2,159 research outputs found
Smeared and unsmeared chiral vertex operators
We prove unboundedness and boundedness of the unsmeared and smeared chiral
vertex operators, respectively. We use elementary methods in bosonic Fock
space, only. Possible applications to conformal two - dimensional quantum field
theory, perturbation thereof, and to the perturbative construction of the
sine-Gordon model by the Epstein-Glaser method are discussed. From another
point of view the results of this paper can be looked at as a first step
towards a Hilbert space interpretation of vertex operator algebras.Comment: 18 pages, latex, no figure
Mechanisms of nonlinear spin-wave emission from a microwave driven nanocontact
We present a micromagnetic study of linear and nonlinear spin-wave modes
excited in an extended permalloy thin film by a microwave driven nanocontact.
We show that the linear mode having the frequency equal to the excitation
frequency (f) is driven by the ac Oersted field component perpendicular to the
static external field (applied in-plane of the sample). The nonlinear mode with
the frequency f /2 is excited as an independent eigenmode within a parametric
longitudinal pumping process (due ac Oersted field component parallel to the
bias field). Spectral positions of those modes are determined both in the space
and phase domain. The results are important for the transfer of information
coded into spin-waves between nanocontacts, and for synchronization of spin
transfer torque nano-oscillators.Comment: 5 pages, 4 figure
Stability of the Wave Bearing on an Elastic Support
Numerical computation predicts that an elastic support can substantially improve the stability of the wave bearing if the dynamic stiffness and damping of this support are in a specific range of values. To experimentally validate this prediction, the housing of a gas bearing was mounted on elastic O-rings and the threshold of sub-synchronous whirl motion was experimentally observed when the bearing runs unloaded with a rotating speed up to 30,000 RPM. The O-ring system was also dynamically characterized by measuring its stiffness and damping at various frequencies up to 500 Hz. Good correlation exists between the experimental data and numerical prediction
Hydrodynamic Analyses and Evaluation of New Fluid Film Bearing Concepts
Over the past several years, numerical and experimental investigations have been performed on a waved journal bearing. The research work was undertaken by Dr. Florin Dimofte, a Senior Research Associate in the Mechanical Engineering Department at the University of Toledo. Dr. Theo Keith, Distinguished University Professor in the Mechanical Engineering Department was the Technical Coordinator of the project. The wave journal bearing is a bearing with a slight but precise variation in its circular profile such that a waved profile is circumscribed on the inner bearing diameter. The profile has a wave amplitude that is equal to a fraction of the bearing clearance. Prior to this period of research on the wave bearing, computer codes were written and an experimental facility was established. During this period of research considerable effort was directed towards the study of the bearing's stability. The previously developed computer codes and the experimental facility were of critical importance in performing this stability research. A collection of papers and reports were written to describe the results of this work. The attached captures that effort and represents the research output during the grant period
Stability of adhesion clusters under constant force
We solve the stochastic equations for a cluster of parallel bonds with shared
constant loading, rebinding and the completely dissociated state as an
absorbing boundary. In the small force regime, cluster lifetime grows only
logarithmically with bond number for weak rebinding, but exponentially for
strong rebinding. Therefore rebinding is essential to ensure physiological
lifetimes. The number of bonds decays exponentially with time for most cases,
but in the intermediate force regime, a small increase in loading can lead to
much faster decay. This effect might be used by cell-matrix adhesions to induce
signaling events through cytoskeletal loading.Comment: Revtex, 4 pages, 4 Postscript files include
Electrophysiological characterization of the hyperdirect pathway and its functional relevance for subthalamic deep brain stimulation
The subthalamic nucleus (STN) receives input from various cortical areas via hyperdirect pathway (HDP) which bypasses the basal-ganglia loop. Recently, the HDP has gained increasing interest, because of its relevance for STN deep brain stimulation (DBS). To understand the HDP's role cortical responses evoked by STN-DBS have been investigated. These responses have short (<2 ms), medium (2–15 ms), and long (20–70 ms) latencies. Medium-latency responses are supposed to represent antidromic cortical activations via HDP. Together with long-latency responses the medium responses can potentially be used as biomarker of DBS efficacy as well as side effects. We here propose that the activation sequence of the cortical evoked responses can be conceptualized as high frequency oscillations (HFO) for signal analysis. HFO might therefore serve as marker for antidromic activation. Using existing knowledge on HFO recordings, this approach allows data analyses and physiological modeling to advance the pathophysiological understanding of cortical DBS-evoked high-frequency activity
Trajectory structures and transport
The special problem of transport in 2-dimensional divergence-free stochastic
velocity fields is studied by developing a statistical approach, the nested
subensemble method. The nonlinear process of trapping determined by such fields
generates trajectory structures whose statistical characteristics are
determined. These structures strongly influence the transport.Comment: Latex file 19 pages, includes 12 EPS figures. Extended version of the
invited talk at the ITCPP, Santorini, 200
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