An anomaly in the necking behavior of polyethylene,Part 2

Dumb-bell shaped specimens of three polyethylenes were subjected to constant uniaxial tensile loads at test temperatures from 298 to 353 K. For the high density polyethylenes, a marked transition appeared in the neck/fracture behavior. At a certain stress level, the instantaneous fracture of the neck formed at high loads was replaced by the formation of a neck that resisted fracture for a considerable time. This transition was more gradual for the medium density polyethylene. Furthermore, at all test temperatures the transition shifts towards higher nominal stresses with increasing molecular weight. Mainly on the basis of measurements of the local strain rate in the neck forming region, a hypothesis is proposed which explains the appearance of the marked transition. The draw ratios and the densities of the fractured neck fibers were also measured and are in accordance with current molecular deformation theories.     

Characterization of mixed syngeneic-allogeneic and syngeneic-xenogeneic islet-graft rejections in mice. Evidence of functional impairment of the remaining syngeneic islets in xenograft rejections

Allogeneic mouse islets or xenogeneic rat islets, or fetal porcine islets were implanted under the renal capsule of C57BL/6 mice either alone or carefully mixed with syngeneic islets. With this experimental model the syngeneic islets, although not rejected themselves, are exposed to cytokines and inflammatory mediators released during either allograft or xenograft rejection. No differences in insulin content could be observed between mixed islet grafts and pure syngeneic islet grafts 6 wk after transplantation. Neither was there any morphological evidence of a non-specific destruction of syngeneic islets. These findings suggest that the mechanisms of both allograft and xenograft rejections are highly specific. The hormone release from the mixed syngeneic-allogeneic grafts was similar to that from pure syngeneic islet grafts. In contrast, a pronounced impairment of both the first and second phases of insulin release was observed 2 wk after implantation in mixed syngeneic-xenogeneic islet grafts. When perfusing the mixed islet graft after completed rejection of the concordant xenogeneic rat islets (6 wk after implantation), the insulin release from the remaining syngeneic mouse islets was identical to that of control grafts. However, syngeneic mouse islets exposed to the rejection mechanism of the discordant xenogenic pig islet-like cell clusters did not attain a complete functional recovery.     

Determination of the absolute configuration of sugar residues using gas chromatography. Method with potential for elimination of references

The effects of the benzodiazepine receptor antagonist flumazenil (Ro 15-1799), the benzodiazepine receptor partial inverse agonist Ro 15-4513 and the benzodiazepine receptor inverse agonist beta-CCM on the behaviour of control and small platform stressed mice studied. Small platform stress was induced by placing the animals on small platforms (d = 3.5 cm) surrounded by water for 24 hours. This technique involves several factors of stress such as rapid eye movement sleep-deprivation, isolation, immobilization, falling into the water and soaking. In the plus-maze test small platform stress induced changes indicating anxiolytic action-an increase of the percentage of entries made onto and the percentage of time spent on the open arms. In control mice flumazenil (2.0 and 10.0 mg/kg), Ro 15-4513 (0.5; 1.0; 2.5; 5.0 and 10.0 mg/kg), and beta-CCM (1.0 and 2.0 mg/kg) exerted dose-dependent anxiogenic effect. The small platform stress induced an enhancement of the anxiogenic effect of flumazenil, but not that of Ro 15-4513 and beta-CCM. The selective enhancement of flumazenil's action may be explained with the mode of action of flumazenil. It is proposed that small platform stress causes changes in the concentration of the endogenous benzodiazepine receptor ligand with stress protective activity and flumazenil acts by blocking the effects of this endogenous ligand.     

Experimental haemorrhage and blood component transfusion in humans: no change in plasma concentration of thrombin-antithrombin complex and plasmin-antiplasmin complex

1. To examine whether insulin resistance in vivo is manifest equally in both muscle and adipose tissues, we measured arteriovenous glucose and lactate fluxes across forearm (muscle) and abdominal subcutaneous (adipose) tissue in nine obese, glucose-intolerant subjects and 13 non-obese subjects of similar age and sex. 2. Compared with non-obese subjects, the forearm of the obese subjects was resistant to insulin stimulation of glucose uptake after a mixed meal. In contrast, adipose tissue showed little evidence of insulin stimulation of glucose uptake, and adipose tissue in subjects in both normal and obese groups behaved very similarly (assessed per 100 g of tissue). 3. For lactate flux, adipose tissue behaved very similarly (per 100 g of tissue) in obese and non-obese subjects, and was a consistent lactate exporter. 4. We conclude that insulin resistance of glucose uptake observed in the forearm of obese subjects is not evident in adipose tissue. Adipose tissue glucose uptake in obese, insulin-resistant subjects is similar to that in lean control subjects, although it occurs at elevated circulating insulin and glucose concentrations.     

Fabrication of silica nano wires on the internal perimeter of narrow bore fused silicia tubing by non-isothermal etching

An method for fabrication of long silica nano wires is presented. The nano structured material is an integral part of the inner surface of narrow bore fused silica capillary tubing. The wire preparation method is based on a hydrothermal action and decomposition of 2-chloro-1,1,2-trifluoroethyl methyl ether at elevated temperature. In our previous work, reproducible nano wire outgrowth could only be accomplished in capillaries with an inner diameter less than10 m [1], and the centre of the capillary lumen remained free of wires. In the present article we report on nano wire outgrowth in capillaries with larger inner diameters. These wires are entangled via carbon nucleating particles and stretch across the entire lumen of the capillary. The long nano wire outgrowth was induced by a time dependent, non isothermal etching of the capillaries. Suggested mechanisms for the growth process are discussed.     

Studies of relaxation phenomena in polymers. I. The use of periodic square and triangular stress functions

In order to evolve the methods of mechanical spectroscopy and find new methods of studying the rise of nonlinear viscoelasticity, periodic square and triangular stress functions have been used. A “new” viscoelastic function is defined, log J₂ = g{log J₁}, where J₁ and J₂ are the compliances at the time (ζ/2 + 2nζ)_n→∞ for an odd, periodic, square function and an even, periodic, triangular function, respectively, with periods of 2ζ. The function shows characteristic shapes for viscoelastic spring and dashpot models. The interrelations between the complex compliance and J₁ and J₂ are developed; and since the sum of J₁ and J₂ at the time ζ/2 agrees very well with the creep compliance at the same time, J₁ and J₂ can be used as an interrelation between complex compliance and creep compliance. Special equipment for measuring the compliances J₁ nd J₂ is described.     

The effect of the oxygen pressure and the growth of whiskers on the oxidation of pure Fe

The weight increase curves of pure iron specimens cold-worked by abrasion with SiC and 7- diamond paste have been registered as a function of pressure and temperature. The oxidation rate increases with temperature and pressure when the pressure is raised from 0.02 to 0.2 bar. When the pressure is further increased to 1.02 bar at 500 and 625°C the oxidation rate decreases. This decrease is attributed to an orientation of the oxide grains in the -Fe₂O₃ surface.     

Further studies on the epoxidation of propylene in a bipolar trickle bed

Further studies on the epoxidation of propylene via electrogenerated hypobromite in a trickle bed have been carried out with the aim of increasing the space-time yield. Factors which have been studied in more detail include electrode material, applied voltage, sense of polarity, cell packing arrangements, electrolyte flow rate and sodium bromide concentration. By suitable choice of conditions a significant increase in space-time yield can be obtained, up to a limit set by the depletion of propylene, without a large increase in energy consumption.