685 research outputs found
Zero Dimensional Field Theory of Tachyon Matter
The first issue about the object (now) called tachyons was published almost
one century ago. Even though there is no experimental evidence of tachyons
there are several reasons why tachyons are still of interest today, in fact
interest in tachyons is increasing. Many string theories have tachyons
occurring as some of the particles in the theory. In this paper we consider the
zero dimensional version of the field theory of tachyon matter proposed by A.
Sen. Using perturbation theory and ideas of S. Kar, we demonstrate how this
tachyon field theory can be connected with a classical mechanical system, such
as a massive particle moving in a constant field with quadratic friction. The
corresponding Feynman path integral form is proposed using a perturbative
method. A few promising lines for further applications and investigations are
noted.Comment: 2 pages, Talk presented at the 6th International Conference of Balkan
Physical Union - BPU6, Istanbul, Turkey, August 22-26. 200
The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations
By taking into account relativistic corrections to the magnetic dipole
operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98
is obtained. In order to check this new value using AGN spectra we present the
measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a
sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database
and from published observations. We select only high signal-to-noise ratio
spectra for which the line shapes of the [OIII] 4959,5007 lines are the same.
We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good
agreement with the theoretical one.Comment: Accepted for publication in the MNRA
On the influence of Stark broadening on Si I lines in stellar atmospheres
We study the influence of Stark broadening and stratification effects on Si\i
lines in the rapidly oscillating (roAp) star 10 Aql, where the Si\i 6142.48 \AA
and 6155.13 \AA lines are asymmetrical and shifted. First we have calculated
Stark broadening parameters using the semiclassical perturbation method for
three Si\i lines: 5950.2 \AA, 6142.48 \AA and 6155.13 \AA. We revised the
synthetic sp$ calculation code taking into account both Stark width and shift
for these lines. From the comparison of our calculations with the observations
we found that Stark broadening + the stratification effect can explain
asymmetry of the Si\i 6142.48 \AA and 6155.13 \AA lines in the atmospere of
roAp star 10 Aql.Comment: Accepted to A&
Clinical-parasitological screening for respiratory capillariosis in cats in urban environments
Respiratory capillariosis is a widely distributed zoonotic parasitic disease caused by the nematode Capillaria aerophila (Trichocephalida, Trichuridae) that commonly infects wild carnivores butalso cats and dogs. This retrospective study aims to describe cases of respiratory capillariosis incats from the city of Belgrade, Serbia. Between 2015 and 2019, a total of 155 pet cats with or without respiratory symptoms were submitted to physical examination and parasitological examination of the feces. All cats lived indoor but had free access to outdoor. In suburban settlements, wild carnivores commonly share their living environments with owned cats and dogs. It can be assumed that more intense urbanization spreading into the natural habitats of will carnivores creates the opportunity for closer and more frequent contacts between the population of cats and feral carnivores whichmight increase the risk of feline contamination. The findings confirm the existence of capillaries in cats in urban areas of the city of Belgrade, contribute to a better understanding of the epidemiology of this nematode and warn that, because of close contacts between cats of pets and humans, capillaries can cause human infection
New Technologies for Ecosystem Analysis Planning and Management
Planning the rural environment is one of the most intriguing examples of technical challenge where a multi-disciplinary approach plays a crucial role. The agricultural production, both food and non-food, the social role of rural settlements, the state and diffusion of the infrastructural networks, the rural architectonic heritage that in many countries constitutes a major positive value, should be appropriately considered and sinergically interlaced for a sound planning of agricultural biosystems.
Human activities impose a transformation of the extra-urban land that may lead to the modification of the frail equilibrium of whole ecosystems. Sound planning strategies should be therefore pursued, employing a multidisciplinary approach that should take into account geographical, environmental and landscape factors as variables interacting among themselves and with the social and economic aspects. In order to simultaneously analyse all these properties, tools able to manage, interpret and integrate several data are necessary
On the influence of Stark broadening on Cr I lines in stellar atmospheres
Using the semiclassical perturbation method, electron-, proton-, and ionized
helium-impact line widths and shifts for the nine Cr I spectral lines from the
multiplet, have been calculated for a perturbers density of
10 cm and temperatures T =2,500 - 50,000 K. The obtained results
have been used to investigate the influence of Stark broadening effect in the
Cr-rich Ap star CrB atmosphere on line shapes of these lines. It has
been found that the contribution of the proton and He II collisions to the line
width and shift is significant, and it is comparable and sometimes (depending
of the electron temperature) even larger than electron-impact contribution.
Moreover, not only the Stark line width, but, depending on the electron-,
proton-, and He\ii density in stellar atmosphere also the Stark shift may
contribute to the blue as well as to the red asymmetry of the same line. The
obtained results have been used to investigate the influence of Stark
broadening effect on line shapes of Cr\i lines in the atmosphere of Cr-rich Ap
star CrB.Comment: 8 pages, Astron. Astrophys. accepte
- …