bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicted Effects of Shunt Injection on the Rotordynamics of Gas Labyrinth Seals
Authors: Kim N. , Park S.-Y. , Rhode D. L.
Published: January 2003

A recent CFD perturbation model for turbomachinery seal rotordynamics was extended for labyrinth shunt injection with an arbitrarily high pressure gas. A large number of measured cases with labyrinth injection pressure at approximately 13.8 bars (200 psi) were computed and compared with measurements. The drastically reduced (negative) cross-coupled stiffness, which is the primary advantage from the use of shunt injection in gas labyrinth seal applications, was well predicted. The agreement with measurements for k, C, and Ceff was within about 40%, 60% and 10%, respectively. In addition, it was found that moving the injection toward the high pressure end of the seal gives k, C, and Ceff values that are rotordynamically only slightly more stabilizing. Further, the radial distributions of the flow perturbation quantities give support to the two-control volume approach for developing bulk-flow models for labyrinth seal rotordynamics.
Predicted Geometry Effects on Oil Vapor Flow Through Buffer-Gas Labyrinth Seals
Authors: Park S.-Y. , Rhode D. L.
Published: January 2003

Mass transport characteristics of buffer-gas labyrinth seals operating in the flooded, nonmist regime were studied using numerical simulations. Discussion is given of the extension, to account for oil vapor mass transport, of a finite volume computer code that was previously validated using nonoil labyrinth hot-film anemometer as well as leakage measurements. A parametric study was conducted to obtain a first understanding of oil vapor transport from the liquid film on the stator wall and to assist oil seal designers. Various geometry effects with various oil film lengths were investigated. It was found in the present investigation that increasing the buffer gas pressure can increase the oil vapor mass flow to the process gas due to increased evaporation from the liquid oil film. In addition, it was found that buffer-gas mass flow is mainly affected by the clearance and the total flow area of the buffer-gas injection.
Analytical Treatment of In-Plane Parametrically Excited Undamped Vibrations of Simply Supported Parabolic Arches
Authors: Sophianopoulos Dimitris S. , Michaltsos George T.
Published: January 2003

The present work offers a simple and efficient analytical treatment of the in-plane undamped vibrations of simply supported parabolic arches under parametric excitation. After thoroughly dealing with the free vibration characteristics of the structure dealt with, the differential equations of the forced motion caused by a time dependent axial loading of the form P=P0+Pt cos θt are reduced to a set of Mathieu-Hill type equations. These may be thereafter tackled and the dynamic stability problem comprehensively discussed. An illustrative example based on Bolotin’s approach produces results validating the proposed method.
In-Plane Vibrations of a Thin Rotating Disk
Authors: Deshpande Moreshwar , Mote, C. D.
Published: January 2003

A model for the in-plane oscillations of a thin rotating disk has been derived using a nonlinear strain measure to calculate the disk energy. This accounts for the stiffening of the disk due to the radial expansion resulting from its rotation. The corresponding nondimensionalized natural frequencies are seen to depend only on the nondimensionalized rotation speed and have been calculated. The radially expanded disk configuration is linearly stable over the range of rotation speeds studied here. The sine and cosine modes for all nodal diameters couple to each other at all non-zero rotation speeds and the strength of this coupling increases with rotation speed. This coupling causes the reported frequencies of the stationary disk to split. The zero, one and two nodal diameter in-plane modes do not have a critical speed corresponding to the vanishing of the backward travelling wave frequency. The use of a linear strain measure in earlier work incorrectly predicts instability of the rotating equilibrium and the existence of critical speeds in these modes.
Interaction Between the Torsional Vibration of a Circular Rod and an Adjacent Viscous Fluid
Authors: Kim Jin O. , Chun Han Yong
Published: January 2003

This paper deals with the effect of an adjacent viscous fluid on the torsional vibration of a circular rod excited by a transducer at one end. The interaction between the torsional vibration of the rod and the fluid has been studied theoretically and expressed in terms of mechanical impedance. The theoretically-obtained result that the mechanical impedance is proportional to the square root of the viscosity times mass density of the fluid has been confirmed by the experiment measuring electric impedance. This paper demonstrates that a torsionally-vibrating rod can be used as a sensor for measuring the viscosity of a fluid.
Imperfect Interfaces and Discrete Lattice Structures
Authors: Movchan A. B.
Published: January 2003

We propose a model where a lattice structure is used within an interface layer of finite thickness. An evolution problem is set and studied to analyze the structural changes within the interface during the deformation. Numerical examples are presented for the case of a triangular lattice structure.
Transmission and Polarization of Elastic Waves in Irregular Structures
Authors: Platts S. B. , Movchan N. V. , McPhedran R. C. , Movchan A. B.
Published: January 2003

Propagation of elastic waves in an infinite elastic medium containing a finite array of circular cylindrical cavities is considered. It is assumed that the cavities are equally spaced within each layer, but the cylinder radii, as well as the distance between the layers, may vary from layer to layer. Our objective is to analyze the effect of such an irregularity on scattering properties of the system. Using the method of multipole expansions we evaluate for the case of normal incidence the reflection and transmission matrices for a stack of layers, and find a range of frequencies for which polarization or complete reflection of an incident wave takes place. Presented results highlight the effect of variation in radii and distance between the layers on propagation of elastic waves in such structures.
Transformation Textures in Unstable Austenitic Steel
Authors: Kubler R. , Berveiller M. , Cherkaoui M. , Inal K.
Published: January 2003

During the martensitic transformation in elastic-plastic materials, the local transformation strain as well as the plastic flow inside austenite are strongly related with the crystallographic orientation of the austenitic lattice. Two mechanisms involved in these materials, i.e., plasticity by dislocation motion and martensitic phase formation are coupled through kinematical constraints so that the lattice spin of the austenitic grains is different from the one due to classical slip. In this work, the lattice spin ω˙eA of the austenitic grains is related with the slip rate on the slip systems of the two phases, γ˙A and γ˙M, the evolution of the martensite volume fraction f˙ and the overall rotation rate Ω˙ of the grains. This new relation is integrated in a micromechanical model developed for unstable austenite in order to predict the evolution of the austenite texture during TRansformation Induced Plasticity (TRIP). Results for the evolution of the lattice orientation during martensitic transformation are compared with experimental data obtained by X-ray diffraction on a 304 AISI steel.
Thermal Loading of Duplex Steels
Authors: Silberschmidt Vadim V. , Werner Ewald A. , Messner Christof
Published: January 2003

Ferritic-austenitic duplex steels demonstrate a complex deformational behavior even in the absence of mechanical loads. Purely thermal cycling in the temperature interval from 20°C to 900°C can cause either accumulation of inelastic strains (thermal ratchetting) or plastic shakedown, depending on microstructure morphology and/or the strength and thermal properties of the constituting phases. In this paper, a study is undertaken on duplex steel containing nitrogen, including experimental and theoretical analyses at microscopic and macroscopic levels. High-precision dilatometry and roughness measurements are accompanied by thorough numerical simulations based on different microstructural models.
Interaction of Phase Transformation and Diffusion in Steels
Authors: Gamsja¨ger E. , Fischer F. D. , Svoboda J.
Published: January 2003

During continuous casting low alloy steels undergo a proeutectoid γ (austenite)/α (ferrite) transformation at temperatures of about 1000 K and above. The continuous rearrangement of the iron-lattice (fcc to bcc) is accompanied by diffusion of dissolved components (C, Mn). The diffusion coefficient of carbon exceeds that of a substitutionally dissolved element by a factor of 104 to 105 at these temperatures. Therefore, Mn-diffusion does not influence the γ/α phase transformation provided that the mole fraction of Mn and the transformation temperature are low enough. In this case the γ/α transformation in the Fe-C-Mn system finally reaches paraequilibrium rather than orthoequilibrium. The time-dependent driving force of the phase transformation has been evaluated as a function of temperature and composition. Furthermore, the growth kinetics of the ferrite phase was calculated by a numerical routine.
K Variations and Anisotropy: Microstructure Effect and Numerical Predictions
Authors: Li Xu-Dong
Published: January 2003

Computer experiments were performed on simulated polycrystalline material samples that possess locally anisotropic microstructures to investigate stress intensity factor (K) variations and anisotropy along fronts of microcracks of different sizes. The anisotropic K, arising from inhomogeneous stresses in broken grains, was determined for planar microcracks by using a weight function-based numerical technique. It has been found that the grain-orientation-geometry-induced local anisotropy produces large variations in K along front of microcracks, when the crack size is of the order of few grain diameters. Synergetic effect of grain orientation and geometry of broken grains control K variations and evolution along the microcrack front. The K variations may diminish at large crack sizes, signifying a shift of K calculation to bulk stress dependence from local stress dependence. Local grain geometry and texture may lead to K anisotropy, producing unusually higher/lower K at a segment of the crack front. Either K variation or anisotropy cannot be ignored when assessing a microcrack.
Numerical Simulations of the Creep Deformation of MMCs in 4-Point Bending Mode
Authors: Daxner Thomas , Rammerstorfer Franz G. , Segurado Javier , Pettermann Heinz E.
Published: January 2003

The 4-point bending test is a widely used method to determine material parameters. No commonly accepted evaluation methodology is available for materials showing non-linear deformation mechanisms. In the present study micro- and macro-mechanical simulation models of continuously reinforced metal matrix composites are employed to investigate thermo-elasto-plasticity and creep in such experiments. The overall deflection behavior and the underlying mechanisms are identified revealing the interaction of various micromechanical phenomena. Comparisons to a set of experimental results are presented.
Creep Behavior and Deformation Mechanism Map of Sn-Pb Eutectic Solder Alloy
Authors: Shi X. Q. , Wang Z. P. , Yang Q. J. , Pang H. L. J.
Published: January 2003

In this study, a large number of creep tests were carried out using miniature specimens in order to investigate the creep behavior of 63Sn/37Pb eutectic solder alloy over a wide temperature range from −40 to 150°C and stress range from 0.75 to 70 MPa. Based on dislocation and diffusion theories, two unified constitutive models were developed to describe the dislocation-controlled and diffusion-controlled creep behaviors observed. It was found that the two models accurately predict the experimental data. A deformation mechanism map was established for this eutectic solder alloy in order to interpret the creep mechanism under different temperature and loading conditions.
On the Analytical Solution of Pullout Phenomena in Textile Reinforced Concrete
Authors: Zastrau B. , Richter M. , Lepenies I.
Published: January 2003

The bond between the textile reinforcement and the finegrade concrete (cementitious matrix) is essential for the structural behavior of textile reinforced concrete. The analysis of the bond behavior between roving and matrix is important for the development of computational methods analyzing textile reinforced concrete. Therefore, the pullout phenomenon of a roving from a matrix is investigated by analytical methods based on the implementation of various damage models for the interface.
Chip Formation in Cellular Materials
Authors: Laternser Ralf , Ga¨nser Hans-Peter , Taenzer Lars , Hartmaier Alexander
Published: January 2003

The constitutive behavior of cellular materials like wood, especially with respect to the plastic and fracture mechanical properties, differs significantly from that of “classical” materials like steel. From this point of view, it appears interesting to investigate a process like chip formation, where both plasticity and fracture intervene. Finite element simulations of such a process are performed using an elastoplastic constitutive model for isotropic foams to describe the material, and a cohesive zone model to describe the crack. The repartition of the cutting force into the components required for the elasto-plastic deformation of the material and for crack opening is obtained.
Plastic Deformation of a Perforated Sheet With Non-Uniform Circular Holes Along the Thickness Direction
Authors: Chen Fuh-Kuo , Lee Yi-Che
Published: January 2003

For a perforated sheet with circular holes, used in shadow masks, the diameter of the circular hole varies through the thickness, and the non-uniform circular holes are arranged in a triangular pattern. In order to simplify the analysis, a perforated sheet with equivalent circular holes of uniform diameter is proposed such that its plastic behavior is similar to that with the given non-uniform circular holes. In this study, a yield criterion is discussed for the perforated sheet with uniform circular holes by employing an equivalent continuum approach, which is then applied to examine the plastic deformation of the perforated sheet with non-uniform circular holes. The analytical results predicted by the theory, including those for the apparent yield stresses and strain ratios, are verified by the results obtained from the finite element analysis and also from experiments.
Development of Finite Element Techniques for Three-Dimensional Analyses of Thermo-Piezoelectric Materials
Authors: Shang Fulin , Kuna Meinhard , Scherzer Matthias
Published: January 2003

The development and application of smart structures and smart composite materials require efficient numerical tools to analyze the thermo-piezoelectric behavior and stress state. In this paper, finite element (FE) techniques are suggested for three-dimensional coupled thermo-electro-mechanical analyses. The actual thermo-piezoelectric responses of smart structures subjected to thermal loadings can be determined by adopting a procedure TPESAP. The detailed implementation is presented with emphasis on the integration with software ABAQUS. A benchmark problem is discussed afterwards.
The Convergence of a DFT-Algorithm for Solution of Stress-Strain Problems in Composite Mechanics
Authors: Brown C. M. , Dreyer W. , Mu¨ller W. H.
Published: January 2003

This paper addresses the convergence characteristics of an iterative solution scheme of the Neumann-type useful for obtaining homogenized mechanical material properties from a representative volume element. The analysis is based on Eshelby’s idea of “equivalent inclusions” and, within the context of mechanical stress/strain analysis, allows modeling of elastically highly heterogeneous bodies with the aid of discrete Fourier transforms. Within the iterative scheme the proof of convergence depends critically upon the choice of an appropriate, auxiliary stiffness matrix, which also determines the speed of convergence. Mathematically speaking it is based on Banach’s fixpoint theorem and only results in sufficient convergence conditions. However, all cases of elastic heterogeneity that are of practical importance are covered and some evidence is provided that other choices of auxiliary stiffness may result in faster convergence even if this cannot explicitly be shown within the theoretical framework chosen.
Changes in photoluminescence of SrS:Ce induced by synchrotron radiation
Authors: Sato Fumio , Nakamura Tatsuya , Tanaka Katsu , Aihara Satoshi , Saito Nobuo , Inoue Katsuaki , Yagi Naoto , Mizuki Jun-ichiro
Published: January 2003

The effect of x-ray irradiation on the photoluminescence (PL) of SrS:Ce was investigated using synchrotron radiation. SrS films deposited by molecular-beam epitaxy were irradiated by x-ray pulses having an energy of 8.0 keV or 14.5 keV for duration of 17 to 50 ms. PL measurements showed that both the enhancement and deterioration of PL characteristics could be achieved by choosing a combination of shot numbers of x-ray pulses and intervals between pulses. It was found that the enhancement of PL intensity was more remarkable for x-rays of 14.5 keV than for ones of 8.0 keV. The effects of this x-ray irradiation were discussed in terms of x-ray-induced nonthermal atomic movements and thermal annealing by the heat resulting from x-ray absorption.
Influence of the Ar/N2 ratio on the preferred orientation and optical reflectance of reactively sputter deposited titanium nitride thin films
Authors: Banerjee R. , Singh K. , Ayyub P. , Totlani M. K. , Suri A. K.
Published: January 2003

Titanium nitride thin films have been deposited using reactive direct current magnetron sputtering onto stainless steel substrates. The only deposition condition which has been varied is the ratio of argon to nitrogen in the sputtering gas. While the films deposited at low nitrogen partial pressures exhibited a strong (111) preferred orientation, with increasing fraction of nitrogen in the sputtering gas, the preferred orientation of the films changed from (111) to (002). The accompanying changes in the microstructure and growth morphologies of the phases in these thin films have been investigated by x-ray diffraction and transmission electron microscopy. In addition, the effect of orientation on the optical reflectance of the films has been investigated.
Is the effective accommodation coefficient of the spinning rotor gauge temperature dependent?
Authors: Jousten Karl
Published: January 2003

The spinning rotor gauge (SRG) used as a vacuum gauge for the range of 10−4–1 Pa shows good long-term stability. Therefore it is widely used as a reference standard in calibration services. The calibration constant of the SRG is the effective accommodation coefficient σ with values around 1. This effective accommodation coefficient of the gas particles to the rotor is considered to be temperature independent for normal operational temperatures of 18–30 °C. We have carried out investigations that show that σ is slightly temperature dependent both for a baked and an unbaked rotor and vacuum system. The temperature range investigated was 16–40 °C. Relative changes of σ varied from 1×10−4 to 4×10−4/K. As the reason for the temperature dependence we could exclude neither a temperature dependent change of H2O coverage of the rotor nor a temperature dependence of the energy accommodation coefficient.
Accuracy of CT‐based thickness measurement of thin structures: Modeling of limited spatial resolution in all three dimensions
Authors: Prevrhal Sven , Fox Julia C. , Shepherd John A. , Genant Harry K.
Published: January 2003

Measurement of the width of thin structures such as the cortical shell of the vertebral body or femoral neck with computed tomography (CT) is limited by the spatial resolution of the CT system. Limited spatial resolution exists both within the CT image plane and perpendicular to it and can be described by the in‐plane point spread function (PSF) and the across‐plane slice sensitivity profile (SSP), respectively. The goal of this study was to confirm that errors of thickness measurement of thin structures critically depend on the spatial positioning of the object and the spatial resolution limitations of CT in all three dimensions, and to assess the size of the errors themselves. We compared computer models that incorporated both effects to experimentally assessed cortical thicknesses of the European Spine Phantom. Analysis included varying CT slice width, the orientation of measurement and angle β of misalignment of longitudinal scanner and phantom axes. Agreement of models with measurements was good in all configurations with an overall error of 0.17 mm. This showed that PSF and SSP are adequate system characteristics to predict deviation of measured values from true widths. Errors between measurements and true cortical thickness values averaged to 1.5 mm were strongly positively correlated with slice width and β. When the across‐plane partial volume effect was eliminated, limited in‐plane resolution still accounted for overestimation of by 0.68 (137%), 0.27 (27%), and 0.06 mm (4%) for 1.0, and 1.5 mm, respectively. For of 1.0 mm and above, it was shown that although the absolute cortical thickness values might not be accurately measurable, relative differences between two values are reflected in measurement. Implications for cortical thickness measurement are that the spinal cortical shell is too thin, whereas accurate assessment at locations of the femoral neck exhibiting a thicker cortical shell of both difference and absolute values should be possible with CT even for larger misalignment angles, especially when a smaller CT slice width is chosen.
Monte Carlo dosimetry of a new pulsed dose rate brachytherapy source
Authors: Karaiskos P. , Angelopoulos A. , Pantelis E. , Papagiannis P. , Sakelliou L. , Kouwenhoven E. , Baltas D.
Published: January 2003

A new microSelectron pulsed dose rate source has been designed, containing two active pellets instead of one inactive and one active pellet contained in the old design, to facilitate the incorporation of higher activity up to 74 GBq (2 Ci). In this work, Monte Carlo simulation is used to derive full dosimetric data following the AAPM TG‐43 formalism, as well as the dose rate per unit air kerma strength data in Cartesian, “away and along” coordinates for both source designs. The calculated dose rate constant of the new PDR source design was found equal to compared to for the old design. Radial dose functions of the two sources calculated using the point source approximated geometry factors were found in close agreement (within 1%) except for radial distances under 2 mm. At polar angles close to the longitudinal source axis at the sources' distal end, the new design presents increased anisotropy (up to 10%) compared to the old one due to its longer active core. At polar angles close to the longitudinal source axis at the sources' drive wire end however, the old design presents increased anisotropy (up to 18%) due to attenuation of emitted photons through the inactive Ir pellet. These differences, also present in “away and along” dose rate results, necessitate the replacement of treatment planning input data for the new microSelectron pulsed dose rate source.
Spatial resolution of magnetic resonance imaging Fricke‐gel dosimetry is improved with a honeycomb phantom
Authors: Aparecida Silva Nivia , Nicolucci Patricia , Baffa Oswaldo
Published: January 2003

The spatial accuracy of magnetic resonance imaging (MRI) Fricke‐gel dosimetry is limited by diffusion of ferric ions. This paper describes a honeycomb structure to limit diffusion of ions in a three‐dimensional phantom. Such a phantom containing the dosimeter gel was irradiated to a known dose distribution. Maps of dose distributions were produced from the MR images acquired at 2 and 24 hours after the dose was given. The dose distribution maps verified that the honeycomb structure precludes ion diffusion from one honeycomb cell to another, thus improving the usefulness of MRI Fricke‐gel dosimetry.
Validation of a pencil beam model–based treatment planning system for fast neutron therapy
Authors: Bourhis‐Martin E. , Meissner P. , Rassow J. , Baumhoer W. , Schmidt R. , Sauerwein W.
Published: January 2003

Treatment planning systems (TPSs) are used to compute dose delivered to the patient. In the case of fast neutron therapy, TPSs are mostly not of general purpose but are dedicated to one facility. This is due to the few fast neutron facilities worldwide and due to the high variation in the neutron energy distributions. Efforts have been undertaken to develop a new TPS that could be applied to all the existing fast neutron facilities. The University Hospital of Essen operates a fast neutron beam and the TPS used is based on an empirical model. In a previous study, the empirical model has been evolved to a pencil beam model of 35 monoenergetic neutron beams. Monte Carlo techniques have been utilized to compute distributions of the energy deposition due to primary and scattered neutrons in a simple geometry water phantom. The experimental validation of the method is now presented. Depth dose curves in water of monoenergetic neutrons have been derived from the distributions of energy deposition. The resultant depth dose curves have been utilized in order to determine the depth dose curves of the fast neutron beam of the Essen facility for the 14 radiation field sizes available in this facility. This determination requires the initial neutron spectrum. As this spectrum could not be measured at the Essen facility, the initial neutron spectrum of the Physikalisch Technische Bundesanstalt, Braunschweig, Germany, which operates the same cyclotron, was used. The calculated depth dose curves were compared to experimental depth dose curves that have been obtained in water at the University Hospital of Essen. The comparison between calculated and experimental depth dose curves showed significant deviations in the case of large radiation fields and of depth less than 5 cm. In the case of radiation field areas less than and depth more than 5 cm (usual clinical situation), the measured and calculated values are in a good agreement. In the case of clinical situation, the dependence on the radiation field size is relatively well taken into account by the model presented here.
Monte Carlo dose characterization of a new source with balloon for intravascular brachytherapy
Authors: Wang Ruqing , Li X. Allen , Lobdell John
Published: January 2003

Beta emitting source wires or seeds have been adopted in clinical practice of intravascular brachytherapy for coronary vessels. Due to the limitation of penetration depth, this type of source is normally not applicable to treat vessels with large diameter, e.g., peripheral vessel. In the effort to extend application of its beta source for peripheral vessels, Novoste has recently developed a new catheter‐based system, the Corona™ system. It is a source train of 6 cm length and is jacketed by a balloon. The existence of the balloon increases the penetration of the beta particles and maintains the source within a location away from the vessel wall. Using the EGSnrc Monte Carlo system, we have calculated the two‐dimensional (2‐D) dose rate distribution of the Corona™ system in water for a balloon diameter of 5 mm. The dose rates on the transverse axis obtained in this study are in good agreement with calibration results of the National Institute of Standards and Technology for the same system for balloon diameters of 5 and 8 mm. Features of the 2‐D dose field were studied in detail. The dose parameters based on AAPM TG‐60 protocol were derived. For a balloon diameter of 5 mm, the dose rate at the reference point (defined as 2 mm from the balloon surface) is found to be A new formalism for a better characterization of this long source is presented. Calculations were also performed for other balloon diameters. The dosimetry for this source is compared with a source, commonly used for peripheral arteries. In conclusion, we have performed a detailed dosimetric characterization for a new beta source for peripheral vessels. Our study shows that, from dosimetric point of view, the Corona™ system can be used for the treatment of an artery with a large diameter, e.g., peripheral vessel.
Evaluation of external beam radiotherapy and brachytherapy for localized prostate cancer using equivalent uniform dose
Authors: Wang Jian Z. , Li X. Allen
Published: January 2003

Various radiotherapy (RT) modalities, such as external beam radiotherapy (EBRT) and permanent/high‐dose‐rate (HDR) brachytherapy, have been used for the management of localized prostate cancer. Using the linear‐quadratic (LQ) model, we compared the relative merits of these modalities in terms of equivalent uniform dose (EUD) and tumor control probability (TCP). The LQ parameters and determined recently from compiled clinical data, as well as other sets of LQ parameters for prostate cancer, were used to carry out the EUD and TCP calculations. A computer code was developed for this purpose. We calculate the EUD for some common RT modalities, and present the corresponding TCP data predicted for a sample patient group (high‐risk). Biological equivalence of treatment outcome among various RT modalities is demonstrated. The model suggests that the hypofractionation is preferred in terms of tumor control, due to the lower α/β ratio. Also, the current combined treatment schemes (initial brachytherapy boost) provide higher EUD and TCP than these monotherapies. The study shows that EUD is less sensitive to model parameters than TCP, and EUD can be used to compare and to optimize treatment plans involving different RT modalities. Techniques to further optimize and/or to combine external beams with brachytherapy for better treatment outcomes are proposed.
Emission spectra of Gadolinium‐158
Authors: Stepanek Jiri
Published: January 2003

The photon and electron spectra of as result of the ‐reaction on were calculated with IMRDEC Monte Carlo computer program. The relaxation probabilities were taken from EADL file of the Lawrence Livermore National Laboratory. Because this file does not consist of data for some N and O transitions, they were additionally determined by Chen applying the DHS scheme. Two schemes are applied to calculate the energies of the transitions: (1) a simple scheme, and (2) accurate calculation solving the relativistic Dirac equations.
IVBTMC, A Monte Carlo dose calculation tool for intravascular brachytherapy
Authors: Chibani Omar , Li X. Allen
Published: January 2003

A new Monte Carlo code (IVBTMC) is developed for accurate dose calculations in intravascular brachytherapy (IVBT).IVBTMCcalculates the dose distribution of a brachytherapy source with arbitrary size and curvature in a general three‐dimensional heterogeneous medium. Both beta and gamma sources are considered.IVBTMCis based on a modified version of theEGSNRCcode. A voxel‐based geometry is used to describe the target medium incorporating heterogeneities with arbitrary composition and shape. The source term is modeled using appropriate phase‐space data. The phase‐space data are calculated for three widely used sourcesand. To speed up dose calculations for gamma sources, a special version ofIVBTMCbased on the kerma approximation is developed. The accuracy of the phase‐space data model is verified andIVBTMCis validated against other Monte Carlo codes and against reported measurements using radio‐chromic films. To illustrate theIVBTMCcapabilities, a variety of examples are treated.andsources with different lengths and degrees of curvature are considered. Calcified plaques with regular and irregular shapes are modeled. The dose distributions are calculated with a spatial resolution ranging between 0.1 and 0.5 mm. They are presented in terms of isodose contour plots. The dosimetric effects of the source curvature and/or the presence of calcified plaques are discussed. In conclusion,IVBTMChas the capability to perform high‐precision IVBT dose calculations taking into account the realistic configurations of both the source and the target medium. Key Words: Intravascular Brachytherapy, Monte Carlo, Dosimetry, Heterogeneity, Calcified Plaque, Source curvature.
Computer‐assisted detection of colonic polyps with CT colonography using neural networks and binary classification trees
Authors: Jerebko Anna K. , Summers Ronald M. , Malley James D. , Franaszek Marek , Johnson C. Daniel
Published: January 2003

Detection of colonic polyps in CT colonography is problematic due to complexities of polyp shape and the surface of the normal colon. Published results indicate the feasibility of computer‐aided detection of polyps but better classifiers are needed to improve specificity. In this paper we compare the classification results of two approaches: neural networks and recursive binary trees. As our starting point we collect surface geometry information from three‐dimensional reconstruction of the colon, followed by a filter based on selected variables such as region density, Gaussian and average curvature and sphericity. The filter returns sites that are candidate polyps, based on earlier work using detection thresholds, to which the neural nets or the binary trees are applied. A data set of 39 polyps from 3 to 25 mm in size was used in our investigation. For both neural net and binary trees we use tenfold cross‐validation to better estimate the true error rates. The backpropagation neural net with one hidden layer trained with Levenberg–Marquardt algorithm achieved the best results: sensitivity 90% and specificity 95% with 16 false positives per study.
An optimization algorithm for intensity modulated radiotherapy— The simulated dynamics with dose–volume constraints
Authors: Hou Qing , Wang Jun , Chen Yan , Galvin James M.
Published: January 2003

We have developed a new method for optimization in intensity modulated radiation therapy (IMRT) that makes use of simulated dynamics in a classical system of interacting particles. An analogy is drawn between intensity profile optimization in IMRT and relaxation to the equilibrium configuration in a dynamic system. The intensities of beamlets are equivalent to the positions of the virtual particles. The potential energy of the system is defined by the objective function, which determines the equations of motion for the virtual particles. In this paper, we present the implementation of dose constraints and dose–volume constraints. Our strategy is to optimize the dose to the planned target volume (PTV) while keeping all constraints to the organs at risk (OARs) satisfied rigorously. A simple quadratic objective function is used that only includes terms for PTV voxels. By this approach, no additional parameters other than that for prescribing desired dose and constraints, such as importance factors, are needed. The hard constraints that require non‐negative beamlet intensities and that the dose at any voxel in an OAR cannot exceed a maximum tolerance, are implemented as semi‐transmittable potential barriers of infinite height. Dose–volume constraints are handled by placing hard constraints on partial volumes. Handling of the clinically applied constraints was tested using phantoms and clinical cases. Our results show that the dose–volume histogram (DVH) type of plan prescription can be fulfilled with satisfactory PTV coverage. In addition to the convenience of implementation, our method can achieve a high computational efficiency with the understanding of the dynamic behavior of the system.
The impact of increased Al filtration on x‐ray tube loading and image quality in diagnostic radiology
Authors: Behrman Richard H.
Published: January 2003

Previous work has shown that for nine common radiographic projections (AP abdomen, AP cervical spine, LAT cervical spine, PA chest, LAT chest, AP hip, AP lumbar spine, LAT lumber spine, and AP pelvis) increasing the total x‐ray tube filtration from 2.5 mm Al equivalent (the regulatory minimum for general diagnostic radiology) to 4.0 mm Al equivalent, reduces the average effective dose and average skin entrance dose by 9% and 16%, respectively, using a 400 speed screen‐film system.1 In this study, the effects of this filtration increase on x‐ray tube loading and image quality were assessed. For the above projections and filtration increase, mean absolute and percentage increases in tube loading were 2.9 mAs and 15%, respectively, for a constant film density and fixed kVp. Tube current (mA) increases of 25% (a worst case) resulted in no statistically significant loss in focal spot resolution due to blooming for both large (1.2 mm) and small (0.6 mm) focal spot sizes, except at high mA low kVp techniques. The latter losses were below 10%, and when the image receptor blur was incorporated, the total system spatial resolution losses were on the order of one‐quarter to one‐half these values for typical clinical geometries. Radiographs of a contrast phantom taken with 2.5 and 4.0 mm total Al equivalent x‐ray tube filtration were compared at 60, 70, 81, 90, 102, and 121 kVp. No statistically significant changes were observed with regard to (1) test object conspicuity as reported by three observers, (2) image contrast, as measured using a densitometer with a 3 mm aperture (±0.0017 OD, 95% confidence level), and (3) pixel value image noise, image contrast‐to‐noise ratios, and image signal‐to‐noise ratios, as measured using a scanning densitometer with a 12‐bit acquisition depth and 85 μ pixel size (±2.5%, ±3.1%, and ±2.5%, 95% confidence levels, respectively). These results, combined with the linear no‐threshold model for radiation risk and the ALARA principle, suggest that general radiography should be carried out using a minimum of 4.0 mm total Al equivalent filtration.
Inductively coupled transmission of neuro‐active signals: Analysis of optimal parameters
Authors: Tulgar Metin , Soysal Ömer Muhammet
Published: January 2003

Fifteen parameters that play a role in the optimal transmission of therapeutic signals by inductively coupled implantable neurostimulator have been investigated. For this purpose, at first, a model of the system was constructed from which the system transfer function was obtained. Then, the relationship between the transfer gain and each parameter was evaluated using mathematical equations and a specifically built computer program. This study showed that the gain could be increased selecting small values for some parameters (the number of active coil windings, first radii of inner and outer paths of the core, heights of the core base and windings, position under the skin, internal resistances of the active and passive coils, tissue impedance between the contacts of electrode), and high values for the others (the number of passive coil windings, second radii of inner and outer paths of the core, frequency of the signal, relative magnetic permeability of the core). Critical saturation values were another considerable point. The nearest commercially available standard values should be preferred in practical applications.
Respiration‐correlated spiral CT: A method of measuring respiratory‐induced anatomic motion for radiation treatment planning
Authors: Ford E. C. , Mageras G. S. , Yorke E. , Ling C. C.
Published: January 2003

We describe a method for generating CT images at multiple respiratory phases with a single spiral CT scan, referred to as respiratory‐correlated spiral CT (RCCT). RCCT relies on a respiration wave form supplied by an external patient monitor. During acquisition this wave form is recorded along with the initiation time of the CT scan, so as to “time stamp” each reconstructed slice with the phase of the respiratory cycle. By selecting the appropriate slices, a full CT image set is generated at several phases, typically 7–11 per cycle. The CT parameters are chosen to optimize the temporal resolution while minimizing the spatial gap between slices at successive respiratory cycles. Using a pitch of 0.5, a gantry rotation period of 1.5 s, and a reconstruction algorithm results in slice spacing at a given phase for typical respiration periods, and a respiratory motion within each slice that is acceptably small, particularly near end expiration or end inspiration where gated radiotherapy is to occur. We have performed validation measurements on a phantom with a moving sphere designed to simulate respiration‐induced tumor motion. RCCT scans of the phantom at respiratory periods of 4, 5, and 6 s show good agreement of the sphere's motion with that observed under fluoroscopic imaging. The positional deviations in the sphere's centroid between RCCT and fluoroscopy are in the transaxial direction (average over all scans at all phases and in the longitudinal direction. Reconstructed volumes match those expected on the basis of stationary‐phantom scans to within 5% in all cases. The surface distortions of the reconstructed sphere, as quantified by deviations from a mathematical reference sphere, are similar to those from a stationary phantom scan and are correlated with the speed of the phantom. A RCCT scan of the phantom undergoing irregular motion, demonstrates that successful reconstruction can be achieved even with irregular respiration. Limitations from x‐ray tube heating in our current CT unit restrict the length of the scan region to 9 cm for the RCCT settings used, though this will not be a limitation for a multislice scanner. RCCT offers an alternative to the current method of respiration‐triggered axial scans. Multiple phases of respiration are imaged with RCCT in approximately the same scanning time required to image a single phase with a triggered axial scan. RCCT scans can be used in connection with respiratory‐gated treatment to identify the patient‐specific phase of minimum tumor motion, determine residual tumor motion within the gate interval, and compare treatment plans at different phases.
Acoustic and vibration background noise in the collapsed structure of the World Trade Center (L)
Authors: Gabrielson Thomas B. , Poese Matthew E. , Atchley Anthony A.
Published: January 2003

Measurements of acoustic and vibration background noise were made on 18 September 2001 at the southern edge of the World Trade Center collapse. Sensors were deployed in a configuration reasonable for survivor search and near an on-going recovery operation and heavy debris removal. Geophones were placed on steel beams that extended into a deep void and a microphone was lowered below ground level into a pocket in the rubble. Even in what appeared at ground level to be a high-noise environment, weak or distant taps and bangs generated either by the authors or by recovery personnel produced distinct signals from the microphone and geophones.
Analysis of the three-dimensional tongue shape using a three-index factor analysis model
Authors: Zheng Yanli , Hasegawa-Johnson Mark , Pizza Shamala
Published: January 2003

Three-dimensional tongue shape during vowel production is analyzed using the three-mode PARAFAC (parallel factors) model. Three-dimensional MRI images of five speakers (9 vowels) are analyzed. Sixty-five virtual fleshpoints (13 segments along the rostral–caudal dimension and 5 segments along the right–left direction) are chosen based on the interpolated tongue shape images. Methods used to adjust the alignment of MRI images, to set up the fleshpoints, and to measure the position of the fleshpoints are presented. PARAFAC analysis of this 3D coordinate data results in a stable two-factor solution that explains about 70% of the variance.
Effects of prosodic boundary on /aC/ sequences: Acoustic results
Authors: Tabain Marija
Published: January 2003

This study presents various acoustic measures used to examine the sequence /a # C/, where “#” represents different prosodic boundaries in French. The 6 consonants studied are /b d g f s ∫/ (3 stops and 3 fricatives). The prosodic units investigated are the utterance, the intonational phrase, the accentual phrase, and the word. It is found that vowel target values, formant transitions into the stop consonant, and the rate of change in spectral tilt into the fricative, are affected by the strength of the prosodic boundary. F1 becomes higher for /a/ the stronger the prosodic boundary, with the exception of one speaker’s utterance data, which show the effects of articulatory declension at the utterance level. Various effects of the stop consonant context are observed, the most notable being a tendency for the vowel /a/ to be displaced in the direction of the F2 consonant “locus” for /d/ (the F2 consonant values for which remain relatively stable across prosodic boundaries) and for /g/ (the F2 consonant values for which are displaced in the direction of the velar locus in weaker prosodic boundaries, together with those of the vowel). Velocity of formant transition may be affected by prosodic boundary (with greater velocity at weaker boundaries), though results are not consistent across speakers. There is also a tendency for the rate of change in spectral tilt moving from the vowel to the fricative to be affected by the presence of a prosodic boundary, with a greater rate of change at the weaker prosodic boundaries. It is suggested that spectral cues, in addition to duration, amplitude, and F0 cues, may alert listeners to the presence of a prosodic boundary.
Detection and direction-discrimination of diotic and dichotic ramp modulations in amplitude and phase
Authors: Witton Caroline , Simpson Michael I. G. , Henning G. Bruce , Rees Adrian , Green G. G. R.
Published: January 2003

When the source of a tone moves with respect to a listener’s ears, dichotic (or interaural) phase and amplitude modulations (PM and AM) are produced. Two experiments investigated the psychophysical characteristics of dichotic linear ramp modulations in phase and amplitude, and compared them with the psychophysics of diotic PM and AM. In experiment 1, subjects were substantially more sensitive to dichotic PM than diotic PM, but AM sensitivity was equivalent in the dichotic and diotic conditions. Thresholds for discriminating modulation direction were smaller than detection thresholds for dichotic AM, and both diotic AM and PM. Dichotic PM discrimination thresholds were similar to detection thresholds. In experiment 2, the effects of ramp duration were examined. Sensitivity to dichotic AM and PM, and diotic AM increased as duration was increased from 20 ms to 200 ms. The functions relating sensitivity to ramp duration differed across the stimuli; sensitivity to dichotic PM increased more rapidly than sensitivity to dichotic or diotic AM. This was also reflected in shorter time-constants and minimum integration times for dichotic PM detection. These findings support the hypothesis that the analysis of dichotic PM and AM rely on separate mechanisms.