Investigating dc polyethylene threshold by space charge. Currentand electroluminescence measurements

It has been proposed recently that the lowest level of dc field, above which electrical degradation may occur, is associated with the formation of space charges in insulation. Therefore, inference of field levels above which space charge accumulates in a given material may provide fundamental information for material characterization and system design. Threshold field values were estimated through evidence of space charge accumulation derived from conduction current, space charge amplitude and electroluminescence (EL) counts vs, electrical field characteristics. Press-molded plates of polyethylene-based materials were used for this investigation. In order to be able to detect even by EL experiments the presence of the space charge accumulated at low fields, measurements were carried out during both polarization and short-circuit of specimens. It is shown that the threshold corresponding to the onset of EL upon grounding the specimen is close to the space charge accumulation threshold derived from space charge and conduction current measurements. This earlier value is considerably lower than the one previously detected from constant dc-voltage EL measurements, thus confirming that even at low fields and in the presence of voltage reversals or transients, space charges can trigger luminescence phenomena. The methodology developed in this paper enlarges the applicability of the EL technique to accommodate a wider electrical field range in view of insulation characterization     

Evaluation of dc insulation performance based on space-chargemeasurements and accelerated life tests

Space charge observation is becoming the most widely used technique to evaluate polymeric materials for dc insulation applications, particularly HV cables. However, quantities are still lacking that can help to summarize and interpret the huge amount of data resulting from space charge measurements, and that also are associated with the electrical performance of the insulation. The purpose of this paper is to propose test methods and parameters, based on the pulsed electroacoustic technique, which can be used for the evaluation of the electrical performance of polymeric insulation under dc fields. These parameters are related to the space charge magnitude and mobility as well as to the internal electric field amplification, the rate of charge accumulation, and the threshold field above which charge is stored in the insulation. In order to investigate the meaning of the parameters proposed for the assessment of insulation performance, the correlation between these parameters associated with space charge and insulation life is discussed. Examples are reported with reference to five different candidate materials for dc cable insulation     

Electrical ac and dc behavior of epoxy nanocomposites containing graphene oxide

This article deals with the investigation of electrical properties of epoxy‐based nanocomposites containing graphene oxide nanofillers dispersed in the polymer matrix through two‐phase extraction. Broadband dielectric spectroscopy and dc electrical conductivity as a function of electric field have been evaluated in specimens containing up to 0.5 wt % of nanofiller. Nanocomposites containing pristine graphene oxide do not show significant changes of electrical properties. On the contrary, the same materials after a proper thermal treatment at 135°C, able to provoke the in situ reduction of graphene oxide, exhibit higher permittivity and electrical conductivity, without showing large decrease of breakdown voltage. Moreover, a nonlinear behavior of the electrical conductivity is observed in the range of electric fields investigated, i.e. 2–30 kV mm^?1. A new relaxation phenomenon with a very low temperature dependence is also evidenced at high frequency in reduced graphene oxide composites, likely associated to induced polarization of electrically conductive nanoparticles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41923.     

CHEMICAL AND TOXICOLOGICAL CHARACTERIZATION OF AIRBORNE TOTAL SUSPENDED PARTICULATE (TSP) AND PM 10 ORGANIC EXTRACTS

The relationship between chemical composition of airborne particulates and the genotoxicity has been investigated in the atmosphere of Rome, Italy. For this purpose, both total suspended particulate (TSP) and the PM ₁₀ fractions were collected daily inside a green park located in downtown, grouped on a weekly basis and speciated for their burdens of polycyclic aromatic hydrocarbons (PAH) and nitro-PAH. Concurrently, the genotoxicity of the organic extracts was evaluated by the Comet assay (SCGE: single cell gel electrophoresis) on human peripheral blood mononuclear cells (PBMC). The results indicate that organic extracts were able to induce DNA damage and a cytotoxic effect on PBMC. The TSP fraction was more cytotoxic than PM ₁₀ while the genotoxicity of both fractions was comparable. The genotoxic potential of the different samples was highly correlated to the amount of total PAH (correlation coefficient = 0.87), carcinogenic PAH (correlation coefficient = 0.88), B(a)P (correlation coefficient = 0.87) and to a less extend to the concentration of 1-nitropyrene (correlation coefficient = 0.66). The seasonal modulation suggests that in Rome the air is more toxic during winter, however in the warm season oxidized species including nitro-PAHs (evolving from secondary pollution) seem to balance the decrease of PAH concentration rates.     

Effect of Tolrestat on oesophageal transit time and cholecystic motility in type 2 diabetic patients with asymptomatic diabetic neuropathy

The aim of the present study was to investigate the influence of Tolrestat, an aldose-reductase inhibitor, on both oesophageal and cholecystic motility in Type-2 diabetic patients with asymptomatic diabetic neuropathy. Sixty-six patients were randomly assigned to receive Tolrestat 200 mg once daily (33 patients) or were left without specific treatment (33 patients) for 12 months. Efficacy and safety evaluation were done at 4.5 and 12 months by persons blinded to the patient treatment regimen. Scintigraphic evaluation of oesophageal motility showed significant changes in transit time for Tolrestat at 12 months (p < 0.001). There was no significant effect of Tolrestat on cholecystic function in cholecystography, although diabetic patients taking Tolrestat showed a trend toward improvement. The vibration perception threshold at two sites of the dominant leg improved by at least 3 volts in the Tolrestat group and remained unchanged or slightly deteriorated in the control group. Tendon reflexes and blood pressure fall after standing were improved in the Tolrestat group. In conclusion, one-year treatment with Tolrestat significantly improved oesophageal motility and vibration perception in Type-2 diabetic patients with asymptomatic diabetic neuropathy.     

Encoding processes and memory organization: A model of the von Restorff effect.

The mechanisms underlying the improved recall of isolated events (von Restorff effect) were investigated. Participants studied lists of stimuli containing a physical and a semantic isolate while performing a physical task or a lexical decision task. The physical-task group showed a physical but not a semantic isolation effect (IE) in free recall, whereas the lexical-decision group displayed both types of IEs. The recall of the isolates was independent of that of the other words, and isolates were usually reported separately from other words in the list. Event-related potentials recorded at encoding predicted the recall of both types of isolates. In recognition tests, the IE was obtained only when the encoding context was reinstated. These results are consistent with a model of the IE that stresses the role of the encoding processes immediately following the presentation of distinctive events, and that postulates interactions between these processes and subsequent elaboration of the stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of airborne particulate extracts on monocyte oxidative metabolism

The present study was designed to examine the effects of metyrapone in vitro on the activities of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) types 1 and 2, the two intracellular enzymes responsible for the metabolism of glucocorticoids. Enzymatic activities of 11beta-HSD1 and 2 were determined by a radiometric conversion assay using cortisol and cortisone as physiological substrates. The enzyme activity assays were carried out in the absence and presence of metyrapone using sheep liver and kidney microsomes as the source of 11beta-HSD1 and 2, respectively. It was found that metyrapone inhibited the reductase activity of 11beta-HSD1 in a dose-dependent manner with an apparent Ki of 30 microM. Moreover, this inhibition was competitive because the Km for cortisone was increased in the presence of metyrapone. In contrast, metyrapone showed biphasic effects on the dehydrogenase activity of 11beta-HSD1, in that it increased the activity at concentrations lower than 100 microM but decreased it at higher concentrations. However, under similar conditions, metyrapone had little effect on the unidirectional dehydrogenase activity of 11beta-HSD2. In conclusion, the present results provide the first direct evidence that metyrapone is a competitive inhibitor of 11beta-HSD1 reductase, and that it also exerts biphasic effects on 11beta-HSD1 dehydrogenase activity. These findings indicate that metyrapone influences peripheral glucocorticoid metabolism through its regulation of 11beta-HSD1 activity, in addition to its classic inhibitory effects on adrenal steroid biosynthesis. It is therefore imperative that this novel extra-adrenal effect of metyrapone be considered when this drug is used in the diagnosis and treatment of adrenocorticoid-related diseases.