996 research outputs found
A graph of dark energy significance on different spatial and mass scales
The current cosmological paradigm sees the formation and evolution of the
cosmic large-scale structure as governed by the gravitational attraction of the
Dark Matter (DM) and the repulsion of the Dark Energy (DE).
We characterize the relative importance of uniform and constant dark energy,
as given by the Lambda term in the standard LCDM cosmology, in galaxy systems
of different scales, from groups to superclusters.
An instructive "Lambda significance graph" is introduced where the matter-DE
density ratio /rho_Lambda for different galaxy systems is plotted
against the radius R. This presents gravitation and DE dominated regions and
shows directly the zero velocity radius, the zero-gravity radius, and the
Einstein-Straus radius for any fixed value of mass.
Example galaxy groups and clusters from the local universe illustrate the use
of the Lambda significance graph. These are generally located deep in the
gravity-dominated region /rho_Lambda > 2, being virialized. Extended
clusters and main bodies of superclusters can reach down near the border line
between gravity-dominated and DE dominated regions /rho_Lambda = 2. The
scale--mass relation from the standard 2-point correlation function intersects
this balance line near the correlation lenght.
The log /rho_Lambda vs. log R diagram is a useful and versatile way to
characterize the dynamical state of systems of galaxies within the Lambda
dominated expanding universe.Comment: 4 pages, 2 figure
Primordial black holes from a curvaton scenario with strongly non-Gaussian perturbations
We investigate the production of primordial black holes (PBHs) in a mixed
inflaton--curvaton scenario with a quadratic curvaton potential, assuming the
curvaton is in de Sitter equilibrium during inflation with . In this setup, the curvature perturbation sourced by the curvaton is
strongly non-Gaussian, containing no leading Gaussian term. We show that for
, the curvaton contribution to the spectrum of primordial
perturbations on CMB scales can be kept negligible but on small scales the
curvaton can source PBHs. In particular, PBHs in the asteroid mass range
with an abundance
reaching can be produced when the inflationary Hubble scale
GeV and the curvaton decay occurs in the window from
slightly before the electroweak transition to around the QCD transition.Comment: 12 pages + appendices, 7 figure
Kahler potentials for the MSSM inflation and the spectral index
Recently it has been argued that some of the fine-tuning problems of the MSSM
inflation associated with the existence of a saddle point along a flat
direction may be solved naturally in a class of supergravity models. Here we
extend the analysis and show that the constraints on the Kahler potentials in
these models are considerably relaxed when the location of the saddle point is
treated as a free variable. We also examine the effect of supergravity
corrections on inflationary predictions and find that they can slightly alter
the value of the spectral index. As an example, for flat direction field values
we find while the
prediction of the MSSM inflation without any corrections is .Comment: 13 pages, one figure. Typos corrected and a reference adde
Can primordial black holes as all dark matter explain fast radio bursts?
Publisher Copyright: © 2021 American Physical Society.Primordial black holes (PBHs) are one of the most interesting nonparticle dark matter (DM) candidates. They may explain all the DM content in the Universe in the mass regime from about 10-14 M to 10-11 M. We study PBHs as the source of fast radio bursts (FRBs) via magnetic reconnection in the event of collisions between them and neutron stars (NSs) in galaxies. We investigate the energy loss of PBHs during PBH-NS encounters to model their capture by NSs. To an order-of-magnitude estimation, we conclude that the parameter space of PBHs being all DM is accidentally consistent with that to produce FRBs with a rate which is the order of the observed FRB rate.Peer reviewe
On the divergences of inflationary superhorizon perturbations
We discuss the infrared divergences that appear to plague cosmological
perturbation theory. We show that within the stochastic framework they are
regulated by eternal inflation so that the theory predicts finite fluctuations.
Using the formalism to one loop, we demonstrate that the infrared
modes can be absorbed into additive constants and the coefficients of the
diagrammatic expansion for the connected parts of two and three-point functions
of the curvature perturbation. As a result, the use of any infrared cutoff
below the scale of eternal inflation is permitted, provided that the background
fields are appropriately redefined. The natural choice for the infrared cutoff
would of course be the present horizon; other choices manifest themselves in
the running of the correlators. We also demonstrate that it is possible to
define observables that are renormalization group invariant. As an example, we
derive a non-perturbative, infrared finite and renormalization point
independent relation between the two-point correlators of the curvature
perturbation for the case of the free single field.Comment: 12 page
Supergravity origin of the MSSM inflation
We consider the supergravity origin of the recently proposed MSSM
inflationary model, which relies on the existence of a saddle point along a
dimension six flat direction. We derive the conditions that the Kahler
potential has to satisfy for the saddle point to exist irrespective of the
hidden sector vevs. We show that these conditions are satisfied by a simple
class of Kahler potentials, which we find to have a similar form as in various
string theory compactifications. For these potentials, slow roll MSSM inflation
requires no fine tuning of the soft supersymmetry breaking parameters.Comment: v3: 10 pages, no figures; version accepted for publication. Typos
correcte
Optimization of Cloud Task Processing with Checkpoint-Restart Mechanism
International audienceIn this paper, we aim at optimizing fault-tolerance tech- niques based on a checkpointing/restart mechanism, in the context of cloud computing. Our contribution is three-fold. (1) We derive a fresh formula to compute the optimal num- ber of checkpoints for cloud jobs with varied distributions of failure events. Our analysis is not only generic with no assumption on failure probability distribution, but also at- tractively simple to apply in practice. (2) We design an adaptive algorithm to optimize the impact of checkpointing regarding various costs like checkpointing/restart overhead. (3) We evaluate our optimized solution in a real cluster en- vironment with hundreds of virtual machines and Berke- ley Lab Checkpoint/Restart tool. Task failure events are emulated via a production trace produced on a large-scale Google data center. Experiments confirm that our solution is fairly suitable for Google systems. Our optimized formula outperforms Young's formula by 3-10 percent, reducing wall- clock lengths by 50-100 seconds per job on average
Impact of perceived inappropiate cardiopulmonary resuscitation on emergency clinicians' intention to leave the job : Results from a cross-sectional survey in 288 centres across 24 countries
Introduction: Cardiopulmonary resuscitation (CPR) in patients with a poor prognosis increases the risk of perception of inappropriate care leading to moral distress in clinicians. We evaluated whether perception of inappropriate CPR is associated with intention to leave the job among emergency clinicians. Methods: A cross-sectional multi-centre survey was conducted in 24 countries. Factors associated with intention to leave the job were analysed by conditional logistic regression models. Results are expressed as odds ratios with 95% confidence intervals. Results: Of 5099 surveyed emergency clinicians, 1836 (36.0%) were physicians, 1313 (25.7%) nurses, 1950 (38.2%) emergency medical technicians. Intention to leave the job was expressed by 1721 (33.8%) clinicians, 3403 (66.7%) often wondered about the appropriateness of a resuscitation attempt, 2955 (58.0%) reported moral distress caused by inappropriate CPR. After adjustment for other covariates, the risk of intention to leave the job was higher in clinicians often wondering about the appropriateness of a resuscitation attempt (1.43 [1.23-1.67]), experiencing associated moral distress (1.44 [1.24 -1.66]) and who were between 30-44 years old (1.53 [1.21-1.92] compared to Conclusion: Resuscitation attempts perceived as inappropriate by clinicians, and the accompanying moral distress, were associated with an increased likelihood of intention to leave the job. Interprofessional collaboration, teamwork, and regular interdisciplinary debriefing were associated with a lower risk of intention to leave the job.Peer reviewe
GeoTextMESS: result fusion with fuzzy Borda ranking in geographical information retrieval
In this paper we discuss the integration of different GIR systems by means of a fuzzy Borda method for result fusion. Two of the systems, the one by the Universidad Politécnica de Valencia and the one of the Universidad of Jaén participated to the GeoCLEF task under the name TextMess. The proposed result fusion method takes as input the document lists returned by the different systems and returns
a document list where the documents are ranked according to the fuzzy Borda voting scheme. The obtained results show that the fusion method allows to improve the results of the component systems, although the
fusion is not optimal, because it is effective only if the components return
a similar set of relevant documents.Peer ReviewedPostprint (author’s final draft
healthcareCOVID: a national cross-sectional observational study identifying risk factors for developing suspected or confirmed COVID-19 in UK healthcare workers.
To establish the prevalence, risk factors and implications of suspected or confirmed coronavirus disease 2019 (COVID-19) infection among healthcare workers in the United Kingdom (UK). Cross-sectional observational study. UK-based primary and secondary care. Healthcare workers aged ≥18 years working between 1 February and 25 May 2020. A composite endpoint of laboratory-confirmed diagnosis of SARS-CoV-2, or self-isolation or hospitalisation due to suspected or confirmed COVID-19. Of 6,152 eligible responses, the composite endpoint was present in 1,806 (29.4%) healthcare workers, of whom 49 (0.8%) were hospitalised, 459 (7.5%) tested positive for SARS-CoV-2, and 1,776 (28.9%) reported self-isolation. Overall, between 11,870 and 21,158 days of self-isolation were required by the cohort, equalling approximately 71 to 127 working days lost per 1,000 working days. The strongest risk factor associated with the presence of the primary composite endpoint was increasing frequency of contact with suspected or confirmed COVID-19 cases without adequate personal protective equipment (PPE): 'Never' (reference), 'Rarely' (adjusted odds ratio 1.06, (95% confidence interval: [0.87-1.29])), 'Sometimes' (1.7 [1.37-2.10]), 'Often' (1.84 [1.28-2.63]), 'Always' (2.93, [1.75-5.06]). Additionally, several comorbidities (cancer, respiratory disease, and obesity); working in a 'doctors' role; using public transportation for work; regular contact with suspected or confirmed COVID-19 patients; and lack of PPE were also associated with the presence of the primary endpoint. A total of 1,382 (22.5%) healthcare workers reported lacking access to PPE items while having clinical contact with suspected or confirmed COVID-19 cases. Suspected or confirmed COVID-19 was more common in healthcare workers than in the general population and is associated with significant workforce implications. Risk factors included inadequate PPE, which was reported by nearly a quarter of healthcare workers. Governments and policymakers must ensure adequate PPE is available as well as developing strategies to mitigate risk for high-risk healthcare workers during future COVID-19 waves. [Abstract copyright: © 2021 Kua et al.
- …