Theoretical Predictions Research Articles

Integrating Experimental and Computational Insights: A Dual Approach to Ba2CoWO6 Double Perovskites

Double perovskite materials have emerged as key players in the realm of advanced materials due to their unique structural and functional properties. This research mainly focuses on the synthesis and comprehensive characterization of Ba2CoWO6 double perovskite nanopowders utilizing a high-temperature conventional solid-state reaction technique. The successful formation of Ba2CoWO6 powders was confirmed through detailed analysis employing advanced characterization techniques. Rietveld refinement of X-ray diffraction (XRD) and Raman data established that Ba2CoWO6 crystallizes in a cubic crystal structure with the space group Fm-3m, indicative of a highly ordered perovskite lattice. The typical crystallite size, approximately 65 nm, highlights the nanocrystalline nature of the material. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) discovered a distinctive morphology characterized by spherical shaped particles, suggesting a complex particle formation process influenced by synthesis conditions. To probe the electronic structure, X-ray Photoelectron Spectroscopy (XPS) identified cobalt and tungsten valence states, critical for understanding dielectric properties associated with localized charge carriers. The semiconducting character of the synthesized Ba2CoWO6 nanocrystalline material was confirmed through UV-Visible analysis, which revealed an energy bandgap value of 3.3 eV, which aligns well with the theoretical predictions, indicating the accuracy and reliability of the experimental results. The photoluminescence spectrum exhibited two distinct emissions in the blue-green region. These emissions were attributed to the transitions 3P0→3H4, 3P0→3H5, and 3P0→3H6, primarily resulting from the contributions of Ba2+ ions. The dielectric characteristics of the compound were analyzed across a different range of frequencies, spanning from 1 kHz to 1 MHz. Magnetic characterization using Vibrating Sample Magnetometry (VSM) revealed antiferromagnetic behavior of Ba2CoWO6 ceramics at room temperature, attributed to super-exchange interactions between Co3+ and W5+ ions mediated by oxygen ions in the perovskite lattice. Additionally, first-principles calculations based on the Generalized Gradient Approximation (GGA+U) with a modified Becke–Johnson (mBJ) potential were employed to gain a deeper understanding of the structural and electronic properties of the materials. This approach involved systematically varying the Hubbard U parameter to optimize the description of electron correlation effects. These results deliver an extensive understanding of the structural, optical, morphological, electronic, and magnetic properties of Ba2CoWO6 ceramics, underscoring their potential for electronic and magnetic device applications.

Piezoelectret metamaterials with a double-V structure exhibiting tunable piezoelectric effect in a broad range

Piezoelectret metamaterials are a kind of piezoelectrets with distinctive properties such as negative Poisson's ratio and positive piezoelectric d31 coefficient. These materials hold significant promise for applications in sensing and mechanical energy harvesting. In this article, flexible piezoelectret metamaterials with a simple double-V cell structure are designed, and their properties are theoretically analyzed, simulated, and experimentally tested. The results indicate that the effective piezoelectric d33 and d31 coefficients can be tuned over a wide range by adjusting the geometric parameters of the cell. The experimental results are consistent with the theoretical prediction and simulation calculation. Differing from the piezoelectric d33 coefficient, which always has positive polarity, the sign of the piezoelectric d31 coefficient depends on Poisson's ratio of the material. In particular, d31 coefficients are negative for the materials with positive Poisson's ratio, while they have a positive sign when Poisson's ratio is negative. For a piezoelectret metamaterial sample prepared in this study, a large effective piezoelectric d31 coefficient up to 1200 pC/N is achieved experimentally. The significant piezoelectric effects in the piezoelectret metamaterials as well as their excellent mechanical adaptivity to irregular surface structures, such as the curved surfaces of humanoid robots and aircraft wings, introduce a novel solution for diverse applications.

Characterization of the SCR-1 Stellarator Physics: Investigating Plasma Discharge, MHD Equilibrium Calculations, and O-X-B Mode Conversion Feasibility

Abstract The Stellarator de Costa Rica 1 (SCR-1) is a small modular stellarator that serves as a valuable research and training tool for plasma magnetic confinement. This study aimed to analyze the characteristics of SCR-1, including its peripheral systems, technical plasma discharge processes, and advancements in plasma characterization. In addition, this study explored a new heating mechanism and the factors that influence it. The current state of the device and plasma discharge are initially presented. Subsequently, the measurement process was utilized to determine the electronic density and plasma temperature using a single Langmuir probe and the results were compared with theoretical predictions based on the particle and energy balance. Additionally, the VMEC code was employed to calculate magnetic flux surfaces with characteristics such as a low aspect ratio, low beta parameter, negative magnetic shear, and decreasing rotational transform along magnetic flux surfaces. The Mercier criterion was employed to conduct a linear stability analysis, which identified a magnetic well that played a crucial role in the linear stability of the majority of magnetic flux surfaces. Feasibility studies of electron Bernstein waves were conducted using the IPF-FMDC full-wave code. The results obtained from the IPF-FMDC code revealed that the O-X conversion percentage reached a maximum of 63 % when considering radiation reflection in the vacuum vessel. Significant effects of plasma curvature on the O-X wave conversion and normalized electron density scale length were observed, while the change in the SCR-1 heating position did not produce a significant impact. Three damping mechanisms affecting O-X conversion were studied, and one of the principal effects was the SX-FX conversion due to steep electron density gradient. Additionally, stochastic electron heating showed a low electron field amplitude, which is important for limiting the electron Bernstein wave propagation.

High pressure induced superconductivity and chirality-neutral Fermi surface in SrSi2

In this study, we investigate the electronic structure and topological properties of the compound SrSi2 using angle-resolved photoemission spectroscopy (ARPES), electrical transport measurements, and calculations. In contrast to recent theoretical predictions that SrSi2 is a Weyl semimetal with robust Weyl nodes and Fermi arcs, our ARPES measurements on undoped and Ca-doped SrSi2 single crystals show no evidence of the predicted Weyl fermions or Fermi arcs at ambient pressure. Instead, ARPES and transport data show that SrSi2 is a narrow-gap semiconductor at ambient conditions. Our hybrid functional calculations also find a small band gap, in agreement with experiments. However, by applying external pressure, we induce a topological phase transition where the electronic bands overlap and Weyl nodes appear, as confirmed by transport measurements and calculations. Interestingly, we also observe a pressure-induced superconducting transition above 20 GPa. Our results establish SrSi2 as a platform to study the interplay between topological states and superconductivity driven by external pressure. Importantly, our results challenge the previously predicted intrinsic Weyl semimetallic nature of SrSi2 and highlight the need for combined experimental and advanced computational approaches to correctly describe the complex electronic structures in topological materials. Published by the American Physical Society 2024

Synthetic graphs for link prediction benchmarking

Abstract Predicting missing links in complex networks requires algorithms that are able to explore statistical regularities in the existing data. Here we investigate the interplay between algorithm efficiency and network structures through the introduction of suitably-designed synthetic graphs. We propose a family of random graphs that incorporates both micro-scale motifs and meso-scale communities, two ubiquitous
structures in complex networks. A key contribution is the derivation of theoretical upper bounds for link prediction performance in our synthetic graphs, allowing us to estimate the predictability of the task and obtain an improved assessment of the performance of any method. Our results on the performance of classical methods (e.g., Stochastic Block Models, Node2Vec, GraphSage) show that the performance of all methods correlate with the theoretical predictability, that no single method is universally superior, and that each of the methods exploit different characteristics known to exist in large classes of networks. Our findings underline the need for careful consideration of graph structure when selecting a link prediction method and emphasize the value of comparing performance against synthetic benchmarks. We provide open-source code for generating these synthetic graphs, enabling further research on link
prediction methods.

QR-DeepONet: Resolve abnormal convergence issue in deep operator network

Abstract Deep operator network (DeepONet) has been proven to be highly successful in operator learning tasks.
Theoretical analysis indicates that the generation error of DeepONet should decrease as the basis dimension increases, 
thus providing a systematic way to reduce its generalization errors by varying the network hyperparameters.
However, in practice, we found that, depending on the problem being solved and the activation function used, 
the generalization errors fluctuate unpredictably, contrary to theoretical expectations. 
Upon analyzing the output matrix of the trunk net, we determined that this behavior stems from the learned basis 
functions being highly linearly dependent, which limits the expressivity of the vanilla DeepONet.
To address these limitations, we propose QR-DeepONet, an enhanced version of DeepONet using QR decomposition.
These modifications ensured that the learned basis functions were linearly independent and orthogonal to each other.
The numerical results demonstrate that the generalization errors of QR-DeepONet follow theoretical predictions that decrease monotonically as the basis dimension increases and outperform vanilla DeepONet.
Consequently, the proposed method successfully fills the gap between the theory and practice.

Broadening of cloud droplet spectra through eddy hopping: Why did we all have it wrong?

Abstract In situ aircraft observations in adiabatic and close-to-adiabatic cloudy volumes suggest that cloud droplet spectra are often broader than predicted by growth of a droplet population rising from the cloud base. Cloud turbulence has been suggested as one of possible mechanisms for the observed spectral broadening. This paper reviews computational studies of the impact of cloud turbulence on the diffusional growth of cloud droplets in adiabatic cloudy volumes. These studies typically apply direct numerical simulation (DNS) or scaledup DNS approach to represent diffusional growth of cloud droplets embedded within homogeneous isotropic air turbulence. There is also a theory that predicts that the droplet spectral width continuously increases in time because of the individual droplet growth or evaporation within turbulent eddies. This mechanism has been referred to as eddy hopping. This paper expands the discussion in Prabhakaran et al. (J. Atmos. Sci. 2022) and illustrates the fundamental flaw of past computational and theoretical studies. These studies do not consider vertical dispersion of droplet positions that leads to growth of droplets that in the mean move upwards, and to evaporation of those that move downwards. The theoretical prediction comes from confusing spectral broadening with the vertical dispersion of droplet positions when periodic lateral boundaries are used in DNS. Computational examples using a stochastic model mimicking eddy hopping show that droplet spectral width does not continuously increase in time, but it saturates at a small spread. Methodologies for appropriate numerical studies of the adiabatic spectral width evolution in natural clouds are discussed.

Enhanced empirical formulas for α-decay for heavy and superheavy nuclei: Incorporating deformation effects of daughter nuclei

Abstract The latest experimental data of $\alpha$-decay half-lives for 573 nuclei within the range of $52 \leq Z \leq 118$ have been utilized to enhance empirical formulas with updated coefficients. These formulas were enhanced by analyzing the contributions of orbital angular momentum and isospin asymmetry. The effect of deformation of daughter nuclei on the $\alpha$-decay half-life is modeled by incorporating two additional terms, dependent on the quadrupole and hexadecapole deformation parameters, into the empirical formulas for $\alpha$-decay half-lives. Incorporating these deformation-dependent terms, along with angular momentum and isospin asymmetry, improved the standard deviation by approximately $17\%$. The revised empirical formulas for $\alpha$-decay half-lives demonstrated better agreement with experimental data when deformation factors were included. Validation of the modified formulas was conducted through comparisons with recent experimental results and further theoretical predictions. This study presents and compares $\alpha$-decay half-life predictions for several isotopes of superheavy nuclei with $Z = 120-126$, which are yet to be experimentally synthesized. For various isotopes of each element, the variation of $\log_{10} T_{\alpha}$ with changes in neutron number is also explored.

Proton and alpha-particle activation studies of natFe, natCu, natTi and natW targets at low energies

Abstract A study was conducted to examine the production cross sections of nuclear reactions natFe(p,x)56,57,58Co, natCu(p,x)63,65Zn, natTi(p,x)48V, natW(p,x)182m,182g,184g,186Re, natTi(α,x)49,51Cr, natCu(α,x)66,67,68Ga, and natFe(α,x)57Ni,57Co, within the low energy range. Experiments were performed using a 5 MV tandem (Pelletron) accelerator situated at the National Centre for Physics (NCP) in Islamabad, Pakistan we employed the foil activation technique and used an off-line gamma ray spectroscopy system having Genie 2,000 software to detect the reaction products. The data analysis indicated the production of a number of radioisotopes with important applications in nuclear, industrial and medical fields. We compared our measured results with previously evaluated data as well as with theoretical predictions from the TENDL-library, based on TALYS-1.9 code calculations, to validate our findings.

Elastic spherical cloak driven by Bayesian optimization

Abstract The introduction of machine learning algorithms has revolutionized the landscape of invisibility devices design, particularly in the intricate domain of elastodynamics. In this work, we proposed a core-shell configuration to realize elastic sphere cloaks, which was driven by Bayesian optimization algorithm to pinpoint the optimal configuration with high precision. Numerical simulations in solid and aqueous environments are implemented respectively to validate the cloaking efficacy of our design and the parameters identified by the algorithm. The results are in close alignment with theoretical prediction, underscoring the robustness of the proposed method. This approach provides new insights for the designing of elastic wave invisibility devices, and may lead to potential applications in underwater communication and sonar detection.

Design of a Deep Learning-Based Metalens Color Router for RGB-NIR Sensing.

Metalens can achieve arbitrary light modulation by controlling the amplitude, phase, and polarization of the incident waves and have been applied across various fields. This paper presents a color router designed based on metalens, capable of effectively separating spectra from visible light to near-infrared light. Traditional design methods for meta-lenses require extensive simulations, making them time-consuming. In this study, we propose a deep learning network capable of forward prediction across a broad wavelength range, combined with a particle swarm optimization algorithm to design metalens efficiently. The simulation results align closely with theoretical predictions. The designed color router can simultaneously meet the theoretical transmission phase of the target spectra, specifically for red, green, blue, and near-infrared light, and focus them into designated areas. Notably, the optical efficiency of this design reaches 40%, significantly surpassing the efficiency of traditional color filters.

Effects of Solid-to-Fluid Conductivity Ratio on Thermal Convection in Fluid-Saturated Porous Media at Low Darcy Number

Abstract This study presents experimental data on the effects of the solid-to-fluid thermal conductivity ratio on natural convective heat transfer in a fluid-saturated porous medium heated from below. Argon is used as the saturating fluid, while a bed of glass, steel, or aluminum spheres constitutes the solid porous matrix. Emphasis is placed on attaining high Rayleigh numbers while maintaining low Darcy numbers (5.68 × 10−8 ≤Da≤5.22 × 10−7). At low modified Rayleigh numbers (Ra*) corresponding to the Darcy regime, the Nusselt number is independent of the medium conductivity. As Ra* increases and the system transitions into Forchheimer regime, the data diverge, with Nusselt numbers decreasing with increased thermal conductivity ratio at a fixed Ra*. This non-intuitive result is shown to be the result of the traditional choice of Ra* and Da as the controlling parameters since the heat transfer coefficient appears independent of the conductivity ratio. Scaling arguments are used to identify transition points between the regimes, which yield the transition criterion Ra* ~ Prp, where Prp is the modified Prandtl number. When the data are expressed by scaling with Prp, it is shown that the data for multiple parameter combinations collapse onto a single curve, which also agrees well with theoretical predictions. In light of this finding, the data from available literature are assessed, and it is proposed that deviations from theory are likely the result of the strong porous medium condition (low Da) not being satisfied.

Selective Flotation of Galena and Sphalerite from a Pb/Zn Complex Sulfide Ore Using Saline Water: The Effects of Xanthate and Pine Oil Addition

ABSTRACT This study focuses on the effects of saline water on the selective flotation of a Pb/Zn complex sulfide ore. Batch flotation experiments were carried out using NaCl solutions as well as seawater. It was found that increasing NaCl concentration in solution from 1 mM to 500 mM had a positive effect on the Pb and Zn recoveries. When comparing recoveries in the highest NaCl concentration in solution to seawater, Pb recovery decreased by 48%, most likely due to the presence of additional ions such as Ca2+ and Mg2+. On the contrary, Zn recovery in seawater increased by 55%, and this increase could be attributed to the SO4 2- ion effect from seawater. DLVO-like theoretical analyses using pH-dependent charge regulated models of surface charge were employed to study particle-particle and particle-bubble interactions during sulfide ore flotation under different NaCl concentrations and solution pH. The theoretical predictions of the models supported the experimental results, with a stronger particle-bubble attraction predicted by the models at higher NaCl concentrations. Overall, results demonstrated the potential of using the theoretical predictions for describing the various interactions during sulfide ore flotation in saline water.

Mechanisms of Noise Transmission in Velocity Broad-Band Seismometers: Modeling and Analysis

This paper focuses on the noise transmission process, presenting a comprehensive noise transfer model for velocity broad-band seismometers, which elucidate the transmission mechanisms of five distinct noise sources. We analyzed the spectral characteristics of the noise transfer functions across the forward path, feedback path, and data acquisition stages, with a focus on gains, corner frequencies, and the 0 dB point. Numerical simulations and experiments using the CS60 seismometer showed excellent agreement with theoretical predictions, validating the proposed model and associated noise optimization strategies. This study identified effective methods to reduce noise transfer gains, including optimizing the input and feedback mechanical constants and refining gains at various stages.

Enhanced Imbibition in Liquid-Infused Coated Microchannels.

Spontaneous capillary imbibition has the potential to improve the performance of many micro and nanodevices since it does not require an external energy source to drive a fluid flow. Despite this advantage, controlling and reducing the friction exerted by the channel walls, which limits the speed of the liquid, remains a challenge. Here, we demonstrate experimentally that infusing the walls of a channel with a liquid lubricant substantially speeds up the imbibition process and reduces the overall viscous friction. By varying the viscosity of the lubricant, we observe a substantial reduction of the imbibition time of up to 50%. Our experimental results are in good agreement with previous theoretical predictions, providing a solid framework to study low-resistance spontaneous imbibition processes.

Three degrees of freedom rigid-soft coupling biomimetic hip joint driven by dielectric elastomer

Abstract Dielectric elastomer (DE) has an attractive combination of high energy density, large strain, and fast response. A growing number of DE actuators are being used as driving materials in rigid-soft coupling joints. For better structural design, the mapping relations from the musculoskeletal system of the human hip joint to the biomimetic hip joint mechanism have been established. Inspired by the human musculoskeletal system, the configuration of the three-degree-of-freedom rigid-soft coupling hip joint based on DE is proposed. The configuration includes six soft-driving limbs and one passive rigid limb. The soft-driving limb driven by the fiber-constrained dielectric elastomer actuator (FCDEA) does not contain passive rigid joints. Based on the Gent material model, the electromechanical coupling model of FCDEA is established. A mapping model is established between the voltage applied to the soft-driving limb of the biomimetic hip joint and the posture of the moving platform in the case of deflection and torsion. A single FCDEA is prepared and its electro-responsive deformation performance is tested through experiments. As a demonstration, a prototype of the biomimetic hip joint is developed. After applying voltage, the deflection angle and the torsion angle of the biomimetic hip joint are tested and the curve of voltage and rotation angle is drawn. The experimental results agree well with the theoretical predictions. This article can provide theoretical references for improving the performance of rigid-soft coupling hip joints.

Monitoring and Analysis of Circumferential Pressure for Long‐Distance Pipe Jacking Construction in Composite Strata

ABSTRACTAt present, the monitoring methods of mechanical parameters of pipe in the process of pipe jacking construction generally have the disadvantages of low data reliability and poor timeliness. Especially in the jacking construction in complex strata, if the jacking parameters and lubrication grouting parameters cannot be adjusted in real time according to the circumferential pressure, it is easy to cause pipe sticking accident. Based on the Inner Mongolia Water Diversion Project from ChaorHe to Liaoning, this paper adopts the LPWA low‐power wide‐area network wireless sensing system based on 5G and IOT technology to realize the real‐time wireless monitoring of the contact pressure and lubrication grouting pressure of the underground pipe jacking pipe. Through the parameters obtained by the wireless sensing system, the stress characteristics of a specific pipe traversing different strata and under different working conditions were studied, and the change rule of circumferential contact pressure of the pipe and the influence of various factors on it were analyzed. The results show that: by analyzing the circumferential contact pressure obtained by the wireless sensing system, the pressure distribution of the pipe in the top soft and bottom hard strata is right>left>bottom>top; in the full‐section strata, the destruction of the lubricating mud sleeve will lead to the same contact pressure on one side and the bottom of the pipe; when the pipe traverse the interfaces of different rock strata, the stability of the lubricating mud sleeve will be affected, and thus the circumferential contact pressure will be altered. The above results are consistent with the theoretical prediction and can provide reference for the actual project. In conclusion, the wireless sensing system can accurately reflect the distribution of circumferential contact pressure of the pipe under different strata, and provide reliable data support for improving construction efficiency and safety.

The Bottleneck in the Scalar Dissipation Rate Spectra: Dependence on the Schmidt Number

The mean dissipation rate of turbulent energy reaches a constant value at high Taylor–Reynolds numbers (Rλ). This value is associated with the well-scaling dissipation spectrum in Kolmogorov units, where the maximum corresponds to the bottleneck peak. Even the scalar dissipation rate at the high Rλ considered in the present direct numerical simulations attains a constant value as Sc increases. In this scenario, the maximum of the scalar dissipation spectra reaches its peak within the bottleneck, starting at Sc>0.5. A qualitative explanation for the formation of the two bottlenecks is related to the blockage of energy transfer from large to small scales in the inertial ranges. Within the bottleneck, the self-similar, ribbon-like structures transition into the rod-like structures characteristic of the exponential decay range. Investigating the viscous dependence of the bottleneck’s amplitude may be aided by examining the evolution of a passive scalar. As Sc decreases, the scalar spectra undergo changes across the wave number k range. The bottleneck is dismantled, and at very low Sc values, the spectrum tends towards Batchelor’s theoretical prediction, diminishing proportionally to k−17/3. To comprehend the flow structures responsible for the bottleneck, visualizations of θ∇2θ and probability density functions at various Sc values are presented and compared with those of ui∇2ui. The numerical method employed for generating three-dimensional spectra and quantities such as energy and scalar variance dissipation in physical space must be accurate, particularly in resolving small scales. This paper additionally demonstrates that the second-order finite difference scheme conserving kinetic energy and scalar variance in the inviscid limit in viscous simulations accurately predicts the exponential decay range in one-dimensional and three-dimensional turbulent kinetic energy and scalar variance spectra.

Mixed QCD-EW corrections to W-pair production at electron-positron colliders

The discrepancy between the CDF measurement and the Standard Model theoretical prediction for the W-boson mass underscores the importance of conducting high-precision studies on the W boson, which is one of the predominant objectives of proposed future e+e− colliders. We investigate in detail the production of W-boson pairs at e+e− colliders, and compute the next-to-next-to-leading order mixed QCD-EW corrections to both the integrated cross section and various kinematic distributions. By employing the method of differential equations, we analytically calculate the two-loop master integrals for the mixed QCD-EW virtual corrections to e+e− → W+W−. Utilizing the Magnus transformation, we derive a set of canonical master integrals for each integral family. This canonical basis satisfies a system of differential equations in which the dependence on the dimensional regulator is linearly factorized from the kinematics. We then express all these canonical master integrals as Taylor series in ϵ up to ϵ4, with coefficients articulated in terms of Goncharov polylogarithms up to weight four. Upon applying our analytic expressions of these master integrals to the phenomenological analysis of W-pair production, we observe that the O(ααs) corrections are significantly impactful in the α(0) scheme, particularly in certain phase-space regions. However, these mixed QCD-EW corrections can be heavily suppressed by adopting the Gμ scheme.

Experimental investigation of heralded Gaussification of phase-randomized coherent states of light

Probabilistic heralded Gaussification of quantum states of light is an important ingredient of protocols for distillation of continuous variable entanglement and squeezing. An elementary step of the heralded Gaussification protocol consists of interference of two copies of the state at a balanced beam splitter, followed by conditioning on the outcome of a suitable Gaussian quantum measurement on one output mode. When iterated, the protocol either converges to a Gaussian state or diverges. Here, we report on experimental investigation of the convergence properties of iterative heralded Gaussification. We experimentally implement two iterations of the protocol, which requires simultaneous processing of four copies of the input state. We utilize the phase-randomized coherent states as the input states, which greatly facilitates the experiment because these states can be generated deterministically, and their mean photon number can easily be tuned. We comprehensively characterize the input and partially Gaussified states by balanced homodyne detection and quantum state tomography. Our experimental results are in good agreement with theoretical predictions and they provide new insights into the convergence properties of heralded quantum Gaussification.