Acoustic pressure induced period-doubling bifurcations in tympanic membrane oscillations

We demonstrate the possibility of using a quantum-confined semiconductor structure laser operating in the autodyne regime for the investigation of the amplitude-frequency characteristics of the tympanic membrane (TM). Using such a laser, it is established that an increase in the acoustic pressure leads to the appearance of subharmonics in the spectrum of TM oscillations at frequencies equal to one-half and one-quarter of the exciting signal frequency, which is evidence for period-doubling bufurcations.     

Blockchain-oriented dynamic modelling of smart contract design and execution in the supply chain

Recently, the applications of Blockchain technology have begun to revolutionise different aspects of supply chain (SC) management. Among others, Blockchain is a platform to execute the smart contracts in the SC as transactions. We develop and test a new model for smart contract design in the SC with multiple logistics service providers and show that this problem can be presented as a multi-processor flexible flow shop scheduling. A distinctive feature of our approach is that the execution of physical operations is modelled inside the start and completion of cyber information services. We name this modelling concept ‘virtual operation’. The constructed model and the developed experimental environment constitute an event-driven dynamic approach to task and service composition when designing the smart contract. Our approach is also of value when considering the contract execution stage. The use of state control variables in our model allows for operations status updates in the Blockchain that in turn, feeds automated information feedbacks, disruption detection and control of contract execution. The latter launches the re-scheduling procedure, comprehensively combining planning and adaptation decisions within a unified methodological framework of dynamic control theory. The modelling complex developed can be used to design and control smart contracts in the SC.     

A High Order Compact Time/Space Finite Difference Scheme for the Wave Equation with Variable Speed of Sound

We consider fourth order accurate compact schemes, in both space and time, for the second order wave equation with a variable speed of sound. We demonstrate that usually this is much more efficient than lower order schemes despite being implicit and only conditionally stable. Fast time marching of the implicit scheme is accomplished by iterative methods such as conjugate gradient and multigrid. For conjugate gradient, an upper bound on the convergence rate of the iterations is obtained by eigenvalue analysis of the scheme. The implicit discretization technique is such that the spatial and temporal convergence orders can be adjusted independently of each other. In special cases, the spatial error dominates the problem, and then an unconditionally stable second order accurate scheme in time with fourth order accuracy in space is more efficient. Computations confirm the design convergence rate for the inhomogeneous, variable wave speed equation and also confirm the pollution effect for these time dependent problems.     

Use of electrochemical impedance spectroscopy for determining the diffusion layer thickness at the surface of ion-exchange membranes

Three ion-exchange membranes (an AMX homogeneous anion-exchange membrane, a MK-40 heterogeneous cation-exchange membrane, and a Nafion-117 homogeneous cation-exchange membrane) have been studied by electrochemical impedance spectroscopy. Processing of the experimental impedance spectra according to the model developed previously has made it possible to find the Nernst diffusion boundary layer (DBL) thickness δ as a function of current density. The behavior of the AMX membrane has been shown to be close to the “ideal” one described by the model: the impedance spectrum of the membrane is close to the theoretical spectrum and the value of δ is only slightly smaller than the quantity δ _Lev calculated by the Leveque equation derived in terms of classical convective diffusion theory. The behavior of the MK-40 and Nafion membranes markedly differs from the “ideal” behavior: the reactive component of the impedance in the region of medium frequencies corresponding to the maximum point in the low-frequency range of a Warburg type finite-length impedance spectrum is significantly lower than its theoretically predicted value. The value of δ is less than δ _Lev even for underlimiting currents, and the deviation increases with the increasing current density. This specific behavior of the membranes correlate well with the voltammetry data. The behavior of the studied membranes is associated with the surface properties: the heterogeneity (case of MK-40) and, especially, high hydrophobicity of the (Nafion-117) surface facilitate the development of electroconvection. Homogeneity and high hydrophilicity of the surface of the AMX membrane determine its behavior, which is close to the ideal.