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P. Mukherjee

Publications and source records attributed to P. Mukherjee.

49 records · Page 3Linked to original sources
arXiv2005

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.

cond-mat.mtrl-sci↗
arXiv2005

Scaling Behavior of the Portevin-Le Chatelier Effect in an Al-2.5%Mg Alloy

The scaling behavior of the Portevin-Le Chatelier (PLC) effect was studied by deforming Al-2.5%Mg alloy for a wide range of strain rates. To reveal the exact scaling nature, the time series data of true stress vs. time, obtained during deformation, were analyzed by two complementary methods: the finite variance scaling method and the diffusion entropy analysis. From these analyses we could establish that in the entire span of strain rates, PLC effect showed Levy walk property.

cond-mat.mtrl-sci↗
arXiv2005

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.

cond-mat.mtrl-sci↗
arXiv2005

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, Irradiation

cond-mat.mtrl-sci↗
arXiv2000

On dust-correlated Galactic emission in the Tenerife data

Recently correlation analyses between Galactic dust emission templates and a number of CMB data sets have led to differing claims on the origin of the Galactic contamination at low frequencies. de Oliviera-Costa {\em et al} (1999) have presented work based on Tenerife data supporting the spinning dust hypothesis. Since the frequency coverage of these data is ideal to discriminate spectrally between spinning dust and free-free emission, we used the latest version of the Tenerife data, which have lower systematic uncertainty, to study the correlation in more detail. We found however that the evidence in favor of spinning dust originates from a small region at low Galactic latitude where the significance of the correlation itself is low and is compromised by systematic effects in the Galactic plane signal. The rest of the region was found to be uncorrelated. Regions that correlate with higher significance tend to have a steeper spectrum, as is expected for free-free emission. Averaging over all correlated regions yields dust-correlation coefficients of $180\pm47$ and $123\pm16$ $μ$K /MJy sr$^{-1}$ at 10 and 15 GHz respectively. These numbers however have large systematic uncertainties that we have identified and care should be taken when comparing with results from other experiments. We do find evidence for synchrotron emission with spectral index steepening from radio to microwave frequencies, but we cannot make conclusive claims about the origin of the dust-correlated component based on the spectral index estimates. Data with higher sensitivity are required to decide about the significance of the dust-correlation at high Galactic latitudes and other Galactic templates, in particular H$_α$ maps, will be necessary for constraining its origin.

astro-ph↗
arXiv2000

Do wavelets really detect non-Gaussianity in the 4-year COBE data?

We investigate the detection of non-Gaussianity in the 4-year COBE data reported by Pando, Valls-Gabaud & Fang (1998), using a technique based on the discrete wavelet transform. Their analysis was performed on the two DMR faces centred on the North and South Galactic poles respectively, using the Daubechies 4 wavelet basis. We show that these results depend critically on the orientation of the data, and so should be treated with caution. For two distinct orientations of the data, we calculate unbiased estimates of the skewness, kurtosis and scale-scale correlation of the corresponding wavelet coefficients in all of the available scale domains of the transform. We obtain several detections of non-Gaussianity in the DMR-DSMB map at greater than the 99 per cent confidence level, but most of these occur on pixel-pixel scales and are therefore not cosmological in origin. Indeed, after removing all multipoles beyond $\ell = 40$ from the COBE maps, only one robust detection remains. Moreover, using Monte-Carlo simulations, we find that the probability of obtaining such a detection by chance is 0.59. We repeat the analysis for the 53+90 GHz coadded COBE map. In this case, after removing $\ell > 40$ multipoles, two non-Gaussian detections at the 99 per cent level remain. Nevertheless, again using Monte-Carlo simulations, we find that the probability of obtaining two such detections by chance is 0.28. Thus, we conclude the wavelet technique does {\em not} yield strong evidence for non-Gaussianity of cosmological origin in the 4-year COBE data.

astro-ph↗
arXiv1999

Some Comments on the Spin of the Chern - Simons Vortices

We compute the spin of both the topological and nontopological solitons of the Chern - Simons - Higgs model by using our approach based on constrained analysis. We also propose an extension of our method to the non - relativistic Chern - Simons models. The spin formula for both the relativistic and nonrelativistic theories turn out to be structurally identical. This form invariance manifests the topological origin of the Chern - Simons term responsible for inducing fractional spin. Also, some comparisons with the existing results are done.

hep-th↗
arXiv1999

Cosmic Microwave background map making with data between 10 and 90GHz

We use data from the Tenerife 10, 15 and 33 GHz beamswitching experiments along with the COBE 53 and 90 GHz data to separate the cosmic microwave background (CMB) signal from the Galactic signal and create two maps at high Galactic latitude. The new multi-MEM technique is used to obtain the best reconstruction of the two channels. The two maps are presented and known features are identified within each. We find that the Galactic contribution to both the 15 and 33 GHz Tenerife data is small enough to be ignored when compared to the errors in the data and the magnitude of the CMB signal.

astro-ph↗
arXiv1996

Galilean symmetry in a nonabelian Chern Simons matter system

We study the Galilean symmetry in a nonrelativistic model, recently advanced by Bak, Jackiw and Pi, involving the coupling of a nonabelian Chern-Simons term with matter fields. The validity of the Galilean algebra on the constraint surface is demonstrated in the gauge independent formalism. Then the reduced space formulation is discussed in the axial gauge using the symplectic method. An anomalous term in the Galilean algebra is obtained which can be eliminated by demanding conditions on the Green function. Finally, the axial gauge is also treated by Dirac's method. Galilean symmetry is preserved in this method. Comparisions with the symplectic approach reveal some interesting features.

hep-th↗
arXiv1996

Spin of Chern-Simons vortices

We discuss a novel method of obtaining the fractional spin of abelian and nonabelian Chern-Simons vortices. This spin is interpreted as the difference between the angular momentum obtained by modifying Schwinger's energy momentum tensor by the Gauss constraint, and the canonical (Noether) angular momentum. It is found to be a boundary term depending only on the gauge field and, hence, is independent of the matter sector to which the Chern-Simons term couples. Addition of the Maxwell term does not alter the fractional spin.

hep-th↗