Studies on the spin-state equilibria of cobalt ions in the system La1−x Na x Co1−x Nb x O3 (x⩽0·40)

The spin-state equilibria of cobalt ions in the system La_1−x Na _x Co_1−x Nb _x O₃ (x⩽0·40) has been studied by measuring its magnetic susceptibility as a function of temperature in the range 300–600 K. It is found that the behaviour of the samples withx⩽0·10 is similar to that of LaCoO₃, while compositions withx⩾0·20 behave quite differently, exhibiting simple paramagnetic behaviour.     

Water in India’s development: Issues,developmental policy and programmes,and planning approach

The importance of water resources development for sustaining life and the agrarian economy under the conditions prevalent in India is brought out. The inadequacy of drinking water and irrigation facilities inspite of large investments under the various Plans is very disappointing, as also the poor development of the hydroelectric potential. Despite the rich environmental and natural resources of India, there has been very little developmental work due to various reasons, chief of them being non-involvement by specialized technologists in the areas where they matter most. The need for a scientific policy and a planned approach is emphasized so that higher employment generation and rapid economic growth can be achieved.     

Mode I fracture modeling of elastomer-toughened polymers

Analytical models are developed to correlate the mode I fracture toughness of elastomer-toughened polymers with microstructural damage modes occurring around the crack-tip. The total energy dissipation caused by three dominant damage modes, namely, plastic shear band formation, plastic void growth, and plastic deformation of the entire matrix resin, is used as the basis to derive the analytical expression for the mode I fracture toughness of the toughened polymers. Numerical results are presented and compared with available experimental data for a typical toughened epoxy resin. Parametric results involving a number of material and microstructural variables indicate some very interesting trends, and provide some guidelines toward achieving optimum fracture toughness values for these types of material systems.     

Amino acids within residues 181-200 of the nicotinic acetylcholine receptor alpha1 subunit involved in nicotine binding

Hematogenous macrophages and resident brain microglia are agents of demyelination in multiple sclerosis (MS) and paradoxically may also participate in remyelination. In vitro studies have shown that macrophage enrichment of aggregate brain cultures promotes myelination per se and enhances the capacity to remyelinate following a demyelinating episode. It has been hypothesized that remyelination in MS is implemented by surviving dedifferentiated oligodendrocytes or by newly recruited progenitors that migrate, proliferate and synthesize myelin in response to signalling molecules in the local environment. We postulate that macrophage-derived cytokines or growth factors may directly or indirectly promote oligodendroglial proliferation and differentiation, contributing to myelin repair in inflammatory demyelinating disease.     

The role of alloying elements in the design of nickel-base superalloys

The constituents of nickel-base superalloys have been classified into solid solution formers, precipitate formers, carbide formers and surface stabilizers. The characteristics of solutes which would make them most suitable in each category have been specified and appropriate alloying elements have been identified. Nickel-base superalloys are hardened primarily by the precipitation of Ni₃X type compounds. The occurrence and crystallography of precipitation of various kinds of Ni₃X type precipitates have been considered. The role of substitution by alloying elements on mismatch and stability of phases has been discussed. The free electron model and the Engel-Brewer model have been applied for evaluating the stabilities of precipitates, and the role of the alloying elements in determining the stabilities of external and internal surfaces such as grain boundaries have been briefly outlined.     

Influence of alloying elements on the kinetics of massive transformation in gamma titanium aluminides

The effect of alloying elements, Nb and Mn on massive transformation in Ti-45 Al based alloys was studied. The alloy samples were heat treated at 1350 °C for 30 minutes and subsequently cooled to room temperature by furnace cooling, air cooling, and water quenching. The microstructural evolution in various alloys was investigated by a detailed microstructural characterization of the heat-treated samples by optical, scanning, and transmission electron microscopy. It was observed that the volume fraction of the massively transformed gamma in water-quenched samples increased from nil in the Mn-free alloy to ∼70 pct in the alloy containing 2 at. pct Mn. Nb had a minimal effect on the extent of transformation. The effects of Nb and Mn have been rationalized on the basis of the site occupancy of the alloying elements and their possible influence on the phase boundaries and grain size. An attempt has also been made to elucidate the mechanism of massive transformation in these alloys. Based on the results obtained, the influence of Mn and Nb on the kinetics of massive transformation is presented and discussed and, the CCT diagrams for different alloys used in this study are proposed. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Semen quality: is there a paternal effect on pregnancy outcome in in-vitro fertilization/intracytoplasmic sperm injection?

The objective of this study was to investigate the role of the spermatozoon (paternal effects) on implantation and pregnancy outcome in in-vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI). Male individuals of three types were analysed: infertile men with oligoasthenoteratozoospermia (OAT), infertile men with normozoospermia and fertile men (donors). Female counterparts were judged to have comparable egg quality within two groups studied, i.e. infertile women with pure mechanical (tubal) infertility and recipients of donor eggs. There were significantly higher differences in implantation and pregnancy rates in groups using donor spermatozoa and donor egg recipients. Analyses of key set groups revealed a trend toward a poorer implantation and pregnancy outcome when comparing OAT versus normozoospermic patients within IVF, but not within ICSI treatments, in couples with tubal infertility. In couples who were recipients of donor eggs, no differences were observed between OAT patients treated by ICSI and normozoospermic patients treated with IVF. No significant differences were observed in miscarriage rates within any groups studied. In conclusion, the poorer results observed in OAT patients undergoing IVF may be secondary to spermatozoal effects due to a high insemination concentration. Overall, there does not seem to be a significant effect of severe male infertility (OAT) on implantation and pregnancy outcome. However, this does not preclude that specific sperm aberrations may exert a negative effect on embryogenesis and therefore on implantation potential following assisted or in-vivo reproduction.     

Tailored hydrophobic cavities in oligonucleotide-steroid conjugates

BACKGROUND: The extent of adhesion formation following both open and laparoscopic surgery remains unclear. This study aimed to evaluate the extent of postoperative adhesion formation after laparoscopic and open fundoplication in a rat model. METHODS: Fifty-two male Sprague-Dawley rats were randomized into four groups: laparoscopic fundoplication (n = 20), open fundoplication (n = 20), laparoscopy (n = 6) and laparotomy (n = 6). Blood as well as intraperitoneal fluid was sampled for tumour necrosis factor (TNF) alpha measurement by enzyme-linked immunosorbent assay. All the rats were killed 3 weeks after operation, and adhesion formation was evaluated using a standardized scoring system. RESULTS: There were no intergroup differences in body-weight gain after surgery. The overall mortality rate was 19 per cent and death was observed only in the fundoplication groups. Animals that had open fundoplication developed significantly more adhesions than those that underwent laparoscopic fundoplication (34 versus 21). Laparoscopic surgery induced predominantly parietal adhesions, whereas open surgery was more associated with visceral adhesions. The adhesions observed in the laparoscopic groups were significant thinner than those after open surgery and the tenacity of adhesions was decreased in laparoscopic compared with open surgery. The peak plasma level of TNF-alpha was reached during laparoscopic fundoplication, whereas the peak level was observed 3 h after open fundoplication. Intraperitoneal TNF-alpha levels showed no significant differences at 3 h. CONCLUSION: These findings indicate that laparoscopic fundoplication in rats leads to less severe adhesions of a different type (parietal) compared with those seen in the open controls.     

Grain boundary segregation of boron in INCONEL 718

The segregation behavior of boron at grain boundaries in two INCONEL 718⁺ based alloys with different B concentrations was studied. The alloys, one containing 11 ppm of B and the other 43 ppm, were homogenized at 1200 °C for 2 hours followed by water quenching and air cooling. A strong segregation of boron at grain boundaries was observed using secondary ion mass spectrometry after the heat treatment in both the alloys. The segregation was found mainly to be of nonequilibrium type. The homogenized samples were also annealed at 1050 °C for various lengths of time. During annealing, boride particles were observed to first form at grain boundaries and then to dissolve on continued annealing at 1050 °C. The mechanisms of segregation and desegregation of B are discussed.