46,743 research outputs found
Fast scan control for deflection type mass spectrometers
A high speed scan device is reported that allows most any scanning sector mass spectrometer to measure preselected gases at a very high sampling rate. The device generates a rapidly changing staircase output which is applied to the accelerator of the spectrometer and it also generates defocusing pulses that are applied to one of the deflecting plates of the spectrometer which when shorted to ground deflects the ion beam away from the collector. A defocusing pulse occurs each time there is a change in the staircase output
Double-impulse magnetic focusing of launched cold atoms.
We have theoretically investigated three-dimensional focusing of a launched cloud of cold atoms using a pair of magnetic lens pulses (the alternate-gradient method). Individual lenses focus radially and defocus axially or vice versa. The performance of the two possible pulse sequences are compared and found to be ideal for loading both 'pancake' and 'sausage' shaped magnetic/optical microtraps. It is shown that focusing aberrations are considerably smaller for double-impulse magnetic lenses compared to single-impulse magnetic lenses. An analysis of clouds focused by the double-impulse technique is presented
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Evolutionarily stable sexual allocation by both stressed and unstressed potentially simultaneous hermaphrodites within the same population.
Factors influencing allocation of resources to male and female offspring continue to be of great interest to evolutionary biologists. A simultaneous hermaphrodite is capable of functioning in both male and female mode at the same time, and such a life-history strategy is adopted by most flowering plants and by many sessile aquatic animals. In this paper, we focus on hermaphrodites that nourish post-zygotic stages, e.g. flowering plants and internally fertilising invertebrates, and consider how their sex allocation should respond to an environmental stress that reduces prospects of survival but does not affect all individuals equally, rather acting only on a subset of the population. Whereas dissemination of pollen and sperm can begin at sexual maturation, release of seeds and larvae is delayed by embryonic development. We find that the evolutionarily stable strategy for allocation between male and female functions will be critically dependent on the effect of stress on the trade-off between the costs of male and female reproduction, (i.e. of sperm and embryos). Thus, we identify evaluation of this factor as an important challenge to empiricists interested in the effects of stress on sex allocation. When only a small fraction of the population is stressed, we predict that stressed individuals will allocate their resources entirely to male function and unstressed individuals will increase their allocation to female function. Conversely, when the fraction of stress-affected individuals is high, stressed individuals should respond to this stressor by increasing investment in sperm and unstressed individuals should invest solely in embryos. A further prediction of the model is that we would not expect to find populations in the natural world where both stressed and unstressed individuals are both hermaphrodite
Flammability screening tests of resins
Selected flammability characteristics of glass cloth laminates of thermosetting resins are evaluated. A protocol for the evaluation of the flammability hazards presented by glass cloth laminates of thermosetting resins and the usefulness of that protocol with two laminates are presented. The glass laminates of an epoxy resin, M-751 are evaluated for: (1) determination of smoke generation from the laminates; (2) analysis of products of oxidative degradation of the laminates; (3) determination of minimum oxygen necessary to maintain flaming oxidation; (4) evaluation of toxicological hazards
Current status of MCNP6 as a simulation tool useful for space and accelerator applications
For the past several years, a major effort has been undertaken at Los Alamos
National Laboratory (LANL) to develop the transport code MCNP6, the latest LANL
Monte-Carlo transport code representing a merger and improvement of MCNP5 and
MCNPX. We emphasize a description of the latest developments of MCNP6 at higher
energies to improve its reliability in calculating rare-isotope production,
high-energy cumulative particle production, and a gamut of reactions important
for space-radiation shielding, cosmic-ray propagation, and accelerator
applications. We present several examples of validation and verification of
MCNP6 compared to a wide variety of intermediate- and high-energy experimental
data on reactions induced by photons, mesons, nucleons, and nuclei at energies
from tens of MeV to about 1 TeV/nucleon, and compare to results from other
modern simulation tools.Comment: 4 pages, 3 figures, Proc. 11th Conference on the Intersections of
Particle and Nuclear Physics (CIPANP 2012), St. Petersburg, FL, May 28 - June
3, 201
7-Li(p,n) Nuclear Data Library for Incident Proton Energies to 150 MeV
We describe evaluation methods that make use of experimental data, and
nuclear model calculations, to develop an ENDF-formatted data library for the
reaction p + Li7 for incident protons with energies up to 150 MeV. The
important 7-Li(p,n_0) and 7-Li(p,n_1) reactions are evaluated from the
experimental data, with their angular distributions represented using Lengendre
polynomial expansions. The decay of the remaining reaction flux is estimated
from GNASH nuclear model calculations. The evaluated ENDF-data are described in
detail, and illustrated in numerous figures. We also illustrate the use of
these data in a representative application by a radiation transport simulation
with the code MCNPX.Comment: 11 pages, 8 figures, LaTeX, submitted to Proc. 2000 ANS/ENS
International Meeting, Nuclear Applications of Accelerator Technology
(AccApp00), November 12-16, Washington, DC, US
Daylight quantum key distribution over 1.6 km
Quantum key distribution (QKD) has been demonstrated over a point-to-point
-km atmospheric optical path in full daylight. This record
transmission distance brings QKD a step closer to surface-to-satellite and
other long-distance applications.Comment: 4 pages, 2 figures, 1 table. Submitted to PRL on 14 January 2000 for
publication consideratio
Anomalous diffusion in correlated continuous time random walks
We demonstrate that continuous time random walks in which successive waiting
times are correlated by Gaussian statistics lead to anomalous diffusion with
mean squared displacement ~t^{2/3}. Long-ranged correlations of the
waiting times with power-law exponent alpha (0<alpha<=2) give rise to
subdiffusion of the form ~t^{alpha/(1+alpha)}. In contrast correlations
in the jump lengths are shown to produce superdiffusion. We show that in both
cases weak ergodicity breaking occurs. Our results are in excellent agreement
with simulations.Comment: 6 pages, 6 figures. Slightly revised version, accepted to J Phys A as
a Fast Track Communicatio
Finding passwords by random walks: How long does it take?
We compare an efficiency of a deterministic "lawnmower" and random search
strategies for finding a prescribed sequence of letters (a password) of length
M in which all letters are taken from the same Q-ary alphabet. We show that at
best a random search takes two times longer than a "lawnmower" search.Comment: To appear in J. Phys. A, special issue on "Random Search Problem:
Trends and Perspectives", eds.: MEG da Luz, E Raposo, GM Viswanathan and A
Grosber
The diary of an undercover agent in Mexico’s war on drugs
Diario de un agente encubierto [Diary of an undercover agent], by Tomás Borges, Mexico
City, Temas de Hoy, 2013, 342pp., £20 (paperback), ISBN 978607071851
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