Macrostructure and properties of thin walled copper tubes prepared by the downward continuous unidirectional solidification method

The macrostructure and properties of the thin walled copper tube prepared by the downward continuous unidirectional solidification (DCUS) method were studied. The result shows that the macrostructure is closely related to the solid-liquid interface profile, which is influenced by the distance between the cooling water location and the solidification front. The mechanical properties of the thin walled copper tube prepared by the DCUS method are near those of the normal cast copper, and it has good relative density, electrical conductivity, and elongation, which are not greatly affected by casting speed. The thin walled copper tube prepared by the DCUS method also has good processing properties that can be taken to further drawing procedures directly without an intermediate process, and obtains good mechanical properties with the total processing rate of 89.8%.     

Flame instability analysis of diethyl ether-air premixed mixtures at elevated pressures

Combustion characteristics of premixed diethyl ether-air mixtures were studied at different equivalence ratios and elevated initial pressures using schlieren photography and spherically propagating flame. Laminar burning velocities, Markstein number and critical radii at onset of cellular structure were obtained. The results show that an increase in initial pressure leads to a decrease in the unstretched laminar burning velocities. Laminar burning velocities give their peak values at the equivalence ratio o...     

Tectonic rotation in the western South-Dabashan orogenic belt in late Mesozoic

A paleomagnetic study was carried out on Early-Middle Jurassic sediments in the Zhenba area, the western South-dabashan orogenic belt. Stepwise thermal demagnetization isolated the characteristic high temperature component (HTC) (D=37.1°, I=46.1°, α95=10.1°), which passed the fold test. By comparing the corresponding pole of HTC (57.6°N, 196.6°E, A95=9.9°) with coeval reference poles for the Sichuan basin, we detected a 26.5°±9.0° clockwise rotation of the study area relative to the stable Sichuan basin. We...     

市场化进程、融资约束与现金持有价值

选取我国沪深A股上市企业2013—2021年财务数据为样本,运用固定效应模型检验市场化进程对企业现金持有价值的影响及其渠道机制。研究得出：市场化进程对现金持有价值具有显著负向效应,并且融资约束起中介效应;异质性分析中发现在投资者保护度较低、信息不对称程度较高以及企业成长性较高时该效应更明显。进一步研究得出,现金持有水平还有利于缓解企业的经营风险,促进经营业绩。渠道机制表明持有高额的现金能够发挥预防性功能,在市场化进程较低时可以提高现金持有价值;企业要制定较有弹性的现金持有政策以应对不断变化的外部市场环境;对于持有现金政策的制定不可忽略融资约束这一重要中介变量。     

High-resolution algorithm based on temporal-spatial extrapolation

To enhance the resolution of parameter estimation with limited samples received by a short passive array, an iterative nonparametric algorithm for estimating the frequencies and direction-of-arrivals (DOAs) of signals is proposed. The cost function is constructed using l2-norm Gaussian entropy combined with an additional constraint, l2-norm constraint or linear constraint. By minimizing the cost functions in the temporal and the spatial dimensions using corresponding iteration algorithms respectively, the s...     

椭圆型方程组解的性质的某些发展

本文综述了椭圆组解的有界性和解的Ｈｏｌｄｅｒ连续性的某些发展。     

Acerbi—Fusco定理的一个新证明

Ａｃｅｒｂｉ－Ｆｕｓｃｏ利用Ｓｏｂｏｌｅｖ空间ＷＰ（Ｇ，Ｅ＾Ｎ）中函数的逼定理得到了拟凸泛函Ｉ（ｕ，Ｇ）＝∫Ｇｆ（ｕ）ｄｘ，Ｕ∈ＷＰ（Ｇ，Ｅ＾Ｎ），Ｐ≥２，Ｎ〉１极小的部分正则性，Ｅｖａｎｓ－Ｇａｒｉｅｐｙ利用Ｒａｄｏｎ测度的性质重新证明了Ａｃｅｒｂｉ－Ｆｕｓｃｏ定量，本文我们给出一个较为简捷的证明，既不用Ｗ（Ｇ，Ｅ＾Ｎ）中的逼近定理，也不用Ｒａｄｏｎ测度的任何性质。     

4-D parameter estimation of narrowband sources based on parallel factor analysis

A novel algorithm is presented in this paper to jointly estimate frequency, two-dimensional （2-D） direction-of-arrival （DOA）, and range of near-field narrowband sources. The proposed method extends the parallel factor （PARAFAC） analysis model from the common data- and subspace-domain to the cumulant one, and forms three-way arrays by using the five cumulant matrices obtained from the array outputs, and analyzes the uniqueness of low-rank decomposition of the three-way arrays, then jointly estimates source parameters via the low-rank decomposition. In comparison with the conventional methods, the proposed method alleviates the loss of the array aperture, and avoids pairing parameters. What is more important, this algorithm can deal with mixed far-field and near-field sources. Finally, the simulation results validate the performance of the proposed method.