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