We deduce the qualitative phase diagram of a long flexible neutral polymer chain immersed in a poor solvent near an attracting surface using phenomenological arguments. The actual positions of the phase boundaries are estimated numerically from series expansion up to 19 sites of a selfattracting self avoiding walk in three dimensions. In two dimensions, we calculate analytically phase boundaries in some cases for a partially directed model. Both the numerical as well as analytical results corroborate the proposed qualitative phase diagram. PACS number(s) : 68.35.Rh,05.50.+q

It is not always possible for a patient to go to a doctor in critical or urgent period. Telecare Medical Information Systems (TMIS) provides a facility by which a patient can communicate to a doctor through a medical server via internet from home. To hide the secret information of both parties (a server and a patient), an authentication mechanism is needed in TMIS. In 2013, Khan and Kumari proposed the authentication schemes for TMIS. In this paper, we have shown that Khan and Kumari's scheme is insecure against off-line password guessing attack. We have also shown that Khan and Kumari's scheme does not provide any security if the password of a patient is compromised. To improve the security and efficiency, a new authentication scheme for TMIS has been proposed in this paper. Further, the proposed scheme can resist all possible attacks and has better performance than the related schemes published earlier.

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The onset of the "eye phase" (a phase consisting of configurations of eye-type conformations or bubbles in the double-stranded DNA) and its role during the DNA unzipping is studied when a force is applied to the interior of the chain. The directionality of the hydrogen bond introduced here shows oscillations in force-extension curve similar to a "sawtooth" kind of oscillations seen in the protein unfolding experiments. The effects of intermediates (hairpins) and stacking energies on the melting profile have also been discussed.

We show the existence of a force induced triple point in an interacting polymer problem that allows two zero-force thermal phase transitions. The phase diagrams for two different models of mutually attracting but self-avoiding polymers are presented. One of these models has an intermediate phase and it shows a triple point. A general phase diagram with multicritical points in an extended parameter space is also discussed.

Single-molecule manipulation techniques reveal that the mechanical resistance of a protein depends on the direction of the applied force. Using a lattice model of polymers, we show that changing the pulling direction leads to different phase diagrams. The simple model proposed here indicates that in one case the system undergoes a transition akin to the unzipping of a beta sheet, while in the other case the transition is of a shearing (slippage) nature. Our results are qualitatively similar to experimental results. This demonstrates the importance of varying the pulling direction since this may yield enhanced insights into the molecular interactions responsible for the stability of biomolecules.

Smart card-based client-server authentication protocol is well popular for secure data exchange over insecure and hostile networks. Recently, Lee et al. put forward an authentication protocol by utilizing ElGamal cryptosystem and proved that it can withstand known security threats. This article evinces that the protocol of Lee et al. is unwilling to protect various important security vulnerabilities such as forgery attack and off-line password-guessing attack. To vanquish these loopholes, this article presents a robust authentication protocol for client-server communication over any insecure networks. The security explanation of our protocol has done through the formal and informal mechanism and its outcome makes sure that the designed protocol is strong enough to resist the known vulnerabilities. In addition, we have simulated our protocol using ProVerif online software and its results certify that our protocol is safe against private information of the client and server. This paper also has made performance estimation of the presented protocol and others, and the outcome favors the presented protocol. KEYWORDS authentication, forgery attack, identity, password, smart card 1 Int J Commun Syst. 2017;30:e3242.wileyonlinelibrary.com/journal/dac

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