3,314 research outputs found
Cumulative effect of Weibel-type instabilities in counterstreaming plasmas with non-Maxwellian anisotropies
Counterstreaming plasma structures are widely present in laboratory
experiments and astrophysical systems, and they are investigated either to
prevent unstable modes arising in beam-plasma experiments or to prove the
existence of large scale magnetic fields in astrophysical objects.
Filamentation instability arises in a counterstreaming plasma and is
responsible for the magnetization of the plasma. Filamentationally unstable
mode is described by assuming that each of the counterstreaming plasmas has an
isotropic Lorentzian (kappa) distribution. In this case, the filamentation
instability growth rate can reach a maximum value markedly larger than that for
a a plasma with a Maxwellian distribution function. This behaviour is opposite
to what was observed for the Weibel instability growth rate in a bi-kappa
plasma, which is always smaller than that obtained for a bi-Maxwellian plasma.
The approach is further generalized for a counterstreaming plasma with a
bi-kappa temperature anisotropy. In this case, the filamentation instability
growth rate is enhanced by the Weibel effect when the plasma is hotter in the
streaming direction, and the growth rate becomes even larger. These effects
improve significantly the efficiency of the magnetic field generation, and
provide further support for the potential role of the Weibel-type instabilities
in the fast magnetization scenarios
On the entropy of plasmas described with regularized -distributions
In classical thermodynamics the entropy is an extensive quantity, i.e.\ the
sum of the entropies of two subsystems in equilibrium with each other is equal
to the entropy of the full system consisting of the two subsystems. The
extensitivity of entropy has been questioned in the context of a theoretical
foundation for the so-called -distributions, which describe plasma
constituents with power-law velocity distributions. We demonstrate here, by
employing the recently introduced {\it regularized -distributions},
that entropy can be defined as an extensive quantity even for such
power-law-like distributions that truncate exponentially.Comment: Preprint accepted for publication in Phys. Rev.
Surface waves on a quantum plasma half-space
Surface modes are coupled electromagnetic/electrostatic excitations of free
electrons near the vacuum-plasma interface and can be excited on a sufficiently
dense plasma half-space. They propagate along the surface plane and decay in
either sides of the boundary. In such dense plasma models, which are of
interest in electronic signal transmission or in some astrophysical
applications, the dynamics of the electrons is certainly affected by the
quantum effects. Thus, the dispersion relation for the surface wave on a
quantum electron plasma half-space is derived by employing the quantum
hydrodynamical (QHD) and Maxwell-Poison equations. The QHD include quantum
forces involving the Fermi electron temperature and the quantum Bohm potential.
It is found that, at room temperature, the quantum effects are mainly relevant
for the electrostatic surface plasma waves in a dense gold metallic plasma
Sally Ride EarthKAM - Automated Image Geo-Referencing Using Google Earth Web Plug-In
Sally Ride EarthKAM is an educational program funded by NASA that aims to provide the public the ability to picture Earth from the perspective of the International Space Station (ISS). A computer-controlled camera is mounted on the ISS in a nadir-pointing window; however, timing limitations in the system cause inaccurate positional metadata. Manually correcting images within an orbit allows the positional metadata to be improved using mathematical regressions. The manual correction process is time-consuming and thus, unfeasible for a large number of images. The standard Google Earth program allows for the importing of KML (keyhole markup language) files that previously were created. These KML file-based overlays could then be manually manipulated as image overlays, saved, and then uploaded to the project server where they are parsed and the metadata in the database is updated. The new interface eliminates the need to save, download, open, re-save, and upload the KML files. Everything is processed on the Web, and all manipulations go directly into the database. Administrators also have the control to discard any single correction that was made and validate a correction. This program streamlines a process that previously required several critical steps and was probably too complex for the average user to complete successfully. The new process is theoretically simple enough for members of the public to make use of and contribute to the success of the Sally Ride EarthKAM project. Using the Google Earth Web plug-in, EarthKAM images, and associated metadata, this software allows users to interactively manipulate an EarthKAM image overlay, and update and improve the associated metadata. The Web interface uses the Google Earth JavaScript API along with PHP-PostgreSQL to present the user the same interface capabilities without leaving the Web. The simpler graphical user interface will allow the public to participate directly and meaningfully with EarthKAM. The use of similar techniques is being investigated to place ground-based observations in a Google Mars environment, allowing the MSL (Mars Science Laboratory) Science Team a means to visualize the rover and its environment
Contemplating Mindfulness at Work: An Integrative Review
Mindfulness research activity is surging within organizational science. Emerging evidence across multiple fields suggests that mindfulness is fundamentally connected to many aspects of workplace functioning, but this knowledge base has not been systematically integrated to date. This review coalesces the burgeoning body of mindfulness scholarship into a framework to guide mainstream management research investigating a broad range of constructs. The framework identifies how mindfulness influences attention, with downstream effects on functional domains of cognition, emotion, behavior, and physiology. Ultimately, these domains impact key workplace outcomes, including performance, relationships, and well-being. Consideration of the evidence on mindfulness at work stimulates important questions and challenges key assumptions within management science, generating an agenda for future research
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Shake table testing of a tuned mass damper inerter (Tmdi)-equipped structure and nonlinear dynamic modeling under harmonic excitations
This paper presents preliminary experimental results from a novel shaking table testing campaign investigating the dynamic response of a two-degree-of-freedom (2DOF) physical specimen with a grounded inerter under harmonic base excitation and contributes a nonlinear dynamic model capturing the behavior of the test specimen. The latter consists of a primary mass connected to the ground through a high damping rubber isolator (HDRI) and a secondary mass connected to the primary mass through a second HDRI. Further, a flywheel-based rack-and-pinion inerter prototype device is used to connect the secondary mass to the ground. The resulting specimen resembles the tuned mass damper inerter (TMDI) configuration with grounded inerter analytically defined and numerically assessed by the authors in a number of previous publications. Physical specimens with three different inerter coefficients are tested on the shake table under sine-sweep excitation with three different amplitudes. Experimental frequency response functions (FRFs) are derived manifesting a softening nonlinear behavior of the specimens and enhanced vibration suppression with increased inerter coefficient. Further, a 2DOF parametric nonlinear model of the specimen is established accounting for non-ideal inerter device behavior and its potential to characterize experimental response time-histories, FRFs, and force-displacement relationships of the HDRIs and of the inerter is verified
Order parameter oscillations in Fe/Ag/Bi2Sr2CaCu2O{8+delta} tunnel junctions
We have performed temperature dependent tunneling conductance spectroscopy on
Fe/Ag/Bi2Sr2CaCu2O8 (BSCCO) planar junctions. The multilayered Fe
counterelectrode was designed to probe the proximity region of the ab-plane of
BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude
and sign dependent on the energy, decaying with increasing distance from the
junction barrier, in conjunction with the theoretical predictions involving
d-wave superconductors coupled with ferromagnets. The conductance oscillates in
antiphase at E = 0 and E = +/-Delta. Spectral features characteristic to a
broken time-reversal pairing symmetry are detected and they do not depend on
the geometrical characteristics of the ferromagnetic film.Comment: 4 pages and 4 figures Submitted to Physical Review Letter
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