The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) λ of the ionospheric pierce point (IPP) and the IEF’s influence factor (IFF) . The IEF can be used to make a relatively precise distinction between ionospheric daytime and nighttime, whereas the IFF is advantageous for describing the IEF’s variations with day, month, season and year, associated with seasonal variations of total electron content (TEC) of the ionosphere. By combining λ and with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM may further improve ionospheric delay modeling using GPS data.     

额济纳绿洲沙尘暴沉积特征

1 Introduction Oases are unique ecosystems and important residences for our ancestors in arid and semiarid regions of the world, and have deeply been imprinted by human actions, such as Jericho oasis of Jordan Valley, Jarmo oasis of the Euphrates River an…     

Ammonium regeneration in intertidal sediments of the Yangtze estuary during air-exposure

The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification rate (˜500 nmol N cm⁻³ day⁻¹), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×10⁵ t N year⁻¹ in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to the estuarine ecosystem.     

中国西南部强震带大震复发机制

我国西南部鲜水河断裂带、红河断裂带、安宁河断理解带和龙门山断裂带四个测区内，用Ｘ射线法 得的宏观残余应力场和用震源机制解Ｐ轴显示的发震时现今应力场的水平最大主压应力方向基本吻合。这种叠加应力场的水平最大主压力分布方向与发震断裂带总体走 交角约为４０－５５°左右，使断裂带易于发生剪切错动。宏观残余水平最大剪应 值区的分布，也与区内大震震中的分布基本吻合，岩石裂面在３００℃和３００ＭＰａ围压下经１０天     

Stability and accuracy analysis of the central difference method for real‐time substructure testing

The central difference method (CDM) that is explicit for pseudo‐dynamic testing is also believed to be explicit for real‐time substructure testing (RST). However, to obtain the correct velocity dependent restoring force of the physical substructure being tested, the target velocity is required to be calculated as well as the displacement. The standard CDM provides only explicit target displacement but not explicit target velocity. This paper investigates the required modification of the standard central difference method when applied to RST and analyzes the stability and accuracy of the modified CDM for RST. Copyright © 2005 John Wiley & Sons, Ltd.     

Late Quaternary climate and environmental change derived from glacial deposits in the Parlung Zangbo Valley,southeastern Tibetan Plateau

ABSTRACT

This study investigated the late Quaternary climate and environmental characteristics of two tributary valleys (Xingmu and Depu Valleys) in the Parlung Zangbo Valley, southeastern Tibetan Plateau. Optically stimulated luminescence (OSL) samples collected from moraines at the mouth of Xingmu Valley produce a wide age range from 13.9 ka to 76 ka. The ages measured from the lenticular sand are consistent with the relative geomorphic sequence of the landforms. Lenticular sand layers below the moraine were dated to 37.9 ka and 44.7 ka, indicating that fluvial processes were likely dominant in the valley during Marine Isotope Stage (MIS) 3. The outer moraine ridges at the valley mouth were formed during 13.9 ka and 26.5 ka, corresponding to MIS2. At Depu Valley, OSL samples from two sets of lateral and terminal moraines close to the modern glacier, provide ages from 1.4 ka to 29.2 ka. The paleosol layer widely developed during 2.6 cal ka BP and 8.7 cal ka BP in the study area, reflecting a relatively warm condition during the mid-Holocene.     

Internal Microanatomy and Zoological Affinity of the Early Cambrian Olivooides

The early Cambrian pentamerous microfossil Olivooides/Punctatus in South China, which is characterized by a diagnostic stellate tubular apex, has been well-known for its almost complete development sequence that can be confidently traced from embryos and hatched juveniles, to conical adults. However, its zoological affinity remains highly controversial. Here we describe the internal microanatomic structures of the soft-body inside the peridermal theca of Olivooides multisulcatus Qian, 1977, including interradial pairs of tentacles, adradial and perradial frenula, perradial oral marginal lappets and twins of perradial gastric saccule-like humps as well as a circular velarium with striated coronal muscles. Particularly, one specimen shows bifurcated velarial canals along the bell aperture. Both the components of the soft-body and the external theca (or cyst) are arranged in perfect pentaradial symmetry. These characteristics are more compatible with those of living cubomedusans and co-occurring Cambrian athecate embryonic cubozoans. Concerning the presence of peridermal theca, Olivooides most likely represents an extinct thecate stem-group cubomedusae but devoid of both perradial eyes and specialized pedalia. The well-grown soft body inside the peridermal tube displays a set of mixed features of both polyp and medusa.     

Semi-analytical solutions for vertically and laterally loaded piles in multilayered soil deposits

In geotechnical practice, it is of considerable importance to assess the behavior of vertical–lateral coupled loading piles in multilayered soil deposits. This study deals with a semi-analytical formulation for the performance of a pile suffering from combined vertical and lateral loads. The emphasis is on quantifying the mobilization of the subgrade reaction provided by the layered soil stratums. In the proposed method, subgrade reactions, correlated with both the accumulative axial load transfer and side resistances depending upon the pile–soil interaction, are abstracted as a series of nonlinear springs in both vertical and lateral directions. On account of this, an alternative transfer matrix method is applied to characterize the pile reaction along the depth under the identified boundary conditions atop the pile; meanwhile, the condition of static equilibrium, between two specific pile segments located at the border of soil layers, is also essential. On this basis, validation of the solution is conducted by comparing with observations from experiments and predictions obtained from other existing methods. In addition, the influence of properties in shallow soil layer and the vertical load on the lateral response of the pile is also discussed. The results indicate a reduction in the lateral displacement and the maximum bending moment within the pile with the increase in the shallow soil stiffness, but a growth with the increase in vertical load due to the “P-Δ effect.”     

湖南省岳家桥典型岩溶发育区电性特征及构造格架研究

为探讨湖南省益阳市岳家桥地质灾害现状,以区内典型岩溶发育区为研究对象,通过长剖面高密度电法、视电阻率联合剖面法等地球物理方法,研究了地层电性响应特点,利用钻孔数据和综合电法勘探数据建立了三维地层结构模型,揭示了典型区域近地表电性结构形态,构建了区内三维地层构造格架,圈定了岩溶发育范围,并评价了地质灾害程度。研究表明: 因地制宜地利用综合电法勘探,有助于在我国南方含水较多的岩溶发育区快速、有效地进行灾害范围的圈定和评价。     

Model Test on Self-Weight Consolidation of the Red Mud Tailings Placed in the Karsts

The management of tailings depends on its consolidation behavior to great extent. The red mud tailings in Pingguo, Guangxi is of high water content and void ratio. The present paper takes the red mud aluminiferous tailings in Pingguo, Guangxi as prototype. Model tests were carried out to study the consolidation behavior of red mud aluminiferous tailings that were landfilled layer by layer. The layered settlement and the water discharge caused by self-weight consolidation were studied. The influence of the latter landfilled layer of red mud on the previous layer was analyzed. The results show that the settlement at the surface with time can be divided into two stages. During the first stage, a thin layer of water appeared and the thickness kept increasing at the top of the mud surface with the particle of red mud sinking. During the second stage, water drained from the mud and settlement developed slowly. Cracks developed at the surface due to evaporation and the red mud near the surface became unsaturated. When the previous landfilled layer consolidated to the degree that the water content was less than 40%, the later landfilled layer of red mud will have little influence on the settlement of previous landfilled layer.