Dynamic optimisation of the aroma production in brewing fermentation

Several key compounds for the final beer flavour (higher alcohols, esters, vicinal diketones) are produced during the alcoholic fermentation phase. The paper demonstrates the possibility of obtaining various desired final aroma profiles and reducing the total process time using dynamic optimisation of three control variables: temperature, top pressure and initial yeast concentration in the fermentation tank. The optimisation is based on a sequential quadratic programming algorithm, on a dynamic model of the alcoholic fermentation and on an aroma production model. The robustness of the optimal control profile with respect to model uncertainty is discussed.     

Plasma-induced polymerization

Summary Experimental and theoretical data proving the existence of long-lived (living) poly(methyl methacrylate-co-styrene) 5050 random macroradicals are presented.     

Transition and equilibrium processes in metal-ceramic particle systems

The nonlinear motion equation of a spherical particle pushed by the solidification front is determined. In equilibrium, by integrating this equation, we obtain the critical interfacial speed, both in the absence and presence of thermal conductivities. The results are similar to those given by Ştef<anescuet al. only in the case of ionic crystals (n = 2). The analysis of the motion of the particle far from the interface makes it possible to introduce a time constant as a measure of the motion uniformity degree. In such a context, it may be assumed that the lesser the time constant, the quicker the incorporation of the particle by the metal matrix.     

Use of Autocorrelation Analysis in the Evaluation of Piezoelectric Coupling of Modified PLZT Ceramics Subjected to High Electric Fields

Two piezoelectric materials were investigated in electric fields, up to 3 kV/cm to determine whether single-sample testing can be used to evaluate piezoelectric coupling. Autocorrelation analysis of the data showed that the minimal increment of electric field necessary for successive independent measurements on single specimens is 1.3 kV /cm. This value coincides with the breakage field of the sample at resonance. Electrumechanical performance can still be evaluated with a sampling interval slightly lower than 1.3 kV/cm .     

Technology for obtaining samples of layered composite materials with metallic matrix

Layered composite materials significantly improved the mechanical process of fracturing, which means better fracture strength, while preserving surface properties such as hardness, resistance to wear and resistance to high temperatures. The properties are significantly influenced by the interphase mass transfer at the surface matrix-fiber reinforcement. We developed a mathematical model to determine the molar flux at the interface in stationary and in a nonstationary regime. The technological parameters are: hydraulic pressure, reinforced material, alloy type, fiber diameter, mass ratio between the reinforcement and the composite masses and mould preheating temperature. A mould patented in Romania was mounted on a hydraulic press to obtain the samples. We studied the material structure, matrix and fiber element distribution, metallic matrix element distribution and matrix and fiber element content variation. The results recorded revealed a 75% to 120% increase of the fracture strength, which means an improvement of the mechanical process of fracturing. We concluded that the reinforcement material, mass ratio and fiber diameter have a significant influences on the fracture strength.     

Assessment of ventilation efficiency for emergency situations in subway systems by CFD modeling

The ventilation system is the strategic component of the subway systems when incidents involving heavy smoke occur in tunnels. Consequently, the purpose of this study is to investigate the ventilation efficiency in one of the most severe emergency scenario: train on fire (maximum heat release rate reaching 30 MW due to an ultra-fast fire) and stopped in the tunnel, the incident requiring passenger evacuation. Two ventilation strategies are taken into account: tunnel ventilation fan system (mid-tunnel fan plant located in separate construction) in conjunction with stations mechanical ventilation and end-of-station fan plants in conjunction with stations mechanical ventilation. The analysis is performed using computational fluid dynamics (CFD) modeling. The numerical model proposes an original approach based on the introduction of source terms in conservation equations for energy, carbon monoxide (CO) and carbon dioxide (CO₂), in order to deal with the heat, CO, and CO₂ due to fire. Equations expressing the conservation of CO and CO₂ are specially added to the basic equations governing a turbulent non-isothermal airflow in the CFD model. This method allowed achieving values of velocity, temperature, CO and CO₂ concentrations all over the computational domain. In addition, the modeling and simulation methodology complies faithfully to the real operation of the ventilation systems investigated in normal and emergency (fire) conditions. The results show that both ventilation alternatives taken into account lead to the secure evacuation of passengers all over the simulation time. The evacuation process toward the nearest station is not at all disturbed by too high air velocities, high temperatures or critical CO or CO₂ concentrations.     

Nitrogen substituted phenothiazine derivatives: modelling of molecular self-assembling

The study aims to present a detailed theoretical investigation of noncovalent intermolecular interactions between different π–π stacking nitrogen substituted phenothiazine derivatives by applying second-order Møller-Plesset perturbation (MP2), density functional (DFT) and semiempirical theories. The conformational stability of these molecular systems is mainly given by the dispersion-type electron correlation effects. The density functional tight-binding (DFTB) method applied for dimer structures are compared with the results obtained by the higher level theoretical methods. Additionally, the optimal configuration of the investigated supramolecular systems and their self-assembling properties are discussed.     

The influence of hydrostatic pressure and transverse magnetic field on the electric conductivity of the magnetorheological elastomers

Two sets, each of five samples, of magnetorheological elastomers (MREs) based on silicone rubber and carbonyl iron were prepared. One set of samples was obtained by polymerization of the silicone rubber with additives in the absence of the magnetic field, while the other by polymerization of the silicone rubber with additives in the presence of the magnetic field (840 kA/m). The samples from each set differ by volume concentration of the magnetic phase. By means of an experimental setup described in the paper, the electrical resistance R of the samples was measured as a function of the force F applied on the surface of the samples, for fixed values of the transverse magnetic field strength H. From the as-measured dependence R = R(F)_H, the dependence σ = σ(p)_H of the electric conductivity σ on the applied pressure p was determined. The experimental results are discussed in view of possible applications like magneto-mechanical sensors working in hostile media.     

Hybrid Polymer/Clay Nanocomposites: Effect of Clay Size on the Structure of Multilayered Films

The influence of size and surface area of two different types of clay on the structure and characteristics of PEO/clay nanocomposites in the form of multilayered films is discussed. To search for new synergistic properties and/or improve the properties of nanocomposite films already known, we study polymer nanocomposites that have laponite as well as montmorillonite incorporated. While DSC measurements showed that higher laponite amounts gradually suppress the crystallinity of PEO in the nanocomposite, XRD measurements provided evidence that higher montmorillonite amounts ensure an improved final orientation of the clay platelets, parallel to the plane of the multilayered film.