Department of Physics

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We show that non-Markovian effects of the reservoirs can be used as a resource to extract work from an Otto cycle. The state transformation under non-Markovian dynamics is achieved via a two-step process, namely an isothermal process using a Markovian reservoir followed by an adiabatic process. From second law of thermodynamics, we show that the maximum amount of extractable work from the state prepared under the non-Markovian dynamics quantifies a lower bound of non-Markovianity. We illustrate our ideas with an explicit example of non-Markovian evolution. © 2018 American Physical Society.

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Physical Review E

Thermodynamics of non-Markovian reservoirs and heat engines

In this study, both model analysis and electrical characterization of a dielectric barrier discharge based argon plasma jet have been carried at atmospheric pressure in a pin electrode configuration. The plasma and fluid dynamics modules of COMSOL multi-physics code have been used for the modeling of the plasma jet. The plasma parameters, such as, electron density, electron temperature and electrical potential have been analyzed with respect to the electrical parameters, i.e., supply voltage and supply frequency with and without the flow of gas. In all the experiments, gas flow rate has been kept constant at 1 liter per minute. This electrode configuration is subjected to a range of supply frequencies (10-25 kHz) and supply voltages (3.5-6.5 kV). The power consumed by the device has been estimated at different applied combinations (supply voltage & frequency) for optimum power consumption at maximum jet length. The maximum power consumed by the device in this configuration for maximum jet length of ∼26 mm is just ∼1 W. © 2018 Author(s).

AIP Advances

Model analysis and electrical characterization of atmospheric pressure cold plasma jet in pin electrode configuration

We report ultrafast optical measurements of the Dirac line-node semimetal ZrSiS and the Weyl semimetal NbAs, using mid-infrared pump photons from 86 meV to 500 meV to directly excite Dirac and Weyl fermions within the linearly dispersing bands. In NbAs, the photoexcited Weyl fermions initially form a non-thermal distribution, signified by a brief spike in the differential reflectivity whose sign is controlled by the relative energy of the pump and probe photons. In ZrSiS, electron-electron scattering rapidly thermalizes the electrons, and the spike is not observed. Subsequently, hot carriers in both materials cool within a few picoseconds. This cooling, as seen in the two materials' differential reflectivity, differs in sign, shape, and timescale. Nonetheless, we find that it may be described in a simple model of thermal electrons, without free parameters. The electronic cooling in ZrSiS is particularly fast, which may make the material useful for optoelectronic applications. © 2018 Author(s).

Applied Physics Letters

Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs

A study of the surface modification of titanium CP grade 2 implant/target with high intensity picosecond (Nd:YAG) laser, operating at 1064 nm wavelength and pulse duration of 40 ps, in gaseous (air) and liquid (water) medium, is presented. The exposure of Ti to a laser pulse energy of 17 mJ in both media – gaseous and liquid, induced specific surface features and phenomena: (i) enhancement of the implant surface roughness (higher in water). In this context, the damage depth is more prominent in water (as high as ∼40 μm) vs. air (∼14 μm). Also, the appearance of laser induced periodic surface structures (LIPSS) is recorded in both media, at periphery area, while in water they are registered at lower pulse count; (ii) variation of chemical surface content depending on the applied medium. Thus, in the central irradiation region, the oxygen was absent in air while its concentration was relatively high (6.44 wt%) in case of water; (iii) possibility of direct collection of synthesized titanium based nanoparticles in water environment, and (iv) formation of the plasma above the sample in both mediums, more volumetrically confined in water. These investigations showed that surface structuring and observed phenomena are in strong correlation with the medium used. The liquid – water seems like the medium of choice in regard to titanium implant biocompatibility and bio-activity (the water is a favorable medium for build-up of the oxide layer which affects bioactivity). The process of laser interaction with titanium implant targets was accompanied by the formation of plasma plume, which provides the additional sterilizing effect facilitating contaminant-free conditions. © 2017 Elsevier B.V.

Applied Surface Science

Laser-assisted surface modification of Ti-implant in air and water environment

Parabolic optical pulses with their characteristic linear chirp have profound importance in nonlinear optics as they have immense capability to withstand strong nonlinearity which prevents wave-breaking. Moreover, their evolution is self-similar, hence they are typically known as similaritons. Such wave-breaking free parabolic similaritons are widely applicable in all-fiber based devices like, high energy fiber laser sources, bio/chemical sensors, supercontinuum generators, bio-medical imaging and non-invasive surgery tools and so on. To date, theoretical and experimental formation of PPs have been reported for both active and passive optical fibers where PPs are asymptotic solutions of nonlinear Schrodinger equation (NLSE) [1]. It is clearly reported that PPs in active fibers are highly stable and evolve self-similarly over longer propagation distance whereas, passive formation of PPs are a mere intermediate transient state of propagation and with further evolution it becomes unstable [2]. In this context, another two types of similaritons (bright and dark) have been reported which are exact solutions of NLSE and found to propagate self-consistently against their asymptotic counterpart [3]. While encountering the stability issue of PPs in passive medium, it has been seen that high values of dispersion are being detrimental leading to wave-breaking. Hence some dispersion managed schemes have reported that effectively suppresses the excessive dispersive phase accumulation and stabilize the pulse over a few meters [4]. In this paper, we report formation and stable propagation of PPs over few hundreds of meters through a soft glass based tapered Bragg fiber. Instead of employing any dispersion managing technique, we simply have exploited the self-consistent nature of a bright (sechyperbolic) and dark (tanhyperbolic) similaritons and formed parabolic pulses in a decreasing dispersion profile. © 2018 OSA - The Optical Society. All rights reserved.

Optics InfoBase Conference Papers

Towards stable propagation of parabolic pulses through tapered Bragg fiber

We report stable propagation of parabolic similaritons through a specially designed Bragg fiber based on a two-fold engineering including transverse chirping and longitudinal tapering to mitigate the deleterious effect of third order dispersion. © 2018 The Author(s).

Pulse reshaping and stable propagation through a chirpedclad dispersion oscillating bragg fiber

Most of the reports suggest that liquid exfoliated WS2-QDs are unstable; therefore the need of present day is to develop a novel synthesis route for producing long-term stable WS2-QDs. Herein, we report a bottom-up single-step hydrothermal growth of in situ functionalized blue fluorescent WS2-QDs with stable fluorescence in aqueous media without subsequent treatments. Presence of various functional groups over the surface of f-WS2-QDs provides high solubility and stability to f-WS2-QDs in aqueous media preserving its fluorescence. Further, photoluminescence property of f-WS2-QDs has been employed to devise an optical sensor with a high sensitivity (KD ∼104 M-1) and selectivity for ferric (Fe3+) ions. Under the optimal condition, response of the sensor is found to be linear in the range of 0-55 μM with a limit of detection (LOD) of 1.32 μM, which is within the maximum permissible level of Fe3+ (∼5.4 μM) in human drinking water by the USEPA. Further, we have also carried out a detailed evaluation on fluorescence quenching kinetics of f-WS2-QDs. Nonlinear behavior of S-V plot and TRPL measurements suggest that quenching is a mixed phenomenon of dynamic as well as static processes. Finally we have proposed a mechanism for fluorescence quenching of f-WS2-QDs in the presence of Fe3+ © 2018 American Chemical Society.

ACS Applied Nano Materials

In Situ Functionalized Fluorescent WS2-QDs as Sensitive and Selective Probe for Fe3+ and a Detailed Study of Its Fluorescence Quenching

We carried out a comparative study on the electrical and magnetodielectric properties of polycrystalline BiFeO3, Bi0.9Ca0.1FeO2.95, Bi0.9Ba0.05Ca0.05FeO2.95, and Bi0.9Ba0.1FeO2.95 ceramics. The two dielectric anomalies, near 25 K and 281 K, are observed for BiFeO3. Interestingly, the anomaly near 25 K shifts towards a higher temperature above 60 K with Ca and/or Ba doping, attributed to the doping induced chemical pressure. In addition, the room temperature switchable magnetodielectric effect is witnessed for the doped BiFeO3 compounds, due to the quadratic magnetoelectric coupling. This indicates the improved magnetoelectric coupling in BiFeO3 with the Ca and Ba doping. This is essentially due to the enhanced magnetic ordering and reduced leakage current in BiFeO3 after the doping. © 2017 The American Ceramic Society

Journal of the American Ceramic Society

Enhancement in electrical and magnetodielectric properties of Ca- and Ba-doped BiFeO3 polycrystalline ceramics

Zinc oxide (ZnO) and zinc rich zinc oxide (Zn:ZnO) thin films are synthesized using vapor phase trapping assisted thermal chemical vapor deposition (CVD) process. X-ray diffraction measurements indicate the highly textured c-axis growth for Zn:ZnO thin films as compared to ZnO thin film structures. The observed insignificant change in lattice parameters suggests that excess Zn is in interstitial sites. The optical studies substantiate that the excess Zn in ZnO matrix is contributing to the point defects, with integrated luminescence towards the light blue color with respect to that for the pristine ZnO thin film. The electronic carrier concentration is about four orders of magnitude higher for Zn:ZnO thin films, causing Burstein-Moss shift of ∼0.13 eV in Zn:ZnO thin films. © 2017 Elsevier B.V.

Journal of Alloys and Compounds

Zn interstitial defects and their contribution as efficient light blue emitters in Zn rich ZnO thin films

The effect of exfoliated graphite (ExG) with myristic acid phase change material has been investigated to understand the enhancement of thermal conductivity and shape stabilization for the ExG-myristic acid composite system. The thermochemically synthesized ExG is added to myristic acid in 5, 10, and 15 wt\% and the shape stabilized ExG-myristic acid composite samples are prepared. The heat release, solidification time and latent heat of myristic acid and ExG-myristic acid composites are measured using temperature history (T-history) and Differential Scanning Calorimetric (DSC) measurements, respectively. The measured melting temperature and latent heat of fusion of myristic acid are similar to 55 degrees C and similar to 185 kJ/kg, respectively. Latent heat of ExG-myristic acid composite samples has decreased linearly with increasing ExG weight fraction. T-history measurements suggest the reduction in solidification time for ExG-myristic acid composite samples and similar to 55\% reduction in heat release time is observed for 15\% ExG-myristic acid composite sample with respect to pristine myristic acid. The observed reduction in heat release time subtantiates the effective enhancement of thermal conductivity for ExG-myristic acid composite samples.