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21.
Z. Q. Qu C. L. Xu X. Y. Zhang X. L. Yan C. L. Jin 《Monthly notices of the Royal Astronomical Society》2006,370(4):1790-1796
The influence of magnetic fields on the energy level populations of atoms is firstly studied by analysing the Stokes profiles of Fe i 6302.5 forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line-source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase in the level population of the lower level of Fe i 6302.5 (Landé factor g = 2.5 ) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Landé factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Secondly, an experiment utilizing the Hg5461 line in the laboratory on the Earth is carried out to reveal that the exponential relation is independent of variations in temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution. 相似文献
22.
A theoretical model for wind‐sand flow is developed by considering the coupling between wind flow and sand particle motion, the latter subject to the Magnus effect, under different atmospheric stability conditions. Using this model, the characteristics of the wind‐sand flow are discussed in detail. The results show that the atmospheric stability and the Magnus effect both have a strong influence on wind profiles and on the trajectories of sand particles. This approach produces results with characteristics that differ from those previously reported; the latter only applying to atmospheric conditions of neutral stability. The saltating sand reaches a greater height under non‐neutral stability than under neutral stability, while the maximum horizontal distance is greater under unstable conditions and is smaller under stable conditions than under conditions of neutral stability. 相似文献
23.
Zi-Fu Zhao Yong-Fei Zheng Chun-Sheng Wei Fu-Kun Chen Xiaoming Liu Fu-Yuan Wu 《Chemical Geology》2008,253(3-4):222-242
The crustal structure of the Dabie orogen was reconstructed by a combined study of U–Pb ages, Hf and O isotope compositions of zircons from granitic gneiss from North Dabie, the largest lithotectonic unit in the orogen. The results were deciphered from metamorphic history to protolith origin with respect to continental subduction and exhumation. Zircon U–Pb dating provides consistent ages of 751 ± 7 Ma for protolith crystallization, and two group ages of 213 ± 4 to 245 ± 17 Ma and 126 ± 4 to 131 ± 36 Ma for regional metamorphism. Majority of zircon Hf isotope analyses displays negative εHf(t) values of − 5.1 to − 2.9 with crust Hf model ages of 1.84 to 1.99 Ga, indicating protolith origin from reworking of middle Paleoproterozoic crust. The remaining analyses exhibit positive εHf(t) values of 5.3 to 14.5 with mantle Hf model ages of 0.74 to 1.11 Ga, suggesting prompt reworking of Late Mesoproterozoic to Early Neoproterozoic juvenile crust. Zircon O isotope analyses yield δ18O values of − 3.26 to 2.79‰, indicating differential involvement of meteoric water in protolith magma by remelting of hydrothermally altered low δ18O rocks. North Dabie shares the same age of Neoproterozoic low δ18O protolith with Central Dabie experiencing the Triassic UHP metamorphism, but it was significantly reworked at Early Cretaceous in association with contemporaneous magma emplacement. The Rodinia breakup at about 750 Ma would lead to not only the reworking of juvenile crust in an active rift zone for bimodal protolith of Central Dabie, but also reworking of ancient crust in an arc-continent collision zone for the North Dabie protolith. The spatial difference in the metamorphic age (Triassic vs. Cretaceous) between the northern and southern parts of North Dabie suggests intra-crustal detachment during the continental subduction. Furthermore, the Dabie orogen would have a three-layer structure prior to the Early Cretaceous magmatism: Central Dabie in the upper, North Dabie in the middle, and the source region of Cretaceous magmas in the lower. 相似文献
24.
Influence of Structural Non-Stationarity of Surface Roughness on Morphological Characterization and Mechanical Deformation of Rock Joints 总被引:2,自引:2,他引:0
N. Fardin 《Rock Mechanics and Rock Engineering》2008,41(2):267-297
Summary Structural non-stationarity of surface roughness affects accurate morphological characterization as well as mechanical behaviour
of rock joints at the laboratory scale using samples with a size below the stationarity threshold. In this paper, the effect
of structural non-stationarity of surface roughness is investigated by studying the scale dependence of surface roughness
and mechanical behaviour of rock joints. The results show that the structural non-stationarity mainly affects the accurate
characterization of the surface roughness of the fracture samples. It also controls the amount and location of the contact
areas during shear tests, which in turn affects the mechanical properties and asperity degradation of the samples. It is concluded
that for accurate determination of the morphological and mechanical properties of rock joints at laboratory and field scales,
samples with size equal to or larger than the stationarity threshold are required.
Author’s address: Nader Fardin, Rock Mechanics Group, Department of Mining Engineering, Faculty of Engineering, University
of Tehran, P.O. Box: 11365/4563, Tehran, Iran 相似文献
25.
Nonlinear Analysis of Local Site Effects on Seismic Ground Response in the Bam Earthquake 总被引:1,自引:0,他引:1
M. H. T. Rayhani M. H. El Naggar S. H. Tabatabaei 《Geotechnical and Geological Engineering》2008,26(1):91-100
The influence of local geologic and soil conditions on the intensity of ground shaking is addressed in this study. The amplification
of the ground motion due to local site effects resulted in severe damage to dwellings in the Bam area during the 2003 Bam
Earthquake. A unique set of strong motion acceleration recordings was obtained at the Bam accelerograph station. Although
the highest peak ground acceleration recorded was the vertical component (nearly 1 g), the longitudinal component (fault-parallel
motion) clearly had the largest maximum velocity as well as maximum ground displacement. Subsurface geotechnical and geophysical
(down-hole) data in two different sites have been obtained and used to estimate the local site condition on earthquake ground
motion in the area. The ground response analyses have been conducted considering the nonlinear behavior of the soil deposits
using both equivalent linear and nonlinear approaches. The fully nonlinear method embodied in FLAC was used to evaluate the
nonlinear soil properties on earthquake wave propagation through the soil layer, and compare with the response from the equivalent
linear approach. It is shown that thick alluvium deposits amplified the ground motion and resulted in significant damage in
residential buildings in the earthquake stricken region. The comparison of results indicated similar response spectra of the
motions for both equivalent and nonlinear analyses, showing peaks in the period range of 0.3–1.5 s. However, the amplification
levels of nonlinear analysis were less than the equivalent linear method especially in long periods. The observed response
spectra are shown to be above the NEHRP building code design requirements, especially at high frequencies. 相似文献
26.
By using small scale model tests, the interference effect on the vertical load-deformation behavior of a number of equally
spaced strip footings, placed on the surface of dry sand, was investigated. At any stage, all the footings were assumed to
(i) carry exactly equal magnitude of load, and (ii) settle to the same extent. No tilt of the footing was permitted. The effect
of clear spacing (s) among footings on the results was explored. A new experimental setup was proposed in which only one footing
needs to be employed rather than a number of footings. The bearing capacity increases continuously with decrease in spacing
among the footings. The interference effect becomes further prominent with increase in soil friction angle. In contrast to
an increase in the bearing capacity, with decrease in spacing of footings, an increase in the footing settlement associated
with the ultimate state of shear failure was observed. The present experimental observations were similar to those predicted
by the available theory, based on the method of characteristics. As compared to the theory, the present experimental data,
however, indicates much greater effect of interference especially for larger spacing among footings. 相似文献
27.
Diel patterns in the chlorophyll a specific absorption coefficient of surface picoplankton, a*pico (γ) (m2·[mg chlorophyll a]−1), were studied at 7 stations under daily cycle of in situ light condition in the western subarctic Pacific and Japan Sea. All the data were normalized by dividing the anomaly with daily averaged a*pico (γ). Opposite diel patterns were observed for the normalized a*pico (443) and a*pico (675) with maximum toward dawn or dusk and minimum toward midday at 4 stations under low-irradiance (LI) conditions and vice versa at 3 stations under high-irradiance (HI) conditions. The absorption efficiency factors at red absorption peak, Q
a (675), were determined by reconstruction with intracellular chlorophyll a concentration and cell diameter. The normalized Q
a (675) also showed diel pattern with maximum toward midday and minimum toward dawn or dusk under LI. The diel pattern in a*pico (675) and Q
a (675) were primarily caused by changes in intracellular chlorophyll a concentration due to photoadaptation under LI. The diel pattern in a*pico (443) was influenced by pigmentation, as recognized by blue to red ratio [a*pico (443)/a*pico (675)] under HI. This study proposed that the opposite diel pattern in a*pico (γ) might occur for a wide range of algal species. The results presented here have important consequences for the interpretation of diel variations in optical properties observed in the open ocean. 相似文献
28.
Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay 总被引:2,自引:0,他引:2
Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for beth the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are beth the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure. 相似文献
29.
刘连吉 《中国海洋大学学报(自然科学版)》1997,(3)
指出ISD单片语言器件的独特之处,是采用直接模拟存储技术,语音信号以其原本的模拟形式直接存入模拟量存储器中并长远保存。省去了传统的A/D和D/A数模转换机制,能高保真的将语音内容再生。这是一种高新录/放技术。另外,给出的ISD基本录/放电路十分简单易用。可方便地为微机系统、测控仪表电器和广播等设备所采用,使设备具有高效功能 相似文献
30.
在室内水池中观察了黑鲷(Sparusmacrocephalus)和青石斑鱼(Epinephelusawoara)对孔径0.5mm、孔距5.0cm,空气压力0.25kg/cm2固定气泡幕的反应。结果表明,气泡幕对两种海水鱼都有显著的阻拦作用,平均阻拦率分别为黑鲷75.1%、青石斑鱼82.4%。分析显示,气泡幕对两种鱼的阻拦率间无显著差异。在本实验中,该两种鱼对气泡幕均无明显的适应现象 相似文献