9,918 research outputs found
Field Induced Nodal Order Parameter in the Tunneling Spectrum of YBaCuO Superconductor
We report planar tunneling measurements on thin films of
YBaCuO at various doping levels under magnetic fields. By
choosing a special setup configuration, we have probed a field induced energy
scale that dominates in the vicinity of a node of the d-wave superconducting
order parameter. We found a high doping sensitivity for this energy scale. At
Optimum doping this energy scale is in agreement with an induced
order parameter. We found that it can be followed down to low fields at optimum
doping, but not away from it.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
Avoidability of formulas with two variables
In combinatorics on words, a word over an alphabet is said to
avoid a pattern over an alphabet of variables if there is no
factor of such that where is a
non-erasing morphism. A pattern is said to be -avoidable if there exists
an infinite word over a -letter alphabet that avoids . We consider the
patterns such that at most two variables appear at least twice, or
equivalently, the formulas with at most two variables. For each such formula,
we determine whether it is -avoidable, and if it is -avoidable, we
determine whether it is avoided by exponentially many binary words
Cosmology from String Theory
We explore the cosmological content of Salam-Sezgin six dimensional
supergravity, and find a solution to the field equations in qualitative
agreement with observation of distant supernovae, primordial nucleosynthesis
abundances, and recent measurements of the cosmic microwave background. The
carrier of the acceleration in the present de Sitter epoch is a quintessence
field slowly rolling down its exponential potential. Intrinsic to this model is
a second modulus which is automatically stabilized and acts as a source of cold
dark matter with a mass proportional to an exponential function of the
quintessence field (hence realizing VAMP models within a String context).
However, any attempt to saturate the present cold dark matter component in this
manner leads to unacceptable deviations from cosmological data -- a numerical
study reveals that this source can account for up to about 7% of the total cold
dark matter budget. We also show that (1) the model will support a de Sitter
energy in agreement with observation at the expense of a miniscule breaking of
supersymmetry in the compact space; (2) variations in the fine structure
constant are controlled by the stabilized modulus and are negligible; (3)
``fifth''forces are carried by the stabilized modulus and are short range; (4)
the long time behavior of the model in four dimensions is that of a
Robertson-Walker universe with a constant expansion rate (w = -1/3). Finally,
we present a String theory background by lifting our six dimensional
cosmological solution to ten dimensions.Comment: Version to be published in Physical Review
Investigation of Halogenated Components Formed from Chlorination of Natural Waters: Preliminary Studies
Chlorination of power plant cooling water is extensively used as a means of controlling biofouling. This practice presents the potential for formation of halogenated organic compounds hazardous to man and his environment. Accordingly, the organic composition resulting from the chlorination of natural waters (northern Olympic Penn1sula sea water and the Columbia River in Washington State} has been investigated. Nonpolar lipophilic organic halogens were extracted by passing large volumes of water over columns of XAD-2 macroreticular resins. Examination of ether extracts from the resin columns using capillary gas chromatography revealed the presence of halogenated methanes, as well as other electron-capturing components~ that were not found when unchlorinated water was sampled. Examination of the chlorinated water extracts using gas chromatography/mass spectrometry revealed complex mixtures which generally were not separable into individual components~ even when high efficiency WCOT capillary columns were used. The samples were separated into fractions of increasing polarity using a water-deactivated silica gel column. Fractions were thus obtained which were more amenable to GC/MS investigation. Haloforms were identified as the major halogenated product from chlorination of the waters studied. Other halogenated products were found at much lower concentrations
Metallicities of M Dwarf Planet Hosts from Spectral Synthesis
We present the first spectroscopic metallicities of three M dwarfs with known
or candidate planetary mass companions. We have analyzed high resolution, high
signal-to-noise spectra of these stars which we obtained at McDonald
Observatory. Our analysis technique is based on spectral synthesis of atomic
and molecular features using recently revised cool-star model atmospheres and
spectrum synthesis code. The technique has been shown to yield results
consistent with the analyses of solar-type stars and allows measurements of M
dwarf [M/H] values to 0.12 dex precision. From our analysis, we find [M/H] =
-0.12, -0.32, and -0.33 for GJ 876, GJ 436, and GJ 581 respectively. These
three M dwarf planet hosts have sub-solar metallicities, a surprising departure
from the trend observed in FGK-type stars. This study is the first part of our
ongoing work to determine the metallicities of the M dwarfs included in the
McDonald Observatory planet search program.Comment: 13 pages, 2 figures, accepted for publication in ApJ
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