无机盐超细粉体制备技术的回顾与展望

评述了制备无机盐超细粉体的传统方法以及一些传统方法的改进 ,对当前几种新技术做了介绍与展望     

Channel Bed Mobility Downstream from the Elwha Dams,Washington*

Dams are a major source of fragmentation and degradation of rivers. Although substantial research has been conducted on the environmental impacts of large structures in the United States, smaller dams have received less attention. This study evaluated the impact of two dams of moderate size, the Elwha Dams, on the downstream channel system using field data collection at river cross‐sections. The relationship of average boundary shear stress (τ_o) to critical shear stress (τ_cr) served as the basis for determining channel bed material mobility under the two‐year and ten‐year flood events. The channel had the greatest channel bed mobility at the natural cross‐section upstream from the dams, low bed mobility between the structures, and an increase in channel bed mobility in the low gradient river segment near the mouth of the river. Low bed mobility tended to be associated with a lack of channel system complexity, including reduction or loss of bars and low alluvial terraces and their associated young riparian communities. Although these run‐of‐the‐river dams do not modify streamflow greatly, the loss of sediment from the channel system has had a substantial impact on bed mobility and geomorphic and biotic complexity of the Elwha River.     

An automated salt‐tracing gauge for flow‐velocity measurement

This article introduces the SVG (salt‐velocity gauge), a novel automated technique for measuring flow velocity by means of salt tracing. SVG allows a high measuring rate (up to one every 2 seconds), short control section length (down to 10 cm), high accuracy (+[sol ]?1·5 cm s^?1), and unbiased calculation of the mean velocity in experimental conditions with turbulent, supercritical flow. A few cubic centimetres of saturated salt solution (NaCl) are injected into the flow at regular time intervals using a programmable solenoid valve. The tracer successively passes two conductivity probes placed a short distance downstream. The transformation of the signal between the two probes is modelled as a one‐dimensional diffusion wave equation. Model calibration gives an estimation of the mean velocity and the diffusion for each salt plume. Two implementations of the SVG technique are described. The first was an outdoors simulated rainfall experiment in Senegal (conductivity probes at 40 cm apart, 8 Hz measurement rate, salt injections at 10 second intervals). Mean velocity was estimated to range between 0·1 and 0·3 m s^?1. The second was a laboratory‐based flume experiment (conductivity probes at 10 cm apart, 32 Hz, salt injections at 2 second intervals). Another SVG with probes at 34 cm apart was used for comparison. An acoustic Doppler velocimeter (ADV) was also used to give an independent assessment of velocity. Using the 10 cm salt gauge, estimated mean velocity ranged from 0·6 to 0·9 m s^?1 with a standard deviation of 1·5 cm s^?1. Comparisons between ADV, 10 cm SVG and 34 cm SVG were consistent and demonstrated that the salt‐tracing results were unbiased and independent of distance between probes. Most peaks were modelled with r² > 90 per cent. The SVG technology offers an alternative to the dye‐tracing technique, which has been severely criticized in the literature because of the wide interval of recommended values for the correction factor α to be applied to the timings. This article demonstrates that a fixed value of α is inappropriate, since the correction factor varies with velocity, diffusion and the length of the control section. Copyright © 2005 John Wiley & Sons, Ltd.     

The effect of bed mobility on resistance to overland flow

When sediment grains are transported as bed load in overland flow, there is a net transfer of momentum from the flow to the grains. When these grains collide with other grains, whether on the bed or in the flow, streamwise flow velocity decreases and resistance to flow increases. Resistance to flow generated in this manner is termed bed‐load transport resistance. Resistance to flow f over a plane bed may be partitioned into grain resistance f_g and bed‐load transport resistance f_bt. We use the symbols f_btf and f_btm to denote f_bt for flows over fixed beds and over mobile beds, respectively, and we compute the effect of bed mobility on flow resistance f_mob by subtracting f_btf from f_btm. The data for this study come from 54 flume experiments with fixed beds and 38 with mobile beds. On average f_mob is approximately equal to half of f_btm, which is about one‐quarter of f. Hence, f_mob is about one‐tenth of f. Predictive equations are developed for f_btf, f_btm and f_mob using dimensional analysis to identify the relevant independent variables and regression analysis to evaluate the coefficients associated with these variables. Values of f_mob are always positive which implies that mobile beds offer greater resistance to flow than do fixed beds. Evidently bed‐load grains colliding with mobile beds lose more momentum to the bed than do grains colliding with fixed beds. In other words, grain collisions with mobile beds are less elastic than those with fixed beds. Copyright © 2005 John Wiley & Sons, Ltd.     

山东泰安朱家庄自然硫矿床地质概要

山东省泰安朱家庄自然硫矿床,赋存于鲁西断隆古近纪汶东陆相盆地。自然硫矿层在汶口组二段上亚段,泥质灰岩-含泥灰岩-含云灰岩-石膏岩韵律层中的白云岩-石膏岩层段发育。自然硫以胶态、晶态、土态3种形态产出,可划分为顺层型、准顺层型、斑杂型及不顺层型4大类10余种矿石类型。从矿区去膏化作用普遍、自然硫与石膏-硬石膏分别富集轻-重同位素的特征、油气显示明显及地下水主要径流方向自然硫矿化最强等各种证据,表明该矿属生物后生成因的矿床。     

石灰改良膨胀土力学性质的研究

膨胀(?)主要是由强亲水性粘土矿物蒙脱石和伊利石组成的,是具有膨胀性、多裂隙性和超固结性的高塑性粘性土。在铁路施工中,膨胀土不能直接作为路基填土,必需进行改良。通过室内试验的方法来讨论石灰改良膨胀土的力学性质在各种影响因素下的变化规律。     

秦末以来秦都咸阳地貌演变

秦都咸阳地貌演变研究是秦咸阳考古和关中地区历史环境演变研究不容忽视的问题。秦末以来，秦都咸阳地貌演变包括渭河河道北移和咸阳原边坡地貌变化两个方面。通过文献考证与实地考察恢复了秦末、唐、明、清各代渭河的河道位置，秦末以来秦都咸阳段渭河河道北移4100m，平均北移速度1．8764m／a，明代以前北移较慢，以后北移速度显著加快，清顺治至现代北移速度达到5．9701m／a。咸阳原南侧边坡上的中小切沟主要是秦以后形成的。原坡上的村庄平台是历史上人为斩齐原坡，挖掘窑洞，引起原边逐步后退的结果，是咸阳原边坡人为地貌演变的体现。     

江苏王港盐沼的现代沉积速率

江苏海岸湿地总面积超过5000km^2，但围垦活动的加剧使盐沼湿地面积迅速减少；为了达到海岸防护、保滩促淤的目的，先后引种了大米草和互花米草。通过采集江苏王港潮滩盐沼湿地9处柱状样和挖取探槽剖面，以及对沉积剖面样品进行^210Pb和^137Cs测年分析，探讨了^210Pb的本底及影响^210Pb富集的因素，估算了王港盐沼湿地的现代沉积速率。王港潮滩盐沼沉积物对^210Pb的吸附作用较弱；受风暴潮、生物扰动、物源变化及实验误差等因素的影响，在^210Pbex剖面上出现了数据异常点，将这些数据点剔除后计算得到的沉积速率为33cm yr^-1，^137Cs测年显示，该地区1963年以来的平均沉积速率3．1cm yr^-1，与^210Pb法及前人研究结果相一致。根据一个典型剖面的^137Cs测年数据分析，王港潮滩盐沼的沉积过程根据地貌特征的不同可分3个阶段，大米草覆盖阶段滩面高程迅速增加，互花米草的生长提高了滩面淤积速率。     

Daily salinity fluctuation alleviates salt stress on seedlings of the mangrove Bruguiera gymnorhiza

Salinity is a vital factor that regulates leaf photosynthesis and growth of mangroves, and it frequently undergoes large seasonal and daily fluctuations creating a range of environments – oligohaline to hyperhaline. Here, we examined the hypotheses that mangroves benefit opportunistically from low salinity resulting from daily fluctuations and as such, mangroves under daily fluctuating salinity (FS) grow better than those under constant salinity (CS) conditions. We compared growth, salt accumulation, gas exchange, and chlorophyll fluorescence of leaves of mangrove Bruguiera gymnorhiza seedlings growing in freshwater (FW), CS (15 practical salinity units, PSU), and daily FS (0–30 PSU, average of 4.8 PSU) conditions. The traits of FS-treated leaves were measured in seedlings under 15 PSU. FS-treated seedlings had greater leaf biomass than those in other treatment groups. Moreover, leaf photosynthetic rate, capacity to regulate photoelectron uptake/transfer, and leaf succulence were significantly higher in FS than in CS treatment. However, leaf water-use efficiency showed the opposite trend. In addition to higher concentrations of Na⁺ and Cl⁻, FS-treated leaves accumulated more Ca²⁺ and K⁺. We concluded that daily FS can enhance water absorption, photosynthesis, and growth of leaves, as well as alter plant biomass allocation patterns, thereby positively affecting B. gymnorhiza. Mangroves that experience daily FS may increase their adaptability by reducing salt build-up and water deficits when their roots are temporally subjected to low salinity or FW and by absorbing sufficient amounts of Na⁺ and Cl⁻ for osmotic adjustment when their roots are subsequently exposed to saline water.