Field Coefficients Research Articles

Solute cloud evolution in channels with suspended vegetation of different configurations

Suspended vegetation's ability to handle solute accumulation in natural waters through their roots has sparked significant interest and research in using them to improve water quality. This research semi-analytically investigates the unsteady solute cloud evolution in channels with suspended vegetation after the point source release on the water surface, by solving the solute transport model with spatially variable flow field coefficients. Results show that regardless of gap ratio (the ratio of the height of the gap region to the water depth) and vegetation density, the solute cloud evolution in the preasymptotic stage (the dimensionless time ⟨Dz*⟩t*/h*2<1, where ⟨Dz*⟩ is the depth-averaged vertical turbulent diffusion coefficient. t* is the time, and h* is water depth.) can be featured by: the cloud centroid shifts upstream; the longitudinal dispersion coefficient increases; the solute cloud is positively skewed; and the solute accumulates in the vegetation layer on the upstream side and the bottom boundary layer on the downstream side. At around ⟨Dz*⟩t*/h*2∼1, the cloud centroid position and the longitudinal dispersion coefficient approach their asymptotic values, and the solute cloud is basically considered to follow the normal distribution longitudinally. In terms of the influences of configurations on the solute cloud during the whole dispersion process, the cloud centroid moves faster and reaches a farther asymptotic location due to a more serious blockage effect for a smaller gap ratio or larger vegetation density. In addition, a small gap ratio enhances the skewness and kurtosis of the cloud, while the vegetation density has little effect on them. Benefiting from the combined action of the violent velocity shear and the strong shear-scale diffusion which dominates the vertical mixing, the smallest gap ratio or highest vegetation density promotes the vertical mixing and yields the largest asymptotic longitudinal dispersion coefficient. Consequently, the vertical concentration distribution is the most uniform and the longitudinal concentration distribution is the flattest in these two cases.

Revealing Site Occupancy in a Complex Oxide: Terbium Iron Garnet.

Complex oxide films stabilized by epitaxial growth can exhibit large populations of point defects which have important effects on their properties. The site occupancy of pulsed laser-deposited epitaxial terbium iron garnet (TbIG) films with excess terbium (Tb) is analyzed, in which the terbium:iron (Tb:Fe)ratio is 0.86 compared to the stoichiometric value of 0.6. The magnetic properties of the TbIG are sensitive to site occupancy, exhibiting a higher compensation temperature (by 90 K) and a lower Curie temperature (by 40 K) than the bulk Tb3 Fe5 O12 garnet. Data derived from X-ray core-level spectroscopy, magnetometry, and molecular field coefficient modeling are consistent with occupancy of the dodecahedral sites by Tb3+ , the octahedral sites by Fe3+ , Tb3+ and vacancies, and the tetrahedral sites by Fe3+ and vacancies. Energy dispersive X-ray spectroscopy in a scanning transmission electron microscope provides direct evidence of TbFe antisites. A small fraction of Fe2+ is present, and oxygen vacancies are inferred to be present to maintain charge neutrality. Variation of the site occupancies provides a path to considerable manipulation of the magnetic properties of epitaxial iron garnet films and other complex oxides, which readily accommodate stoichiometries not found in their bulk counterparts.

Significance of MHD Cross nanofluid analysis near a stretched surface with double stratification and activation energy

The flow of 2-D cross fluid model with mass and heat transmission over a linearly stretched sheet is analyzed in this paper. Furthermore, we have expanded our study by considering the effects of MHD flow, stagnation point, double stratification, heat generation, radiation effect, nanofluid flow, activation energy and mass diffusion. This type of study has not being investigated previously in literature. The flow generating PDEs are altered into ODEs by deploying suitable transformations. The effects of the parameters involved, namely the Weissenberg number, magnetic field coefficient, Brownian motion coefficient, radiation parameter, Damkohler number, thermophoresis coefficient, Schmidt number, activation energy, heat generation parameter and temperature difference coefficient on the velocity, concentration and energy fields are thoroughly scrutinized. The problem is solved through numerical technique (BVP4c) on MATLAB. The outcomes reveal that the velocity curve upsurges for rising Weissenberg number and decreases due to magnetic parameter. The heat field improves for increasing behavior of the Brownian motion, thermophoresis, heat generation, thermal conductivity and radiation coefficient whereas reverse results are obtained due to Prandtl number and stratification parameter. The concentration improves due to thermophoresis parameter and diffusivity coefficient while reverse outcomes are noticed due to Schmidt number, Damkohler number, temperature difference parameter and Brownian motion parameter.

CFD Analysis of the Heat Transfer and Fluid Flow Characteristics Using the Rectangular Rib Attached to the Fin Surface in a Solar Air Heater

This study discussed the effect of ribbed fin, which was suggested by the authors, on the enhancement of heat transfer and flow characteristics of fluid in a solar air heater. The ribbed fin has a rectangular rib at the base and side surfaces of the fin. Thus, it can increase the heat transfer coefficient in the fluid field of a solar air heater as well as extend the heat transfer area. The simulation was performed with various Reynolds numbers, relative heights, and pitches of the rib. The presence of the rib enhances the heat transfer performance by 3.497 times over a smooth fin. However, the addition of the rib also increases pressure drop. Thus, the thermo-hydraulic performance, which considers both heat transfer enhancement and pressure drop increase, was also discussed. Furthermore, this study developed correlations for the Nusselt number and friction factor as a function of geometric condition of the rib and Reynolds number. The correlations accurately predicted the Nusselt number for the base and side surfaces of the fin and friction factor with mean absolute percent errors of 4.24%, 4.53%, and 7.33%, respectively.

Giant electric field-induced strain and structure evolution of NaTaO3-modified 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 Pb-free ceramics

To acquire giant electric field-induced strain in non-Pb materials is attracting a great deal of attention in the past decade. In the current investigation, the crystal and domain structures as well as the electrical performances of (1-x) (0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xNaTaO3 (BNBT-xNT) specimens were systematically studied to achieve enhanced strain. The introduction of NT makes the phase structure transit from rhombohedral-tetragonal to pseudo-cubic structure. The original domain structure of BNBT is destroyed, and the disorder degree of the local structure increases. Simultaneously, the remnant polarization, coercive field, and piezoelectric coefficients were significantly decreased. The transition from ferroelectric to ergodic relaxation can be effectively modified, thus lowering the transition zone to room temperature. Finally, the BNBT-3NT ceramics achieve marked strain coefficients at room temperature, with a maximum strain of 0.394% under 65 kV/cm and a d33* of 606 pm/V.

An Improved Calculation Method Based on Newton–Raphson Method for Ion Flow Field of UHVDC Transmission Lines at High Altitude

The fast and accurate solution of the total electric field and ion current density is crucial for the electromagnetic environment of ultra high voltage direct current (UHVDC) transmission lines. In this article, an improved method based on Newton–Raphson method (NRM) and upstream finite element method (UFEM) is proposed to calculate the ion flow field under complex conditions. According to the gas motion theory, the corona-onset electric field, ion mobility, and recombination coefficient are obtained at high altitude and put into the ion flow field model in this article. Subsequently, the charge density is used to solve Poisson’s equation, and the current continuity equations are calculated by UFEM. After that, the charge density of the conductor surface is updated based on NRM. These three parts are iterated repeatedly until the convergence conditions are met. According to the test results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 800-kV UHVDC transmission line at high altitude, the validity and rationality of the proposed method are verified. The result demonstrates that due to the reduction of atmospheric pressure at the high altitude, the corona-onset electric field decreases, and the ion mobility and recombination coefficient increase, which makes the total electric field and ion current density at ground level increase. Compared with the traditional methods, the improved method is insensitive to the initial value of the surface charge density. Moreover, this proposed method can effectively improve the convergence ability and achieve the stable and fast calculation of the ion flow field at high altitude.

On the determination and interpretation of the lithospheric induced magnetisation

We present a new technique for reducing the uncertainties inherent in the interpretation of lithospheric magnetic field observations over the Earth. This technique, without involving iterations, provides an improved estimate of the depth-integrated magnetic susceptibility of the crust as compared to previous approaches. Departing from the normal practice of using observations at specific locations, we model directly Gauss coefficients of the lithospheric magnetic field and use an a-priori initial lithospheric thickness model to circumvent magnetic annihilators (i.e. magnetisation distributions that cannot be determined from magnetic data since they have no impact on the lithospheric magnetic field). Of the several initial magnetic layer models tested, we prefer the model where magnetic thickness is based on the Moho or the regional estimate of the Curie depth when it is shallower than the Moho because it is physically reasonable and produces the fewest artefacts. The method is applied to a recent high-degree lithospheric magnetic field model called LCS-1 derived from CHAMP and Swarm magnetic satellite data. The technique is appropriate for regions where induced magnetisation dominates over remanent magnetisation. We show that high degrees of the final depth-integrated magnetic susceptibility variation are dependent only on the corresponding high degrees of the LCS-1 magnetic field model. Thus, the depth-integrated magnetic susceptibility variation is an important quantity derived in the study which enables readily qualitative interpretation of regional geology.

Determination of asymptotic field coefficients for multi-material antiplane V-notches by the weak form quadrature element method

Weak form quadrature element analysis (QEA) of multi-material antiplane V-notches is conducted. Angular eigenfunctions are introduced into the inner subdomains where stress singularity exists, while the outer domain is divided into several quadrature elements according to geometric boundary conditions and material properties. Algebraic equations are established and coefficients are solved for after introducing the minimum potential energy principle. The influence of the first eight terms on improvement of far field stress and displacement estimations is demonstrated. As compared to the computational costs of other methods, much fewer degrees of freedom are needed in the present formulation to achieve the same accuracy of results, exhibiting the merits of QEA of fracture problems.

Crop yield and carbon sink potential with precipitation in maize and potato cropland ecosystems over the summertime monsoon transition zone of China

AbstractChina has significantly enhanced vegetation coverage and terrestrial carbon sink functions through ecological restoration. However, cropland ecosystems are sensitive to a changing climate over the summertime monsoon transition zone of China (SMTZC), which has implications for carbon cycling. For example, it is unclear how changes in precipitation will affect the cropland ecosystem carbon sinks (CSe) and carbon sink potential (CSp), and the mechanisms of tradeoffs that develop between plant and soil organic carbon (SOC) are unclear. Here, we integrated crop yield, total biomass (TB) and water coefficient in a combined field and modelling experimental. We explored the mechanisms of ecosystem carbon cycling and CSp in the SMTZC under different precipitation scenarios. We found that soil organic carbon sink (SOCs) was strongly correlated with the plant organic carbon sink (POCs) and discovered. Significant differences in CSp between ecosystems resulting from interannual precipitation. The C4 (maize, Zea mays) and C3 (potato, Solanum tuberosum L) carbon sinks (CSs) were 68.59, 190.73, 160.37 Mt and 10.21, 30.97, 14.59 Mt for the 3 years, respectively. Precipitation effectively increased TB and yield, but excessive precipitation in them, which was most obvious in C3 ecosystem (R2 &gt; 0.60) and reduced POCs, evident in C4 ecosystem (R2 &gt; 0.16). This study provides data and a scientific basis for increasing CS and achieving carbon neutrality in cropland.

Target area distillation and section attention segmentation network for accurate 3D medical image segmentation.

3D medical image segmentation has an essential role in medical image analysis, while attention mechanism has improved the performance by a large margin. However, existing methods obtained the attention coefficient in a small receptive field, resulting in possible performance limitations. Radiologists usually scan all the slices first to have an overall idea of the target, and then analyze regions of interest in multiple 2D views in clinic practice. We simulate radiologists' recognition process and propose to exploit the 3D context information in a deeper manner for accurate 3D medical images segmentation. Due to the similarity of human body structure, medical images of different populations have highly similar shape and location information, so we use target region distillation to extract the common segmented region information. Particularly, we proposed two optimizations including Target Area Distillation and Section Attention. Target Area Distillation adds positions information to the original input to let the network has an initial attention of the target, while section attention performs attention extraction in three 2D sections thus with large range of receptive field. We compare our method against several popular networks in two public datasets including ImageCHD and COVID-19. Experimental results show that our proposed method improves the segmentation Dice score by 2-4% over the state-of-the-art methods. Our code has been released to the public (Anonymous link).

Imaging Convective Phenomena inside Highly Refractive Cylindrical Enclosures

The conventional refractive index-based optical techniques show limitations in measuring the thermal field inside refractive surfaces due to the curvature effects. The present work reports on the application of lensless Fourier transform digital holographic interferometry for mapping heat transfer phenomena inside highly refracting axisymmetric enclosures. Experiments have been performed to characterize the buoyancy-driven natural convection heat transfer around a vertically oriented heated cylinder placed concentrically inside a relatively large cylindrical enclosure filled with de-ionized water. The experiments were performed under various heating conditions, and the corresponding holograms were analyzed in real-time to show the transients of the temperature field. Quantitative results were obtained in the form of a two-dimensional temperature distribution field and local heat transfer coefficients along the heated surface. Experimental results were validated by comparing the values of the surface temperatures obtained from the analysis with that obtained from the thermocouple data. The work presented highlights the ability of the lensless Fourier transform digital holographic technique to map the real-time temperature field inside a highly refracting enclosure.

Semi-empirical formulas on notch stress field and SIF of orthotropic V-shaped thin plate with initial crack under tensile-bending loads

For orthotropic materials, the solution of notch stress field and stress intensity factor (SIF) is not only related to crack opening angle, crack depth, notch length, geometric parameters, but also obviously influenced by material characteristics and constitutive relation. On the basis of isotropic notch stress field and SIF theoretical formula, a series of multi-parameter models of orthotropic materials were constructed and fitted. The effects of notch depth, crack length, the ratio of notch depth to plate width, opening angle and mechanical properties of composite materials on geometric correction coefficient YI are systematically analyzed. On this basis, a semi-empirical formula of YI is put forward by combining stress field analysis and multi-parameter fitting. The semi-empirical formula is further verified with finite element method, traditional formula and various composite materials. The numerical results show that the simple formula proposed in this paper has higher prediction accuracy. Finally, the proposed formula is extended to the solution of notch stress field and geometric correction coefficient for V-notch-cracked plate under bending load, tension-bending complex loads.

Experimental study on the direct contact condensation of gaseous oxygen jets in crossflow of liquid oxygen

To ensure the safe and stable operation of the oxidant supply system in liquid oxygen (LOX)/kerosene liquid rocket engines, cryogenic visualization experiments on the direct contact condensation of gaseous jets in liquid crossflow are conducted using oxygen as the working fluid. The mass flux of gaseous oxygen (GOX) is 200–800 kg/m2s, while the temperature of LOX is 101 K. Under these operating conditions, violent oscillations occur. To address this problem, this paper proposes an image processing program to facilitate the study of flow patterns, oscillation frequency, plume length, and heat transfer coefficients in unstable flow fields. Three flow patterns are identified, namely condensation oscillation, chugging, and crawling. The effect of the GOX mass flow rate on chugging is investigated. In addition, the flow pattern map with the coordinates of nondimensional GOX mass flux and condensation driving potential is developed. The oscillation frequency, ranging from 120 Hz to 150 Hz, increases monotonically with the GOX mass flow rate and LOX pressure in the test section. The plume shrinks with the increase of the GOX mass flow rate, which differs from the experimental results reported for room-temperature working fluids. The dimensionless plume length varies between 4 and 6 and is fitted by a correlation relationship with discrepancies of ±5%. The heat transfer coefficient ranges from 0.1 MW/m2K to 0.5 MW/m2K and is also fitted by a correlation relationship with discrepancies of ±15%.

Homotopic morphisms between weighted digraphs

&lt;abstract&gt;&lt;p&gt;In this paper, we consider weighted digraphs and prove that homotopic morphisms between weighted digraphs induce the identical homomorphisms on weighted path homology groups with field coefficients.&lt;/p&gt;&lt;/abstract&gt;

Analytical solution for acoustic radiation force on a sphere near a planar boundary.

Acoustic radiation force on a sphere in an inviscid fluid near a planar boundary, which may be rigid or pressure release, is calculated using spherical wave functions to expand the total pressure field. The condition at the boundary is satisfied with the addition of a reflected wave and an image sphere. The total pressure field, which is exact in the linear approximation, is composed of the incident field, the reflected field, and the scattered fields due to the physical sphere and the image sphere. The expansion coefficients for the pressure field are used to evaluate the acoustic radiation force on the sphere using a known analytical expression obtained from integration of the radiation stress tensor. Calculations illustrate the influence of multiple scattering effects on the radiation force acting on the sphere. The model applies to compressible and elastic spheres and for any incident field structure. An approximation is introduced that extends the analytical model to other types of interfaces, including a fluid-fluid interface. The analytical model is validated by comparisons with an independent finite element model.

МОДЕЛИРОВАНИЕ ВОЗБУЖДЕНИЯ ПОВЕРХНОСТНЫХ ПЛАЗМОН-ПОЛЯРИТОНОВ В ПРЯМОУГОЛЬНОМ НАНОРЕЗОНАТОРЕ НА ОСНОВЕ ЗОЛОТА

This paper considers the modeling of surface plasmon polaritons excitation in a limited nanostructure on the basis of a two-dimensional area discrete model, the area interacts with the oscillator. The nanostructure is a rectangle defined on the metal surface at the interface of the gold–silicon oxide, the surface plasmon–polaritons are excited by an electromagnetic radiation point source located above the metal surface. The dynamics of radiation point source is described by a discrete version of the Van der Pol equation with a small nonlinearity of the source parameters. The parameters of the goldsilicon oxide structure (the wave phase speed, the radiation source frequency, the characteristic time in the system, etc.) will be received from the dispersion relation for surface plasmon–polaritons at a single metal–dielectric interface. The distributions of the wave field in the structure will be analyzed at different positions of the point oscillator and different coupling coefficients of the wave field with the oscillators. The resonant wave field mode composition at different positions of the point oscillator and different coupling coefficients will be found using the two-dimensional Fourier transform of the wave field, the time evolution of excited modes of the wave field amplitudes will be also analyzed. In conclusion, the paper gives applicability limits of the considered model for studying the surface plasmon polaritons excitation in a limited nanostructure.

Investigation on favorable pressure gradient in an atmospheric boundary layer wind tunnel using large‐eddy simulation and its impact on wind field and surface pressure measurement

AbstractA constant cross‐section wind tunnel usually experiences a negative pressure gradient (ie, favorable pressure gradient, FPG), resulting in a certain degree of discrepancy between the simulated and idealized atmospheric boundary layer (ABL) flows. To investigate its impact, three large‐eddy simulation (LES) cases were conducted in this study: one simply reproduced a wind tunnel, one removed the FPG by adjusting the ceiling height, and one reduced the FPG by canceling unnecessary boundary layers associated with the tunnel sidewalls and ceiling. The required ceiling height in the second case was estimated based on the pressure gradient in the first case. The FPG was found mainly generated by the contraction effect induced by the boundary layers over the tunnel walls because it can be largely removed in the third case. In addition, we investigated the mean and standard deviation of the surrounding wind field and surface pressure coefficient of an isolated square‐section building model. Because the FPG in the macroscale ABL is negligible compared with the adverse pressure gradient in the microscale near‐wall boundary layers of the building, the influence of the FPG is negligible in a wind tunnel experiment conducted in a relatively large wind tunnel with a safe blockage ratio.

Instabilities of Transonic Turbulent Flow over a Flat-Sided Wedge

The transonic turbulent two-dimensional airflow over a symmetric flat-sided double wedge is studied numerically. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with ANSYS-18.2 CFX finite-volume solver of second order accuracy on a fine mesh. The solutions demonstrate an extreme sensitivity of the flow field and lift coefficient to variation of the angle of attack α or free-stream Mach number M∞. Non-unique flow regimes and hysteresis in certain bands of α and M∞ are identified. Interaction of shock waves and local supersonic regions is discussed. The study confirms a concept of shock wave instability due to a coalescence/rupture of supersonic regions. In addition to the instability of shock wave locations, the numerical simulation shows a buffet onset, i.e., self-exciting oscillations due to instability of a boundary layer separation at the rear of wedge. Curious flow regimes with positive lift at negative angles α and, vice versa, with negative lift at positive angles α, are pointed out. A piecewise continuous dependence of the lift coefficient on two free-stream parameters, α and M∞, is discussed.

A Leray–Serre spectral sequence for Lagrangian Floer theory

We consider symplectic fibrations as in Guillemin-Lerman-Sternberg, and derive a spectral sequence to compute the Floer cohomology of certain fibered Lagrangians sitting inside a compact symplectic fibration with small monotone fibers and a rational base. We show if the Floer cohomology with field coefficients of the fiber Lagrangian vanishes, then the Floer cohomology with field coefficients of the total Lagrangian also vanishes. We give an application to certain non-torus fibers of the Gelfand-Cetlin system in Flag manifolds, and show that their Floer cohomology vanishes.

Influence of Radiation and Convection on 3D-Casson Hybrid Nanofluid Flow in the Presence of Suction Over a Rotary Sheet

The current research looks at how the radiation affects the convective hybrid Casson 3D flow in the presence of suction. The fluid analysed was a hybrid nanofluid made up of Alumina (Al2O3) and Copper (Cu) nanoparticles diffused in base fluid (Water). After simplification, the flow control equations were programmed and solved employing the MATLAB software and the bvp4c code. Figures depict the study’s most important findings, such as the impact of several physical elements such as convection, radiation, and suction on the velocity profile, mass transfer, temperature field, friction factor, and heat transfer coefficient. According to the key findings, the Casson Hybrid nanofluid has a better property than normal fluids. It can also be deduced that as the scale of the radiation constraint strengthens, the temperature field improves. Tables were used to validate our findings with cited papers.