DAC-Less amplifier-less generation and transmission of QAM signals using sub-volt silicon-organic hybrid modulators

We demonstrate generation and transmission of optical signals by directly interfacing highly efficient silicon-organic hybrid (SOH) modulators to binary output ports of a field-programmable gate array. Using an SOH Mach-Zehnder modulator (MZM) and an SOH IQ modulator we generate ON-OFF- keying and binary phase-shift keying signals as well as quadrature phase-shift keying and 16-state quadrature amplitude modulation (16QAM) formats. Peak-to-peak voltages amount to only 0.27 V-pp for driving the MZM and 0.41 V-pp for the IQ modulator. Neither digital-to-analog converters nor drive amplifiers are required, and the RF energy consumption in the modulator amounts to record-low 18 fJ/bit for 16QAM signaling

From ultrahigh to extreme field magnetic resonance: where physics, biology and medicine meet

International audienc

A Comparison between the 3D and the Kirchhoff-Love Solutions for Cylinders under Creep-Damage Conditions

The 3D theory of creep deformation and creep damage growth in a cylindrical body of revolution is considered. Constitutive equations describing the creep deformation and unilateral creep damage in initially isotropic materials with characteristics dependent on the kind of the stress state are discussed. The numerical approach to obtain the 3D solution for a cylinder under creep-damage conditions is developed. The numerical results generated by the proposed 3D theory are compared with the analogous results based on the Kirchhoff-Love model. Thin and moderately thick cylindrical shells of revolution made from the material with the creep and creep damage characteristics dependent on the kind of the stress state are considered in this comparative analysis. The influence of tension–compression asymmetry on the stress–strain state and damage evolution with time in thin and moderately thick cylindrical shells is discussed. If it is assumed that the properties of the shell material do not depend on the kind of the stress state, this could lead to an overprediction of the creep damage growth and a significant underestimation of the failure initiation time

The gravitational analogue to the hydrogen atom (A summer study at the borders of quantum mechanics and general relativity)

This article reports on a student summer project performed in 2006 at the University of Frankfurt. It is addressed to undergraduate students familiar with the basic principles of relativistic quantum mechanics and general relativity. The aim of the project was to study the Dirac equation in curved space time. To obtain the general relativistic Dirac equation we use the formulation of gravity as a gauge theory in the first part. After these general considerations we restrict the further discussion to the special case of the Schwarzschild metric. This setting corresponds to the hydrogen atom, with the electromagnetic field replaced by gravity. Although there is a singularity at the event horizon it turns out that a regular solution of the time independent Dirac equation exists. Finally the Dirac equation is solved numerically using suitable boundary conditions.Comment: 19 pages, 3 figure

Benchmark creep tests for thermal barrier coatings

The topic of this paper involves a number of benchmark creep tests and reference solutions that give the possibility to verify the finite element analysis of stress redistribution in thermal barrier coatings related to commercial software packages. The numerical results have been compared in the benchmark tests with the results obtained by other methods and by other authors. The results of creep studies revealed the magnitudes of the local stresses that correlate with the residual stresses determined in the thermally grown oxide by the luminescence spectroscopy method. The creep properties of Ni-based superalloy substrate have strong influence on the stress state and subsequent failure of EB-PVD thermal barrier coatings. The obtained numerical results demonstrate that the future EB-PVD thermal barrier coatings should be developed simultaneously with the Ni-based superalloy substrate, because the effectiveness of coating is influenced by the composition and properties of the substrate.Тема цієї статті включає в себе ряд тестів на повзучість та еталонні рішення, які дають можливість перевірити аналіз методом скінченних елементів перерозподілу напружень в теплозахисних покриттях, пов'язаний з комерційними пакетами програмного забезпечення. Чисельні результати були порівняні у тестах з результатами, отриманими іншими методами та іншими авторами. Результати досліджень повзучості показали величини локальних напружень, які корелюють із залишковими напруженнями, визначеними в термічно вирощеному оксиді методом люмінесцентної спектроскопії. Повзучість нікелевих жароміцних сплавів підкладки має сильний вплив на напружений стан і подальше руйнування EB-PVD теплозахисних покриттів. Отримані чисельні результати показують, що майбутні EB-PVD теплозахисні покриття повинні бути розроблені одночасно з нікелевою підкладкою, оскільки ефективність покриття залежить від складу і властивостей підкладки

Geometry-dependent critical currents in superconducting nanocircuits

In this paper we calculate the critical currents in thin superconducting strips with sharp right-angle turns, 180-degree turnarounds, and more complicated geometries, where all the line widths are much smaller than the Pearl length $\Lambda = 2 \lambda^2/d$. We define the critical current as the current that reduces the Gibbs free-energy barrier to zero. We show that current crowding, which occurs whenever the current rounds a sharp turn, tends to reduce the critical current, but we also show that when the radius of curvature is less than the coherence length this effect is partially compensated by a radius-of-curvature effect. We propose several patterns with rounded corners to avoid critical-current reduction due to current crowding. These results are relevant to superconducting nanowire single-photon detectors, where they suggest a means of improving the bias conditions and reducing dark counts. These results also have relevance to normal-metal nanocircuits, as these patterns can reduce the electrical resistance, electromigration, and hot spots caused by nonuniform heating.Comment: 29 pages, 24 figure