bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuroendoscopy Training
Authors: Hedaoo Ketan , Sinha Mallika , Chauhan Bhanu Pratap Singh , Bajaj Jitin , Ratre Shailendra , Swamy M.N. , Parihar Vijay , Shakya Jitendra , Sharma Mukesh , Patidar Jayant , Yadav Yad Ram
Published: October 2024

Neuroendoscopy can be learnt by assisting or doing live human surgery, cadaver dissection with or without augmented pulsatile vessel and cerebrospinal fluid (CSF) perfusion, and practicing on live animal, dead animal model, synthetic models, three-dimensional printing model with or without augmentation with animal, cadaver tissue, pulsatile vessel and reconstructed CSF model, virtual reality (VR) simulator, and hybrid simulators (combined physical model and VR model). Neurosurgery skill laboratory with basic and advanced learning should be there in all teaching hospitals. Skills can be transferred from simulation model or VR to cadaver to live surgery. Staged learning (first with simple model to learn basic endoscopic technique, then animal model, and then augmented cadavers) is the preferred method of learning. Although most surveys favor live surgery and practice on animal models and cadavers as the most preferred training model now, in future VR may also become a favored method of learning. This article is based on our experience in over 10,000 neuroendoscopic surgeries, and feedback from over 950 neuroendoscopic fellows or consultants who attended workshops conducted every 6 monthly since 2010. A literature search was done on PubMed and Google Scholar using (neuroendoscopy) AND (learning), and (neuroendoscopy) AND (training), which resulted in 121 and 213 results, respectively. Out of them, 77 articles were finally selected for this article. Most of the training programs typically focus on microneurosurgical training. There is lack of learning facilities for neuroendoscopy in most centers. Learning of neuroendoscopy differs greatly from microneurosurgery; switching from microneurosurgery to neuroendoscopy can be challenging. Postgraduate training centers should have well-equipped neuroendoscopy skill laboratory and the surgical educational curriculum should include neuroendoscopy training. Learning endoscopy is about taking advantages of the technique and overcoming the limitations of endoscopy by continuous training.
An effective approach for correlating Na+ concentrations with sweating rates in wearable sweat sensing platform
Authors: He Anwei , Wang Xiaohe , Zhang Liang , Zhang Haolong , Xu Xingli , Yu Chenyang , Ma Yongquan , Wei Wei , Niu Pengfei
Published: October 2024

Accurately correlating the sweating rate and the concentration of biomarkers in sweat is essential in many sweat-based diagnostic applications. These two measurements are always done simultaneously in wearable sweat sensing platforms. However, concentration measurements of biomarkers are always delayed on the timeline compared with their production, whereas there is no such delay for sweating rate. Thus, a timeline mismatch exists between these two measurements. This means that the concentration vs rate correlation constructed on the basis of such measurements will deviate from the actual correlation. This study demonstrates the existence of this mismatch and explains its cause using sweat Na+ measurements. It also proposes an effective approach that applies a point-by-point compensation for the delay between Na+ measurements and the real-time sweating rates, such that the data on the repositioned concentration vs time curve correspond to exactly the same point on the timeline as their production. A vison sensor is developed to measure the sweating rate with high accuracy at a frequency of more than 0.1 Hz. Off-body and on-body measurements of sweating rate and Na+ concentration are carried out, and concentration–rate correlations are constructed using both measured and repositioned concentration curves. The least squares and random forest methods are employed to fit the constructed correlations and evaluate the reliability of the proposed approach. The use of the repositioned concentration curve gives a constructed correlation that is much closer to the actual one. This study indicates the necessity to rearrange sensor-measured biomarker concentration vs time curves when correlations of concentration with sweating rate need to be constructed and proposes a practical point-by-point data repositioning strategy for doing so. The results presented here will benefit the study of sweat biomarkers with unclear correlations with sweating rate, as well as providing a basis for the development of more reliable sweat-based diagnostic methods.
Directed pulsed neutron source generation from inverse kinematic reactions driven by intense lasers
Authors: Yao Yilin , Wu Zhenbo , Ye Tao , Zhu Shaoping , He Xiantu , Qiao Bin
Published: October 2024

Neutron production driven by intense lasers utilizing inverse kinematic reactions is explored self-consistently by a combination of particle-in-cell simulations for laser-driven ion acceleration and Monte Carlo nuclear reaction simulations for neutron production. It is proposed that laser-driven light-sail acceleration from ultrathin lithium foils can provide an energetic lithium-ion beam as the projectile bombarding a light hydrocarbon target with sufficiently high flux for the inverse p(Li7,n) reaction to be efficiently achieved. Three-dimensional self-consistent simulations show that a forward-directed pulsed neutron source with ultrashort pulse duration 3 ns, small divergence angle 26°, and extremely high peak flux 3 × 1014n/(cm2⋅s) can be produced by petawatt lasers at intensities of 1021 W/cm2. These results indicate that a laser-driven neutron source based on inverse kinematics has promise as a novel compact pulsed neutron generator for practical applications, since the it can operate in a safe and repetitive way with almost no undesirable radiation.
Lagrangian particle tracking at large Reynolds numbers
Authors: Küchler Christian , Ibanez Landeta Antonio , Moláček Jan , Bodenschatz Eberhard
Published: October 2024

In the study of fluid turbulence, the Lagrangian frame of reference represents the most appropriate methodology for investigating transport and mixing. This necessitates the tracking of particles advected by the flow over space and time at high resolution. In the past, the purely spatial counterpart, the Eulerian frame of reference, has been the subject of extensive investigation utilizing hot wire anemometry that employs Taylor’s frozen flow hypotheses. Measurements were reported for Taylor scale Reynolds number Rλ > 104 in atmospheric flows, which represent the highest strength of turbulence observed on Earth. The inherent difficulties in accurately tracking particles in turbulent flows have thus far constrained Lagrangian measurements to Taylor scale Reynolds numbers up to approximately Rλ = 103. This study presents the Lagrangian particle tracking setup in the Max Planck Variable Density Turbulence Tunnel (VDTT), where Taylor scale Reynolds numbers between 100 and 6000 can be reached. It provides a comprehensive account of the imaging setup within the pressurized facility, the laser illumination, the particles used, and the particle seeding mechanism employed, as well as a detailed description of the experimental procedure. The suitability of KOBO Cellulobeads D-10 particles as tracers within the VDTT is illustrated. The results demonstrate that there is no significant charge exhibited by the particles and that the impact of their inertia on the results is negligible across a wide range of experimental conditions. Typical data are presented, and the challenges and constraints of the experimental approach are discussed in detail.
Achieving smooth motion in displacement amplification piezoelectric stick–slip actuator
Authors: Ji Hua-wei , Lin Li-ming , Liu Yu , Chen Zhe-hao , Wu Xin , Ni Jing
Published: October 2024

Traditional piezoelectric stick–slip actuators often suffer from significant backward motion phenomena, which greatly impact their output performance. To overcome this issue, a novel displacement amplification piezoelectric stick–slip actuator was meticulously designed. It integrates an L-shaped displacement amplification mechanism with a parallelogram-compliant mechanism. By dynamically adjusting the compressive force between the stator and the mover, this actuator effectively increases the single-step displacement, resulting in smooth and stable motion output. The design process involved thorough structural feasibility validation and core dimension optimization, utilizing Castigliano’s second theorem and finite element simulation analysis. These efforts successfully yielded a substantial increase in the single-step output displacement. Experimental results demonstrate the actuator’s capability to achieve smooth and stable motion output, even under challenging conditions, such as symmetric excitation signals and horizontal loading. Under specific operating parameters—preloading force of 3 N, input voltage of 100 VP–P, and driving frequency of 625 Hz sinusoidal excitation signal, the actuator achieves an impressive maximum driving speed of 25.22 mm/s, with a substantial maximum load capacity of 2.1 N. Compared to previous studies, the designed actuator exhibits superior adaptability to various excitation signals, offering significant potential for enhancing the performance and expanding the applications of piezoelectric stick–slip actuators.
Interference of single photons with ultralong coherence time
Authors: Wang Manman , Li Yanfeng , Liu Hanqing , Ni Haiqiao , Niu Zhichuan , Wei Xiaogang , Yang Renfu , Hu Chengyong
Published: October 2024

Two-photon interference (TPI) is a fundamental phenomenon in quantum optics and plays a crucial role in optical quantum technologies. TPI is commonly considered as quantum interference with an upper bound of 100% for both the TPI and the beat visibility in contrast to its classical counterpart with a maximum visibility of 50%. However, this is not always the case. Here, we report a simultaneous observation of quantum and classical TPI of single photons with ultralong coherence time, which is five orders of magnitude longer than the photon correlation time. We observe a TPI visibility of 94.3% ± 0.2% well above the 50% classical limit indicating the quantum feature, and a beat visibility of 50% reflecting the classical feature. In addition an anti-bunching central dip due to single-photon anti-correlation, we also observe two bunching side peaks in cross correlation curves for indistinguishable photons. Using the general wave superposition theory and the quantum field approach, we derive the same cross correlation functions, which fully reproduce and explain the experiments. Our results reveal that the quantum and classical features of TPI result from the same interference, as the fourth-order temporal interference arises from the second-order temporal interference between two photons on the timescale of the photon coherence time.
Inducing alternating magnetic fields for real-time non-contact fault localization within electric energy storage component arrays
Authors: Peng Tonghui , Gao Wei , Wu Ya , Ma Yulong , Zhang Shiwu , Hu Yinan
Published: October 2024

With the wide application of electric energy storage component arrays, such as battery cell arrays, capacitor arrays, and inductor arrays, their potential safety risks have gradually drawn the public attention. However, existing technologies cannot realize rapid, precise, and nondestructive localization of the faulty component within these large-scale arrays, especially for a component with an early stage short-circuit fault. To address this challenge, this paper proposes a magnetic field based method and realizes precise fault localization by inducing an alternating magnetic field from the target array, unlike previous research where a static magnetic field was induced. Through establishing a physical model of the short-circuit component as well as the whole array, a spatial filtering algorithm based on beamforming techniques is utilized to process the measured magnetic field data in real time. Both the simulation and experimental results demonstrate the capability of the proposed method in enhancing the security of electric energy storage component arrays. Within an imaging area of 80 × 80 mm2, the proposed method can accurately locate the faulty component out of a nine-component array, with an error of only 0.72 mm for capacitors and 0.91 mm for battery cells.
Machine learning force field for thermal oxidation of silicon
Authors: Cvitkovich Lukas , Fehringer Franz , Wilhelmer Christoph , Milardovich Diego , Waldhör Dominic , Grasser Tibor
Published: October 2024

Looking back at seven decades of highly extensive application in the semiconductor industry, silicon and its native oxide SiO2 are still at the heart of several technological developments. Recently, the fabrication of ultra-thin oxide layers has become essential for keeping up with trends in the down-scaling of nanoelectronic devices and for the realization of novel device technologies. With this comes a need for better understanding of the atomic configuration at the Si/SiO2 interface. Classical force fields offer flexible application and relatively low computational costs, however, suffer from limited accuracy. Ab initio methods give much better results but are extremely costly. Machine learning force fields (MLFF) offer the possibility to combine the benefits of both worlds. We train a MLFF for the simulation of the dry thermal oxidation process of a Si substrate. The training data are generated by density functional theory calculations. The obtained structures are in line with ab initio simulations and with experimental observations. Compared to a classical force field, the most recent reactive force field, the resulting configurations are vastly improved. Our potential is publicly available in an open-access repository.
Three-dimensional simulations of two-phase plug flow in a microfluidic channel
Authors: Virappane Santhosh , Azadi Reza , Mukherjee Neelarun , Tsai Peichun Amy
Published: October 2024

A fundamental understanding of two-phase flow behavior in microfluidics is crucial for various technological applications across different disciplines, including energy, chemical, and material engineering, as well as biomedical, environmental, and pharmaceutical sciences. In this work, we elucidate the flow fields of low Capillary number [Ca ∼O(10−3)] segmented Taylor flows of immiscible CO2 emulsions/bubbles transported by water in a low aspect ratio microchannel. We conducted high-resolution two- and three-dimensional (2D and 3D) numerical simulations using an improved volume-of-fluid two-phase flow solver and validated their accuracy against experimental data. Our results show that 3D simulations are necessary to accurately capture the dynamics of liquid and supercritical CO2 emulsions produced at relatively higher Ca. The 3D simulation results also reveal diverse patterns of spanwise vortices, which are overlooked in 2D simulations. Calculating the Q-criterion in 3D revealed that vortices with relatively higher vorticity magnitudes are adjacent to the sidewalls, with the strongest ones emerging across the microchannel in the third dimension. More specifically, gaseous CO2 bubbles display relatively intense vortex patterns near the interfacial region of the bubble body and the cap due to the influence of the surrounding thin liquid film and slug flow. At higher Ca, liquid and supercritical CO2 emulsions exhibit similar flow dynamics, however, with prominent vortex patterns occurring in the upstream cap region. These findings pinpoint specific areas within the emulsions/bubbles that require attention to enhance stabilization or exchanging mechanisms for low-Ca Taylor flow of emulsions/bubbles.
FePt bimetallic nanoparticles: A highly efficient hydrogen evolution catalyst with tunable d-band center
Authors: Huang Yue , Chang Shao-Zhong , Zi Tao-Qing , Zhu Lin , Gao Li , Cao Yan-Qiang , Syed Jawad Ali Shah , Li Wei-Min , Wu Di , Li Ai-Dong
Published: October 2024

Atomic layer deposition-derived FePt alloy catalysts exhibit superb hydrogen evolution reaction (HER) activity under tuning of their composition, where the electronic structure is modulated by the ligand effect. We demonstrate that HER activity can be correlated with the calculated d-band center via a linear relationship.
Multi-functional programmable active acoustic meta-surface: Acoustic switch, acoustic barrier, and acoustic transmitter
Authors: Pundir Anil , Gupta Arpan , Nag Sarthak
Published: October 2024

An ultra-sparse, broadband programmable Active Acoustic Meta-surface (AAMS) that is demonstrated to function as a multi-functional Active Acoustic Meta-device is developed. Functionalities Acoustic Barrier (AB), Acoustic Switch (AS), and Acoustic Transmitter (AT) have been successfully explored. AB functions at a broadband frequency of 455 to 679 Hz as an approximately 100% acoustic reflector. The functional range of the AS is 425 to 800 Hz, and similarly, the functional range of the AT is 300 to 800 Hz (the full range of the applied frequency sweep). Being a re-configurable device, the AAMS has variable thickness. On a wavelength scale, it varies from 0.10λ to 0.99λ for the said functionalities. Here, λ is the wavelength.
Implementation of frozen density embedding in CP2K and OpenMolcas: CASSCF wavefunctions embedded in a Gaussian and plane wave DFT environment
Authors: Schreder Lukas , Luber Sandra
Published: October 2024

Most chemical processes happen at a local scale where only a subset of molecular orbitals is directly involved and only a subset of covalent bonds may be rearranged. To model such reactions, Density Functional Theory (DFT) is often inadequate, and the use of computationally more expensive correlated wavefunction (WF) methods is required for accurate results. Mixed-resolution approaches backed by quantum embedding theory have been used extensively to approach this imbalance. Based on the frozen density embedding freeze-and-thaw algorithm, we describe an approach to embed complete active space self-consistent field simulations run in the OpenMolcas code in a DFT environment calculated in CP2K without requiring any external tools. This makes it possible to study a local, active part of a chemical system in a larger and relatively static environment with a computational cost balanced between the accuracy of a WF method and the efficiency of DFT, which we test on environment–subsystem pairs. Finally, we apply the implementation to an oxygen molecule leaving an aluminum (111) surface and a ruthenium(IV) oxide (110) surface.
A comparison of neural-network architectures to accelerate high-order h/p solvers
Authors: Marino Oscar A. , Juanicotena Adrian , Errasti Jon , Mayoral David , Manrique de Lara Fernando , Vinuesa Ricardo , Ferrer Esteban
Published: October 2024

High-order solvers are accurate but computationally expensive as they require small time steps to advance the solution in time. In this work, we include a corrective forcing to a low-order solution to achieve high accuracy while advancing in time with larger time steps and achieving fast computations. This work is a continuation of our previous research [Manrique de Lara and Ferrer, “Accelerating high order discontinuous Galerkin solvers using neural networks: 1D Burgers' equation,” Comput. Fluids 235, 105274 (2022) and F. Manrique de Lara and E. Ferrer, “Accelerating high order discontinuous Galerkin solvers using neural networks: 3D compressible Navier-Stokes equations,” J. Comput. Phys. 489, 112253 (2023).], where we compare advanced neural networks: convolutional neural network (CNN) and long short-term memory (LSTM) networks to obtain the corrective forcing that corrects the low-order solution. The CNN exploits local spatial correlations while the LSTM accounts for temporal dependencies in the flow, expanding the validity of the low-order solution. Experimental results on the Taylor–Green vortex problem at Re = 1600, which includes laminar, transitional, and turbulent regimes, demonstrate significant accelerations of these advanced networks over the fully connected network.
Design of an X-band high-efficiency coaxial relativistic klystron oscillator packaged with permanent magnet
Authors: Li Zhimin , Zhang Peng , Ge Xingjun , Dang Fangchao , Yang Fuxiang , Deng Rujin , Chi Hang
Published: October 2024

An X-band high-power microwave (HPM) oscillator packaged with permanent magnets is proposed. The oscillator employs a radially non-uniform modulation cavity structure to enhance the modulation depth of the electron beam, thereby improving the conversion efficiency of the device. Verified by particle-in-cell simulation, the device achieves an HPM output at X-band with a frequency of 9.38 GHz and power of 3.1 GW, corresponding to a power efficiency of 44.5%, under the conditions of a permanent magnet field of 0.4 T, a diode voltage of 600 kV, and a beam current of 11.6 kA.
Tunable phase and electrical characteristics induced by Al content in Zr1−
xAlxN films for temperature sensors with wide temperature range
Authors: Li Yanjie , You Minmin , Ran Yongpeng , Zhu Xiantao , Lin Zude , Liu Jingquan
Published: October 2024

Transition metal nitride (TMN) films hold great promise in temperature sensing due to their excellent stability, but the decreased sensitivity with increasing temperature has limited their adaptability to various temperature scenarios. In this paper, a method for regulating the high-sensitivity temperature range (HSTR) of the temperature sensors based on the zirconium aluminum nitride (Zr1−xAlxN) films by adjusting the Al content is proposed. According to the resistance–temperature (R–T) curves from 4.2 to 300 K, the metal-to-semiconductor transition was observed when Al atoms were doped in ZrN. Moreover, the semiconductor R–T curve gradually shifts to 300 K and then backs to cryogenics by continuously increasing the Al content in Zr1−xAlxN. Interestingly, the phase transition from cubic (c)-ZrN to cubic (c)-Zr1−xAlxN, then to the mixed phases of c-Zr1−xAlxN and wurtzite aluminum nitride (w-AlN), and, finally, to the hexagonal close packed-zirconium (α-Zr) precipitation was observed with increasing Al content, which shows high consistency with R–T characteristics. Moreover, the bandgap energy initially increases and then decreases, which matches well with the phase and electrical transitions. Based on the experimental results, we build a physical model that can clarify the above phase and electrical transition when the Al content in Zr1−xAlxN films changes, proposing that the effect of Al content on the phase and electrical characteristics can realize the control of the HSTR of Zr1−xAlxN films. These findings suggest ideas for developing temperature sensors based on TMN films with high sensitivity across a wide temperature range.
High-precision electrospinning of Ag fluid fibers with electric field-guided deposition on flexible substrates
Authors: Aoboun Assareeya , Pechyen Chiravoot , Shin Dong-Youn
Published: October 2024

This study introduces the approach for precisely controlling the trajectory of fluid jets by employing electric field manipulation to confine fiber deposition to specific areas on flexible substrates, particularly within various electronic device applications. Applying similar polar high voltage to both the nozzle tip and printed circuit board generates complementary electric fields, directing the fluid jet to the desired locations on the flexible substrate. This innovative technique eliminates the necessity for traditional masking methods, resulting in reduced ink consumption, streamlined production processes, and minimized chemical waste. To illustrate practical applications, we fabricate flexible conductive electrodes for media façade applications and real-time sensor monitoring, showcasing the effectiveness of integrating Ag nanoparticles into functional electronic components. With an approximate sheet resistance of 10 Ω/sq2, our system adeptly controls Ag nanoparticle deposition within defined areas. This approach not only aligns fibers precisely but also ensures uniform deposition, making it ideal for various flexible applications. Overall, this study underscores the potential of electric field manipulation to revolutionize surface and coating technology, offering a promising avenue for sustainable and efficient manufacturing processes, particularly in flexible applications. The resulting patterned electrodes can be employed in a wide range of flexible electronic devices, contributing to more sustainable and efficient manufacturing processes in the industry.
Reversal barrier and ferroelectric polarization of strained wurtzite Al1−xScxN ferroelectric alloys
Authors: Xue Yixin , Cui Dongsheng , Kang Mengyang , Wang Yifei , Zhang Hong , Yuan Haidong , Gao Xiangxiang , Su Jie , Lin Zhenhua , Miao Jinshui , Zhang Jincheng , Hao Yue , Chang Jingjing
Published: October 2024

Reducing the reversal barrier of Al1−xScxN ferroelectric alloy is critical for improving the coercive voltage and power consumption of ferroelectric devices. Here, the synergistic effect of alloy composition and strain is introduced to optimize the ferroelectric properties of Al1−xScxN alloys. Because of the increased Al–N ionic bond character and the contribution of Sc-d orbitals, the spontaneous polarization, reversal barrier, and bandgap all reduce as the Sc concentration increases. Strain engineering improves the electron's electric dipole moment, resulting in a significant increase in spontaneous polarization (145.93 μC/cm2 for Al0.625Sc0.375N alloy). Meanwhile, the horizontal tension and vertical compression lower the reversal barrier of Al0.625Sc0.375N alloy to 95.45 meV/f.u., significantly lower than that of orthorhombic HfO2. Interestingly, the bandgap of Al1−xScxN alloy with low Sc concentration rises initially and then decreases as horizontal strain varies from compression to tension, whereas that of Al1−xScxN alloy with high Sc concentration monotonically decreases. The Al1−xScxN alloy exhibits the opposite tendency under vertical strain. These findings provide a thorough understanding of Al1−xScxN ferroelectric alloys and a guideline for designing high-performance Al1−xScxN ferroelectric alloys.
Modeling phase separation in solids beyond the classical nucleation theory: Application to FeCr
Authors: Luneville L. , Tissot O. , Pareige C. , Simeone D.
Published: October 2024

Despite a large amount of work being devoted to study the phase separation in solids, the underlying physical mechanism responsible for such diffusive first-order phase transitions remains difficult to model outside the spinodal regime, i.e., in the nucleation and growth regime. This work presents an alternative of the classical nucleation theory for modeling phase separation in this regime, even for systems far from the solubility limit, i.e., for high degree of meta-stability where the classical nucleation theory does not hold. This method then allows a direct comparison between simulations and experiments always performed in solids with a high degree of meta-stability.
Toward a realistic theoretical electronic spectra of metal aqua ions in solution: The case of Ce(H2O)n3+ using statistical methods and quantum chemistry calculations
Authors: Raposo-Hernández Gema , Pappalardo Rafael R. , Réal Florent , Vallet Valérie , Sánchez Marcos Enrique
Published: October 2024

Accurately predicting spectra for heavy elements, often open-shell systems, is a significant challenge typically addressed using a single cluster approach with a fixed coordination number. Developing a realistic model that accounts for temperature effects, variable coordination numbers, and interprets experimental data is even more demanding due to the strong solute–solvent interactions present in solutions of heavy metal cations. This study addresses these challenges by combining multiple methodologies to accurately predict realistic spectra for highly charged metal cations in aqueous media, with a focus on the electronic absorption spectrum of Ce3+ in water. Utilizing highly correlated relativistic quantum mechanical (QM) wavefunctions and structures from molecular dynamics (MD) simulations, we show that the convolution of individual vertical transitions yields excellent agreement with experimental results without the introduction of empirical broadening. Good results are obtained for both the normalized spectrum and that of absolute intensity. The study incorporates a statistical machine learning algorithm, Gaussian Mixture Models-Nuclear Ensemble Approach (GMM-NEA), to convolute individual spectra. The microscopic distribution provided by MD simulations allows us to examine the contributions of the octa- and ennea-hydrate of Ce3+ in water to the final spectrum. In addition, the temperature dependence of the spectrum is theoretically captured by observing the changing population of these hydrate forms with temperature. We also explore an alternative method for obtaining statistically representative structures in a less demanding manner than MD simulations, derived from QM Wigner distributions. The combination of Wigner-sampling and GMM-NEA broadening shows promise for wide application in spectroscopic analysis and predictions, offering a computationally efficient alternative to traditional methods.
Centrifugal through-flow rotor-stator cavity boundary layer transition based on the effect of roughness
Authors: Yao Yulong , Hu Bo , Wang Hui , Wang Chuan , Yang Yang , Chen Xionghuan
Published: October 2024

In this study, we report a set of compressible Reynolds-averaged Navier–Stokes simulation results of rotor-stator cavity flows under a range of conditions such as surface roughness, Reynolds number, and through-flow coefficient. The main objective is to determine the effect of rotor roughness on the characteristics of the fluid and thermal boundary layers. The boundary layer inside the disk cavity is found to be Batchelor-type within the present parameter range. Increases in Reynolds number, through-flow coefficient, and surface roughness all enhance the flow circulation inside the disk cavity. The thickness of the Ekman layer on the rotor is almost twice that of the stator Bodewadt layer. Rotor roughness significantly affects the turbulent characteristics of the flow when the rotor-stator cavity is rotationally dominated, but the effect is small when the cavity is through-flow dominated. Increasing rotor roughness accelerates the separation of the stator boundary layer, particularly at weak through-flow. On heat transfer, large rotor roughness induces an overall temperature rise in the cavity and reduces the thermal boundary layer thickness. The effects are more pronounced at low Reynolds numbers and small through-flow coefficient. The present results can facilitate the design of high-efficiency rotor-stator cavities.
Large eddy simulation investigation on the effects of the forebody shape of a supercavitating torpedo
Authors: Pham Van-Duyen , Ahn Byoung-Kwon
Published: October 2024

The forebody length of a supercavitating vehicle requires careful consideration during the design process. Variations in this dimension have the potential to profoundly influence the supercavitation characteristics. In this numerical study, we qualitatively and quantitatively explore the characteristics of natural and ventilated supercavitating flow under various forebody lengths. We use the multiphase volume-of-fluid method and the large-eddy simulation framework coupled with the Schnerr–Sauer cavitation model. Three forebody lengths (LF = 10dc, 15dc, and 20dc, where dc is the diameter of the cavitator) are applied to the test model. The numerical simulations effectively predict variations in supercavity geometry, hydrodynamic force, and supercavitating internal flow under the influence of the forebody length. The results indicate that the time required to generate a clear supercavity for the model with a 10dc forebody length is ∼6% and 9% less than for the 15dc and 20dc forebody length models, respectively. Additionally, the 10dc forebody length model experiences about 5% smaller total drag force compared to the longer models. The variations in forebody length significantly influence the supercavitating internal flow and pressure distribution inside the supercavity. Specifically, the ventilation air is distributed as an outer layer of the supercavity for the 10dc forebody length model, whereas it moves along the surface of the models with 15dc and 20dc forebody lengths. In terms of pressure distribution, the 10dc forebody length model exhibits the highest local pressure compared to the models with longer forebody lengths. These observations provide insights into the physical mechanisms underlying the effects of forebody length on supercavity characteristics.
ICF target optimization using generative AI
Authors: Ben Tayeb M. , Tikhonchuk V. , Feugeas J.-L.
Published: October 2024

This paper explores the capabilities of generative artificial intelligence (AI) for target optimization in inertial confinement fusion for energy production. For demonstration purposes, the focus is on optimizing the laser illumination temporal profile assuming a spherical implosion and a given target structure. An optimization protocol is based on the generative AI tool and a dataset for a shock ignition scheme produced with a reference hydrodynamic code. In a first optimization process, the generative AI proposed a family of laser power profiles by introducing a plateau before the shock that doubles the energy gain value of the reference configuration. In a second optimization process, the number of parameters defining the laser power profile is increased according to the results of the first step. The generative AI then suggested more general solutions including multiple plateaus and classical profiles without shock that further double the gain for half the laser energy required. The suggested optimization method can be extended to other configurations of laser-target interaction.
Topological comparison of flexible and semiflexible chains in polymer melts with θ-chains
Authors: Schmitt Maurice P. , Wettermann Sarah , Daoulas Kostas Ch. , Meyer Hendrik , Virnau Peter
Published: October 2024

A central paradigm of polymer physics states that chains in melts behave like random walks as intra- and interchain interactions effectively cancel each other out. Likewise, θ-chains, i.e., chains at the transition from a swollen coil to a globular phase, are also thought to behave like ideal chains, as attractive forces are counterbalanced by repulsive entropic contributions. While the simple mapping to an equivalent Kuhn chain works rather well in most scenarios with corrections to scaling, random walks do not accurately capture the topology and knots, particularly for flexible chains. In this paper, we demonstrate with Monte Carlo and molecular dynamics simulations that chains in polymer melts and θ-chains not only agree on a structural level for a range of stiffnesses but also topologically. They exhibit similar knotting probabilities and knot sizes, both of which are not captured by ideal chain representations. This discrepancy comes from the suppression of small knots in real chains, which is strongest for very flexible chains because excluded volume effects are still active locally and become weaker with increasing semiflexibility. Our findings suggest that corrections to ideal behavior are indeed similar for the two scenarios of real chains and that the structure and topology of a chain in a melt can be approximately reproduced by a corresponding θ-chain.
High-resolution anionic velocity map imaging apparatus for dissociative electron attachment dynamics study
Authors: Xie Jingchen , Gao Xiao-Fei , Fan Mengyuan , Li Hao , Wu Bin , Tian Shan Xi
Published: October 2024

Dissociative electron attachment (DEA) of a molecular target XY, e− + XY → XY− → X + Y−, is an important process in plasma, atmosphere, interstellar space, and ionizing radiation. DEA dynamics, i.e., the formation and fragmentation of an electron–molecule resonant complex, can be unveiled by measuring the product Y− with the velocity map imaging (VMI) technique. However, it is still challenging to achieve a high-resolution VMI measurement. Recently, we developed a high-resolution DEA apparatus that combined the VMI technique with a trochoidal electron monochromator. The energy spread (around 500 meV) of thermally emitted incident electrons can be reduced remarkably, but the monochromatized electrons become diffuse again in energy when being pulsed with an electric pulse applied on the grid electrode because the electron beam must be pulsed in the VMI measurement. Now this long-standing technical contradiction is settled by introducing a parallel resistance-capacitor circuit to the electrode of an electron gun. A delay-line detector is used for the VMI measurement, which allows the three-dimensional velocity or momentum images of multiple anionic yields to be recorded efficiently. Our high-resolution VMI apparatus works at a pulse frequency of 5 kHz and an energy spread of about 120–150 meV, and its credible performances are exhibited by the measurements of the DEA processes of CO(a3Π) and NO2.
Electrohydrodynamic stability of a two-layer plane Poiseuille flow in the presence of interfacial surfactant: Energy budget analysis
Authors: Yadav Sarita , Chattopadhyay Geetanjali
Published: October 2024

The electrohydrodynamic stability of a two-layer plane Poiseuille flow has been examined under the influence of an electric field acting normally to the unperturbed interface of two viscous immiscible fluids. The presence of insoluble surfactant at the interface is considered to achieve passive control over the instability that naturally comes into play in such flows. The fluids considered here for the asymptotic and numerical stability analyses are treated as leaky dielectrics, which are allowed to have different viscosities, densities, permittivities, and conductivities. An asymptotic analysis shows that the two opposite influences from the electrical stresses and the Marangoni stresses in competition at the interface give rise to remarkably different patterns of neutral curves depending upon the ratios of viscosities and thicknesses of the fluid layers. A linear stability analysis utilizing the Chebyshev spectral collocation method for disturbances of all wave numbers is employed numerically to obtain various types of dispersion curves and neutral stability diagrams originating from the associated Orr–Sommerfeld eigenvalue problem. Our results suggest that increasing the electrical conductivity ratio leads to an increase in the growth rate of disturbances, whereas an increase in the electrical permittivity ratio stabilizes the flow as the interfacial surface tension resists the growth of perturbations that are otherwise promoted by electrical stresses. The energy budget calculations show that the presence of the insoluble surfactant is primarily responsible for the viscosity-induced instability triggered by the modified interface deformation. The comparisons with pertinent studies are performed to enhance the quantitative reliability of the present work.
Dynamics of round turbulent offset jets in quiescent and coflowing environments
Authors: Hakimi Fatemeh , Khorsandi Babak
Published: October 2024

This study experimentally investigates the dynamics of turbulent round offset jets introduced into both a quiescent environment and a coflowing stream. The acoustic Doppler velocimeter was employed to precisely measured the velocity field of the jet in a water flume. The results pertaining to the offset jets released into a quiescent background was compared against those of the previous studies and the measurement technique was validated. Coflow confines the offset jets, leading to narrower mean and root mean square (rms) velocity profiles. Furthermore, the spreading and decay rates decrease, indicating that the external flow constrains the growth and development of the offset jets. The effect of coflow becomes more pronounced and the rates further decrease when the offset ratio reduces. The rms velocities of coflowing offset jets increase compared to those of jets in a quiescent background. Moreover, by decreasing the offset ratio, the rms velocities decrease, as the wall proximity further restricts the jet's meandering and intermittency. The velocity spectra of coflowing offset jets have higher values in the inertial subrange compared to those of the offset jets in a quiescent environment. However, this trend reverses within the energy-containing range. This coincides with a decrease in the integral length scales, suggesting that the coflow may suppress the large-scale jet structures mainly responsible for engulfing the ambient fluid into the jet. The observed reduction in spreading and decay rates, as well as integral length scales of the coflowing offset jets, suggest a decrease in jet entrainment, resulting in a reduction in overall jet mixing.
Numerical investigation of the damping rates of free oscillations in fluid energy acquired due to sloshing in rectangular tanks
Authors: Pujari Siddhesh , Rajan Girish Kumar
Published: October 2024

Enhancing the dissipation of fluid energy generated due to sloshing is necessary to eliminate the undesirable hydrodynamic forces it produces on the walls of a mobile container. With this goal, this work investigates the fluid motion due to sloshing in three rectangular tanks (A, B, and C) that undergo sinusoidal displacements from their mean positions for a short duration of time, Ts. Tank A is partially filled with water; tank B is partially filled with water and contains a bottom-mounted baffle at a distance of xb from the left wall; and tank C consists of an oil-layer of thickness, d, floating on a water layer. Three-dimensional simulations are performed to obtain the flow field and temporal evolution of fluid kinetic energy in several cases. The period of evolution includes the initial transient regime; the periodic forced-oscillation regime; and the free-oscillation regime, which comprises the nonlinear and linear damping sub-regimes. In each case, nonlinear and linear damping rates are obtained and analyzed to estimate the timescales for energy dissipation in the respective sub-regimes. Results of detailed parametric studies reveal that damping rates increase significantly due to the baffle (tank B) and oil-layer (tank C), so both are effective in mitigating sloshing. For flow in tank B, nonlinear damping rates are consistently higher than corresponding linear damping rates, and both are non-monotonic functions of xb and Ts. For flow in tank C, the nonlinear (linear) damping rate is a monotonic (non-monotonic) function of d. Reasons for variations in damping rates due to the baffle and the oil-layer are highlighted, and discussions of the physics causing these changes are also presented.
Enhancement of mass transfer in converter by improving the flow of slag and molten steel
Authors: Wang Xi , Liu Guangqiang , Mu Wangzhong , Liu Tie , Liu Kun , Wang Lianyu
Published: October 2024

In top blowing steelmaking, the impact behavior of the supersonic oxygen jet significantly affects the emulsification of slag–metal and the reaction rate in the molten bath. To enhance the mass transfer rate, a swirl-type oxygen lance is proposed. The mass transfer processes between slag and molten steel in the converter during the swirl-type oxygen lance blowing process are investigated. A mixing index Im is proposed to assess the slag–metal mixing degree, and the effects of operating parameters on mass transfer rate and mixing index are discussed. The results demonstrate that compared to the traditional oxygen lance, the swirl-type oxygen lance enhances the stirring intensity of the jet on the molten bath, resulting in a 5.1%–13.0% increase in the mass transfer rate. When the swirl-type oxygen lance is under the condition of H = 45de, the mixing index is the lowest (4.52) and the volumetric mass transfer coefficient is the highest (1.92 × 10−3 m3/s). The energy transferred from the jet to the molten bath can be enhanced by an increase in the flow rate or operation pressure, thereby decreasing the mixing index and increasing the volumetric mass transfer coefficient. Finally, a criterion number equation (Sh = 5.78 × 10−3Re0.43Sc0.33) for the involved mass transfer processes is established, which indicates that increasing the velocity of the slag and molten steel is more effective in enhancing the mass transfer rate than adjusting the liquid phase components in practical steelmaking.
Simultaneous resonance characteristics of cylindrical bubbles under dual-frequency acoustic excitation based on singular-perturbation theory
Authors: Yu Jiaxin , Luo Jinxin , Zhang Xiangqing , Zhang Yuning , Zhang Yuning
Published: October 2024

The simultaneous resonance patterns and dynamic attributes of cylindrical bubbles subjected to dual-frequency acoustic excitation are explored in this article. Specifically, analytical models and local stability analysis are constructed for different types of simultaneous resonance under dual-frequency acoustic excitation. Based on the frequency response curve, the mechanisms whereby the core parameters in dual-frequency excitation influence the resonant dynamic characteristics are then explored. Combined with the Lyapunov exponent and amplitude, frequency, and phase, bifurcation diagrams are illustrated for determining the global stability of the cylindrical bubble dual-frequency resonance system. The conclusions from this research are given as follows: (1) Under dual-frequency acoustic excitation, the simultaneous resonance type can be subdivided into three categories, namely, primary–superharmonic, primary–subharmonic, and superharmonic–subharmonic simultaneous resonances. These dual-frequency resonance types exhibit unique and significant dynamic characteristics. (2) Increasing the total amplitude of dual-frequency acoustic excitation significantly enhances the maximum value of the dual-frequency resonance and the vulnerability to instabilities. The effect of the bubble balance radius is similar to that of the total amplitude. Higher values of the nonlinear coefficient reduce the maximum value of the resonance and increase the likelihood of instability. (3) The total amplitude of dual-frequency acoustic excitation is a key factor affecting the stability of bubbles. As the total amplitude increases, the bubble oscillation gradually transforms from periodic to chaotic.
Cylindrical micro-pressure wave radiation from tunnel portals in deep cuttings
Authors: Miyachi Tokuzo
Published: October 2024

In high-speed railways, micro-pressure waves (MPWs) emitted from tunnel portals can cause significant problems. An MPW is typically a spherical wave. However, in infinitely deep cuttings, an MPW becomes a cylindrical wave and affects larger areas. In this study, the cylindrical MPWs emitted toward infinitely deep cuttings were analytically and numerically investigated. Analytical expressions were introduced, and a far-field approximation using the half-derivative of velocity at the tunnel exit was demonstrated. The analytical solutions agreed with the results of computational fluid dynamics. Finally, the strength of the main source term was demonstrated to be approximately proportional to Δpin(∂pin/∂t)max where pin is the pressure of the compression wave at the tunnel exit, and a linear formula is shown for engineering estimations.