Perfect elastic-viscoplastic field at mode I dynamic propagating crack-tip

The viscosity of material is considered at propagating crack-tip. Under the assumption that the artificial viscosity coefficient is in inverse proportion to power law of the plastic strain rate, an elastic-viscoplastic asymptotic analysis is carried out for moving crack-tip fields in power-hardening materials under plane-strain condition. A continuous solution is obtained containing no discontinuities. The variations of numerical solution are discussed for mode Ⅰ crack according to each parameter. It is shown that stress and strain both possess exponential singularity. The elasticity, plasticity and viscosity of material at crack-tip only can be matched reasonably under linear-hardening condition. And the tip field contains no elastic unloading zone for mode I crack. It approaches the limiting case, crack-tip is under ultra-viscose situation and energy accumulates, crack-tip begins to propagate under different compression situations.

The asymptotic field of mode Ⅰ quasi-static crack growth on the interface between a rigid and a pressure-sensitive material

A mechanical model of the quasi-static interface of a mode I crack between a rigid and a pressure-sensitive viscoelastic material was established to investigate the mechanical characteristic of ship-building engineering hi-materials. In the stable growth stage, stress and strain have the same singularity, ie （σ, ε） ∝ r^-1/（n-1）. The variable-separable asymptotic solutions of stress and strain at the crack tip were obtained by adopting Airy＇s stress function and the numerical results of stress and strain in the crack-tip field were obtained by the shooting method. The results showed that the near-tip fields are mainly governed by the power-hardening exponent n and the Poisson ratio v of the pressure-sensitive material. The fracture criterion of mode I quasi-static crack growth in pressure-sensitive materials, according to the asymptotic analyses of the crack-tip field, can be viewed from the perspective of strain.

Quantum entanglement in the system of two two-level atoms interacting with a single-mode vacuum field

The entanglement properties of the system of two two-level atoms interacting with a single-mode vacuum field are explored. The quantum entanglement between two two-level atoms and a single-mode vacuum field is investigated by using the quantum reduced entropy; the quantum entanglement between two two-level atoms, and that between a single two-level atom and a single-mode vacuum field are studied in terms of the quantum relative entropy. The influences of the atomic dipole-dipole interaction on the quantum entanglement of the system are also discussed. Our results show that three entangled states of two atoms-field, atom-atom, and atom-field can be prepared via two two-level atoms interacting with a single-mode vacuum field.

N_2O Emission from Paddy Field under Different Rice Planting Modes

Measurements of N2O emissions from conventional rice cultivation （CRC）, CRC with straw mulching, system of rice intensification （SRI） and SRI with plastic film mulching were conducted through static chamber/gas-chromatography techniques. The results show that daily fluctuation of N2O emissions in jointing stage are much higher than in others. A type peak of N2O seasonal emission presented between jointing and bearing stages companying with high daily average temperature and low precipitation. Biomass and leaf stomatal conductance were observed. Total quantities of N2O emission were budgeted. The results showed that after jointing stage the average N2O emission flux of SRI with plastic film mulching increased significantly than CRC with straw mulching and SRI, the leaf stomatal conductance of those showed the same trend （p〈 0.05）. Yield and total quantity of N20 emission in CRC with straw mulching enhanced 13. 7% and 10.7% compared with those of CRC, respectively. The total quantity of N20 emissions reduced 3. 6% in SRI with plastic film mulching compared with CRC, however, the yield increase of that was not significant.

ANTIPLANE SHEAR FIELDS NEAR A CRACK-TIP IN A BRITTLE DAMAGED MATERIAL

In this paper,a simplified brittle damage model is proposed according to the Mazars-Lemaitre damage model for concrete.A closed-form solution for a mode Ⅲ crack is obtained based on the simplified model under small scale damage conditions,which allows for discontinuities of displacement-gradient and tangential stress on the damage boundary.It is pointed out that the discontinuities of field variables near the tip region exist for the brittle damaged material induced by the softening effect of the material.

Forward modeling for “earth-ionosphere” mode electromagnetic field

A fixed artificial source(greater than 200 kW) was used and the source location was selected at a high resistivity region to ensure high emission efficiency. Some publications used the "earth-ionosphere" mode in modeling the electromagnetic(EM) fields with the offset up to a thousand kilometer, and such EM fields still have a signal/noise ratio of 10-20 dB. This means that a new EM method with fixed source is feasible, but in their calculation, the displacement in air was neglected. In this work, some three-layer modeling results were presented to illustrate the basic EM fields' characteristics in the near, far and waveguide areas under "earth-ionosphere" mode, and a standard is given to distinguish the boundary of near, far and waveguide areas. Due to the influence of the ionosphere and displacement current in the air, the "earth-ionosphere" mode EM fields have an extra waveguide zone, where the fields' behavior is very different from that of the far field zone.

Nitrogen and Phosphorus Loss Law and Emission Reduction Effects Under Water and Fertilizer Management Integrated Mode in Dike Paddy Field

To achieve the purpose of reducing farm non-point source pollution, we integrated site specific nitrogen management precise irrigation, controlled drainage, and wetland eco-repair system in dike area of Taihu basin. During investigation, it had given prominence for the water and fertilizer coupling effects of precise irrigation and site specific nutrient management, the characteristics of integration on controlled irrigation, controlled drainage and wetland ecosystem non-point source pollution control. Then the water and fertilizer integrated management mode of paddy field was put forward in Taihu basin where the water production efficiency increased to 1.64 kg. m-3, water saved 37.8%, fertilizer use efficiency raised 15,4%, yield raised 10%, and N, P load decreased 26%-72%. The modern agricultural and farmland ecosystems that control and cut down the farm non-point source pollution came into being, which can be a reference by Taihu basin to control its agricultural non-point source pollution and eutrophicated water body.

EXACT SOLUTIONS OF NEAR CRACK LINE FIELDS FOR MODE I CRACK UNDER PLANE STRESS CONDITION IN AN ELASTIC－PERFECTLY PLASTIC SOLID

The near crack line analysis method has been used in the present paper,The classical small scale yielding conditions have been completely abandoned in the analyses and one inappropriate matching condition used to be used at the elasticplastic boundary has been corrected.The reasonable solution of the plastic stresses near the crack line region has been established.By matching the plastic stresses with the exact elastic stresses at the elastic-plastic boundary,the plastic stresses the length of the plastic zone and the unit normal vector of the elastic-plastic boundary near the crock line region have been obtained for a mode I crack under uniaxial tension,as well as a mode I crack under biaxial tension,which shows that for both conditions the plastic stress componentsσy, and σsy.he length of the plastic zone and the unit normal vector of the elastic-plastic boundary are quite the same while the plastic stress σs is different.

Dynamic mode decomposition of the geomagnetic field over the last two decades

Earth’s magnetic field,which is generated in the liquid outer core through the dynamo action,undergoes changes on timescales of a few years to several million years,yet the underlying mechanisms responsible for the field variations remain to be elucidated.In this study,we apply a novel data analysis technique developed in fluid dynamics,namely the dynamic mode decomposition,to analyze the geomagnetic variations over the last two decades when continuous satellite observations are available.The dominant dynamic modes are extracted by solving an eigen-value problem,so one can identify modes with periods longer than the time span of data.Our analysis show that similar dynamic modes are extracted from the geomagnetic secular variation and secular acceleration,justifying the validity of applying the dynamic mode decomposition method to geomagnetic field.We reveal that the geomagnetic field variations are characterized by a global mode with period of 58 years,a localized mode with period of 16 years and an equatorially trapped mode with period of 8.5 years.These modes are possibly related to magnetohydrodynamic waves in the Earth’s outer core.

Preparation and control of entangled states in the two-mode coherent fields interacting with a moving atom via two-photon process

We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter p on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.

Preparation and control of atomic optimal entropy squeezing states for a moving two-level atom under control of the two-mode squeezing vacuum fields

From the viewpoint of quantum information, this paper studies preparation and control of atomic optimal entropy squeezing states （AOESS） for a moving two-level atom under control of the two-mode squeezing vacuum fields. Necessary conditions of preparation of the AOESS are analysed, and numerical verification of the AOESS is finished. It shows that the AOESS can be prepared by controlling the time of the atom interaction with the field, cutting the entanglement between the atom and field, and adjusting squeezing factor of the field. An atomic optimal entropy squeezing sudden generation in different components can alternately be realized by controlling the field-mode structure parameter.

Quantum entanglement between the two-mode fields and atomic entropy squeezing in the system of a moving atom interacting with two-mode entangled coherent field

This paper investigates the entropy squeezing of a moving two-level atom interacting with the two-mode entangled coherent field via two-photon transition by using an entropic uncertainty relation and the degree of entanglement between the two-mode fields by using quantum relative entropy.The results obtained from numerical calculation indicate that the squeezed period,the duration of entropy squeezing and the maximal squeezing can be controlled by appropriately choosing the intensity of the light field,the atomic motion and the field-mode structure.The atomic motion leads to the periodic recovery of the initial maximal degree of entanglement between the two-mode fields.Moreover,there exists a corresponding relation between the time evolution properties of the atomic entropy squeezing and those of the entanglement between the two-mode fields.

Properties study of LiNbO_3 lateral field excited device working on thickness extension mode

This paper investigates the properties of thickness extension mode excited by lateral electric field on LiNbO3 by using the extended Christoffel-Bechmann method. It finds that the lateral field excitation coupling factor for amode （quasi-extensional mode） reaches its maximum value of 28% on Xmcut LiNbO3. The characteristics of a lateral field excitation device made of X-cut LiNbO3 have been investigated and the lateral field excitation device is used for the design of a high frequency ultrasonic transducer. The time and frequency domain pulse/echo response of the LiNbO3 lateral field excitation ultrasonic transducer is analysed with the modified Krimholtz-Leedom-Matthae model and tested using traditional pulse/echo method. A LiNbO3 lateral field excitation ultrasonic transducer with the centre frequency of 33.44 MHz and the -6 dB bandwidth of 33.8% is acquired, which is in good agreement with the results of the Krimholtz-Leedom-Matthae model. Further analysis suggests that the LiNbO3 lateral field excitation device has great potential in the design of broadband high frequency ultrasonic transducers.

HYDROSTATIC STRESS-DEPENDENT PERFECTLY-PLASTIC STRESS FIELDS AT A STATIONARY PLANE-STRESS CRACK-TIP

Under the condition that all the stress components at a crack-tip are the functions ofθonly,making use of equilibrium equations and hydrostatic stress-dependent yield condition,in this paper,we derive the generally analytical expressions of the hydrostatic stress-dependent perfectly-plastic stress fields at a stationary plane-stress crack-tip.Applying these generally analytical expressions to the concrete cracks,the analytical expressions of hydrostatic stress-dependent perfectly-plastic stress fields at the tips of mode I and mode II cracks are obtained.

SUPPLEMENTARY STUDY ON ANISOTROPIC PLASTIC STRESS FIELDS AT A STATIONARY PLANE-STRESS CRACK-TIP

Under the hypothesis that all the perfectly plastic stress components at a orach tip are the functions of θ only, making use of yield conditions and equilibrium equations. we derive the generally analytical expressions of the perfectly plastic stress field at a crack tip. Applying these generally analytical expressions to the concrete cracks, the analytical expressions of perfectly plastic stress fields at the tips of Mode Ⅰ Mode Ⅱ, Mode Ⅲ and Mixed Mode Ⅰ-Ⅱ cracks are obtained.

ANISOTROPIC PLASTIC FIELDS AT A RAPIDLY PROPAGATING PLANE-STRESS CRACK-TIP

Under the condition that all the stress components at a crack-tip are the functions of 0 only, making use of the equations of steady-state motion. Hill anisotropic yield condition and stress-strain relations, we obtain the general solution of anisotropic plastic field at a rapidly propagating plane-stress crack-tip. Applying this general solution to four particular cases of anisotropy, the general solutions of these four particular cases are derived. Finally, we give the anisotropic plastic field at the rapidly propagating plane-stress mode I crack-tip in the case of X=Y=Z

THE ASYMPTOTIC SOLUTION TO THE ANTIPLANE SHEAR DYNAMICCRACK-TIP FIELD IN AN ELASTIC STRAIN-SOFTENING VISCOPLASTIC MATERIAL

The elastic strain softening-viscoplastic model is given in this paper. Using this model, the asymptotic stress and strain equations surrounding the tip of a propagating crock are given and numerical results ale obtained under antiplane shear. The analysis and calculation show that at the crack tip the strain possesses logarithmic singularity (ln(R/r))(1/(n+1)) while the stress is like (ln(R/r))(-n/(n+1)), therefore the asymptotic behaviour of the elastic strain-softening viscoplastic field is revealed under the antiplane shear.

POWER LAW NONLINEAR VISCOELASTIC CRACK-TIP FIELDS

The aim of this paper is to derive the power law type nonlinear viscoelastic crack-tip fields.For the requirement of later derivation,the HRR singular fields and the high-order asymp- totic fields are first examined.That they are essentially the isotropic,incompressible,power law type nonlinear elastic crack-tip fields is illustrated.After a concise review of the elasticity recov- ery correspondence principle for solving the nonlinear viscoelastic problems,the correspondence principle for solving the crack problems of power law type nonlinear viscoelastic materials under the first type boundary condition is proposed.The solution of the crack-tip stress,strain fields for the power law type nonlinear viscoelastic materials,especially for the modified polypropylene, is obtained.

ANISOTROPIC PLASTIC FIELDS AT A RAPIDLY PROPAGATING CRACK-TIP

Under the condition that all the stress components at a crack-tip are the functions of only, making use of the equations of steady-slate motion, stress-strain relations and Hill anisotropic yield conditions, we obtain the general solutions at a crack-tip in both the cases of anti-plane and in-plane strains. Applying these general solutions to the concrete cracks, the anisotropic plastic fields at the rapidly propagating tips of mode III and mode I cracks are derived.

Optical anapole modes in hybrid metal–dielectric nanoantenna for near-field enhancement and optical sensing

Metal–dielectric nanostructures in the optical anapole modes are essential for light–matter interactions due to the low material loss and high near-field enhancement. Herein, a hybrid metal–dielectric nanoantenna composed of six wedgeshaped gold(Au) nanoblocks as well as silica(SiO2) and silicon(Si) nanodiscs is designed and analyzed by the finite element method(FEM). The nanoantenna exhibits flexibility in excitation and manipulation of the anapole mode through the strong coupling between the metal and dielectrics, consequently improving the near-field enhancement at the gap. By systematically optimizing the structural parameters, the electric field enhancement factors at wavelengths corresponding to the anapole modes(AM1 and AM2) can be increased to 518 and 1482, respectively. Moreover, the nanoantenna delivers great performance in optical sensing such as a sensitivity of 550 nm/RIU. The results provide guidance and insights into enhancing the coupling between metals and dielectrics for applications such as surface-enhanced Raman scattering and optical sensing.