The use of randomness in computer science is ubiquitous. Randomized protocols have turned out to be much more efficient than their deterministic counterparts. In addition, many problems in distributed computing and cryptography are impossible to solve without randomness. However, these applications typically require uniform random bits, while in practice almost all natural random phenomena are biased. Moreover, even originally uniform random bits can be damaged if an adversary learns some partial information about these bits. In this thesis, we study how to run randomized protocols in distributed computing and cryptography with imperfect randomness. We use the most general model for imperfect randomness where the weak random source is only required to have a certain amount of min-entropy. One important tool here is the randomness extractor. A randomness extractor is a function that takes as input one or more weak random sources, and outputs a distribution that is close to uniform in statistical distance. Randomness extractors are interesting in their own right and are closely related to many other problems in computer science. Giving efficient constructions of randomness extractors with optimal parameters is one of the major open problems in the area of pseudorandomness. We construct network extractor protocols that extract private random bits for parties in a communication network, assuming that they each start with an independent weak random source, and some parties are corrupted by an adversary who sees all communications in the network. These protocols imply fault-tolerant distributed computing protocols and secure multi-party computation protocols where only imperfect randomness is available. The probabilistic method shows that there exists an extractor for two independent sources with logarithmic min-entropy, while known constructions are far from achieving these parameters. In this thesis we construct extractors for two independent sources with any linear min-entropy, based on a computational assumption. We also construct the best known extractors for three independent sources and affine sources. Finally we study the problem of privacy amplification. In this model, two parties share a private weak random source and they wish to agree on a private uniform random string through communications in a channel controlled by an adversary, who has unlimited computational power and can change the messages in arbitrary ways. All previous results assume that the two parties have local uniform random bits. We show that this problem can be solved even if the two parties only have local weak random sources. We also improve previous results in various aspects by constructing the first explicit non-malleable extractor and giving protocols based on this extractor.

Abstract Title: How to assess risks in weak links in cold chain distribution process? Authors: Shuchang Lu, Yufan Gu & Radzion Predko Tutor: Åsa Gustafsson Examiner: Dr. Lars-Olof Rask Course: 4FE06E - Master Thesis Research Questions: • Why do cold chain products have quality risk? -  What kind of weak links exist in distribution process of cold chain? -  What kind of risks exist in weak links of distribution process of cold chain? -  How to assess risks in weak links of distribution process of cold chain? Background: The increasing food wastes and starving people have made food preserved by cold chain as a significant and profitable issue. An effective and efficiency cold chain can make a big difference in the whole food supply chain around the world. With the improvements of modern technologies, cold chain distribution is experiencing changes. Purpose: To identify weak links in distribution channel of cold chain products. What kind of risks exist in these weak inks and how to assess them. Method: Positivistic is used throughout the paper. Multiple exploratory case study is our way of research our problems. Data were gathered from interview, documents and company’s website. Conclusions: Human handling in delivery process, the way retailers deal with frozen products, how do different participants manage their resources and safety of product and its quality are main reasons for quality risk. Risks in weak links can cause product quality problem in cold chain distribution channel. Therefore, assess these risks can help managers to deal with them. Keywords: Cold chain distribution, quality problem, weak link, risk

This thesis presents a model for the process of sand production that allows us to predict the stability of wellbores and perforation tunnels as well as mass of sand produced. Past analytical, numerical, and empirical models on material failure and erosion mechanisms were analyzed. The sand production model incorporates shear and tensile failure mechanisms. A criterion for sand erosion in failed sand was proposed based on a force balance calculation on the sand face. It is shown that failure, post failure sand mechanics and flow-dominated erosion mechanisms are important in the sand production process. The model has a small number of required input parameters that can be directly measured in the lab and does not require the use of empirical correlations for determining sand erosion. The model was implemented in a numerical simulator. Three different experiments using different materials were simulated and the results were compared to test the model. The model-generated results successfully matched the sand production profiles in experiments. When the post-failure behavior of materials was well-known, the match between the simulation and experiment was excellent. Sensitivity studies on the effect of mechanical stresses, flow rates, cohesion, and permeability show qualitative agreement with experimental observations. In addition, the effect of two-phase flow was presented to emphasize the importance of the water-weakening of the sand. These results show that catastrophic sand production can occur following water breakthrough. Finally the impact of increasing sand cohesion by the use of sand consolidation chemicals was shown to be an effective strategy for preventing sand production. / text

Σε ένα γραμμικό υπόδειγμα βοηθητικών μεταβλητών η ασθενής συσχέτιση των βοηθητικών μεταβλητών με τις ενδογενείς ερμηνευτικές μεταβλητές είναι γνωστή στη βιβλιογραφία ως το ζήτημα των ασθενών βοηθητικών μεταβλητών. Στην παρούσα εργασία διερευνώνται διάφορες πτυχές του εν λόγω ζητήματος και επισημαίνονται πιθανές μέθοδοι για την αντιμετώπισή του. Επίσης, μελετάται η απόδοση των εκτιμητών OLS, TSLS, BTSLS, LIML και Fuller-k κάτω από την υπόθεση των ασθενών βοηθητικών μεταβλητών, μέσω ενός πειράματος Monte Carlo, με τα αποτελέσματα να τεκμηριώνουν τη δυσκολία λήψης αξιόπιστων σημειακών εκτιμήσεων. / Weak instruments arise when the instruments in linear instrumental variables (IV) regression are weakly correlated with the included endogenous variables. We review most of the recent studies on weak instruments and point to several methods that have been proposed to deal with such instruments. Using a Monte Carlo experiment we study the performance of OLS, TSLS, BTSLS, LIML and Fuller-k estimators under weak instruments. Our results indicate the difficulty of obtaining reliable point estimates.

Στην εργασία μελετάται η ανάλυση και ο έλεγχος μετατροπέων αιολικής ενέργειας (ανεμογεννήτριες) και συγκεκριμένα μία ανεμογεννήτρια η οποία χρησιμοποιεί σύγχρονη γεννήτρια με 2 τριφασικά τυλίγματα στο στάτη και με διασύνδεση συνεχούς ρεύματος. Παρουσιάζεται η μοντελοποίηση της γεννήτριας, του ανεμοκινητήρα και της διασύνδεσης συνεχούς ρεύματος. Στη συνέχεια σχεδιάζονται διάφοροι τρόποι ελέγχου ώστε να είναι δυνατή η σύνδεση της ανεμογεννήτριας σε ασθενή δίκτυα μέσης τάσης, σε απομονωμένα φορτία αυτόνομα και σε συνεργασία με υδροηλεκτρικό σταθμό. / In this thesis, the analysis and control of wind energy conversion systems is studied. The chosen wind energy converter consists of an horizontal-axis three-blade pitchable wind turbine, a six-phase synchronous generator and an AC/DC/AC link. The operation is based on a variable-speed constant-frequency scheme that is achieved through two different AC/DC/AC topologies and the appropriate pulsation of the IGBT converters. The aerodynamic torque on the wind turbine is modeled by a special non linear equation, which also includes the pitch angle as an extra variable for the control of the aerodynamic power. The simulation program SIMULINK has been used for the modeling and the study of the various systems under large variations of the wind speed.

Exchange rate determination allows precise modeling of chemical systems, and allows one to infer properties relevant to tumor biology such as enzyme activity and pH. Current exchange rate determination methods found via Contrast Enhanced Saturation Transfer agents are not effective for fast exchanging protons and use non-linear models. A comparison of their effectiveness has not been performed. In this thesis, I compare the effectiveness of current exchange rate measurement methods. I also develop exchange rate measurement methods that are effective for fast exchanging CEST agents and use linear models instead of non-linear models. In chapter 1 I review current exchange rate measurement methods. In chapter 2 I compare several of the current methods of exchange rate measurement, along with several techniques we develop. In chapter 3 I linearize the Quantifying Exchange through Saturation Transfer (QUEST) measurement method analogously to the Omega Plot method, and compare its effectiveness to the QUEST method. In chapter 4, I compare the effectiveness of current exchange rate theories (Transition State Theory and Landau-Zener theory) in the moderate coupling regime, and propose our own combined Eyring-Landau-Zener theory for this intermediate regime. In chapter 5 I discuss future directions for method development and experiments involving exchange rate determination.

Two new specification tests for overidentifying restrictions proposed by Hahn and Hausman (2002:b) are here tested and compared to the classical Sargan test. Power properties are found to be very similar in overall performance, while Sargan generally has better size than the new tests. Also, size is distorted for one of the new tests, thus a tendency to reject prevails. In addition, sometimes severe bias is found which affects the tests’ performances, something that differs from earlier studies.

This thesis presents ground control best practices in weak rock environments including an augmentation to the existing Span Design curve by adding 463 case histories of RMR76 values ranging from 25 to 60. A Neural Network analysis of this data has been added and compared to the existing Span Design data of 292 case histories. Ground support is almost always used in weak rock environments, though the type of support used can vary widely. The development of the weak rock augmented Span Design Curve has also been calibrated to four different support categories; Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill. Category A is considered “Unsupported” with an average Factor of Safety less than 1.2. Categories B, C and D are considered “Supported” with average Factors of Safety greater than 1.2. All categories are compared the original Critical Span Design Curve presented by Lang (1994). However, only Category A can be accurately compared to the original Critical Span Design Curve as it is “Unsupported” as well. Category A yields good results, however, Categories B, C and D do not, but still demonstrate that spans can remain stable at lower RMR76 values. Design of underground man-entry type excavations in North America relies heavily upon empirical analysis. This design requires a higher Factor of Safety than other non-man entry type excavations. A comparison of the calculated ½ span failure Factor of Safety between all the categories is also presented. The contribution this research provides to the mining industry is the "Unsupported" Weak Rock Updated Span Design Curve and awareness pertaining to the potentially detrimental effects of using resin grounted rebar in weak rock masses and the false sense of security that the use of resin grouted rebar may instill. It is also shown that spans in the “Unstable” zone of the new “Unsupported” Weak Rock Updated Span Design Curve can possibly be stabilized if detailed engineering design is applied to obtain “Supported” status.

Ištvermė, suvokiama kaip aerobinis darbingumas, yra svarbiausia iš visų su sveikata susijusių fizinių ypatybių. Šio tyrimo tikslas buvo įvertinti aklųjų ir silpnaregių aerobinės ištvermės ugdymo ypatumus, atliekant aerobinį krūvį. Tyrimai buvo atlikti Lietuvos kūno kultūros akademijos (LKKA) TFV katedroje. Tyrime dalyvavo aklieji ir silpnaregiai vyrai, iš Kauno sveikatos sporto klubo ir LAS Lietuvos aklųjų sąjungos. Jie buvo suskirstyti į dvi grupes sportuojantis ir nesportuojantys. Taip pat tyrime dalyvavo Lietuvos kūno kultūros akademijos studentai. Tikslas - nustatyti ir įvertinti sportuojančių ir nesportuojančių regos negalią turinčių asmenų ištvermės rodiklių kaitą priklausomai nuo negalios sunkumo laipsnio Uždaviniai: 1. Nustatyti ir įvertinti nesportuojančių regos negalią tiriamų asmenų ir įgaliųjų aerobinės ištvermės rodiklių kaitą atliekant 12min. bėgimo testą. 2. Nustatyti ir įvertinti sportuojančių neįgaliųjų, turinčių regos negalią, ištvermės rodiklių kaitą priklausomai nuo negalios sunkumo laipsnio. 3. Palyginti sportuojančių ir nesportuojančių aklųjų, silpnaregių ir nesportuojančių įgaliųjų aerobinės ištvermės rodiklius, 12 min. bėgimo testo metu. Visiems tiriamiesiems buvo atliktas Cooperio testas - 12 min. bėgimas. Tiriamiesiems bėgimo sąlygos vienodos. Tyrimo užduotis– kuo ilgesnį atstumą nubėgti per 12 min. Tiriamieji po trijų minučių apšilimo užduotį atliko bėgdami bėgtakiu. Kas minute buvo registruojamas pulso dažnis. Kiekvienas bėgikas galėjo... [toliau žr. visą tekstą] / Stamina, perceived as aerobic efficiency, is the most important from all physical peculiarities related with health. The purpose of this research was to evaluate training peculiarities of aerobic stamina of blind and weak-eyed persons, while exercising aerobic load. The researches were done in Lithuanian Academy of Physical Education TVF department (Department of Adapted Physical Activity). Blind and weak-eyed men from Kaunas Health Sport Club and LAS Lithuanian the blind union. They were split into two groups: those going in for sports and those do not going in for sports. Students from Lithuanian Academy of Physical Education participated in the research as well. Purpose - To measure and assess the change of stamina indexes of the disabled with sight disability persons going in for sports subject to the heaviness degree of the disability. 1. To measure and assess the change of aerobic stamina indexes of persons with sight disabilities going in for sports and not going in for sports and of healthy people while doing 12 min.-running test 2. To measure and assess the change of stamina indexes of the disabled with sight disability persons going in for sports subject to the heaviness degree of the disability. 3. To compare aerobic stamina indexes of blind persons, weak-eyed persons going in for sports and not going in for sports and healthy persons not going in for sports during the 12 min.-running test. Cooper test – 12 min. running was done to all the people under the... [to full text]

Baigiamajame magistriniame darbe nagrinėjama tema – ikimokyklinio amžiaus aklųjų ir silpnaregių kalbos raidos ypatumai ( lyginamoji analizė). Sunku pervertinti kalbos plėtotės procese pagrindinių – regos ir klausos – analizatorių vaidmenį. Šių analizatorių sutrikimas labai stipriai įtakoja kalbinės veiklos vystymąsi ir suteikia jam tam tikrų ypatumų. Labai dažnai aklo iš prigimties asmens turimų sąvokų turinys kardinaliai skiriasi nuo reginčiųjų. Stokodami vieno iš pasaulio pažinimo būdų aklieji dažnai neadekvačiai vartoja turimas sąvokas. Aklas vaikas gali girdėti kalbą ir mėgdžiodamas jos mokosi. Kartais jis labiau už regintįjį yra motyvuotas ją vartoti, nes tai pagrindinis kanalas komunikuojant su kitais. Ar iš tikrųjų aklųjų kalbinė raiška skiriasi nuo normaliai matančių vaikų? Į šį klausimą bandoma atsakyti šiame magistro darbe. Tyrimo problema: ikimokyklinio amžiaus nereginčių ir silpnaregių vaikų kalbinė raida stokoja normalaus psichofiziologinio pagrindo. Šiuos trūkumus būtina kompensuoti, pasitelkus išlikusius sveikus analizatorius prieš tai tiksliai išsiaiškinus šios grupės vaikų kalbinės raidos pasiekimo skirtumus lyginant su sveikaisiais. Tyrimo objektas: ikimokyklinio amžiaus aklųjų ir silpnaregių bei gerai matančių vaikų kalbos raida ( lyginamoji analizė). Tyrimo tikslas: ištirti ikimokyklinio amžiaus aklųjų ir silpnaregių kalbos raidos ypatybes. Tyrimo uždaviniai: 1. Išanalizuoti psichologinę ir pedagoginę literatūrą apie aklųjų ir silpnaregių kalbinę raidą... [toliau žr. visą tekstą] / SUMMARY The final master‘s study deals with the peculiarities in lingual development of the blind and poor-sighted children at preschool age (the comparative analysis). It is difficult to overestimate the role of the main analyzers, i.e. sight and hearing in the process of lingual development. The disorder of these analyzers affects very strongly the development of lingual activities and renders certain peculiarities to it. Very often the contents of concepts of a person, who is blind by nature, cardinally differ from that of people with normal sight. Lacking one technique for world cognition, the blind persons often inadequately use the concepts available. The sightless child can hear the language and learn it by imitation. Sometimes he is more motivated to use it than a seeing person, since it is the main channel for communication with others. Does really the lingual expression of the blind children differ from that of normally sighted? In this master’s study the attempts were done to answer this question. Problem of study. The lingual development of blind and poor-sighted preschoolers lacks normal psycho-physiological substantiation. These shortcomings should be compensated with help of the remaining healthy analyzers. But before it the differences in achieved lingual development between the children of this group and healthy ones should be find out. Object of study: lingual development in blind and poor-sighted children at preschool age (the comparative analysis). ... [to full text]