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Neural network for enhancement of end milling processes through accurate prediction of temperature in the cutting zone
No full textUnderstanding the complex influence of temperature in the cutting zone in order to achieve a successful and efficient machining process is of critical importance. The temperatures generated during processing have a crucial influence on achieving optimal results. In order to achieve the desired result, and to optimize the process, understanding of this complex interaction is necessary. The focus of this research was on the analysis of the influence of temperature in the cutting zone during the milling process. Particular attention has been paid to the influence of cutting speed, feed rate, and cutting depth on temperature generation. The design of the experiment was carried out according to the central composite design, which included 24 distinct cases. The experiment was performed on a Maho 600C vertical milling machine, using 30CrNiMo8 material. Temperature was measured using a FLIR InfraCAM Western thermal imaging camera. Based on the collected experimental data, artificial neural network and mathematical models which define the dependence of temperature on cutting parameters have been developed. The best performance was demonstrated by the artificial neural network with a 3 × 10x5 × 2x1 architecture, trained using the SCG learning algorithm, which resulted in a mean squared error of 0.000782. A comparative analysis was performed between the values gained by experiments and values provided by neural networks and mathematical models. The results showed that the artificial neural network achieved the smallest deviations. These results demonstrate the quality and reliability of our temperature prediction models for machining processes, which allow us to further optimize these processes and achieve the desired results.Publishe
Multi-Objective Optimization of Tribological Characteristics for Aluminum Composite Using Taguchi Grey and TOPSIS Approaches
Full text linkIn this study, a multi-objective optimization regarding the tribological characteristics of the hybrid composite with a base material of aluminum alloy A356 as a constituent, reinforced with a 10 wt.% of silicon carbide (SiC), size 39 μm, and 1, 3, and 5 wt.% graphite (Gr), size 35 μm, was performed using the Taguchi method, gray relational analysis (GRA), and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) decision-making methods. Tribological tests were carried out on a “block on disc” type tribometer with lubrication. Load, sliding speed, and graphite mass concentration were analyzed as input parameters. As output parameters, wear rate and coefficient of friction were calculated. An analysis of variance (ANOVA) was conducted to identify all parameters that have a significant influence on the output multi-response. It was found that the normal load has the highest influence of 41.86%, followed by sliding speed at 32.48% and graphite
addition at 18.47%, on the tribological characteristics of composites. Multi-objective optimization determined that the minimal wear rate and coefficient of friction are obtained when the load is 40 N, the sliding speed is 1 m/s, and the composite contains 3 wt.% Gr. The optimal combination of parameters achieved by GRA was also confirmed by the TOPSIS method, which indicates that both methods can be used with high reliability to optimize the tribological characteristics. The analysis of worn surfaces using scanning electron microscopy revealed adhesive and delamination wear as dominant mechanisms.Publishe
Турбуленција у атмосфери
Full text linkТурбуленција је хаотично и неправилно кретање флуидa различитих врста. Ваздух који сачињава атмосферу је стишљив флуид и подложан турбуленцији. То значи да турбуленција игра кључну улогу у обликовању динамике и понашања Земљине атмосфере. У раду ће бити речи о томе како турбуленција утиче на атмосферу и климу и зашто компликује покушаје метеоролошких предвиђања. Како се ђаци у средњим школама сусрећу са динамиком флуида у физици, а са друге стране са метеорологијом у географији, овај рад ће дати једну од значајних веза између физике и географије. Такође, рад ће дати увид ђацима зашто је турбуленција један од главних фактора који утичу да временска прогноза погреши у предвиђању. На крају рада биће приказан и оглед који сликовито приказује турбулентно кретање ваздуха.Publishe
Particulate Matter Emission and Air Pollution Reduction by Applying Variable Systems in Tribologically Optimized Diesel Engines for Vehicles in Road Traffic
Full text linkRegardless of the increasingly intensive application of vehicles with electric drives, internal combustion engines are still dominant as power units of mobile systems in various sectors of the economy. In order to reduce the emission of exhaust gases and satisfy legal regulations, as a temporary solution, hybrid drives with optimized internal combustion engines and their associated systems are increasingly being used. Application of the variable compression ratio and diesel fuel injection timing, as well as the tribological optimization of parts, contribute to the reduction in fuel consumption, partly due to the reduction in mechanical losses, which, according to test results, also results in the reduction in emissions. This manuscript presents the results of diesel engine testing on a test bench in laboratory conditions at different operating modes (compression ratio, fuel injection timing, engine speed, and load), which were processed using a zero-dimensional model of the combustion process. The test results should contribute to the optimization of the combustion process from the
aspect of minimal particulate matter emission. As a special contribution, the results of tribological tests of materials for strengthening the sliding surface of the aluminum alloy piston and cylinder of the internal combustion engine and air compressors, which were obtained using a tribometer, are presented. In this way, tribological optimization should also contribute to the reduction in particulate matter emissions due to the reduction in fuel consumption, and thus emissions due to the reduction in friction, as well as the recorded reduction in the wear of materials that are in sliding contact. In this way, it contributes to the reduction in harmful gases in the air.Publishe
Staging Imperial Aspirations: Spolia At Ljuboten And The Symbolic Role Of Antiquity, The Days of St. Emperor Constantine and Helena
No full textThis study examines the deliberate placement of spolia and the
fresco of King Stefan Dušan within St. Nicholas Church at Ljuboten (present-
day North Macedonia). It argues that this visual strategy aimed to showcase
Dušan’s authority and his ambition to claim the legacy of the Byzantine Empire
as a successor to the Roman Empire. The deliberate juxtaposition of spolia with
Dušan’s monumental portrait suggests an intentional evocation of Translatio
Imperii, legitimizing his rule and associating him with the prestige of the past.
The analysis connects architectural elements, the ruler’s portrait, and inscrip-
tions of the west portal to illuminate the power dynamics within the Serbian
nobility and Dušan’s aspirations for imperial dominance.Publishe
TOWARDS THE NEW GENERATION OF EUROCODE 7
No full textBetween 1991. and 1999., three versions of the Construction Eurocodes were published as pre-norms ("EuroNorm Vornnorm", ENV). The duration of each version was 3 years, when they could be used but without the status of fully adopted European Norms (EN). The experiences gained during the application of these pre-norms were used to harmonize and modify the pre-norms according to the final form of the European Norms (EN). Many pre-norms underwent significant changes and revisions until the final transformation into the fully adopted European Norm (EN).
Work on the final version of the Construction Eurocodes began in June 1996 and continued until November 2006, when the final part of Eurocode 9 was ratified.
International working group CEN TC250 (European Committee for Standardization) works on the new generation of Eurocode 7, after the shortcomings were noticed and the problems that appeared during the application of the current Eurocode 7 were considered in detail. The standard has been reorganized so that it now consists of three parts (instead of 2), new chapters were added (methods for soil improvement, the influence of groundwater), design rules were simplified, "alternative" methods were avoided, and the selection of nationally determined parameters was reduced.
The paper presents the key changes in relation to the current Eurocode.Publishe
THE USE OF TRACTOR AGGREGATES ON A MEDIUM-SIZED FARM IN ARABLE PRODUCTION
Full text linkThe intensity of use and work output of tractors and implements were investigated using the example of a medium-sized family farm. The farm is located in central Serbia and cultivates 44 ha of arable land for livestock farming. The farm has 3 tractors, 22 attachments, a self-propelled combine harvester for harvesting small grains, and a combine harvester for silage preparation. In the 2021/22 production year, the tractors were used for a total of 376.92 hours, namely 170.58 hours for the FIAT 78 tractor, 144.17 hours for the IMT-539, and 62.17 hours for the IMT-558. Tractors and attachments were most frequently used to produce wheat (10 h ha-1), silage maize (9.94 h ha-1), soybeans (9.72 h ha-1), oats (9.17 h ha 1), barley (8.58 h ha-1) and grain maize (8.17 h ha-1). The greatest engagement of mechanization was in basic tillage 31%, pre-sowing preparation with a rotary harrow 25%, and the least in spreading mineral fertilizers, protecting plants from diseases, and pests, and destroying weeds 8% of the total working time.Publishe
Tribological Application of Nanocomposite Additives in Industrial Oils
Full text linkThe demand for an improvement in the tribological properties of lubricants used in various industrial plants, the automotive industry, and other power transmissions has resulted in the development of a whole family of improved lubricants based on nanotechnology. Especially important are nanotube additives, which significantly improve the tribological properties of lubricants, primarily by reducing the friction coefficient and wear of the coupled elements but also by reducing the temperature load and increasing the stability of the oil film between the lubricated surfaces. The properties of nanotube-based additives were further improved using elements such as metal oxides and compounds based on titanium, molybdenum, aluminum, etc. This paper presents the results obtained in the field of research and application of nanocomposite lubricant additives. It also gives a partial comparative analysis of the research conducted in this field. The primary goal of this paper is to analyze the research results in the field of the application of nanotubes in lubricants and to indicate the importance of their application, such as improving the tribological properties of machines and reducing power losses. Furthermore, this paper shows the negative impact of nanoparticles on the environment and human health and the costs of applying some types of nanoparticles.Publishe
CONDITIONAL CLAUSES WITH THE CONJUNCTION AKO IN THE 19TH CENTURY SERBIAN LEGAL LANGUAGE
No full textThe aim of the paper is to study the status of conditional subordinate clauses introduced by the conjunction ako in the administrative-legal register of the 19th century Serbian language. The corpus consists of Constitutions introduced during the 19th and early 20th centuries (1835, 1838, 1869, 1888, 1901), as well as of laws from the Collection of Laws,
Regulations and Decrees from the Principality of Serbia. In the analysis we used a combination of semantic-syntactic methods and methods from historical linguistics and functional
stylistics. We have found that conditional clauses with the conjunction ako occur mostly
in law texts, which is a characteristic of both medieval and contemporary Serbian legal
language. The subordinate clause with the conjunction ako represents the ideal surface representation of the deep form of the legal norm. This type of subordinate clause is primarily noted in preposition, and is rarely found in interposition and postposition. It was used with
correlatives, especially in the first part of the 19th century (to, taj, takov, takova, takovo,
zato, u slučaju). On the other hand, we have also found examples without the correlatives.
Sometimes this type of clause can be transformed into a relative clause with the antecedent
embedded into the structure of the relative clause. The tenses used in both the subordinate
and the main clause vary according to the semantic parameter: regular – irregular (unexpected). In the subordinate clause the future tense, imperative, modal verbs and present
tense were used, while past tense and the future form with the verb budem were rarely usedhttps://doi.fil.bg.ac.rs/volume.php?pt=journals&issue=sj-2024-29-1&i=22Publishe
Проблем три тела и стабилна решења
Full text linkУ физици за средњошколце решавање проблема три тела се најчешће провлачи само као појам и наводи се као нерешив. Међутим и ако је аналитички заиста тренутно остао нерешив, развојем рачунара омогућено је да се проблем решава нумерички са задовољавајућим нивоом прецизности. Ово омогућава да се овакви системи детаљније истраже и да се опише њихово необично понашање. У раду биће дат један класичан пример проблема три тела као и нумеричка решења за одређене параметре. Биће показано да постоје конфигурације та три тела које дају стабилан систем, као и колико су ти системи осетљиви на промену. Ово може дати ученицима увид у необично функционисање компелексних система, нелинеарне динамике и хаоса. Такође, може дати и увид у модеран приступ решавању проблема у физици.Publishe