Good Compromise (good + compromise)

Distribution by Scientific Domains

Selected Abstracts

A comparative study of GLS finite elements with velocity and pressure equally interpolated for solving incompressible viscous flows

Yongtao Wei
Abstract A comparative study of the bi-linear and bi-quadratic quadrilateral elements and the quadratic triangular element for solving incompressible viscous flows is presented. These elements make use of the stabilized finite element formulation of the Galerkin/least-squares method to simulate the flows, with the pressure and velocity fields interpolated with equal orders. The tangent matrices are explicitly derived and the Newton,Raphson algorithm is employed to solve the resulting nonlinear equations. The numerical solutions of the classical lid-driven cavity flow problem are obtained for Reynolds numbers between 1000 and 20 000 and the accuracy and converging rate of the different elements are compared. The influence on the numerical solution of the least square of incompressible condition is also studied. The numerical example shows that the quadratic triangular element exhibits a better compromise between accuracy and converging rate than the other two elements. Copyright 2008 John Wiley & Sons, Ltd. [source]

Using evidence for population stratification bias in combined individual- and family-level genetic association analyses of quantitative traits

Lucia Mirea
Abstract Genetic association studies are generally performed either by examining differences in the genotype distribution between individuals or by testing for preferential allele transmission within families. In the absence of population stratification bias (PSB), integrated analyses of individual and family data can increase power to identify susceptibility loci [Abecasis et al., 2000. Am. J. Hum. Genet. 66:279,292; Chen and Lin, 2008. Genet. Epidemiol. 32:520,527; Epstein et al., 2005. Am. J. Hum. Genet. 76:592,608]. In existing methods, the presence of PSB is initially assessed by comparing results from between-individual and within-family analyses, and then combined analyses are performed only if no significant PSB is detected. However, this strategy requires specification of an arbitrary testing level ,PSB, typically 5%, to declare PSB significance. As a novel alternative, we propose to directly use the PSB evidence in weights that combine results from between-individual and within-family analyses. The weighted approach generalizes previous methods by using a continuous weighting function that depends only on the observed P -value instead of a binary weight that depends on ,PSB. Using simulations, we demonstrate that for quantitative trait analysis, the weighted approach provides a good compromise between type I error control and power to detect association in studies with few genotyped markers and limited information regarding population structure. Genet. Epidemiol. 34: 502,511, 2010. 2010 Wiley-Liss, Inc. [source]

Transition Metal Borides: Superhard versus Ultra-incompressible,

Qinfen Gu
Borides of several heavy transition metals have been synthesized by arc melting at ambient pressure. The materials are characterized by either low compressibility or high hardness, some of them showing a good compromise between both properties. The structure,property relationship is revealed based on their crystal structures and a chemical bonding analysis by means of the electron localization function. [source]

Identification of autoregressive models in the presence of additive noise

Roberto Diversi
Abstract A common approach in modeling signals in many engineering applications consists in adopting autoregressive (AR) models, consisting in filters with transfer functions having a unitary numerator, driven by white noise. Despite their wide application, these models do not take into account the possible presence of errors on the observations and cannot prove accurate when these errors are significant. AR plus noise models constitute an extension of AR models that consider also the presence of an observation noise. This paper describes a new algorithm for the identification of AR plus noise models that is characterized by a very good compromise between accuracy and efficiency. This algorithm, taking advantage of both low and high-order Yule,Walker equations, also guarantees the positive definiteness of the autocorrelation matrix of the estimated process and allows to estimate the equation error and observation noise variances. It is also shown how the proposed procedure can be used for estimating the order of the AR model. The new algorithm is compared with some traditional algorithms by means of Monte Carlo simulations. Copyright 2007 John Wiley & Sons, Ltd. [source]

Quantitative assessment of the effect of basis set superposition error on the electron density of molecular complexes by means of quantum molecular similarity measures

Pedro Salvador
Abstract The Chemical Hamiltonian Approach (CHA) method is applied to obtain Basis Set Superposition Error (BSSE)-free molecular orbitals at the Hartree,Fock (HF) and Density Functional Theory (DFT) levels of theory. To assess qualitatively the effect of the BSSE on the first-order electron density, we had previously applied Bader's analysis of the intermolecular critical points located on the electron density, as well as density difference maps for several hydrogen bonded complexes. In this work, Quantum Molecular Similarity Measures are probed as an alternative avenue to properly quantify the electronic relaxation due to the BSSE removal by means of distance indices between the uncorrected and corrected charge densities. It is shown that BSSE contamination is more important at the DFT level of theory, and in some cases, changes on the topology of the electron density are observed upon BSSE correction. Inclusion of diffuse functions have been found to dramatically decrease the BSSE effect in both geometry and electron density. The CHA method represents a good compromise to obtain accurate results with small basis sets. 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

On ACK filtering on a slow reverse channel

Chadi Barakat
Abstract Acknowledgement (ACK) filtering has been proposed as a technique to alleviate the congestion at the input of a slow channel located on the reverse path of a TCP connection. Old ACKs waiting at the input of the slow channel are erased when new ACKs are to be queued. In the literature the case of one-ACK per connection at a time has been studied. In this paper we show that this is too aggressive for short transfers where ACKs arrive in bursts due to the slow start phase, and where the TCP source needs to receive the maximum number of ACKs to increase fast its window. We study first static filtering where a certain ACK queue length is allowed. We show analytically how this length needs to be chosen. We present then some algorithms that adapt the filtering of ACKs as a function of the slow channel utilization rather than the ACK queue length. These algorithms provide a good compromise between reducing the ACK queueing delay and passing a large number of ACKs that guarantee a fast window increase. Copyright 2003 John Wiley & Sons, Ltd. [source]

Systematic quantum chemical study of DNA-base tautomers

M. Piacenza
Abstract The relative energies of the energetically low-lying tautomers of pyridone, cytosine, uracil, thymine, guanine, and iso-cytosine are studied by a variety of different quantum chemical methods. In particular, we employ density functional theory (DFT) using the six functionals HCTH407, PBE, BP86, B-LYP, B3-LYP, and BH-LYP, and the ab initio methods Hartree-Fock (HF), standard second-order Mller-Plesset perturbation theory (MP2), an improved version of it (SCS-MP2), and quadratic configuration interaction including single and double excitations (QCISD) and perturbative triple corrections [QCISD(T)]. A detailed basis set study is performed for the formamide/formamidic acid tautomeric pair. In general, large AO basis sets of at least valence triple-, quality including f-functions (TZV) are employed, which are found to be necessary for an accurate energetic description of the various structures. The performance of the more approximate methods is evaluated with QCISD(T)/TZV(2df,2dp) data taken as reference. In general it is found that DFT is not an appropriate method for the problem. For the tautomers of pyridone and cytosine, most density functionals, including the popular B3-LYP hybrid, predict a wrong energetic order, and only for guanine, the correct sequence of tautomers is obtained with all functionals. Out of the density functionals tested, BH-LYP, which includes a rather large fraction of HF exchange, performs best. A consistent description of the nonaromatic versus aromatic tautomers seems to be a general problem especially for pure, nonhybrid functionals. Tentatively, this could be assigned to the exchange potentials used while the functional itself, including the correlation part, seems to be appropriate. Out of the ab initio methods tested, the new SCS-MP2 approach seems to perform best because it effectively reduces some outliers obtained with standard MP2. It outperforms the much more costly QCISD method and seems to be a very good compromise between computational effort and accuracy. 2003 Wiley Periodicals, Inc. J Comput Chem 1: 83,98, 2004 [source]

Changes in vertebral structure during growth of reared rainbow trout, Oncorhynchus mykiss (Walbaum): a new approach using modelling of vertebral bone profiles

M-H Deschamps
Abstract Severe bone resorption of the vertebral body in reared rainbow trout was thought to be a dysfunction in mineral balance induced by increased growth rate in unfavourable rearing conditions. To verify this assumption, we sampled market-sized trout (c. 250 g) from 20 fish farms with different rearing conditions. Growth rate was also studied by sampling trout reared in three different water temperatures from fry to market-size. Transverse sections of vertebrae were microradiographed, then digitized. Total bone area (Tt-B.Ar.) and bone profiles were obtained using BONE PROFILER 3.23 software and a mathematical model was developed to statistically compare bone profiles using 12 parameters in four vertebra regions. Tt-B.Ar. and bone profiles were found to vary with rearing conditions and growing temperatures, indicating obvious influences of these factors on bone remodelling. However, vertebral resorption was found to be a general phenomenon. In trout from 190 to 235 mm in length, vertebrae underwent important remodelling resulting in large resorption of the middle area, while the transition and peripheral areas showed an increase in bone deposition. Changes in vertebra architecture seem to be a good compromise between the need to mobilize stored minerals during growth while maintaining vertebral biomechanical properties. [source]

Methane steam reforming at microscales: Operation strategies for variable power output at millisecond contact times

AICHE JOURNAL, Issue 1 2009
Georgios D. Stefanidis
Abstract The potential of methane steam reforming at microscale is theoretically explored. To this end, a multifunctional catalytic plate microreactor, comprising of a propane combustion channel and a methane steam reforming channel, separated by a solid wall, is simulated with a pseudo 2-D (two-dimensional) reactor model. Newly developed lumped kinetic rate expressions for both processes, obtained from a posteriori reduction of detailed microkinetic models, are used. It is shown that the steam reforming at millisecond contact times is feasible at microscale, and in agreement with a recent experimental report. Furthermore, the attainable operating regions delimited from the materials stability limit, the breakthrough limit, and the maximum power output limit are mapped out. A simple operation strategy is presented for obtaining variable power output along the breakthrough line (a nearly iso-flow rate ratio line), while ensuring good overlap of reaction zones, and provide guidelines for reactor sizing. Finally, it is shown that the choice of the wall material depends on the targeted operating regime. Low-conductivity materials increase the methane conversion and power output at the expense of higher wall temperatures and steeper temperature gradients along the wall. For operation close to the breakthrough limit, intermediate conductivity materials, such as stainless steel, offer a good compromise between methane conversion and wall temperature. Even without recuperative heat exchange, the thermal efficiency of the multifunctional device and the reformer approaches ,65% and ,85%, respectively. 2008 American Institute of Chemical Engineers AIChE J, 2009 [source]

Evaluation of mobile phase, ion pairing, and temperature influence on an HILIC-MS/MS method for L -arginine and its dimethylated derivatives detection

Giuseppe Paglia
Abstract Asymmetric NG,,NG -dimethylarginine (ADMA) increases in diseases such as renal failure, diabetes mellitus, and hypercholesterolemia. The feasibility and utility of a hydrophilic interaction chromatography (HILIC) method for the separation of free L -arginine (Arg), ADMA, and symmetric NG,,NG, -dimethylarginine (SDMA) on a typical silica column were explored and the impact of some experimental parameters on the chromatographic behavior of these analytes was investigated. The effect of water and TFA content in mobile phase and of column temperature was investigated during the development of a fast and simple HILIC-MS/MS method that might be suitable for the quantification of free Arg, ADMA, and SDMA in plasma for routine analysis. Our results show that a good compromise between efficiency and peak shape with acceptable retention and total chromatographic run time is achieved using an ACN/water (90:10) mobile phase with TFA% as additive ranging from 0.015 to 0.025% and column temperature ranging from 25 to 30C. [source]


Navin Kumar C. Twarakavi
ABSTRACT: A methodology consisting of ordinal logistic regression (OLR) is used to predict the probability of occurrence of arsenic concentrations in different threshold limits in shallow ground waters of the conterminous United States (CONUS) subject to a set of influencing variables. The analysis considered a number of maximum contaminant level (MCL) options as threshold values to estimate the probabilities of occurrence of arsenic in ranges defined by a given MCL of 3, 5, 10, 20, and 50 ,g/l and a detection limit of 1 ,g/l. The fit between the observed and predicted probability of occurrence was around 83 percent for all MCL options. The estimated probabilities were used to estimate the median background concentration of arsenic in the CONUS. The shallow ground water of the western United States is more vulnerable than the eastern United States. Arizona, Utah, Nevada, and California in particular are hotspots for arsenic contamination. The risk assessment showed that counties in southern California, Arizona, Florida, and Washington and a few others scattered throughout the CONUS face a high risk from arsenic exposure through untreated ground water consumption. A simple cost effectiveness analysis was performed to understand the household costs for MCL compliance in using arsenic contaminated ground water. The results showed that the current MCL of 10 ,g/l is a good compromise based on existing treatment technologies. [source]

Ultrastructural identification of peripheral myelin proteins by a pre-embedding immunogold labeling method

Marie-Hlne Canron
Abstract Ultrastructural immunolabeling of peripheral nervous system components is an important tool to study the relation between structure and function. Owing to the scarcity of certain antigens and the dense structure of the peripheral nerve, a pre-embedding technique is likely appropriate. After several investigations on procedures for pre-embedding immunolabeling, we propose a method that offers a good compromise between detection of antigenic sites and preservation of morphology at the ultrastructural level, and that is easy to use and suitable for investigations on peripheral nerve biopsies from humans. Pre-fixation by immersion in paraformaldehyde/glutaraldehyde is necessary to stabilize the ultrastructure. Then, ultrasmall gold particles with silver enhancement are advised. Antibodies against myelin protein zero and myelin basic protein were chosen for demonstration. The same technique was applied to localize a 35 kDa myelin protein. [source]

Double-masked randomised placebo-controlled trial of the effect of prismatic corrections on rate of reading and the relationship with symptoms

Claire I. O'Leary
Abstract Practitioners' decisions on when to intervene in decompensated heterophoria are often based on symptoms, which are in some cases an unreliable indicator of whether an intervention will be helpful. The aim of our study was to determine when prismatic corrections improve performance at a measure of dynamic visual function: the Wilkins Rate of Reading Test (WRRT). All participants manifested an aligning prism (associated heterophoria) on the near Mallett Unit of 0.5, or greater. There were 80 participants, of whom 58 had exophoria, 15 esophoria, and seven hyperphoria. The effect of the aligning prism on the WRRT was compared with a control lens using a double-masked randomised design. For exophoria, an aligning prism of 2, and above has a sensitivity of 67% and a specificity of 79% for improving performance at the WRRT by 5% or more. It is not possible from our data to achieve a good compromise between sensitivity and specificity for the other types of heterophoria. Patients in the horizontal (but not vertical) heterophoria groups had significantly more symptoms than a control group. The patients whose visual performance is improved by prismatic correction are not necessarily those who report the most symptoms. Our data suggest that exophoric patients of any age are likely to have improved visual performance with an intervention if they have an aligning prism of 2, or more, even in the absence of symptoms. We stress that although the Mallett Unit Fixation Disparity test provides useful information, its results need to be considered in the overall context of the patient's symptoms, lifestyle, and the results of other optometric tests. Although this study evaluated prismatic corrections, we note that interventions for decompensated heterophoria include not only prismatic corrections, but also eye exercises and refractive modification. [source]

Matrix vapor deposition/recrystallization and dedicated spray preparation for high-resolution scanning microprobe matrix-assisted laser desorption/ionization imaging mass spectrometry (SMALDI-MS) of tissue and single cells

Werner Bouschen
Matrix preparation techniques such as air spraying or vapor deposition were investigated with respect to lateral migration, integration of analyte into matrix crystals and achievable lateral resolution for the purpose of high-resolution biological imaging. The accessible mass range was found to be beyond 5000 u with sufficient analytical sensitivity. Gas-assisted spraying methods (using oxygen-free gases) provide a good compromise between crystal integration of analyte and analyte migration within the sample. Controlling preparational parameters with this method, however, is difficult. Separation of the preparation procedure into two steps, instead, leads to an improved control of migration and incorporation. The first step is a dry vapor deposition of matrix onto the investigated sample. In a second step, incorporation of analyte into the matrix crystal is enhanced by a controlled recrystallization of matrix in a saturated water atmosphere. With this latter method an effective analytical resolution of 2,m in the x and y direction was achieved for scanning microprobe matrix-assisted laser desorption/ionization imaging mass spectrometry (SMALDI-MS). Cultured A-498 cells of human renal carcinoma were successfully investigated by high-resolution MALDI imaging using the new preparation techniques. Copyright 2010 John Wiley & Sons, Ltd. [source]

Choices and Constraints over Retirement Income Streams: Comparing Rules and Regulations,

The new Simplified Superannuation regulations for Australian superannuation provide tax concessions to retirement income streams which comply with legislated minimum drawdown rules. We evaluate these new drawdown rules against four alternatives, including three formula-based ,rules of thumb' used by financial planners. We find that the new regulations are a substantial improvement on the previous rules for allocated pensions and, when compared with the formula-based rules, are a good compromise in terms of simplicity, adequacy and risk. We also find that welfare is lower for most individuals who follow the Simplified Superannuation rules compared with welfare under an optimal path or a simple fixed percentage drawdown rule, but that outcomes could be improved through a further simplification of the new rules. [source]

Anion Recognition by Neutral Macrocyclic Amides

J. Chmielewski Dr., Micha
Abstract Although amides often serve as anchoring groups in natural and synthetic anion receptors, the structure,affinity relationship studies of amide-based macrocyclic receptors are still very limited. Therefore, we decided to investigate the influence of the size of the macroring on the strength and selectivity of anion binding by uncharged, amide-based receptors. With this aim, we synthesized a series of macrocyclic tetraamides derived from 2,6-pyridinedicarboxylic acid and aliphatic ,,,-diamines of different lengths. X-ray analysis shows that all ligands studied adopt expanded conformations in the solid state with the convergent arrangement of all four hydrogen-bond donors. 1H NMR titrations in DMSO solution revealed a significant effect of the ring size on the stability constants of anion complexes; the 20-membered macrocyclic tetraamide 2 is a better anion receptor than its both 18- and 24-membered analogues. This effect cannot be interpreted exclusively in terms of matching between anion diameter and the size of macrocyclic cavity, because 2 forms the most stable complexes with all anions studied, irrespective of their sizes. However, geometric complementarity manifests in extraordinarily high affinity of 2 towards the chloride anion. The results obtained for solutions were interpreted in the light of solid-state structural studies. Taken together, these data suggest that anion binding by this family of macrocycles is governed by competitive interplay between their ability to adjust to a guest, requiring longer aliphatic spacers, and preorganization, calling for shorter spacers. The 20-membered receptor 2 is a good compromise between these factors and, therefore, it was selected as a promising leading structure for further development of anion receptors. Furthermore, the study of an open chain analogue of 2 revealed a substantial macrocyclic effect. X-ray structure of the acyclic model 14 suggests that this may be due to its ill-preorganized conformation, stabilized by two intramolecular hydrogen bonds. [source]