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Aim. To identify the effect of preterm birth on proliferation and hyperplasia of cardiomyocytes in the early postnatal period of ontogenesis in rats.Materials and methods. Preterm birth (on day 21 and 21.5 of gestation) in Wistar rats was induced by subcutaneous administration of mifepristone. Immunohistochemistry was used to identify and calculate the number of Ki67-positive and Mklp2-positive cardiomyocytes in the left ventricle of preterm and full-term rats on days 1, 2, 3, 4, 5, and 6 of postnatal ontogenesis. Statistical analysis of morphometric parameters was performed using the Shapiro – Wilk test and Mann – Whitney test with the Bonferroni correction.Results. We revealed an increase in the number of Ki67-positive cardiomyocytes in the left ventricle of the rats: on day 1 of postnatal ontogenesis (in the rats born on day 21 of gestation) and on days 3–5 of postnatal ontogenesis (in the rats born on day 21.5 of gestation). Preterm birth in rats did not result in a change in the number of Mklp2-positive cardiomyocytes in the left ventricular wall.Conclusion. A change in the pattern of Ki67 expression by cardiomyocytes in the rats born 12 or 24 hours before full term was demonstrated in the early postnatal period of ontogenesis. An isolated increase in Ki67 expression without a change in Mklp2 expression by cardiomyocytes in the left ventricular wall of preterm rats indicates acceleration of cardiomyocyte hypertrophy. Shorter duration of prenatal development is associated with more pronounced morphological and functional rearrangements in the rat myocardium.

The structure of blood neutrophils, eosinophils, monocytes, and lymphocytes and differential white blood count in adult rats were studied over 120 days after a single intravenous injection of magnetoliposomes based on nanomagnetite. Magnetoliposomes had no effect on the structure of neutrophils, eosinophils, monocytes, and lymphocytes. At the same time, injection of a suspension of magnetoliposomes based on magnetite nanoparticles led to a decrease in lymphocyte count and an increase in the count of monocytes and band and segmented neutrophils in the blood. These changes were transient and the parameters returned to normal by day 40-60 after injection.

Chitosan-modified magnetic nanoparticles are a promising basis for the creation of new diagnostic agents and therapeutic drugs. The cells of erythroid, granulocytic, monocytic, lymphocytic, and megakaryocytic lineages of bone marrow of mature rats were investigated for 120 days after single injection of 0.14 g per 1 kg body weight chitosan-modified magnetic nanoparticles (Fe3O4). Light microscopy was applied to describe the structure of hematopoietic cells and morphometric study was performed on Romanowsky—Giemsa stained smears to measure cells size (µm) and relative number (%). Comparison of the biological effects of nonmodified and modified magnetite nanoparticles on hematopoietic cells of bone marrow revealed the advantages of modification. Chitosan-modified magnetite nanoparticles did not affect the structure of hematopoietic cells in the rat bone marrow, and their injection produced a reversible increase in the relative number of monocytes, stab neutrophils and segmented neutrophils, as well as polychromatic and oxyphilic normoblasts.

The ferromagnetic resonance (FMR) spectra of dilute random assemblies of magnetite nanoparticles with cubic magnetic anisotropy and various aspect ratios are calculated using the stochastic Landau-Lifshitz equation at a finite temperature, T = 300 K, taking into account the thermal fluctuations of the particle magnetic moments. Particles of non-spherical shape in the first approximation are described as elongated spheroids with a given semiaxes ratio a/b, where a and b are the long and transverse semiaxes of a spheroid, respectively. A representative database of FMR spectra is created for assemblies of randomly oriented spheroidal magnetite nanoparticles with various transverse diameters D = 5 - 25 nm, moderate aspect ratios a/b = 1.0 - 1.8, and magnetic damping constants k = 0.1, 0.2. The basic FMR spectra of assemblies with D = 25 nm at different aspect ratios can be considered as representatives of assemblies of single-domain magnetite nanoparticles with transverse diameters D > 25 nm. The database is calculated at exciting frequency f = 4.9 GHz (S-band) to clarify clearly the details of the FMR spectrum that depend on the nature of the particle magnetic anisotropy. The data obtained make it possible to analyze arbitrary combined FMR spectra constructed as weighted linear combinations of FMR spectra of the base assemblies. In addition, using a genetic algorithm, the corresponding inverse problem is solved. The latter consists in determining the volume fractions of the base assemblies in some arbitrary nanoparticle assembly, which is represented by its FMR spectrum.PACS: 75.20.-g; 75.50.Tt; 75.40.Mg

The specific absorption rate of magnetic nanoparticles in a rotating magnetic field has been calculated taking into account both thermal fluctuations of the particle magnetic moments and st...

It is shown that surface domain structure arises in magnetic nanotube with uniaxial anisotropy if surface anisotropy constant is negative and sufficiently high in absolute value. The surface magnetic anisotropy affects also the structure and dynamics of a head-to-head domain wall propagating along the nanotube axis in applied magnetic field. The hopping mode is observed for stationary movement of a head-to-head domain wall. The average speed of the domain wall in the hopping mode is found to be several times less than the stationary velocity of the wall in the absence of surface anisotropy. This effect is important for various applications where fast propagation of the domain wall along the sample is essential.

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau- Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments, and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters the intensity of magneto- dipole interaction is determined mainly by the cluster packing density eta = Np*V/Vcl, where Np is the average number of the particles in the cluster, V is the nanoparticle volume, and Vcl is the cluster volume. The area of the low frequency hysteresis loop and the assembly specific absorption rate have been found to be considerably reduced when the packing density of the clusters increases in the range of 0.005 < eta < 0.4. The dependence of the specific absorption rate on the mean nanoparticle diameter is retained with increase of eta, but becomes less pronounced. For fractal clusters of nanoparticles, which arise in biological media, in addition to considerable reduction of the absorption rate, the absorption maximum is shifted to smaller particle diameters. It is found also that the specific absorption rate of fractal clusters increases appreciably with increase of the thickness of nonmagnetic shells at the nanoparticle surfaces., The paper is accepted for Nanoscale Res. Lett

Chemically synthesized iron oxide nanoparticles and magnetosomes produced by magnetotactic bacteria are of great importance for application in biomedicine. In this paper, we discuss the complicated magnetic anisotropy of the nanoparticles, the influence of the magnetostatic interactions, and thermal fluctuations on the behavior of these assemblies. Numerical simulation for dilute assemblies of iron oxide nanoparticles with combined magnetic anisotropy show that the uniaxial shape anisotropy dominates even for small aspect ratios of the particle, L/D≥1.1–1.2. The quasistatic hysteresis loops are calculated for various clusters of bacterial magnetosomes with diameters D=40–60 nm to understand the influence of magnetostatic interactions. The specific absorption rate (SAR) is calculated for assemblies of magnetic nanoparticles dispersed in solid and liquid media. A new electrodynamic method of measurement is used to obtain the SAR of the assembly of bacterial magnetosomes with average diameter D=48 nm.

The dynamics of the magnetization reversal by means of head-to-head domain-wall propagation is investigated both experimentally and theoretically for magnetic labels made from Fe-rich bistable glass-coated microwires. It is shown that the amplitudes of the electromagnetic harmonics generated by bistable Fe-rich magnetic labels of the length 1―4 cm with metallic nuclear diameter of 10―20 μm are more than 5 times larger than that of similar labels made of Co-rich microwires having high permeability and low coercive force. The electromagnetic harmonics can be detected at the distances up to 15― 20cm from the magnetic label at the signal-to-noise ratio not lower than 2.0.

An automated vibration magnetometer for measuring the magnetization and hysteresis curves of soft magnetic materials at room temperature is described. The vibromagnetometer has a magnetic moment sensitivity of 5∙10–6 Gs∙cm3, a measurement error of less than 3% and a magnetizing field strength range of up to ±200 Oe, which can be extended to ±10000 Oe using more powerful magnetic systems. Hysteresis characteristics of amorphous ferromagnetic microwire and of a printed text sign are presented.

The results of detecting quasi-stationary electric fields onboard the Kosmos-1809 satellite and observing sea storms and typhoons are analyzed jointly. We have detected an amplification of the electric field in the low-latitude ionosphere that is related to the preparatory stage and development of tropical storms and typhoons. In this case, the electric field strength can reach ∼20 mV/m, an anomalously high value for the low-latitude and near-equatorial ionosphere. High-accuracy estimates of the electric field strength are made on the basis of a model of its origination as a result of the generation of an extraneous electric current in the disturbed region of the lower atmosphere and the impact of these currents on the global atmosphere–ionosphere system of currents.

Three-dimensional numerical simulation of equilibrium micromagnetic configurations existing in thin ferromagnetic films with surface anisotropy is carried out taking into account the strong demagnetization field acting on the film magnetization and the true micromagnetic boundary condition on the film surface. The numerical results are obtained in the simplest Neel approximation for surface anisotropy energy, a surface anisotropy constant Ks being a single phenomenological parameter. It is found that the spin canted state has the lowest total energy as compared to various multi-domain configurations in the intermediate range of thickness, Lz,min Lz,max, nearly uniform in-plane magnetization, or the vortex has been obtained depending on the film in-plane aspect ratio. On the other hand, different labyrin...

Cosmos-1809 satellite data on ELF emissions, plasma density, Ne and variations dNe in the ionosphere above the Spitak earthquake zone during a period of enhanced aftershock activity are presented. The data show that small-scale plasma inhomogeneities with d N e N e ≈ 3–8% and with a characteristic scale of 4–10 km along the orbit are excited on geomagnetic field tubes connected to the epicentral region, simultaneously with earthquake related ELF emissions. A generation mechanism for such inhomogeneities under the influence of seismic activity in terms of the dissipative instability of acoustic-gravity waves in the ionosphere is proposed.

A detailed numerical simulation of quasistatic hysteresis loops of dense clusters of interacting magnetic nanoparticles is carried out. Both clusters of magnetically soft and magnetically hard nanoparticles are considered. The clusters are characterized by an average particle diameter D, the cluster radius Rc, the particle saturation magnetization Ms, and the uniaxial anisotropy constant K. The number of particles in the cluster varies between Np = 30 - 120. The particle centers are randomly distributed within the cluster, their easy anisotropy axes being randomly oriented. It is shown that a dilute assembly of identical random clusters of magnetic nanoparticles can be characterized by two dimensionless parameters: 1) the relative strength of magneto-dipole interaction, K/Ms2, and the average particle concentration within the cluster, η = V Np/Vc. Here V is the nanoparticle volume, and Vc is the volume of the cluster, respectively. In the strong interaction limit, Msη/Ha > > 1, where Ha = 2K/Ms is the a...

The magnetization reversal process in a soft magnetic nanotube with a weak helical magnetic anisotropy is studied by means of numerical simulation. The origin of a helical anisotropy is a small off-diagonal correction to the magneto-elastic energy density. The change of the external magnetic field parallel to the nanotube axis is shown to initiate a magnetic hysteresis associated with the jumps of the circular magnetization component of the nanotube at a critical magnetic field H s. For a uniform nanotube, the critical magnetic field H s is investigated as a function of geometrical and magnetic parameters of the nanotube. Using 2D micromagnetic simulation, we study the behavior of a nanotube having magnetic defects in its middle part. In this case, the jump of the circular magnetization component starts at the defect. As a result, two bamboo domain walls appear near the defect and propagate to the nanotube ends. Similar effect may explain the appearance of the bamboo domain walls in a slightly non uniform amorphous ferromagnetic microwire with negative magnetostriction during magnetization reversal process.