bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-adiabatic direct quantum dynamics using force fields: Toward solvation
Authors: Cigrang L. L. E. , Green J. A. , Gómez S. , Cerezo J. , Improta R. , Prampolini G. , Santoro F. , Worth G. A.
Published: May 2024

Quantum dynamics simulations are becoming a powerful tool for understanding photo-excited molecules. Their poor scaling, however, means that it is hard to study molecules with more than a few atoms accurately, and a major challenge at the moment is the inclusion of the molecular environment. Here, we present a proof of principle for a way to break the two bottlenecks preventing large but accurate simulations. First, the problem of providing the potential energy surfaces for a general system is addressed by parameterizing a standard force field to reproduce the potential surfaces of the molecule’s excited-states, including the all-important vibronic coupling. While not shown here, this would trivially enable the use of an explicit solvent. Second, to help the scaling of the nuclear dynamics propagation, a hierarchy of approximations is introduced to the variational multi-configurational Gaussian method that retains the variational quantum wavepacket description of the key quantum degrees of freedom and uses classical trajectories for the remaining in a quantum mechanics/molecular mechanics like approach. The method is referred to as force field quantum dynamics (FF-QD), and a two-state ππ*/nπ* model of uracil, excited to its lowest bright ππ* state, is used as a test case.
Startability analysis of hypersonic overboard spillage internal waverider intake based on new basic flowfield
Authors: Musa Omer , Huang Guoping , Yu Zonghan , Jin Bo , Razzaghi Mohammad Javad Pour
Published: May 2024

The current work is undertaken to examine the capability of a recently developed ICFM (internal conical flow M) basic flowfield [Musa et al., AIAA J. 61, 1–16 (2023)] to design hypersonic internal waverider intakes. The osculating axisymmetric flows concept is employed alongside the streamline-tracing method to design three internal waverider intakes with different contraction ratios, i.e., 6.0, 9.0, and 25. The three intakes have similar capture and throat shapes and entrance areas. Then, the starting characteristics of designed intakes were investigated at different design and off-design conditions. The selected design condition is the flight at Mach 6.0 and 28 km altitude. Viscous computations have been performed at Mach 6.0, 5.0, 4.0, 3.9, 3.8, 3.5, and 3.0 for the intake with a contraction ratio of 6.0, and at Mach 6.0, 5.0, 4.7, and 4.0 for the intake with contraction ratio of 9.0. The intake with a contraction ratio of 25 is simulated at Mach 6.0 and 5.0. Successful intake starting has been achieved up to Mach 3.8 for the first intake and up to Mach 4.7 for the second intake. The intake with a contraction ratio of 25 attained an unstart state in the design condition due to a very high contraction ratio. Thus, the starting limit of internal waverider intakes designed using ICFM basic flowfield is found to be controlled by Van Wie empirical limit. It is concluded that the ICFM basic flowfield can effectively design high-performance fixed-geometry intakes with overboard spillage, demonstrating excellent performance and startability across a wide range of Mach numbers.
Data-driven surrogate modelling of multistage Taylor cone–jet dynamics
Authors: Cândido Sílvio , Páscoa José C.
Published: May 2024

The Taylor cone jet is an electrohydrodynamic flow typically induced by applying an external electric field to a liquid within a capillary, commonly utilized in colloidal thrusters. This flow generation involves a complex multiphase and multiphysics process, with stability contingent upon specific operational parameters. The operational window is intrinsically linked to flow rate and applied electric voltage magnitude. High voltages can induce atomization instabilities, resulting in the production of an electrospray. Our study presents initially a numerical investigation into the atomization process of a Taylor cone jet using computational fluid dynamics. Implemented within OpenFOAM, our numerical model utilizes a volume-of-fluid approach coupled with Maxwell's equations to incorporate electric body forces into the incompressible Navier–Stokes equations. We employ the leaky-dielectric model, subjecting the interface between phases to hydrodynamic surface tension and electric stress (Maxwell stress). With this model, we studied the droplet breakup of a heptane liquid jet, for a range of operation of 1.53–7.0 nL s−1 and 2.4–4.5 kV of extraction. First, the developed high-fidelity numerical solution is studied for the jet breakup and acceleration of the droplets. Second, we integrate a machine learning model capable of extending the parametric windows of operation. Additionally, we explore the influence of extractor and acceleration plates on colloidal propulsion systems. This work offers a numerical exploration of the Taylor cone–jet transition and droplet acceleration using novel, numerically accurate approaches. Subsequently, we integrate machine learning models, specifically an artificial neural network and a one-dimensional convolutional neural network, to predict the jet's performance under conditions not previously evaluated by computationally heavy numerical models. Notably, we demonstrate that the convolutional neural network outperforms the artificial neural network for this type of application data, achieving a 2% droplet size prediction accuracy.
Stationary trajectories in Minkowski spacetimes
Authors: Bunney Cameron R. D.
Published: May 2024

We determine the conjugacy classes of the Poincaré group ISO+(n, 1) and apply this to classify the stationary trajectories of Minkowski spacetimes in terms of timelike Killing vectors. Stationary trajectories are the orbits of timelike Killing vectors and, equivalently, the solutions to Frenet–Serret equations with constant curvature coefficients. We extend the 3 + 1 Minkowski spacetime Frenet–Serret equations due to Letaw to Minkowski spacetimes of arbitrary dimension. We present the explicit families of stationary trajectories in 4 + 1 Minkowski spacetime.
Elucidating the structural and conformational preferences of bioactive chromone and its monohydrate through advanced rotational spectroscopy
Authors: Chen Junhua , Zhang Min , Lan Junlin , Wang Chengxu , Chen Zhikai , Xu Xuefang , Gao Xiuli , Gou Qian
Published: May 2024

Chromones are a class of naturally occurring compounds, renowned for their diverse biological activities with significant relevance in medicine and biochemistry. This study marks the first analysis of rotational spectra of both the chromone monomer and its monohydrate through Fourier transform microwave spectroscopy. The observation of nine mono-substituted 13C isotopologues facilitated a semi-experimental determination of the equilibrium structure of the chromone monomer. In the case of chromone monohydrate, two distinct isomers were identified, each characterized by a combination of O–H⋯O and C–H⋯O hydrogen bonds involving the chromone’s carbonyl group. This study further delved into intermolecular non-covalent interactions, employing different theoretical approaches. The relative population ratio of the two identified isomers was estimated to be about 2:1 within the supersonic jet.
Metastable structures of cation vacancies in semiconducting oxides
Authors: Fowler W. Beall , Stavola Michael , Venzie Andrew , Portoff Amanda
Published: May 2024

The observed metastable characteristics of cation vacancies in Ga2O3 have prompted a wider search for such systems. In this Perspective, we consider a number of defect systems as candidates for metastability. Some of these are already known to have this property, while for others, this suggestion is new. The examples discussed here are but a sampling of a huge number of systems, and these are used to emphasize that the metastability of defect structures is both common and important; it may yield (for example) split vacancy equilibrium configurations and, hence, should be considered in developing defect models and in analyzing their properties.
Superconducting nanowire single-photon detectors with saturated quantum efficiency at 1550 nm on single-crystal diamond substrates
Authors: Qin Zhi , Huang Mingxue , Tao Tao , Wang Xiaohan , Bao Han , Xu Tao , Tu Xuecou , Zhang Labao , Zhao Qingyuan , Jia Xiaoqing , Kang Lin , Chen Jian , Wu Peiheng
Published: May 2024

Single-crystal diamond possesses exceptional physical and optical properties, rendering it an ideal platform for integrated quantum optics. The direct integration of broadband-sensitive and high-performance single-photon detectors on diamond holds significant implications for the realization of integrated diamond quantum optical circuits. In this study, we polished the diamond surface with RMS (root mean square) below 0.6 nm suitable for the deposition and patterning of NbN thin films through ion beam etching. Subsequently, we fabricated superconducting nanowire single-photon detectors directly on the polished diamond substrates and characterized for their electrical and optical properties. The NbN-SNSPD exhibited a high critical current density (2 MA cm−2), a saturated quantum efficiency (QE) below 2.5 K, and a maximum value of QE up to 88% at 4 K. These findings offer a promising solution for fully integrated quantum optical chips on single-crystal diamond substrates.
Impact of the recessed gate depth on the GaN metal-oxide-semiconductor high electron mobility transistor performances: New insights on mobility extraction
Authors: Piotrowicz C. , Mohamad B. , Malbert N. , Bécu S. , Ruel S. , Le Royer C.
Published: May 2024

This paper provides a comprehensive study of the impact of the gate recess depth (RD) on the GaN-on-Si MOS-HEMTs DC performances. IDS = f(VGS) and IDS = f(VDS) measurements are conducted at 25 and 150 °C, respectively, in forward and blocking modes. The gate recessed depth (50, 150, and 350 nm) is modulated by adjusting the plasma etching time, which is a critical step for improving the dielectric/GaN interface quality and the gate channel electron mobility. Three distinct regions can be defined separately: the bottom, the sidewall, and the corner region being the junction between the two previous regions. To assess the impact of gate recessed depth (RD) on the several mobilities around the gate cavity first, we applied our previous methodology allowing us to extract the bottom (μbot) and the entire sidewall region mobility (μT), without distinction from the corner. The mobility of the transverse region was found surprisingly to increase with deeper RD. To gain insight into the impact of the RD on this transverse section, a new extraction methodology is proposed to extract separately the gate corner (μcorner) and sidewall (μSW) mobility. These extractions show that the corner mobility is found to be reduced compared to the sidewall one (μcorner < μSW) evidencing the different weighting contributions over the transverse mobility. Moreover, these mobilities are found to be more degraded compared to the bottom one, highlighting the different contributions on the on-state resistance (RON). Indeed, the on-state resistance is lowered with the shallower RD due to the reduced sidewall resistance contribution (lower sidewall length) and despite the incremental contribution of the bottom resistance (larger effective gate length). However, the shallower RD shows an increase in the drain–source leakage current in reason of a lower gate electrostatic control. Technology Computer Aided Design (TCAD) simulations of the three RD morphologies are carried out to validate the experimental trends and the proposed methodology.
Theoretical modeling of defect diffusion in wide bandgap semiconductors
Authors: Knausgård Hommedal Ylva , Etzelmüller Bathen Marianne , Mari Reinertsen Vilde , Magnus Johansen Klaus , Vines Lasse , Kalmann Frodason Ymir
Published: May 2024

Since the 1940s, it has been known that diffusion in crystalline solids occurs due to lattice defects. The diffusion of defects can have a great impact on the processing and heat treatment of materials as the microstructural changes caused by diffusion can influence the material qualities and properties. It is, therefore, vital to be able to control the diffusion. This implies that we need a deep understanding of the interactions between impurities, matrix atoms, and intrinsic defects. The role of density functional theory (DFT) calculations in solid-state diffusion studies has become considerable. The main parameters to obtain in defect diffusion studies with DFT are formation energies, binding energies, and migration barriers. In particular, the utilization of the nudged elastic band and the dimer methods has improved the accuracy of these parameters. In systematic diffusion studies, the combination of experimentally obtained results and theoretical predictions can reveal information about the atomic diffusion processes. The combination of the theoretical predictions and the experimental results gives a unique opportunity to compare parameters found from the different methods and gain knowledge about atomic migration. In this Perspective paper, we present case studies on defect diffusion in wide bandgap semiconductors. The case studies cover examples from the three diffusion models: free diffusion, trap-limited diffusion, and reaction diffusion. We focus on the role of DFT in these studies combined with results obtained with the experimental techniques secondary ion mass spectrometry and deep-level transient spectroscopy combined with diffusion simulations.
Impedance characterization of dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene diodes: Addressing dielectric properties and trap effects
Authors: Cho Hong-rae , Hyung Park Joon , Kim Somi , Udaya Mohanan Kannan , Jung Sungyeop , Kim Chang-Hyun
Published: May 2024

Dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (DNTT) is a widely used small-molecular p-type organic semiconductor. Despite the broad availability of high-performance DNTT transistors, there is a lack of investigation into other devices based on this semiconductor. In this study, rectifying diodes with DNTT as a single transport medium are fabricated and characterized. Realizing unipolar current rectification from asymmetric metal contacts, a number of physical and electrical properties of DNTT are made accessible. Current–voltage measurement, broad-band impedance spectroscopy, drift-diffusion simulation, and equivalent-circuit modeling are combined to quantify important parameters such as dielectric constant, trap energy, and lifetime. These results provide a practical reference for the design and optimization of diverse electronic devices incorporating DNTT.
The effect of FeGa (0/–) level presence on material properties in dilute AlxGa1−xN layers
Authors: Sun L. , Kruszewski P. , Markevich V. P. , Dawe C. A. , Peaker A. R. , Crowe I. F. , Plesiewicz J. , Prystawko P. , Grzanka Sz. , Grzanka E. , Jakiela R. , Binks D. , Halsall M. P.
Published: May 2024

AlxGa1−xN epilayers are used as the basis of ultraviolet LEDs and detectors. The trap states produced by defects and impurities can play a key role in the device performance. In this work, conventional deep-level transient spectroscopy, photoluminescence (PL), and secondary ion mass spectrometry have been used to characterize a deep-level trap termed as E3 in dilute AlxGa1−xN (x < 0.063) epilayers grown by metal-organic vapor phase epitaxy (MOVPE) on highly conductive ammono-GaN substrates. The AlxGa1−xN epilayers were doped with silicon to about 3 × 1016 cm−3. The electrical and the optical measurements were conducted on Ni/Au Schottky barrier diodes and virgin samples, respectively. First, we observed a general trend that the E3 (FeGa) electron trap concentration significantly changes along the wafers in AlxGa1−xN layers that is fully consistent with previously reported results for GaN materials grown by the MOVPE technique. Second, we report that the activation energies for electron emission for the E1 and E3 traps in dilute AlxGa1−xN exhibit linear variations with Al content. Moreover, low-temperature PL results show a proportional relation between the intensity of the line with its maximum at 1.299 eV and concentration of residual Fe impurity. Finally, we discuss how the presence of defects resulting from Fe contamination may result in degradation of AlxGa1−xN-based devices.
Independent Rydberg atom sensing using a dual-ladder scheme
Authors: Berweger Samuel , Artusio-Glimpse Alexandra B. , Prajapati Nikunjkumar , Rotunno Andrew P. , Schlossberger Noah , Shylla Dangka , Moore Kaitlin R. , Simons Matthew T. , Holloway Christopher L.
Published: May 2024

Rydberg atom-based electric field sensing can provide all-optical readout of radio frequency (RF) fields in a dielectric environment. However, because a single set of optical fields is typically used to prepare the Rydberg state and readout its response to RF fields, it is challenging to perform simultaneous and independent measurements of the RF field(s). Here, we show that using two independent schemes to prepare and readout the same Rydberg state can be used to perform independent measurements in general, which we demonstrate specifically by resolving the RF polarization. We expect this work will be useful for fiber-coupled sensor heads where spatial multiplexing is challenging as well as for complex multi-level sensing schemes.
Dynamics of karyotype evolution
Authors: Kuzmin Elena , Baker Toby M. , Van Loo Peter , Glass Leon
Published: May 2024

In the evolution of species, the karyotype changes with a timescale of tens to hundreds of thousand years. In the development of cancer, the karyotype often is modified in cancerous cells over the lifetime of an individual. Characterizing these changes and understanding the mechanisms leading to them has been of interest in a broad range of disciplines including evolution, cytogenetics, and cancer genetics. A central issue relates to the relative roles of random vs deterministic mechanisms in shaping the changes. Although it is possible that all changes result from random events followed by selection, many results point to other non-random factors that play a role in karyotype evolution. In cancer, chromosomal instability leads to characteristic changes in the karyotype, in which different individuals with a specific type of cancer display similar changes in karyotype structure over time. Statistical analyses of chromosome lengths in different species indicate that the length distribution of chromosomes is not consistent with models in which the lengths of chromosomes are random or evolve solely by simple random processes. A better understanding of the mechanisms underlying karyotype evolution should enable the development of quantitative theoretical models that combine the random and deterministic processes that can be compared to experimental determinations of the karyotype in diverse settings.
Investigating optimal development approaches via bottom hole pressure control in stress-sensitive tight oil reservoirs
Authors: Liu Yunfeng , Zhu Yangwen , Zhu Weiyao , Liao Haiying , Kong Debin
Published: May 2024

After volumetric fracturing, the conventional recovery methods for tight oil reservoirs rely on natural energy depletion. However, the production rate rapidly declines due to their intricate characteristics, such as threshold pressure gradient (TPG), stress sensitivity, and multi-scale porous media. This study plotted permeability loss charts based on stress sensitivity experiments. A pressure distribution equation incorporating TPG and flow in different regions was developed, and production prediction methods for tight oil reservoirs were established. The results revealed the effects of TPG and multi-region flow on pressure distribution, demonstrating the need to control bottom hole pressure (BHP) in tight oil reservoirs. Accordingly, methods to improve tight oil reservoir development were proposed by controlling BHP. Reducing BHP, increasing the imbibition displacement, and improving oil-phase mobility proved conducive to enhanced oil recovery. The development model featuring BHP control for 1000 days with initially rapid and subsequently slower BHP declines demonstrated the highest recovery rate, surpassing depletion development by 7.404%. This research helps us to optimize tight oil reservoir development plans while offering significant practical guidance for developing similar oil reservoirs, which is of the reference value for the industry.
Fourier–Hankel–Abel Nyquist-limited tomography: A spherical harmonic basis function approach to tomographic velocity-map image reconstruction
Authors: Sparling Chris , Rajak Debobrata , Blanchet Valérie , Mairesse Yann , Townsend Dave
Published: May 2024

A new method for the fully generalized reconstruction of three-dimensional (3D) photoproduct distributions from velocity-map imaging (VMI) projection data is presented. This approach, dubbed Fourier–Hankel–Abel Nyquist-limited TOMography (FHANTOM), builds on recent previous work in tomographic image reconstruction [C. Sparling and D. Townsend, J. Chem. Phys. 157, 114201 (2022)] and takes advantage of the fact that the distributions produced in typical VMI experiments can be simply described as a sum over a small number of spherical harmonic functions. Knowing the solution is constrained in this way dramatically simplifies the reconstruction process and leads to a considerable reduction in the number of projections required for robust tomographic analysis. Our new method significantly extends basis set expansion approaches previously developed for the reconstruction of photoproduct distributions possessing an axis of cylindrical symmetry. FHANTOM, however, can be applied generally to any distribution—cylindrically symmetric or otherwise—that can be suitably described by an expansion in spherical harmonics. Using both simulated and real experimental data, this new approach is tested and benchmarked against other tomographic reconstruction strategies. In particular, the reconstruction of photoelectron angular distributions recorded in a strong-field ionization regime—marked by their extensive expansion in terms of spherical harmonics—serves as a key test of the FHANTOM methodology. With the increasing use of exotic optical polarization geometries in photoionization experiments, it is anticipated that FHANTOM and related reconstruction techniques will provide an easily accessible and relatively low-cost alternative to more advanced 3D-VMI spectrometers.
Identification of full-field wind loads on buildings using a mechanism-inspired recursive convolutional neural network with partial structural responses
Authors: Zhang Fubo , Lei Ying , Liu Lijun , Huang Jinshan
Published: May 2024

Indirect identification approaches through structural responses have proven effective for wind load estimation in real-world engineering. Currently, methods for identifying wind loads mainly rely on theoretical inverse identification, with rare research based on the mapping relationship between structural responses and wind loads through machine learning. In this paper, a scheme for identifying full-field wind loads using a recursive convolutional neural network (CNN) inspired by physical mechanisms is proposed. The recursive form of the network, as well as the inspiration for its inputs and outputs, is inspired by the spatial correlation and the mapping relationship between wind loads and structural responses. Thus, the network inputs comprise a fusion of structural acceleration and inter-story displacement responses, while the network outputs represent the independent wind loads on structures. Notably, mismatch test is employed by the network, wherein the training and testing datasets originate from entirely different sources. Specifically, during training, Gaussian white noises that simulate wind loads are utilized, while real wind load data are used for testing. The generalization of the proposed scheme is demonstrated through the identification of full-field wind loads generated by different stationary or non-stationary wind spectra of the 76-story wind-excited benchmark building. Furthermore, the proposed scheme is validated by identifying the full-field wind loads of a 67-story shear wall structure with wind tunnel test data.
Research on the unsteady flow field and aerodynamic noise characteristics in the circular space of ultra-high-speed elevators
Authors: He Qin , Yang Guifa , Zhang Ruijun , Zhang Chenglong , Ma Kai
Published: May 2024

Due to the non-streamlined blunt body shape of the elevator car, intense aerodynamic loads and noise are generated in the annular space when the elevator operates at high speed in a narrow hoistway. This article uses large-eddy simulation and Curle acoustic theory to establish a numerical model of the wellbore flow field under different guiding shapes of the elevator car. First, the mechanism of action between the flow guide shape, vortex characteristics, and aerodynamic load was studied, and the influence of operating speed on aerodynamic load under different flow guide shapes was analyzed. Second, the distribution and spectral characteristics of noise in the annular space under different flow guide shapes were studied from the near field and far field scales. Finally, it can be concluded that increasing the guide surface can significantly reduce the pressure difference between the upper and lower parts of the car, weakening the separation of the tail airflow. The number of guide surfaces, installation position, and vertex offset significantly impact drag and lateral force, with the optimal reduction of 34.65% and 57.6%, respectively. The maximum sound source intensity of near-field noise is mainly concentrated at the arc transition in the upper part of the annular space, and the frequency is mainly concentrated in the range of 500–1000 Hz. The sound pressure level is linearly related to the logarithm of the longitudinal distance, and the noise attenuation speed becomes faster with the increase in the number of guiding surfaces.
Thermoelectric properties of undoped and Bi-doped GeS monolayers: A first-principles study
Authors: Yang H. , Shi H. L. , Han Q. Z. , Yang J. , Ren Y. H. , Zhao Y. H. , Gong L. J. , Liu Q. H. , Shi L. J. , Jiang Z. T.
Published: May 2024

Different from the extensive experimental investigations into the thermoelectric (TE) properties of the bulk IV–VI compounds, less attention has been paid to the TE properties of the monolayer IV–VI compounds. Here, we consider the TE transport properties including the Seebeck coefficient, electronic conductance, thermal conductance, power factor, and figure of merit ZT of the undoped and Bi-doped GeS monolayers. Our results show that for both the undoped and Bi-doped monolayers the anisotropy is widely observed in all their TE properties, and the maximum ZT at a certain temperature along the armchair direction is much greater than that along the zigzag direction. Moreover, Bi doping can lead to an increase of the maximum ZT, and there are more ZT peaks appearing near the zero chemical potential. This indicates that the Bi-doped GeS monolayer can work as a TE material at a lower bias voltage, and especially along the armchair direction it can work at zero bias voltage, which obviously strengthens the reliability of the TE devices. As the temperature increases, the maximum ZT will be uniformally increased along the armchair and zigzag directions for both the undoped and Bi-doped GeS monolayers. In the temperature scope from 300 to 800 K, the maximum ZT along the armchair direction of the Bi-doped GeS monolayer will increase from 3.39 to 4.85, which indicates that this Bi-doped GeS monolayer is a promising TE material in a wide-temperature zone. As an application, we have designed the GeS-based TE couples and found that their efficiencies can be greater than 27% at large temperature differences. This research should be an important guidance for designing a low-voltage, wide-temperature-scope, and high-stability TE device.
On the extreme wall shear stress events in a turbulent pipe flow
Authors: Fei Haoqi , Wang Rui , Lai Pengyu , Wang Jing , Xu Hui
Published: May 2024

This study investigates the extreme wall shear stress events in a turbulent pipe flow by direct numerical simulation at a frictional Reynolds number Reτ≈500. A two-step conditional averaging scheme is implemented to identify the locations of extreme events and construct their spatial structures. Combined with the joint probability density functions of shear stresses, further evidence is provided for the argument that extreme positive events occur below an intense sweep event (Q4), and the formation of the backflow events is predominantly aided by an identifiable oblique vortex. Moreover, the conditional probability distribution of shear stress for varying thresholds used to define extreme events reveals that, when the threshold is above or below the mean, the probability distributions of the extreme positive events or the backflow events generally follow an exponential relationship, suggesting the extreme wall shear stress events are a threshold-independent process. Finally, the conditional space–time proper orthogonal decomposition is performed to extract the dominant modes and characterize the evolution of the extreme events from inception to dissipation, which exhibits morphological features of real flow structures. It is found that the observation of uθ modes can provide a basic representation of the entire variation process and the extreme values return to normal levels in a very short time.
Experimental and numerical study on the pressure drop and flow pattern of liquid foam in a foam generator
Authors: Li Huan , Yu Xiaoyang , Qiu Ke , Fu Zhihao , Lu Shouxiang
Published: May 2024

In the present study, a comprehensive analysis of the pressure drop, flow pattern, and foam structural properties of vertical upward two-phase flow in a Kenics static foam generator of a compressed air foam system was carried out. A liquid with an extremely low surface tension (16.5 mN/m) was used for making the foam. The effects of the number of elements (number of individual elements combined into the mixer), aspect ratio (the ratio of length to diameter of each element), and transition angle (transition angle between elements) of the Kenics mixers on the pressure loss during foam generation were studied in detail over a wide range of Reynolds numbers through experiments and numerical simulation. A new pressure drop correlation was successfully obtained by scaling analysis and the modified Lockhart–Martinelli correlation was proposed to describe the pressure drop during foam generation. Furthermore, the experimental results validated the proposed correlation and exhibited good reliability and predictive accuracy. Finally, four flow patterns for foam generation in vertical pipes that were different from the classical gas–liquid two-phase flow patterns were proposed, and the relationships among the pressure drop, flow pattern, and foam structural properties were explored. This research expands the study of foam generation in vertical tubes containing a built-in spiral structure with low flow resistance. It provides new insights and guidance for developing continuous foam manufacturing.
Study on rotating stall characteristics of centrifugal pumps based on gamma transition model
Authors: Ye Changliang , Huang Wanru , Yan Hongyeyu , Zheng Yuan , Kan Kan , van Esch B. P. M.
Published: May 2024

The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.
Two-dimensional shielded vortices in a shear current
Authors: Zoeller V. , Viúdez A.
Published: May 2024

The interaction of shielded vortices, with a continuous vorticity distribution, and a shear current of weak vorticity amplitude but similar velocity compared to the vortex amplitude is numerically investigated in two-dimensional isochoric flows. Different types of axisymmetric shielded vortices, namely, a neutral unstable vortex, a neutral robust vortex, and a non-neutral vortex are considered. The vortices are linear combinations of vorticity layer-modes, which consist of conveniently normalized cylindrical Bessel functions of order 0, truncated by a zero of the Bessel function of order 1. The vortex–current interaction is investigated by superposing initially the vortices at different initial locations along the cross-flow axis in the shear current. The numerical results show that some shielded vortices, as well as the shear current, remain robust while the vortices cross the shear current and reach a stable equilibrium location, which is of the same sign vorticity as its amount of circulation. There exist two unstable equilibrium locations where most of the vortices persist during a relatively short time interval before heading to their stable equilibrium region in the shear current.
The influence of plug nozzle and Laval nozzle on the flow field and performance of non-premixed rotating detonation combustor
Authors: Zhang Yunzhen , Cheng Miao , Liu Xiangyang , Rong Guangyao , Sheng Zhaohua , Shen Dawen , Wu Kewen , Wang Jianping
Published: May 2024

With the rotating detonation engine's (RDE) development to engineering applications, the selection and optimization of nozzle is garnering great concerns, with the aim to maximize the performance benefits of this pressure gain propulsion system. The present study represents the first effort to explore the distinct impacts of two commonly used nozzles in RDE, namely, the plug nozzle and the Laval nozzle, on the internal flow and performance within the combustion chamber. Three-dimensional numerical simulations are conducted on non-premixed annular RDEs with plug nozzles and Laval nozzles. It is found that the Laval nozzle induces a forward-leaning wavefront structure in the combustion chamber. Furthermore, the overall pressure gain of the RDE is divided into the injection pressure loss, the average pressure gain at the chamber bottom, and the flow losses downstream, by combining the wavefront coordinate averaged flow field, which is proposed and applied in this study, and laboratory coordinate averaged flow field. The results show that, for the performance of the combustion chamber, while Laval nozzles enhance pressure gains at the chamber bottom and reduce exit flow non-uniformity, they also increase downstream losses. By comparing the RDE performance with the ideal performance of deflagration-based combustors, it is found that the premixed control group exceeded the deflagration ideal performance by 30%. Despite lower combustion efficiency, non-premixed configurations nearly match the ideal deflagration performance, underscoring the inherent advantages of RDEs.
Heterogeneous hydrochlorination of lipids mediated by fatty acids in an indoor environment
Authors: Liu Yaqi , Liu Zhuo , Chen Yijing , He Jing , Niu Yuqing , He Yuwei , Wang Yanjie , Ju Yun , Jiang Jie , Zhang Hong , Qiao Lina
Published: May 2024

Fatty acids from cooking fumes and hypochlorous acid (HOCl) released from indoor cleaning adversely affect respiratory health, but the molecular-level mechanism remains unclear. Here, the effect of cooking oil fumes [palmitic acid (PA), oleic acid (OA), and linoleic acid (LA)] on lung model phospholipid (POPG) hydrochlorination mediated by HOCl at the air–water interface of the hanged droplets was investigated. Interfacial hydrochlorination of POPG was impeded by OA and LA, while that of POPG was facilitated by PA. The effect on POPG hydrochlorination increased with the decrease in oil fume concentration. A potential mechanism with respect to the chain length of these oil fumes, regardless of their saturation, was proposed. PA with a short carbon chain looses the POPG packing and leads to the exposure of the C=C double bonds of POPG, whereas OA and LA with a long carbon chain hinder HOCl from reaching the C=C bonds of POPG. These results for short chain and low concentration dependence suggest that the decay of oil fumes or the conversion of short-chain species by indoor interfacial chemistry might be adverse to lung health. These results provide insights into the relationship between indoor multicomponent pollutants and the respiratory system.
Antiferromagnetic ground state and evidence for metamagnetic transition in itinerant-electron compounds YCo12−xFexB6 (x = 1.5, 2, 2.5)
Authors: Vallet-Simond B. , Diop L. V. B. , Isnard O.
Published: May 2024

In contrast to the parent compound YCo12B6, the Fe-doped YCo12−xFexB6 (1.5 ≤ x ≤ 2.5) alloys exhibit an antiferromagnetic ground state. It is further revealed that the antiferromagnetic state gets transformed into a forced ferromagnetic state by way of a magnetic-field-induced metamagnetic transition. The results demonstrate a progressive reinforcement of the antiferromagnetic interactions upon increasing Fe content along the YCo12−xFexB6 series of compounds. The magnetic phase diagram of each (x = 1.5, 2, and 2.5) composition is determined by combining isothermal and isofield magnetization measurements. The composition and temperature dependencies of the critical field are derived and discussed. Whereas for x = 2 and 2.5, the magnetic state changes from antiferromagnetic (AFM) to ferromagnetic (FM) and then to the paramagnetic (PM) state upon heating, exhibiting three distinct temperature regions, a multicritical point of magnetic origin is proposed for the x = 1.5 compound at a temperature of about 117 K. The ordering temperature is found to decrease upon increasing Fe concentration, while the critical field of the AFM-FM metamagnetic phase transition shows the opposite trend. The critical transition field diminishes upon increasing temperature.
Experimental and numerical study on the local crosswind environment of a wide streamlined bridge deck equipped with wind barriers at different angles of attack
Authors: Li Ming , Zhang Haicheng , Lin Zhongyu , Sun Yanguo , Li Mingshui
Published: May 2024

In this study, the effects of wind barriers on the crosswind environment of vehicle safety on a long-span bridge with a streamlined bridge deck were investigated at different angles of attack (AOA). The profiles of the mean and the root mean square (RMS) of the wind pressure coefficients above different traffic lanes were obtained through synchronous pressure measurements. The mean pressure fields around the bridge decks were investigated by computational fluid dynamics (CFD) simulations. The crosswind environment of vehicle safety between the deck with railings and the deck with wind barriers was compared and analyzed in detail at different AOA. The results showed that the wind barriers produce a thicker separation shear layer above the bridge deck and result in a larger negative pressure region in comparison with the case with railings. This leads to a notable reduction in the mean wind pressure coefficients above the deck. The increase in the AOA enhances the above-mentioned reduction effect. It was also found that the wind barriers significantly increase the RMS of the wind pressure coefficients above the deck compared with the railings. The increase in the AOA inhibits this enhancement effect. The results of the equivalent mean pressure coefficients show that the wind barriers reduce the vehicle sideslipping risk more effectively than the vehicle overturning risk. It was also found that the effect of the wind barriers on the reduction of the overturning risk is more sensitive to the change in AOA than the effect on the reduction of the vehicle sideslipping risk.
Assessment of viscosity effects on high-speed coolant pump performance
Authors: Wang Dongcheng , Gu Yandong , Stephen Christopher , Zhao Wenpeng , Ji Qingfeng
Published: May 2024

The high-speed coolant pump facilitates thermal regulation in electric vehicle components, including batteries and motors, by circulating an ethylene glycol solution. This commonly used circulating fluid exhibits a notable negative correlation with temperature in terms of viscosity. Numerical simulations investigate the transient dynamics of a high-speed coolant pump operating at 6000 rpm, driving coolant flow at various temperatures. A high-speed coolant pump test rig is established, and the performance is evaluated under different temperature conditions. The numerical simulations at different temperatures align well with the experimental outcomes. Decreasing temperatures, from 100 to −20 °C, lead to reduced pump head and efficiency due to increased viscosity. Specifically, at a flow rate of 30 L/min, head decreases by 40.03% and efficiency by 44.19%. With escalating viscosity, the best efficiency point shifts toward lower flow rates. Notable impacts on both disk efficiency and hydraulic efficiency are observed due to viscosity fluctuations. It exerts minimal influence on volumetric efficiency at elevated flow rates but has a substantial impact on volumetric efficiency at lower flow rates. Increased fluid viscosity causes uneven pressure distribution within the pump, altering velocity profiles within the impeller. High-viscosity fluids tend to form large-scale vortex structures around the blades, reducing the thrust exerted by the blades on the fluid. Higher viscosity results in larger vortex structures around the blades, reducing thrust and increasing fluid frictional resistance. The study findings provide valuable insights for the advancement of high-efficiency, energy-saving, high-speed coolant pumps tailored for electric vehicles.
Relationship between vorticity near the surface and a long-lived vortex raised above it
Authors: Elikashvili Alexander , Golbraikh Ephim
Published: May 2024

The ability to predict the behavior of vortices is valuable for solving various scientific problems. One such problem is the evolution of tornado-like vortices near the surface and their connection with the original vortex located at a certain height above the surface. This article considers a two-dimensional axisymmetric hydrodynamic model in which the initial vorticity is maintained by an external force. Using the model, the influence of external force and temperature field on the evolution of vorticity near the surface is studied. It is shown that at relatively short times, the behavior of the resulting tornado-like vortices near the surface is universal and weakly depends on the external force and temperature field. However, over time, this influence becomes significant. It is shown that, depending on the presence of an anomaly in the temperature distribution, the vortex formed at the surface can exist for a long time.
Dynamic density functional theory with inertia and background flow
Authors: Mills-Williams R. D. , Goddard B. D. , Archer A. J.
Published: May 2024

We present dynamic density functional theory (DDFT) incorporating general inhomogeneous, incompressible, time-dependent background flows and inertia, describing externally driven passive colloidal systems out of equilibrium. We start by considering the underlying nonequilibrium Langevin dynamics, including the effect of the local velocity of the surrounding liquid bath, to obtain the nonlinear, nonlocal partial differential equations governing the evolution of the (coarse-grained) density and velocity fields describing the dynamics of colloids. In addition, we show both with heuristic arguments, and by numerical solution, that our equations and solutions agree with existing DDFTs in the overdamped (high friction) limit. We provide numerical solutions that model the flow of hard spheres, in both unbounded and confined domains, and compare with previously derived DDFTs with and without the background flow.
Effect of initial water saturation and water film on imbibition behavior in tight reservoirs using nuclear magnetic resonance technique
Authors: Meng Mianmo , Hu Qinhong , Wang Qianyou , Hong Ziqing , Zhang Lisheng
Published: May 2024

Initial water saturation has a significant influence on spontaneous imbibition, and it impacts the imbibition rate and imbibed liquid dynamic distribution among pore networks. At present, the effect of initial water saturation on spontaneous imbibition is still unclear, especially the water film effect caused by initial water saturation varies during imbibition. To address these issues, we prepared the samples with varied initial water saturation through vapor adsorption and then conducted spontaneous imbibitions on these samples, which were monitored by nuclear magnetic resonance (NMR). Samples were selected from tight sandstone reservoirs in the eastern Ordos Basin. From the NMR spectrum corresponding to different imbibition duration, the left wing of the left peak at the initial water saturation is usually higher than the ones after imbibition, mainly caused by the water film effect. When the water film on the surface of large pores is too thin, it is prone to be interpreted as water in small pores because the water film has a quick relaxation time than the water in the center part of pores. The water film effect disappears when the whole pores are filled with water, and the inversed small pores decrease. The relaxation time of the water film is shorter than 0.51 ms in the tested samples. This study is conducive to understanding the effect of initial water saturation on liquid dynamic distribution during imbibition, especially the water film effect variation during imbibition and the T2 value of the water film.