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Estimates of reactive trace gases (NMVOCs, CO and NOx) and their ozone forming potentials during forest fire over Southern Himalayan region
No full textIn the present study, emission of trace gases [non-methane volatile organic compounds (NMVOCs), carbon monoxide (CO) and oxides of nitrogen (NOx)], their ozone forming potentials and ozone sensitivities have been investigated during the forest fire period (2003-2016) over the Southern Himalayan region. Reanalysis data of Global Fire Assimilation System model is used to retrieve the various parameters such as fire radiative power and emission rates of various trace gases. April 2016 is noticed to be anomalous in terms of fire events in the last fourteen years (2003-2016) over the lower Southern Himalayan region. Our estimation shows major contribution of oxygenated compounds (55.2%) amidst all NMVOCs. Mean CO and NOx emission rates are 533.81 and 13.66 mg/m(2)/day, respectively during the forest fire of April months for fourteen years. The emissions of NMVOCs, CO and NOx increased by 90.4, 110.6 and 132.5% and reaches up to 121.1, 958.3 and 25.3 mg/m(2)/day in April 2016 with respect to non-burning period (April 2015). Ozone forming potentials (OFP) of NMVOCs are also examined using the maximum incremental reactivity (MIR) method, which shows similar to 2 times higher OFP for total NMVOCs during 2016 as compared to 2015. Based on the MIR scale, the contribution of top 10 species to OFP are in the decreasing order of formaldehyde, acetaldehyde, ethane, propene, toluene, butane, isoprene, methanol, pentene and hexane. The ratio of NMVOCs/NOx is < 8, which indicates that the photochemical production of O-3 is mainly controlled by the levels of NMVOCs. The surface observations of ozone and CO from a Himalayan station Nainital also showed substantial increase in concentration during the forest fire of April 2016. Our results are valuable for the better understanding of chemical composition of trace gases, their role in O-3 formation and effective control strategies of O-3 pollution during the forest fire events over the lower Himalayan region
Multiwall carbon nanotubes tailored porous carbon fiber paper-based gas diffusion layer performance in polymer electrolyte membrane fuel cell
No full textIn the present investigation, porous carbon fiber paper as a gas diffusion layer (GDL) of polymer electrolyte membrane fuel cell was modified by nano-structuring. It was modified by incorporating multiwall carbon nanotubes (MWCNTs) in chopped carbon fiber preform by two approaches; first by incorporating in the matrix phase and second by the in-situ growth of MWCNTs on the carbon fiber preform by chemical vapor deposition technique, followed by impregnation of phenolic resin and processed to carbonization at 1000 and 1800 degrees C.The effect of MWCNTs incorporation was ascertained by characterizing carbon fiber paper by various techniques. It is found that incorporation of MWCNTs reveals an increase in electrical conductivity from 66 S/cm to 175 S/cm and flexural modulus from 5 GPa to 20 GPa. The extent of increase in electrical conductivity was greater in MWCNTs mixed with phenolic resin as compared to MWCNTs grown over the carbon fiber preform. There is a significant improvement in power density from 361 to 594 mW/cm(2) of MWCNTs grown based GDL. The BET contact angle increases the hydrophobicity of GDL, reduced the blockage of gas diffusion path. Also, higher value of electrical conductivity, surface area and optimal pore sizes results in the enhancement of I-V performance
NbOx based memristor as artificial synapse emulating short term plasticity
Get PDFMemristors can mimic the functions of biological synapse, where it can simultaneously store the synaptic weight and modulate the transmitted signal. Here, we report Nb/Nb2O5/Pt based memristors with bipolar resistive switching, exhibiting synapse like property of gradual and continuously change of conductance with subsequent voltage signals. Mimicking of basic functions of remembering and forgetting processes of biological brain were demonstrated through short term plasticity, spike rate dependent plasticity, paired pulse facilitation and post-titanic potentiation. The device layer interface tuning was shown to affect the device properties shift from digital to analog behaviour. Demonstration of basic synaptic functions in the NbOx based devices makes them suitable for neuromorphic applications
Nonlinear I-V characteristics of two-dimensional superconductors: Berezinskii-Kosterlitz-Thouless physics versus inhomogeneity
No full textOne of the hallmarks of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional superconductors is the universal jump of the superfluid density that can be indirectly probed via the nonlinear exponent of the current-voltage I-V characteristics. Here, we compare the experimental measurements of I-V characteristics in two cases, namely NbN thin films and SrTiO3-based interfaces. While the former display a paradigmatic example of BKT-like nonlinear effects, the latter do not seem to justify a BKT analysis. Rather, the observed I-V characteristics can be well reproduced theoretically by modeling the effect of mesoscopic inhomogeneity of the superconducting state. Our results offer an alternative perspective on the spontaneous fragmentation of the superconducting background in confined two-dimensional systems
EFFECTS OF LOCAL CHEMICAL MINERALOGY ON THE LONG TERM DURABILITY OF REINFORCED CONCRETE STRUCTURES - EFFECTS OF CALCIUM CARBONATE:AN INDIAN PERSPECTIVE USING XRF
No full textAnalyses of chemical constituents in sand were undertaken
after these sand samples were collected from different sources,
including river sand and manufactured sand from all over India,
ensuring a fair representation. Indian subcontinent is home to
20% of the worlds’ population. X-Ray Fluorescence (XRF) results
along with data from X-Ray diffraction suggested that Indian
sand is not necessarily pure silica based sand but all most always
has calcium carbonate as a constituent. Its content varied from a
few percent to majority fraction of the sand at certain locations.
This can chemically react with acidic ground water (hard water)
and make any exposed concrete porous and susceptible to
further degradation based on capillary action. As calcium salts
like carbonate was present in non-negligible amounts, such sand
samples need to be leached with dilute acids and such content
removed to make the sand chemically more stable before
mixing with cement for production of reinforced concrete, for
better durability even in slightly acidic environments with nonpotable
ground water or in areas close to the sea coast or areas
with tidal effects
Modelling aerosol optical properties over urban environment (New Delhi) constrained with balloon observation
No full textVertical variation in aerosol optical properties [e.g. Single Scattering Albedo (SSA) and aerosol extinction coefficient] over a polluted environment is extremely important for better understanding of columnar radiative characteristics. The present case study over a typical polluted environment (New Delhi) discusses the vertical profile (ground to 700 m) of modelled optical properties of atmospheric particles at different altitudes. Here, we used the aerosol physico-chemical data generated in the tethered balloon-based observation conducted at CSIRNPL, New Delhi (28 degrees 38' 10 '' N, 77 degrees 10' 17 '' E) from 21st -27th February 2014. Based on the microscopic observations of individual particles, we developed the aerosol model shapes (coated spheres) for simulating their optical properties. Total three cases were considered for simulating the aerosol optics at varying altitude; Case A: External mixture of coated dust and coated sulfate particles; Case B: External mixture of coated dust, coated sulfate, coated OC (Organic Carbon) and coated EC (Elemental Carbon) (with assumption that 6% EC at ground level); Case C: External mixture of coated dust, coated sulfate, coated OC and coated EC (with assumption that 10% EC at ground level). At 550 nm wavelength, the value of SSA has been found to be highest (i.e. 0.985) at 200 m altitude for Case A while Case B (i.e. 0.9523) and Case C (i.e. 0.9291) show highest values at 500 m altitude. SSA was found to be maximum at 500 m altitude for both Case B and Case C due to the presence of lowest graphitic counts at that particular altitude. Case B and Case C exhibit similar pattern but differ in magnitude, this is due to two EC extremities at ground level i.e. minima (6%) and maxima (10%). The percentage deviation in SSA from ground level to 700 m was found to be highest for Case C (i.e. 5.95%) followed by Case B (i.e. 4.19%) and Case A (i.e. 1.4%). Modelled aerosol optical properties within boundary layer may improve our understanding about the thermodynamics of lower atmosphere
Morphology of Martian Low-Altitude Ionospheric Layer: MGS Observations
No full textAn analysis of the entire data set of 5,600 electron density profiles returned by Mars Global Surveyor's Radio Science Experiment is carried out to study the physical characteristics of Martian low-altitude plasma layer (M layer). Our analysis suggests that this layer is predominantly observed during low and moderate solar activity periods, in northern autumn. The critical ionospheric parameters (electron density and height) of this M layer are found not to show a definitive correlation with solar zenith angle. In contrast to earlier reports where meteoroid ablation was proposed to cause total electron content (TEC) enhancements, we report that the maximum contribution from this layer (TECM) is only about 5.5%, while the contribution is 3.7% during predicted meteor shower, suggesting that M layer occurrence does not depend upon meteor shower nor on dust storm. It is observed that the M layer occurrence increases as the Martian E region becomes prominent and well defined, suggesting that the source which causes M layer possibly leads to more pronounced E layers. Southern hemisphere profiles were found to behave differently from northern hemisphere profiles, possibly due to crustal magnetic fields. Large surges observed in Martian F1 layer peak height during consecutive occultations (similar to 2hr apart) are found not to show any correlation with the occurrence of M layer and are not influenced by dust storms
Morphology induced plasmonic-excitonic interaction revealed by pump-probe spectroscopy
No full textStructure dependent relaxation and recombination dynamics of plasmons in three distinct colloidal plasmonic nanoshapes namely gold nanoflowers (GNF), gold nanopebbles (GNP), gold nanospheres (GNS) and a gold nanoislands film has been investigated with the help of ultrafast pump-probe spectroscopy. The structural transformation study revealed that the geometry plays a vital role in modulating the relaxation time of the plasmons. Further, an organic fluorescent dye (Eosin yellow, EY) is coupled with the aforementioned gold nanoshapes, to decipher the morphology directed excited state intermolecular interaction, amongst the plasmonic-organic hybrids in terms of their temporal and spectral modulations. Indeed, the experimental observations depict a reduction in the fluorescence lifetime of all the hybrids thereby confirming the presence of a non-radiative energy transfer within the hybrids. Variation in the coupling configuration of the EY with the aforementioned gold nanoshapes, lead to a tunable response time, providing a powerful means to alter the optical properties of plasmonic-organic hybrids. Overall, this study may not only help in a better understanding of excited the state dynamics of a coupled hybrid but also pave a way towards the realization of plasmonic-based active photonic devices
Bandgap Engineering and Signature of Ferromagnetism in Ti1-xMnxO2 Diluted Magnetic Semiconductor Nanoparticles: A Valence Band Study
No full textDiluted magnetic semiconductor Ti1-xMnxO2 (0.0 <= x <= 0.06) nanoparticles have been synthesized by sol-gel technique. Phase purity, structural, micro-structural, and vibrational properties of the samples have been studied by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and Raman spectroscopy. UV-Vis and photoluminescence spectroscopy clearly indicate the tuning of bandgap and appearance of different defect states (oxygen vacancies) with Mn-doping, respectively. Chemical states and surface stoichiometry of the samples have been probed by X-ray photoemission spectroscopy (XPS). Shifting of binding energy of Ti2p toward lower value and appearance of Mn2+, Mn3+, and Mn(4+)confirm Mn doping into TiO2 and also indicate that Mn-doping reduces the number of oxygen vacancies in the system. Valence band studies have been done by XPS and ultraviolet photoemission spectroscopy (UPS) valence band spectra. Combined result of valence band spectra and optical data reveals shortening of HOMO-LUMO gap with increasing Mn-concentration. Room temperature ferromagnetism, originating from oxygen vacancies, has been explained on the basis of the bound magnetic polaron (BMP) model. Resistivity measurements have been conducted to examine the semiconducting behavior and to study the electrical conduction mechanism. It is revealed that the thermally activated conduction (Arrhenius) mechanism is valid in the high temperature region whereas Mott's variable-range hopping (VRH) mechanism is applicable in low temperature region
Boosting thermoelectric power factor of free-standing Poly (3,4ethylenedioxythiophene):polystyrenesulphonate films by incorporation of bismuth antimony telluride nanostructures
No full textWe demonstrate that introduction of p-type Bi0.5Sb1.5Te3 nanostructures into the polymer matrix not only causes highly adherent drop-casted films of PEDOT:PSS (on Kapton sheets) to attain a free-standing nature but also brings a significant improvement in their thermoelectric properties. Hall and ESR measurements of these hybrid films clearly show that both the carrier concentration and mobility can be varied with Bi0.5Sb1.5Te3 content. Whereas, results of X-ray diffraction, Raman and X-ray photoelectron spectroscopy confirm the enhancement in chain alignment and better connectivity among PEDOT:PSS and Bi0.5Sb1.5Te3 nanosheets; leading to remarkable enhancement of electrical conductivity. These hybrid films, due to energy filtering of charge carriers at the organic/inorganic interface, exhibit improvement in the Seebeck coefficient also. In fact, such a synergetic combination of improved electrical conductivity and Seebeck coefficient expertly tailors the power factor (from order of similar to 10(-4) to 8.3 mu W/mK(2)) over a vast range. The optimized films are tested for their power conversion ability and a single thermoelement based device exhibits an open circuit voltage similar to 536 mu V and current similar to 134 mu A for a temperature difference of 53 degrees C. Such an evolution of organic-inorganic hybrid films in a flexible, free-standing motif with enhanced thermoelectric properties exhibit good potential for recovering heat from the curved hot surfaces