74 research outputs found
From elongated spanning trees to vicious random walks
Given a spanning forest on a large square lattice, we consider by
combinatorial methods a correlation function of paths ( is odd) along
branches of trees or, equivalently, loop--erased random walks. Starting and
ending points of the paths are grouped in a fashion a --leg watermelon. For
large distance between groups of starting and ending points, the ratio of
the number of watermelon configurations to the total number of spanning trees
behaves as with . Considering the spanning
forest stretched along the meridian of this watermelon, we see that the
two--dimensional --leg loop--erased watermelon exponent is converting
into the scaling exponent for the reunion probability (at a given point) of
(1+1)--dimensional vicious walkers, . Also, we express the
conjectures about the possible relation to integrable systems.Comment: 27 pages, 6 figure
Alpha-1–Adrenergic Receptors in Heart Failure: The Adaptive Arm of the Cardiac Response to Chronic Catecholamine Stimulation
Alpha-1-adrenergic receptors are G-protein coupled receptors (GPCRs) activated by catecholamines. The alpha-1A and alpha-1B subtypes are expressed in mouse and human myocardium, whereas the alpha-1D protein is found only in coronary arteries. There are far fewer alpha-1-ARs than beta-ARs in the non-failing heart, but their abundance is maintained or increased in the setting of heart failure, which is characterized by pronounced chronic elevation of catecholamines and b□eta-AR dysfunction. Decades of evidence from gain- and loss-of-function studies in isolated cardiac myocytes and numerous animal models demonstrate important adaptive functions for cardiac alpha-1-ARs, to include physiological hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Clinical trial data indicate that blocking alpha-1-ARs is associated with incident heart failure in patients with hypertension. Collectively, these findings suggest that alpha-1-AR activation might mitigate the well-recognized toxic effects of beta-ARs in the hyperadrenergic setting of chronic heart failure. Thus, exogenous cardioselective activation of alpha-1-ARs might represent a novel and viable approach to the treatment of heart failure
QuTiP: An open-source Python framework for the dynamics of open quantum systems
We present an object-oriented open-source framework for solving the dynamics
of open quantum systems written in Python. Arbitrary Hamiltonians, including
time-dependent systems, may be built up from operators and states defined by a
quantum object class, and then passed on to a choice of master equation or
Monte-Carlo solvers. We give an overview of the basic structure for the
framework before detailing the numerical simulation of open system dynamics.
Several examples are given to illustrate the build up to a complete
calculation. Finally, we measure the performance of our library against that of
current implementations. The framework described here is particularly
well-suited to the fields of quantum optics, superconducting circuit devices,
nanomechanics, and trapped ions, while also being ideal for use in classroom
instruction.Comment: 16 pages, 12 figure
Coupling ultracold atoms to mechanical oscillators
In this article we discuss and compare different ways to engineer an
interface between ultracold atoms and micro- and nanomechanical oscillators. We
start by analyzing a direct mechanical coupling of a single atom or ion to a
mechanical oscillator and show that the very different masses of the two
systems place a limit on the achievable coupling constant in this scheme. We
then discuss several promising strategies for enhancing the coupling:
collective enhancement by using a large number of atoms in an optical lattice
in free space, coupling schemes based on high-finesse optical cavities, and
coupling to atomic internal states. Throughout the manuscript we discuss both
theoretical proposals and first experimental implementations.Comment: 19 pages, 9 figure
Light dark matter versus astrophysical constraints
Hints of direct dark matter detection coming from the DAMA, CoGeNT
experiments point toward light dark matter with isospin-violating and possibly
inelastic couplings. However an array of astrophysical constraints are rapidly
closing the window on light dark matter. We point out that if the relic density
is determined by annihilation into invisible states, these constraints can be
evaded. As an example we present a model of quasi-Dirac dark matter,
interacting via two U(1) gauge bosons, one of which couples to baryon number
and the other which kinetically mixes with the photon. Annihilation is
primarily into "dark neutrinos" that do not mix with the SM, but which could
provide a small component of dark radiation. The model could soon be tested by
several experiments searching for such light gauge bosons, and we predict that
both could be detected. The model also requires a fourth generation of quarks,
whose existence might increase the production cross section of Higgs bosons at
the Tevatron and LHC.Comment: 11 pages, two figures; references added, published versio
Decoherence Suppression by Cavity Optomechanical Cooling
We consider a cavity optomechanical cooling configuration consisting of a
mechanical resonator (denoted as resonator b) and an electromagnetic resonator
(denoted as resonator a), which are coupled in such a way that the effective
resonance frequency of resonator a depends linearly on the displacement of
resonator b. We study whether back-reaction effects in such a configuration can
be efficiently employed for suppression of decoherence. To that end, we
consider the case where the mechanical resonator is prepared in a superposition
of two coherent states and evaluate the rate of decoherence. We find that no
significant suppression of decoherence is achievable when resonator a is
assumed to have a linear response. On the other hand, when resonator a exhibits
Kerr nonlinearity and/or nonlinear damping the decoherence rate can be made
much smaller than the equilibrium value provided that the parameters that
characterize these nonlinearities can be tuned close to some specified optimum
values
V. Rondot, Tebytnis II, Le temple de Soknebtynis, Le Caire (2004)
OʼConnell Elisabeth R. V. Rondot, Tebytnis II, Le temple de Soknebtynis, Le Caire (2004). In: Topoi, volume 14/2, 2006. pp. 591-599
V. Rondot, Tebytnis II, Le temple de Soknebtynis, Le Caire (2004)
OʼConnell Elisabeth R. V. Rondot, Tebytnis II, Le temple de Soknebtynis, Le Caire (2004). In: Topoi, volume 14/2, 2006. pp. 591-599
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