Spatial Nonuniformity Research Articles

A quantitative study of some sources of uncertainty in opacity measurements

Laboratory (laser and Z-pinch) opacity measurements of well-characterized plasmas provide data to assist inertial confinement fusion, astrophysics and atomic-physics research. In order to test the atomic-physics codes devoted to the calculation of radiative properties of hot plasmas, such experiments must fulfill a number of requirements. In this work, we discuss some sources of uncertainty in absorption-spectroscopy experiments, concerning areal mass, background emission, intensity of the backlighter and self-emission of the plasma. We also study the impact of spatial non-uniformities of the sample.

Spatial Non-Uniformity of Surface Temperature of the Dead Sea and Adjacent Land Areas

Pronounced spatial non-uniformity has been obtained of daytime sea surface temperature (SST) of the Dead Sea and of land surface temperature (LST) over areas adjacent to the Dead Sea. This non-uniformity was observed in the summer months, under uniform solar radiation. Our findings are based on Moderate Resolution Imaging Spectroradiometer (MODIS) data (2002–2016) on board the Terra and Aqua satellites. MODIS data showed that, on average for the 15-year study period, daytime SST over the eastern part of the lake (Te) exceeded by 5 °C that over the western part (Tw). This SST non-uniformity (observed in the absence of surface heat flow from land to sea at the eastern side) was accompanied by spatial non-uniform distribution of land surface temperature (LST) over areas adjacent to the Dead Sea. Specifically, LST over areas adjacent to the eastern side exceeded by 10 °C that over areas adjacent to the western side. Our findings of spatial non-uniformity of SST/LST based on MODIS data were supported by Meteosat Second Generation LST records. Regional atmospheric warming led to a decrease in spatial non-uniformity of SST during the study period. Temperature difference between Te and Tw steadily decreased at the rate of 0.32 °C decade−1, based on MODIS/Terra data, and 0.54 °C decade−1, based on MODIS/Aqua data. Our simulations of monthly skin temperature distribution over the Dead Sea by the Weather Forecast and Research (WRF) model contradict satellite observations. The application to modeling of the observed SST/LST spatial non-uniformity will advance our knowledge of atmospheric dynamics over hypersaline lakes.

Spin Polarization of Nonequilibrium Conduction Electrons in Magnetic Junctions

An original equation for nonequilibrium spin polarization in magnetic junctions based on dynamic equations for magnetic moment was obtained. Spatial nonuniformity of the distribution of carriers is taken into account in the equations, and the magnetic moment is averaged over the ensemble of nonequilibrium spin-injected electrons. The solution to the dynamic equations for the magnetic moment is used to estimate the probability of spin-flip electron transitions upon spin injection, and the solution to the equation for the nonequilibrium spin polarization in magnetic junctions is used to calculate frequencies of photon emission or absorption at energies corresponding to the energy of effective exchange splitting of spin subbands.

Analysis of the Spatial Nonuniformity of the Electric Field in Spectroscopic Diagnostic Methods of Atmospheric Electricity Phenomena.

The spatial nonuniformity of the electric field in air discharges, such as streamers, can influence the accuracy of spectroscopic diagnostic methods and hence the estimation of the peak electric field. In this work, we use a self‐consistent streamer discharge model to investigate the spatial nonuniformity in streamer heads and streamer glows. We focus our analysis on air discharges at atmospheric pressure and at the low pressure of the mesosphere. This approach is useful to investigate the spatial nonuniformity of laboratory discharges as well as sprite streamers and blue jet streamers, two types of transient luminous events taking place above thunderclouds. This characterization of the spatial nonuniformity of the electric field in air discharges allows us to develop two different spectroscopic diagnostic methods to estimate the peak electric field in cold plasmas. The commonly employed method to derive the peak electric field in streamer heads underestimates the electric field by about 40–50% as a consequence of the high spatial nonuniformity of the electric field. Our diagnostic methods reduce this underestimation to about 10–20%. However, our methods are less accurate than previous methods for streamer glows, where the electric field is uniformly distributed in space. Finally, we apply our diagnostic methods to the measured optical signals in the second positive system of N2 and the first negative system of N2+ of sprites recorded by Armstrong et al. (1998, https://doi.org/10.1016/S1364-6826(98)00026-1) during the SPRITE's 1995 and 1996 campaigns.

Features of Mass Transfer of Noncondensable Gases by Primary Coolant of Nuclear Icebreaker Reactors

To study the characteristics of the mass transfer of noncondensable gases in the primary loop of the nuclear icebreaker reactors, models of the core and the up-core space were developed using the Relap5 (USA) and Fluent (USA) codes and modeling of interphase mass transfer and transport of the gas phase by the water coolant was performed on these sections. Spatial non-uniformity of the content of undissolved gases, which arises as a result of vapor-gas bubbles concentrating in the vortex structures of the flow and resulting in a significant reduction of their dissolution rate, was revealed. This must be taken into account in the analysis of the operation of the primary loop equipment of nuclear icebreakers (hydrogen absorption in the titanium alloys of steam-generator piping, nodular corrosion of the zirconium cladding of the fuel rods).

Propagation of Solar Energetic Particles in the Outer Heliosphere: Interplay between Scattering and Adiabatic Focusing

Abstract The turbulence and spatial nonuniformity of the guide magnetic field cause two competitive effects, namely, the scattering effect and the adiabatic focusing effect, respectively. In this work, we numerically solve the five-dimensional Fokker–Planck transport equation to investigate the radial evolutions of these important effects undergone by the solar energetic particles (SEPs) propagating through interplanetary space. We analyze the interplay process between the scattering and adiabatic focusing effects in the context of three-dimensional propagation, with special attention to the scenario of the outer heliosphere, in which some peculiar SEP phenomena are found and explained. We also discuss the radial dependence of the SEP peak intensities from the inner through the outer heliosphere, and conclude that it cannot be simply described by a single functional form such as R −α (R is radial distance), which is often used.

State prediction of an entropy wave advecting through a turbulent channel flow

Survival of entropy waves during their advection throughout a combustor is central to the generation of entropic sound and the subsequent effects upon thermoacoustic stability of the system. However, the decay and spatial non-uniformity of entropy waves are largely ignored by the existing models used for the calculation of entropy noise generation. Recent investigations have demonstrated the complex spatio-temporal dynamics of entropy waves and cast doubts on the sufficiency of the one-dimensional approach, conventionally used for the analysis of these waves. Hence, this paper proposes a novel approach to the low-order modelling of entropy wave evolution wherein the wave is described by the two states of position and amplitude in the streamwise direction. A high-order model is first developed through direct numerical simulation of the advection of entropy waves in a fully developed, heat transferring, compressible, turbulent channel flow. The data are then utilised to build and validate a series of nonlinear, low-order models that provide an unsteady two-dimensional representation of the decaying and partially annihilating entropy waves. It is shown that these models need, at most, approximately 12.5% of the total trace of entropy wave advection to predict the wave dynamics accurately. The results further reveal that the existing linear low-order models are truly predictive only for the entropy waves with less than 2% increase in the gas temperature compared to that of the surrounding flow. Yet, in agreement with the assumption of existing models, it is shown that entropy waves travel with the mean flow speed.

Numerical simulation of turbulent Rayleigh-Bénard mercury convection in a circular cylinder with introducing small deviations from the axisymmetric formulation

Results of DNS are reported for turbulent Rayleigh-Bénard mercury convection (Pr = 0.025) in a cylindrical container with the aspect ratio of unity at the Rayleigh number of Ra = 106. The main goal of the study is to estimate the influence of small deviations from the axisymmetric formulation on the behavior of large-scale circulation (LSC) developing in the container. The deviations examined are a small tilt of the cylinder or prescribed sinusoidal disturbances of the bottom wall temperature. The effects of the computational grid structure in the central region of the flow are investigated as well. It has been shown that the azimuthal low-frequency reorientations of the LSC, which are typical for the axisymmetric problem setting, can be fully suppressed by imposing relatively small non-axisymmetric disturbances of various kinds. Time-averaged 3D velocity and temperature fields, as well as spatial non-uniformities of local heat transfer are analyzed for a “locked” LSC case.

Analysis of lightning discharges activity within the territory of Buryatia in 2010-2016 based on WWLLN data

Thunderstorm activity is the main natural cause of forest fires. The development of new or modernization of existing systems for monitoring and forest fires forecasting requires the involvement of data on the spatial and temporal distribution of thunderstorms in monitorable forest areas. This article discusses the territory of the Republic of Buryatia (Russian Federation). The study of the spatial and temporal components of thunderstorm activity was carried out based on the World Wide Lightning Location Network (WWLLN) data. WWLLN data on thunderstorms locations for 2010-2016 were used. The network registers lightning discharges during the year. The thunderstorm season lasts from May to September. Archival WWLLN data for this period were selected. The resulting dataset allowed us to distinguish areas with different lightning activity. A high degree of spatial nonuniformity of thunderstorm activity in Buryatia was established. The number of lightning discharges begins to increase in May, the maximum is observed in July, and a recession occurs in August. Two daily maximum were revealed: the first maximum of number of lightning discharges is in the interval from 12 to o’clock and the second is about 19 o’clock of local time.

Turbulent radial thermal counterflow in the framework of the HVBK model

We apply the coarse-grained Hall-Vinen-Bekarevich-Khalatnikov (HVBK) equations to model the statistically steady-state, turbulent, cylindrically symmetric radial counterflow generated by a moderately large heat flux from the surface of a cylinder immersed in superfluid 4He. We show that a time-independent solution exists only if a spatial non-uniformity of temperature and the dependence on temperature of the thermodynamic properties are accounted for. We demonstrate the formation of a thermal boundary layer whose thickness grows with temperature of the cylinder's surface, and analyze the properties of the flow in the radial direction, including the local average vortex line density.

Design of dynamic screw pinch experiments for magnetized liner inertial fusion

Magnetic implosion of cylindrical metallic shells (liners) is an effective method for compressing preheated, premagnetized fusion fuel to thermonuclear conditions [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] but suffers from magneto-Rayleigh–Taylor instabilities (MRTI) that limit the attainable fuel pressure, density, and temperature. A novel method proposed by Schmit et al. [Phys. Rev. Lett. 117, 205001 (2016)] uses a helical magnetic drive field with a dynamic polarization at the outer surface of the liner during implosion, reducing (linear) MRTI growth by one to two orders of magnitude via a solid liner dynamic screw pinch (SLDSP) effect. Our work explores the design features necessary for successful experimental implementation of this concept. Whereas typical experiments employ purely azimuthal drive fields to implode initially solid liners, SLDSP experiments establish a helical drive field at the liner outer surface, resulting in enhanced average magnetic pressure per unit drive current, mild spatial nonuniformities in the magnetic drive pressure, and augmented static initial inductance in the pulsed-power drive circuit. Each of these topics has been addressed using transient magnetic and magnetohydrodynamic simulations; the results have led to a credible design space for SLDSP experiments on the Z Facility. We qualitatively assess the stabilizing effects of the SLDSP mechanism by comparing MRTI growth in a liner implosion simulation driven by an azimuthal magnetic field vs one driven with a helical magnetic field; the results indicate an apparent reduction in MRTI growth when a helical drive field is employed.

Railway track degradation: The contribution of a spatially variant support stiffness - Global variation

The effect of large-scale variation in the support stiffness on railway track degradation is studied using a frequency-domain approach. The model used can deal with parametric excitation due to both the discrete sleeper spacing and arbitrary large-scale spatial track non-uniformity. Adopted stiffness profiles are based on realistic datasets in the literature. The sensitivity to degradation is assessed by quantifying the energy dissipation in the substructure over the influence zone. Results show that the effect of spatial stiffness variation generally increases with the speed, for any subgrade condition; system resonance however leads to increased degradation at resonance speeds and increases with the mean value of the track stiffness. The speed is shown to have a larger influence in the presence of non-uniformity than it has for uniform track with a mean value of the same non-uniform track stiffness, independent of this mean value. In general, support stiffness non-uniformity and poor track conditions (in terms of a low overall stiffness) may have comparable effects; the combination of both is a worst-case scenario. Predictions are independent from the randomness for measured datasets and have therefore general validity. Further, an excellent correlation is found between the spatial variation of the dynamic track stiffness, the differential energy dissipation in the substructure, and the work performed by the moving contact load with respect to the track, independent of the train speed. This confirms existing empirical evidence of the dynamic track stiffness for non-uniform track as an indicator for degradation.

Three-dimensional surface charge nonlinear waves at a plasma boundary

The nonlinear behavior of surface charges is here investigated under simplest ideal conditions. A new single equation is deduced from the well-known descriptions, which govern the cold electron plasma motion, for cases when the dependence on all spatial coordinates must be taken into account. It opens new possibilities to reveal and describe conditions of the existence of nonlinear surface charge waves with a solitary structure when there are two different scales of a spatial non-uniformity of wave characteristics for different coordinates in the boundary plane. The simple method to determine parameters, which are necessary for the propagation of surface charge perturbations along the plasma boundary, is also described.

Fast Method for Liquid Crystal Cell Spatial Variations Estimation Based on Modeling the Spectral Transmission.

Liquid crystal phase retarders are utilized by photonic devices and imaging systems for various applications, such as tunable filtering, light modulation, polarimetric imaging, remote sensing and quality inspection. Due to technical difficulties in the manufacturing process, these phase retarders may suffer from spatial non-uniformities, which degrade the performance of the systems. These non-uniformities can be characterized by measuring the spectral transmission at each voltage and each point on the liquid crystal cell, which is time consuming. In this work, we present a new fast and simple method for measuring and computationally estimating the spatial variations of a liquid crystal phase retarder with planar alignment. The method is based on measuring the spectral transmission of the phase retarder at several spatial locations and estimating it at others. The experimental results show that the method provides an accurate spatial description of the phase retarder and can be employed for calibrating relevant systems.

Evaluation method of infrared thermography on children with idiopathic thrombocytopenic purpura: Preliminary

PurposeIdiopathic thrombocytopenic purpura (ITP) is an immune disease with complex pathogenesis. However, the diagnosis of ITP lacks of specificity test index, the diagnosis is still at an exclusive diagnosis level. Clinical studies have found that ITP can cause a disorder of the skin temperature distribution due to the spontaneous immune response. Human skin temperature can be collected by infrared thermography (IRT), and we can speculate on the severity of the immune response by extracting the temperature distribution characteristics. In this paper we will explore the value of IRT for the diagnosis and evaluation on ITP, and try to add new non-invasive inspection tools for ITP laboratory inspection. MethodAccording to the human metabolic function status, a spatial heterogeneity algorithm for skin temperature distribution was proposed in this paper based on infrared thermography. The algorithm was used to quantify the degree of confusion in a target region. Thirty-three subjects were divided into a control group, an ITP1 group and an ITP2 group in this study. The temperature distribution spatial non-uniformity, average temperature and maximum temperature characteristics of 14 ROI regions were extracted from the infrared thermal imaging of every subject. Six target regions with smaller P value were selected and single-dimensional evaluation parameter was extracted by the method of area weighting. At the same time, the sensitivity and specificity of the parameter to ITP were examined. ResultThe 6 target regions selected by the non-uniformity feature had significant differences (P < 0.05) among the three groups with the statistical method of ANOVA, but there were no significantly statistical difference on the regions extracted by average temperature and maximum temperature. It can be found from the ROC curve that the evaluation method proposed in this paper has higher sensitivity and specificity, than the common methods. ConclusionThe skin temperature distribution characteristics of the ITP children can be displayed by an infrared thermography. All of the 6 target regions screened by the spatial non-uniformity algorithm proposed in this paper are torso parts, which match the conclusions of relevant literature research. The method presented in this paper has high sensitivity and specificity to ITP. Although there are some limitations, it can non-invasively and objectively describe the disease state and add a new tool for ITP laboratory examinations. This paper also provides a new method and idea for the medical evaluation of infrared thermography.

Characterization of Process-Induced Nonuniformity Using Asymmetric Metal–Insulator–Semiconductor Capacitive Test Structure

For most large-area applications, spatial nonuniformity of transistor characteristics makes it difficult if not impossible, to achieve adequate performance. Nonuniform parameters may lead to variations in color or gray level, which is commercially not viable. A variation in threshold voltage, mobility or I-V characteristics of an organic thin-film transistor (OTFT) in a pixel circuit can result in unacceptable variation in the current driving the organic light-emitting diode (OLED) which accounts for large nonuniformities in the pixel brightness. Given its importance, a fast and straightforward method for characterization of device variations would be of great help in the process development and optimization. In the present work, a simple, easy to fabricate two-terminal asymmetric metal- insulator-semiconductor (AMIS) capacitive test structure is proposed for quick and accurate characterization of the process-induced nonuniformities in mobility, threshold voltage, and drain current. The capacitance-voltage (C-V) characteristic of the proposed AMIS structure is derived mostly from the channel, and its contribution to the total capacitance at any given frequency depends on channel properties including mobility and threshold voltage. At low frequencies, the C-V characteristics become independent of the series resistances, and hence, complex techniques can be sidestepped for accurate estimation of channel properties. The simulation results are presented to demonstrate the concept using a single AMIS test structure. The experimental results obtained with top contact pentacene based on AMIS arrays are presented to show the concept and advantages of the proposed structure.

Computational study of electrostatic focusing of aerosol nanoparticles using an einzel lens

This study computationally explores the possibility of focusing charged aerosol nanoparticles using electrostatics, similar to focusing of electrons and ions. A non-dimensional electrostatic focusing parameter χe, defined as the ratio of electrostatic potential energy to the kinetic energy of an aerosol nanoparticle, significantly determines focusing performance. The focusing device considered here is a 3-electrode electrostatic (“einzel”) lens. The average focal length of the lens is seen to have an inverse power relationship with χe. For low values of χe ∼3 in this study, the particles are seen to cross the lens axis once, while at higher χe multiple axis cross-over points appear. Similar to electron and ion optics, nanoparticle focusing is also limited by spherical aberration and beam divergence due to finite spread of particles in the inlet cross section of the lens and spatial non-uniformity of the focusing electric field. Other factors that influence focusing performance such as the electrostatic lens geometry, and the distribution of velocity and kinetic energy of the particles at the inlet of the lensing region are recognized, but not considered here for simplicity. In vacuum, good focusing performance (i.e.) a narrow beam of nanoparticles with minimum spherical aberration and small divergence angle is theoretically possible if χe<1 and if spread of particles in the inlet is confined to 20% of radius of the cylindrical lens. The effect of gas pressure is also probed to understand the degradation of focusing performance due to particle-gas interactions. It is seen that, for particles of specified size and density, a certain maximum pressure exists beyond which the device can no longer be efficiently used to focus nanoparticles. Likewise, below a certain pressure, the focusing performance is nearly independent of gas pressure, thereby enabling the selection of an operating pressure for such devices.

Influence of hydrological structure on exchange processes between water and bottom sediments in Mozhaysk Reservoir

The results of studies of exchange processes at the “water – bottom sediments” border for the summer period 2017–18 at the Mozhaisk reservoir are presented. The factors that determine the intensity values of methane and mineral phosphorus fluxes from bottom sediments as well as their spatial non-uniformity, associated with the soils distribution characteristics in the valley-type reservoir, are analysed.

Optimization and Analysis of a Heat Exchanger with Encapsulated Phase Change Material

In this study, the performance of a heat exchanger (HX) with encapsulated phase change material (EPCM) undergoing alternating melting and freezing is studied with the intent of analyzing the thermal behavior and optimizing its performance. The specific application of the EPCM HX is to cool the exiting hot water stream from the steam condenser in a power plant in lieu of a traditional cooling tower. The HX consists of a series of stacked flattened tubes with encapsulated phase change material (PCM) and arranged in lateral sections that are alternately exposed to orthogonal streams of the hot water and the ambient air drawn by a fan. A systems-level code was developed to predict the quasi-steady state and transient performance of the HX. Using large-eddy simulations, new heat transfer and pressure drop correlations for in-line flattened tube banks were developed to predict the HX performance. The capital cost of the HX is minimized using the genetic algorithm for a specific cooling duty and coefficient of performance (COP). The effect of various design parameters on the capital costs is also studied. The study shows that using PCMs with different melting temperatures along the water flow direction enhances the overall heat transfer. It is observed that more PCM is required to meet the desired COP and cooling duty for EPCM HX with a smaller footprint or height due to lower allowable air velocity, thus demanding a higher tube surface area. The transient simulations reveal that the PCM undergoes sensible heat transfer locally due to spatial nonuniformities in heat transfer distribution.

Assessment of the systematic errors caused by diffusion gradient inhomogeneity in DTI-computer simulations.

Diffusion tensor imaging (DTI) is a powerful MRI modality that allows the investigation of the microstructure of tissues both in vivo and noninvasively. Its reliability is strictly dependent on the performance of diffusion-sensitizing gradients, of which spatial nonuniformity is a known issue in the case of virtually all clinical MRI scanners. The influence of diffusion gradient inhomogeneity on the accuracy of the diffusion tensor imaging was investigated by means of computer simulations supported by an MRI experiment performed at the isocenter and 15cm away. The DTI measurements of two diffusion phantoms were simulated assuming a nonuniform diffusion-sensitizing gradient and various levels of noise. Thereafter, the tensors were calculated by two methods: (i) assuming a spatially constant b-matrix (standard DTI) and (ii) applying the b-matrix spatial distribution in the DTI (BSD-DTI) technique, a method of indicating the b-matrix for each voxel separately using an anisotropic phantom as a standard of diffusion. The average eigenvalues and fractional anisotropy across the homogeneous region of interest were calculated and compared with the expected values. Diffusion gradient inhomogeneity leads to overestimation of the largest eigenvalue, underestimation of the smallest one and thus overestimation of fractional anisotropy. The effect is similar to that caused by noise; however, it could not be corrected by increasing SNR. The MRI measurements, performed using a 3T clinical scanner, revealed that the split of the eigenvalues measured 15cm away from the isocenter is significant (up to 25%). The BSD-DTI calibration allowed the reduction of the measured fractional anisotropy of the isotropic medium from 0.174 to 0.031, suggesting that gradient inhomogeneity was the main cause of this error. For the phantom measured at the isocenter, however, the split was almost not observed; the average eigenvalues were shifted from the expected value by ~ 5%.