bluuebunny/crossref_metadata_2025 huggingface dataset:
14N NMR study of the domain structure of tetramethylammonium cadmium chloride (TMCC)
Authors: Mulla‐Osman S. , Michel D. , Czapla Z.
Published: February 2003

Quadrupolar perturbed 14N NMR investigations are performed on single crystals of tetramethylammonium cadmium chloride, (CH3)4NCdCl3 (TMCC), in the temperature range of 297 to 80 K. At the phase transitions at 118 and 104 K the quadrupole coupling tensor (QCT) shows abrupt changes in accordance with their first order type. The largest QCT component is parallel to the hexagonal c‐axis in the high temperature phase and rotates by 90° at the transition into the monoclinic phase II at 118 K. In complete agreement with a recent 35Cl NMR study, the 14N spectra in phase II show clearly a ferro‐elastic twin domain structure. The saturated rotational angle between the epitaxially grown domains of Exp ≈ 4 is in a good agreement with the theoretical value of S = 3.55 calculated from the ferro‐elastic strain tensor. The ordering behaviour below the phase transition at 118 K is related with the rotation of the largest component VZZ of the QCT in a plane perpendicular to the c‐axis and with changes of its principal axes values. The component VZZ is parallel to the N bond direction. A shift of the N atoms within the plane in relation with the phase transition was also found in recent low temperature X‐ray diffraction measurements. In the whole temperature range investigated, the 14N NMR spectra are exclusively determined by the lattice symmetry but not by distortions of the local tetrahedral symmetry at the N sites of the tetramethylammonium groups.
Band offset of quantum wells computed from charge measurements
Authors: Biswas Dipankar , Chakrabarti Satyajit , Dasgupta Sudipto , Kundu Sudakshina , Datta Resmi
Published: February 2003

Band discontinuity is an important parameter for the design of heterojunction based electronic and opto electronic devices. An alternative method for band offset measurement in quantum wells has been outlined in this paper. The band offset is determined from a comparison of experimental results and theoretical computations of the temperature dependent total charge content of a quantum well. In spite of the simplicity of the measurement procedures the result at its best has an error around ±2%.
Charge carrier diffusion in energy landscape created by static charges: Poole–Frenkel model revised
Authors: Novikov S. V.
Published: February 2003

Effect of static charges on charge carrier transport in disordered organic materials is considered. We show that the mobility dependence on temperature and concentration of charged traps differs drastically from the prediction of the model of isolated charged trap (Poole–Frenkel model), yet, by accident, the mobility field dependence remains the same with the logarithm of the mobility being proportional to the square root of the electric field. The ultimate reason for the difference is a long range nature of the Coulomb interaction of a carrier with charged traps. This interaction produces huge fluctuations of carrier energy in the medium overcoming carrier interaction with the isolated static charge. A possibility to observe this quasi‐Poole–Frenkel transport regime in experiments is discussed. We argue that the model of isolated charged trap may be applied only to the case of charge transport in extremely thin transport layers.
Theoretical analysis of d electron effects on the electronic properties of wurtzite and zincblende GaN
Authors: Bouhafs B. , Litimein F. , Dridi Z. , Ruterana P.
Published: February 2003

We investigate the electronic properties of the technologically important wide‐band‐gap semiconductor GaN employing ‘state‐of‐the‐art’ DFT‐LDA calculations using a FP‐LAPW code. The Ga 3d electrons are treated both as core or as valence electrons and the wurtzite as well as the zincblende modifications of GaN are investigated. In particular, we address the influence of the lattice configuration and of the d electrons to the electronic structure of w‐GaN and c‐GaN. Band structures, densities of states, orbital‐resolved densities of states, total and partial valence charge densities, and ionicity factors are analysed in great detail. The calculated values of the energy gaps, bandwidths, spin–orbit, crystal‐field splittings, and the correct band degeneracies are compared to experimental and/or ab initio results. Several features of w‐GaN resemble those of c‐GaN. Most of the calculated band parameters, of band gaps, total and upper‐valence bandwidths, and antisymmetric gap for w‐GaN are close to those of c‐GaN within 1%. The charge distributions have similar features meaning that this material has the same ionicity factor with or without Ga 3d hybridization in both structures. By examining the pressure dependence of the energy band gaps, the value of the hydrostatic deformation potential of the band gap has also been calculated.
Superfluid fraction of a charged boson fluid at non‐integer dimensions and superconducting films
Authors: Kim Sang‐Hoon , Koo Kim Chul , Nahm Kyun
Published: February 2003

The superfluid fraction of a charged boson fluid at non‐integer dimensions between 2 and 3 is studied. Interaction between particles is assumed to be Coulombic, and Bogoliubov approximation is applied for a weak coupling regime. The theoretical results are compared with the superfluid densities of superconducting films, showing an universal splitting behavior. The qualitative similarity between the charged boson fluid and the superconducting films gives a strong clue for the origin of the universality observed in the superconducting films.
Effective nonlinear response in random mixture of coated granular cylinders
Authors: Gao Lei
Published: February 2003

Effective dielectric response of granular composites consisting of coated cylindrical inclusions embedded in a host medium is investigated in both the dilute and nondilute cases. We assume that the shell and the host are linear with the dielectric function ϵs0 and ϵh0, while the core has the field‐dependent dielectric function ϵc = ϵc0 + χc|Ec|β, where ϵc0 and χc are the linear dielectric function and nonlinear susceptibility, respectively. General expressions for the effective linear dielectric function and third‐order nonlinear susceptibility of the three‐phase system are analytically obtained with perturbative expansion method. The partially resonant circumstances, in which the dielectric response of the components satisfies ϵs0 + ϵh0 or ϵs0 + ϵc0 = 0, and the conductance case in which the coated inclusions possess superconducting shells (ϵs0 → ∞) of zero thickness (t → 0), are examined in detail. We show that under the partially resonant conditions the coated cylindrical inclusions are equivalent to solid cylinders with larger nonlinear susceptibility and volume fractions than these of original cylindrical cores, and thus the effective nonlinear susceptibility χe of the composite system may be greatly enhanced. For the conductance case, we find that the coated cylinders behave as solid cylinders with a larger linear dielectric function than ϵc0.
Specific heat capacity of AuTe2I below 100 K
Authors: Gmelin Eberhard
Published: February 2003

The heat capacity of AuTe2I was measured in the temperature range of 0.7 K < T < 100 K. The resulting low temperature limiting Debye temperature and electronic contribution were determined to be θ0 = (140 ± 1.5) K and γ = (1.54 ± 0.04) mJ/mol K2, respectively, the latter in reasonable agreement with earlier results from Hall effect and Shubnikov de Haas experiments.
Polaronic exciton in a parabolic quantum dot
Authors: Senger R. T. , Bajaj K. K.
Published: February 2003

A calculation of the variations of the energy and oscillator strength of the ground state of an exciton in an ionic quantum dot as a function of the dot size, using a parabolic confining potential and a variational approach, is presented. The strong exciton–phonon interaction is taken into account by using an effective potential between the electron and the hole as derived by Pollmann and Büttner. The values of the exciton binding energies calculated using this potential are compared with those obtained using statically screened Coulomb potential and are found to be considerably larger for all values of the quantum dot size. In small quantum dots, the electron–hole correlation is reduced as the single particle energies scale at a much faster rate than the interaction energy. This is manifested in the behavior of oscillator strength, which becomes less dependent on the form of the effective interaction as the quantum dot size is reduced.
Epitaxial formation of a multilayer Pd–Ta surface alloy on a Ta substrate
Authors: Szczepkowicz A. , Ciszewski A.
Published: February 2003

A thick palladium layer (∼5 nm) is deposited onto a curved tantalum surface. The system is submitted to several annealing cycles. Structural changes within 0–5 nm below the surface are observed using Field Ion Microscopy. At 800 K, an atomic intermixing of adsorbate and substrate is observed. Pd atoms are detected within the first five atomic layers of the Ta substrate. At 1100 K, a multilayer alloy is formed at the surface, oriented epitaxially with respect to the Ta{100} planes.
Simultaneous measurements of crystal optical characteristics of deuterated triglycine sulphate
Authors: Kushnir O. S.
Published: February 2003

The birefringence, rotation angle of the optical indicatrix and the gyration along the polar direction are studied in the paraelectric and ferroelectric phases of deuterated triglycine sulphate crystals using the HAUP‐type universal null‐polarimetric technique. The gyration effect in the multidomain ferroelectric phase is found to be negligibly small, in accordance with the symmetry considerations, while the changes in the birefringence and the indicatrix rotation occurring in the course of the phase transition may be described by electrooptical coupling due to the quadratic spontaneous effect.
Structural modulation of spinel ZnCr2Se4 in the vicinity of antiferromagnetic phase transition induced by an applied magnetic field
Authors: Hidaka M. , Yoshimura M. , Takahasi S. , Watanabe S. , Akimitsu J.
Published: February 2003

Magnetic and structural phase transitions of normal‐type spinel ZnCr2Se4 have been studied as functions of applied magnetic field and temperature by means of neutron diffraction. It is found that the spiral spin order of Cr3+ ions is largely affected by the magnetic field, and the satellite‐like magnetic reflections are largely decreased in the magnetic field of 0.6 T < H < 1.2 T and disappear at H ≥ 1.2 T, when the magnetic field was applied vertically to an orthorhombic axis [001]. This means that the spiral configuration of the ferromagnetic CrSe4 chains is perfectly disordered around two‐fold screw axes in an orthorhombic symmetry phase (Fddd structure) by the magnetic field H ≥ 1.2 T, though the structural phase transition (TC) between cubic and orthorhombic symmetry phases simultaneously occurs at the antiferromagnetic phase transition temperature (TN ≈︂ 21 K) in no magnetic field. It is also found that the main reflections show a magnetic field dependence similar to that of the magnetic reflections. Pseudo‐tetragonal displacements of Se ions below TN are modulated by the applied magnetic field. The 3 T magnetic field induces a metastable structural transition at about 15 K, after initially cooling down to about 2 K in no applied magnetic field. The transition is related to the modulation from pseudo‐tetragonal to pseudo‐cubic displacements of Se ions.
Impurity levels in layered semiconductor n‐InSe doped with Ge
Authors: Shigetomi S. , Ikari T.
Published: February 2003

The impurity levels in Ge‐doped n‐InSe have been investigated by using photoluminescence (PL), photocurrent (PC), and Hall effect measurements. Two emission bands related with impurity level are observed at about 1.28 and 1.25 eV in PL spectra at 77 K. In addition to the results of temperature dependence of PC spectra and electron concentration, it is found that the 1.28 and 1.25 eV emission bands are associated with the donor levels at about 0.09 and 0.06 eV below the conduction band, respectively. The effect of excitation intensity of peak energy for the 1.25 eV emission band is characterized by the donor–acceptor recombination. The temperature dependence of mobility is influenced by adding an amount of Ge atom. The scattering mechanism of the 0.05 at.% Ge‐doped sample can be well explained by the combined mechanism of the optical phonon, ionized impurity and neutral impurity scatterings.
Evidence for pseudo‐gap behavior in defect‐doped infinite layer (Ca, Sr)CuO2 thin films
Authors: Norton David P. , Chakoumakos Bryan C. , Budai John D. , Lowndes Douglas H.
Published: February 2003

A distinct crossover between the high temperature and low temperature normal state dc transport properties of epitaxial (Ca, Sr)CuO2 single crystal thin films has been observed. Defect‐doped (Ca, Sr)CuO2 films with dc conductivity behavior ranging from insulating to metallic‐like were obtained by growing stoichiometric and cation‐deficient material under various film growth conditions. The results indicate that 2D variable‐range hopping is the dominant transport mechanism at low temperatures. The high temperature behavior depends on the magnitude of the conductivity, resulting in either activated conduction or a ln ρ ∼ 1/T1/2 dependence that is reminiscent of thermally‐activated tunneling in a granular metal/insulator matrix. The distinct crossover in behavior suggests the possibility of gap formation in the temperature range 150–200 K.
Far infrared magneto‐optical transitions in quantum disks: New results
Authors: Comas F. , Gondar J. L.
Published: February 2003

We have reconsidered the problem of far infrared magneto‐optical transitions in a Quantum‐Disk (QD). For this spectral region we are essentially concerned with intraband electronic transitions and excitonic effects do not contribute. The system is modelled by a cylindrical geometry with a uniform magnetic field B acting along the cylinder axis. The confinement in the radial direction is given by a parabolic potential, while along the cylinder axis we assume two interfaces located at z = ± d/2. We have calculated the transition probabilities for the electron interaction with an electromagnetic radiation field using the dipole approximation. Inaccuracies found in some previous fundamental works on the subject are analyzed and amended. New possible magneto‐optical transitions are predicted and a detailed discussion of their oscillator‐strength is made.
Tight‐binding parameters from the full‐potential linear muffin‐tin orbital method: A feasibility study on NiAl
Authors: Djajaputra David , Cooper Bernard R.
Published: February 2003

We have examined a method of direct extraction of accurate tight‐binding parameters from anab‐initioband‐structure calculation. The linear muffin‐tin potential method, in its full‐potential implementation, has been used to provide the hamiltonian and overlap matrix elements in the momentum space. These matrix elements are Fourier transformed to real space to produce the tight‐binding parameters. The feasibility of this method has been tested on the intermetallic alloy NiAl, usingspdorbitals for each atom. The parameters generated for this alloy have been used as input to a real‐space calculation of the local density of states using the recursion method.
Temperature dependence of the quantum dot lateral size in the Ge/Si(100) system
Authors: Tonkikh A. A. , Dubrovskii V. G. , Cirlin G. E. , Egorov V. A. , Ustinov V. M. , Werner P.
Published: February 2003

The temperature dependence of morphological characteristics of Ge/Si(100) quantum dots grown by molecular beam epitaxy with constant growth rate at different substrate temperatures is investigated. The mean lateral size of quantum dots at 6.2 ML is shown to increase at rising substrate temperature. Comparison of experimental and theoretical results obtained in the frame of kinetic model is performed.
Structural modulation of spinel ZnCr2Se4 in the vicinity of antiferromagnetic phase transition induced by an applied magnetic field
Authors: Hidaka M. , Yoshimura N. , Takahasi S. , Watanabe S. , Akimitsu J.
Published: February 2003

The cover picture of physica status solidi (b) shows a structure model of ZnCr2Se4, a spinel compound which exhibits remarkable structural and magnetic modulations near its antiferromagnetic phase transi‐tion around 20 K as well as under an applied magnetic field. Results of extensive neutron diffraction investigations of these phenomena are reported in this issue's Editor's Choice [1].

The first author, Masanori Hidaka, is at the Department of Fundamental Physics of the Graduate School of Sciences at Kyushu University, and is working on the correlation between functional physical properties and the structure of condensed matter such as high‐TC superconductors, ferro‐antiferromagnetic and ‐electric compounds by neutron or X‐ray diffraction and XANES experiments.
Discontinuous feedbacks, discontinuous optimal controls, and continuous‐time model predictive control
Authors: A. C. C. Fontes Fernando
Published: February 2003

It is known that there is a class of nonlinear systems that cannot be stabilized by a continuous time‐invariant feedback. This class includes systems with interest in practice, such as nonholonomic systems, frequently appearing in robotics and other areas. Yet, most continuous‐time model predictive control (MPC) frameworks had to assume continuity of the resulting feedback law, being unable to address an important class of nonlinear systems. It is also known that the open‐loop optimal control problems that are solved in MPC algorithms may not have, in general, a continuous solution. Again, most continuous‐time MPC frameworks had to artificially assume continuity of the optimal controls or, alternatively, impose some demanding assumptions on the data of the optimal control problem to achieve the desired continuity. In this work we analyse the reasons why traditional MPC approaches had to impose the continuity assumptions, the difficulties in relaxing these assumptions, and how the concept of ‘sampling feedbacks’ combines naturally with MPC to overcome these difficulties. A continuous‐time MPC framework using a strictly positive inter‐sampling time is argued to be appropriate to use with discontinuous optimal controls and discontinuous feedbacks. The essential features for the stability of such MPC framework are reviewed. Copyright © 2003 John Wiley & Sons, Ltd.
Output feedback stabilization of constrained systems with nonlinear predictive control
Authors: Findeisen Rolf , Imsland Lars , Allgöwer Frank , Foss Bjarne A.
Published: February 2003

We present an output feedback stabilization scheme for uniformly completely observable nonlinear MIMO systems combining nonlinear model predictive control (NMPC) and high‐gain observers. The control signal is recalculated at discrete sampling instants by an NMPC controller using a system model for the predictions. The state information necessary for the prediction is provided by a continuous time high‐gain observer. The resulting ‘optimal’ control signal is open‐loop implemented until the next sampling instant. With the proposed scheme semi‐global practical stability is achieved. That is, for initial conditions in any compact set contained in the region of attraction of the NMPC state feedback controller, the system states will enter any small set containing the origin, if the high‐gain observers is sufficiently fast and the sampling time is small enough. In principle the proposed approach can be used for a variety of state feedback NMPC schemes. Copyright © 2003 John Wiley & Sons, Ltd.
Robust model predictive control for nonlinear discrete‐time systems
Authors: Magni L. , De Nicolao G. , Scattolini R. , Allgöwer F.
Published: February 2003

This paper describes a model predictive control (MPC) algorithm for the solution of a state‐feedback robust control problem for discrete‐time nonlinear systems. The control law is obtained through the solution of a finite‐horizon dynamic game and guarantees robust stability in the face of a class of bounded disturbances and/or parameter uncertainties. A simulation example is reported to show the applicability of the method. Copyright © 2003 John Wiley & Sons, Ltd.
Suboptimal control of constrained nonlinear systems via receding horizon constrained control Lyapunov functions
Authors: Sznaier Mario , Suárez Rodolfo , Cloutier James
Published: February 2003

In this paper we propose a new controller design method, based on the combination of receding horizon and control Lyapunov functions, for nonlinear systems subject to input constraints. The main result shows that this control law renders the origin an asymptotically stable equilibrium point in the entire region where stabilization with constrained controls is feasible, while, at the same time, achieving near‐optimal performance. Contrary to other approaches, the proposed controller does not require forcing the trajectory at the end of the prediction horizon to lie in a region where the constraints are not binding, allowing for the use of (potentially substantially) smaller horizons in the optimization. Copyright © 2003 John Wiley & Sons, Ltd.
Model predictive control of constrained piecewise affine discrete‐time systems
Authors: Mayne D. Q. , Raković S.
Published: February 2003

The paper deals with model predictive control of a class of non‐smooth nonlinear systems, namely piecewise affine systems. A novel procedure for solving the associated optimal control problem is presented and its convergence established. Stability properties of the closed‐loop system using model predictive control with the new algorithm are derived. Examples illustrate the proposed algorithm for determining optimal control of constrained piecewise affine systems and the performance of the closed‐loop system. Copyright © 2003 John Wiley & Sons, Ltd.
Predictive control of constrained nonlinear systems via LPV linear embeddings
Authors: Casavola Alessandro , Famularo Domenico , Franzè Giuseppe
Published: February 2003

This paper analyzes the applicability of convex MPC schemes, synthesized for LPV polytopic systems, to nonlinear plants. The nonlinear systems under consideration are those whose trajectories can be embedded within those of a polytopic LPV discrete‐time system. It is postulated that the latter belongs to a polytopic family of linear systems, each member of which is parameterized by the value that a parameter vector assumes in the unit simplex. Such a parameter can be measured on‐line and exploited for feedback while a bound on its rate of change is known and exploited for predictions. Different customizations and improvements of a recently introduced MPC scheme for LPV systems are presented and contrasted in terms of their numerical burdens and control performance. The proposed predictive controllers are proved to quadratically stabilize LPV polytopic systems, as well as any other embedded non‐linear system, in the presence of input and state constraints. Copyright © 2003 John Wiley & Sons, Ltd.
Gain‐scheduling MPC of nonlinear systems
Authors: Chisci Luigi , Falugi Paola , Zappa Giovanni
Published: February 2003

Predictive control of nonlinear systems is addressed by embedding the dynamics into an LPV system and by computing robust invariant sets. This mitigates the on‐line computational burden by transferring most of the computations off‐line. Benefits and conservatism of this approach are discussed in relation with the control of a critical mechanical system. Copyright © 2003 John Wiley & Sons, Ltd.
Efficient optimization approaches to nonlinear model predictive control
Authors: Mahadevan R. , J. Doyle III F.
Published: February 2003

Efficient optimization approaches for nonlinear model predictive control (NMPC) are described in this paper. The first approach is based on the differential flatness property of a system of ordinary differential equations. The nonlinear process model is represented in terms of the flat outputs and their derivatives, and the nonlinear dynamic optimization problem is transformed into a nonlinear programming problem, with exact representation of the system dynamics. The approach is illustrated through the control of substrate concentration of a fed‐batch bioreactor. The second approach is motivated by the idea of differential flatness, but is applicable to broader class of nonlinear systems. Here, the nonlinear process model is recast through the elimination of a subset of the system variables. This results in a nonlinear dynamic optimization with a reduced number of system variables that have to be solved for, as well as the dynamic equations. Applications of this approach to the optimization of a recombinant product in a fed‐batch bioreactor and the control of a chemical reactor are presented. Both the approaches discussed in this paper provide up to a five fold improvement in the solution time for the optimization problem as compared to the traditional formulation. Copyright © 2003 John Wiley & Sons, Ltd.
Efficient scheduled stabilizing model predictive control for constrained nonlinear systems
Authors: Wan Zhaoyang , Kothare Mayuresh V.
Published: February 2003

We present a computationally efficient scheduled model predictive control (MPC) algorithm for constrained nonlinear systems with large operating regions. We design a set of local predictive controllers with estimates of their regions of stability covering the desired operating region, and implement them as a single scheduled MPC which on‐line switches between the set of local controllers and achieves nonlinear transitions with guaranteed stability. This algorithm is computationally efficient and provides a general framework for the scheduled MPC design. The algorithm is illustrated with two examples. Copyright © 2003 John Wiley & Sons, Ltd.
Simulation based strategy for nonlinear optimal control: application to a microbial cell reactor
Authors: Kaisare Niket S. , Lee Jong Min , Lee Jay H.
Published: February 2003

Optimal control of systems with complex nonlinear behaviour such as steady state multiplicity results in a nonlinear optimization problem that needs to be solved online at each sample time. We present an approach based on simulation, function approximation and evolutionary improvement aimed towards simplifying online optimization. Closed loop data from a suboptimal control law, such as MPC based on successive linearization, are used to obtain an approximation of the ‘cost‐to‐go’ function, which is subsequently improved through iterations of the Bellman equation. Using this offline‐computed cost approximation, an infinite horizon problem is converted to an equivalent single stage problem—substantially reducing the computational burden. This approach is tested on continuous culture of microbes growing on a nutrient medium containing two substrates that exhibits steady state multiplicity. Extrapolation of the cost‐to‐go function approximator can lead to deterioration of online performance. Some remedies to prevent such problems caused by extrapolation are proposed. Copyright © 2003 John Wiley & Sons, Ltd.
Nonlinear predictive control of hot strip rolling mill
Authors: Cannon M. , Kouvaritakis B. , Grimble M. , Bulut B.
Published: February 2003

Linear Model Predictive Control (MPC) has been applied successfully to numerous industrial problems, but its various extensions to the nonlinear case have not enjoyed the same measure of success. One of the major obstacles in this development is the prohibitive online computation required to execute receding horizon minimization of the predicted cost. This paper combines recent linear techniques, which allow for significant reductions in online computational load, with Linear Difference Inclusion in order to apply MPC to a rolling mill problem described by a set of algebraic and differential/integral nonlinear equations, discretized to give a suitable time‐varying uncertain linear model. Through successive optimization of an approximate cost derived by linearization about predicted trajectories, we obtain MPC laws with guaranteed stability and convergence to a (possibly local) minimum of the performance index predicted on the basis of the full nonlinear model dynamics. The efficacy of the approach is illustrated by means of simulation results presented at the end of the paper. Copyright © 2003 John Wiley & Sons, Ltd.
Nonlinear receding horizon control of an underactuated hovercraft
Authors: Seguchi Hiroaki , Ohtsuka Toshiyuki
Published: February 2003

This paper describes nonlinear receding horizon control of an underactuated hovercraft with discrete‐valued inputs and its hardware implementation. The hovercraft has two fixed thrusters, and the thrusters generate thrusts of only three discrete values, that is, forward, backward and zero thrusts. Nonlinear receding horizon control is applied to position control of the hovercraft with the discrete‐valued inputs approximated by constrained continuous‐valued inputs. Although nonlinear receding horizon control requires real‐time constrained optimization, a fast algorithm is successfully implemented for the hardware experiment. Copyright © 2003 John Wiley & Sons, Ltd.
The effects of axial deformation and axial force on vibration characteristics of tall buildings
Authors: Swaddiwudhipong S. , Sidji S. Soelarno , Lee S.‐L.
Published: February 2003

A tall building comprising frames and shear walls coupled together is idealized as a shear–flexure cantilever through the continuum approach. The effects of axial deformation as well as axial force in the frames are considered and incorporated in the formulation of the governing equations. Numerical examples are solved through the Galerkin method and the results compared with finite element solutions. The study indicates that the effect of axial deformation in the frame should be considered for tall and/or slender buildings while the effect of axial force in the column should be included for buildings with soft‐storeys resulting from the termination of core walls in the lower portion of the building. Copyright © 2002 John Wiley & Sons, Ltd.
Overstrength and force reduction factors of multistorey reinforced‐concrete buildings
Authors: Elnashai A. S. , Mwafy A. M.
Published: February 2003

This paper addresses the issue of horizontal overstrength in modern code‐designed reinforced‐concrete (RC) buildings. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. The lateral capacity and the overstrength factor are estimated by means of inelastic static pushover as well as time‐history collapse analysis for 12 buildings of various characteristics representing a wide range of contemporary RC buildings. The importance of employing the elongated periods of structures to obtain the design forces is emphasized. Predicting this period from free vibration analysis by employing ‘effective’ flexural stiffnesses is investigated. A direct relationship between the force reduction factor used in design and the lateral capacity of structures is confirmed in this study. Moreover, conservative overstrength of medium and low period RC buildings designed according to Eurocode 8 is proposed. Finally, the implication of the force reduction factor on the commonly utilized overstrength definition is highlighted. Advantages of using an additional measure of response alongside the overstrength factor are emphasized. This is the ratio between the overstrength factor and the force reduction factor and is termed the inherent overstrength (Ω
i). The suggested measure provides more meaningful results of reserve strength and structural response than overstrength and force reduction factors. Copyright © 2002 John Wiley & Sons, Ltd.
Seismic analysis of Tehran Telecommunication Tower using complex fractional modulus
Authors: Horr A. M. , Safi M. , Asadpour N.
Published: February 2003

Seismic response of large concrete tower structures with passive or active damping is important in terms of performance under earthquake loads. The conventional finite element method has been used successfully in linear and nonlinear analyses in large concrete structures. The method can be performed by subdividing the large structure into small uniform elements having approximate shape functions. Although this replaces a single complicated structural system with a number of simple uniform elements, in cases of tall concrete tower structures with cracking and crushing behaviour in the concrete material and yielding in the reinforcement, the computer time and memory can be large. Hence, it is desirable to search for a procedure requiring fewer elements and also less computer time and effort to model the structure. In this respect, attention is paid to the advanced complex damped spectral element method, which benefits from the more accurate and also mathematically complicated shape functions. Use of the advanced spectral element method can help engineers to design a complex structure, such as a tall concrete tower, with lower cost and lower weight. Using a computer program, the proposed formulation has been used to derive the nonlinear dynamic response of the 435‐m Tehran Telecommunication Tower. Copyright © 2002 John Wiley & Sons, Ltd.
Exact method of analysis of shear lag in framed tube structures
Authors: Haji‐Kazemi H. , Company M.
Published: February 2003

Framed tube structures are particularly suitable for tall buildings. Owing to flexural and shear flexibilities of the frame members, the overall bending of the frame is complicated by the occurance of shear lag. The shear lag phenomenon in framed‐tube structures under lateral loads is explained in the literature, but explanation of its origin and comprehensive studies of it is lacking. In this paper an analogy between the shear lag behaviour of a cantilever box representing a uniform framed‐tube building is used for exact analysis of stress and displacement components of perimeter columns. The coefficients of the power series used for the governing equilibrium and compatibility equations are functions of the height and width of the frame panels. Numerical examples are given to demonstrate the accuracy of the proposed method. Copyright © 2002 John Wiley & Sons, Ltd.
Delay in Treatment of Colorectal Cancer: Multifactorial Problem
Authors: Langenbach Mike Ralf , Schmidt Johannes , Neumann Jürgen , Zirngibl Hubert
Published: February 2003

Abstract

The stage of a colorectal carcinoma represents the most important prognostic factor regarding the probability of survival. The primary objective of this study was to document the management of patients with colorectal carcinoma after onset of symptoms. Factors influencing the delay in definitive therapy should thus be determined. Anthropometric, social, and operative data were obtained by standardized questionnaires from 40 patients with colonic cancer and 30 patients with rectal cancer. The influence of delayed treatment on outcome was analyzed. A significant correlation was found for the time between onset of first symptoms and definitive surgical therapy with tumor stage (colon cancer: r = 0.52, p < 0.05; colorectal cancer: r = 0.62, p < 0.05). The time delay in rectal carcinoma patients averaged 224 days and in patients with colonic carcinoma 149 days. Social influences such as profession, type of education, marital status, and quality of health insurance had a significant influence on treatment delay, as did the clinical experience of the physician first contacted. The leading symptom in patients with rectal cancer was peranal hemorrhage, and in patients with colonic cancer it was abdominal pain. The main causes of iatrogenic delay were insufficient clinical investigation and a lack of awareness when typical first symptoms were present. Delayed treatment of colorectal cancer seems to be a multifactorial problem. Causes for such delay are found not only in the patients and their social environments but also in the type and quality of their medical care systems. Intensified education and earlier prevention are the major aims for patients and their physicians.
Hepatoduodenal Ligament Invasion by Gallbladder Carcinoma: Histologic Patterns and Surgical Recommendation
Authors: Kaneoka Yuji , Yamaguchi Akihiro , Isogai Masatoshi , Harada Tohru , Suzuki Masahiko
Published: February 2003

Abstract

A consensus for the optimal management of hepatoduodenal ligament (HDL) invasion by gallbladder carcinoma has yet to be reached. We retrospectively correlated the patterns of HDL invasion with the surgical outcome. From 1985 to 2000, 59 patients underwent combined resection of the extrahepatic bile duct and gallbladder and contiguous organs if required. Pathologic staging (UICC) was stage II, 4; stage III, 14; stage IVa, 10; and stage IVb, 31. Hepatoduodenal ligament invasion was subdivided into lymph node involvement (LNI) and bile duct infiltration (BDI). Patterns of HDL invasion were compared with bile duct morphology, resectability, and outcome. Bile duct infiltration (n = 32) caused stenosis of the bile duct in all cases, whereas LNI (n = 40) caused stenosis in only 4 cases. Resection was complete after extended cholecystectomy (n = 22) in 36%; 4b/5 segmentectomy (n = 10) in 90%; major hepatectomy (n = 2) in 50%; and hepatopancreatoduodenectomy (n = 17) in 53% of cases. Surgery was curative in 75% of patients without BDI, and was < 30% with BDI. The most common factor preventing curative resection in BDI was perineural invasion around the HDL. Perineural invasion occurred in over 70% of cases at either the cut end of the bile duct or in the margin of dissection. The 3‐year survival rates, excluding patients with R2 resection (residual cancer) and death in hospital, were LNI(−)BDI(−) (n = 8), 65.6%; LNI(+)BDI(−) (n = 17), 35.3%; LNI(−)BDI(+) (n = 7), 14.3%; and LNI(+)BDI(+) (n = 17), 5.9%. There were no 5‐year survivors with BDI. In conclusion, perineural invasion in BDI is an important obstacle to complete resection. Hepatopancreatoduodenectomy is a feasible strategy only for LNI(+)BDI(−) disease.
Nitric Oxide‐mediated Liver Injury in the Presence of Experimental Bile Duct Obstruction
Authors: Engin Atilla , Bozkurt B. Şükrü , Altan Nilgün , Memiş Leyla , Bukan Neslihan
Published: February 2003

Abstract

We investigated the possible mechanism of common bile duct (CBD) obstruction‐related liver cell necrosis in a guinea pig model during a 24‐hour period of biliary occlusion. A total of 30 male albino guinea pigs were randomly and equally assigned to two groups. Group 1 underwent sham laparotomy (SL), and group 2 underwent common bile duct ligation (CBDL). All the animals were followed for the first 24‐hours after operation. The liver antioxidant defense was examined by measuring liver total superoxide dismutase (TSOD), copper/zinc‐containing superoxide dismutase (Cu‐ZnSOD), manganese superoxide dismutase (MnSOD), and glutathione peroxidase (GPx) activities as well as the reduced glutathione (GSH) concentration. Severity of necrosis was assessed by blind quantitation of liver specimens using a histologic scoring system. Histologic evidence of grade +2 hepatocellular necrosis was observed in the CBDL group, as was a more than fourfold increase in plasma nitrite plus nitrate [NOx] concentrations in these animals. Although no significant difference was found between the two groups for liver Cu‐ZnSOD activity, the CBDL group showed a marked decrease in MnSOD activity. Concomitant increases in liver GPx activity and the GSH level were measured in the CBDL group. These data supported the hypothesis that excessive production of [NOx] and its derivative peroxynitrite contribute to a coexisting MnSOD deficiency in the mitochondria and lead to liver cell necrosis in cholestatic animals.
A novel testis‐specific RAG2‐like protein, Peas: its expression in pachytene spermatocyte cytoplasm and meiotic chromatin
Authors: Ohinata Yasuhide , Sutou Shizuyo , Mitsui Youji
Published: February 2003

We report a novel gene Peas that constitutes an overlapping gene complex in mammalian genome. We have cloned human and mouse Peas cDNAs (hPEAS/mPeas) and analyzed their tissue and stage‐specific expressions. Peas protein contains six repeated kelch motifs, structurally similar to RAG2, a V(D)J recombination activator, and is evolutionarily conserved among mammals, birds, insects, and nematodes. Northern, RNA in situ hybridization and immunohistochemical analyses showed that mPeas is specifically transcribed in testis, particularly in pachytene spermatocytes in which it is localized to the cytoplasm and meiotic chromatin. It is suggested that Peas may be involved in meiotic recombination process.
Complement component anaphylatoxins upregulate chemokine expression by human astrocytes
Authors: Jauneau Anne-Christine , Ischenko Alexander , Chan Philippe , Fontaine Marc
Published: February 2003

The complement (C) system, a major component of the innate immune system, has been described as a factor implicated in some brain disorders. C activation leads to the release of anaphylatoxins, two proinflammatory polypeptides acting through specific receptors that have been detected on brain cells. Here, we examined the effect of anaphylatoxins on chemokine expression by human astrocytes. We showed that anaphylatoxins significantly increase chemokine mRNA expression. However, anaphylatoxin‐induced chemokine secretion (interleukin‐8) was observed only in the presence of interleukin‐1β. Thus, anaphylatoxins could initiate a chemokine cascade and, at least in part, be involved in pathogenesis of the brain.
Phosphate‐deficient oat replaces a major portion of the plasma membrane phospholipids with the galactolipid digalactosyldiacylglycerol
Authors: Andersson Mats X , Stridh Malin H , Larsson Karin E , Liljenberg Conny , Sandelius Anna Stina
Published: February 2003

The plasma membranes of oat normally resemble those of other eukaryotes in containing mainly phospholipids and sterols. We here report the novel finding that the galactolipid digalactosyldiacylglycerol (DGDG) can constitute a substantial proportion of oat plasma membrane lipids, in both shoots and roots. When oat was cultivated under severe phosphate limitation, up to 70% of the plasma membrane phosphoglycerolipids were replaced by DGDG. Our finding not only reflects a far more developed potential for plasticity in plasma membrane lipid composition than often assumed, but also merits interest in the context of the limited phosphate availability in many soils.
Modular PH and C2 domains in membrane attachment and other functions
Authors: Katan Matilda , Allen Victoria L
Published: February 2003

The pleckstrin homology and C2 domains are modular protein structures involved in mediating intermolecular interactions. Although they represent distinct domains, there are several parallels regarding their function and type of interactions in which they participate. Both domains are stable structural entities that incorporate variable regions which, in different proteins, can be adapted to perform a specific function through binding to membrane phospholipids or specific protein ligands. A number of recent examples illustrate the function of some of these domains in regulated membrane attachment, with an important role in many cellular signalling pathways.
Voltage‐gated potassium channels: from hyperexcitability to excitement
Authors: Pongs Olaf
Published: February 2003

The superfamily of voltage‐activated potassium channels may express structurally and functionally diverse voltage‐activated potassium channels in the nervous system. The roles of some voltage‐activated potassium channel types, e.g. rapidly inactivating (transiently active type) channels and muscarine sensitive muscarine sensitive channels, are beginning to be understood. They may significantly influence dendritic action‐potential back‐propagation, signal to noise ratios in presynaptic excitability or the responsiveness of a neuron to synaptic input. Inherited disorders related to changes in excitability (episodic ataxia, epilepsy, heart arrhythmia) or to defects in sensory perception (hearing loss) have been associated with mutations in a few voltage‐activated potassium channel genes. Most likely, more voltage‐activated potassium channel genes will be linked to related disorders in the near future.
Biogenesis of transport intermediates in the endocytic pathway
Authors: Gu Feng , Gruenberg Jean
Published: February 2003

Evidence is accumulating that membrane traffic between organelles can be achieved by different types of intermediates. Small (<100 nm) and short‐lived vesicles mediate transport from the plasma membrane or the trans‐Golgi network to endosomes, and formation of these vesicles depends on specific adapter complexes. In contrast, transport from early to late endosomes is achieved by relatively large (∼0.5 μm), long‐lived and multivesicular intermediates, and their biogenesis depends on endosomal COP‐I proteins. Here, we review recent work on the formation of these different transport intermediates, and we discuss, in particular, coat proteins, sorting signals contained in cargo molecules and the emerging role of lipid in vesicle biogenesis.
Initiation of DNA replication in eukaryotes: questioning the origin
Authors: Françon Patricia , Maiorano Domenico , Méchali Marcel
Published: February 2003

Although proteins involved in DNA replication in yeast have counterparts in multicellular organisms, the definition of an origin of DNA replication and its control in higher eukaryotes might obey to different rules. Origins of DNA replication that are site‐specific have been found, supporting the notion that specific DNA regions are used to initiate DNA synthesis along metazoan chromosomes. However, the notion that specific sequences will define origins is still being debated. The variety and complexity of transcriptional programs that have to be regulated in multicellular organisms may impose a plasticity that would not be compatible with a fixed origin simply defined at the sequence level. Such a plasticity would be essential to developmental programs where the control of DNA replication could be more integrated to the control of gene expression than in unicellular eukaryotes.
Molecular and cellular activities of Helicobacter pylori pathogenic factors
Authors: Montecucco Cesare , Papini Emanuele , de Bernard Marina , Zoratti Mario
Published: February 2003

Stomach infection with pathogenic strains of Helicobacter pylori causes in some patients severe gastroduodenal diseases. These bacteria produce various virulence factors and, here, we review the recent acquisition on the biochemical mode of action of three major factors. We discuss the role of urease both as buffer of the stomach pH and as source of ammonia. The vacuolating toxin alters the endocytic pathway of non‐polarized cells, inducing the release of acid hydrolases, the depression of extracellular ligand degradation and of antigen processing and, in the presence of ammonia, swelling of late‐prelysosomal compartments. In polarized epithelial monolayers, vacuolating toxin induces an increase of the paracellular permeability, independent of vacuolation. The neutrophil activating protein induces the production of oxygen radicals in human neutrophils and could contribute to the damage of the stomach mucosa. The activities of these factors are discussed in terms of the need of the bacterium of increasing the supply of nutrients from the stomach lumen and from the mucosa.
Extremophiles and their adaptation to hot environments
Authors: Stetter Karl O
Published: February 2003

Water‐containing terrestrial, subterranean and submarine high temperature areas harbor a variety of hyperthermophilic bacteria and archaea which are able to grow optimally above 80°C. Hyperthermophiles are adapted to hot environments by their physiological and nutritional requirements. As a consequence, cell components like proteins, nucleic acids and membranes have to be stable and even function best at temperatures around 100°C. The chemolithoautotrophic archaeon Pyrolobus fumarii is able to grow at 113°C and, therefore, represents the upper temperature border of life. For the first time, (vegetative) cultures of Pyrolobus and Pyrodictium are able to survive autoclaving.