The planetary nebula Abell 48 and its [WN4] central star

We have conducted a multi-wavelength study of the planetary nebula Abell 48 and give a revised classification of its nucleus as a hydrogen-deficient star of type [WN4]. The surrounding nebula has a morphology typical of PNe and importantly, is not enriched in nitrogen, and thus not the 'peeled atmosphere' of a massive star. Indeed, no WN4 star is known to be surrounded by such a compact nebula. The ionized mass of the nebula is also a powerful discriminant between the low-mass PN and high-mass WR ejecta interpretations. The ionized mass would be impossibly high if a distance corresponding to a Pop I star was adopted, but at a distance of 2 kpc, the mass is quite typical of moderately evolved PNe. At this distance, the ionizing star then has a luminosity of ~5000 Lsolar, again rather typical for a PN central star. We give a brief discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars.Comment: EUROWD12 Proceeding

The planetary nebula Abell 48 and its [WN] nucleus

We have conducted a detailed multi-wavelength study of the peculiar nebula Abell 48 and its central star. We classify the nucleus as a helium-rich, hydrogen-deficient star of type [WN4-5]. The evidence for either a massive WN or a low-mass [WN] interpretation is critically examined, and we firmly conclude that Abell 48 is a planetary nebula (PN) around an evolved low-mass star, rather than a Population I ejecta nebula. Importantly, the surrounding nebula has a morphology typical of PNe, and is not enriched in nitrogen, and thus not the `peeled atmosphere' of a massive star. We estimate a distance of 1.6 kpc and a reddening, E(B-V) = 1.90 mag, the latter value clearly showing the nebula lies on the near side of the Galactic bar, and cannot be a massive WN star. The ionized mass (~0.3 M_Sun) and electron density (700 cm^-3) are typical of middle-aged PNe. The observed stellar spectrum was compared to a grid of models from the Potsdam Wolf-Rayet (PoWR) grid. The best fit temperature is 71 kK, and the atmospheric composition is dominated by helium with an upper limit on the hydrogen abundance of 10 per cent. Our results are in very good agreement with the recent study of Todt et al., who determined a hydrogen fraction of 10 per cent and an unusually large nitrogen fraction of ~5 per cent. This fraction is higher than any other low-mass H-deficient star, and is not readily explained by current post-AGB models. We give a discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars. There is now tentative evidence for two distinct helium-dominated post-AGB lineages, separate to the helium and carbon dominated surface compositions produced by a late thermal pulse. Further theoretical work is needed to explain these recent discoveries.Comment: 19 pages, 10 figures, to appear in MNRAS. Version 3 incorporates proof correction

Measurement and analysis of vibrations of the axial-flow compressor caused by inlet flow instability during the flight of aircraft

U radu je prezentovan praktičan primer merenja i analize vibracija na prva dva stepena aksijalnog kompresora sa namerom da se proceni povezanost između poremećene ulazne struje vazduha i pojave otcepljenja strujnica od lopatica kompresora. Poremećenost ulazne struje vazduha je ispitivana tokom različitih režima leta aviona sa maksimalnim potiskom, pod pretpostavkom da postoji nesimetrično strujanje vazduha kroz dvostruki uvodnik i da ono ima uticaj na pojavu vibracija kompresora. Prikazano je merenje vibracija na avionu Galeb G-2 sa motorom Rolls Royce Viper Mk22-6 sa ciljem da se prepozna i definiše minimum neophodnih podataka koji bi ukazali na potencijalnu poremećenu struju vazduha kroz kompresor, kao posledicu nejednake raspodele vazdušne struje u uvodniku. Efikasnost ove metodologije merenja predstavljena je korišćenjem Furijeovih transformacija. Predložena metodologija merenja i analize može se sprovoditi na različitim tipovima aviona u cilju istraživanja pojave otcepljenja strujnica i pumpanja kompresora.This paper presents a practical example of the measurement and analysis of vibrations in the first two stages of the axial-flow compressor with intention to estimate a connection between inlet air flow distortions and appearance of stalling of the compressor blades. The inlet air flow distortions were tested during different regimes of the aircraft flight with a maximum thrust, with an assumption that the asymmetry of air flow through the twin-inlets existed and had effect on vibrations of the compressor. The paper shows the measurement of vibrations on the Galeb G-2 aircraft powered by the Rolls Royce Viper Mk22-6 engine with the aim to recognize and define the minimum necessary data for detection of the potential distorted air flow through the compressor, as consequences of an unequal air flow distribution in the inlets. The detection capability of this methodology of measurement is presented using the fast Fourier transform (FFT). The proposed methodology of measurement and analysis can be implemented in different types of aircraft in order to research the occurrence of stall and surge

Damage tolerance analysis of structural components under general load spectrum

In this investigation fatigue behaviour of damaged structural components under cyclic loads constant amplitude and load spectrum is considered. Primary attention of this investigation is the establishment of computation procedure for the evaluation of the residual life of aircraft attachment lug type structural elements in the presence of initial cracks. In this investigation for residual life estimation and crack growth analysis Strain Energy Density ( SED) method is used. The SED method uses the low-cycle fatigue (LCF) properties of the material in crack growth analysis. In this approach experimentally obtained dynamic properties of the material such as Forman's constants are not required when this method is concerned. The complete computation procedure for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the damaged structural elements. To determine analytic expressions for stress intensity factors (SIF) singular finite elements are used. Results of numerical simulation for crack propagation based on strain density method have been compared with own experimental results

Measurement and analysis of vibrations of the axial-flow compressor caused by inlet flow instability during the flight of aircraft

U radu je prezentovan praktičan primer merenja i analize vibracija na prva dva stepena aksijalnog kompresora sa namerom da se proceni povezanost između poremećene ulazne struje vazduha i pojave otcepljenja strujnica od lopatica kompresora. Poremećenost ulazne struje vazduha je ispitivana tokom različitih režima leta aviona sa maksimalnim potiskom, pod pretpostavkom da postoji nesimetrično strujanje vazduha kroz dvostruki uvodnik i da ono ima uticaj na pojavu vibracija kompresora. Prikazano je merenje vibracija na avionu Galeb G-2 sa motorom Rolls Royce Viper Mk22-6 sa ciljem da se prepozna i definiše minimum neophodnih podataka koji bi ukazali na potencijalnu poremećenu struju vazduha kroz kompresor, kao posledicu nejednake raspodele vazdušne struje u uvodniku. Efikasnost ove metodologije merenja predstavljena je korišćenjem Furijeovih transformacija. Predložena metodologija merenja i analize može se sprovoditi na različitim tipovima aviona u cilju istraživanja pojave otcepljenja strujnica i pumpanja kompresora.This paper presents a practical example of the measurement and analysis of vibrations in the first two stages of the axial-flow compressor with intention to estimate a connection between inlet air flow distortions and appearance of stalling of the compressor blades. The inlet air flow distortions were tested during different regimes of the aircraft flight with a maximum thrust, with an assumption that the asymmetry of air flow through the twin-inlets existed and had effect on vibrations of the compressor. The paper shows the measurement of vibrations on the Galeb G-2 aircraft powered by the Rolls Royce Viper Mk22-6 engine with the aim to recognize and define the minimum necessary data for detection of the potential distorted air flow through the compressor, as consequences of an unequal air flow distribution in the inlets. The detection capability of this methodology of measurement is presented using the fast Fourier transform (FFT). The proposed methodology of measurement and analysis can be implemented in different types of aircraft in order to research the occurrence of stall and surge

Multi-objective fuzzy optimization of sizing and location of piezoelectric actuators and sensors for vibration control based on the particle swarm optimization technique (part 1: Theoretical model)

Određivanje veličine i položaja piezoelektričnih aktuatora i senzora za aktivno upravljanje vibracijama savitljivih struktura obično je bazirano na maksimalnoj efikasnosti upravljanja i postizanja maksimalnog izlaza za modove vibracija od interesa. Integracija piezoelektričnih delova utiče na masu i dinamičke performanse bazične strukutre. Ovo je prvi deo istraživanja koje predstavlja teorijski razvoj višeciljne fazi optimizacione tehnike za određivanje položaja i veličine piezoelektričnih aktuatora i senzora na tankozidnoj kompozitnoj gredi. Kriterijumi optimizacije za određivanje optimalne veličine i položaja piezoelektričnih aktuatora i senzora zasnivaju se na stepenu upravljivosti upravljanih modova. Procedura optimizacije obuhvata ograničenje promene prvobitnih dinamičkih karakteristika i ograničenje u porastu mase. Pseudociljna funkcija, zasnovana na teoriji fazi skupova, daje izraz za globalnu ciljnu funkciju eliminišući upotrebu težinskih koeficijenata i kaznenih funkcija. Optimizacija rojem čestica je upotrebljena za nalaženje optimalne konfiguracije.Sizing and location of the piezoelectric actuators and sensors for vibration control of flexible structures is usually based on maximum control effectiveness and achieving the maximum output for the vibration in the modes of interests. Integration of piezoelectric patches affects the mass and the original dynamic properties of the parent structure. This is the first part of the two-paper research which presents the theoretical development of the multi-objective fuzzy optimization technique of sizing and location of the collocated piezoelectric actuators and sensors on the thin-walled composite beam. The optimization criteria for the optimal size and location of piezoelectric A/Ss are based on the degree of controllability (DC) for controlled modes. The optimization procedure implies the constraining of the original dynamic properties change and the limitation of the mass increase. A pseudogoal function, derived based on the fuzzy set theory, gives an expression for global objective functions eliminating the use of weighting coefficients and penalty functions. the particle swarm optimization technique is used to find the optimal configuration.

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

Multi-objective fuzzy optimization of sizing and location of piezoelectric actuators and sensors for vibration control based on the particle swarm optimization technique (part 1: Theoretical model)

Određivanje veličine i položaja piezoelektričnih aktuatora i senzora za aktivno upravljanje vibracijama savitljivih struktura obično je bazirano na maksimalnoj efikasnosti upravljanja i postizanja maksimalnog izlaza za modove vibracija od interesa. Integracija piezoelektričnih delova utiče na masu i dinamičke performanse bazične strukutre. Ovo je prvi deo istraživanja koje predstavlja teorijski razvoj višeciljne fazi optimizacione tehnike za određivanje položaja i veličine piezoelektričnih aktuatora i senzora na tankozidnoj kompozitnoj gredi. Kriterijumi optimizacije za određivanje optimalne veličine i položaja piezoelektričnih aktuatora i senzora zasnivaju se na stepenu upravljivosti upravljanih modova. Procedura optimizacije obuhvata ograničenje promene prvobitnih dinamičkih karakteristika i ograničenje u porastu mase. Pseudociljna funkcija, zasnovana na teoriji fazi skupova, daje izraz za globalnu ciljnu funkciju eliminišući upotrebu težinskih koeficijenata i kaznenih funkcija. Optimizacija rojem čestica je upotrebljena za nalaženje optimalne konfiguracije.Sizing and location of the piezoelectric actuators and sensors for vibration control of flexible structures is usually based on maximum control effectiveness and achieving the maximum output for the vibration in the modes of interests. Integration of piezoelectric patches affects the mass and the original dynamic properties of the parent structure. This is the first part of the two-paper research which presents the theoretical development of the multi-objective fuzzy optimization technique of sizing and location of the collocated piezoelectric actuators and sensors on the thin-walled composite beam. The optimization criteria for the optimal size and location of piezoelectric A/Ss are based on the degree of controllability (DC) for controlled modes. The optimization procedure implies the constraining of the original dynamic properties change and the limitation of the mass increase. A pseudogoal function, derived based on the fuzzy set theory, gives an expression for global objective functions eliminating the use of weighting coefficients and penalty functions. the particle swarm optimization technique is used to find the optimal configuration.

Factors affecting titratable acidity in raw milk

The value of titratable acidity (TA) as an indicator of raw milk quality has been challenged recently, because milk is refrigerated within minutes after it leaves the cow until it reaches the consumer. Also, high milk protein may interfere with the test or confer falsely high TA values. Samples of milk containing 3.8% protein were used to examine the impact of protein on TA. The effects of milk age and bacterial counts also were investigated. Titratable acidity increased as milk protein content increased but the influence of bacterial populations and age were much more dramatic. As bacterial counts increased, TA values surpassed an acceptable level (upper maximum at .17%) for the KSU Dairy Processing Plant. At the same time, as raw milk increased in age, TA increased to the upper level of acceptability (.17%). Thus, TA appears to be a valid method of evaluating raw milk quality even though it can be influenced by the protein content