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S M King

Publications and source records attributed to S M King.

At least 19 recordsLinked to original sources
PubMed2006

Direct measurement of the singlet generation yield in polymer light-emitting diodes.

In this study, the singlet and triplet exciton generation yields of a representative blue-emitting conjugated polymer are directly compared using simultaneous optical and electrical excitation measurements. After carefully accounting for bimolecular triplet annihilation and knowing the independently measured solid state inter-system-crossing yield of the polymer, a singlet generation yield of 44% is obtained, in the working device, which is clearly in excess of the simple quantum statistical 25% limit.

Journal Article↗
PubMed2006

Femtosecond ground state recovery: measuring the intersystem crossing yield of polyspirobifluorene.

Measurement of the quantum yield of triplet formation has been made for the prototypical conjugated polymer polyspirobifluorene in solution and solid state. An updated method has been described based on femtosecond time resolved ground state recovery following photoexcitation of the polymer. The two components to the recovery of the ground state due to the decay of the singlet and triplet excited states are clearly visible and from these it is possible to calculate Phi(T)=0.05+/-0.01 in solution, this gives k(isc)=5.4 x 10(7) s(-1) which compares favorably with other conjugated polymers. In polymer films an increased triplet yield of Phi(T)=0.12+/-0.02 is found to be independent of temperature, the increased yield is attributed to triplet recombination from charged states.

Journal Article↗
PubMed2006

Transmission of Mycobacterium tuberculosis from an infant.

SETTING: This report investigates the unusual transmission of Mycobacterium tuberculosis from a 12-week-old infant with nosocomially acquired tuberculosis (TB). Compliance with recommendations on the post-exposure management of young children is described. DESIGN: Contacts of an infant case of TB were identified and recommended to undergo baseline and post-exposure tuberculin skin tests (TST) as per Canadian TB standards. TST conversion was measured at least 8 weeks post exposure. Children aged <6 years were recommended to initiate preventive treatment with isoniazid (INH) until their post-exposure TST. Information on TST results and adherence to therapy were analysed from existing medical records. RESULTS: Overall, 17 TST conversions were documented among 732 contacts: both parents, two health care workers (HCWs) who provided close care, and several patients, visitors and one staff member without obvious close contact. Of 65 eligible children, 46% completed post-exposure therapy as recommended. The most common reasons for treatment failure were concern about side effects, perception of low risk and lack of physician support. CONCLUSION: This investigation suggests that all children, including infants, with cough and numerous bacilli or extensive pulmonary disease should be considered infectious. Health care provider education is necessary to resolve the observed low compliance with current post-exposure management guidelines.

Cross Infection↗
PubMed2004

Variegated micelle surfaces: correlating the microstructure of mixed surfactant micelles with bulk solution properties.

Electron paramagnetic resonance, viscosity, and small-angle neutron scattering (SANS) measurements have been used to study the interaction of mixed anionic/nonionic surfactant micelles with the polyampholytic protein gelatin. Sodium dodecyl sulfate (SDS) and the nonionic surfactant dodecylmalono-bis-N-methylglucamide (C12BNMG) were chosen as "interacting" and "noninteracting" surfactants, respectively; SDS micelles bind strongly to gelatin but C12BNMG micelles do not. Further, the two surfactants interact synergistically in the absence of the gelatin. The effects of total surfactant concentration and surfactant mole fraction have been investigated. Previous work (Griffiths et al. Langmuir 2000, 16 (26), 9983-9990) has shown that above a critical solution mole fraction, mixed micelles bind to gelatin. This critical mole fraction corresponds to a micelle surface that has no displaceable water (Griffiths et al. J. Phys. Chem. B 2001, 105 (31), 7465). On binding of the mixed micelle, the bulk solution viscosity increases, with the viscosity-surfactant concentration behavior being strongly dependent on the solution surfactant mole fraction. The viscosity at a stoichiometry of approximately one micelle per gelatin molecule observed in SDS-rich mixtures scales with the surface area of the micelle occupied by the interacting surfactant, SDS. Below the critical solution mole fraction, there is no significant increase in viscosity with increasing surfactant concentration. Further, the SANS behavior of the gelatin/mixed surfactant systems below the critical micelle mole fraction can be described as a simple summation of those arising from the separate gelatin and binary mixed surfactant micelles. By contrast, for systems above the critical micelle mole fraction, the SANS data cannot be described by such a simple approach. No signature from any unperturbed gelatin could be detected in the gelatin/mixed surfactant system. The gelatin scattering is very similar in form to the surfactant scattering, confirming the widely accepted picture that the polymer "wraps" around the micelle surface. The gelatin scattering in the presence of deuterated surfactants is insensitive to the micelle composition provided the composition is above the critical value, suggesting that the viscosity enhancement observed arises from the number and strength of the micelle-polymer contact points rather than the gelatin conformation per se.

Journal Article↗
PubMed2004

Effect of ethanol on the interaction between poly(vinylpyrrolidone) and sodium dodecyl sulfate.

The effect of ethanol on the interaction between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic polymer poly(vinylpyrrolidone) (PVP) has been investigated using a range of techniques including surface tension, fluorescence, electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS), and viscosity. Surface tension and fluorescence studies show that the critical micelle concentration (cmc) of the surfactant decreases to a minimum value around 15 wt % ethanol; that is, it follows the cosurfactant effect. However, in the presence of PVP, the onset of the interaction, denoted cmc(1), between the surfactant and the polymer is considerably less dependent on ethanol concentration. The saturation point, cmc(2), however, reflects the behavior of the cmc in that it decreases upon addition of ethanol. This results in a decrease in the amount of surfactant bound to the polymer [C(bound) = cmc(2) - cmc] at saturation. The viscosity of simple PVP solutions depends on ethanol concentration, but since SANS studies show that ethanol has no effect on the polymer conformation, the changes observed in the viscosity reflect the viscosity of the background solvent. There are significant increases in bulk viscosity when the surfactant is added, and these have been correlated with the polymer conformation extracted from an analysis of the SANS data and with the amount of polymer adsorbed at the micelle surface. Competition between ethanol and PVP to occupy the surfactant headgroup region exists; at low ethanol concentration, the PVP displaces the ethanol and the PVP/SDS complex resembles that formed in the absence of the ethanol. At higher ethanol contents, the polymer does not bind to the ethanol-rich micelle surface.

Journal Article↗
PubMed2004

The structure of metallomicelles.

The morphology of micelles formed by two novel metallosurfactants has been studied by small-angle neutron scattering (SANS) and small-angle-X-ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are Cu(II) complexes of monopendant alcohol derivatives of a) the face-capping macrocycle 1,4,7-triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10-tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X-ray scattering to locate the metal ions. For the 1,4,7,10-tetraazacyclododecane-based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7-triazacyclononane analogue. The X-ray scattering analysis shows that the metal ions are distributed throughout the polar head-group region, rather than at a well-defined radius; this is in good agreement with the SANS-derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.

Journal Article↗
PubMed2004

Interaction between a partially fluorinated alkyl sulfate and gelatin in aqueous solution.

The interaction of a partially fluorinated alkyl sulfate, sodium 1H,1H,2H,2H-perfluorooctyl sulfate (C6F13CH2CH2OSO3Na), with the polyampholyte gelatin has been examined in aqueous solution using surface tension and small-angle neutron scattering (SANS). The 19F chemical shift of each fluorine environment in the surfactant is unaltered by the addition of gelatin, indicating that there is no contact between the gelatin and the fluorocarbon core of the micelle. The chemical shift of the two methylene groups closest to the headgroup is altered when gelatin is present, disclosing the location of the polymer. The critical micelle concentration (cmc) of the surfactant, cmc = 17+/-1 mM, corresponds to an effective alkyl chain (CnH2n+1) length of n = 11. In the presence of gelatin, the cmc is substantially reduced as expected, cmc(1) = 4+/-1 mM, which is also consistent with an effective alkyl chain length of n = 11. In the presence of the fluorosurfactant, the monotonic decay of the SANS from the gelatin-only system is replaced by a substantial peak at an intermediate Q value mirroring the micellar interaction. At low ionic strengths, the gelatin/micelle complex can be described by an ellipsoid. At higher ionic strengths, the electrostatic interaction between the micelles is screened and the peak in the gelatin scattering disappears. The correlation length describing the network structure decreases with increasing SDS concentration as the bound micelles promote a collapse of the network.

Journal Article↗
PubMed2002

The 'family' context of HIV: a need for comprehensive health and social policies.

This paper reports on the findings from a multi-site psychosocial study of Canadian families with HIV-positive mothers. A total of 110 adults, representing 91 families across Canada participated in interviews. Qualitative analysis revealed a number of themes including: a complex web of personal, health and family concerns; the needs of children; family finances; disclosure dilemmas; and social experiences and challenges. These themes reflect an intricate and dynamic picture of parental and family life for adults and children living with HIV infection. Nowhere in the literature do we see HIV framed as a 'family infection'. Surveillance reporting reflects information on infected adults and children but not family groupings. Yet with HIV several family members and multiple generations as well as single or both parents may be infected, highlighting the importance of 'family HIV' as a framework for health policy and programme development. At issue is the problem that medical and other institutions view issues of surveillance, treatment and care through the lens of the infected individual, rather than being family focused. Often it is only in the context of identifying support, or barriers to support, for the medically diagnosed individual that biological or socially created families become a focus of concern. The failure to situate both chronic and life-threatening illnesses within the family setting has serious quality of life and planning consequences for parents and children living with HIV infection as well as other illnesses.

Adolescent↗
PubMed2002

Further evidence for the predictive validity of the unstable elevated exposed plus-maze, a behavioural model of extreme anxiety in rats: differential effects of fluoxetine and chlordiazepoxide.

The unstable elevated exposed plus-maze (UEEPM) is a novel model of extreme anxiety which elicits unconditioned flight/escape behaviour in rats. The current studies aimed to investigate further the predictive validity of the paradigm, by examining the effects on UEEPM behaviour of both clinically effective (chronic fluoxetine) and ineffective (acute fluoxetine and chlordiazepoxide) treatments for panic disorder. In the first experiment, male Brown Norway rats received a single injection of fluoxetine (1.0-10.0 mg/kg p.o.) or chlordiazepoxide (CDP, 1.0-10.0 mg/kg i.p.) 30 min prior to UEEPM exposure. In the second experiment, in order to assess the effects of chronic dosing or handling on baseline UEEPM behaviour, subjects received either 21 days vehicle injection (p.o.) or handling, before being exposed to the test. Finally, rats received 21 days fluoxetine (1.0-10.0 mg/kg) in their food, before being tested in the UEEPM. Acute CDP and fluoxetine had no effect on UEEPM behaviour. Chronic handling and vehicle administration (p.o.) significantly reduced escape in the UEEPM, hence preventing the effects of chronic fluoxetine administration from being investigated by p.o. dosing. Chronic fluoxetine in subjects' food (10.0 mg/kg) significantly attenuated animals' propensity to escape from the UEEPM. The results further support the pharmacological similarity between symptoms of panic in humans and escape in the UEEPM and suggest that the UEEPM may represent a paradigm to facilitate investigation into the neurochemical basis of extreme anxiety disorders.

Animals↗
PubMed2001

The role of infections in primary hemophagocytic lymphohistiocytosis: a case series and review of the literature.

There is a paucity of literature addressing infection-related morbidity and mortality in children with primary hemophagocytic lymphohistiocytosis (HLH), a rare condition characterized by abnormal proliferation of macrophages, hypercytokinemia, and T cell immunosuppression. Therefore, a retrospective chart review was done of patients diagnosed with primary HLH over a 15-year period. Significant infections present at diagnosis, during the course of illness, and just prior to death or at autopsy were noted. Of the 18 children identified with primary HLH, an infectious agent was documented at the initial presentation of HLH in 5. Significant infections occurred during therapy in 10 (56%) of 18. Of the 12 fatal cases, invasive infection was the cause of death in 8 children, and 6 of these deaths were directly attributable to invasive fungal infection. Significant infections were common during therapy in children with primary HLH, and fungal infections were an important cause of mortality in this group.

Bacterial Infections↗
PubMed2001

The Tctex1/Tctex2 class of dynein light chains. Dimerization, differential expression, and interaction with the LC8 protein family.

The Tctex1/Tctex2 family of dynein light chains associates with the intermediate chains at the base of the soluble dynein particle. These components are essential for dynein assembly and participate in specific motor-cargo interactions. To further address the role of these light chains in dynein activity, the structural and biochemical properties of several members of this polypeptide class were examined. Gel filtration chromatography and native gel electrophoresis indicate that recombinant Chlamydomonas flagellar Tctex1 exists as a dimer in solution. Furthermore, yeast two-hybrid analysis suggests that this association also occurs in vivo. In contrast, both murine and Chlamydomonas Tctex2 are monomeric. To investigate protein-protein interactions involving these light chains, outer arm dynein from Chlamydomonas flagella was cross-linked using dimethylpimelimidate. Immunoblot analysis of the resulting products revealed the interaction of LC2 (Tctex2) with LC6, which is closely related to the highly conserved LC8 protein found in many enzyme systems, including dynein. Northern dot blot analysis demonstrated that Tctex1/Tctex2 family light chains are differentially expressed both in a tissue-specific and developmentally regulated manner in humans. These data provide further support for the existence of functionally distinct populations of cytoplasmic dynein with differing light chain content.

Amino Acid Sequence↗
PubMed2001

Influence of circadian phase and test illumination on pre-clinical models of anxiety.

Pre-clinical models of anxiety, particularly the elevated plus-maze (EPM), have been shown to be sensitive to a variety of methodological variations. Recent research has implicated circadian phase of testing in influencing the behavioural profile of 5-HT(1A) ligands on the EPM. The present study investigated the effects of testing animals during the dark and light phases and in light and subjective dark test conditions on baseline behaviour in animal models of anxiety. Eighty singly housed male Sprague-Dawley rats were exposed to a battery of unconditioned, exploratory tests (EPM, open field arena, holeboard) and a new model of extreme anxiety, the unstable elevated exposed plus-maze (UEEPM). Circadian phase of testing failed to consistently alter behaviour on any model. Level of test illumination had no effect on subjects' response to the open field arena, holeboard or UEEPM. Dark testing increased locomotor activity on the EPM (total arm entries, closed arm entries and distance moved) without decreasing open-arm avoidance. The construct of anxiety as measured by a number of different paradigms withstood major intra-laboratory manipulation of circadian phase of testing and illumination of apparatus. It is suggested that the effects of circadian rhythmicity may be confined to the behavioural profiles of serotonergic, particularly 5-HT(1A), ligands on the EPM.

Animals↗
PubMed2001

Dynein motors of the Chlamydomonas flagellum.

Chlamydomonas is a biflagellate unicellular green alga that has proven especially amenable for the analysis of microtubule (MT)-based molecular motors, notably dyneins. These enzymes form the inner and outer arms of the flagellum and are also required for intraflagellar transport. Dyneins have masses of approximately 1-2 MDa and consist of up to 15 different polypeptides. Nucleotide binding/hydrolysis and MT motor activity are associated with the heavy chains, and we detail here our current model for the substructural organization of these approximately 520-kDa proteins. The remaining polypeptides play a variety of roles in dynein function, including attachment of the motor to cargo, regulation of motor activity in response to specific inputs, and their necessity for the assembly and/or stability of the entire complex. The combination of genetic, physiological, structural, and biochemical approaches has made the Chlamydomonas flagellum a very powerful model system in which to dissect the function of these fascinating molecular motors.

Amino Acid Sequence↗
PubMed2001

Safety of the Canadian blood supply in 1980-85: using a paediatric cohort for risk assessment of human immunodeficiency virus (HIV) infection.

The risk of HIV from transfusions in Canada in the period 1980-85 was estimated, using the information from a transfused paediatric cohort. Children who were transfused between January 1980 and November 1985 at a tertiary care paediatric hospital were contacted by letter. With this notification, HIV testing for recipients was recommended. HIV testing histories were obtained. The number tested for HIV was estimated from the questionnaire responses and from data matching with the HIV-testing laboratory. Cases of HIV infection were identified through multiple sources. In this cohort, 11,028 children were transfused a mean of 21 units. Of the 10,220 living recipients, the estimated proportion tested for HIV was 86% to 91%. Thirty-one cases of HIV infection were identified, representing 0.28% of the cohort but 0.34% of those expected to have been tested. The estimated HIV incidence per 1,000 units transfused ranged from 0.028 [95% CI 0.0007, 0.155] in 1980 to 0.445 [95% CI 0.2592, 0.712] in 1985. This suggests that the risk of HIV from transfusions in Canada continued to rise until the implementation of HIV testing of donors in November 1985.

AIDS Serodiagnosis↗
PubMed2001

Pattern electroretinograms after cerebral hemispherectomy.

Cortically blind patients with brain damage restricted to the optic radiations or primary visual cortex may be able to detect and discriminate visual stimuli presented in their field defects, even though they deny seeing them. In contrast, patients who are hemianopic as a result of cerebral hemispherectomy cannot explicitly discriminate visual stimuli in their field defects, even when forced choice procedures are used. A possible explanation for this difference is that retrograde, transneuronal degeneration of the retina, which affects approximately 85% of wavelength-sensitive ganglion cells (approximately 70% of the total) after damage restricted to striate cortex, could be far more extensive after hemispherectomy, rendering the retina incapable of processing and conveying visual information to the brain. To test this, we assessed retinal ganglion cell function by means of electroretinography in three patients with cerebral hemispherectomy who were functionally blind. Steady-state pattern electroretinograms elicited by achromatic and isoluminant-chromatic (red-green) sinusoidal gratings, whose contrast was temporally modulated, were recorded from both blind and sighted hemiretinae. The electroretinograms were qualitatively indistinguishable from those of a control patient with a unilateral striate cortical lesion with documented visual capacity in his field defect. Within-subject analysis of variance revealed significant differences in the amplitude of the second harmonic (2f(0)) component of the averaged signal (diagnostic of retinal ganglion cell function) with respect to stimulus, but no significant differences between blind and sighted hemiretinae. This indicates that many retinal ganglion cells must have survived in the hemispherectomized patients. Isoluminant chromatic stimuli tended to elicit stronger signals than achromatic stimuli, which was unexpected given that wavelength-opponent Pbeta ganglion cells are far more susceptible than broad-band Palpha ganglion cells to transneuronal degeneration after cortical damage. It suggests that the 2f(0) component of the response to isoluminant chromatic stimuli might not reflect the activity of chromatic processes. Overall, the results show that the absence of residual vision in the blind fields of patients with cerebral hemispherectomy cannot be due to complete degeneration of retinal ganglion cells and, by extension, complete degeneration of their subcortical targets. This supports an alternative explanation, which is that intact extrastriate cortex is required for mediating voluntary responses to visual stimuli presented in the scotoma.

Adult↗
PubMed2001

Challenges of parenting for families living with HIV/AIDS.

Given the continual rise of HIV infection in our communities and the improved life span for many who are HIV-positive, social workers in all fields of practice have clients whose lives have been touched by HIV/AIDS. This article reviews relevant literature and reports on the parenting needs that emerged in a Canadian study that examined the experiences of 105 mothers and fathers living with HIV/AIDS. The majority of the children in the study were not HIV-positive. Some themes related to parenting in the literature, and evident in this study, were chronic sorrow, stress and burden, normalization, stigma, secrecy, and disclosure. In the study parenting was found to be a source of joy and an additional challenge in an already complicated life. Important new themes were family life as precious time, focused parenting, the different effects of HIV/AIDS, the parenting preparation needs of fathers, and the efforts to parent affected and infected children differently. Parenting when living with HIV/AIDS requires attention from clinicians and researchers in a range of settings.

Canada↗