13,369 research outputs found
A Birkhoff connection between quantum circuits and linear classical reversible circuits
Birkhoff's theorem tells how any doubly stochastic matrix can be decomposed as a weighted sum of permutation matrices. Similar theorems on unitary matrices reveal a connection between quantum circuits and linear classical reversible circuits. It triggers the question whether a quantum computer can be regarded as a superposition of classical reversible computers
Interplay between multiple scattering, emission, and absorption of light in the phosphor of a white light-emitting diode
We study light transport in phosphor plates of white light-emitting diodes
(LEDs). We measure the broadband diffuse transmission through phosphor plates
of varying YAG:Ce density. We distinguish the spectral ranges where
absorption, scattering, and re-emission dominate. Using diffusion theory, we
derive the transport and absorption mean free paths from first principles. We
find that both transport and absorption mean free paths are on the order of the
plate thickness. This means that phosphors in commercial LEDs operate well
within an intriguing albedo range around 0.7. We discuss how salient parameters
that can be derived from first principles control the optical properties of a
white LED.Comment: 14 pages, 9 figure
A Comparative Study of the Valence Electronic Excitations of N_2 by Inelastic X-ray and Electron Scattering
Bound state, valence electronic excitation spectra of N_2 are probed by
nonresonant inelastic x-ray and electron scattering. Within the usual
theoretical treatments, dynamical structure factors derived from the two probes
should be identical. However, we find strong disagreements outside the dipole
scattering limit, even at high probe energies. This suggests an unexpectedly
important contribution from intra-molecular multiple scattering of the probe
electron from core electrons or the nucleus. These effects should grow
progressively stronger as the atomic number of the target species increases.Comment: Submitted to Physical Review Letters April 27, 2010. 12 pages
including 2 figure pages
Cross-talk between signaling pathways leading to defense against pathogens and insects
In nature, plants interact with a wide range of organisms, some of which
are harmful (e.g. pathogens, herbivorous insects), while others are beneficial
(e.g. growth-promoting rhizobacteria, mycorrhizal fungi, and predatory
enemies of herbivores). During the evolutionary arms race between plants
and their attackers, primary and secondary immune responses evolved to
recognize common or highly specialized features of microbial pathogens
(Chisholm et al., 2006), resulting in sophisticated mechanisms of defense
Photonic Band Gaps of Three-Dimensional Face-Centered Cubic Lattices
We show that the photonic analogue of the Korringa-Kohn-Rostocker method is a
viable alternative to the plane-wave method to analyze the spectrum of
electromagnetic waves in a three-dimensional periodic dielectric lattice.
Firstly, in the case of an fcc lattice of homogeneous dielectric spheres, we
reproduce the main features of the spectrum obtained by the plane wave method,
namely that for a sufficiently high dielectric contrast a full gap opens in the
spectrum between the eights and ninth bands if the dielectric constant
of spheres is lower than the dielectric constant of
the background medium. If , no gap is found in the
spectrum. The maximal value of the relative band-gap width approaches 14% in
the close-packed case and decreases monotonically as the filling fraction
decreases. The lowest dielectric contrast for which a
full gap opens in the spectrum is determined to be 8.13. Eventually, in the
case of an fcc lattice of coated spheres, we demonstrate that a suitable
coating can enhance gap widths by as much as 50%.Comment: 19 pages, 6 figs., plain latex - a section on coated spheres, two
figures, and a few references adde
A first phase in the habitat classification for the Zeeschelde: Bed form classification
Within the scope of the long term vision of the Schelde Estuary and the Development Outline 2010 low dynamic intertidal and shallow water areas are considered to be of high ecological value. Little is known about the occurrence of such valuable reas in the Schelde Estuary, nor are the physical and morphological processes which determine the occurrence of these areas fully understood. Based on the results and recommendations of a 2008-2009 research project in the Westerschelde, a new research project was defined to determine relationships between abiotic (bedforms, hydrodynamics, sediment) and biotic (benthos) characteristics in the Zeeschelde (Belgium) and to set up a classification of deep and undeep subtidal areas. A first phase in the habitat classification comprises of the analysis of bed form occurrence and the setup of a bed form classification based on multibeam echo sounding data. Results show within the different sub areas a variation in bed forms going from hard bed layers to no bed forms to ripples (H ~ 0,1 to 0,3 m | L ~ 10 m) and smaller dunes (H ~ 0,5 to 1 m | L ~ 15 to 25 m). On-going research investigates relationships between the bed form characteristics and flow and sediment characteristics. Preliminary results
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