Measurement of Electrophysiological Signals In Vitro Using High-Performance Organic Electrochemical Transistors

Biological environments use ions in charge transport for information transmission. The properties of mixed electronic and ionic conductivity in organic materials make them ideal candidates to transduce physiological information into electronically processable signals. A device proven to be highly successful in measuring such information is the organic electrochemical transistor (OECT). Previous electrophysiological measurements performed using OECTs show superior signal-to-noise ratios than electrodes at low frequencies. Subsequent development has significantly improved critical performance parameters such as transconductance and response time. Here, interdigitated-electrode OECTs are fabricated on flexible substrates, with one such state-of-the-art device achieving a peak transconductance of 139 mS with a 138 µs response time. The devices are implemented into an array with interconnects suitable for micro-electrocorticographic application and eight architecture variations are compared. The two best-performing arrays are subject to the full electrophysiological spectrum using prerecorded signals. With frequency filtering, kHz-scale frequencies with 10 µV-scale voltages are resolved. This is supported by a novel quantification of the noise, which compares the gate voltage input and drain current output. These results demonstrate that high-performance OECTs can resolve the full electrophysiological spectrum and suggest that superior signal-to-noise ratios could be achieved in high frequency measurements of multiunit activity.     

Optimisation of design and operation of generators for offshore vertical axis wind turbines

A process for optimizing both the design and operation of the generator for a large offshore vertical axis wind turbine (VAWT) is developed. The objectives of the optimization process are to minimize additional costs and losses in the generator to allow for a fair evaluation of the impact of the VAWT environment on the powertrain. A spectrum of torque control strategies was tested based on the ratio, q, of the allowed electrical torque variation to the inherent mechanical torque variation. Equations relating q to the generator losses were established. The effect of q on the energy extracted by the rotor was also investigated and incorporated into the optimization process. This work shows that a variable q strategy with respect to wind speed can improve turbine performance across the range of operational wind speeds depending on the torque loading from the rotor blades. In turn, this also allows for the torque rating of the generator to be reduced from the peak torque rating that would otherwise be expected, creating an opportunity to downscale the generator size, reducing costs. The optimization of powertrain design and operation should be carried out at as high level as is possible, ideally using the fully factored cost of energy (COE) to guard against unexpected losses because of excessive focus in one COE factor (for example reducing upfront cost but in turn reducing availability).     

A lightweight low‐speed permanent magnet electrical generator for direct‐drive wind turbines

The evolution, design and test results of a novel permanent magnet generator for use in direct‐drive wind turbines are presented. This generator topology is based on steel C‐core modules (which make up the rotor) and an air‐cored stator winding. This topology allows a reduction in structural mass for large diameter generators, which can lead to lightweight generators. Copyright © 2009 John Wiley & Sons, Ltd.     

A route set construction algorithm for the transit network design problem

The transit network design problem (TNDP) aims to determine a set of bus routes for a public transportation system, which must be convenient from the viewpoints of both users (people who use public transportation) and operators (companies who own the resources to give the service). This article presents a constructive algorithm for the TNDP. It is specially designed to produce a set of routes that fulfils demand covering constraints, while taking into account the interests of both users and operators. Its general structure is inspired in the Route Generation Algorithm (RGA) of Baaj and Mahmassani, where its original expansion of routes by inserting individual vertices is replaced by a strategy of insertion of pairs of vertices. The algorithm proposed, called Pair Insertion Algorithm (PIA) can be used to generate initial solutions for a local improvement or evolutionary algorithm, as well as to complete an unfeasible solution with respect to demand covering constraints. Numerical results comparing PIA with RGA over a real test case show that both algorithms produce solutions with similar quality from the users viewpoint (in terms of in-vehicle travel time), while the former produces better solutions from the operators viewpoint (in terms of number of routes and total route duration) and requires a higher execution time. Since the TNDP arises in a context of strategic planning, a solution that reduces the operation cost of the system is highly desirable, even though it takes more time to be computed. The experimental study of the proposed algorithm also shows its ability to produce diverse solutions in both decision and objective spaces; this is a useful property when looking at the use of PIA as a subroutine in the context of another algorithm such as metaheuristics, in particular for a multi-objective problem like TNDP.     

The application of regression analysis to problems of landscape evaluation

During the unprecedented period of building activity in the Middle East, architects have become very aware of the way in which the ongoing Islamic tradition and 20th century technology can be reconciled satisfactorily. A substantial volume of building in the earlier days of the construction boom resulted in entirely inappropriate building forms which flagrantly ignored climate, culture and custom. However, in more recent years a more careful synthesis has been evolved which draws on the best of both cultures to provide the basis for an entirely authentic way of architectural expression.     

Simple learning rules to cope with changing environments

We consider an agent that must choose repeatedly among several actions. Each action has a certain probability of giving the agent an energy reward, and costs may be associated with switching between actions. The agent does not know which action has the highest reward probability, and the probabilities change randomly over time. We study two learning rules that have been widely used to model decision-making processes in animals—one deterministic and the other stochastic. In particular, we examine the influence of the rules'' ‘learning rate’ on the agent''s energy gain. We compare the performance of each rule with the best performance attainable when the agent has either full knowledge or no knowledge of the environment. Over relatively short periods of time, both rules are successful in enabling agents to exploit their environment. Moreover, under a range of effective learning rates, both rules are equivalent, and can be expressed by a third rule that requires the agent to select the action for which the current run of unsuccessful trials is shortest. However, the performance of both rules is relatively poor over longer periods of time, and under most circumstances no better than the performance an agent could achieve without knowledge of the environment. We propose a simple extension to the original rules that enables agents to learn about and effectively exploit a changing environment for an unlimited period of time.     

Wind energy for the 1990s and beyond

Electrical power must be available to the consumer in any amount upon demand. Conventional methods of power generation, such as the burning of fossil fuels, hydroelectric plants, and nuclear power plants, have considerable shortcomings. Governmental regulations have increased in quantity and have raised the already rigid standards of producing electric power without further damage to the environment. Electrical power produced by wind energy conversion systems are undergoing extensive research and revitalization as a viable solution to clean air power generation. The basic challenge to scientists and engineers is to develop wind energy conversion systems that produce adequate amounts of power, but at a cost comparable to present conventional methods. This article discusses the background and impact of the modern wind energy conversion system on future power generation.     

Cost-effectiveness of a targeted disinfection program in household kitchens to prevent foodborne illnesses in the United States, Canada, and the United Kingdom

Foodborne illnesses impose a substantial economic and quality-of-life burden on society by way of acute morbidity and chronic sequelae. We developed an economic model to evaluate the potential cost-effectiveness of a disinfection program that targets high-risk food preparation activities in household kitchens. For the United States, Canada, and the United Kingdom, we used published literature and expert opinion to estimate the cost of the program (excluding the educational component); the number of cases of Salmonella, Campylobacter, and Escherichia coli O157:H7 infections prevented; and the economic and quality-of-life outcomes. In our primary analysis, the model estimated that approximately 80,000 infections could be prevented annually in U.S. households, resulting in 138 million dollars in direct medical cost savings (e.g., physician office visits and hospitalizations avoided), 15,845 quality-adjusted life-years (QALYs) gained, 788 million dollars in program costs, and a favorable cost-effectiveness ratio of 41,021 dollars/QALY gained. Results were similar for households in Canada and the United Kingdom (21,950 dollars Can/QALY gained and 86,341 pounds sterling/QALY gained, respectively). When we evaluated implementing the program only in U.S. households with high-risk members (those less than 5 years of age, greater than 65 years of age, or immunocompromised), the cost-effectiveness ratio was more favorable (10,163 dollars/QALY gained). Results were similar for high-risk households in Canada and the United Kingdom (1,915 dollars Can/QALY gained and 28,158 pounds sterling/QALY gained, respectively). Implementing a targeted disinfection program in household kitchens in the United States, Canada, and the United Kingdom appears to be a cost-effective strategy, falling within the range generally considered to warrant adoption and diffusion (<100,000 dollars/QALY gained).