bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanoregulation of MSC spheroid immunomodulation
Authors: Thai Victoria L. , Mierswa Sabrina , Griffin Katherine H. , Boerckel Joel D. , Leach J. Kent
Published: March 2024

Mesenchymal stromal cells (MSCs) are widely used in cell-based therapies and tissue regeneration for their potent secretome, which promotes host cell recruitment and modulates inflammation. Compared to monodisperse cells, MSC spheroids exhibit improved viability and increased secretion of immunomodulatory cytokines. While mechanical stimulation of monodisperse cells can increase cytokine production, the influence of mechanical loading on MSC spheroids is unknown. Here, we evaluated the effect of controlled, uniaxial cyclic compression on the secretion of immunomodulatory cytokines by human MSC spheroids and tested the influence of load-induced gene expression on MSC mechanoresponsiveness. We exposed MSC spheroids, entrapped in alginate hydrogels, to three cyclic compressive regimes with varying stress (L) magnitudes (i.e., 5 and 10 kPa) and hold (H) durations (i.e., 30 and 250 s) L5H30, L10H30, and L10H250. We observed changes in cytokine and chemokine expression dependent on the loading regime, where higher stress regimes tended to result in more exaggerated changes. However, only MSC spheroids exposed to L10H30 induced human THP-1 macrophage polarization toward an M2 phenotype compared to static conditions. Static and L10H30 loading facilitated a strong, interlinked F-actin arrangement, while L5H30 and L10H250 disrupted the structure of actin filaments. This was further examined when the actin cytoskeleton was disrupted via Y-27632. We observed downregulation of YAP-related genes, and the levels of secreted inflammatory cytokines were globally decreased. These findings emphasize the essential role of mechanosignaling in mediating the immunomodulatory potential of MSC spheroids.
Pixel-integrated Mie metasurface long-wave multispectral type II superlattice detector
Authors: Xiao Lei , Fu Jintao , Zhu Peng , Li Nong , Jiang Yongyi , Shi Haofei , Wei Xingzhan , Xiong Wen , Wang Guowei , Sun Tai
Published: March 2024

Dynamic multispectral imaging finds extensive applications in acquiring multidimensional information. The integration of high-performance, dynamic, and long-wavelength multispectral detectors at the pixel level is highly desirable across various applications. However, the development of such detector faces enormous challenges due to the fundamental material and optical system limitations. In this work, we present a pixel-integrated long-wavelength multispectral type II superlattice detector based Mie dielectric metasurface (Mie-multispectral detector) realized by integrating a graphene-assisted depletion Mie metasurface structure (GAMS). The GAMS is featured with a single-layer graphene and electrically gated tuned Mie dielectric grating. This pixel-integrated multispectral detector allows for 340 nm electrical dynamic tuning and D* value of 5 × 1010 Jones. The Mie-multispectral detector offers potential solutions in space exploration, pollutant retrieval, and other relevant fields.
Effects of structural defects on optical properties of InxGa1−xN layers and quantum wells
Authors: Liliental-Weber Z. , dos Reis Roberto
Published: March 2024

This review concentrates on the microstructure of InxGa1−xN layers and quantum wells (QWs) in relation to their optical properties. The microstructure of InxGa1−xN, with a constant In(x) concentration, shifts with layer thickness. Only layers below 100 nm for x = 0.1 are nearly defect-free. A photoluminescence peak is observed at 405 nm, in line with ∼10% In, suggesting band-edge luminescence. Layers with greater thickness and In content present a corrugated surface with numerous structural defects, including V-defects, causing redshifts and multi-peaks in photoluminescence up to 490 nm. These defects, resembling those in GaN, lead to a corrugated sample surface. Atomic force microscopy shows a 3.7-fold larger corrugation in samples with 20 QWs compared to those with 5 QWs measured on 2 × 2 μm2 areas. Like in GaN, dual growth on different crystallographic planes results in varied QW thicknesses, influencing optical traits of devices made from InxGa1−xN layers. The purpose of this review and the chosen subject is to highlight the significant contribution of Wladek Walukiewicz and his group to the current research on the properties of InxGa1−xN, which are crucial alloys in the field of optoelectronics.
Effects of terraces and steps on the 4H-SiC BPD-TED conversion rate: A reaction pathway analysis
Authors: Hirano Atsuo , Sakakima Hiroki , Hatano Asuka , Izumi Satoshi
Published: March 2024

The practical use of 4H-SiC as a semiconductor material alternative to Si has been investigated by several researchers. However, a key challenge impeding its practical implementation is the elimination of killer defects in the epitaxial layer, such as basal plane dislocations (BPDs), which cause bipolar degradations. The conversion of BPDs into threading edge dislocations is crucial to reduce detrimental mobile dislocations. However, their underlying atomistic mechanisms remain unclear. In this study, the effects of the step height and distance from the step on the contraction of BPDs were determined using a reaction pathway analysis. Notably, the step height did not affect the contraction, and the activation energies for the contraction of the partial dislocation pairs with Burgers vectors closed toward the step were 0.4 (C face) and 0.3 eV (Si face) lower than those for expansion. Conversely, for the partial dislocation pairs with Burgers vectors open toward the step, the activation energies for contraction were 0.4 (C face) and 0.2 eV (Si face) higher than those for expansion. Furthermore, the effect of the step diminished when the distance from the step exceeded 3 nm. The results suggest that the steps prevented contraction, and longer terraces reduced this preventive effect. Therefore, a surface morphology with fewer steps and longer terraces would increase the conversion rate. Furthermore, a low-off-angle substrate and surface polishing would increase the conversion rate, whereas step bunching slightly would decrease it. Macrosteps would decrease the conversion rate as the average distance from the surface to BPDs increased.
Vaccination impact on impending HIV-COVID-19 dual epidemic with autogenous behavior modification: Hill-type functional response and premeditated optimization technique
Authors: Majumder Madhuri , Pal Samares , Kumar Tiwari Pankaj
Published: March 2024

An HIV-COVID-19 co-infection dynamics is modeled mathematically assimilating the vaccination mechanism that incorporates endogenous modification of human practices generated by the COVID-19 prevalence, absorbing the relevance of the treatment mechanism in suppressing the co-infection burden. Envisaging a COVID-19 situation, the HIV-subsystem is analyzed by introducing COVID-19 vaccination for the HIV-infected population as a prevention, and the “vaccination influenced basic reproduction number” of HIV is derived. The mono-infection systems experience forward bifurcation that evidences the persistence of diseases above unit epidemic thresholds. Delicate simulation methodologies are employed to explore the impacts of baseline vaccination, prevalence-dependent spontaneous behavioral change that induces supplementary vaccination, and medication on the dual epidemic. Captivatingly, a paradox is revealed showing that people start to get vaccinated at an additional rate with the increased COVID-19 prevalence, which ultimately diminishes the dual epidemic load. It suggests increasing the baseline vaccination rate and the potency of propagated awareness. Co-infection treatment needs to be emphasized parallelly with single infection medication under dual epidemic situations. Further, an optimization technique is introduced to the co-infection model integrating vaccination and treatment control mechanisms, which approves the strategy combining vaccination with awareness and medication as the ideal one for epidemic and economic gain. Conclusively, it is manifested that waiting frivolously for any anticipated outbreak, depending on autogenous behavior modification generated by the increased COVID-19 prevalence, instead of elevating vaccination campaigns and the efficacy of awareness beforehand, may cause devastation to the population under future co-epidemic conditions.
Numerical simulation of enzymatic hydrolysis in a bionic intestinal segmentation reactor
Authors: Liao Qiang , Zhu Tong , Zhang Chang , Huang Yun , Zhu Xianqing , Zhu Xun , Xia Ao
Published: March 2024

Enzymatic hydrolysis plays a critical role in the microbial conversion of lignocellulosic biomass, which has been widely performed in continuous stirred-tank reactors (CSTRs). However, low hydrolysis efficiency in CSTRs hinders the industrial application of lignocellulose to produce biofuels. A bionic intestinal segmentation reactor (BISR) was proposed for efficient enzymatic hydrolysis. In BISR, the dynamic reactor's wall with enzyme secretion led to a 2.0-fold improvement in the conversion of cellobiose as a model substrate compared to the control with a static one. Meanwhile, the reaction rate reached 0.89 mmol/l/s, which was increased by 6.7-fold. Flow fields further illustrated that secondary flow during the segmentation facilitated radial mass transfer between cellobiose and enzyme. Dimensionless secondary flow intensity Sem increased from 0.93 to 2.35 with amplitude, while decreasing from 2.86 to 2.26 with period. More importantly, the analysis of dimensionless Péclet number (Pe) and Damköhler number (Da) indicated that secondary flow could significantly enhance the hydrolysis process controlled by mass transfer.
Cone array formation on Si surfaces by low-energy He plasma irradiation with magnetron sputtering pre-deposited Ta
Authors: Liu Zhe , Li Long , Gao Zeshi , Chen Ze , Yin Chao , Mao Shifeng , Kajita Shin , Ohno Noriyasu , Ye Minyou
Published: March 2024

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1–10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick’s law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms.
Thermoelectric performance of high aspect ratio double-sided silicon nanowire arrays
Authors: Ning Rui , Zeng Yuqiang , Rapp Vi , Zhang Buyi , Yang Lin , Prasher Ravi , Zheng Xiaolin
Published: March 2024

Roughly, 50% of primary energy worldwide is rejected as waste heat over a wide range of temperatures. Waste heat above 573 K has the highest Carnot potential (>50%) to be converted to electricity due to higher Carnot efficiency. Thermoelectric (TE) materials have gained significant attention as potential candidates for efficient thermal energy conversion devices. Silicon nanowires (SiNWs) are promising materials for TE devices due to their unique electrical and thermal properties. In this study, we report the successful fabrication of high-quality double-sided SiNW arrays using advanced techniques. We engineered the double-sided structure to increase the surface area and the number of TE junctions, enhancing TE energy conversion efficiency. We also employed non-agglomeration wire tip engineering to ensure uniformity of the SiNWs and designed effective Ohmic contacts to improve overall TE efficiency. Additionally, we post-doped the double-sided SiNW arrays to achieve high electrical conductivity. Our results showed a significant improvement in the TE performance of the SiNW array devices, with a maximum figure-of-merit (ZT) value of 0.24 at 700 K, fabricated from the single SiNW with ZT of 0.71 at 700 K in our previous work [Yang et al., Nat. Commun. 12(1), 3926(2021)].
DFT study of energetics and optoelectronics properties of B, C, and N binary and ternary honeycomb structures
Authors: Tazekritt S. , Gallouze M. , Kellou A.
Published: March 2024

Using the Full Potential Linear Augmented Plane Wave and the pseudo-potential method based on the Density Functional Theory, we investigate the physical properties of two-dimensional (2D) boron nitride, carbon nitride, and boron carbide as well as their ternary system boron carbon nitride (BCN). The structural and optoelectronic properties are determined and discussed in detail with available theoretical and experimental results. We show that the studied physical properties are influenced and tunable by atom concentration. A high concentration of nitrogen (> 50%) disturbs the honeycomb structure of binary and ternary alloys. Additionally, the optoelectronic properties are very sensitive to the amount of boron and nitrogen atoms. The zero bandgap is only conserved for B3C12N3 and B6C6N6 ternary systems. A large bandgap was observed for B9N9 (∼3.9 eV) and a moderate one for B6N12 and B3N15 (∼2 eV). The coexistence of boron, carbon, and nitrogen atoms with different concentrations has important optical properties as they can absorb light in all spectra. However, they have more active absorption in the ultraviolet than visible regions. It is more interesting to use ternary BCN than binary or pristine alloys with tunable optoelectric properties, by varying the nitrogen content in nanodevices.
Ab initio morphology prediction of Pd, Ag, Au, and Pt nanoparticles on (0001) sapphire substrates
Authors: Ishii Akio , Nakamura Nobutomo
Published: March 2024

We energetically predict the morphology of Pd, Ag, Au, and Pt nanoparticles on (0001) sapphire substrates, using density functional theory (DFT) simulations and the well-known Young–Dupre equation. In all cases, the contact angles exceed 90°, indicating that the nanoparticles are spherical. Notably, Au nanoparticles exhibit a higher contact angle than those of their counterparts. The validity of the proposed abinitio nanoparticle morphology prediction approach based on DFT simulations was assessed in comparison with our previous experimental findings pertaining to the time variation of the full width at half maximum (FWHM) of the resonant peak. Furthermore, the diffusivities of single Pd, Ag, Au, and Pt atoms on the substrate were evaluated by calculating the activation energy, offering insights into the underlying physics governing the timing of FWHM peaks. The analysis confirms a higher diffusivity of Au and Ag compared with Pd and Pt. According to the comparison between DFT and experiment results, although no clear relation is observed between the contact angles and timing of FWHM peaks, the diffusivity of sputtered atoms may influence the timing of FWHM peaks. Thus, timing can help to clarify the nanoparticle size, rather than shape.
Effects of topographical disturbances on flexural wave motion in a viscous fluid
Authors: Prasad Indra Mani , Behera Harekrushna , Tsai Chia-Cheng , Hsu Tai-Wen
Published: March 2024

Main causes of ground disturbances are geological events such as earthquakes, underwater gravity mass flows, volcanic eruptions, and bottom explosions. This paper investigates the effects of transitory ground disturbance on the generation of flexural waves in the presence of a thin floating elastic plate. The problem is formulated using the Stokes stream function and wave potential boundary value problems in a viscous fluid. The expression of the plate deflection is obtained as multiple infinite integrals using the Fourier and Laplace transforms, which is further solved by the steepest descent method. Three types of ground disturbances such as H0(x)=e(−x2/2), H0(x)=e−|x|, and H0(x)=δ(x) are considered. The deflection of the floating elastic plate is investigated in connection to ground disturbances, fluid viscosity, and structural parameters such as mass per unit length of the plate and flexural rigidity. The study reveals that with higher viscosity and flexural rigidity, the amplitude of the plate deflection is reduced. Moreover, these two parameters play a great role in the reduction of plate deflection.
Structure and self-diffusivity of mixed-cation electrolytes between neutral and charged graphene sheets
Authors: Rezlerová Eliška , Moučka Filip , Předota Milan , Lísal Martin
Published: March 2024

Graphene-based applications, such as supercapacitors or capacitive deionization, take place in an aqueous environment, and they benefit from molecular-level insights into the behavior of aqueous electrolyte solutions in single-digit graphene nanopores with a size comparable to a few molecular diameters. Under single-digit graphene nanoconfinement (smallest dimension <2 nm), water and ions behave drastically different than in the bulk. Most aqueous electrolytes in the graphene-based applications as well as in nature contain a mix of electrolytes. We study several prototypical aqueous mixed alkali-chloride electrolytes containing an equimolar fraction of Li/Na, Li/K, or Na/K cations confined between neutral and positively or negatively charged parallel graphene sheets. The strong hydration shell of small Li+ vs a larger Na+ or large K+ with weaker or weak hydration shells affects the interplay between the ions’s propensity to hydrate or dehydrate under the graphene nanoconfinement and the strength of the ion–graphene interactions mediated by confinement-induced layered water. We perform molecular dynamics simulations of the confined mixed-cation electrolytes using the effectively polarizable force field for electrolyte–graphene systems and focused on a relation between the electrochemical adsorption and structural properties of the water molecules and ions and their diffusion behavior. The simulations show that the one-layer nanoslits have the biggest impact on the ions’ adsorption and the water and ions’ diffusion. The positively charged one-layer nanoslits only allow for Cl− adsorption and strengthen the intermolecular bonding, which along with the ultrathin confinement substantially reduces the water and Cl− diffusion. In contrast, the negatively charged one-layer nanoslits only allow for adsorption of weakly hydrated Na+ or K+ and substantially break up the non-covalent bond network, which leads to the enhancement of the water and Na+ or K+ diffusion up to or even above the bulk diffusion. In wider nanoslits, cations adsorb closer to the graphene surfaces than Cl−’s with preferential adsorption of a weakly hydrated cation over a strongly hydrated cation. The positive graphene charge has an intuitive effect on the adsorption of weakly hydrated Na+’s or K+’s and Cl−’s and a counterintuitive effect on the adsorption of strongly hydrated Li+’s. On the other hand, the negative surface charge has an intuitive effect on the adsorption of both types of cations and only mild intuitive or counterintuitive effects on the Cl− adsorption. The diffusion of water molecules and ions confined in the wider nanoslits is reduced with respect to the bulk diffusion, more for the positive graphene charge, which strengthened the intermolecular bonding, and less for the negative surface charge, which weakened the non-covalent bond network.
Investigating the entry of symmetric/asymmetric elastic wedge into water
Authors: Zou Jian , Li Hui , Liu Ruixiang , Lu Lin
Published: March 2024

Understanding the impact of fluid–structure interaction during the entry of a marine vessel into water is crucial for its design. While numerous models have been proposed to investigate the penetration of symmetric elastic wedges into water, in this study, we propose a numerical model that combines the fully nonlinear boundary element method with a mode superposition method to analyze the penetration of symmetric and asymmetric elastic wedges into water. We derive the boundary conditions of the acceleration potential within the flow field for the problem of fluid–structure interaction and use auxiliary functions to decompose the acceleration potential and extract the instantaneous added mass. Following this, the differential equations of the modes of rigid motion and elastic deformation of the body are established and solved. This approach enables the simultaneous solution of the motion and vibrations of the wedge as well as the hydrodynamic pressure. The proposed model also accounts for flow separation while the wedge is submerged, thereby prolonging the simulation. We confirmed the validity of the model through comprehensive examinations based on semi-analytical, computational, and experimental data on the problem of the entry of a symmetric body into water. We then extended our study to encompass the free-falling entry of an asymmetric elastic wedge into water. The results revealed notable discrepancies in the evolution of deformation and jet flow between the right and left boundaries during the entry of the wedge into water.
Microstructural smoothed particle hydrodynamics model and simulations of discontinuous shear-thickening fluids
Authors: Angerman Peter , Prasanna Kumar Sagaya S. , Seto Ryohei , Sandnes Bjornar , Ellero Marco
Published: March 2024

Despite the recent interest in the discontinuous shear-thickening (DST) behavior, few computational works tackle the rich hydrodynamics of these fluids. In this work, we present the first implementation of a microstructural DST model in smoothed particle hydrodynamic (SPH) simulation. The scalar model was implemented in an SPH scheme and tested in two flow geometries. Three distinct ratios of local to non-local microstructural effects were probed: zero, moderate, and strong non-locality. Strong and moderate cases yielded excellent agreement with flow curves constructed via the Wyart–Cates (WC) model, with the moderate case exhibiting banding patterns. We demonstrate that a local model is prone to a stress-splitting instability, resulting in discontinuous stress fields and poor agreement with the WC model. The mechanism of stress splitting has been explored and contextualized by the interaction of local microstructure evolution and the stress-control scheme. Analytic solutions for a body-force-driven DST channel flow have been derived and used to validate the SPH simulations with excellent agreement in velocity profiles. Simulations carried out at increasing driving forces exhibited a decrease in flow. We showed that even the simple scalar model can capture some of the key properties of DST materials, laying the foundation for further SPH study of instabilities and pattern formation.
Reconstruction techniques for complex potentials
Authors: Kravchenko Vladislav V.
Published: March 2024

An approach for solving a variety of inverse coefficient problems for the Sturm–Liouville equation −y″ + q(x)y = ρ2y with a complex valued potential q(x) is presented. It is based on Neumann series of Bessel functions representations for solutions. With their aid the problem is reduced to a system of linear algebraic equations for the coefficients of the representations. The potential is recovered from an arithmetic combination of the first two coefficients. Special cases of the considered problems include the recovery of the potential from a Weyl function, inverse two-spectrum Sturm–Liouville problems, as well as the inverse scattering problem on a finite interval. The approach leads to efficient numerical algorithms for solving coefficient inverse problems. Numerical efficiency is illustrated by several examples.
Non-Hermitian molecular dynamics simulations of exciton–polaritons in lossy cavities
Authors: Sokolovskii Ilia , Groenhof Gerrit
Published: March 2024

The observation that materials can change their properties when placed inside or near an optical resonator has sparked a fervid interest in understanding the effects of strong light–matter coupling on molecular dynamics, and several approaches have been proposed to extend the methods of computational chemistry into this regime. Whereas the majority of these approaches have focused on modeling a single molecule coupled to a single cavity mode, changes to chemistry have so far only been observed experimentally when very many molecules are coupled collectively to multiple modes with short lifetimes. While atomistic simulations of many molecules coupled to multiple cavity modes have been performed with semi-classical molecular dynamics, an explicit description of cavity losses has so far been restricted to simulations in which only a very few molecular degrees of freedom were considered. Here, we have implemented an effective non-Hermitian Hamiltonian to explicitly treat cavity losses in large-scale semi-classical molecular dynamics simulations of organic polaritons and used it to perform both mean-field and surface hopping simulations of polariton relaxation, propagation, and energy transfer.
Clustering of chemically propelled nanomotors in chemically active environments
Authors: Khatri Narender , Kapral Raymond
Published: March 2024

Synthetic nanomotors powered by chemical reactions have been designed to act as vehicles for active cargo transport, drug delivery, and a variety of other uses. Collections of such motors, acting in consort, can self-assemble to form swarms or clusters, providing opportunities for applications on various length scales. While such collective behavior has been studied when the motors move in a chemically inactive fluid environment, when the medium in which they move is a chemical network that supports complex spatial and temporal patterns, through simulation and theoretical analysis we show that collective behavior changes. Spatial patterns in the environment can guide and control motor collective states, and interactions of the motors with their environment can give rise to distinctive spatiotemporal motor patterns. The results are illustrated by studies of the motor dynamics in systems that support Turing patterns and spiral waves. This work is relevant for potential applications that involve many active nanomotors moving in complex chemical or biological environments.
Design and performance of an ultrahigh vacuum spectroscopic-imaging scanning tunneling microscope with a hybrid vibration isolation system
Authors: Chung Pei-Fang , Venkatesan Balaji , Su Chih-Chuan , Chang Jen-Te , Cheng Hsu-Kai , Liu Che-An , Yu Henry , Chang Chia-Seng , Guan Syu-You , Chuang Tien-Ming
Published: March 2024

A spectroscopic imaging-scanning tunneling microscope (SI-STM) allows for the atomic scale visualization of the surface electronic and magnetic structure of novel quantum materials with a high energy resolution. To achieve the optimal performance, a low vibration facility is required. Here, we describe the design and performance of an ultrahigh vacuum STM system supported by a hybrid vibration isolation system that consists of a pneumatic passive and a piezoelectric active vibration isolation stage. We present the detailed vibrational noise analysis of the hybrid vibration isolation system, which shows that the vibration level can be suppressed below 10−8 m/sec/√Hz for most frequencies up to 100 Hz. Combined with a rigid STM design, vibrational noise can be successfully removed from the tunneling current. We demonstrate the performance of our STM system by taking high resolution spectroscopic maps and topographic images on several quantum materials. Our results establish a new strategy to achieve an effective vibration isolation system for high-resolution STM and other scanning probe microscopies to investigate the nanoscale quantum phenomena.
Temporal pre-pulse shaping in dual pulse laser produced plasma for the optimization of the EUV source in tin microdroplet system
Authors: Sizyuk V. , Sizyuk T. , Hassanein A.
Published: March 2024

Dual-laser beams interacting with small droplets of liquid tin are currently the most efficient systems for producing the 13.5 nm EUV photon radiation source required for the next generation microchips. Usually, EUV light is produced during the second main-pulse stage, while the pre-pulse (PP) is used for target preparation, i.e., droplet preheating, vaporization, and target deformation. However, the PP laser energy can be utilized more efficiently if the EUV producing plasma is being developed during the PP stage as well. In this work, we study the ways of optimization of the PP laser temporal shape to achieve conditions for maximum EUV output during the pre-pulse. The size of the deformed droplet is kept optimized for the following main laser pulse. Our simulations showed a significant increase in the EUV output at the pre-pulse stage when a ramping profile is used for the laser temporal shape. Using the ramped square pre-pulse produces 24% gain in the EUV output in comparison with the standard Gaussian temporal profile (i.e., regular Nd:YAG shape) for the same energy of the laser pulse.
Finite element simulations of double diffusion in a staggered cavity filled with a power-law fluid
Authors: Majeed Afraz Hussain , Mahmood Rashid , Liu Dong
Published: March 2024

Double diffusion refers to a phenomenon where two different components of a fluid (such as heat and mass) exhibit distinct diffusive behaviors. In this study, we employ finite element-based numerical simulations to investigate the phenomenon of double diffusion in a non-Newtonian fluid within a staggered cavity. Mathematically, this system can be understood by coupling the two-dimensional continuity, momentum, energy, and concentration equations. Since the governing equations have been written in a dimensionless form, Galerkin's finite element method is used to find a solution. The velocity profile and temperature are calculated in a function space of quadratic polynomials (P2), while the pressure is calculated in a linear (P1) finite element function space. Discrete systems of nonlinear algebraic equations are resolved through the implementation of Newton's method with appropriate damping and PARDISO solver in the inner loops for solving the sparse linear systems. In this work, the data are presented graphically in the form of streamlines, isotherms, iso-concentration, average Nusselt numbers, average Sherwood numbers, and kinetic energy distribution. Code validation and grid independence study are also provided. Moreover, convective mass transfer is significantly correlated with the Lewis number, as demonstrated by the results. As the power-law index increases, convection also exhibits enhanced as a means of transmitting heat and mass.
High-resolution velocity determination from particle images via neural networks with optical flow velocimetry regularization
Authors: Ji Kexin , Hui Xin , An Qiang
Published: March 2024

Particle image velocimetry (PIV) and optical flow velocimetry (OFV) are important velocity measurement methods in the field of fluid dynamics. Nevertheless, the conventional cross correlation-based PIV method is beset by diminished resolution, while the OFV method exhibits computational sluggishness and susceptibility to noise. These constraints have somewhat delimited the applicability of PIV and OFV techniques. Recent attempts have introduced deep learning-based methods for analyzing PIV images, offering high-resolution velocity fields with computational efficiency, but their accuracy needs improvement. This study proposes four neural networks based on the well-established FlowNetS. They incorporate two distinct velocity constraints, namely, first-order velocity smoothing regularization and second-order grad (curl)–grad (div) regularization. In the networks, these constraints are used either independently or in combination with optical flow conservation (OFC). The performances of the networks have been assessed on six different flow configurations, and the results show that the network with the second-order regularization markedly outperforms the original network across all flows, demonstrating an enhanced capacity to capture larger-scale vortices. The network with the first-order regularization also exhibits superior performance compared to the original network except in the case of cylinder flow. Unexpectedly, the introduction of the OFC constraints results in a decline in network performance. This anomaly may stem from the network's inherent capability to capture optical flow features, rendering the OFC constraint less effective in providing guidance. In summary, this study underscores the substantial potential of neural networks incorporated with judicious physical constraints in PIV applications, enabling the determination of high-resolution, high-accuracy flow fields.
Investigating strengthening and softening mechanisms in Al/Ni multilayers via molecular dynamics simulations of uniaxial compression
Authors: Schwarz Fabian , Spolenak Ralph
Published: March 2024

Due to their nanoscale features, nanometric multilayers can have a large variation in properties for varying bilayer heights. While the hardening at small feature sizes and the consequent softening at even smaller feature sizes have been observed for decades, the underlying mechanisms are still under debate. In this study, molecular dynamics uniaxial compression simulations are employed to study the mechanical properties of Al/Ni multilayers for bilayer heights h from 100 nm down to 5 nm. The effect of the microstructure on Young’s modulus and the yield strength was investigated. Furthermore, the mechanical properties of equiatomic and equivolumetric multilayers were compared. A comparison with experimental results from the literature showed good agreement. Both the hardening at intermediate bilayer heights as well as the softening at very small bilayer heights were observed. The results are discussed in the context of possible hardening and softening mechanisms. While the Hall–Petch effect with a h−1/2 scaling is not contradicted, it is shown that, although the underlying mechanisms are different, both the hardening as well as the softening are based on a general size effect with a scaling of ln(h)/h.
Four-wave mixing based spectral Talbot amplifier for programmable purification of optical frequency combs
Authors: Li Zijian , Xie Qijie , Zhang Yuanfei , Zhang Honghui , Huang Chaoran , Shu Chester
Published: March 2024

Optical frequency combs (OFCs) with programmable free spectral range and high optical carrier-to-noise ratio (CNR) play a crucial role in diverse research fields, including telecommunications, spectroscopy, quantum information, astronomy, sensing, and imaging. Unfortunately, the presence of stochastic noise often results in degraded optical CNR, leading to limited communication performance and measurement accuracy in comb-based systems. There is a lack of effective and flexible methods to improve the CNR of OFCs contaminated by broadband noise, hampering their widespread utilization. To address this challenge, we propose a four-wave mixing based spectral Talbot amplifier to purify OFCs flexibly. Our approach employs programmable spectral phase filters followed by a nonlinear Kerr medium to regenerate an OFC with superior CNR. In our experimental demonstration, we regenerated a 165-GHz spaced CNR enhanced OFC from a noise-dominated comb source spaced at 11 GHz, achieving up to ∼11-dB CNR improvement. The technique allows for a user-defined purification factor m to range from 7 to 15. Furthermore, our scheme demonstrates flexibility in adjusting the wavelengths of the regenerated comb lines via a tunable optical delay line without the need for a tunable seed laser. We also investigated the impact of the pump and signal on the regenerated comb experimentally and studied the influence of dispersion mismatch on the suppression of undesired sidebands numerically. Our proposed scheme presents a powerful alternative for programmable purification, manipulation, and detection of noise-dominated spectral waveforms.
Improvement of ferroelectric phase fraction in HfO2 via La-containing co-doping method
Authors: Tian Yushui , Zhou Yulu , Zhao Miao , Ouyang Yifang , Tao Xiaoma
Published: March 2024

In this work, the effect of co-doping lanthanide and VB group elements on the phase fraction of HfO2 is studied by first-principles calculations. A significant increase in the ferroelectric orthorhombic phase fraction can be achieved by doping La with Ta or Nb, which would enhance the ferroelectricity of HfO2. Furthermore, during the screening process, it is observed that oxygen vacancies coupled with dopants can promote the formation of the ferroelectric phase in HfO2. These studies and results provide valuable methods for improving the ferroelectric properties of HfO2.
Heterogeneous ice nucleation of salt solution in porous media
Authors: Lin Xin , Zhang Chao , Hu Shaojie , Chen Renpeng
Published: March 2024

Water ubiquitously exists with dissolved salt in both natural and engineered porous media, such as soil, rock, concrete, and tissue; therefore, its freezing temperature depression behavior is of particular interest to various scientific communities tackling with mechanics and physics of porous media. To date, it remains elusive which physical mechanism accounts for its freezing temperature depression and how dissolved ions affect it. Herein, a series of pore-scale experiments were designated to investigate the freezing temperature of salt solutions in tubes with varying pore diameters, pore solution volumes, solid–liquid interfacial areas, ion concentrations, and ion types. The results reveal two main findings: (i) the freezing temperature depression of pore solutions is governed by the heterogeneous ice nucleation (HIN) at the water–solid interface, as evidenced by the observation that the freezing temperature decreases with the decreasing solid–liquid interfacial areas, regardless of pore diameter and pore solution volume; (ii) the dissolved salts alter HIN processes via changing the osmotic potential across the ice embryo–liquid water interface, as indicated by the observation that the freezing temperature is mainly determined by the salt concentration irrespective of salt types. Furthermore, the classical nucleation theory model is adapted for the freezing behavior of pore solutions by including an osmotic potential term. The model shows excellent performance in capturing experimental data with various pore solution concentrations, further substantiating the HIN as the physical mechanism governing pore solution freezing.
A slow feature analysis approach for the optimization of collective variables
Authors: Gong Shuai , Zheng Zheng
Published: March 2024

Molecular dynamics simulations have become increasingly important in understanding the microscopic mechanisms of various molecular systems. However, the high energy barriers in complicated molecules often make it difficult to observe events of interest within a reasonable timescale. To address this issue, researchers have developed a variety of enhanced sampling methods to explore configuration space by adding bias potentials along the slowly changing collective variables (CVs). In this study, we have developed a new tool that combines slow feature analysis and biasing-enhanced sampling methods to identify effective CVs and enhance the sampling efficiency of configuration space. We have demonstrated the effectiveness of this tool through three general examples.
Deep learning-based data processing method for transient thermoreflectance measurements
Authors: Mao Yali , Zhou Shaojie , Tang Weiyuan , Wu Mei , Zhang Haochen , Sun Haiding , Yuan Chao
Published: March 2024

Pump–probe thermoreflectance has been commonly applied for characterizing the thermal properties of materials. Generally, a reliable and efficient non-linear fitting process is often implemented to extract unknown thermal parameters during the pump–probe thermoreflectance characterizations. However, when it comes to processing large amounts of data acquired from similar structural samples, non-linear fitting process appears to be very time-consuming and labor-intensive to search for the best fitting for every testing curve. Herein, we propose to apply deep learning (DL) approach to nanosecond transient thermoreflectance technique for high-throughput experimental data processing. We first investigated the effect of training set parameters (density and bounds) on the predictive performance of the DL model, providing a guidance to optimize the DL model. Then, the DL model is further verified in the measurement of the bulk sapphire, SiC, diamond samples, and GaN-based multilayer structures, demonstrating its capability of analyzing the results with high accuracy. Compared to the conventional non-linear fitting method (such as Global Optimization), the computation time of the new model is 1000 times lower. Such a data-driven DL model enables the faster inference and stronger fitting capabilities and is particularly efficient and effective in processing data acquired from wafer-level measurements with similar material structures.
Field-dependent Néel relaxation time of magnetic nanoparticles in AC excitation fields: Boundary field between Néel- and Brownian-dominant regions
Authors: Yoshida Takashi , Enpuku Keiji
Published: March 2024

We investigated the field-dependent Néel relaxation time of magnetic nanoparticles (MNPs) in an AC excitation field. Specifically, a fundamental component of the magnetization for immobilized MNPs was studied by numerical simulation while changing the frequency f and amplitude Hac of the field. From the simulation results, we clarified the Hac dependence of the effective Néel relaxation time τN,e and obtained an empirical expression for τN,e(Hac) for the first time. The expression was obtained for the cases when the angle of the easy axis of magnetization in MNPs is fixed and randomly distributed. Using the Hac dependencies of τN,e and the previously reported Brownian relaxation time τB,e, we showed that the behavior of suspended MNPs changes from Brownian-dominant to Néel-dominant when Hac increases, even when the MNP parameters are fixed, and we obtained an expression for the boundary field between them. Furthermore, we classified several types of responses for the suspended MNPs in the AC field using the magnitude relationship among τN,e(Hac), τB,e(Hac), and 1/(2πf). Finally, we experimentally verified the classification, and reasonable agreement was observed between the experiment and analysis. The results are useful for determining suitable MNP parameters and excitation conditions for various biomedical applications.
Influence of a hemispherical bulge on a flat wall upon the collapse jet of cavitation bubbles
Authors: Wang Xiaoyu , Zhang Cheng , Shen Junwei , Zhang Yuning , Xi Xinming , Zhang Yuning
Published: March 2024

Uneven sections along a wall cause local flow deterioration and can result in severe cavitation erosion. This paper investigates the influence of a hemispherical bulge on a flat wall upon the collapse dynamics of a cavitation bubble in terms of the Kelvin impulse theory and high-speed photography based on the Weiss theorem and the image method. The evolution and characteristics of the bubble collapse morphology, the flow field distribution, and the Kelvin impulse (in terms of strength, direction, and directional sensitivity) are analyzed for symmetric and asymmetric configurations. The results show that the bubble collapse jet can be divided into three scenarios: mainly induced by the hemispherical bulge, mainly induced by the flat wall, and broadly equivalent effects of both. Additionally, as the dimensionless distance between the bubble and the flat wall increases, the range of the jet attraction zone induced by the bulge initially increases, subsequently decreases, and ultimately converges to the diameter of the bulge. The maximum width of the attraction zone can reach 3.45 times the radius of the bulge. Finally, the spatial sensitivity of the jet direction is found to be significant near the junction between the flat wall and the bulge.
Intrinsic free carrier absorption limited THz generation from Bi2Te3 and Bi2Se3 topological insulators
Authors: Nivedan Anand , Kumar Sunil
Published: March 2024

We investigate the influence of intrinsic free charge carriers on the ultrashort THz pulse generation efficiency of three-dimensional topological insulators (3dTIs). Wavelength dependence of the optical penetration depth of the femtosecond excitation pulses is exploited to vary the excitation volume within Bi2Te3 and Bi2Se3 crystals and accordingly, the free carrier population, to contribute to THz attenuation. The standard free carrier absorption (FCA) formalism is inadequate to explain wavelength-dependent enhancement in the THz emission as observed in the experiments. Within a modified framework, the THz attenuation by FCA is accounted for accurately, which consistently explains the experimental results for samples having different carrier density and mobility. We conclude that the THz generation efficiency of 3dTIs can be enhanced by engineering samples with high carrier mobility and low intrinsic carrier density and by using excitation wavelengths of minimal penetration depth.
Vapor–liquid equilibrium and thermodynamic properties of saturated argon and krypton from Monte Carlo simulations using ab initio potentials
Authors: Ströker Philipp , Meier Karsten
Published: March 2024

Vapor–liquid equilibria and thermodynamic properties of saturated argon and krypton were calculated by semi-classical Monte Carlo simulations with the NpT + test particle method using ab initio potentials for the two-body and nonadditive three-body interactions. The NpT + test particle method was extended to the calculation of second-order thermodynamic properties, such as the isochoric and isobaric heat capacities or the speed of sound, of the saturated liquid and vapor by using our recently developed approach for the systematic calculation of arbitrary thermodynamic properties in the isothermal–isobaric ensemble. Generally, the results for all simulated properties agree well with experimental data and the current reference equations of state for argon and krypton. In particular, the results for the vapor pressure and for the density and speed of sound of the saturated liquid and vapor agree with the most accurate experimental data for both noble gases almost within the uncertainty of these data, a level of agreement unprecedented for many-particle simulations. This study demonstrates that the vapor–liquid equilibrium and thermodynamic properties at saturation of a pure fluid can be predicted by Monte Carlo simulations with high accuracy when the intermolecular interactions are described by state-of-the-art ab initio pair and nonadditive three-body potentials and quantum effects are accounted for.