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[en] A counter-streaming flow system is a test-bed to investigate the astrophysical collisionless shock (CS) formation in the laboratory. Electrostatic/electromagnetic instabilities, competitively growing in the system and exciting the CS formation, are sensitive to the flows parameters. One of the most important parameters is the velocity, determining what kind of instability contributes to the shock formation. Here we successfully measure the evolution of the counter-streaming flows within one shot using a multi-pulses imaging diagnostic technique. With the technique, the average velocity of the high-density-part () of the flow is directly measured to be of cm/s between 7 ns and 17 ns. Meanwhile, the average velocity of the low-density-part () can be estimated as cm/s. The experimental results show that a collisionless shock is formed during the low-density-part of the flow interacting with each other. (paper)
[en] We study the masses and radii of 65 exoplanets smaller than 4 R ⊕ with orbital periods shorter than 100 days. We calculate the weighted mean densities of planets in bins of 0.5 R ⊕ and identify a density maximum of 7.6 g cm–3 at 1.4 R ⊕. On average, planets with radii up to R P = 1.5 R ⊕ increase in density with increasing radius. Above 1.5 R ⊕, the average planet density rapidly decreases with increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying a rocky core. Including the solar system terrestrial planets with the exoplanets below 1.5 R ⊕, we find ρP = 2.43 + 3.39(R P/R ⊕) g cm–3 for R P < 1.5 R ⊕, which is consistent with rocky compositions. For 1.5 ≤ R P/R ⊕ < 4, we find M P/M ⊕ = 2.69(R P/R ⊕)0.93. The rms of planet masses to the fit between 1.5 and 4 R ⊕ is 4.3 M ⊕ with reduced χ2 = 6.2. The large scatter indicates a diversity in planet composition at a given radius. The compositional diversity can be due to planets of a given volume (as determined by their large H/He envelopes) containing rocky cores of different masses or compositions
[en] The state of the surface of mesh implants and their encapsulation region in herniology is investigated by laser confocal microscopy. A correlation between the probability of developing relapses and the size and density of implant microdefects is experimentally shown. The applicability limits of differential reverse scattering for monitoring the post-operation state of implant and adjacent tissues are established based on model numerical experiments. (optical technologies in biophysics and medicine)
[en] The detection of gravitational waves from the merger of binary black holes by the LIGO Collaboration has opened a new window to astrophysics. With the sensitivities of ground based detectors in the coming years, we will principally detect local binary black hole mergers. The integrated merger rate can instead be probed by the gravitational-wave background, the incoherent superposition of the released energy in gravitational waves during binary-black-hole coalescence. Through that, the properties of the binary black holes can be studied. In this work we show that by measuring the energy density ΩGW (in units of the cosmic critical density) of the gravitational-wave background, we can search for the rare ∼ 100 M ⊙ massive black holes formed in the Universe. In addition, we can answer how often the least massive BHs of mass ≳ 3 M ⊙ form. Finally, if there are multiple channels for the formation of binary black holes and if any of them predicts a narrow mass range for the black holes, then the total ΩGW spectrum may have features that with the future Einstein Telescope can be detected.
[en] The subject of this paper is the design of practical laser experiments that can produce collisionless shocks mediated by the Weibel instability. Such shocks may be important in a wide range of astrophysical systems. Three issues are considered. The first issue is the implications of the fact that such experiments will produce expanding flows that are approximately homologous. As a result, both the velocity and the density of the interpenetrating plasma streams will be time dependent. The second issue is the implications of the linear theory of the Weibel instability. For the experiments, the instability is in a regime where standard simplifications do not apply. It appears feasible but non-trivial to obtain adequate growth. The third issue is collisionality. The need to keep resistive magnetic-field dissipation small enough implies that the plasmas should not be allowed to cool substantially.
[en] Standard perturbation theory (SPT) for large-scale matter inhomogeneities is unsatisfactory for at least three reasons: there is no clear expansion parameter since the density contrast is not small on all scales; it does not fully account for deviations at large scales from a perfect pressureless fluid induced by short-scale non-linearities; for generic initial conditions, loop corrections are UV-divergent, making predictions cutoff dependent and hence unphysical. The Effective Field Theory of Large Scale Structures successfully addresses all three issues. Here we focus on the third one and show explicitly that the terms induced by integrating out short scales, neglected in SPT, have exactly the right scale dependence to cancel all UV-divergences at one loop, and this should hold at all loops. A particularly clear example is an Einstein deSitter universe with no-scale initial conditions Pin ∼ kn. After renormalizing the theory, we use self-similarity to derive a very simple result for the final power spectrum for any n, excluding two-loop corrections and higher. We show how the relative importance of different corrections depends on n. For n ∼ −1.5, relevant for our universe, pressure and dissipative corrections are more important than the two-loop corrections
[en] The light curves of V X Cas, V V and D D are studied in Institute of Astrophysics of the Academy of Science of the Republic of Tajikistan for 40-50 years on the photographic observations. It is established, that the reason of light changes of these variables is existence around of them about 100000 dust clouds, eclipsing these stars from time to time
[en] The electronic structure and physical properties of crystals, meteorites, alloys and salts using Moessbauer effect and X ray diffraction are studied. (M.C.K.)
[pt]Estudam-se as estruturas eletronicas e propriedades fisicas de cristais, meteoritos, ligas e sais usando-se espectroscopia Mossbauer e difracao de raios X. (M.C.K.)
[en] We show how to use multiple tracers of large-scale density with different biases to measure the redshift-space distortion parameter β ≡ b−1f ≡ b−1d ln D/d ln a (where D is the growth factor and a the expansion factor), to, as the signal-to-noise (S/N) of a survey increases, much better precision than one could achieve with a single tracer (to arbitrary precision in the low noise limit). In combination with the power spectrum of the tracers this would allow a more precise measurement of the bias-free velocity divergence power spectrum, f2Pm, with the ultimate, zero noise limit, being that f2Pm can be measured as well as would be possible if velocity divergence was observed directly, with maximum rms improvement factor ∼ [5.2(β2+2β+2)/β2]1/2 (e.g., ≅ 10 times better than a single tracer with β = 0.4). This would allow a determination of fD as a function of redshift with an error as low as ∼ 0.1% (again, in the idealized case of the zero noise limit). The ratio b2/b1 can be determined with an even greater precision than β, potentially producing, when measured as a function of scale, an exquisitely sensitive probe of the onset of non-linear bias. We also extend in more detail previous work on the use of the same technique to measure non-Gaussianity. Currently planned redshift surveys are typically designed with S/N ∼ 1 on scales of interest, which severely limits the usefulness of our method. Our results suggest that there are potentially large gains to be achieved from technological or theoretical developments that allow higher S/N, or, in the long term, surveys that simply observe a higher number density of galaxies
[en] We assume cylindrically symmetric stars which begin collapsing by dissipating energy in the form of heat flux. We wish to study the effects of Carroll-Duvvuri-Trodden-Turner (CDTT) model, f(R) = R+σμ4/R, on the range of dynamical instability. For this purpose, perturbation scheme is applied to all the metric functions, material functions and f(R) model to obtain the full set of dynamical equation which control the evolution of the physical variables at the surface of a star. It is found that instability limit involves adiabatic index Γ which depends on the density profile and immense terms of perturbed CDTT model. In addition, model is constrained by some requirement, e.g. positivity of physical quantities. We also reduce our results asymptotically as μ→0, being the GR results in both the Newtonian and post Newtonian regimes