FREE VIBRATION ANALYSIS AND PHYSICAL PARAMETER IDENTIFICATION OF NON-UNIFORM BEAM CARRYING SPRING-MASS SYSTEMS

To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is developed by using the transfer matrix method of multibody system（MS-TMM）, the transfer matrix of non-u- niform beam is derived, and the natural frequencies are computed. Compared with the numerical assembly method （NAM）, the results by MS-TMM have good agreement with the results by FEM, and are better than the results by NAM. When using the high precision method, the global dynamic equations of the complex multibody system are not needed and the orders of involved system matrices are decreased greatly. For the investigation on the re- verse problem of the physical parameter identification of multibody system, MS-TMM and the optimization tech- nology based on genetic algorithms（GAs） are combined and extended. The identification problem is exchanged for an optimization problem, and it is formulated as a global minimum solution of the objective function with respect to natural frequencies of multibody system. At last, the numerical example of non-uniform beam with attach- ments is discussed, and the identification results indicate the feasibility and the effectivity of the proposed aop- proach.

DFT谱分析在卫星通信业务监测系统中的应用

采用离散傅立叶变换（DFT）实现了对卫星通信业务监测系统中监测信号的频谱分析。频率分辨率的大小直接决定了频谱分析的精度，因此重点研究了DFT的参数选择对频率分辨率的影响，并采用数字移频有效降低了采样频率，提高了频率分辨率，从而提高了对监测信号谱分析的精度。

金士顿KVR533D2N4/1G

继上月威刚与宇瞻送来DDRⅡ内存后,Kingston也送来了一条DDRⅡ533内存,单条容量为1GB,属于unbuffered内条,内存模组采用双面16颗结构。内存颗粒为ELPIDA E5108AB-4A-E。通过SiSoftwareSandra 2004查看得知此内存颗粒的数据深度为64M、位宽为8bit。这样16颗内存颗粒总容量就是1GB,而总位宽是16×8bit=128bit,所以这条内存的物理Bank数应该是2,也就是双Bank的内存条,Sandra的检测信息也证实了这一点。 KingstonKVR533D2N4/1G虽然属于Kingston的ValueRAM系列,但无论是PCB布线还是元件用料都一丝不苟,现在要找一条做工粗糙的DDRⅡ内存恐怕也不简单。

Study on a 5.0 W/80 K single stage Stirling type pulse tube cryocooler

A single stage Stifling pulse tube cryocooler was designed based on REGEN 3.2 and fabricated for testing. The experimental results show that the cooler can provide a cooling capacity of 5.0 W at 79.1 K, and produce a no-load temperature of 57.0 K, operating with an average pressure of 2.50 MPa and a frequency of 60 Hz, performance results that are very close to the calculated values. The cryocooler can be cooled from room temperature to 80 K in 8.5 min. The fast cooldown time is a result of the small regenerator.

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.

Dielectric characteristics and nonlinear properties of ZnO-polypyrrole composites

The nonlinear properties and frequency characteristics of ZnO-polypyrrole composites were investigated at 200 Hz-5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 ℃. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 k Hz. These parameters fall off by increasing frequency up to 1 k Hz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1 k Hz is related to the Maxwell-Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.

The Application of Microwave Low Temperature Plasma in Pretr-eatment of Cotton Fabric

The effect of microwave low temperature plasma pretreatment on desizing and removing natural impurity of cellulose fiber was studied. The influencing factors of pretreatment such as treating power, gas pressures and time were discussed in detail and the final effect had been compared with that of traditional pretreating process of cotton fabric. The results showed that better capillary effect, strength, whiteness and dyeing K/S value could be given by means of microwave low temperature plasma treatment.

Vibrational Spectra and Adsorption of Trisiloxane Superspreading Surfactant at Air/Water Interface Studied with Sum Frequency Generation Vibrational Spectroscopy

The C-H stretch vibrational spectra of the trisiloxane superspreading surfactant Silwet L-77 （（CH3）3Si- O-Si（CH3）（C3H6）（OCH2CH2）7-8OCH3）-O-Si（CH3）3） at the air/water interface are measured with the surface Sum Frequency Generation Vibrational Spectroscopy （SFG-VS）. The spectra are dominated with the features from the -Si-CH3 groups around 2905 cm^-1 （symmetric stretch or SS mode） and 2957 ^-1 （mostly the asymmetric stretch or AS mode）, and with the weak but apparent contribution from the -O-CH2- groups around 2880 ^-1 （symmetric stretch or SS mode）. Comparison of the polarization dependent SFG spectra below and above the critical aggregate or micelle concentration （CAC） indicates that the molecular orientation of the C-H related molecular groups remained unchanged at different surface densities of the Silwet L-77 surfactant. The SFG-VS adsorption isotherm suggested that there was no sign of Silwet L-77 bilayer structure formation at the air/water interface. The Gibbs adsorption free energy of the Silwet surfactant to the air/water interface is -42.2±0.8kcal/mol, indicating the unusually strong adsorption ability of the Silwet L-77 superspreading surfactant.

Extracting Oscillation Frequencies in Spontaneous Emission Rate of an Atom Between Two Mirrors

For an atom in a medium with refractive index n sandwiched between two parallel mirrors, we derive an analytical formula for the spontaneous emission rate based on Fermi＇s golden rule. The oscillations are not transparent in this formula. By performing Fourier transform on scaling variable measuring system size while holding system configuration fixed, we extracted the frequencies of many oscillations in this system. We show that these oscillations correspond to emitted photon closed-orblts going away from and returning to the emitting atom.

Nonlinear Quantum Optical Springs and Their Nonclassical Properties

The original idea of quantum optical spring arises from the requirement of quantization of the frequency of oscillations in the Hamiltonian of harmonic oscillator. This purpose is achieved by considering a spring whose constant （and so its frequency） depends on the quantum states ofanother system. Recently, it is realized that by the assumption of frequency modulation of ω to ω √1＋ μα＋α the mentioned idea can be established. In the present paper, we generalize the approach of quantum optical spring with particular attention to the dependence or trequency to the intensity of radiation field that naturally observes in the nonlinear coherent states, from which we arrive at a physical system has been called by us as nonlinear quantum optical spring. Then, after the introduction of the generalized tlamiltonian of nonlinear quantum optical spring and it＇s solution, we will investigate the nonclassical properties of the obtained states. Specially, typical collapse and revival in the distribution functions and squeezing parameters, as particular quantum features, will be revealed.

A Modified Doppler Frequency Trajectory Undergoing Varying Velocities in HSR Communications

The varying trajectory of Doppler frequency under changing speed motion conditionsare investigated in Highspeed Railway(HSR) scenarios.Based on the geometrical physical parameters,instantaneous Doppler trajectories and expression forms of the change rate arededuced,including acceleration and deceleration cases.These modified models provide more accurate and realisticapproximations in modeling rapidly fading channels.

巧用电脑软件演示声波特性

声波,一种机械振动产生的机械波,与人类生活息息相关。在声波的学习中,有关声音知识是小学科学、中学物理的重点学习内容。教学中,对学生进行各种声波演示实验,教学效果更好。

开启心门 激扬生命——浅谈大课间团体活动对缓解学生人际交往障碍的作用

当前网络的覆盖及自媒体多样化的选择,青少年足不出户却可遍览天下,网购、社交、游戏等均能在虚拟的世界中完成,在虚拟世界里他们春风得意,叱咤风云,但却导致了现实人际交往减少、人际关系走向淡漠,标签为'宅男宅女'的青少年大量出现,'宅'在家里,是这一代青少年很显著的特征,从而造成了个别青少年许多心理障碍与疾病,人际交际障碍是其中之一。

New Solution for the Earth’s Free Wobble and Its Geophysical Implications

In this paper, the theory of the free wobble of the triaxial Earth is developed and new conclusions are drawn: the Euler period should be actually expressed by the first kind of complete elliptic integral; the trace of the free polar motion is elliptic and the orientations of its semi-minor and major axes are approximately parallel to the Earth's principal axes A and B, respectively. In addition, the present theory shows that there is a mechanism of frequency-amplitude modulation in the Chandler wobble, which might be a candidate for explaining the correlation between the amplitude and period of the Chandler wobble.