Magneto-elasto-dynamic analysis of an elastically confined conducting nanowire due to an axial magnetic shock

Vibration of a conducting nanowire embedded in an elastic matrix due to an axial magnetic shock is of concern. Based on Maxwell?s and Cauchy?s equations, a model is proposed to study the problem in the context of nonlocal continuum theory. For solving the equations of motion of the nanowire, an analytical approach and a semi-analytical technique are proposed for low and high levels of small-scale parameter, respectively. The effects of small-scale parameter, stiffness of the surrounding matrix, and duration of the applied magnetic shock on the maximum dynamic elastic fields are examined.     

Longitudinal waves in carbon nanotubes in the presence of transverse magnetic field and elastic medium

In the present paper, the coupling effect of transverse magnetic field and elastic medium on the longitudinal wave propagation along a carbon nanotube (CNT) is studied. Based on the nonlocal elasticity theory and Hamilton's principle, a unified nonlocal rod theory which takes into account the effects of small size scale, lateral inertia and radial deformation is proposed. The existing rod theories including the classic rod theory, the Rayleigh-Love theory and Rayleigh-Bishop theory for macro solids can be treated as the special cases of the present model. A two-parameter foundation model (Pasternak-type model) is used to represent the elastic medium. The influence of transverse magnetic field, Pasternak-type elastic medium and small size scale on the longitudinal wave propagation behavior of the CNT is investigated in detail. It is shown that the influences of lateral inertia and radial deformation cannot be neglected in analyzing the longitudinal wave propagation characteristics of the CNT. The results also show that the elastic medium and the transverse magnetic field will also affect the longitudinal wave dispersion behavior of the CNT significantly. The results obtained in this paper are helpful for understanding the mechanical behaviors of nanostructures embedded in an elastic medium.     

Donor impurity states in elliptical quantum rings subjected to a magnetic field

Within the effective-mass approximation we calculate the energies of a donor impurity in an elliptical quantum ring subjected to a magnetic field. The energies are found to exhibit Aharonov-Bohm oscillations depending on the magnetic field and the eccentricity. As the eccentricity increases, the energies decrease and the period increases.     

Quadrupole magnetic field-flow fractionation: A novel technique for the characterization of magnetic nanoparticles

Quadrupole magnetic field-flow fractionation (MgFFF) is an analytical separation and characterization technique for nano- and micro-sized magnetic particles. It fractionates particles according to their content of magnetite or other magnetic material. The potential and versatility of MgFFF for separation and characterization of magnetic nanoparticles, such as those used for immunospecific labeling of biological cells for magnetic separation, is demonstrated. A broadly polydisperse sample of dextran-coated magnetite nanoparticles was eluted under programmed field decay conditions, and quantitative data concerning the distribution of magnetite content were determined from the elution profile using a data reduction method.     

Effects of external magnetic field on biodistribution of nanoparticles: A histological study

This study investigates the effect of external magnetic fields on the biodistribution of nanoparticles (NP). A NdFeB magnet of 2.4 kG was externally applied over the left femoral artery or right kidney. The 250 nm dextran-coated Fe₃O₄ NP was injected via tail vein in healthy rats, and organs were taken 1 or 24 h later. Prussian blue stain revealed that NP were more rapidly retained in the liver and spleen than in the lungs. NP aggregation observed in the kidney and femoral artery after application of external magnets was time dependent. Hollow organs such as the intestine, colon, and urinary bladder retained little NP.     

Size-dependant heating rates of iron oxide nanoparticles for magnetic fluid hyperthermia

Using the thermal decomposition of organometallics method we have synthesized high-quality, iron oxide nanoparticles of tailorable size up to ∼15 nm and transferred them to a water phase by coating with a biocompatible polymer. The magnetic behavior of these particles was measured and fit to a log-normal distribution using the Chantrell method and their polydispersity was confirmed to be very narrow. By performing calorimetry measurements with these monodisperse particles we have unambiguously demonstrated, for the first time, that at a given frequency, heating rates of superparamagnetic particles are dependent on particle size, in agreement with earlier theoretical predictions.     

Fabrication of water-soluble magnetic nanoparticles by ligand-exchange with thermo-responsive polymers

We report the use of thermo-responsive polymers in the synthesis of Co and γ-Fe₂O₃ nanoparticles using a two-step method involving thermal decomposition of the organometallic complexes in the presence of oleic acid and then followed by ligand-exchange process with thermo-responsive polymer. Among different thermo-responsive polymers investigated, it was found that the polymer based on poly(N-isopropylacrylamide) with a co-monomer component of acrylic acid and acrylamide can be used in the ligand-exchange to coat Co and γ-Fe₂O₃ nanoparticles, respectively. The nanoparticles are found to be water-soluble at temperatures below coil-to-globule phase transition of the coating polymer.     

交变磁场作用下高温超导体温度变化研究

高温超导体在交变的磁场作用下,由于磁通的运动引起能量损耗,损耗的能量一部分通过超导体表面传递到冷却剂中,另一部分将使得超导体的温度升高。文中用数值的方法研究了外加磁场速度在0.0005T/s—5T/s变化情况下超导体的温度变化;当外磁场的速度由小到大变化时,超导板的状态会发生从稳定→不稳定(磁通跳跃)→稳定的变化;慢变磁场作用下超导体的温度在接近冷却剂温度的温区作微幅的周期性变化,当外加磁场速度比较大时,超导体发生磁通跳跃,温度也呈跳跃性变化,进一步加大外磁场速度,磁通和温度呈准周期的振荡型变化,而且振荡幅值随外磁场速度的增加逐渐减小,最后振荡消失,超导体在更高的温区稳定运行,温度呈周期性变化。     

Heat diffusion characteristics of magnetite nanoparticles dispersed hydro-gel in alternating magnetic field

Heat diffusion characteristics of a spherical heat source dispersing magnetite nanoparticles (MNPs) in hydro-gel were investigated numerically and experimentally to evaluate the conditions required for magnetic fluid hyperthermia (MFH). Numerical estimation assumed one-dimensional spherical model and constant heat evolution. Experimental observation was carried out by exposing the magnetite-dispersed hydro-gel in an AC magnetic field with strength and frequency of 3.2 kA/m and 600 kHz, respectively. The temperature distribution observed along the radial axis of the spherical heat source agreed well with the theoretical estimation quantitatively and qualitatively. However, the minor difference existed between the theory and experiment was due to the variation in experimentally determined and actual particle size distributions. Thus, we could conclude that the proposed algorithm could be extended to be used in the estimation of the temperature distribution in intravital conditions with blood flow, metabolism etc., to arrive at biologically significant conclusions helpful for MFH cancer treatment.     

Effect of magnetic field on electron spectrum and probabilities of intraband quantum transitions in spherical quantum-dot-quantum-well

The effect of magnetic field on electron energy spectrum, wave functions and probabilities of intraband quantum transitions in multilayered spherical quantum-dot-quantum-well (QDQW) CdSe/ZnS/CdSe/ZnS is studied. Computations are performed in the framework of the effective mass approximation and rectangular potential barriers model. The wave functions are expanded over the complete basis of functions obtained as exact solutions of the Schrodinger equation for the electron in QDQW without the magnetic field.It is shown that magnetic field takes off the spectrum degeneration with respect to the magnetic quantum number and changes the localization of electron in the nanostructure. The field stronger effects on the spherically-symmetric states, especially in the case of electron location in the outer potential well. The magnetic field changes more the radial distribution of probability of electron location in QDQW than the angular one. The oscillator strengths of intraband quantum transitions are calculated as functions of the magnetic field induction and their selection rules are established.     

Size-controlled magnetic nanoparticles with lecithin for biomedical applications

Lecithin-adsorbed magnetic nanoparticles were prepared by three-step process that the thermal decomposition was combined with ultrasonication. Experimental parameters were three items—molar ratio between Fe(CO)₅ and oleic acid, keeping time at decomposition temperature and lecithin concentration. As the molar ratio between Fe(CO)₅ and oleic acid, and keeping time at decomposition temperature increased, the particle size increased. However, the change of lecithin concentration did not show the remarkable particle size variation.     

Wave propagation in viscoelastic single-walled carbon nanotubes with surface effect under magnetic field based on nonlocal strain gradient theory

The governing equation of wave motion of viscoelastic SWCNTs (single-walled carbon nanotubes) with surface effect under magnetic field is formulated on the basis of the nonlocal strain gradient theory. Based on the formulated equation of wave motion, the closed-form dispersion relation between the wave frequency (or phase velocity) and the wave number is derived. It is found that the size-dependent effects on the phase velocity may be ignored at low wave numbers, however, is significant at high wave numbers. Phase velocity can increase by decreasing damping or increasing the intensity of magnetic field. The damping ratio considering surface effect is larger than that without considering surface effect. Damping ratio can increase by increasing damping, increasing wave number, or decreasing the intensity of magnetic field.     

Morphologies and magnetic properties of FeCo nanoparticles modulated by changing the types of ligands of Co

A new way of preparing FeCo nanoparticles has been developed using the co-precipitation technique based on the appropriate Co precursors of different types of ligands. These new precursors have been prepared by the reaction of cobalt acetate with three various coordination compositions for forming cobalt complex types. This technique provides proper control on nanoparticle size distribution after annealing to 500 °C. The variation of the magnetic properties with the type of ligands of Co can arise from the changes of the microstructures and crystalline anisotropies. Maximum coercivity values of 480 Oe were obtained. It is found that the precursors with special structures can prevent from agglomeration without presence of any surfactants.     

Focusing of Fe3O4 nanoparticles using a rotating magnetic field in various environments

The paper shows the application of a new method – Magnetic Nanoparticles Focusing 3D, MNF-3D – for focusing of magnetic nanoparticles at any point in a three-dimensional space between the rotating magnet system. The results of focusing process of nanoparticles in water, human blood, human serum and polyurethane sponge are presented. Additionally, blood flow was also considered. The effectiveness of nanoparticle focusing was monitored optically and quantitatively by electron spin resonance method. The method enabled focusing of magnetic nanoparticles within a few minutes in different environments. A good efficiency of focusing process was observed for all the samples.     

Bioavailability of magnetic nanoparticles to the brain

This study investigates the bioavailability of carboxymethyl dextran-coated magnetic nanoparticles (CMD-MNP) to the brain. The cytotoxicity of CMD-MNP was assessed by co-culture with C6, a rat glioma cell line. To investigate the effects of an external magnetic field on the biodistribution of nanoparticles in a rat model, a magnet of 0.3 Tesla was applied externally over the cranium and the particles injected via the external jugular vein. Nanoparticles were also injected into rats implanted with C6 tumor cells. Staining of histological samples with Prussian blue to detect iron particles revealed that the external magnetic field enhanced the aggregation of nanoparticles in the rat brain; this enhancement was even more pronounced in the tumor region.     

Ionic magnetic fluid based on cobalt ferrite nanoparticles: Influence of hydrothermal treatment on the nanoparticle size

Magnetic fluid based on cobalt ferrite nanoparticles was obtained using a hydrothermal treatment added to the Massart procedure. This treatment increases the average size of the nanoparticles from 11.9 to 18.7 nm and also improves the dispersity and crystallinity of the cobalt ferrite particles. The nanoparticles obtained after the hydrothermal treatment were dispersed in aqueous solvent by the classical procedure for ionic magnetic fluids. The ferrofluid thus obtained is stable at pH 7 and may be useful for hyperthermia applications.     

The role of copper ions on the structural and magnetic characteristics of MgZn ferrite nanoparticles and thin films

In this study Cu_xMg_0.5−xZn_0.5Fe₂O₄ (x=0-0.5) nanoparticles and thin films were prepared by sol-gel processing. The morphologies of nanoparticles were observed by transmission electron microscope (TEM). The Mössbauer spectroscopy (MS) was employed to determine the site preference of the constitutive elements. Magnetic dynamics of the nanoparticles was studied by the measurement of AC magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel-Brown and Vogel-Fulcher models were employed to distinguish between interacting or non-interacting system. Results exhibited that there is strong interaction between fine particles. X-ray diffraction (XRD) patterns of the thin films indicate the formation of single-phase cubic spinel structure. Atomic force microscope (AFM) was employed to evaluate the surface morphologies of the prepared thin films. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of samples. It was found that with an increase in the amount of copper, the saturation of magnetization and initial permeability increase.     

Ultrasonic investigation of magnetic nanoparticles suspension with PEG biocompatible coating

Water suspension of nanoparticles was studied by ultrasound spectroscopy. Nanoparticles have a core-shell structure with magnetic core Fe₃O₄ and surfactant shells. The surface of magnetic particles was coated with oleate sodium as the primary layer and polyethylene glycol as the secondary layer. The acoustic properties of suspensions, such as velocity and attenuation of ultrasonic waves, have been measured. From experimental data mechanical properties have been determined. Adiabatic compressibility of nanoparticles suspension decreased with increase of temperature. The changes of ultrasonic wave attenuation under the influence of the external magnetic field, show that magnetic liquids with high concentration of magnetic material (despite two surfactant shells) show tendency to aggregate.     

First principles study of the electronic and optical properties of GaAs nanoparticles under the influence of external uniform electric field

We present electronic and optical properties of the hydrogen terminated gallium arsenide nanoparticles using time dependent density functional theory (TD-DFT). The electronic and optical properties of the GaAs nanoparticles were calculated at presence of the uniform external electric field in the range from 0 to 0.51 V/Å. The induced electric filed can decrease the HOMO–LUMO gap of the nanoparticles and the mount of these reductions increases with gain of the electric field strength.