bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental investigation of the effect of wetting-layer states on the gain–current characteristic of quantum-dot lasers
Authors: Matthews D. R. , Summers H. D. , Smowton P. M. , Hopkinson M.
Published: December 2002

Using experimental measurements of the gain–current characteristic as a function of temperature in InGaAs quantum-dot lasers, we demonstrate that it is the population of wetting-layer states that leads to a saturation of the population inversion in dot states and hence to the saturation of gain in a quantum-dot laser. At 300 K, the maximum modal gain for a three-layer structure is reduced from 53 to 14 cm−1.
Magnetization reversal measurements in Gd/Fe multilayer antidot arrays by vector magnetometry using x-ray magnetic circular dichroism
Authors: Lee D. R. , Choi Y. , You C.-Y. , Lang J. C. , Haskel D. , Srajer G. , Metlushko V. , Ilic B. , Bader S. D.
Published: December 2002

Fe K-edge x-ray magnetic circular dichroism (XMCD) was used as vector magnetometry to measure the magnetization rotation while field cycling Gd/Fe multilayer antidot arrays through a hysteresis loop. The measured XMCD hysteresis curves were then compared quantitatively with micromagnetic calculations to reconstruct the microscopic magnetization configurations. The best fit reveals the existence of three types of characteristic domains: two that rotate coherently during magnetization reversal and one that is strongly pinned. The behavior is explained by a simple three-domain energy model, including a phenomenological ansatz for a shape-induced demagnetization energy contribution.
Ultralow loss polycrystalline alumina
Authors: Breeze Jonathan D. , Aupi Xavi , Alford Neil McN.
Published: December 2002

Polycrystalline alumina with extremely low microwave dielectric loss is reported with properties analogous to a theoretical ensemble of randomly oriented, single crystal sapphire grains. By avoiding deleterious impurities and by careful control of microstructure, we show that grain boundaries in aluminum oxide have only a limited influence on the dielectric loss. A method of measuring the electric permittivity and loss tangent of low-loss microwave ceramic dielectrics is reported. The electrical parameters such as relative permittivity and loss tangent are extracted using the radial mode matching technique. The measured values for ultralow loss polycrystalline aluminum oxide agree well with theoretical values modelled on an ensemble of randomly oriented anisotropic single crystal sapphire grains.
Measuring the energetic distribution of ballistic electrons after their refraction at an Au–GaAs interface
Authors: Rakoczy D. , Strasser G. , Smoliner J.
Published: December 2002

In this work, ballistic electron emission microscopy/spectroscopy on biased GaAs–AlAs double-barrier resonant tunneling structures is used to study the energetic distribution of ballistic electrons transmitted through an Au–GaAs interface. Measuring the ballistic current as a function of collector bias, we observe a surprisingly broad energetic distribution of ballistic electrons in the GaAs. This observation can be explained by electron “refraction” effects at the Au–GaAs interface and the influence of inelastic scattering in the drift region of the sample.
Highly aligned, spin polarized thin films of Sr2FeMoO6 by a chemical vapor process
Authors: Rager J. , Berenov A. V. , Cohen L. F. , Branford W. R. , Bugoslavsky Y. V. , Miyoshi Y. , Ardakani M. , MacManus-Driscoll J. L.
Published: December 2002

Highly oriented films of Sr2FeMoO6 were fabricated by ultrasonic spray pyrolysis. A combined organic/inorganic solution was developed and the films were deposited on single-crystal LaAlO3 between 600 °C and 900 °C followed by postannealing at 850 °C or 1200 °C in Ar/5% H2. Optimum films showed a metallic resistivity behavior with less than a 0.25% magnetoresistive effect at 50 K, 1 T, indicative of highly quality intra- and intergranular material. At 4.2 K, the lower bound saturation magnetization, Ms was ∼2.5 μB/f.u. and the transport spin polarization was 60±3%.
Effects of Hf contamination on the properties of silicon oxide metal–oxide–semiconductor devices
Authors: Kang Chang Seok , Onishi Katsunori , Kang Laegu , Lee Jack C.
Published: December 2002

Effects of hafnium (Hf) contamination on the properties of n+-polycrystalline-Si/SiO2/Si metal–oxide–semiconductor (MOS) devices were investigated using p-type Si substrates implanted by Hf ions. Flat-band voltages (Vfb) and substrate doping concentrations (NA) of the MOS capacitors were not dependent on the Hf dose levels of 1×1011–1×1013 atoms/cm2. Leakage current density of the MOS capacitor was also not affected by the implant conditions. Electron channel mobility of n-type MOS field-effect transistors with 45-Å-thick SiO2 as gate dielectrics was not degraded by the implantation of Hf ions into the Si substrates.
Impact of organic contamination on the electrical properties of hydrogen-terminated silicon under ambient conditions
Authors: Liu Yong-Jun , Waugh Damien M. , Yu Hua-Zhong
Published: December 2002

The electrical properties of hydrogen-terminated silicon (H–Si) surfaces were investigated by the assembly and testing of reliable and reproducible mercury–silicon junctions. When a H–Si surface is exposed to air under ambient conditions, the current density–bias voltage curve of the thus formed mercury–silicon junction initially maintains ohmic characteristics for a period of 8–12 h and then evolves to diode behavior. The current density substantially decreases, but can be recovered to a certain extent upon sonication in organic solvents. In agreement with infrared spectroscopic results, organic contamination of H–Si is suggested to play an important role in the transition of the electrical properties.
Graded ferroelectric thin films: Possible origin of the shift along the polarization axis
Authors: Poullain G. , Bouregba R. , Vilquin B. , Le Rhun G. , Murray H.
Published: December 2002

Hysteresis measurements performed on graded Pt/lead zirconate titanate (PZT)/Pt structures with well oxygenated PZT films do not display any shift along the polarization axis (Voffset) as previously reported. On the other hand, when the PZT graded films were grown under low oxygen pressure, an offset voltage was measured. This shift was systematically enhanced after cycling the film as for fatigue measurements. It was also observed that the Voffset is independent of the value of the reference capacitor used in the Sawyer–Tower circuit. We propose an asymmetry in the leakage current of the structure to be at the origin of the shift along the polarization axis.
Surface domain engineering in congruent lithium niobate single crystals: A route to submicron periodic poling
Authors: Busacca A. C. , Sones C. L. , Apostolopoulos V. , Eason R. W. , Mailis S.
Published: December 2002

We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as ∼1 μm. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures.
Vibronic spectrum of the Ag(NH3)2 complex
Authors: Miyawaki Jun , Djafari Schahla , Sugawara Ko-ichi , Takeo Harutoshi
Published: December 2002

We report observation of the resonantly enhanced two-photon ionization (R2PI) spectrum of the Ag(NH3)2 complex formed in a free jet. The origin of the Ã–X̃ band system is located 947 cm−1 lower than that of AgNH3 and shifted from the corresponding Ag (5p2P1/2–5s2S) transition by 9089 cm−1. This indicates that the stabilization of the excited silver atom by the second ammonia molecule is much smaller than that caused by the first one. The well-resolved vibrational progressions are characterized by three vibrational frequencies, 197, 67, and 375 cm−1. We have assigned these to the (AgNH3)–NH3 stretching, (AgNH3)–NH3 bending, and Ag–NH3 stretching modes, respectively, based on the ab initio structure of Dubois et al. [Chem. Phys. Lett. 323, 1 (2000)]. The R2PI signal suddenly disappears ∼500 cm−1 above the origin, which indicates that some nonradiative transition takes place.
Unusual excitation intensity dependence of fluorescence of CdTe nanoparticles
Authors: Wu Fanxin , Lewis James W. , Kliger David S. , Zhang Jin Z.
Published: December 2002

The fluorescence of thiol-capped CdTe nanoparticles have been measured using nanosecond laser spectroscopy. While the bandedge fluorescence intensity of CdTe nanoparticles has been found to increase linearly with excitation intensity at low intensities, an unusual decrease of fluorescence intensity with increasing excitation intensity has been observed at higher intensities. This unusual excitation intensity dependence has been tentatively explained by nonlinear exciton–exciton annihilation or Auger photoionization effect that takes place within the 7 ns excitation laser pulse. In contrast, the fluorescence intensity of CdS nanoparticles increases monotonically with excitation intensity in the same intensity range studied. The results indicate that CdTe nanoparticles show stronger nonlinear optical properties due possibly to stronger quantum confinement effect and could be potentially useful for nonlinear optical applications.
The Electronic Spectra of Aromatic Molecules IV: Excited States of Odd Alternant Hydrocarbon Radicals and Ions
Authors: H C Longuet-Higgins  , J A Pople
Published: December 2002

The lower excited electronic states of some unsaturated hydrocarbon radicals and ions are discussed in terms of molecular orbital theory, taking account of electron interaction. The following results emerge:

In the absorption spectrum of an alternant radical there should appear two long wavelength bands. These arise jointly from excitations of electrons into and out of the singly occupied orbital. The lower frequency band should be weak, and the higher frequency band relatively strong. The existence of a low-lying quartet level is also predicted.

The absorption spectra of the corresponding anion and cation should be closely related, the lowest two excited states being for both types of ion a triplet and a singlet.

The singlet-triplet separation in the ions should be roughly equal to the separation of the two low-lying doublets of the radical.

These generalizations are supported by the experimental data for certain triaryl-methyl systems.
Definitive equations for the fluid resistance of spheres
Authors: C N Davies
Published: December 2002

For calculation of terminal velocities it is convenient to express the Reynolds' number,Re, of a moving sphere as a function of the dimensionless group ψRe2, where ψ is the drag coefficient. The following equations have been fitted by the method of least squares to critically selected data from a number of experimenters:

Re= ψRe2/24 -0.00023363(ψRe2)2+ 0.0000020154(ψRe2)3- 0.0000000069105(ψRe2)4forRe<4 or ψRe2<140. This tends to Stokes' law for low values ofRe.It is specially suited to calculation of the sedimentation of air-borne particles. The upper limit corresponds to a sphere weighing 1.5 μg. falling in the normal atmosphere, that is, one having a diameter of 142 μ for unit density.

logRe=-1.29536+0.986 (logψRe2)-0.046677 (logψRe2)2+0.0011235 (logψRe2)3for 3<Re<10,000 or 100<ψRe2<4.5.107.

Correction for slip in gases should be applied to Stokes' law by the following expression, based on the best results available:

1 +l/a[1.257 + 0.400exp(-1.10a/l)],

where the mean free pathlis given by η/0.499σc.

This conveniently transforms to the following for the sedimentation of particles in air at pressurepcm. mercury

1 +l/pa[6.32.10-4+ 2.01.10-4exp(-2190ap)]
Active and passive membrane properties of rat sympathetic preganglionic neurones innervating the adrenal medulla
Authors: Wilson Jennifer M. M. , Coderre Elaine , Renaud Leo P. , Spanswick David
Published: December 2002

The intravascular release of adrenal catecholamines is a fundamental homeostatic process mediated via thoracolumbar spinal sympathetic preganglionic neurones (AD‐SPN). To understand mechanisms regulating their excitability, whole‐cell patch‐clamp recordings were obtained from 54 retrogradely labelled neonatal rat AD‐SPN. Passive membrane properties included a mean resting membrane potential, input resistance and time constant of ‐62 ± 6 mV, 410 ± 241 MΩ and 104 ± 53 ms, respectively. AD‐SPN were homogeneous with respect to their active membrane properties. These active conductances included transient outward rectification, observed as a delayed return to rest at the offset of the membrane response to hyperpolarising current pulses, with two components: a fast 4‐AP‐sensitive component (A‐type conductance), contributing to the after‐hyperpolarisation (AHP) and spike repolarisation; a slower prolonged Ba2+‐sensitive component (D‐like conductance). All AD‐SPN expressed a Ba2+‐sensitive instantaneous inwardly rectifying conductance activated at membrane potentials more negative than around ‐80 mV. A potassium‐mediated, voltage‐dependent sustained outward rectification activated at membrane potentials between ‐35 and ‐15 mV featured an atypical pharmacology with a component blocked by quinine, reduced by low extracellular pH and arachidonic acid, but lacking sensitivity to Ba2+, TEA and intracellular Cs+. This quinine‐sensitive outward rectification contributes to spike repolarisation. Following block of potassium conductances by Cs+ loading, AD‐SPN revealed the capability for autorhythmicity and burst firing, mediated by a T‐type Ca2+ conductance. These data suggest the output capability is dynamic and diverse, and that the range of intrinsic membrane conductances expressed endow AD‐SPN with the ability to generate differential and complex patterns of activity. The diversity of intrinsic membrane properties expressed by AD‐SPN may be key determinants of neurotransmitter release from SPN innervating the adrenal medulla. However, factors other than active membrane conductances of AD‐SPN must ultimately regulate the differential ratio of noradrenaline (NA) versus adrenaline (A) release secreted in response to various physiological and environmental demands.
Experimental Investigation of Residual Stresses in Layered Materials Using Moire´ Interferometry
Authors: Bowman Keith B. , Mollenhauer David H.
Published: December 2002

As two dissimilar materials are bonded or cocured at elevated temperatures, residual stresses result upon cooling the layered material system to room temperature. It is well known that the free edges of composite laminates experience interlaminar stresses during applied mechanical or thermal loading. These stresses are significant and must be understood. Current experimental methods are not capable of determining the residual stresses along free edges where failure is likely to initiate. This paper describes the initial findings of a novel experimental technique that uses moire´ interferometry and material removal to determine the residual stress distribution resulting from elevated temperature processing at the free edges of layered materials.
Optical Measurements of Shrinkage in UV-Cured Adhesives
Authors: Hudson A. J. , Martin S. C. , Hubert M. , Spelt J. K.
Published: December 2002

This paper describes an optical method that has been developed to accurately measure shrinkage during the cure of adhesives treated with UV light. The experiment was designed to measure changes in the volume of very small quantities of material appropriate to uses in the fiber-optic and micro-electronic industries. A spot-curing device (EFOS Inc.) was used to deliver a controlled exposure of UV-light with a known distribution of wavelengths to the sample. The results indicate that reproducible values for the volumetric shrinkage can be achieved using spot-curing methods. The technique described in this paper, combined with other experimental measurements under development, will assist in the selection of the appropriate adhesive for specific applications and the curing conditions needed to optimize its final properties.
Study of P-V-T-C Relation of EMC
Authors: Chang Yi-San , Hwang Sheng-Jye , Lee Huei-Huang , Huang Durn-Yuan
Published: December 2002

A two-plunger-type dilatometer was designed and fabricated to measure cure-induced volume changes of epoxy molding compound (EMC). The device is suitable for studying volume change of material systems that are fast reacting and with high conversions and high viscosity like commercial EMC. In this paper, the conversion rate was determined by DSC. Interactions of volume change, pressure, temperature, and conversion were measured. In the experiment, two different temperatures: 172°C,180°C and four different pressures: 30, 50, 80, and 100kgf/cm2 were applied. The total number of conditions in this experiment is 8. Volume change of EMC due to thermal expansion, cure shrinkage, and thermal contraction under fixed temperature and pressure was measured. For higher pressure, the final volume change will be higher.
Delamination Risk Evaluation for Plastic Packages Based on Mixed Mode Fracture Mechanics Approaches
Authors: Auersperg J. , Kieselstein E. , Schubert A. , Michel B.
Published: December 2002

The growing application of advanced electronic packages under harsh environmental conditions, extreme temperatures especially in automotive applications is often a reason for damage, fatigue, and failure of entire components and systems. Consequently, their thermo-mechanical reliability is one of the most important preconditions for adopting these technologies in industrial applications. To prevent chips from being exposed to the external environment integrated circuits are usually encapsulated into packages. As a result, a microelectronic package is basically a compound of several materials with quite different Young’s moduli and thermal expansion coefficients. Additionally, various kinds of inhomogeneity, residual stresses from several steps of the manufacturing process contribute to interface delaminations, chip cracking, and fatigue of solder interconnects. This paper intends to investigate mixed mode interface delamination phenomena in micro components by using combined numerical investigations by means of nonlinear FEA and experimental investigations. It explains how experimental data were used as input for the quantitative evaluation of fatigue and fracture of microcomponents. Both numerical and experimental investigations provide the basis for understanding and evaluating failure mechanisms especially in solder joints, as well as several polymer material interfaces, and should support further applications for raising the thermo-mechanical reliability of advanced electronic packages.
Controlling Subcritical Crack Growth at Epoxy/Glass Interfaces
Authors: Ritter John E. , Jacome G. S. , Pelch J. R. , Russell T. P. , Lardner T. J.
Published: December 2002

The resistance of silane bonded epoxy/glass interfaces to subcritical crack growth was studied as a function of the density of primary bonds between the silane and epoxy using the double-cleavage drilled compression test (DCDC). The silane coupling agents propyltriethoxysilane (PES), 3-aminopropyltriethoxysilane (3-APES) and various mixtures of 3-APES and PES were used to systematically control the bonding density since 3-APES can form primary bonds with both the glass and the epoxy, while PES forms primary bonds only with the glass. The resistance of these interfaces to crack growth was tested under both static and cyclic loading in high and low humidity test environments. These tests allowed the separation of the effects on crack growth due to stress corrosion and cyclic fatigue. Experimental results showed that the density of primary bonding between the silane layer and the epoxy controls the cyclic fatigue resistance of the silanized interfaces. Additionally, for 3-APES bonded epoxy/glass interfaces cyclic fatigue crack growth predominates at both high and low humidities but for PES bonded interfaces, crack growth by stress corrosion dominates at high humidity and by cyclic fatigue at low humidities. For a 50% 3-APES/50% PES bonded interface, stress corrosion effects are somewhat greater than cyclic fatigue effects at high humidities but at low humidities the two effects are comparable. When testing the interfaces for durability, PES bonded interfaces showed spontaneous delamination when aged in distilled water for 36h at 94°C. On the other hand, 3-APES and mixtures of 3-APES bonded interfaces did not show any detrimental effect of the cyclic fatigue resistance when aged in distilled water at temperatures up to 98°C.
Determination of Packaging Material Properties Utilizing Image Correlation Techniques
Authors: Vogel D. , Ku¨hnert R. , Dost M. , Michel B.
Published: December 2002

Thermo-mechanical reliability in advanced electronic packaging requires new materials testing approaches. The necessary understanding of the impact of very local material stressing on component reliability leads to the need of materials testing and characterization on microscopic scale. For example, defect initiation and propagation in multilayer structures as in WLP and flip chip technology, the influence of material migration to mechanical behavior or defect development in ultra-thin silicon dies often are not well understood. A key for micro materials testing and characterization is the measurement of strains and displacements inside microscopic regions. Correlation techniques (e.g., microDAC, nanoDAC) are one of the promising tools for that purpose. Their application potentials to micro testing for electronic packaging materials are demonstrated in the paper. More in detail, CTE measurement and crack testing are discussed. First attempts for testing under AFM conditions and their results are considered.
Chemical-Mechanical Planarization of Low-k Polymers for Advanced IC Structures
Authors: Borst Christopher L. , Thakurta Dipto G. , Gill William N. , Gutmann Ronald J.
Published: December 2002

Successful integration of copper and low dielectric constant (low-k) materials is dependent on robust chemical-mechanical planarization (CMP) during damascene patterning. This process includes the direct removal of copper and interaction of the copper slurry with the underlying dielectric. Experiments were designed and performed to examine the CMP of two low-k polymers from Dow Chemical Company, bis-benzocyclobutene (BCB*, k=2.65) and “silicon-application low-k material” (SiLK* resin, k=2.65) with both acidic slurries suitable for copper damascene patterning and a KH phthalate-based model slurry developed for SiLK. Blanket polymer films were polished in order to determine the interactions that occur when copper and liner materials are removed by the damascene CMP process. Removal rates were obtained from material thickness measurements, post-CMP surface topography from AFM scans, and post-CMP surface chemistry from XPS measurements. Physically based wafer-scale models are presented which are compatible with the experimental results.
Near-Threshold Fatigue Crack Growth at 63Sn37Pb Solder Joints
Authors: Kang Ki-Ju , Choi Seon-Ho , Bae Tae-Sung
Published: December 2002

Fatigue tests were performed using single lap-joint specimens to obtain near-threshold fatigue crack growth data of solder joint under mode-II load. Attention was focused on the effect of high temperature aging and microstructures separately from the intermetallics. As a result, it was shown that the long cast time yielded the intermetallics and microstructures of the solder invariable regardless of aging condition. The granular micro-structure of the air-cooled specimens was shown to be inferior to the laminated micro-structure of the furnace-cooled specimens. Also, transition of fatigue crack behavior with ΔJ and the procedure of fatigue crack propagation from the pre-crack tip were discussed.
An Analytical Cure Model for Underfill Epoxies
Authors: Mahajan R. L. , Malhotra C. P. , Sharma R. K.
Published: December 2002

An analytical model relating the degree of cure of an underfill epoxy to the heat transfer coefficient of the heating process and time is presented. The model was verified experimentally by partially curing samples of a commercial underfill epoxy in two different heating environments for various times and scanning the samples in a differential scanning calorimeter to determine the degree of cure. A simplified equation can be used to relate the time required to achieve a given degree of cure to the heat transfer coefficient and the isothermal cure time.
Application of Ice Particles for Precision Cleaning of Sensitive Surfaces
Authors: Shishkin D. V. , Geskin E. S. , Goldenberg B.
Published: December 2002

This study was concerned with the use of the ice-air jet. It was demonstrated that at the optimal range of process conditions this jet constitutes a precision tool for selective material removal operations. Number of experiments was carried out in order to demonstrate this technology. Various electronic devices (computers, calculators, electronic games and watches, camera and lenses) were disassembled and electronic boards were contaminated by grease and metal powder. Then the boards were cleaned and reassembled. The computer, calculators and watches worked normally. Other experiments involved degreasing, depainting and deicing of liquid crystals, optical glass, removal emulsion from a film, etc. The feasibility of the damage free and pollution free decontamination of highly sensitive, highly countered surfaces was demonstrated. A low-cost ice-air cleaning will enable us to use it for processing large surfaces at a high rate. On-line degreasing of metal in the course of rolling or prior to machining illustrates this application. A generic environmentally friendly surface processing technology is emerging as the result of the presented study.
Creep Analysis and Thermal-Fatigue Life Prediction of the Lead-Free Solder Sealing Ring of a Photonic Switch
Authors: Lau J. , Mei Z. , Pang S. , Amsden C. , Rayner J. , Pan S.
Published: December 2002

Thermal reliability of the solder sealing ring of Agilent Technologies’ bubble-actuated photonic cross-connect switches has been investigated in this paper. Emphasis is placed on the determination of the thermal-fatigue life of the solder sealing ring under shipping/storing/handling conditions. The solder ring is assumed to obey the Garofalo-Arrhenius creep constitutive law. The nonlinear responses such as the deflections, stresses, creep strains, and creep strain energy density of the 3-D photonic package have been determined with a commercial finite element code. In addition, isothermal fatigue tests have been performed to obtain the relationship between the number of cycle-to-failure and the strain energy density. Thus, by combining the finite element results and the isothermal fatigue test results, the average thermal-fatigue life of the solder sealing ring is readily determined and is found to be more than adequate for shipping/storing/handling the photonic switches.
Decentralized Control of Rigid Robots Driven by Current-Fed Induction Motors
Authors: Guerrero-Ramı´rez Gerardo , Tang Yu
Published: December 2002

The problem of controlling a rigid manipulator driven by induction motors to follow a desired trajectory using the decentralized control technique is considered in this paper. Parameter uncertainties of the rigid robot are considered. First, a PI controller is used to force an induction motor to work in the current-command mode, then based on a fourth-order reduced model of induction motors, a current controller is proposed using only local measurements of each link (link position, velocity and stator currents of the induction motor). The rotor flux is estimated through a closed-loop observer. Provided that the flux observer is properly initialized, this controller is singularity-free and guarantees the uniform ultimate stability of the closed-loop system. Simulations are presented to illustrate the performance of this controller.
Transient and Steady-State Dynamic Finite Element Modeling of Belt-Drives
Authors: Leamy Michael J. , Wasfy Tamer M.
Published: December 2002

In this study, a dynamic finite element model is developed for pulley belt-drive systems and is employed to determine the transient and steady-state response of a prototypical belt-drive. The belt is modeled using standard truss elements, while the pulleys are modeled using rotating circular constraints, for which the driver pulley’s angular velocity is prescribed. Frictional contact between the pulleys and the belt is modeled using a penalty formulation with frictional contact governed by a Coulomb-like tri-linear friction law. One-way clutch elements are modeled using a proportional torque law supporting torque transmission in a single direction. The dynamic response of the drive is then studied by incorporating the model into an explicit finite element code, which can maintain time-accuracy for large rotations and for long simulation times. The finite element solution is validated through comparison to an exact analytical solution of a steadily-rotating, two-pulley drive. Several response quantities are compared, including the normal and tangential (friction) force distributions between the pulleys and the belt, the driven pulley angular velocity, and the belt span tensions. Excellent agreement is found. Transient response results for a second belt-drive example involving a one-way clutch are used to demonstrate the utility and flexibility of the finite element solution approach.
Multi-Input Square Iterative Learning Control With Bounded Inputs
Authors: Driessen Brian J. , Sadegh Nader
Published: December 2002

In this paper, we present a very simple modification of the iterative learning control algorithm of S. Arimoto et al. (1984, “Bettering Operation of Robots by Learning,” J. Robot Syst., 1(2), pp. 123–140) to the case where the inputs are bounded. The Jacobian condition presented in K. Avrachenkov (1998, “Iterative Learning Control Based on Quasi-Newton Methods,” Conference on Decision Control, pp. 170–174) is specified instead of the usual condition specified by Arimoto et al. (1984). (See also K. L. Moore, 1993, Iterative Learning Control for Deterministic Systems, Advances in Industrial Control Series, Springer-Verlag, London, UK.) In particular, the former is a condition for monotonicity in the distance to the solution instead of monotonicity in the output error. This observation allows for a simple extension of the methods of Arimoto et al. (1984) to the case of bounded inputs since the process of moving an input back to a bound if it exceeds it does not affect the contraction mapping property; in fact, the distance to the solution, if anything, can only decrease even further. The usual Jacobian error condition, on the other hand, is not sufficient to guarantee the chopping rule will converge to the solution, as proved herein. To the best of our knowledge, these facts have not been previously pointed out in the iterative learning control literature.
Comparison of Adaptive Control Techniques Applied to Diesel Engine Idle Speed Regulation
Authors: Memering Douglas W. , Meckl Peter H.
Published: December 2002

Two self-tuning adaptive algorithms are developed for a heavy-duty diesel engine in order to tune the idle governor to the specific parameters of a given engine. Engine parameters typically vary across engines and over time, thus causing potentially detrimental effects on engine idle speed performance. Self-tuning controllers determine the specific parameters of a given engine, and then adjust the controller algorithm accordingly. Recursive least squares is used to do the parameter identification, whose samples are synchronized with the discrete injection events of the diesel engine for good convergence. Both Minimum Variance and Pole Placement Self-Tuning Regulators are developed and simulated on the nonlinear diesel engine model. The results show successful tuning of each adaptive controller to the specific parameters of a given engine model, with parameter convergence occurring within 30 seconds.
Accuracy Considerations in a 3-D Ultrasonic Positioning System Based on the Difference in Time of Flights
Authors: Unnikrishnan Nishant , Ray Probir Kumar , Mahajan Ajay , Chu Tsuchin
Published: December 2002

This paper presents a method to improve the accuracy of an ultrasonic 3-D positioning system that uses the differences in the time of flights from a single transmitter to multiple receivers. The paper presents techniques to overcome errors in ultrasonic systems due to critical issues such as misalignment of transducers, changes in the speed of sound, arrival time of signals, etc. Further, the work presented here is not just applicable to ultrasonic systems but to all systems based on wave theory. This work will impact applications in robotics, virtual reality, precision measurement devices and probes, guidance of autonomous vehicles, and vibration analysis.
On the Flow Rate Dynamics in Time-Pressure Dispensing Processes
Authors: Chen, X. B. , Schoenau, and G. , Zhang W. J.
Published: December 2002

Time-pressure dispensing has been widely employed in electronics packaging manufacturing, where the fluid (such as encapsulant, epoxy, adhesive, etc.) in a syringe is driven by pressurized air and delivered onto boards or substrates. In such a process, the flow rate dynamics is critical in controlling the amount of fluid dispensed, yet extremely difficult to represent due to its complex behavior. This paper presents the development of a model of the flow rate dynamics in time-pressure dispensing, taking into account both air compressibility and fluid inertia. Experiments have been conducted to verify the effectiveness of the model developed.
Identification of Friction Coefficient for Constrained Robotic Tasks
Authors: Sharf I. , Gilardi G. , Crawford C.
Published: December 2002

Correct modeling of friction forces during constrained robotic operations is critical to high-fidelity contact dynamics simulation. Such simulations are particularly important for the development, mission planning and operations analysis of space robotic systems. Most existing friction models employ the coefficient of friction to capture the relationship between the friction force and the normal load. Hence, accurate identification of this parameter is prerequisite to accurate simulation. This issue is particularly important for space robotic operations since friction characteristics of materials are very different in space. In this manuscript, the problem of identification of the coefficient of friction is investigated experimentally and numerically. The motivating application being space manipulator systems, our principal objective is to develop a practical off-line identification algorithm, requiring minimum number of measurements from sensors available on space robots. To this end, a strategy is proposed to determine the coefficient of friction by using only the measured end-effector forces. The key idea behind the method is that during one-point contact, these forces represent the contact force and hence, can be directly used to calculate the coefficient of friction. The proposed approach is tested with the experimental data from peg insertion experiments conducted on a planar robotics test-bed with a specially designed contact interface. The algorithm is generalized to arbitrary complex geometries and applied to identify the coefficient of friction for a simulated battery drop test.
Robust Nonlinear Control of a Novel Indexing Valve Plate Pump: Simulation Studies
Authors: Zhang X. , Nair S. S. , Manring N. D.
Published: December 2002

A robust adaptive pressure control strategy is proposed for a novel indexing variable-displacement pump. In the proposed approach, parametric uncertainties and unmodeled dynamics are identified to the extent possible using a model free learning network and used to decouple the dynamics using physical insights derived from careful reduced order modeling. The swash plate motion control is then carefully designed to provide the desired pressure response characteristics showing improved performance with learning. The proposed control framework and designs are validated using a detailed nonlinear simulation model.
Optimal Biped Walking Locomotion Solved by Trajectory Planning Method
Authors: Ono Kyosuke , Liu Rongqiang
Published: December 2002

This paper describes an optimal trajectory planning of walking locomotion for a planar biped walking mechanism which has thighs, shanks and small feet. The biped mechanism was modeled to be a 3-degree-of-freedom (dof) link system composed of a stance leg and a 2-dof swing leg. The one step walking locomotion is divided into two phases, i.e., the swing motion of 2-dof swing until knee collision and the swing motion of the straight leg until toe collision. It is assumed that the knee collision of the swing leg and the toe collision at the foot exchange are plastic and occur instantly. The motion of the swing and stance legs in the first phase is solved by the optimal trajectory planning based on the function approximation method. Under the full-actuated condition at the hip, knee and ankle joints, we obtained the optimal trajectory solution with a minimum square integral of input torque. We also obtained a sub-optimal walking locomotion for an under-actuated system whose ankle is a passive joint. The validity of the optimal trajectory solution is confirmed by a forward dynamic simulation. The optimal trajectory solution for the human body parameter values exhibits a natural and stable walking locomotion with the step length of 0.33 m and a step period of 0.62 s.
A New Yaw Dynamic Model for Improved High Speed Control of a Farm Tractor
Authors: Bevly David M. , Gerdes J. Christian , Parkinson Bradford W.
Published: December 2002

This paper presents the system identification of a new model for the farm tractor’s yaw dynamics in order to improve automatic control at higher speeds and understand controller limitations from neglecting these dynamics. As speed increases, higher order models are required to maintain accurate lateral control of the vehicle. Neglecting these dynamics can cause the controller to become unstable at the bandwidths required for accurate control at higher speeds. The yaw dynamic model, which is found to be dominated by a second order response, is identified for multiple speeds to determine the effect of velocity on the model. The second order yaw dynamics cannot be represented by the traditional bicycle model. An analytical derivation shows that the model characteristics can, however, be captured by a model consisting of a significant (non-negligible) relaxation length in the front tire. Experimental results are presented showing that the new yaw dynamic model can provide lateral control of the tractor to within 4 cm (1σ) at speeds up to 8 m/s. These results are shown to be an improvement, at high speeds, over controllers based on models (such as a kinematic model) previously used for control of farm equipment.
Actuator Fault Estimation Scheme for Flight Applications
Authors: Yee Jiong-Sang , Liang Wang Jian , Jiang Bin
Published: December 2002

The paper presents a new actuator fault estimation scheme based on the augmented error method that estimates the actuator effectiveness on-line. The proposed scheme is applied to a fault-tolerant flight control system design for an F4-E fighter aircraft. The output of a nominal H∞ controller is continuously reconfigured to compensate for any loss of actuator effectiveness. Simulation results demonstrate good fault estimation and flying qualities obtained using the proposed scheme under the actuator fault conditions.
Two-Degree-of-Freedom Optimal Preview Tracking Control: A Mechatronic Design Example
Authors: She Jin-Hua , Xin Xin , Ohyama Yasuhiro
Published: December 2002

A design method for digital tracking control is described and applied to control an arm robot with structured uncertainties. A two-degree-of-freedom control system configuration provides the desired feedback and input-output performances independently. Regarding controller design, first, sampled-data H∞ control and linear matrix inequality approaches are used to design a reduced-order output feedback controller. Then, the feedforward controller is parameterized based on the feedback controller, with the free parameter being chosen based on a preview strategy.
Transient Thermal Management of a Handset Using Phase Change Material (PCM)
Authors: Hodes Marc , Weinstein Randy D. , Pence Stephen J. , Piccini Jason M. , Manzione Lou , Chen Calvin
Published: December 2002

The power density of portable electronic devices continues to increase because packaging advances reduce their size even as features are added and enhanced. Designing thermal management systems to accommodate steady-state conditions as opposed to fixed duty cycles can substantially increase cost, size, and weight. The feasibility of transient thermal management of handsets using phase change materials (PCMs) was experimentally investigated using an ABS handset mock-up. At selected intervals of time, the nonuniform case temperature of the handset was measured using an infrared (IR) camera, while thermocouples measured the temperatures of the PCM and simulated power amplifier (heater). Transient and steady-state heat transfer rates by natural convective and radiation from the handset to the environment were numerically computed from the temperature data in the thermal images. The effects of PCM material, power supplied to the handset, and handset orientation on the time required for the handset case to reach a given (maximum) temperature and “recovery” time were examined.
Fractal Structures in PbF2/Pb(NO3)2 Precipitate Systems
Authors: Mandalian Lara , Sultan Rabih
Published: December 2002

Tree-like aggregates (dendrites) have been reported in a variety of precipitate systems. We here explore different routes for the growth of dendrites of PbF2 and Pb(NO3)2. The PbF2 ramifications form via the interdiffusion of coprecipitates (F- into Pb2+) in microslides (Liesegang-type experiments) and via the infiltration of electrolyte through cracks, thus simulating geochemical fractals. The Pb(NO3)2 dendrites are grown by evaporation of dilute solutions of the salt. Images of the various patterns obtained are analyzed and their fractal dimensions are determined. The location of the edges of successive "cascades" in dendritic patterns obeys a spacing law similar to that of Liesegang bands.
Study of the Influence of Water on Oxidative Properties of Fe3+ in ZSM-5 Zeolite Channels
Authors: Čík Gabriel , Hubinová Milada , Šeršeň František , Brezová Vlasta
Published: December 2002

The interactions of phenol and thiophene with Fe3+ ions have been studied in ZSM-5 zeolite channels in the presence of water. The Fe-ZSM-5 was prepared by the ion exchange of Fe3+ for Na+. The Fe3+ ions in zeolite channels have unsaturated co-ordination spheres and oxidize organic substrates (phenol, thiophene) at room temperature. The interaction of Fe3+ with phenol gives rise to the stabilized cation-radical PhOH•+ and thiophene forms low oligomers (2-6 monomeric units). The oligomers are present in the neutral as well as oxidized form as cation-radicals (polarons). The formation of dications (bipolarons) has not been observed.
Incorporation of Aluminum and Iron Into the ZSM-12 Zeolite: Synthesis and Characterization of Acid Sites
Authors: Košová Gabriela , Čejka Jiří
Published: December 2002

Zeolite ZSM-12 with aluminum and iron in the framework was synthesized in a broad range of Si/Al (Si/Fe) ratios using triethylmethylammonium bromide as structure-directing agent with the aim to characterize the type and concentration of acid sites in dependence on the Si/Al (Si/Fe) ratio and calcination procedure. It was shown that the minimum Si/Al ratio achieved for (Al)ZSM-12 is around 35, which is very close to the minimum Si/Fe ratio ca 37 for (Fe)ZSM-12. The rate of crystallization of (Al)ZSM-12 and (Fe)ZSM-12 depends on the concentration of Al and Fe in the reaction mixture. The higher was the concentration of these trivalent cations, the slower was the apparent crystallization rate. It is suggested that the crystallization rate is controlled by the number of nucleation centers, which depends on the amount of trivalent cations (Al, Fe) in the reaction mixture. Zeolites (Al)ZSM-12 and (Fe)ZSM-12 were calcined under a variety of carefully controlled conditions to investigate the resulting concentration of Brønsted and Lewis acid sites. FTIR spectroscopy used to study the adsorption of acetonitrile-d3 and pyridine on Brønsted and Lewis acid sites revealed that both sites are present in significant concentrations in all calcined (Al)ZSM-12 and (Fe)ZSM-12 zeolites. The highest concentrations of Brønsted sites especially at low Si/Al or Si/Fe ratios were achieved via calcination of the zeolites in a stream of ammonia followed by a repeated sodium ion exchange and further calcination in a stream of air.
Steric Hindrance in the Solute-Solvent Interactions of 2-Substituted 4,5-Dimethoxypyridazin-3(2H)-ones: An Infrared Spectral and Theoretical Study
Authors: Šamalíková Mária , Perjéssy Alexander , Liu Quing , Loos Dušan , Konečný Václav , Dehne Heinz , Sokolowski Siegmar , Šusteková Zora
Published: December 2002

Infrared spectra for a series of 2-substituted 4,5-dimethoxypyridazin-3(2H)-ones (1) were measured in hexane (n-C6H14)-CHCl3 and CH3CN-D2O binary mixtures. The solute-solvent interactions of pyridazinones 1 were studied by correlation of v(C=O) values with mole fractions of the less polar components of binary mixtures. The different solute-solvent interacting species were distinguished and compared with those for 3-methyl-4-phenylthiazol-2(3H)-one (2) and previously investigated 1-methylpyrrolidin-2-one (3). The steric effects of the substituents adjacent to the C=O group amplified by the geometrical requirements of the six-membered pyridazin-3(2H)-one ring appeared to be the main factor governing the existence of individual hydrogen-bonded species. The solute-solvent interactions are sterically most restricted in pyridazinones 1, while in thiazolones 2 they are freer and almost comparable to those in the sterically least hindered 1-methylpyrrolidin-2-ones 3. The above results were confirmed by inspection of calculated semiempirical AM1 and PM3 and ab initio 6-31G* geometrical data for methyl derivatives 1h, 2 and 3.
Time-Resolved Tryptophan Fluorescence of Fragment 1-86 of Factor X and the Influence of Membrane Binding
Authors: Häfner Angelika , Beneš Martin , Mérola Fabienne , Duportail Guy , Schneider Friedemann W. , Hof Martin
Published: December 2002

Membrane binding of the N-terminus of the prothrombinase reaction enzyme, fragment 1-86 of factor X (FX F1-86), to phospholipid vesicles was studied using time-resolved fluorescence spectroscopy of the tryptophan residue Trp41 which is located in the membrane binding part of this protein (Gla domain). Fluorescence lifetimes were determined by the time-correlated single photon counting technique using synchrotron radiation as the excitation source. Different negatively charged lipid vesicles containing either phosphatidylserine or phosphatidylglycerol mixed with phosphatidylcholine were investigated. Pure synthetic lipids (dilauroyl and dioleoyl lipids) as well as natural lipids (from egg yolk or bovine brain) were used in membrane binding studies. Multiexponential data analysis supports the results already found for FX F1-86 in the presence of calcium ions. For all lipid systems we obtained decay times in the range of 0.2, 0.6, 2.6, 5.6 ns. Moreover, a long-lifetime component with minor contribution to the decay amplitude (<5%) was found. The fluorescence lifetimes do not show any wavelength dependence. There was no change in the fluorescence decay times upon membrane binding, which might indicate that a lipid-specific conformational change in the Gla domain of factor X does not take place upon membrane binding.