4,753 research outputs found
Modelling end-pumped solid state lasers
The operation dynamics of end-pumped solid-state lasers are investigated by means of a spatially resolved numerical rate-equation model and a time-dependent analytical thermal model. The rate-equation model allows the optimization of parameters such as the output coupler transmission and gain medium length, with the aim of improving the laser output performance. The time-dependent analytical thermal model is able to predict the temperature and the corresponding induced thermal stresses on the pump face of quasi-continuous wave (qcw) end-pumped laser rods. Both models are found to be in very good agreement with experimental results
Wi-Fi network testing using an integrated Evil-Twin framework
This work intends to present a newly developed Wi- Fi vulnerability analysis and exploitation framework with the objective of increasing Wi-Fi security. The developed framework focuses primarily on client-side vulnerabilities, currently a weak- ness on Wi-Fi connections, but can be extended to support any type of Wi-Fi attack. The framework was designed and is in- tended to be used by security auditors when performing intrusion tests on Wi-Fi networks. It can also be used as a proof-of-concept tool meant to teach and raise awareness of the risks involved when using Wi-Fi technologies. The developed framework is based on open-source software and is also available as open- source software, allowing developers to extend its functionality.info:eu-repo/semantics/acceptedVersio
Characterisation and calibration of a scintillating fibre detector with > 4000 multi-anode photomultiplier channels
In the Kaos spectrometer at the Mainz Microtron a high-resolution coordinate
detector for high-energy particles is operated. It consists of scintillating
fibres with diameters of 4000 multi-anode
photomultiplier channels. It is one of the most modern focal-plane detectors
for magnetic spectrometers world-wide. To correct variations in the detection
efficiency, caused by the different gains and the different optical
transmittances, a fully automated off-line calibration procedure has been
developed. The process includes the positioning of a radioisotope source
alongside the detector plane and the automated acquisition and analysis of the
detector signals. It was possible to characterise and calibrate each individual
fibre channel with a low degree of human interaction.Comment: Nucl. Instrum. Meth. A (2012
A proposal for relative time petri nets
Copyright © 2005, IEEEPetri nets are a graph-based modelling formalism which has been widely used for the formal specification and analysis of concurrent systems. A common analysis technique is that of state space exploration (or reachability analysis). Here, every possible reachable state of the system is generated and desirable properties are evaluated for each state. This approach has the great advantage of conceptual simplicity, but the great disadvantage of being susceptible to state space explosion, where the number of states is simply too large for exhaustive exploration. Many reduction techniques have been suggested to ameliorate the problem of state space explosion. In the case of timed systems, the state space is infinite, unless analysis is restricted to a bounded time period. In this paper, we present a Petri net formalism based on the notion of relative time (as opposed to the traditional approach of dealing with absolute time). The goal is to derive a finite state space for timed systems which have repeating patterns of behaviour, even though time continues to advance indefinitely.Joseph Kuehn, Charles Lakos, Robert Esse
Component-based design and analysis: a case study
©2003 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.In this paper, we introduce a component-based design methodology and present a practical analysis approach that makes use of the modular nature of component-based designs to alleviate the state space explosion problem, a well-known obstacle to system verification. In addition, the approach is illustrated by application to a non-trivial case study: the production cell. It is shown that not only the basic consistency property, viz. the freedom from unexpected reception and deadlock, but also other important safety properties in the design can be proved.Yan Jin, Charles Lakos, Robert Esse
Femtosecond study of the interplay between excitons, trions, and carriers in (Cd,Mn)Te quantum wells
We present an absorption study of the neutral and positively charged exciton
(trion) under the influence of a femtosecond, circularly polarized, resonant
pump pulse. Three populations are involved: free holes, excitons, and trions,
all exhibiting transient spin polarization. In particular, a polarization of
the hole gas is created by the formation of trions. The evolution of these
populations is studied, including the spin flip and trion formation processes.
The contributions of several mechanisms to intensity changes are evaluated,
including phase space filling and spin-dependent screening. We propose a new
explanation of the oscillator strength stealing phenomena observed in p-doped
quantum wells, based on the screening of neutral excitons by charge carriers.
We have also found that binding heavy holes into charged excitons excludes them
from the interaction with the rest of the system, so that oscillator strength
stealing is partially blockedComment: 4 pages, 4 figure
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