bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverted Brayton Cycle Employment for Low-Temperature Cogenerative Applications
Authors: Bianchi M. , di Montenegro G. Negri , Peretto A.
Published: July 2002

The employment of cogeneration plants for thermal and electric power production is constantly increasing especially for low power requirements. In most cases, to match these low power needs, the cogeneration plant is built up with diesel or gasoline engine or with gas turbine units. In this paper, the performance, in terms of the most utilized cogenerative indexes, of an inverted Brayton cycle working with the gas exhausted by the open power plant have been evaluated. Subsequently, the analysis of a cogenerative gas turbine equipped with IBC was carried out and the benefits numerically calculated. It resulted that the IBC employment may increase of about five percentage points the plant electric efficiency, making this solution particularly attractive for cogenerative applications.
Pressure Surface Separations in Low-Pressure Turbines—Part 2: Interactions With the Secondary Flow
Authors: Brear Michael J. , Hodson Howard P. , Gonzalez Paloma , Harvey Neil W.
Published: July 2002

This paper describes a study of the interaction between the pressure surface separation and the secondary flow on low-pressure turbine blades. It is found that this interaction can significantly affect the strength of the secondary flow and the loss that it creates. Experimental and numerical techniques are used to study the secondary flow in a family of four low-pressure turbine blades in linear cascade. These blades are typical of current designs, share the same suction surface and pitch, but have differing pressure surfaces. A mechanism for the interaction between the pressure surface separation and the secondary flow is proposed and is used to explain the variations in the secondary flows of the four blades. This mechanism is based on simple dynamical secondary flow concepts and is similar to the aft-loading argument commonly used in modern turbine design.
Metallurgical Considerations for Life Assessment and the Safe Refurbishment and Requalification of Gas Turbine Blades
Authors: Daleo J. A. , Ellison K. A. , Boone D. H.
Published: July 2002

Metallurgical analysis of rotating blades operating in advanced gas turbine engines is important in establishing actual operating conditions, degradation modes, remaining life, and most importantly, the proper repair and rejuvenation techniques to be used in developing optimum component life strategies. The elevated firing temperatures used in the latest engine designs result not only in very high metal surface temperatures but also in very high temperature gradients and concommitant thermal strains induced in part by the complex and efficient cooling systems. This has changed the primary function of today’s superalloy-coating systems from one of hot corrosion protection to moderating high temperature oxidation reactions. Furthermore, as a result of the high thermal strains induced by the cooling systems, long-term metallurgical structural stability issues now revolve around optimizing both thermal mechanical fatigue (TMF) resistance and creep life. Thus the gradual change to directionally solidified (DS) and single crystal (SC) alloys throughout the industry. The use of DS and SC alloys coated with state of the art TBC, platinum modified aluminide and MCrAlY coatings with or without subsequent aluminizing applied by vacuum plasma spray (VPS), high velocity oxygen fuel (HVOF), physical vapor deposition (PVD), air plasma spray (APS), and by chemical vapor deposition (CVD) methods along with the widespread use of internal aluminide coatings have made today’s rotating components prohibitively expensive to replace after only one cycle of operation. It is therefore, or should now be a high priority for all cost conscious gas turbine users to help develop reliable repair and rejuvenation strategies and techniques to minimize their operating cost. Traditional metallurgical considerations required for life assessment and the reliable refurbishment and requalification of gas turbine blades are reviewed along with some new exciting techniques. Examples of component degradation modes are presented. Appropriate attention to metallurgical issues allows turbine users to more successfully and economically operate their turbines.
Computations of Low Pressure Fluid Flow and Heat Transfer in Ducts Using the Direct Simulation Monte Carlo Method
Authors: Yan Fang , Farouk Bakhtier
Published: July 2002

High Knudsen number (Kn) gas flows are found in vacuum and micro-scale systems. Such flows are usually in the slip or transition regimes. In this paper, the direct simulation Monte Carlo (DSMC) method has been applied to compute low pressure, high Kn flow fields in partially heated channels. Computations were carried out for nitrogen, argon, hydrogen, oxygen and noble gas mixtures. Variation of the Kn is obtained by reducing the pressure while keeping the channel width constant. Nonlinear pressure profiles along the channel centerline are observed. Heat transfer from the channel walls is also calculated and compared with the classical Graetz solution. The effects of varying pressure, inlet flow and gas transport properties (Kn, Reynolds number, Re and the Prandtl number, Pr respectively) on the wall heat transfer (Nusselt number, Nu) were examined. A simplified correlation for predicting Nu¯ as a function of the Peclet number, Pe¯ and Kn¯ is presented.
Three Component Velocity Field Measurements in the Stagnation Region of a Film Cooled Turbine Vane
Authors: Polanka Marc D. , Cutbirth J. Michael , Bogard David G.
Published: July 2002

The showerhead region of a film-cooled turbine vane in a gas turbine engine involves a complex interaction between mainstream flow and coolant jets. This flow field was studied using three component laser Doppler velocimeter measurements in a simulated turbine vane test facility. Measurements were focused around the stagnation row of holes. Low and high mainstream turbulence conditions were used. The spanwise orientation of the coolant jets, typical for showerhead coolant holes, had a dominating effect. Very high levels of turbulence were generated by the mainstream interaction with the coolant jets. Furthermore, this turbulence was highly anisotropic, with the spanwise component of the turbulent fluctuations being twice as large as the other components. Finally, there was an interaction of the high mainstream turbulence with the coolant injection resulting in increased turbulence levels for the spanwise velocity component, but had little effect on the other velocity components.
Stress Relaxation in Prestressed Composite Laminates
Authors: Suvorov A. P. , Dvorak G. J.
Published: July 2002

Viscoelastic deformation caused in symmetric laminated plates by release of fiber prestress and by uniform thermomechanical loads is analyzed on the constituent, ply and overall laminate scales with the Transformation Field Analysis (TFA) method (G. J. Dvorak, Proc. R. Soc. Lond., 1992, A437, pp. 311–327). Fiber prestress is applied in individual plies prior to matrix cure and released after matrix consolidation. Linear or nonlinear viscoelastic constitutive relations are used to evaluate the inelastic deformation rates in terms of current constituent stress averages. The TFA method regards both thermal and inelastic strains as piecewise uniform eigenstrains acting in superposition with mechanical loads and fiber prestress release on an elastic laminate. Interactions between the eigenstrains at the three different size scales are described by certain influence functions derived from micromechanical analysis of the plies and laminates. Applications describe stress relaxation in two carbon/epoxy laminates after cooling from the curing temperature and release of optimized fiber prestress, that allows maximum tensile load application while keeping both interior and free-edge stresses within prescribed strength limits. Subsequent viscoelastic deformation under constant rate loading, and stress relaxation caused by a sustained application of an elevated temperature to a laminate without prestress are also analyzed. Results are presented in the form of initial failure maps that identify overall stress states which may or may not initiate a specific damage mode in the laminate.
Control of Transient Thermal Response During Sequential Open-Die Forging: A Trajectory Optimization Approach
Authors: Frazier W. G. , Seshacharyulu T. , Medeiros S. C. , Prasad Y. V. R. K.
Published: July 2002

A trajectory optimization approach is applied to the design of a sequence of open-die forging operations in order to control the transient thermal response of a large titanium alloy billet. The amount of time the billet is soaked in furnace prior to each successive forging operation is optimized to minimize the total process time while simultaneously satisfying constraints on the maximum and minimum values of the billet’s temperature distribution to avoid microstructural defects during forging. The results indicate that a “differential” heating profile is the most effective at meeting these design goals.
Antiplane Crack Problem in Functionally Graded Piezoelectric Materials
Authors: Li Chunyu , Weng G. J.
Published: July 2002

In this paper the problem of a finite crack in a strip of functionally graded piezoelectric material (FGPM) is studied. It is assumed that the elastic stiffness, piezoelectric constant, and dielectric permitivity of the FGPM vary continuously along the thickness of the strip, and that the strip is under an antiplane mechanical loading and in-plane electric loading. By using the Fourier transform, the problem is first reduced to two pairs of dual integral equations and then into Fredholm integral equations of the second kind. The near-tip singular stress and electric fields are obtained from the asymptotic expansion of the stresses and electric fields around the crack tip. It is found that the singular stresses and electric displacements at the tip of the crack in the functionally graded piezoelectric material carry the same forms as those in a homogeneous piezoelectric material but that the magnitudes of the intensity factors are dependent upon the gradient of the FGPM properties. The investigation on the influences of the FGPM graded properties shows that an increase in the gradient of the material properties can reduce the magnitude of the stress intensity factor.
Thermodynamics of Thin Film Epitaxy
Authors: Cammarata R. C. , Sieradzki K.
Published: July 2002

The mechanics of thin film epitaxy is developed using an equilibrium thermodynamics formalism and linear elasticity. A virtual variation approach is employed that leads to a direct identification of the important volume and surface thermodynamic parameters characterizing mechanical equilibrium. In particular, the equilibrium volume stress state of an epitaxial film as a function of the film thickness, surface free energies, and surface stresses is obtained. It is shown how this formalism can be used to determine the critical thickness for epitaxy.
Effect of Nonlinear Elastic Behavior on Bilayer Decohesion of Thin Metal Films From Nonmetal Substrates
Authors: Baker S. P. , Wang X. , Hui C.-Y.
Published: July 2002

Nonlinear unloading behavior has been observed in thin metal films on substrates. In the present work, the effects of this nonlinear unloading behavior on the strain energy release rate in bilayer decohesion experiments, in which a highly stressed overlayer (“driver”) is used to decohere a layer (“target”) from a substrate, is modeled. Cases where either the driver or the target layer are nonlinear are considered. For particular combinations of stiffnesses and thicknesses, the difference between linear and nonlinear unloading behavior can be quite large (several hundred percent) at experimentally observed stress levels. For practical cases of CR/CU and CU/glass driver/target layer combinations, the maximum difference is about 25%.
Domain Dynamics in a Ferroelastic Epilayer on a Paraelastic Substrate
Authors: Gao Y. F. , Suo Z.
Published: July 2002

This paper models the domain dynamics in a ferroelastic epilayer within the time-dependent Ginzburg-Landau (TDGL) framework. Constrained on a paraelastic substrate of square symmetry, the epilayer has rectangular symmetry, and forms domains of two variants. The domain wall energy drives the domains to coarsen. The spontaneous strains induce an elastic field, which drives the domains to refine. The competition between coarsening and refining selects an equilibrium domain size. We model the epilayer-substrate as a nonequilibrium thermodynamic system, evolving by the changes in the elastic displacements and the order parameters. The free energy consists of two parts: the bulk elastic energy, and the excess surface energy. The elastic energy density is taken to be quadratic in the strains. The surface energy density is expanded into a polynomial of the order parameters, the gradients of the order parameters, and the strains. In this expansion, the surface stress is taken to be quadratic in the order parameters. The evolution equations are derived from the free energy variation with respect to the order parameters. The elastic field is determined by superposing the Cerruti solution. Examples of computer simulation are presented.
Phase Transformation and Its Effect on Flank Wear in Machining Steels
Authors: Kim Wonsik , Kwon Patrick
Published: July 2002

In machining, the main wear mechanism on the flank surface of a tool is commonly believed to be abrasive wear [1,9]. Accordingly, work materials with a higher concentration of hard inclusions are expected to develop higher flank wear rates. However, the previous turning experiment [9] with plain carbon steels containing varying amounts of cementite inclusions did not exhibit the expected flank wear behavior. Other imperative phenomenon must be occurring at the tool-work material interface during machining, which diminishes the abrasive action of the cementite inclusions. To investigate this behavior, a series of turning tests with AISI 1045, 1070, and 4340 steels have been conducted; and the newly generated surface layers are examined for phase identification using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM). At high cutting speeds (>200 m/min), flank wear is diminished as the cementite phase at the newly formed surface dissociates and diffuses into the matrix of the austenitic phase. Because the heated austenite phase is cooled extremely rapidly, martensitic and in some case even retained austenitic phases are formed. This is the evidence of phase transformation, which explains the flank wear data observed in [9]. In addition, phase transformation explains the scatter in flank wear data in the literature because the onset of phase transformation depends on the exact composition of the work materials as well as interfacial conditions such as temperature and pressure. This paper reports the experimental evidence of phase transformation and its consequence on flank wear in machining annealed steels.
Modeling Chip-Evacuation Forces and Prediction of Chip-Clogging in Drilling
Authors: Mellinger Jeffrey C. , Burak Ozdoganlar O. , DeVor Richard E. , Kapoor Shiv G.
Published: July 2002

One of the fundamental difficulties of the drilling process is the evacuation of the chips from the drilled hole. As the hole depth increases, the chips tend to cluster together and clog the flutes, causing increased forces, poor hole quality, elevated drill temperatures, and drill breakage. In this paper, a model for chip evacuation has been developed to predict the force and torque arising from the evacuation of the discontinuous chips. The model considers the pressure on a differential chip section being created by the forces required to push the chips out of the hole. The two coefficients of friction required by the model are established via a calibration procedure. The effectiveness of both the calibration and the force models has been assessed via a set of validation experiments. The model can be used to predict the depth when chip-clogging occurs, indicating the need for a pecking cycle, and the depth where the drill experiences an excessive amount of torque, which may result in drill breakage.
Simultaneous Short and Long Wavelength Infrared Pyrometer Measurements in a Heavy-Duty Gas Turbine
Authors: Markham J. R. , Latvakoski H. M. , Frank S. L. F. , Lu¨dtke M.
Published: July 2002

Advanced thermal barrier coatings (TBCs) are increasingly being used in high-performance turbine engines. For optimized use of the coatings, accurate surface temperature measurements are required in the combustion environment. Current on-engine pyrometers, which use short infrared wavelengths to accurately measure the temperatures of metal surfaces, show increased uncertainties when used on TBCs. Studies have suggested that long infrared wavelengths are a suitable alternative. Therefore, to evaluate the response of both wavelength regions, simultaneous measurements with short and long wavelength infrared pyrometers have been accomplished in the first stage turbine of a Siemens V84.3A 60 Hz 180 MW engine at the Berlin Gas Turbine Development and Manufacturing Center.
A Methodology for Predicting the Variance of Fatigue Life Incorporating the Effects of Manufacturing Processes
Authors: Yang Xiaoping , Liu C. Richard
Published: July 2002

It is well known that there is a large variance of fatigue life associated with the data of fatigue tests under nominally identical conditions. Understanding and controlling this variance are essential to enhance the safety and competitiveness of designing and manufacturing fatigue critical products. However, no analytical model quantitatively linking input variables with the variance of fatigue life has been found in current literature. To address this issue, a methodology for analytically predicting the variance of fatigue life is proposed. Using this methodology, the variance of fatigue life can be decomposed into individual components. The significance of this decomposition is two-fold. First, it provides a tool for pinpointing key driving factors of the variance of fatigue life, which is essential for the variance reduction of fatigue life. Second, the time consuming and costly fatigue tests to obtain critical variance information for reliability design may be divided into less time consuming tests for obtaining variance information for individual variables contributing to fatigue variance. Based on the variance prediction tool, a methodology for systematically incorporating manufacturing influence into the prediction of variance and average value of fatigue life is proposed. A verification model is built to predict the variance and average value of fatigue life of a structure with a central hole in the high cycle fatigue regime. The predicted fatigue life matches the actual average fatigue life well. Statistical analysis shows that the predicted variances of the fatigue life are equal to those estimated from actual fatigue life.
Prediction of Thread Quality by Detection and Estimation of Tapping Faults
Authors: Mezentsev Oleg A. , DeVor Richard E. , Kapoor Shiv G.
Published: July 2002

A method is proposed for predicting the internal thread height as a function of tapping process faults and relating it to the standardized thread quality tolerances. Based on the mechanistic tapping model [6], a method of estimating the magnitudes of the faults has been proposed. The effects of tap-hole axes misalignment and tap runout on thread height have been revealed by the mechanistic tapping process model. Based on this model and data obtained from the process estimated process fault values have been used to predict thread height and then predict thread pitch diameter. Using standard tolerances for pitch diameter, an assessment of thread quality can then be made. Validation experiments have been run on several materials for different combinations of process faults. Results of thread measurements showed excellent correspondence with the model predictions.
Adaptive Boundary Control of an Axially Moving String System
Authors: Fung Rong-Fong , Wu Jinn-Wen , Lu Pai-Yat
Published: July 2002

This paper proposes an adaptive boundary control to an axially moving string system, which couples with a mass-damper-spring (MDS) controller at its right-hand-side (RHS) boundary. Unknown parameters appearing in the system equation are assumed constant and estimated on-line by using adaptation laws. The adaptive computed-torque control algorithm applied to robot manipulators of lumped systems is extended to design the adaptive boundary controller for the coupling system. It is found that the control force and update laws depend only on the displacement, velocity and slope of the string at the RHS boundary. Lyapunov stability guarantees the convergence of the tracking error to zero. Finally, the performance of the proposed controller is demonstrated by numerical simulations.
Study of Mixing and Augmentation of Natural Convection Heat Transfer by a Forced Jet in a Large Enclosure
Authors: Kuhn Shine-Zen (Joseph) , Kang Hwan Kook , Peterson Per F.
Published: July 2002

This paper presents an experimental study of gas mixing processes and heat transfer augmentation by a forced jet in a large cylindrical enclosure with an isothermal bottom heating/cooling surface. Cold/hot air was injected at several positions with varying pipe diameters and injection orientations, and was removed from the top of the enclosure. Under natural convection, the mean Nusselt number was correlated by the enclosure Rayleigh number RaD1/3, and under strong forced convection, by the jet Reynolds number Rej2/3. A combining rule for mixed convection was found for both the stabilizing (cooled surface) and destabilizing (heated surface) density gradients. Using the ratio of forced and free convection Nusselt numbers, this correlation could be further reduced to predict forced-jet augmentation as a function of the Archimedes number, with a correction factor to account for jet orientation and enclosure aspect ratio.
Perspectives in Modeling Film Cooling of Turbine Blades by Transcending Conventional Two-Equation Turbulence Models
Authors: Azzi A. , Lakehal D.
Published: July 2002

The paper presents recent trends in modeling jets in crossflow with relevance to film cooling of turbine blades. The aim is to compare two classes of turbulence models with respect to their predictive performance in reproducing near-wall flow physics and heat transfer. The study focuses on anisotropic eddy-viscosity/diffusivity models and explicit algebraic stress models, up to cubic fragments of strain and vorticity tensors. The first class of models are direct numerical simulation (DNS) based two-layer approaches transcending the conventional k−ε model by means of a nonisotropic representation of the turbulent transport coefficients; this is employed in connection with a near-wall one-equation model resolving the semi-viscous sublayer. The aspects of this new strategy are based on known channel-flow and boundary layer DNS statistics. The other class of models are quadratic and cubic explicit algebraic stress formulations rigorously derived from second-moment closures. The stress-strain relations are solved in the context of a two-layer strategy resolving the near-wall region by means of a nonlinear one-equation model; the outer core flow is treated by use of the two-equation model. The models are tested for the film cooling of a flat plate by a row of streamwise injected jets. Comparison of the calculated and measured wall-temperature distributions shows that only the anisotropic eddy-viscosity/diffusivity model can correctly predict the spanwise spreading of the temperature field and reduce the strength of the secondary vortices. The wall-cooling effectiveness was found to essentially depend on these two particular flow features. The non-linear algebraic stress models were of a mixed quality in film-cooling calculations.
Direct measurement of residual gas effect on the sensitivity in TAMA300
Authors: Takahashi R. , Saito Y. , Fukushima M. , Ando M. , Arai K. , Tatsumi D. , Heinzel G. , Kawamura S. , Yamazaki T. , Moriwaki S.
Published: July 2002

A laser interferometer gravitational wave detector requires an ultrahigh vacuum in the tubes in which the laser beams pass. TAMA300, involves two 300-m vacuum tubes, and is kept at 2×10−6 Pa of vacuum pressure so as to reduce scattering effects due to residual-gas molecules. The sensitivity attained so far is 2×10−18 m/Hz around 1 kHz. By introducing a Xe gas into the entire system of TAMA300, we directly observed the residual-gas effect on the sensitivity. It was found that Xe-gas pressure of 0.03 Pa induces an increase in the mirror displacement noise of 3×10−18 m/Hz. This noise level is consistent with a calculated optical fluctuation of the laser beam due to residual-gas scattering.
Method for seed and underlayer optimization of perpendicular magnetic recording media
Authors: Svedberg Erik B. , Van de Veerdonk Rene , Howard Kent J. , Madsen Lynnette D.
Published: July 2002

A set of seed and underlayers for thin film perpendicular recording media has been optimized using a technique involving simultaneous thickness and composition gradients on a single test wafer. Magnetron sputtering under ultrahigh vacuum conditions in Ar gas was used for the deposition of the layers. The structure being optimized consisted of a Ta seed layer, RuxCo1−x, Co63Cr37 underlayers, and a Co68Cr18Pt8B6 hard magnetic layer. One of the layers in the stack on a wafer has been deposited so that both a thickness variation and composition variation occurred. The method allows cross terms between thickness and the individual compositional terms to be investigated. Coercivity and squareness of the samples was measured by magneto-optical Kerr rotation. The results showed that for the range of thickness under investigation, the highest coercivity and squareness does not occur for the same set of conditions. Maximum squareness is reached without a radio frequency (rf) bias, while the coercivity increases further with the application of a −25 V rf bias.
Reduction of metallic oxides by late Ar–H2–N2 postdischarges. II. Applications to iron oxides
Authors: Belmonte T. , Thiébaut J. M. , Michel H. , Cardoso R. P. , Maliska A.
Published: July 2002

In this second part of a study dealing with the reduction of metallic oxide, iron oxide (Fe2O3) is treated by Ar–N2–H2 post discharges. The influence of the composition of both the gas mixture and the temperature on the reduction kinetics was measured between 783 and 868 K. If CuO is reduced to Cu (see Part I of the study), Fe2O3 is reduced to Fe2N1−x or Fe depending on the gas mixture composition. Measurements of the activation energies of the reduction reactions suggest that the reduction mechanisms of Fe2O3 are limited by the diffusion of oxygen in ε- Fe2N1−x. Similar conclusions to those drawn in the case of copper suggest that atomic nitrogen can reduce these oxides, but the reduction kinetics by this specie is much slower than by H. It is also confirmed that atomic hydrogen seems to affect the internal reaction at the interfaces of the sublayer oxides and modifies the activation energy of the growth processes. Finally, the reduction of titanium oxide (TiO2) at 873 K is not observed, and the reduction kinetics, and thus the treatment temperature, seems to depend on the metal–oxygen binding energy.
Study of the properties of thin films of silicon nitride and silicon oxide using effective medium theories
Authors: Henda Redhouane
Published: July 2002

Effective medium theories (EMTs) find widespread applications in the general area of condensed matter. In this article, EMTs are used to investigate the properties of thin films of silicon nitride (SiNx) and silicon oxide (SiOx) produced by the low-pressure chemical vapor deposition technique. Experimental data on the technologically important properties, such as the optical constants and density, of these materials are compared with theoretical predictions using Clausius–Mossotti, Maxwell-Garnett, and Bruggemann equations. For both materials, the results show a good agreement between theoretical predictions as obtained from the solution of the Bruggemann equation and the experimental data up to the percolation threshold. The experimental results agree fairly well with the calculated results obtained through the solution of the Maxwell-Garnett equation, but the latter fails to predict the transition present in the composition versus optical constant curves of both materials.
Calculated energy transfer in an accommodation pump
Authors: Hobson J. P.
Published: July 2002

In an accommodation pump gas is transferred from one point to another at the same temperature without the application of any external mechanical or electrical forces to the gas—only temperature gradients are used. If there is no continuous flow a static and unchanging pressure difference develops between the two points, requiring no additional input of energy to the gas. Little attention has been paid to the energy transfer, i.e., the number of calories per mole of gas pumped, in this process. A simple model is presented in which this energy transfer is analytically calculated for a single-stage Pyrex accommodation pump, upper temperature room (295 K), lower temperature liquid nitrogen (77.4), gas helium, compression ratio 1.2, and pressure in the free molecular range. Under these conditions the physical adsorption of helium on pump surfaces is quantitatively negligible. The model calculates the energy difference between a true accommodation pump with atomically rough (leached) and smooth surfaces and a nonpump with exactly the same geometrical dimensions, but with all surfaces rough. The energy differences are assigned to accommodation pumping. It is found that an energy in the range of 300 calories per mole of gas pumped is required, independent of the overall size of the pump, but becoming smaller as the cold volume is reduced relative to the warm volume. The results are extended to multistage pumps, which are ponderous to calculate analytically, but which bear a simple relationship to a single-stage pump.
Surface morphology of evaporated CuInS2 thin films grown by single source thermal evaporation technique
Authors: Akaki Youji , Komaki Hironori , Yoshino Kenji , Ikari Tetsuo
Published: July 2002

Single source thermal evaporation technique was carried out for CuInS2 thin films on the glass substrates. The films were annealed from 100 °C to 500 °C in air. The crystal structures of the films were examined by x-ray diffraction and surface morphology investigated by optical microscope. The CuInS2 thin films were grown by annealing at 200 °C. The sample indicated high resistivity and n-types conductivity examined by a four-point probe method and thermoprobe analysis, respectively.
Density and temperature in an inductively amplified magnetron discharge for titanium deposition
Authors: Ricard A. , Nouvellon C. , Konstantinidis S. , Dauchot J. P. , Wautelet M. , Hecq M.
Published: July 2002

In order to determine the titanium neutral density, a direct current (dc) plasma discharge, amplified by a radio-frequency (rf) coil, was studied by absorption spectrometry. The argon pressure varied from 5 to 40 mTorr. The dc and rf powers varied between 100 and 1500 W and 0 and 500 W, respectively. The plasma gas temperature necessary for the density calculation was evaluated by analyzing the N2 rotational spectrum in an Ar–N2 gas mixture. When increasing the rf power a decrease of titanium neutral density was found. This decrease is related to the increased titanium ion density. When using the rf coil, the titanium degree of ionization can be up to 90%.
Femoral neck trabecular patterns predict osteoporotic fractures
Authors: Lee Richard L. , Dacre Jane E. , Hart Deborah J. , Spector Tim D.
Published: July 2002

In this paper we show that texture analysis of femoral neck trabecular patterns can be used to predict osteoporotic fractures. The study is based on a sample of 123 women aged 44–66 years with and without fractures. We analyzed trabecular patterns using the Co‐occurrence Matrix texture analysis algorithm and compared the predictive utility of the textural data with densitometry. Logistic regression was used to estimate the predictive utility, of clinical and textural data per standard deviation. Reproducibility was also demonstrated using paired films at 1‐year intervals Bone mass estimated by DEXA measurements of the spine and hip were the most predictive of fractures giving a two‐fold increase in fractures per s.d. bone mass loss (95% CI: 1.2–3.1, Age was also highly predictive with fracture risk increasing by 1.07‐fold per year (95% CI: 1.01–1.14, Trabecular texture was found to give a lower, but significant, prediction of fracture of 1.5‐fold per s.d. trabecular pattern loss (95% CI: 0.96–2.31, Combining age, weight, and trabecular texture increased the fracture prediction to 1.78‐fold per s.d. (95% CI: 1.19–2.67). Combining trabecular texture with densitometry increased the predictive ability to 2.06‐fold per s.d. (95% CI: 1.32–3.22) and combined with age and weight as well increased to 2.1‐fold per s.d. (95% CI: 1.32–3.35). This shows that osteoporotic trabecular texture changes can be “measured.” Moreover, the combination of age, weight, and trabecular texture is more predictive than either alone. We propose therefore that this trabecular texture analysis is both reproducible and clinically meaningful. The application of such methods could be used to improve the estimation of fracture risk in conjunction with other clinical data, or where densitometry data cannot be obtained (e.g., in retrospective studies).
Implementation of the isocenter‐shift technique for smoothing MLC field edge on a 3D treatment planning system
Authors: Xue Jinyu , Zhang Pengpeng , Wu Jackie , Wang Zhiheng , Sibata Claudio
Published: July 2002

Stepped leaf edges are the major limitation of conforming to the prescribed treatment contour defined by the conventional multileaf collimator (MLC), which produces a scalloped dose pattern. The commercial HD‐270 MLC™ (HDI) technique provides a software solution of the conventional MLC to achieve smoothed edge and optimal penumbra of the MLC shaped field. We implemented the HDI functionality on a 3D treatment planning system and compared the dosimetric effects of the HDI delivery in simulation with those in experiment for a number of the MLC fields. The fields from the contour of varied shapes with different sizes of the leaf stepping were tested for the HDI delivery. There is a good agreement of the dose distribution between the calculation as implemented in the planning system and the measurement performed on the treatment machine. It has been shown that the HDI delivery significantly smoothes the stepped field edge with the reduced isodose undulation and effective penumbra. A problem may be present when the HDI is applied for the treatment of the circular contour of smaller diameter, and the conformity of the MLC shaping may not be achievable satisfactorily with the existing system. The optimization of leaf configuration is suggested to improve the conformity of the HDI technique. The HDI planning then can be used to assist in the decision making of applying the HDI treatment delivery.
Dosimetric characterization of a bi‐directional micromultileaf collimator for stereotactic applications
Authors: Bucciolini M. , Russo S. , Buonamici F. Banci , Pini S. , Silli P.
Published: July 2002

A 6 MV photon beam from Linac SL75‐5 has been collimated with a new micromultileaf device that is able to shape the field in the two orthogonal directions with four banks of leaves. This is the first clinical installation of the collimator and in this paper the dosimetric characterization of the system is reported. The dosimetric parameters required by the treatment planning system used for the dose calculation in the patient are: tissue maximum ratios, output factors, transmission and leakage of the leaves, penumbra values. Ionization chambers, silicon diode, radiographic films, and LiF thermoluminescent dosimeters have been employed for measurements of absolute dose and beam dosimetric data. Measurements with different dosimeters supply results in reasonable agreement among them and consistent with data available in literature for other models of micromultileaf collimator; that permits the use of the measured parameters for clinical applications. The discrepancies between results obtained with the different detectors (around 2%) for the analyzed parameters can be considered an indication of the accuracy that can be reached by current stereotactic dosimetry.
Experimental investigation of dose calibrator response for brachytherapy solutions contained in 5 mL plastic syringes and 2 mL conical glass v‐vials as a function of filling mass
Authors: Zimmerman B. E. , Cessna J. T. , Dorton J. A.
Published: July 2002

The effect of measurement geometry on the determination of the activity of solutions containing for use in brachytherapy applications has been investigated for 5 mL plastic syringes and 2 mL conical glass dose vials as a function of filling mass. New dial settings for the syringes over a filling mass range of 1 to 3 g have been determined to be and (expanded, uncertainties) for the NIST Capintec CRC‐12 and Capintec CRC‐35R, respectively, with any effect due to the filling mass lying within the uncertainty in the activity calibration. A filling mass effect was observed in the dose vials, causing a 10.5% reduction in the chamber response from a 2 g filling mass to 1 g. Dial settings at 2 g were experimentally found to be and (expanded uncertainties) for the NIST Capintec CRC‐12 and Capintec CRC‐35R, respectively. The appropriate dial settings for the same vials with a 1 g filling mass were found to be and for CRC‐12 and CRC‐35R, respectively. Differences of up to ±45% in the activity determination were observed between values obtained with the manufacturer's recommended setting and the settings obtained experimentally for each specific geometry. Calibration factors were also determined for a Vinten 671 Radionuclide Calibrator, giving values of and (expanded uncertainties), respectively, for the 1 and 2 g dispensings. This study demonstrates that experimentally determined calibration factors for the exact measurement geometry are necessary when measuring radionuclides in configurations other than the manufacturer's standard geometry, especially when nuclides that emit low‐energy radiations are involved.
Vessel size measurements in angiograms: A comparison of techniques
Authors: Hoffmann Kenneth R. , Nazareth Daryl P. , Miskolczi László , Gopal Anant , Wang Zhou , Rudin Stephen , Bednarek Daniel R.
Published: July 2002

As interventional procedures become more complicated, the need for accurate quantitative vascular information increases. In response to this need, many commercial vendors provide techniques for measurement of vessel sizes, usually based on derivative techniques. In this study, we investigate the accuracy of several techniques used in the measurement of vessel size. Simulated images of vessels having circular cross sections were generated and convolved with various focal spot distributions taking into account the magnification. These vessel images were then convolved with Gaussian image detector line spread functions (LSFs). Additionally, images of a phantom containing vessels with a range of diameters were acquired for the 4.5″, 6″, 9″, and 12″ modes of an image intensifier–TV (II–TV) system. Vessel sizes in the images were determined using a first‐derivative technique, a second‐derivative technique, a linear combination of these two measured sizes, a thresholding technique, a densitometric technique, and a model‐based technique. For the same focal spot size, the shape of the focal spot distribution does not affect measured vessel sizes except at large magnifications. For vessels with diameters larger than the full‐width‐at‐half‐maximum (FWHM) of the LSF, accurate vessel sizes (errors ∼0.1 mm) could be obtained by using an average of sizes determined by the first and second derivatives. For vessels with diameters smaller than the FWHM of the LSF, the densitometric and model‐based techniques can provide accurate vessel sizes when these techniques are properly calibrated.
An analog experiment of the parametric instability
Authors: Berthet R. , Petrosyan A. , Roman B.
Published: July 2002

We show how a simple electronic parametric oscillator can be used to exhibit both supercritical and subcritical bifurcations to a subharmonic oscillatory state as the pump frequency is varied, and study the scaling behavior of the oscillation amplitude in the vicinity of the tricritical point.
Undergraduate experiment to measure the speed of sound in liquid by diffraction of light
Authors: Luna Diego A. , Real Mariano A. , Durán Débora V.
Published: July 2002

Diffraction of light by an ultrasonic phase grating enables a direct measurement of the wavelength of acoustic waves in liquids. If the acoustic frequency is known independently, it can be combined with the measured acoustic wavelength to determine the speed of sound in liquid. The method of Debye and Sears based on a visual display of the diffraction pattern on a distant screen is used. Measurements carried out with a He–Ne laser and an ultrasonic nebulizer provide an excellent experiment for an undergraduate laboratory with a minimum of equipment. A sound velocity of 1536 m/s with an uncertainty of 1% is obtained for distilled water.
Pyrotechnic shock response predictions combining statistical energy analysis and local random phase reconstruction
Authors: Bodin E. , Brévart B. , Wagstaff P. , Borello G.
Published: July 2002

Numerous pyrotechnic devices are used on satellites to separate structural subsystems, deploy appendages, and activate on-board operating subsystems. The firing of these pyrotechnic mechanisms leads to severe impulsive loads which could sometimes lead to failures in electronic systems. The objective of the present investigation is to assess the relevance of a method combining deterministic calculations and statistical energy analysis to predict the time overall shock environment of electronic equipment components. The methods are applied to the low- and high-frequency ranges, respectively, which may be defined using a modal parameter based on the effective transmissibility. Initially, in order to address the problem of the low-frequency content of the mechanical shock pulse, the linear dynamic response of the equipment was calculated using direct time integration of a finite element model of the structure. The inputs in the form of the accelerations measured in all three directions at each of the four bolted interfaces were injected into the model. The high-frequency content of the shock response is taken into account by considering the intrinsic dynamic filtering of the equipment. This frequency filter magnitude is extrapolated from the transfer function given by statistical energy analysis between the different imposed accelerations and the response accelerations. Their associated phases are synthesized by considering pseudo-modal phase variations around the group velocity of the structural flexural waves. Combining the effects of the high-frequency filter outputs and the low-frequency finite element calculations yields good predictions of the equipment shock time response over the whole frequency range of interest.
On the effect of viscosity in scattering from partially coated infinite cylinders
Authors: Ginsberg Jerry H.
Published: July 2002

This paper considers the two-dimensional problem of scattering of a plane wave incident on an infinite cylinder that is coated with strips of pressure-release material extending over quadrants on the illuminated and shadowed sides, with the remainder of the surface considered to be rigid. Transitions from soft to rigid surfaces correspond to discontinuous boundary conditions. Ideal fluid theory predicts an infinite pressure gradient at these transitions, which suggests that viscous effects may be significant. The present work is a quantitative analysis of the global effect on acoustic scattering of viscosity effects arising in the vicinity of the discontinuity. The analysis represents the scattered field in terms of acoustic and vortical contributions. Both contributions are represented by series expansions in terms of azimuthal harmonics and associated cylindrical wave functions. The amplitudes of these harmonics are determined by satisfying a pair of discontinuous boundary conditions. Results obtained by using the method of weighted residuals are shown to be less accurate than those obtained from a collocation procedure. The results for surface pressure and farfield directivity indicate that viscous effects are important only if the Reynolds number is extremely small.
Audiogram of a harbor porpoise (Phocoena phocoena) measured with narrow-band frequency-modulated signals
Authors: Kastelein Ronald A. , Bunskoek Paulien , Hagedoorn Monique , Au Whitlow W. L. , de Haan Dick
Published: July 2002

The underwater hearing sensitivity of a two-year-old harbor porpoise was measured in a pool using standard psycho-acoustic techniques. The go/no-go response paradigm and up–down staircase psychometric method were used. Auditory sensitivity was measured by using narrow-band frequency-modulated signals having center frequencies between 250 Hz and 180 kHz. The resulting audiogram was U-shaped with the range of best hearing (defined as 10 dB within maximum sensitivity) from 16 to 140 kHz, with a reduced sensitivity around 64 kHz. Maximum sensitivity (about 33 dB re 1 μPa) occurred between 100 and 140 kHz. This maximum sensitivity range corresponds with the peak frequency of echolocation pulses produced by harbor porpoises (120–130 kHz). Sensitivity falls about 10 dB per octave below 16 kHz and falls off sharply above 140 kHz (260 dB per octave). Compared to a previous audiogram of this species (Andersen, 1970), the present audiogram shows less sensitive hearing between 2 and 8 kHz and more sensitive hearing between 16 and 180 kHz. This harbor porpoise has the highest upper-frequency limit of all odontocetes investigated. The time it took for the porpoise to move its head 22 cm after the signal onset (movement time) was also measured. It increased from about 1 s at 10 dB above threshold, to about 1.5 s at threshold.
Prediction of the generation of acoustic waves due to the penetration of pulsed microwaves in multilayer media
Authors: Guilliorit Emmanuel , Bacon Christophe , Hosten Bernard
Published: July 2002

The acoustic wave generation in a body irradiated by a pulsed microwave is predicted theoretically. The irradiated body is a viscoelastic multilayer rod inserted into a waveguide or an uniformly irradiated viscoelastic plate. The model is based on Maxwell’s equations, the heat equation, and thermoviscoelasticity theory. It is validated experimentally by means of four tests performed on three different specimens. The two first specimens are homogeneous rods used to evaluate and verify the mechanical and electromagnetic characteristics of two different materials. The third specimen is a composite rod made up of these materials. Two tests are performed with this specimen. The comparison between the experimental results and the theoretical computations leads to the validation of the theoretical model.
Propagation of quasiplane nonlinear waves in tubes and the approximate solutions of the generalized Burgers equation
Authors: Bednarik Michal , Konicek Petr
Published: July 2002

This paper deals with using the generalized Burgers equation for description of nonlinear waves in circular ducts. Two new approximate solutions of the generalized Burgers equation (GBE) are presented. These solutions take into account the boundary layer effects. The first solution is valid for the preshock region and gives more precise results than the Fubini solution, whereas the second one is valid for the postshock (sawtooth) region and provides better results than the Fay solution. The approximate solutions are compared with numerical results of the GBE. Furthermore, the limits of validity of the used model equation are discussed with respect to boundary conditions and radius of a circular duct.