ABSTRACT: The detection of gradual trends in water quality time series is increasing in importance as concern grows for diffuse sources of pollution such as acid precipitation and agricultural non-point sources. A significant body of literature has arisen dealing with trend detection in water quality variables that exhibit seasonal patterns. Much of the literature has dealt with seasonality of the first moment. However, little has been mentioned about seasonality in the variance, and its effect upon the performance of trend detection techniques. In this paper, eight methods of trend detection that arise from both the statistical literature as well as the water quality literature have been compared by means of a simulation study. Varying degrees of seasonality in both the variances and the means have been introduced into the artificial data, and the performances of these procedures are analyzed. Since the focus is on lake and ground water quality monitoring, quarterly sampling and short to moderate record lengths are examined. 相似文献
Objective: This study was designed to evaluate the performance of a pelvic restraint cushion (PRC), a submarining countermeasure that deploys under the thighs when a crash is detected in order to block the forward motion of the pelvis.
Methods: Sled tests approximating low- and high-speed frontal impacts were conducted with 4 female postmortem human subjects (PMHS) restrained by a lap and shoulder belt in the right front passenger seat. The subjects were tested with and without a PRC.
Results: The PRC is effective in reducing forward motion of the PMHS pelvis and reduces the risk of injury due to lap belt loading in a high-speed frontal crash.
Conclusions: Although small sample size limits the utility of the study's findings, the results suggest that the PRC can limit pelvic forward motion and that pelvic injury due to PRC deployment is not likely. 相似文献
This research investigated the possibility of using recycled asphalt concrete as surface course in airport pavement. The basic properties of recycled asphalt binder after short- and long-term aging were firstly tested and compared with those of the virgin asphalt. Then, a series of laboratory tests were performed to evaluate the performance of recycled asphalt concrete (containing 40% and 70% RAP), in which the HMA mixture without RAP was used as a control. Furthermore, an experimental pavement consisting of three sections (corresponding to 0%, 40% and 70% RAP content) was constructed to verify the laboratory test results. These results indicated that the recycled asphalt could achieve the similar properties against long-term aging as virgin asphalt. Recycled asphalt concrete containing 40% RAP could be used as surface course in airport pavement as it exhibited similar performance as control mixture both from the laboratory and experimental pavement test results. On the contrary, recycled asphalt concrete containing 70% RAP was not recommended as its fatigue property was much poorer compared with that of virgin asphalt mixture. 相似文献
Acute, laboratory toxicity tests were performed by the National Oceanic and Atmospheric Administration (NOAA) on 1543 surficial sediment samples collected during 1991 through 1997 throughout 25 estuaries and marine bays. Selected areas were sampled along the Atlantic, Gulf of Mexico, and Pacific coasts. The toxicity of each sample was determined with 10-day amphipod survival tests performed with solid-phase (bulk) sediments. Collectively, the 1543 samples tested through 1997 represented a total area of approximately 7300 km2. Toxicity was observed with the amphipod survival tests in samples that represented approximately 6% of the combined area. Using similar tests conducted on samples collected in different, but overlapping, study areas, the U.S. Environmental Protection Agency (EPA) estimated that approximately 7% of the combined estuarine area sampled was toxic. Generally, toxicity was most severe in northeastern and southwestern estuaries and least prevalent in southeastern and northwestern areas. However, considerable portions of the Pacific coast have not been tested with the same methods. In tests of CYP1A enzyme induction (n=464), samples were toxic that represented about 5% of the combined study areas. Toxicity was much more widespread, however, when the results of two sub-lethal tests were analyzed. Significant results occurred in samples that represented approximately 25% and 39% of the study areas in tests of sea urchin fertilization (n=1309) and microbial bioluminescence (n=1215), respectively. 相似文献
Though measurement instruments and methods have their natural precision limits, long term monitoring, which is so importantfor environmental studies, requires to set up and maintaincertain standards regarding precision. The elementaryrequirement is to produce measurements with a prescribed numberof valid digits. If the technology further develops and allowsto increase the number of valid digits, the change should bedocumented. In this paper we discuss a simple procedure for validity assessment of the last digits of data in a data base.It may be useful for both calibration control of an instrumentas well as for preliminary data analysis in scientific studies.The procedure utilizes the assumption that, under normalconditions, the last digits of the observed data can usually beconsidered as uniformly distributed random numbers. Failures ordeliberate changes in the observation mechanism can be detectedif particular digits occur more frequently than the others. Thedecision about proper representations of the last digits is doneby means of the familiar chi-square statistics. 相似文献
To obtain reliable diffusion parameters for diffusion testing, multiple experiments should not only be cross-checked but the internal consistency of each experiment should also be verified. In the through- and in-diffusion tests with solution reservoirs, test interpretation of different phases often makes use of simplified analytical solutions. This study explores the feasibility of steady, quasi-steady, equilibrium and transient-state analyses using simplified analytical solutions with respect to (i) valid conditions for each analytical solution, (ii) potential error, and (iii) experimental time. For increased generality, a series of numerical analyses are performed using unified dimensionless parameters and the results are all related to dimensionless reservoir volume (DRV) which includes only the sorptive parameter as an unknown. This means the above factors can be investigated on the basis of the sorption properties of the testing material and/or tracer. The main findings are that steady, quasi-steady and equilibrium-state analyses are applicable when the tracer is not highly sorptive. However, quasi-steady and equilibrium-state analyses become inefficient or impractical compared to steady state analysis when the tracer is non-sorbing and material porosity is significantly low. Systematic and comprehensive reformulation of analytical models enables the comparison of experimental times between different test methods. The applicability and potential error of each test interpretation can also be studied. These can be applied in designing, performing, and interpreting diffusion experiments by deducing DRV from the available information for the target material and tracer, combined with the results of this study. 相似文献
Selected results from the degradation of reactive-dye hydrolysates after UV irradiation, ozonation and sodium peroxodisulphate (NaPS) treatment are presented. Reactive dyes with representative chromophores and anchor groups were chosen for the research project. Different stages of oxidative decolourisation were examined and determined by water parameters for biological degradation (BOD). The paper focuses on toxicity tests with Pseudomonas putida to consider whether the oxidative treatments result in products with a risk for the environment. Tests were performed with the AQUALYTIC® Sensomat System, which measures biological oxygen demand (BOD). It was determined that the chosen oxidative treatments had as a rule no bearing on respiration of P. putida. Experiments with hydrolysates after short-term UV irradiation resulted in a slightly increased but not long-lasting toxicity in comparison with treatments with ozone or NaPS. Toxic effects were found in tests with hydrolysates of metalliferous dyes. During oxidative treatment, metals were liberated from the chromophores. This did cause complete inhibition of respiration of P. putida. Dye Blue E, a member of a dye class with chlorotriazine anchor groups, was itself found to be toxic, caused by the reactivity of the anchor group. The hydrolysate is only of minor toxicity. 相似文献