13,489 research outputs found
A bibliography of electrothermal thruster technology, 1984
Electrothermal propulsion concepts are briefly discussed as an introduction to a bibliography and author index. Nearly 700 citations are given for resistojets, thermal arcjets, pulsed electrothermal thrusters, microwave heated devices, solar thermal thrusters, and laser thermal thrusters
On the theory of composition in physics
We develop a theory for describing composite objects in physics. These can be
static objects, such as tables, or things that happen in spacetime (such as a
region of spacetime with fields on it regarded as being composed of smaller
such regions joined together). We propose certain fundamental axioms which, it
seems, should be satisfied in any theory of composition. A key axiom is the
order independence axiom which says we can describe the composition of a
composite object in any order. Then we provide a notation for describing
composite objects that naturally leads to these axioms being satisfied. In any
given physical context we are interested in the value of certain properties for
the objects (such as whether the object is possible, what probability it has,
how wide it is, and so on). We associate a generalized state with an object.
This can be used to calculate the value of those properties we are interested
in for for this object. We then propose a certain principle, the composition
principle, which says that we can determine the generalized state of a
composite object from the generalized states for the components by means of a
calculation having the same structure as the description of the generalized
state. The composition principle provides a link between description and
prediction.Comment: 23 pages. To appear in a festschrift for Samson Abramsky edited by
Bob Coecke, Luke Ong, and Prakash Panangade
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
NONLOCALITY OF A SINGLE PHOTON REVISITED AGAIN
Comment on L. Hardy, Phys. Rev. Lett. {\bf 73}, 2279 (1994). It is argued
that the experiment proposed by Hardy should not be considered as a single
photon experiment.Comment: 5 pages, LaTe
EPR-Bell Nonlocality, Lorentz Invariance, and Bohmian Quantum Theory
We discuss the problem of finding a Lorentz invariant extension of Bohmian
mechanics. Due to the nonlocality of the theory there is (for systems of more
than one particle) no obvious way to achieve such an extension. We present a
model invariant under a certain limit of Lorentz transformations, a limit
retaining the characteristic feature of relativity, the non-existence of
absolute time resp. simultaneity. The analysis of this model exemplifies an
important property of any Bohmian quantum theory: the quantum equilibrium
distribution cannot simultaneously be realized in all
Lorentz frames of reference.Comment: 24 pages, LaTex, 4 figure
Cathode degradation and erosion in high pressure arc discharges
The various processes which control cathode erosion and degradation were identified and evaluated. A direct current arc discharge was established between electrodes in a pressure-controlled gas flow environment. The cathode holder was designed for easy testing of various cathode materials. The anode was a water cooled copper collector electrode. The arc was powered by a dc power supply with current and voltage regulated cross-over control. Nitrogen and argon were used as propellants and the materials used were two percent thoriated tungsten, barium oxide impregnated porous tungsten, pure tungsten and lanthanum hexaboride. The configurations used were cylindrical solid rods, wire bundles supported by hollow molybdenum tubes, cylindrical hollow tubes, and hollow cathodes of the type used in ion thrusters. The results of the mass loss tests in nitrogen indicated that pure tungsten eroded at a rate more than 10 times faster than the rates of the impregnated tungsten materials. It was found that oxygen impurities of less than 0.5 percent in the nitrogen increased the mass loss rate by a factor of 4 over high purity nitrogen. At power levels less than 1 kW, cathode size and current level did not significantly affect the mass loss rate. The hollow cathode was found to be operable in argon and in nitrogen only at pressures below 400 and 200 torr, respectively
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.
Pressure-temperature phase diagram of ferromagnetic superconductors
The symmetry approach to the description of the (P,T) phase diagram of
ferromagnet superconductors with triplet pairing is developed. Taking into
account the recent experimental observations made on UCoGe it is considered the
case of a crystal with orthorhombic structure and strong spin-orbital coupling.
It is shown that formation of ferromagnet superconducting state from a
superconducting state is inevitably accompanied by the first order type
transition.Comment: 4 pages, 1 figur
Experimental Realization of Teleporting an Unknown Pure Quantum State via Dual Classical and Einstein-Podolski-Rosen Channels
We report on a quantum optical experimental implementation of teleportation
of unknown pure quantum states. This realizes all the nonlocal aspects of the
original scheme proposed by Bennett et al. and is equivalent to it up to a
local operation. We exhibit results for the teleportation of a linearly
polarized state and of an elliptically polarized state. We show that the
experimental results cannot be explained in terms of a classical channel alone.Comment: 11 pages LaTeX, 3 figures, 1 page figures captions. The figures and
figures captions are not encapsulated; please print them separatel
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