The utility of ICS International Chronostratigraphic Charts(ICS Charts)relies on the accuracy and precision of reported geochronologic dates and their relationship to the bases of global chronostratigraphic units.Howe...The utility of ICS International Chronostratigraphic Charts(ICS Charts)relies on the accuracy and precision of reported geochronologic dates and their relationship to the bases of global chronostratigraphic units.However,an examination of some early Paleozoic dates(i.e.,Cambrian-Ordovician boundary and lowest Ordovician)on the ICS Charts shows that they differ from originally reported and late recalculated dates.Thus,they record a numerical precision that differs from these revised dates.The dates assigned to the bases of formal early Paleozoic chronostratigraphic units may be interpreted by the lay reader as precise determinations.展开更多
To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was ...To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention,gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.展开更多
文摘The utility of ICS International Chronostratigraphic Charts(ICS Charts)relies on the accuracy and precision of reported geochronologic dates and their relationship to the bases of global chronostratigraphic units.However,an examination of some early Paleozoic dates(i.e.,Cambrian-Ordovician boundary and lowest Ordovician)on the ICS Charts shows that they differ from originally reported and late recalculated dates.Thus,they record a numerical precision that differs from these revised dates.The dates assigned to the bases of formal early Paleozoic chronostratigraphic units may be interpreted by the lay reader as precise determinations.
基金supported by the National Basic Research Program(No.2016YFB1102704)the Youth Innovation Promotion Association,CAS
文摘To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention,gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.
