Excitation of surface plasmons at a SiO2/Ag interface by silicon quantum dots: Experiment and theory

The excitation of surface plasmons (SPs) by optically excited silicon quantum dots (QDs) located near a Ag interface is studied both experimentally and theoretically for different QD-interface separations. The Si QDs are formed in the near-surface region of an SiO2 substrate by Si ion implantation and thermal annealing. Photoluminescence decay-rate distributions, as derived from an inverse Laplace transform of the measured decay trace, are determined for samples with and without a Ag cover layer. For the smallest, investigated Si-QDs-to-interface distance of 44 nm the average decay rate at lambda=750 nm is enhanced by 80% due to the proximity of the Ag-glass interface, with respect to an air-glass interface. Calculations based on a classical dipole oscillator model show that the observed decay rate enhancement is mainly due to the excitation of surface plasmons that are on the SiO2/Ag interface. By comparing the model calculations to the experimental data, it is determined that Si QDs have a very high internal emission quantum efficiency of (77±17)%. At this distance they can excite surface plasmons at a rate of (1.1±0.2)×104 s¿1. From the model it is also predicted that by using thin metal films the excitation of surface plasmons by Si QDs can be further enhanced. Si QDs are found to preferentially excite symmetric thin-film surface plasmons

Optical control of solar sails using distributed reflectivity

The dynamics of solar sails with a variable surface reflectivity distribution are investigated. When changing the reflectivity across the sail film, which can be achieved using electro-chromic coatings, the solar radiation pressure forces and torques across the sail film can be controlled without changing the attitude of the spacecraft relative to the Sun and without using mechanical systems. The paper presents two approaches. First, a continuous reflectivity distribution is presented to control the sail attitude under the influence of, for example, gravity gradient torques in Earth orbit. The second approach assumes discrete on/o reflectivity regions across the surface. Both concepts of `optical reconfiguration' of solar sails enable a more flexible steering of the spacecraft and minimize actuation effort

Too Big to Nail: How Investor-State Arbitration Lacks an Appropriate Execution Mechanism for the Largest Awards

Typically, when an international arbitration tribunal renders an award, it includes a specific date by which the defendants must pay the award. If the defendants refuse to pay the award by the mandated deadline and the defendants are not seeking that the award be set aside, then the claimants have the ability to seize assets of the defendants through national courts that could enforce the tribunal’s judgment. Those courts may issue orders to seize a party’s assets in their jurisdiction as a way to enforce all or part of the tribunal’s award. This presents an uphill battle for the claimants, particularly if the defendant is a sovereign entity. States have sovereign-immunity laws that prevent their national courts from seizing most assets of another state, except for those assets largely used for a commercial purpose. Although seizing such assets is possible and has been done, it is a costly and time-consuming process. As the size of the award increases, the costs and time required to seize assets increase exponentially. And when awards become especially massive, it becomes particularly difficult for the claimant to seize assets that would be valued anywhere near the award amount. The degree of difficulty becomes so large that it might not even be worth attempting to seize the defendant’s assets. Arbitration panels are likely to face more and more disputes involving higher and higher awards. Project-finance transactions and public-private partnerships, which have capital costs in the hundreds of billions of dollars, are becoming increasingly popular as investment mechanisms, particularly in developing countries. Nearly all these transactions use international arbitration in their contracts. Disputes that arise from these transactions could result in massive awards on a sizable scale. Barring adopting new investment treaties, states could be prevented from engaging in recalcitrant behavior by having the international community develop additional incentives to motivate states to comply with large awards rendered against them. This includes better involvement of multinational organizations—to put additional pressure on the state—and the private sector—to determine the best entity to execute the award against the state

Direct numerical simulation of heat transport in dispersed gas-liquid two-phase flow using a front tracking approach

In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of heat transport in dispersed gas-liquid two-phase flow using the Front Tracking (FT) approach. Our model extends the FT model developed by van Sint Annaland et al. (2006) to non-isothermal conditions. In FT an unstructured dynamic mesh is used to represent and track the interface explicitly by a number of interconnected marker points. The Lagrangian representation of the interface avoids the necessity to reconstruct the interface from the local distribution of the fractions of the phases and, moreover, allows a direct and accurate calculation of the surface tension force circumventing the (problematic) computation of the interface curvature. The extended model is applied to predict the heat exchange rate between the liquid and a hot wall kept at a fixed temperature. It is found that the wall-to-liquid heat transfer coefficient exhibits a maximum in the vicinity of the bubble that can be attributed to the locally decreased thickness of the thermal boundary layer