Gravity and Centrifugal Casting of Light Metal Alloys using rapidly produced sand moulds

Traditional sand casting is a well understood method to produce metal shapes and has been used for many years in industry. It is a relatively simple method but has a significant drawback, with the requirement of a pattern to form the internal cavity. Patterns are produced at high cost through Computer Numerical Controlled machining or wood pattern making with significantly high lead times. Rapid Prototyping is seen as a solution to this problem, with the ability to produce sand moulds directly from Computer Aided Design platforms and thus eliminate the requirement of a pattern. Through layered manufacturing, the sand mould can be produced with complex internal geometry directly, minimising labour costs and involving short waiting times. While initial research was mainly concerned with the use of Selective Laser Sintering, with the advent of 3D printing, pattern-less sand moulds can be produced more easily and cheaply. With the process gaining more and more popularity, there was a need to scientifically assess the suitability of the process for sand casting as well as, establish influences of typical process parameters on significant responses. Critical mould properties, such as permeability and compressive strength, were investigated with respect to varying time and temperature of baking. To this end, mathematical models of permeability and compressive strength were developed. Also, the influence of mould material, mould coating, alloy type and pouring temperatures were investigated in static sand casting of light metals. Further work utilised the centrifugal casting process using these 3D printed moulds to establish links between process factors, such as rotational speed and cast strength using light metals. Compressive strength results for the rapidly produced materials were acceptable compared to traditional values. Permeability was however lower than commonly used foundry sand. Results showed, nevertheless, that permeability and compressive strength were both improved by baking times and temperatures. Significant model effects were established for ZP131 and ZCast501 with respect to increased compressive strength and mould permeability. Multi-factorial experiments involving simultaneous variation of factors such as mould materials, surface coatings, alloys and pouring temperatures were conducted and static casting results in general show good as-cast mechanical properties with the factors having significant effects on surface roughness, percent elongation and hardness. Centrifugal casting of aluminium alloys initially produced below average tensile properties, due to the large presence of hydrogen porosity. However, upon degassing, much improved tensile strengths were obtained, being superior to both static casting and traditionally sand cast aluminium. Also a Magnesium alloy was successfully trialled with the centrifugal process using 3D printed moulds in spite of numerous practical difficulties. Substantial data relating to the process factors for mould materials and casting processes was produced. Analysis of factor influences facilitated optimum process configurations for the production of moulds and castings. These combinations of factors at optimum levels comprehensively showed that light metals such as aluminium and magnesium alloys could be successfully processed by rapidly produced moulds, both statically and centrifugally

Inference of natural language predicates in the open domain

Inference of predicates in natural language is a common task for humans in everyday scenarios, and thus for natural language processing by machines, such as in question answering. The question Did Arsenal beat Man United? can be affirmed by a text Arsenal obliterated Man United on Saturday if an inference is drawn that the text predicate obliterate entails beat in the question. In a world of vast and varied text resources, automatic language inference is necessary for bridging this gap between records and queries. A promising model of such inference between predicates is an Entailment Graph (EG), a structure of meaning postulates such as x obliterates y entails x defeats y. EGs are constructed using unsupervised distributional methods over a large corpus, learning representations of natural language predicates contained within. Entailment is directional, and correctly, EGs fail to confirm the opposite, that x defeats y entails x obliterates y; these distinctions are important for language understanding applications. In an EG, postulates are typically defined for a predicate argument pair (x, y) over a fixed vocabulary of such binary valence predicates, which relate two arguments. However, EG meaning postulates are limited in terms of their predicates in two ways. First, using the conventional approach, entailments may only be learned for predicates of the same valence, typically binary to binary entailment, ignoring entailments between valencies and their applications. For example, the binary relation Arsenal defeats Man United leads to an inference in humans that Arsenal is the winner, a unary relation applying to the subject Arsenal. Yet using conventional means, it is not possible to learn these in EGs. Second, only a limited vocabulary of predicates may be learned in training. This is because of the natural Zipfian frequency distribution of predicates in text corpora, which includes an unbounded long tail of rarely-mentioned predicates like obliterate. This distribution simultaneously makes it impractical to learn entailments for every predicate in a language by reading corpora, and also very likely that many of these unlearned predicates may be involved in real queries. This thesis explores inference in the open domain of natural language predicates beyond a fixed vocabulary of binary predicates. First, Entailment Graph valency is addressed. The distributional learning method is refined to enable learning entailments between predicates of different valencies. This improves recall in question answering by leveraging all available predicates in the reference text to answer questions. Second, the problem of overall predicate sparsity in EGs is explored, in which Language Model encoding is applied unsupervised with an EG. This provides a means of approximating missing premise predicates at test-time, which improves both recall and precision. However, while approximating missing hypothesis predicates is shown to be possible in principle, it remains a challenge. Finally, a behavioral study is presented on Large Language Models (containing one billion parameters or more) which investigates their ability to perform language inference involving fully open-domain premise and hypothesis predicates. While superficially performant, this class of model is found to merely approximate language inference, utilizing unsound methods to mimic reasoning including memorized training data and proxies learned from corpus distributions, which have no direct relationship with meaning

The micro-foundations of alignment among sponsors and contractors on large engineering projects

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2006.Includes bibliographical references (p. 216-230).Large engineering projects design, engineer and construct much of the world's energy, transportation and defense infrastructure. These large scale engineering endeavors are highly visible, have long lasting impacts and are of major economic significance. Yet despite their importance they frequently suffer from cost overruns and long delays and deliver systems with operational shortcomings. A contributing factor to the challenge of large projects is that the project enterprise is created by separate firms being brought together by the project sponsor, typically via formal contracts. Success requires multiple firms with hundreds (possibly thousands) of engineers working together to efficiently create complex product systems within an environment of high uncertainty. In an attempt to improve project outcomes, sponsors often endeavor to create "alignment" between themselves and their key contractors. In practice, alignment has proved difficult to create and to sustain. This research explores the policies and actions taken by firms that give rise to alignment. The large engineering projects studied for this research were offshore oil and gas field developments. grounded theory method, supplemented by formal dynamic model building, was used to investigate the causal mechanisms that support, or inhibit, the generation of alignment. The research revealed that alignment is founded on the collective understanding of the project, incorporating the firm's separate interests, and inter-firm trust. Furthermore the two antecedents of alignment act together to form a self-enforcing alignment mechanism. Six factors (system architecture, organizational design, contract design, risk, metrics and incentives) were identified that establish the inter-firm interactions through which collective understanding and inter-firm trust are created. These findings are organized into a framework that guides policy selection with a view to enabling the generation, and sustainment, of alignment.(cont.) A grounded theory method, supplemented by formal dynamic model building, was used to investigate the causal mechanisms that support, or inhibit, the generation of alignment. The research revealed that alignment is founded on the collective understanding of the project, incorporating the firm's separate interests, and inter-firm trust. Furthermore the two antecedents of alignment act together to form a self-enforcing alignment mechanism. Six factors (system architecture, organizational design, contract design, risk, metrics and incentives) were identified that establish the inter-firm interactions through which collective understanding and inter-firm trust are created. These findings are organized into a framework that guides policy selection with a view to enabling the generation, and sustainment, of alignment.by Nicholas McKenna.Ph.D

Executing major projects through Contractors

Thesis (S.M.)--Massachusetts Institute of Technology, System Design and Management Program, 2005.Includes bibliographical references (p. 112-115).Project based organizational structures are utilized in many industries. The firms engaged in these significant endeavors, project sponsor and contractor alike, risk both capital and reputation in the market-place with each new project. Delivering projects effectively provides all the firms involved with desirable financial outcomes and market advantage. This thesis sets out to identify and understand the mechanisms established by the contracting structure that in part determine the outcome of the project. It is suggested that the nature of the relationship between project sponsor and contractor shapes the outcome of the project to a significant extent. Complex and challenging projects are made more so by the adversarial relationships that frequently exist between the sponsor and contractor(s). This thesis unpacks the underlying mechanisms that determine that relationship and begins to establish a theory of the project organization that could lead to improved project execution performance.by Nicholas A. McKenna.S.M

End-use demand in commercial office buildings: case-study and modelling recommendations

While considerable progress has been made on developing high-resolution stochastic models of electricity demand for the domestic sector, non-domestic models remain relatively undeveloped. This paper provides general recommendations about how such models might be structured for commercial offices, based on detailed analysis of high-resolution end-use demand data for a single multi-tenanted office building. The results indicate that modelling of commercial office buildings could be viewed as analogous to modelling a group of dwellings with partial residency (to represent individual office units within the building), with communal heating and communal spaces, a limited number of work related appliances, and occupant activities restricted to those related to work

Reconstitution Properties of Thymus Stem Cells in Murine Fetal Liver

Injection of day-12 murine fetal liver cells into thymus lobes of Thy-1 congenic adult recipients results in a wave of thymocyte development. The kinetics of repopulation by donor cells reaches a peak after 20–25 days. The frequency of thymic stem cells (TSC) in day-12 fetal liver was estimated, by limit dilution, as 1 in 4x104 cells. Within 8 hr of injection into a thymus lobe, fetal liver TSC commit to T-cell development, losing stem-cell activity. When fetal liver cells are maintained in culture for 7 days, with no exogenous cytokines added, and then injected intra-thymically (I.T.), thymus recolonization is not observed. However, TSC can be maintained in culture for 7 days with IL-1β, IL-3, IL-6, or LIF added, alone or in combination, with steel factor (SLF). Poisson analysis of fetal liver cells cultured with SLF and IL-3 together revealed a precursor frequency of 1 in 1.8x 105 cells. In contrast, the frequency of TSC in adult bone marrow was estimated by limit dilution as 1 in 12,000 cells

Do walking strategies to increase physical activity reduce reported sitting in workplaces: a randomized control trial

Background Interventions designed to increase workplace physical activity may not automatically reduce high volumes of sitting, a behaviour independently linked to chronic diseases such as obesity and type II diabetes. This study compared the impact two different walking strategies had on step counts and reported sitting times. Methods Participants were white-collar university employees (n = 179; age 41.3 ± 10.1 years; 141 women), who volunteered and undertook a standardised ten-week intervention at three sites. Pre-intervention step counts (Yamax SW-200) and self-reported sitting times were measured over five consecutive workdays. Using pre-intervention step counts, employees at each site were randomly allocated to a control group (n = 60; maintain normal behaviour), a route-based walking group (n = 60; at least 10 minutes sustained walking each workday) or an incidental walking group (n = 59; walking in workday tasks). Workday step counts and reported sitting times were re-assessed at the beginning, mid- and endpoint of intervention and group mean± SD steps/day and reported sitting times for pre-intervention and intervention measurement points compared using a mixed factorial ANOVA; paired sample-t-tests were used for follow-up, simple effect analyses. Results A significant interactive effect (F = 3.5; p < 0.003) was found between group and step counts. Daily steps for controls decreased over the intervention period (-391 steps/day) and increased for route (968 steps/day; t = 3.9, p < 0.000) and incidental (699 steps/day; t = 2.5, p < 0.014) groups. There were no significant changes for reported sitting times, but average values did decrease relative to the control (routes group = 7 minutes/day; incidental group = 15 minutes/day). Reductions were most evident for the incidental group in the first week of intervention, where reported sitting decreased by an average of 21 minutes/day (t = 1.9; p < 0.057). Conclusion Compared to controls, both route and incidental walking increased physical activity in white-collar employees. Our data suggests that workplace walking, particularly through incidental movement, also has the potential to decrease employee sitting times, but there is a need for on-going research using concurrent and objective measures of sitting, standing and walking

Core-collapse Supernovae from the Palomar Transient Factory: Indications for a Different Population in Dwarf Galaxies

We use the first compilation of 72 core-collapse supernovae (SNe) from the Palomar Transient Factory (PTF) to study their observed subtype distribution in dwarf galaxies compared to giant galaxies. Our sample is the largest single-survey, untargeted, spectroscopically classified, homogeneous collection of core-collapse events ever assembled, spanning a wide host-galaxy luminosity range (down to M_r ≈ –14 mag) and including a substantial fraction (>20%) of dwarf (M_r ≥ –18 mag) hosts. We find more core-collapse SNe in dwarf galaxies than expected and several interesting trends emerge. We use detailed subclassifications of stripped-envelope core-collapse SNe and find that all Type I core-collapse events occurring in dwarf galaxies are either SNe Ib or broad-lined SNe Ic (SNe Ic-BL), while "normal" SNe Ic dominate in giant galaxies. We also see a significant excess of SNe IIb in dwarf hosts. We hypothesize that in lower metallicity hosts, metallicity-driven mass loss is reduced, allowing massive stars that would have appeared as "normal" SNe Ic in metal-rich galaxies to retain some He and H, exploding as Ib/IIb events. At the same time, another mechanism allows some stars to undergo extensive stripping and explode as SNe Ic-BL (and presumably also as long-duration gamma-ray bursts). Our results are still limited by small-number statistics, and our measurements of the observed N(Ib/c)/N(II) number ratio in dwarf and giant hosts (0.25^(+0.3)_(–0.15) and 0.23^(+0.11)_(–0.08), respectively; 1σ uncertainties) are consistent with previous studies and theoretical predictions. As additional PTF data accumulate, more robust statistical analyses will be possible, allowing the evolution of massive stars to be probed via the dwarf-galaxy SN population

Preschool and School Meal Policies: An Overview of What We Know about Regulation, Implementation, and Impact on Diet in the UK, Sweden, and Australia

School meals make significant contributions to healthy dietary behaviour, at a time when eating habits and food preferences are being formed. We provide an overview of the approaches to the provision, regulation, and improvement of preschool and primary school meals in the UK, Sweden, and Australia, three countries which vary in their degree of centralisation and regulation of school meals. Sweden has a centralised approach; all children receive free meals, and a pedagogical approach to meals is encouraged. Legislation demands that meals are nutritious. The UK system is varied and decentralised. Meals in most primary schools are regulated by food-based standards, but preschool-specific meal standards only exist in Scotland. The UK uses food groups (starchy foods, fruit and vegetables, proteins and dairy) in a healthy plate approach. Australian States and Territories all employ guidelines for school canteen food, predominantly using a “traffic light” approach outlining recommended and discouraged foods; however, most children bring food from home and are not covered by this guidance. The preschool standards state that food provided should be nutritious. We find that action is often lacking in the preschool years, and suggest that consistent policies, strong incentives for compliance, systematic monitoring, and an acknowledgement of the broader school eating environment (including home provided food) would be beneficial