14,332 research outputs found
Experimental Outlook for the Pentaquark
A critical look is taken at both positive and null evidence for the
pentaquark. Potential problems with experiments will be discussed
and the question of what conclusion can be drawn from both the positive and the
null results is examined. First the question of existence of the
pentaquark is considered, followed by a discussion of new experiments that are
either planned or in progress to answer questions about its mass, width and
isospin. Finally, indirect evidence for the parity of the is
examined, and suggestions for experiments to measure its parity directly are
given.Comment: MESON2004 conference proceedings, 10 pages, 1 figur
Responses of salmonids to habitat changes
Streams in western North America provide spawning and rearing habitats for several species of salmon and trout that are of substantial economic importance in the region. Timber that grows on lands through which these streams flow is also economically important, and its harvest can substantially change habitat conditions and aquatic production in salmonid streams. Undisturbed forests, the streams that flow through them, and the salmonid communities in these streams have intrinsic scientific, genetic, and cultural values in addition to their economic importance. The complex relations between salmonids and their physical environment, and the changes in these relations brought about by timber harvest, have been investigated extensively (see the bibliography by Macdonald et al. 1988). However, in spite of considerable evidence of profound changes in channel morphology and in light, temperature, and flow regimes associated with timber harvests, much uncertainty exists about the responses of salmonids to these changes
A general numerical analysis program for the superconducting quasiparticle mixer
A user-oriented computer program SISCAP (SIS Computer Analysis Program) for analyzing SIS mixers is described. The program allows arbitrary impedance terminations to be specified at all LO harmonics and sideband frequencies. It is therefore able to treat a much more general class of SIS mixers than the widely used three-frequency analysis, for which the harmonics are assumed to be short-circuited. An additional program, GETCHI, provides the necessary input data to program SISCAP. The SISCAP program performs a nonlinear analysis to determine the SIS junction voltage waveform produced by the local oscillator. The quantum theory of mixing is used in its most general form, treating the large signal properties of the mixer in the time domain. A small signal linear analysis is then used to find the conversion loss and port impedances. The noise analysis includes thermal noise from the termination resistances and shot noise from the periodic LO current. Quantum noise is not considered. Many aspects of the program have been adequately verified and found accurate
1-1.4 Micron Spectral Atlas of Stars
We present a catalog of J-band (1.08 um to 1.35 um) stellar spectra at low
resolution (R ~ 400). The targets consist of 105 stars ranging in spectral type
from O9.5 to M7 and luminosity classes I through V. The relatively featureless
spectra of hot stars, earlier than A4, can be used to remove the atmospheric
features which dominate ground-based J-band spectroscopy. We measure equivalent
widths for three absorption lines and nine blended features which we identify
in the spectra. Using detailed comparison with higher resolution spectra, we
demonstrate that low resolution data can be used for stellar classification,
since several features depend on the effective temperature and gravity. For
example The CN index (1.096 - 1.104 um) decreases with temperature, but the
strength of a blended feature at 1.28 um (consisting of primarily P beta)
increases. The slope of a star's spectrum can also be used to estimate its
effective temperature. The luminosity class of a star correlates with the ratio
of the Mg I (1.1831 um) line to a blend of several species at 1.16 um. Using
these indicators, a star can be classified to within several subclasses.
Fifteen stars with particularly high and low metal abundances are included in
the catalog and some spectral dependence on metal abundance is also found.Comment: 35 pages, 10 figures (3a-e are in gif format. For complete high
resolution figures, go to http://www.astro.ucla.edu/~malkan/newjspec/) ;
Accepted for published in ApJS; For associated spectra files, see
http://www.astro.ucla.edu/~malkan/newjspec
Improved Mean-Field Scheme for the Hubbard Model
Ground state energies and on-site density-density correlations are calculated
for the 1-D Hubbard model using a linear combination of the Hubbard projection
operators. The mean-field coefficients in the resulting linearized Equations of
Motion (EOM) depend on both one-particle static expectation values as well as
static two-particle correlations. To test the model, the one particle
expectation values are determined self-consistently while using Lanczos
determined values for the two particle correlation terms. Ground state energies
and on-site density-density correlations are then compared as a function of
to the corresponding Lanczos values on a 12 site Hubbard chain for 1/2 and 5/12
fillings. To further demonstrate the validity of the technique, the static
correlation functions are also calculated using a similar EOM approach, which
ignores the effective vertex corrections for this problem, and compares those
results as well for a 1/2 filled chain. These results show marked improvement
over standard mean-field techniques.Comment: 10 pages, 3 figures, text and figures as one postscript file -- does
not need to be "TeX-ed". LA-UR-94-294
The Virtues of Scientific Practice: MacIntyre, Virtue Ethics, and the Historiography of Science
âPracticeâ has become a ubiquitous term in the history of science, and yet historians have not always reflected on its philosophical import and especially on its potential connections with ethics. In this essay, we draw on the work of the virtue ethicist Alasdair MacIntyre to develop a theory of âcommunal practicesâ and explore how such an approach can inform the history of science, including allegations about the corruption of science by wealth or power; consideration of scientific ethics or âmoral economiesâ; the role of values in science; the ethical distinctiveness (or not) of scientific vocations; and the relationship between history of science and the practice of science itself
The Virtues of Scientific Practice: MacIntyre, Virtue Ethics, and the Historiography of Science
âPracticeâ has become a ubiquitous term in the history of science, and yet historians have not always reflected on its philosophical import and especially on its potential connections with ethics. In this essay, we draw on the work of the virtue ethicist Alasdair MacIntyre to develop a theory of âcommunal practicesâ and explore how such an approach can inform the history of science, including allegations about the corruption of science by wealth or power; consideration of scientific ethics or âmoral economiesâ; the role of values in science; the ethical distinctiveness (or not) of scientific vocations; and the relationship between history of science and the practice of science itself
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