Optimum Number (optimum + number)

Distribution by Scientific Domains


Selected Abstracts


Optimizing the point spread function in phase-encoded magnetic resonance microscopy

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2004
A.G. Webb
Abstract Three-dimensional phase-encoded magnetic resonance microscopy is the most promising method for obtaining images with isotropic spatial resolutions on the order of a few micrometers. The attainable spatial resolution is limited by the available gradient strength (Gmax) and the molecular self-diffusion coefficient (D) of the sample. In this study, numerical simulations in the microscopic-size regime are presented in order to show that for given values of Gmax and D, there exists an optimum number of phase-encoding steps that maximize the spatial resolution in terms of minimizing the full-width at half-maximum (FWHM) of the image point spread function (PSF). Unlike the case of "macroscopic" imaging, in which diffusion plays an insignificant role in determining spatial resolution, acquiring data beyond this optimal value actually degrades the image PSF. An alternative version of phase encoding, using a variable phase-encoding time rather than a variable gradient strength, is analyzed in terms of improvements in the image PSF and/or reductions in the data acquisition time for a given spatial resolution. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 22A: 25,36, 2004. [source]


Optimization of ordered distance sampling,

ENVIRONMETRICS, Issue 2 2004
Ryan M. Nielson
Abstract Ordered distance sampling is a point-to-object sampling method that can be labor-efficient for demanding field situations. An extensive simulation study was conducted to find the optimum number, g, of population members to be encountered from each random starting point in ordered distance sampling. Monte Carlo simulations covered 64 combinations of four spatial patterns, four densities and four sample sizes. Values of g from 1 to 10 were considered for each case. Relative root mean squared error (RRMSE) and relative bias were calculated for each level of g, with RRMSE used as the primary assessment criterion for finding the optimum level of g. A non-parametric confidence interval was derived for the density estimate, and this was included in the simulations to gauge its performance. Superior estimation properties were found for g > 3, but diminishing returns, relative to the potential for increased effort in the field, were found for g > 5. The simulations showed noticeable diminishing returns for more than 20 sampled points. The non-parametric confidence interval performed well for populations with random, aggregate or double-clumped spatial patterns, but rarely came close to target coverage for populations that were regularly distributed. The non-parametric confidence interval presented here is recommended for general use. Copyright © 2004 John Wiley & Sons, Ltd. [source]


ON THE EVOLUTION OF DIFFERENTIATED MULTICELLULARITY

EVOLUTION, Issue 2 2009
Martin Willensdorfer
Most conspicuous organisms are multicellular and most multicellular organisms develop somatic cells to perform specific, nonreproductive tasks. The ubiquity of this division of labor suggests that it is highly advantageous. In this article I present a model to study the evolution of specialized cells. The model allows for unicellular and multicellular organisms that may contain somatic (terminally differentiated) cells. Cells contribute additively to a quantitative trait. The fitness of the organism depends on this quantitative trait (via a benefit function), the size of the organism, and the number of somatic cells. The model allows one to determine when somatic cells are advantageous and to calculate the optimum number (or fraction) of reproductive cells. I show that the fraction of reproductive cells is always surprisingly high. If somatic cells are very small, they can outnumber reproductive cells but their biomass is still less than the biomass of reproductive cells. I discuss the biology of primitive multicellular organisms with respect to the model predictions. I find a good agreement and outline how this work can be used to guide further quantitative studies of multicellularity. [source]


Streamflow estimation using optimal regional dependency function

HYDROLOGICAL PROCESSES, Issue 25 2009
Abdüsselam Altunkaynak
Abstract The determination of spatial dependency of regionalized variable (ReV) is important in engineering studies. Regional dependency function that leads to calculation of weighting coefficients is required in order to make regional or point-wise estimations. After obtaining this dependency function, it is possible to complete missing records in the time series and locate new measurement station. Also determination of regional dependency function is also useful to understand the regional variation of ReV. Point Cumulative Semi-Variogram (PCSV) is another methodology to understand the regional dependency of ReV related to the magnitude and the location. However, this methodology is not useful to determine the weighting coefficient, which is required to make regional and point-wise estimations. However, in Point Semi-Variogram (PSV) proposed here, weighting coefficient depends on both magnitude and location. Although the regional dependency function has a fluctuating structure in PSV approach, this function gradually increases with distance in PCSV. The study area is selected in Mississippi river basin with 38 streamflow stations used for PCSV application before. It is aimed to compare two different geostatistical models for the same data set. PSV method has an ability to determine the value of variable along with optimum number of neighbour stations and influence radius. PSV and slope PSV approaches are compared with the PCSV. It was shown that slope slope point semi-variogram (SPSV) approaches had relative error below 5%, and PSV and PCSV methods revealed relative errors below 10%. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Rainfall network design using kriging and entropy

HYDROLOGICAL PROCESSES, Issue 3 2008
Yen-Chang Chen
Abstract The spatial distribution of rainfall is related to meteorological and topographical factors. An understanding of the weather and topography is required to select the locations of the rain gauge stations in the catchment to obtain the optimum information. In theory, a well-designed rainfall network can accurately represent and provide the needed information of rainfall in the catchment. However, the available rainfall data are rarely adequate in the mountainous area of Taiwan. In order to provide enough rainfall data to assure the success of water projects, the rainfall network based on the existing rain gauge stations has to be redesigned. A method composed of kriging and entropy that can determine the optimum number and spatial distribution of rain gauge stations in catchments is proposed. Kriging as an interpolator, which performs linear averaging to reconstruct the rainfall over the catchment on the basis of the observed rainfall, is used to compute the spatial variations of rainfall. Thus, the rainfall data at the locations of the candidate rain gauge stations can be reconstructed. The information entropy reveals the rainfall information of the each rain gauge station in the catchment. By calculating the joint entropy and the transmitted information, the candidate rain gauge stations are prioritized. In addition, the saturation of rainfall information can be used to add or remove the rain gauge stations. Thus, the optimum spatial distribution and the minimum number of rain gauge stations in the network can be determined. The catchment of the Shimen Reservoir in Taiwan is used to illustrate the method. The result shows that only seven rain gauge stations are needed to provide the necessary information. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Design techniques of two-layer architectures for WDM optical networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2001
Andrea Borella
Abstract A general method for designing multilayered WDM optical networks, based on the combined use of single-and multi-hop connection modes, is presented. It takes into account variable values for the number of users and wavelengths in each cluster. Closed form expressions are derived for the transmission capacity and the optimum number of channels for intra-cluster communications, either in the case of uniform or non-uniform traffic distribution. The analytical approach is particularly useful in the presence of constraints on the number of wavelengths, due to technological limits or non-linear phenomena, when sub-optimal solutions must be necessarily addressed. The proposed method is integrated with the adoption of well-known selection procedures, like simulated annealing or genetic algorithms, to reduce the computational effort. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Second law analysis of hydrogen liquefiers operating on the modified Collins cycle

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2001
M. T. Syed
Abstract Hydrogen liquefaction systems have been the subject of intense investigations for many years. Some established gas liquefaction systems, such as the precooled Linde,Hampson systems, are not used for hydrogen liquefaction in part because of their relatively low efficiencies. Recently, more promising systems employing the modified Collins cycle have been introduced. This paper reports on second law analyses of a hydrogen liquefier operating on the modified Collins cycle. Two different modifications employing the cycle in question were attempted: (1) a helium-refrigerated hydrogen liquefaction system and (2) a hydrogen-refrigerated hydrogen liquefaction system. Analyses were carried out in order to identify potential areas of development and efficiency improvement. A computer code capable of computing system and component efficiencies; exergy losses; and optimum number and operating conditions of compressors, expanders, aftercoolers, intercoolers, and Joule,Thomson valves was developed. Evaluation of the thermodynamic and transport properties of hydrogen at different temperature levels was achieved by employing a hydrogen property code developed by researchers at the National Bureau of Standards (currently NIST). A parametric analysis was carried out and optimal decision rules pertaining to system component selection and design were reached. Economic analyses were also reported for both systems and indicated that the helium-refrigerated hydrogen liquefier is more economically feasible than the hydrogen-refrigerated hydrogen liquefier. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Branch Network and Modular Service Optimization for Community Banking

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2002
G. Ioannou
In the information society, what is clearly changing is the role and image of bank branches in order to satsify in a more efficient way customers' needs. This paper develops an integrated approach to assist the bank's management in reconfiguring a branch network according to the dictates of the market. We are seeking the optimum number of branches and the optimum mix of services that each branch should offer in order to maximize the revenue,generating measures of the branches within a community. The problem is modeled using a linear program that accounts for community performance as a function of performance variables that are explained by a set of external and internal factors, which reflect community characteristics and modular branch banking parameters, respectively. The relationships between factor and performance variables are identified using regression analysis. An iterative algorithm allows convergence to a solution that provides the best configuration of branches after all possible branch mergers and modular branch adjustments are accomplished. [source]


OPTIMIZATION CRITERIA FOR BATCH RETORT BATTERY DESIGN AND OPERATION IN FOOD CANNING-PLANTS

JOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2003
R. SIMPSON
ABSTRACT Optimization of thermal processing in the commercial sterilization of canned foods is of great interest because the canning industry plays an important role within the economy of the food processing sector. Many food canning plants operate in a batch mode with a battery of individual batch retorts. The aim of this study was to propose and analyze several criteria and methodologies for optimum design and operation of such retort systems. Two criteria were proposed in the case of choosing the optimum number of retorts to be installed when designing a new batch-operated canning line. The third criterion dealt with seeking optimum process conditions for maximizing output from a fixed number of retorts when processing small batches of different products and container sizes. In the case of new plant design optimization, one objective was to determine the optimum number of retorts that would minimize on-going processing costs related to labor and energy. Retort scheduling (programming) was studied from which a simple mathematical expression was derived for this purpose. A second objective was to determine the optimum number of retorts that would maximize the net present value of initial investment. Approaches based upon engineering economics were studied from which to develop a mathematical procedure for this purpose. In the case of maximizing output from a fixed number of retorts for different products and container sizes, isolethal processes were identified for various product/containers from which a common set of process conditions could be chosen for simultaneous processing of different product lots in the same retort. [source]


Disjunctive optimization design models for complex liquid,liquid multistage extractors

AICHE JOURNAL, Issue 10 2001
Juan A. Reyes-Labarta
A new method for the optimal design of multicomponent liquid,liquid extraction processes using multistage countercurrent extractor systems is proposed. The method determines the optimum number of equilibrium stages and flow rates needed to obtain a specified product separation and recovery, and accounts for the possibility of side feed streams and product extractions. A superstructure is proposed that has embedded all potential configurations and interconnections. Based on this superstructure representation, the problem is formulated as an optimization problem using generalized disjunctive programming (GDP) to minimize the total cost of the process, subject to design specifications. The robustness and computational efficiency of the model is illustrated with different cases involving single and complex countercurrent cascades in a quaternary liquid,liquid system. [source]


Rapid diversification of mating systems in ciliates

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009
SUJAL S. PHADKE
Ciliates are a diverse group of microbial eukaryotes that exhibit tremendous variety in several aspects of their mating systems. To understand the evolutionary forces driving mating system diversification in ciliates, we use a comparative approach synthesizing data from many ciliate species in light of recent phylogenetic analyses. Specifically, we investigate the evolution of number of mating types, mode of mating type inheritance, and the molecular determinants of mating types across the taxonomic diversity of ciliates, with an emphasis on three well-studied genera: Tetrahymena, Paramecium, and Euplotes. We find that there have been many transitions in the number of mating types, and that the requirement of nuclear reorganization may be a more important factor than genetic exchange in determining the optimum number of mating types in a species. We also find that the molecular determinants of mating types and mode of inheritance are evolving under different constraints in different lineages of ciliates. Our results emphasize the need for further detailed examination of mating systems in understudied ciliate lineages. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 187,197. [source]


Laser-capture microdissection in prostate cancer research: establishment and validation of a powerful tool for the assessment of tumour,stroma interactions

BJU INTERNATIONAL, Issue 6 2008
Chitranjan J. Shukla
OBJECTIVES To describe our experience with the optimization and validation of laser-capture microdissection (LCM) for biomarker analysis in prostate tissues. As LCM allows the separation of benign and malignant epithelial structures and stromal elements, it not only allows identification of the source of the biomarker, but might also accentuate gene or protein expression changes by reducing contamination by other cellular elements. MATERIALS AND METHODS In all, 19 fresh-frozen prostate tissue samples were subjected to LCM, with the cDNA being analysed using quantitative polymerase chain reaction for several genes, to identify the optimum number of cells for capture, as well as gene markers assessing for the purity of the captured cells. The localization was further confirmed by in situ hybridization. RESULTS Prostate-specific antigen (PSA) and cytokeratin 8, were expressed solely by epithelial cells, whereas hepatocyte growth factor (HGF) and tissue inhibitor of metalloproteinases-3 (TIMP3) were expressed only by stromal cells, and the levels of transcripts of these genes were unaltered between benign and malignant tissues. CONCLUSIONS These data suggest that PSA, cytokeratin 8, HGF and TIMP3 are reliable gene markers of purity of epithelial and stromal compartments for LCM of prostate tumours. Although this technique is not new and is increasingly used in laboratories, it needs optimization and stringent validation criteria before data analysis. This applies to all tissue types subjected to LCM. [source]