Increase In Magnetic Field Strength Research Articles

Selective CO2 Photoconversion on Low-Coordinate TiO2

The selective conversion of CO2 into desired hydrocarbon products remains a challenge in photocatalysis. In this issue of Chem, Feng and colleagues report a strong-magnetic-field-assisted strategy for forming active low-coordinate (100) facets on TiO2 nanotubes, enabling selective photoconversion of CO2 into the C2 product C2H5OH under visible light.

Rotating spin-1/2 Bose–Einstein condensates in a gradient magnetic field with spin–orbit coupling

We study the ground-state phases of two-dimensional rotating spin–orbit coupled spin-1/2 Bose–Einstein condensates (BECs) in a gradient magnetic field. The competition between gradient magnetic field, spin–orbit coupling and rotation leads to a variety of ground-state phase structures. In the weakly rotation regime, as the increase of gradient magnetic field strength, the BECs experiences a phase transition from the unstable phase to the single vortex-line phase. The unstable phase presents the vortex lines structures along the off-diagonal direction. With magnetic field gradient strength increasing, the number of vortex lines changes accordingly. As the magnetic field gradient strength increases further, the single vortex-line phase with a single vortex line along the diagonal direction is formed. The phase diagram shows that the boundary between the two phases is linear with the relative repulsion λ ≥ 1 and is nonlinear with λ < 1. In the relatively strong rotation regime, in addition to the unstable phase and the single vortex-line phase, the vortex-ring phase is formed for the strong magnetic field gradient and rapid rotation. The vortex-ring phase shows the giant and hidden vortex structures at the center of ring. The strong magnetic field gradient makes the number of the vortices around the ring unchanged.

Effects of static magnetic field on Chlorella vulgaris: growth and extracellular polysaccharide (EPS) production

In this study, Chlorella vulgaris treated with static magnetic field (SMF) was investigated in terms of the algal density, biomass, extracellular polysaccharide content and distribution, percentage of algal aggregation, total protein content, enzyme activity, malondialdehyde content, and nutrient removal. The algal density and biomass under 800 G SMF were highest on the 16th day and were 29.02% and 35.67% greater than the control group (0 G group), respectively. Soluble EPS decreased with an increase in magnetic field strength, while bound EPS exhibited an opposite trend. Algal aggregation occurred in all treatment groups, with the aggregation percentage in the high magnetic field-treated groups being lower than that in the control group. Total protein content of the 800 G group was the lowest at 1.13 μg (106 cells)-1 and the enzyme activity of treated algae was higher than that of the control group. SMF affected the growth and reproduction of C. vulgaris by affecting the antioxidant response.

Experimental Observation and Numerical Analysis of the Arc Plasma Axial Motion in a Magnetically Rotating Arc Plasma Generator

To better understand the arc plasma axial motion under an axial magnetic field, a high-speed charge-coupled device camera was used to observe the arc plasma images in a magnetically rotating arc plasma generator. Experimental results indicate that the arc plasma moves towards the cathode bottom as the magnetic field strength increases, while a higher arc current facilitates the cathode arc root to move to the cathode terminus. A two-dimensional coupled model was used to analyze the arc plasma axial motion under different magnetic field strengths. The numerical simulation shows that the arc plasma is axially compressed and curves towards the cathode bottom. It is proposed that the arc plasma structure is derived from the strong backflow from the anode outlet, which is induced by the low-pressure region near the cathode. Moreover, the coupled model predicts the movement of the cathode arc root in agreement with the experimental results. It is inferred that the movement of the cathode arc root is relevant to the energy flux, which is transported from the arc column plasma to the cathode surface.

Accelerated MR spectroscopic imaging-a review of current and emerging techniques.

Over more than 30 years in vivo MR spectroscopic imaging (MRSI) has undergone an enormous evolution from theoretical concepts in the early 1980s to the robust imaging technique that it is today. The development of both fast and efficient sampling and reconstruction techniques has played a fundamental role in this process. State‐of‐the‐art MRSI has grown from a slow purely phase‐encoded acquisition technique to a method that today combines the benefits of different acceleration techniques. These include shortening of repetition times, spatial‐spectral encoding, undersampling of k‐space and time domain, and use of spatial‐spectral prior knowledge in the reconstruction. In this way in vivo MRSI has considerably advanced in terms of spatial coverage, spatial resolution, acquisition speed, artifact suppression, number of detectable metabolites and quantification precision. Acceleration not only has been the enabling factor in high‐resolution whole‐brain 1H‐MRSI, but today is also common in non‐proton MRSI (31P, 2H and 13C) and applied in many different organs. In this process, MRSI techniques had to constantly adapt, but have also benefitted from the significant increase of magnetic field strength boosting the signal‐to‐noise ratio along with high gradient fidelity and high‐density receive arrays. In combination with recent trends in image reconstruction and much improved computation power, these advances led to a number of novel developments with respect to MRSI acceleration. Today MRSI allows for non‐invasive and non‐ionizing mapping of the spatial distribution of various metabolites’ tissue concentrations in animals or humans, is applied for clinical diagnostics and has been established as an important tool for neuro‐scientific and metabolism research. This review highlights the developments of the last five years and puts them into the context of earlier MRSI acceleration techniques. In addition to 1H‐MRSI it also includes other relevant nuclei and is not limited to certain body regions or specific applications.

Gamma-ray and optical properties of the flat spectrum radio quasar 3C 279 flare in June 2015

The flat spectrum radio quasar 3C 279 was observed in an extremely high activity state on June 16, 2015 (MJD 57189). In this paper, we investigate the properties of this flaring episode in the high energy γ-ray and optical bands using data from the Fermi-LAT, SMARTS, and SPOL observations during the period June 1-30, 2015 (MJD 57174-57203). The highest emission state in the γ-ray band detected by the Fermi-LAT exhibits a peak flux of ∼ 2×10−7 erg cm−2 s−1 which is more than 25 times the flux level measured in the low activity state of the source. The temporal analysis of the daily Fermi-LAT light curve suggests that the giant flaring episode has characteristic rise and decay times less than one day. The optical daily light curves in B, V, R, and J bands also indicate the flaring activity from 3C 279 with flux levels peaking for two days on June 16-17, 2015 (MJD 57189-57190). The discrete correlation function analysis indicates a time lag of 1 day or longer between the γ-ray and optical peaks during the flaring episode. The γ-ray emission is also observed to show a harder-when-brighter behaviour whereas optical emission exhibits an opposite behaviour. The γ-ray emission region during the flare is observed to be very compact and is located close to the base of the jet. The degree of linear polarization in the wavelength range 500-700 nm measured using SPOL during this period is also highly variable with a peak of ∼ 30% one day after the γ-ray flare. Near simultaneous γ-ray flux points show a linear anti-correlation with the degree of polarization during the period of γ-ray flare. The significant drop in the degree of linear polarization suggests a sudden increase in the tangled magnetic field strength in the emission region.

Influence of the Phase Transitions of Water in Permafrost on Natural and Technological Electromagnetic Fields

Frozen ground deformations, resulting from the volumetric changes, associated with the phase changes of water are accompanied by the phenomenon of electromagnetic emission. Based on monitoring data from an experimental site near Yakutsk, this study has shown that the vertical component of magnetic field strength increases at low frequencies in the spectrum of accepted signals in the spring and autumn periods. Seasonal increases in the natural electromagnetic field are attributed to electromagnetic emission which is observed in the frequency range 5-300 kHz when permafrost soils thaw or freeze. Monitoring data on the seasonal increase of natural and technological fields, strength at low frequencies, are presented. In sandy soils, the relative increase of the natural field was 543 % during thawing in May and 208 % during freezing in October. The relative increase of the field strength of a radio station was 1014 % in May and 178% in October. Electromagnetic emission in sandy soils was found to result in a twice higher relative increase in natural magnetic field strength upon thawing than upon freezing. The relative increase in magnetic field strength of radio stations is six times greater during spring thawing compared to autumn freezing. This is explained by better conditions for radio wave distribution on the line during the spring

Microscopic characteristics of magnetorheological fluids subjected to magnetic fields

With the aim of studying the microscopic characteristics of a magnetorheological fluid (MRF) in a magnetic field, the theoretical analyses of the particles dynamics in a magnetic field are presented, and a model for the particle motion is proposed. Based on these analyses, a three-dimensional numerical simulation of the microstructure of MRFs in different magnetic fields is performed. Furthermore, the microstructures of the MRFs are investigated using industrial computed tomography (CT) imaging. The numerical simulation and industrial CT results indicate that the chain structure of the same MRF becomes more apparent as the magnetic field strength increases, and in the same external magnetic field, this chain structure also becomes more apparent with an increase in the particle volume fraction. The lengths of particle chains in different magnetic fields are also captured in the industrial CT experiments. When the magnetic field strength is 12 mT, the particle chains of the MRF with a particle volume fraction of 30% reach more than 10 mm in length, which bridge the inner diameter of the container, and the dense clusters-like structure is formed, the clusters-like structure becomes denser with an increase in magnetic field. Moreover, the particle chain lengths of MRF with high particle volume fractions increase sharply with the magnetic field. The experiments demonstrated that the industrial CT is an efficient method to study the microstructures of MRFs by providing particledistributions of MRFs more clearly and intuitively.

Experimental analysis of magnetic field effects on compressor energy saving cooling system

A research on different refrigerants with and without influence of the magnetic field is provided in this paper. The magnetic field degree viz is four gauss. The condenser exit row was 3000, 6000, 9000 and 12000 gauss. Magnetic fields at condenser exit lines are found to reduce the consumption of the compressor energy. Through applying magnet fields on R134a, compressor energy savings was observed up to 1.35%, 6.23%, 5.40% and 4.19%, respectively, in gauss levels of 3000, 6000, 9000 and 12000, while R152a savings in energy levels were up 13.10%, 15.59% and 25.86% and R407a saving in power up to 7.3%, 9.19%, 13.05% and 12.40%. The coolant R152a saves energy in contrast to other coolant compressors. As the magnetic field strength increases, a vapor refrigeration system decreases the energy consumption of the compressor.

Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields.

We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.

Micromagnetic simulation of magnetic domain structures evolution of FeGa alloys by phase-field method

The stabilization of magnetic domains and their temporal evolution in FeGa alloys are predicted by combining micromagnetic model with phase-field method in this paper. The total free energy includes magnetocrystalline anisotropy energy, exchange energy, magnetostatic energy, external field energy and elastic energy. Under the diverse magnetic fields, domain structures are various because of the different total free energy and magnetization processes. The results show that when magnetic field direction along [1 0 0], with different magnetic strength, the directions of magnetization vectors all parallel to the magnetic field direction and the magnetized area forms a single domain structure eventually. When the magnetic field along [1 1 1] direction, the magnetic domains form striped domains. The direction and strength of magnetic field can effectively control the structures of magnetic domains. The total free energy increases with the increase of magnetic field strength and evolutionary steps. The system is stable with the stabilization of total free energy.

Effect of Magnetization on Impedance Characteristics of a Capacitive Discharge Using Push-Pull Driven Cylindrical Electrodes

The impedance characteristics of a 13.56-MHz capacitively driven, symmetric magnetized discharge, created in argon and helium using an array of cylindrical electrodes, are presented. It is found that the discharge produced in argon is largely capacitive, while it tends to becoming inductive as the axial magnetic field strength increases. However, an opposing trend is seen in the case of helium discharge. On the other hand, the effective resistance is seen to continuously decrease for both helium as well as argon. The effect of increasing the radio frequency (RF) power levels is seen to have a marginal effect in the plasma density formed between the discharge electrodes, whereas the density rise is quite significant with the increase in the magnetic field. This behavior has been attributed to power mode transition from ion to electron heating inside the discharge.

A characterization of ABL-101 as a potential tracer for clinical fluorine-19 MRI.

The two main challenges that prevent the translation of fluorine-19 (19 F) MRI for inflammation monitoring or cell tracking into clinical practice are (i) the relatively low signal-to-noise ratio generated by the injected perfluorocarbon (PFC), which necessitates long scan times, and (ii) the need for regulatory approval and a high biocompatibility of PFCs that are also suitable for MRI. ABL-101, an emulsion of perfluoro(t-butylcyclohexane), is a third-generation PFC that is already used in clinical trials, but has not yet been used for 19 F MRI. The objective of this study was therefore to assess the performance of ABL-101 as a 19 F MRI tracer. At magnetic field strengths of 3, 9.4 and 14.1T, the CF3 groups of ABL-101 generated a large well-separated singlet with T2 /T1 ratios of >0.27, >0.14 and>0.05, respectively. All relaxation times decreased with the increase in magnetic field strength. The detection limit of ABL-101 in a 0.25mm3 voxel at 3T, 37°C and with a 3-minute acquisition time was 7.21mM. After intravenous injection, the clearance half-lives of the ABL-101 19 F MR signal in mouse (n=3) spleen and liver were 6.85±0.45 and 3.20±0.35days, respectively. These results demonstrate that ABL-101 has 19 F MR characteristics that are similar to those of PFCs developed specifically for MRI, while it has clearance half-lives similar to PFCs that have previously been used in large doses in non-MRI clinical trials. Overall, ABL-101 is thus a very promising candidate tracer for future clinical trials that use 19 F MRI for cell tracking or the monitoring of inflammation.

Integrated Fluxes in Magneto-Hydrodynamic Mixed Convection in a Cavity Sustained by Conjugate Heat Transfer

Abstract A numerical study of magneto-hydrodynamic mixed convection in a cavity has been conducted to investigate the influence of magnetic field on integrated flux of thermal energy, linear momentum, and kinetic energy. Shear force through lid motion establishes the forced convection effect and buoyancy force due to differential heating of the moving lid and the stationary interface ensures the natural convection phenomenon. Additionally, conduction through the solid slab with prescribed temperature at the outer surface attached to the cavity induces conjugate heat transfer. Further, the top and bottom walls throughout the domain are kept insulated and a uniform horizontal magnetic field is applied on the interface toward left. Fluid flow and heat transfer characteristics are examined for a range of Hartmann number (Ha): 0, 10, 50, and 120 at fixed values of Reynolds number, Grashof number, and Prandtl number of 300, 9 × 104 and 0.71, respectively. The result shows that the transport of heat in the near wall regions of the fluid domain is primarily governed by diffusion, whereas advection appears stronger in the central region of the cavity. Increase in magnetic field strength from Ha = 0 to 120 gradually suppresses the recirculating structure of the flow signifying a reduction in advective strength as depicted by the decrease in the value of total integrated heat flux from 25.15×10-3 to 6.0×10-3. The reduction in heat flux, momentum fluxes, and kinetic energy fluxes with increase in magnetic field has been well correlated in the range of 0≤Ha≤120.

Investigation of the Chain Formation Effect on Thermal Conductivity of Magnetorheological Fluids

Chain formation is one of the factors influencing the changes in the rheological properties of magnetorheological (MR) fluids as thermal conductivity. After applying the magnetic field, the particles make some clusters in the direction of the applied field. In this work, a variation of thermal conductivity of the MR fluid was investigated experimentally, and the cluster formation inside the fluid was visualized by appropriate computational fluid dynamics simulations. The experimental results show that with the increase in magnetic field strength and dispersed particle volume fraction, as well as the decrease in the size of dispersed particles, more particles joined together in the direction of the external applied magnetic field. It was found that the more and longer chains of particles are formed, the variation of thermal conductivity of the MR fluid is more considerable. The experimental results showed that the thermal conductivity of the MR fluid with 15% dispersed particle volume fraction is increased up to 117% by applying an magnetic field. The increase in the thermal conductivity has been observed in experimental studies, and the longer and the more strong chain formations have shown in computational fluid dynamics simulation that its trend is in good agreement with experimental results.

Crystalline membrane morphology beyond polyhedra.

Elastic crystalline membranes exhibit a buckling transition from sphere to polyhedron. However, their morphologies are restricted to convex polyhedra and are difficult to externally control. Here we study morphological changes of closed crystalline membranes of superparamagnetic particles. The competition of magnetic dipole-dipole interactions with the elasticity of this magnetoelastic membrane leads to concave morphologies. Interestingly, as the magnetic field strength increases, the symmetry of the buckled membrane decreases from 5-fold to 3-fold, to 2-fold and, finally, to 1-fold rotational symmetry. This gives the ability to switch the membrane morphology between convex and concave shapes with specific symmetry and provides promising applications for membrane shape control in the design of actuatable microcontainers for targeted delivery systems.

Effect of external magnetic field on cyclic voltammetry of exfoliated graphene-based magnetic composites with conductive polymer and carbon dots

Abstract Cyclic voltammetric performance of magnetic graphene composites expanded at 90, 900 and 2000 °C and their composites with polyaniline and carbon dots was monitored under external magnetic fields at maximum 1191 Gauss generated from 7 A current supply. These composites showed the enhanced performances accompanied by the increase of magnetic field strength. The enhancement of the capacitance was further achieved, when iron oxide nanoparticles were further added on magnetic graphene composites, when polyaniline was in-situ combined with magnetic graphene composites or when carbon dot was hydrothermally loaded on magnetic graphene composites. These results clarify the remarkable effect of the external magnetic field on the electrochemical performance of magnetic graphene composites. This research should offer a breakthrough on the adoption of the magnetic field in energy science and technology.

Kinetic Particle-in-cell Simulations of the Transport of Astrophysical Relativistic Jets in Magnetized Intergalactic Medium

Abstract We present results from fully kinetic particle-in-cell simulations of the transport of astrophysical relativistic jets in magnetized intergalactic medium. As opposed to magnetohydrodynamic simulations, the results show that a strong charge-separation electric field, induced by the different responses between jet electrons and ions to the magnetic fields, significantly enhances the energy exchange between different species of charged particles and electromagnetic fields, thus playing a key role in determining the collimation and shape of the jet spectral energy distribution (SED). It is found that when the magnetic field strength increases, the jet collimation also increases while the power-law slope of the jet SED decreases; this provides potential enlightenment on related astrophysical observations.

NMR shutter-speed elucidates apparent population inversion of 1 H2 O signals due to active transmembrane water cycling.

PurposeThe desire to quantitatively discriminate the extra‐ and intracellular tissue 1H2O MR signals has gone hand‐in‐hand with the continual, historic increase in MRI instrument magnetic field strength [B 0]. However, recent studies have indicated extremely valuable, novel metabolic information can be readily accessible at ultra–low B 0. The two signals can be distinguished, and the homeostatic activity of the cell membrane sodium/potassium pump (Na+,K+,ATPase) detected. The mechanism allowing 1H2O MRI to do this is the newly discovered active transmembrane water cycling (AWC) phenomenon, which we found using paramagnetic extracellular contrast agents at clinical B 0 values. AWC is important because Na+,K+,ATPase can be considered biology’s most vital enzyme, and its in vivo steady‐state activity has not before been measurable, let alone amenable to mapping with high spatial resolution. Recent reports indicate AWC correlates with neuronal firing rate, with malignant tumor metastatic potential, and inversely with cellular reducing equivalent fraction. We wish to systematize the ways AWC can be precisely measured.MethodsWe present a theoretical longitudinal relaxation analysis of considerable scope: it spans the low‐ and high–field situations.ResultsWe show the NMR shutter‐speed organizing principle is pivotal in understanding how trans–membrane steady–state water exchange kinetics are manifest throughout the range. Our findings illuminate an aspect, apparent population inversion, which is crucial in understanding ultra‐low field results.ConclusionsWithout an appreciation of apparent population inversion, significant misinterpretations of future data are likely. These could have unfortunate diagnostic consequences.

Functional Magnetic Resonance Spectroscopy at 7 T in the Rat Barrel Cortex During Whisker Activation.

Nuclear magnetic resonance (NMR) spectroscopy offers the opportunity to measure cerebral metabolite contents in vivo and noninvasively. Thanks to technological developments over the last decade and the increase in magnetic field strength, it is now possible to obtain good resolution spectra in vivo in the rat brain. Neuroenergetics (i.e., the study of brain metabolism) and, especially, metabolic interactions between the different cell types have attracted more and more interest in recent years. Among these metabolic interactions, the existence of a lactate shuttle between neurons and astrocytes is still debated. It is, thus, of great interest to perform functional proton magnetic resonance spectroscopy (1H-MRS) in a rat model of brain activation and monitor lactate. However, the methyl lactate peak overlaps lipid resonance peaks and is difficult to quantify. The protocol described below allows metabolic and lactate fluctuations to be monitored in an activated brain area. Cerebral activation is obtained by whisker stimulation and 1H-MRS is performed in the corresponding activated barrel cortex, whose area is detected using blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD fMRI). All steps are fully described: the choice of anesthetics, coils, and sequences, achieving efficient whisker stimulation directly in the magnet, and data processing.