10,320 research outputs found
The Nonlinear Permittivity Including Non-Abelian Self-interaction of Plasmons in Quark-Gluon Plasma
By decomposing the distribution functions and color field to regular and
fluctuation parts, the solution of the semi-classical kinetic equations of
quark-gluon plasma is analyzed. Through expanding the kinetic equations of the
fluctuation parts to third order, the nonlinear permittivity including the
self-interaction of gauge field is obtained and a rough numerical estimate is
given out for the important \vk =0 modes of the pure gluon plasma.Comment: 7 pages, shortened version accepted by Chin.Phys.Let
Atomic Scale Sliding and Rolling of Carbon Nanotubes
A carbon nanotube is an ideal object for understanding the atomic scale
aspects of interface interaction and friction. Using molecular statics and
dynamics methods different types of motion of nanotubes on a graphite surface
are investigated. We found that each nanotube has unique equilibrium
orientations with sharp potential energy minima. This leads to atomic scale
locking of the nanotube.
The effective contact area and the total interaction energy scale with the
square root of the radius. Sliding and rolling of nanotubes have different
characters. The potential energy barriers for sliding nanotubes are higher than
that for perfect rolling. When the nanotube is pushed, we observe a combination
of atomic scale spinning and sliding motion. The result is rolling with the
friction force comparable to sliding.Comment: 4 pages (two column) 6 figures - one ep
Activated O2 dissociation and formation of oxide islands on the Be(0001) surface: Another atomistic model for metal oxidation
By simulating the dissociation of O2 molecules on the Be(0001) surface using
the first-principles molecular dynamics approach, we propose a new atomistic
model for the surface oxidation of sp metals. In our model, only the
dissociation of the first oxygen molecule needs to overcome an energy barrier,
while the subsequent oxygen molecules dissociate barrierlessly around the
adsorption area. Consequently, oxide islands form on the metal surface, and
grow up in a lateral way. We also discover that the firstly dissociated oxygen
atoms are not so mobile on the Be(0001) surface, as on the Al(111) surface. Our
atomistic model enlarges the knowledge on metal surface oxidations by perfectly
explaining the initial stage during the surface oxidation of Be, and might be
applicable to some other sp metal surfaces.Comment: 5 pages, 4 figure
The d* dibaryon in the extended quark-delocalization, color-screening model
The quark-delocalization, color-screening model, extended by inclusion of a
one-pion-exchange (OPE) tail, is applied to the study of the deuteron and the
d* dibaryon. The results show that the properties of the deuteron (an extended
object) are well reproduced, greatly improving the agreement with experimental
data as compared to our previous study (without OPE). At the same time, the
mass and decay width of the d* (a compact object) are, as expected, not altered
significantly.Comment: 9 pages, no figures, LaTeX, subm. to Phys. Rev.
Power-law cosmological solution derived from DGP brane with a brane tachyon field
By studying a tachyon field on the DGP brane model, in order to embed the 4D
standard Friedmann equation with a brane tachyon field in 5D bulk, the metric
of the 5D spacetime is presented. Then, adopting the inverse square potential
of tachyon field, we obtain an expanding universe with power-law on the brane
and an exact 5D solution.Comment: 8 pages, 1 figure, accepted by IJMP
Quantum oscillations in adsorption energetics of atomic oxygen on Pb(111) ultrathin films: A density-functional theory study
Using first-principles calculations, we have systematically studied the
quantum size effects of ultrathin Pb(111) films on the adsorption energies and
diffusion energy barriers of oxygen atoms. For the on-surface adsorption of
oxygen atoms at different coverages, all the adsorption energies are found to
show bilayer oscillation behaviors. It is also found that the work function of
Pb(111) films still keeps the bilayer-oscillation behavior after the adsorption
of oxygen atoms, with the values being enlarged by 2.10 to 2.62 eV. For the
diffusion and penetration of the adsorbed oxygen atoms, it is found that the
most energetically favored paths are the same on different Pb(111) films. And
because of the modulation of quantum size effects, the corresponding energy
barriers are all oscillating with a bilayer period on different Pb(111) films.
Our studies indicate that the quantum size effect in ultrathin metal films can
modulate a lot of processes during surface oxidation
Stretching Semiflexible Polymer Chains: Evidence for the Importance of Excluded Volume Effects from Monte Carlo Simulation
Semiflexible macromolecules in dilute solution under very good solvent
conditions are modeled by self-avoiding walks on the simple cubic lattice
( dimensions) and square lattice ( dimensions), varying chain
stiffness by an energy penalty for chain bending. In the absence
of excluded volume interactions, the persistence length of the
polymers would then simply be with , the bond length being the lattice spacing,
and is the thermal energy. Using Monte Carlo simulations applying the
pruned-enriched Rosenbluth method (PERM), both and the chain length
are varied over a wide range ), and
also a stretching force is applied to one chain end (fixing the other end
at the origin). In the absence of this force, in a single crossover from
rod-like behavior (for contour lengths less than ) to swollen coils
occurs, invalidating the Kratky-Porod model, while in a double crossover
occurs, from rods to Gaussian coils (as implied by the Kratky-Porod model) and
then to coils that are swollen due to the excluded volume interaction. If the
stretching force is applied, excluded volume interactions matter for the force
versus extension relation irrespective of chain stiffness in , while
theories based on the Kratky-Porod model are found to work in for stiff
chains in an intermediate regime of chain extensions. While for in
this model a persistence length can be estimated from the initial decay of
bond-orientational correlations, it is argued that this is not possible for
more complex wormlike chains (e.g. bottle-brush polymers). Consequences for the
proper interpretation of experiments are briefly discussed.Comment: 23 pages, 17 figures, 2 tables, to be published in J. Chem. Phys.
(2011
Real photons produced from photoproduction in collisions
We calculate the production of real photons originating from the
photoproduction in relativistic collisions. The
Weizscker-Williams approximation in the photoproduction is
considered. Numerical results agree with the experimental data from
Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). We find
that the modification of the photoproduction is more prominent in large
transverse momentum region.Comment: 2 figure
Quantum dynamics of a vibrational mode of a membrane within an optical cavity
Optomechanical systems are a promising candidate for the implementation of
quantum interfaces for storing and redistributing quantum information. Here we
focus on the case of a high-finesse optical cavity with a thin vibrating
semitransparent membrane in the middle. We show that robust and stationary
optomechanical entanglement could be achieved in the system, even in the
presence of nonnegligible optical absorption in the membrane. We also present
some preliminary experimental data showing radiation-pressure induced optical
bistability.Comment: 6 pages, 2 figures. Work presented at the conference QCMC 2010 held
on 19-23 July 2010 at the University of Queensland, Brisbane, Australi
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