Equal Radii Research Articles

Characterization of ultrasonic induced damage on multi-scale pore/fracture in coal using gas sorption and μ-CT 3D reconstruction

Ultrasonic physical stimulation is a promising approach of coalbed methane enhancement recovery. This study is devoted to quantitatively characterizing the damage of multi-scale pores and fractures in coal induced by power ultrasonic stimulation using the gas sorption and CT image-based 3D reconstruction. The gas sorption tests show that the ultrasound treatment (3 kW, 25 Hz, 2 h) increased the maximum N2 sorption quantities (by 75.44 %–111.8 %), the average pore diameter by 12.15 %–20.81 %, and the pore surface area (by 30.99 %–56.02 %) in the tested coal. The mesopore volumes increase by 16.46 %–79.15 %, and the macropore volumes increase by 2.38 %–14.82 % after the ultrasound treatment, which reveals that the ultrasound implemented in this study is more efficient for structure modification in pore with scale of 2–50 nm. The CT image-based characterization shows that fracture volume increased by 8.11 %–11.81 %, and the fracture surface increased by 13.92 % −21.63 %, and the average equivalent diameter increased by 6.76 %–10.74 %, and the porosity increased by 8.1 %–11.86 % for the tested coal subjected to ultrasound treatment. Based on the pore network model, the fracture connectivity was quantitatively analyzed, and it shows that pore throat number increased by 17.62 %–45.76 %, and the average equal radius of pore throat increased by 3.86 %–4.83 %. The proportion of connected fractures in the total fractures was increased by a maximum of 12.78 % in the tested coal after ultrasound treatment. The results show that ultrasound stimulation can significantly improve the multi-scale structure of pores and fractures of coal, which will promote gas desorption, diffusive and Darcian flow flux in coal seam, and enhance coalbed methane production.

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Highly Selective Photocatalytic Conversion of Glucose on Holo-Symmetrically Spherical Three-Dimensionally Ordered Macroporous Heterojunction Photonic Crystal

Effect of Rotor-Stator Spacing on Compressor Performance at Variable Operating Conditions

This paper investigates the effect of rotor-stator spacing and operating conditions on compressor performance and the rotor-stator interaction mechanism. We focus on the interaction between the rotor wake and the stator’s flow field through several unsteady numerical simulations aiming at a transonic compressor stage in the equal radius flow path with two-axial spacing at three operating conditions. The simulation results indicate that the time-averaged efficiency almost declined by 0.6 points due to mixing loss in the spacing ranging from close to far at nominal and low load operating conditions. The deep upstream wake leads to corner separation at high load conditions due to close spacing, imposing a fluctuating efficiency at the frequency where the stator wake near the shroud oscillates, as found by the dominant frequency screening method. Under all conditions, the wake transport can reduce the static pressure on the pressure surface and weaken the hub leakage flow afterward.

Computationally Attractive and Location Robust Estimator for IoT Device Positioning

Locating a device is a basic element for many Internet of Things (IoT) applications. In particular, it often demands an algorithm having low complexity to limit the energy consumption and most important, sufficient robustness without knowing the device in the near-field for point localization or in the far-field for direction of arrival (DOA) estimation. This article proposes a new localization algorithm that can achieve the two purposes, with the theoretical analysis to validate the optimal accuracy and the real data experiment to support the promising performance. The first objective is achieved by a closed-form solution and the second is accomplished by using the modified polar representation (MPR) of the source position, based on a new formulation for the localization problem. While the MPR localization method has been introduced before, it is not sufficiently robust for IoT application to handle the large equal radius (LER) scenario or the presence of sensor position errors. The proposed algorithm uses a different MPR formulation, which is able to handle the LER scenario, sensor position errors, and has low computational complexity.

Dual circularly polarized semi‐cylindrical hybrid dielectric resonator antenna for X and Ku ‐band applications

A hybrid dielectric resonator antenna (HDRA) with a single-probe generating circular polarization (CP) simultaneously at X and Ku-bands is presented in this article. A novel hybrid structure of semi-circular patch and semi-cylindrical dielectric resonator (DR) of equal radius are combined with a single-point probe feed to achieve dual-functional wide CP bands. The asymmetric nature of the semi-circle and semi-cylinder produces two orthogonal modes in their respective bands for CP radiation. The measured impedance bandwidth obtained by the proposed structure is 36.49% (3750 MHz) at X-band and 14.23% (2100 MHz) at the Ku-band range of frequencies. Axial ratio (AR) bandwidth of 30.39% (3100 MHz) is obtained at X-band and 13.24% (1950 MHz) at Ku-band. The measured gains are 9.54 dBic at 9.6 GHz and 6.55 dBic at 15 GHz. An excellent agreement between the computed and measured results validates the design of the dual functional circularly polarized HDRA.

Geometry of Gyrogroups via Klein’s Approach

Using Klein's approach, geometry can be studied in terms of a space of points and a group of transformations of that space. This allows us to apply algebraic tools in studying geometry of mathematical structures. In this article, we follow Klein's approach to study the geometry $(G, \mathcal{T})$, where $G$ is an abstract gyrogroup and $\mathcal{T}$ is an appropriate group of transformations containing all gyroautomorphisms of $G$. We focus on $n$-transitivity of gyrogroups and also give a few characterizations of coset spaces to be minimally invariant sets. We then prove that the collection of open balls of equal radius is a minimally invariant set of the geometry $(G, \Gamma_m)$ for any normed gyrogroup $G$, where $\Gamma_m$ is a suitable group of isometries of $G$.

Influence of the Process Input Parameters on the Cross-Wire Weld Breaking Force

Cross-wire welding is a type of electric resistance welding called projection welding that is used in the production of a variety of products. This paper deals with the case where steel wires of equal radii are joined together to form a reinforced steel mesh. The objective of the study is to determine the correlation between the welding parameters and the breaking force of the weld. Each weld is cut out from the given wire mesh and tested separately by destructive testing on the universal testing machine. A modular testing fixture was constructed for the tests. Although the tests are still in the initial stage, the results already give a good insight into the influence of the process input parameters on the breaking strength of the weld.

An Improved Upper Bound on the Number of Billiard Ball Collisions

We give a new upper bound $K_+$ on the number of totally elastic collisions of $n$ hard spheres with equal radii and equal masses in $R^d$. Our bound satisfies $\log K_+ \leq c(d) n \log n$.

Stationary Sets and Asymptotic Behavior of the Mean Curvature Flow with Forcing in the Plane

We consider the flat flow solutions of the mean curvature equation with a forcing term in the plane. We prove that for every constant forcing term the stationary sets are given by a finite union of disks with equal radii and disjoint closures. On the other hand for every bounded forcing term tangent disks are never stationary. Finally in the case of an asymptotically constant forcing term we show that the only possible long time limit sets are given by disjoint unions of disks with equal radii and possibly tangent.

Research on Photo Catalytic Performance of TiO2 Film Doped with Li+

Based on sol-gel method and spin coating process, TiO2 film doped with Li+ is prepared by utilizing analytical pure butyl titanate, lithium nitrate, absolute ethanol, glacial acetic acid, acetylacetone and deionized water as raw material. The Li+ ion which has equal radius as Ti4+ ion is chosen in experiments for doping and modification. Experimental results show certain increase of catalytic efficiency in TiO film doped with Li+. However, the increase level of catalytic efficiency gradually shows some decrease when the dopant amount changes from 0.025mol to 0.1mol. Catalytic efficiency is raised to 25.7% when the dopant amount is 0.025mol.

Ultrahigh-Q system of a few coaxial disks

Abstract Resonant modes of high contrast dielectric disk have finite Q-factors in the subwavelength range due to radiation leakage into the surrounding space. That leakage can be reduced considerably (a few times) by exploiting of the mechanism of destructive interference of two modes for avoided crossing of resonances (ACR) (Rybin et al. M. V. Rybin, K. L. Koshelev, Z. F. Sadrieva, et al., “High-Q Supercavity Modes in Subwavelength Dielectric Resonators,” Phys. Rev. Lett., vol. 119, p. 243901, 2017.). In the present paper we report suppression of radiation leakage by a few orders in magnitude via the ACR in the structure of three and four different coaxial disks. For fine multi-scale tuning of disks we reveal the ultrahigh-Q resonances of order 105 for the case of three disks and of order 106 for the case of four coaxial disks of equal radii.

Fluctuating Number of Energy Levels in Mixed-Type Lemon Billiards

In this paper, the fluctuation properties of the number of energy levels (mode fluctuation) are studied in the mixed-type lemon billiards at high lying energies. The boundary of the lemon billiards is defined by the intersection of two circles of equal unit radius with the distance 2B between the centers, as introduced by Heller and Tomsovic. In this paper, the case of two billiards, defined by B=0.1953,0.083, is studied. It is shown that the fluctuation of the number of energy levels follows the Gaussian distribution quite accurately, even though the relative fraction of the chaotic part of the phase space is only 0.28 and 0.16, respectively. The theoretical description of spectral fluctuations in the Berry–Robnik picture is discussed. Also, the (golden mean) integrable rectangular billiard is studied and an almost Gaussian distribution is obtained, in contrast to theory expectations. However, the variance as a function of energy, E, behaves as E, in agreement with the theoretical prediction by Steiner.

Improved KNN algorithms of spherical regions based on clustering and region division

The KNN classification algorithm is one of the most commonly used algorithm in the AI field. This paper proposes two improved algorithms, namely KNNTS, and KNNTS-PK+. The two improved algorithms are based on KNNPK+ algorithm, which uses PK-Means ++ algorithm to select the center of the spherical region, and sets the radius of the region to form a sphere to divide the data set in the space. The KNNPK+ algorithm improves the classification accuracy on the premise of stabilizing the classification efficiency of KNN classification algorithm. In order to improve the classification efficiency of KNN algorithm on the premise that the accuracy of KNN classification algorithm remains unchanged, KNNTS algorithm is proposed. It uses tabu search algorithm to select the radius of spherical region, and uses spherical region division method with equal radius to divide the data set in space. On the basis of the first two improved algorithms, KNNTS-PK+ algorithm combines them to divide the data sets in space. Experiments are carried out on the new data set and the classification results were obtained. Results revealed show that the two improved algorithms can effectively improve the classification accuracy and efficiency after the data samples are cut reasonably.

Propagation of a planar shock wave along a convex–concave ramp

The propagation of a normal shock wave along a coupled convex–concave surface of equal radii has been analysed experimentally and numerically in this study. The experimental and numerical studies were conducted using a similar geometry as of that used by Ram et al. (J. Fluid Mech., vol. 768, 2015, pp. 219–239) for studying the shock wave transition from regular reflection to Mach reflection. Many interesting flow features such as shock wave transitions over the ramp, characteristics of the induced flow behind the shock wave and the development of a stationary separation shock wave have been observed in the study. The numerical results are validated with experimental data. While the shock wave transitions over the ramp are found to depend mainly on the ramp geometry, the characteristics of the stationary shock wave and the flow separation in the concave region of the ramp surface have been found to vary with the shock wave Mach numbers.

ПОРОМАСШТАБНОЕ МОДЕЛИРОВАНИЕ ПОТОКА ЖИДКОСТИ В ПРОНИЦАЕМЫХ СФЕРАХ С ИСПОЛЬЗОВАНИЕМ ПРОЕКЦИОННОГО МЕТОДА ДЛЯ НЕСЖИМАЕМЫХ УРАВНЕНИЙ НАВЬЕ-СТОКСА

The direct numerical simulation (DNS) is an effective and useful tool in the two-phase fluid flow studying. The projection method on the staggered grid was applied in this paper to solve the incompressible Navier-Stokes equations in irregular domains at the pore-scale level (irregular boundary is presented by its level-set function). The permeability of porous medium which was constructed by the random positioning of penetrable spheres of equal radii were numerically calculated and validated by comparing with theoretical estimations of permeability based on the numerical solution of the lattice-Boltzmann equation in irregular domains in previous works. All numerical calculations were performed using PARIS simulator.

BVRcIc Observations, Third-body Orbital Study, and Analysis of the UV Leo-type, Pre-W UMA Binary V642 Virginis

Abstract V642 Vir is a polar spotted, well-detached, UV Leo-type, low-mass, pre-WUMa (T1 ∼ 4250K, ∼K6V) eclipsing binary. It was observed in 2020 April, May, and June at the Dark Sky Observatory in North Carolina, USA with the 0.81 m reflector of Appalachian State University. A total of 88 timings were used in our 22-year period study which included 12 Transiting Exoplanet Survey Satellite (TESS) timings. The O − C plots show a low-amplitude oscillation of residuals that points to the existence of an orbiting third body, a dwarf of minimum mass, 0.15 M ⊙ in an eccentric orbit (e = 0.41), with an orbital period of 20.07 yr. The odd light curves of V642 Virginis indicate that it has polar spots similar to UV Leo and the recently published V1023 Per. Its present large polar spot region indicates that it must have a strong magnetic field and that it is synchronously rotating. The BVRcIc simultaneous Wilson–Devinney Program solution gives a detached binary (primary and secondary components are underfilling their respective Roche Lobes, with 76% and 78% fill outs respectively). The cool spot region models near the pole of the primary component (centered at 10° colatitude) and is angled toward the secondary component. Its large radius (68°) and T-fact (Tspot/Tsurface = 0.69) also attest to the conclusion of the strength of the magnetic field. The small ΔT in the components (∼318 K) and mass ratio near unity (0.9542 ± 0.0005) show that the stars are similar in spectral type (secondary ∼K9V). The inclination is high, ∼86.87 ± 0.04°, yet there is no time of constant light due to the two stars’ essentially equal radii.

The effects of microstructural parameters on the electrochemical properties of LSM-LSCF composite cathode by the particle-based discrete element method

In this paper, the particle packing-based discrete element method is applied to study the correlations between the microstructural parameters and electrochemical performances of LSM-LSCF composite electrodes. Firstly, through the verification of domain size independence and the comparison with the percolation theory, the computational domain size and effectiveness of the particle packing are determined. Then, the changes of the electrochemical reaction sites in the composite electrode with the LSM volume fraction under two different ratios of particle radius are investigated, including the LSM-LSCF-pore three-phase boundaries (TPBs) per electrode volume, TPBs per electrolyte surface, and percolated LSCF-pore double phase boundaries (DPBs). The distribution characteristics of the LSM-LSCF-pore TPBs within and outside the threshold volume fraction zone at different particle size ratio cases are obtained. When the particles are of equal radius, the formation of both percolated e−, O2−, and O2 transport paths is in the LSM volume fraction range of 0 to 0.7, due to the electronic conducting path is fully connected. The distribution characteristics of the LSCF-pore DPBs within the electrode in the percolation area and outside the percolation area are obtained respectively. This work is of great significance for the follow-up study of the physical and electrochemical processes within porous composite electrodes based on large-scale complex morphology.

A simple and easy method to quantify the cool island intensity of urban greenspace

Accurately and easily quantifying the greenspace cool island intensity (GCII) is important to understand the cooling effect of urban greenspace for better urban greenspace planning and management. This study proposed two new methods (i.e., equal area method and equal radius method) to estimate GCII and compared them with two old methods (i.e., turning point method and fixed radius method) in terms of the GCII magnitudes, spatial variations, relationships with greenspace size, and the estimation of optimal greenspace size in cooling the environment (i.e., threshold value of efficiency (TVoE)). We performed the analysis based on Landsat derived land surface temperature (LST) in seven Chinese cities with varied climate background and geographic variations. The results showed that: (1) Different methods significantly impacted the estimated GCIIs with higher values by the turning point method and lower values by the equal area method. (2) GCIIs by different methods were positively and significantly correlated with each other and characterized similar spatial heterogeneities. (3) GCIIs by all methods showed significantly positive logarithmic relationships with greenspace area with higher R2 observed by the equal area method. (4) The four methods estimated close TVoEs with no significant difference among them. We recommend the equal radius method to quantify GCII for its equal effectiveness but easier calculation compared to other methods.

Classical Casimir free energy for two Drude spheres of arbitrary radii: A plane-wave approach

We derive an exact analytic expression for the high-temperature limit of the Casimir interaction between two Drude spheres of arbitrary radii. Specifically, we determine the Casimir free energy by using the scattering approach in the plane-wave basis. Within a round-trip expansion, we are led to consider the combinatorics of certain partitions of the round trips. The relation between the Casimir free energy and the capacitance matrix of two spheres is discussed. Previously known results for the special cases of a sphere-plane geometry as well as two spheres of equal radii are recovered. An asymptotic expansion for small distances between the two spheres is determined and analytical expressions for the coefficients are given.

A conceptual methodology for site exclusion boundary and site large early release frequency for multi-unit nuclear power plants site

Probabilistic Safety Assessment (PSA) risk metrics Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) are currently applied for single NPP unit. The purpose of the work is to arrive at quantitative value for LERF for a site consisting of many NPPs. For this objective, the work proposes to define an exclusion boundary for the whole site (site exclusion boundary) which is different from exclusion boundary for one NPP. At a site, the exclusion boundaries of the individual NPPs may overlap or can be separate. In the present research, various concepts of total exclusion boundary length for the site are delineated upon using the exclusion radius/boundary of individual NPPs. A case study for a hypothetical site consisting of three NPP units was considered for the demonstration of the proposed methodology. The NPPs have same power level and equal radius of exclusion boundary. LERF results are available for individual NPPs and those accident sequences are relevant that (initiating events are independent events or common cause events) that cause release of more than 4% of core I-131 radioactive nuclide within 10 h of accident. The radionuclide dispersion was calculated using Gaussian plume model for dose at various locations on the site exclusion boundary for the multiple NPP site. The calculation of site LERF was carried out for various locations on the site exclusion boundary for a specific configuration of NPPs at site.