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[en] Bulk Cu90W10 nanocomposites were fabricated by combination of mechanical alloying and warm pressing. The microstructure, mechanical properties, pin-on-disk dry sliding wear and corrosion behaviors were investigated. The W particles with average size of ∼112 nm are uniformly distributed in the Cu matrix and such nanostructured Cu−W alloys demonstrate excellent high temperature stability. After annealing at 600 °C for 1 h, the W particle size only increased ∼12% and hardness only decreased ∼5%. The plastic deformation region in Cu90W10 extends only about 3 μm below which the microstructure has recovered to the initial state and no chemical nanolayering was formed. Electrochemical corrosion tests show that the surface of Cu90W10 nanocomposite was severely damaged. The corrosion products were identified as predominantly gravel-like CuCl crystals with size of 0.5–4 μm and minor amount of very fine tungsten oxides nanoparticles with size of 50–80 nm. - Highlights: • Bulk dense Cu−W nanocomposites with W precipitates of ∼112 nm were fabricated. • Nanostructured Cu−W alloys demonstrate excellent high temperature stability. • Unlike Cu−Ag, dry sliding wear of Cu−W did not induce chemical nanolayering. • Annealed Cu−W shows slightly higher corrosion resistance in 3.5 wt.% NaCl solution than the as pressed one.
[en] Photon enhanced thermionic emission (PETE) is a new concept in solar energy conversion, combining thermal and photovoltaic carrier excitations with thermionic emission. A solar-power-driven thermionic energy converter operates by illuminating the solar light condensed by a large-scale Fresnel lens to convert heat energy into electrical energy. By enhancing the efficiency of converting solar radiation into the emitter internal energy, the output power and efficiency of the thermionic energy converter can be greatly improved. In this study, using numerical simulations, the effects of emitter temperature and output characteristics on a thermionic energy converter were investigated. The results showed that the higher rate of the heating power represented the higher temperature of an emitter, as well as output current density, and efficiency. In addition, by reducing the diameter of a collector and thermal conductivity of insulation materials, or increasing the diameter of emitter, the temperature of emitter, output current density, and efficiency could be notably improved. It is also worth mentioning that the main factor that affected the emitter temperature in the process of heat transfer was heat conduction between solids. In conclusion, adequate illumination, reasonable size of collector and emitter, as well as appropriate insulation measurements could efficiently improve the output characteristics of thermionic energy converter. (author)
[en] Anomalous X-ray pulsars (AXPs) are now established to exhibit significant X-ray variability and be prolific glitchers, with some glitches being accompanied by large radiative changes. An open issue is whether AXP glitches are generically accompanied by radiative changes, relevant for understanding magnetar physical properties. Here we report on an analysis of archival X-ray data from the AXP 1E 1841-045, obtained between 1993 and 2007. This AXP, located in the center of the supernova remnant Kes 73, has exhibited three glitches between 2002 and 2007, as determined by RXTE monitoring since 1999. We have searched for evidence of phase-averaged flux variability that could be present if glitches in AXPs are usually accompanied by radiative changes. We find no evidence for glitch-correlated flux changes from this source after 1999, supporting the existence of radiatively silent glitches in AXPs.
[en] Objective: To investigate the relationship between changes of blood levels of motilin gastrin and development of GER in children with bronchial asthma. Methods: Altogether 98 children with various forms of bronchial asthma were studied, in which 40 patients were complicated with symptomatic GER. Serum gastrin and plasma motilin levels were measured with RIA in all these 98 children and 30 controls. Barium swallow was performed in 76 children (including all the 40 with symptomatic GER) and anatomic GER was demonstrated in 31 patients (all with symptomatic GER except 4 in young infants who could not tell about symptom). No anatomic GER was shown in children without GER symptoms. Results: The blood levels of motilin and gastrin in all patients with symptomatic GER (barium swallow positive or not) were significantly lower than those in patients without GER symptoms and controls (P<0. 001). The hormone levels in asthmatic children without GER symptoms were still significantly lower than those in controls (P<0. 01). Conclusion: Plasma motilin and serum gastrin levels were markedly decreased in asthmatic children, especially in those with symptomatic and/or anatomic GER. Lowered motilin and gastrin levels might lead to development of GER and GER could further aggravate the attack of asthma. (authors)
[en] Highlights: • Latent thermal storage enables solar-powered residential heating, cooling and hot water. • Sizing method minimizes the phase change material mass and temperature fluctuations. • 29 kWh solar thermal storage provides 87% annual energy saving in Phoenix Arizona. • Exergy efficiencies up to 90% are achieved for the thermal energy storage system. - Abstract: A thermal network model is developed to study the performance of a solar thermal-powered heating, cooling and hot water system comprised of evacuated tube collectors, a latent heat thermal energy storage unit and related heat exchangers, and an absorption chiller/heat pump. The system performance is studied for a residential building in a hot climate zone (Phoenix, Arizona) on two typical solar days representative of a relatively cold day and a relatively hot day. A systematic sizing methodology is presented to minimize the phase change material mass and the output temperature fluctuations. An exergy analysis is also performed to quantify the second law efficiency of the system. Analysis of the energy performance of the system shows that more than 80% annual energy saving can be achieved by using a solar collector area of 10 m2 coupled with a 29 kWh latent heat thermal energy storage system. The effect of the heat transfer design of the thermal energy storage system, in particular the number of condenser pipes of the input heat pipe and evaporator sections of the output heat pipes embedded within the phase change material, on the thermal and exergetic performance of the system is also investigated. It is shown that increasing the number of pipes decreases the temperature fluctuations and increases the exergy efficiency due to minimized temperature drops. Quantitatively, increasing the number of pipes from 60 to 112, decreases the maximum temperature drops across the latent heat thermal energy storage system from about 30 °C to 15 °C, and increases the exergy efficiency from about 75% to 90%. This study demonstrates the capability of a solar thermal-powered heating, cooling and hot water system integrated with latent heat thermal energy storage to significantly reduce the auxiliary energy input needed to meet the demands of a residential building located in a hot climate zone.
[en] Copper-graphite-silica composites reinforced with different amounts of CrFeC particles (0, 8 and 12 wt%) were fabricated by powder metallurgy technique. The tribological behavior of the composites (noted 0CF, 8CF, 12CF) were studied under ambient conditions using a pin-on-disc machine. The results show that at different sliding speed specimen 8CF has lower wear rate (25–30 mg Km−1) than specimens 0CF (28–78 mg Km−1) and 12CF (40–57 mg Km−1) after the sliding distance of 12 Km. With the sliding distance and sliding speed increase, the friction coefficient and wear rate of specimen 0CF increased rapidly, but that of specimens 8CF and 12CF maintain a relatively stable value. The reason is that the hard CrFeC particles can restrict the plastic deformation of the composites in the process of wear. Furthermore, the wear mechanism of specimen 0CF is mainly delamination wear. The addition of CrFeC particles can decrease delamination, but high content of CrFeC particles cause the abrasive wear due to the formation of thick mechanically mixed layer. (paper)
[en] In this paper, a novel method to simulate soil heat flux for large spatial scale is proposed. This method is constructed with the ratio of soil heat flux and net radiation (G0/Rn) and surface characteristic parameters, such as ratio vegetation indices, surface temperature, surface shortwave infrared reflectance, soil moisture content, solar zenith angle. Field calibration is carried out using measured data in 2009 from Yingke, Huazhaizi, Arou, and Dayakou stations located in Heihe River Basin, Northwest of China. The estimated soil heat flux is compared with field observation data from Yingke and Arou stations in 2008. The overall deviation basis and correlation coefficient between the soil heat flux estimation and measured data are 13.4% and 0.804 in the Yingke station and 12.5% and 0.893 in the Arou station respectively, and also the correlation coefficient are 0.905 in the Maliantan station and 0.817 in the Binggou station respectively. Results indicated that the proposed method performed well in Heihe River Basin. This new method could be an optimal choice to estimate surface soil heat flux for large spatial scale in the future
[en] The aerodynamic roughness is one of the major parameters in describing the turbulent exchange process between terrestrial and atmosphere. Remote Sensing is recognized as an effective way to inverse this parameter at the regional scale. However, in the long time the inversion method is either dependent on the lookup table for different land covers or the Normalized Difference Vegetation Index (NDVI) factor only, which plays a very limited role in describing the spatial heterogeneity of this parameter and the evapotranspiration (ET) for different land covers. In fact, the aerodynamic roughness is influenced by different factors at the same time, including the roughness unit for hard surfaces, the vegetation dynamic growth and the undulating terrain. Therefore, this paper aims at developing an innovative aerodynamic roughness inversion method based on multi-source remote sensing data in a semiarid region, within the upper and middle reaches of Heihe River Basin. The radar backscattering coefficient was used to inverse the micro-relief of the hard surface. The NDVI was utilized to reflect the dynamic change of vegetated surface. Finally, the slope extracted from SRTM DEM (Shuttle Radar Topography Mission Digital Elevation Model) was used to correct terrain influence. The inversed aerodynamic roughness was imported into ETWatch system to validate the availability. The inversed and tested results show it plays a significant role in improving the spatial heterogeneity of the aerodynamic roughness and related ET for the experimental site
[en] Superparamagnetic sodium alginate nanoparticles with diameter around 25–30 nm were prepared with a water-in-oil emulsion method. The resulted magnetic SA nanoparticle was activated with glutaraldehyde and epichlorohydrin to form nanoscale support. Candida rugosa lipase (CRL), hereby chosen as a model enzyme, was covalently immobilized on the resulted magnetic support. The structure and magnetic behavior of the magnetic nanoparticles were confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. Based on the structural character of enzyme (containing functional residues that are ideal reaction sites for the immobilization of enzyme repeatedly), the regeneration of support was investigated by reactivating the deactivated immobilized lipase with glutaraldehyde. And the results indicated that these regenerated supports remained to be efficient for lipase immobilization. Finally, all of the immobilized CRL prepared by different generations of supports displayed excellent reusability and applicability.
[en] A fracture mechanics finite element analysis model of cylindrical pressure vessel with an opening nozzle is established through setting singular elements in the forefront of cracks. A stress intensity factor (SIF) automatically-calculated software of surface inclined cracks at the intersection of cylindrical vessels and nozzles which can be communicated with ANSYS program is programmed with Visual Basic. Based on the calculated SIF values of the cracks of different geometries subjected to internal pressure, the SIF curves varying with relative depths of cracks, crack relative radians, diameter ratio of vessels and nozzles and crack inclined angle have been obtained. (authors)