Observation of crack initiation during hot tearing

While the general mechanisms of hot tearing are understood, i.e. the inability of liquid to feed imposed strain on the mushy material, work continues on improving the understanding of the mechanisms at play. A hot tear test rig that measures the temperature and load imposed on the mushy zone during solidification has been successfully used to study hot tearing. The mould has now been modified to incorporate a window above the hot spot region to allow observation of hot tear formation and growth. Combining information from visual observation with load and temperature data has led to a better understanding of the mechanism of hot tearing. Tests were carried out on an Al-0.5 wt-% Cu alloy. It was found that load development began at about 90% solid and a hot tear formed a short time later, at between 93% and 96% solid. Hot tearing started at a very low load.

Crack depths in desiccating plastic concrete

The depths of cracks in desiccating plastic concrete are estimated by considering the effects of the suction (negative pore pressure) associated with desiccation and applying five failure models derived from fracture, theories combined with theories drawn from geotechnical engineering under the assumption that plastic concrete is a frictional particulate material. The estimated crack depths vary with the depth of desiccation, the suction profile, and a small number of material parameters that depend on the model adopted and are comparatively easy to estimate accurately. Four of the models predict excessively large crack depths. The fifth, however, predicts shallower crack depths that increase with the age of the concrete and are consistent with those of analogous desiccation cracks in coal mine tailings. It thus offers a relatively robust method of estimating the depth of desiccation cracks. Confirmation of this with data for plastic concrete is clearly desirable but not possible at present.

Fatigue crack propagation in a sintered 2xxx series aluminium alloy

Many potential applications for sintered aluminium are limited by the poor fatigue properties of the material. In order to increase understanding of the fatigue mechanisms in sintered aluminium, fatigue tests were carried out on a sintered 2xxx series aluminium alloy, AMB-2712. The alloy has a fatigue endurance strength of approximately 145 MPa (R = 0.1). Three regions were identified on the fatigue fracture surfaces. Region I contains the initiation site and transgranular crack propagation. When the size of the cyclic plastic zone ahead of the crack becomes comparable to the grain size, microstructural damage at the crack tip results in a transition to intergranular propagation. Region 2 mainly contains intergranularly fractured material, whilst the final fracture area makes up Region 3, in the form of dimple coalescence and intergranular failure. Transgranular fractographic features observed on fatigued specimens include fissure-type striations, cross-hatched grains, furrowed grains and grains containing step-like features. (c) 2006 Elsevier B.V. All rights reserved.

Timing analysis of assembler code control-flow paths

Timinganalysis of assembler code is essential to achieve the strongest possible guarantee of correctness for safety-critical, real-time software. Previous work has shown how timingconstrain ts on controlflow paths through high-level language programs can be formalised using the semantics of the statements comprisingthe path. We extend these results to assembler-level code where it becomes possible to not only determine timingconstrain ts, but also to verify them against the known execution times for each instruction. A minimal formal model is developed with both a weakest liberal precondition and a strongest postcondition semantics. However, despite the formalism’s simplicity, it is shown that complex timingb ehaviour associated with instruction pipeliningand iterative code can be modelled accurately.

Programs as paths: An approach to timing constraint analysis

A program can be decomposed into a set of possible execution paths. These can be described in terms of primitives such as assignments, assumptions and coercions, and composition operators such as sequential composition and nondeterministic choice as well as finitely or infinitely iterated sequential composition. Some of these paths cannot possibly be followed (they are dead or infeasible), and they may or may not terminate. Decomposing programs into paths provides a foundation for analyzing properties of programs. Our motivation is timing constraint analysis of real-time programs, but the same techniques can be applied in other areas such as program testing. In general the set of execution paths for a program is infinite. For timing analysis we would like to decompose a program into a finite set of subpaths that covers all possible execution paths, in the sense that we only have to analyze the subpaths in order to determine suitable timing constraints that cover all execution paths.

BEM-ESTAR SUBJETIVO E AUTOEFICÁCIA EM DEPENDENTES DE COCAÍNA/CRACK

Este estudo teve por objetivo identificar e descrever associações entre bem-estar subjetivo, construto formado por satisfação geral com a vida e afetos positivos e negativos,e autoeficáciapara abstinência de drogas em dependentes de cocaína/crack em processo de abstinência. Utilizou, para avaliar as variáveis, as Escalas de Afetos Positivos e Negativos, de Satisfação Geral com a Vida, de Autoeficácia para Abstinência de Drogas, de Avaliação para Mudança da Universidade de Rhode Island e um questionário de dados sócio-demográficos e socioculturais. Participaram 70 homens, dependentes de cocaína/crack, jovens e de baixa escolaridade.Eram pessoas de rendimentos de até três salários mínimos (63%), que foram internadas mais de uma vez (65%), autodeclaradas abstinentes no momento da coleta dos dados. Os participantes possuíam níveis médiosde autoeficácia para abstinência de drogas, níveis baixos de bem-estar subjetivo, e estavam satisfeitos com suas vidas. Cálculos de correlação de Pearson revelaram que não há associação entre bem-estar subjetivoe autoeficácia para abstinência de drogas, entre prontidão para mudança no consumo de drogas e bem-estar subjetivo, nem entre prontidão para mudança no consumo de drogas eautoeficácia para abstinência de drogas. Resultados de análise de variância revelaram que não houve diferençasnos níveis de bem-estar subjetivo entreos diferentes os agrupamentos de prontidão para mudanças nem entre as médias de autoeficácia para abstinência de drogas entre os diferentes agrupamentos de prontidão para mudanças no consumo de drogas. A discussão abordou os resultados diante do fato de a internação dos participantes ter sido involuntária ou voluntária, do tempo de internação, do seu estágio de prontidão para mudar seu comportamento de consumo de drogas e das características de seu grupo de abstinência diante da literatura da área. Finalmente, apontou, em conclusão, limitações e agenda de pesquisa futura.

"Crack down on the celebrity junkies": does media coverage of celebrity drug use pose a risk to young people?

This study analysed news media content to examine the role played by celebrity drug use in young people's perceptions of drug use. We know that young people have access to discourses of drug use through music and other media which may emphasise short term gains (of pleasure or sexual success) over longer term health and social problems. This study goes beyond a simple modelling approach by using Media Framing Analysis (MFA) to take an in-depth look at the messages themselves and how they are 'framed'. New stories about Amy Winehouse's drug use were used and we conducted focus groups with young people asking them questions about drugs, celebrity and the media. Frames identified include: 'troubled genius', 'losing patience' and 'glamorization or gritty realism'. Initially, the press championed Winehouse's musical talent but soon began to tire of her recklessness; the participants tended to be unimpressed with Winehouse's drug use, characterising her as a promising artist who had 'gone off the rails'. Young people were far more critical of Winehouse than might be expected, demonstrating that concerns about the influence of celebrity drug use and its impact on future health risk behaviour among young people may have been over-simplified and exaggerated. This study illustrates the need to understand young people and their frames of reference within popular culture when designing drug awareness information relevant to them. Furthermore, it indicates that critical media skills analysis may contribute to health risk education programmes related to drug use.