Theoretical and experimental studies on a compact stretcher with large spectral bandwidth and high transmission efficiency

To ensure safe and effective amplification for the chirped pulse amplification laser facility, many factors such as pulse spectral width, pulse duration, grating parameters and incidence angle parameter are considered carefully in the design of the pulse stretcher. A compact four pass Offner stretcher design is given out. Experiment results show that the stretcher has broad spectral width, large stretching ratio and high transmission efficiency. By comparison, the calculated result of the dispersion effect on the pulse duration is completely consistent with the experiment result.     

Theoretical and experimental study on broadband terahertz atmospheric transmission characteristics

Broadband terahertz(THz) atmospheric transmission characteristics from 0 to 8 THz are theoretically simulated based on a standard Van Vleck–Weisskopf line shape, considering 1696 water absorption lines and 298 oxygen absorption lines.The influences of humidity, temperature, and pressure on the THz atmospheric absorption are analyzed and experimentally verified with a Fourier transform infrared spectrometer(FTIR) system, showing good consistency. The investigation and evaluation on high-frequency atmospheric windows are good supplements to existing data in the low-frequency range and lay the foundation for aircraft-based high-altitude applications of THz communication and radar.     

An experimental and theoretical study of the modelling of road traffic noise and its transmission in the urban environment

This paper describes experiments conducted on the modelling of traffic noise using a $\text{1}\text{80th}$ scale model of a subdivision of a city. The emphasis in this study was on the correct evaluation of ground absorption effects. There were essentially four phases to the study. First, the applicability of various scaling law regimes was examined. It was shown that $\text{1}\text{80th}$ scaling using air as a transmission medium was at least a practical choice. The second phase concerned itself with the choice of materials for the model, particularly that which was to simulate the ground. An impedance measuring apparatus was developed and used to test materials. The third part of the work concerned itself with the development of an anechoic enclosure and a sound source to simulate traffic noise; modulated Hartmann whistles were used for this purpose. Finally, a model of part of a residential area of Calgary was built and sound transmission measurements obtained. These results were compared with field measurements. It was shown that good agreement existed between the field and model measurements.     

空气中声源激发的浅海水下声场传播实验研究

为了了解空气中声源激发的水下声场传播特性,对此开展实验研究。2010年在南海北部海域进行了一次空气中声源激发水下声场实验,在水下成功地接收到远至4km处大功率扬声器在空中发射的脉冲声信号。本文通过分析实验数据,研究空气中声源激发的浅海水下声场传播特点。针对接收阵拾取的声传播信号信噪比低的特点,综合利用脉冲压缩以及波束形成方法提高接收信号的信噪比,得到收发距离1~4km、频率200~1000Hz范围内的传播损失实验值。在理论上,采用波数积分方法进行了声场数据模拟,结果表明理论计算的传播损失与实验结果较为一致。     

电容加载平板传输线型PFN理论与实验研究

介绍了一种电容加载双导体平板传输线型PFN,分析了PFN的波传播特性,提出通过减小加载电容间距提高PFN上限截止频率、减小阻抗色散的方法;采用损耗线模型分析了串联PFN的端部反射系数,研究了减小反射系数的方法;分析了串联PFN的磁耦合问题,从理论和实验两方面研究了PFN几何参数和排布方式对电流脉冲的影响。基于串联PFN和Tesla变压器技术,研制成功一台长脉冲功率源,输出电压脉冲幅度超过300 kV,脉冲宽度110 ns,前沿小于10 ns,功率超过2 GW。     

电容加载平板传输线型PFN理论与实验研究

 介绍了一种电容加载双导体平板传输线型PFN,分析了PFN的波传播特性,提出通过减小加载电容间距提高PFN上限截止频率、减小阻抗色散的方法;采用损耗线模型分析了串联PFN的端部反射系数,研究了减小反射系数的方法;分析了串联PFN的磁耦合问题,从理论和实验两方面研究了PFN几何参数和排布方式对电流脉冲的影响。基于串联PFN和Tesla变压器技术,研制成功一台长脉冲功率源,输出电压脉冲幅度超过300 kV,脉冲宽度110 ns,前沿小于10 ns,功率超过2 GW。     

水面船尾流的声散射实验研究

介绍尾流湖上实验,从水平和竖直两个方向探测尾流.用A式和B式两种显示方式绘出了尾流的轨迹图,测量了尾流的几何尺度.然后利用瞬时频率序列分析方法,对尾流回波(混响)进行了分析.最后,利用比较法测量了尾流的声散射强度.     

Broadening the bandwidth of piezoelectric transducers by means of transmission lines

The transfer functions of a transducer at emission and reception of ultrasonic waves are recalled and then verified. In order to broaden its bandwidth, an original method based on transmission lines properties is described.     

An axiomatic measure of one-way quantum information

I introduce an algorithm to detect one-way quantum information between two interacting quantum systems, i.e. the direction and orientation of the information transfer in arbitrary quantum dynamics. I then build an information-theoretic quantifier of one-way information which satisfies a set of desirable axioms. In particular, it correctly evaluates whether correlation implies one-way quantum information, and when the latter is transferred between uncorrelated systems. In the classical scenario, the quantity measures information transfer between random variables. I also generalize the method to identify and rank concurrent sources of quantum information flow in many-body dynamics, enabling to reconstruct causal patterns in complex networks.     

数字纳米云纹法的实验研究

提出了一种新的测量物质纳米级变形的云纹方法———数字纳米云纹法,在测量过程中,借助于各种电镜,采用具有周期结构的晶体物质的晶格或一些过渡金属、贵金属材料规则的表面原子重构作为试件栅。该试件栅的节距可达到亚纳米的量级,使得该方法可以在纳观范围内测量物体的面内位移,应变。参考栅采用计算机绘制的正弦型数字栅。详细地论述了该数字栅的制作方法,数字纳米云纹条纹的形成机理,及位移、应变的测量方法,云纹条纹的相移方法和倍增方法。     

弱信号在Hodgkin-Huxley神经元单向耦合系统中的传输特性

研究了阈下信号在含噪声的Hodgkin-Huxley神经元单向耦合系统中的传输特性.结果表明,各单元中均存在随机共振现象,可见噪声有助于提高信号的检测和传输;另外,耦合实现了信号的传输,且随着耦合强度的增强信号的传输效率增加,在耦合强度达到某一程度时两神经元实现了有时延的一致放电;并且接收元的信噪比最优值处的噪声强度随着耦合强度的提高而减小,最终与驱动元的一致;另外在耦合强度过强时,接收元出现过耦合放电,但是最终会被不断增强的噪声抑制,此现象有助于解释神经元的自放电及神经系统的自调节.研究表明噪声和耦合在 关键词： Hodgkin-Huxley神经元模型 随机共振 噪声 单向耦合系统     

An experimental study on the acoustic absorption of sand panels

Potentially sand panels could be used as novel sound absorbing materials that are fire resistant, environmentally friendly, mechanically strong and have good durability. However, the performance of sand panels as sound absorbers has not yet been studied. Results of measurements in a reverberation chamber of the random-incidence absorption coefficients of 13 different sand panel compositions and configurations with air gaps are reported. Also the flow resistivities and bulk densities have been measured. The results prove that sand panels could offer effective and wide-band acoustic absorption. As is the case with conventional sound absorbing materials, adding an air space is found to be the most effective way to widen the absorption bands and improve the overall absorption. Comparisons of the measured sand panel absorption data with predictions of the Delany and Bazley and Voronina models reveal that, while neither model is very accurate, the former gives more accurate predictions especially for sand panels with lower flow resistivity and smaller thickness.     

树状分形结构形成过程的实验研究

对大量金属小球在强电场作用下运动形态的演化全过程用联机摄像装置进行了实时拍摄,通过用Sandbox方法计算其稳定状态的分维数,系统地研究了分维数随电压的变化关系.结果表明：在一定电压范围内金属小球聚集体通过自组织过程形成稳定的树状分形结构,其分维数随外加电压的增加而减小.该结果对研究耗散结构的形成机理和外界动力对耗散结构的形貌影响具有参考价值. 关键词： 分形生长 自组织过程 树状结构 分维数     

An experimental and kinetic modeling study on the oxidation of 1,3-dioxolane

The modern catalytic or enzymatic advances allow the production of novel biofuel. Among them, 1,3-dioxolane can be produced from formaldehyde and ethylene glycol, both can be obtained from biomass. In this study, the oxidation of 1,3-dioxolane is studied at stoichiometric conditions. The ignition delay times of 1,3-dioxolane/O₂/inert mixtures were measured in a shock tube and in a rapid compression machine at pressures of 20 to 40 bar and temperatures ranging from 630 to 1300 K. The pressure profiles recorded in the rapid compression machine show a first stage of ignition enlightening the influence of the low temperature chemistry of combustion. Furthermore, mole fraction profiles of the stable intermediates produced during the oxidation of 1,3-dioxolane were measured in a jet-stirred reactor at 10 bar. Following these observations, a detailed kinetic model was developed with reaction rate coefficients and thermochemical data calculated by theoretical calculations or estimated by analogies to suitable molecules. In order to get an insight into the most important reaction pathways brute force sensitivity analysis and reaction pathway analysis were performed with the proposed model and discussed. It became clear that in the fuel-in-air case for the alkylhydroperoxide of 1,3-dioxolane the ring opening beta-scission pathway is favored against the further alkane-like second addition to molecular oxygen, which leads to a limited negative temperature coefficient.     

THz波在金属镀层空芯波导中传输的理论和实验研究

本文基于微扰法求得不同金属镀层空心圆波导中各模式的损耗系数,对金属镀层空芯波导中THz波传输损耗随金属材料、波导结构等参数的变化关系进行了数值模拟.根据数值分析结果,优化设计并拉制了内径为1.1 mm的镀银空芯波导,实验测得当THz波的频率为2.5 THz时,传输损耗为8.6 dB/m,实现了THz波短距离的有效传输. 关键词： 太赫兹波 金属空芯波导 传输损耗     

An experimental study of the blue whirl onset

This paper focuses on the blue whirl's formation conditions and onset mechanism. The blue whirl is experimentally generated using a forced-ventilation fire whirl apparatus, where the swirl intensity can be actively adjusted. It also allows the blue whirl to form in the laminar regime, without requiring a turbulent fire whirl as the inducer. Transverse particle image velocimetry (PIV) measurement is performed to understand the swirling flow near the vortex core and to quantify the swirl intensity in terms of circulation. The result demonstrates that a stable blue whirl can be formed only when the circulation is above a threshold value of about 0.07 m²/s, for the current experimental setup. Then, by examining the formation process during the blue whirl onset, a strong correlation can be confirmed between the circulation jumping and the flame regime transformation from a weak fire whirl to a blue whirl. To understand the critical condition for vortex breakdown, we further propose a new swirl number, $S_P$, based on balancing the pressure differences associated with the centrifugal and the radial-converging effects. As a result, the turning point in the $S_P$ curve agrees well with the emergence of the recirculation zone, verifying the relevance of the proposed vortex breakdown mechanism in determining the blue whirl onset.     

An experimental investigation on the directional distribution of incident energy for the prediction of sound transmission loss

It is suggested from a previous theoretical study that an angular distribution function can be successfully used for describing the directional distribution of incident energy on the wall, instead of the field incidence assumption being used in the prediction of sound transmission loss. This study is devoted to an experimental investigation on the directionality of incidence sound field for validating the underlying assumption in the theoretical work. To this end, the directional magnitudes of incident energy on a wall in a reverberation chamber are measured by employing the sound intensimetry. The experimental results suggest that the transmission coefficient formula should be revised by introducing a proper angular distribution function as a weighting function for describing the directional energy density distribution, which replaces the conventional field incidence method. The revised formula is applied to the prediction of transmission loss for a double-leaf panel with an air cavity, in which its effectiveness is strongly supported by good agreements between measured and predicted values.     

Molecules on kepler orbits: An experimental study

We have demonstrated experimentally that polar molecules revolve around the inner electrode of a charged cylindrical capacitor in helical trajectories that result from a superposition of a translational motion along and an orbital motion around the cylinder axis. In this way molecular beams can be guided over any given distance. The results have been obtained for nozzle beams of NaCl, NaBr, and NaI seeded in Kr. The capacitor bent into a toroid may be used as a storage ring for polar molecules in high field seeking rotational states.     

振转耦合振子实验研究

介绍一个非常有趣的物理演示实验——振转耦合振子实验.弹簧振子实际上是一个具有两个振动模式的振动系统,两振动模式之间存在着耦合,振动能量将从一种模式向另一模式转移.在共振条件下可以实现能量在两模式之间的来回完全转移.