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U–Th–Pbtotal age determinations in monazite in a noritic anorthosite at the margin of the Koraput anorthosite pluton constrain the time of emplacement and sub-solidus chemical modifications in the Grenvillian-age anorthosite pluton in the Eastern Ghats Province (EGP), India. The monazites hosted within dynamically recrystallized orthopyroxene and plagioclase grains are large (50–500 μm in diameter) and complexly zoned. Based on the textural–chemical heterogeneities, these monazites are classified into three groups. Group-I monazites exhibit a low-ThO2 core mantled by a high-ThO2 rim. By contrast, the group-II monazites exhibit high-ThO2 cores laced by ThO2-poor mantles, and outermost rims with still lower ThO2 contents. Skeletal group-III monazites at polygonized grain/phase boundaries exhibit patchy and concentric zones with decreasing ThO2 towards the margin. The U–Th–Pbtotal chemical ages obtained using electron probe microanalyses exhibit four age clusters. The oldest age population (mean 939 ± 4.5 Ma) obtained in cores in group-I, II and III monazites with patchy zones corresponds with the emplacement of the Koraput anorthosite, and this age population is consistent with 980–930 Ma emplacement ages reported in other EGP anorthosite massifs. Younger monazites mantling the cores in group-II monazites and in group-III monazites with mean ages of 877 ± 5 Ma and 749 ± 18 Ma possibly reflect episodic monazite growth by fluid-aided dissolution–precipitation culminating with the disintegration of Rodinia at ~750 Ma. The youngest age population (mean 574 ± 19 Ma) in the outermost monazite rims and monazite veins represents renewed monazite growth during the Pan African assembly of the Grenvillian-age EGP domain with the proto-Indian cratons.
The first few binary pulsars revealed the richness of evolution possible in binary systems containing neutron stars. Products of different evolutionary routes, in high and low mass binaries, as well as examples of evolution affected by the pulsar wind were among the first ten objects discovered. This article presents a historical review of the impact of binary pulsars on the early development of ideas regarding the evolution of neutron stars in binary systems.
Crab Pulsar (PSR B0531+21) is known to emit pulsed emission in all bands of the electromagnetic spectrum. It also emits giant radio pulses (GRPs) frequently, which are roughly a hundred to million times brighter than the normal pulses. We aim to study whether there is a significant X-ray enhancement correlated with the occurrence of GRPs, using simultaneous observations with the ASTROSAT, the Giant Meterwave Radio telescope (1300 MHz) and the Ooty Radio telescope (325 MHz). This required determination of fixed pipeline offsets between different instruments. We find the offset between ASTROSAT and GMRT to be −30.181 ± 0.095 ms and that between ASTROSAT and ORT to be −18.4 ± 0.2 ms. Our preliminary results with 1300 MHz data also show a break in pulse intensity distribution at ~ 33 Jy in the main pulse and ~ 28 Jy in the inter-pulse.
Direct solar flare neutrons are a valuable diagnostic of high-energy ion acceleration in these events, and COMPTEL improves over all previous cosmic neutron detectors in its capacity for neutron energy measurement. Previous studies of COMPTEL neutron data have worked with an incomplete model of the instrumental response, applying energy-by-energy detection efficiencies. Here we employ statistical regularisation techniques with the full (Monte Carlo simulation derived) response matrix to produce improved estimates of neutron numbers and energy distribution. These techniques are applied to data from the well-observed 15 June 1991 flare. Our improved treatment of the instrumental response results in a reduction of 73% in total neutron numbers, compared with previously deduced values. Implications for the picture of primary ion acceleration in this flare are briefly discussed.
Radiation-tolerant materials, sensors and electronics can enable lightweight space subsystems with reduced packaging requirements and increased operation lifetimes. Such technology can be used within extreme harsh environments related to space exploration, radiation medicine and power generation (combustion and nuclear). Gallium nitride (GaN), a ceramic semiconductor material, is a candidate material due to its stability within high-radiation, high-temperature and chemically corrosive environments. In addition, the wide bandgap of GaN (3.4 eV) can be leveraged for ultraviolet (UV) wavelength photodetection. In metal-semiconductor-metal (MSM) photodetector architectures using Schottky contacts, transparent electrodes (e.g., graphene) can increase sensitivity and improve overall device response. Here we present fabrication and characterization of GaN-based UV photodetectors using graphene electrodes irradiated up to 200 krad total ionizing dose (TID) then tested under UV light and dark conditions. For current-voltage measurements taken at 90, 120 and 200 krad TID, the current-voltage response does not vary significantly. From 90 to 120 krad TID, the responsivity shifts by 2% before dropping off at 200 krad TID. These initial findings suggest that graphene/GaN MSM UV photodetectors can provide robust operation within extreme harsh environments.
This study is a part of the surveillance study on childhood diarrhoea in the Andaman and Nicobar Islands; here we report the drug resistance pattern of recent isolates of Shigella spp. (2006–2011) obtained as part of that study and compare it with that of Shigella isolates obtained earlier during 2000–2005. During 2006–2011, stool samples from paediatric diarrhoea patients were collected and processed for isolation and identification of Shigella spp. Susceptibility to 22 antimicrobial drugs was tested and minimum inhibitory concentrations were determined for third-generation cephalosporins, quinolones, amoxicillin-clavulanic acid combinations and gentamicin. A wide spectrum of antibiotic resistance was observed in the Shigella strains obtained during 2006–2011. The proportions of resistant strains showed an increase from 2000–2005 to 2006–2011 in 20/22 antibiotics tested. The number of drug resistance patterns increased from 13 in 2000–2005 to 43 in 2006–2011. Resistance to newer generation fluoroquinolones, third-generation cephalosporins and augmentin, which was not observed during 2000–2005, appeared during 2006–2011. The frequency of resistance in Shigella isolates has increased substantially between 2000–2006 and 2006–2011, with a wide spectrum of resistance. At present, the option for antimicrobial therapy in shigellosis in Andaman is limited to a small number of drugs.
Sb2O3, Sb-metal, Bi2O3 or Bi-metal, powders were mixed with MgB2 powder. Starting compositions were ((MgB2)(M2O3)x, x = 0.0025, 0.005, 0.015, and (MgB2)(M)y, y = 0.01, M = Sb, Bi. Mixtures were processed by Spark Plasma Sintering (SPS) technique. As obtained composite samples show high density, above 94% of the theoretical density. While the secondary phases indicate on similar reactions, samples show different behavior vs. addition type and amount. This does not directly correlate with the melting temperature of the addition. From the critical current density (Jc) and irreversibility field (Hirr) enhancement viewpoints, optimum additions are oxides for x=0.025, 0.005. Both oxides are improving Jc at high fields, but Sb2O3 is effective up to 10 K, while Bi2O3 is up to 30 K. Metal additions are decreasing Jc and Hirr when compared to pristine MgB2sample.
Prior to 2009 dengue fever had not been reported in the Andaman and Nicobar archipelago. In 2009, a few patients with dengue fever-like illness were reported, some of whom tested positive for dengue antibodies. In 2010, 516 suspected cases were reported, including some with dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS); 80 (15·5%) were positive for dengue antibodies. DENV RNA was detected in five patients and PCR-based typing showed that three of these belonged to serotype 1 and two to serotype 2. This was confirmed by sequence typing. Two clones of dengue virus, one belonging to serotype 1 and the other to serotype 2 appeared to be circulating in Andaman. Emergence of severe diseases such as DHF and DSS might be due to recent introduction of a more virulent strain or because of the enhancing effect of sub-neutralizing levels of antibodies developed due to prior infections. There is a need to revise the vector-borne disease surveillance system in the islands.
Using 0.5 ps pulses of 5.9 eV light to excite electron-hole concentrations varied up to 2x1020 e-h/cm3 corresponding to energy deposition within electron tracks, we measure dipole-dipole quenching rate constants K2 in SrI2 and CsI. We previously reported determination of K2 directly from the time dependence of quenched STE luminescence in CsI. The nonlinear quenching rate decreases rapidly within a few tens of picoseconds as the host excitation density drops below the Förster threshold. In the present work, we measure the dependence of integrated light yield on excitation density in the activated scintillators SrI2:Eu2+ and CsI:Tl+. The “z-scan” method of yield vs. irradiance is applicable to a wider range of materials, e.g. when the quenching population is not the main light-emitting population. Furthermore, because of using an integrating sphere and photomultiplier for light detection, the signal-to-noise is substantially better than the time-resolved method using a streak camera. As a result, both 2nd and 3rd orders of quenching (dipole-dipole and Auger) can be distinguished. Detailed comparison of SrI2 and CsI is of fundamental importance to help understand why SrI2 achieves substantially better proportionality than CsI in scintillator applications. The laser measurements, in contrast to scintillation, allow evaluating the rate constants of nonlinear quenching in a population which has small enough spatial gradient to suppress the effect of carrier diffusion.
Independent outbreaks of dengue virus (DENV) infection and sporadic cases of chikungunya virus (CHIKV) have been recorded in the metropolitan city of Delhi on several occasions in the past. However, during a recent 2010 arboviral outbreak in Delhi many cases turned negative for DENV. This prompted us to use duplex reverse transcriptase–polymerase chain reaction (D-RT–PCR) to establish the aetiology of dengue/chikungunya through sequencing of CprM and E1 genes of dengue and chikungunya viruses. Interestingly, for the first time, both DENV and CHIKV co-circulated simultaneously and in equally dominant proportion during the post-monsoon period of 2010. DENV-1 genotype III and the East Central South African genotype of CHIKV were associated with post-monsoon spread of these viruses.
The effect of anthanum substitution (0-20%) on phase formation, structural evolution and electrical properties of SrBi2Ta2O9 (SBT) ceramics were investigated. X-ray diffraction studies revealed that phase pure SBT bulk samples can be synthesized with lanthanum doping without any phase segregation. Raman spectroscopy was used to understand the lattice vibrational characteristics of La substituted SBT compound. The ferroelectric soft mode at 27 cm−1 was shifted towards the lower frequencies at room temperature with increase in La concentrations. The octahedral stretching mode (O-Ta-O) did not influenced by La substitution in SBT. The x-ray photoemission spectroscopy measurements showed the decrease of binding energy of Bi 4f core levels (5/2 and 7/2) upon La substitution in SBT. The dielectric constant was increased from 120 to 190 up to 10% La doping and decreased with further increase in La concentration.
Zinc oxide (ZnO) nanorods were fabricated directly on silicon substrate with diameters in the range of 70-350 nm and up to 15 νm long using pulsed-laser deposition at a relatively low processing temperature (450°C) without any catalytic template. The influences of substrate temperatures and the oxygen pressures on the formation of ZnO nanorods were investigated. The Raman scattering studies and scanning electron microscopy results indicated that the ZnO nanorods were well aligned along c-axis and isolated from each other. The additional Raman modes at ∼ 477 cm−1 and 574 cm−1 were observed in the c-axis oriented ZnO nanorods which attributed to the activation of the upper and lower surface phonon modes respectively.
We have grown SrBi2Ta2O9 (SBT) thin films on various bottom electrodes such as Pt/TiO2/SiO2/Si (Pt) and LaNiO3/Pt/TiO2/SiO2/Si (LNO) substrates. The substrate temperature and oxygen pressure for the SBT film was maintained at 500 °C and 200 mTorr. As-grown films were post-annealed at a temperature of 800 °C. X-ray diffraction studies revealed that as-grown films were amorphous and crystallized to single phase after annealing. The difficulty of obtaining lowest Raman modes of SBT on platinized silicon substrate was overcome by using conducting oxide electrodes. Films grown on platinized silicon showed maximum value of remanent polarization (2Pr ∼ 21.5 μC/cm2) with coercive field (Ec) of ∼ 67 kV/cm. The degradation of ferroelectric properties of the films was observed with the introduction of 50 nm conducting LaNiO3 electrode at the interface of Pt and SBT film, which was attributed to high resistivity of the oxide electrode layers. Leakage current density was studied with the consideration of the Schottky emission model. The barrier height of the films grown on Pt and LNO were estimated to be 1.27 eV and 1.12 eV, respectively. The reduction of barrier height was attributed to the lower work function of the LNO electrode.
Nanodispersed lead in metallic and amorphous matrices was synthesized by rapid solidification processing. The optimum microstructure was tailored to avoid percolation of the particles. With these embedded particles it is possible to study quantitatively the effect of size on the superconducting transition temperature by carrying out quantitative microstructural characterization and magnetic measurements. Our results suggest the role of the matrices in enhancement or depression of superconducting transition temperature of lead. The origin of this difference in behavior with respect to different matrices and sizes is discussed.
The multilayers of ferroelectric (FE) Pb(Zr, Ti)O3 (PZT) and ferromagnetic (FM) CoFe2O4 (CFO) thin films with 3, 5, and 9 layers having configurations PZT/CFO (PC) and CFO/PZT (CP) were fabricated by pulsed laser deposition technique. We have investigated the effect of inter-diffusion at the interface of multilayers (MLs) and reversing the order of FE and FM layers in the multilayers configuration on the electrical/magnetic properties. The TEM of the films showed that the layer structure was not maintained and the inter-diffusion of the CFO into PZT and vice verse were observed at the interface of MLs. Both the PC and CP configurations of multilayer films exhibited pseudo FE hysteresis loop and proper FM hysteresis loops at room temperature. Reversing the multilayer configuration from CP to PC resulted in increasing the pseudo remanent polarization, however this behavior was not observed in magnetic properties. The frequency and temperature dependences of the impedance and modulus spectroscopy of the multilayer PC and CP films were studied in the ranges of 102 to 106 Hz and 200 to 650 K respectively. The electrical response of all multilayer films investigated could be resolved into two contributions. We attributed these to the grain and grain boundary effects in impedance and modulus formalism. We found that the difference between the grain and grain boundary capacitive effect decreased due to increase of the number of layers.
Transition metal doped (Mn, Fe and V) ZnO ceramics and their thin films were prepared by pulsed laser deposition on glass substrates. The ceramic targets did not show any additional phase formation from XRD measurement, except for high Fe concentrations. Optical absorption showed sub-band gap absorption for Mn doping. The band gap was shifted by 0.06 eV for V doped ZnO as concentration was increased to 10%. Micro Raman spectra showed some defect induced modes for all the transition metals doped ZnO ceramics. In V doped ZnO ceramics there was two phonon induced resonance Raman scattering with increase in dopant concentrations. Raman spectra for thin films did not show any significant additional modes for Mn and Fe. However V doped ZnO thin films showed an additional mode for concentration ≥5 %.
The dielectric response of La- and Dy- doped BiFeO3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25 °C to 300 °C. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed ‘N’-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present.
Lattice dynamical and electronic transition changes due to V and Co doped ZnO have been investigated using optical techniques. Vanadium and Co doped ZnO pellets were prepared using conventional ceramic processing route and thin films were fabricated by pulsed laser deposition. Raman spectra of Zn1-xVxO targets showed many additional peaks in the range of 230 to 350 cm-1 and 750 to 900 cm-1. Integrated intensities of these additional modes decreased with increase of temperature as similar to the host ZnO modes, which precludes electronic Raman scattering to be the origin. Raman peaks for stoichiometric Zn3(VO4)2 and Zn2V2O7 compounds also had additional peaks that can be attributed to the secondary phases formed in the compositions of Zn1-xVxO. Raman spectra of Zn1-xCoxO showed no additional modes besides ZnO modes, however, the intensity of the second order peak at 540 cm-1 was increased due to Co doping. Thin films of Zn1-xCoxO exhibited highly c-axis orientation deposited on (001)Al2O3 substrates. The optical absorption of the films showed that the band gap decreased with increase of Co concentrations at room temperature along with the sub bandgap absorptions due to d-d transitions of Co2+.
To understand amorphous and structurally disordered materials requires the application of a wide-range of advanced physical probe techniques and herein a combined methodology is outlined. The relatively short-range structural sensitivity of solid state NMR means that it is a core probe technique for characterizing such materials. The aspects of the solid state NMR contribution are emphasized here with examples given from a number of systems, with especial emphasis on the information available from 17O NMR in oxygen-containing materials. 17O NMR data for crystallization of pure sol-gel prepared oxides is compared, with new data presented from In2O3 and Sc2O3. Sol-gel formed oxide mixtures containing silica have been widely studied, but again the role and effect of the other added oxide varies widely. In a ternary ZrO2-TiO2-SiO2 silicate sol-gel the level of Q4 formation is dependent not only on the composition, as expected, but also the nature of the second added oxide. Sol-gel formed phosphates have been much less widely studied than silicates and some 31P NMR data from xerogel, sonogel and melt-quench glasses of the same composition are compared. The effect of small amounts of added antibacterial copper on phosphate glass networks is also explored.
Al2O3 and ZrO2 substrates were coimplanted with 175 keV Mo+ and 74 keV S+ at doses of 1×10 cm−2 and 2×1017 cm−2 respectively. The energies of Mo+ and S+ ions were chosen to provide a nearly overlapping depth profiles in both substrates. Rutherford backscattering (RBS), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques were used for characterization. The as implanted surface of Al2O3 became amorphous while as implanted ZrO2 surface remained crystalline. The MoS2 phase was observed in the as implanted ZrO2. The MoS2 phase was observed in the implanted region of Al2O3 and ZrO2 after furnace annealing at 700°C. Thermodynamic calculations were performed to predict the equilibrium binary phase formed in Al2O3 and ZrO2 under the present implant and annealing conditions. The predictions agree with the experimental findings.