Residual stress determination in aluminium using electromagnetic acoustic transducers

The residual stresses in a shrink-fit specimen were measured ultrasonically, using shear-horizonal (SH) waves transmitted and received by noncontacting electromagnetic acoustic transducers. The presence of stress induces a small change in the velocity of the SH-waves. The difference in velocities of orthogonally polarized SH-waves (acoustic birefringence) was measured with a simple time-interval averaging system; this velocity difference can be related to the difference of principal stresses. The presence of material anisotropy (texture) in the specimen also causes relative velocity changes comparable to stress-induced changes. A simple method was used to remove the anisotropy-dependent component of the total relative velocity change, thereby allowing a determination of residual stress. This method consisted of measuring the birefringence in unstressed reference specimens and subtracting it from the birefringence measured at stressed locations. For the specimen used here, good agreement between theoretical and experimental values of stress was obtained.     

Imaging characteristics of toroidal and ellipsoidal mirrors for synchrotron radiation source Indus-1

We discuss and compare the imaging characteristics of toroidal and ellipsoidal mirrors for different horizontal acceptances of synchrotron radiation source Indus-1; using a ray tracing method. It has been shown that the toroidal and ellipsoidal mirrors have similar focussing behaviour at small horizontal acceptances. For large horizontal acceptances, toroidal mirror shows an asymmetry in the focussed image. Though the data used here are for Indus-1, the results are generally valid for any bending magnet synchrotron radiation source incident at grazing angles on these mirrors.     

Transport and harvesting of suspended particles using modulated ultrasound

Polystyrene particles of 9 μm diameter were acoustically concentrated along the axis of a water-filled cylindrical waveguide containing a 3 MHz standing wave field. Modulation of the acoustic field enabled transport of the concentrated particles in the axial direction. Four modulations were investigated; 1, a fixed frequency difference introduced between two transducers; 2, ramping the transducer frequency; 3, tone burst, i.e. sound that is pulsed on and off, allowing intermittent sedimentation under gravity; and 4, switching the sound off to allow continuous sedimentation. The most efficient transport (leaving the fewest particles in suspension) of clumps to one end of the container was achieved with method 1 above. In this system the maximum speed of transport of the axial clumps was 24 mm s^-1. A theory developed here for the transport of particles in a pseudo (i.e. slowly moving) standing wave field predicts an upper limit, which increases with particle size, for the speed of an entrained body. For a single 9 μm diameter particle in a field with a spatial peak pressure amplitude of 0.4 MPa this speed would be 0.5 mm s^-1. The higher experimental speeds observed here emphasize the value of acoustically concentrating particles into relatively large clumps prior to initiating transport.     

靶的厚度对激光产生的x射线输运到靶后能谱的影响

利用一维辐射流体动力学程序MULTI数值模拟研究了功率为10¹⁴W/cm²、脉冲宽度为1ns、波长为0.35μm的短脉冲强激光辐照不同厚度的平面Au靶时，靶厚度对靶背面x射线能谱结构和辐射强度的影响. 关键词： 激光等离子体 辐射流体力学 x射线转换     

Light Scattering and Visibility Condition of Spatial Objects

Considering background radiation of different wave band at different typical time by using Modtran soft, the characteristic of light scattering and the visibility condition of spatial object are discussed. Using bi-directional reflectance distribution function, combining geometry modeling with orbit theory, we numerical calculate light scattering radiation of spatial objects and compare it with the background radiation. The best observation time and station can be obtained by analyzing the conditions of visibility.     

Mechanical measurement of the parameters in a pseudo-stationary ultrasonic field in liquids

After recalling the formulae relating the energy density of a progressive wave with the sonic field parameters, the problem of deducing these parameters in a pseudo-stationary field is discussed. This field is produced in a ‘fixed force interferometer’ by two torsion balances; it is shown how to deduce from the radiation pressure, measured simultaneously at transducer and at reflector, the local pressure and velocity amplitudes, discussing the errors involved in treating pseudo-stationary fields as purely stationary.     

A FTIR study of PVDF irradiated by means of swift heavy ions

Poly(vinylidene difluoride) (PVDF) films were irradiated by means of heavy ions (in the electronic stopping-power range) and electrons. Both types of ionizing radiation induce in the polymer film ionizations and excitations, but swift heavy ions induce a huge density of excitations and ionizations along the ion path. Dose-range goes from 0.3 to 40 MGy. Irradiations were performed with Kr ions in the presence of helium, hydrogen, deuterium, and oxygen. Fourier transform infrared (FTIR) transmission measurements show differences in the nature of the created defects. Triple bonds are characteristic of the Kr ion irradiation. Double bonds, isolated and conjugated, exist for both kinds of radiation, but concentrations are higher with the Kr radiation. The presence of oxygen during irradiation produces oxidization defects. Typical bands of hydroxyls and carbonyls can be seen, respectively, in the 3800-3000 cm^?1 zone and ca. 1850–1730 cm^?1. The formation of conjugated double bonds is enhanced when the Kr irradiation is performed under an O₂ atmosphere. © 1994 John Wiley & Sons, Inc.     

相对论速调管放大器中微波放大机制

解析地研究了电子束在相对论速调管放大器（ＲＫＡ）的调制腔和漂移管中的预群聚；第一次用粒子－波相互作用的场方法导出了在辐射腔中预群聚电子束产生辐射的自洽方程；并且计算了线性区的增益．     

Effect of buffer gas on the generation of eye-safe 1.54 μm radiation using the stimulated Raman scattering technique in CH4

Experimental results on the generation of 1.54 μm eye-safe radiation in pure CH₄, CH₄:He and CH₄:Ar mixtures pumped by the fundamental of an Nd:YAG laser, using the stimulated Raman scattering (SRS) technique, are described. A decrease in the energy conversion efficiency and degradation in the beam quality of S₁ was observed in pure CH₄ at high pump energies. This problem was overcome in CH₄:He and CH₄:Ar mixtures. Compared with the first Stokes (1.54 μm) energy conversion efficiency in pure CH₄, at a pump energy of 126 mJ, an enhancement of 50% in energy conversion efficiency was observed in the CH₄:Ar mixture (60% argon concentration) and as much as 100% in the CH₄:He mixture (60% helium concentration). The use of these buffer gas mixtures improved the spatial beam quality of the Stokes radiation considerably and also resulted in raising the pump threshold for optical breakdown of the Raman gain medium.     

The disorder-longitudinal acoustic mode of oligo (ethylene glycol)-lithium trifluoromethane sulfonate solutions as studied by FT Raman spectroscopy

This work presents the results of Fourier transform Raman spectroscopy investigations of the disorder-longitudinal acoustic mode (D-LAM) of oligo(ethylene glycol) dimethyl ether-lithium trifluoromethane sulfonate solutions in dependence on oligomer chain length, temperature and salt concentration. The peak position and the bandwidth of this mode depend on the long-range conformational disorder of oligo(ethylene glycol) chains. The addition of salt causes a marked increase of the long-range conformational disorder. The frequency shift of the D-LAM combined with changes in the asymmetric CH₂ stretching bands indicate that the increasing long-range conformational disorder is connected with an increasing short-range conformational disorder of oligomer chains in a linear relationship.