Analysis and design of a modular multilevel converter with trapezoidal modulation for medium and high voltage DC-DC transformers

Conventional dual active bridge topologies provide galvanic isolation and soft-switching over a reasonable operating range without dedicated resonant circuits. However, scaling the two-level dual active bridge to higher dc voltage levels is impeded by several challenges among which the high dv/dt stress on the coupling transformer insulation. Gating and thermal characteristics of series switch arrays add to the limitations. To avoid the use of standard bulky modular multilevel bridges, this paper analyzes an alternative modulation technique where staircase approximated trapezoidal voltage waveforms are produced; thus alleviating developed dv/dt stresses. Modular design is realized by the utilization of half-bridge chopper cells. Therefore, the analyzed converter is a modular multi-level converter operated in a new mode with no common-mode dc arm currents as well as reduced capacitor size, hence reduced cell footprint. Suitable switching patterns are developed and various design and operation aspects are studied. Soft switching characteristics will be shown to be comparable to those of the two-level dual active bridge. Experimental results from a scaled test rig validate the presented concept

An integrated aerospace requirement setting and risk analysis tool for life cycle cost reduction and system design improvement

In the early conceptual stage of the service orientated model, decisions regarding the design of a new technical product are largely influenced by Service Requirements. Those decisions, therefore, have to merge both technical and business aspects to obtain desired product reliability and reduced Whole Life Cost (WLC). It is, therefore, critical at that phase to define the risk of potential noncompliance of Service Requirements in order to ensure the right design choices; as these decisions have a large impact on the overall product and service development. This paper presents outcome of research project to investigate different approaches used by companies to analyse Service Requirements to achieve reduced Life Cycle Cost (LCC). Analysis using Weibull distribution and Monte Carlo principle have been proposed here; based on the conducted literature review these are considered as the most widely used techniques in product reliability studies. Based on those techniques, a methodology and its software tool for risk evaluation of failure to deliver a new product against Service Requirements are presented in this paper. This is part of the on-going research project which, apart from analysing the gap between the current Service Requirements achievements and the design targets for a new aircraft engine, it also facilitates an optimisation of those requirements at the minimum risk of nonconformity

Enhancing service requirements of technical product-service systems

Due to the integration of product and services as a new business model, product reliability and strategies for cost reduction at the early design stage have become important factors for many manufacturing firms. It is, therefore, critical at this phase to analyse the risk involved with Service Requirements noncompliance in order to help designers make informed decisions; as these decisions have a large impact on the Product Life Cycle (PLC). An investigation has been performed into how Service Requirements are analysed in a service orientated business to achieve reduced Life Cycle Cost (LCC) and improvements of existing Service Requirements. Weibull distribution and Monte Carlo principle have been proposed to do so; as they are considered as the most widely used in product reliability studies in the industry sector. A generic methodology for risk evaluation of failure to deliver a new product against Service Requirements is presented in this paper. This is part of the ongoing research project which aims to, apart from comparing current and targeted Service Requirements, it also facilitates an optimisation of them at the minimum risk of nonconformity

Oscillations of Third Order Half Linear Neutral Differential Equations

In this paper the oscillation criterion was investigated for all solutions of the third-order half linear neutral differential equations. Some necessary and sufficient conditions are established for every solution of (a(t)[(x(t)±p(t)x(?(t) ) )^'' ]^? )^'+q(t) x^? (?(t) )=0, t?t_0, to be oscillatory. Examples are given to illustrate our main results

Performance of Unsupervised Change Detection Method Based on PSO and K-means Clustering for SAR Images

This paper presents unsupervised change detection method to produce more accurate change map from imbalanced SAR images for the same land cover. This method is based on PSO algorithm for image segmentation to layers which classify by Gabor Wavelet filter and then K-means clustering to generate new change map. Tests are confirming the effectiveness and efficiency by comparison obtained results with the results of the other methods. Integration of PSO with Gabor filter and k-means will providing more and more accuracy to detect a least changing in objects and terrain of SAR image, as well as reduce the processing time

A3 thinking approach to support knowledge-driven design

Problem solving is a crucial skill in product development. Any lack of effective decision making at an early design stage will affect productivity and increase costs and the lead time for the other stages of the product development life cycle. This could be improved by the use of a simple and informative approach which allows the designers and engineers to make decisions in product design by providing useful knowledge. This paper presents a novel A3 thinking approach to problem solving in product design, and provides a new A3 template which is structured from a combination of customised elements (e.g. the 8 Disciplines approach) and reflection practice. This approach was validated using a case study in the Electromagnetic Compatibility (EMC) design issue for an automotive electrical sub-assembly product. The main advantage of the developed approach is to create and capture the useful knowledge in a simple manner. Moreover, the approach provides a reflection section allowing the designers to turn their experience of design problem solving into proper learning and to represent their understanding of the design solution. These will be systematically structured (e.g. as a design checklist) to be circulated and shared as a reference for future design projects. Thus, the recurrence of similar design problems will be prevented and will aid the designers in adopting the expected EMC test results

A framework for geometric quantification and forecasting of cost uncertainty for aerospace innovations

Quantification and forecasting of cost uncertainty for aerospace innovations is challenged by conditions of small data which arises out of having few measurement points, little prior experience, unknown history, low data quality, and conditions of deep uncertainty. Literature research suggests that no frameworks exist which specifically address cost estimation under such conditions. In order to provide contemporary cost estimating techniques with an innovative perspective for addressing such challenges a framework based on the principles of spatial geometry is described. The framework consists of a method for visualising cost uncertainty and a dependency model for quantifying and forecasting cost uncertainty. Cost uncertainty is declared to represent manifested and unintended future cost variance with a probability of 100% and an unknown quantity and innovative starting conditions considered to exist when no verified and accurate cost model is available. The shape of data is used as an organising principle and the attribute of geometrical symmetry of cost variance point clouds used for the quantification of cost uncertainty. The results of the investigation suggest that the uncertainty of a cost estimate at any future point in time may be determined by the geometric symmetry of the cost variance data in its point cloud form at the time of estimation. Recommendations for future research include using the framework to determine the “most likely values” of estimates in Monte Carlo simulations and generalising the dependency model introduced. Future work is also recommended to reduce the framework limitations noted

The ciliary machinery is repurposed for T cell immune synapse trafficking of LCK

Upon engagement of the T cell receptor with an antigen-presenting cell, LCK initiates TCR signaling by phosphorylating its activation motifs. However, the mechanism of LCK activation specifically at the immune synapse is a major question. We show that phosphorylation of the LCK activating Y394, despite modestly increasing its catalytic rate, dramatically focuses LCK localization to the immune synapse. We describe a trafficking mechanism whereby UNC119A extracts membrane-bound LCK by sequestering the hydrophobic myristoyl group, followed by release at the target membrane under the control of the ciliary ARL3/ARL13B. The UNC119A N terminus acts as a “regulatory arm” by binding the LCK kinase domain, an interaction inhibited by LCK Y394 phosphorylation, thus together with the ARL3/ARL13B machinery ensuring immune synapse focusing of active LCK. We propose that the ciliary machinery has been repurposed by T cells to generate and maintain polarized segregation of signals such as activated LCK at the immune synapse

Evidence to Support a Putative Role for Insulin Resistance in Chronic Kidney Disease

Introduction: The primary cause of morbidity and mortality in the renal patient is a cardiovascular event. Insulin resistance (IR) contributes to this event by increasing cardiovascular disease (CVD) and accelerating rates of decline in kidney function. Here we review the historical background of IR in patients with chronic kidney disease (CKD) and present evidence for a role of IR in accelerating cardiovascular and renal diseases. Review: The high prevalence of IR in CKD patients is well documented. It is suggested that increased IR in the renal patient is caused by uremia as well as by other known factors in the general population. Patients with CKD have an alarmingly high risk for cardiovascular morbidity and mortality. There is overwhelming evidence to support a role for IR in increased CVD morbidity and mortality in the general population, which is likely to extend to CKD patients. Some of the traditional treatment measures for IR, such as metformin, may not be applicable to the renal patient. Other options include weight reduction, exercise, treatment of anemia to improve exercise tolerance, treatment of vitamin D deficiency, thiazolidinediones, and dialysis. IR is estimated by studying the relationship between blood glucose and the concomitant insulin level. Such measurement may help identify patients at increased risk for future cardiovascular events and guide treatment measures. Conclusion: Sufficient evidence supports the increased prevalence of IR in kidney patients. Treating IR may retard the progression of CKD and decrease the incidence of cardiovascular events in this high risk population. Keywords: chronic kidney diseass, cardiovascular disease, insulin resistanc

Spectrophotometric method for the determination of Captopril in pharmaceutical formulations

A simple, rapid and sensitive spectrophotometric method has been developed for the determination of captopril in aqueous solution. The method is based on reaction of captopril with 2,3-dichloro 1,4- naphthoquinon(Dichlone) in neutral medium to form a stable yellow colored product which shows maximum absorption at 347 nm with molar absorptivity of 5.6 ×103 L.mole-1. cm-1. The proposed method is applied successfully for determination of captopril in commercial pharmaceutical tablets