759 research outputs found
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 . 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 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
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
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