bluuebunny/crossref_metadata_2025 huggingface dataset:
A cradle-to-cradle approach for successive upcycling of polyethylene to polymer electrolytes to organic acids
Authors: Teo Jerald Y. Q. , Tan Ming Yan , Safanama Dorsasadat , Chien Sheau Wei , Jiang Yixuan , Queh Lewis , Tan Tristan T. Y. , Ding Ning , Fam Derrick W. H. , Lim Jason Y. C.
Published: July 2024

We demonstrate the post-synthetic conversion of polyethylene into functional polymer electrolytes for lithium-ion batteries. To avoid end-of-life polymer electrolytes contributing to polymer waste, we further upcycle them into useful organic acids.
Stannum vacancies at precise interface of 2D/2D g-C3N4/SnS S-scheme heterojunction boost up photocatalysis
Authors: Shi Huiming , Shi Quanquan , Piracha Sanwal , Li Gao
Published: July 2024

Advanced semiconductor photocatalysts have significant potential for efficient alcohol photooxidation.
Dopamine sensing by fluorescent carbon nanoparticles synthesized using artichoke extract
Authors: Puglisi Roberta , Mancuso Laura Maria , Santonocito Rossella , Gulino Antonino , Oliveri Valentina , Ruffino Roberta , Li Destri Giovanni , Muccilli Vera , Cardullo Nunzio , Tuccitto Nunzio , Pappalardo Andrea , Sfuncia Gianfranco , Nicotra Giuseppe , Petroselli Manuel , Pappalardo Francesco , Zaccaria Vincenzo , Trusso Sfrazzetto Giuseppe
Published: July 2024

New fluorescent carbon nanoparticles, obtained using artichoke extract, have been used for the ultrasensitive (sub-nanomolar) and selective detection of dopamine in artificial saliva samples.
Identification method for a fractional-order system in terms of equivalent dynamic properties
Authors: Yuan Minjuan , Xu Wei , Liu Fawang , Wang Liang , Lu Yisha
Published: July 2024

In this paper, we introduce an efficient method for identifying fractional dynamic systems using extended sparse regression and cross-validation techniques. The former identifies equations that fit the data with varying candidate functions, while the latter determines the optimal equation with the fewest terms yet ensuring accuracy. The identified optimal equation is expected to share the same dynamic properties as the original fractional system. Unlike previous studies focusing on efficiently computing fractional terms, this strategy addresses dynamic analysis from a data perspective. Importantly, in the proposed method, we treat the fractional order as a variable to account for its impact on the dynamic properties of the identified equation. This treatment enables the identified equation to successfully capture dynamic behaviors when the fractional order changes. We validate the effectiveness of the method using three classical fractional-order systems as well as an energy harvesting system. Interestingly, we find that, although the identified equations do not contain non-local terms like the original fractional-order systems, they exhibit the same stochastic P-bifurcation phenomena. In other words, we construct an equivalent equation without memory properties, sharing the dynamic properties with the original system.
Sigmoid function model of parallel-connected DC–DC converters and analysis of their dynamic characteristics
Authors: Gu Jia , Lu Yimin , Huang Xianfeng , Yin Zhihong
Published: July 2024

Because of the manufacturing variations of circuit elements and the effects of parasitic parameters, the switching elements of parallel-connected modules cannot be synchronously switched. Consequently, the characteristics of these converters, which are multi-mode, high-order systems, cannot be comprehensively described using reduced-order models based on the symmetry of circuit topology and parameters. It is also difficult to fully describe the characteristics of these systems using discrete mapping models and averaged models. Therefore, we developed a smooth, sigmoid function-based continuous-time model for systems comprising parallel-connected buck converters with average current-sharing control. The proposed model provides a unified description of the continuous and discontinuous conduction modes of the system. The criteria for ensuring the stability of the system were derived based on the Floquet theory. The nonlinear dynamic behavior of the system and the effects of the key parameters on the stability of the system were investigated. The results showed that the system may undergo period doubling bifurcation, border collision bifurcation, and Neimark–Sacker bifurcation as the system parameters varied. The theoretical analysis and simulation results were verified experimentally. Our results provide a basis for the configuration of controller parameters.
Exploring the seasonality and optimal control strategy of HIV/AIDS epidemic in China: The impact of seasonal testing
Authors: Zhang Kai , Xue Ling , Li Xuezhi , He Daihai , Peng Zhihang
Published: July 2024

In this work, we investigate how the seasonal variation in the number of individuals who are tested for an HIV antibody in outpatient clinics affects the HIV transmission patterns in China, which has not been well studied. Based on the characteristics of outpatient testing data and reported cases, we establish a periodic infectious disease model to study the impact of seasonal testing on HIV transmission. The results indicate that the seasonal testing is a driving factor for the seasonality of new cases. We demonstrate the feasibility of ending the HIV/AIDS epidemic. We find that the diagnostic rates related to testing play a crucial role in controlling the size of the epidemic. Specifically, when considering minimizing both infected individuals and diagnostic rates, the level of attention paid to undiagnosed infected individuals is always positively correlated with the optimal diagnostic rates, while the optimal diagnostic rates are negatively correlated with the size of the epidemic at the terminal time.
Enhancement of hydrogen response by forming an Au submonolayer on nanogap Pd nanoparticles
Authors: Nakamura Nobutomo , Yoshikawa Kazushi , Ishii Akio
Published: July 2024

When Pd nanoparticles dispersed on a glass substrate with nanometer order gaps are exposed to H2 gas, H atoms are adsorbed on the nanoparticle surface, and the electrical resistance between the nanoparticles increases because of the tunneling current suppression. In contrast, when Au nanoparticles are exposed to H2 gas, the resistance remains unchanged because H atoms are not adsorbed on the Au surface. Considering these behaviors, the change ratio of the electrical resistance is expected to be smaller when the surface of Pd nanoparticles is partially covered with Au. However, the experimental results show the opposite resistance change. Density functional theory simulation indicates that H atoms are adsorbed and absorbed on the pure Pd surface, but H atoms are adsorbed and tend to remain on the partially covered Pd surface. These results indicate that the decrease in the resistance due to the gap narrowing by hydrogen absorption occurs in Pd nanoparticles, but it does not occur in Au/Pd nanoparticles, resulting in a larger resistivity increase compared with the Pd nanoparticles. This result implies that in certain cases, the low reactivity of Au to H2 contributes to the enhancement of the electrical resistance response.
Impact of oxygen vacancy on luminescence properties of dysprosium-doped zinc oxide thin films
Authors: Mandal Animesh , Banpurkar Arun G. , Shinde Shashikant D. , Jejurikar Suhas M.
Published: July 2024

Pristine and dysprosium-doped ZnO thin films, highly c-axis oriented, were grown on a c-Al2O3 substrate using the pulsed laser deposition technique. During the deposition process, the growth was impacted by changes in the oxygen partial pressure. The structural, optical, and compositional properties of the pristine and dysprosium-doped ZnO thin films were systematically characterized using various state-of-the-art experimental techniques. The crystallinity associated with these films was observed to be highly dependent on the oxygen partial pressure maintained during the growth process. An average optical transparency of more than ∼90% in the visible spectral range (i.e., 400–800 nm) was observed for all specimens. For doped specimens, expected intra-4fn emissions of (dysprosium) Dy3+ ions that emanated from the 4F9/2 energy state were observed in room-temperature photoluminescence spectra under direct excitation. The Jacobian-transformed wavelength-to-energy plot for Dy-doped ZnO thin films in the UV-Visible region revealed intriguing findings. Specifically, it depicted a prominent peak at 2.82 eV, indicative of the energy state of Dy3+ ions, alongside intense band-edge emission and various defect-related emissions. The intensity of these transitions was observed to depend on the oxygen partial pressure kept during deposition. An x-ray photoelectron spectroscopy analysis of the doped specimen confirmed the +3 oxidation state of dysprosium into the ZnO matrix. These results provide a promising approach for controlling the doping and growth strategy of Dy-doped ZnO thin films, thereby opening up a wide range of applications and enhancement for next-generation optoelectronic devices.
Comparative simulations of methanol steam reforming on PdZn alloy using kinetic Monte Carlo and mean-field microkinetic model
Authors: Jiang Yongjie , Huang Yucheng , Guo Hui , Zhu Hong , Chen Zhao-Xu
Published: July 2024

Methanol steam reforming (MSR) is an attractive route for producing clean energy hydrogen. PdZn alloys are extensively studied as potential MSR catalysts for their stability and high CO2 selectivity. Here, we investigated the reaction mechanism using density functional calculations, mean-field microkinetic modeling (MF-MKM), and kinetic Monte Carlo (kMC) simulations. To overcome the over-underestimation of CO2 selectivity by log-kMC, an ads-kMC algorithm is proposed in which the adsorption/desorption rate constants were reduced under certain requirements and the diffusion process was treated by redistributing surface species each time an event occured. The simulations show that the dominant pathway to CO2 at low temperatures is CH3OH → CH3O → CH2O → H2COOH → H2COO → HCOO → CO2. The ads-kMC predicted OH coverage is 2–3 times that of MF-MKM, while they produce similar coverage for other species. Analyses indicate that surface OH promotes the dehydrogenation of CH3OH, CH3O, and H2COOH significantly and plays a key role in the MSR process. The dissociation of water/methanol is the most important rate-limiting/rate-inhibiting step. The CO2 selectivity obtained by the two methods is close to each other and consistent with the experimental trend with temperature. Generally, the ads-kMC results agree with the MF-MKM ones, supporting the previous finding that kMC and MF-MKM predict similar results if the diffusion is very fast and adsorbate interactions are neglected. The present study sheds light on the MSR process on PdZn alloys, and the proposed scheme to overcome the stiff problems in kMC simulations is worthy of being extended to other systems.
Suppressing the Leidenfrost effect by air discharge assisted electrowetting-on-dielectrics
Authors: Wang Liang , Li Xiangming , Wang Zeyu , Tian Hongmiao , Wang Chunhui , Chen Xiaoliang , Shao Jinyou
Published: July 2024

The Leidenfrost effect for a droplet on an over-heated substrate always results in a superhydrophobic state, significantly hindering the water evaporation for heat dissipation. Here, we demonstrate a strategy of air discharge assisted electrowetting-on-dielectrics (ADA-EWOD), overcoming this challenge. This strategy increases the solid surface free energy by generating air discharge near the three-phase contact line of the droplet and combines it with the electromechanical force to decrease the contact angle, which makes ADA-EWOD have stronger wetting capabilities than traditional electrically control methods that only rely on electromechanical force. The water contact angle on an over-heated surface (above 350 °C) is decreased from nearly 180° down to less than 10°. This superhydrophilicity at high temperature reduces the droplet lifetime by at least 10 times, well inhabiting the Leidenfrost effect. Furthermore, we use ADA-EWOD in droplet evaporation for heat dissipation, where a heated silicon wafer at 600 °C is cooled down to less than 200 °C within 20 s. We believe that the present work provides a perspective on suppressing the Leidenfrost effect, which may have important potential applications in the field of heat dissipation.
Predicting bond line thickness of polymeric thermal interface materials based on the rheological properties
Authors: Fan Jianfeng , Ye Zhenqiang , Zeng Xiaoliang , Xu Jian-Bin , Ren Linlin , Sun Rong , Wong Ching-Ping
Published: July 2024

Bond line thickness (BLT) is an essential parameter of thermal conductive composite gels as the thermal interface material (TIM). Extensive research has been performed on designing next-generation TIMs with high thermal conductivity; however, it remains elusive how to link laboratory measurements and the theoretically predicted BLT. Here, we propose a new model to estimate BLT based on a rheological property, in which the TIM is assumed to be a simple power law fluid. To avoid the unrealistic situation of the BLT tending to zero, we introduce a decaying exponential function to describe the influence from fillers during the lid attach process and rebuild the force balance equation. Compared with previously reported models, the theoretical prediction BLT based on the proposed model is in good agreement with the experimental data. Our model has a guiding significance in predicting the BLT, which may help to optimize the thermal performance of TIMs.
Atomistic phase transition mechanism of zero-strain electrode material: Transmission electron microscopy investigation of Li4Ti5O12 spinel lattice upon lithiation
Authors: Kitta Mitsunori , Taguchi Noboru , Ozaki Hiroyuki , Kiyobayashi Tetsu
Published: July 2024

The lithiation mechanism of electrode materials is important for understanding the basic reactions in Li-ion batteries. In particular, zero-strain materials have garnered interest owing to their stable charge–discharge performances. In this study, we investigated the atomistic phase transition mechanism of spinel Li4Ti5O12, a well-known zero-strain material, using high-resolution transmission electron microscopy. A single-crystalline Li4Ti5O12 (100) specimen was prepared and observed in situ at a lattice resolution under electron-beam-assisted lithiation. The lattice fringes originating from the Li plane of the spinel crystal were anisotropically altered during phase transition, suggesting the asymmetrical site shifting of Li atoms during lithiation. This spontaneous symmetry-breaking mechanism for the phase transition is considered essential for the lithiation of spinel lattice.
The interface between ice and alcohols analyzed by atomic force microscopy
Authors: Yanagisawa Ryo , Ueda Tadashi , Nakamoto Kei-ichi , Lu Zhengxi , Onishi Hiroshi , Minato Taketoshi
Published: July 2024

This study investigates the interface between ice and organic solvents using atomic force microscopy (AFM). Atomically flat ice surfaces were prepared and observed by AFM in 1-octanol, 1-hexanol, and 1-butanol. The results show differences in surface roughness influenced by the interaction of ice and alcohols. Young’s modulus of ice was analyzed by force curve measurements, providing valuable insights into the properties of ice in liquid environments. The results showed the characteristics of the ice surface in different solvents, suggesting potential applications in understanding surface and interface phenomena associated with ice under realistic conditions.
Investigating crater formation in nanosecond laser ablation of aluminum foils
Authors: Mohajan Shubho , Beier Nicholas F. , Hussein Amina E.
Published: July 2024

A nanosecond Nd:YAG laser was used to study the laser ablation of aluminum foil in the phase explosion regime at a laser intensity range of 0.63–3.61 ×1012W/cm2. Laser ablation and plasma characteristics were studied using microscopic ablation crater images, plasma emission spectra, and plasma plume images. Measured plasma density using a Stark width of Al I (396.2 nm) showed a strong linear correlation with crater size, with a Pearson correlation coefficient (r) of 0.97. To understand the origin of this linear correlation, plasma temperature was estimated using Bremsstrahlung emission from 512 to 700 nm. The estimated plasma temperature and aspect ratio of the plasma plume were negatively correlated, having r=−0.76. This negative correlation resulted from a laser-plasma interaction, which heated the plasma and increased its hydrodynamic length. The percentages of laser energy used for plasma heating (Ep/EL) and Al foil ablation (EAl/EL) were estimated from plasma temperature. Increased EAl/EL, such as crater size, with increasing laser intensity, confirms that greater mass ablation is the fundamental reason for the strong linear correlation between crater size and plasma density.
The wave passage over a seamount without reflection: Analytical results using the generalized Carrier–Greenspan transform
Authors: Melnikov Ioann , Pelinovsky Efim
Published: July 2024

A method for the transformation of linear shallow water equations based on a generalization of the Carrier–Greenspan transform, well known in the theory of wave rolling on a flat slope, is presented. Thanks to it, the initial equations for waves over arbitrary bathymetry are reduced to a wave equation, from which both the displacement of the free surface and the flow velocity can be obtained simultaneously. Exact solutions in the sum of traveling waves have been obtained for certain configurations of the seabed in the form of seamounts. It is shown that when moving from a more gentle slope to a sharper one, the waveform will integrate a certain number of times, and the maximum amplitude is not reached at the very top of the mountain.
Enhanced magnetic transition temperature through ferromagnetic and antiferromagnetic interaction in cobalt-substituted Fe5GeTe2
Authors: Hu Tao , Ma Yupeng , Lu Longyu , Deng Yazhou , Wang Mingjie , Zhu Kejia , Xi Lei , Xiong Yimin , Kan Xucai , Wang Guopeng , Tian Mingliang , Wang Shouguo
Published: July 2024

Two-dimensional (2D) magnetism is an incredibly intriguing phenomenon in condensed matter physics. The exploration of 2D magnets holds great promise for various applications, even though they often exhibit low magnetic transition temperature. Among these materials, Fe5GeTe2 has emerged as a compelling candidate for room-temperature spintronics due to its intrinsic ferromagnetism and high Curie temperature. In this study, we investigate the impact of Co substitution at the Fe sites in Fe5GeTe2, which induces a transition of the magnetic ground state to the antiferromagnetic state when the substitution level exceeds 0.36. Additionally, we observe the coexistence of ferromagnetic (FM) and antiferromagnetic states in the magnetic transition region of (Fe1−xCox)5GeTe2 crystals. Notably, the interaction between the two magnetic phases results in Néel temperature (TN) up to 374 K, establishing a record among known van der Waals antiferromagnets. Our findings present a strategy for enhancing the magnetic temperature of 2D magnets, paving the way for potential advancements in spintronics applications.
Jump and hysteresis of plasma density in the spatial afterglow of inductively coupled plasmas
Authors: Zhang Yu , Yang Wei , Gao Fei , Wang You-Nian
Published: July 2024

In this work, jump and hysteresis of plasma density between low-density (LD) and high-density (HD) in the spatial afterglow of inductively coupled plasmas are experimentally studied for different gas discharges. A quartz plate with a micropore is used to independently control the pressures in the active plasma and spatial afterglow. The plasma density jump from LD to HD vs the pressure in the spatial afterglow only exists in a larger micropore diameter. By adjusting the pressure back and forth, a hysteresis loop in plasma density is formed. The light intensity and excitation rate vs the pressure corresponds well to the jump and hysteresis of plasma density. Therefore, the abrupt changes in ionization rate are responsible for the jump and hysteresis of plasma density. Compared with argon discharges, the critical pressure for the jump from LD to HD is higher in nitrogen discharges, forming a larger hysteresis loop. For hydrogen discharges, the jump from LD to HD is less significant and the hysteresis loop almost disappears. In argon–hydrogen mixed gas discharges, there is no hysteresis loop in plasma density. Experimental results obtained using Langmuir double probes and spectrometer achieve qualitative agreement in gas discharges mentioned above.
Multiple boundary layer suction slots technique for performance improvement of vertical-axis wind turbines: Conceptual design and parametric analysis
Authors: Zhang Rui , Kuang Limin , Tu Yu , Dong Zhikun , Ping Huan , Zhang Kai , Han Zhaolong , Zhou Dai , Bao Yan
Published: July 2024

Vertical-axis wind turbines (VAWTs) are gaining attention for urban and offshore applications. However, their development is hindered by suboptimal power performance, primarily attributable to the complex aerodynamic characteristics of the blades. Flow control techniques are expected to regulate the flow on the blade surface and improve blade aerodynamics. In the present study, an effective active flow control technique, multiple boundary layer suction slots (MBLSS), is designed for VAWTs performance improvement. The impact of MBLSS on the aerodynamic performance of VAWTs is examined using high-fidelity computational fluid dynamics simulations. The response surface methodology is employed to identify the relatively optimal configuration of MBLSS. Three key parameters are considered, i.e., number of slots (n), distance between slots (d), and slot length (l), which vary from 2 to 4, 0.025c to 0.125c, and 0.025c to 0.075c, respectively. The results show that MBLSS positively affects the power performance and aerodynamics of VAWTs. Parameter n has the most significant effect on VAWT power performance and the importance of d and l is determined by tip speed ratios (TSRs). Tight and loose slot arrangements are recommended for high and low TSRs, respectively. The relatively optimal configuration (n = 2, d = 0.025c, l = 0.05c) results in a remarkable 31.02% increase in the average net power output of the studied TSRs. The flow control mechanism of MBLSS for VAWT blade boundary layer flow has also been further complemented. MBLSS can prevent the bursting of laminar separation bubbles and avoid the formation of dynamic stall vortices. This increases the blade lift-to-drag ratio and mitigates aerodynamic load fluctuations. The wake profiles of VAWTs with MBLSS are also investigated. This study would add value to the application of active flow control techniques for VAWTs.
Synergy effects of cavitation and particle erosion based on the Erosion/Corrosion Research Center erosion model
Authors: Nan Haozhi , Han Wei , Li Rennian , Shen Xiaobo , Dong Yifan , Zhang Yukun
Published: July 2024

This study presents a new synergy model that incorporates the accelerated motion of particles resulting from bubble collapse. The model uses the Erosion/Corrosion Research Center erosion model to predict the combined effect of cavitation and particle erosion on wall surfaces. The results show that, compared with the conventional erosion model, the synergy model reduces the error in the erosion mass loss by up to 24.60%. The significant improvement in prediction accuracy confirms the effectiveness of the synergy model. The severity of sample erosion is positively correlated with the cavitation-inducer angle. The synergy effect leads to an increase in the extent and severity of erosion. Smaller particles demonstrate a more pronounced synergy effect, resulting in significantly accelerated motion and a highly concentrated particle distribution. High erosion rates are associated with high-speed impacts and small-angle impact zones, primarily caused by high-speed cutting erosion. This study presents a novel prediction method for exploring the synergy effect of cavitation and particles on wall erosion and investigates the motion characteristics of particles under this effect.
The effect of a textured surface in the form of triangular prisms on the occurrence and development of cavitation behind the cylinder in microchannels
Authors: Lobasov Alexander S. , Kravtsova Aleksandra Yu.
Published: July 2024

Cavitation flow in a microchannel behind a cylinder with a smooth and textured surface is investigated using mathematical modeling methods. The textured cylinder has 72 triangular prisms on its surface. The height of the prism, normal to the surface of the bluff body, was 100 nm. Profiles of the flow velocity and volume fraction of vapor are constructed. The monitoring of the velocity and pressure at five points behind both the smooth and the textured cylinder was carried out, while the inlet pressure changed up to 30 bars. It is shown that there is no restructuring of the vortex street to a symmetrical form at quite high-pressure values at the inlet to the channel for a rough cylinder. Namely, roughness prevents the flow stabilization. A pressure jump in the microchannel is observed when a cavity appears with a uniform increase in the flow rate. Two pulsation frequencies are determined for each of the flow modes. The first pulsation frequency ranges from 480 to 2200 Hz and is associated with the formation of cavitation. The second pulsation frequency is associated with the hydrodynamic flow around the cylinder and its values range from 26 to 95 kHz. An increase in surface roughness leads to a growth of the cavitation pulsation frequency and intensifies cavitation. At that, the velocity pulsations in the flow before the onset of cavitation increase, and the frequency of hydrodynamic pulsations after its onset decrease. The paper provides an analysis of the drag coefficient of a hydraulic section with rough and smooth cylindrical bluff bodies. The effect of roughness on the change in the hydrodynamic characteristics of the flow is described.
Double diffusive thermogravitational convection in a convex U-shaped porous chamber filled with radiative ternary hybrid nanoliquid
Authors: Hansda Samrat , Chattopadhyay Anirban , Pandit Swapan K. , Sheremet Mikhail A.
Published: July 2024

This research deals with the intricate dynamics of double diffusive thermogravitational convection within a convex U-shaped porous chamber and sheds light on the use of a radiative ternary hybrid nanoliquid. In this configuration, the lower flat boundary is assumed to be thermally hot and densely concentrated while the curved lateral boundaries remain cold and dilute. The other boundaries of the enclosure are kept under adiabatic conditions. The governing Navier–Stokes equations along with thermal and species equations are effectively solved by employing a higher order compact technique. The developed in-house program has been rigorously verified against experimental and computational benchmark results. The research meticulously examines the impact of several pivotal parameters, including the Lewis number (1≤Le≤20), buoyancy ratio (0≤N≤10), Darcy number (10−4≤Da≤10−2), Rayleigh number (104≤Ra≤106), volumetric heat source/sink coefficient (−10≤q≤10), radiation parameter (1≤Rd≤5), aspect parameter of the U-shaped chamber (0.2≤AR≤0.6), and solid particles concentration (0.0≤ϕthnp≤0.04) of the ternary hybrid nanofluid. The findings are eloquently portrayed through graphical representations by showcasing streamlines, iso-solutals, isotherms, and the dimensionless Nusselt (Nuavg) and Sherwood (Shavg) parameters. Our investigation demonstrates that the ternary hybrid nanofluid outperforms both hybrid and mono nanofluids in facilitating double diffusion processes. Moreover, optimal heat transfer efficiency is achieved under conditions characterized by an aspect ratio of AR = 0.2, Rayleigh number Ra=106, Darcy number Da=10−2, buoyancy ratio N = 10, Lewis number Le = 1, and solid volume fraction ϕthnp=0.04.
Multiobjective hydraulic optimization of the diffuser vane in an axial flow pump
Authors: Nguyen Duc-Anh , Lee Hyeong-Jin , Kim Sung , Choi Byung-Lyul , Choi Dong-Hoon , Kim Gyeong Sung , Sun Shuaihui , Kim Jin-Hyuk
Published: July 2024

Separation flows tend to induce a chaotic flow field that eventually leads to energy losses and reduced efficiency. The present study performed a multiobjective optimization to improve the hydraulic performance of an axial flow pump at the best efficiency point (BEP) and critical stall point based on the diffuser vane (DV) geometry. Computational fluid dynamics were applied to predict the hydraulic performance of a series of DV models with design points generated through design of experiment. Six different surrogate models were evaluated based on the R-squared criteria. The nondominated sorting genetic algorithm II was also employed to search for optimum solutions for design variables. Hydraulic performance balance between low and high flow rate conditions was analyzed based on the velocity triangle. After optimization, the efficiency and total head at the BEP of the optimum model were increased by 2.341% and 2.779%, respectively, compared to the reference model. Despite the minimal changes to the hydraulic performance at the critical stall point, the optimal operating range was notably expanded in the high flow rate region. Thorough evaluation of losses attributed to horseshoe, corner, and trailing-edge vortices was conducted in meridional planes, multiple spans, and various cross sections in the DV domain. Additionally, the formation and development of turbulent flow were analyzed in detail by transient simulation. Vibration and noise caused by instabilities in the flow characteristics of the reference model were substantially reduced by 36.76% and 67.342% at the first higher-harmonic frequencies at the BEP and the critical stall point, respectively.
Effect of the inlet spatial fluctuation on the gas–solid continuous rotating detonation flow field characteristics
Authors: Wang Yingnan , Zhang Xiangjun , Liu Peilin , Li Yixiang , Wang Jianping , Ma John Z.
Published: July 2024

Continuous rotating detonation engines have been extensively studied due to their high thermal efficiency. The utilization of solid particles as fuel can effectively reduce costs and enhance detonation performance. We have constructed a compressible gas–solid multimedium flow combustion numerical method, employing the double flux model coupled with fifth-order weighted essentially non-oscillatory and third-order total variation diminishing Runge–Kutta schemes to solve the unsteady multi-component chemical reaction Eulerian–Eulerian equations. Finite-rate methods and surface reaction models are used to simulate the combustion of gaseous mixtures and carbon particles. The effects of the inlet total pressure spatial fluctuations and particle diameter on the flow field characteristics of the continuous rotating detonation engine are investigated. The results indicate that changing the fluctuation period significantly affects the number, propagation direction, and intensity of gas–solid two-phase continuous rotating detonation waves (CRDW). The variation of fluctuation amplitude noticeably alters the combustion characteristics of the two-phase continuous rotating detonation wave, and excessively high amplitudes cannot form continuous rotating detonation waves. Introducing solid particles into fuel significantly mitigates the impact of inlet total pressure spatial fluctuation and promotes propagation stability on the detonation waves. Moreover, when solid particle diameters reach or exceed the micrometer scale, they contribute more favorably to generating a stable detonation flow field. However, excessive particle sizes result in a low surface reaction rate and inadequate contribution of heat released from particle combustion to the propagation of detonation waves.
Active Willis metamaterials with programmable density and stiffness
Authors: Baz A.
Published: July 2024

Investigation and implementation of Active Willis Metamaterials (AWM) have been done exclusively, in all the available literature, by approaches that do not rely on any solid control theory basis. When coupled with piezoelectric control elements, the available approaches have not included, from the first principles, the exact form of the constitutive relationship of the piezoelectric materials. Furthermore, in all these approaches, stability analysis, robustness, ability to accommodate uncertainty or parameter changes, or consideration of disturbance rejection has not been addressed at all. More importantly, the available formulations have always mixed the flow and effort variables of the AWM, resulting in a form that is totally incompatible for the use in generating, investigating, or even designing any appropriate sensing or control applications of the material. In this paper, the piezoelectric-based AWM is modeled, from the first principles, to develop a constitutive coupling form that enables its use in actuation, sensing, and as an integrated controller that can be analyzed, designed, and optimized using the classical, optimal, and robust control system theories. Lagrange dynamics formulation is used to generate the equations governing the Willis coupling, the piezoelectric coupling, as well as the active robust controller. With this developed controlled-based structure of the AWM, the inherent and powerful capabilities of the AWM that lie in its ability to robustly control the material properties themselves such as the compliance (or stiffness) and specific volume (or density) are demonstrated in great detail via several numerical examples. Controlling these properties enables the AWM to be used in numerous important and imaginative applications such as cloaking, beam shifting, beam focusing, as well as many other applications that are limited only by our imagination.
A coupled computational fluid dynamics-discrete element method modeling for the dynamic behavior of the polar detector in a crushed ice environment during polar exploration
Authors: Hu Xinyu , Wei Yingjie , Wang Cong
Published: July 2024

Investigating the dynamic behavior of polar detectors holds significance for the polar exploration of clean energy production. This paper uses computational fluid dynamics and the discrete element method, complemented by laboratory experiments, to systematically explore the water entry dynamics of a projectile passing through a zone of crushed ice accumulation. The research analyzes the influence of different crushed ice accumulation heights (ha) and water entry conditions on cavity formation, flow field distribution, and dynamic characteristics as the projectile passes through the crushed ice zone. Moreover, the influence of multi-body coupling on the movement of crushed ice and fluid is analyzed. The findings reveal alterations in the water entry behavior of the projectile due to the presence of the crushed ice accumulation zone. A notable two-way coupling mechanism between crushed ice and fluid is identified: crushed ice particles influence liquid level fluctuations and cavity evolution, while fluid flow impacts the movement of crushed ice particles. As the height of crushed ice accumulation increases, this coupling effect intensifies, leading to changes in the flow field distribution near the cavity and the hydrodynamic behavior of the projectile. While the alteration in water entry Froude number (Fr) may not significantly alter the evolution pattern of the liquid level flow field, it notably affects the distribution range and formation scale of the flow field characteristics. Additionally, the water entry Fr influences the load characteristics of the projectile as it passes through the crushed ice zone.
Size effect in CoFeB-based anomalous Hall sensor and its applications in pulse detection
Authors: Gu Xiaoyi , Wu Yihong
Published: July 2024

Anomalous Hall effect (AHE) sensor has attracted significant attention in recent years due to its simpler structure and better sensitivity as compared to semiconductor-based Hall sensors. However, up to now, most of the work has been focused on its basic functionalities, with very little attention given to optimizing its performance for practical applications. In this work, we systematically investigated how the lateral dimension affects the performance of CoFeB-based AHE sensors. By adjusting the sensor width while keeping the length and other parameters constant, it is found that although the output signal amplitude decreases with increasing the sensor width, the noise and power consumption also decrease simultaneously, leading to an overall enhancement of the sensor performances with a sensitivity, detectivity, and power efficiency of 8960 Ω/T, 205nT/Hz@1Hz, and 2009 V/WT, respectively. To illustrate the potential applications of AHE sensors, we demonstrate a proof-of-concept experiment to showcase the potential AHE sensor in pulse detection.
Modeling and analysis of a two-stage tri-linear pendulum ultra-low frequency horizontal vibration isolator with experimental investigations
Authors: Li Qiang , Chen Zhiming , Xu Yan , Zhang Shengguo , He Zhaoyun , Li Yaqiong
Published: July 2024

In engineering practice, the external horizontal oscillations always influence the working performance of precise instruments, advanced manufacture equipment, and gravitational wave detection. In order to ensure the normal operation of these instruments, it is necessary to attenuate these vibrations adequately. The pendulum mechanism horizontal vibration isolator is an efficient method. Hence, this paper presents a type of two-stage tri-linear pendulum horizontal vibration isolator (TPHVI). The first-stage TPHVI is connected in series with the second-stage one. The dynamic equations of the two-stage TPHVI are subsequently established so that the vibration isolation performance of the two-stage TPHVI is acquired. The analysis result of the natural frequency of the two-stage TPHVI reveals that it can obtain a low frequency vibration isolation performance when the first-stage TPHVI swings in a small value. As a case study, an experimental rig is constructed. The measured transmissibility keeps in good agreement with the calculated one. The natural frequency of the second-stage TPHVI is 0.25 Hz. The initial vibration isolation frequency is 0.3 Hz. When the external frequency is 0.8 Hz, the transmissibility of the second-stage TPHVI reaches −20 dB. Meanwhile, when the external frequency is 3 Hz, the transmissibility of the second-stage TPHVI is −40 dB. These measured data demonstrate that the proposed two-stage TPHVI can realize low frequency vibration isolation horizontally, which will have broad application prospects in the field of ultra-precision in engineering practice.
A diagnosis method for loss of circulation based on transient-pressure wave analysis and particle swarm optimization
Authors: Zhu Zhongxi , Liu Hong , Wu Desheng , Lei Wanneng
Published: July 2024

Lost circulation during operations poses a significant threat to production processes. In the search for an effective detection method, an impulse-response detection method of lost circulation is introduced. This method involves generating transient pressure waves at the wellhead and analyzing their time-frequency domain characteristics to pinpoint location for lost circulation within the wellbore annulus system. Utilizing the data processing capabilities of machine learning models, this study proposes an integrated model for signal feature classification and diagnosis model for lost circulation. Drawing from extensive experimental data, this model integrates laboratory experiments, signal analysis, and machine learning algorithms. Data preprocessing, including wavelet variation and denoising, precedes the application of an enhanced adaptive noise complete ensemble empirical modal decomposition with adapted noise (ICEEMDAN) alongside energy and sample entropy analysis for feature extraction. By establishing a mapping relationship between signal features and lost circulation changes, we develop an improved backpropagation neural network (IBP) model using the particle swarm optimization (PSO) algorithm for diagnosis (PSO-IBP). Comparative analysis of five models reveals compelling results: ① PSO-IBP achieves an average accuracy of 97.60%, with a standard deviation of 0.356; ② diagnosis accuracy for every lost circulation scenario exceeds 92%, outperforming other models in precision, recall, and F-Score; ③ even with limited training data, PSO-IBP maintains 84% accuracy, demonstrating superior performance. Further analysis highlights the efficacy of PSO-IBP, especially when leveraging ICEEMDAN for signal feature extraction, in accurately diagnosing lost circulation.
Parameter optimization of hot dry rock heat extraction based on discrete element crack network model
Authors: Suo Yu , Dong Muyu , He Wenyuan , Fu Xiaofei , Pan Zhejun
Published: July 2024

Hot-dry-rock (HDR) has long been considered a potential exploitable energy source due to its high energy content, cleanliness, and abundant reserves. However, HDR typically resides in ultra-deep strata with high temperatures and pressures, which makes its extraction a highly complex thermal-hydrological-mechanical (THM) coupling. In this paper, the THM coupling relationship in the geothermal extraction is clarified. It establishes a dynamic porosity and permeability model and creates a pair-well geothermal extraction model. The investigation focuses on understanding the influence of the pressure difference between pair-wells, number of cracks, and injection temperature on the heat extraction temperature, permeability ratio, geothermal reservoir reduction rate, and heat extraction temperature. The research findings indicate the following: (1) Increasing the inter-well pressure difference from 2 to 10 MPa reduces the extraction temperature from 155 to 138 °C. However, the thermal reservoir permeability ratio increases from 1.07 to 1.35. Consequently, the extraction efficiency rises from 6.2 to 12.4 MW. (2) The number of cracks from 200 to 400 led to a decrease in extraction temperature from 160 to 115 °C. However, the thermal reservoir permeability ratio increases from 1.12 to 1.35. In the first 8 years of extraction, the thermal pumping power of 400 cracks exceeded 200 cracks, but later this trend reversed. (3) Elevating the injection temperature from 20 to 60 °C increases the extraction temperature from 142 to 158 °C while reducing the permeability ratio from 1.28 to 1.20. Consequently, the extraction power decreases from 8 to 6 MW. (4) The inter-well pressure difference has the greatest impact on the decrease in extraction temperature, whereas the number of cracks has the greatest impact on the increase in permeability ratio. Injection temperature has the most significant impact on extraction power. This study reveals that increasing the pressure difference between wells, increasing the number of cracks, and lowering the injection fluid temperature will enhance geothermal extraction power. These findings provide valuable insights for geothermal development.
Heterogeneous integration photoferroelectrics for self-powered photoelectric detectors
Authors: Liu Yaping , Zhang Jiayi , Du Hongyu , Qin Tian , Yang Bo , Zhao Shifeng
Published: July 2024

The anomalous photovoltaic effect inherent in ferroelectric materials brings promising opportunities for self-powered photoelectric detectors. However, the photoelectric detection performances in photoferroelectrics are limited by the low photocurrent output due to the recombination and low separation ability of photogenerated carriers. This work proposes a heterogeneous integration technology for self-powered photoelectric detectors by designing a P-type/N-type/P-type (PNP) ferroelectric junction with sandwich structure, in which not only the photogenerated carrier separation is strengthened due to the enhanced polarization derived from the interface compressive stress, but also the carrier recombination is suppressed by the built-in electric field in the depletion layer. Thus, the photocurrent output in the PNP heterojunction is increased by more than seven times at 0 V bias compared with N-type ferroelectric film and exhibits excellent responsivity and detectivity. The temperature stability for repeatable time-resolved self-powered photocurrent demonstrates applicability in high temperature environments. This work provides a feasible strategy for high-performance self-powered photoelectric detectors by heterogeneous integration in photoferroelectrics, promoting ferroelectric photonic applications.
Effect of off-axis electron beam on the performance of a gyroklystron amplifier
Authors: Siddiqui Nazish Fatima , Singh Abhijeet , Sharma Dipendra , Chauhan Madan Singh
Published: July 2024

A crucial part of a gyroklystron is an electron beam. For the efficient operation of the gyroklystron, effective interaction between the radio frequency wave and the electron beam is necessary. Although the manufacturing and assembly of the gyroklystron are complicated, during the assembly process of various components of the gyroklystron, there is some possibility that the components may be misaligned from their actual positions. The operation of a gyroklystron is very sensitive if its components are misaligned. Electron beam misalignment is one type of such misalignment. This paper studies the effect of an off-axis electron beam on gyroklystron performance. Due to misalignment, the electron beam radius will vary in its position as the electron beam gyrates. First, the nonlinear single-mode analysis describing the beam–wave interaction process within the gyroklystron amplifier is discussed. As reported in the literature, an experimental, two-cavity 35 GHz fundamental harmonic gyroklystron amplifier has been used to conduct the present study. The results obtained from the analytically developed approach are benchmarked by the results of the experimental device. Subsequently, the analysis developed has been extended to investigate the impact of the misaligned electron beam on the gyroklystron performance characteristics. The study shows that efficiency, output power and gain decrease with misalignment, whereas bandwidth does not change due to such misalignments. These findings demonstrate the critical role that the misaligned electron beam plays in the operation of a gyroklystron amplifier.