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Notes: Crystalline to amorphous transition and subsequent microstructural evolution in silicon induced by Ar+-ion implantation over a wide range of ion fluences (6×1013–1×1017 cm−2) have been investigated by spectroscopic ellipsometry. In the evaluation of the optical and microstructural properties of the damaged layer, the contribution of the surface overlayer to the measured dielectric spectra was separated by fitting a multilayer model with an effective medium approximation. The best fit to the dielectric spectra for disordered silicon could be obtained by taking our highest-fluence implanted (fluence=1×1017 ions/cm2) amorphous silicon (a-Si) data as reference data instead of a-Si data available in the handbook. The derivative spectra as a function of fluence show a distinct and sharp transition from the crystalline to amorphous phase. The threshold fluence for this transition is derived from fitting. Evaluation of standard sum rules and optical moments for imaginary part of the pseudodielectric function reveals no substantial change in various physical parameters below the transition indicating their insensitivity to point defects, while it shows a large change with fluence above the threshold for amorphization. The disorder induced changes in the effective dielectric constant, number of valence electrons per atom participating in optical transition, Penn gap energy, average bond length, coordination number, effective dispersion oscillator energy, an average strength of the interband optical transition with fluence is discussed on the basis of microstructural evolution and corresponding band structure modification. It is also shown that the dielectric functions of damaged silicon are well represented by a sum of six classical Lorentz oscillators. With increasing fluences, each of the oscillator amplitude decreases and linewidth increases except for the 3.3 eV transition which shows increasing amplitude with fluence. These results are discussed in the context of short-range order/disorder and effective band gap reduction along with flattening of the bands with increasing fluence above the amorphization threshold. © 2001 American Institute of Physics.

Notes: The diffusion of B and Sb in Si, with and without a 20-nm-thick epitaxial CoSi2 layer on top, is investigated, during annealing and oxidation, using doping superlattices (DSLs). CoSi2 layers were grown on Si by molecular beam allotaxy. DSLs were grown by molecular beam epitaxy. They consisted of six spikes with peak concentrations of 1018 cm−3(B) and about 1019 cm−3(Sb) with peak centers spaced 100 nm apart. The shallowest spike was capped with 100 nm of Si followed by 20 nm of CoSi2. Annealing in pure N2 and oxidation in pure O2 were performed at temperatures ranging from 800 to 1200 °C. Concentration depth profiles were measured by secondary ion mass spectrometry. The results showed that the dopant diffusion in Si was markedly different with or without a CoSi2 layer. For specimens without CoSi2 layer, we observed oxidation enhanced diffusion of B and oxidation retarded diffusion of Sb in accordance with the literature. However, the effect of CoSi2 layer was a strong retardation of B diffusion and an enhancement of Sb diffusion. The B diffusivity was retarded by a factor of 2–10 as compared to the thermal diffusivity and by a factor of 20–100 as compared to the corresponding diffusivity for oxidation of Si without a CoSi2 layer. Sb diffusivity was enhanced by a factor of 2 with respect to thermal diffusivity and by about a factor of 5 as compared to the case without a CoSi2 layer. © 1999 American Institute of Physics.

Notes: This study compared the effects of intravenous infusions of ephedrine and mephentermine for maintenance of maternal arterial pressure and neonatal outcome in pregnant women receiving subarachnoid block for lower segment Caesarean section. Sixty patients who developed hypotension following subarachnoid block for Caesarean section were randomly divided into two groups of 30 each to receive an intravenous infusion of ephedrine or mephentermine. Hypotension was defined as a decrease in systolic blood pressure of ≥ 20% from the baseline value or an absolute value of 〈100 mmHg, whichever was higher. The vasopressor infusion was titrated to maintain systolic blood pressure between ‘hypotension’ and baseline values. Baseline haemodynamic parameters, haemodynamic changes subsequent to the start of vasopressor infusion, duration of hypotension and amount of vasopressor required were statistically similar for both groups. Neonatal APGAR scores and acid-base profiles were also comparable. To conclude, mephentermine can be used as safely and effectively as ephedrine for the management of hypotension during spinal anaesthesia in patients undergoing elective Caesarean section.

Notes: Gastric emptying of orange-flavoured glucose (group I), low-fat milk (group II) and breast milk (group III) was evaluated in 45 ASA grade I children of ≤ 5 years of age by using real-time ultrasonography and residual gastric volume and pH was then measured. In 15 more children, residual gastric volume and pH was measured after a midnight fast (group IV). Mean (SD) gastric emptying time in group I was 1.53 (0.25) h (range 1.00–1.75), group II 2.32 (0.31) h (range 1.75–2.75) and group III 2.43 (0.27) h (range 2.00–2.75). According to Robert and Shirley's criteria, no children of group I and II were found to be ‘at risk’ at 2 h and 3 h, respectively, but 13.3% of group III children were labelled as ‘at risk’ at 3 h. The incidence of ‘at risk’ children in group IV was 33.3%. It was concluded that 3% fat milk or 17.5% glucose in a volume of 10 ml.kg−1 (maximum volume of 100 ml) can be given in children safely 3 h and 2 h, respectively, before anaesthesia. More real-time studies are required on breast milk to establish guidelines for its potential use as a pre-operative feed 3 h before anaesthesia.

Notes: Mycobacterium tuberculosis can not only neutralize immune effector functions, but also has the ability to modulate host-signalling cascades involved in the development of these responses. The 19 kDa antigen (Rv3763), a lipoprotein of M. tuberculosis, elicits high levels of interleukin (IL)-12 from macrophages in addition to its powerful immunomodulatory properties, leading to suppression of antigen-presentation signalling cascades. The present study was aimed at analysing the effect of overexpression of this antigen on the immunostimulatory properties of M. bovis Bacille Calmette–Guérin (BCG). We have constructed a recombinant BCG strain (rBCG19N) producing higher levels of the 19 kDa antigen in both the cytoplasmic (approximately eightfold) and extracellular (approximately fivefold) fractions as compared to the wildtype BCG. Immunization of mice with rBCG19N elicited high levels of interferon-gamma (IFN-γ) and relatively low levels of IL-10 against the purified 19 kDa antigen. However, in response to total BCG sonicate, mice immunized with rBCG19N produced significantly high levels of IL-10 with relatively very low levels of IFN-γ. This polarization of the host immune responses towards T-helper 2 subtype resulted in complete abrogation of the protective efficacy of BCG, when rBCG19N was used as a live vaccine against M. tuberculosis challenge in guinea pigs.

Notes: Based on their immunodominant nature and ability to induce appropriate immune responses in the host, several antigens of Mycobacterium tuberculosis have shown promise of protection. However, most of the candidate vaccines developed by employing various strategies have afforded protection that is at best comparable with bacillus Calmette–Guérin (BCG) in animal models. Due to the inherent ability of BCG to prime cellular responses in the host, it has become an attractive vehicle for development of a vaccine against intracellular infections. In this study, we have cloned the genes of three immunodominant antigens of M. tuberculosis viz. the ESAT6 (Rv3875), the 19 kDa lipoprotein (Rv3763) and the 38 kDa antigen (Pst homolog) (Rv0934) in pSD5 under the transcriptional control of Trrn, a strong mycobacterial promoter, and expressed them in BCG. The19 kDa antigen and the 38 kDa antigen were expressed at levels that were approximately five and eightfolds higher in the cytosols of recombinant BCG strains rBCG19T and rBCG38T, respectively, as compared with their corresponding levels in M. bovis BCG. Both these antigens were also secreted into the extracellular medium at enhanced levels (19 kDa antigen fourfold and 38 kDa antigen twofold) by rBCG strains in comparison with the wild type BCG. ESAT6 antigen, which is absent in M. bovis BCG, was also expressed at a very high level in the cytosol of the rBCG strain (rBCGE6T). Evaluation of immune responses induced by these three rBCG strains in mice shows a markedly different pattern. The rBCG strain overexpressing the 38 kDa antigen exhibited a predominant T helper 1 (Th1) response with high levels of interferon-γ (IFN-γ) production, whereas overexpression of the 19 kDa antigen resulted in completely polarized Th2 responses against the BCG sonicate. The rBCG-expressing ESAT6 antigen induced a mixed Th1/Th2 response. Our observations suggest that the 38 kDa antigen may hold excellent promise in the rBCG approach for the development of a vaccine against tuberculosis.

Notes: Fifty four varieties of upland cotton (Gossypium hirsutum L.) were screened for resistance to bacterial blight caused by Xanthomonas malvacearum E. F. Smith, (Dowson) under natural field conditions and artificial Inoculation. In general, moderately high levels of field infection provided useful information on susceptibility of varieties but 11 needed to be1 supplemented with artificial inoculation to confirm resistance. Hypocotyl regions of one week-old seedlings were subjected to artificial inoculation with bacterial blight crude isolate using hypodermic needles. None of the fifty lour varieties tested was immune to disease 18.5 % showed a high level of resistance, 29.6 % were recorded as resistant while 20.4 % were susceptible. Another 18.5 % were highly susceptible and 13.0 % showed inconsistent disease reaction under natural field conditions. However, under artificial inoculation the seedlings showed lesions of varied sizes but none of the varieties was found to be resistant. Statistical analysis showed non-significant (P = 0.05) disease interaction indicating susceptibility to disease at the seedling stage. This may be due to lower levels of resistance in seedlings than in mature cotton plants. The resistant varieties were mainly of African origin and well adapted to local conditions. They are therefore potentially useful as commercial varieties in their own right or as donor parents for blight resistance.