Nonlinear Response Research Articles

A two-step dynamic FEM-FELA approach for seismic slope stability assessment

AbstractThe determination of the factor of safety (FoS) of slopes during seismic excitation can be complex if the relevant effects of pore water pressure accumulation, nonlinear material response and variable shear strength are duly accounted for. A rational two-step approach to tackle this task based on a hydro-mechanically coupled dynamic simulation and finite element limit analyses is henceforth introduced. To ensure accurate transfer of the hydro-mechanical soil state, a mapping concept is presented, accounting for spatial distributions of stresses, excess pore water pressures, inertial forces and shear strength. The proposed approach is compared to limit equilibrium method (LEM) for the case of a large-scale water-saturated open cast mine slope subjected to seismic loading. In comparison with LEM, the new approach to assess seismic slope stability proves to be simpler in its implementation and straightforward, which could be an important asset for practitioners.

Modeling linear and nonlinear viscoelastic oscillatory rheometric stress-strain hysteresis of asphalt binders

AbstractUnderstanding the complex stress-strain hysteresis behavior of asphalt binders under varied conditions is critical for optimizing pavement performance. This study addresses the challenge by analyzing and modeling asphalt binder responses in oscillating shear mode across different aging states (unaged, short-term aged, and long-term aged), stretch amplitudes, frequencies, and temperatures. Fifty-three stress-strain hysteresis loops were meticulously analyzed, revealing distinct stress paths relative to applied stretch levels. A nine-parameter parallel rheological framework model was developed, integrating a four-parameter eight-chain (FEC) hyperelastic model in one network and a FEC hyperelastic model with a linear viscoelastic flow element in series in another. This constitutive model was implemented in LS-DYNA finite element simulations to predict experimentally-measured stress-strain hysteresis loops accurately. The research demonstrates the model’s capability to simulate both linear and nonlinear viscoelastic responses of asphalt binders across a wide range of environmental and loading conditions. This approach significantly enhances our ability to capture and understand the stress-strain behavior critical for asphalt pavement durability and performance optimization.

Large Optical Nonlinearity Enhancement and All‐Optical Logic Gate Implementation in Silver‐Modified Violet Phosphorus

AbstractAs the most stable allotrope of phosphorus, violet phosphorus (VP) has attracted extensive research in the field of all‐optical modulation due to its excellent broadband spatial self‐phase modulation (SSPM) effect. To better exploit the great potential of VP in nonlinear photonics devices, this work explores chemical doping method to artificially enhance the nonlinear optical response of VP. Herein, silver‐modified few‐layer VP (Ag‐VP) is constructed for SSPM experiments. In comparison to pristine VP, a significantly improved third‐order nonlinear susceptibility (χ(3)) and nonlinear optical response for Ag‐VP is obtained in visible light band, and the enhancement ratio increases with the increase of wavelength. Moreover, the excitation threshold of SSPM effect is also significantly reduced, with a reduction ratio up to 3.61. The enhanced nonlinear optical response is attributed to the improved light–matter interaction induced by impurity energy levels. By taking advantage of the outstanding SSPM effect of Ag‐VP, an all‐optical logic gate is designed to demonstrate “OR” logical information transmission. This work provides a new avenue for the design and application of energy‐saving and tunable nonlinear photonic devices in the future.

Giant Modulation of Second-Harmonic Generation in CuInP2S6 by Interfacing with MoS2 Atomic Layers.

Probing and manipulating the intriguing nonlinear optical responses in van der Waals (vdW) ferroelectrics offer opportunities for their applications in nanophotonics. Here, we report the observation of giant and tunable second-harmonic generation (SHG) in ferroelectric CuInP2S6 (CIPS) and CIPS/MoS2 heterostructures. The results show that CIPS, ranging from multilayer to bulk-like samples, all exhibit strong SHG with giant anisotropy. The SHG anisotropy is attributed to the local strain along the a-axis that naturally exists in CIPS, as evidenced by piezoresponse force microscopy measurement. We further realized the strong modulation of SHG in CIPS by interfacing with monolayer MoS2. A combination of polarization, temperature, and thickness-dependent SHG and photoluminescence analyses shows that the nonlinear optical signal control in CIPS/MoS2 heterostructures is unrelated to the polar symmetry of CIPS and MoS2 but is driven by light absorption-mediated interfacial coupling. Our study provides a material platform based on vdW ferroelectric heterostructures for achieving dynamic control of nonlinear optical responses, which shows great potential applications in modern nanophotonics.

Electrically switchable chiral nonlinear optics in an achiral ferroelectric 2D van der Waals halide perovskite.

Two-dimensional (2D) van der Waals (vdW) semiconductors play a key role in developing nanoscale nonlinear optical devices. 2D Ruddlesden-Popper lead halide perovskites (RPPs) expand the potential of using 2D vdW semiconductors in nonlinear optical applications because they exhibit electrically switchable and chiral second-order optical nonlinearity originating from the emergence of ferroelectricity and chirality. However, electrically switchable chiral nonlinear optics has not yet been realized because of the difficulty in electrically manipulating chiral structures. Here, we demonstrate that chiral second-harmonic generation (SHG) can be electrically induced and switched in an achiral biaxial ferroelectric 2D RPP. We observe reversible and continuous electrical switching of SHG circular dichroism and large nonlinear chiroptical activity. Polarization-resolved SHG imaging reveals that electrical poling induces the ferroelectric multidomain structure arising from the biaxial nature of the material, and the planar chirality appears. Our findings show a simple electrical control of the nonlinear chiroptical responses and establish chiral nonlinear optics based on ferroelectric 2D RPPs.

A dynamic strain prediction method for malfunction of sensors in buildings subjected to seismic loads using CWT and CNN.

Structural health monitoring (SHM) is a technique used to evaluate the safety of a structure based on the structural response. In the SHM, sensors may fail to measure the structural response, or data loss can occur during the data transmission and reception. In this regard, this paper proposes a method of predicting the strain response when a sensor installed in a structural member suffers a malfunction. To this end, a convolutional neural network (CNN) is introduced to predict the strain response. Time-history strain data for seismic loads measured in adjacent structural members are set as the input layer of the CNN, and continuous wavelet transform (CWT) results are additionally set in the input layer of the CNN to reflect the dynamic structural behavior during earthquakes in the CNN predictions. Time-history strain data for a member, the target of prediction, are set as the output layer of the CNN. Then, the trained CNN uses the time-history strain data of adjacent members with no sensor failure and the CWT result of the data to predict the strain response of a structural member with sensor failure. A numerical study on the seismic load of a single-span three-story steel moment frame and an experimental study on a single-span three-story reinforced concrete frame were carried out to verify the validity of the proposed method. This study presents a method of applying CWT data to the input layer of the CNN and discusses the effectiveness of CWT data for predicting the nonlinear response of a structural member with damaged sensors.

Unleashing the nonlinear optical response of layered vanadium diselenide towards the deep mid-infrared regime

Broadband nonlinear optical materials towards the deep mid-infrared regime are highly required in medical diagnostics, environmental pollution monitoring, etc. Here, we report the ultra-broadband nonlinear optical absorption behavior of the layered vanadium diselenide (VSe2) towards deep mid-infrared regime experimentally. The layered VSe2 prepared by the liquid-phase exfoliation method exhibits broadband and wavelength-dependent nonlinear saturable absorption and a large modulation depth of over 8% in the 3-10 µm spectral range. By utilizing the layered VSe2 for optical modulation, stable nanosecond pulse with a low Q-switched threshold has been delivered successfully from an erbium-doped ZBLAN fiber laser. The experimental findings can deepen the understanding of the nonlinear optical response of the transition metal dichalcogenides towards the deep mid-infrared regime, and may make inroads for the advancement of mid-IR optoelectronic devices.

Universal nonlinear responses of quantum Hall systems with Galilean invariance

Universal nonlinear responses of quantum Hall systems with Galilean invariance

Cold Sintered ZnO-Polystyrene (PS) Composites with Modified Interfacial Structures and Properties.

Lightweight and integrated electronic devices with high performance have become an inevitable trend in the development of power electronic systems. However, it is challenging to obtain lightweight and miniaturized varistors due to the low threshold electric field. Herein, (1 - x)ZnO-xPS composites with a high threshold electric field are prepared through a cold sintering process at 220 °C for 50 min, utilizing lightweight PS to modulate the grain boundary structures of ZnO varistors. With PS content ≤1.5 wt %, the relative densities of cold sintered composites exceed 95%. PS thin layers with a thickness of 2-10 nm are distributed at the grain boundaries of ZnO, forming the Schottky barrier, which triggers nonlinear current-voltage responses. With the addition of PS, the threshold electric field is dramatically enhanced from 135 to 2703 V·mm-1, higher than that of commercial ZnO varistors, which is further demonstrated by the electric field simulation of the Finite Element Method. The interfacial resistance obtained from impedance analysis increases with the increase of the PS content, and the activation energy of (1 - x)ZnO-xPS composites is higher than that of pure ZnO ceramics. This study provides a promising approach for the development of lightweight and cost-effective varistor materials.

Quantum geometry induced third-order nonlinear transport responses

Quantum geometry induced third-order nonlinear transport responses

Application research on nonlinear partitioned analysis of soil-structure interaction method of seismic response for seawater-seabed-structure.

The analysis of seismic response in marine engineering structures is pivotal for guaranteeing their seismic safety. Such analyses are intricate due to the complexity of fluid-structure and soil-structure interactions. This paper introduces a unified computational framework for wave motion within a water-saturated seabed-bedrock system, employing the Davidenkov model and a modified Massing rule to characterize the nonlinear properties of the saturated seabed. A comparative analysis is conducted between the nonlinear responses of marine sites subjected to linear and nonlinear free-field inputs, with a specific focus on the seismic response of bridges under seawater-seabed-structure interaction. The study demonstrates that the modulus of a nonlinear saturated seabed diminishes, leading to a decrease in the wave impedance ratio between the saturated seabed and bedrock. Consequently, the reflection and transmission coefficients from the bedrock to the saturated seabed increase, amplifying the seismic response. For deepwater bridges, under harder site conditions, the abutment's bottom response is largely insensitive to increasing water depth, whereas the shear at the abutment's base diminishes with increasing water depth. The proposed method is validated through two case studies, with an examination of the impact of saturated sites on the analysis results.

Future Increase in Extreme Precipitation: Historical Data Analysis and Influential Factors

With global warming driving an increase in extreme precipitation, the ensuing disasters present an unsustainable scenario for humanity. Consequently, understanding the characteristics of extreme precipitation has become paramount. Analyzing observational data from 1961 to 2020 across 29 meteorological stations in Heilongjiang Province, China, we employed kriging interpolation, the trend-free pre-whitening Mann–Kendall (TFPW–MK) method, and linear trend analysis. These methods allowed us to effectively assess the spatiotemporal features of extreme precipitation. Furthermore, Pearson’s correlation analysis explored the relationship between extreme precipitation indices (EPIs) and geographic factors, while the geodetector quantified the impacts of climate teleconnections. The results revealed the following: (1) There has been a clear trend in increasing extreme precipitation over the last few decades, particularly in the indices of wet day precipitation (PRCPTOT), very wet day precipitation (R95P), and extremely wet day precipitation (R99P), with regional mean trends of 10.4 mm/decade, 5.7 mm/decade, and 3.4 mm/decade, respectively. This spatial trend showed a decrease from south to north. (2) Significant upward trends were observed in both spring and winter for the maximum 1-day precipitation (RX1day) and the maximum 5-day precipitation (RX5day). (3) The latitude and longitude were significantly correlated with the most extreme precipitation indices, while elevation showed a weaker correlation. (4) Extreme precipitation exhibited a nonlinear response to large-scale climate teleconnections, with the combined influence of factors having a greater impact than individual factors. This research provides critical insights into the spatiotemporal dynamics of extreme precipitation, guiding the development of targeted strategies to mitigate risks and enhance resilience. It offers essential support for addressing regional climate challenges and promoting agricultural development in Heilongjiang Province.

Characterizing the interaction effects of modular components on transtibial prosthesis stance-phase mechanical behavior

Background: Despite evidence that passive prosthesis mechanical properties can directly affect user experience, prosthetists have access to minimal information regarding the mechanical interactions between a prosthetic foot and proximal modular componentry. Objectives: This study quantified the stance phase mechanical behavior of a transtibial prosthetic system through the addition of passive modular componentry to a dynamic response (DR) foot. Study Design: Repeated measures, mechanical characterization. Methods: Maximum displacement and energy return were measured with a materials test machine simulating initial, mid, and terminal stances. Twelve conditions were tested: a DR foot in combination with a hydraulic ankle at 2 resistance settings and 3 different shock-absorbing pylons (SAPs). The roll-over shape of the DR foot with and without hydraulic ankle was measured using a test rig. Results: Adding modular passive components altered displacement and energy return, displaying independent and interaction effects. Generally, the hydraulic ankle and SAP reduced energy return (up to 18%) but decreased (up to 51%) and increased (up to 88%) displacement, respectively, while the combined properties were more complex. Roll-over shape radii decreased with increasing load for the foot alone but exhibited a nonlinear response with the addition of the ankle. Conclusions: Inclusion of modular components in a transtibial prosthetic system can have complex mechanical interactions that independently affect the system's response to load. It is important for clinicians to be aware of the cumulative effects of these interactions to inform the tuning of transtibial prosthesis mechanical behavior. Combinations of hydraulic ankles and SAPs can help clinicians adjust the prosthesis to achieve a balance between user comfort and energy return.

Nonlinear conductivity of aqueous electrolytes: Beyond the first Wien effect.

The conductivity of strong electrolytes increases under high electric fields, a nonlinear response known as the first Wien effect. Here, using molecular dynamics simulations, we show that this increase is almost suppressed in moderately concentrated aqueous electrolytes due to the alignment of the water molecules by the electric field. As a consequence of this alignment, the permittivity of water decreases and becomes anisotropic, an effect that can be measured in simulations and reproduced by a model of water molecules as dipoles. We incorporate the resulting anisotropic interactions between the ions into a stochastic density field theory and calculate ionic correlations as well as corrections to the Nernst-Einstein conductivity, which are in qualitative agreement with the numerical simulations.

Parametric global mode method for dynamical modeling and response analysis of a rotating and length-varying flexible manipulator

Rotating and Length-Varying Flexible Manipulators (RLVFMs) benefit from the ability to transform their length to adapt to complex and demanding workspaces but suffer from increased complexity in nonlinear dynamical characteristics and thus difficulties in modeling. To provide an in-depth understanding of the RLVFMs, this paper proposes a novel dynamical modeling approach for the RLVFMs, called the Parametric Global Modal Method (PGMM), and presents a framework to study their nonlinear responses. It is capable of addressing time-varying boundary conditions and describing the elastic deformation of all flexible components with only one set of modal coordinates. A low-dimensional dynamical model of a RLVFM is developed. The natural characteristic results obtained from the models developed by the PGMM and the finite element method (FEM) are compared for verifications of the PGMM. Via a convergence analysis of responses, the high precision of the model developed by the PGMM is verified to be achieved by using only the first two modes. On this basis, the dynamic responses and computational efficiency of the low-dimensional model are validated through experiments and finite element method (FEM) simulations. Moreover, the responses of the RLVFM under operations of rapid maneuvering are studied and a potential vibration control strategy for the RLVFM is preliminarily demonstrated. This work provides a new way of developing advanced dynamical modeling methods of reconfigurable and deformable multi-component mechanisms for their dynamical design, response analysis, and system control.

Surface-Enhanced Raman Scattering-Based Multimodal Techniques: Advances and Perspectives.

Surface-enhanced Raman scattering (SERS) spectroscopy is a versatile molecular fingerprinting technique with rapid signal readout, high aqueous compatibility, and portability. To translate SERS for real-world applications, it is pertinent to overcome inherent challenges, including high sample variability and heterogeneity, matrix effects, and nonlinear SERS signal responses of different analytes in complex (bio)chemical matrices with numerous interfering species. In this perspective, we highlight emerging SERS-based multimodal techniques to address the key roadblocks to improving the sensitivity, specificity, and reliability of (bio)chemical detection, bioimaging, theragnosis, and theragnostic. SERS-based multimodal techniques can be broadly categorized into two categories: (1) complementary methods or systems that work together to achieve a common goal where each method compensates for the weaknesses of the other to culminate in a single enhanced outcome or (2) orthogonal techniques that are independent and provide separate but corroborating results simultaneously without interfering with each other. These multimodal techniques maximize information gained from a single experiment to achieve enhanced qualitative or quantitative analysis and broaden the range of detectable analytes from small molecules to tissues. Finally, we discuss emerging directions in multimodal platform design, instrument integration, and data analytics that aim to push the analytical limits of holistic detection.

Harmonic imaging for nonlinear detection of acoustic biomolecules.

Gas vesicles (GVs) based on acoustic reporter genes have emerged as potent contrast agents for cellular and molecular ultrasound imaging. These air-filled, genetically encoded protein nanostructures can be expressed in a variety of cell types in vivo to visualize cell location and activity or injected systemically to label and monitor tissue function. Distinguishing GV signal from tissue deep inside intact organisms requires imaging approaches such as amplitude modulation (AM) or collapse-based pulse sequences. However, these approaches have limitations either in sensitivity or require the destruction of GVs, restricting the imaging of dynamic cellular processes. To address these limitations, we developed harmonic imaging to enhance the sensitivity of nondestructive GV imaging. We hypothesized that harmonic imaging, integrated with AM, could significantly elevate GV detection sensitivity by leveraging the nonlinear acoustic response of GVs. We tested this hypothesis by imaging tissue-mimicking phantoms embedded with purified GVs, mammalian cells genetically modified to express GVs, and mice liver in vivo post-systemic infusion of GVs. Our findings reveal that harmonic cross-propagating wave AM (HxAM) imaging markedly surpasses traditional xAM in isolating GVs' nonlinear acoustic signature, demonstrating significant (p < 0.05) enhancements in imaging performance. HxAM imaging improves detection of GV producing cells up to three folds in vitro, enhances in vivo imaging performance by over 10 dB, while extending imaging depth by up to 20%. Investigation into the backscattered spectra further elucidates the advantages of harmonic imaging. These advancements bolster ultrasound's capability in molecular and cellular imaging, underscoring the potential of harmonic signals to improve GV detection.

Large internal stress induced nonlinear current-voltage behavior in nanodiamond strengthened ZnO ceramics.

The modulation of the electrostatic potential barrier at grain boundaries determines the performance of many ceramic-based electronics such as varistors. However, conventional protocols relying on complex doping and annealing processes inevitably increase the inhomogeneity of microstructure, which may jeopardize the performance stability and mechanical reliability in service. Instead of doping, herein we demonstrate an effective strategy to modulate the potential barrier in ZnO-based low-voltage varistors by exploiting internal stress-induced piezoelectric polarization. The local residual stress as large as ~1 GPa can be created in the ZnO matrix by incorporating ultra-stiff nanodiamond particles using a cold sintering process. As a result, the composite with only 2 wt% of nanodiamond exhibits a prominent nonlinear current-voltage response at a low switch voltage of 15.7 V/mm, which is ascribed to the depressed barrier height induced by the distinct effects of positively and negatively charged polarization on grain boundaries. More strikingly, the large internal stress can significantly enhance the strength of the composite by more than 230% compared with the monolith, owing to the highly strengthened grain boundaries and crack-tip bridging from prestressed nanodiamonds. These findings add internal stress as a new dimension to design mechanically robust ceramic electronics with high performance.

A Porphyrin-Based MOF Thin Film with Oriented Nanosheet Arrays for Optimizing a Nonlinear Optical Response.

Developing two-dimensional (2D) hybrid nanosheet arrays integrating inorganic and organic components is highly significant for third-order nonlinear optical (NLO) applications. Herein, an oriented 2D porphyrin-based MOF (ZnTPyP(Co)) thin film composed of vertically stacked ultrathin nanosheets was fabricated via the liquid-phase epitaxial (LPE) layer-by-layer (LBL) method. The prepared ZnTPyP(Co) thin film exhibits an outstanding third-order NLO response with a high third-order nonlinear susceptibility of ∼2.63 × 10-7 esu, which is ascribed to the hybrid nanosheet array structure. Additionally, experimental Z-scan measurement and theoretical calculations also demonstrate that the substitution of Co metal ions in the porphyrinic core can increase the level of delocalization of the porphyrinic group and contribute to the material's enhanced NLO properties. These findings not only provide new film candidates for NLO application but also highlight the potential of 2D MOF nanosheets in advanced optical devices.

Effects of Geometry and Supporting Silicone Layers on the Performance of Conductive Composite High-Deflection Strain Gauges

Piezoresistive sensors composed of nickel nanostrands, nickel-coated carbon fibers, and silicone can be used to measure large physical deflections but exhibit viscoelastic properties and creep, leading to a complex and nonlinear electrical response that is difficult to interpret. This study considers the impact of modifying the geometry and architecture of the sensors on their mechanical and electrical performance. Varying the sensor thickness leads to potentially significant differences in conductive fiber alignment, while adding external layers of pure silicone provides elastic support for the sensors, potentially reducing their extreme viscoelastic nature. The impact of such modifications on both mechanical and electrical behavior was assessed by analyzing strain to failure, the magnitude of hysteresis with cycling, the repeatability of the electro-mechanical response, the strain level at which resistance begins to monotonically decrease, and the drift in electrical response with cycling. The results indicate that thicker single-layer sensors have less electrical drift. Sensors with a multilayered architecture exhibit several improvements in behavior, such as increasing the range of the monotonic region by approximately 52%. These improvements become more significant as the thickness of the pure silicone layers increases.