bluuebunny/crossref_metadata_2025 huggingface dataset:
A Proposal for Integration of Wind Tunnel and Engine Test Programs for the Evaluation of Airframe-Propulsion Compatibility Using Numerical Simulations1
Authors: Davis M. , Baker W. , Power G. , Beale D.
Published: July 2002

The current high-performance aircraft development programs, and the trends in research and development activities suggest a rapidly increasing level of aircraft subsystem integration, particularly between the airframe/inlet and the propulsion system. Traditionally these subsystems have been designed, analyzed, and tested as isolated systems. The interaction between the subsystems is modeled primarily through evaluating inlet distortion in an inlet test and simulating this distortion in engine tests via screens or similar devices. In the current paper, an overview of current techniques for inlet performance and distortion characterization and engine distortion testing is presented. A review of the current state of the art in inlet analysis is also presented along with a discussion of current engine analysis techniques, from a semi-empirical approach to high-fidelity full Navier-Stokes simulations. Finally, a proposal to coordinate the existing test techniques and analysis capabilities to provide a truly integrated inlet-engine test and evaluation capability is outlined.
A Cracked Piezoelectric Material Strip Under Transient Thermal Loading
Authors: Wang B. L. , Mai Y. W.
Published: July 2002

Considered in this paper is a piezoelectric material strip containing an embedded crack or an edge crack perpendicular to its boundaries. The problem is solved for a strip that is suddenly heated or cooled from the top surface. The bottom surface is assumed to be zero temperature or thermally insulated. First the transient temperature and the stress distributions in an uncracked strip are calculated. Then, these stresses are used as the crack surface traction with opposite sign to formulate the mixed boundary value problem. This leads to a singular integral equation of Cauchy-type, which is then solved numerically. The numerically results for stress intensity factor are computed as a function of the normalized time and the crack size. The temperature and the thermal stress distributions for the uncracked problem are also included.
Dynamic Behavior of a Thin-Walled Cylindrical Workpiece During the Turning Process, Part 1: Cutting Process Simulation
Authors: Mehdi K. , Rigal J.-F. , Play D.
Published: July 2002

From a practical point of view, in machining applications, chatter vibration constitutes a major problem during the cutting process. It is becoming increasingly difficult to suppress chatter during cutting at high speeds. Many investigators have regarded chatter vibrations as a “natural” phenomenon during the cutting process and a part of the process itself. In classical machining operations with thick-walled workpieces chatter vibrations occur when the cutting depth exceeds stability limits dependent on the machine tool. On the other hand, in the case of thin-walled cylindrical workpieces, chatter vibration problems are not so simple to formulate. The main purpose of this study is to qualify the dynamic behavior of a thin-walled workpiece during the turning process. It contains two parts: the cutting process simulation and the definition of experimental stability criteria. In the first part, a numerical model, which simulates the turning process of thin-walled cylindrical workpieces, is proposed. This model also permits obtaining workpiece responses to excitation generated by cutting forces. Finally, the stability of the process is discussed.
Influence of Boundary Conditions on Decay Rates in a Prestrained Plate1
Authors: Karp B. , Durban D.
Published: July 2002

Decay of end perturbations imposed on a prestrained semi-infinite rectangular plate is investigated in the context of plane-strain incremental finite elasticity. A separation of variables eigenfunction formulation is used for the perturbed field within the plate. Numerical results for the leading decay exponent are given for three hyperelastic materials with various boundary conditions at the long faces of the plate. The study exposes a considerable sensitivity of axial decay rates to boundary data, to initial strain and to constitutive behavior. It is suggested that the results are relevant to the applicability of Saint-Venant’s principle even though the eigenfunctions are not always self-equilibrating.
Numerical Unsteady Flow Analysis of a Turbine Stage With Extremely Large Blade Loads
Authors: Jo¨cker Markus , Hillion Francois X. , Fransson Torsten H. , Wa˚hle´n Ulf
Published: July 2002

This paper presents the detailed numerical analysis including parametric studies on the aerodynamic excitation mechanisms in a turbine stage due to the unsteady stator-rotor interaction. The work is part of the predesign study of a high-pressure subsonic turbine for a rocket engine turbopump. The pressure level in such turbines can be remarkably high (in this case 54 MPa inlet total pressure). Hence, large unsteady rotor blade loads can be expected, which impose difficult design requirements. The parameter studies are performed at midspan with the numerical flow solver UNSFLO, a 2-D/Q3-D unsteady hybrid Euler/Navier-Stokes solver. Comparisons to 2-D and steady 3-D results obtained with a fully viscous solver, VOLSOL, are made. The investigated design parameters are the axial gap (∼8–29 percent of rotor axial chord length) and the stator vane size and count (stator-rotor pitch ratio ∼1–2.75). For the nominal case the numerical solution is analyzed regarding the contributions of potential and vortical flow disturbances at the rotor inlet using rotor gust computations. It was found that gust calculations were not capable to capture the complexity of the detected excitation mechanisms, but the possibility to reduce excitations by enforcing cancellation of the vortical and potential effects has been elaborated. The potential excitation mechanism in the present turbine stage is found dominant compared to relatively small and local wake excitation effects. The parameter studies indicate design recommendations for the axial gap and the stator size regarding the unsteady rotor load.
Experimental Study of Surface-Mounted Obstacle Effects on Heat Transfer Enhancement by Using Transient Liquid Crystal Thermograph
Authors: Yan W. M. , Hsieh R. C. , Soong C. Y.
Published: July 2002

Effects of surface-mounted obstacles on the local heat transfer enhancement of a base plate are investigated by using transient liquid crystal thermograph technique. To explore the geometry effects of short obstacles, the height less than one hydraulic diameter (d), three cross-sectional shapes of obstacles, i.e., circular, square and diamond, with variations in number of obstacles, obstacle spacing, and free-stream Reynolds number are considered. The maximum number of the obstacles in tandem array is 3 and the spacing between obstacles is 1d, 2d, or 4d. The free-stream Reynolds number ranges from 2100 to 4200. The experimental results reveal that the local heat transfer enhancement in front of leading circular and square obstacles are better than the diamond one, while the influenced area by the obstacle of the diamond shape is most remarkable. The present results disclose that an intermediate height (0.5d) of the protruding elements is more beneficial to the heat transfer enhancement in wake of the obstacle. With the sweepback leading edge of the top surface, the diamond and circular obstacles produce vortical flow across the obstacles and thus enhance heat transfer downstream in wake. Increasing Reynolds number leads to an enhancement in heat transfer performance. The number of and the spacing between the obstacles in tandem array are also influential factors to the flow structure and heat transfer enhancement on the basic plate.
Laser Repetitive Pulse Heating of Steel Surface: A Material Response to Thermal Loading
Authors: Shuja S. Z. , Arif A. F. M. , Yilbas B. S.
Published: July 2002

Laser repetitive pulse heating of the workpiece surfaces results in thermal stresses developed in the vicinity of the workpiece surface. In the present study, laser repetitive pulse heating with a gas assisting process is modelled. A two-dimensional axisymmetric case is considered and governing equations of heat transfer and flow are solved numerically using a control volume approach while stress equations are solved using the finite element method (FEM). In this analysis, a gas jet impinging onto the workpiece surface coaxially with the laser beam is considered. A low-Reynolds number k−ε model is introduced to account for the turbulence. When computing the temperature and stress fields two repetitive pulse types and variable properties of workpiece, and gas jet are taken into account. Temperature predictions were discussed in a previous study. A stress field is examined at present. It is found that the radial stress component is compressive while its axial counterpart is tensile. The temporal behavior of the equivalent stress almost follows the temperature field in the workpiece. The pulse type 1 results in higher equivalent stress in the workpiece as compared to that corresponding to pulse type 2.
Free Vibration Analysis of an Inflated Toroidal Shell
Authors: Jha Akhilesh K. , Inman Daniel J. , Plaut Raymond H.
Published: July 2002

Free vibration analysis of a free inflated torus of circular cross-section is presented. The shell theory of Sanders, including the effect of pressure, is used in formulating the governing equations. These partial differential equations are reduced to ordinary differential equations with variable coefficients using complete waves in the form of trigonometric functions in the longitudinal direction. The assumed mode shapes are divided into symmetric and antisymmetric groups, each given by a Fourier series in the meridional coordinate. The solutions (natural frequencies and mode shapes) are obtained using Galerkin’s method and verified with published results. The natural frequencies are also obtained for a circular cylinder with shear diaphragm boundary condition as a special case of the toroidal shell. Finally, the effects of aspect ratio, pressure, and thickness on the natural frequencies of the inflated torus are studied.
A Study on the Knocking and Misfire Detection System Using Breakdown Voltage Characteristics
Authors: Park J. K. , Chae J. O.
Published: July 2002

Engine knocking and misfire cause a negative effect on the engine power and the exhaust emissions such as HC, CO and NOx. They also cause permanent damages to the three way catalyst (TWC) system. And a heavy knock can cause severe damages to the engine itself, which gives more reason why it must be detected and corrected. This study introduces a new system concept for detecting combustion misfire and knocking using breakdown voltage (BDV) characteristics between spark plug electrodes. This system detects and evaluates the degree of combustion by measuring the breakdown voltage which predicts that the breakdown voltage depends on the pressure and the temperature.
Stochastic Analysis of a 1-D System With Fractional Damping of Order 1/2
Authors: Agrawal Om P.
Published: July 2002

This paper presents an analytical technique for the analysis of a stochastic dynamic system whose damping behavior is described by a fractional derivative of order 1/2. In this approach, an eigenvector expansion method is used to obtain the response of the system. The properties of Laplace transforms of convolution integrals are used to write a set of general Duhamel integral type expressions for the response of the system. The general response contains two parts, namely zero state and zero input. For a stochastic analysis, the input force is treated as a random process with specified mean and correlation functions. An expectation operator is applied on a set of expressions to obtain the stochastic characteristics, namely the variance and covariance responses of the system. Closed form stochastic response expressions are obtained for white noise. Numerical results are presented to show the stochastic response of a fractionally damped system subjected to white noise. Results show that stochastic response of the fractionally damped system oscillates even when the damping ratio is greater than its critical value.
Characterization of Sheet Buckling Subjected to Controlled Boundary Constraints
Authors: Cao Jian , Wang Xi , Mills Francis Joe
Published: July 2002

A wedge strip test is designed to study the onset and post-buckling behavior of a sheet under various boundary constraints. The device can be easily incorporated into a conventional tensile test machine and material resistance to buckling is measured as the buckling height versus the in-plane strain state. The design yields different but consistent buckling modes with easy changes of boundary conditions (either clamped or freed) and sample geometry. Experimental results are then used to verify a hybrid approach to buckling prediction, i.e., the combination of the FEM analysis and an energy-based analytical wrinkling criterion. The FEM analysis is used to obtain the stress field and deformed geometry in a complex forming condition, while the analytical solution is to provide the predictions less sensitive to artificial numerical parameters. A good agreement between experimental data and numerical predictions is obtained.
Motion of AMB Rotor in Backup Bearings
Authors: Zeng Sheng
Published: July 2002

This paper studies numerically the motion of an AMB rotor when it is supported only by backup bearings. Unlike a linear rotor-bearing system, which always undergoes a harmonic motion, the nonlinear AMB rotor-backup bearing system will undergo irregular or chaotic motion at some rotating speeds. The simulations show that in a wide rotating speed range there are several extra resonance frequencies, which are different from those appearing in well-known linear models. When a power failure occurs to AMB machinery, the AMB rotor should pass through all these resonance frequencies. Under some conditions, the full clearance whirl motion of the rotor in backup bearings will happen, which may lead to damage. In this paper several measures that could reduce the nonlinear response and hence avoid the full clearance motion are discussed.
Void formation during silicidation and its influence on the thermal stability of cobalt silicide
Authors: Kim Nam-Sik , Cha Han-Seob , Sung Nag-Kyun , Ryu Hyuk-Hyun , Youn Ki-Seog , Lee Won-Gyu
Published: July 2002

Void formation during silicidation and its influence on the thermal stability of CoSi2 on the poly-Si were investigated. Visible voids were found at the interface of CoSi2/poly-Si on the BF2 doped poly-Si but not on the boron doped one. Void formation during silicidation could be suppressed effectively by two methods: preventing oxidation of poly-Si during dopant activation annealing or removing surface SiOx(Fy) compounds sufficiently in dilute HF before cobalt deposition. It was found that the thermal stability of CoSi2 on the BF2 doped poly-Si with the interface voids was much better than that on the boron doped one or BF2 doped one, without the interface voids. It is verified that interface void formation during silicidation improves the thermal stability of CoSi2 by suppressing the grain grooving from the interface due to the increase of interface energy.
Atomistic feature scale modeling of the titanium ionized physical vapor deposition process
Authors: Kersch A. , Hansen U.
Published: July 2002

We develop a fundamental model to simulate the ionized physical vapor deposition process of a titanium barrier into submicron features. Using molecular dynamics techniques we calculate for typical energies the energy and angular dependent reaction rates of Ti+ with Ti and Ar+ with Ti including the distribution of the etched away particles. The interaction potential is based on Ackland’s model [G. J. Ackland, Philos. Mag. A 66, 917 (1992)] and is extended for particles with a kinetic energy up to 150 eV. The reaction rates are implemented into a cellular automaton feature scale simulator modeling the thin film growth. The reactor and plasma sheath conditions are described in a simple model providing the energy and angular distribution for the feature scale simulator. The multiscale model is applied to barrier deposition into a high aspect ratio feature with different substrate bias conditions. The results show that the barrier growth at high energy is dominated by kinetic energy driven processes.
Numerical study of isotope separation phenomena of noble gases by dc discharge as rarefied gas dynamics
Authors: Asami Mitsufumi , Kano Katsuhiro , Akatsuka Hiroshi
Published: July 2002

A numerical simulation was undertaken on argon and krypton isotope separation in their dc arc discharges through a thin capillary. The mass transport phenomenon of neutral particles as well as of ions in the positive column was treated by direct simulation Monte Carlo method, whereas electrons were treated as background particles, and their behavior was assumed to be already given to evaluate the effects of electron collisions onto neutral particles. The numerical results agreed qualitatively with the isotope separation phenomena of argon and krypton dc discharges. The heavier isotopes were enriched into the region of the cathode, whereas the lighter ones into that of the anode. It was also found that the numerical results explained the pressure difference between the cathode and the anode observed experimentally. The characteristics of drift motion of ions also qualitatively agreed with existing experimental results.
Behavior of fluorocarbon species near temperature controlled and radio frequency biased metal plate in C4F8 plasma
Authors: Doh Hyun-Ho , Horiike Yasuhiro
Published: July 2002

Variations of fluorocarbon species were investigated in the vicinity of metal stage that was installed in C4F8 inductively coupled plasma system with the parameters such as temperature of the stage, distance from the stage, gas residence time, and rf bias voltage applied to the stage. Quadrupole mass analyzer and appearance mass spectrometry have been used for the measurement of fluorocarbon ions, radicals. Densities of all radicals increased with the increase of stage temperature and the decrease of the gap distance between stage and detection point. On the other side, the concentrations of fluorocarbon ions decreased slightly when the stage temperature went down. It has been investigated that the density variation of the radicals dependent on the stage temperature could be controlled with gas residence time. It is considered that the balance between pumping loss rate and surface loss rate has a responsibility for the residence time effects on radical density variations. Finally, constant amounts of radicals were desorbed from the stage along with discharge time when we applied rf bias to the stage. All of the experimental results suggest that dielectric etching chamber should be designed on the basis of the understanding on plasma–wall interaction.
Analysis of Cerium–Zirconium Mixed Metal Oxides by X-Ray Photoelectron Spectroscopy
Authors: Nelson Alan E. , Graves-Brook Melissa K. , Schulz Kirk H.
Published: July 2002

Survey and high-resolution x-ray photoelectron spectra of cerium–zirconium mixed metal oxides prepared by co-precipitation are presented. The spectra were collected using a Mg Kα (1253.6 eV) source operated at 300 W and 15 kV over a binding energy range of 1100–0 eV. The compositions of the mixed metal oxides were confirmed with x-ray fluorescence and Auger electron spectroscopy prior to XPS characterization. The precipitates were formed into 100 μm thick specimens and analyzed in wafer form.
Technical note: Creating a four‐dimensional model of the liver using finite element analysis
Authors: Brock K. K. , Hollister S. J. , Dawson L. A. , Balter J. M.
Published: July 2002

Finite element analysis and two liver CT scans were used to construct a four‐dimensional (4D) model of the liver during breathing. A linear elastic, small deformation mechanical model was applied to one patient to obtain intermediate organ position and shape between exhale and inhale. Known transformations between anatomically defined subsections of the exhale and inhale liver surfaces were applied as constraints to the exhale CT liver model. Intermediate states were then calculated and time weighted to determine a 4D model of the liver as it deforms during the breathing cycle. This model can be used to calculate a more accurate dose distribution during radiotherapy.
Image reconstruction algorithm for a rotating slat collimator
Authors: Zeng Gengsheng L. , Gagnon Daniel , Matthews Christopher G. , Kolthammer Jeffery A. , Radachy Jason D. , Hawkins William G.
Published: July 2002

A slat collimator in single photon emission computed tomography consists of a set of parallel slats. As the collimator spins, the detector measures a one‐dimensional projection data set. A complete data set can be obtained by rotating the detector/collimator assembly around the object (patient) while the collimator spins continuously. The measured projection data are assumed to be weighted planar integrals of the object. This paper describes the development of an approximate three‐dimensional image reconstruction algorithm for a rotating/spinning slat collimator. This algorithm is in filtered backprojection form. Computer simulations were performed to verify the effectiveness of the algorithm.
Underdosage of the upper‐airway mucosa for small fields as used in intensity‐modulated radiation therapy: A comparison between radiochromic film measurements, Monte Carlo simulations, and collapsed cone convolution calculations
Authors: Martens C. , Reynaert N. , De Wagter C. , Nilsson P. , Coghe M. , Palmans H. , Thierens H. , De Neve W.
Published: July 2002

Head‐and‐neck tumors are often situated at an air‐tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons, especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis dose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rim situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta linear accelerator, equipped with the standard multileaf collimator (MLC), was assessed. A and a field, both widthwise collimated by the MLC, were applied with their long side parallel to the cylinder axis. Central axis dose rebuild‐up was studied. Radiochromic film measurements were performed in an in‐house manufactured polystyrene phantom with the films oriented either along or perpendicular to the beam axis. Monte Carlo simulations were performed with BEAM and EGSnrc. Calculations were also performed using the pencil beam (PB) algorithm and the collapsed cone convolution (CCC) algorithm of Helax–TMS (MDS Nordion, Kanata, Canada) version 6.0.2 and using the CCC algorithm of Pinnacle (ADAC Laboratories, Milpitas, CA, USA) version 4.2. A very good agreement between the film measurements and the Monte Carlo simulations was found. The CCC algorithms were not able to predict the interface dose accurately when lateral electronic disequilibrium occurs, but were shown to be a considerable improvement compared to the PB algorithm. The CCC algorithms overestimate the dose in the rebuild‐up region. The interface dose was overestimated by a maximum of 31% or 54%, depending on the implementation of the CCC algorithm. At a depth of 1 mm, the maximum dose overestimation was 14% or 24%.
Automatic delineation of Gd enhancements on magnetic resonance images in multiple sclerosis
Authors: He Renjie , Narayana Ponnada A.
Published: July 2002

A method for automatic identification and delineation of contrast‐enhanced multiple sclerosis (MS) lesions on brain magnetic resonance images is described. This method relies on adaptive local segmentation derived from the morphological “open” and “reconstruction” operations on gray scale images for identification of both lesion and nonlesion enhancements. Nonlesion enhancements from vasculature and extrameningeal tissues are identified by exploiting their topologic relationship to the brain mask. Enhancing structures without a blood–brain‐barrier, such as choroid plexus, are identified and eliminated by spatially mapping the locations of the MS lesions visualized on dual echo images onto the post‐contrast images. Delineation of enhancements is realized using fuzzy connectivity. Both the detection and delineation results are validated using statistical methods.
On the role of intensity‐modulated radiation therapy in radiation oncology
Authors: Schulz R. J. , Kagan A. Robert
Published: July 2002

Physicists are critical members of the radiation therapy team, and rightfully so. Therefore, it is not unreasonable that they be acquainted with the broader aspects of the management of patients who receive radiation treatments, as well as the roles played by surgeons, medical oncologists and other members of the treatment team. The spate of recent technical developments openly embraced by medical physicists, many of whom appear unconcerned by questionable benefits and very high costs, leads the authors to believe that this acquaintance is not as widespread as it should be. The present paper provides a brief review of clinical considerations in radiation oncology, statistics for the most prevalent cancers, and how those cancers that account for over 90% of mortality are currently treated. With these data as background, it then considers the extent to which one of the more widely promoted new technologies is likely to impact upon survival. By providing this modicum of perspective, physicists will be in a better position to evaluate these new technologies in more fundamental clinical terms, and thereby enhance their contributions to the overall care of the cancer patient.
Kymogram detection and kymogram‐correlated image reconstruction from subsecond spiral computed tomography scans of the heart
Authors: Kachelrieß Marc , Sennst Dirk‐Alexander , Maxlmoser Wolfgang , Kalender Willi A.
Published: July 2002

Subsecond single‐slice, multi‐slice or cone‐beam spiral computed tomography (SSCT, MSCT, CBCT) offer great potential for improving heart imaging. Together with the newly developed phase‐correlated cardiac reconstruction algorithms 180°MCD and 180°MCI [Med. Phys. 27, 1881–1902 (2000)] or related algorithms provided by the CT manufacturers, high image quality can be achieved. These algorithms require information about the cardiac motion, i.e., typically the simultaneously recorded electrocardiogram (ECG), to synchronize the reconstruction with the cardiac motion. Neither data acquired without ECG information (standard patients) nor acquisitions with corrupted ECG information can be handled adequately. We developed a method to extract the appropriate information about cardiac motion directly from the measured raw data (projection data). The so‐called kymogram function is a measure of the cardiac motion as a function of time t or as a function of the projection angle α. In contrast to the ECG which is a global measure of the heart's electric excitation, the kymogram is a local measure of the heart motion at the z‐position at projection angle α. The patient's local heart rate as well as the necessary synchronization information to be used with phase‐correlated algorithms can be extracted from the kymogram by using a series of signal processing steps. The kymogram information is shown to be adequate to substitute the ECG information. Computer simulations with simulated ECG and patient measurements with simultaneously acquired ECG were carried out for a multislice scanner providing slices to evaluate these new approaches. Both the ECG function and the kymogram function were used for reconstruction. Both were highly correlated regarding the periodicity information used for reconstruction. In 21 out of 25 consecutive cases the kymogram approach was equivalent to the ECG‐correlated reconstruction; only minor differences in image quality between both methods were observed. For one patient the synchronization information detected by the ECG monitor turned out to be wrong; here, the kymogram constituted the only approach that provided useful reconstructions. Patient studies with 12 and 16 slices indicate the usefulness of our approach for cone‐beam CT scans. Kymogram‐correlated reconstructions also appear to have the potential to improve imaging of pericardial lung areas in general.
Dose distributions for intravascular brachytherapy sources used with balloon catheters
Authors: Piessens Marleen , Reynaert Nick , Potempa Jaroslaw , Thierens Hubert , Wijns William , Verbeke Luc
Published: July 2002

The dose distribution around an intravascular brachytherapyline source with centering balloon catheters was measured with a plastic scintillator, TLD and radiochromic film. The absolute dose rates measured with the three detectors in a solid water phantom at 1, 2 and 3 mm distance from the centering balloon surfaces are in agreement within 3.5%, when the detectors are calibrated with the samesource. The dose rates measured with the plastic scintillator in the solid water phantom are in agreement with those directly measured in water. The measured relative dose distributions can be reproduced by Monte Carlo calculations. Also, the influence of the balloon diameter on the dose rate can be reproduced by the calculations. The dose rate calibration routinely performed with the plastic scintillator was checked for fifty‐one sources with a well chamber and with another dedicated dose rate checking device. These measurements show that the consistency of the calibration of these sources was better than 10%. In a previous paper absolute dose rates for five othersources measured with TLD and radiochromic film in a solid water phantom were compared with those obtained with the plastic scintillator in water [Piessens and Reynaert, “Verification of absolute dose rates for intravascular beta sources,” Phys. Med. Biol.45, 2219–2231 (2000)]. Differences of 25 to 41%, depending on the balloon diameter, were reported. In this paper we show the evidence for three main reasons for these previously observed discrepancies: an inconsistency between a detector calibration performed with a 6 MeV electron beam and with a calibratedsource from NIST (16%), inaccuracies of the measuring distances in the solid water phantom (maximum 7.5%) and a time instability of the plastic scintillator, probably due to radiation damage (6%).
Robert A. Millikan Award Lecture (July 2001): Can “descriptive” end with “A”?
Authors: Watkins Sallie A.
Published: July 2002

Recent reports on science achievement in the United States reveal that much work remains to be done if our students are to be competitive with those of other countries. Although the reports focus on K–12 teaching and learning, the picture they paint has a graphic message for the introductory college physics course as well. I cite sample responses to the problem and call on teachers to formulate their own. I single out a particularly troubling level of intellectual development and consider it in some detail.
Correlation analysis with ScienceWorkshop
Authors: Kraftmakher Yaakov
Published: July 2002

A student experiment on correlation analysis is described. The auto- and cross-correlation functions are determined for periodic signals and noise by means of the ScienceWorkshop data-acquisition system with the DataStudio software from PASCO Scientific. The experiment includes the recovery of periodic electric signals buried in noise and determination of the velocity of sound in air by the use of acoustic noise.
The problem of spherically symmetric electromagnetic radiation
Authors: Comay E.
Published: July 2002

Using Maxwell equations for the radiation’s transverse fields, it is proved that a genuine spherically symmetric electromagnetic radiation cannot exist.
Fizeau fringes at home
Authors: Hernández-Andrés Javier , Valero Eva M. , Nieves Juan L. , Romero Javier
Published: July 2002

We propose an easy and inexpensive laboratory experiment to obtain equal-thickness optical interference using a flatbed scanner and a personal computer to produce Fizeau fringes. Valuable discussions about multiple-beam interference, Fresnel equations, the theory of partial coherence, and colorimetry arise naturally from the interference-fringe results.
Relations between Newtonian mechanics, general relativity, and quantum mechanics
Authors: Savickas D.
Published: July 2002

When Euclidean coordinate lengths are replaced by the metric lengths of a curved geometry within Newton’s second law of motion, the metric form of the second law can be shown to be identical to the geodesic equation of motion of general relativity. The metric coefficients are contained in the metric lengths and satisfy the field equations of general relativity. Because metric lengths are the physically measured lengths, their use makes it possible to understand general relativity directly in terms of physical quantities such as energy and momentum within a curved space–time. The metric form of the second law contains gravitational effects in exactly the same manner as occurs in relativity. Its mathematical derivation uses vectors rather than tensors, and nongravitational forces can occur in this modified second law without a tensor form. Because quantum mechanics is based on Newtonian concepts of energy and momentum, it is shown that when metric lengths replace coordinate lengths in Dirac’s wave equation, it has a covariant form under a metric transformation of the physically measured distances themselves, rather than a coordinate transformation. Metric transformations are also used to describe the Dirac equation for the gravitational central field in a Schwarzschild metric.
The speed of sound in a hard disk gas: A computer simulation
Authors: Román F. L. , González A. , White J. A. , Velasco S.
Published: July 2002

We discuss the simulation of a system consisting of a rectangular box that contains two identical hard disk gases with the same number of particles, separated by an internal movable piston. The piston exhibits a random oscillatory motion with a frequency that depends on the mass of the piston, the mass of the disks, the temperature, and the length of the box. The measurement of this frequency allows us to deduce the speed of sound in the gas. The result is compared with the speed of sound from the usual expression in terms of the isothermal compressibility.
Optical aberrations measurement with a low cost optometric instrument
Authors: Furlan Walter D. , Muñoz-Escrivá L. , Pons A. , Martı́nez-Corral M.
Published: July 2002

A simple experimental method for measuring optical aberrations of a single lens is proposed. The technique is based on the use of an optometric instrument employed for the assessment of the refractive state of the eye: the retinoscope. Experimental results for spherical aberration and astigmatism are obtained.
Aberration correction for time-domain ultrasound diffraction tomography
Authors: Mast T. Douglas
Published: July 2002

Extensions of a time-domain diffraction tomography method, which reconstructs spatially dependent sound speed variations from far-field time-domain acoustic scattering measurements, are presented and analyzed. The resulting reconstructions are quantitative images with applications including ultrasonic mammography, and can also be considered candidate solutions to the time-domain inverse scattering problem. Here, the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth. However, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to “gold standard” ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvements for imaging of large scatterers. The parametric range of applicability for the time-domain diffraction tomography method is increased by about a factor of 2 by aberration correction.
Spectral integration in bands of modulated or unmodulated noise
Authors: Bacon Sid P. , Grimault Nicolas , Lee Jungmee
Published: July 2002

Spectral integration was measured for pure-tone signals masked by unmodulated or modulated noise bands centered at the signal frequencies. The bands were typically 100 Hz wide, and when modulated, they were sinusoidally amplitude modulated at a rate of 8 Hz and a depth of 100%. In experiment 1, thresholds were first measured for each individual pure tone of a triplet in the presence of its respective masker band, and then for those three tones added together at their respective threshold levels, masked by their respective masker bands. Four sets of triplets were used: 250, 1000, 4000 Hz; 354, 1000, 2828 Hz; 500, 1000, 2000 Hz; and 800, 1000, 1200 Hz. When the masker bands were unmodulated, the amount of spectral integration was about 2.4 dB for all triplets, consistent with the integration expected based on the multiband energy detector model. When the bands were modulated, the amount of integration depended upon the spacing between masker bands; for the two widest spacings, the integration was between about 0 and 3 dB, whereas for the two closest spacings, the integration was approximately 5 dB. Experiments 2 and 3 addressed the cause of this greater spectral integration in the presence of the modulated masker bands with closer spacing. The second experiment demonstrated that sensitivity (d′) was proportional to signal power regardless of whether the background noise was modulated or not, and thus the greater integration in dB in the presence of the modulated noise bands could not be accounted for by shallower psychometric functions in those conditions. Instead, the third experiment showed that the greater integration was likely due to the fact that the masker bands were comodulated. In other words, it was probably due to cues related to comodulation masking release when all three bands (and signals) were present.
Effects of signal delay on auditory filter shapes derived from psychophysical tuning curves and notched-noise data obtained in simultaneous masking
Authors: Bacon Sid P. , Repovsch-Duffey Jennifer L. , Liu Li
Published: July 2002

Psychophysical tuning curves (PTCs) measured in simultaneous masking usually sharpen as a short duration signal is moved from the onset to the temporal center of a longer duration masker. Filter shapes derived from notched-noise maskers have not consistently shown this effect. One possible explanation for this difference is that the signal level is fixed in the PTC paradigm, whereas the masker level is usually fixed in the notched-noise paradigm. In the present study, the signal level was fixed at 10 dB SL in both paradigms. The signal was 20 ms in duration, and presented at the onset or temporal center of the 400-ms masker. The masker was a pure tone presented in quiet (PTC) or in the presence of a pure-tone “restrictor” intended to limit off-frequency listening (PTCr), or it was a noise with a spectral notch placed symmetrically or asymmetrically about the 2-kHz signal frequency. Filter shapes were derived from the PTC, PTCr, and notched-noise data using the roex (p, w, t) model. The effects of signal delay and masking paradigm on filter bandwidth were analyzed with a two-factor repeated-measures ANOVA. There was a significant effect of signal delay (the filters sharpened with time) and masking paradigm (the filters derived from the notched-noise data were significantly wider than those derived from either of the PTC measurements, which did not differ from one another). Although the interaction between delay and paradigm was not significant, the filter derived from the notched-noise data sharpened more with time than did the other filters, and thus the bandwidth of the filters from the three paradigms were more similar at the longer delay than at the shorter delay. It is likely that the tuning-curve and notched-noise paradigms measure the same underlying filtering, but that various other factors contribute differentially to the derived filter shapes.
Auditory filter shapes for the bottlenose dolphin (Tursiops truncatus) and the white whale (Delphinapterus leucas) derived with notched noise
Authors: Finneran James J. , Schlundt Carolyn E. , Carder Donald A. , Ridgway Sam H.
Published: July 2002

Auditory filter shapes were estimated in two bottlenose dolphins (Tursiops truncatus) and one white whale (Delphinapterus leucas) using a behavioral response paradigm and notched noise. Masked thresholds were measured at 20 and 30 kHz. Masking noise was centered at the test tone and had a bandwidth of 1.5 times the tone frequency. Half-notch width to center frequency ratios were 0, 0.125, 0.25, 0.375, and 0.5. Noise spectral density levels were 90 and 105 dB re:1 μPa2/Hz. Filter shapes were approximated using a roex(p,r) function; the parameters p and r were found by fitting the integral of the roex(p,r) function to the measured threshold data. Mean equivalent rectangular bandwidths (ERBs) calculated from the filter shapes were 11.8 and 17.1% of the center frequency at 20 and 30 kHz, respectively, for the dolphins and 9.1 and 15.3% of the center frequency at 20 and 30 kHz, respectively, for the white whale. Filter shapes were broader at 30 kHz and 105 dB re:1 μPa2/Hz masking noise. The results are in general agreement with previous estimates of ERBs in Tursiops obtained with a behavioral response paradigm.
Bulk reaction modeling of ducts with and without mean flow
Authors: Kakoty S. K. , Roy V. K.
Published: July 2002

A general formulation for analysis of sound field in a uniform flow duct lined with bulk-reacting sound-absorbing material is presented here. Presented theoretical model predicts the rate of attenuation for symmetric as well as asymmetric modes in rectangular duct lined with loosely bound (bulk-reacting) sound-absorbing material, which allows acoustic propagation through the lining. The nature of attenuation in rectangular ducts lined on two and four sides with and without mean flow is discussed. Computed results are compared with published theoretical and experimental results. The presented model can be used as guidelines for the acoustic design of silencers, air-conditioning ducts, industrial fans, and other similar applications.
Changes in auditory sensitivity with depth in a free-diving California sea lion (Zalophus californianus)
Authors: Kastak David , Schusterman Ronald J.
Published: July 2002

All current data on underwater hearing in pinnipeds are based on tests conducted in small tanks, and may not accurately represent the auditory functioning of free-ranging animals, especially if hearing sensitivity changes with water depth. Underwater auditory thresholds were determined for a California sea lion at depths ranging from 10 to 100 meters. The following results were obtained: (1) False alarm probabilities (responding in the absence of a signal) decreased significantly with depth, indicating that the sea lion adopted a more conservative response criterion in deeper water. (2) Hearing sensitivity generally worsened with depth. (3) There was a significant interaction between depth and frequency, the depth effect being most pronounced at 10 kHz and reversing at 35 kHz. Increasing pressure related to diving probably alters the impedance characteristics of the pinniped ear, in particular affecting the size of the middle-ear air space via expansion of cavernous tissue in the middle-ear cavity. These results show that the middle ear plays a functional role in underwater sound detection in sea lions. However, contrary to previous speculation, the presence of cavernous tissue in the sea lion middle ear does not appear to enhance sensitivity at depth.
The effect of speech compression on second language speech perception learning
Authors: Adachi Takahiro , Yamada Tsuneo
Published: July 2002

In recent years, second language education is sometimes conducted over the Internet. However, the speech used for training is often compressed in order to decrease the number of packets transmitted, without an evaluation of whether the compression causes a decrease in intelligibility. The current study assessed the intelligibility of compressed speech in order to determine whether it is appropriate for use in Internet-based training. English words minimally contrasting in /r/ and /l/, /b/ and /v/, or /s/ and /th/ were recorded from native speakers of English and compressed using several different methods (MP3, WMA, QCELP, ADPCM, etc.). The intelligibility of these speech files was then evaluated by a group of native English speakers and a group of native Japanese speakers, using a minimal-pair identification task. Results showed that: (1) intelligibility scores for Japanese speakers were lower than those for the English speakers, as was expected; and (2) intelligibility of /r/–/l/ stimuli was unaltered by the compression, whereas intelligibility of /s/–/th/ stimuli dropped remarkably in several formats, and that of /b/–/v/ stimuli dropped only in QCELP-compressed words. These findings suggest that some compression formats are not appropriate in speech perception training. Implications for Internet educational materials will be discussed.
Structure of the 8200-Year Cold Event Revealed by a Speleothem Trace Element Record
Authors: Baldini James U. L. , McDermott Frank , Fairchild Ian J.
Published: July 2002

Abrupt first-order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western Ireland during the 8200-year event (the major cooling episode 8200 years before the present) are interpreted as responses to a drier climate lasting about 37 years. Both shifts are centered on 8330 ± 80 years before the present, coinciding with a large oxygen isotope anomaly and a change in the calcite petrography. In this very high resolution (monthly) record, antipathetic second-order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality. Growth rate variations within the event reveal a two-pronged structure consistent with recent model simulations.
Pattern Formation in Homogeneous Polymer Solutions Induced by a Continuous-Wave Visible Laser
Authors: Sigel R. , Fytas G. , Vainos N. , Pispas S. , Hadjichristidis N.
Published: July 2002

We report an unexpected nonphotothermal material organization induced by continuous-wave visible laser light at low power levels. This effect is observed along the laser beam propagation direction in fully transparent entangled solutions of common homopolymers featuring sufficiently high molecular mass and optical anisotropy along the chain backbone. The resulting formation of long-lived stringlike or dotlike patterns on the micrometer scale, probed by dark-field coherent imaging, depends on the molecular mass, architecture, solvent nature, and polymer concentration. Electrostrictive and alignment forces as well as chain cooperativity are responsible for the osmotic compression of the polymer solute. Subsequent waveguiding effects induce autoamplification and “pattern writing” upon prolonged illumination. This wave-medium coupling could potentially lead to photorefractive, microoptics, and nanotechnology applications.