Characterization of 40-year-old calcium silicate pastes by thermal methods and other techniques

Differential thermal analysis, thermogravimetry and evolved gas analysis, as well as the X-ray diffraction, were used to identify and to quantify the products of dicalcium silicate hydration. The samples were 38 years stored in laboratory conditions. The calcium hydroxide, calcium carbonate and calcium silicate hydrate contents were determined and discussed in terms of the specific properties of initial anhydrous phases used.

     

Existential definability of modal frame classes

We prove an existential analogue of the Goldblatt-Thomason Theorem which characterizes modal definability of elementary classes of Kripke frames using closure under model theoretic constructions. The less known version of the Goldblatt-Thomason Theorem gives general conditions, without the assumption of first-order definability, but uses non-standard constructions and algebraic semantics. We present a non-algebraic proof of this result and we prove an analogous characterization for an alternative notion of modal definability, in which a class is defined by formulas which are satisfiable under any valuation (the so-called existential validity). Continuing previous work in which model theoretic characterization for this type of definability of elementary classes was proved, we give an analogous general result without the assumption of the first-order definability. Furthermore, we outline relationships between sets of existentially valid formulas corresponding to several well-known modal logics.     

Enhance limit cycle oscillation in a wind flow energy harvester system with fractional order derivatives

Advances in material science and mathematics in conjunction with technological needs have triggered the use of material and electric components with fractional order physical properties. This paper considers the mathematical model of a piezoelectric wind flow energy harvester system for which the capacitance of the piezoelectric material has fractional order current-voltage characteristics. Additionally the mechanical element is assumed to have fractional order damping. The analysis is focused on the effects of order of derivatives on the appearance and characteristics of limit circle oscillations (LCO). It is obtained that, the order of derivatives to enhance the amplitude of LCO and lower the threshold condition leading to LCO. The domains of efficiency of the system are illustrated in various parameters spaces.     

On simulation of a bistable system with fractional damping in the presence of stochastic coherence resonance

A bistable dynamical system with the Duffing potential, fractional damping, and random excitation has been modelled. To excite the system, we used a stochastic force defined by Wiener random process of Gaussian distribution. As expected, stochastic resonance appeared for sufficiently high noise intensity. We estimated the critical value of the noise level as a function of derivative order \(q\) . For smaller order \(q\) , damping enhancement was reported.     

Nonlinear dynamics of a regenerative cutting process

We examine the regenerative cutting process by using a single degree of freedom nonsmooth model with a friction component and a time delay term. Instead of the standard Lyapunov exponent calculations, we propose a statistical 0-1?test analysis for chaos detection. This approach reveals the nature of the cutting process signaling regular or chaotic dynamics. For the investigated deterministic model, we are able to show a transition from chaotic to regular motion with increasing cutting speed. For two values of time delay showing the different response, the results have been confirmed by the means of the spectral density and the multiscaled entropy.     

Asymptotic properties of solutions of the viscous Hamilton-Jacobi equation

The purpose of the paper is to study properties of solutions of the Cauchy problem for the equation under the assumption . General selfsimilar solutions are constructed. Moreover, for initial data with some decay at infinity, we determine the leading term of the asymptotics of solutions in which is described by either solutions of the linear heat equation or by particular selfsimilar solutions of the original equation.     

Project scheduling with finite or infinite number of activity processing modes – A survey

This paper surveys single-project, single-objective, deterministic project scheduling problems in which activities can be processed using a finite or infinite (and uncountable) number of modes concerning resources of various categories and types. The survey is based on a unified framework of a project scheduling model including resources, activities, objectives, and schedules. Most important models and solution approaches across the class of problems are characterized, and directions for future research are pointed out.