1,860 research outputs found
Fluorescence measurements of expanding strongly-coupled neutral plasmas
We report new detailed density profile measurements in expanding
strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques,
we determine plasma densities in the range of 10^5 to 10^9/cm^3 with a time
resolution limit as small as 7 ns. Strong-coupling in the plasma ions is
inferred directly from the fluorescence signals. Evidence for strong-coupling
at late times is presented, confirming a recent theoretical result.Comment: submitted to PR
Infrared radiometer for measuring thermophysical properties of wind tunnel models
An infrared radiometer is described which was developed to measure temperature rises of wind tunnel models undergoing transient heating over a temperature range of -17.8 C to 260 C. This radiometer interfaces directly with a system which measures the effective thermophysical property square root of rho ck. It has an output temperature fluctuation of 0.26 C at low temperatures and 0.07 C at high temperatures, and the output frequency response of the radiometer is from dc to 400 hertz
Experimental study of laser detected magnetic resonance based on atomic alignment
We present an experimental study of the spectra produced by
optical/radio-frequency double resonance in which resonant linearly polarized
laser light is used in the optical pumping and detection processes. We show
that the experimental spectra obtained for cesium are in excellent agreement
with a very general theoretical model developed in our group and we investigate
the limitations of this model. Finally, the results are discussed in view of
their use in the study of relaxation processes in aligned alkali vapors.Comment: 8 pages, 9 figures. Submitted to Phys. Rev. A. Related to
physics/060523
Vector modulation instability induced by vacuum fluctuations in highly birefringent fibers in the anomalous dispersion regime
We report a detailed experimental study of vector modulation instability in
highly birefringent optical fibers in the anomalous dispersion regime. We prove
that the observed instability is mainly induced by vacuum fluctuations. The
detuning of the spectral peaks agrees with linear perturbation analysis. The
exact shape of the spectrum is well reproduced by numerical integration of
stochastic nonlinear Schrodinger equations describing quantum propagation.Comment: 11 pages, 4 figures, to be published in Optics Letter
From interacting particle systems to random matrices
In this contribution we consider stochastic growth models in the
Kardar-Parisi-Zhang universality class in 1+1 dimension. We discuss the large
time distribution and processes and their dependence on the class on initial
condition. This means that the scaling exponents do not uniquely determine the
large time surface statistics, but one has to further divide into subclasses.
Some of the fluctuation laws were first discovered in random matrix models.
Moreover, the limit process for curved limit shape turned out to show up in a
dynamical version of hermitian random matrices, but this analogy does not
extend to the case of symmetric matrices. Therefore the connections between
growth models and random matrices is only partial.Comment: 18 pages, 8 figures; Contribution to StatPhys24 special issue; minor
corrections in scaling of section 2.
Magneto-optical Trapping of Cadmium
We report the laser-cooling and confinement of Cd atoms in a magneto-optical
trap, and characterize the loading process from the background Cd vapor. The
trapping laser drives the 1S0-1P1 transition at 229 nm in this two-electron
atom and also photoionizes atoms directly from the 1P1 state. This
photoionization overwhelms the other loss mechanisms and allows a direct
measurement of the photoionization cross section, which we measure to be
2(1)x10^(-16)cm^(2) from the 1P1 state. When combined with nearby laser-cooled
and trapped Cd^(+) ions, this apparatus could facilitate studies in ultracold
interactions between atoms and ions.Comment: 8 pages, 11 figure
Free-energy distribution of the directed polymer at high temperature
We study the directed polymer of length in a random potential with fixed
endpoints in dimension 1+1 in the continuum and on the square lattice, by
analytical and numerical methods. The universal regime of high temperature
is described, upon scaling 'time' and space (with for the discrete model) by a continuum model with
-function disorder correlation. Using the Bethe Ansatz solution for the
attractive boson problem, we obtain all positive integer moments of the
partition function. The lowest cumulants of the free energy are predicted at
small time and found in agreement with numerics. We then obtain the exact
expression at any time for the generating function of the free energy
distribution, in terms of a Fredholm determinant. At large time we find that it
crosses over to the Tracy Widom distribution (TW) which describes the fixed
infinite limit. The exact free energy distribution is obtained for any time
and compared with very recent results on growth and exclusion models.Comment: 6 pages, 3 figures large time limit corrected and convergence to
Tracy Widom established, 1 figure changed
Sub-Doppler spectroscopy of Rb atoms in a sub-micron vapor cell in the presence of a magnetic field
We report the first use of an extremely thin vapor cell (thickness ~ 400 nm)
to study the magnetic-field dependence of laser-induced-fluorescence excitation
spectra of alkali atoms. This thin cell allows for sub-Doppler resolution
without the complexity of atomic beam or laser cooling techniques. This
technique is used to study the laser-induced-fluorescence excitation spectra of
Rb in a 50 G magnetic field. At this field strength the electronic angular
momentum J and nuclear angular momentum I are only partially decoupled. As a
result of the mixing of wavefunctions of different hyperfine states, we observe
a nonlinear Zeeman effect for each sublevel, a substantial modification of the
transition probabilities between different magnetic sublevels, and the
appearance of transitions that are strictly forbidden in the absence of the
magnetic field. For the case of right- and left- handed circularly polarized
laser excitation, the fluorescence spectra differs qualitatively. Well
pronounced magnetic field induced circular dichroism is observed. These
observations are explained with a standard approach that describes the partial
decoupling of I and J states
On a Camassa-Holm type equation with two dependent variables
We consider a generalization of the Camassa Holm (CH) equation with two
dependent variables, called CH2, introduced by Liu and Zhang. We briefly
provide an alternative derivation of it based on the theory of Hamiltonian
structures on (the dual of) a Lie Algebra. The Lie Algebra here involved is the
same algebra underlying the NLS hierarchy. We study the structural properties
of the CH2 hierarchy within the bihamiltonian theory of integrable PDEs, and
provide its Lax representation. Then we explicitly discuss how to construct
classes of solutions, both of peakon and of algebro-geometrical type. We
finally sketch the construction of a class of singular solutions, defined by
setting to zero one of the two dependent variables.Comment: 22 pages, 2 figures. A few typos correcte
A class of Poisson-Nijenhuis structures on a tangent bundle
Equipping the tangent bundle TQ of a manifold with a symplectic form coming
from a regular Lagrangian L, we explore how to obtain a Poisson-Nijenhuis
structure from a given type (1,1) tensor field J on Q. It is argued that the
complete lift of J is not the natural candidate for a Nijenhuis tensor on TQ,
but plays a crucial role in the construction of a different tensor R, which
appears to be the pullback under the Legendre transform of the lift of J to
co-tangent manifold of Q. We show how this tangent bundle view brings new
insights and is capable also of producing all important results which are known
from previous studies on the cotangent bundle, in the case that Q is equipped
with a Riemannian metric. The present approach further paves the way for future
generalizations.Comment: 22 page
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