Interpolation formula for the electrical conductivity of nonideal plasmas

On the basis of a quantum-statistical approach to the electrical conductivity of nonideal plasmas we derive analytical results in the classical low-density regime, in the degenerate Born limit, and for the contribution of the Debye-Onsager relaxation effect. These explicit results are used to construct an improved interpolation formula of the electrical conductivity valid in a wide range of temperature and density which allows to compare with available experimental data of nonideal plasmas.Comment: 7 pages, 1 tabl

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

Analytic expression for Taylor-Couette stability boundary

We analyze the mechanism that determines the boundary of stability in Taylor-Couette flow. By simple physical argument we derive an analytic expression to approximate the stability line for all radius ratios and all speed ratios, for co- and counterrotating cylinders. The expression includes viscosity and so generalizes Rayleigh's criterion. We achieve agreement with linear stability theory and with experiments in the whole parameter space. Explicit formulae are given for limiting cases.Comment: 6 pages (LaTeX with REVTEX) including 4 figures (Postscript) Revised, discussion of two additional references. See also http://staff-www.uni-marburg.de/~esse

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

High enthalpy testing of UHTC materials for space applications

Space vehicles are subjected to severe heat loads when entering a planetary atmosphere and require a powerful thermal protection system (TPS). The protection systems’ thermal efficiency can strongly be enhanced by using surface materials with substantial radiative cooling capabilities, which are directly correlated to high operational temperatures. Accordingly, ablative and UHTC materials are well-suited for use in TPS structures. Due to their physical integrity, UHTC materials are an appropriate choice for future reusable space vehicles, which are requiring improved thermal efficiencies compared with state-of-the-art systems, resulting from demands on enhanced flight performance parameters [1]. Advanced stages of material development include experimental characterization and qualification at realistic environmental conditions. Arc-heated facilities, as e.g. DLR’s arc heated facilities LBK with its two test legs L2K and L3K, are well suited for testing materials for thermal protection issues, since they allow for testing at realistic convective and catalytic heat fluxes. During the last decades, several test conditions have been established in L2K and L3K and were applied to both, ablative and UHTC materials. Heat fluxes range up to more than 10 MW/m2.Typical test configurations for UHTC materials are illustrated in Figure 1. Please click Additional Files below to see the full abstract

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

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

High Enthalpy Ablation Testing at DLR Cologne

Testing thermal protection capabilities of ablative materials is one of the main working areas of DLR’s arc heated facilities LBK in Cologne. Work on this particular topic has been intensified about five years ago with the following major focus points: Significant improvement of the facilities testing capabilities with respect to cold wall heat flux rates and stagnation pressure. Ablation testing in Martian atmosphere. Influence of dust particle erosion on ablation

Would ACES Academy Benefit Your University?

In 1989 the Federal Aviation Administration (FAA) entered into a collaborative effort with Embry-Riddle Aeronautical University to design a model Aviation Career Education (ACE) Academy seminar. This collaboration was initially made exclusively with Embry-Riddle with the intent to replicate the program at other institutions after the model was established. The objective of the seminar was to introduce high school juniors and seniors to various aviation careers, allowing them to plan their final semesters in high school and set their higher-education goals. Additional goals of the program included: 1. Guiding high school students in exploring the role of aviation in history. 2. Discussing the airplane as a vehicle and identifying its parts and the principles by which it flies. 3. Taking participants on a flight to give them firsthand experience. 4. Helping students explore careers in aviation and aerospace. 5. Explaining the role of government in aviation and the overall socio-economic benefits of aviation. The FAA contacted Patricia Ryan, director of the Teacher Resource Center at Embry-Riddle, who developed the program with the assistance of Dave Esser, an associate professor in Embry-Riddle\u27s Aeronautical Science Department. The FAA has since offered the program developed by Ryan and Esser at various locations around the nation. In 1994, Ryan and Esser decided the project could be better tailored to meet individual needs if each student was allowed to select a particular career field to explore. The enhanced program was renamed Aviation Career Education Specialization (ACES) Academy