Investigation of electrical and optical properties of polyvinyl acetate doped with some polymers

Polyglycerol (PG) and polytriethanolamine(PTEA) have been prepared. The electrical resistivity (ρ) and the optical absorption of polyvinylacetate (PVAc) doped with polyglycerol (PG), polyaniline (PA), and polytriethanolamine (PTEA) have been studied. It was found that the conduction was mainly ionic in the temperature range from 20 to 120°C. The resistivity decreased with the increase of the dopant cocentration. The optical absorption spectra were determined in the wavelength range 400–2500 nm. The analysis of the absorption spectra showed that the intensity of the bands is remarkably affected by the dopant concentration. The optical energy gap of pure PVAc and the samples containing different dopants were estimated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1558–1563, 2002     

Simulation of bulk free radical polymerization of styrene in tubular reactors

A model that takes into consideration radial and axial changes in velocity in a tubular reactor for the thermal polymerization of styrene is used to simulate the effect of changes in inlet tube wall temperature and tube radius. The reactor performance is sensitive to the changes of these parameters. The method of orthogonal collocation is used to discretize the modeling equation in the radial direction and Gear method to solve the resulting stiff differential equations in the axial direction. It is found that reducing the wall temperature and the tube radius along the direction of the flow of the monomer reduces the variation in conversion between the tube center and tube wall and thus are advantageous.     

Low-Voltage digitally controlled fully differential current conveyor

Design and simulation of a digitally controlled CMOS fully differential current conveyor (DCFDCC) is presented. A novel current division network (CDN) is used to provide the digital control of the current gain between terminals X and Z of this DCFDCC. The proposed DCFDCC operates under low supply voltage of /spl plusmn/1.5 V. The realization of the DCFDCC using the new CDN is presented by two approaches. First approach has linearly proportional current gain with the digitally controlled parameter of the CDN, while the second approach exhibits current gain between terminals X and Z greater than, or equal to, one. Applications of the DCFDCC in realizing second order universal active filter and variable gain amplifier are given. PSPICE simulation confirms the performance of the proposed blocks and its applications.     

Growth hormone secretion and circulating insulin-like growth factor-I (IGF-I) and IGF binding protein-3 concentrations in children with sickle cell disease

Impaired growth involving both height and weight accompanying sickle cell disease (SCD) poses diagnostic and therapeutic problems. We undertook this study to test the hypothesis that this impaired growth is associated with abnormalities of the growth hormone (GH)/insulin-like growth factor-I (IGF-I)/IGF binding protein-3 (IGFBP-3) axis in 21 children with SCD and that SCD is associated with GH resistance. Nine of 21 children with SCD had a defective GH response to both clonidine and glucagon provocation (peak < 10 micrograms/L); these children differed from the 12 others in having slower linear growth velocity (GV and GVSDS), lower circulating concentrations of IGF-I and IGFBP-3, and either partial or complete empty sellae in computed tomographic scans of the hypothalamic-pituitary area. In this group of patients with SCD, it appears that defective GH secretion and consequent low IGF-I production are the major etiological factors causing the slow growth. The two groups with SCD did not differ significantly in dietary intake, body mass index (BMI), midarm circumferences, skinfold thickness, serum albumin concentration, or intestinal absorption of D-xylose. A single injection of GH produced a smaller increase in circulating IGF-I in children with SCD with or without defective GH secretion versus 10 age-matched children with idiopathic short stature (ISS) and 11 children with isolated GH deficiency (GHD), suggesting partial GH resistance in the SCD group. The presence of defective GH secretion, decreased IGF-I synthesis, and partial resistance to GH in short children with SCD suggests that treatment with IGF-I may be superior to GH therapy for improving growth.     

Frequency-dependent activation energy of ac-conductivity in poly(4,4′-N,N-diiminosulphoxide diaminophenyl ether)

Summary The ac conductivity of Poly(4,4′-N,N-diiminosulphoxide diaminophenyl ether) was measured at the temperature range 300–355 K as a function of frequency (range 10 Hz to 100 KHz). The activation energy at each frequency was calculated using the Arrhenius relation. A mathematical formula was suggested to explain the dependence of the activation energy on the applied frequency. It was found that there is a good consistent between the experimental and the calculated value.     

Reliability estimation in a generalized life-model with applicationto the Burr-XII

Estimators of the reliability function in a GLM (generalized life model) are considered. The class of the GLM includes (among others) the Weibull, Pareto, Beta, Gompertz, and Rayleigh distribution. A proper general prior density and the predictive function for general class of distribution proposed by Al-Hussaini(1999) are used to obtain the exact estimate. Also, the Bayes estimates relative to symmetric loss function (quadratic loss), and asymmetric loss function (LINEX loss, and GE loss), are obtained. Comparisons are made between those estimators and the MLE applying to the Burr-XII model using the Bayes approximation due to Lindley. Monte Carlo simulation was used     

A three-unit standby redundant system with repair and preventive maintenance

This paper deals with the reliability of a renewable three-unit system under preventive maintenance activity. The Laplace transform of the reliability function and the mean lifetime of the system have been obtained under the assumption that the failure times, repair times, inspection times and maintenance times are random variables having different distributions. Some special cases also have been obtained.     

Heated fats. Part 3. Biological effect and effect of heating and tempering oils on fatty acid composition of liver,heart and serum lipids of rats

The study deals with the biological effect caused by changes in fats during heating. The study includes feeding experiments and extraction of serum, liver, and heart from the animals tested. The biological study reveals that animals fed heated oil showed retardation of growth, poor efficiencies, rough, greasy mottled coats, and shortned life span.     

Selenium and cadmium induced pulmonary functional impairment and cytotoxicity

Ovalbumin-sensitized (50 mg/kg, i.p.) male Hartley-guinea-pigs (550-610 g; n = 6) were treated 14 days later intratracheally with saline, cadmium (Cd 0.3 mg), selenium (Se 0.3 mg or 0.06 mg) or Se (0.06 mg) with Cd (0.3 mg). After 24 h, baseline dynamic-lung-compliance (Cdynl) and pulmonary-resistance (Rp), and percent change after ovalbumin-aerosol-challenge (10 mg/ml, 60 s) were assessed. Cadmium or Se (0.3 mg), Se (0.06 mg) and/or Cd (0.3 mg) decreased Cdynl (P < 0.05). Selenium (0.3 mg) increased Rp (P < 0.05). Ovalbumin-challenge decreased Cdynl and increased Rp in all groups. Analysis of bronchoalveolar-lavage-fluid (BALF) displayed increased activities of lactate-dehydrogenase (LDH), beta-glucuronidase (beta-G), alkaline-phosphatase (AP), and protein due to 0.3 mg Se, 0.3 mg Cd alone or with 0.06 mg Se (P < 0.05). Findings indicated that, 0.3 mg Se is more detrimental than 0.3 mg Cd to lung-dynamics despite a modest protection by 0.06 mg Se against Cd illustrated by an ameliorated Cdynl and lower protein in BALF.