A statistical model for step and ramp voltage breakdown tests in thin insulators

A spread is observed in times to breakdown when step or ramp voltage tests are applied to thin film insulators which have non-shorting breakdowns and which are cleared of weak spots. Following earlier work on sequences of breakdowns in liquids, we investigated the properties of the spread of observations in thin insulators with a statistical model. Probability density functions are derived for the times to breakdown for step and ramp tests, and a relation is given for the ratio of the mean times to breakdown for ramp and step tests. The results agree with experimental observations on the oxides of aluminum and hafnium. This indicates a randomness of the breakdown process and permits the calculation of ramp breakdown voltages from the measured step breakdown voltages. Quantitative agreement is not obtained for silicon dioxide, probably owing to the lack of independence in the location of consecutive breakdown events.     

Interaction of glucose oxidase with phospholipid vesicles

The interactions between glucose oxidase and phospholipid vesicles were investigated. The investigations were carried on molecules adsorbed on the outer surfaces as well as entrapped in the interior of the vesicles . The adsorption of glucose oxidase on the surfaces of egg egg licithin vesicles, containing varying amounts of cholesterol and stearoylamine was measured by determining the free fraction of glucose oxidase detected in the filtrates. In general an enhancement of enzymic activity was observed upon interaction with the vesicles. The enhancement depends on the lipid composition of the vesicles and the surface concentration of the adsorbed glucose oxidase. It reached a maximal value at a surface concentration of 1.4-10(11) molecules/cm2 (approximately 7.1 - 10(4) A2/molecule) on pure phosphatidylcholine vesicles and about 6.5 - 10(10) molecules/cm2 (approximately 16 - 10(4) A2/molecule) when the vesicles contained cholesterol or cholesterol and stearoylamine. CD measurements indicated that the change in enzymic activity of the adsorbed glucose oxidase was accompanied by conformational modification of the enzyme. In order to entrap glucose oxidase into the vesicles, the lipid was sonicated in the presence of the enzyme. After removal of the free and adsorbed enzyme the amount of the entrapped enzyme was determined by measuring its activity after disintegration of the vesicles with Triton. The enzymic activity of the entrapped glucose oxidase served as a measure for the permeability of the bilayer membrane of the lipid vesicles to glucose. Addition of insulin to the suspension of vesicles containing the entrapped glucose oxidase increased the permeability of glucose by up to 9 - 10(-8) cm/s. This value is the lowest estimate based on the assumption that one glucose oxidase molecule was entrapped in every vesicle.     

Toward the use of self-control in behavior modification.

Analyzes the concept of self-control in terms of a 2-stage process: general cognitive set and specific self-controlling responses. The incorporation of the cognitive set into a fuller understanding of behavior modification is emphasized. The set labeled commitment to change is viewed as an important motivational and mediating component in self-directed or therapist-guided therapy programs. A number of characteristics of this set are posited, and the problems of measuring such a commitment are discussed. Several programs describing techniques oriented to commitment are briefly reviewed. The cognitive set analysis seems especially important for discovering factors contributing to the frequent relapse following treatment for addictions. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigation of surface activity and photoinduced diffusion of metals in solution deposited amorphous films of As2S3

Surface activity of solution deposited (SD) amorphous films of As₂S₃ has been investigated. Silver and copper are readily deposited on such films from appropriate aqueous ionic solutions. The metals diffuse into the films upon irradiation with energetic photons. Structure and properties of SD films have been investigated using electron microscopy, optical spectroscopy and differential scanning calorimetry. The amorphous films tend to crystallize upon metal diffusion. The stability of amorphous films, the deposition of metals on their active surfaces and the photo-induced diffusion may all be attributed to the presence or production of charged defects in amorphous chalcogenide films.     

Imaging and its Applications to Drug Delivery

Non-invasive, gamma, and positron scintigraphy can be used to obtain information on drug absorption, distribution, and elimination, as well as, on drug delivery and release from special formulations and controlled delivery devices. To accomplish this, appropriate gamma and/positron emitting radiotracers must be developed which can be incorporated into the formulation or the drug delivery device. Since these studies are non-invasive, they can be conducted in valuable experimental animals, e.g. primates as well as in humans. There are numerous approaches to aid in defining delivery, release, and absorption of compounds. Beginning with conventional radiotracers, progressing to neutron activated compounds, and finally to compounds radiolabeled with halogens or positron emitters one can chose the approach which will provide the information needed in the most reasonable way. Non-invasive imaging allows one to do this in a more physiological state in both pre-clinical and clinical applications.     

Prolongation of conduction time during premature stimulation in the human atrium is primarily caused by local stimulus response latency

BACKGROUND: Conventional clinical electrophysiological techniques cannot accurately differentiate between local stimulus response latency and propagation time of the atrial response. The purpose of this study was to identify and distinguish local stimulus response latency from impulse propagation time in the human right atrium during programmed electrical stimulation. METHODS: Pacing was performed from two atrial sites (high and low right atrium) in 19 patients, using monophasic action potential recording/pacing combination catheters (interelectrode distance < 2 mm). Local stimulus response latency (interval between stimulus artifact and upstroke of the local monophasic action potential), and propagation time (interval between local and remote monophasic action potential upstroke) were evaluated at a basic cycle length (S1-S1) of 600 ms and as a function of the extrastimulus proximity (interval between extrastimulus and effective refractory period). Data are presented as means +/- SEM. RESULTS: During basic stimulation, local latency was very small (3.8 +/- 1.7 ms). During premature extrastimulation (proximity < 70 ms), local latency increased progressively with decreasing coupling intervals. Prolongation of local latency was most pronounced during stimulation close to the effective refractory period with local stimulus response latency increasing to 18.3 +/- 1.4 ms (380 +/- 7.9%) at 10 ms proximity (P < 0.002) and to 27.9 +/- 3.7 ms (630 +/- 13.2%) at 5 ms proximity, respectively (P < 0.0001). The impulse propagation time between the stimulation site and the remote recording site was on average 54.5 +/- 14.3 ms during basic stimulation, and increased up to 62.1 +/- 13.5 ms (14.0 +/- 8.4%), which was not significant. CONCLUSIONS: The intra-atrial impulse propagation remained essentially unchanged during the entire range of premature stimulation. Local stimulus response latency was negligible and constant during late coupling intervals but increased dramatically when extrastimulation approached the preceding repolarization phase. This has the following clinical impact: first, local stimulus response latency during premature extrastimulation curbs the targeted atrial response interval second, local stimulus response latency, not propagation time, seems responsible for the greater functional than effective refractory period during electrical stimulation; third, local stimulus response latency should be considered in pace mapping for accurate comparison of conduction time before pacing with that during pacing.     

Persisting perfusion defects after bronchoscopic removal or spontaneous expulsion of aspirated foreign objects

Two strains fo S.S.P.E. virus show both haemagglutinin and salt-dependent haemagglutinin. These properties are associated with distinct plaque forms within each strain. The existence of salt-dependent strains in wild-type measles virus suggests that they should be found in the early isolates of all strains of S.S.P.E.     

Formation of benzene polycarboxylic acids in the oxygen oxidation of solid by-products from coal-conversion processes (CCP) in an alkaline medium

Solid and liquid carbonaceous by-products have been obtained in both coal gasification and liquefaction processes. A study of the oxidation of the solid by-products was undertaken to determine what commercial chemicals could be derived from these materials. The oxygen oxidation of various coal-conversion-process by-products in 10% aqueous sodium hydroxide was investigated at 250 °C and a total pressure of 8.27 MPa (gauge). The products isolated were carbon dioxide and the organic extract, a complex mixture of aliphatic and aromatic acids. The benzene polycarboxylic acids were the major component of the organic extract.     

Early discharge of patients with new-onset atrial fibrillation after cardiovascular surgery

The feasibility of monitoring intracellular sodium changes using Na triple quantum filtered NMR without a chemical shift reagent (SR) was investigated in an isolated rat heart during a variety of interventions for Na(i) loading. Perfusion with 1 mM ouabain or without K+ present in the perfusate for 30 min produced a rise of the Na TQF signal with a plateau of approximately 190% and approximately 228% relative to the preintervention level, respectively. Stop-flow ischemia for 30 min resulted in a TQF signal growth of approximately 147%. The maximal Na TQF signal increase of 460% was achieved by perfusion without K+/Ca2+, corresponding to an elimination of the Na transmembrane gradient. The observed values of Na NMR TQF growth in the physiological and pathological ranges are in agreement with reported data by other methods and have a linear correlation with intracellular sodium content as determined in this study by Co-EDTA method and by sucrose-histidine washout of the extracellular space. Our data indicate that the increase in Na TQF NMR signal is determined by the growth of Na(i), and the extracellular Na contribution to the total TQF signal is unchanged at approximately 64%. In conclusion, Na TQF NMR without using SR offers a unique and noninvasive opportunity to monitor alterations of intracellular sodium. It may provide valuable insights for developing cardioprotective strategies and for observing the effects of pharmaceutical treatments on sodium homeostasis.