bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier transport in LPCVD grown Ge-doped β-Ga2O3/4H-SiC isotype heterojunction
Authors: Saquib T. , Akyol F. , Ozden H. , Somaiah N. , Sahoo J. , Muralidharan R. , Nath D. N.
Published: February 2024

We report on the study of electron transport and band offset across β-Ga2O3/4H-SiC N–n isotype heterojunction. N-type β-Ga2O3 of thickness 2.7 μm was grown using low-pressure chemical vapor deposition using germanium (Ge) as the dopant on an n-type 4H-SiC substrate. The grown epilayer having (−201) orientation was verified through XRD. Temperature-dependent I–V and C–V measurements were performed (50–300 K) to investigate the transport properties across the heterojunction. First, lateral diodes were fabricated on β-Ga2O3, and from C–V, n-doping was estimated to be 2.3×1017cm−3 in the epilayer while the Schottky barrier height was estimated to be 1.75 eV. In top-down I–V sweeps, the reverse current across the heterojunction exhibited marginal dependence on temperature, indicating a possible tunnelling-based transport mechanism, while the forward current exhibited an exponential dependence on both temperature and the applied bias. The band diagram indicated the formation of a two-dimensional electron gas (2DEG) at the hetero-interface, which was indirectly confirmed using C–V measurement and TCAD simulation at low temperatures. From the position of the Fermi level in SiC and band diagram, a conduction band offset of 0.4–0.5 eV was estimated between β-Ga2O3 and 4H-SiC.
Nonlinear electro-rheological instability of two moving cylindrical fluids: An innovative approach
Authors: Moatimid Galal M. , Mohamed Yasmeen M.
Published: February 2024

The present article examines the nonlinear stability of two viscoelastic electrified cylindrical fluids immersed in permeable media. The current structure consists of two endless vertical cylinders containing two electrified fluids. An axial unchanged electric field (EF) is applied to the entire construction; additionally, the impact of the surface tension is reflected. The main driving force for understanding this challenge has increasing significance in atmospheric and oceanic dynamics. The viscous potential theory is employed to ease the mathematical processes. The fundamental hydrodynamic equations are combined with Maxwell's equations in the quasi-static approximation to set the boundary-value problem. The appropriate boundary conditions (BCs) are expressed in a nonlinear form; this nonlinearity is achieved by addressing the linearized controlling equations of the motion. The viscoelastic impacts are considered to illustrate how the BCs produce their contributions. Consequently, the equations of motion are tackled without the effects of viscoelasticity parameters. The interface displacement consequently interacts vertically along with the cylindrical axis. The Rayleigh Helmholtz–Duffing oscillator describes the propagation of the interface between the two fluids. The non-perturbative approach (NPA), based on the He's frequency formula, transforms the typical nonlinear differential equation (NDE) into a linear one. The non-dimensional analysis reveals a lot of dimensionless physical numerals. These non-dimensional physical characteristics can be utilized to study the fundamental character of the liquid movement. They are also used to reduce the quantity of variables that are needed to comprehend the framework. A quick explanation of NPA is also presented. The stability study reveals the real/complex coefficients of the NDE. The numerical simulations show that there is a consistent solution and that the increases in the axial EF, as well as axial wavenumber, stabilize the system. The obtained findings help to understand and explain diverse nonlinear progressions that have taken place in fluid mechanics. To show the impact of the different factors and the efficiency of the stability approach, diverse PolarPlot diagrams are graphed for both actual and hypothetical portions.
Grain diameter-dependent tuning of exchange anisotropy in the ion-beam sputtered Co-based full Heusler alloy coupled with antiferromagnet
Authors: Kedia Sanjay Kumar , Kumar Nakul , Sharma Nikita , Chaudhary Sujeet
Published: February 2024

We report an investigation into the substantially large and customizable exchange anisotropy (HEA) and coercivity (HC) in a set of bottom-pinned Ir7Mn93/Co2FeAl bilayer heterostructures fabricated using ion-beam sputtering at room temperature (RT) in the presence of an in-situ in-plane static magnetic field of 1 kOe. This modulation is achieved by controlling the microstructural parameter (i.e., grain diameter) of the antiferromagnetic (AF) Ir7Mn93 (IrMn) layer. These bilayers revealed strong positive exchange anisotropy (PEA) at RT, while negative exchange anisotropy (NEA) became evident when field-cooled to 15 K in the presence of 3 kOe. By systematically controlling the AF grain diameter from ∼5.39 to ∼6.94 nm, the PEA and NEA were found to increase by a factor of ∼2.1 and ∼1.8, respectively. However, once the AF grain diameter exceeded the necessary threshold for thermal stability, further enhancement in grain diameter above ∼6.94 nm led to a reduction in both HEA and HC. This decrease was attributed to a reduction in pinning centers at the AF/FM (ferromagnet) interface. The training data are fitted by utilizing various theoretical models, such as thermal relaxation, Binek's model, and spin relaxation model. The spin relaxation model was found to be applicable to fit the complete range of training data, encompassing both thermal and athermal decay, within the context of frozen and rotatable spins.
Hartree–Fock–Bogoliubov theory for number-parity-violating fermionic Hamiltonians
Authors: Henderson Thomas M. , Tabrizi Shadan Ghassemi , Chen Guo P. , Scuseria Gustavo E.
Published: February 2024

It is usually asserted that physical Hamiltonians for fermions must contain an even number of fermion operators. This is indeed true in electronic structure theory. However, when the Jordan–Wigner (JW) transformation is used to map physical spin Hamiltonians to Hamiltonians of spinless fermions, terms that contain an odd number of fermion operators may appear. The resulting fermionic Hamiltonian thus does not have number parity symmetry and requires wave functions that do not have this symmetry either. In this work, we discuss the extension of standard Hartree–Fock–Bogoliubov (HFB) theory to the number-parity-nonconserving case. These ideas had appeared in the literature before but, perhaps for lack of practical applications, had, to the best of our knowledge, never been employed. We here present a useful application for this more general HFB theory based on coherent states of the SO(2M + 1) Lie group, where M is the number of orbitals. We also show how using these unusual mean-field states can provide significant improvements when studying the JW transformation of chemically relevant spin Hamiltonians.
Re-evaluating the methane adsorption behavior in shale kerogen: Unifying experiment and molecular simulation
Authors: Zhang Chu , Yao Yanbin , Swennen Rudy , Zhang Yuheng
Published: February 2024

The methane adsorption capacity is crucial for evaluating gas-in-place resources and the gas production potential in shale gas reservoirs. There are many reports concerning the interfacial interaction between methane fluid and rock using various thermodynamic models; however, little research has been performed to reveal how methane is adsorbed into nanopores with different scales. In this study, we did methane adsorption experiments on nine Longmaxi Formation shale kerogen. Then, molecular simulation and an improved Ono–Kondo model were used to analyze the methane adsorption behaviors. Results show that methane is preferentially adsorbed in sulfur-containing sites by surface adsorption and pore-filling adsorption, and methane adsorbed in the form of pore-filling contributes dominantly to the total methane adsorption amount. Surface adsorption capacity nS increases with increasing mesopore volume, while pore-filling adsorption capacity nF is affected by both micropore (<2 nm) development and the micropore accessibility of methane. On the one hand, nF increases logarithmically with increasing micropore volume. On the other hand, the mean interplanar distance of the aromatic layers d002 is the key parameter in determining nF because the micropores within the aromatic layer with d002 less than 0.38 nm will be inaccessible for methane. This study is essential for understanding the methane adsorption mechanism and lay the foundation for future investigation of fluids–rock interactions.
A flow control strategy for a near-wall square cylinder using porous media: A direct numerical simulation study
Authors: Chen Gong , Zou Chenqi , Yang Hanming , Chen Shunhua , Xie Peng
Published: February 2024

The topic of flows around a near-wall square cylinder has garnered increasing attention in recent decades. However, there are a few publications that have focused on mitigating the occurrence of a substantial negative lift in near-wall flows. In light of this, the present study has developed a novel flow control strategy that covers porous media at inward corners of a near-wall square cylinder to address this problem. We achieve such a control strategy with the aid of a high-fidelity computational framework at Re = 1000. Direct numerical simulations are employed to account for accurate flow behaviors, and the Cartesian cut-cell method as well as an adaptive mesh refinement algorithm are advocated to simplify grid generation and reduce computational costs. Additionally, a quasi-microscopic flow model is introduced to model the porous medium pore structure, providing an intuitive and accurate description of internal flows within the porous medium. Six porous medium layouts are first designed, and their influences and mechanisms on flow control are assessed using the presented computational framework to identify an optimal strategy. The optimal strategy yields a notable reduction of 52.472% in the lift coefficient. The identified strategy is then applied to a case involving a near-wall square cylinder with a substantial negative lift, where a gap ratio of 0.6 is determined via parameterization. The capacity of the presented strategy in flow control of the near-wall square cylinder is fully explored and demonstrated via the consideration of different porosities. The results indicate that the most effective flow control is achieved when the porosity exceeds 90%, leading to a near-zero lift coefficient. Furthermore, the underlying mechanism contributing to the variations in flow control effectiveness due to different porosities is analyzed.
Origin of the super-resolution of microsphere-assisted imaging
Authors: Maslov Alexey V. , Astratov Vasily N.
Published: February 2024

Theoretical explanation of the super-resolution imaging by contact microspheres created a point of attraction for nanoimaging research during the last decade with many models proposed, yet its origin remains largely elusive. Using a classical double slit object, the key factors responsible for this effect are identified by an ab initio imaging model comprising object illumination, wave scattering, and image reconstruction from the diffracted far fields. The scattering is found by a full-wave solution of the Maxwell equations. The formation of super-resolved images relies on coherent effects, including the light scattering into the waves circulating inside the microsphere and their re-illumination of the object. Achieving the super-resolution of the double slit requires a wide illumination cone as well as a deeply sub-wavelength object-to-microsphere separation. The resultant image has a significantly better resolution as compared to that from the incoherent imaging theory.
Acoustic metamaterials for realizing a scalable multiple phi-bit unitary transformation
Authors: Runge K. , Deymier P. A. , Hasan M. A. , Lata T. D. , Levine J. A.
Published: February 2024

The analogy between acoustic modes in nonlinear metamaterials and quantum computing platforms constituted of correlated two-level systems opens new frontiers in information science. We use an inductive procedure to demonstrate scalable initialization of and scalable unitary transformations on superpositions of states of multiple correlated logical phi-bits, classical nonlinear acoustic analog of qubits. A multiple phi-bit state representation as a complex vector in a high-dimensional, exponentially scaling Hilbert space is shown to correspond with the state of logical phi-bits represented in a low-dimensional linearly scaling physical space of an externally driven acoustic metamaterial. Manipulation of the phi-bits in the physical space enables the implementation of a non-trivial multiple phi-bit unitary transformation that scales exponentially. This scalable transformation operates in parallel on the components of the multiple phi-bit complex state vector, requiring only a single physical action on the metamaterial. This work demonstrates that acoustic metamaterials offer a viable path toward achieving massively parallel information processing capabilities that can challenge current quantum computing paradigms.
Decomposition characteristics of C4F7N-based SF6-alternative gas mixtures
Authors: Gao Wenqiang , Posada Luisa , Shiravand Vahid , Shubhashish Shubhashish , Price Capri , Zhang Boya , Potyrailo Radislav , Younsi Karim , Shan Shiyao , Ndiaye Ibrahima , Cabrera Charlotte , Zhou Jierui , Perret Maxime , Berteloot Thomas , Kieffel Yannick , Laso Andres , Uzelac Nenad , Suib Steven L. , Cao Yang
Published: February 2024

C4F7N [2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile]/CO2 gas mixtures are being developed as an eco-friendly electrical insulator to replace SF6, the most potent greenhouse industrial gaseous dielectric. However, recent studies have reported complicated and often conflicting decomposition pathways for C4F7N/CO2 gas mixtures, which has raised concerns. In this work, the decomposition characteristics of C4F7N/CO2 gas mixtures were studied comprehensively by both designed computations and experiments. Computations were performed starting from fundamental propositions of C4F7N/CO2 decompositions, which were further experimentally verified by pyrolysis, long-term thermal aging with/without catalytic materials (industrial-grade molecular sieves 4A), and electrical decomposition by spark discharge. The results of both computations and experiments suggest that in an ideal thermal decomposition, C4F7N is likely to decompose into C2F6 and small fluoronitriles first at high temperatures. The generation of C3F6 and C2N2 from C4F7N thermal decomposition at lower temperatures appears because of the catalytic effect of incompatible materials, for example, the industrial-grade molecular sieves 4A that we tested. The electron impact dissociation of C4F7N plays an important role in C4F7N electrical decomposition, leading to additional formation of distinctive small molecules of CF4 and C2N2 of low concentrations. It was pointed out based on a real arcing test in a load disconnector that the decomposition of C4F7N gas mixtures in real applications will be at a much moderate and manageable rate than what was obtained from the highly accelerated laboratory tests presented in this work. The signatures of decomposition products extracted in this study provide invaluable guidance for developing decomposition-based diagnosis and fixation of decomposition byproducts toward SF6-free power grids.
Integrated approaches for road extraction and de-noising in satellite imagery using probability neural networks
Authors: Dasari Subhashini , Dutt V.B.S Srilatha Indira
Published: February 2024

Remote sensing plays a crucial role in detecting and monitoring natural resources, extending its applications to various fields, such as geography, topographical surveying, and geoscience disciplines, including land management, forest monitoring, crop identification, soil mapping, and ocean resource finding. Road extraction holds significant importance among these applications, contributing to the development of Geographic Information Systems (GIS). The automatic updating of GIS information has become essential in daily life. Road extraction stands out as a prominent application within remote sensing image systems, addressing challenges related to intensity and width. Intensity challenges involve variations in spectral or color values of roads, while width challenges pertain to the issues associated with the size and structure of roads during the extraction process. Addressing the challenges associated with road extraction from remote sensing imagery is crucial for achieving accurate and efficient results. This paper under consideration compares the conventional and contemporary methods of road extraction, emphasizing completeness and correctness metrics. Conventional methods involve techniques like CLAHistogramEqualization for enhancement and fuzzy c-mean clustering for extraction, resulting in incremental improvements. To enhance results further, images are de-noised using Gray World Optimization and iterative domain-guided image filtering. To improve efficiency in road extraction, the authors proposed a contemporary approach through probability neural networks with de-noised images. The comparison is made based on the completeness and correctness of both conventional and contemporary methods.
In situ grown large-size highly crystalline black phosphorus thin film for self-driven photodetector
Authors: Du Kaixiang , Wang Mingyuan , Liang Zhiping , Lv Quanjiang , Hou Haigang , Lei Shuangying , Liu Guiwu , Liu Junlin , Qiao Guanjun
Published: February 2024

Black phosphorus (BP) thin film has highlighted its potential in the photoelectric detection field due to its wide-spectrum and high-absorption capacity. However, the fabrication of controllable and highly quality BP film in large dimensions remains a huge challenge. Herein, we creatively fabricated a centimeter-size highly crystalline BP thin film on the bare silicon substrate using a space-confined chemical vapor transport technique, and we in situ constructed a self-driven BP-based metal–semiconductor–metal photodetector. The as-constructed photodetector achieves a high responsivity of up to 500 mA/W, an external quantum efficiency of 42.1%, a maximum specific detectivity of 3.82 × 1010 cm Hz1/2 W−1, and a small noise-equivalent-power of 3.97 × 10−15 W Hz−1/2 under zero bias voltage at 1550 nm illumination. This work provides a strategy to effectively prepare BP thin film for in situ manufacturing self-driven photodetector, which marks a significant step forward in the integration of BP into the industrial settings.
The filaments control for tunning digital resistive switching in data storage application and analog behavior as an artificial synapse with CsPbBr3-based memristor
Authors: Zhu Yuanyuan , Chen Mengyao , Lu Hongbing , Mi Pengtao , Luo Daobin , Wang Youqing , Liu Yong , Xiong Rui , Wang Hongjun
Published: February 2024

Implementation of tunable digital and analog resistive switching (RS) behaviors for memristors is crucial toward their development in data storage and energy-efficient computations. Herein, the CsPbBr3 film-based RS memristors with different switching film thickness and adaptable electrodes are constructed, which are implemented by the solution processed method. All the constructed memristors demonstrate stable bipolar switching behaviors, and in special, the gradual analog RS behavior with multi-level conductance is observed for the thin memristor, making it as the promising artificial synapse. As a comparison, the thick memristor demonstrates digital abrupt RS behavior, accompanying with a high memory window (>103), which can be applied in data storage field. Furthermore, the evolution of conductive filaments, stemming from synergetic bromine vacancies and aluminum atoms, is proposed to clarify the distinguished dynamic changes in the RS process. This work provides an optimization strategy to tune RS behavior for CsPbBr3-based RS memristors and paves the way for both data storage and artificial synapse applications.
A compensation method of carrier magnetic interference under pathological conditions for geomagnetic navigation
Authors: Ji Caijuan , Song Chengying , Li Sheng , Gao Yang , Chen Qingwei
Published: February 2024

Geomagnetic navigation has become a hot spot in current research because of its characteristics of passiveness and good concealment. However, the magnetic interference from various ferromagnetic substances, electronic equipment, etc., of the carrier will be superimposed on the geomagnetic field, causing magnetometer measurement errors, thus affecting navigation accuracy. In practice, due to the limited maneuverability of the carrier, sufficient geomagnetic observation data cannot be obtained, resulting in the observation equation used for carrier magnetic interference compensation to be seriously pathological. To achieve the compensation of carrier magnetic interference, this paper proposes the total least squares method based on the ridge regression using the L curve to solve ridge parameters. This method can effectively suppress the measurement noise that exists on both sides of the observation equation, and is suitable for alleviating the pathological effects of carrier magnetic interference compensation. Experimental results show that the compensated magnetometer measurement error is reduced to 3% of the carrier magnetic interference by using the method proposed in this paper, which obtains more stable and accurate parameter estimates.
Impact of carrier extraction on photoinduced phase segregation of mixed-halide perovskites
Authors: Qi Xiaorong , Fang Shuyan , Miao Yuchen , Wu Jun , Yang Liu , Yang Cheng , Wang Xu , Zheng Fei , Zhao Feiyu , Shafique Shareen , Hu Ziyang
Published: February 2024

Photoinduced phase segregation (PHS) poses a significant challenge in the practical utilization of mixed-halide perovskites (MHPs) for photovoltaic applications. In this Letter, we investigate the behavior of PHS within operational photovoltaic devices, extending beyond the conventional focus on single-layer MHPs. Our research explores the influence of carrier extraction on PHS by employing various charge transport layers (CTLs) in combination with perovskite films, utilizing photoluminescence (PL) characterization, mainly reflected through the time-dependent PL redshift. Furthermore, we observe that photovoltaic devices capable of efficient carrier extraction exhibit enhanced photoinduced stability during regular operation conditions such as short-circuit operation, as compared to open-circuit conditions. Our findings reveal that efficient photogenerated carrier extraction from the perovskite film mitigates the occurrence of PHS. This work underscores the significance of carrier extraction by CTLs in achieving the efficiency and stability of MHP-based photovoltaic devices.
Shedding of water droplets by the dual synthetic jet
Authors: Gao Tianxiang , Luo Zhenbing , He Wei , Zhou Yan , Cheng Pan , Wang Dehui , Peng Can , Deng Xiong
Published: February 2024

Taking into account the benefits of the dual synthetic jet (DSJ) actuator's simple form, the absence of an air supply, and powerful jet momentum, as well as the low water adhesion force of the superhydrophobic surfaces, it is possible to make droplet shedding happen easily by combining these two methods. This paper studied the motion of water droplets under the action of the DSJ actuator with inclined outlets on three different kinds of surfaces with different wettability, namely, aluminum (hydrophilic), fluorinated silicon (hydrophobic), and superhydrophobic surfaces. Particle image velocimetry measurements were used to describe the flow field of the DSJ actuator. Then, high-speed photography was adopted to compare the critical air velocity for stable motion of the droplet on the three kinds of surfaces. The droplet mobility at three different surfaces when the jet velocity was the same was compared. The displacement and changes of the contact line of water droplets with different volumes on the superhydrophobic surface under the influence of jets were studied. Besides, choosing a typical case, the effect of the dual synthetic jet on the droplet was quantitatively examined, as well as the aerodynamic drag and lift forces. And some of the phenomenon observed in the experiment was explained using the simulation data. It is hoped that this research would lead to the development of a new method of facilitating droplet transport in applications such as anti-icing, drug delivery, self-cleaning surfaces, etc.
Effect of upstream injection and pylon downstream of the cavity on the mixing characteristics
Authors: Nair Prasanth P. , Suryan Abhilash , Narayanan Vinod
Published: February 2024

Flame stabilizers employing pylons within scramjet engines are becoming more prominent for enhancing fuel penetration and mixing. Studies have highlighted the enhanced mixing efficiency achieved by positioning a pylon ahead of the cavity. Nonetheless, the potential of a pylon positioned downstream of the cavity has not been thoroughly examined. To bridge this gap, the present study explores the effects of fuel injection when a pylon is positioned downstream of the cavity, as well as investigates injection upstream of the cavity. Numerical simulation is employed, utilizing a hybrid Reynolds-averaged Navier–Stokes/large eddy simulation simulation with an improved delayed detached eddy simulation turbulence model. To gain a deeper understanding of the mixing dynamics, additional investigation using dynamic mode decomposition has been performed. The upstream injection with a pylon downstream of the cavity has an improved mixing performance in comparison to the cases without it. The pylon placed downstream also assists in increasing the penetration height. The placement of the pylon leads to an increase in the total pressure loss. The low-frequency vortices are observed within the cavity due to back pressure caused by the pylon. Large-scale and higher-frequency vortices are observed downstream of the pylon. It is found in the modal analysis that the low-frequency vortices within the cavity and high-frequency modes downstream of the pylon enhance the mixing. The acoustic loading is observed to be higher when the pylon is placed downstream of the cavity.
Base on temporal convolution and spatial convolution transformer for fluid prediction through well logging data
Authors: Sun Youzhuang , Zhang Junhua , Zhang Yongan
Published: February 2024

Fluid prediction is important in exploration work, helping to determine the location of exploration targets and the reserve potential of the estimated area. Machine learning methods can better adapt to different data distributions and nonlinear relationships through model training, resulting in better learning of these complex relationships. We started by using the convolution operation to process the log data, which includes temporal convolution and spatial convolution. Temporal convolution is specifically designed to capture time series relationships in time series data. In well log data, time information is often critical for understanding fluid changes and other important details. Temporal convolution learns trends and cyclical changes in the data. The spatial convolution operation makes the model more sensitive to the local features in the logging data through the design of the local receptive field and improves the sensitivity to fluid changes. Spatial convolution helps capture spatial correlations at different depths or locations. This can help the model understand the change of fluid in the vertical direction and identify the spatial relationship between different fluids. Then, we use the transformer module to predict the fluid. The transformer module uses a self-attention mechanism that allows the model to focus on information with different weights at different locations in the sequence. In the well log data, this helps the model to better capture the formation characteristics at different depths or time points and improves the modeling ability of time series information. The fully connected structure in the transformer module enables each position to interact directly with other locations in the sequence. By applying it to the data of Tarim Oilfield, the experimental results show that the convolutional transformer model proposed in this paper has better results than other machine learning models. This study provides a new idea in the field of logging fluid prediction.
Self-supervised learning based on Transformer for flow reconstruction and prediction
Authors: Xu Bonan , Zhou Yuanye , Bian Xin
Published: February 2024

Machine learning has great potential for efficient reconstruction and prediction of flow fields. However, existing datasets may have highly diversified labels for different flow scenarios, which are not applicable for training a model. To this end, we make a first attempt to apply the self-supervised learning (SSL) technique to fluid dynamics, which disregards data labels for pre-training the model. The SSL technique embraces a large amount of data (8000 snapshots) at Reynolds numbers of Re = 200, 300, 400, and 500 without discriminating between them, which improves the generalization of the model. The Transformer model is pre-trained via a specially designed pretext task, where it reconstructs the complete flow fields after randomly masking 20% data points in each snapshot. For the downstream task of flow reconstruction, the pre-trained model is fine-tuned separately with 256 snapshots for each Reynolds number. The fine-tuned models accurately reconstruct the complete flow fields based on less than 5% random data points within a limited window even for Re = 250 and 600, whose data were not seen in the pre-trained phase. For the other downstream task of flow prediction, the pre-training model is fine-tuned separately with 128 consecutive snapshot pairs for each corresponding Reynolds number. The fine-tuned models then correctly predict the evolution of the flow fields over many periods of cycles. We compare all results generated by models trained via SSL and models trained via supervised learning, where the former has unequivocally superior performance. We expect that the methodology presented here will have wider applications in fluid mechanics.
Numerical study of gas invasion law in fractured reservoirs
Authors: Sun Tengfei , Li Yongan , Zhang Yang , Liu Hao
Published: February 2024

Gas invasion during the drilling process in fractured reservoirs poses challenges, affecting drilling efficiency and increasing costs. Therefore, it is crucial to effectively and accurately describe the flow characteristics of subsurface fluids. Addressing the issue of gas invasion in fractured reservoirs, this study considers the influence of matrix deformation and fracture aperture variation on fluid flow and establishes a mathematical model for coupled flow and solid deformation in fractured reservoirs. The numerical formulation of the mathematical model is derived using the finite element method. To better represent real reservoir conditions, discrete fractures are created using MATLAB, and numerical solutions are obtained using the commercial software COMSOL Multiphysics. The accuracy of the model is verified through a comparison between numerical and analytical solutions. This paper first explores the characteristics of fluid flow within a single fracture and rock deformation when encountering a fracture during drilling. It then compares the predictive capability of the coupled model with that of the uncoupled model in estimating gas invasion. Finally, the primary factors influencing gas invasion in fractured reservoirs are analyzed from the perspectives of rock matrix, fractures, and drilling operations.
An improved multiphase lattice Boltzmann flux solver with a modified Cahn–Hilliard equation for multiphase flow with super large density ratio
Authors: Zhang Da , Li Yan , Wang Yan , Shu Chang
Published: February 2024

In this study, a modified Cahn–Hilliard equation with a very simple format was proposed, which can be used to simulate immiscible multi-component/multiphase flow with a super large density ratio. In addition, based on this modified equation and the Navier–Stokes equations, an improved multiphase lattice Boltzmann flux solver (IMLBFS) has been proposed, and its computational ability has been tested by multiple numerical examples, including Laplace law, two bubbles merging, contact angle, bubble rising, and droplet splashing on a thin film. The results show that the proposed IMLBFS can simulate immiscible two-phase flow with a very large density ratio up to 1:5000 or 1:10 000 under various operating conditions, including the Reynolds number reaching 10 000. In addition, IMLBFS also has excellent features such as clear physical properties, freely adjustable source term strength, and effective suppression of mass loss.
Improved faster R-CNN and adaptive Canny algorithm for defect detection using eddy current thermography
Authors: Li Jianyu , Zhang Laibin , Zheng Wenpei
Published: February 2024

Eddy current thermography (ECT) is a non-invasive testing method that combines electromagnetic induction and infrared thermography to identify flaws in materials that conduct electricity. However, ECT faces difficulties in accurately locating and classifying defects owing to its low signal-to-noise ratio and complex defect patterns. In this paper, we propose a new method that integrates an improved faster region-convolutional neural network (R-CNN) and an adaptive Canny algorithm to enhance the defect detection performance of ECT. An improved faster R-CNN is a deep neural network that can automatically detect and locate multiple defects in a single ECT image, whereas the adaptive Canny algorithm is an edge detection technique that can identify defect boundaries. The proposed method was tested using a dataset of ECT images with different types of defects. The results demonstrated that our method achieved better accuracy, precision, and speed than existing methods.
Heat transfer enhancement with additively manufactured rough surfaces: Insights from large-eddy simulations
Authors: Garg Himani , Wang Lei , Fureby Christer
Published: February 2024

To study the impact of additively manufactured (AM) roughness on fluid flow and heat transfer, we performed a series of high-fidelity large-eddy simulations on turbulent heat transfer over a three-dimensional AM rough surface with varying bulk Reynolds number and average roughness height values. We considered rough surfaces created using AM techniques at Siemens based on Nickel Alloy IN939 material with four different mean roughness heights, ks= 1.594, 1.992, 2.630, and 3.984 mm, and the simulations were performed at five bulk Reynolds numbers of 1000, 3000, 6000, 11 700, and 18 000. The temperature was treated as a passive scalar with a Prandtl number of 0.71. To better understand the effect of wall roughness on the momentum and heat transfer mechanism, mean temperature and velocity profiles as well as heat fluxes are presented. The wall-normal Reynolds stress, ⟨ux′ur′⟩, and heat flux, ⟨ur′Θ′⟩, decrease for larger wall roughness heights, Ra, and their respective magnitudes remain very similar for different Ra. A similarity rule for friction factor and heat transfer is used to correlate and interpret the numerical results and compare them with previously existing results, both theoretical and experimental. The assessment of the thermal performance factor illuminates the improvement in heat transfer with the existing surface roughness. By studying the probability density functions of the instantaneous Stanton number, the recirculation zones, which are the result of an adverse pressure gradient, were found to have a profound effect on heat transfer. This is important as it leads to the wall-scaled mean temperature profiles being of larger magnitude than the mean velocity profiles both inside and outside the roughness layer. This means that the temperature wall roughness function, ΔΘ+, differs from the momentum wall roughness function, ΔU+.
Molecular dynamics simulation study of water structure and dynamics on the gold electrode surface with adsorbed 4-mercaptobenzonitrile
Authors: Kwac Kijeong , Yang Nan , Ryan Matthew J. , Zanni Martin T. , Cho Minhaeng
Published: February 2024

Understanding water dynamics at charged interfaces is of great importance in various fields, such as catalysis, biomedical processes, and solar cell materials. In this study, we implemented molecular dynamics simulations of a system of pure water interfaced with Au electrodes, on one side of which 4-mercaptobenzonitrile (4-MBN) molecules are adsorbed. We calculated time correlation functions of various dynamic quantities, such as the hydrogen bond status of the N atom of the adsorbed 4-MBN molecules, the rotational motion of the water OH bond, hydrogen bonds between 4-MBN and water, and hydrogen bonds between water molecules in the interface region. Using the Luzar–Chandler model, we analyzed the hydrogen bond dynamics between a 4-MBN and a water molecule. The dynamic quantities we calculated can be divided into two categories: those related to the collective behavior of interfacial water molecules and the H-bond interaction between a water molecule and the CN group of 4-MBN. We found that these two categories of dynamic quantities exhibit opposite trends in response to applied potentials on the Au electrode. We anticipate that the present work will help improve our understanding of the interfacial dynamics of water in various electrolyte systems.
Quartic-root higher-order topological insulators on decorated three-dimensional sonic crystals
Authors: Geng Zhi-Guo , Shen Ya-Xi , Xiong Zhan , Duan Liwei , Chen Zhaojiang , Zhu Xue-Feng
Published: February 2024

The square-root operation provides a new scheme to create topological phases with unconventional spectrum properties. With the square-root operation, the square-root topological insulators can support paired topological boundary states in two bulk gaps, and the mechanism of square-root has been generalized to 2n-root topological insulators. In this study, we describe the acoustic realization of third-order quartic-root topological insulators based on the original three-dimensional (3D) square-root sonic crystals. By inserting extra sites into the 3D square-root lattice, we can renormalize the coupling parameters and obtain multiple topological boundary states in different bulk gaps with distinct phase profiles. The topological origin is clearly elucidated with the direct sum relation for the 3D quartic-root lattice. We further validate the robustness of the corner states under random bulk disorder and show the diversified localizations of topological edge states at distinct frequencies on different-shaped 3D sonic crystals. Our work extends the quartic-root topological states into a 3D acoustic system and may find potential applications in multi-frequency acoustic devices.
Polymeric surfactants at liquid–liquid interfaces: Dependence of structural and thermodynamic properties on copolymer architecture
Authors: Coldstream Jonathan G. , Camp Philip J. , Phillips Daniel J. , Dowding Peter J.
Published: February 2024

Polymeric surfactants are amphiphilic molecules with two or more different types of monomers. If one type of monomer interacts favorably with a liquid, and another type of monomer interacts favorably with another, immiscible liquid, then polymeric surfactants adsorb at the interface between the two liquids and reduce the interfacial tension. The effects of polymer architecture on the structural and thermodynamic properties of the liquid–liquid interface are studied using molecular simulations. The interface is modeled with a non-additive binary Lennard-Jones fluid in the two-phase region of the phase diagram. Block and gradient copolymer surfactants are represented with coarse-grained, bead-spring models, where each component of the polymer favors one or the other liquid. Gradient copolymers have a greater concentration at the interface than do block copolymers because the gradient copolymers adopt conformations partially aligned with the interface. The interfacial tension is determined as a function of the surface excess of polymeric surfactant. Gradient copolymers are more potent surfactants than block copolymers because the gradient copolymers cross the dividing surface multiple times, effectively acting as multiple individual surfactants. For a given surface excess, the interfacial tension decreases monotonically when changing from a block to a gradient architecture. The coarse-grained simulations are complemented by all-atom simulations of acrylic-acid/styrene copolymers at the chloroform-water interface, which have been studied in experiments. The agreement between the simulations (both coarse-grained and atomistic) and experiments is shown to be excellent, and the molecular-scale structures identified in the simulations help explain the variation of surfactancy with copolymer architecture.
Modeling of three-dimensional blood flow in microchannels using a two-fluid method
Authors: Yadav Shivji Prasad , Sharma Atul , Agrawal Amit
Published: February 2024

This work presents a novel two-fluid method based on our recently proposed viscosity model for red blood cells (RBCs)—for simulating three-dimensional (3D) blood flow in a microchannel of dimension comparable to the diameter of red blood cells and larger. Toward this, whole blood is assumed as a suspension of red blood cells in blood plasma, with each phase considered as interpenetrating continua having its separate mass and momentum conservation equations. The proposed approach-based performance study is presented after comprehensively validating it with experimental data for blood flow in a uniform, sudden expansion-constriction, and Y-shaped bifurcated rectangular microchannels over—an extensive range of size (25–330 μm), flow rates (11.8 μl/h–30 ml/h), and inlet hematocrit (0%–45%). The proposed approach effectively captures significant biophysical and biomechanical insights into blood flow. It highlights a migration of red blood cells toward the center of the microchannel and the formation of a cell-free layer near the wall. Notably, with the introduction of constriction and expansion in the microchannel, it predicts a fivefold enhancement of the cell-free layer. The Fahraeus and Fahraeus–Lindquist effects are also demonstrated in microchannels, with less than 300 μm characteristic dimensions. These findings are consistent with experimental evidence. In addition to experimentally evident phenomena, our simulations unveil several additional flow phenomena and features of blood flow in the microchannel. It is observed that the presence of confluence (merging flow) is more disturbing to the blood flow than the presence of diverging bifurcations (splitting flow). Furthermore, after the confluence, velocity profiles exhibit a local peak that persists up to the microchannel outlet. Primary contribution of this work lies in the proposal of a two-fluid method for simulating 3D blood flow in complex geometries. This approach provides a comprehensive understanding of blood flow dynamics in microchannels and can be applied to optimize dimensions and geometries during the initial phases of plasma separation microdevices development.
The structural and electronic split: Boron vs aluminum hydrides
Authors: Pozdeev Anton S. , Popov Ivan A.
Published: February 2024

We systematically investigated the structural evolution of boron (B) and aluminum (Al) hydrides using various DFT and ab initio methods, aiming to reveal the similarities and differences in their geometric and electronic structures. While B hydrides have been extensively studied both experimentally and theoretically, less is known about its group 13 heavier congener, Al. Extensive global minimum searches of the B2Hx (Al2Hx) and B3Hy (Al3Hy) hydrides (x = [0–6], y = [0–9]) were performed to identify the most stable geometric structures for each stoichiometry. In most of the series, B and Al hydrides exhibit qualitatively different structures, except for the most saturated X2H5 and X2H6 stoichiometries. Chemical bonding analyses employing adaptive natural density partitioning and electron localization function methods identified notable differences between B and Al hydrides in most of the compositions. B hydrides predominantly possess two-center (2c) and three-center (3c) bonding elements, suggesting a relatively balanced electron distribution. On the contrary, Al hydrides tend to retain unpaired electrons or lone pairs on Al atoms, forming a large number of closely lying isomers with various combinations of 1c, 2c, 3c, and 4c bonding elements. Thermodynamic stability analyses revealed that all studied clusters demonstrated stability toward various H/H2 dissociation pathways, with Al hydrides being less stable than B counterparts.
Decay behavior and internal interactions of regularly reflected spherical blast waves
Authors: Almustafa Monjee K. , Nehdi Moncef L.
Published: February 2024

Blast wave reflection is a critical area in military and infrastructure defense, converging shock dynamics, and colliding blast waves. While irregular blast reflections have garnered remarkable attention, research on regularly reflected (RR) blast waves remains comparatively limited. This study presents a detailed literature on shortcomings of post-reflection quantities of RR blast waves and aims to bridge this gap by extensively analyzing RR behaviors of spherical blast waves against a planar surface in air via numerical methods. With 31 scenarios involving a 1 kg charge and scaled distances from 0.5 to 4.0 m/kg1/3, comprehensive field data on parameters including pressure, density, and velocity were gathered using a fan-like gauge array. A dedicated program for tracking the RR shock front was developed, enabling precise trajectory detection and detailed quantitative analyses of RR wave decay. First, accurate empirical trajectory equations for RR waves were formulated along its normal axis. Second, spatial decay analysis was conducted, revealing consistent decay rates for each RR field parameter under 1 m/kg1/3 and diminishing decay rates beyond this threshold. Third, parameter profiles preceding RR shock fronts at various post-reflection distances were examined, while discrepancies and complexities against generalized profiles were uncovered. Qualitatively, this study identified four internal interactions within the reflection phenomenon, categorized by scaled distance ranges, and elucidated the secondary wave's impact on RR wave propagation. The comprehensive quantitative and qualitative findings in this work offer profound insights into blast wave dynamics, addressing several gaps on RR blast wave behaviors and laying a foundation for understanding more complex blast reflection phenomena crucial in various domains.
Advances in biomedical fluid–structure interaction: Methodologies and applications from an interfacing perspective
Authors: Hou Tuo , Wei Xiaoyang , Iqbal AKM Asif , Yang Xiaogang , Wang Jing , Ren Yong , Yan Sheng
Published: February 2024

Fluid–structure interaction (FSI) is a nonlinear multiphysics phenomenon that describes the interactions between incompressible fluid flows and immersed structures, making it invaluable to biomedical research. In this work, the common FSI methodologies in biomedical research were systematically summarized and classified into three groups based on FSI interfaces: fluid–channel interfaces, fluid–particle interfaces, and multi-interface interactions. A discussion of the role of the numerical FSI methods was also made, outlining its indispensable advantage in handling complex geometries, boundary conditions, and thus FSI interfaces. The applications of these methods are discussed in terms of blood vessel-related applications, drug-delivering micropumps, particle dynamics/cell sorting, and particle deformation and rapture. The development progress, current advances, and prospects of FSI's future application in biomedical research were illustrated. It was concluded that with the advances in computation technologies, the rapidly developing FSI methods can achieve state-of-the-art level details, helping to improve our understanding of various biomedical-related problems and the use of FSI techniques in biomedical research is likely to continue to grow.