1,450 research outputs found
Enhanced chiral logarithms in partially quenched QCD
I discuss the properties of pions in ``partially quenched'' theories, i.e.
those in which the valence and sea quark masses, and , are
different. I point out that for lattice fermions which retain some chiral
symmetry on the lattice, e.g. staggered fermions, the leading order prediction
of the chiral expansion is that the mass of the pion depends only on , and
is independent of . This surprising result is shown to receive corrections
from loop effects which are of relative size , and which thus
diverge when the valence quark mass vanishes. Using partially quenched chiral
perturbation theory, I calculate the full one-loop correction to the mass and
decay constant of pions composed of two non-degenerate quarks, and suggest
various combinations for which the prediction is independent of the unknown
coefficients of the analytic terms in the chiral Lagrangian. These results can
also be tested with Wilson fermions if one uses a non-perturbative definition
of the quark mass.Comment: 14 pages, 3 figures, uses psfig. Typos in eqs (18)-(20) corrected
(alpha_4 is replaced by alpha_4/2
Two dimensional lattice Gross--Neveu model with domain-wall fermions
We investigate the two dimensional lattice Gross--Neveu model in large flavor
number limit using the domain-wall fermion formulation, as a toy model of
lattice QCD. We study nonperturbative behaviorn of the restoration of chiral
symmetry of the domain-wall fermions as the extent of the extra dimension
is increased to infinity. We find the the parity broken phase (Aoki
phase) for finite , and study the phase diagram, which is related to the
mechanism of the chiral restoration in limit. The continuum
limit is taken and scaling violation of observables vanishes in
limit. We also examine the systematic dependencies of
observables to the parameters.Comment: 36 pages (26 figures), Latex (epsf style-file needed
Don't bleach chaotic data
A common first step in time series signal analysis involves digitally
filtering the data to remove linear correlations. The residual data is
spectrally white (it is ``bleached''), but in principle retains the nonlinear
structure of the original time series. It is well known that simple linear
autocorrelation can give rise to spurious results in algorithms for estimating
nonlinear invariants, such as fractal dimension and Lyapunov exponents. In
theory, bleached data avoids these pitfalls. But in practice, bleaching
obscures the underlying deterministic structure of a low-dimensional chaotic
process. This appears to be a property of the chaos itself, since nonchaotic
data are not similarly affected. The adverse effects of bleaching are
demonstrated in a series of numerical experiments on known chaotic data. Some
theoretical aspects are also discussed.Comment: 12 dense pages (82K) of ordinary LaTeX; uses macro psfig.tex for
inclusion of figures in text; figures are uufile'd into a single file of size
306K; the final dvips'd postscript file is about 1.3mb Replaced 9/30/93 to
incorporate final changes in the proofs and to make the LaTeX more portable;
the paper will appear in CHAOS 4 (Dec, 1993
Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium
Understanding excited carrier dynamics in semiconductors is crucial for the
development of photovoltaics and efficient photonic devices. However,
overlapping spectral features in optical/NIR pump-probe spectroscopy often
render assignments of separate electron and hole carrier dynamics ambiguous.
Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin
films are directly and simultaneously observed by attosecond transient
absorption spectroscopy (ATAS) in the extreme ultraviolet at the germanium
M_{4,5}-edge (~30 eV). We decompose the ATAS spectra into contributions of
electronic state blocking and photo-induced band shifts at a carrier density of
8*10^{20}cm^{-3}. Separate electron and hole relaxation times are observed as a
function of hot carrier energies. A first order electron and hole decay of ~1
ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous
observation of electrons and holes with ATAS paves the way for investigating
few to sub-femtosecond dynamics of both holes and electrons in complex
semiconductor materials and across junctions.Comment: Includes Supplementary Informatio
Chasing the identification of ASCA Galactic Objects (ChIcAGO): An X-ray survey of unidentified sources in the galactic plane. I : Source sample and initial results
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10 keV) within the Fx 10-13 to 10-11 erg cm -2 s-1 X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3′ of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the Fx 10-13 to 10-11 erg cm -2 s-1 flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei.Peer reviewedSubmitted Versio
Affect and cognition in the context of home: The quest for intangibles
The three papers in this special issue represent an important advance in the effort to understand people's attachment to place. Economic factors do not provide an adequate explanation; it is necessary to seek less tangible influences. There are grounds for looking to the physical setting, and especially the natural environment available to residents. Access to other resources may also be important. And group affiliation can impact both cognitive and affective aspects of the attachment process. In terms of future research to better understand these intangibles, it may help to focus on the sense of place, the factors that make an environment psychologically comfortable. Three variables are proposed as researchable facets of the sense of place: (1) legibility, (2) the perception of and preference for the visual environment, and (3) the compatibility of the setting with human purposes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43517/1/11111_2005_Article_BF01254781.pd
Advancing the Field Designing Brain Healthy Environments for Intergenerational Programs Designing Brain Healthy Environments
Intergenerational relationships are at the center of programs designe
Identification and Synthesis of a Male-Produced Pheromone for the Neotropical Root Weevil Diaprepes abbreviatus
An unsaturated hydroxy-ester pheromone was isolated from the headspace and feces of male Diaprepes abbreviatus, identified, and synthesized. The pheromone, methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate, was discovered by gas chromatography-coupled electroantennogram detection (GC-EAD), and identified by gas chromatography–mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The synthesis yielded an 86:14 mixture of methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (active) and methyl (Z)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (inactive), along with a lactone breakdown product. The activity of the synthetic E-isomer was confirmed by GC-EAD, GC-MS, NMR, and bioassays. No antennal response was observed to the Z-isomer or the lactone. In a two-choice olfactometer bioassay, female D. abbreviatus moved upwind towards the synthetic pheromone or natural pheromone more often compared with clean air. Males showed no clear preference for the synthetic pheromone. This pheromone, alone or in combination with plant volatiles, may play a role in the location of males by female D. abbreviatus
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