649 research outputs found
Task mapping on a dragonfly supercomputer
The dragonfly network topology has recently gained traction in the design of high performance computing (HPC) systems and has been implemented in large-scale supercomputers. The impact of task mapping, i.e., placement of MPI ranks onto compute cores, on the communication performance of applications on dragonfly networks has not been comprehensively investigated on real large-scale systems. This paper demonstrates that task mapping affects the communication overhead significantly in dragonflies and the magnitude of this effect is sensitive to the application, job size, and the OpenMP settings. Among the three task mapping algorithms we study (in-order, random, and recursive coordinate bisection), selecting a suitable task mapper reduces application communication time by up to 47%
Signs of low frequency dispersions in disordered binary dielectric mixtures (50-50)
Dielectric relaxation in disordered dielectric mixtures are presented by
emphasizing the interfacial polarization. The obtained results coincide with
and cause confusion with those of the low frequency dispersion behavior. The
considered systems are composed of two phases on two-dimensional square and
triangular topological networks. We use the finite element method to calculate
the effective dielectric permittivities of randomly generated structures. The
dielectric relaxation phenomena together with the dielectric permittivity
values at constant frequencies are investigated, and significant differences of
the square and triangular topologies are observed. The frequency dependent
properties of some of the generated structures are examined. We conclude that
the topological disorder may lead to the normal or anomalous low frequency
dispersion if the electrical properties of the phases are chosen properly, such
that for ``slightly'' {\em reciprocal mixture}--when , and
--normal, and while for ``extreme'' {\em reciprocal
mixture}--when , and --anomalous
low frequency dispersions are obtained. Finally, comparison with experimental
data indicates that one can obtain valuable information from simulations when
the material properties of the constituents are not available and of
importance.Comment: 13 pages, 7 figure
On micro-structural effects in dielectric mixtures
The paper presents numerical simulations performed on dielectric properties
of two-dimensional binary composites on eleven regular space filling
tessellations. First, significant contributions of different parameters, which
play an important role in the electrical properties of the composite, are
introduced both for designing and analyzing material mixtures. Later, influence
of structural differences and intrinsic electrical properties of constituents
on the composite's over all electrical properties are investigated. The
structural differences are resolved by the spectral density representation
approach. The numerical technique, without any {\em a-priori} assumptions, for
extracting the spectral density function is also presented.Comment: 24 pages, 8 figure and 7 tables. It is submitted to IEEE Transactions
on Dielectrics and Electrical Insulatio
Extracting spectral density function of a binary composite without a-priori assumption
The spectral representation separates the contributions of geometrical
arrangement (topology) and intrinsic constituent properties in a composite. The
aim of paper is to present a numerical algorithm based on the Monte Carlo
integration and contrainted-least-squares methods to resolve the spectral
density function for a given system. The numerical method is verified by
comparing the results with those of Maxwell-Garnett effective permittivity
expression. Later, it is applied to a well-studied rock-and-brine system to
instruct its utility. The presented method yields significant microstructural
information in improving our understanding how microstructure influences the
macroscopic behaviour of composites without any intricate mathematics.Comment: 4 pages, 5 figures and 1 tabl
Neuroprotective effect of magnesium on lipid peroxidation and axonal function after experimental spinal cord injury
Study design: An experimental study examining the neuroprotective effect of magnesium on axonal function and lipid peroxidation in a rat model of acute traumatic spinal cord injury. Objective: To determine the effectiveness of postinjury treatment with magnesium on evoked potentials and lipid peroxidation after spinal cord injury (SCI). Setting: Pamukkale University, Denizli, Turkey. Methods: Spinal cord injury occurred in 30 rats with an aneurysm clip at T9 and the rats were randomly assigned to undergo subcutaneous administration of one of the following at 1 h after injury: (1) Physiological saline (n = 10); (2) MgSO4, 300 mg/kg (n = 10) and (3) MgSO4, 600 mg/kg (n = 10). Spinal somatosensory evoked potentials (SSEPs) were recorded before injury, 30 min after injury and 3 h after injections. Rats were killed 24 h after the injury, and malondialdehyde (MDA) levels were measured. Results: Following SCI, there were significant decreases in the amplitudes of P1 and N1 (P 0.001) and only high-dose magnesium improved the SSEPs (P < 0.01). On the other hand, there was significant difference in lipid peroxide content between high-dose magnesium treated group and both of saline treated and low-dose magnesium treated groups (P < 0.01). Conclusion: These results suggest that magnesium has a dose-dependent neuroprotective effect on SSEPs and lipid peroxidation after experimental spinal cord injury
Phosphorus and humic acid application alleviate salinity stress of pepper seedling
Humic acid is a commercial product that contains many elements which improve the soil fertility and increase the availability of nutrient elements. It consequently affects plant growth and yield and ameliorates the deleterious effects of salt stress. The objective of the study was to determine the effect of humic acids and phosphorus on growth and nutrient content of pepper seedlings (cv. Demre) grown under moderate salt stress in growth chamber conditions. Applications of different levels of phosphorus [0 (P0), 50 (P1), 100 (P2) and 150 (P3) mg kg-1] and humic acid [0 (HA0), 750 (HA1) and 1500 (HA2) mg kg-1] to growing media containing moderate salt dose (8 mM NaCl treatment) were studied. The study was replicated four times with 20 plants in each replicate. Humic acid (HA) and phosphorus applications increased the growth and growth parameter of plants. In company, effects of HA and P application was more effective on growth and growth parameter than each separate effect. The optimum total yield was obtained from 69 mg kg-1 P application with HA2 doses according to regression analysis. Humic acid application significantly increased N, P, K, Ca, Mg, S, Mn and Cu contents of shoot of pepper seedling. Also, N, P, K, Ca, S, Fe, Mn, Zn and Cu contents of root were increased with humic acid application. Na contents of both shoot and root of pepper decreased with increased humic acid doses. It can be concluded that high humic acid doses has positive effects on salt tolerance based on the plant growth parameters and nutrient contents. The present study suggests that HA treatments can ameliorate the deleterious effects of salt stress on pepper plants and HA could offer an economical and simple application to reduce problems of pepper production in moderately saline soil.Keywords: Nutrient uptake, plant growth parameter, salt stress, pepperAfrican Journal of Biotechnology Vol. 9(36), pp. 5845-5851, 6 September, 201
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Footprinting parallel I/O – machine learning to classify application’s I/O behavior
Fractional Equations of Curie-von Schweidler and Gauss Laws
The dielectric susceptibility of most materials follows a fractional
power-law frequency dependence that is called the "universal" response. We
prove that in the time domain this dependence gives differential equations with
derivatives and integrals of noninteger order. We obtain equations that
describe "universal" Curie-von Schweidler and Gauss laws for such dielectric
materials. These laws are presented by fractional differential equations such
that the electromagnetic fields in the materials demonstrate "universal"
fractional damping. The suggested fractional equations are common (universal)
to a wide class of materials, regardless of the type of physical structure,
chemical composition or of the nature of the polarization.Comment: 11 pages, LaTe
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Microwave absorption and radiation from large-area multilayer CVD graphene
Here we experimentally study the microwave absorption and near-field radiation behaviour of
monolayer and few-layer, large-area CVD graphene in the C and X bands. Artificial stacking of CVD graphene reduces the sheet resistance, as verified by non-contact microwave cavity
measurements and four-probe DC resistivity. The proposed multilayer stacked graphene exhibits increased absorption determined by the total sheet resistance. The underlying mechanism could enable us to apply nanoscale graphene sheets as optically transparent radar absorbers. Near-field radiation measurements show that our present few-layer graphene patches with sheet resistance more than 600 /sq exhibit no distinctive microwave resonance and radiate less electromagnetic power with increasing layers; however, our theoretical prediction suggests that for samples to be significant as microwave antennas, doped multilayer graphene with sheet resistance less than 10 /sq is required.This work was funded by the Graphene Research Centre, University of Cambridge, and the
Engineering and Physical Sciences Research Council (EPSRC), UK under a Program Grant
(EP/K01711X/1). M.T.C thanks the Winston Churchill Trust and the International Young
Scientist Research Fellowship, National Natural Science Foundation of China, for generous
financial support. B.W. acknowledges the fund support from the China Scholarship Council and National Natural Science Foundation of China No. 61271017.This is the FINAL published version, also available on the publisher's website at: http://www.sciencedirect.com/science/article/pii/S000862231400540
Seeing into a Public Cloud: Monitoring the Massachusetts Open Cloud
Abstract Cloud users today have little visibility into the performance characteristics, power consumption, and utilization of cloud resources; and the cloud has little visibility into user application performance requirements and critical metrics such as response time and throughput. This paper outlines new efforts to reduce the information gap between the cloud users and the cloud. We first present a scalable monitoring platform to collect and retain rich information on a regional public cloud. Second, we present two motivating use cases that leverage the collected information: (1) Participation in emerging smart grid demand response programs in order to reduce datacenter energy costs and stabilize power grid demands, (2) budgeting available power to applications via peak shaving. This work is done in the context of the Massachusetts Open Cloud (MOC), a new public cloud project that has a central goal of enabling cloud research
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