17,968,791 research outputs found
The assembly of massive galaxies from NIR observations of the Hubble Deep Field South
We use a deep K(AB)<25 galaxy sample in the Hubble Deep Field South to trace
the evolution of the cosmological stellar mass density from z~ 0.5 to z~3. We
find clear evidence for a decrease of the average stellar mass density at high
redshift, 2<z<3.2, that is 15^{+25}_{-5}% of the local value, two times higher
than what observed in the Hubble Deep Field North. To take into account for the
selection effects, we define a homogeneous subsample of galaxies with
10^{10}M_\odot \leq M_* \leq 10^{11}M_\odot: in this sample, the mass density
at z>2 is 20^{+20}_{-5} % of the local value. In the mass--limited subsample at
z>2, the fraction of passively fading galaxies is at most 25%, although they
can contribute up to about 40% of the stellar mass density. On the other hand,
star--forming galaxies at z>2 form stars with an average specific rate at least
~4 x10^{-10} yr, 3 times higher than the z<~1 value. This
implies that UV bright star--forming galaxies are substancial contributors to
the rise of the stellar mass density with cosmic time. Although these results
are globally consistent with --CDM scenarios, the present rendition of
semi analytic models fails to match the stellar mass density produced by more
massive galaxies present at z>2.Comment: Accepted for publication on ApJLetter
The evolution of the galaxy luminosity function in the rest frame blue band up to z=3.5
We present an estimate of the cosmological evolution of the field galaxy
luminosity function (LF) in the rest frame 4400 Angstrom B -band up to redshift
z=3.5. To this purpose, we use a composite sample of 1541 I--selected galaxies
selected down to I_(AB)=27.2 and 138 galaxies selected down to K_(AB)=25 from
ground-based and HST multicolor surveys, most notably the new deep JHK images
in the Hubble Deep Field South (HDF-S) taken with the ISAAC instrument at the
ESO-VLT telescope. About 21% of the sample has spectroscopic redshifts, and the
remaining fraction well calibrated photometric redshifts. The resulting blue LF
shows little density evolution at the faint end with respect to the local
values, while at the bright end (M_B(AB)<-20) a brightening increasing with
redshift is apparent with respect to the local LF. Hierarchical CDM models
overpredict the number of faint galaxies by about a factor 3 at z=1. At the
bright end the predicted LFs are in reasonable agreement only at low and
intermediate redshifts (z=1), but fail to reproduce the pronounced brightening
observed in the high redshift (z=2-3) LF. This brightening could mark the epoch
where a major star formation activity is present in the galaxy evolution.Comment: 14 pages, 2 figures, Astrophysical Journal Letters, in pres
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Inclusive search for supersymmetry using razor variables in pp collisions at root s=13 TeV
Peer reviewe
The Darkside Awakens
The DarkSide program at LNGS aims to perform background-free WIMP searches using two phase liquid argon time projection chambers, with the ultimate goal of covering all parameters down to the so-called neutrino floor. One of the distinct features of the program is the use of underground argon with has a reduced content of the radioactive Ar-39 compared to atmospheric argon. The DarkSide Collaboration is currently operating the DarkSide-50 experiment, the first such WIMP detector using underground argon. Operations with underground argon indicate a suppression of Ar-39 by a factor (1.4 +/- 0.2) x 10(3) relative to atmospheric argon. The new results obtained with DarkSide-50 and the plans for the next steps of the DarkSide program, the 20 t fiducial mass DarkSide-20k detector and the 200 t fiducial Argo, are reviewed in this proceedings.71814th International Conference on Topics in Astroparticle and Underground Physics (TAUP)Sep 07-11, 2015Torino, ITAL
Measurement of the inclusive production cross sections for forward jets and for dijet events with one forward and one central jet in pp collisions at sqrt(s) = 7 TeV
The inclusive production cross sections for forward jets, as well for jets in
dijet events with at least one jet emitted at central and the other at forward
pseudorapidities, are measured in the range of transverse momenta pt = 35-150
GeV/c in proton-proton collisions at sqrt(s) = 7 TeV by the CMS experiment at
the LHC. Forward jets are measured within pseudorapidities 3.2<|eta|<4.7, and
central jets within the |eta|<2.8 range. The double differential cross sections
with respect to pt and eta are compared to predictions from three approaches in
perturbative quantum chromodynamics: (i) next-to-leading-order calculations
obtained with and without matching to parton-shower Monte Carlo simulations,
(ii) PYTHIA and HERWIG parton-shower event generators with different tunes of
parameters, and (iii) CASCADE and HEJ models, including different non-collinear
corrections to standard single-parton radiation. The single-jet inclusive
forward jet spectrum is well described by all models, but not all predictions
are consistent with the spectra observed for the forward-central dijet events.Comment: Submitted to the Journal of High Energy Physic
Understanding Soft Errors in Uncore Components
The effects of soft errors in processor cores have been widely studied.
However, little has been published about soft errors in uncore components, such
as memory subsystem and I/O controllers, of a System-on-a-Chip (SoC). In this
work, we study how soft errors in uncore components affect system-level
behaviors. We have created a new mixed-mode simulation platform that combines
simulators at two different levels of abstraction, and achieves 20,000x speedup
over RTL-only simulation. Using this platform, we present the first study of
the system-level impact of soft errors inside various uncore components of a
large-scale, multi-core SoC using the industrial-grade, open-source OpenSPARC
T2 SoC design. Our results show that soft errors in uncore components can
significantly impact system-level reliability. We also demonstrate that uncore
soft errors can create major challenges for traditional system-level checkpoint
recovery techniques. To overcome such recovery challenges, we present a new
replay recovery technique for uncore components belonging to the memory
subsystem. For the L2 cache controller and the DRAM controller components of
OpenSPARC T2, our new technique reduces the probability that an application run
fails to produce correct results due to soft errors by more than 100x with
3.32% and 6.09% chip-level area and power impact, respectively.Comment: to be published in Proceedings of the 52nd Annual Design Automation
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