Effects of High Intensity Ultrasound on BSCCO-2212 Superconductor

Slurries of powdered Bi2Sr2CaCu2O8+x superconductor in low volatility alkanes were treated with intense ultrasound. Significant enhancements of magnetic irreversibility as well as transport critical current are reported. The effects are dependent on the concentration of the slurry and are optimal for 1.5% wt. slurry loading. Electron microscopy shows that ultrasonic treatment leads to a change in grain morphology and intergrain welding. The observed enhancement of superconducting properties is consistent with the limitations in critical currents in BSCCO superconductor being due to intergrain coupling rather than intragrain pinning strength.Comment: 3 page

Cryptanalysis and improvement of password-authenticated key agreement for session initiation protocol using smart cards

Session Initiation Protocol (SIP) is one of the most commonly used protocols for handling sessions for Voice over Internet Protocol (VoIP)-based communications, and the security of SIP is becoming increasingly important. Recently, Zhang et al. proposed a password authenticated key agreement protocol for SIP by using smart cards to protect the VoIP communications between users. Their protocol provided some unique features, such as mutual authentication, no password table needed, and password updating freely. In this study, we performed cryptanalysis of Zhang et al.'s protocol and found that their protocol was vulnerable to the impersonation attack although the protocol could withstand several other attacks. A malicious attacker could compute other users’ privacy keys and then impersonated the users to cheat the SIP server. Furthermore, we proposed an improved password authentication key agreement protocol for SIP, which overcame the weakness of Zhang et al.’s protocol and was more suitable for VoIP communications

Efficient and flexible password authenticated key agreement for Voice over Internet Protocol session initiation protocol using smart card

Providing a suitable key agreement protocol for session initiation protocol is crucial to protecting the communication among the users over the open channel. This paper presents an efficient and flexible password authenticated key agreement protocol for session initiation protocol associated with Voice over Internet Protocol. The proposed protocol has many unique properties, such as session key agreement, mutual authentication, password updating function and the server not needing to maintain a password or verification table, and so on. In addition, our protocol is secure against the replay attack, the impersonation attack, the stolen-verifier attack, the man-in-the-middle attack, the Denning–Sacco attack, and the offline dictionary attack with or without the smart card

Robust and efficient password authenticated key agreement with user anonymity for session initiation protocol-based communications

A suitable key agreement protocol plays an essential role in protecting the communications over open channels among users using Voice over Internet Protocol (VoIP). This paper presents a robust and flexible password authenticated key agreement protocol with user anonymity for Session Initiation Protocol (SIP) used by VoIP communications. Security analysis demonstrates that our protocol enjoys many unique properties, such as user anonymity, no password table, session key agreement, mutual authentication, password updating freely and conveniently revoking lost smartcards etc. Furthermore, our protocol can resist the replay attack, the impersonation attack, the stolen-verifier attack, the man-in-middle attack, the Denning-Sacco attack, and the offline dictionary attack with or without smartcards. Finally, performance analysis shows that our protocol is more suitable for practical application in comparison with other related protocols