2,355 research outputs found
Improving the Hough Transform gathering process for affine transformations
In this paper, we show that significant wrong evidence can be generated when the Hough Transform (HT) is used to extract arbitrary shapes under rigid transformations. In order to reduce the amount of wrong evidence, we consider two types of constraints. First, we define constraints by considering invariant features. Secondly, we consider constraints defined via gradient direction information. Our results show that these constraints can significantly improve the gathering strategy, leading to identification of the correct parameters. The presented formulation is valid for any rigid transformations represented by affine mappings
DMRG Simulation of the SU(3) AFM Heisenberg Model
We analyze the antiferromagnetic Heisenberg chain by means of
the Density Matrix Renormalization Group (DMRG). The results confirm that the
model is critical and the computation of its central charge and the scaling
dimensions of the first excited states show that the underlying low energy
conformal field theory is the Wess-Zumino-Novikov-Witten
model.Comment: corrections and improvements adde
Non-hermitian topology as a unifying framework for the Andreev versus Majorana states controversy
Zero-energy Andreev levels in hybrid semiconductor-superconductor nanowires mimic all expected Majorana phenomenology, including 2 e2∕ h conductance quantisation, even where band topology predicts trivial phases. This surprising fact has been used to challenge the interpretation of various transport experiments in terms of Majorana zero modes. Here we show that the Andreev versus Majorana controversy is clarified when framed in the language of non-Hermitian topology, the natural description for quantum systems open to the environment. This change of paradigm allows one to understand topological transitions and the emergence of zero modes in more general systems than can be described by band topology. This is achieved by studying exceptional point bifurcations in the complex spectrum of the system’s non-Hermitian Hamiltonian. Within this broader topological classification, Majoranas from both conventional band topology and a large subset of Andreev levels at zero energy are in fact topologically equivalent, which explains why they cannot be distinguishedWe thank J. Cayao for useful discussions in the early stages of this work. Research supported by the Spanish Ministry of Science, Innovation and Universities through Grants PGC2018-097018-B-I00, FIS2015-65706-P, FIS2015-64654-P, FIS2016-80434-P (AEI/FEDER, EU), the FPI programme BES-2016-078122, the Ramón y Cajal programme Grants RYC-2011-09345, RYC-2013-14645, the MarÃa de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), and the European Union’s Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948. We also acknowledge support from CSIC Research Platform on Quantum Technologies PTI-00
Emergence of Bulk CsCl Structure in (CsCl)nCs+ Cluster Ions
The emergence of CsCl bulk structure in (CsCl)nCs+ cluster ions is
investigated using a mixed quantum-mechanical/semiempirical theoretical
approach. We find that rhombic dodecahedral fragments (with bulk CsCl symmetry)
are more stable than rock-salt fragments after the completion of the fifth
rhombic dodecahedral atomic shell. From this size (n=184) on, a new set of
magic numbers should appear in the experimental mass spectra. We also propose
another experimental test for this transition, which explicitely involves the
electronic structure of the cluster. Finally, we perform more detailed
calculations in the size range n=31--33, where recent experimental
investigations have found indications of the presence of rhombic dodecahedral
(CsCl)32Cs+ isomers in the cluster beams.Comment: LaTeX file. 6 pages and 4 pictures. Accepted for publication in Phys.
Rev.
Interplay of couplings between antiferrodistortive, ferroelectric, and strain degrees of freedom in monodomain PbTiO/SrTiO superlattices
We report first-principles calculations on the coupling between epitaxial
strain, polarization, and oxygen octahedra rotations in monodomain
(PbTiO)/(SrTiO) superlattices. We show how the
interplay between (i) the epitaxial strain and (ii) the electrostatic
conditions, can be used to control the orientation of the main axis of the
system. The electrostatic constrains at the interface facilitate the rotation
of the polarization and, as a consequence, we predict large piezoelectric
responses at epitaxial strains smaller than those that would be required
considering only strain effects. In addition, ferroelectric (FE) and
antiferrodistortive (AFD) modes are strongly coupled. Usual steric arguments
cannot explain this coupling and a covalent model is proposed to account for
it. The energy gain due to the FE-AFD coupling decreases with the periodicity
of the superlattice, becoming negligible for .Comment: 5 pages, 4 figure
Au-Cu/SBA(Ti) based catalysts for photocatalytic applications
Comunicación a congresoIn this work, it has been synthesized several Au and Au-Cu alloy photocatalysts supported on two
different mesoporous supports: a non-commercial SBA-15 and a post-synthesis TiO2 modified SBA-15
(TiSBA-15), with which a high dispersion of TiO2 species have been achieved maintaining the SBA-15
structure. In addition, it has also been obtained highly dispersed Au nanoparticles confined in SBA-15
pore channels, as can be observed in Figure 1. The photocatalysts have been preliminary tested in the
preferential CO oxidation in a H2-rich stream (CO-PROX) at room temperature and atmospheric pressure
under simulated solar light irradiation. In spite of the very low gold and copper loading (1.5 wt% and
0.5wt% respectively), the catalysts resulted active and selective in the low temperature photo-CO-PROX.Universidad de Málaga, Campus de Excelencia Internacional AndalucÃa Tec
Geometric magic numbers of sodium clusters: Interpretation of the melting behaviour
Putative global minima of sodium clusters with up to 380 atoms have been
located for two model interatomic potentials. Structures based upon the Mackay
icosahedra predominate for both potentials, and the magic numbers for the
Murrell-Mottram model show excellent agreement with the sizes at which maxima
in the latent heat and entropy change at melting have been found in experiment.Comment: 4 pages, 2 figure
Hypodynamia Alters Bone Quality and Trabecular Microarchitecture
Disuse induces a rapid bone loss in humans and animals; hypodynamia/sedentarity is now recognized as a risk factor for osteoporosis. Hypodynamia also decreases bone mass but its effects are largely unknown and only few animal models have been described. Hypodynamic chicken is recognized as a suitable model of bone loss but the effects on the quality have not been fully explored. We have used ten chickens bred in a large enclosure (FREE group); ten others were confined in small cages with little space to move around (HYPO group). They were sacrificed at 53 days and femurs were evaluated by microcomputed tomography (microCT) and nanoindentation. Sections (4 µm thick) were analyzed by Fourier Transform InfraRed Microspectroscopy (FTIR) to see the effects on mineralization and collagen and quantitative backscattered electron imaging (qBEI) to image the mineral of the bone matrix. Trabecular bone volume and microarchitecture were significantly altered in the HYPO group. FTIR showed a significant reduction of the mineral-to-matrix ratio in the HYPO group associated with an increase in the carbonate content and an increase in crystallinity (calculated as the area ratio of subbands located at 1020 and 1030 cm(-1)) indicating a poor quality of the mineral. Collagen maturity (calculated as the area ratio of subbands located at 1660 and 1690 cm(-1)) was significantly reduced in the HYPO group. Reduced biomechanical properties were observed at the tissue level. Confined chicken represents a new model for the study of hypodynamia because bone changes are not created by a surgical lesion or a traumatic method. Animals have a reduced bone mass and present with an altered bone matrix quality which is less mineralized and whose collagen contains less crosslinks than in control chicken
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