11,542 research outputs found
Effects of Bose-Einstein Condensation on forces among bodies sitting in a boson heat bath
We explore the consequences of Bose-Einstein condensation on
two-scalar-exchange mediated forces among bodies that sit in a boson gas. We
find that below the condensation temperature the range of the forces becomes
infinite while it is finite at temperatures above condensation.Comment: 10 pages, 2 figure
Factors affecting sperm recovery rates and survival after centrifugation of equine semen
Conventional centrifugation protocols result in important sperm losses during removal of the supernatant. In this study, the effect of centrifugation force (400 or 900 × g), duration (5 or 10 min), and column height (20 or 40 mL; Experiment 1); sperm concentration (25, 50, and 100 × 10[superscript 6]/mL; Experiment 2), and centrifugation medium (EZ-Mixin CST [Animal Reproduction Systems, Chino, CA, USA], INRA96 [IMV Technologies, Maple Grove, MN, USA], or VMDZ [Partnar Animal Health, Port Huron, MI, USA]; Experiment 3) on sperm recovery and survival after centrifugation and cooling and storage were evaluated. Overall, sperm survival was not affected by the combination of centrifugation protocol and cooling. Total sperm yield was highest after centrifugation for 10 min at 400 × g in 20-mL columns (95.6 ± 5%, mean ± SD) or 900 × g in 20-mL (99.2 ± 0.8%) or 40-mL (91.4 ± 4.5%) columns, and at 900 × g for 5 min in 20-mL columns (93.8 ± 8.9%; P < 0.0001). Total (TMY) and progressively motile sperm yield followed a similar pattern (P < 0.0001). Sperm yields were not significantly different among samples centrifuged at various sperm concentrations. However, centrifugation at 100 × 10[superscript 6]/mL resulted in significantly lower total sperm yield (83.8 ± 10.7%) and TMY (81.7 ± 6.8%) compared with noncentrifuged semen. Centrifugation in VMDZ resulted in significantly lower TMY (69.3 ± 22.6%), progressively motile sperm yield (63.5 ± 18.2%), viable yield (60.9 ± 36.5%), and survival of progressively motile sperm after cooling (21 ± 10.8%) compared with noncentrifuged semen. In conclusion, centrifuging volumes of ≤ 20 mL minimized sperm losses with conventional protocols. With 40-mL columns, it may be recommended to increase the centrifugal force to 900 × g for 10 min and dilute the semen to a sperm concentration of 25 to 50 × 10[superscript 6]/mL in a milk- or fractionated milk-based medium. The semen extender VMDZ did not seem well suited for centrifugation of equine semen
Scale-free Networks from Optimal Design
A large number of complex networks, both natural and artificial, share the
presence of highly heterogeneous, scale-free degree distributions. A few
mechanisms for the emergence of such patterns have been suggested, optimization
not being one of them. In this letter we present the first evidence for the
emergence of scaling (and smallworldness) in software architecture graphs from
a well-defined local optimization process. Although the rules that define the
strategies involved in software engineering should lead to a tree-like
structure, the final net is scale-free, perhaps reflecting the presence of
conflicting constraints unavoidable in a multidimensional optimization process.
The consequences for other complex networks are outlined.Comment: 6 pages, 2 figures. Submitted to Europhysics Letters. Additional
material is available at http://complex.upc.es/~sergi/software.ht
Boundary Effects in 2+1 Dimensional Maxwell-Chern-Simons Theory
The boundary effects in the screening of an applied magnetic field in a
finite temperature 2+1 dimensional model of charged fermions minimally coupled
to Maxwell and Chern-Simons fields are investigated. It is found that in a
sample with only one boundary -a half-plane- a total Meissner effect takes
place, while in a sample with two boundaries -an infinite strip- the external
magnetic field partially penetrates the material.Comment: revte
Higgs- and Goldstone bosons-mediated long range forces
In certain mild extensions of the Standard Model, spin-independent long range
forces can arise by exchange of two very light pseudoscalar spin--0 bosons. In
particular, we have in mind models in which these bosons do not have direct
tree level couplings to ordinary fermions. Using the dispersion theoretical
method, we find a behaviour of the potential for the exchange of very
light pseudoscalars and a dependence if the pseudoscalars are true
massless Goldstone bosons.Comment: 13 pages (REVTeX), 2 figure
Beyond-Constant-Mass-Approximation Magnetic Catalysis in the Gauge Higgs-Yukawa Model
Beyond-constant-mass approximation solutions for magnetically catalyzed
fermion and scalar masses are found in a gauge Higgs-Yukawa theory in the
presence of a constant magnetic field. The obtained fermion masses are several
orders of magnitude larger than those found in the absence of Yukawa
interactions. The masses obtained within the beyond-constant-mass approximation
exactly reduce to the results within the constant-mass approach when the
condition is satisfied. Possible
applications to early universe physics and condensed matter are discussed.Comment: Revised numerical results. New figures. Several sections rewritte
Direct Measurement of the Fermi Energy in Graphene Using a Double Layer Structure
We describe a technique which allows a direct measurement of the relative
Fermi energy in an electron system using a double layer structure, where
graphene is one of the two layers. We illustrate this method by probing the
Fermi energy as a function of density in a graphene monolayer, at zero and in
high magnetic fields. This technique allows us to determine the Fermi velocity,
Landau level spacing, and Landau level broadening in graphene. We find that the
N=0 Landau level broadening is larger by comparison to the broadening of upper
and lower Landau levels.Comment: 5 pages, 4 figure
Performance of the Micromegas detector in the CAST experiment
The gaseous Micromegas detector designed for the CERN Axion search experiment
CAST, operated smoothly during Phase-I, which included the 2003 and 2004
running periods. It exhibited linear response in the energy range of interest
(1-10keV), good spatial sensitivity and energy resolution (15-19% FWHM at
5.9keV)as well as remarkable stability. The detector's upgrade for the 2004
run, supported by the development of advanced offline analysis tools, improved
the background rejection capability, leading to an average rate 5x10^-5
counts/sec/cm^2/keV with 94% cut efficiency. Also, the origin of the detected
background was studied with a Monte Carlo simulation, using the GEANT4 package.Comment: Prepared for PSD7: The Seventh International Conference on Position
Sensitive Detectors, Liverpool, United Kingdom, 12-16 Sep. 200
Long range neutrino forces in the cosmic relic neutrino background
Neutrinos mediate long range forces among macroscopic bodies in vacuum. When
the bodies are placed in the neutrino cosmic background, these forces are
modified. Indeed, at distances long compared to the scale , the relic
neutrinos completely screen off the 2-neutrino exchange force, whereas for
small distances the interaction remains unaffected.Comment: 8 pages, 2 figure
- …