Observation of second sound in graphite over 200 K

Second sound refers to the phenomenon of heat propagation as temperature waves in the phonon hydrodynamic transport regime. We directly observe second sound in graphite at temperatures of over 200 K using a sub-picosecond transient grating technique. The experimentally determined dispersion relation of the thermal-wave velocity increases with decreasing grating period, consistent with first-principles-based solution of the Peierls-Boltzmann transport equation. Through simulation, we reveal this increase as a result of thermal zero sound—the thermal waves due to ballistic phonons. Our experimental findings are well explained with the interplay among three groups of phonons: ballistic, diffusive, and hydrodynamic phonons. Our ab initio calculations further predict a large isotope effect on the properties of thermal waves and the existence of second sound at room temperature in isotopically pure graphite.

Spectral and numerical analysis for a thermoelastic problem with double porosity and second sound

We study some spectral and numerical properties of the solutions to a thermoelastic problem with double porosity. The model includes Cattaneo-type evolution law for the heat flux to remove the physical paradox of infinite propagation speed of the classical Fourier’s law. Firstly, we prove that the operator determined by the considered problem has compact resolvent and generates a C 0 -semigroup in an appropriate Hilbert space. We also show that there is a sequence of generalized eigenfunctions of the linear operator that forms a Riesz basis. By a detailed spectral analysis, we obtain the expressions of the spectrum and we deduce that the spectrum determined growth condition holds. Therefore we prove that the energy of the considered problem decays exponentially to a rate determined explicitly by the physical parameters. Finally, some numerical simulations based on Chebyshev spectral method for spatial discretization are given to confirm the exponential stability result and to show the distribution of the eigenvalues and the variables of the problem.

Second sound in the crossover from the Bose-Einstein condensate to the Bardeen-Cooper-Schrieffer superfluid

Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid, extending previous work at unitarity. In particular, we investigate the strongly-interacting regime where currently theoretical predictions only exist in terms of an interpolation in the crossover. Working with a quantum gas of ultracold fermionic 6Li atoms with tunable interactions, we show that the second sound speed varies only slightly in the crossover regime. By varying the excitation procedure, we gain deeper insight on sound propagation. We compare our measurement results with classical-field simulations, which help with the interpretation of our experiments.

TO TASTE THE SMELL OF LINGUISTIC SIGNIFICANCE AL-ALAQ SURAH AS A MODEL

The linguistic miracle in the Nobel Qur’an has its own flavor, in terms of drawing, sound, formula, and structure. In Al-Alaq surah, we see the subject of the study, is that the first thing that draws attention to it is the congruence of the sounds of its name (Al-Alaq) and the meaning of its three paragraphs. The first paragraph in the first five verses of the surah, which talks about the beginning of creation, the beginning of learning, and the call to acquire knowledge. As for the second sound (al-lam), which is an approximant sound, repeated in the surah 43 times, it agrees with the second paragraph of the surah, which is the longest, and includes verses (6-14) that talk about the deviation of the unbelievers, and wonder about their actions, and determines four types of people towards the Da'wa. As for the third sound (qaf), which is a very explosive sound, it coincided with the third paragraph, which includes the last five verses (15-19) that challenges the deniers and describes their fate and severe torment. It is nice that these divisions coincided with the comma of the surah, as the first five verses and the last five verses ended with the closed sound syllable (CVC), while the nine verses in the middle of the surah (6-14) ended with the open sound syllable (CVV), and because the comma governed by the soothing pause, prompts us to contemplate the significance of the end. The end of the first five verses and the last five in this passage draws our attention to the intensity in the beginning and at the end of the surah; Therefore, we counted the percentage of the long open syllable (CVV), which gives a kind of feeling of temporal calm, and we found what reinforces this, as it represented (10.6%) in the first five verses and (17.64%) in the last five verses, as for the verses of the second paragraph. In the middle of the surah (6-14), its percentage reached (21.25%), in addition, the counting of the high explosive sounds that ended with the closed vocal syllables (CVC) in the three groups was consistent with that and reinforced it.

Well-posedness and energy decay of swelling porous elastic soils with a second sound and delay term

In this paper we consider a one-dimensional swelling porous-elastic system with second sound and delay term acting on the porous equation. Under suitable assumptions on the weight of delay, we establish the well-posedness of the system by using semigroup theory and we prove that the unique dissipation due to the delay time is strong enough to exponentially stabilize the system when the speeds of wave propagation are equal.

Mach Fronts in Random Media with Fractal and Hurst Effects

An investigation of transient second sound phenomena due to moving heat sources on planar random media is conducted. The spatial material randomness of the relaxation time is modeled by Cauchy or Dagum random fields allowing for decoupling of fractal and Hurst effects. The Maxwell–Cattaneo model is solved by a second-order central differencing. The resulting stochastic fluctuations of Mach wedges are examined and compared to unperturbed Mach wedges resulting from the heat source traveling in a homogeneous domain. All the examined cases are illustrated by simulation movies linked to this paper.

Specificity of the second sound standing waves behavior in a medium with nanoparticles

The experimental studies of the second sound waves propagation in a resonator with a deuterium-helium gel were carried out. The latest experimental results, combined with those obtained in earlier experiments, have shown that the propagation of the second sound waves in gels leads to their significant attenuation and a decrease in the propagation velocity. This behavior differs from the case of the propagation of the sound waves of a two-component system with a strongly slow normal component and may indicate changes in the properties of superfluidity under confined geometry conditions.