40,189 research outputs found
Entanglement enhancement and postselection for two atoms interacting with thermal light
The evolution of entanglement for two identical two-level atoms coupled to a
resonant thermal field is studied for two different families of input states.
Entanglement enhancement is predicted for a well defined region of the
parameter space of one of these families. The most intriguing result is the
possibility of probabilistic production of maximally entangled atomic states
even if the input atomic state is factorized and the corresponding output state
is separable.Comment: accepted for publication in J. Phys.
Generality of rotating partial cavitation in two-dimensional cascades
Numerical simulations of 2-dimensional (2D) unsteady cavitating flows were carried out under various conditions of the number of blades, incidence angles and cavitation numbers. When the incidence angle increased or the cavitation number decreased, the steady balanced cavitation transited to unsteady and non-uniform patterns. Typical patterns reported in the previous studies such as rotating, asymmetric and alternating for 3- and 4-blades were successfully reproduced. In this study, cascades of the larger number of blades were dealt with to consider the generality of unsteadiness by reducing the influence of periodicity. The cavitation is basically triggered in the backward next section. However, the period of time for growing causes complexity in the discrimination of propagation. In most cases of rotating partial cavitation, except for 4-blades, the cavity develops in the second passage of backward direction after the decay of largest cavity. In case of many blades, multiple cavities rotate simultaneously and the particular patterns observed in cascades of small even numbers of blades attenuate.http://deepblue.lib.umich.edu/bitstream/2027.42/84276/1/CAV2009-final90.pd
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
A Si-micromachined 48-stage Knudsen pump for on-chip vacuum
This paper describes a thermal transpiration-driven multistage Knudsen pump for vacuum pumping applications. This type of pump relies upon the motion of gas molecules from the cold end to the hot end of a channel in which the flow is restricted to the free molecular or transitional regimes. To achieve a high compression ratio, 48 stages are cascaded in series in a single chip. A five-mask, single silicon wafer process is used for monolithic integration of the designed Knudsen pump. The pump has several monolithically integrated Pirani gauges to experimentally measure the vacuum pumping characteristics of the pump. It has a footprint of 10.35 × 11.45 mm 2 . For an input power of 1350 mW, the fabricated pump self-evacuates the encapsulated cavities from 760 to ≈50 Torr, resulting in a compression ratio of 15. It also pumps down from 250 to ≈5 Torr, resulting in a compression ratio of 50. Each integrated Pirani gauge requires ≈3.9 mW of power consumption, and its response is sufficiently sensitive in the operating pressure range of 760–1 Torr.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98610/1/0960-1317_22_10_105026.pd
Magnetic phase diagram of Fe1.1Te1-xSex: A comparative study with the stoichiometric superconducting FeTe1-xSex system
We report a comparative study of the series Fe1.1Te1-xSex and the
stoichiometric FeTe1-xSex to bring out the difference in their magnetic,
superconducting and electronic properties. The Fe1.1Te1-xSex series is found to
be magnetic and its microscopic properties are elucidated through Moessbauer
spectroscopy. The magnetic phase diagram of Fe1.1Te1-xSex is traced out and it
shows the emergence of spin-glass state when the antiferromagnetic state is
destabilized by the Se substitution. The isomer shift and quadrupolar splitting
obtained from the Moessbauer spectroscopy clearly brings out the electronic
differences in these two series.Comment: 6 pages, 9 figure
Environment-dependent dissipation in quantum Brownian motion
The dissipative dynamics of a quantum Brownian particle is studied for
different types of environment. We derive analytic results for the time
evolution of the mean energy of the system for Ohmic, sub-Ohmic and super-Ohmic
environments, without performing the Markovian approximation. Our results allow
to establish a direct link between the form of the environmental spectrum and
the thermalization dynamics. This in turn leads to a natural explanation of the
microscopic physical processes ruling the system time evolution both in the
short-time non-Markovian region and in the long-time Markovian one. Our
comparative study of thermalization for different environments sheds light on
the physical contexts in which non-Markovian dissipation effects are dominant.Comment: 10 pages, 6 figures, v2: added new references and paragraph
Microlensing Characterization of Wide-Separation Planets
With their excellent photometric precision and dramatic increase in
monitoring frequency, future microlensing survey experiments are expected to be
sensitive to very short time-scale, isolated events caused by free-floating and
wide-separation planets with mass as low as a few lunar masses. We estimate the
probability of measuring the Einstein radius \theta_E for bound and
free-floating planets. We carry out detailed simulations of the planetary
events expected in next-generation surveys and estimate the resulting
uncertainty in \theta_E for these events. We show that, for main-sequence
sources and Jupiter-mass planets, the caustic structure of wide-separation
planets with projected separations of < 20 AU substantially increases the
probability of measuring the dimensionless source size and thus determining
\theta_E compared to the case of unbound planets. In this limit where the
source is much smaller than the caustic, the effective cross-section to measure
\theta_E to 10% is ~25% larger than the full width of the caustic. Measurement
of the lens parallax is possible for low-mass planetary events by combined
observations from the ground and a satellite located in an L2 orbit; this would
complete the mass measurements for such wide-separation planets. Finally,
short-duration events caused by bound planets can be routinely distinguished
from those caused by free-floating planets for planet-star separations < 20 AU
from either the deviations due to the planetary caustic or (more often) the
low-amplitude bump from the magnification due to the parent star.Comment: 10 pages including 7 figures. ApJ, in pres
Quasi-single field inflation in the non-perturbative regime
In quasi-single field inflation there are massive fields that interact with the inflaton field. If these other fields are not much heavier than the Hubble constant during inflation (H) these interactions can lead to important consequences for the cosmological energy density perturbations. The simplest model of this type has a real scalar inflaton field that interacts with another real scalar S (with mass m). In this model there is a mixing term of the form μπS, where π is the Goldstone fluctuation that is associated with the breaking of time translation invariance by the time evolution of the inflaton field during the inflationary era. In this paper we study this model in the region (μ/H)^2 + (m/H)^2 > 9/4 and m/H∼O(1) or less. For a large part of the parameter space in this region standard perturbative methods are not applicable. Using numerical and analytic methods we study how large μ/H has to be for the large μ/H effective field theory approach to be applicable
Electronic and optical properties of LiBC
LiBC, a semiconducting ternary borocarbide constituted of the lightest
elements only, has been synthesized and characterized by x-ray powder
diffraction, dielectric spectroscopy, and conductivity measurements. Utilizing
an infrared microscope the phonon spectrum has been investigated in single
crystals. The in-plane B-C stretching mode has been detected at 150 meV,
noticeably higher than in AlB2, a non-superconducting isostructural analog of
MgB2. It is this stretching mode, which reveals a strong electron-phonon
coupling in MgB2, driving it into a superconducting state below 40 K, and is
believed to mediate predicted high-temperature superconductivity in hole-doped
LiBC [H. Rosner, A. Kitaigorodsky, and W. E. Pickett, Phys. Rev. Lett. 88,
127001 (2002)].Comment: 4 pages, 4 figure
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