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Search Results: 1 - 10 of 223933 matches for " Radivoje B Pe?i? "
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Radivoje B Pei,Aleksandar Lj Davini?,Dragan S Taranovi?,Danijela M Miloradovi?
Thermal Science , 2010, DOI: tsci100505069p
Abstract: A zero-dimensional, one zone model of engine cycle for steady-state regimes of engines and a simplified procedure for indicator diagrams analysis have been developed at the Laboratory for internal combustion engines, fuels and lubricants of the Faculty of Mechanical Engineering in Kragujevac. In addition to experimental research, thermodynamic modeling of working process of diesel engine with direct injection has been presented in this paper. The simplified procedure for indicator diagrams analysis has been applied, also. The basic problem, a selection of shape parameters of double Vibe function used for modeling the engine operation process, has been solved. The influence of biodiesel fuel and engine working regimes on the start of combustion, combustion duration and shape parameter of double Vibe was determined by a least square fit of experimental heat release curve.
Radivoje B Pei,Sa?a T Milojevi?,Stevan P Veinovi?
Thermal Science , 2010, DOI: tsci10041063p
Abstract: The compression ratio strongly affects the working process and provides an exceptional degree of control over engine performance. In conventional internal combustion engines, the compression ratio is fixed and their performance is therefore a compromise between conflicting requirements. One fundamental problem is that drive units in the vehicles must successfully operate at variable speeds and loads and in different ambient conditions. If a diesel engine has a fixed compression ratio, a minimal value must be chosen that can achieve a reliable self-ignition when starting the engine in cold start conditions. In diesel engines, variable compression ratio provides control of peak cylinder pressure, improves cold start ability and low load operation, enabling the multi-fuel capability, increase of fuel economy and reduction of emissions. This paper contains both theoretical and experimental investigation of the impact that automatic variable compression ratios has on working process parameters in experimental diesel engine. Alternative methods of implementing variable compression ratio are illustrated and critically examined.
Aspects of volumetric efficiency measurement for reciprocating engines
PeiRadivoje B.,Davini? Aleksandar Lj.,Petkovi? Sne?ana D.,Taranovi? Dragan S.
Thermal Science , 2013, DOI: 10.2298/tsci120531153p
Abstract: The volumetric efficiency significantly influences engine output. Both design and dimensions of an intake and exhaust system have large impact on volumetric efficiency. Experimental equipment for measuring of airflow through the engine, which is placed in the intake system, may affect the results of measurements and distort the real picture of the impact of individual structural factors. This paper deals with the problems of experimental determination of intake airflow using orifice plates and the influence of orifice plate diameter on the results of the measurements. The problems of airflow measurements through a multi-process Otto/Diesel engine were analyzed. An original method for determining volumetric efficiency was developed based on in-cylinder pressure measurement during motored operation, and appropriate calibration of the experimental procedure was performed. Good correlation between the results of application of the original method for determination of volumetric efficiency and the results of theoretical model used in research of influence of the intake pipe length on volumetric efficiency was determined. [Acknowledgments. The paper is the result of the research within the project TR 35041 financed by the Ministry of Science and Technological Development of the Republic of Serbia]
Sne?ana D Petkovi?,Radivoje B Pei,Jovanka K Luki?
Thermal Science , 2010, DOI: tsci100505070p
Abstract: During the engine cold start, there is a significantly increased emission of harmful engine exhaust gases, particularly at very low environmental temperatures. Therefore, reducing of emission during that period is of great importance for the reduction of entire engine emission. This study was conducted to test the activating speed of the catalyst at low environmental temperatures. The research was conducted by use of mathematical model and developed computer programme for calculation of non-stationary heat transfer in engine exhaust system. During the research, some of constructional parameters of exhaust system were adopted and optimized at environmental temperature of 22 C. The combination of design parameters giving best results at low environmental temperatures was observed. The results showed that the temperature in the environment did not have any significant influence on pre-catalyst light-off time.
Experimental verification of mathematical model of the heat transfer in exhaust system
Petkovi? Sne?ana,PeiRadivoje,Luki? Jovanka
Thermal Science , 2011, DOI: 10.2298/tsci110517102p
Abstract: A Catalyst convertor has maximal efficiency when it reaches working temperature. In a cold start phase efficiency of the catalyst is low and exhaust emissions have high level of air pollutants. The exhaust system optimization, in order to decrease time of achievement of the catalyst working temperature, caused reduction of the total vehicle emission. Implementation of mathematical models in development of exhaust systems decrease total costs and reduce time. Mathematical model has to be experimentally verified and calibrated, in order to be useful in the optimization process. Measurement installations have been developed and used for verification of the mathematical model of unsteady heat transfer in exhaust systems. Comparisons between experimental results and the mathematical model are presented in this paper. Based on obtained results, it can be concluded that there is a good agreement between the model and the experimental results.
Teaching and learning adaptive hydrometallurgy-nanohydrometallurgy
Journal of Mining and Metallurgy, Section B : Metallurgy , 2005, DOI: 10.2298/jmmb0501017p
Abstract: The weakness of the U.S. mining industry has caused a significant decline in academic programs in mining and metallurgical engineering in the U.S. The author’s view on the reasons for such weaknesses is presented in a historical prospective covering some key events within the last 30 years. Arguably, the decline of U.S. mining industry is due to many reasons, the most important being the lack of modernization, the difficulty to comply with stringent environmental laws, and global market forces, are the most important. The importance of emerging nanotechnologies is viewed as an opportunity for the evolution of one component of metallurgical engineering - hydrometallurgy - into nanohydrometallurgy, thus extending its viability.
Immobilization of invertase and glucoamylase on a macroporous copolymer of etyleneglycoldimethacrylate and glycidyl methacrylate and potential applications in biotechnology
Prodanovi? Radivoje M.,Milosavi? Nenad B.,Jovanovi? Slobodan M.,Vuj?i? Zoran M.
Hemijska Industrija , 2003, DOI: 10.2298/hemind0311536p
Abstract: The optimal conditions for the immobilization of invertase and glucoamylasewere found via their carbohydrate moiety on a macroporous copolymer of ehtyleneglycoldimethacry late and glycidylmethacrylate. Almost all of the added enzyme was bound to the polymer by increasing the time of incubation of the oxidized enzyme with polymer. A specific activity of 5500 U/g for invertase was obtained and 1100 U/g for glucoamylase. The specific productivity for invertase in a packed bed reactor was 3.5 kg/lh and for glucoamylase 1.9 kg/lh. During continuous use in a packed bed the reactor operational half life for invertase was 290 days, while no decrease in activity was observed for glucoamylase. In 50% (v/v) ethanol the immobilized enzymes were five to ten times more stable, and more than 200 times more stable in 25% (v/v) dioxane. The immobilized enzymes retained all activity in petroleum ether after 3 days of incubation. Because of their higher stability over native enzymes, and the large surface area of the polymer immobilized glucoamylase and invertase could be more useful for glycoside synthesis in non-aqueous solvents than native ones.
Immobilization of glucoamylase on macroporous spheres
Milosavi? Nenad B.,Prodanovi? Radivoje M.,Jovanovi? Slobodan M.,Vuj?i? Zoran M.
Acta Periodica Technologica , 2004, DOI: 10.2298/apt0435207m
Abstract: Glucoamylase was covalently immobilized through the spacer-arm of the poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) spheres by using a glutaraldehyde as a coupling agent. The influence of the enzyme load applied to the support on immobilization, yield and specific activity, has been determined. Obtained specific activity was 700 U/g with immobilization yield of 35 %. The Km value for immobilized glucoamylase was 1.28 % (w/v), pH and temperature optimum were 4.5 and 70°C, respectively. The conversion of 20 % (w/w) starch hydrolysate achieved with the immobilized glucoamylase was 97 % after 5 hours.
Covalent immobilization of lipase from Candida rugosa on Eupergit
Bezbradica Dejan I.,?orovi? Jasmina J.,Prodanovi? Radivoje M.,Milosavi? Nenad B.
Acta Periodica Technologica , 2005, DOI: 10.2298/apt0536179b
Abstract: An approach is presented for the stable covalent immobilization of Upase from Candida rugosa on Eupergit with a high retention of hydrolytic activity. It comprises covalent bonding via lipase carbohydrate moiety previously modified by periodate oxidation, allowing a reduction in the involvement of the enzyme functional groups that are probably important in the catalytic mechanism. The hydrolytic activities of the lipase immobilized on Eupergif1 by two conventional methods (via oxirane group and via glutaralde-hyde) and with periodate method were compared. Results of lipase assays suggest that periodate method is superior for lipase immobilization on Eupergit among methods applied in this study with respect to both, yield of immobilization and hydrolytic activity of the immobilized enzyme.
The Open Packing of the Lesser Sac Technique in Infected Severe Acute Pancreatitis  [PDF]
Daniel Cochior, Silviu Constantinoiu, Dumitru Pe?a, Mariana Cochior, Rodica B?rl?, Lucian Pripi?i
Surgical Science (SS) , 2010, DOI: 10.4236/ss.2010.11002
Abstract: Aim: The goal of this study is to evaluate the open packing of the lesser sac (OPLS) in treatment of infected severe acute pancreatitis Methodology: The study was based on 98 cases in which this technique was applied during the period between 19942007, in two departments of surgery (Clinical Hospital CF 2 and Clinical Hospital ?Sf. Maria” Bucharest). The technique was applied based on the therapeutically protocol previously established beginning with 2000. The OPLS technique was analyzed relatively to: timing of surgery, the localization of the infected necrosis or abscesses, growing germs on the cultures, antibiotics received, executed primarily or at reintervention, the number of debridement, hospitalization, morbidity and mortality. The information was statistically processed using SPSS test version 17 for Windows. Results: The OPLS technique improved the control of the local sepsis, in the retrospective/prospective study in 83.7%. Mortality was 16.3% (16/98), with a global mortality of 26.3% (75/285) and a postoperative mortality of 29.5% (66/224). Conclusions: Considering the fact that the intensive care techniques are approximately the same in the last 15 years, we thought that this improvement in the survival rate may be due to the application of OPLS in cases with indication and optimal timing for surgery.
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