Useful Estimate (useful + estimate)

Distribution by Scientific Domains

Selected Abstracts

A note on estimating urban roof runoff with a forest evaporation model

J. H. C. Gash
Abstract A model developed for estimating the evaporation of rainfall intercepted by forest canopies is applied to estimate measurements of the average runoff from the roofs of six houses made in a previous study of hydrological processes in an urban environment. The model is applied using values of the mean rates of wet canopy evaporation and rainfall derived previously for forests and an estimate of the roof storage capacity derived from the data collected in the previous study. Although the model prediction is sensitive to the value of storage capacity, close correlation between the modelled and measured runoff indicates that the model captures the essential processes. It is concluded that the process of evaporation from an urban roof is sufficiently similar to that from a forest canopy for forest evaporation models to be used to give a useful estimate of urban roof runoff. Copyright 2007 John Wiley & Sons, Ltd. [source]

Historical instrumental climate data for Australia,quality and utility for palaeoclimatic studies,

Neville Nicholls
Abstract The quality and availability of climate data suitable for palaeoclimatic calibration and verification for the Australian region are discussed and documented. Details of the various datasets, including problems with the data, are presented. High-quality datasets, where such problems are reduced or even eliminated, are discussed. Many climate datasets are now analysed onto grids, facilitating the preparation of regional-average time series. Work is under way to produce such high-quality, gridded datasets for a variety of hitherto unavailable climate data, including surface humidity, pan evaporation, wind, and cloud. An experiment suggests that only a relatively small number of palaeoclimatic time series could provide a useful estimate of long-term changes in Australian annual average temperature. Copyright 2006 John Wiley & Sons, Ltd. [source]

What controls the C iv line profile in active galactic nuclei?

Alexei Baskin
ABSTRACT The high-ionization lines in active galactic nuclei (AGN), such as C iv, tend to be blueshifted with respect to the lower-ionization lines, such as H,, and often show a strong blue excess asymmetry not seen in the low-ionization lines. There is accumulating evidence that the H, profile is dominated by gravity, and thus provides a useful estimate of the black hole mass in AGN. The shift and asymmetry commonly seen in C iv suggest that non-gravitational effects, such as obscuration and radiation pressure, may affect the line profile. We explore the relation between the H, and C iv profiles using the ultraviolet (UV) spectra available for 81 of the 87 z, 0.5 PG quasars in the Boroson & Green sample. We find the following. (1) Narrow C iv lines (full width at half-maximum, FWHM < 2000 km s,1) are rare (,2 per cent occurrence rate) compared with narrow H, lines (,20 per cent). (2) In most objects where the H, FWHM < 4000 km s,1 the C iv line is broader than H,, but the reverse is true when the H, FWHM > 4000 km s,1. This argues against the view that C iv generally originates closer to the centre, compared with H,. (3) C iv appears to provide a significantly less accurate, and possibly biased estimate of the black hole mass in AGN, compared with H,. (4) All objects where C iv is strongly blueshifted and asymmetric have a high L/LEdd, but the reverse is not true. This suggests that a high L/LEdd is a necessary but not sufficient condition for generating a blueshifted asymmetric C iv emission. (5) We also find indications for dust reddening and scattering in ,normal' AGN. In particular, PG quasars with a redder optical,UV continuum slope show weaker C iv emission, stronger C iv absorption and a higher optical continuum polarization. [source]

Pupillary reflex dilation and skin temperature to assess sensory level during combined general and caudal anesthesia in children,

John Emery MBBS, frca
Summary Background:, Regional anesthesia causes sympathetic blockade, vasodilation and higher skin temperature in anesthetized dermatomes. Measurement of skin temperature changes might provide a useful estimate of the level of caudal anesthesia in children. Pupillary reflex dilation (PRD) allows estimation of the sensory level during combined general/epidural anesthesia in adults, but has not been assessed in children. This study was designed to evaluate skin temperature and PRD as methods of estimating sensory level in children receiving combined general/caudal epidural anesthesia. Methods:, Twenty ASA I and II children aged 10 months,5 years were enrolled. Anesthesia was induced with sevoflurane and N2O in O2 and maintained with 1 MAC isoflurane and air in O2. Caudal epidural anesthesia was achieved by injection of 1 mlkg,1 0.25% bupivacaine. Skin temperature was measured by rapid response infrared thermometry. PRD was measured using an ophthalmic ultrasound biomicroscope (UBM). The three criteria used to estimate sensory level were a drop in skin temperature of 0.5C between dermatomes, PRD of 50% and PRD of 0.2 mm. Results:, A drop in skin temperature of 0.5C between dermatomes allowed estimation of the sensory level in only 20% of patients. PRD of 50%, and PRD of 0.2 mm allowed estimation of the sensory level in 45 and 100% of patients, respectively. PRD was significantly greater above the T10 dermatome compared with L2 (P < 0.01). The maximum pupillary dilation was significantly greater in children over 2 years of age [1.3 0.8 mm sd)] compared with children less than two years of age [0.6 0.3 mm sd)]. Conclusions:, Skin temperature cannot be used to estimate sensory level during combined general/caudal epidural anesthesia. PRD of 0.2 mm is sensitive to the loss of analgesia but is not clinically useful. PRD may be useful above 2 years of age. [source]

Identifying the time of polynomial drift in the mean of autocorrelated processes

Marcus B. Perry
Abstract Control charts are used to detect changes in a process. Once a change is detected, knowledge of the change point would simplify the search for and identification of the special ause. Consequently, having an estimate of the process change point following a control chart signal would be useful to process engineers. This paper addresses change point estimation for covariance-stationary autocorrelated processes where the mean drifts deterministically with time. For example, the mean of a chemical process might drift linearly over time as a result of a constant pressure leak. The goal of this paper is to derive and evaluate an MLE for the time of polynomial drift in the mean of autocorrelated processes. It is assumed that the behavior in the process mean over time is adequately modeled by the kth-order polynomial trend model. Further, it is assumed that the autocorrelation structure is adequately modeled by the general (stationary and invertible) mixed autoregressive-moving-average model. The estimator is intended to be applied to data obtained following a genuine control chart signal in efforts to help pinpoint the root cause of process change. Application of the estimator is demonstrated using a simulated data set. The performance of the estimator is evaluated through Monte Carlo simulation studies for the k=1 case and across several processes yielding various levels of positive autocorrelation. Results suggest that the proposed estimator provides process engineers with an accurate and useful estimate for the last sample obtained from the unchanged process. Copyright 2009 John Wiley & Sons, Ltd. [source]

The use of renal scintigraphy in assessing the potential for recovery in the obstructed renal tract in children

A. Thompson
Objective To assess the value of renal scintigraphy with 99mTc-dimercaptosuccinic acid (DMSA) in predicting functional recovery after the surgical relief of obstructed kidneys in children. Patients and methods Forty-three children underwent surgery to relieve upper urinary tract obstruction; 37 had pelvi-ureteric junction obstruction and six had vesico-ureteric junction obstruction. The indication for surgery was a combination of an obstructed renogram with symptoms of either pain or pyelonephritis. Most children (41) had < 40% function on the affected side before surgery, with just two having hyperfunction (> 55%). In all patients intravenous urography before surgery showed hydronephrosis, and a micturating cystogram was used to exclude coexisting reflux in the presence of an associated megaureter. Diuretic renography (using 99mTc-mercaptoacetyl triglycine or 123I-hippuran) and DMSA scintigraphy were both carried out before surgery and the renography repeated 6 months afterward. Results The renographic drainage curves improved from obstructed to unobstructed or ,dilated unobstructed' on all postoperative studies. Regression analysis showed that preoperative DMSA scan was an excellent predictor of outcome (P < 0.001) whilst the preoperative renogram was a relatively poor predictor of the functional result. In four patients where the initial renographic function was < 10%, DMSA scintigraphy predicted correctly the capacity for recovery in three and the inability to improve in the fourth. Conclusion Before surgery, DMSA scintigraphy in children with upper urinary tract obstruction is a more useful estimate of probable long-term renal function than value from diuresis renography. If there is doubt about the desirability of reconstructive surgery, a DMSA scan may eliminate the need for more invasive methods of estimating recovery, e.g. a period of nephrostomy drainage. [source]

Estimating Human Inbreeding Coefficients: Comparison of Genealogical and Marker Heterozygosity Approaches

A. D. Carothers
Summary We have used genealogies and genomic polymorphisms to estimate individual inbreeding coefficients (F) in 50 subjects with an expected range (based on recent genealogies) of F from 0.0 to 0.0625. The estimates were based on two approaches, using genotypes respectively from 410 microsatellite markers (410-STR panel) and from 10,000 SNPs (10K-SNP panel). The latter was performed in a sub-sample of 15 individuals. We concluded that for both marker panels measures of inbreeding based on the excess of homozygosity over Hardy-Weinberg expectation were not closely correlated with 4-5 generation genealogical F- values. For the 10K-SNP panel we found two alternative measures which correlated more closely with F, based respectively on standard errors and on paired homozygosity of nearby SNPs over distances of 2-4 cM. We propose an empirical method for estimating standard errors and hence individual F- values, based on the variation between individual autosomes. This method could provide useful estimates of average F- values for groups of individuals in population-based studies of the effects of inbreeding/homozygosity on quantitative traits. [source]

Bayesian Detection and Modeling of Spatial Disease Clustering

BIOMETRICS, Issue 3 2000
Ronald E. Gangnon
Summary. Many current statistical methods for disease clustering studies are based on a hypothesis testing paradigm. These methods typically do not produce useful estimates of disease rates or cluster risks. In this paper, we develop a Bayesian procedure for drawing inferences about specific models for spatial clustering. The proposed methodology incorporates ideas from image analysis, from Bayesian model averaging, and from model selection. With our approach, we obtain estimates for disease rates and allow for greater flexibility in both the type of clusters and the number of clusters that may be considered. We illustrate the proposed procedure through simulation studies and an analysis of the well-known New York leukemia data. [source]

On Nonexistence of type II blowup for a supercritical nonlinear heat equation

Hiroshi Matano
In this paper we study blowup of radially symmetric solutions of the nonlinear heat equation ut = ,u + |u|p,1u either on ,N or on a finite ball under the Dirichlet boundary conditions. We assume that the exponent p is supercritical in the Sobolev sense, that is, We prove that if ps < p < p*, then blowup is always of type I, where p* is a certain (explicitly given) positive number. More precisely, the rate of blowup in the L, norm is always the same as that for the corresponding ODE dv/dt = |v|p,1v. Because it is known that "type II" blowup (or, equivalently, "fast blowup") can occur if p > p*, the above range of exponent p is optimal. We will also derive various fundamental estimates for blowup that hold for any p > ps and regardless of type of blowup. Among other things we classify local profiles of type I and type II blowups in the rescaled coordinates. We then establish useful estimates for the so-called incomplete blowup, which reveal that incomplete blowup solutions belong to nice function spaces even after the blowup time. 2004 Wiley Periodicals, Inc. [source]