11,046 research outputs found
Exactly Conservative Integrators
Traditional numerical discretizations of conservative systems generically
yield an artificial secular drift of any nonlinear invariants. In this work we
present an explicit nontraditional algorithm that exactly conserves these
invariants. We illustrate the general method by applying it to the three-wave
truncation of the Euler equations, the Lotka--Volterra predator--prey model,
and the Kepler problem. This method is discussed in the context of symplectic
(phase space conserving) integration methods as well as nonsymplectic
conservative methods. We comment on the application of our method to general
conservative systems.Comment: 30 pages, postscript (1.3MB). Submitted to SIAM J. Sci. Comput
3D Computational Ghost Imaging
Computational ghost imaging retrieves the spatial information of a scene
using a single pixel detector. By projecting a series of known random patterns
and measuring the back reflected intensity for each one, it is possible to
reconstruct a 2D image of the scene. In this work we overcome previous
limitations of computational ghost imaging and capture the 3D spatial form of
an object by using several single pixel detectors in different locations. From
each detector we derive a 2D image of the object that appears to be illuminated
from a different direction, using only a single digital projector as
illumination. Comparing the shading of the images allows the surface gradient
and hence the 3D form of the object to be reconstructed. We compare our result
to that obtained from a stereo- photogrammetric system utilizing multiple high
resolution cameras. Our low cost approach is compatible with consumer
applications and can readily be extended to non-visible wavebands.Comment: 13pages, 4figure
Scaling Behavior of the Landau Gauge Overlap Quark Propagator
The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations are done on three lattices with different lattice spacings and
similar physical volumes to explore the approach of the quark propagator
towards the continuum limit. We have calculated the nonperturbative
momentum-dependent wavefunction renormalization function and the
nonperturbative mass function for a variety of bare quark masses and
extrapolate to the chiral limit.
We find the behavior of and are in good agreement for the
two finer lattices in the chiral limit. The quark condensate is also
calculated.Comment: 3 pages, Lattice2003(Chiral fermions
Scaling behavior of quark propagator in full QCD
We study the scaling behavior of the quark propagator on two lattices with
similar physical volume in Landau gauge with 2+1 flavors of dynamical quarks in
order to test whether we are close to the continuum limit for these lattices.
We use configurations generated with an improved staggered (``Asqtad'') action
by the MILC collaboration. The calculations are performed on
lattices with lattice spacing fm and on lattices
with lattice spacing fm. We calculate the quark mass function,
, and the wave-function renormalization function, , for a
variety of bare quark masses. Comparing the behavior of these functions on the
two sets of lattices we find that both and show little
sensitivity to the ultraviolet cutoff.Comment: 6 pages, 5 figure
Simultaneous real-time visible and infrared video with single-pixel detectors
Conventional cameras rely upon a pixelated sensor to provide spatial resolution. An alternative approach replaces the sensor with a pixelated transmission mask encoded with a series of binary patterns. Combining knowledge of the series of patterns and the associated filtered intensities, measured by single-pixel detectors, allows an image to be deduced through data inversion. In this work we extend the concept of a ‘single-pixel camera’ to provide continuous real-time video at 10 Hz , simultaneously in the visible and short-wave infrared, using an efficient computer algorithm. We demonstrate our camera for imaging through smoke, through a tinted screen, whilst performing compressive sampling and recovering high-resolution detail by arbitrarily controlling the pixel-binning of the masks. We anticipate real-time single-pixel video cameras to have considerable importance where pixelated sensors are limited, allowing for low-cost, non-visible imaging systems in applications such as night-vision, gas sensing and medical diagnostics
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