Stress-corrosion coupled damage localization induced by secondary phases in bio-degradable Mg alloys:phase-field modeling

In this study,a phase-field scheme that rigorously obeys conservation laws and irreversible thermodynamics is developed for modeling stress-corrosion coupled damage(SCCD).The coupling constitutive relationships of the deformation,phase-field damage,mass transfer,and electrostatic field are derived from the entropy inequality.The SCCD localization induced by secondary phases in Mg is numerically simulated using the implicit iterative algorithm of the self-defined finite elements.The quantitative evaluation of the SCCD of a C-ring is in good agreement with the experimental results.To capture the damage localization,a micro-galvanic corrosion domain is defined,and the buffering effect on charge migration is explored.Three cases are investigated to reveal the effect of localization on corrosion acceleration and provide guidance for the design for resistance to SCCD at the crystal scale.

Genome-wide identification and co-expression analysis of GDSL genes related to suberin formation during fruit russeting in pear

Glycine-aspartic acid–serine-leucine(GDSL)type lipases/esterases genes play critical roles in plant development and are related to the responses to abiotic and biotic stress.However,little is known about the GDSL family in pear(Pyrus spp.).Studies have shown GDSL-domain proteins play key roles in suberin deposition.Suberin deposition in the fruit epidermis,also called russeting,is an important defect that negatively affects consumer's appeal in some fruit species,such as pear,apple and grapevine.Fruit russeting is mainly associated with cuticle microcracking and suberin accumulation in the inner part of the epidermal cell walls.To gain insight into the role of the GDSL gene family in suberin deposition and russet development in pear,we performed a genome-wide characterization of the GDSL family,including their identification,chromosomal localization,phylogenetic relationships,and expression patterns,in different tissues/organs in pear.One hundred and thirteen GDSL-type lipases/esterases genes were identified in the pear genome,and a phylogenetic analysis revealed that GDSL family can be classified into four distinct groups.Thirty GDSL genes were co-expressed with five homolog pear genes of three well-known suberin biosynthesis Arabidopsis genes(AtGPAT5,AtASFT,and AtCYP86B1)in the transcriptional co-expression network during pear fruit development.Among the 30 co-expressed GDSL genes,twelve genes were further analyzed by quantitative Real-time PCR,and the results showed the expression levels of the 12 genes were different between the russet exocarp and green exocarp of sand pear at different fruit development stages.Our study provides a detailed overview of the GDSL gene family and lays the foundation for future functional characterization of GDSL genes in P.bretschneideri.

Interaction between bending and mobile charges in a piezoelectric semiconductor bimorph

We study the bending of a two-layer piezoelectric semiconductor plate(bimorph).The macroscopic theory of piezoelectric semiconductors is employed.A set of two-dimensional plate equations is derived from the three-dimensional equations.The plate equations exhibit direct couplings among bending,electric polarization along the plate thickness,and mobile charges.In the case of pure bending,a combination of physical and geometric parameters is identified which characterizes the strength of the interaction between the mechanical load and the distribution of mobile charges.In the bending of a rectangular plate under a distributed transverse mechanical load,it is shown that mobile charge distributions and potential barriers/wells develop in the plate.When the mechanical load is local and self-balanced,the induced carrier distributions and potential barriers/wells are also localized near the loading area.The results are fundamentally useful for mechanically manipulating mobile charges in piezoelectric semiconductor devices.

PROPAGATION OF LOVE WAVES IN PRESTRESSED PIEZOELECTRIC LAYERED STRUCTURES LOADED WITH VISCOUS LIQUID

We investigate analytically the effect of initial stress in piezoelectric layered structures loaded with viscous liquid on the dispersive and attenuated characteristics of Love waves, which involves a thin piezoelectric layer bonded perfectly to an unbounded elastic substrate. The effects of initial stress in the piezoelectric layer and the viscous coefficient of the liquid on the phase velocity of Love waves are analyzed. Numerical results are presented and discussed. The analytical method and the results can be useful for the design of chemical and biosensing liquid sensors.

PARALLEL FINITE ELEMENT ANALYSIS OF HIGH FREQUENCY VIBRATIONS OF QUARTZ CRYSTAL RESONATORS ON LINUX CLUSTER

Quartz crystal resonators are typical piezoelectric acoustic wave devices for frequency control applications with mechanical vibration frequency at the radio-frequency （RF） range. Precise analyses of the vibration and deformation are generally required in the resonator design and improvement process. The considerations include the presence of electrodes, mountings, bias fields such as temperature, initial stresses, and acceleration. Naturally, the finite element method is the only effective tool for such a coupled problem with multi-physics nature. The main challenge is the extremely large size of resulted linear equations. For this reason, we have been employing the Mindlin plate equations to reduce the computational difficulty. In addition, we have to utilize the parallel computing techniques on Linux clusters, which are widely available for academic and industrial applications nowadays, to improve the computing efficiency. The general principle of our research is to use open source software components and public domain technology to reduce cost for developers and users on a Linux cluster. We start with a mesh generator specifically for quartz crystal resonators of rectangular and circular types, and the Mindlin plate equations are implemented for the finite element analysis. Computing techniques like parallel processing, sparse matrix handling, and the latest eigenvalue extraction package are integrated into the program. It is clear from our computation that the combination of these algorithms and methods on a cluster can meet the memory requirement and reduce computing time significantly.

A chromosome-level genome assembly of rugged rose (Rosa rugosa) provides insights into its evolution, ecology, and floral characteristics

Rosa rugosa,commonly known as rugged rose,is a perennial ornamental shrub.It produces beautiful flowers with a mild fragrance and colorful seed pods.Unlike many other cultivated roses,R.rugosa adapts to a wide range of habitat types and harsh environmental conditions such as salinity,alkaline,shade,drought,high humidity,and frigid temperatures.Here,we produced and analyzed a high-quality genome sequence for R.rugosa to understand its ecology,floral characteristics and evolution.PacBio HiFi reads were initially used to construct the draft genome of R.rugosa,and then Hi-C sequencing was applied to assemble the contigs into 7 chromosomes.We obtained a 382.6Mb genome encoding 39,704 protein-coding genes.The genome of R.rugosa appears to be conserved with no additional whole-genome duplication after the gamma whole-genome triplication(WGT),which occurred~100 million years ago in the ancestor of core eudicots.Based on a comparative analysis of the high-quality genome assembly of R.rugosa and other high-quality Rosaceae genomes,we found a unique large inverted segment in the Chinese rose R.chinensis and a retroposition in strawberry caused by post-WGT events.We also found that floral development-and stress response signaling-related gene modules were retained after the WGT.Two MADS-box genes involved in floral development and the stress-related transcription factors DREB2A-INTERACTING PROTEIN 2(DRIP2)and PEPTIDE TRANSPORTER 3(PTR3)were found to be positively selected in evolution,which may have contributed to the unique ability of this plant to adapt to harsh environments.In summary,the high-quality genome sequence of R.rugosa provides a map for genetic studies and molecular breeding of this plant and enables comparative genomic studies of Rosa in the near future.

Extended Kantorovich method for local stresses in composite laminates upon polynomial stress functions

The extended Kantorovich method is employed to study the local stress concentrations at the vicinity of free edges in symmetrically layered composite laminates subjected to uniaxial tensile load upon polynomial stress functions. The stress fields are initially assumed by means of the Lekhnitskii stress functions under the plane strain state. Applying the principle of complementary virtual work,the coupled ordinary differential equations are obtained in which the solutions can be obtained by solving a generalized eigenvalue problem. Then an iterative procedure is established to achieve convergent stress distributions. It should be noted that the stress function based extended Kantorovich method can satisfy both the traction-free and free edge stress boundary conditions during the iterative processes. The stress components near the free edges and in the interior regions are calculated and compared with those obtained results by finite element method（FEM）. The convergent stresses have good agreements with those results obtained by three dimensional（3D） FEM. For generality, various layup configurations are considered for the numerical analysis. The results show that the proposed polynomial stress function based extended Kantorovich method is accurate and efficient in predicting the local stresses in composite laminates and computationally much more efficient than the 3D FEM.

Molecular characteristics of S-RNase alleles as the determ inant of self-i ncompatibility in the style of Fragaria viridi

Strawberry(Fragaria spp.)is a member of the Rosoideae subfamily in the family Rosaceae.The self-incompatibility(SI)of some diploid species is a key agronomic trait that acts as a basic pollination barrier;however,the genetic mechanism underlying SI control in strawberry remains unclear.Two candidate S-RNases(S a-and S^-RNase)identi fi ed in the transcriptome of the styles of the self-incompatible Fragaria viridis 42 were con fi rmed to be SI determinants at the S locus following genotype identi fi cation and intraspeci fi c hybridization using sel fi ng progenies.Whole-genome collinearity and RNase T2 family analysis revealed that only an S locus exists in Fragaria;however,none of the compatible species contained S-RNase.Although the results of interspeci fi c hybridization experiments showed that F.viridis(SI)styles could accept pollen from F.mandshurica(self-compatible),the reciprocal cross was incompatible.S a and S b-RNase contain large introns,and their noncoding sequences(promotors and introns)can be transcribed into long noncoding RNAs(lncRNAs).Overall,the genus Fragaria exhibits S-RNase-based gametophytic SI,and S-RNase loss occurs at the S locus of compatible germplasms.In addition,a type of SI-independent unilateral incompatibility exists between compatible and incompatible Fragaria species.Furthermore,the large introns and neighboring lncRNAs in S-RNase in Fragaria could offer clues about S-RNase expression strategies.

ELECTRICALLY FORCED THICKNESS-SHEAR VIBRATIONS OF QUARTZ PLATE WITH NONLINEAR COUPLING TO EXTENSION

We study electrically forced nonlinear thickness-shear vibrations of a quartz plate resonator with relatively large amplitude. It is shown that thickness-shear is nonlinearly coupled to extension due to the well-known Poynting effect in nonlinear elasticity. This coupling is relatively strong when the resonant frequency of the extensional mode is about twice the resonant frequency of the thickness-shear mode. This happens when the plate length/thickness ratio assumes certain values. With this nonlinear coupling, the thickness-shear motion is no longer sinusoidal. Coupling to extension also affects energy trapping which is related to device mounting. When damping is 0.01, nonlinear coupling causes a frequency shift of the order of 10^-6 which is not insignificant,and an amplitude change of the order of 10^-8. The effects are expected to be stronger under real damping of 10^-5 or larger. To avoid nonlinear coupling to extension, certain values of the aspect ratio of the plate should be avoided.

The axisymmetric Rayleigh waves in a semi-infinite elastic solid

It is well-known that Rayleigh wave,also known as surface acoustic wave(SAW),solutions in semiinfinite solids are plane waves with signatory properties like the distinct velocity and exponentially decaying deformation in the depth.Applications of Rayleigh waves are focused on the deformation and energy in the vicinity of surface of solids and less loss in the propagation.A generalized model of Rayleigh waves in axisymmetric mode is established and solutions are obtained with cylindrical coordinates.It is found that the Rayleigh waves also propagate in the axisymmetric mode with slow decay in radius,confirming the existence of surface acoustic waves is irrelevant to coordinate system.On the other hand,the solutions can be treated as plane waves in regions far away from the source.Furthermore,the particle trajectory of axisymmetric SAW is a line with constant slope rather than the signatory ellipse in Cartesian coordinate case.

Effects of surface impedance on current density in a piezoelectric resonator for impedance distribution sensing

We study the relationship between the surface mechanical load represented by distributed acoustic impedance and the current density distribution in a shear mode piezoelectric plate acoustic wave resonator.A theoretical analysis based on the theory of piezoelectricity and trigonometric series is performed.In the specific and basic case when the surface load is due to a local mass layer,numerical results show that the current density concentrates under the mass layer and is sensitive to the physical as well as geometric parameters of the mass layer such as its location and size.This provides the theoretical foundation for predicting the surface impedance pattern from the current density distribution,which is fundamental to the relevant acoustic wave sensors.

An Analysis of Piezomagnetic-Piezoelectric Semiconductor Unimorphs in Coupled Bending and Extension under a Transverse Magnetic Field

We study the response of a composite beam(unimorph)with a piezomagnetic layer and a piezoelectric semiconductor layer under a transverse magnetic field.A one-dimensional model for coupled bending and extension of the beam is derived from the three-dimensional theory.A simple and analytical solution of the model is obtained,showing that various electromechanical fields develop in the beam through piezomagnetic and piezoelectric couplings as well as semiconduction.In particular,the mobile charges in the semiconductor layer redistribute themselves under the magnetic field.A coupling coefficient is defined to describe the strength of this magneto-semiconduction coupling.The effects of physical and geometric parameters on the fields and the coupling coefficient are examined.The results are fundamental to piezotronics when magnetic effects are involved.

Thickness-Shear Frequencies of an Infinite Quartz Plate with Graded Material Properties Across the Thickness

For quartz crystal resonators of thickness-shear type,the vibration frequency and mode shapes reflect the basic material and structural properties of a quartz crystal plate and the variation with time under attack by erosive gases and liquids that can cause surface and internal degradation in a graded form.Such gradual effects,in turn,will change surface conditions through elastic constants and stiffness and more importantly the gradient of such properties across the thickness with certain depth.Now we study the thickness-shear vibrations of functionally graded material plates with properties of the popular AT-cut quartz crystal varying across the thickness in a general pattern represented by both sine and cosine components of the thickness.The vibration solutions are obtained through the Fourier expansion of the plate deformation.

Frequency–Temperature Analysis of Thickness-Shear Vibrations of SC-Cut Quartz Crystal Plates with the First-Order Mindlin Plate Equations

With the incremental thermal field theory by Lee and Yong,the Mindlin plate equations for the analysis of thickness-shear vibrations of SC-cut quartz crystal with the consideration of thermal effect have been obtained.By assuming straight-crested waves in a rectangular plate,the dispersion relations,frequency spectra,mode shapes,and frequency–temperature relations of the thickness-shear mode of SC-cut quartz crystal plates are calculated with plate configurations.The computational results from SC-cut quartz crystal plates are compared with those from AT-cut,which shows that SC-cut resonators have better frequency–temperature relation as a validation.For practical applications,such results will be useful in the precision design and improvement of SC-cut quartz crystal resonator structures.

Digital analysis of tooth microwear,a potential application for dental microwear monitor

In general,tooth wear is difficult to be noticed until it leads to toothache in vivo.Developing a dynamic dental wear monitoring system to predict tooth wear in daily life is a necessity.The translation between complex surface wear morphology and corresponding digital signal source is a technical limitation to develop this kind of monitoring system.Microwear texture analysis has been widely employed in predicting diet by a palaeontologist.The main question is whether the microwear texture analysis has potential development space to develop a sensor for monitoring tooth wear.According to obtained results,the microwear texture analysis had enough sensitivity to display the surface morphology variations for different chewing foods and various angles.The corresponding sensitive digital signal of tooth microwear surface morphology makes it possible to develop a dental microwear sensor.

SHEAR-HORIZONTAL WAVES IN A ROTATED Y-CUT QUARTZ PLATE WITH AN ISOTROPIC ELASTIC LAYER OF FINITE THICKNESS

We study shear-horizontal （SH） waves in a rotated Y-cut quartz plate carrying an isotropic elastic layer of finite thickness.The three-dimensional theories of anisotropic elasticity and isotropic elasticity are used for the quartz plate and the elastic layer,respectively.A transcen-dental frequency equation that determines the dispersion relations of the waves is obtained.The dispersion relations are obtained and plotted by solving the frequency equation using MATLAB.Approximate dispersion relations are also obtained analytically for two special cases.One is for long waves whose wavelength is much larger than the plate thickness.The other is for the case of a very thin elastic layer.The effects of the elastic layer on the dispersion relations are exam-ined.The results obtained are fundamental and useful to acoustic wave sensors for measuring the mechanical and geometric properties of the elastic layer.

Thermally controlled large deformation in temperaturesensitive hydrogels bilayers

The present work investigates the thermally controlled deformation characteristics in temperature-sensitive hydrogels bilayers.The free energy density for temperature-sensitive hydrogels is modified,upon which the finite element model is developed and implemented through user-defined material subroutine UHYPER in the commercial software ABAQUS.The modified UHYPER implementation allows for more vividly depicting the continuous deformation in phase temperature region for temperature-sensitive hydrogels.Several thermally controlled cases of temperature-sensitive hydrogel including grippers,self-folding boxes,thermally driven origami are presented to illustrate a wide array of complex interesting applications or phenomena.Furthermore,we develop a simple model to theoretically calculate the bending angle of the temperature-sensitive hydrogel bilayers,which has been validated by the finite element simulation results.Our study can provide more insights for optimal design in thermally controlled hydrogels structures.

Flexible,high-strength titanium nanowire for scaffold biomimetic periodontal membrane

A layer of micro-sized periodontal membrane can buffer most chewing forces to protect the interface between the natural tooth root and alveolar bone.Artificial dental implants usually direct contact onto the alveolar bone without a buffer layer,which increases the risk of surface damage.The main purpose of this work was the bionic design of a flexible layer of nanowire scaffold on a titanium implant surface according to the function of the periodontal membrane.Millions of nanowires were woven into a superhydrophilic layer of porous scaffold.The evolution of mechanical properties displayed that the biomimetic nanowire scaffold could absorb a maximum of about 1.59 KJ energy per square centi-meter by low-speed impact.The minimum tensile strength of one nanowire was 2 GPa.A biomimetic flexible periodontal membrane connection functioning between the natural tooth root and alveolar bone has great potential value for developing advanced artificial dental implants for dental restorations.

Nano-frictional mechano-reinforcing porous nanowires scaffolds

Artificial biomaterials with dynamic mechano-responsive behaviors similar to those of biological tissues have been drawing great attention.In this study,we report a TiO_(2)-based nanowire(TiO_(2)NWs)scaffolds,which exhibit dynamic mechano-responsive behaviors varying with the number and amplitude of nano-deformation cycles.It is found that the elastic and adhesive forces in the TiO_(2)NWs scaffolds can increase significantly after multiple cycles of nano-deformation.Further nanofriction experiments show the triboelectric effect of increasing elastic and adhesive forces during the nano-deformation cycles of TiO_(2)NWs scaffolds.These properties allow the TiO_(2)NW scaffolds to be designed and applied as intelligent artificial biomaterials to simulate biological tissues in the future.