Search results for "symmetry"
showing 10 items of 3576 documents
Sviluppo e riduzione asimmetrica del cervello umano.
2011
On the history of torsional stress concentrations in shafts: From electrical analogies to numerical methods
2014
This article proposes a retrospective on experimental and numerical methods developed throughout the past century to solve the torsion problem in shafts, with particular emphasis on the determination of shear stress concentration factors in discontinuities of typical use in shaft design. This article, in particular, presents the theory and related solutions distinguishing between two classes of geometries: shafts with constant cross section and axisymmetric shafts with variable diameter. Emphasis is given to approaches based on physical analog methods and, in particular, those based on electrical analogies proposed since about 1925. Experimental methods based on structural physical models …
Ice deformed in compression and simple shear: control of temperature and initial fabric
2012
AbstractLayered and polycrystalline ice was experimentally deformed in general shear involving axial compression (strain magnitude 0.5-17%) and simple shear (strain magnitude γ = 0.1-1.4). As the temperature is increased from -20°C to -2°C, there is at least a twofold enhancement in octahedral shear strain rate, which coincides with the onset of extensive dynamic recrystallization and a change in grain-size distribution at -15°C. Between -150C and -10°C the c-axis preferred orientation rapidly evolves with the initiation of two-maxima fabrics in shear zones. From -10°C to -2°C there is progressive evolution of a final c-axis pattern that is asymmetric with respect to the direction of shorte…
ββ2ν decay in 48Ca
2001
[EN] A schematic study of the bb2n decay of 48Ca is made in a shell-model approach. The emphasis is especially put on the role of the spin-orbit potential in relation with the contribution of other terms in the strong interaction. This is discussed with a particular attention to the behavior of these ones under the SU(4) symmetry. Different methods in calculating the transition amplitude are also looked at with the aim to determine their reliability and, eventually, why they do not work. Further aspects relative to the failure of the operator expansion method to reproduce the results of more elaborate calculations are examined.
Modeling the remnants of core-collapse supernovae from luminous blue variable stars
2021
LBVs are massive evolved stars that suffer sporadic and violent mass-loss events. They have been proposed as the progenitors of some core-collapse SNe, but this idea is still debated due to the lack of direct evidence. Since SNRs can carry in their morphology the fingerprints of the progenitor stars as well as of the inhomogeneous CSM sculpted by the progenitors, the study of SNRs from LBVs could help to place core-collapse SNe in context with the evolution of massive stars. We investigate the physical, chemical and morphological properties of the remnants of SNe originating from LBVs, in order to search for signatures, revealing the nature of the progenitors, in the ejecta distribution and…
Long-term FRII jet evolution: Clues from three-dimensional simulations
2018
We present a long-term numerical three-dimensional simulation of a relativistic outflow designed to be compared with previous results from axisymmetric, two-dimensional simulations, with existing analytical models and state-of-art observations. We follow the jet evolution from 1~kpc to 200~kpc, using a relativistic gas equation of state and a galactic profile for the ambient medium. We also show results from smaller scale simulations aimed to test convergence and different three-dimensional effects. We conclude that jet propagation can be faster than expected from axisymmetric simulations, covering tens of kiloparsecs in a few million years, until the dentist drill effect produced by the gr…
The classical two-dimensional Heisenberg model revisited: An $SU(2)$-symmetric tensor network study
2021
The classical Heisenberg model in two spatial dimensions constitutes one of the most paradigmatic spin models, taking an important role in statistical and condensed matter physics to understand magnetism. Still, despite its paradigmatic character and the widely accepted ban of a (continuous) spontaneous symmetry breaking, controversies remain whether the model exhibits a phase transition at finite temperature. Importantly, the model can be interpreted as a lattice discretization of the $O(3)$ non-linear sigma model in $1+1$ dimensions, one of the simplest quantum field theories encompassing crucial features of celebrated higher-dimensional ones (like quantum chromodynamics in $3+1$ dimensio…
A fast recursive algorithm to compute local axial moments
2001
The paper describes a fast algorithm to compute local axial moments used in the algorithm of discrete symmetry transform (DST). The basic idea is grounded on fast recursive implementation of respective linear filters by using the so-called primitive kernel functions since the moment computation can be performed in the framework of linear filtering. The main result is that the computation of the local axial moments is independent of the kernel size, i.e. of the order O(1) per data point (pixel). This result is of relevance whenever the DST is used to face with real time computer vision problems. The experimental results confirm the time complexity predicted by the theory.
Luminescence of ODC(II) in quartz and cristobalite glasses
2022
Abstract The results of the optical spectroscopy of twofold coordinated silicon centers – ODC(II) in quartz and cristobalite glasses are presented. The luminescence and excitation spectra attributed to different local symmetry of ODC(II) were investigated under synchrotron excitation in the VUV region. The observed differences in the luminescence and excitation spectra of ODC(II) are caused by the environment and, therefore, short-range order in the samples.
Photoelectron lifetime determination of Ag(1 1 1) films at the Fermi surface
2001
The electronic properties of 10 monolayers Ag(111) films deposited onto Si(111)-7 x 7 substrates at room temperature have been studied by scanning the photoelectron intensity at the Fermi level in different symmetry directions. The main features observed in these profiles correspond to Lorentzian-like peaks produced by the pass of the sp band through the Fermi level. A simple model has been developed, which connects the photoemission peak linewidth with the lifetime of photoelectrons excited from the Fermi level. The obtained inverse photoelectron lifetime values have been found to be in excellent agreement with the typical values of the Ag single crystals. These results support the fact th…