Ultra-low Field Research Articles

Effects of nanotechnology-based devices on postural control in healthy subjects.

The aim of the present preliminary randomized controlled study was to ascertain whether the use of newly developed nanotechnologies-based patches can influence posture control of healthy subjects. Thirty healthy female subjects (age 39.4 years, BMI 22.74 kg/m2) were randomly assigned to two groups: one with active patches and a control group with sham patches. Two patches were applied with a tape: one on the subject's sternum and the other on the C7 apophysis. Body sway during quiet upright stance was recorded with a dynamometric platform. Each subject was tested under two visual conditions, eyes open and closed. We used a blocked stratified randomization procedure conducted by a third party. Subjects wearing the sham patches showed a significant increase of the center of pressure sway area after 4 hours when they performed the habitual moderate-intensity work activities. In the active patch group, a decrease of the sway path was evident, providing evidence of an enhanced balance control. Our preliminary findings on healthy subjects indicate that nanotechnological devices generating ultra-low electromagnetic fields can improve posture control.

Invited Review Article: Instrumentation for nuclear magnetic resonance in zero and ultralow magnetic field.

We review experimental techniques in our laboratory for nuclear magnetic resonance (NMR) in zero and ultralow magnetic field (below 0.1 μT) where detection is based on a low-cost, non-cryogenic, spin-exchange relaxation free 87Rb atomic magnetometer. The typical sensitivity is 20-30 fT/Hz1/2 for signal frequencies below 1 kHz and NMR linewidths range from Hz all the way down to tens of mHz. These features enable precision measurements of chemically informative nuclear spin-spin couplings as well as nuclear spin precession in ultralow magnetic fields.

Enhanced Endurance Organolead Halide Perovskite Resistive Switching Memories Operable under an Extremely Low Bending Radius.

It was demonstrated that organolead halide perovskites (OHPs) show a resistive switching behavior with an ultralow electric field of a few kilovolts per centimeter. However, a slow switching time and relatively short endurance remain major obstacles for the realization of the next-generation memory. Here, we report a performance-enhanced OHP resistive switching device. To fabricate topologically and electronically improved OHP thin films, we added hydroiodic acid solution (for an additive) in the precursor solution of the OHP. With drastically improved morphology such as small grain size, low peak-to-valley depth, and precise thickness, the OHP thin films showed an excellent performance as insulating layers in Ag/CH3NH3PbI3/Pt cells, with an endurance of over 103 cycles, a high on/off ratio of 106, and an operation speed of 640 μs and without electroforming. We suggest plausible resistive switching and conduction mechanisms with current-voltage characteristics measured at various temperatures and with different top electrodes and device structures. Beyond the extended endurance, highly flexible resistive switching devices with a minimum bending radius of 5 mm create opportunities for use in flexible and wearable electronic devices.

Mechanism of soft x-ray continuum radiation from low-energy pinch discharges of hydrogen and ultra-low field ignition of solid fuels

EUV continuum radiation (10–30 nm) arising only from very low energy pulsed pinch gas discharges comprising some hydrogen was first observed at BlackLight Power, Inc. and reproduced at the Harvard Center for Astrophysics (CfA). The source was determined to be due to the transition of H to the lower-energy hydrogen or hydrino state H(1/4) whose emission matches that observed wherein alternative sources were eliminated. The identity of the catalyst that accepts 3 · 27.2 eV from the H to cause the H to H(1/4) transition was determined to HOH versus 3H. The mechanism was elucidated using different oxide-coated electrodes that were selective in forming HOH versus plasma forming metal atoms as well as from the intensity profile that was a mismatch for the multi-body reaction required during 3H catalysis. The HOH catalyst was further shown to give EUV radiation of the same nature by igniting a solid fuel comprising a source of H and HOH catalyst by passing a low voltage, high current through the fuel to produce explosive plasma. No chemical reaction can release such high-energy light. No high field existed to form highly ionized ions that could give radiation in this EUV region that persisted even without power input. This plasma source serves as strong evidence for the existence of the transition of H to hydrino H(1/4) by HOH as the catalyst and a corresponding new power source wherein initial extraordinarily brilliant light-emitting prototypes are already producing photovoltaic generated electrical power. The hydrino product of a catalyst reaction of atomic hydrogen was analyzed by multiple spectroscopic techniques. Moreover, the mH catalyst was identified to be active in astronomical sources such as the Sun, stars and interstellar medium wherein the characteristics of hydrino match those of the dark matter of the Universe.

A study of spin–lattice relaxation rates of glucose, fructose, sucrose and cherries using high-Tc SQUID-based NMR in ultralow magnetic fields

We study the concentration dependence of spin–lattice relaxation rates, T1−1, of glucose, fructose, sucrose and cherries by using high-Tc SQUID-based NMR at magnetic fields of ∼97 μT. The detected NMR signal, Sy(TBp), is fitted to [1 − exp(−TBp/T1)] to derive T1−1, where Sy(TBp) is the strength of the NMR signal, TBp is the duration of pre-polarization and T1−1 is the spin–lattice relaxation rate. It was found that T1−1 increases as the sugar concentrations increase. The increased T1−1 is due to the presence of more molecules in the surroundings, which increases the spin–lattice interaction and in turn enhances T1−1. The T1−1 versus degrees Brix curve provides a basis for determining unknown Brix values for cherries as well as other fruits.

Ultra-Low Field SQUID-NMR using LN2 Cooled Cu Polarizing Field coil

We are developing an Ultra-Low Field (ULF) Magnetic Resonance Imaging (MRI) system using a High-Temperature Superconductor superconducting quantum interference device (HTS rf-SQUID) for food inspection. The advantages of the ULF-NMR (Nuclear Magnetic Resonance) / MRI as compared with a conventional high field MRI are that they are compact and of low cost. In this study, we developed a ULF SQUID-NMR system using a polarizing coil to measure fat of which relaxation time T1 is shorter. The handmade polarizing coil was cooled by liquid nitrogen to reduce the resistance and accordingly increase the allowable current. The measured decay time of the polarizing field was 40 ms. The measurement system consisted of the liquid nitrogen cooled polarizing coil, a SQUID, a Cu wound flux transformer, a measurement field coil for the field of 47 μT, and an AC pulse coil for a 90°pulse field. The NMR measurements were performed in a magnetically shielded room to reduce the environmental magnetic field. The size of the sample was ϕ35 mm × L80 mm. After applying a polarizing field and a 90°pulse, an NMR signal was detected by the SQUID through the flux transformer. As a result, the NMR spectra of fat samples were obtained at 2.0 kHz corresponding to the measurement field Bm of 47 μT. The T1 relaxation time of the mineral oil measured in Bm was 45 ms. These results suggested that the ULF-NMR/MRI system has potential for food inspection.

AC Defluxing of SQUIDs

Magnetic flux trapping is a very serious problem in SQUID-based instrumentation and superconducting electronics. A critical consideration for avoiding flux trapping is a prevention of SQUID sensors or circuits from being exposed to magnetic fields. Unfortunately, this measure cannot be applied, if sensors must be exposed to a strong magnetic field or transients. For example, unavoidable exposures take place in ultralow field magnetic resonance imaging and superparamagnetic relaxation measurements using unshielded thin-film planar SQUID sensors. SQUID sensors stop working after being exposed to magnetic fields of only a few mT in strength. Earlier, we reported successful results of defluxing of planar LTS SQUID-gradiometers using strong decaying ac magnetic pulses. In this paper, we present further experimental results and discuss a possible mechanism to explain the observed defluxing effects. The new ac defluxing technique is much faster and dissipates much less energy than a conventional thermal cycling.

Facile growth of vertically-aligned graphene nanosheets via thermal CVD: The experimental and theoretical investigations

Owing to the distinctively morphological and structural features, vertically-aligned graphene nanosheets (VGs) possess many unique properties and hold great promise for applications in various fields. For controllable preparation and wide application of VGs, the establishing reliable growth method and profound understanding of the growth mechanism are of vital significance. Up to date, VGs are normally produced by plasma-enhanced chemical vapor deposition (PECVD) and it's considered that plasma is an indispensible factor for the vertical alignment of graphene sheets. Herein, for the first time, we report the facile and controllable VGs growth via a thermal CVD by precisely tuning growth parameters. Experimental observations in combination with detailed energy calculations reveal that the flow rate of carbon precursor determines the growth dynamics of graphene in CVD. This work offers a novel and reliable technique for VGs preparation and provides new insights into the intrinsic mechanism of vertical graphene growth. Furthermore, benefiting from the ultra-high density of edge sites, thin thickness, and outstanding electrical conductivity of VGs, the as-prepared VGs exhibit excellent field-emission performance such as ultra-low turn-on electric field and threshold field down to 1.07 and 1.65 V μm−1, respectively.

Micromagnetic simulation of two-body magnetic nanoparticles

Field-induced magnetization dynamics was investigated in a system of two magnetic nanoparticles with uniaxial anisotropies and magnetostatic interaction. By using the micromagnetic simulation, ultralow switching field strength was found when the separation distance between the two particles reaches a critical small value on nanometer scale in the perpendicular configuration where the anisotropic axes of the two particles are perpendicular to the separation line. The switching field increases sharply when the separation is away from the critical distance. The same results were observed when varying the radius of particles. The micromagnetic results are consistent with the previous theoretical prediction where dipolar interaction between two single-domain magnetic particles was considered. Our present simulations offered further proofs and possibilities for the low-power applications of information storage as the two-body magnetic nanoparticles could be implemented as a composite information bit.

Depolarization of nuclear spin polarized 129Xe gas by dark rubidium during spin-exchange optical pumping

Continuous-flow spin-exchange optical pumping (SEOP) continues to serve as the most widespread method of polarizing 129Xe for magnetic resonance experiments. Unfortunately, continuous-flow SEOP still suffers from as-yet unidentified inefficiencies that prevent the production of large volumes of xenon with a nuclear spin polarization close to theoretically calculated values. In this work we use a combination of ultra-low field nuclear magnetic resonance spectroscopy and atomic absorption spectroscopy (AAS) measurements to study the effects of dark Rb vapor on hyperpolarized 129Xe in situ during continuous-flow SEOP. We find that dark Rb vapor in the optical cell outlet has negligible impact on the final 129Xe polarization at typical experimental conditions, but can become significant at higher oven temperatures and lower flow rates. Additionally, in the AAS spectra we also look for a signature of paramagnetic Rb clusters, previously identified as a source of xenon depolarization and a cause for SEOP inefficiency, for which we are able to set an upper limit of 8.3×1015 Rb dimers per cm3.

Field-emission property of self-purification SiC/SiOx coaxial nanowires synthesized via direct microwave irradiation using iron-containing catalyst

SiC/SiOx coaxial nanowires were rapidly synthesized via direct microwave irradiation in low vacuum atmosphere. During the preparation process, only graphite, silicon, silicon dioxide powders were used as raw materials and iron-containing substance was employed as catalyst. Comprehensive characterizations were employed to investigate the microstructure of the products. The results showed that a great quantity of coaxial nanowires with uniform sizes and high aspect ratio had been successfully achieved. The coaxial nanowires consist of a silicon oxide (SiOx) shell and a β-phase silicon carbide (β-SiC) core that exhibited in special tube brush like. In additional, nearly all the products were achieved in the statement of pure SiC/SiOx coaxial nanowires without the existence of metallic catalyst, indicating that the self-removal of iron (Fe) catalyst should be occurred during the synthesis process. Photoluminescence (PL) spectral analysis result indicated that such novel SiC/SiOx coaxial nanowires exhibited significant blue-shift. Besides, the measurement results of field-emission (FE) demonstrated that the SiC/SiOx coaxial nanowires had ultralow turn-on field and threshold field with values of 0.2 and 2.1 V/μm, respectively. The hetero-junction structure formed between SiOx shell and SiC core, lots of emission sites, as well as clear tips of the nanowires were applied to explain the excellent FE properties.

Nanodiamond-enhanced MRI via in situ hyperpolarization

Nanodiamonds are of interest as nontoxic substrates for targeted drug delivery and as highly biostable fluorescent markers for cellular tracking. Beyond optical techniques, however, options for noninvasive imaging of nanodiamonds in vivo are severely limited. Here, we demonstrate that the Overhauser effect, a proton–electron polarization transfer technique, can enable high-contrast magnetic resonance imaging (MRI) of nanodiamonds in water at room temperature and ultra-low magnetic field. The technique transfers spin polarization from paramagnetic impurities at nanodiamond surfaces to 1H spins in the surrounding water solution, creating MRI contrast on-demand. We examine the conditions required for maximum enhancement as well as the ultimate sensitivity of the technique. The ability to perform continuous in situ hyperpolarization via the Overhauser mechanism, in combination with the excellent in vivo stability of nanodiamond, raises the possibility of performing noninvasive in vivo tracking of nanodiamond over indefinitely long periods of time.

Statistical Evaluations of Variations in Dairy Cows' Milk Yields as a Precursor of Earthquakes.

Simple SummaryThere are many reports of abnormal changes occurring in various natural systems prior to earthquakes. Unusual animal behavior is one of these abnormalities; however, there are few objective indicators and to date, reliability has remained uncertain. We found that milk yields of dairy cows decreased prior to an earthquake in our previous case study. In this study, we examined the reliability of decreases in milk yields as a precursor for earthquakes using long-term observation data. In the results, milk yields decreased approximately three weeks before earthquakes. We have come to the conclusion that dairy cow milk yields have applicability as an objectively observable unusual animal behavior prior to earthquakes, and dairy cows respond to some physical or chemical precursors of earthquakes.Previous studies have provided quantitative data regarding unusual animal behavior prior to earthquakes; however, few studies include long-term, observational data. Our previous study revealed that the milk yields of dairy cows decreased prior to an extremely large earthquake. To clarify whether the milk yields decrease prior to earthquakes, we examined the relationship between earthquakes of various magnitudes and daily milk yields. The observation period was one year. In the results, cross-correlation analyses revealed a significant negative correlation between earthquake occurrence and milk yields approximately three weeks beforehand. Approximately a week and a half beforehand, a positive correlation was revealed, and the correlation gradually receded to zero as the day of the earthquake approached. Future studies that use data from a longer observation period are needed because this study only considered ten earthquakes and therefore does not have strong statistical power. Additionally, we compared the milk yields with the subionospheric very low frequency/low frequency (VLF/LF) propagation data indicating ionospheric perturbations. The results showed that anomalies of VLF/LF propagation data emerged prior to all of the earthquakes following decreases in milk yields; the milk yields decreased earlier than propagation anomalies. We mention how ultralow frequency magnetic fields are a stimulus that could reduce milk yields. This study suggests that dairy cow milk yields decrease prior to earthquakes, and that they might respond to stimuli emerging earlier than ionospheric perturbations.

Ultra-low threshold field emission from amorphous BN nanofilms

Abstract In this work, Field emission (FE) properties of mixed phase amorphous boron nitride (BN) nanofilms prepared by plasma enhanced chemical vapor deposition (PECVD) were thoroughly investigated. The results showed that, for mixed amorphous BN nanofilms with a little cubic boron nitride (c-BN) and wurtzite boron nitride (w-BN) nanocrystalline, the turn on field of the nanofilms is as low as ∼0.5 V/μm and the FE current density can reach ∼12 mA/cm2 when the electrical field is only 0.75 V/μm. However, for primary cubic phase nanocrystalline BN films, the FE current density is only 500 μA/cm2; at as high as about 2.5 V/μm. Moreover, the field emission mechanism of the phase amorphous BN nanofilms was further discussed. Field emission enhancement for mixed phase amorphous BN may be originated from electron step-transport in different energy states and multi-channel electron transport in nanocrystalline interface.

Ultralow-field and spin-locking relaxation dispersion in postmortem pig brain.

To investigate tissue-specific differences, a quantitative comparison was made between relaxation dispersion in postmortem pig brain measured at ultralow fields (ULF) and spin locking at 7 tesla (T). The goal was to determine whether ULF-MRI has potential advantages for in vivo human brain imaging. Separate specimens of gray matter and white matter were investigated using an ULF-MRI system with superconducting quantum interference device (SQUID) signal detection to measure T1ULF at fields from 58.7 to 235.0 μT and using a commercial MRI scanner to measure T1ρ7T at spin-locking fields from 5.0 to 235.0 μT. At matched field strengths, T1ρ7T is 50 to 100% longer than T1ULF. Furthermore, dispersion in T1ULF is close to linear between 58.7 and 235 µT, whereas dispersion in T1ρ7T is highly nonlinear over the same range. A subtle elbow in the T1ULF dispersion at approximately 140 µT is tentatively attributed to the local dipolar field of macromolecules. It is suggested that different relaxation mechanisms dominate each method and that ULF-MRI has a fundamentally different sensitivity to the macromolecular structure of neural tissue. Ultralow-field MRI may offer distinct, quantitative advantages for human brain imaging, while simultaneously avoiding the severe heating limitation imposed on high-field spin locking. Magn Reson Med 78:2342-2351, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Ultra-low coercive field of improper ferroelectric Ca3Ti2O7 epitaxial thin films

Hybrid improper ferroelectrics have their electric polarization generated by two or more combined non-ferroelectric structural distortions, such as the rotation and tilting of Ti-O octahedral in the Ca3Ti2O7 (CTO) family. In this work, we prepare the high quality (010)-oriented CTO thin films on (110) SrTiO3 (STO) substrates by pulsed laser deposition. The good epitaxial growth of the CTO thin films on the substrates with the interfacial epitaxial relationship of [001]CTO//[001]STO and [100]CTO//[-110]STO is revealed. The in-plane ferroelectric hysteresis unveils an ultralow coercive field of ∼5 kV/cm even at low temperature, nearly two orders of magnitude lower than that of bulk CTO single crystals. The huge difference between the epitaxial thin films and bulk crystals is most likely due to the lattice imperfections in the thin films rather than substrate induced lattice strains, suggesting high sensitivity of the ferroelectric properties to lattice defects.

The use of the empirical mode decomposition for the identification of mean field aligned reference frames

<p>The magnetic field satellite data are usually referred to geocentric coordinate reference frame. Conversely, the magnetohydrodynamic waves modes in magnetized plasma depend on the ambient magnetic field, and is then useful to rotate the magnetic field measurements into the mean field aligned (MFA) coordinate system. This reference frame is useful to study the ultra low frequency magnetic field variations along the direction of the mean field and perpendicularly to it. In order to identify the mean magnetic field the classical moving average (MAVG) approach is usually adopted but, under particular conditions, this procedure induces undesired features, such as spectral alteration in the rotated components. We discuss these aspects promoting an alternative and more efficient method for mean field aligned projection, based on the empirical mode decomposition (EMD).</p>

スピン交換光ポンピングによる<sup>131</sup>Xeの超偏極と極低磁場における核磁気共鳴信号の増大

Magnetic resonance imaging (MRI) has been used in clinical as major tomographic inspection with CT scans. Compared with CT, MRI has a number of advantages for example no radiation exposure. However, MRI has also disadvantages e.g. large size, high cost and never use to patients who have implant devices or metals because have to use strong field. Therefore, ultra-low-field MRI (ULF-MRI) has attracted attention because of usage of ultra-low fields such as earth field about 40∼50 μT. But there is a fatal weakness of ULF-MRI which SN ratio decreases. In this paper we show that spin-exchange optical pumping (SEOP) can increase 131Xe nuclear magnetic resonance (NMR) signals. We also show that SEOP is possible at very low power LASER with field in pulse sequence of NMR measurement.

Resonance magnetoplasticity in ultralow magnetic fields

Resonance relaxation displacements of dislocations in NaCl crystals placed in crossed static and alternating ultralow magnetic fields in the electron paramagnetic resonance scheme are discussed. The Earth’s magnetic field B Earth ≈ 50μT and other fields in the range of 26–261 μT are used as the static field. New strongly anisotropic properties of the effect have been revealed. Frequency spectra including numerous peaks of paths at low pump frequencies beginning with 10 kHz, as well as the quartet of equidistant peaks at high frequencies (~1.4 MHz at B=B Earth), have been measured. The effect is also observed in the pulsed pump field with a resonance duration of ~0.5 μs. Resonance changes have been detected in the microhardness of ZnO, triglycine sulfate, and potassium hydrogen phthalate crystals after their exposure in the Earth’s magnetic field in the same electron paramagnetic resonance scheme.

Ultralow field magnetization reversal of two-body magnetic nanoparticles

Field induced magnetization reversal was investigated in a system of two magnetic nanoparticles with uniaxial anisotropies and magnetostatic interaction. By using the micromagnetic simulation, ultralow switching field strength was found when the separation distance between the two particles reaches a critical small value (on nanometer scale) in the perpendicular configuration where the anisotropic axes of the two particles are perpendicular to the separation line. The switching field increases sharply when the separation is away from the critical distance. The ultralow field switching phenomenon was missed in the parallel configuration where both the anisotropic axes are aligned along the separation line of the two particles. The micromagnetic results are consistent with the previous theoretical prediction [J. Appl. Phys. 109, 104303 (2011)] where dipolar interaction between two single-domain magnetic particles was considered. Our present simulations offered further proofs and possibilities for the low-power applications of information storage as the two-body magnetic nanoparticles might be implemented as a composite information bit.