bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impurity photovoltaic effect in magnesium‐doped silicon solar cells with two energy levels
Authors: Yuan Jiren , Shen Honglie , Zhong Fulian , Deng Xinhua 
Published: February 2012

AbstractIn this paper, we have carried out a numerical study to evaluate the potential of the impurity photovoltaic (IPV) effect in magnesium‐doped silicon solar cells with two energy levels. We found that the cell efficiency can realize an absolute increase of above 2% due to the IPV effect. The efficiency improvement results from the extension of the infrared response of the solar cell. These results indicate that the IPV effect in silicon solar cells doped with magnesium is a potential means for improving cell efficiency.
The influence of inhomogeneities on broadening of fundamental transition in polar and nonpolar InGaN quantum wells dedicated for green emitters
Authors: Gladysiewicz Marta , Kudrawiec Robert 
Published: February 2012

AbstractBroadening of the fundamental transition was calculated for polar and nonpolar InGaN QWs emitting in the green spectral range within the model of a ‘random quantum’ well (QW) [M. Gladysiewicz and R. Kudrawiec J. Phys.: Cond. Mater. 22, 485801 (2010)]. In order to simulate QW inhomogeneities in this model, it was assumed that the QW width, barrier widths and indium concentration vary with a Gaussian distribution where the nominal QW width, barrier widths and indium concentration correspond to the mean value in this distribution and their fluctuations correspond to the deviation from the main value. In this way the influence of the each parameter (QW width, barrier width, and indium concentration) on the broadening of the fundamental transition was considered independently and, finally, all the parameters were taken into account at the same time. It has been found that the same magnitude of QW width fluctuations and indium concentration fluctuations leads to much larger broadening of the fundamental transition for polar QWs than for nonpolar QWs. It means that the reduction of built‐in electric field in InGaN QWs can be a promising way to improve the homogeneity of light emission from this system. For polar InGaN QWs a significant reduction of polarization‐related electric fields can be obtained by a slight intentional doping in QW and/or barriers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis and characterization of Pt‐TiO2 nanofibers
Authors: Lee Deuk Yong , Cho Nam‐Ihn 
Published: February 2012

AbstractPlatinum (Pt) doped nanofibers were electrospun by using a Pt‐TiO2 precursor solution. The Pt‐TiO2 precursor solution was prepared by mixing the synthesized metal‐organic precursor solution containing Ti and Pt and the TiO2 sol. Amino acid, L‐lysine, was used as a bonding medium between Ti and Pt. The required amount of L‐lysine was determined to be 12 wt%. The dynamic viscosity and surface tension of Pt‐TiO2 solution were 16.6 cP and 21.4 mN/m, respectively. SEM results revealed that the diameters of TiO2 and Pt‐TiO2 nanofibers calcined at 500°C were similar regardless of the Pt presence. However, crystallite sizes of TiO2 and Pt‐TiO2 nanofibers determined by the Scherrer formula were 16 nm and 8 nm, respectively, suggesting that Pt metals may hinder the growth of the crystallite (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Origins of visible‐light emissions in porous silicon
Authors: Tit Nacir , Yamani Zain H. , Pizzi Giovanni , Virgilio Michele 
Published: February 2012

AbstractThe electronic and optical properties of porous silicon (p‐Si) have been theoretically investigated using the minimal sp3‐basis set tight‐binding method, with inclusion of second nearest neighbors and spin‐orbit interactions. A hypothetical model of p‐Si was assumed and calculations of band structures, with focus on bandgap energy Eg, oscillator strength (OS) and recombination rate (RR), were carried varying the porosity and the mean distance d between pores. Similar calculations were also performed for other confined silicon nanostructures as hydrogen‐passivated silicon nanocrystals (Si:H NCs) and silicon nanowires (Si‐NWs). For these two latter systems, the results of Eg versus the size d are found to be in excellent agreement with the available measured photoluminescence (PL) data of experimental p‐Si samples. On one hand, the results show that sizes in the range d = 1‐3 nm are responsible for emission in the visible‐light energy window. On the other hand, our results also suggest that the emission properties of p‐Si is strongly affected by the 2D and 3D quantum confinement (QC) characters of the involved band edge states. Furthermore, our theoretical values for the RR are found to be larger and closer to the experimental ones in the case of Si:H NCs with respect to the case of Si‐NWs. This fact suggests that the intense measured PL features are mainly due to 3D confined nanostructures (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pressure and temperature dependence of GaN/AlGaN high electron mobility transistor based sensors on a sapphire membrane
Authors: Edwards M. J. , Le Boulbar E. D. , Vittoz S. , Vanko G. , Brinkfeldt K. , Rufer L. , Johander P. , Lalinský T. , Bowen C. R. , Allsopp D. W. E. 
Published: February 2012

AbstractThis paper reports a high pressure sensor based on a GaN/AlGaN High Electron Mobility Transistor (HEMT) that uses its 375 mm thick sapphire substrate to provide a robust base and enables device operation up to at least 60 bar (6 MPa). Transduction of changes in ambient pressure occurs via piezoelectric and pyroelectric effects on the channel conductance. The HEMTs were strategically placed along an 8 mm2 GaN/AlGaN/GaN/sapphire chip; where the central 4 mm diameter behaves as a pressure sensitive ‘drumskin’. The location of peak response lies in the HEMT at the geometric centre of the drumskin, demonstrated by the change in IDS when the pressure was increased from 0 to 60 bar. The response of six strategically placed HEMTs along the chip's surface, were compared to a finite element model to predict sensor behaviour. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Small current collapse in AlGaN/GaN HFETs on a‐plane GaN self‐standing substrate
Authors: Sugiyama T. , Honda Y. , Yamaguchi M. , Amano H. , Isobe Y. , Iwaya M. , Takeuchi T. , Kamiyama S. , Akasaki I. , Imade M. , Kitaoka Y. , Mori Y. 
Published: February 2012

AbstractWe measured drain bias stress effects and current collapse in AlGaN/ GaN heterostructure field‐effect transistors (HFETs) on a‐plane and c‐plane GaN substrates. An a‐plane AlGaN/GaN HFET (a‐HFET) shows small current collapse with a threshold voltage (Vth = ‐1.8 V). On the other hand, a c‐plane HFET (c‐HFET) with the same barrier thickness (20 nm) shows a small current collapse, although Vth was negatively large (Vth = ‐4 V).Current collapse in a‐HFET was not large compared with that in conventional c‐HFET on GaN. A c‐HFET on sapphire was also measured. The current collapses in HFETs on sapphire were larger than that in HFETs on a GaN substrate. The current collapses in the thin‐barrier c‐HFET (Vth = ‐1.8 V) were particularly large. Therefore, an a‐plane device is promising for a small or positive Vth with small current collapse. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of high quality III‐N heterostructures using specialized MBE system
Authors: Petrov S. I. , Alexeev A. N. , Krasovitsky D. M. , Chaly V. P. 
Published: February 2012

AbstractThe growth of “thick” (200 nm) AlN layers on sapphire at 1100‐1150 °C using STE3N2 MBE system is shown to be the key step to obtain high quality GaN‐based heterostructures. An appropriate sequence of AlGaN transition layers grown on such an AlN both allows to reduce dislocation density in GaN down to 9×108‐1×109 cm‐2 in comparison with GaN layers grown on “thin” (10nm) low temperature AlN nucleation layer. Maximum electron mobility in 1.5 µm thick GaN silicon doped layer reaches 600‐650 cm2/V.s at electron concentrations (3‐5) ×1016 cm‐3. The results of use of GaN‐based heterostructures grown by STE3N2 for power DHFET production are also shown. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Titanium nitride as promising gate electrode for MOS technology
Authors: Lima Lucas P. B. , Moreira Milena A. , Diniz José A. , Doi Ioshiaki 
Published: February 2012

AbstractTitanium nitride (TiN) films have been grown on Si (100) substrates by DC. reactive magnetron sputtering from a titanium (Ti) metallic target at different nitrogen partial pressures (80–10 sccm) and different power (500–1500 W). The effects of the nitrogen pressure and power on structural and electrical properties of TiN films were investigated by measuring their X‐ray diffraction (crystal orientation), Atomic Force Microscopy (surface roughness), four‐probe technique (electrical resistivity) and film thickness. It is show that deposition rate (13–65 nm/min) decrease with an increase of nitrogen pressure. The films have the grain size (0.001–0.027 μm2) along the sample surface and the size of the grain increase with an increase of nitrogen partial pressure. The X‐ray diffraction measurement show that films were crystalline (with preferred orientation (311)), but some of them were polycrystalline ((311) and (111) preferred orientation). These films have been used as gate electrodes in MOS capacitors, which were fabricated with TiN and SiNxOy as gate electrode and dielectric, respectively. With 20 minutes of annealing time, the extracted TiN work function and flat‐band voltage were about 4.65 eV and ‐0.29 V, which indicates that TiN can be used as mig‐gap electrode for MOS technology. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical and electrical properties of sputtered InNO thin films
Authors: Sparvoli Marina , Mansano Ronaldo D. , Zambom Luis S. , Chubaci José F. D. 
Published: February 2012

AbstractIn this work we study the deposition of indium oxynitride prepared by reactive RF magnetron sputtering. This material shows multi‐functionality in electrical and photonic applications. It shows transparence in visible range, wide band gap, high resistivity, low linkage current and response for light. The deposition processes were performed in a home build magnetron sputtering system, using a four‐inch pure In (99.999%) target, nitrogen and oxygen as process gases. The pressure was kept constant in 1.33 Pa and the RF power (13.56 MHz) was constant 250 W. The optical band gap was estimated for samples deposited with 0%, 10%, 20%, 50%, 80% and 85% of oxygen concentration in the gas mixture and the band gap values obtained were 1.32 eV, 2.47 eV, 2.65 eV, 2.50 eV, 3.04 eV and 3.00 eV, respectively. The IxV analysis shows a low leakage current (∼10‐8 A). The increase in the oxygen concentration in the plasma promotes change in the character of these thin films from conductor to semiconductor material. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photocarrier drift mobility in ZnO at low temperature
Authors: Yamaguchi Hiroyuki , Ishidsuka Yousuke , Komiyama Takao , Chonan Yasunori , Aoyama Takashi 
Published: February 2012

AbstractWe have studied photocarrier drift mobility in ZnO in the temperature range between 30 and 280 K using a conventional time‐of‐flight (TOF) technique. Single crystal grown by the hydrothermal method was used as specimens. An electric field was applied in the direction parallel to the polar surfaces. We observed that shapes of the photocurrent transient changed with both applied electric field and temperature. The slopes of initial decays of the photocurrent became steeper with increase of the applied electric field strength. Transit time estimated from the photocurrent transient was in inverse proportion to the applied electric field. The highest drift mobility of 70 cm2V‐1s‐1 was obtained in the vicinity of 60 K for photoelectrons when the O‐surface was irradiated. While drift mobility showed the same temperature dependence as Hall mobility reported in previous work, its value was much smaller than that of Hall mobility. This discrepancy suggests that the multiple trapping effect due to the photocarrier trap centres is important at the ZnO surfaces. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Access‐polynomial‐based self‐healing group key distribution scheme for resource‐constrained wireless networks
Authors: Wang Qiuhua , Chen Huifang , Xie Lei , Wang Kuang 
Published: February 2012

ABSTRACTThe self‐healing group key distribution scheme with revocation can deal with the problem of distributing session keys for secure group communication over an unreliable wireless network, with the capability to resist packet loss and collusion attack. However, existing access‐polynomial‐based self‐healing key management schemes have some problems, such as the small number of active group members, much redundancy in the key updating broadcast packet, and limited collusion attack resistance capability. In order to increase the number of active group members and improve the performance of self‐healing group key distribution schemes, we propose a self‐healing group key distribution scheme based on the access polynomial and one‐way hash key chain for resource‐constrained wireless networks in this paper. In our proposed scheme, by binding the time at which the user joins the group with the capability of recovering previous group session keys, some novel methods to construct the personal secret, the access polynomial, and the session key updating broadcast packet are presented. Compared with existing schemes under same conditions, analysis and simulation results show that our proposed scheme not only supports much more group members and sessions, but also provides a stronger security, considering that it can deal with more colluding users. Moreover, our proposed scheme is especially suitable to resource‐constrained wireless networks in a very bad environment. Copyright © 2012 John Wiley & Sons, Ltd.
Trust modeling for message relay control and local action decision making in VANETs
Authors: Zhang Jie , Chen Chen , Cohen Robin 
Published: February 2012

ABSTRACTIn this paper, we present a trust‐modeling framework for message propagation and evaluation in vehicular ad hoc networks. In the framework, peers share information regarding road condition or safety, and others provide opinions about whether the information can be trusted. More specifically, our trust‐based message propagation model collects and propagates peers' opinions in an efficient, secure, and scalable way by dynamically controlling information dissemination. The trust‐based message evaluation model allows peers to derive a local action decision about whether to follow the information by evaluating the information in a distributed and collaborative fashion while taking into account others' opinions. Experimental results demonstrate that our proposed trust‐modeling framework promotes network scalability and system effectiveness, which are the two essentially important factors for the popularization of vehicular ad hoc networks, in information propagation and evaluation under the pervasive presence of false information. In particular, we clarify how our relay control serves to decrease the number of inappropriate actions taken on the basis of malicious information and enables honest peers to produce a greater number of deliveries within the network. Copyright © 2012 John Wiley & Sons, Ltd.
Social responsibility in new ventures: profiting from a long‐term orientation
Authors: Wang Taiyuan , Bansal Pratima 
Published: February 2012

AbstractSocially responsible activities help create business value, develop strategic resources, and insure against risks, but also cost money and distract management. These prior findings are mainly based on established corporations and may not extend to new ventures in which the liability of newness may suppress some positive effects and amplify some negative impacts of socially responsible activities. New ventures whose strategic decisions have a long‐term orientation, however, are able to counteract their liability of newness and thereby generate net positive economic returns. We tested these relationships by surveying the chief executive officers and presidents and studying the signature Web sites of 149 new ventures. Copyright © 2012 John Wiley & Sons, Ltd.
Enterprise logic: explaining corporate attention to stakeholders from the ‘inside‐out’
Authors: Crilly Donal , Sloan Pamela 
Published: February 2012

AbstractWhy are some firms more effective than others at addressing stakeholder concerns? Conventional stakeholder theories focus on variables in the external environment and cannot adequately explain variance across firms operating in the same context. Our matched‐pair study of eight global corporations goes inside the firm and investigates the role of managerial cognition on corporate attention to stakeholders. We find that top management's conceptualization of the firm's relationship with society—which we name enterprise logic—prompts distinct foci of attention and potentially constrains how well a single firm can simultaneously attend to multiple stakeholders. These findings highlight the value of an ‘inside‐out’ perspective, centered on managerial cognition, in explaining why some firms address stakeholder concerns more effectively than their peers. Copyright © 2012 John Wiley & Sons, Ltd.
Weldability Evaluation and Microstructure Analysis of Resistance‐Spot‐Welded High‐Mn Steel in Automotive Application
Authors: Saha Dulal Chandra , Han Sangho , Chin Kwang Geun , Choi Ildong , Park Yeong‐Do 
Published: February 2012

AbstractIn this paper, resistance spot weldability of high‐Mn steels were investigated in order to get high reliability in welded joints of automotive components. Microstructural characterizations, cross‐tensile test (CTT), microhardness tests of spot welded parts were conducted. The effects of weld current on the microstructural characteristics, mechanical properties, and fracture modes were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The hardness in the weld nugget was observed to be lower than that in the base metal (BM). In CTT, the failure initiation was observed to occur at the boundary of the weld nugget. Also welding imperfections of welded parts were investigated. Liquation cracking in heat affected zone (HAZ), porosity, and shrinkage cavity were found most common welding defects in welded parts. Furthermore, the effects of welding imperfections on weld quality and failure criteria were identified and discussed.
Formal passive testing of timed systems: theory and tools
Authors: Andrés César , Merayo Mercedes G. , Núñez Manuel 
Published: February 2012

SUMMARYThis paper presents a methodology to perform passive testing of timed systems. In passive testing, the tester does not interact with the implementation under test. On the contrary, execution traces are observed without interfering with the behaviour of the system. Invariants are used to represent the most relevant expected properties of the implementation under test. Intuitively, an invariant expresses the fact that each time the implementation under test performs a given sequence of actions, it must exhibit a behaviour in a lapse of time reflected in the invariant. There are two types of invariants: consequent and observational. The paper gives two algorithms to decide the correctness of proposed invariants with respect to a given specification and algorithms to check the correctness of a log, recorded from the implementation under test, with respect to an invariant. The soundness of this methodology is shown by relating it to an implementation relation. In addition to the theoretical framework, a tool called PASTE has been developed. This tool helps in the automation of the passive testing approach because it implements all the algorithms presented in this paper. PASTE takes advantage of mutation testing techniques in order to evaluate the goodness of an invariant according to its capability to detect errors in logs generated from mutants. An empirical study where PASTE was used to analyse a non‐trivial system is also reported. Copyright © 2012 John Wiley & Sons, Ltd.
Identification of functional differences between recombinant human α and β cardiac myosin motors
Authors: Deacon John C. , Bloemink Marieke J. , Rezavandi Heresh , Geeves Michael A. , Leinwand Leslie A. 
Published: February 2012

Abstract
The myosin isoform composition of the heart is dynamic in health and disease and has been shown to affect contractile velocity and force generation. While different mammalian species express different proportions of α and β myosin heavy chain, healthy human heart ventricles express these isoforms in a ratio of about 1:9 (α:β) while failing human ventricles express no detectable α-myosin. We report here fast-kinetic analysis of recombinant human α and β myosin heavy chain motor domains. This represents the first such analysis of any human muscle myosin motor and the first of α-myosin from any species. Our findings reveal substantial isoform differences in individual kinetic parameters, overall contractile character, and predicted cycle times. For these parameters, α-subfragment 1 (S1) is far more similar to adult fast skeletal muscle myosin isoforms than to the slow β isoform despite 91% sequence identity between the motor domains of α- and β-myosin. Among the features that differentiate α- from β-S1: the ATP hydrolysis step of α-S1 is ~ten-fold faster than β-S1, α-S1 exhibits ~five-fold weaker actin affinity than β-S1, and actin·α-S1 exhibits rapid ADP release, which is >ten-fold faster than ADP release for β-S1. Overall, the cycle times are ten-fold faster for α-S1 but the portion of time each myosin spends tightly bound to actin (the duty ratio) is similar. Sequence analysis points to regions that might underlie the basis for this finding.
Population dynamics of the cactus Mammillaria gaumeri: an integral projection model approach
Authors: Ferrer‐Cervantes Merari Esther , Méndez‐González Martha Elena , Quintana‐Ascencio Pedro‐Francisco , Dorantes Alfredo , Dzib Gabriel , Durán Rafael 
Published: February 2012

AbstractThe Cactaceae family in Mexico is particularly important because members of this family exhibit a high degree of endemism. Unfortunately, many species of the Cactaceae are threatened or endangered. We employed an integral projection model for studies of the population dynamics of Mammillaria gaumeri, an endemic cactus of the Yucatán characterized by a small population size. The integral projection model provides estimates of the asymptotic growth rate, stable size distribution, reproductive values, and sensitivities and elasticities of the growth rate to changes in vital rates. Nine locations of this species were studied along the Yucatan coast over a 9‐year period. Individuals were classified by plant volume. Most population growth rate (λ) values were below unity. The highest elasticity values corresponded to the survival of intermediate size individuals. The percentage of germination in the field was low, and consequently, fecundity values were also low. Reproductive values were observed to increase with plant volume. The stable size distribution of M. gaumeri was skewed toward small individuals. For all years, the kernel showed that individual survival determined the population growth rate.