12,321 research outputs found
An Inexpensive Liquid Crystal Spectropolarimeter for the Dominion Astrophysical Observatory Plaskett Telescope
A new, inexpensive polarimetric unit has been constructed for the Dominion
Astrophysical Observatory (DAO) 1.8-m Plaskett telescope. It is implemented as
a plug-in module for the telescope's existing Cassegrain spectrograph, and
enables medium resolution (R~10,000) circular spectropolarimetry of point
sources. A dual-beam design together with fast switching of the wave plate at
rates up to 100Hz, and synchronized with charge shuffling on the CCD, is used
to significantly reduce instrumental effects and achieve high-precision
spectropolarimetric measurements for a very low cost. The instrument is
optimized to work in the wavelength range 4700 - 5300A to simultaneously detect
polarization signals in the H beta line as well as nearby metallic lines. In
this paper we describe the technical details of the instrument, our observing
strategy and data reduction techniques, and present tests of its scientific
performance.Comment: 32 pages, 15 figures. Accepted for publication in PAS
Ladder proof of nonlocality for two spin-half particles revisited
In this paper we extend the ladder proof of nonlocality without inequalities
for two spin-half particles given by Boschi et al [PRL 79, 2755 (1997)] to the
case in which the measurement settings of the apparatus measuring one of the
particles are different from the measurement settings of the apparatus
measuring the other particle. It is shown that, in any case, the proportion of
particle pairs for which the contradiction with local realism goes through is
maximized when the measurement settings are the same for each apparatus. Also
we write down a Bell inequality for the experiment in question which is
violated by quantum mechanics by an amount which is twice as much as the amount
by which quantum mechanics violates the Bell inequality considered in the above
paper by Boschi et al.Comment: LaTeX, 7 pages, 1 figure, journal versio
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
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
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
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
Impact of the various spin and orbital ordering processes on multiferroic properties of orthovanadate DyVO3
The orthovanadate DyVO3 crystal, known to exhibit multiple structural, spin
and orbital ordering transitions, is presently investigated on the basis of
magnetization, heat capacity, resistivity, dielectric and polarization
measurements. Our main result is experimental evidence for the existence of
multiferroicity below a high TC of 108 K over a wide temperature range
including different spin-orbital ordered states. The onset of ferroelectricity
is found to coincide with the antiferromagnetic C-type spin ordering transition
taking place at 108 K, which indicates that DyVO3 belongs to type II
multiferroics exhibiting a coupling between magnetism and ferroelectricity.
Some anomalies detected on the temperature dependence of electric polarization
are discussed with respect to the nature of the spin-orbital ordered states of
the V sublattice and the degree of spin alignment in the Dy sublattice. The
orthovanadates RVO3 (R = rare earth or Y) form an important new category for
searching for high-TC multiferroics.Comment: 25 pages, 7 figures, 68 references, one supplementary material,
Physical Review B, Published 23 July 201
Rapeseed. 2. Insect control
RAPESEED crops are highly susceptible to attack from a number of insects and, in most cases, some crop protection measures will be necessary to achieve satisfactory yields.
This article discusses the insects that have been a problem in rapeseed crops in Western Australia to date
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