bluuebunny/crossref_metadata_2025 huggingface dataset:
Extensive Xanthomatous Change in an Ovarian Serous Borderline Tumor: More Than Just a Mere Coincidence
Authors: Koul Aakanksha , Shetty Archana , Edupuganti Hima Sree , Mysorekar Vijaya
Published: March 2024

Serous borderline tumors of the ovary fall in between the benign and malignant category. These tumors are often diagnosed early, and the prognosis is usually favorable. However, there are variations in the histopathological findings of borderline ovarian tumors. Xanthomatous change is one such rare change in which deposition of lipid-rich material is seen morphologically as xanthoma cells within tumor tissue and reports of this are sparse. There is postulated literature on xanthomatous change being a contributing factor for progression of cancer. We present a case of a 75-year-old postmenopausal female with complaint of pain abdomen since 3 days, diagnosed radiologically as right ovarian mucinous cystadenoma/cystadenocarcinoma. Histopathology revealed a serous borderline tumor with extensive xanthomatous change. This case presents important thoughts on exploring the connection of xanthomatous change with borderline ovarian tumors, which till date is a matter of debate.
Pathophysiology, Diagnosis, and Management of Portal Hypertension in the Pediatric Population
Authors: Karuvannur Meenal Thadasina , Laique Sobia , Radhakrishnan Kadakkal , Gadani Sameer
Published: March 2024

Portal hypertension is caused by resistance to the portal blood flow, which most commonly occurs in the setting of cirrhosis. Complications of portal hypertension can cause significant morbidity and mortality in the pediatric population. Portal hypertension is diagnosed when the hepatic venous pressure gradient (HVPG) is more than 5 mm Hg, and potential bleeding complications from esophageal and gastric varices are more likely when the HVPG is more than 10 mm Hg. Diagnosis can be made clinically; however, liver biopsy with measurement of the HVPG is ultimately required. The management of portal hypertension in pediatric patients is typically aimed at treatment of the complications. Despite the multiple pharmacologic, endoscopic, surgical, and interventional radiologic management techniques that are available, some pediatric patients will ultimately require liver transplant. Prompt referral is needed in such cases.
Python Red Pitaya Lockbox (PyRPL): An open source software package for digital feedback control in quantum optics experiments
Authors: Neuhaus Leonhard , Croquette Michaël , Metzdorff Rémi , Chua Sheon , Jacquet Pierre-Edouard , Journeaux Alexandre , Heidmann Antoine , Briant Tristan , Jacqmin Thibaut , Cohadon Pierre-François , Deléglise Samuel
Published: March 2024

We present the Python Red Pitaya Lockbox (PyRPL), an open source software package that allows the implementation of automatic digital feedback controllers for quantum optics experiments on commercially available, affordable Field-Programmable Gate Array (FPGA) boards. Our software implements the digital generation of various types of error signals, from an analog input through the application of loop filters of high complexity and real-time gain adjustment for multiple analog output signals, including different algorithms for resonance search, lock acquisition sequences, and in-loop gain optimization. Furthermore, all necessary diagnostic instruments, such as an oscilloscope, a network analyzer, and a spectrum analyzer, are integrated into our software. Apart from providing a quickly scalable, automatic feedback controller, the lock performance that can be achieved by using PyRPL with imperfect equipment, such as piezoelectric transducers and noisy amplifiers, is better than the one achievable with standard analog controllers due to the higher complexity of implementable filters and possibilities of nonlinear operations in the FPGA. This drastically reduces the cost of added complexity when introducing additional feedback loops to an experiment. The open-source character also distinguishes PyRPL from commercial solutions, as it allows users to customize functionalities at various levels, ranging from the easy integration of PyRPL-based feedback controllers into existing setups to the modification of the FPGA functionality. A community of developers provides fast and efficient implementation and testing of software modifications.
Observation of maxon-like ultrasound in elastic metabeam
Authors: Zhang Peng , Liu Yunya , Zhang Keping , Wu Yuning , Chen Fei , Chen Yi , Wang Pai , Zhu Xuan
Published: March 2024

We observe maxon-like dispersion of ultrasonic guided waves in elastic metamaterials consisting of a rectangular beam and an array of cylindrical resonators. The pillars act as asymmetric resonators that induce a strong modal hybridization. We experimentally observe the strongly localized maxon mode with zero group velocity. Our study also demonstrates a unique feature of the maxon with a down-shifting peak frequency in space. To reveal the fundamental mechanism, we conduct comprehensive numerical studies on all frieze group symmetries and key geometric parameters.
Portable Thomson scattering system for temporally resolved plasma measurements under low density conditions
Authors: Yamamoto N. , Yalin A. P.
Published: March 2024

We present the development of a portable Thomson scattering diagnostic system allowing simultaneous spatially and temporally resolved plasma property measurements for low density plasmas. The setup uses a compact pulsed Nd:YAG laser (532 nm) as the light source with suppression by two volume Bragg grating notch filters and dispersion with a single-stage spectrometer before measurement with an intensified camera. A key issue is the detailed light collection and how it impacts the sensitivity and elastic light suppression, for which we have investigated two optical configurations, one based on a 7 × 1 linear fiber bundle and the other based on a slit spatial-filter. We find that the configuration with the slit spatial-filter provides a higher sensitivity by a factor of ∼2 along with more uniform spatial response. We have developed a custom pulsed-plasma setup with a modulation at 20 kHz, representative of the Hall thruster breathing mode oscillation, to show the possibility of temporally resolved measurements for electric propulsion applications. We have successfully recorded the variations in electron number density and temperature with sub-mm spatial resolution and capturing ten temporal points over the 50 µs modulation period. The detection limit of electron density (with the spatial-filter configuration) is ∼1.6 × 1017 m−3, which is ∼1/10 of the plasma density in the acceleration channel of Hall thrusters.
GPAW: An open Python package for electronic structure calculations
Authors: Mortensen Jens Jørgen , Larsen Ask Hjorth , Kuisma Mikael , Ivanov Aleksei V. , Taghizadeh Alireza , Peterson Andrew , Haldar Anubhab , Dohn Asmus Ougaard , Schäfer Christian , Jónsson Elvar Örn , Hermes Eric D. , Nilsson Fredrik Andreas , Kastlunger Georg , Levi Gianluca , Jónsson Hannes , Häkkinen Hannu , Fojt Jakub , Kangsabanik Jiban , Sødequist Joachim , Lehtomäki Jouko , Heske Julian , Enkovaara Jussi , Winther Kirsten Trøstrup , Dulak Marcin , Melander Marko M. , Ovesen Martin , Louhivuori Martti , Walter Michael , Gjerding Morten , Lopez-Acevedo Olga , Erhart Paul , Warmbier Robert , Würdemann Rolf , Kaappa Sami , Latini Simone , Boland Tara Maria , Bligaard Thomas , Skovhus Thorbjørn , Susi Toma , Maxson Tristan , Rossi Tuomas , Chen Xi , Schmerwitz Yorick Leonard A. , Schiøtz Jakob , Olsen Thomas , Jacobsen Karsten Wedel , Thygesen Kristian Sommer
Published: March 2024

We review the GPAW open-source Python package for electronic structure calculations. GPAW is based on the projector-augmented wave method and can solve the self-consistent density functional theory (DFT) equations using three different wave-function representations, namely real-space grids, plane waves, and numerical atomic orbitals. The three representations are complementary and mutually independent and can be connected by transformations via the real-space grid. This multi-basis feature renders GPAW highly versatile and unique among similar codes. By virtue of its modular structure, the GPAW code constitutes an ideal platform for the implementation of new features and methodologies. Moreover, it is well integrated with the Atomic Simulation Environment (ASE), providing a flexible and dynamic user interface. In addition to ground-state DFT calculations, GPAW supports many-body GW band structures, optical excitations from the Bethe–Salpeter Equation, variational calculations of excited states in molecules and solids via direct optimization, and real-time propagation of the Kohn–Sham equations within time-dependent DFT. A range of more advanced methods to describe magnetic excitations and non-collinear magnetism in solids are also now available. In addition, GPAW can calculate non-linear optical tensors of solids, charged crystal point defects, and much more. Recently, support for graphics processing unit (GPU) acceleration has been achieved with minor modifications to the GPAW code thanks to the CuPy library. We end the review with an outlook, describing some future plans for GPAW.
A reactive molecular dynamics model for uranium/hydrogen containing systems
Authors: Soshnikov Artem , Lindsey Rebecca , Kulkarni Ambarish , Goldman Nir
Published: March 2024

Uranium-based materials are valuable assets in the energy, medical, and military industries. However, understanding their sensitivity to hydrogen embrittlement is particularly challenging due to the toxicity of uranium and the computationally expensive nature of quantum-based methods generally required to study such processes. In this regard, we have developed a Chebyshev Interaction Model for Efficient Simulation (ChIMES) that can be employed to compute energies and forces of U and UH3 bulk structures with vacancies and hydrogen interstitials with accuracy similar to that of Density Functional Theory (DFT) while yielding linear scaling and orders of magnitude improvement in computational efficiency. We show that the bulk structural parameters, uranium and hydrogen vacancy formation energies, and diffusion barriers predicted by the ChIMES potential are in strong agreement with the reference DFT data. We then use ChIMES to conduct molecular dynamics simulations of the temperature-dependent diffusion of a hydrogen interstitial and determine the corresponding diffusion activation energy. Our model has particular significance in studies of actinides and other high-Z materials, where there is a strong need for computationally efficient methods to bridge length and time scales between experiments and quantum theory.
Deriving the linear dynamic range of next-generation thin-film photodiodes: Pitfalls and guidelines
Authors: Chandran Hrisheekesh Thachoth , Mahadevan Sudhi , Ma Ruijie , Tang Yu , Zhu Tao , Zhu Furong , Tsang Sai-Wing , Li Gang
Published: March 2024

With the use of next-generation semiconductors, notably organic and perovskite materials with remarkable optoelectronic and mechanical properties, thin-film photodiodes are progressing rapidly to rival their inorganic counterparts. However, to ensure a trustworthy comparison among the reported works, it is imperative that the measurement techniques for the figure of merits be unified and standardized. In this Letter, the possible causes of misrepresentation in the linear dynamic range (LDR) values are thoroughly discussed. The role of unity slope in defining the deviation point is examined, and the chances of misinterpretation when adopting different definitions are explained using a representative organic photodiode system. Furthermore, certain criteria are put out to standardize the LDR representation, which could be a crucial step toward facilitating the progress in this promising field via a more rational comparison of literature reports.
Colossal barocaloric effect of plastic crystals imbedded in silicon frame near room temperature: Molecular dynamics simulation
Authors: Niu Chang , Li Fangbiao , Xu Xiong , Xie Weifeng , Zhai Guangwei , Li Min , Wang Hui
Published: March 2024

Solid-state refrigeration technology has been attracting tremendous attention in recent decades. Plastic crystal pentaerythritol (PE) is a crucial barocaloric material in the solid-state refrigeration field due to its high entropy. However, its refrigeration temperature range and extremely low thermal conductivity are far from meeting the requirements of practical application. Here, we systematically investigate the barocaloric effect (BCE) of composite PE and silicon frame [consisting of silicon nanotube and silicene architectures (SNT-Sil)] and analyze the effects of different silicon models on the BCE performance based on molecular dynamics simulations and statistical analysis. A colossal BCE of PE/silicon frame composite is observed, and refrigeration temperature can be altered to the room temperature range by alloying neopentane (PA) into the PE matrix. It is found that the composite PE0.8PA0.2/SNT-Sil and PE0.9PA0.1/SNT-Sil demonstrate excellent comprehensive refrigeration performance near room temperature (300–320 K), with large isothermal entropy change ΔS (654–842 J kg−1 K−1), adiabatic temperature ΔT (34–47 K), and thermal conductivity κ (4.0–4.2 W m−1 K−1). The microscopic mechanism is discussed through pressure induced changes in bonding, structural, and vibrational properties. Importantly, the plastic crystal/silicon framework is easy to deform and requires smaller input work in the barocaloric refrigeration process compared to other nanomaterials such as carbon framework. This work provides important guidance on improving plastic crystals with colossal comprehensive refrigeration performance for practical applications.
Laser temperature programmed desorption: A flexible technique to study ion-surface interaction
Authors: Minissale M. , Dunand A. , Hiret P. , Faure J.-B. , Grisolia C. , Angot T. , Gallais L. , Bisson R.
Published: March 2024

Understanding the physical–chemical processes ruling the interaction of particles (atoms, molecules, and ions) with surfaces is fundamental in several research fields, such as heterogeneous catalysis, astrochemistry, and nuclear fusion. In particular, the interaction of hydrogen isotopes with plasma facing materials represents a high-priority research task in the fusion community. Such studies are essential to ensure the successful operation of experimental fusion reactors, such as the tokamak ITER. In this work, we present a surface science apparatus developed to study ion-surface interaction in fusion relevant systems. It combines laser-based techniques with contaminant-free ion/molecular beams, mass spectrometry, and surface science tools such as low-energy electron diffraction and Auger electron spectroscopy. It allows to cover a wide range of sample temperatures, from 130 to 2300 K, by changing the heating rate of samples from 0.1 to 135 K/s and maintaining the linearity of the heating ramps, a powerful feature to gain insight on adsorption, absorption, and desorption mechanisms. Experimental calibration and performance are presented in detail. Moreover, to provide a factual overview of the experimental capabilities, we focus on two different applications: the protocol used to clean a W(110) single crystal sample and the development of laser temperature programmed desorption to study helium retention in tungsten.
Linear gyrokinetic theory of two-dimensional ion-temperature-gradient mode in tokamaks
Authors: Qiu Yuefeng , Wang Jie , Wang Shaojie
Published: March 2024

The investigation of the two-dimensional (2D) linear ion-temperature-gradient (ITG) mode in toroidal plasma is carried out in ballooning mode representation. A novel approach to solve the radial envelope structure is proposed by constructing radial differential eigenequation. The important lemma (∂ω/∂θk)|θk=0=0 is proved and employed to construct a numerically solvable eigenequation. We have developed a numerical solver which gives the 2D solution consistent with the results obtained by the gyrokinetic global simulation code. Our newly proposed method presents an alternative solution to the 2D ITG eigenvalue problem.
Some experimental results for converging flow of dilute polymer solution
Authors: Kadyirov Aidar , Zaripov Rinat , Makarushkin Danila
Published: March 2024

This paper presents the results of experimental studies of the flow of a dilute polymer solution in a converging pipe. Three geometries with restriction rates are considered: 2.41, 3.92, and 5.65. A water–glycerin solution of 0.1% polyacrylamide was used as a working fluid. Point velocity measurements are made by using the smoke image velocimetry technique, which previously was proved by the construction of velocity profiles corresponding to the laminar viscoelastic flow in a straight pipe. The influence of the Weissenberg number and the restriction rate of the channel on the velocity profiles are established for both transverse and longitudinal directions. For small Weissenberg numbers, the experimental results are compared with the numerical results obtained using the Giesekus and exponential form of Phan-Thien–Tanner rheological models. Three flow regimes are identified: flow without vortex, vortex enhancement, and divergent flow, which is consistent with published results on the abrupt contraction and converging flows. Vortex length for a wide range of Weissenberg numbers is well predicted by a logarithm function. Modified expression of stretch rate with location of detachment plane can predict the flow regimes and the onset of unsteady flow in converging channels.
Computational study of a thin film flow over a topographical feature using phase-field lattice Boltzmann method
Authors: Singh Garima , Tiwari Naveen
Published: March 2024

The study employs the phase-field lattice Boltzmann method (PFLBM) to explore the dynamics of a thin film flowing over a topographical feature such as a mound or a trench. The mesoscopic nature of PFLBM makes it a suitable technique for problems involving tracking the evolution of a liquid–air interface. PFLBM simulation results are validated with experimental and analytical results confirming the viability of the numerical approach for such problems. The effect of changing the topographical height, aspect ratio, viscosity ratio, and presence of multiple mounds on the film profiles are systematically analyzed. It is observed that a steady-state solution could not be obtained for large height topographical features. The transition from a steady-state interfacial pattern to an unsteady-steady state is found to depend on the width of the topography. Geometry-based condition is employed to deal with the contact points present in the film dynamics beyond rupture. For large contact angles, the unsteady cases result in film rupture and form a continuous array of droplets of equivalent dimensions at a periodic interval. Increasing the aspect ratio reduces the width of the capillary ridge formed above the topographical feature, while the viscosity ratio reduces the maximum height of the ridge. The shapes of the capillary ridges formed over multiple mounds in the flow direction are independent if the separation between the successive mounds is beyond a critical value. This critical value strongly depends on the capillary number and is independent of the dimensions of the mound.
Numerical modeling of structural body deformation under free surface flow based on volume of fluid–discrete element method coupling
Authors: Nan Xuan , Shen Zhihao , Li Guodong , Hou Jingming
Published: March 2024

In this work, we proposed a numerical model based on the coupling of the volume of fluid–discrete element method and bond particle method (BPM). The simulation of particle bonding and the structural body formation process had been presented, and the inter-particle bonding mechanism was introduced. We also tested dam-busting impact elastic and wedge plates at high Reynolds numbers (1.26 × 107 and 2.16 × 106) and compared the results with numerical simulations. The results show that the model has mean errors of 3.9% and 6.5% for the large and the micro-deformations, respectively. It is in perfect agreement with the curve trends of the test and keeps good convergence for different particle sizes. In addition, we also used the model used to study the hydrodynamic changes in underwater box net structures in offshore aquaculture, and the deformation kinematic properties of box nets under different material strengths were evaluated. This numerical model of this study provides the effective theoretical support and engineering guidance for the further study of the behavior of structural bodies under hydrodynamic action.
Numerical simulations of the sedimentation of soft particles in confined Newtonian liquids
Authors: Villone Massimiliano M. , Maffettone Pier Luca
Published: March 2024

The gravitational sedimentation of solid particles in liquids is important in several applications, many of which involve soft particles (e.g., microplastics, microgels, and biological cells). However, there is still little knowledge on the sedimentation of deformable beads. In this work, we employ fully three-dimensional finite-element numerical simulations to investigate the sedimentation of an initially spherical elastic bead in a Newtonian liquid contained inside a square-cross section vessel. In particular, we carry out a wide parametric analysis to understand the effects of inertia, particle deformability, and geometrical confinement on the particle sedimentation dynamics and settling velocity. In addition, the sedimentation of a particle in a Newtonian liquid close to a vertical wall is studied. When the particle sediments at the center of the vessel, the settling velocity increases at increasing inertia and decreases at increasing confinement and deformability. However, at intermediate inertia, the settling velocity passes through a minimum and then rises as the particle gets softer. Correspondingly, the equilibrium deformed shape of the particle shows the appearance of a concavity at the rear. When the sedimentation occurs close to a vertical wall, the closer the particle to the solid surface, the slower its sedimentation. On the other hand, the hydrodynamic interaction between the particle and the wall makes the particle move away from the wall.
Non-linear electro-rheological model of a membrane immersed in Tanner-Power law fluids applied to outer hair cells: Shear-thinning mechanisms
Authors: Ramírez-Torres Luis Antonio , Herrera-Valencia Edtson Emilio , Sánchez-Villavicencio Mayra Luz , Soriano-Correa Catalina , Hernández-Abad Vicente Jesús , Calderas Fausto
Published: March 2024

Flexoelectric actuation employs an applied electric field to induce membrane curvature, which is the mechanism utilized by the outer hair cells (OHC) present in the inner ear. The model developed for this study, representing the OHC, integrates two key components: (i) an approximation of the flexoelectric membrane shape equation for circular membranes attached to the inner surface of a circular capillary, and (ii) the coupled capillary flow of contacting liquid viscoelastic phases characterized by the Tanner-Power law rheological equation of state. A second-order non-linear differential equation for average curvature has been derived, and a robust numerical method has been programmed. This model simplifies to a linear model used previously. The main challenge involves identifying and describing the enhancement in curvature change rate. It was observed that low symmetry, low viscosity, and soft membrane and shear-thickening behavior of the phases enhance the curvature change rate. Additionally, there exists a critical electric field frequency value that maximizes the curvature change rate (resonance effect). The current theory, model, and computational simulations add to the ongoing development comprehension of how biological membrane shape actuation through electromechanical couplings.
A non-axisymmetric temperature field reconstruction method based on the compressive sensing background oriented Schlieren method
Authors: Wu Jun , Pan Zhixiang , Zhang Chenping , Guo Runxia , Chen Jiusheng
Published: March 2024

Measurement of the combustion temperature field is an extremely important issue in industrial production. Temperature is one of the key parameters in combustion studies. With the temperature field distribution of the combustion field obtained, heat transfer, heat convection, and heat radiation can be calculated directly and efficiently. Traditional background oriented Schlieren (BOS) is an effective method for non-axisymmetric temperature field measurements, but it requires simultaneous Schlieren imaging at multiple angles for tomographic reconstruction, which will greatly limit its application. In this paper, the compressive sensing algorithm is introduced into the temperature field reconstruction, which establishes the system of equations between the deflection angle and the refractive index gradient. Then, the reconstruction of the non-axisymmetric temperature field is realized by solving the underdetermined system of equations by the method of solving the sparse solution through the compressive sensing. First, light offsets across the non-axisymmetric temperature field are measured by the under-angled BOS system and image processing method. Second, the spatial refractive index field is reconstructed by the compressive sensing BOS method proposed in this paper. Finally, the spatial temperature field is obtained. The experimental results show that by comparing the iRadon reconstruction algorithm and the compressive sensing reconstruction algorithm, the temperature field reconstructed by the compressive sensing under the condition of the under-angled sampling of projection data had a higher accuracy than that reconstructed by the tomographic reconstruction algorithm under the same condition. The average error of the temperature field was reduced from 34.6 to 29.7 K under the same measurement conditions; however, the accuracy is better maintained by using the compressive sensing algorithm under the condition of undersampling projection.
Three-dimensional modeling of multi-component vacuum arc considering anode vapor in actual magnetic field
Authors: Wang Lijun , Chen Jieli , Zhang Zhefeng , Luo Ming , Xie Yiduo , Wang Xiangyu , Wang Hongjian
Published: March 2024

For vacuum circuit breakers, the anode will change to active mode when the current is high enough. The vapor produced by the anode will become another important source of plasma. In this paper, a three-dimensional (3D) magnetohydrodynamic model considering anode vapor and multiple components is developed to study the vacuum circuit breakers with cup-shaped CuCr contact. The characteristics of arc under the actual magnetic field with different anode temperature distribution and different cathode utilization are simulated. Moreover, the ionization and recombination processes between different kinds of components are considered. The simulation results show that the arc current concentrates toward the center. The current value is high between electrodes slots under the actual magnetic field, which significantly affects the arc characteristics. At the same time, higher anode temperatures will produce more neutral atom vapor area (NAVA). Current is concentrated outside NAVA due to the low conductivity of NAVA. As NAVA expands, the constriction of current on the outside is more severe. The simulation results in this paper are consistent with the experimental results.
Laser-driven quasi-static B-fields for magnetized high-energy-density experiments
Authors: Vlachos C. , Ospina-Bohórquez V. , Bradford P. W. , Pérez-Callejo G. , Ehret M. , Guillon P. , Lendrin M. , Vaisseau X. , Albertazzi B. , Soussan E. , Koenig M. , Malko S. , Kaur C. , Gjevre M. , Fedosejevs R. , Bailly-Grandvaux M. , Walsh C. A. , Florido R. , Suzuki-Vidal F. , McGuffey C. , Saret J. , Beg F. N. , Chodukowski T. , Pisarczyk T. , Rusiniak Z. , Dostal J. , Dudzak R. , Calisti A. , Ferri S. , Volpe L. , Woolsey N. C. , Gremillet L. , Tikhonchuk V. , Santos J. J.
Published: March 2024

We present measurements of magnetic fields generated in laser-driven coil targets irradiated by laser pulses of nanosecond duration, 1.053 μm wavelength, 500 J energy, and ∼1015 W/cm2 intensity, at the LULI2000 facility. Using two perpendicular probing axes, proton deflectometry is used to characterize the coil current and static charge at different times. Results reveal various deflection features that can be unambiguously linked to a looping quasi-steady current of well-understood polarity or to a static charging of the coil surface. Measured currents are broadly consistent with predictions from a laser-driven diode-current source and lumped circuit model, supporting the quasi-steady assessment of the discharges. Peak magnetic fields of ∼50 T at the center of 500-μm-diameter coils, obtained at the moderate laser intensity, open up the use of such laser-driven coil targets at facilities worldwide to study numerous phenomena in magnetized high-energy-density plasmas, and its potential applications.
Nonlinear optical effects in polycrystalline transparent Al2O3 ceramics using femtosecond laser pulses—supercontinuum generation and laser damage
Authors: Wu Xingzhong , Zhou Wenbo , Kodera Yasuhiro , Garay Javier E.
Published: March 2024

Nonlinear optical properties play a key role in technologies such as broadband laser light sources and ultrafast laser machining. With the emergence of transparent nanocrystalline Al2O3 ceramics as an alternative to single crystal alumina (sapphire), it is critical to understand their nonlinear optical behavior. Here, we report the demonstration of supercontinuum generation in polycrystalline alumina ceramics. Substantial broadening was observed when a focused 515 nm pulsed (260 fs) laser propagated through the ceramic sample. The broadening increased with increasing laser power and displayed stokes/anti-stokes asymmetries. At higher incident power, permanent damage was observed. Our results show that transparent nanocrystalline Al2O3 ceramics have a higher material removal rate than single crystal alumina. These results have interesting implications for laser machining as well as integrated photonics.
Experimental and numerical studies on vertical water entry of a cylinder under the influence of current
Authors: Qi Chao , Lyu Xujian , Wang Xu , Ye Haijiang , Shi Hao , Wan Zonghao
Published: March 2024

When a moving object penetrates the free surface, it is often accompanied by complex multiphase flow phenomena. In this work, the complicated impact cavity and flow characteristics of water entry by a cylinder are investigated both experimentally and numerically for different current velocities. A high-speed photography technique is employed to capture the cavity contours under both calm water and flowing water. Under the same working conditions, a three-dimensional simulation using a volume of fraction model is conducted to provide detailed flow field structures and motion behaviors for experimental results. The primary results are as follows: the effect of current causes the cavities to no longer develop symmetrically. The cavity on the upstream side is compressed close to the cylinder surface, while the cavity on the downstream side expands. The asymmetrical distribution of cavities causes different wetting states on both sides of the cylinder. The ensuing pressure difference prompts the cylinder to deflect which is quite different that without considering current. Vortices generated on the upstream side disappear faster, while those generated on the downstream side expand significantly along the flow direction.
Polymeric droplet formation and flow pattern evolution in capillary microchannels: Effect of fluid elasticity
Authors: Duan Lian , Yuan Wenjun , Hao Nanjing , Mei Mei
Published: March 2024

Polymeric droplets are widely employed in fields such as chemical, biomedical, and materials engineering. However, the study of polymeric droplet formation is still insufficient due to the complex elasticity. In this work, the effect of fluid elasticity on the flow patterns for polymeric droplet formation in cross-junction microchannels is investigated by means of finite-volume direct numerical simulations. The volume of fluid method with cell-based adaptive mesh refinement technique is used to capture the interface. Additionally, the rheological behavior of polymeric fluids is described using the exponential Phan-Thien–Tanner constitutive model. The simulated flow behaviors are highly consistent with the experimental observations. The results indicate that three typical flow patterns of dripping, jetting, and threading flows are obtained at different fluid elasticities (denoted by the Weissenberg number Wi) and viscosities (denoted by the Capillary number Ca). Meanwhile, the elastic effect is found to be greater in the dripping flow, significantly reducing the axial tensile stress. It is demonstrated that changes in the stretched state of polymer macromolecules with the same Wi at different Ca lead to variations in the strength of elastic action, which, in turn, affects the extension length and the pinch-off time of droplets. Finally, a relationship equation between the extension length and time of the polymer fluid is established. This present study aims to provide important insight into the preparation of polymeric droplets in microchannels.
Numerical study of double emulsion generation in a flow-focusing microchannel by multiple-relaxation-time lattice Boltzmann method
Authors: Wang Shiteng , Wang Hao , Wu Yuting , Cheng Yi
Published: March 2024

Microfluidic technology applied for the controlled production of double emulsions has gained significant interest in biomedicine and material synthesis. The precise regulation of emulsion size depends on the in-depth study of the formation mechanism. A ternary multiple-relaxation-time lattice Boltzmann model with robust stability and multiphase accuracy is established and applied to investigate the formation mechanism of double emulsions within a flow-focusing microchannel. Integrated with the regularized and convective boundary conditions, the present model proves adept at simulating the complex multiphase flow behavior in microchannels under various properties and operation parameters. Extensive validations involving static and dynamic cases demonstrate the model accuracy in capturing three-phase interactions and multiphase flow fields while also significantly enhancing stability and accommodating a broader range of viscosity ratios. Our systematic investigation involves the influence of flow rate, viscosity ratio, interfacial tension ratio, and orifice section size on the formation of double emulsions. The results show the impact of flow rate on flow patterns and inner phase volume, revealing an expanded operation range of the dripping pattern brought by the increased outer phase flow rate. Notably, two distinct droplet formation mechanisms, i.e., shear mode and squeeze mode, are identified across a wide range of viscosity ratios. Additionally, the investigation of interfacial tension ratios focuses on assessing the effect of various interfacial tension combinations, while alterations in orifice width reveal its significant impact on shear strength and dispersed phase dynamics. This work deepens the understanding of double emulsion mechanics and offers a versatile platform for future research.
Te-vacancy defect triggering photocatalytic overall water splitting for MoTe2/GeN Z-scheme heterostructure
Authors: Bai Yujie , Zhang Haiyang , Huang Beibing , Xu Ning , Niu Xianghong , Zhang Xiuyun , Zhang Qinfang
Published: March 2024

Developing proper semiconductor photocatalysts is urgently needed to solve energy and environmental crises. Especially, photocatalysts for water splitting with a Z-scheme mechanism are desirable materials. Herein, a two-dimensional VTe-MoTe2/GeN heterostructure (VTe-HS), including single Te vacancy, is theoretically proved to function as a direct Z-scheme photocatalyst with the wide light-harvesting range, the effective spatial separation for carriers, and the high catalytic activity for water splitting. An enhanced optical absorption coefficient of 105 cm−1 is observed and the absorption edge (∼1.0 eV) is red-shifted into the infrared light region. Separating photogenerated electron–hole pairs enhances the photocatalytic efficiency due to the staggered band alignment. Interlayer charge migration of about 0.154 electrons induces an intrinsic built-in electric field in the heterostructure, allowing forming the Z-scheme mechanism with a reduction potential of –4.01 eV and an oxidation potential of –7.13 eV. Gibbs free energies confirm that water redox reactions can proceed spontaneously under sunshine. Moreover, the Heyrovsky reaction is kinetically more favorable than the Tafel reaction because of a little energy barrier (0.071 eV). These features show that the VTe-HS is a desirable water-splitting photocatalyst, providing a valuable clue to constructing high-efficiency photocatalysts.
Quantitative study of droplet generation by pressure-driven microfluidic flows in a flow-focusing microdroplet generator
Authors: Zeng Wen , Wang Bohang , Chang Honglong , Neužil Pavel
Published: March 2024

To precisely control the size of droplets is of great importance for the applications of the droplet microfluidics. In a flow-focusing microdroplet generator, the pressure-driven microfluidic device is designed to control the flow rates of the fluids. For a specific geometry of the flow-focusing microchannel, a mathematical model of droplet formation is established, and the nonlinear relation between the droplet length and the driven-pressure ratio can be described by our model. For pressure-driven microfluidic flows, the nonlinear relation between the droplet length and the driving-pressure ratio is measured experimentally in the flow-focusing microchannel. Particularly, by using the closed-loop control method of droplet generation, good agreements are shown between the measured size of droplets and the predicted size of the droplets. As a result, the control precision of the droplet size can be increased drastically by the closed-loop control method of droplet generation. Consequently, monodisperse droplets of extremely small size can be produced in the flow-focusing microdroplet generator.
Numerical study of triggered thermoacoustic instability driven by linear and nonlinear combustion response in a solid rocket motor
Authors: Xu Guanyu , Wang Bing , Jin Bingning , Wang Zhuopu , Liu Peijin
Published: March 2024

Thermoacoustic instability (TAI) has consistently presented challenges to the development of solid rocket motors (SRMs), making the prediction of TAI critically important. Most existing TAI predictions rely on linear instability theory, which is inadequate for predicting certain nonlinear TAI, such as triggered TAI. To address this challenge, this study has constructed the nonlinear response model for the burning rate, known as the nonlinear pressure-coupled response function (PCR). The nonlinear PCR is capable of considering the effects of both frequency and amplitude of pressure oscillations. By integrating the PCR into the computational fluid dynamics framework, this study successfully replicated the nonlinear triggered TAI. When exclusively employing the linear PCR, the model demonstrates typical multi-order resonant modes, and the stability map exhibits either persistent stability or persistent instability, contingent upon the distribution of the linear PCR function. However, by incorporating the nonlinear PCR, this study effectively reproduces nonlinear pulse-triggered instability. This instability arises only when the pulse intensity surpasses the threshold value due to SRM damping. The nonlinear response framework allows for the identification of the instability boundary, facilitating a more comprehensive assessment of SRM performance. This study fills a critical gap in predicting triggered TAI in SRMs, providing insights into nonlinear TAI mechanisms.
Dynamic mode characteristics of flow instabilities in a single-stage compressor under different throttling processes
Authors: Wang Ziwei , Fan Zhaolin , Li Bin , Wang Jiantao , Lu Fengshun , Jiang Xiong
Published: March 2024

To investigate the influence of throttling processes on dynamic characteristics of compressor stability, the rotating stall development of National Aeronautics and Space Administration Stage 35 was simulated with full-annulus Unsteady Reynolds-Averaged Navier–Stokes under different throttling processes. The numerical methods were verified. By combining Dynamic Mode Decomposition and flow field evolution research, the flow structures and dynamic characteristics of “critical mass flow” under different throttling processes were deeply studied; the flow mechanism of flow instabilities under different throttling processes was explored. It is found that the “critical mass flow” corresponds to the beginning of a rapid decrease in mass flow, mainly characterized by shock forward movement and a larger range of spillage flow. Around “critical mass flow,” if the throttle is still tightening, it presents stall pattern 2; otherwise, it presents stall pattern 1. During the pre-stall, both patterns are dominated by tip clearance vortex (TCV)-shock interference. Stall inception disturbance is generated from TCV-shock interference; pattern 1 presents a single disturbance, while pattern 2 presents multiple disturbances. Subsequently, the TCV-shock interference gradually weakens. The single stall disturbance of pattern 1 gradually develops and stabilizes. The multiple stall disturbances in pattern 2 undergo processes including fusion and disappearance, ultimately developing into a single stall cell. During the stable stall, the throttling processes have no significant impact on the speed of the stall cell, and the flow in the un-stalled region is basically consistent with the speedline. However, the tighter the throttle is, the larger the stalled region, and the weaker the flow capacity of the un-stalled region.
Improved theoretical prediction of nanoparticle sizes with the resistive-pulse technique
Authors: Gao Zihao , Ma Long , Liu Zhe , Huang Jun , Liu Hanlian , Huang Chuanzhen , Qiu Yinghua
Published: March 2024

With the resistive-pulse technique (RPT), nanopores serve as the nanofluidic sensors of various analytes for their many physical and chemical properties. Here, we focus on the size measurement and its theoretical prediction for sub-200 nm nanoparticles with RPT. Through systematical investigation of the current blockade of nanoparticles across cylindrical nanopores with simulations, Maxwell's method considering the shape coefficient and access resistances agrees well with simulation results. However, the widely used integration method of the resistance has distinct deviations in various cases. With the introduction of a correction factor β to the integration method, our revised equations can provide good predictions for simulation results. β shows a strong dependence on the diameter ratio (d/D) of the nanoparticle and nanopore. Following the same strategy, modified equations are provided for the accurate size prediction for nanoparticles across conical nanopores, where the integration method is the default convenient way. The correction factor β′ relates to β in cylindrical nanopores. β′ exhibits independence on the pore geometry parameters and diameters of nanoparticles, but dependence on the surface charge density of conical nanopores. Our improved equations can provide theoretical predictions for the accurate size detection of 100–200 nm diameter nanoparticles across cylindrical and conical nanopores.
Experimental investigation on dynamic characteristics of single bubble near wall in shear flow
Authors: Su Zi-Yun , Sun Jiao , Zhang Jia-Wei , Cai Run-Ze , Sun Kang-Fu , Chen Wen-Yi , Yu Chang-Xin
Published: March 2024

The bubble near the wall of shear flow will be subjected to both wall-induced lift and shear-induced lift. The two-lift interaction will markedly change the dynamic behavior of the bubble. In this experiment, the lateral motion of a single bubble (deq=2.33−3.42 mm, Reb=470−680) rising near the vertical wall in a linear shear flow was studied. The positive-synergy and negative-synergy between the wall- and shear-induced lift effects on bubble dynamics were compared. The experiment was carried out in a vertical water tunnel with a curved screen used to generate a stable linear shear flow. Using the shadow method and two charge-coupled device cameras, the movement parameters of the bubble were captured, including the movement trajectory of the bubble, length–diameter ratio, and instantaneous velocity. The lift coefficient CL and drag coefficient CD were obtained by quasi-steady-state analysis and calculation. By fitting the steady lift coefficient, the relation of CL with dimensionless wall distance S* and the Reynolds number Reb was obtained. The results show that there is a critical value of the initial dimensionless distance S* about [S*] = 1.6. When S* > [S*], the bubble is subjected to both wall-induced lift and shear-induced lift. The lift coefficient CL decreases with the increase in S*. When S* < [S*], the bubble receives additional induced lift from the wall. The CL of the smaller bubble was smaller and increases with the increase in S*, while the deformation of the larger bubble will interact with the wall to produce deformation lift away from the wall, presenting larger CL, and decrease with the increase in S*.
Fluid–structure-interactive elasto- and thermo-hydrodynamics of electrokinetic binary fluid flows in compliant micro-confinements
Authors: Roy Apurba , Dhar Purbarun
Published: March 2024

We explore the intricate two-way fluid structure interaction arising due to the flow of a binary system of immiscible Newtonian fluids, composed of upper electrically conducting and lower electrically insulating fluids, flowing within a compliant microchannel, whose walls behave as linear elastic solids. The transport of the fluids along the domain occurs due to the collective impact of pressure gradient and applied electric field. We solve the closed-form system of equations and obtain semi-analytical expressions for the velocity fields and channel wall deformation from the coupled elasto-hydrodynamic problem. We then delineate the effect of four pivotal parameters: (a) Debye–Hückel parameter κ¯, (b) upper wall slip length, ls¯, (c) viscosity ratio, μr, and (d) elasticity ratio, Nr, on the morphological evolution of the wall deformation characteristics and the spatial distribution of the velocity profile of the fluids. Observations establish a positive co-relationship of wall deformation with fluid pressure, showcasing an increased collapsibility with augmented pressure gradients. Consequently, the channel walls show enhanced deformation with a decrease in κ¯, ls¯, μr and with an increase in Nr. We also demonstrate from our model that by properly tuning the applied pressure gradient and electric field, it is possible to achieve counterflow of the two fluids. We also consider the effect of heat generation in the fluids due to viscous dissipation and Joule heating, which dissipates to the surrounding by the mechanism of conjugate heat transfer. Accordingly, we provide semi-analytical expressions for the temperature profile distribution within the channel, and discuss their variation with three thermo-physical parameters: (a) Biot number of the top wall (Bi1), (b) Peclet number of the top fluid (Pe1), and (c) ratio of the thermal conductivities of the upper conducting fluid to that of the upper solid wall (kr2). We establish from our investigation that with the increase in Pe1 and with the decrease in Bi1 and kr2, the overall system temperature enhances. Finally, in order to design a thermally efficient system, we compute the global entropy generation rate in the system and evaluate optimum values of, Pe1, Bi1, and kr2 for which the system exhibits highest second law efficiency. We expect our findings to contribute toward the development of optimized microfluidic devices fabricated from deformable elastic materials.