25,187 research outputs found
Enhancement of magnetoresistance in manganite multilayers
Magnanite multilayers have been fabricated using La0.67Ca0.33MnO3 as the
ferromagnetic layer and Pr0.7Ca0.3MnO3 and Nd0.5Ca0.5MnO3 as the spacer layers.
All the multilayers were grown on LaAlO3 (100) by pulse laser deposition. An
enhanced magnetoresistnace (defined (RH- R0)/R0) of more than 98% is observed
in these multilayers. Also a low field magnetoresistance of 41% at 5000 Oe is
observed in these multilayer films. The enhanced MR is attributed to the
induced double exchange in the spacer layer, which is giving rise to more
number of conducting carriers. This is compared by replacing the spacer layer
with LaMnO3 where Mn exists only in 3+ state and no enhancement is observed in
the La0.67Ca0.33MnO3 / LaMnO3 multilayers as double exchange mechanism can not
be induced by external magnetic fields.Comment: 13 pages, 5 Figure
The late-time development of the Richtmyer–Meshkov instability
Measurements have been made of the growth by the Richtmyer–Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride (SF6) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF6. A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness delta of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for delta at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, ddelta/dt[proportional]t–p (i.e., delta[proportional]t1–p), where 0.67<~p<~0.74 and that a small dependence on the initial wavelength lambda0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard [Phys. Fluids 6, 3765–3775 (1994)]. The influence of the wire mesh and membrane on the mixing process is assessed
Weakly commensurable arithmetic groups, lengths of closed geodesics and isospectral locally symmetric spaces
We introduce the notion of weak commensurabilty of arithmetic subgroups and
relate it to the length equivalence and isospectrality of locally symmetric
spaces. We prove many strong consequences of weak commensurabilty and derive
from these many interesting results about isolength and isospectral locally
symmetric spaces.Comment: 62 page
Localized Charge Transfer Process and Surface Band Bending in Methane Sensing by GaN Nanowires
The physicochemical processes at the surfaces of semiconductor nanostructures
involved in electrochemical and sensing devices are strongly influenced by the
presence of intrinsic or extrinsic defects. To reveal the surface controlled
sensing mechanism, intentional lattice oxygen defects are created on the
surfaces of GaN nanowires for the elucidation of charge transfer process in
methane (CH4) sensing. Experimental and simulation results of electron energy
loss spectroscopy (EELS) studies on oxygen rich GaN nanowires confirmed the
possible presence of 2(ON) and VGa-3ON defect complexes. A global resistive
response for sensor devices of ensemble nanowires and a localized charge
transfer process in single GaN nanowires are studied in situ scanning by Kelvin
probe microscopy (SKPM). A localized charge transfer process, involving the
VGa-3ON defect complex on nanowire surface is attributed in controlling the
global gas sensing behavior of the oxygen rich ensemble GaN nanowires.Comment: 42 pages, 6 figures, Journa
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