Band gap study on zinc-doped cadmium sulphide

Photoconductivity studies on cadium sulphide (CdS) crystals grown by chemical vapour transport method were carried out at room temperature (300°C) over the spectral range between the near ultraviolet and the near infrared. Three samples of CdS crystals, viz. undoped CdS crystal, 0·5 ppm zinc doped CdS crystal, and 1 ppm zinc doped CdS crystal, were used. The variation of photocurrent as a function of applied field, intensity of the incident light, response time, and incident wavelength was studied. It was observed that the band gap decreased linearly as doping concentration increased. This is interpreted as being due to doped impurity atoms acting as traps very close to the conduction band edge. The rise and decay times also decreased linearly as doping concentration increased. This has been interpreted due to more free charge carriers being created in the crystal with increase in doping concentration, thereby making the crystal more photosensitive.     

Initial field trials with the synthetic sex pheromone of the processionary mothThaumetopoea pityocampa (Denis and Schiff.)

Synthetic (Z)-13-hexadecen-11-ynyl acetate has been shown to be highly active in catchingThaumetopoea pityocampa (Denis and Schiff.) males in field trials carried out in different parts of Spain. A variety of formulations containing antioxidants or solid paraffin were tested. Formulations containing 3 and 10% ofE isomer showed a decrease of activity compared with those prepared with pureZ isomer. Dodecyl acetate, also found in the virgin female gland, did not show any synergistic effect when tested in a 9∶1 mixture with the synthetic pheromone. The product exhibited a remarkable persistence of activity under the field conditions even in the absence of stabilizer.     

Oxidation behavior of AlN substrate at low temperature

The oxidation onset and the kinetics of polycrystalline AlN substrates were studied by measuring the weight percent of oxygen in the surface layer and the surface roughness with energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM), respectively. The oxidation started in the temperature range 800–900 °C and the entire surface of the AlN substrate was covered with an Al₂O₃ oxide layer below 1100 °C. The oxidation kinetics followed a linear rate law below 1000 °C and a parabolic rate law above 1100 °C. Above 1100 °C, the surface roughness increased abruptly by the irregular shape of overgrown oxide, which might enhance the adhesion of metal to the AlN surface in a metallization process. With an increase of the oxidation temperature above 1200 °C, the oxide layer split during cooling due to the thermal expansion mismatch between the AlN matrix and the Al₂O₃ oxide layer.     

Photoconductivity of iodine-doped single crystals of phthalocyanine

Single crystals of metal-free phthalocyanine (H₂Pc) and of copper phthalocyanine (CuPc) were grown in the presence of iodine vapour. The presence of iodine enhances the spectral dependence of photoconductivity of H₂Pc in the visible region but of CuPc in the near-IR region. The dark current is decreased but the photocurrent is increased by one order of magnitude in iodine-doped H₂Pc but in the case of iodine-doped CuPc both currents are increased by nearly three orders of magnitude. Introduction of iodine results in about one order of magnitude decrease in response time for both modifications. Thus the introduction of iodine into Pc crystals decreases the energy barrier for conduction and increases the drift mobility of charge carriers thereby enhancing the conductivity of the material.     

Noncontact Ultrasonic Characterization of Ceramics

A noncontact ultrasonic technique for the characterization of piezoelectric ceramics is described. The velocity of a laser-generated surface-acoustic-wave pulse propagating at the surface of the ceramic material is measured by an optical probe. The laser beam has an annular section in order to produce a conveniently strong ultrasonic pulse without overheating the surface. Applications to the characterization of PZT samples are described.     

Kinetics of polyesterification and models, 3. Kinetics and mechanism of pentaerythritol esterification by long-chain carboxylic acids at technological conditions

Kinetics of the esterification of pentaerythritol by long-chain carboxylic acids (C₇ – C₁₈) has been followed by potentiometric titrimetry. A simplified approach for the estimation of the rate constant values and the rate constants of the consecutive processes was developed according to the previous established kinetic law for similar systems. A computer simulation of the component concentrations variation has been carried out in order to prove the selected kinetic model.     

Numerical estimation in blind subjects: Evidence of the impact of blindness and its following experience.

Vision was for a long time considered to be essential in the elaboration of the semantic numerical representation. However, early visual deprivation does not seem to preclude the development of a spatial continuum oriented from left to right to represent numbers (J. Castronovo & X. Seron, 2007; D. Szücs & V. Csépe, 2005). The authors investigated the impact of blindness and its following experience on a 3rd property of the mental number line: its obedience to Weber's law. A group of blind subjects and a group of sighted subjects were submitted to 2 numerical estimation tasks: (a) a keypress estimation task and (b) an auditory events estimation task. Blind and sighted subjects' performance obeyed Weber's law. However, blind subjects demonstrated better numerical estimation abilities than did sighted subjects, especially in contexts involving proprioception, indicating the existence of better mapping abilities between the symbolic representations of numbers and their corresponding magnitude representations, obeying Weber's law (e.g., J. S. Lipton & E. Spelke, 2005). These findings suggest that blindness and its following experience with numbers might result in better accuracy in numerical processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiheme cytochromes from the sulfur-reducing bacterium Desulfuromonas acetoxidans

Two new multiheme cytochromes were isolated from the anaerobic sulfur reducing bacterium Desulfuromonas acetoxidans. They have monomeric molecular masses of 50 and 65 kDa and contain six and eight hemes, respectively. Visible and EPR spectroscopies, in the as-isolated (oxidised) cytochromes, show the presence of only low-spin hemes in the 50-kDa cytochrome, and of high-spin and low-spin hemes in the 65-kDa cytochrome. The EPR spectra of the native 65-kDa cytochrome indicate multiple heme-heme interactions, including integer-spin systems as judged by parallel-mode EPR. The 50-kDa cytochrome has a complex redox pattern, as shown by EPR redox titrations, and contains one heme with unusual characteristics. Both cytochromes cover an extremely wide range of reduction potentials, which go from +100 mV to -375 mV for the 50-kDa cytochrome, and +185 mV to -235 mV for the 65-kDa cytochrome. The two cytochromes were tested for hydroxylamine oxidoreductase activity and polysulfide reductase activity, but neither displayed any activity. In contrast, it was found for the first time that the previously characterised cytochrome c551.5, from the same bacterium is very active in the reduction of polysulfide, which suggests that it acts as a terminal reductase in D. acetoxidans.