The effect of the distance between the notch tip and the position of the middle phase in the FGSs on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to...The effect of the distance between the notch tip and the position of the middle phase in the FGSs on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to the middle layer, the Charpy impact energy reaches its maximum value. This is due to the increment of the absorbed energy by plastic deformation ahead of the notch tip. On the other hand, when the notch tip is far from the middle layer, the Charpy impact energy strongly decreases. Another fundamental motivation of the present work is that for crack arrester configuration, no accurate mathematical or analytical modelling is available up to now. By considering the relationship between the Charpy impact energy and the plastic volume size, a new theoretical model has been developed to link the Charpy impact energy with the distance from the notch apex to the middle phase. This model is a simplified one and the effect of different shapes of the layers and the effect of microstructureon the mechanical properties and plastic region size will be considered in further investigation. The results of the new developed closed form expression show a sound agreement with some recent experimental results taken from the literature.展开更多
With regard to brain acetylcholinesterase and acetylcholine and serum triiodothyronine(T_3) and thyroxine(T_4)profiles,a biphasic response pattern was elicited in Channa punctatus chroni- cally exposed to nonlethal do...With regard to brain acetylcholinesterase and acetylcholine and serum triiodothyronine(T_3) and thyroxine(T_4)profiles,a biphasic response pattern was elicited in Channa punctatus chroni- cally exposed to nonlethal doses of locally used pesticides,namely,Metacid-50 and Carbaryl. Data revealed that these xenobiotics caused significant inhibition of brain acetylcholinesterase activity and a decrease in thyroxine level accompanied by a concurrent increase in acetylcholine accumulation and T_3 level.It is surmised that Metacid-50 and Carbaryl influence both neural and hormonal functions.1989 Academic Press.Inc.展开更多
The torsional impact response of a penny-shaped crack in a nonhomogeneous strip is considered. The shear modulus is assumed to be functionally graded such that the mathematics is tractable. Laplace and Hankel transfor...The torsional impact response of a penny-shaped crack in a nonhomogeneous strip is considered. The shear modulus is assumed to be functionally graded such that the mathematics is tractable. Laplace and Hankel transforms were used to reduce the problem to solving a Fredholm integral equation. The crack tip stress field is obtained by considering the asymptotic behavior of Bessel function. Explicit expressions of both the dynamic stress intensity factor and the energy density factor were derived.And it is shown that, as crack driving force, they are equivalent for the present crack problem. Investigated are the effects of material nonhomogeneity and (strip's) highness on the dynamic fracture behavior. Numerical results reveal that the peak of the dynamic stress intensity factor can be suppressed by increasing the nonhomogeneity parameter of the shear modulus, and that the dynamic behavior varies little with the adjusting of the strip's highness.展开更多
光影响微生物代谢及其与环境和其他生物的相互作用,进而影响不同环境中微生物分布及多样性。然而,随着城市化进程的加剧,灯光污染问题日益严重,给生物体带来了不利影响。光对于某些微生物的生存是必需的,但是夜间人造光(Artificial Ligh...光影响微生物代谢及其与环境和其他生物的相互作用,进而影响不同环境中微生物分布及多样性。然而,随着城市化进程的加剧,灯光污染问题日益严重,给生物体带来了不利影响。光对于某些微生物的生存是必需的,但是夜间人造光(Artificial Light at Night,ALAN)打破了自然的昼夜节律,将通过多种途径显著干扰微生物的自然行为和生态平衡,进而影响微生物的群落和功能。这种影响可能会对城市生态系统的健康和功能产生深远的后果,最终威胁到人类健康。因此,综述重点关注城市灯光,系统阐述了灯光对城市不同生境下微生物的影响,同时讨论了夜间人造光驱动的生态功能变化及其潜在危害,并探讨了人造光在生态修复中的应用。综述最后提出了夜间人造光对城市微生物影响研究的重点关注方向,为城市灯光规划和环境质量提升提供了科学的理论依据。展开更多
文摘The effect of the distance between the notch tip and the position of the middle phase in the FGSs on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to the middle layer, the Charpy impact energy reaches its maximum value. This is due to the increment of the absorbed energy by plastic deformation ahead of the notch tip. On the other hand, when the notch tip is far from the middle layer, the Charpy impact energy strongly decreases. Another fundamental motivation of the present work is that for crack arrester configuration, no accurate mathematical or analytical modelling is available up to now. By considering the relationship between the Charpy impact energy and the plastic volume size, a new theoretical model has been developed to link the Charpy impact energy with the distance from the notch apex to the middle phase. This model is a simplified one and the effect of different shapes of the layers and the effect of microstructureon the mechanical properties and plastic region size will be considered in further investigation. The results of the new developed closed form expression show a sound agreement with some recent experimental results taken from the literature.
文摘With regard to brain acetylcholinesterase and acetylcholine and serum triiodothyronine(T_3) and thyroxine(T_4)profiles,a biphasic response pattern was elicited in Channa punctatus chroni- cally exposed to nonlethal doses of locally used pesticides,namely,Metacid-50 and Carbaryl. Data revealed that these xenobiotics caused significant inhibition of brain acetylcholinesterase activity and a decrease in thyroxine level accompanied by a concurrent increase in acetylcholine accumulation and T_3 level.It is surmised that Metacid-50 and Carbaryl influence both neural and hormonal functions.1989 Academic Press.Inc.
文摘The torsional impact response of a penny-shaped crack in a nonhomogeneous strip is considered. The shear modulus is assumed to be functionally graded such that the mathematics is tractable. Laplace and Hankel transforms were used to reduce the problem to solving a Fredholm integral equation. The crack tip stress field is obtained by considering the asymptotic behavior of Bessel function. Explicit expressions of both the dynamic stress intensity factor and the energy density factor were derived.And it is shown that, as crack driving force, they are equivalent for the present crack problem. Investigated are the effects of material nonhomogeneity and (strip's) highness on the dynamic fracture behavior. Numerical results reveal that the peak of the dynamic stress intensity factor can be suppressed by increasing the nonhomogeneity parameter of the shear modulus, and that the dynamic behavior varies little with the adjusting of the strip's highness.
文摘光影响微生物代谢及其与环境和其他生物的相互作用,进而影响不同环境中微生物分布及多样性。然而,随着城市化进程的加剧,灯光污染问题日益严重,给生物体带来了不利影响。光对于某些微生物的生存是必需的,但是夜间人造光(Artificial Light at Night,ALAN)打破了自然的昼夜节律,将通过多种途径显著干扰微生物的自然行为和生态平衡,进而影响微生物的群落和功能。这种影响可能会对城市生态系统的健康和功能产生深远的后果,最终威胁到人类健康。因此,综述重点关注城市灯光,系统阐述了灯光对城市不同生境下微生物的影响,同时讨论了夜间人造光驱动的生态功能变化及其潜在危害,并探讨了人造光在生态修复中的应用。综述最后提出了夜间人造光对城市微生物影响研究的重点关注方向,为城市灯光规划和环境质量提升提供了科学的理论依据。
