72,480 research outputs found
Non-Linear Canonical Transformations in Classical and Quantum Mechanics
-Mechanics is a consistent physical theory which describes both classical
and quantum mechanics simultaneously through the representation theory of the
Heisenberg group. In this paper we describe how non-linear canonical
transformations affect -mechanical observables and states. Using this we
show how canonical transformations change a quantum mechanical system. We seek
an operator on the set of -mechanical observables which corresponds to the
classical canonical transformation. In order to do this we derive a set of
integral equations which when solved will give us the coherent state expansion
of this operator. The motivation for these integral equations comes from the
work of Moshinsky and a variety of collaborators. We consider a number of
examples and discuss the use of these equations for non-bijective
transformations.Comment: The paper has been improved in light of a referee's report. The paper
will appear in the Journal of Mathematical Physics. 24 pages, no figure
Heat-transfer thermal switch
Thermal switch maintains temperature of planetary lander, within definite range, by transferring heat. Switch produces relatively large stroke and force, uses minimum electrical power, is lightweight, is vapor pressure actuated, and withstands sterilization temperatures without damage
On superconducting instability in non-Fermi liquid: scaling approach
The superconducting instability in a non-Fermi liquid in is
considered. For a particular form of the single particle spectral function with
homogeneous scaling it is shown that the pair susceptibility is also a scaling function of
temperature with power defined by . We find three different regimes
depending on the scaling constant. The BCS result is recovered for and it corresponds to a marginal scaling of the coupling constant. For
the superconducting transition happens above some critical
coupling. In the opposite case of for any fixed coupling the
system undergoes a transition at low temperatures. Possible implications for
theories of high- with a superconducting transition driven by the
interlayer Josephson tunneling are discussed. 1 ps file for fig is attached at
the bottom of the tex file.Comment: 10 pages + 1 fig, LA-UR-275
Quantum tunneling between paramagnetic and superconducting states of a nanometer-scale superconducting grain placed in a magnetic field
We consider the process of quantum tunneling between the superconducting and
paramagnetic states of a nanometer-scale superconducting grain placed in a
magnetic field. The grain is supposed to be coupled via tunneling junction to a
normal metallic contact that plays a role of the spin reservoir. Using the
instanton method we find the probability of the quantum tunneling process and
express it in terms of the applied magnetic field, order parameter of the
superconducting grain and conductance of the tunneling junction between the
grain and metallic contact
Stabilizing the Complex Structure in Heterotic Calabi-Yau Vacua
In this paper, we show that the presence of gauge fields in heterotic
Calabi-Yau compacitifications causes the stabilisation of some, or all, of the
complex structure moduli of the Calabi-Yau manifold while maintaining a
Minkowski vacuum. Certain deformations of the Calabi-Yau complex structure,
with all other moduli held fixed, can lead to the gauge bundle becoming
non-holomorphic and, hence, non-supersymmetric. This leads to an F-term
potential which stabilizes the corresponding complex structure moduli. We use
10- and 4-dimensional field theory arguments as well as a derivation based
purely on algebraic geometry to show that this picture is indeed correct. An
explicit example is presented in which a large subset of complex structure
moduli is fixed. We demonstrate that this type of theory can serve as the
hidden sector in heterotic vacua and can co-exist with realistic particle
physics.Comment: 17 pages, Late
Numerical Hermitian Yang-Mills Connections and Kahler Cone Substructure
We further develop the numerical algorithm for computing the gauge connection
of slope-stable holomorphic vector bundles on Calabi-Yau manifolds. In
particular, recent work on the generalized Donaldson algorithm is extended to
bundles with Kahler cone substructure on manifolds with h^{1,1}>1. Since the
computation depends only on a one-dimensional ray in the Kahler moduli space,
it can probe slope-stability regardless of the size of h^{1,1}. Suitably
normalized error measures are introduced to quantitatively compare results for
different directions in Kahler moduli space. A significantly improved numerical
integration procedure based on adaptive refinements is described and
implemented. Finally, an efficient numerical check is proposed for determining
whether or not a vector bundle is slope-stable without computing its full
connection.Comment: 38 pages, 10 figure
What is moving in silica at 1 K? A computer study of the low-temperature anomalies
Though the existence of two-level systems (TLS) is widely accepted to explain
low temperature anomalies in many physical observables, knowledge about their
properties is very rare. For silica which is one of the prototype glass-forming
systems we elucidate the properties of the TLS via computer simulations by
applying a systematic search algorithm. We get specific information in the
configuration space, i.e. about relevant energy scales, the absolute number of
TLS and electric dipole moments. Furthermore important insight about the
real-space realization of the TLS can be obtained. Comparison with experimental
observations is included
Gap anisotropy and universal pairing scale in a spin fluctuation model for cuprates
We consider the evolution of d-wave pairing, mediated by nearly critical spin
fluctuations, with the coupling strength. We show that the onset temperature
for pairing, T*, smoothly evolves between weak and strong coupling, passing
through a broad maximum at intermediate coupling. At strong coupling, T* is of
order the magnetic exchange energy J. We argue that for all couplings, pairing
is confined to the vicinity of the Fermi surface. We also find that thermal
spin fluctuations only modestly reduce T*, even at criticality, but they
substantially smooth the gap anisotropy. The latter evolves with coupling,
being the largest at weak coupling.Comment: 5 pages, 4 figure
Formation of optimal-order necklace modes in one-dimensional random photonic superlattices
We study the appearance of resonantly coupled optical modes, optical
necklaces, in Anderson localized one-dimensional random superlattices through
numerical calculations of the accumulated phase. The evolution of the optimal
necklace order m* shows a gradual shift towards higher orders with increasing
the sample size. We derive an empirical formula that predicts m* and discuss
the situation when in a sample length L the number of degenerate in energy
resonances exceeds the optimal one. We show how the \emph{extra} resonances are
pushed out to the miniband edges of the necklace, thus reducing the order of
the latter by multiples of two.Comment: 4 pages, 4 figure
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