Measurement of dynamic large-strain deformation maps using an automated fine grid technique

Automatic analysis of the dynamic deformation of a fine grid ruled onto a specimen's surface has allowed whole-field measurement of both in-plane displacement components. A high-speed camera was used to capture images of impacts at velocities of over 500 m/s. The Fourier transform method and phase unwrapping were used to calculate planes of phase coordinates which deform with the specimen. An iterative search algorithm yields the displacements directly by searching for the shifted location of each set of phase coordinates in the image of the deformed specimen. This paper describes the application of a previously proven analysis technique to dynamic deformation. Simple sample preparation and experimental operation make this technique ideal for the dynamic regime.     

The geometry of the SU(2) Kepler problem

The SU(2) Kepler problem is defined and analyzed, which is a Hamiltonian system reduced from the conformal Kepler problem on T^*( ⁸ − {0}) by the use of the symplectic SU(2) action lifted from the SU(2) left action on the SU(2) bundle ⁸ − {0} → ⁵ − {0}. This reduced system has a parameter μ ε su(2) coming from the value of the moment map associated with the symplectic SU(2) action. If μ ≠ 0, the phase space of this system have a bundle structure with base space T^*( ⁵ − {0}) and fibre S². The fibre, a (co)adjoint orbit through μ for SU(2), represents the internal degrees of freedom, called the isospin, of the particle of this system. The SU(2) Kepler problem with μ ≠ 0 is then interpreted as describing the motion of a classical particle with isospin in the Newtonian potential plus a specific repulsive potential together with a Yang-Mills field. This Yang-Mills field is to be referred to as BPST Yang's monopole field in ⁵ − {0};, since it becomes the Belavin-Polyakov-Schwartz-Tyupkin instanton, restricted on S⁴. If μ = 0, the SU(2) Kepler problem reduces to the ordinary Kepler problem. Like the ordinary Kepler problem, the Hamiltonian flows of the SU(2) Kepler problem of negative energy are all closed. It is shown in an explicit manner that the energy manifolds and isoenergetic orbit spaces for the SU(2) Kepler problem of negative energy are both homogeneous manifolds on which SU(4) acts transitively to the right; those homogeneous manifold are classified into two, according as the parameter μ is zero or not. For a certain value of μ, however, they contracts to the manifold which represents the set of all the equilibrium states. The isoenergetic orbit spaces are finally shown to be symplectomorphic to certain Kirillov-Konstant-Souriau coadjoint orbits for U(4), if μ is not the exceptional value mentioned above.     

Reproducibility of optically stimulated luminescence measurements from single grains of Al2O3:C and annealed quartz

We have measured some aspects concerning the performance of a new instrument for the measurement of optically stimulated luminescence (OSL) from single sand-sized grains. The instrument uses a solid-state laser to stimulate OSL from each grain individually. These grains are placed in a regular grid of nine-by-nine holes, which are drilled in the sample disc. We report on tests carried out to determine the precision with which the laser beam can be directed at individual grains in these holes. Single grains of aluminium oxide (Al₂O₃:C) (90–180 μm) and annealed quartz (90–120 μm) were used to test the reproducibility with which the OSL signal can be measured. These experiments suggest that the laser beam can be positioned to within 30 μm and that the reproducibility of OSL measurement is 3.5% on an average.     

Fabrication and testing of high quality small germanium plano-convex lens

In this paper, a new method is designed which is accurate (λ/4, λ=632·8 nm) for finishing the small (less than 2·6 mm diameter and a center thickness of 0·4 mm) and soft germanium plano-convex lens. Special features of this process are as follows: (i) it produces a scratch-free and smooth surface; (ii) a precision blocking jig has been constructed which enables the operators to engage centering work of the plano-convex lenses (i.e. the lenses edge are co-axial with the optical axis); (iii) a modified moiré technique rapidly performs the centering test; and (iv) the simulation model has been developed for evaluating the polishing parameters used in this process.     

On the determination of elastic residual strain fields in rail wheels using moiré interferometry

Moiré interferometry was used to determine the residual strain fields in a rail wheel. Hoop, radial, and shear displacement fields were determined in a whole field manner using a novel four-beam moiré interferometer. Diffraction gratings of 150 lines/mm were employed on the specimen surface. A system of data interpolation utilizing a simple control sample scheme was developed for field environments where sample loading occurs away from the optical device. Agreement was found between the moiré technique and physical measurements of wheel contraction during sectioning. Marginal agreement was found with strain gage measurements.     

Magnetostriction in terms of hexagonal and cubic harmonics up to degree 6

Tables are given which allow the magnetostriction constants ^j_kΛ^μ_l6 and magnetoelastic coupling coefficients ^J_kB^μ_l6 to be evaluated from the Fourier coefficients of Δl/l in various crystallographic planes. The difference between anisotropy coefficients at zero strain and zero stress is given for hexagonal crystals for the first time in terms of the ^j_kB^μ_l . At all stages the indices which indicate the symmetry type of a function (μ, i) are clearly distinguished from those which do not (j, k, l).     

Development of extended field Doppler velocimetry for turbomachinery applications

The development of a portable, single component Doppler global velocimetry (DGV) head, based around a wavelength-stabilised argonion laser and a fast digital image-processing system, is described. The normalised two-dimensional DGV image, in which intensities are linearly related to velocities, can be displayed and updated at the 25 Hz camera frame rate, greatly easing the problem of system alignment. The effect of each individual system component upon the velocity resolution achieved for the system as a whole is discussed, and correction factors are calculated to account for the finite aperture and field of view of real systems and for divergence of the illuminating light sheet. Axial velocities of up to 100 m/s in a straight duct flow have been measured, demonstrating an rms velocity resolution of 2.5 m/s. The potential of the technique for gas turbine applications has been demonstrated by measuring the position of a shock in a transonic flow. At a Mach number of 2.3 and mass flow rate of 0.79 kg/s the velocity change across the shock was measured to be approximately 130 m/s.     

Two-dimensional strain measurement with ESPI

Optical techniques have been applied to the measurement of solid deformations in many instances. Practical difficulties with a particular technique can be overcome, in some circumstances, with attention to experimental detail. However, a common problem is the quantitative interpretation of the optical data thus obtained: this can be a time-consuming process and depends on the operator's skill. This paper describes an electronic speckle pattern interferometer that measures two in-plane displacement components simultaneously. The (phase-stepping) procedures implemented for automated displacement and strain analysis are described. Simultaneous measurement of the two displacement components is particularly important for shear strain measurement, because data from the two in-plane views must be combined. The accuracies of displacement and strain measurements are shown to be ±0·03 μm and ±6 μstrain, respectively. Results are presented for a compact tension specimen.     

Micromechanical thermal deformation analysis of unidirectional boron/aluminum metal-matrix composite

An experiment was conducted to document thermal deformation of a unidirectionally reinforced boron/aluminum metal-matrix composite. The specimen was subject to an isothermal loading of ΔT = − 100 °C and the deformation on a free surface perpendicular to the fibers was measured by microscopic moiré interferometry. The high sensitivity and spatial resolution made it possible to elucidate the micromechanical behavior of the specimen at the fiber level. Multiplied moiré fringe patterns with a contour interval of 35 nm/fringe contour were obtained for a hexagonal array of fibers and a square array of fibers. The stress-induced strains were determined from the fringe patterns by subtracting the free thermal contraction strains. The results revealed a free surface effect and showed asymmetrical and irregular strain distributions inherent in real (non-idealized) composite materials.     

Creep deformation measurement using quartz optical fiber

This paper describes an optical system for high temperature creep strain measurement using quartz optical fiber, super long working distance microscope and digital image processing techniques. In this system one end of the quartz optical fibers is arrayed in a small area on the specimen surface and the other end is illuminated by a laser beam. The fiber ends on the specimen surface form the spot array. The small optical spots on the specimen are tracked by a CCD camera and the images are processed by digital image processing software. The diameter of each quartz fiber is 100 μm and the fibers can be arrayed in a small area. The local strains are determined by measuring the variety of relative distance between two spots. Experimental results of local creep strain on the welding joints of 15CrMo and HK40 at 850°C are obtained.     

In situ synchrotron far infrared micro-spectroelectrochemistry with a grazing angle objective

We demonstrate the use of a grazing angle objective attachment to carry out in situ far infrared micro-spectroelectrochemistry at a copper electrode on a nano-scale. A thin-layer spectrochemical cell made out of Teflon was used, fitted with a 20-μm thick Mylar window; the working electrode was 500 μm in diameter. Measurements were carried out in 0.1 M NaOH solution as a function of applied potential between –1.4 and 0 V vs a Hg/Hg₂SO₄ reference electrode. Spectra were obtained with excellent signal to noise ratio for the surface oxide film, formed on copper electrochemically with less than 1 nL of active solution volume. The surface film at 0 V was about 130 nm thick and consisted mainly of CuO, with possibly some Cu(OH)₂ also present. This interpretation is consistent with previous works and thermodynamic calculations. The technique should be useful in other investigations and the further development of electrochemical surface science.     

Three-dimensional pictures of industrial scenes applying an optical radar

For small scale ranging, a light beam, modulated with a wavelength typical for radio waves, is a suitable means of scanning. The ranging beam can be focussed to illuminate only a small spot. The diffuse reflection on the spot ensures that an echo appears. By applying phase comparison techniques to the ranging and echo beam the optical path length and thus the height of the illuminated surface element can be determined. By systematically deflecting the beam and thereby scanning the scene, a discrete height map is obtained. The realisation of such a small scale ‘optical radar’ is described, the main elements of which are a semiconductor diode laser for emission, an avalanche photo diode for detection, and a two-dimensional beam deflection mechanics for scanning. The typical performance is taking a picture of a volume of about 0·5 m × 0·5 m × 0·5 m within 1s, consisting of about 64 000 pixels.     

Hole formation and charge transfer in Y1−xCaxSr2Cu2GaO7, a new oxide superconductor

The technique of transmission electron energy loss spectrometry (EELS) in parallel detection has been utilized to analyze the fine structures associated with the O K and Cu L₃ absorption edges of recently discovered Y_1−xCa_xSr₂Cu₂GaO₇ (0.1 ≤ x ≤ 0.4) series of compounds, which exhibit superconductivity when annealed under high-pressure oxygen atmosphere. We find subtle but significant changes in EELS spectral features of nonsuperconducting and superconducting specimens of these compounds. A broad pre-edge feature is observed below the O K absorption edge, at about 528.2 eV which emerges with Ca-doping alone. Evidence is presented for another O K secondary pre-edge feature, at about 1.1 eV below the first O K pre-edge feature in only those specimens which have undergone high-pressure oxygen treatment (i.e. superconducting specimens). We interpret the O K pre-edge feature as due to formation of holes on oxygen sites and propose that the first broad pre-edge feature (at 528.2 eV) is associated with holes on oxygen sites other than the CuO₂ planes, which are responsible for normal conductivity. The second smaller pre-edge feature (at 527.1 eV) is most probably associated with holes in the CuO₂ planes, which are associated with superconductivity in this system. The presence of a secondary smaller O K pre-edge feature in the superconducting specimens appears to correlate well with a broad shoulder on the high energy side of the Cu L₃ edge. The results are interpreted in terms of oxidation of CuO₂ planes through charge transfer between copper and oxygen in the CuO₂ planes, i.e. covalent mixing of O and Cu orbitals at the Fermi level as a result of high oxygen pressure annealing.     

Vortex penetration depth of κ-(ET)2Cu[N(CN)2]Br

The magnetic field dependence of the in-plane penetration depth λ_|(H) for single crystal κ-(ET)₂Cu[N(CN)₂]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ_| scales with a characteristic field H^*(T) that coincides with a shoulder in the λ_| vs. H curves. Above that field, λ_| increases sharply toward a second inflection point at H^**(T) that coincides with is close to the irreversibility line measured by magnetization. For fields larger than H^** the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ 300 μm, implying an anisotropy λ/λ_| > 200.     

Aspects of “low field” magnetotransport in epitaxial thin films of the ferromagnetic metallic oxide SrRuO3

Epitaxial thin films of the conductive ferromagnetic oxide SrRuO₃ were grown on an (0 0 1) SrTiO₃ (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]_S and [0 0 1]_S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ₀H=9 T; T)−ρ( μ₀H=0 T; T)]/ρ( μ₀H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, T_C 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO₃ films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization.     

Phase slippage at the interface: normal metal/sliding charge-density wave

Phase slippage is required at the current electrodes of quasi-one-dimensional conductors with a charge density wave (CDW) ground state for the conversion from free to condensed carriers. We have performed at the ESRF high-resolution X-ray measurements of the spatially varying shift q(x) of the CDW satellite wave vector between current contacts on a thin NbSe₃ whisker in the sliding state. Applying direct currents, we observe at 90 K a steep exponential decrease of the shift within a few hundred microns from the contact. The CDW strain profile q(x) reflects the carrier conversion process, via nucleation and growth of phase-dislocation loops. Pulsed current measurements of the shift q show important differences between pulsed and dc current data, revealing a spatially dependent relaxational behaviour of the CDW strain. Using time-resolved high spatial resolution X-ray we observe at 300 μm from the electrode a stretched exponential-type decay of the shift q(t) upon switching off the current (T=75 K): q(t)=q₀[exp(−t/τ)^μ] with τ=23 ms and μ=0.36.     

应力作用下EuTiO3铁电薄膜电热效应的唯象理论研究

基于Laudau-Devonshire的热动力学模型, 计算了EuTiO₃铁电薄膜材料的电热效应. 结果显示在外加应力的调控下, 电极化、电热系数以及绝热温差都会随之变化. 外加垂直于表面的张应力加大, 薄膜的相变温度升高, 绝热温差增加, 最大绝热温差所对应的工作温度向高温区移动. 对于二维平面失配应变u_m =-0.005的薄膜, 当外加张应力σ₃ = 5 GPa时, 其最大电热系数为1.75×10^-3 C/m²·K, 电场变化200 MV/m 时室温下绝热温差ΔT 的最大值可达到14 K 以上, 绝热温差ΔT ≥13 K 的工作温区超过120 K, 表明可以通过调控外部应力来获取室温时较大的绝热温差. 此结果预示着铁电EuTiO₃ 薄膜在室温固态制冷方面可能具有较好的应用前景.     

定向凝固单晶冰的取向确定与选晶

基于六方冰晶偏振光学特性,定义了用于确定冰晶晶体取向的三个参数:光轴倾角α,消光角β和与冰晶基面(0001)面内晶体学择优方向1120与温度梯度的夹角γ,提出了定量判定冰晶晶体取向的理论基础,并在定向凝固平台上采用偏光显微镜成功实现了冰晶晶体取向的精确主动控制,获得了任意取向的单晶冰.本文成功解决了冰晶的定向凝固晶体取向确定和选择的难题,为冰晶生长过程中相关理论问题的研究提供了有效的途径.     

自驱动Janus微球近壁运动特性实验与数值模拟研究

自驱动Janus微球是形状规则但表面构成不同的特殊活性颗粒. 针对微米级Pt-SiO₂型Janus 微球近壁面自驱动现象, 实验测得了微球的自驱动速度V_Janus, 并观察到微球运动过程中与垂直方向存在一偏转仰角ψ, 且ψ角随H₂O₂溶液浓度的增大呈减小趋势. 在此基础上, 建立自驱动Janus微球的数值模型, 通过模拟得到了微球在不同浓度H₂O₂溶液中的偏转仰角ψ及距底面的高度δ, 模拟与实验一致. 利用这些数据进一步讨论了壁面效应对微球旋转特征时间τ_R的影响. 这一工作对于理解Janus 微球的运动机理及发展相关应用具有重要意义.     

Stimulated raman scattering in fiber optic systems

The effect of stimulated Raman scattering (SRS) in fiber optic communications is considered. On one hand, SRS limits the launch power in a multiple-channel communication system; while on the other hand, SRS can provide optical amplification in the 1.3-μm and 1.55-μm windows. In most of the previous work these issues have been treated separately by using different assumptions. A solution is usually obtained by solving differential equations. We present a numerical method that involves the simultaneous solution of integral equations describing SRS in optical fiber. The method is general enough to be applicable for wavelength division multiplexing (WDM), optic frequency division multiplexing (OFDM), and optical amplification. However, it is efficient and simple to program and uses just a few realistic assumptions. A WDM communication system with 10 optical channels in the 1.55-μm window is studied by using this method, The data rate is above 1 Gbps. The system parameters are such that the other nonlinear effects, such as stimulated Brillouin scattering and four-wave mixing, are less significant for the system. Launch power limitations imposed by SRS are investigated for IM / DD and coherent systems. The receiver dynamic range over the wavelengths of interest is an important factor in determining the launch power limitations. An optical amplifier in the 1.3-μm window is also analyzed. The two-pump technique is investigated. With pump power levels of about 500 mw 0-dB gain can be achieved for a 30-km repeaterless link. Finally, the calculated results agree with the experiments.