Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (V$_o$) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two V$_o$ states was found to be sensitive to the ambient environment and to NR post-growth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient indicating a clear role of atmospheric O$_2$ on the surface defect states. A model for surface defect transient behaviour due to band bending with respect to the Fermi level is proposed. The results have implications for a variety of sensing and photovoltaic applications of ZnO NRs

A Comparison of the marginal cost of commissioning officers through the U.S. Naval Academy, Naval Reserve Officers Training Corps, and Officer Candidate School

This thesis calculates and compares the marginal cost of graduating a naval officer from the United States Naval Academy (USNA), Naval Reserve Officers Training Corps (NROTC), and Officer Candidate School (OCS). After defining the variable and fixed cost functions for each commissioning source, the total cost, average cost, and marginal cost per graduate are calculated for fiscal year 1989 graduates. Compared to average cost, the marginal cost per Academy graduate is more in line with the marginal cost per graduate for NROTC, and OCS. The results support the conclusion that a majority of the Naval Academy's costs are fixed in the short-run and that savings realized by reducing the number of graduates would be overstated by using average cost. This thesis recommends using marginal cost to estimate savings from reductions in officer accessions in the short-run.http://archive.org/details/acomparisonofmar1094527681Lieutenant, United States NavyApproved for public release; distribution is unlimited

PXRF analysis of a yellow ochre quarry and rock art motifs in the Central Pilbara

The significance of ochre in Indigenous Australia is well documented. Several large, well-known quarries containing ochre that is highly sought after have been described in the archaeological literature, however less attention has been paid to smaller, regionally and locally significant quarries. In this paper a small yellow ochre quarry (VSTA_20140611_1) from the Central Pilbara, where evidence of paint preparation is preserved in the form of residues in two in situ grinding hollows, is described in order to address this oversight. Portable XRF (pXRF) analysis of the pigment in the quarry itself and the paint in the hollows was undertaken to understand the chemistry of the pigmentaceous minerals, to explore the taphonomy of the ochre seam, and to gauge variation within the source. Chemistry indicates that the VSTA_20140611_1 quarry is composed of an iron mineral (likely a hydroxide such as goethite), with Fe abundances consistently between 10.7 and 30%. Typical of the regional geology, the yellow pigment is consistently siliceous, with an Si abundance of between 5.8 and 20.4%. As there are no painted motifs in the rockshelter containing the VSTA_20140611_1 quarry, nor on the suitable BIF surfaces nearby, it is considered highly likely that the surviving paint produced on-site was used for either body decoration or the adornment of artefacts, rather than for rock art production. Nevertheless, the similarity in chemical composition between the VSTA_20140611_1 pigments and that of motifs painted in sites a few kilometres away suggests that, in addition to immediate processing and use at the site, ochre from this quarry may have been transported to rockshelters in the vicinity and used for rock art production

Correlating densities of centrality and activities in cities : the cases of Bologna (IT) and Barcelona (ES)

This paper examines the relationship between street centrality and densities of commercial and service activities in cities. The aim is to verify whether a correlation exists and whether some 'secondary' activities, i.e. those scarcely specialized oriented to the general public and ordinary daily life, are more linked to street centrality than others. The metropolitan area of Barcelona (Spain) is investigated, and results are compared with those found in a previous work on the city of Bologna (Italy). Street centrality is calibrated in a multiple centrality assessment (MCA) model composed of multiple measures such as closeness, betweenness and straightness. Kernel density estimation (KDE) is used to transform data sets of centrality and activities to one scale unit for correlation analysis between them. Results indicate that retail and service activities in both Bologna and Barcelona tend to concentrate in areas with better centralities, and that secondary activities exhibit a higher correlation

Exciton binding energies in carbon nanotubes from two-photon photoluminescence

One- and two-photon luminescence excitation spectroscopy showed a series of distinct excitonic states in single-walled carbon nanotubes. The energy splitting between one- and two-photon-active exciton states of different wavefunction symmetry is the fingerprint of excitonic interactions in carbon nanotubes. We determine exciton binding energies of 0.3-0.4 eV for different nanotubes with diameters between 0.7 and 0.9 nm. Our results, which are supported by ab-initio calculations of the linear and non-linear optical spectra, prove that the elementary optical excitations of carbon nanotubes are strongly Coulomb-correlated, quasi-one dimensionally confined electron-hole pairs, stable even at room temperature. This alters our microscopic understanding of both the electronic structure and the Coulomb interactions in carbon nanotubes, and has direct impact on the optical and transport properties of novel nanotube devices.Comment: 5 pages, 4 figure

Environmental and economic assessment of sustainability in Mediterranean wheat production

ArticleThis study proposes the application of the Life Cycle Assessment (LCA) and economic evaluations conducted on different cereal production systems in semi-arid environments. Two different crop management systems of durum wheat were analysed by distinguishing Continuous Cropping (CC) and Crop Rotation (CR) with vetch, that are conducted through two different levels of crop intensification (in terms of tillage and fertilization strategies): Conventional (Conv) and Conservative (Cons). The resulting four scenarios were examined using LCA methodology to assess the environmental impacts, and the Production Cost (PC) analysis to estimate the economic results. Overall, the findings of this research provide an opportunity to identify sustainable crops management strategies

Extraordinary sensitivity of the electronic structure and properties of single-walled carbon nanotubes to molecular charge-transfer

Interaction of single-walled carbon nanotubes with electron donor and acceptor molecules causes significant changes in the electronic and Raman spectra, the relative proportion of the metallic species increasing on electron donation through molecular charge transfer, as also verified by electrical resistivity measurements.Comment: 15 pages, 5 figurre