17,666 research outputs found
Distribution of Gamma-Ray Bursts in Halo Neutron Star-Comet Models
The motions of comets and neutron stars have been integrated over five
billion years in the Galactic potential to determine a gamma-ray burst
distribution, presuming that bursts are the result of interactions between
these two families of objects. The comets originate in two distinct populations
- one from ejection by stars in the Galactic disk, and the other from ejection
by stars in globular clusters. No choice of the free parameters resulted in
agreement with both the isotropy data and the data.Comment: 4 pages LaTex and two style files, tarred, compressed, and uuencoded.
One postscript figure. To appear in Astrophysics and Space Science as part of
the proceedings of the 29th ESLAB Symposium 'Toward the Source of Gamma-Ray
Bursts' held in Noordwijk, 1995. A postscript version can be found at
http://astro.queensu.ca/~mark/preprints.htm
The Deutsch Field Gamma-Ray Pulsar - Paper I: The Model Basics
A new model for the high-energy emission from pulsars is developed by
considering charged particle motion in the fields of a spinning, highly
magnetised and conducting sphere in vacuum. A generally applicable
approximation to the particle motion in strong fields is developed and applied
to the numerical modelling, and the radiation emitted by curvature emission is
summed to generate light curves. The model predicts many of the observed
features of pulsar light curves. This paper outlines the basic properties of
the model; a subsequent paper will discuss the statistical properties of a
population of model pulsars and apply the model to the known gamma-ray pulsars.Comment: 11 pages LaTex, 10 postscript figures included with psfig. The paper
can also be found at ftp://astro.queensu.ca/pub/mark/preprints/paper1.ps.Z as
a compressed postscript file. Submitted to MNRA
Genetic Transformation, Regeneration and Analysis of Transgenic Peanut
Crop Production/Industries,
Wave packet dynamics of potassium dimers attached to helium nanodroplets
The dynamics of vibrational wave packets excited in K dimers attached to
superfluid helium nanodroplets is investigated by means of femtosecond
pump-probe spectroscopy. The employed resonant three-photon-ionization scheme
is studied in a wide wavelength range and different pathways leading to
K-formation are identified. While the wave packet dynamics of the
electronic ground state is not influenced by the helium environment,
perturbations of the electronically excited states are observed. The latter
reveal a strong time dependence on the timescale 3-8 ps which directly reflects
the dynamics of desorption of K off the helium droplets
Entanglement-enhanced measurement of a completely unknown phase
The high-precision interferometric measurement of an unknown phase is the
basis for metrology in many areas of science and technology. Quantum
entanglement provides an increase in sensitivity, but present techniques have
only surpassed the limits of classical interferometry for the measurement of
small variations about a known phase. Here we introduce a technique that
combines entangled states with an adaptive algorithm to precisely estimate a
completely unspecified phase, obtaining more information per photon that is
possible classically. We use the technique to make the first ab initio
entanglement-enhanced optical phase measurement. This approach will enable
rapid, precise determination of unknown phase shifts using interferometry.Comment: 6 pages, 4 figure
Evaluation of enzyme immunoassays in the diagnosis of camel (Camelus dromedarius) trypanosomiasis:a preliminary investigation
Three enzyme immunoassays were used for the serodiagnosis of Trypanosoma evansi in camels in the Sudan in order to evaluate their ability to discriminate between infected and non-infected animals. Two assays were used for the detection of trypanosomal antibodies, one using specific anti-camel IgG conjugate and another using a non-specific Protein A conjugate. The third assay detected the presence of trypanosomal antigens using anti-T. evansi antibodies in a double antibody sandwich assay. Inspection of the frequency distribution of assay results suggested that the ELISA for circulating trypanosomal antibodies using specific antisera and the ELISA for circulating antigens can distinguish between non-infected camels and infected camels exhibiting patent infections or not. The ELISA using Protein A conjugate to bind non-specifically to camel immunoglobulin did not appear to discriminate between infected and non-infected animals
Recommended from our members
Nucleosome Assembly Proteins Get SET to Defeat the Guardian of Chromosome Cohesion
Steep sharp-crested gravity waves on deep water
A new type of steady steep two-dimensional irrotational symmetric periodic
gravity waves on inviscid incompressible fluid of infinite depth is revealed.
We demonstrate that these waves have sharper crests in comparison with the
Stokes waves of the same wavelength and steepness. The speed of a fluid
particle at the crest of new waves is greater than their phase speed.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Adaptive Measurements in the Optical Quantum Information Laboratory
Adaptive techniques make practical many quantum measurements that would
otherwise be beyond current laboratory capabilities. For example: they allow
discrimination of nonorthogonal states with a probability of error equal to the
Helstrom bound; they allow measurement of the phase of a quantum oscillator
with accuracy approaching (or in some cases attaining) the Heisenberg limit;
and they allow estimation of phase in interferometry with a variance scaling at
the Heisenberg limit, using only single qubit measurement and control. Each of
these examples has close links with quantum information, in particular
experimental optical quantum information: the first is a basic quantum
communication protocol; the second has potential application in linear optical
quantum computing; the third uses an adaptive protocol inspired by the quantum
phase estimation algorithm. We discuss each of these examples, and their
implementation in the laboratory, but concentrate upon the last, which was
published most recently [Higgins {\em et al.}, Nature vol. 450, p. 393, 2007].Comment: 12 pages, invited paper to be published in IEEE Journal of Selected
Topics in Quantum Electronics: Quantum Communications and Information Scienc
- …