bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of Rac1 GTPase promotes leukemia cell chemotherapy resistance, quiescence and niche interaction
Authors: Wang Ji-Ying , Yu Pei , Chen Shuying , Xing Haiyan , Chen Yirui , Wang Min , Tang Kejing , Tian Zheng , Rao Qing , Wang Jianxiang
Published: May 2013

Leukemia stem cells (LSCs) reside in bone marrow niche and receive important signals from the microenvironment that support self‐renewal, maintain quiescence and endow LSC with the ability of chemotherapy resistance. Rac1 belongs to the small GTP‐binding protein superfamily and is implicated in the interactions of hematopoietic progenitors and bone marrow niche. Our previous studies have shown that Rac1 is over‐expressed in leukemia patients and activation of Rac1 GTPase is closely associated with the efficient migration of leukemia cells. However, the potential functions for Rac1 GTPase in LSCs behaviors and in the residence of leukemia cells in niche remain unknown. In this study, by forced expression of a dominant‐negative form of Rac1 GTPase in a CD34+ myeloid leukemia cell line, as well as bone marrow cells from leukemia patients, we show that inactivation of Rac1 GTPase causes impaired migration and enhances chemotherapeutic sensitivity. Inactivation of Rac1 in leukemia cells also lead to a reduction in the frequency of cells in quiescent state and inhibition of homing to bone marrow niche. Gene expression analysis shows that inactivation of Rac1 down‐regulates the expression of several cell intrinsic cell cycle inhibitors such as p21, p27, and p57, as well as the extrinsic molecules that mediated the interaction of LSC with osteoblastic niche. Furthermore, we show that Rac1 mediated the localization in niche is further attributed to the maintenance of quiescence. Our results provide evidence for the critical role of Rac1 GTPase in leukemia cell chemotherapy resistance, quiescence maintenance and the interaction with bone marrow microenvironment.
Femoral Bone Marrow Adiposity and Cortical Bone Cross‐Sectional Areas in Men With Motor Complete Spinal Cord Injury
Authors: Gorgey Ashraf S. , Poarch Hunter J. , Adler Robert A. , Khalil Refka E. , Gater David R.
Published: May 2013

Objectives

To (1) quantify yellow and red bone marrow (BM) and cortical bone cross‐sectional areas (CSAs) of the femur in persons with motor complete spinal cord injury (SCI) compared with healthy able‐bodied control subjects and (2) determine the relationships between yellow and red BM, cortical CSAs, and thigh composition and measurements from dual‐energy x‐ray absorptiometry in men with complete SCI.

Design

Cross‐sectional.

Settings

Clinical hospital and academic settings.

Methods

Eight persons with motor complete SCI and 6 age‐matched healthy control subjects underwent magnetic resonance imaging of both thighs to measure BM adiposity (BMA) and cortical CSA followed by whole‐body dual‐energy x‐ray absorptiometry to measure bone mineral density and body composition for the SCI group.

Results

Cortical bone CSA adjusted to total subperiosteal bone CSA was 1.5‐2 times lower in men with SCI compared with able‐bodied control subjects across the femoral length (P =.003). Yellow BMA CSA was 2‐3 times greater in men with SCI compared with able‐bodied control subjects (P < .0001). Opposite relationships were found between the yellow BMA CSA and cortical bone CSAs in men with SCI (negative association) and able‐bodied control subjects (positive association). Yellow BMA was negatively associated with bone mineral density and bone mineral content and with skeletal muscle CSA and fat‐free mass (P <.05) in men with SCI. Finally, yellow BMA was positively related to thigh subcutaneous adipose tissue.

Conclusions

After SCI, cortical bone CSA becomes thinner and is associated with greater accumulation of yellow BMA. Yellow BMA is associated with changes in bone CSA and bone mass, as well as increased fat mass, after SCI.
Equality, Democracy, Monogamy: Discourses of Canadian Nation Building in the 2010–2011 British Columbia Polygamy Reference
Authors: Sweet Joanna
Published: May 2013

This article examines how the 2010-2011 Reference re s 293, which considered the constitutionality of the polygamy prohibition, contributed to nation building discourses in Canada. A critical discourse analysis demonstrates that traditional views of monogamous marriage remain an important tenet of nation building in Canada. Discourses in the reference portrayed monogamous marriage as a central national institution and as a means of safeguarding women’s equality rights. These discourses, in turn, had racialized consequences for defining Canadian national identity.
« Des menottes sur des pansements » : La décriminalisation de la tentative de suicide dans les tribunaux du Québec entre 1892 et 1972
Authors: Cellard André , Chapdelaine Élise , Corriveau Patrice
Published: May 2013

Depuis l’époque où le suicide était traité par la justice canadienne au même titre qu’un meurtre prémédité jusqu’à la décriminalisation de la tentative de suicide en 1972, l’évolution de la réaction sociale à l’endroit du comportement suicidaire a connu un renversement spectaculaire. À l’aide d’une analyse des procès pour tentative de suicide au Québec entre 1892 et 1972, nous analyserons dans cet article le déplacement de l’interprétation de la tentative de suicide dans les cours de justice. Nous verrons que si le droit et la science médicale s’opposent à l’occasion pour imposer leur explication de la tentative de suicide, ils ne s’excluent pas mutuellement, se renforçant parfois l’un l’autre. En outre, nous constaterons que la réaction sociale au comportement suicidaire avait commencé à migrer du judiciaire au médical au sein même des cours de justice appelées à juger les personnes accusées de tentative de suicide, procédant ainsi de facto à une décriminalisation avant l’heure.
Bisphosphonate-associated osteonecrosis of the external auditory canal
Authors: Wickham N , Crawford A , Carney A S , Goss A N
Published: May 2013

Background:

Osteonecrosis is a benign condition characterised by necrotic exposed bone, and is associated with bisphosphonate use. Osteonecrosis of the external auditory canal is rare, with only a few reported cases.

Method:

Two case reports of temporal bone osteonecrosis are presented.

Results:

A 64-year-old man with a history of immunoglobulin G kappa multiple myeloma developed a right external auditory canal ulcer 6 years after commencement on clodronate. A 72-year-old woman taking alendronate for osteoporosis, initially diagnosed and treated for right-sided otitis externa, was found to have underlying exposed bone in the right external auditory canal, with a computed tomography scan confirming destruction of the temporal bone.

Conclusion:

With increasing use of both oral and intravenous bisphosphonates in the community for benign conditions such as osteoporosis and for malignant conditions such as breast cancer and multiple myeloma, the diagnosis of bisphosphonate-associated osteonecrosis should always be considered in patients with a temporal bone lesion, and a relevant drug history taken.
Children's knowledge ofwh-quantification in Mandarin Chinese
Authors: ZHOU PENG
Published: May 2013

Wh-words in Mandarin Chinese exhibit quantificational variability. Aside from a typical interrogative reading,wh-words can also have an existential indefinite reading or a universal reading. Which reading it is depends on the linguistic environments in which they occur. The present study investigates Mandarin-speaking children's sensitivity to the linguistic environments for the noninterrogative use ofwh-words: the existential reading and the universal reading. The results show that young children exhibited adultlike sensitivity to the licensing environments for the noninterrogative use ofwh-words. Given the difficulty that children may have in using the input data to learn the interpretation ofwh-words and the early emergence of this knowledge, we propose that the licensing mechanism for the noninterrogative use ofwh-words is innate.
Seasonal dynamics of tuberculosis epidemics and implications for multidrug-resistant infection risk assessment
Authors: LIN Y.-J. , LIAO C.-M.
Published: May 2013

Understanding how seasonality shapes the dynamics of tuberculosis (TB) is essential in determining risks of transmission and drug resistance in (sub)tropical regions. We developed a relative fitness-based multidrug-resistant (MDR) TB model incorporated with seasonality and a probabilistic assessment model to assess infection risk in Taiwan regions. The model accurately captures the seasonal transmission and population dynamics of TB incidence during 2006–2008 and MDR TB in high TB burden areas during 2006–2010 in Taiwan. There is ∼3% probability of having exceeded 50% of the population infected attributed to MDR TB. Our model not only provides insight into the understanding of the interactions between seasonal dynamics of TB and environmental factors but is also capable of predicting the seasonal patterns of TB incidence associated with MDR TB infection risk. A better understanding of the mechanisms of TB seasonality will be critical in predicting the impact of public control programmes.
The Entropy of Random-Free Graphons and Properties
Authors: HATAMI HAMED , NORINE SERGUEI
Published: May 2013

Every graphon defines a random graph on any given number n of vertices. It was known that the graphon is random-free if and only if the entropy of this random graph is subquadratic. We prove that for random-free graphons, this entropy can grow as fast as any subquadratic function. However, if the graphon belongs to the closure of a random-free hereditary graph property, then the entropy is O(n log n). We also give a simple construction of a non-step-function random-free graphon for which this entropy is linear, refuting a conjecture of Janson.
Palliative radiotherapy for bone metastases: assessment of factors influencing dose-fractionation schedules at a UK cancer centre
Authors: Bhalla N. , Wong H. , Ibrahim A. , Green J. A.
Published: May 2013

Context

Meta-analyses demonstrate single-fraction radiotherapy to be as effective as multi-fraction treatment in palliating painful bone metastases, although surveys suggest reluctance in prescribing single fractions.

Aims

Assess the factors influencing the choice of dose-fractionation regimen in an unselected population; examine retreatment rates and subsequent skeletal events.

Methods

Data were extracted from case notes for 120 patients treated in 2000 and 2006 in a single centre serving a defined population; analysis used χ2 and Fisher's exact statistical tests.

Results

An 8 Gy fraction was the commonest regimen prescribed (single-fraction delivery rate 53·6%). Tumour site was a significant factor in choice of dose-fractionation schedule. Patients with metastatic breast carcinoma were significantly less likely to receive single-fraction treatment compared with those with metastatic lung carcinoma (year 2000: p = 0·038, 2006: p = 0·001). There was a significantly higher retreatment rate following single-fraction compared with multi-fraction treatment (11% versus 3%). There were two subsequent neural axis compressions and four pathological fractures.

Conclusions

Single-fraction treatment is the commonest regimen but multiple fractions are still frequently delivered. Better prognosis groups appear more likely to receive multi-fraction treatment, possibly to avoid the need for retreatment. Subsequent skeletal events are rare but carry high morbidity when they occur.
What is a factorial trial?
Authors: Cipriani A. , Barbui C.
Published: May 2013

Randomized controlled trials (RCTs), typically, randomize participants to one of two intervention groups. It has been shown, however, that about 25% of RCTs published in the scientific literature randomize participants to three or more treatment groups. These studies are called ‘multi-arm’ trials: there may be, for instance, two or more experimental intervention groups with a common control group, or two control intervention groups such as a placebo group and a standard treatment group. A special case of multi-arm studies are factorial trials, which address two or more intervention comparisons carried out simultaneously, using four or more intervention groups.
Emotional Robots
Authors: Klein Barbara , Gaedt Lone , Cook Glenda
Published: May 2013

As societies age overall, there will necessarily be a significant increase of those over 80 as well as an increase in people with dementia. We know that loneliness increases with old age, and those living with dementia are particularly at risk of social isolation. Also in advanced old age opportunities for sensory stimulation and engagement in pleasurable activities are reduced. The question is which technologies can be used to extend the range of available interventions that can enhance well-being under these circumstances. Emotional robots have been developed for activity and therapeutic purposes. This article explores the experiences with the emotional robot Paro in Denmark, Germany, and the UK, and provides principles of this robot as an activity or as a therapeutic activity.
ATP-dependent regulation of actin monomer–filament equilibrium by cyclase-associated protein and ADF/cofilin
Authors: Nomura Kazumi , Ono Shoichiro
Published: May 2013

CAP (cyclase-associated protein) is a conserved regulator of actin filament dynamics. In the nematode Caenorhabditis elegans, CAS-1 is an isoform of CAP that is expressed in striated muscle and regulates sarcomeric actin assembly. In the present study, we report that CAS-2, a second CAP isoform in C. elegans, attenuates the actin-monomer-sequestering effect of ADF (actin depolymerizing factor)/cofilin to increase the steady-state levels of actin filaments in an ATP-dependent manner. CAS-2 binds to actin monomers without a strong preference for either ATP– or ADP–actin. CAS-2 strongly enhances the exchange of actin-bound nucleotides even in the presence of UNC-60A, a C. elegans ADF/cofilin that inhibits nucleotide exchange. UNC-60A induces the depolymerization of actin filaments and sequesters actin monomers, whereas CAS-2 reverses the monomer-sequestering effect of UNC-60A in the presence of ATP, but not in the presence of only ADP or the absence of ATP or ADP. A 1:100 molar ratio of CAS-2 to UNC-60A is sufficient to increase actin filaments. CAS-2 has two independent actin-binding sites in its N- and C-terminal halves, and the C-terminal half is necessary and sufficient for the observed activities of the full-length CAS-2. These results suggest that CAS-2 (CAP) and UNC-60A (ADF/cofilin) are important in the ATP-dependent regulation of the actin monomer–filament equilibrium.
Automatic face image annotation based on a single template with constrained warping deformation
Authors: Yang Yang , Liu Yuehu , Liu Jianyi
Published: May 2013

In this study, an automatic face image annotation method is proposed by aligning faces with different expressions to an annotated neutral face. This work is useful in reducing tedious manual work for labelling image data in large databases. However, it is challenging because of the appearance variations caused by non‐rigid face deformations under various expressions. Unlike some conventional approaches acquiring sufficient image templates to model the query appearance, only a single given template is necessary for the proposed method. The authors address the problem through dense image alignment. Specifically, image warping in the alignment process is constrained by prior knowledge about facial shape deformation. The proposed method is independent of the appearance model, and is available for unseen faces. In addition, to initialise warping parameters, the authors present a robust patch‐based estimation method. Context information for feature points is carefully modelled to propagate the searching path for local patch matching. The face annotation experiments are performed on some large expressions, with noisy image qualities and in low image resolutions. Comparison results with conventional methods demonstrate the proposed method's superiority on both accuracy and robustness.
Subsynchronous resonance in a series‐compensated Great Britain transmission network
Authors: Ugalde‐Loo Carlos E. , Ekanayake Janaka B. , Jenkins Nick
Published: May 2013

In Great Britain (GB), increased levels of wind penetration require substantial reinforcements for transmitting power from Scotland to England. In the National Grid 2020 Vision, offshore and onshore infrastructure reinforcements have been proposed, the inland reinforcement including series compensation (fixed capacitors). A possible detrimental effect of onshore series compensation is the appearance of subsynchronous resonance (SSR). SSR caused by the interaction between turbogenerators and a series‐compensated electrical network is studied. A three‐machine system representing the onshore‐reinforced mainland GB system is examined. The effect of series compensation equipment on SSR is assessed. The effects of quadrature boosters in the network are also investigated. Time‐domain simulations are carried out in power systems computed aided design (PSCAD) whereas system modelling and eigenvalue analyses are conducted in MATLAB.
Flexible load shedding strategy considering real‐time dynamic thermal line rating
Authors: Sun Wei‐Qing , Zhang Yan , Wang Cheng‐Min , Song Ping
Published: May 2013

In recent years, real‐time dynamic thermal line rating (RT‐DTLR) technology has been developed and implemented in operations to improve transmission line capacity, so that congestion costs and/or risk of load shedding can be reduced. Power systems obviously benefit from this technology but also bear the risks because of thermal overload of transmission lines. To involve RT‐DTLR technology into conventional power system load shedding strategies, this study explains the concept of flexibility in power system analysis, expresses transmission line capacity constraints into flexible forms and proposes a flexible load shedding strategy considering RT‐DTLR. The two sub‐objective functions, representing load shedding quantity and system risk increment, are normalised and expressed as the confidence levels from system security consideration and load loss consideration, respectively. The proposed method takes advantage of both the advanced hardware and software technologies in smart grids and the simulation results showed that it can trade off the benefits and risks brought about by RT‐DTLR in load shedding.
New controlled switching approach for limitation of transmission line switching overvoltages
Authors: Seyedi Heresh , Tanhaeidilmaghani Shahab
Published: May 2013

In this study, a new controlled switching approach is proposed. This method is applied to the controlled closing of high voltage uncompensated transmission lines. The new approach is a developed version of conventional zero‐crossing controlled switching approach. Performance of the new approach is evaluated and compared with the conventional controlled switching approach, using the electro‐magnetic transients program. The results of simulation studies confirm the advantages of new approach over existing methods.
Voltage stability analysis of unbalanced distribution systems using backward/forward sweep load‐flow analysis method with secant predictor
Authors: Abdel‐Akher Mamdouh
Published: May 2013

This study presents a new method for tracing voltage power curves in unbalanced radial distribution power systems. The proposed method starts with the base case loading conditions and leading to the maximum loading point (MLP) whereas no ill‐conditioning problems were detected. The calculation is performed by first‐order polynomial secant predictor and the solution is corrected using the backward/forward radial power‐flow method. Adaptive stepwise control is implemented to improve the overall solution process and reduce the number of the calculated points along the traced curve. The results calculated using the developed method are for both a 33‐bus radial feeder and the unbalanced IEEE 13‐node and IEEE123‐node feeders. The results show that the developed method accurately traces the voltage power curves up to MLP. Comprehensive analysis on unbalanced scenarios shows that load unbalance greatly affects the stability limit of the study system.
Data size reduction with symbolic aggregate approximation for electrical load pattern grouping
Authors: Notaristefano Antonio , Chicco Gianfranco , Piglione Federico
Published: May 2013

Data size reduction techniques may be helpful in the process of categorising the electrical load consumption patterns on the basis of their shape. Starting from a macro‐class of consumers defined according to certain general criteria on the type of consumers and the period of the year or week, the representative load pattern (RLP) of each consumer can be built by considering the data points in the time domain or a reduced number of features. This study exploits the effects of using the symbolic aggregate approximation (SAX) method to form the reduced set of features. The portion of the time–amplitude plane defining the RLP is partitioned into sub‐portions on the basis of the characteristics of the whole data set. A specific partitioning of the time axis is proposed on the basis of the cumulative distribution function of the RLP variations in time. Each RLP is then coded according to the SAX principles. The resulting codes are then used into a hierarchical clustering procedure. The validity of the clustering results obtained by using the SAX data representation with the proposed non‐uniform partitioning of the time axis is presented and discussed, including comparisons with the results obtained from other data size reduction techniques.
Hybrid converter with ac side cascaded H‐bridge cells against H‐bridge alternative arm modular multilevel converter: steady‐state and dynamic performance
Authors: Adam Grain Philip , Finney Stephen Jon , Williams Barry Wayne
Published: May 2013

This study explorers the operating principles of the hybrid converter with ac side cascaded H‐bridge cells and the H‐bridge alternative arm modular multilevel converter, where the main objective is to compare their steady‐state and transient performance. This comparison focuses on steady‐state aspects such as active and reactive power control and semi‐conductor losses and the transient performance of these converters during ac and dc network faults. To facilitate this comparison, detailed switch models of both high‐voltage direct current (HVDC) converters are developed and simulated in Matlab‐Simulink. The major outcomes are discussed and strengths and weakness associated with each converter are highlighted.
Analytical study of the frequency‐dependent earth conduction effects on underground power cables
Authors: Papadopoulos Theofilos A. , Chrysochos Andreas I. , Papagiannis Grigoris K.
Published: May 2013

In electromagnetic transient analysis, one major issue is the influence of the imperfect earth on the propagation characteristics of transmission line conductors. Extensive research has been published for overhead lines, whereas the corresponding literature for underground cables is significantly less. Recently, new expressions for the calculation of the ground impedance and admittance have been proposed for the homogeneous and the stratified earth case. However, most transient simulation programs still use approximate earth representations. Scope of this study is to compare the proposed formulation with the corresponding approximations, in order to introduce a frequency limit for the use of the approximate earth models, sas well as criteria that dictate the use of a stratified earth model. The resulting propagation characteristics are used in transient calculations, in order to validate the effect of the differences by the various approaches and the need to include a more accurate model in the simulation of underground cable transients.
Enhancement of dark and low‐contrast images using dynamic stochastic resonance
Authors: Chouhan Rajlaxmi , Jha Rajib Kumar , Biswas Prabir Kumar
Published: May 2013

In this study, a dynamic stochastic resonance (DSR)‐based technique in spatial domain has been proposed for the enhancement of dark‐ and low‐contrast images. Stochastic resonance (SR) is a phenomenon in which the performance of a system (low‐contrast image) can be improved by addition of noise. However, in the proposed work, the internal noise of an image has been utilised to produce a noise‐induced transition of a dark image from a state of low contrast to that of high contrast. DSR is applied in an iterative fashion by correlating the bistable system parameters of a double‐well potential with the intensity values of a low‐contrast image. Optimum output is ensured by adaptive computation of performance metrics – relative contrast enhancement factor (F), perceptual quality measures and colour enhancement factor. When compared with the existing enhancement techniques such as adaptive histogram equalisation, gamma correction, single‐scale retinex, multi‐scale retinex, modified high‐pass filtering, edge‐preserving multi‐scale decomposition and automatic controls of popular imaging tools, the proposed technique gives significant performance in terms of contrast and colour enhancement as well as perceptual quality. Comparison with a spatial domain SR‐based technique has also been illustrated.
Zero‐quantised discrete cosine transform coefficients prediction technique for intra‐frame video encoding
Authors: Jridi Maher , Kumar Meher Pramod , Alfalou Ayman
Published: May 2013

One promising solution to reduce the computational complexity of discrete cosine transform (DCT) is to identify the redundant computations and to get rid of them. In this study, the authors present a new method to predict zero‐quantised DCT coefficients for efficient implementation of intra‐frame video encoding by identifying such redundant computations. Traditional methods use the Gaussian statistical model of residual pixels to predict all‐zero or partial‐zero blocks. The proposed method is based on two key ideas. At first, the bounds of DCT coefficients are derived from the intermediate signals of the Loeffler DCT algorithm instead of calculating the sum of absolute difference (SAD) of residual pixels. The sufficiency conditions are then suitably chosen to predict the zero‐quantised coefficients to reduce the arithmetic complexity without degrading the video quality. Simulation results are found to validate the analytical model and show that the proposed prediction eliminates more redundant computations than the existing methods. Moreover, the authors have derived a pipelined VLSI architecture of the proposed prediction scheme which offers a saving of more than 63 and 91% of multiplications of the second stage of one‐dimensional DCT for high and low bit‐rate intra‐video encoding, respectively.
Multi‐sensor tracking and lane estimation in highly automated vehicles
Authors: Thomaidis George , Kotsiourou Christina , Grubb Grant , Lytrivis Panagiotis , Karaseitanidis Giannis , Amditis Angelos
Published: May 2013

Highly automated driving brings the next generation of driver assistance systems for increased safety and comfort. Automated vehicles execute part of the driving tasks whereas the driver is still involved in controlling the vehicle. Higher degrees of automation pose more strict requirements for perception systems in terms of performance and robustness. The HAVEit EU project investigates the application and validation of highly automated vehicle systems, technologies that are going to have a great impact on transport of the future. The purpose of this study is to examine in detail the problem of multi‐sensor fusion for target tracking and road environment perception in an automated vehicle application. A series of algorithms are described for solving the data association and track estimation problems, both at sensor and central levels. The techniques that are used for multi‐sensor lane estimation are also presented. Finally, results from simulated and real‐time tests are given to demonstrate the performance of the algorithm.
Modelling correlation degree between two adjacent signalised intersections for dynamic subarea partition
Authors: Bie Yiming , Wang Dianhai , Qu Xiaobo
Published: May 2013

Correlation degree between adjacent signalised intersections is considered as the most important component in subarea partition algorithm. In this study, contributing factors for subarea partition are selected by taking into consideration the differences with respect to cycle lengths, link length and path flow between upstream and downstream coordinated phases. Their impacts on performance index of subarea partition are further studied using numerical experiments. The study then proceeds to propose a correlation degree index (CI) as an alternative for the performance index in order to reduce the computational complexity. The relationship between CI and the contributing factors is established to predict the correlation degree. Finally, the model is validated using field survey data.
Using VISSIM simulation model and Surrogate Safety Assessment Model for estimating field measured traffic conflicts at freeway merge areas
Authors: Fan Rong , Yu Hao , Liu Pan , Wang Wei
Published: May 2013

A procedure was developed for using Surrogate Safety Assessment Model (SSAM) and VISSIM for safety assessment at freeway merge areas. The simulated conflicts generated by the VISSIM simulation models and identified by the SSAM approach to those measured in the field using traditional traffic conflicts techniques. Of particular interest was to identify if the consistency between the simulated and the field‐measured traffic conflicts could be improved by calibrating the VISSIM simulation models and adjusting the threshold values in SSAM. A two‐stage procedure was proposed to calibrate and validate the VISSIM simulation models. The transferability of the calibrated simulation models was also tested. It was found that the two‐stage calibration procedure reduced the mean absolute prevent error (MAPE) for total conflicts from 78.1 to 33.4%. More specifically, the MAPE value was reduced from 76.6 to 33.5% for the rear‐end conflicts, and from 79.5 to 35.8% for the lane‐change conflicts. Linear regression models and the Spearman rank correlation coefficient were also developed to study the relationship between the simulated and the observed conflicts. Data analysis results showed that there was a reasonable consistency between the simulated and the observed conflicts.
Agent‐based approach for crowded pedestrian evacuation simulation
Authors: Ben Xianye , Huang Xifa , Zhuang Zhaoyi , Yan Rui , Xu Sen
Published: May 2013

Pedestrian evacuation has long been a vital safety concern for any large indoor facility, for example, gymnasium or stadium. To efficiently simulate crowded pedestrian evacuation, an agent‐based modelling approach in the cellular automata (CA) environment is proposed in this study. Different from a stand‐alone CA method which roughly describes the external environment, the proposed agent‐based modelling approach can describe individual behaviour more accurately. In order to verify the crowded pedestrian evacuation simulation and reflect the behaviour of pedestrian crowds’ evacuation, this study simulates four evacuation scenarios as follows: (i) an ordered activity area with no obstacles, (ii) an unordered activity area with no obstacles, (iii) an ordered activity area with obstacles and (iv) an unordered activity area with obstacles. The effects of the parameters on the evacuation simulation process and the effects of maximal endurance capability on the number of casualties are also analysed. Furthermore, the order of evacuation of pedestrians with different competitive capabilities is estimated. The simulation results show that the proposed modelling framework, principles and methods are effective, and the model has a strong capability to describe, represent and explain the reality of evacuation.
Dual‐rate background subtraction approach for estimating traffic queue parameters in urban scenes
Authors: Milla Jose M. , Toral Sergio L. , Vargas Manuel , Barrero Federico J.
Published: May 2013

This study proposes traffic queue‐parameter estimation based on background subtraction, by means of an appropriate combination of two background models: a short‐term model, very sensitive to moving vehicles, and a long‐term model capable of retaining as foreground temporarily stopped vehicles at intersections or traffic lights. Experimental results in typical urban scenes demonstrate the suitability of the proposed approach. Its main advantage is the low computational cost, avoiding specific motion detection algorithms or post‐processing operations after foreground vehicle detection.
Analysis and design of a sliding‐mode strategy for start‐up control and voltage regulation in a buck converter
Authors: Martínez‐Salamero Luis , García Germain , Orellana Marcos , Lahore Cyril , Estibals Bruno , Alonso Corinne , Carrejo Carlos Eduardo
Published: May 2013

This study presents the analysis and design of a sliding‐mode control of a buck converter operating in continuous conduction mode that minimises the energy during start‐up and provides output voltage regulation in front of input voltage perturbations and load disturbances. A linear combination of inductor current and capacitor voltage errors with respect to their corresponding equilibrium values is analysed as a switching surface. A linear matrix inequalities (LMI)‐based analysis to obtain optimum coefficients of the linear combination reveals that the best compromise between inrush current and output response rapidity is the current control given by the switching surface S(x) = iL − IE, where IE is the current coordinate of the equilibrium point. This surface is proposed for start‐up and for rejecting input voltage perturbations, because it is demonstrated that the current control is inherently insensitive to input voltage variations. Output voltage regulation in front of load perturbations or input voltage variations is achieved once the converter is in a steady state by modifying S(x) with the insertion of a PI‐correcting network. The resulting controller is implemented analogically and employs two switching surfaces, that is, one surface for start‐up and another one for output voltage regulation. The theoretical predictions are verified by means of simulation and experimental results.
Analysis and implementation of a new soft switching DC/DC PWM converter
Authors: Lin Bor‐Ren , Chien Chih‐Cheng
Published: May 2013

This study presents a new DC/DC converter with series‐connected transformers to achieve zero voltage switching (ZVS) for power switches, less transformer secondary winding and partial ripple current cancellation. Two three‐level circuits using the same active switches are operated with interleaved half switching cycle. The voltage stress of all switches is clamped at Vin/2. The transformers secondary windings are connected in series to balance the primary side currents. The current‐doubler rectifier is adopted on the output side. Thus, the output inductor ripple currents can be partially cancelled each other and the resultant ripple current at the output capacitor is reduced compared with the output ripple current of the centre‐tapped rectifier topology. Based on the resonant behaviour by the output capacitance of active switches and the leakage inductance (or external inductance), all power switches are turned on at ZVS. Laboratory experiments with a 1 kW prototype, verifying the effectiveness of the proposed converter, are described.
Multilevel inverter topology based on series connected switched sources
Authors: Gupta Krishna Kumar , Jain Shailendra
Published: May 2013

A new topology for multilevel DC–AC conversion is presented in this study. It consists of isolated symmetric input DC sources alternately connected in opposite polarities through power switches. The structure allows synthesis of multilevel waveform using reduced number of power switches as compared to the classical topologies. The working principle of the proposed topology is explained with the help of a single‐phase five‐level inverter. Simulation studies are carried out in MATLAB/Simulink environment and experimental validations are obtained on a laboratory prototype. An exhaustive comparison of the proposed topology against the classical cascaded H‐bridge topology indicates reduction in number of power switches, losses, installation area and converter cost.
Two‐channel control of three‐phase inverters for distortion reduction
Authors: Padmavathi Lakshmanan , Janakiraman Panapakkam Arumugam
Published: May 2013

A new two‐phase, independent control strategy for three‐phase three‐wire static inverters to reduce unbalance in output voltage is proposed. The three‐phase voltage and current signals are processed by the ideal Clarke transform block to yield two single‐phase signals, which contain information regarding unbalance and harmonics which may be present in the three‐phase signals. If the two single‐phase voltage signals could be controlled so that they become equal in magnitude with a phase shift of 90° (ideal alpha beta signals), then the corresponding terminal three‐phase voltage signals would become balanced. Single‐phase observers are employed to control the fundamental components in the two identical d‐q frames created. Simultaneously, when the harmonics are eliminated in the two single‐phase channels, the corresponding three‐phase voltage signals would become distortion free. Feed‐forward compensation can be carried out using the equivalent series‐impedance parameters, estimated on‐line using a simple identification algorithm. This procedure is not sensitive to frequency and can take care of the voltage drop in the distribution transformer. The simulation and experimental results for a field programmable gate array (FPGA) controlled 60 V table top inverter fabricated in the laboratory are provided.
Exact analysis and design of zero voltage switching operation for class E inverter with circuit components varying
Authors: Li Yen‐Fang
Published: May 2013

In this study, an exact circuit model for the class E inverter is proposed to analyse the circuit behaviour in frequency domain without mathematical assumptions. Through this model, a close form formula is proposed to solve the load current and drain–source end voltage of metal oxide semiconductor field effect transistor at switching instants in steady‐state instead of complicated numerical iteration. With these current and voltage at switching instants, the load current can be expressed with exact function and evaluated. By means of the proposed formula and current expression, the optimal and suboptimal conditions for the zero voltage switching (ZVS) operation have been expressed in terms of the shifting angle of load current with respect to drain–source voltage. Further, the ZVS and non‐ZVS operation regions can be marked via calculating the shifting angle and optimal shifting angle, which are proposed in the study. To demonstrate the proposed formulas and ZVS conditions, some examples are given to examine the analysis and ZVS drifting behaviour with comparing of calculation, simulation and experiment. Good agreements from the illustrated examples have given the verification of the analysis and design for the class E inverter.
High‐efficiency parallel quasi‐resonant current source inverter featuring SiC metal‐oxide semiconductor field‐effect transistors for induction heating systems with coupled inductors
Authors: Sarnago Hector , Lucia Oscar , Mediano Arturo , Burdio Jose M.
Published: May 2013

Efficiency and reliability are the two key design parameters when designing induction heating (IH) systems. A parallel quasi‐resonant current source inverter (CSI) is proposed to optimise the converter efficiency and to take advantage of the inherent protection of CSIs. The proposed converter uses a coupled inductor, already present in the system to produce the IH phenomena, in order to reduce the current through the power devices and to ensure zero voltage switching during turn on and turn off transitions. As a consequence, the proposed converter significantly improves the IH system efficiency. An analytical model is proposed to study both operating conditions and efficiency. In addition to this, a 2.2‐kW prototype has been designed and implemented to verify the proposed model and to prove the converter feasibility. To utilise the converter at most, SiC metal‐oxide semiconductor field‐effect transistors have been used, obtaining up to 98.6% efficiency at resonant conditions.
Fast control strategy for stabilising fixed‐speed induction‐generator‐based wind turbines in an islanded distributed system
Authors: Wei Mu , Chen Z.
Published: May 2013

Distributed generation systems (DGS) with fixed‐speed induction‐generator‐based wind turbines (FSWT) are sensitive and vulnerable to voltage disturbances and reactive power deficiency. Consequently, the control and protection strategies for such a DGS should be prompt and precise to avoid undesired wind generator cutting off. This study investigates and analyses the dynamic characteristics of an FSWT to reveal the behaviours of an FSWT under disturbances. Then a fast control strategy for stabilising an islanded DGS is proposed. The main contributions of the control strategy are: the total amount of reactive power compensation and load shedding may be determined precisely; all the operation execution points may be decided accurately to improve DGS stability. Furthermore, the implementation of the fast control strategy is also discussed. A case study is presented to demonstrate the effectiveness of the proposed method.
Cooperative converter for improving the performance of grid‐connected photovoltaic power plants
Authors: Miñambres‐Marcos Víctor , Romero‐Cadaval Enrique , Guerrero‐Martínez Miguel Ángel , Milanés‐Montero María Isabel
Published: May 2013

This study presents a new single‐phase topology for the power injection system of a grid‐connected photovoltaic generation system that is based on the parallel association of two voltage‐source inverters: one is a three‐level inverter with clamping diodes (or neutral point clamped) with a low switching frequency strategy (equal to the grid frequency) and the other is a two‐level inverter which operates with a current hysteresis band strategy and an usual switching frequency (5–20 kHz). The main advantage of the proposed topology is to optimise the system design, allowing high power injection with a significant reduction of system losses (mainly switching losses) and achieving an increase of the energy injected into the grid. The performance of the proposed topology and its control algorithms are tested and validated using a laboratory prototype.
Optimisation tools for large permanent magnet generators for direct drive wind turbines
Authors: Zavvos Aristeidis , McDonald Alasdair , Mueller Markus
Published: May 2013

As wind turbines increase in power output, their size and mass grows as well. The development of offshore wind farms demands higher reliability to minimise the maintenance cost. Direct drive electrical generators offer a reliable alternative to conventional doubly fed induction generator machines since they omit the gearbox from the drive train. A fundamental issue for these generators is their large size which makes them difficult to manufacture, transfer and assemble. This study will investigate an analytical and a finite element analysis optimisation technique developed for minimising the structural mass of a direct drive generator. Both tools seek to minimise the mass of three different permanent magnet direct drive (PMDD) generators with 5 MW nominal power output while keeping a set of deflection criteria under limitations. The results indicate that the structural mass of a 5 MW PMDD generator can be effectively reduced with the help of these design tools. The research concludes in favour of a specific transversal flux PMDD topology, of which the electromagnetic topology benefits the structural design.
Interaction of the dynamics of doubly fed wind generators with power system electromechanical oscillations
Authors: Jafarian Mohammad , Ranjbar Ali Mohammad
Published: May 2013

The interaction of the dynamics of doubly fed wind generators with the electromechanical mode of nearby synchronous generators (SGs) can affect the small signal stability of power systems with high penetration levels of wind power. In this study, a novel approach is developed to investigate these interactions and their impact on the damping of power system oscillations. In this approach it is not necessary to model the dynamic behaviour of system SGs and only the frequencies of system oscillations are important. This approach is based on the sensitivity of SGs electromechanical eigenvalue with respect to variations in the Jacobian matrix of power system. By applying this approach to a test system, two of the wind farm (WF) modes are identified to have interaction with the SG electromechanical mode, one has detrimental and the other has beneficial impact, which decrease the damping of system electromechanical oscillation altogether. By using the modal analysis technique, the WF controller gains are retuned to shift the detrimental and beneficial interacting modes away and towards the frequency of system oscillation, respectively. It is shown that this results in the improvement of system oscillation damping whereas the dynamic performance of WF remains satisfactory.
Feasibility study of photovoltaic powered reverse osmosis and pumping plant configurations
Authors: Carvalho Paulo C. M. , Carvalho Lucas A. D. , Hiluy Filho João J. , Oliveira Renato S. H.
Published: May 2013

The present study has as main goal to make a technical and financial feasibility study of a photovoltaic powered reverse osmosis (PV–RO) and pumping system developed at the Renewable Energies Laboratory, Federal University of Ceará, in Fortaleza, Brazil, with the aim to supply drinking water for human consumption at low cost from brackish water in semi‐arid areas. The research intends to determine parameters like drinking water production, specific energy consumption and specific costs, as well as the optimal system size regarding financial viability. The used configurations allow comparing two strategies: with and without batteries. The research was conducted with different levels of brackish water salinity, to identify a viability limit. The technical and financial analysis show that the unit produces satisfactory and competitive results, comparing with different plants in the world, concluding that, assuming a 2748 mg/l brackish water well, the configuration that brings the best cost/benefit is the no battery plant using 3 PV panels, which provides a daily production of 175 l of drinking water at 324.60 mg/l, with a specific consumption of 3.12 kWh/m3 and presenting a competitive specific cost of 10.32 US$/m3.
Controlled synthesis of buried delta-layers of Ag nanocrystals for near-field plasmonic effects on free surfaces
Authors: Benzo Patrizio , Bonafos Caroline , Bayle Maxime , Carles Robert , Cattaneo Laura , Farcau Cosmin , Benassayag Gérard , Pécassou Béatrice , Muller Dominique
Published: May 2013

We report on the shallow synthesis by low energy ion implantation of delta-layers of Ag nanocrystals in SiO2 at few nanometers under its free surface. Transmission electron microscopy observations, ballistic simulations, and reflectance measurements are coupled to define the conditions for which the synthesis is fully controlled and when, on the contrary, this control is lost. We show that low dose implantation leads to the formation of a well-defined single plane of nanocrystals, while for larger doses, sputtering and diffusion effects limit the control of the size, position, and volume amount of these nanocrystals. This paper provides the experimental evidence of the incorporated dose saturation predicted in the literature when implanting metal ions at high doses in glass matrices. Its consequences on the particle population and the plasmonic optical response of the composite layers are carefully analyzed. We show here that this saturation phenomenon is underestimated in standard simulation predictions due to diffusion of metal atoms towards the surface and nanocrystal nucleation during the implantation process.