The Woody Guthrie Centennial Bibliography

This bibliography updates two extensive works designed to include comprehensively all significant works by and about Woody Guthrie. Richard A. Reuss published A Woody Guthrie Bibliography, 1912–1967 in 1968 and Jeffrey N. Gatten\u27s article “Woody Guthrie: A Bibliographic Update, 1968–1986” appeared in 1988. With this current article, researchers need only utilize these three bibliographies to identify all English-language items of relevance related to, or written by, Guthrie

Glucocorticoids in T cell apoptosis and function

Glucocorticoids (GCs) are a class of steroid hormones which regulate a variety of essential biological functions. The profound anti-inflammatory and immunosuppressive activity of synthetic GCs, combined with their power to induce lymphocyte apoptosis place them among the most commonly prescribed drugs worldwide. Endogenous GCs also exert a wide range of immunomodulatory activities, including the control of T cell homeostasis. Most, if not all of these effects are mediated through the glucocorticoid receptor, a member of the nuclear receptor superfamily. However, the signaling pathways and their cell type specificity remain poorly defined. In this review, we summarize our present knowledge on GC action, the mechanisms employed to induce apoptosis and the currently discussed models of how they may participate in thymocyte development. Although our knowledge in this field has substantially increased during recent years, we are still far from a comprehensive picture of the role that GCs play in T lymphocytes

An experimental investigation of floc characteristics in a diffusive turbulent flow

The work presented aimed at investigating the influence of the physical processes effecting mud flocculation in a grid stirred experiment. Two natural muds from the Gironde estuary (organic and another with the organic content removed) and mud from the Tamar estuary (organic) were used to examine the influence of the biological and chemical compositions on interparticular collision efficiency (i.e. stickiness). For every experiment, the mean sediment concentration were deduced from extracted water samples and by optical methods. The turbulent shearing was estimated from high frequency measurements of the velocity profile. Floc size and settling velocity were obtained by high resolution video observational techniques. The study showed that particles are advected with the large scale turbulent eddies from low to high turbulent shearing regions. It does not imply an instantaneous response and floc properties remained predominantly homogeneous in the water column of the experimental tank. From the measurements made, it is therefore possible to conclude that time scales associated to the turbulent transport are much smaller than the ones associated to flocculation processes. As sediment concentrations increased up to 8 g.l -1 , the increase in particle collision frequency enhanced the flocculation process to such a high degree that only a small percentage of the total floc population fell within the microfloc (< 120 µm) size range. Flocculation is especially significant for trials with organic muds and the effect of floc break-up by inter-particular collisions was not observed, at all shear and concentration levels, during our study. The Gironde mud with the organic components neutralised produced only a minor number of flocs, at all shear and suspended concentration combinations, which exceeded the pre-sieving mesh size of 125 µm. This highlights the important role organic matter plays in the flocculation of natural cohesive sediments. This paper compares the distribution of size and settling velocity of macroflocs and microflocs and mean floc properties for the different sediment types under the various experimental concentration and shear ranges. The findings highlight how floc properties change in response to their ambient environment. ADDITIONAL INDEX WORDS: cohesive sediments, floc size, settling velocity, turbulent shear, grid stirred experimen

The flocculation characteristics of freshly eroded aggregates

In Europe, 260,000 km2 of soils already suffer erosion by water. This worrying level of land degradation is expected to increase in the context of climate change, with situations particularly critical in mountainous environments. As any multi-use resources, there is also a growing human pressure on mountainous rivers. Data is required to obtain a better understanding of the cycles of deposition and erosion and of the respective contributions of natural and human-induced processes to fine, cohesive sediment fluxes. When placed in suspension in rivers, cohesive materials are principally transported as flocs. The quantity of suspended solids exported downstream depends mainly of their morphometric properties, including: size, shape and effective density. Once eroded on hillslopes, the conveyance of fine sediment particles on continental surfaces requires the maintenance of particles in suspension by nearbed turbulence and its advection downstream by the mean flow. Traditional Rouse profile relationships do not readily hold for highly concentrated riverine suspensions (~10 g/l), where processes such as flocculation, hindered settling and stratification interplay. This study aims at improving sediment transport parameterisation, by examining the kinetics of fine soil aggregates (size, settling velocity, density), once immersed in a turbulent flow. Particle properties of three Mediterranean materials (clay loam soil, black marl and molasse, all sampled in Badlands environments) were tested in the grid stirred experiment following the protocol previously used by Gratiot and Manning (2004). Hydrodynamic properties were monitored with ADV and turbidity sensors. For each soil, three sediment loads (1.5; 5; 10 g.l-1) representative of flood conditions were tested. Aggregate properties were obtained after sampling at four depths above the grid, using the LabSFLOC – Laboratory Spectral Flocculation Characteristics – technique (Manning, 2006) and laser techniques. These acquisition heights are associated with the corresponding turbulence dissipation rates G of 1.5, 3, 7 and 19 s-1. Flocculation rates and dynamics are reported and discussed

Sub-daily variability of suspended sediment fluxes in small mountainous catchments &ndash implications for community-based river monitoring

International audienceAccurate estimates of suspended sediment yields depend on effective monitoring strategies. In mountainous environments undergoing intense seasonal precipitation, the implementation of such monitoring programs relies primarily on a rigorous study of the temporal variability of fine sediment transport. This investigation focuses on seasonal and short-term variability in suspended sediment flux in a subhumid region of the Mexican Volcanic Belt. Intensive monitoring was conducted during one year in four contrasting catchments (3 to 630 km2). Analyses revealed significant temporal variability in suspended sediment export over various time scales, with between 63 and 97% of the annual load exported in as little as 2% of the time. Statistical techniques were used to evaluate the sampling frequency required to get reliable estimates of annual sediment yield at the four sites. A bi-daily sampling scheme would be required at the outlet of the 630 km2 catchment, whereas in the three smaller catchments (3-12 km2), accurate estimates would inevitably require hourly monitoring. At the larger catchment scale, analysis of the sub-daily variability of fine sediment fluxes showed that the frequency of sampling could be lowered by up to 100% (i.e. from bi-daily to daily) if a specific and regular sampling time in the day was considered. In contrast, conducting a similar sampling strategy at the three smaller catchments could lead to serious misinterpretation (i.e. up to 1000% error). Our findings emphasise the importance of an analysis of the sub-daily variability of sediment fluxes in mountainous catchments. Characterising this variability may offer useful insights for improving the effectiveness of community-based monitoring strategies in rural areas of developing countries. In regions where historical records based on discrete sampling are available, it may also help assessing the quality of past flux estimates. Finally, the study confirms the global necessity of acquiring more high frequency data in small mountainous catchments, especially in poorly gauged areas

On the determination of the settling flux of cohesive sediments in a turbulent fluid

International audienceIn this paper we compare the settling flux of a cohesive sediment mixture measured in a quiescent fluid with that achieved in a turbulent flow. Experiments were performed in a mixing tank. The turbulence produced mechanically by an oscillating grid maintains a stationary, highly concentrated fluid mud layer in which the concentration is almost uniform. In this layer the turbulence decay with increasing distance from the grid is similar to that obtained in clear water. For steady conditions the settling flux of the fluid mud mixture is balanced by the upward turbulent flux, and its value can be determined from the measured depth of the fluid mud layer. At high concentrations (10–200 g L−1), we show that the settling flux in a turbulent fluid is much larger than estimated in a quiescent fluid (up to two orders of magnitude). Hindering effects in the settling process of cohesive sediments may thus be considerably reduced by turbulence

Dynamics of concentrated benthic suspension layers

This paper describes the dynamics of Concentrated Benthic Suspensions (CBS). CBS is defined as a suspension of cohesive sediment with a notable interaction between the sediment and the turbulent flow field through buoyancy effects, but still displaying near-Newtonian behaviour. The mechanisms which distinguish CBS from low-concentrated suspensions are described, and the focus is on the (hindered) settling and mixing processes. Experiments were carried out in an oscillating grid tank and in an rotating annular flume, simulating entrainment and mixing associated with the turbulent CBS-layer, as occur in tide-driven flows. It is shown that CBS can be modelled as a viscous fluid, and that the entrainment rates quantitatively match relations described in the literature on salt-fresh water induced stratified systems. Numerical simulations with one-dimensional vertical models using k-?: and Prandtl mixing length turbulence closures were carried out for hypothetical open channel flows to study the behaviour of CBS through sensitivity analyses. It is shown that high-concentrated mud suspensions may become saturated, generating a CBS-layer prior to the formation of fluid mud

Analyse de l'incertitude globale pour le suivi des sédiments en suspension par turbidimétrie dans un petit bassin versant montagneux

International audienceA major challenge confronting the scientific community is to understand both patterns of and controls over spatial and temporal variability of suspended sediment dynamics in rivers, as these sediment govern nutriment export, river morphology, siltation of downstream reservoirs and degradation of water quality. High-frequency suspended sediment monitoring programs are required to meet this goal, particularly research in highly erodible mountainous catchments which supply the sediment load of the entire downstream fluvial network. However, in this context, analysis of the data and their interpretation are generally limited by many sources of uncertainty in river monitoring. This paper proposes to estimate the global uncertainty of suspended sediment monitoring using turbidimeter in a small mountainous river catchment (22 km2; Southern French Alps). We first conducted a detailed analysis of the main uncertainty components associated with the turbidity approach, i.e. a widely used method to continuously survey the suspended sediment concentration (SSC). These uncertainty components were then propagated with Monte Carlo simulations. For individual records, SSC uncertainties are found to be on average less than 10%, but they can reach 70%. At the flood scale, the mean and the maximum SSC uncertainties are on average 20% (range, 130%), whereas sediment yield uncertainty is a mean 30% (range, 2050% depending on the flood considered; discharge error, 20%). Annual specific sediment yield (SSY) was then 360 ± 100 t km2 year1. Uncertainty components associated with the automatic pumping procedure, discharge measurement and turbidity fluctuation at the short time scale were found to be the greatest uncertainties. SSC and SSY uncertainties were found highly site- and time-dependent as they vary significantly with the hydro-sedimentary conditions. This study demonstrates that global uncertainty accounts for only a small part of inter-flood SSC and SSY variability. It outlines the controlling factors of land use, relief, geology and rainfall regime on suspended sediment yields