49,388 research outputs found
Infrared Photometry and Dust Absorption in Highly Inclined Spiral Galaxies
We present JHK surface photometry of 15 highly inclined, late-type (Sab-Sc)
spirals and investigate the quantitative effects of dust extinction. Using the
(J - H, H - K) two-color diagram, we compare the color changes along the minor
axis of each galaxy to the predictions from different models of radiative
transfer. Models in which scattering effects are significant and those with
more than a small fraction of the light sources located near the edge of the
dust distribution do not produce enough extinction to explain the observed
color gradients across disk absorption features. The optical depth in dust near
the plane as deduced from the color excess depends sensitively on the adopted
dust geometry, ranging from tau = 4 to 15 in the visual band. This suggests
that a realistic model of the dust distribution is required, even for infrared
photometry, to correct for dust extinction in the bulges of nearly edge-on
systems.Comment: Accepted for publication in the March 1996 AJ. LaTex source which
generates 27 pages of text and tables (no figures). Complete (text + figs)
compressed Postscript preprint is also available at
ftp://bessel.mps.ohio-state.edu/pub/terndrup/inclined.ps.Z (854 Mbyte
Chain Reduction for Binary and Zero-Suppressed Decision Diagrams
Chain reduction enables reduced ordered binary decision diagrams (BDDs) and
zero-suppressed binary decision diagrams (ZDDs) to each take advantage of the
others' ability to symbolically represent Boolean functions in compact form.
For any Boolean function, its chain-reduced ZDD (CZDD) representation will be
no larger than its ZDD representation, and at most twice the size of its BDD
representation. The chain-reduced BDD (CBDD) of a function will be no larger
than its BDD representation, and at most three times the size of its CZDD
representation. Extensions to the standard algorithms for operating on BDDs and
ZDDs enable them to operate on the chain-reduced versions. Experimental
evaluations on representative benchmarks for encoding word lists, solving
combinatorial problems, and operating on digital circuits indicate that chain
reduction can provide significant benefits in terms of both memory and
execution time
Competitive pathways for peptide deamidation
Asparagine (Asn) residues spontaneously – yet non-enzymatically – deamidate to form aspartate under physiological conditions, causing time-dependent changes in the conformation of proteins, limiting their lifetime [1]. The 'molecular clocks' hypothesis [2], suggests that deamidation is a biological molecular timing mechanism that could be set to any desired time interval by genetic control of the protein structure and the immediate environment of the Asn residue. The fact that deamidation occurs over a wide range of biologically relevant time intervals suggests that different mechanisms may be at play. To date deamidation is believed to occur over a succinimide-mediated pathway [3]. A novel route leading to the succinimide intermediate via tautomerization of the Asn side chain amide functionality was recently proposed [4,5]. The current study introduces a new 'competing' route for the deamidation of asparagine residues. The aim is to comparatively analyze the feasibility of this new mechanism against the traditional succinimide route, taking into account the catalytic effect of the solvent environment. For this purpose, QM dynamics and meta-dynamics calculations were performed on a model peptide placed in a periodic water box. These results will identify the lowest energy pathway for asparagine deamidation and will serve as a stepping stone for QM/MM calculations of Asn deamidation in proteins
Recommended from our members
Turning negative into positive: public health mass media campaigns and negative advertising.
Literature suggests that 'negative advertising' is an effective way to encourage behavioral changes, but it has enjoyed limited use in public health media campaigns. However, as public health increasingly focuses on non-communicable disease prevention, negative advertising could be more widely applied. This analysis considers an illustrative case from tobacco control. Relying on internal tobacco industry documents, surveys and experimental data and drawing from political advocacy literature, we describe tobacco industry and public health research on the American Legacy Foundation's "truth" campaign, an example of effective negative advertising in the service of public health. The tobacco industry determined that the most effective advertisements run by Legacy's "truth" campaign were negative advertisements. Although the tobacco industry's own research suggested that these negative ads identified and effectively reframed the cigarette as a harmful consumer product rather than focusing solely on tobacco companies, Philip Morris accused Legacy of 'vilifying' it. Public health researchers have demonstrated the effectiveness of the "truth" campaign in reducing smoking initiation. Research on political advocacy demonstrating the value of negative advertising has rarely been used in the development of public health media campaigns, but negative advertising can effectively communicate certain public health messages and serve to counter corporate disease promotion
Highlights of the SLD Physics Program at the SLAC Linear Collider
Starting in 1989, and continuing through the 1990s, high-energy physics
witnessed a flowering of precision measurements in general and tests of the
standard model in particular, led by e+e- collider experiments operating at the
Z0 resonance. Key contributions to this work came from the SLD collaboration at
the SLAC Linear Collider. By exploiting the unique capabilities of this
pioneering accelerator and the SLD detector, including a polarized electron
beam, exceptionally small beam dimensions, and a CCD pixel vertex detector, SLD
produced a broad array of electroweak, heavy-flavor, and QCD measurements. Many
of these results are one of a kind or represent the world's standard in
precision. This article reviews the highlights of the SLD physics program, with
an eye toward associated advances in experimental technique, and the
contribution of these measurements to our dramatically improved present
understanding of the standard model and its possible extensions.Comment: To appear in 2001 Annual Review of Nuclear and Particle Science; 78
pages, 31 figures; A version with higher resolution figures can be seen at
http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8985.html; Second
version incorporates minor changes to the tex
Determining Reactor Flux from Xenon-136 and Cesium-135 in Spent Fuel
The ability to infer the reactor flux from spent fuel or seized fissile
material would enhance the tools of nuclear forensics and nuclear
nonproliferation significantly. We show that reactor flux can be inferred from
the ratios of xenon-136 to xenon-134 and cesium-135 to cesium-137. If the
average flux of a reactor is known, the flux inferred from measurements of
spent fuel could help determine whether that spent fuel was loaded as a blanket
or close to the mid-plane of the reactor. The cesium ratio also provides
information on reactor shutdowns during the irradiation of fuel, which could
prove valuable for identifying the reactor in question through comparisons with
satellite reactor heat monitoring data. We derive analytic expressions for
these correlations and compare them to experimental data and to detailed
reactor burn simulations. The enrichment of the original uranium fuel affects
the correlations by up to 3 percent, but only at high flux.Comment: 10 pages, 9 figure
New Variants of Pattern Matching with Constants and Variables
Given a text and a pattern over two types of symbols called constants and
variables, the parameterized pattern matching problem is to find all
occurrences of substrings of the text that the pattern matches by substituting
a variable in the text for each variable in the pattern, where the substitution
should be injective. The function matching problem is a variant of it that
lifts the injection constraint. In this paper, we discuss variants of those
problems, where one can substitute a constant or a variable for each variable
of the pattern. We give two kinds of algorithms for both problems, a
convolution-based method and an extended KMP-based method, and analyze their
complexity.Comment: 15 pages, 2 figure
Moire bands in twisted double-layer graphene
A moire pattern is formed when two copies of a periodic pattern are overlaid
with a relative twist. We address the electronic structure of a twisted
two-layer graphene system, showing that in its continuum Dirac model the moire
pattern periodicity leads to moire Bloch bands. The two layers become more
strongly coupled and the Dirac velocity crosses zero several times as the twist
angle is reduced. For a discrete set of magic angles the velocity vanishes, the
lowest moire band flattens, and the Dirac-point density-of-states and the
counterflow conductivity are strongly enhanced
Binary Decision Diagrams: from Tree Compaction to Sampling
Any Boolean function corresponds with a complete full binary decision tree.
This tree can in turn be represented in a maximally compact form as a direct
acyclic graph where common subtrees are factored and shared, keeping only one
copy of each unique subtree. This yields the celebrated and widely used
structure called reduced ordered binary decision diagram (ROBDD). We propose to
revisit the classical compaction process to give a new way of enumerating
ROBDDs of a given size without considering fully expanded trees and the
compaction step. Our method also provides an unranking procedure for the set of
ROBDDs. As a by-product we get a random uniform and exhaustive sampler for
ROBDDs for a given number of variables and size
- …