We study linear perturbations of static, spherically symmetric solutions of scalar-tensor theories (STT) of gravity from the Bergmann-Wagoner-Nordtvedt class, sourced by nonlinear electrodynamics (NED). We obtain a general expression for the effective potential V_ eff governing the perturbation dynamics for theories with arbitrary scalar-electromagnetic interaction of the form L(ψ, F), where ψ is a scalar field and F = F_μν F^μν the electromagnetic invariant. This consideration includes, in particular, arbitrary scalar self-interaction potentials and scalar fields that can be phantom in some regions of space-time (the so-called trapped ghosts). Only radial (monopole) perturbations are considered here as the most likely ones to cause an instability. It is shown, in particular, that if NED has a correct Maxwell weak field limit, the zero charge limit of V_ eff does not contain any trace of NED, and the perturbation dynamics is the same as for vacuum STT solutions. The previously obtained stability results for STT-Maxwell solutions are shown to be extended without change to STT-NED solutions with equal electric and magnetic charges, implying F =0.
The manuscript discusses the challenges of metrological support for rapidly developing technologies, including electronics, radio vision, and security systems. To foster successful technological advancement, it is essential to expand the state standard base into a higher frequency range of 100–1000 GHz. This expansion is crucial for the verification and certification of devices and measuring instruments operating in the terahertz (millimeter) frequency range. Currently, the frequency range of the State Primary Standard for the unit of spectral power density of radio noise radiation, as defined in GET 21-2021, spans from 0.002 to 178.3 GHz. However, this frequency range is insufficient for the precise testing and certification of the high-precision devices and measuring instruments that are currently being developed. The manuscript presents the results of the development and study of the experimental sample of the primary standard of the unit of spectral power density of radio noise radiation in the frequency range of 220–300 GHz. The experimental sample includes a radiometer, a signal generator for the local oscillator channel, a low-temperature noise generator, a matched load, and a standard attenuator. The following characteristics of the experimental sample are achieved: the equivalent noise temperature of a low-temperature noise generator is from 103 K (220 Hz) to 120 K (300 GHz). The sensitivity of the comparator based on the radiometer is 0.86 K. The characteristics of the experimental sample are comparable with the characteristics of similar devices from the world's leading manufacturer, Radiometer Physics (Germany). The developed experimental sample can be used to calibrate low-noise receiving and amplifying devices of the terahertz range, which are finding increasing application in various fields of science and technology. An important area of application of the developed standard is also the verification of radiometers used in passive radar systems. Additionally, it is noteworthy that the developed radiometer (operating within 220–300 GHz) holds potential for scientific problems related to conducting radio astronomical terrestrial observations in the terahertz range, in particular in atmospheric transparency windows at wavelengths of 1.3 and 0.8 mm, where many spectral lines of atoms and molecules are concentrated.
The article considers the most rapidly developing artificial intelligence technology, large language models. The authors analyze their functionality, providing examples and outlining the potential for their use in various areas of activity. The use of special fine-tuning technologies is shown to enable the creation of numerous neuro-employees on the basis of large language models, which can improve the performance of companies. Fine-tuning adds specialized expertise in a particular field and/or certain functional capabilities to the general intelligence of large language models. The authors describe a pilot project implemented by RCAM-ROSTEST in cooperation with the University of Artificial Intelligence to create a neuro-consultant in the field of legal metrology on the basis of the YandexGPT model. The project results confirmed the practical feasibility and high efficiency of such a neuro-employee. Further development and scaling of the project are possible.
The results of two radiotechnical experiments on measuring the parameters of the Earth's gravitational field using signals from low-orbit spacecraft and global navigation satellite systems are presented. The authors' previously proposed method of measuring the acceleration of gravity using signals from a low-orbit satellite, as well as the method of measuring the current height of the geoid based on an onboard bistatic radar system, are experimentally verified. In the first experiment, a signal from the low-orbit small spacecraft RS-44 (DOSAAF-85) with a frequency of about 2.3 GHz was used, in the second experiment primary measurement data from a bistatic radar system installed on board a foreign satellite CYGNSS. As a result of processing the measurement results obtained in the first experiment, a difference was established between the measured and model values of the gravitational acceleration of the low-orbit spacecraft with a standard deviation of 6.3 mGal. Currently, gravity acceleration measurements based on mechanical gravimeters on board a satellite are impossible due to weightlessness. In the second experiment, the measured and model values of the geoid height profile differ from each other by 13.3 cm, which meets modern requirements. The method of measuring the current geoid height based on an onboard bistatic radar system, unlike the classical method of satellite radio altimetry, allows for up to 60 reflected signals and measured heights simultaneously. The experimental results can be used to refine the model of the Earth's gravity field in remote territories and water areas, including the Arctic region.
Measurements of the granulometric composition of aerosols, suspensions and powdery materials in the field of ultrahigh concentrations are in demand in the chemical, gas, and oil industries, where concentrated suspensions of solid particles are used. The existing measuring instruments for particle number concentration in liquids are characterized by an upper limit of the reproduction range of particle number concentration of 10 12 m −3 . However, for metrological support of photometric high-precision measuring instruments for the number concentration of particles in a liquid, it is necessary to expand this range to 10 8 ‒10 18 m −3 . As part of the development of measures for calculating the concentration of particles in the liquid MSK-V, a technology for producing highly concentrated suspensions of monodisperse polystyrene latex spheres has been proposed. The high concentration of the suspension was achieved as a result of an increase in the amount of styrene in the seeded emulsion and, consequently, an increase in the amount of coagulate during synthesis. An algorithm for indirect measurements of the particle number concentration in aqueous suspensions of monodisperse polystyrene latex spheres is described. During the research, equipment from the State primary standard of units of dispersed parameters of aerosols, suspensions and powdery materials GET 163-2020 was used. The particle number concentrations and metrological characteristics of the created measures are determined. The levels of confidence of the error of indirect measurement of the number concentration of particles in water are calculated. It is established that the limits of the relative error of indirect measurements of the number concentration of particles in water are ±4 %. The developed measures of number concentrations of particles in a liquid (MSK-V) will partially cover the need of the domestic market for measures and standard samples for determining the size and number concentration of particles while ensuring the uniformity of measurements of the granulometric composition of aerosols, suspensions, and powdery materials.
