1,663 research outputs found
Impact of Decoherence on Internal State Cooling using Optical Frequency Combs
We discuss femtosecond Raman type techniques to control molecular vibrations,
which can be implemented for internal state cooling from Feshbach states with
the use of optical frequency combs with and without modulation. The technique
makes use of multiple two-photon resonances induced by optical frequencies
present in the comb. It provides us with a useful tool to study the details of
molecular dynamics at ultracold temperatures. In our theoretical model we take
into account decoherence in the form of spontaneous emission and collisional
dephasing in order to ascertain an accurate model of the population transfer in
the three-level system. We analyze the effects of odd and even chirps of the
optical frequency comb in the form of sine and cosine functions on the
population transfer. We compare the effects of these chirps to the results
attained with the standard optical frequency comb to see if they increase the
population transfer to the final deeply bound state in the presence of
decoherence. We also analyze the inherent phase relation that takes place owing
to collisional dephasing between molecules in each of the states. This ability
to control the rovibrational states of a molecule with an optical frequency
comb enables us to create a deeply bound ultracold polar molecules from the
Feshbach state.Comment: 10 pages, 6 figure
Is it possible to measure the Lense-Thirring effect on the orbits of the planets in the gravitational field of the Sun?
Here we explore a novel approach in order to try to measure the
post-Newtonian 1/c^2 Lense-Thirring secular effect induced by the
gravitomagnetic field of the Sun on the planetary orbital motion. Due to the
relative smallness of the solar angular momentum J and the large values of the
planetary semimajor axes a, the gravitomagnetic precessions, which affect the
nodes Omega and the perihelia omega and are proportional to J/a^3, are of the
order of 10^-3 arcseconds per century only for, e.g., Mercury. This value lies
just at the edge of the present-day observational sensitivity in reconstructing
the planetary orbits, although future missions to Mercury like Messenger and
BepiColombo could allow to increase it. The major problems come from the main
sources of systematic errors. They are the aliasing classical precessions
induced by the multipolar expansion of the Sun's gravitational potential and
the classical secular N-body precessions which are of the same order of
magnitude or much larger than the Lense-Thirring precessions of interest. This
definitely rules out the possibility of analyzing only one orbital element of,
e.g., Mercury. In order to circumvent these problems, we propose a suitable
linear combination of the orbital residuals of the nodes of Mercury, Venus and
Mars which is, by construction, independent of such classical secular
precessions. A 1-sigma reasonable estimate of the obtainable accuracy yields a
36% error. Since the major role in the proposed combination is played by the
Mercury's node, it could happen that the new, more accurate ephemerides
available in future thanks to the Messenger and BepiColombo missions will offer
an opportunity to improve the present unfavorable situation.Comment: LaTex2e, A&A macros, 6 pages, no figure, 3 tables. Substantial
revision. More realistic conclusions. Estimations of the impact of
BepiColombo presente
The impact of the Kuiper Belt Objects and of the asteroid ring on future high-precision relativistic Solar System tests
We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and
of the asteroid ring on some proposed high-precision tests of Newtonian and
post-Newtonian gravity to be performed in the Solar System by means of
spacecraft in heliocentric \approx 1 AU orbits and accurate orbit determination
of some of the inner planets. It turns out that the Classical KBOSs (CKBOS),
which amount to \approx 70% of the observed population of Trans-Neptunian
bodies, induce a systematic secular error of about 1 m after one year in the
transverse direction T of the orbit of a test particle orbiting at 1 AU from
the Sun. For Mercury the ratios of the secular perihelion precessions induced
by CKBOs to the ones induced by the general relativity and the solar oblateness
J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse
perturbation induced on a \approx 1 AU orbit by the asteroid ring, which
globally accounts for the action of the minor asteroids whose mass is about 5
10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2
Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given
the very ambitious goals of many expensive and complex missions aimed to
testing gravitational theories to unprecedented levels of accuracy, these notes
may suggest further and more accurate investigations of such sources of
potentially insidious systematic bias.Comment: Latex2e, Elsevier macros, 5 pages, no figures, 1 table. To appear in
Planetary Space Science. Small change in table's captio
On the possibility of measuring the solar oblateness and some relativistic effects from planetary ranging
In this paper we first calculate the post-Newtonian gravitoelectric secular
rate of the mean anomaly of a test particle freely orbiting a spherically
symmetric central mass. Then, we propose a novel approach to suitably combine
the presently available planetary ranging data to Mercury, Venus and Mars in
order to determine, simultaneously and independently of each other, the Sun's
quadrupole mass moment J_2 and the secular advances of the perihelion and the
mean anomaly. This would also allow to obtain the PPN parameters gamma and beta
independently. We propose to analyze the time series of three linear
combinations of the experimental residuals of the rates of the nodes, the
longitudes of perihelia and mean anomalies of Mercury, Venus and Mars built up
in order to absorb the secular precessions induced by the solar oblateness and
the post-Newtonian gravitoelectric forces. The values of the three investigated
parameters can be obtained by fitting the expected linear trends with straight
lines, determining their slopes in arcseconds per century and suitably
normalizing them. According to the present-day EPM2000 ephemerides accuracy,
the obtainable precision would be of the order of 10^-4-10^-5 for the PPN
parameters and, more interestingly, of 10^-9 for J_2. The future BepiColombo
mission should improve the Mercury's orbit by one order of magnitude.Comment: LaTex2e, 11 pages, no figures, 3 tables. Extensively rewritten
version. The role of the classical N-body secular precessions has been
discussed. New observable found for J2. Improved accuracy in it: 10^-9. The
role of BepiColombo discusse
Gravitational time delay of light for various models of modified gravity
We reexamined the gravitational time delay of light, allowing for various
models of modified gravity. We clarify the dependence of the time delay (and
induced frequency shift) on modified gravity models and investigate how to
distinguish those models, when light propagates in static spherically symmetric
spacetimes. Thus experiments by radio signal from spacecrafts at very different
distances from Sun and future space-borne laser interferometric detectors could
be a probe of modified gravity in the solar system.Comment: 10 pages, 2 figures; title, abstract and text improved; accepted for
publication in Phys. Lett.
A prospective registry of emergency department patients admitted with infection
<p>Abstract</p> <p>Background</p> <p>Patients with infections account for a significant proportion of Emergency Department (ED) workload, with many hospital patients admitted with severe sepsis initially investigated and resuscitated in the ED. The aim of this registry is to systematically collect quality observational clinical and microbiological data regarding emergency patients admitted with infection, in order to explore in detail the microbiological profile of these patients, and to provide the foundation for a significant programme of prospective observational studies and further clinical research.</p> <p>Methods/design</p> <p>ED patients admitted with infection will be identified through daily review of the computerised database of ED admissions, and clinical information such as site of infection, physiological status in the ED, and components of management abstracted from patients' charts. This information will be supplemented by further data regarding results of investigations, microbiological isolates, and length of stay (LOS) from hospital electronic databases. Outcome measures will be hospital and intensive care unit (ICU) LOS, and mortality endpoints derived from a national death registry.</p> <p>Discussion</p> <p>This database will provide substantial insights into the characteristics, microbiological profile, and outcomes of emergency patients admitted with infections. It will become the nidus for a programme of research into compliance with evidence-based guidelines, optimisation of empiric antimicrobial regimens, validation of clinical decision rules and identification of outcome determinants. The detailed observational data obtained will provide a solid baseline to inform the design of further controlled trials planned to optimise treatment and outcomes for emergency patients admitted with infections.</p
Gravimagnetic effect of the barycentric motion of the Sun and determination of the post-Newtonian parameter gamma in the Cassini experiment
The most precise test of the post-Newtonian gamma parameter in the solar
system has been achieved in measurement of the frequency shift of radio waves
to and from the Cassini spacecraft as they passed near the Sun. The test relies
upon the JPL model of radiowave propagation that includes, but does not
explicitly parametrize, the impact of the non-stationary component of the
gravitational field of the Sun, generated by its barycentric orbital motion, on
the Shapiro delay. This non-stationary gravitational field of the Sun is
associated with the Lorentz transformation of the metric tensor and the affine
connection from the heliocentric to the barycentric frame of the solar system
and can be treated as gravimagnetic field.
The gravimagnetic field perturbs the propagation of a radio wave and
contributes to its frequency shift at the level up to 4 10^{-13} that may
affect the precise measurement of the parameter gamma in the Cassini experiment
to about one part in 10,000. Our analysis suggests that the translational
gravimagnetic field of the Sun can be extracted from the Cassini data, and its
effect is separable from the space curvature characterized by the parameter
gamma.Comment: 12 pages, 1 figure, accepted to Physical Letters
Analytical approach of late-time evolution in a torsion cosmology
In this letter, we study the late-time evolution of a torsion cosmology only
with the spin- mode. We find three kinds of analytical solutions with a
constant affine scalar curvature. In the first case, it is not physical because
the matter density will be negative. In the second case, it shows that the dark
energy can be mimicked in the torsion cosmological model. In the third case,
the characteristic of late-time evolution is similar to that of the universe of
matter dominant. And we also find a kind of expression with the non-constant
curvature that the periodic character of numerical calculation is only the
reflection of solution in a specific period of evolution. Using these
expressions, we shall be able to predict the evolution over the late-time. From
this prediction, we know the fate of universe that the universe would expand
forever, slowly asymtotically to a halt.Comment: 12pages,6 figure
Astro2010 Decadal Survey Whitepaper: Coordinated Science in the Gravitational and Electromagnetic Skies
It is widely expected that the coming decade will witness the first direct
detection of gravitational waves (GWs). The ground-based LIGO and Virgo GW
observatories are being upgraded to advanced sensitivity, and are expected to
observe a significant binary merger rate. The launch of The Laser
Interferometer Space Antenna (LISA) would extend the GW window to low
frequencies, opening new vistas on dynamical processes involving massive (M >~
10^5 M_Sun) black holes. GW events are likely to be accompanied by
electromagnetic (EM) counterparts and, since information carried
electromagnetically is complementary to that carried gravitationally, a great
deal can be learned about an event and its environment if it becomes possible
to measure both forms of radiation in concert. Measurements of this kind will
mark the dawn of trans-spectral astrophysics, bridging two distinct spectral
bands of information. The aim of this whitepaper is to articulate future
directions in both theory and observation that are likely to impact broad
astrophysical inquiries of general interest. What will EM observations reflect
on the nature and diversity of GW sources? Can GW sources be exploited as
complementary probes of cosmology? What cross-facility coordination will expand
the science returns of gravitational and electromagnetic observations?Comment: 7 pages (plus one coverpage), submitted to the US Astro2010 Decadal
Survey. This is a living document, with updates expected to be posted to this
archive. Those interested in contributing should contact J. S. Bloo
Maxwell's field coupled nonminimally to quadratic torsion: Induced axion field and birefringence of the vacuum
We consider a possible (parity conserving) interaction between the
electromagnetic field and a torsion field of spacetime. For
generic elementary torsion, gauge invariant coupling terms of lowest order fall
into two classes that are both nonminimal and {\it quadratic} in torsion. These
two classes are displayed explicitly. The first class of the type
yields (undesirable) modifications of the Maxwell equations. The second class
of the type doesn't touch the Maxwell equations but rather
modifies the constitutive tensor of spacetime. Such a modification can be
completely described in the framework of metricfree electrodynamics. We
recognize three physical effects generated by the torsion: (i) An axion field
that induces an {\em optical activity} into spacetime, (ii) a modification of
the light cone structure that yields {\em birefringence} of the vacuum, and
(iii) a torsion dependence of the {\em velocity of light.} We study these
effects in the background of a Friedmann universe with torsion. {\it File
tor17.tex, 02 August 2003}Comment: 6 page
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