2,584 research outputs found
Depletion of Available Potassium Nutrient with Changes in Clay Mineralogy During Pedogenesis of ASS Landscapes
Structure and lattice dynamics of the wide band gap semiconductors MgSiN and MgGeN
We have determined the structural and lattice dynamical properties of the
orthorhombic, wide band gap semiconductors MgSiN and MgGeN using
density functional theory. In addition, we present structural properties and
Raman spectra of a MgSiN powder. The structural properties and lattice
dynamics of the orthorhombic systems are compared to wurtzite AlN. We find
clear differences in the lattice dynamics between MgSiN, MgGeN and
AlN, for example we find that the highest phonon frequency in MgSiN is
about 100~cm higher than the highest frequency in AlN and that
MgGeN is much softer. We also provide the Born effective charge tensors
and dielectric tensors of MgSiN, MgGeN and AlN. Phonon related
thermodynamic properties, such as the heat capacity and entropy, are in very
good agreement with available experimental results.Comment: 9 pages, 11 figures, 6 table
Demand Uncertainty and the Regulated Firm
[Introduction] In this paper, we investigate the impact of demand uncertainty on the choice of plant capacity by a regulated firm. Over the past few years, demand uncertainty has become a major element in the decision-making of utilities, and particularly in their decision-making with respect to capacity choices. In a recent study by SRI [1977], it was reported that to maximize expected consumers' surplus, more generating capacity was required for the electric utility industry when operating under demand uncertainty than under demand certainty.1 This finding raises
the question whether the structure of rate regulation of electric utilities provides
the appropriate incentives for them to invest in more capacity under demand
uncertainty then under certainty. The present paper addresses such questions
Wetland mapping from digitized aerial photography
Computer assisted interpretation of small scale aerial imagery was found to be a cost effective and accurate method of mapping complex vegetation patterns if high resolution information is desired. This type of technique is suited for problems such as monitoring changes in species composition due to environmental factors and is a feasible method of monitoring and mapping large areas of wetlands. The technique has the added advantage of being in a computer compatible form which can be transformed into any georeference system of interest
Demand Uncertainty and the Regulated Firm
Demand uncertainty is an important element of many regulated markets. Firms often must select plant size before actual demand is observed, and with some expectation of regulatory action if the actual levels of profit or rate of return do not fall within accepted ranges.
We analyze a model of a regulated firm that faces a relatively complex regime of price regulation, reflecting to at least some extent the multiple aspects suggested by Joskow (1974). The firm behaves as though it expects the current tariff to remain in effect unless, at the actual demand observed after plant size is chosen, one of two things occurs. First, if profits are negative, the firm plans to petition for and expects to receive a new tariff yielding zero economic profits. Second, if the rate of return on capital exceeds some specified maximum, the firm expects the regulator to reduce the tariff so that the firm earns only that maximum
Modelling the evolution of distributions : an application to major league baseball
We develop Bayesian techniques for modelling the evolution of entire distributions over time and apply them to the distribution of team performance in Major League baseball for the period 1901-2000. Such models offer insight into many key issues (e.g. competitive balance) in a way that regression-based models cannot. The models involve discretizing the distribution and then modelling the evolution of the bins over time through transition probability matrices. We allow for these matrices to vary over time and across teams. We find that, with one exception, the transition probability matrices (and, hence, competitive balance) have been remarkably constant across time and over teams. The one exception is the Yankees, who have outperformed all other teams
Numerical experiments on short-term meteorological effects on solar variability
A set of numerical experiments was conducted to test the short-range sensitivity of a large atmospheric general circulation model to changes in solar constant and ozone amount. On the basis of the results of 12-day sets of integrations with very large variations in these parameters, it is concluded that realistic variations would produce insignificant meteorological effects. Any causal relationships between solar variability and weather, for time scales of two weeks or less, rely upon changes in parameters other than solar constant or ozone amounts, or upon mechanisms not yet incorporated in the model
A parallel adaptive mesh refinement algorithm
Over recent years, Adaptive Mesh Refinement (AMR) algorithms which dynamically match the local resolution of the computational grid to the numerical solution being sought have emerged as powerful tools for solving problems that contain disparate length and time scales. In particular, several workers have demonstrated the effectiveness of employing an adaptive, block-structured hierarchical grid system for simulations of complex shock wave phenomena. Unfortunately, from the parallel algorithm developer's viewpoint, this class of scheme is quite involved; these schemes cannot be distilled down to a small kernel upon which various parallelizing strategies may be tested. However, because of their block-structured nature such schemes are inherently parallel, so all is not lost. In this paper we describe the method by which Quirk's AMR algorithm has been parallelized. This method is built upon just a few simple message passing routines and so it may be implemented across a broad class of MIMD machines. Moreover, the method of parallelization is such that the original serial code is left virtually intact, and so we are left with just a single product to support. The importance of this fact should not be underestimated given the size and complexity of the original algorithm
Experiences influencing walking football initiation in 55-75 year-old adults
Adults aged 55 and older are least likely to play sport. Despite research suggesting this population experiences physical and psychological benefits when doing so, limited research focuses on older adult sport initiation, especially in “adapted sports” such as walking football. The aim of this study was to explore initiation experiences of walking football players between 55 and 75 years old. Semistructured interviews took place with 17 older adults playing walking football for 6 months minimum ( Mage = 64). Inductive analysis revealed six higher order themes representing preinitiation influences. Eight further higher order themes were found, relating to positive and negative experiences during initiation. Fundamental influences preinitiation included previous sporting experiences and values and perceptions. Emergent positive experiences during initiation included mental development and social connections. Findings highlight important individual and social influences when initiating walking football, which should be considered when encouraging 55- to 75-year-old adults to play adapted sport. Policy and practice recommendations are discussed
Ignition of thermally sensitive explosives between a contact surface and a shock
The dynamics of ignition between a contact surface and a shock wave is investigated using a
one-step reaction model with Arrhenius kinetics. Both large activation energy asymptotics and
high-resolution finite activation energy numerical simulations are employed. Emphasis is on comparing
and contrasting the solutions with those of the ignition process between a piston and a shock,
considered previously. The large activation energy asymptotic solutions are found to be qualitatively
different from the piston driven shock case, in that thermal runaway first occurs ahead of
the contact surface, and both forward and backward moving reaction waves emerge. These waves
take the form of quasi-steady weak detonations that may later transition into strong detonation
waves. For the finite activation energies considered in the numerical simulations, the results are
qualitatively different to the asymptotic predictions in that no backward weak detonation wave
forms, and there is only a weak dependence of the evolutionary events on the acoustic impedance
of the contact surface. The above conclusions are relevant to gas phase equation of state models.
However, when a large polytropic index more representative of condensed phase explosives is used,
the large activation energy asymptotic and finite activation energy numerical results are found to
be in quantitative agreement
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