Bright core-shell semiconductor quantum wires.

Colloidal CdTe quantum wires are reported having ensemble photoluminescence efficiencies as high as 25% under low excitation-power densities. High photoluminescence efficiencies are achieved by formation of a monolayer CdS shell on the CdTe quantum wires. Like other semiconductor nanowires, the CdTe quantum wires may contain frequent wurtzite-zinc-blende structural alternations along their lengths. The present results demonstrate that the optical properties, emission-peak shape and photoluminescence efficiencies, are independent of the presence or absence of such structural alternations.

The hunger-obesity paradox: obesity in the homeless.

Despite stereotypes of the homeless population as underweight, the literature lacks a rigorous analysis of weight status in homeless adults. The purpose of this study is to present the body mass index (BMI) distribution in a large adult homeless population and to compare this distribution to the non-homeless population in the United States. Demographic, BMI, and socioeconomic variables from patients seen in 2007-2008 were collected from the Boston Health Care for the Homeless Program (BHCHP). This population was compared to non-homeless adults from the National Health and Nutrition Examination Survey (NHANES). Among 5,632 homeless adults, the mean BMI was 28.4 kg/m(2) and the prevalence of obesity was 32.3 %. Only 1.6 % of homeless adults were underweight. Compared to mean BMI in NHANES (28.6 kg/m(2)), the difference was not significant in unadjusted analysis (p = 0.14). Adjusted analyses predicting BMI or likelihood of obesity also showed that the homeless had a weight distribution not statistically different from the general population. Although underweight has been traditionally associated with homelessness, this study suggests that obesity may be the new malnutrition of the homeless in the United States.

Excitation Energy Dependence of Photoluminescence Quantum Yields in Semiconductor Nanomaterials with Varying Dimensionalities.

The excitation energy dependence (EED) of the photoluminescence quantum yield (ΦPL) of semiconductor nanoparticles with varying dimensionalities is reported. Specifically, the EEDs of CdSe quantum dots, CdSe quantum platelets, CdSe quantum belts, and CdTe quantum wires were determined via measurements of individual ΦPL values and photoluminescence efficiency (PLEff(E)) spectra. There is a general trend of overall decreasing efficiency for radiative recombination with increasing excitation energy. In addition, there are often local minima in the PLEff(E) spectra that are most often at energies between quantum-confinement transitions. The average PL lifetimes of the samples do not depend on the excitation energy, suggesting that the EED of ΦPL arises from charge carrier trapping that competes efficiently with intraband carrier relaxation to the band edge. The local minima in the PLEff(E) spectra are attributed to excitation into optically coupled states that results in the loss of carriers in the semiconductor. The EED data suggest that the PLEff(E) spectra depend on the sample synthesis, preparation, surface passivation, and environment.

Unusual presentation of erythema elevatum diutinum with underlying hepatitis B infection.

Erythema elevatum diutinum (EED) is a rare, chronic, cutaneous small vessel vasculitis of unclear pathogenesis. Classically, lesions present as symmetric red to purple plaques, papules, and nodules overlying joints. First-line therapy is dapsone. We present a case of EED with widespread lesions involving the hands, extensor arms and legs, and trunk. Multiple biopsies showed concentric intradermal perivascular inflammation with dermal fibrosis and leukocytoclastic vasculitis (LCV) suggesting EED in various stages of evolution. An extensive workup was positive for underlying hepatitis B infection. Our case represents the clinicopathologic spectrum that EED can present and emphasizes the importance of searching for an underlying etiology.

Blueprint for an Undergraduate Primary Care Curriculum.

In light of the increasing demand for primary care services and the changing scope of health care, it is important to consider how the principles of primary care are taught in medical school. While the majority of schools have increased students' exposure to primary care, they have not developed a standardized primary care curriculum for undergraduate medical education. In 2013, the authors convened a group of educators from primary care internal medicine, pediatrics, family medicine, and medicine-pediatrics, as well as five medical students to create a blueprint for a primary care curriculum that could be integrated into a longitudinal primary care experience spanning undergraduate medical education and delivered to all students regardless of their eventual career choice.The authors organized this blueprint into three domains: care management, specific areas of content expertise, and understanding the role of primary care in the health care system. Within each domain, they described specific curriculum content, including longitudinality, generalism, central responsibility for managing care, therapeutic alliance/communication, approach to acute and chronic care, wellness and prevention, mental and behavioral health, systems improvement, interprofessional training, and population health, as well as competencies that all medical students should attain by graduation.The proposed curriculum incorporates important core features of doctoring, which are often affirmed by all disciplines but owned by none. The authors argue that primary care educators are natural stewards of this curriculum content and can ensure that it complements and strengthens all aspects of undergraduate medical education.

Fast Singlet Exciton Decay in Push-Pull Molecules Containing Oxidized Thiophenes.

A common synthetic strategy used to design low-bandgap organic semiconductors employs the use of "push-pull" building blocks, where electron -rich and electron-deficient monomers are alternated along the π-conjugated backbone of a molecule or polymer. Incorporating strong "pull" units with high electron affinity is a means to further decrease the optical gap for infrared optoelectronics or to develop n-type semiconducting materials. Here we show that the use of thiophene-1,1-dioxide as a strong acceptor in "push-pull" oligomers affects the electronic structure and carrier dynamics in unexpected ways. Critically, the overall excited-state lifetime is reduced by several orders of magnitude relative to unoxidized analogs due to the introduction of low-energy optically dark states and low-energy triplet states that allow for fast internal conversion and intramolecular singlet fission. We found that the electronic structure and excited-state lifetime are strongly dependent on the number of sequential thiophene-1,1-dioxide units. These results suggest that both the static and dynamical optical properties are highly tunable via small changes in chemical structure that have drastic effects on the optoelectronic properties, which can impact the types of applications that involve these materials.

Probing differential optical and coverage behavior in nanotube-nanocrystal heterostructures synthesized by covalent versus non-covalent approaches.

Double-walled carbon nanotube (DWNT)-CdSe heterostructures with the individual nanoscale building blocks linked together by 4-aminothiophenol (4-ATP) have been successfully synthesized using two different and complementary routes, i.e. covalent attachment and non-covalent π-π stacking. Specifically, using a number of characterization methods, we have probed the effects of these differential synthetic coupling approaches on the resulting CdSe quantum dot (QD) coverage on the underlying nanotube template as well as the degree of charge transfer between the CdSe QDs and the DWNTs. In general, based on microscopy and spectroscopy data collectively, we noted that heterostructures generated by non-covalent π-π stacking interactions evinced not only higher QD coverage density but also possibly more efficient charge transfer behavior as compared with their counterparts produced using covalent linker-mediated protocols.

Characterization of plasmonic hole arrays as transparent electrical contacts for organic photovoltaics using high-brightness Fourier transform methods.

We present a methodology for probing light-matter interactions in prototype photovoltaic devices consisting of an organic semiconductor active layer with a semitransparent metal electrical contact exhibiting surface plasmon-based enhanced optical transmission. We achieve high-spectral irradiance in a spot size of less than 100 µm using a high-brightness laser-driven light source and appropriate coupling optics. Spatially resolved Fourier transform photocurrent spectroscopy in the visible and near-infrared spectral regions allows us to measure external quantum efficiency with high sensitivity in small-area devices (<1 mm2). This allows for rapid fabrication of variable-pitch sub-wavelength hole arrays in metal films for use as transparent electrical contacts, and evaluation of the evanescent and propagating mode coupling to resonances in the active layer.

The Magic-Size Nanocluster (CdSe)34 as a Low-Temperature Nucleant for Cadmium Selenide Nanocrystals; Room-Temperature Growth of Crystalline Quantum Platelets.

Reaction of Cd(OAc)2·2H2O and selenourea in primary-amine/secondary-amine cosolvent mixtures affords crystalline CdSe quantum platelets at room temperature. Their crystallinity is established by X-ray diffraction analysis (XRD), high-resolution transmission electron microscopy (TEM), and their sharp extinction and photoluminescence spectra. Reaction monitoring establishes the magic-size nanocluster (CdSe)34 to be a key intermediate in the growth process, which converts to CdSe quantum platelets by first-order kinetics with no induction period. The results are interpreted to indicate that the critical crystal-nucleus size for CdSe under these conditions is in the range of (CdSe)34 to (CdSe)68. The nanocluster is obtained in isolated form as [(CdSe)34(n-octylamine)16(di-n-pentylamine)2], which is proposed to function as crystal nuclei that may be stored in a bottle.

Excitation Energy Dependence of the Photoluminescence Quantum Yields of Core and Core/Shell Quantum Dots.

The photoluminescence (PL) intensity of semiconductor quantum dots (QDs) is routinely monitored to track the chemical and physical properties within a sample or device incorporating the QDs. A dependence of the PL quantum yields (QYs) on the excitation energy could lead to erroneous conclusions but is commonly not considered. We summarize previous evidence and present results from two methodologies that confirm the possibility of a dependence of the PL QYs on the excitation energy. The data presented indicate that PL QYs of CdSe and CdSe/ZnS QDs suspended in toluene are highest for excitation just above the band gap, Eg, of each. The PL QYs decrease with increasing excitation energies up to 1 eV above Eg. The PL intensity decay profiles recorded for these samples at varying emission and excitation energies indicate that the changes in the PL QYs result from the nonradiative relaxation pathways sampled as the charge carriers relax down to the band edge.