16,918 research outputs found
Effect of surface roughness on friction behaviour of steel under boundary lubrication
The friction behaviour of grinded and polished surfaces was evaluated by using a reciprocal sliding tester under lubrication with PAO, PAO + ZnDTP and PAO + ZnDTP + MoDTC. Friction coefficients on the smooth surfaces showed higher values compared to those on the rough surfaces. For lubrication incorporating PAO and PAO + ZnDTP + MoDTC, friction coefficients on both the smoothest and the roughest surfaces decreased with sliding time. On the other hand, friction coefficients between these extremes decreased with sliding time. In this paper, the effects of surface roughness on friction behaviour are discussed
K_l3 form factor with two-flavors of dynamical domain-wall quarks
We report on our calculation of K \to \pi vector form factor by numerical
simulations of two-flavor QCD on a 16^3x32x12 lattice at a \simeq 0.12 fm using
domain-wall quarks and DBW2 glue. Our preliminary result at a single sea quark
mass correponding to m_PS/m_V \simeq 0.53 shows a good agreement with previous
estimate in quenched QCD and that from a phenomenological model.Comment: 6 pages, 5 figures, poster presented at Lattice2005 (Weak matrix
elements); v2: a reference adde
Screening of cosmological constant in non-local cosmology
We consider a model of non-local gravity with a large bare cosmological
constant, , and study its cosmological solutions. The model is
characterized by a function where
and is a real dimensionless parameter. In the
absence of matter, we find an expanding universe solution with
, that is, a universe with decelarated expansion without any fine-tuning
of the parameter. Thus the effect of the cosmological constant is effectively
shielded in this solution. It has been known that solutions in non-local
gravity often suffer from the existence of ghost modes. In the present case we
find the solution is ghost-free if . This is
quite a weak condition. We argue that the solution is stable against the
includion of matter fields. Thus our solution opens up new possibilities for
solution to the cosmological constant problem.Comment: 7 pages, 1 figure, LaTeX, V2:Some clarifications and references adde
Forming Clusters of Galaxies as the Origin of Unidentified GeV Gamma-Ray Sources
Over half of GeV gamma-ray sources observed by the EGRET experiment have not
yet been identified as known astronomical objects. There is an isotropic
component of such unidentified sources, whose number is about 60 in the whole
sky. Here we calculate the expected number of dynamically forming clusters of
galaxies emitting gamma-rays by high energy electrons accelerated in the shock
wave when they form, in the framework of the standard theory of structure
formation. We find that a few tens of such forming clusters should be
detectable by EGRET and hence a considerable fraction of the isotropic
unidentified sources can be accounted for, if about 5% of the shock energy is
going into electron acceleration. We argue that these clusters are very
difficult to detect in x-ray or optical surveys compared with the conventional
clusters, because of their extended angular size of about 1 degree. Hence they
define a new population of ``gamma-ray clusters''. If this hypothesis is true,
the next generation gamma-ray telescopes such as GLAST will detect more than a
few thousands of gamma-ray clusters. It would provide a new tracer of
dynamically evolving structures in the universe, in contrast to the x-ray
clusters as a tracer of hydrodynamically stabilized systems. We also derive the
strength of magnetic field required for the extragalactic gamma-ray background
by structure formation to extend up to 100 GeV as observed, that is about
10^{-5} of the shock-heated baryon energy density.Comment: Accepted by ApJ after minor revisions. Received May 9, Accepted
August 3. 8 pages including 2 figure
Chiral thermodynamics of dense hadronic matter
We discuss phases of hot and dense hadronic matter using chiral Lagrangians.
A two-flavored parity doublet model constrained by the nuclear matter ground
state predicts chiral symmetry restoration. The model thermodynamics is shown
within the mean field approximation. A field-theoretical constraint on possible
phases from the anomaly matching is also discussed.Comment: 8 pages, 2 figures, to appear in the proceedings of 6th International
Workshop on Critical Point and Onset of Deconfinement (CPOD), 23-29 August
2010 at Joint Institute for Nuclear Research, Dubna, Russi
Temperature Chaos, Rejuvenation and Memory in Migdal-Kadanoff Spin Glasses
We use simulations within the Migdal-Kadanoff real space renormalization
approach to probe the scales relevant for rejuvenation and memory in spin
glasses. One of the central questions concerns the role of temperature chaos.
First we investigate scaling laws of equilibrium temperature chaos, finding
super-exponential decay of correlations but no chaos for the total free energy.
Then we perform out of equilibrium simulations that follow experimental
protocols. We find that: (1) rejuvenation arises at a length scale smaller than
the ``overlap length'' l(T,T'); (2) memory survives even if equilibration goes
out to length scales much larger than l(T,T').Comment: 4 pages, 4 figures, added references, slightly changed content,
modified Fig.
Realization of a collective decoding of codeword states
This was also extended from the previous article quant-ph/9705043, especially
in a realization of the decoding process.Comment: 6 pages, RevTeX, 4 figures(EPS
Gauge field for edge state in graphene
By considering the continuous model for graphene, we analytically study a
special gauge field for the edge state. The gauge field explains the properties
of the edge state such as the existence only on the zigzag edge, the partial
appearance in the -space, and the energy position around the Fermi energy.
It is demonstrated utilizing the gauge field that the edge state is robust for
surface reconstruction, and the next nearest-neighbor interaction which breaks
the particle-hole symmetry stabilizes the edge state.Comment: 9 pages, 5 figure
Fermi Surface and Anisotropic Spin-Orbit Coupling of Sb(111) studied by Angle-Resolved Photoemission Spectroscopy
High-resolution angle-resolved photoemission spectroscopy has been performed
on Sb(111) to elucidate the origin of anomalous electronic properties in
group-V semimetal surfaces. The surface was found to be metallic despite the
semimetallic character of bulk. We clearly observed two surface-derived Fermi
surfaces which are likely spin split, demonstrating that the spin-orbit
interaction plays a dominant role in characterising the surface electronic
states of group-V semimetals. Universality/disimilarity of the electronic
structure in Bi and Sb is discussed in relation to the granular
superconductivity, electron-phonon coupling, and surface charge/spin density
wave.Comment: 4 pages, 3 figures. to be published in Phys. Rev. Let
Virtual photon structure functions and positivity constraints
We study the three positivity constraints among the eight virtual photon
structure functions, derived from the Cauchy-Schwarz inequality and which are
hence model-independent. The photon structure functions obtained from the
simple parton model show quite different behaviors in a massive quark or a
massless quark case, but they satisfy, in both cases, the three positivity
constraints. We then discuss an inequality which holds among the unpolarized
and polarized photon structure functions , and
, in the kinematic region , where is the mass squared of the probe (target) photon, and we examine
whether this inequality is satisfied by the perturbative QCD results.Comment: 24 pages, 13 eps figure
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