Molecular kinetics and multiline model for the E-beam pumped XeF(B-X) laser

A physical model of the time-, temperature- and wavelength-dependent behavior of an E-beam pumped XeF(B-X) laser is developed. Correlations with published laser- and fluorescence-efficiency data, laser spectra, gain, and absorption data are discussed.     

Experiments with active phase matching of parallel-amplified Multiline HF laser beams by a phase-locked Mach-Zehnder interferometer

Active phase matching of multiline HF laser beams by means of a phase-locked Mach-Zehnder interferometer was demonstrated by locking the interferometer to the central interference fringe at zero optical path length difference. The central fringe could be found by varying the spectral content of the input beam. Laser amplification in one leg of the interferometer decreased fringe visibility without adversely affecting locking. Single-line fringe patterns produced by an array spectrometer (while the interferometer was operated in its scanning mode) were analyzed to show that no significant dispersion occurred in the amplifier. The techniques developed have potential for measuring dispersion mismatch between larger parallel amplifiers. These experiments demonstrated in principle that a number of multiline HF amplified beams can be recombined and phase-matched to produce a high beam quality output beam.     

Nutritional management ofPinus radiata at Gurnang State Forest,New South Wales

A survey of foliage and soil nutrients and productivity in post first-thinned stands (15 years +) ofP. radiata showed high variability on uniform soil parent material. Site index was significantly related to stand age and soil P. Nutritional monitoring plots in pre-crown closure stands showed P and B deficiency in the foliage and declining concentrations with age. High accumulations of Al and Mn in the foliage in both surveys were unrelated to stand age or site index. A 14-year-old once-thinned stand responded to N and P but not to K, Mg, Ca, B, Cu or Zn. The requirement for P in foliage appears to increase with age, though assessing the critical level is difficult. Nutritional monitoring, supported by fertilizer trials, appears essential to assess nutritional needs and to maintain productivity.     

Histologic studies of human skin test responses to ragweed and compound 48/80. III. Effects of alternate-day steroid therapy

Our previous studies have shown depressed eosinophil responses in skin test reactions to pollen antigens and compound 48/80 in those just completing a 1-wk course of daily steroids. Wheal reactions were unaffected. In this study, 6 ragweed-sensitive atopic subjects were studied before and on the seventh day ("day on") and day 8 ("day off") of a course of alternate-day steroids. Blood neutrophil levels rose on day 7 and were similar to baseline on day 8, whereas blood eosinophil levels were significantly reduced on both days 7 and 8. Neutrophil responses in skin test reactions were depressed on day 7 and normal on day 8. In contrast, the tissue eosinophil responses were depressed significantly, and to similar degree, on both days 7 and 8. These findings are of potential significance in evaluating the clinical effects of steroids in allergic diseases.     

MOLECULAR STRUCTURE OF INTERFACES FORMED WITH PLASMA-POLYMERIZED SILICA-LIKE PRIMER FILMS: PART III. MECHANICAL STRENGTH AND ENVIRONMENTAL DURABILITY OF THE PRIMER/ALUMINUM AND PRIMER/TITANIUM INTERFACES

In order to characterize the properties of film/metal interfaces formed between plasma-polymerized amorphous silica-like (a-SiO 2 ) films and metal substrates, lap joints and wedge test specimens were made from aluminum and titanium adherends that were pretreated with plasma-polymerized a-SiO 2 primer films. High breaking strengths of all the lap joints due to cohesive failures within the adhesive indicated that the adhesive/a-SiO 2 and a-SiO 2 /metal interfaces were very strong. In addition, since failure was cohesive within the adhesive, the different interfacial structures at the a-SiO 2 /aluminum and a-SiO 2 /titanium interfaces were cohesively strong. In order to maximize the environmental stress placed upon the a-SiO 2 /metal interfaces, the a-SiO 2 primer films on the metal adherends were pretreated with silane primers before adhesive bonding. This ensured that differences in environmental durability at the a-SiO 2 /metal interface, if any, would be observed. However, no interfacial failures of pretreated substrates was observed, indicating that the a-SiO 2 /aluminum and a-SiO 2 /titanium interfaces had very high environmental durability. This correlated well with the results obtained in Parts I and II of this work, which supported the formation of strong Al-O-Si and Ti-O-Si bonds at the a-SiO 2 /metal interface.     

Tensile strength elevation of brittle polymers by entanglements

Plots of tensile strength (T) versus reciprocal number average molecular weight (M^?1) have been made using previously reported data for linear polymers tested in the glassy state. Over a wide range of molecular weights there is conformity to Flory's empirical equation T = A - BM^?1, in which A and B are constants. Values of M obtained by extrapolation to T = 0 correlate with critical values of molecular weight which are diagnostic of incipient formation of an entangled network. The entanglement thesis is developed further by reference to a model in which brittle strength is attributed to the breaking of covalent backbone bonds. Theoretical values are calculated which exceed experimental values by a factor of only three. Such close agreement is attributed to the insensitivity of glassy linear polymers to flaws.     

Effect of a diamine additive on the structure-property relationships of rim polyurethane elastomers

Structural and mechanical data have been compared for reaction injection molding (RIM) polyurethanes prepared from uretonimine-modified diphenylmethane 4,4′-diisocyanate (MDI), ethylene glycol (EG), and a polyol (a polyether; M_n ? 5000), in order to investigate the effect of addition of a small amount of a polyetherdiamine (PEDA; M_n ? 400) to the reaction mixture, A series of specimens containing 18 parts and 30 parts EG, with and without the diamine additive, were examined both as-prepared and after thermal annealing. The specimens were compared in terms of their x-ray crystallinity, elongation, flexural modulus, impact strength, and heat-sag behavior. All of the specimens showed evidence for crystalline hard segments, which are more abundant in the series containing 30 parts EG. The crystallinity is lowest in the as-prepared specimens without the PEDA additive, and is increased by annealing for 1 hour at 120°C. The as-prepared specimen with additive has a hard segment crystallinity similar to that of the annealed specimen without additive. These results correlate with the mechanical property data, which improve as a result of annealing and/or the use of a PEDA additive. It is argued that the use of the polyetherdiamine enhances the phase separation and facilitates hard segment crystallization, leading to better heat-sag behavior. It is significant that the unannealed/with PEDA and annealed/without PEDA specimens have similar properties. Use of PEDA additive improves the green strength and impact strength of molded parts.     

Cholesterol vehicle in experimental atherosclerosis. III. Effects of absence or presence of fatty vehicle

Three separate experiments show that cholesterol administered to rabbits in the absence of added fat is more atherogenic than cholesterol fed together with corn oil. When cholesterol is dissolved in the corn oil (by heating) prior to mixing with the diet, it is more atherogenic than when it is suspended in the oil. In every case the lowest serum and liver cholesterol levels were observed in the group not receiving corn oil. Gas chromatography of the fatty acids of the serum cholesterol esters of pooled sera suggest that there are smaller amounts of unsaturated C₁₈ fatty acids in the cholesterol-no fat group. Deficiency in these unsaturated acids may be the cause of the high atherogenicity of the cholesterol-no fat diet. There is also a lower proportion of unsaturated fatty acids in the triglycerides of this group. Heating of corn oil 10 min, at 160–200(°C.) causes an increase of titratable fatty acid in the oil (0.005 m-equiv./g. to 0.088 m-equiv./g. or 0.14% FFA to 2.5% FFA). The relatively large amounts of free unsaturated fatty acids in the heated oil may be the cause of the greater atherogenicity of the solution, as compared to the suspension, of cholesterol in corn oil. Presented at the 33rd Fall Meeting, American Oil Chemists’ So ciety, Los Angeles, Calif., September 28–30, 1959. This work was supported by grants from the National Institutes of Health (H-3299 and A-2131), The Nutrition Foundation Inc., and The John A. Hart-ford Foundation Inc.     

The falling weight impact test applied to some glass-fibre reinforced nylons

Measurements on five glass-fibre reinforced compounds have shown that at fibre weight fractions of 0.3 and 0.5 increased mean fibre length confers greater resistance to impact as measured by a conventional flexed-plate method. The results were consistent with notional fracture surface energies that were deduced from the lengths of crack generated by various low energy blows and from the lengths recorded by flash photography at various stages of impact events. The velocity of impact was not influential over the range investigated (1 to 5 m sec^?1 ). The investigation was not straightforward because when a test specimen of this class of material is impacted at room temperature the observed response is either heavily contaminated with extraneous vibrations due to the absence of an electrical filter or of questionable purity due to the presence of a filter. In that respect, and others, the paper is linked to an earlier one (J. Mater. Sci. 21 (1986) 3153).