The influence of negatively charged heavy ions on Alfven waves in a cometary environment

Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of Alfven waves in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species has been modeled by drifting distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution is  simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures.  We find that for frequencies  ( andbeing respectively the Doppler shifted and hydrogen ion gyro-frequencies ), the peak growth  rate increases with increasing negatively charged oxygen ion densities. On the other hand, for frequencies (being the oxygen ion gyro-frequencies) the region of wave growth increases with increasing negatively charged oxygen ion densities

Near perpendicular propagation of electromagnetic waves in the magnetosphere

The nature of the damping or instability has been investigated for the "ordinary" and "extraordinary" electromagnetic wave, propagating almost perpendicular to a magnetic line of force in the magnetosphere, for a plasma whose particle distribution function exhibits a temperature anisotropy and a loss-cone structure

Femtosecond Laser Fabricated Ag@Au and Cu@Au Alloy Nanoparticles for Surface Enhanced Raman Spectroscopy Based Trace Explosives Detection

Herein we present results from our detailed studies on the fabrication of Ag@Au and Cu@Au alloy nanoparticles (NPs) using the femtosecond laser ablation in liquid technique. The NPs were obtained by ablating the pure Ag, Cu targets (bulk) in HAuCl4 (5 mM) solution. The absorption properties of the obtained NPs colloids were characterized using UV-Visible absorption spectrometer and their size, shape, and crystallinity were investigated using the XRD, FESEM and TEM techniques. The fabricated NPs were utilized for sensing of explosive molecules such as 2,4,6-trinitrophenol (PA), 2,4-dinitrotoluene (DNT) and a common dye methylene blue (MB) using the surface enhanced Raman spectroscopy (SERS) technique. The detection limit in terms of weight was as low as few nano-grams in the case of nitroaromatic explosive compounds (PA, DNT) and few picograms in the case of a common dye molecule (MB). Typical enhancement factors achieved were estimated to be ~104, ~105, and ~107, respectively, for PA, DNT, and MB. The significance of the present work lies in exploring the performance of the prepared NPs being used as SERS substrates for explosives detection using a portable Raman instrument. Such capability enables one to carry the spectrometer to the point of interest in the field and evaluate any hazardous samples within a short period of time