8,100 research outputs found
Effects of sheared flows on ion-temperature-gradient-driven turbulent transport
S. Hamaguchi and W. Horton, Physics of Fluids B: Plasma Physics 4, 319 (1992) https://doi.org/10.1063/1.86028
Origin of Lagrangian Intermittency in Drift-Wave Turbulence
The Lagrangian velocity statistics of dissipative drift-wave turbulence are
investigated. For large values of the adiabaticity (or small collisionality),
the probability density function of the Lagrangian acceleration shows
exponential tails, as opposed to the stretched exponential or algebraic tails,
generally observed for the highly intermittent acceleration of Navier-Stokes
turbulence. This exponential distribution is shown to be a robust feature
independent of the Reynolds number. For small adiabaticity, algebraic tails are
observed, suggesting the strong influence of point-vortex-like dynamics on the
acceleration. A causal connection is found between the shape of the probability
density function and the autocorrelation of the norm of the acceleration
A relativistically covariant version of Bohm's quantum field theory for the scalar field
We give a relativistically covariant, wave-functional formulation of Bohm's
quantum field theory for the scalar field based on a general foliation of
space-time by space-like hypersurfaces. The wave functional, which guides the
evolution of the field, is space-time-foliation independent but the field
itself is not. Hence, in order to have a theory in which the field may be
considered a beable, some extra rule must be given to determine the foliation.
We suggest one such rule based on the eigen vectors of the energy-momentum
tensor of the field itself.Comment: 1 figure. Submitted to J Phys A. 20/05/04 replacement has additional
references and a few minor changes made for clarity. Accepted by J Phys
Stable and unstable regimes in Bose-Fermi mixture with attraction between components
A collapse of the trapped boson- fermion mixture with the attraction between
bosons and fermions is investigated in the framework of the effective
Hamiltonian for the Bose system. The properties of the Rb and K
mixture are analyzed quantitatively at . We find numerically solutions of
modified Gross- Pitaevskii equation which continuously go from stable to
unstable branch. We discuss the relation of the onset of collapse with
macroscopic properties of the system. A comparison with the case of a Bose
condensate of atomic system is given.Comment: 7 pages, 5 figure
On the uniqueness of paths for spin-0 and spin-1 quantum mechanics
The uniqueness of the Bohmian particle interpretation of the Kemmer equation,
which describes massive spin-0 and spin-1 particles, is discussed. Recently the
same problem for spin-1/2 was dealt with by Holland. It appears that the
uniqueness of boson paths can be enforced under well determined conditions.
This in turn fixes the nonrelativistic particle equations of the
nonrelativistic Schrodinger equation, which appear to correspond with the
original definitions given by de Broglie and Bohm only in the spin-0 case.
Similar to the spin-1/2 case, there appears an additional spin-dependent term
in the guidance equation in the spin-1 case. We also discuss the ambiguity
associated with the introduction of an electromagnetic coupling in the Kemmer
theory. We argue that when the minimal coupling is correctly introduced, then
the current constructed from the energy-momentum tensor is no longer conserved.
Hence this current can not serve as a particle probability four-vector.Comment: 19 pages, no figures, LaTex, shortened version for Phys. Lett.
The agrin gene codes for a family of basal lamina proteins that differ in function and distribution
We isolated two cDNAs that encode isoforms of agrin, the basal lamina protein that mediates the motor neuron-induced aggregation of acetylcholine receptors on muscle fibers at the neuromuscular junction. Both proteins are the result of alternative splicing of the product of the agrin gene, but, unlike agrin, they are inactive in standard acetylcholine receptor aggregation assays. They lack one (agrin-related protein 1) or two (agrin-related protein 2) regions in agrin that are required for its activity. Expression studies provide evidence that both proteins are present in the nervous system and muscle and that, in muscle, myofibers and Schwann cells synthesize the agrin-related proteins while the axon terminals of motor neurons are the sole source of agrin
Substorm classification with the WINDMI model
International audienceThe results of a genetic algorithm optimization of the WINDMI model using the Blanchard-McPherron substorm data set is presented. A key result from the large-scale computations used to search for convergence in the predictions over the database is the finding that there are three distinct types of vx Bs -AL waveforms characterizing substorms. Type I and III substorms are given by the internally-triggered WINDMI model. The analysis reveals an additional type of event, called a type II substorm, that requires an external trigger as in the northward turning of the IMF model of Lyons (1995). We show that incorporating an external trigger, initiated by a fast northward turning of the IMF, into WINDMI, a low-dimensional model of substorms, yields improved predictions of substorm evolution in terms of the AL index. Intrinsic database uncertainties in the timing between the ground-based AL electrojet signal and the arrival time at the magnetopause of the IMF data measured by spacecraft in the solar wind prevent a sharp division between type I and II events. However, within these timing limitations we find that the fraction of events is roughly 40% type I, 40% type II, and 20% type III
PRACTICAL APPLICATION OF SUSPENSION CRITERIA SCENARIOS: RADIOTHERAPY.
In 2007, the European Commission (EC) commissioned a group of experts to undertake the revision of Report RP91 'Criteria for Acceptability of Radiological (including Radiotherapy) and Nuclear Medicine Installations' written in 1997. The revised draft report was submitted to the EC in 2010, which issued it for public consultation. The EC commissioned the same group of experts to consider the comments of the public consultation for further improvement of the revised report. The EC intends to publish the final report under its Radiation Report Series as RP162. This paper presents a selection of practical applications of suspension criteria scenarios in radiotherapy, mostly in brachytherapy, with special emphasis on the critical roles and responsibilities of qualified radiotherapy staff (radiation oncologists, medical physicists and radiotherapy technicians)
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