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[en] Highlights: • A model of irreversible Meletis-Georgiou cycle is established. • Heat transfer loss and internal irreversibility of cycle are considered. • Finite time thermodynamic theory is applied. • Work output and thermal efficiency are obtained. • They are also maximized with respect to the volume ratios. - Abstract: An irreversible model of Meletis-Georgiou cycle (MGC) is investigated in this paper. Finite time thermodynamic (FTT) theory is introduced, and internal irreversibility of the cycle (IIC) and heat transfer loss (HTL) are considered. The expressions of the work output (WO) and thermal efficiency (TE) of the MGC are obtained, and they are maximized with respect to the volume ratios. The effects of the IIC on the WO and TE are analyzed, and the optimal cycle performances are obtained. It shows that the compression ratio (CR) has its optimal value, which makes the WO or TE reach to its maximum. Therefore, the relationship between WO and TE is loop-shaped one, which is coincidence with the performance of real engine. The results enrich the theoretical studies of the rotary engine and provide some guidelines for practical devices.
[en] Vanadium dioxide (VO2) has a great potential to be utilized as solar energy switching glazing, even though there exist some intrinsic problems of low luminous transmittance (Tlum) and poor oxidation resistance. Si–Al based anti-reflection (AR) sol–gel coatings processed at low temperature have been developed to tackle these issues assisted by adjusting ramping rate and annealing temperature. Si–Al based AR coating gives large relative enhancement on the transmittance (22% for Tlum, 14% for the whole solar spectrum Tsol,) and successfully maintains IR contrast at 2500 nm wavelength with 18% relative increase in solar modulation (ΔTsol). The optimized Si–Al based AR coating annealing conditions are recorded at 3 °C/min ramping rate and 100 °C annealing temperature. Fluorinated-Si based gel offers a new direction of multifunctional overcoat on thermochromic smart windows with hydrophobicity (contact angle 111°), averaged 14% relatively increased luminous transmittance and enhanced oxidation resistance.
[en] Due to the nonlinear effect and the thermal effect, a single optical fiber has limitations in the output power. A beam combination of laser arrays based on adaptive optics can both improve the output power and ensure higher beam quality. This article puts forward one novel fiber positioner structure based on the flexible hinges amplification mechanism, which is the adaptive fiber optics collimator (AFOC), to correct tip-tilt aberration. The theoretical model was established, and the amplification ratios between the output displacement and device’s structure parameters were calculated. The first 6 orders of the mode shape of the vibration of amplification mechanism was obtained by using a modal analysis. Analysis results revealed an excellent performance for the flexible hinges amplification mechanism. The novel fiber positioner has good prospects for applications in laser beam combination systems for ideal tip-tilt control.
[en] The modeling and state-of-charge estimation of the batteries and ultracapacitors are crucial to the battery/ultracapacitor hybrid energy storage system. In recent years, the model based state estimators are welcomed widely, since they can adjust the gain according to the error between the model predictions and measurements timely. In most of the existing algorithms, the model parameters are either configured by theoretical values or identified off-line without adaption. But in fact, the model parameters always change continuously with loading wave or self-aging, and the lack of adaption will reduce the estimation accuracy significantly. To overcome this drawback, a novel co-estimator is proposed to estimate the model parameters and state-of-charge simultaneously. The extended Kalman filter is employed for parameter updating. To reduce the convergence time, the recursive least square algorithm and the off-line identification method are used to provide initial values with small deviation. The unscented Kalman filter is employed for the state-of-charge estimation. Because the unscented Kalman filter takes not only the measurement uncertainties but also the process uncertainties into account, it is robust to the noise. Experiments are executed to explore the robustness, stability and precision of the proposed method. - Highlights: • A co-estimator is proposed to estimate the model parameters and state-of-charge. • The extended Kalman filter is used for model parameter adaption. • The unscented Kalman filter is designed for state estimation with strong robust. • The dynamic profiles are employed to verify the proposed co-estimator.
[en] In recent years, intense laser facilities have been widely used in laboratory astrophysics,and with the development of imaging and analyzing techniques, important advances have been made in this field. These include self-organized electromagnetic field structures in laser-produced counter-streaming plasmas, turbulent amplification of magnetic fields in laboratory laser-produced shock waves, laboratory formation of a scaled protostellar jet by coaligned poloidal magnetic fields, and modeling of the interaction of the solar wind with a dipole magnetic field using the intense Shenguang II lasers. The results achieved have promoted our understanding of protostellar bodies, jets of Herbig-Haro objects, the shockwave of supernova remains, and the earth's magnetosphere near the pole regions. This article will present an overview of the above topics,as well as some outlook on future laboratory astrophysics research. (authors)
[en] Transparent superhydrophobic coatings, having high water contact angle (>160°) and low sliding angle (<5°), were prepared by using poly(methylhydrosiloxane) (PMHS) and tetraethoxysilane (TEOS) as precursors based on a simple sol–gel process. The influence of different mass ratios of PMHS to TEOS on the transparency and superhydrophobicity of resulting coatings was investigated herein to get the optimum performance coating. The structure, composition and morphology of optimum performance coating were characterized by various technologies including Fourier transform infrared (FT-IR) spectroscopy, thermal analysis, BET, 29Si CP MAS NMR, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The optimum performance coating exhibits superhydrophobicity (CA, 164.7° and SA, 2.7°), a high transparency (transmittance closes to 90%) and a good thermal stability (up to 400 °C). Note that the optimum coating directly from sol–gel process exhibits poor moisture resistance. The low surface energy and high volume-fraction porosity structure are responsible for the superhydrophobicity, transparency and thermal stability of the as-prepared coating, while the poor moisture is attributed to the untreated hydroxyl groups on the surface of coating. The moisture resistance of coating can be improved by further treated by cetyltrimethoxylsilane (CTMS), and the coating could switch from superhydrophobic (164.7°) to superhydrophilic (0°) after heat-treating at 600 °C.
[en] Alternating Fe,Cr layers were deposited on the glass and the pure iron substrates placed in a target chamber of a 200 KeV implanter. Fe-Cr amorphous films have been formed by ion beam mixing with 150 KeV Ar+, P+ and B+ respectively. The doses were varied from 1.5x1015ions/cm2 to 5x1016ions/cm2. The process of ion bombardment was simulated by TRIM-88 program. Microstructures of the ion-mixed Fe-Cr samples were examined by transmission electron microscope (TEM). The anodic polari-zation curves were obtained by means of a potentiodynamic sweep system. Results show that the corrosion resistance of the amorphous film in 1N H2SO4 solution is considerably increased than that of pure iron. It is found by X-ray photoelectron spectroscopy (XPS) analysis that the in-crease of the corrosion resistance is associated with an ultra-thin Cr-rich surface film, which contains a compound of [CrOx (OH)y·nH2O]. (author). 3 refs.; 4 figs.; 3 tabs
[en] In this paper, we investigate the 1/4 BPS Wilson-’t Hooft loops in N=4 supersymmetric Yang-Mills theory. We use the bulk D3-brane solutions with both electric and magnetic charges on its world-volume to describe some of 1/4 BPS Wilson-’t Hooft loops. The D3-brane supersymmetric solutions are derived form requiring κ-symmetry. We find the two consistent constraints for Killing spinors and calculate the conserved charges of straight 1/4 BPS Wilson-’t Hooft loops and expectation values of circular 1/4 BPS Wilson-’t Hooft loops separately.
[en] The nonlinear frequency shift is derived in a transparent asymptotic form for intense Langmuir waves in general collisionless plasma. The formula describes both fluid and kinetic effects simultaneously. The fluid nonlinearity is expressed, for the first time, through the plasma dielectric function, and the kinetic nonlinearity accounts for both smooth distributions and trapped-particle beams. Various known limiting scalings are reproduced as special cases. The calculation avoids differential equations and can be extended straightforwardly to other nonlinear plasma waves
[en] We are developing a compact rubidium atomic beam frequency standard with optical pumping and detection. The cavity for microwave interrogation is an important part of the clock. The cavity in our design is a Ramsey-type, E-bend one, which is the same as the conventional method in most cesium beam clocks. Requirements for the design are proposed based on the frequency shift associated with the cavity. The basic structure of the cavity is given by theoretical analysis and detailed dimensions are determined by means of electromagnetic field simulation with the help of commercial software. The cavity is manufactured and fabricated successfully. The preliminary test result of the cavity is given, which is in good agreement with the simulation. The resonant frequency is 6.835 GHz, equal to the clock transition frequency of 87Rb, and the loaded quality factor is 500. These values are adjustable with posts outside the cavity. Estimations on the Ramsey line width and several frequency shifts are made. (paper)