High-transmission focusing X-ray diffractor: Numerical simulation of the reflecting surface

Models of stepped x-ray diffractors of a new type with ellipsoidal and toroidal step surfaces are calculated in the point x-ray source approximation. The Monte Carlo method is used to obtain an image of the diffraction zones of reflection and to investigate the influence of surface curvature on the shape and area of these zones. Pis’ma Zh. Tekh. Fiz. 25, 11–16 (October 12, 1999)     

A focusing X-ray diffractor: Effect of the crystal bending parameters on the spectral resolution

The dependence of the spectral resolution of a focusing X-ray diffractor on the shape and curvature of the reflecting crystallographic faces in the plane perpendicular to the focusing circle plane is theoretically studied in the point source approximation. The curvature parameters ensuring the best spectral resolution are determined for ellipsoidal and toroidal types of the crystal bending.     

Simulation of the stepped surface of a high-resolution X-ray diffractor

Three possible schemes of a high-resolution stepped X-ray diffractor have been analyzed, including those based on the steps of equal angular widths, the steps of equal heights (i.e., distances from the step edge to the beginning of the next step), and the symmetric steps (where a distance from the step edge to the focusing circumference is equal to the distance from the focusing circumference to the edge of the next step). It is shown that the first and the third schemes provide most stable characteristics.     

反射面对有源抗噪声头靠降噪性能的影响

1引言有源抗噪声头靠是一个双输入双输出的有源噪声控制系统。它通过两个次级声源的控制使得在两人耳处的声压最小,从而在人耳附近产生安静区域,达到降噪的效果。其理论上所能达到的控制效果表     

The fractal properties of a geometric model of the high-resolution X-ray diffractor

Perfect and mosaic crystals are conventionally used in X-ray monochromators operating in the energy range from several hundred to tens of thousands of electronvolts. The focusing X-ray optics for nonparallel beams employs either cylindrical bent crystals (the methods of Johann [1], Johansson [2], and Cauchois [3]) or crystals with spherical or toroidal [4] bending of the crystallographic planes. Special variants of high-resolution stepped-crystal diffractors [5–8] were developed to study the possibility of high-precision focusing of a monochromatic X-ray radiation. The fractal properties of a geometric model of such a high-resolution steppedcrystal diffractor are considered.     

Effect of source spectral shape on task-based assessment of detection and resolution in optical coherence tomography

We demonstrate the effect of the spectral shape of broadband light sources in a task-based approach for assessment of signal detection and resolution in optical coherence tomography. We define two binary tasks: The signal is either present or absent and the signal can be either resolved or not. In a transparent sample bounded by two uniform interfaces we study the minimum detectable change in the index of refraction as well as the minimum resolvable distance between the layers in correlation with the source spectral shape and power. Results show that the area under the receiver operating curve (AUC) for a signal-detection task is not affected by the shape of the spectrum but solely by its optical power, whereas spectral shaping has an effect, which we quantify, on the AUC for the resolution task. Moreover, the AUC is demonstrated in relation to the concept of system sensitivity for a signal-detection task.     

The spectral resolution of high temperature GaAs photon counting soft X-ray photodiodes

Circular mesa GaAs p⁺-i-n⁺ diodes for photon counting soft X-ray spectroscopy have been fabricated and characterised over a temperature range of +80 to -30 °C. The spectroscopic performance of the diodes, as measured by the FWHM of the Mn K_α X-ray line from an ⁵⁵Fe radioisotope, is reported. In addition, we compare the GaAs diodes with previously fabricated and characterised Al_0.8Ga_0.2As p⁺-i-n⁺ diodes of similar geometry.     

钢筋混凝土空间网格结构曲率模态曲面拟合损伤识别研究

本文介绍了钢筋混凝土空间网格结构的体系组成及构造特点;提出了曲率模态曲面拟合损伤识别理论,定义了曲率模态曲面拟合损伤指标CMSFDIi和平均曲率模态曲面拟合损伤指标CMSFDIiA,通过曲率模态与曲面拟合值的差异进行损伤定位,方法仅需利用从损伤结构获得的实测数据即可进行结构损伤识别,无需利用完好结构的基本信息和理论模型;最后通过钢筋混凝土正交正放空腹网架结构实例,验证了方法的有效性。计算结果表明,本文方法不仅可以识别单位置损伤还可以识别多位置损伤,对钢筋混凝土空间网格结构的损伤识别和健康监测是可行的。     

X-ray absorption fine structure combined with X-ray fluorescence spectrometry. Improvement of spectral resolution at the absorption edges of 9-29 keV

X-ray absorption near-edge structure (XANES) suffers from core-hole lifetime broadening at a higher energy absorption edge, such as Sn K (29 keV, Gamma(K) = 8.49 eV). To overcome this problem, emitted Sn Kalpha1 fluorescence from sample was counted using high-energy-resolution fluorescence spectrometer in the XANES measurements. Experimental energy resolution (5.0 eV) was consistent with theoretical values based on the Rowland configuration of the spectrometer. The absorption edge became steeper compared to conventional spectra. The white-line peak due to Sn(II) species became remarkably sharper and more intense in the Sn Kalpha1-detecting Sn K-edge XANES for Pt-Sn/SiO2. To support the semiclassical theory of resonant Raman scattering for the explanation of observed elimination of lifetime width, more resolved XANES data at Cu K, Pb L3, and Sn K in this work were convoluted (filtered) with a Lorentzian of each core-hole lifetime width. The processed data resembled generally well corresponding XANES spectrum measured in transmission mode. The verification based on ab initio XANES calculations was also performed.     

Dependence of surface bonding on deformation

Experiments have shown that the peeling of surface films during deformation is dependent on the mechanical properties of the surface film and the bulk materials and on the amplitude of strain in cyclic deformation. An analysis of these results led to an explanation that has as its major parameters the elastic constants, the relative yield stresses and the relative strain to yielding of the materials involved. The model is applied to diffused as well as discrete surface layers and can be used to predict favorable combinations that are unlikely to debond.     

Development of a high spectral resolution lidar based on confocal Fabry-Perot spectral filters

The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5?GHz and a finesse of 50.7 (312) at 532?nm (1064?nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.     

Dependence of the crystal-liquid phase transition temperature on the size and shape of a nanocrystal

The dependence of the crystal-liquid phase transition (melting) temperature T _m on the size and shape of a nanocrystal with a free surface has been studied proceeding from the Lindemann criterion. It is shown that, with neglect of the surface pressure, the T _m value decreases with a reduction in the isomorphous nanocrystal size. The greater the nanocrystal shape deviation from cubic, the more pronounced the size dependence of T _m. With allowance for the surface pressure, the T _m value increases with decreasing nanocrystal size if the arising pressure compresses the crystal. If the surface pressure produces an extension of the crystal, the decrease in T _m with decreasing size becomes more pronounced. The surface pressure can both suppress and enhance the size-dependent T _m variations.     

Absolute high spectral resolution measurements of surface solar radiation for detection of water vapour continuum absorption

Solar-pointing Fourier transform infrared (FTIR) spectroscopy offers the capability to measure both the fine scale and broadband spectral structure of atmospheric transmission simultaneously across wide spectral regions. It is therefore suited to the study of both water vapour monomer and continuum absorption behaviours. However, in order to properly address this issue, it is necessary to radiatively calibrate the FTIR instrument response. A solar-pointing high-resolution FTIR spectrometer was deployed as part of the 'Continuum Absorption by Visible and Infrared radiation and its Atmospheric Relevance' (CAVIAR) consortium project. This paper describes the radiative calibration process using an ultra-high-temperature blackbody and the consideration of the related influence factors. The result is a radiatively calibrated measurement of the solar irradiation at the ground across the IR region from 2000 to 10?000?cm(-1) with an uncertainty of between 3.3 and 5.9 per cent. This measurement is shown to be in good general agreement with a radiative-transfer model. The results from the CAVIAR field measurements are being used in ongoing studies of atmospheric absorbers, in particular the water vapour continuum.     

Resonance suppression in the extinction spectrum of single and aggregated hemispheres on a reflecting surface

The extinction spectrum from single and aggregated hemispheres whose flat faces lie on a reflecting surface is calculated, and some of the expected resonances are found to disappear for specific choices of the direction and the polarization of the incident wave. This resonance-suppressing effect is fully explained for the case of single hemispheres, whereas for the case of aggregated hemispheres the guidelines for its explanation are given.     

On the spectral resolution of a focusing Bragg spectrometer

The influence of the intensity profile of a wave, focused upon backscattering from a bent crystal, on the spectral resolution of a focusing Bragg spectrometer dynamically reflecting short-wavelength X-ray radiation (λ∼1 Å) is considered in comparison to a nonfocusing flat-crystal spectrometer. Conditions necessary for resolving spectral lines in the spectrometers of both types are formulated.     

Dependence of spectral shape of bremsstrahlung spectra on atomic number of target materials in the photon energy range of 5-30 keV

Dependence of spectral shape of total bremsstrahlung spectra i.e. the sum of ordinary bremsstrahlung (OB) and polarization bremsstrahlung (PB), on the atomic number (Z) of target materials (Al, Ti, Sn and Pb), produced by continuous beta particles of ⁹⁰Sr and ²⁰⁴Tl, has been investigated in the photon energy region of 5-30 keV. It has been found that the spectral shape of total bremsstrahlung spectra, in terms of S (k, Z) i.e. the number of photons of energy k per m_oc² per beta disintegration, is not linearly dependent on the atomic number (Z) of the target material and rather it is proportional to Zⁿ. At lower photon energies, the index values ‘n’ of Z-dependence are much higher than unity, which is due to the larger contribution of PB into OB. The decrease in ‘n’ values with increase of photon energy is due to the decrease in contribution of PB into OB. It is clear that the index ‘n’ values obtained from the modified Elwert factor (relativistic) Bethe-Heitler theory, which include the contribution PB into OB, are in agreement with the experimentally measured results using X-PIPS Si(Li) detector. Hence the contribution of PB into the formation of a spectral shape of total bremsstrahlung spectra plays a vital role.     

Dependence of the thermal coefficient of accommodation and the emissivity on surface roughness

Results are presented of a theoretical and experimental investigation of the dependence of the thermal coefficient of accommodation and emissivity on parameters characterizing surface roughness.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 1, pp. 114–118, January, 1971.     

Reconstruction of the net emission distribution from the total radiance distribution on a reflecting surface

The problem is considered of reconstructing, from a measurement of the total radiance distribution on an emitting surface, the radiance distribution that would be observed in the absence of reflected radiation. An explicit solution of the implied inverse problem is derived for the case in which the reflective properties of the surface are given in terms of a bidirectional reflection distribution function. Also considered are the limiting cases of diffuse and specular reflection. Practical considerations are discussed for application of the theory to the nonintrusive and remote measurement of temperatures and pressures on concave surfaces, either by traditional radiometry or by the use of thermographic phosphors and temperature- and pressure-sensitive paints.