2,420 research outputs found
Matrix Theory, Hilbert Scheme and Integrable System
We give a reinterpretation of the matrix theory discussed by Moore, Nekrasov
and Shatashivili (MNS) in terms of the second quantized operators which
describes the homology class of the Hilbert scheme of points on surfaces. It
naturally relate the contribution from each pole to the inner product of
orthogonal basis of free boson Fock space. These basis can be related to the
eigenfunctions of Calogero-Sutherland (CS) equation and the deformation
parameter of MNS is identified with coupling of CS system. We discuss the
structure of Virasoro symmetry in this model.Comment: 13 pages 1 figur
Dynamical radion superfield in 5D action
We derive 5D N=1 superspace action including the radion superfield. The
radion is treated as a dynamical field and identified as a solution of the
equation of motion even in the presence of the radius stabilization mechanism.
Our derivation is systematic and based on the superconformal formulation of 5D
supergravity. We can read off the couplings of the dynamical radion superfield
to the matter superfields from our result. The correct radion mass can be
obtained by calculating the radion potential from our superspace action.Comment: 29 pages, no figures, LaTeX, some comments adde
Oblique Ion Two-Stream Instability in the Foot Region of a Collisionless Shock
Electrostatic behavior of a collisionless plasma in the foot region of high
Mach number perpendicular shocks is investigated through the two-dimensional
linear analysis and electrostatic particle-in-cell (PIC) simulation. The
simulations are double periodic and taken as a proxy for the situation in the
foot. The linear analysis for relatively cold unmagnetized plasmas with a
reflected proton beam shows that obliquely propagating Buneman instability is
strongly excited. We also found that when the electron temperature is much
higher than the proton temperature, the most unstable mode is the highly
obliquely propagating ion two-stream instability excited through the resonance
between ion plasma oscillations of the background protons and of the beam
protons, rather than the ion acoustic instability that is dominant for parallel
propagation. To investigate nonlinear behavior of the ion two-stream
instability, we have made PIC simulations for the shock foot region in which
the initial state satisfies the Buneman instability condition. In the first
phase, electrostatic waves grow two-dimensionally by the Buneman instability to
heat electrons. In the second phase, highly oblique ion two-stream instability
grows to heat mainly ions. This result is in contrast to previous studies based
on one-dimensional simulations, for which ion acoustic instability further
heats electrons. The present result implies that overheating problem of
electrons for shocks in supernova remnants is resolved by considering ion
two-stream instability propagating highly obliquely to the shock normal and
that multi-dimensional analysis is crucial to understand the particle heating
and acceleration processes in shocks.Comment: 20 pages, 9 figures, accepted for publication in Ap
Observables and Correlation Functions in OSp Invariant String Field Theory
We define BRST invariant observables in the OSp invariant closed string field
theory for bosonic strings. We evaluate correlation functions of these
observables and show that the S-matrix elements derived from them coincide with
those of the light-cone gauge string field theory.Comment: 23 page
Open String on Symmetric Product
We develop some basic properties of the open string on the symmetric product
which is supposed to describe the open string field theory in discrete
lightcone quantization (DLCQ). After preparing the consistency conditions of
the twisted boundary conditions for Annulus/M\"obius/Klein Bottle amplitudes in
generic non-abelian orbifold, we classify the most general solutions of the
constraints when the discrete group is . We calculate the corresponding
orbifold amplitudes from two viewpoints -- from the boundary state formalism
and from the trace over the open string Hilbert space. It is shown that the
topology of the world sheet for the short string and that of the long string in
general do not coincide. For example the annulus sector for the short string
contains all the sectors (torus, annulus, Klein bottle, M\"obius strip) of the
long strings. The boundary/cross-cap states of the short strings are classified
into three categories in terms of the long string, the ordinary boundary and
the cross-cap states, and the ``joint'' state which describes the connection of
two short strings. We show that the sum of the all possible boundary conditions
is equal to the exponential of the sum of the irreducible amplitude -- one body
amplitude of long open (closed) strings. This is typical structure of DLCQ
partition function. We examined that the tadpole cancellation condition in our
language and derived the well-known gauge group .Comment: 56 pages, 11 figures, Late
Effects of Ram-Pressure from Intracluster Medium on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies
Using a simple model of molecular cloud evolution, we have quantitatively
estimated the change of star formation rate (SFR) of a disk galaxy falling
radially into the potential well of a cluster of galaxies. The SFR is affected
by the ram-pressure from the intracluster medium (ICM). As the galaxy
approaches the cluster center, the SFR increases to twice the initial value, at
most, in a cluster with high gas density and deep potential well, or with a
central pressure of because the ram-pressure
compresses the molecular gas of the galaxy. However, this increase does not
affect the color of the galaxy significantly. Further into the central region
of the cluster ( Mpc from the center), the SFR of the disk
component drops rapidly due to the effect of ram-pressure stripping. This makes
the color of the galaxy redder and makes the disk dark. These effects may
explain the observed color, morphology distribution and evolution of galaxies
in high-redshift clusters. By contrast, in a cluster with low gas density and
shallow potential well, or the central pressure of ,
the SFR of a radially infalling galaxy changes less significantly, because
neither ram-pressure compression nor stripping is effective. Therefore, the
color of galaxies in poor clusters is as blue as that of field galaxies, if
other environmental effects such as galaxy-galaxy interaction are not
effective. The predictions of the model are compared with observations.Comment: 19 pages, 9 figures, to appear in Ap
D-branes and Closed String Field Theory
We construct solitonic states in the OSp invariant string field theory, which
are BRST invariant in the leading order of regularization parameter. One can
show that these solitonic states describe D-branes and ghost D-branes, by
calculating the scattering amplitudes.Comment: 8 pages, 2 figures, based on an invited talk presented at the
international workshop "Progress of String Theory and Quantum Field Theory"
(Osaka City University, December 7-10, 2007), to be published in the
proceeding
Noncoplanar spin canting in lightly-doped ferromagnetic Kondo lattice model on a triangular lattice
Effect of the coupling to mobile carriers on the 120
antiferromagnetic state is investigated in a ferromagnetic Kondo lattice model
on a frustrated triangular lattice. Using a variational calculation for various
spin orderings up to a four-site unit cell, we identify the ground-state phase
diagram with focusing on the lightly-doped region. We find that an electron
doping from the band bottom immediately destabilizes a 120 coplanar
antiferromagnetic order and induces a noncoplanar three-sublattice ordering
accompanied by an intervening phase separation. This noncoplanar phase has an
umbrella-type spin configuration with a net magnetic moment and a finite spin
scalar chirality. This spin-canting state emerges in competition between the
antiferromagnetic superexchange interaction and the ferromagnetic
double-exchange interaction under geometrical frustration. In contrast, a hole
doping from the band top retains the 120-ordered state up to a finite
doping concentration and does not lead to a noncolpanar ordering.Comment: 6 pages, 4 figures, accepted for publication in J. Phys.: Conf. Se
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Forced convection heat transfer simulation using dissipative particle dynamics with energy conservation
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Dissipative particle dynamics (DPD) with energy conservation was applied to simulate forced convection in parallel-plate channels with boundary conditions of constant wall temperature (CWT) and constant wall heat flux (CHF). DPD is a coarse-grained version of molecular dynamics. An additional governing equation for energy conservation was solved along with conventional DPD equations where inter-particle heat flux
accounts for changes in mechanical and internal energies when particles interact with surrounding particles. The solution domain was considered to be two-dimensional with periodic boundary condition in the flow direction. Additional layers of particles on top and bottom of the channel were utilized to apply no-slip velocity and temperature boundary conditions. The governing equations for energy conservation were modified based
on periodic fully developed velocity and temperature conditions. The results were shown via temperature profiles across the channel cross section. The Nusselt numbers were calculated from the temperature gradient at the wall using a second order accurate forward difference technique. The results agreed well with the exact solutions to within 2.3%.This work is supported by the National Science Foundation grant (NSF-OISE-0530203)
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