Observations in the statistical analysis of NBG-18 nuclear graphite strength tests

The purpose of this paper is to report on the selection of a statistical distribution chosen to represent the experimental material strength of NBG-18 nuclear graphite. Three large sets of samples were tested during the material characterisation of the Pebble Bed Modular Reactor and Core Structure Ceramics materials. These sets of samples are tensile strength, flexural strength and compressive strength (CS) measurements. A relevant statistical fit is determined and the goodness of fit is also evaluated for each data set. The data sets are also normalised for ease of comparison, and combined into one representative data set. The validity of this approach is demonstrated. A second failure mode distribution is found on the CS test data. Identifying this failure mode supports the similar observations made in the past. The success of fitting the Weibull distribution through the normalised data sets allows us to improve the basis for the estimates of the variability. This could also imply that the variability on the graphite strength for the different strength measures is based on the same flaw distribution and thus a property of the material.     

Theoretical and statistical derivation of a screener for the behavioral assessment of executive functions in children.

The problem of valid measurement of psychological constructs remains an impediment to scientific progress, and the measurement of executive functions is not an exception. This study examined the statistical and theoretical derivation of a behavioral screener for the estimation of executive functions in children from the well-established Behavior Assessment System for Children (BASC). The original national standardization sample of the BASC–Teacher Rating Scales for children ages 6 through 11 was used (N = 2,165). Moderate-to-high internal consistency was obtained within each factor (.80–.89). A panel of experts was used for content validity examination. A confirmatory factor analysis model with 25 items loading on 4 latent factors (behavioral control, emotional control, attentional control, and problem solving) was developed, and its statistical properties were examined. The multidimensional model demonstrated adequate fit, and it was deemed invariant after configural, metric, and scalar measurement invariance tests across sex and age. Given its strong psychometric properties, with further tests of item validity, this instrument promises future clinical and research utility for the screening of executive functions in school-age children. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Isotopic identification of the sources of lead contamination for white storks (Ciconia ciconia) in a marshland ecosystem (Doñana,S.W. Spain)

White storks (Ciconia ciconia) fed in contaminated waters resulting from the Aznacollar acid mining-sludge spillage into the R. Guadiamar, which feeds the eastern flank of the Guadalquivir marshes (Do?ana), S.W. Spain. The sludge was rich in a range of toxic elements, and in organic pollutants such as the aromatic amines. Storks did not exhibit elevated metals in their blood immediately following the accident, but chick blood collected the year following the accident showed genotoxic damage compared to the controls. In this study lead isotope analysis was used to assess if the storks had ingested sludge-derived contaminants. The sludge lead isotope ratio was distinct from that of the Do?ana sediments. The stork blood lead isotope ratios exactly matched that of the sludge. It was concluded that the storks had ingested sludge-derived contaminants. A detailed study of the lead contamination along the R. Guadiamar and the R. Guadalquivir (of which the Guadiamar is a tributary) was also conducted to place the white stork colony lead exposure in the context of the spatial contamination of the storks' habitat.     

Real and Ideal Institutional Frameworks for Managing the Common Arab-Israeli Water Resources

The Oslo A and B agreements of September 1993 and September 1995 were the beginning of a process aimed at a peaceful resolution of the Arab-Israeli conflict. The Israeli-Jordanian Treaty of 1994 addresses issues of water sharing between the two parties. In 1995, Israel and the Palestinians signed an Agreement on Water and Sewage as part of their Interim Agreement. In February 1996, Israel, Jordan, and the Palestinians agreed to a “Declaration of Principles for Joint Development of Water Resources.” The purpose of this paper is to compare the components of the two Agreements with an “ideal” institution for management of shared water resources. The “ideal” institution was formulated by 23 water experts who were interviewed on this issue. The main finding is that in most respects, expert opinions did not differ significantly from the Israeli-Jordanian Treaty of Peace and the Israeli-Palestinian Interim Agreement.     

Modeling the impacts of climate change on the thermal and oxygen dynamics of Lake Volta

Climatic changes influence the thermal and oxygen dynamics of a lake and thus its ecological functioning. The impacts of climatic changes on tropical lakes are so far poorly studied and the extent of the effects is therefore uncertain, most investigations describing only potential effects. In this study, we applied the one-dimensional lake ecosystem model GOTM-ERGOM to quantify the effects of climate change on thermal stratification, oxygen dynamics, and primary production in meso-oligotrophic Lake Volta. GOTM-ERGOM was calibrated and validated using two years of observed data. The validated model was used to evaluate a series of future climate change scenarios. The model simulations showed good agreement with observed water temperature, dissolved oxygen and chlorophyll-a and indicated intensified stratification and reduced oxygen levels in the productive water layers of the lake. However, the longer-lasting stratification (prolonged stability) did not translate into permanent stratification. A relatively small (1?m) upward shift of thermocline depth resulted in an 8%–12% volume loss of the oxygen-rich upper mixed layer, which may be significant for the fisheries of the lake as it diminishes the size of suitable fish habitats. Light limitation of primary production renders the lake somewhat resilient to intensive algae blooms, as traceable in both the present and in the future climate scenarios. In the long term, the ongoing climate change may affect riparian communities that depend on the lake's fisheries for their livelihood. In consequence, future lake management strategies for implementation need to account for the impacts of future climate change.     

A calorimetric examination of coal surfaces

This communication reports the results of some exploratory experiments to examine the surface of coal by (i) flow microcalorimetry (FM) and (ii) vapour sorption calorimetry (VSC). Excepting differential scanning calorimetry, calorimetric methods have not been widely-exploited in coal structure research. The intent of this short communication is to demonstrate that hitherto neglected calorimetric methods are very rewarding when applied to the study of coal surfaces.     

A RANDOM PARAMETER PROCESS FOR MODELING AND FORECASTING TIME SERIES

Abstract. A generalized autoregressive (GAR) process {Z ( t ) ; t = 0 , ±1, …} is defined to satisfy the recurrence relation Z(t) = A_θ (t)Z (t -l)+ u( t ), where {A_θ(t); t = 0,±1, …} is itself a stochastic process depending on a vector parameter θ and where {u( t ); t = 0, ±1, …} is white noise with Eu ² ( t ) = a ². This paper develops theory and methodology and implementing the class of GAR processes for time series modeling and forecasting. Conditions on the 'parameter process' { A _θ ( t ); t = 0, ±1, …} are obtained for the existence of a GAR process; necessary and sufficient conditions on { A_θ ( t ) ; t = 0, ±1, …} for existence of a stationary GAR process are also obtained. Procedures are developed for computing maximum likelihood estimates of the parameters 0 and u² and for computing the minimum mean squared error forecasts for GAR processes.     

CELL-FREE SYNTHESIS OF ETHYL ACETATE BY EXTRACTS FROM SACCHAROMYCES CEREVISIAE

A cell-free preparation has been obtained from Saccharomyces cerevisiae which will synthesize ethyl acetate from ethanol and acetyl-CoA. Ethyl acetate synthesizing activity is stimulated by magnesium ions, the optimal concentration being 8 mM. Subcellular fractionation indicates that the enzyme is associated with material sedimenting at 105 000g .     

The productivity measurement and enhancement system: A meta-analysis.

Meta-analytic procedures were used to examine data from 83 field studies of the Productivity Measurement and Enhancement System (ProMES). The article expands the evidence on effectiveness of the intervention, examines where it has been successful, and explores moderators related to its success. Four research questions were explored and results indicate that (a) ProMES results in large improvements in productivity; (b) these effects last over time, in some cases years; (c) the intervention results in productivity improvements in many different types of settings (i.e., type of organization, type of work, type of worker, country); and (d) moderator variables are related to the degree of productivity improvement. These moderator variables include how closely the study followed the original ProMES methodology, the quality of feedback given, whether changes were made in the feedback system, the degree of interdependence of the work group, and centralization of the organization. Implications based on these findings are discussed for future use of this intervention, and the system is discussed as an example for evidence-based management. (PsycINFO Database Record (c) 2010 APA, all rights reserved)