8,070 research outputs found
Transport theory of multiterminal hybrid structures
We derive a microscopic transport theory of multiterminal hybrid structures
in which a superconductor is connected to several spin-polarized electrodes. We
discuss the non-perturbative physics of extended contacts, and show that it can
be well represented by averaging out the phase of the electronic wave function.
The maximal conductance of a two-channel contact is proportional to , where is the distance between the
contacts, the lattice spacing, is the superconducting
coherence length, and is the cross-over frequency between a
perturbative regime () and a non perturbative regime
(). The intercontact Andreev reflection and elastic
cotunneling conductances are not equal if the electronic phases take a fixed
value. However, these two quantities do coincide if one can average out the
electronic phase. The equality between the Andreev and cotunneling conductances
is also valid in the presence of at least one extended contact in which the
phases take deterministic values.Comment: 20 pages, 11 figures, revised version, biblio update
Symbolic Solution of Linear Differential Equations
An algorithm for solving linear constant-coefficient ordinary differential equations is presented. The computational complexity of the algorithm is discussed and its implementation in the FORMAC system is described. A comparison is made between the algorithm and some classical algorithms for solving differential equations
Thermal power systems small power systems applications project. Decision analysis for evaluating and ranking small solar thermal power system technologies. Volume 1: A brief introduction to multiattribute decision analysis
The principal concepts of the Keeney and Raiffa approach to multiattribute decision analysis are described. Topics discussed include the concepts of decision alternatives, outcomes, objectives, attributes and their states, attribute utility functions, and the necessary independence properties for the attribute states to be aggregated into a numerical representation of the preferences of the decision maker for the outcomes and decision alternatives
Nonadiabatic Josephson current pumping by microwave irradiation
Irradiating a Josephson junction with microwaves can operate not only on the
amplitude but also on the phase of the Josephson current. This requires
breaking time inversion symmetry, which is achieved by introducing a phase
lapse between the microwave components acting on the two{\dag} sides of the
junction. General symmetry arguments and the solution of a specific single
level quantum dot model show that this induces chirality in the Cooper pair
dynamics, due to the topology of the Andreev bound state wavefunction. Another
essential condition is to break electron-hole symmetry within the junction. A
shift of the current-phase relation is obtained, which is controllable in sign
and amplitude with the microwave phase and an electrostatic gate, thus
producing a "chiral" Josephson transistor. The dot model is solved in the
infinite gap limit by Floquet theory and in the general case with Keldysh
nonequilibrium Green's functions. The chiral current is nonadiabatic: it is
extremal and changes sign close to resonant chiral transitions between the
Andreev bound states.Comment: 13 pages, 7 figures, extended versio
Long Range Forces from Two Neutrino Exchange Revisited
The exchange of two massless neutrinos gives rise to a long range force which
couples to weakly charged matter. As has been noted previously in the
literature, the potential for this force is \VN \propto G_{F}^2 / r^5 with
monopole-monople, spin-spin and more complicated interactions. Unfortunately,
this is far too small to be observed in present day experiments. We calculate
\VN explicitly in the electroweak theory, and show that under very general
assumptions forces arising from the exchange of two massless fermions can at
best yield potentials.Comment: 5 pages + 1 figure (not included), UFIFT-HEP-92-28/HUTP-92-A04
Fredholm's Minors of Arbitrary Order: Their Representations as a Determinant of Resolvents and in Terms of Free Fermions and an Explicit Formula for Their Functional Derivative
We study the Fredholm minors associated with a Fredholm equation of the
second type. We present a couple of new linear recursion relations involving
the th and th minors, whose solution is a representation of the th
minor as an determinant of resolvents. The latter is given a simple
interpretation in terms of a path integral over non-interacting fermions. We
also provide an explicit formula for the functional derivative of a Fredholm
minor of order with respect to the kernel. Our formula is a linear
combination of the th and the th minors.Comment: 17 pages, Latex, no figures connection to supplementary compound
matrices mentioned, references added, typos correcte
Eigenvalue Integro-Differential Equations for Orthogonal Polynomials on the Real Line
The one-dimensional harmonic oscillator wave functions are solutions to a
Sturm-Liouville problem posed on the whole real line. This problem generates
the Hermite polynomials. However, no other set of orthogonal polynomials can be
obtained from a Sturm-Liouville problem on the whole real line. In this paper
we show how to characterize an arbitrary set of polynomials orthogonal on
in terms of a system of integro-differential equations of
Hartree-Fock type. This system replaces and generalizes the linear differential
equation associated with a Sturm-Liouville problem. We demonstrate our results
for the special case of Hahn-Meixner polynomials.Comment: 28 pages, Latex, U. Texas at Austin/ Washington University preprin
Search for uncharged faster than light particles
Searching for uncharged particles with spacelike four momentum traveling faster than ligh
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