Thermoelectric property enhancement via pore confinement in template grown bismuth telluride nanowire arrays.

Nanostructuring of thermoelectric materials can lead to thermal-to-electrical conversion efficiencies comparable with mechanical energy conversion. Theory predicts that characteristic length scales of <10 nm are necessary to achieve high thermoelectric figures of merit (zT > 3). While sub-10 nm diameter nanowire arrays have been difficult to fabricate, we present here a novel template for sub-10 nm thermoelectric nanowire array fabrication using anodized aluminum oxide followed by silica wall coating for pore confinement. Electrodeposited bismuth telluride nanowires displayed increasing electrical-to-thermal conductivity ratio as the pore diameter decreased, in agreement with theoretical predictions. Achieving the desired stoichiometric ratio of Bi2Te3 through electrodeposition was non-trivial, which limited the Seebeck coefficient of the nanowires. However, hydrolysis of the nanopore walls led to improved electrodeposition, achieving near stoichiometric bismuth-to-tellurium ratios and ultimately p-type thermoelectric nanowire arrays with a Seebeck coefficient of up to 79 µV K-1.

Intracerebral chondroitinase ABC and heparan sulfate proteoglycan glypican improve outcome from chronic stroke in rats.

Physical and chemical constraints imposed by the periinfarct glial scar may contribute to the limited clinical improvement often observed after ischemic brain injury. To investigate the role of some of these mediators in outcome from cerebral ischemia, we treated rats with the growth-inhibitory chondroitin sulfate proteoglycan neurocan, the growth-stimulating heparan sulfate proteoglycan glypican, or the chondroitin sulfate proteoglycan-degrading enzyme chondroitinase ABC. Neurocan, glypican, or chondroitinase ABC was infused directly into the infarct cavity for 7 d, beginning 7 d after middle cerebral artery occlusion. Glypican and chondroitinase ABC reduced glial fibrillary acidic protein immunoreactivity and increased microtubule-associated protein-2 immunoreactivity in the periinfarct region, and glypican- and chondroitinase ABC-treated rats showed behavioral improvement compared with neurocan- or saline-treated rats. Glypican and chondroitinase ABC also increased neurite extension in cortical neuron cultures. Glypican increased fibroblast growth factor-2 expression and chondroitinase ABC increased brain-derived neurotrophic factor expression in these cultures, whereas no such effects were seen following neurocan treatment. Thus, treatment with glypican or enzymatic disruption of neurocan with chondroitinase ABC improves gross anatomical, histological, and functional outcome in the chronic phase of experimental stroke in rats. Changes in growth factor expression and neuritogenesis may help to mediate these effects.

A meal enriched in saturated fat acutely impairs cognitive performance in obese men.

BACKGROUND: Diets chronically high in saturated fat (SFA) associate with obesity and insulin resistance (IR), which in turn associate with cognitive decline and dementia. However, understanding how acute SFA consumption influences cognition is less clear despite short-term SFA-enriched diets inducing whole-body IR. We examined how consuming meals enriched with SFA or monounsaturated fat (MUFA) acutely influence cognitive function in lean and obese men. We hypothesized that greater diet-induced IR following a SFA-enriched meal would associate with decreased cognitive performance. METHODS: Twelve lean and 12 obese males ingested meals containing no fat (CTL), enriched with SFA, or enriched with MUFA in a single-blind, randomized fashion. Cognitive testing and blood sampling were performed pre- and 2 h post-meal. Oral glucose tolerance (OGTT) and body composition were also assessed. RESULTS: At baseline, fasting glucose, insulin, HOMA-IR, triglyceride, IL-6, and 2-hr glucose during an OGTT were higher in obese men (p < 0.001), while executive function (Stroop Test and Trail Making Test B-A) and working memory (Digit Span Test) were lower in obese men (p < 0.05). In response to the CTL and MUFA-enriched, no differences in cognitive measures were observed in lean or obese subjects. Following a SFA-enriched meal, obese subjects scored worse during cognitive testing (Stroop Test, Trail Making Test B-A, and Digit Span Test) compared to pre-meal scores (p < 0.05). These impairments in cognitive testing scores following the SFA-enriched meal associated with increased HOMA-IR (p < 0.01) and decreased plasma IL-6 (p < 0.05). No changes in cognitive function were observed in lean subjects following a SFA-enriched meal. CONCLUSIONS: These data demonstrate that cognitive performance of obese men acutely worsens following a high-SFA meal. Reductions in cognitive performance associated with increased IR, suggesting that diet-induced IR may acutely decrease cognitive function.

An interfacial and bulk charge transport model for dye-sensitized solar cells based on photoanodes consisting of core-shell nanowire arrays.

Dye-sensitized solar cells (DSSCs) based on ordered photoanode morphologies, such as nanotubes and nanowires, are widely gaining attention because these geometries are believed to enhance interfacial charge transfer and bulk charge transport. Unfortunately, experimental results have yet to show substantial improvement to conversion efficiency over nanoparticle-based DSSCs. A model is developed to characterize the performance of an idealized photoanode based on an ordered array of transparent conductive nanowires coated with an anatase titania shell. The role of the interfacial electric field in nanowire-based DSSCs is explored computationally by turning electron migration ON or OFF. The results show that back-reaction rates are most strongly influenced by the electric field. These electron loss mechanisms can be reduced by several orders of magnitude, leading to improvements in short-circuit current, open-circuit voltage, and fill factor.

Analysis of pyramidal neuron morphology in an inducible knockout of brain-derived neurotrophic factor.

BACKGROUND: The messenger ribonucleic acid (mRNA) for brain-derived neurotrophic factor (BDNF), a regulator of pyramidal neuron dendritic spine density during development, is decreased in the prefrontal cortex of subjects with schizophrenia, and the level of BDNF mRNA expression is positively correlated with dendritic spine density in the same subjects. METHODS: To determine whether reduced BDNF mRNA expression might account for decreased spine density in schizophrenia, a knockout of the BDNF gene was induced in mice during embryogenesis or at 12 weeks of age. Quantitative assessments were made of the dendritic arbor of Golgi-impregnated pyramidal neurons in the prelimbic and anterior cingulate cortices in adulthood. RESULTS: Despite an 80% reduction in BDNF mRNA levels in both knockouts, neither spine density nor other dendritic or somal measures were decreased compared with wild-type animals. CONCLUSIONS: A reduction in BDNF expression alone does not seem to be sufficient to alter pyramidal neuron morphology in mice. This finding suggests that other molecular abnormalities are also required to produce the pyramidal neuron dendritic spine abnormalities observed in schizophrenia.

Eliminating capillary coalescence of nanowire arrays with applied electric fields.

Surface tension induces significant forces on wetted nanostructures, such as vertically oriented nanowire arrays, that can force them to aggregate when dried. This aggregation decreases the homogeneity and surface area of the array, often inhibiting their intended application. These aggregation forces are eliminated by introducing small electric fields ( approximately 100 V/m) during drying, providing a simple approach that is applicable to a broad range of nanowire materials, diameters, lengths, and spacing. A model based on the forces acting on two nanowires shows that electrostatic repulsion, rather than field-induced changes to the surface tension, provides the necessary forces to prevent aggregation. These calculations also highlight the substantial surface tension forces acting on nanostructures and the difficulties associated with preventing their aggregation.