Scientometric Evaluation of Sankhyá - the Indian Journal of Statistics

This paper analyses 199 peer-reviewed articles published in Sankhyā during 2003 to 2007. It examines authorship pattern, collaboration trend among authors, predominant areas of statistical research, and time lag in publications, prolific contributors, degree of collaboration, collaboration density, active sub-domains of statistics and time lag trend. Findings reveal that the number of articles reduced from 24.6% to 14.0% that conforms to the growth trend of statistical publications in India and the author productivity is not in agreement with Lotka’s law. The study also shown an average time lag of fifteen months to publish an article, and a declining trend of time lags following second-degree polynomial type has been observed in this scholarly journal

Chemical potential shift and gap-state formation in SrTiO3−δ_{3-\delta} revealed by photoemission spectroscopy

In this study, we report on investigations of the electronic structure of SrTiO$_3$ annealed at temperature ranging between 550 and 840$^\circ$C in an ultrahigh vacuum. Annealing induced oxygen vacancies (O$_{vac}$) impart considerable changes in the electronic structure of SrTiO$_3$. Using core-level photoemission spectroscopy, we have studied the chemical potential shift ($\Delta\mu$) as a function of annealing temperature. The result shows that the chemical potential monotonously increases with electron doping in SrTiO$_{3-\delta}$. The monotonous increase of the chemical potential rules out the existence of electronic phase separation in the sample. Using valence band photoemission, we have demonstrated the formation of a low density of states at the near Fermi level electronic spectrum of SrTiO$_{3-\delta}$. The gap-states were observed by spectral weight transfer over a large energy scale of the stoichiometric band gap of SrTiO$_3$ system leading finally to an insulator - metal transition. We have interpreted our results from the point of structural distortions induced by oxygen vacancies.Comment: 7 pages, 6 figures, 1 tabl

Novel optically active lead-free relaxor ferroelectric (Ba0.6Bi0.2Li0.2)TiO3

We discovered a near room temperature lead-free relaxor-ferroelectric (Ba0.6Bi0.2Li0.2)TiO3 (BBLT) having A-site compositional disordered ABO3 perovskite structure. Microstructure-property relations revealed that the chemical inhomogeneities and development of local polar nano regions (PNRs) are responsible for dielectric dispersion as a function of probe frequencies and temperatures. Rietveld analysis indicates mixed crystal structure with 80% tetragonal structure (space group P4mm) and 20% orthorhombic structure (space group Amm2) which is confirmed by the high resolution transmission electron diffraction pattern. Dielectric constant and tangent loss dispersion with and without illumination of light obey nonlinear Vogel-Fulture relation. It shows slim polarization-hysteresis (P-E) loops and excellent displacement coefficients (d33 ~ 233 pm/V) near room temperature, which gradually diminish near the maximum dielectric dispersion temperature (Tm). The underlying physics for light-sensitive dielectric dispersion was probed by X-ray photon spectroscopy (XPS) which strongly suggests that mixed valence of bismuth ions, especially Bi5+ ions, are responsible for most of the optically active centers. Ultraviolet photoemission measurements showed most of the Ti ions are in 4+ states and sit at the centers of the TiO6 octahedra, which along with asymmetric hybridization between O 2p and Bi 6s orbitals appears to be the main driving force for net polarization. This BBLT material may open a new path for environmental friendly lead-free relaxor-ferroelectric research.Comment: 23 pages, 5 figure

A Simple Analytical Model of a GaN MODFET to Study its DC and RF Performance

395-400This work presents a theoretical study of a GaN MODFET considering accurate velocity field relation of GaN for a wide range of electric field. The analytical expression of different DC parameters such as drain current, mutual conductance and drain conductance of the device has been derived and their variation over different field regions has been investigated. This work has also been extended to study the RF parameters like cut-off frequency and maximum operating frequency of the device. The threshold voltage of the device is also derived and studied in terms of the thickness of the doped AlGaN layer and mole fraction of AlGaN. The mathematical model presented here is calibrated with the experimentally available results reported earlier and a good agreement has been observed

Photoconductivity and photo-detection response of multiferroic bismuth iron oxide

We report visible light detection with in-plane BiFeO3 (BFO) thin films grown on pre-patterned inter-digital electrodes. In-plane configured BFO film displayed photocurrents with a 40:1 photo-to-dark-current ratio and improved photo-sensing ability for >15000 s (4 hrs) under small bias voltage (42V). Nearly sixty percent of the photo-induced charge carriers decay in 1.0 s and follow a double-exponential decay model. At 373 K the effect of light does not significantly increase the dark current, probably due to reduced mobility. Sub-bandgap weak monochromatic light (1 mw/cm2) shows one fold increase in photo-charge carriers.Comment: 18 pages, 7 figure

Scientometric evaluation of Sankhyá – the Indian Journal of Statistics

This paper critically analyses 199 peer-reviewed articles published in Sankhyā during 2003 to 2007. It examines authorship pattern, collaboration trend among authors, predominant areas of statistical research, and time lag in publications. Subsequent analysis focuses on prolific contributors, degree of collaboration, collaboration density, active sub-domains of statistics and time lag trend. Findings reveal the following: (a) the number of articles reduced from 24.6% to 14.0% that conforms to the growth trend of statistical publications in India; (b) single-authored paper counts only 30%, the rest in collaboration either by two-authors (47%) or three-to-fiveauthors (23%) and average authorship accounts for 1.96 per paper; (c) contributors of Sankhyā worked in highly collaborative manner and the degree of collaboration (CC=0.698) is quite significant; and (d) most of the bilateral and multilateral collaborations has emanated from 12 institutions of 5 different countries. Ranked list of prolific authors has been carried out using fractional counting method. It is observed that author productivity is not in agreement with Lotka’s law, but productivity distribution data partially fits the law when the value of approximated to 2.77 and the number of papers does not exceed two. Broad subject clusters, such as statistics (153) and probability theory (38) constituted about 96% of the contributed articles. Nonparametric inference (18%), parametric inference (15%), design of experiments (10%) and multivariate analysis (8%) are found to be active areas of research in statistics. The study shows an average time lag of fifteen months to publish an article, and a declining trend of time lags following second-degree polynomial type has been observed in this scholarly journal

Substitution driven structural and magnetic properties and evidence of spin phonon coupling in Sr-doped BiFeO3 nanoparticles

The manifestation of dimensionalities and Sr induced modifications in structural, vibrational and magnetic properties of Bi1-xSrxFeO3; (x = 0-0.25) nanoparticles synthesized by a tartaric acid based sol-gel route are reported. X-ray diffraction and electron microscopy studies reveal the phase purity and nanocrystalline nature (45-90 nm) of Bi1-xSrxFeO3 samples. The Sr ions substitution motivated the coexistance of rhombohedral (R3c) and pseudo tetragonal (P4/mmm) structural symmetry for the x = 0.25 sample which leads to enhancement of saturation magnetization due to the distorted cycloid spin structure and uncompensated surface spins, which is in concomitance with the electron paramagnetic resonance (EPR) and Mossbauer studies. The ferromagnetic ordering contribution continuously increases with increasing Sr content from x = 0-0.25 samples with a maximum saturation magnetization of 0.72 emu g(-1) for the x = 0.25 sample which is also endorsed by second order Raman modes. X-ray photoelectron and Mossbauer measurements confirmed the dominance of the Fe3+ oxidation state. Alteration in QS hyperfine parameters and line-width analysis have been probed by Mossbauer analysis with increasing Sr content in BiFeO3 nanoparticles suggesting the destruction of the spin cycloid