ALBERT

Notes: Effects of the shape anisotropy on the thermally activated spin relaxation have been investigated using the stochastic Landau–Lifshitz–Gilbert equation. The relaxation times of a noninteracting particle and a thin film were compared with each other. In a noninteracting particle, the relaxation time largely increased with the shape anisotropy when the damping constant was smaller than a certain critical value. In this study, the critical damping constant was 0.02. However, the effect of the shape anisotropy on the energy barrier was negligible in a thin film. All of these results can be explained from the effect of magnetostatic interaction that is enhanced by precession motion at low damping constant. © 2001 American Institute of Physics.

Notes: A method of measuring the thermal diffusivity of solid material at room temperature using photothermal displacement is proposed. The influence of the parameters, such as the radius and modulation frequency of the pump beam and the sample thickness, was studied. From the minimum position of phase of measured deflection with respect to the pump beam, the thermal diffusivity of the materials can be obtained. The position where phase has the minimum value is determined using multiparameter least-square regression fitting. The experimental values for different samples obtained by applying the method are in good agreement with the literature values. © 2000 American Institute of Physics.

Notes: Influence of the magnetic interactions on distribution of energy barrier and time dependent phenomena of magnetization are investigated by micromagnetic and Monte Carlo simulation. For the magnetic thin film with randomly distributed easy axes in the film plane, the shape of the density function of the energy barrier is significantly changed with the varying magnetic interactions. If the exchange or magnetostatic interaction is strong, the density function of energy barrier has a broad distribution, then magnetization decay with time shows a linear dependence on ln(t). © 1999 American Institute of Physics.

Notes: We have measured the temperature- and field-dependent magnetoresistance in an undoped AlGaN/GaN two-dimensional electron gas sample at temperatures below 10 K. Well-resolved Shubnikov-de Haas oscillations have been observed, as well as spin splitting at magnetic fields above 8 T. The amplitude of the oscillations has been used as a thermometer for the electron temperature, Te, studies as a function of driving current have shown that under high applied electric fields the power input per electron follows a Te4.4 dependence. Comparison with numerical modeling indicates that in this heterostructure, electron-acoustic phonon scattering via the screened piezoelectric interaction is the dominant energy-loss mechanism at low temperatures. © 2001 American Institute of Physics.

Notes: The high cost of fish meal in tilapia diets warrants the potential use of cottonseed meal (CSM) as an alternative source of high quality protein. The effects of varying levels of CSM (0, 25, 50, 75 and 100%) as fish meal protein replacement on growth, blood parameters, spleen characteristics, free and bound gossypol in blood plasma, haemoglobin and haematocrit were determined in tilapia. Gossypol (C30H30O8) is a polyphenolic substance found in cottonseed that has known toxic effects in fish. Tilapias (n = 219, average weight = 11.3 ± 3.9 g) were randomly distributed into 15, 32-L glass aquaria, representing five dietary treatments and three replicates per treatment. Each aquarium containing 13–16 fish was supplied with thermoregulated, recirculating water (27 ± 1 °C) at 1 L min−1 flow rate and photoperiod was constant (12 h L/12 h D). Fish fed 25–50% CSM protein replacement showed similar body weights and total lengths as the controls at the completion of the 16-week trial. Fish fed 75 and 100% CSM protein replacement showed a significant decline in body weight and total length. Fish fed 25–100% CSM protein replacement had significantly lower haematocrit and haemoglobin (ANOVA/LSD, P 〈 0.05) compared with levels in controls. The decline was most prominent in groups fed diets with 50–100% CSM protein replacement. Total and free gossypol concentrations of blood plasma significantly increased with increasing levels of CSM replacement (P 〈 0.05). No gossypol was found in blood plasma of fish from the control group. The occurrence of immature and abnormal erythrocytes was significantly greater among fish fed 75 and 100% CSM diets compared with fish fed 0–50% CSM diets. Spleen-somatic index (spleen weight/body weight × 100) did not differ between control fish and fish fed 50–100% CSM diets. Spleen abnormalities, such as large depositions of haemosiderin and melanin pigments and proliferation of melano-macrophage centres, lymphocytic depletion of the white pulp areas (hypocellularity), and presence of vacuoles and necrotic areas were observed among fish fed 50–100% CSM protein diets. In general, the pathological effects of gossypol in tilapia (low haemoglobin and haematocrit levels, abundance of immature red blood cells or polychromatocytes, abnormal spleen morphology) were similar to the effects of vitamin E and/or vitamin C deficiencies observed in other studies.

Notes: Rainbow trout (Oncorhynchus mykiss) males were fed, during a 9-month period, five experimental diets where fishmeal proteins were gradually replaced with cottonseed meal (CS) proteins (0, 25, 50, 75 and 100%; diets 1–5, respectively). This study was carried out to evaluate the action and tissue concentrations of gossypol. Growth performance of fish was not affected with the increasing levels of CS in the diets. Haemoglobin concentration and haematocrit significantly decreased in fish fed 100% CS compared with other dietary treatments. Gonadosomatic index, plasma sex steroids (testosterone, 11-ketotestosterone and 17,20β-dihydroxy-4-pregnen-3-one) and sperm characteristics (concentration, motility, protein concentration and lactate dehydrogenase activity) were not negatively affected by increasing levels of CS. For the first time, a comprehensive study of gossypol concentrations, total and (+) and (−)-enantiomers, in several tissues (liver, blood plasma, spermatozoa and seminal plasma) was performed. The concentrations of both (+) and (−)-enantiomers significantly increased with increasing levels of CS in the diet. The highest concentrations were found in the liver of fish fed diet 5 (185 ± 18 μg g−1). In blood plasma, the concentrations of total gossypol were 10 times lower than the one found in the liver, but 10 and 100 times higher than the concentrations in the spermatozoa and seminal plasma, respectively. In all tissues studied, the concentration of (+)-enantiomer was higher than the (−)-enantiomer. The ratio (−)-enantiomer/total gossypol did not change significantly with the increasing levels of CS in the diet. The results of the present study indicate that CS can be used over a period of 9 months to replace fishmeal proteins completely without compromising growth and reproduction of rainbow trout males.

Notes: Two consecutive 6-week feeding trials were conducted to determine the amount of haemoglobin powder (BM) that could replace fish meal (FM) in juvenile Japanese eel Anguilla japonica (Temminck et Schlegel) diets. Fish were fed 50% crude protein diets in which each of ten isonitrogenous diets was formulated to contain white fish meal and/or blood meal as the dietary protein source to replace FM by BM as follows: Diet 1 (control), 0% BM; diet 2,12.5% BM; diet 3,25% BM; diet 4, 50% BM; diet 5, 75% BM; diet6,100%BM;diet7,25%BM + 3 Essential Amino Acids (EAA); diet 8, 50% BM + 3 EAA; diet 9, 75% BM + 3 EAA; diet 10, 100 BM + 3 EAA. In the first 6-week period, the results were not consistent with the treatments, and poor adaptation of the fish to the experimental diets and conditions was observed. In the second 6-week period, weight gain, specific growth rate, protein efficiency ratio and protein productive value offish fed diets 2, 3, 4, 7, 8 and 9 were not significantly different from those of fish fed the control diet (P 〉 0.05). However, feed conversion ratios offish fed diets 6 and 10 were lower than that offish fed the control diet (P 〈 0.05). These results demonstrate that FM can be replaced by BM up to 50% without supplementation of three EAA, and up to 75% with three EAA supplementation in juvenile Japanese eel diets.