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Magnetocaloric [Gd.sub.5][Si.sub.2][Ge.sub.2]-based alloys exhibit a well-documented giant magnetocaloric effect at around room temperature. However, as candidate materials for real-world refrigeration devices, they suffer from a number of problems, one of which is large hysteresis losses while cycling in and out of the magnetic field. It has, however, been reported that a small amount of iron reduces these hysteresis losses very significantly, so increasing the total potential cooling capacity of the material. We have investigated the magnetic properties as well as the macro- and microstructural changes for a wide range of iron substitutions for silicon, according to the formula [Gd.sub.5][Si.sub.2-x][Fe.sub.x][Ge.sub.2], where x was varied between 0 and 1. The samples were prepared with an arc- melter and homogenized in an inert atmosphere, after which they were analyzed with a nano-resolution field-emission-gun scanning electron microscope (FEG SEM) and an X-ray diffractometer. The magnetic measurements were made with a cryogenic vibrating-sample magnetometer. The substitution of silicon for iron presented us with some unusual macrostructures and a consistent change in the microstructures of the samples. While most of the iron forms part of the grain-boundary phases, it also results in the formation of a new [Gd.sub.5][(SiGe).sub.3] main phase. We also observed that the addition of iron lowered the Curie temperature of the alloy, but only had a minimal effect on reducing the hysteresis losses, suggesting that this previously observed reduction in the hysteresis losses only occurs with very small substitutions of iron. Index Terms--[Gd.sub.5][Si.sub.2][Ge.sub.2]-type alloys, magnetic hysteresis, magnetocaloric effect, microstructure.

The various effects of temperature on the different microstructural, compositional and the magnetic changes taking place in the different electrodeposited Fe-Pd thin films are discussed. High temperatures are shown to lead to a significant reduction in the coercivities of these films.

Mechanical testing in environmental chambers is typically limited to 450°C. Some specialty chambers have been designed but at a high cost. Furthermore, accurate extensometers in environmental chambers are rare and expensive to operate. A unique solution investigated in this manuscript is the mating of a confocal laser scanning microscope with a sealed environmental chamber fitted with loading clevises for mechanical testing. Such a setup allows the researcher to measure strain data at elevated temperatures in controlled environments. Utilizing a laser light source avoids problems with blackbody radiation at elevated temperatures. Setup and accuracy of the microscope are discussed concerning tensile loading. P91 boiler steel was selected for this work because of the long history of the alloy in the fossil energy industry. Optical strain uncertainty was measured between 1.6% and 3.5%. Other tensile parameters were satisfactorily measured within the experimental error of larger standard specimens. [ABSTRACT FROM AUTHOR]

These experiments examine the role of thyroxine (T 4 ) and triiodothyronine (T 3 ) on the toxicity of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD). The first experiment is a continuation of a study reported previously (Rozman et al., 1984). In this experiment, 60 male Sprague‐Dawley rats were divided into 6 equal groups. Four groups of rats were thyro'idectomized by 3 mCi Na 131 1/kg rat. Five weeks later 2 of the thyroidectomized and 1 of the nontbyroidectomized groups of rats received ip 100 μg TCDD/kg body weight in corn oil/acetone, whereas 3 corresponding groups of rats served as vehicle controls. Two days after dosing and every 7 d thereafter, 7 thyroidectomized control group and 1 thyroidectomized TCDD‐dosed group were given ip 105 μg T 4 /kg body weight. Mortality and body weight were monitored. The course of TCDD toxicity was similar in nonthyroidectomized and thyroidectomized T 4 ‐treated rats but was different in thyroidectomized animals without T 4 replacement therapy. At d 90 after TCDD dosage, mortality was still lower and the mean time to death was increased (p < 0.01) in this group of rats compared to nonthyroidectomized or thyroidectomized T 4 ‐treated rats. However, administration of T 4 starting at d 97 after dosing with TCDD resulted within 2 wk in the same final mortality in thyroidectomized rats as in nonthyroidectomized or thyroidectomized T 4 ‐treated animals, indicating that thyroid hormones modulate the time course of the wasting syndrome but do not affect the ultimate mortality figure. Body weight loss was much slower in thyroidectomized (∼ 1 g/d) than in nonthyroidectomized or thyroidectomized T 4 −treated rats (∼ 8 g/d). In the second experiment the three vehicle control groups of the first experiment were used. Nonthyroidectomized vehicle controls and thyroidectomized T 4 ‐treated controls were maintained as before, whereas thyroidectomized controls received T 3 at 5μg/kg daily. One month later each rat was dosed with TCDD at 100 μg/kg in corn oil/acetone. Toxicity of TCDD was similar in nonthyroidectomized, thyroidectomized T 4 ‐treated, and thyroidectomized T3‐treated rats as judged by mortality, body weight, and food intake, indicating no difference between T 3 and T 4 in the modulation of TCDD toxicity. [ABSTRACT FROM PUBLISHER]

A physiologically based pharmacokinetic model was developed to describe the distribution of hexachlorobenzene (HCB) in the rat after oral administration or injection. The model was based on flow-limited blood perfusion of HCB to tissues and organs of the body. A set of simultaneous differential equations were solved for the different tissue concentrations as a function of time. The model allowed for elimination of HCB by excretion. The model also allowed for differential growth of various tissues over the course of an experiment. Computer simulations using the model indicated that growth of animals during the course of dosing experiments can greatly increase the apparent half-life of HCB. [ABSTRACT FROM AUTHOR]