12,768 research outputs found
Three-dimensional spontaneous magnetic reconnection in neutral current sheets
Magnetic reconnection in an antiparallel uniform Harris current sheet
equilibrium, which is initially perturbed by a region of enhanced resistivity
limited in all three dimensions, is investigated through compressible
magnetohydrodynamic simulations. Variable resistivity, coupled to the dynamics
of the plasma by an electron-ion drift velocity criterion, is used during the
evolution. A phase of magnetic reconnection amplifying with time and leading to
eruptive energy release is triggered only if the initial perturbation is
strongly elongated in the direction of current flow or if the threshold for the
onset of anomalous resistivity is significantly lower than in the corresponding
two-dimensional case. A Petschek-like configuration is then built up for \sim
100 Alfven times, but remains localized in the third dimension. Subsequently, a
change of topology to an O-line at the center of the system (``secondary
tearing'') occurs. This leads to enhanced and time-variable reconnection, to a
second pair of outflow jets directed along the O-line, and to expansion of the
reconnection process into the third dimension. High parallel current density
components are created mainly near the region of enhanced resistivity.Comment: 22 pages, 14 figures (Figs. 3,9,10, and 14 as external GIF-Files
Muzak: on functional music and power
This paper examines the phenomenon of “functional music” and its evolution as a social technology in the control and regulation of work, consumption, and public space. It argues that the practices of functional music articulate some of the characteristic ways in which power is exercised in capitalist societies and, moreover, that changes in the functional music industry indicate wider structural shifts in capitalism toward “post-Fordist” regimes of production and consumption. Through an analysis of the history, forms, and discourses of functional music, this paper examines the cultural and political significance of these transformations
Geometry of intensive scalar dissipation events in turbulence
Maxima of the scalar dissipation rate in turbulence appear in form of sheets
and correspond to the potentially most intensive scalar mixing events. Their
cross-section extension determines a locally varying diffusion scale of the
mixing process and extends the classical Batchelor picture of one mean
diffusion scale. The distribution of the local diffusion scales is analysed for
different Reynolds and Schmidt numbers with a fast multiscale technique applied
to very high-resolution simulation data. The scales take always values across
the whole Batchelor range and beyond. Furthermore, their distribution is traced
back to the distribution of the contractive short-time Lyapunov exponent of the
flow.Comment: 4 pages, 5 Postscript figures (2 with reduced quality
Quantum data processing and error correction
This paper investigates properties of noisy quantum information channels. We
define a new quantity called {\em coherent information} which measures the
amount of quantum information conveyed in the noisy channel. This quantity can
never be increased by quantum information processing, and it yields a simple
necessary and sufficient condition for the existence of perfect quantum error
correction.Comment: LaTeX, 20 page
Indeterminate-length quantum coding
The quantum analogues of classical variable-length codes are
indeterminate-length quantum codes, in which codewords may exist in
superpositions of different lengths. This paper explores some of their
properties. The length observable for such codes is governed by a quantum
version of the Kraft-McMillan inequality. Indeterminate-length quantum codes
also provide an alternate approach to quantum data compression.Comment: 32 page
Synchronized single electron emission from dynamical quantum dots
We study synchronized quantized charge pumping through several dynamical
quantum dots (QDs) driven by a single time modulated gate signal. We show that
the main obstacle for synchronization being the lack of uniformity can be
overcome by operating the QDs in the decay cascade regime. We discuss the
mechanism responsible for lifting the stringent uniformity requirements. This
enhanced functionality of dynamical QDs might find applications in
nanoelectronics and quantum metrology.Comment: 4 pages, 3 figures, submitted to AP
Wirkortäquilibration, Anschlagzeit, "time to peak effect": Bedeutung pharmakokinetisch-dynamischer Prinzipien für die tägliche klinische Praxis
Zusammenfassung: In der anästhesiologischen Pharmakologie spielen im Gegensatz zur internistischen Pharmakologie "Non-steady-state-Phänomene" eine herausragende Rolle. Ihr Verständnis ist eine Conditio sine qua non für die sichere und effiziente Applikation von anästhesierelevanten Medikamenten. Insbesondere die Verfügbarkeit der "optimierten target controlled infusion" ("optimized TCI"), von TCI-Systemen mit Ansteuerung des Effektkompartiments und dem relativ geringen Dosierungsspielraum bei "conscious sedation" unter erhaltener Spontanatmung verlangen von Anästhesisten, sich mit dem Konzept des Konzentrationsverlaufes am Wirkort auseinander zu setzen. Der Leser wird in die grundlegende Problematik eingeführt. Anwendungen der Prinzipien bei der Applikation von Muskelrelaxanzien, Propofol mit TCI-Systemen, volatilen Anästhetika und Opiaten werden erläuter
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