Iranian Journal of Astronomy and AstrophysicsIranian Journal of Astronomy and Astrophysics
http://ijaa.du.ac.ir/
Sat, 21 Jul 2018 06:35:30 +0100FeedCreatorIranian Journal of Astronomy and Astrophysics
http://ijaa.du.ac.ir/
Feed provided by Iranian Journal of Astronomy and Astrophysics. Click to visit.Investigation of Behavior and Trend of Nitrogen Dioxide in Tehran Using OMI Satellite Sensor ...
http://ijaa.du.ac.ir/article_107_22.html
Air pollution is one of the most important problems in the world’s major cities in the last century because it endangers human health and the environment. One of the indicators of air pollution is nitrogen dioxide, which is continuously measured by satellite from space and via ground-based instruments. In this paper, the data for nitrogen dioxide was measured by OMI over Tehran. Wind, surface temperature and horizontal visibility were recorded at Mehrabad Meteorological Station during the period from October 2004 to May 2016 to evaluate the behavior and trends of air pollution. The average amount of nitrogen dioxide during the spring, summer, autumn and winter seasons were 6.99 ×1015, 6.22 ×1015, 16.90 ×1015, and 19.65 ×1015 molec/cm2 with the highest (lowest) value occurring in the winter (summer). Also, the highest (lowest) standard deviation occurred in the winter (summer), which was 14.84 ×1015 (3.73 ×1015). The correlation coefficient of nitrogen dioxide with wind and temperature were -0.04 and -0.59, respectively, which show a greater effect of temperature on nitrogen dioxide changes. Also, the correlation coefficient of nitrogen dioxide with horizontal visibility was -0.20, which indicates a reduction of horizontal visibility with increasing urban pollution in Tehran. The nitrogen dioxide trend was calculated using linear regression after eliminating four, six, and twelve-month periods with 95% confidence. The trend of nitrogen dioxide was 5.76 ×1014 molec/ cm2 per year.Thu, 21 Dec 2023 20:30:00 +0100The dependence of the magnetic field strength of a sunspot umbra on its intensity and ...
http://ijaa.du.ac.ir/article_109_22.html
A partial decrease of the convective energy by the magnetic field of a sunspot causes the temperature of the magnetized plasma to decrease and this leads to a magneto-hydrostatic equilibrium. Thus, we expect a strong relation between magnetic field strength of a sunspot and its temperature/brightness. Here, we investigate this relation in the umbra of the large sunspot in NOAA10930 using spectro-polarimetric data recorded by Solar Optical Telescope on board Hinode. The magnetic field strength is measured by two methods: 1) using the Stokes V profile of the neutral iron 630.25 nm line, and 2) running SIR inversion code on the full Stokes profiles of the two neutral iron 630.15 and 630.25 nm lines. The general behavior is the decreasing of magnetic field strength with temperature/intensity. For intensities less than about 0:2Iph (brightness temperature 4280 K; Iph is the mean photospheric intensity around the sunspot), decreasing magnetic field strength with increasing intensity has a steeper gradient, a power law function clearly explains the non-linear variations of magnetic field strength versus temperature/intensity. For intensities larger than 0:2Iph, at a given intensity, the range of the deviation of magnetic field strength is as large as 0.5 kG. By looking for the location of these points on the studied umbral region, we find that these points are belong to the inner penumbra where penumbral filaments intrude into the dark umbra at two corners of the studied umbral region which shows different magnetic field strengths. This difference can be due to the difference between the evolutionary stages of the penumbral filaments at the two corners during the observation period. For intensities less than 0:2Iph, the observed deviation around the power law behavior is partially due to the presence of umbral dots. Since umbral dots are brighter than the umbra, and the layers of optical depth unity are moved to higher heights, a smaller magnetic field strength may be measured in umbral dots. This causes the data points shift to larger intensities and smaller magnetic field strengths on the corresponding scatter plot. Since the increase in intensity and the decrease in magnetic field strength on different umbral dots are different, the scattering around the power law is explained.Sat, 30 Sep 2017 20:30:00 +0100A meshless discrete Galerkin method for solving the universe evolution differential equations ...
http://ijaa.du.ac.ir/article_110_22.html
In terms of observational data, there are some problems in the standard Big Bang cosmological model. Inflation era, early accelerated phase of the evolution of the universe, can successfully solve these problems. The inflation epoch can be explained by scalar inflaton field. The evolution of this field is presented by a non-linear differential equation. This equation is considered in FLRW model. In FLRW model, we consider the universe as the warped product of real line with a three dimensional homogeneous and isotropic manifold _ which could have positive, negative or zero curvature. The main aim of this paper is the numerical solution of the inflation evolution differential equations using of a meshless discrete Galerkin method. The method reduces the solution of these types of differential equations to the solution of Volterra integral equations of the second kind. Therefore, we solve these integral equations using moving least squares method. Finally, a numerical example is included to show the validity and efficiency of the new technique.Sat, 30 Sep 2017 20:30:00 +0100Radiative heat transfer: many-body effects
http://ijaa.du.ac.ir/article_111_22.html
Heat transfer by electromagnetic radiation is one of the common methods of energy transfer between objects. Using the fluctuation-dissipation theorem, we have studied the effect of particle arrangement in the transmission of radiative heat in many-body systems. In order to show the effect of the structure morphology on the collective properties, the radiative heat transfer is studied and the results are compared for fractal and periodic structures. The calculations for fractals are restricted to the fractal structures based on vicsek model. It is shown that the thermal conductance can be large even for far apart particles in periodic structures. In contrast, it is shown that fractal arranged nanoparticles display complex radiative behavior related to their scaling properties, and heat flux is not of large-range character in such structures. Sat, 30 Sep 2017 20:30:00 +0100