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The effects of time-delayed vibration absorber (TDVA) on the dynamic characteristics of a flexible beam are investigated. First, the vibration suppression effect of a single TDVA on a continuous beam is studied. The first optimization criterion is given, and the results show that the introduction of time-delayed feedback control (TDFC) is beneficial to improving the vibration suppression at the anti-resonance band. When a single TDVA is used, the anti-resonance is located at a specific frequency by the optimum design of TDFC parameters. Then, in order to obtain low-frequency and broad bands for vibration suppression, multiple TDVAs are uniformly distributed on a continuous beam, and the relationship between the dynamic responses and the TDFC parameters is investigated. The obtained relationship shows that the TDVA has a significant regulatory effect on the vibration behavior of the continuous beam. The effects of the number of TDVAs and the nonlinearity on the bandgap variation are discussed. As the multiple TDVAs are applied, according to the different requirements on the location and bandwidth of the effective vibration suppression band, the optimization criteria for the TDFC parameters are given, which provides guidance for the applications of TDVAs in practical projects such as bridge and aerospace. [ABSTRACT FROM AUTHOR]

• Proposing origami/kirigami structures modeling method by affine transformation. • Providing physical interpretation and quantitative research of dynamic behaviors. • Clarifying the coupling effects of nonlinear elastic creases on flexible surfaces. • Conducting experiments on kirigami to show the crease design and effectiveness. A generalized multi-body dynamical modeling method of Origami/Kirigami structures considering the elastic–flexible coupling of surfaces and nonlinear creases is proposed. For different structures with complex spatial configuration and constraints, an Affine Transformation (AT) technique based on Absolute Nodal Coordinate Formulation (ANCF) is proposed to make the modeling more convenient and efficient. The surfaces are discretized by triangle reduced elements, and the constitutive relations of creases are described by nonlinear state-dependent torque constraints. The proof of the topological invariance of configurations is also given. The simulation of the folding capacity and dynamic behaviors on two Origami structures, Origami solar array mechanism, and enclosed Yoshimura Origami, are given, which verifies the effectiveness of the modeling method. Additionally, the quantitative dynamic behaviors contributes to the design principle of a Kirigami structure for multi-stability. Comparisons between theoretical results from modeling and experiments demonstrate the effectiveness of the modeling method and crease design. The AT-ANCF lays a theoretical foundation for dynamic prediction and design for large deformation Origami/ Kirigami structures, which has significant potential applications in dynamic properties design in the fields of aerospace, robotic etc. [ABSTRACT FROM AUTHOR]

Inspired that the neck structure can stabilize the head from body movements and external dynamic vibration by the role of intervertebral disc and surrounding muscles, a novel multi-layer structure with nonlinear elastic components is proposed in this paper. The proposed structure is expected for loading the weight of the end effector and isolating bending vibration with low-frequency in the range of 0.1 Hz to 1 Hz. First, considering the loading, the potential energy, restoring force, and structural configuration in axial direction are defined. Then, the dynamical restoring force and stiffness for bending are modelled for different structural parameters and configurations after the axial weight. According to the functions of the proposed structure required in applications including loading capacity and bending vibration isolation effectiveness, design criteria are carried out. Due to the realization of high-order quasi-zero stiffness property, the effective isolation band for bending vibration can be extended from about 0.08 Hz. In addition, based on the proposed design criteria, the constructed multi-layer structure displays remarkable dynamical stabilization effectiveness in ultralow frequency band. The proposed structure not only provides the biological explanations for car sickness, nausea, and airsickness of humans, but also solves the bottleneck techniques in bio-inspired nonlinear isolation structural design for transverse dynamical stabilization, which has remarkable potential applications in the fields of mechanical arm, sensors in satellite etc. [ABSTRACT FROM AUTHOR]

Background and aims: Soil microorganisms play key roles in soil nutrient turnover and plant community composition; however, the soil microbial community composition and species diversity are often influenced by nutrient enrichment which may affect how soil microbes influence nutrient cycles and the plant community structure. The resistance of soil fungal and bacterial communities to nitrogen (N) and phosphorus (P) additions and whether the responses of the soil microbes and the plant community are simultaneous in a N-limited temperate meadow ecosystem are still unclear. Methods: We carried out a 7-year experiment with N and P additions in a temperate meadow. The community structures of soil bacteria and fungi were examined based on high-throughput sequencing targeting the 16S rRNA and ITS genes, respectively. Results: Nitrogen addition did not influence the community composition or species richness of bacteria, but it did alter the soil fungal community composition and increased fungal operational taxonomic unit (OTU) richness. Phosphorus addition significantly altered the soil fungal and bacterial community compositions, decreased the richness of bacterial OTUs, and increased the OTU richness of fungi. Proteobacteria (38.5%) and Acidobacteria (22.3%) were the most dominant bacteria. Ascomycota were the dominant fungi (42.6%) across all samples. The enrichment of available P in the soil due to P addition reduced the bacterial β-diversity, while the β-diversity of soil fungi was mainly influenced by the concentrations of soil N and P, as well as soil moisture. Conclusions: The sensitivity of soil fungi and bacteria to P addition was stronger than that of N addition, and the response of the soil microbes to N and P additions was more sensitive than that of the plant community. Our results highlight the unequal sensitivity of the soil fungal and bacterial community composition and structure to N and P additions, thereby causing changes in above and belowground community composition and structures in the studied temperate meadow ecosystem. [ABSTRACT FROM AUTHOR]

• Generalizing model reconstruction method based on compressive sensing for dynamic behaviors. • Obtaining accurate governing equations for nonlinear systems with multiple attractors. • Verifying correlation by two nonlinear systems with multiple steady states by experiments. • Realizing the application of the model reconstruction for practical nonlinear dynamic systems. In this study, facing the challenges on model reconstruction for multi-attractor nonlinear systems, the data generation and sparse regression processes in sparse identification method are generalized, referring to compressive sensing, to obtain the accurate description under the least volume of test data set. In the data generation process, we introduce compressive sensing process by an arbitrary initial condition and arbitrary perturbations applied on time domain to transcend the local attractors. In the sparse regression process, the optimum sparse parameter is obtained by bi-optimization criterion according to accuracy and interpretability. Then, accuracy criterion is proposed, and when it discovers the unperceived dynamic behaviors, more dynamic data could be recorded and added into the modeling reconstruction data set by perturbations. It requires less dynamic signals by dynamical compressive sensing with perturbations compared to the previous method with uniform point fetching on the state space. Several numerical cases and two experiments of nonlinear systems with different kinds of multi-attractors are proposed to illustrate the effectiveness of the reconstruction method. In experiment, for the dynamic systems with multi-steady states phenomenon, the most obvious problem is the calibration of the equilibrium at the symmetrical configuration, which cannot be obtained for local dynamic behaviors due to its instability. In applications, this generalized modeling reconstruction method can continuously and compressively sense the dynamic behaviors and the stability of multiple attractors to figure out the accurate governing equations under a small quantity of data. In summary, different from the previous sparse regression algorithm for nonlinear systems with multiple attractors under huge amount of data set assembled offline filling a large enough state space, the proposed model reconstruction process can intelligently sense the dynamic behaviors and give the accurate prediction. [Display omitted] [ABSTRACT FROM AUTHOR]

In this article, the vibration absorption performances of a vibration absorber with time-delayed feedback control for a low frequency primary system are studied. In order to extend the effective working frequency band of the time-delayed vibration absorber, its stiffness is designed as an adjustable parameter. The stiffness value of the beam-structure absorber can be tuned by a group of stoppers that can change the constraint condition of the beam. First, the mechanical model of the proposed delay-coupled system is established. Then, the stability boundaries of the proposed system are derived. Next, the analytical approximate solutions of the system are obtained to reveal the frequency response functions. Moreover, two parameter design principles for low-frequency nonlinear primary system are proposed based on the antiresonance frequency and optimum condition. The results show that, for the low-frequency nonlinear primary system, according to the design principles, the antiresonance frequency band can be tuned and the vibration amplitude can be reduced to zero due to the effect of time-delayed control. Relevant experimental prototype is constructed to verify the efficacy of the proposed vibration absorber with time-delayed control. [ABSTRACT FROM AUTHOR]

This was a post hoc analysis of Systolic Blood Pressure Intervention Trial (SPRINT), aimed to investigate whether intensive blood pressure treatment has differential therapeutic outcomes on patients with different baseline Framingham risk score (FRS). The 9298 SPRINT participants were categorized into low-risk (baseline FRS < 10%), intermediate-risk (FRS = 10%-20%), or high-risk (FRS > 20%) arms. The primary outcome was a composite of myocardial infarction, acute coronary syndrome not resulting in myocardial infarction, stroke, acute decompensated heart failure, or death from cardiovascular causes. Serious adverse events were defined as hypotension, syncope, and bradycardia. Multiple Cox regression was used to calculate hazard ratios for study outcomes with intensive compared with standard SBP treatment between these three groups. After a median follow-up time of 3.26 years, the primary outcome hazard ratio (HR) for intensive versus standard treatment was 0.73 (95% CI: 0.61-0.88, P = .0044) in the high-risk arm. And, for all-cause mortality, the hazard ratio with intensive SBP treatment was 1.58 (95% CI: 0.55-1.06), 0.9 (95% CI: 0.26-9.50), and 0.53 (95% CI: 0.34-0.82) in three arms (all P values for interaction > 0.05). Effects of intensive versus standard SBP control on serious adverse events were similar among patients with different FRS. Our results suggested that regardless of the FRS level, the intensive blood pressure control was beneficial. [ABSTRACT FROM AUTHOR]

In this study, magnetic interaction is applied to a continuous structure as local negative-stiffness components to improve the vibration isolation performances and to extend the vibration isolation band. According to the theory of electromagnetic fields, the mechanical model of interaction force is established. This model is used to discover that the magnetic interaction can induce the negative stiffness property locally using appropriate structural parameters. Because different structural parameters of the magnets can increase the negative stiffness strength with different effects, the parameters of the continuous beam and magnets are adjusted for the design of accurate zero stiffness property locally. Then, the relationship between structural parameters and effective isolation bandwidth is established by deriving the solution of steady state around zero equilibrium. As the nonlinearity and zero-stiffness property only occur locally around zero equilibrium and the system displays the positive-stiffness property for large vibration amplitudes, the effective isolation band is significantly extended, and the amplitude–frequency curve is similar to the linear system at resonance. The relevant experiments demonstrate the remarkable tuning characteristic of structural parameters of magnets on the isolation features, which realize the improvement of isolation/protection effectiveness for time-lasting excitation at a low frequency. This study not only demonstrates the advantages of nonlinearity induced by local magnetic interaction on the improvement of isolation performances but also realizes a continuous structure with local quasi-zero stiffness applied in fields of low-frequency engineering structures. • Realizing adjustable negative stiffness by magnetic interaction. • Utilizing local property of magnetic force to realize quasi-zero-stiffness property. • Building the relation between structural parameters and effective isolation band. • Assembling the relevant experiment of continuous structure under magnetic field. [ABSTRACT FROM AUTHOR]

Abstract This paper generalizes and modifies the Equal-peak method for the design of nonlinear vibration absorber for use in the vibration suppression of nonlinear primary vibration system. For a vibration system with nonlinearity, the most relevant bandwidth is the resonance band, in which the undesirable nonlinear vibration phenomenon occurs because of the dramatically amplified of vibration amplitude. To generalize the Equal-peak method for a complex nonlinear primary system under force/base excitations, we utilize the nonlinear perturbation method and bifurcation theory to investigate the vibration performances and critical conditions for dynamical transition. In addition to the Equal-peak property, another novel advantage, called De-nonlinearity (introduced by coupling nonlinearity), is revealed for vibration control in addition to the known effect of nonlinearity on vibration suppression. It is discovered that by applying the nonlinear vibration absorber with appropriate design on the NL primary system, the Equal-peak property can be accurately realized, and unexpected nonlinear vibration performances can be effectively eliminated. A relevant experimental prototype is carried out to illustrate the Equal-peak and De-nonlinearity properties, which is composed of a primary vibration system with complex nonlinearity and a designed tunable nonlinear vibration absorber. The proposed modified design method for Equal-peak and De-nonlinearity properties has huge potential application in the vibration suppression for low-frequency and strong nonlinearity fields such as ships, aircrafts and ocean platform. Highlights • Explore a modified nonlinear tuning method for the design of nonlinear vibration absorber. • Realize accurate equal-peak property for different parameters changing in large ranges. • Obtain expressions of nonlinear frequencies and peaks for multi-nonlinearity system. • Design appropriate nonlinearity to eliminate undesired nonlinear vibration performances. • Introduce the Origami structure to assemble a tunable nonlinear vibration absorber. [ABSTRACT FROM AUTHOR]

Abstract Background and aims Peripheral arterial disease (PAD) is a clinical manifestation of extracoronary atherosclerosis. Many risk factors are involved in the process of PAD, but the association between serum magnesium (Mg) and PAD is not clear. Our study aimed to investigate whether serum Mg is associated with PAD incidence. Methods A total of 13,826 participants (aged 40–64 years) in the Atherosclerosis Risk in Communities (ARIC) study (1987–1989) without prior PAD were included in the final analysis. Serum Mg levels were measured at visits 1 and 2. PAD was defined as an ankle brachial index less than 0.9, or hospitalization with a PAD diagnosis. Cox regression was used to calculate hazard ratios (HRs) for incidence of PAD and serum Mg. Results During a median follow-up of 24.4 years, 1364 (48.4% female) PAD events were observed. After multiple adjustment, participants in the lowest (≤1.4 mEq/L) category of serum Mg compared with the highest (≥1.8 mEq/L) ones were at higher PAD risk (HR: 1.3; 95% confidence interval (CI): 1.06–1.58) (p value = 0.004). The HRs for PAD in 1.5, 1.6 and 1.7 mEq/L of serum Mg were 1.29 (95% CI: 1.08–1.54), 1.05 (95% CI: 0.89–1.24), and 1.0 (95% CI: 0.85–1.18), respectively. Conclusions Low serum Mg was independently associated with an increased prevalence of PAD in the large population-based study; further studies are needed to confirm our findings. Graphical abstract Image 1 Highlights • Serum magnesium (Mg) was inversely and independently associated with the risk of peripheral arterial disease (PAD). • The relation between serum magnesium and peripheral arterial disease was non-linear. • Serum Mg may become a new biomarker for PAD risk prediction. [ABSTRACT FROM AUTHOR]

Highlights • Propose a novel isolation structure with flexible joints. • Introduce Origami mechanism in vibration isolation/protection structure. • Utilize asymmetrical nonlinearity to extend the effective isolation bandwidth. • Determine the optimal structural parameter of folds for isolation effectiveness improvement. • Carry out the experimental prototype with remarkable isolation/protection property. Abstract This paper proposes a novel isolation/protection structure inspired by structure and forcing method of leg parts of bipeds, the Origami-Joint Flexible (OJF) isolation structure. The vibration performances are studied under impact and ultralow-frequency excitations. According to the mechanical features of the legs of bipeds, the restoring force is considered mainly at the joints. Simulating the structure of bipeds, the flexibility of the proposed structure is realized by using an Origami structure with resilience at its folds. Based on the analysis of potential energy, the restoring and damping forces are nonlinear and symmetrical, depending on both magnitude and direction of motions. Then, solutions for transient and steady states are obtained for different high-energy excitations. Due to the large displacement and strong nonlinearity, the Method of Multiple Scales (MMS) with high-order approximation is utilized for theoretical study. The main theoretical results are verified by experiments. The relevant prototype displays remarkable isolation/protection effectiveness for impact and ultralow-frequency excitations. This study not only shows the advantages of strong asymmetrical nonlinearity of the novel isolation structure with flexible joints but also theoretically explains its control mechanism. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

In recent decades, energy harvesting from external vibration with ultralow frequency has been investigated intensively. A novel energy harvesting device with adjustable nonlinearity for ultralow frequency excitation is proposed and analyzed in this study. The energy harvesting device is made of a mass attached to the base by Elastic Steel Slices (ESSs) and a pair of Quadrilateral-Linkage Structures (QLSs). With the mathematical model, theoretical studies are carried out. The analysis shows that the device is capable for ultralow-frequency vibration energy harvesting since it has adjustable resonance frequency band. With the appearance of the adjustable nonlinearity, the system has a wide band for resonance by the utilization of multi-steady states. Experimental prototypes are assembled and tested. The experimental results show that the beginning frequency of effective energy harvesting can be reduced by over 50% by assembling the QLSs to adjust the stiffness property of the system. In addition, although the stiffness of the device is expressed by nonlinear irrational function, we find that the output voltages generated are large, smooth and stable. The results of this study illustrate that the proposed device is a feasible design for collecting energy from ultralow frequency excitation. [ABSTRACT FROM AUTHOR]

In this study, based on the analysis of multiple nonlinear vibration properties, the criterions of parameter design for different types of excitations and structural nonlinearities are proposed for vibration isolation. For a nonlinear vibration isolation system with Quasi-Zero-Stiffness property, the assembly process and stiffness property with different masses of isolation object are taken into account. In order to improve the isolation effectiveness in a wide frequency band, the relation between vibration performances and parameters is established. The effect of adjustable parameters on the vibration features and the effect mechanisms of multiple time delays are discussed in details based on the method of multiple scales. Because the study takes full consideration of the effect of structural nonlinearity and transition mechanism of vibration performances, the proposed criterions for parameter design could solve the conflict between the improvement of isolation effectiveness and complexity or bifurcation brought by nonlinearity. The results in this paper show that without changing the High-Static-Low-Frequency advantage brought by the nonlinear isolation structure, the isolation effectiveness could be improved in a wide frequency band. [ABSTRACT FROM AUTHOR]

An adaptive vibration isolation system is proposed in this paper to combine the advantages of both linear and nonlinear isolators. Because of the proposed structural piecewise characteristics for different levels of response, the stiffness and damping properties could be designed according to the vibration performances. The adaptive stiffness and damping properties are achieved by the joined utilization of symmetrical precompression triangle-like structure (TLS) and column frame with cam. In order to design the control mechanism with optimum structural parameters, nonlinear vibration performances are analyzed by using averaging method and singularity theory. The parameter plane is divided into transition sets, and then the optimization criterions for structural design are provided according to multiple nonlinear vibration performances including frequency band for effective isolation, multisteady state band and resonance peak, etc. The experiment is carried out to verify the theoretical selection of desirable parameters and indicates the advantages and improvement of vibration isolation/suppression brought by the structural property adaptation. This study provides a novel method of achieving structural property adaptation for the improvement of isolation effectiveness, which shows the intelligent realization by passive components. [ABSTRACT FROM AUTHOR]

This research proposes the parametrical design of Metal Rubber (MR) isolation platform based on the investigation of nonlinear vibration properties under different types of excitation. Based on the mechanical model established by experiments, the restoring force of the isolation platform is proposed as a nonlinear function in consideration of the stiffness nonlinearity and Coulomb friction of metal wires. Then, the perturbation method is utilized to solve the steady states whose local stability is studied by singularity theory. The main results obtained by singularity theory show that there are five different types of vibration property, and the critical conditions for the transformation of different vibration properties are defined by transition sets. For impact excitation, the optimum structural parameters are obtained based on the vibration dissipation time via nonlinear backbone analysis; for periodic excitation, the optimum structural parameters are determined according to multiple standards including the bandwidth for effective isolation, bandwidth for multi-steady states, resonance peak and displacement transmissibility in high frequency band etc. The vibration performances for optimum structural parameters are verified by dynamical experiments. In conclusion, this paper carries out a novel sight of choosing optimum parameters, and therefore provides the guidance for the utilization of MR isolation platform for different types of excitation in engineering practices. [ABSTRACT FROM AUTHOR]

The optimum value of time delay of active control used in a nonlinear isolation system for different types of external excitation is studied in this paper. Based on the mathematical model of the nonlinear isolator with time-delayed active control, the stability, response and displacement transmissibility of the system are analyzed to obtain the standards for appropriate values of time delay and control strengths. The effects of nonlinearity and time delay on the stability and vibration response are discussed in details. For impact excitation and random excitation, the optimal value of time delay is obtained based on the vibration dissipation time via eigenvalues analysis, while for harmonic excitation, the optimal values are determined based on multiple vibration properties including natural frequency, amplitude death region and effective isolation region by the Averaging Method. This paper establishes the relationship between the parameters and vibration properties of a nonlinear isolation system which provides the guidance for optimizing time-delayed active control for different types of excitation in engineering practices. [ABSTRACT FROM AUTHOR]

This study investigates theoretically and experimentally a vibration isolator constructed by an n-layer Scissor-Like Structure (SLS), focusing on the analysis and design of nonlinear stiffness and damping characteristics for advantageous isolation performance in both orthogonal directions. With the mathematical modeling, the influence incurred by different structural parameters on system isolation performance is studied. It is shown that, (a) nonlinear high-static-low-dynamic stiffness and damping characteristics can be seen such that the system can achieve good isolation performance in both directions, (b) an anti-resonance frequency band exists due to the coupling effect between the linear and nonlinear stiffness in the two orthogonal directions within the structure, and (c) all these performances are designable with several structural parameters. The advantages of the proposed system are shown through comparisons with an existing quasi-zero-stiffness vibration isolator (QZS-VI) and a traditional mass-spring-damper vibration isolator (MSD-VI), and further validated by experimental results. [ABSTRACT FROM AUTHOR]

The effect of the nonlinearity and time delay in the Magneto-Rheological fluid (MRF) damper on an isolator system is studied in this study. The mechanical model of the control force of the MRF damper in the skyhook control is introduced as nonlinear piecewise function. The displacement transmissibility of the isolation system is solved by employing the Averaging method. The isolation effectiveness for different values of control coefficients is demonstrated by the displacement transmissibility. The increasing of damping control force of MRF damper reduces the displacement transmissibility to a low level while time delay has different functions in different frequency bands. Moreover, by the analysis of eigenvalues in the manifold given by Averaging method, the unstable and stable region of the steady state can be decided on the parameter plane, which provides the bifurcation criterion induced by nonlinearity and time delay. The main results from theoretical analysis and experimental prototype give an insight into the analysis and design of semi-active control with time delay in control loop and signal processing for isolator system by exploiting nonlinear benefits in vibration suppression effectiveness. [ABSTRACT FROM AUTHOR]

Inspired that the knee joint of birds can buffer the impact and vibration from the foot, a novel vibration isolator constructed by the Knee-Like structure (KLS) is proposed in this paper. Considering that the bones and muscles are very different in material strength, the leg bones are described by rigid rods and the muscles around the knee joint are described by the elastic components. Simulating the construction of the whole leg, in the bionic isolation structure, there are three adjustable structural parameters, which correspond to the angles for ankle and knee, and the length of the thigh. According to the dynamic model, the effects of structural parameters on linear and nonlinear coefficients and the widths for effective isolation bands are illustrated. By the transmissibility curves for different structural parameters by the Harmonic Balance Method (HBM), it discovers that the KLS bionic isolator has optimum design for the knee angle, different from the existing nonlinear isolation structure as the structural parameters monotonously affect the width of isolation band. Then, the analytical solution including transient and steady states are solved by the Method of Multiple Scales (MMS). For different frequency band excitation, the order determinations of excitation and nonlinearity are different. The comparison between the analytical solution and numerical simulation shows that the MMS is applicable for the asymmetric nonlinear nonautonomous dynamic system, and describes the buffering process and steady states for the vibration. The analysis of the proposed KLS bionic isolator not only illustrates the significant vibration isolation effectiveness for ultralow frequency, but also gives the mechanical explanations for the biological phenomenon that the leg knee presents a specific angle for vibration buffering and isolation. • A novel vibration isolator constructed by the Knee-Like structure (KLS) is proposed. • The KLS bionic isolator has optimum design for the knee angle. • The transient and steady states are described. • The KLS bionic isolator illustrates the significant vibration isolation effectiveness for ultralow frequency. • The KLS bionic isolator gives the mechanical explanations for the biological phenomenon. [ABSTRACT FROM AUTHOR]

The nonlinear effect incurred by time delay in vibration control is investigated in this study via a vibration absorber coupled with a continuous beam structure. The stability of the vibration absorber coupled structure system with time-delay coupling is firstly studied, which provides a general guideline for the potential time delay to be introduced to the system. Then it is shown that there is a specific region for the time delay which can bring bifurcation modes to the dynamic response of the coupling system, and the vibration energy at low frequencies can be transferred or absorbed due to the bifurcation mode and the vibration in the corresponding frequency range is thus suppressed. The nonlinear mechanism of this vibration suppression incurred by the coupling time delay is discussed in detail, which provides a novel and alternative approach to the analysis, design, and control of vibration absorbers in engineering practice. [ABSTRACT FROM AUTHOR]

A nonlinear combined structure consisted of isolator and absorber with time-delayed coupling active control is proposed in this study, whose vibration suppression effectiveness and control mechanism are investigated. The mathematical model of the combined structure is obtained and stability analysis for different structural parameters and time delay are firstly carried out, which provides a general guideline for the ranges of active control parameters. Then the combined effect of nonlinearity and time delay on vibration suppression and energy transfer is discussed in details based on the analysis of control mechanism by the method of multiple scales. Since the time-delayed nonlinear absorber can induce internal resonance between different modes, the vibration energy at low frequencies can be transferred to high frequency mode and the vibration of the fundamental frequency range is thus suppressed. This paper provides a novel application of internal resonance in vibration suppression of an Absorber–Isolator-Combined structure. [ABSTRACT FROM AUTHOR]

An n -layer Scissor-Like Structured (SLS) vibration isolation platform is studied in this paper, focusing on the analysis and design of nonlinear stiffness, friction forces and damping characteristics for an advantageous vibration isolation performance. The system nonlinear stiffness and damping characteristics are theoretically investigated by considering the influence incurred by different structural parameters, friction forces and link inertia. Since stiffness and damping properties are both asymmetrical nonlinear functions, and Coulomb friction is piecewise nonlinear function, Perturbation Method (PM) and Average Method (AM) are applied together to achieve better solutions. The vibration isolation performance of the SLS platform is compared with known quasi-zero-stiffness vibration isolators in the literature, and a typical application case study as a vehicle seat suspension is also conducted, subjected to different load masses, and base excitations. The results show that much better vibration isolation performance and loading capacity can be easily achieved with the SLS platform by designing structural parameters, and the scissor-like structure provides a very powerful, practical and passive solution to design and realization of beneficial nonlinear stiffness and damping characteristics in vibration control. [ABSTRACT FROM AUTHOR]

The study proposes a novel vibration isolator with 3D quasi-zero-stiffness (QZS) property. The remarkable feature of the proposed system is to apply symmetrically scissor-like structures (SLS) in the horizontal directions, together with a traditional spring-mass-damper system assembled vertically with positive stiffness. With the mathematical modeling of the proposed system, it is shown that the stiffness and damping properties are nonlinear due to nonlinear geometric relations within the SLSs and both can be adjusted via structural parameters of the system. Theoretical analysis with the harmonic balance method reveals that the system can demonstrate QZS property in 3 directions, and can achieve much better 3D vibration isolation performance, including high-static and quasi-zero-dynamic stiffness, and much larger displacement range around equilibrium, compared with an existing QZS system in the literature. The results provide a novel and significant multi-direction vibration isolation method using structural nonlinearity with noticeable performance but using only passive elements. [ABSTRACT FROM AUTHOR]

The potential beneficial performance of a Multi-Direction Quasi-Zero-Stiffness vibration isolator (MDQZS-VI) with linear time-delayed active control is investigated in this study. From the analysis of vibration property such as natural frequency, it is found that the isolation effectiveness of the MDQZS-VI for different directions can be adjusted respectively. The vertical direction natural frequency and damping property of the MDQZS-VI are dependent on structural parameters while the horizontal direction natural frequency and damping coefficient are related to the active control parameters. Moreover, bifurcation analysis shows that the values of control strength and time-delay have effect on the stability of horizontal vibration. By solving the displacement transmissibility for multi-direction, it is shown that structural parameters and active control coefficients could be designed deliberately so that natural frequencies are reduced and nonlinear damping coefficients are increased which is helpful for vibration suppression. The results provide a useful insight into the analysis and design of multi-direction QZS vibration isolator by exploiting potential nonlinear benefits of the time delay in vibration active control. [ABSTRACT FROM AUTHOR]

Quasi-zero-stiffness (QZS) systems have been extensively studied and used as a useful vibration isolation device. In this paper, the feasibility of the application of a QZS system for vibration measurement is investigated. The structural parameters of the QZS system are first analyzed to ensure that the system is staying at stable equilibriums. Comparisons of the absolute motion of a general and typical vibration platform (e.g., a moving vehicle body) and the motion signal measured from the QZS system attached are then conducted to show the effectiveness of the method under different base excitations. Moreover, the case under which the QZS-based sensor system may not behave well is also studied and potential solutions are discussed. The QZS vibration system is shown to be a useful device for absolute displacement measurement in vibration control systems particularly for moving platforms compared with the exciting methods and would benefit a wide range of engineering practices. [ABSTRACT FROM PUBLISHER]

Abstract: The potential beneficial performance of a quasi-zero-stiffness vibration isolator (QZS-VI) with a simple linear time-delayed active control strategy is investigated in this study. Stability and bifurcation analysis shows that an active control can basically improve the system robustness in stability at the equilibrium position. However, a time-delayed active control can not only further strengthen the robustness of the system in stability, but also noticeably improve system transmissibility performance both in force and base excitations and obviously decrease the settling time of system transient response subject to an impact load. Moreover, it is shown that the controlled stiffness and especially the introduced time delay could be designed deliberately so that undesirable bifurcation and chaotic behaviors can be avoided or greatly suppressed. The results provide a useful insight into the analysis and design of nonlinear vibration isolators by exploiting potential nonlinear benefits of the time delay in vibration control. [Copyright &y& Elsevier]

Abstract: More and more attentions are attracted to the analysis and design of nonlinear vibration control/isolation systems for better isolation performance. In this study, an isolation platform with n-layer scissor-like truss structure is investigated to explore novel design of passive/semi-active/active vibration control/isolation systems and to exploit potential nonlinear benefits in vibration suppression. Due to the special scissor-like structure, the dynamic response of the platform has inherent nonlinearities both in equivalent damping and stiffness characteristics (although only linear components are applied), and demonstrates good loading capacity and excellent equilibrium stability. With the mathematical modeling and analysis of the equivalent stiffness and damping of the system, it is shown that: (a) the structural nonlinearity in the system is very helpful in vibration isolation, (b) both equivalent stiffness and damping characteristics are nonlinear and could be designed/adjusted to a desired nonlinearity by tuning structural parameters, and (c) superior vibration isolation performances (e.g., quasi-zero stiffness characteristics etc.) can be achieved with different structural parameters. This scissor-like truss structure can potentially be employed in different engineering practices for much better vibration isolation or control. [Copyright &y& Elsevier]

• Propose a novel multi-layer structure bio-inspired by the role of avian neck. • Realize enough static loading capacity and zero dynamical stiffness simultaneously. • Obtain design criteria of configuration and parameters for wide-band vibration isolation. • Achieve stabilization effectiveness for excitation with low-frequency and displacement mutation. A novel multi-layer structure with functions for dynamic stabilization and vibration isolation, bio-inspired by the role of an avian neck, is proposed in this paper. Inspired by the fact that an avian neck can stabilize the head from body flapping, we expect that the proposed structure can achieve dynamic stabilization effectiveness under external excitation with a low frequency, large amplitude, and displacement mutations. First, for different configurations of the bio-inspired structure, the key characteristics, such as the elastic deformation energy, restoring force and equivalent dynamic properties are determined by mechanical modeling. It discovers that the proposed bio-inspired structure could achieve the designed loading capacity and dynamic zero stiffness simultaneously. Then according to the analysis of the dynamic behaviors under impact excitation and harmonic excitation by the perturbation method, the optimum criteria for the structural configuration and parameters are carried out. Thus, the effective isolation band begins at zero frequency, and the dynamic behavior could be quickly stabilized. Finally, the constructed multi-layer structure could achieve the stabilization functions of the avian neck. For different strengths of gusts, the amplitude of the top layer is less than a fifth of the excitation from the body. Due to the multiple functions in dynamic stabilization and control, the proposed structure can solve the bottleneck techniques in nonlinear isolation structural design, and it has remarkable potential applications in the fields of mechanical arms, sensors in satellites, etc. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The equal-peak property based extension method to a delay-coupled nonlinear system is studied in this paper. A time-delayed vibration absorber is proposed to realize the equal-peak property for a nonlinear primary system. Firstly, the mechanical model of the nonlinear primary system coupled with the time-delayed vibration absorber is established and the optimization objective is proposed. Then, four conditions to figure out the optimum delay-coupled parameters for the equal-peak property with the minimum resonance peak are carried out. Finally, several case studies with different nonlinear terms are given. The results show that the equal-peak property can be realized by appropriate delay-coupled parameters obtained by the optimization procedure. Besides, by selecting the optimum delay-coupled parameters, the two resonance peaks can be suppressed to the minimum level. The design for the time-delayed vibration absorber by the proposed extension method can solve the bottleneck techniques for equal-peak property in nonlinear primary systems under a wide range of excitation amplitude, which are concerned in manufacturing and aerospace. • A time-delayed vibration absorber is proposed to realize the equal-peak property for nonlinear primary systems. • The design procedure of the delay-coupled parameters for equal-peak is proposed. • The delay-coupled parameters for equal-peak with minimum resonance peaks are obtained. • The proposed absorber is applicable to the primary system with multiple nonlinearities and a wide range of excitation amplitude. [ABSTRACT FROM AUTHOR]

With the development of Internet of Things and the increase of wearable devices, the infinite self-power supply of small devices such as wireless sensors and portable devices has been widely concerned. Considering that the vibration energy in the environment is not affected by day and night, season and climate, and widely distributed, its mechanical energy can be collected. If the low-frequency and small amplitude vibration energy in the environment can be collected and converted into electric energy, it will provide a reliable solution for the self-power supply of these small devices. In this study, we designed a miniaturized energy harvester inspired by bionics. The resonance mechanism improved by nonlinearity is used to realize the amplification of vibration in low width frequency band. And triboelectric nanogenerator (TENG) is used to convert mechanical energy into electrical energy. Through the modeling and dynamic analysis of the system, we find a low resonance frequency band as the working range of the system. Subsequently, a prototype of the bird legs-type TENG was fabricated and tested to verify the design concept. We verify the ability of the prototype to amplify low-frequency vibration and optimized the structural parameters. Moreover, we demonstrate the excellent electrical output performance of the prototype in low-frequency and small external excitation environment and give two application prospects of wearable prototype and vehicle-mounted prototype. • Proposing a novel fully foldable structure with adjustable nonlinearity bio-inspired by bird leg multi-link mechanism. • Realizing amplification of the vibration with low-frequency in a wide range. • Verifying correlation between vibration amplitude and electrical output performance. • Fabricating a wearable prototype that generates electricity while swinging arm. [ABSTRACT FROM AUTHOR]

A novel six-direction sensor for absolute vibration motion is proposed in this study for the measurement of absolute motions by employing multi-direction quasi-zero-stiffness property. Scissor-like structures with pre-deformed springs are applied symmetrically in the proposed sensor. Based on the mathematical modeling of the proposed six-direction sensor, it is shown that the stiffness and damping properties of the sensor are adjustable nonlinear functions which are dependent on the structural parameters of scissor-like structures. And then, by utilizing bifurcation theory and perturbation method, the structural parameters are optimized for the improvement of measurement accuracy. For the realization of the approximate fixed point for a moving vibration object, the vibration from measurement object to the sensor is isolated, and thus the sensor could obtain the absolute motions. Utilizing the signals obtained by the proposed sensor directly, better vibration/suppression effectiveness is achieved. The results provide a novel and significant six-direction absolute motion measurement method by utilizing multi-direction quasi-zero-stiffness property with noticeable isolation performance only with passive elements. [ABSTRACT FROM AUTHOR]

We studied the properties of cubic nonlinear systems with dry friction damping on the prospect of ‘non-resonance’. An approximate method was used to get the frequency-response function. And the critical dry friction which ensures no displacement transmissibility amplified in whole frequency range was determined through the frequency-response function. We also researched those characters which may influence the effect of the non-resonance in this system, and proved those results by empirical experiments. The above conclusions have a theoretical significance for the design of nonlinear vibration isolators. [ABSTRACT FROM AUTHOR]

The double-porosity, dual-permeability theory is employed to predict the wave attenuation and phase velocity dispersion induced by wave-induced meso copic fluid flow. Instead of using an up-scaled, single-porosity approximation scheme proposed by previous researchers, we develop an analytical method to exactly solve the wave equations for double-porosity materials. We first propose a new form of wave equations formulated in terms of displacements. This new form of wave equations enables us to decouple the field equations into two second-order symmetric dynamic systems, namely, the P -system for compressional waves and the S -system for shear wave. We then implement Newton iteration for solving the cubic dispersion equation for compressional waves. Finally, to understand the loss mechanism caused by mesoscopic flow, we compare the attenuation curves of the first ( P 1-wave), the second ( P 2-wave), and the third compressional waves ( P 3-wave), as well as the shear wave ( S -wave), with the mesoscopic flow present to those with the mesoscopic flow absent. Furthermore, the effects of matrix porosity, pore-fluid viscosity, and values of fluid transport coefficient on wave attenuation are also investigated in numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, a general and systematic scheme is provided to research strong and weak resonances derived from delay-induced various double Hopf bifurcations in delayed differential systems. The method of multiple scales is extended to obtain a common complex amplitude equation when the double Hopf bifurcation with frequency ratio k1:k2 occurs in the systems under consideration. By analyzing the complex amplitude equation, we give the conditions of the strong and weak resonances respectively in the analytical expressions. The weak resonances correspond to the codimension-two double Hopf bifurcations since the amplitudes and the phases may be decoupled, but the strong resonances to the codimension-three double Hopf bifurcations in the system. It is seen that the weak resonances happen in the system even for a lower-order ratio, i.e. k1 + k2 ≤ 4. As applications, two examples are displayed. Three cases of the delay-induced resonance with 1:2, 1:3, 1:5 and are discussed in detail and the corresponding normals are represented. Thus, the relative dynamical behaviors can be easily classified in the physical parameter space in terms of nonlinear dynamics. The results show the provided conditions may be used to determine that a resonance is strong or weak. [ABSTRACT FROM AUTHOR]

In order to clarify the dynamic process of feldspar dissolution–precipitation and explore the formation mechanism of secondary porosity, six batch reactor experiments were conducted at 200 °C and pH = 7 measured at room temperature. Temporal evolution of fluid chemistry was analyzed with an inductively coupled plasma optical emission spectrometer (ICP-OES). Solid reaction products were retrieved from six batch experiments terminated after 36, 180, 276, 415, 766 and 1008 h. Scanning electron microscopy (SEM) revealed dissolution features and significant secondary mineral adhered on the feldspar surface. The process of feldspar dissolution–precipitation proceeded slowly and full equilibrium was not achieved after 1008 h. Saturation indices suggested that the albite and K-feldspar dissolution occurred throughout the experiments. The average dissolution rates for albite and K-feldspar were 2.28 × 10−10 and 8.51 × 10−11 mol m−2 s−1, respectively. Based on the experimental data, the reaction process of alkaline feldspar was simulated and the secondary porosity had increased 0.3% after the experiment. [ABSTRACT FROM AUTHOR]

Objective: To determine whether visit-to-visit fasting glucose (VVFG) variability in young adulthood is associated with midlife hippocampal integrity and volume.Research Design and Methods: Multivariable-adjusted linear regression models were used to estimate the association between VVFG variability and brain MRI variables in 543 CARDIA study participants. VVFG variability was defined by the SD of FG (SDFG), the coefficient of variation of the mean FG (CVFG), and the average real variability (ARVFG) over 25 years of follow-up. Hippocampal integrity fractional anisotropy (FA) and tissue volume standardized to intracranial volume were measured by 3T MRI at year 25.Results: After multivariable adjustment, higher FG variability (1-SD increase) was associated with lower hippocampal FA (SDFG -0.015 [95% CI -0.026, -0.004]; CVFG -0.009 [95% CI -0.018, -0.001]; ARVFG -0.011 [95% CI -0.019, -0.002]) and lower hippocampal volume (SDFG -0.012 [95% CI -0.023, -0.001]).Conclusions: Higher VVFG variability in young adulthood is associated with lower midlife hippocampal integrity and volume, suggesting its value in predicting risk for hippocampal structural damage. [ABSTRACT FROM AUTHOR]

Objectives An environment-wide association study (EWAS) may be useful to comprehensively test and validate associations between environmental factors and cardiovascular disease (CVD) in an unbiased manner. Approach and results Data from National Health and Nutrition Examination Survey (1999–2014) were randomly 50:50 spilt into training set and testing set. CVD was ascertained by a self-reported diagnosis of myocardial infarction, coronary heart disease or stroke. We performed multiple linear regression analyses associating 203 environmental factors and 132 clinical phenotypes with CVD in training set (false discovery rate < 5%) and significant factors were validated in the testing set ( P  < 0.05). Random forest (RF) model was used for multicollinearity elimination and variable importance ranking. Discriminative power of factors for CVD was calculated by area under the receiver operating characteristic (AUROC). Overall, 43,568 participants with 4084 (9.4%) CVD were included. After adjusting for age, sex, race, body mass index, blood pressure and socio-economic level, we identified 5 environmental variables and 19 clinical phenotypes associated with CVD in training and testing dataset. Top five factors in RF importance ranking were: waist, glucose, uric acid, and red cell distribution width and glycated hemoglobin. AUROC of the RF model was 0.816 (top 5 factors) and 0.819 (full model). Sensitivity analyses reveal no specific moderators of the associations. Conclusion Our systematic evaluation provides new knowledge on the complex array of environmental correlates of CVD. These identified correlates may serve as a complementary approach to CVD risk assessment. Our findings need to be probed in further observational and interventional studies. [ABSTRACT FROM AUTHOR]

The transplantation of mesenchymal stem cells (MSCs) has been a reported method for alleviating atherosclerosis (AS). Because the availability of bone marrow-derived MSCs (BM-MSCs) is limited, the authors used this study to explore the use of a new type of MSC, human induced pluripotent stem cell-derived MSCs (iPSC-MSCs), to evaluate whether these cells could alleviate AS. iPSC-MSCs were intravenously administered to ApoE knock out mice fed on a high-fat diet (HFD) for 12 weeks. It was reported that systematically administering iPSC-MSCs clearly reduced the size of plaques. In addition, the numbers of macrophages and lipids in plaques were lower in the HFD + iPSC-MSCs group than in the HFD group. Furthermore, iPSC-MSCs attenuated AS-associated inflammation by decreasing the levels of inflammatory cytokines, such as tumor necrosis factor-a and interleukin-6, in serum. In addition, the expression of Notch1 was higher in the HFD group, and injecting iPSC-MSCs reversed this effect. In conclusion, the current study provides the first evidence indicating that iPSC-MSCs may be a new optional MSC-based strategy for treating AS. [ABSTRACT FROM AUTHOR]