Granulocitna rezerva u kronignom eksperimentalnom otrovanju benzenom u štakora

The normal two-fold increase in granulocytes in the peripheral circulation induced by corticosteroids was almost abolished in chronic benzene poisoning in rats.Normalno očekivani dvostruki porast granulocita u perifernoj cirkulaciji nakon primjene kortikosteroida izostao je u štakora kronično otrovanih benzenom

Lead metabolism with special reference to the problem of population exposure

U članku je dat prikaz suvremenih shvaćanja o rnetabolizmu olova i njegovim toksičnim učincima. Za razliku od dosadašnjeg promatranja olova kao profesionalnog otrova težište je postavljeno na problem ekspozicije cjelokupnog stanovništva tim metalom i njegovim mogućim učincima na zdravlje. Zbog toga je posebno obrađen problem trovanja djece olovom kao i metabolizam olova u graviditetu i laktaciji. Na kraju je upozoreno na društveno-ekonomsko značenje opće kontaminacije olovom koja uslijed naglog razvoja motorizacije zahvaća i naše krajeve.Current views on lead metabolism and its toxic effects are surveyed. The problem of lead is no longer considered from the point of view of occupational intoxication, but attention is focussed on total population exposure to lead and its possible health effects. The problem of lead poisoning in children as well as of lead metabolism in pregnancy and lactation is therefore dealt with separately. At the end a varning is given about social and economic significance of general lead contamination which is spreading over the country owing to the fast development of motorization

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

Determination of critical size of corrosion pit on mechanical elements in hydro power plants

Researchers in the field of fracture mechanics, predominantly developing appropriate solution algorithms for problems of solid bodies with cracks. Problems in mechanics generally, related with fracture and fatigue for solid bodies with various geometries of sharp notches, are studied to a much lesser extent. This situation can be explained by analytical difficulties arising in solving problems of elasticity theory for bodies with rounded notches. To solve problems of such class, starting from data on stress concentration in the rounded notch tip with a significant radius of curvature, simplified solutions with are therefore of great importance. Recent years, due to constant rise of computing power and development of numerical methods, re-evaluation of stress concentration factors from a viewpoint of theory of elasticity is present. This is mainly as a feedback from industry, which have requirements toward mega and nanostructures. Corrosion represents an important limitation to the safe and reliable use of many alloys in various industries. Pitting corrosion is a form of serious damage on metals surface such as high-strength aluminum alloys and stainless steel, which are susceptible to pitting when exposed to a corrosive attack in aggressive environments. This is particularly valid for dynamic loaded structures. The basic idea behind this paper is finding links between different scientific and engineering disciplines, which will enable useful level of applicability of existing knowledge. The subject of this paper is application of new method of determine length scale parameter for estimating the mechanistic aspect of corrosion pit under uniaxial/multiaxial high-cycle fatigue loading…

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Effects of operation temperature on thermal expansion and main parameters of radial ball bearings

The research of influence of operation temperature on the thermal expansion and main parameters of radial ball bearings is presented in this paper. The main bearing parameters are identified in accordance with the increasing requests concerning stability and load capacity. A series of finite element analyses is performed for quasi-static analysis of all identified bearing parameters during contact period in referent temperature. Then, the dependence of bearing material characteristics on the operation temperature is discussed. Few series of finite element analyses are performed for a particular radial ball bearing type, with characteristics in accordance with manufacturer specifications, for several operation temperatures. These two problems analyses include consideration of relation between the initial radial clearance, thermal expansion strains, and contact deformations of the parts of the bearing assembly. The results for radial ball bearing parameters are monitored during a ball contact period for different temperatures and the appropriate discussion and conclusions are given. The conclusions about the contribution of developed procedure in defining the optimum operation temperature range are shown

Odgođeni učinci olova na bubrege - faktorska analiza

A late, i.e. delayed, effect of lead on kidney function and blood pressure was studied in 23 workers with a history of occupational lead poisoning. Twenty lead exposed workers with no known history of lead poisoning were a positive control. Four important factors out of 11 combined variables derived from 22 single variables were identified by factor analysis. The first factor comprised the variables kidney function, blood pressure, age, duration of lead exposure and the number of previous lead poisonings. The second factor comprised the variables duration of lead exposure and biological indicators of lead exposure. The third factor correlated the frequency of previous lead poisonings with the renal blood flow, erythrocytic protoporphyrin and age. The fourth factor comprised the variables length of work service, creatinine clearance and erythrocytic protoporphyrin. The results confirm the presence of the adverse late effect of previous occupational lead poisoning on kidney function regardless of treatment. The phenomenon is not a single event but a complex interplay of past lead poisoning, duration of exposure to lead, »normal« age effect on an increase in systolic and diastolic blood pressure and blood creatinine and a decrease in renal function as revealed by decreased creatinine clearance and a slow down in renal flow time. The complexity of dealing with the confounding variable of age and lack of appropriate classification of renal function impairment may account for the conflicting results of chronic lead effect upon kidney function in the past. The kidney appears to be a critical target organ, reflecting the total lead body burden in chronic lead exposure and poisoning. Therefore monitoring of kidney function in lead exposed workers needs to be mandatory.Pojava kasnih (odgođenih) oštećenja funkcije bubrega ispitali smo u radnika koji su ranije u životu bili otrovani olovom. Pozitivna kontrola bili su radnici izloženi olovu koji nikada nisu bili otrovani tim metalom. Pomoću faktorske analize dobivena su četiri značajna faktora iz 22 pojedinačne varijable za koje se pretpostavlja da su vezane uz pojavu kasnih (odgođenih) oštećenja funkcije bubrega olovom. Prvi faktor fine varijable funkcije bubrega, krvnog tlaka, dobi, trajanja izloženosti olovu i broja ranijih otrovanja olovom. Drugi faktor dominantno fine varijable trajanja izloženosti olovu i bioloških pokazatelja izloženosti olovu. Treći faktor povezuje učestalost ranih otrovanja olovom s vremenom protoka hipurana kroz bubrege, eritrocitnog protoporfirina i dobi. Četvrti faktor grupiran je oko varijabli radnog staža, klirensa kreatinina i eritrocitnog protoporfirina. Rezultati potvrđuju pretpostavku kako je ranije preboljeno profesionalno otrovanje olovom kasnije u životu praćeno funkcionalnim oštećenjem bubrega. Kasni (odgođeni) učinci olova na bubrege rezultat su složene interakcije međusobno povezanih varijabli: ranije u životu preboljenog otrovanja olovom, ukupnog vremena provedenog u radu s tim metalom, dobi i dobi pripadajućim promjenama porasta sistoličkog i dijastoličkog krvnog tlaka, porasta sistoličkog i dijastoličkog krvnog tlaka, porasta razine kreatinina u krvi te pada vrijednosti klirensa kreatinina i brzine protoka hipurana kroz bubrege. Stoga se može zaključiti kako je bubreg kritični ciljni organ u metabolizmu ekskrecije olova iz organizma te da praćenje njegove funkcije treba uključiti u skup obaveznih indikatora biološkog nadzora profesionalno izloženih radnika