bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of Peptides That Form Amyloid‐Like Fibrils Capturing Amyloid β1–42 Peptides
Authors: Sato Junichi , Takahashi Tsuyoshi , Oshima Hideo , Matsumura Sachiko , Mihara Hisakazu
Published: July 2007

Amyloid β‐peptide (Aβ) plays a critical role in Alzheimer's disease (AD). The monomeric state of Aβ can self‐assemble into oligomers, protofibrils, and amyloid fibrils. Since the fibrils and soluble oligomers are believed to be responsible for AD, the construction of molecules capable of capturing these species could prove valuable as a means of detecting these potentially toxic species and of providing information pertinent for designing drugs effective against AD. To this aim, we have designed short peptides with various hydrophobicities based on the sequence of Aβ14–23, which is a critical region for amyloid fibril formation. The binding of the designed peptides to Aβ and the amplification of the formation of peptide amyloid‐like fibrils coassembled with Aβ are elucidated. A fluorescence assay utilizing thioflavin T, known to bind specifically to amyloid fibrils, revealed that two designed peptides (LF and VF, with the leucine and valine residues, respectively, in the hydrophobic core region) could form amyloid‐like fibrils effectively by using mature Aβ1–42 fibrils as nuclei. Peptide LF also coassembled with soluble Aβ oligomers into peptide fibrils. Various analyses, including immunostaining with gold nanoparticles, enzyme‐linked immunosorbent assays, and size‐exclusion chromatography, confirmed that the LF and VF peptides formed amyloid‐like fibrils by capturing and incorporating Aβ1–42 aggregates into their peptide fibrils. In this system, small amounts of mature Aβ1–42 fibrils or soluble oligomers could be transformed into peptide fibrils and detected by amplifying the amyloid‐like fibrils with the designed peptides.
Metabolic Syndrome and Cardiovascular Disease: Challenges and Opportunities
Authors: Cooper‐DeHoff, Rhonda M. , Pepine, Carl J.
Published: July 2007

Metabolic syndrome (MetS) has been defined in different ways. However, key components common to most definitions are a constellation of risk factors including abdominal adiposity, impaired fasting glucose, hypertension, and dyslipidemia. A major mediator of MetS appears to be insulin resistance, which relates to the development of the vascular and metabolic dysfunctions that precede overt cardiovascular disease and type 2 diabetes. Evidence suggests that the mechanisms underlying the elevated cardiovascular risk associated with MetS begin with subclinical organ damage. Therapy for MetS targets individual components of the syndrome and includes lifestyle interventions, lipid‐modifying therapy, and antihypertensive agents, particularly those that inhibit the renin‐angiotensin system. Results of trials of angiotensin‐converting enzyme inhibitors and angiotensin receptor blockers have demonstrated reductions in new‐onset diabetes and cardiovascular events in a wide range of patients. Clinical trials to investigate further the role of these drugs in the primary prevention of type 2 diabetes in patients with MetS are currently under way. The purpose of this paper is to review the MetS from the perspective of the cardiology workforce with the hope that a better understanding of the links between MetS and cardiovascular disease could lead to improved management of persons at risk. Copyright © 2007 Wiley Periodicals, Inc.
The Andersen thermostat in molecular dynamics
Authors: E Weinan , Li Dong
Published: July 2007

We carry out a mathematical study of the Andersen thermostat [1], which is a frequently used tool in molecular dynamics. After reformulating the continuous‐ and discrete‐time Andersen dynamics, we prove that in both cases the Andersen dynamics is uniformly ergodic. A detailed numerical analysis is presented, establishing the rate of convergence of most commonly used numerical algorithms for the Andersen thermostat. Transport properties such as the diffusion constant are also investigated. It is proved for the Lorentz gas model where there is intrinsic diffusion that the diffusion coefficient calculated using the Andersen thermostat converges to the true diffusion coefficient in the limit of vanishing collision frequency in the Andersen thermostat. © 2007 Wiley Periodicals, Inc.
Diffractive nonlinear geometrical optics for variational wave equations and the Einstein equations
Authors: Alì Giuseppe , Hunter John K.
Published: July 2007

We derive an asymptotic solution of the vacuum Einstein equations that describe the propagation and diffraction of a localized, large‐amplitude, rapidly varying gravitational wave. We compare and contrast the resulting theory of strongly nonlinear geometrical optics for the Einstein equations with nonlinear geometrical optics theories for variational wave equations. © 2007 Wiley Periodicals, Inc.
Distributions for which div v = F has a continuous solution
Authors: De Pauw Thierry , Pfeffer Washek F.
Published: July 2007

The equation div v = F has a continuous weak solution in an open set U ⊂ ℝm if and only if the distribution F satisfies the following condition: the F(φi) converge to 0 for every sequence {φi} of test functions such that the support of each φi is contained in a fixed compact subset of U, and in the L1 norm, {φi} converges to 0 and {∇φi} is bounded. © 2007 Wiley Periodicals, Inc.
Gas‐Phase Infrared Photodissociation Spectroscopy of Tetravanadiumoxo and Oxo–Methoxo Cluster Anions
Authors: Feyel Sandra , Schwarz Helmut , Schröder Detlef , Daniel Charles , Hartl Hans , Döbler Jens , Sauer Joachim , Santambrogio Gabriele , Wöste Ludger , Asmis Knut R.
Published: July 2007

The infrared spectra of the binary vanadium oxide cluster anions V4O9− and V4O10− and of the related methoxo clusters V4O9(OCH3)− and V4O8(OCH3)2− are recorded in the gas phase by photodissociation of the mass‐selected ions using an infrared laser. For the oxide clusters V4O9− and V4O10−, the bands of the terminal vanadyl oxygen atoms, ν(VOt), and of the bridging oxygen atoms, ν(VObV), are identified clearly. The clusters in which one or two of the oxo groups are replaced by methoxo ligands show additional absorptions which are assigned to the CO stretch, ν(CO). Density functional calculations are used as a complement for the experimental studies and the interpretation of the infrared spectra. The results depend in an unusual way on the functional employed (BLYP versus B3LYP), which is due to the presence of both VO(CH3) single and VO double bonds as terminal bonds and to the strong multireference character of the latter.
A neural network for signal decomposition problems
Authors: Forti Mauro
Published: July 2007

This paper presents the design of a neural network for signal decomposition problems with application examples. For this class of problems the proposed network has the same dynamics as the Hopfield net, but it is shown to realize theO(M2) connection paths among theMneurons with a number of wires and conductances increasing onlylinearlywith increasingM, i.e. reducing this number byone dimensionwith respect to thequadraticallyincreasing number of wires and conductances required in the Hopfield net.

Other advantages of the proposed neural network are discussed in relation to classical examples of decomposition problems. In particular, a new architecture for anN‐bit A/D converter is presented employing 4Nconductances instead of theN(N + 1) Hopfield A/D conductances.
A remark on the wave‐form relaxation method
Authors: Schneider Klau S. R.
Published: July 2007

The wave‐form relaxation method (WRM) is an essential tool to compute the solution of an initial value problem for a broad class of large systems of differential algebraic equations in a reasonable CPU time. In this paper we give a sufficient condition for the convergence of the WRM which is more suitable for applications than that given by Lelarasmeeet al. At the same time we provide a new, short proof for the convergence of the WRM.
Finding all solutions of piecewise linear functions and application to circuit design
Authors: Leenaerts D. M. W. , Hegt J. A.
Published: July 2007

An algorithm is given for solving a set of underdetermined non‐linear functions where some or all unknown variables are confined within a certain interval. the functions must be described by piecewise linear models with virtually no restriction to the dimension of the functions or models. the algorithm is able to find all separate solution points of equations on well‐posed functions and can trace solution spaces, eventually composed of several disjunct branches, without any need for initial points. the presented methodology guarantees to find all solutions within a finite number of steps.

In top‐down circuit design, at each level one must solve a set of underdetermined equations in such a way that the solution space, if non‐empty, is in agreement with solutions found earlier in the hierarchy. the presented algorithm can be used in such a hierarchical environment and guarantees to find all solutions at each level which are not in conflict with solutions found at higher levels.
Recursive digital filters which are free from subharmonics
Authors: Werter Michael J.
Published: July 2007

In recursive digital filters, quantization of signals can result in instabilities such as limit cycles and subharmonics. the aim of this paper is to analyse these instabilities in periodically excited recursive digital filters and to present methods to suppress the unwanted phenomena. A new type of digital filter structure is introduced which is free from subharmonics for discrete‐time periodic input signals with a given period N. Using the theory of cyclotomic polynomials, this structure is extended to suppress subharmonics for input signals which are periodic with a divisor of N. A general principle is described to convert a stable, autonomous state space digital filter into one which is free from subharmonics under any periodic excitation with a given period N.
Odd‐degree selective bandpass digital filters interpolating linear phase and constant group delay
Authors: Abo‐Zahhad Mohammed
Published: July 2007

A novel simultaneous amplitude and phase approximation method is presented for the construction of non‐minimum phase odd‐degree transfer functions of distributed (or digital) bandpass filters interpolating linear phase and constant group delay at a set of frequencies in the passband. the passband amplitude characteristic is equiripple interpolating exact transmission at the same set of frequencies. In addition, the stopband amplitude characteristic is maximally flat and the filter selectivity is achieved by introducing a number of transmission zeros distributed arbitrarily between zero and infinite frequencies. the resulting transfer functions are always stable for all the cases considered. Typical characteristics for filters of ninth to 15th degree are graphically presented. the transfer functions presented are also capable of realization as distributed microwave, switched‐capacitor, digital or wave‐digital filters.
Hysteresis in electronic circuits: A circuit theorist's perspective
Authors: Kennedy Michael Peter , Chua Leon O.
Published: July 2007

In this exposition we hope to dispel some common misconceptions about the nature of hysteresis elements are associated with parasitic dynamics in the circuit and therefore should not be considered part of the static characteristics.

We examine the Schmitt trigger ciruit, which exhibits hysteresis in its transfer characteristic, and study a neuraltype pulse oscillator, one of a class of oscillators which relies for its operation on diriving point hysteresis. We illustrate the concepts of DC characteristics, the dynamic route, the jump phenomenon and parasitic dynamics. We show how a clear understanding of these ciruit theoretic principles leads to better analysis and synthesis methods for hysteretic cirucits.
New Algorithms For Two‐ and Three‐Layer Channel Routin
Authors: Wang Deborah , Kuh Ernest S.
Published: July 2007

In this paper a number of new channel‐routing algorithms are presented. the routing strategy is based on parallel bubble‐sorting and river‐routing techniques. an important concept introduced is the POTENTIAL function, which serves as a measure of the degree of difficulty of a particular channel‐routing problem. Both non‐Manhattan wires and overlapping wires are used.

Although the methods are initially derived for two‐layer routing with two‐terminal nets only, extensions to multiterminal nets and three‐layer routing have been made. Preliminary results indicate that in many instances the new algorithm outperforms the traditional approaches.
Parametric yield optimization of CMOS analogue circuits by quadratic statistical circuit performance models
Authors: Yu T. K. , Kang S. M. , Sacks J. , Welch W. J.
Published: July 2007

A major bottleneck in the design and parametric yield optimization of CMOS integrated circuits lies in the high cost of the circuit simulations. One method that significantly reduces the simulation cost is to approximate the circuit performances by fitted quadratic models and then use these computationally inexpensive models to optimize the parametric yield. In this paper quadratic statistical circuit performance models are applied to maximize the parametric yield of CMOS analogue circuits. It is found that quadratic polynomials may not always model the circuit performances well. However, with engineering knowledge applied to identify and reduce the causes of the errors, accurate performance models and yield maximization can be achieved with a reasonably small number of circuit simulations, as illustrated through examples. Distinctions between the present method and previous applications of quadratic modelling to statistical circuit design are made.
A Computer‐Aided Design Toolkit For Continuous/Discrete Systems Based On Continued Fractions
Authors: Vakilzadian Hamid , Ismail Mohammed
Published: July 2007

This paper presents new algorithms (1) to generate complete mathematical symbolic expressions of continued fraction expansion coefficients in the s‐domain, (2) to determine their numeric values and (3) to perform continued fraction inversion in the s‐domain. A software package in PASCAL and LISP to implement these algorithms is developed. In addition, a simple z‐domain inversion algorithm used in the computer implementation of bilinear s‐z transformation is also included in the software package. These algorithms play an important role in the analysis and synthesis of complex electrical networks and control systems. Especially, the s‐domain expansion and inversion algorithms have potential applications in model simplification and system order reductions. the paper also shows that the package, as such, serves as a comprehensive computer‐aided analysis and design (CAD) toolkit for both continuous and discrete systems. the software is interactive and runs on computers equipped with a PASCAL or LISP compiler. It is noted that the iterative implementation of these methods using the new continued fraction algorithms saves considerable memory space and processing time. Numerical examples and computer data are given to demonstrate the development of the new algorithms and the usefulness of the software toolkit in the CAD design of continuous and discrete systems.
Global properties of continuous piecewise linear vector fields. Part II: Simplest symmetric case in ℝ2
Authors: Lum Robert , Chua Leon O.
Published: July 2007

Among non‐linear vector fields, the simplest that can be studied are those which are continuous and piecewise linear. Among these non‐linear vector fields a large and important subset are those vector fields which are odd symmetric. Associated with these types of vector fields are partitions of the state space into a finite number of regions. In each region the vector field is linear. On the boundary between regions it is required that the vector field be continuous from both regions in which it is linear. This presentation is devoted to the analysis in two dimensions of the simplest possible types of continuous piecewise linear vector fields with odd symmetry, namely those vector fields possessing a pair of symmetric boundary conditions.

As a practical concern the analysis will attempt to ask and answer questions raised about the existence of steady state solutions. Since the local theory of fixed points in a linear vector field is sufficient to determine the stability of fixed points in a piecewise linear vector field, most of the steady state behaviour to be studied will be towards limit cycles. the results will present sufficient conditions for the existence, or non‐existence as the case may be, of limit cycles. Particular attention will be paid to the domain of attraction whenever possible.

With these results qualitative statements may be made for piecewise linear models of physical systems which have odd symmetry.
Low‐passband‐sensitivity switched capacitor filters using a parallel connection of two structurally lossless networks
Authors: Gobet Claude‐Alain , Mitra Sanjit K. , Petraglia Antonio
Published: July 2007

The low‐sensitivity property of IIR digital filters designed using a parallel connection of two allpass sections has already been demonstrated in the past few years. This property is closely related to the use of a particular type of allpass structures, calledstructurally losslessnetworks, which remain allpass regardless of the coefficient quantization. In this paper we provide a general theory for the synthesis of low‐passband‐sensitivity switched capacitor (SC) filters using a similar technique. the design of stray‐insensitive structurally allpass SC sections is emphasized, ensuring the passivity property for the overall filter. Design examples are presented with computer simulations and experimental results to compare the performance of the different proposed structures. Analytical sensitivity calculations are also derived yielding useful formulae for the prediction of the filter sensitivities with respect to capacitor ratios, particularly in the stopband.
A unified framework for gradient algorithms used for filter adaptation and neural network training
Authors: Marcos Sylvie , Macchi Odile , Vignat Christophe , Dreyfus Gérard , Personnaz Léon , Roussel‐Ragot Pierre
Published: July 2007

In this paper we present in a unified framework the gradient algorithms employed in the adaptation of linear time filters (TF) and the supervised training of (non‐linear) neural networks (NN). the optimality criteria used to optimize the parametersHof the filter or network are the least squares (LS) and least mean squares (LMS) in both contexts. They respectively minimize the total or the mean squares of the errore(k)between an (output) reference sequenced(k)and the actual system outputy(k)corresponding to the inputX(k). Minimization is performed iteratively by a gradient algorithm. the indexkin (TF) is time and it runs indefinitely. Thus iterations start as soon as reception ofX(k)begins. the recursive algorithm for the adaptationH(k– 1) →H(k)of the parameters is implemented each time a new inputX(k)is observed. When training a (NN) with a finite number of examples, the indexkdenotes the example and it is upper‐bounded. Iterative (block) algorithms wait until allKexamples are received to begin the network updating. However,Kbeing frequently very large, recursive algorithms are also often preferred in (NN) training, but they raise the question of ordering the examplesX(k).

Except in the specific case of a transversal filter, there is no general recursive technique for optimizing the LS criterion. However,X(k)is normally a random stationary sequence; thus LS and LMS are equivalent whenkbecomes large. Moreover, the LMS criterion can always be minimized recursively with the help of the stochastic LMS gradient algorithm, which has low computational complexity.

In (TF),X(k)is a sliding window of (time) samples, whereas in the supervised training of (NN) with arbitrarily ordered examples,X(k– 1) andX(k)have nothing to do with each other. When this (major) difference is rubbed out by plugging a time signal at the network input, the recursive algorithms recently developed for (NN) training become similar to those of adaptive filtering. In this context the present paper displays the similarities between adaptive cascaded linear filters and trained multilayer networks. It is also shown that there is a close similarity between adaptive recursive filters and neural networks including feedback loops.

The classical filtering approach is to evaluate the gradient by ‘forward propagation’, whereas the most popular (NN) training method uses a gradient backward propagation method. We show that when a linear (TF) problem is implemented by an (NN), the two approaches are equivalent. However, the backward method can be used for more general (non‐linear) filtering problems. Conversely, new insights can be drawn in the (NN) context by the use of a gradient forward computation.

The advantage of the (NN) framework, and in particular of the gradient backward propagation approach, is evidently to have a much larger spectrum of applications than (TF), since (i) the inputs are arbitrary and (ii) the (NN) can perform non‐linear (TF).
A fast, single‐layer, area router for semi‐custom analogue circuits
Authors: Buset Oscar , Declercq Michel , Rahali Fouad , Vaucher Pascal
Published: July 2007

This paper describes the router developed for ALPS, the analogue layout prototyping system. the ALPS router employs some classic techniques and contributes a new, fast implementation of a maze‐running algorithm and a new algorithm for finding two disjoint paths in a graph (the so‐called ‘two path problem’). Discussion of these points is coupled with a review of existing routing algorithms and techniques, and comparisons where possible.
Design criteria for high‐frequencyRC‐active sinusoidal oscillators
Authors: Carlosena Alfonso , Martinez Pedro A. , Porta Sonia
Published: July 2007

High‐frequencyRC‐active sinusoidal oscillators using two op amps are surveyed from a unified viewpoint. Information about their performance is obtained using linear and non‐linear approaches. As a consequence of this analysis, two main criteria are proposed to optimize these systems and to select the best configuration for a given application. the first criterion is related to the feasibility of obtaining an oscillation frequency independent of the op amps used in the design. the second criterion is connected with the level of harmonic distortion present in the signal. Experimental measurements obtained agree closely with the theoretical analysis carried out.
Cellular neural network design for solving specific image‐processing problems
Authors: Śalot Krzysztof
Published: July 2007

This paper is concerned with determining simple CNN‐paradigm‐based circuits for solving specific binary image‐processing problems. Single‐layer CNN templates for performing specified shape extraction, extraction of shapes which contain a desired feature and modified feature detection are derived using a formulated design strategy. the concept of CNNs composed of modified cells is developed and circuits designed for realizing simultaneous detection of distinct features and for extracting horizontal line midpoints are presented.
Loop admittance matrix modification for the digital simulation of power converter circuits
Authors: Zacharias Th. , Milias‐Argitis J. , Makios V.
Published: July 2007

The analysis of the equivalent circuit of power converters presents unique difficulties due to the continuously changing conduction state of power semiconductor switches which introduce open‐ and short‐circuit branches. Presently available methods mainly aim at automatically assembling the loop impedance matrix describing any particular conduction pattern. In this paper a novel powerful method is developed for automatically treating this varying topology circuit analysis problem by direct modification of the corresponding loop admittance matrix. In this way the inversion of any matrix is avoided. In particular, the loop admittance matrix (the solution matrix) for an existing conducting state of the switching elements is constructed by modifying the associated matrix corresponding to the previous conduction pattern. These modifications include a change of reference frame and/or elimination and/or addition of one or more loops on a solution matrix level and are expressed in an algorithmic form suitable for digital computer simulation.
A tight clock synchronization technique for multiprocessor systems
Authors: Liu Jyh‐Charn , Hung Tzu‐Chien
Published: July 2007

In this paper we present a tight clock synchronization scheme for large‐scale multiprocessor systems. the proposed scheme consists of two symmetric loops for transmission of the master clock signals and askew cancellation circuit(SCC) for each node to be synchronized to the master clock. Each clocking signal generated by the master clock source is replicated into two identical copies and the twin signals are transmitted on two symmetric loops in opposite directions. to cancel the time skew between them caused by the transmission network, the time difference between the two clocks' arrival times at any node is first measured and stored in each node. Then each of the leading signals received from the loop in a node is issued to its functional units after the signal is delayed by half the measured phase difference. It is shown that the system clock skew can be made independent of the delay of the transmission lines by the proposed scheme at a low hardware cost.

To explore the feasibility of the proposed scheme, the SCC is designed with a combination of programmable delay element arrays and a phase detector. the floor‐plan of the SCC is implemented by the MAGIC VLSI lay‐out tool based on MOSIS CMOS 2 μm technology and extensively simulated.
System identification using discrete orthogonal functions
Authors: Fahmy M. F. , Haweei T. I. , Elraheem G. J. M. , Gharieb R. R.
Published: July 2007

In this paper a novel method is described for the design of adaptive IIR filters used in system identification. the adaptive filter is implemented as a parallel connection of subsections whose transfer functions constitute a set of discrete orthogonal systems. the adaptation algorithm used, which is of the Gauss‐Newton type, adjusts the parameters of these discrete orthogonal systems in order to match the desired output data of the unknown plant in a least squares sense. Owing to the orthogonality property, which ensures complete independence of subsequent sections, convergence is very rapid. Closed‐form expressions for the gradient signals required to update the filter are given. Illustrative examples have shown that this method always results in much improved adaptation properties compared with the already existing approaches.
A new feasible method for the design of stray‐insensitive optimum switched capacitor networks
Authors: Nacaroǧlu A. , Köksal M.
Published: July 2007

On the basis of signal flow graphs a general method is described for the design of stray‐insensitive switched capacitor networks. to be able to choose the optimum one, the method involves the search of all possible topologies for the specially formed signal flow graph of the given z‐domain transfer function and is easily implemented by digital computer.
Analysis of noise in cascaded non‐linear stages
Authors: Larsen Torben
Published: July 2007

This paper presents a method to analyse noise in cascaded non‐linear stages based on Volterra series for multiport systems. the cascaded stages are partitioned such that internal noise sources from different stages are uncorrelated and linear loading between all stages can be assumed. This partitioning scheme implies that the ensemble average of the magnitude‐squared output response from the last stage in the cascade can be determined as a sum of noise contributions from the individual stages. the method allows both unmodulated (independent) and modulated (dependent) noise sources. A special case of the theory and two related examples are presented to illustrate the method.
New CMOS current mirrors with improved high‐frequency response
Authors: Di Cataldo G. , Palumbo G. , Stivala S.
Published: July 2007

A new CMOS current mirror is presented which has the static characteristic of the cascode current mirror and a high‐frequency performance equivalent to or better than that of the simple current mirror. Moreover, the circuit proposed does not present the instability problem of the improved cascode utilized to increase the high‐frequency response.

The circuit is designed using CMOS 2 μm technology with various aspect ratios and simulated with the SPICE programme.
Design of fixed point state space digital filters with low round‐off noise
Authors: Fahmy M. F. , Yassin Y. M. , Raheem G. A. , Haweel T. I.
Published: July 2007

A simple method is described for the design of fixed‐point recursive digital filters with low round‐off noise. the method is based on reducing to zero as many as possible of the coefficients of the filter state matrices. an optimization procedure is used to get the optimum value of linear transformation that minimizes the total output round‐off noise power. Compared with the existing approaches, this method is characterized by its computational simplicity, very low output round‐off noise (if not the lowest possible) and low coefficient sensitivity. the structure of the proposed technique is modular, which makes it suitable for VLSI implementation. the technique is then employed to obtain a reduced‐order low‐round‐off‐noise filter with characteristics equivalent to some desired FIR specifications. Illustrative examples are given to verify these advantages.
Some dynamic phenomena in delayed cellular neural networks
Authors: Civalleri Pier Paolo , Gilli Marco
Published: July 2007

In this paper we study the dynamic behaviour of delayed cellular neural networks (DCNNs). By means of a rigorous eigenvalue and eigenvector analysis and by numerical simulations we show that simple DCNNs composed of only two cells can exhibit a large variety of dynamic phenomena: stable and unstable closed orbits and chaotic attractors.
The describing function perturbation method for the dominant behaviour analysis of adiabatic negative‐conductance oscillators
Authors: Sommariva Antonino M.
Published: July 2007

Negative‐conductance oscillators are termed adiabatic when their transient operation signal can be represented as a narrowband‐modulated Fourier series with a finite number only of dominant components, including the DC one. the method presented here allows one to perform the complete analysis of such oscillators in a rigorous shortened manner. Indeed, it merges the approach of the describing function technique into the classical frame of perturbation theory, so as to replace the oscillator model in the instantaneous variables with a simplified one in the dominant variables, i.e. the complex envelopes of the dominant components. More precisely, the starting model comprises the input impedance and the open‐circuit voltage of the Thévenin equivalent one‐port of the linear network in the complex frequency domain and the voltage/current characteristic of the non‐linear resistor in the time domain. the final model instead comprises as many such triads as there are dominant components. Each triad is made up of an input impedance and an open‐circuit voltage in the baseband complex frequency domain and a voltage/current describing characteristic in the slow time domain. Standard circuit analysis tools are then used to obtain the equations of the dominant dynamics, steady state and dynamical stability of the oscillator.

To facilitate reading the paper, as soon as a new formula is proposed or derived, the result of its application to the well‐known van der Pol oscillator is also provided. In the end, to highlight the simplicity and efficiency of the method, a much more complex case (an eighth‐order oscillator with three dominant components) is analysed in detail.
An optimized synthesis of a discrete‐time cellular neural network for parallel thinning
Authors: Ho Chun‐Ying , Mori Shinsaku
Published: July 2007

The paper describes a systematic synthesizing method to realize the parallel binary image‐thinning algorithm by a discrete‐time cellular neural network. In contrast with previous studies, this paper starts from very basic local rules (algorithm) and the required cloning templates are calculated step‐by‐step. Mathematical techniques of combiningcompatibletemplates are proposed and optimization of the total number of cloning templates, the operating speed and sensitivity is addressed. Finally, the speed and circuit performances are compared with other studies.
Time domain sensitivity of high‐speed VLSI interconnects
Authors: Liu Nelson , Nakhla Michel , Zhang Qi‐Jun
Published: July 2007

An adjoint method based on the asymptotic wave‐form evaluation (AWE) technique is described for the time domain sensitivity analysis of VLSI interconnect networks that contain linear lumped anddistributedelements. the network sensitivity, which is approximated by a set of poles and residues sensitivities, can be evaluated efficiently with respect to all network components and interconnect parameters. Owing to therecursiverelationship between the time moments of distributed networks, the conventional adjoint approach could not be applied directly. Instead, an alternative approach is presented which solves this problem by introducting the concept ofadjoint momentsfor networks with distributed elements. Examples and comparisons with the sensitivity determined by perturbation are presented. the proposed technique is useful for the identification of critical circuit elements and the performance optimization of high‐speed VLSI designs.
A fourth‐order switched capacitor cascade structure for sigma‐delta converters
Authors: Baher Hussein , Afifi Emad
Published: July 2007

This paper gives details of the design of a switched capacitor circuit for use in oversampling sigma‐delta analogue‐to‐digital converters. the circuit is a fourth‐order cascade of two second‐order sections. Comparison with other multistage structures is also presented. It is shown that the proposed design has advantages over the possible alternative cascade of four first‐order sections. It is also shown that it gives certain improvements in performance over the popular third‐order cascade of a second‐order and a first‐order section, thus justifying the use of a higher order under the given technology and tolerance constraints.
Hybrid notch filters
Authors: Rhodes J. D.
Published: July 2007

Narrow bandwidth bandstop filters or ‘notch filters’ are frequently required in both communication and electronic warfare systems. In the latter case the ability to switch into an ‘allpass’ state with a minimum level of loss and time delay distortion is vital. Furthermore, in both cases a level of 20‐30 dB rejection is normally required. These factors suggest that the ‘hybrid notch filter’† proposed in this paper is an optimum solution for low‐loss designs. Design techniques and experimental results for two fixed tuned filters for cellular base station applications are presented.
Analysis of non‐linear dynamical circuits and systems under the influence of thermal noise
Authors: Finger L. , Uhlmann H.
Published: July 2007

In some electronic systems, such as cryoelectronic circuits, random noise has to be taken into consideration for modelling and simulation. After theoretical considerations an algorithm for the simulation of non‐linear circuits with random noise is developed. Methods for global analysis of non‐linear dynamical systems, such as Lyapunov exponents and the Poincaré map, are applied to systems with noise. the developed algorithms are applied to the cryoelectronic circuit of the ideal DC‐SQUID model. Several non‐linear effects which occur through noise are explained.
Exact solutions of cyclically symmetric oscillator equations with non‐linear coupling. Part II: Coupling with phase shift
Authors: Fox David
Published: July 2007

Several authors have found very simple exact limit cycle solutions in cyclically symmetric systems of N oscillator equations with linear coupling in zero order of a perturbation parameter and non‐linear coupling in first order. In contrast with such solutions in most other non‐linear systems, each of these limit cycles is an exact normal mode of the unperturbed equations with no change in frequency or addition of higher harmonics.

In Part I of this paper it was shown that the construction and analysis of such systems of equations are substantially simplified if the equations are expressed in terms of the normal mode co‐ordinates of the unperturbed system. the effects of the cyclic symmetry, as well as those of a higher symmetry shared by previous authors' models, were studied.

It is shown here that similar results can be obtained in systems if the coupling involves a phase shift. the phase shift places added conditions on the systems, so that some sets of equations, shown to have the simple limit cycle solutions, no longer have them after shift is introduced. the methods of the earlier paper, however, can be used to find families of systems with phase shifts which have such solutions.

A result in Part I, that frequencies in a system with the higher symmetry mentioned above are unchanged from those of the unperturbed system, is not valid if phase shifts are introduced.
A family of modular fully differential witched capacitor filters for simulating ladder filters
Authors: Said A. E. , Hosny E. A. , Sobhy M. I.
Published: July 2007

The switched capacitor filters proposed in this paper are based on the simulation of LC ladder filters through the state variable equations. They include all‐pole and finite transmission zero, lowpass filters, bandpass and highpass filters. the introduced family of filters has a fully differential structure; consequently it has the advantages of improved power supply and common mode rejection ratios and extended dynamic range. Since the proposed family of filters simulates LC ladder filters, it inherits their low passband sensitivities. One of the main advantages of this family of filters is that it has a modular structure composed of key and auxiliary circuits. This modular structure results in easier design and implementation procedures in VLSI fabrication. the double‐sampling concept is applied to the introduced modular blocks, which is essentially needed in high‐frequency applications. A comparison with similar published work available in the literature is presented and illustrative examples are given.
On the restrictions of the sensitivities in single‐amplifier biquadratic active filters
Authors: Leenaerts Domine M. W. , Mladenov Valeri M.
Published: July 2007

The paper deals with the bounds on the sensitivities of the poles and the quality factor to the gain of the amplifier in biquadratic second‐order active filters. to ensure stability, the Fialkow‐Gerst conditions are taken into account. It is not possible to realize biquad filters with a better gain‐sensitivity product not obeying the derived conditions. the result can be applied in filter synthesis and will give the designer more freedom to dimension the filter structure and its component values.
A simulation tool for the analysis and verification of the steady state of circuit designs
Authors: Brachtendorf H. G. , Welsch G. , Laur R.
Published: July 2007

Analogue and microwave design requires accurate and reliable simulation tools and methods to meet the design specifications. System properties are often measured in the steady state. Well‐suited algorithms for calculating the steady state can be classified into shooting methods, finite difference methods and the harmonic balance (HB) technique. Harmonic balance is a frequency domain method which approaches the problem of finding the steady state by a trigonometric polynomial. Depending on the size of the circuit and the number of Fourier coefficients of the polynomial, the resulting system of non‐linear equations can become very large. These non‐linear equations are solved by using Newton's method.

The sparse linear system arising from Newton's method can be solved by direct, stationary or non‐stationary iterative solvers. Iterative methods are normally easy to parallelize or vectorize.

In this paper a tool for the simulation of the steady state of electronic circuits is presented. the steady state is calculated using the harmonic balance technique. Non‐linear equations are solved by Newton's method and linear equations by preconditioned non‐stationary iterative solvers (CGS, Bi‐CGSTAB, BiCGSTAB(2), TFQMR). the run time is reduced dramatically, by up to an order of magnitude.
Symbolic analysis approach to settling time minimization in sc networks
Authors: Handkiewicz Andrzej , Śniatala Pawel
Published: July 2007

The paper presents a method of settling time minimization in switched capacitor (SC) circuits. This problem has been discussed in recent papers because of high‐frequency applications of SC networks. In comparison with the methods elaborated up to now and limited to biquads, the method presented in this paper can be used for an SC circuit containing an arbitrary number of operational amplifiers coupled together in each switching state and modelled as ideal transconductances. the fifth‐order ladder bilinear SC filter is considered for illustration of the method and SPICE simulations.
Swann‐a programme for analysis of switched analogue non‐linear networks
Authors: Valsa Juraj , Vlach Jiri
Published: July 2007

This paper describes SWANN, a programme for fast simulation of non‐linear switched analogue networks. the switches act as open and short circuits and are used to model switching diodes, transistors or thyristors. Non‐linearities of other elements such as capacitors, inductors, resistors, conductors and dependent sources, are modelled by polynomials. Possible inconsistent conditions which can appear in networks with ideal switches are correctly handled. At switching instants the values from left and right are obtained and are available for plotting. Examples show applications in communications and power electronics.
Analysis and simulation of substrate coupling in integrated circuits
Authors: Gharpurey Ranjit , Meyer Robert G.
Published: July 2007

A technique is presented which allows efficient calculation of substrate‐coupling macromodels in integrated circuits. the technique can be used to calculate node‐to‐node resistances or impedances in substrate models. Examples of the technique applied to several test structures are presented.
Analogue placement using guided enumeration
Authors: Abthoff Tobias H. , Johannes Frank M.
Published: July 2007

In this paper a new efficient approach to the placement problem of analogue circuits is presented. In the design of analogue circuits, strong interaction between humans and automatic tools is crucial to obtain good results. Hence there is a strong need for fast algorithms to support an interactive and incremental design style. In the design process, usually many geometric constraints such as symmetry or matching requirements are introduced by the designer to obtain a placement that fulfils all electrical requirements. Most state‐of‐the‐art analogue placement tools employ simulated annealing algorithms and map geometric constraints into the cost function of the annealing algorithm; thus they have to search the whole design space. In our approach an initial global placement is computed establishing neighbourhood relations between all modules. Afterwards the design space is reduced to placements that fulfil these neighbourhood relations and user‐specified geometrical constraints. the reduced design space is fully enumerated to find the optimal solution. the implemented tool achieves typical CPU times of a few seconds for designs of about 40 modules, making it an excellent choice for an interactive design process. Two examples are presented: (i) a high‐speed CMOS comparator lay‐out is compared with lay‐outs published in other papers and (ii) a BiCMOS bandpass amplifier lay‐out that has to be embedded into a mixed‐signal chip is compared with the manual lay‐out of a fabricated chip. We achieved the smallest lay‐out size published for the comparator while fulfilling all required constraints. For the amplifier the synthesized lay‐out is very similar to the manual one and about the same size.
Nullator‐norator approach to analogue circuit diagnosis using general‐purpose analysis programmes
Authors: Farchy Samuil L. , Gadzheva Elisaveta D. , Raykovska Lyudmila H. , Kouyoumdjiev Todor G.
Published: July 2007

In this paper a decomposition approach to diagnosis and fault prediction in large analogue and switched capacitor circuits is proposed, reduced to an analysis of the corresponding nullator‐norator models at a single test frequency. Algorithms for isolation of faulty nodes and subcircuits are presented. the topological conditions for performing diagnosis of faulty nodes and for identification of faulty elements have been considered. the element tolerance variations and measurement errors have been taken into account. the possibilities of the general‐purpose programmes for frequency and worst‐case analysis have been used in the practical implementation of diagnosis and fault prediction. Diagnosis of benchmark circuits has been performed and the results of a computer simulation using the programme PSpice are presented.
A new efficient dcvs circuit synthesis technique used for an improved implementation of a serial/parallel multiplier
Authors: Karoubalis Theodore , Adaos Kostas , Alexiou George Ph. , Kanopoulos Nick
Published: July 2007

This paper describes an efficient technique for the design of fault‐secure VLSI circuits based on differential cascode voltage switch (DCVS) logic. We propose a new synthesis method for constructing DCVS circuits with a near‐optimal transistor count based on binary decision diagrams (BDDs). the time and memory resources required are very low, making the technique practical even for PC‐based synthesis tools. This method is the basis for a CAD tool that allows automatic synthesis of fault‐secure circuits based on the DCVS technology. We finally present an improved design and implementation of a 2's complement serial/parallel multiplier as an application of the proposed technique and algorithm.
Correlation between vitamin D3 deficiency and insulin resistance in pregnancy
Authors: Maghbooli Zhila , Hossein‐nezhad Arash , Karimi Farzaneh , Shafaei Ali‐Reza , Larijani Bagher
Published: July 2007

Background

The serum level of 25‐hydroxyvitamin D deficiency has long been suspected as a risk factor for glucose intolerance and perhaps 1,25‐dihydroxyvitamin D has a role in the regulation of insulin secretion. This study investigates the relation between 25‐hydroxyvitamin D concentrations and insulin resistance in pregnant women.

Methods

A cross‐sectional study was conducted on 741 pregnant women referred to five educating hospital clinics. Universal screening was performed with a GCT‐50 g, and those with plasma glucose levels ≥ 7.2 mmol/L were diagnosed as GDM if they had an impaired GTT‐100 g based on Carpenter and Coustan criteria. The levels of insulin and C‐peptide were measured during OGTT‐100 g test. The homeostasis model assessment index (HOMA) equation was used as the insulin resistance index. The concentrations of 25‐hydroxyvitamin D, and PTH were also measured.

Results

Total prevalence of vitamin D deficiency (<25 nmol/L) was found in 70.6% of pregnant women. Prevalence of severe vitamin D deficiency (<12.5) in GDM patients was higher than in normoglycaemic pregnancies. The regression model revealed a strong correlation between the HOMA index and serum levels of vitamin D.

Conclusions

These results show that a positive correlation of 25(OH) vitamin D concentrations with insulin sensitivity and vitamin D deficiency could be a confirmative sign of insulin resistance. Copyright © 2007 John Wiley & Sons, Ltd.