556 research outputs found
Electron Spin-Lattice Relaxation of doped Yb3+ ions in YBa2Cu3Ox
The electron spin-lattice relaxation (SLR) times T1 of Yb3+‡ ions were
measured from the temperature dependence of electron spin resonance linewidth
in Y0.99Yb0.01Ba2Cu3Ox with different oxygen contents. Raman relaxation
processes dominate the electron SLR. Derived from the temperature dependence of
the SLR rate, the Debye temperature (Td) increases with the critical
temperature Tc and oxygen content x. Keywords: EPR; ESR; Electron spin-lattice
relaxation; Debye temperature; Critical temperatureComment: 5 Pages 4 Figure
START in a five-dimensional conformal domain
In this paper we give a brief review of the pseudo-Riemannian geometry of the
five-dimensional homogeneous space for the conformal group O(4,2). Its topology
is described and its relation to the conformally compactified Minkowski space
is described. Its metric is calculated using a generalized half-space
representation. Compactification via Lie-sphere geometry is outlined. Possible
applications to Jaime Keller's START theory may follow by using its predecessor
- the 5-optics of Yu. B. Rumer. The point of view of Rumer is given extensively
in the last section of the paper.
Keywords. Kaluza,Klein, Rumer, conformal symmetry, hyperbolic space, START,
fifth dimension, action coordinate, 5-opticsComment: Latex, 13 pages, 3 figures, added sections 3.2. Christoffel symbols
and geodesics and 3.3. {\Sigma}- as the space of hyperboloids; accepted for
publication in the special volume of AACA in memory of Prof. Jaime Kelle
Electron Spin-Lattice Relaxation of Er3+ ions in Er0.01Y0.99Ba2Cu3Ox
The temperature dependence of the electron spin-lattice relaxation SLR was
studied in Er0.01Y0.99Ba2Cu3Ox compounds. The data derived from the electron
spin resonance ESR and SLR measurements were compared to those from inelastic
neutron scattering studies. SLR of Er3+ ions in the temperature range from 20 K
to 65 K can be explained by the resonant phonon relaxation process with the
involvement of the lowest excited crystalline-electric-field electronic states
of Er3+. These results are consistent with a local phase separation effects.
Possible mechanisms of the ESR line broadening at lower temperatures are
discussed. Keywords: YBCO; EPR; ESR; Electron spin-lattice relaxation time, T ;
Crystalline-electric-fieldComment: 6 pages, 4 figure
The beta function of N=1 SYM in Differential Renormalization
Using differential renormalization, we calculate the complete two-point
function of the background gauge superfield in pure N=1 Supersymmetric
Yang-Mills theory to two loops. Ultraviolet and (off-shell) infrared
divergences are renormalized in position and momentum space respectively. This
allows us to reobtain the beta function from the dependence on the ultraviolet
renormalization scale in an infrared-safe way. The two-loop coefficient of the
beta function is generated by the one-loop ultraviolet renormalization of the
quantum gauge field via nonlocal terms which are infrared divergent on shell.
We also discuss the connection of the beta function to the flow of the
Wilsonian coupling.Comment: 20 pages, 2 figures. Reference added, minor correction
Optimal Transport, Convection, Magnetic Relaxation and Generalized Boussinesq equations
We establish a connection between Optimal Transport Theory and classical
Convection Theory for geophysical flows. Our starting point is the model
designed few years ago by Angenent, Haker and Tannenbaum to solve some Optimal
Transport problems. This model can be seen as a generalization of the
Darcy-Boussinesq equations, which is a degenerate version of the
Navier-Stokes-Boussinesq (NSB) equations. In a unified framework, we relate
different variants of the NSB equations (in particular what we call the
generalized Hydrostatic-Boussinesq equations) to various models involving
Optimal Transport (and the related Monge-Ampere equation. This includes the 2D
semi-geostrophic equations and some fully non-linear versions of the so-called
high-field limit of the Vlasov-Poisson system and of the Keller-Segel for
Chemotaxis. Finally, we show how a ``stringy'' generalization of the AHT model
can be related to the magnetic relaxation model studied by Arnold and Moffatt
to obtain stationary solutions of the Euler equations with prescribed topology
Two Photon Radiation in W and Z Boson Production at the Tevatron Collider
We present a calculation of two photon radiation in W and Z boson production
in hadronic collisions, based on the complete matrix elements for the processes
q\bar q'\to\ell^\pm\nu\gamma\gamma and q\bar q\to\ell^+\ell^-\gamma\gamma,
including finite charged lepton masses. In order to achieve stable numerical
results over the full phase space, multiconfiguration Monte Carlo techniques
are used to map the peaks in the differential cross section. Numerical results
are presented for the Fermilab Tevatron.Comment: Revtex, 28 pages, 3 figure
High Temperature Expansions and Dynamical Systems
We develop a resummed high-temperature expansion for lattice spin systems
with long range interactions, in models where the free energy is not, in
general, analytic. We establish uniqueness of the Gibbs state and exponential
decay of the correlation functions. Then, we apply this expansion to the
Perron-Frobenius operator of weakly coupled map lattices.Comment: 33 pages, Latex; [email protected]; [email protected]
Dynamical stability of infinite homogeneous self-gravitating systems: application of the Nyquist method
We complete classical investigations concerning the dynamical stability of an
infinite homogeneous gaseous medium described by the Euler-Poisson system or an
infinite homogeneous stellar system described by the Vlasov-Poisson system
(Jeans problem). To determine the stability of an infinite homogeneous stellar
system with respect to a perturbation of wavenumber k, we apply the Nyquist
method. We first consider the case of single-humped distributions and show
that, for infinite homogeneous systems, the onset of instability is the same in
a stellar system and in the corresponding barotropic gas, contrary to the case
of inhomogeneous systems. We show that this result is true for any symmetric
single-humped velocity distribution, not only for the Maxwellian. If we
specialize on isothermal and polytropic distributions, analytical expressions
for the growth rate, damping rate and pulsation period of the perturbation can
be given. Then, we consider the Vlasov stability of symmetric and asymmetric
double-humped distributions (two-stream stellar systems) and determine the
stability diagrams depending on the degree of asymmetry. We compare these
results with the Euler stability of two self-gravitating gaseous streams.
Finally, we determine the corresponding stability diagrams in the case of
plasmas and compare the results with self-gravitating systems
Magnetic Field Structures in a Facular Region Observed by THEMIS and Hinode
The main objective of this paper is to build and compare vector magnetic maps
obtained by two spectral polarimeters, i.e. THEMIS/MTR and Hinode SOT/SP, using
two inversion codes (UNNOFIT and MELANIE) based on the Milne-Eddington solar
atmosphere model. To this end, we used observations of a facular region within
active region NOAA 10996 on 23 May 2008, and found consistent results
concerning the field strength, azimuth and inclination distributions. Because
SOT/SP is free from the seeing effect and has better spatial resolution, we
were able to resolve small magnetic polarities with sizes of 1" to 2", and we
could detect strong horizontal magnetic fields, which converge or diverge in
negative or positive facular polarities. These findings support models which
suggest the existence of small vertical flux tube bundles in faculae. A new
method is proposed to get the relative formation heights of the multi-lines
observed by MTR assuming the validity of a flux tube model for the faculae. We
found that the Fe 1 6302.5 \AA line forms at a greater atmospheric height than
the Fe 1 5250.2 \AA line.Comment: 20 pages, 9 figures, 3 tables, accepted for publication in Solar
Physic
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
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