bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies in Early Etruscan Bucchero
Authors: Ramage Nancy Hirschland
Published: August 2013

Bucchero is a type of Etruscan pottery which is black, both on the surface and in the core. There are many different shades of grey to black which are still considered to be bucchero, but in all cases the core of the pottery must be ‘reduced.’ The process was discovered by the Etruscans, and gave rise to one of the most characteristic products of their culture.

Bucchero varies enormously from period to period, from place to place. In this paper the period to be covered is approximately 650–600 B.C., during which the forms ofbucchero sottilewere established and developed in southern Etruria. The origins of these forms will also be sought in earlier periods, chiefly from the late eighth century onwards. Thebucchero pesanteof the sixth century, and later types continuing in the fifth, will not be considered here.
Survey of an Etruscan City at Doganella, in the Albegna valley
Authors: Perkins Philip , Walker Lucy
Published: August 2013

RICOGNIZIONE TOPOGRAFICA DI UNA CITTA' ETRUSCA A DOGANELLA NELLA VALLE DELL'ALBEGNA

Questa città etrusca della Toscana meridionale, di enormi dimensioni, e munita di una cinta muraria, si trova coperta, per la maggior parte, da terreno attualmento adibito ad uso agricolo. Negli anni tra il 1982 e il 1984, nell'ambito di tre campagne di ricognizione topografica condotte nella Valle dell'Albegna, è stata condotta una esplorazionc sistematica dell'area. La relazione che qui si presenta contiene: la storia degli studi relativi al sito, la descrizione dei resti archeologici osservabili sul terreno, l'esposizione della metodologia impiegata nella ricognizione, l'analisi dei campioni di materiali raccolti, ed una discussione dei vari aspetti generali del sito. A ciò segue un catalogo delle distribuzioni in superficie dei vari materiali ed una appendice sui risultati di due carotaggi del suolo.
The emotional labour of health-care assistants in inpatient dementia care
Authors: BAILEY SIMON , SCALES KEZIA , LLOYD JOANNE , SCHNEIDER JUSTINE , JONES ROB
Published: August 2013

Although there is much written on the emotional labour of nursing, there is little research grounded in the experience of so-called ‘unqualified’ care assistants. This paper is drawn from an ethnographic study conducted with care assistants on three dementia care wards in one mental health trust within the United Kingdom National Health Service (NHS). We describe the emotional labour carried out by care assistants in their attempts to provide personalised care for people whose cognitive degeneration renders conventional relationship-building very difficult, produces unpredictable ‘challenging behaviour’ and calls into question the notion of ‘feeling rules’. This context requires the ability to strike a balance between emotional engagement and detachment, and it is the complexities of this relationship that are the focus of this paper, arguing that a degree of detachment is a prerequisite to engagement in this context. In conclusion, we argue that the contribution of care assistants in this context needs to be better acknowledged, supported and remunerated.
Ways of Watching Sport
Authors: Mumford Stephen
Published: August 2013

There are many ways that we can watch sport but not all of them are philosophically interesting. One can watch it enthusiastically, casually, fanatically or drunkenly. One might watch only because one has bet on the outcome. Some watch a friend or relative compete and have a narrow focus on one individual's performance. A coach or scout on the lookout for new talent may have completely different interests to a supporter of a team. But what of the ways of watching sport that are of philosophical interest?
Chess, Imagination, and Perceptual Understanding
Authors: Coates Paul
Published: August 2013

Chess is sometimes referred to as a ‘mind-sport’. Yet, in obvious ways, chess is very unlike physical sports such as tennis and soccer; it doesn't require the levels of fitness and athleticism necessary for such sports. Nor does it involve the sensory-governed, skilled behaviour required in activities such as juggling or snooker. Nevertheless, I suggest, chess is closer than it may at first seem to some of these sporting activities. In particular, there are interesting connections between the way that we use our perceptual imagination in sports, and also in chess. The same distinction between calculation and natural instinct applies in chess as it does in many physical sports.
Glory in Sport (and Elsewhere)
Authors: Chappell Timothy
Published: August 2013

There is a gap between what we think about ethics, and what we think we think about ethics. This gap appears when elements of our ethical reflection and our moral theories contradict each other, or otherwise come into logical tension. It also appears when something that is important in our ethical reflection is sidelined, or simply ignored, in our moral theories. The gap appears in both ways with an ethical idea that I shall labelglory. This paper's exploration of the idea of glory, and its place in our ethical reflection, is offered as a case-study of how far such reflection can diverge from what we might expect, if we suppose that actual ethical reflection usually or mostly takes the forms that might be predicted by moral theory. I shall suggest that this divergence tells against moral theory, and in favour of less constricted and more flexible modes of ethical reflection.
Livedoid vasculopathy - a thrombotic disease
Authors: Kerk Nina , Goerge Tobias
Published: August 2013

Livedoid vasculopathy is a rare, chronic occlusive disease of vessels supporting the upper layers of the skin. It is characterized by purpuric maculae and recurrent painful ulcerations mostly affecting the lower leg. These ulcerations occur episodically especially in summer time and heal slowly, leaving characteristic porcelain-white scars called atrophie blanche.This review is focused on the current knowledge on livedoid vasculopathy and modern therapy strategies resulting from its etiopathogenetic associations with prothrombotic states. Livedoid vasculopathy and its pathophysiology are clearly distinguished from inflammatory vasculitis and thus require a different therapeutic approach. The prevention of irreversible residual scarring and improving the quality of life of patients in this often misdiagnosed disease is one of the main treatment goals.
Past and Future Implications of Near-Misses and Their Emotional Consequences
Authors: Zhang Qiyuan , Covey Judith
Published: August 2013

The Reflection and Evaluation Model (REM) of comparative thinking predicts that temporal perspective could moderate people’s emotional reactions to close counterfactuals following near-misses ( Markman & McMullen, 2003 ). The experiments reported in this paper tested predictions derived from this theory by examining how people’s emotional reactions to a near-miss at goal during a football match (Experiment 1) or a close score in a TV game show (Experiment 2) depended on the level of perceived future possibility. In support of the theory it was found that the presence of future possibility enhanced affective assimilation (e.g., if the near-miss occurred at the beginning of the game the players who had nearly scored were hopeful of future success) whereas the absence of future possibility enhanced affective contrast (e.g., if the near-miss occurred at the end of the game the players who had nearly scored were disappointed about missing an opportunity). Furthermore the experiments built upon our theoretical understanding by exploring the mechanisms which produce assimilation and contrast effects. In Experiment 1 we examined the incidence of present-oriented or future-oriented thinking, and in Experiment 2 we examined the mediating role of counterfactual thinking in the observed effect of proximity on emotions by testing whether stronger counterfactuals (measured using counterfactual probability estimates) produce bigger contrast and assimilation effects. While the results of these investigations generally support the REM, they also highlight the necessity to consider other psychological mechanisms (e.g., social comparison), in addition to counterfactual thinking, that might contribute to the emotional consequences of near-miss outcomes.
Systems Pharmacology Models for Guiding Drug Design
Authors: Krzyzanski W
Published: August 2013

CPT: Pharmacometrics & Systems Pharmacology(2013) 2, e39; doi:10.1038/psp.2013.15; advance online publication 24 April 2013
Systems Approaches Evolve Clinical Pharmacology
Authors: Waldman SA , van der Graaf PH , Terzic A
Published: August 2013

CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e68; doi:10.1038/psp.2013.48; advance online publication 21 August 2013
Consensus of swarm systems with time delays and topology uncertainties
Authors: Xi Jianxiang , Li Hailong , Cai Ning , Zhong Yisheng
Published: August 2013

Consensus problems for first‐order continuous‐time swarm systems in directed networks with time delays and topology uncertainties are dealt with. The state space of a swarm system is decomposed into a null space and a complement null space. By projecting the state of the system onto the two subspaces, a necessary and sufficient condition for consensus is proposed, and an explicit expression of the consensus function is shown based on the impacts of time delays and topology uncertainties. Sufficient conditions in terms of linear matrix inequalities are given for swarm systems with time‐varying delays and topology uncertainties to achieve consensus. Numerical examples are shown to demonstrate theoretical results.
Joint estimation and identification for stochastic systems with unknown inputs
Authors: Lan Hua , Liang Yan , Yang Feng , Wang Zengfu , Pan Quan
Published: August 2013

Motivated by tracking a manoeuvring target in electronic counter environments, the authors present the problem of joint estimation and identification of a class of discrete‐time stochastic systems with unknown inputs in both the plant and sensors. Based on the expectation‐maximum criterion, the joint optimisation scheme of state estimation, parameter identification and iteration terminate decision were derived. A numerical example of tracking a manoeuvring target accompanied range gate pull‐off is utilised to verify the proposed scheme.
Analytical modelling and parametric sensitivity analysis for the PMSM steady‐state performance prediction
Authors: Kazerooni Maryam , Hamidifar Saeedeh , Kar Narayan C.
Published: August 2013

Inaccuracy in the permanent magnet synchronous motor (PMSM) steady‐state performance calculation corresponds to the parameter error and model imprecision. Accurate determination of the PMSM parameters may encounter various complications because of its rotor structure and drive design. Therefore PMSM performance calculation is generally vulnerable to inaccuracy because of the parameter error. This article studies the effect of parameter error on the inaccuracy of the performance calculations. Several methods for determining the PMSM armature resistance, flux linkage constant and d‐ and q‐axis inductances with varying level of accuracy are proposed. The presented methods are applied to a laboratory PMSM and the sensitivity of the PMSM output power to the equivalent circuit parameters is analysed based on the experimental results. In addition, this study contributes to accurate performance estimations of the PMSM by developing a precise model that incorporates the saturation saliency and core losses. The accuracy of the proposed model is compared with the conventional dq‐axis model and its higher accuracy is validated through experimental results.
Characterising brushless doubly fed machine rotors
Authors: McMahon Richard , Tavner Peter , Abdi Ehsan , Malliband Paul , Barker Darren
Published: August 2013

The brushless doubly fed machine (BDFM) is a robust alternative to the doubly fed induction generator, currently widely used in wind turbines but prone to brush‐gear and slip‐ring failure. The rotor winding plays an important part in a BDFM, coupling the two stator windings. To date, nested‐loop (NL) rotor windings have been exclusively used in practical BDFM. This approach may not be ideal for larger machines, in which form‐wound series‐loop rotor winding may be preferable to large section bars and end‐rings. This study gives a comparative analytical and experimental study of two different brushless doubly fed 160 frame‐size rotors, with NL or series‐wound windings, mounted in identical rotor core laminations operating in the same stator tested at a limited voltage (200 V line). The rotors gave a performance which accords with theoretical predictions from two independent methods, giving insight into the design issues of the different rotor windings from both an electrical and manufacturing viewpoint.
Rim‐drive marine thruster using a multiple‐can induction motor
Authors: Tuohy Paul Michael , Smith Alexander Charles , Husband Mark , Hopewell Paul
Published: August 2013

This study presents the development, analysis, manufacture and testing of a demonstrator multiple‐can line‐start rim‐drive induction motor for use as a bi‐directional electric thruster on‐board a tidal stream turbine. A simple ‘canned’ rotor construction was used to eliminate the requirement for a conventional squirrel‐cage rotor, to minimise the rotor size and weight and improve reliability, all the while providing compatibility with the sub‐sea operating environment. The experimental test results on a demonstrator 30 kW rim‐drive motor show good agreement with finite‐element analysis predicted results.
Correction of saturated current from measurement current transformer
Authors: Ozgonenel Okan
Published: August 2013

The suggested study presents an easy and effective way to compensate for the distorted secondary current of measurement‐type current transformers (CTs). The suggested compensating algorithm is based on estimating the magnetising current from a Fröhlich hysteresis approach. The efficiency of the proposed technique was first proved using computer simulations. The prototype compensating device was then tested in a laboratory environment using a 5/1A, 10VA, C0,5 measurement‐type CT. The proposed compensation algorithm is dependent on CT burden and X/R ratio of the line where CT is connected. The outcomes of the study demonstrate that the technique is able to reconstruct the secondary current with an acceptable error and can be applied to any measurement‐type CT regardless of its size and winding topology.
Clarification on power system stabiliser design
Authors: Ma Jin , Wang Hao Jing , Lo Kowk Lun
Published: August 2013

The application of power system stabiliser (PSS) since 1960s has exerted a great effect on improving power system dynamic stability and has become a very important auxiliary excitation control measure to deal with low frequency oscillation. The common design approach is to compensate for the phase lag caused by the excitation system, and thereby increase damping of the system. Is that the real key in stabilising the system? This study clarifies the damping torque concept and analyses the flaws of the damping torque‐based PSS design theory. The key parameters in PSS design to stabilise the power system are fully investigated, based on which the study reveals the real nature of the PSS working mechanism. It has been shown in the study that phase compensation is not the necessary condition in stabilising the system; stabiliser gain is very important for controller design. Case studies in the real power system validate the analysis results.
Extended smart meters‐based remote detection method for illegal electricity usage
Authors: Bat‐Erdene Byambasuren , Lee Bumjoo , Kim Min‐Young , Ahn Tae Hong , Kim Donghan
Published: August 2013

Power delivery systems that use power lines can communicate with other electrical systems, monitor the quality of electrical energy and provide an economical solution for automatic meter reading (AMR). Energy meters can be connected to a low‐voltage power system by power line carriers for all consumers. Illegal electricity usage in the power delivery system can be easily detected if AMR is installed in the system, which consists of a terminal smart meter (TSM) and a gateway smart meter (GSM). This study proposes a novel remote detection method for illegal electricity usage that uses both TSM and GSM, where the TSM and the GSM are installed on the power system of each consumer and on the node of the power system feeder, respectively. TSM and GSM simultaneously disconnect an electrical source for a very short period of time. After this, the proposed detection method sends a low‐voltage signal with a high frequency from the TSM to the GSM during the time of disconnection. Once the signal has passed, the proposed detection method detects illegal electricity usage by measuring the amount of time it was disconnected. This study presents the structure of the proposed detection method as well as the mathematical model, proof, simulation and experimental results.
Optimal multi‐area generation schedule considering renewable resources mix: a real‐time approach
Authors: Soroudi Alireza , Rabiee Abbas
Published: August 2013

One of the key role players in deregulated electricity markets is a retailer. This study proposes a multi‐area dynamic economic dispatch (MA‐DED) model for a retailer, taking into account hydrothermal generating units, wind power generation and power pool market, to supply the overall demand of the system for a given horizon. The uncertainties in wind power generations, energy prices and demand of the system are also modelled to make the proposed approach more practical in case of real‐time operation of practical power systems. Scenario‐based approach is adopted for uncertainty modelling. In order to make the proposed MA‐DED applicable in real‐time operation of power systems, optimality condition decomposition (OCD) technique is employed along with parallel computation ability. The proposed approach is examined on two interconnected power networks, to demonstrate its applicability for real‐time scheduling of joint thermal and undispatchable renewable energy resources. DED, multi‐area, OCD, real‐time, uncertainty modelling, scenario‐based approach.
Comprehensive review of generation and transmission expansion planning
Authors: Hemmati Reza , Hooshmand Rahmat‐Allah , Khodabakhshian Amin
Published: August 2013

Investment on generation system and transmission network is an important issue in power systems, and investment reversibility closely depends on performing an optimal planning. In this regard, generation expansion planning (GEP) and transmission expansion planning (TEP) have been presented by researchers to manage an optimal planning on generation and transmission systems. In recent years, a large number of research works have been carried out on GEP and TEP. These problems have been investigated with different views, methods, constraints and objectives. The evaluation of researches in these fields and categorising their different aspects are necessary to manage further works. This study presents a comprehensive review of GEP and TEP problems from different aspects and views such as modelling, solving methods, reliability, distributed generation, electricity market, uncertainties, line congestion, reactive power planning, demand‐side management and so on. The review results provide a comprehensive background to find out further ideas in these fields.
Authenticated voltage control of partitioned power networks with optimal allocation of STATCOM using heuristic algorithm
Authors: Mehrjerdi Hasan , Ghahremani Esmaeil , Lefebvre Serge , Saad Maarouf , Asber Dalal
Published: August 2013

This study presents a secondary voltage control based on an optimisation algorithm to locate the control buses and regulate the voltage. Control buses are the buses where compensators will be installed on these buses to regulate voltage and avoid voltage violations. Firstly, partitioning algorithm using fuzzy C‐means has been implemented on the power network. Partitioning techniques split the power system into regions to avoid the propagation of disturbances between regions by using local controllers. Then, a number of buses are labelled as control buses displaying the critical point for voltage control in each region. The control algorithm is a decentralised controller which tries to eliminate voltage violations in power system resulting from load variations and disturbances. The decentralised controllers are implemented using flexible AC transmission system (FACTS) devices such as static synchronous compensator (STATCOM). The methodology is applied to the IEEE 118‐bus network. The results show the performance and ability of the partitioning algorithm and bus control selection to regulate the voltage and avoid propagation of disturbances between regions.
TQCR‐media access control: two‐level quality of service provisioning media access control protocol for cognitive radio network
Authors: Mishra Vishram , Chiew Tong Lau , Chan Syin , Mathew Jimson
Published: August 2013

Recently cognitive radio has been proposed to solve the problem of spectrum scarcity with the help of an opportunistic utilisation of unused spaces in the spectrum. The implementation of cognitive radio for real‐time application faces with the challenge of real‐time media access control (MAC) design. To this end the authors propose an energy efficient cognitive radio MAC protocol with two level of quality of service (QoS) support: two level quality of service provisioning in cognitive radio (TQCR)‐MAC. The data traffic in the cognitive radio network is classified as real‐time traffic and non‐real‐time traffic, with former having higher priority over latter. The proposed protocol utilises variable interframe spaces for implementing different priorities to data and also exploits the combination of multiple channels and time division multiple access (TDMA) scheme to further improve the QoS provisioning. The TDMA slots in different channels are used as the data carrier segment, in which a real‐time data can take over the time slots reserved by non‐real‐time data. Thus, non‐real traffic may suffer from starvation, and hence a guarantee on the non‐real‐time data is provided with the help of a starvation prevention algorithm. The performance analysis of the proposed MAC protocol is done against two similar MAC protocols, which shows that the performance is improved significantly, especially when the network is either biased towards real‐time or non‐real‐time data traffic.
High‐efficiency two‐switch tri‐state buck–boost power factor correction converter with fast dynamic response and low‐inductor current ripple
Authors: He Mingzhi , Zhang Fei , Xu Jianping , Yang Ping , Yan Tiesheng
Published: August 2013

Two‐switch tri‐state buck–boost power factor correction (PFC) converter operating in pseudo‐continuous conduction mode is proposed and analysed in this study. Different from tri‐state boost PFC converter, the proposed two‐switch tri‐state buck–boost PFC converter does not need additional power switch to provide the additional degree of control freedom. Therefore it does not increase the complexity and affect the power conversion efficiency of the PFC converter as in the case of tri‐state boost PFC converter. For the proposed two‐switch tri‐state buck–boost PFC converter, the current control loop and voltage control loop are decoupled, a simple voltage control loop with faster dynamic response can be designed to realise output voltage regulation and the additional degree of control freedom introduced by inductor current freewheeling stage helps to achieve unity power factor control. The operation principle, the input current, the inductor current ripple, the switch component stress and the small‐signal characteristics of the proposed two‐switch tri‐state buck–boost PFC converter are analysed. The simulation and experimental results show that the proposed two‐switch tri‐state buck–boost PFC converter benefits with fast dynamic response, high‐efficiency and low‐inductor current ripple over single‐switch buck–boost PFC converter or two‐switch buck–boost PFC converter operating in continuous conduction mode and discontinuous conduction mode.
Instant voltage compensator based on a three‐leg converter
Authors: Kwon Jung‐Min , Kim Kyu‐Tae , Kwon Bong‐Hwan
Published: August 2013

This study proposes an instant voltage compensator (IVC)‐based on a three‐leg converter. It provides single ac–ac power conversion without large energy storage elements, so the size and cost are reduced. It operates as a boost converter when the line voltage is lower than the rated output voltage and as a buck converter when the line voltage is higher than the rated output voltage. Only one leg among the three legs is switched at a high frequency, whereas the other legs are switched at the line frequency. Therefore the power conversion efficiency is higher than that of a conventional IVC where all of the legs are controlled by a high switching frequency. The output voltage is regulated faster using a weighted‐error proportional and integral controller. Experimental results are obtained with a 3 kW prototype to verify that the proposed IVC quickly compensates for the voltage sag and swell of the line voltage.
Implementation of sensorless control of induction machines using only fundamental PWM waveforms of a two‐level converter
Authors: Gao Qiang , Asher Greg M. , Sumner Mark
Published: August 2013

This study reports the implementation of a sensorless control scheme for AC machines that requires neither a fundamental model observer nor a test‐signal. The model is based on saliency detection through the use of fundamental PWM excitation and the measurement of the derivatives of the line currents induced by the PWM voltage vectors. Derivation of the rotor position is possible at low and zero speeds without separate test signals and also at higher speed without the knowledge of the machine's fundamental model. Experimental results showing fully sensorless induction motor control at low and higher speeds validate the principle of this method.
Enhanced fault ride through performance of self‐excited induction generator‐based wind park during unbalanced grid operation
Authors: El Moursi Mohamed , Goweily Khaled , Badran Ebrahim A.
Published: August 2013

This study presents novel control design for improving the performance of large‐scale wind park (LSWP) based on self‐excited induction generator under unbalanced voltage conditions. A dual controller for static synchronous compensator (STATCOM) employing controller by employing positive‐ and negative‐sequence synchronous frames is implemented and analysed in response to severely unbalanced voltage conditions. The test system simulated represents a wind park rated at 100 MW connected to a weak electrical grid. The potential of the dual STATCOM controller is evaluated and analysed for severely unbalanced voltage conditions at the grid interface of LSWP. The dual controller with STATCOM overloading capability is tested and compared with the performance of the positive‐sequence controller in response to different types of asymmetrical grid faults at low short‐circuit ratios. The simulations performed using PSCAD/EMTDC demonstrate superior performance of dual STATCOM control strategy for improving unbalanced operation, fault ride through capability and transient stability margin in response to severely unbalanced voltage conditions.
Digital pulse‐width modulation controller based on fully table look‐up for system‐on‐a‐chip applications
Authors: Tu Steve Hung‐Lung , Chiu Morris M.‐H.
Published: August 2013

Design and implementation of a fully table look‐up digital pulse‐width modulation (DPWM) controller for high‐frequency DC–DC buck conversion is presented. The controller comprises a 1 bit analogue comparator, a digital error process unit and a fully table look‐up multi‐phase DPWM. The interface of analogue‐to‐digital conversion is performed with the analogue comparator. Moreover, the proposed programmable memory is based on the table look‐up multi‐phase approach for the functions of the proportional‐integral‐derivative (PID) compensation, which alleviates the penalty of using large chip‐area multipliers. As a result, the approach is very suitable for system‐on‐a‐chip (SOC) implementation. A prototype test chip is realised to validate the mechanism of the proposed architecture.
A novel circuit for removing the entire current harmonic distortion generated by ohmic phase‐cutting devices
Authors: Fathabadi Hassan
Published: August 2013

In this study and for the first time, a novel harmonic remover circuit is presented that removes the entire current harmonic distortion generated by the phase‐cutting devices, which have ohmic input impedance (ohmic phase‐cutting devices) such as lighting dimmers. The presented circuit has been designed and an experimental prototype has been built in the laboratory. It has a very exact operation to remove the total harmonic distortion (THD). It really removes the entire harmonic and the THD% of the compensated device is equal to the THD% of the same device without any phase cutting, so if the THD% of the system without any phase cutting is zero then the THD% of the compensated device will also be zero. The real measurement and experimental results are presented to validate the theoretically results and make a comparison between the advantages of this work and other related works.
Doubly fed induction generator‐based off‐grid wind energy conversion systems feeding dynamic loads
Authors: Singh Bhim , Sharma Shailendra
Published: August 2013

This study deals with the operation and control of a doubly fed induction generator (DFIG)‐based off‐grid wind energy conversion system (WECS). Two back‐to‐back connected voltage source converters with intermediate DC‐link supported with a battery energy storage system are used as a voltage and frequency controller (VFC). A field oriented control algorithm is used for VFC to perform as a load leveller, a load balancer, an active filter along with a VFC. Simulation results are verified on a developed prototype of VFC for DFIG‐based off‐grid WECS. The performance of WECS is demonstrated feeding non‐linear and dynamic loads.
Marx dc–dc converter for high‐power application
Authors: Veilleux Etienne , Ooi Boon‐Teck , Lehn Peter W.
Published: August 2013

This study presents a dc–dc converter based on the Marx generator principle of charging capacitors in parallel followed by reconnection in series for discharging and for creating higher voltage. The topology uses solid‐state switches like IGBTs as well as diodes. The concept and the operation of converter are described as well as design steps. The validity of the design is confirmed using PSCAD/EMTDC software package. The topology is compared with the conventional boost where the Marx dc–dc converter is shown to be competitive and even advantageous for higher dc gain. A cascade configuration is also presented and a 5 kW prototype with two stages made of two capacitors per stage is presented for experimental validation of the concept.
Relationship between two‐level space‐vector pulse‐width modulation and carrier‐based pulse‐width modulation in the over‐modulation region
Authors: Fang Hui , Feng Xiaoyun , Song Wensheng , Ge Xinglai , Ding Rongjun
Published: August 2013

For low voltage motor drive applications, in order to enhance the utilisation rate of dc bus voltage and extend the operating boundary of induction motors, the modulation index is often extended from the linear modulation region to the over‐modulation region. The relationship between two‐level space‐vector pulse‐width modulation (SVPWM) and carrier‐based pulse‐width modulation (CBPWM) in the linear modulation region has been widely investigated and it was shown that the conventional SVPWM is a special type of CBPWM algorithm with zero sequence components injection. On the basis of that, this study focuses on investigating their relationship in the over‐modulation region. Firstly, the superposition principle is adopted to analyse the features of SVPWM algorithm in the over‐modulation region. Second, the modulating functions of CBPWM equivalent to SVPWM in the over‐modulation modes I and II are derived, respectively, which are on the basis of the CBPWM regular sampling rule. Theoretical analysis shows that SVPWM is a special type of CBPWM algorithm not only in the linear modulation region but also in the over‐modulation region, which provides a bidirectional bridge for the transformation between SVPWM and CBPWM in the full modulation region. Finally, the validity and effectiveness of the theoretical analysis are verified by simulation and experimental results.
Switching strategy for six switches forced commutated cycloconverter with several advantages
Authors: Khoun Jahan Hossein , Banaei Mohamad Reza
Published: August 2013

Forced commutated cycloconverters (FCCs) are very popular topics today which can generate variable frequency and variable voltage in output. These converters include six switches in each phase where operation of these converters depends on switching strategy. This study describes a novel switching strategy for six switches FCC where this strategy transfers seven input voltages to FCC output. In each switching period, among seven input voltages, there are only two input voltages which surround reference output voltage. Hence, the proposed strategy makes these two input voltages around reference voltage transfer to FCC output in each switching period. As a result, average value of FCC output voltage is the same as reference voltage. Main benefits of this switching strategy are minimisation of total harmonic distortion, reduction of dv/dt stresses on the load, lower harmonic components, high‐voltage modulation index and performance in unbalance or non‐sinusoidal input voltage condition. The operation and performance of the proposed switching strategy has been verified by the simulation and measurement results which were carried out for three‐phase to single‐phase converter. The proposed switching strategy serves as the conceptual platform for extending the principles to other FCC topologies.
Analysis, design and implementation of isolated bidirectional converter with winding‐cross‐coupled inductors for high step‐up and high step‐down conversion system
Authors: Li Wuhua , Xu Chi , Yu Hongbing , Gu Yunjie , He Xiangning
Published: August 2013

In this study, a zero voltage switching (ZVS) isolated bidirectional DC/DC converter is proposed for high step‐up and high step‐down conversion systems. In the low voltage side, an interleaved Buck and Boost converter is employed to reduce the current ripple and improve the power level. In the high voltage side, a modified three‐level structure is adopted to bring each power switch sustain half of the high bus voltage, which makes the low voltage rated MOSFETs available for the performance improvement. Two coupled inductors are interleaved in the low voltage side and in series in the high voltage side, which can not only serve as the filter inductors for the current ripple cancellation, but also as the transformer for isolation, which is named as winding‐cross‐coupled inductors. As a result, the magnetic size can be reduced to enhance the power density. ZVS operation is ensured from light load to full load conditions by the advanced pulse width modulation plus phase shift control strategy. The voltage regulation and transferred power are decoupled for easy design and implementation. Finally, a 1.5 kW 48 V/800 V prototype is built to verify the effectiveness of the proposed converter.
Analysis and implementation of a zero‐voltage switching pulse‐width modulation resonant converter
Authors: Lin Bor‐Ren , Hou Bo‐Ren
Published: August 2013

This study presents an interleaved pulse‐width modulation (PWM) converter to achieve the functions of zero‐voltage switching (ZVS) for all power switches and zero‐current switching (ZCS) for rectifier diodes at the secondary side. A three‐level hybrid DC converter is adopted to reduce the voltage stress of power switched at one‐half of the DC bus voltage and automatically balance the two input capacitor voltages. Therefore MOSFETs with 600 V voltage stress can be used at the second stage DC/DC converter after the three‐phase power factor correction circuit. The fixed frequency PWM is used in three‐level PWM resonant converter to regulate output voltage. Since the selected switching frequency is less than the series resonant frequency, MOSFETs can be turned on at ZVS and rectifier diodes can be turned off at ZCS. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. Interleaved PWM scheme is adopted to share load current and further cancel current ripple at output capacitor side. Thus, output capacitance can be reduced. Finally, experiments are provided to verify the effectiveness of the proposed converter.
Improved trench MOS barrier Schottky rectifier by dielectric engineering
Authors: Ying Wang , Likun Xu , Kun Ding
Published: August 2013

An improved trench MOS barrier Schottky (TMBS) rectifier by dielectric engineering variable K TMBS (VK‐TMBS) is proposed and studied by two‐dimensional numerical simulations. The device shows increasing forward current density and reduction in specific on‐resistance (Rsp), as compared with a regular TMBS rectifier. VK‐TMBS attains a breakdown voltage of 140 V, which is larger than that of the original TMBS. The forward voltage drop of TMBS is 0.64 V at 180 A/cm2, and that of VK‐TMBS is 0.59 V. The Rsp of VK‐TMBS is 26.7% smaller than that of the TMBS. The numerical simulation results indicate that the proposed device features high performance with an improved figure of merit.
Comparative study of economic viability of rural electrification using renewable energy resources versus diesel generator option in Saudi Arabia
Authors: Bawah Umar , Addoweesh Khaled E. , Eltamaly Ali M.
Published: August 2013

The objective of this paper is to assess the economic viability of Saudi Arabia's renewable energy resources in electricity production in the rural and remote areas as against the use of diesel generators (DG). The methodology employed is to pick an existing isolated DG electric station for a rural community and assess the levelized cost of energy (LCOE) generated for incremental generation by adding either DG, wind electric conversion system(WECS), or solar Photo Voltaic (PV) electric system. Cost figures are derived from current technology price indices and consultancies studies as contained in the National Renewable Energy Laboratory cost report of November 2012. The existing power station of Addfa in the Southern region is analyzed based on the requirement to increase its current capacity to cater for surrounding smaller communities. An annual extra energy requirement of 4 GWh is to be met by scenarios of using DG, WECS, PV or a hybrid system. Two ownership structures are considered namely a public utility that pays no tax and a private independent power producer (IPP) that pays tax. Both the constant and current LCOE generated are determined for each ownership structure. The results indicate that the WECS is the first investment choice with a constant LCOE of $0.0922/kWh and $0.1090/kWh for the public utility and the IPP, respectively. The DG is the second choice with LCOE of $0.1082/kWh and $0.1175/kWh, the third is a hybrid DG plus WECS with LCOE of $0.1102/kWh and $0.1234/kWh for each ownership structure, respectively. Finally, the PV electric system ranks fourth with LCOE of $0.2791/kWh and $0.3279/kWh, respectively. The results of sensitivity analysis show that these values of LCOE are more sensitive to the initial capital cost and less sensitive to the operation and management costs.
Electron beam coupling to a metamaterial structure
Authors: French David M. , Shiffler Don , Cartwright Keith
Published: August 2013

Microwave metamaterials have shown promise in numerous applications, ranging from strip lines and antennas to metamaterial-based electron beam driven devices. In general, metamaterials allow microwave designers to obtain electromagnetic characteristics not typically available in nature. High Power Microwave (HPM) sources have in the past drawn inspiration from work done in the conventional microwave source community. In this article, the use of metamaterials in an HPM application is considered by using an effective medium model to determine the coupling of an electron beam to a metamaterial structure in a geometry similar to that of a dielectric Cerenkov maser. Use of the effective medium model allows for the analysis of a wide range of parameter space, including the “mu-negative,” “epsilon-negative,” and “double negative” regimes of the metamaterial. The physics of such a system are modeled analytically and by utilizing the particle-in-cell code ICEPIC. For this geometry and effective medium representation, optimum coupling of the electron beam to the metamaterial, and thus the optimum microwave or RF production, occurs in the epsilon negative regime of the metamaterial. Given that HPM tubes have been proposed that utilize a metamaterial, this model provides a rapid method of characterizing a source geometry that can be used to quickly understand the basic physics of such an HPM device.
Effects of point defects and dislocations on spectral phonon transport properties of wurtzite GaN
Authors: Ma Jinlong , Wang XinJiang , Huang Baoling , Luo Xiaobing
Published: August 2013

The spectral phonon transport properties of bulk wurtzite GaN are investigated with the Monte Carlo method on the basis of the first principle calculations. Contributions of different phonon modes to the thermal conductivity with respect to the phonon frequency, mean free path, and wavelength are studied and the effects of point defects and dislocations are discussed. It is found that the effects of the dislocations are negligible when the dislocation concentration is below 1 × 1010 cm−2. The mode analysis shows that the transverse acoustic phonons contribute to the major part of the thermal conductivity from 100 K to 500 K. The point defects and dislocations reduce the thermal conductivity mainly by restraining the transverse modes with little influence on the longitudinal mode. Above 20% thermal conductivity are contributed by phonons with a mean free path larger than 7 μm in pure crystals at near room temperature. For natural crystals with point defects this length will become ever larger, indicating that the size effects should be taken into consideration when the sample characteristic dimension is less than 10 μm. More than 90% thermal conductivity is contributed by phonons with wavelength less than 10 nm for GaN crystals with and without defects, implying that the quantum confinement effect is negligible when the sample characteristic size is larger than 10 nm.
Strain-induced modification in the magnetic properties of Mn5Ge3 thin films
Authors: Dung Dang Duc , Odkhuu Dorj , Thanh Vinh Le , Cheol Hong Soon , Cho Sunglae
Published: August 2013

Epitaxial ferromagnetic Mn5Ge3 thin films were stabilized on GaSb(001) and GaAs(001) substrates using molecular beam epitaxy. Compared to bulk Mn5Ge3 materials, an enhancement of the Curie temperature above 350 K and about 320 K was observed for Mn5Ge3/GaAs(001) and Mn5Ge3/GaSb(001) heterostructures, respectively. The magnetization was found to decrease from 323 to 245 emu/cm3 for films grown on GaSb(001) and GaAs(001). Anomalous Hall effect measurements provide evidence of the strain-induced large spin polarization from density-functional study. Furthermore, our calculated results in bulk Mn5Ge3 under strain indicate that the strain is the origin of different physical properties of Mn5Ge3 grown on different substrates.
Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions
Authors: Torres Juan F. , Komiya Atsuki , Henry Daniel , Maruyama Shigenao
Published: August 2013

We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm2, a variable height of 1–2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg/ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements.
Effective-mass theory of metal-semiconductor contact resistivity
Authors: Harrison Walter A. , Goebel Andreas , Clifton Paul A.
Published: August 2013

We have calculated the contact resistivity for a metal-silicon interface, using an accurate application of effective-mass theory that includes tunneling and quantum reflection. We found that earlier treatments missed an increase in resistivity of a factor of ten due to the mismatch of the wavefunctions at the interface, not included in the WKB approximation. This arises in effective-mass theory for all metal-semiconductor interfaces. We carried out full numerical calculations of the interface resistivity and describe approximations which lead to explicit formulae for the current flow, allowing one to see the dependence of the resistivity on doping, Schottky-barrier height, temperature, crystal orientation, and choice of metal. Finally, we see how the number and energy distribution of transmitted carriers changes as a function of doping density.