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X-RAY ASTRONOMY EXPERIMENT ON THE INDIAN SATELLITE IRS-P3
AGRAWAL P. C.,PAUL B.,RAO A. R.,SHAH M. R.,MCKERJEE K.,VARIA M. N.,YADAV J. S.,DEDHIA D. K.,MALKAR J. P.,SHAH P.,DAMLE S. V.,MARAR T. M. K.,SEETHA S. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
An x-ray astronomy experiment consisting of three collimated proportional counters and an X-ray Sky Monitor (XSM) was flown aboard the Indian Satellite IRS-P3 launched on March 21, 1996 from SHAR range in India. The Satellite is in a circular orbit of 830 km altitude with an orbital inclination of $98^{\circ}$ and has three axis stabilized pointing capability. Each pointed-mode Proportional Counter (PPC) is a multilayer, multianode unit filled with P-10 gas ($90\%$ Ar + $10\%\;CH_4$) at 800 torr and having an aluminized mylar window of 25 micron thickness. The three PPCs are identical and have a field of view of $2^{\circ}{\times}2^{\circ}$ defined by silver coated aluminium honeycomb collimators. The total effective area of the three PPCs is about 1200 $cm^2$. The PPCs are sensitive in 2-20 keV band. The XSM consists of a pin-hole of 1 $cm^2$ area placed 16 cm above the anode plane of a 32 cm$\times$32 cm position sensitive proportional counter sensitive in 3-8 keV interval. The position of the x-ray events is determined by charge division technique using nichrome wires as anodes. The principal objective of this experiment is to carry out timing studies of x-ray pulsars, x-ray binaries and other rapidly varying x-ray sources. The XSM will be used to detect transient x-ray sources and monitor intensity of bright x-ray binaries. Observations of black-hole binary Cyg X-1 and few other binary sources were carried out in early May and July-August 1996 period. Details of the x-ray detector characteristics are presented and preliminary results from the observations are discussed.
Magnetic Behaviour of Granular GdMnO3 Film
Negi, P.,Agrawal, H. M.,Singh, J. P.,Kumar, H.,Srivastava, R. C.,Asokan, K.,Chae, K. H. Springer Science + Business Media 2017 Journal of superconductivity and novel magnetism Vol.30 No.6
<P>The present study deals with the investigation of magnetic properties along with morphological and microstructure analyses of a multiferroic GdMnO3 film fabricated on Si(100) substrate by the pulsed laser deposition technique. Rutherford backscattering spectroscopic analysis suggests that the film is fabricated in the form of diffused layers having different stoichiometric proportions. Raman spectroscopy signifies that few modes present in the film are associated with MnO6 octahedra and some extra peaks indicating the mixed phase formation in tuning with the Rutherford backscattering spectroscopy. Atomic force microscopy confirms the granular nature of the film. Field-cooled and zero-field-cooled thermal magnetization curves show irreversible behaviour extending well above room temperature, which is associated with spin disorder. The presence of Gd+3 state and Mn+3/Mn+4 mixed states in the uppermost layers of the film was confirmed by near-edge X-ray absorption fine structure. Subsequently, in association with these observations, the film is a weak ferromagnetic at 5 K and even at room temperature.</P>
HARD X-RAY PULSATIONS IN GX 1+4
AGRAWAL P. C.,PAUL B.,RAO A. R.,CHANDA R. K. MAN The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
The x-ray pulsar GX 1+4 was observed by us in four balloon- borne experiments carried out from Hyderabad, India during 1991-1995 period with a hard x-ray telescope. The x-ray telescope consists of two collimated large area xenon-filled proportional counters with an effective area of $2400 cm^2$, a field of view of $5^{\circ}{\times}5^{\circ}$ and sensitive in the energy band of 20 - 100 keV. The pulsar was detected in bright state in two of the four experiments and x-ray pulsations with 120 second period were detected clearly. Pulsation period, rate of change of period with time, pulse fraction, pulse profile and energy spectra of the source were determined from these studies. During March 1995 observation, the x-ray pulse of GX 1+4 was found to be double-peaked compared to a single-peak pulse profile detected in December 1993. Details of these results are presented and their interpretation discussed in terms of the current accretion models of x-ray binaries.
Agrawal, Anju,Sailani, Riya,Gupta, Beena,Khandelwal, C.L.,Sharma, P.D. Korean Chemical Society 2012 대한화학회지 Vol.56 No.2
The kinetics of oxidation of nicotinic acid by peroxomonosulfate (PMS) has been studied in acetate buffers. Stoichiometry of the reaction corresponds to the reaction of one mole of the oxidant with a mole of nicotinic acid. N${\rightarrow}$O product has been confirmed both by UV visible and IR spectroscopy. The reaction is second order viz. first order with respect to each reactant. Activation parameters have also been evaluated. A plausible reaction mechanism is mentioned and the derived kinetic rate law accounts for experimental observations.
Structural and magnetic study of dysprosium substituted cobalt ferrite nanoparticles
Kumar, H.,Srivastava, R.C.,Pal Singh, J.,Negi, P.,Agrawal, H.M.,Das, D.,Hwa Chae, K. North-Holland Pub. Co 2016 Journal of magnetism and magnetic materials Vol.401 No.-
The present work investigates the magnetic behavior of Dy<SUP>3+</SUP> substituted cobalt ferrite nanoparticles. X-ray diffraction studies reveal presence of cubic spinel phases in these nanoparticles. Raman spectra of these nanoparticles show change in intensity of Raman bands, which reflects cation redistribution in cubic spinel lattice. Saturation magnetization and coercivity decrease with increase of Dy<SUP>3+</SUP>concentration in these nanoparticles. Room temperature Mossbauer measurements show the cation redistribution in these nanoparticles and corroborates the results obtained from Raman Spectroscopic measurements. Decrease in magnetization of Dy<SUP>3+</SUP> substituted cobalt ferrite is attributed to the reduction in the magnetic interaction and cation redistribution.
Consequences of electronic excitations in CoFe<sub>1.90</sub>Dy<sub>0.10</sub>O<sub>4</sub>
Kumar, H.,Singh, J.P.,Srivastava, R.C.,Negi, P.,Agrawal, H.M.,Asokan, K.,Won, S.O.,Chae, K.H. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.12
Present work reports the irradiation induced effects in Dy<SUP>3+</SUP> doped cobalt ferrite nanoparticles in the regime of dominant electronic excitation processes induced by 100 MeV O<SUP>7+</SUP> ion irradiation. Irradiation leads to the deterioration of crystalline phase as envisaged by X-ray diffraction. Crystallite size decreases with the increase of irradiation fluence. Disappearance of certain bands in Raman spectra at higher fluence of irradiation confirms the crystalline disorder induced by electronic excitations. Fourier transform infrared spectra show onset of cation migration from tetrahedral site to octahedral site and vice versa. X-ray absorption fine structure measurements depict the preservation of valence state of metal ions after irradiation. These measurements further infer bond breaking process in irradiated materials. Magnetic measurements carried out on these materials indicate slight increase of saturation magnetization at room temperature followed by the decrease of coercive field. Obtained results are discussed on the basis of appropriate mechanism.
Consequences of electronic excitations in CoFe1.90Dy0.10O4
Hemaunt Kumar,Jitendra Pal Singh,R.C. Srivastava,P. Negi,H.M. Agrawal,Kandasami Asokan,원성옥,채근화 한국물리학회 2015 Current Applied Physics Vol.15 No.12
Present work reports the irradiation induced effects in Dy3þ doped cobalt ferrite nanoparticles in the regime of dominant electronic excitation processes induced by 100 MeV O7þ ion irradiation. Irradiation leads to the deterioration of crystalline phase as envisaged by X-ray diffraction. Crystallite size decreases with the increase of irradiation fluence. Disappearance of certain bands in Raman spectra at higher fluence of irradiation confirms the crystalline disorder induced by electronic excitations. Fourier transform infrared spectra show onset of cation migration from tetrahedral site to octahedral site and vice versa. X-ray absorption fine structure measurements depict the preservation of valence state of metal ions after irradiation. These measurements further infer bond breaking process in irradiated materials. Magnetic measurements carried out on these materials indicate slight increase of saturation magnetization at room temperature followed by the decrease of coercive field. Obtained results are discussed on the basis of appropriate mechanism.