bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of the conserved Lys68*:Glu265 intersubunit salt bridge in aspartate aminotransferase kinetics: Multiple forced covariant amino acid substitutions in natural variants
Authors: Deu Edgar , Koch Keith A. , Kirsch Jack F.
Published: July 2002

The role of the Lys68*

Residues pertaining to the opposite subunit.

:Glu265 intersubunit salt bridge that is conserved (Csb) in all known aspartate aminotransferases (AATases), except those of animal cytosolic, Ac (His68*:Glu265), and plant mitochondrial, Pm (Met68*:Gln265), origins, was evaluated in the Escherichia coli AATase. Two double‐mutant cycles, to K68M/E265Q and the charge reversed K68E/E265K, were characterized with the context dependence (C) and impact (I) formalism, previously defined for functional chimeric analysis. Mutations of Lys68* with Glu265 fixed are generally more deleterious than the converse mutations of Glu265 with Lys68* fixed, showing that buried negative charges have greater effects than buried positive charges in this context. Replacement of the charged Lys68*:Glu265 with the K68M/E265Q neutral pair introduces relatively small effects on the kinetic parameters. The differential sensitivity of kcat/KM, L‐Asp and kcat/KM, α‐KG to salt bridge mutagenic replacements is shown by a linear‐free energy relationship, in which the logarithms of the latter second order rate constants are generally decreased by a factor of two more than are those of the former. Thus, kcat/KM, L‐Asp and kcat/KM, α‐KG are 133 and 442 mM−1s−1 for the wild‐type (WT) enzyme, respectively, but their relative order is reversed in the more severely compromised mutants (14.8 and 5.3 mM−1s−1 for K68E). A Venn diagram illustrates apparent forced covariances of groups of amino acids that accompany the naturally occurring salt bridge replacements in the Pm and Ac classes. The more deeply rooted tree indicates that the Csb variant was the ancestral specie.
Reduced antibody response to streptavidin through site‐directed mutagenesis
Authors: Meyer Damon L. , Schultz Jody , Lin Yukang , Henry Andrew , Sanderson James , Jackson Jeffrey M. , Goshorn Steve , Rees Anthony R. , Graves Scott S.
Published: July 2002

Streptavidin provides an effective receptor for biotinylated tumoricidal molecules, including radionuclides, when conjugated to an antitumor antibody and administered systemically. Ideally, one would like to administer this bacterial protein to patients repeatedly, so as to maximize the antitumor effect without eliciting an immune response. Therefore, we attempted to reduce the antigenicity of streptavidin by mutating surface residues capable of forming high energy ionic or hydrophobic interactions. A crystallographic image of streptavidin was examined to identify residues with solvent‐exposed side chains and residues critical to streptavidin's structure or function, and to define loops. Mutations were incorporated cumulatively into the protein sequence. Mutants were screened for tetramer formation, biotin dissociation, and reduced immunoreactivity with pooled patient sera. Patient antisera recognized one minor continuous epitope with binding locus at residue E101 and one major discontinuous epitope involving amino acid residues E51 and Y83. Mutation of residues E51, Y83, R53, and E116 reduced reactivity with patient sera to <10% that of streptavidin, but these mutations were no less antigenic in rabbits. Mutant 37, with 10 amino acid substitutions, was only 20% as antigenic as streptavidin. Rabbits immunized with either streptavidin or mutant 37 failed to recognize the alternative antigen. Biotin dissociated from mutant 37 four to five times faster than from streptavidin. Residues were identified with previously undescribed impact on biotin binding and protein folding. Thus, substitution of charged, aromatic, or large hydrophobic residues on the surface of streptavidin with smaller neutral residues reduced the molecule's ability to elicit an immune response in rabbits.
Presence of the cofactor speeds up folding of Desulfovibrio desulfuricans flavodoxin
Authors: Apiyo David , Wittung‐Stafshede Pernilla
Published: July 2002

Flavodoxin is an α/β protein with a noncovalently bound flavin‐mononucleotide (FMN) cofactor. The apo‐protein adopts a structure identical to that of the holo‐form, although there is more dynamics in the FMN‐binding loops. The equilibrium unfolding processes of Azotobacter vinelandii apo‐flavodoxin, and Desulfovibrio desulfuricans ATCC strain 27774 apo‐ and holo‐flavodoxins involve rather stable intermediates. In contrast, we here show that both holo‐ and apo‐forms of flavodoxin from D. desulfuricans ATCC strain 29577 (75% sequence similarity with the strain 27774 protein) unfold in two‐state equilibrium processes. Moreover, the FMN cofactor remains bound to the unfolded holo‐protein. The folding and unfolding kinetics for holo‐flavodoxin exhibit two‐state behavior, albeit an additional slower phase is present at very low denaturant concentrations. The extrapolated folding time in water for holo‐flavodoxin, ∼280 μsec, is in excellent agreement with that predicted from the protein's native‐state topology. Unlike the holo‐protein behavior, the folding and unfolding reactions for apo‐flavodoxin are best described by two kinetic phases, with rates differing ∼15‐fold, suggesting the presence of a kinetic intermediate. Both folding phases for apo‐flavodoxin are orders of magnitude slower (40‐ and 530‐fold, respectively) than that for the holo‐protein. We conclude that polypeptide–cofactor interactions in the unfolded state of D. desulfuricans strain 29577 flavodoxin alter the kinetic‐folding path towards two‐state and speed up the folding reaction.
Pressure versus temperature unfolding of ribonuclease A: An FTIR spectroscopic characterization of 10 variants at the carboxy‐terminal site
Authors: Torrent Joan , Rubens Peter , Ribó Marc , Heremans Karel , Vilanova Maria
Published: July 2002

FTIR spectroscopy was used to characterize and compare the temperature‐ and pressure‐induced unfolding of ribonuclease A and a set of its variants engineered in a hydrophobic region of the C‐terminal part of the molecule postulated as a CFIS. The results show for all the ribonucleases investigated, a cooperative, two‐state, reversible unfolding transition using both pressure and temperature. The relative stabilities, among the different sites and different variants at the same site, monitored either through the changes in the position of the maximum of the amide I′ band and the tyrosine band, or the maximum of the band assigned to the β‐sheet structure, corroborate the results of a previous study using fourth‐derivative UV absorbance spectroscopy. In addition, variants at position 108 are the most critical for ribonuclease structure and stability. The V108G variant seems to present a greater conformational flexibility than the other variants. The pressure‐ and temperature‐denaturated states of all the ribonucleases characterized retained some secondary structure. However, their spectral maxima were centered at different wavenumbers, which suggests that pressure‐ and temperature‐denaturated states do not have the same structural characteristics. Nevertheless, there was close correlation between the pressure and temperature midpoint transition values for the whole series of protein variants, which indicated a common tendency of stability toward pressure and heat.
Reactivity of peptidyl‐tyrosine to hydroxylation and cross‐linking
Authors: Burzio Luis A. , Waite J. Herbert
Published: July 2002

Tyrosine residues of neuroendocrine peptides are frequently the targets of oxidation reactions, one of which involves hydroxylation to peptidyl‐3, 4‐dihydroxy‐phenyl‐L‐alanine (DOPA). The reactivity in vitro of peptidyl‐DOPA in two neuroendocrine peptides, a neurotensin fragment (pELYENK) and proctolin (RYLPT), was investigated using ultraviolet‐visible scanning spectrophotometry and matrix‐assisted laser desorption ionization mass spectrometry following oxidation by tyrosinase and periodate. The peptides form covalently coupled dimers and trimers, and their masses are consistent with the presence of diDOPA cross‐links. Lysine does not appear to participate in multimer formation because it is efficiently recovered in fragmentation ladders using subtilisin. While multimer formation in the neurotensin‐derived peptide can be blocked effectively by adding N‐acetyl‐DOPA‐ethylester to the reaction medium, the DOPA ethylester couples itself four to five times to each peptide.
X‐ray structure of a novel matrix metalloproteinase inhibitor complexed to stromelysin
Authors: Dunten Pete , Kammlott Ursula , Crowther Robert , Levin Wayne , Foley Louise H. , Wang Ping , Palermo Robert
Published: July 2002

A new class of matrix metalloproteinase (MMP) inhibitors has been identified by screening a collection of compounds against stromelysin. The inhibitors, 2,4,6‐pyrimidine triones, have proven to be potent inhibitors of gelatinases A and B. An X‐ray crystal structure of one representative compound bound to the catalytic domain of stromelysin shows that the compounds bind at the active site and ligand the active‐site zinc. The pyrimidine triones mimic substrates in forming hydrogen bonds to key residues in the active site, and provide opportunities for placing appropriately chosen groups into the S1′ specificity pocket of MMPs. A number of compounds have been synthesized and assayed against stromelysin, and the variations in potency are explained in terms of the binding mode revealed in the X‐ray crystal structure.
Thermodynamic analysis of the binding of component enzymes in the assembly of the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus
Authors: Jung Hyo‐Il , Bowden Simon J. , Cooper Alan , Perham Richard N.
Published: July 2002

The peripheral subunit‐binding domain (PSBD) of the dihydrolipoyl acetyltransferase (E2, EC 2.3.1.12) binds tightly but mutually exclusively to dihydrolipoyl dehydrogenase (E3, EC 1.8.1.4) and pyruvate decarboxylase (E1, EC 1.2.4.1) in the pyruvate dehydrogenase multienzyme complex of Bacillus stearothermophilus. Isothermal titration calorimetry (ITC) experiments demonstrated that the enthalpies of binding (ΔH°) of both E3 and E1 with the PSBD varied with salt concentration, temperature, pH, and buffer composition. There is little significant difference in the free energies of binding (ΔG° = −12.6 kcal/mol for E3 and = −12.9 kcal/mol for E1 at pH 7.4 and 25°C). However, the association with E3 was characterized by a small, unfavorable enthalpy change (ΔH° = +2.2 kcal/mol) and a large, positive entropy change (TΔS° = +14.8 kcal/mol), whereas that with E1 was accompanied by a favorable enthalpy change (ΔH° = −8.4 kcal/mol) and a less positive entropy change (TΔS° = +4.5 kcal/mol). Values of ΔCp of −316 cal/molK and −470 cal/molK were obtained for the binding of E3 and E1, respectively. The value for E3 was not compatible with the ΔCp calculated from the nonpolar surface area buried in the crystal structure of the E3‐PSBD complex. In this instance, a large negative ΔCp is not indicative of a classical hydrophobic interaction. In differential scanning calorimetry experiments, the midpoint melting temperature (Tm) of E3 increased from 91°C to 97.1°C when it was bound to PSBD, and that of E1 increased from 65.2°C to 70.0°C. These high Tm values eliminate unfolding as a major source of the anomalous ΔCp effects at the temperatures (10–37°C) used for the ITC experiments.
Modulation by permeant ions of Mg2+ inhibition of NMDA‐activated whole‐cell currents in rat cortical neurons
Authors: Qian Anqi , Antonov Sergei M. , Johnson Jon W.
Published: July 2002

Whole‐cell N‐methyl‐d‐aspartate (NMDA)‐activated currents were recorded from cultured rat cortical neurons. We report here a powerful effect of changing permeant ion concentrations on the voltage‐dependent inhibition by external Mg2+ (Mg2+ (Mgo2+) of these currents. Internal Cs+ (Csi+) affected Mgo2+ inhibition of the NMDA‐activated currents in a voltage‐dependent manner. A decrease in Csi+ concentration ([Cs+]i) from 125 to 8 mm reduced Mgo2+ IC50 by 1.4‐fold at −105 mV and by 11.5‐fold at – 15 mV. A decrease in external Na+ (Nao+ concentration ([Na+]o) also reduced Mgo2+ IC50. This effect was voltage independent. A decrease in [Na+]o from 140 to 70 mm reduced Mgo2+ IC50 by 1.4‐fold at–105 mV and by 1.6‐fold at–15 mV. Varying external Ca2+ (Cao2+) concentrations ([Ca2+]o) from 0.1 to1 mm did not affect Mgo2+ inhibition, even though changing [Ca2+]o in the same range strongly influenced the magnitude of NMDA‐activated currents in the absence of Mgo2+. However, increasing [Ca2+]o to higher concentrations (2–20 mm) greatly increased Mgo2+ IC50 at hyperpolarized voltages. These data are consistent with a model in which Nai+ and Csi+ modulate Mgo2+ inhibition of NMDA‐activated currents by occupying external permeant ion binding sites. The Mgo2+ IC50 values reported here are similar to Mgo2+KD values calculated from previous single‐channel measurements of Mgo2+ blocking kinetics. This similarity implies that Mgo2+ does not affect gating while blocking the channel.
Comparison of aconitine‐modified human heart (hH1) and rat skeletal (μ1) muscle Na+ channels: an important role for external Na+ ions
Authors: Wright Sterling N.
Published: July 2002

Neurotoxins such as aconitine (AC) bind to receptor site 2 on voltage‐gated sodium channels and modify channel kinetics. Although AC modification typically induces hyperpolarizing shifts in sodium channel activation, the effects on channel inactivation seem to vary depending on the tissue origin of the channel. In the present study, the α subunits of human heart (hH1) and rat skeletal muscle (μ1) sodium channels were transiently expressed in human embryonic kidney (HEK293t) cells. Whole‐cell currents were examined before and after AC modification of the channels to determine whether the toxin had isoform‐specific effects on channel kinetics. The magnitudes of the hyperpolarizing shifts in steady‐state current activation and inactivation were similar for AC‐modified hH1 and μ1 channels, and AC modification did not alter the voltage dependence of macroscopic current decay of either channel subtype. There were two notable differences between hH1 and μ1 channels after AC modification. First, the steady‐state availability of AC‐modified μ1 channels decreased by 5–10 % after very negative conditioning pulses. Second, AC‐modified μ1 channels inactivated completely at all voltages, whereas AC‐modified hH1 channels exhibited sustained inward currents at voltages near the threshold of current activation. Interestingly, AC‐modified hH1 channels inactivated completely if the external solution did not contain sodium ions. The data demonstrate that AC modification affects the activation of hH1 and μ1 channels similarly but affects inactivation of the two channels distinctly. The results also imply that the reduced inactivation of AC‐modified hH1 channels at least partially depends on the presence of extracellular sodium.
Association of upregulated activity of KATP channels with impaired insulin secretion in UCP1‐expressing insulinoma cells
Authors: Nakazaki Mitsuhiro , Kakei Masafumi , Ishihara Hisamitsu , Koriyama Nobuyuki , Hashiguchi Hiroshi , Aso Katsumi , Fukudome Michiyo , Oka Yoshitomo , Yada Toshihiko , Tei Chuwa
Published: July 2002

Insulin‐secreting MIN6 cells overexpressing uncoupling protein‐1 (UCP1) were studied regarding insulin secretion in response to various secretagogues. Overexpression of UCP1 prevented an increase of cytosolic ATP levels induced by glucose. In contrast, glucose utilization was not affected, nor was glycerol phosphate flux. The UCP1‐expressing cells showed an inability to increase cytosolic Ca2+ concentration ([Ca2+]i) in response to glucose or α ketoisocaproate and this resulted in less insulin secretion, whereas initial reduction in [Ca2+]i occurring upon either nutrient addition was not affected. Moreover, the effectiveness of tolbutamide on [Ca2+]i increase was reduced and the dose‐response relations for insulin secretion induced by the agent was shifted toward the right in the UCP1‐expressing cells. The resting membrane potential of the UCP1‐expressing cells was significantly hyperpolarized by 6.2 mV compared with control cells. In the perforated and conventional whole‐cell patch‐clamp configurations, the conductance density of ATP‐sensitive K+ (KATP) channels of the UCP1‐expressing cells was 6‐fold and 1.7‐fold greater than that of the control cells, respectively. The sensitivity of KATP channels for tolbutamide was not different between two groups, indicating that in intact cells more than 6‐fold higher concentrations of tolbutamide were required to reduce the KATP channel currents of UCP1‐expressing cells to the same levels as of the control cells. The current density of the voltage‐dependent Ca2+ channels was not influenced. In conclusion, UCP1‐expressing cells showed a refractoriness to respond to tolbutamide as well as nutrients. An upregulated activity of KATP channels was associated with unresponsiveness to the agent in the cells with impaired mitochondrial function.
Differential effects of sarcoplasmic reticular Ca2+‐ATPase inhibition on charge movements and calcium transients in intact amphibian skeletal muscle fibres
Authors: Chawla Sangeeta , Skepper Jeremy N. , Huang Christopher L.‐H.
Published: July 2002

A hypothesis in which intramembrane charge reflects a voltage sensing process allosterically coupled to transitions in ryanodine receptor (RyR)‐Ca2+ release channels as opposed to one driven by release of intracellularly stored Ca2+ would predict that such charging phenomena should persist in skeletal muscle fibres unable to release stored Ca2+. Charge movement components were accordingly investigated in intact voltage‐clamped amphibian fibres treated with known sarcoplasmic reticular (SR) Ca2+‐ATPase inhibitors. Cyclopiazonic acid (CPA) pretreatment abolished Ca2+ transients in fluo‐3‐loaded fibres following even prolonged applications of caffeine (10 mM) or K+ (122 mM). Both CPA and thapsigargin (TG) transformed charge movements that included delayed (qγ) ‘hump’ components into simpler decays. However, steady‐state charge‐voltage characteristics were conserved to values (maximum charge, Qmax∼ 20–25 nC μF−1; transition voltage, V*∼−40 to −50 mV; steepness factor, k∼ 6–9 mV; holding voltage −90 mV) indicating persistent qγ charge. The features of charge inactivation similarly suggested persistent qβ and qγ charge contributions in CPA‐treated fibres. Perchlorate (8.0 mm) restored the delayed kinetics shown by ‘on’qγ charge movements, prolonged their ‘off’ decays, conserved both Qmax and k, yet failed to restore the capacity of such CPA‐treated fibres for Ca2+ release. Introduction of perchlorate (8.0 mm) or caffeine (0.2 mm) to tetracaine (2.0 mm)‐treated fibres, also known to restore qγ charge, similarly failed to restore Ca2+ transients. Steady‐state intramembrane qγ charge thus persists with modified kinetics that can be restored to its normally complex waveform by perchlorate, even in intact muscle fibres unable to release Ca2+. It is thus unlikely that qγ charge movement is a consequence of SR Ca2+ release rather than changes in tubular membrane potential.
Fast Ca2+ signals at mouse inner hair cell synapse: a role for Ca2+‐induced Ca2+ release
Authors: Kennedy Helen J. , Meech Robert W.
Published: July 2002

Inner hair cells of the mammalian cochlea translate acoustic stimuli into ‘phase‐locked’ nerve impulses with frequencies of up to at least 1 kHz. Little is known about the intracellular Ca2+ signal that links transduction to the release of neurotransmitter at the afferent synapse. Here, we use confocal microscopy to provide evidence that Ca2+‐induced Ca2+ release (CICR) may contribute to the mechanism. Line scan images (2 ms repetition rate) of neonatal mouse inner hair cells filled with the fluorescent indicator FLUO‐3, revealed a transient increase in intracellular Ca2+ concentration ([Ca2+]i) during brief (5–50 ms) depolarizing commands under voltage clamp. The amplitude of the [Ca2+]i transient depended upon the Ca2+ concentration in the bathing medium in the range 0–1.3 mm. [Ca2+]i transients were confined to a region near the plasma membrane at the base of the cell in the vicinity of the afferent synapses. The change in [Ca2+]i appeared uniform throughout the entire basal sub‐membrane space and we were unable to observe hotspots of activity. Both the amplitude and the rate of rise of the [Ca2+]i transient was reduced by external ryanodine (20 μm), an agent that blocks Ca2+ release from the endoplasmic reticulum. Intracellular Cs+, commonly used to record at presynaptic sites, produced a similar effect. We conclude that both ryanodine and intracellular Cs+ block CICR in inner hair cells. We discuss the contribution of CICR to the measured [Ca2+]i transient, the implications for synaptic transmission at the afferent synapse and the significance of its sensitivity to intracellular Cs+.
Expression pattern and functional characteristics of two novel splice variants of the two‐pore‐domain potassium channel TREK‐2
Authors: Gu Wenli , Schlichthörl Günter , Hirsch Jochen R. , Engels Hartmut , Karschin Christine , Karschin Andreas , Derst Christian , Steinlein Ortrud K. , Daut Jürgen
Published: July 2002

Two novel alternatively spliced isoforms of the human two‐pore‐domain potassium channel TREK‐2 were isolated from cDNA libraries of human kidney and fetal brain. The cDNAs of 2438 base pairs (bp) (TREK‐2b) and 2559 bp (TREK‐2c) encode proteins of 508 amino acids each. RT‐PCR showed that TREK‐2b is strongly expressed in kidney (primarily in the proximal tubule) and pancreas, whereas TREK‐2c is abundantly expressed in brain. In situ hybridization revealed a very distinct expression pattern of TREK‐2c in rat brain which partially overlapped with that of TREK‐1. Expression of TREK‐2b and TREK‐2c in human embryonic kidney (HEK) 293 cells showed that their single‐channel characteristics were similar. The slope conductance at negative potentials was 163 ± 5 pS for TREK‐2b and 179 ± 17 pS for TREK‐2c. The mean open and closed times of TREK‐2b at −84 mV were 133 ± 16 and 109 ± 11 μs, respectively. Application of forskolin decreased the whole‐cell current carried by TREK‐2b and TREK‐2c. The sensitivity to forskolin was abolished by mutating a protein kinase A phosphorylation site at position 364 of TREK‐2c (construct S364A). Activation of protein kinase C (PKC) by application of phorbol‐12‐myristate‐13‐acetate (PMA) also reduced whole‐cell current. However, removal of the putative TREK‐2b‐specific PKC phosphorylation site (construct T7A) did not affect inhibition by PMA. Our results suggest that alternative splicing of TREK‐2 contributes to the diversity of two‐pore‐domain K+ channels.
Robust Tolerance Synthesis With the Design of Experiments Approach
Authors: Feng Chang-Xue (Jack) , Kusiak Andrew
Published: July 2002

Design of tolerances impacts quality, cost, and cycle time of a product. Most literature on deterministic tolerance design has focused on developing exact and heuristic algorithms to minimize manufacturing cost. Some research has been published on probabilistic tolerance synthesis and optimization. This paper presents the design of experiments (DOE) approach for concurrent selection of component tolerances and the corresponding manufacturing processes. The objective is to minimize the variation of tolerance stackups. Numerical examples illustrate the methodology. The Monte Carlo simulation approach is used to obtain component tolerances and tolerance stackups. Process shift, the worst case and root sum square tolerance stackup constraints, and setup reduction constraints have been incorporated into the proposed methodology. Benefits of the proposed DOE approach over exact algorithms are discussed. [S1087-1357(00)00202-1]
Numerical Properties of the Discrete Gas Cavity Model for Transients
Authors: Liou Jim C. P.
Published: July 2002

Wylie’s discrete gas cavity model offers a simple way to simulate transients in liquids with a small amount of free gas, and to model vaporous and gaseous cavitations. It uses a constant and gas-free wave speed to avoid interpolations and a weighting factor to control numerical oscillations. The model has an intriguing ability to capture features associated with pressure-dependent wave speeds. This paper describes a von Neumann analysis on this model, shows why the need for the weighting factor and how to select it, and explains why the model exhibits variable wave speed features. [S0098-2202(00)00703-3]
Durability and Damage Development in Woven Ceramic Matrix Composites Under Tensile and Fatigue Loading at Room and Elevated Temperatures
Authors: Haque A. , Rahman M.
Published: July 2002

This paper investigates the damage development in SiC/SiNC woven composites under tensile and cyclic loading both at room and elevated temperatures. The ultimate strength, failure strain, proportional limit, and modulus data at a temperature range of 23°C–1250°C are generated. The tensile strength of SiC/SiNC woven composites has been observed to increase with increased temperatures up to 1000°C. The stress/strain plot shows a pseudo-yield point at 25 percent of the failure strain εf, which indicates damage initiation in the form of matrix cracking. The evolution of damage above 0.25 εf both at room and elevated temperature comprises of multiple matrix cracking, interfacial debonding, and fiber pullout. Although the nature of the stress/strain plot shows damage-tolerant behavior under static loading both at room and elevated temperature, the life expectancy of SiC/SiNC composites degrades significantly under cyclic loading at elevated temperature. This is mostly due to the interactions of fatigue damage caused by the mechanically induced plastic strain and the damage developed by the creep strain. The in-situ damage evolutions are monitored by acoustic event parameters, ultrasonic C-scan, and stiffness degradation. Rate equations for modulus degradation and fatigue life prediction of ceramic matrix composites both at room and elevated temperatures are developed. These rate equations are observed to show reasonable agreement with experimental results. [S0094-4289(00)02304-5]
Software “Reliability”?
Authors: Hanmer Robert S.
Published: July 2002

Many systems composed of both hardware and software components are expected to be failure-free. This article discusses software reliability and presents the reader with an understanding of why it is meaningful to talk in terms of the reliability of software components. Software faults, unlike hardware faults, are not related to the physical properties of the components. They are the products of the design processes and software’s interfaces to other parts of the system. Just how well the software handles software and hardware faults to prevent errors from occurring determines how reliable the software and the system are deemed to be. [S1043-7398(00)00304-2]
Flow Measurements in a Nozzle Guide Vane Passage With a Low Aspect Ratio and Endwall Contouring
Authors: Burd Steven W. , Simon Terrence W.
Published: July 2002

Most turbine cascade studies in the literature have been performed in straight-endwall, high-aspect-ratio, linear cascades. As a result, there has been little appreciation for the role of, and added complexity imposed by, reduced aspect ratios. There also has been little documentation of endwall profiling with these reduced spans. To examine the role of these factors on cascade hydrodynamics, a large-scale nozzle guide vane simulator was constructed at the Heat Transfer Laboratory of the University of Minnesota. This cascade is comprised of three airfoils between one contoured and one flat endwall. The geometries of the airfoils and endwalls, as well as the experimental conditions in the simulator, are representative of those in commercial operation. Measurements with hot-wire anemometry were taken to characterize the flow approaching the cascade. These measurements show that the flow field in this cascade is highly elliptic and influenced by pressure gradients that are established within the cascade. Exit flow field measurements with triple-sensor anemometry and pressure measurements within the cascade indicate that the acceleration imposed by endwall contouring and airfoil turning is able to suppress the size and strength of key secondary flow features. In addition, the flow field near the contoured endwall differs significantly from that adjacent to the straight endwall. [S0889-504X(00)01104-1]
Numerical Prediction of the Hydrodynamic Loads and Vortex-Induced Vibrations of Offshore Structures
Authors: Schulz Karl W. , Kallinderis Yannis
Published: July 2002

An incompressible Navier-Stokes flow algorithm is coupled with an elastic body structural response to numerically investigate the hydrodynamics of several relevant offshore applications. These applications include the effects of surface roughness on a bare cylinder and the study of vortex-induced vibrations (VIV) for a cylinder at high Reynolds numbers. The Reynolds number for the roughness cases was Re=4×106, while the Reynolds number for the VIV cases ranged from 2.25×105⩽Re⩽4.75×105. Additional VIV cases were also performed for two common suppression devices: strakes and fairings. The results from both the roughness and bare cylinder VIV applications were compared to experimental data in order to further validate the numerical scheme and illustrate the effectiveness of applying Navier-Stokes technologies to offshore applications. [S0892-7219(00)00604-X]
Vortex Generators in Lean-Premix Combustion
Authors: Eroglu A. , Do¨bbeling K. , Joos F. , Brunner P.
Published: July 2002

A novel fuel-air mixing technique on the basis of vortex generators has been developed and successfully implemented in the worlds first lean-premix reheat combustor of ABB’s GT24/GT26 series industrial gas turbines. This technique uses a special arrangement of delta-wing type vortex generators to achieve rapid mixing through longitudinal vortices, which produce low pressure drop and no recirculation zones along the mixing section. In this paper, after a short introduction to the topic, the motivation for utilizing vortex generators and the main considerations in their design are explained. A detailed analysis of the flow field, pressure drop and the strength of the vortices generated by a single vortex generator are presented as one of the three main geometrical parameters is varied. The results obtained through water model tests indicate that an optimum vortex generator geometry exists, which produces the maximum circulation at a relatively low pressure drop price. Moreover, the axial velocity distribution along the mixing section stays uniform enough to assure flash-back free operation despite the elevated inlet temperatures encountered in a reheat combustor. After selecting this optimized geometry, the process of the arrangement of multiple vortex generators in an annular combustor segment is described. The optimum arrangement presented here is suitable both for gaseous and liquid fuel injection, since it requires only one injection location per combustor segment.
Mixed-Convection Laminar Film Condensation on an Inclined Elliptical Tube
Authors: Mosaad M.
Published: July 2002

The present theoretical study concerns with mixed-convection laminar film condensation outside an inclined elliptical tube with isothermal surface. The assumptions used are as in the classical Nusselt-Rohsenow theory, however, with considering the interfacial vapor shear by extending a circular-tube shear model developed in a previous study. An equivalent diameter, based on equal surface area, is introduced in the analysis to enable comparison with circular tubes. For zero ellipticity, the approach simplifies to the circular tube model developed in our previous work. A numerical solution has been obtained for a wide range of the independent parameters. The results indicate that the heat transfer performance of the inclined elliptical tube enhances with the increase of tube ellipticity compared to an inclined circular tube of equivalent diameter. For forced-convection-dominated film condensation, the rate of this enhancement in the heat transfer coefficient is found smaller than that for pure-free-convection film.
Analytical Thermal Models of Oblique Moving Heat Source for Deep Grinding and Cutting
Authors: Jin T. , Cai G. Q.
Published: July 2002

Three related analytical thermal models of plane heat source moving obliquely along the surface of a semi-infinite solid are presented. The temperature distribution of grinding zone under deep-cut conditions is investigated with these models. It is proposed that the oblique angle of the heat source plane to its moving direction has an essential influence on the grinding zone temperature rise and its distribution of high efficiency deep grinding (HEDG). Compared with that in creep-feed grinding, HEDG has a different form of heat flux distribution in grinding zone and should be treated with different thermal models. The temperature distribution at the shear zone of orthogonal cutting is also briefly discussed with the thermal models. The models developed in the paper provide a more rational and integrated analytical basis for dealing with the heat transfer problems of inclined moving heat sources.
Forces and Energy in Circular Sawing and Grinding of Granite
Authors: Xu Xipeng , Li Yuan , Malkin Stephen
Published: July 2002

An investigation is reported of the forces and energy in circular sawing and grinding of gray granite. Measurements were made of the forces and power over a wide range of sawing and grinding conditions. Calculated tangential force components were found to be much different than the measured horizontal force components for sawing, but the two forces were almost identical for grinding. The location of the resultant force was proportionally further away from the bottom of the cutting zone with longer contact lengths. For sawing, the normal force per grain was nearly proportional to the calculated undeformed chip thickness. The G-ratios at different sawing rates reached a maximum value at the same intermediate undeformed chip thickness, which was attributed to a transition in the diamond wear mechanism from attrition to fracture at a critical normal force per grain. SEM observations indicated material removal mainly by brittle fracture, with some evidence of ductile plowing especially for grinding and to a lesser extent for sawing. The corresponding fracture energy was estimated to constitute a negligible portion of the total energy expenditure. About 30 percent of the sawing energy might be due to the interaction of the swarf with the applied fluid and bond matrix. Most of the energy for sawing and grinding is attributed to ductile plowing. Analogous to recent studies on grinding of ceramics and glass, the power per unit width was found to increase linearly with the generation of plowed surface area per unit width.
Double Cantilever Beam Measurement and Finite Element Analysis of Cryogenic Mode I Interlaminar Fracture Toughness of Glass-Cloth/Epoxy Laminates
Authors: Shindo Y. , Horiguchi K. , Wang R. , Kudo H.
Published: July 2002

An experimental and analytical investigation in cryogenic Mode I interlaminar fracture behavior and toughness of SL-E woven glass-epoxy laminates was conducted. Double cantilever beam (DCB) tests were performed at room temperature (R.T.), liquid nitrogen temperature (77 K), and liquid helium temperature (4 K) to evaluate the effect of temperature and geometrical variations on the interlaminar fracture toughness. The fracture surfaces were examined by scanning electron microscopy to verify the fracture mechanisms. A finite element model was used to perform the delamination crack analysis. Critical load levels and the geometric and material properties of the test specimens were input data for the analysis which evaluated the Mode I energy release rate at the onset of delamination crack propagation. The results of the finite element analysis are utilized to supplement the experimental data.
Study of Subcooled Film Boiling on a Horizontal Disc:1 Part 2—Experiments
Authors: Banerjee D. , Dhir V. K.
Published: July 2002

Experiments were performed to study subcooled film boiling of performance liquid PF-5060 (made by 3-M Company) on a horizontal copper disc. The experiments were performed for two regimes of film boiling involving departing vapor bubbles (low subcooling) and nondeparting vapor bubbles (high subcooling). By employing high speed digital camera, data were obtained for temporal variation of bubble height, bubble shape and bubble growth rate over one cycle. Heat flux data were deduced from temperatures measured with thermocouples embedded in the solid. The results from the numerical model are compared with experimental data and are found to be in general agreement. Particle Tracking Velocimetry (PTV) experiments were performed for a configuration of non-departing vapor bubbles to study the flow field in the liquid phase. The PTV experiments point to the existence of natural convection flow in the liquid phase and is in qualitative agreement with the predictions available in the literature.
Solarthermal Processing: A Review
Authors: Fletcher Edward A.
Published: July 2002

Research on solarthermal processing and the need for alternative energy sources have reached the point where efforts to develop some industrial processes and expand research to suggest others are at least desirable, if not imperative. This paper presents a rationale for such an effort, describes the underlying thermodynamics, and summarizes much of the research which has been conducted in the years since the end of World War II. Major emphasis is placed on the work that has been done since the imposition of the 1973 oil embargo and the present.
Adaptive Influence Coefficient Control of Single-Plane Active Balancing Systems for Rotating Machinery
Authors: Dyer Stephen W. , Ni Jun
Published: July 2002

Rotating unbalance is a costly source of harmful vibration affecting a wide variety of applications such as high-speed machine tools and turbomachinery. Active balancing technology allows adjustment of a machine’s balance state while conditions change as the machine continues to operate. An adaptive control law for single-plane active balancing is presented here for control of steady-state rotation-synchronous vibration. The adaptive control method, based on the well known “influence coefficient” approach, requires no a priori modeling or estimation of plant dynamics. A control “gain” parameter is introduced and shown to enhance stability robustness of the nonadaptive portion of the control law. A recursive on-line system identification method is presented that uses exponential weighted averaging to mitigate the effects of measurement noise and system nonlinearities. Experimental results establish the efficacy of the adaptive control system even in the face of certain nonlinear and time-varying rotordynamic systems.
Turbine Separation Control Using Pulsed Vortex Generator Jets
Authors: Bons Jeffrey P. , Sondergaard Rolf , Rivir Richard B.
Published: July 2002

The application of pulsed vortex generator jets to control separation on the suction surface of a low-pressure turbine blade is reported. Blade Reynolds numbers in the experimental, linear turbine cascade match those for high-altitude aircraft engines and aft stages of industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets have a 30 deg pitch and a 90 deg skew to the free-stream direction. Jet flow oscillations up to 100 Hz are produced using a high-frequency solenoid feed valve. Results are compared to steady blowing at jet blowing ratios less than 4 and at two chordwise positions upstream of the nominal separation zone. Results show that pulsed vortex generator jets produce a bulk flow effect comparable to that of steady jets with an order of magnitude less massflow. Boundary layer traverses and blade static pressure distributions show that separation is almost completely eliminated with the application of unsteady blowing. Reductions of over 50 percent in the wake loss profile of the controlled blade were measured. Experimental evidence suggests that the mechanism for unsteady control lies in the starting and ending transitions of the pulsing cycle rather than the injected jet stream itself. Boundary layer spectra support this conclusion and highlight significant differences between the steady and unsteady control techniques. The pulsed vortex generator jets are effective at both chordwise injection locations tested (45 and 63 percent axial chord) covering a substantial portion of the blade suction surface. This insensitivity to injection location bodes well for practical application of pulsed VGJ control where the separation location may not be accurately known a priori.
On Dynamics of Bar of Rectangular Cross Section
Authors: Rassoulova N. B.
Published: July 2002

The propagation of nonstationary waves in semi-infinite elastic rectangular bars is studied. It is assumed that two opposite lateral surfaces of the body are free of forces, while the two others are subjects to cross conditions. By introducing three new potential functions, the author succeeded in getting closed-form solutions in Laplace and Fourier transform parameters. Inversion of the transform solutions, carried out by an original method of inversion, is suggested herein.
Rupture of Thin Power-Law Liquid Film on a Cylinder
Authors: Gorla Rama Subba Reddy
Published: July 2002

The dynamic rupture process of a thin power-law type non-Newtonian liquid film on a cylinder has been analyzed by investigating the stability to finite amplitude disturbances. The dynamics of the liquid film is formulated using the balance equations including a body force term due to van der Waals attractions. The governing equation for the film thickness was solved by finite difference method as part of an initial value problem for spatial periodic boundary conditions. A decrease in the cylinder radius will induce a stronger lateral capillary force and thus will accelerate the rupture process. The influence of the power-law exponent on rupture is discussed.
A Dispersive Model for Wave Propagation in Periodic Heterogeneous Media Based on Homogenization With Multiple Spatial and Temporal Scales
Authors: Chen W. , Fish J.
Published: July 2002

A dispersive model is developed for wave propagation in periodic heterogeneous media. The model is based on the higher order mathematical homogenization theory with multiple spatial and temporal scales. A fast spatial scale and a slow temporal scale are introduced to account for the rapid spatial fluctuations as well as to capture the long-term behavior of the homogenized solution. By this approach the problem of secularity, which arises in the conventional multiple-scale higher order homogenization of wave equations with oscillatory coefficients, is successfully resolved. A model initial boundary value problem is analytically solved and the results have been found to be in good agreement with a numerical solution of the source problem in a heterogeneous medium.
Three-Dimensional Elastic-Plastic Finite-Element Analysis of the Flattening of Wire Between Plain Rolls*
Authors: Utsunomiya H. , Hartley P. , Pillinger I.
Published: July 2002

It is normal industrial practice to roll round edged flat wires from round circular wires using plain rolls. Although this is not a complex type of metal forming process, the internal deformation is highly three-dimensional. It is important to be able to determine the lateral spread, elongation and final profile precisely. In this paper, this process has been analyzed using an elastic-plastic finite element program. Firstly, algorithms for integrating the constitutive equations, i.e., return mapping algorithms, are evaluated to determine the most accurate technique. Then, the influences of friction and reduction in thickness on the deformation characteristics are investigated. The lateral spread and the radius of curvature of the free surface are quantitatively in reasonable agreement with those obtained from empirical formulas. The lateral spread increases with friction and with reduction. The variation of elongation in the roll bite is investigated in detail. It is found that the elongation is not uniformly distributed across the cross section. After passing the roll gap, the distribution is compensated by the elastic recovery of wire, otherwise it may cause edge waves.
High-Pressure Steam-Driven Jet Pump—Part II: Parametric Analysis
Authors: Beithou N. , Aybar H. S.
Published: July 2002

The steam-driven jet pump (SDJP) is a device without moving parts, in which steam is used as an energy source to pump cold water from a pressure much lower than the steam pressure to a pressure higher than the steam pressure. In the previous part of this study, the mathematical modeling of the SDJP has been done, and reported. The results of the mathematical modeling of the SDJP have been compared with Cattadori’s experimental results. The comparisons show that the experimental and calculated pressure distributions are in good qualitative agreement. For the same steam inlet pressure of 8.7 MPa, the discharge pressures in the experiment and in the simulation are 9.8 MPa and 9.54 MPa, respectively. The relative difference is two percent. It can be said that the computed discharge pressure is in good agreement with the experimental result. In the current study, a parametric analysis of the SDJP has been done in terms of four independent parameters: steam inlet pressure and temperature, supply water pressure, and temperature. The output parameters are: discharge pressure, temperature, and mass flow rate. As a result of this parametric study, the operation characteristics of the SDJP have been obtained.
Rapid and Accurate Calculation of Water and Steam Properties Using the Tabular Taylor Series Expansion Method
Authors: Miyagawa K. , Hill P. G.
Published: July 2002

In applications where both speed and accuracy of computation of thermodynamic properties are important and particularly where the independent variables are not those used in Helmholtz equations, direct use of such equations can be excessively time-consuming. This paper introduces the enthalpy-pressure version of the tabular Taylor series (TTSE) method, which has the accuracy and computing speed required for application in power industries. The IAPWS formulation for scientific use, IAPWS-95, was used as the basic Helmholtz equation. The speed and accuracy of the TTSE have been compared with the IAPWS formulation for industrial use, IAPWS-IF97, which has been developed to achieve high-speed calculation with good representation of IAPWS-95 values. Test results show that the TTSE accurately represents the basic equation and that the computation speed is higher than that of IF97.
Formulation and Numerical Solution of Non-Local Thermal Equilibrium Equations for Multiple Gas/Solid Porous Metal Hydride Reactors
Authors: Lloyd George M. , Razani A. , Kim Kwang J.
Published: July 2002

The assumption of local thermal equilibrium (LTE) is very common in the study of reacting flows in porous media. The assumption simplifies the structure of the solutions and places fewer constraints on computational methods for the domain and boundary conditions. However, in certain systems, such as gas/solid metal hydride reactors, the boundary conditions may impose high energy transfer rates which produce slowly evolving phase change fronts coupled with rapid kinetics. Overall performance of the systems is proportional to the release or absorption of hydrogen, and this is sensitively related to temperature. Thus, capturing local departures from LTE is required. This paper directly evaluates the influence of these effects by solving an NLTE (non-local thermal equilibrium) formulation for coupled reactors as a function of the interphase heat transfer coefficient, hsf. The reactor dynamics and overall energy balances are compared to solutions previously obtained from LTE calculations. The results appear to be the first NLTE results for coupled reactors. They confirm the existence of NLTE effects and suggest the magnitude of hsf for which they can be minimized.