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Magnetic Properties of Ni-Zn Ferrites by Citrate Gel method

Advances in Materials Physics and Chemistry 2012年第3期2卷 149-154页

作者： K. Rama Krishna K. Vijaya Kumar C. Ravindernathgupta Dachepalli Ravinder Department of Physics Government Polytechnic Nizamabad India Department of Physics Jawaharlal Nehru Technological University Hyderabad College of Engineering Hyderabad India Department of Physics Malla Reddy College of Engineering & Technology Secunderabad India Department of Physics Osmania University Hyderabad India

Ni-Zn ferrite with a nominal composition of Ni1-xZnxFe2O4 (x = 0, 0.2, 0.6, 0.8, 0.9) are prepared by citrate gel method and characterized by X-ray diffraction. Magnetic properties of all samples are obtained by using VSM (Vibrating Sample Magnetometer) in the range of 10 Koe. The saturation magnetization values of the samples are carried out from the B-H loop. The effect of composition on saturation magnetization and magnetic moment are studied in this paper. The results showed that Saturation magnetization and magnetic moment values increases gradually as Zn2+ composition increases, it reaches maximum value 70.28 emu/gm for (x = 0.6) and decreases further with increasing Zn2+ composition.

关键词： Ni-Zn Ferrites Citrate Gel method: Vibrating Sample Magneto Meter Saturation Magnetization Magnetic Moment

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Is it plausible to expect a close encounter of the Earth with a yet undiscovered astronomical object in the next few years?

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Natural Science 2010年第11期2卷 1181-1188页

作者： Lorenzo Iorio 不详

We analytically and numerically investigate the possibility that a still undiscovered body X, moving along an unbound hyperbolic path from outside the solar system, may penetrate its inner regions in the next few years posing a threat to the Earth. By conservatively using as initial position of X the lower bounds on the present‐day distance of X dynamically inferred from the gravitational perturbations induced by it on the orbital motions of the planets of the solar system, both the analyses show that, in order to reach the Earth’s orbit in the next 2 yr, X should move at a highly unrealistic speed , whatever its mass is. For example, by assuming for it a solar ( M ) or brown dwarf mass ( ), now at not less than kau (1 kau=1000 astronomical units), v would be of the order of and of the speed of light c, respectively. By assuming larger present‐day distances for X, on the basis of the lacking of direct observational evidences of electromagnetic origin for it, its speed would be even higher. Instead, the fastest solitary massive objects known so far, like hypervelocity stars (HVSs) and supernova remnants (SRs), travel at , having acquired so huge velocities in some of the most violent astrophysical phenomena like interactions with supermassive galactic black holes and supernova explosions. It turns out that the orbit of the Earth would not be macroscopically altered by a close (0.2 au) passage of such an ultrafast body X in the next 2 yr. On the contrary, our planet would be hurled into the space if a Sun‐sized body X would encounter it by moving at . On the other hand, this would imply that such a X should be now at just 20-30 au, contrary to all direct observational and indirect dynamical evidences.

关键词： Gravitation Celestial Mechanics Planet-Star Interactions methods: Analytical method: Numerical

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