Crystallization kinetics of poly(L-lactide-co-meso-lactide)

The crystallization kinetics of poly(L -lactide-co-meso-lactide) were determined over a range of 0% to 9% mesolactide. The kinetics were fit to the nonlinear Avrami equation and then to the Hoffman–Lauritzen equation modified for optical copolymers. The theory was found to fit the data well. The crystallization half-time was found to increase about 40% for every 1 wt % meso-lactide in the polymerization mixture. The change in crystallization rate is driven mainly by the reduction in melting point for the copolymers. The copolymer crystallization kinetics were also determined in the presence of talc, a nucleating agent for polylactide. The theory again fit the data well, using the same growth parameters and accounting for the talc only through the nucleation density term. © 1996 John Wiley & Sons, Inc.     

HST1, a new member of the SIR2 family of genes

A novel Saccharomyces cerevisiae gene, HST1, was identified from among anonymous cDNAs and the complete corresponding genomic clone was isolated and sequenced. HST1 is very closely related to SIR2, showing 71% sequence identity over 84% of its length. Polymerase chain reaction with degenerate primers on S. cerevisiae DNA identified three additional SIR2-related genes designated HST2, HST3 and HST4. The sequences of HST2, HST3 and HST4 correspond to sequences previously released by the S. cerevisiae genome sequencing project as U33335, NCBI gi:965078; X87331, NCBI gi:829135; and Z48784, YD9346.03, respectively. Disruption of HST1 has shown no phenotype with respect to mechanisms in which SIR2 has a role, namely, regional silencing of HMLα, or in rDNA recombination. The sequence of HST1 has been deposited in the DDBJ, EMBL and GenBank at NCBI database under Accession Number L47120.     

Filament-activated chemical vapour deposition of nitride thin films

We have applied the novel method of hot filament-activated chemical vapour deposition (HFCVD) for low-temperature deposition of a variety of nitride thin films. In this paper the results from our recent work on aluminium, silicon and titanium nitride have been reviewed. In the HFCVD method a hot tungsten filament (1500–1850°C) was utilised to decompose ammonia in order to deposit nitride films at low substrate temperatures and high rates. The substrate temperatures ranged from 245 to 600°C. The film properties were characterised by a number of analytical and optical methods. The effect of various deposition conditions on film properties was studied. All the films obtained were of high chemical purity and had very low or no detectable tungsten contamination from the filament metal.     

Reactions of TATB-Based Explosive with Molten Metal

The reactions of combustion products (CO, H₂O) from the insensitive high explosive LX-17 (92.5 wt% 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 7.5 wt% Kel-F 800 binder) with molten metal (75 a%Nd, 25 a% Fe) were studied, to determine their contribution to the energy release rate of deflagrating LX-17, Kinetic data taken with gas mixtures of CO and H₂O, and larger-scale tests with LX-17, showed that the reactions were slow and incomplete and that there was no significant contribution to the energy release rate. From the tests with JX-17, the effective flame temperature and burn velocity were dependent on confinement of gas products. LX-17 preheated to 500 K - 510 K showed effective flame temperatures of 1100 K - 1400 K and burn rates of 0.08–0.11 mm/s, depending on the extent of gas confinement by the molten metal.