On CHF calculations of second-order magnetic properties using the method of continuous transformation of origin of the current density

Summary A fully analytical formulation is outlined for computing molecular magnetic susceptibilities and nuclear magnetic shieldings via a continuous change of origin of the electronic current density induced by an external magnetic field. The change of origin is described in terms of a (continuous) arbitrary shift functiond(r). Coupled Hartree-Fock second-order magnetic properties of CH₄ and CO₂ molecules have been computed, using the special choiced(r)=r as generating function. A detailed analysis of results obtained with a variety of basis sets reveals that such a method is not as good as previously suggested. Large basis sets must be used to obtain accurate magnetic properties. On the other hand, all the components of theoretical nuclear magnetic shielding evaluated via this approach are independent of the origin of the vector potential. In general, theoretical magnetic susceptibilities depend linearly on the distance between different coordinate frames, but are origin independent for centre-symmetric molecules.     

Invariance of multipole polarisabilities of nuclear magnetic shielding within the approach of continuous transformation of the origin of the current density

Electric multipole polarisabilities of nuclear magnetic shielding of a molecule in the presence of external fields—a uniform magnetic and a non-uniform electric field—calculated via the approach of continuous transformation of the origin of the current density, are shown to be invariant in a translation of the gauge of the vector potential. However, multipole polarisabilities depend upon the origin of the coordinate system for multipole higher than dipole, because of the intrinsic origin dependence of the related operators.     

Three‐dimensional printed magnetophoretic system for the continuous flow separation of avian influenza H5N1 viruses

As a result of the low concentration of avian influenza viruses in samples for routine screening, the separation and concentration of these viruses are vital for their sensitive detection. We present a novel three‐dimensional printed magnetophoretic system for the continuous flow separation of the viruses using aptamer‐modified magnetic nanoparticles, a magnetophoretic chip, a magnetic field, and a fluidic controller. The magnetic field was designed based on finite element magnetic simulation and developed using neodymium magnets with a maximum intensity of 0.65 T and a gradient of 32 T/m for dragging the nanoparticle–virus complexes. The magnetophoretic chip was designed by SOLIDWORKS and fabricated by a three‐dimensional printer with a magnetophoretic channel for the continuous flow separation of the viruses using phosphate‐buffered saline as carrier flow. The fluidic controller was developed using a microcontroller and peristaltic pumps to inject the carrier flow and the viruses. The trajectory of the virus–nanoparticle complexes was simulated using COMSOL for optimization of the carrier flow and the magnetic field, respectively. The results showed that the H5N1 viruses could be captured, separated, and concentrated using the proposed magnetophoretic system with the separation efficiency up to 88% in a continuous flow separation time of 2 min for a sample volume of 200 μL.     

富勒烯的磁化率计算

Ring current theory and the gauge invariant molecule orbital theory were applied to study the magnetic susceptibility of fullerenes. The results show that the diamagnetic susceptibility has anisotropy character. And it was pointed that c60 is of ambiguous aromatic character with anomalous magnetic properties but with the reactivity of a continuous aromatic molecule.     

Continuous microfluidic DNA extraction using phase-transfer magnetophoresis

This paper reports a novel microfluidic-chip based platform using "phase-transfer magnetophoresis" enabling continuous biomolecule processing. As an example we demonstrate for the first time continuous DNA extraction from cell lysate on a microfluidic chip. After mixing bacterial Escherichia coli culture with superparamagnetic bead suspension, lysis and binding buffers, DNA is released from cells and captured by the beads. These DNA carrying beads are continuously transported across the interfaces between co-flowing laminar streams of sample mixture, washing and elution buffer. Bead actuation is achieved by applying a time-varying magnetic field generated by a rotating permanent magnet. Flagella-like chains of magnetic beads are formed and transported along the microfluidic channels by an interplay of fluid drag and periodic magnetic entrapment. The turnover time for DNA extraction was approximately 2 minutes with a sample flow rate of 0.75 μl s(-1) and an eluate flow rate of 0.35 μl s(-1). DNA recovery was 147% (on average) compared to bead based batch-wise extraction in reference tubes within a dilution series experiment over 7 orders of magnitude. The novel platform is suggested for automation of various magnetic bead based applications that require continuous sample processing, e.g. continuous DNA extraction for flow-through PCR, capture and analysis of cells and continuous immunoassays. Potential applications are seen in the field of biological safety monitoring, bioprocess control, environmental monitoring, or epidemiological studies such as monitoring the load of antibiotic resistant bacteria in waste water from hospitals.     

A comparative study to evaluate the performance of coated Fe3O4 nanoparticles for adsorption of asphaltene from crude oil in bench scale

The present study was conducted to evaluate the performance of magnetic Fe₃O₄ nanoparticles coated with polythiophene (PT), Mil-101 (Cr) (MOF), graphene oxide (GO), SiO₂, and chitosan for adsorption of asphaltene from crude oil in a bench scale setup. All nanoparticles were synthesized using co-precipitation method. The characteristics of nanoparticles were verified using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscope (FESEM) analyses. The concentration of nanoparticles was kept constant at the optimum value of 10g?L^?1. The amount of asphaltene adsorption was determined at different contact times of 0.5, 0.75, 1, 2, and 4 hours. The results showed that the adsorption increased with contact time and reached equilibrium after about 2 hours in both continuous and batch experiments. The amount of asphaltene adsorption was lower in continuous experiments compared to batch experiments. However, it was found that magnetic nanoparticles are applicable for inhibition of asphaltene precipitation under flow conditions. Furthermore, polythiophene coating on magnetic Fe₃O₄ nanoparticles had the highest capacity for asphaltene adsorption. Besides, by applying a magnetic field, the magnetic nanoparticles that adsorbed asphaltene can be separated from crude oil to prevent asphaltene aggregation and precipitation.     

INAA at the top of the world: Elemental characterization and analysis of airborne particulate matter collected in the Himalayas at 5,100 m high

A magnetic filter — continuous electrodeionization (CEDI) hybrid separation system was investigated for the purification of the primary coolant in a nuclear power plant. A magnetic filter system with a 3000 Gauss magnetic field and a CEDI system with a cell consisting of 3 compartments were used for the removal of magnetite and nickel ions, respectively. The hybrid separation system achieved removal rates of 98% for magnetite and 99% for the nickel ions demonstrating its feasibility for the purification of primary coolant.The authors gratefully acknowledge the Basic Atomic Energy Research Institute (BAERI) program at the Korea Institute of Science and Technology Evaluation and Planning (KISTEP) for the financial support to carry out this work.     

Continuous sorting of magnetic cells via on-chip free-flow magnetophoresis

The ability to separate living cells is an essential aspect of cell research. Magnetic cell separation methods are among some of the most efficient methods for bulk cell separation. With the development of microfluidic platforms within the biotechnology sector, the design of miniaturised magnetic cell sorters is desirable. Here, we report the continuous sorting of cells loaded with magnetic nanoparticles in a microfluidic magnetic separation device. Cells were passed through a microfluidic chamber and were deflected from the direction of flow by means of a magnetic field. Two types of cells were studied, mouse macrophages and human ovarian cancer cells (HeLa cells). The deflection was dependent on the magnetic moment and size of the cells as well as on the applied flow rate. The experimentally observed deflection matched well with calculations. Furthermore, the separation of magnetic and non-magnetic cells was demonstrated using the same microfluidic device.     

Flow-through immunomagnetic separation system for waterborne pathogen isolation and detection: Application to Giardia and Cryptosporidium cell isolation

Simultaneous sample washing and concentration of two waterborne pathogen samples were demonstrated using a rotational magnetic system under continuous flow conditions. The rotation of periodically arranged small permanent magnets close to a fluidic channel carrying magnetic particle suspension allows the trapping and release of particles along the fluidic channel in a periodic manner. Each trapping and release event resembles one washing cycle.The performance of the magnetic separation system (MSS) was evaluated in order to test its functionality to isolate magnetic-labelled protozoan cells from filtered, concentrated tap water, secondary effluent water, and purified water. Experimental protocols described in US Environmental Protection Agency method 1623 which rely on the use of a magnetic particle concentrator, were applied to test and compare our continuous flow cell separation system to the standard magnetic bead-based isolation instruments. The recovery efficiencies for Giardia cysts using the magnetic tube holder and our magnetic separation system were 90.5% and 90.1%, respectively, from a tap water matrix and about 31% and 18.5%, respectively, from a spiked secondary effluent matrix. The recovery efficiencies for Cryptosporidium cells using the magnetic tube holder and our magnetic separation system were 90% and 83.3%, respectively, from a tap water matrix and about 38% and 36%, respectively, from a spiked secondary effluent matrix. Recoveries from all matrices with the continuous flow system were typically higher in glass tubing conduits than in molded plastic conduits.     

Evaluation of NMR spectroscopy for the quantitative characterization of urea-formaldehyde resins

A comparative evaluation has been made of both proton and (13)C nuclear magnetic resonance techniques in the quantitative characterization of commercial urea-formaldehyde resins. There is good agreement between data derived from (13)C NMR spectra and from (1)H high-field continuous wave, or low-field (Fourier transform) NMR spectra. Low-field continuous wave proton spectra exhibit inferior resolution and provide inaccurate quantitative data. Combination of (13)C and proton NMR with nitrogen analysis gives a quantitative characterization technique for these resins.     

磁性离子交换树脂连续化运行条件的研究

本文针对现行离子交换操作过程和离子交换树脂的不足,研制出一种新磁性离子交换树脂,并对其应用于连续化子离子交换过程的运行条件进行了较详细的研究,结果表明,磁性离子交换树脂应用于连续化操作过程,可增大操作流速或提高工作效率。     

Continuous Re‐hyperpolarization of Nuclear Spins Using Parahydrogen: Theory and Experiment

The continuous re‐hyperpolarization of nuclear spins in the liquid state by means of parahydrogen (para‐H₂) and chemical exchange at low magnetic fields was recently discovered and offers intriguing perspectives for many varieties of magnetic resonance. In this contribution, we provide a theoretical assessment of this effect and compare the results to experimental data. A distinct distribution of polarization is found, which shares some features with experimental data and, interestingly, does not directly correspond to the loss of the singlet order of para‐H₂. We derived expressions for the magnetic field and para‐H₂–substrate interaction time, for which the polarization transfer is maximal. This work sheds light onto the effect of continuous hyperpolarization and elucidates the underlying mechanism, which may facilitate the development of an optimized catalyst. As an application, continuous hyperpolarization may enable highly sensitive nuclear magnetic resonance at very low magnetic fields, for example, for the cost‐efficient screening of drugs.     

The estimation of the aromaticity of five-membered and benzo fused five-membered rings by the hybrid DFT computed magnetic properties

The structures of thiophene, pyrrole, furan, and their benzo derivatives were generated with the hybrid B3LYP density functional theory (DFT) methods employing a 6-31G* basis set. Their magnetic susceptibility anisotropics were calculated on these geometries with a continuous set of gauge transformations. The aromaticity of the heterocycles was discussed in light of their structural uniformity and magnetic susceptibility. The computed structural parameters, order of aromaticity, stability, and reactivity is in excellent agreement with the experimental results. The usefulness of this approach to determine the reactivity is discussed.     

Magnetic field induced assembly of highly ordered two-dimensional particle arrays

Suspended magnetic beads are exposed to an external homogeneous magnetic field which rotates around the axis perpendicular to the field direction. Because of dipolar interactions, magnetic beads assemble in highly ordered two-dimensional hexagonal arrays perpendicular to the rotation axis. By continuous provision of the particle concentration, the growth modes of two-dimensional particle clusters and monolayers are observed. The structure of the resulting assembled objects is analyzed for different field frequencies and particle concentrations. We identify dynamic processes which enhance stability and reduce lattice distortions and, thus, allow for the application of these particle agglomerations as dynamic components in lab-on-a-chip technologies.     

Simultaneous bioassays in a microfluidic channel on plugs of different magnetic particles

Magnetic particles coated with specific biomolecules are often used as solid supports for bioassays but conventional test tube based techniques are time consuming and labour intensive. An alternative is to work on magnetic particle plugs immobilised inside microfluidic channels. Most research so far has focussed on immobilising one type of particle to perform one type of assay. Here we demonstrate how several assays can be performed simultaneously by flushing a sample solution over several plugs of magnetic particles with different surface coatings. Within a microchannel, three plugs of magnetic particles were immobilised with external magnets. The particles featured surface coatings of glycine, streptavidin and protein A, respectively. Reagents were then flushed through the three plugs. Molecular binding occurred between matching antigens and antibodies in continuous flow and was detected by fluorescence. This first demonstration opens the door to a quicker and easier technique for simultaneous bioassays using magnetic particles.     

Two applications of metal cyanide square grid monolayers: studies of evolving magnetic properties in layered films and templating Prussian blue family thin films

Two applications of previously described square grid network monolayers prepared at the air/water interface are explored. The monolayer networks are single layers of Prussian blue like mixed-metal cyanide networks that are formed via the interface-directed condensation of amphiphilic pentacyanometallate complex and subphase metal ions. In the first application, the monolayers are deposited onto solid supports and the magnetic properties of the networks are evaluated, as the transferred films evolve from a monolayer to a bilayer to multilayers. In the second application, the network monolayers are used to derivatize a surface, providing a seed layer for the subsequent deposition of solid-state metal cyanide molecule-based magnets. Improved surface wetting results in continuous, transparent magnetic films.     

Polymerization in a magnetic field. X. Solvent effect in poly(methyl methacrylate) synthesis

The effect of a continuous external magnetic field on the free radical polymerization of methyl methacrylate was studied with respect to some properties of the solvents used in the reaction. The studies were performed through dilatometric technique in and out a magnetic field of 0.25 T. Ten different solvents were used to underline the dependence between the magnetic field presence, the reaction medium, and the development of the polymerization process. The intervened magnetokinetic effects are attributed to the changes in the multiplicity of the radical pairs owing to the magnetic field influence. There is an interdependence among the viscosity and molar polarization of the solvents and the magnetic field effect. © 1996 John Wiley & Sons, Inc.     

Preparative continuous separation of biological particles by means of free-flow magnetophoresis in a free-flow electrophoresis chamber.

For sorting, cells or cellular components can specifically be labeled by antibody-coated magnetic beads. We have developed a device for continuous magnetic sorting based on the flow-chamber of a free-flow electrophoresis system. Magnetically labeled particles are injected into a given continuously flowing chamber buffer and pass an inhomogeneous magnetic field, configurated perpendicular to the flow direction. According to its magnetic moment, the magnetic material is deviated into the direction of the magnetic forces, while nonmagnetic material passes the field without interaction. The magnetic forces can be changed with the electrical current of the solenoids producing the magnetic field. As in the free-flow electrophoresis system, the particle fractions are collected in different vials. On-line control of the experiments can be performed by an optical scanning system. Experiments with model particles achieved a sorting purity of more than 99% at a rate of up to 5 X 10(8) particles per hour. In experiments with blood cells, a high enrichment of either B-or-T-lymphocytes was obtained. In contrast to free-flow electrophoresis, there is no limitation, in principle, regarding the type of chamber buffer to be used. This allows an optimal adaptation of the buffer conditions to the requirements of vital sorting. The preliminary results so far confirm this conclusion.     

Ion beam-induced magnetic patterning at the sub-0.1 μm level

We present a method that allows magnetic patterning of a continuous magnetic film without significant modification of the surface roughness or of the film's optical indices. It involves ion irradiation of Co/Pt multilayers, using either a standard ion implantation technology combined with high resolution masking, or a focussed ion beam. We fabricated arrays of lines or dots whose magnetic properties differ on a sub-100 nm scale. We describe the ion collision physics on which the techniques are based, as well as some of the observed consequences on the micromagnetic properties of the arrays and on the ultimate resolution. Possible applications to high-density information storage are briefly discussed.     

Study of magnetic particles pulse-injected into an annular SPLITT-like channel inside a quadrupole magnetic field

Advantages of the continuous magnetic flow sorting for biomedical applications over current, batch-wise magnetic separations include high throughput and a potential for scale-up operations. A continuous magnetic sorting process has been developed based on the quadrupole magnetic field centered on an annular flow channel. The performance of the sorter has been described using the conceptual framework of split-flow thin (SPLITT) fractionation, a derivative of field-flow fractionation (FFF). To eliminate the variability inherent in working with a heterogenous cell population, we developed a set of monodisperse magnetic microspheres of a characteristic magnetization, and a magnetophoretic mobility, similar to those of the cells labeled with a magnetic colloid. The theory of the magnetic sorting process has been tested by injecting a suspension of the magnetic beads into the carrier fluid flowing through the sorter and by comparing the theoretical and experimental recovery versus total flow-rate profiles. The position of the recovery maxima along the total flow-rate axis was a function of the average bead magnetophoretic mobility and the magnetic field intensity. The theory has correctly predicted the position of the peak maxima on the total flow-rate axis and the dependence on the bead mobility and the field intensity, but has not correctly predicted the peak heights. The differences between the calculated and the measured peak heights were a function of the total flow-rate through the system, indicating a fluid-mechanical origin of the deviations from the theory (such as expected of the lift force effects in the system). The well-controlled elution studies using the monodisperse magnetic beads, and the SPLITT theory, provided us with a firm basis for the future sorter evaluation using cell mixtures.