28,099 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
Tidal Interaction between a Fluid Star and a Kerr Black Hole in Circular Orbit
We present a semi-analytic study of the equilibrium models of close binary
systems containing a fluid star (mass and radius ) and a Kerr black
hole (mass ) in circular orbit. We consider the limit where
spacetime is described by the Kerr metric. The tidally deformed star is
approximated by an ellipsoid, and satisfies the polytropic equation of state.
The models also include fluid motion in the stellar interior, allowing binary
models with nonsynchronized stellar spin (as expected for coalescing neutron
star-black hole binaries) to be constructed. Tidal disruption occurs at orbital
radius , but the dimensionless ratio depends on the spin parameter of
the black hole as well as on the equation of state and the internal rotation of
the star. We find that the general relativistic tidal field disrupts the star
at a larger than the Newtonian tide; the difference is
particularly prominent if the disruption occurs in the vicinity of the black
hole's horizon. In general, is smaller for a (prograde
rotating) Kerr black hole than for a Schwarzschild black hole. We apply our
results to coalescing black hole-neutron star and black hole-white dwarf
binaries. The tidal disruption limit is important for characterizing the
expected gravitational wave signals and is relevant for determining the
energetics of gamma ray bursts which may result from such disruption.Comment: 29 pages including 8 figures. Minor changes and update. To appear in
ApJ, March 20, 2000 (Vol.532, #1
Has there been a recent shallowing of tropical cyclones?
Many aspects of tropical cyclone (TC) properties at the surface have been changing but any systematic vertical changes are unknown. Here, we document a recent trend of high thick clouds of TCs. The global inner-core high thick cloud fraction measured by satellite has decreased from 2002 to 2021 by about 10% per decade. The TC inner-core surface rain rate is also found to have decreased during the same period by a similar percentage. This suppression of high thick clouds and rain has been largest during the intensification phase of the strongest TCs. Hence, these two independent and consistent observations suggest that the TC inner-core convection has weakened and that TCs have become shallower recently at least. For this period, the lifetime maximum intensity of major TCs has not changed and this suggests an increased efficiency of the spin-up of TCs
General-relativistic coupling between orbital motion and internal degrees of freedom for inspiraling binary neutron stars
We analyze the coupling between the internal degrees of freedom of neutron
stars in a close binary, and the stars' orbital motion. Our analysis is based
on the method of matched asymptotic expansions and is valid to all orders in
the strength of internal gravity in each star, but is perturbative in the
``tidal expansion parameter'' (stellar radius)/(orbital separation). At first
order in the tidal expansion parameter, we show that the internal structure of
each star is unaffected by its companion, in agreement with post-1-Newtonian
results of Wiseman (gr-qc/9704018). We also show that relativistic interactions
that scale as higher powers of the tidal expansion parameter produce
qualitatively similar effects to their Newtonian counterparts: there are
corrections to the Newtonian tidal distortion of each star, both of which occur
at third order in the tidal expansion parameter, and there are corrections to
the Newtonian decrease in central density of each star (Newtonian ``tidal
stabilization''), both of which are sixth order in the tidal expansion
parameter. There are additional interactions with no Newtonian analogs, but
these do not change the central density of each star up to sixth order in the
tidal expansion parameter. These results, in combination with previous analyses
of Newtonian tidal interactions, indicate that (i) there are no large
general-relativistic crushing forces that could cause the stars to collapse to
black holes prior to the dynamical orbital instability, and (ii) the
conventional wisdom with respect to coalescing binary neutron stars as sources
of gravitational-wave bursts is correct: namely, the finite-stellar-size
corrections to the gravitational waveform will be unimportant for the purpose
of detecting the coalescences.Comment: 22 pages, 2 figures. Replaced 13 July: proof corrected, result
unchange
Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope
We present a detailed modeling and characterization of our scalable microwave
nanoprobe, which is a micro-fabricated cantilever-based scanning microwave
probe with separated excitation and sensing electrodes. Using finite-element
analysis, the tip-sample interaction is modeled as small impedance changes
between the tip electrode and the ground at our working frequencies near 1GHz.
The equivalent lumped elements of the cantilever can be determined by
transmission line simulation of the matching network, which routes the
cantilever signals to 50 Ohm feed lines. In the microwave electronics, the
background common-mode signal is cancelled before the amplifier stage so that
high sensitivity (below 1 atto-Farad capacitance changes) is obtained.
Experimental characterization of the microwave probes was performed on
ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or
topographical signals can be realized using different reflection modes of the
probe.Comment: 7 figure
A Meta-Analysis of Procedures to Change Implicit Measures
Using a novel technique known as network meta-analysis, we synthesized evidence from 492 studies (87,418 participants) to investigate the effectiveness of procedures in changing implicit measures, which we define as response biases on implicit tasks. We also evaluated these procedures’ effects on explicit and behavioral measures. We found that implicit measures can be changed, but effects are often relatively weak (|ds| \u3c .30). Most studies focused on producing short-term changes with brief, single-session manipulations. Procedures that associate sets of concepts, invoke goals or motivations, or tax mental resources changed implicit measures the most, whereas procedures that induced threat, affirmation, or specific moods/emotions changed implicit measures the least. Bias tests suggested that implicit effects could be inflated relative to their true population values. Procedures changed explicit measures less consistently and to a smaller degree than implicit measures and generally produced trivial changes in behavior. Finally, changes in implicit measures did not mediate changes in explicit measures or behavior. Our findings suggest that changes in implicit measures are possible, but those changes do not necessarily translate into changes in explicit measures or behavior
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