Asymmetric Parameter Research Articles

Realization of robust high-Q resonances of BICsvia eigenfield perturbations in a multiple-notched nanocube metasurface.

Non-radiative bound states in the continuum (BICs) allow the construction of resonances with high-quality (Q) factors and have emerged as an attractive platform for manipulating light-matter interactions on the nanoscale. However, current studies on symmetry-protected BICs (SP-BICs) suffer from a fundamental trade-off between the Q factor and asymmetric parameters, presenting a significant hurdle for practical applications. Here, utilizing the eigenfield perturbations, we successfully break the conventional inverse quadratic law of the SP-BICs and realize the robust high-Q resonances against the asymmetric parameters. We find the introductions of the central notch can efficiently boost the resonance of the electric quadrupole, which results in the enhancement of multiple-mode interference, and thus improving Q factors, while the constant effective refractive index guarantees the resonance with a stable wavelength. Our findings provide a promising strategy for modulating the light-matter interaction and may pave the way for applications in future high-performance optoelectronic devices.

Enhancing underwater unmanned vehicle efficiency through asymmetric dynamics in manta-like swimming

This study explores the hydrodynamic performance of a National Advisory Committee for Aeronautics 0012 foil using computational fluid dynamics with the unsteady Reynolds-averaged Navier–Stokes (URANS) method and shear stress transport k-ω model to assess the impact of asymmetric motion parameters in manta-like swimming. The angles of attack during the mid-upstroke (αmu), mid-downstroke (αmd), and stroke duration (S) are varied to understand their effect. At low Strouhal numbers (StA = 0.2–0.35), a smaller αmd compensates for thrust loss at the start of the upstroke due to a greater αmu. At high Strouhal numbers (StA = 0.5), a greater αmd reduces negative thrust and compensates for the smaller thrust generated by a small αmu during the upstroke. Shorter stroke durations increase asymmetry, leading to more significant positive thrust peaks during the downstroke. If both the angle of attack and S are large, the slower downward speed extends negative thrust, reducing thrust peaks and lowering average thrust. A smaller stroke duration combined with a large angle of attack enhances efficiency due to a greater thrust-to-power ratio, highlighting the interplay between these parameters. A smaller S and greater αmd and StA maximize thrust and efficiency, suggesting aquatic organisms increase thrust while ensuring propulsion efficiency by using a large angle of attack and an asymmetric stroke duration. This study demonstrates how asymmetric parameters interact, providing insights into designing biomimetic underwater vehicles. The findings suggest that asymmetric dynamics enhance propulsion efficiency.

Unveiling asymmetric return spillovers with portfolio implications among Indian stock sectors during Covid-19 pandemic

This paper aims to provide a systematic inquiry into the return spillover dynamics between a network of Indian sectoral indices during the pre- and post-pandemic periods. To analyze the same, this paper uses the asymmetric time-varying parameter vector autoregressions (TVP-VAR) framework. Furthermore, in the spirit of Broadstock et al. (2020), we perform dynamic portfolio exercises based on common hedging techniques and the minimum connectedness portfolio approach to determine what better captures asymmetry. Our daily dataset includes 12 sectoral stocks spanning from January 01, 2017, to May 5, 2023. The findings reveal that negative connectedness dominates throughout the sample period, demonstrating that profit-maximizing agents and risk-averse investors are more likely to react negatively to news. We also show that in the network, the average net transmitters are the banking and other financial service sectors, whereas the net receivers are the information technology, pharmaceutical, and fast-moving consumer goods sectors throughout the period under consideration. Our results show that the minimum connectedness portfolio (MCoP) approach is a very useful method based on Sharpe ratios, as it is either the first or second most profitable among these three competing methods. These results, therefore, yield valuable insights for policymakers and investors

Active dual quasi-BICs in a dielectric metasurface with VO2 for slow light and optical modulation.

We investigate the temperature tunable dual quasi-bound states in the continuum (qBICs) in a silicon/vanadium dioxide (Si/VO2) hybrid metasurface with Q-factor being as large as 9.3 × 106 and 2.8 × 107 by breaking the in-plane C2 symmetry. The far-field scattering of multipoles and near-field distributions confirm that the toroidal dipole and magnetic quadrupole dominate the dual qBICs resonance. The high performance of slow light with ultralarge group index exceeding 5.6 × 105 and the inverse quadratic law between the group index and asymmetric parameter are achieved. By temperature tuning of the VO2 thin film at the sub-10 K scale, a modulation depth of 90% and the ON/OFF ratio exceeding 12.8 dB are obtained. The proposed temperature tunable dual qBICs have potential applications in the fields of tunable slow light, temperature switches, and sensors.

Estimation and model performance of aerosol radiative forcing from Radiative Transfer models using the AERONET data over Kenya, East Africa

The rapid economic growth and a lack of strict implementation of air quality regulations have led to unqualified effects on health, the environment, and the climate. In recent years, there has been an urgent need for the increased characterization of aerosols in terms of optical, micro-physical, and radiative properties and their climatic impacts. In the present study, the aerosol-climate implications were evaluated by aerosol radiative forcing (ARF) at three environmentally specific sites, Malindi (3° S, 40.2° E, 12 m asl), Mbita (0.42° S, 34.20° E, 1125 m asl), and Nairobi (1.0° S, 36.0° E, 1650 m asl), located in Kenya. The aerosol optical properties such as aerosol optical depth (AOD440), single scattering albedo (SSA440), asymmetric parameter (ASY440), and Ångström exponent (AE440-870) showed significant annual and seasonal heterogeneities. They noticed high (low) values during the local dry (wet) seasons, attributed to changes in anthropogenic activities, emission sources, and prevailing dynamics played by the meteorology. The study also utilized measured spectral aerosol optical properties and two radiative transfer models in the short-wave (SW) and long-wave (LW) regions with their respective spectral bands (0.2–4.0 µm) and (4.0–100.0 µm) during 2007–2018. The direct ARF simulated in the SW using the Santa Barbara DISORT Atmospheric Radiative Transfer Model (SBDART) and the Coupled Ocean and Atmospheric Radiative Transfer models (COART) depicted high correspondence, evidenced by relatively high (r > 0.64) correlations over the three sites. The ARF simulated by the two models in the SW and LW regions exhibited significant seasonal heterogeneity, with maximum (minimum) values observed during the local dry (wet) seasons. The results from the present study could form a basis for other climate change studies and increase the accuracy of the existing climate models to enhance climate forecasting over the East Africa region.

Multimodal ultra-high Q-factor C2 asymmetric all-dielectric metasurface induced by quasi-BIC states

A high Q-factor resonant cavity indicates minimal energy loss at the resonance frequency. In this paper, we propose a four-leaf clover sensor with air pillars based on the all-dielectric metasurface and discuss the C2 asymmetric induced quasi-bound states in the continuum(quasi-BIC). Firstly, we obtain dual Fano resonance by C2 symmetric configuration. Secondly, by introducing C2 asymmetric parameters, leading to a new Fano resonance peak, and the Q-factor exceeds 104. Furthermore, When the incident laser changes from TE mode to TM mode, the original Fano resonance peaks gradually disappear, and a new peak is generated near the 1273 nm. The calculated polarization sensitivity is up to 0.012 per degree. The dynamic range (DR) of the peak value of transmission spectrum with polarization is 58 dB. By calculation, we have achieved a maximum sensitivity (S) of 270 nm/RIU for an optical refractive index sensor, with a figure of merit (FOM) value of 2250 RIU-1.

Temperature-dependent dielectric relaxation studies of malononitrile from 10 MHz to 30 GHz using time domain reflectometry technique

Dielectric relaxation investigations of malononitrile have been carried out at different temperatures in the frequency range of 10 MHz–30 GHz using a time domain reflectometry technique. The static dielectric constant (ε0) and relaxation time (τ), and asymmetric distribution parameter (β) of liquid malononitrile at different temperatures have been determined using the Least Squares Fit method. The intermolecular hydrogen bonding in malononitrile has also been discussed with the use of the Kirkwood correlation factor and dielectric relaxation parameters.

Online Split-Phase Identification of Asymmetric Parameters Between Distribution Lines and Ground for Unbalanced Voltage Compensation Based on Power Electronics

Online Split-Phase Identification of Asymmetric Parameters Between Distribution Lines and Ground for Unbalanced Voltage Compensation Based on Power Electronics

Estimation of CLARK Y-14 Airfoil’s Lift Hysteresis in Low-Speed Flow

A phenomenon called hysteresis is responsible for the difference in the separation and the reattachment angles of an airfoil which is seen within the vicinity of the stalling angle of attack. The reason for this is the difference in the expected lift distribution of an airfoil for a particular angle of attack when recovery from stall is achieved. This leads to asymmetric flow parameters around a body even when the boundaries remain symmetric. Empirical results were obtained for a two-dimensional Clark Y-14 airfoil by varying the angle of attack for different Reynold’s numbers in order to estimate how lift characteristics are affected by the formation of hysteresis loops at different Reynolds numbers. It was seen that the extent of the clockwise hysteresis loops of the Clark Y-14 increased with the increase of the Reynolds number up to the Reynolds number of 134072 before starting to decrease again. The stalling angles followed a similar pattern before starting to decrease at a Reynolds number of 164543. These trends observed for the Clark Y-14 airfoil is similar to that of the Eppler 591 and NACA 0018 by Lance W.Traub and W.A Timmer respectively (Timmer, 2008), (Traub, 2016). When analyzing the coefficient of pressure variation for the Clark Y-14 airfoil at a particular Reynolds number, it was seen that a laminar separation bubble was formed for the forward stroke which shifted towards the leading edge of the airfoil which was common for all the Reynolds numbers. In the forward stroke, it could be seen that a laminar separation bubble was formed whereas for the backward stroke no such laminar separation bubble was formed for the same angle of attack which gave rise to the hysteresis loops of the Clark Y-`14 airfoil. It was observed that the laminar separation bubble had a direct impact on the formation of the hysteresis loops giving rise to static stall hysteresis as mentioned in previous research published by various authors. The empirical results obtained were further validated using Computation Fluid Dynamics.

A-shaped switchable asymmetric transmission metasurface based on VO2 in the THz band

The asymmetric transmission of terahertz (THz) waves has attracted considerable interest because of its novel applications in isolators and wireless communication. An A-shaped switchable asymmetric transmission metasurface integrating vanadium dioxide (VO2) in the THz band is proposed, which achieved dynamic control of asymmetric transmission by exploiting insulator-to-metal transition characteristics of VO2. When VO2 is in an insulating state, the proposed metadevice realized an asymmetric transmission effect of the asymmetric transmission parameter reaching up to 0.76 and realized linear polarization conversion with a 95% polarization conversion rate. Furthermore, the proposed metadevice prevented asymmetric transmission and polarization conversion as VO2 transforms in the metallic state. This work provides a new ideal for the design of switchable asymmetric transmission metadevices and has potential applications in wireless communication, sensing, and polarization control.

Vibrational resonance in an asymmetric system modeled by an electronic circuit: Effect of the buffers.

Vibrational resonance (VR) has been extensively studied in symmetric circuits, but research on this phenomenon in asymmetric electronic circuits is understudied. The current study aims to model a novel asymmetric electronic circuit and investigate the occurrence of VR in the circuit. This oscillator shows changes according to four control parameters, with the aid of two buffers. The amplification of signals in electronic circuits gives interesting results, vibrational resonance is one of the phenomena which is based on the amplification of signals. In this study, the asymmetric strength caused by the potentiometers and the frequencies influence are the major aims explored. Interestingly, the circuit shows different types of behaviors that are pointed out through waveform profiles, bifurcation diagrams, largest Lyapunov exponent, and the phase portraits. The dynamic of the system is studied theoretically, numerically and by Pspice Simulation. The Pspice estimates match with numerical simulations. We use the response Q(ω) method, based on the sine and cosine of the Fourier component to study VR. Our discovery suggests that the asymmetric parameter and the amplitude of the high frequency, both affect the occurrence of vibrational resonance.

Asymmetric TVP-VAR connectedness between highly traded commodities and hedging strategies: Evidence from major contagions

The objective of this study is to examine the return interconnectedness and asymmetric spillover effects in global commodity futures markets, with a focus on the impact of contagion. A competent asymmetric time-varying parameter vector autoregressive (TVP-VAR) model was employed for highly traded commodity futures (cocoa, coffee, corn, cotton, soy, sugar, wheat, and oil) between January 1, 2000, and March 31, 2024. This study investigates the connectedness of commodities in three dimensions: asymmetric spillovers, the influence of oil and oil substitutes on the network, and the impact of major contagions. The average total connectedness index (TCI) indicates that the connectedness is significant throughout the period and increases during the invasion. The findings imply that contagion effects trigger a potential alteration in the structure of the network integration level of the commodities, amplifying system-wide dynamic connectivity due to disurptions caused by oil and oil substitutes. The net plot depicts corn and soy as the net transmitters, with their magnitude increasing during the contagions. The pairwise connectedness index (PCI) revealed that corn-soy, corn‒wheat, and soy-wheat were the primary interactors, while oil became a significant interactor, particularly during the oil crash and the COVID-19 outbreak. Additionally, compared with other contagions, GFC had a potential asymmetric effect on the network. Positive returns dominate the interaction between the primary transmitter and receivers, whereas negative returns do not significantly dominate the total network. These investigations contribute to the literature on the food-fuel nexus in terms of asymmetries and the impact of contagions on the futures market. It also identified the optimal portfolio allocation based on the hedging effectiveness of three portfolio construction strategies.

Asymmetric Return Connectedness Among Indian Equity Sectors: Insights from Recent Global Disruptions

This article aims to study asymmetric shock transmission among India’s National Stock Exchange sectoral indexes before and amid the COVID-19 crisis and the Russian–Ukraine feud using an asymmetric time-varying parameter vector autoregressive connectedness technique. The daily closing price of equity sector indexes from 1 January 2018 to 31 March 2023 were used. The research reveals strong sectoral return interconnectedness, with negative returns spillover dominating the assessment period. COVID-19 substantially impacted connectedness more than the Russian–Ukraine feud. The sectors such as bank, private bank and financial services were net transmitters of risk, and information technology was the net recipient of risk throughout the assessment period, indicating these sectors are not much affected by these crises. Sector return spillover patterns were similar during the epidemic and the Russian–Ukraine dispute, except for the oil and gas and metal sectors, which shifted roles. These findings suggest that policymakers must recognize and assess the peculiarities of industries that are high-risk transmitters when formulating strategies to prevent market failure or mitigate risk transmission to others. Investors may benefit from recognizing industries that operate as risk transmitters and receivers to create effective risk-mitigation investment strategies amid turbulent times.

Cumulative ordinal quasi-symmetry model and its separation for square contingency tables with ordered categories

Summary This study deals with square contingency tables, which are two-way contingency tables in which the row and column variables consist of the same classification. When the categorical variables are grouped into ordered categories from quantitative variables by cut points, a score that approximates the distance between the midpoints of the quantitative scale categories may be used to reflect the characteristics of the data. As an asymmetry model based on scores, this study proposes the cumulative ordinal quasi-symmetry model and ordinal marginal homogeneity model based on cumulative probabilities. The asymmetric parameter in the proposed models would be useful for making inferences such as that a row variable is stochastically less than a column variable or vice versa. This study also gives a separation of the cumulative ordinal quasi-symmetry model, that is, the cumulative ordinal quasi-symmetry model holds if and only if both the cumulative quasi-symmetry and ordinal marginal homogeneity models hold. The usefulness of the proposed models and the proposed separation is demonstrated through real data analysis.

Identification of the Asymmetric Transmission Error and Gear Mesh Dynamic Parameters using Full-Spectrum Responses in a Geared-Rotor System

A dominant source of vibration in geared-rotor systems are the gear mesh fault parameters. They include the asymmetric transmission error, phases of transmission error, the gear mesh stiffness, the gear mesh damping and the gear runouts. The present work deals with the experimental identification of aforementioned parameters. A mathematical model of geared-rotor system has been developed using Lagrangian dynamics. Equations of motion are transformed into frequency domain using the full-spectrum response analysis. These transformed equations are used to develop an identification algorithm based on least-squares fit to estimate the transmission error and gear mesh dynamic parameters. The system identification algorithm is initially verified using numerical simulations. The robustness of the algorithm is checked by introducing white Gaussian noise in the simulated responses. A geared-rotor experimental rig was developed and used to measure responses at gear locations in two orthogonal directions. Measured responses are transformed in frequency domain using the full-spectrum analysis and used in the present novel identification algorithm to identify the gear parameters. The identified parameters are validated by comparing the numerically generated full-spectrum response using experimentally estimated parameters and that from the experimental rig. Conflict of Interest Statement The authors declare no conflicts of interest.

Performance analysis of an underwater wireless optical communication link with Lommel beam

In order to mitigate the stochastic interference of underwater channels and improve the quality of underwater communication systems, it is essential to study the performance of the underwater wireless optical communication (UWOC) links utilizing vortex beams with unique attributes. In this paper, the analytical formulae for the bit error rate (BER) and the average capacity of the UWOC link with diffraction-free Lommel beam are derived under the Rytov theory. Simulation results demonstrate that the system with a long wavelength, a high system signal-to-noise ratio(SNR), a small asymmetric parameter and receiving aperture diameter achieves a high average capacity and a low BER. Furthermore, in the underwater channel with a larger kinetic energy dissipation rate per unit mass of fluid and inner scale, a smaller mean-squared temperature dissipation rate, temperature salinity contribution ratio and transmission distance, the performance of the communication link can be improved. Meanwhile, it is found that the performance of the link with carrier Lommel beam are less sensitive to the topological charge, the scaling factor of the beam and the turbulent outer scale. These findings provide theoretical support for the design and implementation of an UWOC link utilizing the Lommel beam.

Rigid covalent bond of α-sulfur investigated via temperature-dependent EXAFS

This study performs extended x-ray absorption fine structure (EXAFS) measurements for the S-K edge in the temperature range of 10 and 300 K in the transmission mode using a photodiode to detect the transmitted x-rays. It provides the first report of temperature variations in the structural parameters of α-S. As the temperature increases from 10 to 300 K in the Fourier transform of kχ(k) the first peak corresponding to the covalent bond of the eight-membered ring becomes slightly low anomalously despite thermal disturbances. However, as in normal materials, the second peak at 300 K decreases to approximately half of that at 10 K, which contains several intra- and inter-ring correlations. All structural parameters of the covalent bond obtained by nonlinear least squares fitting exhibit missing temperature variations. A value of zero for the asymmetric parameter in the EXAFS (C 3) implies that the potential of the covalent bond is symmetric, and the constant value of the mean square relative displacement (MSRD) with temperature implies that the potential is extremely high. The Einstein model fitting for the temperature variation in the MSRD yields an Einstein temperature of 942 K and force constant (K) of 405 N m−1. The value of K is the largest among those of chalcogen elements.

Quasi-bound states in the continuum for electromagnetic induced transparency and strong excitonic coupling

Advancing on previous reports, we utilize quasi-bound states in the continuum (q-BICs) supported by a metasurface of TiO2 meta-atoms with broken inversion symmetry on an SiO2 substrate, for two possible applications. Firstly, we demonstrate that by tuning the metasurface's asymmetric parameter, a spectral overlap between a broad q-BIC and a narrow magnetic dipole resonance is achieved, yielding an electromagnetic induced transparency analogue with a 50 μs group delay. Secondly, we have found that, due to the strong coupling between the q-BIC and WS2 exciton at room temperature and normal incidence, by integrating a single layer of WS2 to the metasurface, a 37.9 meV Rabi splitting in the absorptance spectrum with 50% absorption efficiency is obtained. These findings promise feasible two-port devices for visible range slow-light characteristics or nanoscale excitonic coupling.

Assessment of Black Carbon, optical properties and aerosol radiative forcing at Pranmati basin Himalayan critical zone observatory

The study aimed to understand the optical properties of Black Carbon (BC) and radiative forcing over a data deficient Himalayan region focusing on critical zone observatory employing ground-based measurements by Aethalometer for BC and satellite retrieval techniques for optical properties during mid-May-June 2022 and January–May 2023.BC mass concentration ranged from 0.18 to 4.43 μgm−3, exhibit a mean of 1.47 ± 0.83 μgm−3 with higher summer concentration (1.51 ± 0.94 μgm−3) than winter (1.39 ± 0.61 μgm−3). The average Absorption Ångström Exponent observed to be significantly higher than unity (1.77 ± 0.31) over the studied high-altitude Himalayan region, suggesting the dominance of biomass-burning aerosol. Higher aethalometer derived compensation parameter (K) in winter suggesting locally originated BC while, lower K value in summer suggesting aged BC transported from Indo-Gangetic Plains.Optical properties calculated from “Optical Properties of Aerosol and Cloud” (OPAC) model are used in the “Santa Barbara DISORT Atmospheric Radiative Transfer” (SBDART) model to calculate the aerosol Direct Radiative Force (DRF). The entire studied period is characterized by the predominance of absorbing aerosols, particularly BC, increasing Aerosol Optical Depth, Asymmetric Parameters and decreasing Single Scattering Albedo, leading to a considerable increase in atmospheric radiative forcing (+0.9 Wm−2, top of atmosphere) and Heating Rate (0.36 KDay−1). The mean radiative forcing within atmosphere during summer was higher (+14.29 Wm−2) relative to the winter (+12.00 Wm−2), emphasizing the impact of absorbing aerosols on regional warming and potential glacier melting in the Himalayas at a faster rate. Urgent policy consideration for the reduction of absorbing aerosols is highlighted, recognizing the critical roles of Black Carbon in the changing behaviour of Critical Zone observatory. The study's data serve as a valuable resource to understanding and addressing uncertainties in climate models, aiding effective policy implementation for Black Carbon reduction.

An asymmetric S-curve trajectory planning based on an improved jerk profile

AbstractIn this paper, a method of planning the expanded S-curve trajectory of robotic manipulators is proposed to minimize the execution time as well as to achieve the smoother trajectory generation in the deceleration stage for point-to-point motions. An asymmetric parameter is added to the piecewise sigmoid function for an improved jerk profile. This asymmetric profile is continuous and infinitely differentiable. Based on this profile, two analytical algorithms are presented. One is applied to determine the suitable time intervals of trajectory satisfying the time optimality under the kinematic constraints, and the other is to determine the asymmetric parameter generating the minimum execution time. Also, the calculation procedure for the time-scaled synchronization for all joints is given to decrease unnecessary loads onto the actuators. The velocity, acceleration, jerk and snap (the derivative of jerk) of the joints and the end-effector are equal to zero at two end points of motion. The simulation results through 3 DOF and 6 DOF robotic manipulators show that our approach reduces the jerk and snap of the deceleration stage effectively while decreasing the total execution time. Also, the analysis for a single DOF mass-spring-damper system indicates that the residual vibration could be reduced to 10% more than the benchmark techniques in case velocity, acceleration and jerk are limited to 1.24 m/s, 6 m/s2 and 80 m/s3, respectively and displacement is set to 0.8m. These results manifest that the performance of reducing residual vibrations is good and demonstrate an important characteristic of the proposed profile suitable for point-to-point motion.