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91.
R. Shukla R. S. Ningthoujam S. S. Umare S. J. Sharma Sajith Kurian R. K. Vatsa A. K. Tyagi N. S. Gajbhiye 《Hyperfine Interactions》2008,184(1-3):217-225
Co1???x Ag x Fe2O4 nanoparticles have been prepared by the combustion route. The average crystallite sizes for compositions with x = 0 and 0.2 are found to be 36 and 33 nm respectively from the XRD line broadening. Compared to the pure CoFe2O4, Ag-doping reduces the intrinsic magnetization values (M, M r), but enhances coercivity (H c). Mössbauer spectra show two sextets, indicating occupancies of tetrahedral and octahedral sites by Fe3?+?. Hyperfine fields of 505 and 477 kOe in pure CoFe2O4 have been found for octahedral and tetrahedral sites respectively at liquid nitrogen temperature. The hyperfine field decreases with Ag-doping which also corroborates the magnetization studies. EPR study confirms the room temperature ferromagnetic behavior for Co1???x Ag x Fe2O4 (x = 0.2). The room temperature Mössbauer studies on x?=?0.0 and 0.2 show the ferromagnetic sextets (95%) along with superparamagnetic doublet (5%). However, x = 0.6 sample shows the ferromagnetic sextets only at room temperature. Highly Ag doped samples could be useful for the fabrication of the high-density magnetic materials as well as magnetic drug delivery. 相似文献
92.
Sarita Rai Sajith Kurian V. N. Dwivedi S. S. Das N. B. Singh N. S. Gajbhiye 《Hyperfine Interactions》2009,188(1-3):19-24
Effect of different concentrations of naturally occurring admixture in the form of fine powder of black gram pulse (BGP) on the hydration of Portland cement was studied by isothermal calorimetry and 57Fe Mössbauer spectroscopy. The spectra were recorded for anhydrous cement and the hydration products at room temperature and 77 K. In the presence of BGP, the spectra showed superparamagnetic doublets at room temperature and the sextet at 77 K, due to the presence of fine particles of iron containing component. Mössbauer studies of hydration products confirmed the formation of nanosize hydration products containing Fe3?+?. The isomer shift (δ) and the quadrupole splitting (ΔE Q) values of C4AF in the cement confirmed iron in an octahedral and tetrahedral environment with +3 oxidation state. The high value of quadrupole splitting showed the high asymmetry of the electron environment around the iron atom. The overall mechanism of the hydration of cement in presence of BGP is discussed. 相似文献
93.
E. Muhammad Abdul Jamal P. Mohanan P. A. Joy Philip Kurian M. R. Anantharaman 《Applied Physics A: Materials Science & Processing》2009,97(1):157-165
Nickel–rubber nanocomposites were synthesized by incorporating ferromagnetic nickel nanoparticles in a natural rubber as well
as neoprene rubber matrix. Complex dielectric permittivity and magnetic permeability of these composites were evaluated in
the X-band microwave frequencies at room temperature using cavity perturbation technique. The dielectric loss in natural rubber
is smaller compared to neoprene rubber. A steady increase in the dielectric permittivity is observed with increase in the
content of nickel in both the composites. The magnetic permeability exhibits a steady decrease with increase in frequency
and magnetic loss shows a relaxation at 8 GHz. The suitability of these composites as microwave absorbers is modeled based
on the reflection loss which is dependant on the real and imaginary components of the complex dielectric permittivity and
magnetic permeability. 相似文献
94.
A solitary structure of quasi-static electromagnetic pulse is formed in moderate density plasmas by a propagation of ultra-intense
and ultra-short laser pulse, which is formed after the laser pulse is depleted and slowly propagates in the laser propagation
direction. The structure is sustained by huge magnetic pressure and compensating electric field which are in an electromagnetic
equilibrium together with the plasma motion. The solitary structure is formed when the resonance condition is satisfied and
laser intensity is high enough to induce huge magnetic field pressure. 相似文献
95.
S. Ter-Avetisyan M. Schnürer T. Sokollik P. V. Nickles W. Sandner U. Stein D. Habs T. Nakamura K. Mima 《The European physical journal. Special topics》2009,169(1):117-121
The complex dynamical behavior of the electron sheath in laser driven ion acceleration leads to variations in ion beam pointing
and ion energy modulation. These processes are derived from high resolution particle spectroscopy and 2D-PIC simulations.
The phenomena arise from ion source movement if laser irradiation occurs at oblique incidence. Different laser absorption
processes act in dependence on laser parameter which determines the ion acceleration. 相似文献
96.
In this letter we consider dipole-mediated correlations between DNA and enzymes in the context of their water environment. Such correlations emerge from electric dipole-dipole interactions between aromatic ring structures in DNA and in enzymes. We show that there are matching collective modes between DNA and enzyme dipole fields, and that a dynamic time-averaged polarization vanishes in the water dipole field only if either DNA, enzyme, or both are absent from the sample. This persistent field may serve as the electromagnetic image that, in popular colloquialisms about DNA biochemistry, allows enzymes to “scan” or “read” the double helix. Topologically nontrivial configurations in the coherent ground state requiring clamplike enzyme behavior on the DNA may stem, ultimately, from spontaneously broken gauge symmetries. 相似文献
97.
Liquid phase benzylation of benzene with benzyl chloride was investigated over different compositions of cobalt zinc ferrite (CoxZn1-xFe2O4, x-0.0, 0.25, 0.5, 0.75, 1.0) nano composites, synthesized by sol–gel method. The un-substituted cobalt ferrite catalyst exhibited excellent activity among the series effecting complete conversion of benzyl chloride in 60?min at 90?°C with 100% selectivity for diphenyl methane. The effect of various reaction parameters on the reaction was studied. Higher benzylation activity of cobalt ferrite nanocomposite is attributed to the presence of higher quantities of moderately acidic sites and a good correlation was observed between surface acidity and benzylation activity of catalysts. The catalysts are reusable without any significant structural change as indicated by X-ray Diffraction (XRD) and Atomic Absorption Spectrophotometer (AAS). 相似文献
98.
Powerful coherent emission around the plasma oscillation frequency can be produced from a laser wakefield through linear mode conversion. This occurs when the laser pulse is incident obliquely to the density gradient of inhomogeneous plasmas. The emission spectrum and conversion efficiency are obtained analytically, which are in agreement with particle-in-cell simulations. The emission can be tuned to be a radiation source in the terahertz region and with field strengths as large as a few GV/m, suitable for high-field applications. The emission also provides a simple way to measure the wakefield produced for particle acceleration. 相似文献
99.
Kurian A George SD Nampoori VP Vallabhan CP 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(13-14):2799-2802
A sensitive method based on the principle of photothermal phenomena to study the energy transfer processes in organic dye mixtures is presented. A dual beam thermal lens method can be very effectively used as an alternate technique to determine the molecular distance between donor and acceptor in fluorescein-rhodamine B mixture using optical parametric oscillator. 相似文献
100.
Sheng Z Sentoku Y Mima K Zhang J Yu W Meyer-ter-Vehn J 《Physical review letters》2000,85(25):5340-5343
We study the angular distributions of fast electrons, ions, and bremsstrahlung x/ gamma-rays generated during the interaction of an ultrashort intense laser pulse with solid targets. A relation is found on the angular directions for fast electrons and ions as a function of the particle's kinetic energy, experienced Coulomb potential changes, and the incident angle of the laser pulse. It is valid independent of the acceleration mechanisms and the polarization of the laser pulse, as confirmed by particle-in-cell simulations. The angular distribution of bremsstrahlung x/gamma-rays is presented to show explicitly its correlation with the corresponding angular distributions of electrons. 相似文献