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Non-uniform Distribution (non-uniform + distribution)
Selected AbstractsImplementing quality control on a random number stream to improve a stochastic weather generator,,HYDROLOGICAL PROCESSES, Issue 8 2008Charles R. Meyer Abstract For decades, stochastic modellers have used computerized random number generators to produce random numeric sequences fitting a specified statistical distribution. Unfortunately, none of the random number generators we tested satisfactorily produced the target distribution. The result is generated distributions whose mean even diverges from the mean used to generate them, regardless of the length of run. Non-uniform distributions from short sequences of random numbers are a major problem in stochastic climate generation, because truly uniform distributions are required to produce the intended climate parameter distributions. In order to ensure generation of a representative climate with the stochastic weather generator CLIGEN within a 30-year run, we tested the climate output resulting from various random number generators. The resulting distributions of climate parameters showed significant departures from the target distributions in all cases. We traced this failure back to the uniform random number generators themselves. This paper proposes a quality control approach to select only those numbers that conform to the expected distribution being retained for subsequent use. The approach is based on goodness-of-fit analysis applied to the random numbers generated. Normally distributed deviates are further tested with confidence interval tests on their means and standard deviations. The positive effect of the new approach on the climate characteristics generated and the subsequent deterministic process-based hydrology and soil erosion modelling are illustrated for four climatologically diverse sites. Copyright © 2007 John Wiley & Sons, Ltd. [source] Strengthening of moment-resisting frame structures against near-fault ground motion effectsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 6 2004Babak Alavi Abstract Near-fault ground motions with forward directivity are characterized by a large pulse. This pulse-like motion may cause a highly non-uniform distribution of story ductility demands for code-compliant frame structures, with maximum demands that may considerably exceed the level of code expectations. Strengthening techniques for multi-story frame structures are explored with the objective of reducing maximum drift demands. One option is to modify the code-based SRSS distribution of story shear strength over the height by strengthening of the lower stories of the frame. The modified distribution reduces the maximum story ductility demand, particularly for weak and flexible structures. However, this strengthening technique is less effective for stiff structures, and is almost ineffective in cases in which the maximum demand occurs in the upper stories, i.e. strong and flexible structures. As an alternative, the benefits of strengthening frames with elastic and inelastic walls are evaluated. The effects of adding walls that are either fixed or hinged at the base are investigated. It is demonstrated that strengthening with hinged walls is very effective in reducing drift demands for structures with a wide range of periods and at various performance levels. Wall inelastic behavior only slightly reduces the benefits of strengthening with hinged walls.Copyright © 2004 John Wiley & Sons, Ltd. [source] Transverse imaging and simulation of dsDNA electrophoresis in microfabricated glass channelsELECTROPHORESIS, Issue 23 2008Ramsey I. Zeitoun Abstract We have observed the non-uniform distribution of DNA molecules during PAGE in a microfabricated system. Confocal laser scanning microscopy was used to visualize fluorescently labeled DNA during electrophoretic migration. The distribution of double-stranded DNA larger than 100,bp is observed to transition from a center-biased motion on the transverse plane 1,cm downstream from injection to an edge-biased motion 2,cm downstream. Although this distribution increased with increasing dsDNA size in a cross-linked gel, no similar distribution was found with the same dsDNA molecules in a linear polyacrylamide solution (6%). Simulations of DNA distribution in gels suggest that DNA distribution non-uniformities may be caused by biased electrophoretic migration resulting from motion in an inhomogeneous gel system. [source] Case-control association testing in the presence of unknown relationshipsGENETIC EPIDEMIOLOGY, Issue 8 2009Yoonha Choi Abstract Genome-wide association studies result in inflated false-positive results when unrecognized cryptic relatedness exists. A number of methods have been proposed for testing association between markers and disease with a correction for known pedigree-based relationships. However, in most case-control studies, relationships are generally unknown, yet the design is predicated on the assumption of at least ancestral relatedness among cases. Here, we focus on adjusting cryptic relatedness when the genealogy of the sample is unknown, particularly in the context of samples from isolated populations where cryptic relatedness may be problematic. We estimate cryptic relatedness using maximum-likelihood methods and use a corrected ,2 test with estimated kinship coefficients for testing in the context of unknown cryptic relatedness. Estimated kinship coefficients characterize precisely the relatedness between truly related people, but are biased for unrelated pairs. The proposed test substantially reduces spurious positive results, producing a uniform null distribution of P -values. Especially with missing pedigree information, estimated kinship coefficients can still be used to correct non-independence among individuals. The corrected test was applied to real data sets from genetic isolates and created a distribution of P -value that was close to uniform. Thus, the proposed test corrects the non-uniform distribution of P -values obtained with the uncorrected test and illustrates the advantage of the approach on real data. Genet. Epidemiol. 33:668,678, 2009. © 2009 Wiley-Liss, Inc. [source] Non-isothermal multi-phase modeling of PEM fuel cell cathodeINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2010Nada Zamel Abstract In this study, numerical simulation has been carried out for the heat transfer and temperature distribution in the cathode of polymer electrolyte membrane fuel cells along with the multi-phase and multi-species transport under the steady-state condition. The commercial software, COMSOL Multiphysics, is used to solve the conservation equations for momentum, mass, species, charge and energy numerically. The conservation equations are applied to the solid, liquid and vapor phases in the bipolar plate and gas diffusion (GDL) and catalyst layers of a two-dimensional cross section of the cathode. The catalyst layer is assumed to be a finite domain and the water production in the catalyst layer is considered to be in the liquid form. The temperature distribution in the cathode is simulated and then the effects of the relative humidity of the air stream, the permeability of the cathode and the flow channel shoulder to channel width ratio are investigated. It is shown that the highest temperature change, both in the in-plane and across-the-plane directions, occurs in the GDL, while the highest temperature is reached in the catalyst layer. The distribution of temperature in the bipolar plate is shown to be relatively uniform due to the high thermal conductivity of the plate. A decrease in the inlet relative humidity of the air stream results in the decrease of the maximum temperature due to the absorption of heat during the evaporation of liquid water in the GDL and catalyst layer. The non-uniformity of the temperature distribution, especially in the catalyst layer, is observed with the increase of the permeability of the cathode. Similarly, the decrease of the channel shoulder to channel width ratio leads to a non-uniform distribution of temperature especially under the channel areas. Copyright © 2009 John Wiley & Sons, Ltd. [source] Flavour retention during high temperature short time extrusion cooking process: a reviewINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2001Bhesh Bhandari Research on the stability of flavours during high temperature extrusion cooking is reviewed. The important factors that affect flavour and aroma retention during the process of extrusion are illustrated. A substantial number of flavour volatiles which are incorporated prior to extrusion are normally lost during expansion, this is because of steam distillation. Therefore, a general practice has been to introduce a flavour mix after the extrusion process. This extra operation requires a binding agent (normally oil), and may also result in a non-uniform distribution of the flavour and low oxidative stability of the flavours exposed on the surface. Therefore, the importance of encapsulated flavours, particularly the ,-cyclodextrin-flavour complex, is highlighted in this paper. [source] Biases in the polarization position angles in the NRAO-VLA sky survey point source catalogueMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008R. A. Battye ABSTRACT We have examined the statistics of the polarization position angles determined for point sources in the NRAO-VLA Sky Survey (NVSS), and find that there is a statistically significant bias towards angles which are multiples of 45°. The formal probability that the polarization angles are drawn from a uniform distribution is exponentially small. When the sample of those NVSS sources with polarizations detected with a signal-to-noise ratio ,3 is split either around the median polarized flux density or the median fractional polarization, the effect appears to be stronger for the more highly polarized sources. Regions containing strong sources and regions at low-Galactic latitudes are not responsible for the non-uniform distribution of position angles. We identify clean bias as the probable cause of the dominant effect, coupled with small multiplicative and additive offsets on each of the Stokes parameters. Our findings have implications for the extraction of science, such as information concerning galactic magnetic fields, from large-scale polarization surveys. [source] Electrical and optical properties of thick highly doped p-type GaN layers grown by HVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008A. Usikov Abstract In this paper we report 3-7 ,m thick p-GaN growth by hydride vapor phase epitaxy (HVPE) on sapphire substrates. Mg impurity was used for doping. As-grown GaN layers had p-type conductivity with concentration NA -ND up to 3×1019 cm,3. Mg atom concentration was varied from 1017 to 1020 cm,3. Hydrogen concentration was about 10 times less than that for Mg, which may explain effective p-type doping for as-grown GaN layers. Micro-cathodoluminescence revealed a columnar-like structure of the GaN layers with a non-uniform distribution of material regions having dominant 362 nm or 430 nm luminescence. Use of these thick p-GaN layers to grow InGaN-based blue and green LEDs by the HVPE is demonstrated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electroluminescence uniformity in green LEDs and dual color blue/green stacking LEDsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Grigory Onushkin Abstract The uniformity of Electroluminescence (EL) of green and blue/green stacking InGaN Light Emitting Diodes (LED) has been studied and analyzed by various techniques. Comparative measurements of Photo-Luminescence (PL), Cathode-Luminescence (CL) and EL allow us to conclude that non-uniform distribution of EL in studied LEDs is caused by non-uniformity of acceptors distribution over the p-GaN area. It was found that there are some defective areas in p-GaN having locally low level of acceptor concentration. These areas correspond to the surface hexagonal shaped pyramids on p-GaN surface. The locally low doping level changes the field distribution, injection properties and the EL emission properties for these defective points. Optimization of p-GaN growth conditions will improve the EL uniformity and increase the efficiency of green and blue/green LEDs. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A finite element algorithm for parameter identification of material models for fluid saturated porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2001R. Mahnken Abstract In this contribution an algorithm for parameter identification of geometrically linear Terzaghi,Biot-type fluid-saturated porous media is proposed, in which non-uniform distributions of the state variables such as stresses, strains and fluid pore pressure are taken into account. To this end a least-squares functional consisting of experimental data and simulated data is minimized, whereby the latter are obtained with the finite element method. This strategy allows parameter identification based on in situ experiments. In order to improve the efficiency of the minimization process, a gradient-based optimization algorithm is applied, and therefore the corresponding sensitivity analysis for the coupled two-phase problem is described in a systematic manner. For illustrative purpose, the performance of the algorithm is demonstrated for a slope stability problem, in which a quadratic Drucker,Prager plasticity model for the solid and a linear Darcy law for the fluid are combined. Copyright © 2001 John Wiley & Sons, Ltd. [source] Closed-form minimax time-delay filters for underdamped systemsOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 3 2007Tarunraj Singh Abstract This paper derives closed-form solutions for the parameters of a time-delay filter designed to be robust to uncertainties in frequencies to be cancelled. It is shown that the slope of the magnitude plot of the two time-delay filter is zero at the nominal frequency indicating that it is a local maximum. This information is used for deriving the solution of the parameters of the time-delay filter in closed form. Three time-delay filters are also designed which force a zero of the filter to be located at the nominal frequency of the system. Uniform and non-uniform distributions of the penalty over the uncertain regions are permitted in this formulation. The applicability of the proposed technique for the control of multi-mode systems is also illustrated. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||||||||