Low Magnetic Field Gradients Research Articles

УДОСКОНАЛЕНА МЕТОДИКА ДЕТАЛЬНОЇ МАГНІТНОЇ ЗЙОМКИ ДЛЯ ВИРІШЕННЯ ЗАВДАНЬ НАФТОГАЗОВОЇ ГЕОЛОГІЇ

Background. Nowadays, interest in studying the local anomalous magnetic field to solve the problems of oil and gas geology is growing, and the capabilities of the equipment can significantly increase the speed, accuracy and detail of work. Accordingly, the development and testing of an improved method of detailed magnetic recording in motion becomes relevant. Methods. For areas with low gradient magnetic field, we assessed the accuracy of the survey by comparing the maps obtained from repeated surveys of the site. Results. The survey of the magnetic field was conducted in the movement. The total surveyed area was about 20 square kilometers in the Zinkovsky district of the Poltava region. The inter-profile distance was about 50 meters, the distance between the points of observation on the profile was about 1 meter. This grid of observations allows us to get maps that differ significantly from the maps obtained by the usual density of observations. This technique also allows identifying local anomalies, and drawing conclusions about the fine structure of the magnetic field. The main objects that form anomalies and their geological characteristics are identified. On this basis, interpreted magnetic field anomalies in oil and gas regions were catalogued. Conclusions. We have proposed explanation of tectonic and geochemical factors, which form local anomalies of the magnetic field of the studied areas. Three types of anomalies associated with ravines are distinguished. Positive anomalies over ravines and step-type anomalies, in our opinion, are associated with tectonic movements, and negative anomalies are due to slope wash processes. Alternating magnetic fields in the studied areas may be due to ferruginized deposits.

Adaptive control for downhole nuclear magnetic resonance excitation

Nuclear magnetic resonance (NMR) measurements are performed with the pulse sequence and acquisition parameters set by the operator, which cannot be adjusted in real time according to sample characteristics. In one acquisition cycle, usually thousands of high-power pulses are transmitted and thousands of echo points are acquired. The power consumption cause the RF amplifier to overheat, and large amounts of acquired data may be invalid. Therefore, the optimization of excitation and acquisition processes is necessary to improve measurement efficiency. We explore a scheme for the real-time measurement of the samples by adaptively regulating the pulse sequence, which adapts the variable TE pulse sequence as the reconnaissance mode. The appropriate pulse sequence and reasonable parameters (NE, TE) can be selected according to the relaxation characteristics of the samples.This adaptive control strategy has great significance in guiding both dynamic and static measurements, and it is especially suitable for occasions where low magnetic field gradients and diffusion terms can be ignored. We also design a test circuit for adaptive control, which has the function of automatic parameter adjustment. By adjusting parameters such as the number of refocusing pulses, echo spacing, etc., the effective measurement of the samples can be achieved in practice.

Nanotechnology for purifying nematic liquid crystals based on magnetic separation accompanied by phase transition

Free ions are generally unfavorable in liquid crystal (LC) displays, and LC purification technologies are critically important. The colloidal γ-Fe2O3 magnetic nanoparticles coated with oleic acid (γ-Fe2O3@OA MNPs) have a high ratio of surface to volume, which may adsorb more free ions and are uniform in the LC at room temperature. In this work, the precipitation and separation of the doped colloidal γ-Fe2O3@OA MNPs resulting from the magnetic field accompanied by an isotropic-nematic phase transition are more efficient than in the single case of the phase transition or the magnetic field. The residual ion concentrations have decreased distinctly using the low gradient magnetic field (∇ B ∼ 2 T/m) with the phase transition. In addition, when the doped colloidal γ-Fe2O3@OA MNPs are 0.4 % and 0.2 % by weight, the former concentrations of the residual ions and γ-Fe2O3@OA MNPs are lower than the latter. As a result, the commercial nematic LC can be purified by this approach based on nanotechnology in our study.

A Fluorescent Biosensor for Sensitive Detection of Salmonella Typhimurium Using Low-Gradient Magnetic Field and Deep Learning via Faster Region-Based Convolutional Neural Network.

In this study, a fluorescent biosensor was developed for the sensitive detection of Salmonella typhimurium using a low-gradient magnetic field and deep learning via faster region-based convolutional neural networks (R-CNN) to recognize the fluorescent spots on the bacterial cells. First, magnetic nanobeads (MNBs) coated with capture antibodies were used to separate target bacteria from the sample background, resulting in the formation of magnetic bacteria. Then, fluorescein isothiocyanate fluorescent microspheres (FITC-FMs) modified with detection antibodies were used to label the magnetic bacteria, resulting in the formation of fluorescent bacteria. After the fluorescent bacteria were attracted against the bottom of an ELISA well using a low-gradient magnetic field, resulting in the conversion from a three-dimensional (spatial) distribution of the fluorescent bacteria to a two-dimensional (planar) distribution, the images of the fluorescent bacteria were finally collected using a high-resolution fluorescence microscope and processed using the faster R-CNN algorithm to calculate the number of the fluorescent spots for the determination of target bacteria. Under the optimal conditions, this biosensor was able to quantitatively detect Salmonella typhimurium from 6.9 × 101 to 1.1 × 103 CFU/mL within 2.5 h with the lower detection limit of 55 CFU/mL. The fluorescent biosensor has the potential to simultaneously detect multiple types of foodborne bacteria using MNBs coated with their capture antibodies and different fluorescent microspheres modified with their detection antibodies.

The Effect of pH and Viscosity on Magnetophoretic Separation of Iron Oxide Nanoparticles

Magnetic nanoparticles (MNPs) are used for magnetophoresis-based separation processes in various biomedical and engineering applications. Essential requirements are the colloidal stability of the MNPs and the ability to be separated even in low magnetic field gradients. Bare iron oxide nanoparticles (BIONs) with a diameter of 9.2 nm are synthesized via coprecipitation, exhibiting a high saturation magnetization of 70.84 Am2 kg−1 and no remanence. In our study, zeta potential, dynamic light scattering (DLS), and sedimentation analysis show that the aggregation behavior of BIONs is influenced by pH and viscosity. Small aggregate clusters are formed with either low or high pH values or increased viscosity. Regarding magnetophoresis-based separation, a higher viscosity leads to lower magnetophoretic velocities, similar to how small aggregates do. Additionally, cooperative magnetophoresis, the joint motion of strongly interacting particles, affects the separation of the BIONs, too. Our study emphasizes the effect of pH and viscosity on the physicochemical characteristics of MNPs, resulting in different aggregation behavior. Particularly, for high viscous working media in downstream processing and medicine, respectively, the viscosity should be taken into account, as it will affect particle migration.

Magnetophoresis of Magnetic Pickering Emulsions Under Low Field Gradient: Macroscopic and Microscopic Motion.

Monodispersed iron oxide nanoparticles (IONPs) coated with polystyrenesulfonate (PSS) and cetrimonium bromide (CTAB) have been used to stabilize magnetic Pickering emulsions (MPEs). Magnetophoresis of MPEs under the influence of a low gradient magnetic field (∇B < 100 T/m) was investigated at the macroscopic and microscopic scale. At the macroscopic scale, for the case of pH 7, the MPE achieved a magnetophoretic velocity of 70.9 μm/s under the influence of ∇B at 93.8 T/m. The magnetic separation efficiency of the MPE at 90% was achieved within 30 min for pH 3, 7, and 10. At pH 10, the colloidal stability of the MPE was the lowest compared to that for pH 3 and 7. Thus, MPE at pH 10 required the shortest time for achieving the highest separation efficiency, as the MPE experienced cooperative magnetophoresis at alkaline pH. The creaming rate of the MPE at all conditions was still lower compared to magnetophoresis and was negligible in influencing its separation kinetics profiles. At the microscopic scale, the migration pathways of the MPEs (with diameters between 2.5 and 7.5 μm) undergoing magnetophoresis at ∇B ∼ 13.0 T/m were recorded by an optical microscope. From these experiments, and taking into consideration the MPE size distribution from the dynamic light scattering (DLS) measurement, we determined the averaged microscopic magnetophoretic velocity to be 7.8 ± 5.5 μm/s. By making noncooperative magnetophoresis assumptions (with negligible interactions between the MPEs along their migration pathways), the calculated velocity of individual MPEs was 9.8 μm/s. Such a value was within the percentage error of the experimental result of 7.8 ± 5.5 μm/s. This finding allows for an easy and quick estimation of the magnetophoretic velocity of MPEs at the microscale by using macroscopic separation kinetics data.

Removal of Iron Oxide Scale From Boiler Feed-Water in Thermal Power Plant by Magnetic Separation-Separation Conditions of Oxygenated Treatment Scale

We have been developing the scale removal system utilizing superconducting magnet that can remove iron scale from boiler feed-water in a thermal power plant. The scale removal prevents the plants from the reduction in power generation efficiency. Iron oxide scale consists of the ferromagnetic and the paramagnetic particles, and the optimal separation conditions largely differ depending on the magnetic properties of the particles. So, single separation condition may cause the filter blockage by over capture or inadequate capture. We proposed the two-stage magnetic separation according to the magnetic properties of the aggregates, where the ferromagnetic particles are captured in the 1st stage in low magnetic field and field gradient, and then the paramagnetic ones are captured in the 2nd stage in high magnetic field and field gradient. It was shown that two-stage magnetic separation system for the mixture of ferromagnetic and paramagnetic particles is possible by utilizing one superconducting solenoidal magnet.

Optimized process for the fabrication of PDMS membranes integrating permanent micro-magnet arrays

Here we report on the fabrication of micro-magnet arrays by powder agglomeration in a polymer matrix. The NdFeB@polydimethylsiloxane (PDMS) inner microstructure and the generated magnetic forces were studied, when prepared under two different magnetic field configurations. The initial process uses the classical crosslinking of PDMS mixed with NdFeB powder under a low magnetic field gradient provided by a permanent magnet (LG set-up for low gradient). In contrast, the optimized process uses an intermediate layer, composed of iron microstructures in a PDMS matrix that amplifies and focuses the magnetic field gradient given by the permanent magnet (HG set-up for high gradient). Both processes result in a heterogeneous material that can be described as an array of permanent micro-magnets diluted in a non-magnetic host matrix. The NdFeB@PDMS microstructure was characterized by X-ray tomography and optical microscopy. The magnetic properties were also measured by magnetometry and colloidal probe AFM. Results showed that the HG set-up leads to an array of micro-magnets localized at the surface, with higher compactness and density, resulting in stronger magnetic performances compared to the LG set-up. This technology only implies easy-to-handle and cheap fabrication processes, paving the way for the development of low-cost lab-on-chip devices integrating magnetophoretic trapping functionality.

Adsorption-desorption characteristic of thermo-magneto-responsive poly(N-isopropylacrylamide)-co-acrylic acid composite hydrogel towards chromium (III) ions

The thermo-responsive swelling-shrinking behaviour of the poly(N-isopropylacrylamide) (PNIPAM) hydrogels under the effect of temperature change have mechanistic function upon controlling the uptake and release of Cr3+ ions by the hydrogel networks. In this study, acrylic acid (AA) was co-polymerized with PNIPAM onto the silica-coated magnetic nanoparticles (MNPs) to form thermo-magneto-responsive (PNIPAM-co-AA)-silica-PVP-MNPs composite hydrogels with increased density of Cr3+ binding groups. Its temperature-manipulated adsorption-desorption efficiency as well as their magnetic phase separability were investigated. Chromium-loaded hydrogels shown apparent phase separation under influence of low gradient magnetic field. Desorption of Cr3+ gradually predominated as temperature increased from 298 K to 323 K. Under high initial Cr3+ concentration whereby physical adsorption is prevailing, the re-uptake of Cr3+ occurred when the solution being cooled down to 298 K. Furthermore, the adsorption kinetic analysis revealed that the adsorption of Cr3+ by (PNIPAM-co-AA)-silica-PVP-MNPs hydrogels was governed by surface precipitation of Cr3+.

Effect of inhomogeneous magnetic field on plasma generation in a low magnetic field helicon discharge

Efficient plasma production by a helicon wave in a nonuniform magnetic field near the antenna center is being reported here. Experiments are carried out with different nonuniformities of the magnetic field near the antenna keeping the magnetic field at the center of the antenna &amp;lt;100 G. Coupling efficiencies are studied by measuring the antenna current with and without plasma. Plasma production efficiencies are also estimated in all the different magnetic field topologies. It has been observed that the coupling efficiency increases with the magnetic field nonuniformity. Observation of the beat wave in the axial variation of the axial wave magnetic field suggests the presence of different radial wavemodes. Measurements of the axial wavenumber along with the estimation of the radial wavenumber suggest wave propagation near the resonance cone causing more absorption. It is found that the density obtained by introducing a nonuniform magnetic field results in a higher density than the conventional helicon. Finally, the wavelength is measured for the nonuniform magnetic field near the antenna when the magnetic field is kept at 25 G and 50 G at the antenna center. For the 25 G case, the measured axial wavelength is found to be twice the length of the antenna. This suggests that the half wavelength antenna excites the full wavelength helicon wave. However, in the 50 G case, the measured wavelength is shown to be approximately equal to the antenna length.

Facile synthesis and characterization of thermo-magneto-responsive poly(N-isopropylacrylamide)-magnetite composite hydrogel and its adsorption-desorption study on chromium (III)

Poly(N-isopropylacrylamide)-magnetite composite hydrogels with thermo-magneto-responsiveness were synthesized via layer-by-layer coatings with and without using silanization precursor, namely 3-(trimethoxysilyl)propyl methacrylate (MPS) as bridging agents for polymerizing N-isopropylacrylamide (NIPAM). Dynamic light scattering (DLS) was employed to monitor the temperature dependent change in hydrodynamic diameters, Dh of the hydrogels. The morphological transition from the stage of bare magnetite nanoparticles (MNPs) until PNIPAM-magnetite composite hydrogels was inspected by using transmission electron microscope (TEM). MPS-modified silica-PVP-MNPs showed the lowest suspension stability whereas, PVP-functionalized MNPs showed the sluggish response towards low gradient magnetic field. PNIPAM-silica-PVP-MNPs was selected as adsorbent for the Cr3+ ions the adsorption test. In the temperature manipulated adsorption-desorption test, the adsorption of Cr3+ prevailed as temperature increased from 25 °C to 50 °C and the release of Cr3+ into bulk phase took place when the reaction solution was cooled back to 25 °C as depicted by the drop in normalized adsorption capacity, qe/Ce from 36.22, 59.65 and 54.76 to 17.87, 36.21 and 41.67 for C0 of 20, 60 and 100 mg L−1.

Artificial Magnetotaxis of Microbot: Magnetophoresis versus Self-Swimming.

An artificial magnetotactic microbot was created by integrating the microalgal cell with magnetic microbead for its potential application as biomotor in microscale environment. Here, we demonstrate the remote magnetotactic control of the microbot under a low gradient magnetic field (<100 T/m). We characterize the kinematic behavior of the microbots carrying magnetic microbeads of two different sizes, with diameter of 2 and 4.5 μm, in the absence and presence of magnetic field. In the absence of magnetic field, we observed the microbot showed a helical motion as a result of the misalignment between the thrust force and the symmetry axis after the attachment. The microbot bound with a larger magnetic microbead moved with higher translational velocity but rotated slower about its axis of rotation. The viscous force was balanced by the thrust force of the microbot, resulting in a randomized swimming behavior of the microbot at its terminal velocity. Meanwhile, under the influence of a low gradient magnetic field, we demonstrated that the directional control of the microbot was based on following principles: (1) magnetophoretic force was insignificant on influencing its perpendicular motion and (2) its parallel motion was dependent on both self-swimming and magnetophoresis, in which this cooperative effect was a function of separation distance from the magnet. As the microbot approached the magnet, the magnetophoretic force suppressed its self-swimming behavior, leading to a positive magnetotaxis of the microbot toward the source of magnetic field. Our experimental results and kinematic analysis revealed the contribution of mass density variation of particle-and-cell system on influencing its dynamical behavior.

Agglomeration Dynamics of Magnetite Nanoparticles at Low Magnetic Field Gradient

Agglomeration of magnetite nanoparticles in the aqueous solution is studied at the low magnetic field gradients of 23–34 T/m by monitoring the temporal change of magnetic weight. A conventional electronic balance is used to measure the magnetic weight that is the magnetic force on the magnetic sample by the magnetic field gradient. The magnetic weight grows slowly following the stretched exponential after the instantaneous jump by the Neel and Brown relaxation. Magnetization of the magnetite nanoparticles is estimated from the magnetic weight and compared with the Langevin function. The magnetization is close to the saturation in the studied magnetic field range and the saturation magnetization of the agglomerate of nanoparticles is about 60% of that of the bulk magnetite. Kinetic parameters of the stretched exponential show little the magnetic field dependence in the investigated range. Complex energy landscape is involved in the agglomeration as the stretched exponential dynamics indicates. The half‐life of the response function for the magnetic weight change suggests that the pathways of low energy barriers are activated by magnetic field at the early stage of agglomeration.

Calculation of an optimized design of magnetic shields with integrated demagnetization coils

Magnetic shielding made from permalloy is frequently used to provide a time-stable magnetic field environment. A low magnetic field and low field gradients inside the shield can be obtained by using demagnetization coils through the walls, encircling edges of the shield. We first introduce and test the computational models to calculate magnetic properties of large size shields with thin shielding walls. We then vary the size, location and shape of the openings for the demagnetization coils at the corners of a cubic shield. It turns out that the effect on the shielding factor and the expected influence on the residual magnetic field homogeneity in the vicinity of the center of the shield is negligible. Thus, a low-cost version for the openings can be chosen and their size could be enlarged to allow for additional cables and easier handling. A construction of a shield with beveled edges and open corners turned out to substantially improve the shielding factor.

Synthesis and evaluation of condensed magnetic nanocrystal clusters with in vivo multispectral optoacoustic tomography for tumour targeting

Colloidal clusters of magnetic iron oxide nanocrystals (MIONs), particularly in the condensed pattern (co-CNCs), have emerged as new superstructures to improve further the performance of MIONs in applications pertaining to magnetic manipulation (drug delivery) and magnetic resonance imaging (MRI). Exploitation of the advantages they represent and their establishment in the area of nanomedicine demands a particular set of assets. The present work describes the development and evaluation of MION-based co-CNCs featuring for the first time such assets: High magnetization, as well as magnetic content and moment, high relaxivities (r2 = 400 and r2*=905s−1mMFe−1) and intrinsic loss power (2.3 nH m2 kgFe−1) are combined with unprecedented colloidal stability and structural integrity, stealth and drug-loading properties. The reported nanoconstructs are endowed with additional important features such as cost-effective synthesis and storage, prolonged self-life and biocompatibility. It is finally showcased with in vivo multispectral optoacoustic tomography how these properties culminate in a system suitable for targeting breast cancer and for forceful in vivo manipulation with low magnetic field gradients.

Manipulating cluster size of polyanion-stabilized Fe3O4 magnetic nanoparticle clusters via electrostatic-mediated assembly for tunable magnetophoresis behavior

We report in this article an approach for manipulating the size of magnetic nanoparticle clusters (MNCs) via electrostatic-mediated assembly technique using an electrolyte as a clustering agent. The clusters were surface-tethered with poly(sodium 4-styrenesulfonate) (PSS) through electrostatic compensation to enhance their colloidal stability. Dynamic light scattering was employed to trace the evolution of cluster size. Simultaneously, electrophoretic mobility and Fourier transform infrared spectroscopy analyses were conducted to investigate the possible schemes involved in both cluster formation and PSS grafting. Results showed that the average hydrodynamic cluster size of the PSS/MNCs and their corresponding size distributions were successfully shifted by means of manipulating the suspension pH, the ionic nature of the electrolyte, and the electrolyte concentration. More specifically, the electrokinetic behavior of the particles upon interaction with the electrolyte plays a profound role in the formation of the PSS/MNCs. Nonetheless, the solubility of the polymer in electrolyte solution and the purification of the particles from residual ions should not be omitted in determining the effectiveness of this clustering approach. The PSS adlayer makes the resultant entities highly water-dispersible and provides electrosteric stabilization to shield the PSS/MNCs from aggregation. In this study, the experimental observations were analyzed and discussed on the basis of existing fundamental colloidal theories. The strategy of cluster size manipulation proposed here is simple and convenient to implement. Furthermore, manipulating the size of the MNCs also facilitates the tuning of magnetophoresis kinetics on exposure to low magnetic field gradient, which makes this nano-entity useful for engineering applications, specifically in separation processes.

Two-color magneto-optical trap with small magnetic field for ytterbium

We report a two-color magneto-optical trap (MOT) for ytterbium atoms where the slowing and trapping functions are separately performed by the singlet transition light () and the triplet transition light (), respectively. The two-color MOT is achieved by simultaneously applying laser light on both the broad-linewidth singlet transition and the narrow-linewidth triplet transition. It is highly robust against laser power imbalance even at very low magnetic field gradients, and can operate at magnetic field gradients down to 2 G cm−1 where a conventional MOT using the singlet transition is unable to trap atoms. We load and trap up to atoms directly from an atomic beam at 700 K.

Fabrication of Fe3O4@cyclodextrin magnetic composite for the high-efficient removal of Eu(III)

In this study, the Fe3O4@CD MCs were synthesized by using a simple chemical co-precipitation method for the removal of Eu(III) from aqueous solutions. Compared with Fe3O4, the prepared Fe3O4@CD MCs exhibited higher sorption amount toward Eu(III). In addition, Fe3O4@CD MCs could be easily separated from aqueous solutions by using magnetic separation technique at low magnetic field gradients. The sorption properties of Fe3O4@CD MCs toward Eu(III) were investigated by using a batch technique under environmental conditions. The sorption kinetics of Eu(III) on Fe3O4@CD MCs could achieve equilibrium in a time period of 3h. The pH-dependent and ionic strength-independent Eu(III) sorption on the surface of Fe3O4@CD MCs demonstrated that the sorption mechanism of Eu(III) was inner-sphere surface complexation at low pH, whereas the removal of Eu(III) was achieved by simultaneous precipitation and inner-sphere surface complexation at high pH values. The Langmuir and Freundlich patterns were employed to simulate sorption isotherms of Eu(III) on Fe3O4@CD MCs. Considering the low cost, simple synthesis procedure, high removal efficiency, easy separation and environmental friendliness, it is expected that Fe3O4@CD MCs can be used as a cost-effective material for the purification of Eu(III)-bearing effluents.

Magnetophoresis of superparamagnetic nanoparticles at low field gradient: hydrodynamic effect.

Convective current driven by momentum transfer between magnetic nanoparticles (MNPs) and their surrounding fluid during magnetophoresis process under a low gradient magnetic field (<100 T m(-1)) is presented. This magnetophoresis induced convective flow, which imposed direct hydrodynamic effects onto the separation kinetics of the MNPs under low gradient magnetic separation (LGMS), is analogous to the natural convection found in heat transportation. Herein, we show the significance of the induced convection in controlling the transport behavior of MNPs, even at a very low particle concentration of 5 mg L(-1), and this feature can be characterized by the newly defined magnetic Grashof number. By incorporating fluid flow equations into the existing magnetophoresis model, we reveal two unique features of this convective flow associated with low gradient magnetophoresis, namely, (1) the continuous homogenization of the MNPs solution and (2) accompanying sweeping flow that accelerates the collection of MNPs. According to both simulation and experimental data, the induced convection boosts the magnetophoretic capture of MNPs by approximately 30 times compared to the situation with no convection.

Transmitted light relaxation and microstructure evolution of ferrofluids under gradient magnetic fields

Using light transmission experiments and optical microscope observations with a longitudinal gradient magnetic field configuration, the relationship between the behavior of the transmitted light relaxation and the microstructure evolution of ionic ferrofluids in the central region of an axisymmetric field is investigated. Under a low-gradient magnetic field, there are two types of relaxation process. When a field is applied, the transmitted light intensity decreases to a minimum within a time on the order of 101–102s. It is then gradually restored, approaching its initial value within a time on the order of 102s. This is type I relaxation, which corresponds to the formation of magnetic columns. After the transmission reaches this value, it either increases or decreases slowly, stabilizing within a time on the order of 103s, according to the direction of the field gradient. This is a type II relaxation, which results from the shadowing effect, corresponding to the motion of the magnetic columns under the application of a gradient force. Under a magnetic field with a centripetal high-gradient (magnetic materials subjected to a force pointing toward the center of the axisymmetric field), the transmitted light intensity decreases monotonously and more slowly than that under a low-gradient field. Magnetic transport and separation resulted from magnetophoresis under high-gradient fields, changing the formation dynamics of the local columns and influencing the final state of the column system.