IST Austria Thesis

A proof system is a protocol between a prover and a verifier over a common input in which an honest prover convinces the verifier of the validity of true statements. Motivated by the success of decentralized cryptocurrencies, exemplified by Bitcoin, the focus of this thesis will be on proof systems which found applications in some sustainable alternatives to Bitcoin, such as the Spacemint and Chia cryptocurrencies. In particular, we focus on proofs of space and proofs of sequential work. Proofs of space (PoSpace) were suggested as more ecological, economical, and egalitarian alternative to the energy-wasteful proof-of-work mining of Bitcoin. However, the state-of-the-art constructions of PoSpace are based on sophisticated graph pebbling lower bounds, and are therefore complex. Moreover, when these PoSpace are used in cryptocurrencies like Spacemint, miners can only start mining after ensuring that a commitment to their space is already added in a special transaction to the blockchain. Proofs of sequential work (PoSW) are proof systems in which a prover, upon receiving a statement x and a time parameter T, computes a proof which convinces the verifier that T time units had passed since x was received. Whereas Spacemint assumes synchrony to retain some interesting Bitcoin dynamics, Chia requires PoSW with unique proofs, i.e., PoSW in which it is hard to come up with more than one accepting proof for any true statement. In this thesis we construct simple and practically-efficient PoSpace and PoSW. When using our PoSpace in cryptocurrencies, miners can start mining on the fly, like in Bitcoin, and unlike current constructions of PoSW, which either achieve efficient verification of sequential work, or faster-than-recomputing verification of correctness of proofs, but not both at the same time, ours achieve the best of these two worlds

Accelerated Simulation of Large Scale Power System Transients

RÉSUMÉ Le temps de simulation est un paramètre crucial de l’analyse des transitoires dans les réseaux électriques et il est en train de devenir l’un des facteurs les plus importants pour mesurer les performances et la fiabilité des logiciels. Actuellement, la vitesse et les performances des processeurs ont atteint un point où l’accélération de gain en vitesse et d’opérations en virgule flottante peut être réduite en se concentrant uniquement sur l’aspect vitesse des processeurs individuels. Au contraire, la recherche en informatique et le développement de matériel informatique tendent de plus en plus à rendre les processeurs parallèles plutôt que plus rapides. D'autre part, la simulation des systèmes électriques devient de plus en plus complexe avec l'introduction de modèles complexes tels que les énergies renouvelables, les composantes de réseaux intelligents et l'électronique de puissance. En outre, la demande de puissance sans cesse croissante et l’augmentation de la zone de couverture des réseaux de distribution d’énergie contribuent à l’augmentation de la taille des réseaux de distribution d’énergie et ralentissent encore plus la simulation électromagnétique transitoire de ces réseaux. De nombreux -logiciels de simulation de type EMT effectuent actuellement leurs opérations de manière séquentielle en utilisant un seul - processeur, plutôt que tous les processeurs de la machine. Ce comportement entraîne un temps de simulation long et introduit des difficultés pour simuler des réseaux de systèmes d'alimentation plus avancés et complexes. Ce type de délai devient un obstacle lorsque de grands réseaux, réels ou existants, sont utilisés. Par exemple, simuler le réseau d'Hydro-Québec doté d'une matrice de taille 41555 × 41555 et contenant un grand nombre de dispositifs de commutation et des éléments non linéaires nécessite 1765 secondes pour simuler une seconde avec un pas de temps de 50us. La programmation parallèle multithread est maintenant disponible dans les compilateurs modernes. Elle peut être utilisée pour améliorer de manière significative les performances des calculs EMT. La recherche actuelles dans ce domaine est principalement appliqué à des systèmes moins complexes qui nécessitent l'intervention de l'utilisateur pour le découpage parallèle et manque de généralisation pour toute topologie rencontrée dans les études réels. Cette thèse développe une méthode de parallélisation entièrement automatique applicable aux systèmes à grande échelle avec des topologies arbitraires sans aucune intervention de l'utilisateur.----------ABSTRACT Simulation time is a crucial parameter in power system transient analysis. The simulation needs for electromagnetic transients are continuously increasing. The electromagnetic transient (EMT) type tools are now also used for the simulation of slower electromechanical transients in large scale power systems. The EMT approach for power system analysis is the most accurate approach, but it suffers from computation performance issues. Research on this aspect is currently of crucial importance. Research is timely and should increase the application range of EMT-type tools. In fact very fast EMT-type tools can have a major impact on the simulation and analysis of modern power grids with increased penetration of renewables. Currently, computer processor speed and performance reached a point where not much speed gain and floating-point operation acceleration can be achieved by only focusing on the speed aspect of individual processors. Rather, the trend in computer research and hardware development is becoming more and more focused on making processors parallel rather than faster. Many EMT-Type simulation packages currently perform their operations sequentially by using only one CPU core rather than all machine processors. This behaviour results in long simulation time and introduces major difficulties when simulating large and complex power grids. This type of delay becomes a show stopper when large, real and existing networks are used. Multithreaded parallel programming is now available in modern compilers. It can be used to significantly improve the performance of EMT computations. Current research in this field has been mostly applied to less complicated systems and requires user intervention. This thesis develops a fully automatic parallelization method that is applicable to large scale systems with arbitrary topologies. This PhD thesis presents existing progress in the field of electromagnetic transient simulation acceleration and highlights the different approaches that are adopted to achieve faster EMT simulation. The focus is mainly on threading through CPU exclusively on modern desktop computers used by engineers on daily basis

SNACKs for Proof-of-Space Blockchains

SNACKs are succinct non-interactive arguments of chain knowledge. They allow for efficient and generic solutions to blockchain light-client bootstrapping. Abusalah et al. construct SNACKs in the random oracle model for any \emph{single-chain} blockchain from any graph-labeling proof of sequential work (PoSW) scheme. Their SNACK construction is a PoSW-like protocol over the augmented blockchain. Unlike single-chain blockchains, such as proof-of-work and proof-of-stake blockchains, proof-of-space (PoSpace) blockchains are composed of two chains: a \emph{canonical} proof chain and a data chain. These two chains are related using a signature scheme. In this work, we construct PoSW-enabled SNACKs for any PoSpace blockchain. Combined with the results of Abusalah et al., this gives the first solution to light-client bootstrapping in PoSpace blockchains. The space cost of our construction is \emph{two} hash values in each augmented PoSpace block. Generating SNACK proofs for a PoSpace blockchain is identical to generating SNACK proofs for single-chain blockchains and amounts to looking up a succinct number of augmented blocks

The strategic role of GCC Islamic banks in Malaysia: a knowledge transfer perspective

The recent trend in the field of strategic management has been to emphasize the role of knowledge management as a basis of the competitive advantage of organizations. Historically, the searches for MNCs performance have been oriented around that knowledge is power. In organizations, this expression has become even more relevant than other social settings. Knowledge is a major factor that differentiates successful organizations from the unsuccessful ones. This study aims to investigate the strategic role in knowledge transfer, as well as to review the effect of strategic role as the constituent factor of knowledge transfer which contributes to the success of Islamic banking and financial knowledge performance in GCC Islamic banks subsidiaries in Malaysia. The data were collected through sending out questionnaires to 5 leaders of Upper Managers in GCC Islamic banks in Malaysia, administered 2-items of strategic roles namely: Contributor and Implementer. The respondents’ answers were subjected to SPSS. After that, semi-structured interviews were conducted with respondents. The results indicated that there is positive and significant influence of strategic leadership on knowledge transfer process. GCC Islamic banks subsidiaries in Malaysia are standing at the great extent level of strategic role from knowledge transfer perspective. In addition, the two factors named contributor and implementer lead to achieve the strategic role between headquarter and its subsidiary. The conclusion of this research paper recommended the advanced empirical research studies in future to develop a conceptual unifying model of Islamic banking and financial knowledge transfer within Islamic banks

Financial situation of PN17 companies listed in the Malaysian Stock Exchange

A Practice Note 17 (PN17) Company is a listed company in the Malaysian Stock Exchange that is financially distressed or does not have a core business or has failed to meet minimum capital or equity (Less than 25% of the paid up capital). Financial ratio analysis method can be used to detect the failure of this company. As of 9th August 2010, there are still thirty four companies listed on Malaysian Stock Exchange classified under PN17 List. These companies have entered into PN 17 list in accordance with existing standards. There are also investors who do not know the status of these listed companies. A real and full attention has not been given yet for these companies. Analytical studies and scientific researches are almost still lacking on PN17 Companies listed in the Malaysian Stock Exchange. The aims of this research work is to examine the differences between the financial liquidity ratios (Current, Quick, Cash Ratio) and Altman's Z-score in determining the financial failure of companies, that is using financial ratios and Altman Z Score to examine whether there is different between PN17 companies and Non-PN17 listed in the Malaysian Stock Exchange. It also aimed to determine whether are all the PN17 Companies listed in the Malaysian Stock Exchange financial failure companies, to explore and report the financial situation of companies listed on Malaysian Stock Exchange. The available data collected from the library of Malaysian Stock Exchange covering the period from 2003 to 2009 were used in the analysis. This study answered the research questions formulated. Financial Liquidity ratios and Altman Z-score can be used to detect financial distress of companies, and it is important to compare ratios with the industry average or with a competitor in the same sector. Not all the PN17 Companies are financial failure Companies, It was found that there are financial difficulties companies still listed among the Non-PN17 list. Companies should emphasize on the issue of accounting disclosure

Transfer of Islamic banking knowledge from GCC Islamic bank headquarter to its subsidiary in Malaysia

The Gulf Cooperation Council (GCC) Islamic banks' subsidiaries which have invested in Malaysia have seen the going gets tough. They are strapped by paltry returns and stymied by stiff competition from the local Malaysian banks. Since the increasing competition and the slowdown of the economy have encouraged multinational banks to seek new ways to improve their internal efficiency and their performance, it has given the pivotal importance of knowledge transfer for the competitiveness of multinationals, but the process of transferring knowledge effectively across dispersed units of International Islamic banks has only attracted little and rather fragmented research interest. Thus, there is hardly evidence about how this large-scale knowledge transfer has been achieved and what knowledge has actually been transferred to the GCC Islamic banks investing in Malaysia. Therefore, the aim of this research study is to develop a comprehensive Islamic banking knowledge transfer framework that serves as a basis for future research agenda. The study focused on the cases of the Islamic banks' subsidiaries in Malaysia that are fully owned by GCC Islamic banks. The respondents were the experts who are well aware of their business to answer the survey questionnaire. This study is mixed method type of research study. A survey questionnaire was used as a guideline to compose specific questions related to the conceptual model. This is followed by interviews that were conducted with the respondents to investigate the model’s constructs and then to analyse the generated propositions in order to address the main research questions. This study tested the research propositions and found that, the integration between HQ bank and its subsidiary bank, the strategic role and the ability of the subsidiary bank to engage in Islamic banking knowledge transfer are related to the development of Islamic banking knowledge transfer capabilities. Besides that, the development of Islamic banking knowledge transfer capabilities, as well as organizational and cultural distances between HQ bank and its subsidiary bank are related to the Islamic banking knowledge transfer performance. In short, the findings of this research study have not only contributed to the literature, but also provided valuable information to both managers and policy makers on the matter of transferring the knowledge of Islamic banking. The study recommends the top management to implement KT practices that need to be made known and felt by all levels of bank units' members. Managers have to pay attention to the development of communication technologies, personal contacts, training efforts and relations of trust between the employees, because it is an important factor for a successful knowledge transfer process. Finally, the findings of this study are useful, but need to be strengthened by future research work

Host-parasitoid relationships of Anagyrus sp. near pseudococci (Girault), (Hymenoptera, Encyrtidae), as a basis to improve biological control of pest mealybugs (Hemiptera, Pseudococcidae)

Doutoramento em Engenharia Agronómica - Instituto Superior de AgronomiaThe host-parasitoid relationships of Anagyrus sp. nr. pseudococci were investigated, including host selection behavior, host defenses, host suitability and parasitoid functional response in relation to five mealybug species with different phylogenetic relationships and geographical origins: i) a Mediterranean native species, Planococcus ficus, with a long co-evolutionary history with the parasitoid; ii) three alien species, Planococcus citri, Pseudococcus calceolariae and Pseudococcus viburni, with a more recent co-evolutionary history; and iii) a fourth alien species, Phenacoccus peruvianus, with no previous common history with the parasitoid. The parasitoid recognized as potential hosts and complete development in all five mealybug species, but showed a clear preference for Planococcus spp. Host suitability of the studied mealybugs seems to fit a phylogenetic/biogeographic trend, showing the highest level in Pl. ficus and its closely related congener Pl. citri, followed by the Australasian Ps. calcelolariae, and the Neotropical Ps. viburni and Ph. peruvianus. The functional response of the parasitoid varied between host species, with a type II and type III responses observed for Ps. calceolariae and Pl. ficus, respectively. The results suggest that A. sp. nr. pseudococci has a broader host range and a more generalist behavior in comparison with other Anagyrus species

An Incremental PoSW for General Weight Distributions

A proof of sequential work (PoSW) scheme allows the prover to convince a verifier that it computed a certain number of computational steps sequentially. Very recently, graph-labeling PoSW schemes, found applications in light-client blockchain protocols, most notably bootstrapping. A bootstrapping protocol allows a light client, with minimal information about the blockchain, to hold a commitment to its stable prefix. An incremental PoSW (iPoSW) scheme allows the prover to non-trivially increment proofs: given $\chi,\pi_1$ and integers $N_1,N_2$ such that $\pi_1$ is a valid proof for $N_1$, it generates a valid proof $\pi$ for $N_1+N_2$. In this work, we construct an iPoSW scheme based on the skiplist-based PoSW scheme of Abusalah et al. and prove its security in the random oracle model by employing the powerful on-the-fly sampling technique of Döttling et al. Moreover, unlike the iPoSW scheme of Döttling et al., ours is the first iPoSW scheme which is suitable for constructing incremental non-interactive arguments of chain knowledge (SNACK) schemes, which are at the heart of space and time efficient blockchain light-client protocols. In particular, our scheme works for general weight distributions, which we characterize as incrementally sampleable distributions. Our general treatment recovers the distribution underlying the scheme of Döttling et al. as well as the distribution underlying SNACK-enabled bootstrapping application as special cases. In realizing our general construction, we develop a new on-the-fly sampling technique

Effect of Educational Program on Compliance with Medication Regimen of Myocardial Infarction Patients

Myocardial infarction (MI) is a major cause of death and disability worldwide as well as in Palestine. In Palestine, mortality rate from MI reach 18.7% in males and 7.7% in females. Recently it has become evidenced that there are certain modifiable factors that may contribute to the occurrence of MI. The study aims to determine the effect of an educational program about medication regimen on compliance of myocardial infarction patients in Gaza Strip. A quasi-experimental design (pre-test/post-test) was conducted at two major hospitals with cardiac outpatient clinics in the Gaza Strip. 65 clients suffering from myocardial infarctions were selected randomly from Shifa and Nasser hospital. Pretest and posttest structured interviewing questionnaire was used to collect data about patient's knowledge and reported practices about medication regimen. The educational program was typed and handed out to study participants in the form of a booklet. The study revealed that patients’ knowledge score about MI disease and treatment regimen pre educational was improved significantly post education program. The same as, the percentage of patients who ranking score of compliance as good was improved from 13.8% pre-education program to 72.3% post education. The study concluded that, educational program about medication regimen implicated changes in myocardial infarction subjects' knowledge, and reported practices. This would ultimately increase the quality of life for myocardial infarction patients and decrease the incidence of complications. Keywords: compliance, myocardial infarction, educational program, knowledge, reported practic