We report a simple and highly sensitive solution concentration and refractive index (RI) sensor based on a microfiber knot resonator (MKR). The sensor was assembled using a flexible poly(trimethylene terephthalate) microfiber of 1.3 µm diameter. The resonance peak shifts due to the variation of the concentration of the ambient medium surrounding the MKR were detected. In the mass concentration range of 0.6–1.2%, the concentration sensitivity and resolution of the sensor are 1.7 nm/% and 1.2 × 10−3%, respectively. The highest measured sensitivity of the sensor is about 95.5 nm/RIU (RI unit) and the RI detection limit is about 2.1 × 10−5 in the RI range from 1.39 to 1.41.
The authors first review the recently proposed Das's biometric-based remote user authentication scheme, and then show that Das's scheme is still insecure against some attacks and has some problems in password change phase. In order to overcome the design flaws in Das's scheme, an improvement of the scheme is further proposed. Cryptanalysis shows that our scheme is more efficient and secure against most of attacks; moreover, our scheme can provide strong mutual authentication by using verifying biometric, password as well as random nonces generated by the user and server.
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