6,866 research outputs found
Exchange bias effect and intragranular magnetoresistance in Nd$_{0.84}Sr_{0.16}CoO_3
Electrical transport properties as a function of magnetic field and time have
been investigated in polycrystalline, Nd_{0.84}Sr_{0.16}CoO_3. A strong
exchange bias (EB) effect is observed associated with the fairly large
intragranular magnetoresistance (MR). The EB effect observed in the MR curve is
compared with the EB effect manifested in magnetic hysteresis loop. Training
effect, described as the decrease of EB effect when the sample is successively
field-cycled at a particular temperature, has been observed in the shift of the
MR curve. Training effect could be analysed by the successful models. The EB
effect, MR and a considerable time dependence in MR are attributed to the
intrinsic nanostructure giving rise to the varieties of magnetic interfaces in
the grain interior
Cationic DMPC/DMTAP Lipid Bilayers: Molecular Dynamics Study
Cationic lipid membranes are known to form compact complexes with DNA and to
be effective as gene delivery agents both in vitro and in vivo. Here we employ
molecular dynamics simulations for a detailed atomistic study of lipid bilayers
consisting of a mixture of cationic dimyristoyltrimethylammonium propane
(DMTAP) and zwitterionic dimyristoylphosphatidylcholine (DMPC). Our main
objective is to examine how the composition of the bilayers affects their
structural and electrostatic properties in the liquid-crystalline phase. By
varying the mole fraction of DMTAP, we have found that the area per lipid has a
pronounced non-monotonic dependence on the DMTAP concentration, with a minimum
around the point of equimolar mixture. We show that this behavior has an
electrostatic origin and is driven by the interplay between positively charged
TAP headgroups and the zwitterionic PC heads. This interplay leads to
considerable re-orientation of PC headgroups for an increasing DMTAP
concentration, and gives rise to major changes in the electrostatic properties
of the lipid bilayer, including a significant increase of total dipole
potential across the bilayer and prominent changes in the ordering of water in
the vicinity of the membrane. Moreover, chloride counter-ions are bound mostly
to PC nitrogens implying stronger screening of PC heads by Cl ions compared to
TAP head groups. The implications of these findings are briefly discussed
Shortcuts to Thermodynamic Computing: The Cost of Fast and Faithful Erasure
Landauer's Principle states that the energy cost of information processing
must exceed the product of the temperature and the change in Shannon entropy of
the information-bearing degrees of freedom. However, this lower bound is
achievable only for quasistatic, near-equilibrium computations -- that is, only
over infinite time. In practice, information processing takes place in finite
time, resulting in dissipation and potentially unreliable logical outcomes. For
overdamped Langevin dynamics, we show that counterdiabatic potentials can be
crafted to guide systems rapidly and accurately along desired computational
paths, providing shortcuts that allows for the precise design of finite-time
computations. Such shortcuts require additional work, beyond Landauer's bound,
that is irretrievably dissipated into the environment. We show that this
dissipated work is proportional to the computation rate as well as the square
of the information-storing system's length scale. As a paradigmatic example, we
design shortcuts to erase a bit of information metastably stored in a
double-well potential. Though dissipated work generally increases with erasure
fidelity, we show that it is possible perform perfect erasure in finite time
with finite work. We also show that the robustness of information storage
affects the energetic cost of erasure---specifically, the dissipated work
scales as the information lifetime of the bistable system. Our analysis exposes
a rich and nuanced relationship between work, speed, size of the
information-bearing degrees of freedom, storage robustness, and the difference
between initial and final informational statistics.Comment: 19 pages, 7 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/scte.ht
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