Combustion synthesis of advanced materials: Part I. Reaction parameters

An explanation of combustion (self propagating high temperature) synthesis (SHS) is given together with a historical perspective of the examination of such exothermic reactions. The application of thermochemical functions has been used to predict theoretically the maximum adiabatic temperature, T_ad. This, combined with a knowledge of the ignition temperature, T_ig, and the actual combustion temperature, T_c, has been used to determine the heat loss from the SHS reaction and the amount of heat needed to raise the adjacent, cold, reactant layer to the ignition temperature in order to maintain the self sustaining nature of the propagating mode of the reaction. The pertinent reaction parameters that control self propagating high temperature (combustion) synthesis reactions have been examined. These include: reactant particle size and shape; powder mixing and compaction; green density; reaction stoichiometry; impurities; volatiles and diluents; reaction environment; mode and technique of ignition; heating rate; and the effect of these parameters on the generation of heat, exothermicity and control of the SHS reaction.     

Cell cycle and genetic requirements of two pathways of nonhomologous end-joining repair of double-strand breaks in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, an HO endonuclease-induced double-strand break can be repaired by at least two pathways of nonhomologous end joining (NHEJ) that closely resemble events in mammalian cells. In one pathway the chromosome ends are degraded to yield deletions with different sizes whose endpoints have 1 to 6 bp of homology. Alternatively, the 4-bp overhanging 3' ends of HO-cut DNA (5'-AACA-3') are not degraded but can be base paired in misalignment to produce +CA and +ACA insertions. When HO was expressed throughout the cell cycle, the efficiency of NHEJ repair was 30 times higher than when HO was expressed only in G1. The types of repair events were also very different when HO was expressed throughout the cell cycle; 78% of survivors had small insertions, while almost none had large deletions. When HO expression was confined to the G1 phase, only 21% were insertions and 38% had large deletions. These results suggest that there are distinct mechanisms of NHEJ repair producing either insertions or deletions and that these two pathways are differently affected by the time in the cell cycle when HO is expressed. The frequency of NHEJ is unaltered in strains from which RAD1, RAD2, RAD51, RAD52, RAD54, or RAD57 is deleted; however, deletions of RAD50, XRS2, or MRE11 reduced NHEJ by more than 70-fold when HO was not cell cycle regulated. Moreover, mutations in these three genes markedly reduced +CA insertions, while significantly increasing the proportion of both small (-ACA) and larger deletion events. In contrast, the rad5O mutation had little effect on the viability of G1-induced cells but significantly reduced the frequency of both +CA insertions and -ACA deletions in favor of larger deletions. Thus, RAD50 (and by extension XRS2 and MRE11) exerts a much more important role in the insertion-producing pathway of NHEJ repair found in S and/or G2 than in the less frequent deletion events that predominate when HO is expressed only in G1.     

Acute aortic dissection: association with patent ductus arteriosus

The Cuban recombinant vaccine against the hepatitis B virus was applied to a group of individuals over 65 from a geriatric home in Havana City. Dose of 20 ìg were administered within a scheme from 0.1 to 6 months in order to study its immunogenicity, which was evaluated at 2, 7, and 12 months after the first dose. 47.1% of protective titres and geometrical mean of 6.04 UI/L were obtained after 60 days. 100% of seroconversion (UI/L) and seroprotection (10 UI/L) and geometric mean of 136.93 UI/L were obtained when the immune response was evaluated on the 7th month. Finally, after a year, seroconversion and seroprotection were also of 100%, and the geometric mean was of 204.61 UI/L. It was proved the high immunogenic power of this vaccine, which makes it recommendable to protect this age group from the hepatitis B virus.     

A history of M.S. and Ph.D. programs offered by schools and colleges of optometry in North America

This paper gives an overview of the history of M.S. and Ph.D. graduate programs offered by schools and colleges of optometry. It also highlights some of the contributions of Henry Hofstetter to graduate education.     

Maximum cardiac output during incremental exercise by first-pass radionuclide ventriculography

A flow injection hydride atomic absorption spectrometric (FI-HAAS) method was developed for determining selenium in human milk and whole blood after microwave digestion of the sample. The sample (2 mL human milk or 0.25 mL blood) was introduced into the microwave vessel with 1.5 mL HNO3 and 0.25 mL H2O2 and 300 W (4 min) and 600 W (4 min) were applied. The digestion was completed by heating to 140 degrees C (2-3 h). Se (VI) was reduced to Se (IV) with hydrochloric acid. The instrumental conditions for FI-HAAS (concentrations of reducing agent and carrier acid, flow rate of argon carrier gas, and sample volume injected) were optimized. The detection limit of the proposed method was 0.23 ng/mL (assay) or 115 pg Se (absolute) in biological samples (1.15 ng/mL milk, 10.4 ng/mL blood). The precision values were 5.0% for milk and 4.0% for blood. The accuracy was evaluated with 2 reference materials, National Institute of Standards and Technology Non-Fat Milk Powder (found: 104.3 +/- 7.2 ng/g, certified: 110 +/- 10 ng/g) and Whole Blood Seronorm (found: 81 +/- 7.3 ng/mL, reference: 83 +/- 4 ng/mL). The results show the suitability of the method for selenium determination in human milk and whole blood. The method was applied to whole blood samples obtained from pregnant women and to human milk.     

Intraocular pressure fluctuations during scleral buckling surgery

PURPOSE: The purposes of this study are to measure real-time intraocular pressure (IOP) during scleral buckling and to determine the effects of elevated IOPs on ocular perfusion. PATIENTS AND METHODS: A standard 4-mm, 20-gauge infusion cannula was inserted through the pars plana, connected to a standard hemodynamic monitoring unit with an electronic pressure transducer, and calibrated. The authors measured real-time IOP in 20 eyes undergoing scleral buckling surgery for primary rhegmatogenous retinal detachments and determined the IOP required to close the central retinal artery. Pressure measurements were read from the monitor videoscreen intraoperatively and from a continuous paper tracing postoperatively. RESULTS: The patients ranged in age from 24 to 88 years (mean, 59.7 years). The highest IOP elevations occurred during scleral depression and cryopexy, ranging up to 210 mmHg (mean, 116 mmHg). Pressures at which the central retinal artery closed ranged from 48 to 110 mmHg (mean, 79.2 mmHg). Manipulations of the globes caused IOPs greater than the central retinal artery perfusion pressures in 13 of the 20 patients. The duration of pressures in excess of the central retinal artery perfusion pressure ranged from 6 to 402 seconds (mean, 118.8 seconds). There were no intraoperative or postoperative complications from the infusion cannula. CONCLUSIONS: Conventional scleral buckling surgery causes wide fluctuations in IOP and may impair ocular perfusion. Additional studies are needed to determine the long-term consequences of these pressure elevations.     

A formal model of asynchronous communication and its use in mechanically verifying a biphase mark protocol

We present a formal model of asynchronous communication between two digital hardware devices. The model takes the form of a function in the Boyer-Moore logic. The function transforms the signal stream generated by one processor into that consumed by an independently clocked processor, given the phases and rates of the two clocks and the communications delay. The model can be used quantitatively to derive concrete performance bounds on communications at ISO protocol level 1 (physical level). We use the model to show that an 18-bit/cell biphase mark protocol reliably sends messages of arbitrary length between two processors provided the ratio of the clock rates is within 5% of unity.     

Herd immunity to filarial infection is a function of vector biting rate

Despite the existence of an impressive body of work on human immune responses against filarial infections, the occurrence of a protective response to infection remains unclear. Here, we use a combined modelling and comparative data analysis framework to address this issue for human infections with the filarial parasite, Wuchereria bancrofti. By analogy with previous work, the analysis involves the comparison of observed field patterns of infection with epidemiological patterns predicted by a mathematical model of parasite immunity. Unlike most other human helminths, which are transmitted by ingestion or dermal penetration, exposure to infection with lymphatic filariasis can be measured explicitly in terms of vector mosquito biting rates, thereby also allowing, probably for the first time, examination of the suggested role of exposure in generating herd immunity to macroparasites. Observed field patterns in this study were derived from 19 different published studies, which gave parallel estimates of community exposure rates and the corresponding age--prevalence patterns of infection, while predictions of the epidemiological impact of herd immunity were obtained using a catalytic model framework. The results provide the first conclusive evidence to date that variations in the observed age--prevalence patterns of infection in filariasis can be effectively explained by the occurrence of an exposure-driven acquisition of herd immunity. We discuss this result in terms of implications for the new World Health Organization-led initiative for the global control of this parasitic disease.