• S Sahoo

Articles written in Pramana – Journal of Physics

• Flavour-changing neutral currents in models with extraZ′ boson

New neutral gauge bosonsZ′ are the features of many models addressing the physics beyond the standard model. Together with the existence of new neutral gauge bosons, models based on extended gauge groups (rank &gt; 4) often predict new charged fermions also. A mixing of the known fermions with new states, with exotic weak-isospin assignments (left-handed singlets and right-handed doublets) will induce tree-level flavour-changing neutral interactions mediated byZ exchange, while if the mixing is only with new states with ordinary weak-isospin assignments, the flavour-changing neutral currents are mainly due to the exchange of the new neutral gauge bosonZ′. We review flavour-changing neutral currents in models with extraZ′ boson. Then we discuss some flavour-changing processes forbidden in the standard model and new contributions to standard model processes.

• Dielectric relaxation of binary polar liquid mixture measured in benzene at 10 GHz frequency

The dielectric relaxation times $\tau_{jk}$'s and dipole moments $\mu_{jk}$'s of the binary ($j_{k}$) polar liquid mixture of N,N-dimethyl acetamide (DMA) and acetone (Ac) dissolved in benzene (i) are estimated from the measured real $\sigma_{ijk}^{'}$ and imaginary $\sigma_{ijk}^{''}$ parts of complex high frequency conductivity $\sigma_{ijk}^{*}$ of the solution for different weight fractions $w_{jk}$'s of 0.0, 0.3, 0.5, 0.7 and 1.0 mole fractions $x_{j}$ of Ac and temperatures (25, 30, 35 and 40°C) respectively under 9.88 GHz electric field. $\tau_{jk}$'s are obtained from the ratio of slopes of $\sigma_{ijk}^{''} - w_{jk}$ and $\sigma_{ijk}^{'} - w_{jk}$ curves at $w_{jk} \rightarrow 0$ as well as linear slope of $\sigma_{ijk}^{''} - \sigma_{ijk}^{'}$ curves of the existing method (Murthy et al, 1989) in order to eliminate polar-polar interaction in the latter case. The calculated 𝜏's are in excellent agreement with the reported 𝜏's due to Gopalakrishna's method. $\mu_{jk}$'s are also estimated from slopes 𝛽's of total conductivity $\sigma_{ijk} - w_{jk}$ curves at $w_{jk} \rightarrow 0$ and the values agree well with the reported 𝜇's from G.K. method. The variation of $\tau_{jk}$'s and $\mu_{jk}$'s with $x_{j}$ of Ac reveals that solute-solute molecular association occurs within $0.0-0.3x_{j}$ of Ac beyond which solute-solvent molecular association is predicted. The theoretical dipole moments $\mu_{\text{theo}}$'s are calculated from bond angles and bond moments to have exact 𝜇's only to show the presence of inductive, mesomeric and electromeric effects in the substituent polar groups. The thermodynamic energy parameters are estimated from ln($\tau_{jk}T$) against $1/T$ linear curve from Eyring's rate theory to know the molecular dynamics of the system and to establish the fact that the mixture obeys the Debye-Smyth relaxation mechanism.

• Dielectric behaviour of some amides and formamides dissolved in nonpolar solvents under static electric ﬁeld

Structural and associational aspects of polar amides (𝑗) like formamide, acetamide, Nmethyl acetamide (NMA), N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMA) and acetanilide dissolved in the nonpolar solvent (𝑖) benzene or 1,4-dioxan have been estimated from the measured static relative permittivity $\varepsilon_{0ij}$ and high-frequency permittivity $\varepsilon_{\infty ij}$ at different weight fractions $w_j$s of polar solute at 35°C under static electric ﬁeld using Debye model of polar liquid molecule. The static dipole moments $\mu_s$s are compared with $\mu_j$s reported from conductivity method and theoretical $\mu_{\text{theo}$s to get exact $\mu_{\text{cal}} \cdot \mu_{\text{theo}$s of the molecules are predicted from the available bond angles and bond moments where difference in electron afﬁnity exists between two adjacent atoms of a polar group due to inductive, mesomeric and electromeric effects in them. Solute–solute molecular association for NMA in benzene and solute–solvent association for other amides are ascertained to arrive at their conformational structures.

• Dielectric relaxation of ethanol and 𝑁-methyl acetamide polar mixture in C6H6 at 9.90 GHz

Debye relaxation times $(\tau_{jk})$ and dipole moments $(\mu_{jk})$ of binary ($jk$) polar mixtures of ethanol (EtOH) and 𝑁-methyl acetamide (NMA) dissolved in benzene(i) are studied by studying conductivity of solution at 9.90 GHz for different temperatures, different mole fractions ($x_j$) of ethanol and different weight fractions $(w_{jk})$ of the mixtures, respectively. The variation of $\tau_{jk}−x_j$ from linear slope of imaginary ($\sigma''_{ijk}$) against real ($\sigma'_{ijk}$) part of total conductivity ($\sigma^{\ast}_{ijk}$) curve reveals solute–solute (dimer) or solute–solvent (monomer) molecular associations up to $x_j$ = 0.0−0.3 and thereafter, solute–solvent molecular associations. $\tau_{jk}$s from the ratio of slopes of $\sigma''_{ijk}$−w_{jk}$and$\sigma'_{ijk}$−w_{jk}$ curves exhibit solute–solvent molecular association for all $x_j$s which are consistent with the $\mu_{jk}−x_j$ curves at all temperatures except at 35°C. This signifies the validity of both the proposed methods in estimating 𝜏 and 𝜇. The molecular dynamics of the polar mixture are ascertained from Eyring rate theory. Theoretical dipole moments from bond angles and bond moments ($\mu_{\text{theo}}$) are also calculated to predict associational aspects.

• # Pramana – Journal of Physics

Volume 94, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019