24,095 research outputs found
Growth of graphene on 6H-SiC by molecular dynamics simulation
Classical molecular-dynamics simulations were carried out to study epitaxial
growth of graphene on 6H-SiC(0001) substrate. It was found that there exists a
threshold annealing temperature above which we observe formation of graphitic
structure on the substrate. To check the sensitivity of the simulation results,
we tested two empirical potentials and evaluated their reliability by the
calculated characteristics of graphene, its carbon-carbon bond-length, pair
correlation function, and binding energy.Comment: 7 pages, 5 figure
Genetic variation in the oxytocin system and its link to social motivation in human infants
Frontal brain asymmetry has been linked to motivational processes in infants and adults, with left lateralization reflecting motivation to approach and right lateralization reflecting motivation to withdraw. We examined the hypothesis that variability in infants’ social motivation may be linked to genetic variation in the oxytocin system. Eleven-month-old infants’ brain responses and looking preferences to smiling and frowning individuals were assessed in conjunction with a polymorphism in CD38 (rs3796863) linked to autism spectrum disorder (ASD) and reduced oxytocin. Frontal brain asymmetry and looking preferences differed as a function of CD38 genotype. While non-risk A-allele carriers displayed left lateralization to smiling faces (approach) and a heightened looking preference for the individual who smiled, infants with the CC (ASD risk) genotype displayed withdrawal from smiling faces and a preference for the individual who frowned. Findings demonstrate that the oxytocin system is linked to brain and behavioral markers of social motivation in infancy
Effects of Higher-Order Threshold Corrections in High-E_T Jet Production
Results for higher-order threshold enhancements in high-E_T jet production in
hadron-hadron collisions are presented. Expressions are given for the
next-to-next-to-leading order (NNLO) threshold corrections to the single-jet
inclusive cross section at next-to-leading logarithmic (NLL) accuracy. The
corrections are found to be small for the specific choice of E_T/2 for the
factorization and renormalization scales, and the corrected cross section shows
a substantial reduction of the scale dependence. A comparison to experimental
results from the Tevatron is presented.Comment: 24 pages LaTeX, 5 figure
Innermost Stable Circular Orbit of Inspiraling Neutron-Star Binaries: Tidal Effects, Post-Newtonian Effects and the Neutron-Star Equation of State
We study how the neutron-star equation of state affects the onset of the
dynamical instability in the equations of motion for inspiraling neutron-star
binaries near coalescence. A combination of relativistic effects and Newtonian
tidal effects cause the stars to begin their final, rapid, and
dynamically-unstable plunge to merger when the stars are still well separated
and the orbital frequency is 500 cycles/sec (i.e. the gravitational
wave frequency is approximately 1000 Hz). The orbital frequency at which the
dynamical instability occurs (i.e. the orbital frequency at the innermost
stable circular orbit) shows modest sensitivity to the neutron-star equation of
state (particularly the mass-radius ratio, , of the stars). This
suggests that information about the equation of state of nuclear matter is
encoded in the gravitational waves emitted just prior to the merger.Comment: RevTeX, to appear in PRD, 8 pages, 4 figures include
Innermost Stable Circular Orbit of a Spinning Particle in Kerr Spacetime
We study stability of a circular orbit of a spinning test particle in a Kerr
spacetime. We find that some of the circular orbits become unstable in the
direction perpendicular to the equatorial plane, although the orbits are still
stable in the radial direction. Then for the large spin case ($S < \sim O(1)),
the innermost stable circular orbit (ISCO) appears before the minimum of the
effective potential in the equatorial plane disappears. This changes the radius
of ISCO and then the frequency of the last circular orbit.Comment: 25 pages including 8 figure
Solving the Darwin problem in the first post-Newtonian approximation of general relativity
We analytically calculate the equilibrium sequence of the corotating binary
stars of incompressible fluid in the first post-Newtonian(PN) approximation of
general relativity. By calculating the total energy and total angular momentum
of the system as a function of the orbital separation, we investigate the
innermost stable circular orbit for corotating binary(we call it ISCCO). It is
found that by the first PN effect, the orbital separation of the binary at the
ISCCO becomes small with increase of the compactness of each star, and as a
result, the orbital angular velocity at the ISCCO increases. These behaviors
agree with previous numerical works.Comment: 33 pages, revtex, 4 figures(eps), accepted for publication in Phys.
Rev.
Non-equilibrium initial conditions from pQCD for RHIC and LHC
We calculate the initial non-equilibrium conditions from perturbative QCD
(pQCD) within Glauber multiple scattering theory for AGeV and
ATeV. At the soon available collider energies one will
particularly test the small region of the parton distributions entering the
cross sections. Therefore shadowing effects, previously more or less
unimportant, will lead to new effects on variables such as particle
multiplicities , transverse energy production , and the
initial temperature . In this paper we will have a closer look on the
effects of shadowing by employing different parametrizations for the shadowing
effect for valence quarks, sea quarks and gluons. Since the cross sections at
midrapidity are dominated by processes involving gluons the amount of their
depletion is particularly important. We will therefore have a closer look on
the results for , , and by using two different
gluon shadowing ratios, differing strongly in size. As a matter of fact, the
calculated quantities differ significantly.Comment: typo in ref's removed, ack's added, no change in result
Isospin splitting in heavy baryons and mesons
A recent general analysis of light-baryon isospin splittings is updated and
extended to charmed baryons.
The measured and splittings stand out as being difficult
to understand in terms of two-body forces alone.
We also discuss heavy-light mesons; though the framework here is necessarily
less general, we nevertheless obtain some predictions that are not strongly
model-dependent.Comment: 12 pages REVTEX 3, plus 4 uuencoded ps figures, CMU-HEP93-
Unifying the Phase Diagrams of the Magnetic and Transport Properties of La_(2-x)Sr_xCuO_4, 0 < x < 0.05
An extensive experimental and theoretical effort has led to a largely
complete mapping of the magnetic phase diagram of La_(2-x)Sr_xCuO_4, and a
microscopic model of the spin textures produced in the x < 0.05 regime has been
shown to be in agreement with this phase diagram. Here we use this same model
to derive a theory of the impurity-dominated, low temperature transport. Then,
we present an analysis of previously published data for two samples: x = 0.002
data from Chen et. al., and x = 0.04 data from Keimer et. al. We show that the
transport mechanisms in the two systems are the same, even though they are on
opposite sides of the observed insulator-to-metal transition. Our model of
impurity effects on the impurity band conduction, variable-range hopping
conduction, and coulomb gap conduction, is similar to that used to describe
doped semiconductors. However, for La_(2-x)Sr_xCuO_4 we find that in addition
to impurity-generated disorder effects, strong correlations are important and
must be treated on a equal level with disorder. On the basis of this work we
propose a phase diagram that is consistent with available magnetic and
transport experiments, and which connects the undoped parent compound with the
lowest x value for which La_(2-x)Sr_xCuO_4 is found to be superconducting, x
about 0.06.Comment: 7 pages revtex with one .ps figur
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