779 research outputs found
A BGG-type resolution for tensor modules over general linear superalgebra
We construct a Bernstein-Gelfand-Gelfand type resolution in terms of direct
sums of Kac modules for the finite-dimensional irreducible tensor
representations of the general linear superalgebra. As a consequence it follows
that the unique maximal submodule of a corresponding reducible Kac module is
generated by its proper singular vector.Comment: 11pages, LaTeX forma
Cloning and functional characterization of a complex endo-beta-1,3-glucanase from Paenibacillus sp
A beta-1,3-glucanase gene, encoding a protein of 1,793 amino acids, was cloned from a strain of Paenibacillus sp. in this study. This large protein, designated as LamA, consists of many putative functional units, which include, from N to C terminus, a leader peptide, three repeats of the S-layer homologous module, a catalytic module of glycoside hydrolase family 16, four repeats of the carbohydrate-binding module of family CBM_4_9, and an analogue of coagulation factor Fa5/8C. Several truncated proteins, composed of the catalytic module with various organizations of the appended modules, were successfully expressed and characterized in this study. Data indicated that the catalytic module specifically hydrolyze beta-1,3- and beta-1,3-1,4-glucans. Also, laminaritriose was the major product upon endolytic hydrolysis of laminarin. The CBM repeats and Fa5/8C analogue substantially enhanced the hydrolyzing activity of the catalytic module, particularly toward insoluble complex substrates, suggesting their modulating functions in the enzymatic activity of LamA. Carbohydrate-binding assay confirmed the binding capabilities of the CBM repeats and Fa5/8C analogue to beta-1,3-, beta-1,3-1,4-, and even beta-1,4-glucans. These appended modules also enhanced the inhibition effect of the catalytic module on the growth of Candida albicans and Rhizoctonia solani
Gamma-Ray Emission From Be/X-Ray Binaries
Be/X-ray binaries are systems formed by a massive Be star and a magnetized
neutron star, usually in an eccentric orbit. The Be star has strong equatorial
winds occasionally forming a circumstellar disk. When the neutron star
intersects the disk the accretion rate dramatically increases and a transient
accretion disk can be formed around the compact object. This disk can last
longer than a single orbit in the case of major outbursts. If the disk rotates
faster than the neutron star, the Cheng-Ruderman mechanism can produce a
current of relativistic protons that would impact onto the disk surface,
producing gamma-rays from neutral pion decays and initiating electromagnetic
cascades inside the disk. In this paper we present calculations of the
evolution of the disk parameters during both major and minor X-ray events, and
we discuss the generation of gamma-ray emission at different energies within a
variety of models that include both screened and unscreened disks.Comment: 14 pages, to appear in: "The multiwavelength approach to unidentified
gamma-ray sources", Eds. K. S. Cheng & G.E. Romero, Kluwer Academic Publisher
(Astrophysics and Space Sciences Journal). The present version has two
additional figures respect to the version to be published in the journa
Recommended from our members
Characteristics of regional new particle formation in urban and regional background environments in the North China Plain
Long-term measurements of particle number size distributions were carried out both at an urban background site (Peking University, PKU) and a regional Global Atmospheric Watch station (Shangdianzi, SDZ) from March to November in 2008. In total, 52 new particle formation (NPF) events were observed simultaneously at both sites, indicating that this is a regional phenomenon in the North China Plain. On average, the mean condensation sink value before the nucleation events started was 0.025 sâ1 in the urban environment, which was 1.6 times higher than that at regional site. However, higher particle formation and growth rates were observed at PKU (10.8 cmâ3 sâ1 and 5.2 nm hâ1) compared with those at SDZ (4.9 cmâ3 sâ1 and 4.0 nm hâ1). These results implied that precursors were much more abundant in the polluted urban environment. Different from the observations in cleaner environments, the background conditions of the observed particle homogeneous nucleation events in the North China Plain could be characterized as the co-existing of a stronger source of precursor gases and a higher condensational sink of pre-existing aerosol particles. Secondary aerosol formation following nucleation events results in an increase of particle mass concentration, particle light scattering coefficient, and cloud condensation nuclei (CCN) number concentration, with consequences on visibility, radiative effects, and air quality. Typical regional NPF events with significant particle nucleation rates and subsequent particle growth over a sufficiently long time period at both sites were chosen to investigate the influence of NPF on the number concentration of "potential" CCN. As a result, the NPF and the subsequent condensable growth increased the CCN number concentration in the North China Plain by factors in the range from 5.6 to 8.7. Moreover, the potential contribution of anthropogenic emissions to the CCN number concentration was more than 50%, to which more attention should be drawn in regional and global climate modeling, especially in the polluted urban areas
Single-cell cytometry via multiplexed fluorescence prediction by label-free reflectance microscopy
Traditional imaging cytometry uses fluorescence markers to identify specific structures but is limited in throughput
by the labeling process. We develop a label-free technique that alleviates the physical staining and provides
multiplexed readouts via a deep learningâaugmented digital labeling method. We leverage the rich structural
information and superior sensitivity in reflectance microscopy and show that digital labeling predicts accurate
subcellular features after training on immunofluorescence images. We demonstrate up to three times improvement
in the prediction accuracy over the state of the art. Beyond fluorescence prediction, we demonstrate that
single cellâlevel structural phenotypes of cell cycles are correctly reproduced by the digital multiplexed images,
including Golgi twins, Golgi haze during mitosis, and DNA synthesis. We further show that the multiplexed readouts
enable accurate multiparametric single-cell profiling across a large cell population. Our method can markedly
improve the throughput for imaging cytometry toward applications for phenotyping, pathology, and high-content
screening.Published versio
Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter
The Coronal Multichannel Polarimeter (CoMP) measures not only the
polarization of coronal emission, but also the full radiance profiles of
coronal emission lines. For the first time, CoMP observations provide
high-cadence image sequences of the coronal line intensity, Doppler shift and
line width simultaneously in a large field of view. By studying the Doppler
shift and line width we may explore more of the physical processes of CME
initiation and propagation. Here we identify a list of CMEs observed by CoMP
and present the first results of these observations. Our preliminary analysis
shows that CMEs are usually associated with greatly increased Doppler shift and
enhanced line width. These new observations provide not only valuable
information to constrain CME models and probe various processes during the
initial propagation of CMEs in the low corona, but also offer a possible
cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism,
Sol. Phy
Rare Decays of \Lambda_b->\Lambda + \gamma and \Lambda_b ->\Lambda + l^{+} l^{-} in the Light-cone Sum Rules
Within the Standard Model, we investigate the weak decays of and with the light-cone
sum rules approach. The higher twist distribution amplitudes of
baryon to the leading conformal spin are included in the sum rules for
transition form factors. Our results indicate that the higher twist
distribution amplitudes almost have no influences on the transition form
factors retaining the heavy quark spin symmetry, while such corrections can
result in significant impacts on the form factors breaking the heavy quark spin
symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of
baryon are also employed in the sum rules for a comparison, which can
give rise to the form factors approximately 5 times larger than that in terms
of conformal expansion. Utilizing the form factors calculated in LCSR, we then
perform a careful study on the decay rate, polarization asymmetry and
forward-backward asymmetry, with respect to the decays of , .Comment: 38 pages, 15 figures, some typos are corrected and more references
are adde
The Multiwavelength Approach to Unidentified Gamma-Ray Sources
As the highest-energy photons, gamma rays have an inherent interest to
astrophysicists and particle physicists studying high-energy, nonthermal
processes. Gamma-ray telescopes complement those at other wavelengths,
especially radio, optical, and X-ray, providing the broad, mutiwavelength
coverage that has become such a powerful aspect of modern astrophysics.
Multiwavelength techniques of various types have been developed to help
identify and explore unidentified gamma-ray sources. This overview summarizes
the ideas behind several of these methods.Comment: Proceedings of the Conference "The Multiwavelength Approach to
Unidentified Sources", to appear in the journal Astrophysics and Space
Scienc
Magnetic Catalysis: A Review
We give an overview of the magnetic catalysis phenomenon. In the framework of
quantum field theory, magnetic catalysis is broadly defined as an enhancement
of dynamical symmetry breaking by an external magnetic field. We start from a
brief discussion of spontaneous symmetry breaking and the role of a magnetic
field in its a dynamics. This is followed by a detailed presentation of the
essential features of the phenomenon. In particular, we emphasize that the
dimensional reduction plays a profound role in the pairing dynamics in a
magnetic field. Using the general nature of underlying physics and its
robustness with respect to interaction types and model content, we argue that
magnetic catalysis is a universal and model-independent phenomenon. In support
of this claim, we show how magnetic catalysis is realized in various models
with short-range and long-range interactions. We argue that the general nature
of the phenomenon implies a wide range of potential applications: from certain
types of solid state systems to models in cosmology, particle and nuclear
physics. We finish the review with general remarks about magnetic catalysis and
an outlook for future research.Comment: 37 pages, to appear in Lect. Notes Phys. "Strongly interacting matter
in magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Yee. Version 2: references adde
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
- âŠ