67 research outputs found
Indications for sharp continuous phase transitions at finite temperatures connected with the apparent metal-insulator transition in two-dimensional disordered systems
In a recent experiment, Lai et al. [Phys. Rev. B 75, 033314 (2007)] studied
the apparent metal-insulator transition (MIT) of a Si quantum well structure
tuning the charge carrier concentration . They observed linear temperature
dependences of the conductivity around the Fermi temperature and
found that the corresponding extrapolation exhibits a
sharp bend just at the MIT. Here, reconsidering the data published by Lai et
al., it is shown that this sharp bend is related to a peculiarity of
clearly detectable in the whole range up to 4 K, the
highest measuring temperature in that work. Since this peculiarity seems not to
be smoothed out with increasing it may indicate a sharp continuous phase
transition between the regions of apparent metallic and activated conduction to
be present at finite temperature. Hints from the literature of such a behavior
are discussed. Finally, a scaling analysis illuminates similarities to previous
experiments and provides understanding of the shape of the peculiarity and of
sharp peaks found in .Comment: Revised version (quantitative determination of exponent beta added),
accepted for publication by Physical Review B. Revtex, 10 pages, 9 figure
Removing pose from face images
This paper proposes a novel approach to pose removal from face images based on the inherent symmetry that is present in faces. In order for face recognition systems and expression classification systems to operate optimally, subjects must look directly into the camera. The removal of pose from face images after their capture removes this restriction. To obtain a pose-removed face image, the frequency components at each position of the face image, obtained through a wavelet transformation, are examined. A cost function based on the symmetry of this wavelet transformed face image is minimized to achieve pose removal.Experimental results are presented that demonstrate that the proposed algorithm improves upon existing techniques in the literature
Continuous symmetry of C60 fullerene and its derivatives
Conventionally, the Ih symmetry of fullerene C60 is accepted which is
supported by numerous calculations. However, this conclusion results from the
consideration of the molecule electron system, of its odd electrons in
particular, in a close-shell approximation without taking the electron spin
into account. Passing to the open-shell approximation has lead to both the
energy and the symmetry lowering up to Ci. Seemingly contradicting to a
high-symmetry pattern of experimental recording, particularly concerning the
molecule electronic spectra, the finding is considered in the current paper
from the continuous symmetry viewpoint. Exploiting both continuous symmetry
measure and continuous symmetry content, was shown that formal Ci symmetry of
the molecule is by 99.99% Ih. A similar continuous symmetry analysis of the
fullerene monoderivatives gives a reasonable explanation of a large variety of
their optical spectra patterns within the framework of the same C1 formal
symmetry exhibiting a strong stability of the C60 skeleton.Comment: 11 pages. 5 figures. 6 table
Step-Wise Computational Synthesis of Fullerene C60 derivatives. 1.Fluorinated Fullerenes C60F2k
The reactions of fullerene C60 with atomic fluorine have been studied by
unrestricted broken spin-symmetry Hartree-Fock (UBS HF) approach implemented in
semiempirical codes based on AM1 technique. The calculations were focused on a
sequential addition of fluorine atom to the fullerene cage following indication
of the cage atom highest chemical susceptibility that is calculated at each
step. The effectively-non-paired-electron concept of the fullerene atoms
chemical susceptibility lays the foundation of the suggested computational
synthesis. The obtained results are analyzed from energetic, symmetry, and the
composition abundance viewpoints. A good fitting of the data to experimental
findings proves a creative role of the suggested synthesis methodology.Comment: 33 pages, 11 figures, 2 tables, 2 chart
Avalanche effect in Si heavily irradiated detectors: Physical model and perspectives for application
The model explaining an enhanced collected charge in detectors irradiated to 10^1^5-10^1^6n_e_q/cm^2 is developed. This effect was first revealed in heavily irradiated n-on-p detectors operated at high bias voltage ranging from 900 to 1700V. The model is based on the fundamental effect of carrier avalanche multiplication in the space charge region and in our case is extended with a consideration of p-n junctions with a high concentration of the deep levels. It is shown that the efficient trapping of free carriers from the bulk generation current to the deep levels of radiation induced defects leads to the stabilization of the irradiated detector operation in avalanche multiplication mode due to the reduction of the electric field at the junction. The charge collection efficiency and the detector reverse current dependences on the applied bias have been numerically simulated in this study and they well correlate to the recent experimental results of CERN RD50 collaboration. The developed model of enhanced collected charge predicts a controllable operation of heavily irradiated detectors that is promising for the detector application in the upcoming experiments in a high luminosity collider
Quality enhancement of reconstructed 3D models using coplanarity and constraints
We present a process to improve the structural quality of automatically acquired architectural 3D models. Common architectural features like orientations of walls are exploited. The location of these features is extracted by using a probabilistic technique (RANSAC). The relationships among the features are automatically obtained by labelling them using a semantic net of an architectural scene. An evolutionary algorithm is used to optimise the orientations of the planes. Small irregularities in the planes are removed by projecting the triangulation vertices onto the planes. Planes in the resulting model are aligned to each other. The technique produces models with improved appearance. It is validated on synthetic and real data
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