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Li, Jingfa, Dukui Zheng e Wei Zhang. "Advances of Phase-Field Model in the Numerical Simulation of Multiphase Flows: A Review". Atmosphere 14, n. 8 (19 agosto 2023): 1311. http://dx.doi.org/10.3390/atmos14081311.
Testo completoAbstract (sommario):
The phase-field model (PFM) is gaining increasing attention in the application of multiphase flows due to its advantages, in which the phase interface is treated as a narrow layer and phase parameters change smoothly and continually at this thin layer. Thus, the construction or tracking of the phase interface can be avoided, and the bulk phase and phase interface can be simulated integrally. PFM provides a useful alternative that does not suffer from problems with either the mass conservation or the accurate computation of surface tension. In this paper, the state of the art of PFM in the numerical modeling and simulation of multiphase flows is comprehensively reviewed. Starting with a brief description of historical developments in the PFM, we continue to take a tour into the basic concepts, fundamental theory, and mathematical models. Then, the commonly used numerical schemes and algorithms for solving the governing systems of PFM in the application of multiphase flows are presented. The various applications and representative results, especially in non-match density scenarios of multiphase flows, are reviewed. The primary challenges and research focus of PFM are analyzed and summarized as well. This review is expected to provide a valuable reference for PFM in the application of multiphase flows.
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Sidharth, P. C., e B. N. Rao. "A Review on phase-field modeling of fracture". Proceedings of the 12th Structural Engineering Convention, SEC 2022: Themes 1-2 1, n. 1 (19 dicembre 2022): 449–56. http://dx.doi.org/10.38208/acp.v1.534.
Testo completoAbstract (sommario):
In cases with complicated crack topologies, the computational modeling of failure processes in materials owing to fracture based on sharp crack discontinuities fails. Diffusive crack modeling based on the insertion of a crack phase-field can overcome this. The phase-field model (PFM) portrays the fracture geometry in a diffusive manner, with no abrupt discontinuities. Unlike discrete fracture descriptions, phase-field descriptions do not need numerical monitoring of discontinuities in the displacement field. This considerably decreases the complexity of implementation. These qualities enable PFM to describe fracture propagation more successfully than numerical approaches based on the discrete crack model, especially for complicated crack patterns. These models have also demonstrated the ability to forecast fracture initiation and propagation in two and three dimensions without the need for any ad hoc criteria. The phase-field model, among numerous options, is promising in the computer modeling of fracture in solids due to its ability to cope with complicated crack patterns such as branching, merging, and even fragmentation. A brief history of the application of the phase-field model in predicting solid fracture has been attempted. An effort has been made to keep the conversation focused on recent research findings on the subject. Finally, some key findings and recommendations for future research areas in this field are discussed.
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Chen, Ming, Xiao Dong Hu e Dong Ying Ju. "Phase-Field Simulation of Binary Alloy Crystal Growth Prepared by a Fluid Flow". Materials Science Forum 833 (novembre 2015): 11–14. http://dx.doi.org/10.4028/www.scientific.net/msf.833.11.
Testo completoAbstract (sommario):
Phase field method (PFM) was employed to investigate the crystal growth of Mg-Al alloy, on the basis of binary alloy model, the fluid field equation was coupled into the phase-field models, and the marker and cell (MAC) method was used in the numerical calculation of micro structural pattern. In the cast process, quantitative comparison of different anisotropy values that predicted the dendrite evolution were discussed in detail, and when the fluid flow rate reaches a high value, we can see the remelting of dendrite arms.
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Karim, Eaman T., Miao He, Ahmed Salhoumi, Leonid V. Zhigilei e Peter K. Galenko. "Kinetics of solid–liquid interface motion in molecular dynamics and phase-field models: crystallization of chromium and silicon". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n. 2205 (19 luglio 2021): 20200320. http://dx.doi.org/10.1098/rsta.2020.0320.
Testo completoAbstract (sommario):
The results of molecular dynamics (MD) simulations of the crystallization process in one-component materials and solid solution alloys reveal a complex temperature dependence of the velocity of the crystal–liquid interface featuring an increase up to a maximum at 10–30% undercooling below the equilibrium melting temperature followed by a gradual decrease of the velocity at deeper levels of undercooling. At the qualitative level, such non-monotonous behaviour of the crystallization front velocity is consistent with the diffusion-controlled crystallization process described by the Wilson–Frenkel model, where the almost linear increase of the interface velocity in the vicinity of melting temperature is defined by the growth of the thermodynamic driving force for the phase transformation, while the decrease in atomic mobility with further increase of the undercooling drives the velocity through the maximum and into a gradual decrease at lower temperatures. At the quantitative level, however, the diffusional model fails to describe the results of MD simulations in the whole range of temperatures with a single set of parameters for some of the model materials. The limited ability of the existing theoretical models to adequately describe the MD results is illustrated in the present work for two materials, chromium and silicon. It is also demonstrated that the MD results can be well described by the solution following from the hodograph equation, previously found from the kinetic phase-field model (kinetic PFM) in the sharp interface limit. The ability of the hodograph equation to describe the predictions of MD simulation in the whole range of temperatures is related to the introduction of slow (phase field) and fast (gradient flow) variables into the original kinetic PFM from which the hodograph equation is obtained. The slow phase-field variable is responsible for the description of data at small undercoolings and the fast gradient flow variable accounts for local non-equilibrium effects at high undercoolings. The introduction of these two types of variables makes the solution of the hodograph equation sufficiently flexible for a reliable description of all nonlinearities of the kinetic curves predicted in MD simulations of Cr and Si. This article is part of the theme issue ‘Transport phenomena in complex systems (part 1)’.
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Jeon, Seoyeon, e Hyunjoo Choi. "Trends in Materials Modeling and Computation for Metal Additive Manufacturing". journal of Korean Powder Metallurgy Institute 31, n. 3 (30 giugno 2024): 213–19. http://dx.doi.org/10.4150/jpm.2024.00150.
Testo completoAbstract (sommario):
Additive Manufacturing (AM) is a process that fabricates products by manufacturing materials according to a three-dimensional model. It has recently gained attention due to its environmental advantages, including reduced energy consumption and high material utilization rates. However, controlling defects such as melting issues and residual stress, which can occur during metal additive manufacturing, poses a challenge. The trial-and-error verification of these defects is both time-consuming and costly.Consequently, efforts have been made to develop phenomenological models that understand the influence of process variables on defects, and mechanical/electrical/thermal properties of geometrically complex products. This paper introduces modeling techniques that can simulate the powder additive manufacturing process. The focus is on representative metal additive manufacturing processes such as Powder Bed Fusion (PBF), Direct Energy Deposition (DED), and Binder Jetting (BJ) method.To calculate thermal-stress history and the resulting deformations, modeling techniques based on Finite Element Method (FEM) are generally utilized. For simulating the movements and packing behavior of powders during powder classification, modeling techniques based on Discrete Element Method (DEM) are employed. Additionally, to simulate sintering and microstructural changes, techniques such as Monte Carlo (MC), Molecular Dynamics (MD), and Phase Field Modeling (PFM) are predominantly used.
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Deng, Jinghui, Jie Zhou, Tangzhen Wu, Zhengliang Liu e Zhen Wu. "Review and Assessment of Fatigue Delamination Damage of Laminated Composite Structures". Materials 16, n. 24 (16 dicembre 2023): 7677. http://dx.doi.org/10.3390/ma16247677.
Testo completoAbstract (sommario):
Fatigue delamination damage is one of the most important fatigue failure modes for laminated composite structures. However, there are still many challenging problems in the development of the theoretical framework, mathematical/physical models, and numerical simulation of fatigue delamination. What is more, it is essential to establish a systematic classification of these methods and models. This article reviews the experimental phenomena of delamination onset and propagation under fatigue loading. The authors reviewed the commonly used phenomenological models for laminated composite structures. The research methods, general modeling formulas, and development prospects of phenomenological models were presented in detail. Based on the analysis of finite element models (FEMs) for laminated composite structures, several simulation methods for fatigue delamination damage models (FDDMs) were carefully classified. Then, the whole procedure, range of applications, capability assessment, and advantages and limitations of the models, which were based on four types of theoretical frameworks, were also discussed in detail. The theoretical frameworks include the strength theory model (SM), fracture mechanics model (FM), damage mechanics model (DM), and hybrid model (HM). To the best of the authors’ knowledge, the FDDM based on the modified Paris law within the framework of hybrid fracture and damage mechanics is the most effective method so far. However, it is difficult for the traditional FDDM to solve the problem of the spatial delamination of complex structures. In addition, the balance between the cost of acquiring the model and the computational efficiency of the model is also critical. Therefore, several potential research directions, such as the extended finite element method (XFEM), isogeometric analysis (IGA), phase-field model (PFM), artificial intelligence algorithm, and higher-order deformation theory (HODT), have been presented in the conclusions. Through validation by investigators, these research directions have the ability to overcome the challenging technical issues in the fatigue delamination prediction of laminated composite structures.
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Li, Chang, Shuchao Li, Jiabo Liu, Yichang Sun, Yuhao Wang e Fanhong Kong. "Study on Mechanism of Microstructure Refinement by Ultrasonic Cavitation Effect". Coatings 14, n. 11 (17 novembre 2024): 1462. http://dx.doi.org/10.3390/coatings14111462.
Testo completoAbstract (sommario):
During the solidification process of the alloy, the temperature lies in the range between the solid-phase line and the liquidus. Dendrite growth exhibits high sensitivity to even slight fluctuations in temperature, thereby significantly influencing the tip growth rate. The increase in temperature can result in a reduction in the rate of tip growth, whereas a decrease in temperature can lead to an augmentation of the tip growth rate. In cases where there is a significant rise in temperature, dendrites may undergo fracture and subsequent remelting. Within the phenomenon of ultrasonic cavitation, the release of internal energy caused by the rupture of cavitation bubbles induces a substantial elevation in temperature, thereby causing both dendrite remelting and fracture phenomena. This serves as the main mechanism behind microstructure refinement induced by ultrasonic cavitation. Although dendrite remelting and fracture exert significant influences on the solidification process of alloys, most studies primarily focus on microscopic characterization experiments, which fail to unveil the transient evolution law governing dendrite remelting and fracture processes. Numerical simulation offers an effective approach to address this gap. The existing numerical models primarily focus on predicting the dendrite growth process, while research on remelting and fracture phenomena remains relatively limited. Therefore, a dendrite remelting model was established by incorporating the phase field method (PFM) and finite element difference method (FDM) into the temperature-induced modeling, enabling a comprehensive investigation of the entire process evolution encompassing dendrite growth and subsequent remelting.
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Zhang, Shidong, Kai Wang, Shangzhe Yu, Nicolas Kruse, Roland Peters, Felix Kunz e Rudiger-A. Eichel. "Multiscale and Multiphysical Numerical Simulations of Solid Oxide Cell (SOC)". ECS Meeting Abstracts MA2023-01, n. 54 (28 agosto 2023): 144. http://dx.doi.org/10.1149/ma2023-0154144mtgabs.
Testo completoAbstract (sommario):
Electrochemical applications play a key role for the topic of “green hydrogen” for the de-carbonization of the energy and mobility sectors. Electrochemical systems and processes, including fuel cells and electrolysers, have witnessed several benefits over conventional combustion-based technologies currently being widely used in power plants and vehicles. The ceramic high-temperature technologies by means of SOC exhibits high efficiencies, with a thermoelectric conversion efficiency as high as 60% and a total efficiency of up to 90% in fuel cell operation and even higher in electrolysis mode. The SOC technology, therefore, sees a promising future in the production of green hydrogen and electricity. Providing high operating temperature, over 600 oC, the SOC system shows the capability to operate with diverse types of gas mixtures, for example, hydrogen, ammonia, and carbon-containing mixtures such as methane (CH4), carbon monoxide (CO) in fuel cell operation (SOFC) and steam and/or carbon dioxide (CO2) in electrolysis operation (SOEC). The design of the SOC stack enables a reversible operation (rSOC) between fuel cell and electrolysis modes. It indicates the SOC system can perform with high efficiencies in both operating modes, which also widens the scope of possible applications. Challenges remain when it comes to commercialization of the SOC technology, in both the investment costs (CAPEX) and operating costs (OPEX) aspects. From the technological and scientific point of view, the physical transport phenomena in SOCs need to be understood which can be done by the help of experimental and numerical investigations. Cheaper and long-lasting material alternatives may be found for the cell, stack and system development afterwards. Detailed experimental investigations usually require a lot of effort in time and data analysis. To promote the scientific and technological studies on the SOC technology, numerical investigations by using multiscale and multiphysical models are carried out in this work. The models include an in-house designed/written phase field model (PFM) 1, and an open-source based computational fluid dynamics (CFD) model, openFuelCell2 2 (based on OpenFOAM). The former accounts for the microstructure evolution of the Ni/YSZ composition. The latter addresses the multiphysical transport processes in different phases, i.e., ionic transfer in YSZ, electronic transfer in Ni, and the gas diffusion in the gas phase. The figure below shows the computational domain and different phases in the numerical simulations. The evolution of Ni/YSZ composition can be predicted by the PFM. It is supposed to reproduce the Ni agglomeration that has been observed in SOFC long-term experiments 3. The simulation result shown at the left-most is obtained by performing the PFM simulation (with 96 x 96 x 96 voxels) representing the microstructure change for a certain time duration. The computational domain (192 x 192 x 192 voxels) consists of three phases, namely, YSZ, Ni, and gas, as shown in the middle and on the right side. It is refined in each direction to better capture the triple phase regions (lower right) shared by the three phases, which refers to the active sites that enable the electrochemical reaction to be conducted. By applying different governing equations on these phases, the CFD model, openFuelCell2, can describe the transport phenomena numerically. Hence, the performance degradation of a SOFC due to Ni agglomeration can be captured by carrying out the simulations for different time durations. The effective properties may be derived as well so that they can be used in numerical simulations with larger scales. Acknowledgement The authors would like to thank their colleagues at Forschungszentrum Jülich GmbH for their great support and the Helmholtz Society, the German Federal Ministry of Education and Research as well as the Ministry of Culture and Science of the Federal State of North Rhine-Westphalia for financing these activities as part of the Living Lab Energy Campus. References Q. Li, L. Liang, K. Gerdes, and L.-Q. Chen, Appl. Phys. Lett., 101, 033909 (2012). S. Zhang, S. Hess, H. Marschall, U. Reimer, S. B. Beale, and W. Lehnert, Computer Physics Communications, to be submitted (2023). C. E. Frey, Q. Fang, D. Sebold, L. Blum, and N. H. Menzler, J. Electrochem. Soc., 165, F357 (2018). Figure 1
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Steinberg, A. B., F. Maucher, S. V. Gurevich e U. Thiele. "Exploring bifurcations in Bose–Einstein condensates via phase field crystal models". Chaos: An Interdisciplinary Journal of Nonlinear Science 32, n. 11 (novembre 2022): 113112. http://dx.doi.org/10.1063/5.0101401.
Testo completoAbstract (sommario):
To facilitate the analysis of pattern formation and the related phase transitions in Bose–Einstein condensates, we present an explicit approximate mapping from the nonlocal Gross–Pitaevskii equation with cubic nonlinearity to a phase field crystal (PFC) model. This approximation is valid close to the superfluid–supersolid phase transition boundary. The simplified PFC model permits the exploration of bifurcations and phase transitions via numerical path continuation employing standard software. While revealing the detailed structure of the bifurcations present in the system, we demonstrate the existence of localized states in the PFC approximation. Finally, we discuss how higher-order nonlinearities change the structure of the bifurcation diagram representing the transitions found in the system.
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Yoon, Sungha, Darae Jeong, Chaeyoung Lee, Hyundong Kim, Sangkwon Kim, Hyun Geun Lee e Junseok Kim. "Fourier-Spectral Method for the Phase-Field Equations". Mathematics 8, n. 8 (18 agosto 2020): 1385. http://dx.doi.org/10.3390/math8081385.
Testo completoAbstract (sommario):
In this paper, we review the Fourier-spectral method for some phase-field models: Allen–Cahn (AC), Cahn–Hilliard (CH), Swift–Hohenberg (SH), phase-field crystal (PFC), and molecular beam epitaxy (MBE) growth. These equations are very important parabolic partial differential equations and are applicable to many interesting scientific problems. The AC equation is a reaction-diffusion equation modeling anti-phase domain coarsening dynamics. The CH equation models phase segregation of binary mixtures. The SH equation is a popular model for generating patterns in spatially extended dissipative systems. A classical PFC model is originally derived to investigate the dynamics of atomic-scale crystal growth. An isotropic symmetry MBE growth model is originally devised as a method for directly growing high purity epitaxial thin film of molecular beams evaporating on a heated substrate. The Fourier-spectral method is highly accurate and simple to implement. We present a detailed description of the method and explain its connection to MATLAB usage so that the interested readers can use the Fourier-spectral method for their research needs without difficulties. Several standard computational tests are done to demonstrate the performance of the method. Furthermore, we provide the MATLAB codes implementation in the Appendix A.
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Ainsworth, Mark, e Zhiping Mao. "Fractional phase-field crystal modelling: analysis, approximation and pattern formation". IMA Journal of Applied Mathematics 85, n. 2 (17 marzo 2020): 231–62. http://dx.doi.org/10.1093/imamat/hxaa004.
Testo completoAbstract (sommario):
Abstract We consider a fractional phase-field crystal (FPFC) model in which the classical Swift–Hohenberg equation (SHE) is replaced by a fractional order Swift–Hohenberg equation (FSHE) that reduces to the classical case when the fractional order $\beta =1$. It is found that choosing the value of $\beta $ appropriately leads to FSHE giving a markedly superior fit to experimental measurements of the structure factor than obtained using the SHE ($\beta =1$) for a number of crystalline materials. The improved fit to the data provided by the fractional partial differential equation prompts our investigation of a FPFC model based on the fractional free energy functional. It is shown that the FSHE is well-posed and exhibits the same type of pattern formation behaviour as the SHE, which is crucial for the success of the PFC model, independently of the fractional exponent $\beta $. This means that the FPFC model inherits the early successes of the FPC model such as physically realistic predictions of the phase diagram etc. and, therefore, provides a viable alternative to the classical PFC model. While the salient features of PFC and FPFC are identical, we expect more subtle features to differ. The prediction of grain boundary energy arising from a mismatch in orientation across a material interface is another notable success of the PFC model. The grain boundary energy can be evaluated numerically from the PFC model and compared with experimental measurements. The grain boundary energy is a derived quantity and is more sensitive to the nuances of the model. We compare the predictions obtained using the PFC and FPFC models with experimental observations of the grain boundary energy for several materials. It is observed that the FPFC model gives superior agreement with the experimental observation than those obtained using the classical PFC model, especially when the mismatch in orientation becomes larger.
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Caggiano, Antonio, Christoph Mankel e Eddie Koenders. "Reviewing Theoretical and Numerical Models for PCM-embedded Cementitious Composites". Buildings 9, n. 1 (21 dicembre 2018): 3. http://dx.doi.org/10.3390/buildings9010003.
Testo completoAbstract (sommario):
Accumulating solar and/or environmental heat in walls of apartment buildings or houses is a way to level-out daily temperature differences and significantly cut back on energy demands. A possible way to achieve this goal is by developing advanced composites that consist of porous cementitious materials with embedded phase change materials (PCMs) that have the potential to accumulate or liberate heat energy during a chemical phase change from liquid to solid, or vice versa. This paper aims to report the current state of art on numerical and theoretical approaches available in the scientific literature for modelling the thermal behavior and heat accumulation/liberation of PCMs employed in cement-based composites. The work focuses on reviewing numerical tools for modelling phase change problems while emphasizing the so-called Stefan problem, or particularly, on the numerical techniques available for solving it. In this research field, it is the fixed grid method that is the most commonly and practically applied approach. After this, a discussion on the modelling procedures available for schematizing cementitious composites with embedded PCMs is reported.
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Dehghan, Mehdi, e Vahid Mohammadi. "The numerical simulation of the phase field crystal (PFC) and modified phase field crystal (MPFC) models via global and local meshless methods". Computer Methods in Applied Mechanics and Engineering 298 (gennaio 2016): 453–84. http://dx.doi.org/10.1016/j.cma.2015.09.018.
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Li, Zhi Yong, Zheng Yong Wang, Qu Fan e Zhan Wu. "The Interval Analysis for Uncertainty Heat Transfer Process of Phase Change Thermal Storage Based on Perturbation Method". Advanced Materials Research 838-841 (novembre 2013): 1939–43. http://dx.doi.org/10.4028/www.scientific.net/amr.838-841.1939.
Testo completoAbstract (sommario):
Due to phase change materials (PCMs) composition, machining error, measuring error and other factors, the PCMs thermal physical properties, geometric properties, etc are usually uncertain. As a result, phase change heat transfer process is an uncertainty heat transfer process. But at present, heat transfer characteristics research on phase change thermal storage are all based on certainty heat transfer models (Taken uncertainty factors as certainty factors). In this paper, it is considered factors uncertainty influencing phase change thermal storage heat transfer process. By looked on the variation scope of influence factors as "interval number", based on interval mathematics, perturbation method and finite difference method, "interval number" heat transfer model of phase change thermal storage is established. In this model, the uncertainty variables are decomposed into the sum of the nominal value and the deviation value. PCM uncertainty temperature field can be determined by calculated nominal value and the deviation value of PCM temperature field separately. Comparison between simulation results of the model and experimental data implies that it is necessary to consider influencing factors uncertainty in phase change thermal storage heat transfer analysis.
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Wan, Wan, e Pinlei Chen. "A Fully Coupled Thermomechanical Phase Field Method for Modeling Cracks with Frictional Contact". Mathematics 10, n. 23 (23 novembre 2022): 4416. http://dx.doi.org/10.3390/math10234416.
Testo completoAbstract (sommario):
In this paper, a thermomechanical coupled phase field method is developed to model cracks with frictional contact. Compared to discrete methods, the phase field method can represent arbitrary crack geometry without an explicit representation of the crack surface. The two distinguishable features of the proposed phase field method are: (1) for the mechanical phase, no specific algorithm is needed for imposing contact constraints on the fracture surfaces; (2) for the thermal phase, formulations are proposed for incorporating the phase field damage parameter so that different thermal conductance conditions are accommodated. While the stress is updated explicitly in the regularized interface regions under different contact conditions, the thermal conductivity is determined under different conductance conditions. In particular, we consider a pressure-dependent thermal conductance model (PDM) that is fully coupled with the mechanical phase, along with the other three thermal conductance models, i.e., the fully conductive model (FCM), the adiabatic model (ACM), and the uncoupled model (UCM). The potential of this formulation is showcased by several benchmark problems. We gain insights into the role of the temperature field affecting the mechanical field. Several 2D boundary value problems are addressed, demonstrating the model’s ability to capture cracking phenomena with the effect of the thermal field. We compare our results with the discrete methods as well as other phase field methods, and a very good agreement is achieved.
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Kang, Hoseong, Muyeong Cheon, Chang Hyun Lee, Tae-Ho Kim, Young Taik Hong, Sang Yong Nam e Chi Hoon Park. "Mesoscale Simulation Based on the Dynamic Mean-Field Density Functional Method on Block-Copolymeric Ionomers for Polymer Electrolyte Membranes". Membranes 13, n. 3 (22 febbraio 2023): 258. http://dx.doi.org/10.3390/membranes13030258.
Testo completoAbstract (sommario):
Block copolymers generally have peculiar morphological characteristics, such as strong phase separation. They have been actively applied to polymer electrolyte membranes for proton exchange membrane fuel cells (PEMFCs) to obtain well-defined hydrophilic regions and water channels as a proton pathway. Although molecular simulation tools are advantageous to investigate the mechanism of water channel formation based on the chemical structure and property relationships, classical molecular dynamics simulation has limitations regarding the model size and time scale, and these issues need to be addressed. In this study, we investigated the morphology of sulfonated block copolymers synthesized for PEM applications using a mesoscale simulation based on the dynamic mean-field density functional method, widely applied to investigate macroscopic systems such as polymer blends, micelles, and multi-block/grafting copolymers. Despite the similar solubility parameters of the monomers in our block-copolymer models, very different morphologies in our 3D mesoscale models were obtained. The model with sulfonated monomers, in which the number of sulfonic acid groups is twice that of the other model, showed better phase separation and water channel formation, despite the short length of its hydrophilic block. In conclusion, this unexpected behavior indicates that the role of water molecules is important in making PEM mesoscale models well-equilibrated in the mesoscale simulation, which results in the strong phase separation between hydrophilic and hydrophobic regions and the ensuing well-defined water channel. PEM synthesis supports the conclusion that using the sulfonated monomers with a high sulfonation degree (32.5 mS/cm) will be more effective than using the long hydrophilic block with a low sulfonation degree (25.2 mS/cm).
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Bolteya, Ahmed M., Mohamed A. Elsayad, Ola D. El Monayeri e Adel M. Belal. "Impact of Phase Change Materials on Cooling Demand of an Educational Facility in Cairo, Egypt". Sustainability 14, n. 23 (30 novembre 2022): 15956. http://dx.doi.org/10.3390/su142315956.
Testo completoAbstract (sommario):
Heat gains and losses via building envelopes are impacted by varied characteristics such as geometry, orientation, properties of the building materials, and the type of construction and its interface with the exterior environment. Current studies are investigating the use of phase change materials (PCMs) characterized by high latent heat and low thermal conductivity that may cause temperature time lag and reduce amounts of heat transferred through building envelopes. The prime objectives of this research are evaluating zones’ energy consumption by type for an educational facility in a dry arid climate, examining the effects of a PCM (RT28HC) and polyurethane insulating material, comparing these effects to the existing situation with respect to cooling energy savings and CO2 emissions, and studying the effect of varying PCM thicknesses. The working methodology depended on gathering the real status and actual material of the building, constructing models of the building using Design Builder (DB) simulation software, and comparing the insulation effect of incorporating polyurethane and phase change insulating materials. A parametric study evaluated various PCM thicknesses (6, 12, 18, 24, 30, and 36 mm). Validation was performed primarily for a selected year’s energy usage; simulation results complied with field measurements. The results revealed that an 18 mm PCM had a high efficiency regarding thermal comfort attributes, which reduced cooling energy by 17.5% and CO2 emissions by 12.4%. Consequently, this study has shown the significant potential of PCM regarding improved energy utilization in buildings.
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Xu, Shuai, Ying Wang, Jianying Hu e Zishun Liu. "Atomic Understanding of the Swelling and Phase Transition of Polyacrylamide Hydrogel". International Journal of Applied Mechanics 08, n. 07 (ottobre 2016): 1640002. http://dx.doi.org/10.1142/s1758825116400020.
Testo completoAbstract (sommario):
A polymer network can imbibe copious amounts of solvent (water) and swell, and the resulting state is known as a hydrogel. In this study, we have made the modification for the all-atom consistent valence force field (CVFF) to investigate the swelling property of polyacrylamide (PAM) hydrogel by molecular dynamics simulation. We have built 21 hydrogel models with different solvent contents and calculate the average chemical potential and diffusion coefficient of solvent molecules in PAM hydrogel. We find that when the mass fraction of solvent is about 90%, PAM hydrogel reaches its free swelling limitation and loses the motivation of absorbing solvent. Furthermore, it is also found that PAM hydrogel has a phase transition phenomenon when the values of solvent chemical potential are between [Formula: see text][Formula: see text]kcal/mol and [Formula: see text][Formula: see text]kcal/mol. This study will provide insight into the basic parameters which are widely used in continuum mechanics analysis of hydrogels from atomic point of view and help researchers to improve the continuum mechanics model for neutral hydrogel.
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Madruga, Santiago, e Gonzalo S. Mischlich. "Melting dynamics of a phase change material (PCM) with dispersed metallic nanoparticles using transport coefficients from empirical and mean field models". Applied Thermal Engineering 124 (settembre 2017): 1123–33. http://dx.doi.org/10.1016/j.applthermaleng.2017.06.097.
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Nazzi Ehms, José Henrique, Rejane De Césaro Oliveski, Luiz Alberto Oliveira Rocha, Cesare Biserni e Massimo Garai. "Fixed Grid Numerical Models for Solidification and Melting of Phase Change Materials (PCMs)". Applied Sciences 9, n. 20 (15 ottobre 2019): 4334. http://dx.doi.org/10.3390/app9204334.
Testo completoAbstract (sommario):
Phase change materials (PCMs) are classified according to their phase change process, temperature, and composition. The utilization of PCMs lies mainly in the field of solar energy and building applications as well as in industrial processes. The main advantage of such materials is the use of latent heat, which allows the storage of a large amount of thermal energy with small temperature variation, improving the energy efficiency of the system. The study of PCMs using computational fluid dynamics (CFD) is widespread and has been documented in several papers, following the tendency that CFD nowadays tends to become increasingly widespread. Numerical studies of solidification and melting processes use a combination of formulations to describe the physical phenomena related to such processes, these being mainly the latent heat and the velocity transition between the liquid and the solid phases. The methods used to describe the latent heat are divided into three main groups: source term methods (E-STM), enthalpy methods (E-EM), and temperature-transforming models (E-TTM). The description of the velocity transition is, in turn, divided into three main groups: switch-off methods (SOM), source term methods (STM), and variable viscosity methods (VVM). Since a full numerical model uses a combination of at least one of the methods for each phenomenon, several combinations are possible. The main objective of the present paper was to review the numerical approaches used to describe solidification and melting processes in fixed grid models. In the first part of the present review, we focus on the PCM classification and applications, as well as analyze the main features of solidification and melting processes in different container shapes and boundary conditions. Regarding numerical models adopted in phase-change processes, the review is focused on the fixed grid methods used to describe both latent heat and velocity transition between the phases. Additionally, we discuss the most common simplifications and boundary conditions used when studying solidification and melting processes, as well as the impact of such simplifications on computational cost. Afterwards, we compare the combinations of formulations used in numerical studies of solidification and melting processes, concluding that “enthalpy–porosity” is the most widespread numerical model used in PCM studies. Moreover, several combinations of formulations are barely explored. Regarding the simulation performance, we also show a new basic method that can be employed to evaluate the computing performance in transient numerical simulations.
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Bihdan, O. A., e N. A. Alk Khalaf. "DFT-analysis of protolytic equivalents of 5-(aryl)-4-(methyl,amino)-1,2,4-triazole-3(2H)-thione". Current issues in pharmacy and medicine: science and practice 15, n. 2 (1 agosto 2022): 133–39. http://dx.doi.org/10.14739/2409-2932.2022.2.254474.
Testo completoAbstract (sommario):
The use of modern computer methods in aspects of quantum chemistry and systematic analysis of their results give an idea of the reactivity of organic compounds, as well as to understand the essence of known experimental data, correct predictions, and quantitative estimates. Undoubtedly, theoretical calculations are useful in solving such an urgent problem of modern chemistry as prototropic equilibria and properties of substances in the gas phase, solutions, and solid-state. The aim of the work – until recently assigned to a theoretical vivification in the infusion of solvents on tautomeric equilibrium and acid-base powers і know more broadly practical stasis in the pharmaceutical industry. Materials and methods. The effect of solvation effects on tautomerism and antitropic properties of 1,2,4-triazole derivatives was studied on the example of model compounds. All calculations were performed using the Gauss-View 6.0.1 molecular link visualization program and Gaussian 98, Gaussian 03 software packages and the use of default convergence criteria. After optimizing the geometry, frequency calculations followed. Thus, the stationary structures are confirmed by checking that all ground states have only real frequencies, and all transition states have only one imaginary frequency. The same method and established basis were used to optimize the geometry. Solvation calculations were performed in the framework of continuous models (D-PCM, C-PCM, IEF-PCM, IPCM, SCIPCM) of discrete and combined models using the Hartree–Fock constraint method, the method of density functional theory B3LYP with basic sets 6-31G (d), 6-31G (d,p), 6-31G++ (d,p), cc-pVDZ, as well as semi-empirical methods in the MOPAC6 package. Results. For the first time, various quantum chemical calculations of solvated model compounds using different approaches and models, variation of the basis in non-empirical calculations, identification of the role of electronic correlation effects, method of geometry optimization, etc. were carried out within the theory of self-consistent reaction field. The main stage of this study was to compare trends in the equilibrium change in the relative stability of tautomeric forms of thione-thiol tautomerism of 1,2,4-triazole-2(3H)-thions in the gas phase and different prototropic solvents due to the possibility of using different models and calculation methods for quality predictions of the effect of solvation on the position of tautomeric equilibrium in compounds of this class. It was found that the selected various solvents according to all used quantum chemical methods and models (D-PCM, C-PCM. IEF-PCM, IPCM, SCIPCM) reduce the difference in the stability of tautomeric forms of the investigated compounds in comparison with the gas phase, while the greatest stabilizing effect is observed in the solvation of NH-tautomers derived from 1,2,4-triazole-2(3H)-thiones. Using all energy parameters (∆Etot, ∆E0, ∆H298, ∆G298) allowed to determine the effect of complexation on the relative stability of tautomeric forms of the studied compounds. The difference in the values of the energy levels of HOMO and LUMO – orbitals indicate the reactivity of the molecule and its activation energy, which indicates the chemical reactivity of the molecule to electronic transport and the manifestation of biological activity with intramolecular charge transfer. Conclusions. For the first time, complex quantum chemical calculations of thione-thiol tautomers of 5-(aryl)-4-(methyl, amino)-1,2,4-triazole-3(2H)-thiones were performed and it was found that prototropic solvents reduce the difference in all models. In the stability of tautomeric forms of the investigated compounds in comparison with the gas phase. The calculated values of electronic correlation models on the hydrogen atom make a significant contribution to the relative stability of tautomeric forms, while the use of polarization functions of quantum chemical methods on hydrogen atoms has practically no effect on the tautomeric equilibrium. From the obtained data it becomes clearer that in the gas phase and aprotic solvents the thione tautomer with the center of NH-acidity is the most stable, and the thiol tautomer of 1,2,4-triazole-3(2H)-thione predominates in the transition to polar proton-donor solvents. The obtained data indicate the possibility of conducting an electrophilic substitution reaction (eg, alkylation) in the form of an anion. The partially negative charge of the Nitrogen atoms of the 1,2,4-triazole ring promotes electrophilic addition reactions. In the thionic form, on the contrary, electrophilic substitution reactions are possible.
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Kaderuppan, Shiraz S., Anurag Sharma, Muhammad Ramadan Saifuddin, Wai Leong Eugene Wong e Wai Lok Woo. "Θ-Net: A Deep Neural Network Architecture for the Resolution Enhancement of Phase-Modulated Optical Micrographs In Silico". Sensors 24, n. 19 (26 settembre 2024): 6248. http://dx.doi.org/10.3390/s24196248.
Testo completoAbstract (sommario):
Optical microscopy is widely regarded to be an indispensable tool in healthcare and manufacturing quality control processes, although its inability to resolve structures separated by a lateral distance under ~200 nm has culminated in the emergence of a new field named fluorescence nanoscopy, while this too is prone to several caveats (namely phototoxicity, interference caused by exogenous probes and cost). In this regard, we present a triplet string of concatenated O-Net (‘bead’) architectures (termed ‘Θ-Net’ in the present study) as a cost-efficient and non-invasive approach to enhancing the resolution of non-fluorescent phase-modulated optical microscopical images in silico. The quality of the afore-mentioned enhanced resolution (ER) images was compared with that obtained via other popular frameworks (such as ANNA-PALM, BSRGAN and 3D RCAN), with the Θ-Net-generated ER images depicting an increased level of detail (unlike previous DNNs). In addition, the use of cross-domain (transfer) learning to enhance the capabilities of models trained on differential interference contrast (DIC) datasets [where phasic variations are not as prominently manifested as amplitude/intensity differences in the individual pixels unlike phase-contrast microscopy (PCM)] has resulted in the Θ-Net-generated images closely approximating that of the expected (ground truth) images for both the DIC and PCM datasets. This thus demonstrates the viability of our current Θ-Net architecture in attaining highly resolved images under poor signal-to-noise ratios while eliminating the need for a priori PSF and OTF information, thereby potentially impacting several engineering fronts (particularly biomedical imaging and sensing, precision engineering and optical metrology).
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Li, Jing, Yanning Liao, Shaowei Li, Xu Yang e Naixun Jiao. "Thermal properties of the three-dimensional graphene/paraffin nanocomposite phase change materials". E3S Web of Conferences 341 (2022): 01005. http://dx.doi.org/10.1051/e3sconf/202234101005.
Testo completoAbstract (sommario):
The excellent properties of graphene phase change nanocomposite made it have potential application value in the field of heat storage materials, which was expected to achieve the integration of heat transfer and storage. In order to enhance the thermal performance of paraffin in energy storage, the structure models of n-octadecane and three kinds of graphene/n-octadecane composites were established. Molecular dynamics method was used to study the variation of thermophysical properties. It is found that the strong interaction between graphene and noctadecane restricts the diffusion intensity of n-octadecane molecules, which reflects in the decreasing trend of the self-diffusion coefficient. In addition, the thermal conductivity of each system in the solid state is higher than that of liquid, and abruptly drops near the melting point. The thermal conductivity of the composite PCM always higher than the pure noctadecane and increases with the amount of graphene.
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Pocheć, Michał, Katarzyna M. Krupka, Jarosław J. Panek, Kazimierz Orzechowski e Aneta Jezierska. "Intermolecular Interactions and Spectroscopic Signatures of the Hydrogen-Bonded System—n-Octanol in Experimental and Theoretical Studies". Molecules 27, n. 4 (11 febbraio 2022): 1225. http://dx.doi.org/10.3390/molecules27041225.
Testo completoAbstract (sommario):
n-Octanol is the object of experimental and theoretical study of spectroscopic signatures and intermolecular interactions. The FTIR measurements were carried out at 293 K for n-octanol and its deuterated form. Special attention was paid to the vibrational features associated with the O-H stretching and the isotope effect. Density Functional Theory (DFT) in its classical formulations was applied to develop static models describing intermolecular hydrogen bond (HB) and isotope effect in the gas phase and using solvent reaction field reproduced by Polarizable Continuum Model (PCM). The Atoms in Molecules (AIM) theory enabled electronic structure and molecular topology study. The Symmetry-Adapted Perturbation Theory (SAPT) was used for energy decomposition in the dimers of n-octanol. Finally, time-evolution methods, namely classical molecular dynamics (MD) and Car-Parrinello Molecular Dynamics (CPMD) were employed to shed light onto dynamical nature of liquid n-octanol with emphasis put on metric and vibrational features. As a reference, CPMD gas phase results were applied. Nuclear quantum effects were included using Path Integral Molecular Dynamics (PIMD) and a posteriori method by solving vibrational Schrödinger equation. The latter applied procedure allowed to study the deuterium isotope effect.
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Besagni, Giorgio, Nicolò Varallo e Riccardo Mereu. "Computational Fluid Dynamics Modelling of Two-Phase Bubble Columns: A Comprehensive Review". Fluids 8, n. 3 (3 marzo 2023): 91. http://dx.doi.org/10.3390/fluids8030091.
Testo completoAbstract (sommario):
Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal of developing a predictive tool that can track the complex dynamic phenomena occurring in these types of reactors. For this reason, we present a detailed literature review on the numerical simulation of two-phase bubble columns. First, after a brief introduction to bubble column technology and flow regimes, we discuss the state-of-the-art modelling approaches, presenting the models describing the momentum exchange between the phases (i.e., drag, lift, turbulent dispersion, wall lubrication, and virtual mass forces), Bubble-Induced Turbulence (BIT), and bubble coalescence and breakup, along with an overview of the Population Balance Model (PBM). Second, we present different numerical studies from the literature highlighting different model settings, performance levels, and limitations. In addition, we provide the errors between numerical predictions and experimental results concerning global (gas holdup) and local (void fraction and liquid velocity) flow properties. Finally, we outline the major issues to be solved in future studies.
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Wojtkowiak, Kamil, Aneta Jezierska e Jarosław J. Panek. "Revealing Intra- and Intermolecular Interactions Determining Physico-Chemical Features of Selected Quinolone Carboxylic Acid Derivatives". Molecules 27, n. 7 (1 aprile 2022): 2299. http://dx.doi.org/10.3390/molecules27072299.
Testo completoAbstract (sommario):
The intra- and intermolecular interactions of selected quinolone carboxylic acid derivatives were studied in monomers, dimers and crystals. The investigated compounds are well-recognized as medicines or as bases for further studies in drug design. We employed density functional theory (DFT) in its classical formulation to develop gas-phase and solvent reaction field (PCM) models describing geometric, energetic and electronic structure parameters for monomers and dimers. The electronic structure was investigated based on the atoms in molecules (AIM) and natural bond orbital (NBO) theories. Special attention was devoted to the intramolecular hydrogen bonds (HB) present in the investigated compounds. The characterization of energy components was performed using symmetry-adapted perturbation theory (SAPT). Finally, the time-evolution methods of Car–Parrinello molecular dynamics (CPMD) and path integral molecular dynamics (PIMD) were employed to describe the hydrogen bond dynamics as well as the spectroscopic signatures. The vibrational features of the O-H stretching were studied using Fourier transformation of the autocorrelation function of atomic velocity. The inclusion of quantum nuclear effects provided an accurate depiction of the bridged proton delocalization. The CPMD and PIMD simulations were carried out in the gas and crystalline phases. It was found that the polar environment enhances the strength of the intramolecular hydrogen bonds. The SAPT analysis revealed that the dispersive forces are decisive factors in the intermolecular interactions. In the electronic ground state, the proton-transfer phenomena are not favourable. The CPMD results showed generally that the bridged proton is localized at the donor side, with possible proton-sharing events in the solid-phase simulation of stronger hydrogen bridges. However, the PIMD enabled the quantitative estimation of the quantum effects inclusion—the proton position was moved towards the bridge midpoint, but no qualitative changes were detected. It was found that the interatomic distance between the donor and acceptor atoms was shortened and that the bridged proton was strongly delocalized.
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Pesterev, I. S., N. N. Sosnovsky e B. G. Stepanov. "Radiation by Transducer of Waveguide Type into Conical Half-Spaces Coaxial With It". Journal of the Russian Universities. Radioelectronics 23, n. 1 (28 febbraio 2020): 70–82. http://dx.doi.org/10.32603/1993-8985-2020-23-1-70-82.
Testo completoAbstract (sommario):
Introduction. The present stage of development of hydroacoustic equipment is characterized by a constant improvement of an element base and by an increase in computing power. However, in solving of applied problems one is increasingly faced with a restriction on the realized bandwidth of electroacoustic transducers and antennas. The most of well-known methods of bandwidth expansion do not provide a linear character of the phase-frequency characteristic (PFC) of radiation in the working frequency band, which is of primary importance for the effective formation of relatively short, frequency-tunable, and complex acoustic signals. From this position, the use of a transducer of waveguide type (TWT) is preferential. Its construction and electrical excitation method provides a close to linear phase response of radiation.Aim. The development of a generalized computational model. It has to include particular cases of TWT radiation into cylindrical waveguides coaxial with it and into half-spaces, and also to take into account the influence of waves reflected from the boundaries of the TWT on its field characteristics.Materials and methods. The TWT was presented by a coaxial set of identical water filled piezocylinders with amplitude-phase excitation, provided a mode of broadband radiation in the form of traveling waves. The usage of the method of partial regions allowed one to obtain a solution of the problem of TWT radiation through water filled apertures into the conical adjacent half-spaces, variable in angle.Results. Frequency characteristics of TWT sound pressure results calculated in accordance with the solution of the synthesis problem in the frontal and rear directions for different angles of cone opening were presented and analyzed. Using the proposed computational model of TWT, the possibility of obtaining a bandwidth of the order of 3 octaves was demonstrated. An influence of the thickness of the passive flanges, which are used to link the TWT in the antennas was estimated. The possibility of radiation in the working frequency band of TWT of ultrashort ultra-short single-period pulses for different angles of cone opening was considered. A comparative assessment of the result of calculation with other particular solutions (the radiation by TWT in coaxial water-filled waveguides and also – in half-spaces) was presentedConclusion. An expedient to use a generalized computational model for a more accurate description of the acoustic fields of real antenna models made up of TWT was concluded.
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Zuo, Huiyan, Qiu Yang, Po-Ya Abel Chuang, Ruiming Zhang e Pang-Chieh Sui. "Numerical Investigation of Flow Distribution in PEMFC and Pemwe Stacks Considering Two-Phase Flow in the Stack Headers". ECS Meeting Abstracts MA2024-01, n. 34 (9 agosto 2024): 1687. http://dx.doi.org/10.1149/ma2024-01341687mtgabs.
Testo completoAbstract (sommario):
PEM fuel cell (PEMFC) and PEM water electrolyzer (PEMWE) stacks are assembled by connecting a series of unit cells. The stack headers are conduits formed by the ports of these unit cells; see Fig. 1(a). The flow field in the headers affects the flow uniformity of the stack, which significantly impacts the stack’s performance and lifespan. This study aims to investigate the fluid flows in the stack headers of PEMFC and PEMWE. A specific objective of this study is to understand how two-phase flow (liquid water and gases) in the headers would impact the flow distribution inside the stacks. The present study investigates the flow inside a stack by two-dimensional (2D) and three-dimensional (3D) models, as shown in Figure 1(b) and (c) respectively. The 3D model was constructed with an inlet header and an outlet header with flow resistors in between to represent the unit cells.1,2 CFD simulations using ANSYS Fluent were performed over a 100-cell PEMFC stack based on the k-ε RNG turbulence model. The two-dimensional 100-cell PEMFC stack model was built with COMSOL Multiphysics and considers the diffusion and transport, proton and electron conduction, electrochemical reactions on the catalytic layer, and heat transfer in the unit cells. The flow distribution obtained from the 3D model was used as the boundary conditions for the 2D model to calculate the effects of flow distribution on the overall performance of the stack. It should be pointed out that in the 3D models of PEMFC and PEMWE headers, simulations using the volume of fluid (VOF) model to track the liquid water droplets in a PEMFC and bubbles in a PEMWE were carried out to gain insights into the impact of two-phase flow on stack header flow sharing. The simulation results show the existence of unstable and highly transient turbulence within the PEMFC outlet header, as seen in Figs. 1(d) and 1(e). Jet flows from individual cells cause vortices inside the header, reducing the effective flow area. Liquid water accumulates on the inner wall of the header and is swept out by the cross-flow. In the dead-end region, liquid water undergoes helical motion under the influence of vortices, resulting in a longer residence time in the header and making it less prone to be expelled. This study parametrically investigated the effects of header size and air stoichiometry. As the cross-sectional area of the inlet header decreases from A=1,225 mm2 to A=857.5 mm2, the coefficient of mass flow variation within the stack increases, indicating a decrease in the uniformity of flow distribution inside the stack, as shown in Fig. 1(f). The air stoichiometry also affects the flow distribution inside the stack; as the air stoichiometry λ decreases from 2.2 to 1.4, the uniformity of gas distribution in the stack deteriorates significantly. The methodology used in the present study provides a reference for the parameter design and operating conditions of PEMFC and PEMWE stacks. It helps to gain insights into the optimization of stack header design and energy management. References [1] M. Li, K. Duan, N. Djilali, P.C. Sui, Int. J. Hydrogen Energy, 44 (2019) 30306–30318. [2] B. Chernyavsky, P.C. Sui, B.S. Jou, N. Djilali, Int. J. Hydrogen Energy, 36 (2011) 7136–7151. Figure 1
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Shetty, Reshma A., e Monika Sadananda. "Effect of Mentone® on depression- and anxiety-like profiles and regional brain neurochemistry in the adolescent Wistar Kyoto rat, a putative model of endogenous depression". Indian Journal of Physiology and Pharmacology 66 (10 agosto 2022): 103–10. http://dx.doi.org/10.25259/ijpp_464_2021.
Testo completoAbstract (sommario):
Objectives: Antidepressants, when prescribed to treat adolescent depression tend to induce adverse effects, including suicidal tendencies. This is because the adolescent brain circuitry is still maturing and is therefore extremely vulnerable. As such, the search is on for compounds for use in complementary/alternative medicine. Polyherbal formulations are widely used as therapeutic alternatives for the treatment of depression. Such formulations and plant extracts are being studied in adult rodent models using standard pharmacological parameters, but not much emphasis has been given to testing the same in adolescents and endogenous animal models of depression. Therefore, the present study was focused on testing out the effect of the polyherbal formulation Mentone® on depression- and anxiety-like profiles and brain neurochemistry in the adolescent Wistar Kyoto rat (WKY), a putative model of endogenous and treatment-resistant depression (TRD). Materials and Methods: Mentone®, a polyherbal formulation comprising of four different plant species: Centella asiatica (Brahmi), Evolvulus alsinoides (Shankapushpi), Tinospora cordifolia (Guduchi), and Glycyrrhiza glabra (Yashtimadhu) was tested at two (18 and 36 mg/kg body weight) doses from the post-natal day (pnd) 25 to pnd 42 using standard neurobehavioral paradigms. Vehicular controls were intubated with saline and positive controls with 10 mg/kg body weight of conventional antidepressant, Fluoxetine. From pnd 35 onwards, animals were tested on a battery of tests, including sucrose preference, novel open field, elevated plus maze, and forced swim or Porsolt’s learned helplessness test. On pnd 42, animals were sacrificed and brain regional tissues such as the Prefrontal cortex (PFC), Striatum (Str), Nucleus Accumbens (NAc), and Hippocampus were microdissected out and subjected to reverse phase HPLC for the separation and quantification of monoamines: Norepinephrine (NE), dopamine (DA), serotonin (5-HT) and their metabolites, 3,4-Dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in reference to external standards. Results: Mentone® reversed anhedonia by increasing sucrose consumption in Mentone®-treated as compared to Fluoxetine-treated groups. However, there was no effect on anxiety-related parameters in the novel open field or elevated plus-maze. Mentone® exhibited significant anti-depressant-like effects as indicated by its ability to reduce swim stress-induced immobility in Porsolt’s behavioural despair test with a concomitant increase in climbing or struggling behaviour, signifying reversal of depressive-like symptomatology. HPLC-based separation and quantification of brain regional levels of monoamines and their metabolites revealed increased DA levels in NAc and Str in treated groups with decreased levels of metabolite DOPAC in Mentone®-treated groups indicating increased DA tone. Significantly reduced 5-HT metabolite 5-HIAA levels in both PFC and Str is indicative of increased 5-HT tone in both Mentone®- and Fluoxetine-treated groups. NE was variably affected. Conclusion: While no anxiolytic effects and differential neurochemical effects were observed in brain regional areas in relation to Mentone® and Fluoxetine treatment, anhedonia and forced swim test, which are gold-standard tests for assessing depressive-like profiles indicated an effect of Mentone® that was on par with Fluoxetine. Thus, studies on such Ayurvedic formulations would enable a teasing out or differentiation between anxiolytic-like and depressive-like symptomatology and could constitute a source that holds promise in the development of complementary/alternative therapies for the treatment of depression in general and TRD in particular.
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Jury, Mark R. "An Intercomparison of Observational, Reanalysis, Satellite, and Coupled Model Data on Mean Rainfall in the Caribbean". Journal of Hydrometeorology 10, n. 2 (1 aprile 2009): 413–30. http://dx.doi.org/10.1175/2008jhm1054.1.
Testo completoAbstract (sommario):
Abstract This study examines the spatial variability of mean annual rainfall in the Caribbean in the satellite era 1979–2000. Intercomparisons of gridded rainfall fields from conventional stations, satellite estimators, reanalysis products, and coupled general circulation models (CGCMs) are made, with a focus on the Antilles island chain and their land–sea transitions. The rainfall products are rated for their ability to capture a number of key features, including (i) topographically enhanced precipitation over the larger western Antilles islands of Cuba, Jamaica, Hispanola, and Puerto Rico; (ii) the rain shadow west of Hispanola; (iii) the two dry zones where SSTs are low: north of Venezuela and north of the Lesser Antilles; and (iv) the wet axis extending north of Trinidad. The various monitoring and modeling systems produce gridded rainfall fields at resolutions from 50 to 280 km, from station reconstructions, satellite estimates, blended and reanalysis products, and CGCM climatologies with respect to surface forcing fields. Wet and dry biases were found in many of the reanalysis and satellite products, respectively—either over the whole Caribbean or in a certain sector. The intercomparison found some measure of consensus, but no single product is without discrepancy. High-resolution passive microwave satellite rainfall estimates [Climate Prediction Center’s multisaltellite passive microwave, IR morphed product (cMOR)] appear “most representative”; however, the climatology is short (2003–07) and the field is generally drier than the consensus. Of the conventional products, decadal variability of climate interpolated rain gauges (DEKL), World Climate Research Programme’s (WCRP) blended rain gauges, the Comprehensive Ocean–Atmosphere Data Set (COADS), and an operational climate anomaly monitoring system of NCEP (CAMS) perform well. Among the satellite estimators, the Global Precipitation Climatology Project’s blended gauge and IR satellite (GPCP) and outgoing longwave radiation (OLR) capture the key features and ocean–island transitions. The Center for Ocean–Land–Atmosphere Studies [COLA; the coupled model, part of the Coupled Model Intercomparison Project (CMIP, phase 3)] and the climate forecast system of the NCEP (CFS) models perform reasonably, but NCAR’s Parallel Climate Model (PCM; the CGCM’s historical run of CMIP3) fares poorly. The version 2 hindcast of the operational Medium-Range Forecast (MRF) weather prediction model (REAN) captures the smaller wet zones and topographically enhanced features, but it does not handle the broad oceanic dry zones well, as the input from the operational climate data assimilation system of NCEP (CDAS) has a wet bias. Of the various key rainfall features, high rainfall over southern Cuba and the rain shadow west of Hispanola are poorly handled by most products. The wet axis north of Trinidad and the dry zone north of Venezuela are well represented in many climatologies.
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Munawar, Hafiz Suliman, Siddra Qayyum, Fahim Ullah e Samad Sepasgozar. "Big Data and Its Applications in Smart Real Estate and the Disaster Management Life Cycle: A Systematic Analysis". Big Data and Cognitive Computing 4, n. 2 (26 marzo 2020): 4. http://dx.doi.org/10.3390/bdcc4020004.
Testo completoAbstract (sommario):
Big data is the concept of enormous amounts of data being generated daily in different fields due to the increased use of technology and internet sources. Despite the various advancements and the hopes of better understanding, big data management and analysis remain a challenge, calling for more rigorous and detailed research, as well as the identifications of methods and ways in which big data could be tackled and put to good use. The existing research lacks in discussing and evaluating the pertinent tools and technologies to analyze big data in an efficient manner which calls for a comprehensive and holistic analysis of the published articles to summarize the concept of big data and see field-specific applications. To address this gap and keep a recent focus, research articles published in last decade, belonging to top-tier and high-impact journals, were retrieved using the search engines of Google Scholar, Scopus, and Web of Science that were narrowed down to a set of 139 relevant research articles. Different analyses were conducted on the retrieved papers including bibliometric analysis, keywords analysis, big data search trends, and authors’ names, countries, and affiliated institutes contributing the most to the field of big data. The comparative analyses show that, conceptually, big data lies at the intersection of the storage, statistics, technology, and research fields and emerged as an amalgam of these four fields with interlinked aspects such as data hosting and computing, data management, data refining, data patterns, and machine learning. The results further show that major characteristics of big data can be summarized using the seven Vs, which include variety, volume, variability, value, visualization, veracity, and velocity. Furthermore, the existing methods for big data analysis, their shortcomings, and the possible directions were also explored that could be taken for harnessing technology to ensure data analysis tools could be upgraded to be fast and efficient. The major challenges in handling big data include efficient storage, retrieval, analysis, and visualization of the large heterogeneous data, which can be tackled through authentication such as Kerberos and encrypted files, logging of attacks, secure communication through Secure Sockets Layer (SSL) and Transport Layer Security (TLS), data imputation, building learning models, dividing computations into sub-tasks, checkpoint applications for recursive tasks, and using Solid State Drives (SDD) and Phase Change Material (PCM) for storage. In terms of frameworks for big data management, two frameworks exist including Hadoop and Apache Spark, which must be used simultaneously to capture the holistic essence of the data and make the analyses meaningful, swift, and speedy. Further field-specific applications of big data in two promising and integrated fields, i.e., smart real estate and disaster management, were investigated, and a framework for field-specific applications, as well as a merger of the two areas through big data, was highlighted. The proposed frameworks show that big data can tackle the ever-present issues of customer regrets related to poor quality of information or lack of information in smart real estate to increase the customer satisfaction using an intermediate organization that can process and keep a check on the data being provided to the customers by the sellers and real estate managers. Similarly, for disaster and its risk management, data from social media, drones, multimedia, and search engines can be used to tackle natural disasters such as floods, bushfires, and earthquakes, as well as plan emergency responses. In addition, a merger framework for smart real estate and disaster risk management show that big data generated from the smart real estate in the form of occupant data, facilities management, and building integration and maintenance can be shared with the disaster risk management and emergency response teams to help prevent, prepare, respond to, or recover from the disasters.
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Kimura, Masato, Takeshi Takaishi e Yoshimi Tanaka. "What is the physical origin of the gradient flow structure of variational fracture models?" Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 382, n. 2277 (15 luglio 2024). http://dx.doi.org/10.1098/rsta.2023.0297.
Testo completoAbstract (sommario):
We investigate a physical characterization of the gradient flow structure of variational fracture models for brittle materials: a Griffith-type fracture model and an irreversible fracture phase field model. We derive the Griffith-type fracture model by assuming that the fracture energy in Griffith’s theory is an increasing function of the crack tip velocity. Such a velocity dependence of the fracture energy is typically observed in polymers. We also prove an energy dissipation identity of the Griffith-type fracture model, in other words, its gradient flow structure. On the other hand, the irreversible fracture phase field model is derived as a unidirectional gradient flow of a regularized total energy. We have considered the time relaxation parameter a mathematical approximation parameter, which we should choose as small as possible. In this research, however, we reveal the physical origin of the gradient flow structure of the fracture phase field model (F-PFM) and show that the small time relaxation parameter is characterized as the rate of velocity dependence of the fracture energy. It is verified by comparing the energy dissipation properties of those two models and by analysing a travelling wave solution of the irreversible F-PFM. This article is part of the theme issue ‘Non-smooth variational problems with applications in mechanics’.
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Prusty, Aurojyoti, e Amirtham Rajagopal. "Modeling fracture in brittle materials by higher-order phase field method using C1 non-Sibsonian interpolants". Engineering Computations, 2 agosto 2023. http://dx.doi.org/10.1108/ec-12-2022-0735.
Testo completoAbstract (sommario):
PurposeThis study implements the fourth-order phase field method (PFM) for modeling fracture in brittle materials. The weak form of the fourth-order PFM requires C1 basis functions for the crack evolution scalar field in a finite element framework. To address this, non-Sibsonian type shape functions that are nonpolynomial types based on distance measures, are used in the context of natural neighbor shape functions. The capability and efficiency of this method are studied for modeling cracks.Design/methodology/approachThe weak form of the fourth-order PFM is derived from two governing equations for finite element modeling. C0 non-Sibsonian shape functions are derived using distance measures on a generalized quad element. Then these shape functions are degree elevated with Bernstein-Bezier (BB) patch to get higher-order continuity (C1) in the shape function. The quad element is divided into several background triangular elements to apply the Gauss-quadrature rule for numerical integration. Both fourth-order and second-order PFMs are implemented in a finite element framework. The efficiency of the interpolation function is studied in terms of convergence and accuracy for capturing crack topology in the fourth-order PFM.FindingsIt is observed that fourth-order PFM has higher accuracy and convergence than second-order PFM using non-Sibsonian type interpolants. The former predicts higher failure loads and failure displacements compared to the second-order model due to the addition of higher-order terms in the energy equation. The fracture pattern is realistic when only the tensile part of the strain energy is taken for fracture evolution. The fracture pattern is also observed in the compressive region when both tensile and compressive energy for crack evolution are taken into account, which is unrealistic. Length scale has a certain specific effect on the failure load of the specimen.Originality/valueFourth-order PFM is implemented using C1 non-Sibsonian type of shape functions. The derivation and implementation are carried out for both the second-order and fourth-order PFM. The length scale effect on both models is shown. The better accuracy and convergence rate of the fourth-order PFM over second-order PFM are studied using the current approach. The critical difference between the isotropic phase field and the hybrid phase field approach is also presented to showcase the importance of strain energy decomposition in PFM.
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Kebria, Mahyar Malekzade, e SeonHong Na. "A coupled phase‐field method (PFM) and thermo‐hydro‐mechanics (THM) based framework for analyzing saturated ice‐rich porous materials". International Journal for Numerical and Analytical Methods in Geomechanics, 3 gennaio 2024. http://dx.doi.org/10.1002/nag.3685.
Testo completoAbstract (sommario):
AbstractThis study proposes a novel framework for ice‐rich saturated porous media using the phase‐field method (PFM) coupled with a thermo‐hydro‐mechanical (THM) formulation. By incorporating the PFM and THM approaches based on the continuum theory, we focus on the mechanical responses of fully saturated porous media under freeze‐thaw conditions. The phase transition between liquid water and crystalline ice can be explicitly expressed as captured by evaluating the internal energy and implementing thermal, mechanical, and hydraulic couplings at a diffused interface using PFM. Accurately modeling the coupled mechanical behaviors of ice and soil presents significant challenges. Therefore, in previous numerical frameworks, ad hoc constitutive models were adopted to phenomenologically estimate the overall behavior of frozen soil. To address this, we employ a method that differentiates between the kinematics of the solid and ice constituents, enabling our framework to accommodate distinct constitutive models for each constituent. Within this framework, we naturally introduce anisotropy of frozen soil as it undergoes the freezing process by integrating a transversely isotropic plastic constitutive model for ice. We illustrate the capabilities of our proposed approach through numerical examples, demonstrating its effectiveness in modeling the phase transition process and revealing the overall anisotropic responses of frozen soil.
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Dibua, Obehi G., Anil Yuksel, Nilabh K. Roy, Chee S. Foong e Michael Cullinan. "Nanoparticle Sintering Model: Simulation and Calibration Against Experimental Data". Journal of Micro and Nano-Manufacturing 6, n. 4 (19 novembre 2018). http://dx.doi.org/10.1115/1.4041668.
Testo completoAbstract (sommario):
One of the limitations of commercially available metal additive manufacturing (AM) processes is the minimum feature size most processes can achieve. A proposed solution to bridge this gap is microscale selective laser sintering (μ-SLS). The advent of this process creates a need for models which are able to predict the structural properties of sintered parts. While there are currently a number of good SLS models, the majority of these models predict sintering as a melting process which is accurate for microparticles. However, when particles tend to the nanoscale, sintering becomes a diffusion process dominated by grain boundary and surface diffusion between particles. As such, this paper presents an approach to model sintering by tracking the diffusion between nanoparticles on a bed scale. Phase field modeling (PFM) is used in this study to track the evolution of particles undergoing sintering. Changes in relative density are then calculated from the results of the PFM simulations. These results are compared to experimental data obtained from furnace heating done on dried copper nanoparticle inks, and the simulation constants are calibrated to match physical properties.
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Flachberger, Wolfgang, Jiri Svoboda, Thomas Antretter, Manuel Petersmann e Silvia Leitner. "Numerical treatment of reactive diffusion using the discontinuous Galerkin method". Continuum Mechanics and Thermodynamics, 13 ottobre 2023. http://dx.doi.org/10.1007/s00161-023-01258-0.
Testo completoAbstract (sommario):
AbstractThis work presents a new finite element variational formulation for the numerical treatment of diffusional phase transformations using the discontinuous Galerkin method (DGM). Steep concentration and property gradients near phase boundaries require particular focus on a sound numerical treatment. There are different ways to tackle this problem ranging from (i) the well-known phase field method (PFM) (Biner et al. in Programming phase-field modeling, Springer, Berlin, 2017, Emmerich in The diffuse interface approach in materials science: thermodynamic concepts and applications of phase-field models, Springer, Berlin, 2003), where the interface is described continuously to (ii) methods that allow sharp transitions at phase boundaries, such as reactive diffusion models (Svoboda and Fischer in Comput Mater Sci 127:136–140, 2017, 78:39–46, 2013, Svoboda et al. in Comput Mater Sci 95:309–315, 2014). Phase transformation problems with continuous property changes can be implemented using the continuous Galerkin method (GM). Sharp interface models, however, lead to stability problems with the GM. A method that is able to treat the features of sharp interface models is the discontinuous Galerkin method. This method is well understood for regular diffusion problems (Cockburn in ZAMM J Appl Math Mech 83(11):731–754, 2003). As will be shown, it is also particularly well suited to model phase transformations. We discuss the thermodynamic background by review of a multi-phase, binary system. A new DGM formulation for the phase transformation problem with sharp interfaces is then introduced. Finally, the derived method is used in a 2D microstructural evolution simulation that features a binary, three-phase system that also takes the vacancy mechanism of solid body diffusion into account.
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Grose, Joshua, Obehi G. Dibua, Dipankar Behera, Chee Seng Foong e Michael Cullinan. "Simulation and Property Characterization of Nanoparticle Thermal Conductivity for a Microscale Selective Laser Sintering System". Journal of Heat Transfer, 29 settembre 2022. http://dx.doi.org/10.1115/1.4055820.
Testo completoAbstract (sommario):
Abstract Current Additive Manufacturing (AM) technologies are typically limited by the minimum feature sizes of the parts they can produce. This issue is addressed by the microscale selective laser sintering system (µ-SLS), which is capable of building parts with single micrometer resolutions. Despite the resolution of the system, the minimum feature sizes producible using the µ-SLS tool are limited by unwanted heat dissipation through the particle bed during the sintering process. To address this unwanted heat flow, a particle scale thermal model is needed to characterize the thermal conductivity of the nanoparticle bed during sintering and facilitate the prediction of heat affected zones (HAZ). This would allow for the optimization of process parameters and a reduction in error for the final part. This paper presents a method for the determination of the effective thermal conductivity of copper nanoparticle beds in a µ-SLS system using finite element simulations performed in ANSYS. A Phase Field Model (PFM) is used to track the geometric evolution of the particle groups within the particle bed during sintering. CAD models are extracted from the PFM output data at various timesteps, and steady state thermal simulations are performed on each particle group. The full simulation developed in this work is scalable to particle groups with variable sizes and geometric arrangements. The particle thermal model results from this work are used to calculate the thermal conductivity of the copper nanoparticles as a function of the density of the particle group.
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Holl, Max Philipp, Andrew J. Archer, Svetlana V. Gurevich, Edgar Knobloch, Lukas Ophaus e Uwe Thiele. "Localized states in passive and active phase-field-crystal models". IMA Journal of Applied Mathematics, 9 luglio 2021. http://dx.doi.org/10.1093/imamat/hxab025.
Testo completoAbstract (sommario):
Abstract The passive conserved Swift–Hohenberg equation (or phase-field-crystal [PFC] model) describes gradient dynamics of a single-order parameter field related to density. It provides a simple microscopic description of the thermodynamic transition between liquid and crystalline states. In addition to spatially extended periodic structures, the model describes a large variety of steady spatially localized structures. In appropriate bifurcation diagrams the corresponding solution branches exhibit characteristic slanted homoclinic snaking. In an active PFC model, encoding for instance the active motion of self-propelled colloidal particles, the gradient dynamics structure is broken by a coupling between density and an additional polarization field. Then, resting and traveling localized states are found with transitions characterized by parity-breaking drift bifurcations. Here, we briefly review the snaking behavior of localized states in passive and active PFC models before discussing the bifurcation behavior of localized states in systems of (i) two coupled passive PFC models with common gradient dynamics, (ii) two coupled passive PFC models where the coupling breaks the gradient dynamics structure and (iii) a passive PFC model coupled to an active PFC model.
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Punke, Maik, Vidar Skogvoll e Marco Salvalaglio. "Evaluation of the elastic field in phase‐field crystal simulations". PAMM, 26 settembre 2023. http://dx.doi.org/10.1002/pamm.202300213.
Testo completoAbstract (sommario):
AbstractThe phase‐field crystal model (PFC) describes crystal structures at diffusive timescales through a periodic order parameter representing the atomic density. One of its main features is that it naturally incorporates elastic and plastic deformation. To correctly interpret numerical simulation results or devise extensions related to the elasticity description, it is important to have direct access to the elastic field. In this work, we discuss its evaluation in classical PFC models based on the Swift–Hohenberg energy functional. We consider approaches where the stress field can be derived from the microscopic density field (i.e., the order parameter) and a simple novel numerical routine is proposed. By numerical simulations, we demonstrate that it overcomes some limitations of currently used methods. Moreover, we shed light on the elasticity description conveyed by classical PFC models, characterizing a residual stress effect present at equilibrium. We show explicitly and discuss the evaluation of the elastic fields in prototypical representative cases involving an elastic inclusion, a grain boundary, and dislocations.
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Benoit-Maréchal, Lucas, e Marco Salvalaglio. "Gradient elasticity in Swift-Hohenberg and phase-field crystal models". Modelling and Simulation in Materials Science and Engineering, 24 aprile 2024. http://dx.doi.org/10.1088/1361-651x/ad42bb.
Testo completoAbstract (sommario):
Abstract The Swift-Hohenberg (SH) and Phase-Field Crystal (PFC) models are minimal yet powerful approaches for studying phenomena such as pattern formation, collective order, and defects via smooth order parameters. They are based on a free-energy functional that inherently includes elasticity effects. This study addresses how gradient elasticity (GE), a theory that accounts for elasticity effects at microscopic scales by introducing additional characteristic lengths, is incorporated into SH and PFC models. After presenting the fundamentals of these theories and models, we first calculate the characteristic lengths for various lattice symmetries in an approximated setting. We then discuss numerical simulations of stress fields at dislocations and comparisons with analytic solutions within first and second strain-gradient elasticity. Effective GE characteristic lengths for the elastic fields induced by dislocations are found to depend on the free-energy parameters in the same manner as the phase correlation length, thus unveiling how they change with the quenching depth. The findings presented in this study enable a thorough discussion and analysis of small-scale elasticity effects in pattern formation and crystalline systems using SH and PFC models and, importantly, complete the elasticity analysis therein. Additionally, we provide a microscopic foundation for GE in the context of order-disorder phase transitions.
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Burns, Duncan, Nikolas Provatas e Martin Grant. "Phase field crystal models with applications to laser deposition: A review". Structural Dynamics 11, n. 1 (1 gennaio 2024). http://dx.doi.org/10.1063/4.0000226.
Testo completoAbstract (sommario):
In this article, we address the application of phase field crystal (PFC) theory, a hybrid atomistic-continuum approach, for modeling nanostructure kinetics encountered in laser deposition. We first provide an overview of the PFC methodology, highlighting recent advances to incorporate phononic and heat transport mechanisms. To simulate laser heating, energy is deposited onto a number of polycrystalline, two-dimensional samples through the application of initial stochastic fluctuations. We first demonstrate the ability of the model to simulate plasticity and recrystallization events that follow laser heating in the isothermal limit. Importantly, we also show that sufficient kinetic energy can cause voiding, which serves to suppress shock propagation. We subsequently employ a newly developed thermo-density PFC theory, coined thermal field crystal (TFC), to investigate laser heating of polycrystalline samples under non-isothermal conditions. We observe that the latent heat of transition associated with ordering can lead to long lasting metastable structures and defects, with a healing rate linked to the thermal diffusion. Finally, we illustrate that the lattice temperature simulated by the TFC model is in qualitative agreement with predictions of conventional electron–phonon two-temperature models. We expect that our new TFC formalism can be useful for predicting transient structures that result from rapid laser heating and re-solidification processes.
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Punke, Maik, Steven M. Wise, Axel Voigt e Marco Salvalaglio. "Explicit temperature coupling in phase-field crystal models of solidification". Modelling and Simulation in Materials Science and Engineering, 18 agosto 2022. http://dx.doi.org/10.1088/1361-651x/ac8abd.
Testo completoAbstract (sommario):
Abstract We present a phase-field crystal (PFC) model for solidification that accounts for thermal transport and a temperature-dependent lattice parameter. Elasticity effects are characterized through the continuous elastic field computed from the microscopic density field. We showcase the model capabilities via selected numerical investigations which focus on the prototypical growth of two-dimensional crystals from the melt, resulting in faceted shapes and dendrites. This work sets the grounds for a comprehensive mesoscale model of solidification including thermal expansion.
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Welland, M. J., K. D. Colins, N. Ofori-Opoku, A. A. Prudil e E. S. Thomas. "Multiscale Mesoscale Modeling of Porosity Evolution in Oxide Fuels". Journal of Nuclear Engineering and Radiation Science 6, n. 1 (8 novembre 2019). http://dx.doi.org/10.1115/1.4044405.
Testo completoAbstract (sommario):
Abstract The behavior of fission gas, notably accommodation within intra- and intergranular bubbles, influences the macroscopic properties and overall performance of oxide fuels. This work discusses progress to capture key fission gas-related phenomena with modern mesoscale techniques: the interaction of grain growth and irradiation by a phase-field crystal (PFC) method; overpressurized intragranular bubble migration in a vacancy gradient by a linearized phase-field model; and intergranular bubble interlinkage and percolation by the included phase model (IPM). An outlook on the impact of these models for the investigation of unit mechanisms of fission gas behavior and integration of them into fuel-performance codes is presented.
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te Vrugt, Michael, Max Philipp Holl, Aron Koch, Raphael Wittkowski e uwe thiele. "Derivation and analysis of a phase field crystal model for a mixture of active and passive particles". Modelling and Simulation in Materials Science and Engineering, 29 luglio 2022. http://dx.doi.org/10.1088/1361-651x/ac856a.
Testo completoAbstract (sommario):
Abstract We discuss an active phase field crystal (PFC) model that describes a mixture of active and passive particles. First, a microscopic derivation from dynamical density functional theory (DDFT) is presented that includes a systematic treatment of the relevant orientational degrees of freedom. Of particular interest is the construction of the nonlinear and coupling terms. This allows for interesting insights into the microscopic justification of phenomenological constructions used in PFC models for active particles and mixtures, the approximations required for obtaining them, and possible generalizations. Second, the derived model is investigated using linear stability analysis and nonlinear methods. It is found that the model allows for a rich nonlinear behavior with states ranging from steady periodic and localized states to various time-periodic states. The latter include standing, traveling, and modulated waves corresponding to spatially periodic and localized traveling, wiggling, and alternating peak patterns and their combinations.
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Li, Xinju, Xiaoping Guan, Rongtao Zhou, Ning Yang e Mingyan Liu. "CFD Simulation of Gas Dispersion in a Stirred Tank of Dual Rushton Turbines". International Journal of Chemical Reactor Engineering 15, n. 4 (11 maggio 2017). http://dx.doi.org/10.1515/ijcre-2016-0221.
Testo completoAbstract (sommario):
Abstract3D Eulerian-Eulerian model was applied to simulate the gas-liquid two-phase flow in a stirred tank of dual Rushton turbines using computational fluid dynamics (CFD). The effects of two different bubble treatment methods (constant bubble sizevs. population balance model, PBM) and two different coalescence models (Luo modelvs. Zaichik model) on the prediction of liquid flow field, local gas holdup or bubble size distribution were studied. The results indicate that there is less difference between the predictions of liquid flow field and gas holdup using the above models, and the use of PBM did not show any advantage over the constant bubble size model under lower gas holdup. However, bubble treatment methods have great influence on the local gas holdup under larger gas flow rate. All the models could reasonably predict the gas holdup distribution in the tank operated at a low aeration rate except the region far from the shaft. Different coalescence models have great influence on the prediction of bubble size distribution (BSD). Both the Luo model and Zaichik model could qualitatively estimate the BSD, showing the turning points near the impellers along the height, but the quantitative agreement with experiments is not achieved. The former over-predicts the BSD and the latter under-predicts, showing that the existing PBM models need to be further developed to incorporate more physics.
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Howard, Brian, David E. Haines, Atul Verma, Nicole Kirchhof, Noah Barka, Birce Onal, Mark T. Stewart e Daniel C. Sigg. "Characterization of Phrenic Nerve Response to Pulsed Field Ablation". Circulation: Arrhythmia and Electrophysiology, giugno 2022. http://dx.doi.org/10.1161/circep.121.010127.
Testo completoAbstract (sommario):
Background: Phrenic nerve palsy is a well-known complication of cardiac ablation, resulting from the application of direct thermal energy. Emerging pulsed field ablation (PFA) may reduce the risk of phrenic nerve injury but has not been well characterized. Methods: Accelerometers and continuous pacing were used during PFA deliveries in a porcine model. Acute dose response was established in a first experimental phase with ascending PFA intensity delivered to the phrenic nerve (n=12). In a second phase, nerves were targeted with a single ablation level to observe the effect of repetitive ablations on nerve function (n=4). A third chronic phase characterized assessed histopathology of nerves adjacent to ablated cardiac tissue (n=6). Results: Acutely, we observed a dose-dependent response in phrenic nerve function including reversible stunning (R 2 =0.965, P <0.001). Furthermore, acute results demonstrated that phrenic nerve function responded to varying levels of PFA and catheter proximity placements, resulting in either: no effect, effect, or stunning. In the chronic study phase, successful isolation of superior vena cava at a dose not predicted to cause phrenic nerve dysfunction was associated with normal phrenic nerve function and normal phrenic nerve histopathology at 4 weeks. Conclusions: Proximity of the catheter to the phrenic nerve and the PFA dose level were critical for phrenic nerve response. Gross and histopathologic evaluation of phrenic nerves and diaphragms at a chronic time point yielded no injury. These results provide a basis for understanding the susceptibility and recovery of phrenic nerves in response to PFA and a need for appropriate caution in moving beyond animal models.
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Pinomaa, Tatu, Matti Lindroos, Paul Jreidini, Matias Haapalehto, Kais Ammar, Lei Wang, Samuel Forest, Nikolas Provatas e Anssi Laukkanen. "Multiscale analysis of crystalline defect formation in rapid solidification of pure aluminium and aluminium–copper alloys". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 380, n. 2217 (3 gennaio 2022). http://dx.doi.org/10.1098/rsta.2020.0319.
Testo completoAbstract (sommario):
Rapid solidification leads to unique microstructural features, where a less studied topic is the formation of various crystalline defects, including high dislocation densities, as well as gradients and splitting of the crystalline orientation. As these defects critically affect the material’s mechanical properties and performance features, it is important to understand the defect formation mechanisms, and how they depend on the solidification conditions and alloying. To illuminate the formation mechanisms of the rapid solidification induced crystalline defects, we conduct a multiscale modelling analysis consisting of bond-order potential-based molecular dynamics (MD), phase field crystal-based amplitude expansion simulations, and sequentially coupled phase field–crystal plasticity simulations. The resulting dislocation densities are quantified and compared to past experiments. The atomistic approaches (MD, PFC) can be used to calibrate continuum level crystal plasticity models, and the framework adds mechanistic insights arising from the multiscale analysis. This article is part of the theme issue ‘Transport phenomena in complex systems (part 2)’.
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"*V. S. Yessaulkov ". ""ON CHOOSING APPROPRIATE EQUATIONS FOR MATHENATICAL MODELING OF PROCESSES IN PCM-BASED ENERGY STORAGE SYSTEMS FOR VEHICLES"". Science and Technology of Kazakhstan, 26 giugno 2023, 129–36. http://dx.doi.org/10.48081/jfbh2786.
Testo completoAbstract (sommario):
"With regards to storing thermal energy, latent heat storage are the matter of growing attention over the past years due to their straightforward design, affordable production and maintenance costs, as well as universal applicability. The phase-change materials (PCM) are well-known for their widespread use in aforementioned systems primarily because of their high thermal storage density. Many studies concerning analysing and optimising the design of latent heat storage systems (LHHS) have been carried out in the last years. In relatively recent researches, different research teams have investigated different types of LHHS, using mathematical models of different levels of complexity. The wide variety of different approaches to the mathematical modeling (including different methods, algorithms and applications from different field of pure and applied research) sometimes make it challenging to choose and implement a proper system of equations and criteria without excessive complicacies. This very paper describes and elaborates on the system of equations that can and will be applied to the mathematical modeling of charging/recharging process in PCM-based LHHS for commercial vehicles. After a brief review of previous models, author presents the model and asses its accuracy and possibilities for further development and exploration. "
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Momeni, Davood. "Position-dependent mass quantum systems and ADM formalism". SciPost Physics Proceedings, n. 4 (13 agosto 2021). http://dx.doi.org/10.21468/scipostphysproc.4.009.
Testo completoAbstract (sommario):
The classical Einstein-Hilbert (EH) action for general relativity (GR) is shown to be formally analogous to the classical system with position-dependent mass (PDM) models. The analogy is developed and used to build the covariant classical Hamiltonian as well as defining an alternative phase portrait for GR. The set of associated Hamilton’s equations in the phase space is presented as a first-order system dual to the Einstein field equations. Following the principles of quantum mechanics, I build a canonical theory for the classical general. A fully consistent quantum Hamiltonian for GR is constructed based on adopting a high dimensional phase space. It is observed that the functional wave equation is timeless. As a direct application, I present an alternative wave equation for quantum cosmology. In comparison to the standard Arnowitt-Deser-Misner(ADM) decomposition and quantum gravity proposals, I extended my analysis beyond the covariant regime when the metric is decomposed into the 3+13+1 dimensional ADM decomposition. I showed that an equal dimensional phase space can be obtained if one applies ADM decomposed metric.
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Lazzarini, Laura, Enzo Rotunno, Vincenzo Grillo e Massimo Longo. "Determination of the atomic stacking sequence of Ge-Sb-Te nanowires by HAADF STEM". MRS Proceedings 1512 (2013). http://dx.doi.org/10.1557/opl.2012.1746.
Testo completoAbstract (sommario):
ABSTRACTThe reduction of the active cell size to the nanoscale is crucial for the improvement of the phase change memory devices (PCM) based on Ge-Sb-Te (GST) alloys. The self-assembly of Au catalyzed Ge1Sb2Te4 (GST-124) nanowires (NWs) has been achieved by metal organic chemical vapor deposition. The atomic arrangement of the NWs has been investigated and the stacking sequence has been identified, by combining the direct observation by High Angle Annular Dark Field (HAADF) imaging and simulations. It has been assessed that Ge and Sb atoms can randomly occupy the same sites in the crystal lattice, despite the adverse predictions of the theoretical models elaborated for the bulk material.