14,641 research outputs found
Effective models of two-flavor QCD: from small towards large
We study effective models of chiral fields and Polyakov loop expected to
describe the dynamics responsible for the phase structure of two-flavor QCD. We
consider chiral sector described either using linear sigma model or
Nambu-Jona-Lasinio model and study how these models, on the mean-field level
when coupled with the Polyakov loop, behave as a function of increasing bare
quark (or pion) mass. We find qualitatively similar behaviors for the cases of
linear sigma model and Nambu-Jona-Lasinio model and, relating to existing
lattice data, show that one cannot conclusively decide which or the two
approximate symmetries drives the phase transitions near the physical point
Damage coefficients in low resistivity silicon
Electron and proton damage coefficients are determined for low resistivity silicon based on minority-carrier lifetime measurements on bulk material and diffusion length measurements on solar cells. Irradiations were performed on bulk samples and cells fabricated from four types of boron-doped 0.1 ohm-cm silicon ingots, including the four possible combinations of high and low oxygen content and high and low dislocation density. Measurements were also made on higher resistivity boron-doped bulk samples and solar cells. Major observations and conclusions from the investigation are discussed
Seventy-One New L and T Dwarfs from the Sloan Digital Sky Survey
We present near-infrared observations of 71 newly discovered L and T dwarfs,
selected from imaging data of the Sloan Digital Sky Survey (SDSS) using the
i-dropout technique. Sixty-five of these dwarfs have been classified
spectroscopically according to the near-infrared L dwarf classification scheme
of Geballe et al. and the unified T dwarf classification scheme of Burgasser et
al. The spectral types of these dwarfs range from L3 to T7, and include the
latest types yet found in the SDSS. Six of the newly identified dwarfs are
classified as early- to mid-L dwarfs according to their photometric
near-infrared colors, and two others are classified photometrically as M
dwarfs. We also present new near-infrared spectra for five previously published
SDSS L and T dwarfs, and one L dwarf and one T dwarf discovered by Burgasser et
al. from the Two Micron All Sky Survey. The new SDSS sample includes 27 T
dwarfs and 30 dwarfs with spectral types spanning the complex L-T transition
(L7-T3). We continue to see a large (~0.5 mag) spread in J-H for L3 to T1
types, and a similar spread in H-K for all dwarfs later than L3. This color
dispersion is probably due to a range of grain sedimentation properties,
metallicity, and gravity. We also find L and T dwarfs with unusual colors and
spectral properties that may eventually help to disentangle these effects.Comment: accepted by AJ, 18 pages, 10 figures, 5 tables, emulateapj layou
Influence of retardation effects on 2D magnetoplasmon spectrum
Within dissipationless limit the magnetic field dependence of magnetoplasmon
spectrum for unbounded 2DEG system found to intersect the cyclotron resonance
line, and, then approaches the frequency given by light dispersion relation.
Recent experiments done for macroscopic disc-shape 2DEG systems confirm theory
expectations.Comment: 2 pages,2 figure
On Recognizing Transparent Objects in Domestic Environments Using Fusion of Multiple Sensor Modalities
Current object recognition methods fail on object sets that include both
diffuse, reflective and transparent materials, although they are very common in
domestic scenarios. We show that a combination of cues from multiple sensor
modalities, including specular reflectance and unavailable depth information,
allows us to capture a larger subset of household objects by extending a state
of the art object recognition method. This leads to a significant increase in
robustness of recognition over a larger set of commonly used objects.Comment: 12 page
Dispersion Relations in String Theory
We analyze the analytic continuation of the formally divergent one-loop
amplitude for scattering of the graviton multiplet in the Type II Superstring.
In particular we obtain explicit double and single dispersion relations,
formulas for all the successive branch cuts extending out to plus infinity, as
well as for the decay rate of a massive string state of arbitrary mass 2N into
two string states of lower mass. We compare our results with the box diagram in
a superposition of -like field theories. The stringy effects are traced
to a convergence problem in this superposition.Comment: 17 pages, COLUMBIA-YITP-UCLA/93/TEP/45 (figures fixed up
Role of material properties and mesostructure on dynamic deformation and shear instability in Al-W granular composites
Dynamic experiments with Al-W granular/porous composites revealed
qualitatively different behavior with respect to shear localization depending
on bonding between Al particles. Two-dimensional numerical modeling was used to
explore the mesomechanics of the large strain dynamic deformation in Al-W
granular/porous composites and explain the experimentally observed differences
in shear localization between composites with various mesostructures.
Specifically, the bonding between the Al particles, the porosity, the roles of
the relative particle sizes of Al and W, the arrangements of the W particles,
and the material properties of Al were investigated using numerical
calculations. It was demonstrated in simulations that the bonding between the
"soft" Al particles facilitated shear localization as seen in the experiments.
Numerical calculations and experiments revealed that the mechanism of the shear
localization in granular composites is mainly due to the local high strain flow
of "soft" Al around the "rigid" W particles causing localized damage
accumulation and subsequent growth of the meso/macro shear bands/cracks. The
"rigid" W particles were the major geometrical factor determining the
initiation and propagation of "kinked" shear bands in the matrix of "soft" Al
particles, leaving some areas free of extensive plastic deformation as observed
in experiments and numerical calculations.Comment: 10 pages, 14 figures, submitted to Journal of Applied Physic
A Perturbative Study of a General Class of Lattice Dirac Operators
A perturbative study of a general class of lattice Dirac operators is
reported, which is based on an algebraic realization of the Ginsparg-Wilson
relation in the form
where stands for a non-negative integer.
The choice corresponds to the commonly discussed Ginsparg-Wilson relation
and thus to the overlap operator. We study one-loop fermion contributions to
the self-energy of the gauge field, which are related to the fermion
contributions to the one-loop function and to the Weyl anomaly. We
first explicitly demonstrate that the Ward identity is satisfied by the
self-energy tensor. By performing careful analyses, we then obtain the correct
self-energy tensor free of infra-red divergences, as a general consideration of
the Weyl anomaly indicates. This demonstrates that our general operators give
correct chiral and Weyl anomalies. In general, however, the Wilsonian effective
action, which is supposed to be free of infra-red complications, is expected to
be essential in the analyses of our general class of Dirac operators for
dynamical gauge field.Comment: 30 pages. Some of the misprints were corrected. Phys. Rev. D (in
press
Dips in Partial Wave Amplitudes from Final State Interactions
We consider the dip-peak structures in the J=0 partial wave amplitudes for
processes \gamma\gamma\rightarrow W^+W^-~
\mbox{and}~\gamma\gamma,gg\rightarrow t\overline{t} taking into account the
corresponding Born term process and the rescattering process where the
intermediate state is rescattered through the exchange of Higgs resonance state
in the direct channel.Comment: 9 pages, CPP-93-21, 6 figures not include
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