Design of a modular, high step-up ratio DC–DC converter for HVDC applications integrating offshore wind power

High-power and high-voltage gain dc-dc converters are key to high-voltage direct current (HVDC) power transmission for offshore wind power. This paper presents an isolated ultra-high step-up dc-dc converter in matrix transformer configuration. A flyback-forward converter is adopted as the power cell and the secondary side matrix connection is introduced to increase the power level and to improve fault tolerance. Because of the modular structure of the converter, the stress on the switching devices is decreased and so is the transformer size. The proposed topology can be operated in column interleaved modes, row interleaved modes, and hybrid working modes in order to deal with the varying energy from the wind farm. Furthermore, fault-tolerant operation is also realized in several fault scenarios. A 400-W dc-dc converter with four cells is developed and experimentally tested to validate the proposed technique, which can be applied to high-power high-voltage dc power transmission.

Ultrahigh step-up dc-dc converter for distributed generation by three Degrees of Freedom (3DoF) approach

This paper proposes a novel dc-dc converter topology to achieve an ultrahigh step-up ratio while maintaining a high conversion efficiency. It adopts a three degree of freedom approach in the circuit design. It also demonstrates the flexibility of the proposed converter to combine with the features of modularity, electrical isolation, soft-switching, low voltage stress on switching devices, and is thus considered to be an improved topology over traditional dc-dc converters. New control strategies including the two-section output voltage control and cell idle control are also developed to improve the converter performance. With the cell idle control, the secondary winding inductance of the idle module is bypassed to decrease its power loss. A 400-W dc-dc converter is prototyped and tested to verify the proposed techniques, in addition to a simulation study. The step-up conversion ratio can reach 1:14 with a peak efficiency of 94% and the proposed techniques can be applied to a wide range of high voltage and high power distributed generation and dc power transmission.

Metabolic induction and early responses of mouse blastocyst developmental programming following maternal low protein diet affecting life-long health

Previously, we have shown that a maternal low protein diet, fed exclusively during the preimplantation period of mouse development (Emb-LPD), is sufficient to induce by the blastocyst stage a compensatory growth phenotype in late gestation and postnatally, correlating with increased risk of adult onset cardiovascular disease and behavioural dysfunction. Here, we examine mechanisms of induction of maternal Emb-LPD programming and early compensatory responses by the embryo. Emb-LPD induced changes in maternal serum metabolites at the time of blastocyst formation (E3.5), notably reduced insulin and increased glucose, together with reduced levels of free amino acids (AAs) including branched chain AAs leucine, isoleucine and valine. Emb-LPD also caused reduction in the branched chain AAs within uterine fluid at the blastocyst stage. These maternal changes coincided with an altered content of blastocyst AAs and reduced mTORC1 signalling within blastocysts evident in reduced phosphorylation of effector S6 ribosomal protein and its ratio to total S6 protein but no change in effector 4E-BP1 phosphorylated and total pools. These changes were accompanied by increased proliferation of blastocyst trophectoderm and total cells and subsequent increased spreading of trophoblast cells in blastocyst outgrowths. We propose that induction of metabolic programming following Emb-LPD is achieved through mTORC1signalling which acts as a sensor for preimplantation embryos to detect maternal nutrient levels via branched chain AAs and/or insulin availability. Moreover, this induction step associates with changes in extra-embryonic trophectoderm behaviour occurring as early compensatory responses leading to later nutrient recovery. © 2012 Fleming et al.

EU governance of the internet:analyzing Europol’s role in the development of a EU cyber crime and cyber security policies

In recent years, the European Union has come to view cyber security, and in particular, cyber crime as one of the most relevant challenges to the completion of its Area of Freedom, Security and Justice. Given European societies’ increased reliance on borderless and decentralized information technologies, this sector of activity has been identified as an easy target for actors such as organised criminals, hacktivists or terrorist networks. Such analysis has been accompanied by EU calls to step up the fight against unlawful online activities, namely through increased cooperation among law enforcement authorities (both national and extra- communitarian), the approximation of legislations, and public- private partnerships. Although EU initiatives in this field have, so far, been characterized by a lack of interconnection and an integrated strategy, there has been, since the mid- 2000s, an attempt to develop a more cohesive and coordinated policy. An important part of this policy is connected to the activities of Europol, which have come to assume a central role in the coordination of intelligence gathering and analysis of cyber crime. The European Cybercrime Center (EC3), which will become operational within Europol in January 2013, is regarded, in particular, as a focal point of the EU’s fight against this phenomenon. Bearing this background in mind, the present article wishes to understand the role of Europol in the development of a European policy to counter the illegal use of the internet. The article proposes to reach this objective by analyzing, through the theoretical lenses of experimental governance, the evolution of this agency’s activities in the area of cyber crime and cyber security, its positioning as an expert in the field, and the consequences for the way this policy is currently developing and is expected to develop in the near future.

Statnote 25: Stepwise multiple regression

An investigator may also wish to select a small subset of the X variables which give the best prediction of the Y variable. In this case, the question is how many variables should the regression equation include? One method would be to calculate the regression of Y on every subset of the X variables and choose the subset that gives the smallest mean square deviation from the regression. Most investigators, however, prefer to use a ‘stepwise multiple regression’ procedure. There are two forms of this analysis called the ‘step-up’ (or ‘forward’) method and the ‘step-down’ (or ‘backward’) method. This Statnote illustrates the use of stepwise multiple regression with reference to the scenario introduced in Statnote 24, viz., the influence of climatic variables on the growth of the crustose lichen Rhizocarpon geographicum (L.)DC.

Three-port DC-DC converter for stand-alone photovoltaic systems

System efficiency and cost effectiveness are of critical importance for photovoltaic (PV) systems. This paper addresses the two issues by developing a novel three-port dc-dc converter for stand-alone PV systems, based on an improved Flyback-Forward topology. It provides a compact single-unit solution with a combined feature of optimized maximum power point tracking (MPPT), high step-up ratio, galvanic isolation, and multiple operating modes for domestic and aerospace applications. A theoretical analysis is conducted to analyze the operating modes followed by simulation and experimental work. This paper is focused on a comprehensive modulation strategy utilizing both PWM and phase-shifted control that satisfies the requirement of PV power systems to achieve MPPT and output voltage regulation. A 250-W converter was designed and prototyped to provide experimental verification in term of system integration and high conversion efficiency.

New modular structure DC-DC converter without electrolytic capacitors for renewable energy applications

Electrolytic capacitors are extensively used in power converters but they are bulky, unreliable, and have short lifetimes. This paper proposes a new capacitor-free high step-up dc-dc converter design for renewable energy applications such as photovoltaics (PVs) and fuel cells. The primary side of the converter includes three interleaved inductors, three main switches, and an active clamp circuit. As a result, the input current ripple is greatly reduced, eliminating the necessity for an input capacitor. In addition, zero voltage switching (ZVS) is achieved during switching transitions for all active switches, so that switching losses can be greatly reduced. Furthermore, a three-phase modular structure and six pulse rectifiers are employed to reduce the output voltage ripple. Since magnetic energy stored in the leakage inductance is recovered, the reverse-recovery issue of the diodes is effectively solved. The proposed converter is justified by simulation and experimental tests on a 1-kW prototype.

Developing a scalable model of recombinant protein yield from Pichia pastoris:the influence of culture conditions, biomass and induction regime

Background The optimisation and scale-up of process conditions leading to high yields of recombinant proteins is an enduring bottleneck in the post-genomic sciences. Typical experiments rely on varying selected parameters through repeated rounds of trial-and-error optimisation. To rationalise this, several groups have recently adopted the 'design of experiments' (DoE) approach frequently used in industry. Studies have focused on parameters such as medium composition, nutrient feed rates and induction of expression in shake flasks or bioreactors, as well as oxygen transfer rates in micro-well plates. In this study we wanted to generate a predictive model that described small-scale screens and to test its scalability to bioreactors. Results Here we demonstrate how the use of a DoE approach in a multi-well mini-bioreactor permitted the rapid establishment of high yielding production phase conditions that could be transferred to a 7 L bioreactor. Using green fluorescent protein secreted from Pichia pastoris, we derived a predictive model of protein yield as a function of the three most commonly-varied process parameters: temperature, pH and the percentage of dissolved oxygen in the culture medium. Importantly, when yield was normalised to culture volume and density, the model was scalable from mL to L working volumes. By increasing pre-induction biomass accumulation, model-predicted yields were further improved. Yield improvement was most significant, however, on varying the fed-batch induction regime to minimise methanol accumulation so that the productivity of the culture increased throughout the whole induction period. These findings suggest the importance of matching the rate of protein production with the host metabolism. Conclusion We demonstrate how a rational, stepwise approach to recombinant protein production screens can reduce process development time.

Involvement of phosphoinositide 3-kinase and Akt in the induction of muscle protein degradation by proteolysis-inducing factor

In the present study the role of Akt/PKB (protein kinase B) in PIF- (proteolysis-inducing factor) induced protein degradation has been investigated in murine myotubes. PIF induced transient phosphorylation of Akt at Ser(473) within 30 min, which was attenuated by the PI3K (phosphoinositide 3-kinase) inhibitor LY294002 and the tyrosine kinase inhibitor genistein. Protein degradation was attenuated in myotubes expressing a dominant-negative mutant of Akt (termed DNAkt), compared with the wild-type variant, whereas it was enhanced in myotubes containing a constitutively active Akt construct (termed MyrAkt). A similar effect was observed on the induction of the ubiquitin-proteasome pathway. Phosphorylation of Akt has been linked to up-regulation of the ubiquitin-proteasome pathway through activation of NF-kappaB (nuclear factor kappaB) in a PI3K-dependent process. Protein degradation was attenuated by rapamycin, a specific inhibitor of mTOR (mammalian target of rapamycin), when added before, or up to 30 min after, addition of PIF. PIF induced transient phosphorylation of mTOR and the 70 kDa ribosomal protein S6 kinase. These results suggest that transient activation of Akt results in an increased protein degradation through activation of NF-kappaB and that this also allows for a specific synthesis of proteasome subunits.

Modelling of induction motors for system faults and transient stability studies

The research carried out in this thesis was mainly concerned with the effects of large induction motors and their transient performance in power systems. Computer packages using the three phase co-ordinate frame of reference were developed to simulate the induction motor transient performance. A technique using matrix algebra was developed to allow extension of the three phase co-ordinate method to analyse asymmetrical and symmetrical faults on both sides of the three phase delta-star transformer which is usually required when connecting large induction motors to the supply system. System simulation, applying these two techniques, was used to study the transient stability of a power system. The response of a typical system, loaded with a group of large induction motors, two three-phase delta-star transformers, a synchronous generator and an infinite system was analysed. The computer software developed to study this system has the advantage that different types of fault at different locations can be studied by simple changes in input data. The research also involved investigating the possibility of using different integrating routines such as Runge-Kutta-Gill, RungeKutta-Fehlberg and the Predictor-Corrector methods. The investigation enables the reduction of computation time, which is necessary when solving the induction motor equations expressed in terms of the three phase variables. The outcome of this investigation was utilised in analysing an introductory model (containing only minimal control action) of an isolated system having a significant induction motor load compared to the size of the generator energising the system.

Build-up of the tendency to segregate auditory streams:resetting effects of single deviant tones

The tendency to hear a sequence of alternating low (L) and high (H) frequency tones as two streams can be increased by a preceding induction sequence, even one composed only of same-frequency tones. Four experiments used such an induction sequence (10 identical L tones) to promote segregation in a shorter test sequence comprising L and H tones. Previous studies have shown that the build-up of stream segregation is usually reduced greatly when a sudden change in acoustic properties distinguishes all of the induction tones from their test-sequence counterparts. Experiment 1 showed that a single deviant tone, created by altering the final inducer (in frequency, level, duration, or replacement with silence) reduced reported segregation, often substantially. Experiment 2 partially replicated this finding, using changes in temporal discrimination as a measure of streaming. Experiments 3 and 4 varied the size of a frequency change applied to the deviant tone; the extent of resetting varied with size only gradually. The results suggest that resetting begins to occur once the change is large enough to be noticeable. Since the prior inducers always remained unaltered in the deviant-tone conditions, it is proposed that a single change actively resets the build-up evoked by the induction sequence.

Build-up and resetting of auditory stream segregation in quiet and in complex-tone backgrounds

Thirteen experiments investigated the dynamics of stream segregation. Experiments 1-6b used a similar method, where a same-frequency induction sequence (usually 10 repetitions of an identical pure tone) promoted segregation in a subsequent, briefer test sequence (of alternating low- and high-frequency tones). Experiments 1-2 measured streaming using a direct report of perception and a temporal-discrimination task, respectively. Creating a single deviant by altering the final inducer (e.g. in level or replacement with silence) reduced segregation, often substantially. As the prior inducers remained unaltered, it is proposed that the single change actively reset build-up. The extent of resetting varied gradually with the size of a frequency change, once noticeable (experiments 3a-3b). By manipulating the serial position of a change, experiments 4a-4b demonstrated that resetting only occurred when the final inducer was replaced with silence, as build-up is very rapid during a same-frequency induction sequence. Therefore, the observed resetting cannot be explained by fewer inducers being presented. Experiment 5 showed that resetting caused by a single deviant did not increase when prior inducers were made unpredictable in frequency (four-semitone range). Experiments 6a-6b demonstrated that actual and perceived continuity have a similar effect on subsequent streaming judgements promoting either integration or segregation, depending on listening context. Experiment 7 found that same-frequency inducers were considerably more effective at promoting segregation than an alternating-frequency inducer, and that a trend for deviant-tone resetting was only apparent for the same-frequency case. Using temporal-order judgments, experiments 8-9 demonstrated the stream segregation of pure-tone-like percepts, evoked by sudden changes in amplitude or interaural time difference for individual components of a complex tone, Active resetting was observed when a deviant was inserted into a sequence of these percepts (Experiment 10). Overall, these experiments offer new insight into the segregation-promotIng effect of induction sequences, and the factors which can reset this effect.

Build-up of auditory stream segregation induced by tone sequences of constant or alternating frequency and the resetting effects of single deviants

A sequence of constant-frequency tones can promote streaming in a subsequent sequence of alternating-frequency tones, but why this effect occurs is not fully understood and its time course has not been investigated. Experiment 1 used a 2.0-s-long constant-frequency inducer (10 repetitions of a low-frequency pure tone) to promote segregation in a subsequent, 1.2-s test sequence of alternating low- and high-frequency tones. Replacing the final inducer tone with silence substantially reduced reported test-sequence segregation. This reduction did not occur when either the 4th or 7th inducer was replaced with silence. This suggests that a change at the induction/test-sequence boundary actively resets build-up, rather than less segregation occurring simply because fewer inducer tones were presented. Furthermore, Experiment 2 found that a constant-frequency inducer produced its maximum segregation-promoting effect after only three tones—this contrasts with the more gradual build-up typically observed for alternating-frequency sequences. Experiment 3 required listeners to judge continuously the grouping of 20-s test sequences. Constant-frequency inducers were considerably more effective at promoting segregation than alternating ones; this difference persisted for ~10 s. In addition, resetting arising from a single deviant (longer tone) was associated only with constant-frequency inducers. Overall, the results suggest that constant-frequency inducers promote segregation by capturing one subset of test-sequence tones into an ongoing, preestablished stream, and that a deviant tone may reduce segregation by disrupting this capture. These findings offer new insight into the dynamics of stream segregation, and have implications for the neural basis of streaming and the role of attention in stream formation. (PsycINFO Database Record (c) 2013 APA, all rights reserved)

Scaling up question-answering to linked data

Linked Data semantic sources, in particular DBpedia, can be used to answer many user queries. PowerAqua is an open multi-ontology Question Answering (QA) system for the Semantic Web (SW). However, the emergence of Linked Data, characterized by its openness, heterogeneity and scale, introduces a new dimension to the Semantic Web scenario, in which exploiting the relevant information to extract answers for Natural Language (NL) user queries is a major challenge. In this paper we discuss the issues and lessons learned from our experience of integrating PowerAqua as a front-end for DBpedia and a subset of Linked Data sources. As such, we go one step beyond the state of the art on end-users interfaces for Linked Data by introducing mapping and fusion techniques needed to translate a user query by means of multiple sources. Our first informal experiments probe whether, in fact, it is feasible to obtain answers to user queries by composing information across semantic sources and Linked Data, even in its current form, where the strength of Linked Data is more a by-product of its size than its quality. We believe our experiences can be extrapolated to a variety of end-user applications that wish to scale, open up, exploit and re-use what possibly is the greatest wealth of data about everything in the history of Artificial Intelligence. © 2010 Springer-Verlag.

Zinc-α2-glycoprotein, a lipid mobilizing factor, is expressed in adipocytes and is up-regulated in mice with cancer cachexia

Zinc-α2-glycoprotein (ZAG), a 43-kDa protein, is overexpressed in certain human malignant tumors and acts as a lipid-mobilizing factor to stimulate lipolysis in adipocytes leading to cachexia in mice implanted with ZAG-producing tumors. Because white adipose tissue (WAT) is an endocrine organ secreting a wide range of protein factors, including those involved in lipid metabolism, we have investigated whether ZAG is produced locally by adipocytes. ZAG mRNA was detected by RT-PCR in the mouse WAT depots examined (epididymal, perirenal, s.c., and mammary gland) and in interscapular brown fat. In WAT, ZAG gene expression was evident in mature adipocytes and in stromal-vascular cells. Using a ZAG Ab, ZAG protein was located in WAT by Western blotting and immunohistochemistry. Mice bearing the MAC16-tumor displayed substantial losses of body weight and fat mass, which was accompanied by major increases in ZAG mRNA and protein levels in WAT and brown fat. ZAG mRNA was detected in 3T3-L1 cells, before and after the induction of differentiation, with the level increasing progressively after differentiation with a peak at days 8-10. Both dexamethasone and a β 3 agonist, BRL 37344, increased ZAG mRNA levels in 3T3-L1 adipocytes. ZAG gene expression and protein were also detected in human adipose tissue (visceral and s.c.). It is suggested that ZAG is a new adipose tissue protein factor, which may be involved in the modulation of lipolysis in adipocytes. Overexpression in WAT of tumor-bearing mice suggests a local role for adipocyte-derived ZAG in the substantial reduction of adiposity of cancer cachexia.