496 research outputs found
Astrometric Control of the Inertiality of the Hipparcos Catalog
Based on the most complete list of the results of an individual comparison of
the proper motions for stars of various programs common to the Hipparcos
catalog, each of which is an independent realization of the inertial reference
frame with regard to stellar proper motions, we redetermined the vector
of residual rotation of the ICRS system relative to the extragalactic
reference frame. The equatorial components of this vector were found to be the
following: mas yr,
mas yr, and mas yr.Comment: 8 pages, 1 figur
Microscopic Derivation of Non-Markovian Thermalization of a Brownian Particle
In this paper, the first microscopic approach to the Brownian motion is
developed in the case where the mass density of the suspending bath is of the
same order of magnitude as that of the Brownian (B) particle. Starting from an
extended Boltzmann equation, which describes correctly the interaction with the
fluid, we derive systematicaly via the multiple time-scale analysis a reduced
equation controlling the thermalization of the B particle, i.e. the relaxation
towards the Maxwell distribution in velocity space. In contradistinction to the
Fokker-Planck equation, the derived new evolution equation is non-local both in
time and in velocity space, owing to correlated recollision events between the
fluid and particle B. In the long-time limit, it describes a non-markovian
generalized Ornstein-Uhlenbeck process. However, in spite of this complex
dynamical behaviour, the Stokes-Einstein law relating the friction and
diffusion coefficients is shown to remain valid. A microscopic expression for
the friction coefficient is derived, which acquires the form of the Stokes law
in the limit where the mean-free in the gas is small compared to the radius of
particle B.Comment: 28 pages, no figure, submitted to Journal of Statistical Physic
NMR Simulation of an Eight-State Quantum System
The propagation of excitation along a one-dimensional chain of atoms is
simulated by means of NMR. The physical system used as an analog quantum
computer is a nucleus of 133-Cs (spin 7/2) in a liquid crystalline matrix. The
Hamiltonian of migration is simulated by using a special 7-frequency pulse, and
the dynamics is monitored by following the transfer of population from one of
the 8 spin energy levels to the other.Comment: 10 pages, 3 figure
Tunneling dynamics in relativistic and nonrelativistic wave equations
We obtain the solution of a relativistic wave equation and compare it with
the solution of the Schroedinger equation for a source with a sharp onset and
excitation frequencies below cut-off. A scaling of position and time reduces to
a single case all the (below cut-off) nonrelativistic solutions, but no such
simplification holds for the relativistic equation, so that qualitatively
different ``shallow'' and ``deep'' tunneling regimes may be identified
relativistically. The nonrelativistic forerunner at a position beyond the
penetration length of the asymptotic stationary wave does not tunnel;
nevertheless, it arrives at the traversal (semiclassical or
B\"uttiker-Landauer) time "tau". The corresponding relativistic forerunner is
more complex: it oscillates due to the interference between two saddle point
contributions, and may be characterized by two times for the arrival of the
maxima of lower and upper envelops. There is in addition an earlier
relativistic forerunner, right after the causal front, which does tunnel.
Within the penetration length, tunneling is more robust for the precursors of
the relativistic equation
Xenohormone transactivities are inversely associated to serum POPs in Inuit
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
On Multipartite Pure-State Entanglement
We show that pure states of multipartite quantum systems are multiseparable
(i.e. give separable density matrices on tracing any party) if and only if they
have a generalized Schmidt decomposition. Implications of this result for the
quantification of multipartite pure-state entanglement are discussed. Further,
as an application of the techniques used here, we show that any purification of
a bipartite PPT bound entangled state is tri-inseparable, i.e. has none of its
three bipartite partial traces separable.Comment: 8 Pages ReVTeX, 4 figures (eps); v2: Revised terminology, added two
references and other minor changes; v3: Minor changes, added two references,
added author's middle initial; v4: One footnote remove
A Catching Trap for All Antiproton Seasons
We describe the origin, development, and status of the Los Alamos antiproton
catching trap. Originally designed for the antiproton gravity experiment, it
now is clear that this device can be a source of low-energy antiprotons for a
wide range of physics, both on site, at CERN, and also off site.Comment: 18 pages, LaTeX, 6 figures available upon request, In honor of
Herbert Walthe
Sub-femtosecond determination of transmission delay times for a dielectric mirror (photonic bandgap) as a function of angle of incidence
Using a two-photon interference technique, we measure the delay for
single-photon wavepackets to be transmitted through a multilayer dielectric
mirror, which functions as a ``photonic bandgap'' medium. By varying the angle
of incidence, we are able to confirm the behavior predicted by the group delay
(stationary phase approximation), including a variation of the delay time from
superluminal to subluminal as the band edge is tuned towards to the wavelength
of our photons. The agreement with theory is better than 0.5 femtoseconds (less
than one quarter of an optical period) except at large angles of incidence. The
source of the remaining discrepancy is not yet fully understood.Comment: 5 pages and 5 figure
Langevin Equation for the Rayleigh model with finite-ranged interactions
Both linear and nonlinear Langevin equations are derived directly from the
Liouville equation for an exactly solvable model consisting of a Brownian
particle of mass interacting with ideal gas molecules of mass via a
quadratic repulsive potential. Explicit microscopic expressions for all kinetic
coefficients appearing in these equations are presented. It is shown that the
range of applicability of the Langevin equation, as well as statistical
properties of random force, may depend not only on the mass ratio but
also by the parameter , involving the average number of molecules in
the interaction zone around the particle. For the case of a short-ranged
potential, when , analysis of the Langevin equations yields previously
obtained results for a hard-wall potential in which only binary collisions are
considered. For the finite-ranged potential, when multiple collisions are
important (), the model describes nontrivial dynamics on time scales
that are on the order of the collision time, a regime that is usually beyond
the scope of more phenomenological models.Comment: 21 pages, 1 figure. To appear in Phys. Rev.
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