23,586 research outputs found
On the Uniqueness of Quantum Equilibrium in Bohmian Mechanics
In Bohmian mechanics the distribution is regarded as the
equilibrium distribution. We consider its uniqueness, finding that it is the
unique equivariant distribution that is also a local functional of the wave
function .Comment: 15 pages, no figures, LaTe
Determining the alpha dynamo parameter in incompressible homogeneous magnetohydrodynamic turbulence
Alpha, an important parameter in dynamo theory, is proportional to either the kinetic, current, magnetic, or velocity helicity of the fluctuating magnetic field and fluctuating velocity field. The particular helicity to which alpha is proportional depends on the assumptions used in deriving the first order smoothed equations that describe the alpha effect. In two cases, when alpha is proportional to either the magnetic helicity or velocity helicity, alpha is determined experimentally from two point measurements of the fluctuating fields in incompressible, homogeneous turbulence having arbitrary symmetry. For the other two possibilities, alpha is determined if the turbulence is isotropic
Densities and abundances of hot cometary ions in the coma of P/Halley
On its flight by P/Halley, the Giotto spacecraft carried a High Energy Range Spectrometer (HERS) for measuring the properties of cometary ions picked up by the solar wind in the nearly collisionless regions of the coma. Preliminary estimates of the ion densities observed by HERS were reevaluated and extended; density profiles along the Giotto trajectory are presented for 13 values of ion mass/charge. Comparison with the physical-chemical model of the interaction of sunlight and the solar wind with the comet by other researchers reveals that, with the exception of protons and H2(+), all ion densities were at least an order of magnitude higher than predicted. The high ion densities cannot be explained on the basis of compression of the plasma, but require additional or stronger ionization mechanisms. Ratios of the densities of different ion species reveal an overabundance of carbonaceous material and an underabundance of H2(+) compared to the predictions of the Schmidt. While the densities of solar wind ions (H(+) and He(++)) changed sharply across a magnetic discontinuity located 1.35(10)(exp 5) km from the comet, this feature, which has been called both the 'cometopause' and the 'magnetic pileup boundary' was barely distinguishable in the density profiles of hot cometary ions. This result is consistent with the interpretation that the magnetic pileup boundary detected by Giotto was caused by a discontinuity in the solar wind and is not an intrinsic feature of the interaction of the solar wind with an active comet
The "Unromantic Pictures" of Quantum Theory
I am concerned with two views of quantum mechanics that John S. Bell called
``unromantic'': spontaneous wave function collapse and Bohmian mechanics. I
discuss some of their merits and report about recent progress concerning
extensions to quantum field theory and relativity. In the last section, I
speculate about an extension of Bohmian mechanics to quantum gravity.Comment: 37 pages LaTeX, no figures; written for special volume of J. Phys. A
in honor of G.C. Ghirard
Liver Transplantation to Provide Low-Density-Lipoprotein Receptors and Lower Plasma Cholesterol in a Child with Homozygous Familial Hypercholesterolemia
A six-year-old girl with severe hypercholesterolemia and atherosclerosis had two defective genes at the low-density-lipoprotein (LDL) receptor locus, as determined by biochemical studies of cultured fibroblasts. One gene, inherited from the mother, produced no LDL receptors; the other gene, inherited from the father, produced a receptor precursor that was not transported to the cell surface and was unable to bind LDL. The patient degraded intravenously administered 125I-LDL at an extremely low rate, indicating that her high plasma LDL-cholesterol level was caused by defective receptor-mediated removal of LDL from plasma. After transplantation of a liver and a heart from a normal donor, the patient's plasma LDL-cholesterol level declined by 81 per cent, from 988 to 184 mg per deciliter. The fractional catabolic rate for intravenously administered 125I-LDL, a measure of functional LDL receptors in vivo, increased by 2.5-fold. Thus, the transplanted liver, with its normal complement of LDL receptors, was able to remove LDL cholesterol from plasma at a nearly normal rate. We conclude that a genetically determined deficiency of LDL receptors can be largely reversed by liver transplantation. These data underscore the importance of hepatic LDL receptors in controlling the plasma level of LDL cholesterol in human beings. (N Engl J Med 1984; 311: 1658–64.). © 1984, Massachusetts Medical Society. All rights reserved
Optics in the Schwarzschild space-time
Realistic modelling of radiation transfer in and from variable accretion
disks around black holes requires the solution of the problem: find the
constants of motion and equation of motion of a light-like geodesic connecting
two arbitrary points in space. Here we give the complete solution of this
problem in the Schwarzschild space-time.Comment: 14 pages, 10 figures, type C orbits added, analytic solutions for
time of flight of photons for all 3 types of orbits adde
Celestial mechanics in Kerr spacetime
The dynamical parameters conventionally used to specify the orbit of a test
particle in Kerr spacetime are the energy , the axial component of the
angular momentum, , and Carter's constant . These parameters are
obtained by solving the Hamilton-Jacobi equation for the dynamical problem of
geodesic motion. Employing the action-angle variable formalism, on the other
hand, yields a different set of constants of motion, namely, the fundamental
frequencies , and associated with
the radial, polar and azimuthal components of orbital motion. These
frequencies, naturally, determine the time scales of orbital motion and,
furthermore, the instantaneous gravitational wave spectrum in the adiabatic
approximation. In this article, it is shown that the fundamental frequencies
are geometric invariants and explicit formulas in terms of quadratures are
derived. The numerical evaluation of these formulas in the case of a rapidly
rotating black hole illustrates the behaviour of the fundamental frequencies as
orbital parameters such as the semi-latus rectum , the eccentricity or
the inclination parameter are varied. The limiting cases of
circular, equatorial and Keplerian motion are investigated as well and it is
shown that known results are recovered from the general formulas.Comment: 25 pages (LaTeX), 5 figures, submitted to Class. Quantum Gra
Deriving relativistic momentum and energy. II. Three-dimensional case
We generalise a recent derivation of the relativistic expressions for
momentum and kinetic energy from the one-dimensional to the three-dimensional
case.Comment: 7 page
Critical frequency in nuclear chiral rotation
Within the cranked Skyrme-Hartree-Fock approach the self-consistent solutions
have been obtained for planar and chiral rotational bands in 132La. It turns
out that the chiral band cannot exist below some critical rotational frequency
which in the present case equals omega=0.6MeV. The appearance of the critical
frequency is explained in terms of a simple classical model of two gyroscopes
coupled to a triaxial rigid body.Comment: 4 RevTeX pages, 6 EPS figure
Synopsis of early field test results from the gravity gradiometer survey system
Although the amount of data yielded by the initial airborne and surface tests was modest, it was sufficient to demonstrate that the full gravity gradient tensor was successfully measured from moving platforms both in the air and on the surface. The measurements were effectively continuous with spatial along-track resolution limited only by choice of integration lengths taken to reduce noise. The airborne data were less noisy (800 E squared/Hz typical) than were the Gravity Gradiometer Survey System (GGSS) measurements taken at the surface (5000 E squared/Hz typical). Single tracks of surface gravity disturbances recovered from airborne data were accurate to 3 to 4 mgal in each component of gravity when compared to 5 x 5 mean gravity anomalies over a 90 km track. Multitrack processing yielded 2 to 3 mgal when compared to 5 x 5 mean anomalies. Deflection of the vertical recovery over a distance of 150 km was about one arcsecond
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