Improved functionality and control in the isomerization of a calix[4]arene-capped azobenzene

An improved azobenzene core capped by two calix[4]arene units isomerizes readily between trans and cis configurations via photochemical and/or thermal means. In addition, the presence of acid (particularly HCl) increases the rate of thermal cis→trans conversion. These enhancements to the functional response, control, and understanding of calixarene-capped azobenzene isomerization are important for future application in the dynamic encapsulation of small chemical species.     

The perception of two vocal qualities in a synthesized vocal utterance: ring and pressed voice

Two vocal qualities, ringquality and pressed quality, were analyzed perceptually. Listeners were asked to rate (on a scale from 0 to 10) the “amount of ring” in one listening and the “amount of pressedness” in another listening. The stimulus was the synthesized utterance /ya-ya-ya-ya-ya/. In the continuum representation of ring, the skewing quotient and the cross section of the epilaryngeal tube area were systematically varied, independently and by a covariation rule. In the continuum representation of pressed, the flow amplitude and open quotient were similarly varied. Results indicated that the crossover point between ring and no ring occurred with an epilaryngeal area of around 1.0 cm², and the crossover point between pressed and not pressed quality occurred at an open quotient of about 0.4. Fundamental frequency also had an effect on the perceptions, with a higher fundamental frequency receiving higher ratings of ring and pressed for otherwise the same parameters. Listeners demonstrated highly variable perceptions in both continua with poor intersubject, intrasubject, and intergroup reliability.     

Patterning porous matrices and planar substrates with quantum dots

Silica hydrogels and planar substrates were patterned with CdS nanoparticles using a photolithographic method based on the photo dissociation of thiols and cadmium-thiolate complexes. Silica hydrogels were prepared via a standard base-catalyzed route. The solvent was exchanged with an aqueous solution of CdSO₄ and 2-mercaptoethanol, and the samples were then exposed to a focused ultraviolet beam. Planar substrates were patterned by illuminating a precursor solution spin coated on the substrates. CdS nanoparticles formed in the illuminated spots, and had a diameter below about 2 nm. The diameter of the spots illuminated by the UV beam could be varied from a few hundred to a few μm, on both hydrogels and planar substrates. Samples were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and optical absorption, photoluminescence and Raman spectroscopies. All these techniques confirmed the chemical identity of the CdS nanoparticles. To investigate the mechanism of nanoparticle formation, we took absorption spectra of the precursor solution as a function of irradiation time. In unirradiated solutions, we noticed a maximum at 250 nm, characteristic of Cd-thiolate complexes. The absorption at 250 nm decreased with increasing irradiation time. A new band appeared at 265 nm for exposures around 5 min, and that band shifted to 290 nm in samples exposed for 10 min. A yellow precipitate formed after about 30 min. XRD showed that the precipitate was cubic CdS, with a mean particle size of 1.4 nm. We attribute formation of CdS to the photodissociation of the thiols and of the Cd-thiolates. UV irradiation of these precursors yields a series of species that can react with Cd²⁺, such as RS^·, S²⁻ and H₂S. Small CdS nanoparticles form in the initial stages of illumination, and present absorption bands in the 265–290 nm region. These CdS aggregates grow, coalesce and precipitate for longer irradiation times.     

Comparative PIV and LDA studies of Newtonian and non-Newtonian flows in an agitated tank

The paper presents results of an experimental study of the fluid velocity field in a stirred tank equipped with a Prochem Maxflo T (PMT) type impeller which was rotating at a constant frequency of N = 4.1 or 8.2 s^?1 inducing transitional (Re = 499 or 1307) or turbulent (Re = 2.43 × 10⁴) flow of the fluid. The experiments were performed for a Newtonian fluid (water) and a non-Newtonian fluid (0.2 wt% aqueous solution of carboxymethyl cellulose, CMC) exhibiting mild viscoelastic properties. Measurements were carried out using laser light scattering on tracer particles which follow the flow (2-D PIV). For both the water and the CMC solution one primary and two secondary circulation loops were observed within the fluid volume; however, the secondary loops were characterized by much lower intensity. The applied PMT-type impeller produced in the Newtonian fluid an axial primary flow, whilst in the non-Newtonian fluid the flow was more radial. The results obtained in the form of the local mean velocity components were in satisfactory agreement with the literature data from LDA. Distribution of the shear rate in the studied system was also analyzed. For the non-Newtonian fluid an area was computed where the elastic force dominates over the viscous one. The area was nearly matching the region occupied by the primary circulation loop.     

Comparison of magnetic resonance imaging-based vocal tract area functions obtained from the same speaker in 1994 and 2002

A new set of area functions for vowels has been obtained with magnetic resonance imaging from the same speaker as that previously reported in 1996 [Story et al., J. Acoust. Soc. Am. 100, 537-554 (1996)]. The new area functions were derived from image data collected in 2002, whereas the previously reported area functions were based on magnetic resonance images obtained in 1994. When compared, the new area function sets indicated a tendency toward a constricted pharyngeal region and expanded oral cavity relative to the previous set. Based on calculated formant frequencies and sensitivity functions, these morphological differences were shown to have the primary acoustic effect of systematically shifting the second formant (F2) downward in frequency. Multiple instances of target vocal tract shapes from a specific speaker provide additional sampling of the possible area functions that may be produced during speech production. This may be of benefit for understanding intraspeaker variability in vowel production and for further development of speech synthesizers and speech models that utilize area function information.     

A comparison of vocal tract perturbation patterns based on statistical and acoustic considerations

The purpose of this study was to investigate the relation between vocal tract deformation patterns obtained from statistical analyses of a set of area functions representative of a vowel repertoire, and the acoustic properties of a neutral vocal tract shape. Acoustic sensitivity functions were calculated for a mean area function based on seven different speakers. Specific linear combinations of the sensitivity functions corresponding to the first two formant frequencies were shown to possess essentially the same amplitude variation along the vocal tract length as the statistically derived deformation patterns reported in previous studies.     

A proton NMR study of water in hydrated sodium β-alumina

Proton nmr study of hydrated sodium β-alumina reveals a Pake doublet spectrum due to stationary water molecules. As the temperature is increased from -196C to 192C, linewidth changes indicate that the stationary protons sense the increasingly rapid motion of nearby sodium nuclei and other protons. The interproton spacing computed from the spectra was found to be 1.7A.     

Selectivity behavior of low-capacity, partially sulfonated, macroporous resin beads

Cation-exchange resins with capacities ranging from 0.23 to 3.70 mequiv./g were prepared by sulfonation of highly cross-linked macroporous polystyrene resins. Distribution coefficients for exchange of hydrogen-form resin for polyvalent metal cations in 1 M acid show marked increases with increasing resin capacity.