851 research outputs found

    Prediction of water temperature metrics using spatial modelling in the Eastern and Western Cape, South Africa

    Get PDF
    Key aspects of a river's temperature regime are described by magnitudes, timing and durations of thermal events, and frequencies of extreme exceedance events. To understand alterations to thermal regimes, it is necessary to describe thermal time series based on these statistics. Classification of sites based on their thermal metrics, and understanding of spatial patterns of these thermal statistics, provides a powerful approach for comparing study sites against reference sites. Water temperature regime dynamics should be viewed regionally, where regional divisions have an inherent underpinning by an understanding of natural thermal variability. The aim of this research was to link key water temperature metrics to readily-mapped environmental surrogates, and to produce spatial images of temperature metrics: 37 temperature metrics were derived for 12 months of sub-daily water temperatures at 90 sites in the Eastern Cape and Western Cape provinces, South Africa. These metrics were correlated with 16 environmental variables. Correlations enabled development of multiple regression models which facilitated mapping of temperature metrics over the study area. This approach has the potential to be applied at a national scale as more thermal time series are collected nationally. It is argued that the appropriateness of management decisions in rivers can be improved by including guidelines for thermal metrics at a regional scale. Such maps could facilitate incorporation of a temperature component into management guidelines for water resources

    Rodents as receptor species at a tritium

    Get PDF
    New methods are being employed on the Department of Energy’s Savannah River Site to deal with the disposal of tritium, including the irrigation of a hardwood/pine forest with tritiated water from an intercepted contaminant plume to reduce concentrations of tritium outcropping into Fourmile Branch, a tributary of the Savannah River. The use of this system has proven to be an effective means of tritium disposal. To evaluate the impact of this activity on terrestrial biota, rodent species were captured on the tritium disposal site and a control site during two trapping seasons in order to assess tritium exposure resulting from the forest irrigation. Control site mice had background levels of tritium, 0.02 Bq/mL, with disposal site mice having significantly higher tritium concentrations, meanZ34.86 Bq/mL. Whole body tritium concentrations of the mice captured at the disposal site were positively correlated with tritium application and negatively correlated with precipitation at the site

    The stagnation point von K\'arm\'an coefficient

    Full text link
    On the basis of various DNS of turbulent channel flows the following picture is proposed. (i) At a height y from the y = 0 wall, the Taylor microscale \lambda is proportional to the average distance l_s between stagnation points of the fluctuating velocity field, i.e. \lambda(y) = B_1 l_s(y) with B_1 constant, for \delta_\nu << y \lesssim \delta. (ii) The number density n_s of stagnation points varies with height according to n_s = C_s y_+^{-1} / \delta_\nu^3 where C_s is constant in the range \delta_\nu << y \lesssim \delta. (iii) In that same range, the kinetic energy dissipation rate per unit mass, \epsilon = 2/3 E_+ u_\tau^3 / (\kappa_s y) where E_+ is the total kinetic energy per unit mass normalised by u_\tau^2 and \kappa_s = B_1^2 / C_s is the stagnation point von K\'arm\'an coefficient. (iv) In the limit of exceedingly large Re_\tau, large enough for the production to balance dissipation locally and for - ~ u_\tau^2 in the range \delta_\nu << y << \delta, dU_+/dy ~ 2/3 E_+/(\kappa_s y) in that same range. (v) The von K\'arm\'an coefficient \kappa is a meaningful and well-defined coefficient and the log-law holds only if E_+ is independent of y_+ and Re_\tau in that range, in which case \kappa ~ \kappa_s. The universality of \kappa_s = B_1^2 / C_s depends on the universality of the stagnation point structure of the turbulence via B_1 and C_s, which are conceivably not universal. (vi) DNS data of turbulent channel flows which include the highest currently available values of Re_\tau suggest E_+ ~ 2/3 B_4 y_+^{-2/15} and dU_+/dy_+ ~ B_4/(\kappa_s) y_+^{-1 - 2/15} with B_4 independent of y in \delta_\nu << y << \delta if the significant departure from - ~ u_\tau^2 is taken into account.Comment: 14 pages, 20 figures. This version of the article has been accepted for publication in PRE. Note though that the PRE paper format is differen

    Prediction of water temperature metrics using spatial modelling in the Eastern and Western Cape, South Africa

    Get PDF
    Key aspects of a river’s temperature regime are described by magnitudes, timing and durations of thermal events, and frequencies of extreme exceedance events. To understand alterations to thermal regimes, it is necessary to describe thermal time series based on these statistics. Classification of sites based on their thermal met-rics, and understanding of spatial patterns of these thermal statistics, provides a powerful approach for comparing study sites against reference sites. Water tem-perature regime dynamics should be viewed regionally, where regional divisions have an inherent underpinning by an understanding of natural thermal variability. The aim of this research was to link key water temperature metrics to readi-lymapped environmental surrogates, and to produce spatial images of temperature metrics: 37 temperature metrics were derived for 12 months of sub-daily water temperatures at 90 sites in the Eastern Cape and Western Cape provinces, South Africa

    Effects of Antihypertensive Medications on Quality of Life in Elderly Hypertensive Women

    Get PDF
    The impact of antihypertensive medications on the quality of life of elderly hypertensive women has rarely been systematically evaluated in large clinical trials using drugs from the new generations of pharmaceutic preparations. We carried out a multicenter, randomized double-blind clinical trial with 309 hypertensive women aged 60 to 80 years to assess effects of atenolol, enalapril, and isradipine on measures of quality of life over a 22-week period. The patients had mild to moderate hypertension. Hydrochlorothiazide was added to treatment if monotherapy was inadequate in lowering blood pressure. At the conclusion of the trial the three drug groups did not differ in degree of reduction of diastolic blood pressure or in supplementation with hydrochlorothiazide. Over the 22-week trial, linear trend analysis showed no differences between the treatment groups in change from baseline on quality of life measures of well-being, physical status, emotional status, cognitive functioning, and social role participation. Regarding each of 33 physical side effects over the 22 weeks, we found no general difference between atenolol, enalapril, and isradipine groups on measures of change in distress over symptoms except for enalapril patients who worsened in distress over cough (P = .001) and atenolol patients who worsened in distress over dry mouth (P = .014). Centering on three medications that are relatively new additions to the armamentarium for blood pressure control, the findings underline the increasing opportunities for the physician to select drugs that can control blood pressure while maintaining the quality of life of elderly hypertensive women

    Improvement of the Staggered Fermion Operators

    Get PDF
    We present a complete and detailed derivation of the finite lattice spacing corrections to staggered fermion matrix elements. Expanding upon arguments of Sharpe, we explicitly implement the Symanzik improvement program demonstrating the absence of order aa terms in the Symanzik improved action. We propose a general program to improve fermion operators to remove O(a)O(a) corrections from their matrix elements, and demonstrate this program for the examples of matrix elements of fermion bilinears and BKB_K. We find the former does have O(a)O(a) corrections while the latter does not.Comment: 16 pages, latex, 1 figur

    Au/TiO2(110) interfacial reconstruction stability from ab initio

    Full text link
    We determine the stability and properties of interfaces of low-index Au surfaces adhered to TiO2(110), using density functional theory energy density calculations. We consider Au(100) and Au(111) epitaxies on rutile TiO2(110) surface, as observed in experiments. For each epitaxy, we consider several different interfaces: Au(111)//TiO2(110) and Au(100)//TiO2(110), with and without bridging oxygen, Au(111) on 1x2 added-row TiO2(110) reconstruction, and Au(111) on a proposed 1x2 TiO reconstruction. The density functional theory energy density method computes the energy changes on each of the atoms while forming the interface, and evaluates the work of adhesion to determine the equilibrium interfacial structure.Comment: 20 pages, 11 figure
    • …
    corecore