Differences in loudness of positive and negative Schroeder-phase tone complexes as a function of the fundamental frequency

Tone complexes with positive (m+) and negative (m-) Schroeder phase show large differences in masking efficiency. This study investigated whether the different phase characteristics also affect loudness. Loudness matches between m+ and m- complexes were measured as a function of (1) the fundamental frequency (f0) for different frequency bands in normal-hearing and hearing-impaired subjects, and (2) intensity level in normal-hearing subjects. In normal-hearing subjects, the level of the m+ stimulus was up to 10 dB higher than that of the corresponding m- stimulus at the point of equal loudness. The largest differences in loudness were found for levels between 20 and 60 dB SL. In hearing-impaired listeners, the difference was reduced, indicating the relevance of active cochlear mechanisms. Loudness matches of m+ and m- stimuli to a common noise reference (experiment 3) showed differences as a function of f0 that were in line with direct comparisons from experiment 1 and indicated additionally that the effect is mainly due to the specific internal processing of m+. The findings are roughly consistent with studies pertaining to masking efficiency and can probably not be explained by current loudness models, supporting the need for incorporating more realistic cochlea simulations in future loudness models.     

Modeling of the adsorption and desorption of CO2 on Cu/ZrO2 and ZrO2 catalysts

The interaction between carbon dioxide and two zirconia catalysts-a Cu/ZrO2 catalyst containing 34% copper and a pure ZrO2 catalyst-was studied by pulse adsorption and temperature-programmed desorption methods. Kinetic modeling by nonlinear regression was applied to acquire information on the adsorption and desorption of CO2 relevant in the synthesis of methanol from carbon dioxide. A model that included three types of adsorption sites described well the experimental data for both Cu/ZrO2 and ZrO2. The model assumed first-order kinetics and a Freundlich-type logarithmic dependence of adsorption enthalpy on surface coverage. The parameters of the model were well identified and were in the physically meaningful range. The results indicate that, at 30 degrees C, on both catalysts, carbon dioxide adsorbs reversibly on one type of site and irreversibly on two other types of sites.     

Xanthane sesquiterpenoids: structure, synthesis and biological activity

The aim of this review is to survey the naturally occurring xanthanes and xanthanolides, their structures, biological activities, structure–activity relationships and synthesis. There has been no comprehensive review of this topic previously. On the basis of 126 references, 112 compounds are summarized.     

Study on the applicability of instrumental measures for black-box evaluation of static feedback control in hearing aids

Presented is a report on black-box evaluation of feedback control systems for commercial hearing aids. The aim of the study is to examine the ability of existing instrumental measures to quantify the performance of the feedback control system in black-box settings and on realistic signals, when more than one element of the signal processing chain may be active (compression, noise suppression, microphone directionality, etc.). The evaluation is carried out on 6 different hearing aids and for 10 measures. Thereby it is possible to see which measure is best suited to measuring which specific characteristic of the feedback control system, and serves as a beginning for conducting perceptual tests. The study uses static (but variable) feedback paths and is based on signals recorded from the in-ear microphone of an artificial head, on which the hearing instruments are mounted.     

Effect of Physical Properties and Emulsification Conditions on the Microsphere Size Prepared Using a Solvent Extraction Process

Microspheres were prepared using a hydrocarbon-perfluorocarbon solvent extraction process. The effect of the physical properties and the emulsification conditions on the mean microsphere size was investigated. The viscosity of the dispersed and the continuous phase greatly affected the microsphere size. Smaller microspheres were produced at the same mixing intensity when the viscosity of the dispersed phase decreased. Increased continuous phase viscosity reduced the coalescenceof the droplets and hence smaller microspheres were produced. The mean microsphere size first decreased as the volume ratio of the dispersed phase to the continuous phase increased but upon further increase the mean microsphere size increased. The effect of the volume ratio on the microsphere size was linked to the surfactant concentration. The stability of the studied hydrocarbon-in-fluorocarbon emulsion is poor. One reason for the poor stability is the high density difference between the phases. The emulsion droplets were solidified by siphoning part of the emulsion in the fresh continuous phase, which extracted the solvent from the dispersed phase. The effect of emulsion transfer time between the emulsification and solidification steps on the particle size was studied but no significant effect was observedduring the controlled time interval.     

Quantification of femtomolar concentrations of the CYP3A substrate midazolam and its main metabolite 1'-hydroxymidazolam in human plasma using ultra performance liquid chromatography coupled to tandem mass spectrometry

The benzodiazepine midazolam is a probe drug used to phenotype cytochrome P450 3A activity. In this situation, effective sedative concentrations are neither needed nor desired, and in fact the use of very low doses is advantageous. We therefore developed and validated an assay for the femtomolar quantification of midazolam and 1′-hydroxymidazolam in human plasma. Plasma (0.25 mL) and 96-well-based solid-phase extraction were used for sample preparation. Extraction recoveries ranged between 75 and 92% for both analytes. Extracts were chromatographed within 2 min on a Waters BEH C18 1.7 μm UPLC? column with a fast gradient consisting of formic acid, ammonia, and acetonitrile. Midazolam and 1′-hydroxymidazolam were quantified using deuterium- and ¹³C-labeled internal standards and positive electrospray tandem mass spectrometry in the multiple reaction monitoring mode, which yielded lower limits of quantification of 50 fg/mL (154 fmol/L) and 250 fg/mL (733 fmol/L) and a corresponding precision of <20%. The calibrated concentration ranges were linear for midazolam (0.05–250 pg/mL) and 1′-hydroxymidazolam (0.25–125 pg/mL), with correlation coefficients of >0.99. Within-batch and batch-to-batch precision in the calibrated ranges for both analytes were <14% and <12%. No ion suppression was detectable, and plasma matrix effects were minimized to <15% (<25%) for midazolam (1′-hydroxymidazolam). The assay was successfully applied to assess the kinetics of midazolam in two human volunteers after the administration of single oral microgram doses (1–100 μg). This ultrasensitive assay allowed us to quantify the kinetics of midazolam and 1′-hydroxymidazolam for at least 10 h, even after the administration of only 1 μg of midazolam.