130,597 research outputs found
Understanding pool-riffle dynamics through continuous morphological simulations
No full textPool-riffle dynamics is governed by complex time and spatial interactions between water and sediment flows. In the last few decades, significant advances have been made in characterizing and modeling the hydrodynamics of pool-riffle sequences, and this information has been extensively used as the basis of conceptual models to describe or infer pool-riffle morphodynamics. A lot less attention, however, has been paid to the coupled dynamics of flow and sediment, which is essential to fully understand these complex geomorphic systems. This paper uses an unsteady 1-D flow-morphology and bed-sorting model to analyze pool-riffle dynamics. The model is first applied to a pool-riffle sequence on a 1.1 km reach of the lower Bear Creek, Arkansas, United States. After showing the model's ability to describe the general reach hydrodynamics and morphological evolution over 1 year, the detailed sediment and flow information is used to investigate pool-riffle dynamics in terms of self-maintenance mechanisms. Two effects that have been only marginally explored in the past, i.e., bed sediment sorting and downstream riffle control, are explained and quantified with the help of the model's outputs. The results show that self-maintenance occurs more frequently than previously thought as a result of grain sorting and that erosion or deposition of contiguous riffles also constitutes a self-maintenance mechanism. These findings provide the support for a physically based, integral description of pool-riffle morphodynamics and highlight the importance of flow and sediment variability on pool-riffle self-maintenance. The morphodynamic analysis bridges the gap between observations and current theories based mainly on hydrodynamic information
Recommended from our members
[News Clip: Tar pool]
No full textVideo footage from the WBAP-TV station in Fort Worth, Texas, covering a news story about Ross V. Osterhout who built a pool in his yard out of tar paper for less than $500
An Intergenerational Common Pool Resource Experiment
No full textintergenerational common pool resources;growth and altruism;free-riding intentions
Desiccation of rock pool habitats and its influence onpopulation persistence in a Daphnia metacommunity
No full textHabitat instability has an important influence on species' occurrence and community composition. For freshwater arthropods that occur in ephemeral rock pools, the most drastic habitat instabilities are droughts and the intermittent availability of water. However, although the desiccation of a rock pool is detrimental for planktonic populations, it may also bring certain benefits: the exclusion of predators or parasites, for example, or the coexistence of otherwise competitively exclusive species. The commonness of drought resistant resting stages in many aquatic organisms shows the ecological significance of droughts. We measured daily evaporation in 50 rock pools inhabited by three Daphnia species D. magna, D. longispina and D. pulex over one summer. Daily evaporation and ultimately desiccation showed significantly seasonally influenced correlation with pool surface area, presence of vegetation, ambient temperature, wind and standardized evaporation measures. We used the estimates from this analysis to develop a simulation model to predict changes in the water level in 530 individual pools on a daily basis over a 25-year period. Eventually, hydroperiod lengths and desiccation events could be predicted for all of these rock pools. We independently confirmed the validity of this simulation by surveying desiccation events in the 530 rock pools over a whole season in 2006. In the same 530 rock pools, Daphnia communities had been recorded over the 25 years the simulation model considered. We correlated pool-specific occupation lengths of the three species with pool-specific measures of desiccation risk. Occupation lengths of all three Daphnia species were positively correlated with maximum hydroperiod length and negatively correlated with the number of desiccation events. Surprisingly, these effects were not species-specific
Effect of torch angle on arc properties and weld pool shape in stationary GTAW
No full textIn this paper, a three dimensional numerical simulation is performed on a stationary arc to study the effect of torch angle in gas tungsten arc welding (GTAW) of SS304 stainless steel. A comparison has been made to investigate 90o and 70o torch angles and analyze the effect on arc and weld pool shape. Current density, heat flux and gas shear stress are calculated in the arc region and are used as input to the workpiece to determine the weld pool. Buoyancy and Marangoni shear also affect the weld pool shape and are taken into account. The computed and experimental results are observed symmetric for 90o torch angle. For 70o torch angle, current density and hence the heat flux due to electron contribution is found the maximum behind and heat flux due to conduction and convection is found the maximum ahead of the electrode tip in the welding direction. This makes the maximum of total heat flux symmetric along the arc center. Heat flux due to conduction and convection decreases as the torch angle decreases resulting in a shallow weld pool. The nonsymmetric “w” shaped weld pool is developed by the combined effect of the gas shear and Marangoni convection. It is found that for 70o torch angle, the weld pool becomes non-symmetric, shallow and wide ahead of the electrode tip in the welding direction. The numerical weld pool shapes are verified through experiments
Assessing the health impact of local amenities: a qualitative study of contrasting experiences of local swimming pool and leisure provision in two areas of Glasgow
No full textStudy objective: To assess the health impacts of local public swimming pool and leisure provision.
Design: Retrospective qualitative study using focus groups. Reports from two areas with contrasting experience of provision of a public swimming pool (opening and closure) were compared within the context of general reports about health and neighbourhood.
Setting: Two deprived neighbourhoods in south Glasgow.
Participants: Local adult residents of mixed ages, accessed through local community groups.
Main results: In both areas the swimming pool was reported as an important amenity that was linked to health and wellbeing. However, few residents reported regular use of the pool for physical activity. Use of the pool facility for social contact was directly linked to reports of relief of stress and isolation, and improved mental health. Pool closure was one in a series of amenity closures and area decline and was used to represent other area changes. Health impacts were strongly linked to the pool closure. The pool opening was associated with local area regeneration, similar but less prominent links between swimming pool provision and health were reported. Health benefits of social contact were diffuse and linked to other local amenities as well as the new pool facility.
Conclusions: Although theoretically linked to increased physical activity, the health benefits conveyed by the swimming pool may be more closely linked to the facilitation of social contact, and a supervised facility for young children. The use of qualitative work to investigate area based change provides rich contextual data to strengthen and explain the reported health impacts
Exit-Pool
No full textInternational Ideas Competition Man made reformulate. 4th International Architecture Triennale 2010, Oslo. Project "Exit-Pool" with: F. Marullo, F. Perugini, G. Sponzilli, V. Signore. Second prize with honorable mention
The Role of Rivalry. Public Goods versus Common-Pool Resources
No full textDespite a large theoretical and empirical literature on public goods and common-pool resources, a systematic comparison of these two types of social dilemmas is lacking. In fact, there is considerable confusion about these two types of dilemma situations. As a result, they are often treated alike. In this paper we argue that the degree of rivalry is the fundamental difference between the two games. We show that rivalry implies that both games cannot be represented by the same game theoretic structure. Fur-thermore, we experimentally study behavior in a quadratic public good and a quadratic common-pool resource game with identical Pareto opti-mum but divergent interior Nash equilibria. The results show that partici-pants clearly perceive the differences in rivalry. Aggregate behavior in both games starts relatively close to Pareto efficiency and converges to the respective Nash equilibrium.
Pallet pool
No full textPředložená diplomová práce se zabývá systémem paletového poolu. Hlavním cílem bylo shromáždit informace o dané problematice a analyzovat procesy paletového poolu. Na paletový pool bylo nahlíženo ze dvou různých pohledů z pohledu směny palet mezi uživateli (otevřený paletový pool) a z pohledu možnosti nájmu palet (uzavřený paletový pool). Podmínky směny palet byly objasněny v jediném současném fungujícím otevřeném paletovém poolu, Evropském paletovém poolu (EPP). Práce byla zaměřena na vývoj EPP a současné problémy, se kterými se EPP potýká. Popsána byla kvalita, jednotlivé stupně jakosti a správné značení palet směnitelných v EPP. Další část práce byla zaměřena na uzavřený paletový pool. Procesy pronájmu palet byly vysvětleny u největšího světového pronájemce palet společnosti CHEP. Zmíněny byly i další společnosti provozující uzavřený paletový pool. Poslední část diplomové práce byla zaměřena na procesy otevřeného paletového poolu u konkrétního podniku - společnosti PPL CZ s.r.o. Hodnocení jednotlivých procesů je umístěno v závěru práce.ObhájenoThe presented thesis is focused on pallet pool system. The main objective was to gather imformations about pallet pool and analyze the processes of pallet pool. It was viewed at the issue from two different angles from perspective of exchange pallets among the pallet users (open pallet pool) and from perspective of possibility to rent the pallets (closed pallet pool). The terms of exchange pallets were clarified by the only one open pallet pool, which is currently working The European Pallet Pool (EPP). This thesis was focused on development of the EPP and on the current problems the EPP is facing to. The quality of pallet, the different quality grades and the proper labiling of pallets in EPP were successively described. The processes of rental pallet pool were explained at the world's largest rental pallet pool company the company of CHEP. Then other rental companies were mentioned. The last part of thesis was focused on a specific company, which is part of European Pallet Pool the PPL CZ s.r.o
Combined effect of electric field and surface modification on pool boiling of R-123
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The effect of surface modification and high intensity electric field (uniform and non – uniform) acting separately or in combination on pool boiling of R-123 is presented in this thesis. The effect of surface modification was investigated on saturated pool boiling of R-123 for five horizontal copper surfaces modified by different treatments, namely: an emery polished surface, a fine sandblasted surface, a rough sandblasted surface, an electron beam (EB) enhanced surface and a sintered surface. Each 40 mm diameter heating surface formed the upper face of an oxygen-free copper block, electrically heated by embedded cartridge heaters. The experiments were performed from the convective heat transfer regime to the critical heat flux, with both increasing and decreasing heat flux, at 1.01 bar, and additionally at 2 bar and 4 bar for the emery polished surface. Significant enhancement of heat transfer with increasing surface modification was demonstrated, particularly for the EB enhanced and sintered surfaces. The emery polished and sandblasted surface results are compared with nucleate boiling correlations and other published data. The effect of uniform and non-uniform electric fields on saturated pool boiling of R-123 at 1.01 bar pressure was also examined. This method of heat transfer enhancement is known as electrohydrodynamic abbreviated as EHD-enhancement. A high voltage potential was applied at the electrode located above the heating surface, which was earthed. The voltage was varied from 0 to 30 kV. The uniform electric field was provided through a 40 mm diameter circular electrode of stainless steel 304 wire mesh having an aperture of 5.1 mm, while the non-uniform electric field was obtained by using a 40 mm diameter circular rod electrode with rods 5 and 8 mm apart. The effect of uniform electric field was investigated using all five modified surfaces, i.e. emery polished, fine sandblasted, rough sandblasted, EB enhanced and sintered surfaces, while non – uniform electric field was tested using the emery polished, fine sandblasted, EB enhanced and sintered surfaces. The effect of pressure on EHD enhancement was also examined using emery polished surface at saturation pressure of 2 and 4 bars while the electric field was fix at 20 kV corresponding to 2 MV/m. Further, the bubble dynamics is presented for the emery polished surface obtained using a high-speed high – resolution camera.The Government of Pakista
- …
