27,274 research outputs found
Environmental aspects of soil phosphorus testing
peer-reviewedSoil phosphorus testing in Ireland uses Morgan’s reagent from samples taken to 10 cm
depth for agronomic recommendations. However, its suitability as an environmental
indicator has been questioned in terms of sample depth and extraction solution. Seven
grassland sites were sampled to depths of 2, 5 and 10 cm and extracted for Morgan’s
P, the standard agronomic test, as well as iron-oxide impregnated paper strip P (FeOP),
calcium chloride extractable P (CaCl2-P) and water soluble P (WSP), all proposed
as environmental soil tests. Extractable soil P decreased with increasing sample depth,
as did variances in each test, such that, 2 cm samples had highest concentrations and
variances. The current standard sample depth (10 cm) was linearly related to corresponding
data from samples taken to 2 and 5 cm, indicating that surface soil P can be
consistently estimated from the current standard depth. When soil tests were compared
with dissolved reactive P (DRP) in overland flow collected from two field sites,
certain soil tests were better indicators of P loss than others. The relative difference in
Morgan’s P values at the standard sample depth (10 cm) was reflected in the relative
difference in P loss between the two sites. Average values of DRP collected from two
sites ranged from 0.032 to 0.067 mg/l at the low P site and 0.261 to 0.620 at the high P
site. Average DRP values from the high P site and maximum DRP values from the low
P site were simulated using water-soluble P extraction at water to soil ratios 5 to 250
l/kg. In this study, Morgan’s P to 10 cm gave a good indication of the relative difference in DRP loss between the two sites
A Quantitative Analysis of Suburbanization and the Diffusion of the Automobile
Suburbanization in the U.S. between 1910 and 1970 was concurrent with the rapid diffusion of the automobile. A circular city model is developed in order to access quantitatively the contribution of automobiles and rising incomes to suburbanization. The model incorporates a number of driving forces of suburbanization and car adoption, including falling automobile prices, rising real incomes, changing costs of traveling by car and with public transportation, and urban population growth. According to the model, 60 percent of postwar (1940-1970) suburbanization can be explained by these factors. Rising real incomes and falling automobile prices are shown to be the key drivers of suburbanization.automobile; suburbanization; population density gradients; technological progress
Finite State Markov-Chain Approximations to Highly Persistent Processes
This paper re-examines the Rouwenhorst method of approximating first-order autoregressive processes. This method is appealing because it can match the conditional and unconditional mean, the conditional and unconditional variance and the first-order autocorrelation of any AR(1) process. This paper provides the first formal proof of this and other results. When comparing to five other methods, the Rouwenhorst method has the best performance in approximating the business cycle moments generated by the stochastic growth model. In addition, when the Rouwenhorst method is used, moments computed directly off the stationary distribution are as accurate as those obtained using Monte Carlo simulations.Numerical Methods; Finite State Approximations; Optimal Growth Model
Quantum correlations in nanostructured two-impurity Kondo systems
We study the ground-state entanglement properties of nanostructured Kondo
systems consisting of a pair of impurity spins coupled to a background of
confined electrons. The competition between the RKKY-like coupling and the
Kondo effect determines the development of quantum correlations between the
different parts of the system. A key element is the electronic filling due to
confinement. An even electronic filling leads to results similar to those found
previously for extended systems, where the properties of the reduced
impurity-spin subsystem are uniquely determined by the spin correlation
function defining a one-dimensional phase space. An odd filling, instead,
breaks spin-rotation symmetry unfolding a two-dimensional phase space showing
rich entanglement characteristics as, e.g., the requirement of a larger amount
of entanglement for the development of non-local correlations between impurity
spins. We check these results by numerical simulations of elliptic quantum
corrals with magnetic impurities at the foci as a case study.Comment: Submitted for publication. 8 pages, 4 figures. Revised versio
Recommended from our members
Pursuing Energy-Efficient Behavior in a Regulatory Environment: Motivating Policymakers, Program Administrators, and Program Implementers
This white paper examines how policymakers, program administrators, and program implementers can be motivated to pursue behavioral change in a regulatory environment. For the purposes of this report, behavior change is defined rather broadly, encompassing both behaviors associated with the purchase and installation of energy efficiency technologies as well as behaviors, decisions, and actions that might be thought of as more independent of technology. These include energy use habits, lifestyle choices, and consumption patterns. The insights and lessons discussed in this paper are drawn from a wide variety of sources including interviews with representatives from the energy and utility communities, and program documentation for energy-related programs and projects
A Quantitative Analysis of Suburbanization and the Diffusion of the Automobile
Suburbanization in the U.S. between 1910 and 1970 was concurrent with the rapid diffusion of the automobile. A circular city model is developed in order to access quantitatively the contribution of automobiles and rising incomes to suburbanization. The model incorporates a number of driving forces of suburbanization and car adoption, including falling automobile prices, rising real incomes, changing costs of traveling by car and with public transportation, and urban population growth. According to the model, 60 percent of postwar (1940-1970) suburbanization can be explained by these factors. Rising real incomes and falling automobile prices are shown to be the key drivers of suburbanization.automobile; suburbanization; population density gradients; technological progress
Finite State Markov-Chain Approximations to Highly Persistent Processes
This paper re-examines the Rouwenhorst method of approximating first-order autoregressive processes. This method is appealing because it can match the conditional and unconditional mean, the conditional and unconditional variance and the first-order autocorrelation of any AR(1) process. This paper provides the first formal proof of this and other results. When comparing to five other methods, the Rouwenhorst method has the best performance in approximating the business cycle moments generated by the stochastic growth model. It is shown that, equipped with the Rouwenhorst method, an alternative approach to generating these moments has a higher degree of accuracy than the simulation method.Numerical Methods; Finite State Approximations; Optimal Growth Model
- …