257 research outputs found
Transient simulation of LBE cooled CHTR under natural circulation with 3D multi-physics code ARCH-TH
India is developing a 100kWth Compact High Temperature Reactor (CHTR) to facilitate demonstration of technologies for high temperature process heat applications. CHTR is being designed as thorium based TRISO fueled and beryllium oxide moderated prismatic block type vertical core cooled with lead-bismuth eutectic (LBE) under natural circulation for 1000°C outlet. The new concept of high temperature core requires multi-physics multi-scale modeling based tools for investigating the normal operational behavior as well as anticipated transients of CHTR. In view of that, 3D multi-physics code ARCH-TH is being indigenously developed and validated for coupled neutronics-thermal hydraulic benchmarks. The multi-group diffusion based neutron kinetics in code ARCH-TH is integrated with thermal-hydraulic (TH) capability considering 1D- radial heat conduction in multi-channel system. The 1D based hydraulic in the code is capable to simulate the natural circulation phenomena of coolant in coupled parallel multi-channel system. The steady state operation and case of unprotected transient of control rod withdrawal in CHTR have been simulated with ARCH-TH. The rising transient power in CHTR is being assumed to be arrested with temperature feedbacks in the core cooled with natural circulation of molten metal coolant LBE. The variation of several key parameters defining neutronics and thermal hydraulics of CHTR have been predicted and discussed in detail. It has been found that peak fuel and coolant temperatures are well within the safety limits during transient of inadvertent withdrawal of control rod in CHTR operating at full power during initial core life cycle
Electrical, Thermal and Spectroscopic Characterization of Bulk Bi2Se3 Topological Insulator
We report electrical (angular magneto-resistance, and Hall), thermal (heat
capacity) and spectroscopic (Raman, x-ray photo electron, angle resolved photo
electron) characterization of bulk Bi2Se3 topological insulator, which is being
is grown by self flux method through solid state reaction from high temperature
(950C) melt and slow cooling (2C/hour) of constituent elements. Bi2Se3
exhibited metallic behaviour down to 5K. Magneto transport measurements
revealed linear up to 400% and 30% MR at 5K under 14 Tesla field in
perpendicular and parallel field direction respectively. We noticed that the
magneto-resistance (MR) of Bi2Se3 is very sensitive to the angle of applied
field. MR is maximum when the field is normal to the sample surface, while it
is minimum when the field is parallel. Hall coefficient (RH) is seen nearly
invariant with negative carrier sign down to 5K albeit having near periodic
oscillations above 100K. Heat capacity (Cp) versus temperature plot is seen
without any phase transitions down to 5K and is well fitted (Cp = gammaT +
betaT3) at low temperature with calculated Debye temperature (ThetaD) value of
105.5K. Clear Raman peaks are seen at 72, 131 and 177 cm-1 corresponding to
A1g1, Eg2 and A1g2 respectively. Though, two distinct asymmetric characteristic
peak shapes are seen for Bi 4f7/2 and Bi 4f5/2, the Se 3d region is found to be
broad displaying the overlapping of spin - orbit components of the same.
Angle-resolved photoemission spectroscopy (ARPES) data of Bi2Se3 revealed
distinctly the bulk conduction bands (BCB), surface state (SS), Dirac point
(DP) and bulk valence bands (BVB) and 3D bulk conduction signatures are clearly
seen. Summarily, host of physical properties for as grown Bi2Se3 crystal are
reported here.Comment: 6 Pages Text + Figs; Comments Suggestions welcom
Unexplored photoluminescence from bulk and mechanically exfoliated few layers of Bi2Te3
We report the exotic photoluminescence (PL) behaviour of 3D topological
insulator Bi2Te3 single crystals grown by customized self-flux method and
mechanically exfoliated few layers (18 plus minus 2 nm)/thin flakes obtained by
standard scotch tape method from as grown Bi2Te3 crystals.The experimental PL
studies on bulk single crystal and mechanically exfoliated few layers of Bi2Te3
evidenced a broad red emission in the visible region. These findings are in
good agreement with our theoretical results obtained using the ab initio
density functional theory framework.Comment: Main MS (17 Pages text including 4 Figs): Suppl. info. (4 pages);
Accepted Scientific Report
Observation of inverse a. c. Josephson effect in bulk Y-Ba-Sr-Cu-O up to room temperature
Microwave induced d.c. voltage due to inverse a.c. Josephson effect has been observed across bulk samples of multiphase Y2BaSrCu3O8. Results indicate that weakly coupled superconducting grains probably exist up to 26°C
Comparison of Rates of Fast and Catastrophic Visual Field Loss in Three Glaucoma Subtypes.
Purpose:To compare the distribution of visual field progression rates in three subgroups of glaucoma, being primary angle-closure glaucoma (PACG), POAG, and juvenile open-angle glaucoma (JOAG). Methods:We assessed glaucoma patients treated in an Indian tertiary care setting with at least four visual field assessments. We determined rates from a single eye of each of 525 patients using linear regression of the summary index mean deviation (MD) over time. The main outcome measures were the proportions of fast (<-1.0 to -2.0 dB/y) and catastrophic (<-2 dB/y) visual field progression. Bootstrapped 95% CIs allowed comparison with published data from a large clinical cohort in Canada. Results:The combined proportion of fast and catastrophic progressors in our cohort was less than half that in the Canada dataset (2.3% vs. 5.8%), despite median progression rates differing by only 0.03 dB/y. PACG, POAG, and JOAG represented 45%, 32%, and 12% of our cohort, respectively. Baseline MD values were similarly distributed between these subtypes. All subtypes showed a similar shaped distribution for progression rates, with median progression rates of -0.03, -0.05, and 0.02 dB/y for PACG, POAG, and JOAG, respectively. Combined proportions of fast and catastrophic progression rates did not significantly differ between subtypes. Conclusions:Differences in fast and catastrophic visual field progression can exist despite only small changes in median progression rates, highlighting the importance of considering the full shape of the progression rate distribution when comparing the risk of devastating visual field loss
Decadal variations of sea surface temperature in the eastern Arabian Sea and its impacts on the net primary productivity
Ten-year satellite derived data (January 2007 to
December 2016) were used to investigate the variability of
Chlorophyll-a (Chl-a), sea surface temperature (SST), net
primary production (NPP) in the eastern Arabian Sea (AS).
This study is aimed to show the coupling of physical and
biological processes to understand how temporal, annual
and inter-annual variations occur and the forcing mechanisms
behind these variations in the ocean environments.
This work is linked to Indian Ocean Dipole and the El
Nin˜o/Southern Oscillation, which frequently co-occur and
drives inter-annual changes within the AS. Vertically
Generalized Production Model was used to estimate NPP
using chl-a, Photosynthetically Available Radiation,
euphotic depth, and maximum photosynthetic rate from
SST. The relationship between NPP and SST showed
change in the pattern over the study period. The NPP in the
AS is characterized by an unusual decline during El Nin˜o
events. AS is more productive during summer monsoon
(June–September) due to coastal upwelling, wind driven
mixing and lateral advection processes. There was decline
in NPP after 2014 and this trend continued in the following
years. The present investigation revealed that the strong El
Nin˜o condition was observed in 2015 and productivity of
AS declined by * 19%, while SST increased by * 2%
from an overall average of 2007–2016. Increased SST and
low productivity could result in low fish catch in AS.
Increasing trend in SST could be attributed to the extreme
events like cyclones occurring along the west coast of
India
Possible competition between superconductivity and magnetism in RuSr<SUB>2</SUB>Gd<SUB>1.5</SUB>Ce<SUB>0.5</SUB>Cu<SUB>2</SUB>O<SUB>10-δ</SUB> ruthenocuprate compounds
The RuSr2Gd1.5Ce0.5Cu2O10-δ (Ru-1222) compounds, with varying oxygen content, crystallize in a tetragonal crystal structure (space group I4/mmm). Resistance (R) versus temperature (T) measurements show that the air-annealed samples exhibit superconductivity with superconduting transition temperature (Tc) onset at around 32 K and R=0 at 3.5 K. On the other hand, the N2-annealed sample is semiconducting down to 2 K. Magneto-transport measurements on an air-annealed sample in applied magnetic fields of 3 and 6 T (Tesla) show a decrease in both Tc onset and TR=0. Magnetoresistance of up to 20% is observed in the N2-annealed sample at 2 K and 3 T applied field. The dc magnetization data (M vs T) reveal magnetic transitions (Tmag) at 100 K and 106 K, respectively, for both air- and N2-annealed samples. Ferromagnetic components in the magnetization are observed for both samples at 5 K and 20 K. The superconducting transition temperature (Tc) seems to compete with the magnetic transition temperature (Tmag). Our results suggest that the magnetic ordering temperature (Tmag) of Ru moments in RuO6 octahedra may have direct influence/connection with the appearance of superconductivity in Cu-O2 planes of Ru-1222 compounds
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