Total electron scattering cross-sections for carbon monoxide at low electron energies

Absolute total electron scattering cross-sections for carbon monoxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 22 electron energies varying from 0.73 to 9.14 eV with an accuracy of ±3%. The cross-sections obtained in the present experiment have been compared with other measurements and theoretical computations.     

Thermal infrared cross-sections of C2F6 at atmospheric temperatures

Spectral absorption cross-sections, k_ν (), have been measured in the 8.0 and bands of C₂F₆. Temperature and total (N₂-broadening) pressure have been varied to represent the conditions specified in various models of the terrestrial atmosphere so that the absorption cross-sections can be applied directly to the optical remote-sensing of C₂F₆ in the atmosphere. The measured absolute intensities of the 8.0 and the bands are (1.636±0.003)×10⁻¹⁶ and (, respectively.     

Measurement ofL-shell photoelectric cross-sections in lower intermediateZ elements at 6 keV

L-shell photoelectric cross-sections have been measured at 6 keV for eight elements in the range 40⩽Z⩽53. The measurements agree with theoretical calculations.     

Absorption of external thermal radiation in asymmetrically illuminated droplets

A theoretical model of thermal radiation absorption in semi-transparent droplets at the surface and inside a fuel spray is presented. Asymmetry of droplet illumination is taken into account. Results of Mie calculations of thermal radiation absorption inside large spherical droplets illuminated from a hemisphere are presented. Simple approximations for the angular and radial dependencies of the absorbed radiation power are suggested. These approximations are generalisations of the approximations suggested earlier by the authors for the case of symmetric illumination of droplets. They predict the results close to those which follow from the Mie calculations. Results of approximate calculations for a typical diesel fuel droplet at the periphery of the spray are presented. As in the case of symmetrical droplet illumination, an increased absorption of thermal radiation in the central area of the droplet is predicted. Also, at the illuminated side of the droplet, the absorption of radiation in a thin layer near the surface of the droplet is predicted, as in the case of symmetrical droplet illumination. Absorption of radiation in the central area of the droplet is related to the contribution of radiation in the spectral ranges of semi-transparency. The maximum of radiation absorption near the droplet surface is linked to the contribution of radiation in the vicinity of the diesel fuel absorption peak .     

Absorption cross-sections and lifetimes as a function of size in Si nanocrystals embedded in SiO2

The photoluminescence (PL) emission yield of Si nanocrystals embedded in SiO₂ depends on their size and on Si–SiO₂ interface passivation. In this work we aim at clarifying the relative importance of both contributions by studying lifetimes and absorption cross-sections as a function of size, for samples with and without passivation in forming gas. We find that while the PL lifetime increases steadily (quasi-linear dependence), the radiative lifetime increases exponentially with the nanocrystal size. Thus, as expected, radiative oscillator strengths are much smaller for large nanocrystals, but this reduction is partially compensated by a less effective quenching at interfacial non-radiative states. The absorption cross-section per nanocrystal rises as the nanocrystal size decreases, for all excitation wavelengths, implying that the variation of oscillator strength dominates over the reduction of the density of states. Passivation processes do not affect the emission mechanism and increase the emission yield while reducing the density of non-radiative recombination centers at the Si–SiO₂ interface (P_b centers).     

Measurement of photoabsorption and fluorescence cross-sections for CS2 at 188.2–213 and 287.5–339.5 nm

The photoabsorption and fluorescence cross-sections for carbon disulphide have been measured in the 188.2–213 and 287.5–339.5 nm spectral regions using an argon mini-arc light source. The absorption cross-sections have been measured with an accuracy of ±4.2% whereas the most probable error estimated in the case of fluorescence cross-sections is ±5.1%. The fluorescence quantum yields for CS₂ have also been obtained in the two spectral regions.     

Generation of L sub-shell photo-ionization cross-sections for elements 18?Z?92 at energies .320-115.606 keV (A computer program ‘LSPICS’)

L sub-shell photo-ionization cross-sections, σ_Li, for elements 18?Z?92 at energies .320-115.606 keV have been generated from an empirical relation fitted to Scofield's L sub-shell photo-ionization cross-section values. The excitation energy E for an element is constrained by the condition that only L and higher shell vacancies are produced in the elements. The closeness of generated and existing values of Scofield's L sub-shell data recommends the use of generated values in the fields of atomic and molecular physics and for trace elemental analysis. For this purpose computer software ‘LSPICS’ has been developed. On personal computer LSPICS generates L sub-shell photo-ionization cross-section values in barns just by entering the atomic number of element and excitation photon energy in keV.     

近红外光谱范围人肝癌变和热凝固导致组织吸收和散射特性的变化

研究了人肝的癌变及热凝固导致其对710,730,750,770,790,810,830,850,870和890 nm的钛宝石激光的吸收和散射特性的变化,实验采用双积分球测量系统以及反向倍增法获取肝组织的吸收和散射特性参数.结果表明:人肝的癌变导致其吸收系数发生了显著的减小,其变化的最大值在850 nm,其值为86.12%,而变化的最小值在750 nm,其值为82.65%.正常人肝组织热凝固导致其吸收系数明显变化,其吸收系数的变化的最大值在710 nm,其值为79.55%,而变化的最小值在790 nm,其值为0.72%.人肝癌组织热凝固导致其吸收系数显著地增大,其变化的最大值在810 nm,其值为78.69%,而变化的最小值在710nm,其值为38.16%.人肝的癌变导致了肝组织的散射系数发生了显著的增大,其变化的最大值在710 nm,其值为158.37%,而变化的最小值在890 nm,其值为136.03%.正常人肝组织热凝固导致其散射系数显著地增大,其变化的最大值在890 nm,其值为632.92%,而变化的最小值在710 nm,其值为587.40%.人肝癌组织热凝固导致其散射系数显著地增大,其变化的最大值在810 nm,其值为384.25%,而变化的最小值在710 nm,其值为330.86%.肝组织的吸收和散射特性的变化也随着激光波长的变化而变化.     

中红外吸收光谱的气相过氧化氢浓度测量

气相过氧化氢为强氧化剂,其消毒、灭菌的最终产物为水和氧气,具有无残留、安全、快速消毒以及广泛的材料兼容性等优点.广泛应用于制药、医疗、卫生、生物安全等领域,特别是新冠肺炎、M ERS、S A RS以及甲流等呼吸类传染性疾病的消毒防治.为保证灭菌效果,防止无菌检查的假阴性或者假阳性,需要对过氧化氢的浓度进行监测.基于12...     

Evidence for a proton halo in 27P through measurements of reaction cross-sections at intermediate energies

Measurements of reaction cross-sections ( σ_R's) for some proton-rich nuclei ( N = 11–15 isotones) on carbon target at intermediate energies have been performed on RIBLL of HIRFL. A larger enhancement of the σ_R for ²⁷P has been observed than for its neighboring nuclei. A large difference between the proton and neutron density distributions (proton halo) is necessary to explain the enhanced cross-section for ²⁷P within the framework of the Glauber model. Density distributions with HO-type core plus Yukawa-square tail and rms radii for ²⁷P have been deduced from the measured σ_R data for the first time, which conform the long tail in its densities as predicted by RMF calculations. Received: 23 May 2001 / Accepted: 7 November 2001     

IR signature estimation of an object or a target by taking into account atmospheric effects

In this study, a reference infrared (IR) image of an object or a target was analyzed, and the IR signature was calculated. Background and atmospheric effects were decomposed so that the calculation errors were minimized. Depending on the reference IR image, the IR signature at any distance and any angle was estimated while considering atmospheric effects. Calculated results were obtained from IR images taken from the same distance and angle, and were compared with the estimated results. The comparison of the measured and calculated signatures demonstrated the accuracy of the proposed method of estimation.     

Absorption of sound at a surface exposed to flow and temperature gradients

In noise abatement using porous or fibrous materials, accurate determination of the surface impedance representing the absorber is decisive for simulation quality. The presence of grazing flow and non-homogeneous ambient temperature influence the reaction of the absorber and may suitably be included in a modified “effective” surface impedance. In this paper, this approach is applied to a generic case representative for the engine bay of a heavy truck, where porous shields suppress the radiated noise, e.g. during a pass-by noise test. The change in the absorption is determined numerically by solving the wave propagation through a layer of varying temperature and flow adjacent to the impedance surface for different angles of incidence. The study shows significant impact of both flow and temperature, especially for materials with low absorption. The diffuse field absorption coefficient is also derived and although the effect is less pronounced in this case, it is still important in lower frequencies and in the frequency range typical for IC engine noise. The proposed numerical method is shown to be accurate and efficient for determination of the effective impedance and moreover not limited to thin boundary layers.     

高温环境下NO气体紫外吸收截面的温变特性研究

为了研究NO气体在不同烟气排放温度下的紫外吸收特性变化规律,测量了温度在285～410 K范围内NO气体200～230 nm紫外吸收截面随温度变化规律。采用分辨率为0.2 nm三光栅单色仪、氘灯光源和特制闭式气样室。将NO气体吸收截面分解为离散吸收和连续吸收两部分。结果表明,离散吸收具有等波长间隔分布特征,间隔约为10.5 nm。随温度升高,离散吸收峰值呈现出先抑后扬的非单调变化趋势,最大相对变化率约为19.3%,峰值位置并未出现波长红移或蓝移,谱线半宽也未出现明显的变化;连续吸收截面整体上随温度升高单调增大,且这种增强趋势随波长红移逐渐减弱。利用吸收法在线测量NO浓度时不应假定NO气体吸收截面为常数,应根据对烟气温度对NO吸收截面进行实时补偿计算,能够有效提高NO气体浓度在线测量的精度。     

热凝固致良性前列腺增生组织在590～1 064 nm的吸收和散射特性的变化

研究了自然的和热凝固的良性前列腺增生(BPH)组织在590～1 064 nm光谱范围的光学特性及其差异,实验采用带积分球附件的分光光度计以及反向倍增法获取组织样品的吸收和散射特性参数。结果表明：热凝固导致BPH组织在590～1 064 nm光谱范围的吸收系数明显地减小的,自然的和热凝固的BPH组织的吸收系数都有一个峰值在990 nm处,其值分别为0.438和0.416 mm-1,自然的和热凝固的BPH组织的吸收系数的最大差异在1 064 nm,其值为86.79%,其最小差异在920 nm,其值为4.74%。热凝固导致BPH组织在600～1 064 nm光谱范围的约化散射系数明显地增大,而在590 nm处,热凝固导致BPH组织的约化散射系数却是明显地减小,自然的和热凝固的BPH组织的约化散射系数都有一个峰值在970 nm处,其值分别为1.090和1.449 mm-1,其另一个峰值都在1 050 nm处,其值分别为1.116和1.627 mm-1,自然的和热凝固的BPH组织的约化散射系数的最大差异在1 060 nm,其值为47.73%,其最小差异在600 nm,其值为4.86%。     

Absorption Spectra of Benzene Cation Radical,Chlorobenzene Cation Radical,and Fluorobenzene Cation Radical in Perfluorocarbon Polymer Film at 77K

Absorption spectra of benzene cation radical, chlorobenzene cation radical, and fluorobenzene cation radical have been obtained in perfluorocarbon polymer at 77 K. Cation radicals are formed in good yields and less perturbed electronic absorption spectra are obtained. Results demonstrate that perfluorocarbon polymer is suitable as matrix for spectroscopic investigation of the cation radicals formed by γ-irradiation.     

Solid and Liquid AgI at High Pressure and High Temperature: A X-ray Absorption Spectroscopy Study

We report about recent X-ray absorption spectroscopy (XAS) measurements on solid and liquid AgI under high pressure. The structural behaviour of AgI has been investigated to pressures P～4.3 GPa at room temperature and to P～1.8 GPa at 1100 K. The high temperature/high pressure conditions have been obtained by means of a large-volume press of the Paris-Edinburgh type, coupled with a 10 mm boron/epoxy biconical gasket. The absorption spectra have been collected in transmission mode, both at the K-edge of Ag and I, and the samples have been characterized in situ by energy scanning X-ray diffraction at fixed angles. Our XAS results for solid AgI are compatible with previous X-ray diffraction measurements. For liquid AgI, we observe a slight change in the intensity and a shift in the frequency of the XAS oscillations with respect to what obtained in the case of the ambient pressure liquid.     

Design and Performances of a Carbon Monoxide Sensor Using Mid-Infrared Absorption Spectroscopy Technique at 4.6 µm

Based on infrared absorption spectroscopy technique, a carbon monoxide sensor was developed using the fundamental absorption band of carbon monoxide molecule at the wavelength around 4.6 µm. The developed sensor consists of pulse-modulated wideband incandescence, open ellipsoid light-collector gas-cell, dual-channel detector, and control and signal-processing module. With the prepared standard carbon monoxide gas sample, sensing characteristics on carbon monoxide were investigated using the sensor. Experimental results reveal that the limit of detection is about 10 ppm, the relative error at the limit of detection point is less than 14%, and that is less than 7.8% within the low concentration range of 20～180 ppm. The maximum absolute errors of 50 min long-term measurement on the 0 and 14 ppm CO gas samples are about 3 and 3.17 ppm, respectively, and the standard deviations are as small as 0.18 and 1.25 ppm, respectively. Compared with the reported carbon monoxide detection systems utilizing quantum cascaded lasers and distributed feedback lasers, the proposed sensor shows potential applications in carbon monoxide detection under the circumstances of coal-mine and environmental protection, by virtue of high performance, low cost, simple optical structure, and so on.     

中国遥感卫星辐射校正场陆表热红外发射率光谱野外测量

中国遥感卫星辐射校正场陆表发射率光谱是利用陆表场地进行遥感器红外通道绝对辐射定标的关键因子之一。基于光谱平滑的温度与发射率分离反演迭代算法,利用高精度的BOMEM MR154傅里叶变换红外光谱仪和红外标准板,对敦煌戈壁陆表发射率光谱进行测量。获得了不同时间和地点测量的陆表发射率光谱数据,并与利用CE312通道式红外辐射计在相同区域的测量结果进行比较分析。结果表明各个通道发射率的差别均在0.012以内,具有较好的一致性。利用该发射率光谱测量结果,可以在敦煌戈壁——中国遥感卫星辐射校正陆面场,对目前国内外主流的遥感卫星热红外通道进行在轨场地绝对辐射定标。     

Unsteady deflagration speed of an auto-ignitive dimethyl-ether (DME)/air mixture at stratified conditions

The propagation speed of an auto-ignitive dimethyl-ether (DME)/air mixture at elevated pressures and subjected to monochromatic temperature oscillations is numerically evaluated in a one-dimensional statistically stationary configuration using fully resolved numerical simulations with reduced kinetics and transport. Two sets of conditions with temperatures within and slightly above the negative temperature coefficient (NTC) regime are simulated to investigate the fundamental aspects of auto-ignition and flame propagation along with the transition from auto-ignitive deflagration to spontaneous propagation regimes under thermal stratification. Contrary to the standard laminar flame speed, the steady propagation speed of an auto-ignitive front is observed to scale proportionally to its level of upstream reactivity. It is shown that this interdependence is primarily influenced by the characteristic residence time and the homogeneous auto-ignition delay. Furthermore, the unsteady reaction front in either of the two cases responds distinctly to the imposed stratification. Specifically, the results in both cases show that the dynamic flame response depends on the mean temperature at the flame base T_b and the time-scale of thermal stratification. It is also found that, based on T_b and the propensity of the mixture to two-stage chemistry, the instantaneous peak propagation speed and the overall time taken to achieve that speed differs considerably. A displacement speed analysis is carried out to elucidate the underlying combustion modes that are responsible for such a variation in flame response.     

Twinning structure of M23C6 carbide precipitated at twin-related grain boundaries in Alloy 600

The microstructure features of carbides precipitated at twin boundary and Σ9 grain boundary (GB) in nickel-based Alloy 600 after aging at 715?°C for different time were investigated by high-resolution transmission electron microscopy. The carbides precipitated at incoherent twin boundary and Σ9 GB were identified as M₂₃C₆. The bar-like carbides grow parallel to each other and into each side of grain nearby incoherent twin boundary, while only growth into one side nearby Σ9 GB is observed. The carbides precipitated at incoherent twin and Σ9 GBs contain twins. The carbides have (1?1?1) _matrix // (1?1?1) _M23C6 orientation relationship with the nearby matrix. Based on the experimental results, the formation of twinning microstructure features in the M₂₃C₆ is discussed.