17,278 research outputs found
Is the Mott transition relevant to f-electron metals ?
We study how a finite hybridization between a narrow correlated band and a
wide conduction band affects the Mott transition. At zero temperature, the
hybridization is found to be a relevant perturbation, so that the Mott
transition is suppressed by Kondo screening. In contrast, a first-order
transition remains at finite temperature, separating a local moment phase and a
Kondo- screened phase. The first-order transition line terminates in two
critical endpoints. Implications for experiments on f-electron materials such
as the Cerium alloy CeLaTh are discussed.Comment: 5 pages, 3 figure
Average characteristic polynomials in the two-matrix model
The two-matrix model is defined on pairs of Hermitian matrices of
size by the probability measure where
and are given potential functions and \tau\in\er. We study averages
of products and ratios of characteristic polynomials in the two-matrix model,
where both matrices and may appear in a combined way in both
numerator and denominator. We obtain determinantal expressions for such
averages. The determinants are constructed from several building blocks: the
biorthogonal polynomials and associated to the two-matrix
model; certain transformed functions and \Q_n(v); and finally
Cauchy-type transforms of the four Eynard-Mehta kernels , ,
and . In this way we generalize known results for the
-matrix model. Our results also imply a new proof of the Eynard-Mehta
theorem for correlation functions in the two-matrix model, and they lead to a
generating function for averages of products of traces.Comment: 28 pages, references adde
Superconductivity-Related Insulating Behavior
We present the results of an experimental study of superconducting,
disordered, thin-films of amorphous Indium Oxide. These films can be driven
from the superconducting phase to a reentrant insulating state by the
application of a perpendicular magnetic field (). We find that the high-
insulator exhibits activated transport with a characteristic temperature,
. has a maximum value () that is close to the
superconducting transition temperature () at = 0, suggesting a
possible relation between the conduction mechanisms in the superconducting and
insulating phases. and display opposite dependences on the
disorder strength.Comment: Tex file and 5 figures; Revised version; To appear in Phys. Rev.
Lett. (2004
Structure and kinematics of the molecular spiral arms in M51
Mapping of the CO(1-0) emission from the spiral galaxy was made with the Onsala 20 m antenna. The observations show that the emission is considerably enhanced in spiral arms which appear to originate as intense ridges of emission about 1 kpc from the nucleus. One of the main objectives for the 1986 observations was to study the variations of the tangential velocity component of molecular gas across a spiral arm. The radial velocity was found to have a velocity shift similar to that predicted by the density wave theory. The present (1986) observations of the inner southern spiral arm of M51 show that the tangential velocity component also behaves in a way which conforms with the density wave model. The molecular arms were compared with the H alpha ionized gas arms of Tully (1974) and it was found that the ionized gas appears to have its maximum intensity slightly outside the molecular arm
Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets
The concept of local isotropy in a chemically reacting turbulent wall-jet
flow is addressed using direct numerical simulation (DNS) data. Different DNS
databases with isothermal and exothermic reactions are examined. The chemical
reaction and heat release effects on the turbulent velocity, passive scalar and
reactive species fields are studied using their probability density functions
(PDF) and higher order moments for velocities and scalar fields, as well as
their gradients. With the aid of the anisotropy invariant maps for the Reynolds
stress tensor the heat release effects on the anisotropy level at different
wall-normal locations are evaluated and found to be most accentuated in the
near-wall region. It is observed that the small-scale anisotropies are
persistent both in the near-wall region and inside the jet flame. Two
exothermic cases with different Damkohler number are examined and the
comparison revealed that the Damkohler number effects are most dominant in the
near-wall region, where the wall cooling effects are influential. In addition,
with the aid of PDFs conditioned on the mixture fraction, the significance of
the reactive scalar characteristics in the reaction zone is illustrated. We
argue that the combined effects of strong intermittency and strong persistency
of anisotropy at the small scales in the entire domain can affect mixing and
ultimately the combustion characteristics of the reacting flow
Manipulating the torsion of molecules by strong laser pulses
A proof-of-principle experiment is reported, where torsional motion of a
molecule, consisting of a pair of phenyl rings, is induced by strong laser
pulses. A nanosecond laser pulse spatially aligns the carbon-carbon bond axis,
connecting the two phenyl rings, allowing a perpendicularly polarized, intense
femtosecond pulse to initiate torsional motion accompanied by an overall
rotation about the fixed axis. The induced motion is monitored by femtosecond
time-resolved Coulomb explosion imaging. Our theoretical analysis accounts for
and generalizes the experimental findings.Comment: 4 pages, 4 figures, submitted to PRL; Major revision of the
presentation of the material; Correction of ion labels in Fig. 2(a
The 12C/13C Isotopic Ratio in Photodissociated Gas in M42
We have observed the 158 micron 2P3/2-2P1/2 fine-structure line of 12C II
simultaneously with the F=2-1 and F=1-0 hyperfine components of this transition
in 13C II in the Orion photodissociation region near theta1C . The line
profiles were fully resolved using a heterodyne spectrometer with 0.5 km/s
resolution. The relative intensities of these lines give a 12C/13C isotopic
ratio of R=58 (+6,-5) for the most probable 12C II peak optical depth tau=1.3 .
The constrained range of tau(12C II) between 1.0 and 1.4 corresponds to a range
of 12C/13C between 52 and 61. The most probable value of 58 agrees very well
with that obtained from a relationship between the isotopic ratio and
galactocentric distance derived from CO measurements, but is lower than the
specific value of 67(+-3) obtained for Orion from CO data. An isotopic ratio as
low as 43, as previously suggested based on optical absorption measurements of
the local interstellar medium, is excluded by the C II data at about the 2
sigma level.Comment: 11 pages, 2 postscript figures, uses aaspp4 macro
High Excitation Molecular Gas in the Magellanic Clouds
We present the first survey of submillimeter CO 4-3 emission in the
Magellanic Clouds. The survey is comprised of 15 6'x6' maps obtained using the
AST/RO telescope toward the molecular peaks of the Large and Small Magellanic
Clouds. We have used these data to constrain the physical conditions in these
objects, in particular their molecular gas density and temperature. We find
that there are significant amounts of molecular gas associated with most of
these molecular peaks, and that high molecular gas temperatures are pervasive
throughout our sample. We discuss whether this may be due to the low
metallicities and the associated dearth of gas coolants in the Clouds, and
conclude that the present sample is insufficient to assert this effect.Comment: 18 pages, 3 figures, 5 tables. To appear in Ap
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