870 research outputs found
Portevin-Le Chatelier Effect: a Poisson Process
The Portevin-Le Chatelier (PLC) effect is a kind of plastic instability
observed in many dilute alloys when deformed at certain ranges of strain rate
and temperature. In this letter we establish that the dynamical process
responsible for the PLC effect is Poisson in nature by applying statistical
analysis to the observed experimental data obtained during the PLC effect in a
substitutional alloy, Al-2.5%Mg and in an interstitial alloy, low carbon steel
subjected to uniaxial tensile test at constant imposed strain rate.Comment: 15 pages, 3 figures, 3 table
Effect of meditation on scaling behavior and complexity of human heart rate variability
The heart beat data recorded from samples before and during meditation are
analyzed using two different scaling analysis methods. These analyses revealed
that mediation severely affects the long range correlation of heart beat of a
normal heart. Moreover, it is found that meditation induces periodic behavior
in the heart beat. The complexity of the heart rate variability is quantified
using multiscale entropy analysis and recurrence analysis. The complexity of
the heart beat during mediation is found to be more.Comment: 7 Figure
Effect of heavy ion irradiation on microstructure and electron density distribution of zirconium alloy characterised by X-ray diffraction technique
Different techniques of the X-ray Diffraction Line Profile Analysis (XRDLPA)
have been used to assess the microstructure of the irradiated
Zr-1.0%Nb-1.0%Sn-0.1%Fe alloy. The domain size, microstrain, density of
dislocation and the stacking fault probabilities of the irradiated alloy have
been estimated as a function of dose by the Williamson-Hall Technique, Modified
Rietveld Analysis and the Double Voigt Method. A clear signature in the
increase in the density of dislocation with the dose of irradiated was
revealed. The analysis also estimated the average density of dislocation in the
major slip planes after irradiation. For the first time, we have established
the changes in the electron density distribution due to irradiation by X-ray
diffraction technique. We could estimate the average displacement of the atoms
and the lattice strain caused due to irradiation from the changes in the
electron density distribution as observed in the contour plots
Effect of Temperature on the Complexity of Solid Argon System
We study the measure of complexity in solid Argon system from the time series
data of kinetic energy of single Argon atoms at different equilibrated
temperatures. To account the inherent multi-scale dependence of the complexity,
the multi-scale entropy of the time series of kinetic energy of individual
Argon atoms are computed at different equilibrated temperatures. The
multi-scale entropy study reveals that the dynamics of an atom becomes more
complex at higher temperatures and the result corroborates well with the
variation of the pair correlation function of the atoms in the solid Argon
crystal. Also, we repeat the multi-scale entropy analysis for program generated
Levy noise time series and for time series data obtained from the outcomes of
exponential decay with noise dx(t) = -x(t) dt + sigma dB(t) (Langevin
equation). Our study establishes that the scale dependence of sample entropy
for time series of kinetic energy of individual atoms in solid Argon system has
similar tendency as that of Levy noise time series and the outcomes of
exponential decay with noise (Langevin equation).Comment: 8 pages, 14 figures, Accepted in Indian Journal of Physics for
publicatio
Oscillatory Shannon Entropy in the Process of Equilibration of Nonequilibrium Systems
We present a study of the equilibration process of nonequilibrium systems by
means of molecular dynamics simulation technique. The nonequilibrium conditions
are achieved in systems by defining velocity components of the constituent
atoms randomly. The calculated Shannon en- tropy from the probability
distribution of the kinetic energy among the atoms at different instants during
the process of equilibration shows oscillation as the system relaxes towards
equilibrium. Fourier transformations of these oscillating Shannon entropies
reveal the existance of Debye frequency of the concerned system. From these
studies it was concluded that the signature of the equilibration process of
dynamical systems is the time invariance of Shannon entropy.Comment: 4 pages, 4 figure
Character of the Dislocation Bands in the (A+B) regime of the Portevin-Le Chatelier effect in Al-2.5%Mg alloy
The Portevin-Le Chatelier(PLC) effect has been investigated by deforming
Al-2.5%Mg alloy in the strain rate regime where simultaneously two types (type
B and type A) of serrations appear in the stress strain curve. Our analysis
reveal that in this strain rate regime the entire PLC dynamics for a particular
strain rate experiment is governed by a single band which changes its character
during the deformation.Comment: 13 pages, 4 figure
Studies on Neon irradiated amorphous carbon using X-ray Diffraction technique
Two sets of amorphous carbon materials prepared at different routes are
irradiated with swift (145 MeV) heavy ion (Ne6+). The structural parameters
like the size of ordered grains along c and a axis i.e. Lc & La, the average
spacing of the crystallographic planes (002) i.e. d002 and the fraction of the
amorphous phase of the unirradiated and the irradiated samples are estimated by
X-ray diffraction technique. The fraction of the amorphous phase is generally
found to increase with the irradiation dose for both sets of the samples. The
estimated and values are found to be almost unaffected by irradiation. The
estimated values of corroborate with the increase of disorder in both sets of
the samples with the increasing dose of irradiation. Keywords: X-ray
Diffraction, Amorphous Carbon, Irradiatio
Inertial Oscillations of Pinned Dislocations
Dislocation pinning plays a vital role in the plastic behaviour of a
crystalline solid. Here we report the first observation of the damped
oscillations of a mobile dislocation after it gets pinned at an obstacle in the
presence of a constant static shear load. These oscillations are found to be
inertial, instead of forced as obtained in the studies of internal friction of
solid. The rate of damping enables us to determine the effective mass of the
dislocation. Nevertheless, the observed relation between the oscillation
frequency and the link length is found to be anomalous, when compared with the
theoretical results in the framework of Koehler's vibrating string model. We
assign this anomaly to the improper boundary conditions employed in the
treatment. Finally, we propose that the inertial oscillations may offer a
plausible explanation of the electromagnetic emissions during material
deformation and seismic activities.Comment: 28 pages, 4 figure
Microstructural studies on lattice imperfections in irradiated Titanium and Ti-5%Ta-2%Nb by X-Ray Diffraction Line Profile Analysis
The microstructural parameters like the average domain size, effective domain
size at a particular crystallographic direction and microstrain within the
domains of titanium and Ti-5%Ta-2%Nb, irradiated with 116 MeV O5+ ion, have
been characterized as a function of dose by X-Ray Diffraction Line Profile
Analysis using different model based approaches. Dislocation Density and
stacking fault probabilities have also been estimated from the analysis. The
analysis revealed that there was a significant decrease of the average domain
size with dose as compared to the unirradiated sample. The estimated values of
dislocation density increased significantly for the irradiated samples and was
found to be an order of magnitude more as compared to the unirradiated one.
However, the dislocation density saturated with increase in dose. The
deformation (stacking) fault probabilities were found to be negligible even
with the increase in dose of irradiation
Effect of transient change in strain rate on plastic flow behavior of low carbon steel
Plastic flow behavior of low carbon steel has been studied at room
temperature during tensile deformation by varying the initial strain rate of
3.3x10e-4 1/sec to the final strain rate ranging from 1.33x10e-3 1/sec to
2.0x10e-3 1/sec at a fixed engineering strain of 12%. Haasen plot revealed that
the mobile dislocation density remained almost invariant at the juncture where
there was a sudden increase in stress with the change in strain rate and the
plastic flow was solely dependent on the velocity of mobile dislocations. In
that critical regime, the variation of stress with time was fitted with a
Boltzman type Sigmoid function. The increase in stress was found to increase
with final strain rate and the time elapsed to attain these stress values
showed a decreasing trend. Both of these parameters saturated asymptotically at
higher final strain rate
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