深海热液区主要成分的高温高压拉曼光谱分析

模拟深海热液口环境(最高压力40 MPa,最高温度350℃),对深海热液区的主要成分CO2、CH4及其混合物的水溶液在不同压力和温度条件下的拉曼光谱进行探测和分析,结果显示:常温低压下CO2水溶液的Fermi双峰分别位于1 384.9 cm-1和1 278.3 cm-1处,CH4的水溶液拉曼峰υ1位于2 912.1 cm-1处,均比其气相的拉曼频移小;常温下CO2和CH4水溶液的拉曼特征峰随压力(≤40 MPa)的变化均不明显;在40 MPa的压力下随着温度的升高(≤350℃),CO2水溶液的Fermi双峰分别向高波数区移动了约3.4 cm-1和7.0 cm-1,而CH4水溶液的拉曼峰υ1向低波数区移动了约3.1cm-1;混合后升温过程中CO2的双峰分别向高波数区移动了约4.3 cm-1和3.8 cm-1,CH4的特征峰υ1向低波数区移动了4.5 cm-1。说明在室温到350℃范围内温度的变化对CO2和CH4水溶液拉曼频移有影响,频移量与温度线性相关,而压力在≤40 MPa范围内的改变对拉曼频移影响不明显。     

实验研究不同盐离子对水分子拉曼效应的影响

对流体包裹体中常见的几种盐水溶液进行了拉曼光谱分析.采用了频移参数描述水分子拉曼峰的形变强度,并讨论了频移参数与盐度之间的关系.实验分析结果表明,盐度越大,频移参数越大,水分子拉曼峰形变越大.对频移参数曲线斜率分析显示,盐类对水分子拉曼峰偏移程度影响的强弱顺序为NaCl＞Na2SO4＞NaHCO3＞Na2CO3.讨论了不同阳离子和阴离子对水伸缩振动拉曼峰的影响,结果表明,高价阳离子的影响明显高于低价阳离子;而阴离子对水拉曼峰影响的强弱顺序初步确定为Cl-≈SO2-4-＞HCO-3＞CO2-3≈NO-3.     

Analysis of COMPTEL gamma-ray burst locations and spectra

In its first three years of operation, the COMPTEL instrument on theCompton Gamma-Ray Observatory has measured the locations (mean accuracy 1°) and spectra (0.75-30 MeV) of 18 gamma-ray bursts and continues to observe new events at a rate of 1/month. With good angular resolution and sensitivity at MeV energies, the growing COMPTEL burst catalog is an important new piece of evidence in the on-going GRB mystery. The COMPTEL burst locations are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts indicates the possibility of repetition. The COMPTEL burst spectra are in most cases consistent with a single power law model with spectral index in the range 2–3. However, two bursts show evidence of a spectral break in the MeV range. Measurement of rapid variability at MeV energies in the stronger bursts provides evidence that either the sources are nearby (within the Galaxy) or the gamma-ray emission is relativistically beamed. We present an overview of analysis results obtained from the COMPTEL burst catalog concentrating on the search for burst repetition and the implications of highly variable MeV emission.     

小振幅海洋内波的演变、破碎和所致混合

利用基于谱方法和MPI并行运算的数值模式SpectralModel,直接数值模拟了三维小振幅海洋内波的演变、破碎和所致湍流混合,指出导致其不稳定而破碎的为PSI(parametric subharmonic instability)机制;对于内波破碎所致的湍流混合过程,分析了跨等密度面扩散系数kρ、混合效率γ、浮力通量谱、动能谱以及势能谱等统计性质:内波破碎前,kρ和γ保持低值水平,浮力通量谱值为负,且集中在低波数段;内波破碎后,kρ和γ迅速增大,最大值分别约为0.9×103m2/s和0.18,浮力通量谱值在低波数段为负值,在高波数段为正值,这是因为层化湍流中势能向小尺度运动传递和动能向小尺度运动传递相比更为有效。在内波破碎、强湍流混合阶段,势能谱存在一谱段满足kz3律,P(kz)=0.2N2kz3。此外,与二维模拟结果相比较,导致内波不稳定而破碎的均为PSI机制,kρ、浮力通量谱、势能谱变化趋势大体一致;但三维数值实验中,内波破碎时间提前,湍流衰减加快;KE谱在高波数部分下降速度相对减小,更接近于kz3。     

On the correction of spectra by a displacement reduction factor in direct displacement-based seismic design and assessment

The application of some design and assessment approaches, such as the direct displacement-based design (DDBD) and the capacity spectrum methods, requires the modification of elastic design spectra by some displacement reduction factor, to account for the appropriate energy dissipation capacity of different structures. While several equations to correlate dissipation and hysteresis cycles are available, once the displacement reduction factor has been obtained, the correction of the spectra is operated reducing the displacement demand accordingly and conserving the period of vibration at each point. This procedure is here discussed and proved to be conceptually inappropriate, because the spectral acceleration rather than the period should be kept at each point. The application of this alternative procedure may result in increased shear strength demand in design and in larger required displacement capacity for the same level of strength in assessment, if all other factors are not modified. However, the calibration of the reduction factors applied in DDBD has been extensive, and the method has proved to be effective in predicting displacement demands consistent with those resulting from refined nonlinear time history analysis; therefore, a possible introduction of the proposed correction will require equally extensive studies and possibly compensating corrections in the calculation of the equivalent damping. On the contrary, an appropriate calibration of the factors to be used in the application of the “capacity spectrum” method is still being developed, and the consideration of a constant acceleration may facilitate the derivation of effective equations.     

Recent progress on anomalous X-ray pulsars

I review recent observational progress on Anomalous X-ray Pulsars, with an emphasis on timing, variability, and spectra. Highlighted results include the recent timing and flux stabilization of the notoriously unstable AXP 1E 1048.1–5937, the remarkable glitches seen in two AXPs, and the newly recognized variety of AXP variability types, including outbursts, bursts, flares, and pulse profile changes. I also discuss recent discoveries regarding AXP spectra, including their surprising hard X-ray and far-infrared emission, as well as the pulsed radio emission seen in one source. Much has been learned about these enigmatic objects over the past few years, with the pace of discoveries remaining steady. However additional work on both observational and theoretical fronts is needed before we have a comprehensive understanding of AXPs and their place in the zoo of manifestations of young neutron stars.      

Conditional spectrum‐based ground motion selection. Part I: Hazard consistency for risk‐based assessments

The conditional spectrum (CS, with mean and variability) is a target response spectrum that links nonlinear dynamic analysis back to probabilistic seismic hazard analysis for ground motion selection. The CS is computed on the basis of a specified conditioning period, whereas structures under consideration may be sensitive to response spectral amplitudes at multiple periods of excitation. Questions remain regarding the appropriate choice of conditioning period when utilizing the CS as the target spectrum. This paper focuses on risk‐based assessments, which estimate the annual rate of exceeding a specified structural response amplitude. Seismic hazard analysis, ground motion selection, and nonlinear dynamic analysis are performed, using the conditional spectra with varying conditioning periods, to assess the performance of a 20‐story reinforced concrete frame structure. It is shown here that risk‐based assessments are relatively insensitive to the choice of conditioning period when the ground motions are carefully selected to ensure hazard consistency. This observed insensitivity to the conditioning period comes from the fact that, when CS‐based ground motion selection is used, the distributions of response spectra of the selected ground motions are consistent with the site ground motion hazard curves at all relevant periods; this consistency with the site hazard curves is independent of the conditioning period. The importance of an exact CS (which incorporates multiple causal earthquakes and ground motion prediction models) to achieve the appropriate spectral variability at periods away from the conditioning period is also highlighted. The findings of this paper are expected theoretically but have not been empirically demonstrated previously. Copyright © 2013 John Wiley & Sons, Ltd.     

Model for multiblock columns subjected to base excitation

A new model is presented for multiblock columns subjected to earthquakes, which contains an impact and an opening model. Both in the impact and in the opening model, all the possible opening configurations are investigated because it was found that in many practical cases, unexpected patterns may occur. The model is purely mechanical: assuming rigid blocks and classical (inelastic) impact. The effect of energy dissipation during impact was investigated. Using our model in accordance with the literature, it was found that monolithic blocks are more vulnerable to overturning than multiblock systems.     

Engineering source model for strong ground motion

A new engineering source model consistent with seismological concepts for simulating strong-motion accelerograms (SMAs) is presented in this paper. The source region is modeled as a horizontally layered elastic medium to cater for site dependency. The moment field acting on the rupture plane is decomposed into space and time functions, which is a novel concept. The spatial and temporal components are determined for six well-recorded earthquakes using the corresponding recorded SMA. The obtained spatial variations indicate that they can be modeled as an anisotropic random field. The temporal components of all the six events are transients, with typical frequency spectra. Based on these results, a simplified source model is proposed for the synthesis of SMA during strong earthquakes. The model is validated by simulating strong-motion acceleration time histories at stations deliberately kept out of the modeling exercise. It is found that the present model is efficient in simulating observed time histories. The proposed model is also illustrated by simulating an ensemble of acceleration time histories for the Kutch earthquake of 26th January 2001 using only the few known source parameters.