Biomedical subjects

Michael D Barnes

Publications and source records attributed to Michael D Barnes.

10 recordsLinked to original sources

PubMed2006

Probing the chiroptical response of a single molecule.

Chirally sensitive measurement techniques have generally been restricted to bulk samples. Here, we report the observation of fluorescence-detected circular dichroism (FDCD) from single (bridgedtriarylamine) helicene molecules by using an excitation wavelength (457 nanometers) in the vicinity of an electronic transition that shows circular dichroism in bulk samples. The distributions of dissymmetry (g) parameters by analysis of signals from pure M- and P-type diastereomers are almost perfect mirror images of one another, each spanning a range of both positive and negative values. In addition, we observe a well-defined structure in the histogram of dissymmetry parameters suggestive of specific molecular orientations at the polymer interface. These single-molecule results highlight strong intrinsic circular dichroism responses that can be obscured by cancellation effects in ensemble measurements of a randomly oriented bulk sample.

Journal Article↗

PubMed2006

Coverage-mediated suppression of blinking in solid state quantum dot conjugated organic composite nanostructures.

Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems.

Cadmium Compounds↗

PubMed2006

Knowledge of the effects of indoor air quality on health among women in Jordan.

OBJECTIVE: To assess the extent of knowledge about symptoms relating to respiratory illnesses and home environments among a random sample of 200 urban Jordanian women. METHOD: This customized, validated, cross-sectional questionnaire evaluated the knowledge of these women about the association between the indoor environment and health, the presence or absence of indoor discomforts, symptoms of respiratory illnesses, and behaviors related to the home environment such as cleaning practices. RESULTS: Results showed an alarming rate of smoking in the homes; the extent of knowledge was moderate but higher among those exhibiting symptoms and those with children. Cleaning practices associated with healthy home environments were reported at a high rate but seemed to be based on cultural influences. CONCLUSIONS: This type of information is crucial to the formation of health education programs and policy recommendations for pollutant source and exposure reductions in homes in the Middle East and other developing countries.

Adult↗

PubMed2006

Observation of enhanced energy transfer in individual quantum dot-oligophenylene vinylene nanostructures.

The temporal and spectral properties of luminescence from individual CdSe quantum dot-oligophenylene vinylene nanostructures (single quantum dots with conjugated organic ligands coordinated to the surface) are profoundly modified relative to blended films of the same components. These kinds of composite quantum dot-conjugated organic systems have attracted significant interest as a way to improve efficiency in photovoltaic device applications. By direct functionalization of the dot surface with the conjugated organic ligands, we realize a significant enhancement in energy transfer and luminescence stability.

Journal Article↗

PubMed2005

Computational study of the structure, dynamics, and photophysical properties of conjugated polymers and oligomers under nanoscale confinement.

Computational simulations were used to investigate the dynamics and resulting structures of several para-phenylenevinylene (PPV) based polymers and oligomers (PPV, 2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylene --> MEH-PPV and 2,5,2',5'-tetrahexyloxy-7,8'-dicyano-p-phenylenevinylene --> CN-PPV). The results show how the morphology and structure are controlled to a large extent by the nature of the solute-solvent interactions in the initial solution-phase preparation. Secondary structural organization is induced by using the solution-phase structures to generate solvent-free single molecule nanoparticles. Isolation of these single molecule nanostructures from microdroplets of dilute solution results in the formation of electrostatically oriented nanostructures at a glass surface. Our structural modeling suggests that these oriented nanostructures consist of folded PPV conjugated segments with folds occurring at tetrahedral defects (sp3 C-C bonds) within the polymer chain. This picture is supported by detailed experimental fluorescence and scanning probe microscopy studies. We also present results from a fully quantum theoretical treatment of these systems which support the general conclusion of structure-mediated photophysical properties.

Journal Article↗

PubMed2005

Prevalence and predictors of "heavy" marijuana use in a Canadian youth sample.

In this investigation, secondary analyses were performed on an extensive database for 473 biological and 128 adoptive families. These data, which were gathered as part of the Vancouver Family Survey, were used to examine the prevalence and predictors of "heavy" marijuana use in a Canadian youth sample aged 14-25. Results in this study showed that 12.6% of the sample reported using marijuana once a week or more. These respondents were categorized as "heavy" marijuana users. Higher levels of life problems were associated with this use pattern. Results from a series of regression analyses suggested that the family, personality, and peer domains all contributed significantly in predicting "heavy" marijuana use. Father's alcoholism and peer illicit drug use had direct relationships with heavy marijuana use in this final model. A possible mediated pathway was also suggested with the Addiction Prone Personality influencing use through its relationship with heavier peer drug use.

Adolescent↗

PubMed2004

Quantum mechanical single-gold-nanocluster electroluminescent light source at room temperature.

Electrically contacted gold-nanocluster arrays formed within electromigration-induced break junctions exhibit bright, field-dependent electroluminescence in the near infrared (650-800 nm). Intensity autocorrelation of spatially isolated individual nanocluster emission driven at high electrical frequency (f(ac)= approximately 200 MHz) reveals antibunched electroluminescence at room temperature. These results demonstrate the single quantum nature of several-atom gold molecules and suggest their use as room-temperature electrically driven single-photon sources.

Journal Article↗

PubMed2004

Photon antibunching from oriented semiconducting polymer nanostructures.

Fluorescence intensity correlation measurements reveal that z-oriented nanostructures from single chains of a cyano-substituted polyphenylene vinylene (CN-PPV) polymer act as single-quantum emitters. Photon antibunching is observed for the first time on individual polymer nanostructures with a modulation depth exceeding 90%, providing definitive proof that radiative recombination of molecular excitons occurs at a single localized site within the folded polymer chain.

Journal Article↗

PubMed2003

Size-correlated spectroscopy and imaging of rare-earth-doped nanocrystals.

Isolated europium-doped metal-oxide nanoparticles were probed by size-correlated high-numerical-aperture (far-field) imaging techniques. A modified Digital Instruments Bioscope atomic force microscope mounted upon a Nikon TE300 inverted microscope was used to interrogate (dry) particles ranging in size from 2 to 150 nm on the surface of a glass or quartz coverslip. These experiments revealed several interesting features of doped-nanoparticle luminescence such as Poissonian occupation statistics, size-dependent luminescence efficiency enhancement for particle sizes of <10 nm, and correlation of interesting transient behavior at particle sizes of <5 nm.

Journal Article↗

PubMedDate not supplied

Public health perspectives on the family: an ecological approach to promoting health in the family and community.

The family, as a setting of practice, is increasingly recognized as critical to health promotion. A better understanding of the nature and process through which families take an active part in their own health can serve as the basis for designing and linking health interventions with public health programs. The integrating function of the family, viewed through an ecological context, makes it an effective entry point and central focus in health promotion.

Community Participation↗