34,222 research outputs found
Parrondo-like behavior in continuous-time random walks with memory
The Continuous-Time Random Walk (CTRW) formalism can be adapted to encompass
stochastic processes with memory. In this article we will show how the random
combination of two different unbiased CTRWs can give raise to a process with
clear drift, if one of them is a CTRW with memory. If one identifies the other
one as noise, the effect can be thought as a kind of stochastic resonance. The
ultimate origin of this phenomenon is the same of the Parrondo's paradox in
game theoryComment: 8 pages, 3 figures, revtex; enlarged and revised versio
Universal Phase Diagram for High-Piezoelectric Perovskite Systems
Strong piezoelectricity in the perovskite-type PbZr(1-x)TixO3 (PZT) and
Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) systems is generally associated with the
existence of a morphotropic phase boundary (MPB) separating regions with
rhombohedral and tetragonal symmetry. An x-ray study of PZN-9%PT has revealed
the presence of a new orthorhombic phase at the MPB, and a near-vertical
boundary between the rhombohedral and orthorhombic phases, similar to that
found for PZT between the rhombohedral and monoclinic phases. We discuss the
results in the light of a recent theoretical paper by Vanderbilt and Cohen,
which attributes these low-symmetry phases to the high anharmonicity in these
oxide systems.Comment: REVTeX file. 4 pages,=A0 4 figures embedde
The symplectic Deligne-Mumford stack associated to a stacky polytope
We discuss a symplectic counterpart of the theory of stacky fans. First, we
define a stacky polytope and construct the symplectic Deligne-Mumford stack
associated to the stacky polytope. Then we establish a relation between stacky
polytopes and stacky fans: the stack associated to a stacky polytope is
equivalent to the stack associated to a stacky fan if the stacky fan
corresponds to the stacky polytope.Comment: 20 pages; v2: To appear in Results in Mathematic
Characterization of heat transfer in nutrient materials, part 2
A thermal model is analyzed that takes into account phase changes in the nutrient material. The behavior of fluids in low gravity environments is discussed along with low gravity heat transfer. Thermal contact resistance in the Skylab food heater is analyzed. The original model is modified to include: equivalent conductance due to radiation, radial equivalent conductance, wall equivalent conductance, and equivalent heat capacity. A constant wall-temperature model is presented
Outstanding problems in the phenomenology of hard diffractive scattering
This paper is a summary of the discussion within the Diffractive and Low-x
Physics Working Group at the 1999 Durham Collider Workshop of the
interpretation of the Tevatron and HERA measurements of inclusive hard
diffraction.Comment: 5 pages, 1 figure. Talks and discussions from the UK Phenomenology
Workshop on Collider Physics, Durham, September 199
Knight Shift Anomalies in Heavy Electron Materials
We calculate non-linear Knight Shift vs. susceptibility anomalies
for Ce ions possessing local moments in metals. The ions are modeled with the
Anderson Hamiltonian and studied within the non-crossing approximation (NCA).
The non-linearity diminishes with decreasing Kondo temperature
and nuclear spin- local moment separation. Treating the Ce ions as an
incoherent array in CeSn, we find excellent agreement with the observed Sn
data.Comment: 4 pages, Revtex, 3 figures available upon request from
[email protected]
Prepotentials for local mirror symmetry via Calabi-Yau fourfolds
In this paper, we first derive an intrinsic definition of classical triple
intersection numbers of K_S, where S is a complex toric surface, and use this
to compute the extended Picard-Fuchs system of K_S of our previous paper,
without making use of the instanton expansion. We then extend this formalism to
local fourfolds K_X, where X is a complex 3-fold. As a result, we are able to
fix the prepotential of local Calabi-Yau threefolds K_S up to polynomial terms
of degree 2. We then outline methods of extending the procedure to non
canonical bundle cases.Comment: 42 pages, 7 figures. Expanded, reorganized, and added a theoretical
background for the calculation
Relaxation oscillations, stability, and cavity feedback in a superradiant Raman laser
We experimentally study the relaxation oscillations and amplitude stability
properties of an optical laser operating deep into the bad-cavity regime using
a laser-cooled Rb Raman laser. By combining measurements of the laser
light field with nondemolition measurements of the atomic populations, we infer
the response of the gain medium represented by a collective atomic Bloch
vector. The results are qualitatively explained with a simple model.
Measurements and theory are extended to include the effect of intermediate
repumping states on the closed-loop stability of the oscillator and the role of
cavity feedback on stabilizing or enhancing relaxation oscillations. This
experimental study of the stability of an optical laser operating deep into the
bad-cavity regime will guide future development of superradiant lasers with
ultranarrow linewidths.Comment: 9 pages, 6 figure
Speckle visibility spectroscopy and variable granular fluidization
We introduce a dynamic light scattering technique capable of resolving motion
that changes systematically, and rapidly, with time. It is based on the
visibility of a speckle pattern for a given exposure duration. Applying this to
a vibrated layer of glass beads, we measure the granular temperature and its
variation with phase in the oscillation cycle. We observe several transitions
involving jammed states, where the grains are at rest during some portion of
the cycle. We also observe a two-step decay of the temperature on approach to
jamming.Comment: 4 pages, 4 figures, experimen
Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs
NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance ∼170 nΦ0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1–2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise
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