bluuebunny/crossref_metadata_2025 huggingface dataset:
Pure red electroluminescence from a host material of binuclear gallium complex
Authors: Qiao Juan , Qiu Yong , Wang Liduo , Duan Lian , Li Yang , Zhang Deqiang
Published: December 2002

By using a binuclear gallium complex, bis(salicylidene-o-aminophenolato)-bis(8quinolinoato)-bisgallium(III)[Ga2(saph)2q2], as the host material, organic light emitting diodes (OLEDs) with pure red emission were developed, which used a red fluorescent dye of 4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB). Ga2(saph)2q2 proves to be of much better film-forming ability and a smaller energy gap than tris(8-quinolinolato)aluminum (Alq3). And the doped device with a configuration of indium tin oxide/N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine/Ga2(saph)2q2: DCJTB (2 wt %)/Ga2(saph)2q2/Mg:Ag, exhibited a turn-on voltage as low as 2.2 V, and a pure red emission with Commission Internationale de l’Eclairage (CIE 1931) coordinates of (0.67, 0.33). The improved energy transfer gave a high current efficiency of 2.04 cd/A at 20 mA/cm2, which is about two times higher than that of the doped Alq3 device. This letter indicates that developing host materials is a promising way to achieve excellent red emission OLEDs.
Low temperature electronic transport and electron transfer through organic macromolecules
Authors: Zimbovskaya Natalya
Published: December 2002

It is shown that at low temperatures and moderate electron dephasing the electron transmission function reveals a structure containing information about donor/acceptor sites effectively participating in the electron transfer processes and primary pathways of electrons tunneling through molecular bridges in macromolecules. This important information can be obtained as a result of analysis of experimental low temperature current-voltage characteristics for chosen molecules.
Electrically Conductive Adhesive Formulations for SMT Applications
Authors: Kisiel Ryszard
Published: December 2002

The aim of current research presented in my paper is to establish how adhesive composition influences the performance of joints between SMDs and PCBs. For identifying the best adhesive formulation in SMT applications, the experiment design method based on Taguchi techniques for quality engineering has been used. It was decided to investigate how the following controllable factors: type of isolating resin, levels of weight content of Ag filler, presence of adhesive promoter and spread improver as well as PCB pads finishing influences the performance of adhesive joints. As the figure-of-merit, the individual joint resistance and adhesion between SMDs and PCBs were measured. It was found that the type of resin had the biggest influence on electrical and mechanical properties of adhesive joints.
Study on Failure Mechanism of PCT Reliability for BT Substrate Based CSP (Chip Scale Package)
Authors: Chung C. L. , Fan James , Huang M. L. , Tsai F. J.
Published: December 2002

In this paper, the study on failure mechanism of moisture sensitivity reliability is reported. It focuses on the PCT conditions which are 121°C, 2atm, 100RH%, and 168 hr. The general failure mode is delamination on the interface between die attach material and die backside. Interestingly, the delamination exists as a gap of 20∼40 μm. In addition, the paper discusses the relative materials influences — for example, the moisture uptake of mold compound systems and die backside surface property effects. The degradation of the die attach material was analyzed by Dynamic Mechanic Analysis (DMA). The delamination surfaces are analyzed by Scanning Electron Microscope (SEM), and Optical Microscope (OM). Furthermore, Scanning Acoustic Tomograph (SAT) through scanning results reveals that the mold compound formula affects the amount of moisture uptake, which obviously would affect the PCT reliability.
Strength Evaluation of Notch Structure for Semiconductor Encapsulant Resin
Authors: Kawamura Noriyasu , Kawakami Takashi , Kishimoto Kikuo , Omiya Masaki , Shibuya Toshikazu
Published: December 2002

Plastic encapsulated semiconductor packages may crack at the corner regions of die pads or chips if internal delamination occurs at an elevated temperature during the reflow soldering process. Thus, the structural strength design around the notch structures, which will be formed in the encapsulant resin due to the delamination, is considered one of the most important issues. Especially, it becomes a more critical item of the package development in order to realize the reflow process with lead-free solder materials, whose melting points are higher than that of Sn63-Pb37. In this study, the fracture behavior of notched specimens, which were made of silica particulate-filled epoxy resins and modeled as the corner regions in actual packages, were studied with experimental and numerical analyses. First, the fracture tests of the notch structure of semiconductor encapsulant resin were carried out. A notch tip with several different radii was introduced to the specimen. The specimens were fractured by a three-point bending load. Second, the strength evaluation of the notch structure was carried out. The critical stress distribution σCr=max.[KIC/2πr1/2,σB] was used to determine the crack initiation at the notch tip. It is assumed that a fracture occurs when, at any point near the notch tip, the stress distribution exceeds the critical stress distribution determined by fracture toughness and bending strength. Three-dimensional finite element analysis was carried out to obtain the stress distributions around the notch tip in the specimen. The calculated stress distributions around the notch tip were compared with the critical stress distribution to estimate the fracture load of the specimen. Estimated fracture loads at room temperature and at high temperature were compared with the results of the fracture tests. It was confirmed that the predicted results based on the critical stress distribution corresponded very well with the experimental results. The validity of the criterion was confirmed by studying the fracture behavior of the notched specimens of actual silica particulate filled epoxy resins.
Impact Resistance of SM Joints Formed With ICA
Authors: Wu C. M. Lawrence , Li Robert K. Y. , Yeung N. H.
Published: December 2002

Isotropic conductive adhesives (ICA) have been considered as replacement materials for lead-tin solder alloys. In this paper, the post-impact shear strength of ICA surface mount (SM) joints was obtained experimentally and compared with that of SM lead-tin joints. The dynamic impact energy was provided in the form of three-point bending on the PCB using equipment called the split Hopkinson bar. Strain rates of over 4000/s were used for the impact bending test. The action of impact bending was used to simulate the effect on the PCB and the interconnection as a result of high energy impact on an electronic equipment. Shear test was then performed to examine the change in strength of the ICA joints as a result of impact damage. It was found that the SM ICA joints failed due to impact at a strain rate just over 4000/s. Microstructural examination carried out using a scanning electron microscope revealed that the interface between the ICA and copper pad on the PCB was the weakest region of the joint.
Corrosion Analysis of a Fiber-Optic Transceiver Housing
Authors: Lau J. H. , Jiaa C. L. , Erasmus S. J.
Published: December 2002

The corrosion responses of a fiber-optic transceiver’s housing with zinc alloy die casting material are investigated in this study. Emphasis is placed on the determination of the weight change and corrosion rate of the housing when it is subjected to a 85% relative humidity and 85°C temperature (85%RH/85°C) test condition. Also, the average light optical power, receiver sensitivity, extinction ratio, and mask margin of transceiver modules subjected to 85%RH/85°C and 3.47V at 500, 1000, 1500, and 1600 h are provided. Furthermore, metallography is performed on the surfaces and cross sections of the housing. Finally, measurements are made of the thickness of the oxide layer on the surfaces of the fiber-optic transceiver housing.
Correlation Between the Mechanical Strength and Curing Condition of No-Flow Flip Chip Assemblies
Authors: Tang C. W. , Chan Y. C. , Hung K. C. , Tu P. L.
Published: December 2002

Flip chip is the emerging interconnect technology for the next generation of high performance electronics. To eliminate the process bottlenecks associated with flip chip assembly, a new assembly technique based around “No-flow” underfill formulations has been proposed. In this paper, we have studied the correlation between the mechanical strength and the curing condition of no-flow flip chip assemblies using six different reflow profiles. It is found that both Ni3Sn4 and Cu6Sn5 intermetallics (IMCs) are formed at the solder/substrate pad and UBM (Under Bump Metallization)/solder interfaces respectively. The thickness of both IMCs increase with the increasing heating factor. The characteristics of the mechanical strength of these IMCs have been demonstrated. A correlation between the mechanical strength and the interfacial metallurgical reaction has been discussed. Also, the fastest possible reflow profile for both the cure of the underfill and maximizing the shear strength is identified. Based on the observed relationship of the mechanical strength and underfill curing of no-flow flip chip assemblies with Qn, the reflow profile should be controlled with caution in order to optimize both the mechanical strength and time for underfill cure. Only a clearer understanding of these correlation can allow manufacturers to develop a optimal, high reliable, low cost, high throughput no-flow flip chip assembly process.
Study of Mechanical Behavior of Compliant Micro-Springs for Next Generation Probing Applications
Authors: Ahmad Mudasir , Sitaraman Suresh K.
Published: December 2002

Advances in integrated circuit fabrication have created a need for an innovative, inexpensive, yet reliable probing technology with ultra-fine pitch capability. Research teams at Georgia Tech, Xerox PARC, and NanoNexus, Inc. are developing flexible micro-spring structures that can far exceed the probing needs of the next-generation microelectronic devices. Highly compliant cantilevered springs have been fabricated at pitches as small as 6 μm. These micro-springs are designed to accommodate topological variation in probing surfaces while flexing within the elastic regime. To be able to use the micro-springs for probing applications, several design challenges must be addressed. When the probe head is brought into contact with the bonding pads, the micro-springs will slide across the surface of the bonding pad and establish contact. The bonding pads typically have surface oxides. Thus, from a mechanical standpoint, it is important to ensure that the springs would apply enough force to break through the surface oxides and establish good electrical contact. The damage done to the pads in the process has to be minimal. It is also important that the distance through which the springs will slide across the bonding pad surface does not exceed the pad dimensions. From a mechanical fatigue standpoint, the stress amplitude that the springs will be subjected to, needs to be within the elastic limit of the spring material. This will enhance the life of the micro-spring probes. Typical probing devices are expected to last about half a million touchdowns. Numerical models and sub-models have been developed to simulate the mechanical contact between a single spring and the bonding pad, and to determine the probing force. The model simulates the establishment of contact, sliding, and indentation resulting in plastic deformation of the pad. The length of the scrub mark and the indentation depth are validated with experimental measurements using focused ion beam. The spring geometry parameters are varied and their influence on the penetration depth studied. Finally, the variation of contact resistance with probing force is outlined.
Motion Planning for a Spherical Mobile Robot: Revisiting the Classical Ball-Plate Problem
Authors: Mukherjee Ranjan , Minor Mark A. , Pukrushpan Jay T.
Published: December 2002

In comparison to wheeled robots, spherical mobile robots offer greater mobility, stability, and scope for operation in hazardous environments. Inspite of these advantages, spherical designs have failed to gain popularity due to complexity of their motion planning and control problems. In this paper, we address the motion planning problem for the rolling sphere, often referred in the literature as the “ball-plate problem,” and propose two different algorithms for reconfiguration. The first algorithm, based on simple geometry, uses a standard kinematic model and invokes alternating inputs to obtain a solution comprised of circular arcs and straight line segments. The second algorithm is based on the Gauss-Bonet theorem of parallel transport and achieves reconfiguration through spherical triangle maneuvers. While the second algorithm is inherently simple and provides a solution comprised of straight line segments only, the first algorithm provides the basis for development of a stabilizing controller. Our stabilizing controller, which will be presented in our next paper, will be the first solution to a problem that has eluded many researchers since the kinematic model of the sphere cannot be converted to chained form. Both our algorithms require numerical computation of a small number of parameters and provide the scope for easy implementation.
A General Approach to the Dynamics of Nonholonomic Mobile Manipulator Systems
Authors: Yu Qing , Chen I-Ming
Published: December 2002

This paper studies the dynamic modeling of a nonholonomic mobile manipulator that consists of a multi-degree of freedom serial manipulator and an autonomous wheeled mobile platform. The manipulator is rigidly mounted on the mobile platform, and the wheeled mobile platform moves on the ground subjected to nonholonomic constraints. Forward Recursive Formulation for the dynamics of multibody systems is employed to obtain the governing equation of the mobile manipulator system. The approach fully utilizes the existing equations of motion of the manipulator and that of the mobile platform. Furthermore, terms representing the dynamic interactions between the manipulator and the mobile platform can be observed. The resulting dynamic equation of the mobile manipulator has the minimum number of generalized coordinates and can be used for the purpose of dynamic simulation and control design, etc. The implementation issues of the model are discussed.
Integrated Design and PD Control of High-Speed Closed-loop Mechanisms
Authors: Wu F. X. , Zhang W. J. , Li Q. , Ouyang P. R.
Published: December 2002

The performance of an electromechanical system not only depends on its controller design, but also on the design of its mechanical structure. In order to achieve the excellent performance of the four-bar-link mechanism by employing the simple PD control, we redesign the structure of the four-bar-link mechanism by a mass-redistribution scheme to simplify the dynamic model. Theoretically, we analyze the stability of the closed-loop system consisting of the PD controller and several kinds of four-bar-link mechanisms, and discuss the relations between the performance of the PD controller and its gains and the mechanical design. The obtained results show that the performance of the PD controller may be significantly improved by using the methodology of Design For Control (DFC). The effectiveness of the proposed methodology has also been verified by some simulation studies.
Disturbance Observers for Rigid Mechanical Systems: Equivalence, Stability, and Design
Authors: Schrijver Erwin , van Dijk Johannes
Published: December 2002

Mechanical (direct-drive) systems designed for high-speed and high-accuracy applications require control systems that eliminate the influence of disturbances like cogging forces and friction. One way to achieve additional disturbance rejection is to extend the usual (P(I)D) controller with a disturbance observer. There are two distinct ways to design, represent, and implement a disturbance observer, but in this paper it is shown that the one is a generalization of the other. A general systematic design procedure for disturbance observers that incorporates stability requirements is given. Furthermore, it is shown that a disturbance observer can be transformed into a classical feedback structure, enabling numerous well-known tools to be used for the design and analysis of disturbance observers. Using this feedback interpretation of disturbance observers, it will be shown that a disturbance observer based robot tracking controller can be constructed that is equivalent to a passivity based controller. By this equivalence not only stability proofs of the disturbance observer based controller are obtained, but it also provides more transparent controller parameter selection rules for the passivity based controller.
Template Generation Algorithm Using Vectorized Function Evaluations and Adaptive Subdivisions
Authors: Nataraj P. S. V. , Sheela S.
Published: December 2002

A template generation algorithm is presented in this paper based on interval analysis. The proposed algorithm makes use of vectorized evaluations of the angle-magnitude functions and adaptive subdivisions of the parameter intervals. The algorithm is applicable to any computer programmable transfer function and generates templates to a user-specified accuracy. It is shown through several examples that the proposed algorithm is more efficient than existing interval analysis based template generation algorithms.
Synthesis, Stability Analysis, and Experimental Implementation of a Multirate Repetitive Learning Controller
Authors: Sadegh Nader , Hu Ai-Ping , James Courtney
Published: December 2002

This paper describes a multirate repetitive learning controller with an adjustable sampling rate that may be used as an “add-on” module to enhance the tracking performance of a feedback control system. The sampling rate of the multirate controller is slower than the remainder of the control system, and is selected by the user to achieve the required system performance based on a trade-off between the accuracy and the complexity of the controller. The multirate controller learns the system control input based on the tracking error down-sampled using a weighted averaging filter. The output of the multirate controller is up-sampled through an arbitrary hold mechanism determined by the user. This paper extends the existing stability results for single-rate repetitive learning controllers to the proposed multirate scheme. It provides an explicit procedure for its design and stability analysis. In addition, the proposed multirate repetitive learning controller is implemented on a mechanical system performing a non-colocated control task, where its effectiveness in reducing tracking errors while following periodic reference trajectories is shown experimentally.
Two-Step Controller for 3-D Flexible Link Manipulators: Bandwidth Modulation and Modal Feedback Approach
Authors: Cheong Joono , Chung Wan Kyun , Youm Youngil
Published: December 2002

For joint tracking control of flexible robots, this paper presents a two-step design of controller: the bandwidth modulation with modal feedback approach. First, we focus on the design of rigid part’s motion controller considering the bandwidth of the rigid subsystem. We investigate the relationship between macro joint tracking performance and vibration suppression capability using the bandwidth parameter. After adjusting the bandwidth of rigid motion, the composite control, which is the second step consisting of rigid and flexible sub-controllers, is applied like singular perturbation approach. As the flexible sub-controller, we propose a direct modal feedback controller that is very simple, but effective to suppress the vibration. The validity and effectiveness of the proposed method are verified by experiments using a POSTECH 3-D flexible robot.
Stability and Resolution Analysis of a Phase-Locked Loop Natural Frequency Tracking System for MEMS Fatigue Testing
Authors: Sun X. , Horowitz R. , Komvopoulos K.
Published: December 2002

An analysis of a nonlinear control system that was used to track the natural frequency of a MEMS resonator is presented in this paper. A phase-locked loop system is used to track the natural frequency of the resonator due to fatigue of the spring element. A model for the control system is established and the system behavior is analyzed using an averaging method. The analysis provides a quantitative criterion for selecting the control gain to achieve stability. Simulation results are shown to be in agreement with the theoretical analysis. Tracking accuracy under the presence of Brownian noise and capacitive position sensing noise is also analyzed by using a variance propagation equation for the nonlinear dynamic system utilizing a first-order Taylor series approximation. The theoretically estimated resolution is also found to be in good agreement with simulation results.
Performance of a Smart Direct Fire Projectile Using a Ram Air Control Mechanism
Authors: Chandgadkar Siddharth , Costello Mark , Dano Bertrand , Liburdy James , Pence Deborah
Published: December 2002

The effectiveness of a direct fire penetrator projectile equipped with an actively controlled ram air actuation mechanism is investigated through dynamic simulation. The ram air control mechanism consists of a rotary sleeve valve which directs air flow from an inlet in the center of the nose to side ports. The coupled dynamics of the projectile, inertial measurement unit, and flight control system are included in the system model. This work shows that a ram air control mechanism provides sufficient control authority to significantly reduce dispersion of a direct fire penetrator, even in the presence of moderate levels of sensor bias and noise.
Magnetic Bearing Measurement Configurations and Associated Robustness and Performance Limitations
Authors: Thibeault Nancy Morse , Smith Roy S.
Published: December 2002

We obtain bounds on achievable sensitivity and complementary sensitivity reduction for a magnetic bearing system in three measurement configurations. We use the sensitivity reduction bounds to deduce achievable robustness and performance limits for each system configuration. We then show how these limits vary with varying magnetic bearing physical dimensions and other parameter values as well as varying closed-loop system bandwidth and controller relative degree. Using all of this information, we derive guidelines for designing magnetic bearing systems and their controllers, for each measurement configuration considered, for greatest achievable robustness and performance.
Linear Stability Analysis for the Wall Temperature Feedback Control of Planar Poiseuille Flows
Authors: Pabiou Herve´ , Liu Jun , Be´nard Christine
Published: December 2002

Active control of a planar Poiseuille flow can be performed by increasing or decreasing the wall temperature in proportion to the observed wall shear stress perturbation. In continuation with the work of H. H. Hu and H. H. Bau (1994, Feedback Control to Delay or Advance Linear Loss of Stability in Planar Poiseuille Flow, Proc. R. Soc. London A, 447, pp. 299–312), a linear stability analysis of such a feedback control is developed in this paper. The Poiseuille flow control problem is reduced to a modified Orr-Sommerfeld equation coupled with a heat equation. By solving numerically the coupled equations with a finite element method, many numerical results about the stability of the flow control are obtained. We focus our attention on the interpretation of the numerical results. In particular, the role of two essential parameters—the Prandtl number Pr and the control gain K—is investigated in detail. When Pr>1.31, stabilizing K is negative; while, when Pr<1.31, stabilizing K is positive. And when Pr=1.31, the flow cannot be stabilized by a real K. A comparison between symmetric two-wall control and non-symmetric one-wall control is also made.
Modeling and H2/H∞ MIMO Control of an Earthmoving Vehicle Powertrain
Authors: Zhang Rong , Alleyne Andrew , Prasetiawan Eko
Published: December 2002

Coordination of the power distribution in a Multi-Input Multi-Output (MIMO) electro-hydraulic transmission is investigated for the case of an earthmoving vehicle powertrain. A generalized model of a representative system is presented along with the development of both H2 and H∞ MIMO controller designs. The controllers are developed based on a linearized model of the system about some nominal operating point. Multiple inputs are coordinated to control multiple load outputs simultaneously. Since typical MIMO electrohydraulic transmission systems have significant nonlinear dynamics that vary with system operating conditions, a robust controller design is paramount. The increased robustness of the H∞ controller over the H2 scheme is demonstrated qualitatively in the time domain through both disturbance rejection and trajectory tracking comparisons. A frequency domain criterion quantitatively provides quantifiable comparisons between the two methods. Hardware-in-the-Loop experiments validate the modeling and control performance on an Earthmoving Vehicle Powertrain Simulator (EVPS).
Nonlinear Model Reduction for Dynamic and Automotive System Descriptions
Authors: Liu Zeyu , Wagner John
Published: December 2002

The mathematical modeling of dynamic systems is an important task in the design, analysis, and implementation of advanced control systems. Although most vehicle control algorithms tend to use model-free calibration architectures, a need exists to migrate to model-based control algorithms which may offer greater operating performance. However, in many instances, the analytical descriptions are too complex for real-time powertrain and chassis model-based control algorithms. Thus, model reduction strategies may be applied to transform the original model into a simplified lower-order form while preserving the dynamic characteristics of the original high-order system. In this paper, an empirical gramian balanced nonlinear model reduction strategy is examined. The controllability gramian represents the energy needed to transport the system between states, while the observability gramian denotes the output energy transmitted. These gramians are then balanced and select system dynamics truncated. For comparison purposes, a Taylor Series linearization will also be introduced to linearize the original nonlinear system about an equilibrium operating point, and then a balanced realization linear reduction strategy applied to reduce the linearized model. To demonstrate the functionality of each model reduction strategy, a vehicle suspension system and exhaust gas recirculation valve are investigated, and respective transient performances are compared.
Model Predictive Control of a Fuel Injection System with a Radial Basis Function Network Observer
Authors: Manzie Chris , Palaniswami Marimuthu , Ralph Daniel , Watson Harry , Yi Xiao
Published: December 2002

This paper proposes a new Model Predictive Control scheme incorporating a Radial Basis Function Network Observer for the fuel injection problem. Two new contributions are presented here. First a Radial Basis Function Network is used as an observer for the air system. This allows for gradual adaptation of the observer, ensuring the control scheme is capable of maintaining good performance under changing engine conditions brought about by engine wear, variations between individual engines, and other similar factors. The other major contribution is the use of model predictive control algorithms to compensate for the fuel pooling effect on the intake manifold walls. Two model predictive control algorithms are presented which enforce input, and input and state constraints. In this way stability under the constraints is guaranteed. A comparison between the two constrained MPC algorithms is qualitatively presented, and conclusions are drawn about the necessity of constraints for the fuel injection problem. Simulation results are presented that demonstrate the effectiveness of the control scheme, and the proposed control approach is validated on a four-cylinder spark ignition engine.
Genetic Planning Method and its Application to Planetary Exploration
Authors: Farritor Shane , Dubowsky Steven
Published: December 2002

This paper describes a genetic algorithm planning method for autonomous robots in unstructured environments. It presents the approach and demonstrates its application to a laboratory planetary exploration problem. The method represents activities of the robot with discrete actions, or action modules. The action modules are assembled into an action plan with a Genetic Algorithm (GA). A successful plan allows the robot to complete the task without violating any physical constraints. Plans are developed that explicitly consider constraints such as power, actuator saturation, wheel slip, and vehicle stability. These are verified using analytical models of the robot and environment. The methodology is described in the context of planetary exploration similar to the NASA Mars Pathfinder mission. More aggressive missions are planned where rovers will explore scientifically important areas that are difficult to reach (e.g., ravines, craters, dry riverbeds, and steep cliffs). The proposed approach is designed for such areas.
Initial Investigations Into the Dynamics of Cutting Brushes for Sweeping
Authors: Peel G. M. , Parker G. A.
Published: December 2002

Cutting brushes are used at relatively low speeds by various municipal vehicles and in particular road sweeping units. As the name suggests such brushes are designed to “cut” through debris, especially compacted sand or similar matter. The main deflection plane of a bristle (or tine) is along the mount radius, making the tines very stiff in the direction of rotation, hence the cutting action when the brush is rotated. Exploring the literature shows that very little is known, or understood, about the operation of brushes for mechanical sweeping. In this paper a pseudo-static discretized model is developed to investigate the deformations and forces acting on brushes during ideal operation of a horizontal brush on a flat plane. Due to the numerous different sweeper brushes on the market, one common configuration is used as the basis of the model and the paper will detail only the characteristics of this brush. The brush to be investigated is a “cutting brush,” introduced above, where the tines can only deflect along the mount radius. Having developed a model it is used to predict the forces and torques generated within a horizontally rotating brush. The influence of centrifugal force is analyzed although transient effects are neglected and steady state conditions assumed. The predictions of the model are compared to practical results taken from a test rig and the validity of the model is discussed. Agreement between the model and the practical results will be shown to be good, considering the complexities and practical realities involved in analyzing any system which is friction dependent.
Solvent-Free Synthesis of Sulfonephthaleins, Sulfonefluoresceins and Fluoresceins Under Microwave Irradiation
Authors: Cihelník Simon , Stibor Ivan , Lhoták Pavel
Published: December 2002

An efficient solvent-free synthesis of sulfonephthaleins, sulfonefluoresceins and fluoresceins under microwave irradiation is reported.
Preparation of O-, S- and N-Benzyl Derivatives of 1,6-Anhydro-β-D-hexopyranoses via Aziridine Ring Opening
Authors: Kroutil Jiří , Karban Jindřich , Trnka Tomáš , Buděšínský Miloš , Černý Miloslav
Published: December 2002

The aziridine ring opening of N-tosylepimino carbohydrates 1-6 having D-allo, D-manno, D-galacto and D-talo configurations with benzyl alcohol, benzylamine and phenylmethanethiol afforded 2-, 3- and 4-O-benzyl-, benzylsulfanyl and benzylamino derivatives of 1,6-anhydro-β-D-hexopyranoses of D-gluco, D-galacto and D-manno configurations 7-23 in 44-99% yields. Hexenopyranoses 24-26 were prepared from tosylepimino carbohydrates 1, 4 and 5 by intramolecular rearrangement of the aziridine ring.
Synthesis and QSAR Studies of New Conjugated Benzothiazole Derivatives
Authors: Buffa Radovan , Zahradník Pavol , Foltínová Pavlína
Published: December 2002

A series of new push-pull 2-(ω-phenylalkenyl)benzothiazolium compounds with methyl groups in different positions of the conjugated alkenyl bridge were synthesized by alkylation and condensation. The antimicrobial testing has been carried out and the effect of the alkenyl substituent was investigated by the QSAR Free-Wilson method.
Atom Transfer Radical Polymerization of Styrene and Methyl Methacrylate Induced by RhI(cycloocta-1,5-diene) Complexes
Authors: Opstal Tom , Zedník Jiří , Sedláček Jan , Svoboda Jan , Vohlídal Jiří , Verpoort Francis
Published: December 2002

Rh(I)(diene) complexes, di(μ-docosanoato)bis[(η2:η2-cycloocta-1,5-diene)rhodium(I)] (1) and bis(μ-4-methylphenolato)bis[(η2:η2-cycloocta-1,5-diene)rhodium(I)] (2) are introduced as a new class of catalysts for the atom transfer radical polymerization (ATRP) of vinyl monomers and provide new example of an involvement of rhodium compounds in radical reactions. Single complexes 1 and 2 promote a controlled radical polymerization of methyl methacrylate and styrene affording a medium to good yield of high-molecular-weight polymers with polydispersity index, Mw/Mn, values ranging from 1.45 to 1.65. However, the initiator efficiency found for these reaction systems is rather low, from 0.04 to 0.20. The addition of (Bu)2NH to these polymerization systems has a remarkable positive influence on the catalyst activity and the polymerization control, particularly, in the systems involving complex 1, for which approximately tenfold increase in the initiator efficiency, up to 0.85, and decrease in the polydispersity index, to the value 1.27, has been observed. Dissociation of dinuclear Rh(I)(diene) species to the mononuclear ones is suggested as an important part of the mechanism lying behind the effect of (Bu)2NH additive.
APPLYING INTELLIGENT SOFTWARE AGENTS IN A DISTRIBUTED CHANNEL ALLOCATION SCHEME FOR CELLULAR NETWORKS
Authors: BODANESE ELIANE L. , CUTHBERT LAURIE G.
Published: December 2002

As the demand for mobile services has increased, the need for an efficient allocation of channels is essential to ensure good performance, given the limited spectrum available. Techniques for increasing flexibility in radio resource acquisition are needed to handle the heterogeneity of services and bit rates to be supported in the forthcoming generations of mobile communications. To improve the performance and efficiency of the channel allocation, we propose the use of a particular agent architecture that allows base stations to be more flexible and intelligent, including planning to attempt to balance the load in advance of reactive requests. The simulation results prove that the use of intelligent agents controlling the allocation of channels is feasible and the agent negotiation is an important feature of the system in order to improve perceived quality of service and to improve the load balancing of the traffic.
DISTRIBUTED PROBLEM SOLVING WITHOUT COMMUNICATION — AN EXAMINATION OF COMPUTATIONALLY HARD SATISFIABILITY PROBLEMS
Authors: LIU JIMING , JIN XIAOLONG , HAN JING
Published: December 2002

In this paper, we extend and modify the ERA approach proposed in Ref. 13 to solve Propositional Satisfiability Problems (SATs). The new ERA approach involves a multiagent system where each agent only senses its local environment and applies some self-organizing rules for governing its movements. The environment, which is a two-dimensional cellular environment, records and updates the local values that are computed and affected according to the movements of individual agents. In solving a SAT with the ERA approach, we first divide variables into several groups, and represent each variable group with an agent whose possible positions correspond to the elements in a Cartesian product of variable domains, and then randomly place each agent onto one of its possible positions. Thereafter, the ERA system will keep on dispatching agents to choose their movements until an exact or approximate solution emerges. The experimental results on some benchmark SAT test-sets have shown that the ERA approach can obtain comparable results as well as stable performances for SAT problems. In particular, it can find approximate solutions for SAT problems in only a few steps. The real value of this approach is that it is a distributed asynchronous approach without any centralized control or evaluation, where the agents can cooperate to solve problems without explicit communication.
UNDIRECTED DISCOVERY OF INTERESTING EXCEPTION RULES
Authors: SUZUKI EINOSHIN
Published: December 2002

This paper presents an efficient algorithm for discovering exception rules from a data set without domain-specific information. An exception rule, which is defined as a deviational pattern to a strong rule, exhibits unexpectedness and is sometimes extremely useful. Previous discovery approaches for this type of knowledge can be classified into a directed approach, which obtains exception rules each of which deviates from a set of user-prespecified strong rules, and an undirected approach, which typically discovers a set of rule pairs each of which represents a pair of an exception rule and its corresponding strong rule. It has been pointed out that unexpectedness is often related to interestingness. In this sense, an undirected approach is promising since its discovery outcome is free from human prejudice and thus tends to be highly unexpected. However, this approach is prohibitive due to extra search for strong rules as well as unreliable patterns in the output. In order to circumvent these difficulties we propose a method based on sound pruning and probabilistic estimation. The sound pruning reduces search time to a reasonable amount, and enables exhaustive search for rule pairs. The normal approximations of the multinomial distributions are employed as the method for evaluating reliability of a rule pair. Our method has been validated using two medical data sets under supervision of a physician and two benchmark data sets in the machine learning community.
IMPROVING ENCARTA SEARCH ENGINE PERFORMANCE BY MINING USER LOGS
Authors: LING CHARLES X. , GAO JIANFENG , ZHANG HUAJIE , QIAN WEINING , ZHANG HONGJIANG
Published: December 2002

We propose a data-mining approach that produces generalized query patterns (with generalized keywords) from the raw user logs of the Microsoft Encarta search engine (). Those query patterns can act as cache of the search engine, improving its performance. The cache of the generalized query patterns is more advantageous than the cache of the most frequent user queries since our patterns are generalized, covering more queries and future queries — even those not previously asked. Our method is unique since query patterns discovered reflect the actual dynamic usage and user feedbacks of the search engine, rather than the syntactic linkage structure of web pages (as Google does). Simulation shows that such generalized query patterns improve search engine's overall speed considerably. The generalized query patterns, when viewed with a graphical user interface, are also helpful to web editors, who can easily discover topics in which users are mostly interested.
DIFFUSIVE INSTABILITIES AND CHEMICAL REACTIONS
Authors: BORCKMANS P. , DEWEL G. , DE WIT A. , DULOS E. , BOISSONADE J. , GAUFFRE F. , DE KEPPER P.
Published: December 2002

Diffusive instabilities provide the engine for an ever increasing number of dissipative structures. In this class autocatalytic chemical systems are prone to generate temporal and spatial self-organization phenomena. The development of open spatial reactors and the subsequent discovery in 1989 of the stationary reaction–diffusion patterns predicted by Turing [1952] have triggered a large amount of research. This review aims at a comparison between theoretical predictions and experimental results obtained with various type of reactors in use. The differences arising from the use of reactions exhibiting either bistability of homogeneous steady states or a single one in a CSTR are emphasized.
SOME QUALITATIVE DYNAMICS OF NONLINEAR BOUNDARY CONDITIONS
Authors: RODRÍGUEZ-BERNAL ANÍBAL
Published: December 2002

In this paper we survey some recent results on the behavior of solutions of parabolic equations subjected to nonlinear boundary conditions.

The results range from local existence and regularity of solutions, to global existence, dissipativeness and existence of attractors, and to blow-up in finite time.

Some applications are given to some singular perturbation problems and to pattern formation from boundary flux.
SHORT-WAVE ASYMPTOTICS OF THE INFORMATION ENTROPY OF A CIRCULAR MEMBRANE
Authors: DEHESA J. S. , MARTÍNEZ-FINKELSHTEIN A. , SOROKIN V. N.
Published: December 2002

The spreading of the position and momentum probability distributions for the stable free oscillations of a circular membrane of radius l is analyzed by means of the associated Boltzmann–Shannon information entropies in the correspondence principle limit (n → ∞, m fixed), where the numbers (n, m), n ∈ ℕ and m ∈ ℤ, uniquely characterize an oscillation of this two-dimensional system. This is done by solving the short-wave asymptotics of the physical entropies in the two complementary spaces, which boils down to the calculation of the asymptotic behavior of certain entropic integrals of Bessel functions. It is rigorously shown that the position and momentum entropies behave as 2 ln (l) + ln (4π) - 2 and ln (n) - 2 ln (l) + ln (2π3) when n → ∞, respectively. So the total entropy sum has a logarithmic dependence on n and it does not depend on the membrane radius. The former indicates that the ordering of short-wavelength oscillations is exactly identical for the entropic sum and the single-particle energy. The latter holds for all oscillations of the membrane because of the uniform scaling invariance of the entropy sum.
NONPOTENTIAL EFFECTS IN NONLINEAR DYNAMICS OF MARANGONI CONVECTION
Authors: GOLOVIN A. A. , NEPOMNYASHCHY A. A. , PISMEN L. M.
Published: December 2002

Nonpotential effects in nonlinear evolution of Marangoni convection patterns are investigated analytically and numerically. Three manifestations of nonpotential effects are considered: (i) spatial modulations of hexagonal patterns; (ii) interaction between a short-scale hexagonal pattern and a long-scale slow deformational (Goldstone) mode; (iii) generation of the mean flow by the free-surface deformation in a large-scale Marangoni convection with poorly conducting boundaries. Nonpotential effects are shown to cause various secondary instabilities leading to skewed hexagonal structures, coexisting u- and d-hexagons, oscillating hexagonal patterns, spatially irregular cellular patterns, etc.
AUTOWAVES AND SOLITONS IN A THREE-COMPONENT REACTION–DIFFUSION SYSTEM
Authors: NEKORKIN V. I. , KAZANTSEV V. B.
Published: December 2002

We study the propagation of nonlinear waves in a three-component reaction–diffusion system. The problem of the existence of the stationary pulse-like solutions is reduced to the analysis of homoclinic trajectories of a fourth-order system of nonlinear ODEs. We have obtained the parameter set corresponding to the homoclinic bifurcations that defines the velocity spectra of the traveling pulses. We have shown that the pulses behave like autowaves annihilating in head-on collision and like dissipative solitons crossing each other, reflecting at boundaries. We have provided a qualitative explanation for such a behavior.
STRUCTURE OF A FLAME FRONT PROPAGATING AGAINST THE FLOW NEAR A COLD WALL
Authors: KURDYUMOV VADIM N. , LIÑÁN AMABLE
Published: December 2002

The flashback or propagation of premixed flames against the flow of a reacting mixture, along the low velocity region near a cold wall, is investigated numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the limiting reactant. Flame front propagation and flashback are only possible for values of the near wall velocity gradient below a critical value. The flame propagation becomes chaotic for small values of the Lewis number.
IRREVERSIBLE THERMODYNAMICS OF A SIMPLE ATMOSPHERIC FLOW MODEL
Authors: NICOLIS C.
Published: December 2002

The coexistence of different regimes in a class of atmospheric flow models is analyzed from the standpoint of irreversible thermodynamics. The entropy production, measuring the degree of dissipation within the system is evaluated across the bifurcation point. Some interesting trends are brought out, regarding the relative importance of dissipation in two qualitatively different circulation regimes referred to as zonal and blocked flows. It is shown that in the presence of stochastic disturbances entropy production exhibits critical behavior both in the vicinity of the bifurcation point and in parameter values where the two flow regimes are equally probable.
SELF-SUSTAINED MEAN STREAMING MOTION IN DIAMOND PATTERNS OF A GASEOUS DETONATION
Authors: CLAVIN PAUL
Published: December 2002

A weakly nonlinear analysis of an overdriven detonation is carried out in the neighborhood of the instability threshold. The result leads to a nonlinear integral-differential equation describing the dynamics of the cellular front and exhibiting "diamond" patterns similar to those observed in experiments. An unexpected outcome of the analysis is a self-sustained mean streaming motion associated with the nonlinear dynamics of a weakly unstable detonation front.
PATTERN DYNAMICS OF A MULTI-COMPONENT REACTION–DIFFUSION SYSTEM: DIFFERENTIATION OF REPLICATING SPOTS
Authors: TAKAGI HIROAKI , KANEKO KUNIHIKO
Published: December 2002

Replication and differentiation of spots in a class of reaction–diffusion equations are studied by extending the Gray–Scott model with self-replicating spots so that it includes many chemical species. By examining many possible reaction networks, the behavior of this model is categorized into three types: replication of homogeneous fixed spots, replication of oscillatory spots, and differentiation from "multipotent spots". These multipotent spots either replicate or differentiate into other types of spots with different fixed-point dynamics, and as a result, an inhomogeneous pattern of spots is formed. This differentiation process of spots is analyzed in terms of the loss of chemical diversity and decrease of the local Kolmogorov–Sinai entropy. Initial condition dependence and robustness of a pattern against macroscopic perturbation are also analyzed. Relevance of the results to developmental cell biology is also discussed.