THE STUDY OF MOSSBAUER-EFFECT IN EUBA2CU3O7-Y

EuBa2(Cu1-xFex)3O7-y has been investigated by the Fe-57 and Eu-151 Mossbauer effect. The Fe-57 Mossbauer spectra of the EuBa2(Cu1xFex)3O7-y without or with DC electric current (the current strength I = 0.5A) around the superconducting transition temperature have been measured. The results indicate that the isomer shift (IS) and the quadrupole splitting (QS) of the Fe replacing the Cu(2) vary neither with increasing the Fe content nor with the small DC eletric current passing the superconductor and that the IS and the QS of the Fe replacing the Cu(1) vary with the Fe content. Especially, the IS and the QS of the Fe (D3) replacing the Cu(1) are changed when the small electric current passes the superconductor at 80K.

Characteristics of nonlinear internal waves observed in the northern South China Sea

The South China Sea (SCS) is one of the most active areas of internal waves. We undertook a program of physical oceanography in the northern South China Sea from June to July of 2009, and conducted a 1-day observation from 15:40 of June 24 to 16:40 of June 25 using a chain of instruments, including temperature sensors, pressure sensors and temperature-pressure meters at a site (117.5A degrees E, 21A degrees N) northeast of the Dongsha Islands. We measured fluctuating tidal and subtidal properties with the thermistor-chain and a ship-mounted Acoustic Doppler Current Profiler, and observed a large-amplitude nonlinear internal wave passing the site followed by a number of small ones. To further investigate this phenomenon, we collected the tidal constituents from the TPXO7.1 dataset to evaluate the tidal characteristics at and around the recording site, from which we knew that the amplitude of the nonlinear internal wave was about 120 m and the period about 20 min. The horizontal and vertical velocities induced by the soliton were approximately 2 m/s and 0.5 m/s, respectively. This soliton occurred 2-3 days after a spring tide.

光弹调制器在偏振方向调制中的应用

提出了一种将光弹调制器应用于偏振方向调制的方法．介绍了它的两种基本使用模式，利用琼斯矩阵对其偏振方向调制原理及其两种基本使用模式进行了分析。光弹调制器和1／4波片形成偏振方向调制器件时，光弹调制器处于两块透光轴相互垂直的1／4波片之间．且光弹调制器的振动轴分别和两块1／4波片的透光轴成±45°角，线偏振光通过此器件其偏振方向被调制。实验验证了光弹调制器组合1／4波片调制偏振方向的原理。将光弹调制器应用在偏振方向的调制中．使现有偏振方向调制技术的光谱范围扩展到了紫外波段。

Electrochemical preparation of microelectrodes modified with non-stoichiometric mixed-valent molybdenum oxides

A compact non-stoichiometric molybdenum (VI, V) oxide of blue film was grown on carbon fiber (CF) microelectrode surface be cycling the potential between + 0.2V and - 0.70V in a freshly prepared Na2MoO4 solution containing 5 x 10(-3) mol/L H2SO4. The quantity-of the oxide is controlled by the charge passing the electrode. The electrochemical pretreatment of CF microelectrode not only mises the deposition velocity of molybdenum oxide on CF surface, but also improves greatly the cyclic voltammetric behavior of the molybdenum oxide film prior to the electrodeposition. The cathodic processes are believed to yield the hydrogen molybdenum oxide bronzes HxMoO3(0 < x < 2), or substoichiometric lower molybdenum oxides with the formula MoO3-y(0 < y < 1). The anodic response results from the reversible oxidation of molybdenum bronze/Mo(V) centers [or perhaps Mo(IV) in more reduced coatings], to Mo(VI). Further information was gained about the chemical composition and valent state of Mo from XPS and SEM.

边坡工程的极限分析上限法

Theory of limit analysis include upper bound theorem and lower bound theorem. To deal with slope stability analysis by limit analysis is to approximate the real solution from upper limit and lower limit. The most used method of limit analysis is upper bound theorem, therefore it is often applied to slope engineering in many cases. Although upper bound approach of limit analysis can keep away from vague constitutive relation and complex stress analyses, it also can obtain rigorous result. Assuming the critical surface is circular slip surface, two kinematically admissible velocity fields for perpendicular slice method and radial slice method can be established according to the limit analysis of upper bound theorem. By means of virtual work rate equation and strength reduction method, the upper-bound solution of limit analysis for homogeneous soil slope can be obtained. A log-spiral rotational failure mechanism for homogeneous slope is discussed from two different conditions which represent the position of shear crack passing the toe and below the toe. In the dissertition, the author also establishes a rotational failure mechanics with combination of different logarithmic spiral arcs. Furthermore, the calculation formula of upper bound solution for inhomogeneous soil slope stability problem can be deduced based on the upper bound approach of rigid elements. Through calculating the external work rate caused by soil nail, anti-slide pile, geotechnological grid and retaining wall, the upper bound solution of safety factor of soil nail structure slope, slip resistance of anti-slide pile, critical height of reinforced soil slope and active earth pressure of retaining wall can be obtained by upper bound limit analysis method. Taking accumulated body slope as subject investigated, with study on the limit analysis method to calculate slope safety factor, the kinematically admissible velocity fields of perpendicular slice method for slope with broken slip surface is proposed. Through calculating not only the energy dissipation rate produced in the broken slip surfaces and the vertical velocity discontinuity, but also the work rate produced by self-weight and external load, the upper bound solution of slope with broken slip surface is deduced. As a case study, the slope stability of the Sanmashan landslide in the area of the Three Gorges reservoir is analyzed. Based on the theory of limit analysis, the upper bound solution for rock slope with planar failure surface is obtained. By means of virtual work-rate equation, energy dissipation caused by dislocation of thin-layer and terrane can be calculated; furthermore, the formulas of safety factor for upper bound approach of limit analysis can be deduced. In the end, a new computational model of stability analysis for anchored rock slope is presented after taking into consideration the supporting effect of rock-bolts, the action of seismic force and fissure water pressure. By using the model, not only the external woke-rate done by self-weight, seismic force, fissure water pressure and anchorage force but also the internal energy dissipation produced in the slip surface and structural planes can be totally calculated. According to the condition of virtual work rate equation in limit state, the formula of safety factor for upper bound limit analysis can be deduced.

Effects of the frequency chirp on the fields of a chirped Gaussian pulse passing through a hard-edged aperture

Based on the Huygens-Fresnel diffraction integral and Fourier transform, propagation expression of a chirped Gaussian pulse passing through a hard-edged aperture is derived. Intensity distributions of the pulse with different frequency chirp in the near-field and far-field are analyzed in detail by numerical calculations. In the near-field, amplitudes of the intensity peaks generated by the modulation of the hard-edged aperture decrease with increasing the frequency chirp, which results in the improving of the beam uniformity. A physical explanation for the smoothing effect brought by increasing the frequency chirp is given. The smoothing effect is achieved not only in the pulse with Gaussian transverse profile but also in the pulse with Hermite-Gaussian transverse profile when the frequency chirp increases. (C) 2005 Elsevier B.V. All rights reserved.

The Interaction Between Shock Waves and Solid Spheres Arrays in a Shock Tube

When a shock wave interacts with a group of solid spheres, non-linear aerodynamic behaviors come into effect. The complicated wave reflections such as the Mach reflection occur in. the wave propagation process. The wave interactions with vortices behind each sphere's wake cause fluctuation in the pressure profiles of shock waves. This paper reports an experimental study for the aerodynamic processes involved in the interaction between shock waves and solid spheres. A schlieren photography was applied to visualize the various shock waves passing through solid spheres. Pressure measurements were performed along different downstream positions. The experiments were conducted in both rectangular and circular shock tubes. The data with respect to the effect of the sphere array, size, interval distance, incident Mach number, etc., on the shock wave attenuation were obtained.

Invertible dark-center diffraction of the metal film induced by femtosecond laser

We found reversible dark-center diffraction of the transmitted probe beam passing through the chromium film. which is induced by the pump femtosecond laser. The dark-center diffraction of I he transmitted probe beam appears and disappears with and without the pump beam. A view of diffractive optics with binary phase plate is put forward, which explains the reversible dark-center diffractive optical phenomenon. The pre-ablated hole on the metal film can be regarded as a uniform light filed without phase modulation, the Surrounding Circular part around the pre-ablated hole can be regarded as "phase modulated". Therefore, this diffraction optic view might be helpful for us to understand the phase change of the metal film introduced by the femtosecond laser pulse. (C) 2008 Elsevier B.V, All rights reserved.

Smoothing effect in the broadband laser through a dispersive wedge

The propagation expression of a broadband laser passing through a dispersive wedge is derived on the basis of the Huygens-Fresnel diffraction integral, Smoothing effects caused by the phase perturbation of the dispersive wedge on the intensity profiles are investigated in detail. The phase perturbation of the dispersive wedge induces a relative transverse position shift between the diffraction patterns of different frequency components. The relative transverse position shift is of great benefit to the fill of the intensity peaks of some patterns in the valleys of others when these patterns are overlapped and thus the smoothing effect is achieved. (c) 2006 Elsevier B.V. All rights reserved.

Influence of the chirp on the intensity distributions of an apertured pulse

Starting from the Huygens-Fresnel diffraction integral and the Fourier transform, the propagation expression of a chirped pulse passing through a hard-edged aperture is derived. Using the obtained expression, the intensity distributions of the pulse with different chirp in the near and far fields are analyzed in detail. Due to the modulation of the aperture, many intensity peaks emerge in the intensity distributions of the chirped pulse in the near field. However, the amplitudes of the intensity peaks decrease on increasing the chirp, which results in the smoothing effect in the intensity distributions. The beam smoothing brought by increasing the chirp is explained physically. Also, it is found that the radius of the intensity distribution of the chirped pulse decreases when the chirp increases in the far field. (c) 2005 Elsevier GmbH. All rights reserved.

Smoothing the side lobes of a focused pattern by spectral dispersion in the broadband laser

Starting from the Huygens-Fresnel diffraction integral, the propagation equations of a broadband laser passing through a dispersive lens and a dispersive wedge are derived. Smoothing effect on the side lobes of the focused pattern is achieved as the broadband laser passes through the lens because of the spectral dispersion of the lens. By inserting a dispersive wedge behind the lens, better smoothing effect is realized because a relative position shift between focused patterns of different frequency components is generated due to the spectral dispersion of the wedge. Smoothing effect on the side lobe is obtained even with small bandwidth of the broadband laser as the wedge is used. (c) 2006 Elsevier GmbH. All rights reserved.

Spectral anomalies of focused hollow Gaussian beams at the geometrical focal plane

On the basis of diffraction integral and the expansion of the hard-aperture function into a finite series of complex Gaussian functions, an approximate expression for spatially fully coherent polychromatic hollow Gaussian beams passing through aperture lens is obtained. Detailed numerical results indicate that remarkable spectral changes always occurs near the points where the field amplitude has zero value. The effects of truncation parameter, Fresnel number and the beam order on spectral shifts and spectral switches are investigated numerically. (C) 2008 Elsevier B.V. All rights reserved.

The design and operation of a new clapboard-type internal circulating fluidized-bed gasifier

The design and operation of a new clapboard-type internal circulating fluidized-bed gasifier is proposed in this article. By arranging the clapboard in the bed, the gasifier is thus divided into two regions, which are characterized by different fluidization velocities. The bed structure is designed so that it can guide the circulating flow passing through the two regions, and therefore the feedstock particles entrained in the flow experience longer residence time. The experimental results based on the present new design, operating in the temperature range of 790 degrees C-850 degrees C, indicate that the gas yield is from 1.6-1.9 Nm(3)/kg feedstock, the gas enthalpies are 5,345 kJ/Nm(3) for wood chip and 4,875 kJ/m(3) for rice husk, and a gasification efficiency up to 75% can be obtained.

Characteristics of beam profile of Gaussian beam passing through an axicon

Bessel beam can overcome the limitation of the Rayleigh range of Gaussian beam with the same spot size propagation without any spreading due to diffraction, which is considered as an useful function in guiding particles in the next generation of optical tweezers. The mathematical description of the Bessel beam generated by an axicon is usually based on the Fresnel diffraction integral theory. In this paper, we deduce another type of analytic expression suitable for describing the beam profile generated from the axicon illuminated by the Gaussian beam based on the interferential theory. Compared with the Fresnel diffraction integral theory, this theory does not use much approximation in the process of mathematical analysis. According to the derived expression, the beam intensity profiles at any positions behind the axicon can be calculated not just restricted inside the cross region as the Fresnel diffraction integral theory gives. The experiments prove that the theoretical results fit the experimental results very well. (C) 2004 Elsevier B.V. All rights reserved.

Analytical solution of a multidimensional Langevin equation at high friction limits and probability passing over a two-dimensional saddle

The analytical solution of a multidimensional Langevin equation at the overdamping limit is obtained and the probability of particles passing over a two-dimensional saddle point is discussed. These results may break a path for studying further the fusion in superheavy elements synthesis.