14,915 research outputs found
Charging of DMSP/F6 spacecraft in aurora on 10 January 1983
Spacecraft charging has been widely observed in geosynchronous orbit on the ATS-5 and ATS-6 pair and on the SCATHA spacecraft. An adequate theory for explaining the observations exist. Neither the data or theory can be exported to low polar orbit and its drastically different environment. Evidence of charging on the DMSP F6 spacecraft is presented. A simple model is set up explaining the observations. Two independent instruments on the spacecraft showed charging to a moderate (44 volts) negative potential. The selection spectrometer showed a flux of 2 billion electrons per sq. cm. sec. ster. peaked at 9.5 keV. This was marginally sufficient to overcome the flux of cold ambient ions. Charging calculations are presented showing where simplications are justified and where serious uncertainties exist. More serious charging is predicted for the Shuttle in polar orbit
Towards Quantum Gravity: A Framework for Probabilistic Theories with Non-Fixed Causal Structure
General relativity is a deterministic theory with non-fixed causal structure.
Quantum theory is a probabilistic theory with fixed causal structure. In this
paper we build a framework for probabilistic theories with non-fixed causal
structure. This combines the radical elements of general relativity and quantum
theory. The key idea in the construction is physical compression. A physical
theory relates quantities. Thus, if we specify a sufficiently large set of
quantities (this is the compressed set), we can calculate all the others. We
apply three levels of physical compression. First, we apply it locally to
quantities (actually probabilities) that might be measured in a particular
region of spacetime. Then we consider composite regions. We find that there is
a second level of physical compression for the composite region over and above
the first level physical compression for the component regions. Each
application of first and second level physical compression is quantified by a
matrix. We find that these matrices themselves are related by the physical
theory and can therefore be subject to compression. This is the third level of
physical compression. This third level of physical compression gives rise to a
new mathematical object which we call the causaloid. From the causaloid for a
particular physical theory we can calculate verything the physical theory can
calculate. This approach allows us to set up a framework for calculating
probabilistic correlations in data without imposing a fixed causal structure
(such as a background time). We show how to put quantum theory in this
framework (thus providing a new formulation of this theory). We indicate how
general relativity might be put into this framework and how the framework might
be used to construct a theory of quantum gravity.Comment: 23 pages. For special issue of Journal of Physics A entitled "The
quantum universe" in honour of Giancarlo Ghirard
On the theory of magnetic field dependence of heat conductivity in dielectric in isotropic model
Phonon polarization in a magnetic field is analyzed in isotropic model. It is
shown, that at presence of spin-phonon interaction phonon possess circular
polari-zation which causes the appearance of heat flux component perpendicular
both to temperature gradient and magnetic field.Comment: 5 pages, 0 figure
Spreading with evaporation and condensation in one-component fluids
We investigate the dynamics of spreading of a small liquid droplet in gas in
a one-component simple fluid, where the temperature is inhomogeneous around
0.9Tc and latent heat is released or generated at the interface upon
evaporation or condensation (with Tc being the critical temperature). In the
scheme of the dynamic van der Waals theory, the hydrodynamic equations
containing the gradient stress are solved in the axisymmetric geometry. We
assume that the substrate has a finite thickness and its temperature obeys the
thermal diffusion equation. A precursor film then spreads ahead of the bulk
droplet itself in the complete wetting condition. Cooling the substrate
enhances condensation of gas onto the advancing film, which mostly takes place
near the film edge and can be the dominant mechanism of the film growth in a
late stage. The generated latent heat produces a temperature peak or a hot spot
in the gas region near the film edge. On the other hand, heating the substrate
induces evaporation all over the interface. For weak heating, a steady-state
circular thin film can be formed on the substrate. For stronger heating,
evaporation dominates over condensation, leading to eventual disappearance of
the liquid region.Comment: 12 pages, 14 figure
Quantum Mechanical Interaction-Free Measurements
A novel manifestation of nonlocality of quantum mechanics is presented. It is
shown that it is possible to ascertain the existence of an object in a given
region of space without interacting with it. The method might have practical
applications for delicate quantum experiments.Comment: (revised file with no need for macro), 12, TAUP 1865-91
Bell's theorem without inequalities and without unspeakable information
A proof of Bell's theorem without inequalities is presented in which distant
local setups do not need to be aligned, since the required perfect correlations
are achieved for any local rotation of the local setups.Comment: REVTeX4, 4 pages, 1 figure; for Asher Peres' Festschrift, to be
published in Found. Phy
Nonlocal Effects of Partial Measurements and Quantum Erasure
Partial measurement turns the initial superposition not into a definite
outcome but into a greater probability for it. The probability can approach
100%, yet the measurement can undergo complete quantum erasure. In the EPR
setting, we prove that i) every partial measurement nonlocally creates the same
partial change in the distant particle; and ii) every erasure inflicts the same
erasure on the distant particle's state. This enables an EPR experiment where
the nonlocal effect does not vanish after a single measurement but keeps
"traveling" back and forth between particles. We study an experiment in which
two distant particles are subjected to interferometry with a partial "which
path" measurement. Such a measurement causes a variable amount of correlation
between the particles. A new inequality is formulated for same-angle
polarizations, extending Bell's inequality for different angles. The resulting
nonlocality proof is highly visualizable, as it rests entirely on the
interference effect. Partial measurement also gives rise to a new form of
entanglement, where the particles manifest correlations of multiple
polarization directions. Another novelty in that the measurement to be erased
is fully observable, in contrast to prevailing erasure techniques where it can
never be observed. Some profound conceptual implications of our experiment are
briefly pointed out.Comment: To be published in Phys. Rev. A 63 (2001). 19 pages, 12 figures,
RevTeX 3.
Bohm's interpretation and maximally entangled states
Several no-go theorems showed the incompatibility between the locality
assumption and quantum correlations obtained from maximally entangled spin
states. We analyze these no-go theorems in the framework of Bohm's
interpretation. The mechanism by which non-local correlations appear during the
results of measurements performed on distant parts of entangled systems is
explicitly put into evidence in terms of Bohmian trajectories. It is shown that
a GHZ like contradiction of the type+1=-1 occurs for well-chosen initial
positions of the Bohmian trajectories and that it is this essential
non-classical feature that makes it possible to violate the locality condition.Comment: 18 page
A Simple Algorithm for Local Conversion of Pure States
We describe an algorithm for converting one bipartite quantum state into
another using only local operations and classical communication, which is much
simpler than the original algorithm given by Nielsen [Phys. Rev. Lett. 83, 436
(1999)]. Our algorithm uses only a single measurement by one of the parties,
followed by local unitary operations which are permutations in the local
Schmidt bases.Comment: 5 pages, LaTeX, reference adde
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