43,898 research outputs found
Simulation of Relativistic Force-free Magnetohydrodynamic Turbulence
We present numerical studies of 3-dimensional magnetohydrodynamic (MHD)
turbulence in a strongly magnetized medium in the extremely relativistic limit,
in which the inertia of the charge carriers can be neglected. We have focused
on strong Alfvenic turbulence in the limit. We have found the following
results. First, the energy spectrum is consistent with a Kolmogorov spectrum:
. Second, turbulence shows a Goldreich-Sridhar type
anisotropy: , where and
are wavenumbers along and perpendicular to the local mean magnetic field
directions, respectively. These scalings are in agreement with earlier
theoretical predictions by Thompson & Blaes.Comment: 4 pages; 3 figures; APJL, submitte
Purification through Zeno-like Measurements
A series of frequent measurements on a quantum system (Zeno-like
measurements) is shown to result in the ``purification'' of another quantum
system in interaction with the former. Even though the measurements are
performed on the former system, their effect drives the latter into a pure
state, irrespectively of its initial (mixed) state, provided certain conditions
are satisfied.Comment: REVTeX4, 4 pages, 1 figure; to be published in Phys. Rev. Lett.
(2003
Dynamics of tilt-based browsing on mobile devices
A tilt-controlled photo browsing method for small mobile devices is presented. The implementation uses continuous inputs from an accelerometer, and a multimodal (visual, audio and vibrotactile) display coupled with the states of this model. The model is based on a simple physical model, with its characteristics shaped to enhance usability. We show how the dynamics of the physical model can be shaped to make the handling qualities of the mobile device fit the browsing task. We implemented the proposed algorithm on Samsung MITs PDA with tri-axis accelerometer and a vibrotactile motor. The experiment used seven novice users browsing from 100 photos. We compare a tilt-based interaction method with a button-based browser and an iPod wheel. We discuss the usability performance and contrast this with subjective experience from the users. The iPod wheel has significantly poorer performance than button pushing or tilt interaction, despite its commercial popularity
Schwinger Effect in Non-parallel D1-branes: A Path Integral Approach
We study the Schwinger effect in a system of non-parallel D1-branes for the
bosonic strings using the path integral formalism. We drive the string pair
creation rate by calculating the one loop vacuum amplitude of the setup in
presence of the background electric filed defined along one of the D1-branes.
We find an angle dependent minimum value for the background field and show that
the decaying of vacuum into string pairs takes place for the field above this
value. It is shown that in limit the vacuum
becomes stable and thus no pair creation occurs
Magnetic susceptibility study of hydrated and non-hydrated NaxCoO2-yH2O single crystals
We have measured the magnetic susceptibility of single crystal samples of
non-hydrated NaxCoO2 (x ~ 0.75, 0.67, 0.5, and 0.3) and hydrated Na0.3CoO2-yH2O
(y ~ 0, 0.6, 1.3). Our measurements reveal considerable anisotropy between the
susceptibilities with H||c and H||ab. The derived anisotropic g-factor ratio
(g_ab/g_c) decreases significantly as the composition is changed from the
Curie-Weiss metal with x = 0.75 to the paramagnetic metal with x = 0.3. Fully
hydrated Na0.3CoO2-1.3H2O samples have a larger susceptibility than
non-hydrated Na0.3CoO2 samples, as well as a higher degree of anisotropy. In
addition, the fully hydrated compound contains a small additional fraction of
anisotropic localized spins.Comment: 6 pages, 5 figure
Abelian Chern-Simons field theory and anyon equation on a torus
We quantize the abelian Chern-Simons theory coupled to non-relativistic
matter field on a torus without invoking the flux quantization. Through a
series of canonical transformations which is equivalent to solving the Gauss
constraint, we obtain an effective hamiltonian density with periodic matter
field. We also obtain the many-anyon Schr\"odinger equation with periodic
Aharonov-Bohm potentials and analyze the periodic property of the wavefunction.
Some comments are given on the different features of our approach from the
previous ones.Comment: 24, SNUTP-93-9
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