Different effects of process conditions on PA6/nanoclay composites at nanoclay contents above and below percolation threshold: Rheological,thermo‐dynamical,and thermal properties

The effects of several factors (i.e., nanoclay content (NC), melt temperature, screw speed, and feeding rate), on morphology, rheology, thermodynamics, and thermal stability of PA6/NC samples produced in a co‐rotating twin‐screw extruder were studied. We discuss how changes in the level of these factors can vary diffusion or imposed shear, how these variations in diffusion and/or shear can affect NC dispersion, and how the changes in the state of NC dispersion can influence several properties of the samples. Samples with low NC content, below percolation threshold, showed exfoliated/intercalated structure with negligible sensitivity to changes in the level of the factors; whereas, samples with high NC content, above percolation threshold, showed intercalated with sporadic flocculated structures and noticeable sensitivity to the changes in the level of the factors. Moreover, NC dispersion was found to be mostly diffusion‐controlled: changes that resulted in higher diffusion or residence time (i.e., high melt temperature or low screw speed) also eventuated in better NC dispersion. What is more, percolation threshold was seen to move to lower NC contents as diffusion rate was increased. Moreover, as NC content increased, opposite thermal stability behaviors were observed at above and below the percolation threshold. J. VINYL ADDIT. TECHNOL., 22:259–266, 2016. © 2014 Society of Plastics Engineers     

Effect of Zn and Pb contents on the electrochemical behavior of brass alloys in chloride-free neutral sulfate solutions

Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of brass alloys with various Zn contents (5.5–38.0 mass%) and Cu–38.0Zn–Pb alloy with different Pb contents (1.0–3.4 mass%) in neutral sodium sulfate solutions. The influence of working conditions, e.g., immersion time, sulfate ions concentration and temperature on the electrochemical behavior of the different alloys was also studied. It was found that the initial corrosion rate is relatively high for alloys with the higher zinc content due to dezincification. The dezincification process initiates by selective dissolution of zinc and continues by a simultaneous dissolution of copper and zinc followed by re-deposition of copper. An increase in the lead content and immersion time in the sodium sulfate solution increases the corrosion resistance of the alloy and improves its stability. The stability of the leaded brass was considered to be due to the formation of an insoluble film of lead sulfate on its surface. The impedance data were fitted to theoretical data obtained according to an equivalent circuit model describing the electrode/electrolyte interface. The mechanism of the alloy dissolution was discussed in view of the obtained results.     

Molecular Weight Determination of Palm Olein Polyols by Gel Permeation Chromatography Using Polyether Polyols Calibration

Natural oil polyols have been intensively developed and successfully used for the production of various polymers, notably polyurethanes. The need to access the average molecular weight (MW) and the MW distribution (MWD) has led to the efforts to have a precise and reliable determination method. A series of commercial polyether polyols, with well‐defined MW, was used as a gel permeation chromatography (GPC) calibration standard to determine the MW of palm olein polyols. This GPC analysis was compared to the one calibrated against the commercially available polystyrene (PS) standards and to the number‐average molecular weight (M_n) obtained via vapor pressure osmometry (VPO) technique. For example, the M_n obtained for palm olein polyol E‐135 calibrated against polyether polyols was 2,537 Da, which was closer to the M_n via VPO (1,618 Da), than the M_n obtained using PS as calibration standards (3,836 Da). Hence, this GPC analysis using polyether polyols as calibration standards can offer reassured determination of MWD of palm olein polyols.     

Binary copolymerizations of 8-methacryloxy-quinoline with methyl methacrylate, methyl acrylate, styrene and acrylonitrile

8-methacryloxy-quinoline monomer (MAQ) was prepared by the reaction of 8-hydroxyquinoline with either methacryloyl chloride or methacrylic acid in the presence of triethylamine and N, N′-dicyclohexylcarbodiimide, respectively. Its structure was confirmed by IR and 1 H-NMR spectroscopy. Binary copolymerization of this new monomer with methyl acrylate (MA), acrylonitrile (AN) methyl methacrylate (MMA), styrene(ST), were performed in Dimethylformamide, using 1 mol% azobisisobutyronitrile as initiator at 65 °C. The copolymer compositions were determined from nitrogen analysis except MAQ-AN with 1 H-NMR. Copolymerization Parameters for each system were calculated by both the Finemen-Ross and Kelen-Tüdös methods. The monomer reactivity ratios for the systems MAQ-MA, MAQ-AN, MAQ-MMA and MAQ-ST were found to be r1?=?0.695?±?0.036, r2?=?0.62?±?0.235; r1?=?0.273?±?0.087, r2?=?0.259?±?0.67; r1?=?0.356?±?0.015, r2?=?1.615?±?0.052 and r1?=?0.097?±?0.003, r2?=?0.339?±?0.027 respectively. The Q and e values for MAQ monomer were found to be 1.62 and 1.40.     

Serodiagnosis of cutaneous leishmaniasis: assessment of an enzyme-linked immunosorbent assay using a peptide sequence from gene B protein

An enzyme-linked immunosorbent assay (ELISA) using a 28 amino acid sequence of the repetitive element of gene B protein (GBP) from Leishmania major was developed for serodiagnosis of cutaneous leishmaniasis (CL). The assay was compared to ELISAs using crude amastigote and promastigote antigens from L. donovani and the major surface glycoprotein (Gp63) from either L. donovani or L. major as a solid-phase ligand. The sensitivity of the assays was tested in 33 patients suffering from CL caused by L. major. The sensitivity of the GBP peptide (GBPP) ELISA was 82%. This was higher than in the assays using crude amastigote (67%) or promastigote (67%) antigens, but the difference was not statistically significant. The sensitivity in the assays using Gp63 from L. donovani (52%) or L. major (39%) was significantly lower than in the assay using GBPP (P = 0.019 and P < 0.001, respectively). Plasma samples from healthy Sudanese individuals living in an area endemic for malaria but free of leish-maniasis were negative in all the assays. Significantly higher levels of antibodies were found in the patients who had suffered from the disease for more than eight weeks than in patients with a shorter clinical history (GBPP ELISA; P = 0.038; amastigote ELISA; P = 0.004; and promastigote ELISA; P = 0.017). In the former group, the sensitivities of the five ELISAs were 100% (GBPP), 87% (amastigote), 93% (promastigote), 67% (L. donovani), and 53% (L. major), respectively.     

Decreased uptake of 14C-labeled dicarboxylic amino acids in rapidly growing hepatomas

In contrast to the increased uptake of amino acids which has been found in many neoplastic cells, we have observed a decrease in the net uptake of [14C]aspartate and [14C]glutamate in rapidly growing hepatomas relative to rat host liver. When measured 10 min after s.c. injection, the radioactivity from 14C-labeled dicarboxylic amino acids was greater in liver than in all other tissues examined (blood, skeletal, muscle, heart, spleen, lung, and brain) except kidney, where there was an approximately 2-fold greater uptake of aspartate and 10-fold greater uptake of glutamate. Mean uptakes in the rapidly growing Morris hepatomas 7288CTC and 7777 were 19 to 26% of corresponding values for the host livers. Comparison with uptake of 3H2O indicated that these low values were not solely due to differences in circulation. Decreased uptake was not accompanied by equivalent decreases in the concentration of aspartate and glutamate in the tumors. There were small changes in the net uptake of these amino acids in the slowly growing hepatoma 7787 and no significant differences in regenerating liver and hepatoma 5123C, a tumor of intermediate growth rate. The net uptake of [14C]arginine and [14C]lysine in the hepatomas was similar to that in host livers, except for a 250% increase in uptake of [14C]lysine in hepatoma 5123C. A decreased uptake of the magnitude seen with dicarboxylic amino acids in rapidly growing hepatomas has not been observed with other amino acids.     

Prevention of tooth hypersensitivity caused by the hydrodynamic action of zinc phosphate and composite resin luting cements (SEM) study

This study was done to determine the role of cement liner as a reducing factor to the fluid movement in order to prevent tooth hypersensitivity according to the hydrodynamic theory during cementation of crowns. A total of fourty freshly extracted intact lower molar were selected for this study. After conventional tooth preparation the teeth were sub-divided into four equal groups to identify the role of cement liner in preventing the penetration of used cement into the dentinal tubules. Scanning electron microscopic study proved the efficiency of glass ionomer liner on preventing cement penetration into the dentinal tubules.     

Effects of monomer composition on the mechanical and machinability properties of gel-cast alumina green compacts

In the present work, machinable green gel-cast alumina compacts were prepared by using polyethyleneglycol (400) diacrylate (P4) and polyethyleneglycol (600) dimethacrylate (P6) together with the acrylamide (AAm) comonomer. The glass transition temperatures of copolymers decreased with the increasing of P4 or P6 amount in total copolymer. The green samples obtained in an aqueous system were mechanically analyzed by means of three-point bending. Flexural strength values increased, from 2 MPa to 25 MPa, as the weight ratio of P4 or P6 in total copolymer (AAm-P4 or AAm-P6) decreased from 90% to 3.5%, respectively. The green gel-cast samples prepared by using P4 or P6 were machined easily by using a lathe, drill and milling machine without damaging the samples, which have good surface finish. The binder removal was achieved at lower temperatures than those samples prepared by using only AAm.     

A low-voltage, highly linear voltage-controlled transconductor

A low-voltage fully differential, voltage-controlled transconductor is described. The proposed transconductor achieves a wide input/control voltage range, with a highly linear transconductance factor and truly fully differential output currents. The transconductor is used to implement a G/sub m/-C adaptive forward equalizer (FE) for a 125 Mbps wire line transceiver using digital core transistors with channel length of no more than double the feature size in a typical digital CMOS 180-nm process and supply voltage as low as 1.6 V. The adaptive FE enables IEEE 1394b transceivers to operate over UTP-5 cables for up to 100 m in length. The transconductor stage occupies 1945 /spl mu/m/sup 2/ and consumes an average power of 418 /spl mu/w at 125 Mbps and 1.8-V supply.     

Spectroscopic and clinical aspects of noninvasive glucose measurements

Frequent determination of glucose concentrations in diabetic patients is an important tool for diabetes management. This requires repetitive lancing and finger bleeding. Use of noninvasive (NI) detection techniques offers several advantages, such as the absence of pain and exposure to sharp objects and biohazard materials, the potential for increased frequency of testing, and hence, tighter control of the glucose concentrations, and the potential for a closed-loop system including a monitor and an insulin pump. These potential advantages have led to considerable interest in the commercialization of NI glucose monitoring devices. Review of the scientific, patent, and commercial literature indicates that the spectroscopic basis for NI determination of glucose is not yet well established, and attempts at commercialization may be several steps ahead of our understanding the origin and characteristics of an in vivo glucose-specific or glucose-related signal. Several technologies have potential for leading to viable measuring devices, but most of the data are based on in vitro experimentation. Because of the technical complexity of in vivo glucose measurements, this review aims at discussing the gap between the established need and current technology limitations.