The Helios mechanical despin drive assembly for the high-gain antenna reflector

Helios is the German-American solar probe which comes within 0.31 Astronomical Units of the sun. A special thermal design and a dry lubrication system have resulted in successful operation up to now, with Helios having finished its first orbit around the sun

Towards optimal explicit time-stepping schemes for the gyrokinetic equations

The nonlinear gyrokinetic equations describe plasma turbulence in laboratory and astrophysical plasmas. To solve these equations, massively parallel codes have been developed and run on present-day supercomputers. This paper describes measures to improve the efficiency of such computations, thereby making them more realistic. Explicit Runge-Kutta schemes are considered to be well suited for time-stepping. Although the numerical algorithms are often highly optimized, performance can still be improved by a suitable choice of the time-stepping scheme, based on spectral analysis of the underlying operator. Here, an operator splitting technique is introduced to combine first-order Runge-Kutta-Chebychev schemes for the collision term with fourth-order schemes for the remaining terms. In the nonlinear regime, based on the observation of eigenvalue shifts due to the (generalized) $E\times B$ advection term, an accurate and robust estimate for the nonlinear timestep is developed. The presented techniques can reduce simulation times by factors of up to three in realistic cases. This substantial speedup encourages the use of similar timestep optimized explicit schemes not only for the gyrokinetic equation, but also for other applications with comparable properties.Comment: 11 pages, 5 figures, accepted for publication in Computer Physics Communication

The highly secure anonymous e-voting system of the Czech Pirate Party

The article describes the open-source e-voting system of the Czech Pirate Party including the applications, their modifications and interconnection. Overall, it provides an insight into the highly credible, secure and anonymous voting system used for intra-party direct democracy by the Czech governing party

Rational parameters of seasonal heat accumulators for helios system

Досліджено нестаціонарні процеси теплообміну в геліосистемі з сезонним акумулятором теплоти для періодичної його зарядки в літній період і розрядки в зимовий для різних регіонів України. Проведено чисельні дослідження геліосистеми, що враховують взаємний вплив геліоприймача і сезонного твердотільного акумулятора теплоти з тепловою ізоляцією. Був розглянутий варіант з фіксованими розмірами бака-акумулятора, тому що вибір розмірів зазвичай пов'язаний зі зручністю його розташування в межах заданої ділянки, оскільки при фіксованому об’ємі акумулятора кількість накопиченої енергії визначається тільки його температурою. Ітераційним методом підбиралися умови повного автономного теплопостачання споживача по опалювальному навантаженню. Обґрунтовано можливість підвищення ефективності роботи акумулятора шляхом вибору раціонального його об’єму. Запропоновано метод конструктивного вибору розмірів акумуляторного блоку для різних регіонів. Були отримані залежності температури теплового акумулятора від місяця року, його питомого навантаження від співвідношення об’єму акумулятора та площі сонячних колекторів, а також знайдений аналітичний опис залежності сумарного річного вироблення теплоти в геліосистемі від ефективності сонячного колектора в нормалізованому вигляді. Розраховано річне теплове вироблення геліосистеми, представлене в нормалізованому вигляді щодо навантаження в кінці опалювального сезону, від комплексу параметрів, що визначають конструктивні характеристики геліоколекторів.Non-stationary processes of heat exchange in a solar system with a seasonal heat accumulator for periodic charging of the battery in the summer and discharging in the winter for different regions of Ukraine are investigated. Numerical studies of the solar system have been carried out, taking into account the mutual influence of the solar collector and the seasonal solid-state heat accumulator with thermal insulation. A fixed size of battery tank was considered, because the choice of sizes is usually related to the constrains of its location within a given area, so in the fixed volume of the accumulator the amount of stored energy is determined only by its temperature. Was developed the iterative selection method of the conditions for completely autonomous heat supply of consumer under the heating load. The possibility of increasing the efficiency of the accumulator by choosing its rational volume is justified. The method of the size selection for accumulator block for different regions of Ukraine is proposed. Was obtained the function of the heat accumulator temperature from the month of the year, its specific load from the ratio of the volume of accumulator to the area of the solar collectors, as well as an analytical description of the total annual heat production in the solar system dependence on the efficiency of the solar collector in the normalized form. The annual heat production of the solar system, represented in the normalized form to the load at the end of the heating season, from the parameters of the solar collectors is calculated

Early evolution of electron cyclotron driven current during suppression of tearing modes in a circular tokamak

When electron cyclotron (EC) driven current is first applied to the inside of a magnetic island, the current spreads throughout the island and after a short period achieves a steady level. Using a two equation fluid model for the EC current that allows us to examine this early evolution in detail, we analyze high-resolution simulations of a 2/1 classical tearing mode in a low-beta large aspect-ratio circular tokamak. These simulations use a nonlinear 3D reduced-MHD fluid model and the JOREK code. During the initial period where the EC driven current grows and spreads throughout the magnetic island, it is not a function of the magnetic flux. However, once it has reached a steady-state, it should be a flux function. We demonstrate numerically that if sufficiently resolved toroidally, the steady-state EC driven current becomes approximately a flux function. We discuss the physics of this early period of EC evolution and its impact on the size of the magnetic island.Comment: 12 pages, 7 figure

Technology selection of biogas digesters for OFMSW via multi-criteria decision analysis

Multi-criteria decision analysis (MCDA) techniques are becoming increasingly popular in decision making for technology selection because of their ability to capture the multi-dimensionality of technologies. Biogas typically refers to an odourless gas produced by anaerobic digestion of biomass using microorganisms. Its production can occur naturally in marshes and landfills or more commonly, in specifically designed plants called biogas digesters under controlled conditions. For techno-economic efficiency of a biodigester, several factors such as cost of plant are taken into consideration. This paper examines various available technologies for biogas digesters using defined selection criteria via MCDA and chooses the best alternatives at various scales of biogas production for a case study in South Africa with municipal biowaste as the target feedstock. 14 biogas plants were analysed in this study and the Puxin and Bio4gas digesters were the best alternatives for small and large scale biogas production respectively