柴油机富氧燃烧的试验研究

柴油设备在现代矿山中被广泛使用,其排出的碳烟、氮氧化物等污染物严重影响了井下的生产环境,甚至对井下工作人员的身体健康造成了威胁。该文在实验室环境下通过对柴油机进行富氧燃烧试验来研究柴油机的排放特性,寻找降低柴油机污染物排放的途径。该研究根据柴油机富氧燃烧的机理,设计了柴油机在不同工况下的富氧燃烧试验,对其在各不同工况下排出的碳烟、氮氧化物和一氧化碳进行了对比分析。试验结果表明:柴油机不论在何种工况下的富氧燃烧均可降低碳烟的排放;氮氧化物的排放会随着氧气的增加而上升;一氧化碳的排放也会有所降低,但降低的幅度不大。     

铋磷钼蓝光度法测定铁矿石中磷含量的不确定度评定

采用铋磷钼蓝光度法对铁矿石中磷进行测定,应用统计学理论对其分析结果不确定度的产生原因进行分析,建立测量过程分量的数学模型,分析测量过程不确定度来源及各不确定度分量对总不确定度的影响,确定测定结果的置信区间。给出铁矿石中磷的含量及其置信区间为0.0283%±0.0032%。     

Laboratory and analytical method performance of lead measurements in paint chips, soils, and dusts

The National Lead Laboratory Accreditation Program (NLLAP) recognizes laboratories capable of analyzing lead in paints, soils, and dusts. NLLAP requires successful participation in the Environmental Lead Proficiency Analytical Testing (ELPAT) program. For paint chip analyses, laboratory-to-laboratory variability is about 10% relative standard deviation (RSD) for lead levels near 0.5%, the HUD definition of lead-based paint. For soil analyses, RSDs are about 9 to 10% near relevant federal soil standards and 16% near the lowest state bare soil standard that currently exists. For dust wipe analyses, RSDs range from 10 to 16% for lead levels near relevant HUD standards. Of participating laboratories, 92 to 93% consistently meet ELPAT performance limits. A variety of analytical methods gives similar results. No conclusive significant differences were found among most frequently used hotplate and microwave sample preparation techniques. In addition, several participating laboratories have successfully used ultrasonic extraction methods, a method suitable for use at abatement sites. The three most frequently used instrumental techniques, flame atomic absorption (FAA), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and graphite furnace atomic absorption show no statistically significant differences in ability to meet ELPAT performance limits. However, small statistically significant biases between these methods sometimes occur. The magnitude of biases is less than 5% of the corresponding laboratory mean near relevant federal standards except for lead levels near the lowest HUD lead wipe standard, where biases can be as high as 8%. Other instrumental methods that have been used successfully include ICP-mass spectroscopy, direct current plasma-atomic emission spectroscopy, dithizone spectrophotometry, and anodic stripping voltametry.     

Estimating confidence intervals for cost-effectiveness ratios: an example from a randomized trial

Cost-effectiveness ratios usually appear as point estimates without confidence intervals, since the numerator and denominator are both stochastic and one cannot estimate the variance of the estimator exactly. The recent literature, however, stresses the importance of presenting confidence intervals for cost-effectiveness ratios in the analysis of health care programmes. This paper compares the use of several methods to obtain confidence intervals for the cost-effectiveness of a randomized intervention to increase the use of Medicaid's Early and Periodic Screening, Diagnosis and Treatment (EPSDT) programme. Comparisons of the intervals show that methods that account for skewness in the distribution of the ratio estimator may be substantially preferable in practice to methods that assume the cost-effectiveness ratio estimator is normally distributed. We show that non-parametric bootstrap methods that are mathematically less complex but computationally more rigorous result in confidence intervals that are similar to the intervals from a parametric method that adjusts for skewness in the distribution of the ratio. The analyses also show that the modest sample sizes needed to detect statistically significant effects in a randomized trial may result in confidence intervals for estimates of cost-effectiveness that are much wider than the boundaries obtained from deterministic sensitivity analyses.     

Seven zinc-finger transcription factors are expressed sequentially during the development of anthers in petunia

BACKGROUND: Little is known about the value of heart rate variability in patients with symptomatic coronary artery disease with a preserved left ventricular function. We hypothesized that in these patients heart rate variability might be a helpful adjunct to conventional parameters to predict clinical events. METHODS: In a prospective 2-year follow-up study ambulatory electrocardiographic recordings were performed in 263 consecutive male patients (mean age 56+/-8 years) with stable angina pectoris and a mean left ventricular ejection fraction of 71%+/-12%. Clinical events consisted mainly of coronary events such as percutaneous transluminal angioplasty or coronary artery bypass graft operation. RESULTS: Low measures of standard deviation of normal R-R intervals, standard deviation of the mean R-R intervals of 5 minutes, and two spectral components of heart rate variability were found in patients who had had an event compared with patients with no event. Adjusted for severity of angina, the presence of a previous myocardial infarction, and the use of beta-blockers in a logistic regression model this relation remained statistically significant for SDNN. Healthy volunteers appeared to have the highest measures of heart rate variability. CONCLUSION: In patients with ischemic heart disease and normal or near normal ventricular function decreased heart rate variability is associated with adverse clinical events.     

电感耦合等离子体原子发射光谱法测定低合金钢中硅含量的不确定度评定

采用电感耦合等离子体原子发射光谱法对低合金钢中硅进行测定,应用统计学理论对其分析结果不确定度的产生原因进行分析,建立测量过程分量的数学模型,分析测量过程不确定度来源及各不确定度分量对总不确定度的影响,确定测定结果的置信区间。给出低合金钢中硅的含量及其置信区间为0．472％±0．014％。     

电感耦合等离子体原子发射光谱法测定工业硅中11种成分的不确定度评定

采用电感耦合等离子体原子发射光谱法对工业硅中11种化学成分进行系统的不确定度分析,阐述了测定过程不确定度的主要来源,对各不确定度分量进行了量化计算,提出了量化过程所需各参数的采集和统计计算方法,得出合成标准不确定度、扩展不确定度及测定结果的置信区间。     

Parameter estimation and confidence intervals for Xe-CT ventilation studies: a Monte Carlo approach

Xenon-enhanced computed tomography (Xe-CT) is a technique for the noninvasive measurement of regional pulmonary ventilation from the washin and/or washout time constants of radiodense stable xenon gas, determined from serial computed tomography scans. Although the measurement itself is straightforward, there is a need for methods for the estimation of variability and confidence intervals so that the statistical significance of the information obtained may be evaluated, particularly since obtaining repeated measurements is often not practical. We present a Monte Carlo (MC) approach to determine the 95% confidence interval (CI) for any given measurement. This MC method was characterized in terms of its unbiasedness and coverage of the CI. In addition, 10 identical Xe-CT ventilation runs were performed in an anesthetized dog, and the time constant was determined for several regions of varying size in each run. The 95% CI, estimated from these repeated measurements as the mean +/- 2 x SE, compared favorably with the CI obtained by the MC approach. Finally, a simulation was performed to compare the performance of three imaging protocols in estimating model parameters.     

Prevention of parasitic infections (excluding toxoplasmosis) in immunocompromised patients

Fracture frequency was studied in 107 hypopituitary patients with GH deficiency (GHD) (69 men, mean age 53 years, range 18-74 and 38 women, mean age 54 years, range 31-73). Routine hormonal replacement therapy was given, except GH. Five male patients and 15 female patients with untreated hypogonadism were allocated to a separate group. The mean duration of hypopituitarism was 13.4 years. The prevalence of a history of fractures was assessed using questionnaires. A subsample of the G?teborg WHO MONICA Project was used as a reference population (n = 323). The total fracture frequency was threefold higher (P < 0.001) in patients (24.1%) compared with controls (8.7%) (odds ratio 3.49) (1.85-6.56; 95% confidence intervals). In men (n = 64) the fracture frequency was 25.0%, compared with 7.8% among the controls (P < 0.001). In women (n = 23) the fracture frequency was 21.7%, compared with 9.5% among the controls (P = 0.08). The odds ratios for fracture frequency were 3.97 (1.81-8.40; 95% confidence intervals) and 2.64 (0.89-7.81; 95% confidence intervals) in men and women respectively. In conclusion, adult hypopituitary patients with GHD had a threefold increased fracture frequency compared with controls. Further studies are needed to ascertain whether long-term recombinant human GH treatment can reduce the fracture rate in hypopituitary patients with GHD.     

Decision support issues using a physiology based score

OBJECTIVE: As physiology based assessments of mortality risk become more accurate, their potential utility in clinical decision support and resource rationing decisions increases. Before these prediction models can be used, however, their performance must be statistically evaluated and interpreted in a clinical context. We examine the issues of confidence intervals (as estimates of survival ranges) and confidence levels (as estimates of clinical certainty) by applying Pediatric Risk of Mortality III (PRISM III) in two scenarios: (1) survival prediction for individual patients and (2) resource rationing. DESIGN: A non-concurrent cohort study. SETTING: 32 pediatric intensive care units (PICUs). PATIENTS: 10608 consecutive patients (571 deaths). INTERVENTIONS: None. MEASUREMENTS AND RESULTS: For the individual patient application, we investigated the observed survival rates for patients with low survival predictions and the confidence intervals associated with these predictions. For the resource rationing application, we investigated the maximum error rate of a policy which would limit therapy for patients with scores exceeding a very high threshold. For both applications, we also investigated how the confidence intervals change as the confidence levels change. The observed survival in the PRISM III groups >28, >35, and >42 were 6.3, 5.3, and 0%, with 95% upper confidence interval bounds of 10.5, 13.0, and 13.3%, respectively. Changing the confidence level altered the survival range by more than 300% in the highest risk group, indicating the importance of clinical certainty provisions in prognostic estimates. The maximum error rates for resource allocation decisions were low (e. g., 29 per 100000 at a 95% certainty level), equivalent to many of the risks of daily living. Changes in confidence level had relatively little effect on this result. CONCLUSIONS: Predictions for an individual patient's risk of death with a high PRISM score are statistically not precise by virtue of the small number of patients in these groups and the resulting wide confidence intervals. Clinical certainty (confidence level) issues substantially influence outcome ranges for individual patients, directly affecting the utility of scores for individual patient use. However, sample sizes are sufficient for rationing decisions for many groups with higher certainty levels. Before there can be widespread acceptance of this type of decision support, physicians and families must confront what they believe is adequate certainty.     

Is the Meta-Analysis of Correlation Coefficients Accurate When Population Correlations Vary?

One conceptualization of meta-analysis is that studies within the meta-analysis are sampled from populations with mean effect sizes that vary (random-effects models). The consequences of not applying such models and the comparison of different methods have been hotly debated. A Monte Carlo study compared the efficacy of Hedges and Vevea's random-effects methods of meta-analysis with Hunter and Schmidt's, over a wide range of conditions, as the variability in population correlations increases. (a) The Hunter-Schmidt method produced estimates of the average correlation with the least error, although estimates from both methods were very accurate; (b) confidence intervals from Hunter and Schmidt's method were always slightly too narrow but became more accurate than those from Hedges and Vevea's method as the number of studies included in the meta-analysis, the size of the true correlation, and the variability of correlations increased; and (c) the study weights did not explain the differences between the methods. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of Methane Flux and Oxidation at a Solid Waste Landfill

Methane emissions were measured at several locations at a typical solid waste facility using a static chamber technique. At the entire facility, methane flux varied from ?13.6?to?1,755?g?m?2?day?1. The flux data had an arithmetic mean value of 71.3?g?m?2?day?1 and a geometric mean value of 18.6?g?m?2?day?1. At this site, methane emission was generally lower on the side slopes relative to the flat areas of the landfill. The spatial variability of methane flux was characterized by point kriging and inverse distance weighing (IDW) in an intensive study of a 61×61-m area. The geospatial means in this area obtained by both methods were almost identical (20.9 versus 20.8?g?m?2?day?1). These geospatial means for the area were also similar to the arithmetic mean (24.5?g?m?2?day?1), but 3.4 times the geometric mean (6.5?g?m?2?day?1). Methane oxidation was evaluated at the surface of the landfill and at several depths within the cover soil using stable isotope techniques. The δ?13C of CH4 averaged ?55.4% in the anoxic zone. Methane collected in chambers and in surficial soil probes exhibited more 13C enriched values, ranging from ?55.4 to ?34.5%, due to the preferential uptake of 12CH4 by methanotrophic bacteria. Methane oxidation at the landfill averaged 22% and occurred in the upper 70?cm of the landfill cover soil. Oxidation occurred in all tested locations of the landfill and for all ages of buried waste.     

Confidence intervals or surfaces? Uncertainty on the cost-effectiveness plane

Although cost-effectiveness analysis is not new, it is only recently that economic analysis has been conducted alongside clinical trials. Whereas in the past economic analysts most often used sensitivity analysis to examine the implications of uncertainty for their results, the existence of patient-level data on costs and effects opens up the possibility of statistical analysis of uncertainty. Unfortunately, ratio statistics can cause problems for standard statistical methods of confidence interval estimation. The recent health economics literature contains a number of suggestions for estimating confidence limits for ratios. In this paper, we begin by reviewing the different methods of confidence interval estimation with a view to providing guidance concerning the most appropriate method. We go on to argue that the focus on confidence interval estimation for cost-effectiveness ratios in the recent literature has been concerned more with problems of estimation than with problems of decision-making. We argue that decision-makers are most likely to be interested in one-sided tests of hypothesis and that confidence surfaces are better suited to such tests than confidence intervals. This approach is consistent with decision-making on the cost-effectiveness plane and with the cost-effectiveness acceptability curve approach to presenting uncertainty due to sampling variation in stochastic cost-effectiveness analyses.     

The continuing misinterpretation of the standard error of measurement.

Monographs, texts, and guides designed to inform readers about the meanings and interpretations of test scores frequently misinform instead, because the standard error of measurement is misapplied. The standard error of measurement, ??(1?-?r?I)?, is an estimate of the variability (i.e., the standard deviation) expected for observed scores when the true score is held constant. To set confidence intervals for true scores given an observed score, the appropriate standard error is that for true scores when observed scores are held constant and estimated by ??[r?I(1?-?r?I)]?; and the interval is around the estimated true score rather than around the observed score. Except in the case of perfect reliability, the estimated true score is not the observed score, but is a value regressed toward the mean. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Three-dimensional CT measurement of adult acetabular dysplasia: technique, preliminary results in normal subjects, and potential applications

OBJECTIVE: To assess a three-dimensional computed tomography (3DCT) technique for measurement of acetabular coverage in adults. DESIGN: We used 3DCT to define the geometric centre of the femoral head and to measure centre-edge angles (CEAs) at 10 degrees rotational increments around the acetabular rim. The means, ranges, standard deviations and 95% confidence intervals for the CEAs at the various rotational increments were determined. Inter- and intra-observer variability was measured. The normal values are compared with two example cases of acetabular dysplasia. PATIENTS: The normal hips of 15 subjects aged 1949 years (mean 34.2 years) were measured. RESULTS: The 3DCT measurements are reproducible (mean difference interobserver, 1.7 degrees - 7.9 degrees; mean difference intra-observer, 0.6 degrees-6.9 degrees). Mean normal CEA at the lateral rim was 33 degrees with a 95% confidence interval of 23 degrees - 43 degrees. Mean normal CEAs at 10 rotational increments from anterior to posterior rim were determined, and graphed as a 'normal curve'. CONCLUSION: This new 3DCT method of assessing acetabular dysplasia is simple, reproducible, and applicable to diagnosis, quantification and surgical planning for adult acetabular dysplasia patients.     

The importance of local control in the conservative treatment of breast cancer

The purpose of this study was to examine the meaning of local control, especially on survival, in breast cancer patients treated by lumpectomy with or without radiotherapy. We analyzed the survival results of four major published randomized trials that compare conservation surgery with or without radiation using three different statistical approaches: p-values, confidence intervals, and Bayesian techniques. All four trials report statistically significant increased local control and improved survival for the irradiated patients. Survival based on p-values and confidence intervals shows statistical significance for long-term follow-up of the NSABP-B06 trial, but not for the other trials, probably because of small sample sizes and short follow-up. At 10 years, the overall survival rates for the NSABP-B06 were 65% and 71% for lumpectomy alone or with radiation respectively. Interpreted in a Bayesian framework, the expected advantage in 10-year survival was 6% (the mean of NSABP-B06 10-year survival) with an 83% probability that the 10-year survival difference may lie between 2% and 10%. An 85% probability that 3% of patients will survive at 10 years because of irradiation translates into a 30% reduction in annual odds of death several years after treatment in stage I good prognosis patients and 15% in stage I poor prognosis patients. Analysis of the randomized trials comparing lumpectomy with or without radiation indicate a clear improvement in survival for the irradiated patients associated with increased local control. Combination of improved survival with the reduced psychological and economic costs associated with local recurrence argues well for the inclusion of radiation for many breast cancer patients.     

柴油机故障诊断的现状与展望

柴油机作为广泛使用的动力机械，其状态监测和故障诊断日益受到重视。总结了柴油机故障诊断的国内外现状；简述了柴油机故障诊断的主要方法；分析了柴油机故障诊断的难点；指出了柴油机故障诊断的发展趋势     

Assessing the Impacts of Nutrient Load Uncertainties on Predicted Truckee River Water Quality

This study examined the effects of uncertain model boundary conditions on dissolved oxygen (DO) predictions for the lower Truckee River, Nevada using an augmented version of the EPA’s Water Quality Analysis Simulation Program Version 5 (WASP5) that included periphyton, or attached algae, in eutrophication kinetics. Uncertainty analyses were performed on selected organic nitrogen (ON) and carbonaceous biochemical oxygen demand boundary conditions using Monte Carlo techniques. The stochastic model was run using boundary concentrations assigned from observed probability distributions. Ranges of simulated values were used to construct confidence intervals, the magnitudes of which indicated the uncertainty associated with model predictions. Uncertainty in agricultural ditch return concentrations had minimal effects on in-stream model predictions, as predicted values of daily minimum and maximum DOs, daily average ON, and periphyton biomass all failed to show significant variability as a result of ditch concentration uncertainty. This result indicates that while ditch return nutrient loads are not trivial, their exact concentrations are not needed to make relatively accurate predictions of in-stream DO. However, uncertainty in the upstream ON boundary did result in significant uncertainty during summer months with regard to in-stream model predictions of ON, periphyton biomass, and DO. The model is clearly more sensitive to changes in this boundary than to changes in agricultural ditch concentrations.     

Asymptotically distribution-free (ADF) interval estimation of coefficient alpha.

[Correction Notice: An erratum for this article was reported in Vol 12(4) of Psychological Methods (see record 2007-18729-004). The sentence describing Equation 1 is incorrect. The corrected sentence is presented in the erratum.] The point estimate of sample coefficient alpha may provide a misleading impression of the reliability of the test score. Because sample coefficient alpha is consistently biased downward, it is more likely to yield a misleading impression of poor reliability. The magnitude of the bias is greatest precisely when the variability of sample alpha is greatest (small population reliability and small sample size). Taking into account the variability of sample alpha with an interval estimator may lead to retaining reliable tests that would be otherwise rejected. Here, the authors performed simulation studies to investigate the behavior of asymptotically distribution-free (ADF) versus normal-theory interval estimators of coefficient alpha under varied conditions. Normal-theory intervals were found to be less accurate when item skewness >1 or excess kurtosis >1. For sample sizes over 100 observations, ADF intervals are preferable, regardless of item skewness and kurtosis. A formula for computing ADF confidence intervals for coefficient alpha for tests of any size is provided, along with its implementation as an SAS macro. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of hemodynamic parameters derived from transthoracic electrical bioimpedance with those parameters obtained by thermodilution and ventricular angiography

OBJECTIVE: To determine the limits of agreement between the cardiac output and volumetric data estimated by impedance cardiography with the cardiac output determined by thermodilution and the left ventricular ejection fraction and end-diastolic volume estimated from left ventriculography. DESIGN: A prospective study. SETTING: The cardiac catheterization laboratory of a university-affiliated teaching hospital. PATIENTS: Twenty-four patients with coronary artery disease undergoing elective left- and right heart catheterization. INTERVENTIONS: Cardiac output was measured by the thermodilution method and the ejection fraction and left ventricular volumetric data were determined by ventriculography. These same measurements were obtained by simultaneously performed impedance cardiography using a commercially available bioimpedance device. MEASUREMENTS AND MAIN RESULTS: The patients' mean cardiac output was 4.6 +/- 1.7 L/min by bioimpedance and 5.0 +/- 1.1 L/min by thermodilution. The limits of agreement between the two methods was -4.1 to 3.5 L/min. The 95% confidence intervals for the lower and upper limits of agreement were -2.7 to -5.5 L/min and 2.1 to 4.9 L/min, respectively. The mean ejection fraction was 63 +/- 8% by bioimpedance and 53 +/- 15% by ventriculography. The limits of agreement between the ejection fraction estimated by bioimpedance and ventriculography was -35% to 37%. The 95% confidence intervals for the lower and upper limits of agreement were -22% to -48% and 24% to 50%, respectively. The mean left ventricular end-diastolic volume was 108 +/- 47 mL, as estimated by bioimpedance, and 121 +/- 35 mL, as estimated by ventriculography. The limits of agreement between the left ventricular end-diastolic volume as estimated by bioimpedance and ventriculography was -139 to 113 mL. The 95% confidence intervals for the lower and upper limits of agreement were -184 to -94 mL and 68 to 158 mL, respectively. CONCLUSIONS: The 95% confidence range defining the limits of agreement between cardiac output and volumetric data estimated by bioimpedance, with the cardiac output measurement by thermodilution and the volumetric data estimated from left ventriculography, were wide, making the degree of agreement clinically unacceptable. In the opinion of the authors, impedance cardiography should not replace invasive hemodynamic monitoring at this time.