Self-assembly of an Octa-uranate Cage Complex with a Rigid bis-Catechol Ligand

While the terminally protected tripeptide Boc-Phe-Gly-m-ABA-OMe I (m-ABA, meta-amino benzoic acid) is an excellent gelator of aromatic organic solvents, another similar tripeptide Boc-Leu-Gly-m-ABA-OMe II, where the Phe residue of peptide I is replaced by Leu, cannot form gels with the same solvents. The morphology of the gels of peptide I, characterised by the field-emission scanning electron microscopy and high-resolution transmission electron microscopy, reveals the formation of nanofibrous networks which are known to encapsulate solvent molecules to form gels. The wide-angle X-ray scattering studies of the gels suggest the β-sheet-mediated self-assembly of peptide I in the formation of a nanofibrous network, where π-stacking interactions of Phe play an important role in the self-assembly and gel formation. The dried gel of peptide I observed between crossed polarisers after binding with a physiological dye, Congo red, shows a bluish-green birefringence, a characteristic of amyloid fibrils.     

A cocktail party model of spatial release from masking by both noise and speech interferers

A mathematical formula for estimating spatial release from masking (SRM) in a cocktail party environment would be useful as a simpler alternative to computationally intensive algorithms and may enhance understanding of underlying mechanisms. The experiment presented herein was designed to provide a strong test of a model that divides SRM into contributions of asymmetry and angular separation [Bronkhorst (2000). Acustica 86, 117-128] and to examine whether that model can be extended to include speech maskers. Across masker types the contribution to SRM of angular separation of maskers from the target was found to grow at a diminishing rate as angular separation increased within the frontal hemifield, contrary to predictions of the model. Speech maskers differed from noise maskers in the overall magnitude of SRM and in the contribution of angular separation (both greater for speech). These results were used to develop a modified model that achieved good fits to data for noise maskers (ρ=0.93) and for speech maskers (ρ=0.94) while using the same functions to describe separation and asymmetry components of SRM for both masker types. These findings suggest that this approach can be used to accurately model SRM for speech maskers in addition to primarily "energetic" noise maskers.     

The benefit of binaural hearing in a cocktail party: effect of location and type of interferer

The "cocktail party problem" was studied using virtual stimuli whose spatial locations were generated using anechoic head-related impulse responses from the AUDIS database [Blauert et al., J. Acoust. Soc. Am. 103, 3082 (1998)]. Speech reception thresholds (SRTs) were measured for Harvard IEEE sentences presented from the front in the presence of one, two, or three interfering sources. Four types of interferer were used: (1) other sentences spoken by the same talker, (2) time-reversed sentences of the same talker, (3) speech-spectrum shaped noise, and (4) speech-spectrum shaped noise, modulated by the temporal envelope of the sentences. Each interferer was matched to the spectrum of the target talker. Interferers were placed in several spatial configurations, either coincident with or separated from the target. Binaural advantage was derived by subtracting SRTs from listening with the "better monaural ear" from those for binaural listening. For a single interferer, there was a binaural advantage of 2-4 dB for all interferer types. For two or three interferers, the advantage was 2-4 dB for noise and speech-modulated noise, and 6-7 dB for speech and time-reversed speech. These data suggest that the benefit of binaural hearing for speech intelligibility is especially pronounced when there are multiple voiced interferers at different locations from the target, regardless of spatial configuration; measurements with fewer or with other types of interferers can underestimate this benefit.     

Near-infrared fluorescence microscopy of single-walled carbon nanotubes in phagocytic cells

The uptake of pristine single-walled carbon nanotubes into macrophage-like cells has been studied using the nanotubes' intrinsic near-infrared fluorescence. Macrophage samples that have been incubated in growth media containing suspended single-walled nanotubes show characteristic nanotube fluorescence spectra. The fluorescence intensities increase smoothly with incubation time and external nanotube concentration. Near-infrared fluorescence microscopy at wavelengths above 1100 nm provides high contrast images indicating localization of nanotubes in numerous intracellular vesicles. Nanotube uptake appears to occur through phagocytosis. Population growth of macrophage cultures is unaffected by exposure to single-walled nanotube concentrations of ca. 4 mug/mL for up to 96 h.     

Production of contrast between sibilant fricatives by children with cochlear implants

Speech production by children with cochlear implants (CIs) is generally less intelligible and less accurate on a phonemic level than that of normally hearing children. Research has reported that children with CIs produce less acoustic contrast between phonemes than normally hearing children, but these studies have included correct and incorrect productions. The present study compared the extent of contrast between correct productions of /s/ and /∫/ by children with CIs and two comparison groups: (1) normally hearing children of the same chronological age as the children with CIs and (2) normally hearing children with the same duration of auditory experience. Spectral peaks and means were calculated from the frication noise of productions of /s/ and /∫/. Results showed that the children with CIs produced less contrast between /s/ and /∫/ than normally hearing children of the same chronological age and normally hearing children with the same duration of auditory experience due to production of /s/ with spectral peaks and means at lower frequencies. The results indicate that there may be differences between the speech sounds produced by children with CIs and their normally hearing peers even for sounds that adults judge as correct.     

Intravascular photoacoustic imaging of lipid in atherosclerotic plaques in the presence of luminal blood

Intravascular photoacoustic (IVPA) imaging can characterize atherosclerotic plaque composition on the basis of the optical absorption contrast between different tissue types. Given the high optical absorption of lipid at 1720 nm wavelength, an atherosclerotic rabbit aorta was imaged at this wavelength ex vivo using an integrated intravascular ultrasound (IVUS) and IVPA imaging catheter in the presence of luminal blood. Strong optical absorption of lipid combined with low background signal from other tissues provides a high-contrast, depth-resolved IVPA image of lipid. The ability to image lipid at a single wavelength without removing luminal blood suggests that in vivo detection of lipid in atherosclerotic plaques using combined IVUS/IVPA imaging is possible.     

Localization dominance in the median-sagittal plane: effect of stimulus duration

Localization dominance is an aspect of the precedence effect (PE) in which the leading source dominates the perceived location of a simulated echo (lagging source). It is known to be robust in the horizontal/azimuthal dimension, where binaural cues dominate localization. However, little is known about localization dominance in conditions that minimize binaural cues, and most models of precedence treat the phenomena as "belonging" to the binaural system. Here, localization dominance in the median-sagittal plane was studied where binaural cues are greatly reduced, and monaural spectral/level cues are thought to be the primary cues used for localization. Lead-lag pairs of noise bursts were presented from locations spaced in 15 degrees increments in the frontal, median-sagittal plane, with a 2-ms delay in their onsets, for source durations of 1, 10, 25, and 50-ms. Intermixed with these trials were single-speaker trials, in which lead and lag were summed and presented from one speaker. Listeners identified the speaker that was nearest to the perceived source location. With single-speaker stimuli, localization improves as signal duration is increased. Furthermore, evidence of elevation compression was found with a dependence on duration. With lead-lag pairs, localization dominance occurs in the median plane, and becomes more robust with increased signal duration. These results suggest that accurate localization of a co-located lead-lag pair is necessary for localization dominance to occur when the lag is spatially separated from the lead.     

Speech intelligibility and localization in a multi-source environment.

Natural environments typically contain sound sources other than the source of interest that may interfere with the ability of listeners to extract information about the primary source. Studies of speech intelligibility and localization by normal-hearing listeners in the presence of competing speech are reported on in this work. One, two or three competing sentences [IEEE Trans. Audio Electroacoust. 17(3), 225-246 (1969)] were presented from various locations in the horizontal plane in several spatial configurations relative to a target sentence. Target and competing sentences were spoken by the same male talker and at the same level. All experiments were conducted both in an actual sound field and in a virtual sound field. In the virtual sound field, both binaural and monaural conditions were tested. In the speech intelligibility experiment, there were significant improvements in performance when the target and competing sentences were spatially separated. Performance was similar in the actual sound-field and virtual sound-field binaural listening conditions for speech intelligibility. Although most of these improvements are evident monaurally when using the better ear, binaural listening was necessary for large improvements in some situations. In the localization experiment, target source identification was measured in a seven-alternative absolute identification paradigm with the same competing sentence configurations as for the speech study. Performance in the localization experiment was significantly better in the actual sound-field than in the virtual sound-field binaural listening conditions. Under binaural conditions, localization performance was very good, even in the presence of three competing sentences. Under monaural conditions, performance was much worse. For the localization experiment, there was no significant effect of the number or configuration of the competing sentences tested. For these experiments, the performance in the speech intelligibility experiment was not limited by localization ability.