1,089 research outputs found
Joint Analysis of Cluster Observations: II. Chandra/XMM-Newton X-ray and Weak Lensing Scaling Relations for a Sample of 50 Rich Clusters of Galaxies
We present a study of multiwavelength X-ray and weak lensing scaling
relations for a sample of 50 clusters of galaxies. Our analysis combines
Chandra and XMM-Newton data using an energy-dependent cross-calibration. After
considering a number of scaling relations, we find that gas mass is the most
robust estimator of weak lensing mass, yielding 15 +/- 6% intrinsic scatter at
r500 (the pseudo-pressure YX has a consistent scatter of 22%+/-5%). The scatter
does not change when measured within a fixed physical radius of 1 Mpc. Clusters
with small BCG to X-ray peak offsets constitute a very regular population whose
members have the same gas mass fractions and whose even smaller <10% deviations
from regularity can be ascribed to line of sight geometrical effects alone.
Cool-core clusters, while a somewhat different population, also show the same
(<10%) scatter in the gas mass-lensing mass relation. There is a good
correlation and a hint of bimodality in the plane defined by BCG offset and
central entropy (or central cooling time). The pseudo-pressure YX does not
discriminate between the more relaxed and less relaxed populations, making it
perhaps the more even-handed mass proxy for surveys. Overall, hydrostatic
masses underestimate weak lensing masses by 10% on the average at r500; but
cool-core clusters are consistent with no bias, while non-cool-core clusters
have a large and constant 15-20% bias between r2500 and r500, in agreement with
N-body simulations incorporating unthermalized gas. For non-cool-core clusters,
the bias correlates well with BCG ellipticity. We also examine centroid shift
variance and and power ratios to quantify substructure; these quantities do not
correlate with residuals in the scaling relations. Individual clusters have for
the most part forgotten the source of their departures from self-similarity.Comment: Corrects an error in the X-ray luminosities (erratum
submitted)---none of the other results are affected. Go to
http://sfstar.sfsu.edu/jaco for an electronic fitter and updated quick data
download link
Impact of loss on the wave dynamics in photonic waveguide lattices
We analyze the impact of loss in lattices of coupled optical waveguides and
find that in such case, the hopping between adjacent waveguides is necessarily
complex. This results not only in a transition of the light spreading from
ballistic to diffusive, but also in a new kind of diffraction that is caused by
loss dispersion. We prove our theoretical results with experimental
observations.Comment: Accepted for publication in PRL, 5+8 pages (Paper + Supplemental
material), 4 figure
A novel method to design variable gain amplifier
A novel method to design of Variable gain Amplifiers (VGAs) is proposed. A low power VGA with wide range of gain variation and appropriate bandwidth using new technique is presented in this paper. Moreover, the suggested circuit is simulated in whole process corners and different temperatures in the region of -50 to +70 ºC. The circuit has been designed in a typical 0.35μm CMOS process with a power supply of 3.3V, and simulated by HSPICE software using level 49 parameters (BSIM3v3).Keywords: variable gain amplifier; Operational Transconductance Amplifier; wide gain range; low power; unity gain bandwidt
Evidence for Non-Hydrostatic Gas from the Cluster X-ray to Lensing Mass Ratio
Using a uniform analysis procedure, we measure spatially resolved weak
gravitational lensing and hydrostatic X-ray masses for a sample of 18 clusters
of galaxies. We find a radial trend in the X-ray to lensing mass ratio: at
r2500 we obtain a ratio MX/ML=1.03+/-0.07 which decreases to MX/ML=0.78+/-0.09
at r500. This difference is significant at 3 sigma once we account for
correlations between the measurements. We show that correcting the lensing mass
for excess correlated structure outside the virial radius slightly reduces, but
does not eliminate this trend. An X-ray mass underestimate, perhaps due to
nonthermal pressure support, can explain the residual trend. The trend is not
correlated with the presence or absence of a cool core. We also examine the
cluster gas fraction and find no correlation with ML, an important result for
techniques that aim to determine cosmological parameters using the gas
fraction.Comment: 8 pages, minor modifications, accepted for publication in MNRA
Cleavable Biotin Probes for Labeling of Biomolecules via Azide−Alkyne Cycloaddition
The azide−alkyne cycloaddition provides a powerful tool for bio-orthogonal labeling of proteins, nucleic acids, glycans, and lipids. In some labeling experiments, e.g., in proteomic studies involving affinity purification and mass spectrometry, it is convenient to use cleavable probes that allow release of labeled biomolecules under mild conditions. Five cleavable biotin probes are described for use in labeling of proteins and other biomolecules via azide−alkyne cycloaddition. Subsequent to conjugation with metabolically labeled protein, these probes are subject to cleavage with either 50 mM Na_2S_2O_4, 2% HOCH_2CH_2SH, 10% HCO_2H, 95% CF_3CO_2H, or irradiation at 365 nm. Most strikingly, a probe constructed around a dialkoxydiphenylsilane (DADPS) linker was found to be cleaved efficiently when treated with 10% HCO_2H for 0.5 h. A model green fluorescent protein was used to demonstrate that the DADPS probe undergoes highly selective conjugation and leaves a small (143 Da) mass tag on the labeled protein after cleavage. These features make the DADPS probe especially attractive for use in biomolecular labeling and proteomic studies
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Investigation of physical processes limiting plasma density in H-mode on DIII-D
A series of experiments was conducted on the DIII-D tokamak to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased non-linearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was {le} 3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density {approximately} 1.5 {times} Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flattop. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks
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Investigation of Density Limit Processes in DIII-D
A series of experiments has been conducted in DIII-D to investigate density-limiting processes. The authors have studied divertor detachment and MARFEs on closed field lines and find semi-quantitative agreement with theoretical calculations of onset conditions. They have shown that the critical density for MARFE onset at low edge temperature scales as I{sub p}/a{sup 2}, i.e. similar to Greenwald scaling. They have also shown that the scaling of the critical separatrix density with heating power at partial detachment onset agrees with Borass` model. Both of these processes yield high edge density limits for reactors such as ITER. By using divertor pumping and pellet fueling they have avoided these and other processes and accessed densities > 1.5{times} Greenwald limit scaling with H-mode confinement, demonstrating that the Greenwald limit is not a fundamental limit on the core density
Zonal flows and long-distance correlations during the formation of the edge shear layer in the TJ-II stellarator
A theoretical interpretation is given for the observed long-distance
correlations in potential fluctuations in TJ-II. The value of the correlation
increases above the critical point of the transition for the emergence of the
plasma edge shear flow layer. Mean (i.e. surface averaged, zero-frequency)
sheared flows cannot account for the experimental results. A model consisting
of four envelope equations for the fluctuation level, the mean flow shear, the
zonal flow amplitude shear, and the averaged pressure gradient is proposed. It
is shown that the presence of zonal flows is essential to reproduce the main
features of the experimental observations.Comment: 19 pages, 7 figure
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