bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lowest energy structures of anionic Sin (n = 11–25) clusters
Authors: Li Bao‐xing , Xu Qing 
Published: March 2004

AbstractUsing full‐potential linear‐muffin‐tin‐orbital molecular‐dynamics (FP‐LMTO‐MD) method based on single‐parent evolution algorithm, we have studied the geometric and electronic structures of anionic Si11–25 clusters. For the anionic Sin (n = 11–20) clusters (except for n = 15 and n = 19), the ground state structures are in good agreement with the results obtained by using density functional theory with the gradient‐corrected functionals Perdew‐Wang‐Becke 88 (PWB). For n = 15 and 19, our results are in excellent agreement with those optimized using generalized gradient approximation (GGA) functionals based on single‐parent evolution method. In special, we have found the ground state structures for the anionic Si21–25 clusters using FP‐LMTO‐MD based on single‐parent evolution method. It is found that all the lowest energy structures include a sub‐unit of tricapped trigonal prism (TTP). Some lowest‐energy structures for the anions are different from those of neutrals. In addition, some energy orderings are also different by comparison with those of their corresponding neutral clusters. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time resolved photoluminescence study of Si modulation doped GaN/Al0.07Ga0.93N multiple quantum wells
Authors: Haratizadeh H. , Monemar B. , Paskov P. P. , Holtz P. O. , Pozina G. , Kamiyama S. , Iwaya M. , Amano H. , Akasaki I. 
Published: March 2004

AbstractThe effects of the Si doping level on the recombination dynamics and carrier (exciton) localization in modulation doped GaN/Al0.07Ga0.93N multiple‐quantum‐well (MQW) structures were studied by means of photoluminescence (PL) and time‐resolved PL measurements. All samples with different doping levels show a QW emission which is blue shifted with respect to the 3.48 eV PL peak from the GaN buffer layer. The decay time at the peak position remains nearly constant in the range of 320–420 ps at 2 K for all doping levels. For the undoped and low‐doped samples (3 × 1018 cm−3), which have less free electrons in the QWs, a non‐exponential PL decay behaviour at 2 K is attributed to localized exciton recombination. The more highly doped samples (5 × 1018 cm−3 to 1020 cm−3) show almost exponential decay curves at 2 K, suggesting the recombination of free electrons and localized holes. This localization effect appears even at high electron concentrations to cancel the expected lowering of the radiative lifetime with doping at 2 K; such a lowering is clearly observed at elevated temperatures for the highly doped samples, however. The internal polarization‐induced fields of the medium and highly‐doped samples are partly screened by the electrons originating from the doping in the barriers. Only the PL peak of the undoped and low‐doped samples shows a redshift with time delay, related to the photogenerated carriers. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical field induced order–order transitions in rare earth manganites
Authors: Bärner K. , Annaorazov M. , Yang C. P. , Morchshakov V. 
Published: March 2004

AbstractVaristor‐like electrical transport is found in Nd2/3Sr1/3MnOz and Pr0.7Sr0.3MnO3 compounds, with evidence of magnetic order–order transitions superimposed. The transition temperatures move under a magnetic field which establishes the spin‐dependent character of these phenomena. We also discuss the possibilty that the electrical field induces such transitions, as the transition appears and/or shifts at certain applied currents (or potentials). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Horizontal line nodes in superconducting Sr2RuO4
Authors: Litak G. , Annett J. F. , Györffy B. L. , Wysokiński K. I. 
Published: March 2004

AbstractWe analyze the possibilities of triplet pairing in Sr2RuO4 based upon an idea of interlayer coupling. We have considered two models differing by the effective interactions. In one model the quasi‐particle spectra have horizontal line nodes on all three Fermi surface sheets, while in the other the spectra have line or point nodes on the α and β sheets and no nodes on the γ sheet. Both models reproduce the experimental heat capacity and penetration depth results, but the calculated specific heat is sightly closer to experiment in the second solution with nodes only on the α and β sheets. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Correlation between ferroelectricity and electronic density of states near the Fermi level in BaTiO3
Authors: Hidaka M. , Tokiwa N. , Takahashi S. , Choi J.‐Y. , Lee J. M. 
Published: March 2004

AbstractThe electronic density of states in BaTiO3 is studied by means of X‐ray absorption near‐edge structure in a vicinity of a Ti K edge and Ba L edges. A 4pπ band of the Ti ion and a 5dπ band of the Ba ion having a high‐density unoccupied state occupy a level just above the Fermi level (EF). The pre‐edge peaks give that, in addition to an O2− 2p valence band, the electronic density of states below EF are composed of negative‐charge‐transfer bands 3d1, 3d1$ \underline {\rm L} $ and 3d2$ \underline {\rm L} $2 of Ti ions and 4f1, 4f1$ \underline {\rm L} $ and 4f2$ \underline {\rm L} $2 of Ba ions. The 3d1, 3d1$ \underline {\rm L} $ and 3d2$ \underline {\rm L} $2 bands of Ti ions gives that a mixture of the different oxidation states Ti2+ and Ti3+ is present in addition to Ti4+. The 4f1, 4f1$ \underline {\rm L} $ and 4f2$ \underline {\rm L} $2 bands are induced by a hybridization between Ba2+ 4d and O2– 2p orbitals via an electronic configuration interaction between the 4f and 4d orbitals of the Ba ion. The disappearance of the 4f1, 4f1$ \underline {\rm L} $ and 4f2$ \underline {\rm L} $2 bands in the ferroelectric phase suggests that the collective displacement of Ba ions from ideal ionic sites of the cubic perovskite‐type structure reduces the hybridization between the Ba and O ions. This gives that the effective charge on the O ions is increased and induces a large dipole moment between the O ions and the Ti ions, which are at an off‐center position of TiO6 octahedra in the ferroelectric phase. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of an inclined anisotropy on formation of spatially inhomogeneous phase in two‐dimensional ferromagnet
Authors: Fridman Yu. A. , Klevets Ph. N. , Spirin D. V. 
Published: March 2004

AbstractPhase states of ultrathin magnetic film with an inclined anisotropy are investigated. It is shown, that in a 2D film with easy‐axis, easy‐plane anisotropies, and inclined out‐of‐plane anisotropy the realization of spatially inhomogeneous phase is possible only at specific orientation of an external magnetic field. If orthorhombic anisotropy is implemented in the film plane, then the spatially inhomogeneous phase realizes at arbitrary orientation of in‐plane external field. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shallow donor impurities in different shaped double quantum wells under the electric field
Authors: Kasapoglu E. , Sokmen I. 
Published: March 2004

AbstractThe binding energy of the donor impurity in double triangle quantum well (DTQW), double graded (DGQW) and double square (DSQW) GaAs–(Ga,Al)As quantum wells under the electric field is calculated by using a variational approach. The results have been obtained in the presence electric field applied along the growth direction as a function of the impurity position, barrier width and the geometric shape of the double quantum wells. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Density‐functional‐based tight‐binding approach to phonon spectra of conjugated polymers
Authors: Lynge T. B. , Pedersen T. G. 
Published: March 2004

AbstractWe apply a computationally efficient method for calculating phonon spectra to the two conjugated polymers trans‐polyacetylene and poly(para‐phenylene). The starting point of the calculation is a relaxation of the atomic coordinates based on the Density‐Functional‐Based Tight‐Binding (DFTB) approach of Porezag et al. From the relaxed geometry we calculate the force constant matrix of a suitably sized super cell and calculate the dynamical matrix by Fourier transformation.The only input required for the computation is the parametrized DFTB Hamilton and overlap matrix elements, and as a non‐self consistent TB‐method the present approach is highly efficient and therefore able to treat molecules of considerable size. The method has previously been successfully applied to vibrations in hydrocarbon molecules and single‐wall nanotubes. We demonstrate here that the approach is equally applicable to polymers, as the equilibrium configurations as well as the phonon spectra are found to be in reasonable agreement with other results from the literature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive backstepping control for a class of nonlinear systems using neural network approximations
Authors: Tan K. K. , Huang S. N. , Lee T. H. 
Published: March 2004

AbstractIn this paper, an adaptive neural network (NN) backstepping technique is developed for tracking control of a class of nonlinear systems. NNs are used to compensate for the unknown nonlinear functions in the system. A systematic backstepping approach is established to synthesize the adaptive NN control scheme that ensures the boundedness of all the signals in the closed‐loop system, and yields a small tracking error. The issue of transient performance is also addressed under an analytical framework. The effectiveness of the proposed scheme is demonstrated by computer simulations. Copyright © 2004 John Wiley & Sons, Ltd.
Delay‐dependent anti‐windup strategy for linear systems with saturating inputs and delayed outputs
Authors: Tarbouriech S. , Gomes Da Silva J.M. , Garcia G. 
Published: March 2004

AbstractThis paper addresses the problem of the determination of stability regions for linear systems with delayed outputs and subject to input saturation, through anti‐windup strategies. A method for synthesizing anti‐windup gains aiming at maximizing a region of admissible states, for which the closed‐loop asymptotic stability and the given controlled output constraints are respected, is proposed. Based on the modelling of the closed‐loop system resulting from the controller plus the anti‐windup loop as a linear time‐delay system with a dead‐zone nonlinearity, constructive delay‐dependent stability conditions are formulated by using both quadratic and Lure Lyapunov–Krasovskii functionals. Numerical procedures based on the solution of some convex optimization problems with LMI constraints are proposed for computing the anti‐windup gain that leads to the maximization of an associated stability region. The effectiveness of the proposed technique is illustrated by some numerical examples. Copyright © 2004 John Wiley & Sons, Ltd.
Nonlinear path following control of non‐holonomic vehicles with the human as actuator in a parking application
Authors: Kochem M. , Isermann R. 
Published: March 2004

AbstractThis paper describes and compares several controllers for precision tracking control of non‐holonomic vehicles at low speeds with the driver as actuator in the control loop. A possible application for the developed controllers is a driver assistance system for supporting the driver in a backward parking procedure. The system, designed as a comfort feature, provides the driver with optical and acoustical information through an appropriate human–machine interface (HMI) on how to steer the vehicle into the previously scanned parking spot. Without having an active steering in the vehicle, the driver remains in full control over the vehicle's motion. This paper outlines the main ideas and concepts of the system and focusses on the developed control structures. Finally, experimental results underline the validity of the chosen approach. Copyright © 2004 John Wiley & Sons, Ltd.
Adaptive sliding mode control of air–fuel ratio in internal combustion engines
Authors: Souder Jason S. , Hedrick J. Karl 
Published: March 2004

AbstractA simplified model of an internal combustion engine is used to derive a sliding mode control law. Adaptive update laws are derived for two fueling parameters that describe fuel flow into the cylinders, and a third parameter that describes air flow into the cylinders. The update laws allow the sliding mode control gain, which is usually increased to overcome model uncertainty, to be reduced. This improves the tracking performance of the sliding mode controller in the presence of the feedback time delays. The parameter update laws are modified to bound the parameter values and allow all three parameter update laws to run simultaneously. The effect of the sampling rate on the adaptive sliding mode controller performance and air–fuel ratio biasing via gain selection are also addressed. Copyright © 2004 John Wiley & Sons, Ltd.
Pressure and temperature‐based adaptive observer of air charge for turbocharged diesel engines
Authors: Stefanopoulou A. G. , Storset O. F. , Smith R. 
Published: March 2004

AbstractIn this paper we design an adaptive air charge estimator for turbocharged diesel engines using intake manifold pressure, temperature and engine speed measurements. This adaptive observer scheme does not depend on mass air flow sensors and can be applied to diesel engines with no exhaust gas recirculation (EGR). The performance of the adaptive scheme is shown in simulations to be comparable to conventional air charge estimation schemes if perfect temperature measurements are available. The designed scheme cannot estimate fast transients and its performance deteriorates with temperature sensor lags. Despite all these difficulties, this paper demonstrates that (i) the proposed scheme has better robustness to modelling errors because it provides a closed‐loop observer design, and (ii) robust air charge estimation is achievable even without air flow sensors if good (fast) temperature sensors become available. Finally, we provide a rigorous proof and present the implementation challenges as well as the limiting factors of this adaptation scheme and point to hardware and temperature sensor requirements. Copyright © 2004 John Wiley & Sons, Ltd.
Control of an electro‐mechanical valve actuator for a camless engine
Authors: Haskara İ. , Kokotovic V. V. , Mianzo L. A. 
Published: March 2004

AbstractIn an electro‐mechanical valve actuated engine, the valves are driven by solenoid‐type actuators and cam‐shaft is eliminated. Individual control of each valve provides flexibility in valve timings over all engine conditions and fully exploits the benefits of variable valve timing. This paper pertains to the closed‐loop control of an electro‐mechanical valve actuator. The primary emphasis is on the soft‐seating problem, in which the valve and the moving actuator parts need to be brought to a soft‐stop at the end of their travels. The actuator control features which provide reliable valve motion are discussed in detail. Several illustrative experimental results are also presented. Copyright © 2004 John Wiley & Sons, Ltd.
Modular adaptive robust control of SISO nonlinear systems in a semi‐strict feedback form
Authors: Chantranuwathana Supavut , Peng Huei 
Published: March 2004

AbstractIn this paper, a modular modification of the adaptive robust control (ARC) technique is presented. The modular design has all of the original ARC properties with an estimation‐based update law instead of a Lyapunov‐based update law. In this design, the controller is divided into two modules: a control module and an identification module. A key new idea is to seta prioribounds on the time derivatives of the estimates to be maintained by the update law. As a result, their effects on the system tracking accuracy can be dominated by the control law. A modification is proposed for the standard gradient and least‐square update laws to guarantee the bounds. This modification also makes the controller robust against the generalized (unparameterized) uncertainties considered in the ARC formulation while allowing asymptotic output tracking without the generalized uncertainties. Both the ARC and the modular ARC techniques are applied to a force control problem for an active suspension system. Simulations and experimental results are provided to show that the update law of the modular design is less sensitive to measurement noise which results in smaller force tracking error and smaller control gain. Copyright © 2004 John Wiley & Sons, Ltd.
Exploring the structural effects of internetworking
Authors: Brews Peter J. , Tucci Christopher L. 
Published: March 2004

AbstractExtant theory presents conflicting perspectives on how internetworking might affect the organizational structures of established firms. One prediction is that internetworking could narrow organizational scope and deepen specialization, reduce hierarchy, and increase external partnering. A second contends that internetworking might increase scope, expand hierarchy, and decrease external partnering. Analysis of a multinational sample of 469 firms reveals that deeply internetworked firms are more focused and specialized, less hierarchical, and more engaged in external partnering than less intensively internetworked organizations are. No scope broadening or hierarchy expansion effects are observed. Copyright © 2004 John Wiley & Sons, Ltd.
Three‐dimensional ultrasound‐validated large‐core needle biopsy: is it a reliable method for the histological assessment of breast lesions?
Authors: Delle Chiaie L. , Terinde R. 
Published: March 2004

AbstractObjectiveThe use of three‐dimensional (3D) ultrasound may help to determine the exact position of the needle during breast biopsy, thereby reducing the number of core samples that are needed to achieve a reliable histological diagnosis. The aim of this study was to demonstrate the efficacy of 3D ultrasound‐validated large‐core needle biopsy (LCNB) of the breast.MethodsA total of 360 core needle biopsies was obtained from 169 breast lesions in 146 patients. Additional open breast biopsy was performed in 111 women (127/169 breast lesions); the remaining 42 lesions were followed up for at least 24 months. 3D ultrasound visualization of the needle in the postfiring position was used to classify the biopsy as central, marginal or outside the lesion. Based on this classification it was decided whether another sample had to be obtained.ResultsA median of two core samples per lesion provided for all the lesions a sensitivity for malignancy of 96.9%, specificity of 100%, false‐positive rate of 0% and false‐negative rate of 3.1%, and for the excised lesions a sensitivity of 96.5%, specificity of 100%, false‐positive rate of 0%, false‐negative rate of 3.5% and an underestimation rate of 3.4%.Conclusions3D ultrasound validation of the postfiring needle position is an efficient adjunct to ultrasound‐guided LCNB. The advantages of 3D ultrasound validation are likely to include a reduction in the number of core samples needed to achieve a reliable histological diagnosis (and a possible reduction in the risk of tumor cell displacement), reduced procedure time and lower costs. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Validation of fractional moving blood volume measurement with power Doppler ultrasound in an experimental sheep model
Authors: Hernandez‐Andrade E. , Jansson T. , Ley D. , Bellander M. , Persson M. , Lingman G. , Maršál K. 
Published: March 2004

AbstractObjectiveTo compare fractional moving blood volume (FMBV) estimation using power Doppler ultrasound (PDU) with blood flow estimation using radioactive microspheres (RMS) for evaluation of fetal organ blood perfusion.MethodsBlood flow was measured in the adrenal gland of nine exteriorized fetal lambs. Five fetal lambs underwent total umbilical cord occlusion in order to induce changes in the adrenal blood flow (asphyxia group). Four lambs were used as sham controls (control group). Three RMS injections, with coincident PDU recordings of the adrenal gland, were performed in each lamb. In the asphyxia group, measurements were taken before the cord occlusion, 5 min later and when the mean blood pressure decreased below 25 mmHg. In the control group, the measurements were done with an interval of 5 min. FMBV normalized for attenuation of PDU signals, and mean pixel intensity (MPI) were estimated offline. After completion of the study, adrenal blood perfusion was calculated according to the reference sample microsphere technique, using the isotope activity and expressed in mL/min/100 g. The correlation between RMS and FMBV and MPI, respectively, was analyzed individually for each lamb.ResultsIn the asphyxia group, all lambs showed a marked reduction in the adrenal blood perfusion towards the third RMS injection. In the control group, the adrenal perfusion showed small variations throughout the experiment. In the total material, there was a higher correlation between FMBV and RMS (median, r = 0.90; range, 0.43–0.99) than between MPI and RMS (median, r = 0.55; range, −0.53 to 0.99).ConclusionThe FMBV method of quantifying PDU signals correlates highly with blood flow perfusion estimation using RMS in the fetal lamb adrenal gland. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.
Fractional moving blood volume estimation in the fetal lung using power Doppler ultrasound: a reproducibility study
Authors: Hernandez‐Andrade E. , Thuring‐Jönsson A. , Jansson T. , Lingman G. , Maršál K. 
Published: March 2004

AbstractObjectiveTo evaluate the reproducibility of fractional moving blood volume (FMBV) estimation in the fetal lung using power Doppler ultrasound (PDU).MethodsThe lung blood perfusion of 20 normally grown singleton fetuses at 32–35 weeks of gestation was evaluated by two experienced observers using PDU. Each observer recorded two consecutive sequences of images from the posterior part of the fetal lung and calculated FMBV offline. FMBV expresses the percentage of blood movement within a defined region of interest (ROI). Repeatability and agreement were evaluated by means of the intraclass (intraCC) and interclass (interCC) correlation coefficients.ResultsFMBV was successfully evaluated in 17/20 fetuses by both observers (kappa index 0.82; 95% CI 0.51–0.93). The intraCC for repeatability for Observer A was 0.92 (95% CI 0.78–0.96), and for Observer B 0.90 (95% CI 0.74–0.96). The mean difference between the first and the second measurement was 0.7% (SD 4.5%). The interCC for repeatability over time and between the operators was 0.70 (95% CI 0.56–0.76) and the mean difference between the observers was 0.6% (SD 4.65%). The interCC for agreement was 0.92 (95% CI 0.84–0.95) and the mean difference in FMBV results when both observers analyzed the same sequences offline was 0.6% (SD 3.85%).ConclusionIn the hands of experienced operators, using a well‐defined ROI and standard settings, FMBV estimation is a reproducible method of quantifying power Doppler signals recorded from fetal lung blood perfusion. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.