ALBERT

Notes: Abstract. A rickettsia-like organism was observed in diseased Nile tilapia, Oreochronuis niloticus (L.), from southern Taiwan. Most affected fish were pale and lethargic with haemorrhages and ulcers on the skin. The most significant gross pathological changes were varying degrees of ascites, and enlargement of the spleen, kidney and liver. Marked white nodules (as ring-shaped foci), varying in size, were found in these organs. A Gram-negative, rickettsia-like organism (RLO) frequently appeared as inclusions or within host cell intra-cytoplasmic vacuoles. Fibrin thrombi, perivascular necrosis, chronic inflammatory cells with hypertrophy and RLO-laden cells were characteristic of the disease. White nodules induced in experimental fish were similar to naturally infected cases and RLOs were reisolated in tissue culture using a CHSE-214 cell line. This provides evidence that the systemic granulomas in Nile tilapia were caused by RLOs.

Notes: The working frequency of Mn-Zn ferrites in switching power supply has been increased recently. Therefore, the manufacturing Mn-Zn ferrites with low loss at high frequency is very important. However, there were few reports concerning the core loss of Mn-Zn ferrites.1 It is beneficial to study the parameters affecting the core loss of Mn-Zn ferrites. Therefore, we studied the influence of atmosphere on the hysteresis loss (Wh) and eddy current loss (We) for different compositions in this work. Three compositions, Mn0.70Zn0.21−xFe2.09+xO4 (x=0, 0.01, 0.02), were prepared by traditional ceramic process. The sintering condition is 1385 °C for 4 h. Then, the samples are annealed at 1100 °C for 24 h in different oxygen partial pressure (0.015–1.0 vol %). Experimental results show that both We and Wh have minimum value at different oxygen partial pressure for samples with different composition. Increasing Fe content which raises the Fe++ concentration shifts the We and Wh minimum point to higher annealing oxygen partial pressure. It is mainly due to the oxidation of Fe++ and the transition of conduction mechanism, and it will be further discussed later. We can obtain the lowest core loss for using 10 and 100 kHz are samples with composition x=0 annealed in 0.07 and 0.2 vol % oxygen partial pressure, respectively. Summarily, for application to low loss at different working frequency, it is found that different optimized atmosphere should be controlled during annealing for different composition.

Notes: The effects of elastic strain induced by lattice mismatch on the effective mass and band offset at Γ point are studied in this article. We found that the effective masses (electron, light- and heavy-hole) become anisotropic in a strained layer. The theoretical calculations were made using a method of linear combination of atomic orbitals, and the overlapping integrals are adjusted in accordance with the change of atomic distance. In the kz direction, the effective mass ratios (strain: unstrain) of the electron of InxGa1−xSb/GaSb structure were found to vary from 1 to 3.38 for 0≤x≤1, the corresponding ratios of the light- and heavy-hole are 1 to 3.38 and 1 to 0.99, respectively. In the kx and ky direction, the ratios of the light- and heavy-hole are 1 to 1.02 and 1 to 1.13, respectively. For unstrained and strained interfaces, the band offset ratios of 90:10 and 57:43 (conduction band: valence band) are obtained, respectively. Experimental studies were also performed on the InxGa1−xSb/GaSb strained-layer superlattice sample. It was found that the theoretical calculations agree well with experimental results in this study.

Notes: We obtain undoped n-type GaSb epilayers by low-temperature metalorganic chemical vapor deposition at a low growth temperature of 450 °C reproducibly. Different conduction types of GaSb and different energy levels are compared by photoluminescence spectra. For n-type undoped GaSb, the FWHM of dominant peak and bound exciton are 11 and 1.3 meV, respectively. Because semi-insulating GaSb substrates cannot be obtained, we cannot use the Hall effect to determine the carrier concentration and mobility of the homoepilayer. In order to identify the conduction types of GaSb, ohmic contact and Schottky barrier are made by Au/Ge/Ni and Au, respectively. The concentrations of undoped n-type GaSb homoepilayers obtained from I-V and C-V measurements are 1.44×1017–3.0×1017 cm−3, respectively. The mobility and concentration of undoped p-type GaSb heteroepilayers are 758 cm2/V s and 9.0×1015 cm−3 at 300 K, respectively.

Notes: Undoped GaSb epilayers were grown on GaSb and GaAs substrates using the metalorganic chemical vapor deposition (MOCVD) technique, and photoluminescence (PL). Hall effect measurements were used to characterize the undoped epilayers. For undoped GaSb epilayers, four energy levels revealed by PL spectra are shown to be due to acceptors, using KTdp/dEf va Ef-Ev data obtained from Hall effect results, where p is the hole concentration, Ef and Ev are the Fermi level and the top of valence band, respectively. The acceptor levels lie at 3, 58, 80, and 130 meV above the top of valence band, respectively. The donor level is 15 meV below the bottom of the conduction band. These acceptor levels exist in almost all of the undoped p-type GaSb epilayers grown at high temperature, while the donor level exists only in the undoped n-type GaSb epilayers grown by low-temperature MOCVD. It is found that these levels may be changed using the different growth temperatures.

Notes: Single-phase Fe4N and (Fe1−xNix)4N compounds have been synthesized in a continuous form by heat treating iron and iron-nickel alloy sheets at various temperatures under NH3/H2 atmospheres. The Fe4N sheet has a high room-temperature magnetization value of 179 emu/g (2.14 μB/Fe), which is only slightly less than 218 emu/g (2.19 μB/Fe) observed in pure iron. The magnetic moments of the Fe-Ni alloy nitrides decreased monotonically as x was increased, in contrast to those for the starting alloys Fe1−xNix which exhibited a peak value around x=0.05. The decrease in magnetic moment with nickel content in the alloy nitrides was close to the value anticipated by magnetic dilution from nickel. The coercive force is about 5 Oe and is slightly decreased by the Ni substitution. The Fe-nitride offers a significantly improved corrosion resistance over pure iron. Even further improvement is obtained in the (Fe1−xNix)4N system with only slight sacrifice in magnetic moment. The addition of nickel has been found to noticeably improve the mechanical ductility of the normally brittle Fe4N compound. Theses nitrides also exhibit significantly increased electrical resistivity and wear resistance, and may be useful for a variety of technological applications.

Notes: We report here measurements of quasielastic neutron scattering from n-butane at temperatures of 90, 115, 125 and 190 K and in a momentum transfer range of 0.8–2.4 A(ring)−1. These measurements confirm that between 115 and 125 K butane forms a plastic crystal in which the centers of mass of the butane molecules form a crystalline structure, but the individual molecules are free to rotate. At these two intermediate temperatures, there exists both an elastic peak, characteristic of a solid structure, and quasielastic components arising from the rotational motions of the butane molecules. At 90 K, the butane scatters neutrons only elastically, while at 190 K, the butane scatters neutrons only quasielastically. In both the plastic and the liquid phases, the presence of at least two quasielastic processes must be assumed in order to explain the measurements. In the plastic crystal, we associate a broad Lorentzian component with intramolecular reorientations about the central carbon–carbon bond and a second, relatively narrow, Lorentzian component with whole molecule rotations.The latter process gives rise to a rotational quasielastic peak having a width of 400 μeV, which is constant to within the instrumental resolution of 70 μeV at both temperatures and at all measured momentum transfers. In a continuous diffusion model, this width corresponds to a rotational diffusion constant of 0.277 rad2/ps, a value which is about 3.5 times larger than one extracted from a molecular dynamics simulation of n-butane in the plastic phase recently published by Refson and Pawley [Mol. Phys. 61, 669 (1987); 61, 693 (1987)]. On the other hand, the first process, which corresponds to the carbon–carbon reorientation peak, is about 16 meV wide, indicating that this reorientation occurs on a time scale of about 0.1 ps. The absence of this broad peak in the solid butane at 90 K indicates that this fast carbon–carbon reorientation is coupled to an aspect of the structure or dynamics of the plastic phase. In the scattering from liquid butane at 190 K, there is a third, narrow quasielastic peak which also has a Lorentzian energy distribution. This peak width is about 200 μeV and corresponds to a translational diffusion constant of 0.23 A(ring)2/ps, a result in rough agreement with a recent molecular dynamics simulation of liquid butane by Ullo and Yip. [J. Chem. Phys. 85, 4056 (1986)].