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[en] Solar radiation and sunshine duration data from 69 meteorological stations in China was used to develop the formula for estimating the monthly average daily global radiation on a horizontal surface. Several models and correlations that embrace such variables as the fraction of sunshine duration, the latitude and the altitude have been selected, tested and compared to decide which model is recommended on the basis of statistical error tests. In this study, using the relative duration of sunshine as a single independent variable, the most accurate equation that is expressed in a third order form was obtained for each station. The results show that the coefficients are site dependent. Subsequently, taking the radiation data and geographical parameters at all 69 stations as reference, a countrywide general equation was established. Compared with the equation using the relative duration of sunshine as a single independent variable, the general equation shows relatively lower accuracy, but estimating the global solar radiation by this equation has proved sufficiently reliable. This equation can be used to estimate the monthly average daily global radiation in areas where the radiation data is missing or not available, so that a geographical distribution of global solar radiation across the country may be obtained
[en] The dynamic rotor behavior is significantly affected by the stiffness and damping characteristics of the bearings. Therefore, it is important to identify these bearing parameters. For active magnetic bearings (AMBs), these bearing parameters not only could be identified from rotor dynamic response, but also from electrical control system transfer function. Some identification works from rotor dynamic response have been reported, but identification from electrical control system transfer function is relatively few. In this paper, we deduced the equivalent stiffness and damping expressions with electrical control system transfer function for rotor AMBs and identified these values from electrical control system model. To evaluate the identified results, previous reported results from rotor dynamic response is employed for comparison. We found that for the stiffness, a complete and precise electrical control model will obtain relatively consistent values; however, for the damping, the accurate electrical control model is still not enough and the eddy current loss should be included.
[en] Multiwalled carbon nanotubes-sulfur (MWCNTs-S) composites were synthesized by chemical activation of MWCNTs and capillarity between sulfur and MWCNTs. The MWCNTs activated by potassium hydroxide (denoted as K-MWCNTs) were used as conductive additive. The as-prepared K-MWCNTs-S composites can display excellent cycle stability and rate capability with the initial discharge capacity of 741 mAh g−1 and capacity retention of 80% after 50 cycles compared to pure S. The improvement in the electrochemical performance for K-MWCNTs-S composites is attributed to the interstitial structure of the MWCNTs resulted from the strong chemical etching, which can facilitate the insertion and extraction of Li ions and more better percolation of the electrolyte, and also ascribed to enhanced electronic conductivity of K-MWCNTs-S composites. It is indicated that the K-MWCNTs-S composites can be used as the cathode materials for lithium–sulfur batteries.
[en] On the basis of one simple gain boundary model, the trapped states of positrons at grain boundaries in pure Aluminium are solved and the corresponding positron annihilation lifetime spectra are calculated. The correlations between the atomic density distributions of grain boundaries and the lifetime spectra are discussed and the existing experimental results are explained theoretically
[en] In order to develop compact accelerators with small beam spot, a C-band 5.52 GHz 2 MeV SW accelerating tube is physically designed and studied, which operated in the π/2 mode. Not using any exterior focusing element, transverse emittance growth aroused from space charge effect is restrained efficiently by repeatedly bunching and utilizing dissymmetry field of first cavity. The accelerating tube consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163 mm, excited with 1 MW magnetron. In final dynamics simulation, 2 MeV 150 mA beam pulse current is obtained, and the capture efficiency is more than 30%. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot (Full Width at Half Maximum of density distribution) is about 0.55 mm. (authors)
[en] Graphical abstract: Three-dimensional porous reduced graphene hydrogels with tunable pore size distribution are prepared by using thiourea dioxide in GO suspension with ammonia. - Highlights: • Three-dimensional reduced graphene hydrogels (RGHs) were prepared. • Thiourea dioxide was used as reducing agent with ammonia. • RGHs showed tunable pore size distribution by thiourea dioxide. • RGHs exhibited relatively good electrochemical properties in supercapacitor. - Abstract: In present work, we demonstrate a rapid and easy approach to fabricate three-dimensional (3D) reduced graphene hydrogels (RGHs) by using thiourea dioxide as reducing agents in an aqueous solution of graphene oxide (GO) with ammonia. The transformation of GO suspension to the hydrogels can be confirmed by X-ray powder diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. The hierarchical porosity, structure and surface chemical properties can be demonstrated by N_2 sorption experiments, scanning electron microscopy and X-ray photoelectron spectroscopy. With adding different amounts of thiourea dioxide, the obtained RGHs behave different degree of reduction, controlled specific surface area and pore size distribution, and unlike performances in supercapacitors. Benefiting from well-defined and cross-linked 3D porous network architectures, the supercapacitors based on the RGHs in KOH electrolyte exhibited a high specific capacitance of 258.6, 167.3 and 198.3 F g"−"1 at 0.1 A g"−"1 for RGHs-1, RGHs-2 and RGHs-5, respectively. Furthermore, this capacitance also showed good electrochemical stability and a high degree of reversibility in the repetitive charge/discharge cycling test
[en] Applying the daily global solar radiation data measured at least 10 years, the typical solar radiation year for 30 meteorological stations in China is generated using the Finkelstein-Schafer statistical method. Based on the typical solar radiation data obtained, the geographical difference of solar energy resource of these 30 stations was also analyzed. The results in this paper will fill this gap that complete and detailed typical solar radiation data are not available for China, and will be useful to the designers of solar energy conversion and utilization devices. (author)
[en] Observables that related to the flows in intermediate and relativistic energy heavy ion collisions are discussed. The flow parameters which describe directe flow, squeeze-out and elliptic flow, as well as probing the equation of state, in medium n-n cross section and the dynamical emission are reviewed
[en] In present work, we demonstrate an efficient and facile strategy to fabricate three-dimensional (3D) nitrogen-doped graphene aerogels (NGAs) based on melamine, which serves as reducing and functionalizing agent of graphene oxide (GO) in an aqueous medium with ammonia. Benefiting from well-defined and cross-linked 3D porous network architectures, the supercapacitor based on the NGAs exhibited a high specific capacitance of 170.5 F g"−"1 at 0.2 A g"−"1, and this capacitance also showed good electrochemical stability and a high degree of reversibility in the repetitive charge/discharge cycling test. More interestingly, the prepared NGAs further exhibited high adsorption capacities and high recycling performance toward several metal ions such as Pb"2"+, Cu"2"+ and Cd"2"+. Moreover, the hydrophobic carbonized nitrogen-doped graphene aerogels (CNGAs) showed outstanding adsorption and recycling performance for the removal of various oils and organic solvents. - Graphical abstract: Three-dimensional nitrogen-doped graphene aerogels were prepared by using melamine as reducing and functionalizing agent in an aqueous medium with ammonia, which showed multifunctional applications in supercapacitors and adsorption. - Highlights: • Three-dimensional nitrogen-doped graphene aerogels (NGAs) were prepared. • Melamine was used as reducing and functionalizing agent. • NGAs exhibited relatively good electrochemical properties in supercapacitor. • NGAs exhibited high adsorption performance toward several metal ions. • CNGAs showed outstanding adsorption capacities for various oils and solvents
[en] This paper describes the control and data acquisition of three-dimensional magnetic field mapping device for BESIII. A special motor driving system was adopted to meet the 3D moving requirement, and a control and acquisition software was designed. (authors)