bluuebunny/crossref_metadata_2025 huggingface dataset:
Adopting Sustainable Practices at an Island Ecotourism Destination in Sabah through a Sea Turtle Conservation Project
Authors: Chan Jennifer Kim Lian
Published: December 2023

This case centres on the sustainable ecotourism practices carried out on Libaran Island, Malaysia, through a sea turtle conservation project called the Walai Penyu Conservation Park. This widely recognised and award-winning project was launched and led by an ecotourism practitioner in collaboration with the island community, supported by governmental and non-governmental organisations. The project’s sustainable approaches have had significant positive impacts on the islands’ economy, environment, society, and culture. Among these impacts are the transformation of Libaran Island into an ecotourism destination, the preservation and promotion of local culture, and the generation of income for islanders through tourism job opportunities, village tour services, and handicraft sales. The project also enriches the pristine island environment by keeping its beaches clean, promoting recycling, and conserving endangered marine species (i.e., green turtles and hawksbill turtles). In summary, the project embodies the concept of sustainability and underscores the strong, interdependent relationships among the tourism industry, island communities, government agencies and NGOs.

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© The Author 2023
Path integral factorization and the gravitational effective action
Authors: Draper Patrick , Farkas Szilard , Karydas Manthos
Published: December 2023

We discuss the factorization and continuity properties of fields in the Euclidean gravitational path integral with higher dimension operators constructed from powers of the Riemann tensor. We construct the boundary terms corresponding to the microcanonical ensemble and show that the saddle point approximation to the path integral with a quasilocal energy constraint generally yields a saddle point with discontinuous temperature. This extends a previous result for the Euclidean Schwarzschild–de Sitter geometry in Einstein gravity and shows that it is robust against at least some types of quantum corrections from heavy fields. As an application, we compute the entropy of SdS in D = 4 using the BTZ method. Our result matches the entropy calculated using Wald’s formula.
Chilled sampling for uncertainty quantification: a motivation from a meteorological inverse problem
*
Authors: Héas P , Cérou F , Rousset M
Published: December 2023

Atmospheric motion vectors (AMVs) extracted from satellite imagery are the only wind observations with good global coverage. They are important features for feeding numerical weather prediction (NWP) models. Several Bayesian models have been proposed to estimate AMVs. Although critical for correct assimilation into NWP models, very few methods provide a thorough characterization of the estimation errors. The difficulty of estimating errors stems from the specificity of the posterior distribution, which is both very high dimensional, and highly ill-conditioned due to a singular likelihood, which becomes critical in particular in the case of missing data (unobserved pixels). Motivated by this difficult inverse problem, this work studies the evaluation of the (expected) estimation errors using gradient-based Markov chain Monte Carlo (MCMC) algorithms. The main contribution is to propose a general strategy, called here ‘chilling’, which amounts to sampling a local approximation of the posterior distribution in the neighborhood of a point estimate. From a theoretical point of view, we show that under regularity assumptions, the family of chilled posterior distributions converges in distribution as temperature decreases to an optimal Gaussian approximation at a point estimate given by the maximum a posteriori, also known as the Laplace approximation. Chilled sampling therefore provides access to this approximation generally out of reach in such high-dimensional nonlinear contexts. From an empirical perspective, we evaluate the proposed approach based on some quantitative Bayesian criteria. Our numerical simulations are performed on synthetic and real meteorological data. They reveal that not only the proposed chilling exhibits a significant gain in terms of accuracy of the AMV point estimates and of their associated expected error estimates, but also a substantial acceleration in the convergence speed of the MCMC algorithms.
Breakdown modes in nanosecond pulsed micro-discharges at atmospheric pressure
Authors: Chen Lei , Wu Hao , Chen Zili , Wang Yu , Yi Lin , Jiang Wei , Zhang Ya
Published: December 2023

Nanosecond pulse micro-discharges at atmospheric pressure have garnered attention because of their unique physics and numerous applications. In this study, we employed a one-dimensional particle-in-cell/Monte Carlo collision model coupled with an external circuit, using an unequal weight algorithm to investigate the breakdown processes in micro-discharges driven by pulses with voltage ranging from 1 kV to 50 kV at atmospheric pressure. The results demonstrate that nanosecond pulse-driven microplasma discharges exhibit different breakdown modes under various pulse voltage amplitudes. We present the discharge characteristics of two modes: ‘no-breakdown’ when the breakdown does not occur, and ‘runaway breakdown mode’ and ‘normal breakdown mode’ when the breakdown does happen. In the runaway breakdown mode, the presence of runaway electrons leads to a phenomenon in which the electron density drops close to zero during the pulse application phase. Within this mode, three submodes are observed: local mode, transition mode, and gap mode, which arise from different secondary electron generation scenarios. As the pulse voltage amplitude increases, a normal breakdown mode emerges, characterized by the electron density not dropping close to zero during the pulse application phase. Similarly, three sub-modes akin to those in the runaway breakdown mode exist in this mode, also determined by secondary electrons. In these modes, we find that electron loss during the pulse application phase is dominated by boundary absorption, whereas during the afterglow phase, it is dominated by recombination. Ion losses are primarily governed by recombination. These findings contribute to a better understanding of the discharge mechanisms during the breakdown process.
Robust RGB: D-SLAM in highly dynamic environments based on probability observations and clustering optimization
Authors: Liu Hailin , Tian Liangfang , Du Qiliang , Xu Wenjie
Published: December 2023

Visual simultaneous localization and mapping (SLAM) is the underlying support of unmanned systems. Currently, most visual SLAM methods are based on the static environment assumption so that dynamic objects in the camera’s field of view will seriously disrupt its working performance. In view of this, an RGB-D SLAM approach based on probability observations and clustering optimization for highly dynamic environments is proposed, which can effectively eliminate the influence of dynamic objects and accurately estimate the ego-motion of an RGB-D camera. The method contains a dual static map point detection strategy, which is carried out simultaneously in the current and previous frames. First, to enhance tracking robustness in highly dynamic environments, the probabilities of map points being static, calculated by both reprojection deviation and intensity deviation, are used to weight the cost function for pose estimation. Meanwhile, by taking the previous frames as a reference, a static velocity probability based on sparse scene flow is acquired to preliminarily recognize static map points and further improve the tracking accuracy. Then, an improved map point optimization strategy based on K-means clustering is designed, which effectively takes advantage of the clustering algorithm to refine the static map point labels while alleviating its stubborn problem. Finally, the experimental results on the TUM dataset and real scenes compared with the state-of-the-art visual SLAM methods illustrate that the proposed method achieves an extremely robust and accurate performance for estimating camera pose in highly dynamic environments.
Fusing sensitive degradation features with uncertainty analysis for RUL prediction of rotating machines
Authors: Li Yuxin , Liu Jie , Liu Baonan , Zhang Fengyuan , Yuan Xiaohui , Zhang Yongchuan
Published: December 2023

Recently, deep learning technology-based neural networks have been adopted for remaining useful life (RUL) prediction of rotating machines. However, there are still some shortcomings: (1) an individual degradation feature cannot sufficiently represent the degradation process, which has an adverse impact on the accuracy of prediction results; (2) most recurrent neural network-based prediction methods have difficulty in quantifying the uncertainty of the forecast results. In this paper, a fusing sensitive degradation features with uncertainty analysis for RUL prediction of rotating machines is proposed. Firstly, the statistical features contained in the vibration signal used to monitor the degradation of rotating equipment are extracted to construct the original feature set. Then, the weight coefficients of the monotonicity, correlation and robustness criteria are determined by the self-adjusting analytic hierarchy process. The sensitive features that describe the degradation process are selected from among the statistical features. Furthermore, the sensitive features are fed into residual networks and gated recurrent unit, and the spatial and temporal correlation of the features are considered to establish the health index (HI). Finally, the fitted HI is input into a Gaussian process regression model, and the prediction results with confidence intervals are obtained. To verify the effectiveness and superiority of the proposed method, two public bearing datasets and three model methods are used for comparative experiments.
Fault diagnosis method for planetary gearbox based on intrinsic feature extraction and attention mechanism
Authors: Zhan Shanning , Shao Ruipeng , Men Chengjie , Hao Huimin , Wu Zhifei
Published: December 2023

In a high-noise environment and with a limited number of faulty samples, it becomes challenging to extract a sufficient amount of useful fault information, which makes gear fault diagnosis more difficult. To address these issues, this paper proposes a fault diagnosis method for planetary gearboxes based on intrinsic feature extraction and attention mechanism. The method utilizes the complementary ensemble empirical mode decomposition algorithm to perform modal decomposition on the fault vibration signal, obtaining a series of modal components. By comparing and selecting the modal components that contain a significant amount of fault features, they are then transformed into two-dimensional images with time–frequency properties using wavelet transform. Additionally, a neural network model based on attention mechanism and large-scale convolution is proposed. The preprocessed images are inputted into the network for feature extraction. During this process, the large-scale convolution with residual structure maximizes the retention of effective feature information, while the attention network further filters the features. Finally, the selected features are used for fault classification. The model is validated using the gear datasets from Southeast University and the University of Connecticut. A comparison is made with the Pro-MobileNetV3, channel attention and multiscale convolutional neural network, multiscale dynamic adaptive residual network, and CBAM-ResNeXt50 models. It is found that the accuracy reaches 100% before adding Gaussian noise and 99.68% after adding noise, which is significantly higher than that of other models.
Designer artificial chiral kagome lattice with tunable flat bands and topological boundary states
Authors: Li Xueyan , Wang Dongli , Hu Hao , Pan Yi
Published: December 2023

The kagome lattice is a well-known model system for the investigation of strong correlation and topological electronic phenomena due to the intrinsic flat band, magnetic frustration, etc. Introducing chirality into the kagome lattice would bring about new physics due to the unique symmetry, which is still yet to be fully explored. Here we report the investigation on a two-dimensional chiral kagome lattice utilizing tight binding band calculation and topological index analysis. It is found that the periodic chiral kagome lattice would bring about a robust zero-energy flat band. Furthermore, in the Su–Schrieffer–Heeger type dimer-/trimerized breathing chiral kagome lattice with particular edge terminations, topological corner states or metallic edge states would appear, implying new candidates for the second-order topological insulator. We also proposed the construction strategy for such lattices employing the scanning tunneling microscope atom manipulation technique.
Ketoconazole-loading strategy to improve antifungal activity and overcome cytotoxicity on human renal proximal tubular epithelial cells
Authors: Coksu Irem , Bozkurt Yagmur , Akmayan Ilkgul , Demirci Hasan , Ozbek Tulin , Acar Serap
Published: December 2023

Ketoconazole (KTZ), an antifungal agent used to treat localized or systemic fungal infections by inhibiting ergosterol synthesis, exhibits restricted efficacy within eukaryotic cells owing to its elevated toxicity and limited solubility in water. This study aims to improve the biological activity and overcome cytotoxic effects in the renal system of the hydrophobic KTZ by incorporating it into poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) utilizing biomaterial nano-engineering techniques. KTZ-loaded PLGA NPs (KTZ-NPs) were prepared by single emulsion solvent evaporation method and characterized by using dynamic light scattering (DLS), electrophoretic light scattering (ELS), Fourier transform-infrared (FT-IR) spectroscopy and scanning light microscopy (SEM). Particle size and zeta potential of KTZ-NPs were determined as 182.0 ± 3.27 nm and −27.4 ± 0.56 mV, respectively. Antifungal activity was analyzed with the time-kill and top agar dilution methods on Candida albicans (C. albicans) and Aspergillus flavus (A. flavus). Both KTZ and KTZ-NPs caused a significant decrease in A. flavus cell growth; however, the same effect was only observed in time-killing analysis on C. albicans, indicating a methodological difference in the antifungal analysis. According to the top agar method, the MIC value of KTZ-NPs against A. flavus was 9.1 μg ml−1, while the minimum inhibition concentration (MIC) value of KTZ was 18.2 μg ml−1. The twofold increased antifungal activity indicates that nanoparticular drug delivery systems enhance the water solubility of hydrophobic drugs. In addition, KTZ-NPs were not cytotoxic on human renal proximal tubular epithelial cells (HRPTEpCs) at fungistatic concentration, thus reducing fungal colonization without cytotoxic on renal excretion system cells.
Predictable and adjustable broadband gold nanorods for photothermal effects and foldable performances
Authors: Chen Xi , Liu Jie , Li Xun , Cheng Zhiqun , Deng Tian-Song
Published: December 2023

Colloidal gold nanorods (GNRs) have demonstrated their potential to absorb light within specific wavelength bands and induce photothermal effects. However, the unpredictability and lack of adjustability in the broadband spectrum formed by the self-assembly of gold nanospheres or the coupling of various sizes of GNRs have posed significant challenges. To address this, we have developed broadband GNRs (BGNRs) with a predictable and adjustable extinction band in the visible and near-infrared regions. The BGNRs were synthesized by simply mixing GNRs with different aspect ratios, allowing for control over the bandwidths and positions of the extinction bands. Subsequently, the BGNRs were coated with silica and underwent surface modification. The resulting BGNRs@SiO2 were then mixed with either polydimethylsiloxane (PDMS) or polyvinylidene fluoride (PVDF) to create BGNRs@SiO2/PDMS (or PVDF) films. The BGNRs@SiO2/PDMS and BGNRs@SiO2/PVDF films both exhibit excellent photothermal performance properties. Additionally, the light absorption intensity of the BGNRs@SiO2/PVDF film linearly increases upon folding, leading to significantly enhanced photothermal performance after folding. This work demonstrates that plasmonic colloidal GNRs, without the need for coupling, can yield predictable and adjustable extinction bands. This finding holds great promise for future development and practical applications, particularly in the transfer of these properties to films.
Ultrasound stimulated piezoelectric barium titanate and boron nitride nanotubes in nonconductive poly-ε-caprolactone nanofibrous scaffold for bone tissue engineering
Authors: Çobandede Zehra , Çulha Mustafa
Published: December 2023

Nanomaterials can provide unique solutions for the problems experienced in tissue engineering by improving a scaffold’s physico-bio-chemical properties. With its piezoelectric property, bone is an active tissue with easy adaptation and remodeling through complicated mechanisms of electromechanical operations. Although poly(ε-caprolactone) (PCL) is an excellent polymer for bone tissue engineering, it is lack of conductivity. In this study, piezoelectric barium titanates (BaTiO3) and boron nitride nanotubes (BNNTs) are used as ultrasound (US) stimulated piezoelectric components in PCL to mimic piezoelectric nature of bone tissue. Electric-responsive Human Osteoblast cells on the scaffolds were stimulated by applying low-frequency US during cell growth. Biocompatibility, cell adhesion, alkaline phosphatase activities and mineralization of osteoblast cells on piezo-composite scaffolds were investigated. BaTiO3 or BNNTs as reinforcement agents improved physical and mechanical properties of PCL scaffolds. In vitro studies show that the use of BaTiO3 or BNNTs as additives in non-conductive scaffolds significantly induces and increases the osteogenic activities even without US stimulation. Although BaTiO3 is one of the best piezoelectric materials, the improvement is more dramatic in the case of BNNTs with the increased mineralization, and excellent chemical and mechanical properties.
Therapeutic effect and metabolic fingerprinting of triple-negative breast cancer cells following exposure to a novel pH-responsive, gambogic acid-loaded micelle
Authors: Da Mengting , Li Su , Yang Rui , Jia Zhen , Ma Yulian , Qi Fengxian , Zhao Jiuda , Shen Guoshuang , Chen Daozhen
Published: December 2023

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with a poor prognosis and lacks effective therapeutic targets. The use of gambogic acid (GA), a class of active ingredients in traditional Chinese medicine with anti-tumour potential, is limited in tumour therapy owing to its drawbacks and unclear organ toxicity. In this study, we used the pH-responsive amphiphilic block copolymer, PEOz-PCL, to create nanodrugs for GA delivery to MDA-MB-231 cells. The pH-responsive GA-loaded micelles were prepared through nanoprecipitation with a more homogeneous size. The average particle size was 42.29 ± 1.74 nm, and the zeta potential value was 9.88 ± 0.17 mV. The encapsulation rate was 85.06%, and the drug loading rate was 10.63%. The process was reproducible, and sustained release reached 80% in 96 h at acid pH 5.0. Furthermore, cellular tests using CCK-8, TUNEL, and flow cytometry revealed that pH-responsive GA-loaded micelles killed MDA-MB-231 cells more effectively and had much higher activity and targeting compared with free drugs. Metabolomic analysis of the changes in differential metabolites revealed that pH-responsive GA-loaded micelles may inhibit TNBC cells by causing amino acid anabolism, nucleotide metabolism, and glucose metabolism, as well as by affecting their energy sources. The study outcomes will help understand the mechanism of action and the therapeutic efficacy of pH-responsive GA-loaded micelles in vivo.
A road map to the blow-up for a Kirchhoff equation with external force
Authors: Ghisi Marina , Gobbino Massimo
Published: December 2023

It is well-known that the classical hyperbolic Kirchhoff equation admits infinitely many simple modes, namely time-periodic solutions with only one Fourier component in the space variables. In this paper we assume that, for a suitable choice of the nonlinearity, there exists a heteroclinic connection between two simple modes with different frequencies. Under this assumption, we cook up a forced Kirchhoff equation that admits a solution that blows-up in finite time, despite the regularity and boundedness of the forcing term. The forcing term can be chosen with the maximal regularity that prevents the application of the classical global existence results in analytic and quasi-analytic classes.
Research on variable stiffness asymmetrical resonant linear piezoelectric actuator based on multi-modal drive
Authors: He Liangguo , Yue Xukang , Dou Haotian , Ge Xinfang , Wan Zhikai , Qian An
Published: December 2023

In this paper, a linear piezoelectric motor with variable stiffness and asymmetric resonance is proposed, which is driven by a single harmonic signal. Working in the resonant state improve the output performance of the motor. Motor control is relatively simple and can realize reverse movement under the driving of second-order single harmonic signal. At the same time, the new motor can obtain different operating speed and step distance by changing the clamping position in front and back to meet the requirements of different loads and different working conditions and has strong applicability. By experiment, the first-order optimal operating frequency of the motor prototype at three different stiffness adjustment positions is 88 Hz, 90 Hz and 92 Hz respectively. Under the excitation of 240 Vp–p first-order resonance signal, the corresponding output speed of the motor prototype is 16.116 mm s−1, 20.457 mm s−1 and 25.015 mm s−1 respectively, and the corresponding displacement resolution is 0.18 mm, 0.22 mm and 0.27 mm respectively. When the stiffness adjustment positions is 2 mm, the maximum load of the motor prototype reaches 450 g. The second-order optimal operating frequency at the stiffness adjustment positions 1 mm is 601 Hz. Under the excitation of a 240 Vp–p second-order resonant signal, the reverse output speed of the motor prototype is 13.126 mm s−1, and the corresponding displacement resolution is 0.02 mm.
A versatile and high-load soft gripper enabled by vacuum-assisted bio-inspired interfacial adhesion
Authors: Sun Tianhui , Chen Wenqing , Li Jingyang , Li Xiaosong , Li Xinxin , Meng Yonggang , Tian Yu
Published: December 2023

Soft robotic grippers have gained considerable attention owing to their highly compliant, adaptive, and safe characteristics in a large variety of scenes, especially involving human-machine interactions. However, the low-stiffness nature of the soft material and the multi-finger gripping mechanism make soft grasping systems suffer in applications requiring relatively high load capacity and broad grasping adaptability. Despite extensive efforts to develop soft grippers with tunable stiffness by constructing smart materials and structures, the resultant load capacity is often compromised by sacrificing working efficiency or surface adaptability. In this work, we report a paradigm to design a versatile, high-load (>2 kg), and fast-response (<1 s) pneumatic soft gripper by strengthening the contact interface via bio-inspired controllable adhesion. A mushroom-shaped micropatterned dry adhesive surface is integrated with a soft pneumatic bidirectionally bendable actuator via a vacuum-assisted equal load-sharing design. This gripper extends the adaptable object diameter from 15 mm to infinity and significantly increases the load capacity to over 2 kg without compromising the original compliance. The multifunctional grasping modes and high load capacity are successfully demonstrated by grasping objects with diverse material components, various surface shapes.
Engineered IPMC sensors: modeling, characterization, and application towards wearable postural-tactile measurement
Authors: Nagel William S , Fakharian Omid , Aureli Matteo , Leang Kam K
Published: December 2023

This paper focuses on the modeling and development of engineered ionic polymer-metal composite (eIPMC) sensors for applications such as postural and tactile measurement in mechatronics/robotics-assisted finger rehabilitation therapy. Specifically, to tailor the sensitivity of the device, eIPMCs, fabricated using a polymer-surface abrading technique, are utilized as the sensing element. An enhanced chemoelectromechanical model is developed that captures the effect of the abrading process on the multiphysics sensing behavior under different loading conditions. The fabricated sensors are characterized using scanning electron microscopy imaging and cyclic voltammetry and chronoamperometry. Results show significant improvement in the electrochemical properties, including charge storage, double layer capacitance, and surface conductance, compared to the control samples. Finally, prototype postural-tactile finger sensors composed of different eIPMC variants are created and their performance validated under postural and tactile experiments. The tailored eIPMC sensors show increased open-circuit voltage response compared to control IPMCs, with 7.7- and 4.7-times larger peak-to-peak bending response under postural changes, as well as a 3.2-times more sensitive response under compression during tactile loading, demonstrating the feasibility of eIPMC sensors.
Dynamically reprogrammable stiffness in gecko-inspired laminated structures
Authors: Chen Kai Jun , Sakovsky Maria
Published: December 2023

Adaptive structures are of interest for their ability to dynamically modify mechanical properties post fabrication, enabling structural performance that is responsive to environmental uncertainty and changing loading conditions. Dynamic control of stiffness is of particular importance as a fundamental structural property, impacting both static and dynamic structural performance. However, existing technologies necessitate continuous power to maintain multiple stiffness states or couple stiffness modulation to a large geometric reconfiguration. In this work, reversible lamination of stiff materials using gecko-inspired dry adhesives is leveraged for bending stiffness control. All stiffness states are passively maintained, with electrostatic or magnetic actuation applied for ∼1 s to reprogram stiffness. We demonstrate hinges with up to four passively maintained reprogrammable states decoupled from any shape reconfiguration. Design guidelines are developed for maximizing stiffness modulation. Experimentally, the proposed method achieved a stiffness modulation ratio of up to 14.4, with simulations showing stiffness modulation ratios of at least 73.0. It is anticipated that the stiffness reprogramming method developed in this work will reduce energy requirements and design complexity for adaptation in aerospace and robotics applications.
Nonlinear dynamics of 3D superconducting maglevs with six degrees of freedom: dependence on magnetization strategy and disturbance type
Authors: Huang Chenguang , Diao Yunfei , Liu Yi , Chen Long , Liu Wei , Tao Weifeng , Wang Fusheng
Published: December 2023

Based on the heat diffusion equation, Maxwell’s equations, and translational and rotational dynamic equations, we establish and theoretically validate an electromagnetic-thermal-mechanical coupling model to analyze the levitation performance during normal operation and the nonlinear dynamic behavior under disturbance for 3D maglev systems composed of a six-degree-of-freedom bulk superconductor (SC) and a Halbach-type guideway of permanent magnets (PMs) with different magnetization strategies and different types of disturbances, as well as the change rules of magnetic force and torque during translational or rotational cycle movement. In order to ensure the system security, we propose a generalized electromagnetic restoring force model to theoretically analyze the stability of the SC moving along the directions of various degrees of freedom. The results show that after being disturbed, the SC vibrates along the direction of each degree of freedom, and the vibration center, i.e. equilibrium position, will drift along each vibration direction. With time increasing, the equilibrium position will appear periodically on both sides of the working position. Compared to zero-field cooling magnetization, field cooling magnetization enables the SC to trap more flux in its interior to alleviate the drift phenomenon and reduce the energy loss. This advantage can be further enhanced by adding an extra step of preloading treatment. For the lateral motion, the system has one stable focus point and two unstable saddle points. Whether the system at these saddle points is stable depends on the direction of disturbance-induced velocity. For the rotational motion, the system has only one stable focus point, which means that regardless of the type of disturbance, the SC will finally come back to its stable equilibrium position. Besides, the stability is related to the axis around which the SC rotates, and rotating around the longitudinal axis is more likely to generate larger magnetic force, torque and local temperature rise. Either field cooling magnetization or preloading treatment can effectively improve system stability.
Analogue tachyons in SNAIL transmission lines
Authors: Katayama Haruna , Hatakenaka Noriyuki , Fujii Toshiyuki , Blencowe Miles P
Published: December 2023

Tachyons are hypothetical particles with imaginary mass that travel faster than light. However, methods to experimentally verify whether tachyons exist are lacking. Here, we propose a novel scheme to create analogue tachyons using a transmission line composed of superconducting nonlinear asymmetric inductive elements and to detect them by controlling the wavenumber in order to extend their lifetime. In particular, we numerically demonstrate the exotic property of tachyons where their velocity increases with decreasing energy. Our proposal offers a promising approach to understanding tachyon condensation, which is crucial for elucidating the origins of the Universe, in a realizable laboratory system.
Pressure dynamics of an internal shock wave emission inside a water droplet and potential cavitation
Authors: Tang Mao , Zhang Hongchao , Lu Jian
Published: December 2023

Shock reflected by a spherical interface is involved in shock-droplet interaction. Here, we investigate the pressure dynamics of an internal spherical shock wave and the potential cavitation inside a spherical water droplet. We conduct hydrodynamic simulation and employ the linear geometrical acoustics approximation to analyze the negative pressure and the wavefront at different intervals d between the source point of the shock and the droplet surface. Studies indicate that the negative pressure at a very large d is primarily attributed to the focusing effect of the droplet surface, whereas the collision of the reflected waves contributes to negative pressure at a small d. The caustic, which is the locus of the cusps (singular points) on the shock wavefront is determined by the parametric equations. Notably, the caustic also has singular points owing to the off-axis reflection. Finally, we evaluate the cavitation inside the droplet. Cavitation occurs on the opposite side of the droplet and moves away from the surface with d increasing, which agrees with previous experimental results. Additionally, we demonstrate that cavitation can occur with less damage to the droplet compared to a planar shock impact on a water droplet.
Nonlinear electrostatic kelvin-helmholtz shock waves in a viscous electron-positron-ion plasma with non-maxwellian distribution
Authors: Ahmad Mushtaq , Ahmad Zulfiqar , Farooq M , Usman S
Published: December 2023

A theoretical investigation is carried out for nonlinear electrostatic Kelvin-Helmholtz (K-H) shock waves in a magnetized electron-positron-ion viscous plasma in the presence of transport equations and non-Maxwellian particles by following the generalized (r, q) distribution function. The propagation of electrostatic K-H modes are studied both in the presence of trapped and free electrons. The nonlinear analysis with inclusion of plasma transport properties (magnetic viscosity and heat conduction) lead to nonlinear electrostatic K-H mode in the form of shock like waves by solving the modified Burgers’ equation. The electrostatic K-H shocks are investigated numerically with effect of different plasma parameters such as shear velocity and non-Maxwellian distributed particles. It is observed that the striking features (viz., amplitude and width of dissipative shock through the solution of Burgers’ equation) of the K-H mode are significantly modified by the effects of non-thermality of electrons and positrons both at shoulder and tails along with shear velocity due to viscosity. The relevancy of our work to the observations in space (viz., cometary comae and earth’s ionosphere), astrophysical (viz., pulsars) and laboratory (viz., solid-high intense laser plasma interaction experiments) plasmas is highlighted.
Diffuse reflectance and photoluminescence spectroscopic investigations of Sr2RE8(SiO4)6O2 (RE = rare earth) apatites
Authors: Viegas Jéssica I , Martins Guilherme M , Dias Anderson
Published: December 2023

Apatite-type compounds have attracted attention due to their flexible crystalline structure besides high chemical stability, which increases the interest in understanding and modifying their properties to achieve the requirements for applications in catalysis and energy devices. In order to attend these demands, this paper investigates the optical properties of apatite-type Sr2
RE
8(SiO4)6O2 ceramics (RE = rare earth) by using diffuse reflectance and photoluminescence spectroscopies. Intraconfigurational f-f transitions, charge transfer bands, and energy gaps were identified and detailed discussed in terms of their relationships with the structural features of the rare earth apatites. Although all materials have the same hexagonal space group (P6
3
/m, # 176), the band gaps varied between 3.51 and 3.95 eV, for Eu- and Yb-containing apatites, respectively, showing the influence of their ionic radii and their electronic configurations on this property. In this sense, diffuse reflectance spectroscopy emerges as a powerful tool to study the optical properties of rare earth-containing materials as a complementary technique to photoluminescence spectroscopy. In this work, these techniques were discussed in association, which allowed us to provide a complete set of optical information that improves the understanding of apatite-type materials, as required in advanced technological demands.
Millimeter-wave metalens with extended depth of focal on the short focal length
Authors: Zhang Quansheng , Guo Di , Shen Changsheng , Chen Zhaofu , Bai Ningfeng
Published: December 2023

Millimeter wave (mm-wave) metalens has shown significant progress in recent years. However, the existing works in the literature on the extended depth of focal (EDOF) metalens present limitations for mm-waves. More specifically, the good performance of the EDOF requires a focal length larger than the radius of the metalens, which limits its miniaturization applications. In this work, mm-wave metalens with EDOF on the short focal length was proposed. The focus distribution was equally divided and the spin Hall effect was employed to guarantee the uniform focus intensity. From our analysis, it was demonstrated that the designed metalens can work at mm-wave frequencies and also achieve extended focal depth at half the metalens’ radius. The proposed metalens has the unique characteristics of short focal length (The focal diameter ratio is 0.36) with EDOF. Moreover, it can be used in the mm-wave field for short-distance imaging and detection, also the development of high-power metalens applications may be facilitated.
A Sine-coupled model for constructing N-dimensional non-degenerate discrete hyperchaotic map
Authors: Huang Lilian , Li Chuang , Yang Yan , Mao Yanhao
Published: December 2023

The non-degenerate hyperchaotic systems with the maximum number of positive Lyapunov exponents (LEs) typically have better ergodicity, pseudo randomness, and stronger anti-degeneration property. Therefore, designing non-degenerate hyperchaotic maps with complex dynamics has attracted increasing attention from various research fields in recent years. By introducing the sine function, this paper proposes a construction model of N-dimensional non-degenerate discrete hyperchaotic map. To verify the effectiveness of this model, we provide three sub-maps of different dimensions based on this model as illustrative examples, and the dynamic behavior is explored using multiple numerical measures. The results demonstrate that the sub-maps with concise symmetric structures have complex dynamics, such as ultra-wide non-degenerate hyperchaotic parameter range, state transition phenomenon, and multistability. In particular, coexisting symmetric attractors and quasi-periodic curves switch periodically with the change of initial value. Furthermore, the hyperchaotic sequences generated by the three sub-maps have excellent performance, and the NIST test also further verifies the super randomness and unpredictability of these sequences. Finally, through the DSP hardware platform, the physical realizability of the sub-maps is verified successfully.
The enhanced adsorption mechanism of ethanol on (Fe-Zn) bimetallic-doped Ti2CO2 monolayers: a DFT study
Authors: Zhao Bing , Liu Xin , Zhang Hanmei , Su JiaHui , Feng Yue , Shen Tao
Published: December 2023

Ti2C as a new two-dimensional layered MXene material has a certain potential in the sensor field. The adsorption properties of gases (NH3, NO, ethanol, CO) on intrinsic Ti2CO2 and transition metal atoms (Fe, Zn) doped Ti2CO2 were studied by density functional theory systematically. The geometric structure, adsorption energy, molecular dynamics, energy band structure, density of states, charge transfer, and differential charge density of these molecules at five sites of intrinsic Ti2CO2, Fe-doped Ti2CO2, Zn-doped Ti2CO2, FeZn-adjacent co-doped Ti2CO2 and FeZn-pair co-doped Ti2CO2 were analyzed. The results show that the activity of the substrate can be improved by the introduction of Fe-Zn transition metals. The high adsorption energy of ethanol gas at (A) FeZn site is −1.98eV with the short adsorption distance. The high charge transfer between the metal co-doped Ti2CO2 substrate and ethanol gas was also found. The results suggest that the Fe-Zn bimetallic-doped Ti2CO2 monolayer may be a potential sensing material for the detection of ethanol gas.
The linear response theory approach to the sub-GeV dark matter in the Sun
Authors: Liang Zheng-Liang , Zhang Ping
Published: December 2023

In recent years, the importance of the electronic in-medium effect
in the sub-GeV dark matter (DM) direct detection has been recognized
and a coherent formulation of the DM-electron scattering based on
the linear response theory has been well established in the literature.
In this paper, we apply the formulation to the scattering between
DM particles and solar medium, and it is found that the dynamic structure
factor inherently incorporate the particle-particle scattering and
in-medium effect. Using this tool and taking a benchmark model as
an example, we demonstrate how the in-medium effect affects the scattering
of DM particles in the Sun, in both the heavy and the light mediator
limit. Formulae derived in this work lay the foundation for accurately
calculating the spectra of solar-accelerated DM particles, which is
of particular importance for the detection of DM particles via plasmon
in semiconductor targets.
General parallel cosmology
Authors: Aguiar Gomes Débora , Beltrán Jiménez Jose , Koivisto Tomi S.
Published: December 2023

General (tele)parallel Relativity, G∥R, is the relativistic completion of Einstein's theories of gravity. The focus of this article is the derivation of the homogeneous and isotropic solution in G∥R. The first-principles derivation, based on a non-trivial realisation of the symmetry, supersedes and unifies previous constructions of Riemannian and teleparallel cosmologies, and establishes the uniqueness of the physical solution. The constitutive law and the form of the material and inertial source currents is presented in the tensor (Palatini) formalism and adapted to the cosmological background, which exhibits novel features absent in the previously studied, static solutions to the theory. The results are contrasted with those in incomplete theories, such as sitting at the three corners of the geometrical trinity which correspond to particular reference frames in G∥R.
A thermodynamical model of non-deterministic computation in cortical neural networks
Authors: Stoll Elizabeth A
Published: December 2023

Neuronal populations in the cerebral cortex engage in probabilistic coding, effectively encoding the state of the surrounding environment with high accuracy and extraordinary energy efficiency. A new approach models the inherently probabilistic nature of cortical neuron signaling outcomes as a thermodynamic process of non-deterministic computation. A mean field approach is used, with the trial Hamiltonian maximizing available free energy and minimizing the net quantity of entropy, compared with a reference Hamiltonian. Thermodynamic quantities are always conserved during the computation; free energy must be expended to produce information, and free energy is released during information compression, as correlations are identified between the encoding system and its surrounding environment. Due to the relationship between the Gibbs free energy equation and the Nernst equation, any increase in free energy is paired with a local decrease in membrane potential. As a result, this process of thermodynamic computation adjusts the likelihood of each neuron firing an action potential. This model shows that non-deterministic signaling outcomes can be achieved by noisy cortical neurons, through an energy-efficient computational process that involves optimally redistributing a Hamiltonian over some time evolution. Calculations demonstrate that the energy efficiency of the human brain is consistent with this model of non-deterministic computation, with net entropy production far too low to retain the assumptions of a classical system.
Free Energy of Anisotropic Strangeon Stars
Authors: Chen Shichuan , Gao Yong , Zhou Enping , Xu Renxin
Published: December 2023

Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation? This is actually relevant to the equation of state of cold supra-nuclear matter, which is still under hot debate. Enormous energy is surely needed to understand various observations, such as γ-ray bursts, fast radio bursts and soft γ-ray repeaters. In this paper, the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars, with two anisotropic models to calculate in general relativity. It is found that huge free energy (>1046 erg) could be released via starquakes, given an extremely small anisotropy ((p
t − p
r)/p
r ∼ 10−4, with p
t/p
r the tangential/radial pressure), implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.
Evaluating and benchmarking the EEG signal quality of high-density, dry MXene-based electrode arrays against gelled Ag/AgCl electrodes
Authors: Erickson Brian , Rich Ryan , Shankar Sneha , Kim Brian , Driscoll Nicolette , Mentzelopoulos Georgios , Fernandez-Nuñez Guadalupe , Vitale Flavia , Medaglia John D
Published: December 2023

Objective. To evaluate the signal quality of dry MXene-based electrode arrays (also termed ‘MXtrodes’) for electroencephalographic (EEG) recordings where gelled Ag/AgCl electrodes are a standard. Approach. We placed 4 × 4 MXtrode arrays and gelled Ag/AgCl electrodes on different scalp locations. The scalp was cleaned with alcohol and rewetted with saline before application. We recorded from both electrode types simultaneously while participants performed a vigilance task. Main results. The root mean squared amplitude of MXtrodes was slightly higher than that of Ag/AgCl electrodes (.24–1.94 uV). Most MXtrode pairs had slightly lower broadband spectral coherence (.05 to .1 dB) and Delta- and Theta-band timeseries correlation (.05 to .1 units) compared to the Ag/AgCl pair (p < .001). However, the magnitude of correlation and coherence was high across both electrode types. Beta-band timeseries correlation and spectral coherence were higher between neighboring MXtrodes in the array (.81 to .84 units) than between any other pair (.70 to .75 units). This result suggests the close spacing of the nearest MXtrodes (3 mm) more densely sampled high spatial-frequency topographies. Event-related potentials were more similar between MXtrodes (ρ ⩾ .95) than equally spaced Ag/AgCl electrodes (ρ ⩽ .77, p < .001). Dry MXtrode impedance (x̄ = 5.15 KΩ cm2) was higher and more variable than gelled Ag/AgCl electrodes (x̄ = 1.21 KΩ cm2, p < .001). EEG was also recorded on the scalp across diverse hair types. Significance. Dry MXene-based electrodes record EEG at a quality comparable to conventional gelled Ag/AgCl while requiring minimal scalp preparation and no gel. MXtrodes can record independent signals at a spatial density four times higher than conventional electrodes, including through hair, thus opening novel opportunities for research and clinical applications that could benefit from dry and higher-density configurations.
Economically optimized design point of high-field stellarator power-plant
Authors: Prost Victor , Volpe Francesco A.
Published: December 2023

High temperature superconductors (HTSs) expand the design space of stellarator power-plants (PPs) toward high magnetic fields B, enabling compact major radii R. The present paper scans the space of B, R and other design parameters, finding solutions that are promising from a physics and engineering standpoint, while minimizing the capital cost of the PP and the levelized cost of fusion electricity. Similarly, it identifies minimum-cost design points for next-step burning plasma stellarator experiments of fusion gain

1
<
Q
<
10

. The study assumes advanced stellarator configurations of reduced aspect ratio, heated by neutral beam injection. Plasma-facing, flowing liquid metal (LM) walls protect it from high heat and neutron fluxes. The study relies on analytical first-principle calculations, and established zero-dimensional (0D) empirical scaling laws. Power flows are illustrated by Sankey diagrams. Plasma operating contours are used to determine the reactor’s start-up path. Sensitivity analyses are conducted to identify the most critical reactor parameters within physics, engineering and costing, quantifying their influence on the economics of the PPs. Such 0D study suggests that the assumed next generation HTS, flowing LM walls, and advances in compact plasma configurations could lead to an ignited stellarator PP of aspect ratio

A
∼
4

,

R
⩽
4

 m, B > 9 T, and normalized plasma pressure

β
∼
5
%

which would minimize both the cost of electricity and capital cost while achieving a net electric power of about 1 GW.
Anisotropy of field-controlled shear viscosity of dipolar fluids
Authors: D Fjeldstad Christopher , Pousaneh Faezeh , Troncoso Roberto E , de Wijn Astrid S
Published: December 2023

We numerically study the anisotropic viscous response of dipolar hard spheres in the presence of an electric field. We find that the shear viscosity is sensitive to both the strength and orientation of the field relative to the shearing direction. The effect on the viscosity is strongest when the field is oriented in the shear gradient direction. We investigate the structure of the fluid in detail to explain the mechanism for the changes in viscosity, and show that the reorientation of chain-like clusters plays a crucial role. We show that the anisotropy arises from the polarization of the fluid induced by the field, leading to the orientation of chain-like clusters along the direction of the field.