Experimental and numerical thermo - mechanical analysis of friction stir welding of high - strength alluminium alloy

This paper presents experimental and numerical analysis of the change of temperature and force in the vertical direction during the friction stir welding of high-strength aluminium alloy 2024 T3. This procedure confirmed the correctness of the numerical model, which is subsequently used for analysis of the temperature field in the welding zone, where it is different to determine the temperature experimentally. 3D finite element model is developed using the software package Abaqus; arbitrary Lagrangian-Eulerian formulation is applied. Johnson-Cook material law and Coulomb's Law of friction are used for modelling the material behaviour. Temperature fields are symmetrical with respect to the welding line. The temperature values below the tool shoulder, i.e. in the welding zone, which are reached during the plunge stage, are approximately constant during the entire welding process and lie within the interval 430-502 degrees C. The temperature of the material in the vicinity of the tool is about 500 degrees C, while the values on the top surface of the welding plates (outside the welding zone, but close to the tool shoulder) are about 400 degrees C. The temperature difference between the top and bottom surface of the plates is small, 10-15 degrees C

Optimization of cultivation medium for the production of antibacterial agents

Optimization of the cultivation medium for production of antibiotic effective against pathogenic bacteria Staphylococcus aureus using strain of Streptomyces spp. isolated from the environment represents the aim of this study. After the biosynthesis, the medium was analyzed by determining residual sugar and nitrogen, and the antibiotic activity was determined using diffusion-disc method. Experiments were carried out in accordance with the Box-Behnken design, with three factors varied on three levels (glucose: 10.0, 30.0 and 50.0 g/L; soybean meal: 5.0, 15.0 and 25.0 g/L; phosphates: 0.5, 1.0 and 1.5 g/L) and for the optimization of selected parameters Response Surface Methodology was used. The obtained model with the desirability function of 0.985 estimates that the lowest amounts of residual sugar (0.89 g/L) and nitrogen (0.24 g/L) and the largest possible inhibition zone diameter (21.88 mm) that with its antibiotic activity against S. aureus creates the medium containing 10.0 g/L glucose, 5.0 g/L soybean meal and 1.04 g/L phosphates

Regulating market-led urban expansion in the new master plans of Sofia and Belgrade

Like most European cities, cities in South-east Europe (SEE) have been growing throughout the 20th century, however, since the end of the 1980s, the mechanisms of urban growth and expansion have changed radically: from development fully determined by central planning to market-led urban development. This paper examines how planning in large SEE cities is coping with the challenge to balance the action of the market and achieve planning goals relating to the form of urban growth and expansion. As case studies we analyse the master plans of Sofia and Belgrade and their implementation. We have two research questions: first, whether planning in the two cities has considered the role of the market when defining its objectives, measures and solutions regarding the forms of urban growth and the development of in suburban areas, and, second, whether planning has been able to influence the market or cooperate with it in order to achieve its objectives in suburban development.Rad je rezultat i bilateralnog istraživačkog projekta "Support to Process of Urban Development in Serbia" (SPUDS), No. 160503 [http://p3.snf.ch/Project-160503], 2015-2018, u okviru SCOPES programa uz finansijsku podršku Swiss National Science Foundation

Određivanje brzine korozije metala šava u zavarenom spoju pomoću elektrohemijskih tehnika

To determine corrosion rate of the base metal and weld metal were applied electrochemical techniques: linear polarization resistance, linear sweep voltammetry and electrochemical impedance spectroscopy. The samples were obtained by arc welding steel boiler plate using coated basic electrode. Factory electrode and electrodes, which are produced in the laboratory thinly and thick coated basic electrodes, were used for welding. It was found that the corrosion rate of the weld metal was greater than the corrosion rate of the base metal. The corrosion rate of weld metal obtained by thinly coated electrodes is less than the corrosion rate of weld metal obtained by thick coated basic and factory-coated electrodes. The corrosion rates, determined by different electrochemical techniques are in agreement.Za određivanje brzine korozije osnovnog metala i metala šava u zavarenom spoju primenjene su elektrohemijske tehnike: linearna polarizaciona otpornost, voltametrija sa linearnom promenom potencijala i elektrohemijska impedansna spektroskopija. Uzorci za ispitivanje dobijeni su elektrolučnim zavarivanjem čeličnog kotlovskog lima, uz upotrebu obloženih bazičnih elektroda. Pri zavarivanju je korišćena fabrička elektroda i elektrode koje su proizvedene u laboratorijskim uslovima (tanko obložena i debelo obložena bazična elektroda). Utvrđeno je da je brzina korozije metala šava veća od brzine korozije osnovnog metala. Brzina korozije metala šava dobijenog pomoću tanko obložene elektrode je manja od brzine korozje metala šava dobijenog pomoću debelo obložene i fabričke elektrode. Vrednosti za brzinu korozije, određene različitim elektrohemijskim tehnikama, su u saglasnosti

Measurement of 60CO gamma radiation induced attenuation in multimode step-index POF at 530 nm

As optical fibres are used ever more extensively in space applications, nuclear industry, medicine and high-energy physics experiments, it has become essential to investigate the influence of ionizing radiation on their characteristics. In this work, the radiation-induced attenuation at 530 nm is investigated experimentally in step-index multimode polymethyl-methacrylate plastic optical fibres exposed to low dose-rate gamma radiation. Cumulative doses ranged from 50 Gy to 500 Gy. The radiation induced attenuation has been empirically found to obey the power law RIA= aDb, where D is the total radiation dose and a and b are the constants determined by fitting

Change of temperature and vertical force during friction stir welding

Cilj rada je analiza promene vertikalne sile i temperature tokom procesa zavarivanja trenjem mešanjem (FSW) legura aluminijuma visoke čvrstoće (2024 T3). FSW postupak je složen nelinearan proces praćen velikim plastičnim deformacijama, visokim temperaturama i plastičnim tečenjem materijala u zoni zavarivanja. To je postupak spajanja materijala u tzv. čvrstoj fazi, kombinovanim delovanjem toplote i mehaničkog rada. Analiza promene sile i temperature tokom procesa zavarivanja omogućava bolje razumevanje i kontrolu samog procesa. U radu je analizirana i praćena promena sile u vertikalnom pravcu pomoću dinamometra i promena temperature na gornjoj površini radne ploče u blizini čela valjka alata pomoću termovizijske kamere.The aim of this paper is to analyze changes of vertical force and temperature during friction stir welding process of high strength aluminum alloys (2024 T3). FSW process is a complex nonlinear process accompanied by large plastic deformation, high temperatures and plastic material flow in the welding zone. It is the procedure of material connecting in the so-called solid phase, through the combined action of heat and mechanical work. Analysis of force and temperature changes during the process of welding allows better understanding and control of the process. This paper analyzes the change of force in the vertical direction using a dynamometer and temperature changes on the upper surface of the working panel near the tops of the roller tool using thermal imaging cameras

Могућност примене експлозива amonex у заваривању разнородних челичних плоча и утицај количине експлозива на квалитет завареног споја

Детонацијом експлозивних материја ослобађа се велика количина енергије у врло кратком времену, која се примењује за различите врсте корисног рада, како у привредне, тако и у војне сврхе. Поред приме- не експлозивних материја у убојним средствима и за рушење у рударству и грађевинарству, енергија детонације нашла је примену и у заваривању и об- ради метала. Применом енергије настале детонационим разлагањем експло- зива могуће је извршити заваривање метала, обликовање, резање, утицати на повећање његове чврстоће итд. Технологија заваривања експлозивом почела се развијати половином 20. века, и данас је заступљена за израду делова ва- здухоплова, наоружања и војне опреме, оклопних плоча са повећаном бали- стичком заштитом, специјалних цистерни, топлотних измењивача, посуда под притиском,специјалних индустријских резних алата и свих других производа који се не могу израдити неким другим конвенционалним поступком обраде металних материјала. Такође, значајна предност ове технологије је могућност израде вишеслојних материјала великих површина. Заваривање метала експлозијом остварује се као последица веома брзог судара метала под дејством продуката детонације, уз појаву високог притиска и пластичних деформација у облику таласа на граници споја и адијабатског локалног загревања површинских слојева металних материјала. У оквиру овог рада анализирана је могућност примене привредног екс- плозива Amonex у заваривању плоча од опружног челика 51CrV4 и конструк- ционог челика S355 J2. За изабрани експлозив Amonex, који је произведен у Корпорацији ТРАЈАЛ, претходно су измерене насипна густина и брзина дето- нације, где је коришћена метода мерења времена између две тачке у експлозив- ном пуњењу коришћењем електронског бројача са оптичким давачима. Током свих реализованих експеримената коришћена је иста поставка плоча. Коришћене су плоче димензија 150×200 mm. Горња плоча од опружног челика ознаке 51CrV4 дебљине 3 mm, која је убрзавана енергијом експлозије, била је постављена паралелно са непомичном доњом плочом израђеном од кон- струкционог челика ознаке S355 J2 дебљине 10 mm. Почетно одстојање између плоча износило је 4 mm, где су коришћена по 4 ивично постављена одстој- ника израђена од пластичне масе поли(метил метакрилат), скраћено PMMA. Коришћена су експлозивна пуњења три различите масе експлозива Amonex, који је у одговарајућем слоју био равномерно слободно насут на горњу плочу. Таквим експериментима омогућено је одређивање зависности квалитета зава- реног споја од масе примењеног експлозива. За одређивање квалитета завареног споја примењене су две технике ис- питивања без разарања: метода са течним пенетрантима MR68C и испитивање ултразвучним дефектоскопом ознаке Phasor XS. Потом су плоче исечене за даљу анализу, где су извршени микроскопски преглед пресека заварених споје- ва помоћу оптичког микроскопа типа Leitz Metalloplan, опремљеног камером DFC 295 и софтвером за обраду слике LAS 4.3.1. Ударна жилавост споја из- међу експлозијом заварених плоча испитана је на одговарајуће припремљеним епруветама помоћу Шарпијевог клатна ознаке Schenck trebel. Резултати испитивања показали су да експлозив Amonex може наћи примену у експлозивном заваривању, a најбољи резултати постигнути су код узорка завареног средњом количином експлозива. Код овог узорка добијене су највише вредности ударне жилавости на Шарпијевом клатну, док је код трећег завареног споја дошло до наглог пада ударне жилавости услед формирања међуслоја, растопљене фазе на споју, што је потврђено микроскопском ана- лизом. Ултразвучна дефектоскопија је показала да средњи узорак има највећу површину завареног споја, а узорак са најмање експлозива најмању површину завареног споја.Detonation of explosive substances releases a large amount of energy in a very short time, which is used for various types of useful work, both for economic and military purposes. In addition to the use of explosive substances in ordnance and for demolition in mining and construction, detonation energy has found its application in welding and metal processing. By applying the energy generated by the detonation of explosives, it is possible to weld metal, shape it, cut it, increase its solidity, etc. Explosion welding technology began to develop in the middle of the 20th century, and today it is used for the production of aircraft parts, weaponsand military equipment, armour plates with increased ballistic protection, special tanks, heat exchangers, pressure vessels, special industrial cutting tools and all other products which cannot be produced by any other conventional method of processing metal materials. Also, a significant advantage of this technology is the possibility of manufacturing multi-layer materials of large surfaces. The explosion welding of metals is done as a result of the very fast collision of metals under the effect of detonation products, with the appearance of high pressure and plastic deformations in the form of waves at the fusion line and adiabatic local heating of the surface layers of metal materials. In this paper, the possibility of using commercial explosive Amonex for the welding of plates made of 51CrV4 spring steel and S355 J2 structural steel was analysed. For the selected explosive Amonex, which was produced by TRAJAL Corporation, the bulk density and detonation velocity were previously measured, whereby the method of measuring the time between two points in the explosive charge using an electronic counter with optical sensors was used. During all conducted experiments, the same arrangement of plates was used. Plates of dimension 150×200 mm were used. The upper plate of 3 mm thick 51CrV4 spring steel, which was accelerated by the energy of the explosion, was placed parallel to a stationary lower plate made of 10 mm thick S355 J2 structural steel. The initial distance between the plates was 4 mm, where 4 edge spacers made of plastic mass poly(methyl methacrylate), abbreviated PMMA, were used. Explosive charges of three different masses of Amonex explosive were used, which was evenly and freely poured in the appropriate layer on the upper plate. Such experiments made it possible to determine the dependence of the quality of the welded joint on the mass of the explosive used. To determine the quality of the welded joint, two non-destructive testing techniques were applied: the method with liquid penetrants MR68C and testing with an ultrasonic defectoscope Phasor XS. Then the plates were cut for further analysis, whereby the microscopic examination of the sections of the welded joints was performed using the Leitz Metalloplan optical microscope equipped with a DFC 295 camera and LAS 4.3.1 image processing software. The impact toughness of the joint between the explosion-welded plates was tested on appropriately prepared test tubes using the Charpy pendulum Schenck trebel. The test results showed that Amonex explosive can be used in explosion welding, and the best results were achieved with a sample welded with a medium amount of explosive. In this sample, the highest values of impact toughness were obtained on the Charpy pendulum, while in the third welded joint there was a sudden decrease in impact toughness due to the formation of an intermediate layer, a molten phase at the joint, which was confirmed by microscopic analysis. Ultrasonic defectoscopy showed that the middle sample had the largest area of the welded joint, and the sample with the least explosive had the smallest area of the welded joint

DES-ncRNA: A knowledgebase for exploring information about human micro and long noncoding RNAs based on literature-mining

Noncoding RNAs (ncRNAs), particularly microRNAs (miRNAs) and long ncRNAs (lncRNAs), are important players in diseases and emerge as novel drug targets. Thus, unraveling the relationships between ncRNAs and other biomedical entities in cells are critical for better understanding ncRNA roles that may eventually help develop their use in medicine. To support ncRNA research and facilitate retrieval of relevant information regarding miRNAs and lncRNAs from the plethora of published ncRNA-related research, we developed DES-ncRNA (www.cbrc.kaust.edu.sa/des_ncrna). DES-ncRNA is a knowledgebase containing text- and data-mined information from public scientific literature and other public resources. Exploration of mined information is enabled through terms and pairs of terms from 19 topic-specific dictionaries including, for example, antibiotics, toxins, drugs, enzymes, mutations, pathways, human genes and proteins, drug indications and side effects, mutations, diseases, etc. DES-ncRNA contains approximately 878,000 associations of terms from these dictionaries of which 36,222 (5,373) are with regards to miRNAs (lncRNAs). We provide several ways to explore information regarding ncRNAs to users including controlled generation of association networks as well as hypotheses generation. We show an example how DES-ncRNA can aid research on Alzheimer disease and suggest potential therapeutic role for Fasudil. DES-ncRNA is a powerful tool that can be used on its own or as a complement to the existing resources, to support research in human ncRNA. To our knowledge, this is the only knowledgebase dedicated to human miRNAs and lncRNAs derived primarily through literature-mining enabling exploration of a broad spectrum of associated biomedical entities, not paralleled by any other resource

Evaluacija antioksidativnog potencijala gljive Cordyceps sinensis in vitro

Objective. Prooxidants and antioxidants affect the oxidative balance at the intracellular level. Oxidative stress is a consequence of the overproduction of prooxidants and is caused by disturbances in the balance of oxidative reduction processes. Non-enzymatic low molecular weight antioxidants can be introduced into the body through food. Cordyceps sinensis (C. sinensis) is a medicinal fungus used in traditional Chinese medicine, with rich content of vitamins, various polysaccharides, and many nucleosides. The aim of this study is to evaluate the antioxidant capacity of the dietary supplement C. sinensis. Methods. The capacity of the hydroxyl radical scavenger activity, the total antioxidant activity of FRAP (Ferric Reducing Antioxidant Power) and the DPPH (2,2-diphenyl-1picrylhydrazyl) scavenger activity were measured. Results. C. sinensis at the tested concentrations of 0.0078-2.00 mg/mL had a pronounced ability to remove hydroxyl radicals with IC50 of 0.5 mg/mL, while at concentrations (0.0078-10.00 mg / mL) it showed a moderate reducing ability. C sinensis showed no ability to remove DPPH radicals. Conclusion. C. sinensis effectively removes hydroxyl radicals, for which the body does not have adequate antioxidant protection, so we can include it in the group of free radical scavengers.Cilj. Prooksidansi i antioksidansi utiču na oksidativnu ravnotežu na intracelularnom nivou. Oksidativni stres je posledica prekomerne produkcije prooksidanasa i nastaje usled poremećaja u ravnoteži oksido-redukcionih procesa. Neenzimski antioksidansi male molekulske mase mogu se uneti u organizam preko hrane. Cordyceps sinensis (C. sinensis) lekovita je gljiva koja se koristi u tradicionalnoj kineskoj medicini, ima bogat sadržaj vitamina, raznih polisaharida, kao i mnogih nukleozida. Cilj istraživanja ove studije bila je evaluacija antioksidativnog kapaciteta dijetetskog suplementa C. sinensis. Metode. Mereni su kapacitet "skevindžer" aktivnosti hidroksil radikala, ukupna antioksidativna aktivnost primenom FRAP (Ferric Reducing Antioxidant Power) metode i DPPH (2,2-difenil-1-pikrilhidrazil) - skevindžer aktivnost. Rezultati. C. sinensis je u ispitivanim koncentracijama 0,0078-2,00 mg/mL imao izraženu sposobnost uklanjanja hidroskil radikala, čija je IC50 iznosila 0,5 mg/mL, dok je u koncentracijama 0,0078-10,00 mg/mL pokazao umerenu redukcionu sposobnost. C. sinensis nije pokazao sposobnost uklanjanja DPPH radikala. Zaključak. C. sinensis efikasno neutrališe hidroksilne radikale, za koje organizam nema adekvatnu antioksidativnu zaštitu pa ga možemo uvrstiti u grupu potencijalnih protektora od slobodnih radikala

The microbiome-gut-brain axis in multiple sclerosis

The microbiome-gut-brain axis (MGBA) represents a close two-way relationship between the gut and the central nervous system (CNS) mediated by the immune system, the enteric nervous system (ENS), the vagus nerve, and the gut microbiome. Gut microbes, including bacteria, fungi, and viruses, can communicate with the CNS and modulate the physiology of the brain in health and disease, which marks them as an important MGBA factor. It is becoming increasingly evident that gut microbiome dysbiosis is implicated in the onset and severity of different neurodegenerative and psychiatric diseases including multiple sclerosis (MS). MS is a chronic disease of the CNS associated with different genetic and environmental risk factors. Neuroinflammation and demyelination in the brain and the spinal cord are hallmark features of MS. The accumulating evidence shows that the MGBA, although a relatively new concept, has an important role in MS. Therefore, the purpose of this article is to review recent research on the gut-brain connection in MS, and to highlight MS-associated gut microbiota constituents and the role of bacterial metabolites in MS