CMOS/Bipolar current conveyor design and development

The aim of this research programme was to design and develop a novel CMOS current conveyor, to improve areas such as bandwidth, slew rate, gain, and Powe- Supply Reject Ratio (PSRR). The current conveyor can be used in low frequency applications such as LED drivers for mobile phones and televisions, and high frequency applications such as mixers for up/down converters used in anything from radios to mobile phones. The initial part of the research looked into improving the Power Supply Rejection Ration (PSRR) of the current follower (mirror) by increasing its output impedance. Several types of current mirror were compared using analytical and simulation methods, using a new generic low frequency transistor model which was used to highlight the differences in impedance between BJT and CMOS current mirrors. It was found that the best type of mirror was the regulated cascode current mirror which offered the largest value of output impedance when built from CMOS transistors. Work then moved onto the voltage follower. By initially using a typical CMOS source follower, it was found that the voltage gain suffered from low values transconductance, drain/source resistance, and a larger than expected value of source resistance, which was extracted from simulation and was found to be around 300- 350Q. The best design was a two stage un-buffered amplifier which offered the best Power Supply Rejection (PSRR) voltage gain and bandwidth. Several different types of current conveyor (CCII+) were simulated and the results were compared. It was found that the best types of current conveyor were the cascode type conveyors which offered a voltage gain error of less than 1%. The regulated cascode type current conveyor offered the highest figure of PSRR that of around 60dB. Finally the new cascode type current conveyors were used to build examples of current feedback operational amplifiers (CFOAs), and the cascode type CCIl+ offered a voltage gain error of less than I%, largest bandwidth and best P SRR

A metabolic model of the mitochondrion and its use in modelling diseases of the tricarboxylic acid cycle.

BACKGROUND: Mitochondria are a vital component of eukaryotic cells and their dysfunction is implicated in a large number of metabolic, degenerative and age-related human diseases. The mechanism or these disorders can be difficult to elucidate due to the inherent complexity of mitochondrial metabolism. To understand how mitochondrial metabolic dysfunction contributes to these diseases, a metabolic model of a human heart mitochondrion was created. RESULTS: A new model of mitochondrial metabolism was built on the principle of metabolite availability using MitoMiner, a mitochondrial proteomics database, to evaluate the subcellular localisation of reactions that have evidence for mitochondrial localisation. Extensive curation and manual refinement was used to create a model called iAS253, containing 253 reactions, 245 metabolites and 89 transport steps across the inner mitochondrial membrane. To demonstrate the predictive abilities of the model, flux balance analysis was used to calculate metabolite fluxes under normal conditions and to simulate three metabolic disorders that affect the TCA cycle: fumarase deficiency, succinate dehydrogenase deficiency and α-ketoglutarate dehydrogenase deficiency. CONCLUSION: The results of simulations using the new model corresponded closely with phenotypic data under normal conditions and provided insight into the complicated and unintuitive phenotypes of the three disorders, including the effect of interventions that may be of therapeutic benefit, such as low glucose diets or amino acid supplements. The model offers the ability to investigate other mitochondrial disorders and can provide the framework for the integration of experimental data in future studies.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Heat and mass transfer for a small diameter thermosyphon with low fill ratio

Abstract Thermosyphons of smaller dimensions are more commonly sought after as electronics cooling devices. The interactions of the tube wall and working fluid become more significant as the dimension of a thermosyphon is reduced, particularly for high surface tension fluids such as water. This paper aims to experimentally investigate a water-charged, small diameter (8 mm) thermosyphon as it operates with a low (25%) filling ratio for a relatively long evaporator length of 200 mm. High speed videography provides in-situ flow pattern visualization at different heat input power. The boiling regimes for each level of heat flux are determined by analyzing the flow patterns from the high-speed video footage. The interdependence of the flow regimes and the heat and mass transfer mechanisms is evaluated using the measured wall temperature variations and derived thermosyphon performance metrics, such as the average heat transfer coefficients and thermal resistances. It was observed that the heat and mass transport was dominated by Geyser-type boiling at lower heat fluxes with associated low heat transfer coefficients in the evaporator and condenser. With increasing thermal power, less liquid was observed to return to the evaporator resulting in more aggressive boiling events which improved the heat transfer coefficients in both the evaporator and condenser. For all power levels tested, the dominant thermal resistance was found to be that associated with the condenser. The ultimate failure of the thermosyphon was a result of liquid hold-up in the condenser section and subsequent falling liquid film and evaporator dryout

The Cambridge Face Tracker: Accurate, Low Cost Measurement of Head Posture Using Computer Vision and Face Recognition Software.

PURPOSE: We validate a video-based method of head posture measurement. METHODS: The Cambridge Face Tracker uses neural networks (constrained local neural fields) to recognize facial features in video. The relative position of these facial features is used to calculate head posture. First, we assess the accuracy of this approach against videos in three research databases where each frame is tagged with a precisely measured head posture. Second, we compare our method to a commercially available mechanical device, the Cervical Range of Motion device: four subjects each adopted 43 distinct head postures that were measured using both methods. RESULTS: The Cambridge Face Tracker achieved confident facial recognition in 92% of the approximately 38,000 frames of video from the three databases. The respective mean error in absolute head posture was 3.34°, 3.86°, and 2.81°, with a median error of 1.97°, 2.16°, and 1.96°. The accuracy decreased with more extreme head posture. Comparing The Cambridge Face Tracker to the Cervical Range of Motion Device gave correlation coefficients of 0.99 (P < 0.0001), 0.96 (P < 0.0001), and 0.99 (P < 0.0001) for yaw, pitch, and roll, respectively. CONCLUSIONS: The Cambridge Face Tracker performs well under real-world conditions and within the range of normally-encountered head posture. It allows useful quantification of head posture in real time or from precaptured video. Its performance is similar to that of a clinically validated mechanical device. It has significant advantages over other approaches in that subjects do not need to wear any apparatus, and it requires only low cost, easy-to-setup consumer electronics. TRANSLATIONAL RELEVANCE: Noncontact assessment of head posture allows more complete clinical assessment of patients, and could benefit surgical planning in future

Characterization of Ceramic Matrix Composite Vane Subelements Subjected to Rig Testing in a Gas Turbine Environment

Vane subelements were fabricated from a silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite. A cross-sectional slice of an aircraft engine metal vane was the basis of the vane subelement geometry. To fabricate the small radius of the vane's trailing edge using stiff Sylramic SiC fibers, a unique SiC fiber architecture was developed. A test configuration for the vanes in a high pressure gas turbine environment was designed and fabricated. Testing was conducted using a pressure of 6 atm and combustion flow rate of 0.5 kg/sec, and consisted of fifty hours of steady state operation followed by 102 2-minute thermal cycles. A surface temperature of 1320 C was obtained for the EBC-coated SiC/SiC vane subelement. This paper will briefly discuss the vane fabrication, test configuration, and results of the vane testing. The emphasis of the paper is on characterization of the post-test condition of the vanes

Distributed usability evaluation of the Pennsylvania Cancer Atlas

<p>Abstract</p> <p>Background</p> <p>The Pennsylvania Cancer Atlas (PA-CA) is an interactive online atlas to help policy-makers, program managers, and epidemiologists with tasks related to cancer prevention and control. The PA-CA includes maps, graphs, tables, that are dynamically linked to support data exploration and decision-making with spatio-temporal cancer data. Our Atlas development process follows a user-centered design approach. To assess the usability of the initial versions of the PA-CA, we developed and applied a novel strategy for soliciting user feedback through multiple distributed focus groups and surveys. Our process of acquiring user feedback leverages an online web application (e-Delphi). In this paper we describe the PA-CA, detail how we have adapted e-Delphi web application to support usability and utility evaluation of the PA-CA, and present the results of our evaluation.</p> <p>Results</p> <p>We report results from four sets of users. Each group provided structured individual and group assessments of the PA-CA as well as input on the kinds of users and applications for which it is best suited. Overall reactions to the PA-CA are quite positive. Participants did, however, provide a range of useful suggestions. Key suggestions focused on improving interaction functions, enhancing methods of temporal analysis, addressing data issues, and providing additional data displays and help functions. These suggestions were incorporated in each design and implementation iteration for the PA-CA and used to inform a set of web-atlas design principles.</p> <p>Conclusion</p> <p>For the Atlas, we find that a design that utilizes linked map, graph, and table views is understandable to and perceived to be useful by the target audience of cancer prevention and control professionals. However, it is clear that considerable variation in experience using maps and graphics exists and for those with less experience, integrated tutorials and help features are needed. In relation to our usability assessment strategy, we find that our distributed, web-based method for soliciting user input is generally effective. Advantages include the ability to gather information from users distributed in time and space and the relative anonymity of the participants while disadvantages include less control over when and how often participants provide input and challenges for obtaining rich input.</p