128 research outputs found
Introduction to cryptography
No full textCryptography is a key technology in electronic key systems. It is used to keep data secret, digitally sign documents, access control, etc. Therefore, users should not only know how its techniques work, but they must also be able to estimate their efficiency and security. For this new edition, the author has updated the discussion of the security of encryption and signature schemes and recent advances in factoring and computing discrete logarithms. He has also added descriptions of time-memory trade of attacks and algebraic attacks on block ciphers, the Advanced Encryption Standard, the Secure Hash Algorithm, secret sharing schemes, and undeniable and blind signatures. Johannes A. Buchmann is a Professor of Computer Science and Mathematics at the Technical University of Darmstadt, and the Associate Editor of the Journal of Cryptology. In 1985, he received the Feodor Lynen Fellowship of the Alexander von Humboldt Foundation. Furthermore, he has received the most prestigious award in science in Germany, the Leibniz Award of the German Science Foundation. About the first edition: It is amazing how much Buchmann is able to do in under 300 pages: self-contained explanations of the relevant mathematics (with proofs); a systematic introduction to symmetric cryptosystems, including a detailed description and discussion of DES; a good treatment of primality testing, integer factorization, and algorithms for discrete logarithms; clearly written sections describing most of the major types of cryptosystems....This book is an excellent reference, and I believe it would also be a good textbook for a course for mathematics or computer science majors..." -Neal Koblitz, The American Mathematical Monthly
Towards Overset LES for Aeroacoustic Source Prediction
No full textIn this contribution an application of a computational aeroacoustics code (CAA) as a hybrid Zonal DNS tool is presented. The here used hybrid approach is based on a novel implementation of the Non-Linear Perturbation Equations (NLPE) extended with viscous terms, denoted as overset since a perturbation analysis is performed on top of a background flow. It is found that Direct Noise Computation results of a cylinder in uniform flow show the dipolar sound radiation characteristic as well as the expected decay of sound pressure level with distance. The extension to LES is illustrated with isotropic decaying turbulence, where the expected -5/3 slope of the reference DNS data is recovered with the LES employing the classical Smagorinsky model
Decompounding discrete distributions: A nonparametric Bayesian approach
No full textSuppose that a compound Poisson process is observed discretely in time and assume that its jump distribution is supported on the set of natural numbers. In this paper we propose a nonparametric Bayesian approach to estimate the intensity of the underlying Poisson process and the distribution of the jumps. We provide a Markov chain Monte Carlo scheme for obtaining samples from the posterior. We apply our method on both simulated and real data examples, and compare its performance with the frequentist plug-in estimator proposed by Buchmann and Grübel. On a theoretical side, we study the posterior from the frequentist point of view and prove that as the sample size n→∞, it contracts around the “true,” data-generating parameters at rate 1/√n, up to a n factor.Statistic
Análise de custos dos insumos: um estudo de caso na unidade do SESI alimentação Renaux View, no segundo semestre de 2007, visando melhorar o resultado líquido financeiro
No full textThe base of all economic management of a company is the real knowledge of its costs. For this, the detailed demonstration of the expenses incurred into the production, the prescription acquired in the same period and, consequently, the final liquid result is necessary. The Service of Feeding of the Sesi possesss diverse monitored expenditures monthly. This work was carried through in order more at great length to know the expenditures with the costs of the insumos of the vendidos products (CPV), being this, the expenditure of bigger impact in the final liquid result. From this study, the author, considered itself to identify the reasons to it that take the unit of the Sesi feeding of the regional Itajaí-Brusque, Renaux View (contracting company of the Service of Feeding of the Sesi), to work with these expenditures above of the daily pay-established goal, suggesting action to revert this situation. The research was developed of the following form: first one arose the description of the involved companies, Sesi and Renaux View, and its main characteristics. In function of the date of beginning of the activities of the services given for the Sesi in the Renaux View ((June of 2006), the search of information became necessary on the planning of the CPV for the opening of the together service the management and sub-management of the regional Itajaí-Brusque. In one second stage one became fulfilled the diagnosis of the presented situation and the analysis of the data gotten in relation to the financial controls and results of CPV, front to the daily pay-established goal. It was evaluated, also in this stage, the effective application of the administrative and financial controls, for the collaborators of the Sesi, with the purpose to identify the reasons that take this unit to work above of the goal daily payestablished in relation to the expenditures of CPV and considering new strategies to minimize the differences.A base de toda gestão econômica de uma empresa é o conhecimento real de seus custos. Para isto, é necessária a demonstração detalhada dos gastos incorridos na produção, a receita adquirida no mesmo período e, conseqüentemente, o resultado líquido final. O Serviço de Alimentação do Sesi possui diversas despesas monitoradas mensalmente. Este trabalho foi realizado a fim de conhecer mais detalhadamente as despesas com os custos dos insumos dos produtos vendidos (CPV), sendo esta, a despesa de maior impacto no resultado líquido final. A partir deste estudo, a autora, propôs-se a identificar as razões que levam a unidade do Sesi alimentação da regional Itajaí-Brusque, Renaux View (empresa contratante do Serviço de Alimentação do Sesi), a trabalhar com estas despesas acima da meta pré-estabelecida, sugerindo ações para reverter esta situação. A pesquisa desenvolveu-se da seguinte forma: primeiramente levantou-se o histórico das empresas envolvidas, Sesi e Renaux View, e suas principais características. Em função da data de início das atividades dos serviços prestados pelo Sesi na Renaux View ((junho de 2006), tornou-se necessária a busca de informações sobre o planejamento do CPV para a abertura do serviço junto à gerência e sub-gerência da regional Itajaí-Brusque. Em uma segunda etapa realizou-se o diagnóstico da situação apresentada e a análise dos dados obtidos em relação aos controles financeiros e resultados de CPV, frente à meta pré-estabelecida. Avaliou-se, também nesta etapa, a efetiva aplicação dos controles administrativo-financeiros, pelos colaboradores do Sesi, com a finalidade de identificar as razões que levam esta unidade a trabalhar acima da meta pré-estabelecida em relação às despesas de CPV e propor novas estratégias para minimizar as diferenças
"An Empirical Analysis of Gender Bias in Education Spending in Paraguay"
No full textGender affects household spending in two areas that have been widely studied in the literature. One strand documents that greater female bargaining power within households results in a variety of shifts in household production and consumption. An important source of intrahousehold bargaining power is ownership of assets, especially land. Another strand examines gender bias in spending on children. This paper addresses both strands simultaneously. In it, differences in spending on education are examined empirically, at both the household and the individual level. Results are mixed, though the balance of evidence weighs toward pro-male bias in spending on education at the household level. Results also indicate that the relationship between asset ownership and female bargaining power within the household is contingent on the type of asset.
Application of stereoscopic PIV for hemodynamic studies of life-sized carotid artery models under pulsatile flow condition
No full textOne of the major causes of ischemic stroke is embolism of thrombi (i.e. blood clots) that are formed at the site of the atherosclerotic plaque in the carotid artery bifurcation. Certain hemodynamic factors, such as flow disturbances, shear stress forces, and recirculation are linked to thrombosis by enhancing and facilitating platelet activation and aggregation [1, 2]. Any alterations of the local flow patterns that can, in turn, induce altered hemodynamic factors can impact the level of thrombotic activity. Previous clinical studies have shown the association of certain geometrical features of the plaque, namely severity of stenosis (i.e. narrowing), plaque eccentricity (symmetry), and plaque ulceration (irregular surface) to the frequency of cerebrovascular events [3, 4]. As a gold-standard experimental technique, particle image velocimetry (PIV) can provide detailed analysis of spatially and temporally evolving flows. This technique has extensively been applied to hemodynamic studies, primarily to investigate the potential of thrombosis in mechanical heart valves (ref). To date, only three PIV studies (excluding echo PIV studies) have been reported in carotid artery models; Bale-Glickman et al. [5] applied planar PIV to two patientspecific stenosed carotid artery models, Vetel et al. [6] studied flow in a patient-specific model of a healthy carotid artery using stereo PIV, and Buchmann et al. [7] studied a healthy carotid artery model and compared results using tomographic and stereoscopic PIV. All studies were conducted assuming steady inlet flow; although they provide a baseline understanding of flow patterns, pulsatile flow conditions strongly impact the flow dynamics, introducing flow instabilities and high temporal gradients. We have developed a flow-measurement system applying stereoscopic PIV in a family of life-sized carotid artery models, representing a range of disease progression, under physiologically realistic flow conditions in order to characterize stenosed flow features and investigate the impact of the geometrical features of the plaque on downstream flow patterns. A detailed description of the experimental design features and challenges are described, along with sample results. To demonstrate the capability of this system, flow features extracted from a 70% concentrically stenosed model are presented
Appropriate spatial filtering of 2D and 3D PIV measurements of wall-bounded turbulent flows
No full textThree-dimensional spatial filtering and measurement noise associated with experimental particle image velocimetry (PIV) measurements of wall-bounded flows are investigated via the application of the noiseless transfer function of PIV to the results of direct numerical simulations (DNS) and the comparison with real PIV measurements undertaken at the equivalent spatial resolution. For interrogation region dimensions typical of many PIV experiments the spatial filtering inherent in PIV is shown to significantly underestimate turbulent fluctuations, however in practical experiments this effect is largely offset by measurement noise. In order to determine the noise level and the noise-free effective spatial dynamic range of a given PIV measurement it is therefore necessary to compare experimental measurements in terms of the 1D velocity power spectra and the associated 1D transfer function of PIV, in both the absence of measurement noise and at the equivalent spatial resolution. In this paper the relationship between the 1D transfer function and the 3D transfer function of PIV is explained and a method for identifying the noise dominated scales is demonstrated using data from a tomographic PIV measurement of a turbulent boundary l yer. Following this method filtering is applied to reduce the influence of the noise dominated scales and provide experimental PIV velocity fields inline with that which should be generated by a noise free measure of a given spatial dynamic range
High-speed 3D Particle Tracking using Tomographic Holographic Reconstruction
No full textThis paper demonstrates ultra-high-speed tomographic digital in-line holographic velocimetry measurements of the three-component, three-dimensional velocities and trajectories of micron-sized particles in a supersonic underexpanded jet flow. In high-speed digital in-line holography the depth resolution of the measurement is severely restricted by the limited resolution of the high-speed digital recording array, which leads to significant elongation of the reconstructed particles in the depth direction. It is shown that by applying tomographic digital holography this limitation is relaxed and that accurate reconstruction of the three-dimensional particle intensities can be obtained without the depth-of-field restriction. In the first part, the paper discusses guidelines and limitation as they apply to ultra-high-speed holography at frame rates of up to 1,000,000fps and provides a detailed description and implementation of the high-speed tomographic holographic velocimetry technique. In the second part of this paper, the method is applied to an axisymmetric particle-laden underexpanded jet flow to obtain the time-resolved three-component particle velocities and to asses the measurement uncertainty
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