Department of Physics

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IIT Jodhpur

Ultrahigh-molecular-weight polyethylene (UHMWPE) is of great interest as a next-generation body armor material because of its superior mechanical properties. However, such unique properties depend critically on its microscopic structure characteristics, including the degree of crystallinity, chain alignment, and morphology. Here, we present a highly aligned UHMWPE and its composite sheets containing uniformly dispersed boron nitride (BN) nanosheets. The dispersion of BN nanosheets into the UHMWPE matrix increases its mechanical properties over a broad temperature range. Experiments and simulation confirm that the alignment of chain segments in the composite matrix increases with temperature, leading to an improvement in mechanical properties at high temperature. Together with the large thermal conductivity of UHMWPE and BN, our findings serve to expand the application spectrum of highly aligned polymer nanocomposite materials for ballistic panels and body armor over a broad range of temperatures. © 2018 American Chemical Society.

World University root node

Journal of Physical Chemistry Letters

Mechanically Strong Polymer Sheets from Aligned Ultrahigh-Molecular-Weight Polyethylene Nanocomposites

We report a facile and cost-effective approach to develop self-standing reduced Graphene Oxide (rGO) film based optical sensor and its low-temperature performance analysis where midgap defect states play a key role in tuning the crucial sensor parameters. Graphite oxide (GO) is produced by modified Hummers' method and reduced thermally at 250 °C for 1 h in Argon atmosphere to obtain rGO. Self-standing rGO film is prepared via vacuum filtration. The developed film is characterized by HRTEM, FESEM, Raman, and XRD techniques. The developed sensor exhibits highest sensitivity towards 635 nm illumination wavelength, irrespective of the operating temperature. For a given excitation wavelength, photoresponse study at low temperature (123K-303K) reveals inverse relationship between sensitivity and operating temperature. Highest sensitivity of 49.2% is obtained at 123 K for 635 nm laser at power density of 1.4 mW/mm2. Unlike sensitivity, response- A nd recovery-time demonstrate directly proportional dependence with operating temperature. Power dependent studies establish linear relation between power-density and sensitivity, and a safe limit beyond which sample heating prolongs the recovery time. Wavelength-dependent studies shows that proposed sensor can efficiently operate from visible to near NIR region. To the best of our knowledge such rGO based optical sensor performance at low temperature had not been reported earlier. © 2018 The Author(s).

Fulltext

Scientific Reports

Reduced graphene oxide (rGO) based wideband optical sensor and the role of Temperature, Defect States and Quantum Efficiency

We report the sensitivity of Iron CALorimeter (ICAL) detector to the detection of TeV gamma rays from various astrophysical sources at India-based Neutrino Observatory (INO). The ICAL detector is proposed to be of 51 kton with an average magnetic field of ~ 1.3T. The electromagnetic showers generated by high-energy gamma rays at the atmosphere will produce down-going muons through either muon pair production or pion decay. The gamma rays can be traced by detecting these muons using ICAL. Most of the space- and underground-based experiments have detected them directly and indirectly, but the advantage of using ICAL for their detection is to measure the µ+ to µ- ratio, which is 1in case of pair production, at very high energy (≥ 50 GeV). Here, we have shown its detection ability for the appropriate astrophysical 2FHL sources listed in “The Second Catalog of Hard Fermi-LAT Sources,” where the signal-to-noise ratio is suppressed by factor of 5σ for ICAL running period of five years for spectral index of ≥ 0.45. © Springer Nature Singapore Pte Ltd 2018.

Springer Proceedings in Physics

Sensitivity of ICAL to TeV Gamma Rays at INO

We investigated the translation of a protein through model nanopores using coarse-grained (CG) nonequilibrium molecular dynamics (NEMD) simulations and compared the mobilities with those obtained from previous coarse-grained equilibrium molecular dynamics model. We considered the effects of nanopore confinement and external force on the translation of streptavidin through nanopores of dimensions representative of experiments. As the nanopore radius approaches the protein hydrodynamic radius, rh/rp→1 (where rh is the hydrodynamic radius of protein and rp is the pore radius), the translation times are observed to increase by two orders of magnitude. The translation times are found to be in good agreement with the one-dimensional biased diffusion model. The results presented in this paper provide useful insights on nanopore designs intended to control the motion of biomolecules. © 2018 American Physical Society.

Physical Review E

Translational mobilities of proteins in nanochannels: A coarse-grained molecular dynamics study

CdTe quantum dots were synthesized using water as a solvent medium. Synthesized quantum dots were used to integrate into TiO2 nano-porous electrode using a combination of linker assisted direct adsorption and chemical bath deposition process. Sensitized electrodes were characterized to understand their physical and optical properties for photovoltaic application. © 2018 Elsevier Ltd.

Materials Today: Proceedings

CdTe Sensitized Nano Porous Electrode for Photovoltaic Application

Cadmium telluride (CdTe) quantum dots are integrated with mesoporous titanium dioxide “TiO2” electrode using an in-situ sensitization approach for the first time, where water soluble N-Acetyl Cysteine capped CdTe quantum dots (diameter 4–5 nm) are grown hydrothermally inside mesoporous TiO2 electrode matrix. This in-situ sensitization approach has shown the effective sensitization over the conventional reported sensitization processes. The in-situ CdTe sensitized TiO2 electrodes are further unified with PbS counter electrode to realize the quantum dot sensitized solar cell (QDSSC). The fabricated CdTe QDSSC has shown the optimal short circuit current density 3.35 ± 0.21 mA/cm2 and open circuit voltage 0.58 ± 0.01 V. The observed current density is the highest among such cell configurations, reported till date. The in-situ sensitized CdTe QDs are further treated with zinc sulfide for surface passivation to realize the reduced back recombination, if any. These ZnS passivated CdTe QDs sensitized solar cells in similar device configurations resulted into the significant reduction in the short circuit current density (20%) with the minimal change in open circuit voltage (5%). The impedance spectroscopy measurements suggest that the transmission resistance “Rtr” has increased after ZnS treatment for these electrodes, however, the recombination resistance Rrec has not changed much. The observed high Rtr might be responsible for the observed current deterioration after ZnS surface passivation. These studies suggest that in-situ QD sensitization may provide a new method of integrating QDs into mesoporous TiO2 matrix for effective QDSSC device performance without any additional surface passivation. © 2018 Elsevier Ltd

Solar Energy

A novel process for sensitization and infiltration of quantum dots in mesoporous metal oxide matrix for efficient solar photovoltaics response

The cubic double perovskites A2ZnWO6 (A = Ba, Sr and Ca) are studied to understand the effect of A cation site, using the density functional theory (DFT) based full potential augmented plane wave method (FP-LAPW) with GGA and mBJ exchange correlation potentials. The structural robustness and stability are investigated using the bond lengths and the total energy. The band structure and density of states suggest that all these cubic double perovskites are indirect wide band gap semiconductors. The band gap varies from 3.90 eV (2.97 eV) for Ba2ZnWO6 system to 3.40 eV (2.8 eV) for Ca2ZnWO6 system using mBJ (GGA) exchange correlation potentials. Our studies suggest that A cation site modification has a strong effect on physical and electronic properties, in contrast to the structural robustness. The lattice parameter decreases from 8.19 Å to 7.9 Å from Ba to Ca at alkali cation site and the electronic band gap variation follows the common cation rule. The charge densities show enhanced localization of charges near the zinc and oxygen sites with increasing alkali cation atomic radii. In addition, we discuss the impact of A cation site modification on the dielectric and optical properties for A2ZnWO6 double perovskites. © 2017 Elsevier B.V.

Computational Condensed Matter

Cation modified A2(Ba, Sr and Ca) ZnWO6 cubic double perovskites: A theoretical study

We study the geometric phase for neutrinos at various man-made facilities, such as the reactor and accelerator neutrino experiments. The analysis is done for the three flavor neutrino scenario, in the presence of matter and for general, noncyclic paths. The geometric phase is seen to be sensitive to the CP violating phase in the leptonic sector and the sign ambiguity in . We find that for neutrino experimental facilities where the geometric phase can complete one cycle, all the phase curves corresponding to different values of CP violating phase, converge to a single point, called the cluster point. There are two distinct cluster points for positive and negative signs of Δ31. Thus, the geometric phase can contribute to our understanding of the neutrino mass hierarchy problem. © 2018 IOP Publishing Ltd.

Journal of Physics G: Nuclear and Particle Physics

Geometric phase and neutrino mass hierarchy problem

One of the exciting results in flavor physics in recent times is the RD/RD⁎ puzzle. The measurements of these flavor ratios performed by the B-factory experiments, BaBar and Belle, and the LHCb experiment are about 4σ away from the Standard Model expectation. These measurements indicate that the mechanism of b→cτν¯ decay is not identical to that of b→c(μ/e)ν¯. This charge lepton universality violation is particularly intriguing because these decays occur at tree level in the Standard Model. In particular, we expect a moderately large new physics contribution to b→cτν¯. The different types of new physics amplitudes, which can explain the RD/RD⁎ puzzle, have been identified previously. In this letter, we show that the polarization fractions of τ and D⁎ and the angular asymmetries AFB and ALT in B→D⁎τν¯ decay have the capability to uniquely identify the Lorentz structure of the new physics. A measurement of these four observables will lead to such an identification. © 2018 The Author(s)

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

Resolution of RD/RD⁎ puzzle

In this study, a promising microbial fuel cell (MFC) system has been developed, wherein algae is cultivated in the cathode chamber, algae biomass is harvested and lipids are extracted. The lipid extracted algal (LEA) biomass was then used as an electron donor substrate. The performance of MFCs fed with LEA biomass was compared with that of fruit waste fed MFCs (FP-MFCs), wherein LEA-fed MFC was superior in all aspects. Power density of 2.7 W m−3 was obtained by LEA-fed MFCs which is 145% and 260% higher than FP MFC and control MFC respectively. The volumetric algae productivity of 0.028 kg m−3 day−1 in cathode chamber was achieved. The system was able to generate 0.0136 kWh Kg−1 COD day−1 of electric energy and 0.0782 kWh m−3 day−1 of algal oil energy. The proposed system is a net energy producer which does not rely heavily on the external supply of electron donor substrates. © 2017 Elsevier Ltd