Physical Research Laboratory PRL

Ahmadābād, India

Physical Research Laboratory PRL

Ahmadābād, India
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Venkata Raman V.,Physical Research Laboratory PRL | Anandarao B.G.,Physical Research Laboratory PRL | Janardhan P.,Physical Research Laboratory PRL | Pandey R.,Mls University
Monthly Notices of the Royal Astronomical Society | Year: 2017

We present here Spitzer mid-infrared (IR) spectra and modelling of the spectral energy distribution (SED) of a selection of post-asymptotic giant branch (PAGB) stars. The mid-IR spectra of the majority of these sources showed spectral features such as polycyclic aromatic hydrocarbons (PAHs) and silicates in emission. Our results from SED modelling showed interesting trends of dependence between the photospheric and circumstellar parameters. A trend of dependence is also noticed between the ratios of equivalent widths (EWs) of various vibrational modes of PAHs and the photospheric temperature T* and model-derived stellar parameters for the sample stars. The PAGB mass-loss rates derived from the SED models are found to be higher than those for AGB stars. In a few objects, low- and high-excitation finestructure emission lines were identified, indicating their advanced stage of evolution. Further, IR vibration modes of fullerene (C60) were detected for the first time in the PAGB star IRAS 21546+4721. © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Sahu L.K.,Physical Research Laboratory PRL | Tripathi N.,Physical Research Laboratory PRL | Yadav R.,Physical Research Laboratory PRL
Environmental Pollution | Year: 2017

This paper presents the sources and characteristics of ambient volatile organic compounds (VOCs) measured using PTR-TOF-MS instrument in a metropolitan city of India during winter to summer transition period. Mixing ratios of VOCs exhibited strong diurnal, day-to-day and episodic variations. Methanol was the most dominant species with monthly mean values of 18–22 pbbv. The emission ratios of VOCs relative to benzene calculated from nighttime data were used to estimate the relative contributions of vehicle exhaust and other sources. The increasing daytime ratios of oxygenated-VOCs (OVOCs)/benzene and isoprene/benzene from February to March indicates increasing contribution of photo-oxidation and biogenic sources. Daytime fractions of acetone (18%), acetaldehyde (15%) and isoprene (4.5%) to the sum of measured VOCs in March were higher than those in February. Variations of VOCs at lower temperatures (<25 °C) were predominantly controlled by anthropogenic sources. At high temperatures, particularly in the range of 32–40 °C during March, levels of OVOCs and isoprene were influenced by biogenic emissions. The emissions of OVOCs from vehicle exhaust were estimated to be smaller (20–40%) than those from other sources. The contributions of biogenic and secondary sources to OVOCs and isoprene increased by 10–15% from winter to summer. This study provides evidence that the winter-to-summer transition has an impact on sources and composition of VOCs in tropical urban areas. © 2017 Elsevier Ltd

Sahu L.K.,Tokyo University of Science | Lal S.,Physical Research Laboratory PRL | Thouret V.,CNRS Laboratory for Aerology | Smit H.G.,Jülich Research Center
International Journal of Climatology | Year: 2011

Climatology of tropospheric ozone (O3) and water vapour (H2O) over a metro city of Chennai in southern India has been presented based on the Measurements of OZone and water vapour by Airbus In-service AirCraft (MOZAIC) data during 1996-2001. The seasonal trends in mixing ratio of O3 are discussed in view of annual changes in the transport pattern, rainfall, and its relationship with ambient H2O. The vertical distributions of both O3 and H2O show large seasonal variations. The observed high mixing ratios of O3 in winter and spring months can be attributed to long-range transport of pollutants by the northwesterly winds associated with winter monsoon circulation. The lowest mixing ratio of 15 ppbv of O3 from July to September coincides with the summer monsoon circulation over Indian subcontinent. The surface level mixing ratio of O3 was observed to be below 30 ppbv throughout the year. On the other hand, monthly rainfall and vertical distributions of H2O show just opposite seasonal variations to that of O3 mixing ratio. Chennai is a coastal city; therefore, the seasonal change in surface wind flow causes large variability in H2O concentrations of 6-30 g/kg in the lower troposphere. More or less similar annual patterns of mixing ratios of O3 and H2O are repeated during different years of 1996-1998, except for some small-scale differences. High level of O3 mixing ratio, particularly during the early winter months of year 1997, seems unusual as we do not see such trends for other year of measurements over Chennai. The case studies of profiles of O3, relative humidity (RH), and temperature in view of long-range transport over Chennai during the different seasons have been also discussed. Significant enhancements in tropospheric O3 were observed over Chennai due to transport of air from forest fire regions of Indonesia during October 1997. © 2010 Royal Meteorological Society.

Sahu L.K.,Physical Research Laboratory PRL | Sheel V.,Physical Research Laboratory PRL | Kajino M.,Japan Meteorological Agency | Kajino M.,Pacific Northwest National Laboratory | Nedelec P.,CNRS Laboratory for Aerology
Atmospheric Environment | Year: 2013

This paper analyses MOZAIC (Measurements of Ozone aboard Airbus in-service airCraft) measurements of carbon monoxide (CO) profiles over Bangkok to discuss the seasonality in vertical distribution during year 2005-2006. The mixing ratios of CO were enhanced in the lower troposphere being highest in winter followed by summer and wet seasons. During all the seasons, the mixing ratio of CO decreased rapidly and remained low in the middle troposphere. At higher altitudes (6-12 km), CO shows enhanced values particularly during wet and early winter seasons. The strong seasonality in CO was caused by the seasonal shift in the patterns of the long-range transport and biomass burning (BB) in South and Southeast Asia (S-SE Asia). Flow of cleaner air and negligible BB resulted in the lowest mixing ratio of CO in the wet season. In addition to anthropogenic influence, the long. -range transport and BB caused the higher CO in the winter and summer seasons, respectively. Despite extensive local BB activities in Thailand during the summer season, the moderate levels of CO were attributed to the dilution due to flow of cleaner marine from the Indian and Pacific Oceans. We have also compared the observations with the Model for Ozone And Related Chemical Tracers (MOZART) simulations. Mostly the observations lie between the MOZART-2 and MOZART-4 simulations as they underestimate and overestimate the observed CO, respectively. In the middle and upper troposphere, both the observed and simulated mixing ratios of CO during September-November of year 2006 were higher by 15-30 ppbv compared to the same period of year 2005. Our analysis indicates the impact of El Niño induced extensive BB in Indonesia during the year 2006. © 2012 Elsevier Ltd.

Chakrabortty J.,Physical Research Laboratory PRL | Ghosh P.,Autonomous University of Madrid | Rodejohann W.,Max Planck Institute for Nuclear Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

New data on the lepton mixing angle θ 13 imply that the eμ element of the matrix m νmν†, where m ν is the neutrino Majorana mass matrix, cannot vanish. This implies a lower limit on lepton flavor violating processes in the eμ sector in a variety of frameworks, including Higgs triplet models or the concept of minimal flavor violation in the lepton sector. We illustrate this for the branching ratio of μ→eγ in the type II seesaw mechanism, in which a Higgs triplet is responsible for neutrino mass and also mediates lepton flavor violation. We also discuss processes like μ→eēe and μ→e conversion in nuclei. Since these processes have sensitivity on the individual entries of m ν, their rates can still be vanishingly small. © 2012 American Physical Society.

Bambhaniya G.,Physical Research Laboratory PRL | Goswami S.,Physical Research Laboratory PRL | Khan S.,Physical Research Laboratory PRL | Konar P.,Physical Research Laboratory PRL | And 2 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study the production of heavy neutrinos at the Large Hadron Collider through the dominant s-channel production mode as well as the vector boson fusion process. We consider the TeV scale minimal linear seesaw model containing two heavy singlets with the opposite lepton number. This model is fully reconstructible from oscillation data apart from an overall normalization constant which can be constrained from the metastability of the electroweak vacuum and bounds coming from lepton flavor violation searches. The Dirac nature of heavy neutrinos in this model implies suppression of the conventional same-sign-dilepton signal at the Large Hadron Collider. We analyze the collider signatures with the trilepton final state and missing transverse energy as well as vector boson fusion type signals which are characterized by two additional forward tagged jets. Our investigation reveals that due to stringent constraints on light-heavy mixing coming from lepton flavor violation and metastability bounds, the model can be explored only for a light to moderate mass range of heavy neutrinos. We also note that in case of a positive signal, flavor counting of the final trilepton channel can give information about the mass hierarchy of the light neutrinos. © 2015 American Physical Society.

Pramitha M.,National Atmospheric Research Laboratory NARL | Venkat Ratnam M.,National Atmospheric Research Laboratory NARL | Taori A.,National Atmospheric Research Laboratory NARL | Krishna Murthy B.V.,B1 | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Sources and propagation characteristics of high-frequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of ground-based (MST radar, radiosondes, MF radar) and rocket- and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50-100 km and 150-300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (~9 ms-1 km-1) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10-12 km altitude) and are thus identified to be the source for generating the observed high-phase-speed, high-frequency gravity waves. © Author(s) 2015.

Sahu L.K.,Physical Research Laboratory PRL
Indian Journal of Geo-Marine Sciences | Year: 2014

In the earth-ocean-atmosphere system, the halogenated species take part in the cycles of several key processes involving both gas and heterogeneous interactions. The atmospheric cycles of reactive halogens are very complex specifically for those emitted from natural sources. As far as their roles in the tropospheric chemistry, the halogen compounds particularly those containing bromine (Br) and chlorine (Cl) play key roles. The reaction rate constants of many trace gases with halogen radicals are faster than those with hydroxyl radicals (OH). Near the source regions, however, halogen radicals can greatly influence the oxidizing capacity of the troposphere due to their reactive behaviors. In the lower troposphere, particularly in the marine boundary layer (MBL) and polar boundary layer, the reactive halogen compounds cause substantial destruction of ozone. The in-situ observations are available only for very limited geographical regions mainly in the mid- and high- latitudes of the northern hemisphere. One of the reasons for the lack of studies could be the technological constraint owing to very reactive nature of halogens hence the uncertainty in detection and quantification. Nonetheless, it is imperative to study the photochemistry of halogens in global troposphere for the better understanding of chemistry-climate interactions. Many theoretical aspects related to photochemistry of halogenated species in the troposphere need to be verified by the observations. Present study highlighted recent scientific progress about the roles of reactive halogens and their measurements in the troposphere. In spite of greater scientific opportunities in atmospheric studies of halogens, study over Indian subcontinent and surrounding marine regions are almost nil. © 2014, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.

Bambhaniya G.,Physical Research Laboratory PRL | Chakrabortty J.,Physical Research Laboratory PRL | Goswami S.,Physical Research Laboratory PRL | Konar P.,Physical Research Laboratory PRL
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In this paper we consider the generation of naturally small neutrino masses from a dimension-7 operator. Such a term can arise in the presence of a scalar quadruplet and a pair of vectorlike fermion triplets and enables one to obtain small neutrino masses through the TeV scale linear seesaw mechanism. We study the phenomenology of the charged scalars of this model, in particular, the multilepton signatures at the Large Hadron Collider. Of special importance is the presence of the same-sign-tri-lepton signatures originating from the triply charged scalars. The Standard Model background for such processes is small, and hence this is considered as a confirming evidence of new physics. We also looked for events with three, four, five, and six leptons that have negligible contamination from the Standard Model. We further point out the spectacular lepton flavor violating the four-lepton signal that can be the hallmark for these types of models. We also compute the added contributions in the rate for the Standard Model Higgs decaying to two photons via the charged scalars in this model. © 2013 American Physical Society.

Sahu L.K.,Physical Research Laboratory PRL | Sheel V.,Physical Research Laboratory PRL
Journal of Atmospheric Chemistry | Year: 2014

In this study, we have investigated the seasonality and long-term trends of major biomass burning (BB) sources over South and Southeast Asia (S-SE Asia). The activities of BB and related emissions show bi-modal seasonality in S-SE Asia. From January to May period, the BB dominates in the northern hemisphere parts of S-SE Asia. From July to September, the activities shift to the southern hemisphere where the emissions from Indonesian and Malaysian islands make largest contributions. Overall, the activities of BB are lowest during October-December period in S-SE Asia. The seasonality of BB intensity and rain are just opposite in the phase over India. The climatological (1997-2008) emissions of carbon monoxide (CO), oxides of nitrogen (NOx) and non-methane hydrocarbons (NMHCs) show strong spatio-temporal variation. The trends show large inter-annual variations with highest and lowest values during years 1997 and 2000, respectively. In the southern hemisphere parts of S-SE Asia mainly in Indonesia, the intensity of biomass fires has been modulated by the large scale climatic phenomena like El Niño and Southern Oscillation (ENSO). The annual emissions of trace gases in southern hemisphere region during the El Niño years exceed to those for the normal years. The estimates for northern hemisphere region during the La Niña years were significantly higher than those for the normal years. The Model for Ozone And Related Chemical Tracers (MOZART) simulations of columnar CO and NOx tend to capture the prominent features of BB emissions in S-SE Asia. The impacts of extensive fires in Indonesia during El Niño year of 2006 compared to a normal year of 2005 were clearly seen in the MOZART-4 simulations of both CO and NOx. © 2013 Springer Science+Business Media.

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