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The current study addresses the stability of shock waves propagating through dissipative media, analogous to both granular media and molecular gases undergoing endothermic reactions. In order to investigate the stability, a simple molecular dynamics model was developed to observe shock waves and their structures with the inclusion of energy dissipation. For this, an Event Driven Molecular Dynamics model was implemented in a 2D environment, where a molecule is represented by a disk. The simulations addressed the formation of a shock wave in a gas by the sudden acceleration of a piston. Inelastic collisions were assumed to occur only if an impact velocity threshold is surpassed, representing the activation energy of the dissipative reactions. Parametric studies were conducted for this molecular model, by varying the strength of the shock wave, the activation threshold and the degree of inelasticity in the collisions. The resulting simulations showed that a shock structure does indeed become unstable with the presence of dissipative collisions. This instability manifests itself in the form of distinctive high density non-uniformities behind the shock wave, which take the form of convective rolls. The spacing and size of this ``finger-like" unstable pattern was shown to be dependent on the degree of inelasticity, the activation energy, and the strength of the driving piston. The mechanism responsible for the instability was addressed by studying the time evolution of the material undergoing the shock wave compression and further relaxation. It is found that the gas develops the instability on the same time scales as the clustering instability in homogeneous gases, first observed by Goldhirsch and Zanetti in granular gases. This confirmed that the clustering instability is the dominant mechanism.

Collision strength, the measure of strength for a binary collision, hasn't been defined clearly. In practice, many physical arguments have been employed for the purpose and taken for granted. A scattering angle has been widely and intensively used as a measure of collision strength in plasma physics for years. The result of this is complication and unnecessary approximation in deriving some of the basic kinetic equations and in calculating some of the basic physical terms. The Boltzmann equation has a five-fold integral collision term that is complicated. Chandrasekhar and Spitzer's approaches to the linear Fokker-Planck coefficients have several approximations. An effective variable-change technique has been developed in this dissertation as an alternative to scattering angle as the measure of collision strength. By introducing the square of the reduced impulse or its equivalencies as a collision strength variable, many plasma calculations have been simplified. The five-fold linear Boltzmann collision integral and linearized Boltzmann collision integral are simplified to three-fold integrals. The arbitrary order linear Fokker-Planck coefficients are calculated and expressed in a uniform expression. The new theory provides a simple and exact method for describing the equilibrium plasma collision rate, and a precise calculation of the equilibrium relaxation time. It generalizes bimolecular collision reaction rate theory to a reaction rate theory for plasmas. A simple formula of high precision with wide temperature range has been developed for electron impact ionization rates for carbon atoms and ions. The universality of the concept of collision strength is emphasized. This dissertation will show how Arrhenius' chemical reaction rate theory and Thomson's ionization theory can be unified as one single theory under the concept of collision strength, and how many important physical terms in different disciplines, such as activation energy in chemical reaction theory, ionization energy in Thomson's ionization theory, and the Coulomb logarithm in plasma physics, can be unified into a single one -- the threshold value of collision strength. The collision strength, which is a measure of a transfer of momentum in units of energy, can be used to reconcile the differences between Descartes' opinion and Leibnitz's opinion about the "true'' measure of a force. Like Newton's second law, which provides an instantaneous measure of a force, collision strength, as a cumulative measure of a force, can be regarded as part of a law of force in general.

Orientador: Hans Ingo Weber / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-24T05:43:03Z (GMT). No. of bitstreams: 1 Mattos_MarcioCoelhode_D.pdf: 10130294 bytes, checksum: 5b9cef82256f8fd05f78a1341b08ac10 (MD5) Previous issue date: 1998 / Resumo: Apresentamos neste trabalho uma investigação sobre as mudanças na dinâmica de sistemas com vibroimpacto. Particularmente estamos interessados no estudo da migração das freqüências características destes sistemas. Podemos considerar que um dado sistema com vibroimpacto tende a um sistema com impacto degenerado quando a folga deste sistema tende a zero ou a um valor maior que a amplitude de vibração do sistema na coordenada de impacto. Podemos também denominar estes sistemas como sistemas lineares associados ao sistema com impacto, se o impacto' for a única não linearidade presente no sistema. Mostramos que existe uma relação intrínseca entre a resposta do sistema com impacto e os sistemas lineares associados, ou sistemas degenerados. Para investigar esta relação, analisamos a resposta de sistemas com dois e três graus de liberdade com impacto em uma de suas coordenadas. Além disto, investigamos experimentalmente a resposta de uma viga engastada-livre excitada randomicamente e com impactos em sua extremidade livre. Observamos boa correlação entre os resultados numéricos e, experimentais. Propomos uma função para a migração da primeira freqüência característica da resposta de sistemas com vibroimpacto. O caminho da migração depende da distribuição da energia total fornecida ao sistema entre os diversos modos de vibração dos sistemas lineares associados / Abstract: This works presents an investigation on the changes in the dynamics of vibroimpact systems as their clearance is varied. Particularly we are interested in the migration of the characteristic frequencies of impact systems. We can consider that a given vibroimpact system reaches to a degenerated impact system when the clearance reaches to zero or to a value which is greater than the amplitude of the response of the system at the impact coordinate. We also can call these systems as associated linear systems of a given impact system, if the impact is the only nonlinearity which takes place. We show that there is an intrinsic relation between impact systems and their associated linear systems, or degenerated systems. To investigate this relation we consider the free response of 2-DOF and 3-DOF impact systems with impact in one of their coordinates. On the other hand, we have performed an experimental investigation in a randomly excited cantilever beam with impacts on its free end. We have found good agreement between numerical and experimental results. We have proposed a function for the migration of the first characteristic frequency of impact systems. The migration way depends on distribution of the total energy supplied to system among the vibration modes of the associated linear systems / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23002号 / 理博第4679号 / 新制||理||1671(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 大西 明, 准教授 菅沼 秀夫, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Title: Study of transverse flow of kaons in Au + Au collisions at 1.23A GeV Author: Lukáš Chlad Abstract: The production and propagation of strange hadrons at the threshold energy are important probes of the in-medium hadron's properties and stiffness of the equation of state of nuclear matter. In this thesis, the transverse kaon flow at Au + Au collisions with kinetic beam energy 1.23A GeV measured with the HADES spectrometer is discussed. The motivation for such an analysis and the theoretical introduction are described first, followed by the characterization of the the individual parts of HADES spectrometer. The procedure to identify detected particles from the measured signals is introduced. Finally, the flow analysis and its results are presented. The differential directed and elliptic flow of kaons in measured gold on gold collisions is compared with published data and with kinetic transport model predictions. Keywords: relativistic heavy-ion collisions, transverse flow, kaon flow 1

Highly energetic jets are considered to be a direct probe of hot and dense QCD medium created in heavy ion collisions. Jet measurements performed both at the LHC and RHIC indicate a presence of the jet quenching phenomenon. This thesis summarizes ATLAS jet heavy ion measurements and it reports the first exploratory study of properties of the multi-jet production in heavy ion collisions presented in terms of yield of neighbouring jets. The work is expected to shed a light on the process of the parton energy loss. The measurement is performed using the Pb+Pb collision data collected by ATLAS detector during the 2011 LHC runs at the nucleon-nucleon center of mass energy of 2.76 TeV. 1

The research reported here evolved from the researcher’s ethnographic immersion in an ICT for Development (ICT4D) project in a deep rural part of South Africa. During ethnographic immersion, three key issues emerged from fieldwork. Firstly, the researcher realised his limited understanding of the worldview of research participants. Secondly, he realised his inability to appropriately and ethically do community entry and implement the ICT4D artefact (e.g. ICT4D training and policy), especially because of his limited understanding of the cultural context, underlying values, emancipatory concepts and interests, as well as incomplete insight into the oppressive circumstances that the people in the research setting find themselves in. The third issue relates to an inability to interpret and explain the collisions and conflicts that emerged from introducing, aligning, and implementing the ICT4D artefact. Through critical ethnographic methods and a critical orientation to knowledge, the researcher shows how these inabilities, collisions, and false consciousnesses emerged to be the result of cultural entrapment and ethnocentricity that he and the research participants suffered from. A key argument throughout this thesis is that the emancipation of the researcher is a precursor for the emancipation of the researched. The researcher thus asks: In what ways should ICT4D researchers and practitioners achieve self-emancipation, in order to ensure the ongoing emancipation and empowerment of the deep rural developing community in South Africa? The study subsequently argues the link between the topic of this thesis, namely the issue of ethical research practice, and the primary research question. A unique perspective on these problems is presented as the study looks at emancipatory ICT4D research and practice in context of a deep rural Zulu community in South Africa, and specifically the journey of social transformation that the researcher himself embarked on. The study retrospectively applies Bourdieu’s critical lineage to reflect on the research contribution and how the researcher was eventually able to construct adequate knowledge of the ICT4D social situation. Building onto the idea of critical reflexivity, the researcher argues that critical introspection should also be part of critical ICT4D research in South African contexts. Through confessional writing, the researcher describes experiential knowledge of the worldview collisions that emerged from ICT4D research and practice. In particular, manifestations of the collisions between the typical task-orientated or performance-orientated value system of Western-minded societies and the traditional loyalty-based value system or people-orientated culture of the Zulu people are described. The research contributes by challenging dominant ICT4D discourses and by arguing for an end to a line of ICT4D research and practice where outsiders with a Western task-orientated worldview, like the researcher himself, make unqualified and inadequate assumptions about their own position in ICT4D practice, and about their own understanding of how to “develop” traditional communities in South Africa through ICTs. Following Bourdieu, the researcher argues that one can only build an adequate understanding of the social situation through critical reflexivity, by making the necessary knowledge breaks, and by allowing oneself to be carried away by the game of ICT4D practice. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Informatics / Unrestricted

<p>    </p> <p>Space has become ever more crowded since the launch of Sputnik. The need for predictions of possible collisions between space objects has only ever grown. The development of space, particularly around Earth, increases the density of space objects and skyrockets the number of close approaches between these objects, called conjunctions. This investigation is conducted in the context of probability dilution, a phenomenon leading to a false negative collision prediction where increasing positional uncertainty decreases the predicted likelihood of a collision. Dilution is investigated along two avenues: how to generate accurate collision predictions in an efficient manner and how to obtain better input data with which to make these predictions. Along the first avenue, this research presents a novel analytical rectan- gular probability of collision expression as well as a variety of new covariance scale factor formulations for maximum collision probability that indicate the maximum possible collision risk for any conjunction. Along the second avenue, this research tests new sensor tasking regimes to mitigate dilution, ultimately showing that while dilution can be reduced, shrink- ing the positional covariance through optimal measurement updates may not be enough to avoid false negatives in orbital conjunctions. </p>

Kollisioner, grundstötningar och andra haverier till sjöss har förekommit lika länge som det funnits fartyg. Dessa olyckor är vanligt förekommande och utgör fara för människor, fartyg, miljö, last och ekonomi. Med dagens utvecklade teknologi finns det bra metoder och utrustning för att undkomma grundstötningar och kollisioner, dock är det fortfarande vanligt förekommande händelser. För att kunna minska denna typ av sjöolyckor är det viktigt att undersöka orsaken till varför de inträffar. Syftet med studien är att undersöka och få en djupare förståelse om varför passagerarfartyg går på grund eller kolliderar i svenska havsområden. För att få fram vilka bidragande faktorer som orsakar dessa typer av sjöolyckor granskas och analyseras 29 haverirapporter från Statens haverikommission (SHK) och Transportstyrelsen. Resultat visar att majoriteten av olyckorna sker i farleder runt om i Sverige. Faktorer som bidrar till olyckorna är bland annat brist på rutiner, accepterat möten i för liten marginal, utkik används på fel sätt och brist på framförhållning. Därmed är det betydelsefullt att fartygen ser över sina rutiner och bryggbemanning. / Collisions, groundings and other accidents have been occuring for as long as ships have existed. These accidents are common and pose a danger to people, ships, the environment, cargo and the economy. With today's developed technology there are good methods and equipment to avoid groundings and collisions, although they are still common. To be able to reduce these types of accidents it is important to investigate the reasons behind them. The purpose of this study is to investigate and develop a deeper understanding as to why passenger ships ground or collide within Swedish waters. To obtain the contributing factors behind these types of sea accidents 29 accident reports from The Swedish Accident Investigation Authority (Statens haverikommission - SHK) and the Swedish Transport Agency (Transportstyrelsen) have been reviewed and analyzed. The results show that the majority of accidents happen in fairways around Sweden. Contributing factors to the accidents include a lack of routines, two ships passing with too small of a margin, lookout used incorrectly and a lack of forward planning. It is therefore of importance that ships review their routines and bridge manning.