Evolution of meanders with hyperconcentrated flow in the loess areas

依据中国黄土分布区多沙曲流的水沙资料、河床平面形态和河床大断面测量资料分析认为: 多沙河流来水变率影响河床断面形态和曲流发育; 由于窄深的河槽是高含沙水流输沙的必要条件和结果, 因此随着含沙量的增加, 多沙河流河床断面形态首先出现变窄深的趋势, 随着含沙量的进一步增加, 水流造床能力增大, 河槽会向宽浅方向调整; 一定的河床冲淤强度有利于曲流的发育, 随着含沙量的增加, 多沙河流河床曲率存在先增加后减小的规律。In the loess areas, especially on the Loess Plateau in China, most of the rivers discharging hyperconcentrated flows have developed a typical meandering pattern. Based on the data of thirteen meandering rivers on the Loess Plateau and the Yangchangzi River, the properties of water flow and sediment load of these rivers, the effects of variations of flow and sediment load on channel cross sectional geometry and sinuosity, are analyzed in the paper. The data include the daily flow and sediment load and the geometry of channel cross sections recorded from 1976 to 1980 as well as the plan of channel measured on the landscape maps with a scale of 1 : 50 000 or 1 : 100 000. From these data we extrast parameters reflecting the characteristics of flow and sediment load, channel geometry, and sedimentation in channel and channel adjustment thereupon. Follows are the results of analyses. 1) As the rivers with low sediment concentration, the hyperconcentrated flow dominated rivers have a narrower and more sinuous channel if the fluctuation in water discharge is low. 2) With the increase of sediment concentration, the channel cross sectional geometry is usually widened in the case of the rivers with low sediment concentration. Since a narrow channel is one of the requisite conditions as well as the result of sediment transport of hyperconcentrated flows, the channels become narrow initially as the sediment concentration of hyperconcentrated flow increases. However, if the sediment concentration is larger than a certain value, the energy consumption of sediment transport is lowered down thenceforth with the increase of sediment concentration, and the flow becomes unsaturated and has a higher channel making capacity, so the channel is widened. Revealed by the instantaneous hydrological records, the transition takes place at the sediment concentration of about 400 kg/m3. 3) Both excessive and low intensity of sedimentation in the channel is unfavorable to development of meanders. In the case of the rivers with a low sediment concentration, the energy consumption per unit distance increases with the enlargement of slope and discharge and so the capacity of channel making of the flows; therefore, the channel sinuosity increases initially and decreases later. Regarding the hyperconcentrated flow dominated rivers, the energy consumption of sediment transport is lowered and the channel making capacity as well as magnitude of sedimentation are enlarged accompanying with the increase of sediment concentration, so an initial increase of channel sinuosity is followed by a decrease also. Due to the difference of the mechanism of channel sinuosity adjustment from that of cross section changes, the existence of the asychronism in the adjustment of the two factors is reasonable.published_or_final_versio

A semi-discrete model and its approach to a solution for a wide moving jam in traffic flow

This paper investigates the analytical and numerical solutions to wide moving jams in traffic flow. Under the framework of the Lagrange coordinates, a semi-discrete model and a continuum model correlate with each other, in which the former model approaches the latter as the increment ΔM in the former model vanishes. This implies that the solution to a wide moving jam in the latter model, which can be analytically derived using the known theory, can be conceivably taken as an approximation to that of the former model. These results were verified through numerical simulations. Because a detailed understanding of the traffic phase "wide moving jam" is very important for the further development of Kerner's three-phase traffic theory, this study helps to explain the empirical features of traffic breakdown and resulting congested traffic patterns that are observed in real traffic. © 2011 Elsevier B.V. All rights reserved.postprin

A study of chemical properties of rains on the Tibetan Plateau

Natural rains are generally considered as weakly acidic. Measurements in Lhasa and other three small cities on the Tibetan Plateau reveal that the rainwater on the Plateau is alkaline with bicarbonate as the dominant anion and contains few pollutants. On the basis of the measurements on the Tibetan Plateau, the experiments and calculation, the authors believe that the original pH of natural rainwater in arid and semiarid areas on this planet should be weakly alkaline because of the influence of alkaline dusts. 一般認為天然降雨呈弱酸性,但是觀測顯示青藏高原上拉薩及其它3個城市降水呈堿性,以重碳酸鹽陽離子為主,污染物很少.通過對實測資料和試驗結果的分析計算,認為地球上干旱和半干旱地區天然降水的應呈弱堿性,原因是大氣中漂浮著堿性粉塵

Toxicokinetic behaviors and modes of perfluorooctane sulfonate (PFOS) and perfluorooctane acid (PFOA) on tilapia (Oreochromis niloticus)

Perfluorooctane sulfonate (PFOS) and perfluorooctane acid (PFOA) are widely distributed environmentally persistent organic pollutants found at low levels in human and wildlife ecosystem. The objectives of the current study were to investigate toxicokinetic behaviors and modes of PFOS and PFOA on tilapia (Oreochromis niloticus). The toxicokinetic behaviors and modes of PFOS and PFOA are different in tilapia during experimental periods. Exposure to both PFOS and PFOA was approximately 5 to 6 times higher for male tilapia than for female tilapia. The terminal half-life of PFOA in serum was about 4 times longer for male tilapia than for female tilapia. The apparent volume of distribution for PFOS and PFOA in the serum was about 3 to 4 times higher for female tilapia than for male tilapia. The lymphocytes level decreased rapidly with the increased PFOA concentration. A similar pattern was observed with the PFOS exposure, and it is remarkable that PFOS and PFOA were significantly accumulated in both PFOS and PFOA exposure but PFOA showed a greater effect than PFOS. PFOA blood concentrations were lesser than the limit of quantification in non-exposure tilapia during an uptake period, while measured PFOS concentrations were at least six times lesser than those in PFOS exposure. Tilapia weight gain was also decreased with statistical significance in all PFOA-treated groups, and the effect of PFOA was higher than that of PFOS. The effects of PFOA in survival percent were more pronounced in this case than that of PFOS. Moreover, PFOA had similar mode, and PFOS and PFOA can inhibit the 17β-HSD3 enzyme activity of tilapia.Key words: Toxicokinetic, behaviors, perfluorooctane sulfonate (PFOS), perfluorooctane acid (PFOA), tilapia (Oreochromis niloticus)

Phase-plane analysis of conserved higher-order traffic flow model

The phase-plane analysis is used to study the traveling wave solution of a recently proposed higher-order traffic flow model under the Lagrange coordinate system. The analysis identifies the types and stabilities of the equilibrium solutions, and the overall distribution structure of the nearby solutions is drawn in the phase plane for the further analysis and comparison. The analytical and numerical results are in agreement, and may help to explain the simulated phenomena, such as the stop-and-go wave and oscillation near a bottleneck. The findings demonstrate the model ability to describe the complexity of congested traffic.postprin

Enhanced performance of Si MOS capacitors with HfTaOxNy gate dielectric by using AlOxNy or TaOxNy interlayer

Si MOS capacitors with HfTa oxide and oxynitride as gate dielectric were fabricated. Moreover, AlOxNy or TaOxN y was used as the interlayer between HfTa oxynitride and Si substrate to improve the electrical quality of the capacitors. Experimental results showed that the HfTaOxNy capacitor with TaO xNy interlayer achieved better performance with larger capacitance and smaller leakage current than its counterpart with AlO xNy interlayer. © 2008 IEEE.published_or_final_versio

A simple particle-size distribution model for granular materials

© 2018, Canadian Science Publishing. All rights reserved. Particle-size distribution (PSD) is a fundamental soil property that plays an important role in soil classification and soil hydromechanical behaviour. A continuous mathematical model representing the PSD curve facilitates the quantification of particle breakage, which often takes place when granular soils are compressed or sheared. This paper proposes a simple and continuous PSD model for granular soils involving particle breakage. The model has two parameters and is able to represent different types of continuous PSD curves. It is found that one model parameter is closely related to the coefficient of nonuniformity (Cu) and the coefficient of curvature (Cc), while the other represents a characteristic particle diameter. A database of 53 granular soils with 154 varying PSD curves is analyzed to evaluate the performance of the proposed PSD model, as well as that of three other PSD models in the literature. The results show that the proposed model has improved overall performance and captures the typical trends in PSD evolution during particle breakage. In addition, the proposed model is also used for assessing the internal stability of 27 widely graded soils

Improved electrical properties of Ge p-MOSFET with HfO 2 gate dielectric by using TaO xN y interlayer

The electrical characteristics of germanium p-metal-oxide-semiconductor (p-MOS) capacitor and p-MOS field-effect transistor (FET) with a stack gate dielectric of HfO 2TaO xN y are investigated. Experimental results show that MOS devices exhibit much lower gate leakage current than MOS devices with only HfO 2 as gate dielectric, good interface properties, good transistor characteristics, and about 1.7-fold hole-mobility enhancement as compared with conventional Si p-MOSFETs. These demonstrate that forming an ultrathin passivation layer of TaO xN y on germanium surface prior to deposition of high- k dielectrics can effectively suppress the growth of unstable GeO x, thus reducing interface states and increasing carrier mobility in the inversion channel of Ge-based transistors. © 2008 IEEE.published_or_final_versio

Solitary wave solution to Aw-Rascle viscous model of traffic flow

A traveling wave solution to the Aw-Rascle traffic flow model that includes the relaxation and diffusion terms is investigated. The model can be approximated by the well-known Kortweg-de Vries (KdV) equation. A numerical simulation is conducted by the first-order accurate Lax-Friedrichs scheme, which is known for its ability to capture the entropy solution to hyperbolic conservation laws. Periodic boundary conditions are applied to simulate a lengthy propagation, where the profile of the derived KdV solution is taken as the initial condition to observe the change of the profile. The simulation shows good agreement between the approximated KdV solution and the numerical solution.postprin

Comparative study of HfTa-based gate-dielectric Ge metal-oxide- semiconductor capacitors with and without AlON interlayer

The electrical properties and high-field reliability of HfTa-based gate-dielectric metal-oxide-semiconductor (MOS) devices with and without AlON interlayer on Ge substrate are investigated. Experimental results show that theMOS capacitor with HfTaON/AlON stack gate dielectric exhibits low interface-state/oxide-charge densities, low gate leakage, small capacitance equivalent thickness (∼1.1 nm), and high dielectric constant (∼20). All of these should be attributed to the blocking role of the ultrathin AlON interlayer against interdiffusions of Ge, Hf, and Ta and penetration of O into the Ge substrate, with the latter effectively suppressing the unintentional formation of unstable poorquality low-k GeO x and giving a superior AlON/Ge interface. Moreover, incorporation of N into both the interlayer and high-k dielectric further improves the device reliability under high-field stress through the formation of strong Nrelated bonds. © Springer-Verlag 2009.published_or_final_versionSpringer Open Choice, 01 Dec 201