bluuebunny/crossref_metadata_2025 huggingface dataset:
ELECTROMAGNETIC-LIKE BOOST TRANSFORMATIONS OF WEYL AND MINIMAL SUPER-ENERGY OBSERVERS IN BLACK HOLE SPACETIMES
Authors: BINI DONATO , JANTZEN ROBERT T. , MINIUTTI GIOVANNI
Published: November 2002

The transformation laws for the electric and magnetic parts of the electromagnetic 2-form and the Weyl tensor under a boost are studied using the complex vector approach, which shows the close analogy between the two cases. For a nonnull electromagnetic field, one can always find an observer who sees parallel electric and magnetic fields (vanishing Poynting vector) and also sees a minimum electromagnetic energy density (and minimum electric and magnetic field magnitudes) compared to other observers. For Weyl fields of all Petrov types except III, and boosts along certain directions of the Weyl principal tetrad, the more complicated Weyl transformation closely mimics the electromagnetic boost transformation, allowing one to extend the electromagnetic results directly to the families of boosts along those directions. In particular for black hole spacetimes, the alignment of the electric and magnetic parts of the Weyl tensor (vanishing super-Poynting vector) leads to minimal gravitational super-energy as seen by the Carter observer within the family of all circularly rotating observers at each spacetime point outside the horizon.
DOUBLY STOCHASTIC EFFECTS
Authors: ZAIKIN A.
Published: November 2002

Doubly stochastic effects are effects in which an optimization of both multiplicative and additive noise intensities is necessary to induce ordering in a nonlinear system. I review recent achievements in the investigation of these effects and discuss two phenomena: doubly stochastic resonance and noise-induced propagation in monostable medium. Finally I discuss possible experimental implementations of these phenomena.
A CHARACTERIZATION OF SUPRATHRESHOLD STOCHASTIC RESONANCE IN AN ARRAY OF COMPARATORS BY CORRELATION COEFFICIENT
Authors: MCDONNELL MARK D. , ABBOTT DEREK , PEARCE CHARLES E. M.
Published: November 2002

Suprathreshold Stochastic Resonance (SSR), as described recently by Stocks, is a new form of Stochastic Resonance (SR) which occurs in arrays of nonlinear elements subject to aperiodic input signals and noise. These array elements can be threshold devices or FitzHugh-Nagumo neuron models for example. The distinguishing feature of SSR is that the output measure of interest is not maximized simply for nonzero values of input noise, but is maximized for nonzero values of the input noise to signal intensity ratio, and the effect occurs for signals of arbitrary magnitude and not just subthreshold signals. The original papers described SSR in terms of information theory. Previous work on SR has used correlation based measures to quantify SR for aperiodic input signals. Here, we argue the validity of correlation based measures and derive exact expressions for the cross-correlation coefficient in the same system as the original work, and show that the SSR effect also occurs in this alternative measure. If the output signal is thought of as a digital estimate of the input signal, then the output noise can be considered simply as quantization noise. We therefore derive an expression for the output signal to quantization noise ratio, and show that SSR also occurs in this measure.
INFLUENCE OF DENSITY, OCCUPANCY AND LOCATION OF ELECTRON TRAPS ON SHOT NOISE IN NONDEGENERATE QUASIBALLISTIC TRANSPORT
Authors: VASALLO B. G. , MATEOS J. , PARDO D. , GONZÁLEZ T.
Published: November 2002

An ensemble Monte Carlo simulator self-consistently coupled with a Poisson solver is used to study the influence of the density, occupancy and location of electrons traps on the current fluctuations in nondegenerate quasiballistic structures. Transport and noise are found to depend significantly on the density and location of the traps. In particular, the presence of traps increases the noise level as compared with the purely ballistic case. The nonuniformity of the trap occupancy profiles along the active region of the structures affects markedly (specially for low trap densities) the dependence of shot noise on the applied voltage. The location of the traps with respect to the potential minimum appearing in the structures because of the presence of space charge determines their influence on the noise level, fact which can be of help to identify the trap position.
EMPLOYMENT IMPACT OF CLEANER PRODUCTION ON THE FIRM LEVEL: EMPIRICAL EVIDENCE FROM A SURVEY IN FIVE EUROPEAN COUNTRIES
Authors: RENNINGS KLAUS , ZWICK THOMAS
Published: November 2002

This paper analyses the determinants of employment reactions of firms where environmentally friendly innovations (eco-innovations) were carried out. The data stem from a telephone survey covering more than 1500 firms in five European countries that have recently introduced eco-innovations. We found that product and service innovations create more jobs than process innovations. Moreover, employment impacts differ depending on the intended goals of the innovations. If products and processes are motivated by the goal of cost reduction, they tend to reduce employment. If they are motivated by market share goals, effects can be positive or negative depending on the success of the strategy the firm is following. With respect to skill-biased technogical change, eco-innovations do not differ from other innovations. So, environmental innovations have a small but positive net effect on employment. Thus, environmental support programmes do not counteract labour market policy. A further shift from end-of-pipe technologies to cleaner production, especially towards product and service innovations, would be beneficial for the environment and create jobs.
An Integrated Computational Infrastructure for a Virtual Tokyo Concepts and Examples
Authors: Kraines Steven B. , Wallace David R. , Iwafune Yumiko , Yoshida Yoshikuni , Aramaki Toshiya , Kato Kazuhiko , Hanaki Keisuke , Ishitani Hisashi , Matsuo Tomonori , Takahashi Hiroshi , Yamada Koichi , Yamaji Kenji , Yanagisawa Yukio , Komiyama Hiroshi
Published: November 2002

The evaluation of tradeoffs between technologies and policies for mitigation of environmental problems requires a systematic investigation of effects over the entire region under consideration. When attempting to model such large complex systems, issues such as usability, maintenance, and computing efficiency often become major modeling barriers. In this work a software prototype for integrating the services of computational models over the Internet, called DOME (distributed object‐based modeling environment) is used to facilitate the construction of virtual Tokyo—a simulation platform for evaluating holistically the tradeoffs between various technologies for reducing the emissions of greenhouse gases. In making steps toward this ultimate goal, two models have been developed that use data defining spatial land‐use distributions and the flows of goods expressed as an input‐output table to provide information on the spatial and temporal characteristics of an urban region. Integrated, these models form a preliminary virtual Tokyo model when applied to Tokyo‐specific databases. Given this platform, process models are applied to examine the effectiveness of using photovoltaic (PV) modules on the demand side to reduce conventional electric power generation and, thereby, also reduce carbon dioxide emissions. The results of introducing PV modules on the rooftops of buildings in Tokyo under various installation conditions are presented as a working example of the prototype. For full deployment on usable rooftop space, PV power generation could reduce carbon dioxide emissions from electric power generation by more than 12%. Future work will use the same methods as presented in this paper to examine cost, a critical determinant in the actual feasibility of PV module installation.
Size distribution of geological faults: Model choice and parameter estimation
Authors: Borgos Hilde Grude , Omre Henning , Townsend Chris
Published: November 2002

Geological faults are important in reservoir characterization, since they influence fluid flow in the reservoir. Both the number of faults, or the fault intensity, and the fault sizes are of importance. Fault sizes are often represented by maximum displacements, which can be interpreted from seismic data. Owing to limitations in seismic resolution only faults of relatively large size can be observed, and the observations are biased. In order to make inference about the overall fault population, a proper model must be chosen for the fault size distribution. A fractal (Pareto) distribution is commonly used in geophysics literature, but the exponential distribution has also been suggested. In this work we compare the two models statistically. A Bayesian model is defined for the fault size distributions under the two competing models, where the prior distributions are given as the Pareto and the exponential pdfs, respectively, and the likelihood function describes the sampling errors associated with seismic fault observations. The Bayes factor is used as criterion for the model choice, and is estimated using MCMC sampling. The MCMC algorithm is constructed using pseudopriors to sample jointly the two models. The statistical procedure is applied to a fault size data set from the Gullfaks Field in the North Sea. For this data set we find that the fault sizes are best described by the exponential distribution.
Compatibility issues for mechanical system modelling with standard components
Authors: Hicks B J , Culley S J
Published: November 2002

The success of a product and ultimately the associated company are largely dependent on the ability of the company to generate effective, high-quality and economical design solutions within shortened development times. To achieve increased quality and considerable time savings, standard components can be utilized. In order to establish a suitable solution the designer must evaluate various component types, sizes and combinations until the desired performance capabilities for the design are achieved. However, further improvements in economy and performance can be obtained by the effective utilization of various configurations of standard components. During this phase of evaluation, the designer must consider not only system performance but also component issues such as reliability, suppliers, cost, maintenance and internal practices. The pressure for reduced time to market does not leave room for time-consuming trial-and-error approaches. Today, experimentally validated computer modelling has become the preferred choice for rapidly carrying out the assessment of performance and the evaluation of design alternatives. In using such techniques the designer also demands the capability to assess whether the connected components are suitable both quantitatively and qualitatively. The quantitative issues relate to whether the components are physically connectible and matched in terms of their performance capabilities, while the qualitative issues relate to the utilization of the component or a sequence of components. These may include preferences for suppliers, cost considerations, reliability issues, recommended component combinations and internal practices. These two aspects of the embodiment process are defined as compatibility analysis in this work.

This paper outlines the process for the embodiment of mechanical systems with standard components and identifies the key aspects of compatibility analysis. Following this, the importance of and the requirements for compatibility analysis in modelling mechanical systems are discussed and a strategy to support compatibility analysis within a modelling environment is proposed. This strategy is implemented into an existing system modelling tool and an example study is included to illustrate the benefits to the designer.
A Shannon sampling approach to form error estimation
Authors: Yang T-H , Jackman J
Published: November 2002

Form error estimation is a critical step in verifying that a product satisfies design specifications. It is demonstrated how Shannon sampling can be used to reconstruct surface profiles if they are treated as band-limited signals. To demonstrate its use in form estimation, a Shannon sampling series is applied to flatness error estimation for uniform sample points measured from five common machined surfaces. The results indicate that Shannon sampling provides superior performance over using points directly for estimation.
The disinfection of flexible fibre-optic nasendoscopes out-of-hours: confidential telephone survey of ENT units in England
Authors: Kanagalingam J. , Zainal A. , Georgalas C. , Paun S. , Tolley N. S.
Published: November 2002

We present the results of a confidential telephone survey of ENT units in England on the disinfection of flexible fibre-optic nasendoscopes out-of-hours. The on-call residents of 124 units were contacted and questioned. In 35.1 per cent of units surveyed, the on-call resident was primarily responsible for cleaning the scopes after use. Only 46 per cent of these junior doctors had access to a chemical sterilant to allow for high-level disinfection of these scopes. Provision for disinfection of scopes was poorer in teaching hospitals and in units that served inner city populations. Only 12.1 per cent of Senior House Officers (SHOs) received any training in disinfection techniques and only 25.5 per cent of units kept a register of patients nasendoscoped out-of-hours for purposes of contact tracing.
Descending necrotizing mediastinitis: report of a case following steroid neck injection
Authors: Harar R. P. S. , Cranston C. , Warwick-Brown N.
Published: November 2002

Cervical necrotizing fasciitis is a rare, rapidly progressive, severe bacterial infection of the soft tissues of the neck. Uncommonly, it may descend into the mediastinum. We describe a case of descending necrotizing mediastinitis in a young man, where there was diagnostic confusion and delay, with an eventual fatal outcome. A steroid injection for neck pain is thought to be the source of infection. In this case, the signs of mediastinitis were initially masked, and the diagnosis delayed until cardiopulmonary arrest occurred. Early recognition with a low threshold for computed tomography (CT) scanning is essential. Aggressive multidisciplinary therapy with mediastinal drainage is mandatory.
Participation in health care priority-setting through the eyes of the participants
Authors: Martin Douglas , Abelson Julia , Singer Peter
Published: November 2002

Objectives: The literature on participation in priority-setting has three key gaps: it focuses on techniques for obtaining public input into priority-setting that are consultative mechanisms and do not involve the public directly in decision-making; it focuses primarily on the public's role in priority-setting, not on all potential participants; and the range of roles that various participants play in a group making priority decisions has not been described. To begin addressing these gaps, we interviewed individuals who participated on two priority-setting committees to identify key insights from participants about participation. Methods: A qualitative study consisting of interviews with decision-makers, including patients and members of the public. Results: Members of the public can contribute directly to important aspects of priority-setting. The participants described six specific priority-setting roles: committee chair, administrator, medical specialist, medical generalist, public representative and patient representative. They also described the contributions of each role to priority-setting. Conclusions: Using the insights from decision-makers, we have described lessons related to direct involvement of members of the public and patients in priority-setting, and have identified six roles and the contributions of each role.
Health policy-makers' perceptions of their use of evidence: a systematic review
Authors: Innvær Simon , Vist Gunn , Trommald Mari , Oxman Andrew
Published: November 2002

Objectives: The empirical basis for theories and common wisdom regarding how to improve appropriate use of research evidence in policy decisions is unclear. One source of empirical evidence is interview studies with policy-makers. The aim of this systematic review was to summarise the evidence from interview studies of facilitators of, and barriers to, the use of research evidence by health policy-makers.

Methods: We searched multiple databases, including Medline, Embase, Sociofile, PsychLit, PAIS, IBSS, IPSA and HealthStar in June 2000, hand-searched key journals and personally contacted investigators. We included interview studies with health policy-makers that covered their perceptions of the use of research evidence in health policy decisions at a national, regional or organisational level. Two reviewers independently assessed the relevance of retrieved articles, described the methods of included studies and extracted data that were summarised in tables and analysed qualitatively.

Results: We identified 24 studies that met our inclusion criteria. These studies included a total of 2041 interviews with health policy-makers. Assessments of the use of evidence were largely descriptive and qualitative, focusing on hypothetical scenarios or retrospective perceptions of the use of evidence in relation to specific cases. Perceived facilitators of, and barriers to, the use of evidence varied. The most commonly reported facilitators were personal contact (13/24), timely relevance (13/24), and the inclusion of summaries with policy recommendations (11/24). The most commonly reported barriers were absence of personal contact (11/24), lack of timeliness or relevance of research (9/24), mutual mistrust (8/24) and power and budget struggles (7/24).

Conclusions: Interview studies with health policy-makers provide only limited support for commonly held beliefs about facilitators of, and barriers to, their use of evidence, and raise questions about commonsense proposals for improving the use of research for policy decisions. Two-way personal communication, the most common suggestion, may improve the appropriate use of research evidence, but it might also promote selective (inappropriate) use of research evidence.
Active Pitch Control in Larger Scale Fixed Speed Horizontal Axis Wind Turbine Systems Part I: Linear Controller Design
Authors: Bao Nengsheng , Ye Zhiquan
Published: November 2002

This paper reviews and addresses the principles of linear controller design of the fixed speed wind turbine system in above rated wind speed, using pitch angle control of the blades and applying modern control theory. First, the non-linear equations of the system are built in under some reasonable suppositions. Then, the non-linear equations are linearised at set operating point and digital simulation results are shown in this paper. Finally, a linear quadratic optimal feedback controller is designed and the dynamics of the closed circle system are simulated with digital calculation. The advantages and disadvantages of the assumptions and design method are also discussed. Because of the inherent characteristics of the linear system control theory, the performance of the linear controller is not sufficient for operating wind turbines, as is discussed.
The Mutual Effects of Grid and Wind Turbine Voltage Stability Control
Authors: Akhmatov Vladislav
Published: November 2002

This note considers the results of wind turbine modelling and power system stability investigations. Voltage stability of the power grid with grid-connected wind turbines will be improved by using blade angle control for a temporary reduction of the wind turbine power during and shortly after a short circuit fault in the grid.
Statistical Study of the Instantaneous Values of Traffic Noise Sound Pressure Level
Authors: Fernández Jesús Alba , García Marcelino Ferri , Soriano Jaime Ramis , Mora Juan Antonio Martínez
Published: November 2002

In environmental acoustics the knowledge of the time dependency of the sound level provides relevant information about a sound event. In this sense, it may be said that conventional sound level metres have frequently implemented programs to calculate the fractiles (percentiles) of the distribution of instantaneous sound levels; and there are several indexes to evaluate the noise pollution, based on different statistical parameters. For further analysis of sound, and to obtain the commented indexes, it is accepted that this distribution is normal or gaussian. The questions we've tried to solve in this work are the following: First of all, whether the time dependent distribution of the variable sound pressure level should be considered as Gaussian in general cases or only in some particular ones. On the other hand, we have studied how the frequency of the sampling affects the resulting distribution of a given a sound event. To these ends, a set of road traffic noise events has been evaluated.

Furthermore, even in gaussian distributions of sound pressure levels, the average of the distribution will not be coincident with the equivalent sound pressure level; that is the level of the average quadratic pressure. The difference between this parameter, and its dependence on the standard deviation, is studied.
Cocaine treatment increases expression of a 40 kDa catecholamine‐regulated protein in discrete brain regions
Authors: Sharan Niki , Chong Victor Z. , Nair Venugopalan D. , Mishra Ram K. , Hayes Robert J. , Gardner Eliot L.
Published: November 2002

Previous reports from our laboratory have described brain‐specific catecholamine‐regulated proteins, which bind dopamine and related catecholamines. Evidence from the molecular cloning of a 40 kDa catecholamine‐regulated protein (CRP40) revealed that CRP40 is dopamine‐inducible and has properties similar to those of the 70 kDa heat shock protein (HSP70) family. The present study investigates the effects of acute and chronic cocaine treatment on CRP40 expression in the striatum, nucleus accumbens, prefrontal cortex, and medulla. Acute treatment with cocaine increased CRP40 expression in the nucleus accumbens and striatum, whereas chronic treatment with cocaine increased CRP40 expression in the nucleus accumbens only. Neither of these treatments affected CRP40 levels in the prefrontal cortex or medulla. In addition, pretreatment with the spin‐trapping agent α‐phenyl‐tert‐butylnitrone did not attenuate cocaine‐induced expression of CRP40, suggesting that the observed increases in CRP40 levels were not caused by free radicals. On the other hand, pretreatment with anisomycin, a protein synthesis inhibitor, blocked the cocaine‐induced expression of CRP40. Thus, protein synthesis may be involved in the observed CRP40 level increases. Furthermore, neither acute nor chronic cocaine treatment affected levels of inducible or constitutively expressed HSP70, which indicates a specificity of cocaine's effects on CRP40. Since cocaine has been shown to increase extracellular dopamine levels, these findings suggest that increased expression of CRP40 is associated with high extracellular levels of dopamine (or its metabolites). Elevated levels of CRP40 could play a protective role for dopamine neurons in response to increased oxidative stress that has been shown to be induced by cocaine and that can lead to apoptosis and neurodegeneration. Synapse 47:33–44, 2003. © 2002 Wiley‐Liss, Inc.
Cocaine alters mu but not delta or kappa opioid receptor‐stimulated in situ [35S]GTPγS binding in rat brain
Authors: Schroeder Joseph A. , Niculescu Michelle , Unterwald Ellen M.
Published: November 2002

Chronic cocaine administration produces alterations in mu and kappa opioid receptor density as well as striatal and accumbens opioid‐regulated adenylyl cyclase activity, suggesting a psychostimulant responsive interaction between opioidergic and dopaminergic systems. Stimulation of G‐protein‐coupled opioid receptors inhibits adenylyl cyclase production of cyclic AMP. The present study employed in situ [35S]GTPγS binding to measure opioid receptor‐stimulated activation of G‐proteins in response to acute and chronic cocaine exposure. Male Fischer rats received acute (1 or 3 days) or chronic (14 days) binge pattern cocaine administration. Three and 14 days of cocaine injections resulted in greater increases in the ability of the mu receptor agonist DAMGO to stimulate [35S]GTPγS binding in both the core and the shell of the nucleus accumbens, all regions of the caudate putamen and the cingulate cortex compared with saline‐matched controls. The greatest increases in DAMGO‐stimulated [35S]GTPγS binding were observed in the dorsal areas of the caudate putamen in animals that received 14 days of cocaine. No significant changes in delta (DPDPE), or kappa (dynorphin A1–17) receptor‐stimulated [35S]GTPγS binding were found in any brain region in response to cocaine administration. These results demonstrate that binge pattern cocaine administration induce changes in mu but not delta or kappa opioid receptor‐mediated G‐protein activity. This study provides support for the hypothesis that the addictive properties of both psychostimulants and opiates may share common neurochemical signaling substrates. Synapse 47:26–32, 2003. © 2002 Wiley‐Liss, Inc.
Ultrasound examination of carotid arteries with intima media measurement: An underestimated tool in the diagnosis of takayasu's disease
Authors: Zieliński Tomasz , Wolkanin-Bartnik Jolanta , Makowiecka-Cicśla Magdalena , Florczak Elżbieta , Cybulska Idalia
Published: November 2002

The diagnosis of Takayasu's arteritis is often clinically difficult. The ultrasound examination of the arteries originating from the aortic arch, especially with the assessment of intima media thickness of common carotid arteries, is easily available and can add valuable information. Eighteen patients, 16 women and 2 men, aged 11–62, with established diagnosis of Takayasu's arteritis and 17 age- and sex-matched controls were examined using duplex color doppler ultrasound. The flow in subclavian, common, internal, external carotid and vertebral arteries was visualized. The mean intima media thickness of the common carotid arteries proximal to the bulb (CCA) and in the carotid bulb were measured in different planes, off-line from digitized images by a single reader, helped by a computerized system for averaging and analysis. A total occlusion of left common carotid arteries in three patients and right CCA in one patient was detected. An occlusion of the brachiocephalic trunk was found in one patient and significant narrowing found in two others. A significant (>50%) stenosis or occlusion of at least one subclavian artery was present in a majority of patients (87%), with a predilection for the left subclavian artery. In 5 patients, a steal syndrome grade II or III was found in the vertebral arteries. The value of the mean IMT of the CCA is patients with Takayasu's disease was significantly higher than in controls (mean ± SEM; 1.1 ± 0.1 vs 0.59 ± 0.01 mm). In healthy controls, the intima media thickness of the bulb was higher than that in the CCA (0.7 ± 0.03 vs 0.59 ± 0.01 mm). In patients with Takayasu's disease, that proportion was inversed (0.81 ± 0.05 vs 1.1 ± 0.1 mm). Higher intima media thickness found in the common carotid artery than in the bulb can rise a suspicion of Takayasu's arteritis.
Visibly Pregnant: Toward a Placental Body
Authors: Maher JaneMaree
Published: November 2002

In recent years, feminist theorists have examined the use of visual technologies in pregnancy and argued that these technologies are reconstructing the meaning of pregnancy. The imaged body of gestation can be deployed to distinguish and separate maternal and foetal interests. Drawing on this work, ‘Visibly Pregnant: Toward a placental body’ argues that the use of visual technology also obfuscates that which it purports to make clear. The images produced by these technologies in particular do not locate and acknowledge the significance of the placenta as a point of connection and distinction for the gestating body. The possibilities suggested by a concentration on the placenta show how the morphology of the pregnant body itself rejects the distinction outlined in the technologically produced images of pregnancy and offers some new possibilities for thinking subjectivity.
Second-order luminescent saturation effects in SrGa2S4:Eu
Authors: Manigault P. , Summers C. J. , Stoffers C.
Published: November 2002

This study identified a quadratic energy loss process in europium-doped strontium thiogallate using luminescent decay time analysis. The role of activator–activator cross relaxation in producing the nonlinearity in the luminescent efficiency for SrGa2S4:Eu was assessed. Ground-state depletion did not contribute to the observed saturation, which instead was attributed to interionic energy transfer (cross relaxation). This work provides a deeper understanding of the factors contributing to luminescent saturation. The understanding of these mechanisms will contribute to the optimization of phosphors for cathodoluminescent applications.
Three-dimensional self-consistent simulation of the charging time response in silicon nanocrystal flash memories
Authors: de Sousa J. S. , Thean A. V. , Leburton J. P. , Freire V. N.
Published: November 2002

A numerical model to calculate the tunneling time from the channel of a metal–oxide–semiconductor device into a silicon nanocrystal embedded in SiO2 is presented. Self-consistent simulations of the Kohn–Sham and Poisson equations are performed to study the role of the size, shape, and barrier thickness of a quantum dot (QD). We found that the charging process is very sensitive to the shape of the QD, resulting in changes of several orders of magnitude in the electron transfer and retention times.
Strain and band edges in single and coupled cylindrical InAs/GaAs and InP/InGaP self-assembled quantum dots
Authors: Tadić M. , Peeters F. M. , Janssens K. L. , Korkusiński M. , Hawrylak P.
Published: November 2002

A comparative study is made of the strain distribution in cylindrical InAs/GaAs and InP/InGaP self-assembled quantum dots as obtained from isotropic elasticity theory, the anisotropic continuum mechanical model, and from atomistic calculations. For the isotropic case, the recently proposed approach [J. H. Davies, J. Appl. Phys. 84, 1358 (1998)] is used, while the finite-element method, the valence force field method, and Stillinger–Weber potentials are employed to calculate the strain in anisotropic structures. We found that all four methods result in strain distributions of similar shapes, but with notable quantitative differences inside the dot and near the disk–matrix boundary. The variations of the diagonal strains with the height of the quantum dot, with fixed radius, as calculated from all models, are almost linear. Furthermore, the energies of the band edges in the two types of quantum dots are extracted from the multiband effective-mass theory by inserting the strain distributions as obtained by the four models. We demonstrated that all strain models produce effective potentials for the heavy and light holes which agree very well inside the dot. A negligible anisotropy of all normal strains in the (x,y) plane is found, which, providing the axial symmetry of the kinetic part of the multiband effective-mass Hamiltonian, justifies the use of the axial approximation. Strain propagation along the vertical direction is also considered with the aim to study the influence of strain on the electron coupling in stacks of quantum dots. We found that the interaction between the strain fields of the individual quantum dots makes the effective quantum wells for the electrons in the conduction band shallower, thereby counteracting the quantum mechanical coupling.
Nonlinear superlattice transport limited by Joule heating
Authors: Scheuerer R. , Renk K. F. , Schomburg E. , Wegscheider W. , Bichler M.
Published: November 2002

We studied the effects caused by Joule heating in GaAs/AlAs superlattices. We measured the current–voltage characteristics of superlattice mesas of different cross sections. Each current–voltage characteristic showed a corresponding peak current followed by a region of negative differential conductivity, according to miniband transport in the superlattice. We found that Joule heating in the mesa reduced the peak-current density. Current jumps in the region of negative differential conductivity disappeared for large cross-section mesas indicating a suppression of electron domains. The results are of significance for the development of high-power superlattice oscillators for submillimeter radiation.
Apparent dependence of conductivity of a conducting polymer on an electric field in a field effect transistor configuration
Authors: Lu Jin , Pinto Nicholas J. , MacDiarmid Alan G.
Published: November 2002

A curious effect is reported whereby an electric field apparently greatly affects the conductivity of an organic polymer, poly-3,4-ethylenedioxythiophene (PEDOT), doped to the “metallic” conducting regime when it is used in an all-organic polymer field effect transistor configuration. The response time for change in current in the source/drain PEDOT polymer with a change of gate voltage is slow (⩽∼2 s), suggesting that ionic diffusion is involved in the phenomenon. It is suggested that the electric field changes only the conductivity of the lowly conducting polymer matrix, which contains highly conducting islands of PEDOT, thus changing the extent of percolation of electric charge between metallic islands, and thereby affecting the bulk conductivity of the PEDOT source/drain material.
Combined dislocation and process modeling for local oxidation of silicon structure
Authors: Chidambarrao D. , Liu X. H. , Schwarz K. W.
Published: November 2002

Recent work on modeling dislocation behavior in small semiconductor structures is extended to the level of complexity appropriate to actual manufacturing situations. The dislocation-dynamics code PARANOID is generalized to handle arbitrary geometries and unstructured stress tables, and combined with commercial process-modeling software to study the dislocation configurations which arise during the growth of the well-known local oxidation of silicon “bird’s beak” structure. Experimentally observed dislocation patterns are reproduced with considerable fidelity. The observed Hu loop configuration is matched to 90% accuracy, provided that the long-range thermal mismatch stresses arising from cooldown are included. It is concluded that the main remaining obstacle to predicting dislocation behavior during device manufacture lies in the difficulty of utilizing current three-dimensional process-modeling codes to obtain reliable stress fields.
A comparative study of spontaneous emission and carrier recombination processes in InGaAs quantum dots and GaInNAs quantum wells emitting near 1300 nm
Authors: Bennett A. J. , Stavrinou P. N. , Roberts C. , Murray R. , Parry G. , Roberts J. S.
Published: November 2002

We have undertaken a comparative study of the emission properties of GaInNAs quantum wells and InGaAs quantum dots (QDs) in the temperature range 10 to 70 °C using p–i–n light emitting diodes (LEDs). It is shown that at 10 °C the external quantum efficiency of the QD LED peaks at almost 1% for low current densities, but that this efficiency rapidly falls as the current is increased further. On the other hand the maximum efficiency of the nitride samples is an order of magnitude lower than that seen in the QD LEDs but occurs at much higher currents. It is also shown that emission from the nitride samples is limited by nonradiative recombination at all currents, whereas in the QDs state filling effects and multiple-carrier processes limit the emission efficiency at high carrier densities.
Correlations between embedded single gold nanoparticles in SiO2 thin film and nanoscale crater formation induced by pulsed-laser radiation
Authors: Papernov S. , Schmid A. W.
Published: November 2002

A model SiO2 thin-film system containing gold nanoparticles serving as nanoscale absorbing defects is investigated with the goal of unraveling the connection between the 351 nm pulsed-laser energy absorption process inside a single defect and the resulting film damage morphology. For this purpose, gold nanoparticles are lodged at a well-defined depth inside a SiO2 monolayer film. Particle sites, as well as nanoscale craters generated at these locations after 351 nm irradiation, are mapped by means of atomic force microscopy. The results of this mapping confirm a damage mechanism that involves initiation in the nanoscale defect followed by absorption spreading out to the surrounding matrix. At low laser fluences (below optically detected damage onset), the probability of crater formation and the amount of the material vaporized is, to within ±25% of the average value, almost independent of the particle size. Inhomogeneities in the particle environment are held responsible for variances in the laser-energy absorption process and, consequently, for the observed particle/crater correlation behavior. Investigation of the damage threshold as a function of particle size (2–19 nm range) showed that even few-nanometer-diameter particles can lead to a significant threshold reduction. The “nanoscale” damage threshold is introduced as a laser fluence causing localized melting without significant vaporization.
Transmission electron microscopy of the induced damage by argon implantation in (111) HgCdTe at room temperature
Authors: Aguirre Myriam H. , Cánepa Horacio R. , Walsöe de Reca Noemı́ E.
Published: November 2002

HgCdTe (MCT) is an important semiconductor material used for infrared photovoltaic detectors. Although ion implantation is a widely used technique in the manufacture of devices based on MCT to obtain n/p junctions, a detailed understanding of the n-type behavior of the unannealed damage region has not yet been established. In this work, n/p junctions were formed by Ar++ implantation on MCT (111) grown by the isothermal vapor phase epitaxy method. Structural damage after implantation for different implantation doses (1013, 1014, and 1015 Ar++/cm2) was evaluated by transmission electron microscopy. At high doses, damage distribution exhibits a double region of defects. These were mainly vacancy dislocation loops and lines in the first region, whereas the second zone exhibited small dislocation loops. The observed n-type behavior after implantation was attributed to the generation and diffusion of Hg from the damaged region.
Pulse striations in glow discharge generated by a laser ablation plume
Authors: Hoshi Y. , Yoshida H. , Tsutsui Y.
Published: November 2002

A unique form of striations, pulse striations, has been observed in a glow discharge by means of a laser-triggered pulse. Unlike conventional striations in a discharge tube, pulse striations are generated near an anode placed in free space. Pulse striations are stereoscopic in shape, appear static, and have a relatively short lifetime of around 1 ms. The wavelength of striations was found to be a function of ambient pressure only, while the relationship between wavelength and pressure in pulse striations was similar to that between specific volume and pressure in the polytropic process of neutral gases. Goldstein’s original equation is a function of pressure only and appears to describe more common striation phenomena than Goldstein’s law, which is additionally dependent on the radius of the discharge tube. An upper limit of current density, above which striations do not occur, exists. A lower limit of current density was also found in addition to the optimum current density for initiating striations. Laser-triggered pulse striations may enable the easy control of striation duration.
Langmuir–Blodgett films of polyethylene
Authors: Sorokin A. V. , Bai Mengjun , Ducharme Stephen , Poulsen Matt
Published: November 2002

The possibility to obtain surface layers on water and prepare solid multilayer Langmuir–Blodgett films of medium-density polyethylene is shown. The polymer film on water is stable, demonstrates a reversible surface pressure-area isotherm up to 15 mN/m, and can be deposited onto a substrate using the Langmuir–Blodgett technique in a wide range of surface pressures. The thickness of a single deposited layer is 5.1 nm on average. The dielectric and optical constants of multilayer films are near their bulk values. The films exhibit high dielectric strength of at least 200 MV/m.
Frequency and intensity dependence of the sub-band-gap features observed in the surface photovoltage spectrum of semi-insulating GaAs
Authors: Sharma T. K. , Kumar Shailendra , Rustagi K. C.
Published: November 2002

Surface photovoltage spectroscopy studies on thick semi-insulating GaAs wafers are reported in the range 850–950 nm using the chopped light geometry. We observed some interesting sharp features in the sub-band-gap of SI-GaAs, which were reported recently [Appl. Phys. Lett. 79, 1715(2001); Rev. Sci. Instrum. 73, 1835 (2002)]. In this article, we present the dependence of these features on the chopping frequency and the source intensity. The intensity variation in the above-band-gap region and for the A peak (898 nm) in the sub-band-gap region could be fitted with single component while it is necessary to consider more than one component to fit the data for the Q peak (887 nm) in the sub-band-gap region. A model consistent with the observed features is also proposed.
Quantitative measurement of surface potential and amount of charging on insulator surface under electron beam irradiation
Authors: Mizuhara Y. , Kato J. , Nagatomi T. , Takai Y. , Inoue M.
Published: November 2002

Surface potential and the amount of charging on an insulator surface under electron beam irradiation have been quantitatively measured. For these measurements, a special sample holder was developed. The surface potential was measured using a secondary electron method. The measurement of the surface potential revealed that the sample behaves as a resistor, enabling the present technique to be applied for mapping microarea resistance. The results of measuring the amount of charging revealed that the amounts of charging obtained with different beam currents are the same in spite of different surface potentials. This strongly suggests that the charging phenomenon depends on the distribution of the charge trapping sites.
Reduction of boride enhanced diffusion in MeV-implanted silicon
Authors: Shao Lin , Thompson Phillip E. , Bleiler Roger J. , Baumann Scott , Wang Xuemei , Chen Hui , Liu Jiarui , Chu Wei-Kan
Published: November 2002

We demonstrated that implantation of MeV Si ions into a Si substrate can suppress boride-enhanced diffusion (BED) normally associated with a high B concentration layer. In this study, a molecular-beam-epitaxy grown Si layer with a B concentration of 1021/cm3 over a 10 nm region capped with 100 nm Si was used as a source of BED. A sequence of four B delta-doped layers with 100 nm Si spacers was grown prior to the source layer to monitor the diffusion. Half of the sample was implanted with 1 MeV Si ions at a dose of 1016/cm2, followed by annealing at 800, 900, and 1000 °C for different periods of time. For control samples without the MeV Si implant, BED was observed with enhancements of around 40 while the MeV Si-implanted sample showed a reduced, yet nonvanishing, BED with an enhancement of around 8 after annealing at 800 °C for 1 h. Both BED and suppressed BED with MeV implant show transient behavior with decay after annealing for long periods of time. The effect of high energy implant on B diffusion from surface deposited B layer was also discussed.
Correlation between channel mobility and shallow interface traps in SiC metal–oxide–semiconductor field-effect transistors
Authors: Suzuki Seiji , Harada Shinsuke , Kosugi Ryoji , Senzaki Junji , Cho Won-ju , Fukuda Kenji
Published: November 2002

The shallow interface trap density near the conduction band in silicon carbide (SiC) metal–oxide–semiconductor (MOS) structure was evaluated by making capacitance–voltage measurements with gate-controlled-diode configuration using the n-channel MOS field effect transistors (MOSFETs). The close correlation between the channel mobility and the shallow interface trap density was clearly found for the 4H- and 6H-SiC MOSFETs prepared with various gate-oxidation procedures. This result is strong evidence that a significant cause of the poor inversion channel mobility of SiC MOSFETs is the high density of shallow traps between the conduction band edge and the surface Fermi level at the threshold.
Photodissociation of hydrogen iodide in the A-band region 273–288 nm
Authors: Manzhos Sergei , Loock Hans-Peter , Bakker Bernard L. G. , Parker David H.
Published: November 2002

The photodissociation of hydrogen iodide in the A-band region was investigated between 273 and 288 nm using the photofragment imaging technique. At 17 wavelengths the I* (2P1/2)/I(2P3/2) branching ratio was measured by recording the corresponding hydrogen atomic fragment using multiphoton ionization at 243 nm. The branching ratios are in good agreement with previous measurements and confirm that four (final) states Π3(0+), 3Π(1), 3Σ(1), and Π1(1) are involved in the A-band absorption of HI and that those states dissociate adiabatically to form H+I* and H+I following parallel and perpendicular transitions, respectively. The deficiency of the model of three unbound states and that of the δ-approximation is substantiated.
Diffusion-limited crystal growth in metallic glasses under continuous heating
Authors: Rassolov S. G. , Tkatch V. I. , Selyakova N. I.
Published: November 2002

Mathematical analysis for diffusion-limited growth of a spherical crystal in an infinite matrix under linear heating conditions has been performed, and the exact and approximated solutions of the problem have been obtained. The approximated expression derived for evolution of the growing crystal radius at constant heating rate q formally coincides with the well-known parabolic law derived for isothermal conditions if the real time is replaced by T2/(qQ), with Q being the activation energy of diffusion. Despite a relatively large difference between the exact and approximated values of the crystal size, the accuracy of the volume fraction crystallized is within 1%. A good agreement of the calculated results with the relevant experimental data for the Fe–B metallic glasses implies the validity of the simple analytical relations derived for description of the diffusion-limited crystal growth in metallic glasses at constant rate heating.
Born–Oppenheimer breakdown in a combined-isotopomer analysis of the A 1Σu+–X 1Σg+ system of Li2
Authors: Wang Xuejun , Magnes Jenny , Lyyra A. Marjatta , Ross Amanda J. , Martin Françoise , Dove Peter M. , Le Roy Robert J.
Published: November 2002

New high resolution polarization data have been obtained for the A–X band system of Li2 6,7, and new Fourier transform data for the homonuclear lithium dimers. They are combined with earlier data for Li26,6 and Li2 7,7 in the first systematic combined-isotopomer analysis of data for Li2 . This analysis of 8445 rovibrational transitions yields an improved and internally consistent set of molecular constant for the three Li2 isotopomers, and determines the electronic isotope shift and leading vibrational and rotational Born–Oppenheimer breakdown correction terms for both electronic states.
Cation and anion vacancies in proton irradiated GaInP
Authors: Dekker J. , Oila J. , Saarinen K. , Tukiainen A. , Li W. , Pessa M.
Published: November 2002

Defects in electron irradiated GaInP grown by molecular beam epitaxy have been investigated using deep level transient spectroscopy (DLTS) and positron annihilation spectroscopy (PAS). PAS measurements indicate that vacancies are introduced at a high rate. Core annihilation curves, compared with theoretical calculations, are used to identify the principal defect in n-GaInP as cation vacancies, while phosphorus vacancies are seen in both undoped and n-type GaInP. The concentrations of defects obtained by PAS and Hall are in good agreement with each other. DLTS gives much lower values, possibly due to assumptions in the C–V analysis. These results give support to the identification of the midgap deep level observed using DLTS in irradiated and as-grown n-type and undoped GaInP as the phosphorus vacancy.