An analysis of RNG based turbulence models for homogeneous shear flow

In a recent paper, the authors compared the performance of a variety of turbulence models including the k-epsilon model and the second-order closure model based on Renormalization Group (RNG) Methods. The performance of these RNG models in homogeneous turbulent shear flow was found to be quite poor, apparently due to the value of the constant C(sub epsilon1) in the modeled dissipation rate equation which was substantially lower than its traditional value. However, recently a correction has been made in the RNG based calculation of C(sub epsilon1). It is shown that with the new value of C(sub epsilon1), the performance of the RNG k-epsilon model is substantially improved. On the other hand, while the predictions of the revised RNG second-order closure model are better, some lingering problems still remain which can be easily remedied by the addition of higher order terms

Investigation factors that control trace metal toxicity in coastal systems : a temporal and spatial analysis of kinetically inert copper in Boston Harbor

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.Includes bibliographical references (p. 56-58).(cont.) form of inert Cu. Correlations between Cu concentrations and total suspended solids at one sampling location suggested that sediment resuspension may be a source of inert Cu to coastal waters. Consistently significant inert Cu concentrations at a site near a salt marsh implied that the presence of sulfides may result in formation of inert Cu. No correlation between inert Cu and chlorophyll a was observed, suggesting that biological formation of inert Cu compounds in situ did not occur in this system. Whether Cu is added to surface waters as existing inert Cu compounds or as inert Cu that is formed when exchangeable Cu reacts with certain constituents in surface waters remains a subject for future work.Understanding how Cu reacts with constituents in coastal waters and interacts with biota is important for predicting Cu toxicity. It was recently shown that some of the Cu in coastal waters is present in kinetically inert forms that are not released from strongly bound compounds and do not bind to a strong synthetic ligand, remaining undetectable by competitive ligand exchange / adsorptive cathodic stripping voltammetry (CLE-ACSV) on time scales relevant to natural processes (48 hours). Inert Cu seems to be irreversibly bound to strong ligands or physically sequestered within organic and inorganic matrices such that it is likely non-toxic. The primary objective of this work was to collect an extensive data set on one site, Boston Harbor, in order to examine the sources and sinks of inert Cu in this coastal system. Surface water samples were collected and filtered (0.2 [micro]m) using trace-metal clean techniques from eleven locations in Boston Harbor every two to three weeks from June to November 2002. A strong ligand (salicylaldoxime) and increments of Cu were added to each sample to determine exchangeable Cu using CSV-ACSV. UV-treated samples were analyzed by CLE-ACSV to determine total dissolved Cu concentrations. Inert Cu concentrations were deduced by subtracting exchangeable from total Cu. An average of 46.1% of the total dissolved Cu in Boston Harbor was determined to be inert Cu. Exchangeable Cu concentrations averaged 10.8 nM ([sigma]=5.5 nM); total Cu, 20.6 nM ([sigma]=5.7 nM); inert Cu, 10.7 nM ([sigma]=3.1 nM). Although the fraction of inert Cu was variable among different sites and sampling dates, the concentration of exchangeable Cu remained within a smaller range (5-15 nM), implying that Cu inputs above this level mainly took theby Arthur G. Fitzmaurice, III.S.M

A generalized linear mixed model for longitudinal binary data with a marginal logit link function

Longitudinal studies of a binary outcome are common in the health, social, and behavioral sciences. In general, a feature of random effects logistic regression models for longitudinal binary data is that the marginal functional form, when integrated over the distribution of the random effects, is no longer of logistic form. Recently, Wang and Louis [Biometrika 90 (2003) 765--775] proposed a random intercept model in the clustered binary data setting where the marginal model has a logistic form. An acknowledged limitation of their model is that it allows only a single random effect that varies from cluster to cluster. In this paper we propose a modification of their model to handle longitudinal data, allowing separate, but correlated, random intercepts at each measurement occasion. The proposed model allows for a flexible correlation structure among the random intercepts, where the correlations can be interpreted in terms of Kendall's $\tau$. For example, the marginal correlations among the repeated binary outcomes can decline with increasing time separation, while the model retains the property of having matching conditional and marginal logit link functions. Finally, the proposed method is used to analyze data from a longitudinal study designed to monitor cardiac abnormalities in children born to HIV-infected women.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS390 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Across-country genetic evaluation of meat sheep from Ireland and the United Kingdom

Genetic evaluations in sheep have proven to be an effective way of increasing farm profitability. Much research has previously been conducted on producing within‐country genetic evaluations; however, to date, no across‐country sheep genetic evaluations have been produced between Ireland and the UK. The objective of the present study was to examine the feasibility of an across‐country genetic evaluation of live body weight and carcass composition traits for Texel sheep raised in Ireland and the UK. The benefit of genetic selection based on across‐country genetic evaluations, in comparison with within‐country genetic evaluations, was also quantified. Animal traits included early‐life and postweaning live body weights, and muscle and fat depth ultrasound measurements. Irish and UK data were combined, common animals with progeny with records in both countries were identified and a series of bivariate analyses were performed separately for each trait to produce across‐country genetic evaluations. Fixed effects included contemporary group, age at first lambing of the dam, parity of the dam (Ireland), dam age at lamb's birth (UK), a gender by age of the lamb interaction, a birth type by rearing type of the lamb interaction and country of birth of the lamb. Random effects included the animal additive genetic, dam maternal, litter common environment and residual effect. The model for postweaning weight, muscle depth and fat depth included only the animal additive genetic and litter common environmental random effects. Genetic correlations between the two countries ranged from 0.82 to 0.88 for the various traits. Across‐country breeding values were estimated for all animals and response to selection was predicted using the top 10 and top 20 sires in both within‐ and across‐country analyses for the two countries. Overall, results showed that rates of genetic gain could potentially increase from between 2.59% and 19.63% from selection based on across‐country genetic evaluations compared to within‐country evaluations alone. Across‐country evaluations are feasible and would be of significant benefit to both the Irish and UK sheep industries. In order to realize these potential gains though, there would need to be a switch in emphasis by sheep breeders towards using objective traits as their primary selection criteria

Services surround you:physical-virtual linkage with contextual bookmarks

Our daily life is pervaded by digital information and devices, not least the common mobile phone. However, a seamless connection between our physical world, such as a movie trailer on a screen in the main rail station and its digital counterparts, such as an online ticket service, remains difficult. In this paper, we present contextual bookmarks that enable users to capture information of interest with a mobile camera phone. Depending on the user’s context, the snapshot is mapped to a digital service such as ordering tickets for a movie theater close by or a link to the upcoming movie’s Web page