Linear spatio-temporal instability analysis of ice growth under a falling water film

A linear spatio-temporal stability analysis is conducted for the ice growth under a falling water film along an inclined ice plane. The full system of linear stability equations is solved by using the Chebyshev collocation method. By plotting the boundary curve between the linear absolute and convective instabilities (AI/CI) of the ice mode in the parameter plane of the Reynolds number and incline angle, it is found that the linear absolute instability exists and occurs above a minimum Reynolds number and below a maximum inclined angle. Furthermore, by plotting the critical Reynolds number curves with respect to the inclined angle for the downstream and upstream branches, the convectively unstable region is determined and divided into three parts, one of which has both downstream and upstream convectively unstable wavepackets and the other two have only downstream or upstream convectively unstable wavepacket. Finally, the effect of the Stefan number and the thickness of the ice layer on the AI/CI boundary curve is investigated.

Wave generation by the falling rock in the two-dimensional wave tank

Wave generation by the falling rock in the two-dimensional wave tank is experimentally and numerically studied, where the numerical model utilizes the boundary element method to solve the fully nonlinear potential flow theory. The wave profiles at different times are measured in the laboratory, which are also used to test the numerical model. Comparisons show that the experimental and numerical results are in good agreement, and the numerical model can be used to simulate the wave generation due to the submarine rock falling. Further numerical tests on the influences of the rock size, density, initial position and the falling angle on the wave elevation of the generated waves are performed, respectively. The results show that the size and density of the rock have strong effects on the maximum elevation of the generated wave, while the effects of the initial position and the falling angle of the rock are also significant. When the size or the density of the rock increases, the maximum elevation of the generated wave increases. The same effect on the generated wave would be produced if the initial position of the rock becomes closer to the surface, or the falling angle between the falling route and the vertical direction turns larger. In addition, the present numerical tests reveal that the submarine rock falling provides a new generation method for the breaking wave in the wave tank.

清江茅坪滑坡白岩危岩体崩塌现场测量及其分析

位于茅坪滑坡体后缘的白岩危岩体于2002年8月24日发生了大规模的崩塌。崩落的块石落在滑坡体上，对滑坡体产生了加载作用，影响了该滑坡体的稳定性。为研究茅坪滑坡体的稳定性，有必要弄清滑坡体上崩落块石的堆积情况。论文在对清江隔河岩水库白岩危岩体崩塌现场调查的基础上，估算了崩塌岩体的体积，实地测量了岩体崩塌后堆积体表面块石的尺寸以及各块石空间位置坐标。对测量的结果进行了统计分析。根据所测量的块石尺寸、得到了崩落岩体的块体大小级配累积曲线图和各块石尺度出现的概率，从而阐明了各尺度崩落块石组合情况。根据各块石尺寸和各块石空间位置坐标、分析得到不同尺寸崩落块石落在滑坡体上的空间分布规律，从而为茅坪滑坡的进一步研究打下了基础。

Computation of flow over a rotating body on unstructured Chimera mesh

Flow around moving boundary is ubiquitous in engineering applications. To increse the efficienly of the algorithm to handle moving boundaries is still a major challenge in Computational Fluid Dynamics (CFD). The Chimera grid method is one type of method to handle moving boundaries. A concept of domain de-composition has been proposed in this paper. In this method, sub-domains are meshed independently and governing equations are also solved separately on them. The Chimera grid method was originally used only on structured (curvilinear) meshes. However, in a problem which involves both moving boundary and complex geometry, the number of sub-domains required in a traditional (structured) Chimera method becomes fairly large. Thus the time required in the interior boundary locating, link-building and data exchanging also increases. The use of unstructured Chimera grid can reduce the time consumption significantly by the reduction of domain(block) number. Generally speaking, unstructured Chimera grid method has not been developed. In this paper, a well-known pressure correction scheme - SIMPLEC is modified and implemented on unstructured Chimera mesh. A new interpolation scheme regarding the pressure correction is proposed to prevent the possible decoupling of pressure. A moving-mesh finite volume approach is implemented in an inertial reference frame. This approach is then used to compute incompressible flow around a rotating circular and elliptic cylinder. These numerical examples demonstrate the capability of the proposed scheme in handling moving boundaries. The numerical results are in good agreement with other experimental and computational data in literature. The method proposed in this paper can be efficiently applied to more challenge cases such as free-falling objects or heavy particles in fluid.

Instabilities of a liquid film flowing down an inclined porous plane

The problem of a film flowing down an inclined porous layer is considered. The fully developed basic flow is driven by gravitation. A careful linear instability analysis is carried out. We use Darcy's law to describe the porous layer and solve the coupling equations of the fluid and the porous medium rather than the decoupled equations of the one-sided model used in previous works. The eigenvalue problem is solved by means of a Chebyshev collocation method. We compare the instability of the two-sided model with the results of the one-sided model. The result reveals a porous mode instability which is completely neglected in previous works. For a falling film on an inclined porous plane there are three instability modes, i.e., the surface mode, the shear mode, and the porous mode. We also study the influences of the depth ratio d, the Darcy number delta, and the Beavers-Joseph coefficient alpha(BJ) on the instability of the system.

溶胶-凝胶条波导Sagnac环的乙醇蒸气传感特性

采用有机/无机混合溶胶-凝胶法制作条形光波导,并将条波导接入光纤Sagnac 环中,测量了输出光功率随环境气氛中乙醇蒸气体积分数变化的特性,表明在实验研究的范围内,输出信号与乙醇蒸气体积分数呈正弦变化。根据Sagnac环结构输出特性的基本关系,反映了溶胶-凝胶条波导在乙醇蒸气气氛下产生了双折射效应。观察到双折射相移与乙醇体积分数的亚线性关系。对实验数据拟合,计算了偏振相移的线性项和二次项系数,得到所制备的条波导的双折射对乙醇体积分数的响应为Δn≈4.4×10-2。测量了信号变化的时间演变特性,典型的上升和

基于高精度差动干涉仪的微伽重力仪

本文提出的微伽绝对重力仪基于高精度、高稳定的差动干涉仪。详细研究了重力仪的距离测量技术，自由落体运动的距离测量实验表明，本文提出的高精度差动干涉仪可以满足相对不确定度达6.4×10^(-9)的微伽绝对重力仪要求。而且，差动干涉仪比目前广泛应用于绝对重力仪的Mach-Zehnder干涉仪更稳定。

双频激光干涉仪的最大可测量速度研究

现代制造业对双频激光干涉仪的最大可测量速度提出了越来越高的要求。最大可测量速度是双频激光干涉仪的一项重要指标，它主要受双频激光光源所输出的频差、干涉仪的光学结构以及电子带宽等因素的限制。本文从理论和实验两方面对干涉仪的最大可测量速度进行了研究，搭建了基于自由落体运动的实验装置。实验结果表明，实际最大可测量速度略低于其理论值。另外，文中还分析了上述三种因素对最大可测量速度的影响。实验装置和结果可供工业应用提供参考。

Contributions of Pelagic and Benthic Dietary Sources to Freshwater Mussels: Evidence from Stable Carbon Isotope Analysis

In Gonghu Bay of Lake Taihu, tissue of five mussel species showed delta C-13 values similar to or slightly below that of pelagic suspended particulate organic matter (SPOM). This indicated that mussels in this area either fed non-selectively and so reflected available carbon in the pelagic habitat or selected for phytoplankton. The situation was the same for Anodonta woodiana woodiana and Cristaria plicata in Meiliang Bay; however, for the remaining three species, Hyriopsis cumingii, Arconaia lanceolata, and Lamprotula rochechouarti, tissue had intermediate delta C-13 values, falling between those for pelagic SPOM and benthic sediment organic matter (SOM), suggesting a possible preferential selection of phytoplankton from the pelagic SPOM but more likely reflecting local differences in pelagic SPOM and benthic SOM composition and available organic carbon sources. The mixing model showed that pelagic SPOM accounted for over 98% of carbon incorporated by all mussels in Gonghu Bay and two mussels in Meiliang Bay, suggesting the dietary importance of pelagic food sources for mussels. Less than 50% of the assimilation in H. cumingii, A. lanceolata, and L. rochechouarti came from the pelagic carbon sources in Meiliang Bay, which suggested that these species consumed a mix of benthic and pelagic derived carbon sources.

Whistles of boto, Inia geoffrensis, and tucuxi, Sotalia fluviatilis

Whistles were recorded and analyzed from free-ranging single or mixed species groups of boto and tucuxi in the Peruvian Amazon, with sonograms presented. Analysis revealed whistles recorded falling into two discrete groups: a low-frequency group with maximum frequency below 5 kHz, and a high-frequency group with maximum frequencies above 8 kHz and usually above 10 kHz. Whistles in the two groups differed significantly in all five measured variables (beginning frequency, end frequency, minimum frequency, maximum frequency, and duration). Comparisons with Published details of whistles by other platanistoid river dolphins and by oceanic dolphins suggest that the low-frequency whistles were produced by boto, the high-frequency whistles by tucuxi. Tape recordings obtained on three occasions when only one species was present tentatively support this conclusion, but it is emphasized that this is based on few data. (C) 2001 Acoustical Society of America.

HYDROGRAPHIC VARIATIONS IN SIZE STRUCTURE OF PLANKTON BIOMASS IN A CHANGJIANG FLOODPLAIN LAKE

The size structure of the planktonic community in a Changjiang floodplain lake (Lake Chenhu, Hubei, P. R. China) was described for the inundation period of May through September 1983. The modality of the Sheldon-type size distributions changed hydrographically with the spectral profiles being bimodal during low, rising, mid-high and falling water phases, and trimodal soon after filling and shortly before falling. The modal peaks corresponded respectively to the dominant organisms of chlorophytes and nauplii, while the troughs centered on the bacteria and macrocrustacean size classes in the lake. The slope of the normalized biomass spectrum (an index of plankton size distribution) was less than -1.0 for the filling and falling phases or close to -1.0 for the high water period, indicating that the planktonic biomass tended to decrease or evenly distributes across logarithmically ordered size classes, respectively. This observed variation in the size distribution of the plankton community mainly resulted from changes in water levels and contents of particulate inorganic matter (PIM) in the lake.

CONTRIBUTION OF BACTERIOPLANKTON, PHYTOPLANKTON, ZOOPLANKTON AND DETRITUS TO ORGANIC SESTON CARBON LOAD IN A CHANGJIANG FLOODPLAIN LAKE (CHINA)

The relative compositions of bacterioplankton, phytoplankton, zooplankton and detritus of seston were studied during the course of inundation in a floodplain lake of central Changjiang (China). Peaks in bacterial biomass developed shortly after flooding, coinciding with the initial leaching of organic nutrients from vegetation submerged under floodwater, and again at high water, shortly before the climax of phytoplankton biomass. Rods predominated the bacterial carbon biomass. Phytoplankton developed a postflood bloom at initial falling, corresponding to the drainage of the lake water into the river. While minimal biomass occurred during the advent of flooding, most likely due to disturbance and dilution. Algal biomass was usually dominated by Chlorophyta. Highest biomass of zooplankton was recorded at the end of the flooding in connection with the decline in turbidity, and once again at early drainage, closely associated with high phytoplankton biomass. Copepods (mainly nauplii) always constituted the majority of zooplankton carbon biomass. Peaks in detrital carbon concentrations were recorded at rising and falling water phases, corresponding respectively to the riverine discharge and decomposition of macrophyte mats. At rising water phase, CPOC was abundant. While during other water phases, this predominance was shifted to FPOC alone. Taken together, average contribution of bacterioplankton, phytoplankton, zooplankton and detritus to total seston carbon was 3.29, 21.21, 6.83 and 68.67 %, respectively.

Photovoltaic effect in a photon storage cell

The response of photonic memory effect in I-V characteristics of a specially designed photonic memory cell was reported. When the cell is biased in a storage mode, the optical excitation with the photon's energy larger than the energy gap gives rise to a step-like jump in the current. A set-up was used to measure the transient photocurrent at the biases where the step-like jump showed up. It is proved that the falling transient edge of the photocurrent, as the photoexcitation turns off, mainly maps the decaying of electrons and holes, which were previously stored in the cell during the illumination. Its time constant is a measure of photonic memory time.

Instabilities and transient behaviors of a liquid film flowing down a porous inclined plane

The nonmodal linear stability of a falling film over a porous inclined plane has been investigated. The base flow is driven by gravity. We use Darcy's law to describe the flow in the porous medium. A simplified one-sided model is used to describe the fluid flow. In this model, the influence of the porous layer on the flow in the film can be identified by a parameter beta. The instabilities of a falling film have traditionally been investigated by linearizing the governing equations and testing for unstable eigenvalues of the linearized problem. However, the results of eigenvalue analysis agree poorly in many cases with experiments, especially for shear flows. In the present paper, we have studied the linear stability of three-dimensional disturbances using the nonmodal stability theory. Particular attentions are paid to the transient behavior rather than the long time behavior of eigenmodes predicted by traditional normal mode analysis. The transient behaviors of the response to external excitations and the response to initial conditions are studied by examining the pseudospectral structures and the energy growth function G(t) Before we study the nonmodal stability of the system, we extend the results of long-wave analysis in previous works by examining the linear stabilities for streamwise and spanwise disturbances. Results show that the critical conditions of both the surface mode and the shear mode instabilities are dependent on beta for streamwise disturbances. However, the spanwise disturbances have no unstable eigenvalue. 2010 American Institute of Physics. [doi:10.1063/1.3455503]

Controls on suppression of methane flux from a peat bog subjected to simulated acid rain sulfate deposition

The effect of acid rain SO42− deposition on peatland CH4 emissions was examined by manipulating SO42− inputs to a pristine raised peat bog in northern Scotland. Weekly pulses of dissolved Na2SO4 were applied to the bog over two years in doses of 25, 50, and 100 kg S ha−1 yr−1, reflecting the range of pollutant S deposition loads experienced in acid rain-impacted regions of the world. CH4 fluxes were measured at regular intervals using a static chamber/gas chromatographic flame ionization detector method. Total emissions of CH4 were reduced by between 21 and 42% relative to controls, although no significant differences were observed between treatments. Estimated total annual fluxes during the second year of the experiment were 16.6 g m−2 from the controls and (in order of increasing SO42− dose size) 10.7, 13.2, and 9.8 g m−2 from the three SO42− treatments, respectively. The relative extent of CH4 flux suppression varied with changes in both peat temperature and peat water table with the largest suppression during cool periods and episodes of falling water table. Our findings suggest that low doses of SO42− at deposition rates commonly experienced in areas impacted by acid rain, may significantly affect CH4 emissions from wetlands in affected areas. We propose that SO42− from acid rain can stimulate sulfate-reducing bacteria into a population capable of outcompeting methanogens for substrates. We further propose that this microbially mediated interaction may have a significant current and future effect on the contribution of northern peatlands to the global methane budget.