Leonid meteor spectrum from 110 to 860 nm     

J.F Carbary  J.-H Yee 《Icarus》2003,161(2):223-234

During the Leonid meteor shower on 18 November 1999, the five spectrographic imagers onboard the Midcourse Space Experiment (MSX) satellite recorded the first complete meteor spectra from 110 to 860 nm. The observation occurred at 00:23:36.2 UT, at which time the satellite was pointed at a tangent altitude of 100 km over 37.2°N and 78.2°E. The spectrograph slits were oriented approximately parallel to the horizon at a tangent altitude of 100 km, and the meteor passed approximately perpendicular through the slits’ fields of view. All five spectrographic imagers observed the passage of a bright object (m_v < −2.8 at 100 km) and each recorded several frames of data. In the visible, common meteor emissions were observed from iron, sodium, and oxygen. However, the ultraviolet spectrum displayed a wealth of more intense features, some of which actually caused saturation in the spectrographs. The most intense features appeared between 220 and 300 nm and are attributed to neutral and singly ionized iron and ionized magnesium. Some unknown emissions, possibly from an unidentified molecular species such as iron oxide, appear between 180 and 220 nm. In the far ultraviolet from 110 to 130 nm, oxygen and nitrogen features appear in the spectrum, with some features from ionized iron and magnesium. In particular, the FUV spectrum showed an intense emission from hydrogen Lyman alpha and a much weaker emission from what appeared to be neutral carbon. The atmospheric emissions can be associated with the heating within the meteor shock, while the metallic emissions originate from the fireball of the meteor proper. The ultraviolet emissions were much stronger than those in the visible and near-infrared parts of the spectrum. The energy of emissions in the ultraviolet (110 < λ < 337 nm) exceeded the energy of the visible (337 < λ < 650 nm) by a factor of at least 5.  相似文献   

Extended model of shear modulus reduction for cohesive soils     

Wong  John Kok Hee  Wong  Soon Yee  Wong  Kim Yuen 《Acta Geotechnica》2022,17(6):2347-2363

Acta Geotechnica - The shear modulus of a soil, G, shows a hyperbolic degradation curve relationship with increasing shear strain, γ. G is usually normalized against the small-strain modulus...  相似文献   

State‐led talent return migration programme and the doubly neglected ‘Malaysian diaspora’: Whose diaspora,what citizenship,whose development?          下载免费PDF全文

Sin Yee Koh 《Singapore journal of tropical geography》2015,36(2):183-200

This paper questions the assumptions of ‘diaspora’, ‘citizenship’ and ‘development’ underlying diaspora strategies targeting a specific pool of overseas Malaysian ‘talent’ migrants. I examine the Malaysian state's discursive attempts to construct a carefully contained economic ‘diaspora'—the ‘Malaysian diaspora'—through its talent return migration programme. In this process, there is a portion of the ‘Malaysian diaspora’, especially non‐bumiputeras (sons of soil), who are doubly neglected and excluded: first, from access to full and equal citizenship (which arguably contributed to their emigration in the first place); and second, from eligibility and recognition to participate in Malaysia's talent return migration programme. However, recent political activism calling for electoral reform and overseas voting rights challenges state‐constructed visions of the ‘diaspora’ and their expected roles in advancing ‘development’. This paper concludes by highlighting questions raised by the Malaysian case, linking these explicitly to how diaspora strategies—as they have been conceived, practised and contested—challenge the broader Migration and Development paradigm.  相似文献   

Concerning dispersion relations for the magnetotelluric impedance tensor   总被引：1，自引：0，他引：1  

E. Yee  K. V. Paulson 《Geophysical Journal International》1988,95(3):549-559

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Energy transfer of O(¹S) atoms in collision with O(³P) atoms     

Jeng-Hwa Yee  A. Dalgarno 《Planetary and Space Science》1985,33(7):825-830

Elastic scattering and excitation transfer collision cross-sections in O(¹S)-O(³P) collisions are calculated. These cross-sections are needed in determining the degree of thermalization of the O(¹S) atoms in the nighttime thermosphere. A formula is given for the rate coefficient for the production of an O(¹S) atom with a specific energy in collisions involving an O(¹S) atom of a given initial energy and the ground state O(³P) atoms of a thermal gas. Effective elastic scattering and excitation transfer cross-sections are defined and calculated to be 1.71 × 10^?15 cm² and 6.67 × 10^?16 cm² respectively at a relative collision energy of 0.41 eV.  相似文献   

多尺度空间单元区域划分方法   总被引：20，自引：0，他引：20  

骆剑承  周成虎  梁怡  张讲社  黄叶芳 《地理学报》2002,57(2):167-173

传统空间单元的区域划分通常仅以属性数据作为划分依据，而对单元之间空间依赖关系考虑不周。在尺度空间理论基础上，提出多尺度空间单元区域划分方法，在考虑空间单元属性信息的同时，增加了空间单元的相互依赖关系，使得在空间尺度在由小变大过程中，具有高度空间相互依赖关系的空间单元相互融合，得到不同空间尺度下的区域划分。以江苏省从1978年到1995年的18年社会经济发展数据为基础，进行了全省社会经济发展水平的区域划分的试验，结果表明与实际发展水平的分布情况相吻合。  相似文献   

Simulation of a heavy wintertime precipitation event in California     

Su-Tzai Soong  Jinwon Kim 《Climatic change》1996,32(1):55-77

A coupled mesoscale atmospheric-land surface model is used to simulate a twelve-day heavy precipitation event in California. In addition to the temporal variation of the large-scale flow, local topography played a crucial role in the simulated precipitation and land-surface snow budget through orographically-generated vertical motion and a decrease of atmospheric temperature with increasing altitude. The observed and simulated heavy precipitation occurred at locations where orographic lifting is strong: western slopes of the Sierra Nevada Mountains and the Coastal Range. Due to rainshadow effects, the Central Valley area, which is located at the lee side of the Coastal Range, received only a small amount of precipitation. The snowline appeared at altitudes as low as 750 m above sea level, and most of the precipitation above the 1.8 km level was snow. Maximum rainfall was located near the 1 km elevation along the western slope of the Sierra-Nevada while snowfall maxima appeared along the ridge of the Sierra Nevada Mountains. Snow accumulation was also strongly dependent upon surface elevations. The simulation suggested that over 75% of the fresh snowfall during the study period was added to the existing snow cover at elevations above 1.5 km while much of the snowfall over lower elevations melted.  相似文献   

Finite element modelling for water waves-soil interaction   总被引：1，自引：0，他引：1  

Dong-Sheng Jeng  Yee Shown Lin 《Soil Dynamics and Earthquake Engineering》1996,15(5):283-300

The soil permeability and shear modulus of many marine sediments vary with depth because of consolidation under overburden pressure. However, conventional theories for wave-induced soil response have assumed a homogeneous porous seabed, with constant soil permeability and shear modulus. This paper presents a finite element model for the wave-induced soil response in a porous seabed, with variable permeability and shear modulus as a function of burial depth. The soil matrix considered here is unsaturated and hydraulically anisotropic, and subjected to a three-dimensional short-crested wave system. The present finite element formulation is established by using a combination of semi-analytical techniques and the Galerkin method. The nodal effective stresses directly derived from the governing equations can be calculated accurately in the present model. Verification is available through the reduction to the simple case of homogeneous seabed. Three typical marine materials, course, fine sand and gravel, are considered in this study. The numerical results indicate that the soil permeability affects the wave-induced seabed response significantly especially for gravelled seabed, as does the soil shear modulus for sandy seabed.  相似文献   

Instability in Lagrangian stochastic trajectory models,and a method for its cure     

Eugene Yee  John D. Wilson 《Boundary-Layer Meteorology》2007,122(2):243-261

A number of authors have reported the problem of unrealistic velocities (“rogue trajectories”) when computing the paths of particles in a turbulent flow using modern Lagrangian stochastic (LS) models, and have resorted to ad hoc interventions. We suggest that this problem stems from two causes: (1) unstable modes that are intrinsic to the dynamical system constituted by the generalized Langevin equations, and whose actual triggering (expression) is conditional on the fields of the mean velocity and Reynolds stress tensor and is liable to occur in complex, disturbed flows (which, if computational, will also be imperfect and discontinuous); and, (2) the “stiffness” of the generalized Langevin equations, which implies that the simple stochastic generalization of the Euler scheme usually used to integrate these equations is not sufficient to keep round-off errors under control. These two causes are connected, with the first cause (dynamical instability) exacerbating the second (numerical instability); removing the first cause does not necessarily correct the second, and vice versa. To overcome this problem, we introduce a fractional-step integration scheme that splits the velocity increment into contributions that are linear (U _i ) and nonlinear (U _i U _j ) in the Lagrangian velocity fluctuation vector U, the nonlinear contribution being further split into its diagonal and off-diagonal parts. The linear contribution and the diagonal part of the nonlinear contribution to the solution are computed exactly (analytically) over a finite timestep Δt, allowing any dynamical instabilities in the system to be diagnosed and removed, and circumventing the numerical instability that can potentially result in integrating stiff equations using the commonly applied explicit Euler scheme. We contrast results using this and the primitive Euler integration scheme for computed trajectories in a drastically inhomogeneous urban canopy flow.  相似文献   

Comparison of Wind-tunnel and Water-channel Simulations of Plume Dispersion through a Large Array of Obstacles with a Scaled Field Experiment     

Eugene Yee  Ralph M. Gailis  Alexander Hill  Trevor Hilderman  Darwin Kiel 《Boundary-Layer Meteorology》2006,121(3):389-432

We report on measurements of the near-field dispersion of contaminant plumes in a large array of building-like obstacles at three scales; namely, at full-scale in a field experiment, at 1:50 scale in a wind-tunnel simulation, and at 1:205 scale in a water-channel simulation. Plume concentration statistics extracted from the physical modelling in the wind-tunnel and water-channel simulations are compared to those obtained from a field experiment. The modification of the detailed structure of the plume as it interacts with the obstacles is investigated. To this purpose, measurements of the evolution of the mean concentration, concentration fluctuation intensity, concentration probability density function, and integral time scale of concentration fluctuations in the array plume obtained from the field experiment and the scaled wind-tunnel and water-channel experiments are reported and compared, as well as measurements of upwind and within-array velocity spectra. Generally, the wind-tunnel and water-channel results on the modification of the detailed plume structure by the obstacles were qualitatively similar to those observed in the field experiments. However, with the appropriate scaling, the water-channel simulations were able to reproduce quantitatively the results of the full-scale field experiments better than the wind-tunnel simulations.  相似文献