uk: Математика, природничі науки

description: Although a large number of fluids used in hydraulic fracturing practice exhibit a shear thinning behaviour, little is known on the impact of such a complex fluid rheology on the propagation of a hydraulic fracture. We focus our investigation on the configuration of a semi-infinite hydraulic fracture propagating at a constant velocity in an impermeable linearly elastic material. We allow for the occurrence of a region without fluid of a-priori unknown length at the fracture tip. We use the Carreau rheological model in order to properly account for the shear thinning of fracturing fluid between the low and large shear rates Newtonian limits. We solve this problem numerically combining a Gauss-Chebyshev method for the discretization of the elasticity equation, the quasi-static fracture propagation condition and a finite difference scheme for the width-averaged lubrication flow. This yields in a system of non-linear equations for the fluid pressure in the filled region of the fracture and the extent of the fluid lag region near the fracture tip. We show that for a Carreau rheology, the solution depends on four dimensionless parameters: a dimensionless toughness (function of the fracture velocity, confining stress, material and fluid parameters), a dimensionless transition shear stress (related to both fluid and material behaviour), the fluid shear thinning index and the amplitude of the shear thinning behaviour of the fluid (captured by the ratio of the high and low shear rate viscosities). The solution exhibits a complex structure with up to four distinct asymptotic regions as one moves away from the fracture tip: a region governed by the classical linear elastic fracture mechanics behaviour near the tip, a high shear rate viscosity asymptotic and power-law asymptotic region in the intermediate field and a low shear rate viscosity asymptotic far away from the fracture tip. The occurrence and order of magnitude of the extent of these different viscous asymptotic regions are obtained analytically. Our results also quantify how shear thinning drastically reduces the size of the fluid lag compared to a Newtonian fluid. We also investigate the response obtained with simpler rheological models (powerlaw, Ellis). In most cases, the power-law model does not accurately match the predictions obtained with a Carreau rheology. In the zero lag limit, the Ellis model properly reproduces the results of a Carreau rheology, albeit only for a dimensionless transition shear stress below a critical dimensionless transition shear stress whose expression is given analytically as function of the shear thinning index and magnitude.

uk: вхід без авторизації

name: A semi-infinite hydraulic fracture driven by a shear thinning fluid


Gennady Mishuris

type: Person

cs: Matematika

de: Mathematik

fi: matematiikka

uk: Математика

en: Mathematics

fr: Mathématiques

da: Matematik

es: Matemáticas

nl: Wiskunde

de: Mathematik, Naturwissenschaften

uk: Математика, природничі науки

en: Mathematics, Natural Sciences

description: We discuss the Hydraulic Fracture (HF) model introduced in [1] accounting for the hydraulically induced shear stresses at the crack faces. The model utilizes a general form of the boundary integral operator alongside a revised fracture propagation condition based on the critical value of the energy release rate. The tip asymptotics of the revised model is always consistent with that of the Linear Elastic Fracture Mechanics. We have found that energy release rate criterion takes a more general form in this case and, in fact, plays the role of a natural regulariser in the numerical simulations. As a result, the hydraulically induced tangential tractions may play a significant role in the small toughness and viscosity dominated regimes of crack propagation, while for other regimes the reported results are close to those obtained in the classic model. We have also found that, in case of small toughness or viscosity dominated regimes, the crack redirection angle may change rather significantly for a mixed mode loading [2]. Certain aspects of the recent discussion on the topic [3-5] will be presented and commented. The potential of the revised formulation in tackling some challenges of HF modelling will be demonstrated. References [1] Wrobel, M., Mishuris, G., & Piccolroaz, A. (2017). Energy release rate in hydraulic fracture: Can we neglect an impact of the hydraulically induced shear stress? International Journal of Engineering Science, 111, 28–51. [2] Perkowska, M., Piccolroaz, A., Wrobel, M., & Mishuris, G. (2017). Redirection of a crack driven by viscous fluid. International Journal of Engineering Science, 121, 182–193. [3] Linkov, A. M. (2017). On influence of shear traction on hydraulic fracture propagation. Material Physics and Mechanics, 32, 272–277. [4] Linkov, A. M. (2018). Response to the paper by M. Wrobel, G. Mishuris, A. Piccolroaz “Energy release rate in hydraulic fracture: Can we neglect an impact of the hydraulically induced shear stress?” International Journal of Engineering Science, 127, 217–219. [5] Wrobel, M., Mishuris, G., & Piccolroaz, A. On the impact of tangential traction on the crack surfaces induced by fluid in hydraulic fracture: Response to the letter of A.M. Linkov. Int. J. Eng. Sci. (2018) 127, 217–219

TIB AV-Portal

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type: WebContent

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de: keine Anmeldung erforderlich

uk: вхід без авторизації

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nl: geen login vereist

name: The role of fluid induced shear traction on the surface of a hydraulically driven crack

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery

type: Organization

cs: Video

de: Video

fi: Video

uk: Відео

en: Video

fr: Vidéo

da: Video

nl: Video

es: Video


uk: Математика, природничі науки

description: Well pads with multiple horizontal wells are widely used to develop the unconventional tight and shale oil reservoirs, which is driven by both the economic and environmental considerations. Thus, determining the optimal well spacing, placement configuration, and stimulation design is critical to optimizing hydrocarbon production from multi-well pads in unconventional. Recent research efforts have been devoted to maximizing the oil/gas production or the NPV in unconventional reservoirs by utilizing analytical models and reservoir simulations. However, owing to the complexity and computationally expensive simulation of the field-scale problem, the optimization process is mostly restricted to the parametric-sensitivity analysis, where a single variable is varied while others are fixed as constant values. In this work, a new Generalized Differential Evolution (GDE) algorithm has been developed and successfully applied to optimize the well placement as well as fracture parameters of a multi-well pad under constraints. A new well completion economic model based on the field dataset is developed and incorporated into the optimization framework, allowing us to find a practical optimum scenario for the multi-well pad development. A field case in Cardium tight oil reservoir is finally used to demonstrate the successful application of the newly developed optimization framework. It is shown from optimum solutions that the well spacing between 230 and 280 m is considered to be the optimum range for the multi-well pad development in Cardium tight formation. The optimum fracture half-length ranges from 82 to 97 m, and the optimum value of fracture conductivity is between 220 and 240 md⸱m. Under an optimal design of well placements and fracture parameters, the proppant pumped per stage ranges from 15 to 20 tonnages and fracturing fluid injection volume is between 100 and 130 m3 per stage. In summary, the relationship between the overall NPV and total fracture volume is complicated and it is of practical importance to optimize the total fracture volume and strike a balance between the oil production and stimulation cost in order to achieve a higher NPV.

uk: вхід без авторизації

name: Optimization of Well Placement and Fracture Design for Multi-Well Pads in Unconventional Tight Reservoirs


uk: Математика, природничі науки

description: We describe methodologies and robust flow and mechanics algorithms for modeling diffusive fracture network representations in tight formations. These include a priori and a posteriori error estimates for modeling Biot systems, generating natural fracture networks and applying phase field for stimulation.

uk: вхід без авторизації

name: Phase Field Modeling for Diffusive Networks and Stimulation


uk: Математика, природничі науки

description: The computational modeling of the formation and growth of the pressurized and fluid filled fractures in poroelastic media is difficult with complex fracture topologies. Here we study the fracture propagation by approximating lower-dimensional fracture surface using the phase field function. The major advantages of using phase-field modeling for crack propagation are i) it is a fixed-topology approach in which remeshing is avoided, ii) crack propagation and joining path are automatically determined based on energy minimization, and iii) joining and branching of multiple cracks also do not require any additional techniques. Recently, the phase field approach has been widely employed to different applications and developed for various softwares. The two-field displacement phase-field system solves fully-coupled constrained minimization problem due to the crack irreversibility. Here, this constrained optimization problem is handled by using active set strategy. The pressure is obtained by using a diffraction equation where the phase-field variable serves as an indicator function that distinguishes between the fracture and the reservoir. Then the above system is coupled via a fixed-stress iteration. In addition, we couple with transport system for proppant filled fracture by using a power-law fluid system.The numerical discretization in space is based on Galerkin finite elements for displacements and phase-field, and an Enriched Galerkin method is applied for the pressure equation and transport equation in order to obtain local mass conservation. Nonlinear equations are treated with Newton’s method. Predictor-corrector dynamic mesh refinement allows to capture more accurate interface of the fractures with reasonable number for degrees of freedom. In addition, we will discuss how to couple these phase field model to multi scale and optimization problems.

uk: вхід без авторизації

name: Phase field modeling for fracture propagation in porous medium


uk: Математика, природничі науки

description: Since their inception in the mid-90's, variational phase-field models of fracture [1] have steadily gained popularity. One of their strengths, the ability to handle complex topologies with unknown crack paths and the interaction between multiple cracks, which is a fundamental requirement for the numerical simulation of hydraulic fracturing in complex situations. Following the technique of [2], crack propagation subject to given pressure p acting along the fracture surfaces of a brittle material occupying a domain Ω is computed as the minimizer of the energy functional Eℓ(u,α)=∫Ω12(1−α)2Ae(u):e(u)dx−p∫Ωα÷(u)dx+3Gc8∫Ωαℓ+ℓ|∇α|2dx where u denotes the displacement field, α the phase field representing the fracture geometry and A its Hooke's law. As in [2], in the case of a single pre-existing line or penny-shaped crack in an infinite medium the pressure and volume of fluid recovered from minimizers of (1) can be compared with solutions from the literature [3]. This formalism can also be used to address the issue of hydraulic stimulation of multiple cracks. Symmetry arguments are routinely used to suggest that the propagation of an infinite array of cracks of equal length in an infinite reservoir is possible. Yet a simple stability analysis reveals that this is not the case and that loss of symmetry is always energetically favored [4]. References [1] Bourdin, B., Francfort, G., and Marigo, J.-J., Numerical experiments in revisited brittle fracture. J. Mech. Phys. Solids, (2000), 48(4) 797-826 [2] Bourdin, B., Chukwudozie, C., and Yoshioka, K. (2012). A variational approach to the numerical simulation of hydraulic fracturing. In Proceedings of the 2012 SPE Annual Technical Conference and Exhibition, volume SPE 159154. [3] Sneddon, I. and Lowengrub, M. (1969). Crack problems in the classical theory of elasticity. The SIAM series in Applied Mathematics. John Wiley & Sons. [4] Tanné, E. (2017). Variational phase-field models from brittle to ductile fracture: nucleation and propagation. PhD thesis, Université Paris-Saclay, Ecole Polytechnique.

uk: вхід без авторизації

name: A variational phase field model of hydraulic fracturing


uk: Математика, природничі науки

description: Since their inception in late 90's, the phase-field models of fracture simulation have steadily gained popularity. One of the appeals is its ability to handle complex topologies with unknown crack paths in relatively coarse meshes as well as multiple-crack interaction, which is a fundamental requirement for the numerical simulation of hydraulic fracturing in complex situations and is technically more difficult to achieve with many other methods. In this talk, we will first describe the construction of a phase-field based coupled hydromechanical reservoir simulator. We will then revisit the problem of a single hydraulic fracture propagating in an infinite impermeable medium in order to validate the computation of fracture width and frac pressure from the phase-field model. Finally we will show how a phase-field description of a system of cracks can be leveraged to model flow in a fractured porous medium and describe the coupling of the flow and mechanics problems, and illustrate the properties of this model through various numerical simulations.

uk: вхід без авторизації

name: A variational phase field hydromechanical model of reservoir


uk: Математика, природничі науки

description: The eXtended Finite Element Method (XFEM) has developed to a standard tool in fracture mechanics. The method enriches the approximation space such that inner-element cracks are considered without loss of accuracy. The hybrid explicit-implicit XFEM uses both, an explicit surface mesh and the implicit level-set method for the description of the crack geometry. The implicit description is needed for the integration in cut elements and it defines where to enrich and how. The explicit description facilitates the (non-planar) crack propagation and provides the basis for solving general transport models on the surface mesh in order to consider for the fluid in Hydraulic Fracturing. One may span the full range from the Reynolds equation, general scalar advection-diffusion equations up to Stokes and Navier-Stokes equations. Because the crack surfaces in hydraulic fracturing may be non-planar, these models have to be extended from the flat case to the situation on curved manifolds. Tangential differential calculus and surface operators play an important role and approximations based on finite elements have to be provided. Future research will show which of these transport models are necessary and sufficient in the field of hydraulic fracturing.

uk: вхід без авторизації

name: Explicit-implicit XFEM for Hydraulic Fracturing with emphasis on transport models on curved crack surfaces


uk: Математика, природничі науки

description: Hydraulic fracturing in naturally fractured rocks often leads to the creation of a stimulated zone of enhanced permeability in which the target formation is irreversibly deformed through shear dilation of natural fractures, plastic deformation, and induced bulk damage. The current dominant modeling approach - explicitly accounting for each fracture with microscale resolution of the fracture network (e.g., discrete fracture network or distinct element method) is a computationally expensive and complex task. There also remain large uncertainties with respect to natural fracture distribution and reservoir parameters. Addressing these issues leads to identification of the need to develop up-scaled continuum model that is able to, in an average sense, capture the irreversible behavior of naturally fractured rock masses. We present a novel mathematical approach with the goal of simulating the evolution of the Stimulated Rock Volume (SRV) in a 2D/3D geomechanical model. This is achieved by introducing a homogenized non-local poro-elastic-plastic continuum zone for the stimulated region, described by an internal characteristic length scale. The up-scaled mechanism of fracturing and deformation is described by a non-local Drucker-Prager model coupled to a Biot poroelastic medium, and implemented within a standard Galerkin Finite Element Method framework. We first quantify the evolution of the SRV and pressure change in the reservoir for a typical example of hydraulic fracture stimulation in a tight formation. After the creation of a sufficiently large SRV, the well is shut-in for an extended period of time and the wellbore pressure is allowed to fall-off. The analysis of post-shut pressure curves confirms the existence of the well-known flow regimes- storage and bi-linear flow- characteristic of the simple bi-wing hydraulic fractures in homogenous rocks. Using the existing analytical solution for the finite conductive fracture, the flow capacity of the stimulated zone is calculated and correlated to the size of the stimulated zone through the non-local length scale. The performance of the developed methodology is tested by considering examples of 2D and 3D SRV calculations. For each example, the stimulated zone and the fluid pressure in relation to the local in-situ stress field are quantified. The influence of reservoir complexities, such as sedimentary layering, complex initial in-situ stress field, and wellbore effects on the evolution of the SRV and fluid pressure will be discussed.

uk: вхід без авторизації

name: 3D Simulation of Stimulated Rock Volume Evolution during Hydraulic Fracturing


uk: Математика, природничі науки

description: The inversion of remote tilt measurements to determine the geometry of an evolving hydraulic fracture (HF) is a classically ill-posed problem due to the fact that the elliptic PDE that governs the behaviour of the displacement gradient field rapidly smooths the geometric details of the fracture with distance. Indeed, it is possible to show that it is only possible to obtain reasonable estimates of the first few moments of the crack opening displacement field from such measurements. On the other hand, numerical and analytic models of evolving HF cannot be expected to provide a completely accurate prediction of evolving HF geometries taking place in the field due to the large number of uncertainties in the data and the un-modeled dynamics due to physical processes that have, of necessity, been ignored. Our approach is to feed the time series of tilt data as input to the implicit level set algorithm (ILSA) model for an evolving HF via the Extended Kalman Filter (EKF). Form an inversion point of view, the dynamics from the coupled ILSA model enables the tilt data snapshots in the time series to be connected, where in previous inversion algorithms these data were regarded as independent. We illustrate the EKF-ILSA algorithm using numerical experiments for planar HF propagating in 3D elastic media. By varying the confining stress field, synthetic tiltmeter data are generated that result in substantial changes to the geometry of the evolving HF. The ILSA model is assumed to have no knowledge of this confining stress field except for feedback from the tiltmeters via the Extended Kalman Filter. Indeed, without this feedback the ILSA HF model would propagate with radial symmetry. We compare the EKF-ILSA estimates of the fracture geometry and width with those of the HF used to generate the synthetic data with and without Gaussian noise. We also present results in which the algorithm is tested on real field data from a mining situation in which HF have been deliberately generated to enhance caving in longwall coal mining. The model is able to detect asymmetry in the growth of the HF, which is corroborated by measured intersection times of the HF with monitoring boreholes.

uk: вхід без авторизації

name: Monitoring Evolving Hydraulic Fracture Growth using Tiltmeters and a combined Extended Kalman Filter-Implicit Level Set Algorithm


uk: Математика, природничі науки

description: Models of hydraulic fractures in conventional reservoirs assume that Carter’s leak-off law —the leak-off rate is proportional to the inverse of the square root of the time elapsed since exposure to fracturing fluid — is applicable. The validity of Carter’s leak-off law stems from the cake-building properties of the fracturing fluid. In some situations where water is essentially the fracturing fluid, Carter’s leak-off law can also be justified (through an reinterpretation of the leak-off coefficient) as an early-time solution of the diffusion equation. However, in water flooding operations of very permeable reservoirs, the fracture propagates in a region where the pore pressure perturbations caused by injection of water is quasi-stationary. The talk will present the construction of a new class of solutions for hydraulic fractures propagating under these asymptotic conditions. We will first present a KGD-type model of an hydraulic fracture created by injecting fluid in weak, poorly consolidated rocks. By further assuming a “small” or negligible toughness (with the consequence that the crack aperture is “small”), we prove that the system is characterized by two asymptotic fracture propagation regimes: rock-flow dominated at small time and fracture-flow dominated at large time. The timescale that legislates the transition between the small and large time asymptotic regimes is shown to be a strongly nonlinear function of a dimensionless injection rate. The rock-flow dominated regime is characterized by an increasing injection pressure while the fracture-flow dominated regime is associated with an injection pressure decreasing with time. The peak injection pressure takes place during the transition between the two regimes. The KGD model collapses, however, when the total crack length (two wings) becomes larger than the thickness of the reservoir layer, assumed to be bounded by impermeable strata. The changing geometric ratio of the constant crack height over its length affects the fracture compliance, i.e. the relationship between fracture aperture and net pressure. As this ratio decreases, the non-local elastic interaction characteristic of the KGD model progressively vanishes and for ratio approximately larger than 5 the compliance becomes essentially local as in the PKN model. It will be shown that evolution of the fracture from a KGD to a PKN mode causes an unexpected reversal of the regime of propagation, with the rock-flow dominated regime in the PKN geometry becoming the long-term solution.

uk: вхід без авторизації

name: Hydraulic Fractures in Weak, Permeable Rocks


uk: Математика, природничі науки

description: The model and algorithm for the numerical solution of the three-dimensional problem of hydraulic fracture initiation and further propagation will be presented. The model is fully coupled and takes into account three important processes: elastic deformation of the rock, fluid flow in the fracture, and its further propagation in the rock. The mathematical model consists of three groups of equations. Each of them responses for one process defined above. The elasticity equations are solved by the dual boundary element method (DBEM), the lubrication equations by the finite element method (FEM) improved by simple conservative correction. This correction allows us to preserve the total volume of injected fluid on the discrete level. The fracture propagation criterion gives the system of non-linear equations, which is solved by special modification of relaxation method. In the early stages of propagation we need to explicitly consider the fluid lag, which in general varies along fracture front. It essentially increases needed computational resources. One of the ways to overcome this challenge is to use any approximation of behavior of variables near the fracture front (tip). Are the already developed asymptotic solution applicable here? The results obtained by the model include the initiation pressure for the real configuration of perforated well, the shape of the fracture, its position and orientation, as well as the possibility of reorientation and the size of the domain where it reorients. The cementing and casing of the well can be taken into account. From the point of oilfield engineer's view, the model can be useful in the understanding of the early stage of hydraulic fracturing when there are many stop cases that sometimes lead to an unsuccessful hydraulic fracturing.

uk: вхід без авторизації

name: The fully coupled 3D numerical model of hydraulic fracturing: ways to improve and possible applications


uk: Математика, природничі науки

description: In the talk, we present our recent developments of the modelling of a planar hydraulic fracture in an inhomogeneous reservoir. The hierarchy of models includes the Enhanced Pseudo 3D (EP3D) model [1] coupled with the proppant transport, the Planar 3D model under the modification of the Implicit Level Set Algorithm (ILSA) [2], and the Planar 3D Biot model that accounts for the effect of poroelasticity [3]. In the EP3D model, the three-dimensional fracture is modeled in terms of quantities that are averaged along the fracture’s height dimension. This model is computationally fast, but is limited to a certain shape of the fracture, and takes into account the layered structure of the reservoir only in terms of the confining stress difference. This model is used for the development of the coupling procedure with the proppant transport module. For the latter we use the one-speed transport model with the effective viscosity varying with particle concentration. We demonstrate effects of the Saffman-Taylor instability development, proppant bridging, breakage of the proppant plug due to the displacement instability. The Planar 3D model describes the fracture development in a layered reservoir, where the effects of the poroelasticity are neglected. The model is implemented using a modification of the ILSA approach [2]. In particular, the model accounts for the inhomogeneity of the elastic properties of the reservoir (only the layered structure of the reservoir is allowed), and is able to simulate cases of fracture local closure due to the fluid re-distribution and/or leak-off. The most advanced Planar 3D Biot model describes the fully coupled interaction of the stresses with the fluid filtration. The numerical model is implemented using the Finite Element Method and allows us to account for an arbitrary inhomogeneity of all physical characteristics of the reservoir. In particular, we show that in the case of the layered structure of the formation, where the layers differ only by permeability, the fracture propagation can demonstrate counter-intuitive non-monotonical behavior. Both, Planar 3D and Planar 3D Biot models, are thoroughly verified by comparison with fast approximate solution for the radial fracture [4], and matched with the existing experimental data [5]. Finally, we present results of the multi-parameter and multi-objective optimization for the Net Present Value and the Fracture Production depending on the applied flow rate, volume of fluid and proppant, and other characteristics of the fracturing process. The optimization is based on the fast algorithms for estimation of fracture’s characteristics [6], on the module for computation of the production of the multiply-fractured wellbore, and on application of genetic algorithms [7] for construction of the Pareto front in the space of objective functions. The work was supported by the Ministry of Science and Education of Russian Federation (grant 2016-220-05-2642). Literature 1. E.V. Dontsov, A. P. Peirce. (2015) An enhanced Pseudo-3D model for hydraulic fracturing accounting for viscous height growth, non-local elasticity, and lateral toughness, Eng. Fract. Mech., V. 142, p 116-139 2. E.V. Dontsov, A.P. Peirce. (2017) A multiscale Implicit Level Set Algorithm (ILSA) to model hydraulic fracture propagation incorporating combined viscous, toughness, and leak-off asymptotics. Comput. Methods Appl. Mech. Engrg. V. 313. P. 53–84. 3. A.N. Baykin, S.V. Golovin. (2016) Modelling of hydraulic fracture development in inhomogeneous poroelastic medium. J. Phys.: Conf. Ser., V. 722. 012003 4. Dontsov, E.V. (2016) An approximate solution for a penny-shaped hydraulic fracture that accounts for fracture toughness, fluid viscosity, and leak-off. R.Soc. Open Sci. V. 3. P. 160737. 5. R. Wu, A.P. Bunger, R.G. Jeffrey, E. Siebrits. (2008) A comparison of numerical and experimental results of hydraulic fracture growth into a zone of lower confining stress. ARMA 08-267 6. Dontsov, E. V. (2016) An approximate solution for a penny-shaped hydraulic fracture that accounts for fracture toughness, fluid viscosity and leak-off. Royal Society open science V.3 N.12 P. 160737. 7. Deb, K. (2001) Multi-objective optimization using evolutionary algorithms. John Wiley & Sons.

uk: вхід без авторизації

name: Modelling of a planar hydraulic fracture with three different approaches


General-order observation-driven models

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

uk: вхід без авторизації

name: Extrema of stable processes and number theory


uk: Математика, природничі науки

uk: вхід без авторизації

name: Testing for structural changes in LMSV time series


uk: Математика, природничі науки

uk: вхід без авторизації

name: Asymptotics of bivariate local Whittle estimators with applications to fractal connectivity


uk: Математика, природничі науки

uk: вхід без авторизації

name: On the tail behavior of a class of multivariate conditionally heteroskedastic processes


uk: Математика, природничі науки

uk: вхід без авторизації

name: Representation of homogeneous measures and tail measures of regularly varying time series


uk: Математика, природничі науки

uk: вхід без авторизації

name: Climate event attribution using peaks-over-thresholds modelling

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery


uk: Математика, природничі науки

uk: вхід без авторизації

name: Extremal (in)dependence structures of random scale constructions


uk: Математика, природничі науки

uk: вхід без авторизації

name: Instability of ranks and inference under long memory


uk: Математика, природничі науки

uk: вхід без авторизації

name: Limit theorems for quadratic functionals of heavy-tailed long-memory processes


uk: Математика, природничі науки

uk: вхід без авторизації

name: Scale invariant set functions arising from general iterative schemes


uk: Математика, природничі науки

uk: вхід без авторизації

name: Large deviation for extremes in BRW with regularly varying displacements


uk: Математика, природничі науки

uk: вхід без авторизації

name: Long range dependence for random functions with infinite variance


uk: Математика, природничі науки

uk: вхід без авторизації

name: The Linear Preferential Attachment Model for Social Network Growth


uk: Математика, природничі науки

uk: вхід без авторизації

name: Consistency of Hill Estimators in a Linear Preferential Attachment Model


uk: Математика, природничі науки

uk: вхід без авторизації

name: Efficient simulation of Brown-Resnick processes based on variance reduction of Gaussian processes


uk: Математика, природничі науки

uk: вхід без авторизації

name: Threshold Selection for Multivariate Heavy-tailed Data


uk: Математика, природничі науки

uk: вхід без авторизації

name: Extremal Value Theory of a Stationary SαS Random Fields


Regularly Varying Random Fields

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

uk: вхід без авторизації

name: Heavy tails in a robust newsvendor model


uk: Математика, природничі науки

uk: вхід без авторизації

name: Optimization-based Approaches to Extreme Event Analysis


uk: Математика, природничі науки

uk: вхід без авторизації

name: Group measure space construction, ergodicity and stable random fields


cs: Informatika

de: Informatik

fi: tietojenkäsittelytiede

uk: Комп'ютерні науки

en: Computer Science

fr: Informatique

da: Datalogi

es: Ciencias de la Computación

nl: Informatica

cs: Technické vědy

de: Ingenieurwissenschaften

fi: tekniikka

uk: Інженерія

en: Engineering Sciences

fr: Ingénierie

da: Ingeniørvidenskab

es: Ingeniería

nl: Engineering

uk: вхід без авторизації

name: Open Science Festival 2022 - Keynote: Transition to Open Science: Reform of Recognition and Rewards

Leibniz Universität Hannover (LUH)

addressCountry: DE

addressLocality: Hanover

addressRegion: Lower Saxony


uk: Комп'ютерні науки

description: Wie kann durch Open Science Praktiken wissenschaftliche Integrität befördert werden, wie stehen die Anerkennungssysteme in der Wissenschaft im Widerspruch zur Umsetzung von Open Science Praktiken?

@language: de

uk: вхід без авторизації

name: Open Science Festival 2022 - Panel 1: Open Science: Just science done right!


uk: Комп'ютерні науки

description: Mit internationalen Expert*innen wollen wir diskutieren, inwieweit Datenströme in der Wissenschaft kommerzialisiert sind und wie das auch Open Science betrifft.

uk: вхід без авторизації

name: Open Science Festival 2022 - Panel 2: Who owns science?


uk: Математика, природничі науки

uk: вхід без авторизації

name: Diffusion transformations, Black-Scholes equation and optimal stopping

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery


uk: Математика, природничі науки

uk: вхід без авторизації

name: Convex duality in nonlinear optimal transport


uk: Математика, природничі науки

uk: вхід без авторизації

name: Convergence to the Mean Field Game Limit: A Case Study


uk: Математика, природничі науки

uk: вхід без авторизації

name: Large Deviations for McKean Vlasov Equations and Importance Sampling


uk: Математика, природничі науки

uk: вхід без авторизації

name: Nonzero-sum stochastic differential games with impulse controls: a verification theorem with applications


uk: Математика, природничі науки

uk: вхід без авторизації

name: Markovian representations of stochastic Volterra processes


uk: Математика, природничі науки

uk: вхід без авторизації

name: Optimal investment and consumption with labor income or liability streams in incomplete markets


uk: Математика, природничі науки

uk: вхід без авторизації

name: Optimal make-take fees for market making regulation


uk: Математика, природничі науки

uk: вхід без авторизації

name: Incomplete Equilibrium with Stochastic Interest Rates


uk: Математика, природничі науки

uk: вхід без авторизації

name: Equilibrium with Heterogeneous Information


uk: Математика, природничі науки

uk: вхід без авторизації

name: Optimal Investment & Derivative Demand under Price Impact


uk: Математика, природничі науки

uk: вхід без авторизації

name: Interacting through their hitting times: neuron firing, supercooling & systemic risk


uk: Математика, природничі науки

uk: вхід без авторизації

name: An Infinite-dimensional McKean-Vlasov Stochastic Equation


uk: Математика, природничі науки

uk: вхід без авторизації

name: Optimal investment in an endogenous price impact model


uk: Математика, природничі науки

uk: вхід без авторизації

name: Pricing and Hedging in rough volatility models


uk: Математика, природничі науки

uk: вхід без авторизації

name: Martingale Benamou-Brenier: a probabilistic perspective


uk: Математика, природничі науки

uk: вхід без авторизації

name: Various formulations of martingale optimal transport problem in multi-dimension


uk: Математика, природничі науки

uk: вхід без авторизації

name: Computational Methods for Martingale Optimal Transport: a related problems in robust pricing and hedging

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery


Weak approximation by adapted process

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

uk: вхід без авторизації

name: On the partial hedging of American options


uk: Математика, природничі науки

uk: вхід без авторизації

name: Short- and long-term relative arbitrage in stochastic portfolio theory


uk: Математика, природничі науки

uk: вхід без авторизації

name: Projections of Local Martingale Deflators


Simple bounds for transaction costs

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

uk: вхід без авторизації

name: Volatility derivatives in (rough) forward variance models


uk: Математика, природничі науки

uk: вхід без авторизації

name: High dimensional problems for continuous time models


uk: Математика, природничі науки

uk: вхід без авторизації

name: Measure-valued martingales and optimality of solutions to the Skorokhod embedding problem


Free Banach lattice over a set

uk: Математика, природничі науки

uk: вхід без авторизації


Free Banach lattice over a Banach space

uk: Математика, природничі науки

uk: вхід без авторизації


Free vector lattices

uk: Математика, природничі науки

uk: вхід без авторизації


p-multinorms and Banach lattices

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

uk: вхід без авторизації

name: Multi-normed spaces, based on non-discrete measures, their tensor products and applications


Uo-convergence

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

uk: вхід без авторизації

name: Applications of uo-convergence to vector lattices


uk: Математика, природничі науки

uk: вхід без авторизації

name: Order Convergence & Unbounded Order Convergence in C(X)


Un-convergence and un-topology

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

description: In this talk, we will present algorithms for distributed statistical estimation that can take advantage of the divide-and-conquer approach. We show that one of the key benefits attained by an appropriate divide-and-conquer strategy is robustness, an important characteristic of large distributed systems. Moreover, we introduce a class of algorithms that are based on the properties of the spatial median, establish connections between performance of these distributed algorithms and rates of convergence in normal approximation, and provide tight deviations guarantees for resulting estimators in the form of exponential concentration inequalities. Techniques are illustrated with several examples; in particular, we obtain new results for the median-of-means estimator, as well as provide performance guarantees for robust distributed maximum likelihood estimation.

uk: вхід без авторизації

name: Distributed Statistical Estimation and Rates of Convergence in Normal Approximation


uk: Математика, природничі науки

description: Deep learning has been widely applied and brought breakthroughs in speech recognition, computer vision, and many other domains. The involved deep neural network architectures and computational issues have been well studied in machine learning. But there lacks a theoreti- cal foundation for understanding the approximation or generalization ability of deep learning methods with network architectures such as deep convolutional neural networks with convo- lutional structures. This talk describes a mathematical theory of deep convolutional neural networks (CNNs). In particular, we show the universality of a deep CNN, meaning that it can be used to approximate any continuous function to an arbitrary accuracy when the depth of the neural network is large enough. Our quantitative estimate, given tightly in terms of the number of free parameters to be computed, verifies the efficiency of deep CNNs in dealing with large dimensional data. Some related distributed learning algorithms will also be discussed.

uk: вхід без авторизації

name: Theory of Deep Convolutional Neural Networks and Distributed Learning


uk: Математика, природничі науки

description: This paper proposes a simple, practical and efficient MCMC algorithm for Bayesian analysis of big data. The proposed algorithm suggests to divide the big dataset into some smaller subsets and provides a simple method to aggregate the subset posteriors to approximate the full data posterior. To further speed up computation, the proposed algorithm employs the population stochastic approximation Monte Carlo (Pop-SAMC) algorithm, a parallel MCMC algorithm, to simulate from each subset posterior. Since this algorithm consists of two levels of parallel, data parallel and simulation parallel, it is coined as “Double Parallel Monte Carlo”. The validity of the proposed algorithm is justified mathematically and numerically.

uk: вхід без авторизації

name: Double-Parallel Monte Carlo for Bayesian Analysis of Big Data


uk: Математика, природничі науки

description: State-of-the-art techniques in passive particle-tracking microscopy provide high-resolution path trajectories of diverse foreign particles in biological fluids. In order to analyze experiments often tracking thousands of particles at once, scientists must account for many sources of unwanted variability, such as heterogeneity of the fluid environment and measurement error. To this end, this talk presents a versatile family of hierarchical stochastic process models, along with a scalable split-merge distributed computing strategy for parameter inference. Also presented are several applications to quantifying subdiffusive mobility of tracer particles in human lung mucus.

uk: вхід без авторизації

name: Applications of a Distributed Computational Method for Microparticle Tracking in Biological Fluids


uk: Математика, природничі науки

uk: вхід без авторизації

name: Distributed Kriging: A Divide-and-Conquer Bayesian Approach to Large-Scale Kriging


uk: Математика, природничі науки

description: Many statistical learning problems can be posed as minimization of a sum of two convex functions, one typically a composition of non-smooth and linear functions. Examples include regression under structured sparsity assumptions. Popular algorithms for solving such problems, e.g., ADMM, often involve non-trivial optimization subproblems or smoothing approximation. We consider two classes of primal-dual algorithms that do not incur these difficulties, and unify them from a perspective of monotone operator theory. From this unification we propose a continuum of preconditioned forward-backward operator splitting algorithms amenable to parallel and distributed computing. For the entire region of convergence of the whole continuum of algorithms, we establish its rates of convergence. For some known instances of this continuum, our analysis closes the gap in theory. We further exploit the unification to propose a continuum of accelerated algorithms. We show that the whole continuum attains the theoretically optimal rate of convergence. The scalability of the proposed algorithms, as well as their convergence behavior, is demonstrated up to 1.2 million variables with a distributed implementation.

uk: вхід без авторизації

name: Easily parallelizable and distributable class of algorithms for structured sparsity, with optimal acceleration


uk: Математика, природничі науки

uk: вхід без авторизації

name: Bayesian Regression with Undirected Network Predictors with an Application to Brain Connectome Data


uk: Математика, природничі науки

description: In the field of road safety, crashes involving physical injuries typically occur on roadways, which constrain the events to lie along a linear network. Substantial research efforts have been devoted to the development of methods for point patterns on linear networks. In one such model, we assume that crash coordinates are produced by a Poisson point process whose domain corresponds to edges in the road network. This talk focuses on the analysis of geo-localised accident data in the context of a smart city initiative launched by the City of Quebec (Canada) aiming to identify crash hotspots on the road network based on covariates derived from GPS data. Data originate from three sources: i) a geolocalised traffic accident database whose entries are based on police reports, ii) GPS trajectories obtained from a study on 4,000 drivers involving 55,000 trips and iii) the structure of the road network obtained from the OpenStreetMap (OSM) database. We highlight challenges, both methodological and computational, with the use of those three data sources in producing sensible inference for the covariate effects.

uk: вхід без авторизації

name: Challenges in the prediction of motor vehicle traffic collisions with GPS travel data

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery


uk: Математика, природничі науки

uk: вхід без авторизації

name: On Combination of Inferences After Split-and-Conquer


Online Algorithms for Statistics

uk: Математика, природничі науки

uk: вхід без авторизації


uk: Математика, природничі науки

description: I will give a very pedestrian overview of some problems in spectral geometry — a vast topic covering relations between eigenvalues of boundary value problems for the Laplacian (or for other differential operators) in a Euclidean domain or on a Riemannian manifold, and the underlying geometry. They will include some open problems of various degrees of difficulty.

uk: вхід без авторизації

name: Spectral geometry - from the 19th to 21st century in 50 minutes


Hearing the Shape of the Bunny

uk: Математика, природничі науки

description: It is well-known that one cannot generally hear the shape of a drum: the metric of a compact surface is not uniquely determined by its Laplace-Beltrami spectrum. But one can still seek computational solutions to the inverse problem: given a sequence of eigenvalues, can we compute a surface whose Laplace-Beltrami spectrum approximates the sequence? I will discuss some numerical experiments related to this problem for the case of surfaces of sphere topology, whose discrete conformal parameterization leads to an especially simple formulation of the inverse problem.

uk: вхід без авторизації


uk: Математика, природничі науки

description: A classical approach for surface classification is to find a compact algebraic representation for each surface that would be similar for objects within the same class and preserve dissimilarities between classes. We introduce self functional maps as a novel surface representation that satisfies these properties, translating the geometric problem of surface classification into an algebraic form of classifying matrices. The proposed map transforms a given surface into a universal isometry invariant form defined by a unique matrix. The suggested representation is realized by applying the functional maps framework to map the surface into itself. The key idea is to use two different metric spaces of the same surface for which the functional map serves as a signature. Specifically, in this lecture, we suggest the regular and the scale invariant surface laplacian operators to construct two families of eigenfunctions. The result is a matrix that encodes the interaction between the eigenfunctions resulted from two different Riemannian manifolds of the same surface. Using this representation, geometric shape similarity is converted into algebraic distances between matrices. In contrast to geometry understanding there is the emerging field of deep learning. Learning systems are rapidly dominating the areas of audio, textual, and visual analysis. Recent efforts to convert these successes over to geometry processing indicate that encoding geometric intuition into modeling, training, and testing is a non-trivial task. It appears as if approaches based on geometric understanding are orthogonal to those of data-heavy computational learning. We propose to unify these two methodologies by computationally learning geometric representations and invariants and thereby take a small step towards a new perspective on geometry processing. If time permits I will present examples of shape matching, facial surface reconstruction from a single image, reading facial expressions, shape representation, and finally definition and computation of invariant operators and signatures.

uk: вхід без авторизації

name: Learning Invariants and Representation Spaces of Shapes and Forms


uk: Математика, природничі науки

description: The transmission eigenvalue problem plays a central role in inverse scattering theory. This is a non-selfadjoint problem for a coupled pair of partial differential equations in a bounded domain corresponding to the support of the scattering object. Unfortunately, relatively little is known about the spectrum of this problem. In this talk I will consider the simplest case of the transmission eigenvalue problem for which the domain and eigenfunctions are spherically symmetric. In this case the transmission eigenvalue problem reduces to an eigenvalue problem for ordinary differential equations. Through the use of the theory of entire functions of a complex variable, I will show that there is a remarkable diversity in the behavior of the spectrum of this problem depending on the behavior of the refractive index near the boundary. Included in my talk will be results on the existence of complex eigenvalues, the inverse spectral problem and a remarkable connection (due to Fioralba Cakoni and Sagun Chanillo) between the location of transmission eigenvalues for automorphic solutions of the wave equation in the hyperbolic plane and the Riemann hypothesis.

uk: вхід без авторизації

name: Spectral Theory for the Transmission Eigenvalue Problem


uk: Математика, природничі науки

uk: вхід без авторизації

name: Discussion and open problem session on numerical aspects of spectral geometry


uk: Математика, природничі науки

description: Subspace iteration for computing eigenvalues and eigenvectors, a natural generalization of the power method, is among the most straight-forward methods to analyze and implement. A variant of subpace iteration, called FEAST, that uses rational filters to accelerate convergence toward a targeted invariant subspace (typically selected by enclosing the eigenvalues of interest by a simple contour), has gained significant interest in recent years, having been adopted as part of Intel's Math Kernel Library for matrix eigenvalue problems. Such rational filters are often derived from quadrature approximations of contour integrals---think of approximating Cauchy's integral formula for the indicator function of the region enclosed by the contour. The rational filter governs the iterative convergence of the method, so it is perhaps surprising that quadrature error plays little role in the analysis of the algorithm, and we will explain why this is so. Inspired by this approach, we consider filtered subspace iteration for (possibly) unbounded selfadjoint operators, having in mind differential operators as motivational examples. In this broader context, it is natural to consider errors in approximating the invariant subspace with respect to different norms, and we provide a fairly general framework for analyzing both iteration and discretization errors for eigenvalues and invariant subspaces. The bulk of the computational effort in the algorithm involves approximating the action of the resolvent at a few points along a contour enclosing the eigenvalues of interest. In our numerical examples, such finite-rank approximations of the resolvent are obtained by finite element discretizations.

uk: вхід без авторизації

name: Filtered subspace iteration for selfadjoint operator eigenvalue problems


uk: Математика, природничі науки

description: In this talk,we analyze the connections between the nodal domains of the eigenfunctions of the Dirichlet-Laplacian and the partitions of the domain by k open sets Di which are minimal in the sense that the maximum over the Di's of the groundstate energy of the Dirichlet realization of the Laplacian is minimal. Instead of considering the maximum among the first eigenvalues, we can also consider the p-norm of the vector composed by the first eigenvalues of each subdomain.

uk: вхід без авторизації

name: Minimal k-partition for the p-norm of the eigenvalues


uk: Математика, природничі науки

description: Recently a novel family of eigensolvers, called spectral indicator methods (SIMs), was proposed. Given regions of the complex plane, SIMs compute indicators and use them to detect eigenvalues. Regions that contain eigenvalues are subdivided and the procedure is repeated until eigenvalues are isolated with a specified precision. In this talk, by a special way of using Cayley transformation and Krylov subspaces, a memory efficient eigensolver for sparse eigenvalue problems is proposed. The method uses little memory and is particularly suitable for the computation of many eigenvalues of large problems. The eigensolver is realized in Matlab and tested using various matrices.

uk: вхід без авторизації

name: A Memory Efficient Spectral Indicator Method for Eigenvalue Problems


uk: Математика, природничі науки

description: Tangent vector fields on surfaces are linear operators acting on scalar functions. Taking this classical view as the starting point for the discretization of tangent vector fields on discrete surfaces, leads to interesting operator-based insights and applications. For example, geometric properties of the vector field can be expressed as algebraic properties of its matrix representation. We will present some theoretical properties and applications to geometry processing.

uk: вхід без авторизації

name: On the spectral properties of tangent vector fields on surfaces with applications to geometry processing


uk: Математика, природничі науки

description: In recent years the subject of sharp inequalities for Laplace eigenvalues has received a lot of attention, in particular, due to its connection with minimal surfaces in spheres. In this talk we will explain this connection and give an overview of some recent estimates for Laplace eigenvalues on Riemannian surfaces.

uk: вхід без авторизації

name: Recent advances in shape optimisation of Laplace eigenvalues


uk: Математика, природничі науки

uk: вхід без авторизації

name: Discussion and open problem session on theoretical aspects of spectral geometry


uk: Математика, природничі науки

description: This talk will be part-tutorial and part-research presentation. I will begin by summarizing some applications of spectral geometry, in particular the geometry of the Laplacian operator, appearing in the discrete geometry processing, computer graphics, and machine learning literatures. Using these applications as motivation, I will construct discretizations of the Laplacian suitable for calculations on triangulated surfaces, volumes bounded by a discretized surface, and point clouds. The talk will conclude with some of my own research in spectral geometry for surface correspondence, shape analysis, and applications.

uk: вхід без авторизації

name: Computational Applications of Spectral Geometry


uk: Математика, природничі науки

description: We study eigenvalue asymptotics for a class of Steklov problems, possibly mixed with Dirichlet and/or Neumann boundary conditions, on planar domains with piecewise smooth boundary and with finitely many corners. This includes the famous "sloshing problem" as well as the Steklov problem on polygons. Two interesting features of this problem, which I will explain, are the surprisingly precise asymptotics we can obtain (with error decreasing as the spectral parameter increases) and a connection to a scattering problem on the Steklov portion of the boundary. This is joint work with M. Levitin (Reading), L. Parnovski (UCL), and I. Polterovich (Montreal).

uk: вхід без авторизації

name: Eigenvalue asymptotics for Steklov-type problems on curvilinear polygons


Averages of Laplace eigenfunctions

uk: Математика, природничі науки

description: In this talk we discuss the behavior of Laplace eigenfunctions when restricted to a fixed submanifold by studying the averages given by the integral of the eigenfunctions over the submanifold. In particular, we show that the averages decay to zero when working on a surface with Anosov geodesic flow regardless of the submanifold (curve) that one picks. This is based on joint works with John Toth and Jeffrey Galkowski.

uk: вхід без авторизації


uk: Математика, природничі науки

description: Verified computing is a newly developed methodology to estimate all errors in numerical computing and provide mathematically rigorous results. Recently, there have been several newly developed verified computing methods to give guaranteed eigenvalue estimation for differential operators. In this talk, I will explain basic concepts about verified computing and give a survey on guaranteed eigenvalue estimation methods. Particularly, the newly developed verified eigenvalue estimation method based on finite element method (FEM) will be introduced in detail. Such a method has been successfully applied to various differential operators, for example, the Laplace, the Biharmonic, the Stokes, the Steklov operators. Also, applications of the guaranteed eigenvalue estimation in mathematical proof will be introduced. As an example, I will show the latest result on solution existence proof about the Navier-Stokes equation in 3D space.

uk: вхід без авторизації

name: Guaranteed eigenvalue estimation for differential operators and its application in mathematical proof


uk: Математика, природничі науки

description: How to analyze complex shapes, such as of the highly folded surface of the brain? This talk will show how spectral representations of shapes can benefit neuroimaging. Here, we exploit spectral coordinates derived from the eigenfunctions of the graph Laplacian. Methodologically, we address the inherent instability of spectral shape decompositions. This change of paradigm, exploiting spectral representations, enables an intrinsic processing of brain surfaces. Brain surface matching will be shown as an example.

uk: вхід без авторизації

name: Spectral Matching - Examples on Brain Surfaces


uk: Математика, природничі науки

uk: вхід без авторизації

name: Discussion and open problem session on applications of spectral geometry


uk: Математика, природничі науки

description: The goal of this talk is to study bounds on the Riesz means of mixed Steklov problems. The Riesz mean is a convex function of eigenvalues and has an important role and connection with other spectral quantities. We recall the results known in this direction for the Laplace eigenvalues. Then we introduce the mixed Steklov problem and state the main results. We also discuss some key ideas of the proof.

uk: вхід без авторизації

name: Bounds on the Riesz means of mixed Steklov eigenvalues

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery


Guaranteed lower bounds for eigenvalues

uk: Математика, природничі науки

description: This talk introduces fully computable two-sided bounds on the eigenvalues of the Laplace operator on arbitrarily coarse meshes based on some approximation of the corresponding eigenfunction in the nonconforming Crouzeix-Raviart finite element space plus some postprocessing. The efficiency of the guaranteed error bounds involves the global mesh-size and is proven for the large class of graded meshes. Numerical examples demonstrate the reliability of the guaranteed error control even with inexact solve of the algebraic eigenvalue problem. This motivates an adaptive algorithm which monitors the discretisation error, the maximal mesh-size, and the algebraic eigenvalue error. The accuracy of the guaranteed eigenvalue bounds is surprisingly high with efficiency indices as small as 1.4. This is joint work with Carsten Carstensen.

uk: вхід без авторизації


uk: Математика, природничі науки

description: Computer graphics and geometry processing study the representation, processing, and analysis of 3D shapes, with wide applications to brain imaging, computer vision, computer aided design and engineering, and so on. Intrinsic approaches, usually based on the Laplace-Beltrami operator, have been popular in computer graphics. However, intrinsic approaches cannot capture the spatial embedding of a shape up to rigid motion, and many previous extrinsic methods lack theoretical justification. Instead, we advocate using the Dirichlet-to-Neumann operator as an extrinsic alternative to the Laplacian for geometry processing and shape analysis. We consider the Steklov eigenvalue problem, computing the spectrum of the Dirichlet-to-Neumann operator of a surface bounding a volume. A remarkable property of this operator is that it completely encodes volumetric geometry. We use the boundary element method (BEM) to discretize the operator, accelerated by hierarchical numerical schemes and preconditioning; this pipeline allows us to solve eigenvalue and linear problems on large-scale meshes despite the density of the Dirichlet-to-Neumann discretization. We further demonstrate that our operators naturally fit into existing frameworks for geometry processing, making a shift from intrinsic to extrinsic geometry as simple as substituting the Laplace-Beltrami operator with the Dirichlet-to-Neumann operator.

uk: вхід без авторизації

name: Steklov Spectral Geometry for Extrinsic Shape Analysis


Jones modes in Lipschitz domains

uk: Математика, природничі науки

description: The Jones eigenvalue problem is an overdetermined problem, where the Neumann eigenvalue problem for linear elasticity is coupled with a constraint on the normal trace of the displacement along the boundary. This eigenvalue problem presents interesting features, not least of which is the sensitive dependance on boundary geometry. We prove the existence of eigenpairs of this eigenvalue problem on Lipschitz domains in 2D and 3D, and use numerical methods to approximate the eigenpairs on some simple geometries.

uk: вхід без авторизації


uk: Математика, природничі науки

description: A variety of tasks in inverse problems and data analysis can be formulated as the variational problem of minimizing the Dirichlet energy of a function that takes values in a certain target set and possibly satisfies additional constraints. These additional constraints may be used to enforce fidelity to data or other structural constraints arising in the particular problem considered. I'll present diffusion generated methods for solving this problem for a wide class of target sets and prove some stability and convergence results. I’ll give examples of how these methods can be used for the geometry processing task of generating quadrilateral meshes, finding Dirichlet partitions, constructing smooth orthogonal matrix valued functions, and solving inverse problems for target-valued maps.

uk: вхід без авторизації

name: Diffusion generated methods for target-valued maps


uk: Математика, природничі науки

description: We present a short-time existence result for the surface diffusion equation with an elastic term and without additional curvature regularization. We shall also discuss the asymptotic stability of strictly stable stationary sets.

uk: вхід без авторизації

name: Asymptotic stability of the gradient flow of nonlocal energies


uk: Математика, природничі науки

description: We study the behavior of surface energies defined over couples (E,u) where E is a set and u is a density on the boundary of E. Such energies have been considered in the context of materials science for modelling surface diffusion in a way that takes into consideration explicitly the effect of the free atoms moving on the surface (adatoms) in a regime where the elastic energy is negligible. We discuss regular critical points, existence and uniqueness of minimizers and we characterize the relaxation of the energy functional in a suitable topology. Finally, we will present approximations with phase field and discrete energy.

uk: вхід без авторизації

name: Equilibria configurations for epitaxial crystal growth with adatoms


uk: Математика, природничі науки

description: In this talk we discuss the equilibrium problem for a curved dislocation line in a three-dimensional domain. As the core radius tends to zero, we derive an asymptotic expression to characterize the induced elastic energy. We then obtain the force on the dislocation line as the variation of this expression and identify the highest order terms explicitly. As a main ingredient, we present an explicit asymptotic formula for the induced elastic strain which depends on the curvature of the dislocation line and thus highlights the difference with existing work on straight dislocation lines.

uk: вхід без авторизації

name: Forces on dislocations lines in three dimensions


uk: Математика, природничі науки

description: We consider a shape optimization problem related to the design of polymer scaffolds for bone tissue engineering. Globally, bone loss due to trauma, osteoporosis, or osteosarcoma comprises a major reason for disability. To this day, autograft, i.e., a graft of bone tissue from a different place in the same body, remains the gold standard for large scale bone loss. This is despite major issues, for example donor site morbidity and limited availability. An ideal scaffold to be implanted in place of lost bone tissue must satisfy a number of different criteria, apart from the requirement of biocompatibility. It should be bioresorbable, so that no foreign objects remain after the regeneration time. In particular, however, during the regeneration time, it should provide adequate mechanical stability, while not preventing osteogenesis. Inspired by this biomechanical challenge, we consider the following shape optimization problem. In a periodic setting, by means of homogenization, one can obtain the effective elastic modulus for a given structure of a linearly elastic material occupying a set E⊂Ω=[0,1]3 under a certain loading condition. The objective is to find a set Eopt (the occupied scaffold volume in a unit cell) such that the minimum of the effective elastic modulus for Eopt and of the effective elastic modulus of the complement of the set Ecopt (i.e., of the regenerated bone tissue) is maximized.

uk: вхід без авторизації

name: Shape design of a polymer microstructure for bones


uk: Математика, природничі науки

description: A variational model for epitaxially-strained thin films deposited on substrates is derived by Γ-convergence from the so-called transition-layer model available in the literature. The regularity of energy-minimal film profiles is studied by establishing the internal-ball condition and by implementing some arguments from transmission problems. The possibility of different elastic properties between the film and the substrate is included in the analysis, as well as the surface tensions of all three involved interfaces: film/gas, substrate/gas, and film/substrate. The results relate to both the Stranski-Krastanow and the Volmer-Weber modes. Moreover, geometrical conditions are provided for the optimal wetting angle, i.e., the angle formed at the contact points between films and substrates. In particular, the Young-Dupr\`e law is shown to hold, yielding what appears to be the first analytical validation of such law in the context of Continuum Mechanics for a thin-film model.

uk: вхід без авторизації

name: Analytical validation of the Young-Dupré law for epitaxially-strained thin films


uk: Математика, природничі науки

description: The Minimizing Movement (MM) scheme is a variational method introduced by E. De Giorgi to solve gradient flows in a quite general setting. In finite dimensional Euclidean spaces, when the driving function f is continuously differentiable, it is not difficult to see that all the limit curves are solutions to the ODE system generated by the gradient of f. However, since this vector field is only continuous, solutions may be not unique and there are solutions which cannot be obtained as a direct limit of the MM scheme. In his inspiring 1993 paper “New problems on Minimizing Movements”, De Giorgi raised the conjecture that all the solutions can be obtained as limit of a modifed scheme, obtained by a Lipschitz perturbation of f, converging to f in the Lipschitz norm as the time step goes to 0. We present some ideas of the proof of this conjecture related to nonsmooth calculus and to a new distinguished class of solutions to gradient flows. We will also discuss a partial extension of this result to infinite dimensional Hilbert spaces. In collaboration with Florentine Fleissner.

uk: вхід без авторизації

name: Reverse approximation of gradient flows as Minimizing Movements


uk: Математика, природничі науки

description: In this talk we will establish a quantitative rigidity estimate for two-well nonlinear elastic energies, in the case in which the two wells have exactly one rank-one connection, and we will analyze linearization around a laminate in the setting of two-dimensional solid-solid phase transition. In particular, we will identify by Gamma-convergence an effective limiting model. This limiting description will be given by the sum of a quadratic linearized elastic energy with two surface terms, corresponding to the total length of interfaces created by jumps of the deformation gradient and of the displacement field, respectively.

uk: вхід без авторизації

name: Linearization for solid-solid phase transitions


Discrete optimal transport

uk: Математика, природничі науки

description: Using the finite volume method, one can define a discrete Kantorovich distance with a Riemannian structure based on a Euclidean mesh. We show that in most cases, the limit distance as mesh size tends to zero, in the sense of Gamma- or Gromov-Hausdorff-convergence, is strictly less than the standard Kantorovich distance. This is due to an oscillation effect reminiscent of homogenization. We introduce a geometric condition on the mesh that prevents oscillations and are able to show Gromov-Hausdorff convergence under this condition.

uk: вхід без авторизації


uk: Математика, природничі науки

description: Liftings and their associated Young measures are new tools to study the asymptotic behaviour of sequences of BV-maps under weak* convergence. Their main feature is that they allow to keep track of the precise shape of the jump path and as such are natural objects whenever different ways of approaching a jump need to be distinguished. While this tool has several promising applications, in this talk I will focus on its use to prove lower semicontinuity for linear-growth functionals that depend on the value of the argument function, u(x), besides its gradient. It is well known that in this situation the particular shape of jumps cannot be neglected. Using the theory of liftings, we can prove relaxation theorems under essentially optimal assumptions, generalizing a classical theorem by Fonseca & Müller (1993). The key idea is that liftings provide the right way of localizing the functional in the x and u variables simultaneously under weak* convergence. As a consequence, we are able to implement an optimal measure-theoretic blow up procedure.

uk: вхід без авторизації

name: Liftings of BV-maps and lower semicontinuity


uk: Математика, природничі науки

description: The theory of structured deformations shows good potential to deal with mechanical problems where multiple scales and fractures are present. Mathematically, it amounts to relaxing a given energy functional and to show also the relaxed one has an integral representation. In this seminar, I will focus on a problem for thin objects: the derivation of a 2D relaxed energy via dimension reduction from a 3D energy, incorporating structured deformations in the relaxation procedure. I will discuss the two-step relaxation (first dimension reduction, then structured deformations and viceversa) and I will compare it with another result in which the two relaxation procedures are carried out simultaneously. An explicit example for purely interfacial initial energies will complete the presentation.

uk: вхід без авторизації

name: Dimension reduction in the context of structured deformations


uk: Математика, природничі науки

description: We present a variant of the Cahn-Hilliard energy model for immiscible fluids which incorporates the effect of periodic heterogeneity at small scales. We describe the asymptotic behavior of minimizers using Gamma convergence methods. This talk will address some of the major difficulties in passing to a homogenized limit, which will require heavy exploitation of the self-symmetries of the N-dimensional integer lattice.

uk: вхід без авторизації

name: Effects of periodic homogenization in phase transition problems


uk: Математика, природничі науки

description: We study the mathematical well-posedness of the Crystalline Mean Curvature Flow in all dimensions and for arbitrary anisotropies and (convex) mobilities by means of a variational approach recently developed in collaboration with A. Chambolle, M. Novaga, and M. Ponsiglione.

uk: вхід без авторизації

name: A variational approach to the Crystalline Mean Curvature Flow


uk: Математика, природничі науки

description: We prove that special functions of bounded deformation with small jump sets are close in energy to functions which are smooth in a slightly smaller domain. This permits to generalize the decay estimate by De Giorgi, Carriero, and Leaci to the linearized context in dimension n and to establish the closedness of the jump set for minimizers of the Griffith energy.

uk: вхід без авторизації

name: Approximation of functions with small jump sets and existence of strong minimizers of the Griffith’s energy in dimension n


uk: Математика, природничі науки

description: This talk is devoted to confront two different approaches to the problem of dynamic perfect plasticity. Interpreting this model as a constrained boundary value Friedrichs' system enables one to derive admissible hyperbolic boundary conditions. Using variational methods, we show the well-posedness of this problem in a suitable measure theoretic setting. We prove that this unique variational solution actually coincides with the unique entropic solution of the hyperbolic formulation. Finally, thanks to the finite speed propagation property, we establish a new short time regularity result for the solution.

uk: вхід без авторизації

name: Dissipative boundary conditions and entropic solutions in dynamical perfect plasticity


uk: Математика, природничі науки

description: I will report on recent results with M. Jesenko (Univ. Freiburg) on a homogenization result for Hencky plasticity functionals with non-convex potentials. Also the influence of a small hardening parameter is investigated and it will be shown that homogenization and taking the vanishing hardening limit commute.

uk: вхід без авторизації

name: Homogenization in non-convex Hencky plasticity and the limit of vanishing hardening in Hencky plasticity with non-convex potentials


uk: Математика, природничі науки

description: Epitaxy is a process in which a thin film is grown above a much thicker substrate. Even in the simplest case, with no deposition, and purely elastic interactions, such growth leads to a nonuniform film thickness since the film and the substrate can have different rigidity constants. The resulting system is thus an energy driven one, but quite irregular. Similarly, the evolution of nematic liquid crystals, systems is modeled by a highly complex energy driven system. In this talk I will present some recent results about the regularity of solutions to several equations arising from nematic liquid crystals and epitaxy.

uk: вхід без авторизації

name: Energy driven systems from Liquid Crystals and Epitaxy

name: Banff International Research Station (BIRS) for Mathematical Innovation and Discovery


uk: Математика, природничі науки

description: We consider minimizers of an energy functional arising in cohesive zone models for fracture mechanics. Under smoothness assumptions on the boundary conditions and on the fracture energy density, we show that minimizers are C1,1/2 on each side of the fracture. Moreover, we prove that near non-degenerate points the fracture set is C1,α, for some α∈(0,1). This is joint work with Luis Caffarelli and Alessio Figalli.

uk: вхід без авторизації

name: Optimal regularity and structure of the free boundary for minimizers in cohesive zone models


The wrinkling of a twisted ribbon

uk: Математика, природничі науки

description: We explore a specific system in the mechanics of thin elastic sheets in which geometry and loading conspire to generate fine-scale wrinkling. This system -- a twisted ribbon held with small tension -- was examined experimentally by Chopin and Kudrolli [Phys Rev Lett 111, 174302, 2013]. There is a regime where the ribbon wrinkles near its center. A recent paper by Chopin, Démery, and Davidovitch models this regime using a von Kármán-like variational framework [J Elasticity 119, 137-189, 2015]. Our contribution is to give upper and lower bounds for the minimum energy as the thickness tends to zero. Since the bounds differ by a thickness-independent prefactor, we have determined how the minimum energy scales with thickness. Along the way we find estimates on Sobolev norms of the minimizers, which provide some information on the character of the wrinkling.

uk: вхід без авторизації


uk: Математика, природничі науки

description: The Cahn-Hilliard model is a classical model for microscopic phase transitions in materials, which serves as an important prototype of many phase transition problems in continuum mechanics. I will discuss some recent results regarding second-order Gamma-convergence of these models using a novel rearrangement technique, as well as the application of these results to the study of metastable states for the Allen-Cahn equation.

uk: вхід без авторизації

name: Cahn-Hilliard energies: second-order Gamma-convergence and metastable states


uk: Математика, природничі науки

description: Fracture problems and damage processes have been widely studied in the last twenty years, starting from the pioneristic work of Griffith (and the later approach of Francfort - Marigò) to the more recent Gamma-convergence point of view developed by exploiting the Ambrosio - Tortorelli approximation for image recovery applied to the context of function of Bounded Deformation. In this talk we ill give a brief overview of the state of art of such a topic and we will end by presenting a recent approximation of fluid driven fracture based on a suitable correction of the classical energy with a lower order term that enable the introduction of several application. Some numerical experiments will also be discussed.

uk: вхід без авторизації

name: Approximation of fracture problems via Gamma-convergence: state of art and new results


uk: Математика, природничі науки

description: I will present an analysis of the sets that minimize the Gaussian perimeter plus the norm of the barycenter. These two terms are in competition, and in general the solutions are not the half-spaces. In fact we prove that when the volume is close to one, the solutions are the strips centered in the origin. As a corollary, we obtain that the symmetric strip is the solution of the Gaussian isoperimetric problem among symmetric sets when the volume is close to one. Co-Author: Vesa Julin

uk: вхід без авторизації

name: Stability of the Gaussian isoperimetric problem


uk: Математика, природничі науки

description: Phase field models are often used in situations where sharp interface simulations are difficult, in particular where topological changes can occur. While these are a feature in many applications, we may want to control at least the connectedness of either the phase transition regions or the phases. We present a method which allows us to approximate a relaxation of the perimeter functional under a connectedness constraint in two dimensions and Willmore's curvature energy at connected surfaces in three dimensions. We will give numerical evidence of the effectiveness of the method and describe how it can be implemented in an efficient manner.

uk: вхід без авторизації

name: Keeping it together: A connectedness constraint in phase-field simulations


The mathematics of charged liquid drops

uk: Математика, природничі науки

description: I will present an overview of recent analytical developments in the studies of equilibrium configurations of liquid drops in the presence of repulsive Coulombic forces. Due to the fundamental nature of Coulombic interaction, these problems arise in systems of very different physical nature and on vastly different scales: from femtometer scale of a single atomic nucleus to micrometer scale of droplets in electrosprays to kilometer scale of neutron stars. In the talk, I will focus on Rayleigh's model of perfectly conducting liquid drops and discuss the basic questions of existence vs. non-existence, as well as some qualitative properties of global energy minimizers in these models.

uk: вхід без авторизації


uk: Математика, природничі науки

description: Graphene is locally two-dimensional but not flat. Nanoscale ripples appear in suspended samples and rolling-up often occurs when boundaries are not fixed. In this talk, I explain this variety of graphene geometries by classifying all ground-state deformations of the hexagonal lattice with respect to configurational energies including two- and three-body terms. We prove that all energy minimizers are either periodic in one direction, as in the case of ripples, or rolled up, as in the case of nanotubes. For suspended samples we refine the analysis further and prove the emergence of wave patterning. Specifically, we show that almost minimizers of the configurational energy develop waves with certain wavelength, independently of the size of the sample. The talk is based on joint work with Ulisse Stefanelli.

uk: вхід без авторизації

name: Ripples in graphene: A variational approach


uk: Математика, природничі науки

description: In this talk we consider a large class of Bernoulli-type free boundary problems with mixed periodic-Dirichlet boundary conditions. We show that solutions with non-flat profile can be found variationally as global minimizers of the Alt-Caffarelli energy functional.

uk: вхід без авторизації

name: On the existence and regularity of non-flat profiles for a Bernoulli free boundary problem


uk: Математика, природничі науки

description: We prove the existence of weak solutions to the homogeneous wave equation on a suitable class of time-dependent domains. Using the approach suggested by De Giorgi and developed by Serra and Tilli, such solutions are approximated by minimizers of suitable functionals defined on space-time.

uk: вхід без авторизації

name: A minimization approach (in De Giorgi’s style) to the wave equation on time-dependent domains


uk: Комп'ютерні науки

description: Im Jahr 2021 wurden erstmals Anträge auf Förderung von Open-Access-Publikationskosten bei der Deutschen Forschungsgemeinschaft eingereicht. Während der Open-Access-Tage kann bereits ein erster Überblick über das Antragsaufkommen und über Tendenzen dargestellt werden, die allgemein in den Anträgen erkennbar sind. Der Vortrag wird daher auf die Erkenntnisse eingehen, die im ersten Jahr der Antragsstellung in der Geschäftsstelle der DFG gewonnen wurden. Dadurch wird auch ein Beitrag zu der Diskussion um den Stand der Open-Access-Transformation in Deutschland geleistet.

uk: вхід без авторизації

name: Open-Access-Publikationskostenförderung der Deutschen Forschungsgemeinschaft

Universität Konstanz

addressLocality: Konstanz

addressRegion: Baden-Wurttemberg


uk: Комп'ютерні науки

description: Bei der Antragstellung im DFG-Förderprogramm Open Access Publikationskosten erklären Einrichtungen ihre Bereitschaft, Metadaten zu den geförderten Publikationen an eine datensammelnde Stelle abzuliefern und diese öffentlich zugänglich zu machen. Die Zentralbibliothek des Forschungszentrums Jülich wurde von der Deutschen Forschungsgemeinschaft mit dem begleitenden Monitoring des DFG-Förderprogramms Open Access Publikationskosten beauftragt und ist somit die „datensammelnde Stelle“. Im Vortrag wird das Konzept des Monitoring vorgestellt, welches mit seinen jährlichen Berichten Stand und Entwicklung der Open-Access-Transformation in Deutschland abbilden wird. Ein besonderer Fokus des Vortrags liegt auf dem Datenschema, mit dem Einrichtungen die im Rahmen des Programms geförderten Publikationen melden werden.

uk: вхід без авторизації

name: Monitoring des DFG-Förderprogramms „Open Access Publikationskosten“


uk: Комп'ютерні науки

uk: вхід без авторизації

name: Das OA-Monitoring des Schweizerischen Nationalfonds


uk: Комп'ютерні науки

description: n der deutschen Rechtswissenschaft scheint bereits die Idee von Open Access (OA) einen schweren Stand zu haben: Eine Reihe von Wissenschaftler:innen üben offen Kritik an der Idee oder bezweifeln sogar die Verfassungsmäßigkeit von Open-Access-Vorgaben oder -Richtlinien. Nichtsdestotrotz sind in den letzten Jahren innovative digitale Formate entstanden, die hochwertige rechtswissenschaftliche Inhalte OA veröffentlichen. Nennenswerte Beispiele sind der Verfassungsblog und der Völkerrechtsblog. Diese Plattformen nennen sich „Blogs“, stellen als qualitätsgesicherte Multi-Author-Blogs (QMABs) aber tatsächlich eine neue, innovative, frei verfügbare und genuin digitale Form des wissenschaftlichen Publizierens dar, die zwischen wissenschaftlichen Zeitschriften und traditionellen Medien/Presse angesiedelt ist. In einem QMAB können Expert:innen (in der Regel Wissenschaftler:innen) tagesaktuell Ereignisse analysieren, einordnen und kommentieren. QMABs in der Rechtswissenschaft und den Geistes- und Sozialwissenschaften haben als innovatives Publikationsformat in den vergangenen Jahren eine wachsende Zahl an Autor:innen und Leser:innen hinzugewonnen. Auch die breite Öffentlichkeit nimmt zunehmend Notiz von diesen Plattformen. Gesellschaftspolitische Entwicklungen und Ereignisse sind häufig mit rechtlichen und rechtspolitischen Fragestellungen verknüpft, auf die auch Nicht-Wissenschaftler:innen Antworten suchen. Gleichzeitig haben Wissenschaftler:innen ein Interesse daran, ihre Expertise in den politischen Raum zu tragen. QMAB dienen somit nicht nur dem wissenschaftlichen Binnendiskurs, sondern ermöglichen es auch der breiten Öffentlichkeit, an Fachdiskursen teilzunehmen, etwa über die Kommentarfunktion – und all dies über staatliche Grenzen hinweg. Damit fördern QMABs nicht nur den wissenschaftlichen Austausch und öffnen Diskurse für ein breites Publikum, sondern internationalisieren diese auch. Hierin offenbaren sie ihr partizipatives und kommunikatives Potenzial, das letztlich dem wissenschaftlichen Erkenntnisgewinn zugute kommt. Noch sind QMABs „Exoten“ unter den Wissenschaftspublikationen in den Geistes- und Sozialwissenschaften. Sie sind aber dabei, ihre Position in der wissenschaftlichen Community zu behaupten und werden mittlerweile breit zitiert. Auf den Open-Access-Tagen möchten wir diskutieren, ob QMABs als Ausgangspunkt dienen können, OA (auch in OA-skeptischen Disziplinen) zu etablieren und alternative und inklusivere Formen des wissenschaftlichen Austauschs zu entwickeln.

uk: вхід без авторизації

name: Qualitätsgesicherte Multi-Author-Blogs: Das partizipative Potenzial innovativer Publikationsformate


uk: Комп'ютерні науки

description: Der Vortrag stellt das Projekt „Open Library Economics“ (OLEcon) vor, welches Partizipation durch die Förderung nicht-kommerzieller Publikationsorte ermöglicht. Die „ZBW – Leibniz Informationszentrum Wirtschaft“ unterstützt mit dem Projekt Diamant Open Access Zeitschriften in den Wirtschaftswissenschaften. Das sind solche Zeitschriften, die weder Gebühren für die Autorenschaft noch für die Leserschaft verlangen. Der Vortrag stellt Konzept und Umsetzung von OLEcon vor und geht auf eine Besonderheit bei der Fördermittelvergabe ein: die Förderung muss über ein europaweites Vergabeverfahren ausgeschrieben werden. OLEcon ist Teil eines größeren Vorhabens zur Unterstützung der Open-Access-Transformation an der ZBW. Im Rahmen eines sogenannten Sondertatbestands erprobt die ZBW von 2020 bis 2023 neue Lizenzierungs-, Geschäfts- und Beteiligungsmodelle für Open Access. Dies erfolgt in verschiedenen Tätigkeitsfeldern und beinhaltet auch Verhandlungen mit kommerziellen Verlagen. OLEcon bildet das Gegengewicht zu den Verträgen mit kommerziellen Verlagen: Es werden nicht-kommerzielle Publikationsorte und -infrastruktur gefördert. Zielgruppe für die Förderung von OLEcon sind verlagsunabhängige Zeitschriften, die ihr Geschäftsmodell auf Open Access umstellen wollen bzw. die im Open Access gehalten werden sollen. Es gibt drei Förderelemente für die Zeitschriften. Erstens eine finanzielle Förderung als Übergangsfinanzierung, zweitens ein umfassendes Beratungs- und Serviceangebot und drittens die Vermittlung zu einer nicht-kommerziellen Publikationsplattform. Im letzten Teil des Vortrags gehen wir auf eine Besonderheit bei der Vergabe der Fördermittel durch die ZBW ein: In einem Vergabeverfahren muss die ZBW sicherstellen, dass die Mittel für die Zeitschriften transparent, fair und wirtschaftlich vergeben werden. Wir berichten von unseren Erfahrungen mit der praktischen Umsetzung und stellen die Herausforderungen vor, die es mit sich bringt, wenn ein Verfahren, welches üblicherweise zur Vergabe von öffentlichen Aufträgen wie Bauvorhaben eingesetzt wird, auf die Vergabe von Mitteln an wissenschaftliche Zeitschriften angewendet wird.

uk: вхід без авторизації

name: Partizipation durch Förderung nicht-kommerzieller Publikationsorte in den Wirtschaftswissenschaften ermöglichen: Die Open Library Economics


uk: Комп'ютерні науки

description: The Amsterdam Call for Open Science invites further exploration of the frontiers of Open Science, suggesting this should be done in particular with regard to data sharing and to methods of opening up the scientific process to society. These suggestions come after a great deal of expertise has been achieved in open access to academic publications. Since the Amsterdam Call, Citizen Science has become a well-established domain in most of the scientific disciplines at the European level, but less is known about Citizen Science practices in the Social Sciences and Humanities (SSH), their specificity and needs, together with the diverse ways SSH researchers carry out for open themselves to participation, making a diversity of publics engaging with their methodologies. Two projects coordinated by OpenEdition Center (EHESS, France), involving SSH researchers and journalists (PLACES project) and more largely other professionals and associations (COESO project) are concrete attempts to address the issues of opening the scientific process to society and to give visibility to the specific SSH Citizen Science practices. They achieve that by encouraging and supporting participatory research and mutual learning between academics and citizens. Furthermore, they built on a major French infrastructure committed to open access to the scientific research in the SSH disciplines. The experiences from PLACES and COESO provide an insight to how open access paves the way for citizen science activities in the social sciences and humanities and how these activities can in turn greatly increase the impact of open access activities. Taking stock of them, it will be possible to highlight some aid and barriers to open participation in knowledge production. Particular attention will be given to the data sharing issue, and to the benefits of mutual learning through participatory research in the rise of scientific literacy. These experiences also provide an overview of the significance that open access and open science infrastructures of services have in supporting citizen science activities.

uk: вхід без авторизації

name: From open access to citizen science: opening participation within the SSH disciplines through the PLACES and COESO projects


uk: Комп'ютерні науки

description: In 2014 the Alliance of Science Organisations (Allianz der Wissenschaftsorganisationen), a union of the majority of German research organisations, established Projekt DEAL, a national-level project to negotiate licensing agreements with large scientific publishers. Negotiations between the DEAL consortium and Elsevier, one of the world's largest scientific publishers, began in 2016, and broke down without a successful agreement in 2018; in this time, around 200 German research institutions cancelled their existing license agreements with Elsevier, leading to Elsevier shutting off access to their journal portfolios at those institutions from July 2018 onwards. We aimed to assess the effect of Elsevier access restrictions on the publishing and citing behaviour of researchers from a bibliometric perspective, using a dataset of ~410,000 articles published by researchers from those affected institutions. Our early results show Elsevier’s market share of articles published by researchers from DEAL institutions has fallen over the past 5 years, from a peak of 25.3% in 2015 to 20.6% in 2020; the largest year-on-year loss in market share (>1%) was reported in 2020. Despite a reduction in the proportion of articles published in Elsevier journals, researchers at DEAL institutions have continued to cite Elsevier articles following access restrictions in similar proportions to before, suggesting that researchers use other methods to access and read articles (e.g. interlibrary loans, sharing between co-authors, or “shadow libraries” such as Sci-Hub). We further investigated these behaviours with respect to the timing of contract expirations, research disciplines, collaboration patterns and article OA status. Overall, we find some evidence of reduced willingness amongst researchers at DEAL institutions to publish in Elsevier journals, but no evidence suggesting that researchers are negatively affected in their ability to cite articles following restricted access to those journals.

uk: вхід без авторизації

name: No Deal: Investigating the Influence of Restricted Access to Elsevier Journals on German Researchers’ Publishing and Citing Behaviours


uk: Комп'ютерні науки

description: The scientific publishing market suffers from injustice in several regards. Interestingly, traces of injustice can be found in both open-access (OA) and closed-access (CA) publishing-models. The OA-model makes scientific literature freely accessible for all scholars - but, the costs of publishing have to be assumed by somebody (e.g. the authors via APCs). This, however, may not be possible for authors who do not benefit from financial support for OA-publishing. In succession, such authors cannot publish in the OA-model (instead they must turn to the CA-model) and cannot profit from the citation advantage that was shown for many OA-articles [1]. Researchers (at institutions) who are not able to maintain subscriptions to CA-publications suffer from the CA-model as it builds a barrier to access the required resources. This may result in falling behind the state of the art in the field which along with it may negatively affect future publication success in outlets of high reputation. This study (conducted with data from Scopus and Unpaywall) will research the effect on researchers’ scientific success grounded in the unfairness of both publishing models. We aim to answer three questions. First, is there any limitation for a group of researchers (e.g. from different countries, career stages, career positions) to cite the CA-papers? Second, is there any limitation for researchers to publish in the OA-model and receiving citations? To answer these questions, we try to find the relationship between the groups that researchers belong to and the tendency to cite/publish in the OA- or CA-model. Third, to what extent do these limitations affect the scientific success of scholars? We assess scientific success by comparing the receiving citations for each group. We expect that the tendency to cite OA- and publish CA-articles affects the scientific success of scholars negatively.

uk: вхід без авторизації

name: Impact of Publishing and Citing Open Access Papers on Researchers' Scientific Success


uk: Комп'ютерні науки

description: Die kontinuierliche Fort- und Weiterbildung der mit Open-Access-Themen befassten Mitarbeiter*inInnen an Hochschulbibliotheken ist eine notwendige Voraussetzung zur Absicherung optimaler lokaler Entscheidungs-, Steuerungs- und Entscheidungsprozesse mit Bezug zu Open Access. Über Projekte wie beispielsweise open.access.network oder auch die entstehende Vernetzungs- und Kompetenzstelle Open Access im Land Brandenburg (VuK) entstehen umfangreiche Informations- und Schulungsangebote, die diese Notwendigkeit und den Bedarf aufgreifen. In der Praxis zeigt sich jedoch, dass Fort- und Weiterbildungen oft weniger systematisch und zielführend wirken, als es erwartbar wäre und wünschenswert ist. In einem Projekt des Ministeriums für Forschung, Wissenschaft und Kultur des Landes Brandenburg (MWFK) untersuchten wir mit einer Fallstudie anhand der Hochschulen im Land Brandenburg die konkreten Anforderungen und Rahmenbedingungen zu Fort- und Weiterbildungsprogrammen für die mit Open Access befassten Personen in den Hochschulbibliotheken. Es zeigte sich, dass generische Schulungsformate nicht zuletzt aus arbeitsorganisatorischen und strukturellen Gründen nur eine eingeschränkte Wirkung entfalten können. Um den nachweislich vorhandenen Schulungs- und Fortbildungsbedarf sowie die in der Community vorliegenden Potentiale präziser und wirksamer aufgreifen zu können, schlagen wir ein Set von Maßnahmen und Formaten vor, die dem festgestellten Bedarf unter Berücksichtigung der tatsächlichen Rahmenbedingungen Rechnung tragen. In der Präsentation erläutern wir die Einsichten aus dem Projekt, die vorgeschlagenen Maßnahmen und ihre Verankerung in die seit April 2021 im Aufbau befindliche Vernetzungs- und Kompetenzstelle Open Access im Land Brandenburg (VuK).

uk: вхід без авторизації

name: Zur Vereinbarkeit von Arbeitspraxis und Weiterbildungsbedarf