Magnetic Spheres Research Articles

Numerical Solution of Unsteady A12O3 -Water Nanofluid Flow Past A Magnetic Porous Sliced Sphere

This study aims to investigate the MHD stagnation point flow of Al2O3 -Water nanofluid with mixed convection effect pass a sliced magnetic porous sphere. The unsteady Al2 O3 -Water nanofluid mixed convection boundary layer flows the stagnation point is an interesting study. This implementation of this concept can use in the problems of engineering and industrial fields such as propulsion ships system, oil drilling, chemical piping, and nuclear reactor coolant. In this paper, we consider the effect of magnetic, porosity, and slicing angel parameters towards the velocity and temperature profiles. We construct a mathematical model of MHD flow in Al2O3 -Water nanofluid to obtain dimensional governing equations. Then, the equations converted into non-dimensional equations by using non-dimensional variables and unsimilarity equations using stream function. The solution of the model solved by numerically using the Keller-Box scheme. The velocity and temperature profiles are determined for various non-dimensional parameters such as magnetic parameter, sliced angle, and porosity parameter. We obtain that the velocity of Al2O3 -Water nanofluid decreases but the temperature decreases when magnetic parameters increases. For the porosity parameter increases then the velocity of the fluid decreases but the temperature of the fluid increases. For the sliced angle parameter increases then the velocity of the fluid increases but temperature of the fluid decrease. For the volume fraction parameter increases then the fluid velocity decreaes but the fluid temperature increases.

Spherical optomagnonic microresonators: Triple-resonant photon transitions between Zeeman-split Mie modes

We report a thorough theoretical investigation of magnon-assisted photon transitions in magnetic garnet micron-sized spheres, which operate as optomagnonic resonators. In this case, matching the intraband splitting of optical Mie modes, induced by particle magnetization, to the eigenfrequency of the uniform-precession spin wave, high-efficiency triply resonant optical transitions between these modes, through respective emission or absorption of a cavity magnon, are enabled. By means of rigorous full electrodynamic computations, supported by corresponding approximate analytical calculations, we provide compelling evidence of greatly increased optomagnonic interaction, compared to that in similar processes between whispering gallery modes of corresponding submillimeter spheres, due to the reduced magnon mode volume. We explain the underlying mechanisms to a degree that goes beyond existing interpretation, invoking group theory to derive general selection rules and highlighting the role of the photon spin as the key property for maximizing the respective coupling strength.

3DOF Ultrasonic Motor With Two Piezoelectric Rings.

A novel design of a multiple degrees of freedom (multi-DOF) piezoelectric ultrasonic motor (USM) is presented in the paper. The main idea of the motor design is to combine the magnetic sphere type rotor and two oppositely placed ring-shaped piezoelectric actuators into one mechanism. Such a structure increases impact force and allows rotation of the sphere with higher torque. The main purpose of USM development was to design a motor for attitude control systems used in small satellites. A permanent magnetic sphere with a magnetic dipole is used for orientation and positioning when the sphere is rotated to the desired position and the magnetic field synchronizes with the Earth’s magnetic dipole. Also, the proposed motor can be installed and used for robotic systems, laser beam manipulation, etc. The system has a minimal number of components, small weight, and high reliability. Numerical simulation and experimental studies were used to verify the operating principles of the USM. Numerical simulation of a piezoelectric actuator was used to perform modal frequency and harmonic response analysis. Experimental studies were performed to measure both mechanical and electrical characteristics of the piezoelectric motor.

Quantification of live Gram-positive bacteria via employing artificial antibacterial peptide-coated magnetic spheres as isolation carriers

A novel artificial antibacterial peptide was prepared by minor modification of the amino acids sequence of a natural peptide protonectin. Distinct from protonectin with natural broad-spectrum antibacterial activity, the designed peptide named as Phe11-protonectin displayed obviously improved selectivity towards Gram-positive (G+) bacteria. Adopting Phe11-protonectin as the recognition reagent, a bioluminescent method was established to quantify live G+ bacteria. Phe11-protonectin-coated magnetic spheres were employed as carriers for isolating G+ bacteria from sample matrixes. The isolated bacteria were lysed to release intracellular adenosine triphosphate, followed by bioluminescent signal collection for quantifying the amount of live G+ bacteria. Staphylococcus aureus, Streptococcus mutans and Bacillus cereus were adopted as model bacteria to explore the feasibility of this method. The linear range for G+ bacteria was 2.3 × 103 - 1.2 × 107 CFU mL−1, and the limit of detection was 2.2 × 102 CFU mL−1 (3σ). The quantification process composed of bacteria isolation, bacteria lysis and signal detection was completed within 33 min. Both Gram-negative and dead G+ bacteria displayed very minor interference to the method for quantifying live G+ bacteria. It has been successfully employed for four types of sample matrixes including peach juice, glucose injection, human urine and lake water, revealing its application prospect in food and drug safety control, clinical diagnosis and hygiene monitoring.

Facile construction of Fe, N and P co-doped carbon spheres by carbothermal strategy for the adsorption and reduction of U(vi).

In this work, nitrogen and phosphorus co-doped magnetic carbon spheres encapsulating well-dispersed active Fe nanocrystals (Fe/P-CN) were fabricated via a simple copolymer pyrolysis strategy. Benefiting from heteroatoms doping, Fe/P-CN could primarily adsorb soluble U(vi) ions through abundant functional groups, and subsequently, the adsorbed U(vi) could be reduced to insoluble U(iv) by Fe nanocrystals. Fe/P-CN pyrolyzed at 800 °C (Fe/P-CN-800) exhibited excellent U(vi) removal capacity of 306.76 mg g−1, surpassing nitrogen and phosphorus co-doped carbon spheres and nano zero-valent iron. In addition, the magnetic separation and thermal reactivation properties endow Fe/P-CN-800 with excellent reusability. This research, especially, provides a promising synergistic adsorption and reduction strategy to effectively remove U(vi) using heteroatom-doped composites.

Erratum: “Near-infrared measurement of water temperature near a 1-mm-diameter magnetic sphere and its heat generation rate under induction heating” [J. Appl. Phys. 122, 044901 (2017)

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Facile synthesis of magnetic mesoporous silica spheres by a sol-gel/surface-protected etching/incipient wetness impregnation approach

We recently synthesized the magnetic mesoporous silica spheres (MMSS) by a sol-gel/surface-protected etching/incipient wetness impregnation approach. Silica spheres (SS) were firstly synthesized by the Stöber method, and surface-protected etching allowed convenient conversion of sol-gel derived silica into mesoporous structures (mesoporous silica spheres, MSS). The immobilization of magnetic nanoparticles over MSS supports was addressed by incipient wetness impregnation. XRD, TEM, and nitrogen sorption technique showed successful synthesis as desired. The iron loadings could reach to 32.67 wt% and narrow pore size distribution centered at ca. 4 nm was found. MMSS exhibits superior persulfate (PDS) activation as well as stability for removing the organic compounds. In addition, magnetic separation of the materials offers great prospects for fast and economical reuse.

Magnetic iron oxide nanoparticle-hollow mesoporous silica Spheres:Fabrication and potential application in drug delivery

A facile method is developed for the fabrication of magnetic iron oxide nanoparticle-hollow mesoporous silica spheres (IONP-HMSs) and explored their potential application in drug delivery. Through the self-assembling process of IONPs and the formation of mesoporous silica shells, the IONP-HMSs with hollow interior cavity were obtained. The cetyltrimethyl ammonium bromide (CTAB) encapsulated IONP-containing spheres served as the template to establish the mesoporous silica shells. Typical anti-cancer drug, doxorubicin hydrochloride (DOX) was applied for drug loading and release process of IONP-HMSs, which demonstrated the IONP-HMSs have a high drug loading efficiency and allow pH-trigged release of DOX in vitro. Moreover, the IONP-HMSs exhibited excellent biocompatibility and enhanced DOX therapeutic efficacy to HeLa cells. Compared with traditional methods, the reported microemulsion-based method for the synthesis of IONP-HMSs enables the formation of hollow-structured nanocomposite without any complex template-removing process, which could pave the way to improving the therapeutic efficacy in drug delivery system.

Investigating MTX-Loaded magnetic nanocomposite particles for treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder that initially leads to inflammation in the lining of a joint and other parts of the body, then progresses and causes deformity. It occurs when the immune system attacks the body tissue. Treatments help to mitigate symptoms and impede the progression of this disease; however, it can bring about a range of side effects. In a current study, methotrexate hydrate (MTX)-loaded magnetic nanocomposite spheres were fabricated and examined for their potential to treat collagen-induced arthritis (CIA) in the murine model. The carriers contain MTX, albumin, poly lactic-co-glycolic acid (PLGA), and magnetic nanoparticles (NPs), thereby allowing the drug carriers to accumulate at the targeted limb using a magnet that is attached outside the body. A release rate study of these drug delivery systems concluded a mean of six to seven days for the release of the effective dosage. Also, it was revealed that mice treated with the drug carriers using a magnet to target the carriers brought better results in the overall progression of the disease compared to mice that were treated with only carriers but did not receive a magnet to target the carriers. Analysis of the paw scores of arthritis-induced mice demonstrated a progression in the studied paws. Moreover, these results were stated with a 95% confidence interval revealing that paws treated with the targeted carrier showed lower scores and subsequently a better outcome. These results are further supported by the review of micro-computed tomography (micro-CT) scans of the paws.

Green synthesis of magnetic sodalite sphere by using groundwater treatment sludge for tetracycline adsorption

Abstract Herein, a green approach was developed to recycle groundwater treatment sludge effectively for preparing magnetic sodalite adsorbent (MS) via a one-step alkali hydrothermal route without the addition of exogenous Si/Al sources. The groundwater treatment sludge was a typical solid waste composed of ferrihydrite, boehmite and quartz, and weakly magnetized in its irregular form. After a hydrothermal treatment of 3 M NaOH, ferrihydrite in the sludge was transformed into hematite, with magnetic maghemite as an intermediate. Boehmite and quartz were dissolved under alkaline conditions and recrystallized on the Fe oxide surface to form a sodalite spherical coating. The product prepared at 3 M NaOH was MS3, which had fine spherical particles with diameters between 3 and 5 μm and exhibited a saturation magnetization of 10.4 emu/g. Increasing the NaOH concentration could improve the saturation magnetization of the prepared magnetic adsorbent but could destroy the sodalite sphere. MS3 exhibited a high tetracycline (TC) adsorption capacity of 488.1 mg/g. The adsorption data fitted well with the pseudo-second-order model, whereas the adsorption isotherm fitted well with the Langmuir model. The major adsorption mechanism was the coordination reaction between the –NH2 group on the side chain of a TC molecule and the H atom of the hydroxyl groups on the sodalite surface. This study not only developed a novel and useful method for effectively recycling groundwater treatment sludge but also presented the potential of the prepared magnetic sodalite sphere for application in wastewater treatment.

Construction of Carbon Dots Coated Magnetic Hollow Silica Spheres.

Magnetic hollow silica spheres (MHSS) with uniform cavity size and shell thickness were prepared using functionalized SiO₂ spheres as templates, on which the magnetic particles were uniformly deposited on their surface. The obtained MHSS exhibited a super-paramagnetic behavior at room temperature. Due to large hollow cavity space and super-paramagnetic characteristics, the MHSS were coated with carbon dots with assistance of (3-Aminopropyl) trimethoxysilane (APS). Thus, the preparedMHSS were mixed with citric acid and APS, followed by hydrothermal reaction at 180 °C, to generate carbon quantum dots coated MHSS (MHSS@CDs). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder scattering (XRD), X-ray energy dispersive spectral analysis (EDS), Raman spectra and laser scattering particle analyzer were applied to characterize the MHSS and MHSS@CDs.

Three-dimensional macroassembly of hybrid C@CoFe nanoparticles/reduced graphene oxide nanosheets towards multifunctional foam

Many efforts have been focused on developing the three-dimensional (3D) foams with enhanced absorption performance, improved mechanical behavior and excellent environmental stability. 3D graphene (or reduced graphene oxide) architecture with interconnected conductive network and ultralow density make it the most promising candidate for high-performance microwave absorption application. Unfortunately, they are extremely delicate to handle for the weak van der Waals interactions between neighboring nanosheets. Here, we show a simple approach via three-dimensional macroassembly of hybrid C@CoFe nanoparticles (NPs)/reduced graphene oxide (rGO) nanosheets to fabricate multifunctional foam. Firstly, hybrid hydrogels by in situ sol-gel polymerization form directly in the framework of GO aerogel. And decomposition of metal-citric acid complexes occurs during the heat treatment and formation of metal oxides is followed. RF-derived (RF- resorcinol-formaldehyde) rich carbon source can reduce CoFe 2 O 4 to CoFe alloy via thermal treatment. Such hybrid magnetic carbon spheres not only can absorb electromagnetic (EM) wave, but also act as fillers to support stresses transferred from the reduced graphene oxide nanosheets. The compression modulus of C@CoFe/rGO (CCR) foam can reach 26 MPa. Three-Dimensional macroassembly of C@CoFe NPs/rGO nanosheets generates efficient channels for multiple reflections and scatterings in the framework, which is advantageous for electromagnetic attenuation.

Rh Catalyzed Selective Hydrogenation of Nitroarenes under Mild Conditions: Understanding the Functional Groups Attached to the Nanoparticles

AbstractModifying the surface of metal catalyst is a crucial subject for improving the heterogeneous metal catalysts. It is still a great challenge to understand the structure‐activity relationship (SAR) between the surface supporting groups and the metal particles. Herein, Rh NPs supported on the magnetic silica sphere with various functional groups (−NH2, −SH, −SO3H, −N=CH2, −Cl, −NHCOCH3 and −NHCH2Ph) have been prepared for catalytic hydrogenation of nitroarenes under atmospheric pressure at room temperature. We discover that the chemical state of Rh NPs depends on the supporting groups significantly. The electron‐donating functionalities can effectively elevate the Rh0/Rh3+ ratio, which increase the catalytic performance both in conversion and selectivity. The amino group decorated catalyst has such a good selectivity that no dechlorination reaction is observable in the hydrogenation of 2‐chloro‐3‐nitropyridine. What's more, by introducing magnetic Fe3O4 nuclei and mesoporous silica encapsulating layer, the catalyst can be recovered conveniently by an external magnet, and can be reused 10 cycles without any loss of activity.

Phase diagram for ensembles of random close-packed Ising-like dipoles as a function of texturation

We study random close packed systems of magnetic spheres by Monte Carlo simulations in order to estimate their phase diagram. The uniaxial anisotropy of the spheres makes each of them behave as a single Ising dipole along a fixed easy axis. We explore the phase diagram in terms of the temperature and the degree of alignment (or texturation) among the easy axes of all spheres. This degree of alignment ranges from the textured case (all easy axes pointing along a common direction) to the non-textured case (randomly distributed easy axes). In the former case we find long-range ferromagnetic order at low temperature but, as the degree of alignment is diminished below a certain threshold, the ferromagnetic phase gives way to a spin-glass phase. This spin-glass phase is similar to the one previously found in other dipolar systems with strong frozen disorder. The transition between ferromagnetism and spin-glass passes through a narrow intermediate phase with quasi-long-range ferromagnetic order.

Magnetic Hollow Spheres Assembled from Graphene-Encapsulated Nickel Nanoparticles for Efficient Photocatalytic CO2 Reduction

The exploitation of efficient, robust, and easily recyclable catalysts is highly desirable for photochemical CO2 reduction to produce fuels and chemicals. Herein, we demonstrate the preparation of Ni@GC magnetic hollow spheres composed of metallic Ni nanoparticles surrounded by few-layered graphitic carbon (GC) for photocatalytic CO2 reduction with high efficiency. The Ni@GC hollow spheres were prepared by thermal annealing a Ni-containing metal–organic framework (Ni-MOF) under N2 atmosphere. A series of physiochemical characterizations reveal that the Ni@GC hollow spheres are successfully synthesized with large surface area and highly porous structure. In the presence of Ni–C bonding, the porous Ni@GC material can efficiently accelerate the separation and transportation of photoexcited charges, as well as improve CO2 adsorption. With the cooperation of a ruthenium photosensitizer under visible light irradiation, the Ni@GC catalyst exhibits a high CO2-to-CO conversion activity, giving a superior CO-produc...

Electrochemical immunoassay for the tumor marker CD25 by coupling magnetic sphere-based enrichment and DNA based signal amplification.

Interleukin-2 receptor alpha chain (also called CD25) is a tumor biomarker that is frequently expressed on the surface of hematological tumor cells. The authors describe an electrochemical immunoassay for CD25 that involves (a) enrichment of CD25 from samples by using magnetic nanospheres, and (b) utilization of DNA modulated current as the detection signal. Primary anti-CD25 antibody was immobilized onto F3O4 magnetic nanospheres to capture CD25 from samples. A polycytosine DNA sequence (dC20) was conjugated to the secondary antibody through glutaric dialdehyde via the amino groups on both antibody and the end of the DNA sequence. This leads to the formation of a sandwich structure on the magnetic spheres. dC20 is then reacted with molybdate to form redox molybdophosphate and generate electrochemical current (best measured at 0.2V vs. Ag/AgCl) that is proportional to the concentration of CD25. The method is sensitive, selective, and has a wide linear response that extends from 1pg.mL-1 to 1ng.mL-1. The immunoassay was applied in a recovery test for CD25 in spiked serum samples. Graphical abstract Electrochemical immunoassay for CD25 is reported by initial enrichment of CD25 from samples with magnetic nanospheres and then utilizing DNA generated electrochemical current as detection signal.

Rheological behavior of magnetic colloids in the borderline between ferrofluids and magnetorheological fluids

Magnetic colloids were formulated by dispersion of magnetic oxide spheres in water. Their rheological behavior was investigated for a wide range of particle diameters covering in detail the magnetic single-multidomain transition and therefore spanning the gap between ferrofluids and conventional magnetorheological fluids. The magnetoviscous effect (i.e., the ratio between the viscosity increment under field and the viscosity value in the absence of field) was found to reach a maximum for a critical particle size in the single-multidomain transition region. The observations were explained in terms of magnetization changes with particle size. The results obtained are applicable to any magnetic material (not only iron oxides) and therefore constitute a new route to enhance the magnetorheological effect. For very small particle sizes (in the superparamagnetic region), thermal motion plays a crucial role and the dimensionless viscosity scales with the Peclet number as expected for Brownian Hard Spheres. For larger particle sizes and λ>1, the dimensionless viscosity scales with the Mason number and closely follows the structural viscosity model under the mean magnetization approximation.

Wireless power transmission in endoscopy capsules.

The operating life of endoscopy capsules is limited by the batteries needed for use. The capacity of corresponding batteries, however, is too short to cover the total period of gastrointestinal transit. To overcome this limitation, a novel kind of wireless power transmission was used. It utilizes a permanent magnetic cylinder located outside the patient's body and is turned by an electric motor, thereby generating a rotating magnetic field. This field in turn causes the motor, by a permanent magnetic sphere, located in a liquid bearing inside the endoscopy capsule, to rotate synchronously. The sphere induces an alternating voltage in coils inside the capsule and thus provides the necessary power. This arrangement was able to transmit power of up to 170 mW. This value is clearly higher than the minimum power of 100 mW needed to operate the electronics of the endoscopy capsules that are actually in use. The volume of both the sphere and the induction coil is smaller than the batteries that are actually integrated in the capsules. By this means, the operating time may be prolonged, in principle up to arbitrary values.

From Polymer to Magnetic Porous Carbon Spheres: Combined Microscopy, Spectroscopy, and Porosity Studies

The facile preparation of polymer waste-derived microporous carbon microspheres (SBET800 m2/g) 100-300 μm in size, is reported at first. We have taken advantage of both, the crosslinked nature and the porous texture of the poly(4-ethylstyrene-co-divinylbenzene) microspheres, which allow the incoming anions and cations present in liquid media to enter and to remain segregated into the pores of the polymer microspheres as soon as the solvent is removed. Interestingly, the ZnCl2 phase, when incorporated in the microporous molecular architecture of the polymer, prevents the collapsing of the pore structure of thermosetting polymer spheres during the pyrolysis occurring at 800°C and acts as an activating agent of the carbon phase under formation, being responsible for the formation of an extended mesoporosity (30-200 A and 300-1000 A ranges). More interestingly, porous carbon microspheres with magnetic properties have been prepared from the ZnCl2-activated porous carbon spheres after impregnation with Fe nitrate solution and thermal treatment at 800°C. A multi-technique methodology to characterize more extensively the carbons at the micro/nanoscale is reported in the paper. More in detail, the morphology, structure, porous texture and the surface properties of the carbon and of the magnetic carbon microspheres have been investigated by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, N2 physisorption, diffuse reflectance UV-vis, Raman and infrared spectroscopies. Furthermore, magnetic properties have been revealed at the nano- and at the macroscale by magnetic force microscopy and simple magnetically guided experiments by permanent magnets. The multi-technique methodology presented in the paper allows in elucidating more extensively about the different characteristics of activated carbons. Notwithstanding the huge amount of literature on activated carbons, the precise control of both the structure and the surface has, for the most part, hidden the relevance of other properties at the molecular scale of the assembled architectures. On the other hand, recent studies indicate that by molecular design, nanostructured and porous carbonaceous materials could also be rationally proposed.

Surface dynamics of rough magnetic films

The chirality of Damon-Eshbach (DE) magnons affects the transport of energy and angular momentum at the surface of magnetic films and spheres. We calculate the surface-disorder-limited dephasing and transport lifetimes of surface modes of sufficiently thick high-quality magnetic films such as yttrium iron garnet. In spite of their chirality surface magnons are not protected, but interact strongly with smooth surface roughness. Nevertheless, for long-range disorder the transport is much less affected by the suppressed back scattering (vertex correction). Moreover, in the presence of roughness ferromagnetic resonance under a \textit{uniform} microwave field can gennerate a considerable amount of surface magnons.