298 research outputs found
Considerations of uncertainty in robust optimisation of electromagnetic devices
No full textDue to unavoidable uncertainties related to material properties and manufacturing processes, the robustness of the optimal solution must be considered when designing electromagnetic devices. In this paper, the worst-case optimisation (WCO) and the worst-vertex-based WCO are proposed to evaluate the robustness of both performance and constraints under uncertainty. To reduce computing times when searching for the robust solution a predicted objective function is used, obtained with the help of a kriging algorithm which explores the searching space using the concept of rewards. Finally, to avoid some of the shortcomings of WCO, the concept of average performance evaluation is developed
An innovative method for highly-efficient fabrication of carbon fiber precursors via acrylonitrile emulsion copolymerization coupled to a chemical oscillator
No full textA new synthetic protocol to produce the carbon fiber precursor polyacrylonitrile (PAN) and its block copolymers with polyethylene glycol (PEG) is proposed here. The constant flux of radical species produced at low concentrations during the oscillating Belousov-Zhabotinsky (BZ) reaction was properly exploited to initiate the radical polymerization reaction. Compared with conventional methods, this oscillating initiation decreases the probability of chain termination, thus favouring the production of high molecular weight polymers, and it does not require an inert atmosphere and elevated temperatures to be produced. The solubility of the polymeric chains during the polymerization reaction was improved by adding the anionic micelle-forming surfactant sodium dodecyl sulphate (SDS). Following the initiation step, short oligomer chains are able to overcome the micellar
interface, thereby reaching a favourable environment for the increase of the polymeric chains, thus strongly contributing to the increase of the molecular weight of the fibers’ precursors. The synthesis was conducted by adding the monomer acrylonitrile (AN) to the unperturbed and PEG-perturbed BZ system after the onset of the oscillations, in the absence and presence of increasing amounts of the SDS surfactant. The potentiometric
technique was utilized to detect the dynamics of the oscillatory reaction. Preliminarily, the response of the BZ system to the monomer addition was investigated. Additional information was provided from the study of the effect of the SDS and PEG concentration on the dynamics of the BZ reaction during AN polymerization, thus obtaining a deepening in the understanding of the BZ mechanism. The characterization of the obtained polymers and copolymers, by melting point measurements, molecular weight determinations, Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) analyses, and thermal treatments, indicated that the proposed synthetic method produces carbon fiber precursors with high molecular weight and good thermal stability. The addition of the surfactant was revealed as a good method to improve and/or finely tune the precursor molecular weight. The proposed synthetic protocol represents a valuable alternative to conventional methods to produce highperformant precursors of carbon fibers
SONATA-DIALOGUE FOR BASSOON AND PIANO BY V. ROTARU
No full textIn the pages of this article, the author analyzes the stylistic peculiarities of the Sonata-dialogue for bassoon and piano by Vladimir Rotaru, highlighting the composer’s predilection for the genre of instrumental chamber music, mostly for piano and wind instruments. Th e Sonata-dialogue in question is characterized by a musical language deeply rooted in folklore (with specifi c rhythms of the Moldovan folk dances), by using the principles of improvisation in developing the material and original virtuosity of the solo part. As a performer (soloist) of the sonata, the author suggests some methodical recommendations to bassoon-soloists in order to achieve a successful interpretation of the creation
Vogel-Fulcher analysis of relaxor dielectrics with the tetragonal tungsten bronze structure : Ba6MNb9O30 (M = Ga, Sc, In)
No full textIn-depth analysis of the relaxor behaviour of Ba6MNb9O30 (M= Ga, Sc, In) tetragonal tungsten bronze (TTB) ceramics was carried out. Powder x-ray diffraction and scanning electron microscopy were performed in order to confirm the formation of desired phases and to determine the microstructure. Low-temperature dielectric spectroscopy was used in order to characterise the dielectric properties of these materials; the degree of relaxor behaviour were investigated in relation with the increase of ionic radius of the M-cation on the B-site of the TTB structure. The dynamics of dielectric relaxation of dipoles was studied by fitting the dielectric permittivity data to the Vogel-Fulcher (VF) model in order to monitor the reproducibility and validity of the physical results. Restrictions to the VF fit were attempted besides the regular “free-fit” by constraining some of the fundamental relaxation parameters to physically sensible values. We show that Vogel-Fulcher fits are very sensitive to the fitting range resulting in a large range of fundamental parameters for the dielectric relaxation processes, and that the restriction of the frequency domain due to experimental noise or to instrumentation limits has a dramatic influence on the values obtained.Peer reviewe
Advancements in the integration and understanding of the Sestak–Berggren generalized conversion function for heterogeneous kinetics
No full textKinetic models are relevant to describe heterogeneous kinetic processes; a number of kinetic models and their mathematical expressions have been reported in the literature, many of these based on idealistic conditions in terms of geometrical constrain and driving forces. Alternatively, the semi-empirical Sestak–Berggren (SB) conversion function, which was proposed as a general equation, encompasses a large variety of equations corresponding to different kinetic models. Despite the fact that the SB equation does not provide any physical meaning, it is extremely useful for kinetic analysis as it offers a good fit to experimental data even when they do not follow the ideal conditions assumed for the conventional kinetic models. One limitation of the SB kinetic model is the fact that its conversion function cannot be analytically integrated to provide an exact solution; thus, it cannot be directly applied in kinetic integral methods. The objective of this study aims to propose some solutions for some specific cases, while the mathematical limits for the values of the kinetic exponents m, n, p of the SB model and their validity are also explored. Further ideas for improving the SB equation or finding an alternative for a superior conversion function were explored in this work.The work of I. Roventa has been supported by a grant of the Romanian Ministry of Research, Innovation and Digitalization (MCID), project number 22–Nonlinear Differential Systems in Applied Sciences, within PNRR-III-C9-2022-I8.Peer reviewe
Implementation of new standards in statistics production, in countries in transition
No full textProject Work presented as the partial requirement for obtaining a Master's degree in Statistics and Information Management, specialization in Information Analysis and ManagementDuring the last decade, the Republic of Moldova as a country in transition faced many issues,
including financial crises impact and one more specific event – bank fraud that leaded to closure of
three banks that at the closing date counted 34.2% share of total assets of banking system. As a
consequence, it was a trigger to reassess the supervision approach for banks and it was decided to
implement BASEL III framework in order to have a best conformity with the latest supervision
standards.
Another needs that were identified – is identification of the reaction of the market to such a big
event (closure of three banks) in the mater of financial asset and liabilities distribution between
sectors. The question was focused on distribution part, because all financial liabilities of closed banks
were repaid by loans provided by the National Bank of Moldova (NBM) by reallocating of deposits to
other banks (loans were reallocated by mutual agreements).
I this regards, as the National Bank of Moldova tried to reassess the reasons that lead to closure of
banks, the process of qualitative changes begun. Were identified many loans provided to affiliated
parties, and as a result started an immense investigation on the compliance to all required legal
framework for loan activity of closed banks.
The year 2014 was a very significant for the financial market, because other financial corporations
(non-banking sector) start to increase its market share in loans provided to customers (individuals
and corporates) very accelerated.
At the moment, the National Bank finalized implementation of Monetary and Financial Statistics
Compilation Guide 2016 (International Monetary Fund, 2016), in producing of monetary and financial
statistics. Starting with 2014, external statistics is produced according to Balance of Payment Manual
version 6 (International Monetary Fund, 2009). Current project will be focused on the experience of
the Republic of Moldova in implementation of the financial accounts statistics based on a
consequence of environmental factors that I believe can contributed to successful implementation of
such valuable and useful statistics. I will try to note some experiences from mentioned activities,
which I think are important things that can be considered a problems and will underline ways we
used to solve some difficult situations. The structure of Project Work will be as a step-by-step
description of actions and strategy approves in order to have financial accounts statistics at a final
stage
Pianistic works of composer V. Rotaru in the concert and pedagogical repertoire of the Republic of Moldova
No full textIn this article, the author describes the pianistic heritage of composer V. Rotaru from the perspective of its importance for the concert and pedagogical activity in the Republic of Moldova. Piano miniatures that are different in variety of artistic ideas and content are included in this anthology.
The part of the collection is represented by mobile works, which contain significant technical difficulties and are often used in concert and contest repertoire of Moldova (Expromt, Humoresque, Toccata, cycle Improvisations etc.). Another part of lyrical cantilena piano pieces by the composer is characterized by sincere warmth that is often associated with the landscapes of Moldovan nature. (Doina, Silhouettes, Preludes cycle et al.).
All the works have a number of teaching and performing features, typical figurative and emotional system, evident technical issues and based on the national folklore. All this makes them indispensable in pedagogical and concert competitive repertoire in the special piano course in the secondary and higher educational institutions of the Republic of Moldova
Current Trends in Ceramifiable Polymer Composites Development
No full textAlthough ceramifiable composites have been developed for over 30 years, there is still very broad area for an enhancement of their properties. Following scientific articles in this field, one can find out that since 2013 the number of the papers started to rise significantly [1]. The ceramifiable composites consist of polymer continuous phase and properly designed mix of mineral fillers. Ceramification is an advanced passive flame retardancy process based on formation of continuous ceramic structure on the surface of the composite, which limits transfer of flammable fuel into burning zone as well as oxygen into polymer matrix. Moreover, the ceramic structure provides protection against heat and mechanical stress. In principle, ceramification is improved version of more traditional flame retardancy method based on char formation. However, the ceramic structure formed in ceramification process exhibits outstanding barrier and mechanical properties in comparison to loosely bonded char formed by traditional methods. A key feature characterizing both these methods is lack of toxic or hazardous products formation during flame retardant action. This increases safety of human life and health during a fire accident.Due to silicone elastomers ability to create silica while burning, this group of polymers was firstly selected as continuous phase for ceramifiable composites [2, 3]. The silica created, takes part in the ceramic structure formation, actively improving its properties. On the other hand, silicone rubber exhibits limited ability to incorporate large amount of fillers without a rapid decrease of its mechanical properties. Sufficient amount of mineral fillers is also crucial from the point of view of the ceramification performance. Therefore, recent research in this filed has focused on various organic polymers, much more common in industrial practice and of lower price. Generally, various organic rubbers may be filled with mineral powders up to 300-400 weight parts per hundred parts of their own mass. This allows development of high performance caramifiable composites of much more affordable price. However, high fillers load makes the processability of the composites more challenging, resulting in, for example worse extrudability. This problem must be also addressed in future works. Recently, ethylene-vinyl acetate copolymer (EVA) [4, 5] and styrene-butadiene rubber (SBR) [6] are considered to be the most promising materials for continuous phase for ceramifiable composites.[1] Scopus database, searched words: “ceramifiable” or “ceramizable”,[2] L.G. Hanu, G.P. Simon, J. Mansouri, R.P. Burford, Y.B. Cheng, J. Mater. Process Tech., 153-154 (2004) 401[3] L.G. Hanu, G.P. Simon, Y.B. Cheng, Mat. Sci. Eng. A, 398 (2005) 180[4] G. Xinhao, S. Yucai, W. Tingwei, RSC Adv., 6 (2016) 96984[5] Y-M. Li, C. Deng, Y-Z. Wang, Compos. Sci. Technol., 132 (2016) 116[6] R. Anyszka, D.M. Bieliński, Z. Pędzich, P. Rybiński, M. Imiela, M. Siciński, M. Zarzecka-Napierała, T. Gozdek, P. Rutkowski P., Materials, 9 (2016) 604<br/
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