Influence of wear on deep groove ball bearing service life

Habanje kotrljajnog ležaja je uslovljeno proklizavanjem koje prati kotrljanje kotrljajnih tela duž staza kotrljanja. Usled habanja spregnutih delova ležaja povećava se unutrašnji radijalni zazor. Sa povećanjem unutrašnjeg radijalnog zazora neravnomernost raspodele opterećenja na kotrljajna tela ležaja se povećava, što je uzrok smanjenja radnog veka ležaja. U ovom radu je izvršena analiza uticaja habanja na radni vek ležaja na osnovu klasične teorije radnog veka ležaja i originalnog matematičkog modela raspodele opterećenja na kotrljajna tela ležaja.Frictional sliding which follows rolling of balls along rings raceways causes rolling bearing wear. Internal radial clearance of rolling bearing becomes larger due to wear of rolling elements and raceways. With increasing internal radial clearance, load distribution between rolling elements becomes more unequal. It is cause of decreasing rolling bearing life. Functional dependence of deep groove ball bearing life on wear is presented in this paper. Development of this function is based on classical expressions of bearing life theories and an original mathematical model of load distribution between rolling elements

Influence of wear on deep groove ball bearing service life

Habanje kotrljajnog ležaja je uslovljeno proklizavanjem koje prati kotrljanje kotrljajnih tela duž staza kotrljanja. Usled habanja spregnutih delova ležaja povećava se unutrašnji radijalni zazor. Sa povećanjem unutrašnjeg radijalnog zazora neravnomernost raspodele opterećenja na kotrljajna tela ležaja se povećava, što je uzrok smanjenja radnog veka ležaja. U ovom radu je izvršena analiza uticaja habanja na radni vek ležaja na osnovu klasične teorije radnog veka ležaja i originalnog matematičkog modela raspodele opterećenja na kotrljajna tela ležaja.Frictional sliding which follows rolling of balls along rings raceways causes rolling bearing wear. Internal radial clearance of rolling bearing becomes larger due to wear of rolling elements and raceways. With increasing internal radial clearance, load distribution between rolling elements becomes more unequal. It is cause of decreasing rolling bearing life. Functional dependence of deep groove ball bearing life on wear is presented in this paper. Development of this function is based on classical expressions of bearing life theories and an original mathematical model of load distribution between rolling elements

Afforestation on bare lands – example of Ibar Gorge, Serbia

The afforestation of bare lands, sandstone, and skeletal terrains are one of the biggest challenges forestry scientists face. These terrains are characterized by specific ecological conditions that are generally unfavorable for the growth of woody species. These are usually shallow soils, unstable, and poor in nutrients and moisture. The characteristics of these habitats make said terrains unfavorable for the regeneration of forest vegetation. It is therefore crucial for the success of afforestation to gain detailed knowledge and understanding of environmental conditions. Only after the detailed research and study of field conditions can the selection of species for afforestation, including selection of species characteristics and technology of planting, begin. Mistakes made during previous establishments of green areas are one of the main reasons some species of vascular flora have disappeared. This alone expresses the undeniable importance of knowledge on habitat specifics, work schedule, and selection of species for afforestation. With the aim to implement the future afforestation within the planned scope, it is necessary to organize an effective nursery production of seedlings with characteristics that will suit the environmental conditions of bare lands, sandstones, and skeletal terrains whose afforestation is planned

Mathematical model of load distribution in rolling bearing

Spoljašnje opterećenje kotrljajnog ležaja se sa jednog prstena na drugi prenosi preko kotrljajnih tela. Pri tome je raspodela opterećenja na kotrljajna tela neravnomerna. Stepen neravnomernosti raspodele opterećenja zavisi od unutrašnje geometrije ležaja i intenziteta spoljašnjeg opterećenja. U ovom radu su definisana i razmatrana dva granična slučaja raspodele opterećenja kod kugličnog kotrljajnog ležaja opterećenog spoljašnjim radijalnim opterećenjem. To su idealno ravnomerna i izrazito neravnomerna raspodela opterećenja. Stvarna raspodela opterećenja je između ova dva granična slučaja. Novi matematički model raspodele opterećenja je razvijen na osnovu klasične teorije kotrljajnih ležaja i uvođenjem nove originalne veličine, definisane kao faktor raspodele opterećenja. Razvijeni matematički model obuhvata sve pomenute relevantne uticaje na raspodelu opterećenja u kotrljajnom ležaju (broj kotrljajnih tela u ležaju, unutrašnji radijalni zazor i spoljašnje opterećenje).External load of rolling bearing is transferred from one ring to the other one through the rolling elements. Load distribution between rolling elements is unequal. Degree of load distribution unequality depends on internal geometry of bearing and magnitude of external load. Two boundary load distributions in radially loaded ball bearing were defined and discussed in this paper. These are ideally equal and extremely unequal load distribution. Real load distribution is between these boundary cases. The new mathematical model of load distribution is developed respecting classic rolling bearing theory and by introduction of new, original value defined as load distribution factor. Developed mathematical model includes all main influences on load distribution in rolling bearing (number of rolling elements, internal radial clearance and external load)

Mathematical model of load distribution in rolling bearing

Spoljašnje opterećenje kotrljajnog ležaja se sa jednog prstena na drugi prenosi preko kotrljajnih tela. Pri tome je raspodela opterećenja na kotrljajna tela neravnomerna. Stepen neravnomernosti raspodele opterećenja zavisi od unutrašnje geometrije ležaja i intenziteta spoljašnjeg opterećenja. U ovom radu su definisana i razmatrana dva granična slučaja raspodele opterećenja kod kugličnog kotrljajnog ležaja opterećenog spoljašnjim radijalnim opterećenjem. To su idealno ravnomerna i izrazito neravnomerna raspodela opterećenja. Stvarna raspodela opterećenja je između ova dva granična slučaja. Novi matematički model raspodele opterećenja je razvijen na osnovu klasične teorije kotrljajnih ležaja i uvođenjem nove originalne veličine, definisane kao faktor raspodele opterećenja. Razvijeni matematički model obuhvata sve pomenute relevantne uticaje na raspodelu opterećenja u kotrljajnom ležaju (broj kotrljajnih tela u ležaju, unutrašnji radijalni zazor i spoljašnje opterećenje).External load of rolling bearing is transferred from one ring to the other one through the rolling elements. Load distribution between rolling elements is unequal. Degree of load distribution unequality depends on internal geometry of bearing and magnitude of external load. Two boundary load distributions in radially loaded ball bearing were defined and discussed in this paper. These are ideally equal and extremely unequal load distribution. Real load distribution is between these boundary cases. The new mathematical model of load distribution is developed respecting classic rolling bearing theory and by introduction of new, original value defined as load distribution factor. Developed mathematical model includes all main influences on load distribution in rolling bearing (number of rolling elements, internal radial clearance and external load)

Chemometric methods for the prediction of river water quality parameters and pollutants degradation

Hemometrijske metode se koriste za obradu velikog broja podataka dobijenih u hemijskoj analizi, redukciju podataka i izbor adekvatnog broja potrebnih parametara koji bi bili obuhvaćeni redovnim monitoringom, a sve u cilju predviđanja ponašanja raznih parametara, određivanja međusobnih odnosa, sličnosti i razlika koje uslovljavaju grupisanje parametara, i važnosti svakog parametra u prostorno/vremenskoj varijaciji u kvalitetu rečne vode. Odabrane hemometrijske metode su primenjene u okviru ove doktorske disertacije za analizu i tumačenje uticaja različitih parametara značajnih za inženjerstvo zaštite životne sredine: određivanje i procenu kvaliteta rečnih voda, određivanje porekla zagađujućih materija u rečnoj vodi, predviđanje koncentracija parametara kvaliteta rečnih voda, opis i analizu procesa oksidacije gasnom plazmom dve grupe zagađujućih materija vode, tekstilnih boja i pesticida. U svakoj od oblasti koja je bila obuhvaćena istraživanjem (monitoring i procesi tretmana zagađujućih materija) korišćene su odgovarajuće analitičke tehnike, kao i instrumentalne metode analize, u skladu sa relevantnim standardima. Dobijeni eksperimentalni podaci primenjeni su za modelovanje primenom veštačkih neuronskih mreža (ANN) i Monte Karlo simulacije (MCS). Za redukciju podataka i objašnjenje prostorne i sezonske varijacije kvaliteta rečne vode na različitim lokalitetima od hemometrijskih metoda bila je primenjena metoda glavnih komponenata (PCA). S obzirom da je, kao posledica intenzivnog rasta broja stanovnika u svetu i povećanja stepena industrijalizacije kvalitet rečnih voda narušen, neophodno je svakodnevno pratiti njen kvalitet i analizirati veliki broj podataka: vrednosti fizičkohemijskih, bioloških, izotopskih i hidroloških parametara, lokacije uzorkovanja, sezonske prilike u kojima se merenja obavljaju, itd. Informacije koje se dobiju monitoringom predstavljaju osnovu za strategiju upravljanja prirodnim vodnim resursima, kako bi se održao ili čak unapredio njihov kvalitet. Primenom hemometrijskih tehnika moguće je odrediti eventualne korelacije, trendove i međusobne uticaje svih podataka koji se dobijaju monitoringom i samim tim smanjiti obim istraživanja u smislu redukcije broja parametara kvaliteta i lokacija monitoringa. U okviru ove disertacije analizirani su fizičkohemijski parametri kvaliteta vode i izotopi odabranih elemenata reke Dunav na delu toka kroz Republiku Srbiju. Parametri kvaliteta vode koji su praćeni tokom istraživanja su: temperatura, pH, elektrolitička provodljivost, mutnoća, ukupne suspendovane materije, ukupne čvrste materije, ukupne isparljive suspendovane materije, ukupne rastvorne materije, ukupna tvrdoća, rastvoreni kiseonik i ugljen-dioksid, alkalitet, koncentracije kalcijuma, magnezijuma, natrijuma, kalijuma, gvožđa, bikarbonata, sulfata, hlorida, karbonata, organskog azota (azot po Kjeldalu), neorganskih oblika azota (amonijak, nitrat, nitrit) i fosfora (orto-fosfati), silikata, sadržaj organske materije (utrošak KMnO4, K2Cr2O7), biološka potrošnja kiseonika (BPK), sadržaj hlorofila-a (Cha) i feofitina. Izotopske analize su obuhvatale izotope lakih elemenata (δ18O, δ2H, δ13CDIC, δ13CPOC, δ15NTPN).U prvom delu disertacije su prikazani rezultati ispitivanja koji su imali za cilj određivanje korelacije između sadržaja stabilnih izotopa i hidroloških, fizičkohemijskih i bioloških parametara Dunava primenom analize glavnih komponenata, da bi se predvidele sezonske varijacije kvaliteta reke i interakcije sa podzemnom vodom, kao i način prihranjivanja reke. Pored toga, razvijeni su i optimizovani modeli neuronskih mreža za predviđanje vrednosti pojedinih parametara kvaliteta rečne vode, u slučaju isključivanja pojedinih stanica iz redovnog monitoringa. Za odabir ulaznih promenljivih i procenu njihove značajnosti je primenjena tehnika Monte Karlo simulacije, kako bi se razvio model sa minimalnim brojem ulaznih promenljivih, uz poboljšanje performansi samog modela...Chemometric methods are used in processing of large dataset obtained in chemical analysis, data reduction and selection of an adequate number of required parameters which would be included in regular monitoring; they are applied to predict the behavior of various parameters, determine relationships, similarities and differences which cause parameters grouping and the importance of each parameter in the spatial/temporal variation in river water quality. Within this doctoral dissertation selected chemometric methods were applied to analyse and interpret data and the impact of various parameters which are important for environmental engineering, such as: river water quality determination and assessment, the origin of pollutants in river water, prediction of river water quality parameters, characterization and analysis of degradation of two groups of water pollutants, textile dyes and pesticides by gas plasma oxidation. In each of the areas covered by this research (monitoring and pollutants oxidation), appropriate analytical techniques and instrumental methods were used, in accordance with the relevant standards. The obtained experimental data were applied for the artificial neural networks (ANN) modeling and Monte Carlo simulation (MCS). For data reduction and explanation of spatial and seasonal variation in river water quality at different locations the PCA method was applied. Since rapid population growth in the world and increased industrialization caused decline in the surface water quality, continuous river water quality monitoring is necessary to provide values of physicochemical, biological, isotopic, hydrologic parameters, characteristics of sampling locations, seasonal conditions in which measurements are performed, etc. The information collected from monitoring can be used for the water resource management strategy, in order to maintain or even improve its quality. The chemometric techniques were applied to determine possible correlations, trends and mutual influences of the data obtained by monitoring and thus to reduce the scope of research in terms of reducing the number of examined parameters and monitoring locations. Physicochemical water quality parameters of the Danube through Republic of Serbia and isotopes of selected elements in this research were analyzed. These water quality parameters are continuously measured during the study: temperature, pH, electrolytic conductivity, turbidity, total suspended solids, total solids, total volatile suspended solids, total dissolved solids, total hardness, dissolved oxygen and carbon dioxide, alkalinity, concentrations of calcium, magnesium, sodium, potassium, iron, bicarbonate, sulphate, chloride, carbonate, organic nitrogen (Kjeldahl nitrogen), inorganic forms of nitrogen (ammonia, nitrate, nitrite) and phosphorus (ortho-phosphates), silicate, organic matter content (consumption of KMnO4, K2Cr2O7), biological oxygen demand (BOD), chlorophyll (Cha) and pheophytin content. Isotope analyzes included isotopes of light elements (δ18O, δ2H, δ13CDIC, δ13CPOC,δ15NTPN).In the first part of the dissertation, possible correlation between the stable isotope composition and hydrological, physicochemical and biological parameters of the Danube was examined by applying the principle component analysis, in order to predict seasonal variations of river quality, interaction with groundwater and river recharge. In addition, artificial neural network models have been developed and optimized to predict certain water quality parameters, in order to exclude specific monitoring locations from regular monitoring. To select the input variables and to assess their significance, the Monte Carlo simulation technique was applied; it was performed in order to develop a model with a minimum number of input variables while improving the performance of the model itself

Identification and characterization of rat β-DRE binding factors involved in erythroid-specific induction of transcription

Identifikovali smo i okarakterisali DNK vezujuće proteine koji specifično prepoznaju transkripcioni regulatorni element βDRE iz βbminy-globinskog promotora pacova. βDRE je evolutivno konzervisan u adultnim β-globinskim promotorima sisara. Potvrdili smo da bDRE regulatorni element doprinosi transkripcionoj inducibilnosti βbminy-globinskog gena pacova u pacovskim eritroleukemičnim ćelijama. Korišćenjem "gel mobility shift" i South-Western metoda i kompeticionih eseja, pokazali smo da se za βDRE pacovskog βbminy-globinskog promotora specifično vezuju eritroidno-specifični transkripcioni faktor od 60 kD i dva opšta transkripciona faktora od 35 i 20 kD poreklom iz pacovskih eritroleukemičnih ćelija. Takođe, eritroidna diferencijacija REL ćelija je praćena značajnim povećanjem količine transkripcionog faktora od 60 kD.We have identified and characterized a DNA-binding activity with specificity for the β-globin direct repeat element (βDRE) from rat βbminy-globin promoter, an evolutionarily conserved transcriptional regulatory element in mammalian adult β-globin promoters. We have also confirmed that the βDRE contributed to the transcriptional inducibility of rat βbminy-globin gene in rat erythroleukemia (REL) cells. By using gel mobility shift and South-Western blot competition studies we have shown that 60 kD erythroid-specific transcription factor and 35 kD and 20 kD ubiquitous factors from rat erythroleukemia cells specifically bind to the βDRE from the rat βbminy-globin promoter. Additionally, a significant increase in the quantity of 60 kD transcription factor was observed upon erythroid differentiation of REL cells

Construction variation of packing machine in food processing

U radu je prikazano varijantno konstrukciono rešenje mašine za pakovanje prehrambenih proizvoda. Na osnovu tehno-ekonomske analize pokazano je da originalno i varijantno konstrukciono rešenje imaju približno istu tehničku vrednost, s tim što varijantna konstrukcija ima veću ekonomsku vrednost opravdanost. Ekonomska opravdanost postignuta je pogodnim konstrukcionim rešenjem i primenom domaćih komponenti i tehnologije izrade.The construction variation of packing machine in food processing is shown in this paper. By the techno-economic analyses it is shown that original and new construction has the same construction value, but the new construction has a better economic value – validity. Better economic value has achieved with new construction and engaging domestic components and production technology

Construction variation of packing machine in food processing

U radu je prikazano varijantno konstrukciono rešenje mašine za pakovanje prehrambenih proizvoda. Na osnovu tehno-ekonomske analize pokazano je da originalno i varijantno konstrukciono rešenje imaju približno istu tehničku vrednost, s tim što varijantna konstrukcija ima veću ekonomsku vrednost opravdanost. Ekonomska opravdanost postignuta je pogodnim konstrukcionim rešenjem i primenom domaćih komponenti i tehnologije izrade.The construction variation of packing machine in food processing is shown in this paper. By the techno-economic analyses it is shown that original and new construction has the same construction value, but the new construction has a better economic value – validity. Better economic value has achieved with new construction and engaging domestic components and production technology

Influence of different nutritional preparations on morpho-anatomical characteristics of wild fruit seedlings : doctoral dissertation

Шумске воћкарице које су широко распрострањене, али и оне чије је присуство спорадично или ограничено на мања пространства, од огромне су важности и њихово очување, унапређење и одрживо коришћење генофонда на природним стаништима у складу је са општим интересом очувања биодиверзитета Србије. Основни научни циљеви везани су за истраживање морфолошко-анатомске грађе садница шумских воћкарица (црни орах, орах, мечја леска, оскоруша, дивља трешња) и утицај три различита типа препарата исхране на њихову примарну грађу, како би се одабрао онај препарат, чији је утицај на развој садног материјала био највећи и допринео правилном развоју и оптималном квалитету садница. Оглед је постављен 2011. године у Расаднику Института за шумарство у Београду, а поновљен 2012. и 2013. године. За сваку од пет истраживаних врста формирана су четири блока огледних површина, сваки са по три понављања: контролна површина (у коме биљке нису биле третиране препаратима исхране), и у зависности од типа препарата исхране којима је вршено третирање Osmocote® Exact Standard 5-6 М, контролисано разлагајуће минерално ђубриво, Bactofil® B 10, микробиолошки препарат и Florin 2, комплексно NPK минерално ђубриво. Сетва семена свих врста извршена је почетком априла. Семе је засејано у супстрату Tref PS fine brown, у који су (осим у контролном пољу) непосредно пред сетву додати наведени препарати исхране. За потребе истраживања ове докторске дисертације измерени су следећи морфометријски параметри: висина надземног дела садница, пречник у кореновом врату, дужина корена, маса надземног дела биљке (изданка) у апсолутно сувом стању, маса подземног дела биљке (корена) у апсолутно сувом стању, а осим њих, израчунати су и изведени параметри – однос пречник/висина и индекс квалитета садница...Widely spread forest fruit trees, but also those whose occurrence is sporadic or limited to smaller areas, have an enormous importance and their preservation, improvement and sustainable use in natural habitats are in accordance with the general interest for preservation of the biodiversity in Serbia. The primary scientific objectives are related to the study of morphologicalanatomical structure of seedlings of forest fruit trees (black walnut, walnut, Turkish hazelnut, service tree, and wild cherry) and the impact of three different type nutrition preparations on the primary structure of the said forest fruit trees, with the aim of selecting a preparation that exerts the strongest impact on development of planting material and contributes to adequate development and optimum quality of seedlings. A sample plot was established in 2011 at the seedling nursery of the Institute of Forestry in Belgrade and re-established in 2012 and 2013. For each of five studied species four blocks of sample plots with a repeated pattern were established, which were composed of the control plot (in which plants were not treated with nutrition preparations) and, depending on the type of nutrition preparation applied, plots treated with Osmocote® Exact Standard 5-6 М (controlled release mineral fertiliser), Bactofil® B 10 (micro-biological preparation) and Florin 2, (complex NPK mineral fertiliser). The sowing of seeds of all species was conducted in the beginning of April. The seeds were sown in the Tref PS fine brown substrate, into which, (with the exception of the control plot), the abovementioned nutrition preparations were immediately added. For the purpose of research of this doctoral dissertation, the following morphometric parameters were measured: The height of the surface part of the seedlings, diameter at the root collar, mass of the surface part of plant (sprout) in the absolutely dry condition, mass of the under surface part of plant (root) in the absolutely dry condition. In addition, the following parameters were calculated and obtained: the diameter/height ratio and seedling quality index..