Title: Partonic showers and jets Author: Ondřej Hladík Department: Institute of Theoretical Physics MFF UK Supervisor: Mgr. Alexander Kupčo, Ph.D., Institute of Physics ASCR, v. v. i. Abstract: In the present thesis we compare experimentally measured differential and integrated jets shapes with predictions of quantum chromodynamics (QCD) at the second order (NLO) of perturbative expansion. The measured jet sha- pes were taken from ATLAS experiment at LHC in proton-proton collisions at a center-of-mass energy √ s = 7 TeV and were compared with these predictions. The jets were reconstructed by means of anti-kT jet algorithm with R = 0.6. The predictions at NLO QCD agree with data in wider kinematics region than predictions at leading order (LO). The agreement, however, is still in some kine- matical regions not satisfactory. Keywords: QCD, jets, jet shapes, LHC

We present multi-wavelength studies of the radio galaxy 3C 120 and the blazar CTA 102 during unprecedented gamma-ray flares for both sources. In both studies the analysis of gamma-ray data has been compared with a series of 43 GHz VLBA images from the VLBA-BU-BLAZAR program, providing the necessary spatial resolution to probe the parsec scale jet evolution during the high energy events. To extend the radio dataset for 3C 120 we also used 15 GHz VLBA data from the MOJAVE sample. These two objects which represent very different classes of AGN, have similar properties during the gamma-ray events. The gamma-ray flares are associated with the passage of a new superluminal component through the mm VLBI core, but not all ejections of new components lead to gamma-ray events. In both sources gamma-ray events occurred only when the new components are moving in a direction closer to our line of sight. We locate the g-ray dissipation zone a short distance from the radio core but outside of the broad line region, suggesting synchrotron self-Compton scattering as the probable mechanism for the gamma-ray production.

A dissertation submitted to the Faculty of Science, School of Computational and Applied Mathematics, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015. / Invariant solutions for two-dimensional free and wall jets are derived by consid- ering the Lie point symmetry associated with the appropriate conserved vectors of Prandtl's boundary layer equations for the jets. For the two-dimensional jets we also consider the comparison, advantages and disadvantages between the standard method that uses a linear combination of all the Lie point symme- tries of Prandtl's boundary layer equations to generate the invariant solution with the new method explored in this paper which uses the Lie point sym- metry associated with a conserved vector to generate the invariant solution. Invariant solutions for two-dimensional classical and self-propelled wakes are also derived by considering the Lie point symmetry associated with the appro- priate conserved vectors of Prandtl's boundary layer equations for the wakes. We also consider and discuss the standard method that uses a linear combi- nation of all the Lie point symmetry of Prandtl's boundary layer equations to generate the invariant solutions for the classical and self-propelled wakes.

Dynamics of baroclinic jets on extrasolar planets is studied using three-dimensional general circulation models (GCMs) which solve the traditional hydrostatic primitive equations. The focus is on: i ) baroclinic ow and instability on hot-Jupiters; ii ) detailed GCM intercomparison in a commonly used extrasolar planet setup; and, iii ) equatorial superrotation on Earth-like planets. Stability, non-linear evolution and equilibration of high-speed ageostrophic jets are studied under adiabatic condition relevant to hot-Jupiters. It is found that zonal jets can be baroclinically unstable, despite the planetary size of the Rossby deformation scale, and that high resolution is necessary to capture the process. Non-linear jet evolution is then used as a test case to assess model convergence in ve GCMs used in current hot-Jupiter simulations. The GCMs are also tested under a diabatic condition (thermal relaxation on a short timescale) similar to that used in many hot-Jupiter studies. In the latter case, in particular, the models show signi cant inter- and intra-model variability, limiting their quantitative prediction capability. Some models severely violate global angular momentum conservation. The generation of equatorial superrotation in Earth-like atmospheres, subject to \Held & Suarez-like" zonally-symmetric thermal forcing is also studied. It is shown that transition to superrotation occurs when the meridional gradient of the equilibrium surface entropy is weak in this setup. Two factors contribute to the onset of superrotation | suppression of breaking Rossby waves (generated by midlatitude baroclinic instability) that decelerate the equatorial ow, and, generation of inertial and barotropic instabilities in the equatorial region that provide the stirring to accelerate the equatorial ow. In summary, forcing condition and physical setup used in current hot-Jupiter simulations severely stretch model performance and predictive capability. Superrotation in Earth-like conditions may be common, but its strength decreases with resolution. Broadly, numerical convergence must be assessed in GCM experiments for each problem or setup considered.

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The power generation industry in the state of Victoria, Australia stands to gain significantly from process improvements and optimization which can potentially lead to cleaner production of cost effective electricity. The efficient operation of lignite based tangentially-fired combustion systems depends on critical issues such as ignition and combustion of the fuel, which are largely controlled by burner aerodynamics. The geometry of the burner and the ratio of velocities between the primary and secondary jets play an important role in achieving stable combustion, high burnout of fuel, low production of pollutants and control of fouling. Slot-burners are a vertically aligned stack of rectangular nozzles delivering primary fuel and secondary air jets, and are commonly used in tangentially-fired boilers. To obtain a better understanding of the overall combustion process, it is important to understand the aerodynamics of jet development from these burners. The starting point of this research was a CFD investigation of aerodynamics in the near-burner region of isolated rectangular slot-burners, using isothermal conditions, for various secondary to primary jet velocity ratios (φ). Cross-flow was then added to replicate a near-burner flow field similar to that found in a tangentially-fired furnace and the effect of changing φ in the near-burner region of the developing jets was again investigated. Experiments were carried out on an isothermal physical-burner model to obtain mean velocity and turbulent statistics for different nozzle geometries and a range of φ. A computational fluid dynamics investigation of these same jets was also performed to gain further insights into the complexities of flow field with experimental results used to validate CFD predictions. The primary jet substantially deviated from the geometric axis of the burner towards the furnace wall and became very unstable for higher φ. The causes of unfavourable aerodynamics were discussed and suggestions were made on possible remedies for such behaviour. Conventional lignite combustion in a full-scale tangentially-fired furnace was modelled. The model was used to assess the possibility of utilizing a new type of mechanically thermally dewatered (MTE) coal in existing furnaces.