bluuebunny/crossref_metadata_2025 huggingface dataset:
Gibberellins and Seed Development in Maize. II. Gibberellin Synthesis Inhibition Enhances Abscisic Acid Signaling in Cultured Embryos
Authors: White Constance N. , Rivin Carol J.
Published: July 2002

Abscisic acid (ABA) is required for seed maturation in maize (Zea mays L.) and other plants. Gibberellins (GAs) are also present in developing maize embryos, and mutual antagonism of GAs and ABA appears to govern the choice between precocious germination or quiescence and maturation. Exogenous ABA can also induce quiescence and maturation in immature maize embryos in culture. To examine the role of GAs versus ABA in regulating maize embryo maturation, the effects of modulating GA levels were compared with those of ABA in embryos cultured at successive stages of development. The effects of GA synthesis inhibition or exogenous GA application differed markedly in embryos at different stages of development, indicating changes in both endogenous GA levels and in the capacity for GA synthesis as embryogenesis and maturation progress. In immature embryos, the inhibition of GA synthesis mimicked the effects of exogenous ABA, as shown by the suppression of germination, the acquisition of anthocyanin pigments, and the accumulation of a variety of maturation-phase mRNAs. We suggest that GA antagonizes ABA signaling in developing maize embryos, and that the changing hormone balance provides temporal control over the maturation phase.
Characterization of Sulfate Assimilation in Marine Algae Focusing on the Enzyme 5′-Adenylylsulfate Reductase
Authors: Gao Yu , Schofield Oscar M.E. , Leustek Thomas
Published: July 2002

5′-Adenylylsulfate (APS) reductase was characterized in diverse marine algae. A cDNA encoding APS reductase from Enteromorpha intestinalis (EAPR) was cloned by functional complementation of an Escherichia coli cysH mutant. The deduced amino acid sequence shows high homology with APS reductase (APR) from flowering plants. Based on the probable transit peptide cleavage site the mature protein is 45.7 kD. EAPR expressed as a His-tagged recombinant protein catalyzes reduced glutathione-dependent reduction of APS to sulfite, exhibiting a specific activity of approximately 40 μmol min−1 mg protein−1 and Michealis-Menten kinetic constants of approximately 1.4 mm for reduced glutathione and approximately 6.5 μm for APS. APR activity and expression were studied in relation to the production of 3-dimethylsulfoniopropionate (DMSP), a sulfonium compound produced by many marine algae. A diverse group of DMSP-producing species showed extremely high enzyme activity (up to 400 times that found in flowering plants). Antibodies raised against a conserved peptide of APR strongly cross-reacted with a protein of 45 kD in several chlorophytes but insignificantly with chromophytes. In the chlorophyteTetraselmis sp., APR activity varies significantly during the culture cycle and does not follow the changes in cellular DMSP content. However, a positive correlation was found between cell-based APR activity and specific growth rate.
Assembly, Secretion, and Vacuolar Delivery of a Hybrid Immunoglobulin in Plants
Authors: Frigerio Lorenzo , Vine Nicholas D. , Pedrazzini Emanuela , Hein Mich B. , Wang Fei , Ma Julian K.-C. , Vitale Alessandro
Published: July 2002

Secretory immunoglobulin (Ig) A is a decameric Ig composed of four α-heavy chains, four light chains, a joining (J) chain, and a secretory component (SC). The heavy and light chains form two tetrameric Ig molecules that are joined by the J chain and associate with the SC. Expression of a secretory monoclonal antibody in tobacco (Nicotiana tabacum) has been described: this molecule (secretory IgA/G [SIgA/G]) was modified by having a hybrid heavy chain sequence consisting of IgG γ-chain domains linked to constant region domains of an IgA α-chain. In tobacco, about 70% of the protein assembles to its final, decameric structure. We show here that SIgA/G assembly and secretion are slow, with only approximately 10% of the newly synthesized molecules being secreted after 24 h and the bulk probably remaining in the endoplasmic reticulum. In addition, a proportion of SIgA/G is delivered to the vacuole as at least partially assembled molecules by a process that is blocked by the membrane traffic inhibitor brefeldin A. Neither the SC nor the J chain are responsible for vacuolar delivery, because IgA/G tetramers have the same fate. The parent IgG tetrameric molecule, containing wild-type γ-heavy chains, is instead secreted rapidly and efficiently. This strongly suggests that intracellular retention and vacuolar delivery of IgA/G is due to the α-domains present in the hybrid α/γ-heavy chains and indicates that the plant secretory system may partially deliver to the vacuole recombinant proteins expected to be secreted.
A New Set of Arabidopsis Expressed Sequence Tags from Developing Seeds. The Metabolic Pathway from Carbohydrates to Seed Oil,
Authors: White Joseph A. , Todd Jim , Newman Tom , Focks Nicole , Girke Thomas , de Ilárduya Oscar Martı́nez , Jaworski Jan G. , Ohlrogge John B. , Benning Christoph
Published: July 2002

Large-scale single-pass sequencing of cDNAs from different plants has provided an extensive reservoir for the cloning of genes, the evaluation of tissue-specific gene expression, markers for map-based cloning, and the annotation of genomic sequences. Although as of January 2000 GenBank contained over 220,000 entries of expressed sequence tags (ESTs) from plants, most publicly available plant ESTs are derived from vegetative tissues and relatively few ESTs are specifically derived from developing seeds. However, important morphogenetic processes are exclusively associated with seed and embryo development and the metabolism of seeds is tailored toward the accumulation of economically valuable storage compounds such as oil. Here we describe a new set of ESTs from Arabidopsis, which has been derived from 5- to 13-d-old immature seeds. Close to 28,000 cDNAs have been screened by DNA/DNA hybridization and approximately 10,500 new Arabidopsis ESTs have been generated and analyzed using different bioinformatics tools. Approximately 40% of the ESTs currently have no match in dbEST, suggesting many represent mRNAs derived from genes that are specifically expressed in seeds. Although these data can be mined with many different biological questions in mind, this study emphasizes the import of photosynthate into developing embryos, its conversion into seed oil, and the regulation of this pathway.
Light Differentially Regulates Cell Division and the mRNA Abundance of Pea Nucleolin during De-Etiolation
Authors: Reichler Stuart A. , Balk Janneke , Brown Margaret E. , Woodruff Kathryn , Clark Greg B. , Roux Stanley J.
Published: July 2002

The abundance of plant nucleolin mRNA is regulated during de-etiolation by phytochrome. A close correlation between the mRNA abundance of nucleolin and mitosis has also been previously reported. These results raised the question of whether the effects of light on nucleolin mRNA expression were a consequence of light effects on mitosis. To test this we compared the kinetics of light-mediated increases in cell proliferation with that of light-mediated changes in the abundance of nucleolin mRNA using plumules of dark-grown pea (Pisum sativum) seedlings. These experiments show that S-phase increases 9 h after a red light pulse, followed by M-phase increases in the plumule leaves at 12 h post-irradiation, a time course consistent with separately measured kinetics of red light-induced increases in the expression of cell cycle-regulated genes. These increases in cell cycle-regulated genes are photoreversible, implying that the light-induced increases in cell proliferation are, like nucleolin mRNA expression, regulated via phytochrome. Red light stimulates increases in the mRNA for nucleolin at 6 h post-irradiation, prior to any cell proliferation changes and concurrent with the reported timing of phytochrome-mediated increases of rRNA abundance. After a green light pulse, nucleolin mRNA levels increase without increasing S-phase or M-phase. Studies in animals and yeast indicate that nucleolin plays a significant role in ribosome biosynthesis. Consistent with this function, pea nucleolin can rescue nucleolin deletion mutants of yeast that are defective in rRNA synthesis. Our data show that during de-etiolation, the increased expression of nucleolin mRNA is more directly regulated by light than by mitosis.
Continuing Professional Development: Perspectives from Human Resource
Professionals
Authors: Jones Norman , Fear Nicola
Published: July 2002

Explores several important issues associated with continuing
professional development (CPD). Notes the importance of ensuring that
CPD is driven by the needs of the business, and also considers the issue
of whether CPD should be compulsory or voluntary. Presents the results
of a survey targeted at human resource professionals in South Wales. The
survey explored the attitude of respondents to a variety of CPD issues
and found that, although most organizations had business plans, such
plans were frequently silent on human resource activities which could
enhance general business direction. Respondents, while remaining
over‐whelmingly opposed to compulsory CPD, were in favour of some
certification and recognition for CPD activities.
A factor approach to the analysis of components’ defects in housing stock
Authors: Olubodun Femi
Published: July 2002

This paper seeks to explore and detect underlying relationships between identifiable primary causes of defects in local authority housing stock with the view to identifying which groups of building components are associated with one another. It is primarily based on responses to a questionnaire from building surveyors who were involved in the day‐to‐day diagnosis of defects of a large local authority housing stock. The intercorrelations among the primary defect‐causing factors demanded the application of principal component analysis to determine the factors affecting deterioration of the building fabric. This resulted in the extraction of nine significant factors which combine to exert their influence on the building.
The impact of lecture theatre design on learning experience
Authors: Fleming David , Storr John
Published: July 2002

This exploratory research investigates the issues surrounding the impact of lecture facilities on the student learning experience. Given the growing administrative significance of lecturer/student ratios, room utilization and occupancy levels, the importance of the lecture facility in the academic programmes of universities is central. Facility function must have an effect on future design decisions in regard to both new build facilities and refurbishment projects. The better informed those decisions are, the greater the quality of the learning experiences taking place in them. The methodology and findings of a research project are considered. It was found that generic design criteria can form the basis for benchmarking facility performance.
Liquefaction phenomenon of granular materials and constitutive stability
Authors: Darve Félix
Published: July 2002

Liquefaction phenomenon and its catastrophic nature can be analysed as a particular material behaviour of granular media under certain loading paths. Proposes a definition of liquefaction and its modelling by constitutive relations. Discusses this modelling in relation to the questions of stability and uniqueness. Considers the signs of three scalar quantities: the work of second order, the determinant of the symmetric part of the tangent constitutive tensor and the determinant of the tensor itself. Concludes that the liquefaction path is situated inside a potentially unstable domain and that in some cases this path reaches some states of loss of uniqueness, which are essentially bifurcation points.
Promoting reflective practice in initial teacher training
Authors: Moran Anne , Dallat John
Published: July 2002

Sets out to examine five school‐based initial teacher training
schemes and to assess the most successful aspects of each. Aims in
particular to investigate the ways in which student teachers are
encouraged and assisted systematically to reflect on their practice. All
those interviewed (student teachers, mentors and university tutors)
recognized reflection as a crucial component of the mentoring process
for structuring the analysis of teaching, but considered it a complex
and challenging activity. Mentors lacked confidence in their ability to
analyse and make explicit their implicit theories of teaching.
Furthermore, they were inhibited by a lack of training, the time
available and by the absence of a collaborative and supportive working
environment. Learning to teach undoubtedly involves the mastery of
reflective practice in which teaching performance is developed
simultaneously with thinking about teaching.
Contractile responses of smooth muscle cells differentiated from rat neural stem cells
Authors: Oishi Kazuhiko , Ogawa Yasuhiro , Gamoh Shuji , Uchida Masaatsu K.
Published: July 2002

To characterize the functional differentiation of neural stem cells into smooth muscle cells, multipotent stem cells in the central nervous system (CNS) were isolated from rat embryonic day 14 (E14) cortex and cultured by neurosphere formation in serum‐free medium in the presence of 10 ng ml−1 of basic fibroblast growth factor. Differentiation was induced by the addition of 10 % fetal bovine serum to low‐density cultures (2.5 × 103 cells cm−2). Immunological analyses and reverse transcriptase‐polymerase chain reaction indicated that the differentiated cells expressed smooth‐muscle‐specific marker proteins such as SM‐1, SM‐2, and SMemb myosin heavy chains, SM‐22, basic calponin and α‐smooth‐muscle actin, but not the astrocyte marker glial fibrillary acidic protein. To examine whether smooth‐muscle‐like cells that are differentiated from CNS stem cells possess the characteristics of contractile smooth muscle, we prepared reconstituted collagen gel fibres and measured their contractile tension. The reconstituted fibres were prepared by thermal gelation of collagen and the differentiated cells. The fibres contracted in response to treatment with KCl (80 mm), ACh (100 μm), endothelin‐1 (10 nm), endothelin‐2 (10 nm), and prostaglandin F2α (100 μm). ACh‐induced contraction was partially inhibited by the L‐type voltage‐dependent Ca2+ channel inhibitor nifedipine and by the intracellular Ca2+ chelator 1,2‐bis (2‐aminophenoxy) ethane‐N,N,N’,N'‐tetraacetic acid acetoxymethyl ester, the myosin light chain kinase inhibitor ML‐9, the Rho kinase inhibitor Y‐27632, dibutyryl cAMP and 8‐bromo‐cGMP. These results suggest that CNS stem cells give rise to smooth muscle cells in vitro that have an identical contractile function to smooth muscle in vivo.
Muscle glycogen content and glucose uptake during exercise in humans: influence of prior exercise and dietary manipulation
Authors: Steensberg Adam , van Hall Gerrit , Keller Charlotte , Osada Takuya , Schjerling Peter , Klarlund Pedersen Bente , Saltin Bengt , Febbraio Mark A.
Published: July 2002

There are many factors that can influence glucose uptake by contracting skeletal muscle during exercise and although one may be intramuscular glycogen content, this relationship is at present not fully elucidated. To test the hypothesis that muscle glycogen concentration influences glucose uptake during exercise, 13 healthy men were studied during two series of experiments. Seven men completed 4 h of two‐legged knee extensor exercise 16 h after reducing of muscle glycogen by completing 60 min of single‐legged cycling (Series 1). A further six men completed 3 h of two‐legged knee extensor exercise on two occasions: one after 60 min of two‐legged cycling (16 h prior to the experimental trial) followed by a high carbohydrate diet (HCHO) and the other after the same exercise followed by a low carbohydrate diet (LCHO) (Series 2). Muscle glycogen was decreased by 40 % when comparing the pre‐exercised leg (EL) with the control leg (CL) prior to exercise in Series 1. In addition, muscle glycogen was decreased by the same magnitude when comparing LCHO with HCHO in Series 2. In Series 1, glucose uptake was 3‐fold higher in the first 60 min of exercise, in the presence of unchanged pre‐exercise GLUT4 protein in EL compared with CL, suggesting that the lower glycogen, and not the exercise the day before, might have provided the stimulus for increased glucose uptake. Despite the same magnitude of difference in pre‐exercise glycogen concentration when comparing Series 1 with Series 2, neither direct‐nor isotopic tracer‐determined glucose uptake was higher in LCHO compared with HCHO in Series 2. However, arterial concentrations of insulin and glucose were lower, while free fatty acids and adrenaline were higher in LCHO compared with HCHO. These data suggest that pre‐exercise glycogen content may influence glucose uptake during subsequent exercise. However, this is only the case when delivery of substrates and hormones remains constant. When delivery of substrates and hormones is altered, the potential effect of glycogen on glucose uptake is negated.
Scaling Laws of Hydrodynamic Noise Generation for a Simple Fluid Valve Model
Authors: Prek Matjaz
Published: July 2002

Noise-source mechanisms for the simple fluid valve model were observed and compared with predicted mechanisms. A comparison of the predicted mechanisms with the experimental data indicated that the scaling laws could be further improved by a re-examination of the influence of the impact parameters. This was done by an extended analysis of the influence of geometrical parameters on acoustical characteristics. Additional parameters were determined statistically using nonlinear multiple regression analysis of the experimental data. The estimated correlation between the observed and predicted values for the applied geometrical and hydrodynamic parameters are good. [S0739-3717(00)01303-9]
Manufacturing Block Diagrams and Optimal Adjustment Procedures
Authors: Frey Daniel D. , Otto Kevin N. , Taketani Stan
Published: July 2002

This paper introduces a technique for modeling manufacturing systems using block diagrams. The blocks represent linear transformations of dimensionless noise vectors to normalized quality characteristic vectors. These block diagrams are used to model on-line adjustment procedures using generalized inverses. This adjustment strategy is shown to guarantee minimum quality loss as defined by Taguchi if the required adjustments have no active constraints, and is effective for coupled linear systems. The surface mount of large body packages serves as an example of the modeling techniques. Block diagrams of the surface mount process are developed for a production system incorporating on-line adjustments and for the same system without adjustments. Data from preproduction runs support the model’s predictions of bias, variance, and yield.
Experimental and 3D Finite Element Studies of CW Laser Forming of Thin Stainless Steel Sheets
Authors: Chen Guofei , Xu Xianfan
Published: July 2002

Laser forming as a springback-free and noncontact forming technique has been under active investigation over the last decade. Previous investigations are mainly focused on forming of large and thick workpieces using high power lasers, with less work on precision, micro-scale bending of small and thin sheets. In this work, a 4 W continuous wave argon ion laser is used as the energy source, and the laser beam is focused to a beam diameter of tens of micrometers to induce bending of thin stainless steel sheets. When the laser scanning velocity is above 8 mm/s, bending can be explained by the temperature gradient mechanism, while decreasing the scanning velocity leads to the buckling mechanism of bending. The bending angle is measured at various processing conditions. A fully 3D finite element analysis is performed to simulate the thermo-elasto-plastic deformation process during laser forming. Experimental measurements and computational results agree in trend, and reasons for the deviation are discussed.
Cavitation and Mushrooming in Attack of Thick Targets by Deforming Rods
Authors: Lee M.
Published: July 2002

This paper analyzes the cavitation and mushrooming phenomena occurring in a metal target during the high-speed penetration by a deforming rod. It is motivated by the fact that two mechanisms are involved in the formation of cavity by a deforming rod. First, the flow of the deformed rod products exerting radial stress on the target opens a cavity (mushrooming). Second, the radial inertia of the target as it flows around the head plays another part in the formation of the cavity (cavitation). By examining the dynamics of the flow of deformed rod products, the proposed model can estimate the extent of cavity growth due to the mushrooming effect. Predicted results for the final cavity growth are found to match well with the corresponding test values.
Rapid Indentation of Transversely Isotropic or Orthotropic Half-Spaces
Authors: Brock L. M. , Georgiadis H. G. , Hanson M. T.
Published: July 2002

The canonical problems of rapid indentation by, respectively, a rigid smooth wedge and a rigid smooth cylinder, are examined for a transversely isotropic or orthotropic half-space in plane strain. An exact transient analysis based on integral transforms is carried out for the case of contact zone expansion at a constant subcritical rate. Certain functions in the transform space can be factored in such a manner that the resulting solutions, despite anisotropy, have rather simple forms. This factorization is also exploited to obtain a compact exact formula for the Rayleigh wave speed, which serves as the critical contact zone expansion rate. Aspects of contact zone behavior for the two problems are illustrated for five specific materials.
An International Electronic and Interactive Teaching and Life-Long Learning Platform for Gas Turbine Technology in the 21st Century
Authors: Fransson T. H. , Hillion F.-X. , Klein E.
Published: July 2002

An interactive learning platform which sets a new standard for electronic learning of gas turbine technology in a global life-long learning perspective is presented (Fig. 1). The platform contains a theoretical section in the form of several pages for each chapter available, with a significant number of related interactive simulations, movies, animations, virtual laboratory exercises, virtual study visits and realistic case studies. A significant background information related to historical development in the field, a display of existing components, nomenclature, multi-lingual dictionary and keywords, as well as questions for self-assessment and exams, an electronic communication group and a database of the user’s “successes and failures,” enhance the learning process in a significant way. The program is intended as a platform for an international collaboration on learning heat and power technology. It can be used both in the classroom as well as for self-studies and is as such well adapted for both university and post-university learning, both on and off campus. Tools to facilitate the introduction of new material exist. It is thus hoped that teachers at different universities can join forces and in a noncompetitive way introduce material which can be shared, instead of developing similar simulations with somewhat different interfaces. The long-term goal of the learning platform is of course that users worldwide will have the possibility to access the best teaching material available from any specialist, and that this material will contain supplementary pedagogical information which will enhance the learning both at a university and a post-university level.
Reduction of Noise Transmission in a Duct by Termination Impedance Control of a Sidebranch Resonator
Authors: Utsumi M.
Published: July 2002

This paper investigates the use of a sidebranch resonator subjected to active termination impedance control as a means to reduce noise transmission in a duct. The main purpose of this paper is to establish a method for controlling a broad-band noise, which is characterized by a simultaneous incidence of a large number of frequency components. To this end, a control law is expressed in terms of a controller transfer function, and a new method for accurately implementing the desired frequency characteristic of the controller transfer function over a wide frequency range is presented. In this method, the inverse Laplace transform of the controller transfer function is expressed in terms of a Fourier series. This expression leads to an online computation algorithm that allows us to update the values of base functions of the control force at each digital sampling time. The effectiveness of the algorithm is demonstrated by computer simulation.
Energy Separation and Acoustic Interaction in Flow Across a Circular Cylinder
Authors: Goldstein R. J. , He Boyong
Published: July 2002

Energy separation in a flow around an adiabatic circular cylinder is investigated using a surface-mounted thermocouple. Energy separation mechanisms in different regions around the cylinder are discussed. Velocity measurements near the rear stagnation point and acoustic measurements indicate that shedding vortices and the wind tunnel intrinsic resonant acoustics can strengthen each other when their frequencies match producing strong energy separation.
Effects of Some Modeling Parameters of Finite Element Models of Binder Forming
Authors: Chen Kuo-Kuang , Sa Chung-Yeh
Published: July 2002

This paper studies the effects of some modeling parameters on the accuracy of finite element simulation in sheet-metal forming. A simple stepdie, which simulates binder forming, is used. In this two-dimensional case, a flat blank is bent into an S-shape, which has an exact solution. Four modeling parameters are studied. They are: die close speed, die gap, mass damping, and width of blank. One significant finding of this study reveals that in calculations using explicit finite elements, the simulation speed should be selected with care. The dynamic effects may be prevalent if the simulation speed is too fast. Numerical errors may accumulate and renders the results erroneous if it is too slow.
An Experimental Comparison Between a Recombined Hydrocarbon-Water Fluid and a Model Fluid System in Three-Phase Pipe Flow
Authors: Utvik Ole Harald , Rinde Trygve , Valle Arne
Published: July 2002

In this paper, results are presented from an experimental comparison between a light hydrocarbon system from the North Sea and a model oil system in pipe flow. The experiments were carried out in order to compare similar fluid systems (density, viscosity, oil-water interfacial tension) with respect to pressure drop and flow pattern for horizontal flow. The results show significant deviations with respect to pressure drop and flow patterns for two and three-phase flow. This may contribute to the explanation of the discrepancies often revealed between multiphase models and measurements on multiphase flowlines in the oil and gas industry.
Scaling of Composite Wind Turbine Blades for Rotors of 80 to 120 Meter Diameter
Authors: Griffin Dayton A. , Zuteck Michael D.
Published: July 2002

As part of the U.S. Department of Energy’s Wind Partnerships for Advanced Component Technologies (WindPACT) Program, a scaling study was performed on composite wind turbine blades. The study’s objectives were to assess the scaling of current commercial blade materials and manufacturing technologies for rotors of 80 to 120 meters in diameter, to develop scaling curves of estimated weight and cost for rotor blades in that size range, and to identify practical limitations to the scaling of current conventional blade manufacturing and materials. Aerodynamic and structural calculations were performed for a matrix of baseline blade design parameters, and the results were used as a basis for constructing a computational scaling model. The scaling model was then used to calculate structural properties for a wide range of aerodynamic designs and rotor sizes. Blade designs were evaluated on the basis of power performance, weight, static strength in flapwise bending, fatigue life in edgewise bending, and tip deflection under design loads. Calculated results were compared with weight data for current commercial blades, and limitations were identified for scaling up the baseline blade configurations. A series of parametric analyses was performed to quantify the weight reductions possible by modifying the baseline design and to identify the practical limits of those modifications. The model results provide insight into the competing design considerations involved in scaling up current commercial blade designs.
Surface Texture, Fatigue, and the Reduction in Stiffness of Fiber
Reinforced Plastics
Authors: Arola D. , Williams C. L.
Published: July 2002

In this study the influence of machined surface texture on the fatigue strength of a Graphite/Bismaleimide (Gr/Bmi) laminate was examined. Rectangular beam specimens were machined to achieve specific surface roughness 0.2⩽Ra⩽10.0 μm and then subjected to fully reversed four-point flexural fatigue. The surface texture resulting from machining was evaluated using contact profilometry and the standard surface roughness parameters were used in estimating the effective stress concentration K¯t and effective fatigue notch K¯f factors for the machined surfaces according to models reported in the open literature. Fully reversed flexural fatigue loading of the laminate was conducted at two separate maximum bend loads corresponding to Tsai-Hill ratios for first ply failure of 0.75 and 0.9. It was found that the reduction in stiffness of the Gr/Bmi laminate at both levels of fatigue loading increased with the magnitude of surface roughness. The apparent fatigue stress concentration factors Kf of the machined surfaces determined from experimental results ranged from 1.0 to 1.2. The effective fatigue notch factors estimated using the Arola-Ramulu model for the machined specimens were within 10% of the corresponding Kf determined from experiments.
Active Control of Low-Frequency Sound Radiation From Vibrating Panel Using Planar Sound Sources
Authors: Chen Kean , Koopmann Gary H.
Published: July 2002

Active control of low frequency sound radiation using planar secondary sources is theoretically investigated in this paper. The primary sound field originates from a vibrating panel and the planar sources are modeled as simply supported rectangular panels in an infinite baffle. The sound power of the primary and secondary panels are calculated using a near field approach, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiate sound power. Finally, active reduction for a number of secondary panel arrangements is examined and it is concluded that when the modal distribution of the secondary panel does not coincide with that of the primary panel, one secondary panel is sufficient. Otherwise four secondary panels can guarantee considerable reduction in sound power over entire frequency range of interest.
Numerical Simulation of Laminar Flow and Heat Transfer Over a Blunt Flat Plate in Square Channel
Authors: Yanaoka Hideki , Yoshikawa Hiroyuki , Ota Terukazu
Published: July 2002

Three-dimensional simulations of laminar separated and reattached flow and heat transfer over a blunt flat plate in a square channel are presented. Numerical calculations of Navier-Stokes equations and energy equation are carried out using the finite difference method. Results of three-dimensional calculation are compared with two-dimensional ones and effects of the side walls are described. It is clarified from the present results that the reattachment length increases with an increase of Reynolds number and the flow in the recirculation region becomes three-dimensional. The reattachment line is curved by the side wall effects. Two-dimensionality of the flow is reduced as Reynolds number increases. The horseshoe-vortex formed near the side walls has great effects upon the heat transfer in the redeveloping flow region. The separated shear layer around the center of plate becomes unstable with a further increase of Reynolds number and the vortices are periodically shed from the reattachment flow region. Such vortices exhibit a hairpin-like structure and greatly influence the heat transfer.
Stochastic Response of Offshore Structures by a New Approach to Statistical Cubicization
Authors: Di Paola Mario , Failla Giuseppe
Published: July 2002

This study presents a new statistical cubicization approach for predicting the stochastic response of offshore platforms subjected to a Morison-type nonlinear drag loading. Statistics of the original system are obtained from an equivalent nonlinear system, which is constructed by replacing the Morison drag force by a cubic polynomial function of the relative fluid-structure velocity, up to cubic order. A Volterra series expansion with a finite Fourier series representation is used to approximate the response of the equivalent system. Exact solutions are developed to express the Fourier coefficients of the second and third-order response as functions of the Fourier coefficients of the first-order relative fluid-structure velocity. Response statistics are then computed by ensemble averaging over a suitable number of realizations of the first-order Gaussian response. Response statistics up to the sixth order, computed for a variety of sea conditions, show accuracy and efficiency of the proposed method as compared to digital simulation.
Nonlinear Dynamic Analysis of a Flexible Rotor Supported by Externally Pressurized Porous Gas Journal Bearings
Authors: Wang Cheng-Chi , Lo Cheng-Ying , Chen Cha’o-Kuang
Published: July 2002

This paper studies the nonlinear dynamic analysis of a flexible rotor supported by externally pressurized porous gas journal bearings. A time-dependent mathematical model for externally pressurized porous gas journal bearings is presented. The finite difference method and the Successive Over Relation (S.O.R.) method are employed to solve the modified Reynolds’ equation. The system state trajectory, Poincare´ maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the rotor and journal center in the horizontal and vertical directions under different operating conditions. The analysis reveals a complex dynamic behavior comprising periodic and quasi-periodic response of the rotor and journal center. This paper shows how the dynamic behavior of this type of system varies with changes in rotor mass and bearing number. The results of this study contribute to a further understanding of the nonlinear dynamics of gas-lubricated, externally pressurized, porous rotor-bearing systems.
Modeling and Control of a Deformable Mirror
Authors: Winters S. E. , Chung J. H. , Velinsky S. A.
Published: July 2002

A multi-input multi-output surface shape control system model is developed to study wavefront aberration correction. The plant model represents a deformable mirror and utilizes a finite element model that is validated using an actual prototype deformable mirror and an interferometer system. The sensor model is based on a Shack-Hartmann sensor, and the controller model is based on a least squares approach. The control system model is used to compare an available Gaussian model with the validated finite element model. Results clearly show the efficacy of the approach and the superiority of the finite element based method. The control approach is expected to be implemented on the adaptive optics system of the National Ignition Facility.
Logarithmic Stress Singularities Resulting From Various Boundary Conditions in Angular Corners of Plates Under Bending
Authors: Sinclair G. B.
Published: July 2002

This note considers the occurrence of pure logarithmic singularities in angular elastic plates under bending within the context of classical theory. By paralleling the development of requirements for logarithmic singularities for plates in extension, requirements for log singularities in bending are developed, both for homogeneous boundary conditions on plate edges and for inhomogeneous. Using these singularity requirements, some 50-odd configurations with log singularities are identified, the great majority being for inhomogeneous boundary conditions. [S0021-8936(00)00501-8]
An Investigation of Yield Potentials In Superplastic Deformation
Authors: Khraisheh Marwan K.
Published: July 2002

Recent results (Khraisheh et al., 1995 and 1997) have indicated that superplastic materials exhibit a strong degree of anisotropy and that the plastic flow cannot be described by the isotropic von Mises flow rules. In this study, the yield potential for the model Pb-Sn superplastic alloy is constructed experimentally for different effective strain rates using combined tension/torsion tests. A generalized anisotropic “dynamic” yield function is also proposed to represent the experimentally constructed yield potentials. The anisotropic function is not only capable of describing the initial anisotropic state of the yield potential, it can also describe its evolution through the evolution of unit vectors defining the direction of anisotropy. The anisotropic yield function includes a set of material constants which determine the degree of deviation of the yield potential from the isotropic von Mises yield surface. It is shown that the anisotropic yield function successfully represents the experimental yield potentials, especially in the superplastic region. [S0094-4289(00)01401-8]
Predicting the Influence of Compressibility and Thermal and Flow
Distribution Asymmetry on the Frequency-Response Characteristics of Multitube
Two-Phase Condensing Flow Systems
Authors: Kobus C. J. , Wedekind G. L. , Bhatt B. L.
Published: July 2002

An equivalent single-tube model concept was extended to predict the frequency-response characteristics of multitube two-phase condensing flow systems, complete with the ability to predict the influence of compressibility and thermal and flow distribution asymmetry. The predictive capability of the equivalent single-tube model was verified experimentally with extensive data that encompassed a three-order-of-magnitude range of frequencies, and a wide range of operating parameters. [S0022-1481(00)00601-0]
Heat (Mass) Transfer in a Diagonally Oriented Rotating Two-Pass
Channel With Rib-Roughened Walls
Authors: Park C. W. , Yoon C. , Lau S. C.
Published: July 2002

Naphthalene sublimation experiments have been conducted to examine the effects of channel orientation, rotational Coriolis force, ad a sharp turn, on the local heat (mass) transfer distributions in a two-pass square channel with rib-roughened walls, rotating about a perpendicular axis. The test channel was oriented so that the direction of rotation was perpendicular or at a 45 deg angle to the leading and trailing walls. In the two straight passes of the test channel, there were parallel 90 or 60 deg ribs on the leading and trailing walls. The test channel modeled serpentine cooling passages in modern gas turbine blades. The results showed that the heat (mass) transfer was very low on the leading wall of the first pass when the channel was oriented with the rotating direction normal to the leading and trailing walls. There were regions of very low heat (mass) transfer on both the leading and trailing walls in the turn, especially on the trailing wall in the turn when the channel with transverse ribs was oriented diagonally. For the given diagonal channel orientation, rotational Coriolis forces caused the leading and trailing wall heat (mass) transfer to be high near the outer edges of the walls in the channel with transverse ribs; rotation-induced secondary flows dominated near wall rib-induced secondary flows in the channel with angled ribs, since the heat (mass) transfer was generally higher near the outer edges of the walls than near the inner edges in the first and second straight passes. [S0022-1481(00)00201-2]
Self-Excited Sloshing due to the Fluid Discharge Over a Flexible Cylindrical Weir
Authors: Nagakura Hiroshi , Kaneko Shigehiko
Published: July 2002

This paper presents an analytical model for the self-excited sloshing due to the fluid discharge over a flexible weir, as observed in the cooling circuit of the French fast breeder reactor, Super-Phenix-1. To clarify the instability mechanism, we analyzed the case in which an annular reservoir was divided into an upstream and a downstream plenum by a flexible cylindrical weir. The kinematic and dynamic effects of the discharged fluid on downstream plenum sloshing are discussed in details. Calculations are presented for the cylindrical fluid-structure model with successively increasing fluid level difference between the upstream and downstream plenums, and the instability mechanism is examined. [S0094-9930(00)00901-X]
The Use of Risk-Based Approaches in Post-Construction Standards
Authors: Sims J. Robert , Feigel Richard E.
Published: July 2002

This article provides a general discussion on the application of risk analysis in the development of safety codes and standards, with particular emphasis on the standards currently under development by the ASME Post-Construction Committee. It also provides an exposition of some of the implicit risk-based assumptions incorporated in the basic new construction pressure vessel code (ASME Section VIII, Div. 1). It proceeds to argue that codes and technical safety standards should be developed using explicit rather than implicit risk-based principles. The authors argue that, contrary to popular belief, pressure equipment standards have always incorporated ad hoc, anecdotal risk principles. The article elucidates this through two detailed examples dealing with provisions affecting nearly all vessels produced to Section VIII, Div. 1: i.e., joint efficiency factors and the scope of coverage of the code. The article then proceeds to a discussion of data collection and cost-benefit modeling which would support a migration to a more rigorous risk-based foundation for future code development. The authors argue that the interests of the entire community of code users—users, manufacturers, regulatory authorities, insurers, and the general public—will be better served by the rational incorporation of risk principles as a foundation for code development. Examples of the application of risk-based approaches in two of the Post-Construction Code drafts follow. [S0094-9930(00)02003-5]
Experiments on Active Vibration Control of a Flexible Four-Bar Linkage Mechanism
Authors: Shu-Qing, Yuan , Qing-Yu, Xu , Ling Zhang
Published: July 2002

Experiments are performed to actively suppress vibration of a flexible four-bar linkage mechanism bonded with piezoelectric materials as sensor and actuator. The control system is built up with computer, A/D and D/A converter, low-pass filter, voltage amplifier and charge amplifier etc. Location of the actuator is properly selected to minimize the drive energy. According to the characteristics of the control system. Internal model control strategy is employed to suppress vibration caused by periodic disturbance, i.e., inertial force of the mechanism. Encouraging results are gained when the strategy is realized in the experiments. [S0739-3717(00)01201-0]
Ag2O XPS Spectra
Authors: Hoflund Gar B. , Weaver Jason F. , Epling William S.
Published: July 2002

XPS data have been obtained from a pressed Ag2O powder obtained from AESAR. The Ag2O sample was annealed in vacuum at 300°C for 30 min. This resulted in a surface primarily composed of Ag2O with a small amount of Ag metal present also. The anneal temperature is above that which results in the decomposition of AgO to Ag2O and below the temperature which results in complete reduction. These spectra will be helpful in XPS studies of O/Ag systems such as alumina-supported silver epoxidation catalysts.
AgO XPS Spectra
Authors: Hoflund Gar B. , Weaver Jason F. , Epling William S.
Published: July 2002

XPS data have been obtained from a pressed AgO powder sample obtained from AESAR. Obtaining high-quality XPS data from a single oxide state is difficult because multiple oxide states, hydroxides, and other contaminants are usually present. The AgO sample was annealed in vacuum at 100°C for 30 min to reduce the amounts of contaminants present. The primary contaminant on this sample is a bicarbonate species that was significantly reduced during the anneal. The anneal temperature is below that which results in decomposition of AgO and Ag2O. These spectra will be useful in XPS studies of O/Ag systems such as alumina-supported silver epoxidation catalysts.
Study of Amorphous Carbon Nitride Films by X-ray Photoelectron Spectroscopy
Authors: Chen Dihu , Wei Aixing , Wong S. P. , Peng Shaoqi , Kwok R. W. M.
Published: July 2002

X-ray photoelectron spectroscopy measurements of amorphous carbon nitride films have been performed. The samples were prepared by magnetic filtered plasma deposition, and cleaned by Ar+ ion sputtering before analysis to eliminate the surface contamination. The spectra include standard survey scans and high resolution scans of the photoelectron peaks of C, N, and O atoms. These spectra were collected using a monochromatic Mg Kα x-ray source operated at 300 W (20 mA, 15 kV). The survey scans were collected using an 80 eV pass energy, while high resolution scans were recorded using a 20 eV pass energy. By deconvolution of the XPS spectra, it was found that the XPS C 1s and N 1s signals could be deconvoluted into three and two Gaussian peaks, respectively. A plausible suggestion on the assignments of XPS peaks to C3N4, CNx, and ta-C phases was discussed. The relative abundance of CN bonds, calculated from the area of the respective C 1s Guassian peaks divided by the total area of the C 1s spectra, was determined to be 80%, and the actual nitrogen content in films in terms of atomic percentage is 46%.
Effect of magnetic field configuration in the cathodic polymerization systems with two anode magnetrons
Authors: Zhao J. G. , Yasuda H. K.
Published: July 2002

Direct current glow discharge can be utilized in plasma polymer coating of metal substrates by using the substrate as the cathode (cathodic polymerization). By using an anode equipped with magnetic enhancement, the anode magnetron cathodic polymerization can be effectively operated in low pressure regime, in which a tight barrier type plasma polymer can be formed. When two magnetrons are used against a cathode (substrate), the configurations of magnetic field employed in each magnetron become an important factor of the system. In one case [parallel magnetron (PM)], in which the identical magnetrons are used; magnetic field near the substrate (cathode) emanating from two magnetrons are parallel. In another case [opposite magnetron (OM)], in which magnet arrangement is reversed in one magnetron, magnetic fields near the substrate are opposite. Plasma polymerization with no magnetron shows the edge effect (higher deposition rate near the edge of cathode). With anode magnetrons (OM or PM), the edge effect is eliminated and higher deposition rates, compared to that obtained without magnetron, were obtained in the majority of electrode area. The uniformity of the deposition rate distribution is better with the OM configuration than with the PM configuration. The distance between electrodes influences the distribution of the deposition rate with the PM configuration (less uniform with small distance), but has little effect with the OM configuration. The advantage of having anode magnetrons diminishes at system pressure higher than 50 mTorr.