4,514 research outputs found
Statistical Mechanics of DNA Rupture: Theory and Simulations
We study the effects of the shear force on the rupture mechanism on a double
stranded DNA. Motivated by recent experiments, we perform the atomistic
simulations with explicit solvent to obtain the distributions of extension in
hydrogen and covalent bonds below the rupture force. We obtain a significant
difference between the atomistic simulations and the existing results in the
iterature based on the coarse-grained models (theory and simulations). We
discuss the possible reasons and improve the coarse-grained model by
incorporating the consequences of semi-microscopic details of the nucleotides
in its description. The distributions obtained by the modified model
(simulations and theoretical) are qualitatively similar to the one obtained
using atomistic simulations.Comment: 18 pages, 9 figures. Accepted in J. Chem. Phys. (2013). arXiv admin
note: text overlap with arXiv:1104.305
Glassy magnetic phase driven by short range charge and magnetic ordering in nanocrystalline LaSrFeO: Magnetization, Mossbauer, and polarised neutron studies
The charge ordered LaSrFeO (LSFO) in bulk and
nanocrystalline forms are investigated using ac and dc magnetization,
M\"{o}ssbauer, and polarised neutron studies. A complex scenario of short range
charge and magnetic ordering is realized from the polarised neutron studies in
nanocrystalline specimen. This short range ordering does not involve any change
in spin state and modification in the charge disproportion between Fe
and Fe compared to bulk counterpart as evident in the M\"{o}ssbauer
results. The refinement of magnetic diffraction peaks provides magnetic moments
of Fe and Fe are about 3.15 and 1.57 for bulk, and
2.7 and 0.53 for nanocrystalline specimen, respectively. The
destabilization of charge ordering leads to magnetic phase separation, giving
rise to the robust exchange bias (EB) effect. Strikingly, EB field at 5 K
attains a value as high as 4.4 kOe for average size 70 nm, which is zero
for the bulk counterpart. A strong frequency dependence of ac susceptibility
reveals cluster-glass like transition around 65 K, below which EB
appears. Overall results propose that finite size effect directs the complex
glassy magnetic behavior driven by unconventional short range charge and
magnetic ordering, and magnetic phase separation appears in nanocrystalline
LSFO.Comment: 10 pages, 9 figures. Fig. 1 available upon request or in
http://www.ffn.ub.es/oscar/Articles.html. Accepted in Phys. Rev.
Normal mode analysis for scalar fields in BTZ black hole background
We analyze the possibility of inequivalent boundary conditions for a scalar
field propagating in the BTZ black hole space-time. We find that for certain
ranges of the black hole parameters, the Klein-Gordon operator admits a
one-parameter family of self-adjoint extensions. For this range, the BTZ
space-time is not quantum mechanically complete. We suggest a physically
motivated method for determining the spectra of the Klein-Gordon operator.Comment: 6 pages, no figure, late
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Efficient biometric and password based mutual authentication for consumer USB mass storage devices
A Universal Serial Bus (USB) Mass Storage Device (MSD), often termed a USB flash drive, is ubiquitously used to store important information in unencrypted binary format. This low cost consumer device is incredibly popular due to its size, large storage capacity and relatively high transfer speed. However, if the device is lost or stolen an unauthorized person can easily retrieve all the information. Therefore, it is advantageous in many applications to provide security protection so that only authorized users can access the stored information. In order to provide security protection for a USB MSD, this paper proposes a session key agreement protocol after secure user authentication. The main aim of this protocol is to establish session key negotiation through which all the information retrieved, stored and transferred to the USB MSD is encrypted. This paper not only contributes an efficient protocol, but also does not suffer from the forgery attack and the password guessing attack as compared to other protocols in the literature. This paper analyses the security of the proposed protocol through a formal analysis which proves that the information is stored confidentially and is protected offering strong resilience to relevant security attacks. The computational cost and communication cost of the proposed scheme is analyzed and compared to related work to show that the proposed scheme has an improved tradeoff for computational cost, communication cost and security
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