Jagiellonian University

About: Jagiellonian University is a education organization based out in Krakow, Poland. It is known for research contribution in the topics: Population & Catalysis. The organization has 17438 authors who have published 44092 publications receiving 862633 citations. The organization is also known as: Academia Cracoviensis & Akademia Krakowska.

Radiation from the Relativistic Jet: A Role of the Shear Boundary Layer

Abstract: Recent radio and optical large-scale jet observations suggest a two-component jet morphology, consisting of a fast central spine surrounded by a boundary layer with a velocity shear. We study radiation of electrons accelerated at such boundary layers as an option for standard approaches involving internal shocks in jets. The acceleration process in the boundary layer yields in a natural way a two-component electron distribution: a power-law continuum with a bump at the energy where energy gains equal radiation losses, followed by a cutoff. For such distributions, we derive the observed spectra of synchrotron and inverse Compton radiation, including Comptonization of synchrotron and cosmic microwave background photons. Under simple assumptions of energy equipartition between the relativistic particles and the magnetic field, the relativistic jet velocity at large scales, and a turbulent character of the shear layer, the considered radiation can substantially contribute to the jet radiative output. In the considered conditions the synchrotron emission is characterized by a spectral index of the radio-to-optical continuum being approximately constant along the jet. A characteristic feature of the obtained broadband synchrotron spectrum is an excess at X-ray frequencies, similar to the one observed in some objects by Chandra. As compared to the uniform jet models, the velocity shear across the radiating boundary region leads to a decrease and frequency dependence of the observed jet-counterjet radio brightness asymmetry. We conclude that a careful investigation of the observational data looking for the derived effects can allow us to evaluate the role of the boundary layer acceleration processes and/or impose constraints for the physical parameters of such layers in large-scale jets.

Coffee components and cardiovascular risk: beneficial and detrimental effects

Abstract: Coffee consists of several biological active compounds, such as caffeine, diterpenes, chlorogenic acids, and melanoidins, which may affect human health. The intake of each compound depends on the variety of coffee species, roasting degree, type of brewing method and serving size. The bioavailability and the distribution of each compound and its metabolites also contribute to coffee mechanisms of action. The health benefits of coffee consumption regarding cardiovascular system and metabolism mostly depend on its antioxidant compounds. In contrast, diterpenes and caffeine may produce harmful effects by raising lipid fraction and affecting endothelial function, respectively. Studying the mechanism of action of coffee components may help understanding whether coffee's impact on health is beneficial or hazardous. In this article, we reviewed the available information about coffee compounds and their mechanism of action. Furthermore, benefits and risks for cardiovascular system associated with coffee consumption will be discussed.

Detecting domain walls of axionlike models using terrestrial experiments

Abstract: Stable topological defects of light (pseudo)scalar fields can contribute to the Universe's dark energy and dark matter. Currently, the combination of gravitational and cosmological constraints provides the best limits on such a possibility. We take an example of domain walls generated by an axionlike field with a coupling to the spins of standard-model particles and show that, if the galactic environment contains a network of such walls, terrestrial experiments aimed at the detection of wall-crossing events are realistic. In particular, a geographically separated but time-synchronized network of sensitive atomic magnetometers can detect a wall crossing and probe a range of model parameters currently unconstrained by astrophysical observations and gravitational experiments.

Assessing bee species richness in two Mediterranean communities: importance of habitat type and sampling techniques

Abstract: The decline of bees has raised concerns regarding their conservation and the maintenance of ecosystem services they provide to bee-pollinated wild flowers and crops. Although the Mediterranean region is a hotspot for bee species richness, their status remains poorly studied. There is an urgent need for cost-effective, reliable, and unbiased sampling methods that give good bee species richness estimates. This study aims: (a) to assess bee species richness in two common Mediterranean habitat types: semi-natural scrub (phrygana) and managed olive groves; (b) to compare species richness in those systems to that of other biogeographic regions, and (c) to assess whether six different sampling methods (pan traps, variable and standardized transect walks, observation plots and trap nests), previously tested in other European biogeographic regions, are suitable in Mediterranean communities. Eight study sites, four per habitat type, were selected on the island of Lesvos, Greece. The species richness observed was high compared to other habitat types worldwide for which comparable data exist. Pan traps collected the highest proportion of the total bee species richness across all methods at the scale of a study site. Variable and standardized transect walks detected the highest total richness over all eight study sites. Trap nests and observation plots detected only a limited fraction of the bee species richness. To assess the total bee species richness in bee diversity hotspots, such as the studied habitats, we suggest a combination of transect walks conducted by trained bee collectors and pan trap sampling.