bluuebunny/crossref_metadata_2025 huggingface dataset:
Sustained contractions produced by plateau‐like behaviour in human motoneurones
Authors: Collins D. F. , Burke D. , Gandevia S. C.
Published: July 2002

Electrical stimulation over human muscle can generate force directly by activation of motor axons and indirectly by ‘reflex’ recruitment of spinal motoneurones. These experiments were designed to define the properties of the centrally generated ‘reflex’ force, including the optimal stimulus conditions for producing it in tibialis anterior (TA) and triceps surae (TS), and its interaction with volition. Subjects (n= 21) were seated with their foot strapped to an isometric myograph. Surface EMG was recorded from TS and TA. High‐frequency electrical stimulation (100 Hz) of TS and TA with wide pulse widths (1 ms) was most effective to evoke the sustained centrally generated forces. The maximal force evoked by this mechanism during stimulation of TA for 40 s was ∼42 % of that produced by a maximal voluntary contraction. For both muscle groups, ramp increases and decreases in stimulus frequency (from ∼4 to 100 Hz and back to 4 Hz over 6 s) resulted in marked hysteresis in the force‐frequency plot. After a single ‘burst’ of 100 Hz stimulation during prolonged stimulation at 25 Hz, force remained elevated. Repeated bursts often generated progressively larger force increments. These behaviours were abolished by an anaesthetic nerve block proximal to the stimulation site, confirming the central origin for the ‘extra’ force. After a brief voluntary contraction was performed during 25 Hz stimulation, force remained elevated, and this showed some gradation with voluntary contraction amplitude. Sometimes voluntary contractions alone initiated the sustained central motor output. Involuntary contractions often persisted for many seconds after electrical stimulation ceased. These were not terminated by brief inhibitory inputs to the active motoneurones but could be stopped by the voluntary command to ‘relax completely’. Overall, these centrally generated contractions are consistent with activation of plateau potentials in motoneurones innervating the ankle dorsiflexors and plantarflexors. Large forces can be produced through this mechanism. The interaction with volitional drives suggests that plateau behaviour may contribute significantly to the normal output of human motoneurones.
Spike‐independent release of ATP from Xenopus spinal neurons evoked by activation of glutamate receptors
Authors: Brown Paul , Dale Nicholas
Published: July 2002

As the release of ATP from neurons has only been directly studied in a few cases, we have used patch sniffing to examine ATP release from Xenopus spinal neurons. ATP release was detected following intracellular current injection to evoke spikes. However, spiking was not essential as both glutamate and NMDA could evoke release of ATP in the presence of TTX. Neither acetylcholine nor high K+ was effective at inducing ATP release in the presence of TTX. Although Cd2+ blocked glutamate‐evoked release of ATP suggesting a dependence on Ca2+ entry, neither ω‐conotoxin‐GVIA nor nifedipine prevented ATP release. N‐type and L‐type channels are thus not essential for glutamate‐evoked ATP release. That glutamate receptors can elicit release in the absence of spiking suggests a close physical relationship between these receptors, the Ca2+ channels and release sites. As the dependence of ATP release on the influx of Ca2+ through Ca2+ channel subtypes differs from that of synaptic transmitter release, ATP may be released from sites that are distinct from those of the principal transmitter. In addition to its role as a fast transmitter, ATP may thus be released as a consequence of the activation of excitatory glutamatergic synapses and act to signal information about activity patterns in the nervous system.
Cortically evoked neural volleys to the human hand are increased during ischaemic block of the forearm
Authors: McNulty P. A. , Macefield V. G. , Taylor J. L. , Hallett M.
Published: July 2002

Reorganisation of the motor cortex may occur after limb amputation or spinal cord injury. In humans, transcranial magnetic stimulation (TMS) shows expansion of motor cortical representations of muscles proximal to the injury. Similarly, ischaemic block of the hand can increase acutely the representation of the biceps muscle, measured by increased biceps motor potentials evoked by TMS. It is thought that this increase occurs at the expense of the cortical representation of the paralysed and deafferented hand muscles but this has never been investigated. To study what changes occur in the cortical representation of the hand muscles during ischaemic block, a tungsten microelectrode was inserted into the ulnar or median nerve above the elbow and the size of the neural potential elicited by TMS in fascicles supplying the hand was measured in seven subjects. Prior to ischaemia, TMS evoked EMG responses in the intrinsic hand muscles. In the nerve, a brief motor potential preceded the response in the muscle and was followed by a contraction‐induced sensory potential. During 40 min of ischaemia produced by a blood pressure cuff inflated around the forearm to 210 mmHg, the EMG response to TMS and the sensory potential from the hand were progressively blocked. However, the motor neural evoked potential showed a significant increase in amplitude during the ischaemic period (30.5 %, P= 0.005). The increase in the neural potential suggests that output to the hand evoked from the cortex by TMS was not decreased by ischaemic block. Thus, we conclude that the increased response of biceps to TMS during distal ischaemia is not accompanied by a corresponding decrease in the motor cortical representation of the hand.
Molecular determinants of emerging excitability in rat embryonic motoneurons
Authors: Alessandri‐Haber Nicole , Alcaraz Giséle , Deleuze Charlotte , Jullien Florence , Manrique Christine , Couraud François , Crest Marcel , Giraud Pierre
Published: July 2002

Molecular determinants of excitability were studied in pure cultures of rat embryonic motoneurons. Using RT‐PCR, we have shown here that the spike‐generating Na+ current is supported by Nav1.2 and/or Nav1.3 α‐subunits. Nav1.1 and Nav1.6 transcripts were also identified. We have demonstrated that alternatively spliced isoforms of Nav1.1 and Nav1.6, resulting in truncated proteins, were predominant during the first week in culture. However, Nav1.6 protein could be detected after 12 days in vitro. The Navβ2.1 transcript was not detected, whereas the Nav β1.1 transcript was present. Even in the absence of Navβ2.1, α‐subunits were correctly inserted into the initial segment. RT‐PCR (at semi‐quantitative and single‐cell levels) and immunocytochemistry showed that transient K+ currents result from the expression of Kv4.2 and Kv4.3 subunits. This is the first identification of subunits responsible for a transient K+ current in spinal motoneurons. The blockage of Kv4.2/Kv4.3 using a specific toxin modified the shape of the action potential demonstrating the involvement of these conductance channels in regulating spike repolarization and the discharge frequency. Among the other Kv α‐subunits (Kv1.3, 1.4, 1.6, 2.1, 3.1 and 3.3), we showed that the Kv1.6 subunit was partly responsible for the sustained K+ current. In conclusion, this study has established the first correlation between the molecular nature of voltage‐dependent Na+ and K+ channels expressed in embryonic rat motoneurons in culture and their electrophysiological characteristics in the period when excitability appears.
Developmental profiles of glutamate receptors and synaptic transmission at a single synapse in the mouse auditory brainstem
Authors: Joshi Indu , Wang Lu‐Yang
Published: July 2002

Using whole‐cell recordings from presynaptic terminals and postsynaptic principal neurons in the mouse medial nucleus of the trapezoid body (MNTB), we have characterized properties of the calyx of Held synapse during the first three postnatal weeks. We observed that evoked excitatory postsynaptic currents (EPSCs) mediated by NMDA receptors (NMDAR) increased until postnatal day 11/12 (P11/12) after which they declined to very low or undetectable levels at P16. Meanwhile, EPSCs mediated by AMPA receptors (AMPAR) showed an approximate three‐fold increase in amplitude. These changes were paralleled by NMDAR and AMPAR currents evoked by exogenous NMDA and kainate to MNTB neurons except that whole‐cell kainate currents remained constant after P7/8 while AMPAR‐EPSCs continued to increase. We found that the decay time constant τ for NMDAR‐EPSCs and AMPAR‐EPSCs declined by about 30 % and 70 %, respectively. Analyses of NMDAR‐EPSCs with subunit‐specific pharmacological agents including ifenprodil, N,N,N′,N′‐tetrakis(2‐pyridylmethyl)‐ethylenediamine (TPEN), zinc and Mg2+ revealed subtle developmental changes in subunit composition. As maturation progressed, this synapse displayed a reduction in the number of presynaptic spike failures and the extent of synaptic depression in response to trains of stimuli (50–300 Hz) while the recovery rate from depression accelerated. These results demonstrate profound changes in the size and kinetics of postsynaptic glutamate receptors and in the spike‐firing capability of presynaptic terminals at the calyx of Held‐MNTB synapse during early development. We suggest that these concurrent presynaptic and postsynaptic adaptations represent important steps for synapse consolidation and refinement and ultimately for the development of fast high‐fidelity transmission at this synapse.
Rat nicotinic ACh receptor α7 and β2 subunits co‐assemble to form functional heteromeric nicotinic receptor channels
Authors: Khiroug Serguei S. , Harkness Patricia C. , Lamb Patricia W. , Sudweeks Sterling N. , Khiroug Leonard , Millar Neil S. , Yakel Jerrel L.
Published: July 2002

Rat hippocampal interneurons express diverse subtypes of functional nicotinic acetylcholine receptors (nAChRs), including α7‐containing receptors that have properties unlike those expected for homomeric α7 nAChRs. We previously reported a strong correlation between expression of the α7 and of the β2 subunits in individual neurons. To explore whether co‐assembly of the α7 and β2 subunits might occur, these subunits were co‐expressed in Xenopus oocytes and the functional properties of heterologously expressed nAChRs were characterized by two‐electrode voltage clamp. Co‐expression of the β2 subunit, both wild‐type and mutant forms, with the α7 subunit significantly slowed the rate of nAChR desensitization and altered the pharmacological properties. Whereas ACh, carbachol and choline were full or near‐full agonists for homomeric α7 receptor channels, both carbachol and choline were only partial agonists in oocytes expressing both α7 and β2 subunits. In addition the EC50 values for all three agonists significantly increased when the β2 subunit was co‐expressed with the α7 subunit. Co‐expression with the β2 subunit did not result in any significant change in the current‐voltage curve. Biochemical evidence for the co‐assembly of the α7 and β2 subunits was obtained by co‐immunoprecipitation of these subunits from transiently transfected human embryonic kidney (TSA201) cells. These data provide direct biophysical and molecular evidence that the nAChR α7 and β2 subunits co‐assemble to form a functional heteromeric nAChR with functional and pharmacological properties different from those of homomeric α7 channels. This co‐assembly may help to explain nAChR channel diversity in rat hippocampal interneurons, and perhaps in other areas of the nervous system.
A Geometric Approach for Determining Exact Point Accessibility of Robotic Manipulations
Authors: Rauchfuss Jason W. , Yang Daniel C. H.
Published: July 2002

This paper presents a method of determining the exact point accessibility for an articulated manipulator with joint limits in both the regional and wrist structures. The method is based on the derivation of constraint equations, which define boundary curves on the service sphere separating accessible and non-accessible regions. These constraint equations are defined individually in each specially selected coordinate frame, called the “neutral coordinate frame.” The boundary curves on the service sphere may arise from both regional structure joint limits and wrist joint limits. The resulting constraint equations are solved numerically, and the accessibility regions of any given point can be plotted on its service sphere automatically. The method is demonstrated on a simple articulated manipulator with an Euler angle wrist. [S1050-0472(00)00103-3]
A Finite Element Approach to Transient Thermal Analysis of Work Rolls in Rolling Process
Authors: Lee James D. , Manzari Majid T. , Shen Yin-Lin , Zeng Wenjun
Published: July 2002

The three-dimensional transient thermal problem of work rolls in the entire rolling process has been formulated. It includes the time-varying boundary conditions specified at the roll surface taking the schedule of both rolling and idling cycles into consideration. The corresponding finite element equations are derived and solved by the Runge-Kutta-Verner method. The finite element solutions indicate that the temperature variations in the circumferential direction are overwhelming. Case studies unveil the thermal characteristics of the work rolls in various kinds of mill operations. The effects of the specific heat and the angular velocity of the work rolls are presented. Numerical results are compared with Guo’s analytical solutions. [S1087-1357(00)01604-X]
Fluids Transport Optimization Using Seabed Separation
Authors: Song S. , Kouba G.
Published: July 2002

Terrain slugging is extremely likely to occur sometime during the life of a deep subsea pipeline/riser system. But, can the terrain slugs be mitigated? In this study, we performed transient multiphase flow simulations to explore the feasibility of sea floor separation to mitigate terrain slugging and to optimize fluid transport from wellhead to downstream processing. We considered the effects of separator location and separation efficiency on production system behavior. We found that there is an optimal amount of gas underflow into the liquid line and there is an optimum location for subsea separator. Our study also covered how the operational transient processes, such as startup and shutdown, would affect the performance of the pipeline/separator system. It is necessary to have a good understanding of the performance of subsea separation system before a reliable one can be designed. The results of this study are aimed toward improving the design of sea floor processing for ultra-deepwater production. [S0195-0738(00)00403-9]
A Triaxial-Measurement Shear-Test Device for Soft Biological Tissues
Authors: Dokos Socrates , LeGrice Ian J. , Smaill Bruce H. , Kar Julia , Young Alistair A.
Published: July 2002

A novel shear-test device for soft biological tissue, capable of applying simple shear deformations simultaneously in two orthogonal directions while measuring the resulting forces generated in three axes, is described. We validated the device using a synthetic gel, the properties of which were ascertained from independent tensile and rotational shear tests. Material parameters for the gel were fitted using neo-Hookean analytical solutions to the independent test data, and these matched the results from the device. Preliminary results obtained with rat septal myocardium are also presented to demonstrate the feasibility of the apparatus in determining the shear characteristics of living tissue. [S0148-0731(00)00205-3]
Epicardial Suction: A New Approach to Mechanical Testing of the Passive Ventricular Wall
Authors: Okamoto R. J. , Moulton M. J. , Peterson S. J. , Li D. , Pasque M. K. , Guccione J. M.
Published: July 2002

The lack of an appropriate three-dimensional constitutive relation for stress in passive ventricular myocardium currently limits the utility of existing mathematical models for experimental and clinical applications. Previous experiments used to estimate parameters in three-dimensional constitutive relations, such as biaxial testing of excised myocardial sheets or passive inflation of the isolated arrested heart, have not included significant transverse shear deformation or in-plane compression. Therefore, a new approach has been developed in which suction is applied locally to the ventricular epicardium to introduce a complex deformation in the region of interest, with transmural variations in the magnitude and sign of nearly all six strain components. The resulting deformation is measured throughout the region of interest using magnetic resonance tagging. A nonlinear, three-dimensional, finite element model is used to predict these measurements at several suction pressures. Parameters defining the material properties of this model are optimized by comparing the measured and predicted myocardial deformations. We used this technique to estimate material parameters of the intact passive canine left ventricular free wall using an exponential, transversely isotropic constitutive relation. We tested two possible models of the heart wall: first, that it was homogeneous myocardium, and second, that the myocardium was covered with a thin epicardium with different material properties. For both models, in agreement with previous studies, we found that myocardium was nonlinear and anisotropic with greater stiffness in the fiber direction. We obtained closer agreement to previously published strain data from passive filling when the ventricular wall was modeled as having a separate, isotropic epicardium. These results suggest that epicardium may play a significant role in passive ventricular mechanics. [S0148-0731(00)00305-8]
On Higher-Order Crack-Tip Fields in Creeping Solids
Authors: Nguyen B. N. , Onck P. R. , van der Giessen E.
Published: July 2002

In view of the near-tip constraint effect imposed by the geometry and loading configuration, a creep fracture analysis based on C* only is generally not sufficient. This paper presents a formulation of higher-order crack-tip fields in steady power-law creeping solids which can be derived from an asymptotic development of near-tip fields analogous to that of Sharma and Aravas and Yang et al. for elastoplastic bodies. The higher-order fields are controlled by a parameter named A2*, similar as in elastoplasticity, and a second loading parameter, σ∞. By means of the scaling properties for power-law materials, it is shown that A2* for a flat test specimen is independent of the loading level. Finally, we carry out small-strain finite element analyses of creep in single-edge notched tension, centered crack panel under tension, and single-edge notched bending specimens in order to determine the corresponding values of A2* for mode I cracks under plane-strain conditions. [S0021-8936(00)01202-2]
Characterizing Damping and Restitution in Compliant Impacts via Modified K-V and Higher-Order Linear Viscoelastic Models
Authors: Butcher E. A. , Segalman D. J.
Published: July 2002

[S0021-8936(00)00503-1]
Quantification of Creep Cavitation in Welded Joint and Evaluation of Material Characteristics of Simulated Heat-Affected Zone in X 20 CrMoV 12 1 Steel
Authors: Chung Yong-Keun , Joo Cheol-Hong , Park Jong-Jin , Park Ik-Man , Kim Hyo-Jin
Published: July 2002

X 20 CrMoV 12 1(DIN 17 175) steel has been used for components subjected to high temperature in power plants and chemical and petroleum industries. Therefore, extensive studies have been made on this steel. However, these studies focused mainly on the base metal, and few studies on the welded joint have been reported. Actually, a large number of failures have occurred at the welded joint, so there is increasing need to investigate the characteristics of X 20 CrMoV 12 1 weldment. In this study, the interrupted and creep rupture tests were carried out and quantification of the creep damage was attempted for the X 20 CrMoV 12 1 welded joint. The interrupted and creep rupture tests were performed at four conditions\M650-60, 600-100, 600-120, and 575-150(|SDC-MPa)\Mon the X 20 CrMoV 12 1 welded joint specimens, respectively. It was revealed from the experimental results that creep damage mechanism of a welded joint was mainly creep cavitation, and that the intensively damaged area by creep cavitations was the transition region from fine-grained heat-affected zone (HAZ) to unaffected base metal, namely intercritical HAZ. For both the interrupted and ruptured specimens, quantification of creep damage was attempted by evaluating cavitated area fraction, average diameter, and the number of cavities with creep life fraction. In addition, on the basis of the heat input during the welding, microstructure, microhardness, and grain size of the actual intercritical HAZ, simulated HAZ was made in order to evaluate its material properties. For the simulated HAZ specimens, tensile, charpy impact, and creep rupture tests were carried out. As a result, yield, tensile strength, and elongation of simulated HAZ were similar to those of base metal, respectively, and impact property of simulated HAZ was slightly above base metal. Also, it was found that creep strength of simulated HAZ was inferior to that of the base metal.
Heave Plate Design With Computational Fluid Dynamics
Authors: Holmes Samuel , Bhat Shankar , Beynet Pierre , Sablok Anil , Prislin Igor
Published: July 2002

Computational fluid dynamics (CFD) methods are used to predict the hydrodynamic loads on heave plates. A series of numerical simulations for plates undergoing simple harmonic motion is used to determine the force and moment resultant histories. Then a least mean squares method is used to obtain the appropriate Morison coefficients for the plates under a variety of sea conditions. Finally, force and moment histories are predicted for a plate on a floating platform excited by a random sea motion.
A State-Space-Based Stress Analysis of a Multilayered Spherical Shell With Spherical Isotropy
Authors: Chen W. Q. , Ding H. J.
Published: July 2002

This paper presents an exact static stress analysis of a multilayered elastic spherical shell (hollow sphere) completely based on three-dimensional elasticity for spherical isotropy. Two independent state equations are derived after introducing three displacement functions and two stress functions. In particular, a variable substitution technique is used to derive the state equations with constant coefficients. Matrix theory is then employed to obtain the relationships between the state variables at the upper and lower surfaces of each lamina. By virtue of the continuity conditions between two adjacent layers, a second-order linear algebraic equation and a fourth-order one about the boundary variables at the inner and outer surfaces of a multilayered spherical shell are obtained. Numerical examples are presented to show the effectiveness of the present method.
A New Look at an Old Problem: Newton’s Cradle
Authors: Ceanga V. , Hurmuzlu Y.
Published: July 2002

In this paper we consider the most basic multi-impact system, the so-called “Newton’s Cradle.” The task of developing an analytical method to predict the post impact velocities of the balls in the cradle has baffled investigators in the field of impact research for many years. The impulse-based rigid-body body as well as the alternative compliance-based time-base approaches have failed to produce valid solutions to this problem. Here, we present a new method that produces energetically consistent solutions to the problem. Our method is based on the traditional impulse-momentum-based rigid-body approach. We do, however, resolve the nonuniqueness difficulty in the rigid-body approach by introducing a new constant called the Impulse Transmission Ratio. Finally, we verify our method by conducting a set of experiments and comparing the theoretical predictions with the experimental outcomes.
Analytical Predictions of the Air Gap Response of Floating Structures
Authors: Manuel Lance , Sweetman Bert , Winterstein Steven R.
Published: July 2002

Two separate studies are presented here that deal with analytical predictions of the air gap for floating structures. 1) To obtain an understanding of the importance of first and second-order incident and diffracted wave effects as well as to determine the influence of the structure’s motions on the instantaneous air gap, statistics of the air gap response are studied under various modeling assumptions. For these detailed studies, a single field point is studied here—one at the geometric center (in plan) of the Troll semi-submersible. 2) A comparison of the air gap at different locations is studied by examining response statistics at different field points for the semi-submersible. These include locations close to columns of the four-columned semi-submersible. Analytical predictions, including first and second-order diffracted wave effects, are compared with wave tank measurements at several locations. In particular, the gross root-mean-square response and the 3-h extreme response are compared.
Bolt Head Fillet Stress Concentration Factors in Cylindrical Pressure Vessels
Authors: Srinivasan Gowri , Lehnhoff Terry F.
Published: July 2002

Linear three-dimensional finite element analysis (FEA) was performed on bolted pressure vessel joints to determine maximum stresses and stress concentration factors in the bolt head fillet as a result of the prying action. The three-dimensional finite element models consisted of a segment of the flanges containing one bolt, using cyclic symmetry boundary conditions. The flanges were each 20 mm in thickness with 901.7 mm inner diameter. The outer flange diameter was varied from 1021 to 1041 mm in steps of 5 mm. The bolt circle diameter was varied from 960.2 to 980.2 mm in steps of 5 mm. The bolts used were 16-mm-dia metric bolts with standard head and nut thickness. The threads were not modeled. The internal vessel pressure was 0.6895 MPa (100 psi). Stress concentration factors in the bolt head fillet were calculated, and they ranged from 3.34 to 4.80. The maximum stress in the bolt as well as the stress concentration factors in the bolt head fillet increase with an increase in bolt circle diameter for a given outer flange dimension. Keeping the bolt circle diameter constant, bolt stress and stress concentration factors in the bolt head fillet decrease with increase in outer flange diameter. The maximum stresses in the bolt were also calculated according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and the Verein Deutscher Ingenieur (VDI) guidelines and compared to the results observed through finite element analysis. The stresses obtained through FEA were larger than those predicted by the ASME and VDI methods by a factor that ranged between 2.96 to 3.41 (ASME) and 2.76 to 3.63 (VDI).
Deposit Formation and Mitigation in Aircraft Fuels
Authors: Spadaccini L. J. , Sobel D. R. , Huang H.
Published: July 2002

The development of a viable strategy for limiting coke deposition involves combining synergistic approaches for suppressing deposit buildup and reducing its impact on performance. Candidate approaches, including selection of favorable operating conditions (viz., pressure, temperature, heat flux, residence time, and passage size) and coke-tolerant heat exchanger designs, were investigated to evaluate their effectiveness and provide a basis for combining them into a single design philosophy. These approaches were evaluated through testing of current jet fuels in single-tubes and segments of heat exchanger configurations at temperatures up to 1000°F, pressures up to 1200 psi and liquid hourly space velocities up to 40,000/h. A key result of this work is the ranking of the importance of heat exchanger operating conditions on carbon deposition, with fuel temperature and those parameters that control species diffusion having the most pronounced impact. Residence time and pressure are of lesser importance. Alternative coke-tolerant heat exchanger designs featuring interchannel communication were evaluated and ranked, with several of these concepts demonstrating improvement over continuous passages.
Construction of a Physical Model of the Human Carotid Artery Based Upon In Vivo Magnetic Resonance Images
Authors: Yedavalli R. V. , Loth F. , Yardimci A. , Pritchard W. F. , Oshinski J. N. , Sadler L. , Charbel F. , Alperin N.
Published: July 2002

A method is described for construction of an in vitro flow model based on in vivo measurements of the lumen geometry of the human carotid bifurcation. A large-scale physical model of the vessel lumen was constructed using fused deposition modeling (a rapid prototyping technique) based on magnetic resonance (MR) images of the carotid bifurcation acquired in a healthy volunteer. The lumen negative was then used to construct a flow model for experimental studies that examined the hemodynamic environment of subject-specific geometry and flow conditions. The physical model also supplements physician insight into the three-dimensional geometry of the arterial segment, complementing the two-dimensional images obtained by MR. Study of the specific geometry and flow conditions in patients with vascular disease may contribute to our understanding of the relationship between their hemodynamic environment and conditions that lead to the development and progression of arterial disease.
Adhesion and Reliability of Epoxy/Glass Interfaces
Authors: Ritter John E. , Huseinovic Armin
Published: July 2002

The reliability of microelectronic components is profoundly influenced by the fracture resistance of the polymer/inorganic interfaces and by the progressive debonding of these interfaces in aqueous environments. Consequently, fatigue (slow) crack growth in epoxy/glass interfaces bonded with the silane coupling agent 3-aminopropyltriethoxysilane (3-APES) was studied under static and cyclic loading at 23°C and in either dry or humid conditions using the double cleavage drilled compression (DCDC) test. Crack growth rates under cyclic loading were significantly greater than under static loading, indicating that stress corrosion effects are negligible and that crack tip plasticity controls cyclic fatigue crack growth at silane (3-APES) bonded epoxy/glass interfaces. After aging at 94°C in water, these silane bonded epoxy/glass interfaces exhibited somewhat greater resistance to cyclic fatigue crack growth than the unaged samples; however, after aging at 98°C in water cyclic fatigue crack growth became cohesive and fractal in nature. Mechanisms for fatigue crack growth at silane (3-APES) bonded epoxy/glass interfaces are discussed.
Performance of Rectangular Fin in Wet Conditions: Visualization and Wet Fin Efficiency
Authors: Lin Yur-Tsai , Hsu Kuei-Chang , Chang Yu-Juei , Wang Chi-Chuan
Published: July 2002

An experimental study concerning the performance of a rectangular fin in both dry and wet condition was carried out. The visual observation of the dehumidifying phenomenon identified four regions, including the fully dry, very fine droplet, larger droplet, and film-like region. Experimental results showed that the effect of dry bulb temperature on the wet fin efficiency is very small. The dry fin efficiency is about 15–25 percent higher than that of the corresponding wet fin efficiency. For fully wet condition, the effect of relative humidity on the fully wet fin efficiency is also small. For partially wet surface, a considerable influence of the relative humidity on the fin efficiency is encountered. Test results for the fully wet fin efficiency agree well with some of the previous studies but disagree with some of the previous investigations. The main cause to this controversy may be attributed to the formulation of the relation between the humidity ratio and the fin temperature. The fully wet fin efficiency decrease slightly with increase of fin base temperature. However, the effect of fin base temperature on the dry fin efficiency is relatively small.
The Many Faces of Turbine Surface Roughness
Authors: Bons Jeffrey P. , Taylor Robert P. , McClain Stephen T. , Rivir Richard B.
Published: July 2002

Results are presented for contact stylus measurements of surface roughness on in-service turbine blades and vanes. Nearly 100 turbine components were assembled from four land-based turbine manufacturers. Both coated and uncoated, cooled and uncooled components were measured, with part sizes varying from 2 to 20 cm. Spanwise and chordwise two-dimensional roughness profiles were taken on both pressure and suction surfaces. Statistical computations were performed on each trace to determine centerline averaged roughness, rms roughness, and peak to-valley height. In addition, skewness and kurtosis were calculated; as well as the autocorrelation length and dominant harmonics in each trace. Extensive three-dimensional surface maps made of deposits, pitting, erosion, and coating spallation expose unique features for each roughness type. Significant spatial variations are evidenced and transitions from rough to smooth surface conditions are shown to be remarkably abrupt in some cases. Film cooling sites are shown to be particularly prone to surface degradation.
Synchronization of Vortex Shedding and Heat Transfer Enhancement Over a Heated Cylinder Oscillating With Small Amplitude in Streamwise Direction
Authors: Gau C. , Wu S. X. , Su H. S.
Published: July 2002

Experiments are performed to study the flow structure and heat transfer over a heated cylinder oscillating radially with small amplitude in streamwise direction. Both flow visualization using a smoke wire in the upstream and the local heat transfer measurements based on wall temperatures around the cylinder were made. The excitation frequencies of the cylinder are selected at Fe/Fn=0, 0.5, 1, 1.5, 2, 2.5, and 3. The oscillation amplitude selected is less than a threshold value of A/D=0.06 where synchronization of vortex shedding with the cylinder excitation was not expected. However, experiments indicate that synchronization still occurs which stimulates a great interest to study its enhancement in the heat transfer. Synchronization occurred at Fe/Fn=2 is antisymmetric vortex formation while synchronization at Fe/Fn=2.5 and 3 is symmetric type. The forward motion (advancing into the cross flow) of the cylinder during one cycle of oscillation has an effect to suppress the instability and the vortex formation. This leads to the occurrence of a smaller and symmetric vortex formation and a less enhancement of heat transfer than the case of antisymmetric type Fe/Fn=2. For excitations at lower frequencies Fe/Fn⩽1.5, all the vortex formations occurred are mostly antisymmetric. The dominant mode of the instability in the shear layer is actually the natural shedding frequency Fn of the vortex. A closer excitation frequency to 2Fn causes a greater enhancement in the heat transfer. During the experiments, the Reynolds numbers varies from 1600 to 3200, the dimensionless amplitude A/D from 0.048 to 0.016.
Deformation and Recrystallization Textures in Cross-Rolled Copper Sheet
Authors: Hong Seung-Hyun , Lee Dong Nyung
Published: July 2002

A study has been made of the deformation and recrystallization textures of 99.99% pure copper sheets which were cross rolled by 82 and 96% reduction in thickness and recrystallized in a salt bath at 450°C for 1h. The deformation texture was approximated by the {011}〈755〉 orientation as the major component and {001}〈100〉 as a minor component. These deformation texture components were well simulated using the rate sensitive relaxed constraints model. The {001}〈100〉 orientation was calculated to be metastable while the {011}〈755〉 orientation was located in the middle of the rotation path between the stable orientations in two cross rolling directions. The recrystallization texture in the center layer of the 96% cross-rolled copper sheet was approximated by {86 50 9}〈10 34 94〉 for each rolling direction. The evolution of the recrystallization texture was discussed based on the strain energy release maximization model.
A Feature-Based Approach to Automated Design of Multi-Piece Sacrificial Molds
Authors: Dhaliwal S. , Gupta S. K. , Huang J. , Kumar M.
Published: July 2002

This paper describes a feature-based algorithm for automated design of multi-piece sacrificial molds. Our mold design algorithm consists of the following three steps. First, the desired gross mold shape is created based on the feature-based description of the part geometry. Second, if the desired gross mold shape is not machinable as a single component, then the gross mold shape is decomposed into simpler geometric components to make sure that each component is machinable using 3-axis CNC machining. The decomposition is performed to ensure that each component is accessible to end-milling tools, and decomposed components can be assembled together to form the gross mold shape. Finally, assembly features are added to mold components to eliminate unnecessary degrees of freedom from the final mold assembly to facilitate molding.
An Analysis of Filament Overwound Toroidal Pressure Vessels and Optimum Design of Such Structures
Authors: Li Shuguang , Cook John
Published: July 2002

This paper is concerned with the membrane shell analysis of filament overwound toroidal pressure vessels and optimum design of such pressure vessels using the results of the analysis by means of mathematical nonlinear programming. The nature of the coupling between overwind and linear has been considered based on two extreme idealizations. In the first, the overwind is rigidly coupled with the liner, so that the two deform together in the meridional direction as the vessel dilates. In the second, the overwind is free to slide relative to the linear, but the overall elongations of the two around a meridian are identical. Optimized designs with the two idealizations show only minor differences, and it is concluded that either approximation is satisfactory for the purposes of vessel design. Aspects taken into account are the intrinsic overwind thickness variation arising from the winding process and the effects of fiber pre-tension. Pre-tension can be used not only to defer the onset of yielding, but also to achieve a favorable in-plane stress ratio which minimizes the von Mises equivalent stress in the metal liner. Aramid fibers are the most appropriate fibers to be used for the overwind in this type of application. The quantity of fiber required is determined by both its short-term strength and its long-term stress rupture characteristics. An optimization procedure for the design of such vessels, taking all these factors into account, has been established. The stress distributions in the vessels designed in this way have been examined and discussed through the examples. A design which gives due consideration of possible mechanical damage to the surface of the overwind has also been addressed.
A Boundary Element Method Without Internal Cells for Two-Dimensional and Three-Dimensional Elastoplastic Problems
Authors: Gao X.-W.
Published: July 2002

In this paper, a new and simple boundary element method without internal cells is presented for the analysis of elastoplastic problems, based on an effective transformation technique from domain integrals to boundary integrals. The strong singularities appearing in internal stress integral equations are removed by transforming the domain integrals to the boundary. Other weakly singular domain integrals are transformed to the boundary by approximating the initial stresses with radial basis functions combined with polynomials in global coordinates. Three numerical examples are presented to demonstrate the validity and effectiveness of the proposed method.
The Differential Interfacial Tension Hypothesis (DITH): A Comprehensive Theory for the Self-Rearrangement of Embryonic Cells and Tissues
Authors: Brodland G. Wayne
Published: July 2002

A comprehensive theory, herein named the Differential Interfacial Tension Hypothesis (DITH), for the self-rearrangement of embryonic cells and tissues is presented. These rearrangements include sorting, mixing and formation of checkerboard patterns in heterotypic aggregates of embryonic cells, and total or partial engulfment, separation and dissociation of tissues. This broadly-based theory accounts for the action of all currently known cytoskeletal components and cell adhesion mechanisms. The theory is used to derive conditions for the cell and tissue rearrangements named above. Finite element-based computer simulations involving two or more cell types confirm these conditions.
Survey of Thermal Energy Storage for Parabolic Trough Power Plants
Authors: Herrmann Ulf , Kearney David W.
Published: July 2002

A literature review was carried out to critically evaluate the state of the art of thermal energy storage applied to parabolic trough power plants. This survey briefly describes the work done before 1990 followed by a more detailed discussion of later efforts. The most advanced system is a 2-tank-storage system where the heat transfer fluid (HTF) also serves as storage medium. This concept was successfully demonstrated in a commercial trough plant (13.8MWe SEGS I plant; 120MWht storage capacity) and a demonstration tower plant (10MWe Solar Two; 105MWht storage capacity). However, the HTF used in state-of-the-art parabolic trough power plants 30-80MWe is expensive, dramatically increasing the cost of larger HTF storage systems. Other promising storage concepts are under development, such as concrete storage, phase change material storage, and chemical storage. These concepts promise a considerable cost reduction compared to the direct 2-tank system, but some additional R&D is required before those systems can be used in commercial solar power plants. An interesting and likely cost-effective near-term option for thermal energy storage for parabolic trough power plants is the use of an indirect 2-tank-storage, where another (less expensive) liquid medium such as molten salt is utilized rather than the HTF itself.
Free-Surface Effects in 3D Dislocation Dynamics: Formulation and Modeling
Authors: Khraishi Tariq A. , Zbib Hussein M.
Published: July 2002

Recent advances in 3-D dislocation dynamics include the proper treatment of free surfaces in the simulations. Dislocation interaction and slip is treated as a boundary-value problem for which a zero-traction condition is enforced at the external surfaces of the simulation box. Here, a new rigorous method is presented to handle such a treatment. The method is semi-analytical/numerical in nature in which we enforce a zero traction condition at select collocation points on a surface. The accuracy can be improved by increasing the number of collocation points. In this method, the image stress-field of a subsurface dislocation segment near a free surface is obtained by an image segment and by a distribution of prismatic rectangular dislocation loops padding the surface. The loop centers are chosen to be the collocation points of the problem. The image segment, with proper selection of its Burgers vector components, annuls the undesired shear stresses on the surface. The distributed loops annul the undesired normal stress component at the collocation points, and in the process create no undesirable shear stresses. The method derives from crack theory and falls under “generalized image stress analysis” whereby a distribution of dislocation geometries or entities (in this case closed rectangular loops), and not just simple mirror images, are used to satisfy the problem’s boundary conditions (BCs). Such BCs can, in a very general treatment, concern either stress traction or displacements.
Determination of the Effective Thermal Conductivity Tensor of
Heterogeneous Media Using a Self-Consistent Finite Element Method: Application
to the Pseudo-percolation Thresholds of Mixtures Containing Nonspherical
Inclusions
Authors: Decarlis A. , Jaeger M. , Martin R.
Published: July 2002

This paper concerns the determination of the effective thermal conductivity of heterogeneous media with randomly dispersed inclusions. Inclusions of arbitrary shape can be considered since the self-consistent problem is solved numerically with the finite element method. Results for many different cases of heterogeneous media with axially symmetrical inclusions are presented. Moreover, the influence of the inclusion’s shape on the pseudo-percolation threshold is investigated. [S0022-1481(00)00801-X]
Agent-Based Synthesis of Electromechanical Design Configurations
Authors: Campbell Matthew I. , Cagan Jonathan , Kotovsky Kenneth
Published: July 2002

A new automated approach to engineering design known as A-design is presented that creates design configurations through the interaction of software agents. By combining unique problem solving strategies, these agents are able to generate solutions to open-ended design problems. The A-design methodology makes several theoretical claims through its combination of multiagent systems, multiobjective design selection, and stochastic optimization, and is currently implemented to solve general electromechanical design problems. While this paper presents an overview of the theoretical basis for A-design, it primarily focuses on the method for representing electromechanical design configurations and the reasoning of the agents that construct these configurations. Results from an electromechanical test problem show the generality of the functional representation. [S1050-0472(00)00701-7]
Reliability Analysis of Non-Constant-Size Part Populations in Design for Remanufacture
Authors: Jiang Z. H. , Shu L. H. , Benhabib B.
Published: July 2002

Remanufacture offers significant economic and ecological advantages over other end-of-life options for appropriate products. The goal of this research is to estimate replacement requirements of parts in systems that are remanufactured. In our previous work, a novel repairable-system reliability model that allows system modifications was developed to describe a population of systems that are remanufactured. In this paper, the reliability model is modified to accommodate changes to the population size, while the population is in service, to better describe actual processes. The effects of two types of disturbances to population size, pulse and continuous, on the replacement rate behavior are studied. Analysis of actual industrial data is presented as an example of population replacement under continuous disturbance. This example confirms that a simulation using the reliability model described in this paper yields an estimate for replacement rate with acceptable error bound. [S1050-0472(00)00302-0]
A Control System for Microwave Processing of Materials
Authors: Groombridge P. , Oloyede A. , Siores E.
Published: July 2002

This paper discusses a control system for microwave processing of materials. Microwave joining of ceramics and drying of timber are currently industry practices while microwave joining of engineering plastics and curing of epoxy adhesives are still being researched. In this study, all materials are processed in rectangular sections of waveguide fed by a magnetron with a maximum output power of 2 kW operating at 2.45 GHz. The most significant problems encountered when processing these materials are: (i) maintaining proper tuning to ensure maximum power transfer, (ii) thermal runaway, where the heating rate proceeds so rapidly that the material burns within a few seconds, and (iii) hot spot development, where localized regions heat up at a faster rate than adjacent regions. A computerized automated control system has been developed to alleviate these processing problems and has been successfully employed in joining a range of ceramics and engineering plastics, curing epoxy adhesives and drying wood. Results of preliminary tests obtained using the developed prototype are presented. [S1087-1357(00)71701-1]