Geometric Asymmetry Research Articles

Angstrom Scale Ionic Memristors' Engineering with van der Waals Materials: A Route to Highly Tunable Memory States.

Memristors that mimic brain functions are crucial for energy-efficient neuromorphic devices. Ion channels that emulate biological synapses are still in the early stages of development, especially the tunability of memory states. Here, we demonstrate that cations such as K+, Na+, Ca2+, and Al3+ intercalated in the interlayer spaces of vermiculite result in highly confined channels of size 3-5 Å. They host exotic memristor properties through ion exchange dynamics, even at high salt concentrations of 1 M. The bipolar memristor characteristics observed are tunable with frequency, geometric asymmetry, ion concentration, and intercalants. Notably, we observe polarization-flipping memristor behavior in two cases: one with Al3+ ions and another with devices having a geometric asymmetry ratio greater than 15. This inversion is attributed to the overscreening of counterions due to their accumulation at the channel entrance. Our results suggest that ion exchange dynamics, ion-ion interactions, and ion accumulation/depletion mechanisms, particularly with multivalent ions, can be harnessed to develop advanced memristor devices.

Ratcheting fluid pumps: Using generalized polynomial chaos expansions to assess pumping performance and sensitivity

A large diversity of fluid pumps is found throughout nature. The study of these pumps has provided insights into fundamental fluid dynamic processes and inspiration for the development of micro-fluid devices. Recent work by Thiria and Zhang [Appl. Phys. Lett. 106, 054106 (2015)] demonstrated how a reciprocal, valveless pump with a geometric asymmetry could drive net fluid flow due to an impedance mismatch when the fluid moves in different directions. Their pump's geometry is reminiscent of the asymmetries seen in the chains of contractile chambers that form the insect heart and mammalian lymphangions. Inspired by these similarities, we further explored the role of such geometric asymmetry in driving bulk flow in a preferred direction. We used an open-source implementation of the immersed boundary method to solve the fluid-structure interaction problem of a viscous fluid moving through a sawtooth channel whose walls move up and down with a reciprocal motion. Using a machine learning approach based on generalized polynomial chaos expansions, we fully described the model's behavior over the target 3-dimensional design space, composed of input Reynolds numbers (Rein), pumping frequencies, and duty cycles. Scaling studies showed that the pump is more effective at higher intermediate Rein. Moreover, greater volumetric flow rates were observed for near extremal duty cycles, with higher duty cycles (longer contraction and shorter expansion phases) resulting in the highest bulk flow rates.

All-dielectric structural coloration empowered by bound states in the continuum.

The technological requirements of low-power and high-fidelity color displays have been instrumental in driving research into advanced coloration technologies. At the forefront of these developments is the implementation of dye-free approaches, which overcome previous constraints related to color resolution and fading. Resonant dielectric nanostructures have emerged as a promising paradigm, showing great potential for high efficiency, high color saturation, wide gamut palette, and image reproduction. However, they still face limitations related to color accuracy, purity, and simultaneous brightness tunability. Here, we demonstrate an all-dielectric metasurface empowered by photonic bound states in the continuum (BICs), which supports sharp resonances throughout the visible spectral range, ideally suited for producing a wide range of structural colors. The metasurface design consists of TiO2 ellipses with carefully controlled sizes and geometrical asymmetry, allowing versatile and on-demand variation of the brightness and hue of the output colors, respectively.

Asymmetric thermo-electro-osmotic responses in charged conical nanochannels

Nanofluidic thermo-electric and thermo-osmotic responses have attracted increasing attention for their potential in low-grade heat energy recovery. However, the synergistic influence of geometric asymmetry and electrolyte physical properties on these responses is often overlooked. This study investigates asymmetric thermo-electro-osmotic responses by systematically varying parameters such as conicity, Debye length, and surface charge density within conical nanochannels. We employ the numerical model coupling extended Poisson-Nernst-Planck-Navier-Stokes and energy equations to simulate ion transport, fluid flow, and heat transfer. Results demonstrate pronounced asymmetries in thermo-electric and thermo-osmotic responses between forward and backward nanochannel configurations. The short-circuit current strongly depends on conicity, Debye length, and surface charge density, while the Seebeck coefficient is primarily influenced by Debye length, and surface charge density. Thermo-osmotic flow is significantly affected by all parameters, with flow direction reversals observed under specific conditions. The study highlights that Debye length and surface charge density significantly influence both thermo-electric and -osmotic responses, whereas geometric asymmetry predominantly affects thermo-osmotic response. This study provides a valuable framework for understanding fundamental thermal-driven transport phenomena at the nanoscale. The observed synergistic effects between various parameters offer insights for optimizing thermo-electric energy conversion and fluidic control within conical nanochannels, paving the way for innovative applications in nanofluidic technology and energy recovery systems.

Ultrabroadband coherent perfect absorption with composite graphene metasurfaces.

We investigate the design and performance of a new multilayer graphene metasurface for achieving ultrabroadband coherent perfect absorption (CPA) in the THz regime. The proposed structure comprises three graphene patterned metasurfaces separated by thin dielectric spacer layers. The top and bottom metasurfaces have crossed shape unit cells of varying sizes, while the middle graphene metasurface is square-shaped. This distinctive geometrical asymmetry and the presence of multiple layers within the structure facilitate the achievement of wideband asymmetric reflection under incoherent illumination. This interesting property serves as a crucial step towards achieving near-total absorption under coherent illumination across a broad frequency range. Numerical simulations demonstrate that the absorption efficiency surpasses 90% across an ultrabroadband frequency range from 2.8 to 5.7 THz, i.e., a bandwidth of 2.9 THz. The CPA effect can be selectively tuned by manipulating the phase difference between the two incident coherent beams. Moreover, the absorption response can be dynamically adjusted by altering the Fermi level of graphene. The study also examines the influence of geometric parameters on the absorption characteristics. The results of this research work offer valuable insights into the design of broadband graphene metasurfaces for coherent absorption applications, and they contribute to the advancement of sophisticated optical devices operating in the THz frequency range.

Experimental and numerical investigation on failure behaviour of aluminum-polymer friction stir composite joints

Friction stir composite joints between an aluminum alloy (AA6082-T6) and reinforced polymer (NorylTM GFN2) were studied regarding their failure characteristics. A comprehensive analysis on the mechanical behaviour of the joints was carried out, assessing the resulting deformed shape, the associated strain field and the observed failure modes using a digital image correlation (DIC) system and comparing with a finite elements method (FEM) model. The numerical model evidenced a good fitness to the experimental results since both the displacements and strain fields were found to be very similar. Both numerical and experimental strain fields in the longitudinal direction exhibited a localized spot of highly strained material, clearly indicating the nucleation site. Since secondary bending occurs in structural elements under tension due to geometrical and stiffness asymmetries, as is the case of overlap composite joints, a bending stress is induced, increasing the local stress compared to the nominal tension stress values. The ultimate tensile stress of the joints was found to range between 60.2 and 70.4 MPa, leading to an average joint efficiency of 82.6 %. The bending factor (kb) at the failure region was found to be 2.0, which means that the bending stress accounts for 2/3 of the total stress, acting as main failure catalyst.

Estimation of the Values of Electrical Shock Currents during Live-Line Work in Multi-Circuit, Multi-Voltage HVAC Transmission Lines

This article covers the analysis of voltages induced on the conductors of a de-energized circuit of a multi-circuit, multi-voltage HVAC transmission line. As a result of the multiplied interactions between the circuits in such lines, the expected electrical shock currents (touch currents) to which a lineman performing live work on such a line may be exposed are determined. A number of supporting structures of three- and four-circuit lines with various degrees of geometric asymmetry are analyzed. Analyses have shown that in multi-circuit lines in which circuits of different voltages are carried on a common structure, despite the outage of one of the circuits, touch voltages and electrical shock currents (touch currents) exceeding the permissible values can be expected on its conductors, endangering the safety of the lineman. The arrangements of s in such lines that provide the smallest values of touch currents are indicated.

Probing quantum causality with geometric asymmetry in spatial-temporal correlations

Probing quantum causality with geometric asymmetry in spatial-temporal correlations

Nonreciprocal scattering and unidirectional cloaking in nonlinear nanoantennas.

Reciprocal scatterers necessarily extinguish the same amount of incoming power when excited from opposite directions. This property implies that it is not possible to realize scatterers that are transparent when excited from one direction but that scatter and absorb light for the opposite excitation, limiting opportunities in the context of asymmetric imaging and nanophotonic circuits. This reciprocity constraint may be overcome with an external bias that breaks time-reversal symmetry, posing however challenges in terms of practical implementations and integration. Here, we explore the use of tailored nonlinearities combined with geometric asymmetries in suitably tailored resonant nanoantennas. We demonstrate that, under suitable design conditions, a nonlinear scatterer can be cloaked for one excitation direction, yet strongly scatters when excited at the same frequency and intensity from the opposite direction. This nonreciprocal scattering phenomenon opens opportunities for nonlinear nanophotonics, asymmetric imaging and visibility, all-optical signal processing and directional sensing.

Insights into crystal structure, temperature-dependent magnetization and dielectric relaxation mechanism in Bi substituted samarium iron garnet

The single phase Sm3−xBixFe5O12 with x=0.0,0.2,0.4 and 0.6 samples are synthesized by solid-state reaction method. We have systematically studied the structural, morphological, temperature dependent magnetic and electric properties. All the samples crystallize in simple cubic crystal structure and belongs to Ia3‾d space group. The lattice constant and bond angle between Fe(a)−O−Fe(d) network is enhanced with Bi substitution. As a result, the ferrimagnetic transition temperature is also enhanced from 565K to 569K. We have examined the applicability of Bloch's and Cojocaru's laws to our temperature-dependent magnetization data and find that Bloch's T3/2 law is not suitable due to geometrical asymmetry, long wavelength excitation, and local atomic disorders. However, Cojocaru's law which accounts for the geometrical aspects, provides a better fit to our magnetization data. Further, the impedance plots at room temperature exhibit no relaxation which is attributed to the limited mobility of charge carriers. On the other hand, the high temperature impedance data represents dielectric relaxation at a particular frequency. This frequency is used to determine the relaxation time which is fitted to Arrhenius law and activation energy is evaluated. The activation energy lies in between 0.24−0.32eV which corresponds to the singly ionized oxygen vacancies. The conduction mechanism is analyzed with Variable range hopping model and the average hopping length and hopping energies are also determined for these garnet samples.

Acoustic radiation force on a cylindrical composite particle with an elastic thin shell and an internal eccentric liquid column in a plane ultrasonic wave field

Abstract A model with three-layer structure is introduced to explore the acoustic radiation force (ARF) on composite particles with an elastic thin shell. Combing acoustic scattering of cylinder and the thin-shell theorem, the ARF expression was derived, and the longitudinal and transverse components of the force and axial torque for an eccentric liquid-filled composite particle was obtained. It was found that many factors, such as medium properties, acoustic parameters, eccentricity, and radius ratio of the inner liquid column, affect the acoustic scattering field of the particle, which in turn changes the forces and torque. The acoustic response varies with the particle structures, so the resonance peaks of the force function and torque shift with the eccentricity and radii ratio of particle. The acoustic response of the particle is enhanced and exhibits higher force values due to the presence of the elastic thin shell and the coupling effect with the eccentricity of the internal liquid column. The decrease of the inner liquid density may suppress the high-order resonance peaks, and internal fluid column has less effects on the change in force on composite particle at ka > 3, while limited differences exist at ka < 3. The axial torque on particles due to geometric asymmetry is closely related to ka and the eccentricity. The distribution of positive and negative force and torque along the axis ka exhibits that composite particle can be manipulated or separated by ultrasound. Our theoretical analysis can provide support for the acoustic manipulation, sorting, and targeting of inhomogeneous particles.

Experimental study on the hydrodynamic performance of a multi-DOF WEC-type floating breakwater

A hybrid system consisting of wave energy converters and breakwaters can be applied for both wave energy conversion and shoreline protection. Besides, the cost of wave energy conversion is believed to be reduced by such a combination. In this paper, a two-dimensional asymmetric wave energy converter-type breakwater with a triangle-baffle bottom that can convert wave energy through its heave motion is proposed and investigated experimentally in regular waves. A supporting system is designed and established to allow the model to move in a single degree of freedom or prescribed combination of multiple-degree-of-freedoms. The effects of the geometric asymmetry, the bottom slope, the width-to-draft ratio, and the multiple-degree-of-freedom motion on the wave energy conversion and attenuation performances are analyzed. The results show that the triangle-baffle wave energy converter-type breakwater has much higher wave energy conversion efficiency than its rectangular counterpart with the same displacement. Increasing the bottom slope and allowing pitch motion can improve efficiency, allowing surge motion will reduce efficiency, and the effect of increasing the width is uncertain due to two conflicting effects. The asymmetry, bottom slope, and width only have a limited influence on the wave attenuation, whereas surge and pitch motions reduce the wave attenuation in short waves, analogizing a wavemaker.

Modeling thermocapillary microgear rotation and transferring the concept of asymmetric shape to translational particle propulsion

In this study, we investigate the thermocapillary rotation of microgears at fluid interfaces and extend the concept of geometric asymmetry to the translational propulsion of micrometer-sized particles. We introduce a transient numerical model that couples the Navier–Stokes equations with heat transfer, displaying particle motion through a moving mesh interface. The model incorporates absorbed light illumination as a heat source and predicts both rotational and translational speeds of particles. Our simulations explore the influence of microgear design geometry and determine the scale at which thermocapillary Marangoni motion could serve as a viable propulsion method. A clear correlation between Reynolds number and rotation efficiency can be recognized. To transfer the asymmetry-based propulsion principle from rotational to directed translational motion, various particle geometries are considered. We demonstrate that, under illumination from above, geometrically asymmetric “Christmas tree”-shaped particles move forward. The exploration of breaking geometric symmetry for translational propulsion is mostly ignored in the existing literature, thus warranting further discussion. Therefore, we analyze expected translational speeds in comparison to corresponding microgears to provide insight into this promising propulsion method. Our simulations indicate that translational propulsion speeds of several particle lengths per second can be expected on the micrometer scale.

High Q chiroptical responses with maximum chirality in all-dielectric metasurfaces driven by quasi-bound states in the continuum

Chiral metasurfaces have attracted considerable attention because of their immense potential for diverse applications requiring chiral light-matter interactions. Recently, boosted by a mechanism based on the concept of bound states in the continuum (BICs), high Q factor chiroptical resonances have been exhibited by breaking the inversion symmetries of planar metasurfaces. However, the optical chirality of these chiral metasurfaces is generally intolerable with respect to the structural geometries, especially the geometric asymmetry. Here, we present a novel chiral quasi-BIC with strong optical chirality in an all-dielectric metasurface. By simultaneously breaking the in-plane C2 rotational and mirror symmetries, the chiral metasurface shows enhanced chiroptical resonances with near-unity CD (∼0.996) and high Q factors (∼2274) at terahertz frequencies. Further analyses based on numerical simulations reveal that the CD of the chiroptical resonance depicts exceptional remarkable tolerableness to the geometry asymmetry δ when δ are present in a broad range, while the corresponding Q factor is modulated accordingly. The results may develop a novel approach to manipulating the advanced optical chirality for potential applications requiring strong CD with enhanced light-matter interactions.

Failures of geometrically asymmetric steel-UHPC composite beams

Geometrically asymmetric steel-ultra-high performance concrete (UHPC) composite structures (SUCSs) suffer several typical failure modes during applications in structural engineering. But the competing mechanism of these failure modes remains a challenge to be urgently overcome. In the present paper, the failure modes of the geometrically asymmetric SUCSs under lateral loads are theoretically predicted and numerically studied. Considering both the geometric asymmetry of the structure and the tensile-compressive asymmetry of UHPC, a theoretical model is proposed to predict the critical failure load for each failure mode (e.g., bending and core shear), and then a failure mechanism map is constructed by comparing each critical failure load. The theoretical predictions are in line with the present numerical results and the previous experimental measurements. The results demonstrate that geometric asymmetry, together with some other geometric parameters and material properties, have remarkable influences on the failure modes of structures. This work provides an effective approach for predicting and designing the failure modes of geometrically asymmetric SUCSs in structural engineering applications, such as undersea tunnels, offshore platforms, and nuclear shielding walls.

Stress distribution in multilayer structural element subjected to skew bending

Results of researches on strength and stiffness of diagonally bending sandwich girders having geometric and/or stiffness asymmetry have been given. A mathematical module for calculation of normal strain (strength) and stiffness on bending at any cross-section point of sandwich girder has been proposed. The kinetics of stiffness on bending and strength variation dependences when geometric parameters of a cross-section and tension modulus ratios of girder layers are changing have been examined. It has been established that the strength of a diagonally bending sandwich girder on the whole depends on the position of the centre of stiffness and the position of the neutral plane.

Analysing and Computing the Impact of Geometric Asymmetric Coils on Transformer Stray Losses

Designing and manufacturing transformers often involves variations in heights and thicknesses of windings. However, such geometric asymmetry introduces a significant impact on the magnitude of stray transformer losses. This study examines the effects of asymmetric coils on the generation of stray losses within core clamps and transformer tank walls. A model has been introduced to ascertain the dispersion magnetic field’s value at a specific distance from the coil. The analysis extends to characterising the dispersion magnetic field reaching the tank walls by using electromagnetic simulation by a finite element method. It explores strategies to diminish stray losses, including the placement of magnetic shunts as protective shields for the tank walls. It delves into the efficacy of employing a transformer shell-type configuration to mitigate the magnetic dispersion field. The findings revealed that achieving greater symmetry in transformer coils can minimise stray losses. Specifically, the incorporation of magnetic shunts has the potential to reduce additional losses by 40%, while the adoption of a shell-type configuration alone can lead to a 14% reduction. This work provides valuable insights into optimising transformer designs, contributes a user-friendly tool for estimating additional tank losses, thereby enhancing the knowledge base for transformer manufacturers.

Dual-Channel Transverse Fields Radiofrequency Coils for 1.5 T Magnetic Resonance Imaging.

This theoretical study presents the design and analytical/numerical optimization of novel dual-channel transverse fields radiofrequency (RF) surface coils for 1.5 T Magnetic Resonance Imaging (MRI). The research explores a planar setup with two channels on a row with aligned spatial orientation of the RF coils, aiming to solve a common design drawback of single-channel transverse field RF coils: the reduced Field Of View (FOV) along the direction of the RF field. A significant challenge in this design is the efficient decoupling of two sets of transverse field RF coils to prevent mutual interference. Our modeling approach integrates thin wire theoretical modeling, magnetostatic computation for strip conductor coils, and their full-wave electromagnetic simulation. Key findings at 64 MHz demonstrate that strategic geometric placement among the two-channel RF coil and the introduction of geometrical asymmetry in the design of the individual RF coils does minimize the mutual inductance, paving the way for effective dual-channel MRI applications. This decoupling approach allows to enhance the FOV, providing a theoretical framework for the development of optimized dual-channel transverse field RF coil configurations. The current design was validated with full-wave numerical study at 64 MHz (1H, 1.5 T), has the potential to be extended at lower or higher frequencies, and the presence of lossy samples needs to be considered in the latter case.

Simultaneous effects of the position dependent mass and magnetic field on quantum well with the improved Tietz potential

In this study, we explored the synergistic impact of position-dependent mass and magnetic field on the electronic and optical properties of quantum wells, featuring an enhanced Tietz potential confinement incorporating both standard Morse and improved Rosen–Morse potentials, as influenced by variations in the structural parameter. Calculations were conducted within the framework of effective mass and parabolic band approximations. The diagonalization method was employed, selecting a wave function basis of trigonometric orthonormal functions to determine the eigenvalues and eigenfunctions of the confined electron potential. Our findings reveal that alterations in the sizes and shapes of the quantum wells, magnetic field strength, geometric asymmetry, and confinement parameters lead to significant variations in electron energies, transition between electron states, and the absorption spectrum. These outcomes offer valuable insights for investigating the electronic and structural properties of materials and devising novel materials with tailored optical characteristics.

Comprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects

Comprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects