Observational manifestations of prerecombination protoobjects     

V. K. Dubrovich 《Astronomy Letters》2003,29(1):6-9

We consider the image formation for an extremely distant source in an optically dense, homogeneous, and isotropic medium. We show that the angular size of the image would presently be θ₀ ≈ 10′, irrespective of the initial redshift z. Parameters of the inhomogeneities capable of producing the observed effect were estimated. We note that this effect should be taken into account for the baryon density fluctuations that were damped according to Silk at the prerecombination epoch. The spot radiation spectrum is shown to be a diluted Planckian spectrum with a dilution factor much larger than unity. We also point out the presence of peculiar tangential polarization in the spot, which reaches several tens of percent at the spot edge. All these observational features clearly distinguish the fluctuations under consideration from the standard fluctuations.  相似文献   

A difference method of searching for spectral-spatial fluctuations of the cosmic microwave background radiation     

V. K. Dubrovich  A. T. Bajkova 《Astronomy Letters》2003,29(9):567-572

We consider methods of searching for the spectral-spatial fluctuations of the cosmic microwave background radiation that were formed in the early Universe. Based on the narrow-band spatial-frequency properties of these fluctuations, we suggest a difference method of their search. We describe the method and present our simulation results. This technique is shown to have a significant advantage over the existing methods. We give recommendations to optimize the observing and reduction procedures.  相似文献   

氢氧化物族矿物的氧同位素分馏   总被引：2，自引：0，他引：2  

郑永飞  徐宝龙 《地球化学》1998,27(2):141-152

应用增量方法计算了氢氧化物族矿物的氧同位素分馏,得到常见氢氧化物的18O富集顺序为：褐铁矿＞三水铝石＞针铁矿＞水镁石＞硬水铝石。氢氧化物与其对应的氧化物相比显著地富集18O。三价阳离子的氢氧化物和氧化物的18O富集顺序为：M（OH）3＞MO（OH）＞M2O3。Al（OH）3同质多象变体之间也存在一定的分馏。对于石英-氢氧化物、方解石-氢氧化物和氢氧化物-水体系,本文计算提供了在0-1200℃温度范围内三组内部一致的分馏系数方程。这些理论校准与合成实验结果和／或地表温度下的天然样品相吻合,特别针铁矿、勃姆石和硬水铝石与水之间的氧同位素分馏关系能够满足地质测温的要求。因此,对氢氧化物-水体系的氧同位素分析可望提供表生环境下可靠的地质温度计。  相似文献   

Three-dimensional geometrical ray theory and modelling of transmitted seismic energy of data from the Nevada Test Site     

How-Wei Chen 《Geophysical Journal International》1998,133(2):363-378

This paper presents a geometrically based algorithm for computing synthetic seismograms for energy transmitted through a 3-D velocity distribution. 3-D ray tracing is performed to compute the traveltimes and geometrical spreading (amplitude). The formulations of both kinematic and dynamic ray-tracing systems are presented. The two-point ray-tracing problem is solved by systematically updating the initial conditions and adjusting the ray direction until the ray intersects the specified endpoint. The amount of adjustment required depends on the derivatives of the position with respect to the given starting angles between consecutive rays. The algorithm uses derivatives to define the steepest-descent direction and to update the initial directions. The convergence rate depends on the complexity of the model.
Test seismograms compare favourably with those from a 2-D asymptotic ray theory algorithm and a 3-D Gaussian-beam algorithm. The algorithm is flexible in modelling arbitrary source and recorder geometries for various smoothly varying 3-D velocity distributions. The algorithm is further tested by simulating surface-to-tunnel vibroseis field data. Shear waves as well as compressional waves may be approximately included. Application of the algorithm to a data set from the Rainier Mesa of the Nevada Test Site produced a good fit to the transmitted (first arrival) traveltimes and amplitudes, with approximately 15 per cent variation in the local 3-D velocity.  相似文献   

Optimally accurate second-order time-domain finite difference scheme for the elastic equation of motion: one-dimensional case     

Robert J. Geller  & Nozomu Takeuchi 《Geophysical Journal International》1998,135(1):48-62

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Polarization anomaly of Love waves caused by lateral heterogeneity   总被引：1，自引：0，他引：1  

Reiji Kobayashi 《Geophysical Journal International》1998,135(3):893-897

We calculate surface waves propagating in a laterally heterogeneous structure beneath the Kuril trench, where significant Love-wave polarization anomalies, called quasi-Love waves, are generated. Since 3-D wave propagation in the two-dimensionally heterogeneous structure can be assumed, we apply the 2.5-D finite difference method to the surface-wave calculations. The calculations show that a velocity contrast of 7 per cent at depths of less than 210 km beneath the Kuril trench cannot generate quasi-Love waves, and that an unlikely contrast of 20 per cent is required to generate clear quasi-Love waves. The possible cause of the quasi-Love waves inferred from previous studies on coupled free oscillations is a lateral variation in azimuthal anisotropy. The lateral variation in azimuthal anisotropy beneath the Kuril trench suggests a change in the mantle flow induced by the subducting slab.  相似文献   

Site amplifications in the city of Benevento (Italy): comparison of observed and estimated ground motion from explosive sources     

F. Marrara  P. Suhadolc 《Journal of Seismology》1998,2(2):125-143

A hybrid approach is applied to construct 2-D synthetic seismograms for explosive sources. The computation of the signals has been performed with a hybrid technique, that couples the modal summation method, describing the P-SV propagation from the source to a target area, to the finite difference method, allowing the computation of the 2-D response of the target area. We use this technique to study the site response in the city of Benevento (Southern Italy). The results are compared both with those obtained for the same model, but considering an extended double-couple source and SH wave propagation and with those derived from a direct analysis of experimental data obtained during the Benevento Seismic Risk Project, funded by the Commission of European Communities. The type and depth of the source and the source-receiver distance can provide different excitations, but the response of the target area, in terms of ratios of response spectra, remains in general stable in the high frequency range (>2 Hz). The explosive source does not excite lower frequencies and is therefore unable to provide estimates of site effects in this frequency range. We also show that it is important to consider both P-SV and SH waves when assessing site effects. Finally, a very good definition of a structural model from geological data is fundamental in order to explain the observed data in the time domain. The observed data validate our synthetic modelling for evaluating the site effects and for a tentative seismic microzonation of the city of Benevento.  相似文献   

A method of searching for radial velocity anomalies in the lower mantle using interfering signals     

C. Wright  J. A. Lyons 《Pure and Applied Geophysics》1980,119(1):118-136

Radial velocity anomalies in the lower mantle that give rise to triplications in the travel-time curve for short-periodP waves will produce arrivals havingdT/d values that differe by roughly 0.2–0.5 s/deg. The first two arrivals associated with such triplications will be separated by less than one second over a distance range of 4°–10° they may not, therefore, be separable visually on single seismograms, so that their presence can only be inferred from some measurable property that depends on their mutual interference. If there are lateral variations in the regions of anomalous velocity gradients, the interfering signals will also have different azimuths of arrival. Using two synthetic wavelets we have investigated the effect of interference on bothdT/d and azimuth measurements at the Yellowknife Array. We found that if the interfering pulses have a dominant frequencyv, there is a range of time separations (0.30/v0.55/v) over which the measureddT/d and azimuth values may fluctuate by much more than the differences indT/d and azimuth between the interfering signals. We have evaluated the following empirically defined functions for three different primary signals, and for three different relative amplitudes of the interfering signals:f (t), the drift function, which expresses how the measured slownesses,p, and azimuths, , differ from the slownesses and azimuths of the primary wavelets; f(), the range function, which describes the behaviour of the upper and lower bounds ofp and as a function of the difference in arrival times of the signals, andf , studied the properties of these functions, and have outlined how these properties provide criteria based on the numerical and statistical characteristics of the arrival vectors, and on the waveform of the signal that will enable small radial velocity anomalies to be more clearly delineated.Contribution No. 863 from the Earth Physics Branch.  相似文献   

围海造陆工程泄水口悬浮物扩散规律分析   总被引：1，自引：1，他引：0  

陈杰  蒋昌波  张绍华  胡保安 《海洋科学》2015,39(8):58-62

掌握围海造陆工程泄水口悬浮物扩散规律,对保护海洋水环境质量具有重要意义。选取围海造陆工程泄水口为研究对象,基于泥沙对流扩散方程,推求出泄水口悬浮物扩散平面二维分析解表达式。开展现场观测,确定泄水口源强取值,并对泄水口悬浮物扩散进行理论计算和分析。研究结果显示,围海造陆工程施工后期,泄水口悬浮物流失非常严重。泄水口附近水域出现的最大悬浮物浓度主要由源强的大小来决定,悬浮物扩散范围主要由流速的大小来控制。  相似文献   

加标回收在水质分析中的应用及回收率计算方法   总被引：3，自引：1，他引：2  

李义  禹海清  董建芳  梁志宏 《岩矿测试》2010,29(5):597-600

阐述了水质分析中加标回收分析的方法步骤、条件控制及计算方法。当加标体积影响试样在加标水样中的浓度时,直接使用回收率理论计算公式的计算值,均较其真实的回收率偏低,且其偏低值随加标体积的增加而增大。根据加标回收分析的定义,分别以加标前后被测组分质量浓度(mg/L)的变化或含量(μg)的变化为依据,导出两个计算加标回收率的实用公式。采用该公式,加标体积可以不受严格控制,其计算结果与真实的回收率一致,适用于日常水质分析工作。  相似文献