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Heterogeneous Nature (heterogeneous + nature)
Selected AbstractsAn EasyGrid portal for scheduling system-aware applications on computational GridsCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 6 2006C. Boeres Abstract One of the objectives of computational Grids is to offer applications the collective computational power of distributed but typically shared heterogeneous resources. Unfortunately, efficiently harnessing the performance potential of such systems (i.e. how and where applications should execute on the Grid) is a challenging endeavor due principally to the very distributed, shared and heterogeneous nature of the resources involved. A crucial step towards solving this problem is the need to identify both an appropriate scheduling model and scheduling algorithm(s). This paper presents a tool to aid the design and evaluation of scheduling policies suitable for efficient execution of system-aware parallel applications on computational Grids. Copyright © 2005 John Wiley & Sons, Ltd. [source] REVIEW: Understanding the construct of impulsivity and its relationship to alcohol use disordersADDICTION BIOLOGY, Issue 2 2010Danielle M. Dick ABSTRACT There are well-established links between impulsivity and alcohol use in humans and other model organisms; however, the etiological nature of these associations remains unclear. This is likely due, in part, to the heterogeneous nature of the construct of impulsivity. Many different measures of impulsivity have been employed in human studies, using both questionnaire and laboratory-based tasks. Animal studies also use multiple tasks to assess the construct of impulsivity. In both human and animal studies, different measures of impulsivity often show little correlation and are differentially related to outcome, suggesting that the impulsivity construct may actually consist of a number of more homogeneous (and potentially more meaningful) subfacets. Here, we provide an overview of the different measures of impulsivity used across human and animal studies, evidence that the construct of impulsivity may be better studied in the context of more meaningful subfacets, and recommendations for how research in this direction may provide for better consilience between human and animal studies of the connection between impulsivity and alcohol use. [source] A Polycrystalline Approach to the Cyclic Behaviour of f.c.c. Alloys , Intra-Granular HeterogeneityADVANCED ENGINEERING MATERIALS, Issue 9 2009Xavier Feaugas For several decades, the plastic deformation mechanisms of f.c.c. metals under cyclic loading have received considerable attention. The extensive work on this subject has gradually lead to the identification of the physical processes to be included in a formal scheme of fatigue behavior. Accordingly, we propose a review of the physical mechanisms of plastic deformation in f.c.c. metals and alloys to define the state-of-the-art and motivate future studies. The aim is to demonstrate the importance of a good knowledge of the heterogeneous nature of deformation at the intra-granular scale in defining a physical model of cyclic behavior. A large characterization of the different stages associated with the evolution of heterogeneous dislocation structures during tensile and cyclic loadings is given for an austenitic stainless steel AISI 316L. A unified view of these various structures is proposed in the form of a modified Pedersen's map [,max,=,f(,pcum), where ,max is the maximum plastic strain and ,pcum the cumulative plastic strain] in the case of tensile loading and different kinds of cyclic loading: uni-axial and multi-axial tests under stress or strain amplitude control. The specificities of each domain defined in the map are discussed in terms of long-range internal stresses in order to formalize, in a simple composite scheme, the intra-granular stress,strain field. The importance of taking into account this scheme and the nature of the different dislocations populations in a polycrystalline model is illustrated. [source] On the climate and weather of mountain and sub-arctic lakes in Europe and their susceptibility to future climate changeFRESHWATER BIOLOGY, Issue 12 2009R. THOMPSON Summary 1.,The complex terrain and heterogeneous nature of the mountain environment coupled with remoteness from major centres of human activity makes mountains challenging locations for meteorological investigations. Mountainous areas tend to have more varied and more extreme weather than lowlands. 2.,The EMERGE program has the primary aim of assessing the status of remote mountain and sub-arctic lakes throughout Europe for the first time. In this study, we describe the main features of the climate, ice-cover durations and recent temperature trends of these areas. The main weather characteristics of European mountain and sub-arctic lakes are their cold temperatures and year-round precipitation. Mean annual temperatures are generally close to 0 °C, and maximum summer temperatures reasonably close to 10 °C. 3.,Maritime versus continental settings determine the main differences in annual-temperature range among lake districts (10.5 °C in Scotland to 26.7 °C in Northern Finland), and a similar factor for ice-cover duration. Radiation ranges from low (120 W m,2) in the high latitude sub-arctic and high (237 W m,2) in the southern ranges of the Pyrenees and Rila. Similarly, precipitation is high in the main Alpine chain (250 cm year,1 in the Central Southern Alps) and low in the continental sub-arctic (65 cm year,1 in Northern Finland). 4.,The main temporal patterns in air temperature follow those of the adjacent lowlands. All the lake districts warmed during the last century. Spring temperature trends were highest in Finland; summer trends were weak everywhere; autumn trends were strongest in the west, in the Pyrenees and western Alps; while winter trends varied markedly, being high in the Pyrenees and Alps, low in Scotland and Norway and negative in Finland. 5.,Two new, limnological case studies on Lake Redon, in the Pyrenees, highlight the sensitivity of remote lakes to projected changes in the global climate. These two case studies involve close linkages between extreme chemical-precipitation events and synoptic wind-patterns, and between thermocline behaviour and features of the large-scale circulation. 6.,Individual lakes can be ultra-responsive to climate change. Even modest changes in future air temperatures will lead to major changes in lake temperatures and ice-cover duration and hence probably affect their ecological status. [source] Reconstruction of the Water Table from Self-Potential Data: A Bayesian ApproachGROUND WATER, Issue 2 2009A. Jardani Ground water flow associated with pumping and injection tests generates self-potential signals that can be measured at the ground surface and used to estimate the pattern of ground water flow at depth. We propose an inversion of the self-potential signals that accounts for the heterogeneous nature of the aquifer and a relationship between the electrical resistivity and the streaming current coupling coefficient. We recast the inversion of the self-potential data into a Bayesian framework. Synthetic tests are performed showing the advantage in using self-potential signals in addition to in situ measurements of the potentiometric levels to reconstruct the shape of the water table. This methodology is applied to a new data set from a series of coordinated hydraulic tomography, self-potential, and electrical resistivity tomography experiments performed at the Boise Hydrogeophysical Research Site, Idaho. In particular, we examine one of the dipole hydraulic tests and its reciprocal to show the sensitivity of the self-potential signals to variations of the potentiometric levels under steady-state conditions. However, because of the high pumping rate, the response was also influenced by the Reynolds number, especially near the pumping well for a given test. Ground water flow in the inertial laminar flow regime is responsible for nonlinearity that is not yet accounted for in self-potential tomography. Numerical modeling addresses the sensitivity of the self-potential response to this problem. [source] Identifying connections in a fractured rock aquifer using ADFTsGROUND WATER, Issue 3 2005Todd Halihan Fractured rock aquifers are difficult to characterize because of their extremely heterogeneous nature. Developing an understanding of fracture network hydraulic properties in these aquifers is difficult and time consuming, and field testing techniques for determining the location and connectivity of fractures in these aquifers are limited. In the Clare Valley, South Australia, well interference is an important issue for a major viticultural area that uses a fractured aquifer. Five fracture sets exist in the aquifer, all dipping >25°. In this setting, we evaluate the ability of steady-state asymmetric dipole-flow tests (ADFTs) to determine the connections between a test well and a set of piezometers. The procedure involves dividing a test well into two chambers using a single packer and pumping fluid from the upper chamber to the lower chamber. By conducting a series of tests at different packer elevations, an "input" signal is generated in fracture zones connected to the test well. By monitoring the "output" response of the hydraulic dipole field at piezometers, the connectivity of the fractures between the test well and piezometers can be determined. Results indicate the test well used in this study is connected in a complex three-dimensional geometry, with drawdown occurring above and below areas of potentiometric buildup. The ADFT method demonstrates that the aquifer evaluated in this study cannot be modeled effectively on the well scale using continuum flow models. [source] Is representative elementary area defined by a simple mixing of variable small streams in headwater catchments?HYDROLOGICAL PROCESSES, Issue 5 2010Yuko Asano Abstract The spatial variability of hydrology may decrease with an increase in catchment area as a result of mixing of numerous small-scale hydrological conditions. At some point, it is possible that a threshold area, the representative elementary area (REA), can be identified beyond which an average hydrologic response occurs. This hypothesis has been tested mainly via numerical simulations, with only a few field studies involving simple mixing. We tested this premise quantitatively using dissolved silica (SiO2) concentrations at 96 locations that included zero-order hollow discharges through sixth-order streams, collected under low-flow conditions within the 4·27-km2 Fudoji catchment. The catchment possesses a simple topography consisting almost solely of hillslopes and stream channels, uniform bedrock geology, soil type and land use in the Tanakami Mountains in central Japan. Dissolved SiO2 provides a useful tracer in hydrological studies insofar as it is responsive to flowpath depth on hillslopes of uniform geology. Our results demonstrate that even in a catchment with an almost homogeneous geology and simple topography, dissolved SiO2 concentrations in zero-order hollow discharges largely varied in space and they became similar among sampling locations with area of more than 10,1,100 km2. Relationships between stream order and standard deviation of SiO2 concentration closely matched the theoretical predictions from simple mixing of random fields. That is, our field data supported the existence of the REA and showed that the REA was produced by the simple mixing of numerous small-scale hydrological conditions. The study emphasizes the need to consider both the heterogeneous nature of small-scale hydrology and the landscape structure when assessing the characteristics of catchment runoff. Copyright © 2010 John Wiley & Sons, Ltd. [source] An optimized nested polymerase chain reaction (PCR) approach allows detection and characterization of human immunodeficiency virus type 1 (HIV-1) env and gag genes from clinical samplesJOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 2 2008Dayse Locateli Abstract The needs for development and/or improvement of molecular approaches for microorganism detection and characterization such as polymerase chain reaction (PCR) are of high interest due their sensitivity and specificity when compared to traditional microbiological techniques. Considering the worldwide importance of human immunodeficiency virus type 1 (HIV-1) infection, it is essential that such approaches consider the genetic variability of the virus, the heterogeneous nature of the clinical samples, the existence of contaminants and inhibitors, and the consequent needs for standardization in order to guarantee the reproducibility of the methods. In this work we describe a nested PCR assay targeting HIV-1 virus gag and env genes, allowing specific and sensitive diagnosis and further direct characterization of clinical samples. The method described herein was tested on clinical samples and allowed the detection of HIV-1 presence in all samples tested for the gag gene and 90.9% for the env gene, revealing sensitivities of 1,fg and 100,fg, respectively. Also, no cross-reactions were observed with DNA from infected and noninfected patients and the method allowed detection of the env and gag genes on an excess of 108 and 104 of human deoxyribonucleic acid (DNA), respectively. Furthermore, it was possible to direct sequence all amplified products, which allowed the sub typing of the virus in clinical samples. J. Clin. Lab. Anal. 22:106,113, 2008. © 2008 Wiley-Liss, Inc. [source] PERMEABILITY ANISOTROPY DISTRIBUTIONS IN AN UPPER JURASSIC CARBONATE RESERVOIR, EASTERN SAUDI ARABIAJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2007A. Sahin Most classical reservoir engineering concepts are based on homogeneous reservoirs despite the fact that homogeneous reservoirs are the exception rather than the rule. This is especially true of carbonate reservoirs in the Middle East which are known to be highly heterogeneous. The realistic petrophysical characterization of these kinds of reservoirs is not an easy task and must include the study of directional variations of permeability. Such variation can be incorporated into engineering calculations as the square root of the ratio of horizontal to vertical permeability, a parameter known as the anisotropy ratio. This paper addresses the distribution of anisotropy ratio values in an Upper Jurassic carbonate reservoir in the Eastern Province of Saudi Arabia. Based on whole core data from a number of vertical wells, statistical distributions of horizontal and vertical permeability measurements as well as anisotropy ratios were determined. The distributions of both permeability measurements and anisotropy ratios have similar patterns characterized by considerable positive skewness. The coefficients of variation for these distributions are relatively high, indicating their very heterogeneous nature. Comparison of plots of anisotropy ratios against depth for the wells and the corresponding core permeability values indicate that reservoir intervals with lower vertical permeability yield consistently higher ratios with considerable fluctuations. These intervals are represented by lower porosity mud-rich and/or mud-rich/granular facies. Granular facies, on the other hand, yielded considerably lower ratios without significant fluctuations. [source] Genetic characterization of spoilage pseudomonads isolated from retail-displayed beefLETTERS IN APPLIED MICROBIOLOGY, Issue 3 2008M. Aslam Abstract Aim:, This study genetically characterized Pseudomonas isolated from beef using the random amplification of polymorphic DNA (RAPD) method and correlate predominant genotypes with spoilage changes. Methods and Results:, Pseudomonads were recovered from beef loins and steaks on days 0, 2, 4, 6, 8 and 10. A total of 309 pseudomonads were grouped into 50 RAPD types (>85% similarity). One major RAPD type contained 45% of the isolates comprising 71%, 45%, 31%, 35%, 50% and 37% of isolates from days 0, 2, 4, 6, 8 and 10, respectively, from steaks and 48% of the isolates recovered from beef loins. Nineteen RAPD types consisted of isolates that were shared between more than two sampling times, whereas the remaining 31 types were unique to one particular time. Conclusions:, A genetically diverse Pseudomonas population was present on the loins and steaks at each sampling time. Although pseudomonads associated with beef loins were transferred to the steaks prepared from it, a genetically diverse Pseudomonas population emerged during the retail display. Significance and Impact of the Study:, Information about the heterogeneous nature of Pseudomonas recovered from meat would help understanding the spoilage owing to predominant strains. The meat industry can use the knowledge to develop control strategies for prevalent spoilage strains. [source] Time evolution and temperatures of hypervelocity impact-generated tracks in aerogelMETEORITICS & PLANETARY SCIENCE, Issue 10 2009Gerardo Dominguez Due to the fragile and heterogeneous nature of cometary dust grains, their fragments are found along the walls of tracks that are formed during the capture process. These fragments appear to experience a wide range of thermal alteration and the causes of this variation are not well understood at a theoretical level as physical models of track formation are not well developed. Here, a general model of track formation that allows for the existence of partially and completely vaporized aerogel material in tracks is developed. It is shown that under certain conditions, this general track model reduces to the kinetic "snowplow" model that has previously been proposed. It is also shown, based on energetic considerations, that track formation is dominated by an expansion that is snowplow-like in the later stages of track formation. The equation of motion for this snowplow-like stage can be solved analytically, thus placing constraints on the amount of heating experienced by cometary dust fragments embedded in track walls. It is found that the heating of these fragments, for a given impact velocity, is expected to be greater for those embedded in larger tracks. Given the expected future use of aerogels for sample return missions, the results presented here imply that the choice of aerogel compositions can have a significant effect on the modification of samples captured and retrieved by these collectors. [source] Histologic classification of ductal carcinoma in situMICROSCOPY RESEARCH AND TECHNIQUE, Issue 2 2002Shabnam Jaffer Abstract Prior to the current mammographic era, ductal carcinoma in situ (DCIS) usually presented as a large mass, was classified morphologically by architecture, and treated by mastectomy. The introduction of screening mammography led to an increase in the incidence of DCIS, a decrease in the average size of DCIS, and an increased emphasis on its heterogeneous nature. Thus, a reproducible and prognostically relevant classification system for DCIS is necessary. The ultimate goal of this classification is proper selection of patients for whom lumpectomy would suffice rather than mastectomy. Features to evaluate include: extent and size of disease, adequacy of resection margins, and histology. While none of the proposed histological classification systems were endorsed at the recent Consensus Conference on the Classification of DCIS, nuclear grade was the most important feature common to most of them. Architecture was given secondary importance. By definition, DCIS is a non-invasive clonal proliferation of epithelial cells originating in the terminal duct lobular unit, which would be expected to be monomorphic; however, it is the degree of nuclear pleomorphism that is primarily used to separate DCIS into low, intermediate, and high grades. Architecturally, DCIS has been divided into the following types: comedo, solid, cribriform, micropapillary, and papillary. Different architectural patterns and grades may be present in a given particular case; however, some combinations of patterns occur more frequently than others. Interobserver studies have shown nuclear grading to be interpreted with greater consistency than architecture, and nuclear grading methods have correlated with biological and molecular marker studies. Microsc. Res. Tech. 59:92,101, 2002. © 2002 Wiley-Liss, Inc. [source] When does Parkinson's disease begin?,MOVEMENT DISORDERS, Issue S2 2009Carles Gaig MD Abstract Pathological and neuroimaging studies have shown that in Parkinson's disease (PD) there is a "subclinical" or "premotor" period during which dopaminergic neurons in the substantia nigra (SN) degenerate but typical motor symptoms have not yet developed. Post-mortem studies based on nigral cell counts and evaluating dopamine levels in the striata, and imaging studies assessing the nigrostriatal pathway in vivo, have estimated that this time period could last 3 to 6 years. In addition, emerging evidence indicates that the neuropathological process of PD does not start in the SN but more likely elsewhere in the nervous system: in the lower brainstem and the olfactory bulb, or even more distant from the SN, such as in the peripheral autonomic nervous system. Patients with PD frequently can present non-motor symptoms, such as hyposmia or constipation, years before the development of classical motor signs. The physiopathology of these "premotor" symptoms, though still unclear, is currently thought to be related to early involvement by the pathological process underlying PD of non-dopaminergic lower brainstem structures or autonomic plexuses. However, the answer to the question "when does PD start" remains uncertain. Here, we review clinical, pathological, and neuroimaging data related to the onset of the pathological process of PD, and propose that its onset is non-motor and that non-motor symptoms could begin in many instances 10 and 20 years before onset of motor symptoms. The variable course of the disorder once the motor symptoms develop, suggests that the start and progression of premotor PD is also highly variable andgiven the heterogeneous nature of PD, may differ depending on the cause/s of the syndrome. When and where the neuropathological process develops in PD remains uncertain. © 2009 Movement Disorder Society [source] Taxonomy of pain. (Lehigh Valley Hospital, Center for Pain Management, Allentown, PA) Clin J Pain 2000;16:S114,S117.PAIN PRACTICE, Issue 2 2001Bruce Nicholson: This article discussed the way that research on the pathophysiology of chronic pain has started to challenge the traditional diagnostic and treatment paradigms for the patient with neuropathic pain. It stated that the heterogeneous nature of neuropathic pain indicated that more than one anatomic lesion is most likely responsible for the clinical presentation of a particular syndrome. Conclude that the current taxonomy often falls short of identifying the multifactorial nature of neuropathic pain syndromes and, therefore, may lead to imprecise management of those conditions. It is suggested that an integrated approach to the diagnosis and treatment of neuropathic pain that considers both etiologic factors and possible mechanisms will lead to more effective taxonomy, treatment paradigms, and outcomes. [source] U-Statistics-based Tests for Multiple Genes in Genetic Association StudiesANNALS OF HUMAN GENETICS, Issue 6 2008Zhi Wei Summary As our understanding of biological pathways and the genes that regulate these pathways increases, consideration of these biological pathways has become an increasingly important part of genetic and molecular epidemiology. Pathway-based genetic association studies often involve genotyping of variants in genes acting in certain biological pathways. Such pathway-based genetic association studies can potentially capture the highly heterogeneous nature of many complex traits, with multiple causative loci and multiple alleles at some of the causative loci. In this paper, we develop two nonparametric test statistics that consider simultaneously the effects of multiple markers. Our approach, which is based on data-adaptive U-statistics, can handle both qualitative data such as case-control data and quantitative continuous phenotype data. Simulations demonstrate that our proposed methods are more powerful than standard methods, especially when there are multiple risk loci each with small genetic effects. When the number of disease-predisposing genes is small, the data-adaptive weighting of the U-statistics over all the markers produces similar power to commonly used single marker tests. We further illustrate the potential merits of our proposed tests in the analysis of a data set from a pathway-based candidate gene association study of breast cancer and hormone metabolism pathways. Finally, potential applications of the proposed tests to genome-wide association studies are also discussed. [source] Mitochondrial Membrane Potential Selects Hybridomas Yielding High Viability in Fed-Batch CulturesBIOTECHNOLOGY PROGRESS, Issue 1 2002Brian D. Follstad Prior research (Follstad, B. D.; Wang, D. I. C.; Stephanopoulos, G. Mitochondrial membrane potential differentiates cells resistant to apoptosis in hybridoma cultures. Eur. J. Biochem. 2000, 267, 6534,6540.) identified mitochondrial membrane potential (MMP) as a marker of hybridoma subpopulations resistant to apoptosis caused by a variety of apoptosis inducers. In this study, we investigated the viability of hybridoma cell cultures inoculated with cells of varying MMP in regular fed-batch operation. A hybridoma cell population was separated using FACS into subpopulations based on their mean mitochondrial membrane potential (MMP) as measured using the common mitochondrial stain, Rhodamine 123 (Rh123). These subpopulations showed dramatic differences in their apoptotic death kinetics. Fed-batches inoculated with a high MMP subpopulation reached higher viable cell concentrations and viabilities that were maintained for prolonged periods of time relative to fed-batches inoculated with low MMP subpopulations. These results underline the heterogeneous nature of hybridoma cell cultures and suggest that mitochondrial physiology is a critical parameter determining culture performance. [source] | ||||||||||||||||