45,220 research outputs found
A new model for the double well potential
A new model for the double well potential is presented in the paper. In the
new potential, the exchanging rate could be easily calculated by the
perturbation method in supersymmetric quantum mechanics. It gives good results
whether the barrier is high or sallow. The new model have many merits and may
be used in the double well problem.Comment: 3pages, 3figure
Magnetoelectronic Phenomena at a Ferromagnet-Semiconductor Interface
A Comment on the Letter by P. R. Hammar et al., Phys. Rev. Lett. 83, 203 (1999)
Origin of the roughness exponent in elastic strings at the depinning threshold
Within a recently developed framework of dynamical Monte Carlo algorithms, we
compute the roughness exponent of driven elastic strings at the
depinning threshold in 1+1 dimensions for different functional forms of the
(short-range) elastic energy. A purely harmonic elastic energy leads to an
unphysical value for . We include supplementary terms in the elastic
energy of at least quartic order in the local extension. We then find a
roughness exponent of , which coincides with the one
obtained for different cellular automaton models of directed percolation
depinning. The quartic term translates into a nonlinear piece which changes the
roughness exponent in the corresponding continuum equation of motion. We
discuss the implications of our analysis for higher-dimensional elastic
manifolds in disordered media.Comment: 4 pages, 2 figure
Superconducting correlations in ultra-small metallic grains
To describe the crossover from the bulk BCS superconductivity to a
fluctuation-dominated regime in ultrasmall metallic grains, new order
parameters and correlation functions, such as ``parity gap'' and ``pair-mixing
correlation function'', have been recently introduced. In this paper, we
discuss the small-grain behaviour of the Penrose-Onsager-Yang off-diagonal
long-range order (ODLRO) parameter in a pseudo-spin representation. Relations
between the ODLRO parameter and those mentioned above are established through
analytical and numerical calculations.Comment: 7 pages, 1 figur
A fiber-optic current sensor for aerospace applications
A robust, accurate, broad-band, alternating current sensor using fiber optics is being developed for space applications at power frequencies as high as 20 kHz. It can also be used in low and high voltage 60 Hz terrestrial power systems and in 400 Hz aircraft systems. It is intrinsically electromagnetic interference (EMI) immune and has the added benefit of excellent isolation. The sensor uses the Faraday effect in optical fiber and standard polarimetric measurements to sense electrical current. The primary component of the sensor is a specially treated coil of single-mode optical fiber, through which the current carrying conductor passes. Improved precision is accomplished by temperature compensation by means of signals from a novel fiber-optic temperature sensor embedded in the sensing head. The technology contained in the sensor is examined and the results of precision tests conducted at various temperatures within the wide operating range are given. The results of early EMI tests are also given
Fiber-optic sensors for aerospace electrical measurements: An update
Fiber-optic sensors are being developed for electrical current, voltage, and power measurements in aerospace applications. These sensors are presently designed to cover ac frequencies from 60 Hz to 20 kHz. The current sensor, based on the Faraday effect in optical fiber, is in advanced development after some initial testing. Concentration is on packaging methods and ways to maintain consistent sensitivity with changes in temperature. The voltage sensor, utilizing the Pockels effect in a crystal, has excelled in temperature tests. This paper reports on the development of these sensors, the results of evaluation, improvements now in progress, and the future direction of the work
Discussions on Stability of Diquarks
Since the birth of the quark model, the diquark which is composed of two
quarks has been considered as a substantial structure of color anti-triplet.
This is not only a mathematical simplification for dealing with baryons, but
also provides a physical picture where the diquark would behave as a whole
object. It is natural to ask whether such a structure is sufficiently stable
against external disturbance. The mass spectra of the ground states of the
scalar and axial-vector diquarks which are composed of two-light (L-L),
one-light-one-heavy (H-L) and two-heavy quarks (H-H) respectively have been
calculated in terms of the QCD sum rules. We suggest a criterion as the
quantitative standard for the stability of the diquark. It is the gap between
the masses of the diquark and where is the threshold of the
excited states and continuity, namely the larger the gap is, the more stable
the diquark would be. In this work, we calculate the masses of the type H-H to
complete the series of the spectra of the ground state diquarks. However, as
the criterion being taken, we find that all the gaps for the various diquaks
are within a small range, especially the gap for the diquark with two heavy
quarks which is believed to be a stable structure, is slightly smaller than
that for other two types of diquarks, therefore we conclude that because of the
large theoretical uncertainty, we cannot use the numerical results obtained
with the QCD sum rules to assess the stability of diquarks, but need to invoke
other theoretical framework.Comment: 14 pages, 4 figure
Elastic String in a Random Medium
We consider a one dimensional elastic string as a set of massless beads
interacting through springs characterized by anisotropic elastic constants. The
string, driven by an external force, moves in a medium with quenched disorder.
We present evidence that the consideration of longitudinal fluctuations leads
to nonlinear behavior in the equation of motion which is {\it kinematically}
generated by the motion of the string. The strength of the nonlinear effects
depends on the anisotropy of the medium and the distance from the depinning
transition. On the other hand the consideration of restricted solid on solid
conditions imposed to the growth of the string leads to a nonlinear term in the
equation of motion with a {\it diverging} coefficient at the depinning
transition.Comment: 9 pages, REVTEX, figures available upon request from
[email protected]
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