Channeling of protons through carbon nanotubes

This book contains a thorough theoretical consideration of the process of proton channeling through carbon nanotubes. We begin with a very brief summary of the theoretical and experimental results of studying ion channeling through nanotubes. Then, the process of ion channeling is described briefly. After that, the crystal rainbow effect is introduced. We describe how it was discovered, and present the theory of crystal rainbows, as the proper theory of ion channeling in crystals and nanotubes. We continue with a description of the effect of zero-degree focusing of protons channeled through nanotubes. It is shown that the evolution of the angular distribution of channeled protons with the nanotube length can be divided in the cycles defined by the rainbow effect. Further, we analyze the angular distributions and rainbows in proton channeling through nanotubes. This is done using the theory of crystal rainbows. The angular distributions are generated by the computer simulation method, and the corresponding rainbow patterns are obtained in a precise analysis of the mapping of the impact parameter plane to the transmission angle plane. We demonstrate that the rainbows enable the full explanation of the angular distributions. We also investigate how the effect of dynamic polarization of the carbon atoms valence electrons influences the angular and spatial distributions of protons transmitted through short nanotubes in vacuum and embedded in dielectric media. In addition, we explore the channeling star effect in 1 GeV proton channeling through bundles of nanotubes, which appears when the proton beam divergence angle is larger than the critical angle for channeling.Comment: 58 pages, 22 figures, the book "Channeling of Protons through Carbon Nanotubes" (published by Nova Science Publishers 2011

Constraining Scalar-Tensor gravity models by S2 star orbits around the Galactic Center

The aim of our investigation is to derive a particular theory among the class of scalar-tensor(ST) theories of gravity, and then to test it by studying kinematics and dynamics of S-stars around supermassive black hole (BH) at Galactic Center (GC). We also discuss the Newtonian limit of this class of ST theories of gravity, as well as its parameters. We compare the observed orbit of S2 star with our simulated orbit which we obtained theoretically with the derived ST potential and constrained the parameters. Using the obtained best fit parameters we calculated orbital precession of S2 star in ST gravity,and found that it has the same direction as in General Relativity (GR), but causes much larger pericenter shift.Comment: 13 pages, 1 table, 6 figures. Accepted for publication in Facta Universitatis: Series Phys. Chem. Tech. (Invited lecture at Balkan Workshop 2018

Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84

Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.BPU11 : 11th International Conference of the Balkan Physical Union : Proceedings book; Aug 11 - Sep 1, 2022S02-AA Astronomy and Astrophysic

Distribution of radio spectral index over the Lupus loop

We use all-sky surveys at 408 and 1420 MHz with aim to investigate properties of the Galactic radio source Lupus Loop. We estimate the brightness temperature, surface brightness and radio spectral index of this supernova remnant using the method we have developed. The non-thermal nature of its radiation is confirmed, and also the distribution of spectral index over its area is given

Distribution of radio spectral index over the Lupus loop

We use all-sky surveys at 408 and 1420 MHz with aim to investigate properties of the Galactic radio source Lupus Loop. We estimate the brightness temperature, surface brightness and radio spectral index of this supernova remnant using the method we have developed. The non-thermal nature of its radiation is confirmed, and also the distribution of spectral index over its area is given.17th National Conference of Astronomers of Serbia : Book of abstracts; September 23-27,2014, Belgrad

Constraints on f(R, ɸ) (Sanders-Like) Gravity Potential From Orbit of S2 Star

We investigate the possibility to explain theoretically the S2 star orbital precession around the massive object at the Galactic Centre using Extended Theories of Gravity [1], specifically f(R, φ) a Sanders-like [2] gravitational potential in total absence of dark matter. To this aim an analytic fourth-order theory of gravity, non-minimally coupled with a massive scalar field is considered. The interaction term is given by an analytic functions f(R, φ) where R is the Ricci scalar and φ is the scalar field. We simulated orbit of S2 star around the Galactic Centre in Sanders-like gravity potentials and compared it with NTT/VLT observations. We presented maps of reduced χ 2 over the {α−mφ} parameter space in the case of NTT/VLT observations. The approach we are proposing [3,4] seems reliable to constrain modified gravity models at astronomical level.17th National Conference of Astronomers of Serbia : Book of abstracts; September 23-27,2014, Belgrad

Constraints on f(R, ɸ) (Sanders-Like) Gravity Potential From Orbit of S2 Star

We investigate the possibility to explain theoretically the S2 star orbital precession around the massive object at Galactic Centre using Extended Theories of Gravity, specifically f(R, φ) a Sanders-like gravitational potential in total absence of dark matter. To this aim an analytic fourth-order theory of gravity, non-minimally coupled with a massive scalar field is considered. The interaction term is given by an analytic functions f(R, φ) where R is the Ricci scalar and φ is the scalar field. We simulated orbit of S2 star around Galactic Centre in Sanders-like gravity potentials and compared it with NTT/VLT observations. We presented maps of reduced χ 2 over the {α − mφ} parameter space in the case of NTT/VLT observations. The approach we are proposing seems reliable to constrain modified gravity models at astronomical level

Improvement of graviton mass constraints using GRAVITY's detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center

Here we study the possible improvements of the existing constraints on the upper bound of graviton mass by the analysis of the stellar orbits around the supermassive black hole (SMBH) at the Galactic Center (GC) in the framework of Yukawa gravity. Main motivation for this study is recent detection of Schwarzschild precession in the orbit of S2 star around the SMBH at the GC by the GRAVITY Collaboration in 2020. They indicated that the orbital precession of the S2 star is close to the General Relativity (GR) prediction, but with possible small deviation from it, and parametrized this effect by introducing an ad hoc factor in the parameterized post-Newtonian (PPN) equations of motion. Here we use the value of this factor presented by GRAVITY in order to perform two-body simulations of the stellar orbits in massive gravity using equations of motion in the modified PPN formalism, as well as to constrain the range of massive interaction $\Lambda$. From the obtained values of $\Lambda$, and assuming that it corresponds to the Compton wavelength of graviton, we then calculated new estimates for the upper bound of graviton mass which are found to be independent, but consistent with the LIGO's estimate of graviton mass from the first gravitational wave (GW) signal GW150914. We also performed Markov chain Monte Carlo (MCMC) simulations in order to constrain the bounds on graviton mass in the case of a small deviation of the stellar orbits from the corresponding GR predictions and showed that our method could further improve previous estimates for upper bounds on the graviton mass. It is also demonstrated that such analysis of the observed orbits of S-stars around the GC in the frame of the Yukawa gravity represents a tool for constraining the upper bound for the graviton mass, as well as for probing the predictions of GR or other gravity theories.Comment: 13 pages, 2 tables, 6 figure

Angular and spatial distributions of protons channeled in a bent and radially deformed single-wall boron-nitride nanotubes

This study is devoted to the angular and spatial distribution of protons channeling through a bent and radially deformed single-wall boron-nitride nanotubes (SWBNNTs). These nanotubes are more thermal and chemical stable then carbon nanotubes, and they are good candidates for future channeling experiments. This investigation is continuation of our previous study [1, 2] and now we investigate channeling properties of SWBNNTs as a function of the very realistic effects: bending angle of nanotube and its radial deformation. For the first time we presented here investigation of these effects with boron-nitride nanotubes and combination of both effect. The angular and spatial distributions of channeled protons were generated using the Molière’s expression for the continuum potential of the SWBNNT’s atoms and computer simulation method. We also calculate the total yield of protons channeled in the nanotubes as a function of the bending angle. We demonstrate that varying bending angle and taking into account radial deformation we can get a significant rearrangement of the propagating protons within the boron-nitride nanotube. This investigation may be very useful to give us detailed information on the relevant interaction potentials inside SWBNNTs and for creating nanosized proton beams to be used in different applications in medicine and materials science. © 2019, Editura Academiei Romane. All rights reserved

Constraining Yukawa gravity from planetary motion in the solar system

In this work we used the observed additional perihelion precession in the Solar System, obtained from the observations of planets and spacecrafts, to study the possible existence of Yukawa correction term to the Newtonian gravitational potential. Our study was motivated by previous analyses which indicated the possible discrepancies from Newtonian gravity in this form and at wide range of astrophysical scales. Yukawa gravity was introduced to cure some shortcomings of General Relativity (GR) at galactic and extragalactic scales. We demonstrated that this form of gravity can give the values for orbital precession which are comparable or even in better agreement with observations than the corresponding predictions of GR. The obtained results can be used for setting stronger constraints on variation of the gravitational constant G, as well as on the fundamental constant δ of Yukawa gravity. Moreover, Yukawa gravity could be used to improve the results for the motion of planets, other Solar System bodies, as well as spacecrafts, and as a consequence, it can help us to get more reliable predictions for natural hazards in the Solar System, such as potential impacts by near-Earth objects. © 2019, Geographical Institute "Jovan Cviji" of the Serbian Academy of Sciences and Arts. All rights reserved