400 research outputs found
Lack of class I H-2 antigens in cells transformed by radiation leukemia virus is associated with methylation and rearrangement of H-2 DNA
Transformation of murine thymocytes by
radiation leukemia virus is associated with reduced expression
of the class I antigens encoded in the major histocompatibility
complex (MHC) and increased methylation and altered restriction
enzyme patterns of MHC DNA. These changes may play
a role in host susceptibility to virus-induced leukemogenesis
and accord with the notion that viral genomes play a regulatory
function when they integrate adjacent to histocompatibiity
genes
Recommended from our members
Trabecular Bone in the Bird Knee Responds with High Sensitivity to Changes in Load Orientation
Wolff’s law of trajectorial orientation proposes that trabecular struts align with the orientation of dominant compressive loads within a joint. Although widely considered in skeletal biology, Wolff’s law has never been experimentally tested while controlling for ontogenetic stage, activity level, and species differences, all factors that may affect trabecular bone growth. Here we report an experimental test of Wolff’s law using a within-species design in age-matched subjects experiencing physiologically normal levels of bone strain. Two age-matched groups of juvenile guinea fowl Numida meleagris ran on a treadmill set at either 0° (Level group) or 20° (Incline group), for 10·min per day over a 45-day treatment period. Birds running on the 20° inclined treadmill used more-flexed knees than those in the Level group at midstance (the point of peak ground reaction force). This difference in joint posture enabled us to test the sensitivity of trabecular alignment to altered load orientation in the knee. Using a new radon transform-based method for measuring trabecular orientation, our analysis shows that the fine trabecular bone in the distal femur has a high degree of correspondence between changes in joint angle and trabecular orientation. The sensitivity of this response supports the prediction that trabecular bone adapts dynamically to the orientation of
peak compressive forces.Anthropolog
The Atacama Cosmology Telescope: The LABOCA/ACT Survey of Clusters at All Redshifts
We present a multi-wavelength analysis of eleven Sunyaev Zel'dovich effect
(SZE)-selected galaxy clusters (ten with new data) from the Atacama Cosmology
Telescope (ACT) southern survey. We have obtained new imaging from the Large
APEX Bolometer Camera (345GHz; LABOCA) on the Atacama Pathfinder EXperiment
(APEX) telescope, the Australia Telescope Compact Array (2.1GHz; ATCA), and the
Spectral and Photometric Imaging Receiver (250, 350, and ;
SPIRE) on the Herschel Space Observatory. Spatially-resolved 345GHz SZE
increments with integrated S/N > 5 are found in six clusters. We compute 2.1GHz
number counts as a function of cluster-centric radius and find significant
enhancements in the counts of bright sources at projected radii . By extrapolating in frequency, we predict that the combined
signals from 2.1GHz-selected radio sources and 345GHz-selected SMGs contaminate
the 148GHz SZE decrement signal by ~5% and the 345GHz SZE increment by ~18%.
After removing radio source and SMG emission from the SZE signals, we use ACT,
LABOCA, and (in some cases) new Herschel SPIRE imaging to place constraints on
the clusters' peculiar velocities. The sample's average peculiar velocity
relative to the cosmic microwave background is .Comment: 19 pages, 11 figures, Accepted for Publication in The Astrophysical
Journa
Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements
For the first time, measurements of the cosmic microwave background radiation
(CMB) alone favor cosmologies with dark energy over models without dark
energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing
deflection power spectrum from the Atacama Cosmology Telescope with temperature
and polarization power spectra from the Wilkinson Microwave Anisotropy Probe.
The lensing data break the geometric degeneracy of different cosmological
models with similar CMB temperature power spectra. Our CMB-only measurement of
the dark energy density confirms other measurements from
supernovae, galaxy clusters and baryon acoustic oscillations, and demonstrates
the power of CMB lensing as a new cosmological tool.Comment: 4 pages, 3 figures; replaced with version accepted by Physical Review
Letters, added sentence on models with non-standard primordial power spectr
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the
relationship between the cluster characteristic size (R_500) and the integrated
Compton parameter (Y_500). The UPP scalings are found to be nearly identical to
an adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
high signal to noise ratio subsample of 15 ACT clusters is used to obtain
cosmological constraints. We first confirm that constraints from SZ data are
limited by uncertainty in the scaling relation parameters rather than sample
size or measurement uncertainty. We next add in seven clusters from the ACT
Southern survey, including their dynamical mass measurements based on galaxy
velocity dispersions. In combination with WMAP7 these data simultaneously
constrain the scaling relation and cosmological parameters, yielding \sigma_8 =
0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include
marginalization over a 15% bias in dynamical mass relative to the true halo
mass. In an extension to LCDM that incorporates non-zero neutrino mass density,
we combine our data with WMAP7+BAO+Hubble constant measurements to constrain
\Sigma m_\nu < 0.29 eV (95% C. L.).Comment: 32 pages, 21 figures To appear in J. Cosmology and Astroparticle
Physic
The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data
We present the temperature power spectra of the cosmic microwave background
(CMB) derived from the three seasons of data from the Atacama Cosmology
Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum
between the two channels. We detect and correct for contamination due to the
Galactic cirrus in our equatorial maps. We present the results of a number of
tests for possible systematic error and conclude that any effects are not
significant compared to the statistical errors we quote. Where they overlap, we
cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they
are consistent. The measurements of higher-order peaks in the CMB power
spectrum provide an additional test of the Lambda CDM cosmological model, and
help constrain extensions beyond the standard model. The small angular scale
power spectrum also provides constraining power on the Sunyaev-Zel'dovich
effects and extragalactic foregrounds. We also present a measurement of the CMB
gravitational lensing convergence power spectrum at 4.6-sigma detection
significance.Comment: 21 pages; 20 figures, Submitted to JCAP, some typos correcte
A New Era in Extragalactic Background Light Measurements: The Cosmic History of Accretion, Nucleosynthesis and Reionization
(Brief Summary) What is the total radiative content of the Universe since the
epoch of recombination? The extragalactic background light (EBL) spectrum
captures the redshifted energy released from the first stellar objects,
protogalaxies, and galaxies throughout cosmic history. Yet, we have not
determined the brightness of the extragalactic sky from UV/optical to
far-infrared wavelengths with sufficient accuracy to establish the radiative
content of the Universe to better than an order of magnitude. Among many
science topics, an accurate measurement of the EBL spectrum from optical to
far-IR wavelengths, will address: What is the total energy released by stellar
nucleosynthesis over cosmic history? Was significant energy released by
non-stellar processes? Is there a diffuse component to the EBL anywhere from
optical to sub-millimeter? When did first stars appear and how luminous was the
reionization epoch? Absolute optical to mid-IR EBL spectrum to an
astrophysically interesting accuracy can be established by wide field imagingat
a distance of 5 AU or above the ecliptic plane where the zodiacal foreground is
reduced by more than two orders of magnitude.Comment: 7 pages; Science White Paper for the US Astro 2010-2020 Decadal
Survey. If interested in further community-wide efforts on this topic please
contact the first autho
Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope
We report the first detection of the gravitational lensing of the cosmic
microwave background through a measurement of the four-point correlation
function in the temperature maps made by the Atacama Cosmology Telescope. We
verify our detection by calculating the levels of potential contaminants and
performing a number of null tests. The resulting convergence power spectrum at
2-degree angular scales measures the amplitude of matter density fluctuations
on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The
measured amplitude of the signal agrees with Lambda Cold Dark Matter cosmology
predictions. Since the amplitude of the convergence power spectrum scales as
the square of the amplitude of the density fluctuations, the 4-sigma detection
of the lensing signal measures the amplitude of density fluctuations to 12%.Comment: 4 pages, 4 figures, replaced title and author list with version
accepted by Physical Review Letters. Likelihood code can be downloaded from
http://bccp.lbl.gov/~sudeep/ACTLensLike.htm
The BLAST Survey of the Vela Molecular Cloud: Physical Properties of the Dense Cores in Vela-D
The Balloon-borne Large-Aperture Submillimeter Telescope (BLAST) carried out
a 250, 350 and 500 micron survey of the galactic plane encompassing the Vela
Molecular Ridge, with the primary goal of identifying the coldest dense cores
possibly associated with the earliest stages of star formation. Here we present
the results from observations of the Vela-D region, covering about 4 square
degrees, in which we find 141 BLAST cores. We exploit existing data taken with
the Spitzer MIPS, IRAC and SEST-SIMBA instruments to constrain their
(single-temperature) spectral energy distributions, assuming a dust emissivity
index beta = 2.0. This combination of data allows us to determine the
temperature, luminosity and mass of each BLAST core, and also enables us to
separate starless from proto-stellar sources. We also analyze the effects that
the uncertainties on the derived physical parameters of the individual sources
have on the overall physical properties of starless and proto-stellar cores,
and we find that there appear to be a smooth transition from the pre- to the
proto-stellar phase. In particular, for proto-stellar cores we find a
correlation between the MIPS24 flux, associated with the central protostar, and
the temperature of the dust envelope. We also find that the core mass function
of the Vela-D cores has a slope consistent with other similar (sub)millimeter
surveys.Comment: Accepted for publication in the Astrophysical Journal. Data and maps
are available at http://blastexperiment.info
- …