Measurement of thermal expansion coefficient of nonuniform temperature specimen

A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature.The measuring principle and components of the apparatus are described in detail.The calculation method is derived from the temperature dependence of the therinal expansion coefficient.The apparatus mainly consists of a high temperature environmental chamber,a power circuit of heating,two high-speed pyrometers,and a laser scanning system.A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current.The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation.The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system,respectively.The thermal expansion coefficient in a wide temperature range(1000-3800 K)of the specimen can therefore be obtained.The perfect consistency between the present and previous results justifies the validity of this technique.     

Simultaneous melting and solidification of a columnar dendritic microstructure in a temperature gradient: Numerical modeling and experiments⋆

The European Physical Journal E - We have studied the dewetting dynamics of partially wetting liquid films confined between a soft elastic hemisphere and an elastomer layer by means of systematic...     

Measurement and correction of coupling in BEPCⅡ

The existing linear coupling theory and representation method are introduced briefly. The so-called local and global coupling is discussed in more detail. The vertical orbit distortion excited by a horizontal corrector is represented with the coupling parameters at the corrector and the observation point. The formula is used to measure the coupling in BEPCⅡ. In order to correct the coupling, vertical correctors are used to change the vertical orbit through sextupoles by a least square method. We also introduce and review other frequently used coupling measurement/tuning methods used in our machine.     

Simultaneous Measurement of Concentration and Temperature in Methane–Hydrogen Flames by Laser-Induced Fluorescence

Journal of Russian Laser Research - We analyze the structure of methane–air and methane–hydrogen–air flames stabilized over the porous plate burner, using the method of...     

The electric field gradient and its temperature dependence at111Cd in α-Uranium

The magnitude and temperature dependence of the quadrupole interaction at the¹¹¹Cd site in orthorhombic -Uranium was investigated between 293 and 17 K. The parent activity¹¹¹In was implanted into Uranium metal with an energy of 80 keV and the - TDPAC technique, applied to the 245 keV state in¹¹¹Cd, was used to measure the quadrupole interaction frequency. The derived electric field gradient for Cd in Uranium was found to be highly asymmetric (=1) and led to a quadrupole interaction frequency of _Q=7.10(7) MHz at 293 K. The temperature dependence of the quadrupole interaction is very strong, _Q increases to 14.3(2) MHz at 17 K and shows a linear dependence on the temperature.This work has been partially supported by the BMFT, FRG (03B01B0N/2).Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

Measurement of nuclear moments and radii by collinear laser spectroscopy and by β-NMR spectroscopy

Experiments using laser spectroscopy and nuclear magnetic resonance techniques have been performed at ISOLDE on the unstable isotopes of several light elements. The results include nuclear ground state spins, magnetic dipole and electric quadrupole moments, and the behaviour of mean square nuclear charge radii within isotopic strings. These give important information about the nuclear structure at shell closures and close to the drip lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Controlled focusing of the Å wavelength radiation in case of the ultrasound modulation or temperature gradient

The paper describes diffraction focusing of the spherical X-ray radiation, experimentally discovered outside the crystal with a temperature gradient or ultrasound oscillations in it. The focus distance is shown to decrease with the rise of the temperature gradient if it is antiparallel to the diffraction vector. In the opposite case defocusing is taking place. Similar results are obtained in case of coherent ultrasound excited in the crystal.     

Measurement of sensitivity of transducer in the field of NDT by the reciprocity technique

The sensitivity of a transducer should be an important characteristic inthe field of NDT.But so far,no method for this measurement of the sensitivity of atransducer applied to the ultrasonic flaw detection is available.In this paper thetransducer is regarded as a plane source and the reciprocity parameter under thecondition of the far field is derived.We have calibrated the sensitivity of ultrasonictransducers with the reciprocity technique in the solid sample.The experimentsshow and confirm that the transmitting and receiving sensitivities of the transducerapplied to NDT can be exactly measured.The precision of the measurement is with-in ± 1dB under a certain coupling condition.     

Thermoluminescence and optically stimulated luminescence disadvantages of α-Al2O3:C crystal grown by the temperature gradient technique

Recently, α-Al₂O₃:C crystal with highly sensitive thermoluminescence (TL) and optically stimulated luminescence (OSL) has been successfully grown by the temperature gradient technique. This paper investigates the heating rate dependence of TL sensitivity, light-induced fading of TL signals and thermal stability of OSL of α-Al₂O₃:C crystals. As the heating rate increases, the integral TL response decreases and the dosimetric glow peak shifts to higher temperatures in α-Al₂O₃:C crystals. Light-induced fading of TL increases with the irradiation dose, and TL response decreases as the exposure time increases, especially in the first 15 minutes. With the increasing intensity of the exposure light, the TL fading of α-Al₂O₃:C crystal increases sharply. The OSL response of as-grown α-Al₂O₃:C crystal is quite stable below 373 K and decreases sharply for higher temperatures.     

Measurement of multi-exponential optical decay processes by?phase-shift cavity ring-down

Multi-exponential decay waveforms are common occurrences in cavity ring-down spectroscopy and the respective ring-down times are typically obtained by fitting the ring-down waveform to the sum of exponential decay functions. In phase-shift cavity ring-down (CRD) spectroscopy the measurement of a single phase angle will not provide sufficient information and needs to be complemented by either intensity measurements or phase angle measurements at different modulation frequencies. Here, a formalism analogous to that developed for fluorescence lifetime spectroscopy is adapted to the phase-shift CRD technique and is tested for two types of waveguide CRD systems: (1) a single-mode fiber cavity in which light is confined by two identical Fiber Bragg Gratings and (2) a multimode fiber loop. By measuring the phase angle at different modulation frequencies, lifetimes for up to three different decay processes were obtained.     

Measurement of cluster–cluster interaction in liquids by deposition and AFM of silicon clusters onto HOPG surfaces

Experimental studies have been performed on unisize tungsten clusters constructed on a graphite surface by means of the scanning tunneling microscopy. It was found that the geometry of the clusters changes instantaneously from a monatomic-layer tungsten disk to a diatomic-layer structure between the cluster size of 10 and 11. We concluded that this transition is driven by a change in the dominant interaction from the attractive electrostatic interaction between the cluster and the surface to intracluster cohesive metallic interaction.     

Measurement of velocity distribution in an atomic beam by means of Doppler resonance fluorescence

Introduction Measurement of velocity distribution in atomic beams is of significance to laser spec-troscopy and atomic physics.Previously,workers used to investigate atomic velocity distribu-tion by means of mechanic separators.Recently, spectroscopic methods of measuring veloc-ity distribution are developed,which find velocity distribution from detecting atomic fluo-rescence frequency distribution or from detecting atomic deflection due to radiation force.Un-fortunately,these methods can not realize real time measurement.In this paper we propose a     

Measurements and calculations of ethylene line-broadening by argon in the ν7 band at room temperature

Argon broadening coefficients are measured for 32 vibrotational lines in the ν₇ band of ethylene at room temperature using a tunable diode-laser spectrometer. These lines with 3 ≤ J ≤ 19, 0 ≤ K_a ≤ 4, 2 ≤ K_c ≤ 19 in the P, Q and R branches are located in the spectral range 919–1023 cm^?1. The fitting of experimental line shapes with Rautian profile provides collisional widths slightly larger than those derived from the Voigt profile. The independent theoretical estimation of these line widths is performed by the semiclassical approach of Robert-and-Bonamy type with exact isotropic trajectories generalized to asymmetric tops. Even with a rough atom–atom intermolecular potential model the calculated values show good agreement with experimental results.     

Does human skin truly behave as an array of helical antennae in the millimeter and terahertz wave ranges?

The sweat ducts of the human perspiration system are helically shaped tubes, filled with a conductive aqueous solution. Recent studies have claimed that these ducts act as an array of low-Q helical antennae and are dominant in shaping the spectral response in the subterahertz region. Using local homogenization theory for the skin embedded with sweat ducts, we found that multiple interference effects from the skin layers play the major role in determining the skin electromagnetic characteristics in the millimeter and terahertz regions without the need for the assumption of the sweat ducts acting as low-Q helical antennae.     

Measurement of thermophysical properties by a pulse-heating technique

A technique is described for the dynamic measurement of selected thermophysical properties of electrically conducting solids in the temperature range from 1100 K to the melting point.Based on rapid resistive self-heating of the specimen from room temperature to any desired high temperature in several seconds by the passage of an electical current pulse through it,this technique measures the pertinent quantities such as current,voltage,randiance temperature,with sub-millisecond time resolution.The pulse-heating technique is applied to strip specimens.The radiance temperature is measured by high-speed pyrometry, normal spectral emissivity of the strips is measured by integrating sphere reflectometry.The normal spectral emissivity results are used to compute the true temperature of the specimens.The heat capacity, electrical resistivity,total hemispherical emissivity are evaluated in the temperature range from 1100 K to the melting point.     

Noncontact Measurement of Surface Topography by Mirau Interferometer

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Measurement of Change of ^7Be Decay Rate in Be and Au

We have measured the possible change of the decay rate of ^7Be implanted into hosts of natural beryllium and natural gold. No difference between the ^7 Be decay rates in the two hosts is observed within the experimental precision of 0.12%. This result implies that change of the decay rate of ^7Be implanted in different materials cannot be simply expected from the electron affinity difference consideration lonely and the lattice structure of the host materials should be taken into account.     

Experimental Characterization of Correlation—Functions of Random Surfaces by Speckle Measurement and Complementary Algorithm

A method for the extracting the correlation functions of random surfaces is proposed by using the image speckle intensity.Theoretically,we analyse the integral expression of average intensity of the image speckles,and compare it with the pair of Fourier-Bessel-transform-and-the-inversion of the exponential function of the height-height correlation function of the random surfaces.Then the algorithm is proposed numerically to complement the lacking Bessel function factor in the expression of the average speckle intensity,which changes the intensity data into the pair of the Fourier-Bessel-transforn.Experimentally,we measure the average image speckle intensities versus the radius of the filtering aperture in the 4f system and extract the height-height correlation function by using the proposed algorithm.The results of the practical measurements for three surface samples and the comparison with those by atomic force microscopy validate the feasibility of this method.     

Measurement of Mg Content in Zn1-xMgxO Films by Electron Probe Microanalysis

Zn1-xMgxO films are grown on A-sapphire substrates by molecular beam epitaxy, and Mg content in the Zn1-xMgxO films is measured by electron probe microanalysis （EPMA） when the acceleration voltage, the emission current, and the magnification are set to be 1 k V, 30 μA and 1000, respectively. The dead time is controlled within 17%-20% during the measurement with the receive angle of characteristic x-ray of 45°. The Mg content of the ZnMgO film is calculated by the low energy calibration and the ZAF calibration. By comparing the measurement result with the theoretical analysis and the EPMA result with the inductively coupled plasma （ICP）, one can obtain that the measured value of Mg content of the samples is in good agreement with the theoretical analysis no matter whether the phase separation exists or not, and the correctness of ICP and EPMA is valid when Mg content in the samples is less than 0.5.     

Measurement of Threshold Pressure Gradient of Microchannels by Static Method

The development of oil fields and laboratory experiment present the threshold pressure gradient （TPG） of liquid flow in low permeability porous media, which is called the micro-size effect in porous media. Some micro-size effects in micro-electro-mechanism systems （MEMS） are not always in agreement with each other. We propose an experiment setup to measure the TPG of microchannels by static method in the microchannels with the diameter ranging from 20-320μm. The results present the existence of TPG in microchannel, and show an effect that the TPG of microchannel increases with decreasing hydrodynamic diameter. The relation between TPG and diameter is in agreement with single-log normalization. Additionally, the influence of errors in the experiment shows the data of experiment are valid. Finally, the mechanism of micro-size effects is discussed by revealing the facial force between liquid and solid and theory of boundary liquid, but the explanation is still not good, and needs further study.