Modeling the influence of inherent envelope fluctuations in simultaneous masking experiments

Masked thresholds are measured and simulated for bandpass-noise signals ranging in bandwidth from 4 to 256 Hz in the presence of a masking bandpass noise also ranging in bandwidth from 4 to 256 Hz. Signal and masker are centered at 2 kHz. To investigate the role of temporal processing in simultaneous masking, simulations were performed with the modulation-filterbank model by Dau et al. [J. Acoust. Soc Am. 102, 2906-2919 (1997)]. For a fixed masker bandwidth, thresholds are independent of the signal bandwidth as long as the signal bandwidth does not exceed the masker bandwidth and thresholds decrease with increasing masker bandwidth in those conditions. A simple modulation-low-pass filter (energy integrator) would be sufficient to describe the experimental results in those conditions. In contrast, the processing by a modulation filterbank is necessary to account for the conditions of "asymmetry of masking," where thresholds for signals with bandwidths larger than the masker bandwidth are much lower than those for the reversed condition. In those conditions, the modulation-filterbank model is able to use the inherent higher modulation frequencies of the signal as an additional cue.     

Quasi-triple collisions in low energy ion scattering; A possibility to determine surface debye temperatures

Calculations and measurements of energy spectra of 10 keV Kr⁺ ions, scattered from Cu(100) face at different temperatures, are reported. One of the observed phenomena is the existence of a new peak. From the temperature behaviour of this peak we obtain the surface Debye temperature.     

Modeling cochlear dynamics: interrelation between cochlea mechanics and psychoacoustics

A model of the cochlea was used to bridge the gap between model approaches commonly used to investigate phenomena related to otoacoustic emissions and more filter-based model approaches often used in psychoacoustics. In the present study, a nonlinear and active one-dimensional transmission line model was developed that accounts for several aspects of physiological data with a single fixed parameter set. The model shows plausible excitation patterns and an input-output function similar to the linear-compressive-linear function as hypothesized in psychoacoustics. The model shows realistic results in a two-tone suppression paradigm and a plausible growth function of the 2f(1)-f(2) component of distortion product otoacoustic emissions. Finestructure was found in simulated stimulus-frequency otoacoustic emissions (SFOAE) with realistic levels and rapid phase rotation. A plausible "threshold in quiet" including finestructure and spontaneous otoacoustic emissions (SOAE) could be simulated. It is further shown that psychoacoustical data of modulation detection near threshold can be explained by the mechanical dynamics of the modeled healthy cochlea. It is discussed that such a model can be used to investigate the representation of acoustic signals in healthy and impaired cochleae at this early stage of the auditory pathway for both, physiological as well as psychoacoustical paradigms.     

A self consistent normalized calibration protocol for three dimensional magnetic resonance gel dosimetry

In a clinical setting, mixed and inconsistent results have been reported using Magnetic Resonance Relaxation imaging of irradiated aqueous polymeric gels as a three-dimensional dosimeter, for dose verification of conformal radiation therapy. The problems are attributed to the difficulty of identifying an accurate dose calibration protocol for each delivered gel at the radiation site in a clinical setting. While careful calibration is done at the gel manufacturing site in a controlled laboratory setting, there is no guarantee that the dose sensitivity of the gels remains invariant upon delivery, irradiation, magnetic resonance imaging and storage at the clinical site. In this study, we have compared three different dose calibration protocols on aqueous polymeric gels for a variety of irradiation scenarios done in a clinical setting. After acquiring the three-dimensional proton relaxation maps of the irradiated gels, the dose distributions were generated using the off-site manufacturer provided calibration curve (Cal-1), the on-site external tube gel calibration (Cal-2) and the new on-site internal normalized gel calibration (Cal-3) protocols. These experimental dose distributions were compared with the theoretical dose distributions generated by treatment-planning systems. We observed that the experimental dose distributions generated from the Cal-1 and Cal-2 protocols were off by 10% to 40% and up to 200% above the predicted maximum dose, respectively. On the other hand, the experimental dose distributions generated from the Cal-3 protocol matched reasonably well with the theoretical dose distributions to within 10% difference. Our result suggests that an independent on-site normalized internal calibration must be performed for each batch of gel dosimeters at the time of MR relaxation imaging in order to account for the variations in dose sensitivity caused by various uncontrollable conditions in a clinical setting such as oxygen contamination, temperature changes and shelf life of the delivered gel between manufacturing and MR acquisitions.     

Detection of nanoscale events in dispersed polymer particles containing a charge-transfer fluorescence probe

A probe molecule, which shows an unusually large change in fluorescent properties in response to changes in its environment, was introduced into a monodisperse polystyrene latex. Upon addition of low-molecular-weight compounds, the ensuing swelling process of the latex could be followed via the changes in the fluorescence spectrum of the probe molecule. Polymerization reactions of monomers, introduced into the particles, could also be monitored by means of this approach. Using glycidylmethacrylate as the monomer led to the formation of particles in which two distinctly different surroundings could be detected after such a polymerization. © 1995 John Wiley & Sons, Inc.     

New99mTc-diiodine substituted IDA derivative (DIIODIDA) for hepatobiliary imaging

A new diiodine substituted IDA derivative, 2,4-diiodine-6-methyl IDA (DIIODIDA) was synthesized and labeled with^99mTc. It was established that^99mTc-DIIODIDA had high radiochemical purity. Biodistribution and influence of bilirubin on^99mTc-DIIODIDA biokinetics has been studied in rats and compared to the corresponding results for^99mTc-SOLCOIODIDA. Related to^99mTc-SOLCOIODIDA,^99mTc-DIIODIDA has much better biliary exretion (55.18 versus 43.63%). No change of^99mTc-DIIODIDA biokinetics, under influence of bilirubin was noticed. Biliary excretion of^99mTc-SOLCOIODIDA has been reduced for about 60%. The protein binding of^99mTc-DIIODIDA and^99mTc-SOLCOIODIDA were also determined, using in vitro method of precipitation. These results showed that^99mTc-DIIODIDA hepatobiliary imaging agent is superior to the presently used^99mTc-monoiodine IDA derivatives.     

Study of low energy noble gas ion reflection from monocrystalline surfaces; Influence of thermal vibrations of the surface atoms: II. Calculational evaluation of the sensitivity for model parameters and possibilities for estimation

The sensitivity of the characteristics of low energy noble gas ion reflection from monocrystalline surfaces for thermal properties of the target atoms has been investigated by computer simulation. In addition the uncertainties in comparing experimental results with calculations, introduced by a not well-known interaction potential, have been examined. The calculations have been carried out for 6 keV Ar⁺ ions reflected from a vibrating Cu〈100〉 chain. To achieve the above presented object we varied the mean square value $\text{u}{}^2$ and the correlation coefficients of the atomic thermal displacements. The used ion-atom interaction potential (a Thomas-Fermi potential in the Molière approximation) has been varied by changing the screening length aF. Under certain conditions the shape of the energy spectra of specularly reflected particles depends pronouncedly on both $\text{u}{}^2$ and aF. The effects are the most pronounced for scattering angles between about 20° and 30°. The angular distribution shows also a distinct and simultaneous sensitivity for the used potential and the target-temperature. A most interesting feature is the occurrence of a QT peak at higher temperatures, resulting from quasi triple collisions from surface “thermal pit” structures. At a given scattering angle the cut-off temperature of this QT peak can be related to the mean square displacements of the involved atoms. This cut-off temperature appears to be (almost) independent from the used potential, allowing an estimation of $\text{u}{}^2$. The intensity of the QS peak and the QD peak depend exclusively on the mean square differences of thermal displacements of neighbouring atoms. Correlated atomic displacements have some influence on the angular distributions and on the QT peak intensity. Possibilities to estimate model quantities are discussed briefly.