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[en] The cold start characteristic of hydraulic free piston diesel engine may affect its stable operation. Therefore the specific cold start characteristics, such as BDC or TDC positions, pressure in-cylinder, heat release rate, should be investigated in detail. These parameters fluctuate in some regularity in the cod start process. With the development of the free piston engine prototype and the establishment of test bench, the results are obtained. For the dynamic results, the fluctuation range of TDC and BDC positions is 8 mm and decreases with time. The thermodynamic results show that the combustion process is not stable and the pressure in-cylinder fluctuates largely in the cold start process. In addition, the combustion is rapid and knock happens inevitably. In order to investigate the reasons, a CFD model is established for temperature analysis in-cylinder and heat transfer conditions. It is found that higher start wall temperature will lead to more uniform temperature distribution. The delay period may decreases and heat release will move forward. This reason is analyzed by thermodynamic derivation based on the first law of thermodynamics. Finally, the improvement suggestions of cold start strategy are proposed. - Highlights: • The cold start behaviors of HFPE are investigated in detail. • CFD method is used for simulating temperature distribution in start process. • Thermodynamic derivation uncovers the compression temperature distribution. • The improvement suggestions of cold start strategy are proposed.
[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] 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] A method of fabricating selenium (Se) microwire is demonstrated. A multimaterial fiber with amorphous selenium (a-Se) core and multicomponent phosphate glass cladding is drawn by using a conventional optical fiber drawing technique. Then the a-Se core of the fiber is crystallized by a post thermal process at 150 °C. After the multicomponent phosphate glass cladding is stripped from the multimaterial fiber by marinating the fiber in HF acid solution, a crystalline selenium (c-Se) microwire with high uniformity and smooth surface is obtained. Based on microstructure measurements, the c-Se microwire is identified to consist of most hexagonal state particles and very few trigonal state whiskers. The good photoconduction property of c-Se microwire with high quality and longer continuous length makes it possible to apply to functional devices and arrays. (paper)
[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] Highlights: • An analytical model for inductance of thin-film magnetic devices was developed. • Different device topologies and magnetic permeabilities were addressed. • Inductance of various topologies were calculated and compared with simulation. • The model predicts simulated values with excellent accuracy. - Abstract: A generic analytical model has been developed to fully describe the flux closure through magnetic inductors. The model was applied to multiple device topologies including solenoidal single return path and dual return path inductors as well as spiral magnetic inductors for a variety of permeabilities and dimensions. The calculated inductance values from the analytical model were compared with simulated results for each of the analyzed device topologies and found to agree within 0.1 nH for the range of typical thin-film magnetic permeabilities (∼102 to 103). Furthermore, the model can be used to evaluate behavior in other integrated or discrete magnetic devices with either non-isotropic or isotropic permeability and used to produce more efficient device designs in the future.
[en] The surface microstructure and its evolution during long-term room-temperature storage were studied using transmission electron microscopy for an Al-Zn-Mg-Cu alloy processed by surface abrasion with grinding paper. An altered surface layer (ASL) with thickness of 0.4–0.8 μm was present on the alloy after abrasion. Ultrafine subgrains with width of about 50–120 nm and a high density of dislocations were observed in the ASL. The pre-existing aging-induced η′ and η precipitates dissolved during surface abrasion. During room-temperature aging, relatively pure Zn, Al_2Cu and AlCu phases were observed to precipitate at the extreme surface and subgrain boundaries in the ASL. These phases are very unusual in that they are typically not formed in Al-Zn-Mg-Cu alloys. Mg was not found in these particles, as it remained dissolved in the solid solution of the ASL. Al_2Cu and AlCu phases also precipitated at the grain boundaries in the underlying substrate right below the ASL, as far as 6 μm in depth from the extreme surface. Considerable growth and coarsening of these phases occurred during natural aging over a period of 42 months. The enhanced diffusion accelerated by vacancies, dislocations, and subgrain/grain boundaries was considered to be mainly responsible for the accelerated precipitation and growth of these atypical phases.
[en] Highlights: • A new V35Ti35Fe15Cr10Zr5 high-entropy alloy with a BCC structure was designed and fabricated. • The yield strength of as-cast V35Ti35Fe15Cr10Zr5 HEA increased with increasing the temperature below 500 °C. • At 700 °C, the yield strength of V35Ti35Fe15Cr10Zr5 HEA was about 500 MPa higher than that of candidate alloys. • V35Ti35Fe15Cr10Zr5 alloy has a relative low ductility below 700 °C, while the alloy exhibits a good ductility above 700 °C. Low-activation structural materials for fusion applications beyond 700 °C are desired. High-entropy alloys (HEAs) with excellent properties at elevated temperatures are suitable for use in nuclear reactors. A newly developed V35Ti35Fe15Cr10Zr5 HEA was fabricated by vacuum arc melting and the microstructure of as-cast and annealed sample was found to be composed of BCC solid solution phases. It was interesting to find that the yield strength of as-cast V35Ti35Fe15Cr10Zr5 HEA increased with increasing the temperature below 500 °C, and it was much higher than that of vanadium alloy or martensitic steel for fusion reactors in the temperature range of room temperature to 900 °C. At 700 °C, the yield strength of V35Ti35Fe15Cr10Zr5 HEA was about 500 MPa higher than that of vanadium alloy or martensitic steel, showing promise for high temperature applications. V35Ti35Fe15Cr10Zr5 alloy had a relative low ductility below 700 °C, while the alloy exhibited a good ductility above 700 °C.
[en] Gut microbiota is critical for maintaining body immune homeostasis and thus affects tumor growth and therapeutic efficiency. Here, we investigated the link between microbiota and tumorgenesis in a mice model of subcutaneous melanoma cell transplantation, and explored the underlying mechanism. We found disruption of gut microbiota by pretreating mice with antibiotics promote tumor growth and remodeling the immune compartment within the primary tumor. Indeed, gut microbial dysbiosis reduced the infiltrated mature antigen-presenting cells of tumor, together with lower levels of co-stimulators, such as CD80, CD86 and MHCII, as well as defective Th1 cytokines, including IFNγ, TNFα, IL12p40, and IL12p35. Meantime, splenic APCs displayed blunted ability in triggering T cell proliferation and IFNγ secretion. However, oral administration of LPS restored the immune surveillance effects and thus inhibited tumor growth in the antibiotics induced gut microbiota dysbiosis group. Taken together, these data highly supported that antibiotics induced gut microbiota dysbiosis promotes tumor initiation, while LPS supplementation would restore the effective immune surveillance and repress tumor initiation. - Highlights: • Antibiotics induced gut microbiota dysbiosis promotes tumor initiation in mice. • Gut microbiota disruption compromise APC-Th1 development in tumor. • Orally LPS administration rescues tumor immune surveillance in gut microbiota disrupted mice. • None of the authors have any conflict of interest.
[en] Highlights: • High quality Mg_2Si films were grown on Si (111) and glass substrates with magnetron sputtering, respectively. • The first observation of Photoluminescence (PL) of Mg_2Si films was reported. • The Mg_2Si PL emission wavelengths are almost independence on temperature in the range of 77–300 K. • The strongest PL emissions may be attributed to interstitial Mg donor level to valence band transitions. • The activation energy of Mg_2Si is determined from the quenching of major luminescence peaks. - Abstract: To understand the photoluminescence mechanisms and optimize the design of Mg_2Si-based light-emitting devices, Mg_2Si films were fabricated on silicon (111) and glass substrates by magnetron sputtering technique, and the influences of different substrates on the photoelectric properties of Mg_2Si films were investigated systematically. The crystal structure, cross-sectional morphology, composition ratios and temperature-dependent photoluminescence (PL) of the Mg_2Si films were examined using X-ray diffraction (XRD), Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and PL measurement system, respectively. XRD results indicate that the Mg_2Si film on Si (111) displays polycrystalline structure, whereas Mg_2Si film on glass substrate is of like-monocrystalline structure.SEM results show that Mg_2Si film on glass substrate is very compact with a typical dense columnar structure, and the film on Si substrate represents slight delamination phenomenon. EDS results suggest that the stoichiometry of Mg and Si is approximately 2:1. Photoluminescence (PL) of Mg_2Si films was observed for the first time. The PL emission wavelengths of Mg_2Si are almost independence on temperature in the range of 77–300 K. The PL intensity decreases gradually with increasing temperature. The PL intensity of Mg_2Si films on glass substrate is much larger than that of Mg_2Si film on Si (111) substrate. The activation energy of 18 meV is determined from the quenching of major luminescence peak(1342 nm) as a function of temperature in the Mg_2Si film grown on Si (111) substrate, which is much smaller than that deduced in the sample grown on glass substrate (about 25meV). The small activation energy can be attributed to the additional nonradiative centers originated from relatively poor crystal quality.The physical mechanism responsible for the measured ∼1342 nm and other three longer wavelengths emissions may be respectively result from strong Mg_i donor level to valence band transitions and other defect-related radiative recombination occurred in the Mg_2Si films.