Microchannel bioreactors for bioartificial liver support

An extracorporeal bioartificial liver (BAL) device containing viable hepatocytes has the potential to provide temporary hepatic support to liver failure patients, serving as a bridge to transplantation while awaiting a suitable donor. In some patients, providing temporary hepatic support may be sufficient to allow adequate regeneration of the host liver, thereby eliminating the need for a liver transplant. Although the BAL device is a promising technology for the treatment of liver failure, there are several technical challenges that must be overcome in order to develop systems with sufficient processing capacity and of manageable size. In this study, the authors describe the critical issues involved in developing a BAL device. They also discuss their experiences in hepatocyte culture optimization within the context of a microchannel flat-plate BAL device.     

Caching video objects: layers vs versions?

Because Internet access rates are highly heterogeneous, many video content providers today make available different versions of the videos, with each version encoded at a different rate. Multiple video versions, however, require more server storage and may also dramatically impact cache performance in a traditional cache or in a CDN server. An alternative to versions is layered encoding, which can also provide multiple quality levels. Layered encoding requires less server storage capacity and may be more suitable for caching; but it typically increases transmission bandwidth due to encoding overhead. In this paper we compare video streaming of multiple versions with that of multiple layers in a caching environment. We examine caching and distribution strategies that use both versions and layers. We consider two cases: the request distribution for the videos is known a priori; and adaptive caching, for which the request distribution is unknown. Our analytical and simulation results indicate that mixed distribution/caching strategies provide the best overall performance.A shorter version of this work has appeared in Proc. of IEEE International Conference on Multimedia and Expo (ICME), Vol. 2, pages 45–48, Lausanne, Switzerland, August 2002     

Update strategies for kriging models used in variable fidelity optimization

Many optimization methods for simulation-based design rely on the sequential use of metamodels to reduce the associated computational burden. In particular, kriging models are frequently used in variable fidelity optimization. Nevertheless, such methods may become computationally inefficient when solving problems with large numbers of design variables and/or sampled data points due to the expensive process of optimizing the kriging model parameters in each iteration. One solution to this problem would be to replace the kriging models with traditional Taylor series response surface models. Kriging models, however, were shown to provide good approximations of computer simulations that incorporate larger amounts of data, resulting in better global accuracy. In this paper, a metamodel update management scheme (MUMS) is proposed to reduce the cost of using kriging models sequentially by updating the kriging model parameters only when they produce a poor approximation. The scheme uses the trust region ratio (TR-MUMS), which is a ratio that compares the approximation to the true model. Two demonstration problems are used to evaluate the proposed method: an internal combustion engine sizing problem and a control-augmented structural design problem. The results indicate that the TR-MUMS approach is very effective; on the demonstration problems, it reduced the number of likelihood evaluations by three orders of magnitude compared to using a global optimizer to find the kriging parameters in every iteration. It was also found that in trust region-based method, the kriging model parameters need not be updated using a global optimizer—local methods perform just as well in terms of providing a good approximation without affecting the overall convergence rate, which, in turn, results in a faster execution time.     

Managing database server performance to meet QoS requirements in electronic commerce systems

The performance of electronic commerce systems has a major impact on their acceptability to users. Different users also demand different levels of performance from the system, that is, they will have different Quality of Service (QoS) requirements. Electronic commerce systems are the integration of several different types of servers and each server must contribute to meeting the QoS demands of the users. In this paper we focus on the role, and the performance, of a database server within an electronic commerce system. We examine the characteristics of the workload placed on a database server by an electronic commerce system and suggest a range of QoS requirements for the database server based on this analysis of the workload. We argue that a database server must be able to dynamically reallocate its resources in order to meet the QoS requirements of different transactions as the workload changes. We describe Quartermaster, which is a system to support dynamic goal-oriented resource management in database management systems, and discuss how it can be used to help meet the QoS requirements of the electronic commerce database server. We provide an example of the use of Quartermaster that illustrates how the dynamic reallocation of memory resources can be used to meet the QoS requirements of a set of transactions similar to transactions found in an electronic commerce workload. We briefly describe the memory reallocation algorithms used by Quartermaster and present experiments to show the impact of the reallocations on the performance of the transactions. Published online: 22 August 2001     

Injury trends of passenger car drivers in frontal crashes in the USA

Injuries trends of passenger car drivers in head-on collisions are identified based on crash data extracted from the National Automotive Sampling System. Annual injury incidence levels are estimated for years 1990-2007. Over that period, the number of crashes is predicted to rise by 71%. However, the number of serious injuries to drivers is expected to rise by only 41% and driver fatalities are anticipated to decrease by 9%. Meantime, the types of injuries suffered by drivers are changing. Year-to-year shifts in injury patterns result from changes in vehicle size classes within the US vehicle fleet population and increases in seat belt use and air bag availability. The effectiveness of air bags in saving lives is estimated to be 30%, and with more air bag-equipped cars on the road, the probability of sustaining a life-threatening head or a torso injury is reduced. Air bags, however, are not as effective in preventing upper and lower extremity injuries, and thus arm and leg injuries will become more prevalent in years to come.     

Report of the U.S. Department of Energy Fusion Energy Sciences Advisory Committee (FESAC) Panel Reviewing the Theory and Computing Program

This Panel was set up by the Fusion Energy Sciences Advisory Committee (FESAC) at its November 2000 meeting for the purpose of addressing questions from the Department of Energy concerning the theory and computing/simulation program of the Office of Fusion Energy Sciences. Although the Panel primarily addressed programmatic questions, it acknowledges that the theory and computing in fusion energy sciences has a stellar record of research successes. (A recent FESAC report entitled Opportunities in the Fusion Energy Sciences Program listed a number of theory and computing research highlights.) Last year the National Research Council performed an assessment of the quality of the fusion energy sciences program—including theory and computing—and concluded that the quality of its research is on a par with that of other leading areas of contemporary physical science.     

Effects of diet on rumen proliferation and fecal shedding of Escherichia coil O157:H7 in calves

Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed.     

Effect of a prepartum administration of monensin in a controlled-release capsule on apparent digestibilities and nitrogen utilization in transition dairy cows

The influence of a monensin controlled-release capsule, which was administered 3 wk before the calving date, on diet digestibility and nitrogen utilization was investigated in 16 multiparous dairy cows between approximately 10 and 3 d precalving and 3 and 9 d postcalving. Monensin decreased rumen ammonia from 5.4 to 3.2 mg dl(-1) precalving and from 6.0 to 4.9 mg dl(-1) postcalving. Blood urea concentrations were increased by monensin from 4.93 to 5.28 mM precalving and from 5.27 to 5.81 mM postcalving, but these increases were not statistically significant. Precalving, monensin increased the apparent digestibilities of neutral detergent fiber from 52.8 to 62.1%, of acid detergent fiber from 50.7 to 58.7%, and of gross energy from 60.5 to 66.7%. Postcalving, monensin increased the apparent nitrogen digestibility from 63.7 to 71.5%, which resulted in an improvement in the nitrogen balance from -77.8 to -44.9 g d(-1). The monensin controlled-release capsule contributed to increasing the availability of dietary nitrogen to the transition dairy cow during the critical postcalving period.