Presence Of Local Inhomogeneities Research Articles

Correlation analysis of the results of remote sensing of the atmosphere by a three-band microwave radiometric system

The results of the correlation analysis of the data of measurements of radio-thermal radiation of heterogeneous atmosphere with precipitation by the three-band microwave radiometric system with reception along one direction to the common aperture of the mirror antenna at three frequencies 7.5 GHz, 10 GHz, 22 GHz are presented. Correlation coefficients of output signals of all receiving channels of the system with the results of measurements of meteorological parameters - temperature, intensity of precipitation, humidity of the surface layer of the atmosphere, obtained from the meteorological stations of five cities, nearest to the location of the measuring microwave radiometric complex are calculated. The dependence of measurement results with and without compensation for the influence of external influences at different frequencies on the degree of homogeneity of meteorological parameters of the atmosphere and on the presence of local inhomogeneities in the atmosphere and their remoteness from the location of the measuring microwave radiometric complex is shown.

Enhanced peroxymonosulfate activation in the morphotropic phase boundary of molybdenum doped LaCoO3-δ perovskite

Perovskite oxides, with an ABO3 general formula, have attracted much attention as effective peroxymonosulfate (PMS) activators because of their composition adjustability and chemical stability. A doping strategy has been applied to enhance the PMS activation capability with the modulation of the crystal structure of the parent LaCoO3-δ perovskite by substituting Co atoms located at the B-site, with high valence state transition metals. Herein, a series of LaCo1-xMoxO3-δ perovskites were prepared with different Mo content, showing a phase transformation from rhombohedral to cubic-like structures. LaCo0.95Mo0.05O3-δ compound is located at the so-called morphotropic phase boundary (MPB) boosting PMS activation performance as well as enhanced stability. The presence of local inhomogeneities, observed as oxygen vacancies, has been detected in the MPB region enhancing the catalytic effect of pollutant degradation. Mo doping induced Co reduction that contributed to the enhanced PMS activation. Sulfate radical was identified to be the dominating reactive specie for LaCo1-xMoxO3-δ catalyzed PMS activation. This work contributes first, to clarifying the role of Mo doping to boost PMS activation, and second to highlighting the crucial role of the reduced oxidation state as well as the oxygen vacancies in the MPB for PMS activation. Impressive results were obtained when LaCo0.95Mo0.05O3-δ compound was deposited in a Lab-grade photoreactor with LED technology, reaching a complete removal of paracetamol in the first minute. This study provided new insight into the rational design of PMS activator and developed a new strategy for heterogeneous active PMS at a photoreactor with immobilized catalysts.

Emergence of a cosmological constant in anisotropic fluid cosmology

In this paper, we investigate anisotropic fluid cosmology in a situation where the space–time metric back-reacts in a local, time-dependent way to the presence of inhomogeneities. We derive exact solutions to the Einstein field equations describing Friedmann–Lemaítre–Robertson–Walker (FLRW) large-scale cosmological evolution in the presence of local inhomogeneities and time-dependent backreaction. We use our derivation to tackle the cosmological constant problem. A cosmological constant emerges by averaging the backreaction term on spatial scales of the order of 100 Mpc, at which our universe begins to appear homogeneous and isotropic. We find that the order of magnitude of the “emerged” cosmological constant agrees with astrophysical observations and is related in a natural way to baryonic matter density. Thus, there is no coincidence problem in our framework.

Specific features of the propagation of frequency modulated radio signals in the ionospheric plasma in the presence of local inhomogeneities

The features of the propagation of frequency-modulated radio signals reflected from the anisotropic ionosphere containing local inhomogeneities of the electron concentration are investigated. On the basis of the Hamilton-Lukin bi-characteristic method, mathematical modeling of vertical sounding ionograms was carried out both in the case of propagation of an ordinary wave and in the case of propagation of an extraordinary wave. The results of numerical simulation are presented.

Soil Medium Electromagnetic Scattering Model for the Study of Wireless Underground Sensor Networks

In recent years, there has been keen interest in the area of Internet of Things connected underground, and with this is the need to fully understand and characterize their operating environment. In this paper, a model, based on the Peplinski principle, for the propagation of waves in soils that takes into account losses attributable to the presence of local inhomogeneity is proposed. In the work, it is assumed that the inhomogeneities are obstacles such as stones or pebbles, of moderate size, all identical and randomly distributed in space. A new wave number is obtained through a combination of the multiple scattering theory and the Peplinski principle. Since the latter principle considers the propagation in a homogeneous medium (without obstacles), the wave number it provides is inserted into the one resulting from the former, the multiple scattering theory. The effective wave number thus obtained is compared numerically with that of Peplinski alone on the one hand and with that of multiple scattering alone on the other hand. The phase velocity and the loss tangent are analyzed against the particle concentration at the low‐frequency Rayleigh limit condition (ka≲0.1) and against the frequency at two particle concentrations (c = 0.2 and c = 0.4), two particle radii (a = 0.55 cm and a = 1.10 cm), and 5% and 50% volumetric water content of the soil. Path losses are also compared to each other to examine the effects on transmission of soil containing obstacles. The results obtained suggest that the proposed model has better accuracy in estimating the wave number than previously used schemes.

Critical parameters near the ferromagnetic–paramagnetic phase transition in perovskite manganite Pr0.67Sr0.33Mn1−x Al x O3 (0.025 ≤ x ≤ 0.10)

We have determined the values of critical exponents of three mixed manganite Pr0.67Sr0.33Mn1−xAlxO3 (x = 0.025, 0.05 and 0.1) from the magnetization data versus temperature and magnetic field M(H,T), to learn about their magnetic and magnetocaloric properties. Experimental results revealed that these samples exhibits a continuous (second-order) paramagnetic (PM) to ferromagnetic (FM) phase transition. The critical properties near ferromagnetic–paramagnetic phase transition temperature have been analyzed from data of static magnetization measurements for the samples, using various techniques such as modified Arrott plot (MAP), Kouvel–Fisher (KF) method and critical isotherm (CI) analysis. The critical exponents values estimated from the isothermal magnetization measurements are found to be consistent and comparable to those values predicted short-range 3D Heisenberg model. The field dependence of the magnetic entropy change is also analyzed, which shows the power law dependence, namely \(\Delta S_{\text{M}} \propto H^{n}\), where values n = 0.61–0.62 at Curie temperature (TC) are quite far from than the mean-field predictions (n = 2/3). The deviation from the mean-field behavior is due to the presence of local inhomogeneities in the vicinity of a transition temperatures.

ALTERNATIVE UNIFIED VIEWS ON DARK MATTER AND DARK ENERGY

The simple fact that the present closure contributions in dark matter and dark energy are nearly equal begs the question as to whether they could be different aspects of the same physical phenomenon. Here, we review constraints several postulates as to how this coincidence could be achieved. These include: 1) The possibility that the dark matter decays producing a bulk viscosity in the cosmic fluid; 2) cosmic acceleration produced by the inflow of dark matter from a bulk dimension in brane-world cosmology; and 3) The possibility of relativistic corrections to the Friedmann equation from the presence of local inhomogeneities. Constraints and observational tests of each of these cosmologies are proposed.

Vacuum bubble in an inhomogeneous cosmology

We study the propagation of bubbles of new vacuum in a radially inhomogeneous Lemaitre-Tolman-Bondi background that includes a cosmological constant. This exemplifies the classical evolution of a tunneling bubble through a metastable state with curvature inhomogeneities, and will be relevant in the context of the Landscape. We demand that the matter profile in the LTB background satisfy the weak energy condition. For sample profiles that satisfy this restriction, we find that the evolution of the bubble (in terms of the physically relevant coordinates intrinsic to the shell) is largely unaffected by the presence of local inhomogeneities. Our setup should also be a useful toy model for capturing the effects of ambient inhomogeneities on an inflating region.

The development of theoretical foundations for electromagnetic flaw detection of oil and gas wells

Theoretical foundations of the development of nonstationary electromagnetic (EM) flaw detection of wells as applied to the problem of measuring the wall thickness of casing and lifting pipes of oil and oil-and-gas wells are considered taking into account the diversity of EM properties of metals. Analytical dependences and experimental data on measuring the EM fields formed in the presence of local inhomogeneities of a string, such as small-diameter holes, are analyzed. Main requirements for the engineering parameters of the equipment and principles of interpreting well-logging EM flaw detection are shown.

Influence of local inhomogeneities induced in corneal ablation on the evolution of contrast sensitivity.

The presence of local inhomogeneities in corneal tissue after refractive surgery has an influence on visual performance. Here we focus on the corneal ablation associated with Lasik surgery and its effect on the modulation transfer function (MTF) that we obtained by modifying a personalized Kooijman model. Inhomogeneities induced by the ablation occur in the form of Gaussian-distributed refractive-index variations of a given correlation length. We show how variation of refractive-index deviation and correlation length (size) of the inhomogeneities allows us to obtain pairs of values that are able to achieve a MTF evolution similar to that observed for contrast sensitivity in the same patients. An estimate of the characteristics of the local effects is obtained.

Enhancement of Hyperfine Fields for Iron Atoms in γ ′ -Fe 4-x Ni x N (0.2≤x≤0.8) Compounds

The effect of Ni substitution on hyperfine fields of the iron atoms in the Fe4N is investigated. Nanocrystalline nature of γ′-Fe4−x Ni x N materials was examined by XRD and SEM micrographs. The Mossbauer spectra were modeled for hyperfine field distributions. Hyperfine fields for the iron atoms, (Fec) situated at the corner positions of the fcc lattice, increase dramatically with the Ni atom substitutions and the results are explained by electronic structure and the presence of local inhomogeneities.

Theory of the photoluminescence spectra of porous silicon.

Porous silicon (PS) with its distribution of crystallite sizes is a highly disordered material. We present a theoretical formulation to explain the photoluminescence (PL) spectra of porous silicon. We base our formalism on the quantum confinement model using methods similar to those of Kane and Lifshitz. A minimal set of parameters is employed whose numerical values are obtained from independent experiments and/or microscopic theories. Our work demonstrates (i) a downshift in the PL peak due to the size distribution, thus facilitating the use of smaller and physically reasonable exciton binding energy; (ii) a PL spectrum with a line-shape asymmetry on the energy scale, having a full width at half maximum of \ensuremath{\simeq}350 eV, in consonance with experiments; (iii) the presence of both columns and dots in PS; (iv) the presence of local inhomogeneities. Modifications of our model and extensions to related experimental phenomena are also discussed.