bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical study of ion doping and substrate effects in antiferroelectric thin films
Authors: Wesselinowa Julia M. , Apostolov A. T. , Trimper Steffen 
Published: February 2011

AbstractAntiferroelectric (AFE) thin films are studied under the influence of doping ions and the presence of substrates. Both induce a strong changing of the polarization and lead to a shift of the phase transition temperature. These effects can be understood within the Ising model in a transverse field with additional four spin interaction. To that aim different exchange interactions between the doping ions and the host ions as well as between the AFE thin film and the substrate are assumed. Using a Green's function technique the microscopic spectrum of the elementary excitation is calculated. From here we find that the transition temperature and the polarization is strongly influenced by the magnitude and the kind of stress, tensile or compressive. The competition between surface and substrate effects is discussed.
Substrate induced bandgap in multilayer epitaxial graphene on the 4H‐SiC ($000{\bar {1}}$) surface
Authors: Chen Mohan , Sun Wenlu , Guo Guang‐Can , He Lixin 
Published: February 2011

AbstractWe have investigated the electronic structures of graphene layers epitaxially grown on the 4H‐SiC ($000{\bar {1}}$) surface up to six layers by using first‐principles methods. The graphene layers grown on an ideal SiC interface are found to be p doped, whereas, those grown on a C‐deficient SiC interface are found to be n doped. We discuss the interlayer screening effects from the positions of the Fermi levels of each layer in our simulation. Interestingly, we find that the substrate may induce small atomic distortions in the graphene layers which could open about a 10 meV band gap in each graphene layer.
Avalanche‐like electric‐field‐induced photocurrent gain in resonant tunneling hydrogenated nanocrystalline silicon system
Authors: Chen Jing , Lu Jia Jia , Zhang Rong , Liu Yong Sheng , Shen Wen Zhong 
Published: February 2011

AbstractBy introducing photogeneration into the rate equation of the two‐energy‐level system, we obtain the photocurrent gain effect theoretically in hydrogenated nanocrystalline silicon (nc‐Si:H) structure, which is consistent with the reported experimental data. To understand the carrier‐transport characteristics in such nanostructures, the time‐dependent distributions of the electric field and photocurrent inside nc‐Si:H structure at different absorption coefficients have been calculated. The result shows that the occurrence of photocurrent enhancement is accompanied by an avalanche‐like phenomenon of the electric field during its dynamic process to achieve equilibrium. Further investigation reveals that the physical nature behind this photocurrent gain lies in the existence of the resonant tunneling inside the nc‐Si:H structure.
Investigation of modified p‐n junctions in CSG solar cells
Authors: Lausch Dominik , Werner Martina , Naumann Volker , Schneider Jens , Hagendorf Christian 
Published: February 2011

AbstractIn this paper a method for studying p‐n junctions is described. Different electron and ion beam charactersiation methods are introduced to determine the p‐n‐junction position using two different examples from Crystalline Silicon on Glass (CSG) thin film technology. In a first example lateral and cross section electron beam induced current (EBIC) measurements revealed that oxygen rich columnar growth at textured substrates disturbs strongly the p‐n junction. In a second example diffusion from glass specimen is identified by TOF‐SIMS to influencing the electrical and structural characteristics of the thin Si layer are responsible for the modified p‐n junction. A model describing the formation of both defect structures is introduced. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of the crystal features of mc‐Si PV cells by laser beam induced current (LBIC)
Authors: Moralejo B. , Hortelano V. , González M. A. , Martínez O. , Jiménez J. , Ponce‐Alcántara S. , Parra V. 
Published: February 2011

AbstractIn this work we present LBIC measurements of a set of commercial multicrystalline silicon samples manufac‐tured by different suppliers. The LBIC measurements were obtained with a home‐made system, using several excitation wavelengths, equipped with an autofocus system, and controlling the reflected light. This system keeps constant the distance between the microscope objective and the sample, despite the bowing and the surface roughness characteristic of this type of samples. For the calculation of the Leff maps one needs to consider the distribution of the reflected light, which the maps usually show contrasts corresponding to the different grain orientations. The LBIC maps present networks of dark lines, corresponding to regions with high carrier capture rates. The dark line network does not necessarily match the grain boundaries (GB) revealed in the optical images, but many of them are intragarin defects. The trapping activity of the GB is known to depend on the GB angle. Usually, small angle GBs are decorated with defects that make them electrically active, while the large angles GBs are less decorated, and present a weak electrical activity. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dislocations and cracks at Vickers indentations in GaN and GaAs bulk crystals
Authors: Ratschinski I. , Leipner H. S. , Heyroth F. , Fränzel W. , Hammer R. , Jurisch M. 
Published: February 2011

AbstractThe (0001) surface of GaN single crystals and ($ \bar 1 \bar 1 \bar 1 $)‐oriented GaAs wafers have been deformed using a Vickers indenter with two different orientations at room temperature. Dislocations and cracks at the indentations were observed by means of scanning electron microscopy, cathodoluminescence, light microscopy and transmission electron microscopy. Between dislocations, cracks and the orientation of the indenter, geometrical relations could be found.The GaN and GaAs samples were indented with loads in the range of 0.02 N to 4.90 N and 0.02 N to 1.00 N, respectively. In both materials, the dislocation rosettes correspond to the symmetry of the indented surface. In (0001) GaN, the crack system is predominantly determined by the symmetry and orientation of the indenter. In contrast, the crack formation in ($ \bar 1 \bar 1 \bar 1 $) GaAs is determined by the symmetry of the crystal and consists of different types of radial cracks with different probabilities. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessing the capabilities and limitations of cathodoluminescence microscopy to investigate the optical properties of individual nanostructures
Authors: Stowe David 
Published: February 2011

AbstractUnderstanding the optical properties of individual semiconductor nanostructures is an important step in enabling novel optoelectronic components. The capabilities and limitations of cathodoluminescence microscopy in the scanning and scanning transmission electron microscope in correlating the physical and optical properties of quantum wells, wires and dots is evaluated. In particular the importance of specimen‐electron beam interactions and experimental conditions in maximising spatial resolution are discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of low energy electron irradiation on optical properties of InGaN/GaN light emitting structures
Authors: Vergeles P. S. , Shmidt N. M. , Yakimov E. E. , Yakimov E. B. 
Published: February 2011

AbstractThe effect of low energy e‐beam irradiation on the InGaN related cathodoluminescence in the MQW InGaN/GaN LED structures with different number of quantum wells has been studied. It is shown that the e‐beam exposure leads to an increase of emission intensity and to a formation of new blue‐shifted emission bands. It is shown that the changes in the optical properties are determined by the excess carrier injection. The changes observed were associated with the local changes of InGaN content due to In and/or Ga diffusion stimulated by the excess carrier recombination (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Origin of the Parry arc
Authors: Westbrook C. D. 
Published: February 2011

AbstractLaboratory experiments to determine the preferred orientation of free‐falling hexagonal prisms were performed at Reynolds numbers appropriate to falling ice crystals in the atmosphere. Hexagonal plates orient with their c axis vertical for aspect ratios < 0.9, whilst hexagonal columns fall with their c axis horizontal. A secondary alignment is also observed: regular hexagonal columns fall preferentially with two prism facets aligned vertically and not horizontally – the latter scenario was previously assumed to be responsible for the rare Parry arc. However, if the column is made scalene in its cross‐section, it can orient such that a pair of prism facets is horizontal. This finding indicates that the development of scalene crystals may be key to the production of certain ice‐crystal optical phenomena. Copyright © 2011 Royal Meteorological Society
GRADIENTS IN THE BIOPHYSICAL STRUCTURE OF URBAN RIVERS AND THEIR ASSOCIATION WITH RIVER CHANNEL ENGINEERING
Authors: Gurnell A. M. , Shuker L. , Lee M. , Boitsidis A. J. 
Published: February 2011

ABSTRACTUrban rivers are often engineered to increase flood conveyance and stabilize channel size and position. This paper analyses habitat surveys of 180 urban river stretches of differing engineering type from four river basins (river Tame, West Midlands, UK; tributaries of the lower river Thames, UK; river Botic, Prague, Czech Republic; river Emscher, North‐Rhine Westphalia, Germany). Kruskal–Wallis tests identify significant differences in extent and/or frequency of flow types, bank and bed physical habitats, and vegetation characteristics associated with different styles of engineering. Principal Components Analysis identifies four key environmental gradients in the data set: sediment supply and retention; extent and diversity of in‐channel vegetation and riparian trees; bed and bank sediment calibre; flow type energy and complexity. These gradients discriminate stretches of differing planform, cross section and reinforcement and are significantly correlated with indices of degree and type of bank and bed reinforcement, pollution and presence of alien nuisance plant species. The analytical results illustrate statistically significant associations between different styles and levels of engineering intervention and the number and nature of physical habitats present in urban rivers. The results provide a basis for filtering sites for potential remedial measures prior to site‐specific surveys and modelling, for comparing sites and for tracking trajectories of change at sites that are subject to changes in channel engineering. They provide evidence that river condition and degree of engineering are not inversely related in a simple linear way, and that engineering of urban river channels, in the form of mixed, patchy reinforcement can contribute a great deal to habitat diversity where other controls on flow heterogeneity are more difficult to manipulate. Copyright © 2011 John Wiley & Sons, Ltd.
Science achievement of English language learners in urban elementary schools: Fourth‐grade student achievement results from a professional development intervention
Authors: Santau Alexandra O. , Maerten‐Rivera Jaime L. , Huggins Anne Corinne 
Published: February 2011

AbstractAs part of a 5‐year professional development intervention aimed at improving science and literacy achievement of English language learning (ELL) students in urban elementary schools, this study examined fourth‐grade students' science achievement across a 3‐year (2005–2008) implementation of our professional development intervention consisting of curriculum units and teacher workshops. Analyses were conducted with 1,758 students at six schools that participated in the intervention. The results of this study reveal several central findings. First, students in the treatment group displayed a statistically significant increase in science achievement from pre‐ to posttest. Second, there was no statistically significant difference in achievement gains between students at English to Speakers of Other Languages (ESOL) Levels 1–4 and students who had exited from ESOL or never been in ESOL. Third, there was no significant difference in achievement gains based on the year of participation in the intervention. Finally, students in the treatment group scored substantially lower on National Assessment of Educational Progress (NAEP) and Trends in International Mathematics and Science Study (TIMSS) items than the norm group at the pretest, but higher than the norm group at posttest. These results indicate that ELL students' improved achievement on the science test was a result of effective inquiry‐based science instruction as promoted in the professional development intervention. © 2011 Wiley Periodicals, Inc. Sci Ed 95:771–793, 2011
Secure topology maintenance and events collection in WSNs
Authors: Conti Mauro , Di Pietro Roberto , Gabrielli Andrea , Mancini Luigi V. 
Published: February 2011

AbstractTopology Maintenance Protocols (TMPs) are key for operating Wireless Sensor Networks (WSNs). Their adoption serves a few goals, such as, to save energy, to avoid collisions in communications and to have an adequate number of nodes monitoring the environment—by alternating duty cycles with sleep cycles on the sensor nodes. While effectiveness of TMPs protocols is widely addressed, security is an overlooked feature. Indeed, while different TMPs have been presented in the literature, few of them address the security issues. In particular, only recently a secure TMP protocol that does not require pair‐wise node confidentiality has been proposed: Sec‐TMP. The aim of Sec‐TMP is to enforce event delivery to the Base Station while providing a standard topology maintenance service to the WSN. In this paper, we provide a thorough assessment of our previous preliminary proposal of Sec‐TMP, with particular reference to its effectiveness and security. First, we investigate the energy consumption introduced by TMPs protocols. Second, we show that Sec‐TMP performs well without any assumption neither on the show‐up time of data‐collecting node, nor on their mobility model. In particular, we test Sec‐TMP against a realistic unpredictable data‐collecting mobility scenario, that also brings in new security issues. A thorough security analysis of the proposed solutions to these new issues is also provided. Finally, extensive simulations support the quality of Sec‐TMP as for effectiveness and security. Copyright © 2011 John Wiley & Sons, Ltd.
Protocol for ownership transfer across authorities: with the ability to assign transfer target
Authors: Yang Ming Hour , Hu Hung Yuan 
Published: February 2011

AbstractRadio Frequency Identification (RFID) has been widely deployed for its high capabilities in simple computation, storage, long scan distance, and simultaneous reading. With the combination of mobile devices and readers in recent years, it has been transformed to mobile RFID providing wider services for its users and mobility for its readers. E‐commerce, for instance, has applied many of mobile RFID's deriving services, one of which is the transfer of a tagged item's ownership. To secure such transfer in a mobile RFID environment, we propose a new approach for ownership transfer across different authorities and prove it able to stand most threats for RFID and to prevent Denial of Service (DoS) attacks that derive from asynchrony. Another contribution in this paper is that we can assign transfer targets, which, except our scheme, can only be achieved by Yang et al.'s Cross Authority Ownership Transfer (CAOT) protocol. That scheme, however, involves heavy computation and is not suitable for lightweight tags, whereas this scheme is designed for lightweight tags and has been proved viable on low‐cost passive tags and has better performance than any known ownership transfer schemes. Copyright © 2011 John Wiley & Sons, Ltd.
People‐centric sensing in assistive healthcare: Privacy challenges and directions
Authors: Giannetsos Thanassis , Dimitriou Tassos , Prasad Neeli R. 
Published: February 2011

ABSTRACTAs the domains of pervasive computing and sensor networking are expanding, there is an ongoing trend towards assistive living and healthcare support environments that can effectively assimilate these technologies according to human needs. Most of the existing research in assistive healthcare follows a more passive approach and has focused on collecting and processing data using a static‐topology and an application‐aware infrastructure. However, with the technological advances in sensing, computation, storage, and communications, a new era is about to emerge changing the traditional view of sensor‐based assistive environments where people are passive data consumers, with one where people carry mobile sensing elements involving large volumes of data related to everyday human activities. This evolution will be driven by people‐centric sensing and will turn mobile phones into global mobile sensing devices enabling thousands new personal, social, and public sensing applications. In this paper, we discuss our vision for people‐centric sensing in assistive healthcare environments and study the security challenges it brings. This highly dynamic and mobile setting presents new challenges for information security, data privacy and ethics, caused by the ubiquitous nature of data traces originating from sensors carried by people. We aim to instigate discussion on these critical issues because people‐centric sensing will never succeed without adequate provisions on security and privacy. To that end, we discuss the latest advances in security and privacy protection strategies that hold promise in this new exciting paradigm. We hope this work will better highlight the need for privacy in people‐centric sensing applications and spawn further research in this area. Copyright © 2011 John Wiley & Sons, Ltd.
Minimizing insider misuse through secure Identity Management
Authors: Fuchs Ludwig , Pernul Günther 
Published: February 2011

ABSTRACTTo avoid insider computer misuse, identity, and authorization data referring to the legitimate users of systems must be properly organized, constantly and systematically analyzed, and evaluated. In order to support this, structured and secure Identity Management is required. A comprehensive methodology supporting Identity Management within organizations has been developed, including gathering of identity data spread among different applications, systematic cleansing of user account data in order to detect semantic as well as syntactic errors, grouping of privileges and access rights, and semiautomatic engineering of user roles. The focus of this paper is on the cleansing of identity and account data leading to feedback where insider misuse due to existing privileges which go beyond the scope of the users' current need‐to‐know may occur. The paper in detail presents used data cleansing mechanisms and underlines their applicability in two real‐world case studies. Copyright © 2011 John Wiley & Sons, Ltd.
Depth resolution and inhomogeneity of the sputtering dose with sample rotation and ion beam rastering
Authors: Shard A. G. , Seah M. P. 
Published: February 2011

AbstractSample rotation during sputter depth profiling can improve the measured depth resolution. We examine some of the practical issues of particular relevance to rotation conditions in SIMS. There are many ways of arranging the rotation for sputtering and, to illustrate the issues, one configuration is studied. Through simulations of the spatial distribution of ion dose using a rastered ion beam and sample rotation, we demonstrate that significant variations in the distribution of ion dose across the surface can occur during the profile. With rotational frequencies much lower than raster frequencies, as used for Auger and XPS, these variations are typically small and have the same periodicity as the rotation. If rotational frequencies are similar to, or larger than the raster frequency, then large spatial variations in dose can occur. In this case, extreme care must be taken to ensure that the two frequencies are not related by a simple rational number and that the sputtering ion beam size should be significantly broader than the line spacing of the raster, but significantly smaller than the raster size. Specific recommendations are provided for setting both the rotation frequency and the size of the sputtering ion beam in order to ensure that the relative standard deviation of the ion dose across the analysis area remains lower than 1%. However, the best method may be a stepwise rotation of 90° after each analysis and sputtering cycle. © Crown copyright 2011. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.
A proof of concept phase II non‐inferiority criterion
Authors: Neuenschwander Beat , Rouyrre Nicolas , Hollaender Norbert , Zuber Emmanuel , Branson Michael 
Published: February 2011

AbstractTraditional phase III non‐inferiority trials require compelling evidence that the treatment vs control effect bfθ is better than a pre‐specified non‐inferiority margin θNI. The standard approach compares this margin to the 95 per cent confidence interval of the effect parameter. In the phase II setting, in order to declare Proof of Concept (PoC) for non‐inferiority and proceed in the development of the drug, different criteria that are specifically tailored toward company internal decision making may be more appropriate. For example, less evidence may be needed as long as the effect estimate is reasonably convincing.We propose a non‐inferiority design that addresses the specifics of the phase II setting. The requirements are that (1) the effect estimate be better than a critical threshold θC, and (2) the type I error with regard to θNI is controlled at a pre‐specified level. This design is compared with the traditional design from a frequentist as well as a Bayesian perspective, where the latter relies on the Level of Proof (LoP) metric, i.e. the probability that the true effect is better than effect values of interest. Clinical input is required to establish the value θC, which makes the design transparent and improves interactions within clinical teams. The proposed design is illustrated for a non‐inferiority trial for a time‐to‐event endpoint in oncology. Copyright © 2011 John Wiley & Sons, Ltd.
Extended model‐based designs for more complex dose‐finding studies
Authors: O'Quigley John , Conaway Mark 
Published: February 2011

AbstractWe discuss extensions of model‐based designs, such as the continual reassessment method, for use in dose‐finding studies. Rather than work with a single model to carry out the design and analysis of a dose‐finding study we indicate how the use of several models can greatly increase flexibility. We can appeal to established results on Bayesian model choice and this device makes the inferential problem essentially straightforward. The greater flexibility enables us to take on board many different kinds of added complexity. Examples include extended models to deal with subject heterogeneity, extended models to take account of different treatment schedules and extended models to tackle the problem of partial ordering. Copyright © 2011 John Wiley & Sons, Ltd.