An analysis of random mechanical failures of bucket wheel excavator

In this article random mechanical failures of bucket wheel excavator at open cast mine "Tamnava Zapad" are analysed. Random mechanical failures of mining equipment may represent an important factor in coal production because these types of failures occur unpredictably. Some of the reasons for the occurrence of such failures are unde-tectable defects, unexplainable causes, and unavoidable failures. In addition, here we have failure of equipment that has a large investment and productivity value. Statistical regularity of the component failure distribution of this system is analysed based on dispatcher's reports about EBS system failures in the period 2003-2011. The proposed distribution is analysed by theoretically, using suitable tests. By using statistical distribution we get the expected uptime of the bucket wheel excavator, for each year, which represents an important factor in maintenance programs and periodic inspections/repairs on bucket wheel excavator and mining components, in general

Extended Schatten norms of graphs and combinatorial applications

У овој докторској дисертацији добијени су неки резултети у области теорије графова и њених примена.In this doctoral thesis we obtained some results in graph theory and its applica- tions. In the rst chapter, we give the review of basic notions and theorems of combinatorial theory of graphs, spectral theory of graphs, random graphs and distribution of their eigenvalues. The most detailed consideration is given to adjacency matrix and properties of its spectrum. In particular, in this dissertation we study Energy of graphs and generalizations of it. Energy of graph is the sum of absolute values of eigenvalues of a graph. Schatten norms of graphs represent p-th degree norm of singular values of graph, and the special cases of this norm for p = 1 corresponds to the Energy of graph. In chapter three of this dissertation we are given the most original scientic contribution. We prove the conjecture of Nikiforov about Schatten norms of graphs when p > 2. First we prove that conjecture is true for some special classes of graph (for trees and strongly regular graph with maximal energy). After that, we prove the conjecture in the general case. Auxiliary theorem obtained in the proof of this conjecture is also an original result which gives a sharp upper bound of sum of quadratic of the largest k singular values of graph. A corollary of this theorem which gives an upper bound for sum of squares of the biggest two singular values of graph can be useful in further research. In the subsection 3.3 we give an original theorem about asymptotic properties of spectrum and thus energy of complement graph for a large values of n. In the subsection 3.4 we calculate a mean of p-th degree of singular values and upper bound of geometric mean of almost all graphs. The last chapter shows relation between combinatorial theory of graphs with universal universal algebra and mathematical logic. The central part of this chapter is original and shorter proof of an important theorem which solves a dichotomy conjecture for CSP problem on undirected graphs

Using the ELECTRE MLO Multi-Criteria Decision-Making Method in Stepwise Benchmarking - Application in Higher Education.

This paper describes multi-criteria decision making as a tool for stepwise benchmarking. The ELECTRE MLO ranking method is used. I give a mathematical theorem with a proof which is the answer to the question whether it is better to progress gradually or “to skip steps”. In chapter 3 ELECTRE MLO method is applied to benchmark teaching assistants of one faculty, University of Belgrade according to the marks given by their student

The Reliability of Bucket Wheel Excavator - Review of Random Mechanical Failures

Statistical regularity of random mechanical failures of the bucket wheel excavator will be considered based on dispatcher’s reports about excavator-conveyors-spreader (ECS-III) on the Tamnava - West Field Open Cast Mine in Lazarevac (Serbia) system failures in the period from 2003 to 2011. This kind of failures happens suddenly due to undetectable defects, unexplainable causes, and unavoidable failures. Reliability functions R(t), failure rate λ(t) and failure density f(t) of the bucket wheel excavator will be empirically determined. It was concluded that the random failures could be well approximated by the Exponential distribution. Below, serial reliability configuration of the BWE subsystem was analysed and the failure frequency as well as the values of the failure rate by subsystems were determined. Finally, proactive maintenance approach, which represents the latest innovation in the field of maintenance, will be presented. This approach to maintenance utilizes various technologies in order to achieve extension of operational life and elimination of reactive maintenance

An analysis of random mechanical failures of bucket wheel excavator

In this article random mechanical failures of bucket wheel excavator at open cast mine "Tamnava Zapad" are analysed. Random mechanical failures of mining equipment may represent an important factor in coal production because these types of failures occur unpredictably. Some of the reasons for the occurrence of such failures are unde-tectable defects, unexplainable causes, and unavoidable failures. In addition, here we have failure of equipment that has a large investment and productivity value. Statistical regularity of the component failure distribution of this system is analysed based on dispatcher's reports about EBS system failures in the period 2003-2011. The proposed distribution is analysed by theoretically, using suitable tests. By using statistical distribution we get the expected uptime of the bucket wheel excavator, for each year, which represents an important factor in maintenance programs and periodic inspections/repairs on bucket wheel excavator and mining components, in general

Proučavanje binarnih ravnoteža u rastvorima gadolinijum(III) i aluminijum(III) jona u prisustvu fluorohinolona ofloksacina i maksifloksacina

Предмет ове дисертације је карактеризација прототропних и равнотежа комплексирања јона Al3+ и Gd3+ и офлоксацина и Gd3+ и моксифлоксацина. Проучавања су вршена потенциометријским и спектрофотометријским методама у 0,1 mol/dm3 LiCl и NaCl средини, на (298.0±0.5)К. Проучавање хидролизе Gd3+ јона и комплексирања Gd3+ и офлоксацина, вршено је и ESI MS методом. Биодистрибуција Gd3+ и Al3+ јона у физиолошким условима, проучавана је компјутерском симулацијом, програмом HySS. Проучавањем ових система, наведеним експерименталним техникама и компјутерском симулацијом, добијени су следећи резултати: - Офлоксацин се може протоновати на две функционалне групе (на карбоксилној и терцијарној амино групи у пиперизинском супституенту) и има две константе протоновања logβq,r (q-протон, r-лиганд): Hoflo, logβ1,1=8.212±0.003; H2oflo+, logβ2,1=14.240±0.006; - Моксифлоксацин се може протоновати на две функционалне групе (на карбоксилној групи и на азоту са C7 супституента) и има две константе протоновања logβq,r (q- протон, r-лиганд): Hmoxi, logβ1,1=9.0±0,020; H2moxi+, logβ2,1=15.57±0.050. - Састав и константе стабилности хидролитичких комплекса који се формирају хидролизом Al3+-јона, узети су из литературних извора.The subject of this dissertation is characterization of the prototropic and complexation equilibria in solutions of Al3+ and Gd3+ and ofloxacin and Gd3+ ion and moxifloxacin. Investigations were performed using potentiometric and spectrophotometric methods in 0,1 mol/dm3 LiCl and NaCl ionic medium, at (298.0±0.5)К. The hydrolysis of Gd3+ ions and complexation of Gd3+ and ofloxacin were studied using ESI MS method also. Bio-distribution of Gd3+ and Al3+ ions under physiological conditions, were investigated by computer simulations, using HySS software. Investigation of these systems using the above mentioned experimental techniques and computer simulation, gave the following results: - Ofloxacin can be protonated on two functional groups (on carboxylate and tertiary amino group at pipearizine substituent), with two protonation constants logβq,r (q-proton, rligand):Hoflo, logβ1,1=8.212±0.003; H2oflo+, logβ2,1=14.240±0.006 respectively; - Moxifloxacin can be protonated on two functional groups (on carboxylate gruop and on nitrogen at C7 substituent), with two protonation constants logβq,r (q-proton, r-ligand): Hmoxi, logβ1,1=9.30±0.020; H2moxi+, logβ2,1=15.57±0.050 respectively; - Composition and stability constants of hydrolytic complexes formed by hydrolysis of Al3+ ions have been taken from literature sources. - Potentiometric and ESI MS methods, confirmed the existence of hydrolytic complexes logβp,q (p-metal, q-H): GdOH2+ (-logβ1,-1=7.96±0.01); Gd(OH)3 (logKsp1,-3=17.90±0.1)

Allergen immunotherapy in the polyallergic adolescent

Allergen immunotherapy is the only disease-modifying treatment option for allergic rhinitis, with adherence being its major limitation. We report a case of an adolescent with rhinitis, proven allergy to multiple non-homologous pollens, and troublesome symptoms despite maximal symptomatic therapy during the late spring and early summer months. Allergen immunotherapy to the most clinically relevant allergen was initiated under the supervision of a pediatrician. Shortly before her second year of treatment, she transferred to adult care and maintained a high degree of adherence and a favourable response to immunotherapy. In conclusion, allergen immunotherapy is effective in polyallergic adolescents with good adherence

Uloga strategijskog menadžmenta u kreiranju konkurentske prednosti agro kompleksa Srbije

Uspostavljanjem promenjenog konkurentskog ambijenta na tržištu hrane i prehrambenih proizvoda Srbije, presudnu ulogu i odgovornost za razvoj preuzeli su na sebe privredni subjekti, odnosno menadžment preduzeća. Preuzimajući ulogu glavnog pokretača rasta, menadžment srpskih preduzeća postaje svestan neophodnosti permanentnog usavršavanja znanja i veština, i razvijanja sposobnosti proaktivnog delovanja na dešavanja iz okruženja, zasnovano na principima strategijskog menadžmenta. Imajući u vidu da tržišni uslovi privređivanja bitno menjaju pravila igre, kao i pozicije koje pojedini faktori imaju u kreiranju konkurentske prednosti, javlja se potreba za većom fleksibilnošću u poslovanju. Upravo iz tog razloga, od menadžmenta se očekuje da razvija strategijski pristup u rešavanju problema, sagledavanju šansi i opasnosti, i da na bazi detaljne analize kritičnih faktora poslovnog uspeha definiše adekvatno strategijsko ponašanje. Strategijska orijentacija dobija neprocenjiv značaj u kreiranju diferentnih konkurentskih prednosti. Ukoliko fokus stavimo na poljoprivredni sektor, postaje jasno da bez primene koncepta strategijskog menadžmenta u ovom sektoru nije moguće efikasno uposliti raspoložive potencijale, kao ni očekivati zavidne rezultate u pogledu proizvodnje, izvoza i konkurentnosti na svetskom tržištu

H-colouring revisited

In this paper we give a new, shortened proof of NP-completeness of CSP problem for undirected, non bipartite graphs, of interest for generalization to QCSP problem. We also give some illustrative examples

Optical properties of plastically deformed copper

Pure copper (99.99), prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of 7 cm¡1) and wide ( 40 cm¡1) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen