5,437 research outputs found
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
Matrix metalloproteinase MMP12 is associated with intervertebral disc degeneration
INTRODUCTION: Intervertebral disc (IVD) degeneration is associated with low back pain. However, the molecular changes during the degeneration process is not entirely clear. The loss of nucleus pulposus (NP) integrity is one of the early events of the degeneration. Chondrogenic markers, such as SOX9 and aggrecan, have been commonly used to assess the degree of IVD degeneration. Recent transcriptomic studies have proposed several other candidates that may mark IVD degeneration. These include cartilage oligomeric matrix protein (COMP), matrix gla protein (MGP)[1], fibulin 1 (FBLN1) [2], cytokeratin 18 (KRT18) [3], cadherin-2 (CDH2) [3], cytokeratin 19 (KRT19) [2], and Runt-related transcription factor 2 (RUNX2) [4]. Studies also demonstrated that degenerated NP attains a fibrocartilaginous phenotype [5,6] with increased ...postprin
Perturbative Approach to the Quasinormal Modes of Dirty Black Holes
Using a recently developed perturbation theory for uasinormal modes (QNM's),
we evaluate the shifts in the real and imaginary parts of the QNM frequencies
due to a quasi-static perturbation of the black hole spacetime. We show the
perturbed QNM spectrum of a black hole can have interesting features using a
simple model based on the scalar wave equation.Comment: Published in PR
T-violation tests for relativity principles
We consider the implications of a violation of the equivalence principle or
of Lorentz invariance in the neutrino sector for the T-asymmetry in a
three-flavour framework. We find that additional mixing due to these
mechanisms, while obeying all present bounds, can lead to a substantial
enhancement, suppression, and/or sign change in for the preferred
energies and baselines of a neutrino factory. This in turn allows for the
possibility of improving existing constraints by several orders of magnitude.Comment: 2 pages; Talk given at the 4th NuFact '02 Workshop (Neutrino
Factories Based On Muon Storage Rings), 1-6 Jul 2002, London, England; To
appear in proceeding
Logarithmic perturbation theory for quasinormal modes
Logarithmic perturbation theory (LPT) is developed and applied to quasinormal
modes (QNMs) in open systems. QNMs often do not form a complete set, so LPT is
especially convenient because summation over a complete set of unperturbed
states is not required. Attention is paid to potentials with exponential tails,
and the example of a Poschl-Teller potential is briefly discussed. A numerical
method is developed that handles the exponentially large wavefunctions which
appear in dealing with QNMs.Comment: 24 pages, 4 Postscript figures, uses ioplppt.sty and epsfig.st
Renormalization Flow of Bound States
A renormalization group flow equation with a scale-dependent transformation
of field variables gives a unified description of fundamental and composite
degrees of freedom. In the context of the effective average action, we study
the renormalization flow of scalar bound states which are formed out of
fundamental fermions. We use the gauged Nambu--Jona-Lasinio model at weak gauge
coupling as an example. Thereby, the notions of bound state or fundamental
particle become scale dependent, being classified by the fixed-point structure
of the flow of effective couplings.Comment: 25 pages, 3 figures, v2: minor corrections, version to appear in PR
Multilevel blocking approach to the fermion sign problem in path-integral Monte Carlo simulations
A general algorithm toward the solution of the fermion sign problem in
finite-temperature quantum Monte Carlo simulations has been formulated for
discretized fermion path integrals with nearest-neighbor interactions in the
Trotter direction. This multilevel approach systematically implements a simple
blocking strategy in a recursive manner to synthesize the sign cancellations
among different fermionic paths throughout the whole configuration space. The
practical usefulness of the method is demonstrated for interacting electrons in
a quantum dot.Comment: 4 pages RevTeX, incl. two figure
Frequent epigenetic inactivation of secreted frizzled-related protein 2 (SFRP2) by promoter methylation in human gastric cancer
The role of secreted frizzled-related protein (SFRP) genes in gastric cancer remains largely unknown. We determined the frequency and functional significance of SFRPs hypermethylation in human gastric cancer. The expression and methylation status of four SFRP members (SFRP1, 2, 4, and 5) in primary gastric cancer samples was screened. The biological effects of SFRP were analysed by flow cytometry, cell viability assay and in vivo tumour growth in nude mice. Among the four SFRPs, only SFRP2 was significantly downregulated in gastric cancer as compared to adjacent non-cancer samples (P<0.01). Promoter hypermethylation of SFRP2 was detected in 73.3% primary gastric cancer tissues, 37.5% of samples showing intestinal metaplasia and 20% adjacent normal gastric tissues. Bisulphite DNA sequencing confirmed the densely methylated SFRP2 promoter region. Demethylation treatment restored the expression of SFRP2 in gastric cancer cell lines. Forced expression of SFRP2 induced cell apoptosis, inhibited proliferation of gastric cancer cells and suppressed tumour growth in vivo. Moreover, methylated SFRP2 was detected in 66.7% of serum samples from cancer patients but not in normal controls. In conclusion, epigenetic inactivation of SFRP2 is a common and early event contributing to gastric carcinogenesis and may be a potential biomarker for gastric cancer
Magnetic-film atom chip with 10 m period lattices of microtraps for quantum information science with Rydberg atoms
We describe the fabrication and construction of a setup for creating lattices
of magnetic microtraps for ultracold atoms on an atom chip. The lattice is
defined by lithographic patterning of a permanent magnetic film. Patterned
magnetic-film atom chips enable a large variety of trapping geometries over a
wide range of length scales. We demonstrate an atom chip with a lattice
constant of 10 m, suitable for experiments in quantum information science
employing the interaction between atoms in highly-excited Rydberg energy
levels. The active trapping region contains lattice regions with square and
hexagonal symmetry, with the two regions joined at an interface. A structure of
macroscopic wires, cut out of a silver foil, was mounted under the atom chip in
order to load ultracold Rb atoms into the microtraps. We demonstrate
loading of atoms into the square and hexagonal lattice sections simultaneously
and show resolved imaging of individual lattice sites. Magnetic-film lattices
on atom chips provide a versatile platform for experiments with ultracold
atoms, in particular for quantum information science and quantum simulation.Comment: 7 pages, 7 figure
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