746 research outputs found
Properties of Odd Gap Superconductors
A new class of superconductors with the gap function {\it odd} under time
reversal is considered. Some of the physical properties of these
superconductors such as the Meissner effect, composite condensate, gapless
spectrum and transition from the {\it odd} gap superconductor to the BCS state
at lower temperatures are discussed.Comment: 9 pages + 2 fig, LA-UR-93-299
Developing information skills and system thinking: a resource-based approach to electronic control systems
This paper describes a curriculum development project that addresses the following issue: is it possible
to engage pupils in procedures for developing an electronic control system which mirror those of
professional engineering?
In particular, two key aspects of professional practice were felt to be of critical importance. Firstly,
engineers spend a great deal of time evaluating the potential of devices using data sheets. A major part
of the development was concerned with developing data sheets for the units of a commercially available
electronics systems kit.
Secondly the development sought to emphasise system thinking by encouraging pupils to systematically
plan their overall system, investigate possible sub-systems, conduct practical investigations and, only
then, explore the detailed components required.
The paper describes the outcome of the extensive school trials and presents the published materials
Design and technology preperation and provision - a pilot survey
The paper describes some findings of the preparations made for design and technology and work during the Autumn term of 1990 in a random sample of 28 primary and 27 secondary schools in England and Wales. A preliminary account of part of this survey was presented as DATER 90.
The survey reveals:
wide variations in the amount of time spent in preparation by schools;
a significant minority of primary schools who reported no joint preparation or planning;
wide variations in the amount of time devoted to design and technology in both primary and secondary schools;
very few primary schools making use of food within design and technology;
an overwhelming preponderance of CDT specialist appointed as design and technology coordinators in secondary schools with very few home economists
Sine-Gordon Field Theory for the Kosterlitz-Thouless Transitions on Fluctuating Membranes
In the preceding paper, we derived Coulomb-gas and sine-Gordon Hamiltonians
to describe the Kosterlitz-Thouless transition on a fluctuating surface. These
Hamiltonians contain couplings to Gaussian curvature not found in a rigid flat
surface. In this paper, we derive renormalization-group recursion relations for
the sine-Gordon model using field-theoretic techniques developed to study flat
space problems.Comment: REVTEX, 14 pages with 6 postscript figures compressed using uufiles.
Accepted for publication in Phys. Rev.
Technology insight: virtual visits to industry using the Web
The paper describes the philosophy and structure of a new Web service for technology education that is being
developed by the authors. The fundamental concept is that the site allows pupils and teachers to âvisitâ industry and to
learn how products are designed and made.
Each âvisitâ focuses on a particular product and tells its story through the people involved in its production. The âvisitâ
is complemented by ideas for follow-up activities in schools and hotlinks to other relevant resources on the Web
Restoration of particle number as a good quantum number in BCS theory
As shown in previous work, number projection can be carried out analytically
for states defined in a quasi-particle scheme when the states are expressed in
a coherent state representation. The wave functions of number-projected states
are well-known in the theory of orthogonal polynomials as Schur functions.
Moreover, the functions needed in pairing theory are a particularly simple
class of Schur functions that are easily constructed by means of recursion
relations. It is shown that complete sets of states can be projected from
corresponding quasi-particle states and that such states retain many of the
properties of the quasi-particle states from which they derive. It is also
shown that number projection can be used to construct a complete set of
orthogonal states classified by generalized seniority for any nucleus.Comment: 21 pages, 2 figures, epsf.def style file for printing figure
Monopoles, noncommutative gauge theories in the BPS limit and some simple gauge groups
For three conspicuous gauge groups, namely, SU(2), SU(3) and SO(5), and at
first order in the noncommutative parameter matrix h\theta^{\mu\nu}, we
construct smooth monopole --and, some two-monopole-- fields that solve the
noncommutative Yang-Mills-Higgs equations in the BPS limit and that are formal
power series in h\theta^{\mu\nu}. We show that there exist noncommutative BPS
(multi-)monopole field configurations that are formal power series in
h\theta^{\mu\nu} if, and only if, two a priori free parameters of the
Seiberg-Witten map take very specific values. These parameters, that are not
associated to field redefinitions nor to gauge transformations, have thus
values that give rise to sharp physical effects.Comment: 30 pages, no figure
Spectral properties of the one-dimensional two-channel Kondo lattice model
We have studied the energy spectrum of a one-dimensional Kondo lattice, where
the localized magnetic moments have SU(N) symmetry and two channels of
conduction electrons are present. At half filling, the system is shown to exist
in two phases: one dominated by RKKY-exchange interaction effects, and the
other by Kondo screening. A quantum phase transition point separates these two
regimes at temperature . The Kondo-dominated phase is shown to possess
soft modes, with spectral gaps much smaller than the Kondo temperature.Comment: 4 pages + 2 figures. Submitted for publicatio
Coarse-Graining and Renormalization Group in the Einstein Universe
The Kadanoff-Wilson renormalization group approach for a scalar
self-interacting field theor generally coupled with gravity is presented. An
average potential that monitors the fluctuations of the blocked field in
different scaling regimes is constructed in a nonflat background and explicitly
computed within the loop-expansion approximation for an Einstein universe. The
curvature turns out to be dominant in setting the crossover scale from a
double-peak and a symmetric distribution of the block variables. The evolution
of all the coupling constants generated by the blocking procedure is examined:
the renormalized trajectories agree with the standard perturbative results for
the relevant vertices near the ultraviolet fixed point, but new effective
interactions between gravity and matter are present. The flow of the conformal
coupling constant is therefore analyzed in the improved scheme and the infrared
fixed point is reached for arbitrary values of the renormalized parameters.Comment: 18 pages, REVTex, two uuencoded figures. (to appear in Phys. Rev.
D15, July) Transmission errors have been correcte
Superheavy Dark Matter with Discrete Gauge Symmetries
We show that there are discrete gauge symmetries protect naturally heavy X
particles from decaying into the ordinary light particles in the supersymmetric
standard model. This makes the proposal very attractive that the superheavy X
particles constitute a part of the dark matter in the present universe. It is
more interesting that there are a class of discrete gauge symmetries which
naturally accommodate a long-lived unstable X particle. We find that in some
discrete Z_{10} models, for example, a superheavy X particle has lifetime
\tau_X \simeq 10^{11}-10^{26} years for its mass M_X \simeq 10^{13}-10^{14}
GeV. This long lifetime is guaranteed by the absence of lower dimensional
operators (of light particles) couple to the X. We briefly discuss a possible
explanation for the recently observed ultra-high-energy cosmic ray events by
the decay of this unstable X particle.Comment: 9 pages, Late
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