bluuebunny/crossref_metadata_2025 huggingface dataset:
Studying insect diversity in the tropics
Authors: Godfray H. C. J. , Lewis O. T. , Memmott J.
Published: July 2002

Understanding the extent and causes of insect diversity in the humid tropics is one of the major challenges in modern ecology. We review some of the current approaches to this problem, and discuss how future progress may be made. Recent calculations that there may be more than 30 million species of insect on earth have focused attention on the magnitude of this problem and stimulated several new lines of research (although the true figure is now widely thought to be between five and ten million species). We discuss work based on insecticidal fogging surveys; studies of herbivore and parasitoid specificity; macroecological approaches; and the construction of food webs. It is argued that progress in estimating insect diversity and in understanding insect community dynamics will be enhanced by building local inventories of species diversity, and in descriptive and experimental studies of the trophic structure of communities. As an illustration of work aimed at the last goal, we discuss the construction and analysis of quantitative host–parasitoid food webs, drawing on our work on leaf miner communities in Central America.
Colour vision in billfish
Authors: Fritsches Kerstin A. , Partridge Julian C. , Pettigrew John D. , Marshall N. Justin
Published: July 2002

Members of the billfish family are highly visual predatory teleosts inhabiting the open ocean. Little is known about their visual abilities in detail, but past studies have indicated that these fishes were likely to be monochromats. This study, however, presents evidence of two anatomically distinct cone types in billfish. The cells are arranged in a regular mosaic pattern of single and twin cones as in many fishes, and this arrangement suggests that the different cone types also show different spectral sensitivity, which is the basis for colour vision. First measurements using microspectrophotometry (MSP) revealed a peak absorption of the rod pigment at 484 nm, indicating that MSP, despite technical difficulties, will be a decisive tool in proving colour vision in these offshore fishes. When hunting, billfish such as the sailfish flash bright blue bars on their sides. This colour reflects largely in ultraviolet (UV) light at 350 nm as revealed by spectrophotometric measurements. Billfish lenses block light of wavelengths below 400 nm, presumably rendering the animal blind to the UV component of its own body colour. Interestingly, at least two prey species of billfish have lenses transmitting light in the UV waveband and are therefore likely to perceive a large fraction of the UV peak found in the blue bar of the sailfish. The possible biological significance of this finding is discussed.
Comparative analyses for adaptive radiations
Authors: Harvey Paul H. , Rambaut Andrew
Published: July 2002

Biologists generally agree that most morphological variation between closely related species is adaptive. The most common method of comparative analysis to test for co–evolved character variation is based on a Brownian–motion model of character evolution. If we are to test for the evolution of character covariation, and we believe that characters have evolved adaptively to fill niches during an adaptive radiation, then it is appropriate to employ appropriate models for character evolution. We show here that under several models of adaptive character evolution and coevolution during an adaptive radiation, which result in closely related species being more similar to each other than to more distantly related species, cross–species analyses are statistically more appropriate than contrast analyses. If the evolution of some traits fits the Brownian–motion model, while others evolve to fill niches during an adaptive radiation, it might be necessary to identify the number of relevant niche dimensions and the modes of character evolution before deciding on appropriate statistical procedures. Alternatively, maximum–likelihood procedures might be used to determine appropriate transformations of phylogenetic branch lengths that accord with particular models of character evolution.
A dose reduction x‐ray beam positioning system for high‐speed multislice CT scanners
Authors: Toth Thomas L. , Bromberg Neil B. , Pan Tin‐Su , Rabe Jerry , Woloschek Steven J. , Li Jianying , Seidenschnur George E.
Published: July 2002

The introduction of multislice CT scanners and the associated dose increase compared to single and dual slice scanners has concerned many radiologists, health and medical physicists, as well as members of the regulatory community. Since multislice CT scanners are inherently post‐patient collimated, they are less dose efficient than single slice CT scanners, which use prepatient collimation. The x‐ray beam must be wide enough in the Z axis so that the beam remains on the detector in spite of typical movements due to thermal and mechanical flexing. We describe the x‐ray beam tracking system that is employed on a GE LightSpeed QX/i® scanner to substantially reduce the multislice dose. The tracking system stabilizes the beam on the detector allowing a narrower x‐ray exposure profile compared to the x‐ray exposure profile without tracking. The tracking system measures the position of the beam every few milliseconds and continually repositions a source aperture to hold a narrow beam fixed on the detector. Using a standard LightSpeed QX/i® source collimator and segmented detector, dose reductions of up to 40% were measured when tracking was employed. We also show that tracking has the potential to provide a dose efficiency approaching single slice scanners.
Determination of guidance levels of dose for diagnostic radiography in Taiwan
Authors: Tung C. J. , Tsai H. Y. , Lo S. H. , Guan C. N. , Chen Y. B.
Published: July 2002

The International Atomic Energy Agency has recommended guidance levels of dose for diagnostic radiography for a typical adult patient. These levels were intended to act as thresholds to trigger investigations or corrective actions in ensuring optimized protection of patients and maintaining appropriate levels of good practice. Since guidance levels should be derived from wide scale surveys of exposure factors performed in individual hospitals, a national survey was conducted recently in Taiwan to collect these factors for the most frequent radiographic procedures. A total of 276 completed questionnaires were received and analyzed. In the questionnaire, respondents were asked to check those projections that were routinely performed in their department and to report machine data, patient data, output measurements, and technical factors including kVp, mAs, focus‐to‐film distance, table‐to‐film distance, aluminum filtration, and focal spot size. Based on the survey data, entrance skin exposures in air, i.e., free air exposures at the point of intersection of the x‐ray central beam with the entrance surface of the patient, were estimated using the RADCOMP program. Entrance surface doses to air and tissue with backscatter were then evaluated by the application of the exposure‐dose conversion factor and the backscatter factor obtained from TLD measurements and Monte Carlo simulations. Guidance levels were determined from survey results on the entrance surface dose based on optimization considerations involving the cost‐effectiveness analysis. Except for chest PA and LAT and skull LAT procedures, all guidance levels derived in this work are less than those recommended by the International Atomic Energy Agency. Survey data and guidance levels were provided to the national authorities to help them develop quality control and radiation protection programs for medical exposures.
A variable critical‐volume model for normal tissue complication probability
Authors: Bonta Dacian V. , Fontenla Ernesto , Lu Yong , Chen George T. Y.
Published: July 2002

Predicting late‐term normal‐tissue complication probability (NTCP) after radiotherapy is an important factor in the optimization of conformal radiotherapy. We propose a new NTCP model, based on the properties of the high dose region. The principal assumption of the new model is that a whole‐organ complication will occur when the radiation damage to a normal organ volume (a portion of the total organ) exceeds a threshold value. The dose threshold for complications varies with the size of the volume (percent of the total organ). We hypothesize that a complication occurs if the complication threshold is exceeded for any organ volume. We used the average dose to a volume as a measure of radiation damage to that volume. Also, we used the power law to scale the average dose to various organ volumes to a whole‐organ equivalent dose, and to identify the volume with the most harmful dose‐size combination—the critical volume. We used a logistic distribution to calculate the probability that the patient will develop a complication, given the dose delivered to the critical volume. We used a maximum likelihood fit to estimate the model parameters for late‐term rectal complications in a set of patients treated for prostate carcinoma with external photon beam radiotherapy (EBRT). Good correspondence was found between the experimental data and the model predictions.
Determination of the detective quantum efficiency of a prototype, megavoltage indirect detection, active matrix flat‐panel imager
Authors: El‐Mohri Youcef , Jee Kyung‐Wook , Antonuk Larry E. , Maolinbay Manat , Zhao Qihua
Published: July 2002

After years of aggressive development, active matrix flat‐panel imagers (AMFPIs) have recently become commercially available for radiotherapy imaging. In this paper we report on a comprehensive evaluation of the signal and noise performance of a large‐area prototype AMFPI specifically developed for this application. The imager is based on an array of 512×512 pixels incorporating amorphous silicon photodiodes and thin‐film transistors offering a 26×26 cm2 active area at a pixel pitch of 508 μm. This indirect detection array was coupled to various x‐ray converters consisting of a commercial phosphor screen (Lanex Fast B, Lanex Regular, or Lanex Fine) and a 1 mm thick copper plate. Performance of the imager in terms of measured sensitivity, modulation transfer function (MTF), noise power spectra (NPS), and detective quantum efficiency (DQE) is reported at beam energies of 6 and 15 MV and at doses of 1 and 2 monitor units (MU). In addition, calculations of system performance (NPS, DQE) based on cascaded‐system formalism were reported and compared to empirical results. In these calculations, the Swank factor and spatial energy distributions of secondary electrons within the converter were modeled by means of EGS4 Monte Carlo simulations. Measured MTFs of the system show a weak dependence on screen type (i.e., thickness), which is partially due to the spreading of secondary radiation. Measured DQE was found to be independent of dose for the Fast B screen, implying that the imager is input‐quantum‐limited at 1 MU, even at an extended source‐to‐detector distance of 200 cm. The maximum DQE obtained is around 1%—a limit imposed by the low detection efficiency of the converter. For thinner phosphor screens, the DQE is lower due to their lower detection efficiencies. Finally, for the Fast B screen, good agreement between calculated and measured DQE was observed.
Improved leaf sequencing reduces segments or monitor units needed to deliver IMRT using multileaf collimators
Authors: Langer Mark , Thai Van , Papiez Lech
Published: July 2002

Leaf sequencing algorithms may use an unnecessary number of monitor units or segments to generate intensity maps for delivery of intensity modulated radiotherapy (IMRT) using multiple static fields. An integer algorithm was devised to generate a sequence with the fewest possible segments when the minimum number of monitor units are used. Special hardware related restrictions on leaf motion can be incorporated. The algorithm was tested using a benchmark map from the literature and clinical examples. Results were compared to sequences given by the routine of Bortfeld that minimizes monitor units by treating each row independently, and the areal or reducing routines that use fewer segments at the price of more monitor units. The Bortfeld algorithm used on average 58% more segments than provided by the integer algorithm with bidirectional motion and 32% more segments than did an integer algorithm admitting only unidirectional sequences. The areal algorithm used 48% more monitor units and the reducing algorithm used 23% more monitor units than did the bidirectional integer algorithm, while the areal and reducing algorithms used 23% more segments than did the integer algorithm. Improved leaf sequencing algorithms can allow more efficient delivery of static field IMRT. The integer algorithm demonstrates the efficiencies possible with an improved routine and opens a new avenue for development.
A model for tracking concentration of chemical compounds within a tank of an automatic film processor
Authors: Sobol Wlad T.
Published: July 2002

A simple kinetic model that describes the time evolution of the chemical concentration of an arbitrary compound within the tank of an automatic film processor is presented. It provides insights into the kinetics of chemistry concentration inside the processor's tank; the results facilitate the tasks of processor tuning and quality control (QC). The model has successfully been used in several troubleshooting sessions of low‐volume mammography processors for which maintaining consistent QC tracking was difficult due to fluctuations of bromide levels in the developer tank.
MarCell™ software for modeling bone marrow radiation cell kinetics
Authors: Hasan J. S. , Jones T. D. , Morris M. D.
Published: July 2002

Differential equations were used to model cellular injury, repair, and compensatory proliferation in the irradiated bone marrow. Recently, that model was implemented as MarCell™, a user‐friendly MS‐DOS computer program that allows users from a variety of technical disciplines to evaluate complex radiation exposure. The software allows menu selections for different sources of ionizing radiation. Choices for cell lineages include progenitor, stroma, and malignant, and the available species include mouse, rat, dog, sheep, swine, burro, and man. An attractive feature is that any protracted irradiation can be compared with an equivalent prompt dose (EPD) in terms of cell kinetics for either the source used or for a reference such as 250 kVp x rays or EPD is used to mean a dose rate for which no meaningful biological recovery occurs during the period of irradiation. For human as species, output from MarCell™ includes: risk of 30‐day mortality; risk of whole‐body cancer and leukemia based either on radiation‐induced cytopenia or compensatory cell proliferation; cell survival and repopulation plots as functions of time or dose; and 4‐week recovery following treatment.
Three‐dimensional reconstruction of curves from pairs of projection views in the presence of error. II. Analysis of error
Authors: Bullitt E. , Liu A. , Pizer S. M.
Published: July 2002

We have previously described an approach to 3D intracerebral vascular reconstruction that uses an MRA as a reconstruction base. Additional vessels seen only by angiography are added by segmenting 2D curves from projection angiograms and reconstructing these curves into 3D, building upon the MRA. This paper is the second of two that discuss the specific problem of reconstructing a 3D curve from a given pair of 2D curves in the presence of error. The method presented is capable of detecting and handling many errors produced by misregistration, image distortion, or misdefinition of 2D curves. The first paper gives an algorithm. The current paper discusses factors affecting the accuracy of a reconstructed curve, with emphasis upon registration error. We analyze the spatial accuracy of a reconstructed point in terms of the relationships between pixel size, relative viewing angle, 3D point location, and registration error. We provide a theoretical framework that, given the known error properties of a registration algorithm, allows optimization of the viewing geometry so as to produce the highest precision of point reconstruction. A major focus is the effect of registration error upon the reconstruction of a curve. We subdivide registration error into two types, one of which produces smoothly continuous point placement errors and the other of which produces pixel pairing errors. We test our ability to reconstruct a 3D curve in the presence of both. Finally, we summarize approaches to other sources of error. We conclude with a list of recommendations to optimize reconstruction accuracy. When projection points are associated by the rules of epipolar geometry, viewplane point displacements should not exceed 1.5–2 mm along the axis perpendicular to epipolar planes.
Characteristics of scattered electron beams shaped with a multileaf collimator
Authors: Moran Jean M. , Martel Mary K. , Bruinvis Iaı̈n A. D. , Fraass Benedick A.
Published: July 2002

Characteristics of dual‐foil scattered electron beams shaped with a multileaf collimator (MLC) (instead of an applicator system) were studied. The electron beams, with energies between 10 and 25 MeV, were produced by a racetrack microtron using a dual‐foil scattering system. For a range of field sizes, depth dose curves, profiles, penumbra width, angular spread in air, and effective and virtual source positions were compared. Measurements were made when the MLC alone provided collimation and when an applicator provided collimation. Identical penumbra widths were obtained at a source‐to‐surface distance of 85 cm for the MLC and 110 cm for the applicator. The MLC‐shaped beams had characteristics similar to other machines which use trimmers or applicators to collimate scanned or scattered electron beams. Values of the effective source position and the angular spread parameter for the MLC beams were similar to those of the dual‐foil scattered beams of the Varian Clinac 2100CD and the scanned beams of the Sagittaire linear accelerators. A model, based on Fermi–Eyges multiple scattering theory, was adapted and applied successfully to predict penumbra width as a function of collimator–surface distance.
A statistical investigation of the scaling factor method of beta‐ray dose distribution derivation: The scaling factor for water to bone
Authors: Marcu Silviu M. , Prestwich William V.
Published: July 2002

Reliable methods of estimating doses are essential for the use of beta emitting radionuclides for radiotherapy. The passage of electrons through matter is a very complex phenomenon due to the large number of elastic and inelastic interactions resulting in scattering and energy losses. The analytical solution for the electron transport being intractable, the problem has been addressed by the Monte Carlo technique. Empirical or semiempirical less time consuming methods, such as the scaling factor method, may appear more preferable in practice when dealing with complicated source distributions. The method, proposed by Cross and co‐workers [AECL Report Nos. AECL‐1617 (1982), AECL 10521 (1992)] consists in the derivation of beta‐ray dose distribution in other media from those in water by using a “scaling factor” or “relative attenuation factor” on distance and a closely related renormalization factor imposed by the energy conservation. This work investigates the accuracy of the scaling factor method using a statistical approach, a generalized test, focusing on the particular case of potential interest, the scaling factor for water to bone. The direct comparison of the shapes of the depth dose deposition curves in the two media indicates discrepancies of less than 5% up to at least 60% of the range in bone, a depth within which 95% of the initial energy is deposited. The scaling factor derived by this method, confirms the existing experimentally determined value of [AECL Report No. AECL‐10521 (1992)]. The accuracy of the determination is increased by almost a factor of 10. A way of improving the scaling method, especially for depth over the 60% continuous slowing down approximation range, by using a modulation function is also proposed.
A comparison of the physical imaging properties of Fuji ST‐V, ST‐VA, and ST‐VN computed radiography image plates
Authors: Kengyelics S. M. , Davies A. G. , Cowen A. R.
Published: July 2002

The physical imaging performance of ST‐V, ST‐VA, and ST‐VN computed radiography image plates, read with a Philips AC3 acquisition system, was investigated at 70 kVp with 0.5 mm of copper beam filtration for four different entrance air kerma values: 0.5, 2.6, 26, and 260 μGy. Measurements included characteristic response, presampling‐modulation transfer function, and Wiener spectrum analysis for image plates, sampled at 10 pixels/mm. These results were used to calculate DQE spectral descriptions of system performance. ST‐VN image plates exhibited a slightly superior DQE performance for the two lower entrance air kerma values investigated.
Development of improved methods for internal dosimetry calculations
Authors: Bouchet Lionel G.
Published: July 2002

This dissertation presents improvements in three areas of nuclear medicine dosimetry: diagnostic, therapy, and bone dosimetry. For diagnostic nuclear medicine dosimetry, a series of five pediatric head and brain dosimetric models are developed based on the new adult model of the Medical Internal Radiation Dose Committee (MIRD). The EGS4 Monte Carlo code is used to tabulate absorbed fractions of energy (AFs) for photon and electron sources. Subsequently, radionuclide S values are tabulated for use in pediatric neuroimaging studies. In therapy nuclear medicine dosimetry, a new tool for nonuniform activity distributions is developed based on the MIRD methodology of dose calculation. Three‐dimensional cumulated activity derived from single photon emission computed tomography (SPECT) images can be convoluted with S values calculated for the same voxel arrangement to generate average dose to voxels within the SPECT images. Voxel S values are calculated using the EGS4 code for 21 voxel sizes up to 1.0 cm. A specific absorbed fraction interpolation schema is then derived for other voxel sizes. Examples of the clinical use of this dose calculation method are provided. Finally, in bone dosimetry, three‐dimensional transport models of electrons are developed for trabecular and cortical bone. These models are used with the EGS4‐PRESTA code to calculate AFs. A one‐dimensional transport model is also developed to evaluate improvements using three‐dimensional transport. AFs are then used to calculate bone site‐specific and skeletal‐averaged S values. Differences seen with previously published bone S values are analyzed. These skeletal‐averaged S values are then used to estimate dosimetric advantage of beta‐emitting radionuclides for the palliation of bone pain from bone metastases.
A computer‐aided diagnostic scheme for classification of clustered microcalcifications in mammograms
Authors: Jiang Yulei
Published: July 2002

The hypothesis of this dissertation is that computer‐aided diagnosis (CAD) can improve radiologists' diagnostic performance in breast cancer diagnosis. An automated computerized classification scheme was developed to differentiate malignant from benign clustered microcalcifications. This computer scheme used an artificial neural network (ANN) to analyze eight computer‐extracted image features based on number, size, uniformity, and shape of individual microcalcifications, and on size and shape of a cluster. The features correlated qualitatively with radiologists' perceptual experience. The performance of this computer scheme was evaluated on two independent databases of standard‐view mammograms digitized at 0.1‐mm pixel size: database A contained mammograms from 53 patients with biopsies and database B contained mammograms from 104 patients in a consecutive biopsy series. The computer scheme performed better than radiologists on both databases (p=0.03 and p<0.0001, respectively). An observer performance study was conducted using database B. Ten radiologists read the original standard‐ and magnification‐view mammograms with and without the aid of our computer scheme. The performance of the radiologists improved significantly (p<0.0001) when the computer aid was used: on average, each radiologist recommended 6.4 more biopsies for malignant tumors (p=0.0006) and 6.0 fewer biopsies for benign lesions (p=0.003). We concluded that our computer scheme classifies malignant and benign clustered microcalcifications more accurately than radiologists, and that it can be used to reduce the number of biopsies for benign lesions while maintaining or improving sensitivity for breast cancer diagnosis.
MABDOSE. II: Validation of a general purpose dose estimation code
Authors: Johnson Timothy K. , McClure David , McCourt Steven
Published: July 2002

The MABDOSE software represents a general tool to assess internal radiation dose. A suite of tests are described that validate the dosimetry system's implementation. Methods: The validation suite is divided among tests that verify target digitalization, tumor digitalization and organ replacement, cumulated activity calculation, random number generation, radiation transport, and dose calculation. Results: A comparison between Reference Man organ volumes and MABDOSE organ volumes at (5 mm)3 resolution demonstrates volume correspondence within 10% save for ten organs having dimensions smaller than the target lattice resolution. An accounting of normal organ volume replaced by an arbitrary tumor volume indicates mass is conserved. A comparison between cumulated activities generated by MABDOSE and solutions obtained analytically demonstrates exact correspondence for curve‐fitting algorithms. For mathematical modeling algorithms, cumulated activity solutions converge to their correct values provided sufficient data of high precision are input, accompanied by reasonable initial estimates of rate constants. A comparison of MABDOSE results with the MIRD 3 report demonstrates good agreement (<8% difference) in absorbed fractions for spheres at energies from 20 keV to 2.75 MeV. A comparison of MABDOSE results with the Cristy–Eckerman report demonstrates marginal agreement (specific absorbed fractions within a factor of 2 for all Reference Man organs) at simulation energies of 20, 50, and 100 keV. Lack of exact correspondence is attributed to volume digitalization errors, and to differences in cross‐section libraries, interpolation schemes between cross‐section data points, and random number generators. Finally, the doses reported by MABDOSE correspond to the correct algebraic combination of paired cumulated activities and “S” values. Conclusions: The MABDOSE program has been validated as a general purpose computation tool for use in internal radionuclide dosimetry.
Studies on x‐ray physical analysis and computer‐aided diagnosis of x‐ray CT images [in Japanese]
Authors: Tsuzaka Masatoshi
Published: July 2002

The focus of this thesis was to physically analyze diagnostic x‐rays by using the x‐ray spectrum and to develop an automatic detection method of lymph nodes on chest x‐ray CT images. This dissertation included the following five topics: (1) three issues in terms of the device, method, and data revision on the spectrum measurement of diagnostic x‐rays; (2) development of a doughnut‐shaped parallel ionization chamber dosimeter for monitoring the x‐ray output during the measurement; (3) influence of the size of germanium crystals and different models on the spectral measurement; (4) investigation by Monte Carlo simulation of the influence of the scattered x‐rays from rectangular wave chart for MTF measurements on the determined data; (5) development of a computer‐aided diagnosis (CAD) system for detecting mediastinal lymph nodes on chest CT images of lung cancer patients. In the last topic, the knowledge information processing method was adapted to detect the positions of lymph nodes; anatomical information determined by referring to automatic classified slices by a genetic algorithm (GA) method and lymph node map was useful. This research shows the importance of precise measurements of physical characteristics of x‐rays and the development of CAD systems for chest CT images.
Dosimetry with a fluoroscopic electronic portal imaging device
Authors: Pasma Kasper L.
Published: July 2002

Techniques for dosimetric verification of radiotherapy treatments using a CCD camera based fluoroscopic electronic portal imaging device (EPID) are described. The dosimetric characteristics of the EPID were investigated and a method was developed to derive portal dose images (PDIs) from measured EPID images. EPID and ionization chamber measurements agreed to within 1% (1σ). Subsequently, an algorithm was developed to predict these PDIs using the planning CT data of the patient and the irradiation geometry as determined in the treatment planning process. Furthermore, a method was developed to derive the on‐axis patient dose from an EPID measurement, which was then compared with the intended dose. The method allows the discrimination of errors that are due to changes in patient anatomy and errors due to a deviating cGy/MU value. For 115 prostate cancer patients the differences between the average on‐axis measured portal dose and the predicted portal dose for the three open beams were small: −0.3±2.3% (1σ). However, large (up to 15%) off‐axis differences between measured and predicted PDIs were found, which were caused by frequently occurring gas pockets inside the rectum of the patients during treatment or during acquisition of the planning CT scan. The detected gas pockets did sometimes extend into the tumor volume area as outlined in the CT scan, implying internal organ motion. Finally, methods were developed for pretreatment verification of intensity modulated fields produced with compensators or dynamic multileaf collimation (DMLC). EPID measurements of dose profiles generated with DMLC agreed within 2% (1σ) with predictions and ionization chamber measurements.
A dosimetric leaf‐setting strategy for shaping radiation fields using a multileaf collimator
Authors: Ma Lijun , Yu Cedric , Sarfaraz Merhdad
Published: July 2002

A dosimetric leaf‐setting strategy of using multileaf collimators (MLC) for shaping radiation fields has been developed. Existing MLC leaf‐setting strategies are all based upon geometric criteria. This new approach, however, matches a prescribed field contour with a MLC using clinically consistent dosimetric criteria. The leaf positions are determined using an iterative optimization algorithm. An empirical dose model was developed to compare the dosimetric‐based leaf‐setting strategy with the geometric‐based leaf‐setting strategies. Differences up to half a centimeter in the leaf positions and isodose lines were found between setting the MLC geometrically and setting the MLC dosimetrically. The dosimetric leaf‐setting strategy provides the ability to achieve better dose conformation for a clinically desired isodose line. Since the desired isodose line that covers a treatment volume is typically higher than 50% of the maximum dose, the scalloping effects due to the finite leaf width at the leaf edge or 50% isodose lines are much reduced. Another benefit of the dosimetric leaf‐setting is that it separates the leaf‐setting process from the treatment planning process, and this frees the treatment planning vendors from developing detailed dose models for various existing types and future upgrades of MLC systems.
Fluid dynamics and energetics in ideal gas mixtures
Authors: Ramshaw John D.
Published: July 2002

The generalization of fluid dynamics from pure to multicomponent fluids (fluid mixtures composed of different components or species) requires the introduction of new concepts, some of which are rather subtle and are less widely appreciated than they deserve to be. The purpose of this paper is to provide a simple didactic introduction to some of these concepts based on a detailed analysis of the equations governing the flow of ideal gas mixtures. The treatment is based entirely on a continuum description and makes no explicit use of the kinetic theory of gases. We include a straightforward and physically transparent derivation of the additional heat flux arising from the relative motion of the different species, and show why this flux involves species enthalpies rather than energies. Some of the concepts are reminiscent of those used in turbulence modeling, and these analogies are briefly discussed.
The acoustic calls of blue whales off California with gender data
Authors: McDonald Mark A. , Calambokidis John , Teranishi Arthur M. , Hildebrand John A.
Published: July 2002

The acoustic calls of blue whales off California are described with visual observations of behavior and with acoustic tracking. Acoustic call data with corresponding position tracks are analyzed for five calling blue whales during one 100-min time period. Three of the five animals produced type A-B calls while two produced another call type which we refer to as type D. One of the animals producing the A-B call type was identified as male. Pauses in call production corresponded to visually observed breathing intervals. There was no apparent coordination between the calling whales. The average call source level was calculated to be 186 dB re: 1 μPa at 1 m over the 10–110-Hz band for the type B calls. On two separate days, female blue whales were observed to be silent during respective monitoring periods of 20 min and 1 h.
Effects of middle ear pressure on otoacoustic emission measures
Authors: Zhang Ming , Abbas Paul J.
Published: July 2002

An animal surgical model was established to manipulate pressure in the middle ear. The 2 f1−f2 cochlear microphonic distortion product (CMDP) and distortion product otoacoustic emission (DPOAE) were simultaneously measured in order to analyze the effects of middle ear pressure on sound transmission. The frequency ratio of the two stimulus tones f2/f1 was held at 1.2 and the level ratio L1/L2 was 10 dB. The effect of middle ear pressure on forward transmission was determined from the CMDP data. The effect on backward transmission was determined from the DPOAE data after the effect on forward transmission was subtracted out. The results showed a similar effect on forward and backward transmission. In general, negative pressure had a greater effect than positive pressure. Positive pressures of 10 and 20-cm H2O affected transmission for low-frequency stimuli (f2=1620 and 2680 Hz) but had little effect for high-frequency stimuli (f2=6980 and 10 250 Hz). Negative pressures of −2.5 to −10-cm H2O affected transmission across all frequencies tested. The effect at low frequencies is hypothesized to be related to tympanic membrane stiffness. The effect of negative pressure at high frequencies may be related to changes in the incudostapedial joint.
The unidentified object problem in a shallow ocean
Authors: Gilbert R. P. , Scotti T. , Wirgin A. , Xu Y. S.
Published: July 2002

This work addresses the inverse problem of the identification of a passive three-dimensional impenetrable object in a shallow-water environment. The latter is assumed to have flat perfectly reflecting (sound-soft top and sound-hard bottom) boundaries and therefore acts as a guide for acoustic waves. These waves are employed to interrogate the object and the scattered acoustic wavefield is measured on the surface of a (virtual) vertically oriented cylinder (of finite or infinite radius, corresponding to near- or far-field measurements) fully enclosing the object. The direct scattering problem is resolved in approximate manner by employing, in a local manner, the known separated-variable solution for a scattering by a vertically oriented cylinder in a perfect waveguide. The inverse problem is resolved in the same manner (i.e., with the same approximate field ansatz) by least-squares matching of theoretical fields (for trial objects) to the measured field. Examples are given of successful shape reconstructions for two types of immersed objects. This manner of solving approximately both the forward and inverse problems is generalized to the case of a body of shallow water with an elastic seabed.
Degradation of wren Troglodytes troglodytes song: Implications for information transfer and ranging
Authors: Holland Jo , Dabelsteen Torben , Pedersen Simon Boel , Larsen Ole Næsbye
Published: July 2002

The effects of bird song imply a transfer of information between conspecifics. This communication channel is constrained by habitat-induced degradation. Many studies suggest that birds can utilize features of degraded song to assess relative distance to the signaller (ranging). The degradation of transmitted song in the wren Troglodytes troglodytes is quantified to assess the opportunities offered in received song for both information transfer and ranging. This quantification incorporates three measurable aspects of degradation: signal-to-noise ratio; excess attenuation; blur ratio. Each aspect varies more-or-less predictably with transmission distance, i.e., a criterion for ranging. Significant effects of speaker and microphone elevation indicate a potential for birds to optimize both the opportunity for information transfer and ranging by considering perch location. Song elements are the smallest units of a song being defined as a continuous trace on a sonagram. Main and second-order effects of element type indicate element-specific patterns of degradation which could be a crucial factor in communication in this species. The element variation within a full song offers the potential for effective information transfer over a range of relevant distances and a variety of transmission pathways. It similarly offers highly flexible ranging opportunities.
Guided waves in layered cubic media: Convergence study of a polynomial expansion approach
Authors: Lancellotti Vito , Orta Renato
Published: July 2002

A new numerical method to compute propagation constants and mode functions of a planar layered acoustic waveguide is described. The basic feature is the expansion of velocity and stress fields in each layer on different Legendre polynomial bases, which ensures an exponential convergence rate of the method. No transcendental equation has to be solved and also modes that have very close propagation constants (e.g., coupled Rayleigh waves) are computed with great accuracy. Convergence of the method is studied and a way to estimate and control the error on the solutions is discussed.
Language identification with suprasegmental cues: A study based on speech resynthesis
Authors: Ramus Franck , Mehler Jacques
Published: July 2002

This paper proposes a new experimental paradigm to explore the discriminability of languages, a question which is crucial to the child born in a bilingual environment. This paradigm employs the speech resynthesis technique, enabling the experimenter to preserve or degrade acoustic cues such as phonotactics, syllabic rhythm, or intonation from natural utterances. English and Japanese sentences were resynthesized, preserving broad phonotactics, rhythm, and intonation (condition 1), rhythm and intonation (condition 2), intonation only (condition 3), or rhythm only (condition 4). The findings support the notion that syllabic rhythm is a necessary and sufficient cue for French adult subjects to discriminate English from Japanese sentences. The results are consistent with previous research using low-pass filtered speech, as well as with phonological theories predicting rhythmic differences between languages. Thus, the new methodology proposed appears to be well suited to study language discrimination. Applications for other domains of psycholinguistic research and for automatic language identification are considered.
A cross-cultural study of the factors of sound quality of environmental noise
Authors: Kuwano Sonoko , Namba Seiichiro , Florentine Mary , Da Rui Zheng , Fastl Hugo , Schick August
Published: July 2002

The sound quality of various environmental noises was judged using semantic differential in Japan, Germany, the U.S.A., and China. The sounds used were aircraft noise, train noise, road traffic noise, speech, music, and construction noise. As the result of factor analysis, three factors were extracted in Japan and Germany. They were interpreted as ‘‘powerful,’’ ‘‘pleasant,’’ and ‘‘metallic’’ factors. In the U.S., and China, ‘‘powerful’’ and ‘‘metallic’’ factors were not differentiated. The impression of ‘‘powerful’’ factors were found to show high correlation with LAeq and loudness level based on ISO 532B. There seemed some difference in connotative meanings of the terms ‘‘loud,’’ ‘‘noisy,’’ and ‘‘annoying’’ among the four countries. There was little difference in the impression of high-level aircraft noise, train noise, and road traffic noise among the four countries. They were perceived as negative impression such as ‘‘annoying,’’ ‘‘ugly,’’ ‘‘unpleasant,’’ etc. The validity of other psychophysical measures was examined in relation to these results.
Auditory perception of reverberant surroundings
Authors: Sandvad Jesper
Published: July 2002

Three experiments on perception of reverberant surroundings were performed. In the first experiment, listeners were presented with binaural recordings of a speech signal and a set of photographs taken in different rooms, and were asked to point out where each recording was made. Most listeners performed very well in this task (average number of correct answers was 70%), showing that reverberation contains information on room properties that the listeners are able to extract. In the second experiment, listeners were asked to judge the relative size of different rooms by listening to the recorded signals. The results show substantial individual differences, with some listeners being close to veridical performance while others had only a few correct answers. A scaling analysis suggests that some listeners use the direct/reverberant energy ratio, while others use reverberation time as a cue for room size. In the third experiment, artificial reverberation generated by a geometric room model (including individual reflections) and from a stochastic model (controlling only energy measures) were compared with signals generated directly from measured room impulse responses. The results show comparable performance, suggesting that energy measures are the most important for assessing information on room parameters. [Work supported by ONR Grant No. N00014-96-1-0675.]
Porous piezoelectric ceramic hydrophone
Authors: Marselli Stefano , Pavia Vittorio , Galassi Carmen , Roncari Edoardo , Craciun Floriana , Guidarelli Guido
Published: July 2002

The construction and evaluation of a hydrophone based on porous piezoelectric ceramics with high dhgh figure of merit (FOM) is described. It has been shown that, in order to improve the hydrophone signal-to-noise ratio, a piezoelectric material with a high FOM should be employed. A porous piezoelectric material has been prepared by mixing calcined lead zirconate titanate (PZT) powder with fine particle starch powder. Square plate samples have been cold pressed from this material, which were then heated to eliminate the organic component, sintered, electroded, and poled in a high electric field. An optimum pore volume fraction of approximately 40% has been selected in order to obtain materials with high piezoelectric coefficients and reasonably good mechanical resistance. For this composition a hydrostatic figure of merit of approximately 10−11 m2/N has been obtained that is a few orders of magnitude higher than traditional piezoceramics. Square plate elements were assembled in a planar hydrophone which was made watertight with polyurethane resin. The hydrophone was characterized by different measurements performed in a water tank, by using a pulsed sound technique. Results on acoustical sensitivity measurements, directivity, equivalent noise pressure level, and sensitivity variation with pressure are presented and discussed.
Comparison of electrohydraulic lithotripters with rigid and pressure-release ellipsoidal reflectors. II. Cavitation fields
Authors: Bailey Michael R. , Blackstock David T. , Cleveland Robin O. , Crum Lawrence A.
Published: July 2002

Dramatically different cavitation was produced by two separate acoustic pulses that had different shapes but similar duration, frequency content, and peak positive and negative pressure. Both pulses were produced by a Dornier HM-3 style lithotripter: one pulse when the ellipsoidal reflector was rigid, the other when the reflector was pressure release. The cavitation, or bubble action, generated by the conventional rigid-reflector pulse was nearly 50 times longer lived and 3–13 times stronger than that produced by the pressure-release-reflector pulse. Cavitation durations measured by passive acoustic detection and high-speed video agreed with calculations based on the Gilmore equation. Cavitation intensity, or destructive potential, was judged (1) experimentally by the size of pits in aluminum foil detectors and (2) numerically by the calculated amplitude of the shock wave emitted by a collapsing bubble. The results indicate that the trailing positive spike in the pressure-release-reflector waveform stifles bubble growth and mitigates the collapse, whereas the trough after the positive spike in the rigid-reflector waveform triggers inertially driven growth and collapse. The two reflectors therefore provide a tool to compare effects in weakly and strongly cavitating fields and thereby help assess cavitation’s role in lithotripsy.
Influence of edge boundary conditions on the free vibrations of cross-ply laminated circular cylindrical panels
Authors: Messina Arcangelo , Soldatos Kostas P.
Published: July 2002

This paper deals with the influence of different sets of edge boundary conditions on the dynamic characteristics of shear deformable, cross-ply laminated circular cylindrical panels. The analysis is based on the conjunction of the Ritz method with an appropriate, complete functional basis and its subsequent application on the energy functional of the Love-type version of a unified shear-deformable shell theory [T. Timarci and K. P. Soldatos, J. Sound Vib. 187, 609–624 (1995); J. Eng. Math (to appear January 2000)]. As a result, two different kinds of shear deformable Love-type shell theories are employed and tested, including versions that either fulfill or violate the continuity of the interlaminar stresses along the shell thickness. Although the main theoretical model employed makes use of a certain type of continuous interlaminar stress, the results of the present analysis are initially tested and validated through appropriate comparisons with corresponding numerical results obtained in the relevant literature, mostly on the basis of discontinuous interlaminar plate and shell models. The present approach and analysis are then used for a more thorough investigation of the influence of the edge boundary conditions on the dynamic characteristics of circular cylindrical panels.
Acoustical design of the Tokyo Opera City (TOC) concert hall, Japan
Authors: Hidaka Takayuki , Beranek Leo L. , Masuda Sadahiro , Nishihara Noriko , Okano Toshiyuki
Published: July 2002

The Tokyo Opera City concert hall seats 1632, volume 15 300 m3, and reverberation time, with audience and orchestra, 1.95 s. As part of the design process, measurements on CAD computer and 1:10 wooden models of the hall and full-sized materials samples were conducted over a 5-yr. period. The hall in plan is rectangular. The ceiling is a distorted pyramid, with its peak 28 m above the main floor and nearer the stage than the rear of the hall. This unique shape was analyzed on the models so that all interior surfaces combine to distribute sources on the stage uniformly over the seating areas and to yield optimum values for reverberation time (RT), early decay time (EDT), interaural cross-correlation coefficient (IACCE3), bass ratio (BR), initial-time-delay gap (ITDG), strength (G), and sound diffusion index (SDI) [for definitions see L. Beranek, Concert and Opera Halls: How They Sound (Acoustical Society of America, Woodbury, NY, 1996)]. On the long ceiling facing the stage, Schroeder QRD diffusers provide diffusion, eliminate a possible echo, and strengthen lateral reflections. Performers and critics judge the acoustics excellent.