The chemical effects induced by acoustic cavitation (popularly known as sonochemical effects) in aqueous medium are well-known and are attributed to the production of various radicals during bubble collapse. Under the influence of pressure variation due to acoustic wave, the bubble expands with the evaporation of water at the gas-liquid interface. This water vapor condenses at the gas-liquid interface during compression. At the final moments of bubble collapse, the dynamics of bubble motion is far more rapid than the diffusion dynamics of water vapor. Therefore, not all the water vapor that has entered the bubble during expansion escapes during compression. The entrapped water molecules are subjected to extremely high temperature and pressure reached during bubble collapse and undergo cleavage to produce various radicals. These radicals are then mixed with the bulk, where they induce various chemical reactions. Similar chemical effects have also been demonstrated by hydrodynamic cavitation, produced because of bubble oscillation and collapse driven by pressure variation in liquid flow. In this work, we try to give a numerical explanation to the sonochemical effects induced by hydrodynamic cavitation. Using a simplified ordinary differential equation (ODE) model for the dynamics of argon bubbles (released because of pressure reduction in the flow) with associated heat and mass transfer, we show that the phenomena of water vapor entrapment and cleavage due to extremes of temperature and pressure at bubble collapse also occur in hydrodynamic cavitation. We also try to investigate the effect of several operating parameters on the extent of water vapor entrapment, the extreme conditions of pressure and temperature generated in the bubble during collapse, and the production of radicals.

We demonstrate a simple method to increase the optical density (OD) of cold atom clouds produced by a magneto-optical trap (MOT). A pair of rectangular anti-Helmholtz coils is used in the MOT to generate the magnetic field that produces the cigar-shaped atom cloud. With 7.2x10(8) (87)Rb atoms in the cigar-type MOT, we achieve an OD of 32 as determined by the slow light measurement and this OD is large enough such that the atom cloud can almost contain the entire Gaussian light pulse. Compared to the conventional MOT under the same trapping conditions, the OD is increased by about 2.7 folds by this simple method. In another MOT setup of the cigar-shaped Cs atom cloud, we achieve an OD of 105 as determined by the absorption spectrum of the |6S(1/2),F = 4>-->/6P(3/2),F' = 5> transition.

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We investigate the electron paramagnetic resonance (EPR) of VO 2+ ions in bis (glycinato) Mg (II) monohydrate single crystals at room temperature. Detailed EPR analysis indicates the presence of only one VO 2+ site. The vanadyl complexes are found to take up the substitutional position. The angular variation of the EPR spectra in three planes 𝑎 * 𝑏, 𝑏𝑐 and 𝑐𝑎 * are used to determine principal 𝑔 and 𝐴 tensors. The values of spin Hamiltonian parameters are 𝑔𝑥 = 2.1447 × 10 −4 , 𝑔𝑦 = 1.9974 × 10 −4 , 𝑔𝑧 = 1.9131 × 10 −4 , 𝐴𝑥 = 49 × 10 −4 , 𝐴𝑦 = 60 × 10 −4 , 𝐴𝑧 = 82×10 −4 cm −1 . The optical absorption study is also carried out at room temperature and absorption bands are assigned to various transitions. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental data. By correlating EPR and optical data, different molecular orbital coefficients are evaluated and the nature of bonding in the crystal is discussed.