3,717 research outputs found
Kinetics of Ehrlich ascites tumor growth within millipore chambers in normal and immunized mice.
THE proliferation of malignant cells has been shown to depend not only on intrinsic neoplastic properties but also on environmental circumstances, in vivo (host) or in vitro (medium). In addition, a changing rate of growth in a continuing environment has been documented in tumor-bearing hosts and tissue culture situations. The kinetics of neoplastic cells (i.e. Ehrlich ascites tumor cells-EAT) have been studied with regard to cellular proliferation within cell-tight millipore chambers by Amos and Wakefield (1958) (among others), particularly concerning the growth rate of cells in normal mice and the rate of entry of iso-antibody into the chambers. The present investigations define the growth pattern of Ehrlich ascites tumor cells within the restricted environment of millipore chambers in actively immunized mice. MATERIALS AND METHODS White Swiss mice of both sexes (HA/ICR strain), 3-4 months old, were used in this study. The tumor cells used were Lettre strain, hyperdiploid Ehrlich ascites tumor originally obtained from Roswell Park Memorial Institute and grow
Unveiling a Population of X-ray Non-Detected AGN
We define a sample of 27 radio-excess AGN in the Chandra Deep Field North by
selecting galaxies that do not obey the radio/infrared correlation for
radio-quiet AGN and star-forming galaxies. Approximately 60% of these
radio-excess AGN are X-ray undetected in the 2 Ms Chandra catalog, even at
exposures of > 1 Ms; 25% lack even 2-sigma X-ray detections. The absorbing
columns to the faint X-ray-detected objects are 10^22 cm^-2 < N_H < 10^24
cm^-2, i.e., they are obscured but unlikely to be Compton thick. Using a local
sample of radio-selected AGN, we show that a low ratio of X-ray to radio
emission, as seen in the X-ray weakly- and non-detected samples, is correlated
with the viewing angle of the central engine, and therefore with obscuration.
Our technique can explore the proportion of obscured AGN in the distant
Universe; the results reported here for radio-excess objects are consistent
with but at the low end of the overall theoretical predictions for
Compton-thick objects.Comment: Accepted for publication in the Astrophysical Journal, 15 pages, 10
figures, 4 table
Why Optically--Faint AGN Are Faint: The Spitzer Perspective
Optically--faint X-ray sources (those with f_X/f_R > 10) constitute about 20%
of X-ray sources in deep surveys, and are potentially highly obscured and/or at
high redshift. Their faint optical fluxes are generally beyond the reach of
spectroscopy. For a sample of 20 optically--faint sources in CDFS, we compile
0.4--24 um photometry, relying heavily on Spitzer. We estimate photometric
redshifts for 17 of these 20 sources. We find that these AGN are
optically--faint both because they lie at significantly higher redshifts
(median z ~ 1.6) than most X-ray--selected AGN, and because their spectra are
much redder than standard AGN. They have 2--8 keV X-ray luminosities in the
Seyfert range, unlike the QSO--luminosities of optically--faint AGN found in
shallow, wide--field surveys. Their contribution to the X-ray Seyfert
luminosity function is comparable to that of z>1 optically--bright AGN.Comment: Accepted for publication in the Astrophysical Journa
Recent and future trends in synthetic greenhouse gas radiative forcing
Atmospheric measurements show that emissions of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons are now the primary drivers of the positive growth in synthetic greenhouse gas (SGHG) radiative forcing. We infer recent SGHG emissions and examine the impact of future emissions scenarios, with a particular focus on proposals to reduce HFC use under the Montreal Protocol. If these proposals are implemented, overall SGHG radiative forcing could peak at around 355âmWâm[superscript â2] in 2020, before declining by approximately 26% by 2050, despite continued growth of fully fluorinated greenhouse gas emissions. Compared to âno HFC policyâ projections, this amounts to a reduction in radiative forcing of between 50 and 240âmWâm[superscript â2] by 2050 or a cumulative emissions saving equivalent to 0.5 to 2.8âyears of CO2 emissions at current levels. However, more complete reporting of global HFC emissions is required, as less than half of global emissions are currently accounted for.Natural Environment Research Council (Great Britain) (Advanced Research Fellowship NE/I021365/1)United States. National Aeronautics and Space Administration (Upper Atmospheric Research Program Grant NNX11AF17G)United States. National Oceanic and Atmospheric Administratio
Spitzer Power-law AGN Candidates in the Chandra Deep Field-North
We define a sample of 62 galaxies in the Chandra Deep Field-North whose
Spitzer IRAC SEDs exhibit the characteristic power-law emission expected of
luminous AGN. We study the multiwavelength properties of this sample, and
compare the AGN selected in this way to those selected via other Spitzer
color-color criteria. Only 55% of the power-law galaxies are detected in the
X-ray catalog at exposures of >0.5 Ms, although a search for faint emission
results in the detection of 85% of the power-law galaxies at the > 2.5 sigma
detection level. Most of the remaining galaxies are likely to host AGN that are
heavily obscured in the X-ray. Because the power-law selection requires the AGN
to be energetically dominant in the near- and mid-infrared, the power-law
galaxies comprise a significant fraction of the Spitzer-detected AGN population
at high luminosities and redshifts. The high 24 micron detection fraction also
points to a luminous population. The power-law galaxies comprise a subset of
color-selected AGN candidates. A comparison with various mid-infrared color
selection criteria demonstrates that while the color-selected samples contain a
larger fraction of the X-ray luminous AGN, there is evidence that these
selection techniques also suffer from a higher degree of contamination by
star-forming galaxies in the deepest exposures. Considering only those
power-law galaxies detected in the X-ray catalog, we derive an obscured
fraction of 68% (2:1). Including all of the power-law galaxies suggests an
obscured fraction of < 81% (4:1).Comment: Accepted for publication in the Astrophysical Journal, 27 pages, 20
figures, 5 tables, version with high-resolution figures and online-only
tables available at: http://frodo.as.arizona.edu/~jdonley/powerlaw
Spitzer and Hubble Constraints on the Physical Properties of the z~7 Galaxy Strongly Lensed by Abell 2218
We report the detection of a z~7 galaxy strongly lensed by the massive galaxy
cluster Abell 2218 (z=0.175) at 3.6 and 4.5 um using the Spitzer Observatory
and at 1.1 um using the Hubble Space Telescope. The new data indicate a refined
photometric redshift in the range of 6.6-6.8 depending on the presence of
Ly-alpha emission. The spectral energy distribution is consistent with having a
significant Balmer break, suggesting that the galaxy is in the poststarburst
stage with an age of at least ~50 Myr and quite possibly a few hundred Myr.
This suggests the possibility that a mature stellar population is already in
place at such a high redshift. Compared with typical Lyman break galaxies at
z~3-4, the stellar mass is an order of magnitude smaller (~10^{9} Msun), but
the specific star formation rate (star formation rate/M_{star}) is similarly
large (> 10^{-9} yr^{-1}), indicating equally vigorous star-forming activity.Comment: 11 pages, 2 figures, 2 tables; Accepted for publication in ApJ
The Population of Weak Mg II Absorbers I. A Survey of 26 QSO HIRES/Keck Spectra
We present a search for "weak" MgII absorbers [those with W_r(2796) < 0.3 A
in the HIRES/Keck spectra of 26 QSOs. We found 30, of which 23 are newly
discovered. The spectra are 80% complete to W_r(2796) = 0.02 A and have a
cumulative redshift path of ~17.2 for the redshift range 0.4 < z < 1.4. The
number of absorbers per unit redshift, dN/dz, is seen to increase as the
equivalent width threshold is decreased; we obtained dN/dz = 1.74+/-0.10 for
our 0.02 <= W_r(2796) < 0.3 A sample. The equivalent width distribution follows
a power law with slope -1.0; there is no turnover down to W_r(2796) = 0.02 A at
= 0.9. Weak absorbers comprise at least 65% of the total MgII absorption
population, which outnumbers Lyman limit systems (LLS) by a factor of
3.8+/-1.1; the majority of weak MgII absorbers must arise in sub-LLS
environments. Tentatively, we predict that ~5% of the Lyman-alpha forest clouds
with W_r(1215) > 0.1 A will have detectable MgII absorption to W_r,min(2796) =
0.02 A and that this is primarily a high-metallicity selection effect (Z/Z_sun]
> -1). This implies that MgII absorbing structures figure prominently as
tracers of sub-LLS environments where gas has been processed by stars. We
compare the number density of W_r(2796) > 0.02 A absorbers with that of both
high and low surface brightness galaxies and find a fiducial absorber size of
35h^-1 to 63h^-1 kpc, depending upon the assumed galaxy population and their
absorption properties. The individual absorbing "clouds" have W_r(2796) <= 0.15
A and their narrow (often unresolved) line widths imply temperatures of ~25,000
K. We measured W_r(1548) from CIV in FOS/HST archival spectra and, based upon
comparisons with FeII, found a range of ionization conditions (low, high, and
multi-phase) in absorbers selected by weak MgII.Comment: Accepted Version: 43 pages, PostScript figures embedded; accepted to
ApJ; updated version includes analysis of CIV absorptio
Is Rust Used Safely by Software Developers?
Rust, an emerging programming language with explosive growth, provides a
robust type system that enables programmers to write memory-safe and data-race
free code. To allow access to a machine's hardware and to support low-level
performance optimizations, a second language, Unsafe Rust, is embedded in Rust.
It contains support for operations that are difficult to statically check, such
as C-style pointers for access to arbitrary memory locations and mutable global
variables. When a program uses these features, the compiler is unable to
statically guarantee the safety properties Rust promotes. In this work, we
perform a large-scale empirical study to explore how software developers are
using Unsafe Rust in real-world Rust libraries and applications. Our results
indicate that software engineers use the keyword unsafe in less than 30% of
Rust libraries, but more than half cannot be entirely statically checked by the
Rust compiler because of Unsafe Rust hidden somewhere in a library's call
chain. We conclude that although the use of the keyword unsafe is limited, the
propagation of unsafeness offers a challenge to the claim of Rust as a
memory-safe language. Furthermore, we recommend changes to the Rust compiler
and to the central Rust repository's interface to help Rust software developers
be aware of when their Rust code is unsafe
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