Cryotribology of diamond and graphite

An experimental study was carried out on the tribological behaviour of materials of interest in cryogenic applications, focusing on diamond and graphite. Both natural diamond (referred in the text as diamond) and chemical-vapour-deposition (CVD) diamond (CVD-diamond) were used. The experiment was carried out using a pin-on-disc tribometer capable of operating at cryogenic temperatures, from 4.2 to 293 K. Two basic scenarios of testing were used: (1) frictional coefficient (μ) versus velocity (v) characteristics at constant temperatures; and (2) μ, versus temperature (T) behaviour at fixed sliding speeds. For diamond, graphite, and stainless steel pins, each set of pins against CVD-diamond disc, values of μ are virtually velocity independent. For each of diamond, alumina, and graphite pins, each set against graphite disc, the δμ/δv characteristic is favorable i.e. positive. For diamond and graphite pins against CVD-diamond discs, values of μ are nearly temperature independent in the range 77–293 K. Each μ(T) trace for pin materials sliding on graphite discs has a peak at a temperature in the range 100–200 K. As is the case with diamond/stainless steel pairs, there is a definite correlation between friction and material hardness: μ is inversely proportional to material hardness. Thus μ is higher at higher temperatures, because hardness generally decreases with temperature.     

Synthesis of androst-5-en-7-ones and androsta-3,5-dien-7-ones and their related 7-deoxy analogs as conformational and catalytic probes for the active site of aromatase

A series of androst-5-en-7-ones and androsta-3,5-dien-7-ones and their 7-deoxy derivatives, respectively, were synthesized and tested for their abilities to inhibit aromatase in human placental microsomes. All the steroids inhibited the enzyme in a competitive manner with Ki's ranging from 0.058 to 45 microM. The inhibitory activities of 17-oxo compounds were much more potent than those of the corresponding 17 beta-alcohols in each series. Steroids having an oxygen function (hydroxy or carbonyl) at C-19 were less potent inhibitors than the corresponding parent compounds having a 19-methyl group. 3,5-Dien-7-one 24 and its 19-hydroxy and 19-oxo derivatives (12 and 13) as well as 19-oxo-5-en-7-one 3 caused a time-dependent inactivation of aromatase only in the presence of NADPH in which the kinact values of 19-als 3 and 13 (0.143 and 0.189 min-1, respectively) were larger than those of the corresponding 19-methyl (23 and 24) and 19-hydroxy (1 and 12) steroids, respectively. 19-Nor-5-en-7-one 4 but not its 3,5-diene derivative 14 also inactivated the enzyme in a time-dependent manner. In contrast, 7-deoxy steroids 21 and 27, having a 19-methyl group, did not cause it. The inactivations were prevented by the substrate androstenedione, and no significant effects of L-cysteine on the inactivations were observed in each case. The results suggest that oxygenation at C-19 would be at least in part involved in the inactivations caused by the inhibitors 23 and 24. The conjugated enone structures should play a critical role in the inactivation sequences.     

A 3.5-ns, 500-mW, 16-kbit BiCMOS ECL RAM

A 16-kbit BiCMOS ECL SRAM with a typical address access time of 3.5 ns and 500-mW power dissipation was developed. The RAM was fabricated using half-micrometer, triple-poly, and triple-metal BiCMOS technology. The fast access time with moderate power dissipation has been achieved using new circuit techniques: a grounded-gate, nonlatching-type level converter with a wired-OR predecoder and a direct column sensing scheme having a cascode differential amplifier. As a result of extensive use of high-speed bipolar ECL circuits with self-aligned bipolar transistors, the RAM attains high-speed performance without degrading the low-power BiCMOS RAM characteristics.<>     

Error performance of frequency-hopped d.p.s.k. system

In order to accurately evaluate bit error rates for a frequency-hopped d.p.s.k. system, digital computer experiments were performed. The value of Eb/N0 at the 10?3 error rate without fading was 8.4 dB.     

Secretion and Sex differences in cord serum growth hormone levels of the human fetus (author's transl)

Cord venous growth hormone (GH) and somatostatin levels were measured by radioimmunoassay in 86 infants and 11 anencephalic infants. 1) Cord GH levels were 69.2 +/- 20.2 ng/ml (N = 6, gestational weeks (GW) : 21-30W, mean +/- S.D.), 31.5 +/- 24.3 ng/ml (N = 11, GW : 31-36W), and 17.6 +/- 8.9 ng/ml (N = 71, GW: 37-41). In anencephalic infants, cord GH levels were significantly lower (2.3 +/- 1.4 ng/ml) than those in preterm and fullterm infants. 2) In fullterm infants, cord GH levels of small infants (19.2 +/- 9.2 ng/ml, N = 33, birth weight less than 3,250g) were significantly higher than that of large infants (15.1 +/- 8.1 ng/ml, N = 38, birth weight greater than of equal too 3,250g). On the other hands, cord somatostatin levels were relatively lower in small infants than in large infants. 3) There was a significant difference between male cord GH levels (20.6 +/- 8.9 ng/ml, N = 35) and female cord GH levels (14.6 +/- 8.0 ng/ml, N = 36). These results suggest that fetal GH secretion is suppressed by GH inhibiting factor (somatotropin release inhibiting factor) from mid gestation toward term and there is a sex difference of fetal GH secretion in fullterm fetus.     

A parallel distributed control architecture for multiple robot systems using a network of microcomputers

This paper presents the design and implementation of a parallel distributed control architecture for industrial multiple robot systems. The design methodology is based on a concept of discrete states and actions, and a robotic task is represented as a sequence of primitive actions. For cooperative or exclusive tasks at the synchronous level of multiple robot systems, Petri net representation is applied, and discrete event-driven control is implemented as a data flow network of concurrent processes communicating with each other. Implementation of multiprocessing control on a microcomputer and a network of microcomputers is discussed.