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See detailSpace-time reduced basis approximation and goal-oriented a posteriori error estimation for wave equation
Hoang, Khac Chi; Kerfriden, Pierre; Bordas, Stéphane UL

in Theory and Application of Model Order Reduction (2013, December)

We study numerically the linear second order wave equation with an output quantity of interest which is a linear functional of the field variable using reduced basis approximation methods in the space ... [more ▼]

We study numerically the linear second order wave equation with an output quantity of interest which is a linear functional of the field variable using reduced basis approximation methods in the space-time domain. The essential new ingredient is the a posteriori error estimation of the output quantity of interest. The technique, which is based on the well-known dual-weighted residual (DWR) method is deployed within a reduced basis approximation context. First, we introduce the reduced basis recipe - Galerkin projection onto a space spanned by the reduced basis functions which are constructed from the solutions of the governing PDE at several selected points in the parameter space. Second, in order to construct these basis functions we propose a new “goal-oriented” Proper Orthogonal Decomposition (POD)-Greedy sampling procedure, which is based on these new a posteriori error estimations. Finally, this a posteriori error estimation is also used to evaluate approximately the quality of many output computations in the online stage within the reduced basis procedure. [less ▲]

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See detailSpace-Time Shear-Slip Mesh Update Method for Fluid-Structure Interaction Problems
Schippke, Henning; Zilian, Andreas UL

Presentation (2013)

Many practical problems in engineering consist of a structure surrounded by a fluid. These are all from the theoretical point of view fluid-structure interaction problems, in which the movement of the ... [more ▼]

Many practical problems in engineering consist of a structure surrounded by a fluid. These are all from the theoretical point of view fluid-structure interaction problems, in which the movement of the structure influences the flow field of the fluid and vice versa. In this contribution the structure is described in a total Lagrangian representation based on velocities and the 2nd Piola-Kirchhoff stress state as primal variables in a hybrid-mixed formulation, while the fluid is modelled via the incompressible Navier-Stokes equations with velocities and pressure as unknowns. The governing equations of fluid and structural dynamics are uniformly discretised using space-time finite elements [1]. The discretised model equations of the fluid are stabilised using a SUPG/PSPG approach. Shape and test functions are continuous within the space-time slabs, while across the space- time slabs the shape and test functions are continuous only in space, but discontinuous in time yielding a time-discontinuous Galerkin approach. The space-time discretisation of the coupled system with velocities and pressure as remaining unknowns lays the basis for a mathematically profound analysis due to its methodical uniformity. During the mesh generation of the fluid-structure problem a fitting mesh at the conjoint interface of fluid and structure is generated ensuring natively the geometric continuity. In the discretised flow domain, which model equations are formulated in the Eulerian framework, a mesh-moving scheme needs to be applied to avoid severe mesh distortions. In case of large but regular structural displacements a discontinuous mesh-moving scheme like the Shear-Slip Mesh Update Method (SSMUM) is applicable [2]. In order to increase robustness and conservation behaviour of the classical SSMUM a modification based on the space-time discretisation of the problem described above is investigated. In the Space- Time SSMUM (ST-SSMUM) the alteration of the spatial connectivity takes place continuously in the space-time domain. By avoiding sudden changes in the spatial connectivity between two adjacent space-time slabs any difficulty in evaluating the jump term is circumvented. The properties of the introduced ST-SSMUM is shown by a computation of the flow field of a rotating impeller, which can be interpreted as a simplified water turbine or blood pump. [less ▲]

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See detailSpace-time shear-slip mesh update method for fluid-structure interaction problems
Schippke, Henning; Zilian, Andreas UL

Scientific Conference (2012, September 14)

Space-time discretisations of physical problems involving moving and deforming bodies, boundaries and interfaces have been shown to offer advantageous properties while being methodologically uniform and ... [more ▼]

Space-time discretisations of physical problems involving moving and deforming bodies, boundaries and interfaces have been shown to offer advantageous properties while being methodologically uniform and flexible. Well-known phenomena which are ideally suited to be analysed by space-time methods, are fluid-structure interaction problems in general as well as fluid flows with subdomain phase boundaries or immersed moving objects. In this contribution a short overview of existing mesh- moving techniques is given within the framework of finite element discretisations of the incompressible Navier-Stokes equations in space and time. The investigation is based on a velocity-pressure formulation on the deforming space-time domain in combination with a GLS stabilisation of the balance of momentum as well as the conservation equation of mass. A modification of the shear-slip mesh update method in the framework of space-time finite element discretisation is presented leading to a continuous space-time mesh in the shear-slip layer. The modified mesh moving technique is applied to the classical flow situation of Poiseuille flow incorporating a rotating space-time fluid mesh. Its conservation properties and its quality regarding the approximated solution on moving and deforming meshes are investigated. [less ▲]

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See detailSpace-Time Triplet Loss Network for Dynamic 3D Face Verification
Kacem, Anis UL; Ben Abdessalem, Hamza UL; Cherenkova, Kseniya UL et al

Scientific Conference (2020)

In this paper, we propose a new approach for 3D dynamic face verification exploiting 3D facial deformations. First, 3D faces are encoded into low-dimensional representations describing the local ... [more ▼]

In this paper, we propose a new approach for 3D dynamic face verification exploiting 3D facial deformations. First, 3D faces are encoded into low-dimensional representations describing the local deformations of the faces with respect to a mean face. Second, the encoded versions of the 3D faces along a sequence are stacked into 2D arrays for temporal modeling. The resulting 2D arrays are then fed to a triplet loss network for dynamic sequence embedding. Finally, the outputs of the triplet loss network are compared using cosine similarity measure for face verification. By projecting the feature maps of the triplet loss network into attention maps on the 3D face sequences, we are able to detect the space-time patterns that contribute most to the pairwise similarity between differ-ent 3D facial expressions of the same person. The evaluation is conducted on the publicly available BU4D dataset which contains dynamic 3D face sequences. Obtained results are promising with respect to baseline methods. [less ▲]

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See detailSpace-Time-Frequency candidate Methods for Spectrum Sensing
Lagunas, Eva UL; Najar, Montse; Lagunas, Miguel Angel

in European Signal Processing Conference (EUSIPCO), Barcelona, Spain, August 29- September 2, 2011. (2011, August)

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See detailSpaceborne Gravimetric Satellite Constellations and Ocean Tides: aliasing effects
Visser, P. N. A. M.; Sneeuw, N.; Reubelt, T. et al

in Geophysical Journal International (2010), (181), 789-805

Ocean tides redistribute mass at high temporal frequencies. Satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal ... [more ▼]

Ocean tides redistribute mass at high temporal frequencies. Satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal. Correcting for the effects of ocean tides by means of imperfect models might hamper the observation of other temporal gravity field signals of interest. This paper explores different methods for mitigating aliasing errors for the specific example of observing mass variations due to land hydrology, including temporal filtering of time-series of gravity solutions, spatial smoothing and the use of satellite constellations. For this purpose, an Earth System Model (ESM) was constructed, which included state-of-the-art time varying components for ocean, atmosphere, solid Earth, hydrology, ice-sheets and ocean tides. Using the ESM, we simulated the retrieval of the hydrologically driven gravity field changes using a number of different satellite constellations. We find that (1) the ocean tide aliasing strongly depends on the satellite constellation, the choice of orbital parameters and the length of the data span; (2) the aliasing effect manifests itself differently for different geographical regions; (3) the aliasing causes a peculiar striping pattern along the ground track of the satellite orbits; (4) optimizing the choice of orbital parameters of a single GRACE-type tandem can be more effective at reducing the aliasing of ocean tide model errors than flying more tandems. Finally, we corroborate the experiences with GRACE data analysis that appropriate post-processing techniques can significantly improve the quality of the retrieved gravity changes. [less ▲]

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See detailSpaceborne gravimetry and gravity field recovery
Xu, C.; Weigelt, Matthias UL; Sideris, M. G. et al

in Canadian Aeronautics and Space Journal (2008), 53(3/4), 65--75

As an integrated signal of mass transition and distribution, the Earth's gravity senses the inner and outer mass balance of the Earth. However gravity cannot be measured directly in space but can be ... [more ▼]

As an integrated signal of mass transition and distribution, the Earth's gravity senses the inner and outer mass balance of the Earth. However gravity cannot be measured directly in space but can be derived from other measurements obtained by space vehicles. The dedicated gravity field satellite missions CHAMP, GRACE, and GOCE serve as spaceborne gravimeters by utilizing satellite-to-satellite tracking (SST) and satellite gravity gradiometry (SGG) techniques. In this decade of the geopotentials, these missions will serve different purposes with particular spatial and spectral resolutions. This paper introduces the usefulness of these missions, their impacts on the geosciences the measurement principles, and their implementations. These space sensors will provide a significant number of observations during their mission lifespans. Therefore, global gravity field recovery is a computationally demanding task. Several approaches aimed at this goal are discussed, namely the brute-force approach, the space-wise approach, the time-wise approach, and the proposed torus-based semi-analytical approach. The paper addresses the characteristics of each approach and focuses mainly on the torus-based semi-analytical approach, which can be used to derive the gravity field from any geopotential functional. In this approach, the structure of the normal matrix becomes block-diagonal which leads to a powerful and efficient recovery tool through the use of the fast Fourier transform (FFT). Important issues such as downward continuation, interpolation methods, and regularization approaches are also discussed. To demonstrate the feasibility and efficiency of the torus-based semi-analytical approach of gravity field determination in spaceborne gravimetry, disturbing potential data from CHAMP and GRACE and simulated GOCE gravity gradient tensor data are processed. [less ▲]

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See detailSpaceflight-associated changes in immunoglobulin VH gene expression in the amphibian Pleurodeles waltl
Bascove, Matthieu; Huin-Schohn, Cécile UL; Gueguinou, Nathan UL et al

in FASEB Journal (2009), 23(5), 1607-1615

Understanding why the immune system is depressed during spaceflight is of obvious importance for future human deep-space missions, such as the foreseen missions to Mars. However, little is known about the ... [more ▼]

Understanding why the immune system is depressed during spaceflight is of obvious importance for future human deep-space missions, such as the foreseen missions to Mars. However, little is known about the effects of these flights on humoral immunity. We previously immunized adult Pleurodeles waltl (urodele amphibian) onboard the Mir space station and showed that heavy-chain variable (VH) domains of specific IgM antibodies are encoded by genes belonging to the VHII and VHVI families. We have now determined how these animals use their individual VHII and VHVI genes by screening IgM heavy-chain cDNA libraries and by quantifying IgM heavy-chain transcripts encoded by these genes. Results were compared with those obtained using control animals immunized on Earth under the same conditions as onboard Mir. Our experiments revealed an increase in the expression of IgM heavy-chain mRNAs encoded by the VHII and VHVI.C genes and a strong decrease in the expression of IgM heavy-chain mRNAs encoded by the VHVI.A and VHVI.B genes in spaceflight animals. Consequently, different heavy-chain mRNAs are expressed by spaceflight animals, demonstrating that this environment affects the humoral response. These observations may be due to a change in B-cell selection under spaceflight conditions. [less ▲]

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See detailSpaces - A Replication Scheme for Sharing Tagged Files in Hybrid Wireless Networks
Wehling, Ulf; Rothkugel, Steffen UL

in International Conference on Mobile Ubiquitous Computing, Systems, Services and Technologies (UBICOMM 2007) (2007)

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See detailSpaces and Identities
Colas-Blaise, Marion UL; Freyermuth, Sylvie UL; Kmec, Sonja UL et al

in IPSE (Ed.) Doing Identity. Subjektive Appropriations – Institutional Attributions – Socio-cultural Milieus (2011)

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See detailSpaces and Identities in Border Regions. Politics – Media – Subjects
Wille, Christian UL; Reckinger, Rachel UL; Kmec, Sonja UL et al

Book published by transcript (2016)

Spatial and identity research operates with differentiations and relations. These are particularly useful heuristic tools when examining border regions where social and geopolitical demarcations diverge ... [more ▼]

Spatial and identity research operates with differentiations and relations. These are particularly useful heuristic tools when examining border regions where social and geopolitical demarcations diverge. Applying this approach, the authors of this volume investigate spatial and identity constructions in cross-border contexts as they appear in everyday, institutional and media practices. The results are discussed with a keen eye for obliquely aligned spaces and identities and relinked to governmental issues of normalization and subjectivation. The studies base upon empirical surveys conducted in Germany, France, Belgium and Luxembourg. [less ▲]

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See detailSpaces of the Border - a Practice-theoretical Cultural Studies Perspective in Border Studies
Wille, Christian UL

in Europa Regional (2015), 21(1-2), 60-71

This paper examines how practice-theoretical considerations can be linked with those of a spatial-theoretical nature and translated into a heuristic of spatial analysis from a cultural studies perspective ... [more ▼]

This paper examines how practice-theoretical considerations can be linked with those of a spatial-theoretical nature and translated into a heuristic of spatial analysis from a cultural studies perspective. This question focus results from the understanding that space should be regarded as an emergent aspect of the social and that it is still largely insufficiently defined in Border Studies. Drawing on a number of different spatial concepts, the paper first presents an action-theoretical notion of space and reformulates it in a practice-theoretical framework. It constitutes the point of departure for the development of the spaces of the border model with its analytical categories of social practices, practical knowledge as well as physical-material and social-structural aspects. The diversity of connections between these analytical categories have proven to be heuristically particularly useful. [less ▲]

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See detailSpaces – different modes of space in towns
Pauly, Michel UL; Scheutz, Martin

in Fray, Jean-Luc; Pauly, Michel; Pinheiro, Magda (Eds.) et al Urban Spaces and the complexity of Cities (2018)

introduction to the volume stressing the importance of the spatial turn in urban history and the complexity of towns

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See detailSpaces: Approaches and Perspectives of Investigation
Wille, Christian UL; Hesse, Markus UL

in Wille, Christian; Reckinger, Rachel; Kmec, Sonja (Eds.) et al Spaces and Identities in Border Regions. Politics – Media – Subjects (2016)

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See detailSpanish validation of the Sexual Addiction Screening Test.
Castro-Calvo, Jesus; Ballester-Arnal, Rafael; Billieux, Joël UL et al

in Journal of behavioral addictions (2018), 7(3), 584-600

BACKGROUND AND AIMS: Sexual addiction is a pathological behavior characterized by a combination of excessive sexual desire and impaired ability to control it. Its incidence ranges between 1.2% and 32.2 ... [more ▼]

BACKGROUND AND AIMS: Sexual addiction is a pathological behavior characterized by a combination of excessive sexual desire and impaired ability to control it. Its incidence ranges between 1.2% and 32.2%, although this number may vary depending on the screening tool used. This wide variability is largely due to the use of non-validated instruments (e.g., structural validity relying on exploratory analyses, instruments translated without an additional validation process, or instruments validated in another format). To deal with these limitations, this study tested the psychometric properties of the Spanish paper-and-pencil and online versions of the Sexual Addiction Screening Test (SAST). METHODS: A total of 2,528 participants (1,163 males) completed the Spanish version of the SAST, along with other instruments assessing sexual compulsivity (1,585 = paper-and-pencil, 943 = online). RESULTS: The exploratory factor analysis yielded a four-factor structure explaining 57.39% of the variance for the SAST paper-and-pencil version. This factor structure was then verified for the online version through the use of confirmatory factor analysis [chi(2)(264) = 441.59; chi(2)/df = 1.66; RMSEA = 0.02; CFI = 0.94; IFI = 0.94]. This methodology was also used to support measurement invariance (configural, metric, and scalar invariance) according to gender. The reliability of the total score ranged from .82 to .85. Similarly, correlations with related scales were positive and significant (r between .22 and .71). Temporal stability 1 year after the first application was 0.65 (paper-and-pencil format) and 0.60 (online version). CONCLUSION: These results, together with the absence of questionnaires translated into Spanish to assess this construct, justify the use of the SAST in the evaluation of sexual addiction in Spanish-speaking countries. [less ▲]

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See detailEin spannendes Mosaik. Bevölkerungs- und Raumentwicklung in den USA.
Hesse, Markus UL

in Kommune (2001), 19(7), 19-23

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See detailSpanning L² of a nilpotent Lie group by eigenvectors of invariant differential operators
Ludwig, Jean; Molitor-Braun, Carine UL; Scuto, Laurent

in Mathematische Zeitschrift (2008), 260(4), 717-753

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See detailSpannungsfeld Berufsdomäne - Wirkt sich die Tätigkeit in einer Männer- oder Frauendomäne negativ auf das Karriereverhalten von Frauen und Männern aus?
Sturny, Angelika; Krolak-Schwerdt, Sabine UL; Wintermantel, Margret

in Zeitschrift für Sozialmanagement (2005), 3

Anhand von drei empirischen Studien wurde überprüft, welchen Einfluss die Tätigkeit in einer geschlechtsspezifischen Berufsdomäne (z. B. in einer Männer oder Frauendomäne) auf die Wahrnehmung und das ... [more ▼]

Anhand von drei empirischen Studien wurde überprüft, welchen Einfluss die Tätigkeit in einer geschlechtsspezifischen Berufsdomäne (z. B. in einer Männer oder Frauendomäne) auf die Wahrnehmung und das Erleben erwerbstätiger Männer und Frauen ausübt. Mittelpunkt der Untersuchung waren Erwerbstätige, die in einer Berufsdomäne tätig sind, die nicht mit ihrer Geschlechtsrolle übereinstimmt. [less ▲]

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See detailSpannungsfeld Föderalismus - Die Situation der Universitäten in Kanada
Braband, Gangolf UL

Article for general public (2015)

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See detailSpannungskopfschmerzen in der pädiatrischen Versorgung
Schlarb, Angelika UL; Neumann, Katharina

in Pädiatrische praxis (2013)

Detailed reference viewed: 34 (1 UL)