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Spatial orientation based on the geomagnetic field (GMF) is a widespread phenomenon in the animal kingdom, predominantly observed in long-distance migrating birds, 1 sea turtles, 2 lobsters, 3 and Lepidoptera. 4,5 Although magnetoreception has been studied intensively, the mechanism remains elusive. A crucial question for a mechanistic understanding of magnetoreception is whether animals rely on inclination or polarity-based magnetic information. Inclination-based magnetic orientation utilizes the angle between the magnetic field lines and gravity, indicating poleward and equatorward. In contrast, polarity-based magnetic orientation allows animals to detect the polarity of the GMF, the north and south direction of the field vector. Cataglyphis desert ants are excellent experimental models for testing whether magnetic inclination or polarity of the magnetic field is used for navigation. Desert ants are solitary foragers with exceptional navigational skills. 6 When the ants leave their underground nest for the first time to become foragers, they perform learning walks for up to three days to learn the visual panorama and calibrate their compass systems. 7,8 The ants repeatedly stop their forward movement during learning walks for performing turns (pirouettes), interrupted by stopping phases. Gaze directions during the longest stopping phases are directed toward the nest entrance. 9 We experimentally manipulated look-back behavior systematically by altering polarity or inclination of the GMF. We demonstrate that Cataglyphis ants, contrary to most other insects studied, 10 possess a polarity-sensitive magnetic compass, making them ideal experimental models for narrowing down the evidence for particle-based mechanisms underlying magnetosensation in this insect. [Display omitted] • Cataglyphis ants use the geomagnetic field as a compass for look-back behavior • This magnetic compass is insensitive to the inclination of the magnetic field • Cataglyphis ants use the polarity of the magnetic field to determine directions Grob et al. show that Cataglyphis ants do not rely on the inclination but rather use the polarity of the geomagnetic field for path integration during learning walks in their natural habitat. This suggests a different mechanism for sensing magnetic fields compared with most other insects studied so far. [ABSTRACT FROM AUTHOR]

Using steerable needles to enable course correction and curved trajectories can improve surgical outcomes in numerous clinical interventions including electrode placement for deep brain stimulation. In this work, a physically motivated kinematic model for an actively steered magnetic-tipped needle is used in closed-loop control to perform insertion trajectories. The applied control law is derived using the Lyapunov redesign. Simulation results show this control method to be accurate for a wide range of conditions including randomized target trajectories. Control is performed experimentally in a brain tissue phantom for both initial position offset recovery and curved trajectories. Converged error results average 0.52 mm from target trajectory. Simulation results demonstrate the robustness of the control implementation, while experimental results exceed the accuracy required for the target application, encouraging future use in a clinical setting. Beyond needle insertion, this work has implications in general vehicle steering, as this model and control can apply to systems with similar kinematics such as boats and wheeled vehicles that could benefit from a relaxed slip constraint. [ABSTRACT FROM AUTHOR]

Objective. The measurement of electromyography (EMG) signals with needle electrodes is widely used in clinical settings for diagnosing neuromuscular diseases. Patients experience pain during needle EMG testing. It is significant to develop alternative diagnostic modalities. Approach. This paper proposes a portable magnetomyography (MMG) measurement system for neuromuscular disease auxiliary diagnosis. Firstly, the design and operating principle of the system are introduced. The feasibility of using the system for auxiliary diagnosis of neuromuscular diseases is then studied. The magnetic signals and needle EMG signals of thirty subjects were collected and compared. Main results. It is found that the amplitude of muscle magnetic field signal increases during mild muscle contraction, and the signal magnitudes of the patients are smaller than those of normal subjects. The diseased muscles tested in the experiment can be distinguished from the normal muscles based on the signal amplitude, using a threshold value of 6 pT. The MMG diagnosis results align well with the needle EMG diagnosis. In addition, the MMG measurement indicates that there is a persistence of spontaneous activity in the diseased muscle. Significance. The experimental results demonstrate that it is feasible to auxiliary diagnose neuromuscular diseases using the portable MMG system, which offers the advantages of non-contact and painless measurements. After more in-depth, systematic, and quantitative research, the portable MMG could potentially be used for auxiliary diagnosis of neuromuscular diseases. The clinical trial registration number is ChiCTR2200067116. [ABSTRACT FROM AUTHOR]

Biologging has proven to be a powerful approach to investigate diverse questions related to movement ecology across a range of spatiotemporal scales and increasingly relies on multidisciplinary expertise. However, the variety of animal‐borne equipment, coupled with little consensus regarding analytical approaches to interpret large, complex data sets presents challenges and makes comparison between studies and study species difficult. Here, we present a combined hardware and analytical approach for standardizing the collection, analysis, and interpretation of multisensor biologging data. Here, we present (i) a custom‐designed integrated multisensor collar (IMSC), which was field tested on 71 free‐ranging wild boar (Sus scrofa) over 2 years; (ii) a machine learning behavioral classifier capable of identifying six behaviors in free‐roaming boar, validated across individuals equipped with differing collar designs; and (iii) laboratory and field‐based calibration and accuracy assessments of animal magnetic heading measurements derived from raw magnetometer data. The IMSC capacity and durability exceeded expectations, with a 94% collar recovery rate and a 75% cumulative data recording success rate, with a maximum logging duration of 421 days. The behavioral classifier had an overall accuracy of 85% in identifying the six behavioral classes when tested on multiple collar designs and improved to 90% when tested on data exclusively from the IMSC. Both laboratory and field tests of magnetic compass headings were in precise agreement with expectations, with overall median magnetic headings deviating from ground truth observations by 1.7° and 0°, respectively. Although multisensor equipment and sophisticated analyses are now commonplace in biologging studies, the IMSC hardware and analytical framework presented here provide a valuable tool for biologging researchers and will facilitate standardization of biologging data across studies. In addition, we highlight the potential of additional analyses available using this framework that can be adapted for use in future studies on terrestrial mammals. [ABSTRACT FROM AUTHOR]

The present study shows the development of computational algorithms to represent aircraft instruments such as the attitude indicator or the turn-and-slip indicator; moreover, the algorithms represent a magnetic compass and other instruments that function according to other physical theories. These instruments work by using the gyroscope and magnetic principles and help the pilot in navigation. These are considered to be the basic instruments required to provide location-related and positional information about the actual aircraft attitude. The algorithms developed in this study are capable of working in concordance with other instruments and the physical conditions established. The programming language used was C++ and the algorithms were compiled in independent files and subroutines for computational efficiency, eliminating unnecessary code. The display options were successfully tested. Additionally, an analysis that evaluated the error and approached flight simulation as a function of step time (Δt) is also described. [ABSTRACT FROM AUTHOR]

Influence of Magnetohydrodynamics (MHD) on the fluid in channel flow in the presence of thin needle across the fluid movement is observed in this study. A two-dimensional computational analysis has been performed to see the effects of inlet/outlet conditions with inserted curvilinear shaped body in the channel. In this case, temperature on all boundaries is colder than that of inlet air and flat part of the inserted body. The governing equations are solved by using finite element method and magnetic field is also taken into account. With suitable dimensionless variables, PDEs are transformed into dimensionless PDEs, then raised parameter is simulated against the streamlines, isotherms and temperature distribution at mean position. Effect of Reynolds number, Richardson number, Magnetic hydrodynamic, size and state of needle is observed on local Nusselt number at the mean position. On isotherm profile, Reynolds number has a noticeable impact. With an increase in Re, heat circulation close to the needle increases, and for higher Ri, velocity on the outlet port increases. The inlet and outlet portions of the channel generate streamlines that have a significant impact on the diameter of the needle. Increased needle diameter causes heated lines to be pushed away from the centre. It is also found that the temperature gradient in the flow fields and heat transfer over the heated wall of the cavity are significant, altered by the placement of needle size during various computations. [ABSTRACT FROM AUTHOR]

Homing pigeons (Columba livia) navigate by solar and magnetic compass, and fly home in idiosyncratic but stable routes when repeatedly released from the same location. However, when experienced pigeons fly alongside naive counterparts, their path is altered. Over several generations of turnover (pairs in which the most experienced individual is replaced with a naive one), pigeons show cumulative improvements in efficiency. Here, I show that such cumulative route improvements can occur in a much simpler system by using agent-based simulation. Artificial agents are in silico entities that navigate with a minimal cognitive architecture of goal-direction (they know roughly where the goal is), social proximity (they seek proximity to others and align headings), route memory (they recall landmarks with increasing precision), and continuity (they avoid erratic turns). Agents' behaviour qualitatively matched that of pigeons, and quantitatively fitted to pigeon data. My results indicate that naive agents benefitted from being paired with experienced agents by following their previously established route. Importantly, experienced agents also benefitted from being paired with naive agents due to regression to the goal: naive agents were more likely to err towards the goal from the perspective of experienced agents' memorised paths. This subtly biased pairs in the goal direction, resulting in intergenerational improvements of route efficiency. No cumulative improvements were evident in control studies in which agents' goal-direction, social proximity, or memory were lesioned. These 3 factors are thus necessary and sufficient for cumulative route improvements to emerge, even in the absence of sophisticated communication or thought. Homing pigeons improve their route efficiency in consecutive generations, potentially through social interaction. This study uses artificial agents with a highly limited cognitive architecture to show that although their only "social" capacity is to seek proximity, their behavior matches that of pigeons, and they show cumulative improvements in route efficiency. [ABSTRACT FROM AUTHOR]

The Editors' and Readers' Choice Awards were established in 2022 to celebrate some of the outstanding articles published every year in the Journal of Comparative Physiology A. The recipients of the 2024 Editors' Choice Awards were selected based on votes cast by the Editorial Board on articles published in 2023. In the category Original Paper, this distinction goes to 'Views from 'crabworld': the spatial distribution of light in a tropical mudflat' by Jochen Zeil (J Comp Physiol A 209:859–876, 2023); and in the category Review Article to 'Olfactory navigation in arthropods' by Theresa J. Steele and colleagues (J Comp Physiol A 209:467–488, 2023). The winners of the 2024 Readers' Choice Awards were determined by the number of online accesses of articles published in 2022. In the category Original Paper, the winner is 'Broadband 75–85 MHz radiofrequency fields disrupt magnetic compass orientation in night‑migratory songbirds consistent with a flavin‑based radical pair magnetoreceptor' by Bo Leberecht and colleagues (J Comp Physiol A 208:97–106, 2022). In the category Review Article, the winner is 'Magnetic maps in animal navigation' by Kenneth J. Lohmann and colleagues (J Comp Physiol A 208:41–67, 2022), which already won the Editors' Choice Award in 2023. [ABSTRACT FROM AUTHOR]

Weak oscillating magnetic fields (OMF) in the radiofrequency range are known to disrupt the orientation of birds. However, until now, it has not been experimentally verified that the sensitivity to OMF is a characteristic feature specifically of the magnetic compass and OMF does not influence the celestial compass system as well. Here we studied if OMF affected the star compass of a long-distance migrant, the Garden Warbler. The birds were tested under the natural starry sky under two different conditions: in the natural magnetic field (NMF) and in radiofrequency OMF with the amplitude 20nT and frequency 1.41 MHz (matching the Larmor frequency of a freestanding electron spin in the local NMF of 50,400 nT). This amplitude is about ten times higher than the sensitivity threshold to OMF shown for this species in previous studies. Our experimental results clearly demonstrated that OMF did not influence the celestial (star) compass system: with access to the starry sky garden warblers showed migratory orientation appropriate for autumn migratory season both in the NMF and in the OMF. Thus, the OMF effect is pertinent to the magnetic compass system, not to the avian orientation in general. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids have emerged as a promising field of research in recent years, finding applications in various industries and sectors. The entropy generation and impact of an inclined magnetic field on a water-Ethylene Glycol (50:50) mixture-based nanofluid over a poignant thin needle has been investigated under slip conditions. The flow is swotted using thermal and velocity slip boundary conditions. The numerical effects of an inclined magnetic field on the flow of ferrous and aluminum oxide nanoparticles in a hybrid nanoliquid with as base fluids have been examined. The non-dimensional ODEs along with boundary conditions are solved by numerical technique based on the Runge–Kutta fourth-order method. Velocity profile has been analyzed for the magnetic parameter, inclined angle and volume fractions. The Bejan number provides insights into the balance between heat transfer and entropy generation in a system. From the numerical values of skin friction coefficient and Nusselt number, it is analyzed that Al 2 O3 possesses 1.01% and 1.06% of high heat transfer rate and high surface drag force than Fe 3 O4. Heat transfer profile has been analyzed for entropy generation and the Bejan number. The applications of hybrid nanofluids are vast, and one specific area where they can be utilized is in horizontal needle systems. [ABSTRACT FROM AUTHOR]

Migratory birds possess remarkable accuracy in orientation and navigation, which involves various compass systems including the magnetic compass. Identifying the primary magnetosensor remains a fundamental open question. Cryptochromes (Cry) have been shown to be magnetically sensitive, and Cry4a from a migratory songbird seems to show enhanced magnetic sensitivity in vitro compared to Cry4a from resident species. We investigate Cry and their potential involvement in magnetoreception in a phylogenetic framework, integrating molecular evolutionary analyses with protein dynamics modelling. Our analysis is based on 363 bird genomes and identifies different selection regimes in passerines. We show that Cry4a is characterized by strong positive selection and high variability, typical characteristics of sensor proteins. We identify key sites that are likely to have facilitated the evolution of an optimized sensory protein for night-time orientation in songbirds. Additionally, we show that Cry4 was lost in hummingbirds, parrots and Tyranni (Suboscines), and thus identified a gene deletion, which might facilitate testing the function of Cry4a in birds. In contrast, the other avian Cry (Cry1 and Cry2) were highly conserved across all species, indicating basal, non-sensory functions. Our results support a specialization or functional differentiation of Cry4 in songbirds which could be magnetosensation. [ABSTRACT FROM AUTHOR]

Magnesium alloy, valued for its superior mechanical properties and biocompatibility in biomaterials, faces limitations such as rapid corrosion, poor wear resistance, and unfavorable cell adhesion. To address these challenges and enhance medical magnesium alloy development, this study investigates a magnetic needle grinding process on magnesium alloy. Mg-1.6Ca-2.0Zn alloy, prepared through powder metallurgy and T6 aging treatment, undergoes milling, and magnetic grinding using various needle sizes. The impact is assessed through Vickers hardness, residual stresses, surface roughness, friction and wear tests, electrochemical assessments, and contact angle tests. Results indicate a 22.59% microhardness increase, 30.43 MPa residual compressive stress, increased surface roughness, improved wear and corrosion resistance, and improved hydrophilia after magnetic needle grinding. This research provides a theoretical foundation for advancing medical magnesium alloy industrially. [ABSTRACT FROM AUTHOR]

The mechanism of the magnetic compass sense of migratory songbirds is thought to involve magnetically sensitive chemical reactions of light-induced radical pairs in cryptochrome proteins located in the birds' eyes. However, it is not yet clear whether this mechanism would be sensitive enough to form the basis of a viable compass. In the present work, we report spin dynamics simulations of models of cryptochrome-based radical pairs to assess whether accumulation of nuclear spin polarization in multiple photocycles could lead to significant enhancements in the sensitivity with which the proteins respond to the direction of the geomagnetic field. Although buildup of nuclear polarization appears to offer sensitivity advantages in the more idealized model systems studied, we find that these enhancements do not carry over to conditions that more closely resemble the situation thought to exist in vivo. On the basis of these simulations, we conclude that buildup of nuclear polarization seems unlikely to be a source of significant improvements in the performance of cryptochrome-based radical pair magnetoreceptors. [ABSTRACT FROM AUTHOR]

Viking sailors ruled the North Atlantic Ocean for about three hundred years. Their main sailing route was the 60° 21' 55" latitude between Norway and Greenland. Although they did not have a magnetic compass, in sunshine they used a sun-compass to determine the geographical north (solar Viking navigation: SVN). It has been hypothesized that when the Sun was invisible, Viking navigators determined the direction of polarization of skylight with sunstones (dichroic/birefringent crystals), and then estimated the geographical north using the sun-compass (sky-polarimetric Viking navigation: SPVN). Many details of the hypothetical SPVN have been thoroughly revealed in psychophysical laboratory and planetarium experiments. Combining these results with measured celestial polarization patterns, the success of SPVN was obtained as functions of sailing, meteorological and navigation parameters (sunstone type, sailing date, navigation periodicity, night sailing, cloudiness conditions). What was so far lacking in this experimental and computational archeological approach is the study of the success of SVN and a combined navigation using solar cues in sunshine (SVN) and sky polarization at invisible Sun (SPVN), the latter being the most realistic method. In this work we determine the success of the sole SVN and the combined SVN-SPVN relative to the mere SPVN for three navigator types (determining the intended sailing direction with large, medium or small frequencies) at spring equinox and summer solstice, with and without night sailing. We found that to maximize the sailing success, navigators had to choose different navigation methods depending on the navigation frequency. Using sky polarization with very frequent navigation, resulted in the highest chance to survive a three-week voyage from Norway to Greenland. [ABSTRACT FROM AUTHOR]

The avian magnetic compass can be disrupted by weak narrow-band and broadband radio-frequency (RF) fields in the lower MHz range. However, it is unclear whether disruption of the magnetic compass results from the elimination of the perception pattern produced by the magnetic field or from qualitative changes that make the pattern unrecognizable. We show that zebra finches trained in a 4-arm maze to orient relative to the magnetic field are disoriented when tested in the presence of low-level (~ 10 nT) Larmor-frequency RF fields. However, they are able to orient when tested in such RF fields if trained under this condition, indicating that the RF field alters, but does not eliminate, the magnetic input. Larmor-frequency RF fields of higher intensities, with or without harmonics, dramatically alter the magnetic compass response. In contrast, exposure to broadband RF fields in training, in testing, or in both training and testing eliminates magnetic compass information. These findings demonstrate that low-level RF fields at intensities found in many laboratory and field experiments may have very different effects on the perception of the magnetic field in birds, depending on the type and intensity of the RF field, and the birds' familiarity with the RF-generated pattern. [ABSTRACT FROM AUTHOR]

Many applications of the ocean and aerodynamic engineering, like the design of submarines, missiles, aircraft, rockets, and jet engines, involve flow over surfaces. Moreover, several experimental propulsion methods for seagoing ships, submarines and aerospace crafts are based on magnetohydrodynamics (MHD). This research explores the MHD boundary layer flow over a moving needle (shaped like a paraboloid of revolution). Governing equations are modelled in cylindrical coordinates under axial symmetry constraint, which is then simplified by employing order of magnitude analysis. In the absence of a magnetic field, these equations are self‐similar, and this analysis is already available in the literature. We have applied the local non‐similarity method to derive the boundary layer equations up to the second level of truncation to compute the solutions of non‐similar boundary layer equations. The built‐in MATLAB routine bvp5c is used to solve these equations numerically. This analysis will assist in predicting flow quantities that are important in designing the objects mentioned above. [ABSTRACT FROM AUTHOR]

A magnetic needle headspace single-drop microextraction (MN-HS-SDME) method coupled to HPLC/UV has been developed. Trihexyl(tetradecyl)phosphonium chloride was employed as an ionic liquid (IL) solvent for the headspace extraction of some chlorophenol (CP) compounds from wastewater samples. Despite of the nonmagnetic character of the IL, a significant improvement in the extraction efficiency was obtained by the magnetization of the single-drop microextraction needle using a pair of permanent disk magnets. A simplex method for the fast optimization of the experimental conditions (e.g. stirring speed, ionic strength, pH, extraction time and temperature) was used. The coefficients of determination (R 2) varied between 0.9932 and 0.9989, the limits of detection were from 0.004 to 0.007 μg mL−1 and the relative recoveries were in the range of 88–120% for the studied analytes. The developed MN-HS-SDME HPLC/UV method was successfully applied to the determination of CPs in industrial wastewater. [ABSTRACT FROM AUTHOR]

True north can be determined on Earth by three means: magnetic compasses, stars, and via the global navigation satellite systems (GNSS), each of which has its own drawbacks. GNSS are sensitive to jamming and spoofing, magnetic compasses are vulnerable to magnetic interferences, and the stars can be used only at night with a clear sky. As an alternative to these methods, nature-inspired navigational cues are of particular interest. Celestial polarization, which is used by insects such as Cataglyphis ants, can provide useful directional cues. Migrating birds calibrate their magnetic compasses by observing the celestial rotation at night. By combining these cues, we have developed a bioinspired optical method for finding the celestial pole during the daytime. This method, which we have named SkyPole, is based on the rotation of the skylight polarization pattern. A polarimetric camera was used to measure the degree of skylight polarization rotating with the Sun. Image difference processes were then applied to the time-varying measurements in order to determine the north celestial pole’s position and thus the observer’s latitude and bearing with respect to the true north. [ABSTRACT FROM AUTHOR]

Night-migratory songbirds have a light-dependent magnetic compass sense, the mecha- nism of which is thought to depend on the photochemical formation of radical pairs in cryptochrome (Cry) proteins located in the retina. The finding that weak radiofrequency (RF) electromagnetic fields can prevent birds from orienting in the Earth’s magnetic field has been regarded as a diagnostic test for this mechanism and as a potential source of information on the identities of the radicals. The maximum frequency that could cause such disorientation has been predicted to lie between 120 and 220 MHz for a flavin–tryptophan radical pair in Cry. Here we show that the magnetic orientation capabilities of Eurasian blackcaps (Sylvia atricapilla) are not affected by RF noise in the frequency bands 140 to 150 MHz and 235 to 245 MHz. From a consideration of its internal magnetic interactions, we argue that RF field effects on a flavin-containing radical- pair sensor should be approximately independent of frequency up to 116 MHz and that birds’ sensitivity to RF disorientation should fall by about two orders of mag- nitude when the frequency exceeds 116 MHz. Taken together with our earlier finding that 75 to 85 MHz RF fields disrupt the magnetic orientation of blackcaps, these results provide compelling evidence that the magnetic compass of migratory birds operates by a radical pair mechanism. [ABSTRACT FROM AUTHOR]

This paper proposes a proper compass adjustment method using only a GPS (or any other GNSS receiver) and a single visual reference to enhance the efficiency of compass adjustment. During compass adjustment, the ship proceeds on magnetic courses using a gyroscopic or satellite compass and considering magnetic declination. However, non-magnetic compasses are only compulsory for ships of 500 gross tonnage or upwards (SOLAS V/19.2.5.1). Many ships of less than 500 gross tonnage have only a magnetic compass to indicate heading. In these cases, a minimum of five leading lines or a minimum of five bearings of conspicuous and distant points or sun azimuths are necessary to adjust the compass. This makes compass adjustment more laborious and time consuming. To expedite this process, a reliable and practical method was developed to use the courses over ground given by a GNSS receiver and a single visual reference instead of the headings provided by a gyroscopic or satellite compass. The method is valid for all ships, but is primarily intended for those equipped with only a magnetic compass to indicate heading. [ABSTRACT FROM AUTHOR]

The existence of a magnetic compass system was first demonstrated in birds. Since then, extensive of data have been accumulated on the operation of the magnetic compass in birds and its relationship with visual reception. The currently dominant concept is that the receptor supporting operation of the magnetic compass in birds is located in the retina. The most popular hypothesis for how magnetic field receptors work is the radical pair hypothesis, in which cryptochrome, more specifically, the cryptochrome 4a isoform, is the candidate for the role of the primary magnetoreceptor molecule. Recent research has yielded data on the interaction of cryptochrome with various proteins involved in the phototransduction cascade, along with promising data from electrophysiological studies combining visual (light) and magnetic stimulation. In addition, a number of morphological studies of the avian retina are also helping to narrow the range of possible cells for the role of magnetoreceptor, with double cones being currently the most likely candidate. In this review, we discuss the latest research in this area. [ABSTRACT FROM AUTHOR]

Cluster N is a region of the visual forebrain of nocturnally migrating songbirds that supports the geomagnetic compass of nocturnal migrants. Cluster N expresses immediate‐early genes (ZENK), indicating neuronal activation. This neuronal activity has only been recorded at night during the migratory season. Night‐to‐night variation in Cluster N activity in relation to migratory behaviour has not been previously examined. We tested whether Cluster N is activated only when birds are motivated to migrate and presumably engage their magnetic compass. We measured immediate‐early gene activation in Cluster N of white‐throated sparrows (Zonotrichia albicollis) in three conditions: daytime, nighttime migratory restless and nighttime resting. Birds in the nighttime migratory restlessness group had significantly greater numbers of ZENK‐labelled cells in Cluster N compared to both the daytime and the nighttime resting groups. Additionally, the degree of migratory restlessness was positively correlated with the number of ZENK‐labelled cells in the nighttime migratory restless group. Our study adds to the number of species observed to have neural activation in Cluster N and demonstrates for the first time that immediate early gene activation in Cluster N is correlated with the amount of active migratory behaviour displayed across sampled individuals. We conclude that Cluster N is facultatively regulated by the motivation to migrate, together with nocturnal activity, rather than obligatorily active during the migration season. [ABSTRACT FROM AUTHOR]

Radical-pair reactions have been suggested to be sensitive to the direction of weak magnetic fields, thereby providing a mechanism for the magnetic compass in animals. Discovering the general principles that make radical pairs particularly sensitive to the direction of weak magnetic fields will be essential for designing bioinspired compass sensors and for advancing our understanding of the spin physics behind directional effects. The reference-probe model is a conceptual model introduced as a guide to identify radical-pair parameters for optimal directional effects. Radical pairs with probe character have been extensively shown to enhance directional sensitivity to weak magnetic fields, but investigations on the role of the reference radical are lacking. Here, we evaluate whether a radical has reference character and then study its relevance for optimal directional effects. We investigate a simple radical-pair model with one axially anisotropic hyperfine interaction using both analytical and numerical calculations. Analytical calculations result in a general expression of the radical-pair reaction yield, which in turn provides useful insights into directional effects. We further investigate the relevance of the reference character to robustness against variations of earth-strength magnetic fields and find that the reference character captures robust features as well. Extending this study to radical pairs with more hyperfine interactions, we discuss the interplay between reference character and optimal and robust directional effects in such more complex radical pairs. [ABSTRACT FROM AUTHOR]

Birds appear to be equipped with an innate magnetic compass. One biophysical model of this sense relies on spin dynamics in photogenerated radical pairs in the protein cryptochrome. This study employs a systematic approach to predict the dependence of the compass sensitivity on the relative orientation of the constituent radicals for spin systems comprising up to 21 hyperfine interactions. Evaluating measures of compass sensitivity (anisotropy) and precision (optimality) derived from the singlet yield, we find the ideal relative orientations for the radical pairs consisting of the flavin anion (F•−) coupled with a tryptophan cation (W•+) or tyrosine radical (Y•). For the geomagnetic field, the two measures are found to be anticorrelated in [F•− W•+]. The angle spanned by the normals to the aromatic planes of the radicals is the decisive parameter determining the compass sensitivity. The third tryptophan of the tryptophan triad/tetrad, which has been implicated with magnetosensitive responses, exhibits a comparably large anisotropy, but unfavorable optimality. Its anisotropy could be boosted by an additional ∼50% by optimizing the relative orientation of the radicals. For a coherent lifetime of 1 µs, the maximal relative anisotropy of [F•− W•+] is 0.27%. [F•− Y•] radical pairs outperform [F•− W•+] for most relative orientations. Furthermore, anisotropy and optimality can be simultaneously maximized. The entanglement decays rapidly, implicating it as a situational by-product rather than a fundamental driver within the avian compass. In magnetic fields of higher intensity, the relative orientation of radicals in [F•− W•+] is less important than for the geomagnetic field. [ABSTRACT FROM AUTHOR]

This article discusses the contributions of several early Chinese mathematicians. Zhang Heng proposed a value for pi of approximately 3.16 in AD 100, while Liu Hui estimated pi to be 3.14159 by approximating a circle with polygons with 3072 sides. Zu Chongzhi and his son used polygons with 24,576 sides to prove that pi is between 3.1415926 and 3.1415927. Shen Kuo introduced the magnetic needle compass and made advancements in geometry and spherical trigonometry. Matteo Ricci, an Italian Jesuit, translated Euclid's Elements and collaborated with Xu Guangqi to reform the Chinese calendar. [Extracted from the article]

Magnetoreception is a key element in the sensory repertoire of many organisms, and it has been shown to play a particular role in animal navigation. While the first data to demonstrate a magnetic compass in songbirds through behavioural measures were presented decades ago, studies of behaviour are still the main source of information in learning about the magnetic senses. The behavioural evidence is, however, scattered with sometimes contradictory results. Partly, this is a consequence of a wide spectrum of methods used across multiple research groups studying different model organisms. This has limited the ability of researchers to pin down exactly how and why animals use the Earth's magnetic field. Here, we lay out how a range of methods for testing behaviour spanning from field observations to laboratory manipulations can be used to test for a magnetic sense in animals. To this end, we discuss the principal limitations of behavioural testing in telling us how animals sense the magnetic field, and we argue that behaviour must go hand in hand with other fields to advance our understanding of the magnetic sense. [ABSTRACT FROM AUTHOR]

Animals use the geomagnetic field and astronomical cues to obtain compass information. The magnetic compass is not a uniform mechanism, as several functional modes have been described in different animal groups. The Sun compass requires the internal clock to interpret the position of the Sun. For star compass orientation, night-migrating birds seem to use the star pattern as a whole, without involving the internal clock. Both the astronomical compass mechanisms are based on learning processes to adapt them to the geographic latitude where the animals live and, in long-living animals, to compensate for the seasonal changes. Several mechanisms are used to determine the compass course to a goal. Using information collected during the outward journey is mostly done by path integration: recording the direction with a compass and integrating its twists and turns. Migratory animals have innate programs to guide them to their still unknown goal. Highly mobile animals with large ranges develop a so-called navigational 'map', a mental representation of the spatial distribution of navigational factors within their home region and their migration route. The nature of the factors involved is not yet entirely clear; magnetic intensity and inclination are the ones best supported so far. [ABSTRACT FROM AUTHOR]

Efficient thermal management and electromagnetic interference shielding are crucial for high-power integrated circuits to prevent overheating and ensure reliable performance. Shape-anisotropic CoFe magnetic needles (MNs), which are synthesized via the wet chemical method, are utilized as fillers in composites for microwave absorption and thermal conduction. The atomic ratio of Co2+ to Fe3+ (γ Co/Fe) in the precursor is used as the key parameter to control the composition and microstructure of CoFe MNs. A high γ Co/Fe ratio increases the metallic Co content, enhancing electrical conductivity and residual permeability in the microwave frequency range. The collective orientation of CoFe MNs along the magnetic field of a TEM wave does not significantly affect the real part of the permittivity but facilitates in forming long-range conductive networks, enhancing dielectric losses. The design of composition, along with the collective orientation of magnetic fillers, is an effective strategy for tailoring the properties of composites. The composites consisting of oriented Co 3 Fe 1 MNs (Co 3 Fe 1 -O), with a thickness of 4.4 mm, effectively absorbs S-band microwaves from 2.4 to 4.0 GHz, providing the broadest EAB for a single composite to date. Additionally, Co 3 Fe 1 -O has a thermal conductivity exceeding 0.50 W·m–1·K–1, which is four times higher than that of pure epoxy resin. The formation of long-range conductive networks allows thermal energy to be directly transferred through these networks with minimized phonon scattering. Considering the excellent performance in S-band microwave absorption and high thermal conductivity, Co 3 Fe 1 -O is a highly promising candidate for conformal shielding applications. [Display omitted] • Asymmetric CoFe magnetic needles (MNs) are synthesized via the wet chemical method. • Electromagnetic (EM) properties of CoFe MNs in the S Ku band can be tuned. • Tunable EM properties enable MNs to selectively absorb microwaves in the S Ku band. • Collective orientation of MNs broadens effective absorption bandwidth of S-band. • Long-range conductive networks in oriented MNs facilitate thermal energy transfer. [ABSTRACT FROM AUTHOR]

In evaluating the accuracy of most navigation measuring systems, it is accepted, as a rule, that measurement errors are characterised by a normal distribution. With reference to the compass, the approach of most producers is similar. However, in the case of this measuring device, the dynamics of the ship should also be taken into account. The problem is that any changes in the ship's heading can be measured exclusively with the use of a compass. Until quite recently, this device was built based on mechanical elements, so it possessed its own dynamic properties. This means the appearance of specific, positive feedback (self-reinforcing feedback) because if the compass did not point to the correct heading, it could lead the ship to stray from the correct heading. On the other hand, it could mean an incorrect compass setup, even though the ship had the correct heading. Any incorrect indications of the compass were then interpreted as a ship's departure from the correct heading. This problem was not essential in the era of magnetic compasses because the errors in these compasses are relatively constant, unlike the errors in gyrocompasses, which have an oscillatory and random character and, thus, it is not possible to describe them accurately with mathematical relations. This issue was already perceived before WWII, when the Anschutz Company proposed, among other solutions, using the so-called Schuler period in the construction of gyrocompasses. Fibre optic gyrocompasses do not possess mechanical sensors, so the variability of their indications is of a different character. However, computational processes, as well as applied inertial sensors, also cause certain errors of an oscillatory nature. This raises the following questions: what is the spectrum of the error frequency of such compasses, and what is the influence of the ship's movement on them? The authors attempted to evaluate this phenomenon by performing measurements made on board three hydrographic platforms and comparing them with the headings indicated by other compasses. [ABSTRACT FROM AUTHOR]

Magnetic observations at the Clementinum Observatory were started in July 1839 and data up to 1917 were published in yearbooks. In addition to regular daily observations with a typical 2-hr time step, two categories of data with a higher cadence were provided in the first decade. The first category captures 73 magnetic storms with their magnitude being of at least a moderate level. The second category is the dense observations during the days that had been agreed for joint measurements by the observatories organized in the Göttingen Magnetic Union (GMU), these measurements being known as term-day observations. Whereas four terms per year were set by GMU, many observatories agreed to carry out additional observations in the eight remaining months. The term-day observations also continued being performed for several years after the end of the GMU activities in 1841. Data of 120 term days from January 1840 to December 1849 were published. The declination was observed using the magnetic compass principle, while a bifilar apparatus was used to measure the horizontal intensity. When converting the data to the physical units of the SI, we have achieved the consistency of these high cadence data with previously published regular hourly observations of the geomagnetic field. This requirement was also met by considering the temperature dependence of measurements by the bifilar apparatus in determining the absolute values of horizontal intensity. Revealing the historical observations of the geomagnetic field can serve as a valuable material for studying the space weather in the past and may also contribute to the refinement of global field modelling. [ABSTRACT FROM AUTHOR]

One of the challenges in clinical translation of cell-replacement therapies is the definition of optimal cell generation and storage/recovery protocols which would permit a rapid preparation of cell-treatment products for patient administration. Besides, the availability of injection devices that are simple to use is critical for potential future dissemination of any spinally targeted cell-replacement therapy into general medical practice. Here, we compared the engraftment properties of established human-induced pluripotent stem cells (hiPSCs)-derived neural precursor cell (NPCs) line once cells were harvested fresh from the cell culture or previously frozen and then grafted into striata or spinal cord of the immunodeficient rat. A newly developed human spinal injection device equipped with a spinal cord pulsation-cancelation magnetic needle was also tested for its safety in an adult immunosuppressed pig. Previously frozen NPCs showed similar post-grafting survival and differentiation profile as was seen for freshly harvested cells. Testing of human injection device showed acceptable safety with no detectable surgical procedure or spinal NPCs injection-related side effects. [ABSTRACT FROM AUTHOR]

One of the most unusual features of the avian magnetic compass is its sensitivity to weak oscillating magnetic fields (OMF) in the radiofrequency range. This effect, observed earlier in numerous experiments in European robins Erithacus rubecula and garden warblers Sylvia borin, is usually associated with the radical-pair magnetoreception in the eye, which is the mainstream biophysical model of the avian magnetic compass. We studied the effect of OMF on the orientation behavior of a long-distance migrant, the pied flycatcher Ficedula hypoleuca. The OMF with an amplitude of 190 nT disoriented pied flycatchers, similarly to the species studied earlier. However, the application of OMP with an amplitude of 17 nT did not lead to disorientation in pied flycatchers when tested in round arenas: the birds showed their correct season-specific migratory direction. This finding is in stark contrast with previous results, obtained in garden warblers at exactly the same place and under the same conditions: garden warblers were disoriented by OMF which was an order of magnitude weaker. Moreover, the threshold of sensitivity to OMF amplitude in pied flycatchers is found to be higher than that in both species previously studied, the European robin and the garden warbler. We discuss the variable sensitivity of avian compass to OMF in the context of migration ecology of two long-distance African migrants, the pied flycatcher and garden warbler, and the short-distance migrant, the European robin. Significance statement: Birds are known to use a magnetic compass to determine the proper direction of their flight during seasonal migrations. Many previous experiments demonstrated that operation of this compass is disrupted by weak oscillating magnetic fields (OMF) in the radiofrequency range. Among the two bird species studied so far, a long-distance migrant, garden warbler, is more sensitive to OMF than a short-distance migrant, European robin. This might be a result of finer tuning of the magnetic compass of long-distance migrants, making it less robust to perturbations. In our experiments, however, the magnetic compass of another long-distance migrant, pied flycatcher, remained operational under OMF even stronger than that which disrupted magnetic orientation of European robins. This unexpected result demonstrates high variability of navigational systems of birds and raises questions about their adaptation to behavioral patterns of birds on their migration routes. [ABSTRACT FROM AUTHOR]

Sensitivity to the earth's magnetic field is the least understood of the major sensory systems, despite being virtually ubiquitous in animals and of widespread interest to investigators in a wide range of fields from behavioral ecology to quantum physics. Although research on the use of magnetic cues by migratory birds, fish, and sea turtles is more widely known, much of our current understanding of the functional properties of vertebrate magnetoreception has come from research on amphibians. Studies of amphibians established the presence of a light-dependent magnetic compass, a second non-light-dependent mechanism involving particles of magnetite and/or maghemite, and an interaction between these two magnetoreception mechanisms that underlies the "map" component of homing. Simulated magnetic displacement experiments demonstrated the use of a high-resolution magnetic map for short-range homing to breeding ponds requiring a sampling strategy to detect weak spatial gradients in the magnetic field despite daily temporal variation at least an order of magnitude greater. Overall, reliance on a magnetic map for short-range homing places greater demands on the underlying sensory detection, processing, and memory mechanisms than comparable mechanisms used by long-distance migrants. Moreover, unlike sea turtles and migratory birds, amphibians are exceptionally well suited to serve as model organisms in which to characterize the molecular and biophysical mechanisms underlying the light-dependent 'quantum compass'. [ABSTRACT FROM AUTHOR]

The exceptional navigational capabilities of migrating birds are based on the perception and integration of a variety of natural orientation cues. The "Wulst" in the forebrain of night-migratory songbirds contains a brain area named "Cluster N", which is involved in processing directional navigational information derived from the Earth´s magnetic field. Cluster N is medially joined by the hippocampal formation, known to retrieve and utilise navigational information. To investigate the connectivity and neurochemical characteristics of Cluster N and the hippocampal formation of migratory birds, we performed morphological and histochemical analyses based on the expression of calbindin, calretinin, parvalbumin, glutamate receptor type 1 and early growth response protein-1 in the night-migratory Garden warbler (Sylvia borin) and mapped their mutual connections using neuronal tract tracing. The resulting expression patterns revealed regionally restricted neurochemical features, which mapped well onto the hippocampal and hyperpallial substructures known from other avian species. Magnetic field-induced neuronal activation covered caudal parts of the hyperpallium and the medially adjacent hippocampal dorsomedial/dorsolateral subdivisions. Neuronal tract tracings revealed connections between Cluster N and the hippocampal formation with the vast majority originating from the densocellular hyperpallium, either directly or indirectly via the area corticoidea dorsolateralis. Our data indicate that the densocellular hyperpallium could represent a central relay for the transmission of magnetic compass information to the hippocampal formation where it might be integrated with other navigational cues in night-migratory songbirds. [ABSTRACT FROM AUTHOR]

The avian magnetic compass allows orientation during migration and is shown to function properly under short-wavelength but not long-wavelength visible light. Therefore, the magnetoreceptive system is assumed to be light- and wavelength-dependent and localized in the retina of the eye. Putative candidates for the role of primary magnetosensory molecules are the cryptochromes that are known to be expressed in the avian retina and must be able to interact with phototransduction proteins. Previously, we reported that in migratory birds change in magnetic field direction induces significant effects on electroretinogram amplitude in response to blue flashes, and such an effect was observed only in the nasal quadrant of the retina. Here, we report new electroretinographic, microscopic and microspectrophotometric data on European robins, confirming the magnetosensitivity of the retinal nasal quadrant after applying the background illumination. We hypothesized that magnetoreceptive distinction of this region may be related to its morphology and analyzed the retinal distribution and optical properties of oil droplets, the filtering structures within cones. We found that the nasal quadrant contains double cones with the most intensely colorized oil droplets compared to the rest of the retina, which may be related to its magnetosensory function. [ABSTRACT FROM AUTHOR]

In 1558, the famous natural magician Giambattista della Porta was the first to allude to a method of transmitting secret messages by using manipulated magnetic compasses. Soon thereafter, this idea, known in modern historiography as 'magnetic telegraphy', was spelled out and advertised by many early modern scholars as a promising technology of communication by action at a distance. In 1609, Daniel Schwenter created the most sophisticated design for the fulfillment of this potential: two compass needles were to be magnetized in a highly codified procedure to establish a sympathetic bond between them. Used in a compass circumscribed by an alphabet, one needle would turn to a certain letter whenever the other needle was moved to that same letter. Through 'sympathy', it was thought that this could made to occur even over a distance of many miles. The idea's first critic, the Jesuit, Leonardo Garzoni, was quick to dismiss it as charlatanry, and many later authors argued that the device could not work as there was no such 'sympathy' or magnetism between the two devices. Though only a fanciful pipe dream of natural magic, this pseudo-technology of a magnetic telegraph yet testifies to the imagination of early modern scholars in having prefigured the modern reality of instantaneous global communication. [ABSTRACT FROM AUTHOR]

It is well known that the needle of a compass in a magnetic field deflects, and that a compass near a conductive wire carrying a stable electric current deflects its needle. The only explanation of this observation is that the current-carrying wire creates a magnetic field around it. The strength of the magnetic field at any point near the wire depends on the strength of the current and the distance from the wire. Analysis of the magnetic field created by a long straight current-carrying wire has an important place in magnetism teaching. Therefore, the aim of this study was to develop a low-cost experimental setup to collect real-time data for the analysis of the magnetic field near a long straight wire. [ABSTRACT FROM AUTHOR]

The field of magnetic robotics aims to obviate physical connections between the actuators and end‐effectors. Such tetherless control may enable new ultraminimally invasive surgical manipulations in clinical settings. While wireless actuation offers advantages in medical applications, the challenge of providing sufficient force to magnetic needles for tissue penetration remains a barrier to practical application. Applying sufficient force for tissue penetration is required for tasks such as biopsy, suturing, cutting, drug delivery, and accessing deep‐seated regions of complex structures in organs such as the eye. To expand the force landscape for such magnetic surgical tools, an impact force‐based suture needle capable of penetrating in vitro and ex vivo samples with 3‐degrees‐of‐freedom (DOF) planar motion is proposed. Using custom‐built 14 and 25 G needles, generation of 410 mN penetration force is demonstrated, a 22.7‐fold force increase with more than 20 times smaller volume compared with similar magnetically guided needles. With the Magnetic Pulse Actuated Collisions for Tissue‐penetrating (MPACT)‐Needle, gauze mesh suturing onto an agar gel is demonstrated. In addition, the tip size is reduced to 25 G, a typical needle size for eye interventions, to demonstrate ex vivo penetration in a rabbit eye towards corneal injections and transscleral drug delivery. [ABSTRACT FROM AUTHOR]

Numerous organisms use the Earth's magnetic field as a sensory cue for migration, body alignment, or food search. Despite some contradictory reports, yet it is generally accepted that humans do not sense the geomagnetic field. Here, we demonstrate that a magnetic field resonance mechanism mediates light-dependent magnetic orientation in men, using a rotary chair experiment combined with a two-alternative forced choice paradigm. Two groups of subjects were classified with different magnetic orientation tendencies depending on the food context. Magnetic orientation of the subjects was sensitive to the wavelength of incident light and was critically dependent on blue light reaching the eyes. Importantly, it appears that a magnetic field resonance-dependent mechanism mediates these responses, as evidenced by disruption or augmentation of the ability to orient by radiofrequency magnetic fields at the Larmor frequency and the dependence of these effects on the angle between the radiofrequency and geomagnetic fields. Furthermore, inversion of the vertical component of the geomagnetic field revealed a non-canonical inclination compass effect on the magnetic orientation. These results establish the existence of a human magnetic sense and suggest an underlying quantum mechanical magnetoreception mechanism. [ABSTRACT FROM AUTHOR]