Effects of flow velocity variation on rain driven transportation and the role of rain impact in the movement of solids

Soil Research ◽  
1988 ◽  
Vol 26 (3) ◽  
pp. 443 ◽  
Author(s):  
AJ Moss
Keyword(s):  
Flow Velocity ◽  
Water Erosion ◽  
Velocity Variation ◽  
Constant Intensity ◽  
Modes Of Operation ◽  
Direct Dependence ◽  
Individual Drop ◽  
Drop Impacts

Rain-flow transportation in, and airsplash from, shallow sheet flows of varying velocity were investigated experimentally by using four drop sizes at constant intensity (64 mm h-1). Whereas airsplash yields were negligible, rain-flow transportation reached rates of up to 3 g m-1s-1 and exhibited two distinct modes of operation, or regimes, depending on whether the unimpacted flows were laminar or transitional to turbulent. In the first of these regimes, clouds of particles, suspended by individual drop impacts, were moved downstream before settling back to the bed. In the second regime, general turbulence, imposed by drop bombardment, made the flow everywhere able to entrain and transport particles without direct dependence on individual drop impacts. These findings are combined with those of previous studies to make an assessment of the roles of rain and flow in water erosion.

The Risk of Water Erosion on the Foothills of the Middle High Atlas (Morocco): Tagueleft Basin Case Study : خطر التعرية المائية على السفوح بالأطلس الكبير الأوسط (المغرب): دراسة حالة حوض تاكلفت

2020 ◽  
Vol 4 (3) ◽  
Author(s):  
Rizki Mohamed
Keyword(s):  
Land Degradation ◽  
Local Development ◽  
Remote Sensing Data ◽  
Potential Method ◽  
Water Erosion ◽  
High Atlas ◽  
Negative Impacts ◽  
The Impact

The Tagueleft basin is geographically located in the northern edges of the Middle High Atlas, which is a geomorphological fragile area. The impact of human activity has accelerated water erosion in this mountains area. This is reflected in dynamic and unstable foothills, a decrease in forests density and degradation in the production of the land. On the other hand, land degradation due to human overexploitation of natural resources has increased land degradation in the area. The interest in the risk of erosion on the foothills in the area under study comes in the context of our contribution to clarify the role of geomatical and geomorphological approaches in explaining and identifying the mechanisms responsible for current foothills dynamism through water erosion and its negative impacts on the environment and local development. The aim of the study was to use the EPM (Erosion Potential Méthod) which is formulated by Slobodan Gavrilovic for erosion in mountainous areas and to test the reliability of its results based on fieldwork and remote sensing data. The results of the erosion assessment and its quantification by applying the coefficient (W) for the theoretical model in the area under study have shown that erosion is very important and it touches on wide areas as it appears through the domain classification of the distribution erosion in Tagueleft basin.

Introduction

2019 ◽  
pp. 1-25
Author(s):  
Igor Fedyukin
Keyword(s):  
Early Modern ◽  
The State ◽  
The Self ◽  
Modern State ◽  
Modes Of Operation ◽  
Modern Politics ◽  
Traditional Image

The Introduction defines the notion of “administrative entrepreneurship” and outlines the role the “administrative entrepreneurs” played in building the infrastructure of the early modern state, including schools. Recent historiography has tended to question the traditional image of the “absolutist” state as a powerful unified actor, stressing instead the limits of the rulers’ actual power, the role of social compromises, and the pervasiveness of unofficial clans and patronage networks that structured early modern politics in Europe and elsewhere. Scholars also emphasize the premodern, patrimonial character of bureaucracy in that era. Against this backdrop, the Introduction argues that it might have been the self-seeking projectors who drove the invention and expansion of the state as they strove to invent jobs for themselves and to promote their agendas. The chapter introduces three types of “administrative entrepreneurs”—the “experts,” the “ministers,” and the “functionaries”—and outlines their respective modes of operation.

scholarly journals The Recent Sediment Record as an Indicator of Past Soil-Erosion Dynamics. Study in Dehesa Areas in the Province of Cáceres (Spain)

2019 ◽  
Vol 11 (21) ◽  
pp. 6102
Author(s):  
María Teresa de Tena Rey ◽  
Agustín Domínguez Álvarez ◽  
Lorenzo García-Moruno
Keyword(s):  
Water Erosion ◽  
Recent Sediment ◽  
Sediment Record ◽  
Early 19Th Century ◽  
Sediment Deposits ◽  
Historic Data ◽  
Sediment Model ◽  
Fine Gravel ◽  
Soil Stoniness

The work presented is a study of the recent sediment deposits in a pilot basin in dehesa areas in the province of Cáceres (Spain) through analysis of the sediment record, radiocarbon dating and correlation with historic data to assess the factors that conditioned the deposit in these areas over time. It is a qualitative study based on the important role of sediments as recorders of history, given that sediment facies and their architecture provide one of the best records of past processes and environmental factors. For the study, sediment profile surveys were used to determine the configuration and characteristics of the infill and its chronology. The sediment model of the facies studied is associated with a context of slope water erosion that led to the infill of the watercourse areas, mainly sand and fine gravel, where alterations in the normal rate were detected due to the insertion of a thicker level of materials (soil stoniness) that was able to be dated. The sediment and chronological results obtained can be used to determine the historical events in the area that could have affected the erosion and deposit processes in the basin for the estimated period, from the late 18th to the early 19th century. During this period, pastureland that maintained the ecological balance of the dehesa, with a balanced, stable displacement of soil particles, was converted to cropland, in most cases resulting in soil with a limited profile, overuse and the consequent loss of structure and texture, making it more vulnerable to erosion. Greater remobilisation would have carried thicker material to the watercourses than the material deposited as a result of limited ploughing. This study provides data for the dehesa areas studied with regard to their hydrogeomorphological dynamics, from which past environmental impacts due to tillage can be inferred.

On the Role of Enduring Contact in Powder Lubrication

2005 ◽  
Vol 128 (1) ◽  
pp. 168-175 ◽  
Author(s):  
J. Y. Jang ◽  
M. M. Khonsari
Keyword(s):  
Analytical Solution ◽  
Flow Velocity ◽  
Volume Fraction ◽  
Flow Characteristics ◽  
Kinetic Regime ◽  
Governing Equations ◽  
Wide Range ◽  
Fraction Distribution ◽  
Powder Lubrication

This paper is devoted to a study of the enduring contact between granules of powder lubricants in an effort to better understand the flow characteristics of powder lubricants. Appropriate formulation of the governing equations is reported that can be used for prediction of the flow velocity, pseudo temperature, and volume fraction distribution of powders for a wide range of operating speeds. A set of parametric simulations and a limiting analytical solution is presented for predicting the behavior of a powder lubricant under low operating speeds when the enduring contact tends to dominate the kinetic regime. The limiting solution shows that below a certain sliding speed the volume fraction remains unchanged due to the effect of the enduring contact. It is also shown that below this limiting speed the enduring contact plays a major role and should not be neglected.

scholarly journals Some Possible Causes For Recent Variations Of Patagonian Glaciers

1990 ◽  
Vol 14 ◽  
pp. 351 ◽  
Author(s):  
Renji Naruse ◽  
Masamu Aniya
Keyword(s):  
Flow Velocity ◽  
Air Temperature ◽  
Water System ◽  
Large Change ◽  
Heavy Precipitation ◽  
Field Studies ◽  
Melting Rate ◽  
Velocity Variation ◽  
Ice Flow ◽  
San Rafael

The Patagonian glaciers located in the southern part of the Andes between 46°30′S and 51°30′S are characterized by typical temperate conditions of heavy precipitation, rapid ice flows and high melting rates. During the austral summers of 1983–84 and 1985–86, field studies were made of the ice flow, heat balance and morphology of several glaciers in Patagonia. Coupled with aerial photographic surveys, these revealed that most glaciers had retreated extensively in the recent years, a maximum being 200 m a-1 at San Rafael Glacier from 1974 to 1986. The lower part of Soler Glacier had thinned by a rate of 5.2 m a-1 from 1983 to 1985. This paper presents three possible mechanisms to explain the large variation of temperate glaciers during the last decade, based on analyses of mass balance and dynamics of Patagonian glaciers: (1) The annual melting rate was estimated at about 10–15 m a-1 in water equivalent over the ablation area (from 350 to 1350 m a.s.l.) of Soler Glacier. Monthly mean air temperature in the coldest season (June through August) was estimated at about 0°–4°C near the termini of most glaciers in Patagonia. That temperature coincides with an air temperature which is critical for solid or liquid precipitation. The difference in the surface albedo, that is, 0.7–0.8 for new snow and 0.4–0.55 for bare ice (0.1–0.2 for debris-covered ice), results in different melting rates. Hence, a slight change in air temperature should cause an enhanced change in ice thickness by a positive feedback mechanism. (2) The flow velocity was measured or estimated and was found to change daily and seasonally by factors of 3 to 5 at Soler Glacier. The large flow velocity variation was attributed to difference in the basal sliding velocity. Consequently, a change in the amount of subglacial water or the structure of the basal water system should cause a large change in the ice flow, which in turn results in a retreat or an advance of the glacier-like “mini-surge”. (3) Frequent fluctuations of calving glaciers (e.g. San Rafael and Pio XI glaciers) have been much reported; however, information on the position of the grounding lines is very scarce. The advance or retreat of the glacier front may possibly have been affected by that of the floating terminus. The rate of calving from the ice tongue or spreading of ice shelves should mainly be controlled by the melting rate of ice in the water and by the mechanical properties of ice, and these factors are not directly related to climatic change or the surge phenomenon.

Working through Barriers: Shaping Social Workers’ Engagement in Policy Practice

2019 ◽  
Vol 50 (4) ◽  
pp. 1107-1125 ◽  
Author(s):  
Hani Nouman ◽  
Lia Levin ◽  
Einat Lavee
Keyword(s):  
Social Workers ◽  
Open Systems ◽  
Transformation Process ◽  
Modes Of Operation ◽  
Policy Makers ◽  
Policy Practice ◽  
The Social ◽  
Depth Interviews ◽  
Policy Arena

Abstract Although social workers’ engagement in policy-shaping processes to advance social justice reflects this obligation of the social work profession, many social workers avoid implementing policy practice (PP). Previous studies have identified several barriers limiting social workers’ use of this practice. However, how such barriers can be overcome remains under-studied. In this study, we address this lacuna by examining the role of social workers vis-à-vis their engagement in PP, through the theoretical framework of social psychology of organizations, and therein, through ideas concerning open systems and the formation of roles and praxes in organizations. Drawing on twenty-eight in-depth interviews and three focus groups, we demonstrate how social workers underwent a coping and transformation process that increased their engagement in PP. In certain situations, it was the expectations of colleagues and the challenges posed by them that impelled social workers to re-examine their approach to such engagement and enhance it. We show how social workers can overcome barriers and facilitate their involvement in the policy arena, as well as highlight policy-makers’ role in shaping social workers’ modes of operation.

scholarly journals Aquatic High Intensity Interval Training for Cardiometabolic Health

2016 ◽  
Vol 11 (1) ◽  
pp. 64-76 ◽  
Author(s):  
Elizabeth F. Nagle ◽  
Mary E. Sanders ◽  
Barry A. Franklin
Keyword(s):  
High Intensity ◽  
Interval Training ◽  
Cardiometabolic Health ◽  
Attractive Alternative ◽  
High Intensity Interval Training ◽  
Constant Intensity ◽  
Acute Responses ◽  
Fitness Benefits ◽  
High Intensity Interval

High-intensity interval training (HIIT) has emerged as an attractive alternative to traditional continuous exercise training (CT) programs for clinical and healthy populations who find that they can achieve equal or greater fitness benefits in less time. Land-based HIIT may not be an appropriate choice for some participants. Few studies have explored the acute responses and chronic adaptations of HIIT in an aquatic environment, and no study has compared the cardiometabolic responses of an aquatic-based program to a land-based HIIT program. Shallow-water aquatic exercise (AE) programs utilizing HIIT have elicited comparable and, in some cases, greater physiological responses compared with constant-intensity or continuous AE regimens. Factors that may explain why HIIT routines evoke greater cardiometabolic responses than CT protocols may be based on the types of exercises and how they are cued to effectively manipulate hydrodynamic properties for greater intensities. Favorable aquatic HIIT protocols such as the S.W.E.A.T. system may serve as a beneficial alternative to land-based HIIT programs for clinical, and athletic populations, potentially reducing the likelihood of associated musculoskeletal and orthopedic complications. Hence, the purpose of this review is to examine the role of AE as an alternative safe and effective HIIT modality.

scholarly journals Succession and features distribution plant associations in row of railways

2016 ◽  
Vol 5 (4) ◽  
pp. 31-35
Author(s):  
Nikolay Alexandrovich Nikitin ◽  
Vera Valentinovna Solovieva
Keyword(s):  
Water Erosion ◽  
Processes Of Change ◽  
Ruderal Vegetation ◽  
Soil Lead ◽  
Erosion Processes ◽  
Plant Associations ◽  
Initial Stage ◽  
Motley Grass ◽  
Exchange Structure

ROW is a specific man-made landscape, in which the processes of change occur in its direction and intensity. Erosion processes, in particular the processes of water erosion of soil, lead not only to changes in the soil, but the plant through changes in soil fertility, nutrient richness, and by changing moisture exchange, structure and texture of soils. The main characteristics of flora undergo structural, quantitative and other changes. Vegetation characteristics, composition of plant associations, the speed and direction of succession, from the initial stage of overgrown weeds and ruderal vegetation to sustainable tree and shrub communities also modify. An ecological and geomorphological zoning shows the prevalence of the most eroded soils in the vicinity of the web. The regularity according to which in most habitats anthropogenic disturbed grow motley-grass-wheatgrass association with a reduction of anthropogenic load becomes dominant forb meadow-grass association. The role of indication of Eletrygia repens L. was also identified as an indicator of habitat disturbance.

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