Evidence for the critical role of nanoscale surface roughness on the retention and release of silver nanoparticles in porous media.

Although nanoscale surface roughness has been theoretically demonstrated to be a crucial factor in the interaction of colloids and surfaces, little experimental research has investigated the influence of roughness on colloid or silver nanoparticle (AgNP) retention and release in porous media. This study experimentally examined AgNP retention and release using two sands with very different surface roughness properties over a range of solution pH and/or ionic strength (IS). AgNP transport was greatly enhanced on the relatively smooth sand in comparison to the rougher sand, at higher pH, and lower IS and fitted model parameters showed systematic changes with these physicochemical factors. Complete release of the retained AgNPs was observed from the relatively smooth sand when the solution IS was decreased from 40 mM NaCl to deionized (DI) water and then the solution pH was increased from 6.5 to 10. Conversely, less than 40% of the retained AgNPs was released in similar processes from the rougher sand. These observations were explained by differences in the surface roughness of the two sands which altered the energy barrier height and the depth of the primary minimum with solution chemistry. Limited numbers of AgNPs apparently interacted in reversible, shallow primary minima on the smoother sand, which is consistent with the predicted influence of a small roughness fraction (e.g., pillar) on interaction energies. Conversely, larger numbers of AgNPs interacted in deeper primary minima on the rougher sand, which is consistent with the predicted influence at concave locations. These findings highlight the importance of surface roughness and indicate that variations in sand surface roughness can greatly change the sensitivity of nanoparticle transport to physicochemical factors such as IS and pH due to the alteration of interaction energy and thus can strongly influence nanoparticle mobility in the environment

A Simulation Framework for Real-Time Management and Control of Inventory Routing Decisions

We consider a logistics network where a single warehouse distributes a single item to multiple retailers. Retailers in the network participate in a Vendor Managed Inventory (VMI) program with the warehouse, where the warehouse is responsible for tracking and replenishing the inventory at various retailer locations. The information update occurs every time a vehicle reaches a location and the decision on the delivery quantity and the next location to visit is made. For a small increase of locations in the network, the state space for the solution increases exponentially, making this problem NP-hard. Thus, we propose a solution methodology where in the size of the state space is reduced at each stage. In this work, we use simulation to develop the framework for the real-time control and management of inventory and routing decisions, given this scenario

A Note on Internationally Coordinated Policy Packages Intended to be Robust Under Model Uncertainty

Holtham and Hughes Hallett, and a number of other authors, have suggested that a printout of all 1,000 cases of coordination considered in Frankel and Rockett (1988) should be made available. They wish to check whether, if coordination is restricted to policy packages that they call 'strong' bargains, it would raise welfare a higher percentage of the time. We now make those results available. The results show that if coordination is restricted to packages that are robust with respect to model uncertainty, such as the so-called 'strong' bargains, it does indeed improve the odds in favor of gains from coordination.

Public-Private Partnerships for Technology Growth in the Public Sector

Public-private partnerships (PPP) are a mechanism for financing large infrastructure development such as transportation projects, hospitals, schools, and public works facilities. In addition, the benefits of PPP stretch well into the realm of engineering management. Most notably, PPPs provide the opportunity for more efficient project management, proficient risk mitigation, and enhanced technological innovation. This paper provides a general description of the typical PPP process and how this process can be used to improve management of technology in the public sector

The effect of a gap nonlinearity on recursive parameter identification algorithms

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988.Includes bibliographical references.by Scott E. Schaffer.M.S

Sustainable Transportation: Transforming Utah Through Community Action

Transportation in the United States accounts for 4% of global greenhouse gas emissions. Over half of these emissions come from on-road vehicles. Nationwide, Utah has the third highest rate of car ownership, and the resulting air pollution from on-road vehicles has significant implications for the climate and public health. This fact sheet provides information on how Utah’s government and other entities are working to expand modes of transport that minimize harm to communities and the environment

On the cross-section of Dark Matter using substructure infall into galaxy clusters

We develop a statistical method to measure the interaction cross-section of Dark Matter, exploiting the continuous minor merger events in which small substructures fall into galaxy clusters. We find that by taking the ratio of the distances between the galaxies and Dark Matter, and galaxies and gas in accreting sub-halos, we form a quantity that can be statistically averaged over a large sample of systems whilst removing any inherent line-of-sight projections. In order to interpret this ratio as a cross-section of Dark Matter we derive an analytical description of sub-halo infall which encompasses; the force of the main cluster potential, the drag on a gas sub-halo, a model for Dark Matter self-interactions and the resulting sub-halo drag, the force on the gas and galaxies due to the Dark Matter sub-halo potential, and finally the buoyancy on the gas and Dark Matter. We create mock observations from cosmological simulations of structure formation and find that collisionless Dark Matter becomes physically separated from X-ray gas by up to 20h^-1 kpc. Adding realistic levels of noise, we are able to predict achievable constraints from observational data. Current archival data should be able to detect a difference in the dynamical behaviour of Dark Matter and standard model particles at 6 sigma, and measure the total interaction cross-section sigma/m with 68% confidence limits of +/- 1cm2g^-1. We note that this method is not restricted by the limited number of major merging events and is easily extended to large samples of clusters from future surveys which could potentially push statistical errors to 0.1cm^2g^-1.Comment: 14 pages, 11 figure