37,094 research outputs found
Negative Specific Heat in a Quasi-2D Generalized Vorticity Model
Negative specific heat is a dramatic phenomenon where processes decrease in
temperature when adding energy. It has been observed in gravo-thermal collapse
of globular clusters. We now report finding this phenomenon in bundles of
nearly parallel, periodic, single-sign generalized vortex filaments in the
electron magnetohydrodynamic (EMH) model for the unbounded plane under strong
magnetic confinement. We derive the specific heat using a steepest descent
method and a mean field property. Our derivations show that as temperature
increases, the overall size of the system increases exponentially and the
energy drops. The implication of negative specific heat is a runaway reaction,
resulting in a collapsing inner core surrounded by an expanding halo of
filaments.Comment: 12 pages, 3 figures; updated with revision
A variety of lepton number violating processes related to Majorana neutrino masses
A Majorana type of the neutrino mass matrix induces a class of lepton number
violating processes. Cross sections of these reactions are given in terms of
the neutrino mass matrix element, and a semi-realistic event rate is estimated.
These processes provide mass and mixing parameters not directly accessible by
the neutrino oscillation experiments. If these processes are discovered with a
larger rate than given here, it would imply a new physics of the lepton number
violation not directly related to the Majorana neutrino mass, such as R-parity
violating operators in SUSY models.Comment: 15 pages, 1 figur
Intersubband transitions in nonpolar GaN/Al(Ga)N heterostructures in the short and mid-wavelength infrared regions
This paper assesses nonpolar m- and a-plane GaN/Al(Ga)N multi-quantum-wells
grown on bulk GaN for intersubband optoelectronics in the short- and
mid-wavelength infrared ranges. The characterization results are compared to
those for reference samples grown on the polar c-plane, and are verified by
self-consistent Schr\"odinger-Poisson calculations. The best results in terms
of mosaicity, surface roughness, photoluminescence linewidth and intensity, as
well as intersubband absorption are obtained from m-plane structures, which
display room-temperature intersubband absorption in the range from 1.5 to 2.9
um. Based on these results, a series of m-plane GaN/AlGaN multi-quantum-wells
were designed to determine the accessible spectral range in the mid-infrared.
These samples exhibit tunable room-temperature intersubband absorption from 4.0
to 5.8 um, the long-wavelength limit being set by the absorption associated
with the second order of the Reststrahlen band in the GaN substrates
Widely separated binary systems of very low mass stars
In this paper we review some recent detections of wide binary brown dwarf
systems and discuss them in the context of the multiplicity properties of very
low-mass stars and brown dwarfs.Comment: 2 pages, 1 figure (new version with minor corrections); to appear in
the proceedings of the workshop "Ultra-low mass star formation and
evolution", to be published in A
The Gauge Hierarchy Problem and Higher Dimensional Gauge Theories
We report on an attempt to solve the gauge hierarchy problem in the framework
of higher dimensional gauge theories. Both classical Higgs mass and
quadratically divergent quantum correction to the mass are argued to vanish.
Hence the hierarchy problem in its original sense is solved. The remaining
finite mass correction is shown to depend crucially on the choice of boundary
condition for matter fields, and a way to fix it dynamically is presented. We
also point out that on the simply-connected space even the finite mass
correction vanishes.Comment: LaTeX2e. 12 pages, 3 Postscript figures; Added references, some
comment
Effect of different feeding regimes on reproduction and survival of ablated Penaeus monodon Fabricius
Results of experiments conducted on ablated Penaeus monodon, fed with 4 different feeds (pellet-pellet, mussel-mussel, mussel-pellet and squid-pellet), on survival, spawning, fecundity and hatching rate are given and discussed
Mutation breeding of Phaseolus vulgaris L.: Studies on the effects of irradiation dosage to resolve a suitable procedure of handling M and M generations
Seedling growth studies on gamma-irradiated seeds of Phaseolus vulgaris were conducted in the
greenhouse and the field. No significant differences in germination scores between the unirradiated control
and the seeds exposed to 10, 20, 25, 30, 35 and 40 Krads of gamma radiation were obtained. Exposure
to 100 Krads, however, was lethal to the apical meristem. Growth of the epicotyl under greenhouse conditions
was the most affected by gamma radiation.
Based upon a 30% reduction in epicotyl length the optimum dose for irradiation was 30 Krads.
At this level of irradiation the survival score at harvest under field conditions was 50% of that of the
unirradiated control. Treatment with 30 Krads also gave the highest number of solid chlorophyll mutants.While not all the chlorophyll mutants were scored in the Bs (Sl gle seed bulk) populations, the %
occurrence was consistently higher than that for the corresponding Bp (single pod bulk) populations.
Based on these results, it is recommended that:
a) the most suitable level of gamma radiation to use in a mutation breeding programme is 30 Krads;
b) the M1 seeds should be field-planted at double the planting density of the control;
c) the M1 plants should be harvested such that the Bs (single seed bulk) population be used for screening
of the mutants
Finite temperature Casimir pistons for electromagnetic field with mixed boundary conditions and its classical limit
In this paper, the finite temperature Casimir force acting on a
two-dimensional Casimir piston due to electromagnetic field is computed. It was
found that if mixed boundary conditions are assumed on the piston and its
opposite wall, then the Casimir force always tends to restore the piston
towards the equilibrium position, regardless of the boundary conditions assumed
on the walls transverse to the piston. In contrary, if pure boundary conditions
are assumed on the piston and the opposite wall, then the Casimir force always
tend to pull the piston towards the closer wall and away from the equilibrium
position. The nature of the force is not affected by temperature. However, in
the high temperature regime, the magnitude of the Casimir force grows linearly
with respect to temperature. This shows that the Casimir effect has a classical
limit as has been observed in other literatures.Comment: 14 pages, 3 figures, accepted by Journal of Physics
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