2,866 research outputs found
First Measurement of a Rapid Increase in the AGN Fraction in High-Redshift Clusters of Galaxies
We present the first measurement of the AGN fraction in high-redshift
clusters of galaxies (z~0.6) with spectroscopy of one cluster and archival data
for three additional clusters. We identify 8 AGN in all four of these clusters
from the Chandra data, which are sensitive to AGN with hard X-ray (2-10keV)
luminosity L_{X,H} > 10^43 erg/s in host galaxies more luminous than a rest
frame M_R < -20 mag. This stands in sharp contrast to the one AGN with L_{X,H}
> 10^43 erg/s we discovered in our earlier study of eight low-redshift clusters
with z=0.06-0.31 (average z~0.2). Three of the four high-redshift cluster
datasets are sensitive to nearly L_{X,H} > 10^42 erg/s and we identify seven
AGN above this luminosity limit, compared to two in eight, low-redshift
clusters. Based on membership estimates for each cluster, we determine that the
AGN fraction at z~0.6 is f_A(L_X>10^42;M_R<-20) = 0.028 (+0.019/-0.012) and
f_A(L_X>10^43;M_R<-20) = 0.020 (+0.012/-0.008). These values are approximately
a factor of 20 greater than the AGN fractions in lower-redshift (average z~0.2)
clusters of galaxies and represent a substantial increase over the factors of
1.5 and 3.3 increase, respectively, in the measured space density evolution of
the hard X-ray luminosity function over this redshift range. Potential
systematic errors would only increase the significance of our result. The
cluster AGN fraction increases more rapidly with redshift than the field and
the increase in cluster AGN indicates the presence of an AGN Butcher-Oemler
Effect.Comment: ApJL Accepted, 5 pages, 2 figure
Research Issues in Image Registration for Remote Sensing
Image registration is an important element in data processing for remote sensing with many applications and a wide range of solutions. Despite considerable investigation the field has not settled on a definitive solution for most applications and a number of questions remain open. This article looks at selected research issues by surveying the experience of operational satellite teams, application-specific requirements for Earth science, and our experiments in the evaluation of image registration algorithms with emphasis on the comparison of algorithms for subpixel accuracy. We conclude that remote sensing applications put particular demands on image registration algorithms to take into account domain-specific knowledge of geometric transformations and image content
A Comparative Look at Various Countries\u27 Legal Regimes Governing Automated Vehicles
News and commentary about automated vehicles (AVs) focus on how they look and appear to operate, along with the companies developing and testing them. Behind the scenes are legal regimes—laws, regulations, and implementing bodies of different kinds—that literally and figuratively provide the rules of the road for AVs. Legal regimes matter because public welfare hinges on aspects of AV design and operation. Legal regimes can provide gatekeeping for AV developers and operators seeking to use public roads, and they can allocate liability when something goes wrong. Guiding and complementing legal regimes is public policy. Policy documents such as articulations of national strategies are sometimes used to address issues related to legal regimes and to demonstrate a jurisdiction’s support for AV development.
Building on its long history analyzing AV policy issues, RAND (with support of its Institute for Civil Justice) collaborated with the University of Michigan Law School’s Law and Mobility Program to study the nature of different AV legal regimes around the world. It selected countries known to be active in this domain. The research team reviewed and shared scholarly and gray literature (which is a type of scholarship produced by an entity in which commercial publications are not the primary focus, such as white papers from a government agency), and it also consulted experts in these regimes from the public and private sectors. Under the supervision of the Law and Mobility Fellow (a lawyer), law students collected and studied materials associated with country-specific legal regimes and drafted summaries guided by RAND’s enumeration of key factors. Availability of information about legal regimes varies—access to documentation, especially in English, is uneven, even for officials in different countries working collaboratively on these issues. That constrained availability is reflected in published legal comparisons, and it motivated the research team’s systematic research, which drew from materials in English and other languages. This article summarizes the makeup of AV legal regimes of Australia, China, France, Germany, Japan, and the United Kingdom. It highlights some key contrasts, which will be developed further as the project continues. It focuses on law and policy relating to highly to fully automated vehicles (SAE Levels 4 and 5). Although guided by a common set of topics for each country, each profile reflects the material available and the factors that differentiate national approaches.
The remainder of this article introduces the legal regimes of the covered countries in turn. It then provides an overview of key points of comparison and outlines future work
Analytical modeling for the heat transfer in sheared flows of nanofluids
We developed a model for the enhancement of the heat flux by spherical and
elongated nano- particles in sheared laminar flows of nano-fluids. Besides the
heat flux carried by the nanoparticles the model accounts for the contribution
of their rotation to the heat flux inside and outside the particles. The
rotation of the nanoparticles has a twofold effect, it induces a fluid
advection around the particle and it strongly influences the statistical
distribution of particle orientations. These dynamical effects, which were not
included in existing thermal models, are responsible for changing the thermal
properties of flowing fluids as compared to quiescent fluids. The proposed
model is strongly supported by extensive numerical simulations, demonstrating a
potential increase of the heat flux far beyond the Maxwell-Garnet limit for the
spherical nanoparticles. The road ahead which should lead towards robust
predictive models of heat flux enhancement is discussed.Comment: 14 pages, 10 figures, submitted to PR
Rapidly progressive post-transplant lymphoproliferative disease following withdrawal of sirolimus
Sirolimus, a potent inhibitor of B- and T-cell activation, is a commonly used immunosuppressant after renal transplantation. Withdrawal of sirolimus from the immunosuppression regimen may reduce B-cell surveillance. We present a case of rapidly progressive central nervous system (CNS) polymorphic Epstein-Barr virus (EBV)-related post-transplant lymphoproliferative disorder following the withdrawal of sirolimus
uPAR Induces Expression of Transforming Growth Factor β and Interleukin-4 in Cancer Cells to Promote Tumor-Permissive Conditioning of Macrophages
Cancer cells condition macrophages and other inflammatory cells in the tumor microenvironment so that these cells are more permissive for cancer growth and metastasis. Conditioning of inflammatory cells reflects, at least in part, soluble mediators (such as transforming growth factor β and IL-4) that are released by cancer cells and alter the phenotype of cells of the innate immune system. Signaling pathways in cancer cells that potentiate this activity are incompletely understood. The urokinase receptor (uPAR) is a cell-signaling receptor known to promote cancer cell survival, proliferation, metastasis, and cancer stem cell–like properties. The present findings show that uPAR expression in diverse cancer cells, including breast cancer, pancreatic cancer, and glioblastoma cells, promotes the ability of these cells to condition co-cultured bone marrow–derived macrophages so that the macrophages express significantly increased levels of arginase 1, a biomarker of the alternatively activated M2 macrophage phenotype. Expression of transforming growth factor β was substantially increased in uPAR-expressing cancer cells via a mechanism that requires uPA-initiated cell signaling. uPAR also controlled expression of IL-4 in cancer cells via a mechanism that involves activation of ERK1/2. The ability of uPAR to induce expression of factors that condition macrophages in the tumor microenvironment may constitute an important mechanism by which uPAR promotes cancer progression
The Mass of the Black Hole in the Quasar PG 2130+099
We present the results of a recent reverberation-mapping campaign undertaken
to improve measurements of the radius of the broad line region and the central
black hole mass of the quasar PG 2130+099. Cross correlation of the 5100
angstrom continuum and H-beta emission-line light curves yields a time lag of
22.9 (+4.4 - 4.3) days, corresponding to a central black hole mass MBH= 3.8
(+/- 1.5) x 10^7 Msun. This value supports the notion that previous
measurements yielded an incorrect lag. We re-analyzed previous datasets to
investigate the possible sources of the discrepancy and conclude that previous
measurement errors were apparently caused by a combination of undersampling of
the light curves and long-term secular changes in the H-beta emission-line
equivalent width. With our new measurements, PG 2130+099 is no longer an
outlier in either the R-L or the MBH-Sigma relationships.Comment: 21 pages, 7 figures; Accepted for publication in Ap
Florivory Shapes both Leaf and Floral Interactions
Florivory, or the consumption of flowers, is a ubiquitous interaction that can reduce plant reproduction directly by damaging reproductive tissues and indirectly by deterring pollinators. However, we know surprisingly little about how florivory alters plant traits or the larger community of species interactions. Although leaf damage is known to affect floral traits and interactions in many systems, the consequences of floral damage for leaf traits and interactions are unknown. We manipulated floral damage in Impatiens capensisand measured effects on floral attractive traits and secondary chemicals, leaf secondary chemicals, floral interactions, leaf herbivory, and plant reproduction. We also examined relationships between early season floral traits and floral interactions, to explore which traits structure floral interactions. Moderate but not high florivory significantly increased relative selfed reproduction, leading to a shift in mating system away from outcrossing. Florivory increased leaf secondary compounds and decreased leaf herbivory, although mechanisms other than leaf chemistry may be responsible for some of the reduced leaf damage. Florivory altered four of seven measured interactions, including increased subsequent florivory and reduced flower spiders, although only leaf damage effects were significant after correcting for multiple tests. Pretreatment concentrations of floral anthocyanins and condensed tannins were associated with reduced levels of many floral antagonisms, including florivory, nectar larceny, and flower spider abundance, suggesting these traits play a role in floral resistance. Overall, our results indicate a broad range of community and potential evolutionary consequences of florivory through structuring subsequent floral interactions, altering leaf secondary chemicals, and shaping leaf herbivory
Thermonuclear Burning Regimes and the Use of SNe Ia in Cosmology
The calculations of the light curves of thermonuclear supernovae are carried
out by a method of multi-group radiation hydrodynamics. The effects of spectral
lines and expansion opacity are taken into account. The predictions for UBVI
fluxes are given. The values of rise time for B and V bands found in our
calculations are in good agreement with the observed values. We explain why our
results for the rise time have more solid physical justification than those
obtained by other authors. It is shown that small variations in the chemical
composition of the ejecta, produced in the explosions with different regimes of
nuclear burning, can influence drastically the light curve decline in the B
band and, to a lesser extent, in the V band. We argue that recent results on
positive cosmological constant Lambda, found from the high redshift supernova
observations, could be wrong in the case of possible variations of the
preferred mode of nuclear burning in the earlier Universe.Comment: 20 pages, 5 figures, presented at the conference "Astronomy at the
Eve of the New Century", Puschino, May 17-22, 1999. A few references and a
table added, typos correcte
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