Synthesis and characterization of phosphorescent cyclometalated iridium complexes.

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3.nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CwedgeN2Ir(mu-Cl)2IrCwedgeN2 (CwedgeNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CwedgeN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to lambda(max) values from 510 to 606 nm for the complexes reported here. The strong spin-orbit coupling of iridium mixes the formally forbidden 3MLCT and 3pi-pi* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1-0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CwedgeN2Ir(LX) complexes are surprisingly similar to the fac-IrCwedgeN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CwedgeN2Ir(acac) complexes (i.e., CwedgeN = ppy and tpy) have been determined. Both complexes show cis-C,C', trans-N,N' disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a "CwedgeN2Ir" fragment. NMR data (1H and 13C) support a similar structure for all of the CwedgeN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.

The interaction of bilingualism and stuttering in an adult.

The relation between bilingualism and stuttering was examined in a bilingual adult who stutters. Language ability in English and Afrikaans was assessed through the use of cloze and language proficiency tests. Anticipation, adaptation and consistency of stuttering were investigated. Frequency, distribution and nature of disfluencies on narrative and procedural tasks were analyzed according to a modified version of the Systematic Disfluency Analysis (SDA) (Campbell & Hill, 1987). Results indicated that language ability influenced frequency, distribution and nature of disfluencies. The subject was more proficient and stuttered less in his predominant language. Implications for the interaction of language and stuttering were discussed. Clinical strategies for dealing with bilingual stutterers were considered.

Training to meet the needs of the communicatively impaired population of South Africa: a project of the University of the Witwatersrand.

At a time when South Africa is in the throes of transition, ideologies in the educational, medical, economic and social spheres are being redefined and redirected. The field of speech pathology and audiology is no exception. The Department of Speech Pathology and Audiology, University of the Witwatersrand has acknowledged an urgent need to address the requirements of a multilingual and multicultural South Africa and extend training beyond the white middle-class population. It is the responsibility of the training institutions to redirect the objectives of their curricula in order to meet these needs. This paper describes the changes introduced by the Department. These include teaching of community work principles and primary health care to the speech and hearing therapist, and the training of personnel for an alternative form of service, such as the community speech and hearing worker (CSHW) and the community-based rehabilitation worker (CBRW).

Quasi-phase-matched optical parametric amplification and oscillation in periodically poled LiNbO(3) waveguides.

We report quasi-phase-matched optical parametric amplification and oscillation in a periodically poled LiNbO(3) waveguide. Single-pass parametric gains of 4.1 dB, corresponding to 18%/W efficiency, were achieved at a signal wavelength of 1.55 microm with a pump wavelength of 782.2 nm. We formed a low-finesse cavity resonant at both signal and idler wavelengths by attaching mirrors to the waveguide end faces. Parametric oscillation was observed at wavelengths between 1.4 and 1.7 microm with a peak output power of 700 mW for pump wavelengths between 779 and 782 nm.

Caregiver-child interaction in a rural village in South Africa.

The aim of this study was to describe the caregiver-child interaction in a South African rural village. A social interactional approach was adopted and a triangulation of methods was used. The interaction of nine caregiver-child dyads was observed during a semi-structured play situation, and the caregivers were interviewed concerning their beliefs about, and attitudes towards their child's communication. Interactions were rated according to an interactional profile and common themes found during the interviews, were identified. Interview results showed that although the majority of caregivers assigned importance to interacting and playing with children, their reported actions were not congruent with this. Caregivers played a dominant role during the social play interactions. Support was found for the utilisation of the social interactional approach and a triangulation of methods. Results obtained have important implications for the South African speech-language pathologist.

Iodine spectroscopy and absolute frequency stabilization with the second harmonic of the 1319-nm Nd:YAG laser.

We have frequency doubled a 1319-nm Nd:YAG laser in a quasi-phase-matched LiNbO(3) waveguide and used the asymptotically equal to1-mW second-harmonic output to investigate the (127)I(2) transitions near 660 nm. We reached submegahertz laser-frequency stability at a (vacuum) wavelength of 1319.098 nm by locking the second harmonic to the center of the P(48)6-6 transition.

Surface-emitting second-harmonic generation in a semiconductor vertical resonator.

We experimentally demonstrate a 240-fold increase in the efficiency of an AlGaAs/ALAs surface-emitting second-harmonic generation device by embedding the waveguide core in a monolithic vertical resonant cavity. Calculations indicate that conversion efficiencies of several percent per watt for second-harmonic generation of green or blue light may be expected in an optimized semiconductor resonant vertical-cavity surface emitter.

Language abilities of 18-month-old Zulu speakers.

The receptive, expressive and pragmatic language abilities of 18-month-old Zulu speakers were assessed in order to obtain preliminary norms. Twenty-five participants of the Birth to Ten cohort study were investigated using parent reports, mother-child and tester-child interactions. Data was transcribed and analysed using nonparametric statistics. Results demonstrated that receptively subjects understood two-part instructions. Expressively, the mean lexicon was 4.12 words and mean length of utterance 0.65. Pragmatically, subjects were functioning on a nonverbal level and exhibited culture-specific items. The results provided information which could enable speech, language and hearing therapists to engage in primary and secondary prevention. An appropriate test battery for these children is discussed.

Community work project in Gazankulu: a community-based training experience.

Speech Pathology and Audiology students at the University of the Witwatersrand participated in a field trip to learn about rural community work. In collaboration with rehabilitation workers at Tintswalo Hospital, Gazankulu, projects in pre-school language stimulation, aphasia assessment and intervention, and hearing screening were undertaken. Projects adhered to community work principles. These were successful in terms of both providing a service to the community and teaching students principles and practice of community work.

Measurement of the second-order nonlinear susceptibility of proton-exchanged LiNbO(3).

We have measured the d(33) nonlinear coefficient in proton-exchanged LiNbO(3) by using angle-dependent reflected second-harmonic generation and observed a reduction to

Annealed proton-exchanged LiNbO(3) waveguides.

We report characterization of annealed proton-exchanged waveguides in LiNbO(3). Effective-mode indices and fundamental-mode intensity profiles were measured for a variety of fabrication conditions. Index profile, depth, and surface refractive-index change were determined versus exchange depth and anneal time and are presented in a universal form. An empirical concentration-dependent diffusion model describing the annealing process is presented. The refractive-index dispersion in proton-exchanged and annealed proton-exchanged waveguides was determined for wavelengths between 0.4 and 1.1 microm.