The effects of nanosecond visible laser on metallic materials have been studied experimentally. High laser energies (>1013 W/cm2) created a hydrodynamic regime, where the ablation pressure and the ensuing shock wave are the main mechanisms for material expulsion. Plasma shielding caused a constant material removal despite the increase of energy, while the increase of number of pulses resulted in an almost linear increase of the crater volume, despite the lower depths reached with every subsequent pulse. Our results show that there is a correlation between ablation efficiency and material properties, namely ablation efficiency decreases with melting temperature and bulk modulus. 相似文献
We have developed a Transition Edge Sensor (TES) – Energy Dispersive Spectroscopy (EDS) for Transmission Electron Microscope (TEM) based on a dilution refrigerator. The dilution refrigerator was cooled by liquid helium (L-He), which was supplied from an L-He container separated from the dilution refrigerator. We adopted the hybrid magnetic shields combining a permalloy shield and a NbTi/Nb/Cu superconducting shield to operate the TEM–TES system under a magnetic field of 200 mT. The permalloy shield was used to prevent the ambient magnetic field until the NbTi superconducting shield cooled from room temperature (RT) to 2 K. The critical magnetic field was 220 mT for the TES change from a superconducting state to a normal state. The SQUID – current vs. bias current curve, under the condition that the snout was inserted in the TEM, was equal to the curve of the snout that was out of the TEM. The C (0 0 2) planes could be observed at 120 kV under the condition the snout was inserted in the TEM. 相似文献
We have developed a very large magnetic shielding vessel made from high-Tc Bi-Pb-Sr-Ca-Cu-O superconductor and have experimentally confirmed that this vessel can reduce a weak magnetic field to -100 dB or 1/105. The size of this vessel is 32 cm in diameter, 64 cm in depth and 2.5 cm in thickness. The shielding effect of the vessel does not decrease even at a low frequency like 0.2 Hz. The high attenuation ratio in the low frequency range indicates that magnetic shielding using a high-Tc superconductor is promising for neuromagnetic measurements with SQUID. 相似文献
The Stratospheric Shield was proposed as a geoengineering concept to control the Earth's climate and reverse global warming. This approach seeks to release sulphur dioxide (SO2) aerosols in the stratosphere to decrease the amount of sunlight that reaches the surface of the Earth. It was proposed that this can be done by pumping liquefied SO2 from the ground to the stratosphere in a 30 km long hose supported by aerostats.In this paper we evaluate the dynamic stability of a hose to the sky considering distributed supportive aerostats and an atomiser nozzle that forces a radial discharge of the fluid at the free end of the pipe. We modelled the pipe as a taut string conveying fluid using the finite element method.With a nozzle that discharges the flow straight through, we found that the pipe loses stability by buckling when the tension becomes null at least at one location along its length. This instability can be avoided by having a sufficient minimum tension T0 throughout the whole length of the pipe. The distribution of aerostats does not influence this instability but it modifies the mode shapes and affects the complex frequencies. The atomiser discharging the flow radially at the tip of the pipe has for effect to remove the possibility of an instability; its use is thus recommended. Moreover, we showed that the Coriolis damping can be significant and that by appropriately selecting the number of aerostats as well as the dimensionless flow velocity, stability can be increased. With this in mind, a functional hose to the sky could be designed to maximise Coriolis damping and thus passively damp the motion of the pipe due to forcing from the wind. 相似文献