• Volume 81, Issue 1

July 2013,   pages  1-187

• General editorial on publication ethics

• Novel experimentally observed phenomena in soft matter

Soft materials such as colloidal suspensions, polymer solutions and liquid crystals are constituted by mesoscopic entities held together by weak forces. Their mechanical moduli are several orders of magnitude lower than those of atomic solids. The application of small to moderate stresses to these materials results in the disruption of their microstructures. The resulting flow is non-Newtonian and is characterized by features such as shear rate-dependent viscosities and nonzero normal stresses. This article begins with an introduction to some unusual flow properties displayed by soft matter. Experiments that report a spectrum of novel phenomena exhibited by these materials, such as turbulent drag reduction, elastic turbulence, the formation of shear bands and the existence of rheological chaos, flow-induced birefringence and the unusual rheology of soft glassy materials, are reviewed. The focus then shifts to observations of the liquid-like response of granular media that have been subjected to external forces. The article concludes with examples of the patterns that emerge when certain soft materials are vibrated, or when they are displaced with Newtonian fluids of lower viscosities.

• Plasma response to transient high voltage pulses

This review reports on plasma response to transient high voltage pulses in a low pressure unmagnetized plasma. Mainly, the experiments are reviewed, when a disc electrode (metallic and dielectric) is biased pulsed negative or positive. The main aim is to review the electron loss in plasmas and particle balance during the negative pulse electrode biasing, when the applied pulse width is less than the ion plasma period. Though the applied pulse width is less than the ion plasma period, ion rarefaction waves are excited. The solitary electron holes are reviewed for positive pulsed bias to the electrode. Also the excitation of waves (solitary electron and ion holes) is reviewed for a metallic electrode covered by a dielectric material. The wave excitation during and after the pulse withdrawal, excitation and propagation characteristics of various electrostatic plasma waves are reviewed here.

• Anisotropic cosmological models in $f (R, T)$ theory of gravitation

A class of non-singular bouncing cosmological models of a general class of Bianchi models filled with perfect fluid in the framework of $f (R, T)$ gravity is presented. The model initially accelerates for a certain period of time and decelerates thereafter. The physical behaviour of the model is also studied.

• New perspective in the use of soft rotor formula for $K = 2 \gamma$-band

The use of soft rotor formula (SRF) for the level energies of $K = 2 \gamma$ -band for the shape transitional even $Z$ even $N$ nuclei in the medium mass region is illustrated. With proper treatment, we obtained positive values of the moment of inertia and softness parameter, as opposed to negative values reported in literature. The moments of inertia of the $\gamma$-band are almost equal to the ground state band values. The systematic dependence of the softness parameter on energy ratio $R_{4/2}$ is studied. The effect of the odd–even spin staggering on these parameters is studied in detail. In deformed nuclei, the same parameters for odd and even spin members yield fair energy values.

• A benchmark study on uncertainty of ALICE ASH 1.0, TALYS 1.0 and MCNPX 2.6 codes to estimate production yield of accelerator-based radioisotopes

Radioisotopes find very important applications in various sectors of economic significance and their production is an important activity of many national programmes. Some deterministic codes such as ALICE ASH 1.0 and TALYS 1.0 are extensively used to calculate the yield of a radioisotope via numerical integral over the calculated cross-sections. MCNPX 2.6 stochastic code is more interesting among the other Monte Carlo-based computational codes for accessibility of different intranuclear cascade physical models to calculate the yield using experiment-based cross-sections. A benchmark study has been proposed to determine the codes' uncertainty in such calculations. ${}^{109}$Cd, ${}^{86}$Y and ${}^{85}$Sr production yields by proton irradiation of silver, rubidium chloride and strontium carbonate targets are studied. $^{109}$Cd, $^{86}$Y and $^{85}$Sr cross-sections are calculated using ALICE ASH 1.0 and TALYS 1.0 codes. The evaluated yields are compared with the experimental yields. The targets are modelled using MCNPX 2.6 code. The production yields are calculated using the available physical models of the code. The study shows acceptable relative discrepancies between theoretical and experimental results. Minimum relative discrepancy between experimental and theoretical yields is achievable using ISABEL intranuclear model in most of the targets simulated by MCNPX 2.6. The stochastic code utilization can be suggested for calculating $^{109}$Cd, $^{86}$Y and $^{85}$Sr production yields. It results in more valid data than TALYS 1.0 and ALICE ASH 1.0 in noticeably less average relative discrepancies.

• Systematic study of multiparticle production in nucleus–nucleus interactions at 14.6 A GeV

An experimental analysis of 855 events induced by 14.6 A GeV $^{28}$Si in nuclear emulsion is presented. Mean multiplicities of charged secondary particles produced in the nuclear interactions are studied and compared with the results from the other experiments for the same projectile at 3.7 A GeV as well as data for proton at similar energy (14 GeV). An analysis of pseudorapidity densities of target fragments (black and grey particles) is also performed. The behaviour of the KNO scaling law of the multiplicity distribution for shower particles has been examined. In order to accumulate knowledge about the intermittent behaviour of shower particles, the scaled factorial moments (SFMs) are computed in $\eta$-space and $\phi$-space for a set of data in the $^{28}$Si–AgBr events. Furthermore, validity of limiting fragmentation of shower particles produced in central collision events induced by $^{28}$Si-emulsion interactions has been tested. A crude estimation for the energy density of the nuclear matter formed in the central collision events at our energy has been examined.

• Investigation of invisible oscillation on the photodetachment cross-section of H$_{2}^{-}$ near a hard surface

Induced effects in the photodetached electron spectra from a diatomic negative ion (H$_{2}^{-}$) near a hard surface are investigated. A $z$-polarized laser is used to knock off electrons from H$_{2}^{-}$ in the vicinity of a hard surface. Theoretical imaging method is used to derive a generalized modulation function for the total photodetachment cross-section, which describes invisible oscillation. It is found that the hard surface strongly affects the detached electron flux as well as total photodetachment cross-section. There exists strong dependence on the distance of H$_{2}^{-}$ from the hard surface and also on the separation of atomic centres of H$_{2}^{-}$. Unlike the detached electron flux, no visible oscillations are noted in the photodetachment cross-section.

• Vibrational resonance in the Morse oscillator

The occurrence of vibrational resonance is investigated in both classical and quantum mechanical Morse oscillators driven by a biharmonic force. The biharmonic force consists of two forces of widely different frequencies $\omega$ and $\Omega$ with $\Omega \gg \omega$. In the damped and biharmonically driven classical Morse oscillator, by applying a theoretical approach, an analytical expression is obtained for the response amplitude at the low-frequency $\omega$. Conditions are identified on the parameters for the occurrence of resonance. The system shows only one resonance and moreover at resonance the response amplitude is $1/d\omega$ where $d$ is the coefficient of linear damping. When the amplitude of the high-frequency force is varied after resonance the response amplitude does not decay to zero but approaches a nonzero limiting value. It is observed that vibrational resonance occurs when the sinusoidal force is replaced by a square-wave force. The occurrence of resonance and antiresonance of transition probability of quantum mechanical Morse oscillator is also reported in the presence of the biharmonic external field.

• A simplistic pedagogical formulation of a thermal speed distribution using a relativistic framework

A novel pedagogical technique is presented that can be used in the undergraduate (UG) class to formulate a relativistically extended kinetic theory of gases and thermal speed distribution, while assuming the basic thermal symmetry arguments of the famous Maxwell–Boltzmann distribution as presented at the UG level. The adopted framework can be used by students to understand the physics of a thermally governed system at high temperature and speeds, without having to indulge in high level tensor-based mathematics, as has been done by the previous works on the subject. Our approach, a logical extension of that proposed by Maxwell, will first recapitulate what is taught and known in the UG class and then present a methodology inspired from the Maxwell–Boltzmann framework that will help students to understand and derive the physics of relativistic thermal systems. The methodology uses simple tools well known to undergraduates and involves a component of computational techniques that can be used to involve students in this exercise. We have tried to place the current work in a larger perspective with regard to the earlier works done and emphasize on its simplicity and accessibility to students. Towards the end, interesting implications of the relativistically extended distribution are presented and compared with the Maxwell–Boltzmann results at various temperatures.

• Microwave power coupling with electron cyclotron resonance plasma using Langmuir probe

Electron cyclotron resonance (ECR) plasma was produced at 2.45 GHz using 200 – 750 W microwave power. The plasma was produced from argon gas at a pressure of $2 \times 10^{−4}$ mbar. Three water-cooled solenoid coils were used to satisfy the ECR resonant conditions inside the plasma chamber. The basic parameters of plasma, such as electron density, electron temperature, floating potential, and plasma potential, were evaluated using the current–voltage curve using a Langmuir probe. The effect of microwave power coupling to the plasma was studied by varying the microwave power. It was observed that the optimum coupling to the plasma was obtained for $\sim$ 600 W microwave power with an average electron density of $\sim 6 \times 10^{11}$ cm$^{−3}$ and average electron temperature of $\sim$ 9 eV.

• Nonlinear propagation of ion-acoustic waves in a degenerate dense plasma

Nonlinear propagation of ion-acoustic (IA) waves in a degenerate dense plasma (with all the constituents being degenerate, for both the non-relativistic or ultrarelativistic cases) have been investigated by the reductive perturbation method. The linear dispersion relation and Korteweg de Vries (KdV) equation have been derived, and the numerical solutions of KdV equation have been analysed to identify the basic features of electrostatic solitary structures that may form in such a degenerate dense plasma. The implications of our results in compact astrophysical objects, particularly, in white dwarfs and neutron stars, have been briefly discussed.

• Characterization of pure and copper-doped iron tartrate crystals grown in silica gel

Single crystal growth of pure and copper-doped iron tartrate crystals bearing composition Cu$_{x}$ Fe$_{(1−x)}$ C4H4O6 · $n$H2O, where $x = 0, 0.07, 0.06, 0.05, 0.04, 0.03$, is achieved using gel technique. The elemental analysis has been done using energy-dispersive X-ray analysis (EDAX) spectrum. The characterization studies such as Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), magnetic analysis and thermal analysis have been done for crystals with $x = 0$ for pure iron tartrate and with $x = 0.05$ for copper-mixed iron tartrate crystals. A detailed comparison has been made between pure and doped crystals.

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