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Bobecka and Wesolowski (Studia Math. 152:147–160, [2002]) have shown that, in the Olkin and Rubin characterization of the Wishart distribution (see Casalis and Letac in Ann. Stat. 24:763–786, [1996]), when we use the division algorithm defined by the quadratic representation and replace the property of invariance by the existence of twice differentiable densities, we still have a characterization of the Wishart distribution. In the present work, we show that when we use the division algorithm defined by the Cholesky decomposition, we get a characterization of the Riesz distribution.

The notion of generalized power of a positive definite symmetric matrix and a related notion of generalized Bessel function are used to introduce an extension of the class of matrix generalized inverse Gaussian distributions. The new distributions are shown to arise as conditional distributions of Peirce components of Riesz random matrices. Things are explained in the modern framework of symmetric cones and simple Euclidean Jordan algebra.

The Riesz distributions on a symmetric cone are used to introduce a class of beta-Riesz distributions. Some fundamental properties of these distributions are established. In particular, we study the effect of a projection on a beta-Riesz distribution and we give some properties of independence. We also calculate the expectation of a beta-Riesz random variable. As a corollary, we give the regression on the mean of a Riesz random variable; that is, we determine the conditional expectation E ( U ∣ U + V ) where U and V are two independent Riesz random variables.

Oukessou, M., Hossaini, J., Zine-Filali, R. & Toutain, P.L. Comparative benzylpenicillin pharmacokinetics in the dromedary Camelus dromedarius and in sheep. J. vet. Pharmacol. Therap. 13, 298–303. Benzylpenicillin pharmacokinetics were compared in the dromedary Camelus dromedarius (n=5) and in sheep (n=5) after administration of a single intravenous injection of benzylpenicillin. The data were described by an open three-compartment model with elimination from the central compartment. Body clearance (Clb) was 4.87±0.63 ml/min/kg in the dromedary and 9.17±1.39 ml/min/kg in sheep, the steady-state volumes of distribution (Vss) were 0.151±0.023 l/kg and 0.165±0.038 l/kg and the mean residence times (MRT) 27.34±1.38 min and 14.95±4.16 min in the dromedary and in sheep, respectively. It was concluded that benzylpenicillin elimination occurs more slowly in the dromedary dian in sheep and that use of the same dosage regimen for the two ruminant species may lead to significant differences in plasma concentrations and therapeutic efficacy. P. L. Toutain, INRA Station de Pharmacologie-Toxicologie, 180 chemin de Tournefeuille, Toulouse, France.

In this paper, we report structural parameters, magnetic ordering and the electronic structure of the tetragonal and orthorhombic ternary iron arsenide compound [Formula: see text]. Ab initio calculations are performed by the means of full-potential linearized augmented plane waves plus local orbitals method for both spin states. The local spin density plus Hubbard potential ([Formula: see text]) and generalized gradient plus Hubbard potential ([Formula: see text]) approximations are used to treat the exchange and correlation potentials. The results mainly show that orthorhombic [Formula: see text] compound has an antiferromagnetic spin ordering. Both spin-up and spin-down polarizations are considered to investigate the band structure, density of states and electron charge density. High density of states population at the Fermi level reveals metallic character of this material. The magnetism property arises essentially from the [Formula: see text] orbital of iron atom.

Camels thrive in arid and semiarid areas, although food and water frequently are scarce. However, the mechanisms enabling camels to withstand food deprivation are poorly understood. In this study four female camels were totally deprived of food for 4 days. Their body weight decreased by 6%. Food deprivation caused no change in total plasma protein concentration in the camel, indicating that no alterations in plasma volume occurred. When the first meal was withheld water intake was unchanged. Next day the camels showed signs of hydration with a decreased plasma Na+ concentration and an increased excretion of diluted urine. In the afternoon water intake decreased. Urine K+ excretion fell the first day and urine volume and Na+ excretion from the third day. No activation of the renin-angiotensin-aldosterone system (RAAS) was observed. Plasma and urine urea concentration increased during food deprivation. Plasma glucose concentration and plasma cortisol and thyroxine levels did not change. Body temperature decreased during food deprivation. After refeeding, total plasma proteins increased temporarily by 12%, and a threefold increase in RAAS was seen, implying that both plasma volume and RAAs changed rapidly. Our results show that fluid balance was only slightly affected in the food-deprived camel. We suggest that strategies for the camel to endure food deprivation include maintenance of plasma volume and glucose concentration and a lowering of the body temperature.

Bovine spermatozoa were separated into different density subpopulations utilizing water insoluble hydrocarbon and silicone gels of defined specific gravity. Sperm density profiles were generated for 13 bulls. The separations were found to be repeatable and characteristic of the bull examined. Considerable density variation among animals was demonstrated. Analysis of the separated spermatozoa, before and after freezing, demonstrated that good motility and aerosomal integrity of spermatozoa were maintained. When the least dense fraction of spermatozoa was used for insemination, conception rates were similar to those obtained routinely by artificial insemination with unfractionated spermatozoa. Therefore, this system may be useful in separating spermatozoa of various densities and for removing extraneous matter from semen. However, the sex ratio, among 51 60-day-old fetuses recovered from heifers inseminated with the lowest density fraction of spermatozoa, was 26 males: 25 females.

A thixotropic, silicone based gel (specific gravity 1.0674) has been developed which permits the rapid isolation of human blood lymphocytes. Gel is incorporated within an evacuated blood draw tube containing crystalline EDTA. Lymphocyte separations are performed within the unopened tube. Quantitative yields of lymphocytes from whole blood are obtained with mononuclear cells comprising 93 percent of the recovered cells. In vitro T and B cell mitogenic responses of recovered lymphocytes are normal thus proving the efficacy of this approach to clinical lymphocyte isolations.