The origin of the 90 degree magneto-optical Kerr rotation in CeSb

We calculate the linear magneto-optical Kerr rotation for CeSb in the near-infrared spectral range. Using an exact formula for large Kerr rotation angles and a simplified electronic structure of CeSb we find at \hbar \omega = 0.46 eV a Kerr rotation of 90 degree which then for decreasing \omega jumps to -90 degree as recently observed. We identify the general origin of possible 180 degree polarization rotations as resulting from mainly nonmagnetic optical properties, in particular from the ratio of the dominant interband resonance frequency to the plasma frequency. The dependence of the Kerr rotation on moments and magnetization is discussed.Comment: 6 pages, REVTEX, 5 eps figure

Thermal Modelling and Design of On-board DC-DC Power Converter using Finite Element Method

Power electronic converters are widely used and play a pivotal role in electronics area. The temperature causes around 54 % of all power converters failures. Thermal loads are nowadays one of the bottlenecks in the power system design and the cooling efficiency of a system is primarily determined by numerical modelling techniques. Therefore, thermal design through thermal modelling and simulation is becoming an integral part of the design process as less expensive compared to the experimental cut-and-try approach. Here the investigation is performed using finite element method-based modelling, and also the potential of such analysis was demonstrated by real-world measurements and comparison of obtained results. Thermal modelling was accomplished using finite element analysis software COMSOL and thermo-imaging camera was used to measure the thermal field distribution. Also, the improved configuration of power converter was proposed

Investigation of Heat Sink Efficiency for Electronic Component Cooling Applications

Research and optimisation of cooling of electronic components using heat sinks becomes increasingly important in modern industry. Numerical methods with experimental realworld verification are the main tools to evaluate efficiency of heat sinks or heat sink systems. Here the investigation of relatively simple heat sink application is performed using modelling based on finite element method, and also the potential of such analysis was demonstrated by realworld measurements and comparing obtained results. Thermal modelling was accomplished using finite element analysis software COMSOL and thermo-imaging camera was used to measure the thermal field distribution. Ideas for future research involving improvement of the experimental setup and modelling verification are given

The impacts of uncertainty shocks on the Global Financial Cycle: a multiperspective SVAR analysis

openThis thesis aims to investigate the role of global uncertainty shocks in affecting the Global Financial Cycle (GFC). Three kinds of uncertainty are considered: financial uncertainty, the uncertainty surrounding economic policies and the geopolitical uncertainty. The contribution and the impact of each uncertainty shock is assessed through a SVAR analysis, that employs multiple sets of identification strategies and estimation techniques. Specifically, the uncertainty shocks are identified alternatively with the Cholesky decomposition technique and with the Penalty Function Approach, whereas the VAR models are estimated by means of OLS and Bayesian estimations. We find that the three uncertainty measures have heterogenous effects on the GFC, which are substantially negative and depend on the underlying econometric specification. However, financial uncertainty, as measured by the Global Financial Uncertainty indicator, proves to be the most important driver of GFC, since its shock explains the highest percentage of variance of GFC and triggers the most relevant reaction in GFC in every econometric specification.This thesis aims to investigate the role of global uncertainty shocks in affecting the Global Financial Cycle (GFC). Three kinds of uncertainty are considered: financial uncertainty, the uncertainty surrounding economic policies and the geopolitical uncertainty. The contribution and the impact of each uncertainty shock is assessed through a SVAR analysis, that employs multiple sets of identification strategies and estimation techniques. Specifically, the uncertainty shocks are identified alternatively with the Cholesky decomposition technique and with the Penalty Function Approach, whereas the VAR models are estimated by means of OLS and Bayesian estimations. We find that the three uncertainty measures have heterogenous effects on the GFC, which are substantially negative and depend on the underlying econometric specification. However, financial uncertainty, as measured by the Global Financial Uncertainty indicator, proves to be the most important driver of GFC, since its shock explains the highest percentage of variance of GFC and triggers the most relevant reaction in GFC in every econometric specification

Item analysis of a physics multiple choice test designed for an orientation course

LAUREA MAGISTRALEQuesto lavoro di tesi analizza un test a risposta multipla composto da 8 quesiti di fisica. Il test è stato somministrato a degli studenti del quarto e quinto anno delle scuole superiori che hanno frequentato un corso di orientamento offerto dal Politecnico di Milano ed erano interessati a proseguire gli studi di ingegneria dopo la maturità. Gli item avevano una struttura simile alle domande dell'esame di ammissione a ingegneria, consentendo agli studenti di valutare il livello di conoscenza richiesto per superare il test. Inoltre, il test serviva per affrontare alcuni misconcetti ed errori concettuali comuni tra gli studenti, consentendo al professore che insegnava in classe di sottolineare l’importanza di comprendere questi concetti durante lo studio della fisica. L'analisi svolta utilizzando la Teoria Classica dei Test ci ha aiutato a rilevare gli elementi o i distrattori che necessitavano di revisione. Alcuni item necessitavano di piccole modifiche per migliorare i distrattori, mentre un item aveva una bassa capacità di discriminare tra studenti più e meno bravi, probabilmente a causa dell'elevata difficoltà dell'item. Abbiamo utilizzato il test del chi quadrato per verificare la correlazione tra alcuni fattori. Abbiamo scoperto che gli studenti del quarto anno di scuola superiore tendono a rispondere correttamente a un item più spesso rispetto agli studenti del quinto anno e che gli uomini tendono a rispondere correttamente a un item più spesso delle donne.This thesis work analyses a multiple-choice test consisting of 8 physics items. The test was administered to students doing their fourth and fifth year of high school who were participating in an orientation course offered by Politecnico di Milano and were interested in pursuing engineering studies after high school. The items had a similar structure to the questions found on the engineering entrance exam, allowing students to gauge the level of knowledge required to pass the test. Additionally, the test aimed to address some common misconceptions and conceptual errors among students, enabling the professor teaching the class to emphasize the importance of grasping these concepts while studying physics. The Classical Test Theory analysis helped us to detect the items or distractors that need revision. Some items needed little modifications to improve the distractors, while one item had a low ability to discriminate between high-archiving and low-archiving students probably due to the high item difficulty. We used the chi-squared test to check the correlation among some factors. We discovered that students in their fourth year of high school tend to answer correctly to an item more often than students in their fifth year and that men tend to answer an item correctly more often than women