Granični sloj ioniziranog plina na rotacijskim tijelima pri postojanju magnetskog polja

This paper studies ionized gas flow in the boundary layer on bodies of revolution. The present magnetic field is normal to a nonporous contour of the body. The governing boundary layer equations are brought to a generalized form by general similarity method. The obtained equations are numerically solved by finite differences method. Based on the obtained solutions, diagrams of distributions of physical qualities in the boundary layer are given. Conclusions of behaviour of these quantities for the studied ionized gas problem are also drawn.Istraživano je strujanje ioniziranog plina u graničnom sloju na rotacijskim tijelima. Prisutno magnetsko polje je okomito na neporoznu konturu tijela. Polazne jednadžbe graničnog sloja dovedene su na uopćeni oblik metodom uopćene sličnosti u verziji Saljnikova. Dobivene jednadžbe numerički su riješene metodom konačnih razlika. Na osnovu dobivenih rješenja prikazani su dijagrami raspodjela fizikalnih veličina u graničnom sloju. Izvedeni su zaključci o ponašanju ovih veličina kod razmatranog problema strujanja ioniziranog plina

Computation Method in Failure Analysis of Mechanically Fastened Joints at Layered Composites

This paper considers a computation method in failure analysis of layered composites containing pin-loaded holes. The investigation is focused on developing a reliable computation procedure to analyze initial failure load for pin-loaded holes at layered composite structures. Finite element method (FEM) is used to determine stress distribution around the fastener hole. Combining Chang-Scott-Springer characteristic curve model and Tsai-Wu initial failure criterion are used to determine joint failure. Special attention in this work is paid to pin-load distributions and its effect on the load level of failure and its location. In previous work initial failure analysis was carried out using cosine distribution between pin/lug mechanically fastened joint. Here contact finite element pin/lug model is analysed. The influence of stacking sequences of layered composites containing pin-loaded holes is also investigated. Special attention is paid to failure load and mode analyses in composites with stacking sequence [0/(+/-45)(3)/90(3)](s). The computation results are compared with available experimental results. Good correlations between computation and experimental results are obtained

Uticaj supstituenata na IR, 1H- i 13C-NMR spektralne podatke N-(supstituisanih fenil)-2-cijanoacetamida - korelaciona analiza

Linear free energy relationships (LFER) were applied to the IR, H-1- and C-13-NMR spectral data of N-(substituted phenyl)-2-cyanoacetamides. A variety of substituents were employed for phenyl substitution and fairly good correlations were obtained using the simple Hammett and the Hammett-Taft dual substituent parameter equations. The correlation results of the substituent induced C-13-NMR chemical shifts (SCS) of the Cl, C=O and N-H atom indicated different sensitivity with respect to electronic substituent effects. A better correlation of the SCSc=O with a combination of electrophllic and nucleophilic substituent constants indicated a significant contribution of extended resonance interaction (pi-delocalization) within the pi(1)-unit. The conformations of the investigated compounds were studied using the OFT B3LYP/6-311G** method and, together with the results of C-13-NMR and IR spectroscopic studies, a better insight into the influence of such a structure on the transmission of electronic substituent effects was obtained.Principi linearnih korelacija slobodnih energija (LFER) su primenjeni na IR, 1H- i 13C-NMR spektralne podatke N-(supstituisanih fenil)-2-cijanoacetamida. Pri sintezi N-(supstituisanih fenil)-2-cijanoacetamida izvršen je zadovoljavajući izbor supstituenata u pogledu elektronskih svojstava kako bi se adekvatno sagledao uticaj elektronskih efekata supstituenata na pomeranja u IR, 1H- i 13C-NMR spektralnim podacima. Primenom proste Hametove jednačine dobijene su zadovoljavajuće korelacije. Na osnovu korelacionih rezultata uočen je primaran uticaj elektronskih efekata na SCS (supstituentom indukovana hemijska pomeranja) vrednosti N-H vodonika, C1 i C=O ugljenika ispitivanih jedinjenja. Korelacioni rezultati za C=O ugljenik se značajno popravljaju ako se koristi kombinacija Ϭ+ i Ϭ- konstanti supstituenata, takozvane elektrofilne i nukleofilne konstante supstituenata, što ukazuje na postojanje značajne proširene rezonancione interakcije supstituenata i elektronske gustine karbonilne grupe. Vrednosti konstanti proporcionalnosti pF i pR za sve atome, ukazuju na približno isti doprinos efekta polja i rezonancionog efekta supstituenata. Efekat polja je nešto izraženji na N-H vodoniku, i za sve atome pokazuje značajne razlike u odnosu na njihov položaj u molekulskoj strukturi ispitivanih jedinjenja. Uticaj efekata supstituenata na IR vibracije istezanja N-H (simetrične i antisimetrične), C=O i CN veze je prevashodno elektronske prirode što se može zaključiti na osnovu dobrih korelacija dobijenih primenom Hametove jednačine i Ϭ parametara supstituenata. Osim toga izvršena je optimizacija geometrije ispitivanih jedinjenja primenom DFT B3LYP/ 6-311G**metode, pri čemu je nađeno da je trans-izomer nešto stabilnji, izuzev u slučaju jedinjenja 3. Supstituisana fenil-grupa i amidna grupa, kod trans-izomera, su približno koplanarne, dok se kod cis- izomera uočava značajna devijacija koja je značajno određena elektronskim efektima prisutnog supstituenta. Takođe je ispitivan položaj cis/trans ravnoteže u ugjen-tetrahloridu, i na osnovu rezultata FT/R analize, kada je prisutan H, CH3, OCH3, Br, i COOH supstituent, nađeno je da je cis izomer u velikom višku, a za ostala jedinjenja utvrđeno je postojanje ravnoteže cis- i trans-izomera

Experimental investigation of spillover effect in system of active vibration control

Piezoelektrični aktuatori se uveliko primenjuju za aktivno upravljanje vibracijama na raznim strukturama sa ciljem povećanja performansi sistema. Razvijeni sistem aktivnog upravljanja vibracijama se sastoji od aktivnije strukture, kontrolera i visokonaponskih pojačivača. U ovom radu, kompozitna greda predstavlja osnovnu strukturu za senzorsku (merne trake) i aktuatorsku (dvoslojni PZT piezoelektrični aktuator) platformu. U cilju unapređenja dinamičkih karakteristika aktivnog sistema vršena je promena koeficijenata PID regulatora. Efikasnost sistema aktivnog upravljanja vibracijama za posmatrani mod oscilovanja se može povećati promenom koeficijenata PID regulatora, ali u isto vreme moguće je narušiti stabilnost sistema. Nestabilnost sistema je najčešće uslovljena pojavom 'spillover' efekta. U ovom radu predstavljen je značaj 'spillover' efekta u zatvorenim petljama piezoelektričnih aktivnih struktura, kao i značaj promene koeficijenata PID regulatora na stabilnost sistema. Eksperimentalni rezultati sistema aktivnog prigušenja vibracija su predstavljeni u radu i daju jednu od mogućnosti za povećanje stabilnosti upravljanih struktura.Piezoelectric actuators are widely used in structural systems for active vibration control with the aim to enhance the performance of systems. The developed system of active vibration control consists of active structure, controller and high voltage amplifier. In this paper, the composite beam is host structure for sensor platform (strain gages) and actuator platform (dual layer PZT piezoelectric actuator). In order to improve the dynamic characteristics of active system, the coefficients of PID controller are changed. The effectiveness of active vibration control system at mode of interest can be improved with change of PID coefficients, but the stability of system can be reduced. The instability of the active structure is often perturbed by spillover effect. In this paper the importance of considering spillover effects in closed loop of piezoelectric active structures is demonstrated and shown the importance of change the PID coefficients in stability of active vibration control system. Experimental results which correspond to the developed active vibration control system are presented and affirmed stability on proposed active structure

Experimental investigation of spillover effect in system of active vibration control

Piezoelektrični aktuatori se uveliko primenjuju za aktivno upravljanje vibracijama na raznim strukturama sa ciljem povećanja performansi sistema. Razvijeni sistem aktivnog upravljanja vibracijama se sastoji od aktivnije strukture, kontrolera i visokonaponskih pojačivača. U ovom radu, kompozitna greda predstavlja osnovnu strukturu za senzorsku (merne trake) i aktuatorsku (dvoslojni PZT piezoelektrični aktuator) platformu. U cilju unapređenja dinamičkih karakteristika aktivnog sistema vršena je promena koeficijenata PID regulatora. Efikasnost sistema aktivnog upravljanja vibracijama za posmatrani mod oscilovanja se može povećati promenom koeficijenata PID regulatora, ali u isto vreme moguće je narušiti stabilnost sistema. Nestabilnost sistema je najčešće uslovljena pojavom 'spillover' efekta. U ovom radu predstavljen je značaj 'spillover' efekta u zatvorenim petljama piezoelektričnih aktivnih struktura, kao i značaj promene koeficijenata PID regulatora na stabilnost sistema. Eksperimentalni rezultati sistema aktivnog prigušenja vibracija su predstavljeni u radu i daju jednu od mogućnosti za povećanje stabilnosti upravljanih struktura.Piezoelectric actuators are widely used in structural systems for active vibration control with the aim to enhance the performance of systems. The developed system of active vibration control consists of active structure, controller and high voltage amplifier. In this paper, the composite beam is host structure for sensor platform (strain gages) and actuator platform (dual layer PZT piezoelectric actuator). In order to improve the dynamic characteristics of active system, the coefficients of PID controller are changed. The effectiveness of active vibration control system at mode of interest can be improved with change of PID coefficients, but the stability of system can be reduced. The instability of the active structure is often perturbed by spillover effect. In this paper the importance of considering spillover effects in closed loop of piezoelectric active structures is demonstrated and shown the importance of change the PID coefficients in stability of active vibration control system. Experimental results which correspond to the developed active vibration control system are presented and affirmed stability on proposed active structure

Chemical composition of the mushroom Meripilus giganteus Karst. and bioactive properties of its methanolic extract

Wild Meripilus giganteus Karst belongs to the order Polyporales, in which some members are known to possess a wide range of pharmacological properties. M. giganteus showed to be rich in carbohydrates (74.49 g/100 g) and proteins (15.94 g/100 g), presenting low fat content (1.51 g/100 g). Chemical composition was determined by using chromatographic techniques. Also, various bioactive compounds were detected including all four tocopherol isoforms with d- and ?-tocopherols being predominant (123.35 and 77.80 µg/100 g, respectively); five organic acids (oxalic, malic, quinic, citric and fumaric acids) with predominant malic acid (3.17 g/100 g); and three phenolic acids and related compounds (p-hydroxybenzoic, p-coumaric and cinnamic acids; 1010, 2420 and 340 µg/100 g, respectively). M. giganteus methanolic extract exhibited antioxidant activity tested by five different assays with the strongest potential in TBARS assay (EC 50 0.31 mg/mL); and antimicrobial activities (MIC/MBC 0.0125–5 mg/mL; MIC/MFC 0.025–0.4 mg/mL). Furthermore, treatment of cervical carcinoma cell line (HeLa) led to reduction in cell's viability in MTT assay (IC 50 0.41 mg/mL after 48 h), induced process of apoptosis and inhibited cell's migration in vitro. The analysed extract was not toxic for zebrafish embryos (at 0.5 mg/mL), indicating its biosafety and potential application as a dietary supplement in chemoprevention.This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (grant numbers 173032, 173051 and 47025). Authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support to CIMO (Pest-OE/AGR/UI0690/2015) and L. Barros grant (SFRH/BPD/107855/2015). We would like to thank dr Jelena Dinic for help in performing DAPI/PI staining.info:eu-repo/semantics/publishedVersio

Antioxidant activity relationship of phenolic compounds in Hypericum perforatum L.

<p>Abstract</p> <p>Background</p> <p>The St John's Wort (<it>Hypericum perforatum</it>; Clusiaceae) has been used in traditional and modern medicine for a long time due to its high content of biologically active phenolics. The purpose of this work was to develop a method for their fractionation and identification, and to determine the most active antioxidant compounds in plant extract.</p> <p>Results</p> <p>An LC-MS method which enables fast qualitative and semiquantitative analysis was developed. The composition determined is in agreement with the previous results, where 6 flavonoids, 4 naphthodianthrones and 4 phloroglucinols have been identified. Significant antioxidant activity was determined for most of the fractions by DPPH assay (the lowest IC₅₀of 0.52 μg/ml), NO scavenging (6.11 μg/ml), superoxide scavenging (1.86 μg/ml), lipid peroxidation (0.0079 μg/ml) and FRAP (the highest reduction capacity of 104 mg Fe equivalents/g) assays.</p> <p>Conclusion</p> <p>LC-MS technique has been successfully applied for a quick separation and identification of the major components of <it>H. perforatum </it>fractions. Majority of the fractions analyzed have expressed a very high antioxidative activity when compared to synthetic antioxidants. The antioxidant activity could be attributed to flavonoids and phenolic acids, while phloroglucinols and naphthodianthrones showed no significant activity. It is demonstrated that it is possible to obtain, by fractionation, <it>H. perforatum </it>preparations with significantly increased phloroglucinols-to-naphthodianthrones ratio (up to 95:5).</p

Centar izvrsnosti za računalni vid

Centar izvrsnosti za računalni vid na Fakultetu elektrotehnike i računarstva (FER) osnovan je 2012. godine sa ciljem okupljanja relevantnih istraživača s FER-a i s drugih sastavnica Sveučilišta. U osnivanju Centra sudjelovalo je sedam sastavnica Sveučilišta u Zagrebu. Ciljevi Centra su jačanje međunarodne vidljivosti Sveučilišta u Zagrebu u području računalnog vida, stvaranje kritične mase istraživača za zajednički nastup u većim znanstvenoistraživačkim i razvojnim projektima, poboljšanje kvalitete doktorskih istraživanja u području računalnog vida i poticanje zajedničkog nastupa prema gospodarstvu radi suradnje i transfera tehnologije. U radu je predstavljena motivacija za osnivanje Centra te znanstvene i stručne aktivnosti članova Centra