56,089 research outputs found
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
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
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.
An Intergenerational Common Pool Resource Experiment
No full textintergenerational common pool resources;growth and altruism;free-riding intentions
Member Commitment and the Market and Financial Performance of the Saskatchewan Wheat Pool
No full textSince 2001 several of the largest agricultural co-operatives in Western Canada and the United States have battled impending bankruptcy or ceased operations. In February 2001 Dairyworld Foods was bought out by Montreal dairy processor and cheese producer Saputo Inc. (Saputo; Toronto Stock Exchange). In November 2001, Agricore, formed through a 1998 merger of Alberta Wheat Pool Ltd. and Manitoba Pool Elevators, merged with United Grain Growers to form Agricore United (Agricore United). In the United States, AgWay and Farmland Industries filed for Chapter 11 bankruptcy protection in 2002 (Reuters, 2000), while the Saskatchewan Wheat Pool (hereinafter referred to as SWP or the Pool) underwent a massive debt restructuring in 2003 after four years of consecutive multi-million dollar net losses (SWP Annual Report, 2003). This decline in the market and financial performance of agricultural co-operatives has been associated with a decline in the commitment of the members to their co-operatives (Fulton, 1999; Fulton and Giannakas, 2001; Richards, Klein and Walburger, 1998; Burt and Wirth, 1990). The purpose of this article is to examine the market and financial performance of one of a number of co-operatives that have faced recent financial and market hardships, and to link this performance to member commitment. Specifically, the article examines whether the Pool’s declining market and financial performance is consistent with the predictions that emerge from a model that examines the impact of falling member commitment in a co-operative.Marketing,
Pool-Seq libraries of the 3 P. napi populations
No full textPool-Seq libraries of Spain: Aiguamolls, Sweden: Abisko, and Sweden: Kullaberg. Stored as NCBI bioproject PRJNA449143
Innovative Financing in Early Recovery: The Liberia Health Sector Pool Fund - Working Paper 288
No full textIn post-conflict Liberia, the National Health Plan set out a process for transitioning from emergency to sustainability under government leadership. The Liberia Health Sector Pool Fund, which consists of DfID, Irish Aid, UNICEF, and UNHCR, was established to fund this plan and mitigate this transition by increasing institutional capacity, reducing the transaction costs associated with managing multiple donor projects, and fostering the leadership of the Liberian Health Ministry by allocating funds to national priorities. In this paper, we discuss the design of the health pool fund mechanism, assess its functioning, compare the pooled fund to other aid mechanisms used in Liberia, and look into the enabling conditions, opportunities, and challenges of the pool fundLiberia, national health plan, aid effectivenes
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
Spontaneous formation and degradation of pool-riffle morphology and sediment sorting using a simple fractional transport model
No full textMany gravel bed streams have a typical bed morphology consisting of pool-riffle sequences, which provides important habitat diversity both in terms of flow and substrate. A complete explanation of pool-riffle genesis and self-maintenance remains elusive and, despite advances in understanding the effects of flow spatial and temporal variability, the key sediment processes have been only marginally explored. Here we use a 1D unsteady multi-fraction morphodynamic model to explain the formation and degradation of pool-riffle sequences. Using a 1-year time series of measured flows below bankfull on a stream in which we have removed initial bedforms and sediment sorting our model spontaneously generates pools with finer substrate at narrow sections and riffles with coarser sediment at wider sections, closely resembling the natural bed morphology. Additional experiments show that under our modelling assumptions a variable flow regime is fundamental for development and self-maintenance of the longitudinal grain sorting characteristic of pool-riffle sequences, which could not be obtained or maintained with discharges held constant over relatively long periods
The Restructuring of the Saskatchewan Wheat Pool: Overconfidence and Agency
No full textThis paper examines how agency problems combined with overconfidence and hubris by coop management lead to financial failure in the Saskatchewan Wheat Pool. As a consequence of both of these problems, the Pool made poor investment decisions and ended up in severe financial difficulties. These problems were exacerbated by three additional factors: (1) ownership and control were separated via an A-B share structure, leading to a situation where neither farmer members nor investors had an incentive to monitor management activities; (2) the sheer volume of investment activity undertaken made it virtually impossible for the board to stay on top of what was happening; and (3) as a result of the change financial structure, senior management had available a large amount of debt capital that it could spend.Agribusiness, Crop Production/Industries,
- …
