Longitudinal Inhomogeneity Research Articles

Перенос примеси наночастиц в сосуде с наклонными боковыми границами

Mixtures of components with different densities are stratified in the gravitational field. Colloidal particles with sizes about 10-100 nanometers can be supported by thermal motion in a suspended state, which distinguishes them from roughly dispersed mixtures. In the case of inclined lateral boundaries longitudinal inhomogeneity of the nanoparticles concentration is occurring. In this case, the mechanical equilibrium of the mixture is impossible, and a macroscopic fluid flow occurs. The paper studies the influence of flow on the sedimentation of nanoparticles in colloidal mixtures.

Sensitivity of coronal loop sausage mode frequencies and decay rates to radial and longitudinal density inhomogeneities: a spectral approach

Fast sausage modes in solar magnetic coronal loops are only fully contained in unrealistically short dense loops. Otherwise they are leaky, losing energy to their surrounds as outgoing waves. This causes any oscillation to decay exponentially in time. Simultaneous observations of both period and decay rate therefore reveal the eigenfrequency of the observed mode, and potentially insight into the tubes’ nonuniform internal structure. In this article, a global spectral description of the oscillations is presented that results in an implicit matrix eigenvalue equation where the eigenvalues are associated predominantly with the diagonal terms of the matrix. The off-diagonal terms vanish identically if the tube is uniform. A linearized perturbation approach, applied with respect to a uniform reference model, is developed that makes the eigenvalues explicit. The implicit eigenvalue problem is easily solved numerically though, and it is shown that knowledge of the real and imaginary parts of the eigenfrequency is sufficient to determine the width and density contrast of a boundary layer over which the tubes’ enhanced internal densities drop to ambient values. Linearized density kernels are developed that show sensitivity only to the extreme outside of the loops for radial fundamental modes, especially for small density enhancements, with no sensitivity to the core. Higher radial harmonics do show some internal sensitivity, but these will be more difficult to observe. Only kink modes are sensitive to the tube centres. Variation in internal and external Alfvén speed along the loop is shown to have little effect on the fundamental dimensionless eigenfrequency, though the associated eigenfunction becomes more compact at the loop apex as stratification increases, or may even displace from the apex.

Radiation-reabsorption-induced longitudinal inhomogeneity of the absorption coefficient in neon discharge

A study (based on the magnetic-scanning method) of the absorption of laser radiation with a wavelength of 0.63 μm by neon has revealed a preferred contribution of the central part of extended glow discharge to the absorption signal, which is related to the absorption of its intrinsic radiation.

Light transmission properties in inhomogeneously‐disordered random media

Spatially inhomogeneous disorder exists widely in optical systems. We present a numerical study on the light transport properties and analysis of transmission channels in random media with inhomogeneous disorder. For the case of longitudinal inhomogeneity of disorder we find that the statistics of the transmission channels is independent of the inhomogeneity and the system can be equivalent to a counterpart with homogeneous disorder strength, both of which have the same statistical distribution of the transmission channels. However, for the case of transverse inhomogeneity of disorder, such equivalence does not exist. The distribution of the total transmission is broadened and one most transmitted incident channel emerges.

Ionospheric total electron content: Spatial patterns of variability

AbstractThe distinctive spatial patterns of the ionosphere's total electron content (TEC) response to solar, seasonal, diurnal, and geomagnetic influences are determined across the globe using a new statistical model constructed from 2‐hourly TEC observations from 1998 to 2015. The model combines representations of the physical solar EUV photon and geomagnetic activity drivers with solar‐modulated sinusoidal parameterizations of four seasonal cycles and solar‐modulated and seasonally modulated parameterizations of three diurnal cycles. The average absolute residual of the data‐model differences is 2.1 total electron content unit, 1 TECU = 1016 el m−2 (TECU) (9%) and the root‐mean‐square error is 3.5 TECU (15%). Solar and geomagnetic variability, the semiannual oscillation and the diurnal and semidiurnal oscillations all impact TEC most at low magnetic latitudes where TEC itself maximizes, with differing degrees of longitudinal inhomogeneity. In contrast, the annual oscillation manifests primarily in the Southern Hemisphere with maximum amplitude over midlatitude South America, extending to higher southern latitudes in the vicinity of the Weddell Sea. Nighttime TEC levels in the vicinity of the Weddell Sea exceed daytime levels every year in Southern Hemisphere summer as a consequence of the modulation of the diurnal oscillations by the seasonal oscillations. The anomaly, which is present at all phases of the solar cycle, commences sooner and ends later under solar minimum conditions. The model minus data residuals maximize at tropical magnetic latitudes in four geographical regions similar to the ionosphere pattern generated by lower atmospheric meteorology. Enhanced residuals at northern midlatitudes during winter are consistent with an influence of atmospheric gravity waves.

The response of mesospheric NO to geomagnetic forcing in 2002–2012 as seen by SCIAMACHY

AbstractDaily NO number density, retrieved from measurements of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) from 2002 to 2012 for polar summer in the mesosphere, is used to investigate the response of NO to geomagnetic activity, as expressed by the auroral electrojet (AE) index. Applying the superposed epoch analysis, we observe a clear response of NO to strong geomagnetic forcing at geomagnetic latitudes 55–75°N/S and altitudes above 66 km. The 27 day solar rotation cycle is observed, indicating that some of the observed geomagnetic events are related to solar coronal holes. We find a linear relationship between anomalies of AE and NO at geomagnetic latitudes 55–70°N/S and 70–74 km altitude. A clear auroral oval‐like structure is observed on days of strong geomagnetic forcing in both hemispheres, with small longitudinal inhomogeneities, which might be related to the South Atlantic Anomaly or the magnetic local time. The NO lifetime and production rate per AE anomaly has been derived from a least squares fit to the observations. Comparisons of results from a simple model using this empirical NO production and a lifetime varying from 1.2 days in summer to 10 days in winter to SCIAMACHY observations show good agreement. In particular, the strength and interannual variability of the wintertime maximum is well captured. This suggests that direct production of NO in the upper mesosphere above 72 km contributes substantially to the so‐called energetic particle precipitation indirect effect.

Неустойчивость нормальной сдвиговой волны в упругом волноводе из слабо-неоднородного материала.

The influence of a weak longitudinal inhomogeneity on normal shear waves under different mechanical boundary conditions is investigated. It is shown, that for clamped smooth surfaces of isotropic elastic layer, occurs asymmetric localization of wave energy near the mid-surface layer. On the other side, for mechanically free smooth surfaces, near-surface localization of wave energy appears near mechanically free surfaces of the waveguide, but more intense localization appears again near the mid-surface layer. In both cases, due to the influence of material inhomogeneity on the normal wave, some distortion of amplitude and phase functions occur due to the change of formation coefficients (of frequencies). In both cases of boundary conditions, the weak inhomogeneity of the material leads to presence of frequency zones of transmission or prohibition of the formed wave. It is shown, that it is possible internal resonance in some higher forms.

The longitudinal inhomogeneity of the solar toroidal magnetic field generation

The features of the longitudinal inhomogeneity of the solar magnetic field strength in the region of its generation at mid-latitudes are investigated. For this purpose, the configuration of the large-scale magnetic field was analyzed, which is determined to the greatest extent by its strength. Model calculations have shown that the large-scale magnetic field of the Sun is created by local sources at areas where the generated magnetic field emerges. The source parameters derived from the calculations indicate a significant longitudinal variation of the analyzed field strength. The first harmonic, with one maximum and antipodal minimum, appeared to be the determining one in such a variation. The longitudinal positions of maxima and minima in the northern and southern hemispheres are the same, which indicates the simultaneousness of the generation of the solar toroidal field. The difference between the maximum and minimum can range from 4 to 10 in terms of the values of the magnetic moments of local sources of the large-scale solar magnetic field.

Stationary longitudinal inhomogeneities in areas of mesospheric clouds according to CIPS/AIM data (June–July)

In this paper, the results of a study of the longitudinal inhomogeneity of areas of the global field of noctilucent clouds in the Northern Hemisphere according to data obtained by the CIPS device of the AIM satellite from 2007 to 2012 are presented. An asymmetry in the longitudinal distribution of these cloud formations has been revealed. The revealed fact is interpreted as evidence of the existence of stationary planetary waves in the polar summer mesosphere.

Spatial propagation of quantum light states in longitudinally inhomogeneous waveguides

We study the propagation of quantum states of light in separable longitudinally inhomogeneous waveguides based on the momentum operator. This is carried out in the optical field-strength space E by means of the optical propagator obtained by the path integral formalism. We analyze virtual squeezing appearing in these media and its effect on quantum states of light, that is, Gouy’s quantum phases depending on both the longitudinal inhomogeneity and the quantum state. In addition, it is justified that these media perform unitary Infeld–Plebanski transformations, thus avoiding real squeezing. Likewise, WKB and exact results are presented for the propagation of coherent and squeezed states of light and, additionally, Bessel–Gauss quantum states of light propagating in a power-law parametric family of longitudinally inhomogeneous waveguides are studied in detail.

The dissolved chemical and isotopic signature downflow the confluence of two large rivers: The case of the Parana and Paraguay rivers

Summary The Parana River basin is one of the largest hydrological systems in South America (∼2.6 × 10 6 km 2 ). Downflow the confluence of tributaries, most large rivers exhibit transverse and longitudinal inhomogeneities that can be detected for tens or even hundreds of kilometers. Concordantly, a noticeable cross-sectional chemical asymmetry in the dissolved load was distinguished in the Middle Parana River, after the confluence of its main tributaries (i.e., the Paraguay and Upper Parana rivers). Water chemistry and isotopic signature in three cross-sections along the Middle Parana River, as well as from main and minor tributaries, and some deep (∼105 m bs) and shallow boreholes (∼15 m bs) located near both river banks, were analyzed in order to define the extent of mixing and identify possible contributions from groundwater discharges. Downflow the confluence of the Upper Parana and Paraguay rivers a chemical and isotopic asymmetry was observed, mainly through the values of EC, major ions (Ca 2+ , Na + , Mg 2+ , Cl − and SO 4 2 − ), some trace elements (Fe, U, Th, Ba, Sr, As and REE) and stable isotopes (δ 18 O and δ 2 H). Toward its western margin, higher elemental concentrations which resembled that of the Paraguay River were measured, whereas at the eastern border, waters were more diluted and preserved the chemical signature of the Upper Parana River. This variability remained detectable at least until ∼225 km downflow the confluence, where differences between western and eastern margins were less evident. At ∼580 km downflow the confluence, a slight inversion in the transverse chemical asymmetry was observed. This trend switch can be the result of the input of solutes from minor tributaries that reach the main channel from the East and/or may be due to higher groundwater discharges from the East bank. A mass balance model was applied, as a first approach, to estimate the groundwater inflow using the geochemical tracer 222 Rn. The results indicate that groundwater contributions represent between ∼0.5% and 6% of the total water inputs to the Middle Parana River under baseflow conditions. This implies that the chemical asymmetry in the Middle Parana River is mostly due to the incomplete mixing of the main tributaries. Though the influence of groundwater is not a determining factor in the chemical variability of the river, it may partially explain the higher concentrations of some trace elements found in the eastern margin ∼580 km downflow the confluence.

Azimuthal inhomogeneity in the MHD waveguide in the outer magnetosphere

AbstractGeomagnetic field and plasma inhomogeneities in the outer equatorial part of the magnetosphere create a channel with low Alfvén speeds which spans from the nose to the far flanks of the magnetosphere, in both the morning and the evening sectors. This channel plays the role of a waveguide for fast magnetosonic waves. The waveguide eigenmodes and corresponding Alfvén resonance (field line resonance) regions are directly related to geomagnetic pulsations Pc3 and Pc5. U‐shaped model of the waveguide allows for full analytical investigation of waveguide eigenmodes. Quantities such as mode wave numbers, group velocities, and their energy density distribution are found as functions of coordinate along the waveguide. The linkage of the waveguide magnetosonic oscillation energy to the Alfvén waves in the vicinity of the field line resonance deeper inside the magnetosphere is investigated, and corresponding energy leakage coefficient is found. Thus, the influence of longitudinal (i.e., azimuthal) waveguide inhomogeneity on wave propagation is analytically investigated. Obtained results can be used for interpretation of the observed wave power distribution in the frequency bands of geomagnetic pulsations Pc3 and Pc5, as well as for explanation of their spectral properties in the outer magnetosphere.

The influence of graded inhomogeneity on the thermomagnetic properties of bismuth-antimony alloys

We have studied the influence of a longitudinal graded inhomogeneity in crystals of bismuth-antimony solid solutions on their thermomagnetic properties. It is established that the presence of a temperature and/or composition gradient leads to (i) significant and nontrivial deformation of the magnetothermoelectric potential field under the action of a transverse magnetic field and (ii) the appearance of a stationary vortex electric current. It is shown that, with a certain combination of the mutual orientation of the temperature gradient and composition inhomogeneity, it is possible to significantly reduce the vortex current.

Prominence seismology using the period ratio of transverse thread oscillations

The ratio of the period of the fundamental mode to that of the first overtone of kink oscillations, from here on the "period ratio", is a seismology tool that can be used to infer information about the spatial variation of density along solar magnetic flux tubes. The period ratio is 2 in longitudinally homogeneous thin tubes, but it differs from 2 due to longitudinal inhomogeneity. In this paper we investigate the period ratio in longitudinally inhomogeneous prominence threads and explore its implications for prominence seismology. We numerically solve the two-dimensional eigenvalue problem of kink oscillations in a model of a prominence thread. We take into account three nonuniform density profiles along the thread. In agreement with previous works that used simple piecewise constant density profiles, we find that the period ratio is larger than 2 in prominence threads. When the ratio of the central density to that at the footpoints is fixed, the period ratio depends strongly on the form of the density profile along the thread. The more concentrated the dense prominence plasma near the center of the tube, the larger the period ratio. However, the period ratio is found to be independent of the specific density profile when the spatially averaged density in the thread is the same for all the profiles. An empirical fit of the dependence of the period ratio on the average density is given and its use for prominence seismology is discussed.

The influence of a galvanomagnetic stationary vortex current on the magneto-thermoelectric figure of merit of graded inhomogeneous bismuth-antimony alloys

We have studied the influence of a longitudinal graded inhomogeneity in crystals of bismuth-antimony solid solutions on their effective magnetoresistance, which is one of the parameters determining the efficiency (thermoelectric figure of merit) of a thermoelement operating in the presence of a transverse magnetic field. It is shown that, in a thermoelement operating under the action of an external magnetic field, the negative effect of the crystal inhomogeneity caused by the temperature gradient can be compensated for by its graded composition so as to provide for an increase in the thermoelectric figure of merit of the thermoelement.

Longitudinal inhomogeneity of DC current transport properties in Gd-system HTS tapes – Statistical approach for system design

In this paper, we studied the DC current transport properties of GdBCO-coated conductors, including the longitudinal distribution of critical current. Inhomogeneity of the local critical current was firstly measured by means of TapeStar™ at 77K, and then characterized based on a statistical method. Current transport properties were also measured for different positions and/or distances of potential taps using a four-probe method. It was shown that the longitudinal inhomogeneity of the conductor was described by use of a simplified percolation depinning model that takes account of Gaussian distribution. We further distinguished the above-mentioned inhomogeneity between statistical distribution and random failure. Influence of the aforementioned statistically distributed current transport properties on the magnet performance was also elucidated for simple pancake coils. This information is important as it provides guidance for practical system design.

Accurate and Efficient Modeling to Calculate the Voltage Dependence of Liquid Crystal-Based Reflectarray Cells

Two models that can predict the voltage-dependent scattering from liquid crystal (LC)-based reflectarray cells are presented. The validity of both numerical techniques is demonstrated using measured results in the frequency range 94-110 GHz. The most rigorous approach models, for each voltage, the inhomogeneous and anisotropic permittivity of the LC as a stratified media in the direction of the biasing field. This accounts for the different tilt angles of the LC molecules inside the cell calculated from the solution of the elastic problem. The other model is based on an effective homogeneous permittivity tensor that corresponds to the average tilt angle along the longitudinal direction for each biasing voltage. In this model, convergence problems associated with the longitudinal inhomogeneity are avoided, and the computation efficiency is improved. Both models provide a correspondence between the reflection coefficient (losses and phase-shift) of the LC-based reflectarray cell and the value of biasing voltage, which can be used to design beam scanning reflectarrays. The accuracy and the efficiency of both models are also analyzed and discussed.

Fast magnetohydrodynamic oscillation of longitudinally inhomogeneous prominence threads: an analogue with quantum harmonic oscillator

Previous works indicate that the frequency ratio of second and first harmonics of kink oscillations has tendency towards 3 in the case of prominence threads. We aim to study the magnetohydrodynamic oscillations of longitudinally inhomogeneous prominence threads and to shed light on the problem of frequency ratio. Classical Sturm--Liouville problem is used for the threads with longitudinally inhomogeneous plasma density. We show that the spatial variation of total pressure perturbations along the thread is governed by the stationary Schr\"{o}dinger equation, where the longitudinal inhomogeneity of plasma density stands for the potential energy. Consequently, the equation has bounded solutions in terms of Hermite polynomials. Boundary conditions at the thread surface lead to transcendental dispersion equation with Bessel functions. Thin flux tube approximation of the dispersion equation shows that the frequency of kink waves is proportional to the expression \alpha(2n+1), where \alpha is the density inhomogeneity parameter and n is the longitudinal mode number. Consequently, the ratio of the frequencies of second and first harmonics tends to 3 in prominence threads. Numerical solution of the dispersion equation shows that the ratio only slightly decreases for thicker tubes in the case of smaller longitudinal inhomogeneity of external density, therefore the thin flux tube limit is a good approximation for prominence oscillations. However, stronger longitudinal inhomogeneity of external density may lead to the significant shift of frequency ratio for wider tubes and therefore the thin tube approximation may fail. The tendency of frequency ratio of second and first harmonics towards 3 in prominence threads is explained by the analogy of the oscillations with quantum harmonic oscillator, where the density inhomogeneity of the threads plays a role of potential energy.

Magnetic microscopy for characterization of local critical current in iron-sheathed MgB2 wires

We have developed a characterization method of local critical current in iron-sheathed MgB2 wires. Local homogeneity was visualized by the scanning Hall-probe microscopy (SHPM). The value of local critical current was quantified with the aid of the finite element method (FEM) considering the ferromagnetic properties of the iron sheath. The results suggested that MgB2 wires fabricated by internal Mg diffusion processes still have large longitudinal inhomogeneity and much higher potential than that estimated by the four-probe transport method. This will be very important information for making a correct strategy for further development of MgB2 wires.

Radio seismology of the outer solar corona

Observed oscillations of coronal loops in EUV lines have been successfully used to estimate plasma parameters in the inner corona (< 0.2 R_0, where R_0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma parameters of the outer solar corona (> 0.2 R_0). We use the large Ukrainian radio telescope URAN-2 to observe type IV radio burst at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT in April 14, 2011. The burst was connected to C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio emission shows clear quasi-periodic variations in the emission intensity at almost all frequencies. Wavelet analysis at four different frequencies (29 MHz, 25 MHz, 22 MHz and 14 MHz) shows the quasi-periodic variation of emission intensity with periods of 34 min and 23 min. The periodic variations can be explained by the first and second harmonics of vertical kink oscillation of transequatorial coronal loops, which were excited by the same flare. The apex of transequatorial loops may reach up to 1.2 R_0 altitude. We derive and solve the dispersion relation of trapped MHD oscillations in a longitudinally inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of 0.1), dense (with the ratio of internal and external densities of > 20) magnetic slab with weak longitudinal inhomogeneity may trap the observed oscillations. Seismologically estimated Alfv\'en speed inside the loop at the height of 1 R_0 is 1000 km/s. Then the magnetic field strength at this height is estimated as 0.9 G. Extrapolation of magnetic field strength to the inner corona gives 10 G at the height of 0.1 R_0.