水力学结构成像的大跨距井间层析新方法

一种大跨距井间层析成像系统已经问世，并在佛罗里达州的萨内贝尔岛成功地完成跨距长达５４０ｍ的试验。该系统能够穿过任意沉积地层在所需的跨距之间发送要求频率的声波脉冲，其作法是，产生一系列的相位调制伪随机二进制码，这些代码在进行实时平均和相关计算中不断重复，直到达到期望的信噪比为止。

刺槐苗木干旱胁迫过程中水力学失败和碳饥饿的交互作用

【目的】通过分析刺槐在干旱和复水过程中水力学性状和非结构碳(NSC)储藏的变化,研究在水力学失败和碳饥饿对刺槐苗木的影响,以探讨在经历导致落叶的严重干旱胁迫之后叶片恢复的影响因素。研究的结果可以阐明刺槐干旱和复水过程中水力学结构和碳代谢的交互作用方式,同时为揭示干旱半干旱地区刺槐衰败死亡的生理学机制提供思路和试验证据。【方法】测定3年生刺槐苗在严重干旱导致落叶后和复水后叶片长成时的小枝凌晨和正午水势、枝条正午气穴栓塞、叶片最大光合速率和气孔导度、单株叶面积、枝条和根的非结构碳含量,测定严重干旱后刺槐枝条的栓塞脆弱性,并比较复水后茎干基部和上部新发叶片的叶面积、比叶质量和光合作用及新发小枝的凌晨和正午水势、枝条气穴栓塞。【结果】在干旱导致全部落叶时,凌晨和正午水势分别达到-3.01和-3.73 MPa,显著低于对照;正午导水损失率(PLC)达到91%,显著高于对照;干旱导致刺槐90%以上落叶时其叶片的光合速率为负值,气孔导度也降低到趋近于0。在复水后30天叶片长成时,枝条正午PLC为81%,仍显著高于对照。经历干旱和复水处理的枝条P50(栓塞为50%时的枝条水势)为-1.09 MPa,比对照高0.37 MPa,经历干旱胁迫的枝条抗气穴栓塞能力显著降低。干旱和复水过程均显著降低了刺槐枝条和根的NSC含量,复水过程NSC降低程度更大。复水后的单株总叶面积仅为对照的38%。复水后叶片恢复的主要部位是茎基部和枝条上部,茎基部恢复叶片的叶面积、光合速率、气孔导度均显著大于枝条上部恢复叶片,茎基部新发小枝的凌晨和正午水势显著高于上部新发小枝。【结论】严重干旱导致水势降低,木质部导管栓塞加重,限制了刺槐的水分输导,进而抑制叶片光合作用,导致出现负的碳平衡。在复水阶段,前期严重干旱导致木质部导水能力下降和NSC含量下降限制了复水后新叶的生长,NSC含量降低可能会影响木质部栓塞的即时修复,水力学失败和碳饥饿的交互作用加重了干旱对刺槐的影响。

风对黄花蒿水力学性状和生长的影响

吹风会影响到植物的水力学结构、光合作用、生物量分配以及植物的力学性状,研究风对植物的综合影响有助于深入了解植物应对风胁迫的响应机制。以黄花蒿为研究对象,每天吹风4h,风速为5m/s,吹风处理60d,测定了风吹条件下黄花蒿的水力学特征、光合作用、生物量分配和茎干力学特性。结果表明:在风吹条件下,黄花蒿正午水势显著低于对照,茎干导水损失率(PLC)增加了16%,最大光合速率仅为对照的62%,气孔导度为对照的55%。在试验结束时风吹植株株高仅为对照的68%,但基茎显著高于对照,同时风吹显著降低了黄花蒿的总生物量,但根冠比显著高于对照,风吹显著减小了茎导管直径和导管密度,风吹植物导管直径和导管密度分别为对照的77%和55%,同时,风吹植物茎干导水率显著低于对照,但茎干的抗弯刚度显著高于对照。以上结果表明风吹抑制了植物的水分输导能力,导致叶片水分匮缺,限制了植物的光合作用。风吹增加了茎干的力学稳定性,但同时降低了茎干的水分输导能力,这是植物茎在力学性状和水分输导之间的权衡。这种改变有利于在有风条件下维持植物的力学稳定性,但同时降低了水分输导能力。

Characteristic and optimization of ferrite-rich sulfoaluminate-based composite cement suitable for cold region tunnels

To develop suitable grouting materials for water conveyance tunnels in cold regions,firstly,this study investigated the performance evolution of ferrite-rich sulfoaluminate-based composite cement(FSAC grouting material)at 20 and 3℃.The results show that low temperature only delays the strength development of FSAC grouting material within the first 3 d.Then,the effect of four typical early strength synergists on the early properties of FSAC grouting material was evaluated to optimize the early(£1 d)strength at 3℃.The most effective synergist,Ca(HCOO)_(2),which enhances the low-temperature early strength without compromising fluidity was selected based on strength and fluidity tests.Its micro-mechanism was analyzed by XRD,TG,and SEM methods.The results reveal that the most suitable dosage range is 0.3 wt%−0.5 wt%.Proper addition of Ca(HCOO)_(2)changed the crystal morphology of the hydration products,decreased the pore size and formed more compact hydration products by interlocking and overlapping.However,excessive addition of Ca(HCOO)_(2)inhibited the hydration reaction,resulting in a simple and loose structure of the hydration products.The research results have reference value for controlling surrounding rock deformation and preventing water and mud inrushes during the excavation in cold region tunnels.

Dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in sodium hydroxide solution under atmospheric pressure

The crystal structure, morphology, dissolution kinetics and mechanism of gibbsitic bauxite and pure gibbsite in Na OH solution under atmospheric pressure were systematically investigated by XRD and SEM. The results show that the size of single crystal of gibbsite in gibbsitic bauxite is smaller than that in pure gibbsite, but the interplanar distance is larger than that of pure gibbsite, which result in more defects in the crystal and less energy needed to dissolve in alkaline solution for the gibbsitic bauxite. The dissolution kinetic equations of gibbsitic bauxite and pure gibbsite were established, and the corresponding activation energies were calculated to be 99.144 and 115.149 k J/mol, respectively.

Molecular Dynamics Study on Microstructure of Potassium Dihydrogen Phosphates Solution

Molecular dynamics simulations were carried out to study the internal energy and microstructure of potassium dihydrogen phosphates （KDP） solution at different temperatures. The water molecule was treated as a simple-point-charge model, while a seven-site model for the dihydrogen phosphate ion was adopted. The internal energy functions and the radial distribution functions of the solution were studied in detail. An unusually large local particle number density fluctuation was observed in the system at saturation temperature. It has been found that the specific heat of oversaturated solution is higher than that of unsaturated solution, which indicates the solution experiences a crystallization process below saturation temperature. The radial distribution function between the oxygen atom of water and the hydrogen atom of the dihydrogen phosphate ion shows a very strong hydrogen bond structure. There are strong interactions between potassium cation and oxygen atom of dihydrogen phosphate ion in KDP solution, and much more ion pairs were formed in saturated solution.

Simulation of Random Crack Generation in Concrete Members with Uniform Stress Fields

The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural members with a uniform stress field, where stresses or strains are approximately the same under loading. A mathematical ap- proach of producing a series of random variables of the ultimate tensile strain in concrete is proposed to describe the randomness ofconcrete deformation. With reinforced concrete finite elements a real model calculation method is found for the randomness of initial cracks determined by a minimum tension strain within the uniform stress fields of concrete members. The proposed methods in our paper have as aim to improve the existing method used by FEM and other rela- tive approaches, which normally pay less attention to randomness with consequences that may possibly differ from testing or practice. The method and sample computation as indicated is meaningful and comply with testing and engi- neering practice.

Hydrodynamic Characteristics of Three Rows of Vertical Slotted Wall Breakwaters

In this study, we examine the hydrodynamic characteristics of three rows of vertical slotted wall breakwaters in which the front and middle walls are permeable and partially immersed in a water channel of constant depth, whereas the third wall is impermeable. The wave–structure interaction and flow behavior of this type of breakwater arrangement are complicated and must be analyzed before breakwaters can be appropriately designed. To study the hydrodynamic breakwater performance, we developed a mathematical model based on the eigenfunction expansion method and a least squares technique for predicting wave interaction with three rows of vertical slotted wall breakwaters. We theoretically examined the wave transmission, reflection, energy loss, wave runup, and wave force under normal regular waves. Comparisons with experimental measurements show that the mathematical model results adequately reproduce most of the important features. The results of this investigation provide a better understanding of the hydrodynamic performance of triple-row vertical slotted wall breakwaters.

Hydrodynamic parameters in a flood impacted boulder block ramp： Krzczonówka mountain stream, Polish Carpathians

Boulder block ramps are river engineering structures used to stabilise river beds. Block ramps provide a semi-natural and aesthetically pleasing solution to certain river engineering problems in mountain streams. When constructing block ramps,one can use the dissipative behaviour of large macroroughness elements randomly placed on the river bed to enhance fish migration in an upstream direction thus, in this sense, meeting the requirements of the EU Water Framework Directive. Block ramps are often designed and constructed to replace damaged drop hydraulic structures in the channels of mountain streams. This paper investigates the resilience of a particular block ramp placed in the Krzczonówka stream(Polish Carpathians) in terms of the engineering design function and its durability against damaging. A hydrodynamic analysis of a block ramp is presented before and after a flood event that changed the configuration of the blocks. The seminatural unstructured hydraulic structure was built on the Krzczonowka stream to protect gas pipes which are located beneath it. As a result of several floods, the boulder block chute described in this paper was damaged, and some boulders were dislodged and transported downstream. Our post-flood investigations of bathymetry and velocity revealed that even damaged boulder blocks, removed from the chute and displaced downstream of the structure, still provide significant energy dissipation of the flowing water. The novel of our paper is for the first time showing very detailed analysis of unstructured block ramp hydrodynamics parameters done in the field.Also the novel finding of our investigations shows that before and after the flood event the unstructured block ramp structure, is still fish friendly in terms of hydrodynamics.

A Method to Improve First Order Approximation of Smoothed Particle Hydrodynamics

Smoothed particle hydrodynamics (SPH) is a useful meshless method.The first and second orders are the most popular derivatives of the field function in the mechanical governing equations.New methods were proposed to improve accuracy of SPH approximation by the lemma proved.The lemma describes the relationship of functions and their SPH approximation.Finally,the error comparison of SPH method with or without our improvement was carried out.

Crustal Stress Measurement for Significant Project Construction and Its Application in Design

The hydrofracturing technique has developed into a reliable and practical method for determining the original three-dimensional crustal stress state of underground caverns,the load-bearing capacity of a high pressure cavern itself,and the high pressure hydraulic permeability of rock masses,and has also been extensively used in disposal of nuclear waste,long and deeply-buried traffic channels and high-pressure cavern engineering for hydraulic power plants.The practice shows that the comprehensive measurement of the physical parameters of the rock mass and taking full use of the wall rock load-bearing capacity to optimize the engineering design hold are very useful in ensuring the engineering safety and improving the design level.

Simulation Study on the Structure and Dynamics of Water in Sodium Tetrafluoroborate/Water

The microstructure, IR spectrum, as well as rotation dynamics of water molecule in sodium tetrafluoroborate （NaBF4）/water mixture at room temperatures were studied with molecular dynamics simulation. Different concentrations of water （6.25%, 25.0%, 50.0%, 75.0%, 90.0%, and 99.6%） in NaBF4/water mixture were simulated to understand the structure and dynamics. It was shown that water molecules tend to be isolated from each other in mixtures with more ions than water molecules in both liquids. With increase of the molar fraction of water in the mixture, the rotation bands and the bending bands of water display red shift whereas the O-H stretch bands show blue shift, and the decay of the reorientation correlation function becomes slower. This suggests that the molecules are hindered and their motions are difficult and slow, due to the hydrogen-bond interactions and the inharmonic interactions between the interor intra-molecular modes.

The Problems and Reform and Development of Universities for Audit Teaching

With the development of audit and the main problems of audit education are mainly： large differences in teaching methods, teacher＇ s knowledge structure is incomplete, teachers generally lack practical experience, teachers have not yet formed Auditing echelon teaching case information, and the systematic audit case is difficult to get. Auditing teaching has the following measures： establish research and teaching which reflects both the teacher evaluation system and teacher training active auditing team, there are a variety of ways to improve the operational practice of auditing courses, organizational strength phased development of the system of teaching cases audit system. Audit teaching reform measures are set by the three levels to practice, namely cognitive level of knowledge, knowledge into ability levels and levels of knowledge and innovation.

A coupled strain softening and hardening model for completely weathered granite in a fault zone

his study focused on exploring the specificity of mechanical behavior for completely weathered granite,as a special soil,by consolidated drained triaxial tests.The influences of dry density(1.60,1.70,1.80 and 1.90 g/cm^(3)),confining pressure(100,200,400 and 600 kPa),and moisture content(13.0%,that is,natural moisture content)were investigated in the present work.A newly developed Duncan-Chang model was established based on the experimental data and Duncan-Chang model.The influence of each parameter on the type of the proposed model curve was also evaluated.The experimental results revealed that with varying dry density and confining pressure,the deviatoric stress–strain curves have diversified characteristics including strain-softening,strain-stabilization and strain-hardening.Under high confining pressure condition,specimens with different densities all showed strain-hardening characteristic.Whereas at the low confining pressure levels,specimens with higher densities gradually transform into softening characteristics.Except for individual compression shear failure,the deformation modes of the specimens all showed swelling deformation,and all the damaged specimens maintained good integrity.Through comparing the experiment results,the strain-softening or strain-hardening behavior of CWG specimens could be predicted following the proposed model with high accuracy.Additionally,the proposed model can accurately characterize the key mechanical indicators,such as tangent modulus,peak value and residual strength,which is simple to implement and depends on fewer parameters.

Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe3＋ in polyethylene glycol and the concentration of C1- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe3＋ modulated the hydrolysis kinetics of Fe3＋and prevented the aggregation of β-FeOOH nanorods; while C1- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.

Structure and mechanical properties of pincers for freshwater lobster

The mineral phases and structure of pincer for the freshwater lobster were analyzed and observed by using X-ray diffraction and field-emission scanning electronic microscope with energy dispersive spectroscopy, and the mechanical properties of pincer were determined by using nano-indenter and micro-tribometer. The results showed that the pincers contained Ca, Mg, C, O, Na, etc. elements and there were many amorphous mineral phases in the lobster pincers. There were many concave hollows and convex domes with seta on the surface of pincer, and some spines were observed on the surface of seta, which exhibited non-smooth surface. The exoskeleton of pincer consisted of epicuticle, exocuticle and endocuticle, and the microstructure of exocuticle and endocuticle displayed the twisted plywood structure with chitin protein fibers. The mean hardness and elastic modulus on the surface of fresh pincers were 0.27 GPa and 5.28 GPa, respectively. With the increase in distance from the surface, the hardness and elastic modulus all decreased gradually. This indicated that the transition of hardness and elastic modulus occurred from exocuticle to endocuticle. When the heat treatment temperature was lower than 200°C, the values of hardness and elastic modulus fluctuated slightly, while they increased at the temperature beyond 200°C. As the pincers slid against Si3N4 balls in water and air, the friction coefficients in water were higher than those in air. The research could provide a bio-inspired basis for the structural design of composite materials and anti-friction surface.