Flat Mode Research Articles

Measuring and Extracting the Complex Permittivity of Porous Ceramic Materials in the Y-Band

ABSTRACT Porous ceramics find extensive applications in aerospace and other fields, and the measurement of their electromagnetic parameters is helpful in optimization of material properties and device designs. In this paper, a free-space 8f quasi-optical measurement system consisting of a vector network analyzer, a 325–500 GHz frequency expansion module, and four off-axis parabolic mirrors have been established to measure the transmission parameter S21 of porous ceramics. The complex permittivity was extracted according to the Newton-Raphson iterative method utilizing its measured S21 parameters based on flat mode. The porous ceramics with different porosity and density were measured and the relationships between their permittivity and porosity and density was established, respectively. These results are beneficial to the quality evaluation and application design of porous ceramic materials in the aerospace field.

Dispersionless Flat Mode and Vibrational Anomaly in Active Brownian Vibrators Induced by Stringlike Dynamical Defects.

In recent years, active Brownian particles have emerged as a prominent model system for comprehending the behaviors of active matter, wherein particles demonstrate self-propelled motion by harnessing energy from the surrounding environment. A fundamental objective of studying active matter is to elucidate the physical mechanisms underlying its collective behaviors. Drawing inspiration from advancements in molecular glasses, our study unveils a low-energy "flat mode" within the transverse spectrum of active Brownian vibrators-a nearly two-dimensional, bidisperse granular assembly. We demonstrate that this collective excitation induces an anomalous excess in the vibrational density of states (VDOS) beyond the phononic Debye contribution. We characterize the properties of this flat mode by exploring the parameter space of our experimental system and tuning the packing fraction, the vibrational frequency, the particle size ratio, and the mixture ratio. Additionally, we establish through empirical evidence that stringlike dynamical defects, discerned via the spatial distribution of each particle's contribution to the reduced transverse VDOS, serve as the microscopic origin of the flat mode and its associated anomalies.

Spin waves and orbital contribution to ferromagnetism in a topological metal

Honeycomb and kagome lattices can host propagating excitations with non-trivial topology as defined by their evolution along closed paths in momentum space. Excitations on such lattices can also be momentum-independent, and the associated flat bands are of interest due to strong interactions between heavy quasiparticles. Here, we report the discovery — using circularly polarized X-rays for the unambiguous isolation of magnetic signals — of a nearly flat spin-wave band and large (compared to elemental iron) orbital moment in the metallic ferromagnet Fe3Sn2 with compact AB-stacked kagome bilayers. As a function of out-of-plane momentum, the nearly flat optical mode and the global rotation symmetry-restoring acoustic mode are out of phase, consistent with a bilayer exchange coupling that is larger than the already large in-plane couplings. The defining units of this topological metal are therefore triangular lattices of octahedral iron clusters rather than weakly coupled kagome planes. The spin waves are strongly damped when compared to elemental iron, opening the topic of topological boson–fermion interactions for deeper exploration within this material platform.

Phonons in stringlet-land and the boson peak

Solid materials that deviate from the harmonic crystal paradigm exhibit characteristic anomalies in the specific heat and vibrational density of states (VDOS) with respect to Debye's theory predictions. The boson peak (BP), a low-frequency excess in the VDOS over Debye lawg(ω)∝ω2, is certainly the most famous among them; nevertheless, its origin is still subject of fierce debate. Recent simulation works provided strong evidence that localized one-dimensional string-like excitations (stringlets) might be the microscopic origin of the BP. In this work, we study the dynamics of acoustic phonons interacting with a bath of vibrating 1D stringlets with exponentially distributed size, as observed in simulations. We show that stringlets strongly renormalize the phonon propagator and naturally induce a BP anomaly in the VDOS, corresponding to the emergence of a dispersionless BP flat mode. Additionally, phonon-stringlet interactions produce a strong enhancement of sound attenuation and a dip in the speed of sound near the BP frequency, consistent with experimental and simulation data. The qualitative trends of the BP frequency and intensity are predicted within the model and shown to be in good agreement with previous observations. In summary, our results substantiate with a simple theoretical model the recent simulation results by Hu and Tanaka claiming the origin of the BP from stringlet dynamics.

Magnon Confinement on the Two-Dimensional Penrose Lattice: Perpendicular-Space Analysis of the Dynamic Structure Factor

Employing the spin-wave formalism within and beyond the harmonic-oscillator approx-imation, we study the dynamic structure factors of spin-12 nearest-neighbor quantum Heisenberg antiferromagnets on two-dimensional quasiperiodic lattices with particular emphasis on a mag-netic analog to the well-known confined states of a hopping Hamiltonian for independent electrons on a two-dimensional Penrose lattice. We present comprehensive calculations on the C5v Penrose tiling in comparison with the C8v Ammann–Beenker tiling, revealing their decagonal and octagonal antiferromagnetic microstructures. Their dynamic spin structure factors both exhibit linear soft modes emergent at magnetic Bragg wavevectors and have nearly or fairly flat scattering bands, signifying magnetic excitations localized in some way, at several different energies in a self-similar manner. In particular, the lowest-lying highly flat mode is distinctive of the Penrose lattice, which is mediated by its unique antiferromagnons confined within tricoordinated sites only, unlike their itinerant electron counterparts involving pentacoordinated, as well as tricoordinated, sites. Bringing harmonic antiferromagnons into higher-order quantum interaction splits, the lowest-lying nearly flat scattering band in two, each mediated by further confined antiferromagnons, which is fully demonstrated and throughly visualized in the perpendicular as well as real spaces. We disclose superconfined antiferromagnons on the two-dimensional Penrose lattice.

Spatiotemporal variability of streamflow in the Pearl River Basin: Controls of land surface processes and atmospheric impacts

AbstractTo advance understanding of the spatiotemporal variability of the streamflow in the Pearl River Basin (PRB), we used the Soil and Water Assessment Tool model to simulate the water fluxes from 2010 to 2020 and to identify the underlying controlling mechanisms. The streamflow in the PRB is highly variable and controlled by complex land surface processes and atmospheric impacts over the heterogeneous terrain. Two key factors primarily govern the streamflow: (1) the location of the active precipitation zone, which is determined by the interaction between the monsoon path and uplifting effect of the terrain, and (2) the redistributions resulting from land use and soil characteristics. We observe distinct patterns in the different water fluxes across the different regions. Specifically, surface flow exhibits the highest activity within the precipitation zone. Lateral flow and actual evapotranspiration (AET) have the greatest intensity in the forests and in agricultural regions, respectively, and the aquifer flow is more active in areas with coarse soil textures. The land surface processes of the AET and aquifer retention significantly govern the temporal variability of the streamflow, contributing to the precipitation and streamflow being out of phase in the PRB. Based on the underlying mechanisms driving streamflow variability, we classify the PRB into three substreams: a drought‐prone upstream, a hydrologically active midstream, and a typhoon‐affected downstream, and each substream exhibits distinct spatiotemporal characteristics of streamflow. We find that the time series and probability distributions of the streamflow at different tributaries within each substream are similar. Each probability distribution is multimodal and can be decomposed into three unimodal distributions representing dry, transitional, and wet conditions. Specifically, the PRB features a large and steep dry mode, a flat transitional mode, and a short wet mode.

Research on the 3D indoor positioning technology based on feature light source

Nowadays, positioning technologies mainly consist of three methods: positioning based on satellites, positioning based on RF and positioning based on self-contained sensors. However, due to the complex propagation characteristics of wireless signals in indoor environments, the existing positioning technologies widely used in outdoor environments cannot meet the requirements of indoor applications. Compared to outdoor environments, indoor environments are more complex, and wireless signals are affected by various factors, making it difficult for existing indoor positioning systems to meet the requirements of high accuracy and low cost. Thus, a three-dimensional indoor positioning technology based on a characteristic light source and a spherical lighting device is proposed in this paper to solve the problems. The technology measures the angle of the optical signal through a spherical lighting device, which can receive light in all directions and obtain height information compared with flat mode. Pseudo-source interference caused by the wave nature of light will not be introduced with the use of the particle nature of light. Array layout and optimization algorithms can further improve positioning accuracy. A simulation experiment in Matlab is conducted. The experimental results and the analysis of accuracy confirmed that the positioning accuracy can be controlled within a small error. Three-dimensional indoor positioning technology can achieve high accuracy at a low cost.

Low-threshold single-mode nanowire array flat-band photonic-crystal surface-emitting lasers with high-reflectivity bottom mirrors.

A Si-based nanowire array photonic-crystal surface-emitting laser based on a flat band is designed and simulated. By introducing an air gap between the nanowire and substrate, the bottom reflectivity is significantly enhanced, resulting in much lower threshold and smaller cutoff diameter. Through adjusting the lattice constant (the distance between neighboring nanowires) and nanowire diameter, a photonic crystal structure with a flat band is achieved, in which strong interaction between light and matter occurs in the flat band mode. For the device with a small size, single-mode lasing is obtained with a side-mode suppression ratio of 21 dB, high quality factor of 3940, low threshold gain of 624 cm-1, and small beam divergency angle of ∼7.5°. This work may pave the way for the development of high-performance Si-based surface-emitting nanolasers and high-density photonic integrated circuits.

Softening of a flat phonon mode in the kagome ScV6Sn6

Geometrically frustrated kagome lattices are raising as novel platforms to engineer correlated topological electron flat bands that are prominent to electronic instabilities. Here, we demonstrate a phonon softening at the kz = π plane in ScV6Sn6. The low energy longitudinal phonon collapses at ~98 K and q = frac{1}{3}frac{1}{3}frac{1}{2} due to the electron-phonon interaction, without the emergence of long-range charge order which sets in at a different propagation vector qCDW = frac{1}{3}frac{1}{3}frac{1}{3}. Theoretical calculations corroborate the experimental finding to indicate that the leading instability is located at frac{1}{3}frac{1}{3}frac{1}{2} of a rather flat mode. We relate the phonon renormalization to the orbital-resolved susceptibility of the trigonal Sn atoms and explain the approximately flat phonon dispersion. Our data report the first example of the collapse of a kagome bosonic mode and promote the 166 compounds of kagomes as primary candidates to explore correlated flat phonon-topological flat electron physics.

Cultural mode and organo-mineral amendment effect on growth and yield of rice (Oryza sativa L.) and soil chemical properties in sulfated acid soils of Basse-Casamance

Climatic variability and the scarcity of rainfall have intensified the process of soil salinization, leading to land degradation and loss of rice yield. A field experiment was conducted to study the effect of cultural mode and organo-mineral fertilizers on rice performance and soil chemical properties. A split plot design with four replications and two factors that were cultural mode (flat and ridge) and fertilizers (mineral, organic, organo-mineral, and control) was carried out. Observations on growth, yield parameters, and yield of rice and soil chemical properties (pH and EC) were recorded. The cultural mode influenced significantly rice performance. Height (76.26 cm), tillers (89.93 m-2), panicles (71.66 m-2), biomass (3252.25 kg ha−1), 1000 kernel weight (12.85 g) and yield (1123.14 kg ha−1) were significantly higher in ridge than flat. However, infertility (44.74%), sterility (58.04%), and survival (91.86%) were higher in flat than ridge mode. However, sowing of rice on ridges with mineral and organo-mineral amendments improved yield parameters increasing the yield of rice more than in flat mode. Soil chemical properties were significantly influenced by cultural modes and fertilizers. Ridge mode increased the soil pH and reduced the salinity more than in flat. Organic and organo-mineral fertilizers affected significantly the soil's chemical parameters by improving the pH and reducing the salinity. Ridge mode combined with organo-mineral amendment improved rice performance and soil chemical properties. Cultural modes and fertilizer types were critical elements to improve soil pH, salinity, and yield.

An experimental study to show the effect of forced vertical vibrations on the thermal heat transfer coefficient of a flat plate

The objective of this study is to conduct an experiment that considers the influence of vertical oscillations on the heat transfer coefficient of free convection in an aluminum flat plate component measuring 3 × 100 × 300 mm. The plate is subject to a steady-state heat transfer; whereby it experiences a sustained heat flux ranging from (250–1500) W/m2. The orientation of the flat plate can be either horizontal or inclined at particular angles, specifically at 0°, 30°, 45°, 60°, and 90°. The experimental tests conducted were characterized by an expanded frequency spectrum ranging from 2 to 16 Hz, a variable amplitude range spanning from 1.63 to 7.16 mm, and a range of Rayleigh number values upon activation of the system, with minimum and maximum thresholds of 138.991 and 487.275, respectively. The impact of vibration frequency upon both the amplitude and velocity of vibrations for a heat flow of 250 W/m2, situated at an angle of θ = 0°, was examined. The impact of the Reynolds number upon the total vibrational heat transfer coefficient, as well as the total Nusselt number, was investigated with and without the presence of angle vibration θ = 0°, across diverse degrees of heat flux. This study investigates the impact of the Rayleigh number on the overall Nusselt number under varying conditions of thermal flux, with and without the application of vibration at angles of θ = 30°, 45°, 60°, and 90°. The findings of this analysis demonstrate that there exists a discernible correlation between the incremental amplitude of vibration and the coefficient of heat transfer, manifesting as a negative slope within the range of 0° to 60°. Such correlation reaches its optimal magnitude of 13.2894% under the condition of flat vibration mode, whereas the coefficient of heat transfer declines progressively as vertical vibration is augmented, culminating in a maximum decline of 7.6475%. The present study reports a decrease in the overall vibrational heat transfer coefficient with increasing vibrational Reynolds number. The total Nusselt number was found to increase with or without vibration as the Rayleigh number increased.

Electrochemical etching modes of 4H-SiC in KOH solutions

Electrochemical etching is a promising wet etching technology for preparing porous structures and the flat surface etching of 4H-SiC. In this study, the effects of current density and KOH concentration on the etching of 4H-SiC were investigated. We found that the respective mechanisms for preparing porous structures and flat surface etching differed. The porous and flat etching modes were proposed to clarify the mechanistic differences. In addition, we achieved an etch rate of 1 μm h−1 in flat etching mode, and the sample surface was improved for 4H-SiC applications in the field of optoelectronics and microelectronics through the thermal oxidation of SiC.

Research on the Marketing Strategy of Bytedance Companies in The Internet Industry

This paper aims to investigate the development mode of Internet enterprise service platforms and analyze the marketing strategies that affect their implementation. The research method involves theoretical and empirical analyses, drawing on the theoretical achievements and practical experiences of internet enterprises. Specifically, the paper focuses on ByteDance, a young and successful internet unicorn company that has created several popular products such as Toutiao and TikTok. It analyzes the company's business philosophy and purpose, product profile, SMB commercial marketing strategy, and the problems existing in its marketing strategies. The paper recommends that enterprises should strengthen their technology construction, create a flat management mode, improve their corporate social responsibility, and enhance their corporate culture concept. These recommendations are essential for the survival and growth of companies in the highly competitive internet industry. The paper concludes that in the context of "Internet +", the scale effect of the network economy is significant and the internet marketing market is rapidly developing, providing an excellent opportunity for companies to interact, cooperate, and integrate resources to achieve their goals.

Nylon Membrane-Based Electromembrane Extraction Coupled with Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry for the Determination of Insulin

A rapid and sensitive protein determination method that uses electromembrane extraction (EME) and is coupled with matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) is developed. A flat nylon membrane is used to collect proteins from an aqueous solution and is directly analyzed by MALDI/MS after the addition of the MALDI matrix. Insulin is used as a model protein to investigate the optimum extraction of the parameters. The optimum EME conditions are obtained at 12 V of voltage, 10 min of extraction time, 12 mL sample volume, and 400 rpm agitation rate. The linear dynamic range (LDR) of insulin in an aqueous solution is in the range of 1.0–100.0 nM. The limit of detection (LOD) for insulin in an aqueous solution is 0.3 nM with 103-fold signal-to-noise (S/N) ratio enhancement. Furthermore, the applicability of this method to determine insulin in complicated sample matrices is also investigated. The LDR of insulin in human urine samples is in the range of 5.0–100.0 nM, and the LOD of insulin in urine samples is calculated to be 1.5 nM. The precision and accuracy of this method are evaluated at three different concentration levels, and the coefficient of variation (CV) and relative error are less than 6%. This approach is time-efficient and economical, as the flat membrane mode of EME coupled with MALDI/MS is suitable.

Interactions of xanthates of increasing chain length with pyrite surfaces: A DFT-D and microcalorimetry study

The theoretical technique of computational modelling and the experimental determination of the enthalpy of adsorption of a ligand molecule onto a mineral surface deliver the same output parameters and, therefore, complement each other in investigating the affinity of different ligand types for mineral surfaces. This study ran parallel experimental tests and computational calculations to determine the enthalpy of adsorption of a series of increasing chain length xanthates onto pyrite surfaces. We found that the vertical mode of adsorption was more exothermic than the flat mode adsorption. Most importantly we found that the flat mode adsorption for the 5C xanthate chain demonstrated the effect of van der Waals interaction of the hydrocarbons with the surface. Furthermore, the adsorption of charged xanthate both on hydrated and dry (100) surface gave inconsistent trends with experiments, except for charged xanthate flat adsorption on (111) surface. Significantly, the results of the adsorption of neutral xanthate both on dry and hydrated surfaces showed that although the absolute energy values were different; the trends were similar to the experimental approach. In particular the adsorption of neutral xanthate in water on the surface gave R2 = 0.96 and microcalorimetry gave R2 = 0.95, which indicated a linear correlation between the number of carbon atoms in the alkyl chain and the enthalpy of reaction for both computational and experimental data. The experimentally determined exothermic increase in heat of adsorption for the addition of each CH2 group was found to be −8.17 kJ.mol−1, while the contribution of the thiol head group was 34.9 kJ.mol−1. This study provides a rigorous experimental and computational approach which is intended to afford confidence in modelled data for the screening of new ligands for flotation processes.

Precise Dynamic Symbolic Execution for Nonuniform Data Access in Smart Contracts

Dynamic symbolic execution (DSE) has been successfully adopted for vulnerability detection in desktop and mobile platforms. Unfortunately, we cannot simply extrapolate those techniques to smart contracts. The major challenge is that smart contracts exhibit a nonuniform data access mode. Other than accessing the data via uniform addresses, smart contracts compromise multiple addressing modes, including flat address mode and key-value mode. More seriously, accessing a key-value table usually involves additional hash operations to obtain the keys. In this paper, we propose a DSE framework to resolve the nonuniform data access in smart contracts. More specifically, we exactly track the symbolic variables with concrete addresses and compute the actual/hash keys for table-like accesses. We also take the symbolic keys into account to distinguish data accesses incidentally with the same concrete keys resulting from artificially generated values. We describe the DSE framework in operational semantics. On top of the framework, we implement an integer overflow detector NOVA and a multi-transactional vulnerability detector MTVD. The experiments show that NOVA outperforms state-of-the-art analysis tools in detecting the integer overflows with much higher precision and recall, 94.2% and 93.0%, respectively. MTVD successfully reports three ether leaking vulnerabilities and one suicidal issue from real-world smart contracts.

Continuous Flat Pressing of MDF Quality Control Model Framework and Collaborative Programming Approach Based on Wood Fiber Hot Pressing Mechanism.

The increasing demand for forestry resources is driving the need for smarter systems capable of saving and protecting forests that can optimize agile forestry production. This study uses the continuous hot-pressing process of wooden medium-density fiberboard (MDF) to investigate the possibility of automatic quality control of the continuous flat pressing process. For this purpose, conceptual digital twin modeling for mechanism and sequence parameter control was conducted based on the cellular automata (CA) theory. A distributed coordination mode framework was constructed, and a craft control programming method was proposed for the quality control of MDF continuous flat pressing. Based on the MDF continuous flat press craft mechanism and control standards, a framework of five distributed flat press cooperative control mode elements for the cylinder array of the continuous panel system (CPS) was defined. To satisfy the distributed distance servo and pressure servo demands of the multi-stage hot pressing craft design, five kinds of synergy collaborative control modes of multiple rack groups were constructed using mode elements: For the four types of typical deviations in slab production, i.e., thickness, slope, depression, and bulge, a multi-zone mutual cooperative mode craft control sequence was programmed. According to the type and intensity of real-time deviation, the corresponding regulation sequence was applied. This effectively counteracts the deviation caused by the uncertainty interference due to the multi-field coupling effect in actual production. The application tests demonstrate that the adjustment and response time of the continuous flat press were greatly improved, and the quality superiority rate is controlled above 95%, thereby confirming the effectiveness of the control strategy.

Breakdown of linear spin-wave theory and existence of spinon bound states in the frustrated kagome-lattice antiferromagnet

Spin dynamics of the spin-1/2 kagome lattice antiferromagnet Cs$_2$Cu$_3$SnF$_{12}$ was studied using high-resolution, time-of-flight inelastic neutron scattering. The flat mode, a characteristic of the frustrated kagome antiferromagnet, and the low-energy dispersive mode, which is dominated by magnons, can be well described by the linear spin-wave theory. However, the theory fails to describe three weakly dispersive modes between 9 and 14 meV. These modes could be attributed to two-spinon bound states, which decay into free spinons away from the zone center and at a high temperature, giving rise to continuum scattering.

Hybridization-driven strong anharmonicity in Yb-filled skutterudites

A high-pressure study of the structural and thermal transport properties is carried out on one of the most efficient filled skutterudites, ${\mathrm{Yb}}_{0.3}{\mathrm{Co}}_{4}{\mathrm{Sb}}_{12}$, to understand the relatively low thermal conductivity behavior in this family. By combining x-ray diffraction and Raman scattering measurements, we detect a phase transition at around 12.4 GPa. The mode Gr\"uneisen parameters of the observed phonon modes are obtained from the determined bulk modulus and the phonon frequency shifts with pressure. The strong anharmonicity in this material is demonstrated by the obtained large average Gr\"uneisen parameter. We also find the depressed group velocity within the low-frequency range, the flat guest mode avoided crossing with the acoustic-phonon mode, and the significant contribution of optical phonons. The hybridization of the guest atom and host lattice and the related enhanced anharmonicity are suggested to account for the low lattice thermal conductivity in the studied system. These findings provide new insight into how phonon-phonon interactions lower lattice thermal conductivity in this important thermoelectric family.

Ultra-Low Noise Figure in Optical Fiber Amplifier by Tailoring the Mode Field Profile of Erbium-Doped Fiber

We present a numerical analysis of noise performance improvement of the erbium-doped fiber amplifier by flatting the mode field intensity distribution within the interaction region of erbium ions. Three different refractive index types of erbium-doped fiber were used to study the effect of the pump mode intensity distribution on noise performance. The results show that taking advantage of the depressed refractive index erbium-doped fiber which has a flat mode distribution in the fiber core, the maximum reduction of nearly 0.53 dB for noise figure was achieved across the full C-band. Based on the center depressed refractive index profile, the noise figure was further decreased by about 0.1 dB by reducing the doping radius to 0.71 μm. Finally, maintaining the same gain level of ∼38.3 dB, a NF reduction of ∼0.63 dB was realized by introducing the center depressed refractive index profile and narrowing the erbium doping region. It is suggested that our investigation shows great potential for improving the noise performance of the erbium-doped fiber amplifier.