An experimental study of storing information in a controlled chaotic system with time-delayed feedback

The multistability of a time-delayed feedback system can be used as an alternative for storing information. In this case the information is stored in various temporal patterns by controlling a chaotic system. The capability of storing information can be enhanced since more complex wave forms can be stored, each of which can be used as a memory unit. We showed numerically and experimentally this possibility in a hybrid diode laser system. We also showed that this method is robust to possible errors in the process of coding information.     

Electron microscopes using field emission source

The high brightness and small physical dimensions of a field emission source make it extremely attractive as the source of electrons in scanning electron microscopes. Using this kind of source considerable improvements have been made in this type of instrument so that at the present time the surfaces of solid objects can be viewed at a resolution of 30 Å and thin specimens can be viewed with a resolution of 2.5 Å. The particular nature of the scanning electron microscope allows some unique forms of contrast to be obtained so that the micrographs which can be taken with these microscopes are different in content and quality than those taken on conventional microscopes. As one example, we have been able to study the motion of single heavy atoms on thin carbon films. The resolution is, of course, not as high as that which can be obtained with a field ion microscope but the kind of specimen which can be viewed is different so that the two instruments are complementary in nature.     

一种用于60 GHz通信的S型结构左手材料的设计

基于对S型结构的理论分析,将中心频率设置为60 GHz,通过合理的改变单元结构中相应的尺寸以实现所需电谐振和磁谐振频率,并且经过优化以实现负介电常量和负磁导率的重合频段尽可能理想. 运用反演参量提取方法进行电磁参量提取,可以得到本设计在58.1~61.4 GHz频段内其ε和μ同时为负,即左手频段. 分析散射参量的仿真结果,在58~62 GHz频段内S₂₁大于-3 dB,在59.8~60.4 GHz频段内,S₁₁小于-20 dB,因此该设计结果可以运用于60 GHz通信滤波器和天线等器件的研究与设计.     

适用于循环平稳声场的基于波叠加法的近场声全息技术

在原有的平面循环平稳近场声全息基础上，提出一种基于波叠加法的循环平稳近场声全息技术，可以对具有复杂表面的声源进行全息重建，重建的声源表面声压谱相关密度函数能反映出调制信号的信息.声源表面声压谱相关密度函数全息图形象地反映了调制信号在表面的强弱分布情况，可由此确定调制信号源的产生位置.仿真分析和实验验证表明，基于波叠加法的循环平稳近场声全息技术可以更准确地反映循环平稳声场的调制特性.该方法继承了波叠加法的优点，无需计算边界奇异积分，计算效率高、精度好.     

The measurement of structure-borne sound transmission using impulsive sources

A simple method to measure structure-borne sound transmission is described. Measurement is made of the level difference in the acceleration between two structural elements using a plastic headed hammer as a noise source. The method is at least as accurate as conventional measurements made under steady-state conditions using continuous noise sources and can be carried out with less instrumentation on site and in about a tenth of the time.The portability of the source greatly simplifies the measurements as a hammer can be used to hit structures in a wide variety of positions whereas shakers can only be used in limited situations. In addition, attaching a shaker to a wall can damage the wall surface whereas, with care, a hammer hit will not.     

适用于循环平稳声场的基于波叠加法的近场声全息技术

在原有的平面循环平稳近场声全息基础上,提出一种基于波叠加法的循环平稳近场声全息技术,可以对具有复杂表面的声源进行全息重建,重建的声源表面声压谱相关密度函数能反映出调制信号的信息.声源表面声压谱相关密度函数全息图形象地反映了调制信号在表面的强弱分布情况,可由此确定调制信号源的产生位置.仿真分析和实验验证表明,基于波叠加法的循环平稳近场声全息技术可以更准确地反映循环平稳声场的调制特性.该方法继承了波叠加法的优点,无需计算边界奇异积分,计算效率高、精度好. 关键词： 近场声全息 循环平稳信号 波叠加     

Optical wave propagation in photonic crystal metamaterials

Metamaterials that provide negative refraction can be implemented in photonic crystals (PhCs) through careful design of the devices. Theoretically, we demonstrate that the dispersion can be altered to achieve negative refraction. This can be done through engineering the geometry of the device as well as selecting appropriate materials. The PhC also demonstrates slow light that facilitate sensing chemicals or biological agents. Using metallic materials such as gold nano-particle enables PhCs to guide optical waves in desired pathways. Also using magnetic materials such as highly doped n-GaAs, we can tune the band gap by changing magnetic field. The simulated results are consistent with some of the previously reported experimental results and give us guidance for future experiments.     

Current-induced exchange interactions and effective temperature in localized moment systems

We study theoretically the spin dynamics of a magnetic dimer serving as a contact between two electrodes. We find that the spin-spin coupling in the dimer can be dramatically modified from its equilibrium value. We show that the interaction can be tuned in such a way that it effectively changes its sign. The calculations show that, for large enough bias, the exchange interaction can even be changed from antiferromagnetic to ferromagnetic. The physical principles behind this result can be used as a new tool to achieve magneto-electric effects in molecular magnet systems.     

Improving beampatterns of two-dimensional random arrays using convex optimization

Sensors are becoming ubiquitous and can be combined in arrays for source localization purposes. If classical conventional beamforming is used, then random arrays have poor beampatterns. By pre-computing sensor weights, these beampatterns can be improved significantly. The problem is formulated in the frequency domain as a desired look direction, a frequency-independent transition region, and the power minimized in a rejection-region. Using this formulation, the frequency-dependent sensor weights can be obtained using convex optimization. Since the weights are data independent they can be pre-computed, the beamforming has similar computational complexity as conventional beamforming. The approach is demonstrated for real 2D arrays.     

纳米云纹法条纹倍增技术研究

提出了一种纳米云纹法的条纹倍增技术，可用于单晶材料纳米级变形测量.在测量中，单晶材料的晶格结构由透射电镜（TEM）采集并记录在感光胶片上作为试件栅，几何光栅作为参考栅.对纳米云纹条纹的形成原理，透射电镜放大倍数与试件栅的频率关系，条纹倍增技术，位移、应变测量方法等进行了详细讨论.该方法不仅能够测量连续力学参量，如应变和位移，而且能够表征纳观非连续参量，如位错、夹杂.     

Nuclear Creation and Annihilation Operators and Electromagnetic Multipole Fields

The frequency spectrum of electromagnetic radiation can be written as the Fourier transform of the first-order correlation function of the vector potential. If nuclei are coupled to the radiation field, the Heisenberg equations of motion of the field operators contain nuclear operators and vice versa. Under plausible assumptions the equations of motion for the nuclear operators can be integrated and hence, the equations of the field operators can be solved. The vector potential of the radiated field can then be expressed as a function of solely nuclear quantities. The first-order correlation function deduced from it contains only two-times and one-time averages of simple nuclear creation and annihilation operators. The theory can be used to explain homogeneous line broadening for long-lived nuclei submitted to small fluctuating interactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

R717双蒸发温度三级混流制冷系统的理论分析

文中提出了一种采用氨做制冷剂、可用于获得低至-60℃低温的新型制冷系统,为我国低温冷库的建设提供了一条新型环保技术路线.该制冷系统具有两个蒸发温度回路,高温回路的蒸发温度在-35℃～-28℃之间可调,低温回路的蒸发温度在-50℃～-65℃之间可调.两个回路在低压循环桶处汇合.在对该系统进行热力计算的基础上,分析了系统的...     

用纵向振动法测量弹性模量的实验装置

把待测样品制备成细长棒,受到一定拉力时细长棒有一定伸长,这可等效为弹簧,通过测量由细长棒与质量块构成的振子的固有频率可准确测量劲度系数,若测得了其劲度系数即可得该材料的弹性模量.基于以上思路设计了纵向振动法测量弹性模量的实验装置,使弹性模量测量实验既保留了光杠杆法物理概念清晰的优点,又吸取了振动法的长处.     

The effect of the structure-borne sound transmission between panel and stud via screw connections for a double leaf partition

In additional to the screw connection affecting the sound transmission characteristics of the panel-stud partition,the spacing of screws is also considered as a factor in predicting the sound insulation of the partition.It can be modeled either as a series of independent point connections,or as a line connection depending on the screw spacing.For small screw spacing,the connection between panel and stud can be treated as a line connection,from which a higher sound transmission effect can be achieved.Whilst for a larger screw spacing,it can be treated as an independent point connection,from which a lesser sound transmission through the partition can be achieved accordingly.The distinction between these two kinds of connection is also related to the frequency.Usually,half bending wavelength of a panel will be treated as a distinct frequency.Experimental results of double leaf partition with diverse screw spacing significantly demonstrated their influences on sound reduction.Some prediction methods for partitions with different screw spacing are also reviewed in this paper.It should be noted that the impact of screw spacing effecting on the sound insulation of partitions of wood stud and light-weight metal stud is different.     

Quantification of fluorescent molecules in heterogeneous media by use of the fluorescence decay amplitude analysis

In heterogeneous media, including biological objects, fluorescent molecules of one kind often exist as a mixture of species with different fluorescence parameters. Fractional concentrations of these species can be measured by analyzing their fluorescence decay amplitudes. The amplitudes are linear functions of concentrations of actually fluorescent molecules, i.e., molecules whose fluorescence decay can be measured. Other (quenched) molecules do not influence these amplitudes. The other parameter that has to be measured to calculate these concentrations is the radiative rate constant. The parameter can be excluded by comparison of decay amplitudes of the sample studied and a standard. The comparison should be made taking into account the dependence of the radiation rates on emision wavelength. The method has been tested in experiments with the fluorescent probe 3-methoxybenzanthrone (MBA) bound with phosphatidylcholine bilayer membranes. The probe has a complex fluorescence decay in these membranes. The decay can be described as two exponentials, with decay times of 2 and 12 ns and a blue-shifted fluorescence spectrum of the short-life component as compared with long-life one. The shift was used to correct calculated radiative rate values. After this, about 100% of the MBA molecules were found to be fluorescent in these membranes. Thus, this approach can be used to measure absolute concentrations of subpopulations of fluorescent molecules in heterogeneous biological objects.     

Image encoding based on coherent superposition and basic vector operations

A new method for image encryption based on optical coherent superposition and basic vector operations is proposed in this paper. In this encryption, the original image can be directly separated into two phase masks (PMs). One is a random phase mask (RPM) and the other is a modulation of the RPM by the original image. The mathematical calculation for obtaining the two PMs is quite simple and direct resulting from the simple principle of optical coherent superposition. The arbitrarily selected RPM can be treated as the encrypted result while the PM can be taken as the key for decryption. With this technique, the same encrypted result can be obtained for different images with the same size while the keys for decryption are different. The encryption can be performed digitally and the decryption can be performed optically or digitally. The security of the proposed method is discussed and computer simulation results are presented to verify the validity of proposed method.     

基于图像处理的模拟尾流气泡幕分类识别

提出了一种应用数字图像处理技术对模拟尾流气泡幕分类识别的新方法.文章介绍了BP神经网络的基本结构及其工作原理,通过仿真测试了BP神经网络对模拟尾流气泡幕图像的模式分类.应用灰度图像统计矩法得到了均值﹑归一化系数﹑三阶矩﹑一致性和熵等特征量,设定神经网络学习率为0.1时经过14次循环可以达到训练目标误差为0.001,此时网络对不同压强下的尾流气泡幕分类正确率到达100%.这种方法在处理尾流图像时具有直观、高效、精确等特点,易于应用于对尾流探测、识别等工程技术中.     

A new positioning approach of fiber probe for near-field scanning optical microscope

A fiber probe-based positioning scan approach was established, whose precision can reach as high as 0.8 μm. And a set of modified microscope system was designed utilizing this approach, in which the scanning probe microscope (SPM) combined with an optical microscope was manipulated. The optical microscope and scanning probe can conveniently be switched through a switch panel. The observation period of samples can significantly be shortened. And more reliable images can be provided using this approach. Our design can effectively solve the inherent disadvantages of SPM technology, which makes SPM scan and image more reliably, conveniently, safely and rapidly.     

颗粒介质中的粘滞系数

将颗粒介质看成是等效均匀介质, 其中的声衰减系数和声速等于该颗粒介质中的相应的量值(它们可由作者的理论给出), 等效静态密度可以用二元混合规则求得. 此外, 根据浓颗粒介质中相互作用的声传播理论, 当入射波为平面波时, 相互作用的次级波仍然是平面波. 在这样的情况下, 可以将三维非线性方程组简化为一维情况, 从而算得浓颗粒介质中的粘滞系数, 结果表明, 颗粒介质中的粘滞系数不仅依赖于颗粒的体积分数而且还与频率有关. 根据推导过程可知, 对比于爱因斯坦理论所能应用的限制, 本文的结果可以更广泛地应用于实际介质.     

CFD-DEM simulation of three-dimensional aeolian sand movement

A three-dimensional CFD-DEM model is proposed to investigate the aeolian sand movement.The results show that the mean particle horizontal velocity can be expressed by a power function of heights.The probability distribution of the impact and lift-off velocities of particles can be described by a log-normal function,and that of the impact and lift-off angles can be expressed by an exponential function.The probability distribution of particle horizontal velocity at different heights can be described as a lognormal function,while the probability distribution of longitudinal and vertical velocity can be described as a normal function.The comparison with previous two-dimensional calculations shows that the variations of mean particle horizontal velocity along the heights in two-dimensional and three-dimensional models are similar.However,the mean particle density of the two-dimensional model is larger than that in reality,which will result in the overestimation of sand transportation rate in the two-dimensional calculation.The study also shows that the predicted probability distributions of particle velocities are in good agreement with the experimental results.