Humor u doba COVID-19 pandemije

The research is focused on the very beginning of the COVID-19 pandemic in Croatia – March 2020. The subject of the research are humorous messages related to the pandemic. By combining quantitative and qualitative methods, this research showed how the interviewed respondents experienced the received humorous content related to the coronavirus and what content characteristics of the humorous messages were detected through the content analysis.Istraživanje je usmjereno na sam početak pandemije COVID-19 u Hrvatskoj – ožujak 2020. Predmet istraživanja su humoristične poruke povezane s pandemijom. Kombinacijom kvantitativne i kvalitativne metode, ovo istraživanje je pokazalo kako su ispitanici intervjua doživjeli primljeni humoristični sadržaj vezan uz korona virus te kakve su sadržajne karakteristike humorističnih poruka detektirane kroz analizu sadržaja

Energija i kvalitet obrade abrazivnim vodenim mlazom

Obrada abrazivnim vodenim mlazom je jedna od nedavno razvijenih nekonvencionalnih proizvodnih tehnologija. Danas se sve više koristi u industriji zahvaljujući svojim mnogobrojnim prednostima nad ostalim tehnologijama rezanja. Međutim, da bi obrada abrazivnim vodenim mlazom našla što širu primenu u industriji i da bi se unapredile njene performanse, neophodno je razumevanje brojnih ulaznih i izlaznih parametara ove obrade, kao i uticaj ulaznih parametara na izlazne parametre. U doktorskoj disertaciji: ―Energija i kvalitet obrade abrazivnim vodenim mlazom― predloženi su novi modeli koji definišu uticaj ulaznih parametara obrade abrazivnim vodenim mlazom (radnog pritiska, brzine kretanja rezne glave, protoka abraziva i rastojanja rezne glave od predmeta obrade) na izlazne parametre kao što su širina reza, nagib reza, hrapavost obrađene površine. Predloženi modeli su dobijeni na osnovu opsežnih eksperimentalnih istraživanja. Takođe, dat je nov pristup definisanju geometrije prednje linije reza u zavisnosti od pojedinih, najznačajnijih ulaznih parametara. Na osnovu energije abrazivnog vodenog mlaza i zapremine uklonjenog materijala predmeta obrade, određena je specifična energija obrade za ispitivani materijal. Na osnovu formiranih modela za definisanje putanje abrazivnog vodenog mlaza kroz materijal predmeta obrade, odnosno prednje linije reza, energije abrazivnog vodenog mlaza i specifične energije obrade abrazivnim vodenim mlazom, dobijen je model za određivanje sile rezanja i otpora rezanja pri obradi abrazivnim vodenim mlazom. Rezultati dobijeni pomoću modela su upoređeni sa eksperimentalno dobijenim rezultatima. Model je pokazao dosta dobro poklapanje sa sprovedenim eksperimentom. Sva saznanja, do kojih se došlo tokom izrade doktorske disertacije, ukazuju na činjenicu da od energije abrazivnog vodenog mlaza i specifične energije obrade zavise izlazni parametri koji su analizirani. Ova činjenica može poslužiti kao osnova za buduća istraživanja u oblasti obrade abrazivnim vodenim mlazom.Abrasive water jet machining is one of the recently developed non-conventional production technologies. Due to its many advantages over other cutting technologies it is often used in industry. However, in order to find a wider application of the abrasive water jet machining in industry and improve its performance, it is necessary to perceive a number of input and output parameters of the abrasive water jet machining process, and the impact of the input parameters on the output parameters. This doctoral dissertation, "The energy and quality of abrasive water jet machining", proposes new models for defining the influence of the input parameters of the abrasive water jet machining (operating pressure, traverse speed of cutting head, abrasive flow rate and distance of the cutting head of the workpiece) on the output parameters, such as the width of cut, cut taper, surface roughness. These models are based on extensive experimental investigations. The doctoral dissertation, also, gives insight into the new model for defining the geometry of the front - line of cut, depending on the most important input parameters. Based on the energy of the abrasive water jet and the volume of the removed material of the workpiece, specific energy of the abrasive water jet machining for the tested material is determined. According to developed model for defining the trajectory of the abrasive water jet through the workpiece, and the model for defining the front line of cutting, abrasive water jet energy and specific energy of the abrasive water jet machining, a model for determining the cutting reaction force for the abrasive water jet machining has been developed. The results obtained by the model were compared with the experimental results. The model showed quite good agreement with the conducted experiments. Entire knowledge, achieved while drafting of this doctoral dissertation, indicates that the energy of the abrasive water jet and specific energy of the abrasive water jet machining affect the output parameters which were analyzed in this doctoral dissertation. This fact can be used as a basis for future research in the field of abrasive water jet machining

Numerical Analysis of the Temperature Field in the Cutting Zone in Continuous and Discontinuous Metal Cutting by Turning

Temperature of cutting is a very important indicator of the cutting process. High specific pressures and high temperatures in the narrow cutting zone result in a drop of hardness of the tool material, the intensification of the abrasion and deformation of the cutting elements, losing the cutting abilities, and finally the failure of the cutting tool. The aim of this paper is to calculate the temperature fields using the existing numerical models for the simulation of thermodynamic processes on the wedge of the cutting tool (based on the finite element method). A special accent is given to the numerical calculation of temperatures in the conditions of continuous and discontinuous turning for specific cutting conditions (processing regime, tool geometry and thermo-mechanical characteristics of the tool materials and workpiece materials) using different simulation models. The Third Wave AdvantEdge software package was used for the simulation of orthogonal turning, and some of the results of the calculations of the temperature fields were compared with the results of experimental measurements

Mijalgični encefalomijelitis - enigma na raskršću medicine

Myalgic encephalomyelitis is a complex, multisystem disease with chronic course significantly affecting patients' quality of life. Physical and mental exertion intolerability, muscle pain, and sleep problems are the main features accompanied often with cognitive inefficacy and vegetative symptoms. Prevalence is 7-3000 per 100,000 adults. It is estimated that 90% of the patients are misdiagnosed. Pathogenesis is still only speculative but current research points to disturbances in the immunological system, inflammatory pathways, autonomic and central nervous system, muscle and mitochondria, as well as alterations of gut microbiota and gut permeability. The onset is typically acute, following an infectious disease. Exertional intolerance lasting for more than six months is an important diagnostic factor. The core features must be moderate to severe and present at least 50% of the time. Diagnostic criteria should be fulfilled and differential diagnosis should be made to exclude other potential pathological conditions or to diagnose comorbidities. Brain magnetic resonance imaging morphometry has shown gray matter atrophy in occipital lobes bilaterally, right angular gyrus, and the posterior division of the left parahippocampal gyrus, consistent with memory problems and potentially with impairment of visual processing. Treatment is still symptomatic and of partial benefit. Symptomatic treatment can include medications for controlling pain and sleep problems, graded exercise and cognitive behavioral therapy. Larger controlled trials are needed to shed more light on this challenging condition.Mijalgični encefalomijelitis je složeno, multisistemsko oboljenje sa hroničnim tokom koje značajno utiče na kvalitet života bolesnika. Slaba tolerancija na fizički i mentalni napor, bolovi u mišićima i problemi sa spavanjem glavne su odlike i često su praćene kognitivnom neefikasnošću i vegetativnim simptomima. Prevalencija je 7-3000 na 100.000 odraslih. Procenjuje se da je 90% ovih bolesnika pogrešno dijagnostikovano. Patogeneza je i dalje samo spekulativna, ali trenutna istraživanja ukazuju na poremećaje u imunološkom sistemu, inflamatornom odgovoru, autonomnom i centralnom nervnom sistemu, mišićima i mitohondrijama, kao i promene mikrobiote i propustljivosti creva. Početak bolesti je tipično akutan i prati infektivnu bolest. Netolerancija napora koja traje duže od šest meseci važan je dijagnostički kriterijum. Osnovne karakteristike moraju biti umerene do teške i prisutne najmanje 50% vremena. Isključivanje drugih mogućih patoloških stanja ili komorbiditetnih dijagnoza zahteva zadovoljavanje dijagnostičkih kriterijuma i diferencijalno dijagnostičko sagledavanje. Morfometrijska snimanja mozga magnetnom rezonancom pokazala su atrofiju sive mase u okcipitalnim režnjevima bilateralno, desnom angularnom girusu i posteriornom levom parahipokampalnom girusu, što može dovesti do problema sa pamćenjem i oštećenja vizuelne obrade informacija. Lečenje je i dalje simptomatsko i samo delimično uspešno. Simptomatski tretman može da uključuje lekove za kontrolu bola i problema sa spavanjem, doziranu fizičku aktivnost i kognitivno-bihevioralnu terapiju. Potrebne su veće studije da bi se razjasnilo ovo medicinsko stanje

Flank wear as a function of cutting time

The paper describes one teaching unit - tool wear, which is studied at laboratory classes in the Metal cutting technology course. Through laboratory classes, students gain practical knowledge. The main goal of this teaching unit is to help students to understand the wear process and to define the parameters that describe the wear process. The most important wear parameter is the width of the flank wear of the tool. By monitoring the changes in the values of this parameter, students can see how the wear process is progressing over time. An end mill was taken as an example. The width of the flank wear was measured at intervals of 5 minutes, at distances of 0.1 mm. Based on the measured values, a diagram of tool flank wear was created. Also, the change in the width of the flank wear depending on the cutting time is shown.Publishe

Uticaj brzine rezanja i dubine reza na geometriju prednje linije reza pri obradi abrazivnim vodenim mlazom

Abrasive water jet machining is an unconventional machining process, which is increasingly being used. It is suitable for cutting complex contoured elements, in all types of materials. The major disadvantages of this machining technique are ununiform quality of the machined surface at different depths of cut, lagging of the cut front of the machined surface from the vertical plane and the phenomenon of striation patterns on the cut surface. The striation patterns on machined surface are the trail of the abrasive water jet through the material, and as such, they represents the cut front. Striation may result in different flaws occurring at cutting closed contours and may cause irregularities at cutting angles. The objective of this paper was to determine traverse speed and depth of cut effect on the cut front geometry i.e. on the striation geometry. The experiments were carried out on 6 mm and 10 mm thick samples of aluminum alloy AA 6060 (EN AW-6060; ISO AlMgSi). Samples were machined with several traverse speeds. The lagging of the cut front, at different depths of cut, was measured and analyzed. The obtained results enabled us to define the influence of traverse speed on striation geometry.Publishe

Rigid body dynamics in optimization of the machine tool vibroisolation

Modern design of the machine tool treats the suspending parts as a crucial element of the effective vibration isolation. Therefore the suspending items are specifically developed and subjected to extensive tests before being applied on real objects. These elements ensure accurate levelling and appropriate vibration damping. Usually selection of inadequate support element causes intensive disturbing effects in machining. The paper presents dynamics analysis of the machine tool suspended on flexible mountings. The overall analysis is conceived on a rigid body dynamics. This method enables selection of an optimal supporting configuration. Further on such an effective suspension design prevents a need for expensive monitoring of the dynamic characteristics of the mechanical system, i.e. machine tool and supports. The paper explores dynamics of a real, flexibly supported machine tool. Results are obtained with the assistance of the "SUPPORT" software. Finally the theoretical and computational statements are approved throughout extensive site measurements on the machine tool body with appropriate instrumentation

Tehno-ekonomska analiza obrade abrazivnim vodenim mlazom i elektroerozijske obrade žicom

Nowadays, carefully selected technologies for material machining can significantly affect quality of machined surface and the cost of machining. Stainless steels are increasingly used in modern production. Austenitic stainless steels (type AISI 304 including Č 4580) make up over 50% of total world production of stainless steel. Nowadays, several methods for machining of these materials are available in practice. However, some types of machining cause the change in the material properties. Machined surface quality in the function of traverse speed and costs of the stated machining methods has been selected for comparative analysis of the machining methods. This paper presents an analysis of steel machining technology (4580 type of steel) with two different machining methods - abrasive water-jet and wire electrical- discharge machining. In addition, an economic analysis of the two machining methods has been conducted from the cost standpoint.Nerđajući čelici su danas sve više koriste u savremenoj proizvodnji. Od ukupne svetske proizvodnje nerđajućih čelika, čak 50% čine austenitni nerđajući čelici iz grupe AISI 304, u koju spada i čelik Č 4580. Danas je u praksi dostupno nekoliko metoda za obradu ovih materijala. Međutim, kod nekih vrsta obrade dolazi do promene karakteristika ovih materijala. U ovom radu je vršena obrada čelika Č 4580 sa dva različita postupka obrade – abrazivnim vodenim mlazom i elektroerozionom obradom sa žicom. Za uporednu analizu postupaka obrade izabran je kvalitet obrađene površine u funkciji brzine rezanja i troškovi navedenih postupaka obrade

Effect of machining parameters on jet lagging in abrasive water jet cutting

Glavne karakteristike površine obrađene abrazivnim mlazom vode su razlike u hrapavosti površine na vrhu i na dnu reza i pojava zakrivljenih linija-brazgotina koje su karakteristične za sve procese obrade s koncentriranim tokom velike energije. Zakrivljenost ovih linija je posljedica zaostajanja mlaza. Zaostajanje mlaza je uzrok grešaka pri rezanju radijusa i oštrih kutova. Parametri obrade imaju značajan utjecaj na ovu pojavu. Iz tog razloga nužno je poznavati i definirati utjecaj parametara obrade na ovu pojavu. Cilj ovog rada je istražiti utjecaj parametara obrade na zaostajanje mlaza, odnosno geometriju reza. Uzorci od AISI 304 obrađeni su abrazivnim mlazom vode različitim posmičnim brzinama, radnim tlakovima i protocima abraziva. Zaostajanje mlaza mjereno je na 10 mjernih mjesta preko dubine reza. Na temelju tih rezultata, formiran je odnos između zaostajanja mlaza i parametara obrade.The main characteristics of the surface machined with the abrasive water jet are the differences in surface roughness at the top and bottom of the cut and the appearance of curved lines-striations, which are characteristic for all machining processes with the concentrated stream of high energy. The curvature of these lines is the consequence of jet lagging. Jet lagging is the cause of errors in cutting of radius and sharp corners. The machining parameters have a great influence on this phenomenon. Therefore, it is necessary to know and to define the influence of machining parameters on this phenomenon. The aim of this paper is to investigate the effect of machining parameters on the jet lagging, i.e. cut front geometry. The specimens of AISI 304 were machined by the abrasive water jet under varying traverse speeds, operating pressures and abrasive mass flow rates. The jet lagging was measured at ten monitoring points by the depth of cut. Based on these results, the relationship between the jet lagging and machining parameters has been formed

Facet colouring of nestohedra

A proper colouring of a polytope is a surjective function from the set of facetsto a set ofmcolours such that every two facets associated with the same colour areseparated, i.e. have no vertex in common. The chromatic number of a polytope is theminimalmsuch that there exists a proper colouring of its facets inmcolours. Thistalk presents the chromatic numbers of associahedra and some others interestingmembers of the family of nestohedra