7,032 research outputs found
Phase fluctuations in atomic Bose gases
We improve on the Popov theory for partially Bose-Einstein condensed atomic
gases by treating the phase fluctuations exactly. As a result, the theory
becomes valid in arbitrary dimensions and is able to describe the
low-temperature crossover between three, two and one-dimensional Bose gases,
which is currently being explored experimentally. We consider both homogeneous
and trapped Bose gases.Comment: 4 pages. Title changed Major changes involve extension of theory to
include trapped Bose gases. Deletion of reference to and comparison with
hydrogen experiment. Due to these changes, second author added. Modified
manuscript accepted for PR
Infrared Spectra of Meteoritic SiC Grains
We present here the first infrared spectra of meteoritic SiC grains. The
mid-infrared transmission spectra of meteoritic SiC grains isolated from the
Murchison meteorite were measured in the wavelength range 2.5--16.5 micron, in
order to make available the optical properties of presolar SiC grains. These
grains are most likely stellar condensates with an origin predominately in
carbon stars. Measurements were performed on two different extractions of
presolar SiC from the Murchison meteorite. The two samples show very different
spectral appearance due to different grain size distributions. The spectral
feature of the smaller meteoritic SiC grains is a relatively broad absorption
band found between the longitudinal and transverse lattice vibration modes
around 11.3 micron, supporting the current interpretation about the presence of
SiC grains in carbon stars. In contrast to this, the spectral feature of the
large (> 5 micron) grains has an extinction minimum around 10 micron. The
obtained spectra are compared with commercially available SiC grains and the
differences are discussed. This comparison shows that the crystal structure
(e.g., beta-SiC versus alpha-SiC) of SiC grains plays a minor role on the
optical signature of SiC grains compared to e.g. grain size.Comment: 7 pages, 6 figures. To appear in A&
Scaling behavior in the dynamics of a supercooled Lennard-Jones mixture
We present the results of a large scale molecular dynamics computer
simulation of a binary, supercooled Lennard-Jones fluid. At low temperatures
and intermediate times the time dependence of the intermediate scattering
function is well described by a von Schweidler law. The von Schweidler exponent
is independent of temperature and depends only weakly on the type of
correlator. For long times the correlation functions show a Kohlrausch behavior
with an exponent that is independent of temperature. This dynamical
behavior is in accordance with the mode-coupling theory of supercooled liquids.Comment: 6 pages, RevTex, three postscript figures available on request,
MZ-Physics-10
Investigating 16O with the 15N(p,{\alpha})12C reaction
The 16O nucleus was investigated through the 15N(p,{\alpha})12C reaction at
excitation energies from Ex = 12 231 to 15 700 keV using proton beams from a 5
MeV Van de Graaff accelerator at beam energies of Ep = 331 to 3800 keV. Alpha
decay from resonant states in 16O was strongly observed for ten known excited
states in this region. The candidate 4-alpha cluster state at Ex = 15.1 MeV was
investigated particularly intensely in order to understand its particle decay
channels.Comment: Submitted for Proceedings of Fourth International Workshop on State
of the Art in Nuclear Cluster Physics (SOTANCP4), held from May 13 - 18, 2018
in Galveston, TX, US
Observation of twin beam correlations and quadrature entanglement by frequency doubling in a two-port resonator
We demonstrate production of quantum correlated and entangled beams by second
harmonic generation in a nonlinear resonator with two output ports. The output
beams at wavelength 428.5 nm exhibit 0.9 dB of nonclassical intensity
correlations and 0.3 dB of entanglement.Comment: 5 pages, 7 figure
Stellar activity as noise in exoplanet detection I. Methods and application to solar-like stars and activity cycles
The detection of exoplanets using any method is prone to confusion due to the
intrinsic variability of the host star. We investigate the effect of cool
starspots on the detectability of the exoplanets around solar-like stars using
the radial velocity method. For investigating this activity-caused "jitter" we
calculate synthetic spectra using radiative transfer, known stellar atomic and
molecular lines, different surface spot configurations, and an added planetary
signal. Here, the methods are described in detail, tested and compared to
previously published studies. The methods are also applied to investigate the
activity jitter in old and young solar-like stars, and over a solar-like
activity cycles. We find that the mean full jitter amplitude obtained from the
spot surfaces mimicking the solar activity varies during the cycle
approximately between 1 m/s and 9 m/s. With a realistic observing frequency a
Neptune mass planet on a one year orbit can be reliably recovered. On the other
hand, the recovery of an Earth mass planet on a similar orbit is not feasible
with high significance. The methods developed in this study have a great
potential for doing statistical studies of planet detectability, and also for
investigating the effect of stellar activity on recovered planetary parameters.Comment: Accepted to MNRA
Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets
In the CERN NA63 collaboration we have addressed the question of the
potential inadequacy of the commonly used Migdal formulation of the
Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20
and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of
LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference
target, Ta. For each target and energy, a comparison between simulated values
based on the LPM suppression of incoherent bremsstrahlung is shown, taking
multi-photon effects into account. For these targets and energies, we find that
Migdal's theoretical formulation is adequate to a precision of better than
about 5%, irrespective of the target substance.Comment: 8 pages, 13 figure
Correlation Measurement of Squeezed Light
We study the implementation of a correlation measurement technique for the
characterization of squeezed light which is nearly free of electronic noise.
With two different sources of squeezed light, we show that the sign of the
covariance coefficient, revealed from the time resolved correlation data, is
witnessing the presence of squeezing in the system. Furthermore, we estimate
the degree of squeezing using the correlation method and compare it to the
standard homodyne measurement scheme. We show that the role of electronic
detector noise is minimized using the correlation approach as opposed to
homodyning where it often becomes a crucial issue
- …