Synthesis and characterization of taper- and rodlike si nanowires on Si(x)Ge(1-x) substrate.

Taper- and rodlike Si nanowires (SiNWs) are synthesized successfully on Si and Si(0.8)Ge(0.2) substrates. The growth mechanisms of taper- and rodlike SiNWs are proposed to be oxide-assisted growth (OAG) and vapor-liquid-solid (VLS) growth, respectively. For taperlike SiNWs annealed at 1200 degrees C for 3 h, the emission peaks are found at 772, 478, and 413 nm. On the other hand, for rodlike SiNWs annealed at 1200 degrees C for 4 h, emission peaks are found at 783, 516, and 413 nm. From the field-emission measurements, the taperlike Si nanowires exhibit superior field-emission behavior with a turn-on field of 6.3-7.3 V/mum. The field enhancement, beta, has been estimated to be 700 and 1000 at low and high fields, respectively. The excellent field-emission characteristics are attributed to the perfect crystalline structure and the taperlike geometry of the Si nanowires.

Hyperbaric oxygen as prophylaxis or treatment for radiation myelitis.

This animal study was designed to investigate HBO as a treatment or prophylaxis for radiation myelitis. All animals received identical spinal cord radiation doses of 69 Gy in 10 daily fractions. Group I received no HBO; group II began HBO at the onset of signs of myelitis; group III received HBO with prophylactic intent beginning 6 wk after irradiation; and group IV received both modalities on the same day, but radiation always preceded HBO by at least 4 h. HBO consisted of 90 min oxygen at 2.4 atm abs for 20 daily treatments. Animals were objectively assessed for the loss of certain neurologic reflexes indicative of four levels of myelitis. Although all animals progressed to severe myelitis, group III animals had group-averaged levels of myelitis consistently less than control. The differences were statistically significant for several weeks. Group IV animals progressed to severe myelitis much more rapidly than any other group. Additional study is justified by this trial. Key questions to be answered include the optimal timing of HBO to produce a beneficial rather than detrimental effect.

The allele interaction between apolipoprotein epsilon2 and epsilon4 in Taiwanese Alzheimer's disease patients.

OBJECTIVE: This study aimed to determine the impact of the present of apolipoprotein epsilon (Apoepsilon) 2 on the relationship between Apoepsilon4 and Alzheimer's disease (AD). METHOD: We examined ApoE genotypes in 428 Taiwanese patients with AD and 807 controls; all participants were older than 65 years. RESULTS: The allele frequency of Apoepsilon4 was greater in AD patients than controls, but significantly lower than in Caucasians. The presence of an epsilon2 allele alone was not associated with lower risk for AD, but the presence of an epsilon2 allele was associated with an epsilon4 allele frequency similar to that of controls. CONCLUSION: The low allele frequency of epsilon4 in persons with an epsilon2 allele suggests that this may be part of the protective effect of epsilon2 against AD.

In vivo induction of apoptosis in immature thymocytes by staphylococcal enterotoxin B.

Staphylococcal enterotoxins are potent T cell mitogens. Recent studies have shown that the binding of these toxins to class II MHC molecules on accessory cells is essential for the stimulation of T cells which bear specific V beta segment of TCR. In the present study we show that i.v. administration of staphylococcal enterotoxin B (SEB) results in an enlargement of spleen and lymph nodes but causes thymus atrophy. Elimination of CD4+CD8+ cells predominantly accounted for the shrinkage of thymus, and the lowest level of this cell population was reached 4 days after SEB injection. Furthermore, this decrease in CD4+CD8+ cells was accompanied by a relative increase in the percentages of CD4+CD8-, CD4-CD8+ and CD4-CD8- cells, whereas their absolute numbers actually reduced on day 4. The thymus shrinkage involved apoptosis which was characterized by DNA fragmentation and morphologic changes. The depletion of Thy-1 high, TCR-alpha beta low and TCR-alpha beta intermediate cells also occurred with a kinetic correlated to the reduction of CD4+CD8+ cells. Our results further showed that the percentages of V beta 8+ cells reduced 12 h post SEB injection, increased after 2 days, and decreased again thereafter. SEB thus causes both apoptotic and stimulative effects in the thymus. Apparently, the tremendous loss of double-positive cells (greater than 90% in cell number on day 4) is not simply due to the reduction of V beta 8+ cells, the possible modulatory effect of other factors or hormones which may play a role in the cell death is discussed.

[The urinary screening and identification of amphetamines in clinical toxicology laboratory--VGH].

Amphetamines abuse has recently become a problem in this country. Four case identification, we used Emit-d.a.u. amphetamine assay to screen the amphetamines in human urine, and then confirmed them by gas chromatography-ion trap detector (GC-ITD). From January 1989 to August 1990, 267 urinary samples were requested by the physicians for amphetamine identification. Six samples were accompanied with drug powders used by the patients. Among the 267 samples, 79 were confirmed for the presence for both of methamphetamine and amphetamine. Neither the presence of amphetamine nor methamphetamine itself was detected. Among the six packs of drug powder tested, methamphetamine but not amphetamine was detected in four. We found that fenfluramine and diethylpropion would have false positive amphetamine reactions in Emit-d.a.u. assay. All the samples originated from 34 hospitals were widely distributed in the country. Other drugs concomitantly used included ethanol, morphine, flunitrazepam and ephedrine. Since methamphetamine can be metabolized to amphetamine but not vers versa, our study confirmed the abuse of methamphetamine not amphetamine in this country.

Expression in Pichia pastoris and characterization by circular dichroism and NMR of rhodostomin.

Rhodostomin (Rho) is a snake venom protein isolated from Calloselasma rhodostoma. Rho is a disintegrin that inhibits platelet aggregation by blocking the binding of fibrinogen to the integrin alpha(IIb)beta3 of platelets. Rho produced in Escherichia coli inhibited platelet aggregation with a K(I) value of 263 nM. Although functional, Rho produced in E. coli is misfolded based on our 2D and 3D NMR studies. In order to correct the folding problem, Rho was expressed in Pichia pastoris. The recombinant Rho expressed in P. pastoris inhibited platelet aggregation with a resulting K(I) value of 70 nM. This is the same potency as that of native Rho. CD analysis showed that the secondary structures of Rho are pH-independent and contain 3.5-7.9% alpha-helix, 48.2-50.5% beta-structures, and 42.3-47% coil. The sequential assignment and structure analysis of Rho were obtained using 2D and 3D 15N-edited NMR spectra. These results provide the first direct evidence that highly disulfide-bonded disintegrin can be expressed in P. pastoris with the correct fold. This evidence may serve as the basis for exploring the structure and function relationships as well as the dynamics of disintegrin and its variants.