Experimental investigation of particle velocity distributions in windblown sand movement

With the PDPA (Phase Doppler Particle Analyzer) measurement technology, the probability distributions of particle impact and lift-off velocities on bed surface and the particle velocity distributions at different heights are detected in a wind tunnel. The results show that the probability distribution of impact and lift-off velocities of sand grains can be expressed by a log-normal function, and that of impact and lift-off angles complies with an exponential function. The mean impact angle is between 28° and 39°, and the mean lift-off angle ranges from 30° to 44°. The mean lift-off velocity is 0.81–0.9 times the mean impact velocity. The proportion of backward-impacting particles is 0.05–0.11, and that of backward-entrained particles ranges from 0.04 to 0.13. The probability distribution of particle horizontal velocity at 4 mm height is positive skew, the horizontal velocity of particles at 20 mm height varies widely, and the variation of the particle horizontal velocity at 80 mm height is less than that at 20 mm height. The probability distribution of particle vertical velocity at different heights can be described as a normal function. Supported by the National Natural Science Foundation of China (Grant No. 10532030) and the National Basic Research Program of China (Grant No. G2000048702)     

DPTM simulation of aeolian sand ripple

Aeolian sand ripple and its time evolution are simulated by the discrete particle tracing method (DPTM) presented in this paper. The difference between this method and the current methods is that the former can consider the three main factors relevant to the formation of natural aeolian sand ripples, which are the wind-blown sand flux above the sand bed formed by lots of sand particles with different diameters, the particle-bed collision and after it the rebound and ejection of sand particles in the sand bed, the saltation of high-speed sand particles and the creep of low-speed sand particles, respectively. The simulated aeolian sand ripple is close to the natural sand ripple not only in basic shape and characteristic, particle size segregation and stratigraphy, but also in formation stages. In addition, three important speeds can be obtained by this method, which are the propagation speed of the saturated aeolian sand ripple and the critical frictional wind speeds of emergence and disappearance of sand ripple. Supported by the Key Project of the National Natural Science Foundation of China (Grant No. 10532040)     

Experimental investigation on trap stagnant effect and sand flux in aeolian sand transport

A new isokinetic vertical sand trap is designed in this work, and the new trap has an advantage that airflows in all sampling tubes at different height can simultaneously approach the isokinetic state. The stagnant effect and vertical sand mass flux are experimentally investigated in a wind tunnel. Compared with the traditional passive sand trap, the new design greatly reduces the stagnant effect, and has higher efficiency at different heights and wind speeds. The results obtained in this Letter also show the stagnant effect of the sand trap not only changes the total efficiency of the sand collection, but also the distribution of the vertical sand flux. The new isokinetic sand trap has good performance and can be applied to study the sand flux in aeolian sand transport.     

考虑颗粒形状和破碎的胶结钙质砂力学行为离散元模拟研究

质砂作为一种建筑材料,近年来广泛应用于我国南海岛礁工程建设中。本文通过建立考虑钙质砂真实颗粒形状和颗粒破碎的胶结钙质砂离散元模型,研究了二维剪切条件下试样的宏微观力学行为,包括应力-应变行为、颗粒破碎、胶结破坏、位移场和裂纹随剪应变的演化规律,讨论了颗粒形状、颗粒粒径范围、颗粒强度和水泥胶结强度对胶结钙质砂力学行为的影响规律。结果表明,钙质砂颗粒粒径区间越宽,胶结钙质砂的强度越高。同一级配条件下,考虑真实颗粒形状的胶结钙质砂试样比圆颗粒试样的强度更高,试样总体颗粒破碎率也更高。钙质砂颗粒的强度越高,胶结钙质砂的性能越好。但是提高水泥的强度对胶结钙质砂力学性能的影响并不显著。本文的研究结果可为实际工程中钙质砂的加固提供理论依据。     

Harmful Substances on the Opera Stage: Possible Negative Effects on Singers'' Respiratory Tracts

Objective, quantitative information is lacking in the medical community about actual working conditions for professional singers onstage, and moreover, about which conditions are safe. Physicians, speech-language pathologists, and speech scientists focusing on laryngology should have relevant information about the opera as workplace and the medical sequelae of unhealthy environments. We describe five toxic substances to which singers presenting to our clinics were exposed while working professionally on the opera stage: (1) aromatic diisocyanates, (2) penicillium frequentans in cork granulate, (3) formaldehyde in cork granulate, (4) cobalt and aluminum (pigment components), and (5) quartz sand capable of entering the alveolae. Biological considerations and clinical data for some subjects suggest a direct causal link between the exposures and the patients' complaints and findings. Our observations suggest that whenever singers complain about deleterious conditions such as dry and hot onstage climate or suspicion of the presence of harmful substances, the specific conditions existing in the theater in question should be investigated. Harmful substances are not only poorly tolerated by singers, but also they should be preventable.     

Headspace Solid‐Phase Microextraction (HS‐SPME) for the Determination of Benzene,Toluene, Ethylbenzene,and Xylenes (BTEX) in Foundry Molding Sand

Abstract

The use of headspace solid‐phase microextraction (HS‐SPME) to determine benzene, toluene, ethylbenzene, and xylenes (BTEX) in foundry molding sand, specifically a “green sand” (clay‐bonded sand) was investigated. The BTEX extraction was conducted using a 75 µM Carboxen‐polydimethylsiloxane (CAR‐PDMS) fiber, which was suspended above 10 g of sample. The SPME fiber was desorbed in a gas chromatograph injector port (280°C for 1 min) and the analytes were characterized by mass spectrometry. The effects of extraction time and temperature, water content, and clay and bituminous coal percentage on HS‐SPME of BTEX were investigated. Because green sands contain bentonite clay and carbonaceous material such as crushed bituminous coal, a matrix effect was observed. The detection limits for BTEX were determined to be ≤0.18 ng g^?1 of green sand.     

扎赉特旗油砂在氮气气氛下的热解制油研究

油砂是一种含有沥青或其他重质石油的沉积岩,主要用于提取油砂沥青,以生产合成原油。中国拥有相当数量的油砂资源,目前还未开采,仅处于初步研究阶段。加拿大在20世纪初期就展开了油砂的开采及制油研究工作,并于20世纪70年代由加拿大合成油公司实现了工业化生产。油砂生产的沥青和合成油已占其石油总产量的1／4以上。     

Relationship between swelling and mechanical properties of cross-linked polymers mixed with sand

Cross-linked polymers consisting of acrylamide, sodium acrylate, starch fragments and a cross-linker were synthesized with the same content of carboxyl groups and three degrees of cross-linking Q of 0.04, 0.2 and 1 wt%. An increase in Q gradually reduces the swelling of polymer gels in water; when distributed in sand, polymer gels exhibit maximum swelling at Q = 0.2 wt%. It is shown that the behavior of polymer gels in sand is determined by the balance between the elasticity of swollen polymer gels and the resistance of sand particles