2,639 research outputs found
Smallholder Cash-Cropping, Food-Cropping and Food Security in Mozambique's Cotton Belt
Crop Production/Industries, Food Security and Poverty, Downloads July 2008-June 2009: 12,
Bundle Branch Reentrant Ventricular Tachycardia
Bundle branch reentrant (BBR) tachycardia is an uncommon form of ventricular tachycardia (VT) incorporating both bundle branches into the reentry circuit. The arrhythmia is usually seen in patients with an acquired heart disease and significant conduction system impairment, although patients with structurally normal heart have been described. Surface ECG in sinus rhythm (SR) characteristically shows intraventricular conduction defects. Patients typically present with presyncope, syncope or sudden death because of VT with fast rates frequently above 200 beats per minute. The QRS morphology during VT is a typical bundle branch block pattern, usually left bundle branch block, and may be identical to that in SR. Prolonged His-ventricular (H-V) interval in SR is found in the majority of patients with BBR VT, although some patients may have the H-V interval within normal limits. The diagnosis of BBR VT is based on electrophysiological findings and pacing maneuvers that prove participation of the His- Purkinje system in the tachycardia mechanism. Radiofrequency catheter ablation of a bundle branch can cure BBR VT and is currently regarded as the first line therapy. The technique of choice is ablation of the right bundle. The reported incidence of clinically significant conduction system impairment requiring implantation of a permanent pacemaker varies from 0% to 30%. Long-term outcome depends on the underlying cardiac disease. Patients with poor systolic left ventricular function are at risk of sudden death or death from progressive heart failure despite successful BBR VT ablation and should be considered for an implantable cardiovertor-defibrillator
Thermodynamics of Quantum-Jump-Conditioned Feedback Control
We consider open quantum systems weakly coupled to thermal reservoirs and
subjected to quantum feedback operations triggered with or without delay by
monitored quantum jumps. We establish a thermodynamic description of such
system and analyze how the first and second law of thermodynamics are modified
by the feedback. We apply our formalism to study the efficiency of a qubit
subjected to a quantum feedback control and operating as a heat pump between
two reservoirs. We also demonstrate that quantum feedbacks can be used to
stabilize coherences in nonequilibrium stationary states which in some cases
may even become pure quantum states.Comment: 12 pages, 6 figure
Thermodynamics of stochastic Turing machines
In analogy to Brownian computers we explicitly show how to construct
stochastic models, which mimic the behaviour of a general purpose computer (a
Turing machine). Our models are discrete state systems obeying a Markovian
master equation, which are logically reversible and have a well-defined and
consistent thermodynamic interpretation. The resulting master equation, which
describes a simple one-step process on an enormously large state space, allows
us to thoroughly investigate the thermodynamics of computation for this
situation. Especially, in the stationary regime we can well approximate the
master equation by a simple Fokker-Planck equation in one dimension. We then
show that the entropy production rate at steady state can be made arbitrarily
small, but the total (integrated) entropy production is finite and grows
logarithmically with the number of computational steps.Comment: 13 pages incl. appendix, 3 figures and 1 table, slightly changed
version as published in PR
Nonequilibrium thermodynamics in the strong coupling and non-Markovian regime based on a reaction coordinate mapping
We propose a method to study the thermodynamic behaviour of small systems
beyond the weak coupling and Markovian approximation, which is different in
spirit from conventional approaches. The idea is to redefine the system and
environment such that the effective, redefined system is again coupled weakly
to Markovian residual baths and thus, allows to derive a consistent
thermodynamic framework for this new system-environment partition. To achieve
this goal we make use of the reaction coordinate mapping, which is a general
method in the sense that it can be applied to an arbitrary (quantum or
classical and even time-dependent) system coupled linearly to an arbitrary
number of harmonic oscillator reservoirs. The core of the method relies on an
appropriate identification of a part of the environment (the reaction
coordinate), which is subsequently included as a part of the system. We
demonstrate the power of this concept by showing that non-Markovian effects can
significantly enhance the steady state efficiency of a three-level-maser heat
engine, even in the regime of weak system-bath coupling. Furthermore, we show
for a single electron transistor coupled to vibrations that our method allows
one to justify master equations derived in a polaron transformed reference
frame.Comment: updated and improved version; 19 pages incl. 10 figures and 5 pages
appendi
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