Unidirectional Transmission Research Articles

High wave vector non-reciprocal spin wave beams

We report unidirectional transmission of micron-wide spin waves beams in a 55 nm thin YIG. We downscaled a chiral coupling technique implementing Ni80Fe20 nanowires arrays with different widths and lattice spacing to study the non-reciprocal transmission of exchange spin waves down to λ ≈ 80 nm. A full spin wave spectroscopy analysis of these high wavevector coupled-modes shows some difficulties to characterize their propagation properties, due to both the non-monotonous field dependence of the coupling efficiency, and also the inhomogeneous stray field from the nanowires.

Reconfigurable optical diode based on asymmetrically coupled slow-light waveguide

Controlling the flow of light is fundamental for on-chip optical signal processing. In this paper, we investigate how to realize high contrast, high unidirectional transmission rate, and reconfigurable nonreciprocal light transmission, based on a nonlinear nanocavity asymmetrically side-coupled with a specially designed slow-light waveguide. We analytically and numerically demonstrate that the unusual multiple threshold pump power points for trigging the photon transitions between bistable states, as well as the sensitivity of the dynamic interactions to the relative delay time between the signal light and pump pulse, play crucial roles in this optical diode system. Based on these findings, a high contrast (over 22 dB) and high unidirectional transmission rate (over 70%) optical diode is achieved. More importantly, the conducting direction of the optical diode can be controllably reversed, without the need of changing the signal's wavelength or power as usually done. This approach is promising in the fields of optical information processing and quantum computing.

Unidirectional asymmetry transmission based on quasi-accidental bound states in the continuum.

The unidirectional asymmetry transmission is demonstrated based on quasi-accidental bound states in the continuum by a one-dimensional chiral photonic crystal slab (CPhCs) composed of tilted silicon nano-pillars. The chirality breaks symmetries on the far field polarization and radiation Q-factor between the upward and downward radiation channels. Accordingly, the CPhCs only supports the unidirectional maximal asymmetry transmission at fixed incident and conical angles. The numerical simulation indicates that the CPhCs obtains a circular dichroism of 0.99 and Q-factor of 753.7 at λ = 1.565 μm. In addition, the handedness of polarization is also effectively converted between the incidence and transmission, and the handedness depends on the incident direction and conical angle. Our scheme provides a feasible route for applications in manipulating polarization and chiral sensing.

Research on the function of single jersey based on the 3D channel structure

The main purpose of this experimental study is to determine the thermal properties and the moisture conduction function of a single jersey with a three-dimensional channel structure. As the channel structure of single jersey is gradually applied in the functional sportswear sector, the channel structure has been knitted by single jacquard technology for research purposes. Firstly, the formation principle and the structural unit of knitted fabric with the channel structure were explained. Then, the effects of channel structure with different sizes on thermal insulation, quick-drying, wicking height, and moisture management performance of the fabrics were investigated. Finally, the performance characteristics of the channel structure fabric were analyzed through the channel structure model. The analysis obtains that the channel structure of the sample holds more stagnant air and a large evaporation area. Moreover, as the courses or wales of structural units increase, the thermal insulation rate and the evaporation rate of the fabric improve accordingly. Also, it has a superior effect on the improvement of the wicking effect and the unidirectional transmission of the fabrics. However, when the structural unit exceeds a particular value, the fabric structure begins to deform, which makes its wicking height and unidirectional transmission properties decline. It provides a reference for the design and development of the 3D channel structure of the functional knitted fabric.

Pastoral livestock market integration amidst improvements in physical and communication infrastructure: Evidence from northern Kenya

This article analyses the level of integration in pastoral markets in Kenya using high-frequency data generated through a crowdsourcing endeavour. The vector error-correction model framework was used to estimate the causal relationships between the short- and long-run market price. The results indicate that a higher proportion of price variation in larger markets in the region was due to market price shocks, while variation in the smaller markets originated from the larger markets. Weekly adjustments and the convergence of prices on a long-run equilibrium after experiencing shocks were also observed. Price transmission was also evident between markets operating along different trading routes. However, markets located close to production catchments exhibited lower price trends, despite being connected. These results suggest a strong influence of the recent infrastructural investments on price transmission between markets in the region. The findings imply that more investments would enhance the competitive trading environment and reduce unidirectional price transmission.

Nonreciprocal transmission of electromagnetic waves with nonlinear active plasmonic metasurfaces

Nonreciprocity is important for optical information processing, full-duplex communications, and protection of sensitive laser equipment from unwanted reflections. However, it is very challenging to obtain strong nonreciprocal response in optical frequencies, especially when nanoscale configurations are considered. In this work, we solve this problem by demonstrating a compact bifacial plasmonic metasurface that acts as an ultrathin nonreciprocal transmission filter at near-infrared frequencies. The proposed nanostructure is simple to be practically implemented, since it is composed of two silver nanostripes with different dimensions placed on both sides of an ultrathin active dielectric spacing layer. The introduced gain leads to an exceptional point formation in the linear operation regime, where unidirectional perfect transmission due to loss compensation is achieved from the presented non-Hermitian parity-time symmetric nanoscale system. The demonstrated plasmonic metasurface breaks the Lorentz reciprocity law at the nanoscale when its nonlinear response is considered, mainly due to its spatially asymmetric geometry combined with enhanced nonlinearity. Strong and broadband nonreciprocity with unity transmission contrast from opposite directions is realized under relatively low-input laser intensity values. Furthermore, asymmetric nonlinear third-harmonic generation with a pronounced contrast is also illustrated by the same nonreciprocal metasurface design. The findings of this work can lead to the realization of various self-induced nonreciprocal nanophotonic configurations, such as integrated ultrafast switches, ultrathin protective coatings, and asymmetric directional imaging devices.

New solutions of the soliton type of shallow water waves and superconductivity models

For uni-directional wave transmission in the smooth bottom of shallow sea water and the superconductivity of nonlinear media with dispersion systems, the (1 + 1)-dimensional Camassa-Holm and Landau-Ginzburg-Higgs equations are of particular interest in research to the academics. Analytical wave solutions to the stated models have been successfully constructed in this study, which might have considerable implications in describing the nonlinear dynamical behavior associated with the phenomena. The models we aim to uncover have been put into the form of differential equations with one characteristic variable expending the wave transformation coordinate and, thereupon, the rational (G′/G)-expansion technique is executed. Using the considered technique, diverse soliton solutions in suitable forms arrayed to trigonometric, rational, and hyperbolic functions have been determined. The achieved solutions are figured out in 3D profiles, assigning the free parameters involved in solutions to particular values and discussed their physical significance to bring out the inner context of the tangible incidents in the natural domain. The rational (G′/G)-expansion approach is efficient, concise, and capable of finding analytical solutions to other nonlinear models that can be considered in subsequent studies.

Unidirectional transmission of surface water waves based on evanescent wave modes

In this paper, the unidirectional transmission of surface water waves is experimentally observed by connecting the mode-selective channel and the spatial symmetry-breaking channel. The proposed mode-selective channel contains a symmetry structure but only allows the propagation of anti-symmetric modes in a specific frequency band, while the antisymmetric modes can be excited in the channel with spatial symmetry-breaking. Therefore, the surface water waves can only propagate through the channel when the fundamental plane wave mode is excited at the entrance of the spatial symmetry-breaking channel, but not vice versa. The results of theoretical and numerical analyses indicate that the evanescent wave mode caused by non-Bragg resonances is responsible for the emergence of the antisymmetric mode transmission. The non-Bragg evanescent wave mode, generated by the resonance between the fundamental and higher-order modes, widens the unidirectional transmission band of surface water waves. Limited by the small structure, the experimental observed unidirectional transmission has a wave extinction ratio of 20.49 dB. The simulations closer to the ocean situation show that the bandwidth can reach 0.18 Hz, and the extinction ratio is 46.09 dB. The realization of surface water wave transmission not only enriches our knowledge on ubiquitous wave phenomenon, but also benefits applications in ocean engineering, such as coastal protection, ocean wave control, green energy collection, and reef maintenance.

On-Chip Ultra-Compact Hexagonal Boron Nitride Topological Ring-Resonator in Visible Region

Ultra-compact topological ring-resonators with chirality are important devices for quantum optics. However, there are limited demonstrations of chiral resonators, especially in the visible region. We proposed a topological photonic ring-resonator based on hexagonal boron nitride (hBN) valley photonic crystal (VPC). The spin-valley locking effect in VPC allows achieving robust unidirectional transmission of edge states in the visible region (600 nm–650 nm). As a result, a high quality factor (Q factor) (679.3) with a free spectral range of 15 nm in the visible region can be achieved in a hBN all-pass notch filter (APNF) with a compact size (2.3 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> 2.0 μm). In addition, we investigated the transmission properties of hBN ring-resonators with different shapes and combinations, confirming the flexibility of designing topological ring-resonators based on this principle. This design can be readily integrated with quantum photonic chips for broad applications.

Exceptional Points in Parity--Time-Symmetric Subwavelength Metamaterials

When sources of energy gain and loss are introduced to a wave scattering system, the underlying mathematical formulation will be non-Hermitian. This paves the way for the existence of exceptional points, where eigenmodes are linearly dependent. The primary goal of this work is to study the existence of exceptional points in high-contrast subwavelength metamaterials. We begin by studying a parity--time-symmetric pair of subwavelength resonators and prove that this system supports asymptotic exceptional points. These are points at which the subwavelength eigenvalues and eigenvectors coincide at leading order in the asymptotic parameter. We then investigate the exotic scattering behavior of a metascreen composed of repeating parity-time-symmetric pairs of subwavelength resonators. We prove that the non-Hermitian nature of this structure means that it exhibits asymptotic unidirectional reflectionless transmission at certain frequencies and demonstrate extraordinary transmission close to these frequencies.

Lorentz-force gyrator based on AlScN piezoelectric thin film

This paper reports a chip-scale radio frequency Lorentz-force gyrator based on an aluminum scandium nitride (Al0.7Sc0.3N) thin film. The two-port gyrator, which is essentially a lateral overtone bulk acoustic resonator, consists of a planar coil for Lorentz-force transduction and two top-bottom electrode pairs for piezoelectric transduction. The non-reciprocity is generated by the phase transition in the Lorentz-force coupling when an external vertical magnetic field is applied. The Lorentz-force gyrators based on both AlN and Al0.7Sc0.3N thin films demonstrate good non-reciprocity, i.e., the 180° phase difference, at approximately 517 and 388 MHz, respectively. Thanks to larger piezoelectric constants, the Al0.7Sc0.3N gyrator demonstrates easier impedance matching and a wider fractional bandwidth of 6.3% at a magnetic field of 1.65 T compared to 1.3% for an AlN device. Finally, an isolator consisting of the Lorentz-force gyrator and a shunt resistor is demonstrated over 35 dB of isolation and flat unidirectional transmission.

Plasmonic Metal Mediated Charge Transfer in Stacked Core-Shell Semiconductor Heterojunction for Significantly Enhanced CO2 Photoreduction.

Construction of core-shell semiconductor heterojunctions and plasmonic metal/semiconductor heterostructures represents two promising routes to improved light harvesting and promoted charge separation, but their photocatalytic activities are respectively limited by sluggish consumption of charge carriers confined in the cores, and contradictory migration directions of plasmon-induced hot electrons and semiconductor-generated electrons. Herein, a semiconductor/metal/semiconductor stacked core-shell design is demonstrated to overcome these limitations and significantly boost the photoactivity in CO2 reduction. In this smart design, sandwiched Au serves as a "stone", which "kills two birds" by inducing localized surface plasmon resonance for hot electron generation and mediating unidirectional transmission of conduction band electrons and hot electrons from TiO2 core to MoS2 shell. Meanwhile, upward band bending of TiO2 drives core-to-shell migration of holes through TiO2 -MoS2 interface. The co-existence of TiO2 →Au→MoS2 electron flow and TiO2 →MoS2 hole flow contributes to spatial charge separation on different locations of MoS2 outer layer for overall redox reactions. Additionally, reduction potential of photoelectrons participating in the CO2 reduction is elaborately adjusted by tuning the thickness of MoS2 shell, and thus the product selectivity is delicately regulated. This work provides fresh hints for rationally controlling the charge transfer pathways toward high-efficiency CO2 photoreduction.

Self‐powered virtual olfactory generation system based on bionic fibrous membrane and electrostatic field accelerated evaporation

AbstractOlfactory plays an important role in virtual reality technology. In this work, a bionic fibrous membrane (BFM) integrated with the function of electrostatic field accelerated evaporation (EFAE) is applied for realizing the virtual olfactory generation (VOG) system. The BFM is capable of self‐driven unidirectional liquid transmission and EFAE process is induced on BFM by using an ultrafast voltage‐elevation triboelectric nanogenerator (UVE‐TENG). The output voltage from UVE‐TENG can reach 8 kV within 40 ms, which is enough to maintain all of the functions of VOG system. Meanwhile, the output current from UVE‐TENG is smaller than 1 μA, leading to a safe and human compatible system. The flow rate of the volatile liquid spray from the system emitter can reach 0.1 μl/s, and the average evaporation rate of the BFM device with integrated EFAE function is 0.12 mg/s. Accordingly, the user of this VOG system can feel the generation of odor within 3 s, while the switching of different odor channels can be wirelessly controlled by a mobile phone. This VOG system enhances the user's immersive and interactive experience for virtual reality technology. The similar system composed of UVE‐TENG, reed switch, BFM and EFAE devices also has potential application value in assisted breathing treatment and nasal delivery.image

Constant intensity acoustic propagation in the presence of non-uniform properties and impedance discontinuities: Hermitian and non-Hermitian solutions.

Propagation of sound through a non-uniform medium without scattering is possible, in principle, if the density and acoustic compressibility assume complex values, requiring passive and active mechanisms, also known as Hermitian and non-Hermitian solutions, respectively. Two types of constant intensity wave conditions are identified: in the first, the propagating acoustic pressure has constant amplitude, while in the second, the energy flux remains constant. The fundamental problem of transmission across an impedance discontinuity without reflection or energy loss is solved using a combination of monopole and dipole resonators in parallel. The solution depends on an arbitrary phase angle that can be chosen to give a unique acoustic metamaterial with both resonators undamped and passive, requiring purely Hermitian acoustic elements. For other phase angles, one of the two elements must be active and the other passive, resulting in a gain/loss non-Hermitian system. These results prove that uni-directional and reciprocal transmission through a slab separating two half spaces is possible using passive Hermitian acoustic elements without the need to resort to active gain/loss energetic mechanisms.

Parity-dependent unidirectional and chiral photon transfer in reversed-dissipation cavity optomechanics

Nonreciprocal elements, such as isolators and circulators, play an important role in classical and quantum information processing. Recently, strong nonreciprocal effects have been experimentally demonstrated in cavity optomechanical systems. In these approaches, the bandwidth of the nonreciprocal photon transmission is limited by the mechanical resonator linewidth, which is arguably much smaller than the linewidths of the cavity modes in most electromechanical or optomechanical devices. In this work, we demonstrate broadband nonreciprocal photon transmission in the reversed-dissipation regime, where the mechanical mode with a large decay rate can be adiabatically eliminated while mediating anti-PT-symmetric dissipative coupling with two kinds of phase factors. Adjusting the relative phases allows the observation of periodic Riemann-sheet structures with distributed exceptional points (Eps). At the Eps, destructive quantum interference breaks both the T- and P-inversion symmetry, resulting in unidirectional and chiral photon transmissions. In the reversed-dissipation regime, the nonreciprocal bandwidth is no longer limited by the mechanical mode linewidth but is improved to the linewidth of the cavity resonance. Furthermore, we find that the direction of the unidirectional and chiral energy transfer could be reversed by changing the parity of the Eps. Extending non-Hermitian couplings to a three-cavity model, the broken anti-PT-symmetry allows us to observe high-order Eps, at which a parity-dependent chiral circulator is demonstrated. The driving-phase controlled periodical Riemann sheets allow observation of the parity-dependent unidirectional and chiral energy transfer and thus provide a useful cell for building up nonreciprocal array and realizing topological, e.g., isolators, circulators, or amplifiers.

Acoustic edge mode in spiral-based metamaterials at subwavelength scale

Recently, the quantum effect of condensed matter physics is introduced into the acoustic field, which lays a new pathway to manipulate the acoustic wave. However, the acoustic topological insulator based on Bragg scattering requires their lattice constant to be comparable with the wavelength. In this paper, a novel subwavelength spiral element on the basis of the Archimedean spiral is proposed. Thanks to the central resonator with a slender curved channels scheme, the subwavelength Dirac cone forms in the band structure. The eigenfrequency of the element can be changed by the spiral geometric parameters, which triggers the topological phase transition characterized by opposite valley Chern numbers. The backscattering-immune unidirectional transmission edge state exists at different topological boundaries, suggesting its great robustness even at the sharp bends. Also the topological edge modes along the Z-shaped interfaces are verified by the experiments and the calculation, which provides an effective structure to control the low frequency acoustic wave transmission.

Dynamic risks from climate policy uncertainty: A case study for the natural gas market

A series of policies proposed to deal with climate change has affected the development of the natural gas market. This study aims to investigate whether climate policy uncertainty (CPU) affects natural gas from a dynamic perspective. First, we employ the time-varying Granger causality test to test the impact of CPU on natural gas over time. The results show that events related to climate policy can lead to changes in this impact. Then, we detect the long-, mid-, and short-run changes in this impact by using the frequency-domain Granger causality test. We find that the CPU only holds a significant long-run effect on natural gas. However, considering that raised CPU and declined CPU may have different effects on natural gas, we further apply the asymmetric frequency-domain test, and the results verify that this unidirectional risk transmission has asymmetry. Particularly, we find that increased CPU may lead to a decline in natural gas in the medium run, and this impact lasts until the end of the sample. Thus, market participants invested in natural gas markets should pay attention to the events related to climate policies and the long-run impact of CPU, especially of increased CPU shocks.

Optical Time Domain Reflectometry for Simultaneously Characterizing Forward and Backward Crosstalk Along Multi-Core Fibers

Uncoupled multi-core fibers (MCFs) are promising transmission media for realizing long-haul and large-capacity transmission using space division multiplexing. When the assignment of the signal transmission directions in adjacent cores is unidirectional or bidirectional, the forward and backward crosstalk respectively limits the capacity and distance of the transmission system using uncoupled MCFs. Understanding both the forward and backward crosstalk is crucial for determining an optimal transmission scheme according to traffic demands. In this paper, we propose a novel method based on optical time domain reflectometry for simultaneously characterizing the forward and backward crosstalk along uncoupled MCFs. We measured the forward and backward crosstalk along a four-core fiber by the proposed method. The forward and backward crosstalk obtained with the proposed method agreed well with those measured with unidirectional and bidirectional transmission methods. Since the proposed method enables us to simultaneously evaluate the forward and backward crosstalk along uncoupled MCFs from one end, it would be useful for testing those characteristics during the construction of MCF transmission lines.

In Depth Viral Diversity Analysis in Atypical Neurological and Neonatal Chikungunya Infections in Rio de Janeiro, Brazil.

Chikungunya virus (CHIKV) is an arthropod-borne virus (arbovirus) transmitted by Aedes mosquitoes. The human infection usually manifests as a febrile and incapacitating arthritogenic illness, self-limiting and non-lethal. However, since 2013, CHIKV spreading through the tropics and to the Americas was accompanied by an increasing number of cases of atypical disease presentation, namely severe neuropathies and neonatal infection due to intrapartum vertical transmission. The pathophysiological mechanisms underlying these conditions have not been fully elucidated. However, arbovirus intrahost genetic diversity is thought to be linked to viral pathogenesis. To determine whether particular viral variants could be somehow associated, we analyzed the intrahost genetic diversity of CHIKV in three infected patients with neurological manifestations and three mothers infected during the intrapartum period, as well as their babies following vertical transmission. No statistically supported differences were observed for the genetic variability (nucleotide substitutions/gene length) along the genome between the groups. However, the newborn and cerebrospinal fluid samples (corresponding to virus passed through the placenta and/or the blood–brain barrier (BBB)) presented a different composition of their intrahost mutant ensembles compared to maternal or patient serum samples, even when concurrent. This finding could be consistent with the unidirectional virus transmission through these barriers, and the effect of selective bottlenecks during the transmission event. In addition, a higher proportion of defective variants (insertions/deletions and stop codons) was detected in the CSF and maternal samples and those were mainly distributed within the viral non-structural genes. Since defective viral genomes in RNA viruses are known to contribute to the outcome of acute viral infections and influence disease severity, their role in these atypical cases should be further investigated. Finally, with the in silico approach adopted, we detected no relevant non-conservative mutational pattern that could provide any hint of the pathophysiological mechanisms underlying these atypical cases. The present analysis represents a unique contribution to our understanding of the transmission events in these cases and generates hypotheses regarding underlying mechanisms, that can be explored further.

Transmisión vertical y espacial de precios en el mercado mexicano e internacional de ganado vacuno

From 2000 to 2019, the Mexican beef subsector has undergone significant structural changes; the most important was the concentration of both production and marketing stages. In 2019, the Mexican Federal Commission of Competence revealed that, Mexican households’ income diminished between 16 and 31 % due to a lack of market efficiency. In the case of meat, the reduction may be up to 98 %. In this context, the objective of this study was to examine the degree of spatial price transmission between national and international live cattle prices and the vertical transmission between live cattle prices and carcass meat prices to evaluate market efficiency. The econometric approach consists of the estimation of a vector error correction model, using monthly beef real prices, for the period 1990-2019. Findings from this research provide information for decision-makers and stakeholders in this industry: these comprehend unidirectional transmission of international beef prices to domestic beef prices and from farm price to processor price. Also point to the existence of asymmetric price transmission, which is related to whether cattle and beef prices are increasing or decreasing. Results indicate that a long-run single cointegration relationship exists between international and farmer prices, and between processor and farm price. The direction of price transmission tends to go from producers to processors and from international price to farmer price. When the international price increases, the speed of adjustment tends to be significantly slower, in contrast to when the international price decreases, resulting in a significantly faster rate of adjustment.