A low-frequency and broadband wave-insulating vibration isolator based on plate-shaped metastructures

A metamaterial vibration isolator,termed as wave-insulating isolator,is proposed,which preserves enough load-bearing capability and offers ultra-low and broad bandgaps for greatly enhanced wave insulation.It consists of plate-shaped metacells,whose symmetric and antisymmetric local resonant modes offer several low and broad mode bandgaps although the complete bandgap remains high and narrow.The bandgap mechanisms,vibration isolation properties,effects of key parameters,and robustness to complex conditions are clarified.As experimentally demonstrated,the wave-insulating isolator can improve the vibration insulation in the ranges of[50 Hz,180 Hz]and[260 Hz,400 Hz]by 15 dB and 25 dB,respectively,in contrast to the conventional isolator with the same first resonant frequency.

Prediction of Damping Capacity Demand in Seismic Base Isolators via Machine Learning

Base isolators used in buildings provide both a good acceleration reduction and structural vibration control structures.The base isolators may lose their damping capacity over time due to environmental or dynamic effects.This deterioration of them requires the determination of the maintenance and repair needs and is important for the long-termisolator life.In this study,an artificial intelligence prediction model has been developed to determine the damage and maintenance-repair requirements of isolators as a result of environmental effects and dynamic factors over time.With the developed model,the required damping capacity of the isolator structure was estimated and compared with the previously placed isolator capacity,and the decrease in the damping property was tried to be determined.For this purpose,a data set was created by collecting the behavior of structures with single degrees of freedom(SDOF),different stiffness,damping ratio and natural period isolated from the foundation under far fault earthquakes.The data is divided into 5 different damping classes varying between 10%and 50%.Machine learning model was trained in damping classes with the data on the structure’s response to random seismic vibrations.As a result of the isolator behavior under randomly selected earthquakes,the recorded motion and structural acceleration of the structure against any seismic vibration were examined,and the decrease in the damping capacity was estimated on a class basis.The performance loss of the isolators,which are separated according to their damping properties,has been tried to be determined,and the reductions in the amounts to be taken into account have been determined by class.In the developed prediction model,using various supervised machine learning classification algorithms,the classification algorithm providing the highest precision for the model has been decided.When the results are examined,it has been determined that the damping of the isolator structure with the machine learning method is predicted successfully at a level exceeding 96%,and it is an effective method in deciding whether there is a decrease in the damping capacity.

A vibration isolator with a controllable quasi-zero stiffness region based on nonlinear force design

To achieve stability optimization in low-frequency vibration control for precision instruments,this paper presents a quasi-zero stiffness(QZS)vibration isolator with adjustable nonlinear stiffness.Additionally,the stress-magnetism coupling model is established through meticulous theoretical derivation.The controllable QZS interval is constructed via parameter design and magnetic control,effectively segregating the high static stiffness bearing section from the QZS vibration isolation section.Furthermore,a displacement control scheme utilizing a magnetic force is proposed to regulate entry into the QZS working range for the vibration isolation platform.Experimental results demonstrate that the operation within this QZS region reduces the peak-to-peak acceleration signal by approximately 66.7%compared with the operation outside this region,thereby significantly improving the low frequency performance of the QZS vibration isolator.

Theoretical and experimental investigations on an X-shaped vibration isolator with active controlled variable stiffness

A novel X-shaped variable stiffness vibration isolator(X-VSVI)is proposed.The Runge-Kutta method,harmonic balance method,and wavelet transform spectra are introduced to evaluate the performance of the X-VSVI under various excitations.The layer number,the installation angle of the X-shaped structure,the stiffness,and the active control parameters are systematically analyzed.In addition,a prototype of the X-VSVI is manufactured,and vibration tests are carried out.The results show that the proposed X-VSVI has a superior adaptability to that of a traditional X-shaped mechanism,and shows excellent vibration isolation performance in response to different amplitudes and forms of excitations.Moreover,the vibration isolation efficiency of the device can be improved by appropriate adjustment of parameters.

Impact of surface-reflected seismic waves on the seismic isolation performance of circular tunnel isolation layers

Seismic isolation is an effective strategy to mitigate the risk of seismic damage in tunnels.However,the impact of surface-reflected seismic waves on the effectiveness of tunnel isolation layers remains under explored.In this study,we employ the wave function expansion method to provide analytical solutions for the dynamic responses of linings in an elastic half-space and an infinite elastic space.By comparing the results of the two models,we investigate the seismic isolation effect of tunnel isolation layers induced by reflected seismic waves.Our findings reveal significant differences in the dynamic responses of the lining in the elastic half-space and the infinitely elastic space.Specifically,the dynamic stress concentration factor(DSCF)of the lining in the elastic half-space exhibits periodic fluctuations,influenced by the incident wave frequency and tunnel depth,while the DSCF in the infinitely elastic space remain stable.Overall,the seismic isolation application of the tunnel isolation layer is found to be less affected by surface-reflected seismic waves.Our results provide valuable insights for the design and assessment of the seismic isolation effect of tunnel isolation layers.

A human-sensitive frequency band vibration isolator for heavy-duty truck seats

In this study,a human-sensitive frequency band vibration isolator(HFBVI)with quasi-zero stiffness(QZS)characteristics for heavy-duty truck seats is designed to improve the comfort of heavy-duty truck drivers on uneven roads.First,the analytical expressions for the force and displacement of the HFBVI are derived with the Lagrange equation and d'Alembert's principle,and are validated through the prototype restoring force testing.Second,the harmonic balance method(HBM)is used to obtain the dynamic responses under harmonic excitation,and further the influence of pre-stretching on the dynamic characteristics and transmissibility is discussed.Finally,the experimental prototype of the HFBVI is fabricated,and vibration experiments are conducted under harmonic excitation to verify the vibration isolation performance(VIP)of the proposed vibration isolator.The experimental results indicate that the HFBVI can effectively suppress the frequency band(4-8 Hz)to which the human body is sensitive to vertical vibration.In addition,under real random road spectrum excitation,the HFBVI can achieve low-frequency vibration isolation close to 2 Hz,providing new prospects for ensuring the health of heavy-duty truck drivers.

Application and optimization design of non-obstructive particle damping-phononic crystal vibration isolator in viaduct structure-borne noise reduction

The problems associated with vibrations of viaducts and low-frequency structural noise radiation caused by train excitation continue to increase in importance.A new floating-slab track vibration isolator-non-obstructive particle damping-phononic crystal vibration isolator is proposed herein,which uses the particle damping vibration absorption technology and bandgap vibration control theory.The vibration reduction performance of the NOPD-PCVI was analyzed from the perspective of vibration control.The paper explores the structure-borne noise reduction performance of the NOPD-PCVIs installed on different bridge structures under varying service conditions encountered in practical engineering applications.The load transferred to the bridge is obtained from a coupled train-FST-bridge analytical model considering the different structural parameters of bridges.The vibration responses are obtained using the finite element method,while the structural noise radiation is simulated using the frequency-domain boundary element method.Using the particle swarm optimization algorithm,the parameters of the NOPD-PCVI are optimized so that its frequency bandgap matches the dominant bridge structural noise frequency range.The noise reduction performance of the NOPD-PCVIs is compared to the steel-spring isolation under different service conditions.

Regional dynamic cerebral autoregulation across anterior and posterior circulatory territories:A detailed exploration and its clinical implications

Cerebral autoregulation(CA)is the mechanism that maintains stable cerebral blood flow(CBF)despite fluctuations in systemic blood pressure,crucial for brain homeostasis.Recent evidence highlights distinct regional variations in CA between the anterior(carotid)and posterior(vertebrobasilar)circulations.Noninvasive neuromonitoring techniques,such as transcranial Doppler,transfer function analysis,and near-infrared spectroscopy,facilitate the dynamic assessment of CBF and autoregulation.Studies indicate a robust autoregulatory capacity in the anterior circulation,characterized by rapid adjustments in vascular resistance.On the contrary,the posterior circulation,mainly supplied by the vertebral arteries,may have a lower autoregulatory capacity.in acute brain injuries such as intracerebral and subarachnoid hemorrhage,and traumatic brain injuries,dynamic CA can be significantly altered in the posterior circulation.Proposed physiological mechanisms of impaired CA in the posterior circulation include:(1)Decreased sympathetic innervation of the vasculature impairing compensatory vasoreactivity;(2)Endothelial dysfunction;(3)Increased cerebral metabolic rate of oxygen consumption within the visual cortex causing CBFmetabolism(i.e.,neurovascular)uncoupling;and(4)Impaired blood-brain barrier integrity leading to impaired astrocytic mediated release of vasoactive substances(e.g.nitric oxide,potassium,and calcium ions).Furthermore,more research is needed on the effects of collateral circulation,as well as the circle of Willis variants,such as the fetal-type posterior cerebral artery,on dynamic CA.Improving our understanding of these mechanisms is crucial to improving the diagnosis,prognosis,and management of various cerebrovascular disorders.

A bio-inspired spider-like structure isolator for low-frequency vibration

This paper proposes a quasi-zero stiffness(QZS)isolator composed of a curved beam(as spider foot)and a linear spring(as spider muscle)inspired by the precise capturing ability of spiders in vibrating environments.The curved beam is simplified as an inclined horizontal spring,and a static analysis is carried out to explore the effects of different structural parameters on the stiffness performance of the QZS isolator.The finite element simulation analysis verifies that the QZS isolator can significantly reduce the first-order natural frequency under the load in the QZS region.The harmonic balance method(HBM)is used to explore the effects of the excitation amplitude,damping ratio,and stiffness coefficient on the system’s amplitude-frequency response and transmissibility performance,and the accuracy of the analytical results is verified by the fourth-order Runge-Kutta integral method(RK-4).The experimental data of the QZS isolator prototype are fitted to a ninth-degree polynomial,and the RK-4 can theoretically predict the experimental results.The experimental results show that the QZS isolator has a lower initial isolation frequency and a wider isolation frequency bandwidth than the equivalent linear isolator.The frequency sweep test of prototypes with different harmonic excitation amplitudes shows that the initial isolation frequency of the QZS isolator is 3 Hz,and it can isolate 90%of the excitation signal at 7 Hz.The proposed biomimetic spider-like QZS isolator has high application prospects and can provide a reference for optimizing low-frequency or ultra-low-frequency isolators.

Spatio-temporal isolator in lithium niobate on insulator

In this contribution,we simulate,design,and experimentally demonstrate an integrated optical isolator based on spatiotemporal modulation in the thin-film lithium niobate on an insulator waveguide platform.We used two cascaded travelling wave phase modulators for spatiotemporal modulation and a racetrack resonator as a wavelength filter to suppress the sidebands of the reverse propagating light.This enabled us to achieve an isolation of 27 dB.The demonstrated suppression of the reverse propagating light makes such isolators suitable for the integration with III-V laser diodes and Erbium doped gain sections in the thin-film lithium niobate on the insulator waveguide platform.

Circulating tumor DNA in liquid biopsy: Current diagnostic limitation

With the rapid development of science and technology,cell-free DNA(cfDNA)is rapidly becoming an important biomarker for tumor diagnosis,monitoring and prognosis,and this cfDNA-based liquid biopsy technology has great potential to become an important part of precision medicine.cfDNA is the total amount of free DNA in the systemic circulation,including DNA fragments derived from tumor cells and all other somatic cells.Tumor cells release fragments of DNA into the bloodstream,and this source of cfDNA is called circulating tumor DNA(ctDNA).cfDNA detection has become a major focus in the field of tumor research in recent years,which provides a new opportunity for non-invasive diagnosis and prognosis of cancer.In this paper,we discuss the limitations of the study on the origin and dynamics analysis of ctDNA,and how to solve these problems in the future.Although the future faces major challenges,it also con-tains great potential.

Emulsifying property,antioxidant activity,and bitterness of soybean protein isolate hydrolysate obtained by Corolase PP under high hydrostatic pressure

Enzymatic hydrolysis of proteins can enhance their emulsifying properties and antioxidant activities.However,the problem related to the hydrolysis of proteins was the generation of the bitter taste.Recently,high hydrostatic pressure(HHP)treatment has attracted much interest and has been used in several studies on protein modification.Hence,the study aimed to investigate the effects of enzymatic hydrolysis by Corolase PP under different pressure treatments(0.1,100,200,and 300 MPa for 1-5 h at 50℃)on the emulsifying property,antioxidant activity,and bitterness of soybean protein isolate hydrolysate(SPIH).As observed,the hydrolysate obtained at 200 MPa for 4 h had the highest emulsifying activity index(47.49 m^(2)/g)and emulsifying stability index(92.98%),and it had higher antioxidant activities(44.77%DPPH free radical scavenging activity,31.12%superoxide anion radical scavenging activity,and 61.50%copper ion chelating activity).At the same time,the enhancement of emulsion stability was related to the increase of zeta potential and the decrease of mean particle size.In addition,the hydrolysate obtained at 200 MPa for 4 h had a lower bitterness value and showed better palatability.This study has a broad application prospect in developing food ingredients and healthy foods.

Isolated deep convections over the Tibetan Plateau in the rainy season during 2001–2020

The Tibetan Plateau(TP)is a prevalent region for convection systems due to its unique thermodynamic forcing.This study investigated isolated deep convections(IDCs),which have a smaller spatial and temporal size than mesoscale convective systems(MCSs),over the TP in the rainy season(June-September)during 2001–2020.The authors used satellite precipitation and brightness temperature observations from the Global Precipitation Measurement mission.Results show that IDCs mainly concentrate over the southern TP.The IDC number per rainy season decreases from around 140 over the southern TP to around 10 over the northern TP,with an average 54.2.The initiation time of IDCs exhibits an obvious diurnal cycle,with the peak at 1400–1500 LST and the valley at 0900–1000 LST.Most IDCs last less than five hours and more than half appear for only one hour.IDCs generally have a cold cloud area of 7422.9 km^(2),containing a precipitation area of approximately 65%.The larger the IDC,the larger the fraction of intense precipitation it contains.IDCs contribute approximately 20%–30%to total precipitation and approximately 30%–40%to extreme precipitation over the TP,with a larger percentage in July and August than in June and September.In terms of spatial distribution,IDCs contribute more to both total precipitation and extreme precipitation over the TP compared to the surrounding plain regions.IDCs over the TP account for a larger fraction than MCSs,indicating the important role of IDCs over the region.

Seismic response of a mid-story isolated structure considering SSI in mountainous areas under long-period earthquakes

At present,there is not much research on mid-story isolated structures in mountainous areas.In this study,a model of a mid-story isolated structure considering soil-structure interaction(SSI)in mountainous areas is established along with a model that does not consider SSI.Eight long-period earthquake waves and two ordinary earthquake waves are selected as inputs for the dynamic time history analysis of the structure.The results show that the seismic response of a mid-story isolated structure considering SSI in mountainous areas can be amplified when compared with a structure that does not consider SSI.The structure response under long-period earthquakes is larger than that of ordinary earthquakes.The structure response under far-field harmonic-like earthquakes is larger than that of near-fault pulse-type earthquakes.The structure response under near-fault pulse-type earthquakes is larger than that of far-field non-harmonic earthquakes.When subjected to long-period earthquakes,the displacement of the isolated bearings exceeded the limit value,which led to instability and overturning of the structure.The structure with dampers in the isolated story could adequately control the nonlinear response of the structure,effectively reduce the displacement of the isolated bearings,and provide a convenient,efficient and economic method not only for new construction but also to retrofit existing structures.

Microfluidic platform for circulating tumor cells isolation and detection

Circulating tumor cells(CTCs)are essential biomarkers for liquid biopsies,which are important in the early screening,prognosis,and real-time monitoring of cancer.However,CTCs are less abundant in the peripheral blood of patients,therefore,their isolation is necessary.Recently,the use of microfluidics for CTC sorting has become a research hotspot owing to its low cost,ease of integration,low sample consumption,and unique advantages in the manipulation of micron-sized particles.Herein,we review the latest research on microfluidics-based CTC sorting.Specifically,we consider active sorting using external fields(electric,magnetic,acoustic,and optical tweezers)and passive sorting using the flow effects of cells in specific channel structures(microfiltration sorting,deterministic lateral displacement sorting,and inertial sorting).The advantages and limitations of each method and their recent applications are summarized here.To conclude,a forward-looking perspective is presented on future research on the microfluidic sorting of CTCs.

Frequency domain analysis of pre-stressed elastomeric vibration isolators

Two types of elastomeric vibration isolators used for equipment vibration isolation in aerospace vehicles are considered for the present study. These isolators are constructed using elastomers mounted in steel encasings. These isolators are initially deformed statically and dynamic loads are applied on the deformed configuration. To capture the static deformation, equivalent static load corresponding to its load rating and specified displacements are created. Static deformation is computed using Finite Element methods with four node axi-symmetric element which include the geometric non-linear effect for steel and with standard Yeoh hyper-elastic material model for elastomers(Muhammed and Zu, 2012) [1]. Yeoh material constants are derived from uni-axial tension test data of the elastomer specimen. These isolators are subjected to harmonic and random excitations in the pre-deformed state. For numerical analysis, elastomeric constants at dynamic conditions are obtained as complex function of frequency using Dynamic Mechanical Analyzer(DMA) for a range of frequencies. The standard material model of Yeoh is modified incorporating frequency dependant material characteristics and damping in the range of frequencies of interest. A multiplicative non-separable variables law is derived for Yeoh material model to include the effect of static pre-stress, based on the methodology given in literature(Nashif et al.,1985;Beda et al., 2014) [2,3]. The modifications of Yeoh model suitable for frequency domain analysis is the novelty in the present study. In the analysis, while dynamic loads are applied, the configuration is updated considering initial static loading. The frequency response of the isolators is computed using material properties evaluated at progressive dynamic strains until a match in natural frequency is observed. Appropriate damping corrections are then incorporated to match the test observed transmissibility. Then updated material properties are used to compute the random response which showed good agreement with results of experiments, validating the approach taken for the development of this model.

Effects of Fatigue Characteristics on Static and Dynamic Performance of Eucommia Rubber Isolators

This study aimed to investigate the effect of fatigue characteristics on the static and dynamic performance of Eucommia ulmoides gum isolators, and to explore the performance changes of Eucommia ulmoides gum isolators with different formulations. For this purpose, we used five formulations of Eucommia ulmoides gum isolators and set different fatigue test methods to study the static and dynamic performance changes of Eucommia ulmoides gum isolators with different formulations by changing the amplitude. The experimental results showed that the addition of Eucommia ulmoides gum had an impact on the performance of the isolator, and the number of fatigue cycles would lead to the hardening of the Eucommia ulmoides gum isolator and changes in its static and dynamic performance. In the range of two million vibrations, the performance change of the isolator was significant in the early stage and then tended to be flat, indicating that the impact of fatigue on the performance of the isolator would not continue to persist. It is worth noting that the study found that the addition of 30% Eucommia ulmoides gum had the least impact on the performance of the isolator under fatigue. Therefore, for long-term use of Eucommia ulmoides gum isolators, attention should be paid to their fatigue characteristics to ensure their stability and reliability. Additionally, this study provides a reference for the design and application of Eucommia ulmoides gum isolators. In summary, this study provides important reference value for a deeper understanding of the fatigue characteristics of Eucommia ulmoides gum isolators and for ensuring their stable and reliable performance. .

A viscoelastic metamaterial beam for integrated vibration isolation and energy harvesting

Locally resonant metamaterials have low-frequency band gaps and the capability of converging vibratory energy in the band gaps at resonant cells.It has been demonstrated by several researchers that the dissipatioin of vibratory energy within the band gap can be improved by using viscoelastic materials.This paper designs an integrated viscoelastic metamaterial for energy harvesting and vibration isolation.The viscoelastic metamaterial is achieved by a viscoelastic beam periodically arrayed with spatial ball-pendulum nonlinear energy harvesters.The nonlinear resonator with an energy harvesting function is achieved by placing a free-rolling magnetic ball in a spherical cavity with an additional induction coil.The dynamic equations of viscoelastic metamaterials under transverse excitation are established,and the energy harvesting and vibration isolation characteristics within the dispersion relation of viscoelastic metamaterials are analyzed.The results show that the vibrations of the main body of the viscoelastic metamaterial beam are significantly suppressed in the frequency range of the local resonance band gap.At the same time,the elastic waves are limited in the nonlinear resonator with an energy harvesting function,which improves the energy output.Finally,an experimental platform of viscoelastic metamaterial vibration is established for validation purposes.

Uncertainties of ENSO-related Regional Hadley Circulation Anomalies within Eight Reanalysis Datasets

El Nino-Southern Oscillation(ENSO),the leading mode of global interannual variability,usually intensifies the Hadley Circulation(HC),and meanwhile constrains its meridional extension,leading to an equatorward movement of the jet system.Previous studies have investigated the response of HC to ENSO events using different reanalysis datasets and evaluated their capability in capturing the main features of ENSO-associated HC anomalies.However,these studies mainly focused on the global HC,represented by a zonal-mean mass stream function(MSF).Comparatively fewer studies have evaluated HC responses from a regional perspective,partly due to the prerequisite of the Stokes MSF,which prevents us from integrating a regional HC.In this study,we adopt a recently developed technique to construct the three-dimensional structure of HC and evaluate the capability of eight state-of-the-art reanalyses in reproducing the regional HC response to ENSO events.Results show that all eight reanalyses reproduce the spatial structure of HC responses well,with an intensified HC around the central-eastern Pacific but weakened circulations around the Indo-Pacific warm pool and tropical Atlantic.The spatial correlation coefficient of the three-dimensional HC anomalies among the different datasets is always larger than 0.93.However,these datasets may not capture the amplitudes of the HC responses well.This uncertainty is especially large for ENSO-associated equatorially asymmetric HC anomalies,with the maximum amplitude in Climate Forecast System Reanalysis(CFSR)being about 2.7 times the minimum value in the Twentieth Century Reanalysis(20CR).One should be careful when using reanalysis data to evaluate the intensity of ENSO-associated HC anomalies.

Sedimentary build-ups of pre-salt isolated carbonate platforms and formation of deep-water giant oil fields in Santos Basin,Brazil

In response to the problems of unclear distribution of deep-water pre-salt carbonate reservoirs and formation conditions of large oil fields in the Santos passive continental margin basin,based on comprehensive utilization of geological,seismic,and core data,and reconstruction of Early Cretaceous prototype basin and lithofacies paleogeography,it is proposed for the first time that the construction of pre-salt carbonate build-ups was controlled by two types of isolated platforms:inter-depression fault-uplift and intra-depression fault-high.The inter-depression fault-uplift isolated platforms are distributed on the present-day pre-salt uplifted zones between depressions,and are built on half-and fault-horst blocks that were inherited and developed in the early intra-continental and inter-continental rift stages.The late intra-continental rift coquinas of the ITP Formation and the early inter-continental rift microbial limestones of the BVE Formation are continuously constructed;intra-depression fault-high isolated platforms are distributed in the current pre-salt depression zones,built on the uplifted zones formed by volcanic rock build-ups in the early prototype stage of intra-continental rifts,and only the BVE microbial limestones are developed.Both types of limestones formed into mound-shoal bodies,that have the characteristics of large reservoir thickness and good physical properties.Based on the dissection of large pre-salt oil fields discovered in the Santos Basin,it has been found that both types of platforms could form large-scale combined structural-stratigraphic traps,surrounded by high-quality lacustrine and lagoon source rocks at the periphery,and efficiently sealed by thick high-quality evaporite rocks above,forming the optimal combination of source,reservoir and cap in the form of“lower generation,middle storage,and upper cap”,with a high degree of oil and gas enrichment.It has been found that the large oil fields are all bottom water massive oil fields with a unified pressure system,and they are all filled to the spill-point.The future exploration is recommended to focus on the inter-depression fault-uplift isolated platforms in the western uplift zone and the southern section of eastern uplift zones,as well as intra-depression fault-high isolated platforms in the central depression zone.The result not only provides an important basis for the advanced selection of potential play fairways,bidding of new blocks,and deployment of awarded exploration blocks in the Santos Basin,but also provides a reference for the global selection of deep-water exploration blocks in passive continental margin basins.