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Arctic Soil Governs Whether Climate Change Drives Global Losses or Gains in Soil Carbon
Key uncertainties in terrestrial carbon cycle projections revolve around the timing, direction, and magnitude of the carbon cycle feedback to climate change. This is especially true in carbon-rich Arctic ecosystems, where permafrost soils contain roughly one third of the world's soil carbon stocks, which are likely vulnerable to loss. Using an ensemble of soil biogeochemical models that reflect recent changes in the conceptual understanding of factors responsible for soil carbon persistence, we quantify potential soil carbon responses under two representative climate change scenarios. Our results illustrate that models disagree on the sign and magnitude of global soil changes through 2100, with disagreements primarily driven by divergent responses of Arctic systems. These results largely reflect different assumptions about the nature of soil carbon persistence and vulnerabilities, underscoring the challenges associated with setting allowable greenhouse gas emission targets that will limit global warming to 1.5°C
Partial Covering Arrays: Algorithms and Asymptotics
A covering array is an array with entries
in , for which every subarray contains each
-tuple of among its rows. Covering arrays find
application in interaction testing, including software and hardware testing,
advanced materials development, and biological systems. A central question is
to determine or bound , the minimum number of rows of
a . The well known bound
is not too far from being
asymptotically optimal. Sensible relaxations of the covering requirement arise
when (1) the set need only be contained among the rows
of at least of the subarrays and (2) the
rows of every subarray need only contain a (large) subset of . In this paper, using probabilistic methods, significant
improvements on the covering array upper bound are established for both
relaxations, and for the conjunction of the two. In each case, a randomized
algorithm constructs such arrays in expected polynomial time
Identification of the Early Fermi LAT Gamma-Ray Bright Objects with Extragalactic VLBI sources
A list of 205 gamma-ray strong objects was reported recently as a result of a
3-month integration with the Large Area Telescope on board the Fermi Gamma-Ray
Space Telescope. We attempted identification of these objects,
cross-correlating the gamma-ray positions with VLBI positions of a large
all-sky sample of extragalactic radio sources selected on the basis of their
parsec-scale flux density. The original associations reported by the Fermi team
are confirmed and six new identifications are suggested. A Monte-Carlo analysis
shows that the fraction of chance associations in our analysis is less than 5
per cent, and confirms that the vast majority of gamma-ray bright extragalactic
sources are radio loud blazars with strong parsec-scale jets. A correlation
between the parsec-scale radio and gamma-ray flux is supported by our analysis
of a complete VLBI flux-density-limited sample of extragalactic jets. The
effectiveness of using a VLBI catalog to find associations between gamma-ray
detections and compact extragalactic radio sources, especially near the
Galactic plane, is demonstrated. It is suggested that VLBI catalogs should be
used for future identification of Fermi LAT objects.Comment: 5 pages, 4 figures, 1 table, accepted by the Astrophysical Journal
Letters; minor corrections to the text are made, one panel is added to Figure
1; full table 1 in electronic form can be extracted from the preprint sourc
High Energy Gamma-Ray Emission From Blazars: EGRET Observations
We will present a summary of the observations of blazars by the Energetic
Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory
(CGRO). EGRET has detected high energy gamma-ray emission at energies greater
than 100 MeV from more that 50 blazars. These sources show inferred isotropic
luminosities as large as ergs s. One of the most
remarkable characteristics of the EGRET observations is that the gamma-ray
luminosity often dominates the bolometric power of the blazar. A few of the
blazars are seen to exhibit variability on very short time-scales of one day or
less. The combination of high luminosities and time variations seen in the
gamma-ray data indicate that gamma-rays are an important component of the
relativistic jet thought to characterize blazars. Currently most models for
blazars involve a beaming scenario. In leptonic models, where electrons are the
primary accelerated particles, gamma-ray emission is believed to be due to
inverse Compton scattering of low energy photons, although opinions differ as
to the source of the soft photons. Hardronic models involve secondary
production or photomeson production followed by pair cascades, and predict
associated neutrino production.Comment: 16 pages, 7 figures, style files included. Invited review paper in
"Observational Evidence for Black Holes in the Universe," 1999, ed. S. K.
Chakrabarti (Dordrecht: Kluwer), 215-23
Higher Spin Gravity with Matter in AdS_3 and Its CFT Dual
We study Vasiliev's system of higher spin gauge fields coupled to massive
scalars in AdS_3, and compute the tree level two and three point functions.
These are compared to the large N limit of the W_N minimal model, and
nontrivial agreements are found. We propose a modified version of the
conjecture of Gaberdiel and Gopakumar, under which the bulk theory is
perturbatively dual to a subsector of the CFT that closes on the sphere.Comment: 58 pages; typos corrected, references adde
Eta Carinae -- Physics of the Inner Ejecta
Eta Carinae's inner ejecta are dominated observationally by the bright
Weigelt blobs and their famously rich spectra of nebular emission and
absorption lines. They are dense (n_e ~ 10^7 to 10^8 cm^-3), warm (T_e ~ 6000
to 7000 K) and slow moving (~40 km/s) condensations of mostly neutral (H^0)
gas. Located within 1000 AU of the central star, they contain heavily
CNO-processed material that was ejected from the star about a century ago.
Outside the blobs, the inner ejecta include absorption-line clouds with similar
conditions, plus emission-line gas that has generally lower densities and a
wider range of speeds (reaching a few hundred km/s) compared to the blobs. The
blobs appear to contain a negligible amount of dust and have a nearly dust-free
view of the central source, but our view across the inner ejecta is severely
affected by uncertain amounts of dust having a patchy distribution in the
foreground. Emission lines from the inner ejecta are powered by photoionization
and fluorescent processes. The variable nature of this emission, occurring in a
5.54 yr event cycle, requires specific changes to the incident flux that hold
important clues to the nature of the central object.Comment: This is Chapter 5 in a book entitled: Eta Carinae and the Supernova
Impostors, Kris Davidson and Roberta M. Humphreys, editors Springe
Higher Spin Black Holes from CFT
Higher spin gravity in three dimensions has explicit black holes solutions,
carrying higher spin charge. We compute the free energy of a charged black hole
from the holographic dual, a 2d CFT with extended conformal symmetry, and find
exact agreement with the bulk thermodynamics. In the CFT, higher spin
corrections to the free energy can be calculated at high temperature from
correlation functions of W-algebra currents.Comment: 24 pages; v2 reference adde
Intra-tumor heterogeneity in breast cancer has limited impact on transcriptomic-based molecular profiling
Background: Transcriptomic profiling of breast tumors provides opportunity for subtyping and molecular-based patient stratification. In diagnostic applications the specimen profiled should be representative of the expression profile of the whole tumor and ideally capture properties of the most aggressive part of the tumor. However, breast cancers commonly exhibit intra-tumor heterogeneity at molecular, genomic and in phenotypic level, which can arise during tumor evolution. Currently it is not established to what extent a random sampling approach may influence molecular breast cancer diagnostics. Methods: In this study we applied RNA-sequencing to quantify gene expression in 43 pieces (2-5 pieces per tumor) from 12 breast tumors (Cohort 1). We determined molecular subtype and transcriptomic grade for all tumor pieces and analysed to what extent pieces originating from the same tumors are concordant or discordant with each other. Additionally, we validated our finding in an independent cohort consisting of 19 pieces (2-6 pieces per tumor) from 6 breast tumors (Cohort 2) profiled using microarray technique. Exome sequencing was also performed on this cohort, to investigate the extent of intra-tumor genomic heterogeneity versus the intra-tumor molecular subtype classifications. Results: Molecular subtyping was consistent in 11 out of 12 tumors and transcriptomic grade assignments were consistent in 11 out of 12 tumors as well. Molecular subtype predictions revealed consistent subtypes in four out of six patients in this cohort 2. Interestingly, we observed extensive intra-tumor genomic heterogeneity in these tumor pieces but not in their molecular subtype classifications. Conclusions: Our results suggest that macroscopic intra-tumoral transcriptomic heterogeneity is limited and unlikely to have an impact on molecular diagnostics for most patients.Peer reviewe
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