bluuebunny/crossref_metadata_2025 huggingface dataset:
The terminal abdominal ganglion of the wood cricket Nemobius sylvestris
Authors: Insausti Teresita C. , Lazzari Claudio R. , Casas Jérôme
Published: September 2008

The abdominal cerci of the wood cricket, Nemobius sylvestris, are covered by a variety of hair‐like sensilla that differ in length, thickness, and articulation. Fillings from the cercal nerves with cobalt chloride and fluorescent dyes revealed the projection of sensory axons into the terminal abdominal ganglion of the ventral nerve chain. Two projection areas on each side of the terminal abdominal ganglion midline could be identified: a posterior cercal glomerulus and an anterior bristle neuropil. Axons from some cercal sensilla ascend through the connectives to reach the metathoracic ganglionic mass. As their axons pass through each segmental abdominal ganglion, they project medial arborization. Cross‐sections of the terminal abdominal ganglion and retrograde fills with cobalt chloride and fluorescent dyes from connectives revealed several small cells and seven pairs of giant ascending interneurons organized symmetrically. Giant somata are located contralateral to their axons (diameters between 20 and 45 μm). The cercal projections overlap extensively with the dendritic fields of the giant interneurons. In the terminal abdominal ganglion, we identified nine longitudinal tracts, two major tracts, and seven smaller ones. The functional implications of the neuranatomical organization of the system are discussed on a comparative basis. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.
High‐pressure Brillouin study of the elastic properties of rare‐gas solid xenon at pressures up to 45 GPa
Authors: Sasaki Shigeo , Wada Naoyuki , Kume Tetsuji , Shimizu Hiroyasu
Published: September 2008

The pressure dependences of three adiabatic elastic constants, adiabatic bulk modulus, refractive index, and elastic anisotropy, as well as Cauchy deviation of fcc solid Xe have been determined up to 10 GPa at 296 K by high‐pressure Brillouin scattering spectroscopy. The characteristics of elastic properties at high pressure of rare‐gas solid Xe are investigated by comparison with the previous studies on Ne, Ar, and Kr. Above 10 GPa, the occurrence of splitting in the Brillouin signals and the direction dependence of acoustic velocities for solid Xe clearly show partial phase transformation to the hcp structure reported by the previous X‐ray diffraction and Raman scattering studies. The shear elastic modulus in the hcp phase of solid Xe has also been estimated at pressures up to 45 GPa by using the pressure dependence of the Raman wavenumber shift for the E2g mode. Copyright © 2008 John Wiley & Sons, Ltd.
Eulerian elasto‐visco‐plastic formulations for residual stress prediction
Authors: Qin Xiaoliang , Michaleris P.
Published: September 2008

A stabilized, Galerkin finite element formulation for modeling the elasto‐visco‐plastic response of quasi‐steady‐state processes, such as welding, laser surfacing, rolling and extrusion, is presented in an Eulerian frame. The mixed formulation consists of four field variables, such as velocity, stress, deformation gradient and internal variable, which is used to describe the evolution of the material's resistance to plastic flow. The streamline upwind Petrov–Galerkin method is used to eliminate spurious oscillations, which may be caused by the convection‐type of stress, deformation gradient and internal variable evolution equations. A progressive solution strategy is introduced to improve the convergence of the Newton–Raphson solution procedure. Two two‐dimensional numerical examples are implemented to verify the accuracy of the Eulerian formulation. Copyright © 2008 John Wiley & Sons, Ltd.
On the convergence of discrete schemes for the Perona‐Malik equation
Authors: Bellettini Giovanni
Published: September 2008

We discuss some results on the semi‐discretization and the full‐discretization of the one‐dimensional Perona‐Malik equation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Construction of low‐discrepancy point sets of small size
Authors: Gnewuch Michael
Published: September 2008

We report on recently developed algorithms that construct small point sets in the d ‐dimensional unit cube whose star discrepancies satisfy good and meaningful bounds. These bounds are proved by probabilistic arguments and the algorithms derandomize the corresponding underlying random experiment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hybrid method for the chemical master equation
Authors: Ferm Lars , Hellander Andreas , Lötstedt Per
Published: September 2008

In order to make the solution of the chemical master equation computationally tractable, it is approximated in two different ways: The first two moments of the probability density function are computed or a macroscopic description is coupled to the master equation. In this way the computational complexity is reduced from exponential to polynomial growth of the work in the number of reacting chemical species and the dimension of the problem is lowered. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assimilation of Lagrangian data in oceanography
Authors: Nodet Maëlle
Published: September 2008

Within the framework of Global Ocean Data Assimilation Experiment (GODAE), an increasing amount of data are available. A crucial issue for oceanographers is to exploit at best these observations, in order to improve models, climatology, forecasts, etc. Thanks to the international program Argo and to more localized experiments, a new type of data is now available: positions of floats drifting at depth in the ocean. Unlike other data, mainly Eulerian, these ones are Lagrangian: the measuring instrument move in the flow. I will briefly described methods about 4D‐Var assimilation of Lagrangian data in the OPAVAR ocean model, and show some results assessing the complementarity with temperature data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical case of Lyapunov theorem: about stability on the first approximation
Authors: Trenogin Vladilen A.
Published: September 2008

Analytical case of Lyapunov theorem is considered. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strategies for shotgun identification of integral membrane proteins by tandem mass spectrometry
Authors: Lu Bingwen , McClatchy Daniel B. , Kim Jin Young , Yates John R.
Published: September 2008

Integral membrane proteins (IMPs) are difficult to identify, mainly for two reasons: the hydrophobicity of IMPs and their low abundance. Sample preparation is a key component in the large‐scale identification of IMPs. In this review, we survey strategies for shotgun identification of IMPs by MS/MS. We will discuss enrichment, solubilization, separation, and digestion of IMPs, and data analysis for membrane proteomics.
n‐type silicon solar cells with surface‐passivated screen‐printed aluminium‐alloyed rear emitter
Authors: Bock Robert , Schmidt Jan , Brendel Rolf
Published: September 2008

Aluminium‐doped p‐type (Al‐p+) silicon emitters fabricated by means of a simple screen‐printing process are effectively passivated by plasma‐enhanced chemical‐vapour deposited amorphous silicon (a‐Si). We measure an emitter saturation current density of only 246 fA/cm2, which is the lowest value achieved so far for a simple screen‐printed Al‐p+ emitter on silicon. In order to demonstrate the applicability of this easy‐to‐fabricate p+ emitter to high‐efficiency silicon solar cells, we implement our passivated p+ emitter into an n+np+ solar cell structure. An independently confirmed conversion efficiency of 19.7% is achieved using n‐type phosphorus‐doped Czochralski‐grown silicon as bulk material, clearly demonstrating the high‐efficiency potential of the newly developed a‐Si passivated Al‐p+ emitter. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scientists' teaching orientations in the context of teacher professional development
Authors: Schuster Dwight A. , Carlsen William S.
Published: September 2008

During the past decade science educators have taken steps to identify seminal structures and approaches of science teacher professional development. This literature, which is increasingly informing how and in which contexts professional developers design and implement programs, states that scientists' divergent research interests and knowledge about K‐12 science teachers often limit their involvement in these programs. Conversely, concerns persist that there is very little empirical evidence to support these programmatic recommendations made by the science education literature. This embedded case study was bounded by the contextual similarities between seven professional development workshops with the goal of examining the relationship between scientists' views of teachers as professionals and the pedagogical orientations that the scientists used within these professional development contexts. Multiple methods were employed including systematic classroom observation by nine trained observers, as well as analysis of course materials, interviews, and questionnaires. Altogether, the teacher comments and observation data paint a picture of how the instructors implemented specific pedagogical orientations. Participants appear to have realistic views about the practical roles that research scientists can play in professional development. We explore how these findings merit attention and suggest alternatives to current practice and policy. © 2008 Wiley Periodicals, Inc. Sci Ed 93:635–655, 2009
Effective service delivery and group management in integrated terrestrial‐HAP systems for multicast communications
Authors: Araniti Giuseppe , Iera Antonio , Molinaro Antonella
Published: September 2008

Multicast service delivery can be easily guaranteed to users in disadvantaged areas by effectively integrating HAPs (High Altitude Platforms) into the terrestrial cellular system. HAPs are meant to be as unmanned aerial vehicles, airships or aircrafts, which remain relatively stationary in the stratosphere at short distance from Earth compared to satellites. In the scientific literature, there is evidence of the effectiveness of a UMTS (Universal Mobile Telecommunications Systems) system augmented by the presence of HAPs, which are equipped with UMTS payloads and play the role of additional base stations. This integrated terrestrial‐space platform intrinsically fits the exigencies of rural and emergency scenarios, which are characterized by network resource scarcity, due to either geographical reasons (such as in rural areas) or to temporary resource over‐utilization/reduction (due to emergency status). In this paper, the focus is on the delivery of Multimedia Broadcast/Multicast Services (MBMS) in the reference integrated architecture. Main objectives are designing resource allocation policies to manage multicast groups between space and terrestrial coverages, and analysing their feasibility and performances in terms of offered grade of service. Copyright © 2008 John Wiley & Sons, Ltd.
On the performance anomaly in WiMAX networks
Authors: Detti Andrea , Loreti Pierpaolo , Pomposini Remo
Published: September 2008

The WiMAX system carries a wide range of services in urban and rural environments supporting quality of service. A key element of the QoS framework is the scheduling algorithm adopted by the Base Station (BS). In this paper, we analyze the saturation throughput perceived by Mobile Stations in the cases of two BS scheduling algorithms: Deficit Round Robin (DRR) and time‐based DRR. We demonstrate that the WiFi issue of ‘Performance Anomaly’ also occurs in WiMAX networks: when the BS uses scheduling approaches aimed at achieving throughput‐fairness, like DRR. Performance Anomaly means that when some Mobile Stations (MSs) use a very low bit rate, the throughput of MSs with a high bit rate is dramatically degraded. We propose time‐based DRR as a viable solution to remove the Performance Anomaly. Time‐based DRR is a simple modification of the DRR algorithm that achieves time‐fairness. Its implementation is feasible in WiMAX. The analysis is carried out by means of analytical models supported by NS2 simulations. Two scenarios are considered: the first is suitably set up to highlight and understand the phenomenon of Performance Anomaly; the second examines the impact of Performance Anomaly on a system level focusing on a rural environment. Copyright © 2008 John Wiley & Sons, Ltd.
Geographic rendezvous‐based architectures for emergency data dissemination
Authors: Seada Karim , Helmy Ahmed
Published: September 2008

Communication and information dissemination in times of disasters could have a critical role in aiding the emergency personnel and saving lives. Unfortunately, regular communication becomes more challenging at these times, as the infrastructure might be damaged or overloaded, and the requirements for communication (e.g., response time, capacity) becomes highly critical. Ad‐hoc networks forming between wireless devices have always been considered as a promising technology at disaster recovery situations. In this paper, we examine the need for efficient and robust information dissemination mechanisms on top of infrastructure‐less ad‐hoc networks. We argue that distributed rendezvous‐based approaches are more promising for emergency data dissemination than approaches based on network flooding or centralized storage. We present the design of a geographic rendezvous‐based architecture and evaluate its performance in detail against other variants and traditional approaches. The study shows its efficiency, high success rate in delivering data, and its robustness to failures and mobility; characteristics highly valuable at emergency situations. Copyright © 2008 John Wiley & Sons, Ltd.
Urinary corticosteroid excretion patterns in the okapi (Okapia johnstoni)
Authors: Bennett Cynthia , Fripp Deborah , Othen Leanne , Jarsky Tim , French Jeffrey , Loskutoff Naida
Published: September 2008

Stress is known to alter a variety of biological processes, including behavior and reproduction. It is therefore important to understand the stress levels of animals in captivity, especially those for whom captive breeding is a priority, such as the okapi. Levels of stress hormones can be measured from samples collected noninvasively, such as urine or feces, which are preferable with nondomestic species for whom drawing blood might in itself be a considerable stressor. To understand the excretion of cortisol in urine in the okapi, four (1.3) animals were subject to three injections: saline, 200 IU of an adrenocorticotropic hormone (ACTH) analogue, and 300 IU of the analogue. Their 24‐hr urinary corticosteroid levels were compared with 4 baseline days. Injection with the ACTH analogue significantly increased the urinary corticosteroid levels compared with saline injections and baseline. Eight (3.5) okapi were then observed for 24 hr per day for 5 days to determine their normal patterns of corticosteroid production. The mean corticosteroid levels varied significantly by individual. A significant circadian pattern in urinary corticosteroid was apparent independent of individual or gender, with cortisol rising during the daylight hours and decreasing again at night. Zoo Biol 27:381–393, 2008. © 2008 Wiley‐Liss, Inc.
Bivalvulidan (Myxozoa: Myxosporea) parasites of damselfishes with description of twelve novel species from Australia's Great Barrier Reef
Authors: GUNTER N. L. , ADLARD R. D.
Published: September 2008

Bivalvulidan parasites from the gall bladder of 31 species of damselfishes (family Pomacentridae) were examined for their taxonomic identity and their relatedness to other species of myxozoans. This paper describes 11 novel ceratomyxid species and a novel Myxidium sp. Each species is characterized morphologically and small subunit (SSU) rDNA sequences were used in molecular phylogenetic analyses. Five pomacentrid species were found to harbour multiple infections of bivalvulidan species. One species of Ceratomyxa and Myxidium were found to infect more than a single species of damselfish. Phylogenetic analyses revealed there has been no radiation of ceratomyxids that can be associated with the fish host taxon and that Myxidium queenslandicus n.sp. was more closely related to Zschokkella mugilis and Ellipsomyxa gobii than other members of the genus Myxidium.
From Labour to Capital: Intra-Village Inequality in Rural China, 1988–2006
Authors: Yingying Zhou , Hua Han , Harrell Stevan
Published: September 2008

Economic inequality has increased greatly in China since the end of state socialist industry and collective agriculture, but the story of inequality is much more complex than just the rural–urban and coastal–inland dichotomies or the relative contributions of inter-regional and intra-regional inequality. Even within inland rural areas, inequality between villages and within villages has also increased greatly. In 2005–06, we were fortunate to be able to work with the Sichuan Nationalities Research Institute to re-survey 90 per cent of 300 families in three villages that we had originally surveyed in 1988. On the basis of these surveys and of ethnographic information, we found that income inequality had increased quite dramatically in all three villages. In structural terms, the primary reason for this increase was the shift from labour power to small-scale capital as the primary source of family income, a shift that occurred differently in each village.
Retreat from Equality or Advance towards Efficiency? Land Markets and Inequality in Rural Zhejiang
Authors: Zhang Qian Forrest
Published: September 2008

Based on a 2001 survey, this study finds increased disparities in land distribution in rural Zhejiang. Regression analyses yield three main findings. First, increased disparities in land distribution are associated with growth of land markets. Second, rural households who acquired land through markets significantly increased their farm income. Land markets thus gave rise to a new venue of income generation and increased inequality in farm income. Widening disparities in land rights and farm income, however, did not constitute a further retreat from equality, but instead had compensatory effects on overall inequality, as land markets brought up families who would have fallen at the lower end of income distribution in the absence of such markets. Third, land markets increased efficiency in farming, as households who acquired land were using it more productively. In rural Zhejiang, growth of land markets broadened access to market opportunities and enhanced both efficiency and equity.
Danwei Profitability and Earnings Inequality in Urban China
Authors: Xie Yu , Wu Xiaogang
Published: September 2008

Prior research has debated the relative importance of such factors as human capital, political capital and region in determining workers' earnings in reform-era urban China. This article argues that a main agent of social stratification in contemporary China continues to be the danwei, the work unit. Using data from a 1999 survey we conducted in three large Chinese cities, Wuhan, Shanghai and Xi'an, we assess the extent to which workers' earnings (including regular wages, bonuses and subsidies) depend on the profitability of their danwei. Results show that the financial situation of the danwei is one of the most important determinants of earnings in today's urban China. Furthermore, the importance of danwei profitability does not vary by city or by employment sector.
Is China Abolishing the Hukou System?
Authors: Wing Chan Kam , Buckingham Will
Published: September 2008

In recent years, China has instituted a variety of reforms to its hukou system, an institution with the power to restrict population mobility and access to state-sponsored benefits for the majority of China's rural population. A wave of newspaper stories published in late 2005 understood the latest round of reform initiatives to suggest that the hukou is set to be abolished, and that rural residents will soon be “granted urban rights.” This article clarifies the basic operations of the hukou system in light of recent reforms to examine the validity of these claims. We point out that confusion over the functional operations of the hukou system and the nuances of the hukou lexicon have contributed to the overstated interpretation of the initiative. The cumulative effect of these reforms is not abolition of the hukou, but devolution of responsibility for hukou policies to local governments, which in many cases actually makes permanent migration of peasants to cities harder than before. At the broader level, the hukou system, as a major divide between the rural and urban population, remains potent and intact.
When Communist Party Candidates Can Lose, Who Wins? Assessing the Role of Local People's Congresses in the Selection of Leaders in China
Authors: Manion Melanie
Published: September 2008

This article draws on Party and government documents, Chinese-language books and articles, interviews and firsthand observation, and electoral outcome data to contribute to the emerging literature on the changing role of people's congresses in mainland China. It focuses on the crucially important but neglected relationship between local congresses and local Communist Party committees in the selection of congress and government leaders. It analyses the 1995 reforms to Party regulations and the law, which resulted in electoral losses of more than 17,000 Communist Party candidates in the first set of elections after 1995. It concludes that the reforms created the conditions for local congress delegates to matter – and delegates responded. More broadly, it concludes that congressional assertiveness has significant (although not radical) implications for the relationship between the congresses and Party committees. The winners in the broader (not narrowly electoral) sense of the term are both the congresses and the ruling Communist Party, strengthened as an organization with selection of leaders opened up to more players.
China's Shifting Attitude towards United Nations Peacekeeping Operations
Authors: Stähle Stefan
Published: September 2008

While China has been portrayed as a reluctant supporter of UN peacekeeping in the past, it has voted in favour of every newly established UN peacekeeping operation since the beginning of the new millennium. Previous studies of China's behaviour in UN peacekeeping explained this phenomenon primarily with recent shifts in its foreign and security policy rather than with changes in UN peacekeeping itself. This article analyses China's voting behaviour in the UN Security Council on peacekeeping resolutions in the context of the evolving concepts of UN peacekeeping. It argues that China's recent enthusiasm for these missions is the result of two developments. On the one hand, Beijing was able to reinterpret its understanding of UN peacekeeping after its experience in the 1990s, especially with regard to the use of force; while on the other hand, the way UN peacekeeping missions are conducted was reformed after the Brahimi Report in 2000, which made UN peacekeeping more agreeable to the China.
The Political Economy of Land Reform in China's “Newly Liberated Areas”: Evidence from Wuxi County
Authors: Kai-Sing Kung James
Published: September 2008

A farm survey conducted in Wuxi county in the 1950s found that the Chinese Communist Party had successfully “preserved the rich peasant economy” in the “newly liberated areas”: the landlords were indeed the only social class whose properties had been redistributed, yet without compromising on the magnitude of benefits received by the poor peasants. A higher land inequality in that region, coupled with an inter-village transfer of land, allowed these dual goals to be achieved. Our study further reveals that class status was determined both by the amount of land a household owned and whether it had committed certain “exploitative acts,” which explains why some landlords did not own a vast amount of land. Conversely, it was the amount of land owned, not class status, that determined redistributive entitlements, which was why 15 per cent of the poor peasants and half of the middle peasants were not redistributed any land.
Stationary oscillation of an impulsive delayed system and its application to chaotic neural networks
Authors: Sun Jitao , Lin Hai
Published: September 2008

This paper investigates the stationary oscillation for an impulsive delayed system which represents a class of nonlinear hybrid systems. First, a new concept of S-stability is introduced for nonlinear impulsive delayed systems. Based on this new concept and fixed point theorem, the relationship between S-stability and stationary oscillation (i.e., existence, uniqueness and global stability of periodic solutions) for the nonlinear impulsive delayed system is explored. It is shown that the nonlinear impulsive delayed system has a stationary oscillation if the system is S-stable. Second, an easily verifiable sufficient condition is then obtained for stationary oscillations of nonautonomous neural networks with both time delays and impulses by using the new criterion. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed method.
Electroluminescent characteristics of scandium and yttrium 8-quinolinolates
Authors: Katkova Marina A. , Ilichev Vasilii A. , Konev Alexey N. , Bochkarev Mikhail N. , Vitukhnovsky Alexey G. , Parshin Mikhail A. , Pandey Lesley , Van der Auweraer Mark
Published: September 2008

Efficient electroluminescence (EL) was obtained in organic light-emitting devices using 8-quinolinolate complexes of scandium (Scq3) and yttrium (Yq3) as emitters. Compared to the device based on the analogous Alq3 complex, no notable difference in the EL performances of the Yq3 device can be found; however, the EL characteristics of device with Scq3 were significantly enhanced. The device with the configuration of indium tin oxide/ N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine/Scq3/Yb exhibits a maximum current efficiency of 4.6 cd/A and a maximum power efficiency of 2.6 lm/W at a luminance of 300 cd/m2. The improvement of the performance of this device should be attributed to the higher hole mobility of the Scq3 as compared to Alq3 or a smaller barrier for hole injection into Scq3 compared to Alq3.
Determination of complex refractive index of thin metal films from terahertz time-domain spectroscopy
Authors: Zhou Da-xiang , Parrott E. P. J. , Paul Douglas J. , Zeitler J. Axel
Published: September 2008

Thin metal films alone or incorporated in a multilayer stack structure with dielectric films are good candidates of terahertz absorbers necessary for achieving the maximum responsivity in microbolometer devices. However, the design and optimization of these absorber structures depend on the knowledge of the complex refractive index of metal films in the terahertz frequency range, which is not easy to measure or determine from experiment. This paper presents a novel method that allows fast and reliable extraction of the complex refractive index from terahertz time-domain spectroscopy. It starts with terahertz time-domain transmission measurements, followed by Fourier transforms to obtain the transmission spectrum in the frequency range of 0.1–3 THz, and finally an extraction process using the enhanced “on-the-downhill” algorithm. Some experimental examples are given, all of which show good agreement with theoretical calculations. This extraction method, combined with the scattering matrix model, can help design and optimize complicated absorber structures for terahertz microbolometers.
Direct structural evidence of the change in N-III bonding in (GaIn)(NAs) before and after thermal annealing
Authors: Volz K. , Torunski T. , Rubel O. , Stolz W.
Published: September 2008

The blueshift of the fundamental energy gap of (GaIn)(NAs) upon thermal treatment is well established. However, the physical reason is still controversially discussed in literature. In the present paper we give direct structural evidence using transmission electron microscopy in combination with structure factor calculation that this blueshift—for the metal organic vapor phase epitaxy grown samples investigated here—results solely from a change in the local environment of nitrogen. N is bound to Ga upon growth and moves into an In-rich environment upon annealing to minimize the strain energy of the crystal. The technique presented here can be used to unambiguously determine the reason for the blueshift of differently grown and annealed dilute nitride materials.
Structural, electrical, and optical properties of thermally evaporated nanocrystalline PbTe films
Authors: Wang Jianfei , Hu Juejun , Sun Xiaochen , Agarwal Anuradha M. , Kimerling Lionel C. , Lim Desmond R. , Synowicki R. A.
Published: September 2008

Nanocrystalline PbTe films are deposited on different substrates at room temperature through thermal evaporation. The films are stoichiometric single-phase polycrystalline with (200) texture. Electrical properties of the films are analyzed in the framework of a grain boundary channel conduction model. The index of refraction and extinction coefficient of PbTe films are extracted from infrared spectroscopic ellipsometry measurement in the wavelength range of 2–8 μm, yielding an optical band gap of 0.386 eV and evidence for the presence of an Urbach band tail. The optical band gap is larger than the typical value for bulk material due to quantum confinement effect.
Modeling the electromigration failure time distribution in short copper interconnects
Authors: Dwyer V. M.
Published: September 2008

The electromigration (EM) lifetime in short copper interconnects is modeled using a previously developed means of generating realistic interconnect microstructures combined with the one-dimensional stress evolution equation of Korhonen et al. [J. Appl. Phys. 73, 3790 (1993)]. This initial analysis describes the void nucleation and subsequent growth in lines blocked at one end and terminated with a pad at the other. For short copper interconnects, the failure time is largely spent on void growth, and, for sufficiently short lines (≲50 mm), the growth is largely steady state. This allows for the development of a simple expression for the variation of the failure time with microstructure. Assuming that the diffusion activation energies are normally distributed, the permanence property of summed lognormals leads to a roughly lognormal distribution for EM failure times. Importantly for EM design rules, linear extrapolation on lognormal plot is found to slightly underestimate interconnect reliability.
Deformation mechanism transition caused by strain rate in a pulse electric brush-plated nanocrystalline Cu
Authors: Jiang Zhonghao , Zhang Hanzhuo , Gu Changdong , Jiang Qing , Lian Jianshe
Published: September 2008

Bulk nanocrystalline Cu was synthesized by a pulse electric brush-plating technique. A very large strength (at 2% plastic strain) increase from 644 to 1451 MPa was obtained by compression tests at room temperature and strain rates from 1×10−5 to 3×100 s−1. A transition in plastic deformation mechanism with strain rate from a combination of the thermally activated grain boundary sliding and the dislocation emission-absorption in grain boundaries to one dominated by the dislocation activity has been revealed by the significant changes in strain rate sensitivity and apparent activation volume with strain rate.
Structural instability of epitaxial zinc-blende vanadium pnictides and chalcogenides for half-metallic ferromagnets
Authors: Huang Dan , Zhao Yu-Jun , Chen Li-Juan , Chen Di-Hu , Shao Yuan-Zhi
Published: September 2008

We present a first-principles study of the criteria governing the electronic and structural stability of epitaxial, half-metallic ferromagnetic materials with zinc-blende structure. Upon their application to vanadium pnictides and chalcogenides, we find that the criteria for structural stability are crucial when the optimal match pattern of an epitaxial film with the substrate is considered. Our study shows that thick zinc-blende epitaxial films are difficult to obtain by coherent epitaxial growth for vanadium pnictides and chalcogenides. We suggest that more attention needs to be paid to spin polarized ultrathin films (instead of the thick films) as high spin injection materials.
The role of Ca traces in the passivation of silicon dioxide dielectrics for electron transport in pentacene organic field effect transistors
Authors: Benson Niels , Gassmann Andrea , Mankel Eric , Mayer Thomas , Melzer Christian , Schmechel Roland , von Seggern Heinz
Published: September 2008

Recently, n-type transport in organic field effect transistors (OFETs) incorporating pentacene on a silicon dioxide (SiO2) dielectric has been demonstrated by Ahles et al. [Appl. Phys. Lett. 85, 4499 (2004)]. The electron transport was made possible by modifying the dielectric/semiconductor interface using traces of Ca. While the facilitation of electron current in pentacene remained unclear at that point, an interface near filling of electron trap states in the transistor channel or on the SiO2 dielectric could be suggested as a possible explanation. In the following the influence of the Ca interlayer on the n-type transport in pentacene based OFETs will be correlated with an x-ray photoelectron spectroscopy analysis of the SiO2/Ca interface, in dependence of the Ca layer thickness. It is demonstrated that for low thicknesses an oxidized Ca insulator is formed on the SiO2 dielectric, allowing for the observed pentacene electron transport. The formation of the oxide is suggested to compensate available electron traps, in the form of hydroxyl groups on the SiO2 surface, thus reducing the trap density and isolating remaining interface traps from the transistor channel. Furthermore, it is substantiated for an increased Ca layer thickness, that metallic Ca remains in the oxidized Ca interlayer. This leads to a substantial degradation of the OFET charge carrier transport properties. It is found that up to a Ca layer thickness of ∼12 Å, the metallic Ca fraction in the oxidized Ca layer can be effectively reduced by thermal or cyclic electrical stress, leading to a permanent improvement in the n-type OFET transport properties.
High-mobility microcrystalline silicon thin-film transistors prepared near the transition to amorphous growth
Authors: Chan Kah-Yoong , Knipp Dietmar , Gordijn Aad , Stiebig Helmut
Published: September 2008

Thin-film transistors (TFTs) are core elements of novel display media on rigid or flexible substrates, radio-frequency identification tags on plastic foils, and other large area electronic applications. Microcrystalline silicon TFTs prepared at temperatures compatible with flexible substrates (150–200 °C) have gained much attention as potential elements for such applications due to their high charge carrier mobilities. Understanding the relationship between the structural properties and the charge transport is essential in realizing TFTs with high charge carrier mobility at low temperatures. In this study, top-gate staggered microcrystalline silicon TFTs were realized by plasma-enhanced chemical vapor deposition at maximum temperature of 180 °C. We investigated the correlation between the structural properties of the microcrystalline silicon channel material and the performance of the microcrystalline silicon TFTs. Transistors with the highest charge carrier mobility, exceeding 50 cm2/V s, were realized near the transition to amorphous growth. The results reveal that electronic defects at the grain boundaries of the silicon crystallites are passivated by the amorphous phase near the transition to amorphous growth. The crystalline volume fraction of the channel material will be correlated with the transistor parameters such as charge carrier mobility, threshold voltage, and subthreshold slope.
Switching and characteristic dielectric parameters of a room temperature antiferroelectric liquid crystal mixture
Authors: Kumar Anil , Dhar R. , Agrawal V. K. , Dabrowski R. , Tykarska M.
Published: September 2008

The switching and dielectric properties of a room temperature bicomponent antiferroelectric liquid crystal mixture have been investigated as a function of temperature and frequency. Thermodynamic, optical texture, and dielectric studies carried out on the mixture show the phase sequence of Cr←(12.0 °C)→SmIA∗←(29.1 °C)→SmCA∗←(91.5 °C)→SmC∗←(92.9 °C)→SmA∗←(106.7 °C)→Iso. Spontaneous polarization (Ps), switching time (ts), and torsional bulk viscosity (γϕ) have been determined by using polarization reversal method. Dielectric spectroscopy of the mixture in the frequency range of 0.1 Hz–10 MHz reveals, eight different modes of relaxation in the paraelectric SmA∗, ferroelectric SmC∗, antiferroelectric SmCA∗ and SmIA∗ phases. Origins of these modes have been identified with the help of frequency, temperature, and bias electric field dependence of various dielectric parameters.
First-principles study of the electronic and optical properties in rhombohedral LaAlO3
Authors: Luo Xin , Wang Biao
Published: September 2008

In this paper, the electronic structure, chemical bonding, and optical properties of rhombohedral LaAlO3 are investigated by using the full potential linearized augmented plane wave method with the generalized gradient approximation. The analysis of the electronic density profile, Mulliken charge, and bond population shows a combination of the covalent and ionic natures in the chemical bonding. The calculated complex dielectric function is consistent with the experimental data from the ultraviolet spectroscopic ellipsometry measurement. The optical spectra are assigned to the interband transition from O valence to La conduction bands in the low energy region. Furthermore, absorption spectrum, electron energy-loss spectrum, optical conductivity, reflectivity, and refractive index are derived from the complex dielectric function, and the absorption spectrum exhibits an optical band gap of 6.1 eV, which is consistent with several other experimental measurements.
Multiphoton absorption in CsLiB6O10 with femtosecond infrared laser pulses
Authors: Reddy J. N. Babu , Naik V. B. , Elizabeth Suja , Bhat H. L. , Venkatram N. , Rao D. Narayana
Published: September 2008

Nonlinear absorption and refraction characteristics of cesium lithium borate (CsLiB6O10) crystal have been studied using Z-scan technique. Ti:sapphire laser with 110 fs pulse width operating at 800 nm wavelength and pulse repetition rate of 1 kHz is used as the source of photons. Intensity of the laser pulse is varied from 0.541 to 1.283 T W/cm2 to estimate the intensity dependence of multiphoton absorption coefficients. Using the theory of multiphoton absorption proposed by Sutherland [Handbook of Nonlinear Optics, in 2nd ed., edited by D. G. McLean and S. Kirkpatrick, Dekker, New York (2003)], found that open aperture Z-scan data fit well for the five-photon absorption (5PA) process. 5PA coefficients are obtained by fitting the expressions into the open aperture experimental data for various peak intensities (I00). The nonlinear refractive index n2 estimated from closed aperture Z-scan experiment is 1.075×10−4 cm2/T W at an input peak intensity of 0.723 T W/cm2. The above experiment when repeated with a 532 nm, 6 ns pulsed laser led to an irreversible damage of the sample resulting in an asymmetric open aperture Z-scan profile. This indicates that it is not possible to observe multiphoton absorption in this regime of pulse width using 532 nm laser.
Crystal nucleation in glasses of phase change memory
Authors: Karpov V. G. , Kryukov Y. A. , Mitra M. , Karpov I. V.
Published: September 2008

We propose a theory of field induced crystal nucleation in disordered glass structure applicable to chalcogenide phase change memory. In the region of symmetry breaking strong electric fields, the nucleation is dominated by cylinder shaped particles with bias dependent nucleation barriers. Statistical fluctuations in microscopic structure of a glass translate into probabilistic distributions of induction times and threshold voltages having respectively log-normal and normal shape. These distributions are exponentially sensitive to the applied voltage, temperature, and material parameters.
First-principles anisotropic constitutive relationships in β-cyclotetramethylene tetranitramine (β-HMX)
Authors: Conroy M. W. , Oleynik I. I. , Zybin S. V. , White C. T.
Published: September 2008

First-principles density functional theory calculations have been performed to obtain constitutive relationships in the crystalline energetic material β-cyclotetramethylene tetranitramine (β-HMX). In addition to hydrostatic loading, uniaxial compressions in the directions normal to the {100}, {010}, {001}, {110}, {101}, {011}, and {111} planes have been performed to investigate the anisotropic equation of state (EOS). The calculated lattice parameters and hydrostatic EOS are in reasonable agreement with the available experimental data. The uniaxial compression data show a significant anisotropy in the principal stresses, change in energy, band gap, and shear stresses, which might lead to the anisotropy of the elastic-plastic shock transition and shock sensitivity of β-HMX.
Weak antilocalization and beating pattern in high electron mobility AlxGa1−xN/GaN two-dimensional electron gas with strong Rashba spin-orbit coupling
Authors: Zhou W. Z. , Lin T. , Shang L. Y. , Sun L. , Gao K. H. , Zhou Y. M. , Yu G. , Tang N. , Han K. , Shen B. , Guo S. L. , Gui Y. S. , Chu J. H.
Published: September 2008

The weak antilocalization (WAL) effects of the two-dimensional electron gas (2DEG) in high mobility AlxGa1−xN/GaN heterostructure as well as beating patterns in the Shubnikov–de Haas (SdH) oscillatory magnetoresistance have been investigated by means of magnetotransport measurements before and after illumination. The zero-field spin splitting mainly arising from the Rashba spin-orbit coupling effect is studied using the weak antilocalization and beating patterns analysis, respectively. The Rashba spin-orbit coupling constant α deduced using the weak antilocalization analysis showed a good agreement with that estimated from the analysis of the beating patterns for the sample before and after illumination. For our sample, the electron motion in the high mobility system is in the ballistic regime, the experimental WAL curves were fitted by a simulated quantum conductance correction according to a model proposed by [Golub [Phys. Rev. B 71, 235310 (2005)].
Optical detection and characterization of graphene by broadband spectrophotometry
Authors: Gray Alexander , Balooch Mehdi , Allegret Stephane , De Gendt Stefan , Wang Wei-E
Published: September 2008

The spectra of optical constants, index of refraction (n), and extinction coefficient (k) of graphene and graphite are obtained in the wavelength range of 190–1000 nm (6.53–1.24 eV) using broadband optical spectrophotometry in conjunction with the Forouhi–Bloomer dispersion relations for n and k. Measurement is made possible by the use of a multilayer substrate consisting of bulk Si and a 3000 Å SiO2 film. The effect of multiple internal reflections between the Si/SiO2 and SiO2/graphene interfaces amplifies the attenuating effect of the graphene layer, thereby improving the sensitivity of the reflectance measurement by a factor of 27 in the deep ultraviolet region of the spectrum. Maximum sensitivity is observed in the deep ultraviolet region of the spectrum, where a strong peak in the spectrum of the extinction coefficient of graphene is identified. The proposed method enables fast nondestructive angstrom-level thickness measurements of graphene and graphite. In this work, layers ranging in thickness between 3.8 Å (graphene) and 792.8 Å are detected, measured, and characterized. Reflectance spectra of graphene and graphite on Ni, Co, and Fe substrates are calculated. Differences of 1.1%–2.0% between the bare substrate and the graphene on the substrate are predicted in the deep ultraviolet region of the spectrum, which makes graphene detectable and measurable on these substrates.
Statistical characterization of surface defects created by Ar ion bombardment of crystalline silicon
Authors: Ghazisaeidi M. , Freund J. B. , Johnson H. T.
Published: September 2008

Ion bombardment of crystalline silicon targets induces pattern formation by the creation of mobile surface species that participate in forming nanometer-scale structures. The formation of these mobile species on a Si(001) surface, caused by sub-keV argon ion bombardment, is investigated through molecular dynamics simulation of Stillinger-Weber [Phys. Rev. B 31, 5262 (1985)] silicon. Specific criteria for identifying and classifying these mobile atoms based on their energy and coordination number are developed. The mobile species are categorized based on these criteria and their average concentrations are calculated.
Structure and dynamics of silicon-oxygen pairs and their role in silicon self-diffusion in amorphous silica
Authors: Kuo Chin-Lung , Lee Sangheon , Hwang Gyeong S.
Published: September 2008

Based on gradient corrected periodic density functional theory calculations, we present the formation, structure, and diffusion of SiO pairs in a-SiO2. We find that a SiO pair preferentially undergoes transformation into an O vacancy through a twofold-coordinated Si atom. We determine the pathways for SiO pair→divalent Si→O vacancy transformation and divalent Si diffusion, along with O vacancy diffusion. Based on these results, we also discuss how the presence of SiO pairs can enhance Si self-diffusion in a-SiO2.
Nanotwin and phase transformation in tetragonal Pb(Fe1/2Nb1/2)1−xTixO3 single crystal
Authors: Tu C.-S. , Tseng C.-T. , Chien R. R. , Schmidt V. Hugo , Hsieh C.-M.
Published: September 2008

This work is a study of phase transformation in (001)-cut Pb(Fe1/2Nb1/2)1−xTixO3 (x=48%) single crystals by means of dielectric permittivity, domain structure, and in situ x-ray diffraction. A first-order T(TNT)-C(TNT) phase transition was observed at the Curie temperature TC≅518 K upon zero-field heating. T, TNT, and C are tetragonal, tetragonal nanotwin, and cubic phases, respectively. T(TNT) and C(TNT) indicate that minor TNT domains reside in the T and C matrices. Nanotwins, which can cause broad diffraction peak, remain above TC≅518 K and give an average microscopic cubic symmetry in the polarizing microscopy. Colossal dielectric permittivity (>104) was observed above room temperature with strong frequency dispersion. This study suggests that nanotwins can play an important role in relaxor ferroelectric crystals while phase transition takes place. The Fe ion is a potential candidate as a B-site dopant for enhancing dielectric permittivity.
Structural and dielectric properties of epitaxial SrTiO3 films grown directly on GaAs substrates by laser molecular beam epitaxy
Authors: Wu Z. P. , Huang W. , Wong K. H. , Hao J. H.
Published: September 2008

Epitaxial SrTiO3 films were grown on GaAs (001) substrates without any buffer layers using laser molecular beam epitaxy technique. The reflection high-energy electron diffraction observations have revealed that a layer-by-layer growth of SrTiO3 was achieved at optimized deposition conditions. The crystalline orientation of the as-grown SrTiO3 (001) films rotates 45° in plane with respect to the GaAs substrates. Atomic force microscope studies show that these films possess atomically flat surfaces. The dielectric properties of the heterostructure were also investigated. Our results have clearly demonstrated the practicality of integrating perovskite oxide thin films with GaAs substrates.