Applicability ofMathematicalModels in Defining the Behaviour Kinetics Distinction Among Microbial Strains

Mathematical models were applied to define the behaviour kinetics distinction among microbial strains. In the first series of experiments the growth kinetics of microbial colonies of several S. rimosus mutant strains cultivated on agar plates were compared. Then, the interest was focused on the chosen two strains, in order to express mathematically their differences with respect to their colony growth and antibiotic biosynthesis kinetics. Finally, the behaviour of selected three S. rimosus derivative strains at different culture conditions was subjected to the study, with an aim to define strain distinction parameters. Mathematical models based on the three-dimensional growth concept and describing the microorganism growth, substrate uptake and antibiotic biosynthesis kinetics were developed. The computer simulation was applied to verify the applicability of mathematical models. The excellent agreement of computer simulation with experimental data confirmed the hypothesis that the kinetics parameters can be successfully applied to define the behaviour distinction among different S. rimosus strains. In the case of selected three strains, S. rimosus R6–500, S. rimosus MV9R-1 and MV9R-2, it was established that they can be distinguished by their growth kinetics parameters, their substrate uptake kinetics parameters and their antibiotic biosynthesis kineticsparameters. The strain S. rimosus R6–500 showed to be superior with respect to all kinetics parameters, the strain S. rimosus MV9R-2 showed to be slightly inferior to it, whereas the strain S. rimosus MV9R-1 showed to be inferior with respect to the both mentioned strains, especially because it showed the pronounced active biomass reduction rate at all investigated culture conditions. Based on these and the corresponding previous results one can conclude that appropriate mathematical models can be recommended for defining parameters of microbial behaviour distinction among different microbial strains of S. rimosus species

Failure Analysis of the Stacker Crawler Chain Link

Stacker ARs 2000 presents the final link in the system for continuous overburden removal in the open pit mine "Kostolac" Serbia. Its superstructure leans on three crawlers of the same length, width and height. During the stacker's travel from the erection site to the open pit mine, three crawler chain links fractured, presenting an indication of the problems that were to occur during exploitation. In fact, after only 1000 working hours (about three months), 30 chain links sustained fractures resulting in direct and indirect costs due to the downtime that substantially diminished the effects of the overburden removal system. The goal of the study presented in the paper was to diagnose the cause of chain link breakdown occurrence. Working stresses in the chain link are defined by applying FEM. Experimental investigations define the chemical composition, the tensile properties, the impact toughness and the macro and microhardness. Metallographic examinations are conducted additionally. Based on the results of the numerical-experimental analysis, it can be concluded that chain link breakdown is predominantly caused by (a) substantial deviation of the mechanical properties of the material with respect to those prescribed by the standard and (b) the existence of macro and microcracks in the material structure

Failure Analysis of the Tower Crane Counterjib

Failures of the cranes' structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect

Failure Analysis of the Stacker Crawler Chain Link

Stacker ARs 2000 presents the final link in the system for continuous overburden removal in the open pit mine "Kostolac" Serbia. Its superstructure leans on three crawlers of the same length, width and height. During the stacker's travel from the erection site to the open pit mine, three crawler chain links fractured, presenting an indication of the problems that were to occur during exploitation. In fact, after only 1000 working hours (about three months), 30 chain links sustained fractures resulting in direct and indirect costs due to the downtime that substantially diminished the effects of the overburden removal system. The goal of the study presented in the paper was to diagnose the cause of chain link breakdown occurrence. Working stresses in the chain link are defined by applying FEM. Experimental investigations define the chemical composition, the tensile properties, the impact toughness and the macro and microhardness. Metallographic examinations are conducted additionally. Based on the results of the numerical-experimental analysis, it can be concluded that chain link breakdown is predominantly caused by (a) substantial deviation of the mechanical properties of the material with respect to those prescribed by the standard and (b) the existence of macro and microcracks in the material structure

Failure Analysis of the Tower Crane Counterjib

Failures of the cranes' structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect

Maternal characteristics influencing the duration of breastfeeding in a breastfeeding support group

U radu su prikazani čimbenici koji utječu na trajanje dojenja majki članica grupa za potporu dojenju. Podaci su prikupljeni retrospektivno pomoću anketnog upitnika za samopopunjavanje. Korištene su definicije dojenja SZO. U istraživanju je sudjelovalo 210 članica grupa koje su tijekom prvih šest mjeseci dojenačke dobi došle na sastanak grupe najmanje četiri puta. S navršenih šest mjeseci doji ukupno 83,8% majki, a s navršena tri mjeseca isključivo doji 56% majki. Dojenje dulje od šest mjeseci pozitivno je povezano s prihodima kućanstva, vremenom donošenja odluke o dojenju, namjeravanim trajanjem dojenja i zadovoljstvom savjetima majke voditeljice grupe, a negativno s pušenjem prije trudnoće. U logističkoj regresijskoj analizi prediktori dojenja duljeg od šest mjeseci su namjeravano trajanje dojenja više od šest mjeseci (OR 4,27; 95% CI 1,63-11,17, P= 0,003) i nepušenje prije trudnoće (OR 3,07; 95%CI 1,29-7,30, P=0,011). Ovo je u nas prvo istraživanje karakteristika majki članica grupa za potporu dojenju i čimbenika koji utječu na trajanje dojenja majki u grupama. Buduća istraživanja trebala bi potvrditi zapažanje ove studije da aktivnosti grupa potiču majke u smislu povećanja trajanja dojenja.The study was conducted to analyse factors influencing the duration of breastfeeding among attendees of mother support groups. Data regarding breastfeeding duration was collected retrospectively by a self-reported questionnaire using WHO definitions for breastfeeding. 210 women who were regular attendees of mother support groups (with 4 or more attendances of the group meetings during the first 6 months postpartum) participated in the study. At 6 months post partum 83.8% mothers were breastfeeding and 56% did so exclusively at 3 months. In univariate analysis breastfeeding duration > 6 months was positively associated with family income, time of breastfeeding decision, intended duration of breastfeeding and perceived satisfaction with advice from the mother leader of the group. A negative association was found for maternal smoking. Using logistic regression analysis of factors associated with breastfeeding duration > 6 months, a positive association was found with intended duration of breastfeeding > 6 months (OR 4..27; 95% CI 1.63-11,17, P= 0.003) and maternal non-smoking before pregnancy (OR 3.07; 95%CI 1.29-7.30, P=0.011). This is the first reported study of maternal characteristics and factors influencing the duration of breastfeeding among mother support group attendees. Future research should determine if the decision on the duration of breastfeeding can be modified through attending support groups to enhance breastfeeding duration