Aleksandar Dragić

Bio: Aleksandar Dragić is an academic researcher from University of Belgrade. The author has contributed to research in topics: Cosmic ray & Radon. The author has an hindex of 9, co-authored 55 publications receiving 249 citations.

Forbush decreases - clouds relation in the neutron monitor era

Abstract: The proposed influence of cosmic rays on cloud formation is tested for the effect of sudden intensity changes of CR (Forbush decreases) on cloudiness. An attempt is made to widen the investigated period covered by satellite observation of cloudiness. As an indicator of cloud cover, the diurnal temperature range (DTR - a quantity anticorre- lated with cloudiness) is used. The superposed epoch anal- ysis on a set of isolated Forbush decreases is conducted and the results for a region of Europe are presented. The effect of Forbush decrease on DTR is statistically significant only if the analysis is restricted to high amplitude FDs (above the threshold value of 7% with the respect to undisturbed CR in- tensity). The magnitude of the effect on DTR is estimated to be (0.38± 0.06) C.

Indoor radon measurements by nuclear track detectors: Applications in secondary schools

Abstract: Indoor radon measurements by nuclear track detectors and application of the method in secondary schools in Serbia were performed in the spring 2004. Thirty detectors (type CR-39) were distributed to high school teachers in several cities in Serbia. After three months of the detectors exposure, they were sent back to the Low- Level Laboratory, Institute of Physics, Belgrade. After exposure, the CR-39 detectors were etched in a 6N NaOH at 700C for 3 hours. The tracks were counted by the semiautomatic track-counting system. The preliminary results are presented in this paper.

Measurement of cosmic ray muon flux in the Belgrade ground level and underground laboratories

Abstract: The cosmic-ray muon count rate and energy loss spectra in plastic scintillator detectors are recorded in the Institute of Physics, Belgrade. Measurements are performed at two different levels: at the surface level (78 m a.s.l.) and in the Belgrade underground laboratory at the depth of 25 m.w.e. From experimental data and with the use of GEANT4 computer simulation the flux and vertical intensities have been determined. At ground level the muon flux is determined to be J 1 G = ( 1.37 ± 0.06 ) × 10 - 2 s - 1 cm - 2 and vertical intensity I vG = ( 8.4 ± 0.4 ) × 10 - 3 s - 1 cm - 2 sr - 1 while the same quantities underground are J 1 U = ( 4.5 ± 0.2 ) × 10 - 3 s - 1 cm - 2 and I vU = ( 2.5 ± 0.2 ) × 10 - 3 s - 1 cm - 2 sr - 1 . Their relation to the results of similar measurements worldwide is discussed.

Nuclear Tracks in Solids (Principles and Applications)

Abstract: (1976). Nuclear Tracks in Solids (Principles and Applications) Nuclear Technology: Vol. 30, No. 1, pp. 91-92.

Periodicities in Solar Coronal Mass Ejections

Abstract: Mid-term quasi-periodicities in solar coronal mass ejections (CMEs) during the most recent solar maximum cycle 23 are reported here for the first time using the four-year data (February 5, 1999 to February 10, 2003) of the Large Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). In parallel, mid-term quasi-periodicities in solar X-ray flares (class >M5.0) from the Geosynchronous Operational Environment Satellites (GOES) and in daily averages of Ap index for geomagnetic disturbances from the World Data Center (WDC) at the International Association for Geomagnetism and Aeronomy (IAGA) are also examined for the same four-year time span. Several conceptual aspects of possible equatorially trapped Rossby-type waves at and beneath the solar photosphere are discussed.

The response of clouds and aerosols to cosmic ray decreases

Abstract: A method is developed to rank Forbush decreases (FDs) in the galactic cosmic ray radiation according to their expected impact on the ionization of the lower atmosphere. Then a Monte Carlo bootstrap-based statistical test is formulated to estimate the significance of the apparent response in physical and microphysical cloud parameters to FDs. The test is subsequently applied to one ground-based and three satellite-based data sets. Responses (>95%) to FDs are found in the following parameters of the analyzed data sets. AERONET: Angstrom exponent (cloud condensation nuclei changes), SSM/I: liquid water content, International Satellite Cloud Climate Project (ISCCP): total, high, and middle, IR-detected clouds over the oceans, Moderate Resolution Imaging Spectroradiometer (MODIS): cloud effective emissivity, cloud optical thickness, liquid water, cloud fraction, liquid water path, and liquid cloud effective radius. Moreover, the responses in MODIS are found to correlate positively with the strength of the FDs, and the signs and magnitudes of the responses agree with model-based expectations. The effect is mainly seen in liquid clouds. An impact through changes in UV-driven photo chemistry is shown to be negligible and an impact via UV absorption in the stratosphere is found to have no effect on clouds. The total solar irradiance has a relative decrease in connection with FDs of the order of 10−3, which is too small to have a thermodynamic impact on timescales of a few days. The results demonstrate that there is a real influence of FDs on clouds probably through ions.

Composite analysis with Monte Carlo methods: an example with cosmic rays and clouds

Abstract: The composite (superposed epoch) analysis technique has been frequently employed to examine a hypothesized link between solar activity and the Earth’s atmosphere, often through an investigation of Forbush decrease (Fd) events (sudden high-magnitude decreases in the flux cosmic rays impinging on the upper-atmosphere lasting up to several days). This technique is useful for isolating low-amplitude signals within data where background variability would otherwise obscure detection. The application of composite analyses to investigate the possible impacts of Fd events involves a statistical examination of time-dependent atmospheric responses to Fds often from aerosol and/or cloud datasets. Despite the publication of numerous results within this field, clear conclusions have yet to be drawn and much ambiguity and disagreement still remain. In this paper, we argue that the conflicting findings of composite studies within this field relate to methodological differences in the manner in which the composites have been constructed and analyzed. Working from an example, we show how a composite may be objectively constructed to maximize signal detection, robustly identify statistical significance, and quantify the lower-limit uncertainty related to hypothesis testing. Additionally, we also demonstrate how a seemingly significant false positive may be obtained from non-significant data by minor alterations to methodological approaches.

Generation Of High Energy Ion Beams from a Plasma Focus Modified for Low Pressure Operation

Abstract: This paper reports on the modification of a small plasma focus device (UNU/ICTP PFF) to operate at low pressure for enhanced ion beam generation. For the present operation, the electrode geometry of the plasma focus device is modified to redirect the plasma motion at the end of the axial rundown phase so that normal plasma focus action will not occur. The redirection of the plasma leads to a rapid increase in the plasma resistivity and hence a high localized electric field will be established and as a result, high energy ion beam will be generated. With air as the working gas, pressure as low as 10-3 mbar has been tested. At such a low pressure, breakdown of the discharge must be initiated with the use of a set of twelve plasma injection cable guns. The modified plasma focus has been shown to be able to produce high energy ion beams of nitrogen, argon and hydrogen consistently.