Surface Boundary Research Articles

A Flexible Hierarchical Framework for Implicit 3D Characterization of Bionic Devices.

In practical applications, integrating three-dimensional models of bionic devices with simulation systems can predict their behavior and performance under various operating conditions, providing a basis for subsequent engineering optimization and improvements. This study proposes a framework for characterizing three-dimensional models of objects, focusing on extracting 3D structures and generating high-quality 3D models. The core concept involves obtaining the density output of the model from multiple images to enable adaptive boundary surface detection. The framework employs a hierarchical octree structure to partition the 3D space based on surface and geometric complexity. This approach includes recursive encoding and decoding of the octree structure and surface geometry, ultimately leading to the reconstruction of the 3D model. The framework has been validated through a series of experiments, yielding positive results.

New charged anisotropic solution in f(Q)-gravity and effect of non-metricity and electric charge parameters on constraining maximum mass of self-gravitating objects

In the present article, A new class of singularity-free charged anisotropic stars is derived in f(Q)-gravity regime. To solve the field equations, we assume a particular form of anisotropy along with an electric field and obtain a new exact solution in f(Q)-gravity. The explicit mathematical expression for the model parameters is derived by the smooth joining of the obtained solutions with the exterior Reissner–Nordstrom de-Sitter solution across the bounding surface of a compact star along with the requirement that the radial pressure vanishes at the boundary. We have modeled four self-gravitating pulsar objects such as LMC X-4, PSR J1903+327, PSR J1614-2230, and GW190814 in our current study and predict the radii of these objects that fall between 8 and 10 km. Furthermore, the physical validity of the solution is performed for self-gravitating object PSR J1614-2230 with mass 1.97±0.04M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.97\\pm 0.04~M_{\\odot }$$\\end{document} with radius 10 km. The solution successfully fulfills all the physical requirements along with the stability and hydrostatic equilibrium conditions for a well-behaved model. The non-metricity f(Q)-parameter χ1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi _{_1}$$\\end{document} and electric charge parameter η\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta $$\\end{document} play an important role in the maximum mass of the objects. The maximum mass increases when χ1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi _{_1}$$\\end{document} and η\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta $$\\end{document} increase but a non-collapsing stable object can be obtained when χ1≤0.0205\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi _{_1}\\le 0.0205$$\\end{document} and η≤0.0006\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta \\le 0.0006$$\\end{document}.

An efficient pseudoelastic pure P‐mode wave equation and the implementation of the free surface boundary condition

AbstractBased on the elastic wave equation, a pseudoelastic pure P‐mode wave equation has been recently derived by projecting the wavefield along the wavefront normal direction. This pseudoelastic pure P‐mode wave equation offers an accurate simulation of P‐wave fields with accurate elastic phase and amplitude characteristics. Moreover, considering no S‐waves are involved, it is computationally more efficient than the elastic wave equation, making it an excellent choice as a forward simulation engine for P‐wave exploration. Here, we propose a new pseudoelastic pure P‐mode wave equation and apply the stress image method to it to implement the free surface boundary condition. The new pseudoelastic wave equation offers significantly improved computational efficiency compared to the previous pseudoelastic wave equation. Additionally, the wavefields simulated by this new pseudoelastic wave equation exhibit clear physical interpretations. We evaluate the accuracy of the new wave equation in simulating elastic P‐waves by employing a model with high‐velocity contrasts. We find that this new equation, which purely admits P‐waves, though having exact amplitude and phase behaviour as the elastic waves for transmission components, the amplitudes slightly suffer in the scattering scenario. The difference in amplitude between the elastic and our pseudoelastic increases as the contrast in velocity at the interface (interlayer velocity ratio) increases, especially the S‐wave velocities. This has negative implications on scattering from the free surface boundary condition or the sea bottom interface, especially if the shear wave velocity below the surface or the sea bottom is high. However, in cases where, like for land data in the Middle East, the transition to a free surface is smoother, the accuracy of the pseudoelastic equation is high. In all cases, regardless of the interlayer velocity ratio, the accuracy of the pseudoelastic wave equation in simulating the elastic case, for scattered waves, exceeds that of the acoustic wave equation in phase and amplitude.

Investigating surface and internal waves and viscosity effects in two-layer fluids with a streamlined moving body using fully nonlinear simulation and experiment

Waves generated by a moving submerged moving body were analyzed in a two-layer density fluid. The experiments were performed in a two-dimensional towing tank and compared to the numerical results from a two-dimensional, fully nonlinear numerical towing tank (NTT) based on potential flow. The experimental conditions were determined by the relationship between the depth-dependent Froude number and the critical Froude number in baroclinic mode. The study was performed with various body velocities, changing the upper and lower fluid depth while maintaining the total water depth. An artificial damping coefficient was applied to the entire free surface and interface boundary condition to simulate the viscosity effect of the fluid interface. When the baroclinic mode was dominant, internal precursor soliton waves and depression waves were similar to the experimental results with strong nonlinearity. In contrast, the trailing waves were significantly different from the experimental results without applying an artificial damping scheme. A comparison with the experimental data showed that the effects of the fluid viscosity can be simulated with an appropriate damping coefficient. As the body velocity increases, the depressed or rising waves associated with the baroclinic mode are mixed with the trailing waves of the barotropic mode. As the depth of the upper fluid decreases, the characteristics of the baroclinic mode decrease, and the barotropic mode becomes dominant under the same velocity conditions.

The influence of the bounding surface on the structural ordering of short chains of oligoetherimides.

In this study, we have conducted a comparative analysis of the structural ordering of short oligoetherimide chains (dimers) near the bounding surface, depending on the structure of that surface. In order to clarify the possibility of oligoetherimide ordering along the symmetry axes of graphene, two types of bounding surfaces were considered: graphene, with a regular discrete position of interaction centers (carbon atoms), and a smooth, structureless impermeable wall. The chemical structures of the considered dimers consist of two repeating units of BPDA-P3, ODPA-P3, or aBPDA-P3 thermoplastic polyetherimides. Using all-atom molecular dynamics simulations, the process of structural ordering of the dimers near the surface of the graphene or wall was established. The ODPA-P3 and BPDA-P3 dimers form an ordered state near the graphene surface, while the aBPDA-P3 dimers do not demonstrate structural ordering. The simulation results confirmed that the ordering direction of the BPDA-P3 and ODPA-P3 dimers near the graphene surface is chosen randomly. Comparison of the oligoetherimide structure formed near the attracting wall without a symmetrical location of the interaction centers shows the similarity of the ordering of dimers near the graphene surface and the wall. As in the case of the graphene surface, the ordering of oligoetherimide molecules near the structureless wall demonstrates one direction of ordering. Therefore, we confirmed that the key factor for the onset of ordering is the presence of a confining surface, rather than the symmetrical arrangement of interaction centers in the substrate structure.

A Surface Determination Technique for Dimensional and Geometrical Analysis in Industrial X-ray Computed Tomography

Industrial X-ray computed tomography (XCT) is a nondestructive technique that can measure workpieces with non-accessible internal features or multimaterial components and assess the dimensional properties of assemblies in assembled states. Surface determination is one of its most crucial steps, which consists of determining boundary surfaces between a solid material and the surrounding air or between different solid materials. It allows for extracting surface points and assessing different features of the object from the data acquired through XCT scans. This task is particularly complex because of challenges associated with material properties, artefacts and noise. The main objective of this work is to assess not just the dimensional but also the geometric characteristics of industrial parts, which requires a more accurate definition of surface points. Therefore, we propose a new surface determination technique (SDT) in XCT to achieve subvoxel accuracy in determining surface points. We demonstrated the effectiveness and stability of our method by comparing it with other SDTs documented in the literature or with results from commercial software. The validation involved measuring various attributes, such as diameter, cylindricity and flatness, of a multi-stepped aluminium part calibrated by a coordinate measuring machine.

Anisotropic Durgapal-Fuloria compact stars in f(R) gravity

This study presented a new exact solution for anisotropic compact stellar objects within the framework of f(R)=R+αR2 gravity. In this context, the Durgapal-Fuloria metric potential has been employed to solve the field equation derived for f(R) theory. Furthermore, we have derived the generalized Darmois-Israel junction condition necessary for seamlessly connecting the interior region to the Schwarzschild exterior metric across the boundary hypersurface of the star in the context of f(R) gravity, and the interior solution is matched with the Schwarzschild exterior metric over the bounding surface of a compact star. These junction conditions stipulate that the pressure must not be zero at the boundary and should be proportional to the non-linear terms of f(R) gravity, a crucial aspect often overlooked by many researchers when investigating compact stellar models. Additionally, we derived the values of these parameters by using observational data of various compact stars (CSs), namely Her X-1, SAX J1808.4-3658, SMC X-1, LMC X-4, Cen X-3, 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, and PSR J1416-2230. This approach enables us to investigate the comprehensive analysis of solutions numerically and graphically. We conducted various physical tests, including gradient of energy density and pressures, anisotropy, stability, equilibrium conditions, energy-density constraints, mass function, compactness, redshift, and adiabatic index, to assess the feasibility of our models. Our findings demonstrate the consistent behavior of our models provides a satisfactory physical situation as far as the observational results are confirmed.

Drift Control of High-Dimensional Reflected Brownian Motion: A Computational Method Based on Neural Networks

Motivated by applications in queueing theory, we consider a stochastic control problem whose state space is the d-dimensional positive orthant. The controlled process Z evolves as a reflected Brownian motion whose covariance matrix is exogenously specified, as are its directions of reflection from the orthant’s boundary surfaces. A system manager chooses a drift vector [Formula: see text] at each time t based on the history of Z, and the cost rate at time t depends on both [Formula: see text] and [Formula: see text]. In our initial problem formulation, the objective is to minimize expected discounted cost over an infinite planning horizon, after which we treat the corresponding ergodic control problem. Extending the earlier work by Han et al. [Han J, Jentzen A, Weinan E (2018) Solving high-dimensional partial differential equations using deep learning. Proc. Natl. Acad. Sci. USA 115(34):8505–8510], we develop and illustrate a simulation-based computational method that relies heavily on deep neural network technology. For the test problems studied thus far, our method is accurate to within a fraction of 1% and is computationally feasible in dimensions up to at least [Formula: see text].

A modeling method for thermal steady-state simulation of the four-layer printed circuit board.

Thermal simulation of a Printed Circuit Board (PCB) can help identify potential overheating risks in the circuit. The proposed modeling method combines analytical temperature solutions and numerical approximations. Only Fourier-series analytical solutions related to the prepreg-layer surfaces need to be calculated, rather than the entire structure. Heat transfer through the lateral sides of a PCB is approximately considered as part of the compensated heat flux of the insulating-layer surface boundaries. Heat diffusion within or between metal layers is numerically approximated using the finite volume method. The core layer is treated as "thermally-thick". Temperature-dependent boundary conditions are considered through iterations. A test solver was developed based on the method. The modeling accuracy was validated by comparison with COMSOL Multiphysics for a four-layer structure with a moderate degree of discretization. Additionally, a PCB for generating DC 3.3V was designed, tested, and modeled, with the modeling results confirmed by the thermal images. The electro-thermal analysis of the distribution of electric potential and Joule heating in traces and vias was integrated into the PCB model. The layout maps of the PCB were further adjusted to reduce Joule heating in the output circuit, and the improvement on reducing the IR drop and hotspot temperature was examined.

Transformation of surface [formula omitted]-forces in high grade elasticity

The expression of the elastic energy, postulated for a given material, specifies through the principle of virtual work which external loadings turn out to be admissible. For the elastic bodies, the energy of which depends on the gradients of the placement higher than (H+1) (or, equivalently, on the derivatives of the deformation gradient higher than H), external force densities can be prescribed over the boundary surface, which do work on the H-th derivative of the virtual displacements along the normal direction. Such generalized forces with H=1,2 have been dealt with in the literature, referred to as double and triple forces: when H is increased, however, the analytical evaluation of these work terms may become prohibitive. Each Eulerian H-force density of this kind, acting on the current boundary surface, turns out to be equivalent to a set of diverse actions defined in the Lagrangian configuration. These actions include: (i) surface terms doing work on the virtual displacement vector; (ii) surface terms doing work on the higher order derivatives of the virtual displacement along the normal direction; (iii) edge terms, doing work on the virtual displacement or on its higher order gradients, which may be further reduced. In this study, a recursive algorithm is utilized to generate all these Lagrangian contributions for any H. Such an approach rests on the binomial expansion of the tensor products of complementary surface projectors, symmetrized in the work duality, and on the integration by parts combined with the generalized divergence theorem.

Intelligent computing applications to study the tri-hybrid nanofluid past over the stretched surface

In this study, a recurrent neural network with the Levenberg-Marquardt backpropagation algorithm is used to examine the effects of various parameters on cooling mechanisms involving tri-hybrid nanofluid consisting of Al2O3, Cu, TiO2 and magnetohydrodynamic stagnation point flow. This research focus on nanofluid in the existence of an asymmetrically stretched disc in water, which plays an imprortant role for understanding heat transfer in addition to the dynamics of momentum and thermal boundary surface. Transform the complex partial differential system through suitable similarity transformations into the ordinary differential equations for numerical computing. These equations have been solved numerically by using the Adams method in Mathematica to generate datasets for various parameters.The current study demonstrates that the velocity profile rises with higher magnetic, velocity slip, and mass suction parameters. The fluid thermal level tends to decrease with an increase in mass suction parameters, whereas an increase in the magnetic parameter and Eckert number raises the fluid’s thermal level. Furthermore, it is noticed that the flow resistance and internal friction of the fluid are proportional to the viscosity parameter. The proposed scheme has shown its effectiveness in a wide range of scenarios and cases. This was achieved by comparing the mean square error metric for the squeezing flow tri-hybrid nanofluid problem with the obtained results. In addition, various statistical measures like state transitions, fitness assessments, error histograms, and regression analyses, provide further evidence of the solver’s robustness and reliability. The excellent agreement between the reference datasets and refined numerical solutions through the scheme showcases the method’s effectiveness, achieving remarkable accuracy levels ranging from 10-6 to 10-12.

Determination of five-parameter grain boundary characteristics in nanocrystalline Ni-W by scanning precession electron diffraction tomography

Determining the full five-parameter grain boundary characteristics from experiments is essential for understanding grain boundaries impact on material properties, improving related models, and designing advanced alloys. However, achieving this is generally challenging, in particular at nanoscale, due to their 3D nature. In our study, we successfully determined the grain boundary characteristics of an annealed nickel-tungsten alloy (NiW) nanocrystalline needle-shaped specimen (tip) containing twins using Scanning Precession Electron Diffraction (SPED) Tomography. The presence of annealing twins in this face-centered cubic (fcc) material gives rise to common reflections in the SPED diffraction patterns, which challenges the reconstruction of orientation-specific virtual dark field (VDF) images required for tomographic reconstruction of the 3D grain shapes. To address this, an automated post-processing step identifies and deselects these shared reflections prior to the reconstruction of the VDF images. Combined with appropriate intensity normalization and projection alignment procedures, this approach enables high-fidelity 3D reconstruction of the individual grains contained in the needle-shaped sample volume. To probe the accuracy of the resulting boundary characteristics, the twin boundary surface normal directions were extracted from the 3D voxelated grain boundary map using a 3D Hough transform. For the sub-set of coherent Σ3 boundaries, the expected {111} grain boundary plane normals were obtained with an angular error of <3° for boundary sizes down to 400 nm². This work advances our ability to precisely characterize and understand the complex grain boundaries that govern material properties.

Exploring the effects of the alkaline earth metal cations on the electronic structure, photostability and radiation hardness of lead halide perovskites

The growing interest to the application of perovskite solar cells (PSC) in aerospace requires great attention to the design of new absorber materials with enhanced photostability and radiation hardness. We addressed this challenge through the B-site engineering by partial replacing of Pb2+ in the complex halides with Ca2+, Sr2+, and Ba2+. Change in the material electronic properties suggests the incorporation of the substituent cations in the perovskite lattice. However, when the loading of alkaline earth halides is high, they tend to segregate to the film surface and grain boundaries. The modification of MAPbI3 and Cs0.12FA0.88PbI3 by replacing a 1% of Pb2+ with alkaline earth metal cations resulted in improvements in the photostability and radiation hardness under exposure to gamma rays and electrons beam. Depending on the material formulation, it was possible to mitigate the photochemical and radiation-induced Pb0 formation and the univalent cation phase segregation. The best of the designed perovskite absorbers could successfully tolerate high doses of gamma rays (5.5 MGy) and electron fluences (3 × 1016 e/cm2), thus outperforming significantly the non-modified material. These findings feature the incorporation of alkaline earth metal cations as a promising approach for the development of PSC with enhanced radiation hardness for aerospace applications.

SnSe2 Quantum Dots and Chlorhexidine Acetate Suppress Synergistically Non-radiative Recombination Loss for High Efficiency and Stability Perovskite Solar Cells.

Non-radiative recombination losses limit the property of perovskite solar cells (PSCs). Here, a synergistic strategy of SnSe2QDs doping into SnO2 and chlorhexidine acetate (CA) coating on the surface of perovskite is proposed. The introduction of 2D SnSe2QDs reduces the oxygen vacancy defects and increases the carrier mobility of SnO2. The optimized SnO2 as a buried interface obviously improves the crystallization quality of perovskite. The CA containing abundant active sites of ─NH2/─NH─, ─C═N, CO, ─Cl groups passivate the defects on the surface and grain boundary of perovskite. The alkyl chain of CA also improves the hydrophobicity of perovskite. Moreover, the synergism of SnSe2QDs and CA releases the residual stress and regulates the energy level arrangement at the top and bottom interface of perovskite. Benefiting from these advantages, the bulk and interface non-radiative recombination loss is greatly suppressed and thereby increases the carrier transport and extraction in devices. As a result, the best power conversion efficiency (PCE) of 23.41% for rigid PSCs and the best PCE of 21.84% for flexible PSCs are reached. The rigid PSC maintains 89% of initial efficiency after storing nitrogen for 3100 h. The flexible PSCs retain 87% of the initial PCE after 5000 bending cycles at a bending radius of 5 mm.

An Efficient Progressive Grid Generation Method Considering Internal Quality and Boundary Grid Adjustment

Due to its elegant appearance and high structural efficiency, free-form grid structures are increasingly adopted in architectural design. However, it is a challenging task for engineers to generate a uniform and well-shaped grid on a free-form surface while considering the processing of both interior and boundary of grid, especially for composite surfaces. To generate well-shaped grids with uniform rods, regular cells and smooth visual effects over free-form surfaces, this paper develops an innovative triangular grid generation method capable of automatically managing grid boundary with extending initial surface. In the method, nodes of grid structure are considered to be zero mass particles and are progressively added to the extended surface from geometric center to the boundary of surface. A boundary-processing algorithm is then established to evenly distribute nodes on initial boundary curve, while ensuring that grid cells at the boundary do not exhibit elongation. A mechanical simulation system based on spring-mass model is improved to optimize spatial grid structure, rods of grid are regarded as linear springs, a surface attraction force and an anchoring force are performed on grid nodes. Moreover, the proposed method allows architects change grid direction and rods length easily, which can greatly improve the efficiency of design. Several case studies show that the method can effectively avoid distortion of grids and generate well-shaped grids that can meet aesthetic requirements.

The K‐Profile Parameterization Augmented by Deep Neural Networks (KPP_DNN) in the General Ocean Turbulence Model (GOTM)

AbstractThis study utilizes Deep Neural Networks (DNN) to improve the K‐Profile Parameterization (KPP) for the vertical mixing effects in the ocean's surface boundary layer turbulence. The deep neural networks were trained using 11‐year turbulence‐resolving solutions, obtained by running a large eddy simulation model for Ocean Station Papa, to predict the turbulence velocity scale coefficient and unresolved shear coefficient in the KPP. The DNN‐augmented KPP schemes (KPP_DNN) have been implemented in the General Ocean Turbulence Model (GOTM). The KPP_DNN is stable for long‐term integration and more efficient than existing variants of KPP schemes with wave effects. Three different KPP_DNN schemes, each differing in their input and output variables, have been developed and trained. The performance of models utilizing the KPP_DNN schemes is compared to those employing traditional deterministic first‐order and second‐moment closure turbulent mixing parameterizations. Solution comparisons indicate that the simulated mixed layer becomes cooler and deeper when wave effects are included in parameterizations, aligning closer with observations. In the KPP framework, the velocity scale of unresolved shear, which is used to calculate ocean surface boundary layer depth, has a greater impact on the simulated mixed layer than the magnitude of diffusivity does. In the KPP_DNN, unresolved shear depends not only on wave forcing, but also on the mixed layer depth and buoyancy forcing.

Effects of Horizontal Resolution on Long‐Range Equatorward Radiation of Near‐Inertial Internal Waves in Ocean General Circulation Models

AbstractWind‐generated near‐inertial internal waves (NIWs) are characterized by dominant long‐range equatorward radiation due to the gradient of the planetary vorticity, known as the β‐refraction effect. In this study, we analyze the effects of horizontal model resolution on the long‐range equatorward radiation of NIWs. In a high‐resolution Community Earth System Model (CESM‐HR) with a 0.1° oceanic resolution, about 25% (15%) of NIW energy flux injected downward the surface boundary layer base poleward of 30°N (30°S) radiates into the lower‐latitude region. This ratio decreases to about 15% (8%) in a low‐resolution CESM (CESM‐LR) with a 1° oceanic resolution. The higher long‐range equatorward radiation efficiency in the CESM‐HR than the CESM‐LR is directly attributed to the faster equatorward group velocity of the NIWs of the first three vertical modes, which reflects the better representation of equatorward propagation and beta‐refraction of smaller scale NIWs in the CESM‐HR. The enhancement of equatorward wavenumber induced by the β‐refraction is inhibited in the CESM‐LR, which underrepresent the long‐range equatorward radiation of NIWs. These results underscore the necessity of high‐resolution ocean models in accurately simulating the spatial variabilities of NIWs and their induced turbulent diapycnal mixing in the global ocean.

Construction of mathematical models of thermal conductivity for modern electronic devices with elements of a layered structure

This paper considers a heat conduction process for isotropic layered media with internal thermal heating. As a result of the heterogeneity of environments, significant temperature gradients arise as a result of the thermal load. In order to establish the temperature regimes for the effective operation of electronic devices, linear and non-linear mathematical models for determining the temperature field have been constructed, which would make it possible to further analyze the temperature regimes in these heat-active environments. The coefficient of thermal conductivity for the above structures was represented as a whole using asymmetric unit functions. As a result, the conditions of ideal thermal contact were automatically fulfilled on the surfaces of the conjugation of the layers. This leads to solving one heat conduction equation with discontinuous and singular coefficients and boundary conditions at the boundary surfaces of the medium. For linearization of nonlinear boundary value problems, linearizing functions were introduced. Analytical solutions to both linear and nonlinear boundary value problems were derived in a closed form. For heat-sensitive environments, as an example, the linear dependence of the coefficient of thermal conductivity of structural materials on temperature, which is often observed when solving many practical problems, was chosen. As a result, analytical relations for determining the temperature distribution in these environments were obtained. Based on this, a numerical experiment was performed, and it was geometrically represented depending on the spatial coordinates. This proves that the constructed linear and nonlinear mathematical models testify to their adequacy to the real physical process. They make it possible to analyze heat-active media regarding their thermal resistance. As a result, it becomes possible to increase it and protect it from overheating, which can cause the destruction of not only individual nodes and their elements but also the entire structure

Low-Cost, Scalable Fabrication of Multi-Dimensional Perovskite Solar Cells and Modules Assisted by Mechanical Scribing.

The performance and scalability of perovskite solar cells (PSCs) based on 3D formamidinium lead triiodide (FAPbI3) absorber are often hindered by defects at the surface and grain boundaries of the perovskite. To address this, the study demonstrates the use of pyrrolidinium iodide for the in situ formation of an energetically aligned 1D pyrrolidinium lead triiodide (PyPbI3) capping layer over the 3D FAbI3 perovskite. The thermodynamically stable PyPbI3 perovskitoids, formed through cation exchange reactions, effectively reduce surface and grain boundary defects in the FAPbI3 perovskite. In addition to improved phase stability, the resulting 1D/3D perovskite film forms a cascade energy band alignment with the other functional layers in PSCs, enabling a barrier-free interfacial charge transport. With a maximum power conversion efficiency (PCE) of ≈23.1% and ≈20.7% at active areas of 0.09 and 1.05 cm2, respectively, the 1D/3D PSCs demonstrate excellent performance and scalability. Leveraging this improved scalability, the study has successfully developed a mechanically-scribed 1D/3D perovskite mini-module with an unprecedentedly high PCE of ≈20.6% and a total power output of ≈270mW at an active area of ≈13.0 cm2. The 1D/3D multi-dimensional perovskite film developed herein holds great promise for producing low-cost, high-performance perovskite photovoltaics at both the cell and module levels.

Small molecule induced interfacial defect healing to construct inverted perovskite solar cells with high fill factor and stability

Chemical defects at the surface and grain boundaries of perovskite crystals cause deterioration of conversion efficiency and stability of perovskite solar cells (PSCs). In this study, a multifunctional additive, 5-fluoro-2-pyrimidine carbonitrile (FPDCN) molecule, is added into the perovskite precursor solution in order to passivate the uncoordinated Pb2+ by the cyanogen (–CN) group and pyrimidine N in FPDCN. Interestingly, fluorine (F) atoms interact with FA+ to form hydrogen bonds, which could regulate the perovskite crystallization process for the formation of high-quality perovskite crystals. Besides, the F atoms in FPDCN increase the water contact angle of perovskite films. As a result, the carrier extraction and transport in the perovskite film are significantly enhanced, and the non-radiative recombination is suppressed. The corresponding devices achieve a champion photovoltaic conversion efficiency (PCE) of 20.7 % and a fill factor (FF) of over 83 %. The device based on FPDCN shows long-term stability under a high-humidity atmospheric environment by maintaining 85 % of the initial efficiency after aging of 700 h in the glove box. This study provides a simple and convenient method to prepare stable and efficient PSCs by optimizing the perovskite precursor solution.