1,140 research outputs found
The Pioneer Anomaly in the Light of New Data
The radio-metric tracking data received from the Pioneer 10 and 11 spacecraft
from the distances between 20-70 astronomical units from the Sun has
consistently indicated the presence of a small, anomalous, blue-shifted Doppler
frequency drift that limited the accuracy of the orbit reconstruction for these
vehicles. This drift was interpreted as a sunward acceleration of a_P =
(8.74+/-1.33)x10^{-10} m/s^2 for each particular spacecraft. This signal has
become known as the Pioneer anomaly; the nature of this anomaly is still being
investigated.
Recently new Pioneer 10 and 11 radio-metric Doppler and flight telemetry data
became available. The newly available Doppler data set is much larger when
compared to the data used in previous investigations and is the primary source
for new investigation of the anomaly. In addition, the flight telemetry files,
original project documentation, and newly developed software tools are now used
to reconstruct the engineering history of spacecraft. With the help of this
information, a thermal model of the Pioneers was developed to study possible
contribution of thermal recoil force acting on the spacecraft. The goal of the
ongoing efforts is to evaluate the effect of on-board systems on the
spacecrafts' trajectories and possibly identify the nature of this anomaly.
Techniques developed for the investigation of the Pioneer anomaly are
applicable to the New Horizons mission. Analysis shows that anisotropic thermal
radiation from on-board sources will accelerate this spacecraft by ~41 x
10^{-10} m/s^2. We discuss the lessons learned from the study of the Pioneer
anomaly for the New Horizons spacecraft.Comment: 19 pages, 5 figure
New method for the 3D Ising model
A simple, general and practically exact method is developed for the
equilibrium properties of the macroscopic physical systems with translational
symmetry. Applied to the Ising model in two and three dimension, a modest
calculation gives the spontaneous magnetization and the specific heat to less
than 1% error
The Puzzle of the Flyby Anomaly
Close planetary flybys are frequently employed as a technique to place
spacecraft on extreme solar system trajectories that would otherwise require
much larger booster vehicles or may not even be feasible when relying solely on
chemical propulsion. The theoretical description of the flybys, referred to as
gravity assists, is well established. However, there seems to be a lack of
understanding of the physical processes occurring during these dynamical
events. Radio-metric tracking data received from a number of spacecraft that
experienced an Earth gravity assist indicate the presence of an unexpected
energy change that happened during the flyby and cannot be explained by the
standard methods of modern astrodynamics. This puzzling behavior of several
spacecraft has become known as the flyby anomaly. We present the summary of the
recent anomalous observations and discuss possible ways to resolve this puzzle.Comment: 6 pages, 1 figure. Accepted for publication by Space Science Review
Can the Pioneer anomaly be of gravitational origin? A phenomenological answer
In order to satisfy the equivalence principle, any non-conventional mechanism
proposed to gravitationally explain the Pioneer anomaly, in the form in which
it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave
out of consideration its impact on the motion of the planets of the Solar
System as well, especially those orbiting in the regions in which the anomalous
behavior of the Pioneer probes manifested itself. In this paper we, first,
discuss the residuals of the right ascension \alpha and declination \delta of
Uranus, Neptune and Pluto obtained by processing various data sets with
different, well established dynamical theories (JPL DE, IAA EPM, VSOP). Second,
we use the latest determinations of the perihelion secular advances of some
planets in order to put on the test two gravitational mechanisms recently
proposed to accommodate the Pioneer anomaly based on two models of modified
gravity. Finally, we adopt the ranging data to Voyager 2 when it encountered
Uranus and Neptune to perform a further, independent test of the hypothesis
that a Pioneer-like acceleration can also affect the motion of the outer
planets of the Solar System. The obtained answers are negative.Comment: Latex2e, 26 pages, 6 tables, 2 figure, 47 references. It is the
merging of gr-qc/0608127, gr-qc/0608068, gr-qc/0608101 and gr-qc/0611081.
Final version to appear in Foundations of Physic
Emittance compensation with dynamically optimized photoelectron beam profiles
Much of the theory and experimentation concerning creation of a high-brightness electron beam from a photocathode, and then applying emittance compensation techniques, assumes that one must strive for a uniform density electron beam, having a cylindrical shape. On the other hand, this shape has large nonlinearities in the space-charge field profiles near the beam's longitudinal extrema. These nonlinearities are known to produce both transverse and longitudinal emittance growth. On the other hand, it has recently been shown by Luiten that by illuminating the cathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped bunch is dynamically formed, which then has linear space-charge fields in all dimensions inside of the bunch. We study here this process, and its marriage to the standard emittance compensation scenario that is implemented in most recent photoinjectors. It is seen that the two processes are compatible, with simulations indicating a very high brightness beam can be obtained. The robustness of this scheme to systematic errors is examined. Prospects for experimental tests of this scheme are discussed
Mycotic renal artery degeneration and systemic sepsis caused by infected renal artery stent
AbstractA case of Staphylococcus aureus renal artery stent infection was studied. Fourteen days after the procedure, the patient had a fever, hypotension, and an elevated white blood cell (WBC) count. Blood cultures were positive for S aureus on admission and during the patient's hospitalization, despite intravenous vancomycin therapy. Evaluation included serial CT scans, revealing increasing persistent inflammation with development of multiple renal intraparenchymal abscesses, and arteriography, showing marked degeneration of the renal artery. Therapy required resection of the renal artery/stent and nephrectomy. This case confirms the severe nature of S aureus stent infection; we recommend prophylactic antibiotics before these procedures, as well as expeditious evaluation and consideration for aggressive surgical therapy if this complication is suspected. (J Vasc Surg 1998;28:547-50.
Quantum Phase Fluctuations Responsible for Pseudogap
The effect of ordering field phase fluctuations on the normal and
superconducting properties of a simple 2D model with a local four-fermion
attraction is studied. Neglecting the coupling between the spin and charge
degrees of freedom an analytical expression has been obtained for the fermion
spectral function as a single integral over a simple function. From this we
show that, as the temperature increases through the 2D critical temperature and
a nontrivial damping for a phase correlator develops, quantum fluctuations fill
the gap in the quasiparticle spectrum. Simultaneously the quasiparticle peaks
broaden significantly above the critical temperature, resembling the observed
pseudogap behavior in high-T_c superconductors.Comment: 5 pages, ReVTeX, 1 EPS figure; final version to appear in Physica
The Pioneer anomaly and the holographic scenario
In this paper we discuss the recently obtained relation between the
Verlinde's holographic model and the first phenomenological Modified Newtonian
dynamics. This gives also a promising possible explanation to the Pioneer
anomaly.Comment: 5 pages, Accepted for publication in Astrophysics & Space Scienc
The low-energy phase-only action in a superconductor: a comparison with the XY model
The derivation of the effective theory for the phase degrees of freedom in a
superconductor is still, to some extent, an open issue. It is commonly assumed
that the classical XY model and its quantum generalizations can be exploited as
effective phase-only models. In the quantum regime, however, this assumption
leads to spurious results, such as the violation of the Galilean invariance in
the continuum model. Starting from a general microscopic model, in this paper
we explicitly derive the effective low-energy theory for the phase, up to
fourth-order terms. This expansion allows us to properly take into account
dynamic effects beyond the Gaussian level, both in the continuum and in the
lattice model. After evaluating the one-loop correction to the superfluid
density we critically discuss the qualitative and quantitative differences
between the results obtained within the quantum XY model and within the correct
low-energy theory, both in the case of s-wave and d-wave symmetry of the
superconducting order parameter. Specifically, we find dynamic anharmonic
vertices, which are absent in the quantum XY model, and are crucial to restore
Galilean invariance in the continuum model. As far as the more realistic
lattice model is concerned, in the weak-to-intermediate-coupling regime we find
that the phase-fluctuation effects are quantitatively reduced with respect to
the XY model. On the other hand, in the strong-coupling regime we show that the
correspondence between the microscopically derived action and the quantum XY
model is recovered, except for the low-density regime.Comment: 29 pages, 11 figures. Slightly revised presentation, accepted for
publication in Phys. Rev.
Superfluid Spin-down, with Random Unpinning of the Vortices
The so-called ``creeping'' motion of the pinned vortices in a rotating
superfluid involves ``random unpinning'' and ``vortex motion'' as two
physically separate processes. We argue that such a creeping motion of the
vortices need not be (biased) in the direction of an existing radial Magnus
force, nor should a constant microscopic radial velocity be assigned to the
vortex motion, in contradiction with the basic assumptions of the ``vortex
creep'' model. We point out internal inconsistencies in the predictions of this
model which arise due to this unjustified foundation that ignores the role of
the actual torque on the superfluid. The proper spin-down rate of a pinned
superfluid is then calculated and turns out to be much less than that suggested
in the vortex creep model, hence being of even less observational significance
for its possible application in explaining the post-glitch relaxations of the
radio pulsars.Comment: To be published in J. Low Temp. Phys., Vol. 139, May 2005 [Eqs 11,
15-17 here, have been revised and, may be substituted for the corresponding
ones in that paper
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