Importance and role of fast growing companies: gazelles in modern economies

The importance of small and medium enterprises (SMEs) for the development of national economies is undeniable and it is in many works stand out as a generally accepted position. In this paper, attention is focused at a specific segment of SMEs which comprise particularly dynamic companies that are characterized by fast and steady growth, ability quickly to adapt to market conditions and continuously to function at a high level of performance. These firms are now known as gazelles, the name which was in the 80s of last century first coined by British author David Birch. Gazelles represent relatively small part of total and according to number of studies their share in the total number of companies in national economies is accounting from 3% to the most 5%. Interest for this companies, both at macro level by the creators of economic policy, as well as at micro level by businesses, in recent years is exceedingly increased because of their high potentials for resolving the issue of (un)employment and creating multitude of new products and services and added values which they are created for the society as a whole. In the paper the definitions of these companies are elaborated, the basic features and key factors of their business operation are analyzed, as well as their state (level of development) and their future development prospects in the European Union and the Republic of Serbia. The authors of the paper have used research methods in accordance with the specifics and complexity of the subject of the analysis, relying on the current domestic and international literature and internet sources. The research results clearly showed that gazelles can be an important part of the answer to deep and comprehensive economic and social crisis with which modern societies face today in the world

Fatigue fracture resistance of welded pipes made from high strength steels

Funkcionalnost i sigurnost u eksploataciji su dva bitna zahteva za uspešnu konstrukciju, pa se danas uz zahtev čvrstoće pri projektovanju, mora razmotriti i opasnost od zamornog loma, koja je u velikoj meri zavisna od osobina zavarenih spojeva, kao potencijalnih nosilaca greške. Otkazi zavarenih cevi u naftnoj industriji, nastali kao posledica neotkrivenih grešaka u njihovoj izradi ili usled oštećenja tokom eksploatacije, pored uticaja na pouzdanost i bezbednost u radu, imaju i ekološki uticaj na ţivotnu sredinu. Ovo je podstaklo sprovoĎenje intenzivnih istraţivanja u cilju očuvanja celovitosti cevi u bišotinama i cevovodima. Istraţivanja u okviru ove disertacije imala su za cilj da istraţe ponašanje u slučaju oštećenja usled zamora zavarenih cevi izraĎenih od čelika API J55. Čelici povišene čvrstoće mogu biti prilično osetljivi na nastanak i rast zamorne prsline. Uzimajući u obzir uslove agresivne radne sredine, ovi čelici zahtevaju detaljna istraţivanja njihove otpornosti na zamorni lom i procenu integriteta u navedenim radnim uslovima. Primenom parametara mehanike loma, dobijenih na osnovu eksperimentalnih istraţivanja, izvršena je procena preostalog veka zaštitnih zavarenih cevi sa spoljašnjom aksijalnom površinskom prslinom, izraĎenih od API J55 čelika. Analiziran je istovremeno uticaj opsega napona i vrednosti spoljašnjeg aksijalnog oštećenja na preostali zamorni vek. Jedan od ciljeva ove teze bio je da se istraţe nove metode numeričkog modeliranja rasta prsline, a dobijeni rezultati upravo pokazuju efikasnost primene proširene metode konačnih elemenata – PMKE (Extended Finite Element Metхod - XFEM), kao jedne relativno nove metode, u trodimenzionalnoj simulaciji rasta zamorne prsline na geometriji tipa cevi. Rezultati dobijeni u okviru ove teze ukazuju na značajne mogućnosti primene numeričke simulacije potpomognute eksperimentalnim istraţivanjima u analizi integriteta opreme pod pritiskom.The functionality and safety in exploitation are two important requirements for the successful construction and today, together with the strength requirements, the risk of fatigue fracture, which is largely dependent on the properties of welded joints as potential carriers of errors, must be considered. The failures of the welded pipes in the petroleum industry occurred as a consequence of undetected errors in their design or due to the damage during service, have the impact on the reliability and safety at work, as well as an ecological impact on the environment. This encouraged intensive researches in order to preserve the integrity of pipes in the oil rigs and pipelines. The researches in this thesis were aimed to investigate the behavior in case of damage due to the fatigue of welded pipes made of steel API J55. High strength steels can be quite sensitive to the emergence and growth of the fatigue cracks. Taking into account the conditions and aggressive working environment, these steels require detailed researches of their resistance to the fatigue failure and assess the integrity in the specified operating conditions. Through the application of the fracture mechanics parameters, obtained from experimental research, a residual life of welded protective pipes with an external axial surface crack, made of API J55 steel, was estimated. The impact of the stress range and the value of the external axial damage to the remaining fatigue life were analyzed. One of the goals of this thesis was to investigate new methods of numerical modeling of crack growth, and the results just show the effectiveness of the implementation of the extended finite element method - XFEM, as a relatively new method, in three-dimensional simulation of fatigue crack growth on the pipe geometry. The results obtained in this thesis indicate significant opportunities for the application of numerical simulation, supported by experimental studies, to analyze the integrity of the pressure equipment

Fatigue life prediction of casing welded pipes by using the extended finite element method

The extended finite element (XFEM) method has been used to simulate fatigue crack growth in casing pipe, made of API J55 steel by high-frequency welding, in order estimate its structural integrity and life. Based on the critical value of stress intensity factor KIc, measured in different regions of welded joint, the crack was located in the base metal as the region with the lowest resistance to crack initiation and propagation. The XFEM was first applied to the 3 point bending specimens to verify numerical results with the experimental ones. After successful verification, the XFEM was used to simulate fatigue crack growth, position axially in the pipe, and estimate its remaining life

Elaboration of importance of fast growing companies gazelles: new evidence from Serbia

Small and medium enterprises (SMEs) are one of the key pillars of development of all national economies, both the richest and those less developed. In this paper, attention is focused on the specific segment of SMEs, characterized by rapid and stable growth, ability to quickly adapt to changing market conditions and in the long term to operate at the high performance level. These companies are today known as "Gazelles", a term that was coined by an American author, David Birch. The interest for these companies, both at the macro level of policy creators, as well as at the company level, has grown rapidly in recent years because of their high potential for addressing issues of unemployment, creating a host of new products and services and added value for society as a whole and alike. The paper deals with issues such as definitions and basic characteristics of these companies, the key factors of their business, as well as their level of development in the European Union and the Republic of Serbia

Fatigue life prediction of casing welded pipes by using the extended finite element method

The extended finite element (XFEM) method has been used to simulate fatigue crack growth in casing pipe, made of API J55 steel by high-frequency welding, in order estimate its structural integrity and life. Based on the critical value of stress intensity factor KIc, measured in different regions of welded joint, the crack was located in the base metal as the region with the lowest resistance to crack initiation and propagation. The XFEM was first applied to the 3 point bending specimens to verify numerical results with the experimental ones. After successful verification, the XFEM was used to simulate fatigue crack growth, position axially in the pipe, and estimate its remaining life

Microtensile bond strength of self-etching adhesives to dentin

The aim of this study was to determine micro tensile bond strength of two and one-step self-etching adhesive systems to dentin. 25 intact human third molars were used. Flat surfaces of mid-coronal dentin were exposed and the teeth were divided into 5 groups (n=5). Composite build-ups were made using the following self-etching systems / composite materials: 2-step self-etching system Contax / Ecusphere Carat (DMG), 2-step self-etching system AdheSE / Tetric Ceram (Ivoclar Vivadent), 1-step 2-components self etching system Futurabond NR / Grandio (Voco) and 1-step 1-component self-etching adhesive G Bond / Gradia Direct (GC Corp.). Two-step etch-and-rinse system PQ Clear with Amelogen Universal composite resin (Ultra dent) was used in the control group. Bond strength was assessed with the non-trimming micro tensile technique. Statistical analysis was performed using the 1-way ANOVA, followed by the Tukey test for post-hoc comparisons (p lt 0.05). Investigated self-etching systems showed satisfactory values of micro tensile bond strength to dentin after 24 hours. Two-step self-etching system AdheSE resulted in significantly higher bond strength than all the other groups (p lt 0.001). Micro tensile bond strength of self-etching systems Contax, Futurabond NR and G Bond was comparable to the etch-and-rinse system PQ Clear. .Cilj rada bio je da se odredi jačina veze dvofaznih i jednofaznih samonagrizajućih adhezivnih sistema sa dentinom. Površine dentina su eksponirane na 25 intaktnih trećih molara i zubi su podeljeni u 5 grupa (n=5). Izrađene su kompozitne nadogradnje korišćenjem sledećih samonagrizajućih adheziva / kompozitnih materijala: dvofazni samonagrizajući sistem Contax / Ecusphere Carat (DMG), dvofazni samonagrizajući sistem AdheSE / Tetric Ceram (Ivoclar Vivadent), jednofazni dvokomponentni samonagrizajući sistem Futurabond NR / Grandio (Voco) i jednofazni jednokomponentni samonagrizajući sistem G Bond / Gradia Direct (GC Corp.). Dvofazni adhezivni sistem sa potpunim nagrizanjem PQ Clear sa Amelogen Universal kompozitnim materijalom (Ultradent) korišćen je u kontrolnoj grupi. Jačina veze određena je testom otpornosti mikrouzoraka na kidanje. Rezultati su statistički analizirani jednofaktorskom analizom varijanse (ANOVA) i Tukey testom (p lt 0.05). Ispitivani samonagrizajući sistemi pokazali su zadovoljavajuće vrednosti jačine veze sa dentinom nakon 24 časa. Jačina veze dvofaznog samonagrizajućeg sistema AdheSE bila je značajno viša nego jačina veze u ostalim grupama (p lt 0.001). Jačine veze samonagrizajućih sistema Contax, Futurabond NR i G Bond nisu se statistički značajno razlikovale od jačine veze sistema sa potpunim nagrizanjem PQ Clear.

Transcatheter stenting of arterial duct in duct-dependent congenital heart disease

Introduction. Critical congenital heart diseases (CHD) are mostly duct-dependent and require stable systemic-pulmonary communication. In order to maintain patency of the ductus arteriosus (DA), the first line treatment is Prostaglandin E1 and the second step is the surgical creation of aortic-pulmonary shunt. To reduce surgical risk in neonates with the critical CHD, transcatheter stenting of DA can be performed in selected cases. Case Outline. A four-month old infant was diagnosed with the pulmonary artery atresia with ventricular septal defect (PAA/VSD). The left pulmonary artery was perfused from DA, and the right lung through three major aortopulmonary collaterals (MAPCAs). A coronary stent was placed in the long and critically stenotic DA, with final arterial duct diameter of 3.5 mm, and significantly increased blood supply to the left lung. After the procedure, the infant’s status was improved with regard to arterial oxygen saturation, feeding and weight gain. During the follow-up, one year later, aortography revealed in-stent stenosis. The left pulmonary artery, as well as the branches, was well-developed and the decision was made to proceed with further surgical correction. Conclusion. Stenting of DA can be an effective alternative to primary surgical correction in selected patients with duct-dependent CHD

Prosthetics in paediatric dentistry

Premature loss of teeth in children may lead to both functional and esthetic problems. Missing teeth in both anterior and posterior regions may cause malfunctions in mastication and proper pronunciation. If the missing teeth are not replaced, further complications may occur, including adjacent tooth migration, loss of alveolar bone, and irregular occlusion. Considering the sensitive nature of children, loss of teeth may cause the development of insecurities and low self esteem problems. Due to dynamic nature of growth in children and adolescents, prosthetic appliances must not hinder development of orofacial system, and must meet adequate esthetic and functional standards. Dental prosthetic appliances in paediatrics must be planned with respect to the special conditions that led to tooth loss or damage. Multi-disciplinary approach is needed, under constant supervision of paediatric dentist and orthodontist, as well as regular checkups with clinical and radiographical examinations

Kliničko ispitivanje kompozitnih zalivača fisura

Sistemic fluoride ingestion has been found to be more effective in its caries- reducing benefits on the smooth surfaces than on the pit and fissures. A greater vulnerability to pit and fissure caries determines the need for occlusal surface specific protection. The objective of this study was to investigate clinical effectiveness of 5 different composite sealants during an 18- month observation period. Tested materials were: Superlux Seal-opak (composite with filler particles), Superlux Seal-transparent Estiseal and Fissurit (clear), and Fissurit F (composite with fluoride). They were evaluated according to modified Cvar&Ryge criteria for: retention (R), marginal adaptation (MA), marginal discoloration (MD), surface texture (ST), and secondary caries (SC). The materials were applied in 87 children 6-7 years of age, on 215 first permanent molars, two different materials for each patient. The results were tested for statistical significance by .2 and Fisher's T-test. The results showed good clinical performance of all tested materials with no statistically significant differences. High effectiveness in occlusal caries prevention rated from 97,30% for Fissurit F, and 98% for Superlux Sealopak, to 100% for all other tested sealants. Pit and fissure sealing is an effective prophylactic measure which should be part of the preventive program.Sistemska primena fluorida značajno je doprinela smanjenju incidence karijesa glatkih površina zuba, ali ne i fisura i jamica. Specifičnost okluzalne morfologije zahteva dodatnu profilaktičku meru u vidu zalivanja fisura i jamica specijalno formulisanim materijalima. Cilj ovoga rada bio je ispitivanje kliničke efikasnosti 5 različitih kompozitnih materijala za zalivanje fisura u opservacionom periodu od 18 meseci. Testirani su sledeći materijali, predstavnici tri podvrste kompozitnih zalivača: Superlux Sealopak, (opakni, sa puniocem); Superlux Seal-transparent, Estiseal, i Fissurit (transparentni) i Fissurit F (sa fluorom). Modifikovanim Cvar&Ryge kriterijumima praćeni su retencija (R), marginalna adaptacija (MA), ivična prebojenost (IP,)površinska hrapavost (PH), i pojava sekundarnog karijesa (SK). U ispitivanje je uključeno 87 dece uzrasta 6-7 godina. Svakom pacijentu su na prve stalne molare aplikovana po dva različita materijala na ukupno 215 zuba. Na kraju opservacionog perioda svi testirani materijali pokazali su dobre kliničke osobine bez značajnosti statističkih razlika testiranih.2 i Fisherovim T-testom i visok stepen zaštite od karijesa (od 97,30% za Fissurit F, 98% za Superlux Seal-opak,do 100% za ostale ispitivane materijale). Zalivanje fisura je efikasna profilaktička mera i treba da bude sastavni deo preventivnog programa

Mechanical properties of welded pipes produced by high frequency welding of the steel API J55

Izbor čelika, dimenzija i načina proizvodnje zaštitnih zavarenih cevi je deo procesa konstruisanja, jer je u uskoj vezi sa funkcijom cevi kao konstrukcijske celine u određenim uslovima eksploatacije za predviđeni vek trajanja. Kvalitet zavarenih spojeva u procesu proizvodnje cevi definiše se karakteristikama koje one moraju posedovati da bi zadovoljile određene zahteve, što se postiže izborom odgovarajućih postupaka i parametara zavarivanja, sprovođenjem programa kontrole svih tehnoloških operacija u njihovoj izradi i mehaničkim i tehnološkim ispitivanjima otpornosti i deformacije osnovnog materijala i zavarenih spojeva cevi. U radu su prikazani rezultati ispitivanja mehaničkih osobina uzdužno zavarenih cevi, izrađenih visokofrekventnim kontaktnim zavarivanjem od čelika povećane čvrstoće API J55.Selection of the steel, dimensions and manufacturing methods for protective welded pipes is part of the design process, because it is closely related to the function of tube construction as a whole under certain conditions, for a calculated service life. The quality of welded joints in the process of tubes production is defined by characteristics that they must have to meet certain requirements, which are achieved by choosing appropriate procedures and welding parameters, by controlling all unit operations in their preparation and mechanical and engineering stress and strain tests and base material of welded joints. This paper presents the results of the mechanical properties of longitudinally welded pipes. Casing welded pipe intended for oil and gas wells are made by high frequency contact welding of steel API J55, with increased strength