177 research outputs found
Testing cosmic acceleration for parameterizations using measurements in galaxy clusters
In this paper we study the cosmic acceleration for five dynamical dark energy
models whose equation of state varies with redshift. The cosmological
parameters of these models are constrained by performing a MCMC analysis using
mainly gas mass fraction, , measurements in two samples of galaxy
clusters: one reported by Allen et al. (2004), which consists of points
spanning the redshift range , and the other by Hasselfield et al.
(2013) from the Atacama Cosmology Telescope survey, which consists of data
points in the redshift range . In addition, we
perform a joint analysis with the measurements of the Hubble parameter ,
baryon acoustic oscillations and the cosmic microwave background radiation from
WMAP and Planck measurements to estimate the equation of state parameters. We
obtained that both samples provide consistent constraints on the
cosmological parameters. We found that the data is consistent at the
confidence level with a cosmic slowing down of the acceleration at
late times for most of the parameterizations. The constraints of the joint
analysis using WMAP and Planck measurements show that this trend disappears. We
have confirmed that the probe provides competitive constraints on the
dark energy parameters when a is assumed.Comment: 21 pages, 8 Tables, 11 Figures, accepted for publication in MNRA
Constraints on barotropic dark energy models by a new phenomenological parameterization
In this paper, we propose a new phenomenological two parameter
parametrization of to constrain barotropic dark energy models by
considering a spatially flat FRW universe, neglecting the radiation component,
and reconstructing the effective equation of state (EoS). This two
free-parameter EoS reconstruction shows a non-monotonic behavior, pointing to a
more general fitting for the scalar field models, like thawing and freezing
models. We constrain the free parameters using the observational data of
the Hubble parameter obtained from cosmic chronometers, the
joint-light-analysis type Ia Supernovae sample and a joint analysis from these
data. We obtain a value of today, , and
a transition redshift, (when the Universe
change from an decelerated phase to an accelerated one). The effective EoS
reconstruction and the - plane analysis pointed out a quintom
dark energy, which is consistent with a non parametric EoS reconstruction,
reported by other authors, and using the latest cosmological observations.Comment: This manuscript was accepted to be published in the European Physical
Journal C. 17 pages, 7 figures, 1 tabl
Monitoring of a virtual infrastructure testbed
This paper presents a SNMP-based Monitoring Agents
for Multi-Constrain Resource Scheduling in Grids
(SBLOMARS) as an effective solution for resource usage
monitoring in virtual network environments. SBLOMARS is
different to current large-scale distributed monitoring systems in
three essential aspects: Firstly, it reaches a high level of
generality by the integration of the SNMP protocol and thus,
facilitates to handle heterogeneous operating platforms.
Secondly, it is able to self-configure the polling periods of the
resources to be monitored depending of network context and
finally, it makes use of dynamic software structures to interface
with third parties, allowing to be deployed in a wide range of
devices, from simple mobile access devices to robust
multiprocessor systems or clusters with even multiple hard disks
and storage partitions. SBLOMARS has been deployed in
EmanicsLab, a virtual laboratory constituted by fourteen nodes
distributed in seven European Universities. Although the
research is not yet concluded, available results confirm its
suitability to deal with the challenges of monitoring virtual
networks.Postprint (published version
Modelling non-dust fluids in cosmology
Currently, most of the numerical simulations of structure formation use
Newtonian gravity. When modelling pressureless dark matter, or `dust', this
approach gives the correct results for scales much smaller than the
cosmological horizon, but for scenarios in which the fluid has pressure this is
no longer the case. In this article, we present the correspondence of
perturbations in Newtonian and cosmological perturbation theory, showing exact
mathematical equivalence for pressureless matter, and giving the relativistic
corrections for matter with pressure. As an example, we study the case of
scalar field dark matter which features non-zero pressure perturbations. We
discuss some problems which may arise when evolving the perturbations in this
model with Newtonian numerical simulations and with CMB Boltzmann codes.Comment: 5 pages; v2: typos corrected and refs added, submitted version; v3:
version to appear in JCA
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SCIPP: An Expanded Community of Practice - Community Publishing
SCIPP redefines and expands the existing notions about what makes for a vibrant and robust community of practice by partnering CSUSB students and professors with K-12 students, parents, and educators, along with committed community partners. SCIPP encourages curiosity in ways that leads to critical thinking, exploration, risk taking , confidence building, open-mindedness, and other personal traits that equip them with the softskills to be active, critical, and creative contributors to our communities. SCIPP pedagogy embraces our students\u27 collective wisdom and focuses on relational building where multi-directional communication is promoted and students are viewed as equal stakeholders in their own educations. SCIPP puts collaboration into action which in turn fosters community-based lifelong learning. SCIPP provides the open intellectual space for future university students (our K-12 students) to engage with existing university students in meaningful ways so as to sustain interconnected partnerships facilitating community engagement. It supports parents as experts in the education of their children and acknowledges parents as the first conduits to spark their children’s imagination while they actively participate in education enriching activities and programs. Everyone involved is committed to creating a secure and open atmosphere for dreaming, sharing, and learning. Together we explore the aspects of community publishing through collaborative learning in formal and informal settings relating to digital and printed medias
Diving into the vertical dimension of elasmobranch movement ecology
Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements
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