Understanding the length dependence of molecular junction thermopower

Thermopower of molecular junctions is sensitive to details in the junction and may increase, decrease, or saturate with increasing chain length, depending on the system. Using McConnell's theory for exponentially suppressed transport together with a simple and easily interpretable tight binding model, we show how these different behaviors depend on the molecular backbone and its binding to the contacts. We distinguish between resonances from binding groups or undercoordinated electrode atoms, and those from the periodic backbone. It is demonstrated that while the former gives a length-independent contribution to the thermopower, possibly changing its sign, the latter determines its length dependence. This means that the question of which orbitals from the periodic chain that dominate the transport should not be inferred from the sign of the thermopower but from its length dependence. We find that the same molecular backbone can, in principle, show four qualitatively different thermopower trends depending on the binding group: It can be positive or negative for short chains, and it can either increase or decrease with length

The geography of entrepreneurship in the New York metropolitan area

This article was presented at a conference organized by the Federal Reserve Bank of New York in April 2005, "Urban Dynamics in New York City." The goal of the conference was threefold: to examine the historical transformations of the engine-of-growth industries in New York and distill the main determinants of the city's historical dominance as well as the challenges to its continued success; to study the nature and evolution of immigration flows into New York; and to analyze recent trends in a range of socioeconomic outcomes, both for the general population and recent immigrants more specifically.Business enterprises - New York (N.Y.) ; Economic conditions - New York (N.Y.) ; Federal Reserve District, 2nd ; Urban economics

Characterisation of porous solids using small-angle scattering and NMR cryoporometry

The characteristics of several porous systems have been studied by the use of small-angle neutron scattering [SANS] and nuclear magnetic resonance [NMR] techniques. The measurements reveal different characteristics for sol-gel silicas, activated carbons and ordered mesoporous silicas of the MCM and SBA type. Good agreement is obtained between gas adsorption measurements and the NMR and SANS results for pore sizes above 10 nm. Recent measurements of the water/ice phase transformation in SBA silicas by neutron diffraction are also presented and indicate a complex relationship that will require more detailed treatment in terms of the possible effects of microporosity in the silica substrate. The complementarity of the different methods is emphasised and there is brief discussion of issues related to possible future developments

Floral visitors of Helianthus verticillatus, a rare sunflower species in the southeastern United States

Whorled sunflower (Helianthus verticillatus) is an endangered species of aster found exclusively in the southeastern United States. Evidence suggests that this species is self-incompatible and reliant on insect pollination for seed production. However, little is known about the general biology of this species, including the identity of probable pollinators. Floral visitors were collected and identified during September of 2017 and 2018. A total of 41 species of visitors (29 Hymenoptera, 6 Diptera, 1 Lepidoptera, and 5 miscellaneous) were trapped during seven collection days at one site in Georgia and two in Tennessee. Within a collection day (7:45 to 18:15), there were either 5 or 6 discrete half-hour time periods when insects were trapped. Insect visitor activity peaked during the 11:45-12:15 and 13:45-14:15 collection periods and was least during the 7:45- 8:45 and 9:45-10:15 periods at all three locations. Visitors were identified to genus and species using morphological keys and some with sequences of the COX-1 mitochondrial gene. A rarefaction analysis using the iNext Online package was used to assess species richness, while Simpson’s Diversity Index was used to assess species diversity within and across each location. The most common visitor across all locations was Bombus spp. (bumblebees), followed by Ceratina calcarata (a carpenter bee) and members of the halictid bee tribe Augochlorini at the two Tennessee locations. Pollen on visitors was identified to genus via direct PCR of DNA using Helianthus-specific microsatellites. Pollen grain counts were obtained from the 10 most common visitors and Apis mellifera (honey bee) using a hemocytometer. Of these visitors, Bombus spp., Halictus ligatus (a sweat bee), and Melissodes spp. (long-horned bees) carried the most Helianthus pollen grains. These visitors are likely to be the primary pollinators of H. verticillatus flowers

Once-daily treatment of ADHD with guanfacine: patient implications

The standard of care for treating ADHD is to use a psychostimulant as the first line agent. Recent medical literature reports that approximately 70%–90% of patients with ADHD received some benefit from a stimulant medication. Even though psychostimulants have a high rate of efficacy, an estimated 30%–50% of children and adults may discontinue psychostimulants secondary to adverse effects or inadequate response. Guanfacine has been used for a number of years as an off label alternative to psychostimulants. This article reviews the current literature on the effectiveness of guanfacine in treating ADHD. It also introduces the preliminary data for guanfacine extended release and its effectiveness in decreasing the symptoms of ADHD