Stiffness Degradation of Undisturbed Saturated Soft Clay in the Yangtze Estuary Under Complex Stress Conditions

Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on the saturated soft marine clay in the Yangtze Estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases （or degradation degree increases） significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does.Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.

Expression Analysis of Proline Metabolism-related Genes From Halophyte Arabis stelleri under Osmotic Stress Conditions

Arabis stelleri var. japonica evidenced stronger osmotic stress tolerance than Arabidopsis thaliana. Using an A. thaliana microarray chip, we determined changes in the expression of approximately 2 800 genes between A. stelleri plants treated with 0.2 M mannitol versus mock-treated plants. The most significant changes in the gene expression patterns were in genes defining cellular components or in genes associated with the endomembrane system, stimulus response, stress response, chemical stimulus response, and defense response. The expression patterns of three de novo proline biosynthesis enzymes were evaluated in A. stelleri var. japonica seedlings treated with 0.2 M mannitol, 0.2 M sorbitol, and 0.2 M NaCI. The expression of At-pyrroline-5-carboxylate synthetase was not affected by NaCI stress but was similarly induced by mannitol and sorbitol. The proline dehydrogenase gene, which is known to be repressed by dehydration stress and induced by free L-proline, was induced at an early stage by mannitol treatment, but the level of proline dehydrogenase was increased later by treatment with both mannitol and NaCI. The level of free L-proline accumulation increased progressively in response to treatments with mannitol, sorbitol, and NaCI. Mannitol induced L-proline accumulation more rapidly than NaCI or sorbitol. These findings demonstrate that the osmotic tolerance of the novel halophyte, Arabis stelleri, is associated with the accumulation of L-proline.

Thermal characteristics investigation of high voltage grounded gate-LDMOS under ESD stress conditions

The thermal characteristics of high voltage gg-LDMOS under ESD stress conditions are investigated in detail based on the Sentaurus process and device simulators.The total heat and lattice temperature distributions along the Si–SiO2 interface under different stress conditions are presented and the physical mechanisms are discussed in detail.The influence of structure parameters on peak lattice temperature is also discussed,which is useful for designers to optimize the parameters of LDMSO for better ESD performance.

Development and applications of the quasi‐dynamic triaxial apparatus for deep rocks

The mechanical behaviors of deep rocks have always posed a challenge for the implementation and safe operation of major underground engineering projects.To this end,this study modified the existing mainstream rock mechanics instruments equipped with a dynamic disturbance loading system and developed a second‐generation TFD‐2000/D triaxial instrument.The first‐generation device is equipped with an independent disturbance system and an advanced EDC‐580 all‐digital servo controller,which can apply disturbing load independently,implement the function of cyclic disturbance,and combine dynamic and static disturbances.The instrument was found to be reliable for use in analyzing the damage process of rocks in the disturbance test of marbles.The second‐generation instrument tackles three limitations of the first‐generation instrument:(i)it upgrades the strain measurement system and uses extensometers with linear variable differential transformers to accurately measure deformation;(ii)it uses the self‐balanced chamber to replace the Hoek–Franklin triaxial cell and auto‐balancing triaxial pressure chamber;and(iii)the loading rod is independently equipped with an EDC‐580 all‐digital servo controller,which measures precise loads.The experimental findings confirmed that the second‐generation instrument can be used for rock mechanics testing under cyclic disturbance loading,the disturbance–stress relaxation cycle,and the creep–fatigue cycle.In this sense,the second‐generation instrument can be a useful addition to deep rock mechanical instruments and provide a valuable reference.

Effect of CO_(2)on coal P-wave velocity under triaxial stress

As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO_(2)through P-wave velocity during CO_(2)sequestration in coal.However,the effects of CO_(2)on the coal P-wave velocity under triaxial stress are not clearly discerned.In the present study,different boundary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO_(2).Experiments with helium indicated that the pore pressure primarily affected the P-wave velocity by altering the effective stress.Experiments with CH4 and CO_(2)indicated that matrix swelling induced-cleats porosity decline significantly promoted P-wave velocity.Moreover,CO_(2)caused a wider scale and severe weakening of coal matrix than CH4,thereby significantly decreasing the P-wave velocity,and the decline in P-wave velocity increases with vitrinite content.Furthermore,experiments under different boundary conditions showed that with the boundary condition having more constraints,the decrement of pore pressure on P-wave velocity is more weaken,whereas the improvement of matrix swelling on P-wave velocity is more evident.This study contributes to understanding the mechanism of effect of CO_(2)on P-wave velocity under triaxial stress condition and provides guidance for monitoring CO_(2)sequestration in coal.

The stress release model and results from modelling features of some seismic regions in China

The stress release model is a stochastic point process model developed from the theory of elastic rebound. It can be used to analyse, simulate or predict the seismicity in a certain seismic region. This paper first gives a brief representation of the theory of the stress release model and the method of how to use it to analyse earthquake data, then this model is to fit the earthquake data in North China, Southwest China and Taiwan. The results show that the stress release model fits to the data better than the Poisson model. The different features of stress accumulation and release in these regions imply that the seismic activity is essentially different among these regions.

The Plane Stress Crack-Tip Field for an Incompressible Rubber Material

The crack-tip field under plane stress condition for an incompressible rubbermaterial￣[1] is investigated by. the use of the fully nonlinear equilibrium theory. It isfound thai the crack-tip field is composed of two shrink sectors and one expansion se-ctor. At the crack-tip, stress and strain possess the singularity of R￣(-1) and R￣(-1n), respec-tively, (R is the distance to the crack-tip before deformation, n is the material const-ant). When the crack-tip is approached, the thickness of the sheet shrinks to zerowith the order of R￣(1.4n). The results obtained in this paper are consistent with that ob-tained in [8] when s→∞ .

The Effects of Nonuniform Thermal Boundary Condition on Thermal Stress Calculation of Water-Cooled W/Cu Divertors

The thermal boundary condition has very important effects on the accuracy of thermal stress calculation of a water-cooled W/Cu divertor. In this paper, phase-change heat transfer was simulated based on the Euler homogeneous phase model, and local differences of liquid physical properties were considered under one-sided high heating conditions. The steady-state temperature field and thermal stress field under nonuniform thermal boundary conditions were obtained through numerical calculation. By comparison with the case of traditional uniform thermal boundary conditions, the results show that the distribution of thermal stress under nonuniform thermal boundary conditions exhibits tbe same trend as that under uniform thermal boundary conditions, but is larger in value. The maximum difference of maximum von Mises stress is up to 42% under the highest heating conditions. These results provide a valuable reference for the thermal stress caleulat.ion of water-cooled W/Cu divertors.

Rock mass response for lined rock caverns subjected to high internal gas pressure

The storage of hydrogen gas in underground lined rock caverns(LRCs)enables the implementation of the first fossil-free steelmaking process to meet the large demand for crude steel.Predicting the response of rock mass is important to ensure that gas leakage due to rupture of the steel lining does not occur.Analytical and numerical models can be used to estimate the rock mass response to high internal pressure;however,the fitness of these models under different in situ stress conditions and cavern shapes has not been studied.In this paper,the suitability of analytical and numerical models to estimate the maximum cavern wall tangential strain under high internal pressure is studied.The analytical model is derived in detail and finite element(FE)models considering both two-dimensional(2D)and three-dimensional(3D)geometries are presented.These models are verified with field measurements from the LRC in Skallen,southwestern Sweden.The analytical model is inexpensive to implement and gives good results for isotropic in situ stress conditions and large cavern heights.For the case of anisotropic horizontal in situ stresses,as the conditions in Skallen,the 3D FE model is the best approach.

Quantitative analysis with plastic strain indicators to estimate damage induced by fault-slip

In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a failure criterion are developed for biaxial stress conditions, which are implemented into FLAC3D code. A three-dimensional(3D) mine model encompassing a fault running parallel to a steeply dipping orebody is constructed, whereby static and dynamic analyses are performed to extract stopes and simulate fault-slip in dynamic condition, respectively. In the analysis, the developed biaxial model is applied to the stope wall. The fault-slip simulation is performed, considering shearing of fault surface asperities and resultant stress drop driving the fault-slip. Two methodologies to evaluate damage caused by seismic waves arising from the simulated fault-slip are examined:(i) the ratio of dynamic plastic strain increment to elastic strain limit and(ii) plastic strain energy density. For the former one, two types of strain increments are tested, namely effective shear strain increment and volumetric strain increment.The results indicate that volumetric strain increment is a suitable index for detecting damage near the stope wall, while effective shear strain increment is appropriate for evaluating damage in backfill. The evaluation method with plastic strain energy density is found to be capable of assessing damage accumulated in an extensive area caused by rock mass oscillation due to seismic wave propagation. Possible damage to mine developments in the proximity of a stope is clearly described with the index. The comparison of the two methods clarifies that the former one assesses "instantaneous" damage, which is found to be different from "accumulated" damage calculated using plastic strain energy density, in terms of damage area and its location. It is thus concluded that the combination of the two methodologies leads to more accurate damage assessment as a proper measure against rockburst.

Exploring the factors affecting electric bicycle riders'working conditions and crash involvement in Ningbo,China

The rapid development of the delivery industry brings convenience to modern society.However,the high rates of crashes and the survival of electric bicycle(e-bike)riders in the delivery industry raise concerns.The primary objective of this study is to explore the factors affecting delivery e-bike riders’stressful work pressure and crash involvement in China.Data were collected by a questionnaire survey administered in the city of Ningbo,China.A bivariate ordered probit(BOP)model was developed to simultaneously examine the factors associated with both the working conditions of delivery e-bike riders and their involvement in crashes.The marginal effects for the contributory factors were calculated to quantify their impacts on the outcomes.The results showed that the BOP model can account for commonly unobserved characteristics of the working conditions and crash involvement of delivery e-bike riders.The BOP model results showed that the stressful working conditions of delivery e-bike riders were affected by the number of orders and delivery time and rider age and risky riding behaviors.Delivery rider involvement in crashes was affected by the number of orders,strength of the punishment for traffic violations,and familiarity with traffic regulations.It was also found that stressful working conditions and crash involvement were strongly and positively correlated.The findings of this study can enhance our understanding of the factors that affect the working conditions and delivery rider crash involvement.Based on the results,some suggestions regarding public policy,risky riding behaviors,safety promotion,and stronger corporate governance rules were discussed to increase the targeted safety-related interventions for delivery ebike riders in Ningbo,China.

Melatonin: A master regulator of plant development and stress responses

Melatonin is a pleiotropic molecule with multiple functions in plants. Since the discovery of melatonin in plants, numerous studies have provided insight into the biosynthesis, catabolism, and physiological and biochemical functions of this important molecule. Here, we describe the biosynthesis of melatonin from tryptophan, as well as its various degradation pathways in plants. The identification of a putative melatonin receptor in plants has led to the hypothesis that melatonin is a hormone involved in regulating plant growth,aerial organ development, root morphology, and the floral transition. The universal antioxidant activity of melatonin and its role in preserving chlorophyll might explain its anti-senescence capacity in aging leaves. An impressive amount of research has focused on the role of melatonin in modulating postharvest fruit ripening by regulating the expression of ethylene-related genes.Recent evidence also indicated that melatonin functions in the plant's response to biotic stress,cooperating with other phytohormones and wellknown molecules such as reactive oxygen species and nitric oxide. Finally, great progress has been made towards understanding how melatonin alleviates the effects of various abiotic stresses, including salt, drought, extreme temperature, and heavy metal stress. Given its diverse roles, we propose that melatonin is a master regulator in plants.

A reined global-local approach for evaluation of singular stress ield based on scaled boundary inite element method

A reined global-local approach based on the scaled boundary inite element method（SBFEM） is proposed to improve the accuracy of predicted singular stress ield. The proposed approach is carried out in conjunction with two steps. First, the entire structure is analyzed by employing an arbitrary numerical method. Then, the interested region, which contains stress singularity, is re-solved using the SBFEM by placing the scaling center right at the singular stress point with the boundary conditions evaluated from the irst step imposed along the whole boundary including the side-faces. Beneiting from the semi-analytical nature of the SBFEM, the singular stress ield can be predicted accurately without highly reined meshes. It provides the FEM or other numerical methods with a rather simple and convenient way to improve the accuracy of stress analysis. Numerical examples validate the effectiveness of the proposed approach in dealing with various kinds of problems.

ELASTIC CALCULATION OF STRESSES IN RINGS USING AIRY STRESS FUNCTION

Stress calculation formulae for a ring have been obtained by using Airy stress function of the plane strain field with the decomposition of the solutions for normal stresses of Airy biharmonic equation into two parts when it is loaded under two opposite inside forces along a diameter. One part should fulfill a constraint condition about normal stress distribution along the circumference at an energy valley to do the minimum work. Other part is a stress residue constant. In order to verify these formulae and the computed results, the computed contour lines of equi-maximal shear stresses were plotted and quite compared with that of photo-elasticity test results. This constraint condition about normal stress distribution along circumference is confirmed by using Greens’ theorem. An additional compression exists along the circumference of the loaded ring, explaining the divorcement and displacement of singularity points at inner and outer boundaries.

Advance of tolerance engineering on microbes for industrial production

Industrial microbes have become the core of biological manufacturing,which utilized as the cell factory for production of plenty of chemicals,fuels and medicine.However,the challenge that the extreme stress conditions exist in production is unavoidable for cell factory.Consequently,to enhance robustness of the chassis cell lays the foundation for development of bio-manufacturing.Currently,the researches on cell tolerance covered various aspects,involving reshaping regulatory network,cell membrane modification and other stress response.In fact,the strategies employed to improve cell robustness could be summarized into two directions,irrational engineering and rational engineering.In this review,the metabolic engineering technologies on enhancement of microbe tolerance to industrial conditions are summarized.Meanwhile,the novel thoughts emerged with the development of biological instruments and synthetic biology are discussed.

Study on deformation mechanism of Ti-2Al-2.5Zr alloy tube in the flattening test

The flattening test,using one pair paralleled plates to flatten tube structure radially,is generally employed to examine the ductility of tube used in once through steam generator(OTSG).This study focuses on the stress condition and deformation mechanism analysis on the concentrated stress regions of Ti-2 Al-2.5 Zr alloy tube during the flattening test.Firstly,the finite element analysis was performed using the commercial software ABAQUS to determine the stress condition.Secondly,the Electron BackScattered Diffraction(EBSD)was implemented to observe the microstructure evolution of Ti-2 Al-2.5 Zr alloy.Finally,Schmid law was employed to analyze the activated deformation mechanism under condition of the complex stress.It was found that the condition of the complex stress in stress concentration regions,including tension and compression regions,can be simplified into two directional stresses condition.In grains whose c-axis is nearly towards TD and ND,the strain is mainly accommodated by prismatic slip,whereas in grains whose c-axis deviates about 45°from ND to TD mainly by basal slip.The{10-12}extensive twin and corresponding parent grain orientation mainly relied on the stress condition.Additionally,the intergranular twin pairs connected at common grain boundaries(GBs)with high strain compatibility were found at low angle GBs,which were activated under a combination of macro stress and strain compatibility effect.