108 research outputs found
Improving the modelling of redshift-space distortions: I. A bivariate Gaussian description for the galaxy pairwise velocity distributions
As a step towards a more accurate modelling of redshift-space distortions in
galaxy surveys, we develop a general description of the probability
distribution function of galaxy pairwise velocities within the framework of the
so-called streaming model. For a given galaxy separation , such
function can be described as a superposition of virtually infinite local
distributions. We characterize these in terms of their moments and then
consider the specific case in which they are Gaussian functions, each with its
own mean and dispersion . Based on physical considerations, we
make the further crucial assumption that these two parameters are in turn
distributed according to a bivariate Gaussian, with its own mean and covariance
matrix. Tests using numerical simulations explicitly show that with this
compact description one can correctly model redshift-space distorsions on all
scales, fully capturing the overall linear and nonlinear dynamics of the galaxy
flow at different separations. In particular, we naturally obtain
Gaussian/exponential, skewed/unskewed distribution functions, depending on
separation as observed in simulations and data. Also, the recently proposed
single-Gaussian description of redshift-space distortions is included in this
model as a limiting case, when the bivariate Gaussian is collapsed to a
two-dimensional Dirac delta function. We also show how this description
naturally allows for the Taylor expansion of around
, which leads to the Kaiser linear formula when truncated to second
order, expliciting its connection with the moments of the velocity distribution
functions. More work is needed, but these results indicate a very promising
path to make definitive progress in our program to improve RSD estimators.Comment: 11 pages, 3 figures, 2 table
Multiple satellites in materials with complex plasmon spectra: From graphite to graphene
International audienceThe photoemission spectrum of graphite is still debated. To help resolve this issue, we present photoemission measurements at high photon energy and analyze the results using a Green's function approach that takes into account the full complexity of the loss spectrum. Our measured data show multiple satellite replicas. We demonstrate that these satellites are of intrinsic origin, enhanced by extrinsic losses. The dominating satellite is due to the π+σ plasmon of graphite, whereas the π plasmon creates a tail on the high-binding energy side of the quasiparticle peak. The interplay between the two plasmons leads to energy shifts, broadening, and additional peaks in the satellite spectrum. We also predict the spectral changes in the transition from graphite towards graphene
REPS: REscaled Power Spectra for initial conditions with massive neutrinos
REPS (REscaled Power Spectra) provides accurate, one-percent level, numerical simulations of the initial conditions for massive neutrino cosmologies, rescaling the late-time linear power spectra to the simulation initial redshif
The Terroir Concept Interpreted through Grape Berry Metabolomics and Transcriptomics
Terroir refers to the combination of environmental factors that affect the characteristics of crops such as grapevine (Vitis vinifera) according to particular habitats and management practices. This article shows how certain terroir signatures can be detected in the berry metabolome and transcriptome of the grapevine cultivar Corvina using multivariate statistical analysis. The method first requires an appropriate sampling plan. In this case study, a specific clone of the Corvina cultivar was selected to minimize genetic differences, and samples were collected from seven vineyards representing three different macro-zones during three different growing seasons. An untargeted LC-MS metabolomics approach is recommended due to its high sensitivity, accompanied by efficient data processing using MZmine software and a metabolite identification strategy based on fragmentation tree analysis. Comprehensive transcriptome analysis can be achieved using microarrays containing probes covering ~99% of all predicted grapevine genes, allowing the simultaneous analysis of all differentially expressed genes in the context of different terroirs. Finally, multivariate data analysis based on projection methods can be used to overcome the strong vintage-specific effect, allowing the metabolomics and transcriptomics data to be integrated and analyzed in detail to identify informative correlations
The VVDS type-1 AGN sample: The faint end of the luminosity function
In a previous paper (Gavignaud et al. 2006), we presented the type-1 Active
Galactic Nuclei (AGN) sample obtained from the first epoch data of the
VIMOS-VLT Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN
with redshift up to z=5 and 17.5< I <24.0, selected on the basis of their
spectra. In this paper we present the measurement of the Optical Luminosity
Function up to z=3.6 derived from this sample, we compare our results with
previous results from brighter samples both at low and at high redshift. Our
data, more than one magnitude fainter than previous optical surveys, allow us
to constrain the faint part of the luminosity function up to high redshift. By
combining our faint VVDS sample with the large sample of bright AGN extracted
from the SDSS DR3 (Richards et al., 2006b) and testing a number of different
evolutionary models, we find that the model which better represents the
combined luminosity functions, over a wide range of redshift and luminosity, is
a luminosity dependent density evolution (LDDE) model, similar to those derived
from the major X-surveys. Such a parameterization allows the redshift of the
AGN space density peak to change as a function of luminosity and explains the
excess of faint AGN that we find at 1.0< z <1.5. On the basis of this model we
find, for the first time from the analysis of optically selected samples, that
the peak of the AGN space density shifts significantly towards lower redshift
going to lower luminosity objects. This result, already found in a number of
X-ray selected samples of AGN, is consistent with a scenario of "AGN cosmic
downsizing", in which the density of more luminous AGN, possibly associated to
more massive black holes, peaks earlier in the history of the Universe, than
that of low luminosity ones.Comment: 13 pages, 10 figures, submitted to A&
The MassiveBlack-II simulation: the evolution of haloes and galaxies to z 0
(Abridged for arXiv)We investigate the properties of halos, galaxies and
blackholes to z=0 in the high resolution hydrodynamical simulation
MassiveBlack-II (MBII) which evolves a LCDM cosmology in a comoving volume
Vbox=100(Mpc/h)^3. MBII is the highest resolution simulation of this size which
includes a self-consistent model for star formation, black hole accretion and
associated feedback. We provide a simulation browser web application which
enables interactive search and tagging of halos, subhalos and their properties
and publicly release our galaxy catalogs. Our analysis of the halo mass
function (MF) in MBII reveals that baryons have strong effects, with changes in
the halo abundance of 20-35% below the knee of the MF (Mhalo < 10^13.2 Msun/h
at z=0) when compared to fits based on dark matter only simulations. We provide
a fitting function for the halo MF out to redshift z=11 and discuss how the
onset of non-universality in the MF limits the accuracy of our fit. We study
the halo occupation distribution and clustering of galaxies, in particular the
evolution and scale dependence of stochasticity and bias finding reasonable
agreement with observational data. The shape of the cosmic spectral energy
distribution predicted by MBII is consistent with observations, but lower in
amplitude. The Galaxy Stellar Mass Function (GSMF) function is broadly
consistent with observations at z>=2. At z<2, the population of passive low
mass (for M*<10^9 Msun) galaxies in MBII makes the GSMF too steep compared to
observations whereas at the high mass end (M*>10^11 Msun) galaxies hosting
bright AGNs make significant contributions to the GSMF. The quasar bolometric
luminosity function is also largely consistent with observations. We note
however that more efficient AGN feedback (beyond simple thermal coupling used
here) is likely necessary for the largest, rarest objects/clusters at low
redshifts.Comment: 26 pages, 25 figures. Submitted to MNRAS. High-resolution version and
MBII galaxy catalogs can be found at http://mbii.phys.cmu.edu/data
High Risk of Secondary Infections Following Thrombotic Complications in Patients With COVID-19
Background. This study’s primary aim was to evaluate the impact of thrombotic complications on the development of secondary infections. The secondary aim was to compare the etiology of secondary infections in patients with and without thrombotic complications. Methods. This was a cohort study (NCT04318366) of coronavirus disease 2019 (COVID-19) patients hospitalized at IRCCS San Raffaele Hospital between February 25 and June 30, 2020. Incidence rates (IRs) were calculated by univariable Poisson regression as the number of cases per 1000 person-days of follow-up (PDFU) with 95% confidence intervals. The cumulative incidence functions of secondary infections according to thrombotic complications were compared with Gray’s method accounting for competing risk of death. A multivariable Fine-Gray model was applied to assess factors associated with risk of secondary infections. Results. Overall, 109/904 patients had 176 secondary infections (IR, 10.0; 95% CI, 8.8–11.5; per 1000-PDFU). The IRs of secondary infections among patients with or without thrombotic complications were 15.0 (95% CI, 10.7–21.0) and 9.3 (95% CI, 7.9–11.0) per 1000-PDFU, respectively (P = .017). At multivariable analysis, thrombotic complications were associated with the development of secondary infections (subdistribution hazard ratio, 1.788; 95% CI, 1.018–3.140; P = .043). The etiology of secondary infections was similar in patients with and without thrombotic complications. Conclusions. In patients with COVID-19, thrombotic complications were associated with a high risk of secondary infections
Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world
Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic.
Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality.
Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States.
Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis.
Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection
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