We investigate the deflection and the fluctuation of stresses due to different sizes of granular material in a cylindrical column. It is experimentally observed that the saturation mass systemically increases with gra...We investigate the deflection and the fluctuation of stresses due to different sizes of granular material in a cylindrical column. It is experimentally observed that the saturation mass systemically increases with granule diameter. The results indicate the shielding of vertical stress in silo is varying. We show that the ratio between the horizontal and the vertical stresses, K, decreases with the increase in grainule diameter d. In addition, it has also been found that the presence of larger granules leads to stronger stress fluctuation on the bottom plate of silo.展开更多
The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL...The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous do- main within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the per- meability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interracial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stress- es between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.展开更多
A large number of pyroshock devices are employed in spacecraft and rockets to realize stage separation and appendage deployment.Release of pyroshock devices induces high-level transient shock responses which tend to c...A large number of pyroshock devices are employed in spacecraft and rockets to realize stage separation and appendage deployment.Release of pyroshock devices induces high-level transient shock responses which tend to cause fatal damages in electronic equipment made of crystals and brittle materials.This paper aims to provide methods to isolate pyroshock and guarantee the safety of such equipment against high-frequency shocks.Firstly,stress wave transmission mechanism in stepped rods is investigated,upon which optimal area rate for shock isolation is achieved.Then,two spacecraft-rocket interface structures for pyroshock isolation,namely isolation hole and interim segment,are proposed.Both numerical simulations and experiments are carried out to validate the two shock isolation strategies.It is revealed that the interim segment structure shows better pyroshock isolation performance at the cost of increasing the weight of launching system whereas isolation hole is an optimal choice to reduce pyroshock response without causing weight increase.展开更多
Objective:To investigate the effects of Heijiangdan Ointment(黑绛丹膏,HJD) on oxidative stress in (60)Co γ-ray radiation-induced dermatitis in mice.Methods:Female Wistar mice with grade 4 radiation dermatitis i...Objective:To investigate the effects of Heijiangdan Ointment(黑绛丹膏,HJD) on oxidative stress in (60)Co γ-ray radiation-induced dermatitis in mice.Methods:Female Wistar mice with grade 4 radiation dermatitis induced by ^(60)Co γ-rays were randomly divided into four groups(n=12 per group);the HJD-treated,recombinant human epidermal growth factor(rhEGF)-treated,Trolox-treated,and untreated groups,along with a negative control group.On the 11 th and 21 st days after treatment,6 mice in each group were chosen for evaluation.The levels of superoxide dismutase(SOD),malondialdehyde(MDA),and lactate dehydrogenase(LDH) were detected using spectrophotometric methods.The fibroblast mitochondria were observed by transmission electron microscopy(TEM).The expressions of fibroblast growth factor 2(FGF-2) and transforming growth factor β1(TGF-β1) were analyzed by western blot.Results:Compared with the untreated group,the levels of SOD,MDA and LDH,on the 11 th and 21 st days after treatment showed significant difference(P〈0.05).TEM analysis indicated that fibroblast mitochondria in the untreated group exhibited swelling and the cristae appeared fractured,while in the HJD group,the swelling of mitochondria was limited and the rough endoplasmic reticulum appeared more relaxed.The expressions of FGF-2 and TGF-β1 increased in the untreated group compared with the negative control group(P〈0.05).After treatment,the expression of FGF-2,rhEGF and Trolox in the HJD group were significantly increased compared with the untreated group(P〈0.05),or compared with the negative control group(P〈0.05).The expression of TGF-β1 showed significant difference between untreated and negative control groups(P〈0.05).HJD and Trolox increased the level of TGF-β1 and the difference was marked as compared with the untreated and negative control groups(P〈0.05).Conclusion:HJD relieves oxidative stress-induced injury,increases the antioxidant activity,mitigates the fibroblast mitochondrial damage,up-regulates the expression of growth factor,and promotes mitochondrial repair in mice.展开更多
Depression is a devastating psychiatric disorder widely attributed to defi cient monoaminergic signaling in the central nervous system. However,most clinical antidepressants enhance monoaminergic neurotransmission wit...Depression is a devastating psychiatric disorder widely attributed to defi cient monoaminergic signaling in the central nervous system. However,most clinical antidepressants enhance monoaminergic neurotransmission with little delay but require 4-8 weeks to reach therapeutic efficacy,a paradox suggesting that the monoaminergic hypothesis of depression is an oversimplifi cation. In contrast to the antidepressants targeting the monoaminergic system,a single dose of the N-methyl-D-aspartate receptor(NMDAR) antagonist ketamine produces rapid(within 2 h) and sustained(over 7 days) antidepressant effi cacy in treatment-resistant patients. Glutamatergic transmission mediated by NMDARs is critical for experience-dependent synaptic plasticity and learning,processes that can be modifi ed indirectly by the monoaminergic system. To better understand the mechanisms of action of the new antidepressants like ketamine,we review and compare the monoaminergic and glutamatergic antidepressants,with emphasis on neural plasticity. The pathogenesis of depression may involve maladaptive neural plasticity in glutamatergic circuits that may serve as a new class of targets to produce rapid antidepressant effects.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10675018 and 10674157)
文摘We investigate the deflection and the fluctuation of stresses due to different sizes of granular material in a cylindrical column. It is experimentally observed that the saturation mass systemically increases with granule diameter. The results indicate the shielding of vertical stress in silo is varying. We show that the ratio between the horizontal and the vertical stresses, K, decreases with the increase in grainule diameter d. In addition, it has also been found that the presence of larger granules leads to stronger stress fluctuation on the bottom plate of silo.
基金supported by the National Basic Research Program of China(Grant No.2012CB934101)the National Natural Science Foundation of China(Grant Nos.51175282 and 51375254)
文摘The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous do- main within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the per- meability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interracial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stress- es between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.
基金supports from National Natural Science Foundation of China(No.11902286 and 11972204)。
文摘A large number of pyroshock devices are employed in spacecraft and rockets to realize stage separation and appendage deployment.Release of pyroshock devices induces high-level transient shock responses which tend to cause fatal damages in electronic equipment made of crystals and brittle materials.This paper aims to provide methods to isolate pyroshock and guarantee the safety of such equipment against high-frequency shocks.Firstly,stress wave transmission mechanism in stepped rods is investigated,upon which optimal area rate for shock isolation is achieved.Then,two spacecraft-rocket interface structures for pyroshock isolation,namely isolation hole and interim segment,are proposed.Both numerical simulations and experiments are carried out to validate the two shock isolation strategies.It is revealed that the interim segment structure shows better pyroshock isolation performance at the cost of increasing the weight of launching system whereas isolation hole is an optimal choice to reduce pyroshock response without causing weight increase.
基金Supported by the National Natural Science Foundation of China(No.30973745)
文摘Objective:To investigate the effects of Heijiangdan Ointment(黑绛丹膏,HJD) on oxidative stress in (60)Co γ-ray radiation-induced dermatitis in mice.Methods:Female Wistar mice with grade 4 radiation dermatitis induced by ^(60)Co γ-rays were randomly divided into four groups(n=12 per group);the HJD-treated,recombinant human epidermal growth factor(rhEGF)-treated,Trolox-treated,and untreated groups,along with a negative control group.On the 11 th and 21 st days after treatment,6 mice in each group were chosen for evaluation.The levels of superoxide dismutase(SOD),malondialdehyde(MDA),and lactate dehydrogenase(LDH) were detected using spectrophotometric methods.The fibroblast mitochondria were observed by transmission electron microscopy(TEM).The expressions of fibroblast growth factor 2(FGF-2) and transforming growth factor β1(TGF-β1) were analyzed by western blot.Results:Compared with the untreated group,the levels of SOD,MDA and LDH,on the 11 th and 21 st days after treatment showed significant difference(P〈0.05).TEM analysis indicated that fibroblast mitochondria in the untreated group exhibited swelling and the cristae appeared fractured,while in the HJD group,the swelling of mitochondria was limited and the rough endoplasmic reticulum appeared more relaxed.The expressions of FGF-2 and TGF-β1 increased in the untreated group compared with the negative control group(P〈0.05).After treatment,the expression of FGF-2,rhEGF and Trolox in the HJD group were significantly increased compared with the untreated group(P〈0.05),or compared with the negative control group(P〈0.05).The expression of TGF-β1 showed significant difference between untreated and negative control groups(P〈0.05).HJD and Trolox increased the level of TGF-β1 and the difference was marked as compared with the untreated and negative control groups(P〈0.05).Conclusion:HJD relieves oxidative stress-induced injury,increases the antioxidant activity,mitigates the fibroblast mitochondrial damage,up-regulates the expression of growth factor,and promotes mitochondrial repair in mice.
基金supported by the 973 Program of the Ministry of Science and Technology of China (2013CB835103)the Strategic Priority Research Program of the Chinese Academy of Science (XDB02020200)the National 863 Project of China (2012AA022402)
文摘Depression is a devastating psychiatric disorder widely attributed to defi cient monoaminergic signaling in the central nervous system. However,most clinical antidepressants enhance monoaminergic neurotransmission with little delay but require 4-8 weeks to reach therapeutic efficacy,a paradox suggesting that the monoaminergic hypothesis of depression is an oversimplifi cation. In contrast to the antidepressants targeting the monoaminergic system,a single dose of the N-methyl-D-aspartate receptor(NMDAR) antagonist ketamine produces rapid(within 2 h) and sustained(over 7 days) antidepressant effi cacy in treatment-resistant patients. Glutamatergic transmission mediated by NMDARs is critical for experience-dependent synaptic plasticity and learning,processes that can be modifi ed indirectly by the monoaminergic system. To better understand the mechanisms of action of the new antidepressants like ketamine,we review and compare the monoaminergic and glutamatergic antidepressants,with emphasis on neural plasticity. The pathogenesis of depression may involve maladaptive neural plasticity in glutamatergic circuits that may serve as a new class of targets to produce rapid antidepressant effects.