bluuebunny/crossref_metadata_2025 huggingface dataset:
Repetitive high-power discharge operation of a micro-laser triggered gas switch
Authors: Pouncey J. Cameron , Lehr Jane M.
Published: June 2024

A low-energy, diode-pumped, solid-state passively Q-switched laser operating at a wavelength of 1535 nm has been demonstrated to trigger gas switches. This technology has the potential to bring significant improvements to the operation and reliability of compact pulsed power drivers. Compact pulsed power drivers are often required to operate for hundreds to thousands of shots without maintenance; thus, the reliable operation of the laser triggered switch is significant for the adoption of this technology. A primary limiter of spark gap lifetime is electrode erosion. In the case of a laser triggered switch where the laser is focused on one electrode, an additional source of erosion is the direct ablation of the electrode material by the laser. The micro-laser used in the previous experiments is very low energy, but over thousands of shots, it does damage directly to the target electrode. This damage could potentially interact with the erosion due to the current discharge and impact the operation of the switch. The focus of this paper is to describe experiments undertaken to assess this damage and quantify its effect on switch operation over many discharges at current and energy levels relevant to compact pulsed power systems.
Factorization of large tetra and penta prime numbers on IBM quantum processor
Authors: Dhaulakhandi Ritu , Behera Bikash K. , Seo Felix J.
Published: June 2024

The factorization of large digit integers in polynomial time is a challenging computational task to decipher. The development of Shor’s algorithm sparked a new resolution for solving the factorization problem. However, putting Shor’s algorithm into use in real-world situations presents major difficulties. The algorithm largely depends on the availability of large-scale, fault-tolerant quantum computers, which are not available at present. The need for qubit coherence and error correction makes the algorithm susceptible to noise and decoherence, hindering its practical realization. Therefore, exploring alternative quantum factorization algorithms and investing in quantum computing hardware advancements are vital steps toward overcoming these drawbacks and harnessing the full potential of quantum computing for factorization tasks. This article explores an alternative method of converting the factorization problem into an optimization problem using appropriate analytic algebra. The generalized Grover’s protocol is used to increase the amplitude of the necessary states and, in turn, help in the execution of the quantum factorization of tetra and penta primes as a proof of concept for different integers, including 875, 1 269 636 549 803, and 4375, using three and four qubits of IBMQ Perth (a seven-qubit processor). The fidelity of the quantum factorization protocol with the IBMQ Perth qubits was near unity. A generalization of the method is provided at the end for implementing factorization problems in various cases.
Simulation-trained machine learning models for Lorentz transmission electron microscopy
Authors: McCray Arthur R. C. , Bender Alec , Petford-Long Amanda , Phatak Charudatta
Published: June 2024

Understanding the collective behavior of complex spin textures, such as lattices of magnetic skyrmions, is of fundamental importance for exploring and controlling the emergent ordering of these spin textures and inducing phase transitions. It is also critical to understand the skyrmion–skyrmion interactions for applications such as magnetic skyrmion-enabled reservoir or neuromorphic computing. Magnetic skyrmion lattices can be studied using in situ Lorentz transmission electron microscopy (LTEM), but quantitative and statistically robust analysis of the skyrmion lattices from LTEM images can be difficult. In this work, we show that a convolutional neural network, trained on simulated data, can be applied to perform segmentation of spin textures and to extract quantitative data, such as spin texture size and location, from experimental LTEM images, which cannot be obtained manually. This includes quantitative information about skyrmion size, position, and shape, which can, in turn, be used to calculate skyrmion–skyrmion interactions and lattice ordering. We apply this approach to segmenting images of Néel skyrmion lattices so that we can accurately identify skyrmion size and deformation in both dense and sparse lattices. The model is trained using a large set of micromagnetic simulations as well as simulated LTEM images. This entirely open-source training pipeline can be applied to a wide variety of magnetic features and materials, enabling large-scale statistical studies of spin textures using LTEM.
Mapping the magnon–magnon hybrid state onto the Bloch sphere
Authors: Hu Bo , Xie Zong-Kai , Lu Jie , He Wei
Published: June 2024

We investigate magnon–magnon hybrid states using a non-Hermitian Hamiltonian and the concept of magnon hybridization. By comparing our model with micromagnetic simulations conducted on a synthetic antiferromagnet with strong magnon–magnon coupling, the two-level model reproduces not only the resonance frequencies and linewidths but also the phases and amplitudes of the magnon eigenmode. The coherent coupling between magnons results in both the anticrossing of the energy spectra and the mixing of the linewidths. Specially, it forms a two-level system and makes the eigenmode of the hybrid state as a linear combination of the pure acoustic and optic modes. After that, we map the magnon–magnon hybrid state, including the magnon state of exceptional point, onto a Bloch sphere, which enhances the ability to manipulate hybrid magnons for coherent information processing.
Constant potential energetics of metallic and semiconducting electrodes: A benchmark study on 2D materials
Authors: Oschinski Hedda , Hörmann Nicolas Georg , Reuter Karsten
Published: June 2024

Grand-canonical (GC) constant-potential methods within an implicit solvent environment provide a general approach to compute the potential-dependent energetics at electrified solid–liquid interfaces with first-principles density-functional theory. Here, we use a mindfully chosen set of 27 isostructural 2D metal halides MX2 to analyze the variation of this energetics when the electronic structure changes from metallic to semiconducting and insulating state. Apart from expectable changes due to the opening up of the electronic bandgap, the calculations also show an increasing sensitivity to the numerical Brillouin zone integration and electronic smearing, which imposes computational burdens in practice. We rationalize these findings within the picture of the total interfacial capacitance arising from a series connection of the electrochemical double-layer capacitance and the so-called quantum capacitance resulting from the filling of electronic states inside the electrode. For metals, the electrochemical double-layer capacitance dominates at all potentials, and the entire potential drop takes place in the electrolyte. For semiconductors, the potential drop occurs instead fully or partially inside the electrode at potentials within or just outside the bandgap. For 2D semiconductors, the increased sensitivity to numerical parameters then results from the concomitantly increased contribution of the quantum capacitance that is harder to converge. Fortunately, this understanding motivates a simple extension of the CHE + DL approximation for metals, which provides the approximate GC energetics of 2D semiconductors using only quantities that can be obtained from computationally undemanding calculations at the point of zero charge and a generic double-layer capacitance.
General framework for quantifying dissipation pathways in open quantum systems. I. Theoretical formulation
Authors: Kim Chang Woo , Franco Ignacio
Published: June 2024

We present a general and practical theoretical framework to investigate how energy is dissipated in open quantum system dynamics. This is performed by quantifying the contributions of individual bath components to the overall dissipation of the system. The framework is based on the Nakajima–Zwanzig projection operator technique, which allows us to express the rate of energy dissipation into a specific bath degree of freedom by using traces of operator products. The approach captures system-bath interactions to all orders, but is based on second-order perturbation theory on the off-diagonal subsystem's couplings and a Markovian description of the bath. The usefulness of our theory is demonstrated by applying it to various models of open quantum systems involving harmonic oscillators or spin baths and connecting the outcomes to existing results such as our previously reported formula derived for locally coupled harmonic baths [Kim and Franco, J. Chem. Phys. 154, 084109 (2021)]. We also prove that the dissipation calculated by our theory rigorously satisfies thermodynamic principles such as energy conservation and detailed balance. Overall, the strategy can be used to develop the theory and simulation of dissipation pathways to interpret and engineer the dynamics of open quantum systems.
Propagated (fragment) Pipek–Mezey Wannier functions in real-time time-dependent density functional theory
Authors: Schreder Lukas , Luber Sandra
Published: June 2024

Localization procedures are an important tool for analysis of complex systems in quantum chemistry, since canonical molecular orbitals are delocalized and can, therefore, be difficult to align with chemical intuition and obscure information at the local level of the system. This especially applies to calculations obeying periodic boundary conditions. The most commonly used approach to localization is Foster–Boys Wannier functions, which use a unitary transformation to jointly minimize the second moment of the orbitals. This procedure has proven to be robust and fast but has a side effect of often mixing σ- and π-type orbitals. σ/π-separation is achieved by the Pipek–Mezey Wannier function (PMWF) approach [Lehtola and Jónsson, J. Chem. Theory Comput. 10, 642 (2014) and Jónsson et al., J. Chem. Theory Comput. 13, 460 (2017)], which defines the spread functional in terms of partial charges instead. We have implemented a PMWF algorithm in the CP2K software package using the Cardoso–Souloumiac algorithm to enable their application to real-time time-dependent density functional theory. The method is demonstrated on stacked CO2 molecules, linear acetylenic carbon, boron and nitrogen co-doped graphene, and nitrogen-vacancy doped diamond. Finally, we discuss its computational scaling and recent efforts to improve it with fragment approaches.
Splitter-plate proximity-induced transitions in flow-induced vibration of a triangular prism
Authors: Abhishek  , Saha Sandip K. , Sharma Atul
Published: June 2024

The effect of a splitter-plate downstream of an elastically mounted equilateral triangular prism on flow-induced vibration is numerically investigated at Reynolds number Re = 100, mass ratio m* = 10, damping ratio ζ = 0.005, cylinder-plate gap G* = 0.3, and various angle of attacks α  = 0°–60°. The α = 0° and 60° correspond to vertex and edge of the cylinder facing the free stream. Under the effect of the splitter plate, a single transition from vortex-induced vibration (VIV) to proximity-induced galloping (PIG) in the vibrational response for an axisymmetric circular cylinder is reported, whereas, for the present non-axisymmetric triangular prisms, the varying α exhibits four proximity-induced transitions: VIV to modified VIV at smaller α = 0° and 25°, VIV to PIG at α = 35°, distinct VIV-galloping to combined PIG-galloping at α = 40°, and asymmetric to symmetric-galloping at larger α = 60°. The plate results in more symmetric vibration for high α ≥ 35°, while a reduction is observed for α ≤ 25°. The gap-flow leads to onset (α = 35°) and enhancement (α = 40°) of afterbody re-attachment on the prism, which significantly enhances the galloping instability and vibrational amplitude. A reduction in galloping instability leading to a slight reduction in amplitude is found for α = 60° prism. The study shows that the presence of the splitter-plate downstream influences near-wake structure and far-wake vortex shedding modes, which lead to stabilizing and destabilizing near-wake flow and distinct vibrational characteristics—depending on the angle of attack (α).
Hydrogen-bond linking is crucial for growing ice VII embryos
Authors: Zhang Xuan , Mochizuki Kenji
Published: June 2024

We use molecular dynamics simulations to examine the homogeneous nucleation of ice VII from metastable liquid water. An unsupervised machine learning classification identifies two distinct local structures composing Ice VII nuclei. The seeding method, combined with the classical nucleation theory (CNT), predicts the solid–liquid interfacial free energy, consistent with the value from the mold integration method. Meanwhile, the nucleation rates estimated from the CNT framework and brute force spontaneous nucleations are inconsistent, and we discuss the reasons for this discrepancy. Structural and dynamical heterogeneities suggest that the potential birthplace for an ice VII embryo is relatively ordered, although not necessarily relatively immobile. Moreover, we demonstrate that without the formation of hydrogen-bond links, ice VII embryos do not grow.
A multifractal model for predicting the permeability of dual-porosity media with rough-walled fractures and variable cross-sectional pore channels
Authors: Qiu Chao , Yang Yugui , Huang Bingxiang , Gao Feng , Hou Shanshan , Mu Guangyu
Published: June 2024

The seepage of rock strata is greatly influenced by the pore network and fracture network; however, the prediction of permeability becomes challenging due to the changes in the cross section of pore channels and the morphology of fractures. In this study, a novel pore-fracture permeability model based on a fractal theory is proposed, and the analytical solutions of the model are given. In contrast to the traditional smooth parallel plate and uniform cross section straight capillary, this model not only considers the roughness of the fracture surface, but also the cross section variation and tortuosity of the pore channel. The comparisons between the calculated results and the experimental data verify the reliability of this model. The quantitative analyses of microscopic parameters indicate a positive correlation between the permeability and the fractal dimension, size, and proportion of pores and fractures. Conversely, there is a negative correlation with roughness, tortuosity, and cross-sectional changes. The range in which the seepage contribution of pores cannot be ignored is determined. Two logarithmic relationship expressions for permeability are presented. This study contributes to explore the effects of the geometry and morphology of the pore-fracture media on seepage and supplements the studies on the permeability models.
Infrared spectroscopy of isomers of C3H4+ in superfluid helium droplets
Authors: Singh Amandeep , Feinberg Alexandra J. , Moon Cheol Joo , Erukala Swetha , Kumar Piyush , Choi Myong Yong , Venkataramani Sugumar , Vilesov Andrey F.
Published: June 2024

Superfluid helium nanodroplets are unique nanomatrices for the isolation and study of transient molecular species, such as radicals, carbenes, and ions. In this work, isomers of C3H4+ were produced upon electron ionization of propyne and allene molecules and interrogated via infrared spectroscopy inside He nanodroplet matrices. It was found that the spectrum of C3H4+ has at least three distinct groups of bands. The relative intensities of the bands depend on the precursor employed and its pickup pressure, which indicates the presence of at least three different isomers. Two isomers were identified as allene and propyne radical cations. The third isomer, which has several new bands in the range of 3100–3200 cm−1, may be the elusive vinylmethylene H2C=CH–CH+ radical cation. The observed bands for the allene and propyne cations are in good agreement with the results of density functional theory calculations. However, there is only moderate agreement between the new bands and the theoretically calculated vinylmethylene spectrum, which indicates more work is necessary to unambiguously assign it.
Prediction of three-dimensional flow field inside realistic fibrous filter obtained from x-ray computed tomography images using deep convolutional neural networks
Authors: Hada Kodai , Shirzadi Mohammadreza , Fukasawa Tomonori , Fukui Kunihiro , Ishigami Toru
Published: June 2024

Deep-learning models garnered considerable attention in the field of fluid mechanics for physics discovery and approximation-model generation. This study aims to develop an approximation model to predict the flow field inside realistic fibrous filters based on an image-to-image approach to replace three-dimensional (3D) computational fluid dynamics (CFD) simulations, which are computationally expensive and difficult to apply to realistic fibrous filters. A data-driven framework is proposed using deep convolutional neural networks (CNNs) to provide a per-pixel prediction of the flow field. The model inputs are two-dimensional x-ray computed tomography images, whereas the outputs are the 3D distributions of the velocity vectors and pressure. High-resolution 3D CFD simulations are performed to create a database to train and test the CNN model. The model is applied to surgical and N95 face masks. The relative error of the CNN model over the test dataset is approximately 10% in regions with high velocity and pressure, and the model can provide a detailed high-resolution prediction of the flow field with a speedup of about three orders of magnitudes. A strict generalization test is conducted for completely unseen 3D segments with complex microstructures. The model generalizability still needs more improvements; however, the model can provide a low-resolution 3D flow field for those segments that can be used as the initial condition for CFD simulation to reduce the CFD computational time. This framework can be utilized for other types of filters and provides a basis for the design and optimization of fibrous filters.
A new portable penetrometer for measuring the viscosity of active lava
Authors: Harris M. A. , Kolzenburg S. , Sonder I. , Chevrel M. O.
Published: June 2024

Viscosity is a fundamental physical property of lava that dictates style and rate of effusive transport. Studies of lava viscosity have predominantly focused on measuring re-melted rocks in the laboratory. While these measurements are well-constrained in temperature, shear rate, and oxygen fugacity, they cannot reproduce the complexities of the natural emplacement environment. Field viscosity measurements of active lava are the only way to fully capture lava’s properties, but such measurements are scarce, largely due to a lack of easy-to-use, portable, and accurate measurement devices. Thus, there is a need for developing suitable field instruments to help bolster the understanding of lava. Here, we present a new penetrometer capable of measuring a material’s viscosity under the harsh conditions of natural lava emplacement. This device uses a stainless-steel tube with a semi-spherical tip fixed to a load cell that records axial force when pushed into a material, while simultaneously measuring the penetration depth via a free-moving tube that is pushed backward along the penetration tube. The device is portable (1.5 m long, 5.5 kg in weight) and uses a single-board computer for data acquisition. The penetrometer has an operational range from 2.5 × 102 to 2.1 × 105 Pa s and was calibrated for viscosities ranging from 5.0 × 102 to 1.6 × 105 Pa s. It was deployed to the 2023 Litli-Hrútur eruption in Iceland. These field measurements successfully recorded the in situ viscosities of the lava in the range of 1.2 × 104–3.4 × 104 Pa s, showcasing it as an efficient method of measuring natural lava viscosity.
Potassium doping of vertically aligned multi-walled carbon nanotubes
Authors: Jiménez-Arévalo Nuria , Filoscia Francesco , Marchiani Dario , Frisenda Riccardo , Betti Maria Grazia , Rago Ilaria , Pandolfi Francesco , Cavoto Gianluca , Mariani Carlo
Published: June 2024

Alkali metal doping of multi-walled carbon nanotubes is of great interest, both fundamentally to explore the effect of dopants on quasi-one-dimensional electrical systems and for energy applications such as alkali metal storage. We present an investigation with complementary photoemission and Raman spectroscopies, fully carried out in an ultra-high vacuum, to unveil the electronic and vibrational response of a forest of highly aligned multi-walled carbon nanotubes by in situ potassium doping. The charge donation by the alkali adatoms induces a plasmon mode, and the density of states undergoes an energy shift consistent with electron donation and band filling of the multi-walled carbon nanotube band structure. The π-states in the valence band and the Raman peaks unveil an evolution that can be ascribed to charge donation and partially to a tensile strain exerted by the K adatoms on the carbon lattice. All these effects are thermally reversible, fostering these materials as a potential system for electronic charge harvesting.
Effect of a fixed downstream cylinder on the flow-induced vibration of an elastically supported primary cylinder
Authors: Wang Junlei , Li Shenfang , Yurchenko Daniil , Zhu Hongjun , Bose Chandan
Published: June 2024

This paper numerically investigates the influence of a fixed downstream control cylinder on the flow-induced vibration of an elastically supported primary cylinder. These two cylinders are situated in a tandem arrangement with small dimensionless center-to-center spacing (L/D, L is the intermediate spacing and D is the cylinder diameter). The present two-dimensional (2D) simulations are carried out in the low Reynolds number (Re) regime. The primary focus of this study is to reveal the underlying flow physics behind the transition from vortex-induced vibration to galloping in the response of the primary cylinder due to the presence of another fixed downstream cylinder. Two distinct flow field regimes, namely, steady flow and alternate attachment regimes, are observed for different L/D and Re values. Depending on the evolution of the near-field flow structures, four different wake patterns, “2S,” “2P,” “2C,” and “aperiodic,” are observed. The corresponding vibration response of the upstream cylinder is characterized as interference galloping and extended vortex-induced vibration. As the L/D ratio increases, the lift enhancement due to flow-induced vibration is seen to be weakened. The detailed correlation between the force generation and the near-wake interactions is investigated. The present findings will augment our understanding of vibration reduction or flow-induced energy harvesting of tandem cylindrical structures.
Effect of hydrodynamic and electrical parameters on the dynamics of bubble ascent in the presence of an electric field
Authors: Patel Darshan , Vengadesan S.
Published: June 2024

The present study numerically investigates the dynamics of bubble ascent under the influence of a horizontally applied electric field. We have developed an in-house electrohydrodynamics solver integrated with the open-source solver interFoam. This solver underwent meticulous validation against existing literature and was then employed for conducting simulations. Our investigation reveals the impact of the electric capillary number (CaE) on the occurrence of wobbling. Higher (CaE) values induce wobbling in various steady-state bubble shapes, including ellipsoidal, ellipsoidal cap, dimpled ellipsoidal, and bi-oblate. For the selected conductivity (R) and permittivity ratios(S), (CaE) exhibits negligible influence on bubble rising velocity. However, its effect on deformation is significant for ellipsoidal and ellipsoidal cap shapes while marginal for other configurations. (CaE) minimally affects the shape alteration of the bubble until the onset of wobbling. The overall influence of Bond number (Bo) and Reynolds number (Re) on the dynamics of bubble ascent in the presence of an electric field mirrors their impact in its absence, with one notable exception—the occurrence of wobbling. Wobbling is observed at lower Bo and Re values compared to their counterparts in the absence of an electric field.
Image reconstruction of electrostatic tomography based on the improved residual network
Authors: Liu Xianglong , Li Danyang , Wang Ying , Zhang Kun , Feng Huilin
Published: June 2024

The core of electrostatic tomography (EST) is to solve the inverse problem, but the EST independent measurement data are much smaller than the value that needs to be reconstructed, resulting in a more serious inverse problem. This paper presents an improved ResNet-34 network (P-ResNet), which consists of an input layer, a residual feature extraction layer, and an output layer. The number of residual blocks is 3, 4, 4, and 3. After the second convolution in the main path of each residual block, a ReLU activation function is added to enhance the nonlinear expression ability of the network, and the generalization ability of the model is improved by introducing the L2 regularization loss function. A total of 15 930 sets of samples were simulated for the simulation test. After 200 rounds of iteration, the reconstruction results show that the network achieves high accuracy in EST image reconstruction tasks. In addition, the model is tested under different degrees of Gaussian white noise to verify its anti-noise ability. Compared with the traditional algorithms, the image correlation coefficients of this proposed model network are higher. In addition, this paper designs a small sensor to obtain the induced charge values through the principle of electrostatic induction. The reconstructed results obtained from the experimental data are consistent with the simulation results, which verifies the effectiveness and generalization ability of the proposed model.
A field inversion and symbolic regression enhanced Spalart–Allmaras model for airfoil stall prediction
Authors: He Zizhou , Wu Chenyu , Zhang Yufei
Published: June 2024

A data-driven turbulence modeling method based on symbolic regression (SR) is proposed in this paper to enhance the prediction accuracy of the Spalart–Allmaras (SA) model for airfoil stall. Unlike traditional methods that rely on neural networks and lack physical interpretability, this paper utilizes SR to establish an analytic expression mapping local flow field variables to the SA model correction factor β. The training data are obtained through field inversion with the discrete adjoint method in the flow field of the S809 airfoil. Additionally, a relearning approach proposed in this paper is applied to the SR process to address the issue arising from the multi-solution nature of field inversion. The SA model embedded with β, referred to as the SA-SR model, can be integrated into computational fluid dynamics solvers with negligible computational cost. The generalization performance of the SA-SR model is tested under various conditions and airfoil types. The results indicate that the new model improves the predictive capability for airfoil stall without compromising the performance of the baseline SA model for attached flows.
A fast and smooth one-electron approach for investigating charge transfer states and D1–D0 crossings for systems with odd numbers of electrons
Authors: Qiu Tian , Bian Xuezhi , Tao Zhen , Subotnik Joseph E.
Published: June 2024

We propose an efficient version of ensemble Hartree–Fock/density functional theory to calculate a set of two charge-transfer states for systems with odd-numbers of electrons. The approach does require definitions of donor/acceptor fragments; however, the approach is not very sensitive to such definitions—even in the limit of very strong electronic coupling. The key ansatz is that, by mandating that the vector space spanned by the active orbitals projects equally onto the donor and acceptor fragments, such a constraint eliminates all intra-molecular local excitations and makes it far easier to generate potential energy surfaces that are smooth over a wide region of configuration space. The method is fast, working with only two electron configurations, and should be useful for ab initio non-adiabatic dynamics in the near future.
Stability and deformation of biomolecular condensates under the action of shear flow
Authors: Coronas Luis E. , Van Thong , Iorio Antonio , Lapidus Lisa J. , Feig Michael , Sterpone Fabio
Published: June 2024

Biomolecular condensates play a key role in cytoplasmic compartmentalization and cell functioning. Despite extensive research on the physico-chemical, thermodynamic, or crowding aspects of the formation and stabilization of the condensates, one less studied feature is the role of external perturbative fluid flow. In fact, in living cells, shear stress may arise from streaming or active transport processes. Here, we investigate how biomolecular condensates are deformed under different types of shear flows. We first model Couette flow perturbations via two-way coupling between the condensate dynamics and fluid flow by deploying Lattice Boltzmann Molecular Dynamics. We then show that a simplified approach where the shear flow acts as a static perturbation (one-way coupling) reproduces the main features of the condensate deformation and dynamics as a function of the shear rate. With this approach, which can be easily implemented in molecular dynamics simulations, we analyze the behavior of biomolecular condensates described through residue-based coarse-grained models, including intrinsically disordered proteins and protein/RNA mixtures. At lower shear rates, the fluid triggers the deformation of the condensate (spherical to oblated object), while at higher shear rates, it becomes extremely deformed (oblated or elongated object). At very high shear rates, the condensates are fragmented. We also compare how condensates of different sizes and composition respond to shear perturbation, and how their internal structure is altered by external flow. Finally, we consider the Poiseuille flow that realistically models the behavior in microfluidic devices in order to suggest potential experimental designs for investigating fluid perturbations in vitro.
Modulus alteration of thin polystyrene films by their neighboring PDMS: Soft and hard confinement
Authors: Xiao Yuhan , Bai Pei , Guo Yunlong
Published: June 2024

It is highly demanded to understand the confinement effect on nanoconfined polymers. Recent studies reported a strong perturbation of local dynamics and substantial alteration of glass transition temperature Tg at nanoscale. However, how confinement affects the mechanical properties of polymers is not fully understood. Here, we show that the modulus of thin polymer films could be remarkedly altered through a polymer–polymer interface. The modulus of a thin polystyrene (PS) film next to a polydimethylsiloxane (PDMS) was determined from the PS–PDMS bilayer bulging test. A series of experiments show that the modulus of PS can be increased up to 37%, when the modulus of the neighboring PDMS varies from 1.04 to 4.88 MPa. The results demonstrate a strong sensitivity of mechanical properties of thin polymers to the hard/soft environment, which we attribute to the change of high-mobility layer by the polymer–polymer interface.
Selection of antioxidants for capacitor grade polypropylene film: Insights into electrical performance of the oil-film system
Authors: Li Hua , Wang Yucheng , Huang Ziqin , Zhu Kangyu , Lin Fuchang , Liu Jingqi
Published: June 2024

High voltage power capacitors employ the oil-impregnated polypropylene film as the insulation. The swelling phenomenon might drive the antioxidants and small molecules within the film to migrate into the oil. It is necessary to comprehensively investigate the physical migration mechanism of antioxidants and their impact on the electrical performance of the oil-film combination insulation system and, consequently, formulate the proper selective prescription of antioxidants. Theoretical elucidation of the competitive interaction mechanism between the film and the oil in attracting antioxidant molecules was achieved through the calculation of inter-molecular binding energy, and the migration coefficient ηm was introduced to quantify the migration characteristics of antioxidants. Experimentally, the effects of antioxidants on the space charge distribution of the film, the dielectric properties of the oil, and the breakdown characteristics of both the film and oil were investigated. The experimental conclusions are consistent with theoretical analysis. The lamellar structure antioxidant molecules with ηm > 1 tend to migrate from the film to the oil, which results in increased dielectric loss and decreased breakdown strength of the insulating oil. In addition, the presence of phosphorus atoms in phosphite antioxidants contributes to a reduction in the breakdown strength of the film. For capacitor grade polypropylene film, in addition to the synergistic effect between different types of antioxidants on the thermo-oxidative stability, the structure of the antioxidant molecules and its influence on the electrical performance of the oil–film systems should also be taken into account.
Leakage flow mixing in shrouded axial turbines and its control strategies using casing optimization
Authors: Huang Dongming , Zhang Weihao , Wang Yufan , Jiang Shoumin , Wang Peng , Chen Yun
Published: June 2024

The geometry of the shroud cavity, which accommodates the rotor shroud leakage flow, is very important due to its impact on the leakage flow path as well as the interaction between the leakage flow and mainstream. The research in this paper numerically investigates the potential for reducing the leakage loss by optimization to the casing. The spatial loss audit and the loss breakdown based on loss mechanisms undertaken in the first part of this study are the foundation to develop promising strategies for minimizing the leakage loss. The profiled casing in the exit cavity effectively deflects the leakage jet into the axial direction when it re-enters the mainstream. The mixing loss is significantly reduced due to the notable decrease in axial velocity disparity of the two streams. On this basis, the exit and inlet cavity are further shaped to both form a step. Reductions in the shroud leakage loss are achieved by alleviating the flow nonuniformity in the exit cavity and reducing the leakage flow rate, respectively. The work in this study contributes to the refinement of control methods for the shroud leakage loss.
A compact, low-pressure manifold with uniform flow at low Reynolds number
Authors: Smith Kyle C. , Loud Irwin C. , Rahman Md Habibur , Warden Colby , Do Vu Q.
Published: June 2024

Manifolds that distribute fluid into or that collect fluid from a multiplicity of streams are ubiquitous. We introduce a new theory for manifold design to produce uniform flow among their streams. By constructing a tapered header region that feeds uniformly spaced diffuser channels (constraint A), flow uniformity can be achieved with less than a quarter of the footprint of bifurcating manifolds, provided that diffuser channels are arrayed in triangular form (constraint B) with a design-specific angle that satisfies a compatibility condition between its header and diffuser (constraint C). The associated theory harnesses creeping-flow hydraulics to induce a constant header pressure-gradient, in contrast with past theory that relied on the interplay between kinetic energy, pressure, and viscous losses to uniformize header pressure at finite Reynolds number. Experiments using dye-based flow visualization from manifolds incorporating these three design constraints are shown to produce uniform flows, while designs that violate any of the three constraints produce flow that is biased toward the manifold's ends or its center. Our experiments and three-dimensional simulations of such uniformizing manifolds show maximum deviations from uniformity of ∼10% for Reynolds number as high as ∼10. As expected from creeping-flow theory, simulations confirm that such flow uniformity is facilitated by a uniform header-pressure gradient. Finally, the associated uniformizing manifold is shown to produce lower hydraulic resistance than a rectangular manifold circumscribed around it. In addition to the theory's embodiment in the specific form tested here, it is readily applicable to a variety of header and diffuser-channel cross-sectional types.
Microfluidic flow tuning via asymmetric flow of nematic liquid crystal under temperature gradient
Authors: Li Gu-Yuan , Yu Jia-Jia , Duan Cheng-Cheng , Sun Shouli , Wu Chun-Mei , Li You-Rong
Published: June 2024

In this work, efficient microfluidic flow rate tuning based on the asymmetric flow of nematic liquid crystal 5CB under a horizontal temperature gradient is studied. Rectangular microchannels with the width of 100 μm are fabricated through soft lithography and treated with homeotropic surface anchoring conditions. Polarized optical microscopy is applied to explore the unique optical anisotropic characteristics of the nematic liquid crystal. The asymmetric velocity profiles in the microchannel are obtained by particle tracking velocimetry. The effects of temperature, flow rate, and aspect ratio on the velocity profile and split ratio of the asymmetric flow are quantitatively studied for the first time, while the mechanism of the flow asymmetry of the nematic liquid crystal is discussed. The results show that the asymmetric flow of the nematic liquid crystal occurs after the horizontal temperature gradient is applied, with the velocity in the heated region markedly higher than its counterpart. The split ratio of the asymmetric flow increases with the increase in the temperature gradient and the decrease in the flow rate. The aspect ratio influences the asymmetric flow through approaches of average velocity and surface anchoring strength, while the former is more distinct. The impacts of temperature gradient, flow rate, and aspect ratio on the flow asymmetry of nematic liquid crystals are caused by the coupling between physical properties, velocity field, and director field. Microchannels based on the asymmetric flow characteristics of nematic liquid crystals can act as a novel kind of temperature-controlled microvalve to achieve efficient microfluidic flow tuning.
Isotope shifts in electron affinities and in binding energies of Pb and hyperfine structure of 207Pb−
Authors: Song C. X. , Yan S. T. , Godefroid M. , Bieroń J. , Jönsson P. , Gaigalas G. , Ekman J. , Zhang X. M. , Chen C. Y. , Ning C. G. , Si R.
Published: June 2024

The isotope shifts in electron affinities of Pb were measured by Walter et al. [Phys. Rev. A 106, L010801 (2022)] to be −0.002(4) meV for 207–208Pb and −0.003(4) meV for 206–208Pb by scanning the threshold of the photodetachment channel Pb−(S3/2◦4) − Pb (3P0), while Chen and Ning reported 0.015(25) and −0.050(22) meV for the isotope shifts on the binding energies measured relative to 3P2 using the SEVI method [J. Chem. Phys. 145, 084303 (2016)]. Here we revisited these isotope shifts by using our second-generation SEVI spectrometer and obtained −0.001(15) meV for 207–208Pb and −0.001(14) meV for 206–208Pb, respectively. In order to aid the experiment by theory, we performed the first ab initio theoretical calculations of isotope shifts in electron affinities and binding energies of Pb, as well as the hyperfine structure of 207Pb−, by using the MCDHF and RCI methods. The isotope shifts in electron affinities of 207–208Pb and 206–208Pb are −0.0023(8) and −0.0037(13) meV for the 3P0 channel, respectively, in good agreement with Walter et al.’s measurements. The isotope shifts in binding energies relative to 3P1,2, −0.0015(8) and −0.0026(13) meV for 207–208Pb and 206–208Pb, respectively, are compatible with the present measurements. The hyperfine constant for the ground state of 207Pb− obtained by the present calculations, A(S3/2◦4)=−1118 MHz, differs by a factor of 3 from the previous estimation by Bresteau et al. [J. Phys. B: At., Mol. Opt. Phys. 52, 065001 (2019)]. The reliability is supported by the good agreement between the theoretical and experimental hyperfine parameters of 209Bi.
CO2 injection-based enhanced methane recovery from carbonate gas reservoirs via deep learning
Authors: Huang Yize , Li Xizhe , Elsworth Derek , Liu Xiaohua , Yu Pengliang , Qian Chao
Published: June 2024

CO2 injection is a promising technology for enhancing gas recovery (CO2-EGR) that concomitantly reduces carbon emissions and aids the energy transition, although it has not yet been applied commercially at the field scale. We develop an innovative workflow using raw data to provide an effective approach in evaluating CH4 recovery during CO2-EGR. A well-calibrated three-dimensional geological model is generated and validated using actual field data—achieving a robust alignment between history and simulation. We visualize the spread of the CO2 plume and quantitatively evaluate the dynamic productivity to the single gas well. We use three deep learning algorithms to predict the time histories of CO2 rate and CH4 recovery and provide feedback on production wells across various injection systems. The results indicate that CO2 injection can enhance CH4 recovery in water-bearing gas reservoirs—CH4 recovery increases with injection rate escalating. Specifically, the increased injection rate diminishes CO2 breakthrough time while concurrently expanding the swept area. The increased injection rate reduces CO2 breakthrough time and increases the swept area. Deep learning algorithms exhibit superior predictive performance, with the gated recurrent unit model being the most reliable and fastest among the three algorithms, particularly when accommodating injection and production time series, as evidenced by its smallest values for evaluation metrics. This study provides an efficient method for predicting the dynamic productivity before and after CO2 injection, which exhibits a speedup that is 3–4 orders of magnitudes higher than traditional numerical simulation. Such models show promise in advancing the practical application of CO2-EGR technology in gas reservoir development.
A tantalum oxide based memristive neuron device for anomaly detection application
Authors: Wu Zuheng , Hu Yang , Feng Zhe , Zou Jianxun , Guo Wenbin , Lu Jian , Shi Tuo , Tan Su , Wang Zeqing , Yu Ruihan , Zhu Yunlai , Xu Zuyu , Dai Yuehua
Published: June 2024

Anomaly detection, a data intensive task, is very important in wide application scenarios. Memristor has shown excellent performance in data intensive tasks. However, memristor used for anomaly detection has rarely been reported. In this Letter, a tantalum oxide (TaOx) memristive neuron device has been developed for anomaly detection application. TaOx, a CMOS compatible material, based memristor shows reliable threshold switching characteristics, which is suitable for constructing memristive neuron. Furthermore, the output frequency of the memristive neuron is found to be proportionate to the applied stimulus intensity and at an inflection point starts to decrease, namely, thresholding effect. Based on the thresholding effect of the neuron output, the application of the memristive neuron for anomaly detection has been simulated. The results indicate that the TaOx memristive neuron with thresholding effect shows better performance (98.78%) than the neuron without threshoding effect (90.89%) for anomaly detection task. This work provided an effective idea for developing memristive anomaly detection system.
Time-of-flight technique for estimation of the energy of runaway electron bunches formed in magnetized gas diodes
Authors: Lobanov L. N. , Sharypov K. A. , Shpak V. G. , Shunailov S. A. , Yalandin M. I. , Zubarev N. M.
Published: June 2024

Time-of-flight estimates of the kinetic energy of magnetically insulated bunches of moderately relativistic runaway electrons (RAEs) were obtained with the use of an air diode equipped with a drift section. The measurements have demonstrated that the bunch energy can be controlled by changing the conditions for RAE emission in an air diode with a sharply inhomogeneous electric field, which can be done by varying the cathode geometry and material and the length of the cathode-anode gap. It has been demonstrated that if the measured electron current peaks are resolved to within 10 ps, and the bunch duration and spread in RAE emission moments are close to this resolution, the characteristic energies of the bunches can be estimated with an accuracy of ≈10%. Examples of energy measurements are given for paraxial and tubular bunches accelerated at cathode potentials of up to −250 kV. The estimated characteristic energies of the bunches, even not corrected for drift losses in the fill gas, turned out to be greater than the energies that could be achieved for bunches accelerated in a vacuum diode with due account for the variations in diode voltage.
Plugin-based interoperability and ecosystem management for the MolSSI Driver Interface Project
Authors: Barnes T. A. , Ellis S. , Chen J. , Plimpton S. J. , Nash J. A.
Published: June 2024

The MolSSI Driver Interface (MDI) Project is an effort to simplify and standardize the process of enabling tight interoperability between independently developed code bases and is supported by numerous software packages across the domain of chemical physics. It enables a wide variety of use cases, including quantum mechanics/molecular mechanics, advanced sampling, path integral molecular dynamics, machine learning, ab initio molecular dynamics, etc. We describe two major developments within the MDI Project that provide novel solutions to key interoperability challenges. The first of these is the development of the MDI Plugin System, which allows MDI-supporting libraries to be used as highly modular plugins, with MDI enforcing a standardized application programming interface across plugins. Codes can use these plugins without linking against them during their build process, and end-users can select which plugin(s) they wish to use at runtime. The MDI Plugin System features a sophisticated callback system that allows codes to interact with plugins on a highly granular level and represents a significant advancement toward increased modularity among scientific codes. The second major development is MDI Mechanic, an ecosystem management tool that utilizes Docker containerization to simplify the process of developing, validating, maintaining, and deploying MDI-supporting codes. Additionally, MDI Mechanic provides a framework for launching MDI simulations in which each interoperating code is executed within a separate computational environment. This eliminates the need to compile multiple production codes within a single computational environment, reducing opportunities for dependency conflicts and lowering the barrier to entry for users of MDI-enabled codes.
Are monodisperse phospholipid-coated microbubbles “mono-acoustic?”
Authors: Spiekhout Sander , van Elburg Benjamin , Voorneveld Jason , Jong Nico de , Versluis Michel , Bosch Johannes G. , Segers Tim
Published: June 2024

Phospholipid-coated microbubbles with a uniform acoustic response are a promising avenue for functional ultrasound sensing. A uniform acoustic response requires both a monodisperse size distribution and uniform viscoelastic shell properties. Monodisperse microbubbles can be produced in a microfluidic flow focusing device. Here, we investigate whether such monodisperse microbubbles have uniform viscoelastic shell properties and thereby a uniform “mono-acoustic” response. To this end, we visualized phase separation of the DSPC and DPPE-PEG5000 lipid shell components and measured the resonance curves of nearly 2000 single and freely floating microbubbles using a high-frequency acoustic scattering technique. The results demonstrate inhomogeneous phase-separated shell microdomains across the monodisperse bubble population, which may explain the measured inhomogeneous viscoelastic shell properties. The shell viscosity varied over an order of magnitude and the resonance frequency by a factor of two indicating both a variation in shell elasticity and in initial surface tension despite the relatively narrow size distribution.