On the mechanisms of adenosine induced pulmonary vasoconstriction in rats

The effect of adenosine on pulmonary vessels was studied in isolated perfused rat lungs. Drugs were administered intra-arterially in a fixed volume of 0.1 ml Krebs solution as bolus injections. Adenosine responses were obtained before and 10 min after drug injections. When applied in logarithmically increasing doses (1-100 micrograms/ml), adenosine caused dose-dependent increases in pulmonary perfusion pressure (e.g. pulmonary vasoconstriction) which were readily reversible. Challenging adenosine with quinidine, dihydroergocristine and cyproheptadine (2 micrograms/ml each) did not significantly alter adenosine responses. Pretreatment of lungs with 0.5 mM theophylline, 10 micrograms/ml indomethacin, 30 micrograms/ml tebokan (a PAF antagonist) or 1 microgram/ml methylene blue for 10 min, however, antagonized the vasoconstrictor effect of the drug significantly. From these experiments, it was concluded that the mechanisms underlying the pulmonary vasoconstrictor action of adenosine are complex, and that both types of purinoceptors, prostaglandins, PAF and other vascular endothelial hormones might be involved.     

Shear ductility and toughenability study of highly cross-linked epoxy/polyethersulphone

The objective of the present study was to determine whether the ductility and toughenability of a highly cross-linked epoxy resin, which has a high glass transition temperature, T _g, can be enhanced by the incorporation of a ductile thermoplastic resin. Diglycidyl ether of bisphenol-A (DGEBA) cured by diamino diphenyl sulphone (DDS) was used as the base resin. Polyethersulphone (PES) was used as the thermoplastic modifier. Fracture toughness and shear ductility tests were performed to characterize the materials. The fracture toughness of the DDS-cured epoxy was not enhanced by simply adding PES. However, in the presence of rubber particles as a third component, the toughness of the PES–rubber-modified epoxy was found to improve with increasing PES content. The toughening mechanisms were determined to be rubber cavitation, followed by plastic deformation of the matrix resin. It was also determined, through uniaxial compression tests, that the shear ductility of the DDS-cured epoxy was enhanced by the incorporation of PES. These results imply that the intrinsic ductility, which had been enhanced by the PES addition, was only activated under the stress state change due to the cavitation of the rubber particles. The availability of increasing matrix ductility seems to be responsible for the increase in toughness. This revised version was published online in November 2006 with corrections to the Cover Date.     

Crossing the planes at high speed. Signal integrity issues at splitground and power planes

This article discusses a specific design situation that represents quite a broad class of problems in the study of signal integrity. The article focuses on the effects on high-speed signals that need to cross split ground planes and split power planes that act as signal references or partial references. Such configurations are frequently needed in the layout of printed circuit boards (PCBs), multichip modules (MCMs), and even single-chip modules. Examples of split ground and power planes are discussed first. The conventional effective inductance model is described briefly, and an accurate and efficient transmission line model is then discussed in detail. Examples of modeling and design trade-offs are also presented     

Oral glutamine challenge in cirrhotics pre- and post-liver transplantation: a psychometric and analyzed EEG study

Latent or sub-clinical hepatic encephalopathy is a recognized complication of cirrhosis and is thought to represent one end of the spectrum of neuropsychiatric impairment, which occurrs as a result of portal-systemic shunting. We studied the psychometric, analyzed electroencephalography (EEG), and venous blood ammonia responses to an oral glutamine challenge in 17 patients with cirrhosis and in 4 normal controls. The cirrhotics were attending for liver transplant assessment and had no clinical evidence of hepatic encephalopathy. The oral glutamine challenge was repeated following liver transplantation. Five of sixteen patients (31%) showed impaired performance on at least one of the baseline psychometric tests. There was a correlation between fasting venous ammonia and choice reaction time (r = .7, P < .01). Following glutamine challenge there was a significant increase in blood ammonia from a mean fasting value ranging between 58 micromol/L to 120 micromol/L (P < .01), between significant prolongation of reaction times of 387 ms to 428 ms (P < .01), and an increase in mean EEG amplitude between 68.5 microV to 78.6 microV (P < .001). Four normal controls who were challenged with glutamine and 6 cirrhotic patients who were challenged with water showed no change in any of these parameters. Following orthotopic liver transplantation (OLT) the eight patients studied had normal baseline psychomotor performance with significant improvements in digit symbol, digit span, information processing, number connection tests (P < .05), and reaction time (P < .005). Posttransplantation, there were no significant changes in blood ammonia, analyzed EEG, or choice reaction time in response to oral glutamine challenge (six patients). We conclude that short lived changes in blood ammonia (in cirrhotics) can cause significant impairment of sensitive tests of brain function and that psychometric performance is improved following OLT.     

Recovery of residual oil using the alkali/surfactant/polymer process: effect of alkali concentration

An experimental study was conducted to examine the effectiveness of sodium carbonate in alkali, surfactant and polymer combined slugs in recovering waterflood residual oil. The effects of sodium carbonate concentration on the slug viscosity, interfacial tension, and phase behavior were first examined. Core flood experiments were conducted with unfired linear Berea sandstone cores. The incremental oil recovery, oil cut, residual resistance factor, and chemical propagation were measured for each flood.A significant oil bank was formed for all combined slugs having sodium carbonate concentration ≥1 wt%. The incremental oil recovery, oil cut and the injectivity of the combined slugs greatly improved as sodium carbonate concentration was increased. The effect of sodium carbonate concentration on chemical propagation was dramatic for the synthetic surfactant; a slight delay in surfactant breakthrough and a much slower rate of surfactant propagation were observed at high sodium carbonate concentrations.The results obtained in the present study indicate that the residual oil was recovered by two mechanisms: low interfacial tension and wettability reversal. The former mechanism is dominant at sodium carbonate concentrations ≤1 wt%, whereas the latter plays an important role only at high sodium carbonate concentrations.     

Study of the Polymorphism of Saturated Monoacid Triglycerides II: Polymorphic Behaviour of a 50/50 Mixture of Tripalmitin and Tristearin

The polymorphic behaviour of a 50/50 blend of tripalmitin and tristearin has been investigated in detail using differential scanning calorimetry and X-ray diffraction. The blend is characterized by a greater tendency to β'-crystallization as compared to the pure triglycerides. Tripalmitin and tristearin, when mixed in a 1:1 ratio, are miscible in both the α-form and the β-form. In the β-form, however, demixing occurs, resulting in a 2-phase solid state. The characteristics of the α-form are considerably affected by the crystallization conditions, due to the formation of concentration gradients during crystallization. The β'-form can be obtained from the melt as well as via recrystallization of the α-form, and is characterized by a much higher stability as compared to the pure triglycerides. The X-ray diffraction data of the β'-form of the blend reveal a β₁-crystal structure. The β'-form of the pure triglycerides, however, is characterized by a β'₂-crystal structure. On the basis of the present data, however, no clear structural distinction can be made between β'₂ and β'₁.     

Toxikologie freier Radikale und Antioxidantien unter besonderer Berücksichtigung von Vitamin E

Toxicology of Free Radicals and Antioxidants with Specific Regards to Vitamin E By metabolic activation radicals of xenobiotics can occur in the body which may be toxic by reacting with oxygen. The oxygen radicals formed then react with cellular macromolecules. When reacting with lipids lipid peroxidation occurs. Antioxidants may either inhibit the formation of oxygen radicals or prevent lipid peroxidation. As examples carbon tetrachloride, adriamycin, paraquat and some carcinogens are dealt with. With some toxicity as well as lipid peroxidation are inhibited by vitamin E and other antioxidants. Furthermore, the toxicology of the antioxidants is discussed, because they are themselves transformed into free radicals. Whereas vitamin E has practically no toxic effects, some synthetic antioxidants show carcinogenic effects in animal experiments.