Furrow Erosion and Water and Soil Management

EFFECTS of basic water and soil interactions on erosion are reported. The effects of flow rate and slope on perimeter shear stress are outlined for channels in which the ratio of breadth and depth of the flow cross section stay reasonably constant. Effects of the resulting shear stress on erosion are discussed in terms of coefficients for the equations developed and several data sets. For furrows with a relatively constant breadth to depth ratio, erosion appears to be related to the shear stress by an exponent which varies between two and four depending on the range of cohesive forces holding the soil particles to underlying soil. The data sets studied indicate continuous exponential relationships rather than a "critical shear stress" below which there is no erosion. Following disruption of Portneuf silt loam by tillage or compaction, cohesion increases with time. Maximum rate of cohesion increase occurs when the soils are moist, but have sufficient tension in the water to draw the particles firmly together. Rapid wetting of dry soils disrupts a majority of the bonds between particles, allowing aggregate disintegration which reduces infiltration rates and substantially increases erosion. Considering erosion as an independent factor, not affected by sediment load and carrying capacity, allowed development of equations which appear to describe the whole erosion-deposition process. These findings indicate several management options which can decrease furrow erosion

Symmetries of a class of nonlinear fourth order partial differential equations

In this paper we study symmetry reductions of a class of nonlinear fourth order partial differential equations \be u_{tt} = \left(\kappa u + \gamma u^2\right)_{xx} + u u_{xxxx} +\mu u_{xxtt}+\alpha u_x u_{xxx} + \beta u_{xx}^2, \ee where $\alpha$, $\beta$, $\gamma$, $\kappa$ and $\mu$ are constants. This equation may be thought of as a fourth order analogue of a generalization of the Camassa-Holm equation, about which there has been considerable recent interest. Further equation (1) is a ``Boussinesq-type'' equation which arises as a model of vibrations of an anharmonic mass-spring chain and admits both ``compacton'' and conventional solitons. A catalogue of symmetry reductions for equation (1) is obtained using the classical Lie method and the nonclassical method due to Bluman and Cole. In particular we obtain several reductions using the nonclassical method which are no} obtainable through the classical method

Nonlinear stability of oscillatory wave fronts in chains of coupled oscillators

We present a stability theory for kink propagation in chains of coupled oscillators and a new algorithm for the numerical study of kink dynamics. The numerical solutions are computed using an equivalent integral equation instead of a system of differential equations. This avoids uncertainty about the impact of artificial boundary conditions and discretization in time. Stability results also follow from the integral version. Stable kinks have a monotone leading edge and move with a velocity larger than a critical value which depends on the damping strength.Comment: 11 figure

Interconnecting Governments, Businesses and Citizens – A Comparison of Two Digital Infrastructures

Part 2: Services and InteroperabilityInternational audiencePublic and private organizations in various areas are setting up digital Information Infrastructures (IIs) for interconnecting government, businesses and citizens. IIs can create value by sharing and integrating data of multiple actors. This can be the basis for value added services and especially collaborations of public and private partners can make IIs thrive. Easier access to integrated services and products (jointly) offered by government and businesses may stimulate transparency and innovations. IIs are under development in many domains, including for open data and international trade. However, there are notable differences in the design, characteristics and implementation of the IIs. The objective of this paper is to compare two diverse IIs in order to obtain a better understanding of common and differing elements in the IIs and their impact. Among the differences are the roles of government, businesses and users, in driving, developing and exploitation of the IIs

Groundwater table fluctuations recorded in zonation of microbial siderites from end-Triassic strata

In a terrestrial Triassic–Jurassic boundary succession of southern Sweden, perfectly zoned sphaerosiderites are restricted to a specific sandy interval deposited during the end-Triassic event. Underlying and overlying this sand interval there are several other types of siderite micromorphologies, i.e. poorly zoned sphaerosiderite, spheroidal (ellipsoid) siderite, spherical siderite and rhombohedral siderite. Siderite overgrowths occur mainly as rhombohedral crystals on perfectly zoned sphaerosiderite and as radiating fibrous crystals on spheroidal siderite. Concretionary sparry, microspar and/or micritic siderite cement postdate all of these micromorphologies. The carbon isotope composition of the siderite measured by conventional mass spectrometry shows the characteristic broad span of data, probably as a result of multiple stages of microbial activity. SIMS (secondary ion mass spectrometry) revealed generally higher δ13C values for the concretionary cement than the perfectly zoned sphaerosiderite, spheroidal siderite and their overgrowths, which marks a change in the carbon source during burial. All the various siderite morphologies have almost identical oxygen isotope values reflecting the palaeo-groundwater composition. A pedogenic/freshwater origin is supported by the trace element compositions of varying Fe:Mn ratios and low Mg contents. Fluctuating groundwater is the most likely explanation for uniform repeated siderite zones of varying Fe:Mn ratios reflecting alternating physiochemical conditions and hostility to microbial life/activity. Bacterially mediated siderite precipitation likely incorporated Mn and other metal ions during conditions that are not favourable for the bacteria and continued with Fe-rich siderite precipitation as the physico-chemical conditions changed into optimal conditions again, reflecting the response to groundwater fluctuations

Furrow Erosion and Water and Soil Management

EFFECTS of basic water and soil interactions on erosion are reported. The effects of flow rate and slope on perimeter shear stress are outlined for channels in which the ratio of breadth and depth of the flow cross section stay reasonably constant. Effects of the resulting shear stress on erosion are discussed in terms of coefficients for the equations developed and several data sets. For furrows with a relatively constant breadth to depth ratio, erosion appears to be related to the shear stress by an exponent which varies between two and four depending on the range of cohesive forces holding the soil particles to underlying soil. The data sets studied indicate continuous exponential relationships rather than a "critical shear stress" below which there is no erosion. Following disruption of Portneuf silt loam by tillage or compaction, cohesion increases with time. Maximum rate of cohesion increase occurs when the soils are moist, but have sufficient tension in the water to draw the particles firmly together. Rapid wetting of dry soils disrupts a majority of the bonds between particles, allowing aggregate disintegration which reduces infiltration rates and substantially increases erosion. Considering erosion as an independent factor, not affected by sediment load and carrying capacity, allowed development of equations which appear to describe the whole erosion-deposition process. These findings indicate several management options which can decrease furrow erosion

Factors Affecting Furrow Erosion

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Aspectos epidemiológicos da meningite meningocócica no município de São Paulo (Brasil), no período de 1968 a 1974 Epidemiological aspects of meningococcal meningitis in the city of S. Paulo, Brazil from 1968 through 1974

Estudo epidemiológico da meningite meningocócica no município de São Paulo no período de janeiro de 1968 a junho de 1974. A partir de julho de 1971 uma epidemia causada pelo meningococo sorogrupo C ocorreu na área. Em abril de 1974 foi observado o início de uma segunda epidemia determinada pelo meningococo sorogrupo A. Os maiores coeficientes de morbidade durante o período estudado ocorreram: nos meses frios; nos distritos sanitários da periferia do município; no grupo etário de 0 a 4 anos, no sexo masculino. No primeiro mês das duas epidemias diferiu significantemente o grupo etário mais atingido. A letalidade decresceu de 15,0% em 1968-1970 para 7,9% em 1971-1974. Ela apresentou, durante o período epidêmico, uma variação sazonal no sentido inverso ao da morbidade.<br>An epidemiological study of meningococcal meningitis in the city of S. Paulo, Brazil (population in 1970: 5.931.935 inhabitants) during the period ranging from January 1968 to June 1974 was undertaken. Two outbreaks of meningococcal meningitis occurred during this period in the area under study. The first one began in July 1971, due to serogroup C Neisseria meningitidis; the second one began in april 1974, when the first outbreak had not yet finished and was caused by serogroup A Neisseria meningitidis. The attack rates were higher during the colder months. The majority of the cases occurred in the peripheric districts. Males and infants were at greatest risk. There ivas, however, a significant difference in the age of groups affected by the disease in the first month of both epidemics. The case-fatality ratios (deaths/cases) decreased from 15% (pre-epidemic period of 1968-1970) to 7,9% (epidemic period of 1971-1974.). There was a seasonal variation in the case-fatality ratio during the epidemic period: in colder months it decreased and in warmer months it increased