Linear thermoacoustic instability in the time domain

An approximate time-domain description of the development of the thermoacoustic instability in gas-filled tubes is developed by exploiting the difference between the instability time scale and the period of standing waves. The perturbation results compare very favorably with the exact frequency-domain theory of Rott. The perturbation results are further simplified by introducing a short-stack approximation which is numerically much simpler and only slightly less accurate. An approximate expression for the critical temperature gradient accounting for viscous effects and other design features is also derived. In addition to the fundamental mode of a tube closed at both ends, the theory includes higher modes as well as open-end boundary conditions

The rate of satellite glints in ZTF and LSST sky surveys

We assess the impact of satellite glints -- rapid flashes produced by reflections of a sunlight from flat surfaces of rotating satellites -- on current and future deep sky surveys such as the ones conducted by the Zwicky Transient Facility (ZTF) and the Vera C. Rubin Observatory upcoming Legacy Survey of Space and Time (LSST). In addition to producing a large number of streaks polluting the images, artificial satellites and space debris also generate great amount of false point-source alerts hindering the search for new rapid astrophysical transients. To investigate the extent of this problem, we perform an analysis of isolated single frame events detected by ZTF in more than three years of its operation, and, using three different methods, assess the fraction of them related to artificial satellites to be at least 20\%. The satellites causing them occupy all kinds of orbits around the Earth, and the duration of flashes produced by their rotation is from a fraction of a second down to milliseconds, with mean all-sky rate of up to 80,000 per hour.Comment: Proceedings of 17th INTEGRAL/BART Workshop (IBWS-2023). arXiv admin note: text overlap with arXiv:2202.0571

SEARCH FOR ISOLATED BLACK HOLES: PAST, PRESENT, FUTURE

The critical property of a black hole is the presence of an event horizon. It may be detected only by means of a detailed study of the emission features of its surroundings. The temporal resolution of such observations has to be comparable to rg /c, which is in the 10−6–10 s range, depending on the mass of the black hole. At SAO RAS we have developed the MANIA hardware and software complex, based on the panoramic photon counter, and we use it in observations on the 6m telescope for searching and investigating the optical variability of various astronomical objects on time scales of 10−6–103 s. We present here the hardware and methods used for these photometric, spectroscopic and polarimetric observations, together with the principles and criteria for object selection. The list of objects includes objects with featureless optical spectra (DC white dwarfs, blazars) and long microlensing events

A Simplified Model for Linear and Nonlinear Processes in Thermoacoustic Prime Movers. Part II. Nonlinear Oscillations

The simplified quasi-one-dimensional model of thermoacoustic devices formulated in Part I [Watanabe et al., J. Acoust. Soc. Am. 102, 3484–3496 (1997)] is studied in the nonlinear regime. A suitable numerical method is described which is able to deal with the steep waveforms that develop in the system without inducing spurious oscillations, appreciable numerical damping, or numerical diffusion. The results are compared with some experimental ones available in the literature. Several of the observed phenomena are reproduced by the model. Quantitative agreement is also reasonable when allowance is made for likely temperature nonuniformities across the heat exchangers

Principles of Manufacturing of DC On-Board Harness for a Spacecraft Based on 3D Technology

This article describes in detail principles of manufacturing of DC on-board harness for spacecraft based on a new 3D design technology. This technology puts together all activities of on-board harness production, starting from electrical design and up to the final product readiness. Based on the analysis performed we proposed: necessary software, methods of wires and connector contacts connection, applicable wires and connectors available in Russian and European markets, shielding and insulating materials, test methods. The article discusses benefits of lightweight supply buses technology implementation (as compared to bundle of wires), which are: mass reduction, electrical performances stability improvement, lesser capacity between supply lines, better interference immunity, better thermal performances

Nonlinear wave interactions in bubble layers

Due to the large compressibility of gas bubbles, layers of a bubbly liquid surrounded by pure liquid exhibit many resonances that can give rise to a strongly nonlinear behavior even for relatively low-level excitation. In an earlier paper [Druzhinin et al., J. Acoust. Soc. Am. 100, 3570 (1996)] it was pointed out that, by exciting the bubbly layer in correspondence of two resonant modes, so chosen that the difference frequency also corresponds to a resonant mode, it might be possible to achieve an efficient parametric generation of a low-frequency signal. The earlier work made use of a simplified model for the bubbly liquid that ignored the dissipation and dispersion introduced by the bubbles. Here a more realistic description of the bubble behavior is used to study the nonlinear oscillations of a bubble layer under both single- and dual-frequency excitation. It is found that a difference-frequency power of the order of 1% can be generated with incident pressure amplitudes of the order of 50 kPa or so. It appears that similar phenomena would occur in other systems, such as porous waterlike or rubberlike media

Overcoming the adverse effects of substrate on the waveguiding properties of plasmonic nanoparticle chains

International audienceWe have studied numerically the propagation of surface plasmon polaritons (SPPs) in linear periodic chains of plasmonic nanoparticles of different shapes. The chains are deposited on top of a thick dielectric substrate. While in many commonly considered cases the substrate tends to suppress the SPP propagation, we have found that this adverse effect is practically absent in the case when the nanoparticles have the shape of oblate spheroids with sufficiently small aspect ratio (e.g., nanodisks) whose axis of symmetry coincides with the axis of the chain

On Some Statistical Properties of GRBs with Measured Redshifts Having Peaks in Optical Light Curves

We studied the subset of optical light curves of gamma-ray bursts with measured redshifts and well-sampled R band data that have clearly detected peaks. Among 43 such events, 11 are promptoptical peaks (P), coincident with gamma-ray activity, 22 are purely afterglows (A), and 10 more carrythe signatures of an underlying activity (A(U)). We studied pair correlations of their gamma-ray andoptical parameters, e.g. total energetics, peak optical luminosities, and durations. The main outcomeof our study is the detection of source frame correlations between both optical peak luminosity and total energy and the redshift for classes A and A(U), and the absence of such a correlation for class Pevents. This result seems to provide evidence of the cosmological evolution of a medium around the burst defining class A and A(U) energetics, and the absence of cosmological evolution of the internal properties of GRB engines. We also discuss some other prominent correlations