Robustness of asymptotic accelerated life test plans to small‐sample settings

Much of the statistical literature on optimal test planning for accelerated life testing utilize asymptotic methods to derive optimal test plans. While sufficient effort is made to assess the robustness of these test plans to the choice of design parameters and distribution assumptions, there is very little literature on the performance of asymptotic test plans relative to small samples (on the order of 10‐15 samples). An alternative concern is that the asymptotic test plans may not necessarily be the true “optimal” test plan for a given sample size. The purpose of this research is to present exact or “near‐exact” methods for developing test plans and compare the performance of these test plans with corresponding asymptotic test plans in small‐sample settings. The optimal location of design points and sample allocation is determined using each method for lognormal and Weibull lifetime distributions with both complete and Type 1 right‐censored data under two selected acceleration factor models. The investigations reveal that asymptotic test plans tend to corroborate quite well with exact test plans and thus are suitably robust to small‐sample settings in terms of optimal variance.     

Speciation of copper in high chloride concentrations,in the context of corrosion of copper canisters

Canisters with a cast iron insert for mechanical strength and a 50-mm thick copper shell as corrosion protection are planned to be used for disposal of spent nuclear fuel in Sweden and Finland. Chloride can be considered “beneficial”, as it promotes active dissolution of copper rather than passivation (which might result in pitting), but a high concentration of chloride in solution would increase the driving force for corrosion through the formation of soluble copper chloro complexes. Thermodynamic calculations are performed in this study with the PHREEQC software and three of its accompanying databases, and a comparison with experimental data is performed to select the database to be used when evaluating repository performance. The activity coefficient models are given special attention. For the assessment of chloride-assisted corrosion of a KBS-3 canister, chloride concentrations pessimistically up to 5 mol/kg are used (in Finland and Sweden, the groundwater and bentonite porewater chloride concentrations are not expected to exceed 1 mol/kg). The resulting copper solubilities are then considered in different mass transport cases.     

Dynamics of lipid droplets in the endometrium and fatty acids and oxylipins in the uterine lumen,blood, and milk of lactating cows during diestrus

Our objective was to investigate the lipid content of uterus, blood plasma, and milk at early, mid, and late diestrus. Lactating cows (n = 30) had the estrous cycle and ovulation synchronized by administration of exogenous hormones. Cows were blocked by parity and assigned randomly to receive transcervical uterine flushing and biopsy on d 5 (early diestrus), 10 (mid diestrus) or 15 (late diestrus) of the estrous cycle. Flushing and endometrial biopsy were performed in the uterine horn ipsilateral to the corpus luteum. The recovered flushing was used for analyses of lipid composition by liquid chromatography-tandem mass spectrometry and the biopsy was used for investigation of lipid droplet abundance in endometrial cryosections using a neutral lipid fluorescent dye. In addition, blood and milk samples were collected from all cows on d 5, 10, and 15. All blood samples were used to measure the concentration of progesterone in plasma, and all milk samples were used to determine milk composition. Subsamples of blood plasma and milk were also used to evaluate the composition of fatty acids and oxylipins using the same methodology used for uterine flushing samples. The abundance of lipid droplets in the endometrium increased 1.9-fold from d 5 to 10, and 2-fold from d 10 to 15. Concentration of long-chain fatty acids and oxylipins in uterine flushing were, on average, 2.2 and 2.5 times greater in samples collected on d 15 compared with those collected on d 5 and 10. These differences were not observed in blood and milk, suggesting that accumulation of fatty acids and oxylipins in the uterus is regulated locally. In addition to concentration, the profile of individual fatty acids and oxylipins in uterine lumen changed substantially during diestrus. The main categories with increased abundance at late diestrus were mono- and polyunsaturated fatty acids, and oxylipins derived from arachidonic acid, dihomo-γ-linolenic acid, and docosahexaenoic acid. In conclusion, fatty acids and oxylipins accumulate in the uterine lumen during diestrus and might work as a mechanism to supply these lipids to the developing conceptus at late diestrus, when the onset of elongation occurs and substantial synthesis of biomass and cell signaling by lipid mediators are required.     

MADE3D: Enabling the next generation of high-torque density wind generators by additive design and 3D printing

Forschung im Ingenieurwesen - Direct-drive wind turbine generators are increasing in popularity, thanks to recent project developments—especially offshore, where reliability and efficiency...     

基于Web的齿轮减速器设计优化系统开发

采用最新齿轮强度计算标准,利用ASP和网页制作技术,在Visual Basic、Visual Inter-Dev6.0环境下开发出了基于Web和齿轮设计制造专家咨询的减速器远程优化设计系统,从而实现减速器的远程优化设计,详细设计校核,齿轮的设计与制造的专家咨询,精度检索等。在减轻齿轮工程技术人员的劳动强度,提高工作效率,实现齿轮计算机辅助工程分析(CAE)等方面做出了一定的探索。     

Petrophysics studies of sedimentary rocks from a cross-hole seismic test site

In order to provide a site for studying in detail seismic wave propagation over a large range of frequencies through layered sedimentary rocks, four vertical boreholes of approximately 260 m depth and maximum distance apart of 95 m have been drilled through five cyclical sequences of shallow-dipping sandstone, mudrock and limestone formations in the Carboniferous Limestone series in northern England. Two of the boreholes were fully cored and a number of core samples from these were carefully preserved, at 1 m intervals in the first and at selected intervals in the second. Bulk density, porosity and P- and S-wave velocities and attenuation in the vertical and horizontal directions have been made on a total of 180 specimens from the preserved core samples. Permeability and electrical properties have been measured for the sandstone samples. Multiple linear regression equations have been derived relating the P- and S-wave velocities to porosity and clay content. These equations indicate the relative importance of increases in porosity and in clay content on decreases in all velocities, and the relative insensitivity to changes in clay content of PH- and SH-wave velocities. For the samples tested, the average anisotropy observed under in situ stress conditions is approximately 0.5% for limestones (porosities to 12%) and 5% for sandstones (porosities in the range 2 to 18%). For mudrocks (porosities in the range 2 to 15%), the average anisotropy is 21% for P waves and 27% for S waves. The results have been used to confirm the magnitudes of anisotropy observed in cross-hole seismic tomography at the site, in modelling the seismic response of sedimentary rocks with an appreciable clay content, and in modelling velocity dispersion and attenuation for rocks at the site over a wide range of frequencies.     

Sources of pharmaceutical pollution in the New York City Watershed

An investigation was carried out in the New York City Watershed for the presence of selected pharmaceuticals. In four seasonal sampling events between August 2003 and May 2004, surface water was collected from eight reservoir keypoints and effluent was collected from four wastewater treatment plants. We evaluated the following twelve compounds: amoxicillin, atenolol, caffeine, carbamazepine, cephalexin, estrone, 17alpha-ethinylestradiol, 17beta-estradiol, ibuprofen, sulfamethoxazole, trimethoprim, and valproic acid. In the treated effluents, carbamazepine was detected most frequently (100%; concentration range: 22-551 ng/L), followed by atenolol (94%; ND - 14,200 ng/L), trimethoprim (83%; ND - 37,000 ng/L), ibuprofen (61%; ND - 14,600 ng/L), and caffeine (49%; ND - 37,200 ng/L), while estrone was detected once (56 ng/L). In the reservoir keypoint samples, only ibuprofen (2.5%; ND - 932 ng/L) and caffeine (2.9%; ND - 177 ng/L) were detected. The other analytes were not detected in any sample. It is expected that investigation of other wastewater treatment plants in the New York City Watershed would show that their effluents are also a potential source of pharmaceuticals, but that these pharmaceuticals are unlikely to be detected in the Watershed's surface waters.     

Temporal and spatial patterns of contaminants in Lake Erie watersnakes (Nerodia sipedon insularum) before and after the round goby (Apollonia melanostomus) invasion

Temporal and spatial trends in contaminant concentrations were assessed in Lake Erie watersnakes, a threatened (USA)/endangered (Canada) species restricted to western Lake Erie. Temporal changes in plasma contaminant levels were determined in 1990 and 2003, and spatial patterns in 2003 at 12 sites, throughout the species' range. During this period, the watersnakes' diet changed from fish (75%) and amphibians (25%) that avoid zebra mussels, to round gobies (95%) that feed extensively on zebra mussels. Temporal trends indicate that watersnakes on Pelee and North Bass Islands showed a marginal increase in hexachlorobenzene levels, and a significant decline in dieldrin, oxychlordane, and heptachlor epoxide, likely reflecting declines in aerial deposition and clearing of local vineyards. The contaminants with the greatest burdens, sum PCBs and p,p'-DDE, remained stable in the snakes, consistent with trends in other local biota, suggesting that although the dietary switch to round gobies meant consumption of a more contaminated diet, their diet remained at the same trophic position. We suggest that the watersnakes' PCB and p,p'-DDE temporal patterns reflect the lack of change in sediment concentrations with minimal influence from their dietary switch. Similar to top avian predators, PCBs, p,p'-DDE, and technical chlordane, are most prevalent in watersnakes; this ranking remains unchanged. In 2003, the watersnakes demonstrated significant spatial differences in concentrations of p,p'-DDE, dieldrin, technical chlordane and its metabolites. Their 2003 concentrations of p,p'-DDE, and to a lesser extent PCBs, exceed the recommended interim no-observable effects levels on watersnake embryonic survival. Further investigations are required to determine if these higher levels of PCBs, p,p'-DDE, and technical chlordane, affect reproductive and physiological parameters of the Lake Erie watersnake. Until concentrations of sediment contaminants decline in western Lake Erie, these endangered/threatened watersnakes will continue to be exposed to higher concentrations of persistent organic pollutants.