1,584 research outputs found
High Magnetic Field ESR in the Haldane Spin Chains NENP and NINO
We present electron spin resonance experiments in the one-dimensional
antiferromagnetic S=1 spin chains NENP and NINO in pulsed magnetic fields up to
50T. The measured field dependence of the quantum energy gap for B||b is
analyzed using the exact diagonalization method and the density matrix
renormalization group method (DMRG). A staggered anisotropy term (-1)^i d(S_i^x
S_i^z + S_i^z S_i^x) was considered for the first time in addition to a
staggered field term (-1)^i S_i^x B_st. We show that the spin dynamics in high
magnetic fields strongly depends on the orthorhombic anisotropy E.Comment: 4 pages, RevTeX, 4 figure
Eta invariants for flat manifolds
Using H. Donnelly result from the article "Eta Invariants for G-Spaces" we
calculate the eta invariants of the signature operator for almost all
7-dimensional flat manifolds with cyclic holonomy group. In all cases this eta
invariants are an integer numbers. The article was motivated by D. D. Long and
A. Reid article "On the geometric boundaries of hyperbolic 4-manifolds, Geom.
Topology 4, 2000, 171-178Comment: 18 pages, a new version with referees comment
On operad structures of moduli spaces and string theory
Recent algebraic structures of string theory, including homotopy Lie
algebras, gravity algebras and Batalin-Vilkovisky algebras, are deduced from
the topology of the moduli spaces of punctured Riemann spheres. The principal
reason for these structures to appear is as simple as the following. A
conformal field theory is an algebra over the operad of punctured Riemann
surfaces, this operad gives rise to certain standard operads governing the
three kinds of algebras, and that yields the structures of such algebras on the
(physical) state space naturally.Comment: 33 pages (An elaboration of minimal area metrics and new references
are added
Electromagnetic Polarization Effects due to Axion Photon Mixing
We investigate the effect of axions on the polarization of electromagnetic
waves as they propagate through astronomical distances. We analyze the change
in the dispersion of the electromagnetic wave due to its mixing with axions. We
find that this leads to a shift in polarization and turns out to be the
dominant effect for a wide range of frequencies. We analyze whether this effect
or the decay of photons into axions can explain the large scale anisotropies
which have been observed in the polarizations of quasars and radio galaxies. We
also comment on the possibility that the axion-photon mixing can explain the
dimming of distant supernovae.Comment: 18 pages, 1 figur
Network development in biological gels: role in lymphatic vessel development
In this paper, we present a model that explains the prepatterning of lymphatic vessel morphology in collagen gels. This model is derived using the theory of two phase rubber material due to Flory and coworkers and it consists of two coupled fourth order partial differential equations describing the evolution of the collagen volume fraction, and the evolution of the proton concentration in a collagen implant; as described in experiments of Boardman and Swartz (Circ. Res. 92, 801â808, 2003). Using linear stability analysis, we find that above a critical level of proton concentration, spatial patterns form due to small perturbations in the initially uniform steady state. Using a long wavelength reduction, we can reduce the two coupled partial differential equations to one fourth order equation that is very similar to the CahnâHilliard equation; however, it has more complex nonlinearities and degeneracies. We present the results of numerical simulations and discuss the biological implications of our model
Enhancement of low-mass dileptons in heavy-ion collisions
Using a relativistic transport model for the expansion stage of S+Au
collisions at 200 GeV/nucleon, we show that the recently observed enhancement
of low-mass dileptons by the CERES collaboration can be explained by the
decrease of vector meson masses in hot and dense hadronic matter.Comment: 12 pages, RevTeX, 3 figures available from [email protected]
Magnetotransport in Two-Dimensional Electron Systems with Spin-Orbit Interaction
We present magnetotransport calculations for homogeneous two-dimensional
electron systems including the Rashba spin-orbit interaction, which mixes the
spin-eigenstates and leads to a modified fan-chart with crossing Landau levels.
The quantum mechanical Kubo formula is evaluated by taking into account
spin-conserving scatterers in an extension of the self-consistent Born
approximation that considers the spin degree of freedom. The calculated
conductivity exhibits besides the well-known beating in the Shubnikov-de Haas
(SdH) oscillations a modulation which is due to a suppression of scattering
away from the crossing points of Landau levels and does not show up in the
density of states. This modulation, surviving even at elevated temperatures
when the SdH oscillations are damped out, could serve to identify spin-orbit
coupling in magnetotransport experiments. Our magnetotransport calculations are
extended also to lateral superlattices and predictions are made with respect to
1/B periodic oscillations in dependence on carrier density and strength of the
spin-orbit coupling.Comment: 8 pages including 8 figures; submitted to PR
Dilepton Production at SPS-energy Heavy Ion Collisions
The production of dileptons is studied within a hadronic transport model. We
investigate the sensitivity of the dilepton spectra to the initial
configuration of the hadronic phase in a ultrarelativistic heavy ion collision.
Possible in medium correction due to the modifications of pions and the pion
form factor in a hadronic gas are discussed.Comment: Dedicated to Gerry Brown in honor of the 32nd celebration of his 39th
birthday. 31 pages Latex including 13 eps-figures, uses psfig.sty and
epsf.st
The ZEUS Forward Plug Calorimeter with Lead-Scintillator Plates and WLS Fiber Readout
A Forward Plug Calorimeter (FPC) for the ZEUS detector at HERA has been built
as a shashlik lead-scintillator calorimeter with wave length shifter fiber
readout. Before installation it was tested and calibrated using the X5 test
beam facility of the SPS accelerator at CERN. Electron, muon and pion beams in
the momentum range of 10 to 100 GeV/c were used. Results of these measurements
are presented as well as a calibration monitoring system based on a Co
source.Comment: 38 pages (Latex); 26 figures (ps
Dissipation effects in spin-Hall transport of electrons and holes
We investigate the spin-Hall effect of both electrons and holes in
semiconductors using the Kubo formula in the correct zero-frequency limit
taking into account the finite momentum relaxation time of carriers in real
semiconductors. This approach allows to analyze the range of validity of recent
theoretical findings. In particular, the spin-Hall conductivity vanishes for
vanishing spin-orbit coupling if the correct zero-frequency limit is performed.Comment: 5 pages, no figures, version to appear in Phys. Rev.
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