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The influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components of the instantaneous velocity vector and the instantaneous suspended particle concentration with an acoustic particle flux profiler. The measurements were carried out in clear water and in particle-laden open-channel flows. In both cases, they clearly show the predominance of ejection and sweep phases that are part of a burst cycle. The analysis further demonstrates the importance of the ejection and sweep phases in sediment resuspension and transport. Ejections pick up the sediment at the bed and carry it up through the water column close to the surface. It is shown that ejections and sweeps are in near equality in the near-bottom layer, whereas ejections clearly dominate in the remaining water column. The implications of these results for sediment transport dynamics are discussed. CE Database subject headings: Open channel flow: Sediment transport; Suspended sediments; Turbulence; Sediment concentration; Flow measurement.

To determine the suspended load component of sediment transport in open-channel flow, the vertical distribution of the concentration of suspended particles is of importance. It is usual to determine this distribution by solving the diffusion-convection equation under appropriate boundary conditions. The exponent in the resulting equation is the Rouse number, defined as [Mathematical Expression Omitted]. The [Mathematical Expression Omitted]-value has been the subject of much research. In natural alluvial channels the sediment-laden flow is usually in capacity (saturation) condition, implying that the flow will charge (saturate) itself with particles available in the bed load and/or on the bed itself. However, simulation of sediment-laden flow in a laboratory flume is achieved typically by externally adding particles to the flow. Consequently, it is not certain that the flow was in capacity condition. The resulting [Mathematical Expression Omitted]-values are often values for noncapacity conditions. They should not be used for natural alluvial channels, because they are misleading. Reported herein are experiments performed in the laboratory under noncapacity, as well as under capacity, conditions. This study focuses on the experimental determination of the [Mathematical Expression Omitted]-value, which incorporates the ratio of the sediment flux [c[prime].sub.s]v[prime] and the momentum flux u[prime]v[prime], as well as the velocity and concentration profiles, [Mathematical Expression Omitted] and [Mathematical Expression Omitted], respectively. For experiments with small particles, [d.sub.50] = 0.135 mm, the [Mathematical Expression Omitted]-values at capacity condition are smaller than unity; at noncapacity condition, the [Mathematical Expression Omitted]-values are usually larger than the ones at capacity condition, but all are still smaller than unity.

The fluid mechanics of suspension flow were examined via experiments on uniform flow, noncapacity flow and capacity flow. The results suggested that changes in the velocity distribution across the vertical can be attributed to the presence of solid particles suspended in the flow. Moreover, the study's analysis method and use of DLDV presented several problems involving shear velocity, mean section velocities, velocity profile and energy loss.

The lipid content and composition from an axolemma-rich preparation isolated from squid retinal axons was analyzed.The lipids, which accounted for 45.5% of the dry weight of this membrane, were composed of 22% cholesterol, 66.7% phospholipids and 5.2% free fatty acids. The negatively charged species phosphatidyl ethanolamine (37%), phosphatidyl serine (10%) and lysophosphatidyl ethanolamine (4%) made up 51% of the phospholipids. The amphoteric phosphatidyl choline and sphingomyelin accounted for 39% and 4%, respectively.The relative distribution of fatty acids in each of the isolated phospholipids was studied. The most remarkable feature of these phospholipids was the large proportion of long-chain polyunsaturated fatty acids. The 22∶6 acyl chain accounted for 37% in phosphatidyl ethanolamine, 21.7% in phosphatidyl choline, 17.5% on phosphatidyl serine and 20.3% in sphingomyelin (all expressed as area %).The molar fraction of unsaturated fatty acids reached 65% in phosphatidyl ethanolamine and 42.0 and 44.8% in phosphatidyl choline and phosphatidyl serine, respectively. The double bond index in these species varied between 1.0 and 2.6.The lipid composition of the axolemma-rich preparation isolated from squid retinal axons appears to be similar to other excitable plasma membranes in two important features: (a) a low cholesterol/phospholipid molar ratio of 0.61; and (b) the polyunsaturated nature of the fatty acid of their phospholipids.This particular chemical composition may contribute a great deal to the molecular unstability of excitable membranes. [ABSTRACT FROM AUTHOR]

Oat arginine decarboxylase is synthesized as a 66-kDa proenzyme, but the soluble enzyme is found in oats as a complex of 42- and 24-kDa polypeptide fragments, both derived from the 66-kDa precursor. We report here that this proteolytic cleavage is the result of a processing enzyme, distinct from arginine decarboxylase itself, that leads to activation of the arginine decarboxylase. The proteolysis is resistant to a standard set of protease inhibitors, but is inhibited by high concentrations of Zn2+, as is the activation of arginine decarboxylase. Agmatine, putrescine, spermidine, and spermine, as well as the arginine decarboxylase inhibitor difluoromethylarginine, each had no effect on the reaction. Oat arginine decarboxylase is thus similar to some other amino acid decarboxylases in requiring a proteolytic cleavage for activation; however, it differs in that the other examples are auto-catalytic self-processing.

We have examined soluble oat (Avena sativa) arginine decarboxylase by probing its structure with polyclonal antibodies that separately recognize amino-terminal and carboxyl-terminal antigens and with a monoclonal antibody that immunoprecipitates enzyme activity. These experiments indicated that oat arginine decarboxylase is clipped from a 66,000-D precursor polypeptide into 42,000- and 24,000-D produce polypeptides. Both of these are found in the enzyme and may be held together by disulfide bonds. A full-length precursor protein could not be detected in plants but could be produced by expression of the cDNA in Escherichia coli. Analysis of the expression of the cDNA in E. coli, with antibodies and using pulse labeling with [(35)S]methionine, indicated that the bulk of the expressed protein was the full-length 66,000-D form. Small amounts of 42,000- and 24,000-D polypeptides could also be detected. A reconstruction experiment, adding a radioactively labeled full-length protein isolated from E. coli to powdered oat leaves, supported the idea that the protein extraction method used for western blots was not likely to result in artifactual proteolytic degradation.