Exploration of playa surface crusts in Qehan Lake, China through field investigation and wind tunnel experiments

Globally,many lakes are drying up,leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere.Therefore,understanding the characteristics and spatial distribution of playa surface crusts is important to recognize the manifestation of salt dust storms.The objective of this study was to explore the playa surface crust types as well as their spatial distribution and evolution of Qehan Lake in Inner Mongolia Autonomous Region,China to understand the salt dust release potential of different types of playa surface crusts.Various crust characteristics were investigated by field sampling in Qehan Lake,and playa surface crusts were further divided into five types:vegetated areas,salt crusts,clay flats,curly crusts,and margins.It should be noted that curly crusts were distributed in clay flats and covered only a small area in Qehan Lake.The spatial distribution characteristics of playa surface crust types were obtained by supervised classification of remote sensing images,and the salt dust release potential of crusts was explored by the wind tunnel experiments.The field investigation of Qehan Lake revealed that playa surface crust types had a circum-lake band distribution from the inside to the outside of this lake,which were successively vegetated areas,clay flats,salt crusts,and margins.The spatial distribution patterns of playa surface crust types were mainly controlled by the hydrodynamics of the playa,soil texture,and groundwater.There was a significant negative correlation between crust thickness and electrical conductivity.The results of the wind tunnel experiments showed that the initial threshold of friction wind velocity for the salt dust release was higher in clay flats(0.7–0.8 m/s)than in salt crusts(0.5–0.6 m/s).Moreover,the particle leap impact processes occurring under natural conditions may reduce this threshold value.Salinity was the main factor controlling the difference in the initial threshold of friction wind velocity for the salt dust release of clay flats and salt crusts.This study provides a scientific reference for understanding how salt dust is released from a lakebed,which may be used for ecological restoration of dry salt lakes.

On the horizontal distribution of algal-bloom in Chaohu Lake and its formation process

Based on the remote sensing images of algae, the present work analyzes the horizontal distribution characteristics of algal blooms in Chaohu Lake, China, which also reveals the frequency of algal blooms under different wind directions. Further, an unstructured-grid, three-dimensional finite-volume coastal ocean model （FVCOM） is applied to investigate the wind-induced currents and the transport pro- cess to explain the reason why algal blooms occur at the detected places. We first deduce the primary distribution of biomass from overlaid satellite images, and explain the formation mechanism by analyzing the pollution sources, and simulating the flow field and transportation process under prevailing wind over Chaohu Lake. And then, we consider the adjustment action of the wind on the corresponding day and develop a two-time scale approach to describe the whole formation process of algae horizontal distribution in Chaohu Lake. That is, on the longer time scale, i.e., during bloom season, prevailing wind determines the primary distribution of biomass by inducing the characteristic flow field; on the shorter time scale, i.e., on the day when bloom occurs, the wind force adjusts the primary distribution of biomass to form the final distribution of algal bloom.

Determining soil redistribution in Dian Lake catchment by combined use of caesium-137 and selected chemical properties

Recent development in the use of the environmental radionuclide caesium-137 for documenting rates and soil redistribution on the cultivated or uncultivated land and estimating rates of sediment deposition on represents an important advance that overcomes many of the limitations of the conventional techniques commonly applied in such investigations. A study on soil redistribution （including soil erosion and deposition） was carried out in the Dian Lake catchment, Yunnan Province, using ^137Cs and selected chemical properties. The average soil erosion rate was 1,280.2 t km^2 yr^-1. Soil erosion rate occurring on different parts of the slope was significantly different on different parts of the slope, increasing.from the top. the bottom to the middle slope. The average soil erosion rate is also different with the land use type and that of the cultivated land （1, 672. 8 t km^-2 yr^-1） is higher than oJ the uncultivated land （1.161.2t km^-2 yr^-1 ）. The result shows that landform, slope gradient and land use type are key factors that influence the size of soil erosion. In addition, we also find the SOC and TN contents and amount of the soil erosion to be correlated in the soil. With the soil erosion occurring, there are land degradation and the local eco-environmental problems, such as water eutrophication in Dian Lake.

穿湖隧道超大尺度混凝土施工期的温度效应

穿湖隧道对混凝土的防渗要求很高,而混凝土的温度效应与其开裂息息相关.采用高性能双光栅温度-应变式传感器对隧道浇筑过程中混凝土的温度以及应变进行监测,分析了其变化规律.对混凝土浇筑完成后的现场情况进行了调研,发现侧墙存在裂缝且引起了渗漏.依据现场施工情况,运用有限元法对浇筑的隧道进行模拟,将数值模拟结果与现场监测数据进行对比,验证了数值模拟结果的准确性,并对影响混凝土内外温差的因素进行了参数分析.研究结果表明:混凝土入模温度越高,其内外温差就越大;入模温度升高10℃,内外温差增加1.46℃;在夏季施工时,应注意对混凝土原料进行降温处理,保证混凝土入模温度小于30℃;环境温度下降越多,混凝土内外温差就越大;环境温度下降20℃,内外温差增加6.38℃;当环境温度降低时,应注意采取保温措施;当养护过程中需要进行保温时,建议采用木模板进行养护,但拆模时间不宜早于6 d,否则会导致混凝土表面温度迅速下降,内外温差急剧增大.

湖底隧道工程排水与消防系统设计

为将隧道受水灾和火灾可能性降至最低,以湖底隧道工程为依托,针对隧道排水与消防系统设计要点进行总结分析,应用排水与消防系统,能及早准确地预警水情与火灾,并实现即时现场报警与远程报警。该系统有效提升了隧道防汛预警和识别火灾的精准度以及应急抢险的智能化水平,能更好地保障人民群众的生命财产安全,可供类似隧道工程参考。

基于AHP-Cloud方法的城中湖隧道关键适用技术绩效评价研究

城中湖隧道是典型的复杂工程项目,需要在项目前期对关键技术适用性进行科学评价,以提供辅助决策依据。以东湖通道工程为研究对象,基于技术经济、生态工程、低碳交通多维视角,分析其关键适用技术要点,联合AHP法及云模型评价方法,构建绩效评价指标体系及评价模型,测评适用技术绩效等级,搜索识别关键不利绩效指标,弥补技术管理工作的不足。实证分析表明:湖底城市隧道空气净化系统关键技术绩效等级为中等,其不利绩效指标数居首,需紧密结合隧道工程稳定运营要求、充分调研技术可靠度、模拟技术对环境的影响、进行技术绩效评价,以降低不适用性风险。

Anomalous spin Josephson effect in spin superconductors

The spin superconductor state is the spin-polarized triplet exciton condensate,which can be viewed as a counterpart of the charge superconductor state.As an analogy of the charge Josephson effect,the spin Josephson effect can be generated in the spin superconductor/normal metal/spin superconductor junctions.Here we study the spin supercurrent in the Josephson junctions consisting of two spin superconductors with noncollinear spin polarizations.For the Josephson junctions with out-of-plane spin polarizations,the possibleπ-state spin supercurrent appears due to the Fermi momentum-splitting Andreev-like reflections at the normal metal/spin superconductor interfaces.For the Josephson junctions with in-plane spin polarizations,the anomalous spin supercurrent appears and is driven by the misorientation angle of the in-plane polarizations.The symmetry analysis shows that the appearance of the anomalous spin Josephson current is possible when the combined symmetry of the spin rotation and the time reversal is broken.

湖底隧道联络通道冻结加固施工技术研究

【目的】湖底隧道施工通常具有地质条件复杂、难度系数大、危险性高等特点,为研究冻结法在隧道下穿湖底联络通道中的施工技术要点,依托某实际地铁工程展开研究。【方法】结合地质勘察资料,综合湖底特殊地质条件及水文概况,设计采用冻结加固技术预先对周围土体进行处理,合理设计和优化开挖与构筑施工技术,对相关施工风险进行分析并提出解决措施。【结果】结果表明,冻结法施工具有较高的安全可靠性,且适用于各种复杂的水文地质,如软土、流砂以及高水压和高地压地层。【结论】本研究对城市地铁湖底联络通道的安全和有效施工具有一定的参考意义。

Research progress and development trends of highway tunnels in China

The highway tunnel system in China has in recent years surpassed Europe, the United States, and other developed countries in terms of mileage, scale, complexity, and technical achievement. Much scientific research has been conducted, and the results have greatly facilitated the rapid development of China＇s highway tunnel building capacity. This article presents the historical development of highway tunneling in China, according to specific charac- teristics based on construction and operation. It provides a systematic analysis of the major achievements and chal- lenges with respect to construction techniques, operation, monitoring, repair, and maintenance. Together with future trends of highway tunneling in China, suggestions have been made for further research, and development prospects have been identified with the for a Chinese-style highway aim of laying the foundation tunnel construction method and technical architecture.

Effects of fundamental structure parameters on dynamic responses of submerged floating tunnel under hydrodynamic loads

This paper investigates the effects of structure parameters on dynamic responses of submerged floating tunnel （SFT） under hydrodynamic loads. The structure parameters includes buoyancy-weight ratio （BWR）, stiffness coefficients of the cable systems, tunnel net buoyancy and tunnel length. First, the importance of structural damp in relation to the dynamic responses of SPT is demonstrated and the mechanism of structural damp effect is discussed. Thereafter, the fundamental structure parameters are investigated through the analysis of SFT dynamic responses under hydrodynamic loads. The results indicate that the BWR of SFT is a key structure parameter. When BWR is 1.2, there is a remarkable trend change in the vertical dynamic response of SFT under hydrodynamic loads. The results also indicate that the ratio of the tunnel net buoyancy to the cable stiffness coefficient is not a characteristic factor affecting the dynamic responses of SFT under hydrodynamic loads.

Experimental analysis of sand particles' lift-off and incident velocities in wind-blown sand flux

The probability distributions of sand particles＇ lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry （PDA） in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the X^2-test for these probability distributions, that the probability density functions （pdf＇s） of the sand particles＇ lift-off and incident velocities as well as their vertical com- ponents are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions, These pdf＇s depend on not only the sand particle diameter but also the wind speed.

An analytic study on the deflection of subway tunnel due to adjacent excavation of foundation pit

Predicting and estimating the response of sub- way tunnel to adjacent excavation of foundation pit is a research focus in the field of underground engineering. Based on the principle of two-stage method and incre- mental method, an analytic approach is suggested in this paper to solve this problem in an accurate and rapid way, and the upheavals of tunnel due to adjacent excavation are solved by analytic method. Besides, the presented method is used in the practical engineering case of Shenzhen Metro Line 11 and verified by numerical simulation and in situ measurement. Finally, a parametric analysis is performed to investigate the influence of different factors on tunnel＇s deflection. Some useful conclusions have been drawn from the research as below： The deflection results of tunnel obtained from analytic method are nearly consistent with the results getting from numerical analysis and measured data, which verified the accuracy and rationality of pre- sented method. The excavation size has a significant impact on both the displacement values and influenced range of tunnel. However, the relative distance only impacts the displacement values of tunnel, but not the influenced range of tunnel. It may provide certain reference to analyze the deflection of subway tunnel influenced by adjacent excavation.

Enhanced piezoresistivity in Ni-silicone rubber composites

This paper reports that the nickel-silicone rubber composites with enhanced piezoresistivity were synthesized with much reduced nickel concentration. A large piezosensitivity of 0.716/kPa and a gauge factor of 600 have been obtained for a composite sample with filler-polymer ratio of 2.7：1 by weight. Measurements of resistance as a function of uniaxial force reveal that the piezoresistance arises predominantly from the internal heterogeneity of the material and the effect of geometrical changes of samples under pressure is negleetably small. The nonlinear current-voltage characteristic of the composite depends strongly on the filler content, the initial compression and the electrical current flowing in the sample. Ohmic behaviour has been observed only in the highly compressed samples. The breakdown strength decreases with increasing filler content of the composite. Both I - V and R - f characteristics indicates that the resistivity of the composites decreases with electrical field, suggesting that the composite may also be used to make voltage sensitive resistors for protecting circuits. All the experimental results favour a quantum tunnelling mechanism of conductivity. It finds that the concept ＇negative resistance＇, often used to describe the phenomena that current decreases with increasing voltage, is not appropriate and should be avoided.

Aeroelastic modeling of wind loading on a cable-net supported glass wall

Wind loading study on a cable-net supported glass wall is conducted by means of wind tunnel tests. An equiva- lent aeroelastic model is designed and constructed. Response of displacements of the wall is measured and analyzed. In order to design a glass wall under wind loading, the ＂wind- vibration factor＂ is estimated and discussed. In fact, the mech- anism of wind acting on the wall is commonly known not only as positive pressure, but also as negative pressure caused by the flow separation on the corners of the building. Due to the diffidence in the mechanism of wind acting, two typi- cal response cases are classified. The results show that the dynamic response of the structure caused by the negative pressure is stronger than that of the positive pressure case. To determine the aerodynamic wind loading on a flexible part of structure on a building, wind tunnel study may be useful and play an important role.

Experimental study on correlation between turbulence and sound in a subsonic wind tunnel

In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91 mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quadrupole sources of aerodynamic noise at different velocities is investigated, and it is demonstrated that the contribution of the monopole is dominant, while the shares due to the dipole and quadrupole remain less important. In addition, it is found that the sound waves have a modest impact on the measured longitudinal turbulence and are generated essentially by eddies.

A PRELIMINARY RESEARCH ON THE CLIMATIC RECORDS OF LACUSTRINE DEPOSITS OF QINGTU LAKE IN THE LAST 6000 YEARS

A preliminary study on the advance and the retreat of Qingtu Lake and its climatic records of the Holocene lacustrine deposits has been made through comprehensive analysis. The study shows that the modes characteristics of climatic change in Eastern Hexi Corridor was provided with the corresponding relationship of warm moist and cold dry during the scale longer than hundred years. As a result of climatic changes and human activities, Qingtu Lake cycle has undergone four lake retreated and three lake advanced stages since 6000 a B.P. Based on the study on lacustrine sedimentary color, grain size, Fe 3+ /Fe 2+ and organic matter, the authors put forward that a warm period existed during the phase of 335-480 A.D. in the studied area. This warm period could be further testified by a lot of evidences obtained from the historical documents and the natural records of Qingtu Lake. In brief, the evolution of lakes in Eastern Hexi Corridor is characterized by sedimentary continuity, fast sedimentary rate and high resolution, it not only indicate the paleoenvironmental and climatic change in Holocene, but also can reflect the intensity of Eastern Asia monsoon.

Lithium Behavior in Salt-water System Explored by Molecular Dynamics Simulation

The molecular dynamics simulation method was adopted to study the transient characteristics of Li^+,CO3^2-,and SO4^2- in Na^+,K^+,Li^+,Cl^-,and SO4^2-/H2O system.The composition of Na^+,K^+,Li^+,Cl^-,SO4^2- and CO3^2- was selected to optimize the initial structural model and conduct dynamic simulation.The mean azimuth shift and diffusion coefficient of Li^+,CO3^2-,and SO4^2- in the system,the radial distribution function and potential energy between Li^+ and -OW,SO4^2- and -OW as well as CO3^2- and -OW,and the dielectric constant of hydrogen bond were expounded and analyzed.At the same time,the Li enrichment behavior in the evaporation process of salt lake brine was analyzed based on the simulated data.The results show that the simulation results are in good agreement with the experimental values,which verifies that,compared with other ions,the crystallization of Li^+ and SO4^2- occurs earlier after reaching saturation.

Stabilization variation of organic conductor surfaces induced by π-π stacking interactions

The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscopy（STM）.The three bulk-truncated surfaces are all ac-surface,which are terminated with TCNQ molecular arrays.On the ac-surface of PrQ（TCNQ） 2,the TCNQ molecules form a tetramer structure with a wavelike row behavior and a 纬 angle of about 18掳 between adjacent molecules.Moreover,the dimer structures are resolved on both ac-surfaces of MPM（TCNQ） 2 and MEM（TCNQ） 2.In addition,the tetramer structure is the most stable structure,while the dimer structures are unstable and easily subject to the STM tip disturbance,which results in changeable unit cells.The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the ＇蟺-atom model＇.

Formation and local electronic structure of Ge clusters on Si（111）-7×7 surfaces

We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunnelling spectroscopy （STS）. Atom-resolved STM images reveal that the Ce atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ce clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the ＇dark sites＇ of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ce clusters. Low-temperature STS of the Ce clusters reveals that there is a band gap on the Ce cluster and the large voltage threshold is about 0.9 V.