bluuebunny/crossref_metadata_2025 huggingface dataset:
TAILORING THE TWO DIMENSIONAL ELECTRON GAS DISTRIBUTION BY SELECTIVE DOPING OF THE QUANTUM WELL
Authors: Anwar A.F.M. , Carrol R.D.
Published: February 2008

The effect of doping the quantum well (QW) on the distribution of two dimensional electron gas (2DEG) in high electron mobility transistors (HEMT) is discussed. In con‐ventional HEMTs the QW is unintentionally doped to utilize the higher mobility of the QW material. The overlap between the carrier and the dopant distribution may be minimized by selectively doping the QW.
A COMPREHENSIVE AND COMPUTATIONALLY EFFICIENT MODELING STRATEGY FOR SIMULATION OF BORON ION IMPLANTATION INTO SINGLE‐CRYSTAL SILICON WITH EXPLICIT DOSE AND IMPLANT ANGLE DEPENDENCE
Authors: Park Changhae , Klein Kevin M. , Tasch Al F. , Simonton Robert B. , Novak Steve , Lux Gayle
Published: February 2008

A comprehensive and computationally efficient modeling strategy for the rapid and accurate simulation of implanted impurity distribution profiles in single‐crystal silicon has been developed. This modeling strategy exploits the advantages of both Monte Carlo simulation and semi‐empirical models by combining the two approaches in a complementary manner. The dual Pearson semi‐empirical model is used to accurately and efficiently model the dose and implant angle dependence of impurity profiles as well as the dependence on energy. This new comprehensive model allows convenient and accurate simulation of implanted boron distribution profiles in single‐crystal silicon as a function of dose, tilt angle, and rotation angle, in addition to ion energy, and it has been demonstrated by implementation in the process simulation code SUPREM III.
SIMULATION OF MOS CIRCUITS USING SPECTRAL TECHNIQUE IN RELAXATION FRAMEWORK
Authors: Palusinski O.A. , Guarini M.W.
Published: February 2008

Waveform relaxation has potential to overcome problem of excessive computer run times which are necessary for simulation of larger circuits with the use of existing simulators. One of the attractive features of waveform relaxation is its suitability for parallel implementation. Amount of data necessary for interchange between parallel processors after each iteration influences the overall performance of simulation. Method of integration based on Chebyshev series provides for representation of solutions in the most compact form which makes it very attractive for parallel implementations. This paper presents some results of numerical experiments with the spectral integration applied in the relaxation framework to a number of MOS circuits.
A MULTIGRID ALGORITHM WITH TIME‐DEPENDENT, LOCALLY REFINED GRIDS FOR SOLVING THE NONLINEAR DIFFUSION EQUATION ON A NONRECTANGULAR GEOMETRY ‐ PRACTICAL ASPECTS
Authors: Joppich W.
Published: February 2008

The numerical solution of the diffusion equation in VLSI process simulation leads to large systems of nonlinear equations which have to be solved at every time step. For this purpose, a multigrid (MG) algorithm with locally refined grids is constructed. It is demonstrated that the method used here yields typical MG algorithm convergence rates, and reduces the amount of work considerably. The local refinements are controlled by an estimation of the discretization error which is calculated within the nonlinear MG method (FAS) and requires no extra computational work.
CONNECTING WAVEFORM RELAXATION CONVERGENCE PROPERTIES TO THE A‐ STABILITY OF MULTIRATE INTEGRATION METHODS
Authors: White J. , Odeh F.
Published: February 2008

Application of the waveform relaxation algorithm to the differential‐algebraic equations generated by problems in circuit and semiconductor device simulation have demonstrated that the method often contracts uniformly in time. In addition, instabilities in the underlying multirate integration method have not been observed. In this paper, it is proved that multirate A‐stability and waveform relaxation uniform contractivity are connected, and use the result to show that the first and second‐order backward‐difference based multirate methods are A‐stable when applied to block diagonally‐dominant problems.
AN EFFICIENT SOLUTION FOR DIELECTRIC‐LOADED OR RIDGED WAVEGUIDES PROBLEMS
Authors: PICHON L. , BOURHATTAS A. , RAZEK A.
Published: February 2008

We present in this paper an efficient finite element analysis for different types of waveguides . The computations are performed with “edge elements” . These finite elements avoid all the “spurious modes”, the non‐physical numerical fields obtained from the solution of eigenvalue problems with classical finite elements formulations.Both dielectric‐loaded waveguides and ridged waveguides (waveguides with sharp edges) are analyzed. Comparisons of our results with previously published ones show theaccuracy of the numerical technique.
ON THE INHERENT GEOMETRY OF ELECTROMAGNETISM AND THE GEOMETRY OF ELECTROMAGNETIC SYSTEMS
Authors: Baldomir D , Hammond P
Published: February 2008

The paper explores the geometrical structure of electrodynamics using the algebra of differential forms. Stokes' theorem links the local to the global geometrical features of electromagnetic systems. The gauge invariance of the potentials is shown to be linked to the geometry of a circle in the complex plane, which exhibits the inner geometry of electrodynamics. The total geometry of a system is a combination of this inner geometry with the usual space‐time geometry. The application of these geometrical features to computation is explained.
A USER ORIENTED SHELL FOR ELECTROMAGNETIC CAD OF AXISYMMETRIC DEVICES
Authors: Stochniol A. , Freeman E.M. , Lowther D.A.
Published: February 2008

A special shell for a general purpose FEM package (MagNet) for the electromagnetic CAD of axisymmetric devices is presented. The basic idea of the shell is that a script file may be quickly and easily created for every basic design. Then the whole FEM solution procedure is conducted automatically. Any design changes can be easily and quickly made and a whole sequence of CAD tasks can be prepared and run automatically without any user intervention. An open boundary technique is built into the shell to deal with unbounded problems.
MATHEMATICAL DESIGN OPTIMIZATION OF A PERMANENT MAGNET SYNCHRONOUS MOTOR WITH FD FIELD CALCULATION METHOD
Authors: Russenschuck S. , Andresen E. Ch.
Published: February 2008

A six pole 3 kW synchronous motor with rare earth magnet excitation is used as an ex‐ample for mathematical design optimization on the basis of the FD field calculation method. The nonlinear field of the machine at full load, excited by both the rotor magnets and the stator current, is determined. The resulting vector‐optimization problem is transformed into a scalar problem, i.e. only one objective is minimized, while the others are considered by nonlinear constraints. Either the magnet mass or the machine volume is minimized for a restricted power input. The results of the investigations are presented by the material contours, flux plots and by the electrical and mechanical data of the optimized machines.
TWO‐DIMENSIONAL APPROXIMATIONS TO THREE‐DIMENSIONAL FIELDS IN AN ACTUATOR
Authors: Carpenter C.J. , Affane W.
Published: February 2008

Fig.1 shows a permanent magnet bistable actuator operated by switching the current in alternate directions. It is characterised by long air gaps, and, for mechanical reasons, the cross‐section of the moving part (armature) is much smaller than those of other parts. These features make the magnetic field problem essentially 3‐dimensional, although the main flux path is confined to the longitudinal (x,y) plane. The amount of detail requires a 2D mesh of about 3000 elements in this cross‐section and about 500 elements in the transvers cross‐section, so that a full 3D solution would require a substantial calculation. The dynamic force characteristic requires a magnetic field distribution for each level of current in the coil and each position of the armature, thus creating strong incentives to use 2D approximations.
ON THE OPTIMAL DESIGN OF AIR‐CORED SOLENOID INDUCTORS OF RECTANGULAR CROSS‐SECTION
Authors: Di Barba P. , Savini A. , Rudnicki M.
Published: February 2008

An attempt is made of formulating the optimal design problem of air‐cored inductors in a systematic and straightforward way. The numerical solution is obtained by means of nonlinear constrained optimization techniques. Reference is made to air‐cored multilayer inductors of rectangular cross section.
MAGNETOSTATIC FIELD CALCULATION OF 3‐D NON‐LINEAR MODEL BY RELUCTANCE NETWORK METHOD (Problem No.13‐TEAM Workshop)
Authors: Wiak S. , Pelikant A. , Turowski J.
Published: February 2008

Magnetostaic field analysis of 3‐D nonlinear model problem (No.10 ‐ TEAM Workshop) is carried out by the authors using the Reluctance Network Method. The components and resultant flux density are computed and compared with measurements and results obtained by other authors and shaw reasonable convergence and much less CPU time.
A THREE‐DIMENSIONAL LUMPED‐PARAMETER MODEL FOR MHD DEVICES
Authors: Geri A. , Veca G.M.
Published: February 2008

In this paper the authors apply a three‐dimensional lumped parameter model (3D‐LPM) to evaluate the behaviour of an electromagnetic d.c. pump. Whit reference to the same device we compare the numerical approach with those illustrated in previous papers where we have described a bi‐dimensional model (2D‐LPM) and a quasi‐three‐dimensional lumped parameter model (3d‐LPM). The aim of this study is to note some important aspects of the full three‐dimensional (3D) analysis.
GEORGE GREEN — MILLER AND SELF‐MADE MATHEMATICIAN FROM NOTTINGHAM
Authors: Krawczyk Andrzej
Published: February 2008

In 1993 the 200th anniversary of George Green, a great physicist and mathematician's, birth was celebrated. His contribution to world's science is beyond the question. This can best be seen in the frequency of mentioning his name and quoting his works in other physicists' and mathematicians' works. Some of historians of science and researchers are deeply convinced that George Green together with Maxwell originated modern electromagnetism. George Green is also famous for his inventions as far as light, stress and accoustic theories are concerned but electromagnetism ows him most of all. Indeed, none of those who have ever dealt with mathematical electromagnetism will question George Green's part and position. In nearly each paper referring to it, Green's function or Green's identities are the terms that are mentioned or quoted. Without these notions contemporary numerical techniques such as finite element method (first Green's identity) or boundary element method (second Green's identity) or integral methods (Green's function) are hard to imagine.
COUPLING OF ELECTRIC AND MAGNETIC EQUATIONS IN ELECTROMAGNETIC DEVICES WITH FINITE ELEMENT METHOD
Authors: Bouissou Stefan , Piriou Francis
Published: February 2008

To extend the field application of numerical simulation, it is necessary in many applications to consider the electric circuit. Usually the magnetic equations are solved using the 3D finite element method which implies the solution of a non‐linear equations system. To solve the electric circuit equations a mesh or a state variable method can be used. It may be noted that the electric equation system obtained with these methods can also be non‐linear in presence of semi‐conductor components in the electric circuit. If the interaction between the magnetic and electric circuits is important both non‐linear matrix systems must be solved simultaneously.
APPLICATION OF 3‐D FINITE DIFFERENCE METHOD FOR INDUCTANCE CALCULATION OF AIR‐CORE COILS SYSTEM
Authors: Zakrzewski K. , Lukaniszyn M.
Published: February 2008

The paper deals with the inductance calculation of air‐core coils system by means of 3‐D analysis of magnetic field of the coils with rectangular cross‐section. The possibility of mutual and self‐inductance calculation is presented. For magnetic field calculation, the Finite Difference Method with application of fast calculating procedures was applied. The method of calculation has been verified by experiments. The obtained difference between calculating and measurement results is equal to a few percent. The computer program is usefull especially for asymmetrical configuration of the coils.
END COMPONENT OF STATOR LEAKAGE REACTANCE OF SQUIRREL CAGE INDUCTION MOTORS
Authors: Yannopoulos‐Lascaratos P.P. , Tegopoulos J.A.
Published: February 2008

Maximum axial and radial flux densities due to peripheral stator current The flux desnity, Bsper, is found by using the Biot‐Savart law expressed in cylindrical coordinates. Thus
ANALYTICAL CALCULATION OF TRAVELLING WAVE INDUCTION HEATING SYSTEMS
Authors: Dughiero F. , Lupi S. , Siega P.
Published: February 2008

In this paper an analytical method, based on Fourier's series, which allows to determine the eddy currents distribution in travelling wave induction heaters with cylindrical symmetry is described. The method is particularly suitable for parametric analyses of heating systems with magnetic or non‐magnetic, solid, bimetallic or hollow loads, with inductors (with or without external magnetic yoke) of the transverse flux or travelling wave type. Useful results can be obtained also for the heating of “flat” metal loads, by inductors facing one side of the load.
ACCURACY OF MODELLING NON‐EQUILIBRIUM ELECTRON TRANSPORT IN SILICON USING HYDRODYNAMIC TRANSPORT EQUATIONS
Authors: Cheng Ming‐C. , Wen Ying
Published: February 2008

Accuracy of hydrodynamic transport equations using the energy‐dependent relaxation times has been studied for electron transport in Si 〈100〉. The concept of the hydro‐kinetic transport model is used to describe non‐equilibrium electron transport phenomena and to examine the validity for the assumption of energy‐dependent relaxation times. It has been shown that under the influence of a drastic increase in field the relaxation times might also strongly depend on the average velocity near the peak of strong velocity overshoot. In addition, the velocity dependence is found to be more pronounced at lower temperatures in Si 〈100〉.
THERMOMAGNETIC ANALYSIS OF SEMICONDUCTOR DEVICES USING TRENDY
Authors: Dima G. , Krabbenborg B. , Mouthaan T. , Profirescu  , Wallinga H.
Published: February 2008

This paper describes the two‐dimensional numerical solution of the system of partial differential equations governing the carrier and heat transport in a semiconductor structure in the presence of a magnetic field. The model is based on a thermodynamic approach and it was implemented in the thermomagnetic module of 2D process/device simulator TRENDY. The influence of temperature gradients on the response of a magnetic field sensor is presented in the paper.
UNIFIED SIMULATION MODEL FOR JUNCTION‐CONTROLLED FIELD‐EFFECT TRANSISTRORS
Authors: Schwierz Frank , Nakov Valentin , Roßberg Matthias
Published: February 2008

An simple model for the simulation of the electrical behaviour of several types of junction controlled field‐effect transistors is proposed. It is based on the calculation of the carrier concentration in the channel by means of a self‐consistent solution of Schrödinger and Poisson's equation in the direction perpendicular to the current flow. Based on the carrier concentration the dc, the small‐signal, and also the noise properties of the devices may be simulated. The calculated characteristics of a sub‐quarter micron gate GaAs MESFET, a δ‐doped GaAs FET and a Velocity Modulation Transistor will be presented and discussed.
NUMERICAL INVESTIGATION OF CARRIER TRANSPORT IN DOUBLE HETEROSTRUCTURE
Authors: Fardi Hamid Z.
Published: February 2008

Numerical device simulation is developed to study the steady‐state and transient current‐voltage characteristics of double heterostructure AlGaAs/GaAs PNPN electro‐photonic device when its performance is influenced by the presence of interface and bulk recombination mechanism. The simulation results show that the holding current and voltage and the breakover point are strongly affected by varying the minority carrier lifetime at outer heterojunctions. Numerical results also indicate that shortening the minority carrier lifetime in the inner PN homojunction region only increases the OFF‐state current. These results are in agreement with experimental data on AlGaAs/GaAs PNPN devices. The numerical modelling approach taken in this study is shown to be essential in the design and optimization of PNPN switch.
ACCURACY OF FINITE ELEMENTS IN COMPUTING THE SYNCHRONOUS REACTANCES OF SURFACE AND BURIED PERMANENT MAGNET BRUSHLESS MOTORS
Authors: Wing Mitchell , Gieras Jacek F.
Published: February 2008

The increased use of permanent magnet synchronous motors in small to medium power applications has made it imperative that these motors' performance can be modelled successfully. The accuracy of calculating the synchronous reactances determines the success of the modelling technique. An analytical method and the finite element method are used to calculate the synchronous reactances of two prototype synchronous motors. The calculations are compared with measurement for both motors. The results show that the finite element method is more reliable in obtaining synchronous reactances than the analytical method for rotor designs that are very intricate, although both methods show reasonable accuracy.
THE COMPARISON OF THE METHODS USED FOR ESTIMATION OF CURRENT TRANSFORMER METROLOGICAL PROPERTIES
Authors: Leśniewska E.
Published: February 2008

In the paper, research results on applying field methods in the process determining the parameters of a current transformer equivalent circuit have been published. The metrological characteristics were determined by solving a non‐linear electrical circuit, that is, the equivalent circuit of a current transformer, assuming different values of the forcing current and load. The method gave satisfactory results (the curve 1 in Figure 1) but was found to be time and labour‐consuming. The determination of non‐linear characteristics of RFe and Xµ elements of the equivalent circuit of a current transformer, using field methods, required carrying out a number of calculations of field distributions at the current transformer no‐load state, with different forcing currents and allowing for the magnetization characteristic of the core as well. The total magnetic energy at no‐load state is related to the main flux which permits to determine the Xµ magnetizing reactance, for a given saturation state of the core. On the basis of the calculated distribution of the vector potential, the Bmax magnetic flux density may be calculated in each element of the core and then, the total core losses and the RFe resistance may be calculated using the p = ƒ(Bmax) characteristics of the core sheet loss. Using field methods makes it possible to determine the X2r leakage reactance of the secondary winding, on the basis of the magnetic energy related to the leakage flux of the secondary winding, independently from the shape or localization of the core and the windings as well, while using the analytic method, the formulas used are true only for cylindrical coaxial windings located on the same column of the core. These formulas have been derived with the assumption that the distribution of the flux in the gap between the windings is uniform and that the flux is divided equally between the primary and the secondary windings, which is not true actually. The obtained characteristics of the RFe and the Xµ non‐linear elements, approximated by n‐degree polynomial, and also X2r were used as the input data for solving the non‐linear circuit, in order to determine the error characteristics.
END WINDING LEAKAGE CALCULATION OF A SQUIRREL‐CAGE INDUCTION MOTOR FOR DIFFERENT LOAD CONDITIONS
Authors: De Weerdt R. , Hameyer K. , Belmans R.
Published: February 2008

The calculation of the end winding leakage of a squirrel‐cage induction motor using a three‐dimensional finite element method is discussed. The end winding inductance is thought to consist of a leakage, describing the flux linked with the end winding only, and a mutual part, describing the flux linked with both end winding and end ring. Both leakage and mutual inductance are found to vary for different load conditions.
QUASI 3D MAGNETIC FIELD COMPUTATION FOR ANISOTROPIC SHEET LAYER STRUCTURE
Authors: Pietruszka Maria , Napieralska‐Juszczak Ewa
Published: February 2008

The paper presents quasi 3D magnetic field computation for anisotropic layer structure of transformer core, but this computation method can be also applied to other magnetically non‐homogeneous structures. To compute magnetic flux density vectors in the layers of the structure the authors applied a new method based on the assumption that different distribution of the magnetic flux in particular layers results from the tendency to reach the minimum of the magnetic field energy.
EFFICIENT SIMULATION ALGORITHM FOR THE FULL VECTORIAL WAVE PROPAGATION IN THE POLARISATION DEPENDENT STRUCTURES OF INTEGRATED OPTICS
Authors: Kunz Albrecht , Šumichrast L'ubomir
Published: February 2008

Propagation of electromagnetic waves through InP‐based integrated optics structures is directly simulated by solving the full vectorial wave equation in parabolic approximation for the transversal components Hx and Hy of the magnetic intensity vector H. A novel scheme based on the alternating‐directions split‐step finite‐difference technique in combination with the Crank Nicolson scheme is introduced providing exact treatment of the field quantities at the dielectric interfaces between waveguide core and cladding. The method described is applied to the solution of the fundamental mode in a buried rectangular dielectric waveguide and to the numerical optimization of a tapered matching structure.
THE APPLICATION OF THE SUPERCONDENSED TLM NODE TO PROPAGATION PROBLEMS IN INHOMOGENEOUS ANISOTROPIC MATERIALS
Authors: Trenkic V. , Christopoulos C. , Benson T.M.
Published: February 2008

A super‐condensed TLM node for modelling inhomogeneous anisotropic media on an arbitrarily graded mesh without using stubs is developed. It requires less storage, computationally is more efficient and can operate on a higher time step than existing TLM nodes. Complete derivation, implementation and validation of the new node are presented in the paper.
SIMULATION OF AN ELECTROMAGNETIC ACTUATOR BY A COUPLED MAGNETO‐MECHANICAL MODELLING
Authors: Gaspalou B. , Colamartino F. , Marchand C. , Ren Z.
Published: February 2008

This paper presents a model for the simulation of dynamic behaviours of a coupled magneto‐mechanical system. The magnetic equation is solved with the help of the finite element method. The local magnetic material saturation is considered. The moving band technique is used for accounting the movement. The magnetic torque of permanent magnet synchronous machine is calculated from the field solution according to virtual work principle and then introduced in the mechanical motion equation to calculate the shaft position. The complete differential equation system is solved with an iterative procedure.
ANALYSIS OF THE DISPLACEMENT FORCE ON THE FERROMAGNETIC MATRIX IN MAGNETIC FIELDS
Authors: Cie&sacutela Antoni , Matras Andrzej
Published: February 2008

The magnetic filter with the superconductive electromagnet as the source of the field is considered. The manufacturing process with that device needs the cycling removal of the filter. The matrix displacement (treated as a porous ferromagnetic material) in magnetic the field causes forces on the matrix filter and the electromagnetic winding. In the paper the mathematical model for two construction variants of the filter is presented: with “long” matrix and compensation windings. The simulation results are shown.
ANALYSIS AND OPTIMIZATION OF PLANAR THICK FILM NI‐FERRITE INDUCTOR
Authors: Jenei S.M. , Aleksić O.S. , Živanov L.D. , Raković D.I.
Published: February 2008

Ni‐ferrite powder average grain size less than 0.9µm was used for the ferrite paste preparation. Ferrite paste was printed on Al2O3 substrate and fired 850°C/10min. After Ni‐ferrite thick film characterization had been done, simple planar inductor geometry, such as square spirals, were printed on it. Measurements were done, using an HP 4194A impedance analyser. The experimental results were summarized and compared with theoretical predictions given by the electromagnetic analysis using the method of current images for the reason of accounting the effect of magnetic substrate. The computer program, developed here, allows determination of the required thickness of the substrate which will produce inductance enhancement of the given permeability of the substrate material. The same results can also be used to determine the permeability of magnetic film or substrate quickly and are directly applicable to the design of the planar inductors.
ON THE BROWNIAN MOVEMENT OF A ROTATOR AND ITS APPLICATION TO NONLINEAR DIELECTRIC RELAXATION
Authors: Coffey W.T. , Rybarschry C. , SCHRÖER W.
Published: February 2008

The Debye theory of dielectric relaxation as corrected for inertial effects has as yet been only considered in the linear approximation. There, the rise and decay transients are identical. Here a method recently developed for the treatment of a rotator in a periodic potential is applied to calculate the transient behaviour when the linear approximation is discarded. The Kramers equation for the problem is expanded in a set of orthogonal functions which lead to a set of linear differential difference equations giving the relaxation behaviour. It is shown that the Mori formalism for the problem leads to the same set of differential difference equations as the Kramers equation.
Wave Soldering: A look into the future
Authors: Manko H.H.
Published: February 2008

This paper deals with the thermal, chemical and metallurgical interactions between the printed circuit board and the solder wave. Special attention is devoted to the quality of the final solder fillet as a function of each variable. The individual zones inside of a solder wave is analysed. Their effect on the printed circuit and their components is explained. Guidelines for production parameters, i.e., solder temperature, conveyor speed, depths of immersion, impedance angle, hole‐to‐wire ratio, etc., are outlined. The wave solder operation cannot be isolated from fluxing and preheating; therefore, these two additional operations are also analysed. This will be limited, however, to those aspects directly related with wave dynamics. The paper concludes with a discussion of voids and entrapment in the solder fillet as they relate to the wave soldering process. A case history is used to outline the effect of voids on quality. Suggestions are made to avoid fillet imperfections such as blow holes, voids and incomplete fillets. Proper touch‐up procedures is also covered.
The laminate PDR 100—characteristics and technology
Authors: Meozzi A.
Published: February 2008

The production process of the PDR 100 epoxy glass based laminate, as developed by Philips, Holland, produced laboratory results which, with appropriate modifications, were applied by MAS SpA to achieve successful production of a laminate with proven consistency of quality. Industrial tests were carried out on material of varying thickness. The preparation of the resin mix, which differed in composition from that used by the Philips pilot plant, is described in detail, followed by the impregnation process, with emphasis on the precautionary measures necessary. The processes of pressing and finishing of the laminates are discussed, the emphasis again being on the prevention of contamination. The presence of titanium dioxide in the epoxy resin is fully explained and details are given of two technological processes of impregnation. The paper concludes with a summary of the typical properties and characteristics of the PDR laminates.
Manual soldering
Authors: Leonida G.
Published: February 2008

Mass soldering has not entirely replaced manual soldering and it is possible to enumerate various applications of the latter. The basic tool for the manual process is the soldering iron, with its vital major component, the bit. Parameters to be taken into account include power available at the bit, maximum bit temperature, thermal capacity and recovery time. Considerable detail is provided on the criteria that govern the choice of soldering iron bits, and a few useful soldering aids described. Although individual styles of hand soldering emerge, following the preferred practice should guarantee reliable joints. After an outline of the optimal operating procedure, some information is given on touch‐up, desoldering and structural joints. This article is an extract from the book “Handbook of Printed Circuit Design, Manufacture, Components and Assembly” by G. Leonida, published by Electrochemical Publications Limited, 8 Barns Street, Ayr, Scotland.
MAINTENANCE OF STEEL STRUCTURES WITHIN THE CENTRAL ELECTRICITY GENERATING BOARD
Authors: Shaw T.R.
Published: February 2008

The Central Electricity Generating Board is responsible for the operation and maintenance of 233 Generating Stations, 602 Transmission Sub‐Stations, 7,780 miles of Overhead and 602 miles of Underground Transmission Lines. The current building and reinforcement programme is involving considerable financial and technical investment. To support this investment, part of the Board's policy is to promote the issue of Standards and Specifications with the object of controlling quality and the consequent reduction of maintenance down times. The contribution to this policy by incorporating anti‐corrosion techniques in Steel Structures Standards and Specifications can be considerable. Ultimately, of course, maintenance becomes a necessity and for this purpose the Standards and Specifications produced extend themselves to the materials used, principally paint, with the object of reducing maintenance periods to a minimum.
Unfolding the fold of cyclic cysteine‐rich peptides
Authors: Shehu Amarda , Kavraki Lydia E. , Clementi Cecilia
Published: February 2008

We propose a method to extensively characterize the native state ensemble of cyclic cysteine‐rich peptides. The method uses minimal information, namely, amino acid sequence and cyclization, as a topological feature that characterizes the native state. The method does not assume a specific disulfide bond pairing for cysteines and allows the possibility of unpaired cysteines. A detailed view of the conformational space relevant for the native state is obtained through a hierarchic multi‐resolution exploration. A crucial feature of the exploration is a geometric approach that efficiently generates a large number of distinct cyclic conformations independently of one another. A spatial and energetic analysis of the generated conformations associates a free‐energy landscape to the explored conformational space. Application to three long cyclic peptides of different folds shows that the conformational ensembles and cysteine arrangements associated with free energy minima are fully consistent with available experimental data. The results provide a detailed analysis of the native state features of cyclic peptides that can be further tested in experiment.
Engineering and characterization of a single chain surrogate light chain variable domain
Authors: Morstadt Lucia , Bohm Andrew , Yüksel Deniz , Kumar Krishna , Stollar B. David , Baleja James D.
Published: February 2008

The surrogate light chain (SLC) is a key regulator of B cell development in the bone marrow, resulting in mature B cells that produce antibodies that are capable of interacting with antigens. The SLC comprises two noncovalently interacting proteins: VpreB and 14.1. We engineered a construct to represent the complete immunoglobulin‐like domain of the SLC variable domain in a single protein chain that could be bacterially expressed. In this construct, the incomplete immunoglobulin domain of VpreB (residues 1–102) was linked to the J‐segment of 14.1 (residues 40–53), which provided one β‐strand to complete the V‐like domain (VpreBJ). Because VpreBJ has the interface to VH chains, but lacks the unique region of 14.1, which is important for SLC signaling, we predict that a properly folded VpreBJ would have the potential to act as a dominant negative mutant of the surrogate light chain. X‐ray crystallography of VpreBJ at 2.0 Å resolution showed that the engineering was successful. With its two β‐pleated sheets, packed face‐to‐face, the single chain VpreBJ resembles a mature light chain immunoglobulin V‐domain (VL). The surface that would normally interact with the VH chain interacts with a crystallographically related VpreBJ molecule. The presence of dimeric species in solution was verified by analytical ultracentrifugation. VpreBJ is easily overexpressed in bacteria, while retaining the native conformation of an immunoglobulin domain, and thus may serve as an important reagent for future studies in B‐cell development.
Comparison of structural and functional stream assessment methods to detect changes in riparian vegetation and water pH
Authors: RIIPINEN MIIRA P. , DAVY‐BOWKER JOHN , DOBSON MICHAEL
Published: February 2008

1. Streams draining conifer plantations are often assumed to suffer from reduced ecosystem function due to acidity and diminished basal food resources. Evidence exists for the deleterious impacts of conifer plantations on stream ecosystem function and also of the negative impacts of acidification. This study compared the performance of a measure of ecosystem function (leaf litter decomposition) with structural measures (shredder species richness; shredder abundance; ASPT (Average Score Per Taxon) and seven different acidity index scores) in determining the impacts of conifer plantations and acidification on streams.

2. The study was conducted in the Derbyshire Peak District (U.K.) from January to April 2003. Five pairs of sites with broadleaved versus coniferous riparian vegetation were selected for comparison. Three of the broadleaved sites and two of the coniferous sites were also acid (mean pH < 6.1).

3. Breakdown rates of alder and oak leaves as well as shredder species richness and abundance were determined from mesh bags. Benthic samples were also collected on the same sampling dates and these were used to calculate the various index scores for each site. Community composition was investigated using redundancy analysis.

4. Clear differences in mesh bags were observed between the two riparian vegetation types: all parameters measured were higher in conifer sites than broadleaved sites. Leaf litter breakdown also differed between pH classes: mass loss was higher in neutral than acid sites. Structural index scores were unable to differentiate between the riparian vegetation types and with the exception of the species level Acid Water Indicator Community score, no structural index was able to differentiate between the two acidity classes.

5. The results suggest that stream function (leaf litter breakdown) responds to differences in riparian land use and stream acidity more strongly overall than community structure (structural indices). This in turn suggests that stream structure and function may be only loosely coupled. Therefore, the use of water quality indices should ideally be combined with functional measures to obtain a complete assessment of stream ecosystems.
MG132 proteasome inhibitor modulates proinflammatory cytokines production and expression of their receptors in U937 cells: involvement of nuclear factor‐κB and activator protein‐1
Authors: Ortiz‐Lazareno Pablo C. , Hernandez‐Flores Georgina , Dominguez‐Rodriguez Jorge R. , Lerma‐Diaz Jose M. , Jave‐Suarez Luis F. , Aguilar‐Lemarroy Adriana , Gomez‐Contreras Piedad C. , Scott‐Algara Daniel , Bravo‐Cuellar Alejandro
Published: February 2008

In response to inflammatory stimuli, monocytes/macrophages secrete greater quantities of the proinflammatory cytokines tumour necrosis factor‐α (TNF‐α), interleukin‐1β (IL‐1β) and IL‐6. The inflammatory process and the innate immune response are related to the activation of several transcription factors, such as nuclear factor κB (NF‐κB) and activator protein 1 (AP‐1). The proteasome is a multimeric protease complex, which plays a vital role in several cellular functions, including the regulation of transcription factors like NF‐κB. In this study, we used the human monocyte cell line U937 stimulated with lipopolysaccharide (LPS) and phorbol 12‐myristate 13‐acetate (PMA) as a model to investigate the in vitro effects of MG132, a proteasome inhibitor, on the release of TNF‐α, IL‐1β and IL‐6 and on the expression of their membrane and soluble receptors TNF‐R1, IL‐1R1 and IL‐6R. We also analysed the effects of MG132 on the activation of NF‐κB and AP‐1 and on the IκB molecule. MG132 significantly inhibited the secretion of those proinflammatory cytokines. MG132 increased the release of the soluble receptors TNF‐R1 and IL‐1R1 from U937 cells and decreased their cell‐surface expression. MG132 also increased IL‐6R cell‐surface expression and decreased its release. Proteasome inhibition also led to an increase in LPS+PMA‐induced AP‐1 activation and the attenuation of LPS+PMA‐induced IκB degradation, resulting in the abolition of NF‐κB activation. Our experiments strongly suggest that the proteasome is an important factor in the regulation of proinflammatory cytokines and their receptors.
Genomics and the immune system
Authors: Pipkin Matthew E. , Monticelli Silvia
Published: February 2008

While the hereditary information encoded in the Watson–Crick base pairing of genomes is largely static within a given individual, access to this information is controlled by dynamic mechanisms. The human genome is pervasively transcribed, but the roles played by the majority of the non‐protein‐coding genome sequences are still largely unknown. In this review we focus on insights to gene transcriptional regulation by placing special emphasis on genome‐wide approaches, and on how non‐coding RNAs, which derive from global transcription of the genome, in turn control gene expression. We review recent progress in the field with highlights on the immune system.
Characterization of hydration products of mineral trioxide aggregate
Authors: Camilleri J.
Published: February 2008

Objective  To characterize the hydration products of white mineral trioxide aggregate (MTA).

Methodology  Mineral trioxide aggregate, white Portland cement and bismuth oxide were evaluated using X‐ray diffraction (XRD) analysis and Rietveld XRD. The cements were tested un‐hydrated and after hydration and curing for 30 days at 37 °C. Analysis of hydrated cement leachate was performed weekly for five consecutive weeks from mixing using inductively coupled plasma atomic emission spectroscopy after which the cements were viewed under the scanning electron microscope to evaluate the cement microstructure. Quantitative energy dispersive analysis with X‐ray was performed and atomic ratios were plotted.

Results  Both Portland cement and MTA produced calcium silicate hydrate (C‐S‐H) and calcium hydroxide (CH) on hydration. The tricalcium aluminate levels were low for MTA which resulted in reduced production of ettringite and monosulphate. On hydration the bismuth level in the hydrated MTA decreased; bismuth oxide replaced the silica in the C‐S‐H and was leached out once the C‐S‐H decomposed with time. Both MTA and Portland cement released a high amount of calcium ions which decreased in amount over the 5‐week period.

Conclusions  The hydration mechanism of MTA is different to that of Portland cement. In MTA the bismuth oxide is bound to the C‐S‐H and is leached out from the cement with time as the C‐S‐H decomposes. MTA produces a high proportion of calcium ions from CH a by‐product of hydration and also by decomposition of C‐S‐H. The release of calcium ions reduces with time.
Decalcifying effect of 15% EDTA, 15% citric acid, 5% phosphoric acid and 2.5% sodium hypochlorite on root canal dentine
Authors: Pérez‐Heredia M. , Ferrer‐Luque C. M. , González‐Rodríguez M. P. , Martín‐Peinado F. J. , González‐López S.
Published: February 2008

Aim  To evaluate and compare ex vivo the decalcifying effect of 15% EDTA, 15% citric acid, 5% phosphoric acid and 2.5% sodium hypochlorite on root canal dentine.

Methodology  Two 2‐mm‐thick slices were cut from the coronal third of the root of 10 human incisors. Each slice was sectioned into two equal parts. Specimens were assigned to one of four groups (n = 10) for immersion in 20 mL of either 15% EDTA, or 15% citric acid, 5% phosphoric acid or 2.5% NaOCl, for three time periods (5, 10 and 15 min). The concentration of Ca2+ extracted from the dentine was measured by atomic absorption spectrophometry. The amount of calcium extracted was analysed using the Kruskal–Wallis test for global comparisons and the Mann–Whitney U‐test for pairwise comparisons.

Results  In the three time periods, 15% EDTA and 15% citric acid extracted the largest amount of calcium, with no significant differences between them. The 2.5% NaOCl solution extracted insignificant amounts of calcium, whereas 15% EDTA extracted 86.72% of the calcium in the first 5 min, and 15% citric acid and 5% phosphoric acid had a similar pattern of calcium removal (77.03% and 67.08% in first 5 min, respectively).

Conclusions  Solutions of 15% EDTA, 15% citric acid and 5% phosphoric acid decalcify root dentine, with most calcium extracted during the first 5 min of action. The efficacy of 15% citric acid and 15% EDTA solutions was significantly greater than that of 5% phosphoric acid solution at each time period (5, 10 and 15 min).
Endogenous Oestradiol Regulates Progesterone Receptor Expression in the Brain of Female Rat Fetuses: What is the Source of Oestradiol?
Authors: Jahagirdar V. , Quadros P. S. , Wagner C. K.
Published: February 2008

Testosterone secreted by male testes during fetal development is aromatised to oestradiol (E2) or reduced to the androgen, dihydrotestosteorne (DHT), within specific tissues. The female brain is assumed to develop in the relative absence of gonadal steroid hormones, as the ovary is steroidogenically quiescent until later in postnatal life. However, the proximity of a female fetus to male littermates in utero can increase her exposure to testosterone, and thereby its metabolites. To date, it is has been difficult to dissociate the effects of male‐derived E2 from those of DHT on the developing female brain. In the present study, anogential distance (AGD) in females was used as an androgen‐dependent bioassay, whereas progesterone receptor (PR) expression within the medial preoptic nucleus (MPN) was used as an E‐dependent measure. Pregnant dams received the aromatase inhibitor, 1,4,6‐androstatriene‐3,17‐dione (ATD), or vehicle from embryonic day 16 (ED16) to ED21. On ED22, AGD and PR‐immunoreactivity (‐ir) were measured in females that had zero, one, or two males (0–2M) or females that had three, four, or five males (3–5M) in the uterine horn. AGD was significantly greater in 3–5M females compared to 0–2M females, suggesting that male littermates are the source of androgenic exposure in the female fetus. ATD treatment significantly decreased PR‐ir in the MPN, demonstrating E2 regulation of PR. However, the total number of males in the uterine horn did not effect PR expression. There was no correlation between PR‐ir and AGD, suggesting that these measures are influenced independently. Together, these results suggest that although male littermates provide a significant source of androgens to female fetuses, the amount of E2 aromatised from male‐derived testosterone may not be the only biologically relevant source of androgens or E2. Alternative sources of E2 may be essential in ensuring the normal development of the female brain.
Distribution and Regional Stressor‐Induced Regulation of Corticotrophin‐Releasing Factor Binding Protein in Rainbow Trout (Oncorhynchus mykiss)
Authors: Alderman S. L. , Raine J. C. , Bernier N. J.
Published: February 2008

The corticotrophin‐releasing factor (CRF) system plays a key role in the co‐ordination of the physiological response to stress in vertebrates. Although the binding protein (BP) for CRF‐related peptides, CRF‐BP, is an important player in the many functions of the CRF system, the distribution of CRF‐BP and the impact of stressors on its expression in fish are poorly understood. In the present study, we describe the distribution of CRF‐BP in the brain and peripheral tissues of rainbow trout (Oncorhynchus mykiss) using a combination of real‐time reverse transcriptase‐polymerase chain reaction, in situ hybridisation and immunohistochemistry. Our results indicate a widespread and highly localised distribution of CRF‐BP in the central nervous system, but do not support a significant peripheral production of the protein. Major expression sites in the brain include the area ventralis telencephali, nucleus preopticus, anterior and lateral tuberal nuclei, and the posterior region of the pituitary pars distalis. We further characterise changes in CRF‐BP gene expression in three discrete brain regions after exposure to 8 h and 24 h of social stress or hypoxia. The plasma cortisol concentration in subordinate fish was much higher than in dominant fish and controls, and was indicative of a relatively severe stressor. By contrast, the increase in plasma cortisol concentration in fish exposed to hypoxia was characteristic of the response to a mild stressor. Changes in CRF‐BP gene expression were only observed after 24 h of either stressor, and were region‐specific. CRF‐BP mRNA in the telencephalon increased in both subordinate fish and fish exposed to hypoxia, but CRF‐BP in the preoptic area only increased after 24 h of hypoxia exposure. In the hypothalamus, CRF‐BP mRNA levels decreased in dominant fish relative to controls after 24 h. Taken together, our results support a diverse role for CRF‐BP in the central actions of the fish CRF system, but a negligible role in the peripheral functions of circulating CRF‐related peptides. Furthermore, the differential changes in forebrain CRF‐BP mRNA appear to occur independently of the hypothalamic‐pituitary‐inter‐renal axis.
Birthweight percentiles by gestational age and gender for children in the North of Mexico
Authors: Ríos Jesús Manuel , Tufiño‐Olivares Edith , Reza‐López Sandra , Sanín Luz Helena , Levario‐Carrillo Margarita
Published: February 2008

The objective of this study was to determine the 10th, 50th and 90th percentiles of birthweight, by gestational age and sex, for newborns covered by the Mexican Institute of Social Security (IMSS) in the State of Chihuahua. To generate the database, we used IMSS hospitals’ records in the State of Chihuahua, covering the period between 1 January 2000 and 31 December 2004. We included singleton live births only, and excluded babies with congenital malformations. The birthweights of 88 368 children born at 21–44 weeks of gestation comprised our data. From these data, we calculated the 10th, 50th and 90th percentiles for each sex, at 32–44 weeks of gestation. The observed cutoffs for the 10th percentile in our population were 40–250 g higher than those reported in other references with Mexican populations. These results constitute an updated birthweight reference that will allow the identification of newborns in the North region of the country with low birthweight‐for‐gestational age. Such information can be a useful instrument for preventing or diminishing associated risks.