bluuebunny/crossref_metadata_2025 huggingface dataset:
Mobility of a Two‐Dimensional Hole Gas in a SiSiGeSi Quantum Well Based on a New Wave Function
Authors: Kundu S. , Raychaudhuri S. , Ghosh S.
Published: July 2007

The distribution of two‐dimensional holes in a SiGe quantum well (QW) depends significantly on the well width, as it is nearly sinusoidal for very narrow wells and becomes of double heterojunction type for wider wells. In this paper a new wave function has been proposed to account for the distribution at all well widths. The temperature variation of mobility has been studied along with the well width dependence of the mobility. The relative contributions of different scattering mechanisms have been studied. The effect of screening has also been included. The results when compared with mobilities computed for other standard wave functions agree well with the sinusoidal wave function for very thin wells and with the Fang‐Howard wave function for much wider wells. For intermediate well widths, the mobilities based on the new wave function show better agreement with experimental data than for the other two wave functions that are, respectively, valid only at the two extremes.
Electronic Structure of Metal Azides
Authors: Gordienko A. B. , Zhuravlev Yu. N. , Poplavnoi A. S.
Published: July 2007

Calculations of energy band structure, density of states, electronic density, and chemical bond parameters for a series of MeN3, where Me  Na, K, Rb, Cs, Ag, Tl have been given. The density functional theory and pseudopotential technique in mixed basis have been used. The valence band has been shown to be essentially formed from azideion states for alkali metal azides. The conduction band contains two subbands separated by a band gap. The first band is responsible for the anion states, while the second one is responsible for the cation ones. Silver d‐states and thallium s‐states have been seen to change greatly the structure of both the valence and conduction bands for AgN3 and TlN3, viz. the upper valence bands are of a mixed anion‐cation nature, the conduction band bottom consists of cation states, but the anion contributions increase when the energy grows.
Calculated Crystal Field Parameters in RCo5 and RNi5 Systems
Authors: Novák P.
Published: July 2007

We report an ab‐initio calculation of the crystal field parameters Blm of rare earth (R) ions in intermetallic RM5 compounds (M  Ni, Co). The parameter with given l and m is calculated by integrating the product of the spherical (l,m) component of the crystal potential and the radial density of 4f electrons of the rare earth ion. The potential results from the self‐consistent calculation of the electronic structure of RM5 using the full potential LAPW method, while the density of the 4f electrons is taken from an LSDA‐SIC atomic calculation, in which the electron occupation numbers are fxed to their values in the corresponding RM5 system. The sensitivity of results to the parameters which enter the calculation is tested.
Inelastic Electron Interactions in the Energy Range 50 eV to 10 keV in Insulators: Alkali Halides and Metal Oxides
Authors: Akkerman A. , Boutboul T. , Breskin A. , Chechik R. , Gibrekhterman A. , Lifshitz Y.
Published: July 2007

Calculations of electron inelastic mean free paths and stopping powers for several alkali halides (KF, KCl, KBr, and KI) and metal oxides (BeO, MgO, SiO2, and Al2O3) have been performed in the 50 eV to 10 keV energy range. The complex dielectric formalism, improved to include the energy gap, was used for estimating the valence part of the transport characteristics, whereas the part related to electron‐core interactions was evaluated according to Gryzinski's theory. An extended comparison of these calculations with the available experimental data as well as with other theoretical predictions is presented. Trends of the energy dependence of the inelastic mean free path and stopping power in alkali halides are studied. The role of the plasmon deexcitation process as a source for low‐energy electrons in secondary electron emission spectra is discussed. The presented data can be used in Monte‐Carlo simulations of electron transport in the considered materials.
Study of Balance Equations for Hot‐Electron Transport in an Arbitrary Energy Band (II))
Authors: Wu Hang‐Sheng , Wu M. W. , Huang Xian‐Xiang
Published: July 2007

In the present paper it is pointed out that the frictional forces and the energy transfer rate appearing in the balance equations for the hot‐electron transport problem all depend explicitly on the electric field. Their expressions are rederived with the electric field dependent corrections to O(E1) included. These expressions are identical with those of Lei‐Ting except that in the latter the electron energy appearing in the delta function and the distribution function are replaced by coresponding new‐defined field dependent ones. The significance of such substitutions for obtaining the correct result is discussed in detail.
Dielectric Investigation of α‐LiIO3
Authors: Jacobsohn L. G. , Lunkenheimer P. , Laeri F. , Vietze U. , Loidl A.
Published: July 2007

The dielectric properties of hexagonal lithium iodate (α‐LiIO3) single crystals have been studied at frequencies 10−2 Hz⩽v⩽109 Hz and temperatures 100K ⩽ T ⩽ 500 K. Pure and iron doped crystals were investigated. Below approximately 10 kHz, the electric response of the LiIO3 crystals is almost entirely dominated by the accumulation of space charges at the electrodes. At least two types of ionic charge carriers seem to contribute to the observed conductivity. In addition, dc measurements revealed that electronic conductivity cannot be neglected in α‐LiIO3. At frequencies above some 100 kHz the real part of the conductivity σ follows a power law σ′ ∼ vs with relatively small exponents s for both, the doped and the undoped compounds. The temperature dependence of σ in this region behaves thermally activated with two energy barriers. The high‐frequency limit of the dielectric constant ε∞ has been determined. In addition, the data have been evaluated using the modulus formalism.
Screening of active ingredients of herbal medicine for interaction with CYP450 3A4
Authors: Lee S. S. , Zhang B. , He M. L. , Chang V. S. C. , Kung H. F.
Published: July 2007

A two‐step algorithm is adopted in the screening of herbal species which possess significant inhibitory effects on cytochrome P450 3A4 (CYP450 3A4). The algorithm comprises an initial stage of high throughput screening with Herbochip®for the identification of herbal fractions that exhibit interactions with CYP450 3A4. Fifty commonly used TCM species were screened with seven showing a positive signal reflecting interaction. In the inhibition assays that followed, six of the seven species gave a signal.Sophora flavescensstood out as it gave the highest number of wells with a response, the highest maximum index was 0.96, and the median index was 0.55. The selection of TCM species with inhibitory effects on CYP450 carries the potential role of its use to boost the effects of known therapeutic agents, a mechanism that has been exploited in the design of regimens for the treatment of HIV infection. Copyright © 2007 John Wiley & Sons, Ltd.
Protective effect of Lycium barbarum on doxorubicin‐induced cardiotoxicity
Authors: Xin Yan‐Fei , Zhou Guo‐Liang , Deng Zu‐Yue , Chen Yun‐Xiang , Wu Yue‐Guo , Xu Pan‐Sheng , Xuan Yao‐Xian
Published: July 2007

The objective of this work was to explore the hypothesis that Lycium barbarum (LB) may be protective against doxorubicin (DOX)‐induced cardiotoxicity through antioxidant‐mediated mechanisms. Male SD rats were treated with distilled water or a water extract of LB (25 mg/kg, p.o.) daily and saline or DOX (5 mg/kg, i.v.) weekly for 3 weeks. Mortality, general condition and body weight were observed during the experiment. DOX‐induced cardiotoxicity was assessed by electrocardiograph, heart antioxidant activity, serum levels of creatine kinase (CK) and aspartate aminotransferase (AST) and histopathological change. The DOX group showed higher mortality (38%) and worse physical characterization. Moreover, DOX caused myocardial injury manifested by arrhythmias and conduction abnormalities in ECG (increased QT and ST intervals and ST elevation), a decrease of heart antioxidant activity, an increase of serum CK and AST, as well as myocardial lesions. Pretreatment with LB significantly prevented the loss of myofibrils and improved the heart function of the DOX‐treated rats as evidenced from lower mortality (13%), normalization of antioxidative activity and serum AST and CK, as well as improving arrhythmias and conduction abnormalities. These results suggested that LB elicited a typical cardioprotective effect on DOX‐related oxidative stress. Furthermore, in vitro cytotoxic study showed the antitumor activity of DOX was not compromised by LB. It is possible that LB could be used as a useful adjunct in combination with DOX chemotherapy. Copyright © 2007 John Wiley & Sons, Ltd.
A class of optimal solutions of the matrix Nehari‐extension problem
Authors: Halikias G. D.
Published: July 2007

The degrees of freedom that are available in the solution set of the multivariable Nehari‐extension problem are used to minimize an 𝒢2‐type cost and an ‘entropy‐like’ cost associated with the smaller singular values of the (optimal) error system. The optimal extensions are constructed via a diagonalization procedure based on a (normalized) Schmidt pair of the Hankel operator induced by the function which is approximated.
Allowable parameter variations and robustness recovery in LQG regulators
Authors: Kim Sang Woo , Kwon Wook Hyun , Lee Joon Hwa
Published: July 2007

In this paper, the bounds of allowable parameter variations in the LQG regulator for fixed weighting matrices are obtained and the asymptotic properties of these bounds with respect to weighting matrices are analysed. It is shown that the guaranteed bounds of allowable parameter variations, which are independent of weighting matrices, are often small but not necessarily small under some conditions. It is also shown that under some conditions, the allowable bounds of the LQG regulator can become as large as those of the LQ regulator. In addition, a loop transfer recovery method for perturbed systems is derived under which the LQG regulator may possess the same robustness as the LQ regulator. Examples are given to validate these results.
H∞ estimation for discrete‐time linear uncertain systems
Authors: Xie Lihua , de Souza Carlos E. , Fu Minyue
Published: July 2007

This paper is concerned with the problem of H∞ estimation for linear discrete‐time systems with time‐varying norm‐bounded parameter uncertainty in both the state and output matrices. We design an estimator such that the estimation error dynamics is quadratically stable and the induced operator norm of the mapping from noise to estimation error is kept within a prescribed bound for all admissible uncertainties. A Riccati equation approach is proposed to solve the estimation problem and it is shown that the solution is related to two algebraic Riccati equations.
A factorization principle for stabilization of linear control systems
Authors: Ball Joseph A. , Helton J. William , Verma Madanpal
Published: July 2007

By introducing a fictitious signal y0 if necessary we define a transform magnified image which generalizes the passage from the scattering to the chain formalism in circuit theory. Given a factorization 𝒫˜ = ⊖R of 𝒫˜ where R is a block matrix function with a certain key block equal to a minimal phase (or outer) matrix function, we show that a given compensator u = Ky is internally stabilizing for the system 𝒫 if and only if a related compensator K′ is stabilizing for ⊖. Factorizations 𝒫˜ = ⊖R with ⊖ having a certain block upper triangular form lead to an alternative derivation of the Youla parametrization of stabilizing compensators. Factorizations with ⊖ equal to a J‐inner matrix function (in a precise weak sense) lead to a parametrization of all solutions K of the H∞ problem associated with 𝒫. This gives a new solution of the H∞ problem completely in the transfer function domain. Computation of the needed factorization 𝒫˜ = ⊖R in terms of a state‐space realization of 𝒫 leads to the state‐space formulas for the solution of the H∞ problem recently obtained in the literature.
Design of minimax controllers for linear systems with non‐zero initial states under specified information structures
Authors: Didinsky Garry , Başar Tamer
Published: July 2007

In this paper, we obtain the solution to the discrete‐time, linear‐quadratic, finite‐horizon disturbance rejection problem, withhard boundson the disturbance and with a known or an unknown non‐zero initial state. It is shown that there exist two regions in the space of initial conditions: one where a pure‐strategy saddle point exists, and the other where no pure‐strategy saddle point exists. In the latter region, the structure of the minimax controller is fixed throughout, and a saddle point exists in the class of mixed policies. The paper also develops a general algorithm for the construction of such saddle points under different information structures, and illustrates this algorithm on a numerical example.
Stability margins of singular perturbation systems via state‐feedback control
Authors: Cheng Chiu‐Pin , Li Tzuu‐Hseng S. , Sun York‐Yih
Published: July 2007

The gain and phase margins of singular perturbation systems are analysed under unmodelled high‐frequency dynamics control, composite control, and the original full‐order linear quadratic (LQ) control. The analysis is on the basis that there is a good relation between the minimum singular value of return difference transfer matrix and the stability margins. We begin with the examination of stability margins of subsystems and then show that state‐feedback control design of subsystems could preserve gain and phase margins for the original full‐order singularly perturbed system if the singular perturbation parameter epsiv; is sufficiently small.

The effectiveness of ε on stability margins is formulated and determined. It is found that the effectiveness can be evaluated by a simple method. Two examples are exploited to illustrate the analytic results.
Robust system‐parameter identification: The influence functional approach
Authors: Asato Michael S. , Poor H. Vincent
Published: July 2007

The influence functional, developed by Martin and Yohai, is an asymptotic robustness measure of a parameter estimate's sensitivity to the infinitesimal occurrence of correlated outlier contamination of a measurement sequence. Here, the usefulness of the influence functional as a tool for characterizing estimator robustness in system parameter identification is explored. In particular, this utility is illustrated by examining the influence functional as a measure of robustness for the choice of the error‐shaping function in the correlation or instrumental variables approach to system parameter identification.
Optimal H2 and H∞ fixed‐order dynamic compensation using canonical forms
Authors: Byrns Edward V. , Sweriduk Gregory D. , Calise Anthony J.
Published: July 2007

This paper presents a technique for designing fixed order dynamic compensators in controller canonical form which are robust to both structured and unstructured uncertainty. The formulation uses an approach which combines an H2 and H∞ optimization process. Specifically, a quadratic performance index is minimized subject to a constraint on the H∞ norm of the closed loop transfer function from disturbances to controlled outputs. This provides robustness to unstructured uncertainty. To provide robustness to structured uncertainty, an upper bound is computed for the worst case parameter variations, and it is then included in the derivation of the optimality conditions. A robust controller for a jetfoil boat is used to demonstrate this design technique.

For the specific case of no structured uncertainty, the results of this approach using the canonical form compensator are analytically related to the previously published results for a fixed‐order dynamic compensator. It is demonstrated that the use of the canonical form greatly simplifies the system of necessary conditions.
A modified variable structure control algorithm for stabilization of uncertain dynamical systems
Authors: Nersisian Ashot , Zanasi Roberto
Published: July 2007

A modified VS feedback is suggested for robust stabilization of continuous‐time dynamical systems in the presence of parametric and external time‐varying disturbances satisfying the ‘matching conditions’. The main feature of the proposed algorithm is that it contains additional switching ‘integral’ terms which track the unknown disturbances and make it possible to achieve the typical VSS robustness by using switching terms in the control law with arbitrarily small amplitude. This result can be achieved only if the derivatives of the disturbances are bounded.
A non‐recursive method for solving the general discrete‐time riccati equations related to the H∞ control problem
Authors: Chen Ben M. , Saberi Ali , Shamash Yacov
Published: July 2007

In this paper we propose a nonrecursive method for solving the general discrete‐time algebraic Riccati equation related to the H∞ control problem (H∞‐DARE). We have achieved this by casting the problem of solving a given H∞‐DARE to the problem of solving an auxiliary continuous‐time algebraic Riccati equation associated with the H∞ control problem (H∞‐CARE) for which the well known nonrecursive methods of solving are available. The advantages of our approach are: it reduces the computation involved in the recursive algorithms while giving much more accurate solutions, and it readily provides the properties of the general H∞‐DARE.
H∞‐control with measurement‐feedback for Pritchard‐Salamon systems
Authors: Keulen Bert Van
Published: July 2007

In this paper we extend the finite‐dimensional results for theH∞‐control problem with measurement‐feedback to a large class of infinite‐dimensional systems, allowing for a certain type of unboundedness in the input and output operators (the Pritchard‐Salamon class). The main result of the paper relates the solvability to the suboptimalH∞‐control problem to the existence of stabilizing solutions to certain operator Riccati equations. Furthermore, a characterization of all suboptimal controllers is given.
H∞control via measurement feedback for affine nonlinear systems
Authors: Isidori Alberto
Published: July 2007

This paper summarizes some recent results on the problem of disturbance attenuation via measurement feedback, with internal stability, for an affine nonlinear system. The solution of the problem is shown to be related to the existence of solutions of a pair of Hamilton‐Jacobi inequalities innindependent variables, associated with state feedback and, respectively, output‐injection design.
Robust H∞ identification of linear periodic discrete‐time systems
Authors: Arambel Pablo O. , Tadmor Gilead
Published: July 2007

System identification algorithms for linear time‐invariant (LTI) systems have been developed recently, which provide induced norm bounds on the difference between the true system and the identified one. The error bounds then allow the use of robust control design techniques with guarantees on performance of the real system. This note concerns the adaptation of robust H∞ identification techniques to linear periodic discrete‐time (LPDT) systems. The paper focuses on the algorithm proposed by Helmicki et al.13 and is based on a frequency‐domain approach to LPDT systems.
Identification in ℋ︁∞ with nonuniformly spaced frequency response measurements
Authors: Akcay HÜSeyin , Gu Guoxiang , Khargonekar Pramod P.
Published: July 2007

In this paper, the problem of ‘system identification in ℋ︁∞’ is investigated in the case when the given frequency response data are not necessarily on a uniformly spaced grid of frequencies. A large class of robustly convergent identification algorithms is derived. A particular algorithm is further examined and explicit worst case error bounds (in the ℋ︁∞ norm) are derived for both discrete‐time and continuous‐time systems. An example is provided to illustrate the application of the algorithms.
Finite horizon H∞ with parameter variations
Authors: Subrahmanyam M. B.
Published: July 2007

In this paper we consider the finite horizon H∞ performance robustness problem with parameter variations. Assuming a nominal model, an iterative procedure is given to synthesize a suboptimal H∞ controller, which yields the required performance even under parameter variations. As a byproduct, an expression for the variation of performance due to parameter variations is given for this specific controller. An example which illustrates the methodology is worked out under parameter uncertainties.
Robust performance control of uncertain nonlinear systems: A self‐tuning approach
Authors: Lee T. S. , Chen B. S.
Published: July 2007

The problem of output regulation with a guaranteed H∞ performance, besides robust stability, for a class of feedback linearizable nonlinear systems via self‐tuning controllers is investigated. The H∞ performance consists of the desired disturbance attenuation and internal finite L2‐gain stability. We show that, under the perturbations of matched parametric uncertainties, the sufficient condition for the existence of a self‐tuning controller reduces to the solvability of a single Hamilton‐Jacobi‐Isaacs inequality (or algebraic Riccati equation) which indicates that the design can be performed as if the system uncertainties were absent. Under certain situations, the sufficient condition is also necessary. Once a solution of this nonlinear differential inequality (or algebraic equation) is available, a desired self‐tuning controller with gradient‐type parameter estimator can easily be constructed. The present work falls into the category of singular nonlinear H∞ control since the desired H∞ performance does not require any penalty on control input variables. The results also provide an immediate application to H∞ self‐tuning model reference control in linear systems under full state measurement.
An explicit finite difference method for finite‐time observers
Authors: James Matthew R.
Published: July 2007

In this paper we present a numerical method for estimating the current state of a nonlinear control system. We use finite differences to discretize a modified version of the finite‐time observer equations in James. The discretized equations are simple and easily programmed. The convergence and accuracy of the scheme is proved, and the scheme enjoys a number of important properties: availability of rate of convergence estimates, good robustness characteristics, and the ability to handle certain types of discontinuities in the observations. The major disadvantage is that the number of grid points required increases exponentially with the number of state dimensions.
Stochastic robustness synthesis applied to a benchmark control problem
Authors: Marrison Christopher I. , Stengel Robert F.
Published: July 2007

Stochastic robustness synthesis is used to find compensators that solve a benchmark problem. The synthesis minimizes a robustness cost function that is the weighted quadratic sum of stochastic robustness metrics. These metrics — probability of instability, probability of actuator saturation, and probability of settling time violation — are estimated using Monte Carlo analysis. A simple search method minimizes the robustness cost by selecting values for the design parameters of a linear quadratic Gaussian regulator. The resulting compensators are robust, require low actuator authority, and compare well with previous designs.
Control of nonholonomic systems with extended base space dynamics
Authors: Reyhanoglu Mahmut , Bloch Anthony M. , Harris Mcclamroch N.
Published: July 2007

This paper extends certain results in Reference 1 to a more general class of nonholonomic systems with extended base space dynamics. This extension is important in applications for which control actuator dynamics are significant. These nonlinear control systems are referred to as nonholonomic control systems owing to certain nonintegrability assumptions which are made. The class of systems considered in this paper are characterized by general nonlinear base space dynamics that are input‐output decouplable. Controllability results for this class of nonholonomic control systems are presented.
LTR design of proportional‐integral observers
Authors: Niemann H. H. , Stoustrup J. , Shafai B. , Beale S.
Published: July 2007

This paper applies the proportional‐integral (PI) observer in connection with loop transfer recovery (LTR) design for continuous‐time systems. We show that a PI observer makes it possible to obtain time recovery, i.e., exact recovery fort→∞, under mild conditions. Based on an extension of the LQG/LTR method of proportional (P) observers, a systematic LTR design method is derived for the PI observer. Our recovery design method allows time recovery and frequency (normal) recovery to be done independently. Furthermore, we give explicit expressions for the recovery error when asymptotic recovery cannot be obtained. A design example demonstrates the advantages of time recovery in the non‐minimum phase case.
Bootstrap significance test of synchronous spike events—A case study of oscillatory spike trains
Authors: Ito Hiroyuki
Published: July 2007

The purpose of this monograph is two folds. Firstly, we introduce challenging spike data to the statistical analysis. The data of two neurons recorded from the cat visual pathway show various non‐stationary characteristics not fitted by the Poisson spike train. Spike firings of both neurons are strongly periodic and tightly synchronized. Our second purpose is a case study of applications of various statistical methods for the significance test of the time‐varying spike synchrony. We provide various general remarks to the statistical analysis of the synchronous spike activities. At first, we apply the unitary event analysis. The significance limit for the coincident spike events by the Poisson distribution is compared with the limit given by the non‐parametric test based on the bootstrap samplings. The bootstrap test performs superior to the Poisson test in two respects: (1) avoids false positives due to the sudden change of spike density; and (2) takes into account the non‐stationary change of the spiking pattern at different sampling windows. When the spike trains are highly periodic, the histogram of the number of accidental coincident spike events over the bootstrap samples has a systematically larger variance than the Poisson distribution. We find that a large variance originates from the correlation between the successive coincident spike events in the structured spike trains. The significance of the time‐varying synchrony is tested by another statistical method by Ventura et al., which is based on the adaptive smoothing method and the bootstrap significance test. Copyright © 2007 John Wiley & Sons, Ltd.
Youden Index and the optimal threshold for markers with mass at zero
Authors: Schisterman Enrique F. , Faraggi David , Reiser Benjamin , Hu Jessica
Published: July 2007

The Youden Index is often used as a summary measure of the receiver operating characteristic curve. It measures the effectiveness of a diagnostic marker and permits the selection of an optimal threshold value or cutoff point for the biomarker of interest. Some markers, while basically continuous and positive, have a spike or positive mass of probability at the value zero. We provide a flexible modeling approach for estimating the Youden Index and its associated cutoff point for such spiked data and compare it with the standard empirical approach. We show how this modeling approach can be adjusted to take covariate information into account. This approach is applied to data on the Coronary Calcium Score, a marker for
atherosclerosis. Published in 2007 by John Wiley & Sons, Ltd.
Vakuummeßgeräte für Totaldruck
Authors: Kündig Charles
Published: July 2007

Advances in the technical/technological development has resulted in a large growth of vacuum applications and the employment of vacuum techniques in almost all technical fields. In response to this expansion, the number of commercial vacuum gauges has increased. For the engineer or technician it has become more difficult, to make the right choice of the gauge. The present paper is intended as a guide. First, the most important measuring principles are dicussed. Thereafter modern equipment is decribed with application notes for different pressure ranges.
Stand der Kernfusionsforschung
Authors: Hofmann J. V. , Milch I. , Wagner F.
Published: July 2007

The aim of nuclear fusion research is to reproduce on earth the energy generating process of the sun and derive energy from the fusion of atomic nuclei. This is to be done by confining the fuel, a low‐density hydrogen plasma, in magnetic fields and heating it to high temperatures of over 100 million degrees.

Research has made major progress on the way to a burning plasma. JET, the joint European experiment, is just a factor of 6 short of achieving plasma ignition. ITER, the test reactor now being planned in international cooperation, is intended to produce the first burning plasma providing energy over a long period.
Hochtemperatur‐Supraleitungs‐Technologie — Herstellung und Anwendungspotentiale
Authors: Auge J. , Barth R.
Published: July 2007

The discovery of high‐temperature‐superconductors, which exhibit a transition temperature above 77 K, was supposed to be the best way to achieve superconductivity at room temperature. The research of the recent years turned out, that further problems have to be solved. Especially the layered structure of the new ceramic superconductors reveals in several drawbacks in the preparation techniques. The purpose of this article is to give a comprehensive overview about different preparation techniques of high temperature superconductors. A summary of their cryoelectronic applications will be presented.
Properties of Si3N4and AIN Films Produced by Reactive Ion Plating and Gas Discharge Sputtering
Authors: Monz K. H. , Danh Nguyen Quang , Huter M. , Rille E. P. , Pulker H. K.
Published: July 2007

Thin films of Silicon‐ and Aluminiumnitride were produced by Reactive Low Voltage Ion Plating and low pressure dc‐Magnetron Sputtering. The films show excellent adherence, high hardness and abrasion resistance, and are dense and homogeneous. Both processes, applied at optimum conditions, enable the production of films with nearly identical optical properties. Such optimized deposition conditions in both processes yielded a mean refractive index of n550= 2.05 ± 0.03 for Si3N4and of n550= 2.12 ± 0.01 for AIN films. The region of high optical transmission was found to be between 0.23 and 9.5μm (Si3N4) and between 0.2 and 12.5 μm (AIN). In the visible range both metal nitride films are free of optical absorption (k <10−3). These materials, together with their oxynitride phases, offer interesting applications for the deposition of optical multilayer systems with very high spectral stability.
Thermochromes VO2 für die Beschichtung von Architekturglas
Authors: Christmann T. , Kriegseis W. , Niessner A. , Schalch D. , Scharmann A. , Werling M.
Published: July 2007

In recent years vanadium dioxide films were discussed as thermochromic window coatings. Up to now it is not possible to deposit films, the properties of which are well‐suited for technical application. In the following properties of reactively rf sputtered VO2 films on a laboratory scale are reported. Besides optical measurements, analytical techniques as photoelectron spectometry, electron energy loss spectrometry, and secondary ion mass spectrometry are applied to VO2 films for the first time. We expect that these investigations will result in a better understanding of the metal‐to‐semiconductor transition, and other film properties as for example electronic defects and diffusion profiles at the interfaces and their effects on the band structure, thus aiming at superior film processing. In the following a survey over first results is presented.
Sample Exposition System for Plasma Analysis of a Fusion Reactor
Authors: Alessandrini C. , Apicella M. L. , Bella L. Dalla , Maddaluno G.
Published: July 2007

Plasma diagnosis of a fusion reactor can be performed by means of samples which first are exposed to the plasma and then investigated by surface analysis techniques. Construction and tests of such a diagnosis system are described. This system uses a demountable sample chamber in which the samples can be transported under UHV conditions to a distant laboratory for surface analysis.
Ionenstrahltechnologien – Werkzeug für das 21. Jahrhundert
Authors: Mucha A. , Schröer A.
Published: July 2007

Die Oberflächen‐ und Dünnschichttechnologie zeigte in den 10 Jahren ein kontinuierliches Wachstum und fand Eingang in eine Reihe neuer Anwendungsbereiche. Einige Produkte wie z.B. die CD‐Produktion oder wärmedämmendes Architekturglas wären ohne die Dünnschichttechnik nur äußerst schwer zu realisieren. Die Ionenstrahlverfahren stellen mit die jüngsten Entwicklungen auf diesem Gebiet dar und bieten dem Anwender neue Veredelungsmöglichkeiten seiner Werkstoffe. Die Beschichtung bzw. Modifizierung der Oberfläche kann auf nahezu alle Werkstoffklassen, wie z.B. Stahl, Polymere, Keramiken und Halbleiter durchgeführt werden.

Die Ionenimplantation führt u.a. zur einer Härtung der Substratwerkstoffe im oberflächennahen Bereich. Da keine eigentliche Schicht aufgebracht wird, sind Schichtablösungen ausgeschlossen. Dadurch ist dieses Verfahren für den medizinischen, Pharmazeutischen oder lebensmitteltechnischen Bereich von hoher Bedeutung. Der modifizierte Erkstoff bleibt in seinen Vollmaterialeigenschaften unverändert und verhält sich zudem nicht toxisch.

Durch den Ionenstrahlbeschuß konnte bei Präzisionswerkzeugen bis zu 10fache Standzeitveränderungen erzielt werden. Auch die Ionenstrahlbehandlung von Keramikbauteilen führt zu einem verbesserten Verchleißverhalten.

In Kombination mit einer Beschichtungsquelle können unterschiedlichste Schichtsysteme haftfest bei Temperaturen unterhalb von 250°C abgeschieden werden. Die Ionenstrahlgestützte Beschichtung kann ebenfalls für nahezu alle Werkstoffklassen angewendet werden.

Die Ionenstrahlverfahren werden auch in Ergänzung zu anderen Beschichtungstechnologien eingesetzt. Eine nachträgliche Stickstoffimplantation in hartverchromte Bauteile bewirkt eine deutliche Verbesserung des Verschleißverhaltens.

Die Ionenstrahlverfahren — konventionelle Ionenimplantation, Ionenstrahlgestützte Beschichtung, Plasma‐Immersions‐Ionenimplantation — sind sehr flexible und leistungsfähige Techniken um Problemstellungen im Bereich der Hochleistungswerkstoffen zu bearbeiten und zu lösen.
Asymmetric Bipolar Pulsed DC
Authors: Sellers Jeff , Pfähler Jürgen
Published: July 2007

Zusammenfassung Asymmetric Bipolar Pulsed DC wurde als Energieform entwickelt, um isolierende Schichten in einem reaktiven PVD‐Prozess vom metallischen Target kostengünstig und mit hohen Raten langzeitstabil abzuscheiden. Die „Forward Power”︁ (negativer Bereich) arbeitet als Stromquelle, da Ionen bewegt werden müssen. Die „Revers Power”︁ (positiver Bereich) arbeitet als Spannungsquelle, da Elektronen zur Kompensation einer positiven Aufladung bewegt werden müssen. Mit dieser Technik wird die Targetvergiftung vermieden. Außer allen üblichen Parameter eines DCG (DC Generator) gibt es beim RPG (Reactive Plasma Generator) 3 weitere programmierbare Parameter:

Frequenz (50–250KHz)

Duty Cycle (0–40%)

Amplitude des positiven Anteils genannte Reverse Bias Voltage (50–120V) Damit kann der Anwender den RPG (Reactive Plasma Generator) schnell für einen bestimmten Prozess optimieren. Es werden auch andere Quellentechniken mit der vorliegenden verglichen und erörtert. Außerdem wird der Einsatz des RPG (Reactive Plasma Generators) in Verbindung mit PVD‐ und CVD‐Prozessen beschrieben.
Ausgasungsmessungen von Metallen, Plasten und Kohlenstoff
Authors: Schindler N.
Published: July 2007

Es wird eine Meßapparatur zur gasartselektiven Gasabgabemessung vorgestellt und die notwendige Meßdatenaufbereitung beschrieben. Die damit gemessenen partiallen und totalen Gasabgaberaten von einigen wichtigen Metallen, Plasten, Kohlenstoffen und Schichten nach verschiedenen Vorbehandlungen werden dargestellt. Diese Gasabgaberaten werden quantitativ verglichen und qualitativ ausgewertet. Für jedes Gas wurde eine separate Leitwertkorrektur vorgenommen. Für Metalle wurde der Einfluß von gasabgabereduzierenden Schichten und von Reinigungsprozeduren untersucht. Die Messungen an verschiedenen Plasten zeigen den jeweiligen Anteil von Kohlenwasserstoffen an der Gesamtausgasung dieser Stoffe. Für Messungen an Graphitproben wird der Anteil der Wasserstoffausgasung diskutiert.
Lichtbogengestützte Prozesse zur Beschichtung von Kunststoffen
Authors: Hasse B. , Hinz H.‐P. , Müller R. , Siefert W.
Published: July 2007

In den letzten zehn Jahren haben plasmagestützte Beschichtungsverfahren verstärkt an Bedeutung gewonnen. Viele neue Schichteigenschaften sind erst durch diese Verfahren realisierbar geworden, wie beispielsweise hohe Haftung und Einstellbarkeit von Schichtstrukturen. Eines der neuen plasmagestützten Beschichtungsverfahren ist das lichtbogengestützte Aufdampfen. Die Funktionsweise dieses Verfahrens wird beschrieben ebenso wie die Eigenschaften der mit dieser Aufdampfquelle hergestellten Schichten.
Beschichtung von Kunststoffgehäusen zur Sicherung der elektromagnetischen Verträglichkeit elektronischer Geräte
Authors: Blasek G.
Published: July 2007

Die zunehmende Belastung der Umwelt erfordert im Interesse der technischen Sicherheit sensibler Geräte und der Gesundheit der Menschen Maßnahmen, die elektromagnetische Verträglichkeit elektrisch/elektronischer Geräte zu gewährleisten. Eine wichtige Maßnahme ist die Schirmung bei den zunehmend eingesetzten Kunststoffgehäusen. Das stellt eine neue Herausforderung an eine produktive, kostengünstige Beschichtungstechnik. Für die massenweise Beschichtung von Gehäusen haben die galvanotechnischen und die vakuumtechnischen Verfahren die besten Voraussetzungen, mit Abstrichen sind auch das thermische Spritzen und das Leitlackieren geeignet. Aus ökologischer und wohl auch ökonomischer Sicht sind vakuumtechnische Verfahren günstiger als galvanotechnische und gewinnen an Bedeutung. Nachteilig sind aber die begrenzte Schichthomogenität und die thermische Belastung der Objekte. An der Verbesserung der Leistungsfähigkeit vakuumtechnischer Verfahren wird gearbeitet. Gute Chancen haben kombinierte vakuumtechnisch‐galvanotechnische Verfahren.
VAKUUMWAAGEN Teil 1: Einleitung und Makrowaagen
Authors: Robens Erich , Gast Theodor , Jenemann Hans R.
Published: July 2007

Waagen, bei denen sich das zu wägende Gut im Vakuum befindet, werden als Vakuumwaagen bezeichnet. Makrowaagen sind für Lasten von mehr als 100 g ausgelegt. Zum Vergleich von Masseprototypen ohne Auftrieb wurden Vakuum‐Komparatorwaagen entwickelt. Große Vakuumwaagen werden zur Molekulargewichtsbestimmung und zur Messung der Gasdichte verwendet. Für chemische Untersuchungen unter reduziertem Gasdruck und zur thermogravimetrischen Analyse werden Vakuum‐Analysenwaagen mit elektrischer Meßwerterfassung eingesetzt. Zur Steuerung von Produktionsprozessen in kontrollierter Atmosphäre dienen Wägezellen unterschiedlicher Bauart.
Modern Solid Lubricants, Especially Based on MoS2
Authors: Pflüger E. , Savan A.
Published: July 2007

The structure of PVD‐deposited MoS2 films, viewed in relation to the defectfree crystalline form, present opportunities to intervene in order to improve and adapt the film properties to different tribological situations. By using modern PVD deposition technologies, it is possible to create new film structures by multilayering and co‐deposition. Significant reductions in the friction coefficient, and increases in the sliding lifetime in humid atmospheres have been measured. The historical use of MoS2 in spacecraft can be extended to industrial environments such as in dry or reduced‐lubricant machining. Anti‐adhesive properties are additionally important, for example in extruding and moulding.
Solution structure of agelenin, an insecticidal peptide isolated from the spider Agelena opulenta, and its structural similarities to insect‐specific calcium channel inhibitors
Authors: Yamaji Nahoko , Sugase Kenji , Nakajima Terumi , Miki Takafumi , Wakamori Minoru , Mori Yasuo , Iwashita Takashi
Published: July 2007

Agelenin, isolated from the Agelenidae spider Agelena opulenta, is a peptide composed of 35 amino acids. We determined the three‐dimensional structure of agelenin using two‐dimensional NMR spectroscopy. The structure is composed of a short antiparallel β‐sheet and four β‐turns, which are stabilized by three disulfide bonds. Agelenin has characteristic residues, Phe9, Ser28 and Arg33, which are arranged similarly to the pharmacophore of the insect channel inhibitor, ω‐atracotoxin‐Hv1a. These observations suggest that agelenin and ω‐atracotoxin‐Hv1a bind to insect calcium channels in a similar manner. We also suggest that another mode of action may operate in the channel inhibition by ω‐agatoxin‐IVA and ω‐atracotoxin‐Hv2a.
The effect of aluminium on NTPDase and 5′‐nucleotidase activities from rat synaptosomes and platelets
Authors: Kaizer Rosilene Rodrigues , Maldonado Paula Acosta , Spanevello Rosélia Maria , Corrêa Maísa C. , Gonçalves Jamile F. , Becker Lara Vargas , Morsch Vera Maria , Schetinger Maria Rosa Chitolina
Published: July 2007

Aluminium (Al), a neurotoxic compound, has been investigated in a large number of studies both in vivo and in vitro. In this study, we investigated the effect in vivo of long‐term exposure to Al on NTPDase (nucleoside triphosphate diphosphohydrolase) and 5′‐nucleotidase activities in the synaptosomes (obtained from the cerebral cortex and hippocampus) and platelets of rats. Here, we investigated a possible role of platelets as peripheral markers in rats. Rats were loaded by gavage with AlCl3 50 mg/(kg day), 5 days per week, totalizing 60 administrations. The animals were divided into four groups: (1) control (C), (2) 50 mg/kg of citrate solution (Ci), (3) 50 mg/kg of Al plus citrate (Al + Ci) solution and (4) 50 mg/kg of Al (Al). ATP hydrolysis was increased in the synaptosomes from the cerebral cortex by 42.9% for Al + Ci and 39.39% for Al, when compared to their respective control (p < 0.05). ADP hydrolysis was increased by 13.15% for both Al and Al + Ci, and AMP hydrolysis increased by 32.7% for Al and 27.25% for Al + Ci (p < 0.05). In hippocampal synaptosomes, the hydrolysis of ATP, ADP and AMP, was increased by 58.5%, 28.5% and 25.92%, respectively, for Al (p < 0.05) and 36.7%, 22.5% and 37.64% for Al + Ci, both when compared to their respective controls. ATP, ADP and AMP hydrolysis, in platelets, was increased by 172.3%, 188.52% and 92.1%, respectively in Al + Ci, and 317.9%, 342.8% and 177.9%, respectively, for Al, when compared to their respective controls (p < 0.05). Together, these results indicate that Al increases NTPDase and 5′‐nucleotidase activities, in synaptosomal fractions and platelets. Thus, we suggest that platelets could be sensitive peripheral markers of Al toxicity of the central nervous system.
Ossicular chain reconstruction improves bone conduction threshold in chronic otitis media
Authors: Lee H-S , Hong S-D , Hong S H , Cho Y-S , Chung W-H
Published: July 2007

This study aimed to assess the elevation of bone conduction threshold in patients with chronic otitis media and to investigate the mechanism of this phenomenon. One hundred and six patients with unilateral chronic otitis media who had undergone a tympanomastoidectomy were reviewed retrospectively. The differences in the bone conduction thresholds between the diseased and normal sides were assessed and compared according to the duration of the disease and the presence of cholesteatoma. Post-operative changes in the bone conduction threshold were also assessed. The mean bone conduction thresholds were significantly elevated on the diseased side, ranging from 3.4 to 11.6 dB across frequencies, with a maximal elevation at 2000 Hz. The duration of disease and the presence of cholesteatoma did not affect the degree of the bone conduction elevation. After ossicular reconstruction, bone conduction thresholds improved significantly at all frequencies, with the greatest improvement being observed at 2000 Hz. These results suggest that the elevation in the bone conduction threshold in chronic otitis media is mainly caused by a change in the conductive mechanism in the middle ear.
Significance of Streptococcus milleri in acute rhinosinusitis with complications
Authors: Rankhethoa N M , Prescott C A J
Published: July 2007

Objectives:

To assess the significance of Streptococcus milleri in acute rhinosinusitis with complications.

Methods:

A retrospective case note review was undertaken of in-patients at both the Red Cross Children's Hopital and the Groote Schuur Hospital (for adults), Cape Town, South Africa, between 1999 and 2003, with a diagnosis of acute rhinosinusitis with complications. The following were documented: age, gender, complications, organisms cultured and their sensitivity, type and number of operations, and length of hospital stay.

Results:

Seventy-one case notes were reviewed, for 30 female and 41 male patients, representing 38 adults and 33 children. Streptococcus milleri was the most commonly implicated organism (52.1 per cent; 37/71). Patients from whom this organism was isolated tended to require more than one operative procedure, and had a protracted hospital stay.
Dynamics of the parasite Marteilia refringens (Paramyxea) in Mytilus galloprovincialis and zooplankton populations in Alfacs Bay (Catalonia, Spain)
Authors: CARRASCO N. , LÓPEZ-FLORES I. , ALCARAZ M. , FURONES M. D. , BERTHE F. C. J. , ARZUL I.
Published: July 2007

Since the first description of Marteilia refringens (Paramyxea) in flat oysters Ostrea edulis in 1968 in the Aber Wrach, Brittany (France), the life-cycle of this parasite has remained unknown. However, recent studies, conducted in the ‘claire’ system, have proposed the planktonic copepod Acartia grani as a potential intermediate host for the parasite. Nevertheless, experimental transmission of the parasite through the copepod has failed. Recent studies in this field have reported the presence of the parasite in zooplankton from the bays of the Delta de l'Ebre, a more complex and natural estuarine environment than that of the claire. As a result, 2 new Marteilia host species were proposed: the copepods Oithona sp. (Cyclopoida) and an indeterminate Harpaticoida. Consequently, the objective of the present work was to study the dynamics of Marteilia in the zooplankton community from one of the bays, Alfacs Bay, as well as the dynamics of the parasite in cultivated mussels during 1 complete year. Six different zooplankton taxa appeared to be parasitized by M. refringens, including copepods (3 Calanoida, Acartia discaudata, A. clausi and A. italica; 1 Cyclopoida, Oithona sp.; and 1 Harpacticoida, Euterpina acutifrons), and larval stages of decapod crustaceans (zoea larvae of Brachyura, probably Portumnus sp.). These taxa are thus proposed as new subjects for study, since they could be intermediate hosts in the infection process of mussels by Marteilia.
Heavenly cords and prophetic authority in the Quran and its Late Antique context
Authors: van Bladel Kevin
Published: July 2007

The asbāb mentioned in five passages of the Quran have been interpreted by medieval Muslims and modern scholars as referring generally to various “ways”, “means”, and “connections”. However, the word meant something more specific as part of a biblical-quranic “cosmology of the domicile”. The asbāb are heavenly ropes running along or leading up to the top of the sky-roof. This notion of sky-cords is not as unusual as it may seem at first, for various kinds of heavenly cords were part of Western Asian cosmologies in the sixth and seventh centuries ce. According to the Quran, a righteous individual may ascend by means of these cords to heaven, above the dome of the sky, where God resides, only with God's authorization. The heavenly cords are a feature of quranic cosmology and part of a complex of beliefs by which true prophets ascend to heaven and return bearing signs.