Uniqueness of a Negative Mode About a Bounce Solution

We consider the uniqueness problem of a negative eigenvalue in the spectrum of small fluctuations about a bounce solution in a multidimensional case. Our approach is based on the concept of conjugate points from Morse theory and is a natural generalization of the nodal theorem approach usually used in one dimensional case. We show that bounce solution has exactly one conjugate point at $\tau=0$ with multiplicity one.Comment: 4 pages,LaTe

Efficient Spatial Redistribution of Quantum Dot Spontaneous Emission from 2D Photonic Crystals

We investigate the modification of the spontaneous emission dynamics and external quantum efficiency for self-assembled InGaAs quantum dots coupled to extended and localised photonic states in GaAs 2D-photonic crystals. The 2D-photonic bandgap is shown to give rise to a 5-10 times enhancement of the external quantum efficiency whilst the spontaneous emission rate is simultaneously reduced by a comparable factor. Our findings are quantitatively explained by a modal redistribution of spontaneous emission due to the modified local density of photonic states. The results suggest that quantum dots embedded within 2D-photonic crystals are suitable for practical single photon sources with high external efficiency

Highly efficient single photon emission from single quantum dots within a two-dimensional photonic bandgap

We report highly efficient single photon generation from InGaAs self-assembled quantum dots emitting within a two-dimensional photonic bandgap. A strongly suppressed multiphoton probability is obtained for single quantum dots in bulk GaAs and those emitting into the photonic bandgap. In the latter case, photoluminescence saturation spectroscopy is employed to measure a ~17 times enhancement of the average photon extraction efficiency, when compared to quantum dots in bulk GaAs. For quantum dots in the photonic crystal we measure directly an external quantum efficiency up to 26%, much higher than for quantum dots on the same sample without a tailored photonic environment. The results show that highly efficient quantum dot single photon sources can be realized, without the need for complex nanopositioning techniques

Scenarios of cost-effective emission controls after 2020

Although emissions of most air pollutants are expected to significantly decline in the coming decades, the magnitude of the remaining impacts of poor air quality on human health and ecosystems will still be substantial. Technical and non-technical measures will be still available to reduce emissions and resulting impacts below the "current legislation" baseline levels. However, these additional measures come at certain costs. It is estimated that full implementation of all available technical emission control measures would require up to 0.32% of GDP in 2030, and thereby increase total costs of air pollution control by more than 50%. The GAINS optimization offers a tool for a systematic analysis of the cost-effectiveness of further measures. This report presents a series of illustrative optimization calculations addressing the health and ecosystems impact indicators that have been employed for earlier cost-effectiveness analyses for the 2005 Thematic Strategy on Air Pollution and the 2012 revision of the Gothenburg protocol. As a first step, a series of calculations determined for each of these endpoints the increase in emission control costs for gradually tightened "gap closure" targets between the current legislation and the full application of all available technical measures. Costs increase most rapidly for improvements of health impacts (for ozone and PM), while significant progress at comparably low costs is possible for eutrophication and acidification. In a second step, illustrative joint optimizations for multiple targets have been conducted, aiming at arbitrarily chosen gap closure targets of 25/50/75% for all impact indicators in 2030. The costs of the portfolios of measures that meet these targets range from Euros 0.3 bn/yr to Euros 9.9 bn/yr for the most ambitious case. In a further step, the temporal interactions between emission reductions that have been optimized for a more distant year (e.g., 2030) and potential interim targets for earlier years are discussed. While there are several alternatives for securing temporal consistency of targets over time to avoid regret investments, the choice of the temporal path of environmental ambitions remains a political decision, depending on the weight given to environmental improvements in the near term versus the long-term target. All calculations presented in this report must be considered as illustrative, since they do not yet include the forthcoming final TSAP baseline scenario that will build on the latest expectations of economic development and energy use

A Simplified Model to Predict Long-Term Ozone Concentrations in Europe

In the preparation process for the Second Sulphur Protocol of the Convention on Long-range Transboundary Air Pollution, integrated assessment models played an important role in identifying cost-effective strategies for reducing SO2 emissions in Europe. Applying this effect-based approach to other environmental problems (e.g., photo-oxidants) seems appealing. In view of the timetable adopted for the current preparation of an updated Protocol on emissions of nitrogen oxides, an integrated assessment tool for ozone is required in the very near future. The paper presents an outline of an integrated assessment model for tropospheric ozone in Europe, with modules on emissions, emission control technologies and costs, ozone formation and environmental impacts. In its central part the paper focuses on the core element of such an approach, i.e., a concise description of the relationships between the precursor emissions (nitrogen oxides and volatile organic compounds) and regional ozone levels, which must be computationally efficient for use in an integrated assessment model. Critical levels, i.e., threshold levels protecting vegetation from damage, have been recently established using long-term exposure measures. Consequently, to be suitable for integrated assessment models, source-receptor relationships should be able to describe the long-term changes of ozone, e.g., over a six-month period. Based on numerous scenario runs of the EMEP ozone model, polynomial source-receptor relationships have been statistically identified. Using national annual emissions of NO, and VOC, the model predicts regional responses of the six-month mean of early afternoon ozone concentrations. From this concentration measure, excess exposure as used in the definition of the critical levels can be derived. The paper introduces the methodology of the approach, evaluates the results and discusses areas of further work. The suggested model formulation can be incorporated into the framework of an integrated assessment model, enabling (i) the assessment of costs and environmental benefits from alternative strategies to reduce precursor emissions and (ii) the identification of cost-optimized strategies to achieve environmental targets

Semiclassical theory of spin-orbit interactions using spin coherent states

We formulate a semiclassical theory for systems with spin-orbit interactions. Using spin coherent states, we start from the path integral in an extended phase space, formulate the classical dynamics of the coupled orbital and spin degrees of freedom, and calculate the ingredients of Gutzwiller's trace formula for the density of states. For a two-dimensional quantum dot with a spin-orbit interaction of Rashba type, we obtain satisfactory agreement with fully quantum-mechanical calculations. The mode-conversion problem, which arose in an earlier semiclassical approach, has hereby been overcome.Comment: LaTeX (RevTeX), 4 pages, 2 figures, accepted for Physical Review Letters; final version (v2) for publication with minor editorial change

Detection of the Mass of Airborne Particles in an online Optical Sensor System by Correlation of Geometric and Inertial Filtering

AbstractWe present a method combining inertial and geometric filtering to approximate the mass of particles for optical particle detection systems. The method consists of three measurement steps and is based on the difference of the filtering behavior of geometric and inertial filters based on particle size and particle density respectively. Our measurements show the feasibility using polystyrene latex particles with sizes 300/500/900nm and silica particles with diameters 500nm and 1000nm