Backward Coupling Research Articles

Bidirectional Allostery Mechanism in Catch-Bond Formation of CD44 Mediated Cell Adhesion.

Catch-bonds, whereby noncovalent ligand-receptor interactions are counterintuitively reinforced by tensile forces, play a major role in cell adhesion under mechanical stress. A basic prerequisite for catch-bond formation, as implicated in classic catch-bond models, is that force-induced remodeling of the ligand binding interface occurs prior to bond rupture. However, what strategy receptor proteins utilize to meet such specific kinetic control remains elusive. Here we report a bidirectional allostery mechanism of catch-bond formation based on theoretical and molecular dynamics simulation studies. Binding of ligand allosterically reduces the threshold force for unlocking of otherwise stably folded force-sensing element (i.e., forward allostery), so that a much smaller tensile force can trigger the conformational switching of receptor protein to high binding-strength state via backward allosteric coupling before bond rupture. Such bidirectional allostery fulfills the specific kinetic control required by catch-bond formation and is likely to be commonly utilized in cell adhesion. The essential thermodynamic and kinetic features of receptor proteins essential for catch-bond formation were identified.

Stochastic Differential Games and a Unified Forward–Backward Coupled Stochastic Partial Differential Equation with Lévy Jumps

We establish a relationship between stochastic differential games (SDGs) and a unified forward–backward coupled stochastic partial differential equation (SPDE) with discontinuous Lévy Jumps. The SDGs have q players and are driven by a general-dimensional vector Lévy process. By establishing a vector-form Ito-Ventzell formula and a 4-tuple vector-field solution to the unified SPDE, we obtain a Pareto optimal Nash equilibrium policy process or a saddle point policy process to the SDG in a non-zero-sum or zero-sum sense. The unified SPDE is in both a general-dimensional vector form and forward–backward coupling manner. The partial differential operators in its drift, diffusion, and jump coefficients are in time-variable and position parameters over a domain. Since the unified SPDE is of general nonlinearity and a general high order, we extend our recent study from the existing Brownian motion (BM)-driven backward case to a general Lévy-driven forward–backward coupled case. In doing so, we construct a new topological space to support the proof of the existence and uniqueness of an adapted solution of the unified SPDE, which is in a 4-tuple strong sense. The construction of the topological space is through constructing a set of topological spaces associated with a set of exponents {γ1,γ2,…} under a set of general localized conditions, which is significantly different from the construction of the single exponent case. Furthermore, due to the coupling from the forward SPDE and the involvement of the discontinuous Lévy jumps, our study is also significantly different from the BM-driven backward case. The coupling between forward and backward SPDEs essentially corresponds to the interaction between noise encoding and noise decoding in the current hot diffusion transformer model for generative AI.

Spatiotemporal Coupling Analysis of Urbanization and Ecosystem Services in Southeastern Fujian

Revealing the spatiotemporal coupling relationship between urbanization and ecosystem services can help to clarify regional development differences, optimize the implementation path of urbanization, and improve the quality of ecosystem services. Taking southeastern Fujian, a region with a good ecological foundation and strong urbanization potential, as a case study, the levels of multidimensional urbanization systems and typical ecosystem services of this region in the years 2000, 2010, and 2020 were quantified using the index comprehensive evaluation method and the InVEST model. The Pearson correlation coefficient and the coupling coordination degree model were used to analyze the spatiotemporal coupling relationship between urbanization and ecosystem services, and suggestions for improving regional coordinated development were proposed. The results showed that： ① The comprehensive urbanization level in southeastern Fujian increased continuously, with an average annual growth rate of 7.3%, of which social urbanization was the fastest, followed by economic urbanization and population urbanization, and spatial urbanization was relatively backward. Ecosystem services tended to decline, especially food and water provision services, which decreased by 61.9% and 46.9%, respectively. The spatial distribution showed a mismatch pattern of "high urbanization level and weak ecosystem services" in the southeast coastal area and "low urbanization level and strong ecosystem services" in the northwest inland area. ② The correlation between urbanization and ecosystem services was mainly negative. The negative effect of economic and social urbanization on ecosystem services was weaker than that of population and spatial urbanization, with a clear weakening tendency. As population and spatial urbanization slowed down sharply and economic and social urbanization accelerated, the driving force of urbanization development gradually shifted from "quantitative increase" to "qualitative improvement." Thus, the decline of ecosystem services was alleviated. ③ Comprehensive urbanization and various ecosystem services experienced three stages of "imbalance-transition-reconciliation," with an average increase of 60.5% to 120.6% in the coupling coordination degree. However, highly coordinated regions remained scarce, indicating that there is still significant room for improvement. The relative relationship between urbanization and ecosystem services evolved from urbanization lag to ecosystem services lag. The fluctuation problem of backward coupling coordination level caused by excessive urbanization had initially appeared in the southeastern coastal area. Therefore, in future construction, southeastern Fujian should improve economic quality and social benefits； strengthen the overall management, protection, and restoration of ecological space； and enhance the order and stability of the coordinated development of urbanization and ecosystem services.

Reliable intracavity reflection for self-injection locking lasers and microcomb generation

Self-injection locking has emerged as a crucial technique for coherent optical sources, spanning from narrow linewidth lasers to the generation of localized microcombs. This technique involves key components, namely a laser diode and a high-quality cavity that induces narrow-band reflection back into the laser diode. However, in prior studies, the reflection mainly relied on the random intracavity Rayleigh backscattering, rendering it unpredictable and unsuitable for large-scale production and wide-band operation. In this work, we present a simple approach to achieve reliable intracavity reflection for self-injection locking to address this challenge by introducing a Sagnac loop into the cavity. This method guarantees robust reflection for every resonance within a wide operational band without compromising the quality factor or adding complexity to the fabrication process. As a proof of concept, we showcase the robust generation of narrow linewidth lasers and localized microcombs locked to different resonances within a normal-dispersion microcavity. Furthermore, the existence and generation of localized patterns in a normal-dispersion cavity with broadband forward–backward field coupling is first proved, as far as we know, both in simulation and in experiment. Our research offers a transformative approach to self-injection locking and holds great potential for large-scale production.

Cloud and droplet dynamics during a human coughing event under fully mixed and unmixed room conditions

The study of cloud and droplet dynamics during potential transmission events, such as coughing, is essential for understanding the spread and deposition of aerosols and droplets carrying airborne diseases. This paper reports the refinement of a complex model that couples momentum, temperature, and humidity for accurately simulating the dynamics of aerosol clouds and the dispersion of larger droplets under various conditions within an environmental chamber. The model is then employed to quantify aerosol/droplet exposure of a person standing 1 m away from a host. In addition, a statistical framework sheds light on the impact of backward coupling (droplet to cloud), which is negligible compared to forward coupling (cloud to droplet). The near-field study also provides detailed information on droplet behavior, laying the foundation for large-scale far-field studies.

Synchronization onset for contrarians with higher-order interactions in multilayer systems.

We investigate the impact of contrarians (via negative coupling) in multilayer networks of phase oscillators having higher-order interactions. We report that the multilayer framework facilitates synchronization onset in the negative pairwise coupling regime. The multilayering strength governs the onset of synchronization and the nature of the phase transition, whereas the higher-order interactions dictate the backward critical coupling. Specifically, the system does not synchronize below a critical value of the multilayering strength. The analytical calculations using the mean-field Ott-Antonsen approach agree with the simulations. The results presented here may be useful for understanding emergent behaviors in real-world complex systems with contrarians and higher-order interactions, such as the brain and social system.

Reduction of electromagnetic coupling between parallel high speed interconnects using defected Microstrip structure

In the context of designing printed circuit boards (PCBs) for the upcoming fifth generation double data rate (DDR5) technology, the issue of electromagnetic coupling emerges as a significant challenge. To address this concern, a comprehensive approach to mitigating both forward and backward coupling is proposed in this paper. The presented research introduces an innovative solution by incorporating a Defect Microstrip Structure (DMS) with a meticulously designed mitered meander shape. This unique structure is strategically imposed within the victim microstrip lines, aiming to effectively curtail coupling effects between interconnected microstrip lines. By embedding the mitered meander DMS onto the microstrip line, the electromagnetic (EM) coupling strength is substantially reduced. The reduction in coupling is primarily attributed to the achievement of an optimized ratio between capacitive and inductive coupling among the interconnected microstrip lines. The effectiveness of the proposed method is rigorously evaluated through a series of full-wave electromagnetic simulations. These simulations encompass microstrip lines etched both with and without the integration of the mitered meander-shaped DMS. The analytical framework leverages the ANSYS Structure Simulator (HFSS), a powerful tool for evaluating electromagnetic behaviour.

Three-dimensional femtosecond laser inscription of type a-based high-efficiency first-order waveguide Bragg gratings

A novel type of waveguide Bragg grating (WBG) is demonstrated based on femtosecond laser-induced Type A refractive index modifications, namely based of the photochemistry of silver species in a specialty ortho-phosphate glass matrix. First-order WBGs are reported in the near-infrared and down to 736 nm in the visible. Relative transmission measurements with a 500 µm long WBGs lead to narrow-bandwidth attenuations (sub-nm spectral FWHM) from 2.29 dB to 6.25 dB for periods from 240 nm to 280 nm, respectively. The corresponding estimated backward coupling coefficients show high values from 1.66 mm-1 up to 2.69 mm-1. Additionally, we report on a true 3D helix-shaped WBG that shows an even stronger relative attenuation of 10.3 dB for a 500 µm long WBG, equivalently corresponding to a backward coupling coefficient of 3.7 mm-1. These novel results pave the way for new silver-based laser-inscribed integrated photonic devices, among which the combination of Bragg gratings to form active/passive optical resonators, but also the direct inscription of WBG at the glass interface for enhanced sensing applications.

Femtosecond-laser-inscribed Bragg grating in hollow-core fiber for highly sensitive optofluidic sensing.

An optofluidic sensor based on a Bragg grating in hollow-core fiber (HCF) is experimentally demonstrated. The grating is inscribed into the HCF by femtosecond laser illumination through a phase mask. Periodic index modulation is introduced into the silica material surrounding the hollow core, causing cladding mode resonance, and multiple reflection peaks are observed in the grating spectrum. These reflection peaks later shift to longer wavelengths when high-index liquid is infiltrated into the HCF. The new reflection peak results from the backward coupling of the liquid core mode of the waveguide, the mode field of which overlaps with the grating modulation surrounding the liquid core. The resonant wavelength of the liquid-core fiber grating increases with the index value of the infiltrating liquid, and optofluidic refractive index sensing is realized with the device. The highest refractive index sensitivity, 1117 nm/RIU, is obtained experimentally in the index range of 1.476-1.54. The infiltrated hollow-core fiber Bragg grating also exhibits high temperature sensitivity due to the high thermal-optic coefficient of the liquid, and a sensitivity of -301 pm/°C is achieved in the temperature range of 25°C to 60°C.

Numerical Investigation of on-Chip Multi-Gas Sensing Using a Low-Repetition-Frequency Microcavity Kerr Comb With Backward Interference Structure

By integrating a microcavity Kerr frequency comb with an interferometric arm structure for backward coupling with a slot sensing waveguide, we present a new on-chip multi-gas sensing device. The microcavity used for frequency comb generation has a novel symmetric double-ring structure with a large roundtrip length, which makes it possible to obtain high-resolution frequency-resolved absorption spectra. In the meanwhile, a flat octave-spanning broadband spectrum is obtained by dispersion engineering of the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -based micro-rings with a horizontal single slot structure. Without the use of an additional gas cell, the large-length sensing waveguide allows for improved integration. A multiple soliton comb with high pump-to-frequency comb conversion efficiency under the optimization of the microcavity structure to improve pump depletion was obtained. The simulation shows its high stability and application feasibility, and the sensing performance of several gas species in different wavelength regions is verified and analyzed.

Explosive synchronization of multi-layer complex networks based on star connection between layers with delay

Explosive synchronization (ES) is a kind of first-order jump phenomenon that exists in physical and biological systems. In recent years, researchers have focused on ES between single-layer and multi-layer networks. Most research on complex networks with delay has focused on single-layer or double-layer networks, multi-layer networks are seldom explored. In this paper, we propose a Kuramoto model of frequency weights in multi-layer complex networks with delay and star connections between layers. Through theoretical analysis and numerical verification, the factors affecting the backward critical coupling strength are analyzed. The results show that the interaction between layers and the average node degree has a direct effect on the backward critical coupling strength of each layer network. The location of the delay, the size of the delay, the number of network layers, the number of nodes, and the network topology are revealed to have no direct impact on the backward critical coupling strength of the network. Delay is introduced to explore the influence of delay and other related parameters on ES.

Traffic-driven explosive synchronization with adaptive local routing in complex networks

Despite extensive researches on explosive synchronization, the interplay between it and traffic dynamics has not received enough attentions. In this paper, we develop a traffic-driven Kuramoto-like synchronization model, in which pathway and strength of synchronization are determined by directed flow between the oscillator and its neighbors. We show how combining this model with an adaptive traffic routing based on local dynamic information of phase mismatches induces the explosive synchronization with hysteresis loop, width of which is produced by the difference between forward and backward critical coupling strengths and can be maximized by adjustable routing factors. We demonstrate the validity of such a mechanism in producing explosive synchronization phenomenon for different traffic flow levels, initial frequency distributions, network structures, as well as for both homogeneous and heterogeneous networks. Interestingly, it is found that the critical strength of forward coupling is easily affected by these factors, but backward transition behavior is robust with respect to them. All results indicate that our study can provide a new insight for the control of synchronization behavior in the real-world complex systems.

Supermode Bragg grating inscribed in a strongly coupled seven-core fiber and its responses to temperature and curvature.

A Bragg grating is successfully inscribed in a piece of strongly coupled seven-core fiber (SCF). There are two separate Bragg resonance notches observed in the transmission spectrum, corresponding to backward coupling of HE11-like and HE12-like supermodes of the SCF. The mode coupling mechanism of the Bragg grating is theoretically investigated via modeling and analyzing modal properties of the SCF. The theoretical results agree well with the experimental results. Since the SCF is spliced between two standard single mode fibers with central alignments at both ends, the transmission spectrum of the device also contains a set of interference fringe due to modal interference between the supermodes. The device's responses to temperature and curvature are experimentally measured, respectively. The obtained temperature sensitivities and curvature sensitivities of the supermode Bragg grating notches are 9.55 pm/°C and 9.55 pm/°C, -1.8 pm/m-1 and -112.3 pm/m-1, respectively. The obtained temperature sensitivity and curvature sensitivity of one of the interference spectrum dips are 11.8 pm/°C and -3909.8 pm/m-1, respectively. This device is potentially useful for simultaneous measurement of temperature and curvature.

Anomalous broadband Floquet topological metasurface with pure site rings

Photonic and acoustic topological insulators exhibiting one-way transportation that is robust against defects and impurities are typically realized in coupled arrays of two-dimensional ring resonators. These systems have produced a series of applications, including optical isolators, delay lines, and lasers. However, the structures are complicated because an additional coupler ring between neighboring rings is needed to construct photonic pseudospin. A photonic anomalous Floquet topological insulator is proposed and experimentally demonstrated in the microwave regime. This improved design takes advantage of the efficient and backward coupling of negative-index media. The results contribute to the understanding of topological structures in metamaterials and point toward a unique direction for constructing useful topological photonic devices.

Reconfigurable Spoof plasmonic Coupler for Dynamic Switching between Forward and Backward Propagations

AbstractA reconfigurable coupler constructed using two spoof surface plasmon polariton (SSPP) waveguides and a spoof localized surface plasmon (SLSP) resonator to achieve switching between the forward and backward coupling of SSPP waves is proposed. By changing the bias voltage applied to the varactor diodes loaded in the SSPP waveguide, the dispersion of the plasmonic structure is adjusted to achieve a reversed group velocity. Consequently, the direction of the coupled SSPP waves can be dynamically controlled at the same operating frequency. The tunability of this coupler can be further improved by incorporating varactor diodes into the SLSP resonator, where forward–backward coupling can be achieved at multiple frequencies.

Cortical signatures of precision grip force control in children, adolescents, and adults.

Human dexterous motor control improves from childhood to adulthood, but little is known about the changes in cortico-cortical communication that support such ontogenetic refinement of motor skills. To investigate age-related differences in connectivity between cortical regions involved in dexterous control, we analyzed electroencephalographic data from 88 individuals (range 8-30 years) performing a visually guided precision grip task using dynamic causal modelling and parametric empirical Bayes. Our results demonstrate that bidirectional coupling in a canonical 'grasping network' is associated with precision grip performance across age groups. We further demonstrate greater backward coupling from higher-order to lower-order sensorimotor regions from late adolescence in addition to differential associations between connectivity strength in a premotor-prefrontal network and motor performance for different age groups. We interpret these findings as reflecting greater use of top-down and executive control processes with development. These results expand our understanding of the cortical mechanisms that support dexterous abilities through development.

Explosive synchronization of multi-layer complex networks based on inter-layer star network connection

Explosive synchronization (ES) is a first-order transition phenomenon that is ubiquitous in various physical and biological systems. In recent years, researchers have focused on explosive synchronization in a single-layer network, but few in multi-layer networks. This paper proposes a frequency-weighted Kuramoto model in multi-layer complex networks with star connection between layers and analyzes the factors affecting the backward critical coupling strength by both theoretical analysis and numerical validation. Our results show that the backward critical coupling strength of each layer network is influenced by the inter-layer interaction strength and the average degree. The number of network layers, the number of nodes, and the network topology can not directly affect the synchronization of the network. Enhancing the inter-layer interaction strength can prevent the emergence of explosive synchronization and increasing the average degree can promote the generation of explosive synchronization.

A compact parallel coupled meander lines shaped composite right/left-handed transmission line (CRLH-TL) based symmetric quasi-0 dB coupler

AbstractIn this paper, parallel coupled meander lines (PCML) composite right/left-handed transmission line (CRLH-TL) based symmetrical quasi-0 dB coupled-line coupler is presented. Proposed coupler shows measured backward wave coupling level of 0.81 dB at frequency of 6.17 GHz with 3 dB fractional bandwidth (FBW) of 12.64%. Throughout the 3 dB frequency range (5.78–6.56 GHz), isolation and insertion loss of the coupler is better than 24 dB. Overall size of the proposed coupler is 19.6 × 12.1 mm. An equivalent lumped LC circuit model of the coupler is demonstrated. Measured results of the coupler show good agreement with the electromagnetic (EM) simulated and lumped LC circuit model simulated results, which validates proposed coupler design and its performance.

Explosive synchronization induced by traffic processes in complex networks

An abundance of studies on synchronization focus on the characteristics of synchronization itself, but ignore the guiding role of information transfer between dynamic units on the synchronization process. In reality, continuous interactions between dynamic units are costly and sometimes unnecessary. Here we perform both traffic and synchronization processes in the same network and propose a model based on a constant-density traffic. Each node delivers packets with preference according to frequency mismatch and degree, and its synchronization behavior is only determined by the received packets. Explosive synchronization (ES) can be induced in both heterogeneous and homogeneous networks, as well as in both symmetric and asymmetric frequency distributions. We have concluded that the correlation between the average reception degree and the natural frequency is a key feature for the emergence of ES. Furthermore, at different packet densities, the forward and backward critical couplings and the width of the hysteretic loop in ES all exhibit nonmonotonic behavior and have minimum values. ES can still appear even if the packet density is very low.

Design of the quasi-0 dB backward wave-coupled line coupler using CRLH-TL based on stepped-impedance open stub-loaded dual-mode resonator

ABSTRACTThis paper demonstrates symmetric backward wave quasi-0 dB coupled line coupler (CLC) based on the globe shaped composite right/left-handed transmission line (GS-CRLH-TL). The proposed CLC shows quasi-0 dB backward wave coupling with measured maximum backward coupling level of −0.72 dB at 3.07 GHz. −3 dB bandwidth of the backward coupling region is from 2.75 GHz to 3.34 GHz, corresponding to fractional bandwidth (FBW) of 19.16%. The designed CLC shows good isolation of more than 43 dB in the backward coupling region in −3 dB frequency range from 2.75 GHz to 3.34 GHz. The measured value of return loss, at the center frequency 3.07 GHz, is more than 26.4 dB. Overall size of the fabricated CLC including 50 Ω feedline is 0.631λg × 0.455λg where λg is the guided wavelength at 3.07 GHz. Good concurrence is obtained between the simulated results, equivalent LC circuit model results and the measured results.