Assessing soil erosion rates on manually-tilled hillslopes in the Sichuan Hilly Basin using Cs-137 and Pb-210(ex) measurements

IEECAS SKLLQG

Late Pliocene-Pleistocene changes in mass accumulation rates of eolian deposits on the central Chinese Loess Plateau

IEECAS SKLLQG

A study of shear viscosity of interfacial films containing alkyl metal phosphates

Experimental data are presented to show the influence of alkyl metal phosphates, Shengli resin fraction, and NaCl, on the shear viscosity of interfacial films and the stability of emulsions. It was found that the alkyl metal phosphates and the Shengli resin fraction could enhance the shear viscosity of interfacial films and the stability of emulsions. NaCl (0.01-0.03 mol L-1) could change the shear viscosity of interfacial films containing alkyl metal phosphates and the Shengli resin fraction. The shear viscosity of interfacial films containing ethyl iron phosphate and the Shengli resin fraction decreased with the increase of the concentration of NaCl. On the other hand, NaCl could decrease the stability of the emulsions. (C) 2004 Elsevier B.V. All rights reserved.

Stability shear stress and equilibrium cross-sectional geometry of sheltered tidal channels

This study relates tidal channel cross-sectional area (A) to peak spring discharge (Q) via a physical mechanism, namely the stability shear stress ( tau sub(S)) just necessary to maintain a zero gradient in net along-channel sediment transport. It is assumed that if bed shear stress ( tau ) is greater than tau sub(S), net erosion will occur, increasing A, and reducing tau similar to (Q/A) super(2) back toward tau sub(S). If tau < tau sub(S) there will be net deposition, reducing A and increasing tau toward tau sub(S). A survey of the literature allows estimates of Q and A at 242 sections in 26 separate sheltered tidal systems. Assuming a single value of tau sub(S) characterizes the entire length of a given tidal channel, it is predicted that along-channel geometry will follow the relation Ah sub(R) super(1) super(/) super(6) similar to Q. Along-channel regressions of the form Ah sub(R) super(1) super(/) super(6) similar to Q super( beta ) give a mean observed value for beta of 1.00 plus or minus 0.06, which is consistent with this concept. Results indicate that a lower bound on tau sub(S) (and an upper bound on A) for stable channels is provided by the critical shear stress ( tau sub(C)) just capable of initiating sediment motion. Observed tau sub(S) is found to vary among all systems as a function of spring tidal range (R sub(sp)) according to the relation tau sub(S) approximately 2.3 R sub(sp) super(0.79) tau sub(C). Observed deviations from uniform tau sub(S) along individual channels are associated with along-channel variation in the direction of maximum discharge (i.e., flood-versus ebb-dominance).

Estimation of wind erosion rates by using Cs-137 tracing technique: A case study in Tariat-Xilin Gol transect, Mongolian Plateau

Wind erosion is one of the major environmental problems in semi-arid and arid regions. Here we established the Tariat-Xilin Gol transect from northwest to southeast across the Mongolian Plateau, and selected seven sampling sites along the transect. We then estimated the soil wind erosion rates by using the Cs-137 tracing technique and examined their spatial dynamics. Our results showed that the Cs-137 inventories of sampling sites ranged from 265.63 +/- 44.91 to 1279.54 +/- 166.53 Bq.m(-2), and the wind erosion rates varied from 64.58 to 419.63 t.km(-2).a(-1) accordingly. In the Mongolia section of the transect (from Tariat to Sainshand), the wind erosion rate increased gradually with vegetation type and climatic regimes; the wind erosion process was controlled by physical factors such as annual precipitation and vegetation coverage, etc., and the impact of human activities was negligible. While in the China section of the transect (Inner Mongolia), the wind erosion rates of Xilin Hot and Zhengxiangbai Banner were thrice as much as those of Bayannur of Mongolia, although these three sites were all dominated by typical steppe. Besides the physical factors, higher population density and livestock carrying level should be responsible for the higher wind erosion rates in these two regions of Inner Mongolia.

Effect of shear on the crystallization behavior of glass bead filled polypropylene

Linkam CSS450 optical shearing stage, wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering(SAXS) were used to investigate the effect of shear on crystal structure and crystallization morphology of the glass bead filled polypropylene( PP). The results indicate that the glass bead worked as nucleating agent for the glass bead filled PP, compared with pure PP it restrained the formation of beta-crystal after shear treatment. When the mean size of glass bead is smaller(4 mu m) shear rate had less effect on the formation of beta-crystal of PP obviously.

Shear-enhanced crystallization of a thermoplastic polyimide derived from 3,3 ',4,4 '-oxydiphthalic dianhydride and 4,4 '-oxydianiline

The aim of this work is to investigate the effect of consecutive shear on the crystallization of an amorphous aromatic polyimide (PI) derived from 3,3',4,4'oxydiphthalic dianhydride (3,3',4,4'-ODPA) and 4,4-oxydianiline (ODA). At 260 degrees C, the increase of shear rate or shear time leads to the increase of crystallinity. Indeed, increasing shear rate can also accelerate the crystallization behavior. Moreover, it was found that a new melting peak appeared at higher temperature for long time or high rate sheared sample. The enhancement of crystallization behavior appears directly linked to the increase of crystal thickness. Particularly, the effect of shear temperature was investigated, and the results revealed that the crystallization of the PI was more sensitive to shear at 260 degrees C, which was 10 degrees above the glass transition temperature (250 degrees C) of the PI. Possible mechanism was proposed to illustrate the effect of consecutive shear on the crystallization of the PI polymer.

Online study of the formation of PA6 droplets in PP matrix under shear flow

Breakup process of polyamide 6 (PA6) in polypropylene (PP) matrix under shear flow was online studied by using a Linkam CSS 450 stage equipped with optical microscopy. Both tip streaming and fracture breakup modes of PA6 droplets were observed in this study. It was reported that the droplet would break up by tip streaming model when the radio of the droplet phase viscosity to the matrix phase viscosity (n(r) = n(d)/n(m)) is smaller than 0.1 (Taylor, Proc R Soc London A 1934, 146, 501; Grace, Chem Eng Commun 1982, 14, 225; Bartok and Mason, J Colloid Sci 1959, 14, 13; Rumscheidt and Mason, J Colloid Sci 1961, 16, 238; de Bruijn, Chem Eng Sci 1993, 48, 277). However, the tip streaming model was observed even when the viscosity ratio was much greater than 0.1 (n(r) = 1.9). In this study for the tip streaming mode, small droplets were ruptured from the tip of the mother droplet. On the other hand, the mother droplet was broken into two or more daughter droplets with one or several satellite droplets between them for the fracture mode. It was found that PA6 droplet was much elongated at first, and then broke up via tip streaming or fracture to form daughter droplets or small satellite droplets with the shape of fiber or ellipse.

Influence of shear on crystallization behavior of the beta phase in isotactic polypropylene with beta-nucleating agent

Wide-angle X-ray diffraction (WAXD) was used to investigate the effects of shear on the crystallization behavior of polypropylene (PP) with beta-nucleating agent. The melt was subjected to shear at the shear rate from 0.5 to 60 s(-1) for 5 s with a CSS450 shear stage. For the PP with low content of the additive, the formation mechanism of the beta crystals is almost the same as that of pure isotactic polypropylene (iPP), viz., shear induces. Otherwise, for the samples with high content of the additive, the formation mechanism of the beta form are nucleating agent induces. The results clearly show that shear restrains the formation of high beta phase for the melt with additive.

Crystallization kinetics in shearing-induced oriented and stretched poly(ethylene oxide)

Isothermal crystallization kinetics in the melting of poly(ethylene oxide) (PEO) were investigated as a function of the shear rate and crystallization temperature by optical microscopy. The radial growth rates of the spherulites are described by a kinetics equation including shearing and relaxation combined effects and the free energy for the formation of a secondary crystal nucleus. The free-energy difference between the liquid and crystalline phases increased slightly with rising shearing rates. The experimental findings showed that the influence of the relaxation of PEO, which is related to the shear-induced orientation and stretch in a PEO melt, on the rate of crystallization predominated over the influence of the shearing. This indicated that the relaxation of PEO should be more important so that the growth rates increase with shearing, but it was nearly independent of the shear rate within the measured experimental range.

Transition from crazing to shear deformation in ABS/PVC blends

ABS/PVC blends were prepared over a range of compositions by mixing PVC, SAN, and PB-g-SAN. All samples were designed to have a constant rubber level of 12 wt % and the ratio of total-SAN to PVC in the matrix of the blends varied from 70.5/17.5 to 18/80. Transmission electron microscope and scanning electron microscope have been used to study deformation mechanisms in the ABS/PVC blends. Several different types of microscopic deformation mechanisms, depending on the composition of blends, were observed for the ABS/PVC blends. When the blend is a SAN-rich system, the main deformation mechanisms were crazing of the matrix. When the blend is a PVC-rich system, crazing could no longer be detected, while shear yielding of the matrix and cavitation of the rubber particles were the main mechanisms of deformation. When the composition of blend is in the intermediate state, both crazing and shear yielding of matrix were observed. This suggests that there is a transition of deformation mechanism in ABS/PVC blends with the change in composition, which is from crazing to shear deformation.

Polymer concentration, shear and stretch field effects on the surface morphology evolution during the spin-coating

Polymer concentration and shear and stretch field effects on the surface morphology evolution of three different kinds of polymers (polystyrene (PS), polybutadiene (PB) and polystyrene-b-polybutadiene-b-polystyrene (SBS)) during the spin-coating were investigated by means of atomic force microscopy (AFM). For PS and SBS, continuous film, net-like structure and particle structure were observed at different concentrations. For PB, net-like structures were not observed and continuous films and radial array of droplets emerged. Moreover, we compared surface morphology transitions on different substrate locations from the center to the edge. For PS, net-like structure, broken net-like structure and irregular array of particles were observed. For SBS, net-like structure, periodically orientated string-like structure and broken-line structure appeared. But for PB, flower-like holes in the continuous film, distorted stream-like structure and irregular distributions of droplets emerged. These different transitions of surface morphologies were discussed in terms of individual material property.