Indian Institute of Technology Indore

About: Indian Institute of Technology Indore is a education organization based out in Indore, Madhya Pradesh, India. It is known for research contribution in the topics: Fading & Support vector machine. The organization has 1606 authors who have published 4803 publications receiving 66500 citations.

A Particle Module for the PLUTO Code. I. An Implementation of the MHD-PIC Equations

Abstract: We describe an implementation of a particle physics module available for the PLUTO code, appropriate for the dynamical evolution of a plasma consisting of a thermal fluid and a non-thermal component represented by relativistic charged particles, or cosmic rays (CR). While the fluid is approached using standard numerical schemes for magnetohydrodynamics, CR particles are treated kinetically using conventional Particle-In-Cell (PIC) techniques. The module can be used to describe either test particles motion in the fluid electromagnetic field or to solve the fully coupled MHD-PIC system of equations with particle backreaction on the fluid as originally introduced by \cite{Bai_etal.2015}. Particle backreaction on the fluid is included in the form of momentum-energy feedback and by introducing the CR-induced Hall term in Ohm's law. The hybrid MHD-PIC module can be employed to study CR kinetic effects on scales larger than the (ion) skin depth provided the Larmor gyration scale is properly resolved. When applicable, this formulation avoids to resolve microscopic scales offering a substantial computational saving with respect to PIC simulations. We present a fully-conservative formulation which is second-order accurate in time and space and extends to either Runge-Kutta (RK) or corner-transport-upwind (CTU) time-stepping schemes (for the fluid) while a standard Boris integrator is employed for the particles. For highly-energetic relativistic CRs and in order to overcome the time step restriction a novel sub-cycling strategy that retains second-order accuracy in time is presented. Numerical benchmarks and applications including Bell instability, diffusive shock acceleration and test particle acceleration in reconnecting layers are discussed.

Multiplicity dependence of π, K, and p production in pp collisions at √ s = 13 TeV

Abstract: This paper presents the measurements of $\pi ^{\pm }$, $\mathrm {K}^{\pm }$, $\text {p}$ and $\overline{\mathrm{p}} $ transverse momentum ($p_{\text {T}}$) spectra as a function of charged-particle multiplicity density in proton–proton (pp) collisions at $\sqrt{s}\ =\ 13\ \text {TeV}$ with the ALICE detector at the LHC. Such study allows us to isolate the center-of-mass energy dependence of light-flavour particle production. The measurements reported here cover a $p_{\text {T}}$ range from 0.1 to 20 $\text {GeV}/c$ and are done in the rapidity interval $|y|<0.5$. The $p_{\text {T}}$-differential particle ratios exhibit an evolution with multiplicity, similar to that observed in pp collisions at $\sqrt{s}\ =\ 7\ \text {TeV}$, which is qualitatively described by some of the hydrodynamical and pQCD-inspired models discussed in this paper. Furthermore, the $p_{\text {T}}$-integrated hadron-to-pion yield ratios measured in pp collisions at two different center-of-mass energies are consistent when compared at similar multiplicities. This also extends to strange and multi-strange hadrons, suggesting that, at LHC energies, particle hadrochemistry scales with particle multiplicity the same way under different collision energies and colliding systems.

Silicon nanowires prepared by metal induced etching (MIE): good field emitters

Abstract: Micro-Raman scattering and electron field emission characteristics of silicon nanowires (SiNWs) synthesized by metal induced chemical etching (MIE) are studied. Scanning electron microscopy images reveal the growth of well aligned vertical SiNWs which show red-shifted and asymmetrically broadened Raman line-shapes. The relationship between Raman shift and crystallite size, as derived from a bond-polarizability model, has been used to estimate the confinement sizes in SiNWs. The Si optical phonon peak for SiNWs showed an increase in red-shift and full width at half maxima with decreasing diameter of the SiNWs due to quantum confinement of optical phonons. The field emission characteristics of these SiNWs are studied by carrying out current–voltage measurements followed by a theoretical analysis using the Fowler–Nordheim equation. The electron field emission increased with decreasing diameter of SiNWs. Field emission from these SiNWs exhibits significant enhancement in turn-on field and total emission current with decreasing nanowire diameter. The reported results in the current study indicate that MIE is a simple technique to prepare well-aligned SiNWs with potentials for applications in field emission devices.

Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

Abstract: In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.