bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved method for measuring photoacid generator kinetics in polymer thin films using normalized interdigitated electrode capacitance data
Authors: Berger Cody M. , Henderson Clifford L.
Published: July 2004

A data analysis method is presented that can be used to calculate kinetic rate constants for photoacid generation (Dill C values) in polymer and chemically amplified photoresist thin films using capacitance versus exposure dose data from resist coated interdigitated electrode (IDE) sensors. It is shown that the use of normalized IDE capacitance data can reduce or eliminate errors and variations in measured Dill C values obtained from our previous analysis method that are created by environmental factors such as humidity fluctuations and IDE factors such as variations in electrode geometry and size. Using this normalization method, the Dill C rate constants for 248 nm exposure of triphenylsulfonium triflate (TPS–Tf), triphenylsulfonium perfluoro-1-butanesulfonate (TPS–Nf), bis(4-tert-butylphenyl)iodonium triflate (TBI–Tf), and bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonate (TBI–Nf) in poly(p-hydroxystyrene) (PHOST) were found to be 0.046, 0.040, 0.055, and 0.056 cmcm2/mJ, respectively. These results are shown to compare well with values obtained for these same systems using our original IDE data analysis method (0.045 cm2/mJ for TPS–Tf/PHOST, 0.039 cm2/mJ for TPS–Nf/PHOST, 0.056 cm2/mJ for TBI–Tf/PHOST, and 0.054 cm2/m/J for TBI–Nf/PHOST). The normalization method has a significant advantage in that it permits the determination of a Dill C parameter for a particular polymer-photoacid generator system using a single resist film coated IDE and a single exposure experiment.
Automatic generation of anatomy‐based MLC fields in aperture‐based IMRT
Authors: Beaulieu Frédéric , Beaulieu Luc , Tremblay Daniel , Lachance Bernard , Roy René
Published: July 2004

We have developed an algorithm to automatically generate anatomy‐based MLC fields. For each beam, a first field is adjusted to the projection of the target in a beam's eye view, allowing subsequent fields to be derived from this conformal field by removing the overlapping surface of each organ at risk, respectively. The projections are based on a surface sampling of the anatomical structures. On top of the MLC mechanical constraints, verification constraints are imposed on the MLC segments, in order to get reliable dosimetry using a commercial dose calculation engine. Thus, in each direction, the aperture's cross‐section must be greater than a specified threshold, in our case 2 cm. Furthermore, junctions are not tolerated in order to avoid underdosage, for instance from the tongue‐and‐groove effect. The use of such MLC fields simplifies the verification process. The performance of the algorithm is illustrated for head and neck, thorax and prostate cases. Only a fraction of a second of CPU time is required to perform the segmentation for each beam.
Electron beam therapy with coil‐generated magnetic fields
Authors: Nardi Eran , Barnea Gideon , Ma Chang‐Ming
Published: July 2004

This paper presents an initial study on the issues involved in the practical implementation of the use of transverse magnetic fields in electron beam therapy. By using such magnetic fields the dose delivered to the tumor region can increase significantly relative to that deposited to the healthy tissue. Initially we calculated the magnetic fields produced by the Helmholtz coil and modified Helmholtz coil configurations. These configurations, which can readily be used to generate high intensity magnetic fields, approximate the idealized magnetic fields studied in our previous publications. It was therefore of interest to perform a detailed study of the fields produced by these configurations. Electron beam dose distributions for 15 MeV electrons were calculated using the ACCEPTM code for a 3T transverse magnetic field produced by the modified Helmholtz configuration. The dose distribution was compared to those obtained with no magnetic field. The results were similar to those obtained in our previous work, where an idealized step function magnetic field was used and a 3T field was shown to be the optimal field strength. A simpler configuration was also studied in which a single external coil was used to generate the field. Electron dose distributions are also presented for a given geometry and given magnetic field strength using this configuration. The results indicate that this method is more difficult to apply to radiotherapy due to its lack of symmetry and its irregularity. For the various configurations dealt with here, a major problem is the need to shield the magnetic field in the beam propagation volume, a topic that must be studied in detail.
A graph‐searching method for MLC leaf sequencing under constraints
Authors: Chen Yan , Hou Qing , Galvin James M.
Published: July 2004

A new leaf‐sequencing algorithm for step‐and‐shoot IMRT that is based on a graph‐searching technique is described. An iterative process guided by a quantitative measure for the complexity of the initial or residual intensity pattern is used to identify the field segments shaped by a multileaf collimator (MLC). Given a user selected number of intensity levels, the algorithm searches deliverable segment candidates considering all intensity levels and two collimator positions separated by 90 degrees. The candidates for each intensity level are obtained as the least number of segments to cover the areas with equal or higher intensity. The shape of a deliverable segment is adjusted by leaving out certain beam elements for later delivery if this results in a simpler residual intensity pattern and the segment is still deliverable. For a MLC design that does not allow leaf interdigitation, it is initially assumed that a single segment cannot cover two disjoined areas. Among all candidates the segment with the greatest reduction of the complexity of the residual intensity distribution is chosen for the current step of iteration. The iterative process generates a set of deliverable segments of simply connected areas. These segments are combined later under specific MLC constraints. Different orders of segment combination are considered for minimizing the beam‐on time. The final segments are sequenced to minimize the leaf travel. This algorithm has been tested using randomly generated intensity distributions and clinical cases for the Varian, Siemens, and Elekta MLC systems. The results show that as the number of intensity levels is increased, the numbers of segments and MUs increase only modestly. Using two collimator angles results in decreases in the required number of segments and the number of monitor units that can be as much as 20%.
Elastographic versus x‐ray CT imaging of radio frequency ablation coagulations: An in vitro study
Authors: Liu Wu , Techavipoo Udomchai , Varghese Tomy , Zagzebski James A. , Chen Quan , Lee Fred T.
Published: July 2004

Techniques to image elasticity parameters (i.e., elastography) have recently become of great interest to researchers. In this paper we use conventional ultrasound elastography and x‐ray CT to image radio frequency (RF) ablation sites of excised canine liver enclosed in gelatin. Thermal coagulations of different sizes were produced by applying the RF procedure for various times and end point temperatures. Dimensions, areas and volumes computed from CT and elastography were compared with those on whole mount pathology specimens. Ultrasound elastography exhibited high contrast for the thermal coagulations and performed better than CT. The correlation between pathology and elastography for this sample set of 40 thermal coagulations for volume estimation, for area estimation) is better than the correlation between pathology and CT for volume estimation, for area estimation).
MRI/TRUS data fusion for prostate brachytherapy. Preliminary results
Authors: Reynier Christophe , Troccaz Jocelyne , Fourneret Philippe , Dusserre André , Gay‐Jeune Cécile , Descotes Jean‐Luc , Bolla Michel , Giraud Jean‐Yves
Published: July 2004

Prostate brachytherapy involves implanting radioactive seeds for instance) permanently in the gland for the treatment of localized prostate cancers, e.g., cT1c‐T2a N0 M0 with good prognostic factors. Treatment planning and seed implanting are most often based on the intensive use of transrectal ultrasound (TRUS) imaging. This is not easy because prostate visualization is difficult in this imaging modality particularly as regards the apex of the gland and from an intra‐ and interobserver variability standpoint. Radioactive seeds are implanted inside open interventional MR machines in some centers. Since MRI was shown to be sensitive and specific for prostate imaging whilst open MR is prohibitive for most centers and makes surgical procedures very complex, this work suggests bringing the MR virtually in the operating room with MRI/TRUS data fusion. This involves providing the physician with bi‐modality images (TRUS plus MRI) intended to improve treatment planning from the data registration stage. The paper describes the method developed and implemented in the PROCUR system. Results are reported for a phantom and first series of patients. Phantom experiments helped characterize the accuracy of the process. Patient experiments have shown that using MRI data linked with TRUS data improves TRUS image segmentation especially regarding the apex and base of the prostate. This may significantly modify prostate volume definition and have an impact on treatment planning.
Feldkamp‐type VOI reconstruction from super‐short‐scan cone‐beam data
Authors: Yu Hengyong , Wang Ge
Published: July 2004

Based on the fan‐beam reconstruction formula recently developed by Noo et al. [Phys. Med. Biol.47, 2525–2546 (2002)] we develop a Feldkamp‐type algorithm for the reconstruction of a volume of interest (VOI) from super‐short‐scan data. With either a circular or spiral scanning locus in our VOI reconstruction scheme, we first estimate fan‐beam data from cone‐beam data using the popular “cosine correction” scheme, and perform reconstruction based on Noo's FBP‐type fan‐beam reconstruction. Our proposed algorithm is tested using the three‐dimensional (3‐D) Shepp–Logan phantom. The experimental results show that the new algorithm can be applied to multi‐source 4‐D CT with significantly superior temporal resolution and temporal consistency relative to the Katsevich algorithm, which is the state of the art for exact helical cone‐beam reconstruction.
Quantitation of respiratory motion during 4D‐PET/CT acquisition
Authors: Nehmeh S. A. , Erdi Y. E. , Pan T. , Yorke E. , Mageras G. S. , Rosenzweig K. E. , Schoder H. , Mostafavi H. , Squire O. , Pevsner A. , Larson S. M. , Humm J. L.
Published: July 2004

We report on the variability of the respiratory motion during 4D‐PET/CT acquisition. The respiratory motion for five lung cancer patients was monitored by tracking external markers placed on the abdomen. CT data were acquired over an entire respiratory cycle at each couch position. The x‐ray tube status was recorded by the tracking system, for retrospective sorting of the CT data as a function of respiration phase. Each respiratory cycle was sampled in ten equal bins. 4D‐PET data were acquired in gated mode, where each breathing cycle was divided into ten 500 ms bins. For both CT and PET acquisition, patients received audio prompting to regularize breathing. The 4D‐CT and 4D‐PET data were then correlated according to their respiratory phases. The respiratory periods, and average amplitude within each phase bin, acquired in both modality sessions were then analyzed. The average respiratory motion period during 4D‐CT was within 18% from that in the 4D‐PET sessions. This would reflect up to 1.8% fluctuation in the duration of each 4D‐CT bin. This small uncertainty enabled good correlation between CT and PET data, on a phase‐to‐phase basis. Comparison of the average‐amplitude within the respiration trace, between 4D‐CT and 4D‐ PET, on a bin‐by‐bin basis show a maximum deviation of . This study has proved the feasibility of performing 4D‐PET/CT acquisition. Respiratory motion was in most cases consistent between PET and CT sessions, thereby improving both the attenuation correction of PET images, and co‐registration of PET and CT images. On the other hand, in two patients, there was an increased partial irregularity in their breathing motion, which would prevent accurately correlating the corresponding PET and CT images.
Physical performance evaluation of a 256‐slice CT‐scanner for four‐dimensional imaging
Authors: Mori Shinichiro , Endo Masahiro , Tsunoo Takanori , Kandatsu Susumu , Tanada Shuji , Aradate Hiroshi , Saito Yasuo , Miyazaki Hiroaki , Satoh Kazumasa , Matsushita Satoshi , Kusakabe Masahiro
Published: July 2004

We have developed a prototype 256‐slice CT‐scanner for four‐dimensional (4D) imaging that employs continuous rotations of a cone‐beam. Since a cone‐beam scan along a circular orbit does not collect a complete set of data to make an exact reconstruction of a volume [three‐dimensional (3D) image], it might cause disadvantages or artifacts. To examine effects of the cone‐beam data collection on image quality, we have evaluated physical performance of the prototype 256‐slice CT‐scanner with 0.5 mm slices and compared it to that of a 16‐slice CT‐scanner with 0.75 mm slices. As a result, we found that image noise, uniformity, and high contrast detectability were independent of coordinate. A Feldkamp artifact was observed in distortion measurements. Full width at half maximum (FWHM) of slice sensitivity profiles (SSP) increased with coordinate though it seemed to be caused by other reasons than incompleteness of data. With regard to low contrast detectability, smaller objects were detected more clearly at the midplane than at though circular‐band like artifacts affected detection. The comparison between the 16‐slice and the 256‐slice scanners showed better performance for the 16‐slice scanner regarding the SSP, low contrast detectability, and distortion. The inferiorities of the 256‐slice scanner in other than distortion measurement (Feldkamp artifact) seemed to be partly caused by the prototype nature of the scanner and should be improved in the future scanner. The image noise, uniformity, and high contrast detectability were almost identical for both CTs. The 256‐slice scanner was superior to the 16‐slice scanner regarding the PSF, though it was caused by the smaller transverse beam width of the 256‐slice scanner. In order to compare both scanners comprehensively in terms of exposure dose, noise, slice thickness, and transverse spatial resolution, was calculated, where was exposure dose (CT dose index), σ was magnitude of noise, was slice thickness (FWHM of SSP), and was transverse spatial resolution (FWHM of PSF). The results showed that the value was 25% larger for the 16‐slice scanner, and that the 256‐slice scanner was 1.25 times more effective than the 16‐slice scanner at the midplane. The superiority in value for the 256‐slice scanner might be partly caused by decrease of wasted exposure with a wide‐angle cone‐beam scan. In spite of the several problems of the 256‐slice scanner, it took a volume data approximately resolution for a wide field of view (approximately 100 mm long) along the axis in a 1 s scan if resolution was defined by the FWHM of the PSF or the SSP, which should be very useful to take dynamic 3D (4D) images of moving organs.
Geometric studies on variable radius spiral cone‐beam scanning
Authors: Ye Yangbo , Zhu Jiehua , Wang Ge
Published: July 2004

The goal is to perform geometric studies on cone‐beam CT scanning along a three‐dimensional (3D) spiral of variable radius. First, the background for variable radius spiral cone‐beam scanning is given in the context of electron‐beam CT/micro‐CT. Then, necessary and sufficient conditions are proved for existence and uniqueness of PI lines inside the variable radius 3D spiral. These results are necessary steps toward exact cone‐beam reconstruction from a 3D spiral scan of variable radius, adapting Katsevich's formula for the standard helical cone‐beam scanning. It is shown in the paper that when the longitudinally projected planar spiral is not always convex toward the origin, the PI line may not be unique in the envelope defined by the tangents of the spiral. This situation can be avoided by using planar spirals whose curvatures are always positive. Using such a spiral, a longitudinally homogeneous region inside the corresponding 3D spiral is constructed in which any point is passed by one and only one PI line, provided the angle ω between planar spiral's tangent and radius is bounded by for some positive . If the radius varies monotonically, this region is larger and one may allow . Examples for 3D spirals based on logarithmic and Archimedean spirals are given. The corresponding generalized Tam–Danielsson detection windows are also formulated.
Impact of resolution and noise characteristics of digital radiographic detectors on the detectability of lung nodules
Authors: Saunders Robert S. , Samei Ehsan , Hoeschen Christoph
Published: July 2004

One of the unanswered questions in digital radiography is the connection between physical image quality metrics and clinical detection performance. In this paper, we examine the impact of two physical metrics, resolution and noise, on the detectability of nodules in a pulmonary background for specific digital radiographic detectors. A detection experiment was performed on a simulated image set using anatomical backgrounds from a high‐quality lung radiograph and three different simulated nodule sizes (2–3.5 mm). The resolution and noise of the resulting images were modified using existing routines to simulate a selenium‐based and a cesium iodide‐based flat‐panel detector at comparable exposures. A location‐known‐exactly (LKE) observer performance experiment was performed in which four experienced chest radiologists and three physicists specializing in chest radiology scored the images. The data from the observer experiment were analyzed by receiver operating characteristic (ROC) methodology. The detectability, as measured by the parameter was higher for the selenium detector than the cesium iodide detector for all nodule sizes by an average of 8.5%. For one nodule size (2.75 mm), the difference between detectors was statistically significant . The findings indicate that for the particular task studied, the superior resolution performance of the selenium‐based detector provided better detectability of subtle lung nodules even though the images had greater noise than images obtained with the cesium iodide detector.
Treatment planning dosimetric parameters for seed at short distances: Effects of air channels and neighboring seeds based on Monte Carlo study
Authors: Patel Neil S. , Chiu‐Tsao Sou‐Tung , Shih J. Allen , Ho Yunsil , Tsao Hung‐Sheng , Harrison Louis B.
Published: July 2004

The dose distributions around two different arrangements of a single radioactive seed in water, (1) with air channels at the ends, and (2) surrounded by two nonactive (“dummy”) seeds on both longitudinal ends, were calculated using MCNP4C Monte Carlo simulations at distances up to 1 cm. The contributions from beta particles and electrons emitted by were included in the calculations. The effects of (a) the air channels at the seed ends and (b) the interference effect of the dummy seeds on the dose distribution were quantified and compared. It was found that the dummy seeds do not cause significant dose reduction for radial distances beyond 0.05 cm from the seed center. It is decided to report the dose rate values and the dosimetric parameters in TG43 format for a single seed with air channels for use in treatment planning computer systems. The dose rate constant (at 1 cm) of seed, Λ, is The values of radial dose function, are within 1% from the TG43 recommended polynomial fit, except for distances within 0.08 cm. The anisotropy function, attains large values near the seed ends and shallow angles (up to 8), as well as many values greater than 2 at the polar angle. Treatment planning systems involving intravascular brachytherapy do not compromise the accuracy for dosimetry of multiple seed trains by summing single seed values in water.
Quantitative characterization of edge enhancement in phase contrast x‐ray imaging
Authors: Monnin P. , Bulling S. , Hoszowska J. , Valley J.‐F. , Meuli R. , Verdun F. R.
Published: July 2004

The aim of this study was to model the edge enhancement effect in in‐line holography phase contrast imaging. A simple analytical approach was used to quantify refraction and interference contrasts in terms of beam energy and imaging geometry. The model was applied to predict the peak intensity and frequency of the edge enhancement for images of cylindrical fibers. The calculations were compared with measurements, and the relationship between the spatial resolution of the detector and the amplitude of the phase contrast signal was investigated. Calculations using the analytical model were in good agreement with experimental results for nylon, aluminum and copper wires of 50 to 240 μm diameter, and with numerical simulations based on Fresnel–Kirchhoff theory. A relationship between the defocusing distance and the pixel size of the image detector was established. This analytical model is a useful tool for optimizing imaging parameters in phase contrast in‐line holography, including defocusing distance, detector resolution and beam energy.
Extended parallel backprojection for standard three‐dimensional and phase‐correlated four‐dimensional axial and spiral cone‐beam CT with arbitrary pitch, arbitrary cone‐angle, and 100% dose usage
Authors: Kachelrieß Marc , Knaup Michael , Kalender Willi A.
Published: July 2004

We have developed a new approximate Feldkamp‐type algorithm that we call the extended parallel backprojection (EPBP). Its main features are a phase‐weighted backprojection and a voxel‐by‐voxel 180° normalization. The first feature ensures three‐dimensional (3‐D) and 4‐D capabilities with one and the same algorithm; the second ensures 100% detector usage (each ray is accounted for). The algorithm was evaluated using simulated data of a thorax phantom and a cardiac motion phantom for scanners with up to 256 slices. Axial (circle and sequence) and spiral scan trajectories were investigated. The standard reconstructions (EPBPStd) are of high quality, even for as many as 256 slices. The cardiac reconstructions (EPBPCI) are of high quality as well and show no significant deterioration of objects even far off the center of rotation. Since EPBPCI uses the cardio interpolation (CI) phase weighting the temporal resolution is equivalent to that of the well‐established single‐slice and multislice cardiac approaches 180°CI, 180°MCI, and ASSRCI, respectively, and lies in the order of 50 to 100 ms for rotation times between 0.4 and 0.5 s. EPBP appears to fulfill all required demands. Especially the phase‐correlated EPBP reconstruction of cardiac multiple circle scan data is of high interest, e.g., for dynamic perfusion studies of the heart.
Blind deconvolution of audio-frequency signals using the self-deconvolving data restoration algorithm
Authors: Caron James N.
Published: July 2004

A signal processing algorithm has been developed in which a filter function is extracted from degraded data through mathematical operations. The filter function can be used to restore much of the degraded content of the data through use of a deconvolution process. The operation can be performed without prior knowledge of the detection system, a technique known as blind deconvolution. The extraction process, designated self-deconvolving data reconstruction algorithm, is applied here to audio-frequency signals showing significant qualitative improvement. Degradation arising from the process of electronic recording and reproduction is significantly reduced.
Travel-time sensitivity kernels in ocean acoustic tomography
Authors: Skarsoulis E. K. , Cornuelle B. D.
Published: July 2004

Wave-theoretic ocean acoustic propagation modeling is combined with the peak arrival approach for tomographic travel-time observables to derive the sensitivity kernel of travel times with respect to sound-speed variations. This is the Born–Fréchet kernel relating the three-dimensional spatial distribution of sound-speed variations with the induced travel-time variations. The derivation is based on the first Born approximation of the Green’s function. The application of the travel-time sensitivity kernel to an ocean acoustic waveguide gives a picture close to the ray-theoretic one in the case of high frequencies. However, in the low-frequency case, of interest in ocean acoustic tomography, for example, there are significant deviations. Low-frequency travel times are sensitive to sound-speed changes in Fresnel-zone-scale areas surrounding the eigenrays, but not on the eigenrays themselves, where the sensitivity is zero. Further, there are areas of positive sensitivity, where, e.g., a sound-speed increase results in an increase of arrival times, i.e., a further delay of arrivals, in contrast with the common expectation. These findings are confirmed by forward acoustic predictions from a coupled-mode code.
Nonlinear tube waves in permeable formations: Difference frequency generation
Authors: Tserkovnyak Yaroslav , Johnson David Linton
Published: July 2004

We extend earlier work on nonlinear tube wave propagation in permeable formations to study, analytically and numerically, the generation and propagation of a difference frequency, Δω=ω1−ω2, due to an initial pulse consisting of carrier frequencies ω1 and ω2. Tube waves in permeable formations have very significant linear dispersion/attenuation, which is specifically addressed here. We find that the difference frequency is predicted to be rather easily measurable with existing techniques and could yield useful information about formation nonlinear properties.
Sensorless control of a thermoacoustic refrigerator
Authors: Shearer Tony L. , Hofmann Heath F. , Smith Robert W. M. , Garrett Steven L.
Published: July 2004

A method for commanding the frequency of the signal that drives an electrodynamic sound source to maintain the coupled thermoacoustic resonator at its resonance frequency is described. The method uses only the current and voltage applied to the source terminals to select the operating frequency, thereby eliminating the need for pressure and displacement sensors used in previous phase-locked-loop frequency tracking systems. An equivalent circuit model of the coupled electro-mechanical system is used to extract piston position and pressure from the measured input current and voltage waveforms. Parameters of the electro-mechanical model can be obtained from a least-squares fit of the model using measured current, voltage, position, and force over the frequency range of interest. Parameters thus obtained are in good agreement with individual physical measurements of those same parameters. Results are presented for the implementation of this controller in a large thermoacoustic chiller.
The role of high-CF fibers in speech perception: Comments on Horwitz et al. (2002) (L)
Authors: Strickland Elizabeth A. , Viemeister Neal F. , Van Tasell Dianne J. , Preminger Jill E.
Published: July 2004

In a recent paper, Horwitz et al. [J. Acoust. Soc. Am. 111, 409–416 (2002)] concluded that listeners with high-frequency hearing impairment show a decrement in the perception of low-frequency speech sounds that is due to loss of information normally carried by auditory-nerve fibers with high characteristic frequencies (CFs). However, in their own study and in other studies, highpass-filtered noise did not degrade the perception of lowpass-filtered speech in listeners with normal hearing. An alternate conclusion proposed by Strickland et al. [J. Acoust. Soc. Am. 95, 497–501 (1994)] is that information conveyed by high-CF fibers is not necessary for speech perception. To reconcile these opposite conclusions, we suggest that the hearing-impaired listeners tested by Horwitz et al. may not have had normal hearing even in the low frequencies, and that the conclusion from Strickland et al. remains correct: high-CF fibers are not necessary for normal speech perception.
The effects of real and illusory glides on pure-tone frequency discrimination
Authors: Lyzenga J. , Carlyon R. P. , Moore B. C. J.
Published: July 2004

Experiment 1 measured pure-tone frequency difference limens (DLs) at 1 and 4 kHz. The stimuli had two steady-state portions, which differed in frequency for the target. These portions were separated by a middle section of varying length, which consisted of a silent gap, a frequency glide, or a noise burst (conditions: gap, glide, and noise, respectively). The noise burst created an illusion of the tone continuing through the gap. In the first condition, the stimuli had an overall duration of 500 ms. In the second condition, stimuli had a fixed 50-ms middle section, and the overall duration was varied. DLs were lower for the glide than for the gap condition, consistent with the idea that the auditory system contains a mechanism specific for the detection of dynamic changes. DLs were generally lower for the noise than for the gap condition, suggesting that this mechanism extracts information from an illusory glide. In a second experiment, pure-tone frequency direction-discrimination thresholds were measured using similar stimuli as for the first experiment. For this task, the type of the middle section hardly affected the thresholds, suggesting that the frequency-change detection mechanism does not facilitate the identification of the direction of frequency changes.
A partial field decomposition algorithm and its examples for near-field acoustic holography
Authors: Nam Kyoung-Uk , Kim Yang-Hann
Published: July 2004

In this paper we introduce a practical algorithm that can accurately implement partial field decomposition for near-field acoustic holography (NAH). Unlike other methods, the algorithm does not require sensors near sources because it uses calculations rather than measured signals in order to decompose a holography image into the images of individual sources. Therefore it makes holography measurement easier than other methods. The algorithm is composed of five steps: measurement of pressure on a hologram plane, estimation of pressure on a source plane, selection of maximum pressure, estimation of the sound field from one source, and estimation of the remaining sound field. In this paper we also report two experiments that verify and demonstrate the algorithm. In one experiment six speakers are operated independently. The other is a vortex shedding experiment. Their results show that the decomposition method is useful for identifying hidden sources and estimating the power of individual sources.
Scatterer size estimation in pulse-echo ultrasound using focused sources: Calibration measurements and phantom experiments
Authors: Bigelow Timothy A. , O’Brien William D.
Published: July 2004

In a companion paper [T. A. Bigelow and W. D. O’Brien Jr., J. Acoust. Soc. Am. 116, 578 (2004)], theory, supported by simulations, showed that accurate scatterer size estimates could be obtained using highly focused sources provided that the derived generalized attenuation-compensation function was used and the velocity potential field near the focus could be approximated as a three-dimensional Gaussian. Herein, the theory is further evaluated via experimental studies. A calibration technique is developed to find the necessary equivalent Gaussian dimensions for a focused source using reflections obtained from a rigid plane scanned through the focus. Then, the theoretical analysis of focused sources is validated experimentally using three spherically focused ultrasound transducers to estimate the radius of glass beads imbedded in tissue mimicking phantoms. Both the impact of focusing (f/1, f/2, and f/4) and the effect of scatterer type (comparing glass bead results to simulation results that used scatterers with Gaussian impedance distributions) were tested. The simulated differences agree with the measured differences to within 2.5% provided that the comparison is made between the same scatterer type and sources with the same equivalent Gaussian dimensions. The improvement provided by the generalized attenuation-compensation function is greatly influenced by the type of scatterer whose size is being estimated and decreases as the wavelength dependence of the Gaussian depth of focus is reduced.
Levitation force induced by pressure radiation in gas squeeze films
Authors: Minikes Adi , Bucher Izhak , Haber Shimon
Published: July 2004

An analytical and numerical study on the levitation force induced by pressure radiation in gas squeeze films is investigated. The levitation phenomenon is known to occur when a planar object is placed at close proximity to a vibrating piston. The existing analytical approaches are based on either conventional acoustic radiation, where the fluid is assumed inviscid or on a variant of the Reynolds equation that incorporates viscous effects. Alas, these solutions are often in poor agreement with accurate numerical results and, at best, describe appropriately cases that include a limited range of object weights and vibration frequencies. In this work, two cases are addressed: the flow induced by vibrations perpendicular to a flat surface and that by flexural wave propagation parallel to the surface. For the first case, numerical and second-order analytical perturbation solutions are obtained and compared, proving them to be in good agreement. In addition, a novel, analytical expression for the levitation force is also suggested that proves to be valid for a wider physical range of squeeze numbers and vibration amplitudes. For the second and more complex case (recently used in noncontacting transportation systems where the driving surface exhibited flexural traveling waves), the skin-friction force exerted on the flat surface is derived analytically based on a first-order perturbation solution, and the levitation force is analyzed numerically. Some insights on the physical behavior are then highlighted and discussed.
Age reduces response latency of mouse inferior colliculus neurons to AM sounds
Authors: Simon Henry , Frisina Robert D. , Walton Joseph P.
Published: July 2004

Age and stimulus rise time (RT) effects on response latency were investigated for inferior colliculus (IC) neurons in young-adult and old CBA mice. Single-unit responses were recorded to unmodulated and sinusoidal amplitude modulated (SAM) broadband noise carriers, presented at 35 to 80 dB SPL. Data from 63 young-adult and 76 old phasic units were analyzed to identify the time interval between stimulus onset and driven-response onset (latency). When controlling for stimulus sound level and AM frequency, significant age-related changes in latency were identified. Absolute latency decreased with age at all stimulus AM frequencies, significantly so for equivalent rise times (RT)⩽12.5 ms. The linear correlation of latency with AM stimulus RT was significant for both young-adult and old units, and increased significantly with age. It is likely that both the decrease in absolute latency and the increase in latency/RT correlation with age are consistent with a reduction of inhibitory drive with age in the IC. These latency changes will result in age-related timing variations in brainstem responses to stimulus onsets, and therefore affect the encoding of complex sounds.
Quantitative analysis of the vibration modes in a finite set of coupled spheres
Authors: Hladky-Hennion Anne-Christine , Devos Arnaud , de Billy Michel
Published: July 2004

This paper deals with the propagation of waves along a one-dimensional chain made up of welded spheres. First, a theoretical analysis allows the vibration modes of the chain to be quantitatively described. It has been validated by a comparison between numerical results, using the finite element method and experimental results, restricted to sets of two or three coupled spheres. It is numerically and experimentally verified that the peaks associated with the Rayleigh modes broaden out as the mode number increases and that the passband structure is strongly influenced by the characteristics of the welding between the cells of the periodic structure. The interest of such an approach is then illustrated by the examination of an inverse problem, in which the analytical model is used to deduce the characteristics of the welding.
Prediction of the characteristics of two types of pressure waves in the cochlea: Theoretical considerations
Authors: Andoh Masayoshi , Wada Hiroshi
Published: July 2004

The aim of this study was to predict the characteristics of two types of cochlear pressure waves, so-called fast and slow waves. A two-dimensional finite-element model of the organ of Corti (OC), including fluid–structure interaction with the surrounding lymph fluid, was constructed. The geometry of the OC at the basal turn was determined from morphological measurements of others in the gerbil hemicochlea. As far as mechanical properties of the materials within the OC are concerned, previously determined mechanical properties of portions within the OC were adopted, and unknown mechanical features were determined from the published measurements of static stiffness. Time advance of the fluid–structure scheme was achieved by a staggered approach. Using the model, the magnitude and phase of the fast and slow waves were predicted so as to fit the numerically obtained pressure distribution in the scala tympani with what is known about intracochlear pressure measurement. When the predicted pressure waves were applied to the model, the numerical result of the velocity of the basilar membrane showed good agreement with the experimentally obtained velocity of the basilar membrane documented by others. Thus, the predicted pressure waves appeared to be reliable. Moreover, it was found that the fluid–structure interaction considerably influences the dynamic behavior of the OC at frequencies near the characteristic frequency.
Stability analysis of injection molding flows
Authors: Bogaerds Arjen C. B. , Hulsen Martien A. , Peters Gerrit W. M. , Baaijens Frank P. T.
Published: July 2004

We numerically investigate the stability problem of the injection molding process. It was indicated by Bulters and Schepens [Bulters and Schepens (2000)] that surface defects of injection molded products may be attributed to a flow instability near the free surface during the filling stage of the mold. We examine the stability of this flow using the extended Pom–Pom constitutive equations. The model allows for controlling the degree of strain hardening of the fluids without affecting the shear behavior considerably. To study the linear stability characteristics of the injection molding process we use a transient finite element algorithm that is able to efficiently handle time dependent viscoelastic flow problems and includes a free surface description to take perturbations of the computational domain into account. It is shown that the fountain flow, which is a model flow for the injection molding process, is subject to a viscoelastic instability. If the various rheologies are compared, we observe that the onset of unstable flow can be delayed by increasing the degree of strain hardening of the fluid (by increasing the number of arms in the Pom–Pom model). The most unstable disturbance which is obtained after exponential growth is a swirling flow near the fountain flow surface which is consistent with the experimental findings.
Rheo-nuclear magnetic resonance of emulsion systems
Authors: Hollingsworth K. G. , Johns M. L.
Published: July 2004

This paper uses the technique of rheo-nuclear magnetic resonance (rheo-NMR) [reviewed by P. T. Callaghan, Rep. Prog. Phys. 62, 599–670 (1999)] to perform a systematic study of emulsion rheology. Rheo-NMR uses NMR velocimetry to produce velocity maps, from which it is possible to quantify rheological parameters, with apparent wall slip being measured directly. The study is initially conducted on silicone oil-in-water emulsions. Xanthan gum, an important emulsion thickener and stabilizer in the food industry, is then investigated. Finally, the technique is applied to a commercial mayonnaise, which is a complex product comprising a concentrated oil in water emulsion with various thickeners and stabilizers in the continuous phase. Rheological parameters (based on either a power-law fluid or a Hershel–Bulkley analysis) and apparent slip characteristics are extracted from the velocity maps for these materials, across a wide range of shear rates. Comparison with conventional rheological measurement and analysis is presented; reasonably good agreement is produced between the two methods.
A semi-empirical approach for modeling charged soft microgel particles
Authors: Tan B. H. , Tam K. C. , Lam Y. C. , Tan C. B.
Published: July 2004

We describe a unified semi-empirical approach for predicting the viscosity of dilute and concentrated hard and soft sphere systems. A variable specific volume, k was introduced to convert the mass concentration to effective volume fraction. With increasing particle concentration, the concentration of free counter-ions in the solution can be large enough to induce an osmotic de-swelling of soft particles, resulting in the particle shrinkage. The viscosity data for four different microgel systems at different neutralization degree showed excellent agreement with the modified Krieger–Dougherty model.
Effect of long branches on the rheology of polypropylene
Authors: Gotsis A. D. , Zeevenhoven B. L. F. , Tsenoglou C.
Published: July 2004

In order to study the rheology of long chain branched polymers, branches have been added on linear polypropylene precursors in varying amounts using reactive modification with peroxydicarbonates. The branched polypropylene samples show distinct strain hardening, something absent from the linear melt; this considerably improves the melt strength of the modified polymer. The zero shear viscosity and the elasticity measured by the relaxation spectrum also increase with the number of branches per molecule. Two models are applied to describe strain hardening of the viscosity during the course of elongation. The model parameters were found to vary systematically with the degree of branching and, therefore, their values can be used as a measure of this. Consequently, fluidity, elasticity, strain hardening, and melt strength are all related to the degree of long chain branching.
Large shear deformation of particle gels studied by Brownian dynamics simulations
Authors: Rzepiela A. A. , van Opheusden J. H. J. , van Vliet T.
Published: July 2004

Brownian dynamics (BD) simulations have been performed to study structure and rheology of particle gels under large shear deformation. The model incorporates soft spherical particles, and reversible flexible bond formation. Two different methods of shear deformation are discussed, namely affine and nonaffine deformation, the second being novel in simulation studies of gels. Also two dynamic descriptions of the model are presented, with and without inertia effects. Nonaffine deformation resulted in a slower increase of the stress at small deformation than affine deformation. At large deformation both models gave similar stress responses, although the inertia model resulted in lower stresses. The particle gels, regardless of the model used, were observed to fracture into lumps that compactified due to local reorganization. A reversible yielding transition, as observed in polymer gels, was not found. Fractal properties of the gels were irreversibly lost at large deformation.
Steady-shear rheological properties of model compatibilized blends
Authors: Velankar S. , Van Puyvelde P. , Mewis J. , Moldenaers P.
Published: July 2004

Block copolymers may be added as surface-active compatibilizers in order to control the morphology of blends of immiscible polymers. The effects of such added compatibilizers on the rheological properties of droplet–matrix blends are investigated experimentally. Model blends composed of polyisobutylene (PIB) droplets in a polydimethylsiloxane (PDMS) matrix, compatibilized with a diblock copolymer of PIB and PDMS, are studied here. The viscosity ratio of the blends, i.e., the ratio of the viscosity of the droplets to that of the matrix, is varied from 0.1 to 2.7. The viscosity and the first normal stress difference under steady shear conditions, and complex moduli after cessation of shear are measured. It is found that addition of the compatibilizer slightly raises the magnitude of the terminal complex viscosity of blends at all ratios of viscosity. Furthermore, with addition of the compatibilizer, the terminal relaxation time is found to increase sharply at high viscosity ratios, whereas the steady shear N1 is found to increase at low viscosity ratios. These experimental observations are consistent with Marangoni stress caused by flow-induced gradients in the compatibilizer concentration on the surface of compatibilized drops. It is shown that, qualitatively, the effects of the Marangoni stress are somewhat analogous to an increase in drop viscosity.
Cognitive Control Signals for Neural Prosthetics
Authors: Musallam S. , Corneil B. D. , Greger B. , Scherberger H. , Andersen R. A.
Published: July 2004

Recent development of neural prosthetics for assisting paralyzed patients has focused on decoding intended hand trajectories from motor cortical neurons and using this signal to control external devices. In this study, higher level signals related to the goals of movements were decoded from three monkeys and used to position cursors on a computer screen without the animals emitting any behavior. Their performance in this task improved over a period of weeks. Expected value signals related to fluid preference, the expected magnitude, or probability of reward were decoded simultaneously with the intended goal. For neural prosthetic applications, the goal signals can be used to operate computers, robots, and vehicles, whereas the expected value signals can be used to continuously monitor a paralyzed patient's preferences and motivation.
Nanoparticles: Strained and Stiff
Authors: Gilbert Benjamin , Huang Feng , Zhang Hengzhong , Waychunas Glenn A. , Banfield Jillian F.
Published: July 2004

Nanoparticles may contain unusual forms of structural disorder that can substantially modify materials properties and thus cannot solely be considered as small pieces of bulk material. We have developed a method to quantify intermediate-range order in 3.4-nanometer-diameter zinc sulfide nanoparticles and show that structural coherence is lost over distances beyond 2nanometers. The zinc-sulfur Einstein vibration frequency in the nanoparticles is substantially higher than that in the bulk zinc sulfide, implying structural stiffening. This cannot be explained by the observed 1% radial compression and must be primarily due to inhomogeneous internal strain caused by competing relaxations from an irregular surface. The methods developed here are generally applicable to the characterization of nanoscale solids, many of which may exhibit complex disorder and strain.
The (Me
5
C
5
)Si
+
Cation: A Stable Derivative of HSi
+
Authors: Jutzi Peter , Mix Andreas , Rummel Britta , Schoeller Wolfgang W. , Neumann Beate , Stammler Hans-Georg
Published: July 2004

The reaction of decamethylsilicocene, (Me
5
C
5
)
2
Si, with the proton-transfer reagent Me
5
C
5
H
2
+
B(C
6
F
5
)
4
–
produces the salt (Me
5
C
5
)Si
+
B(C
6
F
5
)
4
(2), which can be isolated as a colorless solid that is stable in the absence of air and moisture. The crystal structure reveals the presence of a cationic π complex with an η
5
-pentamethylcyclopentadienyl ligand bound to a bare silicon center. The
29
Si nuclear magnetic resonance at very high field (δ = – 400.2 parts per million) is typical of a π complex of divalent silicon. The (η
5
-Me
5
C
5
)Si
+
cation in 2 can be regarded as the “resting state” of a silyliumylidene-type (η
1
-Me
5
C
5
)Si
+
cation. The availability of 2 opens new synthetic avenues in organosilicon chemistry. For example, 2 reacted with lithium bis(trimethylsilyl)amide to give the disilene
E
-{(η
1
-Me
5
C
5
)[N(SiMe
3
)
2
]Si}
2
(3).