2,840 research outputs found
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 with multiplicity one.Comment: 4 pages,LaTe
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
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
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