2,909 research outputs found

    Driver-pressure-impact and response-recovery chains in European rivers: observed and predicted effects on BQEs

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    The report presented in the following is part of the outcome of WISER’s river Workpackage WP5.1 and as such part of the module on aquatic ecosystem management and restoration. The ultimate goal of WP5.1 is to provide guidance on best practice restoration and management to the practitioners in River Basin Management. Therefore, a series of analyses was undertaken, each of which used a part of the WP5.1 database in order to track two major pathways of biological response: 1) the response of riverine biota to environmental pressures (degradation) and 2) the response of biota to the reduction of these impacts (restoration). This report attempts to provide empirical evidence on the environment-biota relationships for both pathways

    Optical properties of arrays of quantum dots with internal disorder

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    Optical properties of large arrays of isolated quantum dots are discussed in order to interpret the existent photoluminescence data. The presented theory explains the large observed shift between the lowest emission and absorption energies as the average distance between the ground and first excited states of the dots. The lineshape of the spectra is calculated for the case when the fluctuations of the energy levels in quantum dots are due to the alloy composition fluctuations. The calculated lineshape is in good agreement with the experimental data. The influence of fluctuations of the shape of quantum dots on the photoluminescence spectra is also discussed.Comment: 7 pages (twocolumn) LATEX, 6 Postscript figure

    Eight-band calculations of strained InAs/GaAs quantum dots compared with one, four, and six-band approximations

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    The electronic structure of pyramidal shaped InAs/GaAs quantum dots is calculated using an eight-band strain dependent k⋅p\bf k\cdot p Hamiltonian. The influence of strain on band energies and the conduction-band effective mass are examined. Single particle bound-state energies and exciton binding energies are computed as functions of island size. The eight-band results are compared with those for one, four and six bands, and with results from a one-band approximation in which m(r) is determined by the local value of the strain. The eight-band model predicts a lower ground state energy and a larger number of excited states than the other approximations.Comment: 8 pages, 7 figures, revtex, eps

    How quantum bound states bounce and the structure it reveals

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    We investigate how quantum bound states bounce from a hard surface. Our analysis has applications to ab initio calculations of nuclear structure and elastic deformation, energy levels of excitons in semiconductor quantum dots and wells, and cold atomic few-body systems on optical lattices with sharp boundaries. We develop the general theory of elastic reflection for a composite body from a hard wall. On the numerical side we present ab initio calculations for the compression of alpha particles and universal results for two-body states. On the analytical side we derive a universal effective potential that gives the reflection scattering length for shallow two-body states.Comment: final publication version, new lattice results on alpha particle compression, 5 pages, 2 figure

    Electronic structure of strained InP/GaInP quantum dots

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    We calculate the electronic structure of nm scale InP islands embedded in Ga0.51In0.49PGa_{0.51}In_{0.49}P. The calculations are done in the envelope approximation and include the effects of strain, piezoelectric polarization, and mixing among 6 valence bands. The electrons are confined within the entire island, while the holes are confined to strain induced pockets. One pocket forms a ring at the bottom of the island near the substrate interface, while the other is above the island in the GaInP. The two sets of hole states are decoupled. Polarization dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia

    Wave function mapping conditions in Open Quantum Dots structures

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    We discuss the minimal conditions for wave function spectroscopy, in which resonant tunneling is the measurement tool. Two systems are addressed: resonant tunneling diodes, as a toy model, and open quantum dots. The toy model is used to analyze the crucial tunning between the necessary resolution in current-voltage characteristics and the breakdown of the wave functions probing potentials into a level splitting characteristic of double quantum wells. The present results establish a parameter region where the wavefunction spectroscopy by resonant tunneling could be achieved. In the case of open quantum dots, a breakdown of the mapping condition is related to a change into a double quantum dot structure induced by the local probing potential. The analogy between the toy model and open quantum dots show that a precise control over shape and extention of the potential probes is irrelevant for wave function mapping. Moreover, the present system is a realization of a tunable Fano system in the wave function mapping regime.Comment: 6 pages, 6 figure

    Effect of deconfinement on resonant transport in quantum wires

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    The effect of deconfinement due to finite band offsets on transport through quantum wires with two constrictions is investigated. It is shown that the increase in resonance linewidth becomes increasingly important as the size is reduced and ultimately places an upper limit on the energy (temperature) scale for which resonances may be observed.Comment: 6 pages, 6 postscript files with figures; uses REVTe

    Multi-Exciton Spectroscopy of a Single Self Assembled Quantum Dot

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    We apply low temperature confocal optical microscopy to spatially resolve, and spectroscopically study a single self assembled quantum dot. By comparing the emission spectra obtained at various excitation levels to a theoretical many body model, we show that: Single exciton radiative recombination is very weak. Sharp spectral lines are due to optical transitions between confined multiexcitonic states among which excitons thermalize within their lifetime. Once these few states are fully occupied, broad bands appear due to transitions between states which contain continuum electrons.Comment: 12 pages, 4 figures, submitted for publication on Jan,28 199

    Efficient Passive ICS Device Discovery and Identification by MAC Address Correlation

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    Owing to a growing number of attacks, the assessment of Industrial Control Systems (ICSs) has gained in importance. An integral part of an assessment is the creation of a detailed inventory of all connected devices, enabling vulnerability evaluations. For this purpose, scans of networks are crucial. Active scanning, which generates irregular traffic, is a method to get an overview of connected and active devices. Since such additional traffic may lead to an unexpected behavior of devices, active scanning methods should be avoided in critical infrastructure networks. In such cases, passive network monitoring offers an alternative, which is often used in conjunction with complex deep-packet inspection techniques. There are very few publications on lightweight passive scanning methodologies for industrial networks. In this paper, we propose a lightweight passive network monitoring technique using an efficient Media Access Control (MAC) address-based identification of industrial devices. Based on an incomplete set of known MAC address to device associations, the presented method can guess correct device and vendor information. Proving the feasibility of the method, an implementation is also introduced and evaluated regarding its efficiency. The feasibility of predicting a specific device/vendor combination is demonstrated by having similar devices in the database. In our ICS testbed, we reached a host discovery rate of 100% at an identification rate of more than 66%, outperforming the results of existing tools.Comment: http://dx.doi.org/10.14236/ewic/ICS2018.

    Localized states in strong magnetic field: resonant scattering and the Dicke effect

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    We study the energy spectrum of a system of localized states coupled to a 2D electron gas in strong magnetic field. If the energy levels of localized states are close to the electron energy in the plane, the system exhibits a kind of collective behavior analogous to the Dicke effect in optics. The latter manifests itself in ``trapping'' of electronic states by localized states. At the same time, the electronic density of states develops a gap near the resonance. The gap and the trapping of states appear to be complementary and reflect an intimate relation between the resonant scattering and the Dicke effect. We reveal this relation by presenting the exact solution of the problem for the lowest Landau level. In particular, we show that in the absence of disorder the system undergoes a phase transition at some critical concentration of localized states.Comment: 28 pages + 9 fig
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