Tribological Aspects of the Process of Winding the Steel Rope Around the Winch Drum

Proper winding of the steel rope around the winch drum is great importance, mostly for: prolonging the service life of the rope, reduction of deformations of the body and the sides of the drum if the winding of the rope is multilayered, increasing of the safety factors, easier unwinding of the rope while lowering the load, even running of the drive unit, etc. The focus of this paper is on the analysis of the friction which occurs in the process of winding and unwinding the rope around the winch drum. Friction force is in its highest intensity when the rope passes from one layer to another, if the winding of the rope is multilayered. As the result of the research, certain mechanisms of winding of the rope from the aspects of the friction force were obtained, and the effects of the forces on the sides of the drum were analyzed

M-GAM method in function of tourism potential assessment: Case study of the Sokobanja basin in eastern Serbia

The Sokobanja basin is an area in Eastern Serbia with diverse geological and geomorphological features. Also, it is an area with developed spa tourism. The Sokobanja basin has numerous geoheritage features, which tourist potential has not been discovered yet. In this article, several geosites were analyzed, which present significant geoheritage formations. Geosites were selected by authors of this article based on the degree of their attractiveness for the geotourism development. The main goal of this article is to emphasize the geotourism potential of the Sokobanja basin and to determine the current state and geotourism potential of evaluated geosites by applying the modified geosite assessment model (M-GAM). A total of seven geosites were evaluated throughout the basin. The values of the investigated parameters were entered into the matrix of the M-GAM based on the number of points. Based on the research and the results obtained, it can be concluded that the Sokobanja basin has the potential for the development of geotourism, but it is necessary to improve additional values to become a true geotourism destination

The Effects of Aggressive Environments on the Properties of Fly Ash based Geopolymers

This paper analyzes the effects of two different aggressive environments, concentrated ammonium nitrate solution (480 g/dm(3)) and sodium sulphate solution (50 g/dm(3)), on the structure and mechanical strength of fly ash based geopolymers. Geopolymer samples were subjected to the aggressive solutions over a period of 365 days. It was found that exposure to the NH4NO3 and Na2SO4 solutions caused small decrease in geopolymer strength (10-20 %). The most valuable insight into the structural changes caused by testing of the geopolymer samples in the aggressive solutions was provided by means of Si-29 MAS NMR. It was found that the immersion of geopolymer samples in the NH4NO3 solution caused breaking of Si-O-Al bonds in the aluminosilicate geopolymer gel structure. On the other hand, treatment of the geopolymer samples with the Na2SO4 solution resulted in breaking of Si-O-Si bonds in geopolymer gel structure and leaching of Si. It was concluded that the major changes in the geopolymer structure were associated with the changes in the pH values of aggressive solutions during the testing

Synthesis and characterization of binding materials based on alkali-activated fly ash and blast furnace slag.

Извршена је синтеза и карактеризација везивних материјала на бази алкално активираног индустријског отпадног материјала: - смеше електрофилтерског пепела и згуре високе пећи и - механички активираног електрофилтерског пепела. Синтеза везива на бази алкално активиране смеше електрофилтерског пепела и згуре високе пећи извршена је употребом раствора натријум-силиката као активатора, на температури од 95 С у току 24 h и при различитим условима синтезе: различитим масеним уделима електрофилтерског пепела и згуре високе пећи (100-0; 75-25; 50-50; 25-75; 0-100), различитим вредностима модула активатора (SiO2/Na2O: 0,5; 1,0; 1,5) и различитој концентрацији активатора (% Nа2О: 4; 7; 10). Испитиван је утицај услова синтезе на физичко-механичке и структурне карактеристике синтетисаних везива. Утврђено је да чврстоће на савијање и притисак синтетисаних везива у највећој мери зависе од састава смеше и односа вода/везиво. Време везивања у великој мери зависи од концентрације активатора, а скупљање при сушењу од температуре реакције у прва 24 сата. На основу детаљне карактеризације структуре синтетисаних везива закључено је да продукти реакције алкалне активације у погледу хемијског састава и структуре зависе од састава смеше. Главни продукт алкалне активације електрофилтерског пепела је натријум-алумосиликатни гел (N-A-S-H гел). Главни продукти алкалне активације згуре високе пећи су калцијум-силикохидратни гел са супституцијом силицијума алуминијумом у структури (C-A-S-H гел) и хидроталкит. При уделу згуре од 25% у смеши као главни продукт реације формира се N-A-S-H гел са делимично инкорпорираним Са2+ у структури, или С-N-A-S-H гел. При уделима згуре од 50-75%, продукти реакције састоје се од C-A-S-H гела и С-N-A-S-H гела измешених у структури на нанометарском нивоу. Закључено је да је присуство...Synthesis and characterization of binding materials based on alkali-activated industrial waste material was conducted, involving: - blends of fly ash and blast furnace slag and - mechanically activated fly ash. Synthesis of binders based on alkali-activated blends of fly ash and blast furnace slag was conducted by use of sodium silicate solution as an activator, at the temperature of 95 ºC during 24 h, with different synthesis conditions: different fly ash - blast furnace slag mass ratios (100-0; 75-25; 50-50; 25-75; 0-100), different moduli of the activator (SiO2/Na2O: 0.5; 1.0; 1.5) and different activator concentration (% Nа2О: 4; 7; 10). Influence of synthesis conditions on physical-mechanical and structural characteristics of synthesized binders was investigated. It was found that the flexural and compressive strengths mostly depended on the composition of the blends and the water/binder ratio. The setting time highly depended on the activator concentration, while the drying shrinkage was mostly affected by the reaction temperature during the first 24 h. Based on detailed structural characterization of the synthesized binders it was concluded that the chemical composition of alkali activation raction products varied as a function of the blend composition. The main reaction product of alkali-activated fly ash is sodiumaluminosilicate gel (N-A-S-H gel). The main reaction product of alkali-activated blast furnace slag are calcium silicate hydrate gel with substituted silicon by aluminum in the structure (C-A-S-H gel) and hydrotalcite. With the 25% content of slag in the blend the N-A-S-H gel with partially incorporated Са2+ in the structure, or С-N-A-S-H gel, was formed as the main reaction product. With the 50-75% content of slag in the blend the reaction products comprised of C-A-S-H gel and С-N-A-S-H gel intermixed within the structure on a nanometer level. It was concluded that the presence of blast furnace slag in the blend with fly ash affected the improved reactivity of fly ash in the reaction of alkali activation due to lowering the water/binder ratio and the availability of soluble..

Istraživanje alternativnih pogona motornih vozila

Ecology problems of transport appertain „first class“ pollution in urban environment. The forecast about the reserves of crude petroleum have always imposed the need for intensified researches on substitution of conventional mineral fuels. The term „lternative fuels“ is primarily connected with the IC engine and it has developed because of long lasting strict use of petroleum fuels as primary fuels for its drive. If the problem is generalized to the area of motor vehicles, then we can discuss alternative (hybrid) drives, that, beside IC engine as a drive unit, also include electric motor. Applicability of the use of some fuel is rated: by the quality of its energetic transformation through the process of obtainment of work, which directly defines output performance of the drive unit, by production cost, by suitability and safety of transport, storage and manipulation, by natural resourses of raw materials for its obtainment and by its toxic characteristics. The current state and possible perspectives by using motor vehicles alternative drives are analyzed in this paper. The most frequently currently used alternative drives/fuels: electric drive, hybrid drive, liquid petroleum gas, natural gas, bio-diesel, ethanol and methanol are observed. It are showed an example computer simulation (in Matlab) of a complex hybrid electric vehicle in two different driving modes. simulated hybrid electric vehicle is of combined type, similar to Toyota Prius cars. Also, in paper are presented an economic (costbenefit) analysis of different introduction strategies, as well as different elements thereof, for different kinds motor vehicles alternative drives. A cost-benefit analysis is undertaken for increasing the number of various kinds of motor vehicles alternative drives in the Serbian transport sector

Linking arithmetic to algebra

Proceedings of the 12th ICMI study conference: The future of the teaching and learning algebr