Tribology of Polymeric Materials Part 2 - Properties and tribological behaviour of polymeric materials

Tribološka ispitivanja mogu se provesti na nekoliko razina, od mikrorazine do nanorazine. Na toj osnovi mogu se istražiti korelacije između viskoelastičnosti, krhkosti i tribološkog ponašanja materijala na osnovi polimera koje odražavaju utjecaje sastava, orijentacije u magnetnom polju i obrade površine. Relacija između stupnja viskoelastičnog oporavka i krhkosti analizirana je u radu 2006. U raspravi su istaknuta znatna poboljšanja svojstava, uključivo i tribološka, dodatkom anorganskih mikročestica i nanočestica punila. Uočen je utjecaj površinske i međupovršinske napetosti u multifaznim sustavima na tribološka svojstva. Opisane su računalne simulacije tribološkog ponašanja kao dopuna eksperimentima. Predstavljene su osnovne razlike izme|u mikrotribologije i nanotribologije.Tribological investigations can be conducted at several size scales, from micro-level to nano-level. On this basis we can develop correlations between viscoelasticity, brittleness and tribological behaviour of polymer-based materials that reflect the effects of composition, orientation in the magnetic field and surface treatments. The relationship between the degree of viscoelastic recovery after sliding wear and brittleness was analyzed in 2006. Significant improvements of properties, including the tribological ones are discussed, by addition of inorganic micro-particles and nano-particles of fillers. The importance of surface and interface tensions in multiphase systems on tribological properties has been noted. Computer simulations of tribological behaviour as supplement to experiments are described. The basic differences between microand nano-tribology are presented

A new lower bound for doubly metric dimension and related extremal differences

In this paper a new graph invariant based on the minimal hitting set problem is introduced. It is shown that it represents a tight lower bound for the doubly metric dimension of a graph. Exact values of new invariant for paths, stars, complete graphs and complete bipartite graph are obtained. The paper analyzes some tight bounds for the new invariant in general case. Also several extremal differences between some related invariants are determined

Značaj sistema javnih skladišta za finansiranje agro-biznis sektora

The aim of this study was to determine the economic viability of the use of warehouse receipts for the storage of wheat and corn, based on the analysis of trends in product prices, storage costs in public warehouses and interest rate of loans against warehouse receipts. Agricultural producers are urged to sell grain at the harvest time when the price of agricultural products is usually lowest, mostly because of their needs for financial sources. Instead of selling products, farmers can store them in the public warehouses and use short-time financing by lending against warehouse receipt with usually lowest interest rate. In following months, farmers can sell products at higher price and repay short-term loan. This study showed that strategy of using public warehouses and postponing the sale of grains after harvest is profitable strategy for agricultural producers.Cilj ovog rada je da se utvrdi ekonomska isplatljivost korišćenja javnih skladišta za skladištenje pšenice i kukuruza na osnovu analize kretanja cena proizvoda, troškova skladištenja i kamatne stope na kredite koji kao zalogu imaju robni zapis. Poljoprivredni proizvođači su usled potreba za finansijskim sredstvima često primorani da prodaju žitarice odmah nakon žetve kada je cena po pravilu najniža. Umesto prodaje, poljoprivrednici mogu uskladištiti proizvod u javnim skladištima i koristiti robni zapis kao obezbeđenje za kratkoročni kredit koji često ima nisku kamatnu stopu. U mesecima nakon žetve poljoprivrednik prodaje robu po višoj ceni i vraća kredit. Ovaj rad je ukazao na profitabilnost strategije skladištenja robe u javim skladištima i odlaganje prodaje proizvoda za period nakon žetve

On some interconnections between combinatorial optimization and extremal graph theory

The uniting feature of combinatorial optimization and extremal graph theory is that in both areas one should find extrema of a function defined in most cases on a finite set. While in combinatorial optimization the point is in developing efficient algorithms and heuristics for solving specified types of problems, the extremal graph theory deals with finding bounds for various graph invariants under some constraints and with constructing extremal graphs. We analyze by examples some interconnections and interactions of the two theories and propose some conclusions