9,888 research outputs found
LC compensators for power factor correction of nonlinear loads
No full textThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2004 IEEEA method is presented for finding the optimum fixed LC compensator for power factor correction of nonlinear loads where both source voltage and load current harmonics are present. The LC combination is selected because pure capacitive capacitors alone would not sufficiently correct the power factor. Optimization minimizes the transmission loss, maximizes the power factor, and maximizes the efficiency. The performance of the obtained compensator is discussed by means of numerical examples
Immobilization of Polymer-Decorated Liquid Crystal Droplets on Chemically Tailored Surfaces
No full textWe demonstrate that the assembly of an amphiphilic polyamine on the interfaces of micrometer-sized droplets of a thermotropic liquid crystal (LC) dispersed in aqueous solutions can be used to facilitate the immobilization of LC droplets on chemically functionalized surfaces. Polymer 1 was designed to contain both hydrophobic (alkylfunctionalized) and hydrophilic (primary and tertiary amine-functionalized) side chain functionality. The assembly of this polymer at the interfaces of aqueous dispersions of LC droplets was achieved by the spontaneous adsorption of polymer from aqueous solution. Polymer adsorption triggered transitions in the orientational ordering of the LCs, as observed by polarized light and bright-field microscopy. We demonstrate that the presence of polymer 1 on the interfaces of these droplets can be exploited to immobilize LC droplets on planar solid surfaces through covalent bond formation (e.g., for surfaces coated with polymer multilayers containing reactive azlactone functionality) or through electrostatic interactions (e.g., for surfaces coated with multilayers containing hydrolyzed azlactone functionality). The characterization of immobilized LC droplets by polarized, fluorescence, and laser scanning confocal microscopy revealed the general spherical shape of the polymer-coated LC droplets to be maintained after immobilization, and that immobilization led to additional ordering transitions within the droplets that were dependent on the nature of the surfaces with which they were in contact. Polymer 1-functionalized LC droplets were not immobilized on polymer multilayers treated with poly(ethylene imine) (PEI). We demonstrate that the ability to design surfaces that promote or prevent the immobilization of polymer-functionalized LC droplets can be exploited to pattern the immobilization of LC droplets on surfaces. The results of this investigation provide the basis of an approach that could be used to tailor the properties of dispersed LC emulsions and to immobilize these droplets on functional surfaces of interest in a broad range of fundamental and applied contexts
LC compensators based on transmission loss minimization for nonlinear loads
No full textThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2004 IEEEThis paper presents a method employing the penalty function search algorithm to determine the LC compensator value for the optimal power factor correction in nonsinusoidal systems. The objective of the proposed method is to minimize the transmission loss while the power factor and efficiency are taken as constraints and utilized in order to solve the multiobjective optimization problem by transforming it into a single objective one. Examples show that the load nonlinearity can have a significant impact on optimal compensator sizes
Differential proteome profiling analysis of murine skeletal muscle following a single bout of exercise
No full textSkeletal muscle is a plastic tissue, capable of generating large forces to move the body while maintaining the highly organized structure required for its biomechanical efficiency. Skeletal muscle also has the capacity to adapt to the increased functional demands associated with exercise. Differential proteome profiling can be used to obtain a global view of proteins that change expression following a single bout of eccentrically biased exercise, as well as the gender-specific nature of this response. In this study, exercise-naïve male and female mice ran downhill (-15°) on a treadmill at 25 m/min for 15 min and 800 μg of total biceps brachii extract was electrophoresed on pH 5.0-8.0 2-D gels. The resulting spots that changed at least +/- two-fold, and were shown to be significantly different (p \u3c 0.05) relative to unexercised controls of the appropriate gender using PDQuest 8.0, were then analyzed by LC/MS/MS and identified using Bioworks Sequest 3.3.1. The expression change patterns were followed at 0, 24, 48, 72 and 168 hours post-exercise and evaluated relative to a pre-exercise control. Proteins changing expression in both male and female skeletal muscle postexercise are concentrated among metabolic, cytoskeletal, and stress proteins. These data indicate that exercise-naïve skeletal muscle is disrupted by the unfamiliar mechanical and energetic demands of exercise. Post-exercise protein expression patterns further suggest that structural components of the contractile apparatus and various metabolic pathways within the muscle adjust to meet these new demands. This skeletal muscle response to exercise occurs in two phases, a stochastic phase and a sustained response phase. The stochastic phase occurs immediately post-exercise. Although initial protein expression changes may seem random and disorganized, it is likely that metabolic pathways are working to establish a new homeostatic point. The stochastic phase is also often where exercise-naïve gender differences are resolved. After the initial shock of strenuous exercise has been overcome, the true exercise-induced response of different proteins is revealed during the sustained response phase. Protein expression in this phase either demonstrates similar trends in both males and females or is gender-specific. Trends observed in well-studied proteins agree satisfactorily with the literature, such as a decrease in intermediate filament protein abundance and an increase in the abundance of small stress proteins. This study verifies the dynamic nature of the mouse skeletal muscle proteome, and facilitates a deeper understanding of the underlying mechanisms of physiological adaptation and damage mitigation in muscle
LC-API/MS in Drug Metabolism and Pharmacokinetic Studies
No full textThe use of API interfaces with quadrupole mass spectrometers has been shown to give rise to good sensitivity, selectivity, and robustness for the interfacing of LC to MS. Since their introduction in the 1990s the technique has rapidly become widespread, but at the outset of this research programme, there were still a number of problems associated with it, particularly when dealing with complex sample matrices. The aim of this research programme was to study illustrative examples of the kinds of problems associated with the analysis of biological samples using LC-API-MS in an attempt to arrive at strategies which could be employed to eliminate, or at least compensate for, the problems.
Commonly reported problems include the occurrence of matrix effects - a change in response of the target analyte(s) as a result of the presence in the samples of co /late eluting interferences. An investigation which compared ESI with APCI ionisation illustrated a significant drawback in the accepted methodology for the elimination of matrix effects.
Optimal LC conditions for a number of assays may use non-MS-friendly mobile phases. A simple and convenient solution to this problem was found to be the post column addition of organic modifier, which reproducibly and reliably enhanced sensitivity. This approach was initially used for a range of dihydropyridine calcium channel blockers and was subsequently applied to a range of chiral compounds from different therapeutic groups to illustrate that this was applicable as a generic technique for increasing sensitivity (typically by around an order of magnitude) in low organic mobile phases.
Strategies to develop and validate methods for the determination of endogenous analytes in a biological fluid were investigated. This involved the use of a surrogate matrix, to develop a method for the determination of endogenous testosterone in human serum and the use of non-matrix calibration standards for the successful development and validation of a method for the analysis of indolyl 3 acryloylglycine (IAG) in human urine.
As a result of observations suggesting promotion of ionisation of deltamethrin in liver tissue sample extracts, it was postulated that this was due to the presence of high concentrations of surfactants. After confirming the effect, a series of systematic investigations were performed to attempt to understand the mechanism to be able to utilise this as a general method for the enhancement of signal with low sensitivity analytes. It was found that the type of surfactant and concentration used was directly associated with an increased (or decreased) response.
Although there remain a number of problems associated with the use of LC-API-MS, the work undertaken for this thesis has successfully demonstrated a number of techniques that can be applied to overcome these problems. Knowledge of the nature of the sample undergoing analysis, the required analytical conditions, and where required careful application of one of the techniques described will ensure that a robust method can be readily developed
Langmuir Films of Flexible Polymers Transferred to Aqueous/Liquid Crystal Interfaces Induce Uniform Azimuthal Alignment of the Liquid Crystal
No full textWe reported recently that amphiphilic polymers can be assembled at interfaces created between aqueous phases and thermotropic liquid crystals (LCs) in ways that: (i) couple the organization of the polymer to the order of the LC and (ii) respond to changes in the properties of aqueous phases that can be characterized as changes in the optical appearance of the LC. This investigation sought to characterize the behavior of aqueous-LC interfaces decorated with uniaxially compressed thin films of polymers transferred by Langmuir-Schaefer (LS) transfer. Here, we report physicochemical characterization of interfaces created between aqueous phases and the thermotropic LC 4-cyano-4′-pentylbiphenyl (5CB) decorated with Langmuir films of a novel amphiphilic polymer (polymer 1), synthesized by the addition of hydrophobic and hydrophilic side chains to poly(2-vinyl-4,4′-dimethylazlactone). Initial characterization of this system resulted in the unexpected observation of uniform azimuthal alignment of 5CB after LS transfer of the polymer films to aqueous-5CB interfaces. This paper describes characterization of Langmuir films of polymer 1 hosted at aqueous-5CB interfaces as well as the results of our investigations into the origins of the uniform ordering of the LC observed upon LS transfer. Our results, when combined, support the conclusion that uniform azimuthal alignment of 5CB is the result of long-range ordering of polymer chains in the Langmuir films (in a preferred direction orthogonal to the direction of compression) that is generated during uniaxial compression of the films prior to LS transfer. Although past studies of Langmuir films of polymers at aqueous-air interfaces have demonstrated that in-plane alignment of polymer backbones can be induced by uniaxial compression, these past reports have generally made use of polymers with rigid backbones. One important outcome of this current study is thus the observation of anisotropy and long-range order in Langmuir films of a novel flexible polymer. A second important outcome is the observation that the existence, extent, and dynamics of this order can be identified and characterized optically by transfer of the Langmuir film to a thin film of LC. Additional characterization of Langmuir films of two other flexible polymers [poly(methyl methacrylate) and poly(vinyl stearate)] using this method also resulted in uniform azimuthal alignment of 5CB, suggesting that the generation of long-range order in uniaxially compressed Langmuir films of polymers may also occur more generally over a broader range of polymers with flexible backbones
A strategy for continuing professional education in statistics
No full textIn a world that is producing ever increasing amounts of data, there is unrelenting
pressure to provide a quality service for design, collection, analysis, interpretation and
reporting for these data. There is a corresponding need for a recognised professional
qualification that attests to the ability of individual statisticians to provide this service.In 1993 the Royal Statistical Society (RSS) began awarding Chartered Statistician
(CStat) status to suitably qualified statisticians. By the end of 1995 over 1600 statisticians
world-wide had received this qualification. The RSS simultaneously recognised a
responsibility for maintaining professional standards after the awards had been made.
Consequently, in 1996, the Society began to explore a strategy for maintaining and
continuing the development of its professionally qualified statisticians.In this paper we report our views about this strategic exercise. We argue that
continuing education is essential for the maintenance of a professional statistician’s
portfolio of skills and expertise, and that this will help a quality service to be delivered.
We argue for a flexible system based on credits, with an element of compulsion that can
evolve as the profession develops
Sex differences in Cognitive Abilities Test scores: a UK national picture
No full textBackground and aims. There is uncertainty about the extent or even existence of sex differences in the mean and variability of reasoning test scores ( Jensen, 1998; Lynn, 1994, ; Mackintosh, 1996). This paper analyses the Cognitive Abilities Test (CAT) scores of a large and representative sample of UK pupils to determine the extent of any sex differences.
Sample. A nationally representative UK sample of over 320,000 school pupils aged 11-12 years was assessed on the CAT (third edition) between September 2001 and August 2003. The CAT includes separate nationally standardized tests for verbal, quantitative, and non-verbal reasoning. The size and recency of the sample is unprecedented in research on this issue.
Methods. The sheer size of the sample ensures that any sex difference will achieve statistical significance. Therefore, effect sizes (d) and variance ratios (VR) are employed to evaluate the magnitude of sex differences in mean scores and in score variability, respectively.
Results. The mean verbal reasoning score for girls was 2.2 standard score points higher than the mean for boys, but only 0.3 standard points in favour of girls for non-verbal reasoning (NVR), and 0.7 points in favour of boys for quantitative reasoning (QR). However, for all three tests there were substantial sex differences in the standard deviation of scores, with greater variance among boys. Boys were over represented relative to girls at both the top and the bottom extremes for all tests, with the exception of the top 10% in verbal reasoning.
Conclusions. Given the small differences in means, explanations for sex differences in wider domains such examination attainment at age 16 need to look beyond conceptions of `ability'. Boys tend to be both the lowest and the highest performers in terms of their reasoning abilities, which warns against the danger of stereotyping boys as low achievers
Optimizing collection purification and characterization of salivary dopamine and its metabolites as biomarkers for Parkinson\u27s disease
No full textGiven that submandibular glands are affected in the early stages of Parkinson’s disease (Ma, Gao, Li, Ma, & Feng, 2019) , identification and quantification of salivary dopamine and its metabolites, homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid, can be used as a potential diagnostic tool to monitor the initiation and progression of the disease. A sensitive assay method was developed for the determination of dopamine and metabolites through LC-ESI-MS. Although further optimization of the protocol is required for the quantification of these analytes in human salivary samples, the postulated method has laid the foundation for the collection, purification and identification of dopamine and its metabolites as potential biomarkers for Parkinson’s disease
The effect of human body temperature on the proteo-transcriptomic responses of commensal and pathogenic Escherichia coli
No full textWhen Escherichia coli (E. coli) infects a host, it is exposed to a severe temperature shift, going from ambient (23°C) to host temperature (37°C). In order to survive, both commensal and pathogenic E. coli have developed elaborate mechanisms to sense this environmental change and use it as an adaptation cue. While previous efforts in the laboratory focused on studying how a shift from ambient to host temperature affect the expression of the bacteria transcriptome, in the present study we have combined data from high throughput RNA sequencing with liquid-chromatography-coupled mass spectrometry (LC-MS) to uncover key pathways whose regulation changes on both the transcriptome and the proteome level in response to temperature. Commensal (MG1655), enteropathogenic (E2348/69) and uropathogenic (CFT073) strains were grown to a mid-exponential phase, whole cell extracts (n=5) were isolated and proteins were labeled using tandem mass tags (TMT). LC-MS was used to identify and quantify the proteins expressed by each strain, and those proteins which had a significant change in abundance between the two temperatures (as FC ≥ 2 and p-value \u3c 0.05) were grouped into by molecular function. For each strain, we identified over 2000 proteins expressed in given conditions. Around 6% of all identified proteins of commensal strain, 5% of uropathogenic and 1.4% of enteropathogenic had significant changes in abundances between 37°C and 23°C, and were associated with attachment to host cells, nutrient uptake, immune system evasion, virulence and toxin release, energy production and other processes crucial for bacterial survival inside the host. Surprisingly, despite the high temperature regulation seen at both the transcriptome and the proteome level independently, the correlation between temperature regulated transcripts and corresponding proteins appeared lower, possibly hinting at the importance of processes such as post-transcriptional processing and translational regulation in fine tuning the response of E. coli to the outside environment
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