Determination of prestressing levels for cable trusses as a function of their stability

U radu se analizira stabilnost prethodno napregnutih kabelskih rešetki na djelovanje statičkih i dinamičkih opterećenja. Krutost elastičnog sustava kabelskih rešetki varirana je promjenom sila prednaprezanja. Rezultati analiziranih modela za različite razine zategnutosti pokazali su da je u pogledu zadovoljenja uvjeta dinamičke otpornosti potrebna mnogo veća sila zatezanja za kabelske rešetke s dijagonalnim štapovima u odnosu na one s vertikalnim štapovima. Izvedeni zaključci su preporuka za primjenu metoda za proračun kao i utvrđivanje sila prednaprezanja pod kojima su ispunjeni uvjeti stabilnosti.The stability of prestressed cable trusses subjected to static and dynamic loads is analysed in the paper. The stiffness of the elastic cable truss system was varied by changing the prestressing force. Modelling results for different levels of tension show that, in terms of satisfying dynamic resistance conditions, a much greater tensile force is required for cable grids with diagonal members, compared to those with vertical rods. The conclusions derived constitute recommendations for the use of calculation methods, as well as for the determination of prestressing forces under which stability criteria are fulfilled

NGC 300: an extremely faint, outer stellar disk observed to 10 scale lengths

We have used the Gemini Multi-object Spectrograph (GMOS) on the Gemini South 8m telescope in exceptional conditions (0.6" FWHM seeing) to observe the outer stellar disk of the Sculptor group galaxy NGC 300 at two locations. At our point source detection threshold of r' = 27.0 (3-sigma) mag, we trace the stellar disk out to a radius of 24', or 2.2 R_25 where R_25 is the 25 mag/arcsec**2 isophotal radius. This corresponds to about 10 scale lengths in this low-luminosity spiral (M_B = -18.6), or about 14.4 kpc at a cepheid distance of 2.0 +/- 0.07 Mpc. The background galaxy counts are derived in the outermost field, and these are within 10% of the mean survey counts from both Hubble Deep Fields. The luminosity profile is well described by a nucleus plus a simple exponential profile out to 10 optical scale lengths. We reach an effective surface brightness of 30.5 mag/arcsec**2 (2-sigma) at 55% completeness which doubles the known radial extent of the optical disk. These levels are exceedingly faint in the sense that the equivalent surface brightness in B or V is about 32 mag/arcsec**2. We find no evidence for truncation of the stellar disk. Only star counts can be used to reliably trace the disk to such faint levels, since surface photometry is ultimately limited by nonstellar sources of radiation. In the Appendix, we derive the expected surface brightness of one such source: dust scattering of starlight in the outer disk.Comment: ApJ accepted -- 30 pages, 13 figures -- see ftp://www.aao.gov.au/pub/local/jbh/astro-ph/N300 for full resolution figures and preprin

Radial migration in galactic disks caused by resonance overlap of multiple patterns: Self-consistent simulations

We have recently identified a new radial migration mechanism resulting from the overlap of spiral and bar resonances in galactic disks. Here we confirm the efficiency of this mechanism in fully self-consistent, Tree-SPH simulations, as well as high-resolution pure N-body simulations. In all barred cases we clearly identify the effect of spiral-bar resonance overlap by measuring a bimodality in the changes of angular momentum in the disk, dL, whose maxima are near the bar's corotation and outer Lindblad resonance. This contrasts with the smooth distribution of dL for a simulation with no stable bar present, where strong radial migration is induced by multiple spirals. The presence of a disk gaseous component appears to increase the rate of angular momentum exchange by about 20%. The efficiency of this mechanism is such that galactic stellar disks can extend to over 10 scale-lengths within 1-3 Gyr in both Milky Way size and low-mass galaxies (circular velocity ~100 km/s). We also show that metallicity gradients can flatten in less than 1 Gyr rendering mixing in barred galaxies an order of magnitude more efficient than previously thought.Comment: replaced with accepted version: 5 pages, 5 figures (one new figure added), minor change

Evolution of Galactic Discs: Multiple Patterns, Radial Migration and Disc Outskirts

We investigate the evolution of galactic disks in N-body Tree-SPH simulations. We find that disks, initially truncated at three scale-lengths, can triple their radial extent, solely driven by secular evolution. Both Type I (single exponential) and Type II (down-turning) observed disk surface-brightness profiles can be explained by our findings. We relate these results to the strong angular momentum outward transfer, resulting from torques and radial migration associated with multiple patterns, such as central bars and spiral waves of different multiplicity. We show that even for stars ending up on cold orbits, the changes in angular momentum exhibit complex structure as a function of radius, unlike the expected effect of transient spirals alone. Focussing on one of our models, we find evidence for non-linear coupling among m=1, 2, 3 and 4 density waves, where m is the pattern multiplicity. We suggest that the naturally occurring larger resonance widths at galactic radii beyond four scale-lengths may have profound consequences on the formation and location of breaks in disk density profiles, provided spirals are present at such large distances. We also consider the effect of gas inflow and show that when in-plane smooth gas accretion of ~5 M_sun/yr is included, the outer disks become more unstable, leading to a strong increase in the stellar velocity dispersion. This, in turn, causes the formation of a Type III (up-turning) profile in the old stellar population. We propose that observations of Type III surface brightness profiles, combined with an up-turn in the stellar velocity dispersions beyond the disk break, could be a signature of ongoing gas-accretion. The results of this study suggest that disk outskirts comprised of stars migrated from the inner disk would have relatively large radial velocity dispersions, and significant thickness when seen edge-on. [Abridged]Comment: Replaced with accepted version. New Fig. 5 added, Section 10 decreased in size, old Fig. 17 removed. Conclusions remain the same. High-resolution version can be found at http://www.ivanminchev.co

Trophic chain Yersinia pseudotuberculosis

This paper tries to reproduce two types of trophic chains on the example of an aquatic ecosystem model, with the participation of planktonic and benthic organisms: "yersinia - infusoria - daphnia - fish" and "yersinia - insect larvae - fish". The concentration of Yersinia pseudotuberculosis during primary infection (infusoria culture medium) was 109/ml. In the first hours after infection, the concentration of bacteria in the infusoria decreased (105cfu/mass ). In daphnia, which consumed infected infusoria, the concentration of Yersinia pseudotuberculosis decreases in the first 3-5 days (from 105 to 103 cfu/10 individuals), then the reproduction of Yersinia pseudotuberculosis in daphnia continues, and on the 11th day it reaches 107 cfu/10 individuals. The concentration of Yersinia pseudotuberculosis in the intestines of fish fed infected daphnia (107cfu/10 individuals) is continuously decreasing: 105 cfu (after 24 hours) and 102-101 cfu/individuals (after 15-30 days)

Survival of Yersinia pseudotuberculosis in soil

The dynamics of the pseudotuberculous microbes population number in the soil was monitored with the use of bacteriological method. The number of this microbe increased during the first week to 106 -5x106 CFU/ml, after which it stabilized until the third week at level 106, after which there is a continuous decline in the number of Yersinia pseudotuberculosis until the end of the second month, when their growth stops

Supplementary data for article: Mandić, B. M.; Vlajić, M. D.; Trifunović, S. S.; Simić, M. R.; Vujisić, L. V.; Vučković, I. M.; Novaković, M. M.; Nikolić-Mandić, S. D.; Tešević, V. V.; Vajs, V. V.; et al. Optimisation of Isolation Procedure for Pyrrolizidine Alkaloids from Rindera Umbellata Bunge. Natural Product Research 2015, 29 (9), 887–890. https://doi.org/10.1080/14786419.2014.991929

Supplementary material for: [https://doi.org/10.1080/14786419.2014.991929]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1692

An Oxygen Abundance Gradient into the Outer Disk of M81

The extended HI disk and tidal tails of M81 present an interesting environment to study the effects of galaxy interaction on star formation and chemical evolution of the outer disk of a large spiral galaxy. We present H{\alpha} imaging of the outer disk of M81 and luminosities for 40 HII regions out to about 3 times the optical radius. We have also obtained MMT spectra for 21 HII regions out to more than twice the optical radius. We derive strong line oxygen abundances for all HII regions using R_{23} based and [NII]/[OII] based calibrations and electron temperature abundances for seven regions spanning a galactocentric distance between 5.7 and 32 kpc. We also comment on the abundances of HII regions near KDG 61 and the "tidal dwarf" candidate HoIX. Our results constitute the most radially extended metallicity study for M81 to date. With this extended data set, we find an overall oxygen abundance gradient of -0.013 dex/kpc over the entire radial range. This is significantly flatter than what has been found in previous studies which were limited to the optical disk. From our temperature based abundances, we find a gradient of -0.020 dex/kpc and present the possibility of a broken gradient from these data, but note the need to obtain more temperature based abundances at intermediate galactocentric distances (~10-20 kpc) to verify whether or not this may be the case. We discuss our main result of a rather flat gradient for M81 in the context of simulations and observations of abundance gradients in other galaxies. We find that the shallow abundance gradient of M81 is likely a result of the interaction history of this galaxy.Comment: 41 pages, 11 figures, accepted for publication in MNRA

Supplementary data for article: Mandić, B. M.; Vlajić, M. D.; Trifunović, S. S.; Simić, M. R.; Vujisić, L. V.; Vučković, I. M.; Novaković, M. M.; Nikolić-Mandić, S. D.; Tešević, V. V.; Vajs, V. V.; et al. Optimisation of Isolation Procedure for Pyrrolizidine Alkaloids from Rindera Umbellata Bunge. Natural Product Research 2015, 29 (9), 887–890. https://doi.org/10.1080/14786419.2014.991929

Supplementary material for: [https://doi.org/10.1080/14786419.2014.991929]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/1692

Rehabilitation and construction of bridges damaged in NATo-bombardment of SR Yugoslavia in 1999

Structural engineers from Serbia and nearby countries have long tradition in area of design and construction of bridges. Beside ancient stone bridges from the past centuries, in the second half of the XX century, significant professional and science level in all areas of bridge construction have been achieved. Many of projects from that time have become famous all around the globe and were object of pride for everyone included in realization of those. Regretfully, during seventy eight days, in the period from 24th March till the 10th July 1999, in NATO bombardment of SR Yugoslavia, 44 road, 17 railway and one road railway bridge have been totally or partially destroyed. In this article have been described structural damages, rehabilitation and construction, with short description of characteristic cases of bridges, which have been object of bombardment