Observational detection of meteor-produced VLF electromagnetic radiation

In November 1998, Croatian Physical Society's expedition to Mongolia was undertaken. The goal was to make measurements of the puzzling electrophonic sounds and very low frequency (VLF) radio emission from meteors during the anticipated Leonid meteor storm. During the night of 16/17 November 1998, an extremely high fireball activity of the Leonid meteors occured. During this period, we performed measurements of the VLF radiation from meteors. Here we present a positive signal which consists of a sequence of sharp, short VLF bursts, coincident with the appearance of meteor that was recorded by the video camera. This is the first completely controlled instrumental recording of such an event

INFLUENCE OF BIOSTIMULANT ON SEED GERMINATION OF SOME FLOWER SPECIES

U ovom istraživanju ispitan je učinak biostimulatora na energiju klijanja, klijavost, masu svježe i suhe tvari klijanaca kod prkosa, slamnatog cvijeta, kadife i cinije. Energija klijanja i klijavost su ispitane laboratorijski, a po završetku ispitivanja obavljeno je mjerenje svježe i suhe tvari klijanaca. Statističkom obradom podataka analizom varijance utvrđeno je da tretman biostimulatorima pozitivno utječe na poboljšanje energije klijanja, a kod nekih vrsta i na klijavost. Mase svježe i suhe tvari klijanaca su uglavnom bile na strani tretmana sa biostimulatorom, pogotovo kada je u pitanju masa svježe tvari što govori u prilog pojačanom usvajanju vode i boljoj aktivnosti korijena u fazi klijanja koje može biti od presudnog značaja za preživljavanje klijanaca. Na kraju istraživanja može se zaključiti da je tretman biostimulatorima u fazi klijanja ispitivanih vrsta dao pozitivan učinak na ispitivana svojstva.In this research influence of biostimulant on germination energy, germination, seedlings fresh matter content and dry matter content of Moss rose, Strawflower, Mexican marigold and Zinnia was investigated. Germination energy and germination were tested in laboratory and by finishing the testing seedlings fresh matter content and dry matter content were recorded. Statistical analysis of data using analysis of variance method showed that treatment with biostimulant positively affects on germination energy and by some species on germination as well. Seedlings fresh and dry matter content were mostly higher in treated plants, especially in case of fresh matter content. This leads to assumption of higher water absorption and higher root activity in germination phase which can be of crucial significance for seedlings survival. At the end of investigation it can be concluded that treatment with biostimulant in germination phase of mentioned species gave positive results in the first place by increasing germination energy and seedlings fresh matter content

Opažanje niskofrekventnog elektromagnetskog zračenja proizvedenog meteorom

In November 1998, Croatian Physical Society\u27s expedition to Mongolia was undertaken. The goal was to make measurements of the puzzling electrophonic sounds and very low frequency (VLF) radio emission from meteors during the anticipated Leonid meteor storm. During the night of 16/17 November 1998, an extremely high fireball activity of the Leonid meteors occured. During this period, we performed measurements of the VLF radiation from meteors. Here we present a positive signal which consists of a sequence of sharp, short VLF bursts, coincident with the appearance of meteor that was recorded by the video camera. This is the first completely controlled instrumental recording of such an event.Ekspedicija Hrvatskog fizikalnog društvo uputila se u Mongoliju u studenom 1998 radi promatranja očekivane kiše meteora i mjerenja neobičnih elektrofonskih šumova i niskofrekventnog elektromagnetskog zračenja proizvedenog meteorima. U noći 16/17 studenog 1998. došlo je do izrazito pojačane aktivnosti sjajnih meteora Leonida. U tom smo periodu mjerili elektromagnetske valove VLF i istovremeno snimali meteore. Ovdje izvješćujemo o zabilježenom signalu elektromagnetskih valova koji se sastojao od niza kratkotrajnih niskofrekventnih impulsa, koji se pojavio istovremeno s meteorom. Ovo je prvo instrumentalno bilježenje te pojave načinjeno u potpuno kontroliranim uvjetima

Luminosity indicators in dusty photoionized environments

The luminosity of the central source in ionizing radiation is an essential parameter in a photoionized environment, and one of the most fundamental physical quantities one can measure. We outline a method of determining luminosity for any emission-line region using only infrared data. In dusty environments, grains compete with hydrogen in absorbing continuum radiation. Grains produce infrared emission, and hydrogen produces recombination lines. We have computed a very large variety of photoionization models, using ranges of abundances, grain mixtures, ionizing continua, densities, and ionization parameters. The conditions were appropriate for such diverse objects as H II regions, planetary nebulae, starburst galaxies, and the narrow and broad line regions of active nuclei. The ratio of the total thermal grain emission relative to H$\beta$ (IR/H$\beta$) is the primary indicator of whether the cloud behaves as a classical Str\"{o}mgren sphere (a hydrogen-bounded nebula) or whether grains absorb most of the incident continuum (a dust-bounded nebula). We find two global limits: when $IR/H\beta<100$ infrared recombination lines determine the source luminosity in ionizing photons; when $IR/H\beta\gg100$ the grains act as a bolometer to measure the luminosity.Comment: 12 pages 3 figures. Accepted ASP Sept.9

Biologically active adamantane derivatives

Derivati adamantana prekrivaju vrlo široko područje biološke aktivnosti. U ovom prikazu obrađeni su karakteristični primjeri: virustatici i antiparkinsonici, antibiotici, citostatici, hipoglikernici, antiaritmici i antihipertonici, sedativi i antidepresanti, imunosupresivni agensi i spazmolitici. Veća biološka aktivnost derivata adamantana u odnosu na poznate lijekove posljedica je veće otpornosti prema metabolitičkoj razgradnji, veće lipofilnosti i bržeg transporta kroz membrane stanica.Adamantane derivatives cover a very broad spectrum of biological activities. In this review characteristic examples are described: virustatics and antiparkinsonics, antibiotics, cytostatics, hypoglycemics, sedatives and antidepressants, antiarrythmics and antihypertonics, immunosuppressive agents and spasmolytics. A higher biological activity of adamantane derivatives than that of some known drugs is a consequence of their higher lipophilicity more rapid transport through cell membranes and higher resistance to metabolitic degradation

Observational detection of meteor-produced VLF electromagnetic radiation

In November 1998, Croatian Physical Society's expedition to Mongolia was undertaken. The goal was to make measurements of the puzzling electrophonic sounds and very low frequency (VLF) radio emission from meteors during the anticipated Leonid meteor storm. During the night of 16/17 November 1998, an extremely high fireball activity of the Leonid meteors occured. During this period, we performed measurements of the VLF radiation from meteors. Here we present a positive signal which consists of a sequence of sharp, short VLF bursts, coincident with the appearance of meteor that was recorded by the video camera. This is the first completely controlled instrumental recording of such an event

Relation between the luminosity of young stellar objects and their circumstellar environment

We present a new model-independent method of comparison of NIR visibility data of YSOs. The method is based on scaling the measured baseline with the YSO's distance and luminosity, which removes the dependence of visibility on these two variables. We use this method to compare all available NIR visibility data and demonstrate that it distinguishes YSOs of luminosity >1000L_sun (low-L) from YSOs of <1000L_sun (high-L). This confirms earlier suggestions, based on fits of image models to the visibility data, for the difference between the NIR sizes of these two luminosity groups. When plotted against the ``scaled'' baseline, the visibility creates the following data clusters: low-L Herbig Ae/Be stars, T Tauri stars, and high-L Herbig Be stars. The T Tau cluster is similar to the low-L Herbig Ae/Be cluster, which has ~7 times smaller ``scaled'' baselines than the high-L Herbig Be cluster. We model the shape and size of clusters with different image models and find that low-L Herbig stars are the best explained by the uniform brightness ring and the halo model, T Tauri stars with the halo model, and high-L Herbig stars with the accretion disk model. However, the plausibility of each model is not well established. Therefore, we try to build a descriptive model of the circumstellar environment consistent with various observed properties of YSOs. We argue that low-L YSOs have optically thick disks with the optically thin inner dust sublimation cavity and an optically thin dusty outflow above the inner disk regions. High-L YSOs have optically thick accretion disks with high accretion rates enabling gas to dominate the NIR emission over dust. Although observations would favor such a description of YSOs, the required dust distribution is not supported by our current understanding of dust dynamics.Comment: 20 pages, 12 figures, Accepted for publication in the Astrophysical Journa

Schelling Segregation with Strategic Agents

Schelling's segregation model is a landmark model in sociology. It shows the counter-intuitive phenomenon that residential segregation between individuals of different groups can emerge even when all involved individuals are tolerant. Although the model is widely studied, no pure game-theoretic version where rational agents strategically choose their location exists. We close this gap by introducing and analyzing generalized game-theoretic models of Schelling segregation, where the agents can also have individual location preferences. For our models, we investigate the convergence behavior and the efficiency of their equilibria. In particular, we prove guaranteed convergence to an equilibrium in the version which is closest to Schelling's original model. Moreover, we provide tight bounds on the Price of Anarchy.Comment: Accepted at SAGT 2018, 19 pages, 9 figure

Probing the envelopes of massive young stellar objects with diffraction limited mid-infrared imaging

Massive stars form whilst they are still embedded in dense envelopes. As a result, the roles of rotation, mass loss and accretion in massive star formation are not well understood. This study evaluates the source of the Q-band, lambda=19.5 microns, emission of massive young stellar objects (MYSOs). This allows us to determine the relative importance of rotation and outflow activity in shaping the circumstellar environments of MYSOs on 1000 AU scales. We obtained diffraction limited mid-infrared images of a sample of 20 MYSOs using the VLT/VISIR and Subaru/COMICS instruments. For these 8 m class telescopes and the sample selected, the diffraction limit, ~0.6", corresponds to approximately 1000 AU. We compare the images and the spectral energy distributions (SEDs) observed to a 2D, axis-symmetric dust radiative transfer model that reproduces VLTI/MIDI observations of the MYSO W33A. We vary the inclination, mass infall rate, and outflow opening angle to simultaneously recreate the behaviour of the sample of MYSOs in the spatial and spectral domains. The mid-IR emission of 70 percent of the MYSOs is spatially resolved. In the majority of cases, the spatial extent of their emission and their SEDs can be reproduced by the W33A model featuring an in-falling, rotating dusty envelope with outflow cavities. There is independent evidence that most of the sources which are not fit by the model are associated with ultracompact HII regions and are thus more evolved. We find that, in general, the diverse 20 micron morphology of MYSOs can be attributed to warm dust in the walls of outflow cavities seen at different inclinations. This implies that the warm dust in the outflow cavity walls dominates the Q-band emission of MYSOs. In turn, this emphasises that outflows are an ubiquitous feature of massive star formation.Comment: Accepted for publication in A&A. The images in this version have been compressed. A high resolution version is available on reques