A new zirconium-rich master alloy for the grain refinement of magnesium alloys

A new zirconium-rich magnesium-zirconium master alloy (designated AM-cast) has been developed by the CRC for Cast Metals Manufacturing in collaboration with Australian Magnesium Corporation for use as a grain refiner for magnesium alloys that do not contain aluminium. This work describes the microstructural characteristics of this new grain refiner and its grain refining ability when added to different magnesium alloys under various conditions (alloying temperature from 680 °C to 750 °C; weight of melt from 1 kg to 150 kg and sample thickness from 7 mm to 62 mm). Owing to its highly alloyable microstructure, AM-cast can be readily introduced into molten magnesium at any temperature when assisted by a few minutes of stirring or puddling. Little sludge has been found at the bottom of the alloying vessel in these trials due to the fine zirconium particles contained in the master alloy. The recovery of zirconium is normally in the range from 40% to 60% with respect to 1% zirconium addition as the master alloy. It is shown that this new master alloy is an excellent grain refiner for aluminium-free magnesium alloys.

Density evolution and power profile optimization for iterative multiuser decoders based on individually optimum multiuser detectors

Iterative multiuser joint decoding based on exact Belief Propagation (BP) is analyzed in the large system limit by means of the replica method. It is shown that performance can be improved by appropriate power assignment to the users. The optimum power assignment can be found by linear programming in most technically relevant cases. The performance of BP iterative multiuser joint decoding is compared to suboptimum approximations based on Interference Cancellation (IC). While IC receivers show a significant loss for equal-power users, they yield performance close to BP under optimum power assignment.

Independent detectors for expansion and rotation, and for orthogonal components of deformation

It is well known that optic flow - the smooth transformation of the retinal image experienced by a moving observer - contains valuable information about the three-dimensional layout of the environment. From psychophysical and neurophysiological experiments, specialised mechanisms responsive to components of optic flow (sometimes called complex motion) such as expansion and rotation have been inferred. However, it remains unclear (a) whether the visual system has mechanisms for processing the component of deformation and (b) whether there are multiple mechanisms that function independently from each other. Here, we investigate these issues using random-dot patterns and a forced-choice subthreshold summation technique. In experiment 1, we manipulated the size of a test region that was permitted to contain signal and found substantial spatial summation for signal components of translation, expansion, rotation, and deformation embedded in noise. In experiment 2, little or no summation was found for the superposition of orthogonal pairs of complex motion patterns (eg expansion and rotation), consistent with probability summation between pairs of independent detectors. Our results suggest that optic-flow components are detected by mechanisms that are specialised for particular patterns of complex motion.

The growth of six saxicolous lichens transplanted to lime-rich and lime-poor substrates in south Gwynedd, Wales

The objectives of this study were to investigate: (1) whether foliose lichen thalli could be transplanted from one substrate to another and (2) whether such transplants could be used to study the influence of the substrate on growth. Hence, six saxicolous lichens, with contrasting distributions on lime-rich and lime-poor substrates in South Gwynedd, Wales, were transplanted onto slate, granite, asbestos and cement. Fragments of the perimeters of thalli were glued to the different substrates using Bostic adhesive. Parmelia conspersa (Ehrh. Ex Ach.)Ach. and Parmelia saxatilis (L.)Ach., fragments increased in area over 15 months on slate and granite but decreased in area or did not survive on asbestos and cement. Fragments of Xanthoria parietina (L.)Th.Fr. and Physcia tenella (Scop.)DC. em Bitt. did not survive on slate and granite while some fragments survived but grew poorly on asbestos and cement. Parmelia glabratula ssp. fuliginosa (Fr. ex Duby)Laund. fragments decreased in area on all substrates and especially on cement and asbestos while Physcia orbicularis (Neck.)Poetsch fragments increased in area on granite and cement, decreased on asbestos and did not change significantly on slate. The results suggested that the distribution of P. conspersa and P. saxatilis was determined primarily by physico-chemical properties of the substrate. By contrast, P. glabratula ssp. fuliginosa may have responded to the transplant procedure while X. parietina, Ph. tenella and Ph. orbicularis may require nutrient enrichment to grow successfully on a substrate.

The creep properties of a series of zinc-rich zinc-aluminium alloys

The compressive creep behaviour of six sand cast zinc-rich alloys: No3 and No5, corresponding to BS 1004A and BS 1004B, respectively, alloy No2, ILZRO,.16 and two newer alloys ACuZinc5 and ACuZinc10 was investigated. The total creep contraction of the alloys was found to be well correlated using an empirical equation. On the basis of this equation, a parametrical relationship was derived which allowed the total creep contraction to be related to the applied stress, the temperature and the time of test, so that a quantitative assessment of compressive creep of the alloys could be made under different testing conditions. The primary creep and secondary creep rates were found for the alloys at different temperatures and stresses. Generally, the primary creep contraction was found to increase with copper content, whereas secondary creep rates decreased in the order No3, ACuZinc10, ACuZinc5 and No2. ILZRO.16 was tested only at the highest stress and two higher temperatures. The results showed that ILZRO.16 had higher creep resistance than all the other alloys. Thus, based on the above empirical equation, alloy No2 was found to have a substantially better total creep resistance than alloys No3 and No5, and slightly better than ACuZinc5 and ACuZinc10 for strains up to 1%. Both ACuZinc alloys had higher creep strength than commercial alloys No3 and No5. Alloy No5 had much higher creep resistance than alloy No3 under all conditions. The superior creep resistance of alloy No2 was considered to be due to the presence of small precipitates of -phase in the zinc matrix and a regular eutectic morphology. The stress exponents and activation energies for creep under different testing conditions were found to be consistent with some established creep-controlling mechanisms; i.e. dislocation climb for alloy No3, dislocation climb over second phase particles for alloys No5, No2, ACuZinc10, controlled by lattice diffusion in the zinc-rich phase. The lower creep resistance of alloy No3 was mainly due to the lower creep strength of copper-free primary particles having greater volume than eutectic in the microstructure. Alloys No5, ACuZinc5 and ACuZinc10 showed much better creep resistance than alloy No3, based on the precipitation-hardening due to the presence of small -phase precipitates. The primary dendrites in both ACuZinc alloys however were not of much benefit in improving the creep resistance of the alloys.

The design of gas chromatography ionisation detectors:a study of the electron capture detector and the home ionisation detector

DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT

Rich and poor, white and black, free and slave: The social history of Cuba's tobacco farmers, 1763--1817

Tobacco was of primary importance to Spain, and its impact on Cuba's economy and society was greater than just the numbers of farms, workers, or production, demonstrated by the Spanish crown's outlay of monies for capital assets, bureaucrats' salaries, and payments to farmers for their crop. This study is a micro- and macro-level study of rural life in colonial Cuba and the interconnected relationships among society, agricultural production, state control, and the island's economic development. ^ By placing Cuba's tobacco farmers at the forefront of this social history, this work revisits and offers alternatives to two prevailing historiographical views of rural Cuba from 1763 (the year Havana returned to Spanish control following the Seven Years' War) to 1817 (the final year of the 100-year royal monopoly on Cuban tobacco). Firstly, it argues against the primacy of sugar over other agricultural crops, a view that has shaped decades of scholarship, and challenges the thesis which maintains the Cuban tobacco farmer was almost exclusively poor, white, and employed free labor, rather than slaves, in the production of their crop. ^ This study establishes the importance of tobacco as an agricultural product, and argues that Cuban tobacco growers were a heterogeneous group, revealing the role that its cultivation may have played in helping some slaves earn their freedom. ^

The development of an optimized system of narcotic and explosive contraband mimics for calibration and training of biological detectors

Current commercially available mimics contain varying amounts of either the actual explosive/drug or the chemical compound of suspected interest by biological detectors. As a result, there is significant interest in determining the dominant chemical odor signatures of the mimics, often referred to as pseudos, particularly when compared to the genuine contraband material. This dissertation discusses results obtained from the analysis of drug and explosive headspace related to the odor profiles as recognized by trained detection canines. Analysis was performed through the use of headspace solid phase microextraction in conjunction with gas chromatography mass spectrometry (HS-SPME-GC-MS). Upon determination of specific odors, field trials were held using a combination of the target odors with COMPS. Piperonal was shown to be a dominant odor compound in the headspace of some ecstasy samples and a recognizable odor mimic by trained detection canines. It was also shown that detection canines could be imprinted on piperonal COMPS and correctly identify ecstasy samples at a threshold level of approximately 100ng/s. Isosafrole and/or MDP-2-POH show potential as training aid mimics for non-piperonal based MDMA. Acetic acid was shown to be dominant in the headspace of heroin samples and verified as a dominant odor in commercial vinegar samples; however, no common, secondary compound was detected in the headspace of either. Because of the similarities detected within respective explosive classes, several compounds were chosen for explosive mimics. A single based smokeless powder with a detectable level of 2,4-dinitrotoluene, a double based smokeless powder with a detectable level of nitroglycerine, 2-ethyl-1-hexanol, DMNB, ethyl centralite and diphenylamine were shown to be accurate mimics for TNT-based explosives, NG-based explosives, plastic explosives, tagged explosives, and smokeless powders, respectively. The combination of these six odors represents a comprehensive explosive odor kit with positive results for imprint on detection canines. As a proof of concept, the chemical compound PFTBA showed promise as a possible universal, non-target odor compound for comparison and calibration of detection canines and instrumentation. In a comparison study of shape versus vibration odor theory, the detection of d-methyl benzoate and methyl benzoate was explored using canine detectors. While results did not overwhelmingly substantiate either theory, shape odor theory provides a better explanation of the canine and human subject responses.