3,501 research outputs found
Fuel cycles in nuclear reactors
Series numbering from publisher's list"61"--stamped on cover"Unclassified. NYO-2131."Originally issued by the first author as an Sc. D. thesis, Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1959Contract AT(30-1)-207
Localized states in strong magnetic field: resonant scattering and the Dicke effect
We study the energy spectrum of a system of localized states coupled to a 2D
electron gas in strong magnetic field. If the energy levels of localized states
are close to the electron energy in the plane, the system exhibits a kind of
collective behavior analogous to the Dicke effect in optics. The latter
manifests itself in ``trapping'' of electronic states by localized states. At
the same time, the electronic density of states develops a gap near the
resonance. The gap and the trapping of states appear to be complementary and
reflect an intimate relation between the resonant scattering and the Dicke
effect. We reveal this relation by presenting the exact solution of the problem
for the lowest Landau level. In particular, we show that in the absence of
disorder the system undergoes a phase transition at some critical concentration
of localized states.Comment: 28 pages + 9 fig
Improved Fan Control
Cooling large computer enclosures is an increasingly difficult task, usually requiring multiple fans and/or multiple rotors per fan. A technique is disclosed that reduces stress on a power distribution system for multiple fans by delaying individual fan control signals at the final distribution point near the fans
Excitonic Effects and Optical Spectra of Single-Walled Carbon Nanotubes
Many-electron effects often dramatically modify the properties of reduced
dimensional systems. We report calculations, based on an many-electron Green's
function approach, of electron-hole interaction effects on the optical spectra
of small-diameter single-walled carbon nanotubes. Excitonic effects
qualitatively alter the optical spectra of both semiconducting and metallic
tubes. Excitons are bound by ~ 1 eV in the semiconducting (8,0) tube and by ~
100 meV in the metallic (3,3) tube. These large many-electron effects explain
the discrepancies between previous theories and experiments.Comment: 6 pages, 3 figures, 2 table
Treatment-based classification of low back pain – who are the unclear classifications?
A recent focus in low back pain research has been to identify patient subgroups that respond best to certain treatments. To integrate these subgroup findings into a useable form, a treatment-based classification algorithm for LBP was created.1,2 To allow the algorithm to be comprehensive – eg, provide a classification for all patients – additional criteria are provided to assist therapists’ decisions for patients who do not clearly meet a treatment subgroup (unclear classifications).
Recent research found that approximately 34% of patients will receive unclear classifications using the algorithm.3 It has also been shown that the reliability of the classification decision for unclear classifications is poor – significant variability between raters exists.3 In addition to poor reliability, outcomes for patients receiving unclear classifications may be inferior to outcomes of those receiving clear classifications.4 Thus the aim of the present study was to determine if people receiving unclear classifications are different from those with clear classifications in the hopes to refine the classification algorithm
Broom Snakeweed Extracts Dosed to Late-Term Pregnant Cattle Do Not Cause Premature Parturition
Broom snakeweed [Gutierrezia sarothrae (Pursh) Britton and Rusby] and threadleaf snakeweed [G. microcephala (DC.) A. Gray] are found on many rangelands in western North America. Snakeweeds are generally unpalatable; however, animals will graze them when other forage is not available and there are field reports that pregnant cows that graze snakeweeds may abort calves. Subsequent feeding studies using fresh cut snakeweed, ground and gavaged into pregnant cattle have failed to reproduce abortions, though it was evident that at high doses snakeweed quickly damaged the rumen microflora resulting in severe rumen atony, bloating and acidosis. We report here an attempt to solvent extract the snakeweeds, mix the extracts with ground alfalfa hay, and test the extracts for abortifacient activity in late-term pregnant cattle. The dosed extracts again appear to be unable to reproduce snakeweed induced abortions in cattle. Extracts from snakeweed chemotype 1 plant appear to be quite toxic to the rumen and caused complete rumen stasis after 2-3 days. In contrast, cattle receiving chemotype 2 extracts were able to tolerate over twice the dosage as that given for chemotype 1 extracts. We conclude that broom snakeweed plants are unlikely to be directly responsible for cattle abortions observed in cattle grazing snakeweed infested rangelands. It is more likely that cattle may be affected by rumen toxicity and/or might suffer from poor nutritional factors given the lack of quality forage that might be available on rangelands with high snakeweed infestation
Recent Decisions
Comments on recent decisions by William J. Daner, William T. Huston, James D. Matthews, Benedict R. Danko, John E. Lindberg, Maynard R. Bissonnette, Joseph H. Harrison, Peter J. Donahue, Louis J. Mustico, Donald John Tufts, Henry M. Shine, Jr., Arthur L. Beaudette, Luke R. Morin, John F. Mendoza, and Thomas A. Muscatello
Resonant scattering in a strong magnetic field: exact density of states
We study the structure of 2D electronic states in a strong magnetic field in
the presence of a large number of resonant scatterers. For an electron in the
lowest Landau level, we derive the exact density of states by mapping the
problem onto a zero-dimensional field-theoretical model. We demonstrate that
the interplay between resonant and non-resonant scattering leads to a
non-analytic energy dependence of the electron Green function. In particular,
for strong resonant scattering the density of states develops a gap in a finite
energy interval. The shape of the Landau level is shown to be very sensitive to
the distribution of resonant scatterers.Comment: 12 pages + 3 fig
Surface Instabilities on Liquid Oxygen in an Inhomogeneous Magnetic Field
Liquid oxygen exhibits surface instabilities when subjected to a sufficiently
strong magnetic field. A vertically oriented magnetic field gradient both
increases the magnetic field value at which the pattern forms and shrinks the
length scale of the surface patterning. We show that these effects of the field
gradient may be described in terms of an ``effective gravity'', which in our
experiments may be varied from 1g to 360g.Comment: 4 pages, 5 embedded figures in eps forma
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