2,878 research outputs found
Creating effective focus cues in multi-plane 3D displays.
Focus cues are incorrect in conventional stereoscopic displays. This causes a dissociation of vergence and accommodation, which leads to visual fatigue and perceptual distortions. Multi-plane displays can minimize these problems by creating nearly correct focus cues. But to create the appearance of continuous depth in a multi-plane display, one needs to use depth-weighted blending: i.e., distribute light intensity between adjacent planes. Akeley et al. [ACM Trans. Graph. 23, 804 (2004)] and Liu and Hua [Opt. Express 18, 11562 (2009)] described rather different rules for depth-weighted blending. We examined the effectiveness of those and other rules using a model of a typical human eye and biologically plausible metrics for image quality. We find that the linear blending rule proposed by Akeley and colleagues [ACM Trans. Graph. 23, 804 (2004)] is the best solution for natural stimuli
Stable and Metastable vortex states and the first order transition across the peak effect region in weakly pinned 2H-NbSe_2
The peak effect in weakly pinned superconductors is accompanied by metastable
vortex states. Each metastable vortex configuration is characterized by a
different critical current density J_c, which mainly depends on the past
thermomagnetic history of the superconductor. A recent model [G. Ravikumar, et
al, Phys. Rev. B 61, R6479 (2000)] proposed to explain the history dependent
J_c postulates a stable state of vortex lattice with a critical current density
J_c^{st}, determined uniquely by the field and temperature. In this paper, we
present evidence for the existence of the stable state of the vortex lattice in
the peak effect region of 2H-NbSe_2. It is shown that this stable state can be
reached from any metastable vortex state by cycling the applied field by a
small amplitude. The minor magnetization loops obtained by repeated field
cycling allow us to determine the pinning and "equilibrium" properties of the
stable state of the vortex lattice at a given field and temperature
unambiguously. The data imply the occurence of a first order phase transition
from an ordered phase to a disordered vortex phase across the peak effect.Comment: 20 pages, 10 figures. Corresponding author: S. Ramakrishna
Violent Hard X-ray Variability of Mrk 421 Observed by NuSTAR in 2013 April
The well studied blazar Markarian 421 (Mrk 421, =0.031) was the subject of
an intensive multi-wavelength campaign when it flared in 2013 April. The
recorded X-ray and very high energy (VHE, E100 GeV) -ray fluxes are
the highest ever measured from this object. At the peak of the activity, it was
monitored by the hard X-ray focusing telescope {\it Nuclear Spectroscopic
Telescope Array} ({\it NuSTAR}) and {\it Swift} X-Ray Telescope (XRT). In this
work, we present a detailed variability analysis of {\it NuSTAR} and {\it
Swift}-XRT observations of Mrk 421 during this flaring episode. We obtained the
shortest flux doubling time of 14.015.03 minutes, which is the shortest
hard X-ray (379 keV) variability ever recorded from Mrk 421 and is on the
order of the light crossing time of the black hole's event horizon. A pattern
of extremely fast variability events superposed on slowly varying flares is
found in most of the {\it NuSTAR} observations. We suggest that these peculiar
variability patterns may be explained by magnetic energy dissipation and
reconnection in a fast moving compact emission region within the jet. Based on
the fast variability, we derive a lower limit on the magnetic field strength of
~G, where is the
Doppler factor in units of 10, and is the characteristic X-ray
synchrotron frequency in units of ~Hz.Comment: 23 pages, 5 figures, 2 tables, to appear in the Astrophysical Journa
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