23,540 research outputs found
Parity-Violating Nuclear Force as derived from QCD Sum Rules
Parity-violating nuclear force, as may be accessed from parity violation
studies in nuclear systems, represents an area of nonleptonic weak interactions
which has been the subject of experimental investigations for several decades.
In the simple meson-exchange picture, parity-violating nuclear force may be
parameterized as arising from exchange of \pi, \rho, \omega, or other meson(s)
with strong meson-nucleon coupling at one vertex and weak parity-violating
meson-nucleon coupling at the other vertex. The QCD sum rule method allows for
a fairly complicated, but nevertheless straightforward, leading-order
loop-contribution determination of the various parity-violating MNN couplings
starting from QCD (with the nontrivial vacuum) and Glashow-Salam-Weinberg
electroweak theory. We continue our earlier investigation of parity-violating
\pi NN coupling (by Henley, Hwang, and Kisslinger) to other parity-violating
couplings. Our predictions are in reasonable overall agreement with the results
estimated on phenomenological grounds, such as in the now classic paper of
Desplanques, Donoghue, and Holstein (DDH), in the global experimental fit of
Adelberger and Haxton (AH), or the effective field theory (EFT) thinking of
Ramsey-Musolf and Page (RP).Comment: 17 pages, 5 figure
Algebraic Structure of Discrete Zero Curvature Equations and Master Symmetries of Discrete Evolution Equations
An algebraic structure related to discrete zero curvature equations is
established. It is used to give an approach for generating master symmetries of
first degree for systems of discrete evolution equations and an answer to why
there exist such master symmetries. The key of the theory is to generate
nonisospectral flows from the discrete spectral
problem associated with a given system of discrete evolution equations. Three
examples are given.Comment: 24 pages, LaTex, revise
A cryogenic dc-dc power converter for a 100kW synchronous HTS generator at liquid nitrogen temperatures
A dc-dc converter has been developed for retrofitting inside the vacuum space of the HTS rotor of a synchronous generator. The heavy copper sections of the current leads used for energising the HTS field winding were replaced by cryogenic power electronics; consisting of the converter and a rotor control unit. The converter board was designed using an H-bridge configuration with two 5A rated wires connecting the cryogenic boards to the stator control board located on the outside of the generator and drawing power from a (5A, 50V) dc power source. The robustness of converter board was well demonstrated when it was powered up from a cold start at 82K. When charging the field winding with moderate currents (30A), the heat in-leak to the ācoldā rotor core was only 2W. It continued to function down to 74K, surviving several quenches. However, the quench protection function failed when injecting 75A into the field winding, resulting in the burn out of one of the DC-link capacitors. The magnitudes of the critical currents measured with the original current leads were compared to the quench currents, which was defined as the current which triggered quench protection protocol. The difference between the two currents was rather large, (~20A). However, additional measurements using a single HTS coil in liquid nitrogen found that this reduction should not be so dramatic and in the region of 4A. Our conclusions identified the converterās switching voltage and its operating frequency as two parameters, which could have contributed to lowering the quench current. Magnetic fields and eddy currents are expected to be more prominent the field winding and its impact on the converter also need further investigation
Super-soft symmetry energy encountering non-Newtonian gravity in neutron stars
Considering the non-Newtonian gravity proposed in the grand unification
theories, we show that the stability and observed global properties of neutron
stars can not rule out the super-soft nuclear symmetry energies at
supra-saturation densities. The degree of possible violation of the
Inverse-Square-Law of gravity in neutron stars is estimated using an Equation
of State (EOS) of neutron-rich nuclear matter consistent with the available
terrestrial laboratory data.Comment: Version accepted by Physical Review Letter
Evolution of magnetic component in Yang-Mills condensate dark energy models
The evolution of the electric and magnetic components in an effective
Yang-Mills condensate dark energy model is investigated. If the electric field
is dominant, the magnetic component disappears with the expansion of the
Universe. The total YM condensate tracks the radiation in the earlier Universe,
and later it becomes thus is similar to the cosmological constant.
So the cosmic coincidence problem can be avoided in this model. However, if the
magnetic field is dominant, holds for all time, suggesting that it
cannot be a candidate for the dark energy in this case.Comment: 12 pages, 4 figures, minor typos correcte
Suppression of Superconducting Critical Current Density by Small Flux Jumps in Thin Films
By doing magnetization measurements during magnetic field sweeps on thin
films of the new superconductor , it is found that in a low temperature
and low field region small flux jumps are taking place. This effect strongly
suppresses the central magnetization peak leading to reduced nominal
superconducting critical current density at low temperatures. A borderline for
this effect to occur is determined on the field-temperature (H-T) phase
diagram. It is suggested that the small size of the flux jumps in films is due
to the higher density of small defects and the relatively easy thermal
diffusion in thin films in comparison with bulk samples.Comment: 7 figures Phys. Rev. B accepted scheduled issue: 01 Feb 200
A multiple exp-function method for nonlinear differential equations and its application
A multiple exp-function method to exact multiple wave solutions of nonlinear
partial differential equations is proposed. The method is oriented towards ease
of use and capability of computer algebra systems, and provides a direct and
systematical solution procedure which generalizes Hirota's perturbation scheme.
With help of Maple, an application of the approach to the dimensional
potential-Yu-Toda-Sasa-Fukuyama equation yields exact explicit 1-wave and
2-wave and 3-wave solutions, which include 1-soliton, 2-soliton and 3-soliton
type solutions. Two cases with specific values of the involved parameters are
plotted for each of 2-wave and 3-wave solutions.Comment: 12 pages, 16 figure
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