Department of Physics

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The rotational diffusion coefficient is an essential parameter in determining the mechanistic features of biomolecules in both crowded and confined environments. Understanding the influence of nanoconfinement on rotational diffusion is vital in conceptualizing dynamics of biomolecules (such as proteins) in nanopores. The control of the translational movement of biomolecules is practiced widely in nanopore experiments. However, the restrictions on the translational movement may affect other dynamic properties such as rotational diffusion. In this paper, we use a coarse-grained molecular dynamics approach to study the rotational dynamics of a sample protein under the influence of cylindrical nanopore confinement. Our simulation reveals a 2-fold reduction in magnitude from the bulk rotational diffusion coefficient value as the confinement radius reaches double the size of protein's hydrodynamic radius. However, the changes in the rotational diffusion coefficient are relatively small compared to the changes in the translational diffusion coefficient. Interestingly, the rotational anisotropy also varies considerably when pore radii approach protein dimensions. Our simulations point out that the confinement effects cause the breakdown of small angular displacement theory when the pore radius is close to the protein hydrodynamic radius. © 2019 American Chemical Society.

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Journal of Physical Chemistry B

Rotational Diffusion of Proteins in Nanochannels

Quantum key distribution (QKD) is a key exchange protocol which is implemented over free space optical links or optical fiber cable. When direct communication is not possible, QKD is performed over fiber cables, but the imperfections in detectors used at the receiver side and also the material properties of fiber cables limit the long-distance communication. Free space-based QKD is free from such limitations and can pave the way for satellite-based quantum communication to set up a global network for sharing secret messages. To implement free space optical links, it is essential to study the effect of atmospheric turbulence. Here, an analysis is made for satellite-based quantum communication using QKD protocols. We assume two specific attacks, namely PNS (photon number splitting) and IRUD (intercept-resend with unambiguous discrimination), which could be main threats for future QKD-based satellite applications. The key generation rates and the error rates of the considered QKD protocols are presented. Other parameters such as optimum signal and decoy states mean photon numbers are calculated for each protocol and distance. Further, in SARG04 QKD protocol with two decoy states, the optimum signal-state mean photon number is independent of the link distance and is valid for the attacks considered here. This is significant, highlighting its use in a realistic scenario of satellite quantum communication. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

Fulltext

Quantum Information Processing

Analysis of atmospheric effects on satellite-based quantum communication: a comparative study

The violation of Leggett-Garg-type inequalities (LGtIs) is studied on a two-level atom, driven by an external field in the presence of a squeezed thermal reservoir. The violations are observed in the underdamped regime where the spontaneous transition rate is much smaller compared to the Rabi frequency. An increase in thermal effects is found to decrease the extent of violation as well as the time over which the violation lasts. With the increase in the value of the squeezing parameter the extent of violation of LGtIs is seen to reduce. The violation of LGtIs is favored by an increase in the driving frequency. Further, the interplay of the degree of violation and strength of the measurements is studied. It is found that the maximum violation occurs for ideal projective measurements. © 2019 American Physical Society.

Physical Review A

Violation of Leggett-Garg-type inequalities in a driven two-level atom interacting with a squeezed thermal reservoir

Structural, electronic and optical properties of Cu2ZnGe(S/Se)4 semiconductor materials in their kesterite and stannite phase have been investigated using density functional theory (DFT) approach using full potential linearized augmented plane wave (FP-LAPW) method. Modified Becke-Johnson (mBJ) exchange correlation is used for computing physical properties. These kesterite and stannite Cu2ZnGeS4 and Cu2ZnGeSe4 are direct band semiconductors with band gap values ∼1.15 eV and 1.0 eV for Cu2ZnGeS4 and 0.64 eV and 0.24 eV for Cu2ZnGeSe4, respectively at Γ point. A scissor correction of 1 eV raised these band gap values equal to the experiment values. Optical properties are investigated in terms of refractive index, extinction coefficient, reflectivity, optical conductivity, and optical absorption using dielectric constant. © 2018 Elsevier B.V.

Computational Condensed Matter

Theoretical studies on structural, electronic and optical properties of kesterite and stannite Cu2ZnGe(S/Se)4 solar cell absorbers

Abstract: This article discusses approaches to the synthesis of composite cathode materials based on lithium-intercalated transition metal phosphates (by the example of iron–lithium phosphate). Among various methods and approaches to the synthesis, solid-state synthesis with a preliminary mechanochemical treatment of a mixture of starting materials was chosen as a variant of the compromising of simplicity and processability. In a series of experiments, different factors were sequentially varied in order to identify their influence on the properties of the final product. The article further presents the results of a systematic study of the electrochemical properties of LiFePO4-based material using a set of electrochemical methods: galvanostatic and potentiostatic intermittent titration and cyclic voltammetry. An original approach to graphical presentation of the potential–lithium ion concentration dependence in the LiFePO4 electrode was developed: for LixFePO4 solid solutions, the dependence was plotted against the lithium ion concentration; in the case of Li1 – xFePO4 solid solutions, against the lithium vacancies’ concentration. This approach allowed correctly calculating and introducing the correction parameter z into the modified Randles–Ševčik equation, in order to determine the diffusion coefficient according to the cyclic voltammetry method. Analysis of the galvanostatic and potentiostatic intermittent titration transients was carried out in terms of the developed models that allow describing lithium transport in the diffusion layer with a permeable inner boundary (a mathematical model of heterogeneous system with two phases in equilibrium and an interphase boundary). A good agreement has been found between theoretically calculated and experimental current and potential transients. When varying the composition of the electrode with respect to lithium, kinetic parameters of lithium intercalation were determined: the lithium diffusion coefficient and the phase transition constant. © 2019, Pleiades Publishing, Ltd.

Russian Journal of Electrochemistry

LiFePO4-Based Composite Electrode Material: Synthetic Approaches, Peculiarities of the Structure, and Regularities of Ionic Transport Processes

Ni–Co pigmented anodized alumina as spectrally selective coating is realized using electrodeposition. Ni and Co metals are pigmented into nanoporous alumina by the reduction of metallic ion from aqueous solution. The measured spectral absorptance and thermal emittance are ∼0.90 ± 0.05 and 0.14 ± 0.04, in 0.2–2.5 μm and 2.5–25 μm wavelength window, respectively for the optimized Ni–Co co-pigmented alumina spectrally selective coatings. The optimized solar selective coating samples are heat treated in open environmental condition at 300 °C for 100 h to evaluate their thermal stability. The absorptance is nearly unaffected after heat treatment, whereas slight enhancement in thermal emittance is observed as compared to the unheated sample. After thermal evaluation, corrosion characteristics are also evaluated and observed that Ni–Co co-pigmented coatings are more corrosion resistant than anodized alumina structures, suggesting that these co-pigmented solar selective coating may be suitable for mid temperature absorbers in ambient conditions. © 2019 Elsevier B.V.

Journal of Alloys and Compounds

Corrosion resists Ni, Co co-pigmented nanoporous anodized alumina as spectral selective coating structure for solar thermal applications

n-ZnO nanorod/p-si hetrojunction diode is synthesized using a simple chemical solution method on p-type silicon substrates for light emitting diode applications. The grown ZnO nanorods showed highly textured hexagonal crystallographic phase along c-axis. An intense band to band photoluminescence peak is observed at 377 nm in conjunction with the weak deep-level emissions in visible region centred at 500 nm. The current–voltage measurements show diode-like characteristics. The work will also discuss the emission response with bias field for these solution processed n-ZnO/p-Si heterostructures under dark and UV conditions in the context of possible UV photo-response and light emitting diode applications. © Springer Nature Switzerland AG 2019.

Springer Proceedings in Physics

Light emitting diode and uv photodetector characteristics of solution processed n-zno nanorods/ p-si heterostructures

We present a short review on phonon anomalies near magnetic ordering in magnetic materials using the noticed Raman shifts and any change in intensities near such magnetic ordering. The observed variation in specific optical phonon modes is discussed considering the spin-orbital-phonon coupling in various systems. The consequences of spin-orbital-phonon coupling include the impact on bond strength, which results in specific phonon mode anomalies near magnetic ordering. There are several experimental observations based on temperature-dependent Raman and IR spectroscopic measurements in the vicinity of magnetic ordering temperature, suggesting a crucial spin-phonon coupling in certain materials, giving rise to the exotic physical properties such as magnetoelectric, and piezomagnetic effects in such materials. The review will discuss the microscopic origin of spin-orbital-phonon coupling in these systems. © 2019, Springer Nature Singapore Pte Ltd.

Effect of Magnetic Ordering on Phonon Raman Spectra in Magnetic Systems

We report efficient detection of alpha radiation on highly textured and vertically aligned along (002) Gallium-doped Zinc Oxide (ZnO:Ga) nanorods on a glass substrate with an average diameter ~150 ± 10 nm. Photoluminescence measurement showed near band emission 393 nm, in agreement with the bandgap value ~3.22 eV, measured by UV-Vis spectroscopy. The developed ZnO:Ga nanorod scintillator is coupled with a commercially available photomultiplier tube and 1K Multichannel Analyser to fabricate an alpha radiation detector. The performance of the alpha radiation detector is evaluated using various activities alpha radiation sources. A large pulse height spectrum is recorded by the detector for different alpha sources against the background spectrum. The calculated detection efficiency and Minimum Detectable Activity (MDA) showed that the detector is highly sensitive to alpha radiation. The repeatability and reproducibility of the performance are studied by evaluating the response of a single scintillator for numerous exposures and by studying inter-batch response variations, respectively. The response is repeatable within ±1% whereas reproducibility varies from ±20% for extremely low activity alpha sources to ±5% for high activity alpha sources. The performance of ZnO:Ga nanorod scintillator grown on glass substrate demonstrates that it can be a promising material system for the detection of alpha radiation. © 2019, The Author(s).

Scientific Reports

Efficient Alpha Radiation Detector using Low Temperature Hydrothermally Grown ZnO:Ga Nanorod Scintillator

We used temperature-dependent neutron diffraction measurements on FeVO4 to understand the temperature driven anisotropy and observed that the maximum change for a&amp;b lattice parameters in conjunction with a large contraction in angle β as a function of temperature. The least changes are observed for the c lattice parameter and in γ angle. From these structural parameters, it can be said that, FeVO4 exhibits large structural anisotropy with lowering temperature. The large change in lattice parameters in magnetic phases i.e. below 22K explains the strong magnetostructural coupling in FeVO4. © 2019 Author(s).