Implementing aspects of management accounting in a low volume manufacturing engineering concern

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

The creep behaviour of pressure diecast zinc-aluminium based alloys

The creep behaviour of three pressure diecast commercial zinc-aluminium based alloys: Mazak 3, corresponding to BS 1004A, and the new alloys ZA.8 and ZA.27 with a series of alloys with compositions ranging from 0% to 30% aluminium was investigated. The total creep elongation of commercial alloys was shown to be well correlated using an empirical equation. Based on this a parametrical relationship was derived which allowed the total creep extension to be related to the applied stress, the temperature and the time of test, so that a quantitative assessment of creep of the alloys could be made under different conditions. Deviation from the normal creep kinetics occurred in alloys ZA.8 and ZA.27 at very low stresses, 150°C, due to structural coarsening combined with partial transformation of ε -phase into T' phase. The extent of primary creep was found to increase with aluminium content, but secondary creep rates decreased in the order Mazak 3, ZA.8 and ZA.27. Thus, based on the above equation, ZA.8 was found to have a substantially better total creep resistance than ZA.27, which in turn was marginally better than Mazak 3 for strains higher than 0.5%, but inferior for smaller strains, due to its higher primary creep extension. The superior creep resistance of ZA.8 was found to be due to the presence of strictly-orientated, thin plate-like precipitates of ε(CuZn4) phase in the zinc matrix of the eutectic and the lamellarly decomposed β phase, in which the precipitation morphology and orientation of ε in the zinc matrix was determined. Over broad ranges of temperature and stresses, the stress exponents and activation energies for creep were found to be consistent with some proposed creep rate mechanisms; i.e. viscous glide for Mazak 3, dislocation climb over second phase particles for ZA.8 and dislocation climb for ZA.27, controlled by diffusion in the zinc-rich phase. The morphology of aluminium and copper-rich precipitates formed from the solid solution of zinc was clearly revealed. The former were found to further increase the creep rate of inherently low creep resistant zinc, but the latter contributed significantly to the creep resistance. Excess copper in the composition, however, was not beneficial in improving the creep resistance. Decomposition of β in copper-containing alloys was found to be through a metastable Zn-Al phase which is strongly stabilised by copper, and the final products of the decomposition had a profound effect on the creep strength of the alloys. The poor creep resistance of alloy ZA.27 was due to the presence of particulate products derived from decomposed β-phase and a large volume of fine, equiaxed products of continuously decomposed α-dendrites.

The mechanical properties and formability of dual-phase steel

In recent years dual phase steels comprising of 5-20% martensite in a ferrite matrix have come into the limelight of high strength cold formable steels because of their potential for vehicle weight saving. They show the following features: no yield point; relatively low initial flow stress; high initial workhardening rate; well sustained work hardening. As a consequence of these characteristics, dual phase steels exhibit a better combination of strength and elongation than other HSLA steels. In this thesis, a broad view of the factors which influence their properties is presented. Mechanical properties and forming ability of a commercially available dual phase steel and an AL-Si killed steel processed to dual phase form are investigated to ascertain the effect of their microstructure on their properties. It is found that the yield phenomena are masked by the transformation induced stresses present during processing and so yield point could be recovered under suitable ageing treatment; that apart from giving the above properties dual phasing gives rise to very low strain-rate sensitivity and a low R value ~ 1; that the mechanical response under rolling conditions is not different from those under tension; that there is a danger of damage to tooling during forming operations of these steels if fracture should precede instability as a result of grain size dependent strength found for these steels. It is also found that very little deformation of the martensite islands took place during deformation except at high strains. The work-hardening and the strength levels can be controlled by either decreasing the grain size or increasing the martensite volume fraction, but it is found that increasing martensite has a detrimental effect on ductility and the ductility and fracture strength can be controlled better by refining the grain size. A remarkable effect found in the dual phase steel tested is that the compressive strength is higher than the tensile strength. The reason for this observation is not yet clear but it is suggested that it might be due to the introduction of emissary type dislocations into the ferrite lattice as a result of twins formed in the martensite during transformation from austenite. The twins are envisaged to be {111} <112> in character.

The study of ultra-low energy deposition of hydrogenated amorphous carbon thin films

This thesis is dedicated to the production and analysis of thin hydrogenated amorphous carbon films. A cascaded arc plasma source was used to produce a high density plasma of hydrocarbon radicals that deposited on a substrate at ultra low energies. The work was intended to create a better understanding of the mechanisms responsible for the film formation, by an extensive analysis on the properties of the films in correlation with the conditions used in the plasma cell. Two different precursors were used: methane and acetylene. They revealed a very different picture for the mechanism of film formation and properties. Methane was less successful, and the films formed were soft, with poor adhesion to the substrate and decomposing with time. Acetylene was the better option, and the films formed in this case were harder, with better adhesion to the substrate and stable over time. The plasma parameters could be varied to change the character of films, from polymer-like to diamond-like carbon. Films deposited from methane were grown at low deposition rates, which increased with the increase in process pressure and source power and decreased with the increase in substrate temperature and in hydrogen fraction in the carrier gas. The films had similar hydrogen content, sp3 fractions, average roughness (Ra) and low hardness. Above a deposition temperature of 350°C graphitization occurred - an increase in the sp2 fraction. A deposition mechanism was proposed, based upon the reaction product of the dissociative recombination of CH4+. There were small differences between the chemistries in the plasma at low and high precursor flow rates and low and high substrate temperatures; all experimental conditions led to formation of films that were either polymer-like, soft amorphous hydrogenated carbon or graphitic-like in structure. Films deposited from acetylene were grown at much higher deposition rates on different substrates (silicon, glass and plastics). The film quality increased noticeably with the increase of relative acetylene to argon flow rate, up to a certain value, where saturation occurred. With the increase in substrate temperature and the lowering of the acetylene injection ring position further improvements in film quality were achieved. The deposition process was scaled up to large area (5 x 5 cm) substrates in the later stages of the project. A deposition mechanism was proposed, based upon the reaction products of the dissociative recombination of C2H2 +. There were large differences between the chemistry in the plasma at low and medium/high precursor flow rates. This corresponded to large differences in film properties from low to medium flow rates, when films changed their character from polymer-like to diamond-like, whereas the differences between films deposited at medium and high precursor flow rates were small. Modelling of the film growth on silicon substrates was initiated and it explained the formation of sp2 and sp3 bonds at these very low energies. However, further improvements to the model are needed.

Energy saving and solar electricity in fan-ventilated greenhouses

Greenhouse cultivation is an energy intensive process therefore it is worthwhile to introduce energy saving measures and alternative energy sources. Here we show that there is scope for energy saving in fan ventilated greenhouses. Measurements of electricity usage as a function of fan speed have been performed for two models of 1.25 m diameter greenhouse fans and compared to theoretical values. Reducing the speed can cut the energy usage per volume of air moved by more than 70%. To minimize the capital cost of low-speed operation, a cooled greenhouse has been built in which the fan speed responds to sunlight such that full speed is reached only around noon. The energy saving is about 40% compared to constant speed operation. Direct operation of fans from solar-photovoltaic modules is also viable as shown from experiments with a fan driven by a brushless DC motor. On comparing the Net Present Value costs of the different systems over a 10 year amortization period (with and without a carbon tax to represent environmental costs) we find that sunlight-controlled system saves money under all assumptions about taxation and discount rates. The solar-powered system, however, is only profitable for very low discount rates, due to the high initial capital costs. Nonetheless this system could be of interest for its reliability in developing countries where mains electricity is intermittent. We recommend that greenhouse fan manufacturers improve the availability of energy-saving designs such as those described here.

Statnote 36: Do the data fit the Poisson distribution

In previous Statnotes, many of the statistical tests described rely on the assumption that the data are a random sample from a normal or Gaussian distribution. These include most of the tests in common usage such as the ‘t’ test ), the various types of analysis of variance (ANOVA), and Pearson’s correlation coefficient (‘r’) . In microbiology research, however, not all variables can be assumed to follow a normal distribution. Yeast populations, for example, are a notable feature of freshwater habitats, representatives of over 100 genera having been recorded . Most common are the ‘red yeasts’ such as Rhodotorula, Rhodosporidium, and Sporobolomyces and ‘black yeasts’ such as Aurobasidium pelculans, together with species of Candida. Despite the abundance of genera and species, the overall density of an individual species in freshwater is likely to be low and hence, samples taken from such a population will contain very low numbers of cells. A rare organism living in an aquatic environment may be distributed more or less at random in a volume of water and therefore, samples taken from such an environment may result in counts which are more likely to be distributed according to the Poisson than the normal distribution. The Poisson distribution was named after the French mathematician Siméon Poisson (1781-1840) and has many applications in biology, especially in describing rare or randomly distributed events, e.g., the number of mutations in a given sequence of DNA after exposure to a fixed amount of radiation or the number of cells infected by a virus given a fixed level of exposure. This Statnote describes how to fit the Poisson distribution to counts of yeast cells in samples taken from a freshwater lake.

A low mortality, high morbidity Reduced Intensity Status Epilepticus (RISE) model of epilepsy and epileptogenesis in the rat

Animal models of acquired epilepsies aim to provide researchers with tools for use in understanding the processes underlying the acquisition, development and establishment of the disorder. Typically, following a systemic or local insult, vulnerable brain regions undergo a process leading to the development, over time, of spontaneous recurrent seizures. Many such models make use of a period of intense seizure activity or status epilepticus, and this may be associated with high mortality and/or global damage to large areas of the brain. These undesirable elements have driven improvements in the design of chronic epilepsy models, for example the lithium-pilocarpine epileptogenesis model. Here, we present an optimised model of chronic epilepsy that reduces mortality to 1% whilst retaining features of high epileptogenicity and development of spontaneous seizures. Using local field potential recordings from hippocampus in vitro as a probe, we show that the model does not result in significant loss of neuronal network function in area CA3 and, instead, subtle alterations in network dynamics appear during a process of epileptogenesis, which eventually leads to a chronic seizure state. The model’s features of very low mortality and high morbidity in the absence of global neuronal damage offer the chance to explore the processes underlying epileptogenesis in detail, in a population of animals not defined by their resistance to seizures, whilst acknowledging and being driven by the 3Rs (Replacement, Refinement and Reduction of animal use in scientific procedures) principles.

Low-complexity BCH codes with optimized interleavers for DQPSK systems with laser phase noise

The presence of high phase noise in addition to additive white Gaussian noise in coherent optical systems affects the performance of forward error correction (FEC) schemes. In this paper, we propose a simple scheme for such systems, using block interleavers and binary Bose–Chaudhuri–Hocquenghem (BCH) codes. The block interleavers are specifically optimized for differential quadrature phase shift keying modulation. We propose a method for selecting BCH codes that, together with the interleavers, achieve a target post-FEC bit error rate (BER). This combination of interleavers and BCH codes has very low implementation complexity. In addition, our approach is straightforward, requiring only short pre-FEC simulations to parameterize a model, based on which we select codes analytically. We aim to correct a pre-FEC BER of around (Formula presented.). We evaluate the accuracy of our approach using numerical simulations. For a target post-FEC BER of (Formula presented.), codes selected using our method result in BERs around 3(Formula presented.) target and achieve the target with around 0.2 dB extra signal-to-noise ratio.