Architectural Model of a Dryland Gravel Braided River,based on 3D UAV Oblique Photogrammetric Data:A Case Study of West Dalongkou River in Eastern Xinjiang,China

Three-dimensional unmanned aerial vehicle(UAV)oblique photogrammetric data were used to infer mountainous gravel braided river lithofacies,lithofacies associations and architectural elements.Hierarchical architecture and lithofacies associations with detailed lithofacies characterizations were comprehensively described to document the architectural model,architectural element scale and gravel particle scale.(1)Nine lithofacies(i.e.,Gmm,Gcm,Gcc,Gci,Gcl,Ss,Sm,Fsm and Fl)were identified and classified as gravel,sand and fine matrix deposits.These are typical depositional features of a mountainous dryland gravel-braided river.(2)Three architectural elements were identified,including channel(CH),gravel bar(GB)and overbank(OB).CH can be further divided into flow channel and abandoned channel,while GB consists of Central Gravel bar(CGB)and Margin Gravel bar(MGB).(3)The gravel bar is the key architectural element of the gravel braided river,with its geological attributes.The dimensions of GBs and their particles are various,but exhibit good relationships with each other.The grain size of GB decreases downstream,but the dimensions of GB do not.The bank erosion affects the GB dimensions,whereas channel incision and water flow velocity influence the grain size of GB.The conclusions can be applied to the dryland gravel braided river studies in tectonically active areas.

关于Braided双代数的一些注记

本文首先讨论了余半单Ｈｏｐｆ代数的Ｂｒａｉｄｅｄ结构的有限性．其次，对于左Ｈ－模代数Ａ，通过构造新的代数结构Ａ＃σＨ，推广了Ｄｏｉ．Ｙ．在文献［２］中的部分结果．

近三十年沿海发达地区防洪功能变迁研究 ——以粤港澳大湾区为例

沿海发达地区作为中国城镇化进程最为迅猛、经济活力最为旺盛的地区,人口密集、地势低平,其防洪功能的重要性日益凸显。然而,目前对于该区域的防洪功能研究尚显不足,多采用传统的研究方法和服务功能评估,较少结合该区域的生态系统特点以及具备空间可视化优势的防洪功能模型进行深入探讨。鉴于此,文章以高度发达的粤港澳大湾区为例,采用Nature Braid模型,系统评估1990—2020年间的区域防洪功能变迁,并进一步探讨了其供需匹配的现状。研究结果显示,在1990—2020年间,粤港澳大湾区的防洪功能在空间分布上呈现出“四周高、中部低”的特点,而在时间变化上则整体呈现下降趋势。2020年,防洪功能的供需匹配特征总体上表现为空间错位,供需不平衡问题较为突出。因此,在未来的土地利用规划中,为实现区域生态、环境与经济社会的可持续发展,粤港澳大湾区需要加强对现有生态空间的保护,并合理调整土地利用结构。

Investigation on the Thermal Conductivity of 3-Dimensional and 4-Directional Braided Composites

It is vital to choose a factual and reasonable micro-structural model of braided composites for improving the calculating precision of thermal property of 3-D braided composites by finite element method （FEM）. On the basis of new microstructure model of braided composites proposed recently, the model of FEM calculation for thermal conductivity of 3-dimennsional and 4-directional braided composites is set up in this paper. The curves of coefficient of effective thermal conductivity versus fiber volume ratio and interior braiding angle are obtained. Furthermore, comparing the results of FEM with the available experimental data, the reasonability and veracity of calculation are confirmed at the same time.

Internal Strain Measurement in 3D Braided Composites Using Co-braided Optical Fiber Sensors

3D braided composite technology has stimulated a great deal of interest in the world at large. But due to the three-dimensional nature of these kinds of composites, coupled with the shortcomings of currently-adopted experimental test methods, it is difficult to measure the internal parameters of this materials, hence causes it difficult to understand the material performance. A new method is introduced herein to measure the internal strain of braided composite materials using co-braided fiber optic sensors. Two kinds of fiber optic sensors are co-braided into 3D braided composites to measure internal strain. One of these is the Fabry-Parrot (F-P) fiber optic sensor; the other is the polarimetric fiber optic sensor. Experiments are conducted to measure internal strain under tension, bending and thermal environments in the 3D carbon fiber braided composite specimens, both locally and globally. Experimental results show that multiple fiber optic sensors can be braided into the 3D braided composites to measure the internal parameters, providing a more accurate measurement method and leading to a better understanding of these materials.

Pollutant mixing and transport process via diverse transverse release positions in a multi-anabranch river with three braid bars

A multi-anabranch river with three braid bars is a typical river pattern in nature, but no studies have been conducted to describe mixing characteristics of pollutants in the river. In this study, a physical model of a typical multi-anabranch river with three braid bars was established to explore the pollutant mixing characteristics in different branches. The multi-anabranch reach was separated into seven branches, B1, B2, B3, B4, B5, B6, and BT, by three braid bars. Five tracer release positions located 2.9 m upstream from the inlet section of the multi-anabranch reach were adopted, and the distances from the five positions to the left bank of the upstream main channel were 1/6B, 1/3B, 1/2B, 2/3B, and 5/6B （B is the width of the upstream main channel）, respectively. The longitudinal velocities and pollutant concentrations in the seven branches were measured. The planar flow field and mixing characteristics of pollutants from the bottom to the surface in the multi-anabranch river were obtained and analyzed. The results show that the pollutant release positions are the main influencing factors in the pollutant transport process, and the diversion points and pollutant release positions jointly influence the percentage ratios of the pollutant fluxes in branches B 1, B2, and B3 to the pollutant flux in the upstream main channel.

Relationship between energy dissipation rate and channel morphology in the development of the model braided channel

A certain pattern of channel is the product of its self-adjustment under given boundary, discharge and sediment conditions. Based upon the principle of process-response model, an experimental study with 18 runs is carried out in LESRC. This paper is focused on the variation of the energy dissipation versus the channel morphology during and after the bedmaking process of braided channel. The results show that there exists a good empirical relationship between the energy dissipation rate and channel morphology. According to this relationship and the theory of minimum rate of energy dissipation, the authors explain the metamorphosis of the model channel with the development of the braided river.

Study on Braiding Parameters of a Biodegradable Nerve Regeneration Conduit with Regular Braided Structure

A biodegradable nerve regeneration conduit has been developed by the regular braided technique on a spindle-braiding machine. The geometry property indexes of braided nerve conduit consist of pitch, density, wall thickness and porosity etc. In this article, the influences of the braiding parameters i.e. the linear density of yarn, gear ratio and spindle number of the braiding machine on these geometry property indexes of nerve conduit were discussed from which the optimal braiding parameters were obtained.

Tensile Properties of 3-Dimension-4-directional Braided C_f/Si C Composite based on Double-scale Model

The longitude tensile properties of 3-Dimension-4-directional（3D-4d） braided C/Si C composites（CMCs） were investigated with the help of a double scale model. This model involves micro-scale and unit-cell scale. In micro-scale, the tensile properties of fiber tows which involves matrix cracking, interfacial debonding, and fiber failure are studied. The unit-cell scale model can reflect the braided structure and simulate the tensile properties of 3D-4d CMCs by introducing the tensile properties of fiber tows into it. Quasi-static tensile tests of 3D-4d braided CMCs were performed on a PWS-100 test system. The predicted tensile stressstrain curve by the double scale model is in good agreement with that of the experimental results.

Preparation and Characterization of Resistive Strain Sensor Based on Braided Skin-Core Rope

This study proposed a new yarn-like strain sensor on the basis of the braided skin-core rope,and investigated the effect of braiding structures on the sensing properties of sensors.The morphology and electromechanical properties of the strain sensor with different braiding structures were compared and evaluated.The results show that the sensing performance of the sensor from a braided skin-core rope depends on both the number of yarns in braiding and the metallized process of braided rope.Generally,the present stretchable skin-core rope-based sensor provides a basis for the formation of a highly sensitive sensing structure.

Effects of Fiber Volume Fraction on Damping Properties of Three-Dimensional and Five-Directional Braided Composites

The effects of fiber volume fraction on damping properties of carbon fiber three-dimensional and five-directional( 3D-5Dir)braided carbon fiber / epoxyres in composite cantilever beams were studied by experimental modal analysis method. Meanwhile,carbon fiber plain woven laminated / epoxy resin composites with different fiber volume fraction were concerned for comparison. The experimental result of braided specimens shows that the first three orders of natural frequency increase and the first three orders of the damping ratios of specimens decrease, when the fiber volume fraction increases. Furthermore,larger fiber volume fraction will be valuable for the better anti-exiting property of braided composites,and get an opposite effect on dissipation of vibration energy. The fiber volume fraction is an important factor for vibration performance design of braided composites. The comparison between the braided specimens and laminated specimens reveals that 3D braided composites have a wider range of damping properties than laminated composites with the same fiber volume fractions.

Torque and Topology of Braided DNAs under Tension

Double helix DNAs become intertwined around one another during replication and recombination.Here we used magnetic tweezers to make braided DNA molecules and measured their torques under various catenations(Ca)at forces ranging from 0.3 to 8 pN.Images of braided DNA constructs under tensions were captured by scanning electron microscopy which showed major and minor grooves of DNAs and plectonemes of the braids.When the two DNA molecules were braided,the extension decreased as the catenation increased from 0 to 50 turns.We used a thermodynamic Maxwell relation to deduce the torque by integrating the change in the braid extension as a function of the force.The torque increased with the catenation,force and intertether distance until the catenation reached a buckling point.Under the condition of 2 pN force and Ca=20,the torque was computed to be 31,21 and 15 pN nm for the braids of which the intertether distances were 54%,31%and 26%of the DNA contour length,respectively.At an 8.03 pN holding force,the torque was computed to be 76 pN nm as the catenation increased from 0 to 30 turns,or as the catenation density varied from 0 to 0.053.The torque reached a plateau when the catenation increased above 20,indicating formation of braid-plectonemes.The twist modulus increased with the catenation prior to reaching a peak.Before reaching the peak,the moduli were higher than those of a single twisted DNA under the same catenation and applied force.Our experimental data agrees well with the calculation results by a recently developed semiflexible polymer model.Our measurements of the nonlinear torque of the braid establish new fundamental properties of DNA intertwining,which is key to understanding DNA replication and gene expression.The speaker will also introduce briefly other projects in the Xiao group including direct measurements of theforce spectrum of single unlabeled proteins such as adhesive nano-fibers for biofilm,the screening of integrin-targeted peptides drugs by single cell approaches,and the micromechanical approach for determining the survival rate of stem cells.

Modification of Longitudinal Modulus of 3D Full Five Directional Braided Composite Materials Base on Energy Theory

The aim of this paper is to investigate the longitudinal modulus of three dimensional full five directional (3Df5d) braided composite. First, the analytical model of the internal unit cell is established based on its topological structure. Then, according to the intrinsic relation of different cells, the axial moduli of internal, surface and corner cells are systematically deduced, and the influence of corner-cell periodic discontinuity on the moduli is also analyzed. Finally, considering the actual shape of axial yarns after consolidation, the longitudinal moduli of the different cells are modified based on energy theory. The technology factor λ is also proposed in this modification. The results show that the axial mechanical properties of this material can be strongly designable. The straightness of the axial yarns greatly affects the longitudinal modulus. Technology factor λ is between 1 to 2, corresponding to the minimum and the maximum modulus, respectively.

Flow patterns and critical criteria of thermally stratified shear flow in braided rivers

Flow characteristics of thermally stratified shear flow in braided rivers are particularly complicated and poorly understood. In this study, a series of typical flow patterns was examined and their critical criteria were determined. Four flow patterns were identified: mixed, locally unstable, continuously stratified, and two-layer flow. Temperature distributions of the four types of flow patterns were analyzed and compared.The critical Froude numbers for unstable flow, FDcr1, and stable flow, FDcr2, were determined to be 6 and 1, respectively, and comparison of FDcr1 and FDcr2 to the peak Froude numbers, FD1 at the outer bank and FD2 at the inner bank along the anabranch, allowed the flow patterns to be assessed. Then, a discriminant based on initial Jeffreys-Keulegan stability parameters was established to distinguish the flow stages from twolayer flow to completely mixed flow. It is indicated that the three critical Jeffreys-Keulegan parameters increased with the diversion angle of braided rivers. Results also show that, compared to the stratified flow in straight and curved channels, it was more difficult for braided stratified flow to maintain as two-layer flow, and it more easily became mixed flow. Consequently, empirical expressions for stability criteria of the thermally stratified shear flow in braided rivers are presented.

Torsion properties of poly (glycolide-co-L-lactide) biodegradable braided regeneration conduits for peripheral nerve repair

BACKGROUND： Poly （glycolide-co-L-lactide） （PGLA） braided regeneration conduits have been shown to be biocompatible for the repair of damaged nerve. Mechanical properties, such as radial compression and torsion, greatly influence nerve regeneration and functional recovery. OBJECTIVE： To observe the influence of conduit parameters and coating methods on torsion properties in an in vitro-degradation environment and at normal temperature. DESIGN, TIME AND SE＇I-FING： An in vitro, comparative study using repeated measures was performed at the College of Textiles, Donghua University, China from January 2005 to December 2007. MATERIALS： PGLA fiber and yarn （Shanghai Bio-TianQing, China）, as well as torsion property testing instrument （LaiZhou Electronic Instrument, China）, were used in the present study. METHODS： A total of 16 types of conduits were constructed according to braiding structures （regular/triaxial）, angles （50°/55°/60°/65°）nd coating methods （coated/uncoated）. At normal temperature, torsion properties of all conduits were tested at a predefined constant angle of 90°. Coated and uncoated conduits, which were triaxial and 65°, were incubated in a 5% CO2 incubator at 37 ℃ to simulate an in vitro degradation environment, and then torsion properties were tested at 4, 7, 11, 14, 17, 21,24, and 28 days in culture. MAIN OUTCOME MEASURES： Maximal torsion strength and torsion strength-torsion angle curve of conduits at normal temperature, as well as torsion strength-torsion angle curve, loss of torsion strength, and change in maximal torsion strength in an in vitro degradation environment. RESULTS： At normal temperature, the torsion properties of the triaxial structure were superior to the regular structure. Coated conduits performed better than uncoated ones, and the larger braiding angles exhibited superior torsion properties （P 〈 0.05）. In the in vitro degradation environment, with degradation time, torsion strength of uncoated conduits was deceased gradually and the loss of torsion strength was increased fast. Torsion strength of coated conduits was increased first and decreased afterwards; the loss of torsion strength was decreased slowly till 14 days; both became identical after 14 days （P 〉 0.05）. CONCLUSION： Torsion properties of coated conduits with a triaxial structure and large braiding angle were superior to uncoated conduits with regular structures and small braiding angles.

Effective Thermal Conductivity for 3D Five-Directional Braided Composites Based on Microstructural Analysis

A method for predicting effective thermal conductivities(ETCs) of three-dimensional five-directional(3D5D) braided composites is presented. The effective thermal conductivity prediction method contains a digital image processing technology. Multiple scanning electron microscopy(SEM)images of composites are analyzed to obtain actual microstructural features. These actual microstructural features of 3D5D braided composites are introduced into representative volume element(RVE) modeling. Apart from applying actual microstructural features,compression effects between yarns are considered in the modeling of RVE,making the RVE more realistic. Therefore,the ETC prediction method establishes a representative unit cell model that better reflects the true microstructural characteristics of the 3D5D braided composites. The ETCs are predicted with the finite element method. Then thermal conductivity measurements are carried out for a 3D5D braided composite sample.By comparing the predicted ETC with the measured thermal conductivity, the whole process of the ETC prediction method is proved to be effective and accurate,where a relative error of only 2.9 % is obtained.Furthermore,the effects of microstructural features are investigated,indicating that increasing interior braiding angles and fiber fill factor can lead to higher transverse ETCs. Longitudinal ETCs decrease with increasing interior braiding angles,but increase with increasing fiber fill factor. Finally,the influence of variations of microstructure parameters observed in digital image processing are investigated. To explore the influence of variations in microstructural features on variations in predicted ETCs,the actual probability distributions of microstructural features obtained from the 3D5D braided composite sample are introduced into the ETC investigation. The results show that,compared with the interior braiding angle,variations in the fiber fill factor exhibit more significant effects on variations in ETCs.

Elastic Modulus Prediction of Three-dimension-4 Directional Braided C_f/SiC Composite Based on Double-scale Model

Double-scale model for three-dimension-4 directional（3D-4d） braided C/SiC composites has been proposed to investigate its elastic properties. The double-scale model involves micro-scale that takes fiber/ matrix/porosity in fibers tows into consideration with unit cell which considers the 3D-4d braiding structure. Micro-optical photographs of composites have been taken to study the braided structure. Then a parameterized finite element model that reflects the structure of 3D-4d braided composites is proposed. Double-scale elastic modulus prediction model is developed to predict the elastic properties of 3D-4d braided C/SiC composites. Stiffness and eompliance-averaging method and energy method are adopted to predict the elastic properties of composites. Static-tension experiments have been conducted to investigate the elastic modulus of 3D-4d braided C/SiC composites. Finally, the effect of micro-porosity in fibers tows on the elastic modulus of 3D-4d braided C/SiC composites has been studied. According to the conclusion of this thesis, elastic modulus predicted by energy method and stiffness-averaging method both find good agreement with the experimental values, when taking the micro-porosity in fibers tows into consideration. Differences between the theoretical and experimental values become smaller.

Theoretical prediction of stiffness and strength of three-dimensional and four-directional braided composites

Based on unit cell model, the 3D 4-directional braided composites can be simplified as unidirectional composites with different local axial coordinate system and the compliance matrix of unidirectional composites can be defined utilizing the bridge model. The total stiffness matrix of braided composites can be obtained by the volume average stiffness of unidirectional composites with different local axial coordinate system and the engineering elastic constants of braided composites were computed further. Based on the iso-strain assumption and the bridge model, the stress distribution of fiber bundle and matrix of different unidirectional composites can be determined and the tensile strength of 3D 4-directional braided composites was predicted by means of the Hoffman＇s failure criterion for the fiber bundle and Mises＇ failure criterion for the matrix.

DETERMINATION OF INTERNAL STRAIN IN 3-D BRAIDED COMPOSITES USING OPTIC FIBER STRAIN SENSORS

A reliable understanding of the properties of 3-D braided composites is of primary importance for proper utilization of these materials. A new method is introduced to study the mechanical performance of braided composite materials using embedded optic fiber sensors. Experimental research is performed to devise a method of incorporating optic fibers into a 3-D braided composite structure. The efficacy of this new testing method is evaluated on two counts. First, the optical performance of optic fibers is studied before and after incorporated into 3-D braided composites, as well as after completion of the manufacturing process for 3-D braided composites, to validate the ability of the optic fiber to survive the manufacturing process. On the other hand, the influence of incorporated optic fiber on the original braided composite is also researched by tension and compression experiments. Second, two kinds of optic fiber sensors are co-embedded into 3-D braided composites to evaluate their respective ability to measure the internal strain. Experimental results show that multiple optic fiber sensors can be co-braided into 3-D braided composites to determine their internal strain which is difficult to be fulfilled by other current existing methods.

Generalized braided Hopf algebras

The concept of （f, σ）-pair （B, H）is introduced, where B and H are Hopf algebras. A braided tensor category which is a tensor subcategory of the category ^HM of left H-comodules through an （f, σ）-pair is constructed. In particularly, a Yang-Baxter equation is got. A Hopf algebra is constructed as well in the Yetter-Drinfel＇d category H^HYD by twisting the multiplication of B.