4,035 research outputs found
Ab initio study of magnesium alanate, Mg(AlH4)2
Magnesium alanate Mg(AlH4)2 has recently raised interest as a potential
material for hydrogen storage. We apply ab initio calculations to characterize
structural, electronic and energetic properties of Mg(AlH4)2. Density
functional theory calculations within the generalized gradient approximation
(GGA) are used to optimize the geometry and obtain the electronic structure.
The latter is also studied by quasi-particle calculations at the GW level.
Mg(AlH4)2 is a large band gap insulator with a fundamental band gap of 6.5 eV.
The hydrogen atoms are bonded in AlH4 complexes, whose states dominate both the
valence and the conduction bands. On the basis of total energies, the formation
enthalpy of Mg(AlH4)2 with respect to bulk magnesium, bulk aluminum and
hydrogen gas is 0.17 eV/H2 (at T = 0). Including corrections due to the zero
point vibrations of the hydrogen atoms this number decreases to 0.10 eV/H2. The
enthalpy of the dehydrogenation reaction Mg(AlH4)2 -> MgH2 +2Al+3H2(g) is close
to zero, which impairs the potential usefulness of magnesium alanate as a
hydrogen storage material.Comment: 5 pages, 3 figure
Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania)
The present study was performed during a stay at the University of Münster financed by a grant awarded by the German Academic Exchange Service (DAAD) in 2014. Data used in the present study were provided by the National Institute for Earth Physics (Romania) and processed within the National Data Centre in Magurele. Seismic Analysis Code (SAC) (Goldstein and Snoke, 2005) and GMT (Wessel et al., 2013) codes were used. We thank the College of Physical Sciences (University of Aberdeen) and the Santander Mobility Award for providing travel grant to LDS to complete this manuscript. We are grateful as well to the anonymous reviewer for his useful remarks which helped us to improve the paper.Peer reviewedPostprin
Strong solidity of group factors from lattices in SO(n,1) and SU(n,1)
We show that the group factors of ICC lattices in either SO(n,1) or SU(n,1),
n \geq 2, are strongly solid in the sense of Ozawa and Popa. This strengthens a
result of Ozawa and Popa showing that these factors do not have Cartan
subalgebras
Fashion Object Detection for Tops & Bottoms
Fashion is one of the largest world's industries and computer vision
techniques have been becoming more popular in recent years, in particular, for
tasks such as object detection and apparel segmentation. Even with the rapid
growth in computer vision solutions, specifically for the fashion industry,
many problems are far for being resolved. Therefore, not at all times,
adjusting out-of-the-box pre-trained computer vision models will provide the
desired solution. In the present paper is proposed a pipeline that takes a
noisy image with a person and specifically detects the regions with garments
that are bottoms or tops. Our solution implements models that are capable of
finding human parts in an image e.g. full-body vs half-body, or no human is
found. Then, other models knowing that there's a human and its composition
(e.g. not always we have a full-body) finds the bounding boxes/regions of the
image that very likely correspond to a bottom or a top. For the creation of
bounding boxes/regions task, a benchmark dataset was specifically prepared. The
results show that the Mask RCNN solution is robust, and generalized enough to
be used and scalable in unseen apparel/fashion data
Exotic complex Hadamard matrices, and their equivalence
In this paper we use a design theoretical approach to construct new,
previously unknown complex Hadamard matrices. Our methods generalize and extend
the earlier results of de la Harpe--Jones and Munemasa--Watatani and offer a
theoretical explanation for the existence of some sporadic examples of complex
Hadamard matrices in the existing literature. As it is increasingly difficult
to distinguish inequivalent matrices from each other, we propose a new
invariant, the fingerprint of complex Hadamard matrices. As a side result, we
refute a conjecture of Koukouvinos et al. on (n-8)x(n-8) minors of real
Hadamard matrices.Comment: 10 pages. To appear in Cryptography and Communications: Discrete
Structures, Boolean Functions and Sequence
The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior
We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described
Arithmetic core generation using bit heaps
International audienceA bit heap is a data structure that holds the unevaluated sum of an arbitrary number of bits, each weighted by some power of two. Most advanced arithmetic cores can be viewed as involving one or several bit heaps. We claim here that this point of view leads to better global optimization at the algebraic level, at the circuit level, and in terms of software engineering. To demonstrate it, a generic software framework is introduced for the definition and optimization of bit heaps. This framework, targeting DSP-enabled FPGAs, is developed within the open-source FloPoCo arithmetic core generator. Its versatility is demonstrated on several examples: multipliers, complex multipliers, polynomials, and discrete cosine transform
Observational consequences of the Standard Model Higgs inflation variants
We consider the possibility to observationally differentiate the Standard
Model (SM) Higgs driven inflation with non-minimal couplingto gravity from
other variants of SM Higgs inflation based on the scalar field theories with
non-canonical kinetic term such as Galileon-like kinetic term and kinetic term
with non-minimal derivative coupling to the Einstein tensor. In order to ensure
consistent results, we study the SM Higgs inflation variants by using the same
method, computing the full dynamics of the background and perturbations of the
Higgs field during inflation at quantum level. Assuming that all the SM Higgs
inflation variants are consistent theories, we use the MCMC technique to derive
constraints on the inflationnoary parameters and the Higgs boson mass from
their fit to WMAP7+SN+BAO data set. We conclude that a combination of a Higgs
mass measurement by the LHC and accurate determination by the PLANCK satellite
of the spectral index of curvature perturbations and tensor-to-scalar ratio
will enable to distinguish among these models. We also show that the
consistency relations of the SM Higgs inflation variants are distinct enough to
differentiate the models.Comment: 22 pages, 4 figure
- …