Aquaterra Incognita: Lost Land Beneath The Sea

The author proposes scientific recognition of an existing, previously undefined and unnamed global feature. Aquaterra is suggested as the new name for the lands that were alternately exposed and inundated as ice sheets advanced and retreated over the past 120,000 years. The vertical amplitude of sea level change amounts to 130 meters, and the aggregate global area of aquaterra equates to the continent of North America. The time period coincides with the total span during which modern humans are known to have existed.     

Lattice Boltzmann simulation of turbulence-induced flocculation of cohesive sediment

Both the floc formation and floc breakup of cohesive sediment are affected by turbulent shear which is recognized as one of the most important parameters, and thus, on the settling and transport of cohesive sediment. In this study, the development of floc characteristics at early stage and steady-state of flocculation were investigated via a three-dimensional lattice Boltzmann numerical model for turbulence-induced flocculation. Simulations for collision and aggregation of various size particles, floc growth, and breakup in isotropic and homogenous turbulent flows with different shear stresses were conducted. Model results for the temporal evolution of floc size distribution show that the normalized floc size distributions is time-independent during early stage of flocculation, and at steady-state, shear rate has no effect on the shape of normalized floc size distribution. Furthermore, the size, settling velocity, and effective density of flocs at the non-equilibrium flocculation stage do not change significantly for shear stresses in the range 0–0.4 N m^?2. The relationships between floc size and settling velocity established during floc growth stages and that during steady-states are different.     

Particulate contribution to extinction of visible radiation: Pollution, haze, and fog

A data set acquired by eight particle-dedicated instruments set up on the SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique, which is French for Instrumented Site for Atmospheric Remote Sensing Research) during the ParisFog field campaign are exploited to document microphysical properties of particles contributing to extinction of visible radiation in variable situations. The study focuses on a 48-hour period when atmospheric conditions are highly variable: relative humidity changes between 50 and 100%, visibility ranges between 65 and 35 000 m, the site is either downwind the Paris area either under maritime influence. A dense and homogeneous fog formed during the night by radiative cooling. In 6 h, visibility decreased down from 30 000 m in the clear-sky regime to 65 m within the fog, because of advected urban pollution (factor 3 to 4 in visibility reduction), aerosol hydration (factor 20) and aerosol activation (factor 6). Computations of aerosol optical properties, based on Mie theory, show that extinction in clear-sky regime is due equally to the ultrafine modes and to the accumulation mode. Extinction by haze is due to hydrated aerosol particles distributed in the accumulation mode, defined by a geometric mean diameter of 0.6 μm and a geometric standard deviation of 1.4. These hydrated aerosol particles still contribute by 20 ± 10% to extinction in the fog. The complementary extinction is due to fog droplets distributed around the geometric mean diameter of 3.2 μm with a geometric standard deviation of 1.5 during the first fog development stage. The study also shows that the experimental set-up could not count all fog droplets during the second and third fog development stages.     

天然地震接收函数揭示的青藏

1998年 6～ 1 1月 ,中国地质科学院与法国 Joseph大学地球物理及构造研究所合作 ,在青海共和至玉树公路沿线 ,布置了40台 Minititan三分量地震仪和 1 3台 CEIS单分量地震仪 ,进行天然地震观测 .研究区位于班公—怒江断裂以北、柴达木以东、中祁连断裂以南和龙门山断裂以西的区域 .沿线穿过南祁连、东昆仑、巴颜喀拉、金沙江等 ,横穿了青藏高原东部的大部分区域(图 1 ) .此剖面是第一次穿越青藏高原东部的地震探测剖面 ,它有利于与中部已有的研究成果进行对比 ,便于探讨在印度大陆向北俯冲的过程中 ,对青藏高原东部深部特征的影响 ,特别是…     

The influence of preform on the modes of vibrating beams

A theoretical analysis is presented of a vibratory system in which it is possible to eliminate an unwanted mode of vibration by using that mode as an initial deformation of the system. The analysis shows that this is possible in straight beams with end restraints in axial deformation. The mathematical problem leads to an eigenvalue problem of a type not normally encountered. In the paper examples are given for the changes in eigenfrequency and mode shape produced by the initial preformed shape of the beam for cases where the preform is proportional to a mode of the straight beam and when the preform is unrelated to any mode. The analysis shows that, while elimination of a mode in the strict sense is not achieved, the results can be interpreted for practical purposes in this way.     

Response of fixed offshore structures in random sea

An integrated model is developed for the short-term and long-term dynamic response of an offshore structure subjected to random wave excitation. A discrete linear, elastic model of the upper structure is coupled with an iterative linear quasi-three-dimensional finite element model for the pile-soil medium, and the system is subjected to stochastic storms described by mean rate of arrival, joint probability distribution of storm duration and average intensity, and a random process that describes the variations of a statistical wave height measure during each storm. Sarpkaya's 1977 experimental information is used to specify values for C_M and C_D, in Morison's equation, consistent with the flow and response characteristics. Soil (clay) degradation, due to cyclic excitation, is followed during the passage of a storm. The indicator of soil degradation is taken to be the value of the horizontal foundation stiffness and the stiffness degradation is modelled by a homogeneous Markov process.     

Solubility equilibrium constant of α-hopeite

The saturation curve for synthetic α-hopeite, Zn₃(PO₄)₂·4H₂O in dilute phosphoric acid solutions has been determined at 25°C as a function of pH. Interpretation of the data in terms of a model which assumes the formation of the ion-pairs ZnHPO₄⁰ and ZnH₂PO₄⁺ in these solutions resulted in the solubility product constant for α-hopeite of 10^?35.3±0.1. The data show that the formation of hopeite may influence both the availability of zinc in soils and the zinc levels in natural water systems.