Superdiffusive heat conduction in semiconductor alloys -- II. Truncated L\'evy formalism for experimental analysis

Nearly all experimental observations of quasi-ballistic heat flow are interpreted using Fourier theory with modified thermal conductivity. Detailed Boltzmann transport equation (BTE) analysis, however, reveals that the quasi-ballistic motion of thermal energy in semiconductor alloys is no longer Brownian but instead exhibits L\'evy dynamics with fractal dimension $\alpha < 2$. Here, we present a framework that enables full 3D experimental analysis by retaining all essential physics of the quasi-ballistic BTE dynamics phenomenologically. A stochastic process with just two fitting parameters describes the transition from pure L\'evy superdiffusion as short length and time scales to regular Fourier diffusion. The model provides accurate fits to time domain thermoreflectance raw experimental data over the full modulation frequency range without requiring any `effective' thermal parameters and without any a priori knowledge of microscopic phonon scattering mechanisms. Identified $\alpha$ values for InGaAs and SiGe match ab initio BTE predictions within a few percent. Our results provide experimental evidence of fractal L\'evy heat conduction in semiconductor alloys. The formalism additionally indicates that the transient temperature inside the material differs significantly from Fourier theory and can lead to improved thermal characterization of nanoscale devices and material interfaces

Dynamic Thermal Analysis of a Power Amplifier

This paper presents dynamic thermal analyses of a power amplifier. All the investigations are based on the transient junction temperature measurements performed during the circuit cooling process. The presented results include the cooling curves, the structure functions, the thermal time constant distribution and the Nyquist plot of the thermal impedance. The experiments carried out demonstrated the influence of the contact resistance and the position of the entire cooling assembly on the obtained results.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Een jongpaleolithische nederzetting te Kanne

status: publishe

Application of Structure Functions for the Investigation of Forced Air Cooling

This paper presents thermal analyses of a power amplifier placed in a wind tunnel. All the investigations are based on the transient temperature measurements performed during the circuit cooling process. The measured cooling curves were used to compute the cumulative and differential structure functions for the circuit with a heat sink. These functions helped to determine the optimal values of circuit model parameters necessary for numerical thermal simulations. The experiments demonstrated the influence of the wind speed on the value of the heat transfer coefficient and consequently on the temperature of the entire structure.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Site néolithique à Thieusies

status: publishe