bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the factors that stabilize a designed two‐stranded antiparallel β‐sheet
Authors: Espinosa Juan F. , Syud Faisal A. , Gellman Samuel H.
Published: July 2002

Autonomously folding β‐hairpins (two‐strand antiparallel β‐sheets) have become increasingly valuable tools for probing the forces that control peptide and protein conformational preferences. We examine the effects of variations in sequence and solvent on the stability of a previously designed 12‐residue peptide (1). This peptide adopts a β‐hairpin conformation containing a two‐residue loop (D‐Pro‐Gly) and a four‐residue interstrand sidechain cluster that is observed in the natural protein GB1. We show that the conformational propensity of the loop segment plays an important role in β‐hairpin stability by comparing 1 with DP→ N mutant 2. In addition, we show that the sidechain cluster contributes both to conformational stability and to folding cooperativity by comparing 1 with mutant 3, in which two of the four cluster residues have been changed to serine. Thermodynamic analysis suggests that the high loop‐forming propensity of the DPG segment decreases the entropic cost of β‐hairpin formation relative to the more flexible NG segment, but that the conformational rigidity of DPG may prevent optimal contacts between the sidechains of the GB1‐derived cluster. The enthalpic favorability of folding in these designed β‐hairpins suggests that they are excellent scaffolds for studying the fundamental mechanisms by which amino acid sidechains interact with one another in folded proteins.
Synaptic physiology of the flow of information in the cat's visual cortex in vivo
Authors: Hirsch Judith A. , Martinez Luis M. , Alonso José‐Manuel , Desai Komal , Pillai Cinthi , Pierre Carhine
Published: July 2002

Each stage of the striate cortical circuit extracts novel information about the visual environment. We asked if this analytic process reflected laminar variations in synaptic physiology by making whole‐cell recording with dye‐filled electrodes from the cat's visual cortex and thalamus; the stimuli were flashed spots. Thalamic afferents terminate in layer 4, which contains two types of cell, simple and complex, distinguished by the spatial structure of the receptive field. Previously, we had found that the postsynaptic and spike responses of simple cells reliably followed the time course of flash‐evoked thalamic activity. Here we report that complex cells in layer 4 (or cells intermediate between simple and complex) similarly reprised thalamic activity (response/trial, 99 ± 1.9 %; response duration 159 ± 57 ms; latency 25 ± 4 ms; average ± standard deviation; n= 7). Thus, all cells in layer 4 share a common synaptic physiology that allows secure integration of thalamic input. By contrast, at the second cortical stage (layer 2+3), where layer 4 directs its output, postsynaptic responses did not track simple patterns of antecedent activity. Typical responses to the static stimulus were intermittent and brief (response/trial, 31 ± 40 %; response duration 72 ± 60 ms, latency 39 ± 7 ms; n= 11). Only richer stimuli like those including motion evoked reliable responses. All told, the second level of cortical processing differs markedly from the first. At that later stage, ascending information seems strongly gated by connections between cortical neurons. Inputs must be combined in newly specified patterns to influence intracortical stages of processing.
Simultaneous imaging of Ca2+ signals in interstitial cells of Cajal and longitudinal smooth muscle cells during rhythmic activity in mouse ileum
Authors: Yamazawa Toshiko , Iino Masamitsu
Published: July 2002

Electrical rhythmicity in smooth muscle cells is essential for the movement of the gastrointestinal tract. Interstitial cells of Cajal (ICC) lie adjacent to smooth muscle layers and are implicated as the pacemaker cells. However, the pace making mechanism remains unclear. To study the intercellular interaction during electrical rhythm generation, we visualized changes in intracellular Ca2+ concentration ([Ca2+]i) in smooth muscle cells and myenteric ICC within segments of mouse ileum loaded with a fluorescent Ca2+ indicator, fluo‐3. We observed rhythmic [Ca2+]i changes in longitudinal smooth muscle cells travelling rapidly through the smooth muscle cell layer. Between the rhythmic Ca2+ transients, we found brief Ca2+ transients localized to small areas within smooth muscle cells. The amplitude but not the periodicity of rhythmic [Ca2+]i transients in both cell types was partially inhibited by nicardipine, an L‐type Ca2+ channel antagonist, suggesting that the rhythmic [Ca2+]i transients reflect membrane potential depolarizations corresponding to both slow waves and triggered Ca2+ spikes. Longitudinal smooth muscle cells and myenteric ICC showed synchronous spontaneous [Ca2+]i transients in eight out of 21 ileac preparations analysed. In the remaining preparations, the synchrony between ICC and smooth muscle cells was absent, although the rhythmicity of the smooth muscle cells was not disturbed. These results suggest that myenteric ICC may play multiple roles including pace making for physiological bowel movement.
β‐Alanine and taurine as endogenous agonists at glycine receptors in rat hippocampus in vitro
Authors: Mori Masahiro , Gähwiler Beat H. , Gerber Urs
Published: July 2002

Electrophysiological and pharmacological properties of glycine receptors were characterized in hippocampal organotypic slice cultures. In the presence of ionotropic glutamate and GABAB receptor antagonists, pressure‐application of glycine onto CA3 pyramidal cells induced a current associated with increased chloride conductance, which was inhibited by strychnine. Similar chloride currents could also be induced with β‐alanine or taurine. Whole‐cell glycine responses were significantly greater in CA3 pyramidal cells than in CA1 pyramidal cells and dentate granule cells, while responses to GABA were similar among these three cell types. Although these results demonstrate the presence of functional glycine receptors in the hippocampus, no evidence for their activation during synaptic stimulation was found. Gabazine, a selective GABAA receptor antagonist, totally blocked evoked IPSCs in CA3 pyramidal cells. Glycine receptor activation is not dependent on transporter‐controlled levels of extracellular glycine, as no chloride current was observed in response to sarcosine, an inhibitor of glycine transporters. In contrast, application of guanidinoethanesulfonic acid, an uptake inhibitor of β‐alanine and taurine, induced strychnine‐sensitive chloride current in the presence of gabazine. These data indicate that modulation of transporters for the endogenous amino acids, β‐alanine and taurine, can regulate tonic activation of glycine receptors, which may function in maintenance of inhibitory tone in the hippocampus.
Characterization of the cross‐bridge force‐generating step using inorganic phosphate and BDM in myofibrils from rabbit skeletal muscles
Authors: Tesi C. , Colomo F. , Piroddi N. , Poggesi C.
Published: July 2002

The inhibitory effects of inorganic phosphate (Pi) on isometric force in striated muscle suggest that in the ATPase reaction Pi release is coupled to force generation. Whether Pi release and the power stroke are synchronous events or force is generated by an isomerization of the quaternary complex of actomyosin and ATPase products (AM.ADP.Pi) prior to the following release of Pi is still controversial. Examination of the dependence of isometric force on [Pi] in rabbit fast (psoas; 5‐15 °C) and slow (soleus; 15‐20 °C) myofibrils was used to test the two‐step hypothesis of force generation and Pi release. Hyperbolic fits of force‐[Pi] relations obtained in fast and slow myofibrils at 15 °C produced an apparent asymptote as [Pi]∞ of 0.07 and 0.44 maximal isometric force (i.e. force in the absence of Pi) in psoas and soleus myofibrils, respectively, with an apparent Kd of 4.3 mm in both. In each muscle type, the force‐[Pi] relation was independent of temperature. However, 2,3‐butanedione 2‐monoxime (BDM) decreased the apparent asymptote of force in both muscle types, as expected from its inhibition of the force‐generating isomerization. These data lend strong support to models of cross‐bridge action in which force is produced by an isomerization of the AM.ADP.Pi complex immediately preceding the Pi release step.
Site Effects on Seismic Behavior of Pipelines: A Review
Authors: Liang Jianwen , Sun Shaoping
Published: July 2002

Post-earthquake investigations showed that local site condition had significant effect on seismic behavior of pipelines: almost all seismic damages to buried pipelines were either due to permanent ground deformation such as fault movement, landslide and lateral spread, or found in nonuniform ground, and there were few cases that pipelines were damaged only by wave propagation. Earthquake field observations did clearly indicate that relatively high strain occurred in pipelines laid through nonuniform ground. In this paper, an updated and detailed review of site effects on seismic behavior of pipelines is presented. For the purpose, quantitative analysis of damage, earthquake field observation, theoretical and experimental study, and related seismic design are discussed, and research needs are pointed out. [S0094-9930(00)01702-9]
Random Excitation Forces in Heat Exchanger Tube Bundles
Authors: Taylor C. E. , Pettigrew M. J.
Published: July 2002

Random excitation forces can cause low-amplitude tube motion that will result in long-term fretting-wear or fatigue. To prevent these tube failures in heat exchangers, designers and troubleshooters must have guidelines that incorporate random or turbulent fluid forces. Experiments designed to measure fluid forces were conducted at the Chalk River Laboratories and at other laboratories worldwide. The data from these experiments were studied and collated, to determine suitable guidelines for random excitation forces. In this paper, a guideline for random excitation forces in single-phase cross flow is presented in the form of normalized spectra that are applicable to a wide range of flow conditions and tube frequencies. In particular, the experimental results used in this study were conducted over the full range of flow conditions found in the liquid region of a nuclear steam generator. The proposed guidelines are applicable to steam generators, condensers, reheaters and other shell-and-tube heat exchangers. They may be used for flow-induced vibration analysis of new or existing components, as input to vibration analysis computer codes and as specifications in procurement documents. [S0094-9930(00)00603-X]
Bicycle Drive System Dynamics: Theory and Experimental Validation
Authors: Fregly Benjamin J. , Zajac Felix E. , Dairaghi Christine A.
Published: July 2002

Bicycle pedaling has been studied from both a motor control and an equipment setup and design perspective. In both cases, although the dynamics of the bicycle drive system may have an influence on the results, a thorough understanding of the dynamics has not been developed. This study pursued three objectives related to developing such an understanding. The first was to identify the limitations of the inertial/frictional drive system model commonly used in the literature. The second was to investigate the advantages of an inertial/frictional/compliant model. The final objective was to use these models to develop a methodology for configuring a laboratory ergometer to emulate the drive system dynamics of road riding. Experimental data collected from the resulting road-riding emulator and from a standard ergometer confirmed that the inertial/frictional model is adequate for most studies of road-riding mechanics or pedaling coordination. However, the compliant model was needed to reproduce the phase shift in crank angle variations observed experimentally when emulating the high inertia of road riding. This finding may be significant for equipment setup and design studies where crank kinematic variations are important or for motor control studies where fine control issues are of interest. [S0148-0731(00)02004-5]
Key Durability Issues With Mullite-Based Environmental Barrier Coatings for Si-Based Ceramics
Authors: Lee Kang N.
Published: July 2002

Plasma-sprayed mullite 3Al2O3s˙2SiO2 and mullite/yttria-stabilized-zirconia (YSZ) dual layer coatings have been developed to protect silicon-based ceramics from environmental attack. Mullite-based coating systems show excellent durability in air. However, in combustion environments, corrosive species such as molten salt or water vapor penetrate through cracks in the coating and attack the Si-based ceramics along the interface. Thus the modification of the coating system for enhanced crack-resistance is necessary for long-term durability in combustion environments. Other key durability issues include interfacial contamination and coating/substrate bonding. Interfacial contamination leads to enhanced oxidation and interfacial pore formation, while a weak coating/substrate bonding leads to rapid attack of the interface by corrosive species, both of which can cause a premature failure of the coating. Interfacial contamination can be minimized by limiting impurities in coating and substrate materials. The interface may be modified to improve the coating/substrate bond. [S0742-4795(00)03203-8]
A Study of Combustion Characteristics of Gasified Coal Fuel
Authors: Hasegawa T. , Sato M. , Nakata T.
Published: July 2002

The development of integrated, coal-gasification combined cycle (IGCC) systems provides cost-effective and environmentally sound options for meeting future coal-utilizing power generation needs in the world. The Japanese government and the Electric Power Industries in Japan promoted research and development of an IGCC system. We have being working on developing a low-NOx combustion technology used in gas turbine combustors for IGCC. Each gaseous fuel produced from some raw materials contained CO and H2 as the main combustible components, and a small amount of CH4. Compositions and calorific values of gasified coal fuels varied widely depending on raw materials and gasifier types. Gaseous fuel, produced in various gasifiers, has a calorific value of 4–13 MJ/m3, which is about one-tenth to one-third that of natural gas. The flame temperatures of fuels increase as the fuel calorific value rises. When the fuel calorific value rises 8 MJ/m3 or higher, the flame temperature is higher than that of natural gas, and so NOx production from nitrogen fixation is expected to increase significantly. Also, some gasified coal fuels contain fuel nitrogen, such as ammonia, if the hot/dry type gas cleaning system is employed. These factors affect the combustion characteristics of the gasified coal fuel. In this paper, we clarified the influence of gasified coal fuel properties on NOx and CO emissions through experiments using a small diffusion burner and through numerical analysis based on reaction kinetics. The main results were as follows: 1 NH3 conversion to NOx increases with increasing CH4 concentration in gaseous fuel. 2 If gaseous fuel contains CH4, there will be some specific equivalence ratio in the primary combustion zone for the minimum NH3 conversion to NOx in the two-staged combustion. 3 Its specific equivalence ratio in the primary combustion zone increases with decreasing CH4 concentration in gaseous fuel. 4 If the fuel contains a small percent of CH4, there is no influence of the CO/H2 molar ratio in the fuel on the conversion rate of NH3 to NOx, while there is an influence in the case where fuel contains no CH4. The conversion rate increases with rises in the CO/H2 molar ratio. 5 As the pressure increases, the conversion rate of NH3 to NOx slightly decreases and the CO emission declines significantly.
The Surface Temperature of a Half-Plane Subjected to Rolling/Sliding Contact With Convection
Authors: Fischer F. D. , Werner E. , Knothe K.
Published: July 2002

Based on earlier works by the authors an analytical expression for the surface temperature of a halfplane heated by fast moving rolling/sliding contact and cooled by convection on the surface of the halfplane is presented by applying the Laplace transformation technique and the solution of a Volterra integral equation of the second kind. [S0742-4787(00)00604-4]
Comparisons of Diesel Spray Liquid Penetration and Vapor Fuel Distributions With In-Cylinder Optical Measurements
Authors: Ricart Laura M. , Reltz Rolf D. , Dec John E.
Published: July 2002

The performance of two spray models for predicting liquid and vapor fuel distribution, combustion and emissions is investigated. The model predictions are compared with extensive data from in-cylinder laser diagnostics carried out in an optically accessible heavy-duty, D. I. diesel engine over a wide range of operating conditions. Top-dead-center temperature and density were varied between 800 K and 1100 K and 11.1 and 33.2 kg/m3, respectively. Two spray breakup mechanisms were considered: due to Kelvin-Helmholtz (KH) instabilities and to Rayleigh-Taylor (RT) instabilities. Comparisons of a wide range of parameters, which include in-cylinder pressure, apparent heat release rate, liquid fuel penetration, vapor distribution and soot distribution, have shown that a combination of the KH and the RT mechanisms gives realistic predictions. In particular, the limited liquid fuel penetration observed experimentally was captured by including these two competing mechanisms in the spray model. Furthermore, the penetration of the vapor fuel ahead of the liquid spray was also captured. A region of high soot concentration at the spray tip was observed experimentally and also predicted by the KH-RT spray breakup model. [S0742-4795(00)01504-0]
Boundary Layer Transition Induced by Periodic Wakes
Authors: Wu Xiaohua , Durbin Paul A.
Published: July 2002

Turbulent wakes swept across a flat plate boundary layer simulate the phenomenon of wake-induced bypass transition. Benchmark data from a direct numerical simulation of this process are presented and compared to Reynolds-averaged predictions. The data are phase-averaged skin friction and mean velocities. The predictions and data are found to agree in many important respects. One discrepancy is a failure to reproduce the skin friction overshoot following transition. [S0889-504X(00)00503-1]
Yield Functions and Flow Rules for Porous Pressure-Dependent Strain-Hardening Polymeric Materials
Authors: Lee J. H. , Oung J.
Published: July 2002

To characterize the response of progressively damaged glassy polymers due to the presence and evolution of voids, yield functions and flow rules were developed systematically for a pressure-dependent matrix following the modified von Mises criterion. A rigid-perfectly plastic material was first assumed. The upper bound method was used with a velocity field which has volume preserving and shape changing portions. Macroscopic yield criterion in analytical closed form was first obtained for spherical voids which is valid for all possible macroscopic strain rate fields. Macroscopic yield criteria in analytical closed form were then obtained for cylindrical voids for the special cases of axisymmetric and plane-strain modes of deformation. The upper-bound solutions were subsequently improved to better match analytical solutions for pure hydrostatic loading. Characteristics of the yield function as a function of pressure dependency and void fraction were studied in detail. Generalization of the model for spherical voids to include elasticity as well as strain hardening of the matrix was then obtained. An example for the uniaxial response of a progressively damaged material was then used to illustrate one possible application of the full set of constitutive equations. [S0021-8936(00)02902-0]
Dynamic Friction Measurements at Sliding Velocities Representative of High-Speed Machining Processes
Authors: Espinosa H. D. , Patanella A. J. , Fischer M.
Published: July 2002

Understanding high speed machining processes requires knowledge of the dynamic friction response at the tool-workpiece interface, the high strain rate response of the workpiece material and its fracture mechanisms. In this paper, a novel experimental technique, consisting in the independent application of an axial static load and a dynamic torque, is used to investigate time resolved dynamic friction. Shear stress wave propagation along an input bar, pressing statically against an output bar, is analyzed. The quasi-static and kinetic friction coefficients of Ti-6Al-4V sliding against 1080 Steel, Al 6061-T6 sliding against 1080 Steel, and Al 6061-T6 sliding against Al 7075-T6, with various surface characteristics, are investigated. Sliding velocities up to 6.9 m/s are achieved. Surface roughness is varied to understand its role on the frictional response of the sliding interfaces. The dependence of friction coefficient on material strain-rate sensitivity is also assessed. Measured friction coefficients compared well with values reported in the literature using other experimental techniques. The experimental methodology discussed in this article provides a robust method for direct measurement of the quasi-static and dynamic friction coefficients representative of high-speed machining, metal-forming and ballistic penetration processes. [S0742-4787(00)01304-7]
Rise Height for Negatively Buoyant Fountains and Depth of Penetration for Negatively Buoyant Jets Impinging an Interface
Authors: Friedman P. D. , Katz J.
Published: July 2002

A vertical jet or fountain, whose velocity is opposite to the direction of its buoyant force, reverses direction after reaching a maximum penetration depth. This penetration depth is measured from the jet exit or, if present, the location of the undisturbed interface. This paper shows that the penetration depth is only a function of a Richardson number divided by a jet spreading factor. If no interface is present, the spreading factor is one; otherwise the spreading factor is only a function of distance between the jet exit and the interface. As long as the jet is fully turbulent, the penetration depth is independent of Reynolds and Weber numbers. These trends are applicable to a broad range of fluid systems including air jets impacting liquids as well as miscible and immiscible liquid-liquid systems with only slight density differences. [S0098-2202(00)00304-7]
A Linear Stability Analysis of Cavitation in a Finite Blade Count Impeller
Authors: Horiguchi Hironori , Watanabe Satoshi , Tsujimoto Yoshinobu
Published: July 2002

The linear stability analysis of cavitation in flat plate cascades corresponding to 2, 3, 4, and 5-bladed impeller was carried out to clarify the effect of the blade count on cavitation instabilities. Each blade is treated independently so that all possible modes in those impellers can be found. In steady flow analysis the alternate blade cavitation was found only for impellers with even number of blades. For 2 or 4-bladed impeller, it was confirmed that there exists no additional destabilizing mode to those found in the previous analysis in which the inter-blade phase difference of disturbance was assumed. It was shown that the modes with total cavity volume fluctuation depend on the inlet duct length while the modes without total cavity volume fluctuation are independent on the system. [S0098-2202(00)01304-3]
Effect of Entrance Shape on Erosion in the Throat of Chokes
Authors: McLaury Brenton S. , Shirazi Siamack A. , Burden Tim L.
Published: July 2002

Erosion is a complex phenomenon that depends on many factors such as fluid properties, solid particle properties, flow stream velocity, flow geometry, and type of metal. Flow modeling and particle tracking are important tools for predicting erosion. In erosion modeling, it is important to account not only for the factors that influence erosion, but also for changes in some of these factors that occur as the erosion process continues. For example, the change in the geometry resulting can have a significant impact on the erosion results. Geometry changes result when corners, found in couplings and chokes, are eroded with time. This change in geometry due to erosion can drastically change the flow field, especially the turbulent kinetic energy and dissipation rate. Recognizing this change is imperative, since the prediction of particle behavior is heavily dependent on the turbulent kinetic energy. Furthermore, more particle impingements occur in regions with higher turbulent kinetic energy. This paper shows that neglecting the change in the flow field solution resulting from the change in geometry can cause erroneous erosion predictions. A computational study was performed on a choke geometry to demonstrate the importance of incorporating the change in geometry resulting from erosion. Predicted turbulent kinetic energy contours are presented as a function of the changing choke geometry. The predicted erosion rates along the choke are also examined for the various scenarios, and these results are compared to experimental results. Additionally, experimental results obtained from laser doppler velocimeter (LDV) measurements also demonstrate the change in fluctuating velocity (turbulent kinetic energy) as a result of rounding of the entrance of the choke. Results from this study show that it is necessary to update the flow geometry and flow model based on the changing geometry due to erosion. [S0195-0738(00)01004-9]
A Design Method of an Automotive Wheel-Bearing Unit With Discrete Design Variables Using Genetic Algorithms
Authors: Choi Dong-Hoon , Yoon Ki-Chan
Published: July 2002

In order to improve the efficiency of the design process and the quality of the resulting design, this study proposes a design method for determining design variables of an automotive wheel-bearing unit of double-row angular-contact ball bearing type by using a genetic algorithm. The desired performance of the wheel-bearing unit is to maximize system life while satisfying geometrical and operational constraints without enlarging mounting space. The design variables selected are number of balls, initial contact angle, standard ball diameter, pitch circle diameter, preload, distance between ball centers, and wheel offset, which must be selected at the preliminary design stage. The use of gradient-based optimization methods for the design of the unit is restricted because this design problem is characterized by the presence of discrete design variables such as the number of balls and standard ball diameter. Therefore, the design problem of rolling element bearings is a constrained discrete optimization problem. A genetic algorithm using real coding and dynamic mutation rate is used to efficiently find the optimum discrete design values. To effectively deal with the design constraints, a ranking method is suggested for constructing a fitness function in the genetic algorithm. A computer program is developed and applied to the design of a real wheel-bearing unit model to evaluate the proposed design method. Optimum design results demonstrate the effectiveness of the design method suggested in this study by showing that the system life of an optimally designed wheel-bearing unit is enhanced in comparison with that of the current design without any constraint violations. It is believed that the proposed methodology can be applied to other rolling element bearing design applications.
An Efficient Finite Element Procedure for Analysis of High-Speed Spiral Groove Gas Face Seals
Authors: Faria Marco Tulio C.
Published: July 2002

An efficient and accurate finite element procedure is specially devised to analyze the performance of gas-lubricated spiral groove face seals operating at high speeds. The procedure is based on the Galerkin weighted residual method with a new class of high-order shape functions, which are derived from an approximate solution to the nonlinear Reynolds equation within an element. Static and dynamic performance characteristics, such as seal opening force, flow leakage and frequency-dependent dynamic force coefficients, are determined to study the effects of high speeds on the behavior of spiral groove gas face seals.
Experimental Nonlinear Dynamics of a Shape Memory Alloy Wire Bundle Actuator
Authors: Mosley Michael J. , Mavroidis Constantinos
Published: July 2002

In this paper, the nonlinear dynamics of a new Shape Memory Alloy (SMA) actuator that possesses impressive payload lifting capabilities are presented. This actuator consists of 48 SMA wires mechanically bundled in parallel forming one powerful muscle. It was designed to lift up to 45.4 kg (100 lbs), which is approximately 300 times its weight. This SMA actuator was tested in open-loop experiments with different loads and different inputs, such as step, ramp, sinusoid, and half sinusoid, and its dynamic characteristics were evaluated. An important observation made during the dynamic analysis was the unpredictability of the actuator’s response when low to moderate voltages were applied. This characteristic suggests possible chaotic behavior of the actuator, which could affect the system design and cause control difficulties in fine and high accuracy tasks. An investigation into chaos was conducted using time histories, phase plots, Poincare´ maps, and power spectrum density plots. As shown in the diagrams presented in this paper, system response to sinusoidal inputs with a larger mean voltage is periodic, whereas lower mean voltages produce unpredictable responses that indicate chaotic behavior.
Three-Dimensional Axisymmetric Stress Analysis of Superconducting Magnets Using Green’s Function Solution
Authors: Vaghar M. R. , Garmestani H.
Published: July 2002

A closed-form Green’s function solution for the axisymmetric stresses in an elastic coil of superconducting magnets is presented, which provides the components of stress throughout the coil and includes the shear stress in addition to the normal stresses. The Green’s function method permits the development of a solution irrespective of the type of magnetic body forces within the coil. Green’s functions are derived by using finite Hankel transforms appropriate for a cylindrical coil.
Pyrolysis and Ignition Characteristics of Pulverized Coal Particles
Authors: Taniguchi Masayuki , Okazaki Hirofumi , Kobayashi Hironobu , Azuhata Shigeru , Miyadera Hiroshi , Muto Hidetaka , Tsumura Toshikazu
Published: July 2002

Pyrolysis and ignition characteristics of pulverized coals were examined under similar burning conditions to those of industrial burners. In the early stage, fine particles (less than 37 μm) were mainly pyrolyzed by convective heat transfer from surrounding gas. The coals ignited when pyrolyzed volatile matter mixed with surrounding air and formed a combustible mixture. Pyrolysis of large particles was delayed, but accelerated after ignition by radiant heat transfer from coal flames. The effects of radiant heat transfer were strong for intermediate-size particles (37–74 μm). Ignition temperature was examined analytically by using a modified distributed activation energy model for pyrolysis. The calculated results agreed with experimental ones obtained from both laboratory-scale and semi-industrial-scale burners.
Capacity Control for Refrigeration and Air-Conditioning Systems: A Comparative Study
Authors: Yaqub Mohammad , Zubair Syed M.
Published: July 2002

The capacity control of a vapor-compression refrigeration system is investigated for three different capacity control schemes. In a hot-gas by-pass control scheme, the refrigerant is by-passed from the compressor and injected back into the suction line to decrease the cooling capacity, whereas in cylinder-unloading scheme, one or more cylinders are unloaded to decrease the refrigerant mass flow rate in the system, which decreases the cooling capacity. However, in suction gas throttling, the suction gas throttled at the inlet of the compressor, decreases the refrigerant mass flow rate, and hence a corresponding decrease in the system capacity. These schemes are investigated for HFC-134a by considering finite size of the components that are used in the refrigeration systems. The models consider the finite-temperature difference in the heat exchangers, thus allowing the variations in the condenser and evaporator temperatures with respect to capacity and external fluid inlet temperatures. A comparative study is performed among these schemes in terms of the system coefficient of performance (COP), the operating temperatures, and percentage of refrigerant mass fraction as a function of the percentage of full-load system capacity.
Closed-Form Representation of Beam Response to Moving Line Loads
Authors: Sun Lu
Published: July 2002

Fourier transform is used to solve the problem of steady-state response of a beam on an elastic Winkler foundation subject to a moving constant line load. Theorem of residue is employed to evaluate the convolution in terms of Green’s function. A closed-form solution is presented with respect to distinct Mach numbers. It is found that the response of the beam goes to unbounded as the load travels with the critical velocity. The maximal displacement response appears exactly under the moving load and travels at the same speed with the moving load in the case of Mach numbers being less than unity.
The Properties of Asperities of Real Surfaces
Authors: Wu Jiunn-Jong
Published: July 2002

The properties of asperities are investigated. It is found that the asperity size distribution of asperities can be estimated by the auto-correlation function. New definitions for asperity and asperity curvature are employed. It is found that asperity curvature can be estimated by root mean square curvature of profile. With the finding of this paper, the statistical contact model can be used more accurately.
Hysteresis Behavior and Modeling of Piezoceramic Actuators
Authors: Zhou X. , Chattopadhyay A.
Published: July 2002

A new theory is developed to model the hysteresis relation between polarization and electric field of piezoceramics. An explicit formulation governing the hysteresis is obtained by using saturation polarization, remnant polarization, and coercive electric field. A new form of elastic Gibbs energy is proposed to address the coupling relations between electrical field and mechanical field. The nonlinear constitutive relations are derived from the elastic Gibbs energy and are applicable in the case of high stroke actuation. The hysteresis relations obtained using the current model are correlated with experimental results. The static deflection of a cantilever beam with surface-bonded piezoelectric actuators is analyzed by implementing the current constitutive relations. Numerical results reveal that hysteresis is an important issue in the application of piezoceramics.
Stress Concentration Reduction at a Reinforced Hole Loaded by a Bonded Circular Inclusion
Authors: Chau K. T. , Wei X. X.
Published: July 2002

This paper considers analytically the stress concentration in an infinite plane loaded by a circular inclusion, which is bonded to a reinforced hole in the plane. The pulling force of the inclusion is modeled by distributed body force. The infinite plane, the reinforced ring, and the circular inclusion can be of different elastic properties. Airy stress function with body force potential was used to solve the problem analytically. Numerical results show that the maximum tensile hoop stress at the hole boundary in the plane can be reduced to becoming negligible if an optimum stiffness ratio between the plane and the rivet is chosen (normally a harder material for the reinforced ring comparing to the plane is needed). An optimum thickness of the reinforced ring can also be determined to further reduce the hoop stress concentration. Therefore, the results of the present study provide a new theoretical basis for designing a reinforced rivet hole.
Rapid Liquid Fuel Mixing for Lean-Burning Combustors: Low-Power Performance
Authors: Leong M. Y. , Smugeresky C. S. , McDonell V. G. , Samuelsen G. S.
Published: July 2002

Designers of advanced gas turbine combustors are considering lean direct injection strategies to achieve low NOx emission levels. In the present study, the performance of a multipoint radial airblast fuel injector Lean Burn injector (LBI) is explored for various conditions that target low-power gas turbine engine operation. Reacting tests were conducted in a model can combustor at 4 and 6.6 atm, and at a dome air preheat temperature of 533 K, using Jet-A as the liquid fuel. Emissions measurements were made at equivalence ratios between 0.37 and 0.65. The pressure drop across the airblast injector holes was maintained at 3 and 7–8 percent. The results indicate that the LBI performance for the conditions considered is not sufficiently predicted by existing emissions correlations. In addition, NOx performance is impacted by atomizing air flows, suggesting that droplet size is critical even at the expense of penetration to the wall opposite the injector. The results provide a baseline from which to optimize the performance of the LBI for low-power operation.
Cutting Fluid Aerosol Generation due to Spin-off in Turning Operation: Analysis for Environmentally Conscious Machining
Authors: Chen Zhong , Wong Kinwah , Li Wei , Liang Steven Y. , Stephenson David A.
Published: July 2002

This paper presents an analytical model for the prediction of shop floor aerosol generation rate and particulate size distribution due to the spin-off motion of cutting fluid from a rotational workpiece in a turning operation. Based on the theory of atomization and principles of fluid motion, the model analyzes the generation of cutting fluid aerosol associated with the formation of rotating cylindrical peripheral disk and liquid sheet on the workpiece surface. In coupling with fluid flow rate analysis and Rosin and Rammler distribution model, the airborne particulate generation rate and size distribution are expressed in terms of fluid properties, fluid application condition, and machining process parameters. Experiments were performed with the use of the light scattering particle measurement devices to calibrate and verify the analytical models. Under various fluid flow rates and workpiece rotational speeds, experimental data have shown reasonable agreement with model predictions. The predictive models developed in this paper can be used as a basis for human exposure and health hazard analysis. It can also facilitate the control and optimization of the use of cutting fluids in achieving a balanced consideration of process productivity and environmental consciousness.
Tip Clearance Effects in a Turbine Rotor: Part I—Pressure Field and Loss
Authors: Xiao Xinwen , McCarter Andrew A. , Lakshminarayana Budugur
Published: July 2002

This paper presents an experimental investigation of the effects of the tip clearance flow in an axial turbine rotor. The effects investigated include the distribution and the development of the pressure, the loss, the velocity, and the turbulence fields. These flow fields were measured using the techniques of static pressure taps, rapid response pressure probes, rotating five-hole probes, and Laser Doppler Velocimeter. Part I of this paper covers the loss development through the passage, and the pressure distribution within the passage, on the blade surfaces, on the blade tip, and on the casing wall. Regions with both the lowest pressure and the highest loss indicate the inception and the trace of the tip leakage vortex. The suction effect of the vortex slightly increases the blade loading near the tip clearance region. The relative motion between the turbine blades and the casing wall results in a complicated pressure field in the tip region. The fluid near the casing wall experiences a considerable pressure difference across the tip. The highest total pressure drop and the highest total pressure loss were both observed in the region of the tip leakage vortex, where the loss is nearly twice as high as that near the passage vortex region. However, the passage vortex produces more losses than the tip leakage vortex in total. The development of the loss in turbine rotor is similar to that observed in cascades. Part II of this paper covers the velocity and the turbulence fields.
A Study of Convective Heat Transfer in a Model Rotor–Stator Disk Cavity
Authors: Roy R. P. , Xu G. , Feng J.
Published: July 2002

In this study, the fluid (air) temperature field and the convective heat flux distribution on the rotor disk surface were measured and computed in a model rotor–stator disk cavity. Both mainstream flow and secondary air flow were provided. The radial distribution of convective heat transfer coefficient on the rotor disk surface, which was calculated as the ratio of the local heat flux and the local temperature difference across the thermal boundary layer on the disk, is also reported. In the experiments, the disk rotational Reynolds number, Reϕ, ranged from 4.65×105 to 8.6×105, and the nondimensional secondary air flow rate, cw, ranged from 1504 to 7520. The secondary air was supplied at the cavity hub. All experiments were carried out at the same mainstream air flow rate, Rem=5.0×105. The cavity fluid temperature distribution was measured by traversing miniature thermocouples, and the rotor disk surface temperature and heat flux were measured by a quasi-steady thermochromic liquid crystal technique in conjunction with resistance temperature detectors embedded in the disk. The measurements are compared with predictions from the commercial CFD code Fluent. The Fluent simulations were performed in the rotationally symmetric mode using a two-zone description of the flow field and the RNG k-ε model of turbulence. The convective heat transfer coefficient distribution on the rotor disk surface exhibited the influence of the source region and the core region of air flow in the cavity. In the source region, which is radially inboard, the convective heat transfer was dominated by the secondary air flow rate. In the core region, which is radially outboard, the heat transfer was dominated by the rotational motion of the fluid relative to the rotor disk. An empirical correlation for the local Nusselt number on the rotor disk surface is suggested for the core region.
A Study of Beta Processing of Ti-6Al-4V: Is it Trivial?
Authors: Prasad Y. V. R. K. , Seshacharyulu T. , Medeiros S. C. , Frazier W. G.
Published: July 2002

Deformation of Ti-6Al-4V alloy in the β phase field is generally considered to be trivial since the material is highly workable at these temperatures and does not normally pose problems during processing. In view of this, studies on the hot deformation behavior of β are scanty compared to those on the α−β deformation. This paper is focussed on understanding the β deformation characteristics in Ti-6Al-4V with a view to examine whether such studies help in optimizing the process design and achieving microstructural control. The emphasis has been on the two industrial grades, viz. commercial purity (CP) versus extra-low interstitial (ELI), and also on the effect of starting microstructure (transformed β versus equiaxed α+β). The stress-strain curves obtained in compression exhibited steady-state behavior at strain rates lower than 1 s−1 and oscillatory/softening behavior at higher strain rates. Kinetic analysis of the flow stress data obtained at different temperatures and strain rates has shown that the stress exponent is about 3.6-3.8 and the apparent activation energy is in the range 150-287 kJ/mole, which is comparable to that of self-diffusion in β phase (150 kJ/mol). Dynamic recrystallization (DRX) of β is identified as the microstructural mechanism in all the cases except in ELI grade with transformed β starting structure. The prior β grain size in the DRX region exhibits a good correlation with the Zener-Hollomon parameter. In case of ELI grade, a mechanism of large grained superplasticity involving sliding of prior colony boundaries has been identified. However, deformation close to the transus in ELI grade causes nucleation of voids which may grow during soaking at the deformation temperature under the influence of tensile residual stress. The results clearly show that a study of β deformation mechanisms holds the key during hot working of Ti-6-4. More importantly, the processing schedule used for CP grade Ti-6-4 should not be used for ELI grade to achieve microstructural control and avoid defects.
Solids Transport in Multiphase Flows—Application to High-Viscosity Systems
Authors: King Matthew J. S. , Fairhurst C. Paul , Hill Trevor J.
Published: July 2002

Solids transport in multiphase systems falls under the umbrella of “flow assurance.” Unlike issues such as waxes and hydrates, solids transport has received relatively little attention to date. This is especially true for solids transport in high-viscosity fluids such as Venezuelan crude, where viscosities around the 300–400-cP mark are commonly encountered. This paper describes some experiments performed on the BP Amoco 6-in. multiphase flow test facility located at Sunbury. These looked at the transport of field representative sand through a pipeline dip. Several fluids were selected for these experiments to examine the influence of liquid viscosity on the results. These were water, oil, and two different carboxymethylcellulose solutions (150 and 300 cP). These experiments showed that, in slug flow, water and low-viscosity oil were able to transport the sand uphill, whereas neither high-viscosity solution was able to transport the solids. This feature was examined in comparison to the model for solids transport in near-horizontal pipes discussed in this paper. Three-phase flow experiments (water-oil-air) were also performed to investigate the effect of oil or water prewetting of the solids on solids transport. If prewetted by water, the sand could not be moved by oil slugs. Once water was added to the system, the sand became increasingly mobile.
Laser Bending of Tubes: Mechanism, Analysis, and Prediction
Authors: Li Wenchuan , Yao Y. Lawrence
Published: July 2002

Laser bending of tubes is a process in which laser-induced thermal distortion is used to bend tubes without hard tooling or external forces. Mechanisms of the process are examined to better understand the deformation characteristics such as wall thickness variation, cross-section ovalization, bending radius, and asymmetry. Factors important to these characteristics are experimentally and numerically investigated. Temporal and spatial distributions of temperature and stress/strain obtained from experimentally validated simulation models are also used to better understand additional phenomena accompanying the process, and to help devise ways to improve the process such as reducing asymmetry. A closed-form expression for the bending angle is proposed.
Stress-Based Forming Limits in Sheet-Metal Forming
Authors: Stoughton Thomas B.
Published: July 2002

A strain-based forming limit criterion is widely used throughout the sheet-metal forming industry to gauge the stability of the deformed material with respect to the development of a localized neck prior to fracture. This criterion is strictly valid only when the strain path is linear throughout the deformation process. There is significant data that shows a strong and complex dependence of the limit criterion on the strain path. Unfortunately, the strain path is never linear in secondary forming and hydro-forming processes. Furthermore, the path is often found to be nonlinear in localized critical areas in the first draw die. Therefore, the conventional practice of using a path-independent strain-based forming limit criterion often leads to erroneous assessments of forming severity. Recently it has been reported that a stress-based forming limit criterion appears to exhibit no strain-path dependencies. Subsequently, it has been suggested that this effect is not real, but is due to the saturation of the stress-strain relation. This paper will review and compare the strain-based and stress-based forming limit criteria, looking at a number of factors that are involved in the definition of the stress-based forming limit, including the role of the stress-strain relation.