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Notes: We have previously shown that the corrosion behavior of ternary NdFeB magnets is affected by their oxygen, carbon, and nitrogen contents. The corrosion was measured in autoclaves which give accelerated testing environments of high heat and humidity. In this study, we relate this corrosion behavior in both NdFeB and NdFeCoAlB magnets to effects upon their microstructure. When the oxygen and carbon contents are low in ternary NdFeB magnets, a thick Nd-rich phase (α-Nd and/or NdOx) forms along grain boundaries and their triple junctions. As the oxygen and carbon contents increase, the Nd-rich coating along the boundaries becomes thinner and agglomerates into the triple junctions. With thin grain boundaries, the pathways for corrosion propagation are hindered, thus improving corrosion resistance. With increases in oxygen, the α-Nd and unstable NdOx are changed to stable Nd2O3. Nitrogen increases also aid in the process of conversion to Nd2O3 which leads to better corrosion resistance. Two different features are seen in the microstructure of NdFeCoAlB magnets. The grain boundary phase (Nd3Co) is very stable. Any oxygen in the system appears as fully oxidized Nd2O3. Easily corroded α-Nd and NdOx are not detected. All of these factors combine to produce excellent corrosion resistance in this variety of NdFeCoAlB magnets.

Notes: Abnormal grain growth was found in sintered Nd-Fe-B magnets which are made from powder milled after hydrogen decrepitation. The abnormal grain size in the magnets sintered at 1000 °C for 1.5 h was as large as 400 μm. The formation of abnormally large grains reduced the magnetic properties. As sintering temperature increased, the number of large grains increased and coercivity reduced. However, abnormal grain growth was rarely found when the magnets were fabricated without hydrogen decrepitation. A grain growth mechanism is discussed in relation to the effect of hydrogenation and sintering process.

Notes: The effects of vanadium substitution on the magnetic properties of Sm-Fe-Ti-V melt-spun ribbons and the magnetic properties and microstructure of sintered Sm-Fe-Ti based magnets are reported. The highest coercivity, Hc =10.65 kOe, was obtained in a heat-treated melt-spun Sm8 Fe75.5 Ga0.5 Ti8 V8 alloy. This is the highest value of the coercivities reported in alloys with the ThMn12 -type structure. Bulk magnets were prepared by the usual powder metallurgy technique. However, their highest coercivity (∼2 kOe) was much less than that of the corresponding ribbons. The low coercivity of sintered magnets has been attributed to their nonuniform microstructure.

Notes: A technique has been developed that allows single-shot measurement of the electric field over an extended area. A LiTaO3 crystal, covering the entire active area of the GaAs photoconductive switch, coupled the surface field with the polarization of an optical probe pulse. When imaged onto a two-dimensional detector array, this system produced snapshots of the surface field profile with 200-ps time resolution and 3-μm spatial resolution. The technique was used to monitor the collapse of the electric field in the GaAs as it was switched with a λ=1.06 μm optical pulse. The switching speed and generation of field enhancements were found to be dependent on the illumination configuration and the electric field. In particular, the switching efficiency was found to decrease with increasing field.

Notes: The effects of growth temperature, substrate offcut, and dislocation pileup formation on threading dislocation density (TDD) in compositionally graded SiGe buffers are explored. To investigate dislocation glide kinetics in these structures, a series of identical samples graded to 30% Ge were grown at temperatures between 650 and 900 °C on (001)-, (001) offcut 6° towards an in-plane 〈110〉-, and (001) offcut 6° towards an in-plane 〈100〉-oriented Si substrates. The field threading dislocation density (field TDD) in the on-axis samples varied exponentially with temperature, from 3.7×106 cm−2 at 650 °C to 9.3×104 cm−2 at 900 °C. The activation energy for dislocation glide in this series, calculated from the evolution of field TDD with growth temperature, was 1.38 eV, much lower than the expected value for this composition. This deviation indicates that strain accumulating during the grading process at low growth temperatures is forcing further dislocation nucleation, resulting in a deviation from pure glide-limited relaxation. The TDD of samples grown on offcut substrates exhibited a more complicated temperature dependence, likely because films grown on offcut substrates have an increased tendency towards saturation in dislocation reduction reactions at high temperature. Dislocation reduction processes were further explored by initiating compositional grading up to 15% Ge at 650 °C and continuing the grade to 30% Ge at 900 °C. The low temperature portion of this growth provided an excess concentration of threading dislocations which could subsequently be annihilated during the high temperature portion of the growth, enabling a comparison of reduction rates for different substrate offcuts. Combining these results with threading dislocation densities in a variety of other samples, a complete picture of strain relaxation kinetics in compositionally graded SiGe/Si emerges. Generally, strain relaxation in these structures is limited by dislocation glide, and threading dislocation densities are independent of final Ge content. However, we theorize that dislocation pileup formation inhibits the strain relaxation process and is therefore accompanied by a rise in field threading dislocation density. Based on these results, we now have a predictive model for TDD in compositionally graded SiGe/Si over a wide range of growth conditions. © 2001 American Institute of Physics.

Notes: Abstract: Ligand-induced up-regulation of recombinant dopamine D2 receptors was assessed using C6 glioma cells stably expressing the short (415-amino-acid; D2S) and long (444-amino-acid; D2L) forms of the receptor. Overnight treatment of C6-D2L cells with N-propylnorapomorphine (NPA) caused a time- and concentration-dependent increase in the density of receptors, as assessed by the binding of radioligand to membranes prepared from the cells, with no change in the affinity of the receptors for the radioligand. The effect of 10 µM NPA was maximal after 10 h, at which time the density of D2L receptors was more than doubled. The agonists dopamine and quinpirole also increased the density of D2L receptors. The receptor up-regulation was not specific for agonists, because the antagonists epidepride, sulpiride, and domperidone caused smaller (30–60%) increases in receptor density. Prolonged treatment with 10 µM NPA desensitized D2L receptors, as evidenced by a reduced ability of dopamine to inhibit adenylyl cyclase, whereas treatment with sulpiride was associated with an enhanced responsiveness to dopamine. The magnitude of NPA-induced receptor up-regulation in each of four clonal lines of C6-D2L cells (mean increase, 80%) was greater than in all four lines of C6-D2S cells (33%). Inactivation of pertussis toxin-sensitive G proteins had no effect on the basal density of D2L receptors or on the NPA-induced receptor up-regulation. Treatment with 5 µg/ml of cycloheximide, on the other hand, decreased the basal density of receptors and attenuated, but did not prevent, the NPA-induced increase. Chimeric D1/D2 receptors were used to identify structural determinants of dopamine receptor regulation. Treatment with the D1/D2 agonist NPA decreased the density of D1 and chimeric CH4 and CH3 receptors. The latter two receptors have D1 sequence from the amino-terminus to the amino-terminal end of transmembrane region (TM) VII and VI, respectively. CH2, with D1 sequence up to the amino-terminal end of TM V, and thus the third cytoplasmic loop of the D2 receptor, was up-regulated by NPA or the D2-selective agonist quinpirole. Quinpirole treatment decreased the density of CH3 and had no effect on CH4 or D1 receptors. The different responses of CH2 and CH3 to agonist treatment suggest a role for TM V and the third cytoplasmic loop in the direction of receptor regulation.

Notes: Abstract: Human nerve growth factor (NGF) was cloned and engineered for expression in a baculovirus-infected Spodoptera frugiperda (SF-9) insect cell system. Culture supernatants contained 2–3 mg/L of recombinant human NGF. The human NGF produced by this system was purified to apparent homogeneity with a single-step affinity chromatography procedure using a high-affinity monoclonal antibody originally raised against murine NGF. The purification procedure yielded 1–2 mg of pure, human NGF per liter of culture supernatant; i.e., approximately 60% recovery of the human NGF originally released into the culture medium. Although the gene transacted into the SF-9 cells coded for pro-NGF, the NGF recovered after purification was 〉 95% fully processed, mature protein. The KD for the affinity of the pure, recombinant human NGF for NGF receptor in PC12 membranes is 0.20 ± 0.05 nM. Activation of neurite outgrowth in PC12 cells occurs with ED50 values of 85 ± 20 pM and 9.6 ± 1.5 pM for a 3-day primary response and a 1-day secondary response, respectively. The pure, recombinant human NGF also stimulates a significant increase in dopamine content of PC12 cells with an ED50 of 5.8 ± 2.7 pM. These binding and biological activation properties are consistent with values observed using murine NGF purified from sub-maxillary glands.