bluuebunny/crossref_metadata_2025 huggingface dataset:
A new single operational amplifier active RC bandpass network with reduced sensitivity to amplifier gain‐bandwidth product
Authors: Soliman Ahmed M.
Published: July 2007

A new configuration for realizing a low sensitivity active RC bandpass filter suitable for hybrid integrated realization is given. The network consists of a single operational amplifier (OA) and two identical passive RC bandpass building blocks. The active element sensitivities are given. The frequency limitation equations of the filter based on the one‐pole rolloff model of the OA are derived. It is found that the choice of the element ratios of the passive RC networks plays an important role in the overall performance of the active resonator. Two cases are discussed in detail: one has the advantage of having better element ratios, and the other has the advantage of having lower sensitivities. The given network is less sensitive to the amplifier' gain‐bandwidth product than other low sensitivity active RC bandpass networks using two operational amplifiers.
Generalized interdigital filters made of multilayer striplines
Authors: Jokela Kari
Published: July 2007

In the first part of this paper is presented a relatively simple loss analysis method for many coupled line structures. The corresponding equivalent circuit consists of uncoupled lossy transmission lines whose parameters are determined relatively easily without a complex numerical field analysis by using fringing‐capacitance curves for rectangular strips. In the narrowband case further approximations are possible. The increase of the accuracy is most significant if the couplings between strips are tight.

In the second part a realization of the generalized interdigital filter using a multilayer structure consisting of polyphenyleneoxide plates is discussed. The repeatability of the filters is improved with the aid of thin polyethylene films. The shorts are made by the copper coating that also effectively suppresses higher‐order modes. The fine tuning of the filter can be made by tuning screws. The improvement of the design accuracy without tuning elements using a computer simulation is also discussed. Finally, the effects of the losses are studied, connecting the loss analysis presented with ring resonator measurements.
Characterization theorems for bounded and positive two‐variable functions
Authors: Delsarte Ph. , Genin Y. , Kamp Y.
Published: July 2007

The aim of this paper is a two‐variable extension of some classical results by Carathéodory and Schur, characterizing the classes of positive and bounded analytic functions. It is shown how these functions can be approximated by a convergent sequence of polynomials of the same class. The particular case where bounded two‐variable functions reduce to rational inner functions is described. As an application, the integral representation of positive functions is used to generate the complete family of two‐variable reactances of the first degree.
Approximation of fir digital filters by bilinear transformation
Authors: Sallai Gy.
Published: July 2007

The approximation of the finite‐impulse‐response (FIR) digital filters using the bilinear transformation of a restricted class of the rational functions is considered. The reference rational functions are constructed for maximally flat selective and quadrature filters. The proposed method can be directly used for both even and odd degree filters, and yields simple explicit expressions for the filter coefficients.
Intermodulation distortion in uhf transistors
Authors: Stewart R. D. , Kasim T. A.
Published: July 2007

Intermodulation distortion in transistors operating between 1 and 2 GHz has been studied. Four sources of nonlinearity in the transistor were examined and characterized by polynomials which were expressed in terms of the voltages at the transistor junctions. By incorporating these nonlinearities into a linear model, a nonlinear UHF transistor model was derived. The nodal equations of this nonlinear model were successively solved by expressing each nodal voltage in terms of a Volterra series expansion of the input voltage. Based on this analysis, predictions of the intermodulation distortions in two types of transistor were made; these predictions compared favourably with meansurements.
An optimum approximation for the interchange of a second‐order transfer function by a transfer function with decreased pole Q‐factor
Authors: Filanovsky I. M. , Stromsmoe K. A.
Published: July 2007

This article presents a method for the interchange of a second‐order circuit with high Q‐factor poles by a more complicated network that consists of several low Q‐factor stages. The ratio of the substituting circuit transfer function to the given second‐order transfer function approximates unity with a minimum deviation over the whole jw‐axis. The method is applicable to all types of second‐order transfer functions with arbitrary zero locations. The approximation error decreases in a geometric progression with the number of low Q‐factor stages. A method for determining the poles and zeros of the approximating transfer function is described and examples of interchanging are given.
Explicit design formulae for wideband bandpass filters
Authors: Rhodes J. D. , Al‐Jadir S. J.
Published: July 2007

A new design technique is developed for the realization of wideband bandpass filters synthesized in the form of a lowpass filter cascaded with a highpass filter. For the maximally flat and chebyshev response cases, approximate explicit design formulae are provided to allow a direct design technique to be used.

Results obtained by using this design technique agree with those obtained by direct synthesis and offer a significant improvement over the direct lowpass—highpass cascade obtained by frequency scaling.
Optimization of large change tolerances of linear integrated circuits
Authors: Filipkowski Andrzej , Tue Le , Michalski Zdzisław
Published: July 2007

Optimization of element tolerances is a very important but also time consuming part of integrated circuit design. In this paper an algorithm is presented for the worst case optimal assignment of large change tolerances, in which a significant simplification of the problem is obtained for a class of linear circuits. This is due to taking advantage of the bilinear dependence of the network functions on element values and to some simplifications assumed. The minimal cost of the circuit is the objective function.
Exact analysis of inhomogeneous ladder networks having a tridiagonal interaction matrix
Authors: Haley Stephen B.
Published: July 2007

A projection‐recurrence method is applied to active and passive ladder networks with a tridiagonal interaction matrix to obtain a factorization of the response functions. The factors are partial chain parameters, determined by third order recurrences. For a ladder with N nodes, the number of arithmetic operations to calculate response functions ranges from 4N to 6N. A diagrammatic representation is developed for passive ladders which makes it possible to obtain the partial chain parameters by inspection, and a compact formula for the node‐voltage response is presented for active doubly‐terminated ladders.
A new method of inhomogeneous ladder network synthesis
Authors: Brown David P.
Published: July 2007

A procedure to synthesize ladder networks in which each series arm impedance is fiz(s) and each shunt arm admittance is giy(s) is presented. Given a specified network function T(s), the function G = z(s)y(s) is first established by a polynomial decomposition. Then the appropriate chain parameters associated with T(s) are constructed as polynomials in G. The constants fi, gi are determined from a straightforward continued fraction expansion of a related RL impedance function in G. Necessary and sufficient conditions for the steps in the procedure are established and examples are included.
Multiloop feedback unsymmetrical active filters using quads
Authors: Gonuleren Ali Nur
Published: July 2007

In this paper, a general design procedure for high order unsymmetrical active filters is presented using a special configuration of quads. Quads are 4th order subsection blocks using biquads in a special manner. It is shown that the determination of network parameters is not dependent on frequency range, and that the design procedure is simpler than other multiloop feedback (MF) topologies. The transmission zeros of the transfer function are derived directly from the zeros of the biquadratic blocks and thus feedforward or summation techniques are not required.
A comparison of semiconductor controlled sources for the design of active rc impedances
Authors: Brugger U. W. , Leuenberger R. , Hosticka B. J. , Moschytz G. S.
Published: July 2007

A feasibility study of the four types of controlled sources realized in bipolar form is undertaken. The results are used in designing a PCM lowpass filter of which the total amplitude variance due to passive and active non‐idealities is minimized. The circuit yield is determined using Monte Carlo simulation.

For this particular application, a comparison shows preferable behaviour using transimmitances (e.g. operational transconductance amplifiers) than using gain elements such as the opamp.
An efficient method of statistical analysis for LC ladder filters
Authors: Kida Takuro , Kurogochi Katsumi
Published: July 2007

New tolerance measures for lossless or dissipative ladder filters and their numerical evaluation procedures are proposed. The proposed measures provide the approximate values of the statistical mean and variance of the variation of the operating propagation function or characteristic function in nepers. These measures are derived by utilizing a first‐ to fourth‐order Taylor series approximation and can be evaluated easily by a series of simple algebraic operations. Simple formulae are also presented which estimate the error incurred by the neglected terms of this Taylor series approximation.
When is a device passive?
Authors: Moylan P. J. , Chua L. O. , Szeto E. W.
Published: July 2007

Passivity is perhaps the most basic concept in circuit theory. Unfortunately, the existing definitions of passivity are too restrictive and often contradict one another. In this paper, a new passivity definition is proposed which is applicable to all n‐port and (n + 1)‐terminal devices—including time‐varying, non‐linear, and distributed circuit elements. This definition generalizes and reconciles several recent conflicting definitions.
Characterization of integration algorithms for the timing analysis of mos vlsi circuits
Authors: De Micheli Giovanni , Sangiovanni‐Vincentelli Alberto
Published: July 2007

Displacement techniques used for the timing analysis of VLSI circuits are presented under a new perspective. Their numerical properties such as stability, accuracy, consistency and convergence are investigated.
Loop equation formulation for switched capacitor networks containing nullors
Authors: Bruton L. T. , Bailey G. R. , Battacharjee G.
Published: July 2007

A method is given for determining the loop equations of an ideal active switched capacitance (SC) network containing switches, capacitors and nullors. These equations are obtained directly by row‐column operations on the passive unswitched loop elastance matrix. the results are extended for the P‐ phase case. It is shown that the loop charges can be solved for and that the branch voltages can be obtained from the loop charges.
Transfer functions interpolating an ideal amplitude with arbitrary phase and delay
Authors: Jarry P.
Published: July 2007

A method is presented to generate polynomials with phase values and delay (first derivative) specified at given frequencies. Then a closed form solution is described for the scattering transfer function S12(p) of a resistively terminated lossless reciprocal two‐port network with ideal amplitude and arbitrary phase and delay.
The solvability and monotonical properties of a certain class of D.C. non‐linear networks
Authors: Tadeusiewicz Michal
Published: July 2007

The problem of the existence and uniqueness of solutions for a certain class of non‐linear networks, including locally active elements and controlled sources, is considered in the paper. the conditions under which the input characteristics of the network are monotonically increasing are also analysed. Two theorems relating to the problem in question, containing some results in terms of the network topology, are formulated.
Detection of harmonic burst signals
Authors: Simon Gy.
Published: July 2007

The proposed procedure and the corresponding circuits for the recognition of a frequency from a set of possible input frequencies in the frame of a time‐window interval seem to be advantageous as they lead to simpler hardware than the well‐known energy detector. A unique feature is the single channel processing possibility. In addition the decision on the presence or absence of a given frequency is much faster than with a filter bank of resonators in a nearly lossless resonators. the frequency response is however not monotonic in frequency but has a somewhat periodic shape. the cases of the real lossy or unstable circuits are also dealt with. Some aspects of circuit realizations are given.
Subharmonic phase‐lock criteria for a class of weakly non‐linear high‐order oscillators
Authors: Calandra E. F. , Sommariva A. M.
Published: July 2007

Subharmonic frequency entrainment of high‐order weakly non‐linear oscillators is investigated. For the class of circuits considered, equations are first derived which provide the first approximation values for the amplitudes and phases of the two main spectral components of the steady‐state waveform. Necessary and sufficient stability criteria are then derived in explicit from.

The example worked out (a negative conductance double‐tuned oscillator) shows the efficiency and ease of use of the proposed method.
A multiplier‐free dft algorithm using differential coding of coefficients
Authors: Kocsis Ferenc
Published: July 2007

The proposed procedure is a new, practically multiplier‐free DFT algorithm which is especially suitable for the computation of longer transforms. the method is based on the realization of prime‐length transforms using a single kind of optimized FIR filter. the transform coefficients have been coded differentially and the approximation is signal independent. the accuracy has been characterized by the ratio of the squared sum of the DFT coefficients and the squared sum of the errors of the approximating coefficients. the algorithm producing the approximate sequence is simple, its computational and memory requirements are minimal. and finally, for some transform lengths the characteristics of the algorithms have been derived.
Uniqueness of the asymptotic behaviour of autonomous and non‐autonomous, switched and non‐switched, linear and non‐linear systems of dimension 2
Authors: Azzouz Abdennasser , Hasler Martin
Published: July 2007

An explicit criterion is given which guarantees that the solutions of a system of two first‐order differential equations have a unique asymptotic behaviour as t'→ + ∞. the equations are allowed to be time‐dependent, with isolate discontinuities (switching), and non‐linear. In particular, continuously differentiable and piecewise linear systems, as far as the dependence on the state variables is concerned, are considered. the particular case of a linear system switched back and forth between two 2 × 2 matrices is treated in detail, with an outline of an algorithm to decide on the converence to zero of the solutions.

The case of switching between N matrices is a straightforward generalization that is, however, not covered in this paper. It is shown that the problem of unique asymptotic behaviour of piecewise linear systems can always be treated by considering such switched linear systems. Furthermore, an example shows that even some continuously differentiable systems may be reduced to this case. Finally, the connection with the work of Brayton and Tong on the stability of differential equations, also using sets of matrices, is given.
Dynamic partitioning method for piecewise‐linear VLSI circuit simulation
Authors: Tejayadi O. , Hajj I. N.
Published: July 2007

This paper presents a method for dynamically partitioning circuit equations for time‐point relaxation‐based electrical circuit simulation techniques. the non‐linear element characteristics are approximated by piecewise‐linear (PWL) functions. the dynamic partitioning is carried out at every iteration during the solution process by comparing integers representing region numbers in the PWL functions, and only those PWL elements that change regions are involved in the repartitioning process. In many instances the circuit is automatically partitioned into completely d.c.‐disconnected subcircuits, which result in speeding up the convergence of the relaxation process. the approach has been implemented in a computer program for transient analysis of MOS VLSI circuits. Computational speeds of two orders of magnitude or more as compared to standard circuit simulation have been observed in solving small circuits on a serial computer without much loss in accuracy. the speed improvement is expected to be higher as the size of the circuit increases. Simulation using the dynamic partitioning method on a parallel computer indicates an efficient use of the processors, and corresponding improvement in speed.
Analysis of the optimal double side‐band converter
Authors: Belevitch Vitold
Published: July 2007

The optimal double side‐band converter, a novel circuit briefly presented in a previous paper,' is a rectifier bridge operating between selective terminations and containing an infinite number of resonant circuits. the circuit performance was justified by considering a finite number of resonant circuits and then letting that number become infinite. This limit process was erroneously handled, and is now corrected, so that the results for the infinite circuit (which were correct) are rigorously validated.
Dynamics of the inclusions appearing in the return maps of chua's circuit I. The creation mechanism
Authors: Kahlert Claus
Published: July 2007

The island‐like inclusions that appear inside the range of the return map in Chua's circuit are investigated further. the condition for the creation of a new inclusion is shown to be closely related to the selection rule for the critical curve ø. Moreover, a solution of this problem can also be given in terms of λ, the boundary of the return map's domain, and so in simpler form. the phases of the special trajectories that mark the creation of an inclusion turn out to be virtually invariant through all values of the canonical parameter ρ. Moreover, the phase difference between subsequent creations appears to be close to a constant too. This fact allows one to formulate explicit expressions for the limiting behaviour of the creation curves.
A serial charge redistribution logarithmic A/D converter
Authors: Lefas C. C.
Published: July 2007

The present paper describes the design and prototype construction of a serial charge redistribution logarithmic A/D converter (LADC). the LADC uses only two capacitors and has an eight‐bit digital word. It directly converts the input to logarithmic code and is suitable for use with digital systems implementing the sign‐log number system. the conversion is completed in 128 steps (clock cycles). the input dynamic range is four decades and the relative error is 3.7 per cent. A capacitor ratio accuracy of 0.4 per cent is required to keep conversion errors within 1 LSB.
Sc filters based on scattering parameters
Authors: Limperis A. , Haritantis I.
Published: July 2007

A systematic method for the simulation of LC ladders and unit‐element filters by means of switched capacitor (SC) circuits is proposed. the method is based on the use of wave equivalents of various two‐port subnetworks which are now realized by the same type of SC symmetric subcircuits. These subcircuits serve as the structural unit‐blocks for realizing high‐order circuits. Parasitic‐free circuits of practical interest can be developed. Examples of high‐order circuits are given. This wave method is simple in its concept and also in the circuit design. Through the alternative solutions which are described, the flexiblity of the method is demonstrated.
Some fundamental properties of second‐order active RC filters with composite operational amplifiers
Authors: Urbaś Aleksander , Osiowski Jerzy
Published: July 2007

Second‐order active RC filters employing N identical operational amplifiers (OAs) are considered. the way to achieve the highest‐order zero sensitivities of the dominant poles is shown. It leads to composite operational amplifiers (COAs) with a gain function of a polynomial form. the analysis of sensitivities, errors and location shifts of dominant poles as well as the effects of parasitic poles is also provided. the results have been confirmed by numerical analysis and an experimental verification.
On weak completeness and weak non‐degeneracy of networks
Authors: Milić Mirko M. , Novak Ladislav A.
Published: July 2007

The graph‐theoretic properties depending on the element types and their controllability but not on the particular form of constitutive relations of elements are considered. New concepts such as normal partition pair of the branch set, weak completeness and weak non‐degeneracy are introduced and their properties are investigated in detail. These properties may then be used to formulate purely topological methods of analysing some dynamical aspects of nonlinear RLC networks.
Improved description of base dynamics in the modelling of bipolar transistors
Authors: Sipilä Markku , Porra Veikko , Valtonen Martti
Published: July 2007

An improved non‐linear high‐frequency model for the bipolar transistor is presented, based on considerations of the dynamics of the charge stored in the base region. the model incorporates higher‐order circuit elements in order to obtain increased accuracy in circuit simulation at high frequencies. the model is derived from device physics by solving the diffusion equation in the base region by means of a quasi‐static expansion. the result is a more accurate circuit representation, which can be added to existing bipolar transistor models. Simulation examples are given and the possible convergence problems associated with the model are discussed.
Periodic, intermittent and chaotic states of clocked autonomous digital systems
Authors: Deane J. H. B. , Jefferies D. J.
Published: July 2007

The one‐dimensional full return map for the repetitively triggered monostable multivibrator is derived analytically and some of its properties under iteration by computer are investigated. It is found that the monostable can exhibit periodic, intermittent and chaotic behaviour as the triggering frequency is varied. the predictions of the theory are verified experimentally, suggesting that such methods may be used with confidence as a design tool.
An interval method for finding all operating points of non‐linear resistive circuits
Authors: Kolev L. V. , Mladenov V. M.
Published: July 2007

A new method for finding the set of all d.c. operating points of non‐linear electronic circuits is suggested. it is applicable in the case where the circuit equations are written in the hybrid‐representation form. In the general case, the non‐linear elements involved may be described by non‐monotone continuous characteristics.

The method suggested is based on interval analysis techniques. Unlike other non‐interval methods, this approach guarantees that all operating points will be found within prescribed accuracy in a finite number of steps.

The computational efficiency of the present method is illustrated by a numerical example.
Variable dimension algorithms for solving resistive circuits
Authors: Vandenberghe Lieven , Vandewalle Joos
Published: July 2007

Variable dimension algorithms are a recent class of globally convergent algorithms for solving sets of non‐linear equations. This paper introduces a simple circuit‐theoretical interpretation of the underlying idea and describes its advantages as compared to the globally convergent methods better known in circuit theory, such as the generalized Katzenelson algorithm. the convergence criterion is also stated in topological terms, and these conditions turn out to coincide with very general sufficient conditions for existence of solutions. the approach taken here can therefore be seen as a constructive way to prove solvability of resistive circuits. the paper also discusses how to implement the algorithm in an efficient and practical way.
Dissipativity as a unified approach to sandberg‐willson‐type properties of non‐linear transistor networks
Authors: Marinov Corneliu A.
Published: July 2007

A class of circuits is considered consisting of semiconductor devices (non‐linearly modelled bipolar transistors and junction diodes), non‐linear capacitors and inductors, all connected to a non‐linear resistive multiport. This multiport is described by a global piecewise continuously differentiable operator, while the other non‐linearities are of piecewise linear type. Sufficient conditions for the existence, uniqueness, stability, boundedness and source‐related continuity of the solutions are derived for both direct current and dynamic regimes. All these results are obtained by using the dissipativity property exhibited by the functions appearing in the circuit equations and are extensions of well known results of Sandberg and Willson.
Resistive circuit topologies that admit several solutions
Authors: Fosséprez Marc , Hasler Martin
Published: July 2007

Necessary and sufficient conditions are given that a resistive circuit may have several but finitely many solutions. Whether it actually has several solutions depends on the values of the sources and linear resistors as well as on the characteristics of the non‐linear resistors. Such circuits are required for static memory applications of all kinds, including associative memories realized by neural networks. These criteria are given both in terms of linear circuits and circuit topology. In the same way the minimal memory circuits are characterized. They constitute the building blocks for more complicated memory circuits.
Inpatients with eating disorders: Demographic, diagnostic, and service characteristics from a nationwide pediatric sample
Authors: Calderon Rose , Stoep Ann Vander , Collett Brent , Garrison Michelle M. , Toth Karen
Published: July 2007

Objective:

This study describes the demographic and clinical characteristics of youth hospitalized with an eating disorder, using the Pediatric Health Information System (PHIS) database.

Method:

Descriptive and inferential statistics were used to examine and compare PHIS inpatients (N = 1,713) with a primary discharge diagnosis of anorexia, bulimia, or eating disorder, not otherwise specified.

Results:

Of pediatric inpatients with eating disorders, 92% were female and 78% were non‐Hispanic white. Their mean age was 15.3 years; 71% had anorexia; 68% had one or more comorbid psychiatric disorders; 53% stayed on a psychiatric unit; the mean length of stay was 15.7 days. Private insurance paid for 55% of hospital stays. Patients without private insurance were more likely than patients with private insurance to be Black or Hispanic and to have comorbid psychiatric diagnoses.

Conclusion:

This study provides new information that can be used by hospitals to anticipate developmental and treatment needs of future inpatients with eating disorders. © 2007 by Wiley Periodicals, Inc. Int J Eat Disord 2007
Effects of social comparisons with peers on women's body satisfaction and exercise behavior
Authors: Wasilenko Kari A. , Kulik James A. , Wanic Rebekah A.
Published: July 2007

Objective:

Although exposure to thin‐ideal females in the media has been shown to increase women's body dissatisfaction, only a few studies have examined the effects of comparisons with peers, and no prior work has studied the effects of peer comparisons in a naturalistic setting or on objective behavior.

Method:

Female undergraduates (n = 45) in a campus gym who exercised on a target apparatus were assigned to have a fit‐peer, unfit‐peer, or no‐peer (control) exercise within their view on a nearby apparatus. Objective time spent exercising and body satisfaction reports were collected.

Results:

Exposure to a fit peer had undermining effects on women's body satisfaction and exercise duration, whereas an unfit peer produced no compensating greater body satisfaction but did elicit longer exercise duration relative to controls.

Conclusion:

Incidental comparisons with fit versus unfit peers can affect women's body satisfaction and fitness‐related behavior in a naturalistic setting. © 2007 by Wiley Periodicals, Inc. Int J Eat Disord 2007
Structurally Characterized Erbium Alkoxides for Use as an Amphoteric Dopant in PErZT Ceramic Thin Film and Nanoparticles
Authors: Boyle Timothy J. , Ottley Leigh Anna M. , Brewer Luke N. , Sigman Jennifer , Clem Paul G. , Richardson Jacob J.
Published: July 2007

A family of erbium alkoxides [Er(OR)3] was prepared from the reaction of Er[N(SiMe3)2]3 with a series of alcohols (HOR) in selected solvents and crystallographically characterized as: [Er(μ‐Onep)2(Onep)]4, (1), [Er4(μ4‐O)(μ3‐Onep)(μ‐Onep)5(Onep)4(py)3] (3), Er3(μ3‐OtBu)2(μ‐OtBu)3(OtBu)4(HOtBu)2 (4), Er3(μ3‐O)(μ‐OtBu)4(OtBu)3(py)3 (7), Er(dmp)3(solv)3 [solv = thf (9), py (10)], [Er(η‐dip)(dip)2]2 (11), Er(dip)3(thf)2 (12), [Er(μ‐OH)(dbp)2(thf)]2 (15), Er(dbp)3(py)2 (16), [Er(μ‐tps)(tps)2]2 (17), Er(tps)3(solv)3 [solv = thf (18) and (py) (19)] where Onep = neopentoxide (OCH2CMe3), OtBu = tert‐butoxide (OCMe3), dmp = 2,6‐dimethylphenoxide [OC6H3(Me)2‐2,6], dip = 2,6‐diisopropylphenoxide [OC6H3(CHMe2)2‐2,6], dbp = 2,6‐di‐tert‐butylphenoxide [OC6H3(CMe3)2‐2,6], tps = triphenylsiloxide [OSi(C6H5)3], tol = toluene, thf = tetrahydrofuran, and py = pyridine. The structures observed and data collected for the Er family of compounds are, in general, consistent with those reported previously for the Dy congeners over the range of solvated mono‐, di‐, tri‐, and tetranuclear species. Representative members of the Er(OR)3 precursors were used for the production of a PErZT precursor solution, which was subsequently used to generate thin films and nanoparticles. Further, these select Er precursors were used to generate Er2O3 nanoparticles. The full characterization of this family of compounds is reported along with the results of the materials investigations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Pyrrolidino DNA with Bases Corresponding to the 2‐Oxo Deletion Mutants of Thymine and Cytosine: Synthesis and Triplex‐Forming Properties
Authors: Mayer Alain , Leumann Christian J.
Published: July 2007

The dual recognition properties of pyrrolidino DNA species as parallel triplex‐forming oligonucleotides were previously found to be strongly dependent upon the nature of the pyrimidine bases. In the structure–activity study presented here we were able to exclude this differential binding being due to their 2‐oxo function. We had previously reported on the incorporation of pyrrolidino C‐nucleosides into triplex‐forming 2′‐deoxyoligonucleotides (TFOs). The basic nitrogen atom that replaces the 4′‐oxygen atom of the 2′‐deoxysugar in such modified units introduces a positive charge in the third strand, and this is able to produce favourable electrostatic interaction with the negatively charged DNA target duplex. A first series of pyrrolidino pseudonucleosides with the bases isocytosine and uracil proved successful for GC base‐pair recognition, but was unsuccessful for AT base‐pair recognition within the parallel triplex binding motif. Here we report on the synthesis of the two novel 2′‐deoxypyrrolidino nucleosides carrying the bases pyridin‐2‐one and 2‐aminopyridine, their phosphoramidite building blocks and theirincorporation into TFOs. Pyrrolidinylpyridin‐2‐one (dp2P) and ‐2‐aminopyridine (dp2AP), prepared as part of a structure–activity profiling of pyrrolidino DNA in triplex binding, are deletion mutants of T and C, respectively. We found by Tm measurements that neither modification increased triplex binding efficiency relative to the iso‐C‐ and ‐U‐containing pyrrolidino TFOs. These experiments clearly show that the C4 carbonyl function, although important for triplex binding through indirect contributions in general, is not responsible for the differential binding of the latter two aminonucleosides and suggest that TFO conformation is more important. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
The Use of Lithium Amides in the Palladium‐Mediated Synthesis of [Carbonyl‐11C]Amides
Authors: Itsenko Oleksiy , Blom Elisabeth , Långström Bengt , Kihlberg Tor
Published: July 2007

Weakly nucleophilic amines were converted into the corresponding lithium amides and used in either one‐ or two‐pot palladium‐mediated reactions with [11C]carbon monoxide and aryl iodides. It was found that palladium acyl complexes may be prepared in a separate step and have sufficient lifetime to be used in a subsequent reaction with a nucleophile. This two‐pot procedure was used for the labelling synthesis of eleven amides (nine of which are analogues of WAY‐100635, a 5‐HT1A radioligand) from weakly nucleophilic amines. The results were compared to a direct one‐pot procedure using lithium amides. Both approaches extend the scope of palladium‐mediated carbonylation using [11C]carbon monoxide and aryl iodides allowing use of weakly nucleophilic amines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Stereospecific Side Chain Activation in Cyclobutadiene–Fe(CO)3 Chemistry: A Theoretical and Experimental Study on the Structure and Configurational Stability of Cationic, Radical and Anionic Intermediates
Authors: Pfletschinger Anja , Schneider Ulrich , Lex Johann , Schmalz Hans‐Günther
Published: July 2007

The configurational stability of reactive intermediates (cation, radical and anion) derived from ethylcyclobutadiene–Fe(CO)3 by formal abstraction of a hydride, a hydrogen atom or a proton from the pseudobenzylic position was investigated. Density functional calculations (Becke3lyp) predicted that all these reactive intermediates can be regarded as planar chiral structures having a significant configurational stability. The racemization barriers were calculated to be 38.8 kcal mol–1 for the cationic, 16.9 kcal mol–1 for the radical and 44.8 kcal mol–1 for the anionic intermediate. In an experimental part of the study, derivatives of the 1‐hydroxyethyl‐substituted complex, which was enantioselectively prepared by CBS reduction of the acetyl complex, were subjected to SN1‐type as well as single‐electron‐transfer‐driven umpolung reactions. The observed stereospecificity of these transformations (retention of configuration) is in accordance with the predicted configurational stability of the involved reactive intermediates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Cover Picture: Unusual Influence of the Structures of Transition Metal Complexes on Catalytic C–S and C–Se Bond Formation Under Homogeneous and Heterogeneous Conditions (Eur. J. Org. Chem. 21/2007)
Authors: Beletskaya Irina P. , Ananikov Valentine P.
Published: July 2007

The cover picture shows that tuning the size of the catalyst particles provides a powerful synthetic tool for controlling not only the selectivity and yield, but also the direction of the chemical transformation. Soluble mononuclear and dinuclear phosphine complexes of palladium are excellent catalysts for stereoselctive E–E (E = S, Se) bond addition to alkynes. However, these complexes are poor catalysts for E–H bond addition to alkynes. Increasing the size of the catalyst particles changes the reactivity: polymeric species of nickel and palladium become efficient catalysts of E–H bond addition under heterogeneous conditions, while they are totally inactive in E?E bond addition. The unique self‐organized catalytic system shown in the background (magnified by scanning electron microscopy) combines the best features on the polynuclear metal complex and supported catalyst. Details are presented in the Microreview by I. P. Beletskaya and V. P. Ananikov on p. 3431 ff.
The influence of stereotypes on decisions to shoot
Authors: Correll Joshua , Park Bernadette , Judd Charles M. , Wittenbrink Bernd
Published: July 2007

Using a videogame to simulate encounters with potentially hostile targets, three studies tested a model in which racial bias in shoot/don't‐shoot decisions reflects accessibility of the stereotype linking Blacks to danger. Study 1 experimentally manipulated the race‐danger association by asking participants to read newspaper stories about Black (vs. White) criminals. As predicted, exposure to stories concerning Black criminals increased bias in the decision to shoot. Studies 2 and 3 manipulated the number of White and Black targets with and without guns in the context of the videogame itself. As predicted, frequent presentation of stereotypic (vs. counterstereotypic) targets exacerbated bias (Study 2) and—consistent with our process account—rendered stereotypes more accessible (Study 3). Copyright © 2007 John Wiley & Sons, Ltd.
State‐space discrimination and clustering of atmospheric time series data based on Kullback information measures
Authors: Bengtsson Thomas , Cavanaugh Joseph E.
Published: July 2007

Statistical problems in atmospheric science are frequently characterized by large spatio‐temporal data sets and pose difficult challenges in classification and pattern recognition. Here, we consider the problem of identifying geographically homogeneous regions based on similarities in the temporal dynamics of weather patterns. Two disparity measures are
proposed and applied to cluster time series of observed monthly temperatures from locations across Colorado, U.S.A. The two disparity measures are based on state‐space models, where the monthly temperature anomaly dynamics and seasonal variation are represented by latent processes. Our disparity measures produce clusters consistent with known atmospheric flow structures. In particular, the temporal anomaly pattern is related to the topography of Colorado, where, separated by the Continental Divide, the flow structures in the western and eastern parts of the state have different dynamics. The results further suggest that seasonal variation may be affected by locally changing solar radiation levels primarily associated with elevation variations across the Rocky Mountains. The general methodology is outlined and developed in the Appendix. We conclude with a discussion of extensions to time varying and non‐stationary systems. Copyright © 2007 John Wiley & Sons, Ltd.
Factors influencing retention of coarse particulate organic matter in streams
Authors: Quinn John M. , Phillips Ngaire R. , Parkyn Stephanie M.
Published: July 2007

Input of terrestrial coarse particulate organic matter (CPOM: leaves and small wood, >1 mm) adds food resources and habitat to streams. Restoration projects often aim to increase CPOM through riparian planting, but this relies on inputs being retained within the restored reach, and quantitative knowledge of factors influencing retention processes is limited. We investigated retention characteristics under base‐flow conditions in 65 stream reaches in pasture, native forests and pine plantations (with and without recent logging) in five contrasting New Zealand regions, using three CPOM analogues, namely 30 cm dowels, soaked ginkgo leaves and waterproof paper triangles. These differed significantly in geometric mean retention distance (Sp), with greatest retention (smallest Sp) of dowels > ginkgos > triangles. Retention efficiency was greater in riffles and glides than in pools. Objects trapping CPOM differed between land uses and regions in predictable ways. For example, in relatively unshaded pasture streams, instream and encroaching vegetation riparian was more important, and wood less important, than in forest. Catchment‐area‐ and width‐specific Sp values were more informative for comparisons amongst sites than deposition velocities (vdep). Catchment‐area‐specific Sp values varied 10‐fold amongst regions and threefold amongst land uses. Stepwise multiple regression models explained 71–74% of variance in Sp for the different CPOM analogues and showed that flow (+ influence; i.e., Sp increases with flow) was the most important factor, followed by submerged wood (−), with periphyton biomass (−) also significant in all models. A comparison with results from Spain showed similar relationships between Sp of plastic CPOM analogues and discharge under base‐flow conditions. Restoring riparian vegetation is expected to ultimately enhance instream CPOM by increasing input and retention by wood. Our findings indicate that this should prioritize small streams if the aim is to optimize the restoration of CPOM influence on instream processes. Copyright © 2007 John Wiley & Sons, Ltd.
Contribution of dead wood to the carbon flux in forested streams
Authors: Elosegi Arturo , Díez Joserra , Pozo Jesús
Published: July 2007

Dead wood has been identified as an important structural component of stream ecosystems, and researchers have stressed its role in retaining sediments and organic matter, increasing habitat diversity and providing refugia for aquatic organisms. Because it is a highly refractory compound, known to take very long periods to break down underwater, it has been considered a slow source of dissolved or fine particulate organic matter. We evaluated the contribution of dead wood to the total carbon flux in two headwater forested streams in northern Spain, one running under mature deciduous forest, the other under eucalyptus plantations. Breakdown rates were measured from branches (10 cm long, 3 cm in diameter) of alder, oak and eucalyptus, the main species present at the streams, applied to the standing crop of fine dead wood following four different models and compared with the breakdown loss of leaf litter calculated in a previous work for the same reaches. Calculations showed breakdown losses of fine wood (FW, diameter 1–5 cm) to range from 6·0 to 12·3 g ash‐free dry mass (AFDM) m−2y−1at the deciduous stream and from 4·6 to 7·1 g AFDM m−2y−1at the eucalyptus stream. Conservative assumptions show that fine wood breakdown losses amount to 21% of the mass lost by leaf breakdown at the deciduous stream and to 9% of leaf breakdown at the eucalyptus stream. So, fine dead wood contributes to a significant fraction of the total breakdown of allochthonous organic matter in the studied streams; other sizes of dead wood (twigs, coarse wood) increase the breakdown by an order of magnitude, and thus can result in a large part of the carbon flux being derived from wood. Copyright © 2007 John Wiley & Sons, Ltd.
Living trees provide stable large wood in streams
Authors: Opperman Jeff J. , Merenlender Adina M.
Published: July 2007

Large wood exerts strong influences on stream channel morphology and aquatic ecosystems. Previously, in‐stream large wood has generally been equated with dead wood. However, in streams in Northern California we found that living wood – trees that entered the channel but remained rooted and living – represented a major portion of the functional in‐stream large wood. We hypothesized that living wood will tend to be more stable, due to an attached root wad, and more persistent, due to lack of decay, than similarly sized dead wood. Living wood may provide important in‐stream structure in streams with riparian corridors that lack large conifers. We surveyed 20 stream reaches in Northern California with riparian corridors dominated by broadleaved trees and found that a high proportion of wood jams had key pieces that were still living. Living wood was capable of serving as a key piece for a wood jam at a smaller size than dead wood and had a greater influence on channel morphology. We found that only 74% of the jams without living wood persisted over 1–2 years while 98% of those with living key pieces remained in place. Due to living wood, the range of tree species and sizes that provide stable and functional in‐stream large wood may be broader than previously described. Copyright © 2007 John Wiley & Sons, Ltd.
Size and position matter: riparian plant establishment from fluvially deposited trees
Authors: Francis Robert A.
Published: July 2007

The sprouting of fluvially deposited trees is an important process for floodplain woodland regeneration along dynamic rivers. This paper investigates how tree size and relative elevation of the location of fluvially deposited trees affects their survival. The survival of newly deposited trees along the River Tagliamento, Italy, was monitored over three field campaigns (2001, 2003 and 2005). A significant negative correlation was found between relative elevation and tree survival, while tree length was significantly positively correlated to survival. Consequently, larger trees deposited at lower elevations have a greater likelihood of regeneration, although the influence of these factors varied according to genera. Copyright © 2007 John Wiley & Sons, Ltd.
Validating multiple‐period density‐forecasting models
Authors: Dowd Kevin
Published: July 2007

This paper examines the problem of how to validate multiple‐period density forecasting models. Such models are more difficult to validate than their single‐period equivalents, because consecutive observations are subject to common shocks that undermine i.i.d. The paper examines various solutions to this problem, and proposes a new solution based on the application of standard tests to a resample that is constructed to be i.i.d. It suggests that this solution is superior to alternatives, and presents results indicating that tests based on the i.i.d. resample approach have good power.  Copyright © 2007 John Wiley & Sons, Ltd.
Forecasting German GDP using alternative factor models based on large datasets
Authors: Schumacher Christian
Published: July 2007

This paper discusses the forecasting performance of alternative factor models based on a large panel of quarterly time series for the German economy. One model extracts factors by static principal components analysis; the second model is based on dynamic principal components obtained using frequency domain methods; the third model is based on subspace algorithms for state‐space models. Out‐of‐sample forecasts show that the forecast errors of the factor models are on average smaller than the errors of a simple autoregressive benchmark model. Among the factor models, the dynamic principal component model and the subspace factor model outperform the static factor model in most cases in terms of mean‐squared forecast error. However, the forecast performance depends crucially on the choice of appropriate information criteria for the auxiliary parameters of the models. In the case of misspecification, rankings of forecast performance can change severely.  Copyright © 2007 John Wiley & Sons, Ltd.
Effect of PTFE Content in Gas Diffusion Media and Microlayer on the Performance of PEMFC Tested under Ambient Pressure
Authors: Velayutham G. , Kaushik J. , Rajalakshmi N. , Dhathathreyan K. S.
Published: July 2007

Polytetrafluoroethylene (PTFE) content in the fuel cell electrode plays an important role on the performance of polymer electrolyte membrane fuel cell (PEMFC) when the cell is tested under low temperature and under ambient pressure. PTFE is added to the PEM fuel cell electrode to improve the mechanical strength and to help in removing the product water formed on the cathode; however, higher PTFE loading increases the resistance and thus decreases the performance of the cell and very low PTFE content has the disadvantage of water flooding in long‐term operation. We have investigated the effect of the PTFE content in the gas diffusion media (carbon paper) and in the microlayer on the performance of PEMFC operating at ambient pressure. The PTFE contents in these two layers have to be finely matched to get the best performance of the cells. The polarisation behaviour, electrochemical surface area and the electrochemical impedance spectra have been analysed. The results are presented in this paper.