Magnetic maps in animal navigation

In addition to providing animals with a source of directional or ‘compass’ information, Earth’s magnetic field also provides a potential source of positional or ‘map’ information that animals might exploit to assess location. In less than a generation, the idea that animals use Earth’s magnetic field as a kind of map has gone from a contentious hypothesis to a well-established tenet of animal navigation. Diverse animals ranging from lobsters to birds are now known to use magnetic positional information for a variety of purposes, including staying on track along migratory pathways, adjusting food intake at appropriate points in a migration, remaining within a suitable oceanic region, and navigating toward specific goals. Recent findings also indicate that sea turtles, salmon, and at least some birds imprint on the magnetic field of their natal area when young and use this information to facilitate return as adults, a process that may underlie long-distance natal homing (a.k.a. natal philopatry) in many species. Despite recent progress, much remains to be learned about the organization of magnetic maps, how they develop, and how animals use them in navigation.

The archaeomagnetic field recorded in ancient kiln walls in Si Satchanalai, Sukhothai

Archaeological dating is crucial in archaeology as it is a key to understand human history. However, traditional dating methods used by archaeologists such as potassium-argon dating and luminescence dating can provide ambiguous age results, e.g., argon loss during the dating returns young apparent ages. Therefore, I plan to establish an archaeomagnetic secular variation (ASV) curve to resolve this problem and use the ASV curve as an alternative tool to date archaeological artefacts. However, archaeomagnetic data in Thailand are absent from literature. Therefore, the ASV curve cannot be constructed from the archaeomagnetic data for this locality. To provide archaeomagnetic data to construct the ASV curve, the directions of the Earth’s magnetic field recorded in kiln walls from Ban Ko Noi (KN123, age 1,370 ± 100 A.D.), Si Satchanalai were measured. The mean declination and inclination of 49.6° and 32.6° with 95% confidence limit of 5.4° were determined from 10 samples from kiln KN123. Mean directions from this study were also compared with the directions of the Earth’s magnetic field in Thailand during 1,370 A.D. from the global archaeomagnetic field model ARCH3k.1. Declination and inclination from this study show significant departure from the field predicted by the ARCH3k.1 model.

Influences of the Earth’s Magnetic Field on the Transient Electromagnetic Process in the Geoelectric Field: an Experimental Study

—A mathematical model of the influence of the Earth’s magnetic field (the Hall effect) on results of the controlled source transient electromagnetic (TEM) method has been elaborated. For identification of this effect, we propose a schematic layout of the experimental grounded system with a pulsed loop source and signals recording by radial receive lines equally spaced relative to the loop. The 2018–2019 special field experiments were conducted in the Tatar region of the West Siberian Lowland with an aim to estimate the Hall effect contributions to the TEM method. To detect the Hall effect, transient electromagnetic responses were measured mainly by four receive lines radiating from a 500×500 m square loop. Analysis of the TEM results processing aimed at improving the signal quality and reducing the interference revealed a great similarity in signals from the radial lines, which is theoretically possible only under the Hall effect. Comparison of the field signals with the theoretical ones enabled estimation of the components caused by the Hall effect, in particular, conductivity at ~0.002 S/m.

JOM-4S Overhauser Magnetometer and Sensitivity Estimation

The Overhauser magnetometer is a scalar quantum magnetometer based on the dynamic nuclear polarization (DNP) effect in the Earth’s magnetic field. Sensitivity is a key technical specification reflecting the ability of instruments to sense small variations of the Earth’s magnetic field and is closely related to the signal-to-noise ratio (SNR) of the free induction decay (FID) signal. In this study, deuterated 15N TEMPONE radical is used in our sensor to obtain high DNP enhancement. The measured SNR of the FID signal is approximately 63/1, and the transverse relaxation time T2 is 2.68 s. The direct measurement method with a single instrument and the synchronous measurement method with two instruments are discussed for sensitivity estimation in time and frequency domains under different electromagnetic interference (EMI) environments and different time periods. For the first time, the correlation coefficient of the magnetic field measured by the two instruments is used to judge the degree of the influence of the environmental noise on the sensitivity estimation. The sensitivity evaluation in the field environment is successfully realized without electrical and magnetic shields. The direct measurement method is susceptible to EMI and cannot work in general electromagnetic environments, except it is sufficiently quiet. The synchronous measurement method has an excellent ability to remove most natural and artificial EMIs and can be used under noisy environments. Direct and synchronous experimental results show that the estimated sensitivity of the JOM-4S magnetometer is approximately 0.01 nT in time domain and approximately 0.01 nT/ in frequency domain at a 3 s cycling time. This study provides a low-cost, simple, and effective sensitivity estimation method, which is especially suitable for developers and users to estimate the performance of the instrument.

Multi-Acquisition and Multi-Dimensional Earth's Field Nuclear Magnetic Resonance Spectroscopy

<p>In this thesis we investigate the ways in which the sensitivity, resolution and overall performance of an Earth's field NMR system can be improved without significantly compromising its simplicity, portability or affordability. We investigate the limits of the information obtainable using this device and present a range of methods for calculating and analyzing NMR spectroscopy experiments detected in the Earth's magnetic field. We demonstrate significant improvements in the performance of a commercial Earth's field NMR device, the Terranova-MRI, through several apparatus developments. First-order shimming is added to the system in order to counter any local inhomogeneity of the Earth's field. The spectral resolution of the instrument is further improved through the introduction of a field locking system to counter the natural temporal drift in the magnitude of the Earth's magnetic field. External noise interference is reduced through the use of Faraday screening, effectively increasing the signal-to-noise ratio (SNR) performance of the device. We explore three signal enhancement methodologies for optimizing the SNR performance of the system. Prepolarization, with an electromagnet as well as a permanent magnet array, is considered and compared to dynamic nuclear polarization (DNP) and hyperpolarization via optical pumping. We present a detailed theoretical discussion of DNP in low-fields and demonstrate the application of this technique for signal enhancement in EFNMR. An apparatus for performing DNP in the Earth's field is presented and optimized. A density matrix approach to simulating one- and two-dimensional Earth's field NMR experiments is presented. These numerical simulations, along with a perturbation theory approach to calculating one-dimensional EFNMR spectra of tightly coupled heteronuclear systems, are explored and compared to experimental spectra of the tetrahydroborate and ammonium ions. These systems are of particular interest for NMR detected in the Earth's field because they contain strongly coupled nuclei of differing spin, a situation previously unexplored in the literature. Multi-dimensional Earth's field NMR spectroscopy methods, in particular the correlation spectroscopy (COSY) experiment, are implemented and optimized through the use of shimming, field stabilization and noise screening. The 2D COSY spectrum of monofluorobenzene is analyzed and compared to calculated spectra in order to determine the indirect spin-spin coupling constants of this molecule in the Earth's magnetic field. A 2D COSY spectrum of 1,4-difluorobenzene is also presented and compared to simulation. The SNR performance of COSY in the Earth's field is greatly improved through the use of DNP for signal enhancement. A high-quality, 2D COSY EFNMR spectrum with DNP acquired from 2,2,2- trifluoroethanol is presented and compared to simulation. The particular features of this spectrum, which result from the use of DNP for signal enhancement, are discussed with reference to a density matrix simulation and to a one-dimensional spectrum calculated using perturbation theory. The strong indirect spin-spin coupling regime in fields weaker than the Earth's magnetic field is explored through exact calculations and density matrix simulations of a 13C-enriched methyl group. A novel multi-dimensional EFNMR method for observing such spectra is discussed. This experiment allows for the resolution of strongly coupled NMR spectra both in the Earth's magnetic field, in the directly detected domain, and in weaker fields, in the indirectly detected domain. In the final section of this thesis, residual dipolar coupling is observed by EFNMR for the first time in a system of poly-[gamma]-benzyl-L-glutamate (PBLG) in dichloromethane. The form of the EFNMR spectrum of this liquid crystalline system is discussed and compared to equivalent high-field (9.4T) spectra.</p>

Experimental Study of the Velocity of the Electrovortex Flow of In-Ga-Sn in Hemispherical Geometry

The paper describes the application of the thermocorrelation method for measuring the velocity in a current-carrying liquid. An electrovortex flow occurs when the current passing through a conducting medium interacts with its own magnetic field. Measurements of the velocity of the turbulent electrovortex flow of the liquid metal (eutectic alloy In-Ga-Sn) were carried out in a hemispherical container in the range of currents of 100–450 amperes in the presence and absence of compensation of the Earth’s magnetic field. The efficiency of the thermocorrelation method in a current-carrying liquid has been demonstrated. The dependences of the axial velocity on the current and the velocity profiles along the axis were obtained. It was found that the presence of the Earth’s magnetic field leads to a significant decrease in the average value of the axial velocity in the entire range of currents.

Multi-Acquisition and Multi-Dimensional Earth's Field Nuclear Magnetic Resonance Spectroscopy

<p>In this thesis we investigate the ways in which the sensitivity, resolution and overall performance of an Earth's field NMR system can be improved without significantly compromising its simplicity, portability or affordability. We investigate the limits of the information obtainable using this device and present a range of methods for calculating and analyzing NMR spectroscopy experiments detected in the Earth's magnetic field. We demonstrate significant improvements in the performance of a commercial Earth's field NMR device, the Terranova-MRI, through several apparatus developments. First-order shimming is added to the system in order to counter any local inhomogeneity of the Earth's field. The spectral resolution of the instrument is further improved through the introduction of a field locking system to counter the natural temporal drift in the magnitude of the Earth's magnetic field. External noise interference is reduced through the use of Faraday screening, effectively increasing the signal-to-noise ratio (SNR) performance of the device. We explore three signal enhancement methodologies for optimizing the SNR performance of the system. Prepolarization, with an electromagnet as well as a permanent magnet array, is considered and compared to dynamic nuclear polarization (DNP) and hyperpolarization via optical pumping. We present a detailed theoretical discussion of DNP in low-fields and demonstrate the application of this technique for signal enhancement in EFNMR. An apparatus for performing DNP in the Earth's field is presented and optimized. A density matrix approach to simulating one- and two-dimensional Earth's field NMR experiments is presented. These numerical simulations, along with a perturbation theory approach to calculating one-dimensional EFNMR spectra of tightly coupled heteronuclear systems, are explored and compared to experimental spectra of the tetrahydroborate and ammonium ions. These systems are of particular interest for NMR detected in the Earth's field because they contain strongly coupled nuclei of differing spin, a situation previously unexplored in the literature. Multi-dimensional Earth's field NMR spectroscopy methods, in particular the correlation spectroscopy (COSY) experiment, are implemented and optimized through the use of shimming, field stabilization and noise screening. The 2D COSY spectrum of monofluorobenzene is analyzed and compared to calculated spectra in order to determine the indirect spin-spin coupling constants of this molecule in the Earth's magnetic field. A 2D COSY spectrum of 1,4-difluorobenzene is also presented and compared to simulation. The SNR performance of COSY in the Earth's field is greatly improved through the use of DNP for signal enhancement. A high-quality, 2D COSY EFNMR spectrum with DNP acquired from 2,2,2- trifluoroethanol is presented and compared to simulation. The particular features of this spectrum, which result from the use of DNP for signal enhancement, are discussed with reference to a density matrix simulation and to a one-dimensional spectrum calculated using perturbation theory. The strong indirect spin-spin coupling regime in fields weaker than the Earth's magnetic field is explored through exact calculations and density matrix simulations of a 13C-enriched methyl group. A novel multi-dimensional EFNMR method for observing such spectra is discussed. This experiment allows for the resolution of strongly coupled NMR spectra both in the Earth's magnetic field, in the directly detected domain, and in weaker fields, in the indirectly detected domain. In the final section of this thesis, residual dipolar coupling is observed by EFNMR for the first time in a system of poly-[gamma]-benzyl-L-glutamate (PBLG) in dichloromethane. The form of the EFNMR spectrum of this liquid crystalline system is discussed and compared to equivalent high-field (9.4T) spectra.</p>