Experimental Study on the Variation of Optical Imaging Characteristics with Zenith Angle due to Internal Solitary Waves in Sunglint

Internal solitary waves(ISWs)change the roughness of the sea surface,thus producing dark and bright bands in optical images.However,reasons for changes in imaging characteristics with the solar zenith angle remain unclear.In this paper,the optical imaging pattern of ISWs in sunglint under different zenith angles of the light source is investigated by collecting optical images of ISWs through physical simulation.The experiment involves setting 10 zenith angles of the light source,which are divided into area a the optical images of ISWs in the three areas show dark-bright mode,single bright band,and bright-dark mode,which are consistent with those observed by optical remote sensing.In addition,this study analyzed the percentage of the dark and bright areas of the bands and the change in the relative gray difference and found changes in both areas under different zenith angles of the light source.The MODIS and ASAR images display a similar brightness-darkness distance of the same ISWs.Therefore,the relationship between the brightness-darkness distance and the characteristic half-width of ISWs is determined in accordance with the eKdV theory and the imaging mechanism of ISWs of the SAR image.Overall,the relationship between them in the experiment is almost consistent with the theoretical result.

Effect of attack angle on the electromagnetic wave transmission characteristics in the hypersonic plasma sheath of a re-entry vehicle

The attack angle may greatly affect the hypersonic plasma sheaths around the re-entry vehicle,thereby affecting the transmission characteristics of electromagnetic(EM)waves in the sheaths.In this paper,we propose an integrated three-dimensional(3D)model with various attack angles and realistic flying conditions of radio attenuation measurement C-II(RAM C-II)re-entry tasks for analyzing the effect of the attack angle on the transmission characteristics of EM waves in the sheaths.It is shown that the electron density and collision frequency of the sheath on the windward side can be increased by an order of magnitude with the increase of the attack angle.Meanwhile,the thickness of the sheath on the leeward side is increased where the electron density and collision frequency are reduced.The EM waves are mainly reflected on the windward plasma sheath due to the cutoff effect,and the radio-frequency(RF)blackout is mitigated if the antenna is positioned on the leeward side.Thus,by planning the trajectory properly and installing the antenna accordingly during the re-entry,it is possible to provide an approach for mitigation of the RF blackout problem to an extent.

Jet Characteristics and Optimization of a Cavitation Nozzle for Hydraulic Fracturing Applications

Hydraulic jetting is a form of fracturing that involves using a high-pressure jet of water to create fractures in the reservoir rock with a nozzle serving as the central component of the hydraulic sandblasting perforation tool.In this study,the flow behavior of the nozzle is simulated numerically in the framework of a SST k-ωturbulence model.The results show that the nozzle structure can significantly influence the jet performance and related cavitation effect.Through orthogonal experiments,the nozzle geometric parameters are optimized,and the following configuration is found accordingly:contraction angle 20°,contraction segment length 6 mm,cylindrical segment diameter 6 mm,cylindrical segment length 12 mm,spread segment length 10 mm,and spread angle 55°.

Analysis on Genetic Characteristics of Leaf Angle in Waxy Corn

The leaf angle in waxy corn is a significant trait for breeding corn with compact plant type, which is beneficial to improve yield. According to the Griffing method II, the GCA （general combining ability） and SCA （specific combining ability） of leaf angle trait in the 7 waxy corn inbred lines and 21 combinations were esti-mated, and the genetic characteristics of leaf angle in corn were also analyzed. The results showed that among the 7 inbred lines, the GCA values ranked as N22 〉N8 〉 N28 〉 N7 〉 N23 〉 N27 〉 N4. The GCA of N27 showed great negative ef-fect, and the genetic variance of its SCA was lower. It suggested that the N27 can be used as an ideal parent for breeding excel ent combinations with smal leaf angle and compact plant type. The inheritance of leaf angle trait in waxy corn is in ac-cordance with the model of ＂additive - dominant - epistatic＂. The efficiency of leaf angle trait is control ed by recessive genes. The broad heritability of leaf angle trait in waxy corn is relative low （68.5%）, but its narrow heritability is relatively high （72.62%）. In the breeding practices, the early-generation selection is more suitable for the leaf angel trait.

Research on Torque-Angle Characteristic of Large Gap Magnetic Drive System

The principle and design method of the large gap magnetic drive system is studied in this work. The calculation model of the torque-angle characteristic in the large gap magnetic drive system driven by traveling wave magnetic field is established. The calculation model is computed by using MATLAB software, and the pattern of the system’s torque-angle characteristic is obtained by analyzing study results. These results indicate that: torque-angle characteristic and the driving torque of the system can be adjusted by changing the electric current of coil, the magnetization of permanent magnetic gear, the inner diameter of permanent magnetic gear, the coupling distance between electromagnet and permanent magnetic gear, the outer diameter of permanent magnetic gear, and the axial length of permanent magnetic gear.

Strength and deformation characteristics of irregular columnar jointed rock mass: A combined experimental and theoretical study

The irregularity of jointed network poses a challenge to the determination of field mechanical param-eters of columnar jointed rock mass(CJRM),and a reasonable prediction of deformation and strength characteristics of CJRM is important for engineering construction.The Voronoi diagram and three-dimensional printing technology were used to make an irregular columnar jointed mold,and the irregular CJRM(ICJRM)specimens with different dip directions and dip angles were prepared.Uniaxial compression tests were performed,and the anisotropic strength and deformation characteristics of ICJRM were described.The failure modes and mechanisms were revealed in accordance with the final appearances of the ICJRM specimens.Based on the model test results,the empirical correlations for determining the field deformation and strength parameters of CJRM were derived using the dip angle and modified joint factor.The proposed empirical equations were used in the Baihetan Project,and the calculated mechanical parameters were compared with the field test results and those obtained from the tunneling quality index method.Results showed that the deformation parameters determined by the two proposed methods are all consistent with the field test results,and these two methods can also estimate the strength parameters effectively.

An impact angle constraint integral sliding mode guidance law for maneuvering targets interception

An integral sliding mode guidance law(ISMGL)combined with the advantages of the integral sliding mode control(SMC)method is designed to address maneuvering target interception problems with impact angle constraints.The relative motion equation of the missile and the target considering the impact angle constraint is established in the longitudinal plane,and an integral sliding mode surface is constructed.The proposed guidance law resolves the existence of a steady-state error problem in the traditional SMC.Such a guidance law ensures that the missile hits the target with an ideal impact angle in finite time and the missile is kept highly robust throughout the interception process.By adopting the dynamic surface control method,the ISMGL is designed considering the impact angle constraints and the autopilot dynamic characteristics.According to the Lyapunov stability theorem,all states of the closed-loop system are finally proven to be uniformly bounded.Simulation results are compared with the general sliding mode guidance law and the trajectory shaping guidance law,and the findings verify the effectiveness and superiority of the ISMGL.

Microscopic and Dynamic Rheological Characteristics of Crumb Rubber Modified Asphalt

A test for crumb rubber modified asphalt containing 20% crumb rubber particles（30 mesh） was performed using a scanning electron microscope（SEM）.The experimental results indicate that the crumb rubber particles are evenly distributed in the asphalt.Shear rate sweep and shear-temperature sweep tests on the crumb rubber modified asphalt at-20-80 ℃ using a dynamic shear rheology（DSR） instrument,were carried out.The tests show that the complex modulus decreases with increasing temperature;at equivalent temperature,higher load frequencies lead to a larger complex modulus,and this value increasingly decreases as the temperature increases;the phase angle increases with temperature and decreases as the load frequency increases.It can be concluded that the rutting resistance limiting temperature of crumb rubber modified asphalt is 78 ℃,and the anti-fatigue limiting temperature is 16 ℃,which shows that the asphalt has preferable rutting resistance characteristics at high temperature,as well as anti-fatigue characteristics.In addition,the complex modulus master curve at different temperatures was plotted according to the time temperature equivalence principle,which allows the study of the dynamic state behavior of crumb rubber modified asphalt at a wide range of load frequency.

Influence of Blade Thickness on Transient Flow Characteristics of Centrifugal Slurry Pump with Semi-open Impeller

As the critical component, the impellers of the slurry pumps usually have blades of a large thickness. The increasing excretion coefficient of the blades affects the flow in the impeller resulting in a relatively higher hydraulic loss, which is rarely reported. In order to investigate the influence of blade thickness on the transient flow characteristics of a centrifugal slurry pump with a semi-open impeller, transient numerical simulations were carried out on six impellers, of which the meridional blade thickness from the leading edge to trailing edge varied from 5-10 mm, 5-15 mm, 5-20 mm, 10-10 mm, 10-15 mm, and 10-20 mm, respectively. Then, two of the six impellers, namely cases 4 and 6, were manufactured and experimentally tested for hydraulic performance to verify the simulation results. Results of these tests agreed reasonably well with those of the numerical simulation. The results demonstrate that when blade thickness increases, pressure fluctuations at the outlet of the impeller become severe. Moreover, the standard deviation of the relative velocity in the middle portion of the suction sides of the blades decreases and that at the outlet of the impeller increases. Thus, the amplitude of the impeller head pulsation for each case increases. Meanwhile, the distribution of the time-averaged relative flow angle becomes less uniform and decreases at the outlet of the impeller. Hence, as the impeUer blade thickness increases, the pump head drops rapidly and the maximum efficiency point is offset to a lower flow rate condition. As the thickness of blade trailing edge increases by 10 mm, the head of the pump drops by approximately 5 m, which is approximately 10 % of the original pump head. Futhermore, it is for the first time that the time-averaged relative flow angle is being considered for the analysis of transient flow in centrifugal pump. The presented work could be a useful guideline in engineering practice when designing a centrifugal slurry pump with thick impeller blades.

Experimental study on aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds

In this study, experiments were carried out to investigate aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds using a 1:25 scaled sectional model wind-tunnel testing. Pressure measurements of two typical sections, one train-head section and one train-body section, at the windward and leeward tracks were conducted under the smooth and turbulence flows with wind attack angles between-6° and 6°, and the corresponding aerodynamic force coefficients were also calculated using the integral method. The experimental results indicate that the track position affects the mean aerodynamic characteristics of the vehicle, especially for the train-body section. The fluctuating pressure coefficients at the leeward track are more significantly affected by the bridge interference compared to those at the windward track. The effect of turbulence on the train-head section is less than that on the train-body section. Additionally, the mean aerodynamic force coefficients are almost negatively correlated to wind attack angles, which is more prominent for vehicles at the leeward track. Moreover, the lateral force plays a critical role in determining the corresponding overturning moment, especially on the train-body section.

Remote Sensing Monitoring of Surface Characteristics in the Badain Jaran, Tengger, and Ulan Buh Deserts of China

Deserts and sandy land in northern China are very susceptible to sandy desertification and are the main source of sand-dust storms of Asian dust. However, because of the complex factors involved, descriptions of the relationship between sandy desertification and surface characteristics in these regions are lacking. We monitored the surface characteristics and their changes in time using information about soil, vegetation, and landforms in the Badain Jaran Desert(BJD), Tengger Desert(TD), and Ulan Buh Desert(UBD) in the northern China. The monitoring was done using tasseled cap angle(TCA), disturbance index(DI), and topsoil grain size index(TGSI) from Moderate Resolution Imaging Spectroradiometer(MODIS) images combined with a decision tree classification. Results showed that the TD had higher topsoil fine sand content, and the ratio of non-vegetated to vegetated areas was similar with that in the UBD. Northeast-southwest coarse sand dunes with thin interdune(NECTI) dominated the BD, fine sand dunes(FSD) dominated the TD, and a combination of northeast-southwest coarse sand dunes with wide interdune(NECWI) and northwest-southeast coarse sand dunes with wide interdune(NWCWI) dominated the UBD. From 2000 to 2015, in the BJD the area of the NECTI, non-sand dune(Non) and potential sand sources(PSS) increased, whereas the area of the NECWI, FSD and NWCWI decreased, indicating a improve process in the BJD. In the TD, the area covered by Non increased, whereas the area covered by PSS, NECWI, NECTI, FSD, and NWCWI decreased from 2000 to 2015. The area covered by the various surface characteristic types fluctuated annually in the UBD from 2000 to 2015. Changes in surface characteristics reflect the combined effects of natural conditions and human activity. The findings of our study will assist scientists and policy makers in proposing different management techniques to combat sandy desertification for the different surface characteristics of these regions.

Prediction of loess soil-water characteristic curve by mercury intrusion porosimetry

Mercury intrusion porosimetry(MIP)is a simple and fast way to obtain the pore distribution of soil and can be used to estimate the soil-water characteristic curve(SWCC).In previous studies,soil was assumed to be a perfect wettability material,and the contact angle(CA)of the soil-water interface was taken as zero in the SWCC prediction method.However,the CA has proved to be much greater than zero even for hydrophilic soils according to some soil wettability experiments,and it has a significant effect on predicting the SWCC.In this research,a method for predicting the SWCC by MIP,which takes the CA as a fitting coefficient,is proposed.The pore size distribution curves are measured by MIP,and the SWCCs of two loess soils are measured by pressure plate and filter paper tests.When the CA is taken as70°and 50°for the wetting and drying process,respectively,the SWCCs predicted by the pore size distribution curves agree well with the measured SWCCs.The predicted suction range of the proposed method is 0-105 k Pa.The consistency of the results suggests that utilizing the MIP test to predict the SWCC with a proper CA is effective for loess.

Simulation Studies of Rib Structure Effect on Discharge Characteristics of Plasma Display Panel

To investigate the effect of the rib structure on the discharge characteristics of the plasma display panel, the potential distribution, particles density distribution and ions incident angle distribution were examined by simulation of a two-dimensional particle-in-cell/Monte Carlo collision, with two kinds of rib structure： the stripe rib structure and the Waffle rib structure. The results showed that the distribution of electric potential at the corner of the discharge cell was almost the same for these two rib structures while in the centre there was a difference between these two rib structures. The striation phenomenon could be observed in both cases. The distribution of density also indicated that the striation phenomenon was accompanied by the firing of discharge, and the Waffle rib structure might reduce the density humps. In the cell with a stripe rib structure, the profiles of the surface charge density along the sustained dielectric layer presented a better fluctuating distribution than that in the cell with a Waffle rib structure. The spatial potential and particle density in the discharge bulk showed that the Waffle ribs could weaken the striation phenomenon, which could be explained by the decrease in the particle numbers in the discharge cell. The simulation results of the ion incident angle showed that most ions impacted the sustained dielectric layer in the normal stripe rib cell with an incident angle in the range of 6° to 19° while with the Waffle rib structure the incident angle of most ions was in the range of 4° to 19°. The Waffle rib structure did not affect the angle distribution of incident ions significantly.

Effects of different characteristic surfaces at initial stage of frost growth

The effects of surface energy on phase change of water vapor at initial stage of frost growth were studied to find an effective method of restraining frost growth.The mechanism of restraining frost growth by low energy surface(bigger contact angle) was analyzed based on crystal growth theory.Then,the phase change of water vapor and the process of frost growth on the copper and wax energy surfaces were observed using microscope.The results indicate that it is difficult for wax surface(low energy surface),on which there are still water droplets at 100 s,to form critical embryo,so frost growth can be restrained in a way.Water formation,droplet growth,ice formation and dendritic ice growth processes happen on both surfaces,ordinally.But the ice beads,with larger average diameter and sparse distribution on the wax surface,form later(at about 300 s) than that on the copper surface,and the dendritic ice also appears later.All of these support that ice crystal formation and dendritic crystal growth at initial stage of frost growth can be retarded on the low energy surface.

Investigation of hypersonic flows through a cavity with sweepback angle in near space using the DSMC method

Near space has been paid more and more attentionin recent years due to its military application value.However,flow characteristics of some fundamental configurations(e.g.,the cavity)in near space have rarely been investigated due to rarefied gas effects,which make the numerical simulation methods based on continuous flow hypothesis lose validity.In this work,the direct simulation Monte Carlo(DSMC),one of the most successful particle simulation methods in treating rarefied gas dynamics,is employed to explore flow characteristics of a hypersonic cavity with sweepback angle in near space by considering a variety of cases,such as the cavity at a wide range of altitudes 20-60 km,the cavity at freestream Mach numbers of 6-20,and the cavity with a sweepback angle of 30°-90°.By analyzing the simulation results,flow characteristics are obtained and meanwhile some interesting phenomena are also found.The primary recirculation region,which occupies the most area of the cavity,causes pressure and temperature stratification due to rotational motion of fluid inside it,whereas the pressure and temperature in the secondary recirculation region,which is a small vortex and locates at the lower left corner of the cavity,change slightly due to low-speed movement of fluid inside it.With the increase of altitude,both the primary and secondary recirculation regions contract greatly and it causes them to separate.A notable finding is that rotation direction of the secondary recirculation region would be reversed at a higher altitude.The overall effect of increasing the Mach number is that the velocity,pressure,and temperature within the cavity increase uniformly.The maximum pressure nearby the trailing edge of the cavity decreases rapidly as the sweepback angle increases,whereas the influence of sweepback angle on velocity distribution and maximum temperature within the cavity is slight.

Crushing Characteristics of Filament Wound Carbon Fiber/Epoxy Tube under Quasi-static Compression Condition

We investigated the effect of structural factor and amide grafted multi-walled carbon nanotubes（MWNTs-NH2） on crushing characteristics of filament wound CFRP tube under quasi-static compression conditon. It was found that CFRP tubes sequentially showed the brittle fracturing mode, the local buckling fracturing mode and transverse shearing fracturing mode with increasing winding angle, respectively, with the characterizations by mechanical testing, SEM and optical microscopy. Moreover, crack propagation initiated by pre-crack and subsequent failure in the tube were strongly dependent on pre-crack angle due to defl ection and penetration competition of crack evolution. The simulated compression failure behavior correlated well with the experimental results, revealing that the Chang-Chang failure criterion was effective in representing the quasistatic crushing characteristics of the tube. In addtion, the MWNTs-NH2 were sucessfully obtained by multistep functionization. The compressvie properties of the tubes were signifi cantly improved by the addition of the MWNTs-NH2 due to their uniform dispersion and high interfacial chemical reactivity, whereas the as-received MWNTs and other functionalized MWNTs were not as effective.

Moment-angle复形轨道构型空间的欧拉示性数

设I^m为m维标准方体,K'为单纯复形K的重心重分.将K'上的锥形按一定规则逐片线性嵌入I^m的典范单纯剖分中,从而得到K对应的一类方体复形cc(K).根据cc(K)的构造过程,计算了cc(K)的f-向量,即各个维数的胞腔个数.通过投射(D^d)m→J^m的拉回,可定义cc(K)上的moment-angle复形Z_(K.d).将Z_(K,d)放入轨道构型空间的框架中,得到轨道构型空间F_G(Z_(K,d,n)).由F_G(Z_(K,d,n))的组合结构和著名的Inclusion-exclsion原理,给出了轨道构型空间FG(Z_(K,d,n))的欧拉示性数利用f-向量表示的计算公式,并且提供了一种计算Z_(K,d)欧拉示性数的新方法.

Analysis on the Writing Characteristic Featuresof The Great Gatsby

The Great Gatsby is considered the masterpiece of F.Scott Fitzgerald.The reason why it is one of the greatest novels all over the world is not only because of its showing the cruel social reality in America during 1920s and the selflessness and merciless of human nature at that time,but also the novel's unique narrative angle that Fitzgerald wrote the novel from the first person perspective.Fitzgerald com posed the figure "Nick Carraway" as the narrator of the story of Gatsby.And the plots of the novel are ingeniously conceived and well-knit.It gets coherence between the beginning and the end,and the plots linked together.So the novel makes a strong impression on readers.

Determination of key soil characteristic parameters using angle of repose and direct shear stress test

Discrete element modelling(DEM)is a numerical method for examining the dynamic behavior of granular media.In order to build an accurate simulation model and provide more comprehensive soil characteristic parameters for the design and optimization of various soil contact machinery,in this paper,the discrete element simulation method(EDEM)combined with experimental approach is used to investigate the soil contact characteristic parameters in East Asia.In this study,Hertze-Mindlin(no slip)was used as a particle contact model by taking particle contact parameters and soil JKR(Johnson-Kendall-Roberts)surface energy as determinants,and repose angle,internal friction angle,and cohesive force as evaluation indexes.The method of Plackett-Burman,Stepest ascent,and Box-Behnken were used to gradually reduce the range of parameters needed for simulation until the most accurate value was determined.The results show that the restitution coefficient,static friction coefficient,and rolling friction coefficient between soil particles have significant effects on the DEM model,and their value of them are 0.596,0.725,and 0.16,respectively.Based on these parameters used for the repose angle test and direct shear stress test,the value of repose angle is 31.97°,the internal friction angle is 27.61°,and the cohesive force is 33.06 kPa.The relative errors with the actual measured values are 9.54%,1.87%,and 2.31%,respectively.In order to further test whether the simulation parameters of soil obtained by repose angle test and direct shear stress test are consistent with the real soil,comparison test between field test and discrete element simulation was used.The results show that the error in height of ridge between the simulated soil and the actual soil is 4.06%,which is within the acceptable range.It also indicates that the calibrated and optimized soil simulation model can accurately represent the real soil.The research provides theoretical basis and technical support for the study of soil contact parts by using the discrete element method,combined with repose angle test and direct shear stress test.

Spatio-temporal Characteristics of Area Coverage and Observation Geometry of the MISR Land-surface BRF Product: A Case Study of the Central Part of Northeast Asia

The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.