50 research outputs found
The Discrete Logarithm Problem
No full textFor large prime numbers p, computing discrete logarithms of elements of the multiplicative group (Z/pZ) ∗ is at present a very difficult problem. The security of certain cryptosystems is based on the difficulty of this computation. In this expository paper we discuss several generalizations of the discrete logarithm problem and we describe various algorithms to compute discrete logarithms
The automorphism group of the non-split Cartan modular curve of level 11
No full textWe derive equations for the modular curve X-ns(11) associated to a non-split Cartan subgroup of GL(2)(F-11). This allows us to compute the automorphism group of the curve and show that it is isomorphic to Klein's four group. (C) 2014 Elsevier Inc. All rights reserved.Postprint (published version
Modelling of the economic feasibility of large-scale electricity storage technologies: A German case study
No full textThis joint master program entails two master degrees, the MSc. Electric Power Industry at Comillas ICAI Madrid and the MSc. Engineering and Policy Analysis at Delft University of Technology. Electricity storage is often portrayed as the solution for the challenges that an increasing capacity of intermittent generation brings. If the electricity storage facilities are to be introduced in the grid by private investors though, just like any other asset, they require a business case. This study is part of the DNV GL StRe@M project whose goals include the modelling of the economic feasibility of electricity storage facilities in future German electricity grid scenarios from a price-taking investor’s perspective by comparing costs and revenues. The two revenue streams considered in the StRe@M project come from the spot and reserve market, and this study focuses on modelling the latter for Germany. This thesis also provides a cost and revenue framework to assess the revenues from both markets and the resulting profits. First a qualitative study maps the German reserve market and the characteristics of its products to identify opportunities for electricity storage and the impacts of regulation thereon. Next a quantitative model is designed to assess the revenue potential of the future secondary reserve market by forecasting its demand and price levels. The modelling scope is limited to the secondary reserve (energy) market (named aFRR in Germany) only because of its relative market size, the low number of participants and data availability. A bottom-up approach was tried by looking for a quantified relation between (1) historical time series of forecast errors for load and solar and wind generation and (2) system imbalances or activated aFRR directly – a positive causal relation which often appears in literature. As no quantified relation could be found an alternative top-down stochastic approach then used the historical probability distribution of activated aFRR in 2015 to establish a stochastic function for aFRR demand in future scenarios up to a few years, preserving the properties of the historical probability distribution. An effort was made to scale this stochastic function for an increasing renewable penetration but no workable scaling could be obtained. The future prices to accompany the forecasted volumes were determined from a regression analysis on historical aFRR price time series. Regression components included the aFRR volume and the spot price. The design of the cost and revenue framework, used to process the potential revenues from the spot and reserve market, was based on comparing samples of a stochastic reserve market revenue with a deterministic spot market revenue and aggregating this into a distribution for the profit. To conclude the first dispatch and profit results of the StRe@M modelling are presented for a German electricity scenario in February 2020 with an 80 percent RES share, which should be used with great caution. The modelled lithium-ion battery technology and variable-speed PSH show positive profits on average, but the fixed-speed PSH does not. The main limitation of this model is the lack of the scaling effect for renewable penetration, for which a scenario analysis is probably most suited.Technology, Policy and ManagementEngineering and Policy Analysis (EPA)Erasmus Mundus Joint Master program of Economics and Management of Network Industries (EMIN
Simulation of silicon dioxide LPCVD from teos
No full textIn this study, a model is constructed as a basis for an optimization tool for silicon dioxide low pressure chemica! vapor deposition (LPCVD) from the precursor gas tetra-ethyl-ortho-silicate (TEOS) in ASM International's A412, hot wall, vertical 300 mm multi-wafer reactor. The model consists of a chemistry model based on elementaryr reactions and a transport model for multi-component gas flow, heat and mass transfer. Model simulation results have been validated against experimental data on growth rate and uniformities. The model semi-quantitavely predicts the dependence of growth rate and uniformity on pressure, TEOS flow rate and temperature. It also provides a basis for understanding experimental observations, such as the importance of the interwafer distance, the need for the use of multiple inlets and the need for a wafer rotation. The developed simulation tool can be used in further optimization studies with respect to reactor design ansd process operation.Kramers Laboratorium voor Fysische TechnologieApplied Science
Aspects of an exergy analysis for comparison of salt recovery processes
No full textIn this study a qualitative exergy analysis of the evaporation crystallization process and the extractive crystallization process is presented. This is done to give a better insight in the exergy household of salt recovery processes. This can lead to a better design. In the evaporation crystallization process the largest exergy losses are caused by the evaporation and condensation of the water. Because of the higher process temperature, more steam is needed for the heating of the feed. In the extractive crystallization the largest entropy changes come from the mixing and the demixing in the crystallizer and the liquid-liquid separator. These entropy changes are smaller than those from the evaporation and condensation. The streams in the extractive process are much larger, but the temperature differences are smaller. It is probably better to operate the crystallizer at a lower temperature than the liquid-liquid separator. There are several possibilities to treat the waste water in the extractive crystallization process. All of them cost a significant amount of exergy.Applied SciencesApplied Thermodynamics and Phase BehaviourProcess EquipmentExtractive Crystallization Projec
Ontwerp van een voorzetapparaat voor een mozaïekprinter waarmee het afdrukken van met een schrijftelefoon gemaakte afbeeldingen mogelijk gemaakt wordt
No full textHet voorzetapparaat past het uit beeldadressen bestaande beeldsignaal van de schrijftelefoon aan aan de printer, waaraan zeven simultane helderheidssignalen toegevoerd moeten worden. De omzetting wordt verkregen met behulp van o.a. een geheugen, waarin de beeldinformatie deel voor deel wordt ingelezen en uitgelezen. Het voorzetapparaat bestuurt tevens de printer.Electrical Engineering, Mathematics and Computer ScienceTransmissie van Informati
Modelling of phase equilibria of Water-Organic solvent-Electrolyte systems
No full textIn this study the phase behaviour of water-organic solvent-electrolyte systems is studied. The understanding of these systems will be used to select an organic solvent for the extractive crystallization of sodium chloride. For the design of this process, the knowledge of the phase behaviour around the critical solution temperatures is very relevant. The model that is used to calculate the liquid-liquid equilibrium of water-organic solvent systems, mean ionic activity coefficient and solubility of aqueous electrolytes and the liquid-liquid-solid equilibria for mixed solvent electrolyte systems is a modification of the model that was proposed by Peng. There are six adjustable parameters: four energy parameters and two volume parameters. Two of the energy parameters are calculated from the ternary SLLE data, the other parameters are calculated from mean ionic solvent LLE data and water-electrolyte activity coefficient data of aqueous electrolytes. The modifications of the original model include a temperature dependency of the binary energy parameters and the electrolyte volume parameter, and the introduction of a temperature dependent ternary energy parameter. Computer programs were written in Fortran to calculate the binary systems water-organic solvent and water-electrolyte with their consecutive parameters. Also programs were made to calculate the solubility of electrolytes in pure water, and to calculate the parameters and solubility of the ternary system. Six binary water-organic solvent systems were calculated, the average error was 2.6%. The region around the critical point was calculated with success even if the concentrations were strongly diverting. The activity coefficient data of seven water-electrolyte systems were calculated over a wide range of temperature and concentration. For the 1-1 electrolytes the average error was 1.1 %, for salts composed of higher charged ions the errors were larger. The largest concentration was 6 molal. The solubility of three aqueous electrolytes systems were correlated. An attempt was made to use the equilibrium constants that were calculated from the solubility in pure water, and to predict the solubility in the ternary system. It is also possible to correlate the equilibrium constant from the solubility data of the ternary system. The two energy parameters that are calculated from the ternary data, were correlated from experimental data of the ternary system water-DIP A-sodium chloride. It has not yet been possible to calculate the phase split, probably due to computational problems. However this theses has shown that it is possible to calculate both liquid-liquid equilibria up to the critical region and aqueous electrolyte systems over a large range of temperature and concentration with the same model.Applied SciencesApplied Thermodynamics and Phase Behaviou
Counting points on curves over families in polynomial time
No full textThis note concerns the theoretical algorithmic problem of counting rational points on curves over finite fields. It explicates how the algorithmic scheme introduced by Schoof and generalized by the author yields an algorithm whose running time is uniformly polynomial time for curves in families
Self-portrait through the father-in-law:On Frida Vogels' De vader van Artenio (Artenio's father)
No full textReview essay of the autobiographical novel De vader van Artenio by the Dutch author Frida Vogels.De vader van Artenio bestaat uit herinneringen aan ‘een ander’. Frida Vogels beschrijft ook zichzelf, maar doet dat zachtzinniger dan in haar eerdere werk
Writing with a scalpel:On the autobiographical project of Annie Ernaux and her influence on Édouard Louis
No full textThe autobiographical work of the famous French author Édouard Louis is clearly influenced by that of Annie Ernaux. Yet, there are important differences, which have everything to do with perspective.Literaire ster Édouard Louis borduurt onverbloemd voort op het werk van Annie Ernaux. Maar er zijn ook verschillen, en die hebben alles te maken met perspectief
