Data-driven modeling on anisotropic mechanical behavior of brain tissue with internal pressure

Brain tissue is one of the softest parts of the human body,composed of white matter and grey matter.The mechanical behavior of the brain tissue plays an essential role in regulating brain morphology and brain function.Besides,traumatic brain injury(TBI)and various brain diseases are also greatly influenced by the brain's mechanical properties.Whether white matter or grey matter,brain tissue contains multiscale structures composed of neurons,glial cells,fibers,blood vessels,etc.,each with different mechanical properties.As such,brain tissue exhibits complex mechanical behavior,usually with strong nonlinearity,heterogeneity,and directional dependence.Building a constitutive law for multiscale brain tissue using traditional function-based approaches can be very challenging.Instead,this paper proposes a data-driven approach to establish the desired mechanical model of brain tissue.We focus on blood vessels with internal pressure embedded in a white or grey matter matrix material to demonstrate our approach.The matrix is described by an isotropic or anisotropic nonlinear elastic model.A representative unit cell(RUC)with blood vessels is built,which is used to generate the stress-strain data under different internal blood pressure and various proportional displacement loading paths.The generated stress-strain data is then used to train a mechanical law using artificial neural networks to predict the macroscopic mechanical response of brain tissue under different internal pressures.Finally,the trained material model is implemented into finite element software to predict the mechanical behavior of a whole brain under intracranial pressure and distributed body forces.Compared with a direct numerical simulation that employs a reference material model,our proposed approach greatly reduces the computational cost and improves modeling efficiency.The predictions made by our trained model demonstrate sufficient accuracy.Specifically,we find that the level of internal blood pressure can greatly influence stress distribution and determine the possible related damage behaviors.

The Concept of Human Rights in the Constitution and Its Functional Significance

To practice the constitutional provision that “The state respects and protects human rights”, we should clarify its connotation. The understanding of human rights is a natural requirement and the key. In domestic academia, human rights are considered natural rights and interpreted as “moral rights that everyone should enjoy as a human being”, hoping to provide theoretical support for the development of the system centered on the basic rights of citizens in China.Although it reveals the universal moral connotation of human rights, it does not cover the normative connotation of human rights as common international standards. Therefore, it is impossible to fully clarify the functional significance of the provision. It is conducive to scientifically clarifying the relationship between human rights and basic civil rights,better improving the institutional protection of human rights in China,and promoting the building of a community with a shared future for mankind to interpret human rights as common international standards that everyone should enjoy for human dignity based on the development of the international legal order under the Charter of the United Nations since the end of the World War Ⅱ.

Statement by Minister Peng Peiyun at the International Conference on Population and Development

The stabilization of the world population and the achievement of sustained development depend not only on the endeavours of governments of nations,but also on further strengthening and promotion of international cooperation,The developed countries should make eforts to improve the international economic environment,increase funds for population and development programmes and transfer technology at preferable conditions.

On the yield functions in Lagrangian stress space of elastic-plastic materials with internal constraints

In the present paper it is shown that the elastic range in the second Piola-Kirchhoff stress space can be chosen in a hyperplane which is through the origin of Lagrangian stress space and perpendicular to the normal of the constraint manifold at the plastic configuration, if the determinate stress response of the elastic-plastic material with simple internal constraints with some condition is correctly chosen, otherwise, it is in general in a hypersurface and the normal flow rule by Ⅱ yushin＇s postulate will have an indeterminate part. The choice of deterrninate stress response is probable because of its indeterminacy. Therefore the yield function should be a function of the second Piola-Kirchhoff stress lying in the hyperplane so that it is more simple and the back stress as the geometric center of the elastic range in general is inside the elastic range. Finally some examples are concerned.

Ordered Rate Constitutive Theories for Non-Classical Thermoviscoelastic Fluids with Internal Rotation Rates

The paper presents constitutive theories for non-classical thermoviscoelastic fluids with dissipation and memory using a thermodynamic framework based on entirety of velocity gradient tensor. Thus, the conservation and the balance laws used in this work incorporate symmetric as well as antisymmetric part of the velocity gradient tensor. The constitutive theories derived here hold in coand contra-variant bases as well as in Jaumann rates and are derived using convected time derivatives of Green’s and Almansi strain tensors as well as the Cauchy stress tensor and its convected time derivatives in appropriate bases. The constitutive theories are presented in the absence as well as in the presence of the balance of moment of moments as balance law. It is shown that the dissipation mechanism and the fading memory in such fluids are due to stress rates as well as moment rates and their conjugates. The material coefficients are derived for the general forms of the constitutive theories based on integrity. Simplified linear (or quasi-linear) forms of the constitutive theories are also presented. Maxwell, Oldroyd-B and Giesekus constitutive models for non-classical thermoviscoelastic fluids are derived and are compared with those derived based on classical continuum mechanics. Both, compressible and incompressible thermoviscoelastic fluids are considered.

GENERAL CONSTITUTIVE EQUATIONS OF AN ER SUSPENSION BASED ON THE INTERNAL VARIABLE THEORY

A microstructural constitutive theory of ER suspensions was formulated in this investigation. The framework was based on the internal variable theory and the mechanism analysis. The ER suspension consists of fine particles with high dielectric constant and the supporting fluid. Under the action of the electric field, the polarized particles will aggregate together to form the chain-like structures along the direction of the electric field. As the size and orientation of the particle aggregates are volatile, and they adjust according to the applied electric field and strain rate, the energy conservation equation and the force equilibrium equation were thus established to determine the orientation and size of the aggregates. Following that, a three-dimensional, explicit form of the constitutive equation was derived based on the interaction energy and the dissipation function of the system. The response of the system under the action of a simple shearing load was considered and discussed in detail. It is found that the shear-thinning viscosity of an ER suspension is wed approximated by the power-law proportional to (Mn)(-D.82).

Rate Constitutive Theories of Orders n and 1n for Internal Polar Non-Classical Thermofluids without Memory

In recent papers, Surana et al. presented internal polar non-classical Continuum theory in which velocity gradient tensor in its entirety was incorporated in the conservation and balance laws. Thus, this theory incorporated symmetric part of the velocity gradient tensor (as done in classical theories) as well as skew symmetric part representing varying internal rotation rates between material points which when resisted by deforming continua result in dissipation (and/or storage) of mechanical work. This physics referred as internal polar physics is neglected in classical continuum theories but can be quite significant for some materials. In another recent paper Surana et al. presented ordered rate constitutive theories for internal polar non-classical fluent continua without memory derived using deviatoric Cauchy stress tensor and conjugate strain rate tensors of up to orders n and Cauchy moment tensor and its conjugate symmetric part of the first convected derivative of the rotation gradient tensor. In this constitutive theory higher order convected derivatives of the symmetric part of the rotation gradient tensor are assumed not to contribute to dissipation. Secondly, the skew symmetric part of the velocity gradient tensor is used as rotation rates to determine rate of rotation gradient tensor. This is an approximation to true convected time derivatives of the rotation gradient tensor. The resulting constitutive theory: (1) is incomplete as it neglects the second and higher order convected time derivatives of the symmetric part of the rotation gradient tensor;(2) first convected derivative of the symmetric part of the rotation gradient tensor as used by Surana et al. is only approximate;(3) has inconsistent treatment of dissipation due to Cauchy moment tensor when compared with the dissipation mechanism due to deviatoric part of symmetric Cauchy stress tensor in which convected time derivatives of up to order n are considered in the theory. The purpose of this paper is to present ordered rate constitutive theories for deviatoric Cauchy strain tensor, moment tensor and heat vector for thermofluids without memory in which convected time derivatives of strain tensors up to order n are conjugate with the Cauchy stress tensor and the convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n are conjugate with the moment tensor. Conservation and balance laws are used to determine the choice of dependent variables in the constitutive theories: Helmholtz free energy density Φ, entropy density η, Cauchy stress tensor, moment tensor and heat vector. Stress tensor is decomposed into symmetric and skew symmetric parts and the symmetric part of the stress tensor and the moment tensor are further decomposed into equilibrium and deviatoric tensors. It is established through conjugate pairs in entropy inequality that the constitutive theories only need to be derived for symmetric stress tensor, moment tensor and heat vector. Density in the current configuration, convected time derivatives of the strain tensor up to order n, convected time derivatives of the symmetric part of the rotation gradient tensor up to orders 1n, temperature gradient tensor and temperature are considered as argument tensors of all dependent variables in the constitutive theories based on entropy inequality and principle of equipresence. The constitutive theories are derived in contravariant and covariant bases as well as using Jaumann rates. The nth and 1nth order rate constitutive theories for internal polar non-classical thermofluids without memory are specialized for n = 1 and 1n = 1 to demonstrate fundamental differences in the constitutive theories presented here and those used presently for classical thermofluids without memory and those published by Surana et al. for internal polar non-classical incompressible thermofluids.

Randomized control study in the influence of different training methods of Tai Chi on Chinese medicine constitution of international students with depression or depression tendency

Objective： To evaluate the effect of different training methods of Tai Chi on Chinese medicine constitution of international students with depression or depression tendency. Methods： Thirty-eight Africa international students were randomly divided into the physical exercise group who receiving the simple physical exercise of simplified 24-form Tai Chi （physical exercise group） and the breathing group who receiving both deep breathing method plus simple physical exercise （breathing group）. The average scores of Chinese medicine gentleness and various biased constitutional types in the two groups were compared. Results： The average score of thirty-eight students with biased constitution in both groups decreased significantly compared with that before training （P 〈 0.05）. Compared with that before training, the average scores of biased constitutional types in the breathing group, including Qi deficiency, Yang deficiency, phlegm-dampness and Qi stagnation, were significantly decreased （P 〈 0.05）. The average scores of Yang deficiency, blood stasis and Qi stagnation constitutional types of students in simple physical group after training were also significantly decreased after training （P 〈 0.05）. Moreover, the average scores of biased constitutional types, including Qi deficiency, Yang deficiency, Yin deficiency, phlegm and dampness, Qi-stagnation, in the breathing group were significantly lower than those of the simple exercise group, suggesting the superior therapeutic effect of breathing training method （P 〈 0.01）. Conclusion： When combines with the deep breathing method, Tai Chi training achieves better effect on improving the biased constitutional types which may be related to depression or depression tendency, including Qi deficiency, Yang deficiency, Yin deficiency, phlegm and dampness, Qi-stagnation.

Constitution of the Chinese Association for International Understanding

正(Approved by the Third Plenary Sessionof the Tenth Executive Council on May 11, 2012)Chapter I General Rules Article 1 The Chinese Association for International Understanding is a national non-governmental organization(NGO) in the People’s Republic of China.

Improvement on the Modeling of Rate-Dependent Plasticity and Cyclic Hardening by Bodner-Partom Model

An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening behaviors of metals. The extended model （new B-P） contains two isotropic internal variables： one plays the role of representing the fast hardening in smaller inelastic strain range, while the other evolutes at slower speed accompanied by larger accumulated inelastic deformation, such as cyclic hardening. To examine the validity of the extended constitutive model, the rate-dependent plasticity of a Ni-base superalloy Udimet 720Li at 650℃ and 700℃ are characterized using both models. Not only numerical simulations are conducted for various loading conditions by implementing both models into ABAOUS using a user material subroutine, also a systematic comparison between two models is completed. Numerical results show that the extended material constants in the new model provide more flexible capability in modeling the inelastic behavior of the material with sound accuracy.

Factors affecting the geographical distribution of invasive species in China

Frequent international trade has accelerated alien species invasion. However, data on the distribution of invasive species after their introduction and research on the factors that determine their geographical distribution are lacking. This study analyzed the distributional trends of invasive species in China and the drivers for such trends, by identifying the effect of international trade from a dynamic analysis of 13 main invasive insect pests in three time periods - before China’s reform and opening up in 1978, from 1979 to 2001, and after China’s accession to the World Trade Organization in 2001. The results showed that the abundance of invasive species gradually decreased from south to north and from southeast coast to inland. Guangdong(442 species) and Yunnan(404 species) provinces have the highest abundance of invasive species. Among the 13 key invasive insects investigated, 3, 10 and 13 occurred chronologically in the three periods, and invaded 7, 28 and 34 provinces, respectively. Alien pests are found to invade China through Xinjiang, the Bohai Rim and the southeast. Value of imports was a strong predictor of the number of invasive species in China, and followed by temperature heterogeneity, in explaining the richness pattern of invasive animal, plants and insects, but not that of microorganisms. This study provides a scientific basis for furthering international quarantine and effective invasive species control.

A MICROMECHANICS CONSTITUTIVE THEORY FOR FORWARD TRANSFORMATION PLASTICITY WITH SHEAR AND DILATATION EFFECT:I,NONPROPORTIONAL LOADING HISTORY

A micromechanics constitutive theory which takes into account both the dilatation and shear ef- fects of the transformation is proposed to describe the macroscopic plastic behavior of structure ceramics during forward transformation under different temperatures.Under some basic assumptions,the analytic expressions of the Helmholtz and complementary free energy of the constitutive element are derived in a self-consistent manner by using the Mori-Tanaka's method which takes into account the interaction between the transformed inclusions.In the framework of Hill-Rice's internal variable constitutive theory,the forward transformation yield function and incremental stress strain relations,in analogy to the theory of metal plasticity,for non-proportional loading histories are obtained.

THE BIOLOGICAL AND CLINICAL RELEVANCE OF THE GASTRIC ECL CELLS

The acid-producing (oxyntic) part of thestomach harbors mucus cells, parietal cells,chief cells, and endocrine cells, such as theECL cells, A-like (X) cells and somatostatin(D) cells. The ECL cells constitute one of thelargest endocrine cell populations in thebody. The ECL cell can be defined as

Bedding plane-embedded augmented virtual internal bonds for fracture propagation simulation in shale

To effectively simulate the fracture propagation in shale,the bedding plane(BP)effect is incorporated into the augmented virtual internal bond(AVIB)constitutive relation through BP tensor.Comparing the BP-embedded AVIB with the theory of transverse isotropy,it is found the approach can represent the anisotropic properties induced by parallel BPs.Through the simulation example,it is found that this method can simulate the stiffness anisotropy of shale and can represent the effect of BPs on hydraulic fracture propagation direction.Compared with the BP-embedded virtual internal bond(VIB),this method can account for the various Poisson’s ratio.It provides a feasible approach to simulate the fracture propagation in shale.

The Constitutional Analysis of Human Rights Legislative Protection

The paths for applying the international human rights conventions in China should be recognized as follows: On the premise of respecting the Constitution of China, systematic human rights which could coordinate the relationship between the Constitution of China and international human rights conventions. The source of the human rights legislation obligations of the legislative organs of China is the Constitution of China, not the international human rights conventions. The legislature should understand and grasp the main contents of the human rights legislation obligations of the legislature according to Paragraph 3 of Article 33 of the Constitution while the interpretation of this clause must be based on the relevant provisions of the international human rights conventions. Human rights legislative obligations of the legislature can be classified into two types: legislative protecting obligations and legislative relief obligations of human rights. The NPC and its Standing Committee should be structurally responsible for the human rights legislation obligation, and the State Council and other organs of the State not for the legislation protection of human rights. A special human rights law should be enacted by the NPC.

A Comprehensive Review of Experience with the Application of the Mechanical Threshold Stress Model

Accurate prediction of stress-strain behavior of metals as a function of arbitrary temperature and strain rate paths has remained a challenge. The Mechanical Threshold Stress constitutive model is one formalism that has emerged following several decades of research. Vast experience has accumulated with the application of the Mechanical Threshold Stress model over a wide variety of pure metals and alloys. Out of this has arisen common trends across metal systems. The magnitude of activation energies presents one example of this, where these variables consistently increase in magnitude as the obstacle to dislocation motion transitions from short range to long range. Trends in strain hardening are also observed. In Face-Centered Cubic metals the magnitude of strain hardening scales with the stacking fault energy;trends in Body-Centered Cubic metals are less clear. Model parameters derived for over twenty metals and alloys are tabulated. Common trends should guide future application of the MTS model and further model development.