The movement of lenticular pores in UO2 nuclear fuel elements

A simple theory is developed which describes the motion of lenticular pores in a temperature gradient and takes into account evaporation and condensation rates in the pore surfaces. This mechanism, rather than diffusion within the pore, is likely to govern the pore motion if the pores are filled with helium, and it also gives the experimentally favoured $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>5</mtext><mtext>2</mtext>}}$ temperature-dependent factor in the pore velocity. Experimental velocities for UO₂ are reproduced quite well by the theory provided that the O/U ratios were slightly greater than 2 in the hot pore region. At temperatures around 2000 K the latter ratio is critical in giving the equilibrium vapour pressure in the pore and hence the pore velocity.     

On the Execution of Large Batch Programs in Unreliable Computing Systems

The execution of long-running batch programs imposes severe reliability constraints on a computing system since the occurrence of a failure during its execution is more likely and that once occurred, a failure would destroy all the processing perfonned thus far. This paper studies the execution delay and machine resources consumed in supporting the running of large batch programs in a computing environment interrupted by failures. The effect of checkpoints and their optimal insertion are also considered. The results are applicable to arbitrary law of failure.     

Morphometric video analysis of the engine-driven nickel-titanium Lightspeed instrument system

Two hundred and sixteen Lightspeed instruments were evaluated microscopically for the presence of corrosion, surface debris, and alloy defects. The instruments were assessed morphometrically for consistency of physical design and dimensions by measuring and analyzing eight parameters of the instrument pilot tips, heads, and shafts. Results from visual inspection showed that none of the instruments were corroded; 23 presented surface porosities, and 17 had sharp strips of alloy. Data obtained by morphometric analysis indicated the mean diameter of the head of only 7 of 18 sizes met the +/- 0.02 mm allowable tolerance set forth by the American Dental Association (ADA) Specification No. 28. Observation and video analysis indicated that instruments of the same size adhere to the same basic design, but that morphometric variations do exist. The visual and intersize analysis indicated that the Lightspeed is not an instrument of any one determined shape that changes only in diameter. Rather, it is a series of instruments that show gradual shifts in both size and shape as the instrument size increases. Lightspeed instruments are a new type of nickel-titanium endodontic instrument that cannot be evaluated using the standards proposed by the American National Standards Institute/ADA Specification No. 28 for files and reamers.     

New NO-donors with antithrombotic and vasodilating activities, Part 17. Arylazoamidoximes and 3-arylazo-1,2,4-oxadiazol-5-ones

Seven arylazoamidoximes (3), six phenoxycarbonyl derivatives (4), and six 1,2,4-oxadiazol-5-ones (5) have been prepared and their structure and purity established by spectroscopy and elemental analysis. In the EI mass spectra ready elimination of NO from the title amidoximes was observed. A new addition reaction of 3a with hydrochloric acid to 4-chlorophenylhydro-azoamidoxime 7 is described. The compounds were tested for nitric oxide dependent biological properties, i.e. platelet aggregation, antithrombotic effects, and decrease in blood pressure. In arterioles of rats 5/19 compounds inhibited the formation of thrombi with a laser beam by > or = 20% 2 h after oral administration of 60 mg/kg. Among these are three amidoximes (3a, 3e, 3f), one phenoxycarbonyl derivative (4a), and one oxadiazolone (5a). With the 4-chlorophenylazoamidoxime 3c a long lasting (24 h) decrease of blood pressure in spontaneously hypertensive rats was observed. Microsomal fractions of rat liver oxidize arylazoamidoximes and generate nitric oxide (e.g. 3a and 3b). NO was measured by the oxyhemoglobin assay. The influence of SOD, pretreatment of the rats with dexamethasone, as well as kinetic parameters were determined. Type 3 compounds, therefore, are a new class of NO donors. Type 4 and 5 compounds function as their prodrugs.