Modulational Instability of Ion-Acoustic Waves in Pair-Ion Plasma

The modulational instability (MI) of ion-acoustic waves (IAWs) is examined theoretically in a four-component plasma system containing inertialess electrons featuring a non-thermal, non-extensive distribution, iso-thermal positrons, and positively as well as negatively charged inertial ions. In this connection, a non-linear Schrödinger equation (NLSE), which dominates the conditions for MI associated with IAWs, is obtained by using the reductive perturbation method. The numerical analysis of the NLSE reveals that the increment in non-thermality leads to a more unstable state, whereas the enhancement in non-extensivity introduces a less unstable state. It also signifies the bright (dark) ion-acoustic (IA) envelope solitons mode in the unstable (stable) domain. The conditions for MI and its growth rate in the unstable regime of the IAWs are vigorously modified by the different plasma parameters (viz., non-thermal, non-extensive q-distributed electron, iso-thermal positron, the ion charge state, the mass of the ion and positron, non-thermal parameter α, the temperature of electron and positron, etc.). Our findings may supplement and add to prior research in non-thermal, non-extensive electrons and iso-thermal positrons that can co-exist with positive as well as negative inertial ions.

Through-Plane and In-Plane Thermal Diffusivity Determination of Graphene Nanoplatelets by Photothermal Beam Deflection Spectrometry

In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.

Joint estimation of Robin coefficient and domain boundary for the Poisson problem

We consider the problem of simultaneously inferring the heterogeneous coefficient field for a Robin boundary condition on an inaccessible part of the boundary along with the shape of the boundary for the Poisson problem. Such a problem arises in, for example, corrosion detection, and thermal parameter estimation. We carry out both linearised uncertainty quantification, based on a local Gaussian approximation, and full exploration of the joint posterior using Markov chain Monte Carlo (MCMC) sampling. By exploiting a known invariance property of the Poisson problem, we are able to circumvent the need to re-mesh as the shape of the boundary changes. The linearised uncertainty analysis presented here relies on a local linearisation of the parameter-to-observable map, with respect to both the Robin coefficient and the boundary shape, evaluated at the maximum a posteriori (MAP) estimates. Computation of the MAP estimate is carried out using the Gauss-Newton method. On the other hand, to explore the full joint posterior we use the Metropolis-adjusted Langevin algorithm (MALA), which requires the gradient of the log-posterior. We thus derive both the Fréchet derivative of the solution to the Poisson problem with respect to the Robin coefficient and the boundary shape, and the gradient of the log-posterior, which is efficiently computed using the so-called adjoint approach. The performance of the approach is demonstrated via several numerical experiments with simulated data.

An on-chip test structure to measure the Seebeck coefficient of thermopile sensors

Thermopile sensors have a wide range of applications in consumer and industry. Seebeck coefficient is a basic thermal parameter of thermopile sensors. Extracting the Seebeck coefficient of both materials and thermocouple in thermopile sensors is of great importance. In this work, an on-chip test structure is designed. It consists of a substrate, a framework, supporting legs and a sensitive region which has a resistor serving as both heater and temperature detector. A set of on-chip test structures are fabricated along with a thermopile sensor. Its measurement results are analyzed and compared with apparatus measurement results. These results are consistent with each other, and the validity of structure is verified.

Analytical Solution and Quasi-Periodic Behavior of a Charged Dilaton Black Hole

With the vast breakthrough brought by the Event Horizon Telescope, the theoretical analysis of various black holes has become more critical than ever. In this paper, the second-order asymptotic analytical solution of the charged dilaton black hole flow in the spinodal region is constructed from the perspective of dynamics by using the two-timing scale method. Through a numerical comparison with the original charged dilaton black hole system, it is found that the constructed analytical solution is highly consistent with the numerical solution. In addition, several quasi-periodic motions of the charged dilaton black hole flow are numerically obtained under different groups of irrational frequency ratios, and the phase portraits of the black hole flow with sufficiently small thermal parameter perturbation display good stability. Finally, the final evolution state of black hole flow over time is studied according to the obtained analytical solution. The results show that the smaller the integral constant of the system, the greater the periodicity of the black hole flow.

Thermal Conductivity in Aged Li-Ion Cells under Various Compression Conditions and State-of-Charge

Thermal conductivity (TC) is a parameter, which significantly influences the spatial temperature gradients of lithium ion batteries in operative or abuse conditions. It affects the dissipation of the generated heat by the cell during normal operation or during thermal runaway propagation from one cell to the next after an external short circuit. Hence, the thermal conductivity is a parameter of great importance, which concurs to assess the safety of a Li-ion battery. In this work, an already validated, non-destructive measurement procedure was adopted for the determination of the evolution of the through-plane thermal conductivity of 41 Ah commercially available Li-ion pouch cells (LiNiMnCoO2-LiMn2O4/Graphite) as function of battery lifetime and state of charge (SOC). Results show a negative parabolic behaviour of the thermal conductivity over the battery SOC-range. In addition, an average decrease of TC in thickness direction of around 4% and 23% was measured for cells cycled at 60 °C with and without compression, respectively. It was shown that pretension force during cycling reduces battery degradation and thus minimises the effect of ageing on the thermal parameter deterioration. Nevertheless, this study highlights the need of adjustment of the battery pack cooling system due to the deterioration of thermal conductivity after certain battery lifetime with the aim of reducing the risk of battery overheating after certain product life.