Localized Electron States Near a Metal-Semiconductor Nanocontact

The electronic structure of nanowires in contact with metallic electrodes of experimentally relevant sizes is calculated by incorporating the electrostatic polarization potential into the atomistic single particle Schr\"odinger equation. We show that the presence of an electrode produces localized electron/hole states near the electrode, a phenomenon only exhibited in nanostructures and overlooked in the past. This phenomenon will have profound implications on electron transport in such nanosystems. We calculate several electrode/nanowire geometries, with varying contact depths and nanowire radii. We demonstrate the change in the band gap of up to 0.5 eV in 3 nm diameter CdSe nanowires and calculate the magnitude of the applied electric field necessary to overcome the localization.Comment: 11 pages 4 figure

Transferable atomic multipole machine learning models for small organic molecules

Accurate representation of the molecular electrostatic potential, which is often expanded in distributed multipole moments, is crucial for an efficient evaluation of intermolecular interactions. Here we introduce a machine learning model for multipole coefficients of atom types H, C, O, N, S, F, and Cl in any molecular conformation. The model is trained on quantum chemical results for atoms in varying chemical environments drawn from thousands of organic molecules. Multipoles in systems with neutral, cationic, and anionic molecular charge states are treated with individual models. The models' predictive accuracy and applicability are illustrated by evaluating intermolecular interaction energies of nearly 1,000 dimers and the cohesive energy of the benzene crystal.Comment: 11 pages, 6 figure

Heat transfer characteristics of hypersonic waveriders with an emphasis on the leading edge effects

The heat transfer characteristics in surface radiative equilibrium and the aerodynamic performance of blunted hypersonic waveriders are studied along two constant dynamic pressure trajectories for four different Mach numbers. The inviscid leading edge drag was found to be a small (4 to 8 percent) but not negligible fraction of the inviscid drag of the vehicle. Although the viscous drag at the leading edge can be neglected, the presence of the leading edge will influence the transition pattern of the upper and the lower surfaces and therefore affect the viscous drag of the entire vehicle. For an application similar to the National Aerospace Plane (NASP), the present study demonstrates that the waverider remains a valuable concept at high Mach numbers if a state-of-the-art active cooling device is used along the leading edge. At low Mach number (less than 5), the study shows the surface radiative cooling might be sufficient. In all cases, radiative cooling is sufficient for the upper and lower surfaces of the vehicle if ceramic composites are used as thermal protection

Coarse-grained interaction potentials for polyaromatic hydrocarbons

Using Kohn-Sham density functional theory (KS-DFT), we have studied the interaction between various polyaromatic hydrocarbon molecules. The systems range from mono-cyclic benzene up to hexabenzocoronene (hbc). For several conventional exchange-correlation functionals potential energy curves of interaction of the $\pi$-$\pi$ stacking hbc dimer are reported. It is found that all pure local density or generalized gradient approximated functionals yield qualitatively incorrect predictions regarding structure and interaction. Inclusion of a non-local, atom-centered correction to the KS-Hamiltonian enables quantitative predictions. The computed potential energy surfaces of interaction yield parameters for a coarse-grained potential, which can be employed to study discotic liquid-crystalline mesophases of derived polyaromatic macromolecules

The Loving of the Game: A Study of Basketry in the Mammoth Cave Area

The production and marketing of baskets in the Mammoth Cave area of Kentucky from 1880 to the present is observed in light of the cultural, technical, aesthetic, ad traditional aspects involved. The process of making a white oak ribbed basket is documented, as well as the technical and aesthetic variables from which the basket maker renders his product. The changing role of social organization and communication in the production and marketing of a traditional craft objects is also considered

Unsolved Problems in Virtual Knot Theory and Combinatorial Knot Theory

This paper is a concise introduction to virtual knot theory, coupled with a list of research problems in this field.Comment: 65 pages, 24 figures. arXiv admin note: text overlap with arXiv:math/040542

Identifying ENSO Phase Impacts on Area Yield Insurance Rates: An Application of Non-Parametric Analysis

The paper reports results of non-parametric analysis of peanut, corn, and cotton yield distributions by the ElNino Southern Oscillation (ENSO) phases in the Southeastern U.S. For validation purposes, the historical yield data is complemented by a set of simulated peanut yields generated using daily weather data. The hypothesis, justified by the observed South-Eastern climate differences and research on ENSO cycles and planting dates, is that different climate conditions during ENSO cycles translate into different yield distributions and, therefore, insurance premiums (loss to coverage ratios). Kernel density estimates of historical county yield data show consistent patterns in the actuarially fair rate schedules grouped by ENSO phases and geographical areas. In particular, corn and cotton yield insurance premiums appear to be the most dependent on the ENSO phases and are the highest, regardless of coverage, during ElNino and the lowest during LaNina. Peanut premiums are higher during Neutral years and lowest during LaNina. The results appear to be robust to the transformations used to make the yield series stationary. While these dependencies do not necessarily correspond to the precipitation and solar radiation characteristics of the corresponding ENSO cycles in the Southeastern US, drawing direct analogies with yield variability is premature as many less documented factors, like the spacing of sunny and rainy days, may be just as important. The comparisons of the empirical and simulated peanut yield distributions show that they are similar in many ways and that the dissimilarities can be explained by known factors. These findings should be more relevant for the area yield insurance as opposed to the APH arrangements as the yield data used in designing contracts for the former reflects the systemic risk more influenced by climate than by the farm-level, basis risk factors accommodated in the APH plans.Risk and Uncertainty, Q140, C220, G220,

Synthesis, Characterisation and Biological Activity of Novel Carboxylate Complexes Incorporating Phenanthroline and Benzimidazole Ligands

This thesis reports results in two related areas: (1) the synthesis, characterisation and biological activity of soluble metal carboxylate complexes incorporating 1,10-phenanthroline and related ligands and (ii) the synthesis, characterisation and biological activity of Copper(II) complexes containing benzimidazole type ligands. 2,2-dimethylpentanedioic acid (2-dmepdaH2) and 3,3-dimethylpentanedioic acid (3-dmepdaHs) were reacted with copper (II) acetate to yield the novel soluble complexes [Cu(2-dmepda)(H2O)3]2 (1) and [Cu(3-dmepda)(H2)]3]2(2). Reaction of (1) and (2) with either 1,10-phenanthroline or 2,2’-bipyridine generated a series of novel soluble dicarboxylate complexes. The X-ray crystal structure of [Cu(2-dmepda)(bipy)(EtOH)]2-2EtOH and [Cu(3-dmepda)(bipy)(h2o)]2 were determined. The anti-Candida activity of all the soluble 2-dmpeda and 3-dmpeda complexes were determined. Significantly only the two non-phenanthroline complexes [Cu(2-dmepd)]H2O)3]2, [Cu(3-dmepda)(H2O),]2 and [Cu92-dmepda](phen)(H2O)]2.0.5phen(3) exhibited fungitoxic activity. A range of novel metal acetate (metal=Cu(II, Mn(II) and Zn(II) complexes incorporating the chelating 1,10-phenanthroline and the non-chelating 1,7-and 4,7-phenanthroline ligands were synthesised and characterised. The anti-Candida activity of these complexes was studies. Whereas the 1,10-phenanthroline complexes possessed good to moderate anti-fungal activity the complexes containing the non-chelating phenanthroline ligands were essentially inactive. 21 novel Copper(II) complexes were synthesised using simple Benzimidazole and Benzimidazole carboxylic acid ligands. These compounds were characterised using spectroscopic and physical methods. The X-ray crystal structure of [Cu(BZDtac)(1,10-phen)2]BZDtac.5H2)(BZDtacH=Benzimidazolylthioacetic acid were determined. The chloride,nitrate and sulphate salts of copper(II) were reacted with the chelating ligand Thiabendazole (TBZH) to yield salt like compounds. The reaction with copper (11) acetate yielded the previously unknown [Cu(TBZ)2(H2O)2]n. The X-ray crystal structure of [Cu(TBZH)2C1]C1.H2O.EtOH was determined. 7 novel Copper(II) (a,w-dicarboxylate) complexes incorporating Thiabendazole wee generated and characterised. The anti-Candida activity of all of the benzimidazole and thiabendazole complexes was examined. Unlike 1,10-phenanthroline the ‘metal free’ benzimidazole and thiabendazole were inactive against the pathogen, however, a range of their copper complexes were found to exhibit very good anti-fungal activity. The chemotherapeutic potential of a number of the complexes generated during this study was examined against human derived cancer cell line. Sever of the copper(II) complexes were found to exhibit significant activity