Emissione di Corpo Nero e applicazioni astrofisiche

Il presente elaborato si propone di illustrare un modello teorico di radiazione termica, quello di Corpo Nero, descrivendo i passi che permisero di definirne le proprietà. Successivamente vengono analizzati alcuni oggetti astrofisici ai quali tale modello può essere applicato

Physics-based large-signal sensitivity analysis of microwave circuits using technological parametric sensitivity from multidimensional semiconductor device models

The authors present an efficient approach to evaluate the large-signal (LS) parametric sensitivity of active semiconductor devices under quasi-periodic operation through accurate, multidimensional physics-based models. The proposed technique exploits efficient intermediate mathematical models to perform the link between physics-based analysis and circuit-oriented simulations, and only requires the evaluation of dc and ac small-signal (dc charge) sensitivities under general quasi-static conditions. To illustrate the technique, the authors discuss examples of sensitivity evaluation, statistical analysis, and doping profile optimization of an implanted MESFET to minimize intermodulation which makes use of LS parametric sensitivities under two-tone excitatio

When self-consistency makes a difference

Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of selfconsistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. In this contribution we show two examples, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling is proved to be be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximations; in the discussion we exploit a Wiener approach, but of course the strategy should be tailored to the specific problem under consideratio

Behavioral modeling of GaN-based power amplifiers: impact of electrothermal feedback on the model accuracy and identification

In this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics

Effects of Type Ia Supernova feedback in young globular clusters

Through 3D hydrodynamical simulations, we explore the impact of Type Ia supernovae (SNe) explosions on the star formation history and chemical properties of second-generation stars in young globular clusters of different masses. Considering clusters with a first generation of asymptotic giant branch (AGB) stars at masses of 10^5 and 10^6 solar masses, moving at a constant velocity through a uniform gas with densities of 10^(−24) and 10^(−23) g/cm^3, second-generation (SG) stars form as the first-generation AGB stars release their ejecta. During this phase, external gas accretion occurs, and SNe Ia explosions begins, carving hot and tenuous bubbles. Three simulated models are analyzed: in the low mass and low density scenario, we observe hiatuses in star formation, with the second generation dominated by a He-rich (Y>0.33) and metal-poor ([Fe/H]<-1.5) population, depicting a scenario highly affected by Type Ia SN feedback without retaining ejecta. In the high mass and low density scenario, continuous star formation is observed, with dominance of He-rich and metal-poor populations similar to the lower mass model. In the high mass and high density scenario, which exhibits the highest star formation rate, the majority of stars form from a mix of AGB ejecta and pristine gas, showing modest helium enrichment. Each model shows a lower SG final mass compared to the corresponding models without SNeIa

Joint estimation of phase and phase diffusion for quantum metrology

Phase estimation, at the heart of many quantum metrology and communication schemes, can be strongly affected by noise, whose amplitude may not be known, or might be subject to drift. Here, we investigate the joint estimation of a phase shift and the amplitude of phase diffusion, at the quantum limit. For several relevant instances, this multiparameter estimation problem can be effectively reshaped as a two-dimensional Hilbert space model, encompassing the description of an interferometer phase probed with relevant quantum states -- split single-photons, coherent states or N00N states. For these cases, we obtain a trade-off bound on the statistical variances for the joint estimation of phase and phase diffusion, as well as optimum measurement schemes. We use this bound to quantify the effectiveness of an actual experimental setup for joint parameter estimation for polarimetry. We conclude by discussing the form of the trade-off relations for more general states and measurements.Comment: Published in Nature Communications. Supplementary Information available at http://www.nature.com/ncomms/2014/140404/ncomms4532/extref/ncomms4532-s1.pd