Mechanics of DNA packaging and ejection from elastic phage capsid

This study intends to investigate how the elasticity of a bacterial phage can affect the process of DNA packaging and ejection. For this purpose, we propose a unified continuum and statistical mechanics model by taking into account the effects of DNA bending deformation, electrostatic repulsion between DNA-DNA strands and elastic deformation of the phage capsid. Based on such a model, we derive the quantitative relations between packaging force, elasticity of capsid, DNA length remaining in the capsid, osmotic pressure and ejection time. The theoretically predicted results are found to agree very well with in vitro experimental observations in the lit-erature.

Electric-magnetic-force characteristics of rare earth barium copper oxide superconductor high-field coils based on screening effect and strain sensitivity

Rare earth barium copper oxide(REBCO)is the most researched and commercialized second-generation high-temperature superconducting material.Due to the anisotropic structure,strong deformation sensitivity,and central field errors caused by screening current effects,it is still a challenge for commercialization applications.In this study,the transversely isotropic constitutive relationship is selected as the mechanical model based on the structural characteristics of REBCO tapes,and suitable microelements are selected to equate the elastic constants using their average stress-strain relationships.Then,a two-dimensional axisymmetric model for coils wound by single-layer tapes is constructed to analyze the dependence of the electric-magnetic-force distribution in the tape on the strain.Finally,the anisotropic approximation of the homogenized bulk method is used to equate large-turn high-field coils,and the electric-magnetic-force distribution characteristics of the coils with/without screening effects and mechanical strain conditions are investigated,respectively.The results reveal that the mechanical strain has a weakening effect on the electromagnetic field distribution of superconducting tapes,but causes a significant enhancement in the force field distribution.In the presence of 0.5% mechanical strain,the maximum weakening of the peak value of the current density and the critical current density inside the high-field coil can reach about 8% and 13%,respectively,with a nearly 5 times increase in the peak stress.The screening current makes the current field distribution inside the coil improve by about 10 times.The screening current induced magnetic field can reach up to 0.8 T,making the relative error of the high-field coil center up to 7.8%.

Degradation of critical current in Bi2212 composite wire under compression load

Since Bi2Sr2Ca1Cu2O8＋x（Bi2212） wires are subject to mechanical loadings, degradation of critical current will occur. The effect of compressive loadings on the critical current of Bi2212 wire is studied by considering micro-buckling of filament. A Bi2212 wire is regarded as a unidirectional filament-reinforced composite in the theoretical analysis. By considering the influence of inclusion, the micro-buckling wavelength can be derived by using a two-dimensional model. Based on the experimental results, the critical current is fitted as a function of buckling wavelength. It is found that the decrease of the critical current is directly proportional to the reciprocal of square of the buckling wavelength. Change of micro-buckling wavelength with material parameters is discussed. A critical strain in the wire with a filament bridge is analyzed using the finite element method.

Numerical simulation of the behaviors of test square for prehistoric earthen sites during archaeological excavation

During the process of archaeological excavation in the regions of Southeast China, collapse of test square usually occurs due to poor site-specific conditions. In this paper, the fast Lagrangian analysis of continua in three dimensions（FLAC3D） is employed to reveal the behaviors of test square. Taking the archaeological works in Liangzhu prehistoric earthen sites as the research background, the paper first introduces the geological setting, excavation procedure and monitoring scheme of the studied test square. Then, the deformation of four sides of the test square is modeled using FLAC3D. By comparison, it shows that the numerical results are consistent with the results from field monitoring. The result suggests that the numerical simulation can be effectively applied to representing the actual behaviors of the test square,which is helpful for determination of excavation scheme and stability evaluation of the test square during archaeological excavation.

Study on Original Ecological Tridimensional Slope Vegetation

No matter from the perspective of slope protection, landscape effect and construction cost, or from the perspective of ecological benefit, the development of original ecological tridimensional vegetation has become the inevitable trend for slope vegetation in pursuit of protecting ecological condition, decreasing soil erosion, maintaining ecological balance and beautifying environment of slope. The concept of original ecological tridimensional slope vegetation is proposed in this paper, and the original ecological tridimensional slope vegetation is studied through theoretical analysis and experiments. Specifically, the mechanical effect of slope vegetation in reinforcing the cohesion and shear strength of soil mass is firstly discussed, and then experiments are performed to study the water interception and containing function of slope under various vegetation conditions. Moreover, the relation between soil moisture and cohesion, the relation between root distribution density and cohesion, and the relation between root distribution density and soil shear strength are also studied based on experiments.Finally, based on field observation, the soil erosion states of slope under various vegetation conditions are comparatively studied. It is found that the original ecological tridimensional slope, which combines grass,shrub and tree, can generate comprehensive slope protection effects, and hence strengthen the slope protection ability and bring multiple slope protection benefits. Thereby, the theoretical foundation for developing original ecological tridimensional slope vegetation is established.

Thermoelastic stress analysis of multilayered films in a micro-thermoelectric cooling device

This paper presents an analytical solution for the thermoelastic stress in a typical in-plane＇s thin-film micro- thermoelectric cooling device under different operating con- ditions. The distributions of the permissible temperature fields in multilayered thin-films are analytically obtained, and the characteristics, including maximum temperature dif- ference and maximum refrigerating output of the thermo- electric device, are discussed for two operating conditions. Analytical expressions of the thermoelastic stresses in the layered thermoelectric thin-films induced by the tempera- ture difference are formulated based on the theory of mul- tilayer system. The results demonstrate that, the geometric dimension is a significant factor which remarkably affects the thermoelastic stresses. The stress distributions in layers of semiconductor thermoelements, insulating and support- ing membrane show distinctly different features. The present work may profitably guide the optimization design of high- efficiency micro-thermoelectric cooling devices.

Specific adhesion of a soft elastic body on a wavy surface

This paper aims at developing a stochastic-elastic model of a soft elastic body adhering on a wavy surface via a patch of molecular bonds. The elastic deformation of the system is modeled by using continuum contact mechanics, while the stochastic behavior of adhesive bonds is modeled by using Bell＇s type of exponential bond association/dissociation rates. It is found that for sufficiently small adhesion patch size or stress concentration index, the adhesion strength is insensitive to the wavelength but decreases with the amplitude of surface undulation, and that for large adhesion patch size or stress concentration index, there exist optimal values of the surface wavelength and amplitude for maximum adhesion strength.

Tunability of Band Gaps in Two-Dimensional Phononic Crystals with Magnetorheological and Electrorheological Composites

The elastic wave propagation properties of phononic crystals(PnCs)composed of an elastic matrix embedded in magnetorheological and electrorheological elastomers are studied in this paper.The tunable band gaps and transmission spectra of these materials are calculated using the finite element method and supercell technology.The variations in the band gap characteristics with changes in the electric/magnetic fields are given.The numerical results show that the electric and magnetic fields can be used in combination to adjust the band gaps effectively.The start and stop frequencies of the band gap are obviously affected by the electric field,and the band gap width is regulated more significantly by the magnetic field.The widest and highest band gap can be obtained by combined application of the electric and magnetic fields.In addition,the band gaps can be moved to the low-frequency region by drilling holes in the PnC,which can also open or close new band gaps.These results indicate the possibility of multi-physical field regulation and design optimization of the elastic wave properties of intelligent PnCs.

THE NONLINEAR MAGNETOELASTIC PROPERTIES OF <110> ORIENTED TB_(0.27)DY_(0.73)FE_(1.95) POLYCRYSTALLINE ALLOYS UNDER COUPLED MAGNETOMECHANICAL LOADING

In the paper, the nonlinear magnetoelastic properties of composition Tb0.27Dy0.73 Fel.95 〈 110 〉 oriented polycrystalline alloys are investigated under coupled loads of high mag- netic field and compressive stress. The magnetization and magnetostriction are measured simul- taneously under applied magnetic field from -800 to 800 kA/m and compressive stress from 0 to 25 MPa at room temperature. The strain coefficient and relative permeability are obtained by differential calculation from the experimental curves. The results show that the values of satura- tion magnetization （M~） under different compressive stresses remain invariably constant in the region of the high magnetic field. The saturation magnetostriction （As） increases with increasing compressive stress and reaches 1680 ~ 10-6 under 25 MPa. According to the increase of the com- pressive stress, the hysteretic loop area of magnetization and magnetostriction increases, while the maximum relative permeability and strain coefficient decrease. Additionally, the influence of the bias magnetic field on the mechanical property is taken into account. The stress-strain relation- ship is nonlinear and sensitive to the applied external magnetic fields along the axis of rod. The results obtained are a useful complement to the existing experiments for theoretical approaches and engineering applications.

Damage Analysis of Superconducting Composite Wire with Bridging Model

The multi-filamentary Bi2Sr2CaCu2O8＋x （Bi-2212） round wires are made of super- conducting filaments, metal Ag and Ag alloy, which are typical composite structure. Since the filament is brittle, there are various defects and cracks in the Bi-2212 round wire after heat treat- ment. In this paper, we assume that the filaments in the wire are uniformly arranged. Adopting the bridging model which is often used in the fiber-reinforced composite, we calculate the ulti- mate strength of the round wire. The effects of the volume fraction, elastic modulus and interface shear strength are discussed in detail.

The effects of interface scattering on thermoelectric properties of film thermoelectric materials

A theoretical model taking into consideration the interface effects is established to predict the Seebeck coefficient and the electrical conductivity for a polycrystalline thermoelectric(TE)thin film.The interface scattering mechanisms(including the film-surface scattering and grain-boundary scattering)of the transport electrons in the film materials are revealed.The relations between the Seebeck coefficient,the electrical conductivity and the interface parameters(the film-surface reflection coefficient and the grain-boundary transmission coefficient)are then discussed with respect to the proposed model.The differences in the TE properties between the films and bulk materials caused by size restriction are investigated.The results indicate that the higher grain number leads to stronger grain-boundary scattering and more distinct size effects of the TE properties.In contrast to the surface effect,the grain-boundary effect plays a main role in the TE properties of TE films with polycrystalline structures.

Tunability of Band Gaps of Programmable Hard-Magnetic Soft Material Phononic Crystals

In this paper,the elastic wave band gap characteristics of two-dimensional hard-magnetic soft material phononic crystals(HmSM-PnCs)under the applied magnetic field are studied.Firstly,the relevant material parameters of hard-magnetic soft materials(HmSMs)are obtained by the experimental measurement.Then the finite element model of the programmable HmSM-PnCs is established to calculate its band structure under the applied magnetic field.The effects of some factors such as magnetic field,structure thickness,structure porosity,and magnetic anisotropy encoding mode on the band gap are given.The results show that the start and stop frequencies and band gap width can be tunable by changing the magnetic field.The magnetic anisotropy encoding mode has a remarkable effect on the number of band gaps and the critical magnetic field of band gaps.In addition,the effect of geometric size on PnC structure is also discussed.With the increase of the structure thickness,the start and stop frequencies of the band gap increase.

Design of a conduction-cooled 4 T superconducting racetrack for a multi-field coupling measurement system

A conduction-cooled superconducting magnet producing a transverse field of 4 T has been designed for a new generation multi-field coupling measurement system, which will be used to study the mechanical behavior of superconducting samples at cryogenic temperatures and intense magnetic fields. A compact cryostat with a two-stage GM cryocooler is designed and manufactured for the superconducting magnet. The magnet is composed of a pair of flat racetrack coils wound by NbTi/Cu superconducting composite wires, a copper and stainless steel combinational former and two Bi2Sr2CaCu20~ superconducting current leads. The two coils are connected in series and can be powered with a single power supply. In order to support the high stress and attain uniform thermal distribution in the superconducting magnet, a detailed finite element （FE） analysis has been performed. The results indicate that in the operating status the designed magnet system can sufficiently bear the electromagnetic forces and has a uniform temperature distribution.

Effective multi-field properties of electro-magneto-thermoelastic composites estimated by finite element method approach

A finite element approach based on the micromechanics was performed to estimate the multi-field properties of electro-magneto-thermoelastic composites. The thermal field and the involved pyroelectric and pyromagnetic effect of the multi-phase composite materials were taken into account in the investigation and implemented in the finite element modeling. The multi- fields related to the electric field, magnetic field, deformation and temperature field, as well as their coupling effects of the smart composites under periodic boundary conditions were obtained numerically. Especially, by means of the homogenization approximation, the effective thermal ex- pansion coefficients, pyroelectric coefficients, pyromagnetic coefficients and other elastic, electric, and magnetic properties for the piezoelectric material, piezomagnetic material and magnetoelec- tric material were calculated, respectively. Some results are compared to the theoretical predictions by the well-known Mori-Tanaka method to show good agreements.

EFFECT OF MAGNETIC NANOPARTICLES ON THE MECHANICAL PROPERTIES OF TYPE-II SUPERCONDUCTORS

In this paper, the effect of magnetic nanoparticles on the mechanical properties of a type-II superconductor is investigated both theoretically and numerically. Magnetic part of the pinning force associated with the interaction between a finite-size spheroidal magnetic inclusion and an Abrikosov vortex is calculated in the London approximation. It is found that the size and shape of magnetic nanoparticles result in different enhancements of vortex pinning in large-k type-II superconductors. Meanwhile, the screening current induced by a magnetic spheroid suffer the action of Lorentz force, which will lead to prestress in the superconductor, so further numerical calculations are needed to explore the interaction between the spheroidal magnetic particle and superconductor. The distribution of displacement, stress and strain in the superconductor are finally obtained. It is shown that different sizes and shapes of nanoparticles also can change the distributions of these quantities.