bluuebunny/crossref_metadata_2025 huggingface dataset:
Screening crystallisation conditions using fluorescence correlation spectroscopy
Authors: Schmauder Ralf , Schmidt Thomas , Abrahams Jan Pieter , Kuil Maxim E.
Published: September 2002

We investigate the potential of fluorescence correlation spectroscopy (FCS) in screening for crystallisation conditions. Solutions that nucleate protein crystals must have different interactions than solutions that do not give rise to crystals. Due to these different interactions the average mean squared displacement of the individual proteins changes. By monitoring protein self-diffusion, we can distinguish crystallising from non-crystallising solutions. The method introduced can be applied at extremely low concentrations in femtoliter volumes as an early diagnostic for molecular association. Based on our preliminary findings FCS has the potential to become a routine screening method for crystallography.
Correlation between the osmotic second virial coefficient and solubility for equine serum albumin and ovalbumin
Authors: Demoruelle Kristen , Guo Bin , Kao Shangming , McDonald Heather M. , Nikic Dragan B. , Holman Steven C. , Wilson W. William
Published: September 2002

The Haas – Drenth – Wilson (HDW) (Haas et al., 1999) theoretical model was used to correlate osmotic second virial coefficient (B) values with solubility (S) values for equine serum albumin (ESA) and ovalbumin for corresponding solution conditions. The best fit from the theoretical model was compared to experimental S versus B data. B values were experimentally measured using static light scattering. Solubilities of ESA were estimated using a sitting drop method. When the experimental data for S versus B were plotted, an excellent fit for ESA was obtained according to the HDW model. The results showed that the coordination number (z) in the crystal lattice was 6, and the adjustable parameter (A) was 0.072. For ovalbumin, previously reported solubility data in aqueous ammonium sulfate solutions were utilized. The solubility data for ovalbumin were correlated with the measured B values obtained in our laboratory. The resulting best fit from the HDW model showed that z = 6 and A = 0.084.
Thermodynamic relationships between protein-solvent and protein-protein interactions
Authors: Costenaro Lionel , Ebel Christine
Published: September 2002

How the solvent modulates the weak inter-particle interactions in solution and affects macromolecule solubility is not yet understood. Well-established thermodynamic relationships link second virial coefficient and preferential solute binding parameter. We present the meaning of these thermodynamic parameters and the way to measure them. When a solvation shell has a composition different from the bulk solvent, a negative contribution is found in the second virial coefficient corresponding to an effective attraction between the macromolecules in solution. A quantitative evaluation using simple models of solvated particles in solution suggests that solvation could induce, at high or low concentration of a small molecule solute, attractive inter-particle interactions corresponding to favorable crystallization conditions.
Effects of a magnetic field and magnetization force on protein crystal growth. Why does a magnet improve the quality of some crystals?
Authors: Ataka Mitsuo , Wakayama Nobuko I.
Published: September 2002

Probable reasons why some protein crystals grown in a magnet exhibited better quality than control are discussed as follows. (1) Sedimenting three-dimensional nuclei are able to have the same orientation as the underlying, mother crystal into which the nuclei merge. (2) Protein solution may become more viscous, leading to reduction of convection. (3) If an upward force is generated by use of an inhomogeneous magnetic field, the effects of the density differences can be made less significant, causing the reduction of natural convection and the retardation of crystal sedimentation.
Crystallization of the collagen-like polypeptide (PPG)10 aboard the International Space Station. 2. Comparison of crystal quality by X-ray diffraction
Authors: Berisio Rita , Vitagliano Luigi , Vergara Alessandro , Sorrentino Giosuè , Mazzarella Lelio , Zagari Adriana
Published: September 2002

Crystals of the collagen-like polypeptide (PPG)10 were obtained within the Advanced Protein Crystallization Facility on board the International Space Station, during the STS-105/STS-108 mission. The duration of this mission was such to ensure that the crystallization process had reached its end. Crystals were grown both in the presence and in the absence of agarose gel, to compare the quality of the crystals obtained from these different environments. As a result, crystals grown in the absence of agarose on Earth as well as in microgravity showed X-ray diffraction up to 1.15 Å. The intensity/sigma ratio was slightly higher for microgravity grown crystals. Crystals grown in agarose gel, both in microgravity and on ground, showed a comparable diffraction power, with a resolution limit of 1.45 Å.
Understanding salt or PEG induced attractive interactions to crystallize biological macromolecules
Authors: Tardieu Annette , Bonneté Françoise , Finet Stéphanie , Vivarès Denis
Published: September 2002

Phase diagrams of biological macromolecules are governed by an appropriate combination of interaction potentials in solution. Repulsive regimes favor solubility, whereas the presence of attractive potentials may induce a variety of phase transitions, including the desired macromolecular crystallization. The forces at work may be analyzed with a combination of small angle X-ray scattering and of numerical treatments. From the results obtained with a variety of model systems, the respective advantages and drawbacks of using monovalent salts or PEGs as crystallizing agents are discussed.
Experimental observations and numerical modelling of diffusion-driven crystallisation processes
Authors: Carotenuto Luigi , Piccolo Chiara , Castagnolo Dario , Lappa Marcello , Tortora Alessandra , Garcìa-Ruiz Juan Manuel
Published: September 2002

This paper reports experimental results and modelling on the crystallisation processes induced by counter diffusion method of a precipitant agent in a lysozyme protein solution. Comparison between experimental observations and numerical simulations in the presence of convection and sedimentation and without them (suppressed using gel) provides a validation of the model. Different values of the initial protein concentration are used, in order to investigate the effects of supersaturation conditions on the process, and in particular on nucleation. The model and the experimental approach may represent a useful methodology for the determination of the parameters and conditions that may lead to protein crystallisation. A Mach-Zehnder interferometer is used to monitor the transport dynamics in
situ in the fluid phase by observing the compositional field. The effect of the solute transport gives rise to a "nucleation front" that propagates inside the protein solution. The crystal formation, caused by progressing of the front, results in a modulation in time and in space (similar to Liesegang patterns), due to the non-linear interplay among transport, crystal nucleation and growth. Both experimental observation and numerical modelling show spatial and size distributions of crystals that demonstrate comparable evidences of the phenomena.
Granada Crystallisation Box: a new device for protein crystallisation by counter-diffusion techniques
Authors: Garcia-Ruíz Juan Ma. , Gonzalez-Ramirez Luis Antonio , Gavira José Antonio , Otálora Fermín
Published: September 2002

Granada Crystallisation Box (GCB) is a new crystallisation device designed to perform counter-diffusion experiments. Here we describe the device and its use for protein crystallisation purposes. GCB allows one to explore and exploit the coupling between crystallisation and diffusion. The role of viscous fluids, gels and/or microgravity can be enhanced by using capillary volumes, creating a perfect diffusive mass transport scenario. The use of capillaries also reduces the consumption of macromolecules and avoids the handling of crystals for X-ray diffraction data collection.
Lysozyme crystal growth kinetics in microgravity
Authors: Otálora Fermín , García-Ruiz Juan Manuel , Carotenuto Luigi , Castagnolo Dario , Novella María Luisa , Chernov Alexander A.
Published: September 2002

Mach-Zehnder interferometry is applied to quantitatively characterize growth of lysozyme crystals in microgravity. Experiments were performed by the Free Interface Diffusion technique into APCF FID reactors using large seeds. Tracking of the experiments using interferometry allowed to monitor the onset of supersaturation and the seed growth. A large and stable concentration depletion zone around the growing crystal developed, whose time evolution was analyzed. The interferograms were analyzed taking into account finite thickness of the cell by integrating the concentration over the straight lines through the optical path. It was concluded that there may be a quasi-steady state growth mode at the stage when the spacial concentration distribution did not change but its absolute value over all the cell was slowly diminishing. From this portion of the data, an estimate was made of the dimensionless parameter βR/D where β is the face kinetic coefficient, R is the effective crystal size and D is the lysozyme diffusivity in solution, as followed from the steady state model. For the assumed quasi steady state data portion, the parameter varies between 0.7 and 0.9 suggesting mixed diffusion-interface kinetic controlled growth.
Observation of cholesterol nucleation in a magnetic field
Authors: Sandarac Nachiappan Meenakshi , Ashok M. , Kalkura S. Narayana
Published: September 2002

The in vitro studies on the nucleation, growth and other fundamental aspects of cholesterol crystallization have received considerable attention, as it plays a vital role in the formation of atheroclerotic plaques and gallbladder stones. The cholesterol was crystallized in methanol, ethanol, acetone and isopropanol at the physiological temperature of 37°C in the presence and absence of a low static magnetic field at 0.1 T. The presence of magnetic field was found to have a significant effect on the metastable zone width and induction period of cholesterol.
Sugar-mediated lattice contacts in crystals of a plant glycoprotein
Authors: Hogg Tanis , Kuta Smatanova Ivana , Bezouska Karel , Ulbrich Norbert , Hilgenfeld Rolf
Published: September 2002

Pokeweed antiviral protein, PAP-S
aci
, isolated from seeds of the Chinese pokeweed plant, Phytolacca acinosa, belongs to the family of type-1 ribosome-inactivating proteins (RIPs). Type-1 RIPs are ~30-kDa N-glycosidases that inactivate eukaryotic and prokaryotic ribosomes via a site-specific depurination of ribosomal RNA (rRNA). Here we describe the preliminary X-ray structure determination at 1.7 Å resolution of one PAP isoenzyme from seeds, PAP-S1
aci
, after crystallisation from a heterogeneous mixture of two isoenzymes. PAP-S1
aci
possesses a rare type of glycosylation, specifically, N-linked N-acetyl-D-glucosamine monosaccharide (GlcNAc) substitutions at canonical Asn-Xaa-Ser/Thr sequons. One GlcNAc residue was found to play a critical role in crystal lattice formation, forming a packing interface across a crystallographic two-fold with the identical sequon of an adjacent monomer. This observation suggests that deglycosylation protocols for the crystallisation of glycoproteins should be designed to allow for exploitation of the crystal packing potential of the innermost core sugar residue (N-linked GlcNAc or O-linked GalNAc).
Strong and specific effects of cations on lysozyme chloride solubility
Authors: Bénas Philippe , Legrand Laurent , Riès-Kautt Madeleine
Published: September 2002

The influence of salt nature and concentration on tetragonal lysozyme chloride crystal solubility is presented for a set of mono-, di- and trivalent cations (Cs+, Rb+, Mn2+, Co2+ and Yb3+). The results show that cations have as strong an effect on protein solubility as anions and that they present their own particular effects as co-ions. Indeed, after decreasing at low ionic strength, lysozyme solubility increases with high concentration of polyvalent cations, probably due to co-ion binding and therefore the concomitant increase of the net charge of the protein-salt complex. These new results are discussed in order to progress in the understanding of the crystallisation process at the atomic level.
An overview on 2-methyl-2,4-pentanediol in crystallization and in crystals of biological macromolecules
Authors: Anand Kanchan , Pal Debnath , Hilgenfeld Rolf
Published: September 2002

2-Methyl-2,4-pentanediol (MPD) is the most popular chemical additive used for crystallization of biological macromolecules. However, the mechanism of its action on proteins in aqueous solution is not well understood. We have carried out a systematic analysis of the conformation and environment of MPD molecules bound to proteins. We find that the majority of MPD molecules adopt their most stable conformer. They prefer to bind to hydrophobic sites with a distinct preference for leucine side chains. Most MPD binding sites involve amino-acid residues in helical or β-sheet structures. MPD binding to proteins is penetrative, leading to displacement of water molecules in grooves and cavities (sometimes ligand-binding and active sites) on the protein surface. This results in a large reduction of solvent-accessible area, which can have significant implications for protein stability. The packing of the MPD molecules by the protein is not optimal and usually some other solvent molecules are also bound along with it. Our analysis suggests that MPD is not as strong a denaturant as often suggested. It promotes stabilization of the protein by preferential hydration, which is facilitated by attachment of MPD molecules to the hydrophobic surface.
View on biocrystallization from Jena, 2002
Authors: Chernov A. A. , DeLucas L. J.
Published: September 2002

An introductory report of the ICCBM9 meeting in Jena, Germany, 2002, is given.
Flood defence and the surveyor: what’s new?
Authors: Wynn Peter
Published: September 2002

The long historical background to flood defence is outlined. It is noted that many of the concerns and approaches are not new. However in some areas changes are occurring. The freshwater flooding across much of England and Wales in spring 1998 hastened new approaches to the relationship between flood defence agencies and the public. Recent published guidance on flood proof construction is described and reviewed, and a role for the building surveyor is identified.
Strength and durability performance of HPC incorporating pozzolans at elevated temperatures
Authors: Balendran R.V. , Rana T.M. , Maqsood T. , Tang W.C.
Published: September 2002

The inclusion of pozzolans like pulverised fuel ash (PFA), silica fume (SF) and metakaolin (MK) enhances the properties of concrete both in fresh and hardened states. In the case of high performance concrete (HPC), their role in enhancing the workability, strength and durability is extremely significant. However HPC has been observed to be more vulnerable than normal strength concrete when exposed to elevated temperatures. This paper presents an overview and discusses the strength and durability performance of high‐performance pozzolanic concretes incorporating PFA, SF, and MK subjected to elevated temperatures. Various researchers have demonstrated that addition of silica fume causes HPC to perform poorly when subjected to elevated temperatures. Higher loss of strength and spalling risks are also associated with it. Addition of PFA and MK has been found to improve the fire performance of HPC both in terms of residual strength and durability.
Contractor selection for small building works in Hong Kong
Authors: Yiu C.Y. , Lo S.M. , Ng S. Thomas , Ng Michael M.F.
Published: September 2002

Contractor selection models have been developed for large scale works with the assumption of the availability of contractor’s information for the clients. However, a similar study of small building works, especially building maintenance and repair works, is almost ignored. In light of the small amount of work, the employment of building consultants for the selection of contractors in small works is often not feasible, and the cost of acquiring the contractor’s information is often prohibitively high. This research uses case studies to show that a contractor selection model for large scale works does not perform well in small works without the advice of the consultant. The high proportion of specification costs in small works contracting deters the detailed design and documentation stage. A wider variation of tender sums is therefore expected and revealed in the case studies. This paper reviews the building procurement mechanism in small building works in Hong Kong and argues that the employment of a property management agent is conducive to the contractor selection process. Accordingly, further investigations are warranted for a contractor selection model for small building works.
Understanding buyer information acquisition for the purchase of logistics services
Authors: Bienstock Carol C.
Published: September 2002

During the last several decades, logistics has increasingly emerged as a source of sustainable competitive advantage. This article incorporates recent work in services marketing on customer information acquisition, with research on industrial buying behavior to help logistics service providers understand and manage their customers’ information acquisition and purchase activities for logistics services.
The electronic supply chain
Authors: Williams Lisa R. , Esper Terry L. , Ozment John
Published: September 2002

The advent of the Internet and electronic communications has enabled companies to be more responsive to their customers. However, the same technological advancements are changing the marketplace and providing an impetus for changes in strategic alliance and partnership structures. Successful leaders of the future will have to understand how to operate in the new marketplace and within the evolving organizational structures where alliances and partnerships are changing. The purpose of this article is to shed light on the current and future organizational structures in the logistics industry. Toward that end, traditional supply chain management (SCM), electronic supply chain management (eSCM), and the resulting impact on strategic alliances and partnerships will be explored. Additionally, considering the inherent ability of the eSC to be dynamic and adaptable, the new type of leader that is likely to be most successful in this new structure is discussed.
How international firms are coping with supply chain issues in China
Authors: Jiang Bin
Published: September 2002

Foreign firms face many supply chain‐related difficulties in China. These include China’s overburdened, underdeveloped physical infrastructure; inexpert, underfunded state‐owned distribution companies; an enormous, fragmented distribution and logistics sector; and regional protectionism. Additionally, foreign firms face bureaucratic restrictions that prohibit them from legally importing, selling, and servicing products in a straightforward manner. Companies are looking to strengthen their supply chains in China in an effort to leverage the country’s cheap labor costs. This strengthening of the supply chain can be accomplished through three methods: the cluster approach; the use of non‐Chinese 3PLs; and the use of local carriers.
Evaluating the impact of electronic data interchange on the ingredient supply chain of a food processing company
Authors: Owens Stephen F. , Levary Reuven R.
Published: September 2002

A model of an electronic data interchange (EDI) enabled ingredient supply chain for a food processing company was developed, the model was simulated and its performance was compared with a simulation model of the current ingredient supply chain process of a US food processing company. The simulation results indicated that an EDI enabled system, which removed many of the time delays associated with the current process, significantly reduced swings in raw materials inventory and allowed significant reductions in raw materials safety stock without increasing the risk of production delays due to out‐of‐stock ingredients.
The impact of QM maturity upon the extent and effectiveness of customer relationship management systems
Authors: Li Jing , Fok Wing , Fok Lillian , Hartman Sandra
Published: September 2002

Investigates the relationships between organizational adoption and extent of use of two kinds of programs. Specifically, contends that organizations may vary considerably in QM maturity. Argues that QM maturity organizations will be characterized by perceptions that the culture is different in ways which are supportive of QM, and that the organization is performing at higher levels. Moreover, such organizations will be more likely to have moved toward adopting customer relationship management systems to improve their customer services, and have done so in qualitatively better ways. In turn, such adoptions will lead to perceptions by those in the organizations that their customer relationship systems are, in fact, providing better services. Exploratory research provides support for these ideas.
Wireless product identification: enabler for handling efficiency, customisation and information sharing
Authors: Kärkkäinen Mikko , Holmström Jan
Published: September 2002

More sophisticated customer demand chains and electronic business pose new challenges to supply chain management. Delivery sizes decrease as a result of more deliveries directly to the point of use. Customers are demanding products and deliveries customised to their specific needs. Also, the information concerning small, customised deliveries has to be shared in volatile supply networks. This article analyses the opportunities of wireless product identification technology in transforming supply chain management. A new concept of item level supply chain management and enabling steps to achieve the benefits are proposed. Innovative companies already use wireless product identification with great benefits in specific functional areas, e.g. manufacturing and warehousing. However, the biggest potential is in supply chain wide solutions, i.e. item level supply chain management.
Improving supply chain relations: an empirical case study
Authors: Wagner Beverly A. , Macbeth Douglas K. , Boddy David
Published: September 2002

This paper reflects on a three‐year EPSRC research project (1994‐1997), called "Implementing Partnering in the Supply Chain", that studied the development of collaboration between two companies, IDV Operations Ireland Limited and Killeen Corrugated and the complex processes involved in fostering their business relationship. The paper illustrates strategic motivation; both corporate and local, of the companies involved. The principal theoretical outcome of the research, “A Partnering Change Model”, provides a structure for analysis. The case describes the outcomes according to this analysis and, finally, conclusions and managerial implications are presented.
The Influence of Lubricant Film Thickness on Friction Coefficients During Slow Speed Deep Drawing Operations
Authors: Gilmour K. R. , Paul S. , Leacock A. G.
Published: September 2002

During some deep drawing operations liquid lubricants are used under the blankholder to reduce friction coefficients. Under the clamping action of the blankholder, lubricants will be squeezed out resulting in a changing film thickness after the initial application of the blankholder load. A relationship between kinetic friction coefficient values and the loading duration of the blankholder can be observed from analysis of results recorded during simulative testing. By using a numerical model to combine empirical measurements, friction coefficients during boundary lubrication, lubricant film thickness with sheet surface topography data, it can be shown that the coefficient of friction can reliably be predicted for a given loading duration.
Application of Foil Bearings to Turbomachinery Including Vertical Operation
Authors: Walton J. F. , Hesmat H.
Published: September 2002

A review is made of the function of compliant surface bearings in serving the needs of modern turbomachinery. This service extends over a wide spectrum of severe operational and environmental conditions such as extreme low and high temperatures, speeds over 100,000 rpm, and the use of cryogenics as lubricants. The importance of using appropriate simulators that duplicate the actual equipment in evaluating the application of compliant bearings is demonstrated via two specific examples; one, a simulator to evaluate bearings for an air cycle machine and another for an advanced cryogenic device. In view of the known difficulties in using hydrodynamic bearings in vertical machines a new preloaded compliant journal bearing design is offered which performs as well with a vertically mounted shaft as it does in horizontal operation. In terms of the location of the first two rigid-body criticals, the test data show the compliant bearing’s vertical operation to be at most 15 percent lower than for the horizontal case, whereas the maximum vibrational amplitude stayed the same for both modes of operation. This new class of hydrodynamic compliant surface journal bearings now makes possible development of oil-free machines capable of all attitude operation, such as aircraft gas turbine engines undergoing severe pitch maneuvers or machines that must be operated vertically due to space constraints.
Development of a Maintenance Program for Major Gas Turbine Hot Gas Path Parts
Authors: Moritsuka H. , Fujii T. , Takahashi T.
Published: September 2002

The thermal efficiency of gas turbine combined cycle power generation plants increase significantly in accordance with turbine inlet temperature. Gas turbine combined cycle power plants operating at high turbine inlet temperature are popular as a main thermal power station among our electric power companies in Japan. Thus, gas turbine hot gas parts are working under extreme conditions which will strongly affect their lifetime as well as maintenance costs for repaired and replaced parts. To reduce the latter is of major importance to enhance cost effectiveness of the plant. This report describes a gas turbine maintenance management program of main hot gas parts (combustor chambers, transition pieces, turbine first stage nozzles and first stage buckets) for management persons of gas turbine combined cycle power stations in order to obtain an optimal gas turbine maintenance schedule considering rotation, repair and replacement, or exchange of those parts.
Real-Time On-Line Performance Diagnostics of Heavy-Duty Industrial Gas Turbines
Authors: Gu¨len S. C. , Griffin P. R. , Paolucci S.
Published: September 2002

This paper describes the results of real-time, on-line performance monitoring of two gas turbines over a period of five months in 1997. A commercially available software system is installed to monitor, analyze and store measurements obtained from the plant’s distributed control system. The software is installed in a combined-cycle, cogeneration power plant, located in Massachusetts, USA, with two Frame 7EA gas turbines in Apr. 1997. Vendor’s information such as correction and part load performance curves are utilized to calculate expected engine performance and compare it with measurements. In addition to monitoring the general condition and performance of the gas turbines, user-specified financial data is used to determine schedules for compressor washing and inlet filter replacement by balancing the associated costs with lost revenue. All measurements and calculated information are stored in databases for real-time and historical trending and tabulating. The data is analyzed ex post facto to identify salient performance and maintenance issues.
A Comparison of Two Finite Element Reduction Techniques for Mistuned Bladed Disks
Authors: Moyroud F. , Fransson T. , Jacquet-Richardet G.
Published: September 2002

The high performance bladed disks used in today’s turbomachines must meet strict standards in terms of aeroelastic stability and resonant response level. One structural characteristic that can significantly impact on both these areas is that of bladed disk mistuning. To predict the effects of mistuning, computational efficient methods are much needed to make free-vibration and forced-response analyses of full assembly finite element (FE) models feasible in both research and industrial environments. Due to the size and complexity of typical industrial bladed disk models, one must resort to robust and systematic reduction techniques to produce reduced-order models of sufficient accuracy. The objective of this paper is to compare two prevalent reduction methods on representative test rotors, including a modern design industrial shrouded bladed disk, in terms of accuracy (for frequencies and mode shapes), reduction order, computational efficiency, sensitivity to intersector elastic coupling, and ability to capture the phenomenon of mode localization. The first reduction technique employs a modal reduction approach with a modal basis consisting of mode shapes of the tuned bladed disk which can be obtained from a classical cyclic symmetric modal analysis. The second reduction technique uses Craig and Bampton substructure modes. The results show a perfect agreement between the two reduced-order models and the nonreduced finite element model. It is found that the phenomena of mode localization is equally well predicted by the two reduction models. In terms of computational cost, reductions from one to two orders of magnitude are obtained for the industrial bladed disk, with the modal reduction method being the most computationally efficient approach.
Three Practical Examples of Magnetic Bearing Control Design Using a Modern Tool
Authors: Spirig M. , Schmied J. , Jenckel P. , Kanne U.
Published: September 2002

The use of magnetic bearing in industrial applications has increased due to their unique properties. Nowadays efficiency and predictability in handling rotors on magnetic bearings is asked with the same standard as conventional rotors on oil or roller bearings. First of all one must be aware of the special technical properties of magnetic bearing designs. The dynamic behavior of the rotor combined with requirements of the application define the desired bearing characteristic. With modern tools covering the mechanical aspects as well as the electronic controllers and their digital implementation on a DSP, these properties can be designed. However, despite the use of such efficient tools engineering practice is needed. Therefore this paper summarizes the major steps in the control design process of industrial applications. Three rotors supported on magnetic bearing with their specific dynamic behavior are presented: a very small high speed spindle (120,000 rpm); a small industrial turbo molecular pump rotor (36,000 rpm); and a large multistage centrifugal compressor (600 to 6300 rmp). The results of the analyses and their experimental verification are given.
Manufacturing Effects in Microfabricated Gas Bearings: Axially Varying Clearance
Authors: Piekos E. S. , Breuer K. S.
Published: September 2002

The effect of axially-varying clearance on microfabricated gas journal bearings is explored. This variation commonly arises from difficulties inherent to etching deep, narrow channels. Two types of clearance variation commonly observed in etched bearings are investigated: taper and bow. Both shapes are shown to have a detrimental effect on load capacity and bearing stability compared to a cylindrical bearing with the minimum clearance. For the same variation magnitude, taper is shown to have a more serious effect, including complete closure of the stability corridor at low speed for some cases. Methods are suggested for estimating variable-clearance bearing performance using cylindrical bearing data.
The Coefficient of Friction During Hot Rolling of Low Carbon Steel Strips
Authors: Lenard John G. , Barbulovic-Nad Leon
Published: September 2002

Hot rolling tests were performed on low carbon steel strips with the objective of determining the coefficient of friction as a function of the process variables. The growth of the scale prior to rolling was controlled and the thickness of the layer of scale at the entry remained in the range of 20–100 μm, somewhat higher than in the finishing train of a hot strip mill. Roll separating forces, roll torques, the speed, the reduction and the entry temperature were monitored. The effective coefficient of friction was determined by using a one-dimensional model of the flat rolling process. The coefficient was chosen to allow matching the measured and calculated roll force and the roll torque. An empirical relation, connecting the coefficient of friction to process variables was obtained by non-linear regression analysis.
A New Postulation of Viscosity and Its Application in Computation of Film Thickness in TFL1
Authors: Zhang Chaohui , Luo Jianbin , Wen Shizhu
Published: September 2002

In this paper, a viscosity modification model is developed which can be applied to describe the thin film lubrication problems. The viscosity distribution along the direction normal to solid surface is approached by a function proposed in this paper. Based on the formula, lubricating problem of thin film lubrication (TFL) in isothermal and incompressible condition is solved and the outcome is compared to the experimental data. In thin film lubrication, according to the computation outcomes, the lubrication film thickness is much greater than that in elastohydrodynamic lubrication (EHL). When the velocity is adequately low (i.e., film thickness is thin enough), the pressure distribution in the contact area is close to Hertzian distribution in which the second ridge of pressure is not obvious enough. The film shape demonstrates the earlobe-like form in thin film lubrication, which is similar to EHL while the film is comparatively thicker. The transformation relationships between film thickness and loads, velocities or atmosphere viscosity in thin film lubrication differ from those in EHL so that the transition from thin film lubrication to EHL can be clearly seen.
Effects of Elevated Temperatures on Rocking Vibration of Rotating Disk and Spindle Systems
Authors: Tseng Chaw-Wu , Shen Jr-Yi , Ku C.-P. R. , Shen I. Y.
Published: September 2002

This paper studies how temperature variations affect natural frequencies of rocking vibration of a rotating disk and spindle system through mathematical modeling and experimental measurements. Existing literature has shown that both radial bearing stiffness krr and natural frequency ω01B of one-nodal-diameter disk modes could substantially affect natural frequencies ω01U of rocking vibration. In this paper, a preliminary experiment first identifies that relaxation of bearing stiffness krr is the dominating factor to shift the natural frequency ω01U at elevated temperatures. In addition, the bearing relaxation primarily results from thermal mismatch between the bearing raceways and the rotating hub. Guided by the experimental results, a mathematical model is developed to determine how temperature variations affect bearing contact angles, bearing preloads, and subsequently the radial bearing stiffness krr. Based on the bearing stiffness krr and disk frequency ω01B at elevated temperatures, one can predict natural frequency ω01U of rocking vibration through the mathematical model by Shen and Ku (1997). Finally, ω01U of a rotating disk and spindle system are measured in a thermal chamber to validate the theoretical predictions.
A Microscopic Wear Measurement Method for General Surfaces
Authors: Jeng Yeau-Ren , Lin Zhi-Way , Shyu Shiuh-Hwa
Published: September 2002

A method was developed to measure the wear of general engineering surfaces based on the roughness parameters of the worn surfaces. This method does not require any information of the initial surface. The surface height distribution is described using Johnson translatory system where the loss of surface height is attributed to wear. Experiments of engine running in were conducted to validate the method. The results show that the current method can determine wear comparable to surface roughness. The current approach simplifies the profilometrical wear measurement and extends such a measurement to non-Gaussian surfaces.
Thermal EHL of Rough Rolling/Sliding Line Contacts Using a Mixture of Two Fluids at Dynamic Loads
Authors: Kumar Punit , Jain S. C. , Ray S.
Published: September 2002

The behavior of the thermal elastohydrodynamic lubrication film in rough rolling/sliding line contacts at dynamic loads is investigated numerically. The lubricant is assumed to be a mixture of Newtonian and Ree-Eyring fluids. The results show that the maximum pressure in the contact region undergoes a noteworthy change with time due to dynamic loading and the effect of moving surface roughness. The variation of minimum film thickness and coefficient of friction with the composition of the lubricant is found to be dependent upon the reference viscosity ratio. The superposition of the effects of moving surface roughness and dynamic loading is shown to determine the behavior of time dependent film thickness and coefficient of friction.
Elastic-Plastic Finite Element Analysis for the Head-Disk Interface With Fractal Topography Description
Authors: Komvopoulos K. , Ye N.
Published: September 2002

An elastic-plastic contact analysis based on a finite element model and real surface topographies was performed to elucidate the evolution of deformation at the head-disk interface. The topographies of the head and disk surfaces were represented by an equivalent profile generated using a modified two-variable Weierstrass-Mandelbrot function, with fractal parameters determined from images of head and disk surfaces. A region of the equivalent rough surface profile was selected for analysis based on topography scale considerations and contact simulation results. The evolution of plasticity and the likelihood of cracking in the overcoat and the magnetic layer are interpreted in light of results for the subsurface von Mises equivalent stress, equivalent plastic strain, and maximum first principal stress. The finite element model provides insight into the elastic-plastic deformation behavior of the layered medium in terms of the thickness, mechanical properties, and residual stress in the carbon overcoat.
Formulas for Entraining Velocity in Lubricated Line Contacts
Authors: Ciulli Enrico
Published: September 2002

The knowledge of the entraining velocity is necessary for the investigation of lubricated contacts. The entraining velocity is the average of the surface velocities of the two bodies in contact relative to the contact itself; its estimation can be actually not always immediate. In this work the general case of two pairing cylindrical surfaces in planar relative motion is analyzed from a kinematical point of view. Formulas for the evaluation of the entraining velocity are presented that are directly applicable to any case of connected members of a mechanism. The physical meaning of the terms of the proposed formulas is also briefly investigated from a lubrication point of view.
The Effects of Slider Material on the Gasification of Carbon
Authors: Ramirez Ainissa G. , Sinclair Robert , Harkins C. Girvin , Lin A. Robert
Published: September 2002

The influence of alumina and titanium carbide, components of magnetic recording sliders, on the carbon gasification reaction was investigated. Pure alumina and titanium carbide powders were each combined with graphite powder and subjected to thermogravimetric analysis (TGA). The molar ratio ranged from 0 to 20 mol percent; graphite powder was the balance. From the thermogravimetric analysis, the activation energy Ea of the reactions was determined. It was found that the activation energy for carbon gasification reduced slightly for increasing alumina mole percentage. Titanium carbide additions markedly increased the activation energy. This increase indicates a competitive oxidation reaction that forms titanium oxide, as confirmed by X-ray diffraction (XRD). As a result of these observations, titanium oxide was also mixed with graphite powders and analyzed by TGA. Titanium oxide has an activation energy behavior that becomes more complex with increasing mole percentage: the activation energy first increases and then decreases. These data are presented and the oxidation reaction is proposed.
Development of a Three-Dimensional Semi-Analytical Elastic-Plastic Contact Code
Authors: Jacq C. , Ne´lias D. , Lormand G. , Girodin D.
Published: September 2002

A three-dimensional elastic-plastic contact code based on semi-analytical method is presented and validated. The contact is solved within a Hertz framework. The reciprocal theorem with initial strains is then introduced, to express the surface geometry as a function of contact pressure and plastic strains. The irreversible nature of plasticity leads to an incremental formulation of the elastic-plastic contact problem, and an algorithm to solve this problem is set up. Closed form expression, which give residual stresses and surface displacements from plastic strains, are obtained by integration of the reciprocal theorem. The resolution of the elastic-plastic contact using the finite element (FE) method is discussed, and the semi-analytical code presented in this paper is validated by comparing results with experimental data from the nano-indentation test. Finally, the resolution of the rolling elastic-plastic contact is presented for smooth and dented surfaces and for a vertical or rolling loading. The main advantage of this code over classical FE codes is that the calculation time makes the transient analysis of three-dimensional contact problems affordable, including when a fine mesh is required.
Uncertainty Reduction in Gas Turbine Performance Diagnostics by Accounting for Humidity Effects
Authors: Mathioudakis K. , Tsalavoutas T.
Published: September 2002

The paper presents an analysis of the effect of ambient humidity on the performance of industrial gas turbines and examines the impact of humidity on methods used for engine condition assessment and fault diagnostics. First, the way of incorporating the effect of humidity into a computer model of gas turbine performance is described. The model is then used to derive parameters indicative of the “health” of a gas turbine and thus diagnose the presence of deterioration or faults. The impact of humidity magnitude on the values of these health parameters is studied and the uncertainty introduced, if humidity is not taken into account, is assessed. It is shown that the magnitude of the effect of humidity depends on ambient conditions and is more severe for higher ambient temperatures. Data from an industrial gas turbine are presented to demonstrate these effects and to show that if humidity is appropriately taken into account, the uncertainty in the estimation of health parameters is reduced.
Modeling and Identification of Gas Journal Bearings: Self-Acting Gas Bearing Results
Authors: Belforte G. , Raparelli T. , Viktorov V.
Published: September 2002

A mathematical model is elaborated with analytical relations for transfer functions and for gas-film stiffness and damping coefficients for self-acting and externally pressurized gas journal bearings with four supply orifices positioned at the center plane for rotating shaft displacements near the bearing center. Averaging and corrective coefficients are elaborated. In this paper static and dynamic characteristics of self-acting gas bearings are investigated. Results derived using the developed mathematical model are compared with the results derived from numerical computations of a non-linear distributed parameter model of the gas bearings. The results obtained demonstrate that analytical data are in good agreement with the numerical data for wide range of parameters and the mathematical model developed makes the simple calculation of static and dynamic characteristics of self-acting gas bearings possible. Derived analytical relations for transfer functions and for gas-film coefficients of gas bearings provide an efficient means for designing rotor-bearing systems.
Numerical Analysis of Dynamic Coefficients for Gas Film Face Seals
Authors: Liu Yuchuan , Shen Xinmin , Xu Wanfu
Published: September 2002

A numerical analysis of stiffness and damping coefficients for gas film face seals in three degrees of freedom is presented in this paper. By applying small perturbation approximation, the steady and perturbed Reynolds equations, taking account of both hydrodynamic and hydrostatic effects, are obtained and solved by finite element method. Several numerical samples, including externally pressurized annular thrust gas bearings and spiral groove thrust gas bearings, validate the model and numerical algorithm. The results show that the interactions between axial and angular perturbation are negligible. Hence, in the dynamic analysis of gas film face seals, the perturbation in three degrees of freedom can be simplified as two independent ones, an axial movement and an angular wobble around two orthogonal axes perpendicular to axial direction.
Applying the Representative Interactive Flamelet Model to Evaluate the Potential Effect of Wall Heat Transfer on Soot Emissions in a Small-Bore Direct-Injection Diesel Engine
Authors: Hergart C. , Peters N.
Published: September 2002

Capturing the physics related to the processes occurring in the two-phase flow of a direct-injection diesel engine requires a highly sophisticated modeling approach. The representative interactive flamelet (RIF) model has gained widespread attention owing to its ability of correctly describing ignition, combustion, and pollutant formation phenomena. This is achieved by incorporating very detailed chemistry for the gas phase as well as for the soot particle growth and oxidation, without imposing any significant computational penalty. This study addresses the part load soot underprediction of the model, which has been observed in previous investigations. By assigning flamelets, which are exposed to the walls of the combustion chamber, with heat losses calculated in a computational fluid dynamics (CFD) code, predictions of the soot emissions in a small-bore direct-injection diesel engine are substationally improved. It is concluded that the experimentally observed emissions of soot may have their origin in flame quenching at the relatively cold combustion chamber walls.
Tubular Solid Oxide Fuel Cell/Gas Turbine Hybrid Cycle Power Systems: Status
Authors: Veyo S. E. , Shockling L. A. , Dederer J. T. , Gillett J. E. , Lundberg W. L.
Published: September 2002

The solid oxide fuel cell (SOFC) is a simple electrochemical device that operates at 1000°C, and is capable of converting the chemical energy in natural gas fuel to AC electric power at approximately 45% efficiency (net AC/LHV) when operating in a system at atmospheric pressure. Since the SOFC exhaust gas has a temperature of approximately 850°C, the SOFC generator can be synergistically integrated with a gas turbine (GT) engine generator by supplanting the turbine combustor and pressurizing the SOFC, thereby enabling the generation of electricity at efficiencies approaching 60% or more. Conceptual design studies have been performed for SOFC/GT power systems employing a number of the small recuperated gas turbine engines that are now entering the marketplace. The first hardware embodiment of a pressurized SOFC/GT power system has been built for Southern California Edison and is scheduled for factory acceptance tests beginning in Fall 1999 at the Siemens Westinghouse facilities in Pittsburgh, PA. The hybrid power cycle, the physical attributes of the hybrid systems, and their performance are presented and discussed.