412 research outputs found
Anti-phase locking in a two-dimensional Josephson junction array
We consider theoretically phase locking in a simple two-dimensional Josephson
junction array consisting of two loops coupled via a joint line transverse to
the bias current. Ring inductances are supposed to be small, and special
emphasis is taken on the influence of external flux. Is is shown, that in the
stable oscillation regime both cells oscillate with a phase shift equal to
(i.e. anti-phase). This result may explain the low radiation output
obtained so far in two-dimensional Josephson junction arrays experimentally.Comment: 11 pages, REVTeX, 1 Postscript figure, Subm. to Appl. Phys. Let
Fluctuation force exerted by a planar self-avoiding polymer
Using results from Schramm Loewner evolution (SLE), we give the expression of
the fluctuation-induced force exerted by a polymer on a small impenetrable
disk, in various 2-dimensional domain geometries. We generalize to two polymers
and examine whether the fluctuation force can trap the object into a stable
equilibrium. We compute the force exerted on objects at the domain boundary,
and the force mediated by the polymer between such objects. The results can
straightforwardly be extended to any SLE interface, including Ising,
percolation, and loop-erased random walks. Some are relevant for extremal value
statistics.Comment: 7 pages, 22 figure
THEORY OF PHASE-LOCKING IN SMALL JOSEPHSON JUNCTION CELLS
Within the RSJ model, we performed a theoretical analysis of phase-locking in
elementary strongly coupled Josephson junction cells. For this purpose, we
developed a systematic method allowing the investigation of phase-locking in
cells with small but non-vanishing loop inductance.The voltages across the
junctions are found to be locked with very small phase difference for almost
all values of external flux. However, the general behavior of phase-locking is
found to be just contrary to that according to weak coupling. In case of strong
coupling there is nearly no influence of external magnetic flux on the phases,
but the locking-frequency becomes flux-dependent. The influence of parameter
splitting is considered as well as the effect of small capacitive shunting of
the junctions. Strongly coupled cells show synchronization even for large
parameter splitting. Finally, a study of the behavior under external microwave
radiation shows that the frequency locking-range becomes strongly
flux-dependent, whereas the locking frequency itself turns out to be
flux-independent.Comment: 26 pages, REVTEX, 9 PS figures appended in uuencoded form at the end,
submitted to Phys. Rev. B
Electron Refrigeration in the Tunneling Approach
The qualities of electron refrigeration by means of tunnel junctions between
superconducting and normal--metal electrodes are studied theoretically. A
suitable approximation of the basic expression for the heat current across
those tunnel junctions allows the investigation of several features of the
device such as its optimal bias voltage, its maximal heat current, its optimal
working point, and the maximally gained temperature reduction. Fortunately, the
obtained results can be compared with those of a recent experiment.Comment: 4 pages, 4 Postscript figures, uses eps
Intrinsic mechanism of phase locking in two-dimensional Josephson junction networks in presence of an external magnetic field
We present numerical simulations of the dynamics of two-dimensional Josephson
junction arrays to study the mechanism of mutual phase locking. We show that in
the presence of an external magnetic field two mechanisms are playing a role in
phase locking: feedback through the external load and internal coupling between
rows due to microwave currents induced by the field. We have found the
parameter values (junction capacitance, cell loop inductance, impedance of the
external load) for which the interplay of both these mechanisms leads to the
in-phase solution. The case of unshunted arrays is discussed as well.Comment: 13 pages, incl. 6 ps figures, Subm. to Europhysics Letter
Aerothermodynamic radiation studies
We have built and made operational a 6 in. electric arc driven shock tube which alloys us to study the non-equilibrium radiation and kinetics of low pressure (0.1 to 1 torr) gases processed by 6 to 12 km/s shock waves. The diagnostic system allows simultaneous monitoring of shock radiation temporal histories by a bank of up to six radiometers, and spectral histories with two optical multi-channel analyzers. A data set of eight shots was assembled, comprising shocks in N2 and air at pressures between 0.1 and 1 torr and velocities of 6 to 12 km/s. Spectrally resolved data was taken in both the non-equilibrium and equilibrium shock regions on all shots. The present data appear to be the first spectrally resolved shock radiation measurements in N2 performed at 12 km/s. The data base was partially analyzed with salient features identified
Perturbative calculation of the scaled factorial moments in second-order quark-hadron phase transition within the Ginzburg-Landau description
The scaled factorial moments are studied for a second-order
quark-hadron phase transition within the Ginzburg-Landau description. The role
played by the ground state of the system under low temperature is emphasized.
After a local shift of the order parameter the fluctuations are around the
ground state, and a perturbative calculation for can be carried out.
Power scaling between 's is shown, and a universal scaling exponent
is given for the case with weak correlations and weak
self-interactions.Comment: 12 pages in RevTeX, 12 eps figure
Casimir effect for the scalar field under Robin boundary conditions: A functional integral approach
In this work we show how to define the action of a scalar field in a such a
way that Robin boundary condition is implemented dynamically, i.e., as a
consequence of the stationary action principle. We discuss the quantization of
that system via functional integration. Using this formalism, we derive an
expression for the Casimir energy of a massless scalar field under Robin
boundary conditions on a pair of parallel plates, characterized by constants
and . Some special cases are discussed; in particular, we show that
for some values of and the Casimir energy as a function of the
distance between the plates presents a minimum. We also discuss the
renormalization at one-loop order of the two-point Green function in the
theory submitted to Robin boundary condition on a plate.Comment: 16 pages, 2 figures. Version 2: contains a new section on the
renormalization of the two-point Green function in the presence of a flat
boundary. Accepted for publication in J. Phys.
The Casimir effect for the Bose-Gas in Slabs
We study the Casimir effect for the perfect Bose-gase in the slab geometry
for various boundary conditions. We show that the grand canonical potential per
unit area at the bulk critical chemical potential has the standard
asymptotic form with universal Casimir terms.Comment: 6 pages, submitted to Europhysics LettersWe study the Casimir effect
for the perfect Bose-gase in the slab geometry for various boundary
conditions. We show that the grand canonical potential per unit area at the
bulk critical chemical potential has the standard asymptotic form
with universal Casimir term
The bulk correlation length and the range of thermodynamic Casimir forces at Bose-Einstein condensation
The relation between the bulk correlation length and the decay length of
thermodynamic Casimir forces is investigated microscopically in two
three-dimensional systems undergoing Bose-Einstein condensation: the perfect
Bose gas and the imperfect mean-field Bose gas. For each of these systems, both
lengths diverge upon approaching the corresponding condensation point from the
one-phase side, and are proportional to each other. We determine the
proportionality factors and discuss their dependence on the boundary
conditions. The values of the corresponding critical exponents for the decay
length and the correlation length are the same, equal to 1/2 for the perfect
gas, and 1 for the imperfect gas
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