2,999 research outputs found
Exclusion Statistics in a two-dimensional trapped Bose gas
We briefly explain the notion of exclusion statistics and in particular
discuss the concept of an ideal exclusion statistics gas. We then review a
recent work where it is demonstrated that a {\em two-dimensional} Bose gas with
repulsive delta function interactions obeys ideal exclusion statistics, with a
fractional parameter related to the interaction strength.Comment: 10 pages, RevTeX. Proceedings of the Salerno workshop "Theory of
Quantum Gases and Quantum Coherence", to appear in a special issue of J.Phys.
B, Dec. 200
How do electronic carriers cross Si-bound alkyl monolayers?
Electron transport through Si-C bound alkyl chains, sandwiched between n-Si
and Hg, is characterized by two distinct types of barriers, each dominating in
a different voltage range. At low voltage, current depends strongly on
temperature but not on molecular length, suggesting transport by thermionic
emission over a barrier in the Si. At higher voltage, the current decreases
exponentially with molecular length, suggesting tunneling through the
molecules. The tunnel barrier is estimated, from transport and photoemission
data, to be ~1.5 eV with a 0.25me effective mass.Comment: 13 pages, 3 figure
Differential cross sections for pion charge exchange on the proton at 27.5 MeV
We have measured pion single charge exchange differential cross sections on
the proton at 27.5 MeV incident kinetic energy in the center of
momentum angular range between and . The extracted cross
sections are compared with predictions of the standard pion-nucleon partial
wave analysis and found to be in excellent agreement.Comment: ReVTeX v3.0 with aps.sty, 23 pages in e-print format, 7 PostScript
Figures and 4 Tables, also available via anonymous ftp at
ftp://helena.phys.virginia.edu/pub/preprints/scx.p
Optical Clocks in Space
The performance of optical clocks has strongly progressed in recent years,
and accuracies and instabilities of 1 part in 10^18 are expected in the near
future. The operation of optical clocks in space provides new scientific and
technological opportunities. In particular, an earth-orbiting satellite
containing an ensemble of optical clocks would allow a precision measurement of
the gravitational redshift, navigation with improved precision, mapping of the
earth's gravitational potential by relativistic geodesy, and comparisons
between ground clocks.Comment: Proc. III International Conference on Particle and Fundamental
Physics in Space (SpacePart06), Beijing 19 - 21 April 2006, to appear in
Nucl. Phys.
Observation of anomalous spin-state segregation in a trapped ultra-cold vapor
We observe counter-intuitive spin segregation in an inhomogeneous sample of
ultra-cold, non-condensed Rubidium atoms in a magnetic trap. We use spatially
selective microwave spectroscopy to verify a model that accounts for the
differential forces on two internal spin states. In any simple understanding of
the cloud dynamics, the forces are far too small to account for the dramatic
transient spin polarizations observed. The underlying mechanism remains to be
elucidated.Comment: 5 pages, 3 figure
Conductance statistics from a large array of sub-10 nm molecular junctions
Devices made of few molecules constitute the miniaturization limit that both
inorganic and organic-based electronics aspire to reach. However, integration
of millions of molecular junctions with less than 100 molecules each has been a
long technological challenge requiring well controlled nanometric electrodes.
Here we report molecular junctions fabricated on a large array of sub-10 nm
single crystal Au nanodots electrodes, a new approach that allows us to measure
the conductance of up to a million of junctions in a single conducting Atomic
Force Microscope (C-AFM) image. We observe two peaks of conductance for
alkylthiol molecules. Tunneling decay constant (beta) for alkanethiols, is in
the same range as previous studies. Energy position of molecular orbitals,
obtained by transient voltage spectroscopy, varies from peak to peak, in
correlation with conductance values.Comment: ACS Nano (in press
Low-energy Pion-nucleon Scattering
This paper contains the results of an analysis of recent low-energy
pion-nucleon scattering experiments. Obtained are phase shifts, the
pion-nucleon coupling constant and an estimate of the Sigma term.Comment: 30 pages, 11 figures, LaTe
Orthogonal methods based ant colony search for solving continuous optimization problems
Research into ant colony algorithms for solving continuous optimization problems forms one of the most
significant and promising areas in swarm computation. Although traditional ant algorithms are designed for combinatorial
optimization, they have shown great potential in solving a wide range of optimization problems, including continuous
optimization. Aimed at solving continuous problems effectively, this paper develops a novel ant algorithm termed "continuous orthogonal ant colony" (COAC), whose pheromone deposit mechanisms would enable ants to search for
solutions collaboratively and effectively. By using the orthogonal design method, ants in the feasible domain can explore
their chosen regions rapidly and e±ciently. By implementing an "adaptive regional radius" method, the proposed
algorithm can reduce the probability of being trapped in local optima and therefore enhance the global search capability and accuracy. An elitist strategy is also employed to reserve the most valuable points. The performance of the COAC is
compared with two other ant algorithms for continuous optimization of API and CACO by testing seventeen functions
in the continuous domain. The results demonstrate that the proposed COAC algorithm outperforms the others
Stable nondegenerate optical parametric oscillation at degenerate frequencies in Na:KTP
We report the realization of a light source specifically designed for the
generation of bright continuous-variable entangled beams and for
Heisenberg-limited inteferometry. The source is a nondegenerate, single-mode,
continuous-wave optical parametric oscillator in Na:KTP, operated at frequency
degeneracy and just above threshold, which is also of interest for the study of
critical fluctuations at the transition point. The residual
frequency-difference jitter is 150 kHz for a 3 MHz cold cavity half-width
at half maximum. We observe 4 dB of photon-number-difference squeezing at 200
kHz. The Na:KTP crystal is noncritically phase-matched for a 532 nm pump and
polarization crosstalk is therefore practically nonexistent
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