bluuebunny/crossref_metadata_2025 huggingface dataset:
Checkpoint activation regulates mutagenic translesion synthesis
Authors: Kai Mihoko , Wang Teresa S.-F.
Published: January 2003

Cells have evolved checkpoint responses to arrest or delay the cell cycle, activate DNA repair networks, or induce apoptosis after genomic perturbation. Cells have also evolved the translesion synthesis processes to tolerate genomic lesions by either error-free or error-prone repair. Here, we show that after a replication perturbation, cells exhibit a mutator phenotype, which can be significantly affected by mutations in the checkpoint elements Cds1 and Rad17 or translesion synthesis polymerases DinB and Polζ. Cells respond to genomic perturbation by up-regulation of DinB in a checkpoint activation-dependent manner. Moreover, association of DinB with chromatin is dependent on functional Rad17, and DinB physically interacts with the checkpoint-clamp components Hus1 and Rad1. Thus, translesion synthesis is a part of the checkpoint response.
A biochemical framework for RNA silencing in plants
Authors: Tang Guiliang , Reinhart Brenda J. , Bartel David P. , Zamore Phillip D.
Published: January 2003

RNA silencing phenomena were first discovered in plants, yet only the RNA interference pathway in animals has been subject to biochemical analysis. Here, we extend biochemical analysis to plant RNA silencing. We find that standard wheat germ extract contains Dicer-like enzymes that convert double-stranded RNA (dsRNA) into two classes of small interfering RNAs, as well as an RNA-dependent RNA polymerase activity that can convert exogenous single-stranded RNA into dsRNA. In this plant embryo extract, an endogenous microRNA (miRNA) that lacks perfect complementarity to its RNA targets nonetheless acts as a small interfering RNA. The miRNA guides an endonuclease to cleave efficiently wild-typeArabidopsis PHAVOLUTAmRNA, but not a dominant mutant previously shown to perturb leaf development. This finding supports the view that plant miRNAs direct RNAi and that miRNA-specified mRNA destruction is important for proper plant development. Thus, endonuclease complexes guided by small RNAs are a common feature of RNA silencing in both animals and plants.
Yeast DNA polymerase zeta (ζ) is essential for error-free replication past thymine glycol
Authors: Johnson Robert E. , Yu Sung-Lim , Prakash Satya , Prakash Louise
Published: January 2003

DNA polymerase zeta (Polζ) promotes the mutagenic bypass of DNA lesions in eukaryotes. Genetic studies inSaccharomyces cerevisiaehave indicated that relative to the contribution of other pathways, Polζ makes only a modest contribution to lesion bypass. Intriguingly, however, disruption of theREV3gene, which encodes the catalytic subunit of Polζ, causes early embryonic lethality in mice. Here, we present genetic and biochemical evidence for the requirement of yeast Polζ for predominantly error-free replication past thymine glycol (Tg), a DNA lesion formed frequently by free radical attack. These results raise the possibility that, as in yeast, in higher eukaryotes also, Polζ makes a major contribution to the replicative bypass of Tgs as well as other lesions that block synthesis by replicative DNA polymerases. Such a preeminent role of Polζ in lesion bypass would ensure that rapid cell divisions continue unabated during early embryonic development, thereby minimizing the generation of DNA strand breaks, chromosome aberrations, and the ensuing apoptotic response.
Multipotent cell lineages in early mouse development depend on SOX2 function
Authors: Avilion Ariel A. , Nicolis Silvia K. , Pevny Larysa H. , Perez Lidia , Vivian Nigel , Lovell-Badge Robin
Published: January 2003

Each cell lineage specified in the preimplantation mammalian embryo depends on intrinsic factors for its development, but there is also mutual interdependence between them. OCT4 is required for the ICM/epiblast lineage, and at transient high levels for extraembryonic endoderm, but also indirectly through its role in regulatingFgf4expression, for the establishment and proliferation of extraembryonic ectoderm from polar trophectoderm. The transcription factor SOX2 has also been implicated in the regulation ofFgf4expression. We have used gene targeting to inactivateSox2, examining the phenotypic consequences in mutant embryos and in chimeras in which the epiblast is rescued with wild-type ES cells. We find a cell-autonomous requirement for the gene in both epiblast and extraembryonic ectoderm, the multipotent precursors of all embryonic and trophoblast cell types, respectively. However, an earlier role within the ICM may be masked by the persistence of maternal protein, whereas the lack of SOX2 only becomes critical in the chorion after 7.5 days postcoitum. Our data suggest that maternal components could be involved in establishing early cell fate decisions and that a combinatorial code, requiring SOX2 and OCT4, specifies the first three lineages present at implantation.
Fgfr1regulates patterning of the pharyngeal region
Authors: Trokovic Nina , Trokovic Ras , Mai Petra , Partanen Juha
Published: January 2003

Development of the pharyngeal region depends on the interaction and integration of different cell populations, including surface ectoderm, foregut endoderm, paraxial mesoderm, and neural crest. Mice homozygous for a hypomorphic allele ofFgfr1have craniofacial defects, some of which appeared to result from a failure in the early development of the second branchial arch. A stream of neural crest cells was found to originate from the rhombomere 4 region and migrate toward the second branchial arch in the mutants. Neural crest cells mostly failed to enter the second arch, however, but accumulated in a region proximal to it. Both rescue of the hypomorphicFgfr1allele and inactivation of a conditionalFgfr1allele specifically in neural crest cells indicated thatFgfr1regulates the entry of neural crest cells into the second branchial arch non-cell-autonomously. Gene expression in the pharyngeal ectoderm overlying the developing second branchial arch was affected in the hypomorphicFgfr1mutants at a stage prior to neural crest entry. Our results indicate thatFgfr1patterns the pharyngeal region to create a permissive environment for neural crest cell migration.
Future proof signal conditioning
Authors: Turner Brian
Published: January 2003

Despite the rapid growth in the implementation of sophisticated software‐based control systems, today’s process industries still rely heavily on sensors and associated conditioning electronics to provide accurate data from the processes. While most instrumentation manufacturers have focused their attention on products and system software beyond such front end signal conditioning, Status Instruments have decided to invest in the design of a highly versatile front end conditioning module which can be adapted to meet an ever increasing number of applications simply by downloading a new piece of software from their Web site.
Force/torque sensing applied to industrial robotic deburring
Authors: Norberto Pires J. , Ramming John , Rauch Stephen , Araújo Ricardo
Published: January 2003

Force/torque sensing is very important for several automatic and industrial robotic applications. Basically, if precise control of the forces that arise from contact between tools and parts is required to successfully complete the automatic task, then a force/torque sensor is needed along with some force/torque control technique. In this paper we focus on force/torque sensing aspects applied to industrial robotic tasks. Concentrating on a particular type of force/torque sensor, we demonstrate how to use them and how to integrate them into force/torque control applications using robots. Finally, an industrial application is presented where force control was fundamental for the success of the task.
A sensor for the sugar cane harvester topper
Authors: McCarthy Stuart , Billingsley John
Published: January 2003

A robust low cost refractometer has been developed together with signal conditioning algorithms to enable sucrose content to be measured during the mechanical harvesting of the sugar cane plant. This technology will be applied to the harvester process that removes the tops of the cane to assist the harvester operator to cut the cane at the optimum cutting height.
Document delivery – breaking the mould
Authors: Baker David
Published: January 2003

This article takes a personal look – retrospectively and prospectively – at the application of information and communications technology within library and information services in UK higher education (UKHE). It looks particularly at the ways in which document delivery has been transformed into a central driver in Internet‐based library service developments and considers recent innovations and likely future pathways. It focuses on the results of programmes such as the Joint Information Systems Committee’s e‐Lib Programme and subsequent attempts to provide radical alternatives to the dominant design of traditional inter‐library loan and document supply services, and it draws on first‐hand experience of the innovation process through projects such as EDDIS and Agora.
The English experience – library and information services, delivering access collaboratively
Authors: Warren Geoff
Published: January 2003

This article explores a range of issues associated with cross‐sectoral collaboration across different kinds of library and information service providers in England, the purpose of joint‐working being the widening and improving of access to “content and services” for users. Much of this will be applicable across the UK as a whole. It covers three main areas: diversity of user demand; historical and current collaborative mechanisms; and opportunities to further improve the quality of access.
Formation and the colour development in cobalt spinel pigments
Authors: Fernández Ana L. , de Pablo Liberto
Published: January 2003

Nanocrystalline cobalt spinels were synthesized under hydrothermal conditions, starting from metal chlorides. The color properties in these systems mainly depend upon the preparative method and cation distributions, which have been determined by X‐ray powder diffraction using Rietveld refinements and visible near infrared absorption spectra. We observe the influence of tetrahedral and octahedral preference of cations such as Co2+, Cr3+, Mn3+ upon the formation and the color development of cobalt spinel pigments. All the samples prepared revealed the formation of single spinel with particle size at about 0.8‐2.1 μm; CoAl2O4 reveals king's blue, CoMn2O4 dark blue and CoCr2O4 bluish green. Cobalt blues developed giving deep absorption characteristic of tetrahedral Co2+ ions at about 550‐680 nm; therefore, color changed from king's blue to bluish green in CoCr2O4, showing the absorption band of octahedral Cr3+ ions owing to the large excess octahedral crystal field stabilization energy.
Novel pyridine‐2(1H)‐thione and thieno‐[2,3‐b]pyridine derivatives containing arylazo moiety: synthesis, characterization and dyeing properties
Authors: Elgemeie Galal H. , Helal Maher H. , Abbas Emam M. , Abdel Mowla Ebtissam A.
Published: January 2003

Several new pyridine‐2(1H)‐thione and thieno[2,3‐b]pyridine derivatives containing an arylazo function were obtained. The application and characteristics for the synthesised dyes are demonstrated.
Soybean oil modified polyesteramide resins
Authors: Shende Pradeep , Dabhade Shrikant , Kulkarni Milind
Published: January 2003

Polyesteramide resin based on the condensation of hydroxyethylamide derivatives of fatty acids of soybean {N, N′‐bis(2 hydroxyethyl)soybean amide} and various dibasic acid and anhydride were synthesized. Physico‐chemical characteristics and film forming properties of these resins were determined to prove its suitability as a vehicle for surface coatings. The study reveals that resins can be used for the baked type of finishes.
Do relationship portfolios and networks provide the key to successful relationship management?
Authors: Zolkiewski Judy , Turnbull Peter
Published: January 2003

The importance of effective planning and management of an organization’s array of customer and supplier relationships is self‐evident, yet relatively little research has been published which develops our academic or managerial understanding of the conceptual and practical problems inherent in this issue. This paper is written from an interaction and network perspective and critically reviews existing customer and supplier portfolio analysis and considers the implications of using such an approach for the management of relationships. The notion of relationship portfolios in the context of network theory is reviewed and the authors suggest that portfolios provide an alternative method of network conceptualization and analysis and that such portfolios may be a key factor in successful relationship management.
Effects of suppliers’ marketing program variables on industrial buyers’ relationship satisfaction and commitment
Authors: Abdul‐Muhmin Alhassan G.
Published: January 2003

Relationship satisfaction and commitment are two key constructs in the evolving paradigm of relationship marketing in business‐to‐business markets, and a substantial and growing literature exists on their antecedents and consequences, especially within the context of supplier‐retailer relationships. However, relatively little research has examined these constructs within the context of supplier‐manufacturing firm relationships in general, and foreign supplier‐manufacturing firm relationships in particular. Even fewer studies have examined the effects of suppliers’ marketing program variables on relationship satisfaction and commitment in such contexts. The author examines how foreign suppliers’ marketing program variables affect Saudi industrial buyers’ satisfaction and commitment to long‐term relationships with the suppliers. Results of a survey conducted among buyers for manufacturing establishments in the Eastern Province of Saudi Arabia indicate that only the product and price‐related variables of foreign suppliers’ marketing program variables are significantly related to the buyers’ relationship satisfaction and commitment. Theoretical and managerial implications of the findings are outlined and discussed.
Influence of the Combustor Aerodynamics on Combustion Instabilities From Equivalence Ratio Fluctuations
Authors: Sattelmayer T.
Published: January 2003

Gas turbine combustors are often susceptible to self-excited oscillations, which lead to unacceptable levels of pressure, velocity, and heat release fluctuations. Although instabilities can occur in systems with locally constant equivalence ratio, it is very important to take into account the influence of equivalence ratio fluctuations, which are generated in the fuel air mixer in the unstable case. These fluctuations are convected into the flame and lead to an additional mechanism for the generation of heat release fluctuations. Moreover, entropy waves are produced in the flame, which travel through the combustor and generate additional pressure waves during the acceleration of the flow at the combustor exit. To date, available theories use the physically unrealistic assumption that the equivalence ratio waves as well as the entropy waves are convected downstream without any spatial dispersion due to the combustor aerodynamics. An analytical approach is presented, which allows us to take the spatial dispersion into consideration. For that purpose, the response of the burner and the combustor to an equivalence ratio impulse or an entropy impulse is calculated using the Laplace transformation and a more general transfer function for harmonic waves is derived. The obtained expression has three parameters, which represent the influence of the burner or the combustor aerodynamics, respectively. This equation can be used in numerical codes, which represent the combustion system through a network of acoustic multiports, if the equivalence ratio and the entropy are added to the vector of variables considered. The parameters required for the dynamic combustor model can be deduced from a detailed CFD analysis of the combustor flow in case of the application of the theory to a particular combustor design. As an example, a simple model combustor is used to demonstrate the application of the theory. It is highlighted how the spatial dispersion of the equivalence ratio and entropy fluctuations can be included in the stability analysis. The calculated examples reveal that the influence of both variables on the generation of instabilities is highly overpredicted if the spatial dispersion is not taken into account. Furthermore, it can be deduced from the study that burner and combustor designs with a wide range of convective time scales have advantages with respect to the stability of the combustor.
Chebyshev Polynomials Fits for Efficient Analysis of Finite Length Squeeze Film Damped Rotors
Authors: Rodrigues F. A. , Thouverez F. , Gibert C. , Jezequel L.
Published: January 2003

The nonlinear behavior of the hydrodynamic forces generated by squeeze film dampers makes dynamical analyses of rotor-bearing systems incorporating such devices a complex and often long task. When steady-state orbits are to be sought, approximate methods (e.g., harmonic balance method, trigonometric collocation method) can be used in order to save computation cost. However, numerical integration in the time domain cannot be avoided if one wishes to calculate transient responses, or to carry out more meticulous analyses concerning the effects of the damper nonlinear nature on the motion of the system. For finite length squeeze film dampers, neither the short nor the long bearing approximations can be suitably applied, and the fluid pressure field has to be estimated numerically, thus rendering rotordynamics predictions even longer and, for engineering purposes computationally prohibitive. To surmount this problem, the present paper proposes a straightforward procedure to derive polynomial expressions for the squeeze film damper (SFD) forces, for given damper geometry and boundary conditions. This is achieved by applying Chebyshev orthogonal polynomial fits over force data generated by numerically solving the two-dimensional pressure field governing equation. For both transient and steady-state calculations, the use of the SFD forces polynomial expressions is seen to be very efficient and precise.
Control System Design for Active Lubrication With Theoretical and Experimental Examples
Authors: Santos I. F. , Scalabrin A.
Published: January 2003

This work focuses on the theoretical and experimental behavior of rigid rotors controlled by tilting-pad journal bearings with active oil injection. Initially the mathematical model of the active bearing is presented: The equations that describe the dynamics of hydraulic actuators are introduced into the equations of the lubricant, resulting in a new form of Reynolds’ equation for active lubrication. The global model of the system is obtained by coupling the equation of motion of the rigid rotor with the stiffness and damping of the active oil film. This global model is then used to design the control system of the active bearing based on root locus curves. The active system stability is analyzed by calculating its eigenvalues and frequency response curves. The theoretical and experimental results show that this kind of bearing can significantly reduce the vibration level of rotating machinery.
Flow Characterization and Performance of a Powder Lubricated Slider Bearing
Authors: Pappur Manjunath , Khonsari M. M.
Published: January 2003

This paper presents a systematic development of the theory of powder lubrication with the appropriate formalism based on the fundamentals of fluid mechanics. The theory is capable of predicting flow velocity, fluctuation (pseudo-temperature), powder volume fraction, and slip velocity at the boundaries. An extensive set of parametric simulations covering granular size, surface roughness, volumetric flow, load and speed are performed to gain insight into the performance of a powder lubricated thrust bearing. The results of the simulations are compared to published experimental results. Good agreement between the theoretical and experimental results attests to the capability of the model and its potential for design of powder lubricated bearings.
Design Study of Part-Flow Evaporative Gas Turbine Cycles: Performance and Equipment Sizing—Part I: Aeroderivative Core
Authors: A˚gren N. D. , Westermark M. O. J.
Published: January 2003

The evaporative gas turbine cycle is a new high-efficiency power cycle that has reached the pilot testing stage. This paper presents calculation results of a new humidification strategy based on part flow humidification. This strategy involves using only a fraction of the compressed air for humidification. Thermodynamically, it can be shown that not all the air needs to be passed through the humidification system to attain the intrinsic good flue gas heat recovery of an EvGT cycle. The system presented also includes live steam production and superheating by heat from the hottest flue gas region. The humidifier only uses the lower temperature levels flue gas heat, where it is best suited. The analyzed system is based on data for the aeroderivative Rolls Royce Trent as a gas turbine core. Part II of this two-part paper presents the results based on data for the industrial gas turbine ABB GTX100. Simulation results include electric efficiency and other process datas as functions of degree of part flow. A detailed model of the humidifier is also used and described, which produces sizing results both for column height and diameter. Full flow humidification generates an electric efficiency of 51.5% (simple cycle 41%). The efficiency increases when the humidification air flow is reduced, to reach a maximum of 52.9% when air flow to the humidification amounts to around 12% of the intake air to the compressor. At the same time, total heat exchanger area is reduced by 50% and humidifier volume by 36% compared to full flow humidification. This calls for a recommendation not to use all the compressed air for humidification.
Design Study of Part-Flow Evaporative Gas Turbine Cycles: Performance and Equipment Sizing—Part II: Industrial Core
Authors: A˚gren N. D. , Westermark M. O. J.
Published: January 2003

This is Part II of a two-part paper and presents calculation results of a part-flow EvGT cycle based on gas turbine data for the ABB GTX100 (modified for intercooling). The evaporative gas turbine cycle is a new high-efficiency cycle that has reached the pilot testing stage. This paper presents calculation results of a new humidification strategy based on part-flow humidification. This strategy involves using only a fraction of the compressed air for humidification. Thermodynamically, it can be shown that not all the air needs to be passed through the humidification system to attain the intrinsic good flue gas heat recovery of an EvGT cycle. The presented system also includes live steam production and superheating, by heat from the hottest flue gas region, for injection. The humidifier then only uses the lower temperature levels, where it is best suited. The analyzed system is based on data for the ABB GTX100.gas turbine in intercooled mode. Part I of this two-part paper presents the results based on data for the aeroderovative Rolls Royce Trent. Simulation results include electric efficiency and other process data as function of degree of part flow. A detailed model of the humidifier is used, which produces sizing results both for column height and diameter. Paper I includes detailed description of the modeling. For the GTX100 system, full-flow humidification generates an electric efficiency of 52.6% (simple cycle 36.2%). The efficiency is virtually unaffected if the air portion to humidification is cut to 60% of accessible compressor air (represents 48% of compressor intake). If 30% of air from the compressor after cooling bleed (24% of intake) is led to the humidifier, the efficiency is reduced to 52.2%. On the other hand is the total heat exchanger area reduced by 20% and column volume by 50%. This calls for a recommendation not to use all the compressed air for humidification. It is recommended to use 15–30% of compressor intake air. The exact economic optimum depends on local fuel prices, CO2 taxes, interest rates, etc.
A Micro-Contact Model for Boundary Lubrication With Lubricant/Surface Physiochemistry
Authors: Zhang H. , Chang L. , Webster M. N. , Jackson A.
Published: January 2003

A model is developed to study the tribological behavior of sliding micro-contacts. It provides a building block to the modeling of tribo-contacts in boundary lubrication. Three contact variables are calculated at the asperity-level by relating them to the state of contact and the state of asperity deformation. These variables include micro-contact friction force, load carrying capacity and flash temperature. The deformation of the contacting asperity is either elastic, elasto-plastic, or fully plastic. Furthermore, the asperity may be covered by the lubricant/additive molecules adsorbed on the surface, protected by a surface oxide layer or other chemical reaction films, or in direct contact with no boundary protection. The possibility of the contact in each of these three states is represented by a corresponding contact probability. A numerical method is developed to determine the contact state and contact variables in the course of an asperity-to-asperity collision. The asperity flash temperature, which governs the kinetics of lubricant/surface adsorption/desorption, is first calculated by integrating the Jaeger equation over the contact area and in time. Then, the probability of contact covered by an adsorbed film is determined using the Volmer adsorption isotherm, and the probability of contact protected by the oxide layer is estimated using a classical wear theory. For elastic/elasto-plastic deformation of the asperity, the friction coefficient is given by the linear combination of the friction coefficients of the three contact states with their contact probabilities as the weighting factors. For fully plastic deformation of the asperity, the contact pressure and friction force become dependent of each other. The shear stress is approximated by a linear function of the contact probabilities, and the contact pressure and friction coefficient then calculated. Meanwhile, the influence of fresh surface generation due to plastic flow on the contact probabilities is also modeled. Insights are provided into the asperity collision through numerical studies of a sample problem. In addition, parametric studies are carried out to analyze the effects of lubricant and surface parameters on the micro-contact severity and its load capacity.
Analysis of EHL Circular Contact Shut Down
Authors: Zhao Jiaxin , Sadeghi Farshid
Published: January 2003

In this paper, an isothermal study of the shut down process of elastohydrodynamic lubrication under a constant load is performed. The surface mean velocity is decreased linearly from the initial steady state value to zero. The details of the pressure and film thickness distributions in the contact area are discussed for the two stages of shut down process, namely the deceleration stage and the subsequent pure squeeze motion stage with zero entraining velocity. The nature of the balance between the pressure, the wedge and the squeeze terms in Reynolds equation enables an analytical prediction of the film thickness change on the symmetry line of the contact in the deceleration period, provided that the steady state central film thickness relationship with velocity is known. The results indicate that for a fixed deceleration rate, if the initial steady state surface mean velocity is large enough, the transient pressure and film thickness distributions in the deceleration period solely depend on the transient velocity. The pressure and film thickness at the end of the deceleration period are then the same and do not depend on the initial steady state velocity. From the same initial steady state velocity, larger deceleration rates provide higher central pressure increase, but also preserve a higher film thickness in the contact area at the end of the deceleration period. Later in the second stage when the axisymmetric pressure and film thickness patterns typical of pure squeeze motion form, the pressure distribution in the contact area resembles a Hertzian contact pressure profile with a higher maximum Hertzian pressure and a smaller Hertzian half contact width. As a result, the film thickness is close to a parabolic distribution in the contact area. The volume of the lubricant trapped in the contact area is then estimated using this parabolic film thickness profile.
Prevention of Nozzle Wear in Abrasive Water Suspension Jets (AWSJ) Using Porous Lubricated Nozzles
Authors: Anand Umang , Katz Joseph
Published: January 2003

This paper introduces a novel method for preventing nozzle wear in abrasive water jets. It consists of using a porous nozzle, surrounded by a reservoir containing high-viscosity lubricant, which is exposed to the same driving pressure as the flow in the nozzle. The pressure difference across the porous medium, generated due to the high-speed flow in the nozzle, continuously forces lubricant through it. The resulting thin oil film forming on the walls of the nozzle protects the walls from the impact and shear caused by the abrasive particles. The porous nozzles were manufactured using Electric Discharge Machining and examined with Scanning Electron Microscopy. Two test facilities were used for evaluating the porous lubricated nozzles. The first was a two-dimensional facility, supporting a 145 μm wide nozzle with windows on both sides, which enabled visualization of the oil film and measurements of the liquid and abrasive-particle velocities using Particle Image Velocimetry. The measured slip velocities were also compared to computed values from a simple numerical model involving one-way coupling. The second facility used a 200 μm axisymmetric nozzle to determine the extent of nozzle wear under different conditions. We found that the presence of an oil film substantially reduced the extent of nozzle wear, from 111 percent of the diameter, when the nozzle was not lubricated, to 4 percent, when the oil viscosity was 1800 mm2/s and its flow rate was 2.4 percent of the water flow (over the same period). The wear increased as the lubricant flow rate and viscosity decreased. The presence of the oil film also improved the coherence of the jet.
Predicting Critical Friction in a Two-Roll Cross Wedge Rolling Process
Authors: Li and Qiang , Lovell Michael R.
Published: January 2003

Excessive interfacial slip is one of the primary failure mechanisms in the cross wedge rolling (CWR) process. In order to predict operating conditions that lead to excess interfacial slip, an analytical method is presented for determining the critical rolling condition in a two-roll CWR operation. Based on a transverse section of the tool-workpiece contact interface, the method uses Bowden and Oxley’s friction models to obtain the critical rolling condition in CWR as a direct function of tool geometry and workpiece area reduction. The relative accuracy of the results obtained from each friction model is then ascertained and discussed by comparing the analytical results to experiments.
Studies of Jet Fuel Freezing by Differential Scanning Calorimetry and Cold-Stage Microscopy
Authors: Widmor N. , Ervin J. S. , Zabarnick S. , Vangness M.
Published: January 2003

Aircraft which fly at high altitude or encounter extremely cold environments have the potential for fuel freezing and, consequently, catastrophic failure of the fuel system. Thus, it is important to study the freezing of hydrocarbon jet fuels. In the current work, a differential scanning calorimeter is used to study thermal characteristics and phase transitions of freezing jet fuel. In addition, a cold-stage microscope is used to record images of the resulting crystalline microstructure. A kinetic representation for the freezing of jet fuel is presented. Kinetic mechanisms that describe the liquid-to-solid phase transformation in fuels are necessary for the development of computational fluid dynamics models that can be used by aircraft designers.
Internal Reforming Solid Oxide Fuel Cell Gas Turbine Combined Cycles (IRSOFC-GT)—Part II: Exergy and Thermoeconomic Analyses
Authors: Massardo A. F.
Published: January 2003

The aim of this work is to investigate the performance of internal reforming solid oxide fuel cell (IRSOFC) and gas turbine (GT) combined cycles. A mathematical model of the IRSOFC steady-state operation was presented in Part I of this work coupled to the thermodynamic analysis of a number of proposed IRSOFC-GT combined cycles, taking into account the influence of several technological constraints. In the second part of this work, both an exergy and a thermoeconomic analysis of the proposed cycles have been carried out using the TEMP code developed by the author. A suitable equation for IRSOFC cost evaluation based on cell geometry and performance has been proposed and employed to evaluate the electricity generation cost of the proposed combined systems. The results are presented and the influence of several parameters is discussed: external reformer operating conditions, fuel-to-air ratio, cell current density, compressor pressure ratio, etc. Diagrams proposed by the author for cost versus efficiency, cost versus specific work, and cost versus system pressure are also presented and discussed.
On the Surface Dimple Phenomena in Elliptical TEHL Contacts With Arbitrary Entrainment
Authors: Wang Jing , Yang Peiran , Kaneta Motohiro , Nishikawa Hiroshi
Published: January 2003

Theoretical analysis and optical interferometry experiments are performed to investigate the dimple phenomena in thermal elastohydrodynamic lubrication (TEHL) of elliptical contacts under pure sliding conditions. The lubricant entrainment is along the major and minor axes of the Hertzian contact ellipse or at some intermediate angle. Good agreement is achieved between theoretical and experimental results and the surface dimple phenomena occurring in glass-steel conjunctions are explained by the temperature-viscosity wedge mechanism. The influence of the angle between the minor axis and the entrainment vector on the position and shape of the dimple, the central and minimum film thickness, the temperature distribution and the frictional coefficient is discussed.
Dwell Sensitive Fatigue Response of Titanium Alloys for Power Plant Applications
Authors: Bache M. R. , Evans W. J.
Published: January 2003

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality, and periods of dwell loading at peak stress on cyclic strain accumulation.
Failure Analysis of Inlet Guide Vanes
Authors: McAlpin R. L. , Talley P. L. , Bernstein H. L. , Holm R. E.
Published: January 2003

The common failure modes of variable inlet guide vanes (VIGVs or IGVs) on industrial gas turbines are reviewed. These mechanisms include corrosion, cracking, and wear of the IGVs, their bushings and thrust washers. A new mechanism for IGV failure is described through a case history and metallurgical examination. High-cycle fatigue cracking in multiple IGV’s was found at a location different from the expected cracking location. The failure is caused by a combination of wear loss and galling of the IGV metal shafts against the polymer bushings, combined with deterioration of the polymer matrix. Finite element analysis is used to verify the loading mode, maximum stress location, and crack propagation direction.
Application of Pulse Detonation Combustion to Turbofan Engines
Authors: Mawid M. A. , Park T. W. , Sekar B. , Arana C.
Published: January 2003

The potential performance gain of utilizing pulse detonation combustion in the bypass duct of a turbofan engine for possible elimination of the traditional afterburner was investigated in this study. A pulse detonation turbofan engine concept without an afterburner was studied and its performance was assessed. The thrust, specific fuel consumption (SFC), and specific thrust of a conventional turbofan with an afterburner and the new pulse detonation turbofan engine concept were calculated and compared. The pulse detonation device performance in the bypass duct was obtained by using multidimensional CFD analysis. The results showed that significant performance gains can be obtained by using the pulse detonation turbofan engine concept as compared to the conventional afterburning turbofan engine. In particular, it was demonstrated that for a pulse detonation bypass duct operating at a frequency of 100 Hz and higher, the thrust and specific thrust of a pulse-detonation turbofan engine can nearly be twice as much as those of the conventional afterburning turbofan engine. SFC was also shown to be reduced. The effects of fuel-air mixture equivalence ratio and partial filling on performance were also predicted. However, the interaction between pulse detonation combustion in the bypass duct and the engine fan, for potential fan stall, and engine nozzle have not been investigated in this study.
Design Development of Unitized Titanium Structure
Authors: Groneck D. , Harmon D.
Published: January 2003

Traditional airframe primary structure is fabricated from wrought product forms that are transformed by machining, forming, and joining into structural components. These individual parts are assembled together by fasteners to create the airframe. Significant cost and cycle-time savings can be achieved by switching from multipiece builtup assembly to a single-piece net shape casting. The reduction in number of discrete parts provides a significant reduction in both direct and indirect costs. In particular, the inherent low material costs and excellent producibility characteristics of cast metallic parts may provide a significant contribution to the goal to reduce acquisition costs. Under the program reported herein, and in conjunction with a casting vendor, prototype titanium (Ti-6Al-4V) cast airframe components were designed and fabricated. The typical overall dimensions of each casting are 50inches×40inches×30inches, and weigh approximately 190 pounds per casting. The castings were modeled on generic aircraft fuselage structure, that incorporated smooth inner moldline surface and integral webs and keels, capped by a T-element, web stiffeners, access holes, and other detail features. Multiple castings are joined to create the airframe structure. A rapid prototyping method was utilized to create the pattern, which eliminated the requirement for expensive metal tooling. The prototype castings successfully demonstrated the producibility of this generic airframe structure.
Integrated Vehicle Comparison of Turbo-Ramjet Engine and Pulsed Detonation Engine
Authors: Kaemming T.
Published: January 2003

The pulsed detonation engine (PDE) is a unique propulsion system that uses the pressure rise associated with detonations to efficiently provide thrust. A study was conducted under the direction of the NASA Langley Research Center to identify the flight applications that provide the greatest potential benefits when incorporating a PDE propulsion system. The study was conducted in three phases. The first two phases progressively screened a large matrix of possible applications down to three applications for a more in-depth, advanced design analysis. The three applications best suited to the PDE were (1) a supersonic tactical aircraft, (2) a supersonic strike missile, and (3) a hypersonic single-stage-to-orbit (SSTO) vehicle. The supersonic tactical aircraft is the focus of this paper. The supersonic, tactical aircraft is envisioned as a Mach 3.5 high-altitude reconnaissance aircraft with possible strike capability. The high speed was selected based on the perceived high-speed fuel efficiency benefits of the PDE. Relative to a turbo-ramjet powered vehicle, the study identified an 11% to 21% takeoff gross weight (TOGW) benefit to the PDE on the baseline 700 n.mi. radius mission depending on the assumptions used for PDE performance and mission requirements. The TOGW benefits predicted were a result of the PDE lower cruise specific fuel consumption (SFC) and lower vehicle supersonic drag. The lower vehicle drag resulted from better aft vehicle shaping, which was a result of better distribution of the PDE cross-sectional area. The reduction in TOGW and fuel usage produced an estimated 4% reduction in life cycle cost for the PDE vehicle. The study also showed that the simplicity of the PDE enables concurrent engineering development of the vehicle and engine.
Integrating Subsystems and Engine System Assessments
Authors: Van Griethuysen V. J. , Glickstein M. R. , Hodge E. S.
Published: January 2003

In the past, system and subsystem level assessments for propulsion systems have been a long and drawn out serial process, typically taking several months to a year or more. Data exchange from one subsystem group to the next was a manual process. This was particularly the case when different computer platforms were being utilized to run the models. Each group would optimize their particular subsystem as a separate entity. There were no approaches available to facilitate the evaluation of how a particular subsystem, when combined with the engine, would impact the overall integrated system. The availability of tools to facilitate direct interface of the various subsystem models with engine performance decks was not available. As a result, the lead times for various iterations were such that not all of the groups were even working on the same configuration. Fortunately, software technology has been evolving, and the ability to integrate models is now becoming available. This paper describes work in progress of an innovative methodology for high-level integration of complex flight systems. This new approach will facilitate rapid integration and optimization of propulsion and secondary subsystems in a truly concurrent manner, providing capability for top-level evaluation of complex and highly integrated flight system architectures
Development of a Temporally Modulated Fuel Injector With Controlled Spray Dynamics
Authors: Chang H. , Nelson D. , Sipperley C. , Edwards C.
Published: January 2003

It is now well established that combustion instability in liquid-fueled gas turbines can be controlled through the use of active fuel modulation. What is less clear is the mechanism by which this is achieved. This results from the fact that in most fuel modulation strategies not only is the instantaneous mass flow rate of fuel affected but so too are the parameters which define the post-atomization spray that takes part in the combustion. Specifically, experience with piezoelectric modulated sprays has shown that drop size, velocity, cone angle, and patternation are all affected by the modulation process. This inability to decouple changes in the fueling rate from changes in the spray distribution makes understanding of the mechanism of instability control problematic. This paper presents the results of an effort to develop an injector which can provide temporal modulation of the fuel flow rate but without concomitant changes in spray dynamics. This is achieved using an atomization strategy which is insensitive to both fuel flow rate and combustor acoustics (an over-pressured spill-return nozzle) coupled with an actuator with flat frequency response (a low-mass voice coil). The design and development of the actuator (and its control system) are described, and a combination of phase-Doppler interferometry and imaging are used to establish its performance. Results show that the system is capable of producing sprays which have little variation in cone angle or spray distribution function despite variations in mass flow rate (number density) of greater than 50% over a range of frequencies of interest for control of combustion instability (10 Hz to 1 kHz).
Technical Risks and Mitigation Measures in Combustion Turbine Project Development
Authors: Grace D. , Scheibel J.
Published: January 2003

Project developers, insurers, financiers, and maintenance organizations have an interest in quantifying technical risks and evaluating risk mitigation alternatives for combustion turbine (CT) power plants. By identifying exposure to risk early in the project development process, optimal procurement decisions, and mitigation measures can be adopted for improved financial returns. This paper describes a methodology used to quantify all nonfuel O&M costs, including scheduled and unplanned maintenance, and business interruption costs due to unplanned outages. The paper offers examples that demonstrate the impact of technical risk on project profitability. An overview of activities required for addressing technical risk as part of the equipment selection and procurement process is provided, and areas of technical improvements for reducing life cycle costs are described.
Development of Low NOx Combustion Technology in Medium-Btu Fueled 1300°C-Class Gas Turbine Combustor in an Integrated Coal Gasification Combined Cycle
Authors: Hasegawa T. , Hisamatsu T. , Katsuki Y. , Sato M. , Koizumi H. , Hayashi A. , Kobayashi N.
Published: January 2003

The development of integrated coal gasification combined cycle (IGCC) systems ensures higher thermal efficiency and environmentally sound options for supplying future coal utilizing power generation needs. The Japanese government and electric power industries in Japan promoted research and development of an IGCC system using an air-blown entrained-flow coal gasifier. On the other hand, Europe and the United States are now developing the oxygen-blown IGCC demonstration plants. Gasified coal fuel produced in an oxygen-blown entrained-flow coal gasifier, has a calorific value of 8–13 MJ/m3 which is only 1/5–1/3 that of natural gas. However, the flame temperature of medium-Btu gasified coal fuel is higher than that of natural gas and so NOx production from nitrogen fixation is expected to increase significantly. In the oxygen-blown IGCC, a surplus nitrogen produced in the air-separation unit (ASU) is premixed with gasified coal fuel (medium-Btu fuel) and injected into the combustor, to reduce thermal-NOx production and to recover the power used for the ASU. In this case, the power to compress nitrogen increases. Low NOx emission technology which is capable of decreasing the power to compress nitrogen is a significant advance in gas turbine development with an oxygen-blown IGCC system. Analyses confirmed that the thermal efficiency of the plant improved by approximately 0.3% (absolute) by means of nitrogen direct injection into the combustor, compared with a case where nitrogen is premixed with gasified coal fuel before injection into the combustor. In this study, based on the fundamental test results using a small diffusion burner and a model combustor, we designed the combustor in which the nitrogen injection nozzles arranged on the burner were combined with the lean combustion technique for low-NOx emission. In this way, we could reduce the high-temperature region, where originated the thermal-NOx production, near the burner positively. And then, a combustor with a swirling nitrogen injection function used for a gas turbine, was designed and constructed, and its performance was evaluated under pressurized conditions of actual operations using a simulated gasified coal fuel. From the combustion test results, the thermal-NOx emission decreased under 11 ppm (corrected at 16% O2 ), combustion efficiency was higher than 99.9% at any gas turbine load. Moreover, there was different effects of pressure on thermal-NOx emission in medium-Btu fuel fired combustor from the case of a natural gas fired combustor.