Models of G time variations in diverse dimensions

A review of different cosmological models in diverse dimensions leading to a relatively small time variation of the effective gravitational constant G is presented. Among them: 4-dimensional general scalar-tensor model, multidimensional vacuum model with two curved Einstein spaces, multidimensional model with multicomponent anisotropic "perfect fluid", S-brane model with scalar fields and two form field etc. It is shown that there exist different possible ways of explanation of relatively small time variation of the effective gravitational constant G compatible with present cosmological data (e.g. acceleration): 4-dimensional scalar-tensor theories or multidimensional cosmological models with different matter sources. The experimental bounds on G-dot may be satisfied ether in some restricted interval or for all allowed values of the synchronous time variable.Comment: 27 pages, Late

Evidence for grain growth in T Tauri disks

In this article we present the results from mid-infrared spectroscopy of a sample of 14 T Tauri stars with silicate emission. The qualitative analysis of the spectra reveals a correlation between the strength of the silicate feature and its shape similar to the one which was found recently for the more massive Herbig Ae/Be stars by van Boekel et al. (2003). The comparison with theoretical spectra of amorphous olivine with different grain sizes suggests that this correlation is indicating grain growth in the disks of T Tauri stars. Similar mechanisms of grain processing appear to be effective in both groups of young stars.Comment: 4 pages A&A lette

Quantum phase transition in ultrahigh mobility SiGe/Si/SiGe two-dimensional electron system

The metal-insulator transition (MIT) is an exceptional test bed for studying strong electron correlations in two dimensions in the presence of disorder. In the present study, it is found that in contrast to previous experiments on lower-mobility samples, in ultra-high mobility SiGe/Si/SiGe quantum wells the critical electron density, $n_{\text{c}}$, of the MIT becomes smaller than the density, $n_{\text{m}}$, where the effective mass at the Fermi level tends to diverge. Near the topological phase transition expected at $n_{\text{m}}$, the metallic temperature dependence of the resistance should be strengthened, which is consistent with the experimental observation of more than an order of magnitude resistance drop with decreasing temperature below $\sim1$ K.Comment: Misprints corrected. As publishe

Angular dependence of the ferromagnetic resonance parameters of [Ti/FeNi]6/Ti/Cu/Ti/[FeNi/Ti]6 nanostructured multilayered elements in the wide frequency range

Magnetically soft [Ti(6)/FeNi(50)]6/Ti(6)/Cu(500)/Ti(6)/[FeNi(50)/Ti(6)]6 nanostructured multilayered elements were deposited by rf-sputtering technique in the shape of elongated stripes. The easy magnetization axis was oriented along the short size of the stripe using deposition in the external magnetic field. Such configuration is important for the development of small magnetic field sensors employing giant magnetoimpedance effect (GMI) for different applications. Microwave absorption of electromagnetic radiation was experimentally and theoretically studied in order to provide an as complete as possible high frequency characterization. The conductor-backed coplanar line was used for microwave properties investigation. The medialization for the precession of the magnetization vector in the uniformly magnetized GMI element was done on the basis of the Landau–Lifshitz equation with a dissipative Bloch–Bloembergen term. We applied the method of the complex amplitude for the analysis of the rotation of the ferromagnetic GMI element in the external magnetic field. The calculated and experimental dependences for the amplitudes of the imaginary part of the magnetic susceptibility tensor x-component and magnetoabsorption related to different angles show a good agreement. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Russian Science Foundation, RSF: 18-19-00090Funding: This research was funded by the Russian Science Foundation, grant number 18-19-00090

Front Propagation of Spatio-temporal Chaos

We study the dynamics of the front separating a spatio-temporally chaotic region from a stable steady region using a simple model applicable to periodically forced systems. In particular, we investigate both the coarsening of the front induced by the inherent `noise' of the chaotic region, and the long wavelength dynamics causing the front to develop cusps

Improved Perturbative QCD Approach to the Bottomonium Spectrum

Recently it has been shown that the gross structure of the bottomonium spectrum is reproduced reasonably well within the non-relativistic boundstate theory based on perturbative QCD. In that calculation, however, the fine splittings and the S-P level splittings are predicted to be considerably narrower than the corresponding experimental values. We investigate the bottomonium spectrum within a specific framework based on perturbative QCD, which incorporates all the corrections up to O(alpha_S^5 m_b) and O(alpha_S^4 m_b), respectively, in the computations of the fine splittings and the S-P splittings. We find that the agreement with the experimental data for the fine splittings improves drastically due to an enhancement of the wave functions close to the origin as compared to the Coulomb wave functions. The agreement of the S-P splittings with the experimental data also becomes better. We find that natural scales of the fine splittings and the S-P splittings are larger than those of the boundstates themselves. On the other hand, the predictions of the level spacings between consecutive principal quantum numbers depend rather strongly on the scale mu of the operator \propto C_A/(m_b r^2). The agreement of the whole spectrum with the experimental data is much better than the previous predictions when mu \simeq 3-4 GeV for alpha_S(M_Z)=0.1181. There seems to be a phenomenological preference for some suppression mechanism for the above operator.Comment: 26 pages, 16 figures. Minor changes, to be published in PR

Comparing the QCD potential in Perturbative QCD and Lattice QCD at large distances

We compare the perturbatively calculated QCD potential to that obtained from lattice calculations in the theory without light quark flavours. We examine E_tot(r) = 2 m_pole + V_QCD(r) by re-expressing it in the MSbar mass m = m^MSbar(m^MSbar) and by choosing specific prescriptions for fixing the scale mu (dependent on r and m). By adjusting m so as to maximise the range of convergence, we show that perturbative and lattice calculations agree up to 3*r_0 ~ 7.5 GeV^-1 (r_0 is the Sommer scale) within the uncertainty of order Lambda^3 r^2.Comment: Version to appear in Eur.J.Phys; 16 pages, 7 figure

Four-Loop Decoupling Relations for the Strong Coupling

We compute the matching relation for the strong coupling constant within the framework of QCD up to four-loop order. This allows a consistent five-loop running (once the $\beta$ function is available to this order) taking into account threshold effects. As a side product we obtain the effective coupling of a Higgs boson to gluons with five-loop accuracy.Comment: 11 page

Улучшение модели репутации и доверия путем внедрения индикаторов надежности для внутригрупповой коммуникации между автономными транспортными средствами

Reputation and Trust models have successfully been implemented to ensure security and maintain nodes’ trustworthiness in decentralized networks, including autonomous vehicles (AVs). However, the implementations of these models usually lack of objective parameters to calculate the initial Reputation values. In this study, we employ reliability-based approach to evaluate the initial Reputation value