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[en] In an attempt to improve the forecasting accuracy of crude oil price fluctuations, a new neural network architecture is established in this work which combines Multilayer perception and ERNN (Elman recurrent neural networks) with stochastic time effective function. ERNN is a time-varying predictive control system and is developed with the ability to keep memory of recent events in order to predict future output. The stochastic time effective function represents that the recent information has a stronger effect for the investors than the old information. With the established model the empirical research has a good performance in testing the predictive effects on four different time series indices. Compared to other models, the present model is possible to evaluate data from 1990s to today with extreme accuracy and speedy. The applied CID (complexity invariant distance) analysis and multiscale CID analysis, are provided as the new useful measures to evaluate a better predicting ability of the proposed model than other traditional models. - Highlights: • A new forecasting model is developed by a random Elman recurrent neural network. • The forecasting accuracy of crude oil price fluctuations is improved by the model. • The forecasting results of the proposed model are more accurate than compared models. • Two new distance analysis methods are applied to confirm the predicting results.
[en] Highlights: • CaO_2/MW pretreatment synergistically enhanced WAS solubilization and CH_4 production. • MW irradiation facilitated more "·OH generation from CaO_2. • The optimal pretreatment condition for methane production was determined. • The growths of both hydrogenotrophic and acetate-utilizing methanogens were promoted. • The dewaterability of WAS was improved considerably by CaO_2/MW treatment. - Abstract: To investigate the effects of combined calcium peroxide (CaO_2) and microwave pretreatment on anaerobic digestion of waste activated sludge, lab-scale experiments were conducted to measure the solubilization, biodegradation, and dewaterability of the waste activated sludge. Additionally, the synergistic effects between CaO_2 and microwave were studied, and the microbial activity and methanogenic archaea community structure were analyzed. Combined pretreatment considerably facilitated the solubilization and subsequent anaerobic digestion of the waste activated sludge. The optimal pretreatment condition was CaO_2 (0.1 g/gVSS)/microwave (480 W, 2 min) for methane production during the subsequent anaerobic digestion process. Under this condition, 80.2% higher CH_4 accumulation yield was achieved after 16 d of anaerobic digestion when compared with the control. The synergistic effects of CaO_2/microwave pretreatment resulted from the different mechanisms of CaO_2 and microwave treatments. Further, microwave irradiation increased "·OH generation from CaO_2 and significantly alleviated the inhibitory effect of CaO_2 on methanogens. The activities of hydrolytic enzymes and acid-forming enzymes in the waste activated sludge were improved after CaO_2 (0.1 g/gVSS)/microwave (480 W, 2 min) pretreatment. Methanogenesis enzyme activity was also higher after CaO_2 treatment (0.1 g/gVSS)/microwave (480 W, 2 min) following a lag period. Illumina MiSeq sequencing analysis indicated that acetate-utilizing methanogen (Methanosaeta sp.) and H_2/CO_2-utilizing methanogen (Methanospirillum sp.) abundance improved greatly following CaO_2 (0.1 g/gVSS)/microwave (480 W, 2 min) pretreatment. The percentage of CH_4 in biogas with CaO_2/microwave pretreatment increased by 25.4% relative to the control. The dewaterability of the waste activated sludge also improved considerably after anaerobic digestion with combined CaO_2/microwave treatment. Therefore, CaO_2/microwave pretreatment can be used as an effective method to recover energy from waste activated sludge.
[en] Highlights: • The features of three different power generation schemes, including closed Brayton cycle, non-reheating combined cycle and reheating combined cycle, coupled with high temperature gas-cooled reactor (HTGR) were investigated and compared. • The effects and mechanism of reactor core outlet temperature, compression ratio and other key parameters over cycle characteristics were analyzed by the thermodynamic models.. • It is found that reheated combined cycle has the highest efficiency. Reactor outlet temperature and main steam parameters are key factors to improve the cycle’s performance. - Abstract: With gradual increase in reactor outlet temperature, the efficient power conversion technology has become one of developing trends of (very) high temperature gas-cooled reactors (HTGRs). In this paper, different cycle power generation schemes for HTGRs were systematically studied. Physical and mathematical models were established for these three cycle schemes: closed Brayton cycle, simple combined cycle, and reheated combined cycle. The effects and mechanism of key parameters such as reactor core outlet temperature, reactor core inlet temperature and compression ratio on the features of these cycles were analyzed. Then, optimization results were given with engineering restrictive conditions, including pinch point temperature differences. Results revealed that within the temperature range of HTGRs (700–900 °C), the reheated combined cycle had the highest efficiency, while the simple combined cycle had the lowest efficiency (900 °C). The efficiencies of the closed Brayton cycle, simple combined cycle and reheated combined cycle are 49.5%, 46.6% and 50.1%, respectively. These results provide insights on the different schemes of these cycles, and reveal the effects of key parameters on performance of these cycles. It could be helpful to understand and develop a combined cycle coupled with a high temperature reactor in the future.
[en] Highlights: • Different rank coals were hydrogasified using a two-stage pressurized reactor. • Yields of CO, CO_2, CH_4, C2–C3, water and light aromatics were determined. • Coal structures were characterized by chemical titration, solid state "1"3C NMR and FTIR. • The highest sums of CH_4 and C_2H_6 yields were obtained for two lignite coals. • Relations between products and coal properties or structures were surveyed. - Abstract: The pressurized hydrogasification of different rank coals was carried out using a laboratory two-stage reactor to investigate the influences of volatile matter hydrocracking on the formations of gaseous products (CO_2, CO, CH_4 and C2–C3) and liquid products (water and light aromatics). Experiments were conducted by way of comparison under the N_2 atmosphere. Fourier transform infrared spectroscopy (FTIR), solid state "1"3C nuclear magnetic resonance technique ("1"3C NMR) and chemical titration analysis were used to semi-quantitatively or quantitatively determine the main functional groups in the coals. It was found that through the hydrocracking at 700 °C, the summed yields of CH_4 and C_2H_6 from two lignite coals reached as high as 21.2–22.9% (daf. coal), higher than those even from two subbituminous coals. This result was associated with the abundance of longer alkyl groups in two lignite coals. Two lignite coals were the most enriched with carboxyl groups, which was proved to be the principal precursor of CO_2. The hydrocracking at 700 °C allowed a distinct part of CO_2 to convert into CO by the reversal gas water shift reaction, while the changes in the yields of H_2O were indistinct. The hydrocracking at 700 °C was also favorable for the production of BTX (benzene, toluene and xylene) and naphthalene. The simple linear regression was used to assess the correlations of the yields of main gaseous products (CH_4, C_2H_6, CO_2 and CO) and liquid products (H_2O and BTX) obtained under varying conditions to some relevant coal properties such as volatile matter content and total oxygen content as well as to some structural parameters such as aliphatic ratio and carboxyl group content.
[en] Vanadium nitride has been the hot material for supercapacitors due to its excellent electrical conductivity and high specific capacitance. However, vanadium nitride nanoparticle usually suffers a poor performance due to its aggregation and lack of effective contact. In this work, one-dimensional (1D) vanadium nitride nanofibers are prepared by a combination of electrostatic spinning and high-temperature calcination in ammonia. The cross-linked nanofibers composed of nanoparticles construct a facile transport path for charge and electrolyte ion. Moreover, vanadium nitride nanoparticles encapsulated into carbon prevent grain growth and aggregation, which provide more active sites for electrolyte ion. Owing to this unique structure, vanadium nitride nanofibers exhibit high specific capacitance of 291.5 F g"−"1 at 0.5 A g"−"1 and rate capability with a capacitance of 105.1 F g"−"1 at 6 A g"−"1. In addition, we find that annealing temperature has significant influence on the performance of vanadium nitride, which associates with fibrous structure and crystallinity, and a limited potential window can greatly improve the cycling stability (retains 50% of initial capacitance after 1000 cycles)
[en] HTR-10GT is a testing project coupling the reactor HTR-10 with direct gas turbine cycle. Its thermal cycle can be taken as a closed, recuperated and inter-cooled Brayton cycle. The present study is focused on the thermal cycle performance of HTR-10GT under practical conditions of leakage, pressure losses, etc.. Through thermodynamic analysis, the expression of cycle efficiency for actual thermal cycle is derived. By establishing a physical model with friction loss and leakage, a set of governing equation are constructed based on some reasonable assumptions. The results of actual cycle efficiency have been calculated for different leakage amount at different locations while the effects of leakage under different power level have also been calculated and analyzed. (authors)
[en] The helium circulator is a key component of 10 MW high temperature gas-cooled reactor (HTR-10), which has the helium coolant circulate inside the primary loop of the reactor. Before delivery, the performance experiment of the circulator was carried out in the factory at 0.426 MPa, 250 deg. C nitrogen condition. In the paper, by using dimensional methodology, the experiment results are converted to those on 3.0 MPa, 250 deg. C helium condition which is real working condition on the reactor. Then the circulator performances are analyzed. Finally, the operating performances on HTR-10 are predicted. The paper concludes that the circulator design was made correctly and the performances are satisfied with HTR-10 operating requirements
[en] In this paper, the radiation grafting of aluminium oxide and methacrylic acid by electron beams was studied. The grafted samples were characterised by infrared spectroscopy and electron spin resonance spectroscopy. In addition, the radiation grafting mechanism of inorganic oxides and organic monomers has been investigated. (author)
[en] The importance of the nuclear power industry is demonstrated from the energy supply and environmental protection standpoint; then the HTGR gas turbine cycle is analyzed and the results show that the electric generation efficiency is 47.9%; finally, the technical advantages of the HTGR compared with other advanced reactor types are illustrated. It is concluded that the HTGR has great future potential to be one of the advanced reactors in the generation IV nuclear power system