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In the background of cloud, self-destructing data mainly aims at protecting the data privacy. All the data and its copies will become destructed or unreadable after a user-specified period, without any user intervention. Besides, anyone cannot get the decryption key after timeout, neither the sender nor the receiver. The Washington's Vanish system is a system for selfdestructing data under cloud computing, and it is vulnerable to "hopping attack" and "sniffer attack". We propose a new scheme in this paper, called SafeVanish, to prevent hopping attacks by way of extending the length range of the key shares to increase the attack cost substantially, and do some improvement on the Shamir Secret Sharing algorithm implemented in the Original Vanish system. We present an improved approach against sniffing attacks by using the public key cryptosystem to protectt from sniffing operations. In addition, we evaluate analytically the functionality of the proposed SafeVanish system.

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A transient solid/liquid/vapor unified mathematical model for plasma deposition manufacturing was developed to investigate the fluid flow and heat transfer of the molten pool and deposition layer. The level-set approach was adopted to deal with the liquid/vapor interface boundary conditions, which considered surface tension gradient (the major driving forces for the melt flow), interface curvatures, buoyancy, and convection heat loss. The mixture continuum model was applied to describe melting and solidification processes at the solid/liquid interface. Moreover, the effects of main processing parameters on the thickness of the deposition layer, full depth of the molten pool and penetration depth of the substrate have been studied further. The experiments agree well with the simulation results.

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