大学物理实验教学体系改革与实践

本文就大学物理实验的教学体系、教学模式改革进行了探讨和实践。     

Topological Structure of Entropy of 4-Dimensional Axisymmetric Black Holes

Using the relationship between the entropy and the Euler characteristic, an entropy density is introduced to describe the inner topological structure of the entropy of 4-dimensional axisymmetric black holes. It is pointed out that the density of entropy is determined by the singularities of the timelike Killing vector field of spacetime, and these singularities carry the topological numbers, Hopf indices and Brouwer degrees, which are topological invariants. At last, Kerr–Newman black hole as an example of axisymmetric black holes is given. What’s more, the entropy and the latent heat of the topological phase transition of the black hole mentioned above are calculated and the latent heat just lies in the range of the energy of gamma ray bursts. This work is supported in part by the NSFs of China under Grant No. 10575068 and of Shanghai Municipal Committee of Science and Technology under Grant No. 04ZR14059 and Shanghai Leading Academic Discipline Project under Project Number: T0104.     

Calculating vibrational mode contributions to sound absorption in excitable gas mixtures by decomposing multi-relaxation absorption spectroscopy

Sound relaxational absorption spectroscopy of excitable gas mixtures is potentially applied for gas composition detection. The relaxation of vibrational modes of gas molecules determines the sound relaxational absorption. However, to our knowledge, the contribution of each vibrational mode available in gas mixtures to sound multi-relaxation absorption has not been calculated in existing literature. In this paper, based on the decoupled expression of the effective isochoric molar heat for a gas mixture, a sound multi-relaxation absorption spectrum is decomposed into the sum of single-relaxation spectra. From this decomposable characteristic, the contribution of each vibrational mode available in the gaseous medium to the multi-relaxation absorption is obtained at room temperature. For various gas compositions including carbon dioxide, methane, nitrogen etc., the calculated contributions of vibrational modes are verified by the comparison with experiment data. We prove the following views with quantifiable outcomes that the primary molecular relaxation process associated with the lowest mode plays the major role in acoustic relaxational absorption of gas mixtures; the mode with lower vibrational frequency provides higher contribution to the primary relaxation process. This work could provide a deeper insight into the relationship between the sound relaxational absorption spectroscopy and gas molecules.     

基于过模波导的高功率微波准相干功率合成器

研究了一种用于功率合成的GW级高功率微波功率合成器。该合成器工作在X波段,输入微波由2路工作频率不同的X波段的微波源产生。为了满足输出功率和功率容量的要求,用于功率合成的微波源工作段波导的过模因子为12.7,这给功率合成器的设计带来了一定的困难。着重讨论了如何利用过模波导设计X波段高功率合成器,研究了如何抑制过模波导的高次模式并提高其功率容量和传输效率。设计的功率合成器单路传输效率达到99.0%以上,允许的最大输出功率达到5.6 GW以上,还可以按照需求适当增大高度,以进一步提高其功率容量而不影响传输效率。     

塞曼激光陀螺磁屏蔽设计与实现

为提高塞曼激光陀螺精度,分析了塞曼激光陀螺磁的磁敏感特性,指出敏感轴方向是塞曼激光陀螺的最大磁灵敏度方向,该方向为产生磁误差的主要方向。研究了低频磁场屏蔽理论与加工工艺关键技术,结合激光陀螺的环境适应性要求,实现了固态激光陀螺磁屏蔽结构。在三轴磁试验台上进行了陀螺磁敏感性测试,陀螺磁灵敏度值减少到原来的1/1000,实测系数达到2.0(°)/(h.mT),该值满足中等精度激光陀螺的实用要求。     

Highly stable,frequency-controlled mode-locked erbium fiber laser comb

A mode-locked Er:fiber laser-based optical frequency comb with high stability in the repetition frequency and carrier-envelope offset (CEO) frequency is realized. The CEO beat signal was detected right after the supercontinuum generation by a compact single-beam f–2f self-referencing interferometer, which does not require further delay compensation. The stabilized repetition frequency has an out-of-loop tracking stability of 1.3×10^-13/ for an integration time τ less than 1000 s, which is limited by the stability of the frequency measurement system. The stabilized CEO frequency has a residual fluctuation of 0.52 mHz measured with a 1 s gate time. This is, to our knowledge, the highest tracking stability realized for fiber laser-based optical frequency comb. PACS 06.30.Ft; 42.60.Lh; 42.55.Wd     

X射线荧光光谱研究粮食中生命有机碳与碳化学循环

采用X射线荧光光谱(XRF)方法测定六种粮食:稻谷(大米)、小麦(面粉)、黄豆、小米、高粱和玉米中生命有机碳含量和化学元素组成,建立一种新方法测定它们的蛋白质含量.粮食中生命有机碳平均含量约为44%.黄豆中的蛋白质含量最高(42.74%),小米蛋白质含量28.56%,麦子蛋白质含量27.57%,玉米蛋白质含量24.99...     

烧结金属纤维板大空间自然对流实验研究

实验研究了烧结金属纤维板在大空间下的自然对流换热,分析了倾角、孔隙率、纤维丝经、Ra数和金属纤维导热系数对换热性能的影响.实验结果表明:存在最优的角度(60°左右)使烧结金属纤维板的自然对流换热性能最好,但倾斜角度对烧结金属纤维板的换热影响没有光板显著;加热面的平均Nu数随着纤维直径和孔隙率的增加均先增加后减小;在实验...     

Effect of incommensurate potential on the resonant tunneling through Majorana bound states on the topological superconductor chains

We study the transport through the Kitaev chain with incommensurate potentials coupled to two normal leads by the numerical operator method. We find a quantized linear conductance of e ² / h, which is independent to the disorder strength and the gate voltage in a wide range, signaling the Majorana bound states. While the incommensurate potential suppresses the current at finite voltage bias, and then narrows the linear response regime of the I-V curve which exhibits two plateaus corresponding to the superconducting gap and the band edge, respectively. The linear conductance abruptly drops to zero as the disorder strength reaches the critical value 2g _s + 2Δ with Δ the p-wave pairing amplitude and g _s the hopping between neighbor sites, corresponding to the transition from the topological superconducting phase to the Anderson localized phase. Changing the gate voltage also causes an abrupt drop of the linear conductance by driving the chain into the topologically trivial superconducting phase, whose I-V curve exhibits an exponential shape.     

Functional organic single crystals for solid‐state laser applications

Because of long‐range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid‐state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state‐of‐the‐art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light‐emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.