bluuebunny/crossref_metadata_2025 huggingface dataset:
On the spanning vectors of Lusztig cones
Authors: Bédard Robert
Published: July 2002

For each reduced expression

i

{\mathbf i}

of the longest element

w
0

w_0

of the Weyl group

W
W

of a Dynkin diagram

Δ
\Delta

of type

A
A

,

D
D

or

E
E

, Lusztig defined a cone

C

i

{\mathcal C}_{\mathbf i}

such that there corresponds a monomial in the quantized enveloping algebra

U

{\mathbf U}

of

Δ
\Delta

to each element of

C

i

{\mathcal C}_{\mathbf i}

and he asked under what circumstances these monomials belong to the canonical basis of

U

{\mathbf U}

. In this paper, we consider the case where

i

{\mathbf i}

is a reduced expression adapted to a quiver

Ω
\Omega

whose graph is

Δ
\Delta

and we describe

C

i

{\mathcal C}_{\mathbf i}

as the set of non-negative integral combination of spanning vectors. These spanning vectors are themselves described by using the Auslander-Reiten quiver of

Ω
\Omega

and homological algebra.
Kazhdan-Lusztig cells and decomposition numbers
Authors: Geck Meinolf
Published: July 2002

We consider a generic Iwahori–Hecke algebra

H
H

associated with a finite Weyl group. Any specialization of

H
H

gives rise to a corresponding decomposition matrix, and we show that the problem of computing that matrix can be interpreted in terms of Lusztig’s map from

H
H

to the asymptotic algebra 

J
J

. This interpretation allows us to prove that the decomposition matrices always have a lower uni-triangular shape; moreover, we determine these matrices explicitly in the so-called defect 

1
1

case.
Automation and the Organization of Production in the Japanese Automobile
Industry: Nissan and Toyota in the 1950s
Authors: Daito Eisuke
Published: July 2002

Rather than appearing full-blown in the 1970s, flexible production
techniques were developed gradually in the Japanese automobile industry.
After World War II, drawing on indigenous expertise derived from the cotton
textile and aircraft industries, pioneering automakers Nissan and Toyota
adapted Western-style automation technology, particularly transfer machines,
to local conditions. In addition to building flexibility into as many
aspects of this inherently inflexible technology as possible, manufacturers
also worked to adapt labor and supplier relations to the needs of the new
technology within the constraints of the local environment.
Reframing the Past: Thoughts about Business Leadership and Decision Making under Uncertainty
Authors: Lamoreaux Naomi R.
Published: July 2002

How do business leaders make decisions in the face of uncertainty? More important, how do business and economic historians write a narrative that links a business problem, its proposed solution, and the outcome of this action without allowing the success or failure of the decision to determine the trajectory of the story? Counterfactual hypotheses and contextual analysis provide two tools that can help historians minimize the distortions of hindsight and recover a sense of the contingency that surrounds all decisions.
Competition, Collusion, and Confusion: The State and the Reorganization of the British Cotton Industry, 1931–1939
Authors: Greaves Julian I.
Published: July 2002

British industrial policy in the 1930s has generated considerable historical controversy. This article furthers the debate by using the cotton industry as a case study. The biggest constraint on active government policies toward cotton was not institutional inertia or “industrial diplomacy,” as some historians claim, but the sheer practical difficulty of intervening in such a complex industry. Cotton also poses problems for historians who see British industrial policy in the 1930s as largely about restraining competition. The government feared that restriction would make matters worse in the cotton industry and was therefore hesitant about backing schemes designed to limit competition. Its dilemma was how best to maintain private-sector confidence.
Foveate vision in deep–sea teleosts: a comparison of primary visual and olfactory inputs
Authors: Collin Shaun P. , Lloyd Darren J. , Wagner Hans–Joachim
Published: July 2002

The relative importance of vision in a foveate group of alepocephalid teleosts is examined in the context of a deep–sea habitat beyond the penetration limits of sunlight. The large eyes of
Conocara
spp. possess deep convexiclivate foveae lined with Müller cells comprising radial shafts of intermediate filaments and horizontal processes. Photoreceptor cell (171.8 × 10
3
rods mm
−2
) and retinal ganglion cell (11.9 × 10
3
cells mm
−2
) densities peak within the foveal clivus and the perifoveal slopes, respectively, with a centro–peripheral gradient between 3:1 (photoreceptors) and over 20:1 (ganglion cells). The marked increase in retinal sampling localized in temporal retina, coupled with a high summation ratio (13:1), suggest that foveal vision optimizes both spatial resolving power and sensitivity in the binocular frontal visual field. The elongated optic nerve head is comprised of over 500 optic papillae, which join at the embryonic fissure to form a thin nervous sheet behind the eye. The optic nerve is divided into two axonal bundles; one receiving input from the fovea (only unmyelinated axons) and the other from non–specialized retinal regions (25% of axons are myelinated), both of which appear to be separated as they reach the visual centres of the central nervous system. Comparison of the number of primary (first–order) axonal pathways for the visual (a total of 63.4 × 10
6
rod photoreceptors) and olfactory (a total of 15.24 × 10
5
olfactory nerve axons) inputs shows a marked visual bias (ratio of 41:1). Coupled with the relative size of the optic tecta (44.0 mm
3
) and olfactory bulbs (0.9 mm
3
), vision appears to play a major role in the survival of these deep–sea teleosts and emphasizes that ecological and behavioural strategies account for significant variation in sensory brain structure.
Voxel size effects in three‐dimensional nuclear magnetic resonance microscopy performed for trabecular bone dosimetry
Authors: Rajon D. A. , Jokisch D. W. , Patton P. W. , Shah A. P. , Bolch W. E.
Published: July 2002

An important problem in internal dosimetry is the assessment of energy deposition by beta particles within trabecular regions of the skeleton. Recent dosimetry methods for trabecular bone are based on Monte Carlo particle transport simulations within three‐dimensional (3D) images of real human bone samples. Nuclear magnetic resonance (NMR) microscopy is a 3D imaging technique of choice due to the large signal differential between bone tissue and the water‐filled marrow cavities. Image voxel sizes currently used in NMR microscopy are between and but the images are time consuming to acquire and can only be performed at present for in vitro samples. It is therefore important to evaluate what resolution is best suitable in order to properly characterize the trabecular microstructure, to adequately predict the tissue dosimetry, and to minimize imaging time. In this work, a mathematical model of trabecular bone, composed of a distribution of spherical marrow cavities, was constructed. The mathematical model was subsequently voxelized with different voxel sizes to to simulate 3D NMR images. For each image, voxels are assigned to either bone or marrow according to their enclosed marrow fraction. Next, the images are coupled to the EGS4 electron transport code and absorbed fractions to bone and marrow are calculated for a marrow source of monoenergetic electrons. Radionuclide S values are also determined for the voxelized images with results compared to data calculated for the pure mathematical sample. The comparison shows that for higher energy electrons good convergence of the results is seen even within images of poor resolution. Above 400 keV, a voxel resolution as large as results in dosimetry errors below For low‐energy electrons and high‐resolution images, the self‐dose to marrow is also determined to within 5% accuracy. Nevertheless, increased voxelization of the image overestimates the surface area of the bone‐marrow interface leading to errors in the cross‐dose to bone as high as 25% for some low‐energy beta emitters.
Testing of the stability of intensity modulated beams generated with dynamic multileaf collimation, applied to the MM50 Racetrack Microtron
Authors: Dirkx M. L. P. , Heijmen B. J. M.
Published: July 2002

Recently, we have published a method for the calculation of required leaf trajectories to generate optimized intensity modulated x‐ray beams by means of dynamic multileaf collimation [Phys. Med. Biol. 43, 1171–1184 (1998)]. For the MM50 Racetrack Microtron it has been demonstrated that the dosimetric accuracy of this method, in combination with the dose calculation algorithm of the Cadplan 3D treatment planning system, is adequate for a clinical application (within 2% or 0.2 cm). Prior to initiating patient treatment with dynamic multileaf collimation (DMLC), tests have been performed to investigate the stability of DMLC fields generated at the MM50, (i) in time, (ii) subject to gantry rotation and (iii) in case of treatment interrupts, e.g., caused by an error detected by the treatment machine. The stability of relative dose profiles, normalized to a reference point in a relatively flat part of the modulated beam profile, was assessed from measurements with an electronic portal imaging device (EPID), with a linear diode array attached to the collimator and with film. The dose in the reference point was monitored using an ionization chamber. Tests were performed for several intensity modulated fields using 10 and 25 MV photon beams. Based on film measurements for sweeping 0.1 cm leaf gaps it was concluded that in an 80 days period the variation in leaf positioning was within 0.05 cm, without requiring any recalibration. For a uniform 10×10 field, realized dynamically by a scanning 0.4×10 slit beam, a maximum variation in slit width of 0.01 cm was derived from ionization chamber measurements, both in time and for gantry rotation. For a clinical example, the dose in the reference point reproduced within 0.2% (1 SD) over a period of 100 days. Apart from regions with very large dose gradients, variations in the relative beam profiles measured with the EPID were generally less than 1% (1 SD). For different gantry angles the dose profiles also reproduced within 1%, showing that gravity has a negligible influence. No significant deviations between uninterrupted and interrupted treatments could be observed, indicating that the effects of acceleration and deceleration of the leaves are negligible and that a DMLC treatment can be finished correctly after a treatment interrupt. Our previous and present studies have demonstrated that the dosimetric accuracy and stability of intensity modulated beams, generated at the MM50 by means of dynamic multileaf collimation, are adequate for clinical use. Patient treatment using dynamic multileaf collimation has been started in our clinic.
Monte Carlo simulation of dynamic wedged fields
Authors: Shih Rompin
Published: July 2002

This thesis studied the dosimetric characteristics of the dynamic wedge (DW) for a linear accelerator using a Monte Carlo technique based on the EGS4/BEAM system. The geometry of a linear accelerator was simulated. For the DW technique, the segmented treatment table (STT) contains information on the collimator position versus cumulative weighting of monitor units. The simulation of DW was accomplished by weighting the incidence electron fluence with the STT. Calculations were performed for DW and physical wedge (PW) with wedge angles ranging from 15° to 60° for both 6 and 18 MV photon beams and for a whole range of field sizes. The calculated percentage depth doses and beam profiles agreed with the corresponding measurements within 2%. Our calculations show that the effects of a DW on the spectrum and angular distributions (as well as electron contamination) are much less significant than with a PW. A 45° PW in the 6 MV photon beam results in a 30% increase in mean photon energy due to beam hardening. It also results in a 5% dose reduction in the build‐up region due to filtration of contaminated electrons. Neither this mean photon energy increase nor dose reduction is found for a DW. Field size dependence of a DW was also investigated thoroughly. The mean photon energy on the beam axis was reduced by 12.3% as the field size increases from 4×4 to 20×20 for both DW and open fields. The dose in the build‐up region is increased up to 10% due to the increase of the contaminated electrons for a large field size. The results of this work should improve radiotherapy treatment planning with dynamic wedges.
Dosimetric characteristics of the CDC‐type miniature cylindrical brachytherapy sources
Authors: Pérez‐Calatayud J. , Ballester F. , Serrano‐Andrés M. A. , Lluch J. L. , Puchades V. , Limami Y. , Casal E.
Published: July 2002

The low dose rate CDC‐type miniature cylindrical sources are available, with one or three active beads, for use in source trains in automatic and manual afterloading systems for gynecological brachytherapy. Absolute dose rate distributions in water have been calculated around these sources using the Monte Carlo GEANT3 code and they are presented as conventional two‐dimensional Cartesian lookup tables. The AAPM Task Group 43 formalism for dose calculation has been also applied. The dose rate constant obtained for the one bead source is and the value for the three bead source is Finally, for the treatment planning systems based on Sievert‐type algorithms, the attenuation coefficients that best reproduce Monte Carlo dose rate distribution are given.
Surface area overestimation within three‐dimensional digital images and its consequence for skeletal dosimetry
Authors: Rajon D. A. , Patton P. W. , Shah A. P. , Watchman C. J. , Bolch W. E.
Published: July 2002

The most recent methods for trabecular bone dosimetry are based on Monte Carlo transport simulations within three‐dimensional (3D) images of real human bone samples. Nuclear magnetic resonance and micro‐computed tomography have been commonly used as imaging tools for studying trabecular microstructure. In order to evaluate the accuracy of these techniques for radiation dosimetry, a previous study was conducted that showed an overestimate in the absorbed fraction of energy for low‐energy electrons emitted within the marrow space and irradiating the bone trabeculae. This problem was found to be related to an overestimate of the surface area of the true bone‐marrow interface within the 3D digital images, and was identified as the surface‐area effect. The goal of the present study is to better understand how this surface‐area effect occurs in the case of single spheres representing individual marrow cavities within trabecular bone. First, a theoretical study was conducted which showed that voxelization of the spherical marrow cavity results in a 50% overestimation of the spherical surface area. Moreover, this overestimation cannot be reduced through a reduction in the voxel size (e.g., improved image resolution). Second, a series of single‐sphere marrow cavity models was created with electron sources simulated within the sphere (marrow source) and outside the sphere (bone trabeculae source). The series of single‐sphere models was then voxelized to represent 3D digital images of varying resolution. Transport calculations were made for both marrow and bone electron sources within these simulated images. The study showed that for low‐energy electrons the 50% overestimate of the bone‐marrow interface surface area can lead to a 50% overestimate of the cross‐absorbed fraction. It is concluded that while improved resolution will not reduce the surface area effects found within 3D image‐based transport models, a tenfold improvement in current image resolution would compensate the associated errors in cross‐region absorbed fractions for low‐energy electron sources. Alternatively, other methods of defining the bone‐marrow interface, such as with a polygonal isosurface, would provide improvements in dosimetry without the need for drastic reductions in image voxel size.
The effect of gamma ray penetration on angle‐dependent sensitivity for pinhole collimation in nuclear medicine
Authors: Smith Mark F. , Jaszczak Ronald J.
Published: July 2002

The sensitivity of a pinhole collimator for gamma ray imaging in nuclear medicine is dependent on the angle of incidence of the gamma rays. The effect of penetration near the pinhole aperture on angle‐dependent sensitivity was investigated using experimental measurements and numerical modeling. Projection data measurements were acquired with Tc‐99m and I‐131 point sources using tungsten pinhole inserts with 1.0 to 4.0 mm diameter apertures. Curves of the form where θ is the angle of the incident ray with the surface of the detector crystal, were fit to sensitivity measurements from the projection data. Experimentally measured values were between 3.3 and 4.1 for Tc‐99m and between 5.1 and 7.2 for I‐131. Penetration near the pinhole aperture was modeled using (1) an expression for effective pinhole diameter that is a generalization of Anger's formula for normally incident photons and (2) a photon transport simulation code. Experimentally measured sensitivity exponents from new and previously reported experimental observations were modeled within 15% by the numerical simulations. For modeling using the generalized expression for effective diameter the average error was 1.4% and the standard deviation was 7.7%. For the photon transport simulation code the average error was 1.5% and the standard deviation also was 7.7%. The effect of pinhole aperture design parameters on angle‐dependent sensitivity for high resolution pinhole apertures was modeled using a photon transport simulation code. The sensitivity exponents were greater for 364 keV photons than for 140 keV photons and were greater for small aperture diameters, small acceptance angles, and large aperture channel heights. These results provide theoretical justification for incorporating sensitivity corrections, with greater than the value of 3 for an impenetrable pinhole, in filtered backprojection and iterative reconstruction algorithms for single photon emission computed tomography (SPECT) pinhole imaging. Simulated I‐131 SPECT studies for uniformly active cylinders showed that activity concentrations were underestimated toward the outside of the cylinders when a rather than the correct sensitivity correction was applied in image reconstruction.
Approximate 3D iterative reconstruction for SPECT
Authors: Gilland David R. , Jaszczak Ronald J. , Riauka Terence A. , Coleman R. Edward
Published: July 2002

Compared with slice‐by‐slice approaches for SPECT reconstruction, three‐dimensional iterative methods provide a more accurate physical model and an improved SPECT image. Clinical application of these methods, however, is limited primarily by their computational demands. This paper investigates methods for approximate 3D iterative reconstruction that greatly reduce this demand by excluding from the reconstruction the smaller magnitude elements of the system matrix. A new method is described which is designed to control the resulting bias in the SPECT image for a given reduction in computation. The approximate methods were compared to fully 3D iterative reconstruction in terms of SPECT image bias and visual quality. All methods were incorporated into the ML‐EM algorithm and applied to data from 3D mathematical and experimental brain phantoms. The SPECT images reconstructed by the approximate methods exhibited a positive bias throughout the image that was in general smaller with the new method (in the range of 2%–6%). The bias was smallest in locally hot regions and largest in locally cold regions. The high quality brain phantom images demonstrated the capability of the new method in realistic imaging contexts. The time per iteration for an entire 3D brain phantom on a modern workstation using the approximate 3D method was 7.9 s.
Extended random‐dot models for radiographic image noise analysis [In Japanese]
Authors: Yamada Isao
Published: July 2002

The object of this thesis was to study the basic characteristics of radiographic image noise using a microscopic theoretical model. Radiographic images obtained by screen‐film systems contain various noise sources: quantum mottle, structure mottle and film granularity. These noise sources affect the signal detectability in the radiographic image. A two‐dimensional microstructure model for radiographic image noise is proposed, i.e., an extended random‐dot model which obeys triple Poisson process. Rigorous expressions of mean transmittance and autocorrelation function were obtained. By using numerical calculations, it is shown that this model can explain basic characteristics of radiographic image noise. Next, a random‐dot model containing a signal is used to evaluate the theoretical detectability of computer‐generated random‐dot images, i.e., idealized models of nuclear‐medicine images. Theoretical detectability of a random‐dot model containing a signal are calculated and compared with the results of receiver operating characteristics analysis (ROC). The results of ROC analysis were in agreement with the calculated theoretical detectability.
Characteristics of clinical electron beams: Current and optimal
Authors: Ebert Martin A.
Published: July 2002

This thesis presents the results of two investigations into the characteristics of electron beams for application in radiation therapy. The first involves modeling the interactions between the applicator of a Siemens Mevatron KD2 linear accelerator, and the accelerator's electron beam. EGS4 Monte Carlo code is used to simulate narrow beams incident on sections of applicator trimming plate edges in order to investigate the characteristics of scattering off these edges. A model for scatter from irregular apertures is developed based on a superposition of scatter kernels from edge elements. This model is found to give central‐axis depth dose and profile data consistent with measured results. The model is also used to obtain detailed information of the characteristics of particles scattered from the electron applicator. In the second investigation, optimal electron beam properties are determined by inversion of desired dose distributions using a simulated annealing optimization method. This technique is used for several regular desired dose distributions, and various intuitive results are obtained regarding the effects electron energy and angular modulation have on resulting dose distributions. The technique is also used for several complex desired dose distributions, indicating the relative influence energy and angular modulation can have on dose conformation with electrons.
Magnetic resonance imaging in radiotherapy treatment planning
Authors: Moerland Marinus A.
Published: July 2002

The aim of this study is to investigate the capabilities of magnetic resonance imaging (MRI) in radiotherapy treatment planning (RTP) and to explore the MR image distortions and how these distortions can be reduced or, if necessary, corrected in order to integrate MRI into RTP in a reliable manner. Image distortions and the efficacy of correction methods were evaluated in phantom, volunteer, and patient studies. From the measurement, analysis, and correction of machine‐related geometric distortions in MRI, it was concluded that MR image corrections are necessary in applications which require mm accuracy and that correction methods, based on 3D maps of static field inhomogeneity and gradient nonlinearity, are feasible in clinical practice. From the measurement and numerical analysis of object‐related geometric distortions, it was concluded that these distortions can be reduced to the order of the pixel size by imaging at 0.5 T and using gradients on the order of 3 Furthermore, in a study on volunteers, fast MRI scan techniques were used to measure the respiration induced kidney movement and in a study on patients with prostate cancer, the value of MRI for the evaluation of brachytherapy was demonstrated. The MR image artifacts induced by the I‐125 seeds were used to evaluate the dose distributions and dose volume histograms of permanent prostate implants.
Accelerator‐based boron neutron capture therapy
Authors: Howard William Bruce
Published: July 2002

Boron neutron capture therapy (BNCT) is a promising therapy modality for cancer. Clinical trials are under way. BNCT works by a selective loading of tumor cells with and subsequent irradiation of the tumor with thermal neutrons. The reaction is induced which releases 2.3 MeV of energy. In accelerator‐based BNCT, neutrons for this therapy are produced using particle induced reactions. Three reactions, =2.5 MeV, =3.0–4.0 MeV, and =2.6 MeV were investigated. Complete data for the reaction were not previously available. Therefore, 28 thick target neutron spectra were measured, on an absolute basis, using time‐of‐flight techniques. Proton energies of 3.0, 3.4, 3.7, and 4.0 MeV and laboratory angles of 0°–145° were used. The accuracy of the data was confirmed by measuring a different reaction. Monte Carlo techniques were used to design therapy beams. Using and therapy times of 12–25 and 27–60 min, respectively, were predicted (tumor depth 2–6 cm, 15 RBE‐Gy total tumor dose, 10 kW accelerator beam power, 30 ppm boron tumor concentration). The total tumor dose includes four components [fast neutron, thermal neutron, gamma, and which are estimated by using energy‐dependent fluence‐to‐kerma conversion factors. Using and a 1 mA beam current, nearly equivalent therapy beam parameters were predicted with 4.0 and 3.7 MeV protons. For equivalent accelerator beam power, 3.7 MeV protons would produce higher dose rates. Using resulted in lower dose rates. Facility shielding is presented.
A software tool for the quantitative evaluation of 3D dose calculation algorithms
Authors: Harms William B. , Low Daniel A. , Wong John W. , Purdy James A.
Published: July 2002

Current methods for evaluating modern radiation therapy treatment planning (RTP) systems include the manual superposition of calculated and measured isodose curves and the comparison of a limited number of calculated and measured point doses. Both techniques have significant limitations in providing quantitative evaluations of the large number of dose data generated by modern RTP systems. More sophisticated comparison techniques have been presented in the literature, including dose‐difference and distance‐to‐agreement (DTA) analyses. A software tool has been developed that uses superimposed isodose plots, dose‐difference, and DTA distributions to quantify errors in computed dose distributions. Dose‐difference and DTA analyses are overly sensitive in regions of high‐ and low‐dose gradient, respectively. The logical union of locations that fail both dose‐difference and DTA acceptance criteria, termed the composite evaluation, is calculated and displayed. The composite evaluation provides a method for the physicist to efficiently identify regions that fail both the dose‐difference and DTA acceptance criteria. The tool provides a computer platform for the quantitative comparison of calculated and measured dose distributions.
An interlaboratory measurement of screen‐film speed and average gradient according to ISO 9236‐1
Authors: Buhr Egbert , Bergmann Detlef , Hoeschen Dietmar , Ailliet Marc , Sirand‐Rey Gérard , Gazzola Carlo , Uras Sergio
Published: July 2002

The speed and average gradient of a conventional screen‐film system was measured at four European laboratories. This is the first interlaboratory comparison in which the measurement conditions described in ISO 9236‐1 were applied. The four laboratories used calibrated measurement equipment. The values obtained by the four laboratories were within a range of 14% for the speed and within a range of 8% for the average gradient. These variations are consistent with the expected measurement uncertainty.
A simple technique for alignment of perineal needle template to ultrasound image grid for permanent prostate implants
Authors: Mutic Sasa , Low Daniel A. , Nussbaum Gilbert H. , Williamson Jeffrey F. , Haefner Delena
Published: July 2002

Proper alignment of a needle template and ultrasound software grid is required to accurately deliver permanent prostate seed implants optimized using pretreatment volume studies. Correct alignment may also reduce tissue edema, morbidity, and the time and labor required to deliver permanent prostate seed implants. A technique has been developed to rapidly assess (and, if necessary, improve) the alignment using a custom‐designed water phantom. Verification of needle positions can be conducted within 1 mm and requires less than ten minutes. We have instituted the technique as a part of our periodic quality assurance program.
Catheter autoreconstruction in computed tomography based brachytherapy treatment planning
Authors: Milickovic N. , Giannouli S. , Baltas D. , Lahanas M. , Kolotas C. , Zamboglou N. , Uzunoglu N.
Published: July 2002

The aim of this study is to develop an automatic reconstruction of brachytherapy catheters using CT (computed tomography) data. Previously no such automatic facility has existed in any treatment planning software. To achieve this facility we have developed tools for the automatic reconstruction (which we term autoreconstruction) of plastic and metallic catheters. These algorithms overcome a number of difficulties which arise when a large number of catheters are present. These include situations with intersecting catheters and with loop techniques. The time required for the catheter reconstruction process using our autoreconstruction method is significantly reduced. The accuracy of our autoreconstruction is at least as high as the classical manual slice‐by‐slice method.
Motion of a hanging chain after the free end is given an initial velocity
Authors: Bailey Herb
Published: July 2002

One end of a chain is attached to the ceiling and the free end is given a sharp horizontal blow. The resulting pulse travels to the top of the chain, and a few seconds later the reflected pulse causes the free end to give a kick. The free end kicks again and again at regular intervals. The time between kicks is constant and has been accurately predicted by the solution of an ordinary differential equation. Close observation of the nature of successive kicks shows that they are not always in the same direction, but they do follow a pattern that repeats every four kicks. We have modeled this experiment by solving the wave equation with variable tension and summing the resulting series solution. The lateral deflection as a function of time and distance along the chain was calculated. The predicted deflection of the free end is in good agreement with experimental results obtained from a movie of the chain motion.
Psychoacoustic correlates of individual noise sensitivity
Authors: Ellermeier Wolfgang , Eigenstetter Monika , Zimmer Karin
Published: July 2002

In environmental noise surveys, self-reported noise sensitivity, a stable personality trait covering attitudes toward a wide range of environmental sounds, is a major predictor of individual noise-annoyance reactions. Its relationship to basic measures of auditory functioning, however, has not been systematically explored. Therefore, in the present investigation, a sample of 61 unselected listeners was subjected to a battery of psychoacoustic procedures ranging from threshold determinations to loudness scaling tasks. No significant differences in absolute thresholds, intensity discrimination, simple auditory reaction time, or power-function exponents for loudness emerged, when the sample was split along the median into two groups of “low” vs “high” noise sensitivity on the basis of scores obtained from a psychometrically evaluated questionnaire [Zimmer and Ellermeier, Diagnostica 44, 11–20 (1998)]. Small, but systematic differences were found in verbal loudness estimates, and in ratings of the unpleasantness of natural sounds, thus suggesting that self-reported noise sensitivity captures evaluative rather than sensory aspects of auditory processing.
Electromagnetic articulograph based on a nonparametric representation of the magnetic field
Authors: Kaburagi Tokihiko , Honda Masaaki
Published: July 2002

Electromagnetic articulograph (EMA) devices are capable of measuring movements of the articulatory organs inside and outside the vocal tract with fine spatial and temporal resolutions, thus providing useful articulatory data for investigating the speech production process. The position of the receiver coil is detected in the EMA device on the basis of a field function representing the spatial pattern of the magnetic field in relation to the relative positions of the transmitter and receiver coils. Therefore, the design and calibration of the field function are quite important and influence the accuracy of position detection. This paper presents a nonparametric method for representing the magnetic field, and also describes a method for determining the receiver position from the strength of the induced signal in the receiver coil. The field pattern in this method is expressed by using a multivariate spline as a function of the position in the device’s coordinate system. Because of the piecewise property of the basis functions and the freedom in the selection of the rank and the number of the basis functions, the spline function has a superior ability to flexibly and accurately represent the field pattern, even when it suffers from fluctuations caused by the interference between the transmitting channels. The position of the receiver coil is determined by minimizing the difference between the measured strength of the received signal and the predicted one from the spline representation of the magnetic field. Experimental results show that the error in estimating the receiver position is less than 0.1 mm for a 14×14-cm measurement area, and this error can be further reduced by using a spline-smoothing technique.
Measurements of two types of dilatational waves in an air-filled unconsolidated sand
Authors: Hickey Craig J. , Sabatier James M.
Published: July 2002

This study consists of laboratory measurements of dilatational waves propagating through an air-filled unconsolidated sand. One excitation technique consists of a loudspeaker suspended in the air above the packing of sand. A second excitation technique uses a mechanical shaker in contact with the sand. The transmitted signals are received using microphones and geophones located at various depths within the sand. An interpretation based on measured phase speeds indicates that the transmitted energy from the suspended loudspeaker source is partitioned primarily but not exclusively into the type-II dilatational wave. This wave attenuates rapidly and is only detected at depths of less than about 15 cm for this particular sample. At the deeper depths the detected signal is associated with the type-I dilatational wave. The mechanical shaker produces only a type-I dilatational wave. Both the geophone and microphone sensors can detect both types of dilatational waves.
Direct experimental investigations of acoustic modes guided by a solid–solid interface using optical interferometry
Authors: Matteï Ch. , Jia X. , Quentin G.
Published: July 2002

This paper presents direct field measurements of acoustic modes guided by the interface between two transparent solids. The measurement technique is based on the acousto-optical interaction inside the solid between the acoustic field and the probe laser beam of an interferometer. The main advantage of the method is its ability to measure acoustic strain fields in areas of difficult access with the classic detection methods. Moreover, it gives complete information about the dilatation strain field inside the solid, e.g., amplitude and phase. The propagation of a real velocity mode (Stoneley wave) is first illustrated. Then the situation of complex velocity modes is investigated for a Plexiglas–fused quartz slip interface. This material combination supports two possible interface modes theoretically. These modes are simultaneously observed and the differences between their behavior are measured.
Responses of auditory nerve fibers to trains of clicks
Authors: Wickesberg Robert E. , Stevens Hanna E.
Published: July 2002

Responses of auditory nerve fibers to trains of clicks were recorded in ketamine anesthetized chinchillas. By varying the number of clicks and the interclick interval, this study examined whether “post-onset adaptation,” described in psychoacoustic experiments on localization, occurred in auditory nerve fibers. The results showed that the number of action potentials recorded from a nerve fiber in response to a train of clicks was a power function of the number of clicks. For interclick intervals of 2 ms or greater the exponent of the power function was 0.5, and this exponent did not change over a 20-dB range of intensities. The timing of action potentials relative to the click stimuli was measured using synchronization coefficients. The coefficients increased with interclick interval, decreased with increasing intensity, and were greater for fibers with low rates of spontaneous activity than for high spontaneous fibers. Recovery functions showed that for interclick intervals of 2 ms or more, the responses to the second click were at least 70% of the response to the initial click. The recovery depended upon the number of clicks in the train. These findings indicate that auditory nerve fibers respond to high rates of stimulus presentation and do not display the adaptation observed in localization studies.
One-channel time-reversal in chaotic cavities: Theoretical limits
Authors: Draeger Carsten , Fink Mathias
Published: July 2002

One-channel time-reversal experiments in closed chaotic cavities produce excellent, but not perfect, time-reversed focusing. This paper investigates such experiments by a simple eigenmode analysis of the system. It shows that the process is, even for long reversed signals, subject to an information loss during recording and re-emission which prevents perfect time-reversal. This fact can be expressed by a simple equation, called the cavity equation, which states that the signal of a one-channel time-reversal is equal to the signal of a perfect time-reversal after convolution with the backscattering impulse response of the reversal point (i.e., from this point to this point). The latter convolution describes the introduction of the loss of information. Furthermore, arguments are presented suggesting that one third of the total energy of the time-reversed wave field is actually contained in the refocusing wavefront. The predictions are verified by numerical finite-difference time-domain simulations.
Sensitivity measurements of piezoelectric polymer hydrophones from 0.2–2 MHz using a broadband-pulse technique
Authors: Harris Gerald R. , Gammell Paul M.
Published: July 2002

It is widely recognized that the sensitivity of hydrophones used to measure medical diagnostic ultrasound fields should be uniform over several octaves above the center frequency (i.e., above the mean of the upper and lower −3 dB frequencies in the transmitted acoustic-pressure spectrum). However, a bandwidth extending to at least ten times below the diagnostic pulse-center frequency is needed for accurate (error ≈5%) measurement of the peak rarefactional pressure. Since at present it is not common for manufacturers of medical-use hydrophones to provide sensitivity information below 1–2 MHz, a study was undertaken to determine these low-frequency sensitivities. The technique uses broadband, plane-wave pressure pulses generated by electrical short-pulse excitation of a thick piezoelectric ceramic disk. The hydrophone response is calculated from measurements of the source transducer and hydrophone-voltage waveforms. The frequency responses of both needle-type and spot-poled membrane polymer hydrophones were measured using this technique. The spot-poled membrane hydrophones had −3-dB bandwidths extending below 0.2 MHz, the lower limit for the calibration technique. The needle-type hydrophones studied, however, all exhibited a response roll-off of greater than 3 dB in the frequency range studied. Therefore, given the above bandwidth criterion as a function of diagnostic pulse-center frequency, the sensitivity to at least 0.2 MHz should be established for diagnostic-use hydrophones, because a uniform response below 1 MHz cannot be assumed.
Calculation of surface wave motions due to a subsurface point force: An application of elastodynamic reciprocity
Authors: Achenbach J. D.
Published: July 2002

The elastodynamic reciprocity theorem for two time-harmonic elastodynamic states of the same body is used to determine the surface wave motions generated by a subsurface point load of arbitrary direction in an isotropic, homogeneous, elastic half-space. The actual surface wave motions due to the point load expressed in a suitably general form represent one of the states, while the other one is an appropriately selected auxiliary solution consisting of incoming and outgoing surface waves. A direct application of the reciprocity theorem yields the desired information on the generated surface wave motion.
The Effect of Branching on the Melt Rheology of Polyethylene
Authors: Boghetich L. , Kratz R. F.
Published: July 2002

Melt viscosity data were obtained for linear and branched ethylene polymers over temperatures of 150 to 250°C and shear rates of about one to 300 sec−1. A capillary rheometer was employed, and the appropriate corrections were made for the several sources of significant error in shear stress and shear rate. These corrected data were analyzed in terms of the Ree-Eyring inverse hyperbolic sine relationship for viscous flow. The molecular structure was determined by infrared absorption analyses and molecular weight determinations. The rheological character of these polyethylenes was found to depend on the weight-average length of the polymer backbone and on the branching. The major contribution to the viscosity depended on the length of the backbone and was associated with the longer relaxation times. An additional contribution to the viscosity depended on molecular segments about equal to the interbranch distance, and was associated with the shorter relaxation times. The temperature effect was found to depend on the number of the long-chain branches, as interpreted by the reduced variable procedure applied to the shear rate.
Concentration Redistribution Phenomena in the Shear Flow of Monolayers of Suspended Particles
Authors: Brandt Alan , Bugliarello George
Published: July 2002

The full range of phenomena occurring in the flow of suspensions remains still unexplored. This paper describes phenomena observed in a neutrally buoyant suspension consisting of a single layer (a monolayer) of rigid spherical particles, flowing through a 220-cm long rectangular channel of high-aspect ratio (1:16) with its minor dimension (116in.) 1.6 times larger than the particle diameter. The flow was investigated over a range of particle Reynolds numbers between 101 and 407, and of concentrations between 1.7 and 5%. Concentration distributions obtained from a detailed analysis of direct photographic observations show the existence of four consecutive regions as the suspension moves down the channel: (a) an initial region, close to the channel entrance, characterized by essentially uniform particle distribution. (b) A region in which the particles move away from the wall forming a particle-free layer next to it. The core containing the particles does not have a uniform concentration distribution but exhibits marked concentration peaks at its outer margin. (c) A region in which the core has narrowed, the peaks have merged, and the concentration has become uniform. (d) A region of instability characterized by the onset of waves in the configuration of the core, followed, as the flow progresses downstream, by a breaking up of the core and by the formation of groups of particles separated by axial gaps of suspending liquid. The transitions between these regions are not sharply bounded, each region evolving gradually into the next. The process is accelerated by increases in flow velocity, and decelerated by increases in concentration. The phenomena point to the existence of a hydrodynamic force leading to the formation of the core, and possibly of concentration-dependent particle interactions opposing such a formation and contributing to the onset of instabilities.
Dynamic Intrinsic Viscosity of Macromolecules with Internal Viscosity. III. Effect of Molecular Weight, Excluded Volume, and Hydrodynamic Interaction
Authors: Peterlin A. , Reinhold Chr.
Published: July 2002

The frequency dependence of the complex intrinsic viscosity and elastic modulus of a macromolecule with internal viscosity is calculated for the Gaussian coil and the coil with excluded volume in a wide range of molecular weight and hydrodynamic interaction. Due to limitations in eigenvalues and because of coil rotation in laminar flow the results obtained are sufficiently accurate only for a large number of coil segments and for small internal viscosity. Hydrodynamic interaction enhances the effect of internal viscosity so that the macromolecule seems to be stiffer than in the free-draining case. The non-Gaussian character of intrachain distances has a very small effect. Finite internal viscosity yields a nonvanishing limiting viscosity at ω→∞ which at sufficiently large M increases as M1/6. The relative limiting viscosity [η]∞′/[η]0 as a function of molecular weight (Z∼M), hydrodynamic interaction (h), non-Gaussian character of the coil (ε), and internal viscosity (φ) can be well represented by a single master curve if plotted against ν1φ/Zf. The eigenvalue ν1 is unity for the free-draining coil and asymptotically increases as a linear function of h and ε. Molecular weight enters the abscissa of the master curve implicitly through ν1 and explicitly through Z.
The Steady-State Compliance of Polymer Solutions
Authors: Kusamizu Sumio , Holmes Larry A. , Moore Arthur A. , Ferry John D.
Published: July 2002

The steady-state compliance (Je) has been derived from low-frequency dynamic viscoelastic measurements on solutions of several sample of polystyrene, poly-α-methyl styrene, polyvinyl acetate, and cellulose tributyrate in several different solvents including a Θ solvent for polystyrene. The molecular weight (M) distributions were reasonably sharp. Maximum concentrations (c) ranged from 0.17 g/ml (M=860,000) to 0.55 g/ml (M=19,800). In general, Je changes with increasing concentration from a value close to the Zimm theory prediction to a value close to the Rouse theory prediction, the transition occurring in the neighborhood of c[η]=3, where [η] is the intrinsic viscosity. However, for polystyrenes of molecular weights 19,800 and 51,000, values of Je were abnormally small, and some of those for cellulose tributyrate appeared to be abnormally large. Otherwise, there is no marked influence of the chemical nature of either polymer or solvent. The change in behavior with increasing concentration near c[η]=3 is attributed to an overlapping of molecular domains which is sufficient to alter the hydrodynamic interaction. A further change, observed by other investigators at higher concentrations, where the dependence of Je on c and M becomes quite different, is attributed to domination of the behavior by entanglements which develop at a higher degree of overlapping.
Limits of Linear Viscoelasticity and Yield of a Filled and Unfilled Epoxy Resin
Authors: Ishai O. , Bodner S. R.
Published: July 2002

An experimental program was performed to determine the limit of linear viscoelastic response, the onset of yielding, and the condition of gross yielding for a pure and quartz particle filled epoxy resin. The onset of yielding was investigated by a number of different tests, e.g., examination of hysteresis loops, photoelasticity. The tests were performed in both tension and compression over a range of loading times. The limit stresses were found to depend strongly on the loading times.