Search

AbstractTungsten (W) and boron carbide (B4C) coatings deposited on metallic substrates have received considerable attention in recent years because of their potential application in nuclear fusion devices, especially as plasma facing materials (PFMs). In the present study, W and B4C coatings have been deposited by vacuum plasma spraying technology. The tritium retention behaviors of the W and B4C coatings were investigated and comparatively studied by using β-ray-induced X-ray spectrometry (BIXS). The effects of tritium exposure temperature were examined as well. The obtained results showed that much stronger X-ray peaks of Ar(Kα) appeared in the BIXS spectra for the B4C coatings as compared with those for the W coatings, indicating of higher tritium absorbability for the B4C coatings owing to large amount of micro-pores in the coatings. After exposed to tritium gas at 923 K, significantly enhanced tritium retentions were detected for both the W and B4C coatings as compared with those exposed at 573 K.

AbstractTungsten coating as a plasma-facing material on copper alloys is an important issue of a tokamak fusion device. Tungsten tile was created by means of plasma-spraying technology. The properties of the tungsten coating are as follows: low porosity of 4.7%, ˜92% of the theoretical tungsten bulk density, and high thermal conductivity of ˜79.7 W/m·K, which are interesting properties for the plasma-facing material. To alleviate the stress concentration, the tile was designed with rounded edges with a radius of 5 mm. The fatigue performance of the tungsten tile was tested at 5 MW/m2in an electron beam facility. No damage was observed after 38 cycles at 250 s per cycle. It is concluded that the rounded-edge design is helpful in reducing the maximum stress and in improving the resistant heat load property, which was proved by finite element analysis.

When isolate NIOI of self-inducing Phytophthora boehmeriae was grown on medium containing the fungicide ethazol, the fungus produced oospore-free sectors from which self-sterile cultures were recovered. Self-sterile cultures were also recovered from three of six other isolates tested. Single hyphal fragment cultures and single zoospore cultures derived from these self-sterile cultures were of A1A2, A1, A2, and A0 types. Conversion of self-fertile species of Phytophthora to A1 and A2 types is suggested as another possible evolutionary origin of the two sexes in lower organisms, in addition to previously reported mating type change as a possible origin of sexes.

Litterfall is a good indicator of overall forest functions in forest ecosystems. Globally, forest litterfall has been extensively investigated, however, there is a lack of long‐term data analysis to show the various litterfall components in relation to environmental factors on the monthly and yearly scales. Here, monthly (May–October) and annual (1981–2018) litterfall including leaves, twigs, bark, reproductive, and miscellaneous fractions were collected in a mixed mature Pinus koraiensisforest on Changbai Mountain in Northeast, China, across 30 years. Based on these long‐term litterfall data, we analyzed the seasonal and annual variations in different litterfall fractions and the internal/external drivers. We observed that both the leaf and total litterfall exhibited a strong, similar seasonal pattern, with the highest levels between September and October, and the annual litterfall had an “S‐shaped” increasing pattern from 1981 to 2018. The other litterfall fractions showed distinct monthly and yearly fluctuations across the 30 years. Mean monthly evapotranspiration and temperature (minimum and maximum) were the best predictors for monthly litterfall. By contrast, the models that best predicted the annual litterfall production included mean annual precipitation and mean monthly precipitation and temperature in May and October. Our study, using a unique dataset of detailed long‐term litterfall dynamics, has potentially major significance for enhancing our understanding of the role of climatic factors controlling forest litterfall amount and seasonality in temperate mixed mature forests. This insight is of paramount importance for modeling and estimating soil carbon sequestration and nutrient cycling of temperate forests under climate change. Forest litterfall is very important for nutrient cycling in forest ecosystems. Many researchers have studied forest litterfall, but still, there is an obvious lack of long‐term data analysis to show the relationships between forest litterfall and environmental factors. In this study, we analyzed the monthly and annual litterfalls of various components (leaf, reproductive, twig, bark, and miscellaneous litterfall) collected over 30 years in a mixed broad‐leaved Pinus koraiensisold‐growth forest on Changbai Mountain in northeastern China, in relation to climatic factors. We found that the highest monthly values of both leaf and total litterfall occurred during September‐October, and the annual litterfall of all components had an increasing trend from 1981 to 2018. The monthly litterfall was strongly influenced by the mean monthly evapotranspiration and temperature (minimum and maximum). The annual litterfall was mainly influenced by the mean annual precipitation, mean monthly precipitation, and temperature in May and October. These long‐term data based findings have important implications for better understanding the role of climatic factors on forest litterfall dynamics under climate change. Leaf and total litterfall exhibited a strong and similar seasonal patternThere was an “S‐shaped” increasing pattern in the annual litterfallContrasting climatic factors controlled seasonal and annual litterfall dynamics Leaf and total litterfall exhibited a strong and similar seasonal pattern There was an “S‐shaped” increasing pattern in the annual litterfall Contrasting climatic factors controlled seasonal and annual litterfall dynamics

Pressure reducing valve is an extremely significant equipment of energy dissipation for the water supply by gravity with pressure reducing technology in hydropower stations, and which has a pronounced effect on the normal technical water supply even safety operation for the hydropower units. A three-dimensional numerical calculation of flow field and cavitation characteristics towards a combined type pressure reducing valves was carried out based on the system of technical water supply in this paper. The numerical results show that the investigated valve could meet the requirements of technological supply water pressure and great pressure loss was caused when the water flow was accelerated by narrow overflowing section between throttling cone and valve seat. At working operation, obvious cavitation phenomenon was observed on the surface of throttling cone, and the maximum volume fraction of vapor reached 0.537%. Based on above researches, this paper introduces an optimization model for profile line design of throttling cone. The optimal results show that the cavitation performance is effectively improved with identical pressure drop compared with original results.

The cavitation flow phenomena may occur in the bulb tubular turbine at some certain operation conditions, which even decrease the performance of units and causes insatiably noise and vibration when it goes worse. A steady cavitating flow numerical simulations study is carried out on the bulb tubular unit with the same blade pitch angle and different guide vane openings by using the commercial code ANSYS CFX in this paper. The phenomena of cavitation induction areas and development process are obtained and draws cavitation performance curves. The numerical results show that the travelling bubble cavity is the main types of cavitation development over a wide operating range of discharge and this type of cavitation begins to sensitive to the value of cavitation number when the discharge exceeding a certain valve, in this condition, it can lead to a severe free bubble formation with the gradually decrement of cavitation number. The reported cavitation performance curves results indicate that the flow blockage incident would happen because of a mount of free bubble formation in the flow passage when the cavity developed to certain extend, which caused head drop behavior and power broken dramatically and influenced the output power.

Performance prediction about the forward generation condition based on a bidirectional through-flow turbine runner was conducted. The model characteristic curves and efficiency curve under reverse generation condition were plotted. In order to improve the reverse performance, exit guide vanes were lied behind the runner, the forward and reverse operating performance about a runner lied post-guide vane were numerically simulated. The results shows that the flow field distribution on forward generation condition did not significantly change after exit guide vanes were lied, and the energy conversion efficiency decreased. After exit guide vanes were lied, flow pattern of runner intake on under reverse generation condition were bettered, and the energy conversion efficiency increased. This study confirms that the exit guide vanes can improve the hydraulic performance of the turbine on reverse generation condition in view of numerical simulation.