12,256 research outputs found
Detection of X-ray-Emitting Hypernova Remnants in M101
Based on an ultra deep (230 ks) ROSAT HRI imaging of M101, we have detected 5
X-ray sources that coincide spatially with optical emission line features
previously classified as supernova remnants in this nearby galaxy. Two of these
coincidences (SNR MF83 and NGC5471B) most likely represent the true physical
association of X-ray emission with shock-heated interstellar gas. MF83, with a
radius of ~ 134 pc, is one of the largest remnants known. NGC5471B, with a
radius of 30 pc and a velocity of at least 350 km/s (FWZI), is extremely bright
in both radio and optical. The X-ray luminosities of these two shell-like
remnants are and (0.5-2 keV), about an order
of magnitude brighter than the brightest supernova remnants known in our Galaxy
and in the Magellanic Clouds. The inferred blastwave energy is for NGC5471B and ergs for MF83.
Therefore, the remnants likely originate in hypernovae, which are a factor of
more energetic than canonical supernovae and are postulated as
being responsible for Gamma-ray bursts observed at cosmological distances. The
study of such hypernova remnants in nearby galaxies has the potential to
provide important constraints on the progenitor type, rate, energetics, and
beaming effect of Gamma-ray bursts.Comment: 10 pages, 2 gif figures, Accepted for publication in Astrophysical
Journal Letter
PAMELA Positron Excess as a Signal from the Hidden Sector
The recent positron excess observed in the PAMELA satellite experiment
strengthens previous experimental findings. We give here an analysis of this
excess in the framework of the Stueckelberg extension of the standard model
which includes an extra gauge field and matter in the hidden sector.
Such matter can produce the right amount of dark matter consistent with the
WMAP constraints. Assuming the hidden sector matter to be Dirac fermions it is
shown that their annihilation can produce the positron excess with the right
positron energy dependence seen in the HEAT, AMS and the PAMELA experiments.
Further test of the proposed model can come at the Large Hadron Collider. The
predictions of the flux ratio also fit the data.Comment: 9 pages,3 figures; Breit-Wigner enhancement emphasized; published in
PR
FMRI Clustering and False Positive Rates
Recently, Eklund et al. (2016) analyzed clustering methods in standard FMRI
packages: AFNI (which we maintain), FSL, and SPM [1]. They claimed: 1) false
positive rates (FPRs) in traditional approaches are greatly inflated,
questioning the validity of "countless published fMRI studies"; 2)
nonparametric methods produce valid, but slightly conservative, FPRs; 3) a
common flawed assumption is that the spatial autocorrelation function (ACF) of
FMRI noise is Gaussian-shaped; and 4) a 15-year-old bug in AFNI's 3dClustSim
significantly contributed to producing "particularly high" FPRs compared to
other software. We repeated simulations from [1] (Beijing-Zang data [2], see
[3]), and comment on each point briefly.Comment: 3 pages, 1 figure. A Letter accepted in PNA
Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic symmetry dependent lineshapes and laser induced modification
The dynamics of autoionizing Rydberg states of oxygen are studied using
attosecond transient absorption technique, where extreme ultraviolet (XUV)
initiates molecular polarization and near infrared (NIR) pulse perturbs its
evolution. Transient absorption spectra show positive optical density (OD)
change in the case of and autoionizing states of oxygen
and negative OD change for states. Multiconfiguration
time-dependent Hartree-Fock (MCTDHF) calculation are used to simulate the
transient absorption spectra and their results agree with experimental
observations. The time evolution of superexcited states is probed in
electronically and vibrationally resolved fashion and we observe the dependence
of decay lifetimes on effective quantum number of the Rydberg series. We model
the effect of near-infrared (NIR) perturbation on molecular polarization and
find that the laser induced phase shift model agrees with the experimental and
MCTDHF results, while the laser induced attenuation model does not. We relate
the electron state symmetry dependent sign of the OD change to the Fano
parameters of the static absorption lineshapes.Comment: 15 pages, 8 figure
Chandra View of DA 530: A Sub-Energetic Supernova Remnant with a Pulsar Wind Nebula?
Based on a Chandra ACIS observation, we report the detection of an extended
X-ray feature close to the center of the remnant DA 530 with 5.3 sigma above
the background within a circle of 20'' radius. This feature, characterized by a
power-law with the photon index gamma=1.6+-0.8 and spatially coinciding with a
nonthermal radiosource, most likely represents a pulsar wind nebula. We have
further examined the spectrum of the diffuse X-ray emission from the remnant
interior with a background-subtracted count rate of ~0.06 counts s^-1 in
0.3-3.5 keV. The spectrum of the emission can be described by a thermal plasma
with a temperature of ~0.3-0.6 keV and a Si over-abundance of >~7 solar. These
spectral characteristics, together with the extremely low X-ray luminosity,
suggest that the remnant arises from a supernova with an anomalously low
mechanical energy (<10^50 ergs). The centrally-filled thermal X-ray emission of
the remnant may indicate an early thermalization of the SN ejecta by the
circum-stellar medium. Our results suggest that the remnant is likely the
product of a core-collapsed SN with a progenitor mass of 8-12 Msun. Similar
remnants are probably common in the Galaxy, but have rarely been studied.Comment: 23 pages, 7 figures, accepted for publication in ApJ; complete the
abstract on astro-ph and correct some typo
Bioelectronic DNA detection of human papillomaviruses using eSensorâ„¢: a model system for detection of multiple pathogens
BACKGROUND: We used human papillomaviruses (HPV) as a model system to evaluate the utility of a nucleic acid, hybridization-based bioelectronic DNA detection platform (eSensorâ„¢) in identifying multiple pathogens. METHODS: Two chips were spotted with capture probes consisting of DNA oligonucleotide sequences specific for HPV types. Electrically conductive signal probes were synthesized to be complementary to a distinct region of the amplified HPV target DNA. A portion of the HPV L1 region that was amplified by using consensus primers served as target DNA. The amplified target was mixed with a cocktail of signal probes and added to a cartridge containing a DNA chip to allow for hybridization with complementary capture probes. RESULTS: Two bioelectric chips were designed and successfully detected 86% of the HPV types contained in clinical samples. CONCLUSIONS: This model system demonstrates the potential of the eSensor platform for rapid and integrated detection of multiple pathogens
Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows
We study the kinematically narrow, low-ionization line emission from a
bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with
Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance
transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas
outflow. Emission in MgII near and redward of systemic velocity, in concert
with the observed absorption, yields a P Cygni-like line profile similar to
those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the
MgII emission is spatially resolved, and extends significantly beyond the
emission from stars and HII regions within the galaxy. Assuming the emission
has a simple, symmetric surface brightness profile, we find that the gas
extends to distances > ~7 kpc. We also detect several narrow FeII*
fine-structure lines in emission near the systemic velocity, arising from
energy levels which are radiatively excited directly from the ground state. We
suggest that the MgII and FeII* emission is generated by photon scattering in
the observed outflow, and emphasize that this emission is a generic prediction
of outflows. These observations provide the first direct constraints on the
minimum spatial extent and morphology of the wind from a distant galaxy.
Estimates of these parameters are crucial for understanding the impact of
outflows in driving galaxy evolution.Comment: Submitted to ApJL. 6 pages, 4 figures. Uses emulateapj forma
Discovery of Stable and Selective Antibody Mimetics from Combinatorial Libraries of Polyvalent, Loop-Functionalized Peptoid Nanosheets.
The ability of antibodies to bind a wide variety of analytes with high specificity and high affinity makes them ideal candidates for therapeutic and diagnostic applications. However, the poor stability and high production cost of antibodies have prompted exploration of a variety of synthetic materials capable of specific molecular recognition. Unfortunately, it remains a fundamental challenge to create a chemically diverse population of protein-like, folded synthetic nanostructures with defined molecular conformations in water. Here we report the synthesis and screening of combinatorial libraries of sequence-defined peptoid polymers engineered to fold into ordered, supramolecular nanosheets displaying a high spatial density of diverse, conformationally constrained peptoid loops on their surface. These polyvalent, loop-functionalized nanosheets were screened using a homogeneous Förster resonance energy transfer (FRET) assay for binding to a variety of protein targets. Peptoid sequences were identified that bound to the heptameric protein, anthrax protective antigen, with high avidity and selectivity. These nanosheets were shown to be resistant to proteolytic degradation, and the binding was shown to be dependent on the loop display density. This work demonstrates that key aspects of antibody structure and function-the creation of multivalent, combinatorial chemical diversity within a well-defined folded structure-can be realized with completely synthetic materials. This approach enables the rapid discovery of biomimetic affinity reagents that combine the durability of synthetic materials with the specificity of biomolecular materials
Differential Regularization of Topologically Massive Yang-Mills Theory and Chern-Simons Theory
We apply differential renormalization method to the study of
three-dimensional topologically massive Yang-Mills and Chern-Simons theories.
The method is especially suitable for such theories as it avoids the need for
dimensional continuation of three-dimensional antisymmetric tensor and the
Feynman rules for three-dimensional theories in coordinate space are relatively
simple. The calculus involved is still lengthy but not as difficult as other
existing methods of calculation. We compute one-loop propagators and vertices
and derive the one-loop local effective action for topologically massive
Yang-Mills theory. We then consider Chern-Simons field theory as the large mass
limit of topologically massive Yang-Mills theory and show that this leads to
the famous shift in the parameter . Some useful formulas for the calculus of
differential renormalization of three-dimensional field theories are given in
an Appendix.Comment: 25 pages, 4 figures. Several typewritten errors and inappropriate
arguments are corrected, especially the correct adresses of authors are give
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