Browsing by Author "Atul K. Srivastava"

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Black carbon and chemical characteristics of PM10 and PM 2.5 at an urban site of North India
(2009) Suresh Tiwari; Atul K. Srivastava; Deewan S. Bisht; Tarannum Bano; Sachchidanand Singh; Sudhamayee Behura; Manoj K. Srivastava; D.M. Chate; B. Padmanabhamurty
The concentrations of PM10, PM2.5 and their water-soluble ionic species were determined for the samples collected during January to December, 2007 at New Delhi (28.63° N, 77.18° E), India. The annual mean PM10 and PM2.5 concentrations (± standard deviation) were about 219 (± 84) and 97 (±56) μgm -3 respectively, about twice the prescribed Indian National Ambient Air Quality Standards values. The monthly average ratio of PM 2.5/PM10 varied between 0.18 (June) and 0.86 (February) with an annual mean of ∼0.48 (±0.2), suggesting the dominance of coarser in summer and fine size particles in winter. The difference between the concentrations of PM10 and PM2.5, is deemed as the contribution of the coarse fraction (PM10-2.5). The analyzed coarse fractions mainly composed of secondary inorganic aerosols species (16.0 μgm-3, 13.07%), mineral matter (12.32 μgm-3, 10.06%) and salt particles (4.92 μgm-3, 4.02%). PM2.5 are mainly made up of undetermined fractions (39.46 μgm-3, 40.9%), secondary inorganic aerosols (26.15 μgm-3, 27.1%), salt aerosols (22.48 μgm-3, 23.3%) and mineral matter (8.41 μgm-3, 8.7%). The black carbon aerosols concentrations measured at a nearby (∼300 m) location to aerosol sampling site, registered an annual mean of ∼14 (±12) μgm-3, which is significantly large compared to those observed at other locations in India. The source identifications are made for the ionic species in PM10 and PM2.5. The results are discussed by way of correlations and factor analyses. The significant correlations of Cl-, SO 4 2-, K+, Na+, Ca2+, NO 3 - and Mg 2+ with PM2.5 on one hand and Mg2+ with PM 10 on the other suggest the dominance of anthropogenic and soil origin aerosols in Delhi. © 2010 Springer Science+Business Media B.V.
Colony interactions and mycoparasitism between Acremonium furcatum and Aspergillus spp.
(Martinus Nijhoff/Dr. W. Junk Publishers, 1981) Atul K. Srivastava; D.B. Singh; Bharat Rai
Colony interactions and mycoparasitism between Acremonium furcatum and ten species of Aspergillus were studied in dual cultures. It was observed that A. furcatum overgrew the colonies of all the ten species of Aspergillus studied. During the mycoparasitic interactions frequent coiling, penetration and growth of hyphae of A. furcatum inside the conidiophores of six species of Aspergillus were observed. © 1981 Martinus Nijhoff/Dr W. Junk Publishers.
Decomposition and competitive colonization of leaf litter by fungi
(1983) Bharat Rai; Atul K. Srivastava
[No abstract available]
Gravity modulation of thermal instability in a viscoelastic fluid saturated anisotropic porous medium
(2012) Beer S. Bhadauria; Atul K. Srivastava; Nirmal C. Sacheti; Pallath Chandran
The present paper deals with a thermal instability problem in a viscoelastic fluid saturating an anisotropic porous medium under gravity modulation. To find the gravity modulation effect, the gravity field is considered in two parts: a constant part and an externally imposed time-dependent periodic part. The time-dependent part of the gravity field, which can be realized by shaking the fluid, has been represented by a sinusoidal function. Using Hill's equation and the Floquet theory, the convective threshold has been obtained. It is found that gravity modulation can significantly affect the stability limits of the system. Further, we find that there is a competition between the synchronous and subharmonic modes of convection at the onset of instability. Effects of various parameters on the onset of instability have also been discussed. © 2012 Verlag der Zeitschrift für Naturforschung, Tübingen.
Impacts of black carbon on environment and health
(Elsevier, 2021) Shani Tiwari; Bing Chen; Sachchidanand Singh; A.K. Singh; Atul K. Srivastava
During the last few decades, black carbon (BC) has attracted significant attention among scientific communities due to its observable hostile effects on air quality, agriculture, forests, human health, the economy, and environment. BC is a light-absorbing particle in the atmosphere that is emitted mainly from fossil fuels, biomass burning, and vehicular emissions. Although ample studies on BC aerosol characteristics have been carried out worldwide, significant uncertainties remain due to the different emission sources and their interactions with complex atmospheric processes. Thus, an in-depth understanding of BC and its potential impacts is greatly needed. This chapter presents a brief overview of the characteristics, sources, and transport mechanisms of BC and its impacts on the environment as well as human health. In addition, the chapter also highlights instructions to the public, policymakers, and local environmental bodies to control BC emissions. © 2021 Elsevier Inc. All rights reserved.
Intra-urban variability of particulate matter (PM2.5 and PM10) and its relationship with optical properties of aerosols over Delhi, India
(Elsevier Ltd, 2015) Suresh Tiwari; Philip K. Hopke; Atar S. Pipal; Atul K. Srivastava; Deewan S. Bisht; Shani Tiwari; Abhay K. Singh; Vijay K. Soni; Shiv D. Attri
Highly time-resolved measurements of particulate matter (PM: PM2.5 and PM10) were made at three different sites across Delhi (CCRI: a highly traffic site, IMD: a less traffic site and IITM: an urban background site) from 1st December, 2011 to 30th June, 2013. Also, coarse mode (PM10-2.5) mass was estimated as the difference between PM10 and PM2.5. In addition, columnar aerosol optical properties such as aerosol optical depth (AOD) and Angstrom exponent (AE) were studied concurrently over IMD. The mean mass concentrations of PM2.5, PM10-2.5 and PM10 were 118.3±81.7, 113.6±70.4 and 232.1±131.1μgm-3, respectively. Among the three sites, relatively higher mass concentrations of PM2.5 (~35% and 3%) were observed at CRRI compared to IMD and IITM.PM10 and PM10-2.5 were higher at these sites by ~31% and 19%; and 27% and 40%, respectively, compared to CRRI. Coefficients of divergence (COD) and correlation coefficients (r) were calculated between site pairs to assess the spatial and temporal heterogeneity of PM and moderate spatial divergence was found over the three sites. Traffic emission particles (PM2.5) exhibited high spatial heterogeneity as well. The mass concentrations of PM2.5 and PM10 were found to be higher during the night compared to the day. The mean PM2.5/PM10 ratio was ~51%, indicating generally equal amounts of coarse and fine mode PM in the Delhi urban atmosphere. AOD and PM2.5 were positively correlated and a negative correlation was observed between AE and PM10-2.5. PM2.5 particles were significantly correlated with AOD during post-monsoon and winter. Because of the lower vehicular emissions on weekends compared to weekdays, PM at CRRI, IMD, and IITM were separated by day of week and large heterogeneities were found. During weekdays, the mass concentrations of PM10 were ~4, 2, and 12% higher than on weekends. However, for PM2.5, weekend values were 5, 7, and 9% higher for CRRI, IMD and IITM, respectively. © 2015 Elsevier B.V.
Linear stability of solutal convection in a mushy layer subjected to gravity modulation
(Elsevier B.V., 2011) Atul K. Srivastava; B.S. Bhadauria
This study concentrates on instability problem due to solutal convection in a mushy layer of solidifying binary alloys, under the effect of gravity modulation. The gravitational field consists of two parts: a constant part and an externally imposed time-dependent periodic part. The time-dependent part of the gravity is expressed in Fourier series. Using Hill's equation and the Floquet theory, the convective threshold is obtained and effect of gravity modulation is examined. We compare our result with some known results. Further with the help of different graphs we discuss the effect of various physical parameters on the stability of the mushy region. © 2010 Elsevier B.V.
Long-Term Trend in Black Carbon Mass Concentration Over Central Indo-Gangetic Plain Location: Understanding the Implied Change in Radiative Forcing
(John Wiley and Sons Inc, 2024) Bharat Ji Mehrotra; Atul K. Srivastava; Amarendra Singh; Dirgha Parashar; Nabankur Majumder; R.S. Singh; Arti Choudhary; Manoj K. Srivastava
For the first-time, analysis of a decade long measurement of Black Carbon mass concentration (BC) was carried out at a representative central Indo-Gangetic Plain (IGP) location, Varanasi (25.30°N, 83.03°E, 79 m asl), from 2009 to 2021 to understand its physical, optical, and radiative impacts. During the 13-year study period, the daily BC mass concentration was found to vary between 0.07 and 46.23 μg m−3 (mean 9.18 ± 6.53 μg m−3) and showed a strong inter-annual and intra-annual variations. The inter-annual variability of BC showed a significant decreasing trend (−0.47 μg m−3 yr−1), with a maximum during the post-monsoon (−1.86 μg m−3 yr−1) and minimum during the pre-monsoon season (−0.31 μg m−3 yr−1). The Black Carbon Aerosol Radiative Forcing (BC-ARF) at the top of the atmosphere (BC-ARFT), surface (BC-ARFS), and within the atmosphere (BC-ARFA) was found to be 10.3 ± 6.4, −30.1 ± 18.9, and 40.5 ± 25.2 W m−2, respectively. BC-ARF also showed a strong inter-annual variability with a decreasing trend for BC-ARFT (−0.47 W m−2 yr−1) and BC-ARFA (−1.94 W m−2 yr−1), while it showed an increasing trend for BC-ARFS (1.33 W m−2 yr−1). Concentrated weighted trajectories (CWT) and potential source contribution function (PSCF) analyses were performed at the station to determine the potential source sectors and transport routes of BC aerosols. These analyses revealed that the long-range source of BC at Varanasi originates from the upper and lower IGP, central highlands, southern peninsular region, Pakistan, and even from the Central East Asia region. © 2024. American Geophysical Union. All Rights Reserved.
Magneto-convection in an anisotropic porous layer with Soret effect
(2012) Atul K. Srivastava; B.S. Bhadauria; Vinod K. Gupta
Thermal instability in an electrically conducting two component Boussinesq fluid-saturated-porous medium has been investigated, in the presence of Soret coefficient. The porous medium is confined between two horizontal surfaces, and subjected to a constant vertical magnetic field. Flow in the porous medium is characterized by generalized Darcy model, which includes the time derivative term. Performing linear and non-linear stability analysis, the effect of magnetic field on the stability of flow through porous medium has been investigated. The normal mode method is used in linear stability analysis, while a weak non-linear analysis based on a minimal representation of double Fourier series method is used in non-linear analysis. The critical Rayleigh number, wave number for stationary and oscillatory modes, and frequency of oscillations are obtained analytically using linear theory. Effects of various parameters on stationary, oscillatory and finite amplitude convection, rate of heat and mass transfer have been obtained analytically and presented graphically.© 2011 Published by Elsevier Ltd.
Magnetoconvection in an anisotropic porous layer using thermal nonequilibrium model
(2011) Atul K. Srivastava; B.S. Bhadauria; Jogendra Kumar
In the present article, we investigate the onset of thermal convection in an electrically conducting fluid-saturated porous medium, when the fluid and solid phases are not in local thermodynamic equilibrium. The porous medium is heated from below and cooled from above. The Darcy model with anisotropic permeability is used for porous medium, while two energy equations, each representing the solid and fluid phases separately, have been considered as energy equations. The linear stability theory is used to compute the critical Rayleigh number and the corresponding wavenumber for the onset of convective motion. Effects of various parameters on thermal stability has been examined. © 2011 by Begell House Inc.
Microbial decomposition of leaf litter as influenced by fertilizers
(Martinus Nijhoff/Dr. W. Junk Publishers, 1982) Bharat Rai; Atul K. Srivastava
A urea and NPK-mixture at concentration of 5, 10 and 15 mg g-1 air dry litter stimulated microbial populations, microbial activity and rate of decomposition of the litter. The stimulation was more pronounced as the concentration of the fertilizers was increased. However, this trend was reverse after two months in case of urea except for bacterial population. Fewer fungal species were isolated from the fertilizer-treated litter, together with a certain degree of alteration in the composition of mycoflora. © 1982 Martinus Nijhoff/Dr W. Junk Publishers.
Microbial decomposition of leaf litter as influenced by pesticides
(Martinus Nijhoff/Dr. W. Junk Publishers, 1983) Bharat Rai; Atul K. Srivastava
The application of dithane M-45, 2, 4-D and carbofuran at the rates of 1, 5 and 10 mg (active ingredients) per g air-dry litter caused insignificant variations in the microbial populations in decomposing leaf litter. The qualitative nature of mycoflora, was altered, a little, with regard to the total number of species and relative abundance of a few species. The variations in CO2 evolution was significant only in relation to the fungicidal treatment. Percent weight loss of treated and untreated litter differed insignificantly at the end except in the case of fungicidal treatment. The present study infers that the used concentrations of the test pesticides may be recommended in tropical forestry as their application does not pose any potential threat to the process of natural decomposition of the leaf litter. © 1983 Martinus Nijhoff/Dr W. Junk Publishers.
Study of heat transport by stationary magneto-convection in a Newtonian liquid under temperature or gravity modulation using Ginzburg-Landau model
(2012) P.G. Siddheshwar; B.S. Bhadauria; Pankaj Mishra; Atul K. Srivastava
The present paper deals with a weak non-linear stability problem of magneto-convection in an electrically conducting Newtonian fluid, confined between two horizontal surfaces, under a constant vertical magnetic field, and subjected to an imposed time-periodic boundary temperature (ITBT) or gravity modulation (ITGM). In the case of ITBT, the temperature gradient between the walls of the fluid layer consists of a steady part and a time-dependent oscillatory part. The temperature of both walls is modulated in this case. In the problem involving ITGM, the gravity field has two parts: a constant part and an externally imposed time periodic part, which can be realized by oscillating the fluid layer. The disturbance is expanded in terms of power series of amplitude of convection, which is assumed to be small. Using Ginzburg-Landau equation, the effect of modulations on heat transport is analyzed. Effect of various parameters on the heat transport is also discussed.© 2011 Published by Elsevier Ltd.
Time dependent perturbation theory and tones in cascaded erbium-doped fiber amplifier systems
(1997) Yan Sun; Adel A. M. Saleh; John L. Zyskind; David L. Wilson; Atul K. Srivastava; J.W. Sulhoff
The time dependent perturbation theory of the gain dynamics of erbium-doped fiber amplifiers (EDFA's) is presented in this paper. The perturbed output is expressed explicitly in terms of the input perturbation. The general theory is then applied to sinusoidal tones; the results agree well with the experiment.
Volatile and non-volatile metabolites of actinomycetes and the growth of some litter decomposing fungi
(1981) Bharat Rai; Atul K. Srivastava; D.B. Singh
[No abstract available]