bluuebunny/crossref_metadata_2025 huggingface dataset:
What Challenges for Global Development Research are Posed by a More Decolonial Approach? Colonial Genealogies and Responses
Authors: Camfield Laura
Published: December 2024

The increasing appetite for decolonial approaches in development research challenges conventional methodologies rooted in colonial legacies. While the relationship between colonialism and development is well documented, the colonial underpinnings of key research methods, such as surveys and big data, have received less attention. This paper critically examines how these methods, as tools of colonial governance, continue to predominate in development research and reduce the space for decolonial alternatives. It highlights the continuities between colonial-era data practices, such as population censuses, and contemporary methods like big data, arguing that they can perpetuate power asymmetries and “data colonialism”. In contrast, decolonial methodologies emphasise reflexivity, relationality, and the active participation of indigenous communities. However, there is potential for these methods to be co-opted or instrumentalized within the global development research ecosystem, if they are adopted without a critical understanding of the relationship between power and knowledge. This paper evaluates emerging decolonial alternatives, including methodologies grounded in indigenous knowledge systems and ethical frameworks such as Ubuntu and relationality, assessing their potential to resist such co-option. The paper concludes by arguing that while decolonial research offers a more holistic and ethically grounded alternative to conventional methods, its influence is limited by the persistence of deeper structural inequities. These include the dominance of Northern epistemologies and the commodification of research methods and expertise within academia. Future development research must not only adopt decolonial approaches but also actively deconstruct the existing power dynamics within the field to create equitable and inclusive knowledge systems.
Very low subthreshold swing normally-off diamond FET and its logic inverters
Authors: Liang Yuesong , Wang Wei , Niu Tianlin , Chen Genqiang , Wang Fei , He Shi , Zhang Minghui , Wang Yanfeng , Wen Feng , Wang Hong-Xing
Published: December 2024

A normally-off field effect transistor with 15 nm LaB6 gate material directly deposited on hydrogen-terminated diamond surface has been fabricated and characterized. The reason for the normally-off operation could be attributed to the low work function of LaB6 layer, which can deplete holes in the channel. Due to the formation of C–B bond of interface and the thin thickness of LaB6, the subthreshold swing is as low as 70.6 mV/dec and interface state density is as low as 2 × 1011 cm−2eV−1. The maximum drain current density (IDSmax), extrinsic transconductance (Gm), threshold voltage (VTH), and on/off ratio for the device with 8-μm gate length are −60 mA/mm, 5 mS/mm, −1.1 V, and 109, respectively. The low-field mobility (μ0) without vertical-field degradation is 187 cm2/V s. The trapped charge density and fixed charge density are 8.75 × 1011 and 1.26 × 1012 cm−2, respectively. The LaB6/H-diamond logic inverters coupling with different load resistors show distinct inversion characteristics with a peak gain of 4.7 V/V.
How graph neural network interatomic potentials extrapolate: Role of the message-passing algorithm
Authors: Kang Sungwoo
Published: December 2024

Graph neural network interatomic potentials (GNN-IPs) are gaining significant attention due to their capability of learning from large datasets. Specifically, universal interatomic potentials based on GNN, usually trained with crystalline geometries, often exhibit remarkable extrapolative behavior toward untrained domains, such as surfaces and amorphous configurations. However, the origin of this extrapolation capability is not well understood. This work provides a theoretical explanation of how GNN-IPs extrapolate to untrained geometries. First, we demonstrate that GNN-IPs can capture non-local electrostatic interactions through the message-passing algorithm, as evidenced by tests on toy models and density-functional theory data. We find that GNN-IP models, SevenNet and MACE, accurately predict electrostatic forces in untrained domains, indicating that they have learned the exact functional form of the Coulomb interaction. Based on these results, we suggest that the ability to learn non-local electrostatic interactions, coupled with the embedding nature of GNN-IPs, explains their extrapolation ability. We find that the universal GNN-IP, SevenNet-0, effectively infers non-local Coulomb interactions in untrained domains but fails to extrapolate the non-local forces arising from the kinetic term, which supports the suggested theory. Finally, we address the impact of hyperparameters on the extrapolation performance of universal potentials, such as SevenNet-0 and MACE-MP-0, and discuss the limitations of the extrapolation capabilities.
Why do similar 1D-polyhedron-chain copper chloride semiconductors have 2-order-distinct luminescence quantum efficiencies?
Authors: Miao Ruonan , Wu Huaxin , Liang Tianyuan , Fan Jiyang
Published: December 2024

The “green” copper halides with one-dimensional polyhedron chains are very interesting novel semiconductors. These weakly interacting parallel quantum wires (1D polyhedron chains) play key roles in their photophysical properties. Unlike Cs3Cu2I5, which has been much investigated, its homologous compounds Cs3Cu2Cl5 and CsCu2Cl3 remain less studied and their properties are controversial. Both of them are composed of specific 1D-polyhedron-chains. We report the synthesis and comparatively study the photophysical properties of the single crystals of Cs3Cu2Cl5 and CsCu2Cl3. They exhibit green and orange emissions, respectively. Surprisingly, their luminescence quantum efficiencies have a giant difference of over two orders of magnitude (96.7% vs 0.7%). The CsCu2Cl3 crystals exhibit much slower radiative transition and substantially faster nonradiative transition. The experiment in combination with the density functional theory calculation reveals that their 1D-polyhedron-chains have distinct bonding structures and degrees of distortion. This leads to different distributions of electron wave functions and different concentrations of carrier-trapping chlorine vacancies, which account for their highly contrasted quantum efficiencies. The CsCu2Cl3 and Cs3Cu2Cl5 crystals exhibit easy phase transition between each other driven by the changed temperature or ethanol erosion owing to their resembling skeleton structures of 1D polyhedral chain.
Broadband and omnidirectional attenuation of bulk waves in transversely isotropic soil by cross-like metamaterials
Authors: Cai Runcheng , Jin Yabin , Pennec Yan , Djafari-Rouhani Bahram , Rabczuk Timon , Zhuang Xiaoying
Published: December 2024

Metamaterials with bandgap properties have been widely studied and applied in the attenuation of surface and bulk waves propagating in the soil. However, most of the studies consider soil as the isotropic medium and ignore the general anisotropy property from the practical point of view. In this work, we consider the transversely isotropic constitutive model of soil and propose a cross-like metamaterial consisting of concrete inclusion and rubber coating to achieve broadband attenuation for omnidirectional bulk waves. The proposed cross-like metamaterials have more and wider bandgaps compared to circle and square metamaterials, and they have better wave attenuation performance in transversely isotropic soil with higher degrees of anisotropy. The transmission spectra of cross-like metamaterials demonstrate the wave attenuation effect of bandgaps. Furthermore, we build the full-scale transmission model considering the subway tunnel condition and demonstrate the practical wave attenuation performance of cross-like metamaterials in frequency and time domains. We also find that a larger depth of the metamaterial region will enhance wave attenuation in the bandgaps while considering rubber viscosity can enhance wave attenuation in the overall frequency ranges. The variations of omnidirectional bandgaps with rubber thickness, geometric parameters, and hollow concrete sizes are discussed. This study presents an appropriate way to design metamaterials for broadband omnidirectional bulk wave attenuation in transversely isotropic soil, which can be easily extended to other anisotropic media.
Study of the N2 vibrational relaxation behaviors via the CO rovibrational thermometry
Authors: He Dong , Liu Tielou , Li Renjie , Hong Qizhen , Li Fei , Sun Quanhua , Si Ting , Luo Xisheng
Published: December 2024

This paper performed a comprehensive study of the thermal nonequilibrium effects of CO/Ar mixtures with various degrees of N2 additions and probed the N2 relaxation behaviors via the CO rovibrational thermometry. The rovibrational temperature time histories of shock-heated CO/N2/Ar mixtures were measured via a laser-absorption technique, and the corresponding vibrational relaxation data were summarized at 1890–3490 K. The measured results were compared with predictions from the Schwartz–Slawsky–Herzfeld (SSH) formula and the state-to-state (StS) approach (treating CO and N2 as pseudo-species). The vibrational state-specific inelastic rate coefficients for N2–N2 collisions were supplemented using the mixed quantum–classical calculations. The StS predictions, informed by experimentally measured pressures, showed good agreement with experimental data. Additionally, the impact of coupling between flow dynamics and StS kinetics behind reflected shock waves was evaluated using two different one-dimensional approaches, which provide limiting bounds (accounting for unsteady flow and end wall effects) in post-reflected shock flow conditions. Moreover, the vibrational relaxation data of the N2–N2 system were modified via sensitivity analysis to improve the performance of the SSH formula. Further analysis highlighted that the vibration–vibration–translation path provides an efficient way for vibrational energy transfer between CO and N2, resulting in almost the same vibrational temperature time histories for CO and N2. Therefore, the N2 relaxation behaviors can be characterized by the CO rovibrational thermometry, considering N2 is infrared inactive. Finally, the heat sink effects and the reflected-shock-bifurcation phenomena were highlighted.
Limiting and achievable efficiencies of solar-to-hydrogen in heterojunction photocatalysts
Authors: Li Quan , Zhao Guangting , Huang Hao , Tao Maoxiang , Wang Ling-Ling , Zhu Xiaojun , Luo Nan-Nan
Published: December 2024

Although two-dimensional heterojunctions are regarded as potential photocatalysts for water splitting due to their high solar-to-hydrogen (STH) efficiency, it remains unclear whether there is a theoretical limit to the STH efficiency of such materials. This uncertainty significantly hinders the design and optimization of these photocatalytic materials. Here, the limiting efficiencies of different types of heterojunctions are investigated by developing a user-friendly computational program and by creatively utilizing mapping to visualize the changes in STH efficiency as a function of overpotentials for water redox reactions or bandgap widths. From the efficiency maps, it is clear that the STH efficiencies of type-I, type-II, and Z-scheme heterojunctions all exhibit a limiting value. Specifically, the limiting efficiencies of type-I and type-II heterojunctions are the same, both at 17.12%, while the efficiency of Z-scheme heterojunctions is higher, reaching 37.83%. Taking type-I γ-SnS/hBN heterojunction as a case study, first-principles calculations show that the limiting efficiency of type-I heterojunctions is readily achievable. Through a literature survey and data analysis, it is found that the limiting efficiency of type-II heterojunctions is also attainable, whereas that of Z-scheme heterojunctions is quite challenging. These results are consistent with the predictions from the STH efficiency maps. This work not only confirms the existence of an STH efficiency limit in different types of heterojunctions but also provides theoretical guidance for the rational design of heterojunction photocatalysts.
Narrow-bandgap titanium sesquioxide with resonant metasurfaces for enhanced infrared absorption
Authors: Babicheva Viktoriia E. , Lock Evgeniya , Kim Heungsoo
Published: December 2024

We report on the structural, chemical, and optical properties of titanium sesquioxide Ti2O3 thin films on single-crystal sapphire substrates by pulsed laser deposition. The thin film of Ti2O3 on sapphire exhibits light absorption of around 25%–45% in the wavelength range of 2–10 μm. Here, we design an infrared photodetector structure based on Ti2O3, enhanced by a resonant metasurface, to improve its light absorption in mid-wave and long-wave infrared windows. We show that light absorption in the mid-wave infrared window (wavelength 3–5 μm) in the active Ti2O3 layer can be significantly enhanced from 30%–40% to more than 80% utilizing a thin resonant metasurface made of low-loss silicon, facilitating efficient scattering in the active layer. Furthermore, we compare the absorptance of the Ti2O3 layer with that of conventional semiconductors, such as InSb, InAs, and HgCdTe, operating in the infrared range with a wavelength of 2–10 μm and demonstrate that the absorption in the Ti2O3 film is significantly higher than in these conventional semiconductors due to the narrow-bandgap characteristics of Ti2O3. The proposed designs can be used to tailor the wavelengths of photodetection across the near- and mid-infrared ranges.
Influence of amplitude and harmonic frequencies on the velocity of Faraday superwalkers
Authors: P P Pranav , Badvelu Pranay Prabha , Arumuru Venugopal
Published: December 2024

Faraday waves, arising from the vertical oscillation of a liquid bath, have long fascinated researchers for their role in studying non-equilibrium phenomena. The recent discovery of “superwalkers,” which are millimeter droplets exhibiting parabolic bouncing with high velocities on a vibrating liquid bath, has shown wave–particle interactions beyond classical theories. This study systematically investigates how key forcing parameters, such as the amplitude ratio, harmonic frequency, and phase angle difference between the dual-frequency excitation input signals, affect the velocity and walking dynamics of these superwalking droplets on a narrow straight channel. Experiments were performed using a mechanically vibrated silicone oil bath, with droplet motion tracked via a camera and particle-tracking algorithms. The investigated harmonic frequency pairs are (40, 80) Hz, (50, 100) Hz, and (70, 140) Hz, with amplitude ratios incrementally varied from 1 to 4.5 and phase angle differences between 120° and 150°. Results demonstrate a direct proportionality between amplitude ratio and droplet velocity, achieving velocities exceeding 60 mm/s for 1.9–2 mm droplets, surpassing previously reported results. Notably, the harmonic frequency determined the effective droplet size range exhibiting superwalking behavior. Higher frequencies limited mobility to smaller droplets (0.7–1.6 mm), while allowing initially stationary droplets to walk at substantial velocities. Conversely, lower frequencies enabled walking for larger droplets up to 2 mm. To explain these complex dynamics, a new correlation parameter (a/f.15) was formulated, revealing a linear relationship with droplet velocity across all frequencies and diameters investigated. The established quantitative relationships will be useful for precise control over droplet dynamics, enabling potential applications in microfluidics, surface manufacturing, and exploratory quantum analogy.
Modulation of the 2DEGs mediated by 3d-4f exchange interaction via the stacking sequences
Authors: Lin Zeguo , Ding Zhaoqing , Wang Zhen , Yang Mingyu , Wu Xiaofeng , Wang Lifen , Liu Xiaoran , Yang Fang , Guo Jiandong
Published: December 2024

Spin-polarized two-dimensional electron gases (2DEGs) at complex oxide heterointerfaces exhibit intriguing properties and provide great opportunities for spintronics devices. In this work, we investigate the modulation of 2DEGs' properties at the interfaces between LaTiO3 and EuTiO3 films by altering the stacking sequences of the heterostructures. We demonstrate that different stacking sequences lead to distinct mechanisms for compensating the polar discontinuity at the interfaces, which significantly influence the coupling between itinerant electrons and local moments. As a result, an asymmetric metallic and magnetic behavior of 2DEGs at LaTiO3/EuTiO3 vs EuTiO3/LaTiO3 interfaces is observed. These findings establish a method for controlling the exchange interaction between the conducting 3d electrons of 2DEGs and the 4f localized moments of Eu2+ ions. This approach not only deepens our understanding of the physics of complex oxide heterostructures but also opens up an avenue for manipulating spin-polarized 2DEGs, with potential implications for the design of next-generation oxide-based spintronic devices.
Diamagnetic levitation of water realized with a simple device consisting of ordinary permanent magnets
Authors: Naito Tomoya , Suzuki Tomoaki , Ikezoe Yasuhiro
Published: December 2024

Diamagnetic levitation is an appealing technique for levitating objects at room temperature without subjecting the sample to potentially damaging control fields, such as high-intensity laser light or sound pressure. However, owing to the extremely low magnetic susceptibility of diamagnetic materials, except for bismuth and graphite, diamagnetic levitation generally necessitates the use of exceptionally strong magnets, such as those found in world-class high-field facilities. This study simulated the magnetic field distribution in a narrow valley formed between two adjacent rectangular cuboid magnets with antiparallel magnetizations, at a spatial resolution of 5 μm. The simulations indicated the generation of a strong magnetic force field, B∂B/∂z(>40 000 T2/m), which could lift not only light organic compounds but also dense metallic compounds. Moreover, the addition of another pair of smaller sized magnets provided a local potential minimum that satisfied the conditions for non-contact levitation. Based on these results, a compact magnetic levitation system was developed by combining four small commercially available magnets. Experimental results showed that a water droplet of approximately 0.3 mm diameter was levitated. The experimental space was nearly sealed and highly resistant to external disturbances, such as vibrations, allowing the water to remain in a non-contact levitated state unless the operator intentionally shook the experimental table or directed airflow to displace the water away. The device is expected to facilitate various applications in materials science and fluid dynamics as well as promote preliminary ground-based research on space-related experiments designed to be conducted in microgravity environments.
Perspectives on epitaxial InGaP for quantum and nonlinear optics
Authors: Akin Joshua , Zhao Yunlei , Haque A. K. M. Naziul , Fang Kejie
Published: December 2024

Nonlinear optical materials are essential for the development of both nonlinear and quantum optics and have advanced recently from bulk crystals to integrated material platforms. In this Perspective, we provide an overview of the emerging InGaP χ(2) nonlinear integrated photonics platform and its experimental achievements. With its exceptional χ(2) nonlinearity and low optical losses, the epitaxial InGaP platform significantly enhances a wide range of second-order nonlinear optical effects, from second-harmonic generation to entangled photon pair sources, achieving efficiencies several orders of magnitude beyond the current state of the art. Moreover, the InGaP platform enables quantum nonlinear optics at the few- and single-photon levels via passive nonlinearities, which has broad implications for quantum information processing and quantum networking. We also examine the current limitations of the InGaP platform and propose potential solutions to fully unlock its capabilities.
Preserving positivity in density-explicit field-theoretic simulations
Authors: Quah Timothy , Delaney Kris T. , Fredrickson Glenn H.
Published: December 2024

Field-theoretic simulations are numerical methods for polymer field theory, which include fluctuation corrections beyond the mean-field level, successfully capturing various mesoscopic phenomena. Most field-theoretic simulations of polymeric fluids use the auxiliary field (AF) theory framework, which employs Hubbard–Stratonovich transformations for the particle-to-field conversion. Nonetheless, the Hubbard–Stratonovich transformation imposes significant limitations on the functional form of the non-bonded potentials. Removing this restriction on the non-bonded potentials will enable studies of a wide range of systems that require multi-body or more complex potentials. An alternative representation is the hybrid density-explicit auxiliary field theory (DE-AF), which retains both a density field and a conjugate auxiliary field for each species. While the DE-AF representation is not new, density-explicit field-theoretic simulations have yet to be developed. A major challenge is preserving the real and non-negative nature of the density field during stochastic evolution. To address this, we introduce positivity-preserving schemes that enable the first stable and efficient density-explicit field-theoretic simulations (DE-AF FTS). By applying the new method to a simple fluid, we find thermodynamically correct results at high densities, but the algorithm fails in the dilute regime. Nonetheless, DE-AF FTS is shown to be broadly applicable to dense fluid systems including a simple fluid with a three-body non-bonded potential, a homopolymer solution, and a diblock copolymer melt.
Thermodynamic and kinetic insights into the origin of spin-gapless semiconducting behavior in Ti2CoSi Heusler compound
Authors: Li Guijiang , Sun Qihang , Zheng Yi , Dong Zhihua
Published: December 2024

In this study, the origin of spin-gapless semiconducting behavior in Ti2CoSi was theoretically revealed. It was discovered that Ti2CoSi is stable in Cu2MnAl-type structure at the ground state. However, the Hg2CuTi-type structure is thermodynamically preferred in Ti2CoSi at high temperatures, which is responsible for the experimentally observed spin-gapless semiconducting behavior. Comparative analysis of data revealed that the kinetic arrest of atomic diffusion, caused by the rapid-cooling method, led to the formation of a Ti2CoSi phase with a structure similar to the Hg2CuTi-type in thin film samples. This study proposed that the physical properties and applications of Heusler compounds in devices are closely dependent on their structure, which can be adjusted by carefully controlling the thermodynamic states and kinetic process during sample fabrication. The calculation results indicate that the style and strength of interatomic chemical bonds are the inherent factors that aid in determining the phase stability in solids. These results not only suggest that thermodynamic states and kinetic processes during the sample preparation determine the spin-gapless semiconductor characteristic in Ti2CoSi but also are helpful in designing and exploring magnetic functional materials for technological applications.
Short-time collective dynamics of an ionic liquid: A computer simulation study with non-polarizable and polarizable models, and ab initio molecular dynamics
Authors: Paschoal Vitor Hugo , Ribeiro Mauro C. C.
Published: December 2024

Molecular dynamics (MD) simulation is used to study the intermolecular dynamics in the THz frequency range of the ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, [C2C1im][FSI]. Non-polarizable and polarizable models for classical MD simulation are compared using as quality criteria ab initio molecular dynamics (AIMD) and experimental data from far-infrared (FIR) spectroscopy and previously published data of inelastic x-ray scattering (IXS). According to data from IXS spectroscopy, incorporating polarization in the classical MD simulation has relatively little effect on the dispersion curve (excitation frequency vs wavevector) for longitudinal acoustic modes. When the AIMD simulation is used as a reference, the polarizable model leads the time correlation functions of velocity, mass, and charge currents to relax abnormally quickly. The charge current spectra from the AIMD simulation and the non-polarizable model agree with the experimental FIR spectrum, while the polarizable model gives an excessively broad band. When compared to the non-polarizable model, the polarizable model does improve the calculation of transport coefficients (diffusion coefficient, viscosity, and conductivity); however, it yields overdamped short-time collective dynamics.
Assessment of electron–proton correlation functionals for vibrational spectra of shared-proton systems by constrained nuclear-electronic orbital density functional theory
Authors: Yang Yuzhuo , Zhang Yuzhe , Yang Yang , Xu Xi
Published: December 2024

Proton transfer plays a crucial role in various chemical and biological processes. A major theoretical challenge in simulating proton transfer arises from the quantum nature of the proton. The constrained nuclear-electronic orbital (CNEO) framework was recently developed to efficiently and accurately account for nuclear quantum effects, particularly quantum nuclear delocalization effects, in quantum chemistry calculations and molecular dynamics simulations. In this paper, we systematically investigate challenging proton transfer modes in a series of shared-proton systems using CNEO density functional theory (CNEO-DFT), focusing on evaluating existing electron–proton correlation functionals. Our results show that CNEO-DFT accurately describes proton transfer vibrational modes and significantly outperforms conventional DFT. The inclusion of the epc17-2 electron–proton correlation functional in CNEO-DFT produces similar performance to that without electron–proton correlations, while the epc17-1 functional yields less accurate results, comparable with conventional DFT. These findings hold true for both asymmetrical and symmetrical shared-proton systems. Therefore, until a more accurate electron–proton correlation functional is developed, we currently recommend performing vibrational spectrum calculations using CNEO-DFT without electron–proton correlation functionals.
Effects of gust on the aerodynamics of multi-rotors
Authors: Narayanan Shrivathsan , Govindarajan Bharath
Published: December 2024

Understanding the aerodynamics of multi-rotor systems under temporally varying discrete gusts is the focus of this work. Axial and edgewise 1-minus-cosine profiles of varying amplitude (0.1ΩR–0.3ΩR) and gust durations (0.3–15 s) were studied for the rigid, unarticulated Harrington single and coaxial rotors, and the Advanced Precision Composites (APC) 12x6E (a commercial off-the-shelf propeller) quad-rotor in hover. An in-house free vortex method (FVM) was utilized to study the time and frequency domain of thrust, span-wise angle of attack distribution, and the rotor wake structure across the gust event. It was observed that edgewise gusts produced higher frequency components in the thrust signal compared to axial gusts for all rotor systems. Strong wake–wake and blade–vortex interactions (BVI) were observed particularly for edgewise gusts, leading to strong variations in the sectional angle of attack and the thrust values. The wake interactions are more pronounced in the APC quad-rotor system, which operates at a low reduced frequency, essentially resulting in a quasi-steady response of the wake to the gust, resulting in a considerably higher number of BVI events, increased peak rotor loads, and higher frequency content. This study can aid in the understanding of the gust response of small- and medium-scale rotors.
Excited state properties from the Bethe–Salpeter equation: State-to-state transitions and spin–orbit coupling
Authors: Himmelsbach Paula , Holzer Christof
Published: December 2024

The formalism to calculate excited state properties from the GW–Bethe–Salpeter equation (BSE) method is introduced, providing convenient access to excited state absorption, excited state circular dichroism, and excited state optical rotation in the framework of the GW–BSE method. This is achieved using the second-order transition density, which can be obtained by solving a set of auxiliary equations similar to time-dependent density functional theory (TD-DFT). The proposed formulation therefore leads to no increase in the formal computational complexity when compared to the corresponding ground state properties. We further outline the calculation of fully relaxed spin–orbit coupling matrix elements within the GW–BSE method, allowing us to include perturbative corrections for spin–orbit coupling in aforementioned properties. These corrections are also extended to TD-DFT. Excited state absorption and perturbative spin–orbit coupling corrections within GW–BSE are evaluated for a selected set of molecular systems, yielding promising results.
Distinct deformation mechanisms of silicate glasses under nanoindentation: The critical role of structure
Authors: Yan Ziming , Lu Ranran , Ding Linfeng , Wang Lianjun , Zhang Zhen
Published: December 2024

We use large-scale molecular dynamics simulations to investigate the indentation response of three silica-based glasses with varying compositional complexities. Our primary goal is to clarify the roles of the typical network-modifying species, namely, sodium, and the secondary network-forming species, namely, boron, in influencing the mechanical behavior of the glasses under localized stress. The distinct mechanical responses of the glasses are linked to structural features such as bond strength, network connectivity, and atomic packing density. The enhanced nanoscale ductility of sodium silicate and sodium borosilicate glasses, compared to silica, is attributed to the structural flexibility induced by Na atoms, which depolymerize the network, and by B species in mixed coordination. We also find that shear flow, driven by network flexibility, is the dominant deformation mechanism in the sodium silicate and sodium borosilicate glasses, while densification dominates in silica due to its low packing density. The evolution of short-to-intermediate-range structures is responsible for the distinct deformation behaviors of the glasses. These results highlight the critical role of structure in determining the deformation mechanisms of silicate glasses under sharp contact loads, providing insights for improving the mechanical performance of these materials.
Stabilizing complex-Langevin field-theoretic simulations for block copolymer melts
Authors: Willis J. D. , Matsen M. W.
Published: December 2024

Complex-Langevin field-theoretic simulations (CL-FTSs) provide an approximation-free method of calculating fluctuation corrections to the self-consistent field theory (SCFT) of block copolymer melts. However, the complex fields are prone to the formation of hot spots, which causes the method to fail. This problem has been attributed to an invariance under complex translations, which allows the system to drift away from the real-valued saddle-point of SCFT. Here, we apply dynamical stabilization to CL-FTSs of diblock copolymer melts, whereby the drift is suppressed by a small imaginary force on the composition field. The force needs to be sufficient to hold the system near the real saddle-point but also small enough not to significantly bias the statistics. Although larger forces are required as the fluctuations become more intense, we are able to lower the invariant polymerization indices of the CL-FTSs by several orders of magnitude before this becomes a problem. The new CL-FTS results are then used to test conventional Langevin simulations (L-FTSs), in which the instability is removed by a partial saddle-point approximation to the pressure field. As found previously, the L-FTSs agree accurately with the CL-FTSs, provided that the comparison is performed using a Morse calibration.
Predicting the depth of rock cutting by abrasive water jet using support vector machine optimized with whale optimization algorithm
Authors: Li Zhongtan , Ge Zhaolong , Deng Qinglin , Zhou Zhe , Zhu Chun , Liu Lei , Yao Zhi
Published: December 2024

The utilization of abrasive water jet (AWJ) has garnered notable attention in subsurface engineering, as well as unconventional natural gas development, geothermal energy extraction, and tunnel excavation. The efficiency of construction operations is contingent upon rock fragmentation, which is controlled by AWJ parameters and rock properties. Currently, the parameter settings for rock fragmentation by AWJ predominantly rely on empirical approaches, and existing prediction models have large errors due to a limited number of training samples. In this study, we propose a combined support vector machine (SVM) and whale optimization algorithm (WOA) model. To test the model's predictive performance for rock-breaking depth, a database consisting of eight input parameters is constructed. These parameters include AWJ pressure, target distance, lateral velocity, abrasive types, mass flow rate, abrasive particle size, rock types, and rock uniaxial compressive strength. Additionally, to demonstrate the superiority of the WOA-SVM model, three other predictive models based on the back propagation (BP) network, SVM, and Random Forest (RF) are established, compared, and evaluated. The results show that the optimized WOA-SVM model is the most accurate in predicting rock cutting depth, achieving a precision rate of 0.972 25 compared to other models (BP: 0.9536; RF: 0.9681; SVM: 0.9687). Furthermore, sensitivity analysis highlights that lateral velocity exhibits the highest impact on the model, followed by jet pressure and the uniaxial compressive strength of rock. This underscores the critical importance of prioritizing the adjustment of lateral velocity, AWJ pressure, and rock properties when engaging in rock-cutting operations.
Transient charge carrier dynamics in organic solar cell devices studied by simultaneous optical and electric detection
Authors: Miura Tomoaki , Muramatsu Naoya , Takeuchi Tomoaki , Seki Kazuhiko , Ikoma Tadaaki
Published: December 2024

For the clarification of dynamics of photogenerated carriers in practical organic solar cell devices, we have developed a methodology to simultaneously acquire reflection-mode transient optical absorption (ΔA) and transient electric current (Δi) signals. For a typical polythiophene:fullerene bulk heterojunction solar cell device, both the ΔA and Δi signals due to the photogenerated carriers are characterized by the power-law decays of ∝t−α, which are interpreted by detrapping-limited recombination at earlier times than ∼1 μs and trap-free diffusion/drift at later times. Furthermore, we have succeeded in observing switching of the power index α for ΔA signals as well as for Δi signals; the time at which switching occurs indicates the extraction of carriers by electrodes (transit times). From the transit times for ΔA and Δi, transit mobilities μtrΔA and μtrΔi are obtained, which are on the same order. It has been found from the comparison of the cell parameters among several devices fabricated under similar conditions that the device-to-device variation of photon energy conversion efficiency (0.5%–2%) is strongly correlated with the ratio μtrΔA/μtrΔi. It is considered that the charge accumulation at the active layer/electrode interfaces induces a delay between the carrier transport and electrode collection, which significantly lowers the power conversion efficiency. Our simultaneous optical and electrical detection thus allows us to diagnose carrier dynamics in individual devices that affect the solar cell performance.
Broadband transparency in terahertz free-standing anapole metasurface
Authors: Otoo Isaac Appiah , Basharin Alexey , Matveev Grigorii , Fedorov Georgy , Karvinen Petri , Ayyagari Surya Revanth , Pashnev Daniil , Urbanowicz Andrzej , Jorudas Justinas , Kašalynas Irmantas , Svirko Yuri , Kuzhir Polina
Published: December 2024

We report on an all-dielectric compound anapole metasurface featuring metaatoms based on concentric disks and rings arranged in a square lattice. In this free-standing metasurface, the radiating multipole components cancel each other out in the far field, regardless of the angle of incidence and the polarization of incoming radiation. To demonstrate experimentally a broadband transparency in the terahertz range, we fabricated a silicon metasurface with a total thickness of 60 μm using electron beam lithography and plasma deep etching techniques. Terahertz time-domain spectroscopy experiments revealed that the transmittance spectra measured at various incident angles and polarization states agree well with the respective modeling data. The proposed compound anapole approach has strong application potential for broadband terahertz photonics and sensing devices.
Transparent pn junction in CuCrO2/WO3 for enhanced photovoltaic response and stability via high entropy perovskite Ba(Ti0.2Zr0.2Sn0.2Hf0.2Ce0.2)O3 transition layer
Authors: Jia Chengyu , He Bo , Wang Rui , Wang Dingwei , Cao Jun , Shi Lei , Pan Jiaqi , Zhao Zhiguo , Li Chaorong
Published: December 2024

A transparent pn junction comprising CuCrO2/Ba(Ti0.2Zr0.2Sn0.2Hf0.2Ce0.2)O3/WO3 was synthesized using a sol-gel-hydrothermal-annealing method. The CuCrO2/BaTiZrSnHfCe/WO3 achieves a transmittance of ∼83%–88%, with photovoltaic enhancement of ∼4.0 × 103-folds compared to the intrinsic device [photovoltaic conversion efficiency (PCE) of ∼1.22%], and it also demonstrates good stability over 5 months. This is mainly attributed to the BaTiZrSnHfCe HEO solid solution. In addition to an appropriate Fermi level/high QY, the BaTiZrSnHfCe HEO, with carrier inducing/injecting/driving by synergism of high entropy lattice distortion and charge compensation, can improve kinetic equilibrium for achieving PCE-transparency while increasing holes via Cu vacancies/interstitial oxygen. Moreover, inorganic CuCrO2, BaTiZrSnHfCe HEO, and WO3 maintain good structural stability, indicating promising applications for CuCrO2/BaTiZrSnHfCe/WO3 in optoelectronic devices.
A non-local way around the no-global-symmetries conjecture in quantum gravity?
Authors: Borissova Johanna , Eichhorn Astrid , Ray Shouryya
Published: December 2024

The no-global-symmetries conjecture is central to the swampland program that delineates the boundary between effective field theories that can be obtained from a quantum theory of gravity to those that cannot. The conjecture states that virtual black-hole configurations in the path integral generate terms that violate all global symmetries in the effective action for matter. Because of its central role, it is crucial to understand limitations to the validity of this conjecture. In the context of the Lorentzian path integral over spacetime geometries, we explore whether virtual black-hole configurations can be suppressed dynamically. To that end, we work in a spherically symmetric setting and make use of horizon-detecting curvature invariants which vanish on the horizon. By constructing a non-local gravitational action from the inverse of such curvature invariants, we can achieve destructive interference of black-hole configurations in the path integral. Given that non-local gravitational actions appear generically as the result of integrating out matter degrees of freedom from a theory for quantum gravity and matter, our exemplary construction reinforces discussions about the role of non-locality in assessing arguably universal properties of quantum gravity within the framework of path integrals.
A nested sequence of inequivalent Rindler vacua : universal relic thermality of Planckian origin
Authors: Lochan Kinjalk , Padmanabhan T
Published: December 2024

The Bogoliubov transformation connecting the standard inertial frame mode functions to the standard mode functions defined in the Rindler frame R
0, leads to the result that the inertial vacuum appears as a thermal state with temperature

T
0

=

a
0

/

2
π

where a
0 is the acceleration parameter of R
0. We construct an infinite family of nested Rindler-like coordinate systems

R
1

,

R
2

,

…

within the right Rindler wedge, with time coordinates

τ
1

,

τ
2

,

…

,

and acceleration parameters

a
1

,

a
2

,

…

by shifting the origin along the inertial x-axis by amounts

ℓ
1

,

ℓ
2

,
⋯

. We show that, apart from the inertial vacuum, the Rindler vacuum of the frame Rn
also appears to be a thermal state in the frame

R

n
+
1

with the temperature

a

n
+
1

/

2
π

. In fact, the Rindler frame

R

n
+
1

attributes to all the Rindler vacuum states of

R
1

,

R
2

,

…

R
n

, as well as to the inertial vacuum state, the same temperature

a

n
+
1

/

2
π

. We further show that our result is discontinuous in an essential way in the coordinate shift parameters. For a Rindler frame Ri
, this thermality turns on with smallest non-zero

ℓ
i

allowed in the semiclassical framework and remains insensitive to

(

ℓ
i

,

a

i
−
1

)

thereafter, indicating its universal Planckian origin. Similar structures can be introduced in the right wedge of any spacetime with bifurcate Killing horizon, like, for e.g. Schwarzschild spacetime. Apart from providing unsuppressed observables capturing Planck scale effects, these results have important implications for quantum gravity (QG) when flat spacetime is treated as the ground state of QG. Furthermore, a frame with the shift

ℓ

and the corresponding acceleration parameter

a
(
ℓ
)

can be thought of as a Rindler frame which is instantaneously comoving with the Einstein’s elevator moving with a variable acceleration. Our result suggests that the quantum temperature associated with such an Einstein’s elevator is the same as that defined in the comoving Rindler frame. The implications of these results are wide ranging, from having a definitive signature of Planck shifts in the horizon to the existence of a new set of observers in black hole exterior having thermodynamic description of the horizon they perceive.
Flat space gravity at finite cutoff
Authors: Banihashemi Batoul , Shaghoulian Edgar , Shashi Sanjit
Published: December 2024

We study the thermodynamics of Einstein gravity with vanishing cosmological constant subjected to conformal boundary conditions. Our focus is on comparing the series of subextensive terms to predictions from thermal effective field theory, with which we find agreement for the boundary theory on a spatial sphere, hyperbolic space, and flat space. We calculate the leading Wilson coefficients and observe that the first subextensive correction to the free energy is negative. This violates a conjectured bound on this coefficient in quantum field theory, which we interpret as a signal that gravity does not fully decouple in the putative boundary dual.
Resolving emission rates from overlapping capacitance transients of deep levels in SiC
Authors: Wang Zilan , Li Haoyang , Liu Bo , Yang Jiapeng , Lin Tianxiang , Ling Francis C C , Wang Lai
Published: December 2024

With the development of new materials and devices, defect characterization techniques, such as deep level transient spectroscopy, face the challenge of providing more accurate defect information and identification. However, nonexponential capacitance features are introduced for various reasons, making the widely adopted rate window technique encounter difficulties during analysis, which may lead to incorrect conclusions. In this study, the capacitance transients of a SiC junction barrier Schottky diode were systematically analyzed, revealing an overlap of majority and minority carrier trap emission signals within the same measurement temperature. Additionally, the capacitance transients of electron traps contained two similar emission rates. If the selection of rate window is inappropriate, it not only becomes difficult to distinguish each trap, but also false signals may appear. By comparing the rate window and exponential fitting method, the emission rates, activation energy, and capture cross-section can be calculated separately, and this comparative analysis may help improve reliability. Furthermore, the concentration profiles of each trap as a function of depth are analyzed by applying different voltages, and the possible origins of these traps are discussed.
Comprehensive scrutiny on the low temperature magnetism and hyperthermia efficiency of greenly synthesized biocompatible Zn0.25Ca0.25Fe2.5O4 nanoparticles
Authors: Tiwari Sudeep , Bano Anisha , Kamali Saeed , Williams Aleia , Johnson Jacqueline , Johnson Charles , Anandhi J Shebha , Patil Sagar Anandrao , Khot Vishwajeet M , Roychowdhury Parikshit , Eyal Anna , Kumar Sudhish
Published: December 2024

The present study comprehensively scrutinizes the complex magnetism and hyperthermia efficiency of greenly synthesized Zn0.25Ca0.25Fe2.5O4 nanoparticles (ZNCF NPs). ∼23 nm sized ZNCF NPs in single phase fcc-spinel symmetry were successfully produced through sugarcane juice-mediated self-combustion tactics. Biocompatibility examination against BEAS-2B cell lines indicated a safer limit of ZNCF NPs as 1 mg. Exhaustive field (upto ±70 kOe) and temperature-dependent (10 K to 300 K) dc-magnetization measurements showed that ZNCF NPs are in the ferrimagnetic (FiM) phase at low temperatures and superparamagnetic (SPM) along with minute magnetically hard FiM component at 300 K. 57Fe-Mössbauer analysis validated SPM (43%) and FiM (57%) at 293 K and FiM state at low temperatures. Observed isomer shift revealed that the majority of Fe ions are in a high spin Fe3+ state along with Fe2+ ions in ZNCF NPs. Shifting in the real part of ac—susceptibility data toward the higher temperature side upon increasing frequency and obeying Vogel–Fulcher law affirmed collective freezing of superspins below freezing temperature (T
f = 200 K). Dynamic scaling fit yielded relaxation time of ∼10−12 s, Mydosh parameter (=0.021) and critical exponent (8.9) ascertaining superspin glass (SSG) state in ZNCF NPs below glass temperature (T
g = 220 K). Furthermore, SSG phase at low temperatures is approved by archetypal experimental signatures like ageing, memory and rejuvenation. The induction heating characteristics of ZNCF NPs probed via infrared thermography yielded intrinsic loss parameter in the 0.26 nHm2 kg−1–5.10 nHm2 kg−1 range. Linear response theory provided non-zero power dissipation for ZNCF (suspension in de-ionized water) functioning range of 6–8 nm with an optimum particle size of ∼7 nm. A prudent analysis asserted that only 18% of NPs contribute to a non-zero SAR value. Overall, this research is an exhaustive investigation of the complex magnetism and hyperthermia efficiency suitable for mild hyperthermia applications.