Sensitivity analysis of temperature in heated soft tissues with respect to time delays

Axisymmetric tissue region heated by an external heat flux is considered. The mathematical model is based on the dual-phase lag equation supplemented by appropriate boundary and initial conditions. This equation, in relation to the Pennes’ equation, has two additional parameters, namely the relaxation time and the thermalization time. The aim of this research is to estimate the temperature changes due to changes of these parameters. To achieve this, sensitivity analysis methods are used. The basic problem and additional ones related to the sensitivity functions are solved using the implicit scheme of the finite difference method. The performed computations show that the temperature changes caused by changes in the relaxation and thermalization times are larger for higher values of the external heat flux and shorter times of its action.

Two-dimensional WSe2 flakes under high power optical excitation

Quasi-2D layers of transition metal dichalcogenides are promising candidates for creating saturable absorbers for pulsed lasers. However, the peculiarities of intense electromagnetic radiation’s influence on such structures have not been thoroughly studied. This paper explores the dynamics of photoexcited carriers in WSe2 flakes through experimental studies. These studies found that WSe2 flakes significantly change their optical properties under the influence of a high-power optical pump, allowed estimating the thermalization time of these structures (about 2 ps), and found that full relaxation takes more than 10 ps. The concentration of carriers in the semiconductor surface layer was estimated to be about 1028 m–3. It was found that standard description models of the optical response based on exciton resonances and absorption by free carriers could not adequately describe the experiments’ results. Thus, for an accurate description of the optical response, it was necessary to consider the effects associated with Coulomb screening that are caused by the high concentration of photo-excited carriers of the optical pumping densities used in this experiment.

Universal bounds on transport in holographic systems with broken translations

We study the presence of universal bounds on transport in homogeneous holographic models with broken translations. We verify numerically that, in holographic systems with momentum dissipation, the viscosity to entropy bound might be violated but the shear diffusion constant remains bounded by below. This confirms the idea that \eta/sη/s loses its privileged role in non-relativistic systems and that, in order to find more universal bounds, one should rather look at diffusion constants. We strengthen this idea by showing that, in presence of spontaneously broken translations, the Goldstone diffusion constant satisfies a universal lower bound in terms of the Planckian relaxation time and the butterfly velocity. Additionally, all the diffusive processes in the model satisfy an upper bound, imposed by causality, which is given in terms of the thermalization time – the imaginary part of the first non-hydrodynamic mode in the spectrum – and the speed of longitudinal sound. Finally, we discuss the existence of a bound on the speed of sound in holographic conformal solids and we show that the conformal value acts as a lower (and not upper) bound on the speed of longitudinal phonons. Nevertheless, we show that the stiffness \partial p/\partial \epsilon∂p/∂ϵ is still bounded by above by its conformal value. This suggests that the bounds conjectured in the past have to be considered on the stiffness of the system, related to its equation of state, and not on the propagation speed of sound.

Effect of massive potentials and the Gauss–Bonnet gravity on the holographic thermalization

We perform a numerical study to recognize the difference between various massive potentials in the massive gravity on the holographic thermalization in the AdS and AdS–Gauss–Bonnet gravities in 4[Formula: see text]+[Formula: see text]1 dimensions. In this space–time, three different massive potentials contribute to the graviton mass. We analyze the effects of these terms on the time evolution of entanglement entropy and the corresponding thermalization time. We also trace the effect of Gauss–Bonnet coupling on the thermalization process. The behavior of the holographic mutual information and size of the kinks, appearing in a large interval, are also studied.

Numerical model of biological tissue heating using the models of bio–heat transfer with delays

The numerical model of thermal processes in domain of biological tissue subjected to an external heat source is discussed. The model presented is based on the second order dual–phase–lag equation (DPLE) in which the relaxation time and thermalization time thermalization time (τq and τT) are tak n into account. In this paper the homogeneous, cylindrical skin tissue domain is considered. The most important aim of the research is to compare the results obtained using the classical model (the first-orderDPLE) with the numerical solution resulting from the higher order form of this equation. At the stage of numerical computations the Finite Difference Method (FDM) is applied. In the final part of the paper the examples of computations are shown.