bluuebunny/crossref_metadata_2025 huggingface dataset:
The likelihood of aggregation during protein renaturation can be assessed using the second virial coefficient
Authors: Ho Jason G.S. , Middelberg Anton P.J. , Ramage Paul , Kocher Hans P.
Published: March 2003

Protein aggregation is commonly observed during protein refolding. To better understand this phenomenon, the intermolecular interactions experienced by a protein during unfolding and refolding are inferred from second virial coefficient (SVC) measurements. It is accepted that a negative SVC is indicative of protein–protein interactions that are attractive, whereas a positive SVC indicates net repulsive interactions. Lysozyme denatured and reduced in guanidinium hydrochloride exhibited a decreasing SVC as the denaturant was diluted, and the SVC approached zero at approximately 3 M GdnHCl. Further dilution of denaturant to renaturation conditions (1.25 M GdnHCl) led to a negative SVC, and significant protein aggregation was observed. The inclusion of 500 mM L‐arginine in the renaturation buffer shifted the SVC to positive and suppressed aggregation, thereby increasing refolding yield. The formation of mixed disulfides in the denatured state prior to refolding also increased protein solubility and suppressed aggregation, even without the use of L‐arginine. Again, the suppression of aggregation was shown to be caused by a shift from attractive to repulsive intermolecular interactions as reflected in a shift from a negative to a positive SVC value. To the best of our knowledge, this is the first time that SVC data have been reported for renaturation studies. We believe this technique will aid in our understanding of how certain conditions promote renaturation and increase protein solubility, thereby suppressing aggregation. SVC measurements provide a useful link, for protein folding and aggregation, between empirical observation and thermodynamics.
Structure and dynamics of the DNA‐binding protein HU of B. stearothermophilus investigated by Raman and ultraviolet‐resonance Raman spectroscopy3
Authors: Serban Doinita , Arcineigas Sandra F. , Vorgias Constantinos E. , Thomas George J.
Published: March 2003

The histone‐like protein HU of Bacillus stearothermophilus (HUBst) is a 90‐residue homodimer that binds nonspecifically to B DNA. Although the structure of the HUBst:DNA complex is not known, the proposed DNA‐binding surface consists of extended arms that project from an α‐helical platform. Here, we report Raman and ultraviolet‐resonance Raman (UVRR) spectra diagnostic of subunit secondary structures and indicative of key side‐chains lining the proposed DNA‐binding surface. Raman conformation markers show that the DNA‐binding arms of the dimer contain β‐stranded structure in excess (eight ± two residues per subunit) of that reported previously. Important among side‐chain markers are Met (701 cm−1), Ala (908 cm−1), Arg (1082 cm−1), and Pro (1457 cm−1). The Ala marker undergoes a substantial shift (908 → 893 cm−1) on deuteration of alanyl peptide sites, indicating a coupled side‐chain/main‐chain mode of diagnostic value in the identification of exchange‐protected alanines. A large subset of alanines (67%) in the α‐helical core exhibits robust resistance to exchange. A quantitative study of NH → ND exchange exploiting newly identified amide II′ markers of helical (1440 cm−1) and nonhelical (1472 cm−1) conformations of HUBst indicates unexpected flexibility at the dimer interface, which is manifested in rapid exchange of 80% of peptide sites. The results establish a basis for subsequent Raman and UVRR investigations of HUBst:DNA complexes and provide a framework for applications to other DNA‐binding architectural proteins.
Tautomerism, acid‐base equilibria, and H‐bonding of the six histidines in subtilisin BPN′ by NMR
Authors: Day Regina M. , Thalhauser Craig J. , Sudmeier James L. , Vincent Matthew P. , Torchilin Ekaterina V. , Sanford David G. , Bachovchin Christopher W. , Bachovchin William W.
Published: March 2003

We have determined by 15N, 1H, and 13C NMR, the chemical behavior of the six histidines in subtilisin BPN′ and their PMSF and peptide boronic acid complexes in aqueous solution as a function of pH in the range of from 5 to 11, and have assigned every 15N, 1H, Cε1, and Cδ2 resonance of all His side chains in resting enzyme. Four of the six histidine residues (17, 39, 67, and 226) are neutrally charged and do not titrate. One histidine (238), located on the protein surface, titrates with pKa = 7.30 ± 0.03 at 25°C, having rapid proton exchange, but restricted mobility. The active site histidine (64) in mutant N155A titrates with a pKa value of 7.9 ± 0.3 and sluggish proton exchange behavior, as shown by two‐site exchange computer lineshape simulation. His 64 in resting enzyme contains an extremely high Cε1‐H proton chemical shift of 9.30 parts per million (ppm) owing to a conserved Cε1‐H…O=C H‐bond from the active site imidazole to a backbone carbonyl group, which is found in all known serine proteases representing all four superfamilies. Only His 226, and His 64 at high pH, exist as the rare Nδ1‐H tautomer, exhibiting 13Cδ1 chemical shifts ∼9 ppm higher than those for Nε2‐H tautomers. His 64 in the PMSF complex, unlike that in the resting enzyme, is highly mobile in its low pH form, as shown by 15N‐1H NOE effects, and titrates with rapid proton exchange kinetics linked to a pKa value of 7.47 ± 0.02.
Unexpected similarity in regulation between an archaeal inositol monophosphatase/fructose bisphosphatase and chloroplast fructose bisphosphatase
Authors: Stieglitz Kimberly A. , Seaton Barbara A. , Head James F. , Stec Boguslaw , Roberts Mary F.
Published: March 2003

Hyperthermophilic archaea have an unusual phosphatase that exhibits activity toward both inositol‐1‐phosphate and fructose‐1,6‐bisphosphate, activities carried out by separate gene products in eukaryotes and bacteria. The structures of phosphatases from Archaeoglobus fulgidus (AF2372) and Methanococcus jannaschii (MJ0109), both anaerobic organisms, resemble the dimeric unit of the tetrameric pig kidney fructose bisphosphatase (FBPase). A striking feature of AF2372, but not of MJ0109, is that the sulfhydryl groups of two cysteines, Cys150 and Cys186, are in close proximity (4 Å). A similar arrangement of cysteines has been observed in chloroplast FBPases that are regulated by disulfide formation controlled by redox signaling pathways (ferredoxin/thioredoxin). This mode of regulation has not been detected in any other FBPase enzymes. Biochemical assays show that the AF2372 phosphatase activity can be abolished by incubation with O2. Full activity is restored by incubation with thiol‐containing compounds. Neither the C150S variant of AF2372 nor the equivalent phosphatase from M. jannaschii loses activity with oxidation. Oxidation experiments using Escherichia coli thioredoxin, in analogy with the chloroplast FBPase system, indicate an unexpected mode of regulation for AF2372, a key phosphatase in this anaerobic sulfate reducer.
Rational design, synthesis, and verification of affinity ligands to a protein surface cleft
Authors: Baumann Herbert , Öhrman Sara , Shinohara Yasuro , Ersoy Oguz , Choudhury Devapriya , Axén Andreas , Tedebark Ulf , Carredano Enrique
Published: March 2003

The structure‐based design, synthesis, and screening of a glucuronic acid scaffold library of affinity ligands directed toward the catalytic cleft on porcine pancreas α‐amylase are presented. The design was based on the simulated docking to the enzyme active site of 53 aryl glycosides from the Available Chemicals Directory (ACD) selected by in silico screening. Twenty‐three compounds were selected for synthesis and screened in solution for binding toward α‐amylase using nuclear magnetic resonance techniques. The designed molecules include a handle outside of the binding site to allow their attachment to various surfaces with minimal loss of binding activity. After initial screening in solution, one affinity ligand was selected, immobilized to Sepharose (Amersham Biosciences), and evaluated as a chromatographic probe. A column packed with ligand‐coupled Sepharose specifically retained the enzyme, which could be eluted by a known inhibitor.
Prediction of the plant β‐barrel proteome: A case study of the chloroplast outer envelope
Authors: Schleiff Enrico , Eichacker Lutz Andreas , Eckart Kerstin , Becker Thomas , Mirus Oliver , Stahl Tanja , Soll Jürgen
Published: March 2003

In the postgenomic era, the transformation of genetic information into biochemical meaning is required. We have analyzed the proteome of the chloroplast outer envelope membrane by an in silico and a proteomic approach. Based on its evolutionary relation to the outer membrane of Gram‐negative bacteria, the outer envelope membrane should contain a large number of β‐barrel proteins. We therefore calculated the probability for the existence of β‐sheet, β‐barrel, and hairpin structures among all proteins of theArabidopsis thalianagenome. According to the existence of these structures, a number of candidates were selected. This protein pool was analyzed by TargetP to discard sequences with signals that would direct the protein to other organelles different from chloroplasts. In addition, the pool was manually controlled for the presence of proteins known to function outside of the chloroplast envelope. The approach developed here can be used to predict the topology of β‐barrel proteins. For the proteomic approach, proteins of highly purified outer envelope membranes of chloroplasts fromPisum sativumwere analyzed by ESI‐MS/MS mass spectrometry. In addition to the known components, four new proteins of the outer envelope membranes were identified in this study.
Tightly winding structure of sequential model peptide for repeated helical region in Samia cynthia ricini silk fibroin studied with solid‐state NMR
Authors: Nakazawa Yasumoto , Bamba Mie , Nishio Satoko , Asakura Tetsuo
Published: March 2003

There are many kinds of silks from silkworms and spiders with different structures and properties, and thus, silks are suitable to study the structure‐property relationship of fibrous proteins. Silk fibroin from a wild silkworm, Samia cynthia ricini, mainly consists of the repeated similar sequences by about 100 times where there are alternative appearances of the polyalanine (Ala)12–13 region and the Gly‐rich region. In this paper, a sequential model peptide, GGAGGGYGGDGG(A)12GGAGDGYGAG, which is a typical sequence of the silk fibroin, was synthesized, and the atomic‐level conformations of Gly residues at the N‐ and C‐terminal ends of the polyalanine region were determined as well as that of the central Ala residue using 13C 2D spin diffusion solid‐state nuclear magnetic resonance (NMR) under off‐magic angle spinning. In the model peptide with α‐helical conformation, the torsion angle of the central Ala residue, the 19th Ala, was determined to be (ϕ, ψ) = (−60°, −50°), which was a typical α‐helical structure, but the torsion angles of two Gly residues, the 12th and 25th Gly residues, which are located at the N‐ and C‐terminal ends of the polyalanine region, were determined to be (ϕ,ψ) = (−70°, −30°) and (ϕ,ψ) = (−70°, −20°), respectively. Thus, it was observed that the turns at both ends of polyalanine with α‐helix conformation in the model peptide are tightly wound.
Soft Elastohydrodynamic Lubrication With Roughness
Authors: Kim Andrew T. , Seok Jongwon , Tichy John A. , Cale Timothy S.
Published: March 2003

A “soft” elastohydrodynamic lubrication model for a conformal one-dimensional sliding contact is presented. We describe surface-surface and fluid-surface interactions in conditions where asperities are in direct contact (mixed lubrication), and the effective film thickness is comparable in size to the roughness of the bounding surfaces. In the conditions considered, surfaces have a low elastic modulus, and fluid pressures have a low magnitude, relative to those found in most tribology applications. An interesting coupling is exhibited between the surface roughness, the global elasticity, and the fluid pressure. As opposed to typical tribological applications in conformal mixed lubrication contact, fluid pressure is strong enough to cause significant elastic displacement of the mean boundary surfaces. The deformation is taken into account in an iterative process to compute the resulting spatially dependent stresses, deformations and fluid pressures.
Statistical Aspects of Lifetime in the Presence of UV Radiation
Authors: Zeifman Michael I. , Ingman Dov
Published: March 2003

The reliability function of a component cannot be satisfactorily estimated from experiments, because: (i) an accurate estimation of the lifetime distribution tails, controlling the most important domain of high reliability, requires a very large sample and (ii) reliability tests under normal operational conditions are necessarily very lengthy. Hence the urgent need for a physical model for component lifetime statistics. The paper presents an application of the recently developed model for damage accumulation in polymeric materials to the long-term constant stress rupture experiments on Kevlar Composite, which is widely used in fiber optics. The strong dependence of the experimentally observed distribution shape on the load applied to a component has been previously explained in the framework of two different damage mechanisms: kinetic crack growth and chemical deterioration; the resultant 3-parameter lifetime distribution was predicted to be essentially non-Weibull. The proposed model, based on a single micro-mechanical damage mechanism, leads to a 2-parameter Weibull lifetime distribution with the shape parameter depending on the applied load by a simple inverse power law. Both distribution models were fitted to experimental lifetime data for different stress levels and the corresponding goodness of fit was compared by the usual likelihood ratio test. The proposed model describes the experimental data better — especially in the most important domain of low stress and long (of the order of years) lifetime. The model is physically sound and permits improved design of the accelerated tests and more accurate interpretation of their results, and finally quantitative prediction of the reliability function of the loaded polymeric component.
Compression of a Single Transverse Ridge in a Circular Elastohydrodynamic Contact
Authors: Glovnea R. P. , Choo J. W. , Olver A. V. , Spikes H. A.
Published: March 2003

A detailed experimental study has been made of the behavior of a 100 nm high transversely oriented ridge in an elastohydrodynamic (EHD) contact. Ultra-thin film interferometry has been used to measure film profiles accurately over a very wide range of lubricant film thicknesses, from a few nanometers up to nearly one micron. This enables the recovery of the amplitude of the inlet perturbation geometry with increasing EHD film thickness to be quantified and compared with numerical predictions. In pure rolling under very thin film conditions, corresponding to a smooth surface EHD film thickness of 10 nm, the surfaces near the ridge were squashed down, leading to a constriction in the film of only about 9 percent of the height of the un-deformed ridge. As the EHD film thickness increased, this deformation recovered until the ridge constriction regained about 90 percent of its original height at film thicknesses of about 1 μm. However this relatively rapid recovery only occurred in pure rolling and is attributed to the local perturbation of film convergence which the ridge generates while in the inlet region. This propagates through the contact at the mean speed of the surfaces and—in pure rolling—acts to diminish the effect of local squeeze. When sliding was present, the ridge remained almost fully deformed even when the mean film thickness was as much as twice the height of the original ridge. In this case, the ridge travels through the contact at a different speed from the mean of the two surfaces. The consequent decoupling of the ridge and the convergence perturbation results in a large local pressure due to squeeze which acts to inhibit recovery of the ridge. The general trend of the behavior of the lubricated ridge is shown to be in good agreement with earlier theoretical results.
Numerical Three-Dimensional Pressure Patterns in a Recess of a Turbulent and Compressible Hybrid Journal Bearing
Authors: Helene Mathieu , Arghir Mihai , Frene Jean
Published: March 2003

The present work investigates the flow in the feeding recess of a hybrid journal bearing. Numerical integration of the complete Navier-Stokes equations was performed with an appropriate turbulence model. Of primary concern is the pressure field on the rotating journal surface that is commonly known as the recess pressure pattern. The goal of the work is to determine the influences of fluid compressibility, operating conditions and recess geometry. Reference parameters selected for this study comprise feeding Reynolds number Rea of 2.105, sliding Reynolds number Rec of 5.103 and recess depth over film thickness ratio e/H of 2.2. Compressibility was considered first. Three values of the axial exit Mach number were selected for computation, namely 0.2, 0.45, and 0.7. As no significant variation was found, the Mach number was fixed at 0.45 in subsequent studies concerning other parameters:     Feeding Reynolds number, Rea       2.104,2.105,4.105     Recess depth, e/H           0, 2.2, 8     Feedhole axis inclination        90°, 135°, 165°     Feedhole location (Figs. 1(a) and 13)   centered, downstream offset.

As each parameter is varied, wire mesh plot of pressure and its sectional profiles are examined and effects of varying various parameters are discussed in reference to flow processes as they may affect the support characteristics of the hybrid journal bearing.
Theoretical Analysis of the Incompressible Laminar Flow in a Macro-Roughness Cell
Authors: Arghir Mihai , Roucou Nicolas , Helene Mathieu , Frene Jean
Published: March 2003

The present work deals with the analysis of the incompressible laminar shear driven flow in a channel of which one of the walls carries a macro roughness pattern while the opposite one has a parallel velocity. The problem is discussed from the standpoint of lubrication theory and it is shown that the usual simplified models as the Reynolds or the Stokes equations are not applicable. Numerical results are presented for three types of two dimensional macro-roughness and two versions of a three dimensional one. It is shown that a pressure generation effect occurs with increasing the relative importance of convective inertia. Previous analyses found in the literature discussed only the increase of the shear stress due to the presence of the macro roughness but the lift effect due to the pressure generation has never been enlightened up to now. It is further discussed that, extrapolated to a very large number of macro roughness characterizing a textured surface, this new effect could be added to the other lift generating mechanisms of the lubrication theory. It could thus bring a different light on inertia effects stemming from the use of textured surfaces.
Evaluating Thermal Performance of a PTFE-Faced Tilting Pad Thrust Bearing
Authors: Glavatskih Sergei B.
Published: March 2003

This paper compares and analyses operating characteristics of equalizing tilting pad thrust bearings with babbitt and polytetrafluoroethylene (PTFE) composite facings. Each bearing arrangement included six pads with an outer diameter of 228.6 mm and 60 percent offset. The babbitted bearing was typical of design in general use. A PTFE composite was applied instead of the babbitt to a similar bearing. Bearings were tested at different load-speed combinations in the fully flooded mode. Pad temperature distributions, collar temperatures and bearing friction torque were continuously measured. Test results show that the PTFE composite provides excellent thermal insulation so that pad thermal crowning is eliminated. PTFE-faced bearings operate with lower power loss and slightly higher collar temperatures compared to similar babbitted bearings.
Spreading Characteristics of Molecularly Thin Lubricant on Surfaces With Groove-Shaped Textures: Effects of Molecular Weight and End-Group Functionality
Authors: Zhang Hedong , Mitsuya Yasunaga , Yamada Maiko
Published: March 2003

Effects of molecular weight and end-group functionality on spreading of molecularly thin perfluoropolyether (PFPE) film over solid surfaces with groove-shaped textures have been studied by experiments and Monte Carlo simulations. In the experiments, lubricant spreading on a surface with groove-shaped textures was measured by making use of the phenomenon in which diffracted light weakens in the lubricant-covered region. It is found that grooves serve to accelerate spreading and this effect increases for deeper grooves, and also the accelerating rate becomes larger for a lubricant having a larger molecular weight or functional end-groups. In the simulations, the Monte Carlo method based on the Ising model was extended to enable us to evaluate the effect of molecular weight on the spreading of non-functional lubricant inside a groove. The validity of the newly developed simulation method was well confirmed from the agreement between the simulation and experimental results.
Environmental Impact of Fossil Fuel Fired Co-Generation Plants Using a Numerically Standardized LCA Scheme
Authors: Widiyanto Anugerah , Kato Seizo , Maruyama Naoki , Kojima Yoshimasa
Published: March 2003

This paper describes the LCA environmental impacts resulting from fuel fired co-generation systems using our NETS (Numerical Eco-load Total Standard, [1]) scheme having GUI (Graphic User Interface). Following a brief introduction of the NETS evaluation method, firstly the total eco-load from commercial electricity power plants in Japan is numerically calculated in the NETS unit. We take here almost all factors into account including fuel mining, transportation and processing, plant manufacturing, assembling and its building construction, fuel consumption and maintenance during twenty durable years, plant dismantling and waste processing, thermal efficiency and delivery loss, etc. This evaluation greatly helps in the eco-load estimation of co-generation plants when electricity purchase is needed during the plant operation with a minimum eco-load. Next, co-generation systems are paid attention to their ecological effectiveness. Here, we select different fuel fired co-generation plants of natural gas, heavy oil, and coal. Environmental impacts resulting from the respective plants include fossil fuel depletion and natural resources depletion, global warming due to green house gases, ozone layer depletion due to CFC type gas emission, various water and air pollution, rain acidification due to NOx and SOx, waste processing, recycling etc. Each item can be successfully calculated from the inventory database accumulated by authors. Hourly energy demands of electricity and heat (steam, hot water and cold water) are set to a typical model for eight office buildings and two hotels. The NETS method is applied to the co-generation model, resulting in the best cost-operating scheme of co-generation plants with a minimum environmental impact.
An Experimental Study of Controlled Gas-Phase Combustion in Porous Media for Enhanced Recovery of Oil and Gas
Authors: Sanmiguel Javier E. , Mehta S. A. (Raj) , Moore R. Gordon
Published: March 2003

This paper describes an experimental study aimed at establishing fundamental information on the various processes and relevant controlling mechanisms associated with gas-phase combustion in porous media, especially at elevated pressures. A novel apparatus has been designed, constructed and commissioned in order to evaluate the effects of controlling parameters such as operating pressure, gas flow rate, type and size of porous media, and equivalence ratio on combustion characteristics. The results of this study, concerned with lean mixtures of natural gas and air and operational pressures from atmospheric (88.5 kPa or 12.8 psia) to 433.0 kPa (62.8 psia), will be presented. It will be shown that the velocity of the combustion front decreases as the operating pressure of the system increases, and during some test operating conditions, the apparent burning velocities are over 40 times higher than the open flame laminar burning velocities.
Semi-Analytical Dynamic Analysis of Spiral-Grooved Mechanical Gas Face Seals
Authors: Miller Brad A. , Green Itzhak
Published: March 2003

A novel semi-analytical formulation is presented for the linearized dynamic analysis of spiral-grooved mechanical gas face seals. The linearized rotordynamic properties of the gas film are numerically computed and then represented analytically by a constitutive model consisting of a cosine modified Prony series. The cosine modification enables the Prony series to characterize the gas film properties of face seals in applications with large compressibility numbers. The gas film correspondence principle is then employed to couple the constitutive model to the dynamics of the mechanical face seal. Closed-form solutions are presented for the transient natural response to initial velocity conditions, the steady-state response to rotor runout and initial stator misalignment, the transmissibility ratios, and the stability threshold. Results from the closed-form solutions are all within a few percent of the results from a full nonlinear numerical simulation.
Analysis of Contact Mechanics for Rotor-Bristle Interference of Brush Seal
Authors: Stango R. J. , Zhao H. , Shia C. Y.
Published: March 2003

Brush seals have proven to be an attractive alternative to labyrinth seals for turbomachinery applications. This innovation in seal technology utilizes both the high temperature capability of special-alloy wire and the flexural adaptability of fibers to accommodate a wide range of operating conditions that are encountered during service. The effectiveness of the seal is principally derived from the bristles ability to endure forces imparted by both the fluid and shaft, and yet maintain contact between the filament tips and the surface of the rotor. Consequently, contact forces generated along the interface of the fiber tip and rotor are an important consideration for both the design and performance of the rotor-seal assembly. This paper focuses on evaluating brush seal forces that arise along the surface of the rotor due to the dimensional disparity or interference between the rotor-fiber. Filament tip contact forces are computed on the basis of an in-plane, large deformation mechanics analysis of a cantilever beam, and validation of the model is assessed by using an electronic balance for measuring the shear and normal force exerted by a bristle tip onto a flat, hardened surface. Formulation of the mechanics problem is briefly reviewed, and includes the effect of Coulombic friction at the interface of the fiber tip and rotor. Filament contact force is used as a basis for computing bearing stress along the fiber-rotor interface. Results are reported for a range of brush seal design parameters in order to provide a better understanding of the role that seal geometry, friction, and bristle flexural rigidity play in generating rotor contact force.
Elastohydrodynamic Lubrication Analysis of Gear Tooth Surfaces From Micropitting Tests
Authors: Tao J. , Hughes T. G. , Evans H. P. , Snidle R. W. , Hopkinson N. A. , Talks M. , Starbuck J. M.
Published: March 2003

The paper presents numerical results for the elastohydrodynamic lubrication of gear teeth using real surface roughness data taken from micropitting tests carried out on an FZG gear testing machine. Profiles and load conditions corresponding to four load stages in the micropitting test protocol are considered. Elastohydrodynamic film thickness and pressure analyses are presented for conditions having a slide/roll ratio of 0.3 during the single tooth contact phase of the meshing cycle. Comparisons are also included showing the elastohydrodynamic response of the tooth contacts at different times in the meshing cycle for one of the load stages. The rheological model adopted is based on Ree-Eyring non-Newtonian shear thinning, and comparisons are also included of models having constant and different pressure-dependent specifications of the Eyring shear stress parameter τ0. Parameters obtained from the micro EHL analyses are presented that quantify the degree of adversity experienced by the surfaces in elastohydrodynamic contact. These quantify extreme pressure behavior, extreme proximity of surfaces, and pressure cycling within the overall contact and indicate that the different fluid models considered lead to significantly different pressure and film thickness behavior within the contact.
Improvement of the THD Performance of a Misaligned Plain Journal Bearing
Authors: Bouyer J. , Fillon M.
Published: March 2003

This numerical study deals with the improvement of the thermohydrodynamic performance of a 100 mm plain journal bearing submitted to a constant misalignment torque under steady-state conditions. The performance of the misaligned journal bearing is improved by adding either a local or a global defect to the bearing geometry. The influence on bearing performance of the local defect, situated in the zone of minimum film thickness, is analyzed by using various widths and lengths of defect. A global defect, which is conical in shape and is located at one end of the bearing, is also studied under varying direction and magnitude of misalignment torque. Our main focus was on hydrodynamic pressure, temperature distributions at the film/bush interface, oil flow rate, power losses and film thickness. The defects significantly improved the performance of the bearing. The minimum film thickness increased by more than 60 percent and the temperature decreased, whilst the axial flow rate was barely affected. Thus, the defects can be an effective solution for misaligned bearings when they are submitted to extreme operating conditions.
Gas-Liquid Cylindrical Cyclone (GLCC©) Compact Separators For Wet Gas Applications
Authors: Wang Shoubo , Gomez Luis E. , Mohan Ram S. , Shoham Ovadia , Kouba Gene E.
Published: March 2003

Gas-Liquid Cylindrical Cyclone (GLCC©1) separators are becoming increasingly popular as attractive alternatives to conventional separators as they are simple, compact, less expensive, have low-weight, and require little maintenance. However, present studies focus on GLCC designs and applications at relatively lower gas velocities (below the minimum velocity for onset of liquid carry-over in the form of annular/mist flow). With appropriate modifications, GLCCs can be used for wet gas (high gas liquid ratio, GLR) applications, characterized by higher gas velocities, to knock out the liquid droplets from the gas core. The objectives of this study are to design a novel GLCC capable of separating liquid from a wet gas stream; conduct experimental investigations to evaluate the GLCC performance improvement in terms of operational envelope for liquid carry-over; and, quantify the liquid extraction from the gas stream. GLCC design considerations/guidelines for wet gas application are also provided based on the experimental studies at low pressures. This investigation extends the capabilities of compact separators for wet gas applications for insitu gas volume fraction (GVF) greater than 95%.
Determination of the Skin Factor for a Well Produced at a Constant Bottomhole Pressure
Authors: Kutasov I. M. , Kagan M.
Published: March 2003

A new technique has been developed for analyzing the constant bottomhole pressure (BHP) test data. The method presented in this paper allows to calculate the skin factor for damaged and stimulated oil wells. Advantages of the BHP test are: (1) they do not require that the well be shut in; (2) the fluid production can be easily controlled (at constant flow rate tests the BHP is changing with time); and (3) wellbore storage effects on the test data are short-lived. It is assumed that the instantaneous flow rate and time data are available from a well produced against a constant bottomhole pressure. Only records of the flowing time and flow rate data are required to compute the value of the skin factor. A semi theoretical equation is used to approximate the dimensionless flow rate. This formula is used to obtain a quadratic equation for determining the skin factor. The accuracy of the basic quation will be shown below. The paper includes an example of calculation.
A Gas-Liquid Flowmeter Combining Vertical and Horizontal Pressure Fluctuations Induced by Local Void Fraction Variations
Authors: Toma P. , Ridley R. , Chen M.
Published: March 2003

Two AC signals generated by two sensors mounted in two elbows at the ends of vertical and horizontal branches of a metering pipe are simultaneously recorded and analyzed. The AC signals are mainly due to fluctuations in stagnation-pressure caused by the local oscillations of local void fraction and to transport velocity of the gas-liquid flow. Features extracted from stochastic interpretation of the two signals are strongly related to gas and liquid flowrates. Laboratory and field testing of the new meter demonstrated that, for the same gas and liquid flowrates, probability distribution functions (PDF) determined from statistical analysis of “vertical” and “horizontal” AC signals are unique. For broad ranges of gas-liquid ratios, features extracted from the PDF are linearly related to gas and liquid flowrates.
Operation Performance of a Small Air-Lift Pump for Conveying Solid Particles
Authors: Fujimoto Hitoshi , Ogawa Satoshi , Takuda Hirohiko , Hatta Natsuo
Published: March 2003

The pump performance of a small air-lift system for conveying solid particles is investigated experimentally. The total length of the vertical lifting pipe is 3200 mm, and the inner diameter of the pipe is 18 mm. The gas injector is set at a certain point of the pipe. The flows in the lifting pipe are water/solid two-phase mixtures below the gas injection point, and air/water/solid three-phase mixtures above it. The time-averaged characteristics of the flows are examined for various experimental conditions. The effects of particle diameter, particle density, the gas-injection point, and the volume flux of air on the pump performance are studied systematically. The critical boundary at which the particles can be lifted is discussed in detail based upon one-dimensional mixture model.
A CFD Based Correlation for Erosion Factor for Long-Radius Elbows and Bends
Authors: Wang Jianrong , Shirazi Siamack A.
Published: March 2003

A model for predicting sand erosion in 90 degree elbows and bends has been developed based on computational fluid dynamics (CFD), particle tracking and erosion data. After the flow field was obtained from the flow (CFD) model, particles were introduced into the flow and particle trajectories were computed using a Lagrangian approach. A model was also implemented that accounts for the interaction between the particles and the target material. Based on predicted particle impingement velocities, erosion rates and penetration rates were predicted using the empirical equations for erosion ratio. The predicted penetration rates are compared with available experimental data for several different elbows. The agreement between the predicted penetration rates and the experimental data is good. In addition, based on many predictions and erosion rate results, a new CFD based correlation is developed that can be used for an approximate engineering calculation to account for effects of elbow radius on erosion in long-radius elbows. This equation is for computing the ratio of the wall thickness loss (or the penetration rate) in a long-radius elbow to the penetration rate of a standard (short-radius) elbow. The results from the correlation agree well with the trend of available data in the literature.
Strength Evaluation of Plastic Packages During Solder Reflow Process Using Stress Intensity Factors of V-Notch
Authors: Ikeda Toru , Arase Isao , Ueno Yuya , Miyazaki Noriyuki , Ito Nobutaka , Nagatake Mami , Sato Mitsuru
Published: March 2003

A crack initiated from a V-notch corner in the molding resin, such as a corner of die pad, is one of the main causes of the failure in plastic packages. The stress intensity factors of the asymptotic solution of a corner of jointed dissimilar materials are utilized for the evaluation of a solder reflow crack in a quad flat package (QFP). First, we estimate the critical vapor pressure, which causes a crack from a corner in the molding resin, using the critical stress intensity factor of a V-notch corner. This critical factor was measured by V-notched three-point bending tests and the displacement extrapolation method along with the three dimensional (3-D) finite element method (FEM). Moisture concentration in the QFP after absorption is analyzed, and vapor pressure caused by the solder reflow process is estimated. The critical moisture absorption time, which results in crack occurrence during the solder reflow process, can be predicted using this evaluation technique. Furthermore, we perform infrared solder reflow tests of the QFP for verifying the present failure evaluation technique.
Digital Signal Processing in a Novel Flip Chip Solder Joint Defects Inspection System
Authors: Liu Sheng , Ume I. Charles
Published: March 2003

Digital signal processing methods in a novel flip chip solder joint quality inspection system are presented. Laser ultrasound and interferometric system is a new approach for solder joint inspection. It has many advantages such as being noncontact, nondestructive, fast, accurate and low cost. Furthermore, it can be used on-line in assembly line or off-line during process development. In this system, signals recorded are ultrasound waveforms. Because noise is present, signal processing methods are developed to increase signal-to-noise ratio, and to extract solder joint quality information from those waveforms. Signals are analyzed both in frequency domain and time domain. In the frequency domain, digital filtering and Bartlett power spectrum estimation method are used, and defects can be detected from the frequency shifting. A series of experimental results are presented, showing that power spectrum estimation can greatly increase the signal-to-noise ratio than when only time domain averaging is used. This speeds up the data acquisition and analysis process. In the time domain, “error ratio” is used to measure the difference between a good chip and a chip with defect. Results indicate that error ratio method not only can detect whether a chip has solder joint defect or not, but can also locate that defect. Overall, signal processing plays a very important role in this flip chip quality inspection system.
Large Deflection of Thin Plates Under Certain Mixed Boundary Conditions—Cylindrical Bending
Authors: Xue Yibin , Jairazbhoy Vivek A. , Niu Xiaoting , Qu Jianmin
Published: March 2003

Considered in this paper is the large deflection of a thin beam. One end of the beam is fixed (clamped) to a rigid wall, while the other end is placed on a flat surface of arbitrary orientation. Under the assumption that the axial deformation of the neutral axis is negligible, a closed form analytical solution to the deflection curve is obtained in terms of elliptical functions. The analytical solution is shown to have certain scalability properties with respect to the beam length and cross-section. By using appropriate bending rigidity, the same solution can be used for a thin plate under large cylindrical bending. In addition, a finite element analysis using nonlinear shell elements is also conducted showing the axial strain of the neutral axis to be less than one percent of the overall deformation. Therefore, it is valid to assume that the axial strain is negligible.
Temperature and Strain Rate Effects on Tensile Strength and Inelastic Constitutive Relationship of Sn-Pb Solders
Authors: Nose Haruo , Sakane Masao , Tsukada Yutaka , Nishimura Hideo
Published: March 2003

This paper describes the tensile strength and inelastic constitutive relationship of six types of Sn-Pb solders. Static tension tests were carried using 5Sn-95Pb, 10Sn-90Pb, 40Sn-60Pb, 60Sn-40Pb, 63Sn-37Pb, and 62Sn-36Pb-2Ag solders at the strain rates of 0.001–10.0%/s between temperatures of 313 K and 398 K. Strain rates faster than 2.0%/s were needed to obtain the time-independent Young modulus and yield stress of the solders. Tensile strength increased with increasing strain rates up to 10%/s. Parametric equations for predicting tensile strength, Young’s modulus and yield stress of Sn-Pb solders were developed as a function of temperature and Sn content. Plastic and creep constitutive equations were also proposed as a function of temperature and Sn content. The stress amplitude predicted by these equations agreed with the experimental results within ±2 MPa.
An Experimental Assessment of Numerical Predictive Accuracy for Electronic Component Heat Transfer in Forced Convection—Part II: Results and Discussion
Authors: Rodgers Peter J. , Eveloy Vale´rie C. , Davies Mark R.
Published: March 2003

Numerical predictive accuracy is assessed for component-printed circuit board (PCB) heat transfer in forced convection using a widely used computational fluid dynamics (CFD) software. In Part I of this paper, the benchmark test cases, experimental methods and numerical models were described. Component junction temperature prediction accuracy for the populated board case is typically within ±5°C or ±10%, which would not be sufficient for temperature predictions to be used as boundary conditions for subsequent reliability and electrical performance analyses. Neither the laminar or turbulent flow model resolve the complete flow field, suggesting the need for a turbulence model capable of modeling transition. The full complexity of component thermal interaction is shown not to be fully captured.
Impact Resistance of SM Joints Formed With ICA
Authors: Wu C. M. Lawrence , Li Robert K. Y. , Yeung N. H.
Published: March 2003

Isotropic conductive adhesives (ICA) have been considered as replacement materials for lead-tin solder alloys. In this paper, the post-impact shear strength of ICA surface mount (SM) joints was obtained experimentally and compared with that of SM lead-tin joints. The dynamic impact energy was provided in the form of three-point bending on the PCB using equipment called the split Hopkinson bar. Strain rates of over 4000/s were used for the impact bending test. The action of impact bending was used to simulate the effect on the PCB and the interconnection as a result of high energy impact on an electronic equipment. Shear test was then performed to examine the change in strength of the ICA joints as a result of impact damage. It was found that the SM ICA joints failed due to impact at a strain rate just over 4000/s. Microstructural examination carried out using a scanning electron microscope revealed that the interface between the ICA and copper pad on the PCB was the weakest region of the joint.
Analytical Solutions for Heat Transfer During Cyclic Melting and Freezing of a Phase Change Material Used in Electronic or Electrical Packaging
Authors: Chakraborty Suman , Dutta Pradip
Published: March 2003

In this paper, we develop an analytical heat transfer model, which is capable of analyzing cyclic melting and solidification processes of a phase change material used in the context of electronics cooling systems. The model is essentially based on conduction heat transfer, with treatments for convection and radiation embedded inside. The whole solution domain is first divided into two main sub-domains, namely, the melting sub-domain and the solidification sub-domain. Each sub-domain is then analyzed for a number of temporal regimes. Accordingly, analytical solutions for temperature distribution within each sub-domain are formulated either using a semi-infinity consideration, or employing a method of quasi-steady state, depending on the applicability. The solution modules are subsequently united, leading to a closed-form solution for the entire problem. The analytical solutions are then compared with experimental and numerical solutions for a benchmark problem quoted in the literature, and excellent agreements can be observed.
Thermomechanical Stress Analysis of Multi-Layered Electronic Packaging
Authors: Wen Yujun , Basaran Cemal
Published: March 2003

An accurate estimate of thermal stresses in multilayered microelectronics structures along the bonded interfaces is crucial for design and prediction of delamination-related failures. Compared with a numerical method, analytical closed-form solution can offer a more rapid method to obtain the stresses at the interfaces. An analytical model for ply-level sub-laminate analysis is investigated in this paper. The theory presented treats each layer as a beam-type plate with orthotropic material properties. As an example, the results are shown for a three-layer beam problem with special orthotropic material properties. Analytical model results are compared with the finite element analysis results, as a first order approximation.
Stress and Reliability Analysis of Electronic Packages With Ultra-Thin Chips
Authors: Shkarayev Sergey , Savastiouk Sergey , Siniaguine Oleg
Published: March 2003

This research concerns itself with a stress and reliability analysis of electronic packages with ultra-thin chips based on the finite element method. The effect of chip and substrate thickness, substrate material, presence of underfill, dimensions, and shape of the bump on stress reduction is analyzed. Obtained results clearly show that chip thinning, when used with an appropriate design of the entire package, can significantly decrease stresses and stress intensity factors and improve the reliability of the package. The developed software provides an effective design tool to quantify the reliability, stresses, and deflections of a package with ultra-thin chips.
The Strength of the Silicon Die in Flip-Chip Assemblies
Authors: Cotterell B. , Chen Z. , Han J.-B. , Tan N.-X.
Published: March 2003

The mechanical reliability of silicon dies is affected by the defects introduced by surface grinding and edge dicing. The ring-on-ring and the four-point-bend test have been used in this study to separate the distribution in strength for these two types of defect. At low probabilities of failure, it is the “strength” of the edge defects that dominate the reliability. However, if the edges of the die are only lightly stressed compared with the surface, edge defects are unlikely to cause fracture. In this case the use of the four-point-bend test, which is sensitive to both edge and surface defects, will result in an underestimate of the reliability and if only one test is to be performed the ring-on-ring test is preferable to the four-point-bend test. Generally, for a full reliability estimate, the distributions of both types of defect need to be determined.
Heat Transfer and Flow Friction Characteristics for Compact Cold Plates
Authors: Liu Chang-Yuan , Hung Ying-Huei
Published: March 2003

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.