混凝土箱梁相似模型结构噪声对比分析*

为探讨混凝土箱梁噪声的时变特性,以京沪高铁32 m混凝土简支箱梁为原型,制作了1:10的缩尺模型,通过模态试验的方法验证箱梁模型与原型的相似关系,通过声学试验验证箱梁声学计算模型的正确性。然后,建立了箱梁缩尺模型与原型两种计算模型,利用有限元和边界元法求出两种模型的瞬态结构噪声。研究发现,箱梁缩尺模型与箱梁原型的材料参数满足一定关系,模型试验的方法能够验证箱梁模型与箱梁原型之间符合相似关系,箱梁模型的振动噪声测试结果能真实反映原型振动噪声水平。两种模型的结构噪声在时域内声压级及对应场点的声压存在一定相似关系。该研究可为箱梁缩尺模型结构噪声反演至箱梁原型提供依据,所采用的方法和得到的结果对桥梁结构振动与声辐射实验研究具有参考作用。     

选区激光烧结瞬态温度场模拟与测试方法研究

采用有限元方法,考虑实际的边界条件和热物性参量的变化,对Al2O3覆膜陶瓷粉末的选区激光烧结过程瞬态三维温度场进行动态模拟.通过比色测温法对红外热成像系统的发射系数进行修正后,对选区激光烧结过程瞬态温度场进行测试.数值模拟和实测结果显示,两者吻合较好.     

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利用通用有限元程序ANSYS对中国氦冷固态氚增殖剂实验包层模块(CH HCSB TBM)第一壁进行了稳态热分析。结果表明,第一壁铍保护板和RAFM钢的最高温度符合热工安全设计要求。对第一壁表面热流密度随时间变化的瞬态情况进行了分析,给出了随时间变化的结果。对第一壁两种典型的事故情形开展了初步分析,并对分析结果和事故影响进行了相应讨论。     

Time-resolved optical spectroscopy of CsI(Tl) crystals by pulsed electron beam irradiation

Properties of the color and emission centers induced with an electron pulse beam at temperature within 80-300 K have been studied in CsI(Tl) crystals. It has been established by optical spectrometry with time resolution that initial color centers in this crystal are only Tl⁰ and V_k centers, which spontaneously recombine emitting visible light at 2.25 and 2.55 eV. It has been shown that the emission decay kinetics at 80 K include two fast exponential components with decay constants 3 and 14 μs as well as slow hyperbolic component with the power index depending on the wavelength of the emitting light. The temperature effect on the emission kinetics has been studied and it has been directly proved that the emission rise stage at the temperature above 170 K is caused by the recombination of electrons, which are thermally released from single Tl⁰ centers, with V_kA centers. The origin of scintillations in CsI(Tl) crystal is discussed in terms of the tunnel electron transitions from ground state of Tl⁰ centers to ground state of V_k centers at different distances from each other.     

Photo-degradation of imidazolium ionic liquids

Degradation of imidazolium ionic liquid, [bmim⁺][TFSA⁻] and iodide solution of [bmim⁺][TFSA⁻] by UV-laser irradiation has been studied through ground-state absorption and transient absorption spectroscopy. We found that excited state [bmim⁺]* undergoes degradation efficiently.     

Transient absorption measurement system using pulsed energetic ion

This article reports a highly sensitive transient absorbance measurement system using pulsed energetic ions. The ions were pulsed by a beam chopper, which was synchronized with the cyclotron, and accelerated to the desired energy around 18 MeV/u. H, He, C and Ne ions can be used for the transient absorption measurement. The optical system can measure an absorbance smaller than 1.0×10⁻⁴ in the wavelength range of 400–740 nm.     

High-sensitive analysis of DNA fragments by capillary gel electrophoresis using transient isotachophoresis preconcentration and fluorescence detection

In this report aimed on further development of a high-sensitivity capillary gel electrophoresis (CGE) method for analysis of DNA fragments, we firstly explored online transient isotachophoresis (tITP) preconcentration combined with fluorescence detection (FD). The fluorescence signal (excitation: 488 nm; emission: 590 nm) was generated using the intercalating dye of ethidium bromide (EB). It was found when the leading electrolyte (LE) was injected behind the sample zone, such a special tITP mode has significant advantages to solve the bubble formation issue and to improve the analytical performance stability. Two standard DNA samples, a 50 bp DNA step ladder and the φX174/HaeIII digest, were used to evaluate the qualitative and quantitative abilities of the tITP-FD approach. A highly diluted sample (10,000-fold in the water, e.g. the φX174/HaeIII digest diluted from 500 μg/ml to the 50 ng/ml level) was enriched and detected; the LOD was down to 0.09 ng/ml for the 72 bp fragment, apparently improved more than 1000-fold in comparison with UV detection. Although the RSD of peak areas (n = 3) was around 15.5% for the sample was electrokinetically injected, good linearity of peak area response showed that the proposed method is suitable for quantitative analysis.     

Sensor array data profiling for gas identification

The paper presents a new method of qualitative identification of gas. It is based on a dynamic response of sensor array with the emphasis on the processing of discrete measurement data. The information needed for identification of test samples is obtained in course of profiling the data from calibration measurements. This operation consists of the following steps: classification of data sets, selection of representative data sets, parameterization of classifiers associated with representative data sets and determination of data records. In our work Discriminant Function Analysis was used for data classification. The information saved in data record describes: the sequential number of discrete measurement, combination of gas sensors in this measurement which are best for classification of calibration samples, and the parameters of associated classifier. They are identifiers of gas class. The procedure of data record determination itself is time consuming. However this operation will be performed only at the stage of the development of the measurement instrument and when its malfunction is diagnosed. The routine use of the instrument will be restricted to gas identification task, which only utilizes the results of profiling.The identification of unknown gas is performed on the base of data records and measurement data obtained for this gas. Data records guide the preparation of data sets, separately for each class of gases. These data sets are used as input of the discriminant functions which have parameter values also indicated by data records. It was shown in the present contribution, that the qualitative identification of nine test gas samples (vapors of ethanol, acetic acid and ethyl acetate in air) with our method was very accurate and fast.     

Transient Nearest Neighbor Random Walk on the Line

We prove strong theorems for the local time at infinity of a nearest neighbor transient random walk. First, laws of the iterated logarithm are given for the large values of the local time. Then we investigate the length of intervals over which the walk runs through (always from left to right) without ever returning.