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1.
本文演示了紧凑的绿色和近红外双色连续波激光光源,其发射波长分别为516 nm和775 nm。设计并制造了级联的周期性极化掺镁铌酸锂晶体,用于同时转换通信波长的二次谐波(SHG)和三次谐波(THG),可以在相同温度下获得绿色和近红外激光的输出。通过建立一个单程激光测量系统,在2 W泵浦功率下获得516 nm的0.15 mW绿光和775 nm的1.19 mW的光,晶体温度控制在30.8 ℃。实验结果将为单激光器泵浦的紧凑型双波长共线激光器提供重要的案例。  相似文献   
2.
Applied Mathematics and Mechanics - Mechanical models of residually stressed fibre-reinforced solids, which do not resist bending, have been developed in the literature. However, in some residually...  相似文献   
3.
研究了一类特殊情形m=1的重心权Hermite有理插值,证明了该插值函数的二阶导数r1?x在插值节点和非插值节点处分别以Oh2d-1Oh2d-3的速度收敛于函数f?x。数值例子进一步验证了方法的有效性。  相似文献   
4.
证明6维严格近凯勒流形中的二阶平行拉格朗日子流形一定是全测地的,这推广了L.Vrancken等人文中的一个重要结果.特别地,得到了齐性近凯勒S3×S3中该类拉格朗日子流形的完全分类.  相似文献   
5.
A connected graph G=(V,E) is called a quasi-tree graph if there exists a vertex v_0∈V(G) such that G-v_0 is a tree.In this paper,we determine all quasi-tree graphs of order n with the second largest signless Laplacian eigenvalue greater than or equal to n-3.As an application,we determine all quasi-tree graphs of order n with the sum of the two largest signless Laplacian eigenvalues greater than to 2 n-5/4.  相似文献   
6.
本文利用参数变易法研究了时间尺度上二阶变系数线性动力学方程的解与Ulam稳定性问题. 特别地,在不同的系数情形下建立了二阶常系数线性动力学方程的Ulam稳定性理论.  相似文献   
7.
In the light of recent developments in computer technology, a promising and efficient way to design a material with a desired property would be to solve the inverse problem: use a physical property to predict structure. Here, we discuss the basic idea and mathematical foundation of the inverse approach, and proposed strategies for its utilization in the design of materials over nano‐ to macro‐scales. At the nano‐scale, analyzed strategies include scanning of a high‐dimensional space of chemical compounds for those compounds that have a targeted property, and identification of correlations in large databases of materials. However, unlike utilization of inverse approach at nano‐scale where full structural information ‐ atoms and their positions‐ is linked to targeted properties, at the meso‐ and macro‐scale, only partial structural information, manifested via structural motifs or representative volume elements, is available. We discuss the role of partial structural information in the inverse approach to the design of materials at those scales. Risks and limitations of the inverse approach are analyzed and dependence of the approach on factors such as structure parametrization, approximations in theoretical models, and feedback from structural characterization, is addressed.

  相似文献   

8.
In the maritime environment slamming is a phenomenon known as short duration impact of water on a floating or sailing structure. Slamming loads are local and could induce very high local stresses. This paper reports a series of impact test results and investigate the slamming loads and pressures acting on a square based pyramid. In this study the slamming tests have been conducted at constant velocity impact with a hydraulic high speed shock machine. This specific experimental equipment avoids the deceleration of the structure observed usually during water entry with drop tests. Three velocities of the rigid pyramid have been used (10, 13 and 15 m s−1). Time-histories of local pressures, accelerations and slamming loads were successfully measured. The relationship between the pressure magnitude and the impact velocity is obtained and the spatial distribution of pressures on pyramid sides is characterized. The impact velocity was found to have a negligible influence in predicting the maximum pressure coefficient.  相似文献   
9.
通过?30 mm杀爆燃弹外场炮击实验,模拟车辆、装备油箱被炮火击中后二次爆炸场景,采用高速照相机、红外热成像仪分别记录引爆柴油过程和爆炸火球的温度场,对比评估普通柴油、含水型柴油和抑爆型柴油的爆炸特性。实验结果显示:炮弹射击油箱瞬间,柴油液滴被抛撒出油箱,与空气快速混合形成气溶胶,并在炸药能量作用下引发爆炸,形成爆炸火球;不同类型柴油的爆炸火球均经历3个发展阶段,但其尺寸、扩展速率和表面温度等有较大差别,普通柴油和含水型柴油的火球这3个参数比较接近,都大于抑爆型柴油;含水型柴油的油箱毁伤容积为108.00 dm3,远高于普通柴油的57.65 dm3和抑爆型柴油的38.15 dm3。研究表明,抑爆柴油中的高分子聚合物能起到较好的抑爆作用。  相似文献   
10.
The unit of time of the International System of Units (SI), the “atomic second” was defined through a constant of physics in 1967. It is derived from the frequency of the hyperfine transition of the atom of cesium 133. From the astronomical definition of the second until today, the accuracy of the realization of the second has improved by eight orders of magnitude, with a rate that has increased since the development of the cesium frequency standards, to reach parts in 1016 for the best clocks today. In 2018, when the new SI was adopted, the time metrology community proved that a new generation of frequency standards operating in optical wavelengths has uncertainties at the level of 10–18, and challenge the implementation of high accurate frequency and time comparison techniques to decide on a revision of the definition of the second. Herein, the progress in the definition and realization of the second from astronomy until today is reviewed, an inventory of the present resources is assembled and a brief view for the future given.  相似文献   
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