8,349 research outputs found
Dynamic Trust Federation in Grids
Grids are becoming economically viable and productive tools. Grids provide a way of utilizing a vast array of linked resources such as computing systems, databases and services online within Virtual Organizations (VO). However, today’s Grid architectures are not capable of supporting dynamic, agile federation across multiple administrative domains and the main barrier, which hinders dynamic federation over short time scales is security. Federating security and trust is one of the most significant architectural issues in Grids. Existing relevant standards and specifications can be used to federate security services, but do not directly address the dynamic extension of business trust relationships into the digital domain. In this paper we describe an experiment in which we highlight those challenging architectural issues and we will further describe how the approach that combines dynamic trust federation and dynamic authorization mechanism can address dynamic security trust federation in Grids. The experiment made with the prototype described in this paper is used in the NextGRID project for the definition of requirements for next generation Grid architectures adapted to business application need
Pulsar Kicks With Modified URCA and Electrons in Landau Levels
We derive the energy asymmetry given the proto-neutron star during the time
when the neutrino sphere is near the surface of the proto-neutron star, using
the modified URCA process. The electrons produced with the anti-neutrinos are
in Landau levels due to the strong magnetic field, and this leads to asymmetry
in the neutrino momentum, and a pulsar kick. The magnetic field must be strong
enough for a large fraction of the eletrons to be in the lowest Landau level,
however, there is no direct dependence of our pulsar velocity on the strength
of the magnetic field. Our main prediction is that the large pulsar kicks start
at about 10 s and last for about 10 s, with the corresponding neutrinos
correlated in the direction of the magnetic field. We predict a pulsar velocity
of 1.03 km/s, which reaches 1000 km/s if T
K.Comment: 11 pages, 6 figure
Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II
Extremely radiation hard sensors are needed in particle physics experiments
to instrument the region near the beam pipe. Examples are beam halo and beam
loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial
diamond sensors are widely used. In this paper single crystal sapphire sensors
are considered as a promising alternative. Industrially grown sapphire wafers
are available in large sizes, are of low cost and, like diamond sensors, can be
operated without cooling. Here we present results of an irradiation study done
with sapphire sensors in a high intensity low energy electron beam. Then, a
multichannel direction-sensitive sapphire detector stack is described. It
comprises 8 sapphire plates of 1 cm^2 size and 525 micro m thickness,
metallized on both sides, and apposed to form a stack. Each second metal layer
is supplied with a bias voltage, and the layers in between are connected to
charge-sensitive preamplifiers. The performance of the detector was studied in
a 5 GeV electron beam. The charge collection efficiency measured as a function
of the bias voltage rises with the voltage, reaching about 10 % at 950 V. The
signal size obtained from electrons crossing the stack at this voltage is about
22000 e, where e is the unit charge.
The signal size is measured as a function of the hit position, showing
variations of up to 20 % in the direction perpendicular to the beam and to the
electric field. The measurement of the signal size as a function of the
coordinate parallel to the electric field confirms the prediction that mainly
electrons contribute to the signal. Also evidence for the presence of a
polarisation field was observed.Comment: 13 pages, 7 figures, 3 table
Pulsar Kicks With Sterile Neutrinos and Landau Levels
We use a model with two sterile neutrinos obtained by fits to the MiniBoone
and LSND experiments. Using formulations with neutrinos created by URCA
Processes in a strong magnetic field, so the lowest Landau level has a sizable
probability, we find that with known paramenters the assymetric sterile
neutrino emissivity might account for large pulsar kicks.Comment: 3 pages, 1 figur
A breeding site model for regional, dynamical malaria simulations evaluated using in situ temporary ponds observations
Daily observations of potential mosquito developmental habitats in a suburb of Kumasi in central Ghana reveal a strong variability in their water persistence times, which ranged between 11 and 81 days. The persistence of the ponds was strongly tied with rainfall, location and size of the puddles. A simple power-law relationship is found to fit the relationship between the average pond depth and area well. A prognostic water balance model is derived that describes the temporal evolution of the pond area and depth, incorporating the power-law geometrical relation. Pond area increases in response to rainfall, while evaporation and infiltration act as sink terms. Based on a range of evaluation metrics, the prognostic model is judged to provide a good representation of the pond coverage evolution at most sites. Finally, we demonstrate that the prognostic equation can be generalised and equally applied to a grid-cell to derive a fractional pond coverage, and thus can be implemented in spatially distributed models for relevant vector- borne diseases such as malaria
Analytical 1D-calculation of a 1-turn Coil Parameters for the Magneto-Forming Technology
In this paper, we will present an analytical modelling of a one-turn coil dedicated to
magnetic-pulse technologies. The goal is to be able to determine the main useful parameters
of an inductor by calculating the magnetic vector potential “A” diffusion. The concerned
parameters are electromagnetic (electromagnetic fields, magnetic flux and electric current
densities), electrical (resistance and inductance, maximum field coefficient) and
electromechanical (Lorentz force density and maximum force coefficient). The results
obtained will then be compared to numerical computations performed onto some test cases.
In order to get an approximate but robust analytical solution, it is proposed to assume an
axial symmetry and to solve the problem in the harmonic working condition before studying
the transient state
Mosquito breeding site water temperature observations and simulations towards improved vector-borne disease models for Africa
An energy budget model is developed to predict the water temperature of typical mosquito larval developmental habitats. It assumes a homogeneous mixed water column driven by empirically derived fluxes. The model shows good agreement at both hourly and daily time scales with 10-min temporal resolution observed water temperatures, monitored between June and November 2013 within a peri-urban area of Kumasi, Ghana. There was a close match between larvae development times calculated using either the model-derived or observed water temperatures. The water temperature scheme represents a significant improvement over assuming the water temperature to be equal to air temperature. The energy budget model requires observed minimum and maximum temperatures, information that is generally available from weather stations. Our results show that hourly variations in water temperature are important for the simulation of aquatic-stage development times. By contrast, we found that larval development is insensitive to sub-hourly variations. Modelling suggests that in addition to water temperature, an accurate estimation of degree-day development time is very important to correctly predict the larvae development times. The results highlight the potential of the model to predict water temperature of temporary bodies of surface water. Our study represents an important contribution towards the improvement of weather-driven dynamical disease models, including those designed for malaria early forecasting systems
Mosquito breeding site water temperature observations and simulations towards improved vector-borne disease models for Africa
An energy budget model is developed to predict the water temperature of typical mosquito larval developmental habitats. It assumes a homogeneous mixed water column driven by empirically derived fluxes. The model shows good agreement at both hourly and daily time scales with 10-min temporal resolution observed water temperatures, monitored between June and November 2013 within a peri-urban area of Kumasi, Ghana. There was a close match between larvae development times calculated using either the model-derived or observed water temperatures. The water temperature scheme represents a significant improvement over assuming the water temperature to be equal to air temperature. The energy budget model requires observed minimum and maximum temperatures, information that is generally available from weather stations. Our results show that hourly variations in water temperature are important for the simulation of aquatic-stage development times. By contrast, we found that larval development is insensitive to sub-hourly variations. Modelling suggests that in addition to water temperature, an accurate estimation of degree-day development time is very important to correctly predict the larvae development times. The results highlight the potential of the model to predict water temperature of temporary bodies of surface water. Our study represents an important contribution towards the improvement of weather-driven dynamical disease models, including those designed for malaria early forecasting systems
Role of ejecta clumping and back-reaction of accelerated cosmic rays in the evolution of Type Ia supernova remnants
We investigate the role played by initial clumping of ejecta and by efficient
acceleration of cosmic rays (CRs) in determining the density structure of the
post-shock region of a Type Ia supernova remnant (SNR) through detailed 3D MHD
modeling. Our model describes the expansion of a SNR through a magnetized
interstellar medium (ISM), including the initial clumping of ejecta and the
effects on shock dynamics due to back-reaction of accelerated CRs. The model
predictions are compared to the observations of SN 1006. We found that the
back-reaction of accelerated CRs alone cannot reproduce the observed separation
between the forward shock (FS) and the contact discontinuity (CD) unless the
energy losses through CR acceleration and escape are very large and independent
of the obliquity angle. On the contrary, the clumping of ejecta can naturally
reproduce the observed small separation and the occurrence of protrusions
observed in SN 1006, even without the need of accelerated CRs. We conclude that
FS-CD separation is a probe of the ejecta structure at the time of explosion
rather than a probe of the efficiency of CR acceleration in young SNRs.Comment: 12 pages, 11 Figures; accepted for publication on ApJ. Version with
full resolution images can be found at
http://www.astropa.unipa.it/~orlando/PREPRINTS/sorlando_clumping.pd
The Quality of Medical Care in Low-Income Countries: From Providers to Markets
Jishnu Das provides a perspective on a research article by Paul Garner and colleagues that reports a systematic review of 80 studies comparing the quality of private versus public ambulatory health care in low and middle income countries
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