Reconfigurable metamaterial for asymmetric and symmetric elastic wave absorption based on exceptional point in resonant bandgap

Elastic wave absorption at subwavelength scale is of significance in many engineering applications.Non-Hermitian metamaterials show the ability in high-efficiency wave absorption.However,the single functionality of metamaterials is an important limitation on their practical applications for lack of tunability and reconfigurability.Here,we propose a tunable and reconfigurable non-Hermitian piezoelectric metamaterial bar,in which piezoelectric bars connect with resonant circuits,to achieve asymmetric unidirectional perfect absorption(UPA)and symmetric bidirectional perfect absorption(PA)at low frequencies.The two functions can be arbitrarily switched by rearranging shunted circuits.Based on the reverberation-ray matrix(RRM)method,an approach is provided to achieve UPA by setting an exceptional point(EP)in the coupled resonant bandgap.By using the transfer matrix method(TMM)and the finite element method(FEM),it is observed that a non-Hermitian pseudo-band forms between two resonant bandgaps,and the EP appears at the bottom of the pseudo-band.In addition,the genetic algorithm is used to accurately and efficiently design the shunted circuits for desired low-frequency UPA and PA.The present work may provide new strategies for vibration suppression and guided waves manipulation in wide potential applications.

Microwave absorption and bandwidth study of Y_(2)Co_(17)rare earth soft magnetic alloy with easy-plane anisotropy

The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-performance microwave absorbing material.In this paper,Y_(2)Co_(17)alloy was prepared by a reduction-diffusion method,and its micropowder was prepared as polyurethane(PU)based composite absorbing materials(Y_(2)Co_(17)/PU composites).The microwave properties of composites with different volume fractions were calculated.The composites showed outstanding absorption characteristics in the range of 20-30 vol%,and the minimum reflection loss(RL)was less than-50 d B.When the volume fraction was25%,the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm,and the Ku-band at a thickness of1.08 mm.The absorption mechanism was analyzed by the interface reflection model.The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses.The effective absorption bandwidth values were in good agreement with the theoretical expectation.

A Footpad Structure with Reusable Energy Absorption Capability for Deep Space Exploration Lander:Design and Analysis

The footpad structure of a deep space exploration lander is a critical system that makes the initial contact with the ground,and thereby plays a crucial role in determining the stability and energy absorption characteristics during the impact process.The conventional footpad is typically designed with an aluminum honeycomb structure that dissipates energy through plastic deformation.Nevertheless,its effectiveness in providing cushioning and energy absorption becomes significantly compromised when the structure is crushed,rendering it unusable for reusable landers in the future.This study presents a methodology for designing and evaluating structural energy absorption systems incorporating recoverable strain constraints of shape memory alloys(SMA).The topological configuration of the energy absorbing structure is derived using an equivalent static load method(ESL),and three lightweight footpad designs featuring honeycomb-like Ni-Ti shape memory alloys structures and having variable stiffness skins are proposed.To verify the accuracy of the numerical modelling,a honeycomb-like structure subjected to compression load is modeled and then compared with experimental results.Moreover,the influence of the configurations and thickness distribution of the proposed structures on their energy absorption performance is comprehensively evaluated using finite element simulations.The results demonstrate that the proposed design approach effectively regulates the strain threshold to maintain the SMA within the constraint of maximum recoverable strain,resulting in a structural energy absorption capacity of 362 J/kg with a crushing force efficiency greater than 63%.

Estimation of mass transfer coefficient in ozone absorption by linear least square fitting and Simplex search methods

For physical ozone absorption without reaction,two parametric estimation methods,i.e.the common linear least square fitting and non-linear Simplex search methods,were applied,respectively,to determine the ozone mass transfer coefficient during absorption and both methods give almost the same mass transfer coefficient.While for chemical absorption with ozone decomposition reaction,the common linear least square fitting method is not applicable for the evaluation of ozone mass transfer coefficient due to the difficulty of model linearization for describing ozone concentration dissolved in water.The nonlinear Simplex method obtains the mass transfer coefficient by minimizing the sum of the differences between the simulated and experimental ozone concentration during the whole absorption process,without the limitation of linear relationship between the dissolved ozone concentration and absorption time during the initial stage of absorption.Comparison of the ozone concentration profiles between the simulation and experimental data demonstrates that Simplex method may determine ozone mass transfer coefficient during absorption in an accurate and high efficiency way with wide applicability.

A correction method for the telluric absorptions and application to Lijiang Observatory

Observing a telluric standard star for correcting the telluric absorption lines of spectrum will take a significant amount of precious telescope time,especially in the long-term spectral monitoring project.Beyond that,it is difficult to select a suitable telluric standard star near in both time and airmass to the scientific object.In this paper,we present a method of correcting the telluric absorption lines by combining the advantages of long slit spectroscopy.By rotating the slit,we observed the scientific object and a nearby comparison star in one exposure,so that the spectra of both objects should have the same telluric transmission spectrum.The telluric transmission spectrum was constructed by dividing the observed spectrum of the comparison star by its stellar template,and was used to correct the telluric absorption lines of the scientific object.Using the long slit spectrograph of the Lijiang 2.4-meter telescope,we designed a long-term spectroscopic observation strategy,and finished a four-year spectroscopic monitoring for a pair of objects(an active galactic nucleus and a non-varying comparison star).We applied this method to correct the telluric absorption lines of the long-term monitored spectra by the Lijiang 2.4-meter telescope,and investigated the variation of the telluric absorptions at Lijiang Observatory.We found that the telluric absorption transparency is mainly modulated by the seasonal variability of the relative humidity,airmass and seeing.Using the scatter of the [O Ⅲ] λ5007 fluxes emitted from the narrow-line region of active galactic nuclei as an indicator,we found that the correction accuracy of the telluric absorption lines is 1%.

Microwave absorption properties regulation and bandwidth formula of oriented Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU composite synthesized by reduction-diffusion method

As concepts closely related to microwave absorption properties,impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms.In this work,reduction–diffusion method was innovatively applied to synthesize rare earth alloy Y_(2)Fe_(17).In order to regulate the electromagnetic parameters of absorbers,the Y_(2)Fe_(17)N_(3-δ)particles were coated with silica(Y_(2)Fe_(17)N_(3-δ)@SiO_(2))and absorbers with different volume fractions were prepared.The relationship between impedance matching,matching thickness,and the strongest reflection loss peak(RLmin)was presented obviously.Compared to the microwave absorption properties of Y_(2)Fe_(17)N_(3-δ)/PU absorber,Y_(2)Fe_(17)N_(3-δ)@SiO_(2)/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness,light weight,strong absorbing intensity,and broad bandwidth.Based on microwave frequency bands,the microwave absorption properties of the absorbers were analyzed and the related parameters were listed.As an important parameter related to perfect matching,reflection factor(√ε_(r)/μ_(r))was discussed combined with microwave amplitude attenuation.According to the origin and mathematical model of bandwidth,the formula of EAB(RL<-10 dB)was derived and simplified.The calculated bandwidths agreed well with experimental results.

ABSORPTION KINETICS OF HYDROGEN SULPHIDE USING ISOTHERMAL AND ISOVOLUMETRIC METHOD

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AN INVESTIGATION ON NEAR-INFRARED ABSORPTION METHOD FOR MEASURING SUGAR FROM COTTON

In this paper, the authors investigated the feasibility of near-infrared to measure sugar at cotton fibre. The simple regression equations are generated by respectively correlating thc absorption data(by using 1640nm and 2100nm wavelengths) with sugar( glucose, fructose and sucrose) and the regression modes possess a high coefficient of correlation. The differences for absorption of various sugars at some (?)velengths are diseussed.

USE OF FINITE-DIFFERENCE TIME-DOMAIN METHOD FOR CALCULATING EM ABSORPTION IN LOSSY DIELECTRIC SCATTERER

The problem for calculating EM energy absorption by lossy dielectric scatterer ir-radiated by plane wave are discussed.The factors affecting the accuracy of computation arediscussed.The calculated results of EM energy absorption and its distribution in homogeneousand layered homogenous lossy dielectric spheres are presented,and a comparison of these resultswith analytical solution is given.The calculation is carried out for dielectric cylinder on conduct-ing ground as well,and the results are compared with the image theory.All the computationsshew that the finite-difference time-domain method can give satisfactory results.

High voltage DC leakage detection for double-lined hazardous waste landfill based on finite element method

According to the structural characteristics of hazardous waste landfill, a new model based on the finite element method （FEM） is developed. The detection layer is considered as a sealed space and it is assumed that total current flows through the leak for the high resistivity of geomembrane liner. The leak current is regarded as a positive point current ＋I and the other current source is -I. Electrical potential of an arbitrary point in detection layer satisfies Poisson equation. Experiments for detecting leaks in liner were carried out. Excellent agreement between experimental data and simulated model data validates the new model. Parametric curves for a single leak show that with optimum selection of field survey parameters leaks can be detected effectively. For multiple leaks, the simulated results indicate that they are detectable when leak separation is larger than measurement spacing.

In-depth investigation on the factors affecting the performance of high oil-absorption resin by response surface method

A series of high oil-absorption resins with low cross-linking degree were synthesized by suspension polymerization using stearyl methacrylate(SMA),2-Ethylhexyl methacrylate(EHMA),and styrene(St)as monomers.Response surface methodology(RSM)with central composite design(CCD)was also applied to determine the optimal parameters that are mainly known to affect their synthesis.Thus,the effects of the monomer mass ratio(EHMA:SMA),the rigid monomer(St)dosage,the porous agent(acetone)dosage,and their pairwise interaction on the resin's oil-absorption capacity were analyzed,highlighting PSES-R_(2) as the resin with the optimum performance.The pure oil-absorption rates of PSES-R_(2) for gasoline,diesel,and kerosene were 11.19 g·g^(-1),16.25 g·g^(-1),and 14.84 g·g^(-1),respectively,while the oil removal rates from oily wastewater were 98.82%,65.11%,and 99.63%,respectively.

New Numerical Method to Calculate the True Optical Absorption of Hydrogenated Nanocrystalline Silicon Thin Films

The enhanced optical absorption measured by Constant Photocurrent Method (CPM) of hydrogenated nanocrystalline silicon thin films is due mainly to bulk and/or surface light scattering effects. A new numerical method is presented to calculate both true optical absorption and scattering coefficient from CPM absorption spectra of nanotextured nano-crystalline silicon films. Bulk and surface light scattering contributions can be unified through the correlation obtained between the scattering coefficient and surface roughness obtained using our method.

Influence of in vitro Methods, Receptor Fluids on Percutaneous Absorption and Validation of a Novel in vitro Method

In vitro experiment using excised skin has been valuable for studying the mechanism of percutaneous absorption. Based on previously established static diffusion cell system in this laboratory, a novel model-peifused glass diffusion cell system is desboed. The results of initial comporative study on percutaneous absorption between glass perfused diffusion cell and static diffusion cell, ih vitro and in vivo permeation as well as factors affecting permeation with seven radiolabelled chemicals are presented. The results demonstrate that the peifused diffusion cell system, which used a perfusion nuid betow the suiface of skin to take up the materials which penetrated the skin, is more similar to physiologic condition,convenient and automatic than that of the static cell. It well predicts the in vivo percutaneous absorption if appropriate areptor fluid is chosen. The results also show that the selection of receptor fluid is critical for in vitro permeation of chemicals with different soubility

Chemical Analysis of Magnesia and Magnesia-Alumina Refractory Materials——Flame atomic absorption spectrometric method for determination of calcium oxide content

1 Scope This standard specifics the determination of calcium oxide coutent by flame atomic absorption spectrometric method.

Sound absorption property of wood for five eucalypt species

The sound absorption coefficients of wood and wood boards for five eucalypt species (Eucalyptus urophylla, Euca-lyptus urophylla E. grandis, Eucalyptus urophylla E. tereticornis, Eucalyptus urophylla E. camaldulensis and Eucalyptus cloeziana) that were collected from plantation in Dongmen Forestry Center of Guangxi Province, China were tested with stand-ing wave method and their sound absorption properties were also compared. The results showed that the sound absorption co-efficients of the five eucalypt wood species did not change evidently below 1000 Hz, but above 1000 Hz their sound absorption coefficients increased with the increasing frequency. The difference in sound absorption coefficient among five species of eucalypt wood is not evident at the tested frequency range (200-2000 Hz), but the sound absorption property of Eucalyptus urophylla at low frequency is better than that of other four species. The sound absorption coefficient of the tangential-sawn board is higher than that of the radial-sawn board. The sound absorption property of eucalypt wood of 0.5 cm in thickness is much better than that of 1.0 cm in thickness. It is concluded that wood sound absorption properties of eucalypts are affected by their board thickness and the type of sawn timber within the testing frequency, but the variance of wood sound absorption property among the five tested species is not significant.

State of the Art and Prospects in Metal-Organic Framework-Derived Microwave Absorption Materials

Microwave has been widely used in many fields,including communication,medical treatment and military industry;however,the corresponding generated radiations have been novel hazardous sources of pollution threating human’s daily life.Therefore,designing high-performance microwave absorption materials(MAMs)has become an indispensable requirement.Recently,metal-organic frameworks(MOFs)have been considered as one of the most ideal precursor candidates of MAMs because of their tunable structure,high porosity and large specific surface area.Usually,MOF-derived MAMs exhibit excellent electrical conductivity,good magnetism and sufficient defects and interfaces,providing obvious merits in both impedance matching and microwave loss.In this review,the recent research progresses on MOF-derived MAMs were profoundly reviewed,including the categories of MOFs and MOF composites precursors,design principles,preparation methods and the relationship between mechanisms of microwave absorption and microstructures of MAMs.Finally,the current challenges and prospects for future opportunities of MOF-derived MAMs are also discussed.

Effects of core position of locally resonant scatterers on low-frequency acoustic absorption in viscoelastic panel

Locally resonant sonic materials, due to their ability to control the propagation of low-frequency elastic waves, have become a promising option for underwater sound absorption materials. In this paper, the finite element method is used to investigate the absorption characteristics of a viscoelastic panel periodically embedded with a type of infinite-long noncoaxially cylindrical locally resonant scatterers(LRSs). The effect of the core position in the coating layer of the LRS on the low-frequency(500 Hz–3000 Hz) sound absorption property is investigated. With increasing the longitudinal core eccentricity e, there occur few changes in the absorptance at the frequencies below 1500 Hz, however, the absorptance above 1500 Hz becomes gradually better and the valid absorption(with absorptance above 0.8) frequency band(VAFB)of the viscoelastic panel becomes accordingly broader. The absorption mechanism is revealed by using the displacement field maps of the viscoelastic panel and the steel slab. The results show two typical resonance modes. One is the overall resonance mode(ORM) caused by steel backing, and the other is the core resonance mode(CRM) caused by LRS. The absorptance of the viscoelastic panel by ORM is induced mainly by the vibration of the steel slab and affected little by core position. On the contrary, with increasing the core eccentricity, the CRM shifts toward high frequency band and decouples with the ORM, leading to two separate absorption peaks and the broadened VAFB of the panel.

Parameterization of the Absorption of the H_(2)O Continuum,CO_(2),O_(2),and Other Trace Gases in the Fu-Liou Solar Radiation Program

The absorption properties of the water vapor continuum and a number of weak bands for H2O, O2, CO2, CO, N2O, CH4, and O3 in the solar spectrum are incorporated into the Fu-Liou radiation parameterization program by using the correlated k-distribution method (CKD) for the sorting of absorption lines. The overlap absorption of the H2O lines and the H2O continuum (2500-14500 cm-1) are treated by taking the two gases as a single-mixture gas in transmittance calculations. Furthermore, in order to optimize the computation efforts, CO2 and CH4 in the spectral region 2850-5250 cm-1 are taken as a new single-mixture gas as well. For overlap involving other absorption lines in the Fu-Liou spectral bands, the authors adopt the multiplication rule for transmittance computations under which the absorption spectra for two gases are assumed to be uncorrelated. Compared to the line-by-line (LBL) computation, it is shown that the errors in fluxes introduced by these two approaches within the context of the CKD method are small and less than 0.48% for the H2O line and continuum in the 2500-14500 cm-1 solar spectral region, -1% for H2O (line)+H2O (continuum)+CO2+CH4 in the spectral region 2850-5250 cm-1, and -1.5% for H2O (line)+H2O (continuum)+O2 in the 7700-14500 cm-1 spectral region. Analysis also demonstrates that the multiplication rule over a spectral interval as wide as 6800 cm-1 can produce acceptable errors with a maximum percentage value of about 2% in reference to the LBL calculation. Addition of the preceding gases increases the absorption of solar radiation under all sky conditions. For clear sky, the increase in instantaneous solar absorption is about 9%-13% (~12 W m^2) among which the H2O continuum produces the largest increase, while the contributions from O2 and CO2 rank second and third, respectively. In cloudy sky, the addition of absorption amounts to about 6-9 W m-2. The new, improved program with the incorporation of the preceding gases produces a smaller solar absorption in clouds due to the reduced solar flux reaching the cloud top.

Heat Absorption and Joule Heating Effects on Transient Free Convective Reactive Micropolar Fluid Flow Past a Vertical Porous Plate

Mathematical model for an unsteady,incompressible,electrically conducting micropolar fluid past a vertical plate through porous medium with constant plate velocity has been investigated in the present study.Heat absorption,Joulian dissipation,and first-order chemical reaction is also considered.Under the assumption of low Reynolds number,the governing transport equations are rendered into non-dimensional form and the transformed first order differential equations are solved by employing an efficient finite element method.Influence of various flow parameters on linear velocity,microrotation velocity,temperature,and concentration are presented graphically.The effects of heat absorption and chemical reaction rate decelerate the flow is particularly near the wall.Skin friction and wall couple stress increases as heat absorption increases but the reverse phenomenon is observed in the case of chemical reaction rate.Wall mass transfer rate increases for chemical reaction and Sherwood number increases for heat absorption.Finite element study is very versatile in simulating unsteady micropolar rheo-materials processing transport phenomena.However,a relatively simple reaction effects restricted to first order.

Computational Analysis of the Effect of Nano Particle Material Motion on Mixed Convection Flow in the Presence of Heat Generation and Absorption

The present study is concerned with the physical behavior of the combined effect of nano particle material motion and heat generation/absorption due to the effect of different parameters involved in prescribed flow model.The formulation of the flow model is based on basic universal equations of conservation of momentum,energy and mass.The prescribed flow model is converted to non-dimensional form by using suitable scaling.The obtained transformed equations are solved numerically by using finite difference scheme.For the analysis of above said behavior the computed numerical data for fluid velocity,temperature profile,and mass concentration for several constraints that is mixed convection parameterλt,modified mixed convection parameterλc,Prandtl number Pr,heat generation/absorption parameterδ,Schmidt number Sc,thermophoresis parameter Nt,and thermophoretic coefficient k are sketched in graphical form.Numerical results for skin friction,heat transfer rate and the mass transfer rate are tabulated for various emerging physical parameters.It is reported that in enhancement in heat,generation boosts up the fluid temperature at some positions of the surface of the sphere.As heat absorption parameter is decreased temperature field increases at position X=π/4 on the other hand,no alteration at other considered circumferential positions is noticed.