Highly Monodisperse Colloidal Magnesium Nanoparticles by Room Temperature Digestive Ripening

Nanoclusters of 25 nm sized Mg-THF have been prepared by the solvated metal atom dispersion method. Room-temperature digestive ripening of these nanoclusters in the presence of hexadecylamine (HDA) resulted in highly monodisperse colloidal Mg-HDA nanoparticles of 2.8 ± 0.2 nm. An insight into the room-temperature digestive ripening process was obtained by studying the disintegration of clusters for various Mg:HDA ratios. The Mg colloids are quite stable with respect to precipitation of particles under Ar atmosphere. Using this procedure, pure Mg(0) nanopowders were obtained in gram scale quantities. The Mg powder precipitated from the colloid was fully hydrided at 33 bar and 118 °C. Initial desorption of H2 from samples of MgH2 was achieved at a remarkably low temperature, 115 °C compared to >350 °C in bulk Mg, demonstrating the importance of the size on the desorption temperatures.

Rapid, selective, and reversible Nitroxide Radical Coupling (NRC) reactions at amibient temperature

High activation of polystyrene with bromine end groups (PSTY-Br) to their incipient radicals occurred in the presence of Cu(I)Br, Me6TREN, and DMSO solvent. These radicals were then trapped by nitroxide species leading to coupling reactions between PSTY-Br and nitroxides that were ultrafast and selective in the presence of a diverse range of functional groups. The nitroxide radical coupling (NRC) reactions have the attributes of a “click” reaction with near quantitative yields of product formed, but through the reversibility of this reaction, it has the added advantage of permitting the exchange of chemical functionality on macromolecules. Conditions were chosen to facilitate the disproportionation of Cu(I)Br to the highly activating nascent Cu(0) and deactivating Cu(II)Br2 in the presence of DMSO solvent and Me6TREN ligand. NRC at room temperature gave near quantitative yields of macromolecular coupling of low molecular weight polystyrene with bromine chain-ends (PSTY-Br) and nitroxides in under 7 min even in the presence of functional groups (e.g., −≡, −OH, −COOH, −NH2, =O). Utilization of the reversibility of the NRC reaction at elevated temperatures allowed the exchange of chain-end groups with a variety of functional nitroxide derivatives. The robustness and orthogonality of this NRC reaction were further demonstrated using the Cu-catalyzed azide/alkyne “click” (CuAAC) reactions, in which yields greater than 95% were observed for coupling between PSTY-N3 and a PSTY chain first trapped with an alkyne functional TEMPO (PSTY-TEMPO-≡).

Temperature characteristics of the billet and the dies in a small batch forging production

The work reported herein is part of an on-going programme to develop a computer code which, given the geometrical, process and material parameters of the forging operation, is able to predict the die and the billet cooling/heating characteristics in forging production. The code has been experimentally validated earlier for a single forging cycle and is now validated for a small batch production. To facilitate a step-by-step development of the code, the billet deformation has so far been limited to its surface layers, a situation akin to coining. The code has been used here to study the effects of die preheat-temperature, machine speed and rate of deformation the cooling/heating of the billet and the dies over a small batch of 150 forgings. The study shows: that there is a pre-heat temperature at which the billet temperature changes little from one forging to the next; that beyond a particular number of forgings, the machine speed ceases to have any pronounced influence on the temperature characteristics of the billet; and that increasing the rate of deformation reduces the heat loss from the billet and gives the billet a stable temperature profile with respect to the number of forgings. The code, which is simple to use, is being extended to bulk-deformation problems. Given a practical range of possible machine, billet and process specifics, the code should be able to arrive at a combination of these parameters which will give the best thermal characteristics of the die-billet system. The code is also envisaged as being useful in the design of isothermal dies and processes.

Effect of fumigation temperature on the efficacy of phosphine against strongly resistant psocids liposcelis bostrychophila (Pscodoptera: Liposcelididae)

Species of Liposcelis psocids have emerged as major pests of stored grain in Australia in recent years. Several populations have been detected with high resistance to phosphine, the major chemical treatment. Highest resistance has been detected in the cosmopolitan species Liposcelis bostrychophila. As part of a national resistance management strategy to maintain the viability of phosphine, we are developing minimum effective dosage regimes (concentration x time) required to control all life stages of resistant L. bostrychophila at a range of grain temperatures. Four concentrations of phosphine, 0.1, 0.17, 0.3 aid 1 mg/L, were evaluated for their effectiveness against strongly resistant L. bostrychophila at a series of fumigation temperatures: 20, 25, 30 and 35°C. Results were recorded as the least number of days taken to achieve population extinction. We found that, at any fixed concentration of phosphine, time to population extinction decreased as fumigation temperature increased from 20 to 30°C. For example, at 0.1 mg/L, it took more than 14 days at 20°C to completely control these insects, whereas at 30°C it took only seven days. Increase in fumigation temperature from 25OC to 30°C dramatically reduced the exposure period needed to achieve population extinction of resistant psocids. For example, a dose of 0.17 mg/L over six days at 30°C completely controlled strongly resistant L. bostrychophila populations that can survive at 1 mg/L and 25°C over the same exposure period. Findings from our study will be used to formulate recommendations for registered dosage rates and fumigation periods for use in Australia.

Temperature dependence of the dielectric constant of diamond

The temperature dependence of the dielectric constant of diamond has been measured over the temperature range 50-2OO"c. The value of E-ldc dT over this range is + 1 x 10-j. Details of the method of measuring the temperature coefficient of dielectric constant are also given. The magnitude and sign of c-ldc, dT for diamond has been theoretically calculated using Maxwell's relationship and Kramers-Heisenberg theory. The agreement between theoretical and experimental values is extremely good.

NMR relaxation study of disorder in the mixed system BP x GPI(1-x) and the low temperature transition from classical to quantum rotation

1H NMR spin-lattice relaxation time (T1) studies have been carried out in the temperature range 100 K to 4 K, at two Larmor frequencies 11.4 and 23.3 MHz, in the mixed system of betaine phosphate and glycine phosphite (BPxGPI(1-x)), to study the effects of disorder on the proton group dynamics. Analysis of T1 data indicates the presence of a number of inequivalent methyl groups and a gradual transition from classical reorientations to quantum tunneling rotations. At lower temperatures, microstructural disorder in the local environments of the methyl groups, result in a distribution in the activation energy (Ea) and the torsional energy gap (E01). For certain values of x, the magnetisation recovery shows biexponential behaviour at lower temperatures.

Natural convection from a vertical cone in a porous medium due to the combined effects of heat and mass diffusion with non-uniform wall temperature/concentration or heat/mass flux and suction/injection

An analysis has been carried out to study the non-Darcy natural convention flow of Newtonian fluids on a vertical cone embedded in a saturated porous medium with power-law variation of the wall temperature/concentration or heat/mass flux and suction/injection with the streamwise distance x. Both non-similar and self-similar solutions have been obtained. The effects of non-Darcy parameter, ratio of the buoyancy forces due to mass and heat diffusion, variation of wall temperature/concentration or heat/mass flux and suction/injection on the Nusselt and Sherwood numbers have been studied.

Microprocessor-based temperature indicator using a thermistor as the sensor

A novel microprocessor-based temperature indicator has been developed and described. This indicator provides a linear performance over a wide dynamic temperature range of 0-100°C with an accuracy of ±0-l°C. The interfacing module reduces computing time required by the microprocessor for solving the thermistor equation. Test results are given to support the theory.

The sputtering temperature of a cooling cylindrical rod with an insulated core

By a standard application of Jones's method associated with the Wiener-Hopf technique an explicit solution is obtained for the temperature distribution inside a cylindrical rod with an insulated inner core when the rod is allowed to enter into a fluid of large extent with a uniform speed, and a simple integral expression is derived for the value of the sputtering temperature of the rod at the points of entry. Numerical results under certain special circumstances are also obtained and presented in the form of a table.

Effect of Temperature Variation on Sister Chromatid Exchange Frequency in Cultured Human Lymphocytes

The effect of temperature variation on sister chromatid exchange (SCE) frequencies in human lymphocytes was studied. An increase as well as decrease in incubation temperature of cells leads to a higher frequency of sister chromatid exchanges than in cultures grown at 37°C. In addition, it was observed that mitotic: index and cell cycle duration were affected by low temperature.

High-temperature superconductivity in La- and Lu-substituted YBa2,Cu3,O7, and related oxides

The perovskites, Y0.75La0.25Ba2Cu3O7 and Y0.75Lu0.25Ba2Cu3O7, show high-Tc superconductivity (with zero resistance at or above 80 K), just as the parent compound YBa2Cu3O7. The Lu-substituted oxide, with the smallest unit-cell parameters, shows the highest Tc besides exhibiting a 100% Meissner effect. Hc1, in these oxides is around 25 mT, but the Hc2, is large. The thermopower of YBa2Cu3O7 shows a sharp transition to zero at the superconducting transition, reinforcing the bulk nature of the superconductivity. Preliminary studies show that ErBa2Cu3O7 and Er0.5Y0.5Ba2Cu3O7 are both high-temperature superconductors with zero resistance in the 82-90 K range.

Mechanism of high-temperature superconductivity in YBa2Cu3O7−δ: Crucial role of oxygen

Oxygen atoms in the middle Cu---O layer of YBa2Cu3O7 consisting of strings of corner-connected (CuO4)∞ units are shown to be crucial for superconductivity. Importance of hole-hole pairing giving rise to O---O bonds is also indicated.

Temperature dependence of 35Cl NQR in 2,6-dichloropyridine

Chlorine NQR in 2,6-dichloropyridine has been investigated in the temperature range 77 K to room temperature and a single resonance line has been observed throughout. Using this data, torsional frequencies of the molecule have been evaluated on the basis of both the Bayer theory and the modified Bayer theory incorporating Tatsuzaki correction.

Quantitative assessment of total and Gram-positive aerobic bacteria in fresh and ambient-temperature-stored sub-tropical marine fish

The current study was undertaken to enumerate Gram-positive bacteria in fresh sub-tropical marine fish and determine the effect of ambient storage (25°C) on the Gram-positive bacterial count. Total and Gram-positive bacteria were enumerated in the muscles, gills and gut of fresh and stored Pseudocaranx dentex, Pagrus auratus and Mugil cephalus on tryptone soya agar (TSA) and TSA with 0.25% phenylethyl alcohol (PEA), respectively. Initial studies indicated that PEA significantly reduced total aerobic bacterial count (TABC) whereas control Gram-positive bacteria were not affected by 0.25% PEA. TABC significantly increased in all fish body parts, whereas Gram-positive aerobic bacterial count (GABC) significantly increased only in the muscles and gills during ambient storage for 15 h. The TABC of the fish species increased from 4.00, 6.13 and 4.58 log cfu g-1, respectively in the muscles, gills, and gut to 6.31, 7.31 and 7.23 log cfu g-1 by the end of storage. GABC increased from 2.00, 3.52 and 2.20 log cfu g-1 to 4.70, 5.85 and 3.36 log cfu g-1. Within each species, TABC were significantly higher in the gills compared to that of muscles and gut; however, no significant differences were found in GABC between muscles and gills. This study demonstrated the potential importance of Gram-positive bacteria in sub-tropical marine fish and their spoilage.

New temperature fluctuation method for direct determination of thermal activation energy of deep levels in semiconductors

A new method is suggested where the thermal activation energy is measured directly and not as a slope of an Arrhenius plot. The sample temperature T is allowed to fluctuate about a temperature T0. The reverse-biased sample diode is repeatedly pulsed towards zero bias and the transient capacitance C1 at time t1 is measured The activation energy is obtained by monitoring the fluctuations in C1 and T. The method has been used to measure the activation energy of the gold acceptor level in silicon.