172,154 research outputs found
Giant Tunneling Magnetoresistance, Glassiness, and the Energy Landscape at Nanoscale Cluster Coexistence
We present microscopic results on the giant tunneling magnetoresistance that
arises from the nanoscale coexistence of ferromagnetic metallic (FMM) and
antiferromagnetic insulating (AFI) clusters in a disordered two dimensional
electron system with competing double exchange and superexchange interactions.
Our Monte Carlo study allows us to map out the different field regimes in
magnetotransport and correlate it with the evolution of spatial structures. At
coexistence, the isotropic O(3) model shows signs of slow relaxation, and has a
high density of low energy metastable states, but no genuine glassiness.
However, in the presence of weak magnetic anisotropy, and below a field
dependent irreversibility temperature , the response on field cooling
(FC) differs distinctly from that on zero field cooling (ZFC). We map out the
phase diagram of this `phase coexistence glass', highlight how its response
differs from that of a standard spin glass, and compare our results with data
on the manganites.Comment: Final published versio
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Wear of SLS Materials under Plastic and Elastic Contact Conditions
Sliding wear behaviour of two SLS materials: LaserForm and DirectSteel has been
investigated using Fretting tests, Pin-on-disc tests and microfretting tests. Wear
test conditions were determined by calculating Hertzian pressure for various loading
conditions, and wear tests were performed under both plastic and elastic contact
conditions. Wear analysis was subsequently done to find out the wear resistance
of materials. The wear volumes are presented against applied loads and dissipated
energies. It has been found out that LaserForm is better than DirectSteel and there
is no clear relation between hardness and wear resistance of materials.Mechanical Engineerin
Can re-entrance be observed in force induced transitions?
A large conformational change in the reaction co-ordinate and the role of the
solvent in the formation of base-pairing are combined to settle a long standing
issue {\it i.e.} prediction of re-entrance in the force induced transition of
DNA. A direct way to observe the re-entrance, i.e a strand goes to the closed
state from the open state and again to the open state with temperature, appears
difficult to be achieved in the laboratory. An experimental protocol (in direct
way) in the constant force ensemble is being proposed for the first time that
will enable the observation of the re-entrance behavior in the
force-temperature plane. Our exact results for small oligonucleotide that forms
a hairpin structure provide the evidence that re-entrance can be observed.Comment: 12 pages and 5 figures (RevTex4). Accepted in Europhys Lett. (2009
Spinning flavour branes and fermion pairing instabilities
We consider probe Dp-branes, p=3,5,7, in global AdS_5 x S^5, rotating along
an internal direction in the S^5. These are dual to strongly interacting N=4
SYM on S^3 with massless fundamental flavours, in the presence of an R-symmetry
chemical potential for flavour fermions. For massless, "AdS-filling" Dp-brane
embeddings at zero temperature, we find an infinite set of threshold values of
the chemical potential at which instabilities are triggered. The onset of
instability is always preceded by metastability of the zero density state. From
the onset values of the chemical potential, we infer that unstable directions
favour a homogeneous condensate of a bilinear made from fermion harmonics, or
Cooper pairing. We confirm this picture both numerically and analytically. The
linearized analysis showing the appearance of instabilities involves a charged
scalar in global AdS space coupled to a (large) constant background gauge
potential. The resulting frequency space correlator of the fermion bilinear at
strong coupling displays poles in the upper half plane. In contrast, the
correlator at zero coupling exhibits Pauli blocking due to occupation of states
below the Fermi level, but no instabilities. The end-point of the strong
coupling instability is not visible in our setup.Comment: 44 pages, 10 figures, uses late
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