bluuebunny/crossref_metadata_2025 huggingface dataset:
Pharmacokinetics and elimination of moxifloxacin after oral and intravenous administration in man
Authors: Stass H. , Kubitza D.
Published: July 2002

The pharmacokinetics of moxifloxacin and its metabolites M1 (sulpho-compound) and M2 (acyl-glucuronide) were characterized in 12 healthy male volunteers in an open, randomized, crossover study. After an overnight fast the volunteers were given a single 400 mg dosage of moxifloxacin either as a tablet or a 1 h infusion with a washout phase of at least 1 week between the two treatments. Multiple plasma, faeces and urine samples were collected for the analysis of moxifloxacin and metabolites using validated HPLC with fluorescence detection. The AUC for both formulations was comparable with bioequivalence criteria fulfilled, with Cmax after oral treatment approximately 31% lower. Following oral administration, absorption was fast with low to medium variability (mean dissolution and absorption time 2.4 h). The absolute bioavailability was 86%. The excretion of moxifloxacin and its metabolites was quantified in a subset of eight subjects. More than 96% of the dose was recovered from urine and faeces after oral dosing, and >98% following iv administration of the drug. M1, which is strongly bound to plasma proteins (90%), was mainly eliminated into faeces (approximately 37–38% of the administered dose) and to a minor extent into urine (2.5% of the administered dose) by active tubular secretion. M2 (only 5% bound to plasma protein) was only found in urine, where it amounted to approximately 14% of the dose. Plasma concentrations of the metabolites were much lower than those of the parent compound. Moxifloxacin was well tolerated with few adverse events and no clinically relevant changes in laboratory values.
Pharmacodynamics of levofloxacin and ofloxacin against Streptococcus pneumoniae
Authors: Bauernfeind A.
Published: July 2002

The aim of this study was to compare the bactericidal efficacy of levofloxacin and ofloxacin against Streptococcus pneumoniae at different dosage regimens for both agents. An in-vitro pharmacodynamic model was used. Levofloxacin kinetics of 500 mg, administered od or bd, were compared with ofloxacin kinetics of 400 mg od or bd. Killing by 3 log 10 (99.9%) was achieved up to an MIC of 0.5 mg/L (500 mg od) or 1 mg/L (500 mg bd). For levofloxacin killing of S. pneumoniae was unimpaired in mixed cultures with Haemophilus influenzae. For ofloxacin, killing by 2 log 10 was achieved up to an MIC of 0.5 mg/L for 400 mg od and up to an MIC of 1 mg/L for 400 mg bd. Killing by 3 log 10 was not achievable by 400 mg od, but was achieved up to an MIC of 0.5 mg/L for 400 mg bd. Killing of S. pneumoniae with identical MICs of levofloxacin was not influenced by their susceptibility to penicillin G. These data, together with the two-fold higher activity of levofloxacin in comparison with ofloxacin, indicate good therapeutic perspectives for levofloxacin over ofloxacin in the treatment of S. pneumoniae infections.
Tobacco mosaic virus and the study of early events in virus infections
Authors: Shaw John G.
Published: July 2002

In order to establish infections, viruses must be delivered to the cells of potential hosts and must then engage in activities that enable their genomes to be expressed and replicated. With most viruses, the events that precede the onset of production of progeny virus particles are referred to as the early events and, in the case of positive–strand RNA viruses, they include the initial interaction with, and the entry of, host cells and the release (uncoating) of the genome from the virus particles. Though the early events remain one of the more poorly understood areas of plant virology, the virus with which most of the relevant research has been performed is tobacco mosaic virus (TMV). In spite of this effort, there remains much uncertainty about the form or constituent of the virus that actually enters the initially invaded cell in a plant and about the mechanism(s) that trigger the subsequent uncoating (virion disassembly) reactions. A variety of approaches have been used in attempts to determine the fate of TMV particles that are involved in the establishment of an infection and these are briefly described in this review. In some recent work, it has been proposed that the uncoating process involves the bidirectional release of coat protein subunits from the viral RNA and that these activities may be mediated by cotranslational and coreplicational disassembly mechanisms.
Tobacco mosaic virus virulence and avirulence
Authors: Dawson William O.
Published: July 2002

In celebration of a century of research on tobacco mosaic virus that initiated the science of virology, I review recent progress relative to earlier contributions concerning how viruses cause diseases of plants and how plants defend themselves from viruses.
Identification of in vivo mRNA targets of GLD-1, a maxi-KH motif containing protein required for C. elegans germ cell development
Authors: Lee Min-Ho , Schedl Tim
Published: July 2002

Caenorhabditis elegans GLD-1, a KH motif containing RNA-binding protein of the GSG/STAR subfamily, controls diverse aspects of germ line development, suggesting that it may have multiple mRNA targets. We used an immunoprecipitation/subtractive hybridization/cloning strategy to identify 15 mRNAs that are putative targets of GLD-1 binding and regulation. For one target, therme-2 yolk receptor mRNA, GLD-1 acts as a translational repressor to spatially restrict RME-2 accumulation, and thus yolk uptake, to late-stage oocytes. We found that GLD-1 binds sequences in both 5′ coding and the 3′ untranslated region of rme-2 mRNA. Initial characterization of the other 14 targets shows that (1) they are coexpressed with GLD-1; (2) they can have mutant/RNA-mediated interference depletion phenotypes indicating functions in germ line development or as maternal products necessary for early embryogenesis; and (3) GLD-1 may coregulate mRNAs corresponding to functionally redundant subsets of genes within two gene families. Thus, a diverse set of genes have come under GLD-1-mediated regulation to achieve normal germ line development. Previous work identified tra-2 as a GLD-1 target for germ line sex determination. Comparisons of GLD-1-mediated translational control of rme-2 and tra-2suggests that the mechanisms may differ for distinct target mRNA species.
Compatibility of Varian 2100C gated operations with enhanced dynamic wedge and IMRT dose delivery
Authors: Kubo H. Dale , Wang Lili
Published: July 2002

An enhanced dynamic wedge (EDW) is one of the latest technical innovations frequently used in the radiotherapy department. Its usage is enthusiastically supported by radiation therapists. Intensity modulated radiotherapy (IMRT) is the other, which has become popular within the past several years. Its usage is not as straightforward as the EDW. However, its ability to further increase dose conformity to the target and to spare the surrounding normal tissues has been evidenced. Both of these treatment modalities demand sophisticated software, which controls precision motion and speed of jaws or multileaf collimators as well as dose rate. This paper deals with the question of how accurately the EDW profiles and IMRT dose distributions be maintained when the additional constraint of linear accelerator gating is invoked. For this, square pulses mimicking breathing were used in gated and nongated modes for film dosimetry and ion chamber measurements using the Varian 2100C linear accelerator. The results show no observable difference between gated and nongated EDW profiles and IMRT dose distribution regardless of the machine repetition rate. Also studied in this paper are the “fuzzy” dose distributions caused by realistic finite gate window settings.
Inverse planning anatomy‐based dose optimization for HDR‐brachytherapy of the prostate using fast simulated annealing algorithm and dedicated objective function
Authors: Lessard Etienne , Pouliot Jean
Published: July 2002

An anatomy‐based dose optimization algorithm is developed to automatically and rapidly produce a highly conformal dose coverage of the target volume while minimizing urethra, bladder, and rectal doses in the delivery of an high dose‐rate (HDR) brachytherapy boost for the treatment of prostate cancer. The dwell times are optimized using an inverse planning simulated annealing algorithm (IPSA) governed entirely from the anatomy extracted from a CT and by a dedicated objective function (cost function) reflecting clinical prescription and constraints. With this inverse planning approach, the focus is on the physician's prescription and constraint instead of on the technical limitations. Consequently, the physician's control on the treatment is improved. The capacity of this algorithm to represent the physician's prescription is presented for a clinical prostate case. The computation time (CPU) for IPSA optimization is less than 1 min (41 s for 142 915 iterations) for a typical clinical case, allowing fast and practical dose optimization. The achievement of highly conformal dose coverage to the target volume opens the possibility to deliver a higher dose to the prostate without inducing overdosage of urethra and normal tissues surrounding the prostate. Moreover, using the same concept, it will be possible to deliver a boost dose to a delimited tumor volume within the prostate. Finally, this method can be easily extended to other anatomical sites.
Clearance assurance for stereotactic radiosurgery and radiotherapy
Authors: Furhang Eli E. , Hanley Joseph , Chiu‐Tsao Sou‐Tung , Toner Sean , Fan Pei , Gliedman Paul , Harrison Louis B.
Published: July 2002

The nature of stereotactic radiotherapy (SRT)/radiosurgery (SRS) requires the use of oblique noncoplanar beams to avoid critical structures and maximize target coverage. These beams are delivered via a combination of gantry, collimator, and couch rotations. Such beam orientations could result in the gantry colliding with the patient or couch. The outcome can be patient injury, damaged equipment, and unrealized treatment. Our objective in this work was to create a treatment planning tool that utilizes each unique patient geometry to quantify clearance for stereotactic beams. Emphasis was placed on developing a general platform that can completely, yet easily, define any user system. Gantry components were described by providing component dimensions to software that generates thousands of surface points. Table components were described as a combination of boxes and measured surface points. During the treatment planning process isocenter coordinates, patient dimensions and beam orientation were specified. Gantry components were then transformed into the table reference frame. The shortest distance between the gantry and patient or couch was computed and compared to a safety margin. This clearance assurance algorithm was developed in response to the need to reduce patient setup time, and to increase the range of potentially useful beams. The software was verified by measuring minimum gantry–table distances at multiple beam orientations and comparing to calculations. Differences between calculated and measured clearances were on the order of 1 cm. The software enabled the safe delivery of noncoplanar oblique beams that are difficult to visualize. The software was used successfully to assure clearance for 50 patients (366 beams). This useful clinical tool became an integral part of the stereotactic quality assurance protocol at St Luke's–Roosevelt Hospital Center.
Optimal pitch in spiral computed tomography
Authors: Wang Ge , Vannier Michael W.
Published: July 2002

The focus of this paper is to analytically optimize spiral/helical computed tomography (CT) protocols based on a simplified imaging model. Spiral CT was approximately modeled as follows: Using the half‐scan raw data interpolation method, the variance of the spiral CT slice sensitivity profile is equal to the sum of squared detector collimation divided by 12 and squared table increment divided by 24. Image noise variance is inversely proportional to tube current and detector collimation. The maximum continuous scanning time is inversely proportional to tube current. Slice thickness, image noise, and signal‐to‐noise ratio were, respectively, optimized for a given scanning coverage, consistently resulting in pitch of square root of 2. To avoid longitudinal aliasing, at least 2–3 transverse slices should be reconstructed per collimation. When the simplified spiral CT model is valid and a scanning range specified, 1.4 pitch is required for optimal image quality. The method can be applied to more accurate spiral CT models.
Analysis and convergence of the iterative convolution/superposition dose reconstruction technique for multiple treatment beams and tomotherapy
Authors: McNutt T. R. , Mackie T. R. , Paliwal B. R.
Published: July 2002

An iterative convolution/superposition (C/S) algorithm has been created to reconstruct dose distributions in patients from exit dose measurements during a radiotherapy treatment. The method is based on an extended phantom which includes the patient CT representation and an electronic portal imaging device (EPID). The patient CT is assumed to be a true and rigid representation of the patient at the time of treatment. The C/S method computes the dose throughout the extended phantom which allows the exit dose to be predicted in the EPID. The process is then reversed to take the exit dose measurement and infer what the dose distribution must have been to produce the measured exit dose. The dose distribution is modeled without knowledge of the incident intensity distribution, and includes the effects of scatter in the computation. The iterative method begins by assuming that the exit primary energy fluence (PEF) is equal to the exit dose, the PEF is then backprojected through the extended phantom and superposed with the dose deposition kernel to determine a new prediction of the exit dose. The ratio of the computed PEF to exit dose is then multiplied by the measured exit dose image to produce a better representation of the exit PEF. Successive iterations then converge to the exit PEF image that would produce the measured exit dose image. Once convergence is established, the dose distribution is determined by backprojecting the exit PEF followed by superposition with the dose deposition kernel. The method is used to reconstruct the dose from a simulated dynamic wedge and verified with film. Convergence and termination of the algorithm is then investigated with no noise and in the presence of noise. The method is then expanded to handle multiple treatment beams by separating the representation of the EPID from the patient or phantom representation in the computation process. Investigation of the effects of noise during the process of iterative dose reconstruction is necessary to understand the capabilities of the algorithm using exit dose images that may contain significant amounts of noise. The capability of the algorithm is evaluated for multiple field treatments to a cube phantom and a prostate patient CT representation in the presence of noise. The method is then used to simulate the dose reconstruction process for tomotherapy using 72 intensity‐modulated fan beams. Dose reconstruction is shown to be capable of verifying the dose distributions in patients including multiple beams and dynamic collimation, provided the patient CT is known at the time of treatment.
Correlation of medical dosimetry quality indicators to the local tumor control in patients with prostate cancer treated with iodine‐125 interstitial implants
Authors: Nath Ravinder , Roberts Kenneth , Ng Michelle , Peschel Richard , Chen Zhe
Published: July 2002

The treatment of prostate cancer by interstitial implants has been extensively studied with mixed results by one institution or another. A recent study from Hahnemann [Int. J. Radiat. Oncol., Biol., Phys. 21 955–960 (1991)] reported results that were extremely poor compared to those reported in an earlier study at Yale [Int. J. Radiat. Oncol., Biol., Phys. 14, 1153–1157 (1988)] or those in an Eastern Virginia Study [Cancer 63, 2415–2420 (1989)]; differences in 5‐yr survival rates being more than a factor of 2. Such large discrepancies from institution to institution led us to a reexamination of the dosimetry. This study analyzed quantitatively three‐dimensional dosimetric parameters of 110 prostate cancer patients treated with interstitial implants. The study searched for “cutoff” values in each parameter that divided the patients into two groups with statistically significant differences in the local recurrence‐free survival rates. A comparison of the three‐dimensional isodose surfaces of patients with favorable values in all of the parameters to those patients with all unfavorable parameters show how these characteristics translated into poor dose coverage and much inhomogeneity within the implant even for cases that met the traditional criteria for adequacy (160 Gy to the tumor volume). Patients in the favorable group had 10‐yr survival rates higher by a factor of up to 2 compared to those in the unfavorable group. The strong correlation of three‐dimensional volume‐dose parameters to the local control rate observed in this study further emphasizes how important it is to assess the three‐dimensional dosimetric adequacy of interstitial implants before deciding on their clinical efficacy. If implants are performed with appropriate attention to dosimetry parameters, excellent clinical results are obtained. On the other hand, if dosimetry parameters are not correct, the implant results can be poor.
A method of beam–couch intersection detection
Authors: Muthuswamy Moorthy S. , Lam Kwok L.
Published: July 2002

At the time of treatment planning it would be useful to know whether part of the treatment beam passes through the patient/couch support assembly before it passes through the patient. In the previous work of Yorke, the range of gantry angles leading to beam–couch intersection was found as a function of couch translation for symmetric field sizes and for zero couch rotation. Yorke's method has been extended to include couch rotation, dual independent jaws, and multi‐leaf collimator (MLC) field shapes. In addition, the new method is also applicable in the situation of the couch top located above the isocenter. For a clinically treatable, field configuration in a linac, the range of gantry angles leading to beam–couch intersection are different by 6.7 degrees for a couch rotation angle of 25 degrees when compared to no couch rotation. The new method agrees with data within the setup and measurement uncertainties for a variety of field sizes including an oval shaped MLC field, and various couch locations, couch, and collimator rotation angles.
Accuracy of a photogrammetry‐based patient positioning and monitoring system for radiation therapy
Authors: Rogus Ronald D. , Stern Robin L. , Kubo Hideo D.
Published: July 2002

A photogrammetry system designed to reduce simulator‐to‐treatment and treatment‐to‐treatment patient positioning errors has been developed. Two complete systems have been installed in our department: one in the simulator room and one in a treatment room. Each system consists of three charge‐coupled device (CCD) cameras; a ring of infrared LEDs around the lens of each camera; and several small, circular, retroreflective markers that are applied to the patient. The markers reflect infrared light directly back to the cameras, producing a binary image of oval hot spots when the image is thresholded. The three‐dimensional position of each marker is calculated by conventional photogrammetry methods. At simulation, marker positions are measured, then transferred to the treatment room system. The system may be used to actively position patients, and to passively monitor a patient's position and motion during treatment. Studies have focused on measuring the system's temporal stability, precision, and accuracy; on optimal positioning of markers and cameras; and on assessing the system's capability to reduce the positioning error. The repeatability of measuring a marker's position is <0.1 mm in each orthogonal direction. The accuracy is approximately 0.5 mm over a field of view. The system drift over four hours is approximately ±0.2 mm. The photogrammetry system has been used to actively position a lead BB, embedded within a head phantom, at the isocenter; repeatability was ±0.3 mm, as determined radiographically. The system has also been used to passively monitor the positioning of several head and neck patients that were set up by a therapist; setup errors of up to 10 mm in each orthogonal direction were measured, as well as the motion of the patient during treatment.
The impact of edema on planning and prostate implants
Authors: Yue Ning , Dicker Adam P. , Nath Ravinder , Waterman Frank M.
Published: July 2002

Permanent transperineal interstitial and prostate implants are generally planned to deliver a specific dose to a clinically defined target volume; however, the post‐implant evaluation usually reveals that the implant delivered a lower or higher dose than planned. This difference is generally attributed to such factors as source placement errors, overestimation of the prostate volume on CT, and post‐implant edema. In the present work we investigate the impact of edema alone. In routine prostate implant planning, it is customary to assume that both the prostate and seeds are static throughout the entire treatment time, and post‐implant edema is not taken into consideration in the dosimetry calculation. However, prostate becomes edematous after seed implantation, typically by 50% in volume [Int. J. Radiat. Oncol., Biol., Phys. 41, 1069–1077 (1998)]. The edema resolves itself exponentially with a typical half‐life of 10 days. In this work, the impact of the edema‐induced dynamic change in prostate volume and seed location on the dose coverage of the prostate is investigated. The total dose delivered to the prostate was calculated by use of a dynamic model, which takes edema into account. In the model, the edema resolves exponentially with time, as reported in a separate study based on serial CT scans [Int. J. Radiat. Oncol., Biol., Phys. 41, 1069–1077 (1998)]. The model assumes that the seeds were implanted exactly as planned, thus eliminating the effect of source placement errors. Implants based on the same transrectal ultrasound (TRUS) images were planned using both and sources separately. The preimplant volume and planned seed locations were expanded to different degrees of edema to simulate the post‐implant edematous prostate on day 0. The model calculated the dose in increments of 24 h, appropriately adjusting the prostate volume, seed locations, and source strength prior to each time interval and compiled dose‐volume histograms (DVH) of the total dose delivered. A total of 30 such DVHs were generated for each implant using different combinations of edema half‐life and magnitude. In addition, a DVH of the plan was compiled in the conventional manner, assuming that the prostate volume and seeds were static during treatment. A comparison of the DVH of the static model to the 30 edema corrected DVHs revealed that the plan overestimated the total dose by an amount that increased with the magnitude of the edema and the edema half‐life. The maximum overestimation was 15% for and 32% for For more typical edema parameters (a 50% increase in volume and a 10 day half‐life) the static plan for overestimated the total dose by about 5%, whereas that for overestimated it by about 12%.
Classical illustrations of CP violation in kaon decays
Authors: Rosner Jonathan L. , Slezak Scott A.
Published: July 2002

It is easy to construct classical two-state systems illustrating the behavior of the short-lived and long-lived neutral K mesons in the limit of CP conservation. The emulation of CP violation is more tricky, but is provided by the two-dimensional motion of a Foucault pendulum. Analogies are drawn between the pendulum and observables in neutral kaon decays. An emulation of CP and CPT violation using electric circuits is also discussed.
Sounds produced by Australian Irrawaddy dolphins,Orcaella brevirostris
Authors: Van Parijs Sofie M. , Parra Guido J. , Corkeron Peter J.
Published: July 2002

Sounds produced by Irrawaddy dolphins, Orcaella brevirostris, were recorded in coastal waters off northern Australia. They exhibit a varied repertoire, consisting of broadband clicks, pulsed sounds and whistles. Broad-band clicks, “creaks” and “buzz” sounds were recorded during foraging, while “squeaks” were recorded only during socializing. Both whistle types were recorded during foraging and socializing. The sounds produced by Irrawaddy dolphins do not resemble those of their nearest taxonomic relative, the killer whale, Orcinus orca. Pulsed sounds appear to resemble those produced by Sotalia and nonwhistling delphinids (e.g., Cephalorhynchus spp.). Irrawaddy dolphins exhibit a vocal repertoire that could reflect the acoustic specialization of this species to its environment.
Dispersion of interface waves in sediments with power-law shear speed profiles. I. Exact and approximate analytical results
Authors: Godin Oleg A. , Chapman David M. F.
Published: July 2002

In the upper tens of meters of ocean bottom, unconsolidated marine sediments consisting of clay, silt, or fine sand with high porosity are “almost incompressible” in the sense that the shear wave velocity is much smaller than the compressional wave velocity. The shear velocity has very large gradients close to the ocean floor leading to strong coupling of compressional and shear waves in such “soft” sediments. The weak compressibility opens an avenue for developing a theory of elastic wave propagation in continuously stratified soft sediments that fully accounts for the coupling. Elastic waves in soft sediments consist of “fast” waves propagating with velocities close to the compressional velocity and “slow” waves propagating with velocities on the order of the shear velocity. For the slow waves, the theory predicts the existence of surface waves at the ocean-sediment boundary. In the important special case of the power-law depth-dependence of shear rigidity, phase and group velocities of the interface waves are shown to scale as a certain power of frequency. An explicit, exact solution was obtained for the surface waves in sediments characterized by constant density and a linear increase of shear rigidity with depth, that is, for the case of shear speed proportional to the square root of the depth below the sediment-water interface. Asymptotic and perturbation techniques were used to extend the result to more general environments. Theoretical dispersion relations agreed well with numerical simulations and available experimental data and, as demonstrated in a companion paper [D. M. F. Chapman and O. A. Godin, J. Acoust. Soc. Am 110, 1908 (2001)] led to a simple and robust inversion of interface wave travel times for shear velocity profiles in the sediment.
Energy-independent factors influencing noise-induced hearing loss in the chinchilla model
Authors: Hamernik Roger P. , Qiu Wei
Published: July 2002

The effects on hearing and the sensory cell population of four continuous, non-Gaussian noise exposures each having an A-weighted Leq=100 dB SPL were compared to the effects of an energy-equivalent Gaussian noise. The non-Gaussian noise conditions were characterized by the statistical metric, kurtosis (β), computed on the unfiltered, β(t), and the filtered, β(f ), time-domain signals. The chinchilla (n=58) was used as the animal model. Hearing thresholds were estimated using auditory-evoked potentials (AEP) recorded from the inferior colliculus and sensory cell populations were obtained from surface preparation histology. Despite equivalent exposure energies, the four non-Gaussian conditions produced considerably greater hearing and sensory cell loss than did the Gaussian condition. The magnitude of this excess trauma produced by the non-Gaussian noise was dependent on the frequency content, but not on the average energy content of the impacts which gave the noise its non-Gaussian character. These results indicate that β(t) is an appropriate index of the increased hazard of exposure to non-Gaussian noises and that β(f ) may be useful in the prediction of the place-specific additional outer hair cell loss produced by non-Gaussian exposures. The results also suggest that energy-based metrics, while necessary for the prediction of noise-induced hearing loss, are not sufficient.
Two Scholte–Stoneley waves on doubly fluid-loaded plates and shells
Authors: Sessarego J.-P. , Sagéloli J. , Gazanhes C. , Überall H.
Published: July 2002

Previous theoretical and experimental studies of sound scattering from plates and from evacuated cylindrical or spherical shells with one-sided water loading have demonstrated the existence of a water-borne Scholte–Stoneley wave, and its acoustic excitation, in addition to that of the Lamb-type plate or shell wave modes. For two-sided water loading two Scholte–Stoneley waves, of symmetric (S) and antisymmetric (A) nature, were predicted on plates, with only the A wave surviving for the case of one-sided loading, while for loading with two different fluids, again two such waves have been demonstrated theoretically. In the present investigation, these two Scholte–Stoneley waves are studied experimentally via short-pulse scattering from water-immersed, thin-walled cylindrical shells filled alternatingly with air, water, and alcohol, and a theoretical analysis of their dispersion curves is presented.
Novel acoustic wave resonance scattering formalism
Authors: Rhee Huinam , Park Youngjin
Published: July 2002

A novel formalism for the exact isolation of resonances from Rayleigh normal modes (or partial waves) for acoustic wave scattering from submerged fluid or elastic bodies is proposed. The resonance scattering function consisting purely of resonance information is proposed. Both the magnitude and phase of isolated resonances can be correctly obtained by using the proposed formalism while previous works based on classical resonance scattering theory can give only magnitude correctly. The reason previous works could produce correct magnitude information for acoustic wave scattering (no mode conversion) is explained. Plane compressive wave scattering from a variety of submerged bodies is analyzed by utilizing the proposed resonance scattering function and the isolated resonances are compared with previously published studies. The exact π-phase shifts through the resonance and at the anti-resonance caused by the interaction between adjacent resonances, which have never been reported before, show that the proposed formalism properly extracts the resonances from each partial wave.
The effects of frequency region and bandwidth on the temporal modulation transfer function
Authors: Strickland Elizabeth A. , Viemeister Neal F.
Published: July 2002

Temporal resolution was examined as a function of frequency region and listening region. The first experiment demonstrated that amplitude- and frequency-modulated tones are not appropriate stimuli to study temporal resolution as a function of frequency region, due to the availability of other cues in addition to temporal ones. In the other experiments, thresholds for detection of sinusoidal amplitude modulation of a noise band were measured as a function of frequency region, bandwidth, and level of surrounding notched noise masker. Temporal modulation transfer functions (TMTFs) measured in low- and high-frequency regions did not differ in sensitivity or in cutoff frequency, suggesting that initial “critical band” filtering did not affect temporal resolution. When the upper cutoff frequency of the noise was held constant, TMTF sensitivity increased with noise bandwidth, while the cutoff frequency of the TMTF did not show measurable change. These results are consistent with the predictions of an envelope detector model if peripheral filtering in the lower-frequency range is assumed to be approximately twice as wide as that estimated by measuring thresholds for a tone in notched noise. Restricting the listening region with notched noise increased thresholds for low modulation frequencies but not for high. This is consistent with other data showing that upward spread of excitation may increase the effective modulation depth, but only for low modulation frequencies.
Echolocation range of captive and free-ranging baiji (Lipotes vexillifer), finless porpoise (Neophocaena phocaenoides), and bottlenose dolphin (Tursiops truncatus)
Authors: Akamatsu T. , Wang D. , Nakamura K. , Wang K.
Published: July 2002

The interclick intervals of captive dolphins are known to be longer than the two-way transit time between the dolphin and a target. In the present study, the interclick intervals of free-ranging baiji, finless porpoises, and bottlenose dolphins in the wild and in captivity were compared. The click intervals in open waters ranged up to 100–200 ms, whereas the click intervals in captivity were in the order of 4–28 ms. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging, sometimes up to 140 m. Additionally, the difference of waveform characteristics of clicks between species was recognized in the frequency of maximum energy and the click duration.
Exposure-response relationships for transportation noise
Authors: Miedema Henk M. E. , Vos Henk
Published: July 2002

This article presents synthesis curves for the relationship between DNL and percentage highly annoyed for three transportation noise sources. The results are based on all 21 datasets examined by Schultz [J. Acoust. Soc. Am. 64, 377–405 (1978)] and Fidell et al. [J. Acoust. Soc. Am. 89, 221–233 (1991)] for which acceptable DNL and percentage highly annoyed measure could be derived, augmented with 34 datasets. Separate, nonidentical curves were found for aircraft, road traffic, and railway noise. A difference between sources was found using data for all studies combined and for only those studies in which respondents evaluated two sources. The latter outcome strengthens the conclusion that the differences between sources cannot be explained by differences in study methodology.
Effects of noise and spectral resolution on vowel and consonant recognition: Acoustic and electric hearing
Authors: Fu Qian-Jie , Shannon Robert V. , Wang Xiaosong
Published: July 2002

Current multichannel cochlear implant devices provide high levels of speech performance in quiet. However, performance deteriorates rapidly with increasing levels of background noise. The goal of this study was to investigate whether the noise susceptibility of cochlear implant users is primarily due to the loss of fine spectral information. Recognition of vowels and consonants was measured as a function of signal-to-noise ratio in four normal-hearing listeners in conditions simulating cochlear implants with both CIS and SPEAK-like strategies. Six conditions were evaluated: 3-, 4-, 8-, and 16-band processors (CIS-like), a 6/20 band processor (SPEAK-like), and unprocessed speech. Recognition scores for vowels and consonants decreased as the S/N level worsened in all conditions, as expected. Phoneme recognition threshold (PRT) was defined as the S/N at which the recognition score fell to 50% of its level in quiet. The unprocessed speech had the best PRT, which worsened as the number of bands decreased. Recognition of vowels and consonants was further measured in three Nucleus-22 cochlear implant users using either their normal SPEAK speech processor or a custom processor with a four-channel CIS strategy. The best cochlear implant user showed similar performance with the CIS strategy in quiet and in noise to that of normal-hearing listeners when listening to correspondingly spectrally degraded speech. These findings suggest that the noise susceptibility of cochlear implant users is at least partly due to the loss of spectral resolution. Efforts to improve the effective number of spectral information channels should improve implant performance in noise.
Modeling of scattering by objects on the seabed
Authors: Fawcett J. A. , Fox W. L. J. , Maguer A.
Published: July 2002

This paper describes some of the theory and implementation issues of modeling the backscattered energy from cylindrical or spherical objects lying on the seabed. The model utilizes a single-scatter approximation; this approximation is compared to full multiple scattering solutions to verify its accuracy. The effects of various parameters such as grazing angle of the incident energy, receiver/scatterer geometry, and the bottom half-space geoacoustic parameters are investigated numerically. The paper is concluded with a comparison of modeled time series with experimental scattering data obtained for a steel-shelled cylinder and a solid aluminum sphere lying on a sandy seabed.
Iterative inverse scattering algorithms: Methods of computing Fréchet derivatives
Authors: Norton Stephen J.
Published: July 2002

Iterative approaches to the nonlinear inverse scattering problem generally attempt to find the scattering distribution that best predicts the data by minimizing a global error norm (e.g., the mean-square error) which quantifies the misfit between a set of measured data and data predicted on the basis of a forward calculation. A crucial quantity in this minimization is the Fréchet derivative of the error norm which tells us how to update the current estimate of the scattering distribution to reduce the global error at each iteration. This paper demonstrates how to compute the Fréchet derivative using three different, but fundamentally equivalent, methods: the conventional adjoint method, the Lagrange multiplier method, and the integral equation method. The first two begin with the wave equation, while the latter method is based on a Lippmann–Schwinger integral equation. These techniques are not only far more efficient, but also numerically less error prone, than “brute force” methods for computing derivatives based, for example, on finite differences. For simplicity, a variational approach is employed in which the fields and scattering distribution are represented by continuous functions, but the finite-dimensional (discretized) problem is shown to follow directly from the continuous-space results.
A matched-peak inversion approach for ocean acoustic travel-time tomography
Authors: Skarsoulis E. K.
Published: July 2002

A new approach for the inversion of travel-time data is proposed, based on the matching between model arrivals and observed peaks. Using the linearized model relations between sound-speed and arrival-time perturbations about a set of background states, arrival times and associated errors are calculated on a fine grid of model states discretizing the sound-speed parameter space. Each model state can explain (identify) a number of observed peaks in a particular reception lying within the uncertainty intervals of the corresponding predicted arrival times. The model states that explain the maximum number of observed peaks are considered as the more likely parametric descriptions of the reception; these model states can be described in terms of mean values and variances providing a statistical answer (matched-peak solution) to the inversion problem. A basic feature of the matched-peak inversion approach is that each reception can be treated independently, i.e., no constraints are posed from previous-reception identification or inversion results. Accordingly, there is no need for initialization of the inversion procedure and, furthermore, discontinuous travel-time data can be treated. The matched-peak inversion method is demonstrated by application to 9-month-long travel-time data from the Thetis-2 tomography experiment in the western Mediterranean sea.
Backscattering enhancements associated with subsonic Rayleigh waves on polymer spheres in water: Observation and modeling for acrylic spheres
Authors: Hefner Brian T. , Marston Philip L.
Published: July 2002

Unlike most common solids, “plastic” polymer solids typically have shear and Rayleigh wave phase velocities less than the speed of sound in water. Subsonic Rayleigh waves on smooth objects in water are not classified as leakey waves and it is necessary to reexamine backscattering mechanisms. Also the intrinsic material dissipation of the Rayleigh wave can be significant. Backscattering by acrylic or polymethlmethacrylate (PMMA) spheres in water is analyzed and measured in the region ka=1.5–7 and it is found that prominent low-lying resonance peaks of the form function |f| exist. The peaks can be modeled with quantitative ray theory as the result of coupling of subsonic Rayleigh waves with sound through acoustic tunneling. The most prominent maximum of |f|=5.63 occurs at ka=1.73 and is associated with the quadrupole (or n=2) partial wave. In addition to explaining the scattering, the target strength is found to be sufficiently large that such spheres may be useful for passive low frequency targets.
Pseudostatic corrections for the forced vibroacoustic response of a structure-cavity system
Authors: Tournour Michel , Atalla Noureddine
Published: July 2002

The analysis of the coupled vibroacoustic behavior of a structure–cavity system is often performed using the in vacuo structure modes and the rigid cavity modes. Unfortunately, the use of such a modal basis can result in a poor convergence when the high-frequency modes of one of the two subsystems are coupled to the low-frequency modes of the other subsystem. This problem is made critical by the lack of a reliable criterion for selecting the number of kept modes for each subsystem. This paper shows that the effect of modal truncation is critical for the convergence of the method and that the convergence can be greatly improved using pseudostatic corrections for both the structure and the cavity. The theory behind the proposed technique is presented together with two generic problems exhibiting strong coupling: (i) an elastic cylindrical cavity filled with air; and (ii) an elastic plate coupled to a rectangular cavity filled with water.
Multiple neural networks-integrated underwater target classification based on fuzzy theory
Authors: Su Tong
Published: July 2002

In the area of underwater target recognition, in order to process various target feature data extracted from underwater radiating noise signals, a target classification method based on the integration of multiple fuzzy clustering neural networks and fuzzy comprehensive analysis is put forward in this paper. An adaptive fuzzy clustering neural network classifier is constructed and a relative studying algorithm is described for the first class classification, which is applied separately to different kinds of feature data from LOFAR spectrum, bispectrum, and wavelet transformation. Based on fuzzy comprehensive analysis of the outputs and probabilities of the above neural network classifiers and the category and distribution of test samples, the second class fuzzy classifying rules are designed to preprocess and assess the categories of ships. More than 4000 passive sonar signal samples are collected and many tests are done, and the results show the feasibility, adaptability, and effectiveness of the present method.
Rheological behavior of a hydrophobically associating water soluble polymer
Authors: Aubry T. , Moan M.
Published: July 2002

We have investigated experimentally the behavior of a water soluble associating polymer system, hydrophobically modified (hydroxypropyl)guar, with very few randomly distributed hydrophobic substituents along the chains. We focus mainly on the rheological effects due to the superposition of the reversible hydrophobic interaction network on the physical entanglement network in dense macromolecular systems of that kind. Both linear and nonlinear response to transient, steady, and oscillatory shear flow prove that, in the semidilute and moderately concentrated regime, the hydrophobically associating polymer behaves like a classical dense macromolecular system whose long-time dynamics can be described using only one long relaxation time, identified as a retarded disengagement time, much larger than the association lifetime. The temporary hydrophobically associating network can be destroyed when applying a critical shear stress τc, which is studied as a function of polymer concentration.
Steady shear and dynamic rheological properties of xanthan gum solutions in viscous solvents
Authors: Zirnsak M. A. , Boger D. V. , Tirtaatmadja V.
Published: July 2002

An extensive examination of the first normal stress difference and linear viscoelastic properties of xanthan gum solutions has been conducted in relation to molecular theories in the literature. The first normal stress difference, storage modulus, and loss modulus are reported for 0.01–0.04% w/w solutions of xanthan gum in high viscosity (wheat syrup and water) solvents. The average length of the xanthan molecules used was determined by light scattering to be (1.25±0.05)×103 nm. The storage and loss moduli obtained show a frequency dependence consistent with theories that included a relaxation time spectrum, while the first normal stress difference exhibits dependence on shear rate consistent with theories of suspensions of rigid particles. Both the first normal stress difference and the solute contribution to the storage modulus were found to vary linearly with concentration and with the solvent viscosity to the power of 2/3. Extensional viscosity measurements of a xanthan gum solution are in good agreement with the predictions for semi-dilute suspensions of rigid rods.
Prediction of the wax content of the incipient wax-oil gel in a pipeline: An application of the controlled-stress rheometer
Authors: Singh Probjot , Fogler H. Scott , Nagarajan Nagi
Published: July 2002

High molecular weight paraffins are known to form gels of complex morphology at low temperatures due to the low solubility of these compounds in aromatic or naphthene-base oil solvents. The characteristics of these gels are strong functions of the shear and thermal histories of these samples. A model system of wax and oil was used to understand the gelation process of these mixtures. A significant depression in the gel point of a wax-oil sample was observed by either decreasing the cooling rate or increasing the steady shear stress. The wax-oil sample separates into two layers of different characteristics, a gel-like layer and a liquid-like layer, when sheared with a controlled-stress rheometer at high steady shear stresses and low cooling rates. The phase diagram of the model wax-oil system, obtained using a controlled-stress rheometer, was verified by analyzing the wax content of the incipient gel deposits formed on the wall of a flow loop. Based on the rheological measurements, a law has been suggested for the prediction of the wax content of the gel deposit on the laboratory flow loop walls. The wax content of the incipient gel formed on the wall of a field subsea pipeline was predicted to be much higher than that for the flow loop at similar operating conditions. This variation in the gel deposit characteristics is due to the significant differences in the cooling histories in the two cases.