4,811 research outputs found
Investigation of relationships between linears, total and hazy areas, and petroleum production in the Williston Basin: An ERTS approach
The author has identified the following significant results. ERTS-1 imagery in a variety of formats was used to locate linear, tonal, and hazy features and to relate them to areas of hydrocarbon production in the Williston Basin of North Dakota, eastern Montana, and northern South Dakota. Derivative maps of rectilinear, curvilinear, tonal, and hazy features were made using standard laboratory techniques. Mapping of rectilinears on both bands 5 and 7 over the entire region indicated the presence of a northeast-southwest and a northwest-southeast regional trend which is indicative of the bedrock fracture pattern in the basin. Curved lines generally bound areas of unique tone, maps of tonal patterns repeat many of the boundaries seen on curvilinear maps. Tones were best analyzed on spring and fall imagery in the Williston Basin. It is postulated that hazy areas are caused by atmospheric phenomena. The ability to use ERTS imagery as an exploration tool was examined where petroleum and gas are presently produced (Bottineau Field, Nesson and Antelope anticlines, Redwing Creek, and Cedar Creek anticline). It is determined that some tonal and linear features coincide with location of present production in Redwing and Cedar Creeks. In the remaining cases, targets could not be sufficiently well defined to justify this method
Ultrafast harmonic mode-locking of monolithic compound-cavity laser diodes incorporating photonic-bandgap reflectors
We present the first demonstration of reproducible harmonic mode-locked operation from a novel design of monolithic semiconductor laser comprising a compound cavity formed by a 1-D photonic-bandgap (PBG) mirror. Mode-locking (ML) is achieved at a harmonic of the fundamental round-trip frequency with pulse repetition rates from 131 GHz up to a record high frequency of 2.1 THz. The devices are fabricated from GaAs-Al-GaAs material emitting at a wavelength of 860 nm and incorporate two gain sections with an etched PBG reflector between them, and a saturable absorber section. Autocorrelation studies are reported which allow the device behavior for different ML frequencies, compound cavity ratios, and type and number of intra-cavity reflectors to be analyzed. The highly reflective PBG microstructures are shown to be essential for subharmonic-free ML operation of the high-frequency devices. We have also demonstrated that the single PBG reflector can be replaced by two separate features with lower optical loss. These lasers may find applications in terahertz; imaging, medicine, ultrafast optical links, and atmospheric sensing
Investigation of relationships between linears, tonal and hazy anomalies, and petroleum production in the Williston Basin: An ERTS approach
There are no author-identified significant results in this report
Hydrogen dynamics and light-induced structural changes in hydrogenated amorphous silicon
We use accurate first principles methods to study the network dynamics of
hydrogenated amorphous silicon, including the motion of hydrogen. In addition
to studies of atomic dynamics in the electronic ground state, we also adopt a
simple procedure to track the H dynamics in light-excited states. Consistent
with recent experiments and computer simulations, we find that dihydride
structures are formed for dynamics in the light-excited states, and we give
explicit examples of pathways to these states. Our simulations appear to be
consistent with aspects of the Staebler-Wronski effect, such as the
light-induced creation of well separated dangling bonds.Comment: 9 pages, 8 figures, submitted to PR
The Value of Literacy Practices
The concepts of literacy events and practices have received considerable attention in educational research and policy. In comparison, the question of value, that is, ‘which literacy practices do people most value?’ has been neglected. With the current trend of cross-cultural adult literacy assessment, it is increasingly important to recognise locally valued literacy practices. In this paper we argue that measuring preferences and weighting of literacy practices provides an empirical and democratic basis for decisions in literacy assessment and curriculum development and could inform rapid educational adaptation to changes in the literacy environment. The paper examines the methodological basis for investigating literacy values and its potential to inform cross-cultural literacy assessments. The argument is illustrated with primary data from Mozambique. The correlation between individual values and respondents’ socio-economic and demographic characteristics is explored
Used-habitat calibration plots: a new procedure for validating species distribution, resource selection, and step-selection models
“Species distribution modeling” was recently ranked as one of the top five “research fronts” in ecology and the environmental sciences by ISI's Essential Science Indicators (Renner and Warton 2013), reflecting the importance of predicting how species distributions will respond to anthropogenic change. Unfortunately, species distribution models (SDMs) often perform poorly when applied to novel environments. Compounding on this problem is the shortage of methods for evaluating SDMs (hence, we may be getting our predictions wrong and not even know it). Traditional methods for validating SDMs quantify a model's ability to classify locations as used or unused. Instead, we propose to focus on how well SDMs can predict the characteristics of used locations. This subtle shift in viewpoint leads to a more natural and informative evaluation and validation of models across the entire spectrum of SDMs. Through a series of examples, we show how simple graphical methods can help with three fundamental challenges of habitat modeling: identifying missing covariates, non-linearity, and multicollinearity. Identifying habitat characteristics that are not well-predicted by the model can provide insights into variables affecting the distribution of species, suggest appropriate model modifications, and ultimately improve the reliability and generality of conservation and management recommendations
Construction and Measurements of an Improved Vacuum-Swing-Adsorption Radon-Mitigation System
In order to reduce backgrounds from radon-daughter plate-out onto detector
surfaces, an ultra-low-radon cleanroom is being commissioned at the South
Dakota School of Mines and Technology. An improved vacuum-swing-adsorption
radon mitigation system and cleanroom build upon a previous design implemented
at Syracuse University that achieved radon levels of
0.2Bqm. This improved system will employ a better pump and
larger carbon beds feeding a redesigned cleanroom with an internal HVAC unit
and aged water for humidification. With the rebuilt (original) radon mitigation
system, the new low-radon cleanroom has already achieved a 300
reduction from an input activity of Bqm to a
cleanroom activity of Bqm.Comment: 5 pages, 4 figures, Proceedings of Low Radioactivity Techniques (LRT)
2015, Seattle, WA, March 18-20, 201
Thermally stimulated H emission and diffusion in hydrogenated amorphous silicon
We report first principles ab initio density functional calculations of
hydrogen dynam- ics in hydrogenated amorphous silicon. Thermal motion of the
host Si atoms drives H diffusion, as we demonstrate by direct simulation and
explain with simple models. Si-Si bond centers and Si ring centers are local
energy minima as expected. We also describe a new mechanism for break- ing Si-H
bonds to release free atomic H into the network: a fluctuation bond center
detachment (FBCD) assisted diffusion. H dynamics in a-Si:H is dominated by
structural fluctuations intrinsic to the amorphous phase not present in the
crystal.Comment: 4 pages, 5 figures, In press EPL (Jun. 2007
Ab initio estimate of temperature dependence of electrical conductivity in a model amorphous material: hydrogenated amorphous silicon
We present an ab initio calculation of the DC conductivity of amorphous
silicon and hydrogenated amorphous silicon. The Kubo-Greenwood formula is used
to obtain the DC conductivity, by thermal averaging over extended dynamical
simulation. Its application to disordered solids is discussed. The conductivity
is computed for a wide range of temperatures and doping is explored in a naive
way by shifting the Fermi level. We observed the Meyer-Neldel rule for the
electrical conductivity with E_MNR = 0.06 eV and a temperature coefficient of
resistance, TCR ~ -2.0% K^-1 for a-Si:H. In general, experimental trends are
reproduced by these calculations, and this suggests the possible utility of the
approach for modeling carrier transport in other disordered systems.Comment: 9 pages, 8 figures, submitted to PRB Comments: corrected typos,
referee's comments include
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