bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison study of the convergence characteristics and robustness for four variants of SIMPLE‐family at fine grids
Authors: Zeng M. , Tao W.Q.
Published: March 2003

A comparative study is performed to reveal the convergence characteristics and the robustness of four variants in the semi‐implicit method for pressure‐linked equations (SIMPLE)‐family: SIMPLE, SIMPLE revised (SIMPLER), SIMPLE consistent (SIMPLEC), and SIMPLE extrapolation (SIMPLEX). The focus is concentrated in the solution at fine grid system. Four typical fluid flow and heat transfer problems are taken as the numerical examples (lid‐driven cavity flow, flow in an axisymmetric sudden expansion, flow in an annulus with inner surface rotating and the natural convection in a square enclosure). It is found that an appropriate convergence condition should include both mass conservation and momentum conservation requirements. For the four problems computed, the SIMPLEX always requires the largest computational time, the SIMPLER comes the next, and the computational time of SIMPLE and SIMPLEC are the least. As far as the robustness is concerned, the SIMPLE algorithm is the worst, the SIMPLER comes the next and the robustness of SIMPLEX and SIMPLEC are superior to the others. The SIMPLEC algorithm is then recommended, especially for the computation at a fine grid system. Brief discussion is provided to further reveal the reasons which may account for the difference of the four algorithms.
Soldermask laser direct imaging – an enabling technology
Authors: Albin David , Barclay Brewster
Published: March 2003

The use of laser direct imaging (LDI) processing for outer layer circuit pattern generation and the benefits already obtained with this process have encouraged attention to be focussed on the possibility of using laser direct imaging soldermask (LDISM) in the secondary imaging stage of printed circuit board (PCB) fabrication. As feature sizes on advanced interconnects have continued to diminish and the accompanying spacing between circuit features decreases, the requirement for accurately placing and scaling solder dams and apertures has become more critical in order to ensure that a high yield of finished product can be obtained. Consequently the traditional process of creating photographic artworks for soldermask exposure is rapidly becoming a crucial step that can have significant yield implications due to both environmental conditions and registration issues. The use of LDISMs in combination with specially developed LDI exposure systems is an enabling technology which can offer the benefits of a “standard” mask application process and the positional accuracy and individual image scaling required for guaranteeing improved yields for high density interconnect (HDI) panels.
Recycling technologies for the treatment of end of life printed circuit boards (PCBs)
Authors: Goosey Martin , Kellner Rod
Published: March 2003

New legislation to encourage the recycling of end of life electronics and moves to implement sustainable development in electronics manufacturing have focussed attention on the large quantity of printed circuit boards (PCBs) being consigned to landfill. Also, in a recent investigation conducted on behalf of the UK's Department of Trade and Industry, the need for new methodologies for dealing with end of life circuit boards was identified as a priority issue. Within the UK it is estimated that ∼50,000 tonnes per annum of PCB scrap is currently generated and investigations indicate that only ∼15 per cent is subjected to any form of recycling, with the remainder consigned to landfill. This paper reports the results of a scoping study carried out to identify the technologies and processes that can be used to recycle materials from end of life PCBs.
A core value model for implementing total quality management in small organisations
Authors: Hansson Jonas , Klefsjö Bengt
Published: March 2003

Total quality management (TQM) has been recognised and used during the last decades by organisations all over the world to develop a quality focus and improve organisational performance. In spite of this, TQM implementation is still problematic for many organisations. In this perspective important factors to succeed with the organisational change that TQM implementation implies will be discussed in this paper. Also presented is a multiple‐case study of TQM implementation processes in small organisations with a focus on core value aspects. An overarching implementation model is presented based on the multiple‐case study analysis and the theoretical frame. This model implies that TQM implementation will start with core values committed leadership, everybody’s commitment and customer orientation.
Align your management processes for effectiveness
Authors: Sussland Willy A.
Published: March 2003

Waves of restructuring have left enterprises with a patchwork of processes, and ultimately in a strategic quandary. The ensuing misalignment of style, strategies, systems, and structures causes dysfunctions inside and outside the organization, and sub‐optimizes the effectiveness of the whole enterprise. To overcome such problems, the best‐in‐class have introduced a company‐wide framework. Having studied such management systems, the author has developed the “Process of management” that purposely connects the key management processes from the development of the strategies, to their implementation, and to the performance audit performed by management. This article sets out the advocated models and methods and shows how they help improve strategic and organizational effectiveness. The “Process of management” is strategy focused and action oriented.
Directors’ responsibilities and participation in the strategic decision making process
Authors: Scherrer Phillip S.
Published: March 2003

The purpose of the article is to discuss the role of the boards of directors in the corporate governance process. The article argues that directors need to be more actively involved in the strategic decision making process of the corporation. Passive directors and inside directors do not have the incentive to insure that corporate governance policies are followed. Prior cases were reviewed and current topical information is included. Current corporate governance issues are discussed. The lack of board involvement is addressed. The results of the research include litigation statistics and a comparison of “older versus new” corporations directors’ involvement in the strategic decision making process. The article concludes that directors need to be actively involved in the affairs of their corporations to insure corporate governance compliance. The article recommends that corporations have a majority of outside directors that do not have conflicts of interest and who are involved in the corporation.
Three-Dimensional Heat Transfer of a Confined Circular Impinging Jet With Buoyancy Effects
Authors: Ichimiya Koichi , Yamada Yoshio
Published: March 2003

This paper describes the heat transfer and flow characteristics of a single circular laminar impinging jet including buoyancy force in a comparatively narrow space with a confined wall. Temperature distribution and velocity vectors in the space were obtained numerically by solving three-dimensional governing equations for the Reynolds number Re=umD/ν=400-2000 and the dimensionless space, H=h/D=0.25-1.0. After impingement, heat transfer behavior on the impingement surface is divided into a forced convection region, a mixed convection region, and a natural convection region in the radial direction. The local heat flux corresponding to these three regions was visualized using a thermosensitive liquid crystal. Moreover, with the increase in Reynolds number, Re, and dimensionless space, H, the recirculation flow on the impingement surface moves downstream and its volume increases correspondingly. The Nusselt number averaged from r=0 to the minimum point of peripherally averaged Nusselt number, Num, was evaluated as a function of Re and H.
The Effect of Dissolving Salts in Water Sprays Used for Quenching a Hot Surface: Part 2—Spray Cooling
Authors: Cui Qiang , Chandra Sanjeev , McCahan Susan
Published: March 2003

The effect of adding one of three salts (NaCl, Na2SO4 or MgSO4) to water sprayed on a hot surface was studied experimentally. A copper test surface was heated to 240°C and quenched with a water spray. The variation of surface temperature during cooling was recorded, and the surface heat flux calculated from these measurements. Surface heat flux during cooling with pure water sprays was compared with that obtained using salt solutions. Dissolved NaCl or Na2SO4 increased nucleate boiling heat transfer, but had little effect on transition boiling during spray cooling. MgSO4 increased both nucleate and transition boiling heat flux. Enhanced nucleate boiling was attributed to foaming in the liquid film generated by the dissolved salts. MgSO4 produced the largest increase in nucleate boiling heat transfer, Na2SO4 somewhat less and NaCl the least. A concentration of 0.2 mol/l of MgSO4 produced the greatest heat flux enhancement; higher salt concentrations did not result in further improvements. During transition boiling particles of MgSO4 adhered to the heated surface, raising surface roughness and increasing heat transfer. Addition of MgSO4 reduced the time required to cool a hot surface from 240°C to 120°C by an order of magnitude.
Exact Solution of the Navier-Stokes Equations for the Fully Developed, Pulsating Flow in a Rectangular Duct With a Constant Cross-Sectional Velocity1
Authors: Tsangaris S. , Vlachakis N. W.
Published: March 2003

The Navier-Stokes equations have been solved in order to obtain an analytical solution of the fully developed laminar flow in a duct having a rectangular cross section with two opposite equally porous walls. We obtained solutions both for the case of steady flow as well as for the case of oscillating pressure gradient flow. The pulsating flow is obtained by the superposition of the steady and oscillating pressure gradient solutions. The solution has applications for blood flow in fiber membranes used for the artificial kidney.
Hydrodynamic Force and Heat/Mass Transfer From Particles, Bubbles, and Drops—The Freeman Scholar Lecture
Authors: Michaelides Efstathios E.
Published: March 2003

Recent advances on the analytical form of the hydrodynamic force and heat/mass transfer from a particle, bubble, or drop are examined critically. Also some of the recent computational studies, which help strengthen or clarify our knowledge of the complex velocity and temperature fields associated with the momentum and heat/mass transfer processes are also mentioned in a succinct way. Whenever possible, the processes of energy/mass exchange and of momentum exchange from spheres and spheroids are examined simultaneously and any common results and possible analogies between these processes are pointed out. This approach results in a better comprehension of the transport processes, which are very similar in nature, as well as in the better understanding of the theoretical expressions that are currently used to model these processes. Of the various terms that appear in the transient equations, emphasis is given to the history terms, which are lesser known and more difficult to calculate. The origin, form, and method of computation of the history terms are pointed out as well as the effects of various parameters on them. Among the other topics examined here are the differences in the governing and derived equations resulting by finite Reynolds and Peclet numbers; the origin, theoretical validity and accuracy of the semi-empirical expressions; the effects of finite internal viscosity and conductivity of the sphere; the effects of small departures from the spherical shape; the effects of the finite concentration; and the transverse, or lift, components of the force on the sphere.
Simulation of Swirling Gas-Particle Flows Using Different Time Scales for the Closure of Two-Phase Velocity Correlation in the Second-Order Moment Two-Phase Turbulence Model1
Authors: Yu Y. , Zhou L. X. , Zheng C. G. , Liu Z. H.
Published: March 2003

Three different time scales—the gas turbulence integral time scale, the particle relaxation time, and the eddy interaction time—are used for closing the dissipation term in the transport equation of two-phase velocity correlation of the second-order moment two-phase turbulence model. The mass-weighted averaged second-order moment (MSM) model is used to simulate swirling turbulent gas-particle flows with a swirl number of 0.47. The prediction results are compared with the PDPA measurement results taking from references. Good agreement is obtained between the predicted and measured particle axial and tangential time-averaged velocities. There is some discrepancy between the predicted and measured particle axial and tangential fluctuation velocities. The results indicate that the time scale has an important effect. It is found that the predictions using the eddy interaction time scale give the right tendency—for example, the particle tangential fluctuation velocity is smaller than the gas tangential fluctuation velocity, as that given by the PDPA measurements.
Analytic Formulation of Reciprocal Screws and Its Application to Nonredundant Robot Manipulators
Authors: Kim Doik , Chung Wan Kyun
Published: March 2003

One of the most important and widely used concepts in the kinematic analysis of robot manipulators is the reciprocal screw. However, there are no general expressions and easy methods to obtain the reciprocal screw in an analytic manner. This paper suggests an analytic formulation of the reciprocal screws of arbitrarily aligned screw systems. Since the reciprocal screws obtained in this paper are represented by the direction vectors and the position vectors of the given screws, we can analyze the relation between the reciprocal screw system and the given screw system easily. With the results, to find a reciprocal screw is to solve an algebraic equation of the corresponding system of screws. In order to show the usefulness of the result, several examples related to the robot manipulator are provided. For a nonredundant serial manipulator, the pseudo inverse of the Jacobian matrix is shown to be equivalent to the wrench matrix obtained by the reciprocity. For a parallel manipulator, a leg is isolated to obtain an independent part from the manipulator and is analyzed analytically. The proposed method can be applied to any arbitrarily aligned screw system.
Dynamic Analysis of Impact Tools by Using a Method Based on Stress Wave Propagation and Impulse-Momentum Principle
Authors: Elı´as Dante A. , Chiang Luciano E.
Published: March 2003

We present a numerical method derived from the Impulse-Linear Momentum Principle that can be used in the design of impact tools for rock drilling. This method allows the prediction of energy transmission to rock, the profiles of stress, displacement and velocity, all of which are important in the dynamic analysis of such tools. Using the Impulse-Linear Momentum Principle in an algorithmic manner, multibody interaction is simplified, and also different load and boundary conditions such as external forces, initial strains, and initial body separations can be directly considered. The accuracy of the method has been contrasted theoretically with both one-dimensional and three-dimensional FEM analysis, as well as experimentally.
Comparison of Semi-Empirical Correlations and a Navier-Stokes Method for the Overall Performance Assessment of Turbine Cascades
Authors: Cravero C. , Satta A.
Published: March 2003

Turbomachinery flows can nowadays be investigated using several numerical techniques to solve the full set of Navier-Stokes equations; nevertheless the accuracy in the computation of losses is still a challenging topic. The paper describes a time-marching method developed by the authors for the integration of the Reynolds averaged Navier-Stokes equations in turbomachinery cascades. The attention is focused on turbine sections and the computed aerodynamic performances (outlet flow angle, profile loss, etc.,) are compared to experimental data and/or correlations. The need for this kind of CFD analysis tools is stressed for the substitution of standard correlations when a new blade is designed.
Modeling and Qualitative Experiments on Swirling Bubbly Flows: Single Bubble With Rossby Number of Order 1
Authors: Magaud F. , Najafi A. F. , Angilella J. R. , Souhar M.
Published: March 2003

The behavior of an isolated bubble in a single-phase swirling flow is investigated theoretically and experimentally. The Rossby number is such that the liquid flow can be approximated by a solid-body rotation superposed to a uniform axial velocity. The equations of the motion of the bubble are solved analytically and numerically, by assuming that the bubble is small and does not modify the water flow. Two kinds of bubbles have been considered: clean bubbles and bubbles with a contaminated interface. In the latter case the bubble is treated as a solid sphere. In both cases a critical angular velocity ωc for the rotating device is found. When ω<ωc the trajectory of the bubble is a conical spiral which converges to the pipe axis, and when ω>ωc the trajectory is a cosine conical spiral: the bubble migrates to the center in an oscillating manner. The numerical value of ωc, together with the terminal velocity of the bubble, are found to be in good agreement with experimental observations, provided the bubble is treated as a solid sphere.
Distributed Object-Based Modeling in Design Simulation Marketplace
Authors: Senin Nicola , Wallace David R. , Borland Nicolas
Published: March 2003

Predictive integrated system modeling is now a pressing issue in the design of complex products ranging from home air conditioners to automobiles and aircraft. While product development organizations have official top-down development processes, it is generally understood that in practice individual participants perform their work in an informal marketplace, bartering service exchange relationships to get what they need to resolve their part of the problem. The authors envision a distributed simulation service marketplace running in parallel with the activities of design participants. This paper develops an object model representation to enable this vision for a decentralized design simulation marketplace. A prototype implementation, called DOME (Distributed Object-based Modeling Environment), is used to illustrate the concept on a beverage container design problem.
Force Equilibrium Approach for Linearization of Constrained Mechanical System Dynamics
Authors: Kang Ju Seok , Bae Sangwoo , Lee Jang Moo , Tak Tae Oh
Published: March 2003

The purpose of this study is to derive a linearized form of dynamic equations for constrained mechanical systems. The governing equations for constrained mechanical systems are generally expressed in terms of Differential-Algebraic Equations (DAEs). Conventional methods of linearization are based on the perturbation of the nonlinear DAE, where small amounts of perturbations are taken to guarantee linear characteristics of the equations. On the other hand, the proposed linearized dynamic equations are derived directly from a force equilibrium condition, not from the DAEs, with small motion assumption. This approach is straightforward and simple compared to conventional perturbation methods, and can be applicable to any constrained mechanical systems that undergo small displacement under external forces. The modeling procedure and formulation of linearized dynamic equations are demonstrated by the example of a vehicle suspension system, a typical constrained multibody system. The solution is validated by comparison with conventional nonlinear dynamic analysis and modal test results.
Active Balancing of a Flexible Linkage With Redundant Drives
Authors: Yu Yue-Qing , Lin Jing
Published: March 2003

The dynamic balancing of flexible linkages, which is a challenging topic in the dynamics of mechanisms, is accomplished by active control with redundant drives for the first time in the present study. The mathematical modal and dynamic equations of flexible mechanisms with redundant actuators are derived. The optimum shaking force and shaking moment balancing of a flexible linkage have been obtained through an active way of additional actuators. The effectiveness and advantage of redundant drives on the dynamic balancing of flexible mechanisms is fully demonstrated by an example of four-bar linkages.
Elastic Fields of Quantum Dots in Multilayered Semiconductors: A Novel Green’s Function Approach
Authors: Yang B. , Pan E.
Published: March 2003

We present an efficient and accurate continuum-mechanics approach to predict the elastic fields in multilayered semiconductors due to buried quantum dots (QDs). Our approach is based on a novel Green’s function solution in anisotropic and linearly elastic multilayers, derived within the framework of generalized Stroh formalism and Fourier transforms, in conjunction with the Betti’s reciprocal theorem. By using this approach, the induced elastic fields due to QDs with general misfit strains are expressed as a volume integral over the QDs domains. For QDs with uniform misfit strains, the volume integral involved is reduced to a surface integral over the QDs boundaries. Further, for QDs that can be modeled as point sources, the induced elastic fields are then derived as a sum of the point-force Green’s functions. In the last case, the solution of the QD-induced elastic field is analytical, involving no numerical integration, except for the evaluation of the Green’s functions. As numerical examples, we have studied a multilayered semiconductor system of QDs made of alternating GaAs-spacer and InAs-wetting layers on a GaAs substrate, plus a freshly deposited InAs-wetting layer on the top. The effects of vertical and horizontal arrays of QDs and of thickness of the top wetting layer on the QD-induced elastic fields are examined and some new features are observed that may be of interest to the designers of semiconductor QD superlattices.
Stabilization of Frictional Sliding by Normal Load Modulation
Authors: Cochard A. , Bureau L. , Baumberger T.
Published: March 2003

This paper presents the stability analysis of a system sliding at low velocities (<100 μm⋅s−1) under a periodically modulated normal load, preserving interfacial contact. Experiments clearly evidence that normal vibrations generally stabilize the system against stick-slip oscillations, at least for a modulation frequency much larger than the stick-slip one. The mechanical model of L. Bureau, T. Baumberger, and C. Caroli validated on the steady-state response of the system, is used to map its stability diagram. The model takes explicitly into account the finite shear stiffness of the load-bearing asperities, in addition to a classical state and rate-dependent friction force. The numerical results are in excellent quantitative agreement with the experimental data obtained from a multicontact frictional system between glassy polymer materials. Simulations at larger amplitude of modulation (typically 20 percent of the mean normal load) suggest that the nonlinear coupling between normal and sliding motion could have a destabilizing effect in restricted regions of the parameter space.
Mathematical Model and Simulation of a Thermal Diffusion Column
Authors: Vela´squez Juan E. , Chejne Farid , Hill Alan F. J.
Published: March 2003

A two-dimensional mathematical model, in stationary state was developed for the separation of species in a thermal diffusion column working with total reflux. The model was applied to a gas mixture of CO2 and N2. The existence of convective currents along the column was verified, the separation of species due to the temperature gradient was predicted and the effect of the thermal gradient and of the operation pressures on the composition profiles was analyzed.
Heat Transfer in Two-Pass Rotating Rectangular Channels (AR=2) With Five Different Orientations of 45 Deg V-Shaped Rib Turbulators
Authors: AL-Hadhrami Luai , Griffith Todd , Han Je-Chin
Published: March 2003

An experimental study was made to obtain heat transfer data for a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90 deg and 135 deg with respect to the plane of rotation). The V-shaped ribs are placed on the leading and trailing surfaces. Five different arrangements of 45 deg V-shaped ribs are studied. The Reynolds number and rotation number ranges are 5000–40000, and 0.0–0.21, respectively. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10; and the inlet coolant-to-wall density ratio (Δρ/ρ) is maintained around 0.115 for every test. The results show that the rotation-induced secondary flow enhances the heat transfer of the first pass trailing surface and second pass leading surface. However, the first pass leading and the second pass trailing surfaces show a decrease in heat transfer with rotation. The results also show that parallel 45 deg V-shaped rib arrangements produce better heat transfer augmentation than inverted 45 deg V-shaped ribs and crossed 45 deg V-shaped ribs, and a 90 deg channel orientation produces greater rotating effect on heat transfer than a 135 deg orientation.
Carrier spilling revisited: On-bevel junction behavior of different electrical depth profiling techniques
Authors: Clarysse T. , Eyben P. , Duhayon N. , Xu M. W. , Vandervorst W.
Published: March 2003

It is well known that the electrical junction depth position measured along a beveled surface, as is routinely done in the spreading resistance probe (SRP) technique, is shallower than the corresponding metallurgical junction as seen by secondary ion mass spectrometry. The amount of on bevel junction shift (i.e., the difference in electrical on bevel versus metallurgical junction depth) in SRP has previously been attributed to a combination of material removal during the beveling (i.e., one-dimensional zero-field Poisson model) and pressure enhanced carrier spilling (enhanced permittivity). Recently the interest in the application of two-dimensional electrical characterization techniques such as scanning capacitance microscopy, with virtually zero pressure, and scanning spreading resistance microscopy, with a much smaller contact, on beveled surfaces has emerged in order to meet the needed resolutions. The data from these techniques, however, indicate that our present understanding of the carrier-spilling phenomenon is incomplete. Based on a detailed intercomparison of the depth profiles on well-calibrated, junction isolated samples, the shapes of the calibration curves, current–voltage curves, and device simulations, an improved carrier spilling model is proposed that incorporates a uniform surface state density of 5×1012/eV/cm2, with a neutral (Fermi-pinning) level of 0.28 eV above mid-band gap.
Fabrication and characterization of silicon nanocrystals by thermal oxidation ofa-Si:H films in air
Authors: Kohli Sandeep , Theil Jeremy A. , Snyder Rick. D. , Rithner Christopher D. , Dorhout Peter K.
Published: March 2003

Hydrogenated amorphous silicon (a-Si:H) and Si–O–H heterogeneous thin films have been examined for their potential to photoluminesce. In this study, 50 nm a-Si:H films were deposited and oxidized to understand how film morphology affects their optical properties. Glancing angle x-ray diffraction (XRD), x-ray reflectivity, x-ray photoelectron spectroscopy, optical absorption spectroscopy in the wavelength range 250–1000 nm, and Fourier transform infrared measurements were used to complement room temperature photoluminescence (PL) studies. The results are discussed in light of the standard models for room temperature visible PL for a-SiOx:H films and silicon nanocrystals. The PL peak at 1.6 eV arises from silicon nanocrystals. Modeling this band to estimate the quantum dot size indicates that the mean silicon crystallite diameter is ∼5 nm, while XRD analysis gives ∼9±1 nm. The discrepancy in the estimation of crystallite size by the XRD method and PL analysis is attributed to the columnar growth of the silicon nanocrystals.
Analysis of the I–V characteristics of Al/4H-SiC Schottky diodes
Authors: Zhang Jingyan , Harrell William R.
Published: March 2003

The capability of silicon carbide in general to operate at high temperatures, and the fact that the electron mobility of the 4H-SiC polytype is twice that of the 6H polytype, has led to significant interest in 4H-SiC devices. Experimental data for Al/4H-SiC Schottky diodes is limited, and in this article we present forward and reverse I–V characteristics measured over a temperature range of 298–378 K. An analysis of the results shows that the charge transport mechanism is dominated by thermionic emission at forward biases less than 0.3 V, and series resistance at forward biases greater than 0.9 V. However, for a forward bias in the range of 0.3–0.9 V, we found the data fitted the space-charge-limited emission model. The competing mechanisms of thermionic emission and space-charge-limited emission lead to nonideal I–V characteristics, resulting in an increase in measured ideality factor. Space-charge-limited currents are dependent on the trap distribution in the material, and the estimated trap density is 4.4×1015 cm−3 eV−1. In the reverse direction, the I–V curves follow Bardeen’s model for metal–semiconductor contacts with an interfacial layer. Comparison with results published on 6H-SiC Schottky devices shows no significant differences, and our data falls within the spread found in the literature for all SiC results.
Growth and characterization of modulation-doped double barrier quantum well infrared photodetectors
Authors: Luna E. , Guzmán A. , Sánchez-Rojas J. L. , Tijero J. M. G. , Hey R. , Hernando J. , Muñoz E.
Published: March 2003

In this article, we report on the growth by molecular beam epitaxy of a series of modulation-doped AlGaAs/AlAs/GaAs structures designed to work as quantum well infrared photodetectors in the 3–5 μm transmission atmospheric window. Growth conditions based on particular aspects of the surface reconstructions observed in the constituent layers are used. The performance of the modulation doped samples is analyzed by a number of characterization techniques and compared with that of a detector with doping in the well and otherwise the same structure. Responsivity measurements performed at various bias voltages reveal a strong photovoltaic behavior of the detectors. The value of the zero volts responsivity and of the external voltage required to quench the photovoltaic signal are highly dependent on the doping profile. A controlled photovoltaic operation may then be achieved by a proper design of the dopant location.
Role of O(1D) in the oxidation of Si(100)
Authors: Kaspar Tiffany , Tuan Allan , Tonkyn Russell , Hess Wayne P. , Rogers J. W. , Ono Yoshi
Published: March 2003

Oxidation of silicon with neutral atomic oxygen species generated in a rare gas plasma has recently been shown to produce high-quality thin oxides. It has been speculated that atomic oxygen in the first excited state, O(1D), is a dominant reactive species in the oxidation mechanism. In this study, we investigate the role of O(1D) in silicon oxidation in the absence of other oxidizing species. The O(1D) is generated by laser-induced photodissociation of N2O at 193 nm. We find that, at 400 °C, O(1D) is effective in the initial stages of oxidation, but the oxide growth rate decreases dramatically past 1.5 nm. Oxide films thicker than 2 nm were not achieved regardless of oxidation time or N2O partial pressure (0.5–90 mTorr), indicating O(1D) cannot be a dominant reactive species in thicker rapid oxidation mechanisms. We suggest that quenching of O(1D) to O(3P) (ground state) during diffusion through thicker oxides results in drastically slower oxidation kinetics. In contrast, oxidation with a vacuum ultraviolet excimer lamp operating at 172 nm resulted in rapid oxide growth up to 4 nm. Thus, other species produced in plasmas and excimer lamps, such as molecular and atomic ions, photons, and free and conduction band electrons, likely play a dominant role in the rapid oxidation mechanism of thicker oxides (>2 nm).
Patterning SiO2 thin films using synchrotron radiation stimulated etching with a Co contact mask
Authors: Wang Changshun , Moré Sam Dylan , Wang Zhihong , Yamamura Shusaku , Nonogaki Yoichi , Urisu Tsuneo
Published: March 2003

Patterning SiO2 thin film on the Si(100) surface was successfully demonstrated using a synchrotron radiation (SR) stimulated etching technique with SF6 + O2 as the reaction gas and a Co contact mask. The etching stopped completely at the SiO2/Si(100) interface. After the complete removal of SiO2 by SR etching, the Si surface was flat (Ra = 0.1 nm) and a well-ordered self-assembled monolayer (SAM) of dodecene was deposited on the SR etched region area selectively. Co was found to show sufficient resistivity against the SR etching and to be easily removed by dilute (∼ 0.01 N) HNO3, without damaging the SAM. The SR etching of the SiO2 thin films on the Si surface with the Co contact mask was found to be a suitable patterning technique for the area-selective deposition of alkyl SAMs.
Investigation of basic imaging properties in digital radiography. 10. Structure mottle of II–TV digital imaging systems
Authors: Kume Yuichiro , Doi Kunio , Ohara Ken , Giger Maryellen Lissak
Published: March 2003

Single‐frame images obtained with image intensifier (II)–TV digital systems contain a large amount of structure mottle. In the present study, we examined several II–TV digital systems by use of Wiener spectral analysis and noted considerable variation of the structure mottle over the wide spatial frequency range. We found that the structure mottle in these systems may originate in the input phosphor, the output phosphor, and/or the electronic components, and that the Wiener spectra of structure mottle seem to depend on the specific combination of these components. The results of observer performance studies indicated that structure mottle can significantly decrease the detection of low‐contrast objects in a single‐frame image when the exposure incident on the II is greater than approximately 0.1 mR. In addition, we showed that the structure mottle can be removed by subtraction of a uniformly exposed mask. This simple procedure will improve the quality of radiologic images obtained with II–TV digital systems. Note, however, that the structure mottle is largely eliminated by subtraction in digital subtraction angiography (DSA) images.
Equivalent spectra as a measure of beam quality
Authors: Boone John M.
Published: March 2003

The concept of the equivalent spectrum (Seq) is introduced, where Seq is defined as an idealized energy spectrum which results in identical attenuation properties as the actual spectrum of a given x‐ray tube. Seq is described by two parameters, the equivalent aluminum filtration Aleq and the equivalent kilovoltage kVeq, which are evaluated iteratively using aluminum attenuation data. Published spectral data are used to demonstrate the merits of the equivalent spectrum technique, and experimental results are also presented. The technique is shown to be sensitive to changes in total filtration and, indirectly, to the waveform properties of the x‐ray system. The use of the Seq may result in a better description of spectral properties for reporting purposes, and aid in standardizing radiographic techniques within an institution.
Measurement of total‐body oxygen, nitrogen, and carbon in vivo by photon activation analysis
Authors: Ulin Kenneth , Zamenhof Robert G.
Published: March 2003

A method has been developed to measure total‐body oxygen, nitrogen, and carbon in vivo using the x‐ray beam of a 45‐MV betatron and a whole‐body counter. Following x‐ray irradiation of living tissue, the positron emitting activation products 15O, 11C, and 13N are produced. The decay of these radionuclides has been measured in both phantoms and animals, and a computer curve‐fitting algorithm used to resolve the decay curve into separate contributions from 15O, 11C, and 13N. The decay curve was corrected for interfering activity from 30P, 38K, and 34mCl, and in the case of live animals, also corrected for a substantial fraction of 11C lost through exhalation. Activation uniformity profiles have been measured for phantoms up to 30 cm in thickness. With a radiation dose of 20 cGy, total‐body O, N, and C were measured in dead rats with estimated accuracies of ±1.4%, ±4.5%, and ±1.5% [1 standard deviation (SD)], respectively. With a radiation dose of 40 cGy, total‐body O, N, and C were measured in living rats with estimated accuracies of ±1.4%, ±6.9%, and ±1.5% (1 SD), respectively. It is anticipated that total‐body O, N, and C similarly could be measured in human subjects with a radiation dose of 1–2 cGy and with accuracies comparable to those obtained in rats. Although most of the measurements were made using a beam energy of 45 MV, we have shown that useful results may be achievable with a beam energy as low as 25 MV. This accurate, convenient, and safe technique for total‐body O, C, and N measurement should have applications in the study of nutritional status in health and disease, both in human subjects and in animals.
Exposure and organ dose estimation in diagnostic radiology
Authors: McGuire E. Lynn , Dickson Paul A.
Published: March 2003

This paper discusses a methodology which uses a specially developed computer program that enables estimation of output parameters of an x‐ray machine from a single test exposure. Exposure at skin entrance values can be estimated, as well as using the data from the program for organ dose estimates. To perform the estimation procedure, curves and analytical expressions for the curves are presented for conversion of half‐value layers to total filtration and for conventional mR/mAs output curves. Results are given showing that the estimation procedure is reasonably accurate.
Accurate measurement of characteristic curves of II–TV digital systems by use of aluminum stepwedge technique
Authors: Fujita Hiroshi , Doi Kunio
Published: March 2003

In order to determine accurately the relative x‐ray intensities transmitted through the different steps of an aluminum stepwedge and incident on an image intensifier (II)–TV digital system, we used a 100‐mm camera which was attached to the II output. The characteristic curves of an II–TV digital system, which relate the output pixel value to the input relative x‐ray intensity, were determined at 65 and 90 kV by the use of the aluminum attenuation curves measured at the two energies. We found that the two curves agreed within the experimental errors; this result indicates that the characteristic curve does not depend on the x‐ray beam quality used. Furthermore, for accurate measurement of the characteristic curve, it is necessary to collimate the x‐ray beams to a narrow width, approximately 0.6×10 cm, so that the effect of veiling glare from the thinner to the thicker parts of the stepwedge is eliminated.
Effect of background correction on left ventricular ejection fraction calculation through analysis of a simple cardiac model
Authors: Grove D. E. , Stein R. A. , Nosil J.
Published: March 2003

The dependence of the left ventricular ejection fraction calculation on the background correction in gated cardiac blood pool studies is examined by analyzing a simple cardiac model. It is shown that the ejection fraction is relatively insensitive to the background correction when an accurately determined variable region of interest is used, but that with a fixed region of interest the background correction must be accurately estimated. A similar ejection fraction–background correction relationship is obtained in the analysis of clinical cardiac data. Based on the cardiac model, two methods are suggested which, with further investigation and refinement, may lead to a more accurate and consistent technique for determining ejection fraction and background.
Monte Carlo simulation of spectroscopic imaging data
Authors: Harpen Michael D.
Published: March 2003

Presented is a quantitative analysis of fat and water spectroscopic imaging. Nuclear magnetic resonance (NMR) signal decay curves obtained from conventional and spectroscopic imaging of a variety of fat and water samples in a phantom and of bone marrow, adipose tissue, and muscle from a clinical scan are analyzed to determine the transverse relaxation times and percent contribution to total signal of the fat and water fractions. The variance–covariance structure of parameter estimations obtained by the spectroscopic imaging technique is compared with those obtained by the conventional in‐phase imaging technique by means of a Monte Carlo simulation.
Determination of nominal accelerating potential
Authors: Nizin Paul , Kase Kenneth
Published: March 2003

We present a simple linear relationship between the nominal accelerating potential (NAP) and the ratios of ionization measurements made with constant source–detector distance and at two different phantom thicknesses. This relationship can be used as a standard, unambiguous method for determining NAP for use in dosimetry and quality control.
Validity of lung correction algorithms
Authors: Tang Walter L. , Khan Faiz M. , Gerbi Bruce J.
Published: March 2003

Our studies have compared the “effective tissue–air ratio (TAR) method” (ICRU Report No. 24), “equivalent TAR method,” and the “generalized Batho method” (currently used by the TP‐11 computer treatment planning system) with measured results for different energy photon beams using two lung inhomogeneities to simulate a lateral chest field. Significant differences on the order of 3%–15% were found when comparing these various methods with measured values.
Differences in electron depth‐dose curves calculated with EGS and ETRAN and improved energy‐range relationships
Authors: Rogers D. W. O. , Bielajew A. F.
Published: March 2003

For 1–50 MeV electrons incident on a water phantom there are systematic differences in the depth‐dose curves calculated by the Monte Carlo codes EGS and ETRAN (and its descendants SANDYL, CYLTRAN, ACCEPT, and the ITS system). Compared to ETRAN, the EGS code calculates a higher surface dose and a slightly slower dose falloff past the dose maximum. The discrepancy in the surface dose is shown to exist because the modified Landau energy‐loss straggling distribution used in ETRAN underestimates the mean energy loss by about 10% since it underestimates the number of large energy loss events. Comparison to experimental data shows a preference for the EGS depth‐dose curves at 10 and 20 MeV. Since various dosimetry protocols assign electron beam energies based on measured depth‐dose curves in water, formulas based on these more accurate EGS4 calculations are presented: (i) relating the mean energy of an incident electron beam to R50, the depth at which the dose in a water phantom falls to 50% of its maximum value; and (ii) relating the most probable energy of the incident beam to the projected range of the depth‐dose curve. A study is presented of the effects of the incident electron spectrum on the calculated depth‐dose curve.
The development of high‐efficiency cathode converters for a multiwire proportional chamber positron camera
Authors: Marsden P. K. , Bateman J. E. , Ott R. J. , Leach M. O.
Published: March 2003

A high‐efficiency cathode converter for 511‐keV photons has been developed for incorporation into a multiwire proportional chamber (MWPC) positron camera. The converter consists of a honeycomb pattern produced in a 1‐mm‐thick lead sheet to leave lead walls with a thickness of ∼60 μm. The converter also serves as the cathode of an MWPC, the gap between the converter and the anode wire plane being 2.5 mm. This small gap results in a high secondary electron extraction efficiency without the need for additional drift voltages. Measurements of the efficiencies of a plane converter and of two types of structured converters in a single section MWPC are described and the efficiency is found to increase in proportion to the converter surface area. This result justifies the use of a simple theoretical model whereby an extrapolation to the efficiency of a detector consisting of a stack of 20 MWPC sections, each section having two converters, is made. The efficiency of this proposed system is calculated to be 17% for 511‐keV photons.
A quantitative assessment of portal film contrast as a function of beam energy
Authors: Amols H. I. , Reinstein L. E. , Lagueux B.
Published: March 2003

Portal film contrast on a specially designed test phantom has been studied as a function of photon beam energy and object‐to‐film distance. The results provide important insights into the physical processes responsible for image contrast. In particular, theoretical calculations of Compton scatter reactions in the phantom can be used to predict visual film contrast. Good agreement between theory and experiment can be achieved by evaluating the double differential Compton cross sections [dσ(E,θ)/dE dθ] in the test object without resorting to variable parameters or artificial normalization. These calculations demonstrate the importance of low‐energy photons, object‐to‐film distance, and object size on portal film contrast.
Subtraction of simultaneously acquired dual radionuclide images
Authors: Sloboda R. S.
Published: March 2003

The physical aspects of a simultaneous dual radionuclide technique incorporating computer subtraction for the diagnosis of infection using 67Ga citrate and 99mTc methylene diphosphonate (MDP) or sulfur colloid are considered. The efficacy of the data acquisition protocol and the interpretation of the subtracted images are shown to depend significantly on fundamental imaging system parameters. Measurement of these parameters using simple phantoms and their role in elucidating the technique is detailed. Subtracted images produced by three variations of the basic method arising from different normalization algorithms in current usage are compared. Simple phantoms are again used in assessing the accuracy of each variation. Clinical results are reported elsewhere.
Selenium‐75: A potential source for use in high‐activity brachytherapy irradiators
Authors: Weeks K. J. , Schulz R. J.
Published: March 2003

A study was made to find a high‐specific‐activity radioisotope having a longer half‐life and lower gamma‐ray energies than 192Ir in order to replace 192Ir in high‐activity afterloading brachytherapy devices. Based upon a number of considerations, 75Se was selected. The present paper describes the physical properties of 75Se, its method of production, and the properties of an encapsulated source that was fabricated to prove the accuracy of our initial calculations.
Potential exposure to metal fumes, particulates, and organic vapors during radiotherapy shielding block fabrication
Authors: DeMeyer Colleen L. , Whitehead Lawrence W. , Jacobson A. P. , Brown Don G.
Published: March 2003

The shielding‐block fabrication areas of three hospitals were surveyed to assess inhalation exposure to lead (Pb), cadmium (Cd), bismuth (Bi), and tin (Sn) fumes, as well as styrene and methyl chloride vapors. Area and personal breathing zone samples were collected for various steps in the block fabrication process. Only 3 of 16 air samples for metals resulted in detectable levels of Pb and/or Cd. The levels were well below the Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits, excluding a sample which contained a visible metal fragment. Bi and Sn were not detected in any samples. Methyl chloride and styrene vapors were not detected in any air samples during foam cutting procedures. Total particulates (TP) were measurable in 11 of 17 air samples (ranging from 0.01 to 2.1 mg/m3). TP values were below the OSHA federal standard for nuisance particulates, which is 15 mg/m3. The data suggest that the materials and procedures sampled do not present an inhalation hazard to employees who construct shielding blocks. Precautions should, however, be exercised to prevent exposure under extreme procedural conditions such as soldering or overheating of alloy, and by other means such as ingestion. Care should also be taken during cleanup or housekeeping to prevent re‐entrainment into the work atmosphere of mechanically generated metal particles or materials condensed within melting pots (which may be high in metal content).