First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z < 0.6

High Energy Astrophysic

Vibration based damage detection of bridge structures

The task of identifying damage to the load-bearing beams of large-span bridge structures using vibration diagnostic methods has been implemented, taking into account experimental uncertainties associated with natural phenomena and technological processes. The methodology for localizing damage is based on the analysis of dynamic characteristics of the structure, such as natural frequencies and modes of vibration. The study presents research on a finite element model of a bridge structure using a method for determining a damage indicator based on normalizing the values of vibration modes with respect to the values of vibration area

Spatial anomalies in spectral-kinetic properties of Pr³⁺ - Doped LiY<inf>1-x</inf>Lu<inf>x</inf>F<inf>4</inf> mixed crystals

© 2020 We present the spectral-kinetic including excited state absorption spatial-dependent features of Pr3+ - doped LiY1-xLuxF4 mixed crystals grown by Bridgeman technique

Driver-witness electron beam acceleration in dielectric mm-scale capillaries

We investigated a corrugated mm-scale capillary as a compact accelerating structure in the driver-witness acceleration scheme, and suggested a methodology to measure the acceleration of the witness bunch. The accelerating fields produced by the driver bunch and the energy spread of the witness bunch in a corrugated capillary and in a capillary with a constant inner radius were measured and simulated for both on-axis and off-axis beam propagation. Our simulations predicted a change in the accelerating field structure for the corrugated capillary. Also, an approximately twofold increase of the witness bunch energy gain on the first accelerating cycle was expected for both capillaries for the off-axis beam propagation. These results were confirmed in the experiment, and the maximum measured acceleration of 170keV/m at 20 pC driver beam charge was achieved for off-axis beam propagation. The driver bunch showed an increase in energy spread of up to 11%, depending on the capillary geometry and beam propagation, with a suppression of the longitudinal energy spread in the witness bunch of up to 15%

Structural and Dielectric Relaxations in Vitreous and Liquid State of Monohydroxy Alcohol at High Pressure

2-Ethyl-1-hexanol monoalcohol is a well-known molecular glassformer, which for a long time attracts attention of researchers. As in all other monohydroxy alcohols, its dielectric relaxation reveals two distinct relaxation processes attributed to the structural relaxation and another more intense process, which gives rise to a low-frequency Debye-like relaxation. In this monoalcohol, the frequency separation between these two processes reaches an extremely high value of 3 orders of magnitude, which makes this substance a rather convenient object for studies of mechanisms (supposedly common to all monoalcohols) leading to vitrification of this type of liquids. In this work, we apply two experimental techniques, dielectric spectroscopy and ultrasonic measurements (in both longitudinal and transverse polarizations) at high pressure, to study interference between different relaxation mechanisms occurring in this liquid, which could shed light on both structural and dielectric relaxation processes observed in a supercooled liquid and a glass state. Application of high pressure in this case leads to the simplification of the frequency spectrum of dielectric relaxation, where only one asymmetric feature is observed. Nonetheless, the maximum attenuation of the longitudinal wave in ultrasonic experiments at high pressure is observed at temperatures ≈50 K above the corresponding temperature for the transverse wave. This might indicate different mechanisms of structural relaxation in shear and bulk elasticities in this liquid

Fission Dynamics in the Proton Induced Fission of Actinide Nuclei at Intermediate Energies

A multi-parameter correlation study of the reactions 232Th(p,f), 238U(p,f) and 242Pu(p,f) at E_{p}=13, 20, 40 and 55 MeV has been conducted. The fission fragment mass, total kinetic energy distributions, double differential neutron spectra and \gamma-ray spectra have been measured. The three humped shape of mass distributions has been observed up to higher proton energy. Pre-equilibrium, pre-scission and post-scission neutron and \gamma-ray multiplicities measured in coincidence with primary fission fragments provided access to fission dynamics. Shell structure effects were observed in fission fragment mass distributions even at high excitation energy. Manifestation of the nuclear shell Z = 28 near fragment mass A_{fr} = 78 has been detected

Characteristics of Symmetric and Asymmetric Fission Modes as a Function of the Compound Nucleus Excitation in the Proton-Induced Fission of 233^{233}Pa, 239^{239}Np and 243^{243}Am

International audienceAverage preequilibrium $\langle M_n^{preeq}\rangle$ average statistical prescission $\langle M_n^{stpre}\rangle$ and postscission $\langle M_n^{post}\rangle$ neutron multiplicities as well as average gamma-ray multiplicity $\langle M_{gamma}\rangle$, average energy emitted by gamma-rays $\langle E_{gamma}\rangle$ and average energy per one gamma quantum $\langle\varepsilon_{gamma}\rangle$ as a function of mass and total kinetic energy (TKE) of fission fragments were measured in the proton-induced reactions p+^{232}Th \to ^{233}Pa, p+^{238}U \to ^{239}Np and p+^{242}Pu \to ^{243}Am (at proton energy E_p=13, 20, 40 and 55 MeV). The fragment mass and energy distributions (MEDs) have been analyzed in terms of the multimodal fission. The decomposition of the experimental MEDs onto the MEDs of the distinct modes has been fulfilled in the framework of a method that is free from any parameterization of the distinct fission mode mass distribution shapes. The main characteristics for symmetric and asymmetric modes have been studied in their dependence on the compound nucleus composition and proton energy. The manifestation of multimodal fission in average gamma-ray multiplicities $\langle E_{gamma}\rangle$ of fission fragments was also studied in this work

First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z &lt; 0.6

We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to 108M⊙, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lg/LX < 0.3 (Lg and LX being the g band and 0.2-6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of -0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10-5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey