A fractional derivative model for nuclides transport in heterogeneous fractured media.

Nuclide transport in fractured media involves the advection, dispersion, adsorption, etc. The dispersion and adsorption properties of the rock matrix have spatial variability, which results in an anomalous transport of nuclides. In this study, a time-fractional advection-diffusion equation (t-FADE) model is utilized to capture the sub-diffusion transport behavior with heavy-tail property, including the breakthrough curves (BTCs) of uranium and thorium transport in granite plates. Moreover, hydrodynamic dispersion of tritiated water, strontium and cesium in granite fractures are also studied. The results indicate that BTCs of nuclides transport in the granite fractures are unimodal and asymmetric. The decrease of the fractional order α reflects the stronger sub-diffusion. Furthermore, small initial velocity enhances sub-diffusion effect of nuclides and lengthens the breakout time of BTCs, which results in obvious heavy-tail phenomena. The analysis results demonstrate that the t-FADE model can accurately describe sub-diffusion behavior of nuclides transport. At last, the advantages of the t-FADE model in prediction and remediation of nuclides contamination are put forward.

Propagation of terahertz elastic longitudinal waves in piezoelectric semiconductor rods.

Terahertz elastic waves travelling in piezoelectric semiconductors (PSs) with the deformation-polarization-carrier coupling have a huge potential application in elastic wave-based devices. To reveal wave propagation characteristics of terahertz elastic waves in rod-like PS structures, we present three typical rod models based on the Hamilton principle and the linearization of the nonlinear current, which are extensions of the classical, Love, and Mindlin-Herrmann rod models for elastic media to those for PS materials. Using the derived equations, the analytical dispersion relations of the elastic longitudinal waves propagating in an n-type PS rod are obtained, which can be reduced to those for piezoelectric and elastic rods by sequentially dropping the corresponding electron- and piezoelectricity-related terms. The Mindlin-Herrmann rod model is more accurate for analysis of terahertz elastic longitudinal wave in rod-like PS structures. The effects of the interaction between the piezoelectricity and semiconducting properties on the dispersion behaviors of terahertz elastic longitudinal waves are investigated in detail. Numerical results show that both phase and group velocities have a 50%-60% reduction in the terahertz range in comparison with those in the low frequency range, and the effective tuning range of the initial electron concentration is different for longitudinal waves with different frequencies. It lays the theoretical foundations for the design of terahertz elastic wave-based devices.

Waves Propagating in Nano-Layered Phononic Crystals with Flexoelectricity, Microstructure, and Micro-Inertia Effects.

The miniaturization of electronic devices is an important trend in the development of modern microelectronics information technology. However, when the size of the component or the material is reduced to the micro/nano scale, some size-dependent effects have to be taken into account. In this paper, the wave propagation in nano phononic crystals is investigated, which may have a potential application in the development of acoustic wave devices in the nanoscale. Based on the electric Gibbs free energy variational principle for nanosized dielectrics, a theoretical framework describing the size-dependent phenomenon was built, and the governing equation as well as the dispersion relation derived; the flexoelectric effect, microstructure, and micro-inertia effects are taken into consideration. To uncover the influence of these three size-dependent effects on the width and midfrequency of the band gaps of the waves propagating in periodically layered structures, some related numerical examples were shown. Comparing the present results with the results obtained with the classical elastic theory, we find that the coupled effects of flexoelectricity, microstructure, and micro-inertia have a significant or even dominant influence on the waves propagating in phononic crystals in the nanoscale. With increase in the size of the phononic crystal, the size effects gradually disappear and the corresponding dispersion curves approach the dispersion curves obtained with the conventional elastic theory, which verify the results obtained in this paper. Thus, when we study the waves propagating in phononic crystals in the micro/nano scale, the flexoelectric, microstructure, and micro-inertia effects should be considered.

Achromatic metasurfaces by dispersion customization for ultra-broadband acoustic beam engineering.

Metasurfaces, the ultra-thin media with extraordinary wavefront modulation ability, have shown great promise for many potential applications. However, most of the existing metasurfaces are limited by narrow-band and strong dispersive modulation, which complicates their real-world applications and, therefore require strict customized dispersion. To address this issue, we report a general methodology for generating ultra-broadband achromatic metasurfaces with prescribed ultra-broadband achromatic properties in a bottom-up inverse-design paradigm. We demonstrate three ultra-broadband functionalities, including acoustic beam deflection, focusing and levitation, with relative bandwidths of 93.3%, 120% and 118.9%, respectively. In addition, we reveal a relationship between broadband achromatic functionality and element dispersion. All metasurface elements have anisotropic and asymmetric geometries with multiple scatterers and local cavities that synthetically support internal resonances, bi-anisotropy and multiple scattering for ultra-broadband customized dispersion. Our study opens new horizons for ultra-broadband highly efficient achromatic functional devices, with promising extension to optical and elastic metamaterials.

Tunable Fluid-Type Metasurface for Wide-Angle and Multifrequency Water-Air Acoustic Transmission.

Efficient acoustic communication across the water-air interface remains a great challenge owing to the extreme acoustic impedance mismatch. Few present acoustic metamaterials can be constructed on the free air-water interface for enhancing the acoustic transmission because of the interface instability. Previous strategies overcoming this difficulty were limited in practical usage, as well as the wide-angle and multifrequency acoustic transmission. Here, we report a simple and practical way to obtain the wide-angle and multifrequency water-air acoustic transmission with a tunable fluid-type acoustic metasurface (FAM). The FAM has a transmission enhancement of acoustic energy over 200 times, with a thickness less than the wavelength in water by three orders of magnitude. The FAM can work at an almost arbitrary water-to-air incident angle, and the operating frequencies can be flexibly adjusted. Multifrequency transmissions can be obtained with multilayer FAMs. In experiments, the FAM is demonstrated to be stable enough for practical applications and has the transmission enhancement of over 20 dB for wide frequencies. The transmission enhancement of music signal across the water-air interface was performed to demonstrate the applications in acoustic communications. The FAM will benefit various applications in hydroacoustics and oceanography.

Lotus Metasurface for Wide-Angle Intermediate-Frequency Water-Air Acoustic Transmission.

Only 0.1% of the acoustic energy can transmit across the water-air interface because of the huge acoustic impedance mismatch. Enhancing acoustic transmission across the water-air interface is of great significance for sonar communications and sensing. However, due to the interface instability and subwavelength characteristics of acoustic metamaterials, wide-angle intermediate-frequency (10 kHz-100 kHz) water-air acoustic transmission remains a great challenge. Here, we demonstrate that the lotus leaf is a natural low-cost acoustic transmission metasurface, namely, the lotus acoustic metasurface (LAM). Experiments demonstrate the LAM can enhance the acoustic transmission across the water-air interface, with an energy transmission coefficient of about 40% at 28 kHz. Furthermore, by fabricating artificial LAMs, the operating frequencies can be flexibly adjusted. Also, the LAM allows a wide-angle water-to-air acoustic transmission. It will enable various promising applications, such as detecting and imaging underwater objects from the air, communicating between ocean and atmosphere, reducing ocean noises, etc.

Matrix Metalloproteinase-9-Responsive Surface Charge-Reversible Nanocarrier to Enhance Endocytosis as Efficient Targeted Delivery System for Cancer Diagnosis and Therapy.

Nanoparticles, that can be enriched in the tumor microenvironment and deliver the payloads into cancer cells, are desirable carriers for theranostic agents in cancer diagnosis and treatment. However, efficient targeted delivery and enhanced endocytosis for probes and drugs in theranostics are still major challenges. Here, a nanoparticle, which is capable of charge reversal from negative to positive in response to matrix metalloproteinase 9 (MMP9) in tumor microenvironment is reported. This nanoparticle is based on a novel charge reversible amphiphilic molecule consisting of hydrophobic oleic acid, MMP9-cleavable peptide, and glutamate-rich segment (named as OMPE). The OMPE-modified cationic liposome forms an intelligent anionic nanohybrid (O-NP) with enhanced endocytosis through surface charge reversal in response to MMP9 in vitro. Successfully, O-NP nanohybrid performs preferential accumulation and enhances the endocytosis in MMP9-expressing xenografted tumors in mouse models, which improve the sensitivity of diagnosis agents and the antitumor effects of drugs in vivo by overcoming their low solubility and/or nonspecific enrichment. These results indicate that O-NP can be a promising delivery platform for cancer diagnosis and therapy.

Real-time monitoring of caspase-3/8 activity by self-assembling nanofiber probes in living cells.

Caspase-3/8 are key members of the cysteine-aspartyl protease family with pivotal roles in apoptosis. We have designed and synthesized self-assembling probes, Nap-GFFpYDEVD-AFC and Nap-GFFpYIETD-AFC, with fluorescence 'turn-on' properties for real-time monitoring of Caspase-3/8 activity in living cells.

Torsional whole-life transformation ratchetting under pure-torsional and non-proportional multiaxial cyclic loadings of NiTi SMA at human-body temperature: Experimental observations and life-prediction model.

Torsional whole-life transformation ratchetting is investigated under pure-torsional and non-proportional multiaxial loadings of NiTi SMA micro-tubes at human-body temperature (310 K), where three paths of torsional loadings and five paths of multiaxial ones are considered. It is observed that the evolution of the torsional whole-life transformation ratchetting depends strongly on the loading paths and stress levels, and the fatigue lives of pure-torsional loadings decrease faster than that of uniaxial and multiaxial ones with the increase of peak stress. Based on the experimental investigations, a life-prediction model which depends on the applied stress levels is proposed for NiTi SMA micro-tubes, where the martensite transformation and reorientation of NiTi SMAs are considered. The predicted fatigue lives under uniaxial, torsional and non-proportional multiaxial loadings are mostly located within the triple error band.

In-hospital, short-term and long-term adverse clinical outcomes observed in patients with type 2 diabetes mellitus vs non-diabetes mellitus following percutaneous coronary intervention: A meta-analysis including 139,774 patients.

BACKGROUND: Several studies have shown that patients with type 2 diabetes mellitus (T2DM) have worse clinical outcomes in comparison to patients without diabetes mellitus (DM) following Percutaneous Coronary Intervention (PCI). However, the adverse clinical outcomes were not similarly reported in all the studies. Therefore, in order to standardize this issue, a meta-analysis including 139,774 patients was carried out to compare the in-hospital, short-term (<1 year) and long-term (≥1 year) adverse clinical outcomes in patients with and without T2DM following PCI. METHODS: Electronic databases including MEDLINE, EMBASE, and the Cochrane Library were searched for Randomized Controlled Trials (RCTs) and observational studies. The adverse clinical outcomes which were analyzed included mortality, myocardial infarction (MI), major adverse cardiac events (MACEs), stroke, bleeding, target vessel revascularization (TVR), target lesion revascularization (TLR), and stent thrombosis. Risk Ratios (RR) with 95% confidence intervals (CI) were used to express the pooled effect on discontinuous variables and the analysis was carried out by RevMan 5.3 software. RESULTS: A total number of 139,774 participants were assessed. Results of this analysis showed that in-hospital mortality and MACEs were significantly higher in patients with T2DM (RR 2.57; 95% CI: 1.95-3.38; P = .00001) and (RR: 1.38; 95% CI: 1.10-1.73; P = .005) respectively. In addition, majority of the short and long-term adverse clinical outcomes were also significantly higher in the DM group as compared to the non-DM group. Stent thrombosis was significantly higher in the DM compared to the non-DM group during the short term follow-up period (RR 1.59; 95% CI: 1.16-2.18;P = .004). However, long-term stent thrombosis was similarly manifested. CONCLUSION: According to this meta-analysis including a total number of 139,774 patients, following PCI, those patients with T2DM suffered more in-hospital, short as well as long-term adverse outcomes as reported by most of the Randomized Controlled Trials and Observational studies, compared to those patients without diabetes mellitus.

An analysis of the thickness vibration of an unelectroded doubly-rotated quartz circular plate.

The scalar differential equation in the thickness eigendisplacement for the doubly-rotated quartz plates is applied to analyze thickness vibrations of an unelectroded circular plate with free edges at the neighborhood of the pure thickness vibration mode. The scalar differential equation is transformed into an elliptical coordinate system. With the boundary conditions of free edges, the frequencies and the modes are solved in terms of the Mathieu function and the Modified Mathieu function. The results of frequencies of the fundamental harmonic and its third overtone of an AT-cut quartz circular plate by the present approach agree well with the existing theoretical results and the experiment results. The frequencies and modes of an SC-cut quartz circular plate are investigated by the present approach. The frequencies are close to each other when the order of the harmonics is the same. A rotation angle of the symmetric axes of the vibration modes are observed that is dependent on the anisotropic material constants and the order of the harmonics. This approach has potential applications in the design of the doubly-rotated quartz circular resonators.

Broadband single-phase hyperbolic elastic metamaterials for super-resolution imaging.

Hyperbolic metamaterials, the highly anisotropic subwavelength media, immensely widen the engineering feasibilities for wave manipulation. However, limited by the empirical structural topologies, the reported hyperbolic elastic metamaterials (HEMMs) suffer from the limitations of the relatively narrow frequency width, inflexible adjustable operating subwavelength scale and difficulty to further improve the imaging resolution. Here, we show an inverse-design strategy for HEMMs by topology optimization. We design broadband single-phase HEMMs supporting multipolar resonances at different prescribed deep-subwavelength scales, and demonstrate the super-resolution imaging for longitudinal waves. Benefiting from the extreme enhancement of the evanescent waves, an optimized HEMM at an ultra-low frequency can yield an imaging resolution of ~λ/64, representing the record in the field of elastic metamaterials. The present research provides a novel and general design methodology for exploring the HEMMs with unrevealed mechanisms and guides the ultrasonography and general biomedical applications.

High-transmission acoustic self-focusing and directional cloaking in a graded perforated metal slab.

A design strategy and its modeling for high-transmission acoustic self-focusing and directional cloaking in a two-dimensional (2D) and an axisymmetric three-dimensional (3D) gradient-index phononic crystal (GRIN-PC) are reported in this paper. A gradient perforated aluminum slab sandwiched by water is considered. A low-loss directional cloaking device is achieved by controlling the matching coefficient between the slab and the water. The anisotropy coefficient that affects the scattering properties is also introduced. Furthermore, the phase discontinuity for directional cloaking inside and outside the slab is overcome by introducing a non-gradient slab having a lower group velocity behind the GRIN slab as an acoustic delay device. In addition, an axisymmetric 3D directional cloaking structure is obtained by rotating the corresponding 2D structure around the slab axis.

Hybrid acoustic metamaterial as super absorber for broadband low-frequency sound.

A hybrid acoustic metamaterial is proposed as a new class of sound absorber, which exhibits superior broadband low-frequency sound absorption as well as excellent mechanical stiffness/strength. Based on the honeycomb-corrugation hybrid core (H-C hybrid core), we introduce perforations on both top facesheet and corrugation, forming perforated honeycomb-corrugation hybrid (PHCH) to gain super broadband low-frequency sound absorption. Applying the theory of micro-perforated panel (MPP), we establish a theoretical method to calculate the sound absorption coefficient of this new kind of metamaterial. Perfect sound absorption is found at just a few hundreds hertz with two-octave 0.5 absorption bandwidth. To verify this model, a finite element model is developed to calculate the absorption coefficient and analyze the viscous-thermal energy dissipation. It is found that viscous energy dissipation at perforation regions dominates the total energy consumed. This new kind of acoustic metamaterials show promising engineering applications, which can serve as multiple functional materials with extraordinary low-frequency sound absorption, excellent stiffness/strength and impact energy absorption.

Inverse design of high-Q wave filters in two-dimensional phononic crystals by topology optimization.

Topology optimization of a waveguide-cavity structure in phononic crystals for designing narrow band filters under the given operating frequencies is presented in this paper. We show that it is possible to obtain an ultra-high-Q filter by only optimizing the cavity topology without introducing any other coupling medium. The optimized cavity with highly symmetric resonance can be utilized as the multi-channel filter, raising filter and T-splitter. In addition, most optimized high-Q filters have the Fano resonances near the resonant frequencies. Furthermore, our filter optimization based on the waveguide and cavity, and our simple illustration of a computational approach to wave control in phononic crystals can be extended and applied to design other acoustic devices or even opto-mechanical devices.

Band structure calculation of SH waves in nanoscale multilayered piezoelectric phononic crystals using radial basis function method with consideration of nonlocal interface effects.

In this paper, the radial basis function (RBF) collocation method based on the nonlocal Eringen piezoelectricity theory is developed to compute the band structures of nanoscale multilayered piezoelectric phononic crystals taking account of nonlocal interface effects. Detailed calculations are performed for anti-plane transverse waves propagating obliquely or vertically in the system. The correctness of the present method is verified by comparing the numerical results with those obtained by applying the transfer matrix method in the case of nonlocal perfect interfaces. The effects of nonlocal interface imperfections are considered by comparing with the nonlocal perfect interfaces. In addition, the influences of the piezoelectric constant, the nanoscale size, the impedance ratio and the incidence angle on the cut-off frequency and band structures are investigated and discussed in detail. Numerical results show that the nonlocal interface discontinuity has more obvious effect on the low-frequency band structures at the microscopic scale than at the macroscopic scale. Furthermore, at the macroscopic scale, the nonlocal interface imperfection has an obvious effect on the high frequency waves, but the effect on the low frequency waves is not obvious, and the nonlocal interface imperfection has no effect on the cut-off frequency at the microscopic scale.

Two-dimensional locally resonant elastic metamaterials with chiral comb-like interlayers: Bandgap and simultaneously double negative properties.

In this paper, bandgap and dynamic effective properties of two-dimensional elastic metamaterials with a chiral comb-like interlayer are studied by using the finite element method. The effects of the geometrical parameters of the chiral comb-like interlayer on the band edges are investigated and discussed. Combined with the analysis of the vibration modes at the band edges, equivalent spring-mass/pendulum models are developed to investigate the mechanisms of the bandgap generation. The analytically predicted results of the band edges, including the frequency where the double negative properties appear, and the numerical ones are generally in good agreement. The research findings in this paper have relevant engineering applications of the elastic metamaterials in the low frequency range.

Unified analytical expressions of the three-dimensional fundamental solutions and their derivatives for linear elastic anisotropic materials.

Novel unified analytical displacement and stress fundamental solutions as well as the higher order derivatives of the displacement fundamental solutions for three-dimensional, generally anisotropic and linear elastic materials are presented in this paper. Adequate integral expressions for the displacement and stress fundamental solutions as well as the higher order derivatives of the displacement fundamental solutions are evaluated analytically by using the Cauchy residue theorem. The resulting explicit displacement fundamental solutions and their first and second derivatives are recast into convenient analytical forms which are valid for non-degenerate, partially degenerate, fully degenerate and nearly degenerate cases. The correctness and the accuracy of the novel unified and closed-form three-dimensional anisotropic fundamental solutions are verified by using some available analytical expressions for both transversely isotropic (non-degenerate or partially degenerate) and isotropic (fully degenerate) linear elastic materials.

Anti-plane transverse waves propagation in nanoscale periodic layered piezoelectric structures.

In this paper, anti-plane transverse wave propagation in nanoscale periodic layered piezoelectric structures is studied. The localization factor is introduced to characterize the wave propagation behavior. The transfer matrix method based on the nonlocal piezoelectricity continuum theory is used to calculate the localization factor. Additionally, the stiffness matrix method is applied to compute the wave transmission spectra. A cut-off frequency is found, beyond which the elastic waves cannot propagate through the periodic structure. The size effect or the influence of the ratio of the internal to external characteristic lengths on the cut-off frequency and the wave propagation behavior are investigated and discussed.