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[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[en] The intensity distribution in Fresnel diffraction through a slit includes numerous small fluctuations referred to as ripples. These ripples make the modelling of the intensity distribution complicated. In this study, we examine the characteristics of the Fresnel diffraction intensity distribution to deduce the rule for the peak position and then propose two types of quantum-mathematical models to obtain the distance between the edge and the peak point. The analysis and simulation indicate that the error in the models is below . The models can also be used to detect the edges of a diffraction object, and we conduct several experiments to measure the slit width. The experimental results reveal that the repetition accuracy of the method can reach . (paper)
[en] Supernovae (SNe) are the most brilliant optical stellar-class explosions. Over the past two decades, several optical transient survey projects discovered more than ∼ 100 so-called superluminous supernovae (SLSNe) whose peak luminosities and radiated energy are ≳ 7 × 1043 erg s−1 and ≳ 1051 erg respectively, at least an order of magnitude larger than those of normal SNe. According to their optical spectra features, SLSNe have been split into two broad categories of type I that are hydrogen-deficient and type II that are hydrogen-rich. Investigating and determining the energy sources of SLSNe would be of outstanding importance for understanding their stellar evolution and explosion mechanisms. The energy sources of SLSNe can be determined by analyzing their light curves (LCs) and spectra. The most prevailing models accounting for the SLSN LCs are the 56Ni cascade decay model, the magnetar spin-down model, the ejecta-circumstellar medium interaction model and the jet-ejecta interaction model. In this review, we present several energy-source models and their different combinations. (invited reviews)
[en] Large-scale exfoliation of defect-free and few-layer graphene by an inexpensive and environmentally-friendly route has been a significant challenge for a long time. Here we show that high-quality, few-layer graphene with high stability and low defect content can be obtained from natural graphite via a simple stirring process in urea/glycerol, with yields of up to 12 wt.%. We also demonstrate that this facile method can be applied to the exfoliation of other two-dimensional materials, such as molybdenum disulfide and boron nitride. The as-prepared graphene was further composited with polyvinylidene fluoride (PVDF) and the composite exhibited a low percolation threshold of 0.05 vol.%. The incorporation of low (4.5 vol.%) graphene amounts led to a significant increase in the thermal conductivity of the graphene–PVDF composites. .
[en] In this paper we collect 19 hydrogen-deficient superluminous supernovae (SLSNe) and fit their light curves, temperature evolution, and velocity evolution based on the magnetar-powered model. To obtain the best-fitting parameters, we incorporate the Markov chain Monte Carlo approach. We get rather good fits for seven events (χ 2/dof = 0.24–0.96) and good fits for another seven events (χ 2/dof = 1.37–3.13). We find that the initial periods (P 0) and magnetic strength (B p) of the magnetars that supposedly power these SLSNe are in the range of ∼1.2–8.3 ms and G, respectively; the inferred masses of the ejecta of these SLSNe are between 1 and , and the values of the gamma-ray opacity are between 0.01 and 0.82 cm2 g−1. We also calculate the fraction of the initial rotational energy of the magnetars harbored in the centers of the remnants of these SLSNe that is converted to the kinetic energy of the ejecta and find that the fraction is ∼19%–97% for different values of P 0 and B p, indicating that the acceleration effect cannot be neglected. Moreover, we find that the initial kinetic energies of most of these SLSNe are so small ( erg) that they can be easily explained by the neutrino-driven mechanism. These results can help clarify some important issues related to the energy-source mechanisms and explosion mechanisms and reveal the nature of SLSNe.
[en] We report the growth process of FeTe 1−x Sex ( ) monolayer films on SrTiO 3 (STO) substrates through molecular beam epitaxy and discuss the possible ways to improve the film quality. By exploring the parameters of substrate treatment, growth control and post growth annealing, we successfully obtain a series of FeTe 1−x Sex monolayer films. In the whole growth process, we find the significance of the temperature control through surface roughness monitored by the reflection high-energy electron diffraction and scanning tunneling microscopy. We obtain the best quality of FeSe monolayer films with the STO substrate treated at T = 900–950°C before growth, the FeSe deposited at T = 310°C during growth and annealed at T = 380°C after growth. For FeTe 1−x Sex ( ), both the growth temperature and annealing temperature decrease to T = 260°C. According to the angle-resolved photoemission spectroscopy measurements, the superconductivity of the FeTe 1−x Sex film is robust and insensitive to Se concentration. All the above are instructive for further investigations of the superconductivity in FeTe 1−x Sex films. (paper)
[en] Shannon information-entropy uncertainty is used to analyze fragments in the measured 140A MeV Ca + 9Be and Ni + 9Be reactions. A scaling phenomenon is found in the information-uncertainty difference of fragments between the reactions. The scaling phenomenon is explained in the manner of canonical ensemble theory, and is reproduced in simulated reactions using the antisymmetric molecular dynamics (AMD) and AMD + GEMINI models. The probes based on information uncertainty, requiring no equilibrium state of reaction, can be used in the non-equilibrium system, and bridge the results of the static thermodynamics models and the evolving dynamical transport models. (paper)
[en] Broad-lined Type Ic supernovae (SNe Ic-BL) are of great importance because their association with long-duration gamma-ray bursts (LGRBs) holds the key to deciphering the central engine of LGRBs, which refrains from being unveiled despite decades of investigation. Among the two popularly hypothesized types of central engine, i.e., black holes and strongly magnetized neutron stars (magnetars), there is mounting evidence that the central engine of GRB-associated SNe (GRB-SNe) is rapidly rotating magnetars. Theoretical analysis also suggests that magnetars could be the central engine of SNe Ic-BL. What puzzled the researchers is the fact that light-curve modeling indicates that as much as of 56Ni was synthesized during the explosion of the SNe Ic-BL, which is unfortunately in direct conflict with current state-of-the-art understanding of magnetar-powered 56Ni synthesis. Here we propose a dynamic model of magnetar-powered SNe to take into account the acceleration of the ejecta by the magnetar, as well as the thermalization of the injected energy. Assuming that the SN kinetic energy comes exclusively from the magnetar acceleration, we find that although a major fraction of the rotational energy of the magnetar is to accelerate the SN ejecta, a tiny fraction of this energy deposited as thermal energy of the ejecta is enough to reduce the needed 56Ni to 0.06 M ⊙ for both SN 1997ef and SN 2007ru. We therefore suggest that magnetars could power SNe Ic-BL in aspects both of energetics and of 56Ni synthesis.
[en] Highlights: • A new fabrication method for silicon nanowires/micropillars structure is proposed. • The method is using lithography and metal-assisted chemical etching to fabricate silicon nanowires/micropillars structure. • The optimal light trapping properties of silicon nanowires structure were systemically investigated including etching concentration, etching time and etching temperature. • The average reflectance of silicon nanowires/micropillars structure was 1.96% in the wavelength range of 300–1000 nm. - Abstract: In this paper, a new fabrication method for silicon nanowires/micropillars structure is proposed. This method is using lithography and metal-assisted chemical etching to fabricate the structure of silicon nanowires/micropillars. In the experiment, to obtain the optimal light trapping properties of silicon nanowires/micropillars structure, the optimal light trapping properties of silicon nanowires were systemically investigated, including etching concentration, etching time and etching temperature. And then, a large-area uniform, controllable and optimal light trapping silicon nanowires/micropillars structure was fabricated using lithography and metal-assisted chemical etching method. This controllable and facile method for silicon nanowires/micropillars structure will expand its application in the field of optoelectronic devices and solar cells.
[en] To determine Z-score equations and reference ranges for Doppler flow velocity indices of cardiac outflow tracts in normal fetuses. A prospective cross-sectional echocardiographic study was performed in 506 normal singleton fetuses from 18 to 40 weeks. Twelve pulsed-wave Doppler (PWD) measurements were derived from fetal echocardiography. The regression analysis of the mean and the standard deviation (SD) for each parameter were performed against estimated fetal weight (EFW) and gestational age (GA), in order to construct Z-score models. The correlation between these variables and fetal heart rate were also investigated. Strong positive correlations were found between the twelve PWD indices and the independent variables. A linear-quadratic regression model was the best description of the mean and SD of most parameters, with the exception of the velocity time interval (VTI) of ascending aorta against EFW, which was best fitted by a fractional polynomial. Z-score equations and reference values for PWD indices of fetal cardiac outflow tracts were proposed against GA and EFW, which may be useful for quantitative assessment of potential hemodynamic alternations, particularly in cases of intrauterine growth retardation and structural cardiac defects.