bluuebunny/crossref_metadata_2025 huggingface dataset:
Creating an online library to support a virtual learning community
Authors: Sandelands Eric
Published: July 2002

Describes how an independent business school, International Management Centres (IMC), has created a virtual library in partnership with database publisher Anbar Electronic Intelligence. Outlines the action learning methodology used by IMC in delivering management development programmes, and the virtual business school model being developed and used. Examines the relationship between the partner organizations, highlighting the benefits each gains from the collaboration. Analyzes the benefits being experienced by IMC faculty and students from the virtual library investment to‐date, anticipated benefits, and future investment in online information resources.
Guanxi and the realities of career development: a Chinese perspective
Authors: Li Ji , Wright Philip C.
Published: July 2002

Understanding and utilizing guanxi presents a continuing challenge for western firms in China. This article reviews current research, highlighting two different types of guanxi: person‐to‐person and firm‐to‐firm. Based on interviews with 43 Chinese managers, it is suggested that firm‐to‐firm guanxi may be the more valuable to western companies, as most expatriate managers are sojourners, destined to stay only a relatively short time in China. The ramifications for career planning are discussed within the context of a model that illustrates how firm‐to‐firm guanxi can be created.
Novel α7‐like nicotinic acetylcholine receptor subunits in the nematode Caenorhabditis elegans
Authors: Mongan Nigel P. , Jones Andrew K. , Smith Graham R. , Sansom Mark S.P. , Sattelle David B.
Published: July 2002

We have used reverse‐transcription‐polymerase chain reaction (RT‐PCR) and DNA sequencing techniques to confirm the transcription of seven (six α and one non‐α) novel candidate nicotinic acetylcholine receptor (nAChR) subunit‐encoding genes identified in the genome sequence of the nematode Caenorhabditis elegans. Compared to vertebrate nAChR subunits, they most closely resemble the homomer‐forming, neuronal α7 subunit. Comparison of the predicted amino acid sequences of the new nAChR subunits with those described previously in C. elegans reveals five subunits (four α and one non‐α) which resemble the DEG‐3‐like group of subunits. To date, this highly divergent nAChR subunit group is unique to C. elegans. ACR‐22 is the first non‐α member of the DEG‐3‐like group of subunits to be identified. Two new members of the related ACR‐16‐like nAChR group of subunits have also been shown to be transcribed, making the ACR‐16‐like subunit group the largest in C. elegans. Residues in the α subunit second transmembrane region (M2) which contribute to the channel lining show variations with implications for channel function. For example, in ACR‐22, the highly conserved 0′ lysine of M2 is replaced by histidine. Restrained molecular dynamics simulations have been used to generate molecular models of homo‐pentameric M2 helix bundles for the novel subunits, enabling identification and display of pore‐lining and protein interface residues. The number and diversity of genes encoding C. elegans nAChR subunits with similarities to the homomer‐forming vertebrate α7 subunits and the identification of related non‐α subunits, only found in C. elegans to date, suggest that at least some of these subunits may contribute to heteromers in vivo.
Effects of charged amino acids at b and c heptad positions on specificity and stability of four‐chain coiled coils
Authors: Vu Colynda , Robblee James , Werner Karin M. , Fairman Robert
Published: July 2002

An understanding of the balance of chemical forces responsible for protein stability and specificity of structure is essential for the success of efforts in protein design. Specifically, electrostatic interactions between charged amino acids have been explored extensively to understand the contribution of this force to protein stability. Much research on the importance of electrostatic interactions as specificity and stability determinants in two‐stranded coiled coils has been done, but there remains significant controversy about the magnitude of the attractive forces using such systems. We have developed a four‐stranded coiled‐coil system with charged residues incorporated at b and c heptad positions to explore the role of charge interactions. Here, we test quantitatively the effects of varying sidechain length on the magnitude of such electrostatic interactions. We synthesized peptides containing either aspartate or ornithine at both b and c heptad positions and tested their ability to self‐associate and to hetero‐associate with one another and with peptides containing glutamate or lysine at the same positions. We find that interactions between glutamate and either lysine or ornithine are more favorable than the corresponding interactions involving aspartate. In each case, charged interactions provide additional stability to coiled coils, although helix propensity effects may play a significant role in determining the overall stability of these structures.
Analysis of inhibitor binding in influenza virus neuraminidase
Authors: Smith Brian J. , Colman Peter M. , Von Itzstein Mark , Danylec Basil , Varghese Joseph N.
Published: July 2002

2,3‐didehydro‐2‐deoxy‐N‐acetylneuraminic acid (DANA) is a transition state analog inhibitor of influenza virus neuraminidase (NA). Replacement of the hydroxyl at the C9 position in DANA and 4‐amino‐DANA with an amine group, with the intention of taking advantage of an increased electrostatic interaction with a conserved acidic group in the active site to improve inhibitor binding, significantly reduces the inhibitor activity of both compounds. The three‐dimensional X‐ray structure of the complexes of these ligands and NA was obtained to 1.4 Å resolution and showed that both ligands bind isosterically to DANA. Analysis of the geometry of the ammonium at the C4 position indicates that Glu119 may be neutral when these ligands bind. A computational analysis of the binding energies indicates that the substitution is successful in increasing the energy of interaction; however, the gains that are made are not sufficient to overcome the energy that is required to desolvate that part of the ligand that comes in contact with the protein.
Constrained modeling of spin–labeled major coat protein mutants from M13 bacteriophage in a phospholipid bilayer
Authors: Bashtovyy Denys , Marsh Derek , Hemminga Marcus A. , PÁLI Tibor
Published: July 2002

The family of three‐dimensional molecular structures of the major coat protein from the M13 bacteriophage, which was determined in detergent micelles by NMR methods, has been analyzed by constrained geometry optimization in a phospholipid environment. A single‐layer solvation shell of dioleoyl phosphatidylcholine lipids was built around the protein, after replacing single residues by cysteines with a covalently attached maleimide spin label. Both the residues substituted and the phospholipid were chosen for comparison with site‐directed spin labeling EPR measurements of distance and local mobility made previously on membranous assemblies of the M13 coat protein purified from viable mutants. The main criteria for identifying promising candidate structures, out of the 300 single‐residue mutant models generated for the membranous state, were 1) lack of steric conflicts with the phospholipid bilayer, 2) good match of the positions of spin‐labeled residues along the membrane normal with EPR measurements, and 3) a good match between the sequence profiles of local rotational freedom and a structural restriction parameter for the spin‐labeled residues obtained from the model. A single subclass of structure has been identified that best satisfies these criteria simultaneously. The model presented here is useful for the interpretation of future experimental data on membranous M13 coat protein systems. It is also a good starting point for full‐scale molecular dynamics simulations and for the design of further site‐specific spectroscopic experiments.
NO donors potentiate the β‐adrenergic stimulation of ICa,L and the muscarinic activation of IK,ACh in rat cardiac myocytes
Authors: Abi‐Gerges Najah , Szabo Gabor , Otero Angela S. , Fischmeister Rodolphe , Méry Pierre‐François
Published: July 2002

The effects of nitric oxide (NO) donors on the L‐type Ca2+ current (ICa,L) and the muscarinic activated K+ current (IK,ACh) were studied in isolated rat cardiac myocytes. The nitrosothiol S‐nitroso‐N‐acetyl‐d,d‐penicillamine (SNAP, 1 pm‐1 μm) strongly potentiated the stimulation of the ICa,L elicited by subthreshold concentrations of isoprenaline (Iso, 0.1–0.5 nm) in ventricular myocytes. The effect of SNAP was mimicked by 2‐(N,N‐diethylamino)‐diazenolate‐2‐oxide (DEANO, 1 pm‐1 nm), a NONOate that spontaneously releases NO in a pH‐controlled manner, and was blunted by 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide (100 μm), a NO trap. 1H‐[1,2,4]Oxadiazolo[4,3‐a]quinoxaline‐1‐one (10 μm), a guanylyl cyclase inhibitor, did not alter the effect of SNAP. SNAP (1 pm‐1 μm) did not modify the effect of L858051 (0.1–0.3 μm), a forskolin analogue that activates adenylyl cyclase, on ICa,L and did not enhance the basal ICa,L in the presence of rolipram (1 μm), a phosphodiesterase type 4 inhibitor. Superfusion with Rp‐CPT‐cAMPS (500 μm), or internal dialysis with cAMP‐dependent protein kinase (cA‐PK) inhibitory peptide (PKI; 20 μm), inhibitors of the cA‐PK, blunted the effect of SNAP (1 nm and 1 μm) on the Iso‐stimulated (1‐100 pm) ICa,L. SNAP (1 nm and 1 μm) potentiated the threshold stimulation of ICa,L elicited by internal GTP‐γS (10 μm), a non‐hydrolysable analogue of GTP. SNAP (1 pm‐1 μm) and DEANO (1 μm) potentiated the stimulation of IK,ACh elicited by low concentrations of ACh (1–2 nm) in rat atrial myocytes. The threshold stimulation of IK,ACh elicited by internal 5′‐guanylylimidodiphosphate (10 μm) was also potentiated by NO donors. SNAP (1 μm) did not modify IK,ACh reconstituted in human embryonic kidney 293 cells, in the absence or in the presence of ACh (1 or 10 nm). Taken together, these data suggest that NO is a cGMP‐independent modulator of G‐protein‐coupled muscarinic and β‐adrenergic receptor actions on cardiac ion channels. Although this action of NO seemed to occur at the level of G proteins, it appeared to require a component distinct from receptors, G proteins or their effectors.
FEM Analysis of Hydrostatic Pressure Generated Within Lubricant Entrapped Into Pocket on Workpiece Surface in Upsetting Process
Authors: Azushima Akira
Published: July 2002

In order to investigate into the quantitative relationship between the hydrostatic pressure generated within the surface pocket of the workpiece and the normal pressure acting on the real contact area at the interface of metal forming such as drawing, rolling, forging and so on, the hydrostatic pressure is calculated accompanied with reduction in height in upsetting of cylinders having a central conical impression or a central conical dent filled with lubricant on the top surface, using the rigid-plastic finite element method. The formulated is based on the plasticity theory. The material is assumed to be rigid perfectly plastic material. It is assumed that the hydrostatic pressure is generated accompanied with a volume change in the surface pocket for compressible lubricants. The results obtained from the calculation are as follows: (1) The hydrostatic pressure generated within the lubricant in a central conical impression in cylindrical upsetting approaches the yield stress at a reduction in height of about 4 percent; (2) The hydrostatic pressure generated within the lubricant in a central conical dent in cylindrical upsetting having an annular asperity increases linearly and abruptly with increasing height reduction when the contact area ratio is small and the bulk deformation is elastic, and it increases gradually and the maximum value approaches the normal pressure acting on the contact area when the contact area ratio becomes large and the bulk deformation is plastic. [S0742-4787(00)00503-8]
A Numerical Investigation of the Detachment of the Trailing Particle From a Chain Sedimenting in Newtonian and Viscoelastic Fluids
Authors: Patankar N. A. , Hu H. H.
Published: July 2002

Particles sedimenting in a viscoelastic fluid form chains. It has been observed in experiments that, sometimes, the last particle in the chain gets detached. In this paper, we investigate this phenomenon. It is known that a long chain falls faster than a single particle in fluids. This long body effect tends to detach the last particle from the chain. The wake effect and the normal stress effect are the mechanisms that work against the long body effect. The last particle is not detached if the inertial wake effects are strong enough to cause substantial drag reduction on it. The detachment is also restricted by the elastic normal stress of the viscoelastic fluid. [S0098-2202(00)01003-8]
Zener’s Crack and the M-Integral
Authors: Suo Z.
Published: July 2002

In a pair of bonded solids, the interface may block dislocation gliding. The pileup may cause a crack to nucleate either on the interface, or in one of the solids. The model, proposed by Zener half a century ago, has been analyzed in various forms. This note shows that the energy release rate of the crack can be calculated by an application of the M-integral. Both solids are anisotropic, and the interface is flat. The result leads to a discussion of the crack orientation. [S0021-8936(00)00701-7]
Antiplane Deformations for Anisotropic Multilayered Media by Using the Coordinate Transform Method
Authors: Lin Ru-Li , Ma Chien-Ching
Published: July 2002

Green’s functions for anisotropic elastic multilayered media subjected to antiplane shear deformation are presented in this study. The antiplane shear deformation due to a concentrated shear force and screw dislocation in an arbitrary layer was investigated in detail. A linear coordinate transformation is introduced in this study to simplify the problem. The linear coordinate transformation reduces the anisotropic multilayered problem to an equivalent isotropic problem without complicating the geometry of the problem. Explicit analytical solutions were derived using the Fourier transform and the series expansion technique. The complete solutions for the multilayered problem consist only of the simplest solutions obtained from an infinite homogeneous medium with concentrated loadings. Numerical results for the full-field stress distribution in multilayered media subjected to a point body force are presented. These numerical results were compared with the solutions obtained by considering the multilayered medium as one layer with effective elastic constants determined from the averaged material constants of the multilayered medium. It is found that the shear stress τyz of the homogeneous one layer solution is a very good approximation of the result for the multilayered medium; however, the shear stress τxz in these two solutions has a large discrepancy due to the fact that τxz is discontinuous at the interfaces of the multilayered medium. [S0021-8936(00)01703-7]
Wall Shear Stress and Differential Pressure in Large-Diameter Horizontal Multiphase Pipelines
Authors: Maley Lisa C. , Jepson W. Paul
Published: July 2002

When a slug is formed a mixing vortex is created which contains pulses of bubbles which are shot toward the bottom of the pipe where they may impact and collapse. Bubble collapse creates high localized pressure, temperature, and wall shear stress, which cause a reduction in corrosion inhibitor efficiency. The average wall shear stress can be calculated using a conventional equation. However, using a conventional equation will not give the fluctuations in wall shear stress, which can be significant for slug flow conditions. Wall shear stress instruments are generally not accurate for fluids other than water, therefore, it would be beneficial to develop a relationship between the fluctuations in wall shear stress and the fluctuations in differential pressure. A differential pressure transducer, which can be used with any fluid, can be used to measure the fluctuations in differential pressure and then translate those values to fluctuations in wall shear stress. This study shows that wall shear stress fluctuations are related to differential pressure fluctuations to the 1.16 power. [S0195-0738(00)00604-X]
Modeling and Simulation of Elastic Structures with Parameter Uncertainties and Relaxation of Joints
Authors: Qiao S. L. , Pilipchuk V. N. , Ibrahim R. A.
Published: July 2002

Joint preload uncertainties and associated geometrical nonlinearities have a direct impact on the design process and decision making of structural systems. Thus, it is important to develop analytical models of elastic structures with bolted joint stiffness uncertainties. The conventional boundary value problem of these systems usually involves time-dependent boundary conditions that will be converted into autonomous ones using a special coordinate transformation. The resulting boundary conditions will be combined with the governing nonhomogeneous, nonlinear partial differential equation that will include the influence of the boundary conditions uncertainty. Two models of the joint stiffness uncertainty are considered. The first represents the uncertainty by a random variable, while the second considers the relaxation process of the joint under dynamic loading. For a single mode random excitation the response statistics will be estimated using Monte Carlo simulation. The influence of joint uncertainty on the response center frequency, mean square, and power spectral density will be determined for the case of clamped-clamped beam. For the case of joints with time relaxation the response process is found to be nonstationary and its spectral density varies with time. Under random excitation, the response bandwidth is found to increase as the excitation level increases and becomes more stationary. Under sinusoidal excitation, it is shown that the relaxation process of the joints may result in bifurcation of the response amplitude, when even all excitation parameters are fixed.
Dynamic Plastic Response of a Submarine Oil Pipeline to an Underwater Explosion Bubble
Authors: Zong Z. , Lam K. Y.
Published: July 2002

Dynamic plastic response of a submarine oil pipeline to an underwater explosion bubble is studied in this paper. A detailed fluid-structure analysis is given to find the fluid forces acting on the pipeline. Assuming the pipeline is made from rigid, perfectly plastic material, we obtain the hydroplastic equation governing the dynamic plastic deflection of such a pipeline. The equation is analytically solved. Three examples are given to discuss the features of the dynamic plastic response and the applicability range of the present analysis. The relation between the half pipe length and maximum permanent plastic deflection is also given. [S0021-8936(00)01004-7]
Static and Dynamic Characterization of Some Tensegrity Modules
Authors: Murakami H. , Nishimura Y.
Published: July 2002

A set of procedures was presented for characterizing static and dynamic response of tensegrity modules. The procedures were applied to two tensegrity modules: a six-bar spherical module and a two-stage cylindrical module with three bars at each stage. The singular value decomposition of the initial equilibrium matrix revealed prestress and infinitesimal mechanism modes. The prestress stiffening effect of infinitesimal mechanism modes was found to be isotropic at each node. In the initial quasi-static loading, infinitesimal mechanisms exhibited soft response. As the deformation advanced, the stiffness of tensegirty modules increased almost quadratically with infinitesimal mechanism amplitudes. Modal analyses revealed that the lowest modes were those of infinitesimal mechanism modes and their natural frequencies were an order of magnitude smaller than those of higher deformation modes.
Phonon Heat Conduction in Thin Films: Impacts of Thermal Boundary Resistance and Internal Heat Generation
Authors: Zeng Taofang , Chen Gang
Published: July 2002

The measured thermal resistance across a thin film deposited on a substrate often includes the internal thermal resistance within the film and the thermal boundary resistance (TBR) across the film-substrate interface. These two resistances are frequently lumped and reported as an equivalent thermal conductivity of the film. Two fundamental questions should be answered regarding the use of this equivalent thermal conductivity. One is whether it leads to the correct temperature distribution inside the film. The other one is whether it is applicable for thin films with internal heat generation. This paper presents a study based on the Boltzmann transport equation (BTE) to treat phonon heat conduction inside the film and across the film-substrate interface simultaneously, for the cases with and without internal heat generation inside the film. Material systems studied include SiO2 and diamond films on Si substrates, representative of thin-film materials with low and high thermal conductivity. It is found that for a SiO2 film on a Si substrate, the film thermal conductivity and TBR can be treated independently, while for a diamond film on a Si substrate, the two are related to each other by the interface scattering. When the free surface behaves as a black phonon emitter, the TBR for thin diamond films with internal heat generation is the same as that without the internal heat generation. When the free surface is adiabatic, however, the TBR increases and approaches the value of the corresponding black surface as the film thickness increases. Results of this study suggest that great care must be taken when extending the effective thermal conductivity measured for thin films under one experimental condition to other application situations.
Nonlinear Transient Behavior of a Sliding System With Frictionally Excited Thermoelastic Instability
Authors: Zagrodzki P. , Lam K. B. , Al Bahkali E. , Barber J. R.
Published: July 2002

A transient finite element simulation is developed for the two-dimensional thermoelastic contact problem of a stationary layer between two sliding layers, with frictional heat generation. The Petrov-Galerkin algorithm is used to discretize the sliding layers because of the high Peclet numbers involved. The results in the linear, full contact regime were validated by comparison with the analytical predictions of Lee and Barber (1993). After separation occurs, there is a non-monotonic transition to a steady state with the contact regions separated by the same wavelength. During the transition, the migration speed exhibits values lower than those in either the linear regime or the final steady state. When several wavelengths are unstable, the final steady state is generally that corresponding to the longest unstable wavelength, even though other modes have more rapid growth rates in the linear regime.
Direct Numerical Simulation of Flow and Heat Transfer From a Sphere in a Uniform Cross-Flow
Authors: Bagchi P. , Ha M. Y. , Balachandar S.
Published: July 2002

Direct numerical solution for flow and heat transfer past a sphere in a uniform flow is obtained using an accurate and efficient Fourier-Chebyshev spectral collocation method for Reynolds numbers up to 500. We investigate the flow and temperature fields over a range of Reynolds numbers, showing steady and axisymmetric flow when the Reynolds number is less than 210, steady and nonaxisymmetric flow without vortex shedding when the Reynolds number is between 210 and 270, and unsteady three-dimensional flow with vortex shedding when the Reynolds number is above 270. Results from three-dimensional simulation are compared with the corresponding axisymmetric simulations for Re>210 in order to see the effect of unsteadiness and three-dimensionality on heat transfer past a sphere. The local Nusselt number distribution obtained from the 3D simulation shows big differences in the wake region compared with axisymmetric one, when there exists strong vortex shedding in the wake. But the differences in surface-average Nusselt number between axisymmetric and three-dimensional simulations are small owing to the smaller surface area associated with the base region. The shedding process is observed to be dominantly one-sided and as a result axisymmetry of the surface heat transfer is broken even after a time-average. The one-sided shedding also results in a time-averaged mean lift force on the sphere.
Experimental and Theoretical Study of Heating/Drying of Moist Paper Sheet With a Gas-Fired Infrared Emitter
Authors: Seyed-Yagoobi J. , Husain A. N.
Published: July 2002

Infrared (IR) radiation is used for heating/drying of moist paper in the paper making process owing to its penetration characteristic inside porous media and a high absorptivity of water in the IR wavelength range. However, there is a lack of fundamental understanding of the transport phenomena occurring within moist paper during IR heating/drying. A series of experiments has been conducted along with the development of a theoretical model to fundamentally understand IR heating/drying of moist paper. The experimental results confirm the IR radiation energy penetration into the paper sheet and the theoretical analysis indicates that the penetration depth decreases with increasing sheet moisture content.
Feature Based Fabrication in Layered Manufacturing
Authors: Qian Xiaoping , Dutta Debasish
Published: July 2002

To address the conflicting requirements between holding specified surface quality and decreasing build time in layered manufacturing, we present a feature-based fabrication methodology whereby the curvature effects are localized within each decomposed volume. However, staircase interaction between the boundaries of the decomposed neighboring volumes creates geometric incompatibility for deposition, which further results in undesired material properties. This paper proposes a novel concept, feature interaction volume, to eliminate the staircase interaction. Based on this concept, a feature based volume decomposition algorithm is developed. This algorithm enables each decomposed volume to be fabricated independently and compatibly. Implementation and example results are also presented.
In Situ Detailed Chemistry Calculations in Combustor Flow Analyses
Authors: James S. , Anand M. S. , Razdan M. K. , Pope S. B.
Published: July 2002

In the numerical simulation of turbulent reacting flows, the high computational cost of integrating the reaction equations precludes the inclusion of detailed chemistry schemes, therefore reduced reaction mechanisms have been the more popular route for describing combustion chemistry, albeit at the loss of generality. The in situ adaptive tabulation scheme (ISAT) has significantly alleviated this problem by facilitating the efficient integration of the reaction equations via a unique combination of direct integration and dynamic creation of a look-up table, thus allowing for the implementation of detailed chemistry schemes in turbulent reacting flow calculations. In the present paper, the probability density function (PDF) method for turbulent combustion modeling is combined with the ISAT in a combustor design system, and calculations of a piloted jet diffusion flame and a low-emissions premixed gas turbine combustor are performed. It is demonstrated that the results are in good agreement with experimental data and computations of practical turbulent reacting flows with detailed chemistry schemes are affordable.
A Semi-Analytical Model to Predict the Capillary Limit of Heated Inclined Triangular Capillary Grooves
Authors: Catton Ivan , Stroes Gustave R.
Published: July 2002

This paper presents a one-dimensional, semi-analytical model for prediction of the wetted length supported by inclined triangular capillary grooves subject to heating from below. The model utilizes a macroscopic approach employing the concept of an apparent contact angle. Constant liquid properties are assumed and no specific account is taken of surface roughness. The concept of accommodation theory is introduced to account for the change in the radius of curvature of the liquid-vapor interface between the liquid reservoir and the groove proper. Empirical input is required in the form of the axial heat flux profile and the axial profile of the liquid height in the groove. To assist other researchers in the implementation of the model, this paper concludes with a series of design curves. These curves can readily be used to estimate the wetted length (capillary limit) in inclined heated triangular capillary grooves for a variety of operating conditions.
A Method to Accelerate Convergence and to Preserve Radiative Energy
Balance in Solving the P1 Equation by Iterative
Methods
Authors: Li Genong , Modest Michael F.
Published: July 2002

An acceleration method is proposed particularly for the P1 equation. The radiative energy balance is used as a constraint to correct iterative solutions. The method not only accelerates convergence but also preserves the radiative energy balance, the latter being of great importance when radiation calculations are coupled with flow calculations. This acceleration method can be applied to other elliptical problems with boundary conditions of the second and/or the third kind.
Determination of Friction Condition by Geometrical Measurement of Backward Extruded Aluminum Alloy Specimen
Authors: Im Yong-Taek , Cheon Jae-Seung , Kang Seong-Hoon
Published: July 2002

The proper determination of friction condition during metal forming operations is imperative for successful process design and production of parts. Through the years, various methods of determining the friction condition have been proposed, but all methods have some drawbacks. In this study, a new type of friction test named tip test based on backward extrusion of AL6061-O is proposed. The experimental set-up of this method induces the formation of a sharp radial tip on the extruded end of the workpiece. It has been found that the simple geometrical measurement of this radial tip position can be used to effectively determine the friction condition.
Midspan Flow-Field Measurements for Two Transonic Linear Turbine Cascades at Off-Design Conditions
Authors: Jouini D. B. M. , Sjolander S. A. , Moustapha S. H.
Published: July 2002

The paper presents detailed midspan experimental results from two transonic linear turbine cascades. The blades for the two cascades were designed for the same service and differ mainly in their leading-edge geometries. One of the goals of the study was to investigate the influence of the leading-edge metal angle on the sensitivity of the blade to positive off-design incidence. Measurements were made for incidence values of −10.0, 0.0, +4.5, +10.0, and +14.5 deg relative to design incidence. The exit Mach numbers varied roughly from 0.5 to 1.2 and the Reynolds numbers from about 4×105 to 106. The measurements include the midspan losses, blade loadings and base pressures. In addition, the axial-velocity-density ratio (AVDR) was extracted for each operating point. The AVDR was found to vary from about 0.98 at −10.0 deg of incidence to about 1.27 at +14.5 deg. Thus, the data set also provides some evidence of the influence AVDR on axial turbine blade performance. Detailed experimental results for turbine blade performance at off-design incidence are very scarce in the open literature, particularly for transonic conditions. Among other things, the present results are intended to expand the database available in the open literature. To this end, the key aerodynamic results are presented in tabular form, along with the detailed geometry of the cascades. The results could be used in the development of new or improved correlations for use in the early stages of design. They could also be used to evaluate the ability of current CFD codes to capture reliably the variation in losses and other aerodynamic quantities with variations in blade incidence.
Three-Dimensional Computational Model of Left Heart Diastolic Function With Fluid–Structure Interaction
Authors: Lemmon Jack D. , Yoganathan Ajit P.
Published: July 2002

Aided by advancements in computer speed and modeling techniques, computational modeling of cardiac function has continued to develop over the past twenty years. The goal of the current study was to develop a computational model that provides blood–tissue interaction under physiologic flow conditions, and apply it to a thin-walled model of the left heart. To accomplish this goal, the Immersed Boundary Method was used to study the interaction of the tissue and blood in response to fluid forces and changes in tissue pathophysiology. The fluid mass and momentum conservation equations were solved using Patankar’s Semi-Implicit Method for Pressure Linked Equations (SIMPLE). A left heart model was developed to examine diastolic function, and consisted of the left ventricle, left atrium, and pulmonary flow. The input functions for the model included the pulmonary driving pressure and time-dependent relationship for changes in chamber tissue properties during the simulation. The results obtained from the left heart model were compared to clinically observed diastolic flow conditions for validation. The inflow velocities through the mitral valve corresponded with clinical values (E-wave=74.4 cm/s, A-wave=43 cm/s, and E/A=1.73). The pressure traces for the atrium and ventricle, and the appearance of the ventricular flow fields throughout filling, agreed with those observed in the heart. In addition, the atrial flow fields could be observed in this model and showed the conduit and pump functions that current theory suggests. The ability to examine atrial function in the present model is something not described previously in computational simulations of cardiac function. [S0148-0731(00)01302-9]
Deterministic Stress Modeling of Hot Gas Segregation in a Turbine
Authors: Busby J. , Sondak D. , Staubach B. , Davis R.
Published: July 2002

Simulation of unsteady viscous turbomachinery flowfields is presently impractical as a design tool due to the long run times required. Designers rely predominantly on steady-state simulations, but these simulations do not account for some of the important unsteady flow physics. Unsteady flow effects can be modeled as source terms in the steady flow equations. These source terms, referred to as Lumped Deterministic Stresses (LDS), can be used to drive steady flow solution procedures to reproduce the time-average of an unsteady flow solution. The goal of this work is to investigate the feasibility of using inviscid lumped deterministic stresses to model unsteady combustion hot streak migration effects on the turbine blade tip and outer air seal heat loads. The LDS model is obtained from an unsteady inviscid calculation. The inviscid LDS model is then used with a steady viscous computation to simulate the time-averaged viscous solution. The feasibility of the inviscid LDS model is demonstrated on a single-stage, three-dimensional, vane-blade turbine with a hot streak entering the vane passage at midpitch and midspan. The steady viscous solution with the LDS model is compared to the time-averaged viscous, steady viscous, and time-averaged inviscid computations. The LDS model reproduces the time-averaged viscous temperature distribution on the outer air seal to within 2.3 percent, while the steady viscous has an error of 8.4 percent, and the time-averaged inviscid calculation has an error of 17.2 percent. The solution using the LDS model is obtained at a cost in CPU time that is 26 percent of that required for a time-averaged viscous computation. [S0889-504X(00)00601-2]
High-Frequency Acoustic Emission Generated by Underwater Explosion with Cylindrical Symmetry
Authors: Likhterov L.
Published: July 2002

A high-frequency part of the acoustic spectrum excited by an underwater explosion with cylindrical symmetry is investigated theoretically. It is assumed that the liquid is inviscid, the surface tension is negligible, and the model for the explosive source is infinite in extent. A simple solution can be obtained when the adiabatic exponent is equal to 1.625. This, fortunately, gets into the interval of permissible heat ratio values. It is shown that, in the first approximation, the spectral density of the acoustic energy emitted by the underwater explosion with cylindrical symmetry varies as the minus 4/3 power of the frequency and decreases approximately by 4 decibels per octave. [S0739-3717(00)01202-2]
Fabrication and characterization of a micromachined 5 mm inductively coupled plasma generator
Authors: Hopwood J. , Minayeva O. , Yin Y.
Published: July 2002

The electron temperature and ion density produced by a microfabricated plasma generator are characterized in both argon gas and air. The plasma generator sustains a discharge by inductively coupling 450 MHz rf power into a small (10 mm diameter) vacuum chamber. The inductively coupled plasma source is surface micromachined on a glass wafer by electroplating a planar spiral inductor and two interdigitated capacitors. A plasma can be sustained using gas pressures between 0.1 and 10 Torr and rf powers between 0.3 and 3 W. The ion density increases from 1010 to 1011 cm−3 over this range of power. The electron temperature decreases from 4 to 2 eV as the pressure increases from 0.1 to 1 Torr.
Structure of the (0001) Surface of α-Alumina
Authors: Wei P. S. P. , Smith A. W.
Published: July 2002

The (0001) surface of α-Al2O3 has been studied by low-energy electron scattering. Interesting features in the LEED pattern, the energy loss spectrum and the LEED intensity profile, have been observed. The results are discussed in terms of the characteristics of the corundum structure.
Nanomechanical properties of molecular organic thin films
Authors: Caro J. , Fraxedas J. , Gorostiza P. , Sanz F.
Published: July 2002

Using atomic force microscopy we have studied the nanomechanical response to nanoindentations of surfaces of highly oriented molecular organic thin films (thickness⩽1000 nm). The Young’s modulus E can be estimated from the elastic deformation using Hertzian mechanics. For the quasi-one-dimensional metal tetrathiafulvalene tetracyanoquinodimethane E∼20 GPa and for the α phase of the p-nitrophenyl nitronyl nitroxide radical E∼2 GPa. Above a few GPa, the surfaces deform plastically as evidenced by discrete discontinuities in the indentation curves associated to molecular layers being expelled by the penetrating tip.
Wave optical calculations of electron probes
Authors: Rafferty B. , Groves T. R.
Published: July 2002

Electron probes used in electron-beam lithography systems are pushing towards the 1 nm scale. This exceeds the limit of accuracy of conventional knife-edge measuring techniques and conventional modeling methods. The only true way to accurately model such probes as their dimensions approach the 1 nm level is to use a wave optical method. Probe sizes are commonly estimated using the root-sum-of-squares method; i.e., by summing in quadrature the individual effects of the geometrical aberrations and diffraction. This method is relatively accurate when the probe size is greater than ∼10–15 nm, but fails with probes of smaller dimensions due to the inherent erroneous assumption that the effect of individual aberrations on the probe size can be treated independently. In this article we present a method for modeling an electron probe both on and off axis using a wave optical method. This method is commonly used to calculated probe sizes in the electron microscopy community but has not been applied to e-beam lithography systems until now. The wave optical method combines the effects of all geometrical aberrations, diffraction, electron source size, and defocus while fully adhering to the physics of the probe formation process. The challenge with applying this method to an e-beam lithography system is the relatively large field size (0.1–10 mm); in electron microscopy 50 nm is considered a large field size for high-resolution work!
Barrier height enhancement in the Au/n-GaAs Schottky diodes with anodization process
Authors: Bı̇ber M. , Temı̇rcı̇ C. , Türüt A.
Published: July 2002

We have fabricated Au/n-GaAs Schottky barrier diodes with different surface treatments. Prior to Au evaporation on the n-GaAs(100), the first kind of samples has consisted of dip in the 5H2SO4+H2O2+H2O solution and then H2O+HCl solution, followed by a rinse in de-ionized water (sample AuG1), the second kind of sample has consisted of several steps of anodization in aqueous 4C2H6O2+2H2O+0.1H3PO4 electrolyte with pH=2.02 each followed by a dip in diluted aqueous HCl solution and a subsequent rinse in de-ionized water (sample AuG2), and the third kind of samples one anodization step only (MIS sample AuG3). We have found the lowest values of both the barrier heights and ideality factors for the reference sample AuG1. The anodization, on the other hand, has increased the barrier heights as well as the ideality factors. Furthermore, the barrier heights of approximately 0.80, 0.90, and 1.01 eV for the AuG1, AuG2, and AuG3 diodes, respectively, have been obtained adding the contribution due to image force effect.
Growth and structure control of HfO2−x films with cubic and tetragonal structures obtained by ion beam assisted deposition
Authors: Manory Rafael R. , Mori Takanori , Shimizu Ippei , Miyake Shoji , Kimmel Giora
Published: July 2002

Hafnium oxide films were grown by ion beam assisted deposition on water-cooled Si (100) substrates, under conditions of oxygen starvation, using hafnium vapor and an oxygen ion beam. The transport ratio (TR), i.e., the ratio between the arrival rate of hafnium to that of oxygen, was varied between 0.5 and 10, and ion energy was varied between 1 and 20 keV. The films were analyzed using x-ray diffraction and x-ray photoelectron spectroscopy. Films having the CaF2 cubic structure with a lattice parameter of about 0.512 nm were repeatedly obtained. In addition, at 20 keV ion energy and TR values of 4 and above, films with a tetragonal structure were obtained. The latter structure, believed to be a distortion of the cubic structure, has a c/a ratio of 1.01 and its space group is considered to be different from the high temperature tetragonal HfO2 structure. The new tetragonal structure also presents high Knoop hardness, with values between 15 and 25 GPa. Substrate rotation speed was found to affect the structure and the orientation of the films. All films exhibit a stoichiometry in the vicinity of HfO1.6, with the tetragonal films apparently being Hf2O3. These structures are attributed to a very fast cooling rate during film formation. Films deposited without substrate water cooling, or with substrate heating up to 500 °C contain a large component of the monoclinic phase. The new cubic and tetragonal structures are stable at room temperature and upon annealing up to 450 °C in vacuum, but convert to the monoclinic structure upon annealing at 500 °C in air, indicating that their low oxygen content is a key factor for their stability.
Aluminum oxide films deposited in low pressure conditions by reactive pulsed dc magnetron sputtering
Authors: Seino T. , Sato T.
Published: July 2002

The reactive pulsed dc sputtering technique is widely used for the deposition of oxide films. The operating pressure for sputtering is commonly above 0.13 Pa. In this study, however, aluminum oxide (alumina) films were deposited at operating pressures from 0.06 to 0.4 Pa using a sputtering system equipped with a scanning magnetron cathode and a pulsed dc power supply. The pulsed dc power was found to be useful not only to reduce arcing, but also to sustain the discharge at low pressure. The electrical breakdown field, intrinsic stress, O/Al ratio, refractive index, and surface roughness were investigated. Both a low intrinsic stress and an O/Al ratio around the stoichiometry were required to get the film having a high breakdown field. A low operating pressure of 0.1 Pa was found to provide the necessary stress and O/Al ratio targets. A 50-nm-thick alumina film having a maximum breakdown field of 7.4 MV/cm was obtained.
Early stages of interface reactions between AlN and Ti thin films
Authors: Pinkas M. , Frage N. , Froumin N. , Pelleg J. , Dariel M. P.
Published: July 2002

The early stages of interface reactions between AlN and Ti thin films were investigated using x-ray diffractions, Auger electron spectroscopy, cross section transmission electron microscopy (XTEM), and high resolution XTEM. The AlN/Ti bilayers were deposited on a molybdenum substrate using reactive and nonreactive magnetron sputtering techniques. After deposition, the bilayers were heat treated for 1–10 h at 600 °C in a nitrogen atmosphere. Decomposition of the AlN layer took place at the AlN/Ti interface and its products, Al and N, reacted with Ti to produce a AlN/Al3Ti/Ti2N/Ti3Al/α-(Ti, Al)ss phase sequence. This phase sequence is not consistent with the Ti–Al–N phase diagram and is believed to be the outcome of the particular conditions that prevail in the thin film and correspond to a particular set of kinetic parameters. A model that explains the development of the phase sequence and predicts its evolution after prolonged heat treatments is put forward. The applicability of such a solid-state reaction technique for producing functionally graded coating for wear and corrosion resistance applications is discussed.
Growth of Face-Centered-Cubic Metals on Sodium Chloride Substrates
Authors: Matthews J. W.
Published: July 2002

Films of gold, silver, copper, nickel, palladium, and platinum were prepared by evaporation of the metals in ultrahigh vacuum onto hot, vacuum cleaved, sodium chloride substrates. Nickel, palladium, and platinum films that completely covered the surface were single crystals in the orientation of the substrate. Complete gold, silver, and copper films were polycrystals in which there was a tendency for the (111) metal plane to be parallel to the (001) salt surface. Later, it was found that single crystal foils of gold, silver, and copper were obtained if the salt substrate was exposed to air prior to the deposition of metal upon it. Careful comparison of the growth of gold on clean and on air-contaminated salt surfaces has shown that the effect of air is not to improve the alignment of the initial gold nuclei, but is to increase the number of nuclei generated per unit area. This increase causes nuclei to coalesce earlier in film growth. The stage in film growth at which coalescence occurs influences the orientation changes that accompany coalescence, and thereby influences the orientation of the complete film.
LEED analysis of the polar (0001)−Cd and (0001̄)−S surfaces of cadmium sulfide
Authors: Chang Shih−Chia , Mark Peter
Published: July 2002

A LEED analysis of the clean polar surfaces of CdS prepared by ion bombardment−thermal anneal technique reveals: (1) Only integral−order beams and six−fold symmetry from the (0001) −Cd face, and integral−order beams, as well as very diffuse √3×√3−30 deg reconstruction and mild facet formation, from the (0001̄) −S face; (2) Primary Bragg diffraction peaks can be extracted from LEED intensity−profile data via a structure factor analysis, which in turn can be used to obtain the inner potential (14.7 V), the lattice constant in the surface plane (4.10 Å), and the spacing between the CdS dipole layers normal to the surface plane (6.68 Å). The nominal bulk values for these dimensions are 4.14 and 6.71 Å, respectively. Exposure to oxygen (1 Torr−sec) has only a slight transient effect on the Cd face, even after subsequent annealing. Such exposure strongly reduces the LEED intensities of the S face, and subsequent annealing to 400°C produces macroscopic facets that can be detected by LEED and by transmission electron microscopy.
Geometrical and electronic structure of Si(001) and Si(111) surfaces: A status report
Authors: Eastman D. E.
Published: July 2002

A critical review of recent studies of the geometrical and electronic structure of the Si(001) and Si(111) surfaces is given. Emphasis is placed on low-energy electron diffraction (LEED) studies of the geometrical structure, photoelectron spectroscopy studies of the electronic structure, and theoretical studies of the electronic and geometric structure of the Si(111)–(2×1), Si(111)–(7×7), Si(111)–(1×1)X, and Si(001)–(2×1) surfaces.