1,169 research outputs found
The strength of countable saturation
We determine the proof-theoretic strength of the principle of countable
saturation in the context of the systems for nonstandard arithmetic introduced
in our earlier work.Comment: Corrected typos in Lemma 3.4 and the final paragraph of the
conclusio
Band structure of SnTe studied by Photoemission Spectroscopy
We present an angle-resolved photoemission spectroscopy study of the
electronic structure of SnTe, and compare the experimental results to ab initio
band structure calculations as well as a simplified tight-binding model of the
p-bands. Our study reveals the conjectured complex Fermi surface structure near
the L-points showing topological changes in the bands from disconnected
pockets, to open tubes, and then to cuboids as the binding energy increases,
resolving lingering issues about the electronic structure. The chemical
potential at the crystal surface is found to be 0.5eV below the gap,
corresponding to a carrier density of p =1.14x10^{21} cm^{-3} or 7.2x10^{-2}
holes per unit cell. At a temperature below the cubic-rhombohedral structural
transition a small shift in spectral energy of the valance band is found, in
agreement with model predictions.Comment: 4 figure
Magnetic Properties of Ni-Fe Nanowire Arrays: Effect of Template Material and Deposition Conditions
The objective of this work is to study the magnetic properties of arrays of
Ni-Fe nanowires electrodeposited in different template materials such as porous
silicon, polycarbonate and alumina. Magnetic properties were studied as a
function of template material, applied magnetic field (parallel and
perpendicular) during deposition, wire length, as well as magnetic field
orientation during measurement. The results show that application of magnetic
field during deposition strongly influences the c-axis preferred orientation
growth of Ni-Fe nanowires. The samples with magnetic field perpendicular to
template plane during deposition exhibits strong perpendicular anisotropy with
greatly enhanced coercivity and squareness ratio, particularly in Ni-Fe
nanowires deposited in polycarbonate templates. In case of polycarbonate
template, as magnetic field during deposition increases, both coercivity and
squareness ratio also increase. The wire length dependence was also measured
for polycarbonate templates. As wire length increases, coercivity and
squareness ratio decrease, but saturation field increases. Such magnetic
behavior (dependence on template material, magnetic field, wire length) can be
qualitatively explained by preferential growth phenomena, dipolar interactioComment: 26 pages, 7 figures, 5 Tables Submitted to Physical Review
An Array of Descending Visual Interneurons Encoding Self-Motion in Drosophila
The means by which brains transform sensory information into coherent motor actions is poorly understood. In flies, a relatively small set of descending interneurons are responsible for conveying sensory information and higher-order commands from the brain to motor circuits in the ventral nerve cord. Here, we describe three pairs of genetically identified descending interneurons that integrate information from wide-field visual interneurons and project directly to motor centers controlling flight behavior. We measured the physiological responses of these three cells during flight and found that they respond maximally to visual movement corresponding to rotation around three distinct body axes. After characterizing the tuning properties of an array of nine putative upstream visual interneurons, we show that simple linear combinations of their outputs can predict the responses of the three descending cells. Last, we developed a machine vision-tracking system that allows us to monitor multiple motor systems simultaneously and found that each visual descending interneuron class is correlated with a discrete set of motor programs
Tin telluride: a weakly co-elastic metal
We report resonant ultrasound spectroscopy (RUS),
dilatometry/magnetostriction, magnetotransport, magnetization, specific heat,
and Sn M\"ossbauer spectroscopy measurements on SnTe and
SnCrTe. Hall measurements at K indicate that our
Bridgman-grown single crystals have a -type carrier concentration of cm and that our Cr-doped crystals have an -type
concentration of cm. Although our SnTe crystals are
diamagnetic over the temperature range , the Cr-doped crystals are room temperature ferromagnets with a Curie
temperature of 294 K. For each sample type, three-terminal capacitive
dilatometry measurements detect a subtle 0.5 micron distortion at K. Whereas our RUS measurements on SnTe show elastic hardening near the
structural transition, pointing to co-elastic behavior, similar measurements on
SnCrTe show a pronounced softening, pointing to
ferroelastic behavior. Effective Debye temperature, , values of SnTe
obtained from Sn M\"ossbauer studies show a hardening of phonons in the
range 60--115K ( = 162K) as compared with the 100--300K range
( = 150K). In addition, a precursor softening extending over
approximately 100 K anticipates this collapse at the critical temperature, and
quantitative analysis over three decades of its reduced modulus finds with , a value
indicating a three-dimensional softening of phonon branches at a temperature
K, considerably below . We suggest that the differences in
these two types of elastic behaviors lie in the absence of elastic domain wall
motion in the one case and their nucleation in the other
Particle dependence of elliptic flow in Au+Au collisions at 200 GeV
The elliptic flow parameter () for and
has been measured at mid-rapidity in Au + Au collisions at
GeV by the STAR collaboration. The values for both
and saturate at moderate , deviating
from the hydrodynamic behavior observed in the lower region. The
saturated values and the scales where the deviation begins are
particle dependent. The particle-type dependence of shows features
expected from the hadronization of a partonic ellipsoid by coalescence of
co-moving quarks. These results will be discussed in relation to the nuclear
modification factor () which has also been measured for and
by the STAR collaboration.Comment: 6 pages, 3 figures, Strange Quark Matter 2003 Conference (SQM 2003):
updated with 2 figures from original talk that did not appear in the journa
Applying laboratory thermal desorption data in an interstellar context: sublimation of methanol thin films
Methods by which experimental measurements of thermal desorption can be applied in astrophysical environments have been developed, using the sublimation of solid methanol as an example. The temperature programmed desorption of methanol from graphitic, amorphous silica and polycrystalline gold substrates was compared, with the kinetic parameters of desorption extracted by either a leading edge analysis or by fitting using a stochastic integration method. At low coverages, the desorption shows a substrate-dependent fractional order. However, at higher coverages methanol desorption is zeroth order with kinetic parameters independent of substrate. Using a kinetic model based on the stochastic integration analyses, desorption under astrophysically relevant conditions can be simulated. We find that the chemical and morphological nature of the substrate has relatively little impact on the desorption temperature of solid methanol, and that the substrate independent zeroth-order kinetics can provide a satisfactory model for desorption in astrophysical environments. Uncertainties in the heating rate and the distribution of grain sizes will have the largest influence on the range of desorption temperature. These conclusions are likely to be generally applicable to all species in dust grain ice mantles
New results from the NA57 experiment
We report results from the experiment NA57 at CERN SPS on hyperon production
at midrapidity in Pb-Pb collisions at 158 GeV/ and 40 GeV/.
, and yields are compared with those from the STAR
experiment at the higher energy of the BNL RHIC. , , \
and preliminary transverse mass spectra are presented and interpreted
within the framework of a hydro-dynamical blast wave model.Comment: 8 pages, 3 figures, contribution to the proceedings of The XXXVIIIth
Rencontres de Moriond "QCD and High Energy Hadronic Interactions
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