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In this paper, we study and compare the optical and X-ray counterparts of subparsec supermassive black hole binaries (SMBHBs). With that aim, we simulated the profiles of optical spectral lines emitted from the broad line region (BLR) as well as X-ray spectral lines emitted from the relativistic accretion disks around both black holes and compared them with each other. The obtained results showed that SMBHBs could cause a specific, but different variability of the lines from the optical part and Fe K$\alpha$ line, leaving potentially detectable imprints in their profiles. Since these imprints depend on the orbital phase of the system, they could be used for reconstructing the Keplerian orbits of the components in the observed SMBHBs. Moreover, such signatures in the optical and X-ray line profiles of the observed SMBHBs could be used as a tool for the detection of these objects as well as for studying their properties., Comment: 18 pages, 1 table, 10 figures. Accepted for publication in Advances in Space Research

Here we investigate the giant radio galaxy DA 240, which is a FR II source. Specifically, we investigate its flux density, as well as the spectral index distribution. For that purpose, we used publicly available data for the source: Leahy's atlas of double radio-sources and NASA/IPAC Extragalactic Database (NED). We used observations at 326 MHz (92 cm) and at 608 MHz (49 cm) and obtained spectral index distributions between 326 and 608 MHz. For the first time we give spectral index map for these frequencies. We found that the synchrotron radiation is the dominant radiation mechanism over most of the area of DA 240, and also investigated the mechanism of radiation at some characteristic points, namely its core and the hotspots. The results of this study will be helpful for understanding the evolutionary process of the DA 240 radio source., Comment: 9 pages, 5 figures. Accepted for publication in Contrib. Astron. Obs. Skalnate Pleso (Invited lecture at V Meeting on Astrophysical Spectroscopy - A&M DATA 2023)

We studied the in-plane angular magnetoresistance (AMR), in the normal state, of underdoped superconducting Sr1-xLaxCuO2 , which has the simplest crystal structure among cuprates. The measurements of two underdoped thin films with different dopings were performed in intense magnetic field H (up to 22 T). The longitudinal magnetoresistance at temperature T is negative and scales with H/T. For both samples, the AMR is anisotropic and shows an unexpected dependence on H intensity. While at the low magnetic field, one observes essentially twofold AMR oscillations for the more doped sample, fourfold ones start to grow under the high magnetic field, resulting in the coexistence of the two. For the less doped film at the low magnetic field, both twofold and fourfold AMR components exist. With the increase of the magnetic field, the fourfold component survives a pi/4 phase shift, during which its amplitude vanishes, at a magnetic field Hc such as: 16 T < Hc < 17 T. As a result, at the high magnetic field above Hc, the angular dependence of the in-plane magnetoresistance turns out to be the same for both samples. We tentatively ascribe the above features to the presence of anti-ferromagnetism in the CuO2 planes of underdoped Sr1-xLaxCuO2., Comment: 9 pages 5 figures

In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction $\Lambda$ and universal constant $\delta$) with the Schwarzschild precession of the S-stars assuming that the observed values as indicated by the GRAVITY Collaboration will have a small deviation from GR prediction. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant $\delta$, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction $\delta$ and find that this parameter has strong influence on range of Yukawa interaction $\Lambda$. For that purpose we use PPN equations of motion in order to calculate the simulated orbits of S-stars in GR and Yukawa gravity. Using MCMC simulations we obtain the best-fit values and uncertainties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories., Comment: 25 pages, 2 tables, 5 figures. Published in J. Cosmol. Astropart. P

We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data., Comment: 0 pages, 8 figures. Accepted for publication in Adv. Space Res

The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy's Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index $\alpha$ is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN., Comment: 8 pages, 5 figures, 1 FITS file. Accepted for publication in Adv. Space Res

We estimate the parameters of Hybrid Palatini gravity model with the Schwarzschild precession of S-stars, specifically of S2, S38 and S55 stars. We also take into account case of bulk mass distribution near Galactic Center. We assume that the Schwarzschild orbital precession of mentioned S-stars is the same like in General Relativity (GR) in all studied cases. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. The astronomical data analysis of S38 and S55 orbits showed that also in these cases orbital precession is close to the GR prediction. Based on this observational fact, we evaluated parameters of the Hybrid Palatini Gravity model with the Schwarzschild precession of the S2, S38 and S55 stars and we estimated the range of parameters of Hybrid Palatini gravity model for which the orbital precession is like in GR for all tree stars. We also evaluated parameters of the Hybrid Palatini Gravity model in case of different values of bulk mass density distribution of extended matter. We believe that proposed method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center., Comment: 23 pages, 6 figures. Accepted for publication in Universe

After giving a short overview of previous results on constraining of Extended Gravity (EG) by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian (pN) approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first pN approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the EG theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some EG models including power-law f(R), general Yukawa-like corrections, scalar-tensor gravity (STG), and non-local gravity (NLG) theories formulated in both metric and Palatini formalism. In this consideration we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these EG models for which the orbital precession is like in GR. We then compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, STG and NLG theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the GC., Comment: 19 pages, 7 figures. Accepted for publication in Universe

In this study we investigate possible applications of observed S2 orbit around Galactic Center for constraining the Yukawa gravity at scales in the range between several tens and several thousands astronomical units (AU) to obtain graviton mass constraints. In our model we suppose that bulk distribution of matter (includes stellar cluster, interstellar gas distribution and dark matter) exists near Supermassive Black Hole (SMBH) in our Galactic Center. We obtain the values of orbital precession angle for different values of mass density of matter and we require that the value of orbital precession is the same like in General Relativity (GR). From that request we determine gravity parameter $\lambda$ and the upper value for graviton mass. We found that in the cases where the density of extended mass is higher, the maximum allowed value for parameter $\lambda$ is smaller and the upper limit for graviton mass is higher. It is due to the fact that the extended mass causes the retrograde orbital precession. We believe that this study is a very efficient tool to evaluate a gravitational potential at the Galactic Center, parameter $\lambda$ of the Yukawa gravity model, and to constrain the graviton mass., Comment: 7 pages, 6 figures, 2 tables. Accepted for publication in Eur. Phys. J. D

We use the Fundamental Plane of Elliptical Galaxies to constrain the so-called Hybrid Gravity, a modified theory of gravity where General Relativity is improved by further degrees of freedom of metric-affine Palatini formalism of $f(\cal R)$ gravity. Because the Fundamental Plane is connected to the global properties of elliptical galaxies, it is possible to obtain observational constraints on the parameters of Hybrid Gravity in the weak field limit. We analyze also the velocity distribution of elliptical galaxies comparing our theoretical results in the case of Hybrid Gravity with astronomical data for elliptical galaxies. In this way, we are able to constrain the Hybrid Gravity parameters $m_\phi$ and $\phi_0$. We show that the Fundamental Plane, i.e. $v_c/\sigma$ relations, can be used as a standard tool to probe different theories of gravity in the weak field limit. We conclude that Hybrid Gravity is able to explain elliptical galaxies with different stellar kinematics without the dark matter hypothesis., Comment: 7 pages, 5 figures. Accepted for publication in Eur. Phys. J. D

Here we study the potential observational signatures of supermassive black hole binaries (SMBHBs) in the Fe K$\alpha$ line profiles emitted from the accretion disks around their components. We simulated the Fe K$\alpha$ line emission from the relativistic accretion disks using ray tracing method in Kerr metric. The obtained profiles from the SMBHBs are then compared with those in the case of the single supermassive black holes (SMBHs). We considered two models of the SMBHBs: a model when the secondary SMBH is embedded in the accretion disk around the primary, causing an empty gap in the disk, and a model with clearly separated components, where the accretion disks around both primary and secondary give a significant contribution to the composite Fe K$\alpha$ line emission of a such SMBHB. The obtained results showed that both models of SMBHBs can leave imprints in the form of ripples in the cores of the emitted Fe K$\alpha$ line profiles, which may look like an absorption component in the line profile. However, in the case of the composite line profiles emitted from two accretion disks, these ripples could have much higher amplitudes and strongly depend on orbital phase of the system, while for those emitted from a disk with an empty gap, the corresponding ripples mostly have lower amplitudes and do not vary significantly with orbital phase. The present day X-ray telescopes are not able to detect such signatures in the observed X-ray spectra of SMBHBs. However this will be possible with the next generation of X-ray observatories, which will also enable application of such effects as a tool for studying the properties of these objects., Comment: 16 pages, 5 figures, 1 table. Presented as invited talk at the 12th Serbian Conference on Spectral Line Shapes in Astrophysics (http://www.scslsa.matf.bg.ac.rs/press12/day5/Jovanovic.pdf) and accepted for publication in "Contributions of the Astronomical Observatory Skalnat\'e Pleso (CAOSP)"

Non-local theories of gravity have recently gained a lot of interest because they can suitably represent the behavior of gravitational interaction in the ultraviolet regime. Furthermore, at infrared scales, they give rise to notable cosmological effects which could be important to describe the dark energy behavior. In particular, exponential forms of the distortion function seem particularly useful for this purpose. Using Noether Symmetries, it can be shown that the only non-trivial form of the distortion function is the exponential one, which is working not only for cosmological mini-superspaces, but also in a spherically symmetric spacetime. Taking this result into account, we study the weak field approximation of this type of non-local gravity, and comparing with the orbits of S2 stars around the Galactic center (NTT/VLT data), we set constraints on the parameters of the theory. Non-local effects do not play a significant role on the orbits of S2 stars around Sgr A*, but give richer phenomenology at cosmological scales than the $\Lambda$CDM model. Also, we show that non-local gravity model gives better agreement between theory and astronomical observations than Keplerian orbits., Comment: 11 pages, 6 figures. Accepted for publication in Phys. Rev. D

Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as $m_g < 1.2 \times 10^{-22}$ eV (Abbott et al., 2016). In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center. Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity (Borka et al., 2013) and graviton mass (Zakharov et al., 2016) from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around $5 \times 10^{-23}$ eV or slightly better than current estimates obtained with LIGO observations., Comment: 16 pages, 1 Figure, 1 Table, corrected minor typos

We demonstrate that the existence of a Noether symmetry in $f(R)$ theories of gravity gives rise to a further gravitational radius, besides the standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Tully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis., Comment: 9 pages, 2 figures, to be published in JCAP

The fundamental plane (FP) of galaxies can be recovered in the framework of $f(R)$ gravity avoiding the issues related to dark matter to fit the observations. In particular, the power-law version $f(R)\propto R^n$, resulting from the existence of Noether symmetries for $f(R)$, is sufficient to implement the approach. In fact, relations between the FP parameters and the corrected Newtonian potential, coming from $R^n$, can be found and justified from a physical point of view. Specifically, we analyze the velocity distribution of elliptical galaxies and obtain that $r_c$, the scale-length depending on the gravitational system properties, is proportional to $r_e$, the galaxy effective radius. This fact points out that the gravitational corrections induced by $f(R)$ can lead photometry and dynamics of the system. Furthermore, the main byproduct of such an approach is that gravity could work in different ways depending on the scales of self-gravitating systems., Comment: 18 pages, 3 tables, 8 figures. Accepted for publication in Phys. Dark Universe

We use radio-continuum all-sky surveys at 1420 and 408 MHz with the aim to investigate properties of the Galactic radio source Lupus Loop. The survey data at 1435 MHz, with the linear polarization of the southern sky, is also used. We calculate properties of this supernova remnant: the brightness temperature, surface brightness and radio spectral index. For determining borders and calculation of its properties, we use the method we have developed. The non-thermal nature of its radiation is confirmed. The distribution of spectral index over its area is also given. A significant correlation between the radio spectral index distribution and the corresponding polarized intensity distribution inside the loop borders is found, indicating that the polarization maps could provide us information about the distribution of interstellar medium, and thus could represent one additional way to search for new Galactic loops., Comment: 12 pages, 7 figures. Accepted for publication in Rev. Mex. AA

Here we present a short overview and main results of our investigations of several effects which can induce shifts in the broad Fe K$\alpha$ line emitted from relativistic accretion disks around single and binary supermassive black holes. We used numerical simulations based on ray-tracing method in the Kerr metric to study the role of classical Doppler shift, special relativistic transverse Doppler shift and Doppler beaming, general relativistic gravitational redshift, and perturbations of the disk emissivity in the formation of the observed Fe K$\alpha$ line profiles. Besides, we also investigated whether the observed line profiles from the binary systems of supermassive black holes could be affected by the Doppler shifts due to dynamics of such systems. The presented results demonstrate that all these effects could have a significant influence on the observed profiles of the broad Fe K$\alpha$ line emitted from relativistic accretion disks around single and binary supermassive black holes., Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Astrophysics and Space Science

We consider possible signatures for the so called {\it hybrid gravity} within the Galactic Central Parsec. This modified theory of gravity consists of a superposition of the metric Einstein-Hilbert Lagrangian with an $f(R)$ term constructed {\it \`{a} la Palatini} and can be easily reduced to an equivalent scalar-tensor theory. Such an approach is introduced in order to cure the shortcomings related to $f(R)$ gravity, in general formulated either in metric or in metric-affine frameworks. Hybrid gravity allows to disentangle the further gravitational degrees of freedom with respect to those of standard General Relativity. The present analysis is based on the S2 star orbital precession around the massive compact dark object at the Galactic Centre where the simulated orbits in hybrid modified gravity are compared with astronomical observations. These simulations result with constraints on the range of hybrid gravity interaction parameter $\phi_0$, showing that in the case of S2 star it is between -0.0009 and -0.0002. At the same time, we are also able to obtain the constraints on the effective mass parameter $m_{\phi}$, and found that it is between -0.0034 and -0.0025 AU$^{-1}$ for S2 star. Furthermore, the hybrid gravity potential induces precession of S2 star orbit in the same direction as General Relativity. In previous papers, we considered other types of extended gravities, like metric power law $f(R)\propto R^n$ gravity, inducing Yukawa and Sanders-like gravitational potentials, but it seems that hybrid gravity is the best among these models to explain different gravitational phenomena at different astronomical scales., Comment: 11 pages, 4 figures, accepted for publication in Astroparticle Physics

We investigate the possibility to explain theoretically the observed deviations of S2 star orbit around the Galactic Centre using gravitational potentials derived from modified gravity models in absence of dark matter. To this aim, an analytic fourth-order theory of gravity, non-minimally coupled with a massive scalar field is considered. Specifically, the interaction term is given by analytic functions $f(R)$ and $f(R,\phi)$ where $R$ is the Ricci scalar and $\phi$ is a scalar field whose meaning can be related to further gravitational degrees of freedom. We simulate the orbit of S2 star around the Galactic Centre in $f(R)$ (Yukawa-like) and $f(R,\phi)$ (Sanders-like) gravity potentials and compare it with NTT/VLT observations. Our simulations result in strong constraints on the range of gravity interaction. In the case of analytic functions $f(R)$, we are not able to obtain reliable constraints on the derivative constants $f_1$ and $f_2$, because the current observations of S2 star indicated that they may be highly mutually correlated. In the case of analytic functions $f(R,\phi)$, we are able to obtain reliable constraints on the derivative constants $f_0$, $f_R$, $f_{RR}$, $f_{\phi}$, $f_{\phi\phi}$ and $f_{\phi R}$. The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around Galactic Centre., Comment: 9 pages, 6 figure to appear in Phys. Rev. D

We apply color-spin and flavor-spin quark-quark interactions to the meson and baryon constituent quarks, and calculate constituent quark masses, as well as the coupling constants of these interactions. The main goal of this paper was to determine constituent quark masses from light and open bottom hadron masses, using the fitting method we have developed and clustering of hadron groups. We use color-spin Fermi-Breit (FB) and flavor-spin Glozman-Riska (GR) hyperfine interaction (HFI) to determine constituent quark masses (especially $b$ quark mass). Another aim was to discern between the FB and GR HFI because our previous findings had indicated that both interactions were satisfactory. Our improved fitting procedure of constituent quark masses showed that on average color-spin (Fermi-Breit) hyperfine interaction yields better fits. The method also shows the way how the constituent quark masses and the strength of the interaction constants appear in different hadron environments., Comment: 15 pages, 6 tables, 1 figure. Accepted for publication in Mod. Phys. Lett. A

We consider possible signatures for Yukawa gravity within the Galactic Central Parsec, based on our analysis of the S2 star orbital precession around the massive compact dark object at the Galactic Centre, and on the comparisons between the simulated orbits in Yukawa gravity and two independent sets of observations. Our simulations resulted in strong constraints on the range of Yukawa interaction $\Lambda$ and showed that its most probable value in the case of S2 star is around 5000 - 7000 AU. At the same time, we were not able to obtain reliable constrains on the universal constant $\delta$ of Yukawa gravity, because the current observations of S2 star indicated that it may be highly correlated with parameter $\Lambda$ in the range $(0 <\delta < 1)$. For $\delta > 2$ they are not correlated. However, the same universal constant which was successfully applied to clusters of galaxies and rotation curves of spiral galaxies ($\delta=1/3$) also gives a satisfactory agreement with the observed orbital precession of the S2 star, and in that case the most probable value for the scale parameter is $\Lambda \approx 3000 \pm 1500$ AU. Also, the Yukawa gravity potential induces precession of S2 star orbit in the same direction as General Relativity for $\delta > 0$ and for $\delta < -1$, and in the opposite direction for $-1 <\delta < 0$. The future observations with advanced facilities, such as GRAVITY or/and European Extremely Large Telescope, are needed in order to verify these claims., Comment: 16 pages, 8 figures, accepted for publication in JCAP

We used a model of a relativistic accretion disk around a supermassive black hole (SMBH), based on ray-tracing method in the Kerr metric, to study the variations of the composite Fe K$\alpha$ line emitted from two accretion disks around SMBHs in a binary system. We assumed that the orbit of such a binary is approximately Keplerian, and simulated the composite line shapes for different orbital elements, accretion disk parameters and mass ratios of the components. The obtained results show that, if observed in the spectra of some SMBH binaries during their different orbital phases, such composite Fe K$\alpha$ line profiles could be used to constrain the orbits and several properties of such SMBH binaries., Comment: 8 pages, 4 figures, 2 tables. Accepted for publication in special issue of Advances in Space Research on "Spectral Line Shapes in Astrophysics and Related Phenomena"

One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole system in their cores. Here we present an observational evidence for the first spectroscopically resolved sub-parsec orbit of a such system in the core of Seyfert galaxy NGC 4151. Using a method similar to those typically applied for spectroscopic binary stars we obtained radial velocity curves of the supermassive binary system, from which we calculated orbital elements and made estimates about the masses of components. Our analysis shows that periodic variations in the light and radial velocity curves can be accounted for an eccentric, sub-parsec Keplerian orbit of a 15.9-year period. The flux maximum in the lightcurve correspond to the approaching phase of a secondary component towards the observer. According to the obtained results we speculate that the periodic variations in the observed H{\alpha} line shape and flux are due to shock waves generated by the supersonic motion of the components through the surrounding medium. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into black hole mass growth process., Comment: 29 pages, 10 figures, published in ApJ, 759, 118

We study some possible observational signatures of $R^n$ gravity at Galactic scales and how these signatures could be used for constraining this type of $f(R)$ gravity. For that purpose, we performed two-body simulations in $R^n$ gravity potential and analyzed the obtained trajectories of S2-like stars around Galactic center, as well as resulting parameter space of $R^n$ gravity potential. Here, we discuss the constraints on the $R^n$ gravity which can be obtained from the observations of orbits of S2-like stars with the present and next generations of large telescopes. We make comparison between the theoretical results and observations. Our results show that the most probable value for the parameter $r_c$ in $R^n$ gravity potential in the case of S2-like stars is $\sim$100 AU, while the universal parameter $\beta$ is close to 0.01. Also, the $R^n$ gravity potential induces the precession of S2-like stars orbit in opposite direction with respect to General Relativity, therefore, such a behavior of orbits qualitatively is similar to a behavior of Newtonian orbits with a bulk distribution of matter (including a stellar cluster and dark matter distributions)., Comment: 12 pages, 12 figures, accepted in Phys. Rev. D

In this paper we present the main results of our investigation of the $cq \bar{q} \bar{q}$ single-charm scalar tetraquarks and their SU(3)$_\mathrm{F}$ representations: $\bar{15}_S$, $\bar{3}_S$, $6_A$ and $\bar{3}_A$. We use the Fermi-Breit interaction Hamiltonian with SU(3) flavor symmetry breaking to determine the masses of the single-charm tetraquarks. We also discuss mass spectra obtained from meson and baryon mass fits. The mass spectra are very similar to those obtained with Glozman-Riska hyperfine interaction, and they indicate that some of the experimentally detected states may have tetraquark nature., Comment: 13 pages, 6 tables, 2 figures. Accepted for publication in Rom. J. Phys

We use observations of the continuum radio emission at 1420, 820, 408, 34.5 and 22 MHz to estimate the mean brightness temperatures of the HB 21 supernova remnant (SNR) at five frequencies. We also presented mean spectral index of HB 21. The spectra of HB 21 are estimated for mean temperatures versus frequency for 1420, 820, 408, 34.5 and 22 MHz. We also presented $T-T$ plots of three frequency pairs: between 1420--34.5, 1420--22, 34.5--22 MHz. We noticed flatter spectral indices at frequencies below 408 MHz. Probably this is due to the absorption by thermal plasma at low frequencies., Comment: 8 pages, 8 figures, accepted in Rev. Mex. AA

The average brightness temperatures and surface brightnesses at 22 MHz are derived for the four main Galactic radio-continuum loops (Loops I, II, III and IV, hereafter radio-loops). Also the radio-continuum spectra for the radio-loops are presented. Adding the average brightness temperatures at 22 MHz derived here with the average brightness temperatures derived from spectra published previously at 408, 820 and 1420 MHz we obtained clearly non-thermal spectral indices for all radio-loops. Our derived spectral indices are slightly shallower than those measured by previous works., Comment: 11 pages, 2 tables, 9 figures. Accepted for publication in Open Astronomy Journal

The estimated brightness of the Cygnus loop supernova remnant (SNR) at 2720, 1420, 820, 408 and 34.5 MHz are presented. The observations of the continuum radio emission are used to calculate the mean brightness temperatures and surface brightnesses of this loop at the five frequencies in wide spectral range, using the method we have previously developed for large radio loops. The spectrum for mean temperatures versus frequency between the five frequencies is estimated and the spectral index of Cygnus loop is also obtained. Also, from our results can be concluded that Cygnus loop evolves in the low density environment and the initial energy of supernova explosion was relatively low. The obtained results confirm non-thermal origin of the Cygnus radio loop and show that our method is applicable to almost all remnants., Comment: 12 pages, 5 tables, 11 figures. Accepted for publication in RevMexAA

We present several applications of the layered electron gas model to electron energy loss spectroscopy of free-standing films consisting of $N$ graphene layers in a scanning transmission electron microscope. Using a two-fluid model for the single-layer polarizability, we discuss the evolution of high-energy plasmon spectra with $N$, and find good agreement with the recent experimental data for both multi-layer graphene with $N<10$, and thick slabs of graphite. Such applications of these analytical models help shed light on several features observed in the plasmon spectra of those structures, including the role of plasmon dispersion, dynamic interference in excitations of various plasmon eigenmodes, as well as the relevance of the bulk plasmon bands, rather than surface plasmons, in classifying the plasmon peaks., Comment: 11 pages, 6 figures. Accepted for publication in Phys. Rev. B

SiGe islands are used to induce tensile strain in the Si channel of Field Effect Transistors to achieve larger transconductance and higher current driveabilities. We report on x-ray diffraction experiments on a single fully-processed and functional device with a TiN+Al gate stack and source, gate, and drain contacts in place. The strain fields in the Si channel were explored using an x-ray beam focused to 400 nm diameter combined with finite element simulations. A maximum in-plane tensile strain of about 1% in the Si channel was found, which is by a factor of three to four higher than achievable for dislocation-free tensile strained Si in state-of-the-art devices., Comment: The following article has been submitted to Applied Physics Letters. After it is published, it will be found at http://apl.aip.org/

We use the color-spin and flavor-spin interaction Hamiltonians with SU(3) flavor symmetry breaking to obtain meson and baryon mass formulas. Adjusting these masses with experimental masses we determine the constituent quark masses. We discuss the constituent quark masses obtained from meson and baryon mass fits. The results for constituent quark masses are very similar in case of two different phenomenological models: Fermi-Breit and Glozman-Riska hyperfine interactions., Comment: 4 pages, 4 tables. Accepted for publication in Phys. Rev. D

Signatures of antiferromagnetism (AF) in the underdoped Ln2-xCexCuO4 (Ln = Nd, Pr,...) family are observed even for doping levels for which superconductivity exists. We have looked for a similar property in a different electron-doped cuprate family, Sr1-xLaxCuO2, which consists of CuO2 planes separated by Sr/La atoms, and is exempt of the possible influence of magnetic rare earth ions. We report in-plane magnetoresistance measurements in the normal state of underdoped, superconducting, c-axis oriented, epitaxial Sr1-xLaxCuO2 thin films. This probe is sensitive to spin arrangement and we find that the in-plane magnetoresistance, which is negative and does not saturate for T, exhibits an angular dependence when measured upon rotating a magnetic field within the CuO2 planes. The analysis reveals a superposition of fourfold and twofold angular oscillations. Both of these increase in amplitude with increasing field and decreasing and appear below a temperature, which gets higher with decreasing doping levels. Our results demonstrate that these magnetoresistance oscillations, also observed for the Ln2-xCexCuO4 (Ln = Nd, Pr,...) family and attributed to an AF signature, are, without ambiguity, a property of CuO2 planes. Besides, these oscillations vary with doping in an unusual way compared to previous results: fourfold oscillations are essentially present in the more underdoped samples while only twofold oscillations are visible in the less underdoped ones. This intriguing observation appears to be a consequence of spin dilution with increasing doping level., Comment: 25 pages, 6 figures

The in-plane penetration depth of Sr$_{0.88}$La$_{0.12}$CuO$_{2+x}$ thin films at various doping obtained from oxygen reduction has been measured, using AC susceptibility measurements. For the higher doping samples, the superfluid density deviates strongly from the s-wave behavior, suggesting, in analogy with other electron-doped cuprates, a contribution from a nodal hole pocket, or a small gap on the Fermi surface such as an anisotropic s-wave order parameter. The low value of the superfluid densities, likely due to a strong doping-induced disorder, places the superconducting transition of our samples in the phase-fluctuation regime.

In this paper we estimated the temperatures and brightnesses of the Monoceros radio loop at 1420, 820 and 408 MHz. Linear spectrum is estimated for mean temperatures versus frequency between 1420, 820 and 408 MHz. The spectral index of Monoceros loop is also obtained. The brightness temperatures and surface brightnesses of the loop are computed using data taken from radio-continuum surveys at the three frequencies. The spectral index of the loop is also obtained from $T-T$ plots between 1420 - 820, 1420 - 408 and 820 - 408 MHz. The obtained results confirm non-thermal origin of the Monoceros radio loop., Comment: 9 pages, 7 tables, 5 figures. Accepted for publication in Astron. Nachr

We have epitaxially grown c-axis oriented SrxLa1-xCuO2 thin films by rf sputtering on KTaO3 substrates with x = 0.12. The as-grown deposits are insulating and a series of superconducting films with various Tc(R=0) up to 26 K have been obtained by in-situ oxygen reduction. Transport measurements in the ab plane of these samples have been undertaken. We report original results on the temperature dependence of the Hall effect and on the anisotropic magnetoresistance (T > Tc). We discuss the magnitude of upper critical fields and anisotropy, the Hall effect, which presents changes of sign indicative of the existence of two types of carriers, the normal state magnetoresistance, negative in parallel magnetic field, a possible signature of spin scattering. These properties are compared to those of hole-doped cuprates, such as BiSr(La)CuO with comparable Tc., Comment: 4 pages, 4 figures; to appear in Proceedings of LT25, Journal of Physics : Conference Series

Single phase, c-axis oriented, e-doped, Sr1-xLaxCuO2 thin films were epitaxially grown on KTaO3 and DyScO3 substrates by reactive rf sputtering. As-grown films being insulating due to oxygen excess, oxygen reduction is necessary to observe superconductivity. Two different procedures were employed to reach superconductivity. On one hand an in-situ reduction process was conducted on a series of films deposited on both types of substrates. On the other hand, an ex-situ reduction procedure was performed sequentially on a single film deposited on DyScO3. The study of the influence of oxygen reduction on the structural and electronic properties of the thin films is presented and discussed., Comment: 27 pages, 10 figures, to appear in Physica C

We develop a new estimation technique for recovering depth-of-field from multiple stereo images. Depth-of-field is estimated by determining the shift in image location resulting from different camera viewpoints. When this shift is not divisible by pixel width, the multiple stereo images can be combined to form a super-resolution image. By modeling this super-resolution image as a realization of a random field, one can view the recovery of depth as a likelihood estimation problem. We apply these modeling techniques to the recovery of cloud height from multiple viewing angles provided by the MISR instrument on the Terra Satellite. Our efforts are focused on a two layer cloud ensemble where both layers are relatively planar, the bottom layer is optically thick and textured, and the top layer is optically thin. Our results demonstrate that with relative ease, we get comparable estimates to the M2 stereo matcher which is the same algorithm used in the current MISR standard product (details can be found in [IEEE Transactions on Geoscience and Remote Sensing 40 (2002) 1547--1559]). Moreover, our techniques provide the possibility of modeling all of the MISR data in a unified way for cloud height estimation. Research is underway to extend this framework for fast, quality global estimates of cloud height., Comment: Published in at http://dx.doi.org/10.1214/09-AOAS243 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org)