Frequency dependence of MR relaxation times. I. Paramagnetic ions

T1 and T2 of paramagnetic ions in free and chelated form were measured over the range of clinical magnetic resonance imaging field strengths (0.02-1.5 T). T1 values agreed with published data; however, to our knowledge, the field dependence of T2 has not been systematically studied before Mn2+, Cr3+, and Fe3+ all showed T2 reduction at high field strengths, although reduction due to Fe3+ was minimal. This is believed to be due to "contact" interactions, which have been previously noted for manganese. No such T2 reduction was seen in the chelates, except that dysprosium chelate (but not free ion) showed an anomalous decrease in T2 at high field strengths, which may possibly be explained by a dephasing effect caused by the large magnetic moment of Dy3+.     

A student-enacted simulation approach to software engineering education

In some cases, real-world application of software engineering concepts does not effectively map with current undergraduate curriculums. Typically, a student's first "hands-on" experience working on large-scale software development projects is via an intern position or his/her first full-time position. However, prior exposure to the corporate project environment would greatly improve a student's performance in industry. In order to develop students for successful careers in software engineering, specifically for software development, they must be immersed not only in the software development lifecycle and paradigms, but also in the workings of large project teams. Currently, most undergraduate software engineering courses are taught by presenting the concepts and methodologies and assigning fragmented three-to-four person group projects. In the Department of Computer Science, Georgetown University, Washington, DC, a two-course approach to undergraduate software engineering education has been developed that incorporates the practical application of coursework in a large team setting. The first course presents a firm software design basis, while the second course demonstrates corporate-level software engineering concepts with a semester-long software development simulation where the entire class is the development team. This paper presents the experiences from offering this software engineering simulation approach.     

A simulation based supply partner selection decision support tool for service provision in Dell

Partner selection is an important aspect of all outsourcing processes. Traditional partner selection typically involves steps to determine the criteria for outsourcing, followed by a qualification of potential suppliers and concluding with a final selection of partner(s). Reverse auctions (RAs) have widely been used for partner selection in recent times. However, RAs, although proven successful in initial price reduction strategies for product and service provision, can suffer from reduced effectiveness as the number of executions increases.This paper illustrates Dell’s experience of such diminishing returns for its outsourced after sales product repair service and presents the development of a new partner selection methodology, which incorporates a new process improvement stage to be executed in combination with the final selection phase. This new methodology is underpinned by the development of a computer based simulation supply partner selection decision support tool for service provision. The paper highlights the significant additional cost saving benefits and improvement in service achievable through the use of advanced simulation based decision supports.     

Implications of failure criteria choices on the rapid concept design of composite grillage structures using multiobjective optimisation

Grillage topologies are commonly used in many composite structural applications to produce low mass designs that have a high stiffness. While composite failure criteria are being compared in many different simple structures, for example plates and tubes, literature must also compare more complicated applications, including grillages, as there are distinct differences in behaviour. This paper therefore performs analysis of grillage structures with more up to date failure criteria, taken from the world wide failure exercise, than previously investigated. The grillage theory selected is that of Navier theory with elastic equivalent properties due to its low computational expense for use with a genetic algorithm to optimise a composite structure. The results take an example from leisure boatbuilding showing the grillages produced from the different limit states, comparing the cost and mass. The final results show that the method allows a rapid analysis of grillages and that the selection of the limit state has an important effect on the optimised grillage topology.     

Atomic Afterimages

This article examines the recirculation of Robert Del Tredici's photographs of the Cold War nuclear weapons complex. Originally published in his groundbreaking book, At Work in the Fields of the Bomb (1987), a number of Del Tredici's photographs have been republished in a series of post‐Cold War US Department of Energy reports. The article examines the post‐Cold War circulation of Del Tredici's images in these official government reports and analyzes shifts in their meaning across different historical periods. Ultimately, this paper raises questions about the critical stance of Del Tredici's photographs as they are republished in government reports and examines ways in which the meaning of his photographs responds to both Cold War and post‐Cold War contexts.     

Global data and control in multicomputers: Operating system primitives and experimentation with a parallel branch-and-bound algorithm

The static distribution of work among tasks is not possible in many parallel applications. Therefore, it is essential to implement convenient and efficient abstractions for ‘work sharing’ on multicomputers. This paper compares the utility of two operating system facilities for the implementation of such ‘work sharing’: (1) a system for the migration of processes from heavily to less loaded processors and (2) a more general OS construct for the implementation of arbitrary distributed objects. Both were implemented as extensions to the Intel iPSC/1 operating system on a 32-node hypercube. Their experimental evaluation is based on a parallel implementation of a branch-and-bound algorithm. Two sets of results are attained. First, the necessity of the constructs for dynamic work sharing is demonstrated for applications with dynamic data domains, such as parallel branch-and-bound algorithms. This is followed by measurements that demonstrate the acceptable cost of process migration for a specific parallel branch-and-bound algorithm. These measurements are then compared with results attained with the construct for the implementation of distributed objects. Second, when using branch-and-bound to solve the Travelling Salesperson Problem (TSP), evaluation of the resulting parallel TSP program shows that some analytical and simulation results attained in past, published work may not hold.     

The current and residual value of superphosphate,Christmas Island C-grade ore,and Calciphos as fertilizers for a subterranean clover pasture

The effectiveness in the year of application of three phosphorus fertilizers, superphosphate, Christmas Island C-grade ore, and 500°C calcined Christmas Island C-grade ore (Calciphos), was measured for 5 consecutive years in a field experiment on a lateritic soil. The residual value of the phosphorus fertilizers was also measured for 6 years. Dry matter production of subterranean clover-based pasture and bicarbonate extractable soil phosphorus were used as indicators of fertilizer effectiveness.Despite the use of very large amounts of C-grade ore and Calciphos, the plateau of the pasture yield versus fertilizer applied curve for these fertilizers did not reach the yield plateau achieved with superphosphate in either the short or long term.C-grade ore and Calciphos were 3% and 8% as effective as superphosphate for dry matter production in the year of application. Relative to superphosphate applied in the current year the effectiveness of superphosphate decreased by about 70% between the first and second year after application and decreased by a further 14% from year 3 to year 6. C-grade ore and Calciphos remained about 2% and 9% as effective as currently applied superphosphate each year.The residual value of superphosphate as measured by bicarbonate-extracted soil phosphorus decreased by about 60% from year 2 to year 7. The residual value of Calciphos was very low for year 2, doubled from year 2–4 and thereafter decreased gradually to its original value by year 7. The residual value of C-grade ore was extremely low throughout the experiment. Thus after year 2, compared to pasture yield, bicarbonate extracted soil phosphorus overestimated the residual value of superphosphate and calciphos.It follows that neither C-grade ore or Calciphos are suitable replacement fertilizers for superphosphate for use on pastures growing on lateritic soils in south-western Australia.     

Phosphorus content in soil, uptake by plants and balance in three European long-term field experiments

The fate of phosphorus (P) derived from mineral fertilisers and organic manures, and the effective P balance, have been assessed in three long-term field experiments at Rothamsted (UK), Bad Lauchstaedt (Germany) and Skierniewice (Poland). This paper discusses the plant availability, uptake and overall utilisation of P over the last 30 years, based on soil test P availability indices and crop analyses determined by the standard methods used in each of the three countries. The data suggest that differences in soil type significantly influence the dynamics of P at the three locations, but most significantly between a loess Chernozem at Bad Lauchstaedt with a high organic matter content and the soils at the other two locations which have a low organic matter content. The application of P either as inorganic fertiliser or organic manure had a considerable influence on the availablity, uptake, leaching or fixing of P, but the crop recovery rate of P from mineral fertiliser did not exceed 35% with the smallest recovery (average 18%) occurring in the soil with the highest clay content at Rothamsted. At Bad Lauchstaedt and Rothamsted the most efficient utilisation of P (averages of 47% and 37%, respectively) was from soils treated with farmyard manure (FYM), with the greater quantity of P either leached or fixed (8 and 25 kg ha^-1 y^-1, respectively) occurring in soils treated with superphosphate. At Skierniewice, however, the reverse was true. Overall, the most efficient crop utilisation from mineral P (30% average) was from the loamy sand at Skierniewice. P balances for the three locations show that quantitatively, for the same P input, the amount of P either leached from or fixed in the plough layer of Broadbalk field, Rothamsted, was 2–3 times greater than at Skierniewice and 3–6 times greater than at Bad Lauchstaedt. The results suggest that differences in the soil physico-chemical properties, climate, the availability of other major nutrients, and the form in which P is applied, all influence the effectiveness of P fertilisation and P balance. The investigation highlights the importance of maintaining long-term field experiments and archived soil and crop samples on a world-wide basis for understanding nutrient cycling and fertility dynamics.     

Transient behavior of run-around heat and moisture exchanger system. Part IІ: Sensitivity studies for a range of initial conditions

Part І of this paper [17] developed and verified the numerical model for simultaneous heat and moisture transfer in the run-around membrane energy exchanger (RAMEE) system to determine the transient behavior of the system under different initial and operating conditions.This paper presents the transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio. Also the system quasi-steady state operating conditions are predicted as the system approaches its asymptotic operating condition. The transient responses are predicted with changes in various parameters. These include: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the storage volume ratio and the initial salt solution concentration have significant impacts on the transient response of the system and heat transfer between the RAMEE system and the surrounding environment can change the system quasi-steady conditions substantially.     

High-Performance Switched Reluctance Brushless Drives

Switched reluctance (SR) drives offer the advantages of simple and robust motor construction, high speeds, high overall efficiencies over a wide operating range of torque and speed, simple power converter circuits with a reduced number of switches, and excellent controllability. The basis of these claims is explained. The history of the SR system, in particular the extensive research at Nottingham and Leeds Universities, and the basic operating principles and design considerations for motors and power converters are reviewed. Alternative configurations are discussed. The difficulties of establishing a simple mathematical model for the motor and of calculating torque and inverter VA requirements are examined. A comparison of the VA requirements for SR and pulsewidth modulation (PWM) is given for a 7.85-kW system. Measured drive performance is discussed in terms of efficiency over an operating envelope, specific output, controllability, and power converter ratings. Earlier traction drives, incorporating a constant power range and including regeneration, are reported together with the constant torque industrial drives and more recent traction extensions. The long-term potential of the drive is discussed for a wide range of applications. A comprehensive list of references is provided.