This project revised a magneto-optical ac susceptometer aiming to improve the experimentalapproach to investigate the magnetization dynamics of magnetic nano arrays.First the experimental setp was equipped with a new Helmholtzcoil which enables strongerAC magnetic eld compared to the installed coils on the system. That includes i.e. higherRMS magnetic eld amplitudes and a higher cut-o frequency in order to increase thefrequency range for magnetization dynamic measurements. Therefore dierent coil prototypeswere fabricated and tested in table top experiments using dierent additive manufacturingmethods, before the coil was installed on the cryostat and calibrated in thesoftware.In the second part of the project magnetization dynamics of nanostructures were studiedwith this new setup. As a rst step the general functionality of the Set-Up was testedusing a continuous ferromagnetic lm. Subsequently patterned circular discs were investigatedaiming to improve the calibration of the newly designed Helmholtzcoil. Startingfrom pattern with non coupled elements the project lastly investigated frequency dependentthermally active square articial spin ice (sASI), measuring freezing dynamics usingthe frequency dependent AC susceptometer.

In this thesis, a study of the inverse magnetostriction (the Villari effect) of Co nanowires and films is presented. The main objective was to investigate the stability of the Co nanowires’ magnetic properties, i.e., the coercivity and the saturation field under stress, in order to exploit them in flexible spintronic applications, for example, as spin injectors and detectors in spin transport circuits. To achieve our goal, we measured the hysteresis loops for the reference Co films samples and Co nanowires under various values of stress applied by curving the samples in specific molds by a homemade longitudinal magneto-optical Kerr effect (L-MOKE) setup at room temperature. In comparison with bulk Co, the Co film samples demoted their magnetostrictive behavior by one order of magnitude, due to a positive surficial magnetostrictive behavior at the interfaces. The Co nanowires reduced their magnetostrictive behavior further by about two orders of magnitude compared to the bulk Co, which means that they are magnetically stable to stress. This reduction in the magnetostrictive constant value may be related not only to the surface magnetostriction of the in-plane surfaces but also to the contribution of the out of plane surfaces. However, the extremely weak magnetostrictive response of the Co nanowires to stress is considered a promising feature that makes exploiting Co-nanowires in flexible spintronic devices interesting.

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Intake and exhaust orifice noise contributes to interior and exterior vehicle noise. The order noise radiated from the orifice of the intake and exhaust systems is caused by the pressure pulses generated by the periodic charging and discharging process and propagates to the open ends of the duct systems. The propagation properties of these pulses are influenced by the dimensions and acoustic absorption properties of the different devices in the intake/exhaust line (muffler, turbocharger, catalyst, intercooler, particulate filter, etc.). Additional to this pulse noise, the pulsating flow in the duct system generates flow noise by vortex shedding and turbulence at geometrical discontinuities. Several turbochargers, catalytic converters, Diesel particulate filters and intercoolers elements were investigated and analyzed by performing two-port acoustic measurements with and without mean flow at both cold conditions (room temperature) and hot conditions (running engine test bed) to investigate these devices as noise reduction elements. These measurements were performed in a frequency range of 0 to 1200 Hz at no flow conditions and at flow speeds: 0.05 and 0.1 Mach. A new concept for the acoustic modeling of the catalytic converters, Diesel particulate filters and Intercoolers, and a new geometrical model for the turbocharger were developed. The whole test configuration was modeled and simulated by means of 1-D gas dynamics using the software AVL-Boost. The results were validated against measurements. The validation results comprised the acoustic transmission loss, the acoustic transfer function and the pressure drop over the studied test objects. The results illustrate the improvement of simulation quality using the new models compared to the previous AVL-Boost models. / <p>QC 20111115</p>

Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and will manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. When searching for a line, the energy resolution and performance of the calorimeter are key factors. In this thesis, these are investigated using beam test data, taken at CERN in 2006. Four statistical methods that can be used to search for DM spectral lines are, then, studied in terms of their power and coverage. The methods are based on both hypothesis tests and confidence interval calculations. Two peak finding methods are also tested on a simulated data set representing one year of realistic data, obtained with the Large Area Telescope (LAT) on-board the Gamma-ray Large Area Space Telescope (GLAST). The data set is called Service Challenge 2 (SC2) and contains a variety of gamma-ray sources, including different DM components. Finally, an upper limit on &lt; σν &gt; γγ, based on SC2, is calculated. / QC 20101126

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