The primary goal of the American football helmet has been protection of players against skull fractures and other traumatic brain injuries (TBI) [Cantu 2003, Benson 2009]. TBI can result from short, high magnitude linear impact events typical of when the head impacts a hard surface [Gilcrhist 2003, Doorly 2007]. The modern helmet, which has evolved and become well designed to mitigate TBI injuries, does not offer sufficient protection against injury such as concussion, and the incident rate remains high in sport [Broglio 2009, Rowson 2012]. Researchers speculate rotation of the head leads to shear strain on the brain tissue, which may be the underlying mechanism of injury leading to concussive type injuries [Gennarelli 1971, Ommaya 1974, Gennarelli 1982, Prange 2002, Gilcrhist 2003, Aare 2003, Zhang 2004, Takhounts 2008, Greenwald 2008, Meaney 2011]. This has led researchers to investigate new liner materials and technologies to improve helmet performance and include concussive injury risk protection by attempting to address rotational acceleration of the brain [Mills 2003, Benson 2009, Caserta 2011, Caccese 2013]. To improve current football helmet designs, technology must be shown to reduce the motion of the brain, resulting in lower magnitudes of dynamic response thus reducing maximum principal strain and the corresponding risk of injury [Margulies 1992, Zhang 2004, Mills 2003, Kleiven 2007, Yoganandan 2008 Caserta 2011, McAllister 2012, Caccese 2013, Post 2013, Fowler 2015, Post 2015a/b]. Recent research has studied the use of decoupling liner systems in addition to the existing liner technology, to address resultant rotational acceleration. However, none of this previous work has evaluated the results in terms of the relationship between brain motion, tissue strain, and injury risk reduction. This thesis hypothesises the use of decoupling strategies to reduce the dominant coordinate component of acceleration in order to decrease maximum principal strain values. The dominant component of acceleration, defined as the coordinate component with the highest contribution to the resultant acceleration for each impact, is a targetable design parameter for helmet innovation. The objective of this thesis was to demonstrate the effect liner strategies to reduce the dominant component of rotational acceleration to decrease maximum principal strain in American football helmets.

In high impact human activities, much of the impact shock wave is dissipated through internal body structures, preventing excessive accelerations from reaching vital organs. Mechanisms responsible for this attenuation, including lower limb joint compression and spinal compression have been neglected in existing whole-body simulation models. Accelerometer data on one male subject during drop landings and drop jumps from four heights revealed that peak resultant acceleration tended to decrease with increasing height in the body. Power spectra contained two major components, corresponding to the active voluntary movement (2 Hz 14 Hz) and the impact shock wave (16 Hz 26 Hz). Transfer functions demonstrated progressive attenuation from the MTP joint towards the C6 vertebra within the 16 Hz 26 Hz component. This observed attenuation within the spine and lower-limb joint structures was considered within a rigid body, nine-segment planar torque-driven computer simulation model of drop jumping. Joints at the ankle, knee, hip, shoulder, and mid-trunk were modelled as non-linear spring-dampers. Wobbling masses were included at the shank, thigh, and trunk, with subject-specific biarticular torque generators for ankle plantar flexion, and knee and hip flexion and extension. The overall root mean square difference in kinetic and kinematic time-histories between the model and experimental drop jump performance was 3.7%, including ground reaction force root mean square differences of 5.1%. All viscoelastic displacements were within realistic bounds determined experimentally or from the literature. For an equivalent rigid model representative of traditional frictionless pin joint simulation models but with realistic wobbling mass and foot-ground compliance, the overall kinetic and kinematic difference was 11.0%, including ground reaction force root mean square differences of 12.1%. Thus, the incorporation of viscoelastic elements at key joints enables accurate replication of experimentally recorded ground reaction forces within realistic whole-body kinematics and removes the previous need for excessively compliant wobbling masses and/or foot-ground interfaces. This is also necessary in cases where shock wave transmission within the simulation model must be non-instantaneous.

Collapsing magnetic traps (CMTs) have been suggested as one of the mechanisms that could contribute to particle energisation in solar flares. The basic idea behind CMTs is that charged particles will be trapped on the magnetic field lines below the reconnection region of a flare. This thesis discusses a number of important new aspects in particle energisation processes in CMTs, based on the model by Giuliani et al. (2005). In particular, we extend previous studies of particle acceleration in this CMT model to the relativistic regime and compare our results obtained using relativistic guiding centre theory with results obtained using the non-relativistic guiding centre theory. The similarities and differences found are discussed. We then present a detailed study of the question, what leads to the trapping or escape of particle orbits from CMTs. The answer to this question is investigated by using results from the non-relativistic orbit calculations with guiding centre theory and a number of simple models for particle energy gain in CMTs. We find that there is a critical pitch angle dividing trapped particle orbits from the escaping particle orbits and that this critical pitch angle does not coincide with the initial loss cone angle. Furthermore, we also present a calculation of the time evolution of an anisotropic pressure tensor and of the plasma density under the assumptions that they evolve in line with our kinematic MHD CMT model and that the pressure tensor satisfies the double-adiabatic Chew-Goldburger-Low (CGL) theory. Finally, we make a first step to introduce Coulomb scattering by a Maxwellian background plasma into our guiding centre equations by changing them into a set of stochastic differential equations. We study the influence of a static background plasma onto selected particle orbits by pitch angle scattering and energy losses, and look at its effect on the particle energy and the trapping conditions.

This dissertation concentrates on analysis of one of the most important breeding measure in the breeding Czech warmblood in Acceleration program. This measure?s aim is to raise quality this breed?s sports performance, thanks to the performance there will be better possibility to use it among competition horses from breeding advanced countries ensured. From collected documents there was made a detailed overview of stallions, who were in program since 2005 to 2012 and their application in breeding was also assessed. The breeding benefit of these preferred sires was based on the results of performance tests of sires? daughters and sons and also on results of subsequent sport testing their descendants. At least all of these facts mentioned above are evaluated and discussed.

Mining, process and energy industries suffer from billions of dollars of worldwide losses every year due to Vapour Cloud Explosions (VCE). Moreover, explosion accidents are often tragic and lead to a high number of severe injuries and fatalities. The VCE scenario is complex and controlled by various mechanisms. The interplay among them is still not entirely understood. Understanding all these intricate processes is of vital importance and requires detailed experimental diagnostics. Coupling accurate numerical simulations to well documented experiments can allow an elaborate description of these phenomena. This thesis focuses on explosions occurring on configurations that are either semi-confined or confined. In such configurations, the explosion is generally initiated by a mild ignition and a subsonic flame front emerges from the ignition source. An important feature of self-propagating flames lies in their intrinsically unstable nature. When they propagate in an environment with high levels of confinement and congestion, which is the case in most industrial sites, a Flame Acceleration (FA) process is often observed that can give rise to very fast flames, known for their destructive potential. In some cases, the FA process can create the appropriate conditions for the initiation of detonations, which corresponds to a rapid escalation of the explosion hazard. To reproduce the confinement and congestion conditions that one can find in industrial sites, the university of Munich TUM equipped a confined chamber with a series of obstacles and analysed the influence of repeated obstructions on the propagation of hydrogen/air deflagrations. This experimental study showed a strong influence of the mixture composition on the acceleration process. A Deflagration to Detonation Transition (DDT) has also been observed for a certain range of equivalence ratio. This configuration is therefore ideal to study the mechanisms of flame acceleration as well as the intricate DDT process. A numerical study of both scenarios is performed in this thesis: -First for a lean premixed hydrogen/air mixture, a strong flame acceleration is observed experimentally without DDT. The characteristic features of the explosion are well reproduced numerically using a Large Eddy Simulation (LES) approach. The crucial importance of confinement and repeated flame-obstacle interactions in producing very fast deflagrations is highlighted. -DDT is observed experimentally for a stoichiometric hydrogen/air mixture. This thesis focuses on the instants surrounding the DDT event, using Direct Numerical Simulations (DNS). Particular attention is drawn to the impact of the chemistry modelling on the detonation scenario. The failure of preventive measures is often observed in many explosion accidents. To avoid a rapid escalation of the explosion scenario, mitigative procedures must be triggered when a gas leak or an ignition is detected. Metal salts (like potassium bicarbonate and sodium bicarbonate) have received considerable attention recently because well-controlled experiments showed their high efficiency in inhibiting fires. The last part of the thesis focused on the mechanism of flame inhibition by sodium bicarbonate particles. First, criteria based on the particle sizes are established to characterize the inhibition efficiency of the particles. Second, two dimensional numerical simulations of a planar flame propagating in a stratified layer of very fine sodium bicarbonate particles showed that under certain conditions these powders can act as combustion enhancers. These results echo a number of experimental observations on the possible counter-effects of the inhibitors.

O principal objetivo desse trabalho foi investigar a possibilidade da detecção sub-ppb (10-9 g/g) de elementos químicos presentes em amostras líquidas, analisadas por meio da espectrometria de raios-X, seja por STXRF (Synchrotron Total reflection X-ray Fluorescence), ou PIXE (Particle Induced X-ray Emission). Na ausência de padrões certificados, foram preparados em laboratório padrões líquidos multielementares com concentrações variando de 1 a 20 ppm, posteriormente micropipetados sobre substrato de Lucite, constituindo assim amostras adequadas para análises STXRF. Visando controlar a manipulação volumétrica, foi utilizado como padrão interno ítrio, em função do qual foi determinada a curva de sensibilidade relativa para o método. Após pré-concentração das amostras, estas foram micropipetadas sobre substratos de Lucite, Mylar e Kimfoil e as análises foram realizadas no Laboratório Nacional de Luz Síncontron LNLS, em Campinas, SP e no Laboratório de Análise de Materiais por feixes Iônicos LAMFI, no IFUSP. Os limites de detecção para ambos os métodos foram determinados e comparados. Como esperado, a STXRF apresenta limites de detecção uma ordem de grandeza inferior ao PIXE para elementos com 20<Z<40, alcançando, após pré-concentração, um limite inferior de 0,3 ppb para o Zn. A comparação entre medidas elementares absolutas de mesmas amostras pelos métodos STXRF e PIXE indicou substantiva sub avaliação das incertezas analíticas, mas apenas um pequeno desvio sistemático entre resultados de ambos os métodos. Para demonstrar o método, foram analisadas amostras de água do Rio Toledo, afluente do Rio S. Francisco e fonte de água da cidade de Toledo no oeste do estado do Paraná (24°43´S; 53°44´W), trabalho realizado em colaboração com o Núcleo de Biotecnologia e Desenvolvimento de Processos Químicos NBQ da Universidade Estadual do Oeste do Paraná UNIOESTE. Finalmente foi verificada a possibilidade de preparar as amostras micropipetadas para a STXRF sobre substratos de filme fino (Mylar com 2,4 m de espessura e Kimoil com 2 m) ao invés dos tradicionais discos espessos de acrílico, resultando na redução de um fator 3 no limite de detecção. / The main goal of this work was to investigate the feasibility of sub-ppb (10-9 g/g) detection of trace elements in liquid samples analyzed by STXRF (Synchrotron Total reflection X-ray Fluorescence) and by PIXE (Particle Induced X-ray Emission). For STXRF calibration, and due to the absence of certified liquid standards, a set of multielementary liquid standards was prepared in house, with concentrations varying from 1 to 20 ppm in water, and then micro-pipetted on regular 30 mm diameter Lucite discs. Ytrium was used as an internal standard and the relative sensitivity curves were found relative to it. Real water samples for trace element analysis, were first preconcentrated (to a factor of 5) and then micropipetted on Lucite and also on Lylar and Kimfoil thin films. All the STRXF and PIXE analysis were made respectively in the Laboratório Nacional de Luz Síncrotron LNLS , in Campinas, SP, and in the Laboratório de Análise de Materiais por feixes Iônicos LAMFI, USP. As expected, the minimum elementary detection limits for STXRF for elements with 20<Z<40, were one order of magnitude lower than the PIXE ones, reaching, after pre-concentration, 0.3 ppb for Zn. Comparison of STXRF and PIXE data of the same samples, showed some slight differences in absolute concentrations, but an overall and important underestimation of the experimental uncertainties. To exemplify the use of trace-element analysis in liquids, several samples from Toledo River, the main water supply of Toledo City (24°43´S; 53°44´W), were collected and analyzed over one year, in a collaboration with the Núcleo de Biotecnologia e Desenvolvimento de Processos Químicos NBQ from the Universidade Estadual do Oeste do Paraná UNIOESTE. The STXRF analysis of samples pipetted on Mylar and Kimfol, though not dense substrates, showed to be possible, and resulted in a 3 fold reduction of the minimum detection limits for STXRF analysis.

We develop a simple one-zone model of the steady-state Crab nebula spectrum encompassing both the radio/soft X-ray and the GeV/multi-TeV observations. By solving the transport equation for GeV-TeV electrons injected at the wind termination shock as a log-parabola momentum distribution and evolved via energy losses, we determine analytically the resulting differential energy spectrum of photons. We find an impressive agreement with the observed spectrum of synchrotron emission, and the synchrotron self-Compton component reproduces the previously unexplained broad 200-GeV peak that matches the Fermi/Large Area Telescope (LAT) data beyond 1 GeV with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) data. We determine the parameters of the single log-parabola electron injection distribution, in contrast with multiple broken power-law electron spectra proposed in the literature. The resulting photon differential spectrum provides a natural interpretation of the deviation from power law customarily fitted with empirical multiple broken power laws. Our model can be applied to the radio-to-multi-TeV spectrum of a variety of astrophysical outflows, including pulsar wind nebulae and supernova remnants, as well as to interplanetary shocks.

Magister Scientiae - MSc / Beams of polarized protons play an important part in the study of the spin dependence of the nuclear force by measuring the analyzing power in nuclear reactions. The source at iThemba LABS produces a beam of polarized protons that is pre-accelerated by an injector cyclotron (SPC2) to a energy of 8 MeV before acceleration by the main separated-sector cyclotron to 200 MeV for physics research. The polarized ion source is one of the two external ion sources of SPC2. Inside the ion source hydrogen molecules are dissociated into atoms in the dissociator and cooled to a temperature of approximately 30 K in the nozzle. The atoms are polarized by a pair of sextupole magnets and the nucleus is polarized by RF transitions between hyperfine levels in hydrogen atoms. The atoms are then ionized by electrons in the ionizer. The source has various sensitive devices, which influence beam intensity and polarization. Nitrogen gas is used to prevent recombination of atoms after dissociation. The amount of nitrogen and the temperature at which it is used plays a very important role in optimizing the beam current. The number of electrons released in the ionizer is influenced by the size and shape of the filament. Optimization of the source will ensure that beams of better quality (a better current and stability) are produced. / South Africa

The extreme temperatures and nonthermal nature of the solar corona and solar wind arise from an unidentified physical mechanism that preferentially heats certain ion species relative to others. Spectroscopic indicators of unequal temperatures commence within a fraction of a solar radius above the surface of the Sun, but the outer reach of this mechanism has yet to be determined. Here we present an empirical procedure for combining interplanetary solar wind measurements and a modeled energy equation including Coulomb relaxation to solve for the typical outer boundary of this zone of preferential heating. Applied to two decades of observations by the Wind spacecraft, our results are consistent with preferential heating being active in a zone extending from the transition region in the lower corona to an outer boundary 20-40 solar radii from the Sun, producing a steady-state super-massproportional a-to-proton temperature ratio of 5.2-5.3. Preferential ion heating continues far beyond the transition region and is important for the evolution of both the outer corona and the solar wind. The outer boundary of this zone is well below the orbits of spacecraft at 1 au and even closer missions such as Helios and MESSENGER, meaning it is likely that no existing mission has directly observed intense preferential heating, just residual signatures. We predict that the Parker Solar Probe will be the first spacecraft with a perihelion sufficiently close to the Sun to pass through the outer boundary, enter the zone of preferential heating, and directly observe the physical mechanism in action.

Magnetic reconnection is an important mechanism for the restructuring of magnetic fields, and the conversion of magnetic energy into plasma heating and non-thermal particle kinetic energy in a wide range of laboratory and astrophysical plasmas. In this thesis, reconnection is studied in two semi-collisional plasma environments: flares in the solar corona, and the start-up phase of the Mega-Ampere Spherical Tokamak (MAST) magnetic confinement device. Numerical simulations are presented using two different plasma descriptions; the test-particle approach combined with analytical magnetohydrodynamic fields is used to model populations of high-energy particles, and a two-fluid approach is used to model the bulk properties of a semi-collisional plasma. With the first approach, a three-dimensional magnetic null-point is examined as a possible particle acceleration site in the solar corona. The efficiency of acceleration, both within the external drift region and in the resistive current sheet, is studied for electrons and protons using two reconnection models. Of the two models, it is found that the fan-reconnection scenario is the most efficient, and can accelerate bulk populations of protons due to fast and non-uniform electric drifts close to the fan current-sheet. Also, the increasing background field within the fan-current sheet is shown to stabilise particle orbits, so that the energy gain is not limited by ejection. With the second approach, the effects of two-fluid physics on merging flux-ropes is examined, finding fast two-fluid tearing-type instabilities when the strength of dissipation is weak. The model is then extended to the tight-aspect ratio toroidal-axisymmetric geometry of the MAST device, where the final state after merging is a MAST-like spherical tokamak with nested flux-surfaces and a monotonically increasing q-profile. It is also shown that the evolution of simulated 1D radial density profiles closely resembles the Thomson scattering electron density measurements in MAST. An intuitive explanation for the origin of the measured density structures is proposed, based upon the results of the toroidal Hall-MHD simulations.