3,315 research outputs found
Chandra Imaging and Spectroscopy of the Eastern XA Region of the Cygnus Loop Supernova Remnant
The XA region of the Cygnus Loop is a bright knot of X-ray emission on the
eastern edge of the supernova remnant resulting from the interaction of the
supernova blast wave with density enhancements at the edge of a precursor
formed cavity. To study the nature and origin of the X-ray emission we use high
spatial resolution images from Chandra. Our goal is to probe the density of
various spectral extraction regions to form a picture of the cavity wall and
characterize the interaction between this supernova and the local interstellar
medium. We find that a series of regions along the edge of the X-ray emission
appears to trace out the location of the cavity wall. The best fit plasma
models result in two temperature component equilibrium models for each region.
The low temperature components have densities that are an order of magnitude
higher than the high temperature components. The high density plasma may exist
in the cavity wall where it equilibrates rapidly and cools efficiently. The low
density plasma is interior to the enhancement and heated further by a reverse
shock from the wall. Calculations of shock velocities and timescales since
shock heating are consistent with this interpretation. Furthermore, we find a
bright knot of emission indicative of a discrete interaction of the blast wave
with a high density cloud in the cavity wall with a size scale ~0.1 pc. Aside
from this, other extractions made interior to the X-ray edge are confused by
line of sight projection of various components. Some of these regions show
evidence of detecting the cavity wall but their location makes the
interpretation difficult. In general, the softer plasmas are well fit at
temperatures kT~0.11 keV, with harder plasmas at temperatures of kT~0.27 keV.
All regions display consistent metal depletions most notably in N, O, and Ne at
an average of 0.54, 0.55, and 0.36 times solar
The informal sector, firm dynamics, and institutional participation
The informal microfirm sector is believed to be large, accounting for 20-40 percent of employment in many developing countries. The literature tends to view the sector as the disadvantaged sector of a segmented labor market, as existing to evade government regulations, or as constrained by lack of access to government services. The authors offer a unique theoretical framework to analyze informality and microfirm growth behavior -- one that emphasizes the entrepreneurial nature of informal firms and sees informality as a secondary characteristic. First, they assume that informal firms in developing countries have dynamics similar to firms in industrial countries: entrepreneurs have unobserved, differing cost structures that determine their long-run size and survival -- structures that they can only discover by going into business. Second, informality can be thought of as a decision to participate in societal institutions. Access to mechanisms that ensure property rights, pool risk, or enforce contracts become more important as a firm grows, and the entrepreneur will be willing to pay for them through"taxes"in a way that was not the case as a small firm. The combination of these assumptions generates several of the stylized facts emerging from cross-sectional data and identified in existing models -- informal firms tend to remain small and have high rates of mortality, and lower productivity -- without recourse to government-induced distortions in labor or product markets. Further, the framework predicts that firms whose cost structures dictate that they should expand will make the transition to formality as they grow. Using detailed observations from Mexico, the authors find their view consistent with patterns of formality and growth of microfirms.Public Health Promotion,Small and Medium Size Enterprises,Small Scale Enterprise,Decentralization,Microfinance,Private Participation in Infrastructure,Small Scale Enterprise,Microfinance,Governance Indicators,Environmental Economics&Policies
Environmental Impact on the Southeast Limb of the Cygnus Loop
We analyze observations from the Chandra X-ray Observatory of the southeast
knot of the Cygnus Loop supernova remnant. In this region, the blast wave
propagates through an inhomogeneous environment. Extrinsic differences and
subsequent multiple projections along the line of sight rather than intrinsic
shock variations, such as fluid instabilities, account for the apparent
complexity of the images. Interactions between the supernova blast wave and
density enhancements of a large interstellar cloud can produce the
morphological and spectral characteristics. Most of the X-ray flux arises in
such interactions, not in the diffuse interior of the supernova remnant.
Additional observations at optical and radio wavelengths support this account
of the existing interstellar medium and its role in shaping the Cygnus Loop,
and they demonstrate that the southeast knot is not a small cloud that the
blast wave has engulfed. These data are consistent with rapid equilibration of
electron and ion temperatures behind the shock front, and the current blast
wave velocity v_{bw} approx 330 km/s. Most of this area does not show strong
evidence for non-equilibrium ionization conditions, which may be a consequence
of the high densities of the bright emission regions.Comment: To appear in ApJ, April 1, 200
Strength in Numbers: An Examination Into the Liability of Corporate Entities for Consumer and Employee Data Breaches
DIRBE Minus 2MASS: Confirming the CIRB in 40 New Regions at 2.2 and 3.5 Microns
With the release of the 2MASS All-Sky Point Source Catalog, stellar fluxes
from 2MASS are used to remove the contribution due to Galactic stars from the
intensity measured by DIRBE in 40 new regions in the North and South Galactic
polar caps. After subtracting the interplanetary and Galactic foregrounds, a
consistent residual intensity of 14.69 +/- 4.49 kJy/sr at 2.2 microns is found.
Allowing for a constant calibration factor between the DIRBE 3.5 microns and
the 2MASS 2.2 microns fluxes, a similar analysis leaves a residual intensity of
15.62 +/- 3.34 kJy/sr at 3.5 microns. The intercepts of the DIRBE minus 2MASS
correlation at 1.25 microns show more scatter and are a smaller fraction of the
foreground, leading to a still weak limit on the CIRB of 8.88 +/- 6.26 kJy/sr
(1 sigma).Comment: 25 pages LaTeX, 10 figures, 5 tables; Version accepted by the ApJ.
Includes minor changes to the text including further discussion of zodiacal
light issues and the allowance for variable stars in computing uncertainties
in the stellar contribution to the DIRBE intensitie
Mapping the interstellar medium in galaxies with Herschel/SPIRE
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies
M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both
methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies
Radial distribution of gas and dust in spiral galaxies: The case of M 99 (NGC 4254) and M 100 (NGC 4321)
By combining Herschel-SPIRE data with archival Spitzer, H i , and CO maps, we investigate the spatial distribution of gas and dust in the two famous grand-design spirals M 99 and M 100 in the Virgo cluster. Thanks to the unique resolution and sensitivity of the Herschel-SPIRE photometer, we are for the first time able to measure the distribution and extent of cool, submillimetre (submm)-emitting dust inside and beyond the optical radius. We compare this with the radial variation in both the gas mass and the metallicity. Although we adopt a model-independent, phenomenological approach, our analysis provides important insights. We find the dust extending to at least the optical radius of the galaxy and showing breaks in its radial profiles at similar positions as the stellar distribution. The colour indices f350/f500 and f250/f350 decrease radially consistent with the temperature decreasing with radius. We also find evidence of an increasing gas to dust ratio with radius in the outer regions of both galaxies
SPIRE imaging of M 82: Cool dust in the wind and tidal streams
M 82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the M 81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind
1/f noise of Josephson-junction-embedded microwave resonators at single photon energies and millikelvin temperatures
We present measurements of 1/f frequency noise in both linear and
Josephson-junction-embedded superconducting aluminum resonators in the low
power, low temperature regime - typical operating conditions for
superconducting qubits. The addition of the Josephson junction does not result
in additional frequency noise, thereby placing an upper limit for fractional
critical current fluctuations of (Hz) at 1 Hz for
sub-micron, shadow evaporated junctions. These values imply a minimum dephasing
time for a superconducting qubit due to critical current noise of 40 -- 1400
s depending on qubit architecture. Occasionally, at temperatures above 50
mK, we observe the activation of individual fluctuators which increase the
level of noise significantly and exhibit Lorentzian spectra
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