Stability Analysis of Steel Welded Tubes Forming Process Using Numerical Simulations

In this paper, the research results of the stability of steel welded tubes forming process are presented. The aim of this research is to determine influence of geometrical and tribological parameters on stability of the process and to determine optimal values of influential process parameters. A research plan with variation of influential parameters was made, on the basis of which experimental and numerical experiments were performed. Tube forming was performed in one operation in a two-part tool made of hard metal by a combination of widening and narrowing. The geometrical factors observed during experiments are length, outer diameter and thicknesses of steel welded tube as a billet. Friction conditions in contact between tool and tubular workpiece are considered in two cases, the first one when standard machine oil is used as a lubricant and the second one when tube billet surface is phosphated. Based on results of experiments, influencing factors on stability of tube forming process were analysed and optimal production technology was recommended, including optimal values of influencing factors. Results obtained by experimental research were confirmed through numerical experiments based on finite element method

Gravitational microlensing of AGN dusty tori

We investigated the gravitational microlensing of active galactic nucleus dusty tori in the case of lensed quasars in the infrared domain. The dusty torus is modeled as a clumpy two-phase medium. To obtain spectral energy distributions and images of tori at different wavelengths, we used the 3D Monte Carlo radiative transfer code SKIRT. A ray-shooting technique has been used to calculate microlensing magnification maps. We simulated microlensing by the stars in the lens galaxy for different configurations of the lensed system and different values of the torus parameters, in order to estimate (a) amplitudes and timescales of high magnification events, and (b) the influence of geometrical and physical properties of dusty tori on light curves in the infrared domain. We found that, despite their large size, dusty tori could be significantly affected by microlensing in some cases, especially in the near-infrared domain (rest-frame). The very long time-scales of such events, in the range from several decades to hundreds of years, are limiting the practical use of this method to study the properties of dusty tori. However, our results indicate that, when studying flux ratios between the images in different wavebands of lensed quasars, one should not disregard the possibility that the near and mid-infrared flux ratios could be under the influence of microlensing.Comment: 10 pages, 6 figures, 1 table, MNRAS accepted. V3: corrected values in Table

The Myhrr-exuding tomb of St Symeon of Serbia at Studenica: A fresh look

The latest results of the investigation of the royal tombs at the monastery of Studenica, Serbia, have inspired a reconsideration of the place of burial of some members of the Nemanjić family. There is further evidence that the tomb and sarcophagus of the ktetor, Stefan Nemanja, formed part of the original design for the church. Based on their construction and comparative material, it is assumed that the relics of St Symeon, upon their translation to Studenica, were laid in the sarcophagus from which they exuded myrrh. The myrrh-exuding of St Symeon is looked at against the broader background of cult practice in the Byzantine world. [Projekat Ministarstva nauke Republike Srbije, br. 177003: Srednjovekovno nasleđe Balkana - institucije i kultura]The latest results of the investigation of the royal tombs at the monastery of Studenica, Serbia, have inspired a reconsideration of the place of burial of some members of the Nemanjić family. There is further evidence that the tomb and sarcophagus of the ktetor, Stefan Nemanja, formed part of the original design for the church. Based on their construction and comparative material, it is assumed that the relics of St Symeon, upon their translation to Studenica, were laid in the sarcophagus from which they exuded myrrh. The myrrh-exuding of St Symeon is looked at against the broader background of cult practice in the Byzantine world. [Projekat Ministarstva nauke Republike Srbije, br. 177003: Srednjovekovno nasleđe Balkana - institucije i kultura

Triangles bridge the scales: Quantifying cellular contributions to tissue deformation

In this article, we propose a general framework to study the dynamics and topology of cellular networks that capture the geometry of cell packings in two-dimensional tissues. Such epithelia undergo large-scale deformation during morphogenesis of a multicellular organism. Large-scale deformations emerge from many individual cellular events such as cell shape changes, cell rearrangements, cell divisions, and cell extrusions. Using a triangle-based representation of cellular network geometry, we obtain an exact decomposition of large-scale material deformation. Interestingly, our approach reveals contributions of correlations between cellular rotations and elongation as well as cellular growth and elongation to tissue deformation. Using this Triangle Method, we discuss tissue remodeling in the developing pupal wing of the fly Drosophila melanogaster.Comment: 26 pages, 18 figure

Integrisani pristup konstruisanja u funkciji razvoja nove generacije reznih elemenata za bagere kontinualnog dejstva

Proces kopanja kod bagera kontinualnog dejstva neposredno vrše vedrice sa reznim elementima (rezni zubi i nož vedrice) koji se nalaze na frontu rezanja. Da bi se stenski materijal razorio potrebno je na njega delovati određenom silom, koja zavisi od vrste stenskog materijala, tehnologije iskopavanja, geometrije reznih elementa i dr. Rezni zubi svojom oštricom dospevaju na ograničene površine stenskog materijala i vrše naprezanja dovoljna za njihovo razaranje. Primenom reznih zuba raspoloživa sila rezanja se koncentriše na malu dužinu rezanja, i na taj način se olakšava prodiranje kompletne vedrice u materijal. Razoreni materijal se preko odgovarajućih površina reznih elemenata transportuje u kašiku. Da bi ispravno izvršili svoju osnovnu funkciju, rezni zubi moraju zadovoljiti više zahteva, kao što su povoljna geometrija, visoka otpornost na abrazivno habanje, velika mehanička čvrstoća i žilavost itd. Faktori na koje se mora obratiti pažnja pri konstruisanju su geometrija zuba, dimenzionisanje zuba, izbor materijala, montaža zuba na vedrici I tehnologija njegove izrade. Zbog toga je proces konstruisanja reznih zuba kod bagera kontinualnog dejstva vezan za sledeće probleme: a) Kompleksnost procesa konstruisanja vezana za visok nivo korelacije osnovnih svojstava konstrukcije, zbog čega su krajnji izgled, dimenzije i tehnologija izrade reznih zuba veoma osetljivi na tekuće izmene tokom procesa konstruisanja; b) Veliki uticaj specifičnih zahteva korisnika i težnja unikatnoj proizvodnji, zbog čega je pored fleksibilnosti u tehnologiji izrade, neophodno je obezbediti fleksibilnost u svim fazama realizacije reznih zuba, počevši od rane faze razvoja i procesa konstruisanja; c) Složenost definisanja spoljašnjeg opterećenja i usvajanje odgovarajućih pretpostavki, kao osnova pri proračunu nosivosti i optimizacije oblika reznih zuba; d) Specifičnost tehnologije izrade reznih zuba, koja se ogleda u definisanju velikog broja kompleksnih tehničko-tehnoloških parametara livenja; e) Izrada fizičkog prototipa reznog zuba zahteva značajno vreme pripreme i realizacije, dok je ispitivanje fizičkog prototipa na bageru u eksploatacionim uslovima otežano i zahteva značajne vremenske i finansijske izdatke. Postojeća znanja i odgovarajuća literatura ne objašnjavaju i ne daju preporuke za rešavanje predhodnih problema. Zbog toga ne postoji sistemski pristup, pa se proces konstruisanja izvodi na bazi iskustva i minimalnih poboljšanja postojećih rešenja, koristeći se pri tom grubim pretpostavkama i izvođenjem zaključaka bez ulaženja u suštinu problema. Ovakav pristup predstavlja problem u trenutku kada se želi napraviti iskorak i generisati konstrukciono i tehnološki bolje rešenje reznih elemenata, kao što je to slučaj sa razvojem nove generacije modularnih reznih zuba. U okviru doktorske disertacije razmatrana je problematika uvođenja sistemskog procesa konstruisanja reznih elemenata, kroz koncept integrisanog razvoja proizvoda. Ovakav pristup predstavlja alternativu postojećem stanju procesa razvoja reznih elemenata, koji se na relativno jednostavan način može inkorporirati i primeniti u proizvodnom procesu. Cilj primene integrisanog pristupa konstruisanja je u tome da pre same izrade reznog elementa postoji jasna predstava o tome kako će proizvod izgledati, kako i na koji način će usvojena tehnologija proizvodnje uticati na krajnji kvalitet, kako će se ponašati u radnim uslovima i dr. Takođe, obezbeđuje se prednost koja se ogleda u smanjenju troškova, samim tim što se u većem delu analize tokom konstruisanja koriste CAD/CAE/CAM alati, čime se značajno smanjuje vreme potrebno za testiranja u laboratoriji ili eksploatacionim uslovima. Sa druge strane, smanjuje se vreme od trenutka postavljanja zahteva za proizvodom do njegovog dolaska na tržište, jer se smanjuje broj razvojnih ciklusa, automatskim odbacivanjem nezadovoljavajućih rešenja konstrukcije. Težište ovakvog pristupa se prenosi na konceptualno projektovanje I preliminarno konstruisanje, čime se utiče na kasnije smanjenje broja konstrukcionih izmena I izmena u proizvodnom procesu. Ovakvim pristupom se obezbeđuju osnovni uslovi i realizuje težnja ka unikatnoj proizvodnji reznih elemenata, posebno prilagođenih specifičnim uslovima radne sredine, bageru, vedrici, itd.The process of digging in continuous excavators is directly performed by the buckets with cutting elements (cutting teeth and bucket knife) which are positioned on the front of excavators. In order to destroy rock material, it is necessary to exert sufficient force on it, which is dependent on the type of rock material, digging technology, shape of cutting elements, etc. The edges of cutting teeth settle on limited surfaces of rock material and exert pressure sufficient for their destruction. By the use of cutting teeth the available cutting force is concentrated on a small cutting length, thus facilitating the penetration of the entire bucket into the material. The destroyed material is lifted into the bucket by way of appropriate surfaces of cutting elements. In order to properly perform their basic function, cutting teeth must meet several requirements, such as appropriate geometry, high resistance to abrasive wear, high mechanical strength and resilience, etc. The factors that must be considered when designing are teeth geometry, teeth sizing, selection of materials, installation of the teeth on the bucket and its manufacturing technology. Therefore, the process of designing cutting teeth of continuous excavators involves the following issues: a) The complexity of the design process related to the high level of correlation between basic properties of construction, which is why the final appearance, size and manufacturing technology of cutting teeth are very sensitive to the changes in the design process b) Due to strong influence of specific demands of users and tendency towards unique manufacture, it is necessary to ensure flexibility both in manufacturing technology and at all stages of cutting teeth manufacture, starting with the early stages of development and design process; c) The complexity of defining the external load and adoption of appropriate assumptions as the basis for ascertaining the lifting power and optimizing the shape of cutting teeth; d) The specific technology of cutting teeth manufacture, which is reflected in defining a large number of complex technical and technological parameters of casting; e) Manufacture of a physical prototype of the cutting tooth requires considerable time for preparation and implementation, while the testing of the physical prototype on the excavator in exploitation conditions is difficult and requires both longer period of time and considerable financial expenditures. The existing knowledge and appropriate literature neither explain nor provide recommendations for solving the aforementioned problem. Due to the lack of a systematic approach, the manufacturing process is performed on the basis of experience and minimal improvement of existing solutions, using only rough assumptions and drawing conclusions without addressing the problem itself. This approach presents a problem when a more constructive and technologically advanced solution of cutting elements is to be produced, as is the case with the development of a new generation of modular cutting teeth. The issue addressed in this PhD thesis refers to the introduction of a systematic process of designing cutting elements, through the concept of integrated product development. Such an approach presents an alternative solution to the current state of the development process of cutting elements, which can be incorporated and applied in the production process comparatively easily. The main goal of applying an integrated approach to constructing is to form a clear idea of how the product will look like prior to manufacturing the cutting elements, how the adopted production technology will affect the ultimate quality, how it will function in working conditions, etc. Moreover, the advantage of this approach is reflected in the reduction of costs, on account of the fact that CAD/CAE/CAM tools are used in the major part of the analysis during the design. This significantly reduces the time required for the testing in laboratory or exploitation conditions. On the other hand, there is a reduction in the time starting from the moment of the product demand to its launch on the market, because the number of development cycles is reduced by automatic rejection of unsatisfactory design solutions. The focus of this approach is transferred to the conceptual design and preliminary construction, which affects the later reduction in the number of structural changes and changes in the production process. This approach provides the basic conditions and enables the tendency towards unique production of cutting elements, specifically tailored to the specific conditions of working environment, excavators, bucket, etc

Сriteria for Ваsing Ехрlеtivе („Ехсеssivе“) Negation

Analizirani su problemi vezani za ekspletivnu („suvišnu“) negaciju i posmatrana je mogućna veza između ekspletivne negacije u subordiniranoj vremenskoj klauzi, zatim klauzama bojazni i dvostrukog negiranja pri univerzalnoj negaciji.Тwo problems related to expletive negation (EN) are analyzed in the article: а) possible connection between EN in subordinate temporal clause as in example РіSAĆU DОК (NE) РАDNЕ МRАК (I shall write until dark fals), then in clauses of „fear“ like PLASIM SE DA NIJE KASNO (Ifear that it is (not) late) and twofold negation at universal negation (ТNUN) in sentences like NIKO NIJE DOSАО (Nobody came). b) possible connection mentioned in a) is onwards considered and analyzed as a typological feature of Scrbo-Croatian language, then the other Slavic languages and in comparison to several Indo-European languages. Сonclusion of the analysis brings: the factors that influence the degree of „excessiveness“ of EN, dependence EN on aspectual formalization between the verbs in main and temporal subordinate clause. Finally, several distributive criteria for genuine and pseudo-negation in tempo ral subordinate clause containing EN are found. Problem posed in a) is not resolved because semantic factors constraint the connection between EN and ТNUN, and induct analysis to consider EN and ТNUN as two different typological features

Thermodynamic properties of microorganisms: determination and analysis of enthalpy, entropy, and Gibbs free energy of biomass, cells and colonies of 32 microorganism species

Thermodynamic analysis is an important part of chemical engineering. However, its application in biotechnology has been hampered by lack of data on thermodynamic properties of microorganism biomass. In this paper, a review was made of methods for estimation of thermodynamic properties of biomass, including standard enthalpy of combustion hC⁰, enthalpy of formation hf⁰, entropy s⁰, and Gibbs free energy of formation gf⁰. These parameters were calculated on molar and mass specific basis for 32 microorganism species, including 14 bacteria, 7 yeast and 11 algae species. It was found that hf⁰, s⁰, gf⁰ are, respectively, similar for all the analyzed species, due to the fact that all living organisms have a common ancestor and thus a similar chemical composition. Furthermore, all the analyzed microorganisms have negative hf⁰, originating from partial oxidation of all other elements by oxygen and nitrogen. A brief review was given of microorganism endogenous and growth metabolic rates. Finally, based on the determined thermodynamic properties, entropy of individual E. coli and Pseudomonas cells were determined and entropy of a Pseudomonas colony during its lifespan was calculated and analyzed. Three periods can be distinguished in the existence of a microorganism colony: (a) accumulation period when cell number, mass and entropy increase, (b) steady state period when they are approximately constant, and (c) decumulation period when they decrease

Biothermodynamics of Viruses from Absolute Zero (1950) to Virothermodynamics (2022)

Biothermodynamics of viruses is among the youngest but most rapidly developing scientific disciplines. During the COVID-19 pandemic, it closely followed the results published by molecular biologists. Empirical formulas were published for 50 viruses and thermodynamic properties for multiple viruses and virus variants, including all variants of concern of SARS-CoV-2, SARS-CoV, MERS-CoV, Ebola virus, Vaccinia and Monkeypox virus. A review of the development of biothermodynamics of viruses during the last several decades and intense development during the last 3 years is described in this paper