Search

Single molecule tracking experiments inside a hydrated polymer network have shown that the tracer motion is subdiffusive due to the viscoelastic environment inside the gel-like network. This property can be related to the negative autocorrelation of the instantaneous displacements at short times. Although the displacements of the individual tracers exhibit Gaussian statistics, the displacement distribution of all the trajectories combined from different spatial locations of the polymer network exhibits a non-Gaussian distribution. Here, we analyze many individual tracer trajectories to show that the central portion of the non-Gaussian distribution can be well approximated by an exponential distribution that spreads sublinearly with time. We explain all these features seen in the experiment by a generalized Langevin model for an overdamped particle with algebraically decaying correlations. We show that the degree of non-Gaussianity can change with the extent of heterogeneity, which is controlled in our model by the experimentally observed distributions of the motion parameters. [ABSTRACT FROM AUTHOR]

The expansion dynamics and spectral behaviour of plasma produced by a Nd:YAG laser (λ =1.064 lm, pulse width: 8 ns) from barium target and expanding in 0.45 T transverse magnetic field in vacuum (10-5 Torr pressure) are investigated using time-of-flight optical emission spectroscopy. The experiments are carried out at various laser fluences from 12 to 31 J/cm². The temporal profiles of neutral (Ba I 553.5 and 577.7 nm) lines are temporally broadened, while that of ionic (Ba II 413.0 and 455.4 nm) lines show strong confinement in the presence of a magnetic field. In the absence of magnetic field, the temporal profile of Ba I 553.5 nm is exactly reproduced by fitting with two Shifted Maxwell Boltzmann (SMB) Distribution components, while in the presence of a magnetic field the profile could only be fitted with three components. The field enhanced and field induced SMB components of neutral profile are correlated with populations of ground state, metastable states, and long-lived Rydberg states present in the barium plasma, while SMB components of ionic lines are explained on the basis of the presence of super-elastic collisions among the excited species in the plasma. The spatial variation of electron temperature and temporal variation of electron density are deduced and correlated to the different collisional processes in the barium plasma. The ionic profiles show efficient confinement in the presence of a magnetic field at higher fluences. [ABSTRACT FROM AUTHOR]

Lateral interaction between two geometrically modified plasma plumes in the presence of a transverse magnetic field has been investigated. Characteristic behavior of both seed plumes and the interaction region in the presence of the field is compared with those for the field free case. Contrary to the field free case, no sharp interaction zone is observed; rather large enhancement in emission intensities in both seed and interaction regions is observed in the case of a magnetic field. The observed results are explained on the basis of atomic analysis of the spectral lines from the interaction region of the interacting plumes. The physical processes responsible for higher electron temperature and increased ionic line emission from singly as well as doubly ionized aluminum are briefly discussed. [ABSTRACT FROM AUTHOR]

A new experimental set-up which consists of a pulse magnetic field system has been developed to capture the different phases of expanding plasma plume across the transverse magnetic field, varying from 0 to 0.57 T. Two internally synchronized ICCD cameras mounted in the orthogonal direction have been used to record the two directional projections (across and along the magnetic field directions) of the plasma plume. The plume takes the conventional ellipsoidal shape in the absence of a magnetic field. Well-defined cavity-like structures have been observed in a plane perpendicular to the field direction, which are dominant at the early stage of the plasma and comparatively lower magnetic fields. As the time evolves, the cavity changes to jet/cone-like structures which in turn change to slab-like structures with a further increase in time delay. On the other hand, well separated intensity columns (striation-like structures) appeared in a plane parallel to the magnetic field direction, which are more apparent at a higher magnetic field. Based on the projections of plume images in two perpendicular planes, the three dimensional structure of the plasma plume is modeled as an elliptical cylinder-like structure. The time dependence of dynamics and geometry of the plasma plume in the presence of a magnetic field are correlated with the expansion in diamagnetic and non-diamagnetic regimes. The validity of plasma instability, which is responsible for observed striation-like structures, is also discussed. [ABSTRACT FROM AUTHOR]

The effects of mass and pressure of ambient gas on the propagation dynamics of two laser-blow-off plasma plumes created in close proximity are investigated. A time gated fast imaging technique is used for recording the images of the laterally colliding plumes under different experimental conditions. Pressure is varied from 0.1 to 3 mbar in three ambient, i.e., helium, neon, and argon. Emphasis is given on the nature of shock-shock interaction under different ambient conditions. It has been observed that the shock-velocity, shape, strength, and their interactions are strongly dependent on the mass and density of the ambient gases. The role of the interacting shocks and their subsequent reflections on the formation and geometrical shape of the interaction region in different ambient conditions is briefly described. [ABSTRACT FROM AUTHOR]

An experimental investigation of the laser produced plasma induced shock wave in the presence of confining walls placed along the axial as well as the lateral direction has been performed. A time resolved Mach Zehnder interferometer is set up to track the primary as well as the reflected shock waves and its effect on the evolving plasma plume has been studied. An attempt has been made to discriminate the electronic and medium density contributions towards the changes in the refractive index of the medium. Two dimensional spatial distributions for both ambient medium density and plasma density (electron density) have been obtained by employing customised inversion technique and algorithm on the recorded interferograms. The observed density pattern of the surrounding medium in the presence of confining walls is correlated with the reflected shock wave propagation in the medium. Further, the shock wave plasma interaction and the subsequent changes in the shape and density of the plasma plume in confined geometry are briefly described. [ABSTRACT FROM AUTHOR]

Interactions of two Li plasma plumes and shock waves are investigated at various pressures (~10-5 to 3 mbar) in the argon gas ambient. Fast imaging and optical emission spectroscopy are used to study the plume dynamics and characteristic emission of plasmas. The plasma plumes are created in laser-blow-off geometry. The expansion of plasma plumes in the ambient gas leads to the formation of an interaction zone. The formation of interaction zone is dependent on the ambient pressure and below a certain pressure, no significant change is observed in the shape and size of the interaction plasma. In the higher pressure, formation of interaction zone and its shape are dependent on ambient pressure. Dynamics of seed plasmas and interaction zone are also affected by the shock-shock interactions. The shock-shock interaction depends on the angle of incidence (α) between two shock waves at the initial time of interaction but as the plumes expand, the shock-shock interaction does not follow α dependence. [ABSTRACT FROM AUTHOR]

We report a systematic investigation of two plume interactions at different spatial separation (3-7 mm) in laser-blow-off. The plasmas plumes are created using Laser-blow-off (LBO) scheme of a thin film. The fast imaging technique is used to record the evolution of seed plasmas and the interaction zone which is formed as a result of interaction of the two seed plasmas. Time resolved optical emission spectroscopy is used to study evolution of optical emissions of the species present in the different regions of the plasmas. Neutral Li emissions (Li I 670.8 nm (2s ²S1/2 ← 2p ²P3/2,1/2) and Li I 610.3 nm (2p ²P3/2, 1/2 ← 3d ²D3/2, 5/2)) are dominant in the plasmas but significant differences are observed in the emission and estimated plasma parameters of the seed and the interaction zone. The transport of plasma species from the seed plasmas to the interaction zone is discussed in the terms of plume divergence, kinetic energy of particles, and ion acoustic speed. An attempt is made to understand the formation and dynamics of the interaction zone in the colliding LBO seed plasmas. [ABSTRACT FROM AUTHOR]

Unlike a typical spin–phonon coupling, an exhibition of unconventional spin–phonon coupling, which is mediated via magnetostriction effect, is reported in a hole-doped double perovskite Pr1.5Sr0.5CoMnO6. Various investigations including electronic and crystal structures, spin structure, transport property, lattice dynamics, and theoretical density of states analysis by density-functional theory (DFT) have been performed. A substantial increase in the mean oxidation states of Co ions and a concurrent abrupt decrease in the resistivity upon Sr doping is observed, thus altering its underlying transport mechanism. An insulating and ferromagnetic (FM) ground state is predicted by DFT calculations. The neutron diffraction data analysis reveals a complex crystal structure of Pr1.5Sr0.5CoMnO6, which consists of B-site disordered monoclinic (P21/n) and orthorhombic (Pnma) structures, highlighting the presence of an anti-site disorder in the system. The analysis also suggests an overall FM ordering of Co/Mn spins below 150 K for the monoclinic phase, whereas no such magnetic ordering is found for the orthorhombic phase. More interestingly, the neutron powder diffraction study perceives the presence of a strong magnetostriction effect in the system. Raman spectroscopy unravels the presence of a spin–phonon coupling, which is essentially mediated by the magnetostriction effect. [ABSTRACT FROM AUTHOR]

The characteristics of plasma plume produced by front and back ablation of thin films have been investigated using fast imaging and optical emission spectroscopy. Ablation geometry dependence of the plume dynamics, its geometrical aspect and composition is emphasized. Also, the effect of an ambient environment and the beam diameter of an ablating laser on the front and back ablations is briefly discussed. Analysis of time resolved images and plasma parameters indicates that the energetic and spherical plasma formed by front ablation is strikingly different in comparison to the slow and nearly cylindrical plasma plume observed in the case of back ablation. Further shock formation, plume confinement, thermalization and validity of different expansion models in these two ablation geometries are also presented. The present study demonstrates the manipulation of kinetic energy, shape, ion/neutral compositions and directionality of the expanding plume by adjusting the experimental configuration, which is highly relevant to its utilization in various applications e.g., generation of energetic particles, tokamak edge plasma diagnostics, thin film deposition, etc. [ABSTRACT FROM AUTHOR]

The effect of the atomic mass of the ablating target on the formation and expansion of the interaction region in laterally colliding plasmas has been studied. Fast imaging and optical emission spectroscopy have been utilized as diagnostic tools to investigate the characteristic features of the seed plasma as well as interaction zone formed by different target materials (i.e., carbon, aluminium, and nickel). The present results reveal that dynamical, spectral, and geometrical features of the induced interaction zone depend on the mass of the ablated species and spatial separation between the interacting plumes. It has been observed that a sharp, intense, and more directional interaction zone is formed by the interaction of heavier plume species in comparison to that observed for a lighter atomic mass target. Further, the difference in the plasma parameters in seed and interaction regions are explained from the analysis of emission from both the regions for aluminium plasma. [ABSTRACT FROM AUTHOR]

Preparation and characterization of polymer electrolyte films of PEO+10wt.% LiPF6+xwt.% BMIMPF6 (1-butyl-3-methylimidazolium hexafluorophosphate) containing dopant salt lithium hexafluorophosphate (LiPF6) and ionic liquid (BMIMPF6) having common anion PF6- are reported. The ionic conductivity of the polymer electrolyte films has been found to increase with increasing concentration of BMIMPF6 in PEO+10 wt.% LiPF6 due to the plasticization effect of ionic liquid. DSC and XRD results show that the crystallinity of polymer electrolyte decreases with BMIMPF6 concentration which, in turn, is responsible for the increase in ionic conductivity. FTIR spectroscopic study shows the complexation of salt and/or ionic liquid cations with the polymer backbone. Ion dynamics behavior of PEO+LiPF6 as well as PEO+LiPF6+BMIMPF6 polymer electrolytes was studied by frequency dependent conductivity, σ(f) measurements. The values σ(f) at various temperatures have been analyzed in terms of Jonscher power law (JPL) and scaled with respect to frequency which shows universal power law characteristics at all temperatures. [ABSTRACT FROM AUTHOR]