We model high molecular weight homopolymers in semidilute concentration via Dissipative Particle Dynamics (DPD). We show that in model reduction methodologies for polymers it is not enough to preserve system properties (i.e., density ρ, pressure p, temperature T, radial distribution function g(r)) but preserving also the characteristic shape and length scale of the polymer chain model is necessary. In this work we apply a DPD-model-reduction methodology for linear polymers recently proposed; and demonstrate why the applicability of this methodology is limited upto certain maximum polymer length, and not suitable for solvent coarse graining.
A variational multi scale approach to model blood flow through arteries is proposed. A finite element discretization to represent the coarse scales (macro size), is coupled to smoothed dissipative particle dynamics that captures the fine scale features (micro scale). Blood is assumed to be incompressible, and flow is described through the Navier Stokes equation. The proposed cou- pling is tested with two benchmark problems, in fully coupled systems. Further refinements of the model can be incorporated in order to explicitly include blood constituents and non-Newtonian behavior. The suggested algorithm can be used with any particle-based method able to solve the Navier-Stokes equation.
The development of the forward osmosis (FO) process has been constrained by the slow development of appropriate draw solutions. Two significant concerns related to draw solutions are the draw solute leakage and intensive-energy requirement in recycling draw solutes after the FO process. FO would be much attractive if there is no draw solute leakage and the recycle of draw solutes is easy and economic.In this study, polyelectrolytes of a series of polyacrylic acid sodium salts (PAA-Na), were explored as draw solutes in the FO process. The characteristics of high solubility in water and flexibility in structural configuration ensure the suitability of PAA-Na as draw solutes and their relative ease in recycle through pressure-driven ultrafiltration (UF) membrane processes. The high water flux with insignificant salt leakage in the FO process and the high salt rejection in UF recycle processes reveal the superiority of PAA-Na to conventional ionic salts, such as NaCl, when comparing their FO performance via the same membranes. The repeatable performance of PAA-Na after recycle indicates the absence of any aggregation problems. The overall performance demonstrates that polyelectrolytes of PAA-Na series are promising as draw solutes, and the new concept of using polyelectrolytes as draw solutes in FO processes is applicable. The magnetic nanoparticle draw solutes can generate reasonably high osmotic pressure in FO system due to the functional groups on the nanoparticles surface and they can be regenerated through magnetic field and reused as draw solutes. Thermo-responsive magnetic nanoparticles are able to be regenerated with high efficiency as the thermo-responsive property can assist the regeneration in a low-strength magnetic field.
Water Security was a central theme of WANA Forum 2010, where regional experts warned that the wars of the 21st century will be fought over water. Climate change will only exacerbate problems in a region already stressed by lack of water, food and political and social unrest. Across the Arc of Crisis, from Somalia, Sudan and Egypt in Africa to Yemen, Iraq, Pakistan, and Afghanistan in West Asia, water scarcity in the region has already lead to drought and famine, loss of livelihood, the spread of water-borne diseases, forced migrations and open conflict. Water scarcity is closely linked to food and health security, making better water management a key stepping stone for poverty reduction and economic growth. If nothing changes, most of the WANA countries will encounter, in less than a generation, serious problems in managing inland freshwater, the availability of which, in sufficient quantity and quality, may become, as it is already the case in several of these countries, a main challenge for economic and social development. Wastage and pollution will then be such that « water stress » will affect, in a way or another, most of the populations of WANA countries and the poorest first of all. The effects of global warming will increase current trends. On the other hand, water scarcity in the WANA region is an issue of growing concern. With heavy demand from agriculture, growing populations and virtually no remaining untapped water sources, the need to establish water-management strategies in the region is of vital importance. WANA countries can be divided into three major agro-ecologies, each facing slightly different challenges. Rain-fed areas are dependent on a low and extremely variable rainfall, resulting in minimal yields, a problem exacerbated by frequent drought. Rainfall occurs in the form of intense and unpredictable storms, and as a result, the crusting soils are unable to absorb the moisture, which rapidly becomes lost through evaporation or runoff. Irrigated areas utilize rivers and groundwater sources, which are becoming depleted from over-use. Water scarcity is a manmade phenomenon brought about by the increasing demands of the population for water. The imbalance in the population-water resources equation strains society and has an adverse impact on domestic hygiene, public health, and cost of domestic water, and could impart political problems as serious as bringing down governments. On the social side, water scarcity adversely impacts job opportunities, farm incomes, credibility and reliability of agricultural exports, and the ability of the vulnerable to meet the cost of domestic water. Economically, the adverse impact is displayed in the loss of production of goods, especially agricultural goods, the loss of working hours because of the hardships society faces as a result of water scarcity. Thus, there is a need for preventive policy in the context of water security, and a process of networking to exchange the views of experts and specialists in this area, because, there is considerable knowledge of water scarcity in the WANA region, but what is needed is to consider ways that contribute to addressing this scarcity.
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