bluuebunny/crossref_metadata_2025 huggingface dataset:
Contact order and ab initio protein structure prediction
Authors: Bonneau Richard , Ruczinski Ingo , Tsai Jerry , Baker David
Published: October 2002

Although much of the motivation for experimental studies of protein folding is to obtain insights for improving protein structure prediction, there has been relatively little connection between experimental protein folding studies and computational structural prediction work in recent years. In the present study, we show that the relationship between protein folding rates and the contact order (CO) of the native structure has implications for ab initio protein structure prediction. Rosetta ab initio folding simulations produce a dearth of high CO structures and an excess of low CO structures, as expected if the computer simulations mimic to some extent the actual folding process. Consistent with this, the majority of failures in ab initio prediction in the CASP4 (critical assessment of structure prediction) experiment involved high CO structures likely to fold much more slowly than the lower CO structures for which reasonable predictions were made. This bias against high CO structures can be partially alleviated by performing large numbers of additional simulations, selecting out the higher CO structures, and eliminating the very low CO structures; this leads to a modest improvement in prediction quality. More significant improvements in predictions for proteins with complex topologies may be possible following significant increases in high–performance computing power, which will be required for thoroughly sampling high CO conformations (high CO proteins can take six orders of magnitude longer to fold than low CO proteins). Importantly for such a strategy, simulations performed for high CO structures converge much less strongly than those for low CO structures, and hence, lack of simulation convergence can indicate the need for improved sampling of high CO conformations. The parallels between Rosetta simulations and folding in vivo may extend to misfolding: The very low CO structures that accumulate in Rosetta simulations consist primarily of local up–down β–sheets that may resemble precursors to amyloid formation.
Docking of protein models
Authors: Tovchigrechko Andrei , Wells Christopher A. , Vakser Ilya A.
Published: October 2002

An adequate description of entire genomes has to include information on the three‐dimensional (3D) structure of proteins. Most of these protein structures will be determined by high‐throughput modeling procedures. Thus, a structure‐based analysis of the network of protein–protein interactions in genomes requires docking methodologies that are capable of dealing with significant structural inaccuracies in the modeled structures of proteins. We present a systematic study of the applicability of our low‐resolution docking method to protein models of different accuracies. A representative nonredundant set of 475 cocrystallized protein–protein complexes was used to build an array of models of each protein in the set. A sophisticated procedure was created to generate the models with RMS deviations of 1, 2, 3, …, 10 Å from the crystal structure. The docking was performed for all the models, and the predictions were compared with the configurations of the original cocrystallized complexes. Statistical analysis showed that the low‐resolution docking can determine the gross structural features of protein–protein interactions for a significant percent of complexes of highly inaccurate protein models. Such predictions may serve as starting points for a more detailed structural analysis, as well as complement experimental and computational data on protein–protein interactions obtained by other techniques.
Folding and stability of the ligand‐binding domain of the glucocorticoid receptor
Authors: McLaughlin Stephen H. , Jackson Sophie E.
Published: October 2002

A complex pathway involving many molecular chaperones has been proposed for the folding, assembly, and maintenance of a high‐affinity ligand‐binding form of steroid receptors in vivo, including the glucocorticoid receptor. To better understand this intricate folding and assembly process, we studied the folding of the ligand‐binding domain of the glucocorticoid receptor in vitro. We found that this domain can be refolded into a compact, highly structured state in vitro in the absence of chaperones. However, the presence of zwitterionic detergent is required to maintain the domain in a soluble form. In this state, the protein is dimeric and has considerable helical structure as shown by far‐UV circular dichroism. Further investigation of the properties of this in vitro refolded state show that it is stable and resistant to denaturation by heat or low concentrations of chemical denaturants. A detailed analysis of the unfolding equilibria using three different structural probes demonstrated that this state unfolds via a highly populated dimeric intermediate state. Together, these data clearly show that the ligand‐binding domain of the glucocorticoid receptor does not require chaperones for folding per se. However, this in vitro refolded state binds the ligand dexamethasone only weakly (Kd = 45 μM) compared to the in vivo assembled receptor (Kd = 3.4 nM). We suggest that the role of Hsp90 and associated chaperones is to bind to, and stabilize, a specific conformational state of the receptor which binds ligand with high affinity.
The Isolated Points of Ĝρ and the w*‐Strongly Exposed Points of Pρ(G)0
Authors: Miao Tianxuan
Published: October 2002

Let G be a separable locally compact group and let Ĝ be its dual space with Fell's topology. It is well known that the set P(G) of continuous positive‐definite functions on G can be identified with the set of positive linear functionals on the group C*‐algebra C*(G). We show that if π is discrete in Ĝ, then there exists a nonzero positive‐definite function ϕπ associated with π such that ϕπ is a w*‐strongly exposed point of P(G)0, where P(G)0={f ∈ P(G):f(e)⩽ 1. Conversely, if some nonzero positive‐definite function ϕπ associated with π is a w*‐strongly exposed point of P(G)0, then π is isolated in Ĝ. Consequently, G is compact if and only if, for every π∈Ĝ, there exists a nonzero positive‐definite function associated with π that is a w*‐strongly exposed point of P(G)0. If, in addition, G is unimodular and π∈Ĝρ, then π is isolated in Ĝρ if and only if some nonzero positive‐definite function associated with π is a w*‐strongly exposed point of Pρ(G)0, where ρ is the left regular representation of G and Ĝρ is the reduced dual space of G. We prove that if Bρ(G) has the Radon–Nikodym property, then the set of isolated points of Ĝρ (so square‐integrable if G is unimodular) is dense in Ĝρ. It is also proved that if G is a separable SIN‐group, then G is amenable if and only if there exists a closed point in Ĝρ. In particular, for a countable discrete non‐amenable group G (for example the free group F2 on two generators), there is no closed point in its reduced dual space Ĝρ.
Xanthine oxidase, but not neutrophils, contributes to activation of cardiac sympathetic afferents during myocardial ischaemia in cats
Authors: Tjen‐A‐Looi Stephanie C. , Fu Liang‐Wu , Longhurst John C.
Published: October 2002

Activation of cardiac sympathetic afferents during myocardial ischaemia causes angina and induces important cardiovascular reflex responses. Reactive oxygen species (ROS) are important chemical stimuli of cardiac afferents during and after ischaemia. Iron‐catalysed Fenton chemistry constitutes one mechanism of production of hydroxyl radicals. Another potential source of these species is xanthine oxidase‐catalysed oxidation of purines. Polymorphonuclear leukocytes (PMNs) also contribute to the production of ROS in some conditions. The present study tested the hypothesis that both xanthine oxidase‐catalysed oxidation of purines and neutrophils provide a source of ROS sufficient to activate cardiac afferents during ischaemia. We recorded single‐unit activity of cardiac afferents innervating the ventricles recorded from the left thoracic sympathetic chain (T1‐5) of anaesthetized cats to identify the afferents' responses to ischaemia. The role of xanthine oxidase in activation of these afferents was determined by infusion of oxypurinol (10 mg kg−1, I.V.), an inhibitor of xanthine oxidase. The importance of neutrophils as a potential source of ROS in the activation of cardiac afferents during ischaemia was assessed by the infusion of a polyclonal antibody (3 mg ml−1 kg−1, I.V.) raised in rabbits immunized with cat PMNs. This antibody decreased the number of circulating PMNs and, to a smaller extent, platelets. Since previous data suggest that platelets release serotonin (5‐HT), which activates cardiac afferents through a serotonin receptor (subtype 3,5‐HT3 receptor) mechanism, before treatment with the antibody in another group, we blocked 5‐HT3 receptors on sensory nerve endings with tropisetron (300 μg kg−1, I.V.). We observed that oxypurinol significantly decreased the activity of cardiac afferents during myocardial ischaemia from 1.5 ± 0.4 to 0.8 ± 0.4 impulses s−1. Similarly, the polyclonal antibody significantly reduced the discharge frequency of ischaemically sensitive cardiac afferents from 2.5 ± 0.7 to 1.1 ± 0.4 impulses s−1. However, pre‐blockade of 5‐HT3 receptors eliminated the influence of the antibody on discharge activity of the afferents during ischaemia. This study demonstrates that ROS generated from the oxidation of purines contribute to the stimulation of ischaemically sensitive cardiac sympathetic afferents, whereas PMNs do not play a major role in this process.
Excitability changes in human peripheral nerve axons in a paradigm mimicking paired‐pulse transcranial magnetic stimulation
Authors: Chan Jane H. L. , Lin Cindy S.‐Y. , Pierrot‐Deseilligny Emmanuel , Burke David
Published: October 2002

A peripheral nerve model was developed to determine whether changes in axonal excitability could affect the findings in studies of cortical processes using paired‐pulse transcranial magnetic stimulation (TMS). The recovery of axonal excitability from a conditioning stimulus smaller than the test stimulus was qualitatively similar to that with suprathreshold conditioning stimuli. There was an initial decrease in excitability, equivalent to refractoriness at conditioning‐test intervals < 4 ms, an increase in excitability, equivalent to supernormality, at intervals of 5–20 ms and a second phase of decreased excitability, equivalent to late subnormality at intervals > 30 ms. H reflex studies using conditioning stimuli below threshold for the H reflex established that these excitability changes could be faithfully translated across an excitatory synapse. Changing membrane potential by injecting polarising current altered axonal excitability in a predictable way, and produced results similar to those reported for many disease states using paired‐pulse TMS. Specifically, axonal hyperpolarisation produced a smaller decrease in excitability followed by a greater increase in excitability. This study supports the view that changes in excitability of the stimulated axons should be considered before synaptic mechanisms are invoked in the interpretation of findings from paired‐pulse TMS studies.
Carbachol triggers RyR‐dependent Ca2+ release via activation of IP3 receptors in isolated rat gastric myocytes
Authors: White Carl , McGeown J. Graham
Published: October 2002

Possible interactions between different intracellular Ca2+ release channels were studied in isolated rat gastric myocytes using agonist‐evoked Ca2+ signals. Spontaneous, local Ca2+ transients were observed in fluo‐4‐loaded cells with linescan confocal imaging. These were blocked by ryanodine (100 μm) but not by the inositol 1,4,5‐trisphosphate receptor (IP3R) blocker, 2‐aminoethoxydiphenyl borate (100 μm), identifying them as Ca2+ sparks. Caffeine (10 mm) and carbachol (10 μm) initiated Ca2+ release at sites which co‐localized with each other and with any Ca2+ spark sites. In fura‐2‐loaded cells extracellular 2‐aminoethoxydiphenyl borate and intracellular heparin (5 mg ml−1) both inhibited the global cytoplasmic [Ca2+] transient evoked by carbachol, confirming that it was IP3R‐dependent. 2‐Aminoethoxydiphenyl borate and heparin also increased the response to caffeine. This probably reflected an increased Ca2+ store content since 2‐aminoethoxydiphenyl borate more than doubled the amplitude of transients evoked by ionomycin. Ryanodine completely abolished carbachol and caffeine responses but only reduced ionomycin transients by 30 %, suggesting that blockade of carbachol transients by ryanodine was not simply due to store depletion. Double labelling of IP3Rs and RyRs demonstrated extensive overlap in their distribution. These results suggest that carbachol stimulates Ca2+ release through co‐operation between IP3Rs and RyRs, and implicate IP3Rs in the regulation of Ca2+ store content.
Prenatal hypoxia impairs circadian synchronisation and response of the biological clock to light in adult rats
Authors: Joseph Vincent , Mamet Julie , Lee Fuchun , Dalmaz Yvette , Van Reeth Olivier
Published: October 2002

The aim of this study was to test the hypothesis that prenatal hypoxia in rats might lead to consistent changes in the entrainment of the circadian clock by light. Pregnant female rats were placed in a chamber provided with hypoxic gas (10 % O2‐90 % N2) at gestational day 5 and returned to normoxia before delivery. Once adult, rats born to hypoxic mothers had significant alterations in their circadian rhythm of locomotor activity (recorded in freely accessible running wheels). Under a regular 12/12 light/dark (LD) cycle, they showed a phase advance of their rhythm of activity (mean phase advance of 87 min) and were less active than control rats. After an abrupt 6 h phase delay in the LD cycle, rats from the prenatal hypoxic group (PNH) took significantly more time to resynchronise to the new LD cycle compared to controls (+53 %; 6.0 ± 1.5 vs. 9.2 ± 0.5 days respectively). Under constant darkness, PNH and control rats had a similar period of activity (24.27 ± 0.20 vs. 24.40 ± 0.13) but the response of PNH rats to a light pulse in the early subjective night was less marked than that of control rats (101 ± 9 vs. 158 ± 13 min). When submitted to acute restraint stress, PNH rats had a prolonged secretion of corticosterone compared to controls. These results indicate that prenatal hypoxia is a factor that has long lasting consequences for the functional output of the biological clock and the hormonal response to stress.
A New Thermal-Fatigue Life Prediction Model for Wafer Level Chip Scale Package (WLCSP) Solder Joints
Authors: Lau John H. , Pan Stephen H. , Chang Chris
Published: October 2002

A new empirical equation for predicting the thermal-fatigue life of wafer level chip scale package (WLCSP) solder joints on printed circuit board (PCB) is presented. The solder joints are subjected to thermal cycling and their crack lengths at different thermal cycles are measured. Also, the average strain energy density around the crack tip of different crack lengths in the corner solder joint is determined by a time-dependent nonlinear fracture mechanics with finite element method. The solder is assumed to be a temperature-dependent elastic-plastic and a time-dependent creep material.
An Endoscopic and Robotic Tooth-like Compliance and Roughness Tactile Sensor
Authors: Dargahi J.
Published: October 2002

This paper reports on design, fabrication and testing of a prototype Polyvinylidene Fluoride (PVDF) tactile sensor for endoscopic and robotic applications. The sensor can measure both compliance and surface roughness. It consists of rigid and compliant elements. A relative deformation between adjacent parts of the contact object is used to measure the compliance, and the deformation of the compliant element of the sensor is used to measure the profile of a rough surface. The sensor in miniaturized form can be integrated with both endoscopic graspers and robotic end effectors. The theoretical analysis of the sensor is made and compared with experimental values. The advantages and limitations of the sensor are also discussed.
Reliability of Anisotropically Conductive Adhesive Joints on a Flip-Chip/FR-4 Substrate
Authors: Liu Johan , Lai Zonghe
Published: October 2002

A reliability study on anisotropically conductive adhesive joints on a Flip-Chip/FR-4 assembly has been carried out. In the study, nine types of anisotropic conductive adhesive (ACA) and one nonconductive film (NCF) were used. In total, nearly one-thousand single joints were subjected to reliability tests in terms of temperature cycling between −40°C and 125°C with a dwell time of 15 minutes and a ramp rate of 110°C/min. The test chip used for this extensive reliability test had a pitch of 100 μm. Therefore, this work was particularly focused on evaluation on the reliability of ultra fine pitch flip-chip interconnections using anisotropically conductive adhesives on a low-cost substrate. The reliability was characterized by single contact resistance measurement using the four-probe method during temperature cycling testing up to 3000 cycles. The Mean Time To Failure (MTTF) (defined as 50% failure of all tested joints) are 650, 2500, and 3500 cycles when the failure definition is defined as 20% increase, larger than 50 mΩ and larger than 100 mΩ, respectively, using the in-situ electrical resistance measurement technique. Using the discontinuous (manual) measurement at room temperature by taking out the sample from the cycling chamber, the MTTF for the same joint system is around 2500 cycles in the case that the failure criteria is defined as 20% of the resistance increase, far better than the results from the in-situ measurement. The results show clearly that in optimized conditions, high reliability flip-chip anisotropically conductive adhesive joints on low-cost substrate can be achieved.
Design of Circular Cross-Section Corner-Filleted Flexure Hinges for Three-Dimensional Compliant Mechanisms
Authors: Lobontiu Nicolae , Paine Jeffrey S. N.
Published: October 2002

The paper introduces the circular cross-section corner-filleted flexure hinges as connectors in three-dimensional compliant mechanism applications. Compliance factors are derived analytically for bending, axial loading and torsion. A circular cross-section corner-filleted flexure hinge belongs to a domain delimited by the cylinder (no fillet) and the right circular cross-section flexure hinge (maximum fillet radius). The analytical model predictions are confirmed by finite element simulation and experimental measurements. The circular cross-section corner-filleted flexure hinges are characterized in terms of their compliance, precision of rotation and stress levels.
Kinematics of the Full-Toroidal Traction Drive Variator
Authors: Raghavan Madhusudan
Published: October 2002

We present a geometric derivation of the kinematics of the steering action and the roller displacement in a full-toroidal continuously variable traction drive variator. In particular, expressions relating the inclination of the roller to its displacement for designs incorporating a caster angle are derived. These results are useful in the design of the control system for the variator.
Bubble Shape in Non-Newtonian Fluids
Authors: De Kee and D. , Chan Man Fong C. F. , Yao J.
Published: October 2002

The study of the behavior of bubbles in complex fluids is of industrial as well as of academic importance. Bubble velocity-volume relations, bubble shapes, as well as viscous, elastic, and surfactant effects play a role in bubble dynamics. In this note we extend the analysis of Richardson to a non-Newtonian fluid.
Parametric Design and Reliability Analysis of Wire Interconnect Technology Wafer Level Packaging
Authors: Lin Y. T. , Peng C. T. , Chiang K. N.
Published: October 2002

The demands for electronic packages with lower profile, lighter weight, and higher input/output (I/O) density have led to rapid expansion in flip chip, chip scale package (CSP) and wafer level packaging (WLP) technologies. The urgent demand high I/O density and good reliability characteristics have led to the evolution of ultra high-density non-solder interconnection, such as wire interconnect technology (WIT). New technology, which uses copper posts to replace the solder bumps as interconnections, has improved reliability. Moreover, this type of wafer level package produces higher I/O density, as well as ultra fine pitch. This research focuses on the reliability analysis, material selection and structural design of WIT packaging. This research employs finite element method (FEM) to analyze the physical behavior of packaging structures under thermal cycling conditions to compare the reliability characteristics of conventional wafer level and WIT packages. Parametric studies of specific parameters will be performed, and the plastic and temperature-dependent material properties will be applied to all models.
Alternative Causality Assignment Procedures in Bond Graph for Mechanical Systems
Authors: Marquis-Favre Wilfrid , Scavarda Serge
Published: October 2002

This paper proposes to extend the set of causality assignment procedures. The proposed alternative procedures are mainly inspired by formulations developed in the mechanical domain. They enable Lagrange equations, Hamilton equations, and Boltzmann-Hamel equations to be obtained, as well as formulations with the Lagrange multipliers. In the context of system modeling a varied set of mechanical oriented equations are available in a systematic way from the bond graph representation and the proposed corresponding procedures provide an algorithmic frame for programming these mathematical formulations. The graphical features of the bond graph tool and the causality stroke concept enable formulations to be methodically obtained, formulations that can otherwise be very awkward to express. Also these procedures emphasize certain interesting properties of the bond graph tool e.g.: there is a clear distinction between the energy topology of a system and its dynamic equations; it also enables graphic structural analyses to be undertaken; and finally it can play a pedagogical role in engineering education.
Stress integration procedures for inelastic material models within the Finite Element Method
Authors: Kojic´ Milosˇ
Published: October 2002

A review of numerical procedures for stress calculation in the inelastic finite element analysis is presented. The role of stress integration within a time (load) step in the incremental-iterative scheme for the displacements based FE formulation is first given briefly. Then, the basic relations of the explicit algorithms, as the first ones developed in the 70s, are presented. The shortcomings of these algorithms are pointed out. The implicit procedures are presented in some detail, with the emphasis on a general return mapping procedure and the governing parameter method (GPM). Derivation of the consistent tangent moduli represents an important task in the inelastic FE analysis because the overall equilibrium iteration rate depends on these moduli. The basic concepts of this derivation are presented. An important field, very challenging in today’s stage of design and technology, is the large strain deformation of material. A review of the approaches in the large strain domain that includes the rate and the total formulations is given in some detail. Special attention is devoted to the multiplicative decomposition of deformation gradient concept, since that concept is generally favored today. Some unresolved issues, such as the use of the stress and strain measures, are discussed briefly. A number of selected numerical examples illustrate the main topics in the stress integration task, as well as the applications of the stress integration algorithms to various material models. Some concluding remarks and an outline of further research topics are given at the end of the paper. This review article includes 205 references.
A Three-dimensional Finite Element Model for Arterial Clamping
Authors: Gasser Thomas C. , Schulze-Bauer Christian A. J. , Holzapfel Gerhard A.
Published: October 2002

Clamp induced injuries of the arterial wall may determine the outcome of surgical procedures. Thus, it is important to investigate the underlying mechanical effects. We present a three-dimensional finite element model, which allows the study of the mechanical response of an artery–treated as a two-layer tube-during arterial clamping. The important residual stresses, which are associated with the load-free configuration of the artery, are also considered. In particular, the finite element analysis of the deformation process of a clamped artery and the associated stress distribution is presented. Within the clamping area a zone of axial tensile peak-stresses was identified, which (may) cause intimal and medial injury. This is an additional injury mechanism, which clearly differs from the commonly assumed wall damage occurring due to compression between the jaws of the clamp. The proposed numerical model provides essential insights into the mechanics of the clamping procedure and the associated injury mechanisms. It allows detailed parameter studies on a virtual clamped artery, which can not be performed with other methodologies. This approach has the potential to identify the most appropriate clamps for certain types of arteries and to guide optimal clamp design.
Influence of Tooth Profile Modification on Helical Gear Durability
Authors: Wagaj Parag , Kahraman Ahmet
Published: October 2002

A nonlinear finite element contact mechanics model of a helical gear pair was used to study the effect of intentional tooth profile modifications on durability of helical gear pairs. Both two-dimensional (2D) and three-dimensional (3D) modifications were considered. A detailed parametric study was performed to quantify the changes in the contact and bending stresses as a function of tooth profile modification parameters as compared to an unmodified gear pair baseline. The combined influence of modification parameters and torque transmitted on the maximum stresses is described. Results indicate that both bending and contact stresses of a helical gear pair are increased significantly when 2D modifications are applied, potentially causing an underestimation of the actual stress values when the modifications are not included in stress calculations. When properly selected, 3D modifications cause significantly less stress increases.
Designing Two-Revolute Manipulators for Prescribed Feasible Workspace Regions
Authors: Ceccarelli Marco
Published: October 2002

In this paper the concept of feasible workspace regions is introduced and used to design two-revolute manipulators for a workspace prescribed through arbitrarily given workspace points. A design formulation has been proposed to derive an analytical procedure for defining the feasible workspace regions as regions within which feasible solutions for the manipulator design can be obtained. The feasible workspace regions have been geometrically characterized and specific topologies have been shown through illustrative examples. The design algorithm has been completed with a closed form formulation for geometrical parameters and it gives the opportunity to discuss the number and characteristics of multiple solutions.
Adaptive Continuously Variable Compression Braking Control for Heavy-Duty Vehicles
Authors: Druzhinina Maria , Stefanopoulou Anna , Moklegaard Lasse
Published: October 2002

Modern heavy-duty vehicles are equipped with compression braking mechanisms that augment their braking capability and reduce wear of the conventional friction brakes. In this paper we consider a heavy-duty vehicle equipped with a continuously variable compression braking mechanism. The variability of the compression braking torque is achieved through controlling a secondary opening of the exhaust valve of the vehicle’s turbocharged diesel engine using a variable valve timing actuator. A model reference adaptive controller is designed to ensure good vehicle speed tracking performance in brake-by-wire driving scenarios in presence of large payload and road grade variations. The adaptive controller is integrated with backstepping procedure to account for compression braking actuator dynamics, with observers for various unmeasured quantities and with compensation schemes for actuator saturation. In addition to speed tracking, the vehicle mass and road grade are simultaneously estimated if persistence of excitation-type conditions hold. The final version of the controller is successfully evaluated on a high order crank angle model of a vehicle with a six-cylinder engine.
Efficiency of Advanced Ground Transportation Technologies
Authors: Kreith Frank , West Ron E. , Isler Beth E.
Published: October 2002

This paper presents thermodynamic analyses of ten different scenarios for using natural gas to power motor vehicles. Specifically, it presents a comparison between different types of automotive vehicles using fuels made from natural gas feedstock. In comparing the various fuel-vehicle options, a complete well-to-wheel fuel cycle is considered. This approach starts with the well at which the feedstock is first extracted from the ground and ends with the power finally delivered to the wheels of the vehicle. This all-inclusive comparison is essential in order to accurately and fairly compare the transportation options. This study indicates that at the present time hybrid-electric vehicles, particularly those using diesel components, can achieve the highest efficiency among available technologies using natural gas as the primary energy source. Hydrogen spark ignition, all-electric battery-powered, and methanol fuel cell vehicles rank lowest in well-to-wheel efficiency because of their poor fuel production efficiencies.
Accelerated Life Testing (ALT) in Microelectronics and Photonics: Its Role, Attributes, Challenges, Pitfalls, and Interaction With Qualification Tests1
Authors: Suhir E.
Published: October 2002

Accelerated life tests (ALTs) are aimed at revealing and understanding the physics of the expected or occurred failures, i.e., are able to detect the possible failure modes and mechanisms. Another objective of the ALTs is to accumulate representative failure statistics. Adequately designed, carefully conducted, and properly interpreted ALTs provide a consistent basis for obtaining the ultimate information of the reliability of a product—the predicted probability of failure after the given time of service in the given conditions. Such tests can dramatically facilitate the solution to the cost effectiveness and time-to-market problems. ALTs should play an important role in the evaluation, prediction and assurance of the reliability of microelectronics and optoelectronics devices and systems. In the majority of cases, ALTs should be conducted in addition to the qualification tests required by the existing standards. There might also be situations when ALTs can be (and, probably, should be) used as an effective substitution for such standards, or, at least, as the basis for the improvement of the existing qualification specifications. We describe different types (categories) of accelerated tests, with an emphasis on the role that ALTs should play in the development, design, qualification, and manufacturing of microelectronics and photonics products. We discuss the challenges associated with the implementation and use of the ALTs, potential pitfalls (primarily those associated with possible “shifts” in the mechanisms and modes of failure), and the interaction of the ALTs with other types of accelerated tests. The role of the nondestructive evaluations is also briefly outlined. The case of a laser welded optoelectronic package assembly is used to illustrate some concepts addressed.  “All life is an experiment. The more experiments you make the better”  Ralph Waldo Emerson  “In the long run we are all dead”  John Maynard Keynes
A Cavitation Erosion Model for Ductile Materials
Authors: Berchiche N. , Franc J. P. , Michel J. M.
Published: October 2002

An analytical model is proposed for the prediction of cavitation erosion of ductile materials. It is based upon a physical analysis of the work-hardening process due to the successive bubble collapses. The material is characterized by its classical stress-strain relationship and its metallurgical behavior is analyzed from microhardness measurements on cross sections of eroded samples. The flow aggressiveness is determined from pitting tests, using the material properties to go back to the impact loads. The histogram of impact loads is applied numerically a large number of times on the material surface and the evolution of the mass loss with the exposure time is computed. The approach is supported by experimental tests.
Influence of Connection Geometry and SVC-IVC Flow Rate Ratio on Flow Structures within the Total Cavopulmonary Connection: A Numerical Study
Authors: Khunatorn Yottana , Mahalingam Shankar , DeGroff Curt G. , Shandas Robin
Published: October 2002

The total cavopulmonary connection (TCPC) is a palliative cardiothoracic surgical procedure used in patients with one functioning ventricle that excludes the heart from the systemic venous to pulmonary artery pathway. Blood in the superior and inferior vena cavae (SVC, IVC) is diverted directly to the pulmonary arteries. Since only one ventricle is left in the circulation, minimizing pressure drop by optimizing connection geometry becomes crucial. Although there have been numerical and in–vitro studies documenting the effect of connection geometry on overall pressure drop, there is little published data examining the effect of SVC-IVC flow rate ratio on detailed fluid mechanical structures within the various connection geometries. We present here results from a numerical study of the TCPC connection, configured with various connections and SVC:IVC flow ratios. The role of major flow parameters: shear stress, secondary flow, recirculation regions, flow stagnation regions, and flow separation, was examined. Results show a complex interplay among connection geometry, flow rate ratio and the types and effects of the various flow parameters described above. Significant changes in flow structures affected local distribution of pressure, which in turn changed overall pressure drop. Likewise, changes in local flow structure also produced changes in maximum shear stress values; this may have consequences for platelet activation and thrombus formation in the clinical situation. This study sheds light on the local flow structures created by the various connections and flow configurations and as such, provides an additional step toward understanding the detailed fluid mechanical behavior of the more complex physiological configurations seen clinically.
Self-sealing, Large Bore Arterial Punctures: A Counterintuitive New
Phenomenon
Authors: Roeder Blayne A. , Babbs Charles F. , Schoenlein William E. , Kokini Klod , Sadeghi Farshid
Published: October 2002

The human femoral artery can bleed dangerously following the removal of a catheter during cardiac catheterization. In this study, a modified technique of needle insertion, simply inserting the needle bevel-down instead of the standard bevel-up approach, was tested as a means to reduce bleeding after catheter removal. Large bore needle punctures were made in surgically exposed arteries of anesthetized pigs using either a standard technique (45 degree approach, bevel up) or a modified technique (25 degree approach, bevel down). For half the punctures, topical phenylephrine solution (1 mg/ml) was applied to the adventitia of the artery to cause constriction. Median bleeding rates were reduced from 81 to less than 1 ml/min/100 mmHg intraluminal pressure by the modified technique with application of phenylephrine. In most cases zero bleeding, that is self-sealing, of the arteries occurred. It is postulated that a flap-valve of tissue created by the modified technique produced this self-sealing behavior. Sophisticated modeling studies are needed to fully understand this new phenomenon.
Mucosal Folding in Biologic Vessels
Authors: Hrousis Constantine A. , Wiggs Barry J. R. , Drazen Jeffrey M. , Parks David M. , Kamm Roger D.
Published: October 2002

A two-layer model is used to simulate the mechanical behavior of an airway or other biological vessel under external compressive stress or smooth muscle constriction sufficient to cause longitudinal mucosal buckling. Analytic and finite element numerical methods are used to examine the onset of buckling. Post-buckling solutions are obtained by finite element analysis, then verified with large-scale physical model experiments. The two-layer model provides insight into how the stiffness of a vessel wall changes due to changes in the geometry and intrinsic material stiffnesses of the wall components. Specifically, it predicts that the number of mucosal folds in the buckled state is diminished most by increased thickness of the inner collagen-rich layer, and relatively little by increased thickness of the outer submucosal layer. An increase in the ratio of the inner to outer material stiffnesses causes an intermediate reduction in the number of folds. Results are cast in a simple form that can easily be used to predict buckling in a variety of vessels. The model quantitatively confirms that an increase in the thickness of the inner layer leads to a reduction in the number of mucosal folds, and further, that this can lead to increased vessel collapse at high levels of smooth muscle constriction.
A Baseline and Vision of Ultrasonic Guided Wave Inspection Potential
Authors: Rose Joseph L.
Published: October 2002

Ultrasonic guided wave inspection is expanding rapidly to many different areas of manufacturing and in-service inspection. The purpose of this paper is to provide a vision of ultrasonic guided wave inspection potential as we move forward into the new millennium. An increased understanding of the basic physics and wave mechanics associated with guided wave inspection has led to an increase in practical nondestructive evaluation and inspection problems. Some fundamental concepts and a number of different applications that are currently being considered will be presented in the paper along with a brief description of the sensor and software technology that will make ultrasonic guided wave inspection commonplace in the next century.
Multi-axial Spine Biomechanical Testing System with Speckle
Displacement Instrumentation
Authors: Chung S. M. , Teoh S. H. , Tsai K. T. , Sin K. K.
Published: October 2002

This paper reports on the design and development of a multi-axis (up to 6 axes) mechanical tester for spinal research and testing. The developed spine tester allowed true motion to be simulated on a specimen in pure or combined modes. To demonstrate the capability of the new tester, flexural stiffness properties of sheep lumbar motion segments were evaluated together with a non-contact speckle displacement measurement system. The flexural stiffness of the specimens was measured and compared under constrained and non-constrained testing conditions; with relieving of shear forces (non-constrained), it was found that the specimen behaved in a ‘stiffer’ manner.
Increased thickness of buried oxide layer of silicon on insulator in separation by implantation of oxygen with water plasma
Authors: Chen Jing , Chen Meng , Dong Yemin , Wang Xiang , Zheng Zhihong , Wang Xi
Published: October 2002

An implanter without an ion mass analyzer has been used to successfully fabricate silicon on insulator (SOI) materials by H2O+, HO+, and O+ ion implantation using water plasma. Based on the consideration that the masses of those three ions are very close, this fabrication makes it possible to form a single buried oxide (BOX) layer by choosing the appropriate implantation energy and dose. Cross-sectional transmission electron microscopy results indicated that the BOX thickness of the SOI materials fabricated using a water plasma approach is increased more than 50% over that made by the conventional separation by implantation of oxygen (SIMOX) process. Secondary ion mass spectroscopy depth profile analysis on the as-implanted wafers showed that there are two hydrogen enrichment peaks around both sides of the projected range Rp of oxygen, which correspond to the two interfaces of the BOX layer of the annealed samples. The heavily damaged region with hydrogen-induced defects appears to be the adsorption center for the outside oxygen to diffuse into the silicon during the high-temperature annealing process, and consequently, broaden the thickness of the BOX layer. The finding in the present work may provide a possible solution to reduce the cost of the conventional SIMOX–SOI wafers while maintaining a desirable BOX thickness.
Getter requirements for a cathode ray tube with a diamond coated field emitter electron source
Authors: Nemanič Vincenc , Žumer Marko , Zajec Bojan , Tyler Talmage
Published: October 2002

A single diamond coated field emitter (FE) tip could be used as a replacement for the thermionic cathode in small electron beam devices offering better optoelectronic performance. The most important parameter limiting the use of field emitting sources is their short lifetime, which is closely related to the pressure level within the pinched off device. Aside from the initial evacuation of the tube and bakeout, getter selection and the activation procedure would seem to play the crucial role. In the present study, the pressure of miniature cathode ray tubes (CRTs) was measured by a spinning rotor gauge (SRG) after the initial evacuation and bakeout procedures, again after activation of the getters, and finally during operation under typical conditions. After the evaporation of barium getters by the prescribed procedures, the pressure did not drop, but increased slowly. The accumulated gas was shown to be methane. In CRTs with a thermionic electron source, getter pumping action could be triggered by switching on the cathode heater, which efficiently cracked the generated methane. In CRTs with a diamond coated FE tip, there was no way to decrease the residual methane pressure to the desired (i.e., safe) level. The emitters, previously approved and characterized in ultrahigh vacuum, were thus irreversibly damaged ab initio. Ba getters consequently cannot be applied in devices applying diamond coated FE tips just because of geometrical constraints, as usually stated, but mainly because of methane generation. In CRTs with nonevaporable getters, a much lower pressure increase was registered by the SRG during several days. This means that they could maintain the residual atmosphere at the level that may provide a means for long-term operation of devices with diamond coated FE electron sources.
Process and realization of a three-dimensional gold electroplated antenna on a flexible epoxy film for wireless micromotion system
Authors: Basset Philippe , Kaiser Andreas , Collard Dominique , Buchaillot Lionel
Published: October 2002

The process and realization of a light and low resistive antenna for wireless communications by inductive coupling at 13.56 MHz is presented. The antenna is realized on an insulated substrate made of SU-8 resist in order to prevent the losses due to eddy currents from occurring and to strongly decrease its weight. The conductor is obtained by electroplating 24 μm of gold in a mold of AZ-4562 resist. A Q factor of 29 has been obtained with a maximum of 37 at 19 MHz, for antenna dimensions of 1.5×1.5 cm2. This antenna is the key component for a wireless power supplied microrobot.
Room temperature oscillation of self-organized In0.2Ga0.8As/GaAs quantum wire lasers grown on (221)A GaAs substrates by molecular beam epitaxy
Authors: Kanamori H. , Hyodo K. , Ohno Y. , Shimomura S. , Hiyamizu S. , Okamoto Y.
Published: October 2002

Self-organized In0.2Ga0.8As/GaAs quantum wires (QWRs) grown on a (221)A GaAs substrate by molecular beam epitaxy (MBE), which has the narrowest linewidth of photoluminescence peak among self-organized QWRs reported so far, have been applied to an active region of a graded-index separate confinement heterostructure laser structure. Since Si is not a good n-type dopant for (221)A GaAs in the MBE growth, a Sn-doped GaAs/AlAs superlattice layer was used for an n-type cladding layer. The laser operated at room temperature at an emission wavelength of 894 nm under pulsed current conditions with a threshold current of 182 mA (the threshold current density of 2.8 kA/cm2). This result indicates that (221)A InGaAs/GaAs QWRs have sufficient quality for laser devices.
Selective and deep plasma etching of SiO2: Comparison between different fluorocarbon gases (CF4, C2F6, CHF3) mixed with CH4 or H2 and influence of the residence time
Authors: Gaboriau F. , Cartry G. , Peignon M-C. , Cardinaud Ch.
Published: October 2002

SiO 2 is a well suited material for integrated optic applications and is also attractive for microelectromechanical system and micro-optical electromechanical system fabrication. Such optical components require deep oxide etching (several microns) and subsequent high selectivity with respect to the mask. In this article, we describe the influence of various process parameters (gas mixture, pressure, plasma power, and residence time) on the selective etching of SiO2 with respect to Si in inductively coupled plasma (ICP) fluorocarbon with the aim of finding the best compromise between high selectivity and high oxide etch rate. Oxide etch rate is improved by decreasing pressure or increasing source power within the acceptable process windows, respectively, 3–20 mTorr and 1000–2000 W, but the gain in selectivity is low (×1.5). Adding methane rather than more commonly usual hydrogen resulted in higher selectivity without significant decrease in the oxide etch rate. A relatively good correlation is found between the selectivity and the (C+H)/F ratio of the precursor molecule. However, we show that varying the hydrofluorocarbon mixture does not allow us to improve both oxide etch rate and selectivity. In this regard, the residence time is the most significant parameter: choosing the appropriate amount of methane mixed with C2F6, and decreasing tR leads to an improvement in both the selectivity (×7) and the oxide etch rate (×1.5). Finally, the influence of these parameters on pattern transfer is investigated.
Photoresist selectivity mechanism in SiO2 etching by inductively coupled plasma using fluorocarbon gases
Authors: Imai Shin-ichi , Motomura Hideki , Tachibana Kunihide
Published: October 2002

The generation of large molecular species in an inductively coupled plasma using fluorocarbon gases was investigated to elucidate the selective etching mechanism of SiO2 to photoresist. In this study, the source gases C2F6, C4F8, and C5F8 were used to provide a range of fluorine-to-carbon content ratios. It was found that larger quantities and a wider variety of large-mass species are generated in C5F8 plasma than in C2F6 and C4F8 plasmas. Our results also revealed that the gas residence time was an important parameter for controlling the radical composition of the plasma. With increased residence time, the ratio of species with larger masses than the parent molecule to the sum of all product species increased in the C2F6 plasma, whereas this ratio decreased in the C4F8 and C5F8 plasmas. The ratio of larger mass species correlates apparently with the selectivity of SiO2 to photoresist etch rates. However, in any explanation of physical mechanisms, the redeposition of etching byproducts should be taken into account as well as the dependence of polymer deposition tendency on substrate materials under biased etching conditions.