Vol 37, No 1 (2023)

The existence of the magnetic compass system was first shown in birds. Since then, a large amount of data has been accumulated on the performance of the avian magnetic compass and its relationship with visual reception. The current dominant concept is that the receptor for the magnetic compass in birds is located in the retina. The most popular hypothesis for the mechanism of operation of magnetic field receptors is the radical pair model, and a candidate for the role of the primary magnetoreceptor molecule is cryptochrome, and more specifically, its isoform, cryptochrome 4a. In recent years, data have been published on the interaction of cryptochrome with some proteins involved in the phototransduction cascade, as well as promising data from electrophysiological studies combining light and magnetic stimuli. In addition, a number of morphological studies of the avian retina also allow us to narrow down the range of promising cells for the role of a magnetoreceptor, and the double cone is currently the most likely candidate. In this review, we discuss the latest research data in this area.

It is known that some animals can react to very small changes in the magnetic field – a thousand times smaller than the geomagnetic field – and use this to navigate the Earth’s magnetic landscape. However, the nature of the molecular magnetic sensor remains unclear, although it has been established that the magnetic sense is associated with vision. It is generally accepted that the operation of a magnetic sensor is based on a magnetochemical reaction. Cryptochromes of photoreceptors lining the retina contain photoinduced spin-correlated pairs of radicals involved in the formation of a nerve impulse and sensitive to a magnetic field. Therefore, the animal could sense the magnetic field as a change in the brightness of large visual fields and orient itself by their contrast. However, the sensitivity of individual sensors – of radical pairs – is known to be very low. Previously, it has been assumed that this difficulty is overcome by a statistical increase in contrast sensitivity due to the parallel processing by the brain of the primary signals of millions of photoreceptors. In the present work, this hypothesis is tested. It has been found that the threshold sensation of brightness contrast almost linearly depends on the logarithm of the angular size of contrasting stimulus, which is typical for the physiology of sensations that obey the Weber-Fechner law. Contrast sensitivity increases with the number of photoreceptors involved in stimulus recognition, however this increase is not quantitatively sufficient to reliably explain the magnetic navigation of animals.

The mandibular sound conduction hypothesis suggests that dolphins have functionally replaced the external pinna with an “acoustic window” in the low jaw. Using industrial tomography, the lower jaws 3D models of the odontocetes six species were built. In the obtained models, the analysis of the bone thickness in the area of the supposed “acoustic window” showed a dependence of the bone wall thickness on the size of the animal. The area of the greatest thinning of the lateral wall of the lower jaw in the studied samples was determined mainly in the upper angle of the proximal part of the lower jaw or near the lower angle of the lower jaw, and not in the center, as previously assumed.

Local field potentials (LFP) recorded in the olfactory bulb (OB) are known to be largely generated in local neural networks, are directly related to the processing of olfactory information, and are influenced by various factors, including anesthetics. Using 8-electrode arrays implanted in the dorsal regions of 6 adult male Norway rats OBs, the effects of xylazine-tiletamine-zolazepam (XTZ) anesthesia on the spectral characteristics and coherence of the LFP in the frequency range 1–150 Hz were studied in 2 hours long chronic experiments. It is shown that the most significant changes in the rat OB LFP under XTZ-anesthesia are observed in the high γ frequency band. A statistically significant increase in the power (2–4 times) and coherence (up to 50%) of this band was observed in the LFP of all animals within 10–15 minutes from the anesthesia onset. At the same time, during wakefulness, the dominant frequencies of this band were 70–80 Hz, and within 10–15 minutes from the anesthesia onset they increased to 110–130 Hz. During anesthesia, a gradual shift of these dominant frequencies to a lower range (90–110 Hz) was observed, while their total power, in contrast to the coherence, was statistically significantly reduced when the animal started recovering from anesthesia

The KURS radio engineering system for measuring motion parameters during rendezvous and docking has some disadvantages: the accuracy of measurement with multiple reflections of the wave can drop, the technical equipment is available on both docking vehicles (active and passive parts), it is expensive both in terms of energy resources and in terms of cost. An analysis of existing visual systems has shown that such systems successfully solve the problems of visual odometry on UAVs, robots, and similar devices. However, to use such systems, it is necessary to know the internal parameters of the camera (calibration). Classical calibration using a checkerboard pattern is difficult to perform in outer space. In connection with all of the above, this paper proposes methods for estimating the focal length of the camera, based on the analysis of the available video sequence with the footage of the process of rendezvous of spacecraft. The proposed approaches are based on the maximum likelihood method (MLE) and maximum a posteriori estimation (MAP) of the functional depending on the Euler angles and focal length. The results of these methods are compared, showing the advantages of MAP over MLE and the possibility of their practical application.