Aggregate stability

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Agroforestry: Can trees change aggregate stability ?

Agroforestry: Can trees change aggregate stability ?

. Next analysis to better explain our results : Soil organic matter content /Root morphological traits / Microbial activity & metabolic diversity Soil erodibility = the ability of soils to resist erosion, assessed by measuring soil aggregate stability (Le Bissonnais 1996).

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Spatial variability of soil aggregate stability at the scale of an agricultural region in Tunisia

Spatial variability of soil aggregate stability at the scale of an agricultural region in Tunisia

4.3. Importance of geological information for MWD prediction in Mediterranean area In the study area, the pattern of the geological map at 1/50000 explained much of the spatial organization of topsoil aggregate stability. Therefore, the primary driver of topsoil aggregate stability in the study area was the nature of the substrates and surface deposits, which could be used as a first order proxy for MWD. This conclusion was consistent with results from the pedotransfer approach because most factors involved in pedotransfer functions, i.e., texture, iron content and organic carbon content, directly depended on information included in the geological map. In our study area, land use and management primarily consist of rain fed cereals and leguminous crops managed in a traditional tillage management system with very low organic inputs. The relative homogeneity in farming management might explain that the low effect of this factor on MWD values.
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Effects of vegetation type on soil resistance to erosion: relationship between aggregate stability and shear strength

Effects of vegetation type on soil resistance to erosion: relationship between aggregate stability and shear strength

However, even though a superior aggregate stability may reduce runoff and erosion risk, in filtration may in turn increase, thus augmenting the risk of shallow landslides on steep slopes during heavy precipitation events ( Ghestem et al., in press ). The only way to resolve this apparent con flict is to ensure that aggregate stability and cohesion are improved simultaneously. A small number of studies over the past 30 years have suggested a link between shallow landslides and erosion processes, although quantitative data relating the two are limited ( Al-Durrah and Bradford 1981; Frei et al., 2003; Ghidey and Alberts 1997; Nearing and West 1988; Watson and La flen 1986 ). A major factor governing substrate mass movement is the shear strength of soil ( Terzaghi 1942 ). Shear strength within a soil matrix is the result of resistance to movement at interparticle contacts, due to particle interlocking, physical bonds formed across the contact areas (resulting from surface atoms sharing electrons at interparticle contacts), and chemical bonds, or cementation ( Craig, 2004 ). The two major active components in resistance of soil shear stress are i) the cohesion c, which is the summation of the effect of particle interlocking and cementation and ii) the internal angle of friction Φ. Φ is the angle measured between the normal force and resultant force that is attained when failure occurs in response to a shearing stress.
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Aggregate stability as an indicator of soil susceptibility to runoff and erosion : validation at several levels

Aggregate stability as an indicator of soil susceptibility to runoff and erosion : validation at several levels

The objective of our work was to extend the validation of soil aggregation characterisation as a simple and relevant method to evaluate soil susceptibility to runoff and water erosion. This was done through comparisons of topsoil aggregate stability and field-assessed susceptibility to runoff and erosion. Aggregate stability was determined through immersion and subsequent wet-sieving of <2-mm air-dried soil samples into water, which actually tests aggregate resistance to slaking (Le Bissonnais, 1996). Susceptibility to runoff and erosion was determined at three levels: first through measurements of runoff and soil loss from microplots (1 m 2 ) under simulated rainfall in a southern French Regosol; second through three-year measurements of runoff and soil loss on runoff plots (100 to 800 m 2 ) in Benin, Cameroon and Mexico, with additional data on Syria from the literature; and lastly, soil susceptibility to erosion was determined through the semi-quantitative assessment of the frequency of erosion features, on vineyard hillslopes in southern France.
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Trait-based approach for agroecology: contribution of service crop root traits to explain soil aggregate stability in vineyards

Trait-based approach for agroecology: contribution of service crop root traits to explain soil aggregate stability in vineyards

in agriculture. 5. Conclusion In this study, we did not confirm the hypothesis that root functional markers would have a higher contribution than soil properties to explain aggregate stability in soils with low soil organic carbon content; SOC had higher potential than root functional markers to predict aggre- gate stability overall and in situations with the lowest soil organic carbon contents. However we highlighted some positive relations between root functional markers and soil aggregate stability that encourages research efforts for the study of plant traits and ecosystem services in agriculture. Soil aggregate stability in cropped soils re- sults from complex interactions between soil management strategies, soil properties and plant functional markers, and this study highlighted that service crop communi- ties have an impact on soil stabilization even after a short growth period. Within herbaceous species, we showed that the root mean diameter is an important functional marker to explain soil aggregate stability as it is linked to the root water-soluble concentration and exudation, which have a marked impact on the soil aggregate stability. We also suggest that Fabaceae species may be more efficient than Poaceae species in increasing soil aggregate stability on a short time scale under low SOC contents. Moreover we underlined the predominant role of the past manage- ment strategy in soil stabilization, which directly drives soil organic carbon and the rooting efficiency of service crops. Functional approach is a powerful tool for gaining insight into how plants influence ecosystems and how they respond to environmental factors on a broad scale, and it enables comparison of studies and general application of the findings across a wide range of environments. Plant functioning patterns could be identified on the basis of plant traits, and plant traits may thus reveal ideotypes of service crops and expand the pool of species of interest to provide services in agriculture.
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Short-term dynamics of soil aggregate stability in the field

Short-term dynamics of soil aggregate stability in the field

2 Institut National de la Recherche Agronomique (Inra), UMR1221 LISAH, 2 place Viala, F-34060 Montpellier, France. Abstract Aggregate stability is a key property affecting the movement and storage of water, seedling emergence and soil sensitivity to erosion. Many studies have shown that aggregate stability changes through time. Field monitoring studies performed with a relatively large (monthly) time step showed seasonal trend of aggregate stability. But shorter time step monitoring are required to explore dynamics of aggregate stability at short term. For now, biological activity was recognized to be the main factor of aggregate stability dynamic. But previous studies were currently based on the external stimulation of aggregate stability. The objectives of the study were to assess variations in aggregate stability at short time steps in the field and to identify the factors controlling these variations of stability. A six months field monitoring was performed at short time step (two to five days) on a bare field on
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Organic matter contribution to aggregate stability in silty loam cultivated soils. carbon input effects.

Organic matter contribution to aggregate stability in silty loam cultivated soils. carbon input effects.

Chapitre 2 – Variables biologiques Thus, the control treatment showed a steady state with a very low aggregate stability that is common in a silty soil with low organic matter content (Le Bissonnais & Arrouays, 1997). Our experimental set up has advantages not commonly found in the literature. First, we aimed to describe the whole kinetics of aggregate stability after the addition of an organic source, so we incubated aggregates for 253 days whereas few papers performed similarly long incubations. Second, we applied a wide range of C additions, from 0 to 20 g C kg -1 soil. If we consider 10 cm depth residue incorporation in a cultivated soil with a bulk density of 1.3 Mg m -3 , the C additions correspond to a range from 0 to 26 Mg C ha -1 and the highest rate corresponds to ~ 4-5 times a current agronomic rate of maize residue input. Nevertheless, several circumstances may lead to a localized high concentration of C in cultivated soils. For example, when a residue is incorporated by tillage its distribution is very heterogeneous leading to local zones with a high concentration of substrates (hot spots). Direct drilling leaves organic residues on the soil surface creating very high C contents at the mulch-soil interface. In horticulture, high C inputs are not uncommon. Besides, our goal in using a wide range of C inputs was to evaluate the potential response of soil aggregate stability to infer quantitative relationships. The carbon contents and levels of aggregate stability attained with the higher dose of straw addition at the end of
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K-stability and parabolic stability

K-stability and parabolic stability

1. Introduction The Calabi program is concerned with finding canonical metrics on K¨ahler manifolds. The idea is to look for critical points of the Calabi functional, i.e. the L 2 -norm of the scalar curvature, within a prescribed K¨ahler class. Such metrics are called extremal metrics. The existence problem for extremal metrics is open, even for complex surfaces. The Donaldson-Tian-Yau conjecture roughly says that the existence of extremal metrics with integral K¨ahler class should be equivalent to some algebro-geometric notion of stability of the corresponding polarized complex manifold.
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Convergent trends in aggregate and firm volatility

Convergent trends in aggregate and firm volatility

Figure 8 - Volatility of Growth Rate of aggregate final sales and firm-level sales 7 Variance Decomposition To understand the mechanics of convergence in my sample, I’ve decomposed the variance of the aggregate growth rate of turnover in the Amadeus Database into a variance and covariance component. Firstly I verified that my sample displayed similar characteristics at the aggregate level to those of GDP for the European Union. Contrary to aggregate total sales, my sample exhibits a recovery of sorts in 2008. This is due to the fact that although aggregate total sales was still steeped in recession there was a moderate recovery as part of the European Union’s double dip recession that evidently mostly affected firms the size of our sample. Another reason is the fact that our sample’s size varies. Both of these facts together mean that there is a certain level of noise to the growth rate of the AMADEUS database’s aggregate sales. This influence may tend to induce an upward bias in the trend of volatility of the growth rate of total sales in my sample precisely at those periods with more observations. This problem is particularly evident in the year 2001 of my sample where a sharp increase in the number of observations induces a notably sharp rise in the volatility of growth. Another way to observe this problem would be to look at lower levels of aggregation, for example two-digit NACE sector levels. To conduct variance decomposition, the following notation is introduced. Let be the growth rate of aggregate real sales deflated by the aggregate PPI for the EU17, be the growth rate of real sales for firm i , and be the share of sales for firm i in the total sales of its country from the AMADEUS sample, all in year t. Let be the growth rate of real sales for each sector m deflated by sector-specific deflators. Let be the growth rate of rate of real sales for each country k deflated by the aggregate PPI for the EU17. Also, let denote the variance of for any generic variable Z, and be the covariance between and .
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Costs of aggregate hydrocarbon reserve additions

Costs of aggregate hydrocarbon reserve additions

Comparison of Changes in Quantities. Table 2 shows the quantities of aggregate reserve additions indexed to base 1982 for the three techniques: Divisia, BOE thermal conversion (5.5), and BOE fixed price conversion (10.0). In all years the Divisia index exceeds the thermal index. But the differences are quite modest until the latter half of the 1990s; after 1997 they become appreciable. In 12 years out of 19 the Divisia index exceeds the price ratio index; the contrary years are almost all early on. Beyond 1997 the difference between the Divisia numbers and the fixed coefficient approach is marked. In the last year (2001) the Divisia quantity index is 1.56 (relative to 1982); under thermal conversion the quantity index is 1.40; and price ratio conversion index is 1.36, which happens to be quite close to the thermal index. Annual percentage changes in these indexed quantities are shown in Table 3 and
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Ecofriendly recycled aggregate concrete and bioreceptivity

Ecofriendly recycled aggregate concrete and bioreceptivity

6. V.W. Tam, V., K. Wang, C.M. Tam, Assessing relationships among properties of demolished concrete, recycled aggregate and recycled aggregate concrete using regression analysis, J. Hazard. Mater. 152(2) (2008) 703–714. 7. T.C. Hansen, Recycling of Demolished Concrete and Masonry, Taylor & Francis (1992), K. Ramamurthy, M.S. Mathews, Influence of parent concrete on the properties of recycled aggregate concrete, Constr. Build. Mater. 23(2) 829–836.

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Study of Volta River Aggregate Samples

Study of Volta River Aggregate Samples

Four samples of stone and sand were submitted to the Division of Building Research for determination of alkali.. reactivity.[r]

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Cement-aggregate reaction in Kingston, Ontario

Cement-aggregate reaction in Kingston, Ontario

From the studies in this laboratory which have been summarized above, it is considered justifiable to conclude that, with proper air-entrainment, concretes made with the reactive limesto[r]

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Kingston study of cement-aggregate reaction

Kingston study of cement-aggregate reaction

Kingston study of cement-aggregate reaction Swenson, E. G.; Legget, R. F. https://publications-cnrc.canada.ca/fra/droits L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

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Alkali reactivity of dolomitic limestone aggregate

Alkali reactivity of dolomitic limestone aggregate

Alkali reactivity of dolomitic limestone aggregate Swenson, E. G.; Gillott, J. E. https://publications-cnrc.canada.ca/fra/droits L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

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Rheological modeling of carbon nanotube aggregate suspensions

Rheological modeling of carbon nanotube aggregate suspensions

controlled by the state of aggregation and CNT orientation. The FP description was modified to incorporate aggregation/disaggregation kinetics and a detailed derivation for the AO model is included in this section. The AO distribution function in the AO model is written as ␺ 共x,t, ␳ , n兲, where n 苸关0,1兴 describes the state of aggregation 共n=0 corresponds to CNTs that are free from entanglement and n = 1 represents a CNT aggregate network兲. It is assumed that the flow is steady and homogeneous and that different populations 共n兲 are present within the control volume considered in the balance equation. In more complex flow situations where spatial flow inhomogeneity is present, the material derivative in the FP equation contains the orientation distribution function gradient and it does not reduce to the tem- poral partial derivative. Such spatial dependence does not introduce great difficulties in numerical modeling and is commonly encountered in the simulation of forming processes involving flows in complex geometries. There is, however, also evidence in Fig. 3 show- ing local inhomogeneity in terms of CNT concentration. This type of inhomogeneity has not been taken into account in the current modeling because the kinetic theory approach uses a spatial averaging which filters this type of inhomogeneity. In order to take into account this type of inhomogeneity, Brownian dynamics or finer kinetic theory descrip- tion such as the one proposed by Dhont and Briels 共2005兲 should probably be used. In this paper, the orientation distribution is assumed to depend on the orientation and popu- lation conformational coordinates only, reducing ␺ 共x,t, ␳ , n兲 to ␺ 共 ␳ , n兲. ␺ 共 ␳ , n兲 describes the fraction of CNTs oriented in the direction ␳ and belonged to a population n. It contains information about CNT orientation and aggregation state and the remaining task is to modify the FP equation accordingly.
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The DMM bound: multivariate (aggregate) separation bounds

The DMM bound: multivariate (aggregate) separation bounds

Abstract In this paper we derive aggregate separation bounds, named after Davenport-Mahler- Mignotte (DMM), on the isolated roots of polynomial systems, specifically on the minimum distance between any two such roots. The bounds exploit the structure of the system and the height of the sparse (or toric) resultant by means of mixed volume, as well as recent advances on aggregate root bounds for univariate polynomials, and are applicable to arbitrary positive dimensional systems. We improve upon Canny’s gap theorem [7] by a factor of O(d n−1 ), where d bounds the degree of the polynomials, and n is the number of
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Price Dynamics, financial fragility and aggregate volatility

Price Dynamics, financial fragility and aggregate volatility

These results potentially represent major advances in our understanding of macro-economic fluctuations and the unfolding of crisis. Yet, they abstract away from the actual mechanics of crisis and the temporal dimension embedded in the idea of fluctuation, as they are essentially static and asymptotic: they describe the limit properties of a sequence of economies as the number of firms or of sectors tends towards infinity. Therefore, their relevance is conditional on the existence of a model that provides a micro-economic description of the gen- eration and the propagation of shocks and allows to reproduce dynamically the emergence of aggregate volatility. Agent-based models, which allow to simulate the evolution of complex economic systems formed by heterogeneous interact- ing agents (see LeBaron and Tesfatsion, 2008, for an introduction), are the ideal candidate to provide micro-foundations to these results that crucially rely on non-linearity and deviation from Gaussian standards.
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Aggregate calibration of microscopic traffic simulation models

Aggregate calibration of microscopic traffic simulation models

In summary, the contributions of this thesis are (i) a general formulation for the problem of aggregate calibration in the presence of day-to-day variation in vari[r]

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Price dynamics, financial fragility and aggregate volatility

Price dynamics, financial fragility and aggregate volatility

capture part of the profit (the part that is distributed), the other part consists in retained earnings that increase the firm’s capital and therefore allows the firm to expand. The assumption that each household manages the same num- ber of firms (he receives compensation from all firms whose index is the same as his, see above) is certainly over-simplistic but the distribution of wealth among households has little impact on the dynamics of our model given that consump- tion behavior is independent of the level of income (see subsection 2.4). The assumption that firms are funded by banks rather than by households is con- sistent with the fact that there are neither motives nor means for savings in a setting where there is no capital accumulation and the only financial assets are intra-period loans. As a matter of fact, in absence of capital accumula- tion, aggregate budgetary balance implies that all income should be spent on consumption.
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