175,017 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
The Contribution of Hot Electron Spin Polarization to the Magnetotransport in a Spin-Valve Transistor at Finite Temperatures
The effect of spin mixing due to thermal spin waves and temperature
dependence of hot electron spin polarization to the collector current in a
spin-valve transistor has been theoretically explored. We calculate the
collector current as well as the temperature dependence of magnetocurrent at
finite temperatures to investigate the relative importance of spin mixing and
hot electron spin polarization. In this study the inelastic scattering events
in ferromagnetic layers have been taken into account to explore our interests.
The theoretical calculations suggest that the temperature dependence of hot
electron spin polarization has substantial contribution to the magnetotransport
in the spin-valve transistor.Comment: 8 pages and 6 figure
Quantum entanglement and Hawking temperature
The thermodynamic entropy of an isolated system is given by its von Neumann
entropy. Over the last few years, there is an intense activity to understand
thermodynamic entropy from the principles of quantum mechanics. More
specifically, is there a relation between the (von Neumann) entropy of
entanglement between a system and some (separate) environment is related to the
thermodynamic entropy? It is difficult to obtain the relation for many body
systems, hence, most of the work in the literature has focused on small number
systems. In this work, we consider black-holes --- that are simple yet
macroscopic systems --- and show that a direct connection could not be made
between the entropy of entanglement and the Hawking temperature. In this work,
within the adiabatic approximation, we explicitly show that the Hawking
temperature is indeed given by the rate of change of the entropy of
entanglement across a black hole's horizon with regard to the system energy.
This is yet another numerical evidence to understand the key features of black
hole thermodynamics from the viewpoint of quantum information theory.Comment: 10 pages, 5 figures (To appear in Eur. Phys. J. C
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
An Algorithm to Generate Classical Solutions for String Effective Action
It is shown explicitly, that a number of solutions for the background field
equations of the string effective action in space-time dimension D can be
generated from any known lower dimensional solution, when background fields
have only time dependence. An application of the result to the two dimensional
charged black hole is presented. The case of background with more general
coordinate dependence is also discussed.Comment: 12 page
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