Local failure mechanism of sand-blocking fence in latticed dune along desert roads

The latticed dunes in the Tengger Desert are widely distributed,and the sand-blocking fence placed here are highly susceptible to local failure due to complex wind-sand activities,posing a serious threat to the safe operation of the highway.To explore the local failure mechanism of sand-blocking fence in the latticed dune area,the local failure of sand-blocking fence in the latticed dune areas along the Wuhai-Maqin Highway in China was observed.Taking the first main ridge of the latticed dune as the placement location,the structure of the wind-sand flow field of sand-blocking fence placed at top,the bottom and the middle of windward slope was analyzed by Computational Fluid Dynamics(CFD).The results show that when placed at top of the first main ridge,the wind speed near the sand-blocking fence is the highest,up to 15.23 m/s.Therefore,the wind load strength on the sand barrier is correspondingly larger,up to 232.61 N∙m-2.As the strength of material continues to decrease,the nylon net is prone to breakage.The roots of the angle steel posts are susceptible to hollowing by vortex action,which can cause sand-blocking fence to fall over in strong wind conditions.When placed at the bottom of windward slope,wind speed drop near sand-blocking fence is greatest,with the decrease of 12.48-14.32 m/s compared to the original wind speed.This is highly likely to lead to large-scale deposition of sand particles and burial of the sand-blocking fence.When placed in the middle of windward slope,sand-blocking fence is subjected to less wind load strength(168.61N∙m-2)and sand particles are mostly deposited at the bottom of windward slope,with only a small amount of sand accumulating at the root of sand-blocking fence.Based on field observations and numerical modelling results,when the sand-blocking fence is placed in latticed dune area,it should be placed in the middle of the windward slope of the first main ridge as a matter of priority.Besides the sand-blocking fence should be placed at the top of the first main ridge,and sand fixing measures should be added.

Flow field, sedimentation, and erosion characteristics around folded linear HDPE sheet sand fence: Numerical simulation study

Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy areas. The wind and sand flow in the region is notably bi-directional. To shield railroads from sand, a unique sand fence made of folded linear high-density polyethylene(HDPE) is used, aligning with the principle that the dominant wind direction is perpendicular to the fence. This study employed field observations and numerical simulations to investigate the effectiveness of these HDPE sand fences in altering flow field distribution and offering protection. It also explored how these fences affect the deposition and erosion of sand particles. Findings revealed a significant reduction in wind speed near the fence corner;the minimum horizontal wind speed on the leeward side of the first sand fence(LSF) decreased dramatically from 3 m/s to 0.64 m/s. The vortex area on the LSF markedly impacted horizontal wind speeds. Within the LSF, sand deposition was a primary occurrence. As wind speeds increased, the deposition zone shrank, whereas the positive erosion zone expanded. Close to the folded corners of the HDPE sand fence, there was a notable shift from the positive erosion zone to a deposition zone. Field tests and numerical simulations confirmed the high windproof efficiency(WE) and sand resistance efficiency(SE) in the HDPE sand fence. Folded linear HDPE sheet sand fence can effectively slow down the incoming flow and reduce the sand content, thus achieving good wind and sand protection. This study provides essential theoretical guidance for the design and improvement of wind and sand protection systems in railroad engineering.

Protective benefit of folded linear HDPE board sand fences along the Golmud-Korla Railway,China:Field observation and wind tunnel study

The Milan Gobi area of the Golmud-Korla Railway in northwest China is located in the lower dispersal area of the mountain pass and has strong winds with evident double wind direction characteristics.This study introduced a novel sand fence deployment technique,termed‘folded linear deployment',designed to position the sand fence orthogonally to the two predominant wind directions for optimal protection.This study used wind tunnel and field tests to evaluate the wind and sand flow characteristics,as well as the windproof and sandresistant performance of folded linear HDPE(Highdensity polyethylene)board sand fences.The results suggest that the airflow around the fence creates clear zoning characteristics.The deceleration area on the BSF(backwind side of the sand fence)is much larger than that on the DSF(downwind side of the sand fence).Thus,sand particles are primarily deposited on the BSF.At different wind speeds,the airflow at 2 and 5 h on the DSF is not disturbed.The WSP(wind speed profile)presents a logarithmic distribution.The airflow is disturbed at 1-20 h on the BSF,and the WSP gradually deviates from the logarithmic law.However,as the airflow moves away from the fence,the WSP gradually approaches a logarithmic distribution.Meanwhile,the WPE(windproof efficiency)and SRE(sand-resistant efficiency)of the sand fence exceed 80%.In addition,the results of wind tunnel tests are compared with those of field tests.The overall dispersion is good,and the best dispersion is found at z/H=2.00,indicating good agreement between the two test results.This study provides a scientific basis for the design of sand hazard control measures,similar to the railway project in the Gobi Gale area.

基于多特征SAD-Census变换的立体匹配算法

视差不连续区域和重复纹理区域的误匹配率高一直是影响双目立体匹配测量精度的主要问题,为此,本文提出一种基于多特征融合的立体匹配算法。首先,在代价计算阶段,通过高斯加权法赋予邻域像素点的权值,从而优化绝对差之和(Sum of Absolute Differences,SAD)算法的计算精度。接着,基于Census变换改进二进制链码方式,将邻域内像素的平均灰度值与梯度图像的灰度均值相融合,进而建立左右图像对应点的判断依据并优化其编码长度。然后,构建基于十字交叉法与改进的引导滤波器相融合的聚合方法,从而实现视差值再分配,以降低误匹配率。最后,通过赢家通吃(Winner Take All,WTA)算法获取初始视差,并采用左右一致性检测方法及亚像素法提高匹配精度,从而获取最终的视差结果。实验结果表明,在Middlebury数据集的测试中,所提SAD-Census算法的平均非遮挡区域和全部区域的误匹配率为分别为2.67%和5.69%,测量200~900 mm距离的平均误差小于2%;而实际三维测量的最大误差为1.5%。实验结果检验了所提算法的有效性和可靠性。

Effect of fence opening configurations on dune development

Fences have been widely used in coastal protection engineering for their low cost,simple deployment,and easy integration with ecosystems.The effects of fence porosity and height on dune development have been investigated while not much attention has been paid to the effects of fence opening configurations,such as opening size and geometry,and porosity distributions.In this study,we deployed eight fences with same height and similar porosity,but different opening configurations on a sandy beach in Pingtan,Fujian Province.Results indicate that there is a similar two-dune-one-trough pattern for all fences at the beginning of dune development,and opening size,orientation,and geometry,and porosity distribution control the leeward dune peak locations.Fences with small openings and non-uniform porosity have high trapping efficiency,and upper denser porosity may be the optimal design as these fences have the highest trapping efficiency and capacity.The conclusions from this study can provide guidance on practical fence design.

Dramatical hydro-sedimentary changes induced by bamboo fences over mangrove tidal flat of the largest delta in Beibu Gulf, southwestern China

Mangrove forest is one of the most important ecological and environmental resources by effectively promoting tidal flat deposition and preventing the coastal region from typhoon.However,there have been mass loss of mangrove forests due to anthropogenic activities.It is an urgent need to explore an effective way for mangrove restoration.Here,three rows of bamboo fences with hydro-sedimentary observation set over Aegiceras corniculatum mangrove tidal flat of the Nanliu Delta,the largest delta of Beibu Gulf,China,were conducted to analyze the hydro-sedimentary variations induced by bamboo fences.Results identified that the mean horizontal velocity Um per burst(20 min)decreased by as much as 71%and 40%in comparison with those without bamboo fences in March and November,respectively,when the tidal current entering the bamboo area during flood.The maximum of mean horizontal flow velocity Um-max at bamboo area was 50%–75%of that without bamboo fences during ebb tide.The suspended sediment concentration of bamboo area suggested a maximum reduction of 57%relative to bare flat during flood,and was 80%lower than bare flat at ebb peak.Moreover,the turbulent kinetic dissipationεat flood tide was significantly higher than that at ebb tide,while the bamboo fences greatly increased the turbulent kinetic dissipationεby 2 to 5 times relative to bare flat,resulting in an increase of the bed elevation by inhibiting the sediment incipient motion and intercepting suspended sediment.The siltation rate at the bamboo area was 140%and 29.3%higher than that at the bare flat and the region covered with A.corniculatum,respectively.These results highlight that bamboo fences can effectively attenuate tidal current and thus promote siltation over mangrove flat,which contribute great benefit to mangrove survival.

Characteristics of snow cover distribution along railway subgrade and the protective effect of snow fences

Railways built in cold,snowy,and lightly populated areas are subjected to wind and snow disasters.In this study,we selected a snow hazard prevention and control section of the Altay–Zhundong Railway in Xinjiang Uygur Autonomous Region of China as the research object.We investigated the deposited snowfall variation characteristics on the two sides and in the embankment pavement area of snow fences with different porosities,fence heights,and arrangement distances using single-factor tests and orthogonal tests based on global atmospheric reanalysis climate data,field survey data,and a multi-phase flow analysis model.The results showed significant differences in the characteristics of snow cover distribution and snow cover thickness between the embankment and the cutting in the absence of snow protection measures.The maximum snow cover thickness of the embankment pavement decreased by 12.6%relative to the cutting pavement.The snow cover thickness of the embankment exhibited an increasing trend from windward shoulder to leeward shoulder,whereas the snow cover thickness of the cutting presented a declining trend from windward shoulder to leeward toe.In the collaborative prevention and control of snow fences and embankments,the three factors can be ranked in terms of their sensitivity to deposited snowfall within the influence scope of snow fences as follows:fence height>arrangement distance>porosity.At the same time,fence height yielded a significant relationship for the influence scope of snow fences(P<0.05).The three factors can also be ranked in terms of their sensitivity to deposited snowfall on the pavement as follows:porosity>fence height>arrangement distance.For the embankment protection of the Altay–Zhundong Railway against wind and snow,snow fence with a porosity of 75%,a fence height of 4.8 m,and an arrangement distance from the embankment of 60 m produced the best snow control effect.By revealing the characteristics of snow cover distribution along railway subgrade and the protective effect of snow fences,this study provides valuable references for the engineering applications of railway construction in areas prone to wind and snow disasters.

Fences and hydropower:Important but overlooked Human Footprint

Human activities have impacted 77%of the terrestrial ecosystems(excluding Antarctica),and the remaining areas are becoming increasingly endangered.Mapping spatiotemporal dynamics of Human Footprint has been used to evaluate the cumulative interference on terrestrial environments globally.However,fences and hydropower,two widespread and rapidly expanding infrastructures,have not been considered regarding Human Footprint,despite their complicated and extensive effects on ecosystem functioning and species survival.Previous work has proved that fences increase habitat fragmentation,disrupt migratory routes,inadvertently trap and kill wildlife,and hinder genetic exchange.Hydropower construction also caused habitat loss,fragmentation,and degradation.These impacts have received global concern,but fences around the world are difficult to be detected due to the limitations of current cartographic technologies.Furthermore,the effect of hydropower on the terrestrial environment has been underestimated,making the research on this topic at a global scale still in its infancy.Therefore,building an observation network of global fences and hydropower is a necessary step to move forward in the assessment of the impact of human activities on our planet,but also to better provide scientific support for policy-making regarding global biodiversity conservation,the identification of protected areas,and the prioritization of ecological restoration areas.

Effects of long-term fencing on soil microbial community structure and function in the desert steppe,China

One of the goals of grazing management in the desert steppe is to improve its ecosystem.However,relatively little is known about soil microbe communities in the desert steppe ecosystem under grazing management.In this study,we investigated the diversity and aboveground biomass of Caragana korshinskii Kom.shrub communities in long-term fencing and grazing areas,combined with an analysis of soil physical-chemical properties and genomics,with the aim of understanding how fence management affects plant-soil-microbial inter-relationships in the desert steppe,China.The results showed that fence management(exclosure)increased plant diversity and aboveground biomass in C.korshinskii shrub area and effectively enhanced soil organic carbon(233.94%),available nitrogen(87.77%),and available phosphorus(53.67%)contents.As well,the Shannon indices of soil bacteria and fungi were greater in the fenced plot.Plant-soil changes profoundly affected the alpha-and beta-diversity of soil bacteria.Fence management also altered the soil microbial community structure,significantly increasing the relative abundances of Acidobacteriota(5.31%-8.99%),Chloroflexi(3.99%-5.58%),and Glomeromycota(1.37%-3.28%).The soil bacterial-fungal co-occurrence networks under fence management had higher complexity and connectivity.Based on functional predictions,fence management significantly increased the relative abundance of bacteria with nitrification and nitrate reduction functions and decreased the relative abundance of bacteria with nitrate and nitrite respiration functions.The relative abundances of ecologically functional fungi with arbuscular mycorrhizal fungi,ectomycorrhizal fungi,and saprotrophs also significantly increased under fence management.In addition,the differential functional groups of bacteria and fungi were closely related to plant-soil changes.The results of this study have significant positive implications for the ecological restoration and reconstruction of dry desert steppe and similar areas.

第251首Over the Fence-中的戏剧独白特征

狄金森第251首Over the Fence-具有戏剧独白的一些典型特征,如叙述者为充满童趣的小女孩,体现戏剧情境的词语包括"fence"、"strawberries"和"nice",揭示戏剧冲突的词汇或从句包括"over the fence"、"but"和"if"条件句。对这些特征的阐释可提供多元解读狄金森诗歌作品的空间,从而既有助于管窥当时社会的总体风貌和两性不平等问题,还能更加丰富对狄金森诗歌作品思想深度和艺术特色的相关研究。

仓库三维重建系统中改进双目匹配SAD算法研究

利用双目立体视觉技术实现危险化学品仓库的三维重建是库内安全监测的有效手段,立体匹配是其中的重点和难点。提出一种利用加权SAD算法和灰度共生矩阵的双目立体像对稠密匹配算法,该算法对传统SAD匹配算法做出改进,引进服从二维高斯分布的加权系数求出初始视差图,然后结合灰度共生矩阵的4个纹理特征,利用图像纹理信息对空洞进行填充,得到了优化的视差结果。实验结果表明,该算法在标准数据集及仓库模型具有较好的适用性。

Impact of pond and fence aquaculture on reservoir environment

With the rapid development of aquaculture in lakes and reservoirs, its negative effects on water quality and aquatic organisms are clearly emerging. Toward a better understanding of these effects, chemical and biological monitoring was conducted in the Fangbian Reservoir to study the relationship between aquaculture and eutrophication. As a domestic water supply source, this reservoir has reached the mesotrophic level. The concentrations of total nitrogen （TN） and total phosphorus （TP） in the Fangbian Reservoir have frequently exceeded the prescriptive level according to the Environmental Quality Standardgfor SurJace Water （GB3838-2002）. Pond and fence aquaculture feeding is the main cause of high levels of nitrogen and phosphorus, accounting for nearly half of the total pollution, and causing the reservoir environmental capacity to be exceeded. The amounts of nitrogen and phosphorus that went directly to the reservoir through the residual bait and fish droppings in fence aquaculture were 42 768 kg per year and 10 856 kg per year respectively, from 2007 to 2009. About 2 913 kg of nitrogen and 450 kg of phosphorus were imported to the reservoir through the exchange of water from the culturing ponds at the same time. Therefore, controlling the aquaculture scale and promoting eco-aquaculture are key measures for lessening the eutrophication degree and improving the water quality.

Mechanism and effects of snow accumulations and controls by lightweight snow fences

This paper investigates the snowdrifts caused by lightweight fences along the lines on the flatland through the computational fluid dynamics method. The characteristic ambient flows around the solid fences and the porous fences with varied heights and bottom wind gaps are simulated in the numerical model, and the working mechanism of ＂interception＂ and ＂scouring＂ of the lightweight fences are analyzed. Based on the friction velocities near the ground, two sets of criteria are proposed to evaluate the deposition and erosion effects of different fences. According to flow separation and reattachment, the simplified relationships between the most likely positions for snow accumulations and fence parameters are devel- oped. The study indicates that the capabilities for snow interception by the solid fence without wind gap and the distance from which to the second snow coverage center both increase with the fence height. Furthermore, it is found that the scouring range for snow surface increases significantly with the size of wind gap, and the snow accumulation rate on the leeward side decreases with the increasing fence porosity.

The blocking effect of the sand fences quantified using wind tunnel simulations

Fences are one of the most effective measures to prevent and control wind-blown sand disasters,and the blocking effect of fences is largely determined by their porosity and height(H).This study employed wind tunnel experiments to measure wind velocities on both sides of wire mesh sand fences with porosities of 75%,63%,56%,36%and heights of 10,5 and 2 cm.The effects of porosity and height on the blocking effect of the fences were evaluated on the basis of velocity variability,flow field,and the wind velocity reduction coefficient.Results show that the smaller the porosity,the stronger the blocking effect.The fence with a porosity of 36%had the strongest windproof efficiency of 0.70 and longest protection range of 9 H,and thus showed the best applicability in preventing and controlling wind-blown sand disasters.The fence with a porosity of 56%showed a windproof efficiency of 0.31 and a protection range of 7 H,which could be considered for adoption.However,fences with porosities of 75%and 63%were not recommended to be adopted,because their windproof efficiency and protection range were very small.Overall,the higher the fence,the stronger the blocking effect.The highest fence(10 cm)had the longest protection range of 90 cm,which was the best in application.Nevertheless,the 5 and 2 cm fences were almost consistent with 10 cm fence in windproof efficiency,which was still suitable for wind and sand fixation.

Synthesis and Langmuir-Blodgett Film Analysis of Atropisomers of “Picket Fence” Porphyrin

Four ＂picket fence＂ porphyrin atropisomers were respectively synthesized from the four corresponding atropisomers of meso-tetra（o-aminophenyl）porphyrin that had been chromatographed on a column eluted with petroleum ether and ethyl acetate. Results show that each atropisomer could be successfully synthesized by controlling the acylation temperature at 0 ℃. They were characterized by 1H NMR, HRMS, IR, UV-Vis and Langmuir-Blodgett（LB） film analyses. Although the results of HRMS, IR, UV-Vis analyses indicate there is no remarkable difference among the atropisomers, the results of the 1H NMR and the mean molecular areas obtained by LB film technique imply that the atropisomers are significantly discrepant. The former shows that the chemical shifts of the methyl and amide protons of each atropisomer are distinct, while the later presents that the different atropisomer molecules can occupy the different surface areas at the air/water interface.

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert, China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions： no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m（i.e., 13 H, where H denotes the fence height） downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.

Comparative evaluation of concrete sand-control fences used for railway protection in strong wind areas

Concrete-plate fences have been widely adopted for windblown sand control and mitigation along railways.However,the inclination angles of inserting the concrete plate with respect to the vertical direction,i.e.,straight or obliquely inserted concrete plates(SIP or OIP),significantly influence the efficiency of sand-control.This study performs a comparative evaluation of the SIP and OIP sand-control fences using wind tunnel testing and field monitoring data collected from the Lanzhou–Wulumuqi High-Speed Railway Project.The results show that the fence’s ability to reduce the wind speed and the sand-retaining efficiency gradually weakens with the increasing wind speed.Compared with the SIP fence,the OIP fence has a better wind speed reduction capability,stronger ability to capture fine particles below the top of the fence;it is more efficient for sand-retaining and induces stronger eddy intensity.Generally,the wind tunnel test and field monitoring results are consistent,whereas wind tunnel tests incline to overestimate wind speed reduction and sand-control efficiency.The study also finds that the aeolian sand accumulated around the fence can weaken the protection efficiency,and hence cleaning the aeolian sand accumulated around the fence should be done periodically to ensure the designed functions.

Cory's Acceptance of His African American Identity in Fences

Fences is one of the masterpieces of August Wilson's plays, and Wilson tells a story about a black family's life experiences. In this play, Cory, the second son in this family is seeking for his identity in the society. From Cory's conflict and compromise with his father, it's obvious to see Cory's pursuance for his American identity and his acceptance of his African identity.With the two identity, he finally becomes an intact man in the society.

Comparison Between Full-Scale and Model Experiments of Oil Fences

This study examines the performance of an air expansion oil fence system as deployed in two different configurations. Geometric and tension characteristics of the oil fence are investigated for （1） the system attached to two vessels and （2） the system attached to one vessel with spreading devices. Since full-scale testing can be time consuming and expensive, another component of the study was to examine how well models would perform. A scaling technique was developed and a set of experiments were conducted with a 1/20-th scale model of the oil fence in a towing tank facility. Performance resalts from the model tests were compared with those conducted at sea. The tension （N） in the full-scale results were represented by R = avb, where v is the current velocity in m/s and the values for a and b used for comparison purposes. Both sets of full-scale and model tests were conducted with an oil fence opening of 120 m and 160m. In the full-scale experiment with spreading devices attaahed to the forward ends of the oil fence, the horizontal distance of the spreading devices has a tendency to linearly increase as the current velocity increases when the warp length is as short as 50 m, but to linearly decrease as the current velocity increases when the warp length is extended to 100 m and 150 m. The spreading distance at uniform current velocitys in the model test increases as the warp length is extended. While there is no significant difference of spreading distance between the cases of 100 m and 150 m, the spreading distance becomes shorter when the warp length is 50 m.

Effects of Wind Fences on the Wind Environment around Jang Bogo Antarctic Research Station

This study investigated the flow characteristics altered by Jang Bogo Antarctic Research Station using computational fluid dynamics(CFD) modeling. The topography and buildings around Jang Bogo Station were constructed with computeraided-design data in the CFD model domain. We simulated 16 cases with different inflow directions, and compared the flow characteristics with and without Jang Bogo Station for each inflow direction. The wind data recorded by the site’s automatic weather station(AWS) were used for comparison. Wind rose analysis showed that the wind speed and direction after the construction of Jang Bogo Station were quite different from those before construction. We also investigated how virtual wind fences would modify the flow patterns, changing the distance of the fence from the station as well as the porosity of the fence. For westerly inflows, when the AWS was downwind of Jang Bogo Station, the decrease in wind speed was maximized(-81% for west-northwesterly). The wind speed reduction was also greater as the distance of the fence was closer to Jang Bogo Station. With the same distance, the fence with medium porosity(25%–33%) maximized the wind speed reduction.These results suggest that the location and material of the wind fence should be selected carefully, or AWS data should be interpreted cautiously, for particular prevailing wind directions.