The similarities and differences in seepage flow evolution laws of CH4 and CO2 during complete stress- strain process of samples were comparatively analyzed. The results show that the seepage flow evolution laws of CH...The similarities and differences in seepage flow evolution laws of CH4 and CO2 during complete stress- strain process of samples were comparatively analyzed. The results show that the seepage flow evolution laws of CH4 and CO2 are extremely similar during the stress-strain process, showing that the character- istic first decreased and then increased. A mathematical model was also established according to the rela- tionship of seepage velocity and axial strain. However, due to the strong adsorption ability of CO2, the coal samples generated a more serious ''Klinkenberg effect'' under the condition of CO2. Owing to this, the CO2 seepage flow resulted into occurrence of ''stagnation'' phenomenon during the late linear elastic stage II. In the strain consolidation stage III, the increment rate of CH4 seepage velocity was significantly greater than that of CO2. In the stress descent stage IV, when the axial load reached the peak pressure of coal, the increment rates of CH4 seepage velocity presented a turning point. But the changing rate of CO2 seepage velocity still remained slow and a turning point was presented at one time after the peak of thestrain pressure, which showed an obvious feature of hysteresis.展开更多
The mechanical performance of recycled aggregate concrete （RAC） is investigated. An experiment on the complete stress-strain curve under uniaxial compression loading of RAC is carried out. The experimental results i...The mechanical performance of recycled aggregate concrete （RAC） is investigated. An experiment on the complete stress-strain curve under uniaxial compression loading of RAC is carried out. The experimental results indicate that the peak stress, peak strain, secant modulus of the peak point and original point increase with the strength grade of RAC enhanced. On the contrary, the residual stress of RAC decreases with the strength grade enhancing, and the failure of RAC is often broken at the interface between the recycled aggregate and the mortar matrix. Finally, the constitutive model of stress-strain model of RAC has been constituted, and the results from the constitutive model of stress-strain meet the experiment results very well.展开更多
Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stres...Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.展开更多
A micromechanics-based model is established. The model takes the interaction among sliding cracks into account, and it is able to quantify the effect of various parameters on the localization condition of damage and d...A micromechanics-based model is established. The model takes the interaction among sliding cracks into account, and it is able to quantify the effect of various parameters on the localization condition of damage and deformation for brittle rock subjected to compressive loads. The closed-form explicit expression for the complete stress-strain relation of rock containing microcracks subjected to compressive loads was obtained. It is showed that the complete stress-strain relation includes linear elasticity,nonlinear hardening,rapid stress drop and strain softening.The behavior of rapid stress drop and strain softening is due to localization of deformation and damage. Theoretical predictions have shown to be consistent with the experimental results.展开更多
The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irr...The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irreversible changes of their microscopic structures due to microcrack growth. The complete stress-strain relation including linear elasticity, nonlinear hardening,rapid stress drop and strain softening was obtained. The influence of all microcracks with different sizes and orientations were introduced into the constitutive relation by using the probability density function describing the distribution of orientations and the probability density function describing the distribution of sizes. The influence of Weibull distribution describing the distribution of orientations and Rayleigh function describing the distribution of sizes on the constitutive relation were researched. Theoretical predictions have shown to be consistent with the experimental results.展开更多
Mycoplasma ovipneumoniae, a kind of mycoplasma bacteria, commonly infects the respiratory tract causing respiratory disease in sheep and goats worldwide. Here, the complete genome sequence of M. ovipneumoniae strain N...Mycoplasma ovipneumoniae, a kind of mycoplasma bacteria, commonly infects the respiratory tract causing respiratory disease in sheep and goats worldwide. Here, the complete genome sequence of M. ovipneumoniae strain NM2010 isolated from a sheep in China was reported for the ifrst time.展开更多
The aim of this research is to clarify whether the midline axis of the complete upper denture (CUD) is the axis of its torsion during loading, apart from the known bending deflection. Furthermore the present study is ...The aim of this research is to clarify whether the midline axis of the complete upper denture (CUD) is the axis of its torsion during loading, apart from the known bending deflection. Furthermore the present study is intended to estimate the influence of the anterior notches on the torsional deformation of the CUD. Using commercial edentulous molds and standardized procedures, six identical CUDs were fabricated with an initial fraenal notch of 5 mm. Two additional notch conditions were produced by deepening the notch to a total depth of 9 mm and by creating an incisal diastema of 7 mm. Five biaxial (also known as “fish bone”) strain gauges were cemented onto the palatal section of the dentures so that their middle axis coincided with the midline axis of the outer surface of the denture. For the denture specimen used in this study, the specific point of torsion was detected 2 cm from the point of contact of the two artificial central incisors. The presence of a deep fraenal notch and the combination of the deep fraenal notch with the presence of an incisal diastema increased the torsion of the CUD to a significant level (P = 0.006 and P = 0.05, respectively). It was shown that the midline can be the CUD’s axis of torsion. Biaxial strain gauges could be a reliable method of measuring the torsional deformation of the CUD.展开更多
The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding, the applicability of complete plastic model assumption and the shear stress formula were researc...The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding, the applicability of complete plastic model assumption and the shear stress formula were researched. Based on the shear stress formula of circular shaft under pure torsion in elastic stage, the formula of torque in elastic stage and the definition of yield, it is obtained that the yielding stage of plastic metal shaft under pure torsion is only a surface phenomenon of torque-torsion angle relationship, and the distribution of shear stress is essentially different from that of tensile stress when yielding under uniaxial tension. The pure torsion platform-torsion angle and the shape of torque-torsion angle curve cannot change the distribution of shear stress on the shaft cross-section. The distribution of shear stress is still linear with the maximum shear stress ts. The complete plasticity model assumption is not in accordance with the actual situation of shaft under torsion. The experimental strength data of nine plastic metals are consistent with the calculated results of the new limiting strain energy strength theory （LSEST）. The traditional yield stress formula for plastic shaft under torsion is reasonable. The shear stress formula based on the plane assumption in material mechanics is applicable for all loaded stages of torsion shaft.展开更多
Aerobic anoxygenic phototrophic bacteria(AAPB)are photoheterotrophic prokaryotes able to use both light and dissolved organic matter as energy sources.Roseicitreum antarcticum ZS2-28^(T)was isolated from intertidal se...Aerobic anoxygenic phototrophic bacteria(AAPB)are photoheterotrophic prokaryotes able to use both light and dissolved organic matter as energy sources.Roseicitreum antarcticum ZS2-28^(T)was isolated from intertidal sediment in the Larsemann Hills,Princess Elizabeth Land,Antarctica,and was able to produce bacteriochlorophyll a.It is the type strain of the sole species within the genus Roseicitreum.The complete genome sequence of the bacterium was determined using Illumina HiSeq X and PacBio RSII systems.The genome of R.antarcticum ZS2-28^(T)was 4253095 bp and consisted of one chromosome and four plasmids.A number of genes related to the bacteriochlorophyll a production,photosynthetic reaction,cold adaptation,salt adaptation,ultra-violet resistance and DNA damage repairing were found in the genome.In addition to genomic islands and typeⅣsecretion systems,genes related to gene transfer agents were detected in the genome of R.antarcticum ZS2-28^(T),suggesting that this bacterium can adapt to its environment by acquiring exogenous nucleic acids.The annotated complete genome sequence provides genetic insights into the environmental adaptation and ecological function of R.antarcticum ZS2-28^(T)in Antarctic coastal area.展开更多
Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for stressstrain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tens...Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for stressstrain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tension, direct shear and uniaxial compression were presented, respectively. The three derived stressstrain curves were generalized as a unified formula. Beyond the onset of strain localization, a linear strain-softening constitutive relation for localized band was assigned. The size of the band was controlled by internal or characteristic length according to gradient-dependent plasticity. Elastic strain within the entire specimen was assumed to be uniform and decreased with the increase of plastic strain in localized band. Total strain of the specimen was decomposed into elastic and plastic parts. Plastic strain of the specimen was the average value of plastic strains in localized band over the entire specimen. For different heights, the predicted softening branches of the relative stressstrain curves in uniaxial compression are consistent with the previously experimental results for normal concrete specimens. The present expressions for the post-peak stressdeformation curves in uniaxial tension and direct shear agree with the previously numerical results based on gradient-dependent plasticity.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 51074197 and 50674111)the Natural Science Foundation of CQ CSTC (No. 2010BB6118)the Fundamental Research Funds for the Central Universities (No. CDJXS11241181)
文摘The similarities and differences in seepage flow evolution laws of CH4 and CO2 during complete stress- strain process of samples were comparatively analyzed. The results show that the seepage flow evolution laws of CH4 and CO2 are extremely similar during the stress-strain process, showing that the character- istic first decreased and then increased. A mathematical model was also established according to the rela- tionship of seepage velocity and axial strain. However, due to the strong adsorption ability of CO2, the coal samples generated a more serious ''Klinkenberg effect'' under the condition of CO2. Owing to this, the CO2 seepage flow resulted into occurrence of ''stagnation'' phenomenon during the late linear elastic stage II. In the strain consolidation stage III, the increment rate of CH4 seepage velocity was significantly greater than that of CO2. In the stress descent stage IV, when the axial load reached the peak pressure of coal, the increment rates of CH4 seepage velocity presented a turning point. But the changing rate of CO2 seepage velocity still remained slow and a turning point was presented at one time after the peak of thestrain pressure, which showed an obvious feature of hysteresis.
基金Supported by the Fund of Hunan Provincial Construction Department(No.06-468-8)
文摘The mechanical performance of recycled aggregate concrete （RAC） is investigated. An experiment on the complete stress-strain curve under uniaxial compression loading of RAC is carried out. The experimental results indicate that the peak stress, peak strain, secant modulus of the peak point and original point increase with the strength grade of RAC enhanced. On the contrary, the residual stress of RAC decreases with the strength grade enhancing, and the failure of RAC is often broken at the interface between the recycled aggregate and the mortar matrix. Finally, the constitutive model of stress-strain model of RAC has been constituted, and the results from the constitutive model of stress-strain meet the experiment results very well.
基金Project(50774090) supported by the National Natural Science Foundation of China
文摘Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.
文摘A micromechanics-based model is established. The model takes the interaction among sliding cracks into account, and it is able to quantify the effect of various parameters on the localization condition of damage and deformation for brittle rock subjected to compressive loads. The closed-form explicit expression for the complete stress-strain relation of rock containing microcracks subjected to compressive loads was obtained. It is showed that the complete stress-strain relation includes linear elasticity,nonlinear hardening,rapid stress drop and strain softening.The behavior of rapid stress drop and strain softening is due to localization of deformation and damage. Theoretical predictions have shown to be consistent with the experimental results.
文摘The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irreversible changes of their microscopic structures due to microcrack growth. The complete stress-strain relation including linear elasticity, nonlinear hardening,rapid stress drop and strain softening was obtained. The influence of all microcracks with different sizes and orientations were introduced into the constitutive relation by using the probability density function describing the distribution of orientations and the probability density function describing the distribution of sizes. The influence of Weibull distribution describing the distribution of orientations and Rayleigh function describing the distribution of sizes on the constitutive relation were researched. Theoretical predictions have shown to be consistent with the experimental results.
基金supported by the Nationai Key Technology R&D Program of China (2011BAD18B01)
文摘Mycoplasma ovipneumoniae, a kind of mycoplasma bacteria, commonly infects the respiratory tract causing respiratory disease in sheep and goats worldwide. Here, the complete genome sequence of M. ovipneumoniae strain NM2010 isolated from a sheep in China was reported for the ifrst time.
文摘The aim of this research is to clarify whether the midline axis of the complete upper denture (CUD) is the axis of its torsion during loading, apart from the known bending deflection. Furthermore the present study is intended to estimate the influence of the anterior notches on the torsional deformation of the CUD. Using commercial edentulous molds and standardized procedures, six identical CUDs were fabricated with an initial fraenal notch of 5 mm. Two additional notch conditions were produced by deepening the notch to a total depth of 9 mm and by creating an incisal diastema of 7 mm. Five biaxial (also known as “fish bone”) strain gauges were cemented onto the palatal section of the dentures so that their middle axis coincided with the midline axis of the outer surface of the denture. For the denture specimen used in this study, the specific point of torsion was detected 2 cm from the point of contact of the two artificial central incisors. The presence of a deep fraenal notch and the combination of the deep fraenal notch with the presence of an incisal diastema increased the torsion of the CUD to a significant level (P = 0.006 and P = 0.05, respectively). It was shown that the midline can be the CUD’s axis of torsion. Biaxial strain gauges could be a reliable method of measuring the torsional deformation of the CUD.
文摘The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding, the applicability of complete plastic model assumption and the shear stress formula were researched. Based on the shear stress formula of circular shaft under pure torsion in elastic stage, the formula of torque in elastic stage and the definition of yield, it is obtained that the yielding stage of plastic metal shaft under pure torsion is only a surface phenomenon of torque-torsion angle relationship, and the distribution of shear stress is essentially different from that of tensile stress when yielding under uniaxial tension. The pure torsion platform-torsion angle and the shape of torque-torsion angle curve cannot change the distribution of shear stress on the shaft cross-section. The distribution of shear stress is still linear with the maximum shear stress ts. The complete plasticity model assumption is not in accordance with the actual situation of shaft under torsion. The experimental strength data of nine plastic metals are consistent with the calculated results of the new limiting strain energy strength theory （LSEST）. The traditional yield stress formula for plastic shaft under torsion is reasonable. The shear stress formula based on the plane assumption in material mechanics is applicable for all loaded stages of torsion shaft.
基金the National Key R&D Program of China(Grant no.2018YFC1406903)the National Natural Science Foundation of China(Grant nos.91851201 and 41476171).
文摘Aerobic anoxygenic phototrophic bacteria(AAPB)are photoheterotrophic prokaryotes able to use both light and dissolved organic matter as energy sources.Roseicitreum antarcticum ZS2-28^(T)was isolated from intertidal sediment in the Larsemann Hills,Princess Elizabeth Land,Antarctica,and was able to produce bacteriochlorophyll a.It is the type strain of the sole species within the genus Roseicitreum.The complete genome sequence of the bacterium was determined using Illumina HiSeq X and PacBio RSII systems.The genome of R.antarcticum ZS2-28^(T)was 4253095 bp and consisted of one chromosome and four plasmids.A number of genes related to the bacteriochlorophyll a production,photosynthetic reaction,cold adaptation,salt adaptation,ultra-violet resistance and DNA damage repairing were found in the genome.In addition to genomic islands and typeⅣsecretion systems,genes related to gene transfer agents were detected in the genome of R.antarcticum ZS2-28^(T),suggesting that this bacterium can adapt to its environment by acquiring exogenous nucleic acids.The annotated complete genome sequence provides genetic insights into the environmental adaptation and ecological function of R.antarcticum ZS2-28^(T)in Antarctic coastal area.
文摘Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for stressstrain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tension, direct shear and uniaxial compression were presented, respectively. The three derived stressstrain curves were generalized as a unified formula. Beyond the onset of strain localization, a linear strain-softening constitutive relation for localized band was assigned. The size of the band was controlled by internal or characteristic length according to gradient-dependent plasticity. Elastic strain within the entire specimen was assumed to be uniform and decreased with the increase of plastic strain in localized band. Total strain of the specimen was decomposed into elastic and plastic parts. Plastic strain of the specimen was the average value of plastic strains in localized band over the entire specimen. For different heights, the predicted softening branches of the relative stressstrain curves in uniaxial compression are consistent with the previously experimental results for normal concrete specimens. The present expressions for the post-peak stressdeformation curves in uniaxial tension and direct shear agree with the previously numerical results based on gradient-dependent plasticity.
