17,889 research outputs found
Initial stages of cavitation damage and erosion on copper and brass tested in a rotating disk device
In view of the differences in flow and experimental conditions, there has been a continuing debate as to whether or not the ultrasonic method of producing cavitation damage is similar to the damage occurring in cavitating flow systems, namely, venturi and rotating disk devices. In this paper, the progress of cavitation damage during incubation periods on polycrystalline copper and brass tested in a rotating disk device is presented. The results indicate several similarities and differences in the damage mechanism encountered in a rotating disk device (which simulates field rotary devices) and a magnetostriction apparatus. The macroscopic erosion appears similar to that in the vibratory device except for nonuniform erosion and apparent plastic flow during the initial damage phase
Influence of Mo6+ on Dielectric properties of Copper Ferrites
Two series of copper ferrites are prepared using the chemical compositional formula Cu1.0-3y Fe2.0-2x Mox + yO4.0. They are calcinated at 750 C and sintered at 950C.When x =y = 0.0, the ε′ of the basic copper ferrite is probably due to electronic exchange interactions of copper and iron ions as Cu2+↔ Cu1+ and Fe3+↔ Fe2+. The observed value of dielectric constant (є′) decreases as a function of substituent concentration (x) up to x = 0.20 and for further values of ‘x’ it found to increase. In the case of ‘C’ (x = 0) series ferrites є′ decreases with substituent concentration (y) up to y = 0.04, later it found to increase. The dispersion of ac resistivity with frequency is observed indicating their strong dependence on frequency as in the case of dielectric behaviour. These results are explained with different possible mechanisms
Electronic phase separation in the rare earth manganates, (La1-xLnx)0.7Ca0.3MnO3 (Ln = Nd, Gd and Y)
All the three series of manganates showsaturation magnetization
characteristic of ferromagnetism, with the ferromagnetic Tc decreasing with
increasing in x up to a critical value of x, xc (xc = 0.6, 0.3, 0.2
respectively for Nd, Gd, Y). For x > xc, the magnetic moments are considerably
smaller showing a small increase around TM, the value of TM decreasing slightly
with increase in x or decrease in . The ferromagnetic compositions (x xc)
show insulator-metal (IM) transitions, while the compositions with x > xc are
insulating. The magnetic and electrical resistivity behavior of these
manganates is consistent with the occurrence of phase separation in the
compositions around xc, corresponding to a critical average radius of the
A-site cation, , of 1.18 A. Both Tc and TIM increase linearly when < rA
> > or x xc as expected of a homogenous ferromagnetic phase. Both Tc
and TM decrease linearly with the A-site cation size disorder at the A-site as
measured by the variance s2. Thus, an increase in s2 favors the insulating AFM
state. Percolative conduction is observed in the compositions with > <
rAc >. Electron transport properties in the insulating regime for x > xc
conforms to the variable range hopping mechanism. More interestingly, when x >
xc, the real part of dielectric constant (e') reaches a high value (104-106) at
ordinary temperatures dropping to a very small (~500) value below a certain
temperature, the value of which decreases with decreasing frequency.Comment: 27 pages; 11 figures, Submitted to J.Phys:Condens Matte
Understanding of the phase transformation from fullerite to amorphous carbon at the microscopic level
We have studied the shock-induced phase transition from fullerite to a dense
amorphous carbon phase by tight-binding molecular dynamics. For increasing
hydrostatic pressures P, the C60-cages are found to polymerise at P<10 GPa, to
break at P~40 GPa and to slowly collapse further at P>60 GPa. By contrast, in
the presence of additional shear stresses, the cages are destroyed at much
lower pressures (P<30 GPa). We explain this fact in terms of a continuum model,
the snap-through instability of a spherical shell. Surprisingly, the relaxed
high-density structures display no intermediate-range order.Comment: 5 pages, 3 figure
GRNN-Immune Based Strategy for Estimating and Optimizing the Vibratory Assisted Welding Parameters to Produce Quality Welded Joints
Welding is the process of producing permanent joints with the application of pressure and/or heat energy. During welding operation, weldments may be subjected to uneven thermal stresses. These stresses influence the metallurgical structure of the component. Due to this, the strength of the weld joint is reduced. Therefore, vibratory weld treatment during welding has been proposed in the present work to enhance the flexural and impact strength of weldments. However, it is found that the mechanical properties have shown nonlinear behavior with the chosen input parameters. Hence, an efficient Neural Network (NN) based prediction tool is developed to approximate the mechanical properties of weldments without performing the experiments, output values can be predicted for the given input values. Further, an immune based strategy is integrated to the developed prediction tool in order to obtain desired quality welded joints.Welding is the process of producing permanent joints with the application of pressure and/or heat energy. During welding operation, weldments may be subjected to uneven thermal stresses. These stresses influence the metallurgical structure of the component. Due to this, the strength of the weld joint is reduced. Therefore, vibratory weld treatment during welding has been proposed in the present work to enhance the flexural and impact strength of weldments. However, it is found that the mechanical properties have shown nonlinear behavior with the chosen input parameters. Hence, an efficient Neural Network (NN) based prediction tool is developed to approximate the mechanical properties of weldments without performing the experiments, output values can be predicted for the given input values. Further, an immune based strategy is integrated to the developed prediction tool in order to obtain desired quality welded joints
Mg II Absorption Systems in SDSS QSO Spectra
We present the results of a MgII absorption-line survey using QSO spectra
from the SDSS EDR. Over 1,300 doublets with rest equivalent widths greater than
0.3\AA and redshifts were identified and measured. We
find that the rest equivalent width ()
distribution is described very well by an exponential function , with
and \AA. Previously reported power law
fits drastically over-predict the number of strong lines. Extrapolating our
exponential fit under-predicts the number of \AA systems,
indicating a transition in near \AA. A combination of
two exponentials reproduces the observed distribution well, suggesting that
MgII absorbers are the superposition of at least two physically distinct
populations of absorbing clouds. We also derive a new redshift parameterization
for the number density of \AA lines:
and \AA. We find that the distribution steepens with decreasing redshift,
with decreasing from \AA at to \AA at
. The incidence of moderately strong MgII lines does not
show evidence for evolution with redshift. However, lines stronger than
\AA show a decrease relative to the no-evolution prediction with
decreasing redshift for . The evolution is stronger for
increasingly stronger lines. Since in saturated absorption lines is an
indicator of the velocity spread of the absorbing clouds, we interpret this as
an evolution in the kinematic properties of galaxies from moderate to low z.Comment: 50 pages, 26 figures, accepted for publication in Ap
Droplet Fluctuations in the Morphology and Kinetics of Martensites
We derive a coarse grained, free-energy functional which describes droplet
configurations arising on nucleation of a product crystal within a parent. This
involves a new `slow' vacancy mode that lives at the parent-product interface.
A mode-coupling theory suggests that a {\it slow} quench from the parent phase
produces an equilibrium product, while a {\it fast} quench produces a
metastable martensite. In two dimensions, the martensite nuclei grow as
`lens-shaped' strips having alternating twin domains, with well-defined front
velocities. Several empirically known structural and kinetic relations drop out
naturally from our theory.Comment: 4 pages, REVTEX, and 3 .eps figures, compressed and uuencoded,
Submitted to Phys. Rev. Let
Reconstruction of Causal Networks by Set Covering
We present a method for the reconstruction of networks, based on the order of
nodes visited by a stochastic branching process. Our algorithm reconstructs a
network of minimal size that ensures consistency with the data. Crucially, we
show that global consistency with the data can be achieved through purely local
considerations, inferring the neighbourhood of each node in turn. The
optimisation problem solved for each individual node can be reduced to a Set
Covering Problem, which is known to be NP-hard but can be approximated well in
practice. We then extend our approach to account for noisy data, based on the
Minimum Description Length principle. We demonstrate our algorithms on
synthetic data, generated by an SIR-like epidemiological model.Comment: Under consideration for the ECML PKDD 2010 conferenc
Seed nitrogen and fatty acids reflecting yield variation in groundnut (Arachis hypogaea)
This article does not have an abstract
Equivariant map superalgebras
Suppose a group acts on a scheme and a Lie superalgebra
. The corresponding equivariant map superalgebra is the Lie
superalgebra of equivariant regular maps from to . We
classify the irreducible finite dimensional modules for these superalgebras
under the assumptions that the coordinate ring of is finitely generated,
is finite abelian and acts freely on the rational points of , and
is a basic classical Lie superalgebra (or ,
, if is trivial). We show that they are all (tensor products
of) generalized evaluation modules and are parameterized by a certain set of
equivariant finitely supported maps defined on . Furthermore, in the case
that the even part of is semisimple, we show that all such
modules are in fact (tensor products of) evaluation modules. On the other hand,
if the even part of is not semisimple (more generally, if
is of type I), we introduce a natural generalization of Kac
modules and show that all irreducible finite dimensional modules are quotients
of these. As a special case, our results give the first classification of the
irreducible finite dimensional modules for twisted loop superalgebras.Comment: 27 pages. v2: Section numbering changed to match published version.
Other minor corrections. v3: Minor corrections (see change log at end of
introduction
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