Preparation of Silicon Nitride Whiskers from Diatomaceous Earth: I, Reaction Conditions

Whiskers and powder of silicon nitride were prepared by the carbothermal reduction and nitridation of diatomaceous earth in the presence of flowing N₂ and NH₃. The optimum temperature for the formation of Si₃N₄ whiskers was 1350°C and the yield reached almost 20% after 24 h. The α-Si₃N₄ content decreased with increasing nitridation temperature. Yields of the whiskers were dependent on NH₃ concentration and the total gas feed rate. The maximum yield of inside whiskers was obtained for a 25 vol% NH₃/N₂ mixture, while the maximum quantity of outside whiskers was produced for 75 vol% NH₃/N₂. The sum of the yield of the inside and outside whiskers increased with decreasing total gas feed rate. However, no nitridation of SiO₂ was observed at a feed gas rate below 0.18 mmol·min⁻¹. The yield of the inside whiskers increased gradually with increasing reaction time up to 36 h, whereupon a constant value was attained. Although the amount of outside whiskers produced was relatively small, the quantity seemed to increase until 60 h.     

Computer simulation of deformation and fracture of small crystals by molecular dynamics method

Body-centred cubic iron whiskers having [100] and [110] axes were pulled in a molecular dynamics simulation using a supercomputer. The upper yield stress close to the theoretical strength was found. Above the upper yield stress, phase transformation was observed; at the same time the stress was greatly reduced. A new possible mechanism of twinning is proposed. The whiskers were pulled until they had broken into two pieces. Copper small crystals with and without a notch were sheared. It was observed that the edge dislocations were created at the surface and moved through and escaped from the crystals. Copper small single crystals with a notch were pulled. A half-dislocation was created near the tip of the notch. Sharp yield stress was observed. In medium deformation dislocations on different slip planes were created. Due to the cutting of dislocations the tensile stress increased.     

Thickness dependence of signal/background ratio of inner-shell electron excitation loss in eels

The influence of the specimen thickness on the core-edge loss intensity has been studied using the relative specimen thickness (t_R) as the standard rule for the specimen thickness in EELS. The core-edge loss intensity monotonously increased with the increasing relative specimen thickness, 0 < t_R ? 1, and monotonously decreased with increasing relative specimen thickness, t_R ? 1, behind the maximum of core-edge intensity at t_R ? 1. “Optimum specimen thickness” to get the highest core-edge intensity is suggested for the thickness of t_R = 1. The thickness-dependent factor T(t_R) should be considered in a practical measurement in EELS.     

Multijoint Inspection Robot

Developing a remote inspection system is an urgent necessity for reducing the down time of facility and occupational radiation exposure to inspection personnel in nuclear facilities.     

Surgical management of aortic regurgitation associated with ventricular septal defect

The intracarotid amobarbital procedure was carried out in 8 male and 7 female candidates to temporal lobectomy, and a female candidate to frontal lesionectomy, aged 18-50 (mean 32.5) years. Language and memory were tested after injection in each hemisphere. Both were measured by the Montreal procedure. In 9 patients language and memory were evaluated with the Seattle procedure too. In 12 patients the left hemisphere was dominant for language; three had bilateral dominance. In 1 patient the Seattle procedure demonstrated the dominant hemisphere by relatively slowness of speech during the drug effect in the left hemisphere. Memory was defined to be in the left hemisphere in 12 patients, in the right in 2, bilateral in 1 and in another lateralization was not possible. In 1 patient memory dominance was determined by the Montreal protocol alone because of lack of cooperation. These early results indicate that the methods may be complementary for determination of language and memory dominance in epilepsy surgery candidates.     

Interaction between crack and arbitrarily shaped hole with stress and displacement boundaries

The interaction between a crack and an arbitrarily shaped hole under stress and displacement boundaries in an infinite plane subjected to a remote uniform load is studied. The Green's functions of a point dislocation for the problems are derived and are then used to analyze the interaction problem. The superposition principle is employed to reduce the original problem to two subsidiary problems. The complex stress functions of each problem are composed of two parts, in which the second parts are always holomorphic. Using analytical continuation in conjunction with rational mapping function, the stress functions are obtained in closed form. The interaction of a hole or an inclusion with a crack is solved using dislocations to model the crack and solving a system of singular integral equations. Stress intensity factors for crack tips and stress concentration factors for inclusion corner are determined and plotted for various cases. The affecting ranges of hole and inclusion are investigated.     

An Escherichia coli protein that exhibits phosphohistidine phosphatase activity towards the HPt domain of the ArcB sensor involved in the multistep His-Asp phosphorelay

The Escherichia coli sensory kinase, ArcB, possesses a histidine-containing phosphotransfer (HPt) domain, which is implicated in the His-Asp multistep phosphorelay. We searched for a presumed phosphohistidine phosphatase, if present, which affects the function of the HPt domain through its dephosphorylation activity. Using in vivo screening, we first identified a gene that appeared to interfere with the His-Asp phosphorelay between the HPt domain and the receiver domain of OmpR, provided that the gene product was expressed through a multicopy plasmid. The cloned gene (named sixA) was found to encode a protein consisting of 161 amino acids, which has a noticeable sequence motif, an arginine-histidine-glycine (RHG) signature, at its N-terminus. Such an RHG signature, which presumably functions as a nucleophilic phosphoacceptor, was previously found in a set of divergent enzymes, including eukaryotic fructose-2,6-bisphosphatase, E. coli periplasmic phosphatase and E. coli glucose-1-phosphate phosphatase, and ubiquitous phosphoglycerate mutase. Otherwise, the entire amino acid sequences of none of these enzymes resembles that of SixA. It was demonstrated in vitro that the purified SixA protein exhibited the ability to release the phosphoryl group from the HPt domain of ArcB, but the mutant protein lacking the crucial histidine residue in the RHG signature did not. Evidence was also provided that a deletion mutation of sixA on the chromosome affected the in vivo phosphotransfer signalling. These results support the view that SixA is capable of functioning as a phosphohistidine phosphatase that may be implicated in the His-Asp phosphorelay through regulating the phosphorylation state of the HPt domain.     

Development of high-efficiency a-Si solar cell submodule with a size of 30 cm × 40 cm

We have achieved a stabilized conversion efficiency of 8.9% in a single-junction a-Si solar cell and 10.6% in a double-junction a-Si/a-SiGe solar cell for a size of 1 cm², which are the world's highest values achieved so far for this size and structure. We have been investigating the improvement of stability in a-SiGe film with regard to the bottom cell i-layer, and the control of E_opt in a-SiGe film in order to confirm the tandem cell design. On the other hand, uniformity of ± 1% has been obtained in conversion efficiency for many small cells fabricated in a size of 30 cm × 40 cm, evaluated by using a-Si single-junction structure. As a result, we have achieved the stabilized high-effective area conversion efficiency of 8.64% in a 30 cm × 40 cm a-Si/a-Si tandem submodule. The combination of the above techniques and further optimization can be expected to achieve a stabilized conversion efficiency of more than 10% for a 30 cm × 40 cm double-junction a-Si/a-SiGe submodule.