bluuebunny/crossref_metadata_2025 huggingface dataset:
Memory Analysis of Solid Model Representations for Heterogeneous Objects
Authors: Jackson T. R. , Cho W. , Patrikalakis N. M. , Sachs E. M.
Published: July 2002

Methods to represent and exchange parts consisting of Functionally Graded Material (FGM) for Solid Freeform Fabrication (SFF) with Local Composition Control (LCC) are evaluated based on their memory requirements. Data structures for representing FGM objects as heterogeneous models are described and analyzed, including a voxel-based structure, finite-element mesh-based approach, and the extension of the Radial-Edge and Cell-Tuple-Graph data structures with Material Domains representing spatially varying composition properties. The storage cost for each data structure is derived in terms of the number of instances of each of its fundamental classes required to represent an FGM object. In order to determine the optimal data structure, the storage cost associated with each data structure is calculated for several hypothetical models. Limitations of these representation schemes are discussed and directions for future research also recommended.
Stochastic Dislocation Dynamics for Dislocation-Defects Interaction: A Multiscale Modeling Approach
Authors: Hiratani Masato , Zbib Hussein M.
Published: July 2002

A stochastic dislocation dynamics (SDD) model is developed to investigate dislocation glide through dispersed obstacles. The model accounts for: 1) the dynamics of the flight process between successive meta-stable dislocations under various drag mechanism using discrete dislocation dynamics, and 2) thermal activation processes for meta-stable pinned dislocations using a stochastic force. The integration of the two processes allows one to examine the transient regime of dislocation motion between obstacle-controlled motion and drag-controlled motion. Result pertaining to the stress-strain rate behavior in copper are obtained. The stress and temperature dependence of the average dislocation velocity show obstacle-controlled region below the critical resolved shear stress (CRSS) and drag controlled region above the CRSS, which is in good qualitative agreement with experimental data. In the transient region right below the CRSS, negative temperature sensitivity is observed due to the competition between the drag effects in dislocation flight process and thermal activation process.
A Hybrid Disassembly Sequence Planning Approach for Maintenance
Authors: Li , J. R. , Tor , and S. B. , Khoo L. P.
Published: July 2002

This paper describes a hybrid approach to handle disassembly sequence planning for maintenance. The product under maintenance is first modeled using a novel hybrid graph known as Disassembly Constraint Graph (DCG) which embodies complete disassembly information and can be used to prune the search space of disassembly sequences. Subsequently, a novel Tabu-enhanced GA engine is invoked to generate the near optimal disassembly sequences. A case study was used to illustrate the effectiveness of the proposed approach. The details of the DCG, the TS-enhanced GA engine and the fitness function used are presented in this paper.
Rapid Three-Dimensional Segmentation of the Carotid Bifurcation From Serial MR Images
Authors: Ladak H. M. , Milner and J. S. , Steinman D. A.
Published: July 2002

The current trend in computational hemodynamics is to employ realistic models derived from ex vivo or in vivo imaging. Such studies typically produce a series of images from which the lumen boundaries must first be individually extracted (i.e., two-dimensional segmentation), and then serially reconstructed to produce the three-dimensional lumen surface geometry. In this paper, we present a rapid three-dimensional segmentation technique that combines these two steps, based on the idea of an expanding virtual balloon. This three-dimensional technique is demonstrated in application to finite element meshing and CFD modeling of flow in the carotid bifurcation of a normal volunteer imaged with black blood MRI. Wall shear stress patterns computed using a mesh generated with the three-dimensional technique agree well with those computed using a mesh generated from conventional two-dimensional segmentation and serial reconstruction. In addition to reducing the time required to extract the lumen surface from hours to minutes, our approach is easy to learn and use and requires minimal user intervention, which can potentially increase the accuracy and precision of quantitative and longitudinal studies of hemodynamics and vascular disease. [S0148-0731(00)00201-6]
Dynamic Mechanical Stretch of Organotypic Brain Slice Cultures Induces Differential Genomic Expression: Relationship to Mechanical Parameters
Authors: Morrison Barclay , Meaney David F. , Margulies Susan S. , McIntosh Tracy K.
Published: July 2002

Although the material properties of biological tissues are reasonably well established, recent studies have suggested that the biological response of brain tissue and its constituent cells may also be viscoelastic and sensitive to both the magnitude and rate of a mechanical stimulus. Given the potential involvement of changes in gene expression in the pathogenic sequelae after head trauma, we analyzed the expression of 22 genes related to cell death and survival and found that a number of these genes were differentially regulated after mechanical stretch of an organotypic brain slice culture. Twenty-four hours after stretch, the expression of BDNF, NGF, and TrkA was significantly increased, whereas that of bcl-2, CREB, and GAD65 was significantly decreased (MANOVA followed by ANOVA, p<0.05). Expression of CREB and GAD65 was negatively correlated with strain, whereas expression of APP695 was negatively correlated with strain rate (all p<0.05). This study demonstrates that a subset of genes involved in cell death and survival are differentially regulated after dynamic stretch in vitro and that the expression of specific genes is correlated with mechanical parameters of that stretch. [S0148-0731(00)00303-4]
Block Control Principle for Mechanical Systems
Authors: Utkin Vadim I. , Chen De-Shiou , Chang Hao-Chi
Published: July 2002

In this paper, a generalized design procedure for sliding mode control of nonlinear mechanical systems is proposed. The design approach combines the essential idea of the block control principle, utilizing some of the components of the state vector as a virtual control, with the basic concept of zero dynamics. For mechanical systems governed by a set of interconnected second-order equations, the block control principle cannot be directly applied. To facilitate the controller design, we assume that control systems can be transformed into a regular form consisting of second-order equations. The proposed design approach consists of reducing the original plant into the regular form, constructing a switching manifold, and enforcing sliding mode in the manifold such that the reduced order system in sliding mode has desired dynamics. Stabilization of the mechanical system with unstable zero dynamics is taken into consideration. It is shown that the approach has the advantage of decomposing the original problem into subproblems of lower dimensions, and each of them can be handled independently. As an example, control of a rotational inverted pendulum system is examined. The performance of the proposed approach is validated by both numerical and experimental results. [S0022-0434(00)01601-4]
Control of Deep-Hysteresis Aeroengine Compressors1
Authors: Wang Hsin-Hsiung , Krstic´ Miroslav , Larsen Michael
Published: July 2002

Frequencies of higher-order modes of fluid dynamic phenomena participating in aeroengine compressor instabilities far exceed the bandwidth of available (affordable) actuators. For this reason, most of the heretofore experimentally validated control designs for aeroengine compressors have been via low-order models—specifically, via the famous Moore-Greitzer cubic model (MG3). While MG3 provides a good qualitative description of open-loop dynamic behavior, it does not capture the main difficulties for control design. In particular, it fails to exhibit the so-called “right-skew” property which distinguishes the deep hysteresis observed on high-performance axial compressors from a small hysteresis present in the MG3 model. In this paper we study fundamental feedback control problems associated with deep-hysteresis compressors. We first derive a parametrization of the MG3 model which exhibits the right skew property. Our approach is based on representing the compressor characteristic as a convex combination of a usual cubic polynomial and a nonpolynomial term carefully chosen so that an entire family of right-skew compressors can be spanned using a single parameter ε. Then we develop a family of controllers which are applicable not only to the particular parametrization, but to general Moore-Greitzer type models with arbitrary compressor characteristics. For each of our controllers we show that it achieves a supercritical (soft) bifurcation, that is, instead of an abrupt drop into rotating stall, it guarantees a gentle descent with a small stall amplitude. Two of the controllers have novel, simple, sensing requirements: one employs only the measurement of pressure rise and rotating stall amplitude, while the other uses only pressure rise and the mass flow rate (1D sensing). Some of the controllers which show excellent results for the MG3 model fail on the deep-hysteresis compressor model, thus justifying our focus on deep-hysteresis compressors. Our results also confirm experimentally observed difficulties for control of compressors that have a high value of Greitzer’s B parameter. We address another key issue for control of rotating stall and surge—the limited actuator bandwidth—which is critical because even the fastest control valves are often too slow compared to the rates of compressor instabilities. Our conditions show an interesting trade-off: as the actuator bandwidth decreases, the sensing requirements become more demanding. Finally, we go on to disprove a general conjecture in the compressor control community that the feedback of mass flow rate, known to be beneficial for shallow-hysteresis compressors, is also beneficial for deep-hysteresis compressors. [S0022-0434(00)03101-4]
Adaptive Control With Asymptotic Tracking Performance and Its Application to an Electro-Hydraulic Servo System
Authors: Sun Zongxuan , Tsao Tsu-Chin
Published: July 2002

This paper presents a discrete-time adaptive controller, which incorporates internal model principle for asymptotic tracking performance of systems with parametric uncertainties, unmodeled dynamics and disturbances. Global stability and tracking performance of the adaptive system are derived under conditions on the system’s stabilizability and bounds of noise and unmodeled dynamics. It is shown that asymptotic tracking can be achieved while the unmodeled dynamics and disturbances exist. The adaptive algorithm is applied to an electrohydraulic servo system for periodic trajectory tracking and disturbance rejection. Experimental results based on an eighth-order adaptive system updated at 2560 Hz demonstrate the adaptive system’s ability in high bandwidth tracking performance under effects of system variations and finite word length real-time computation. [S0022-0434(00)03301-3]
Neural Network Based, Discrete Adaptive Sliding Mode Control for Idle Speed Regulation in IC Engines
Authors: Li Xiaoqiu , Yurkovich Stephen
Published: July 2002

An adaptive sliding mode control design method is proposed for discrete nonlinear systems where explicit knowledge of the system dynamics is not available. Three-layer feedforward neural networks are used as function approximators for the unknown dynamics. The control law is designed based on the outputs of the approximators, and the sliding surface is defined in terms of a stable polynomial of the system outputs. Convergence of the state trajectories into a small sliding sector is proved. The method is applied to the internal combustion (IC) engine idle speed control problem. Simulation and experimental results are provided. [S0022-0434(00)01702-0]
High Strain Extension of Open-Cell Foams
Authors: Mills N. J. , Gilchrist A.
Published: July 2002

The high strain tensile deformation of open-cell foams is analyzed, using a Kelvin foam lattice model. The stretching, bending, and twisting of elastic cell edges is analyzed, and the deformed cell shapes predicted. The stress-strain relation and Poisson’s ratio are predicted for strains up to 40% for tension in the [100] and [111] directions of the BCC lattice. The latter prediction is closest to stress-strain curves for polyurethane foams, especially when the cell shape anisotropy is taken into account. The change from edge bending to extension as the main deformation mechanisms, for strains exceeding 20% increases the slope of the stress-strain curve. A comparison is made with irregular cell structure models. [S0094-4289(00)01001-X]
Influence of Heat Treatment on the Mechanical Properties and Damage Development in a SiC/Ti-15-3 MMC
Authors: Miller David A. , Lagoudas Dimitris C.
Published: July 2002

Titanium alloys are commonly heat-treated to meet specific design requirements. In an effort to possibly create a better composite, the influence of heat treatments on the damage evolution and strength of a SiC/Ti-15-3 metal matrix composite (MMC) was studied. Heat treatments of 450°C and 700°C for 24 hours were performed on axial and transverse unidirectional specimens. These specimens, in addition to specimens in the as-received condition, were tested under nonproportional loading paths and then microstructurally analyzed to determine the induced damage. The axial composite with the 450°C heat treatment showed the highest elastic modulus and the lowest stiffness reduction than the other heat treatment conditions. The transverse composite in the as-received condition showed the highest room temperature elastic modulus and the lowest stiffness reduction compared with other heat treatment conditions. Typical damage modes of Ti MMC’s, such as fiber/matrix debonding and matrix microcracking, were seen in all heat treatments. A micromechanics model based on the Mori-Tanaka averaging scheme was implemented to simulate the effects of micro-cracking induced damage on composite stiffness reduction. [S0094-4289(00)01101-4]
A Technique to Measure Interfacial Toughness Over a Range of Phase Angles
Authors: Kuhl Adam , Qu Jianmin
Published: July 2002

An experimental technique using sandwiched Brazil-nut specimens to quantitatively characterize interfacial fracture toughness over a wide range of phase angles is presented. Specimens are made by sandwiching a thin layer of adhesive material between two metal substrates. Tensile loads are applied to the specimens at various loading angles. Through the use of fracture mechanics and finite element analysis, interfacial fracture toughness as a function of loading phase angle is determined from the experimentally obtained critical load and loading direction. The fracture toughness curves for several different Cu/adhesive systems are obtained. [S1043-7398(00)00302-9]
Multiobjective Optimal Placement of Convectively and Conductively Cooled Electronic Components on Printed Wiring Boards
Authors: Queipo Nestor V. , Gil Guy F.
Published: July 2002

This paper presents a solution methodology for the optimal placement of convectively and conductively air-cooled electronic components on planar printed wiring boards considering thermal and electrical/cost design objectives. The methodology combines the use of a heat transfer solver for the prediction of the temperature distribution among the electronic components and a genetic algorithm for the adaptive search of optimal or near optimal solutions and a multiobjective optimization strategy (Pareto optimization and multiattribute utility analysis). After proper validation of the elements of the solution methodology (heat transfer solver/genetic algorithm) in isolation, the methodology under consideration is tested using a placement problem (case study) that considers as optimization criteria the minimization of an estimate of the failure rate of the system of components due to thermal overheating (via an Arrhenius relation) and the minimization of the total wiring length given some interconnectivity requirements. Results corresponding to the case study are presented and discussed for both Pareto optimization and multiattribute utility analysis. [S1043-7398(00)00801-X]
Sand Production Management
Authors: Salama Mamdouh M.
Published: July 2002

Sand production may be inevitable in many fields that have a relatively low formation strength. Sand erosion and settling predictions and sand monitoring are important elements of any effective sand production management strategy. Sand erosion predictions are used to establish tolerable sand production rates, and, thus, well productivity, and to develop cost-effective inspection frequency for critical components. Prediction of critical flow rate to prevent sand settling is important for flowlines that are not designed for pigging. Quantitative sand monitoring is essential in verifying the effectiveness of sand control procedures and in generating an important input parameter for erosion and sand settling predictions. This paper presents equations for predicting sand erosion rate and sand settling flow rate, and assesses the accuracy of these equations. In addition, the paper presents an assessment of the sensitivity of commercially available nonintrusive acoustic and intrusive electrical resistance sand monitors. [S0195-0738(00)00201-6]
Dimensional Instability Studies in Machining of Inconel 718 Nickel Based Superalloy as Applied to Aerogas Turbine Components
Authors: Subhas B. K. , Bhat R. , Ramachandra K. , Balakrishna H. K.
Published: July 2002

Inconel 718 alloy is used extensively in aerogas turbines and this alloy is most difficult to machine and highly prone to dimensional instability after machining. Such detrimental phenomenon poses an enormous problem in engine assembly and affects structural integrity. This paper highlights the systematic research work undertaken to study the plastic deformation characteristics of Inconel 718, and the effect of process variables on machined surface, subsurface, and dimensional instability. Also illustrated is the technique developed for simultaneous optimization of several process variables such as cutting speed, feed, depth of cut, rake angle, and tool nose radius to control the residual stresses and dimensional instability within the acceptable tolerance band of the component. Prediction equations were developed for residual stress, dimensional instability, tool life, surface finish, and material removal rate. Predicted data were validated experimentally. This paper also presents the qualitative and quantitative data on dimensional instability with specific case studies of jet engine components, and it clearly illustrates the approach followed to develop a technique to control such detrimental effect. [S0742-4795(00)00901-7]
Three-Dimensional Sintering of Two-Component Metal Powders With Stationary and Moving Laser Beams
Authors: Zhang Yuwen , Faghri A. , Buckley C. W. , Bergman T. L.
Published: July 2002

Melting and resolidification of a mixture of two metal powders with significantly different melting points under irradiation of a stationary or a moving Gaussian laser beam were investigated numerically and experimentally. The liquid motion driven by capillary and gravity forces as well as the shrinkage of the powder bed caused by the overall density change were taken into account in the physical model. The liquid flow was formulated by using Darcy’s law, and the energy equation was given using a temperature transforming model. Prediction were compared with experimental results obtained with nickel braze and AISI 1018 steel powder. The effects of laser properties and the scanning velocity on the laser sintering process were also investigated. An empirical correlation that can be used to predict the cross-sectional area of the heat affected zone is proposed. [S0022-1481(00)70201-5]
Static Balancing of Spatial Parallel Platform Mechanisms—Revisited
Authors: Ebert-Uphoff Imme , Gosselin Cle´ment M. , Laliberte´ Thierry
Published: July 2002

This article discusses the development of statically balanced spatial parallel platform mechanisms. A mechanism is statically balanced if its potential energy is constant for all possible configurations. This property is very important for robotic manipulators with large payloads, since it means that the mechanism is statically stable for any configuration, i.e., zero actuator torques are required whenever the manipulator is at rest. Furthermore, only inertial forces and moments have to be sustained while the manipulator is moving. The application that motivates this research is the use of parallel platform manipulators as motion bases in commercial flight simulators, where the weight of the cockpit results in a large static load. We first present a class of spatial parallel platform mechanisms that is suitable for static balancing. The class of mechanisms considered is a generalization of the manipulator described by Streit (1991, “Spatial Manipulator and Six Degree of Freedom Platform Spring Equilibrator Theory,” in Second National Conference on Applied Mechanisms and Robotics, VIII.B, pp. 1-1–1-6). Then sufficient conditions on the kinematic parameters that guarantee static balancing are derived for this class. Finally a particular mechanism is studied in more detail to show the practicability of its design. [S1050-0472(00)01401-X]
Comparison of Torque Transmitting Shaft Connectivity Using a Trilobe Polygon Connection and an Involute Spline
Authors: Kahn-Jetter Zella L. , Hundertmark Eugene , Wright Suzanne
Published: July 2002

The results of a finite element analysis of a trilobe polygon shaft connection used as an alternative for a spline for torque transmission is presented. These results are compared to the results of a finite element analysis previously performed on an involute spline. It is shown that the tensile stress in the polygon shaft is significantly smaller than in the involute spline and is smaller than all the other stresses in both the shaft and the hub in the polygon connection. Furthermore, the magnitudes and distributions of the maximum principal compressive stress, the shear stress, and the Von Mises stress are nearly the same on the shaft and the hub. It appears that polygonal connections can be more advantageous than splined connections because of lower stresses and the lack of stress concentrations typical of splines. [S1050-0472(00)00601-2]
Flank Wear Estimation in Turning Through Wavelet Representation of Acoustic Emission Signals
Authors: Kamarthi S. V. , Kumara S. R. T. , Cohen P. H.
Published: July 2002

This paper investigates a flank wear estimation technique in turning through wavelet representation of acoustic emission (AE) signals. It is known that the power spectral density of AE signals in turning is sensitive to gradually increasing flank wear. In previous methods, the power spectral density of AE signals is computed from Fourier transform based techniques. To overcome some of the limitations associated with the Fourier representation of AE signals for flank wear estimation, wavelet representation of AE signals is investigated. This investigation is motivated by the superiority of the wavelet transform over the Fourier transform in analyzing rapidly changing signals such as AE, in which high frequency components are to be studied with sharper time resolution than low frequency components. The effectiveness of the wavelet representation of AE signals for flank wear estimation is investigated by conducting a set of turning experiments on AISI 6150 steel workpiece and K68 (C2) grade uncoated carbide inserts. In these experiments, flank wear is monitored through AE signals. A recurrent neural network of simple architecture is used to relate AE features to flank wear. Using this technique, accurate flank wear estimation results are obtained for the operating conditions that are within in the range of those used during neural network training. These results compared to those of Fourier transform representation are much superior. These findings indicate that the wavelet representation of AE signals is more effective in extracting the AE features sensitive to gradually increasing flank wear than the Fourier representation. [S1087-1357(00)71401-8]
A New Sequence Evolution Approach to Assembly Planning
Authors: Fujimoto H. , Sebaaly M. F.
Published: July 2002

Assembly planning is the problem of finding the best or optimal sequence to assemble a product, starting from its design data. It is still solved manually in most advanced assembly plants, despite the large amount of related research. One of the main reasons might be the use of exact- and/or linear-solution approaches. This paper introduces a different approach by applying a modified genetic algorithm (GA). A “best” solution is generated without searching the complete candidate space, while search is performed on a sequence population basis. The GA is modified to cope with sequence nonlinearity and constraints. [S1087-1357(00)70401-1]
Flow Characteristics of a Powder Lubricant Sheared Between Parallel Plates
Authors: Zhou Lei , Khonsari M. M.
Published: July 2002

This paper is devoted to the understanding of the flow characteristics of a powder lubricant. An accurate and realistic model is introduced to investigate the mechanism of powder lubrication sheared between two infinitely wide parallel plates. In this theory, the solid volume fraction, v, together with flow velocity and granular temperature are directly obtained from a set of complete governing equations (mass, momentum and pseudo-energy conservation equations). The boundary conditions take into account the effect of slip velocity and the wall surface roughness. A set of parametric simulation results is presented. It is shown that viscous dissipation plays an important role in the pseudo-energy equation. [S0742-4787(00)01901-9]
Vapor-Deposited Polythiophene by XPS
Authors: Dillingham T. R. , Cornelison D. M. , Townsend S. W.
Published: July 2002

High quality polythiophene films have been grown using a vapor-deposition process using polythiophene powder as the starting material. The powder was placed in an open quartz crucible (housed in a tungsten basket) and heated by running a high current (10–20 A) through it. The evaporated material was deposited onto a glass substrate placed roughly 3 cm above the crucible. The as-deposited, undoped polythiophene film has been characterized using x-ray photoelectron spectroscopy and is contrasted with the initial polythiophene powder. The reported spectra include survey and high resolution scans for the major photoelectron peaks. It is noted that these results compare favorably with previously published spectra from polythiophene grown using the more conventional chemical or electrochemical methods.
Electrical Properties and Superconductivity of Rhenium and Molybdenum Films
Authors: Frieberthauser P. E. , Notarys H. A.
Published: July 2002

Electrical and superconducting properties of rhenium and molybdenum films prepared by electron beam evaporation have been measured as a function of substrate temperature, film thickness, and substrate material. The films were prepared at residual pressures of 5×10−8 Torr. In addition, films of each material were prepared by reactive deposition at nitrogen pressures in the 10−5 Torr range. Rhenium films prepared at low residual pressures exhibited superconductivity with onset temperatures from 2.5–4.9 K depending on thickness and substrate temperature. However, rhenium films prepared by reactive deposition in nitrogen had onset temperatures from 4.6–5.5 K. Transition temperatures from 3.3–3.8 K were observed in molybdenum films at thicknesses greater than 6000 Å when deposited at substrate temperatures of 600 °C. Crystal structure and preferred orientation were determined by x-ray diffraction methods.
Standards and Vacuum Measurement Accuracy
Authors: Ruthberg Stanley
Published: July 2002

Present capabilities for precision and accuracy are compared with the needs at the working level. A measurements structure is sketched by which reference standards accuracies are propagated. Uncertainties are prescribed for a number of prevalent measurement methods including precision U-tube manometer, McLeod gauge, volumetric pressure division, and dynamic expansion. The development at the National Bureau of Standards of direct absolute measurements standards of high precision and their use in dynamic environments stabilized to better than one part in 103 and ranging from the medium to the ultrahigh vacuum are described. These methods include precision liquid columns for the upper pressure range, interferometer manometer and modified McLeod gauges for the high vacuum range, and a torsion microbalance or Vane gauge for the ultrahigh vacuum range.
The Temperature Difference between a Sample and Its Surrounding Liquid Nitrogen Bath
Authors: Fuller O. M. , Ternan M.
Published: July 2002

A vacuum microbalance was used to measure nitrogen gas adsorption on solids. The hangdown tube containing the solid sample was immersed in a liquid nitrogen constant temperature bath. By making modifications to the hangdown tube configuration, it was possible to reduce the temperature difference between the sample and the bath to less than 0.01 K. Adsorption and desorption experiments were performed using a sample having pore radii of 2500 Å. The results show that, contrary to a previous report, the microbalance adsorption technique can be used to study capillary condensation in large radius pores.
Freeze Drying: A Unique Approach to the Synthesis of Ultrafine Powders
Authors: Roehrig F. K. , Wright T. R.
Published: July 2002

The freeze-dry process and its application in the general area of inorganic materials synthesis will be discussed. Details of the process will be given as well as its capabilities for producing ultrafine powders such as Pb–10 v/o MgO, WC, and W2C, ultrafine grained consolidated materials such as W–25 Re will be shown. Also, the application of the process for producing dispersion-strengthened systems such as Cu–ThO2 and Cu–W will be discussed.
Lasers for the Cleaning of Statuary: Initial Results and Potentialities
Authors: Lazzarini L. , Marchesini L. , Asmus J. F.
Published: July 2002

Cleaning is one of the most difficult operations encountered in the restoration of statuary. The fact that known cleaning methods are not entirely satisfactory has stimulated continuing research into new methods and processes. A novel method is proposed for cleaning superficial black scabs or patinas from works of art in marble or other stone by means of laser radiation. Surface cleaning results with a ruby laser are reported and compared with conventional techniques. Preliminary analyses of the laser process are quite favorable and indicate improved selectivity and graduation, self-limiting encrustation removal, and remarkably rapid surface coverage. Finally, the results of cleaning tests with various laser types are presented and discussed, and possible future developments and pratical applications of this new method of cleaning statuary are presented.
Design and operation of scroll-type dry primary vacuum pumps
Authors: Liepert A. , Lessard P.
Published: July 2002

Since being rediscovered three decades ago, scroll technology has been successfully adapted to vacuum use. Several innovations have allowed scroll-type pumps to produce vacuums lower than 10 mTorr; the pumps are used in many applications requiring an inexpensive, dry, long-lived pump. In this article, we detail the scroll design procedure, focusing on the trade offs between the need for sufficient vacuum and low manufacturing cost. As an illustrative example, we consider the design requirements for a high helium compression scroll design for use in leak detectors. We also present guidelines for proper pump operation, including the need for gas ballasting, high-water operation, and proper pump isolation schemes.
Field emitters for space application
Authors: Huq S. E. , Kent B. J. , Stevens R. , Lawes R. A. , Xu N. S. , She J. C.
Published: July 2002

We report on the development of a miniature ion trap mass spectrometer to be deployed on European Space Agency’s Rosetta Mission [Rosetta Comet Rendezvous Mission, ESA publication SC1(93)7 (1993)] to analyze the comet P46/Wirtanen. The mission is due to be launched in 2003 and following a long journey through space the comet rendezvous will take place in 2011 at a distance of approximately 465 million miles from earth. The instrument has been developed on a stringent space budget of <75 g in weight, 1 W maximum power consumption, and resolution down to <1 amu. Silicon field emitters have been successfully used as the electron source for producing ions by impact ionization. Mass spectra have been obtained for a number of gases at pressures in the region of 10−4 Torr.
Generation of a capacitively coupled microplasma and its application to the inner-wall modification of a poly(ethylene terephthalate) capillary
Authors: Yoshiki Hiroyuki , Oki Akio , Ogawa Hiroki , Horiike Yasuhiro
Published: July 2002

A parallel-plate capacitively coupled microplasma excited by a conventional operating frequency of 13.56 MHz has been generated both in a quartz tube with an inner radius of 1 or 2 mm and in a capillary, whose cross section is 65–500 μm×500–5000 μm, on a 20 mm×20 mm quartz chip. To attain a plasma ignition at a low rf power without reflection, a π-type matching circuit was miniaturized and suitably designed to satisfy the resonance condition with the excitation frequency, so that an atmospheric He discharge was obtained at an incident power of 1–3 W. The atomic excitation temperature in the atmospheric discharge was evaluated to be about 1900 K in terms of the atomic emission spectrum. Low-power (2–3 W) glow discharge of pure Ar was also attained at the pressure p given by (pd)min=0.5–0.8 Torr cm, where d is a discharge gap. The microplasma was applied to the inner-wall modification of a poly(ethylene terephthalate) (PET) capillary to demonstrate the electro-osmosis flow (EOF) control on a microcapillary electrophoresis (CE) chip. We found that the mobility of the EOF (μEOF) of the PET capillary treated by the downstream O2 plasma was 5.1×10−4 cm2/V s, which is about three times larger than that of the untreated PET capillary.
Chiral pattern formation: Combined transmission electron microscopy and atomic force microscopy study of tetracyanoquinodimethane thin film grown by vacuum evaporation
Authors: Li J. C. , Liu W. M. , Xue Z. Q.
Published: July 2002

Quasi-two-dimensional chiral patterns have been successfully obtained in the growth of tetracyanoquinodimethane (TCNQ) thin films by vacuum thermal evaporation. The influences of electrostatic effects, substrate temperatures, and other growth factors were discussed based upon experimental studies. It was shown that, contrary to previous reports, charged particles were not essential for chiral pattern formation. By a combined transmission electron microscopy and atomic force microscopy study, we found that chiral pattern growth is strongly related to a special “rod-like” growth property of TCNQ thin films. A simple growth model was thus briefly proposed, without involving any trapped electrostatic charges on the growing island.
Optical characterization of strained InGaAsN/GaAs multiple quantum wells
Authors: Héroux J. B. , Yang X. , Wang W. I.
Published: July 2002

Low-temperature transmittance and room-temperature photoreflectance spectra are presented for a series of InxGa1−xAs1−yNy/GaAs (x≈15%) strained-layer multiple quantum well structures grown by molecular-beam epitaxy with a nitrogen concentration ranging from 0% to 1.7%. Nitrogen incorporation causes an increase of the conduction band offset and effective mass. Moreover, the variation of the valence band alignment can be explained by the lowered compressive strain in the wells; the unstrained valence band offset remains constant. Results are described using the formalism of the band anticrossing model.
SIMS and EID observations of propane adsorbed on aluminum
Authors: Dawson P. H.
Published: July 2002

The slow adsorption of propane on aluminum has been observed using SIMS. The adsorbed hydrocarbon species give rise to a characteristic ’’cracking pattern’’ in the mass spectrum. The main ion peaks resulting are C3H8 +, C3H7 +, C3H5 +, C3H3 +, C2H5 +, and CH3 +. The hydrocarbon ions have very low energies. Electron-induced desorption of hydrocarbon ions was also observed, but in this case the cross sections for ionic desorption were very small.
Characterization of anodic barrier films on tantalum and 1100 aluminum by ISS/SIMS
Authors: McCune R. C.
Published: July 2002

Ion scattering spectrometry (ISS) and concurrent secondary ion mass spectrometry (SIMS) were used to determine the depth profiles of anodic barrier oxide films grown on tantalum and type 1100 aluminum. The sputter rate in each case was determined from the film thickness measured by the anodic overvoltage, and the penetration time determined by the decrease in intensity of the metal oxide fragment observed using SIMS. A mixture of helium and neon ions was used to sputter aluminum oxide films in order to observe ion scattering of helium by oxygen, while taking advantage of the higher sputtering rate available with neon. A comparison of sputter rates for helium and neon on tantalum oxide indicated that neon sputtered the film at a rate eight times that of helium. SIMS depth profiling of the residual boron in the anodic aluminum oxide indicated a mixing effect which did not permit adequate resolution of the interface between the oxide film and the underlying metal.
Surface studies during molecular beam epitaxy of gallium arsenide
Authors: Ploog Klaus
Published: July 2002

Molecular beam epitaxy (MBE) has emerged as a practical growth technique from surface studies of the interactions of thermal molecular beams with solid surfaces under UHV conditions. From this origin, a number of surface analytical techniques have been applied in situ to assure that the desired conditions have been reached before and are being maintained during the crystal growth. The incorporation into the growth apparatus of surface diagnostic techniques, such as Auger electron spectroscopy (AES), reflection high energy electron diffraction (RHEED), and secondary ion mass spectroscopy (SIMS), is contributing important details on fundamental processes, which lead to the growth of high-quality monocrystalline GaAs films by MBE. The formation of reconstructed surface structures on GaAs(100) as a function of growth parameters were observed during growth by RHEED. AES has been used, for example, to determine the relative Ga/As ratios for different reconstructed surface structures, to investigate the impurity contamination on substrate surfaces, and to study the surface segregation of Sn in MBE GaAs during doping. Finally, impurities incorporated during the growth of GaAs by MBE may be detected by SIMS immediately after growth and within the reaction chamber. The MBE technique has also enabled us to alter the surface composition in a well-defined and reproducible manner and has been used to prepare flat, well-ordered clean surfaces, which are essential for surface experiments. Experiments suitable in the MBE apparatus include low energy electron diffraction (LEED), low energy electron loss spectroscopy (LEELS), photoelectron spectroscopy (UPS and XPS), and Raman scattering.
The statistical theory of turbomolecular pumps
Authors: Chu J. G. , Hua Z. Y.
Published: July 2002

The working principle of a modern turbomolecular pump is analyzed from the point of view of statistical mechanics. The pumping action is mainly due to the collision probabilities of the gas molecules with the upper and lower blade surfaces caused by the high-speed relative motion between the rotating blades and the gas molecules. In turbomolecular pumps the molecular drag action only serves as an approximate mathematical description when the rotating speed of the blades is not very high, and both the pumping speed and the compression ratio will saturate as the blade speed approaches the average thermal velocity of the gas molecules, i.e., they cannot increase limitlessly with increasing blade speed as suggested by the molecular drag principle. Finally, the compression ratio of a multistage pump with blades of finite lengths under different rotating speeds are calculated and compared with the experimental results.
Hydrogen-related memory traps in thin silicon nitride films
Authors: Kapoor Vikram J. , Bailey Robert S. , Stein Herman J.
Published: July 2002

The internal photoelectric-effect technique in combination with multiple internal reflection measurements has been used for quantitative measurement of impurities and defect-related traps in the thin Si3N4 insulating film of a metal–nitride–oxide–semiconductor device, and their correlation with film processing conditions. The hydrogen content in the film showed an increase of approximately 3% for a decrease of deposition temperatures from 950 to 700 °C and corresponding increase in trapped electron density from 0.55×1018 to 2.0×1018 cm3. The multiple internal reflection measurements indicated that the variation in the hydrogen content in the Si3N4 film was predominantly related to a variation in hydrogen-to-silicon bonding while the hydrogen bonded to nitrogen was relatively constant. The results suggest that hydrogen, in addition to excess silicon, and perhaps other structural defects, plays a role in determining trapped electron densities in silicon nitride.
Direct-current-magnetron deposition of molybdenum and tungsten with rf-substrate bias
Authors: Bensaoula A. , Wolfe J. C. , Ignatiev A. , Fong F-O. , Leung T-S.
Published: July 2002

It has recently been shown that the stress of many refractory thin films deposited by dc-magnetron sputtering can be influenced by the sputtering pressure. Usually the transition from compressive to tensile stress is too sharp for pressure to be a reliable variable for stress control. This is particularly true in applications such as x-ray optics and lithography where extremely low stress is required owing to minimal substrate rigidity. In this paper, we show that there exists a broad region of the parameter space of current, pressure, and rf-substrate bias where tungsten and molybdenum may be deposited with low stress. A detailed study of the effects of these parameters upon stress, plasma etch rate, and resistivity is reported.
TiN coating adhesion studies using the scratch test method
Authors: Valli J. , Mäkelä U. , Matthews A. , Murawa V.
Published: July 2002

The development of the scratch test method of adhesion assessment is reported. The tangential friction force between the indenter and coating is recorded rather than the acoustic emission which has previously been used to detect the critical load. This method is shown to provide a sensitive and simple means of condition monitoring. Results obtained with this new technique are compared to those obtained by the authors and others using the conventional system, showing that good agreement is achieved. The results of tests on a number of substrate/interface/pretreatment combinations are reported. The implications of the method are discussed especially with regard to the influence of friction on adhesion.
Aluminum etching in boron tribromide plasmas
Authors: Keaton A. Landauer , Hess D. W.
Published: July 2002

Aluminum etching in BBr3 plasmas was characterized by studying the etch rates of aluminum and native aluminum oxide films as functions of electrode temperature, reactant flow rate, and rf power in a parallel plate plasma etcher. For comparison, BCl3 etch data were also determined. Reproducible, controllable, residue-free aluminum etching in BBr3 plasmas was achieved with aluminum etch rates of 1.5 nm/s at 40 °C and 0.31 W/cm2. The most significant difference between BBr3 and BCl3 etchants was the temperature dependence of the native oxide etch rate. For BBr3 on anodized aluminum electrodes, the apparent activation energy was 0.08 eV/molecule, a factor of ∼4 higher than in BCl3; this difference was attributed to different rate-controlling steps in the reaction sequence. The activation energy for aluminum etching was 0.01 eV/molecule, essentially the same as that obtained for BCl3 plasmas.
Thermal dry process soldering
Authors: Moskowitz P. A. , Yeh H. L. , Ray S. K.
Published: July 2002

The use of nonflammable and nontoxic gases CF4, CF2Cl2, and SF6 for the reflow and bonding of Pb/Sn solder has been demonstrated. It has been found that a concentration of these gases on the order of 1%–5% in a 760 Torr atmosphere of nitrogen or argon is sufficient for soldering.
Ion–molecule reactions in a direct current silane glow discharge
Authors: Weakliem H. A. , Estes R. D. , Longeway P. A.
Published: July 2002

We have measured the composition distribution of positive silane ions in a dc silane glow discharge as a function of pressure, flow, and cathode-to-anode separation. The ions were sampled through the anode and were analyzed by a mass spectrometer. When the sampling aperture is close to the negative glow, the monosilane ions are dominant, whereas when the aperture is moved further from the negative glow, successively larger ions are found to dominate. The physical properties of the amorphous silicon films which are deposited on the anode also depend on the distance to the cathode. Correlations between the properties of the films and the ionic composition of the plasma have been made and we have discussed the implications of these results with regard to the mechanism by which the solid film is formed from gaseous species.
Application of glow discharge mass spectrometry and sputtered neutral mass spectrometry to materials characterization
Authors: Chu Paul K. , Huneke John C. , Blattner Richard J.
Published: July 2002

Postsputtering ionization using an inert gas plasma to decouple the sputtering and ionization processes minimizes matrix effects commonly associated with conventional secondary ion mass spectrometry. Glow discharge mass spectrometry (GDMS) utilizes ions generated in a dc inert gas plasma to sputter atoms into the ambient plasma from the surface of a cathode composed of the material to be studied. The sputtered atoms, predominantly neutral, are then ionized in the plasma by Penning and electron impact ionization. GDMS provides excellent sensitivity and signal stability, and has found wide uses for characterization of bulk materials such as metals and GaAs. The sensitivity and large sampling volume also make it ideal for determining nonuniform trace contaminants in materials, e.g., U and Th in metals. Sputtered neutral mass spectrometry uses either low-energy plasma ions (direct bombardment mode or DBM) or an independent focused ion beam (separate bombardment mode or SBM) to sputter atoms into a low-pressure high-frequency plasma for electron impact ionization. DBM offers better depth resolution than conventional surface analytical techniques and is ideal for thin-film studies. The plasma electrons compensate for sample charging in SBM and make this method ideal for the analysis of insulating material such as phosphosilicate glass.
Sputter profiling of passive films in Fe–Cr alloys: A quantitative approach by Auger electron spectroscopy
Authors: Lorang G. , Da Cunha Belo M. , Langeron J. P.
Published: July 2002

The study deals with Auger electron spectroscopy depth profiling of passive films grown on Fe–Cr and Fe–Cr–Mo alloys. Sputter profiles are shown to follow exponential laws related in passive overlayers with the kinetic energy of Auger electrons (inelastic mean-free-path effect). For Cr and Fe LMV transitions, profiles can be decomposed in the interface region in two contributions produced, respectively, by the oxidized species of the film and by the metallic elements ‘‘seen’’ from the alloy substrate throughout this thin passive film (< 4 nm). The method provides an internal estimate of the sputter rate in oxide layers. With a previous calibration of Auger intensities in pure oxides and alloys, a quantitative depth distribution of oxidized elements is proposed assuming a layer-by-layer etching model.