Contrasting models for lactation curve analysis

Several statistical models have been proposed for the genetic evaluation of production traits in dairy cattle based on test-day records. Three main approaches have been put forward in the literature: random regression, orthogonal polynomials, and, more recently, character process models. The aim of this paper is to show how these different approaches are related, to compare their performance for the genetic analysis of lactation curves, and to assess equivalence between sire and animal models for repeated measures analyses. It was found that, with an animal model, a character process model with 11 parameters performed better, regarding the likelihood criterion, than a quartic random regression model (with 31 parameters). However, although the likelihood was higher, the genetic variance was very different with the character process model from the unstructured model, which raises important issues concerning model selection criteria. There are advantages in combining methodologies. A quadratic random regression model for the environmental part, combined with a character process model for the residual, performed better than the quartic random regression model and had fewer parameters. A character process structure allowing for a correlation pattern modeled the residual better than a simple quadratic variance, and had only one extra parameter.     

Multilayer oxide formation on platinum

The growth of multilayer oxide (oxide II) on smooth Pt was investigated as a function of cd and temperature in 0·5 and 1 M H₂SO₄. The pretreatment of the electrode is an essential feature in the forming of oxide 11: eg depending on the history of the electrode, oxide 11 was formed in 0·5 H₂SO₄ at cd of 100 mA/cm² at temperatures above 14 or 22°C. During the oxidation the potential—time curve shows a maximum, characteristic for the forming of oxide II.     

Multiple-marker mapping for selective DNA pooling within large families

Selective DNA pooling is a very powerful method for quantitative trait loci (QTL) mapping. It considerably reduces genotyping costs while maintaining high statistical power. Applied to a daughter design, milk samples of offspring with extreme phenotypic values for a trait of interest are assigned to high and low groups, respectively, and within each group the pooled DNA is used for densitometric estimation of allele frequencies in the 2 groups. A single-marker test for linkage between marker and QTL considers marker allele frequency differences between high and low groups. Single-marker across-sire test statistics are strongly affected by the number of sires that are heterozygous for a given marker and the QTL status (homozygous or heterozygous) of these sires, which decreases the accuracy of QTL mapping. Here we propose a simple method to deal with this problem by taking information from multiple linked markers into account. In particular, given the single-marker test statistics, a multiple-marker method was developed to predict test statistics for markers for which a sire was homozygous (or at any other location on the chromosome). Power and map resolution of the proposed method were assessed by simulation, and we show that for the same data set, multiple-marker mapping performed better than the commonly used single-marker analyses.     

Aerobic and anaerobic degradation of a range of alkyl sulfides by a denitrifying marine bacterium

A pure culture of a bacterium was obtained from a marine microbial mat by using an anoxic medium containing dimethyl sulfide (DMS) and nitrate. The isolate grew aerobically or anaerobically as a denitrifier on alkyl sulfides, including DMS, dimethyl disulfide, diethyl sulfide (DES), ethyl methyl sulfide, dipropyl sulfide, dibutyl sulfide, and dibutyl disulfide. Cells grown on an alkyl sulfide or disulfide also oxidized the corresponding thiols, namely, methanethiol, ethanethiol, propanethiol, or butanethiol. Alkyl sulfides were metabolized by induced or derepressed cells with oxygen, nitrate, or nitrite as electron acceptor. Cells grown on DMS immediately metabolized DMS, but there was a lag before DES was consumed; with DES-grown cells, DES was immediately used but DMS was used only after a lag. Chloramphenicol prevented the eventual use of DES by DMS-grown cells and DMS use by DES-grown cells, respectively, indicating separate enzymes for the metabolism of methyl and ethyl groups. Growth was rapid on formate, acetate, propionate, and butyrate but slow on methanol. The organism also grew chemolithotrophically on thiosulfate with a decrease in pH; growth required carbonate in the medium. Growth on sulfide was also carbonate dependent but slow. The isolate was identified as a Thiobacillus sp. and designated strain ASN-1. It may have utility for removing alkyl sulfides, and also nitrate, nitrite, and sulfide, from wastewaters.     

Bias and power in the estimation of a maternal family variance component in the presence of incomplete and incorrect pedigree information

Several studies over the last 15 yr have estimated the magnitude of cytoplasmic inheritance of production and type traits in dairy cattle. Pedigree information can be used to assign maternal lineages, and the between-maternal lineage variance is then assumed to be an estimate of cytoplasmic inheritance. Two potential sources of bias and reduction of the power of estimation of cytoplasmic inheritance using such a method are 1) incomplete and 2) incorrect pedigree information being used in the assignment of maternal lineages. The theoretical bias introduced by these two sources of error is investigated and the results of a simulation study varying the number of families, the percentage of pedigree errors, and the level of incomplete lineage assignment are presented. Pedigree errors were found to have the biggest impact. A pedigree error rate of 8% per generation would result in a 75% reduction in the estimable magnitude of a 5% true component of variance after nine generations. The effect that these mechanisms have on the power of estimation are discussed and investigated by simulation. It was concluded that using historical pedigree, with incomplete and incorrect maternal family information, to assign maternal lineage would cause a downward bias in the magnitude of the cytoplasmic effect estimated. In the future, it will be possible to overcome pedigree problems by using molecular information to directly assign cytoplasmic lineage groups.     

Quantitative model of cellulite: three‐dimensional skin surface topography,biophysical characterization,and relationship to human perception*

Regional Meeting of the International Society for Bioengineering and the Skin, Orlando, Florida, October 28–30, 2004. Gynoid lipodystrophy (cellulite) is the irregular, dimpled skin surface of the thighs, abdomen, and buttocks in 85% of post‐adolescent women. The distinctive surface morphology is believed to result when subcutaneous adipose tissue protrudes into the lower reticular dermis, thereby creating irregularities at the surface. The biomechanical properties of epidermal and dermal tissue may also influence severity. Cellulite‐affected thigh sites were measured in 51 females with varying degrees of cellulite, in 11 non‐cellulite controls, and in 10 male controls. A non‐contact high‐resolution three‐dimensional laser surface scanner was used to quantify the skin surface morphology and determine specific roughness values. The scans were evaluated by experts and naїve judges (n = 62). Body composition was evaluated via dual‐energy X‐ray absorptiometry; dermal thickness and the dermal‐subcutaneous junction were evaluated via high‐resolution 3D ultrasound and surface photography under compression. Biomechanical properties were also measured. The roughness parameters Svm (mean depth of the lowest valleys) and Sdr (ratio between the roughness surface area and the area of the xy plane) were highly correlated to the expert image grades and, therefore, designated as the quantitative measures of cellulite severity. The strength of the correlations among naїve grades, expert grades, and roughness values confirmed that the data quantitatively evaluate the human perception of cellulite. Cellulite severity was correlated to BMI, thigh circumference, percent thigh fat, architecture of the dermal‐subcutaneous border (ultrasound surface area, red‐band SD from compressed images), compliance, and stiffness (negative correlation). Cellulite severity was predicted by the percent fat and the area of the dermal‐subcutaneous border. The biomechanical properties did not significantly contribute to the prediction. Comparison of the parameters for females and males further suggest that percent thigh fat and surface area roughness deviation are the distinguishing features of cellulite.     

French wheel tracking round robin test on a polymer modified bitumen mixture

In the framework of the RILEM TC 206-ATB TG3, a Round Robin Test (RRT) has been performed in order to evaluate the reproducibility of the French Wheel Tracking Test (FWTT) on a mix made with Polymer Modified Bitumen (PmB). For this mixture, some particular problems had been reported, such as excessive heating of the sample due to friction and sticking of the binder to the wheel. Two procedures, called anti-overheating and anti-sticking procedures, have been proposed by the group in order to improve the reproducibility of the wheel tracking tests. These procedures are assessed. Causes of scattering are discussed. Differences between the tyres used during this RRT as a possible origin of scattering are discussed, as well as temperature peaks and over-compaction of specimens.