Matching Conditions Research Articles

Coupling strength comparison in optical fiber with multiple sector shape stress elements

AbstractThe maximum stress oscillation amplitude and maximum coupling strength of the optical fiber with multiple sector stress elements are studied. Optimized fiber structure with craft feasible is designed and the related structural parameters are given. Comparing the research results, it is found that the optical fiber with triple sector stress elements can achieve the strongest coupling strength to realize the single circular polarization state conversion by the shortest coupling distance. In addition, though the maximum coupling strength is decreased as the number of stress elements increases, it remains the same order of magnitude as the triple sector's. So from the craft perspective, whether it is an optical fiber with triple sector stress elements or the other optical fiber with more sector stress elements, the optical fiber with the property of single circular polarization transmission can be achieved if the spinning rate satisfies the phase matching condition.

Zero‐sum game for nonlinear multiagent systems with full‐state constraints

AbstractThis paper addresses the zero‐sum game problem for strict‐feedback nonlinear multiagent systems with full‐state constraints. Specifically, this paper focuses on the zero‐sum game scenario, wherein multiple agents aim to optimize the control strategies while considering the conflicting objectives of their opponents. To handle the full‐state constraints, a one‐to‐one nonlinear mapping technique is employed to convert the original strict‐feedback system into a more manageable pure‐feedback system without state constraints. In order to find a Nash equilibrium for virtual control signals and external disturbances, a simplified reinforcement learning algorithm is proposed, which tackles the challenges posed by solving the Hamilton–Jacobi–Isaacs equation. Unlike the existing optimal control strategies that deal with matching conditions, the optimal control strategy for strict‐feedback nonlinear systems needs to address the computational complexity issue arising from the repeated derivation of the virtual controller. To overcome the high‐order virtual controller problem, an approach based on the dynamic surface technique is introduced. By incorporating an approximation term of the high‐order virtual controller into the value function, the computational complexity challenge is effectively resolved. Based on the Lyapunov stability theorem, it is proved that all signals of the closed‐loop systems are semi‐global uniformly ultimately bounded and the tracking control performance can be guaranteed. Finally, simulation results are given to verify the effectiveness of the proposed control strategy.

Efficient strong-field THz generation from DSTMS crystal pumped by 1030 nm Yb-laser

We report collinear strong-field terahertz (THz) generation from the organic crystal 4-N, N-dimethlamino-4-N-methyl-stilbazolium 2,4,6-trimethyl benzenesulfonate (DSTMS), driven by an industrial-grade ytterbium (Yb) laser operating at 1030 nm. The laser pulse duration is compressed from 800 to 90 fs by using a multi-pass-cell compressor. The output THz energy reaches 0.4 μJ, with a conversion efficiency of 0.22%. The spectrum covers over 0.1–6 THz with a peak electric field of 236 kV/cm. The phase matching condition and material absorption are illustrated. We demonstrate that a 1030 nm Yb-laser is used to pump organic crystal DSTMS for efficient THz generation in a simple collinear geometry, which provides a promising THz source based on an industrial-grade ultrafast laser.

All-fiberized sorter for nondestructively splitting the orbital angular momentum modes

Orbital angular momentum (OAM) mode sorter is crucial for various OAM (de)multiplexing applications. However, it is challenging to sort the OAM mode without destroying its helical phase. Here, an all-fiber non-destructive OAM mode sorter is proposed for splitting the high purity (>90%) OAM beam with specific topological charge, polarization state and wavelength. By controlling the asymmetrical microfiber coupling region, only the specific OAM mode satisfies the phase matching condition. The all-fibered OAM sorter is optimized to splitting the third order OAM mode with the maximum coupling efficiency 91.02% and the purity 94.71%. The Multiple modes sorter can be realized through the multistage cascaded structure. The proposed all-fiber OAM sort will be a prospective component to expand the OAM beam fiber system.

Fault estimation for a class of nonlinear systems using the improved intermediate estimator

AbstractThis paper focused on fault estimation in Lipschitz nonlinear systems by providing an improved intermediate estimator (IIE). The core feature of an intermediate estimator is to simultaneously estimate the fault and states of the system without considering the matching condition. Since fault estimation is the first step of the process to compensate for its effect, the system performance can be further improved by making more accurate fault estimation. The structure of the nominal intermediate estimator (NIE) was modified by being inspired by the proportional‐integral (PI) controller to improve the performance characteristics of the estimator, such as convergence rate, overshoot, and steady‐state error. The estimation equation was assumed as such in the proposed estimator structure that the estimated fault would have a PI structure of the output estimation error. This has increased the number of design parameters, improving the estimator performance in transient and steady‐state. The NIE can be indeed known as a particular case of the IIE since the proposed estimator benefits from all the advantages of an NIE while improving the estimation performance. The states of the error system were proven to be uniformly ultimately bounded according to Lyapunov stability theory and using the LMI method, as well as the appropriate selection of parameters. The analysis of the theory, simulation, and comparing the results of the proposed method with the NIE method reveal the capabilities and advantages of the proposed method.

Crosstalk-Free Multiplane Full-Color Holography Based on the Space Division Method

This paper has proposed a full-color holography based on the space division method to provide a new solution for three-dimensional color holographic display. The hologram is divided into three different regions for the R, G, and B trichromatic hologram components, which will be designed separately at the corresponding positions. The projection images at different projection depths are preprocessed to meet dimension matching and position matching conditions. Different color images are reconstructed on a single plane and 19 planes in simulations and experiments, respectively, which verify the feasibility of the method. The designed phase-only holograms were fabricated on the silica substrate to obtain the diffraction optical element (DOE). Expect for one DOE, three lasers, and one CCD, no additional optical components are required to prompt a compact and simple experimental setup, which is expected to be used to realize full-color display.

First-principles screening of metal–organic frameworks for entangled photon pair generation

The transmission of strong laser light in nonlinear optical materials can generate output photons sources that carry quantum entanglement in multiple degrees of freedom, making this process a fundamentally important tool in optical quantum technology. However, the availability of efficient optical crystals for entangled light generation is severely limited in terms of diversity, thus reducing the prospects for the implementation of next-generation protocols in quantum sensing, communication and computing. To overcome this, we developed and implemented a multi-scale first-principles modeling technique for the computational discovery of novel nonlinear optical devices based on metal–organic framework (MOF) materials that can efficiently generate entangled light via spontaneous parametric down-conversion (SPDC). Using collinear degenerate type-I SPDC as a case study, we computationally screen a database of 114 373 synthesized MOF materials to establish correlations between the structure and chemical composition of MOFs with the brightness and coherence properties of entangled photon pairs. We identify a subset of 49 non-centrosymmetric mono-ligand MOF crystals with high chemical and optical stability that produce entangled photon pairs with intrinsic G(2) correlation times τc∼10−30 fs and pair generation rates in the range 104−1010s−1mW−1mm−1 at 1064 nm. Conditions for optimal type-I phase matching are given for each MOF and relationships between pair brightness, crystal band gap and optical birefringence are discussed. Correlations between the optical properties of crystals and their constituent molecular ligands are also given. Our work paves the way for the computational design of MOF-based devices for optical quantum technology.

Cold plasma-induced effects on electromagnetic wave scattering in waveguides: a mode-matching analysis

This article presents advancements in an analytical mode-matching technique for studying electromagnetic wave propagation in a parallel-plate metallic rectangular waveguide. This technique involves projecting the solution onto basis functions and solving linear algebraic systems to determine scattering amplitudes. The accuracy of this method is validated via numerical assessments, which involve the reconstruction of matching conditions and conservation laws. The study highlights the impact of geometric and material variations on reflection and transmission phenomena in the waveguide.

Wave interaction with multiple adjacent floating solar panels with arbitrary constraints

The problem of wave interaction with multiple adjacent floating solar panels with arbitrary types and numbers of constraints is considered. All the solar panels are assumed to be homogeneous, with the same physical properties, as well as modeled by using the Kirchhoff-Love plate theory. The motion of the fluid is described by the linear velocity potential theory. The domain decomposition method is employed to obtain the solutions. In particular, the entire fluid domain is divided into two types, the one below the free surface, and the other below elastic plates. The velocity potential in the free surface domain is expressed into a series of eigenfunctions. By contrast, the boundary integral equation and the Green function are employed to construct the velocity potential of fluid beneath the entire elastic cover, with unknowns distributed along two interfaces and jumps of physical parameters of the plates. All these unknowns are solved from the system of linear equations, which is established from the matching conditions of velocity potentials and edge conditions. This approach is confirmed with much higher computational efficiency compared with the one only involving eigenfunction expansion for the fluid beneath each plate. Extensive results and discussions are provided for the reflection and transmission coefficients of water waves, maximum deflection, and principal strain of the elastic plates; especially, the influence of different types and numbers of edge constraints are investigated in detail.

Frequency sweep study on the generation of dual-mode second harmonics (DMSH) on an isotropic nonlinear elastic cylindrical rod by T(0,1) mode

Nonlinear ultrasonic (NLU) guided wave (GW) measurements are more sensitive to microscale defects than linear measurements. This nonlinear phenomenon is helpful for early-stage damage detection in material for nondestructive evaluation (NDE) and structural health monitoring (SHM) applications. The amplitude of the higher harmonics generated in the material serves as the basis for the NLU measurement. Recent studies have reported the presence of dual-mode second harmonic (DMSH) on an isotropic nonlinear elastic plate and cylindrical structures. The fundamental non-dispersive mode shear horizontal SH0 and torsional T(0,1) modes can generate simultaneously propagating dual-mode second harmonic(DMSH) on plate and cylindrical guided media respectively. For the case of cylinders, at phase matching condition two dominant second harmonic fundamental longitudinal (l(0,1)) and orthogonal torsional (t(0,1)┴) mode are generated with significant amplitude. The particle vibration of the t(0,1)┴ mode was present in both orthogonal directions compared to conventional T(0,1) mode and hence called orthogonal torsional mode. The present work aims to study the behaviour of DMSH at different frequencies through a frequency sweep study on a weakly nonlinear elastic cylinder of circular cross-section via numerical simulations and validated experimentally for some selected cases. The wave propagation of the T(0,1) mode at several selected frequencies from 300 kHz to 2.2 MHz is chosen to explore the second harmonic mode for better understanding. At frequencies below 1.25 MHz, l(0,1) mode is faster than t(0,1)┴ mode; above 1.25 MHz, it was the other way around. The behaviour of harmonics was observed to be in accordance with the group and phase velocities at the corresponding frequencies in the dispersion curves. The evidence for the presence of DMSH was validated experimentally for some selected frequency cases at different propagation distances. The significance of DMSH is explored via numerical simulations and found that t(0,1)┴ mode is sensitive towards material degradation, while all other generated wave modes were not affected. Research shows that enough energy is available in the generated DMSH to be noticed experimentally and in numerical simulations. This improved understanding of the generation of DMSH across different frequencies would be helpful in new advanced NLU-based NDE and SHM applications.

Fully integrated and broadband Si-rich silicon nitride wavelength converter based on Bragg scattering intermodal four-wave mixing

Intermodal four-wave mixing (FWM) processes have recently attracted significant interest for all-optical signal processing applications thanks to the possibility to control the propagation properties of waves exciting distinct spatial modes of the same waveguide. This allows, in principle, to place signals in different spectral regions and satisfy the phase matching condition over considerably larger bandwidths compared to intramodal processes. However, the demonstrations reported so far have shown a limited bandwidth and suffered from the lack of on-chip components designed for broadband manipulation of different modes. We demonstrate here a silicon-rich silicon nitride wavelength converter based on Bragg scattering intermodal FWM, which integrates mode conversion, multiplexing and de-multiplexing functionalities on-chip. The system enables wavelength conversion between pump waves and a signal located in different telecommunication bands (separated by 60 nm) with a 3 dB bandwidth exceeding 70 nm, which represents, to our knowledge, the widest bandwidth ever achieved in an intermodal FWM-based system.

Research on Dual Fuel Combustion Characteristics of PFI Natural Gas +DI Gasoline in Large Cylinder Diameter Engine

A 3D simulation model of a single cylinder of a natural gas engine was established. PFI natural gas DI gasoline was used to control the time matching between injection and ignition, so that gasoline could form a small active stratified area near the spark plug. The combustion characteristics under different matching conditions were studied, and finally compared with pure natural gas. It is found that gasoline can be used in large cylinder diameter natural gas engine in a small range, which can accelerate the combustion of natural gas fuel, shorten the time used by CA0-CA5 by 77.6%, shorten the time used by CA5-CA90 by 26.5%, and increase the indicated thermal efficiency of natural gas engine by 1.4%.

High-efficiency low-power 13C-15N cross polarization in MAS NMR

Biomolecular solid-state magic angle spinning (MAS) NMR spectroscopy frequently relies on selective 13C-15N magnetization transfers, for various kinds of correlation experiments. Introduced in 1998, spectrally induced filtering in combination with cross polarization (SPECIFIC-CP) is a selective heteronuclear magnetization transfer experiment widely used for biological applications. At MAS frequencies below 20 kHz, commonly used for 13C-detected MAS NMR experiments, SPECIFIC-CP transfer between amide 15N and 13Cα atoms (NCA) is typically performed with radiofrequency (rf) fields set higher than the MAS frequency for both 13C and 15N channels, and high-power 1H decoupling rf field is simultaneously applied. Here, we experimentally explore a broad range of NCA zero-quantum (ZQ) SPECIFIC-CP matching conditions at the MAS frequency of 14 kHz and compare the best high- and low-power matching conditions with respect to selectivity, robustness, and sensitivity at lower 1H decoupling rf fields. We show that low-power NCA SPECIFIC-CP matching condition gives rise to 20% sensitivity enhancement compared to high-power conditions, in 2D NCA spectra of microcrystalline assemblies of HIV-1 CACTD-SP1 protein with inositol hexakis-phosphate (IP6).

Regulating the electrical performance of contact-separation mode triboelectric nanogenerators based on double-sided groove textures

The contact-separation mode triboelectric nanogenerators (CS-TENGs) is a kind of micro/nano electromechanical power system based on the contact electrification and electrostatic induction. With the expansion of application field of the CS-TENG, regulating the electrical performance becomes essential. In this paper, simple and effective methods for the CS-TENG output regulation based on the double-sided groove textures are proposed. To do this, groove textures on both Cu contact electrode and PDMS dielectric layer are fabricated, and influences and mechanisms of the alignment angle (the angle between the direction of groove textures on the Cu electrode and that on the PDMS dielectric layer), matching condition (textures sidewall contact and non-contact) and applied pressure on the CS-TENG output are explored through output tests, contact and electrostatic simulations. It is shown that altering the alignment angle, matching condition and applied pressure of groove texture on the Cu contact electrode and PDMS dielectric layer, could simply regulate the output of CS-TENG, where changing the alignment angle is the most effective. Under low and high applied pressures, the variations of the output voltage with alignment angle from 0˚–90˚ reach to 343.8% and 297.2%, respectively, and CS-TENG at 0˚ angle outputs the maximum voltage under both pressures, while the minimum voltages under the two pressures are exhibited from different angles. The change of contact area induced by the longitudinal deformation and transverse expansion of the groove textures is the main reason for the output regulations.

Efficient Cascaded Third‐Harmonic Generation in Sampled‐Grating Periodically‐Poled Lithium Niobate Waveguides

AbstractPeriodically poled thin‐film lithium niobate (PPTFLN) waveguides enable efficient quadratic nonlinear processes due to the strong light confinement and the utilization of the largest nonlinear coefficient d33 of lithium niobate. Here, an efficient third harmonic (TH) generation is reported with a normalized conversion efficiency of 6481% W−2 cm−4 in a sampled‐grating PPTFLN waveguide under the pump of a continuous laser, which is improved by 4 orders of magnitude compared with reported results. Such an efficient TH generation is realized by cascaded second‐harmonic (SH) generation and sum‐frequency (SF) generation supported by a sampled‐grating domain structure with two Fourier coefficients of 0.44 and 0.37, respectively. Phase matching conditions for the SH and cascaded SF processes are simultaneously achieved by finely tuning the geometric dispersion, domain structure, and operating temperature of the PPTFLN waveguides.

Vacuum energy of scalar fields on spherical shells with general matching conditions

In this work we analyze the spectral zeta function for massless scalar fields propagating in a D-dimensional flat space under the influence of a shell potential. The static nature of the potential, and the spherical symmetry, allows us to focus on the spatial part of the field which satisfies a one-dimensional Schrodinger equation endowed with a point potential. The shell potential is defined in terms of the two-interval self-adjoint extensions of the one-dimensional Schrodinger equation that describes the radial part of the scalar field. After performing the necessary analytic continuation, we utilize the spectral zeta function of the system to compute the vacuum energy of the field.

Deadzone-adapted disturbance suppression control for global practical IOS and zero asymptotic gain to matched uncertainties

For control-affine nonlinear systems with a disturbance and unknown parameters satisfying a matching condition but not having a known bound, we introduce a direct adaptive control scheme with three design elements: (a) nonlinear damping, (b) single-gain adjustment, and (c) deadzone in the update law. Combining these three ingredients for the first time, we guarantee the following previously unattained property: an attenuation of the plant state to an assignable small level, despite unknown bounds on the parameters and disturbance, without a drift of the gain, state, and input. Given the tools and results, we refer to the proposed scheme as a Deadzone-Adapted Disturbance Suppression (DADS) Controller.

Collapsing Shear‐Free Anisotropic Embedding Star Model in f(R)$f(R)$ Gravity

AbstractThe current paper studied the dynamics of shear‐free and spherically symmetric collapsing stars by incorporating the features of anisotropic dissipative fluid in the realm of gravity. A complete radiative star model that describes the early static configuration obeying the embedding class 1 approach is generated. To acquittance the exact solutions of the geometric variables, a specific form of pressure anisotropy along with a time‐dependent Karmarkar condition is employed, leading to a spacetime solution that seems to be potentially reliable and regular throughout the collapse process. The matching conditions have been thoroughly investigated between the interior geometry and the Vaidya outgoing solution over the junction interface. The physical attributes of our solutions to the Einstein field equations under two viable and cosmologically well‐consistent models of are manifested. The presented features are in a stable equilibrium state and sustainable to model a dynamic structure of gravitational collapse without forming the black hole.

A single sequence of intermittent hypoxia does not alter stretch reflex excitability in able-bodied individuals.

Spasticity attributable to exaggerated stretch reflex pathways, particularly affecting the ankle plantar flexors, often impairs overground walking in persons with incomplete spinal cord injury. Compelling evidence from rodent models underscores how exposure to acute intermittent hypoxia (AIH) can provide a unique medium to induce spinal plasticity in key inhibitory pathways mediating stretch reflex excitability and potentially affect spasticity. In this study, we quantify the effects of a single exposure to AIH on the stretch reflex in able-bodied individuals. We hypothesized that a single sequence of AIH will increase the stretch reflex excitability of the soleus muscle during ramp-and-hold angular perturbations applied to the ankle joint while participants perform passive and volitionally matched contractions. Our results revealed that a single AIH exposure did not significantly change the stretch reflex excitability during both passive and active matching conditions. Furthermore, we found that able-bodied individuals increased their stretch reflex response from passive to active matching conditions after both sham and AIH exposures. Together, these findings suggest that a single AIH exposure might not engage inhibitory pathways sufficiently to alter stretch reflex responses in able-bodied persons. However, the generalizability of our present findings requires further examination during repetitive exposures to AIH along with potential reflex modulation during functional movements, such as overground walking.

Near-perfect sound absorption using hybrid resonance between subwavelength Helmholtz resonators with non-uniformly partitioned cavities

We present near-perfect sound absorption using a metasurface composed of meta-atoms (MAs) which are subwavelength Helmholtz resonators (HRs) with cavities non-uniformly partitioned by membranes. By embedding the membranes at different horizontal locations in the cavities, we break geometrical symmetry between the MAs so as to derive hybrid resonance between the MAs at our target frequency. The resonance frequency of each MA is determined by delicately adjusting the locations of the membranes, resulting in perfect absorption at the target frequency which is different from the resonance frequencies of MAs. The metasurface is designed to satisfy impedance matching conditions with air at one or more target frequencies with the aid of a theoretical model for frequency-dependent effective acoustic impedance. The theoretical model is established with physical reality by considering the higher-order eigenmodes of the membrane, the visco-thermal losses in narrow orifices, and the end corrections of the subwavelength HR. The designed metasurface is fabricated and its absorption performance is verified experimentally in an impedance tube. Near-perfect absorption of sound is achieved at the target frequency of 500 Hz, which is 12.3% lower than that of near-perfect absorption by previous metasurfaces inducing hybrid resonance between HRs without membranes.