Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailStability of a spin-triplet nematic state near to a quantum critical point
Hannappel, Gregor; Pedder, Christopher UL; Kruger, Frank et al

in Physical Review. B: Condensed Matter and Materials Physics (2016), 93(23), 5105

We analyze a model of itinerant electrons interacting through a quadrupole density-density repulsion in three dimensions. At the mean field level, the interaction drives a continuous Pomeranchuk ... [more ▼]

We analyze a model of itinerant electrons interacting through a quadrupole density-density repulsion in three dimensions. At the mean field level, the interaction drives a continuous Pomeranchuk instability towards d-wave, spin-triplet nematic order, which simultaneously breaks the SU(2) spin-rotation and spatial rotational symmetries. This order results in spin antisymmetric, elliptical deformations of the Fermi surfaces of up and down spins. We show that the effects of quantum fluctuations are similar to those in metallic ferromagnets, rendering the nematic transition first-order at low temperatures. Using the fermionic quantum order-by-disorder approach to self-consistently calculate fluctuations around possible modulated states, we show that the first-order transition is pre-empted by the formation of a nematic state that is intertwined with a helical modulation in spin space. Such a state is closely related to d-wave bond density wave order in square-lattice systems. Moreover, we show that it may coexist with a modulated, p-wave superconducting state. [less ▲]

Detailed reference viewed: 144 (9 UL)
Peer Reviewed
See detailThe stability of academic self-concept profiles – a latent transition analysis
Franzen, Patrick UL; Arens, A. Katrin; Niepel, Christoph UL

Poster (2019, November 06)

Detailed reference viewed: 76 (6 UL)
Full Text
Peer Reviewed
See detailThe Stability of Flood Defences on Permeable Soils: The London Avenue Canal Failures in New Orleans
Kanning, W; Van Baars, Stefan UL; Vrijling, J.K.

in Sixth International Conference on Case Histories in Geotechnical Engineering (2008, August)

The two failures of the London Avenue Canal floodwalls contributed largely to the flooding of central New Orleans due to hurricane Katrina. In this paper, both failures are analyzed and compared to each ... [more ▼]

The two failures of the London Avenue Canal floodwalls contributed largely to the flooding of central New Orleans due to hurricane Katrina. In this paper, both failures are analyzed and compared to each other since the flood defenses are both located on permeable soils. Photo’s observation and calculations are used for the analysis. Both failures are caused by the permeable sand layer below the floodwall that allowed high pore water pressures to develop below the floodwall. However, the south breach seems to be caused by the piping failure mechanism and the north breach by loss of stability. At the South breach, the impermeable top layer was thicker than at the North breach, increasing the stability. The North beach was less vulnerable for piping and the lack of stability caused a large breach. The London Avenue Canal failures are a clear yet tragic example of the failure of flood defenses on permeable soils. The failures show that multiple failure mechanism may occur and since there are many flood defenses on permeable soils world wide, the lessons from Katrina can be used to prevent future catastrophes. [less ▲]

Detailed reference viewed: 99 (0 UL)
Full Text
Peer Reviewed
See detailStability of functionalized platform molecules on Au(111)
Jasper-Tönnies, Torben; Poltavskyi, Igor UL; Ulrich, Sandra et al

in Journal of Chemical Physics (2018), 149

Trioxatriangulenium (TOTA) platform molecules were functionalized with methyl, ethyl, ethynyl, propynyl, and hydrogen and sublimated onto Au(111) surfaces. Low-temperature scanning tunneling microscopy ... [more ▼]

Trioxatriangulenium (TOTA) platform molecules were functionalized with methyl, ethyl, ethynyl, propynyl, and hydrogen and sublimated onto Au(111) surfaces. Low-temperature scanning tunneling microscopy data reveal that >99% of ethyl-TOTA and methyl-TOTA remain intact, whereas 60% of H-TOTA and >99% of propynyl-TOTA and ethynyl-TOTA decompose. The observed tendency toward fragmentation on Au(111) is opposite to the sequence of gas-phase stabilities of the molecules. Although Au(111) is the noblest of all metal surfaces, the binding energies of the decomposition products to Au(111) destabilize the functionalized platforms by 2 to 3.9 eV (190–370 kJ/mol) and even render some of them unstable as revealed by density functional theory calculations. Van der Waals forces are important, as they drive the adsorption of the platform molecules. [less ▲]

Detailed reference viewed: 135 (3 UL)
Full Text
Peer Reviewed
See detailStability of Heart Rate Variability Indices Reflecting Parasympathetic Activity
Bertsch, K.; Hagemann, D.; Naumann, E. et al

in Psychophysiology (2012), 49(5), 672-682

Detailed reference viewed: 145 (1 UL)
Full Text
Peer Reviewed
See detailStability of stochastic differential equations in manifolds
Arnaudon, Marc; Thalmaier, Anton UL

in Séminaire de Probabilités, XXXII (1998)

Detailed reference viewed: 214 (8 UL)
Peer Reviewed
See detailStability or stagnation, or why the school is not the way reformers would like.
Tröhler, Daniel UL

in Encounters on Education = Encuentros sobre Educación = Rencontres sur l’Éducation (2008), 9

Detailed reference viewed: 88 (0 UL)
Full Text
Peer Reviewed
See detailStabilization of a Class of Nonlinear Affine Fractional-Order Systems
Ndoye, Ibrahima UL; Zasadzinski, Michel; Darouach, Mohamed et al

in 14th International IEEE/IFAC Conference Methods and Models in Automation and Robotics, MMAR’09, Poland, June 24-26, 2009 (2009)

This paper deals with the asymptotical stabilization of nonlinear affine fractional-order systems. Two static control laws are considered: state and output feedbacks. The asymptotic stability is proven ... [more ▼]

This paper deals with the asymptotical stabilization of nonlinear affine fractional-order systems. Two static control laws are considered: state and output feedbacks. The asymptotic stability is proven using a proposed generalization of the Gronwall-Bellman lemma. [less ▲]

Detailed reference viewed: 105 (1 UL)
Full Text
Peer Reviewed
See detailStabilization of a Class of Nonlinear Affine Fractional-Order Systems using Generalizations of Bellman-Gronwall Lemma
Ndoye, Ibrahima UL; Zasadzinski, Michel; Radhy, Nour-Eddine et al

in 17th IEEE Mediterranean Conference on Control & Automation MED'09, Thessaloniki, Greece, 2009 (2009)

This paper presents a result of stabilization of nonlinear affine fractional-order systems using generalizations of Gronwall-Bellman lemma. Two case are treated: the nonlinear and the linear state ... [more ▼]

This paper presents a result of stabilization of nonlinear affine fractional-order systems using generalizations of Gronwall-Bellman lemma. Two case are treated: the nonlinear and the linear state feedback stabilization. [less ▲]

Detailed reference viewed: 96 (1 UL)
Full Text
Peer Reviewed
See detailStabilization of Singular Fractional-Order Systems : An LMI Approach
Ndoye, Ibrahima UL; Zasadzinski, Michel; Radhy, Nour-Eddine et al

in 18th IEEE Mediterranean Conference on Control & Automation, Morocco, June 23-25, 2010 (2010)

This paper presents the asymptotical stabilization problem of linear singular fractional-order systems. The results are obtained in terms of linear matrix inequalities, which are derived using the ... [more ▼]

This paper presents the asymptotical stabilization problem of linear singular fractional-order systems. The results are obtained in terms of linear matrix inequalities, which are derived using the decomposition on the matrices of the original system. An illustrative example is provided to illustrate the proposed [less ▲]

Detailed reference viewed: 145 (3 UL)
Full Text
Peer Reviewed
See detailStabilization with the Dynamic Cervical Implant: a novel treatment approach following cervical discectomy and decompression.
Matge, Guy; Berthold, Christophe; Gunness, Vimal Raj Nitish et al

in Journal of neurosurgery. Spine (2015), 22(3), 237-45

OBJECT: Although cervical total disc replacement (TDR) has shown equivalence or superiority to anterior cervical discectomy and fusion (ACDF), potential problems include nonphysiological motion ... [more ▼]

OBJECT: Although cervical total disc replacement (TDR) has shown equivalence or superiority to anterior cervical discectomy and fusion (ACDF), potential problems include nonphysiological motion (hypermobility), accelerated degeneration of the facet joints, particulate wear, and compromise of the mechanical integrity of the endplate during device fixation. Dynamic cervical stabilization is a novel motion-preserving concept that facilitates controlled, limited flexion and extension, but prevents axial rotation and lateral bending, thereby reducing motion across the facet joints. Shock absorption of the Dynamic Cervical Implant (DCI) device is intended to protect adjacent levels from accelerated degeneration. METHODS: The authors conducted a prospective evaluation of 53 consecutive patients who underwent DCI stabilization for the treatment of 1-level (n = 42), 2-level (n = 9), and 3-level (n = 2) cervical disc disease with radiculopathy or myelopathy. Forty-seven patients (89%) completed all clinical and radiographic outcomes at a minimum of 24 months. Clinical outcomes consisted of Neck Disability Index (NDI) and visual analog scale (VAS) scores, neurological function at baseline and at latest follow-up, as well as patient satisfaction. Flexion-extension radiography was evaluated for device motion, implant migration, subsidence, and heterotopic ossification. Cervical sagittal alignment (Cobb angle), functional spinal unit (FSU) angle, and range of motion (ROM) at index and adjacent levels were evaluated with WEB 1000 software. RESULTS: The NDI score, VAS neck and arm pain scores, and neurological deficits were significantly reduced at each postoperative time point compared with baseline (p < 0.0001). At 24 months postoperatively, 91% of patients were very satisfied and 9% somewhat satisfied, while 89% would definitely and 11% would probably elect to have the same surgery again. In 47 patients with 58 operated levels, the radiographic assessment showed good motion (5 degrees -12 degrees ) of the device in 57%, reduced motion (2 degrees -5 degrees ) in 34.5%, and little motion (0-2 degrees ) in 8.5%. The Cobb and FSU angles improved, showing a clear tendency for lordosis with the DCI. Motion greater than 2 degrees of the treated segment could be preserved in 91.5%, while 8.5% had a near segmental fusion. Mean ROM at index levels demonstrated satisfying motion preservation with DCI. Mean ROM at upper and lower adjacent levels showed maintenance of adjacent-level kinematics. Heterotopic ossification, including 20% minor and 15% major, had no direct impact on clinical results. There were 2 endplate subsidences detected with an increased segmental lordosis. One asymptomatic anterior device migration required reoperation. Three patients underwent a secondary surgery in another segment during follow-up, twice for a new disc herniation and once for an adjacent degeneration. There was no posterior migration and no device breakage. CONCLUSIONS: Preliminary results indicate that the DCI implanted using a proper surgical technique is safe and facilitates excellent clinical outcomes, maintains index-and adjacent-level ROM in the majority of cases, improves sagittal alignment, and may be suitable for patients with facet arthrosis who would otherwise not be candidates for cervical TDR. Shock absorption together with maintained motion in the DCI may protect adjacent levels from early degeneration in longer follow-up. [less ▲]

Detailed reference viewed: 93 (3 UL)
Full Text
Peer Reviewed
See detailStable 3D extended finite elements with higher order enrichment for accurate non planar fracture
Agathos, Konstantinos; Chatzi, Eleni; Bordas, Stéphane UL

in Computer Methods in Applied Mechanics & Engineering (2015)

We present an extended finite element method (XFEM) for 3D nonplanar linear elastic fracture. The new approach not only provides optimal convergence using geometrical enrichment but also enables to ... [more ▼]

We present an extended finite element method (XFEM) for 3D nonplanar linear elastic fracture. The new approach not only provides optimal convergence using geometrical enrichment but also enables to contain the increase in conditioning number characteristic of enriched finite element formulations: the number of iterations to convergence of the conjugate gradient solver scales similarly to and converges faster than the topologically-enriched version of the standard XFEM. This has two advantages: (1) the residual can be driven to zero to machine precision for at least 50% fewer iterations than the standard version of XFEM; (2) additional enrichment functions can be added without significant deterioration of the conditioning. Numerical examples also show that our new approach is up to 40% more accurate in terms of stress intensity factors, than the standard XFEM. [less ▲]

Detailed reference viewed: 206 (5 UL)
Full Text
Peer Reviewed
See detailStable 3D extended finite elements with higher order enrichment for accurate non planar fracture
Agathos, Konstantinos UL; Chatzi, Eleni; Bordas, Stéphane UL

in Computer Methods in Applied Mechanics & Engineering (2016), 306

An extended finite element method (XFEM) for three dimensional (3D) non-planar linear elastic fracture is introduced, which provides optimal convergence through the use of enrichment in a fixed area ... [more ▼]

An extended finite element method (XFEM) for three dimensional (3D) non-planar linear elastic fracture is introduced, which provides optimal convergence through the use of enrichment in a fixed area around the crack front, while also improving the conditioning of the resulting system matrices. This is achieved by fusing a novel form of enrichment with existing blending techniques. Further, the adoption of higher order terms of theWilliams expansion is also considered and the effects in the accuracy and conditioning of the method are studied. Moreover, some problems regarding the evaluation of stress intensity factors (SIFs) and element partitioning are dealt with. The accuracy and convergence properties of the method as well as the conditioning of the resulting stiffness matrices are investigated through the use of appropriate benchmark problems. It is shown that the proposed approach provides increased accuracy while requiring, for all cases considered, a reduced number of iterations for the solution of the resulting systems of equations. The positive impact of geometrical enrichment is further demonstrated in the accuracy of the computed SIFs where, for the examined cases, an improvement of up to 40% is achieved. [less ▲]

Detailed reference viewed: 84 (2 UL)
Full Text
Peer Reviewed
See detailStable 3D XFEM/vector-level sets for non-planar 3D crack propagation and comparison of enrichment schemes
Agathos, Konstantinos UL; Ventura, Giulio; Chatzi, Eleni et al

in International Journal for Numerical Methods in Engineering (2017)

We present a three-dimensional (3D) vector level set method coupled to a recently developed stable extended finite element method (XFEM). We further investigate a new enrichment approach for XFEM adopting ... [more ▼]

We present a three-dimensional (3D) vector level set method coupled to a recently developed stable extended finite element method (XFEM). We further investigate a new enrichment approach for XFEM adopting discontinuous linear enrichment functions in place of the asymptotic near-tip functions. Through the vector level set method, level set values for propagating cracks are obtained via simple geometrical operations, eliminating the need for solution of differential evolution equations. The first XFEM variant ensures optimal convergence rates by means of geometrical enrichment, i.e., the use of enriched elements in a fixed volume around the crack front, without giving rise to conditioning problems. The linear enrichment approach significantly simplifies implementation and reduces the computational cost associated with numerical integration. The two dicretization schemes are tested for different benchmark problems, and their combination to the vector level set method is verified for non-planar crack propagation problems. [less ▲]

Detailed reference viewed: 320 (28 UL)
Full Text
Peer Reviewed
See detailStable and variable characteristics of the time perspective in humans.
Klapproth, Florian UL

in KronoScope (2011), 11

Today, many definitions and measures of the time perspective exist in parallel, with more or less common meaning. This article presents the most prominent conceptualizations of time perspective, which ... [more ▼]

Today, many definitions and measures of the time perspective exist in parallel, with more or less common meaning. This article presents the most prominent conceptualizations of time perspective, which differ not only in the way of assessing the concept, but also in their assumed variability. The author then reports on an experiment that investigated the relationship between two different conceptualizations of the time perspective, and that examined the role emotions play in the variable part of the time perspective. Finally, conclusions are drawn with respect to the experimental results and the conceptualizations of the time perspective as expressed in the Introduction. [less ▲]

Detailed reference viewed: 105 (1 UL)
Peer Reviewed
See detailStable convergence of generalized $L^2$ stochastic integrals and the principle of conditioning
Peccati, Giovanni UL; Taqqu, Murad S.

in Electronic Journal of Probability (2007), 12

Detailed reference viewed: 70 (0 UL)
Peer Reviewed
See detailStable convergence of multiple Wiener-It\^o integrals
Peccati, Giovanni UL; Taqqu, Murad S.

in Journal of Theoretical Probability (2008), 21(3), 527--570

Detailed reference viewed: 144 (0 UL)
Full Text
Peer Reviewed
See detailStable distributions for alternative UCITS
Fadiga, Ismael; Schiltz, Jang UL

Scientific Conference (2016, July 16)

Detailed reference viewed: 223 (4 UL)
Full Text
Peer Reviewed
See detailStable extended finite element method: Convergence, Accuracy, Properties and Diffpack implementation
Paladim, Daniel; Natarajan, Sundarajan; Bordas, Stéphane UL et al

in International Conference on Extended Finite Element Methods - XFEM 2013, September 11 – 13, 2013, Lyon, France (2013)

Problems involving singularities and moving boundaries, especially when they involve discontinuities, create difficulties for the finite element method. On another, albeit related, front, two diametrally ... [more ▼]

Problems involving singularities and moving boundaries, especially when they involve discontinuities, create difficulties for the finite element method. On another, albeit related, front, two diametrally opposed approaches are attempting to simplify the CAD to Analysis pipeline: isogeometric methods on the one hand [1] aim at coupling the geometry and field approximations, whilst implicit boundary definition-based methods attempt to decouple them [3,4,5]. We examine in this paper one instance of the latter approach, and rely on partition of unity enrichment of the field variable to capture discontinuities along material interface or domain boundaries. We study in particular the stable generalized finite element method of Babuˇka and Banerjee [6] for higher order approximations in two and three dimensions and propose a generic implementation within the C++ library Diffpack from inuTech GmbH [7]. In a companion paper, the implementation of enrichment within Diffpack is presented in more detail. We will present results obtained with our 3D implementation of partition of unity enrichment within Diffpack. This implementation represents the interfaces through level-sets and palliates blending problems using various approaches. We study here the stabilisation approach proposed in [6] in more detail and pay particular attention to the global convergence rate of the approach and to the stability and the local flux converence close to the interfaces. [less ▲]

Detailed reference viewed: 338 (1 UL)
Full Text
See detailThe stable GFEM. Convergence, accuracy and Diffpack implementation
Alves Paladim, Daniel; Natarajan, Sundarajan; Bordas, Stéphane UL et al

Presentation (2015, May 12)

Detailed reference viewed: 75 (1 UL)