The structures and properties of hydrogen silsesquioxane (HSQ) films produced by curing were studied in the temperature range of 240-340 uC for various curing times. The experimental results show that the transformation of the cage structure to the network structure is the major reaction in the studied temperature range. The cage-network transformation can be explained by two-stage zero order kinetics. The rate constant of the first stage is 10-35 times more than that of the second stage. The activation energy and frequency factor of the cage-network transformation are 64.63 kJ mol 21 and 2.76 6 10 4 s 21 for the first stage while those of the second stage are 38.59 kJ mol 21 and 4.11 s 21 , respectively. The difference is probably because the network structure of the second stage limits the structural transformation and results in a small frequency factor. The porosity of the cured HSQ films increases rapidly with curing time in the first 10 min and then slowly for the remaining time. The FE-SEM (Field Emission-Scanning Electron Miscroscope) result suggests the formation of nano-pores in the cured film. The evolution of porosity is probably due to the outgassing of the reaction sideproduct (SiH 4 ), the trapped solvent (4-methylpentan-2-one) or the cage/network transformation. The last two factors contribute significantly as shown by the refractive index results of the cured films. The increasing film thickness with increasing curing time and temperature indicates the evolution of porosity in the HSQ film.
For the salvage of thrombosed AV fistulas, a device using rotational mechanism is more time-saving with a higher immediate success rate and secondary patency rate. However, the long-term patency results were not different.
Plasma levels of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide production, correlate with endothelial dysfunction and the development of cardiovascular events in patients with uremia. It is not known whether endothelial dysfunction contributes to the dysfunction of arteriovenous fistulas (AVFs) in hemodialysis patients. Here, we studied the predictive value of baseline plasma ADMA for symptomatic restenosis of an AVF after percutaneous transluminal angioplasty in dialysis patients. We obtained baseline plasma ADMA levels before percutaneous transluminal angioplasty in 100 consecutive patients with dysfunctional AVFs. Patients were followed up clinically for up to 6 mo after angioplasty for recurrent dysfunction. During the 6 mo after angioplasty, 46 patients experienced recurrent dysfunction of their AVF; of these, follow-up fistulography showed restenosis at the same location in 41, new stenosis at different locations in two, and no significant stenosis in three patients. Up to 60% of the patients with high levels of ADMA (Ͼ0.910 M) had target lesion restenosis compared with 25% of those with low levels (Ͻ0.910 M; P Ͻ 0.001). In multivariate analysis, plasma ADMA independently nearly tripled the risk for recurrent symptomatic stenosis of an AVF after percutaneous transluminal angioplasty (hazard ratio 2.65; 95% confidence interval 1.33 to 5.28). These results suggest a role for ADMA in the progression of symptomatic restenoses of AVFs after percutaneous transluminal angioplasty and call for preventive strategies that target ADMA and/or endothelial dysfunction to decrease the risk for AVF restenosis.
The thermoelectric performance of synthetic conductive polymers, poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), is explored. The effects of the dielectric solvent, dimethyl sulfoxide (DMSO), and of the ratio of PEDOT to PSS in the polymeric PEDOT/PSS thin films were studied systematically. Within the parameter range studied in this work, the variation of electrical conductivity overwhelmed the variation of the Seebeck coefficient, and the optimal power factor is basically determined by the highest electrical conductivity, because the Seebeck coefficient remains small over a wide range of DMSO concentrations and PEDOT:PSS ratios.
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