arXiv subjects

R. Mitra

Publications and source records attributed to R. Mitra.

7 recordsLinked to original sources

arXiv2024

Helicity oscillations in Rayleigh-Bénard convection of liquid metal in a cell with aspect ratio 0.5

In this paper, we present numerical and experimental results on helicity oscillations in a liquid-metal Rayleigh-Bénard (RB) convection cell, with an aspect ratio of 0.5. We find that helicity oscillations occur during transitions of flow states that are characterised by significant changes in the Reynolds number. Moreover, we also observe helicity oscillations at flow conditions where the temporal gradient of the change in the Reynolds number is significantly smaller than that of the helicity. Notably, the helicity oscillations observed during the transient double-roll state exhibit characteristics remarkably similar to those associated with the Tayler Instability.

physics.flu-dyn↗

arXiv2022

Electric Dipole Moments and Static Dipole Polarizabilities of Alkali--Alkaline-Earth Molecules: Non-relativistic versus relativistic coupled-cluster theory analyses

We analyze the electric dipole moments (PDMs) and static electric dipole polarizabilities of the alkali--alkaline-earth (Alk-AlkE) dimers by employing finite-field coupled-cluster methods, both in the frameworks of non-relativistic and four-component spinfree relativistic theory. In order to carry out comparative analyses rigorously, we consider those Alk-AlkE molecules made out of the lightest to the medium-heavy constituent atoms (Alk: Li to Rb and AlkE: Be through Sr). We present behaviour of electron correlation effects as well as relativistic effects with the size of the molecules. Uncertainties to the above quantities of the investigated Alk-AlkE molecules are inferred by analyzing our results from different form of Hamiltonian, basis set, and perturbative parameter in a few representative molecules. We have also provided empirical relations by connecting average polarizabilities of the Alk-AlkE molecules with their PDMs, and atomic numbers and polarizabilities of the corresponding Alk and AlKE atoms, which can be used to roughly estimate the average polarizabilities of other heavier Alk-AlkE molecules. We finally give our recommended results, and compare them with the literature values.

physics.atom-ph↗

arXiv2021

Towards CP Violation Studies on Superheavy Molecules: Theoretical and Experimental Perspective

Molecules containing superheavy atoms can be artificially created to serve as sensitive probes for study of symmetry-violating phenomena. Here, we provide a detailed theoretical study for diatomic molecules containing the superheavy lawrencium nuclei. The sensitivity to time-reversal violating properties was studied for different neutral and ionic molecules. The effective electric fields in these systems were found to be about 3-4 times larger than other known molecules on which electron electric dipole moment experiments are being performed. Similarly, these superheavy molecules exhibit an enhancement of more than 5 times for parity- and time-reversal-violating scalar-pseudoscalar nucleus-electron interactions. We also briefly comment on some experimental aspects by discussing the production of these systems.

physics.atom-ph↗

arXiv2019

A Comparative Analysis of Non-relativistic and Relativistic Calculations of Electric Dipole Moments and Polarizabilities of Heteronuclear Alkali Dimers

We analyze the molecular electric dipole moments (PDMs) and static electric dipole polarizabilities of heteronuclear alkali dimers in their ground states by employing coupled-cluster theory, both in the non-relativistic and four-component relativistic frameworks. The roles of electron correlations as well as relativistic effects are demonstrated by studying them at different levels of theory, followed by a comprehensive treatment of error estimates. We compare our obtained values with the previous non-relativistic calculations, some of which include lower-order relativistic corrections, as well as with the experimental values, wherever available. We find that the PDMs are very sensitive to relativistic effects, as compared to polarizabilities; this aspect can explain the long-standing question on the difference between experimental values and theoretical results for LiNa. We show that consideration of relativistic values of PDMs improves significantly the isotropic Van der Waals $C_6$ coefficients of the investigated alkali dimers over the previously reported non-relativistic calculations. The dependence of dipole polarizabilities on molecular volume is also illustrated.

physics.atom-ph↗

arXiv2019

Mercury Hydroxide as a Promising Triatomic Molecule to Probe P,T-odd Interactions

In the quest to find a favourable triatomic molecule for detecting electric dipole moment of an electron (eEDM), we identify mercury hydroxide (HgOH) as an extremely attractive candidate from both experimental and theoretical viewpoints. Our calculations show that there is a four-fold enhancement in the effective electric field of HgOH compared to the recently proposed ytterbium hydroxide (YbOH) [Phys. Rev. Lett. 119, 133002 (2017)] for eEDM measurement. Thus, in the (010) bending state associated with the electronic ground state, it could provide better sensitivity than YbOH from a theoretical point of view. We have also investigated the potential energy curve and permanent electric dipole moment of HgOH, which lends support for its experimental feasibility. Moreover, we propose that it is possible to laser cool the HgOH molecule by adopting the same technique as that in the diatomic polar molecule, HgF, as shown in [Phys. Rev. A 99, 032502 (2019)].

physics.atom-ph↗

arXiv2019

Analysis of Electric Dipole Moment of $^{225}$Ra Atom using the Relativistic Normal Coupled-cluster Theory

In view of the large differences in the previous calculations of enhancement factors to the parity and time-reversal violating (P,T-odd) electric dipole moment (EDM) of $^{225}$Ra due to nuclear Schiff moment (NSM) and tensor-pseudotensor (T-PT) electron-nucleus (e-N) interactions between the relativistic coupled-cluster (RCC) theory and other many-body methods, we employ the relativistic normal coupled-cluster (RNCC) theory to explain the discrepancies. The normalization of the wave function in the RNCC theory becomes unity by construction. This feature removes the ambiguity associated with the uncertainties in calculations that could arise due to mismatch in cancellation of the normalization factor of the wave function in a truncated RCC method. Moreover, all the terms in the expression for EDM using the RNCC method naturally terminate, in contrast to the RCC approach. By taking an average of the results from two variants each of both the RCC and RNCC methods, we recommend enhancement factors to the EDM of 225Ra due to NSM as $-$6.29(1) $\times 10^{-17} |e| $cm $( |e| fm^3)$ and due to T-PT e-N coupling constant as $-$12.66(14) $\times {10^{-20} \langle σ_N \rangle | e | }$cm, for the nuclear Pauli spinor, $σ_N$. This is corroborated by analyzing the dipole polarizability ($α_d$) value of $^{225}$Ra, which is obtained as 244(13) $ea_0^3$. We also compare our results for all three properties with previous calculations that employ different many-body methods. Our $α_d$ value agrees very well with the results that are obtained by carrying out rigorous analyses using other variants of RCC methods.

physics.atom-ph↗

arXiv2016

The role of crystallographic orientation of martensitic variants on cleavage crack propagation

Cleavage crack propagation has been investigated in a low-carbon lath-martensitic steel using electron back-scattered diffraction technique. The ability of different martensitic boundaries within prior-austenite grain, such as sub-block, block and packet boundaries to resist cleavage crack propagation has been estimated in terms of Kurdjumov-Sachs crystallographic variants. Crystallographic study of crack path indicated that block boundaries are more effective in cleavage crack deviation as compared to packet boundaries, whilst sub-block boundaries are ineffective in that respect. Moreover, characterizing the boundaries in terms of misorientation angle (angle-axis pair) may be misleading if their effectiveness in retarding cleavage crack propagation is considered.

cond-mat.mtrl-sci↗