Browsing by Author "Ashok Kumar Singh"

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Antimutagenic potential of neem leaves extract against cadmium-induced genotoxicity in root meristem cells of Allium cepa L.
(2011) Aradhana Singh; Ashok Kumar Singh
In this study, the Allium cepa root tip cells were exposed to ethanolic extract of neem leaves in order to assess its effectiveness against the genotoxic effects of cadmium by the use of chromosome aberration assay. Incubation of the Allium roots in CdCl2 solution lowered the mitotic index value and also induced different types of chromosomal abnormalities. Preincubation of onion roots in the ethanolic extract of neem leaves caused a slight increase in mitotic index and significant decrease in the total number of chromosomal abnormalities induced by the heavy metal alone. These data suggest a protective action of neem leaves extract against heavy metal toxicity.
Cadmium toxicity to photosynthesis and associated electron transport system of Nostoc linckia
(Springer-Verlag, 1991) Yasmin Husaini; Ashok Kumar Singh; L.C. Rai
[No abstract available]
Climatic Water Balance of a Tropical Deciduous Forest of India
(1980) Ashok Kumar Singh; Kailash Nath Misra
[No abstract available]
Comparative analyses of genotoxicity, oxidative stress and antioxidative defence system under exposure of methyl parathion and hexaconazole in barley (Hordeum vulgare L.)
(Springer Verlag, 2015) Pragyan Dubey; Amit Kumar Mishra; Ashok Kumar Singh
The present study aims to evaluate the comparative effects of methyl parathion and hexaconazole on genotoxicity, oxidative stress, antioxidative defence system and photosynthetic pigments in barley (Hordeum vulgare L. variety karan-16). The seeds were exposed with three different concentrations, i.e. 0.05, 0.1 and 0.5 % for 6 h after three pre-soaking durations 7, 17 and 27 h which represents G1, S and G2 phases of the cell cycle, respectively. Ethyl methane sulphonate, a well-known mutagenic agent and double distilled water, was used as positive and negative controls, respectively. The results indicate significant decrease in mitotic index with increasing concentrations of pesticides, and the extent was higher in methyl parathion. Chromosomal aberrations were found more frequent in methyl parathion than hexaconazole as compared to their respective controls. Treatment with the pesticides induced oxidative stress which was evident with higher contents of H2O2 and lipid peroxidation, and the increase was more prominent in methyl parathion. Contents of total phenolics were increased; however, soluble protein content showed a reverse trend. Among the enzymatic antioxidants, activities of superoxide dismutase and peroxidase were significantly up-regulated, and more increase was noticed in hexaconazole. Increments in total chlorophyll and carotenoid contents were observed up to 0.1 % but decreased at higher concentration (0.5 %), and the reductions were more prominent in methyl parathion than hexaconazole as compared to their respective controls. Methyl parathion treatment caused more damage in the plant cells of barley as compared to hexaconazole, which may be closely related to higher genotoxicity and oxidative stress. © 2015, Springer-Verlag Berlin Heidelberg.
Cyclopeptide alkaloids from Zizyphus sativa bark
(2008) Manoj Bhushan Pandey; Ashok Kumar Singh; Virendra Pratap Singh; Vidya Bhushan Pandey
A new cyclopeptide alkaloid, sativanine-M (1), together with known alkaloid nummularine-P have been isolated from the stem bark of Zizyphus sativa and identified by spectral analysis.
Day time observations of precursors at low latitude
(Springer Netherlands, 1996) U.P. Singh; Ashok Kumar Singh; D.P. Singh; R.P. Singh
Whistler precursors observed during day time at low latitude ground station Gulmarg (Geomag. Lat. 24° 10′ N) and their morphological features are reported. Transverse resonance interaction between whistler mode wave and counter streaming energetic electrons as the probable generation mechanism has been worked out. Minimum anisotropy required for wave amplification, parallel energy of resonating electrons and wave growth rate relevant to generation mechanism is studied. © 1996 Kluwer Academic Publishers.
Daytime Obserations of chorus emissions at low latitude
(Canadian Science Publishing, 1994) R.P. Singh; U.P. Singh; Ashok Kumar Singh; D.P. Singh
DISCRETE VERY-LOW-FREQUENCY CHORUS EMISSIONS OBSERVED DURING THE DAYTIME AT GROUND STATION GULMARG (GEOMAG. LAT. 24°10′N) ARE REPORTED. THE GENERATION OF THESE EMISSIONS IS EXPLAINED IN TERMS OF TRANSVERSE RESONANCE INTERACTION BETWEEN WHISTLER WAVES AND COUNTER-STREAMING ENERGETIC ELECTRONS. THE THEORY IS TESTED BY EVALUATING DIFFERENT PARAMETERS. © 1994 Canadian Science Publishing. All rights reserved.
Differential sensitivity of barley (Hordeum vulgare L.) to chlorpyrifos and propiconazole: Morphology, cytogenetic assay and photosynthetic pigments
(Academic Press Inc., 2015) Pragyan Dubey; Amit Kumar Mishra; Pratiksha Shukla; Ashok Kumar Singh
The present investigation was performed to evaluate the effects of an insecticide and fungicide, namely, chlorpyrifos (CP) and propiconazole (PZ) on barley (Hordeum vulgare L. variety Karan-16). The seeds were treated with three concentrations of CP and PZ, i.e., 0.05%, 0.1% and 0.5% for 6 hours after different pre-soaking durations of 7, 17 and 27 hours. Different pre-soaking durations (7, 17 and 27 h) represent three phases of the cell cycle i.e., G1, S and G2, respectively. Double distilled water and ethyl methane sulfonate were used as negative and positive controls, respectively. As compared to their respective controls, treated root tip meristematic cells of barley showed significant reductions in the germination percentage, seedling height, mitotic index and comparative increase in chromosomal aberrations against both the pesticides, and the magnitude was higher in CP. After treatment with the pesticides, chlorophyll and carotenoid contents increased up to 0.1% but reduced at 0.5% and the decrease was more prominent in CP as compared to PZ. In treated cells, fragmentation, stickiness, bridges, multipolar anaphase and diagonal anaphase were observed as aberrations. As compared to control, chromosomal aberrations were higher in CP as compared to PZ. The results of the present study concluded that CP induced chromosomal aberrations were more frequent than PZ; hence it has higher probability to cause genotoxicity in barley. © 2015 Elsevier Inc.
Effect of a Point/Line Heat Source on Hydromagnetic Free Convection between Vertical Walls due to Induced Magnetic Field
(Springer, 2022) Naveen Dwivedi; Ashok Kumar Singh
The hydromagnetic natural convective flow of an incompressible electrically conducting and viscous liquid amid non-conducting vertical walls with a constant point heat source/sink under the impact of the induced magnetic field has been studied. A wavelet function is used to formulate the point heat source. The considered problem is described by a group of simultaneous ODEs with significant boundary conditions, and their solutions have been acquired for the induced magnetic field, the velocity field and the temperature field by applying the Laplace technique. The skin friction, induced current density and mass flux have also been discussed. The influences of controlling parameters on the fluid flow are discussed with the tables and graphs. The valuable consequence of this investigation is that an enhancement in the length of point heat source enhances the induced magnetic field, velocity, induced current density and temperature field. © 2020, The National Academy of Sciences, India.
Effect of line/point heat source and Hall current with induced magnetic field on free convective flow in vertical walls
(Springer, 2022) Naveen Dwivedi; Ashok Kumar Singh
In this research, the hydromagnetic natural convection of an incompressible fluid with point heat source by considering the influence of Hall current and induced magnetic field between infinite vertical walls is studied. The Laplace transform procedure is utilized to determine the analytical solutions of the acquired mathematical model with the wavelet function. With the derived solution of velocity, induced magnetic field, temperature field, and induced current density, the flow character is investigated with the influence of the physical parameters (namely Hall current, Hartmann number, and point heat source) for the presented boundary conditions. Also, the skin friction and volumetric flow rate are derived through the velocity expression. Numerical and graphical results are introduced to formalize the solution of the model. The valuable result from the investigation is that an increase in the length of the point heat source leads to enhance both components of induced current density, induced magnetic field, and primary velocity profiles. Moreover, it is noticeable that an enhancement in the Hall current has a reverse connection with both components of the induced current density, induced magnetic field, while the direct connection with the primary velocity component. There are numerous engineering applications such as the metal cutting, grinding, welding, laser hardening of metals, and many others in which the calculation of temperature field is modeled as a problem involving a point heat source. © 2021, Indian Association for the Cultivation of Science.
Effect of point/line heat source and Hall current on free convective flow between two vertical walls
(Springer, 2020) Naveen Dwivedi; Ashok Kumar Singh
The influence of a point heat source and Hall current on the laminar hydromagnetic free convective flow of an incompressible and electrically conducting viscous liquid between two vertical walls has been studied. A wavelet function is utilised to mathematically formulate the point or line heat source. The incidental equations on the flow have been processed subject to the Boussinesq approximation. A unified analytical solution of basic equations like thermal energy and momentum has been derived by employing Laplace transform technique. The impacts of the pertinent physical parameters, such as Hall parameter, magnetic field and point heat source, on the velocity field are explained graphically. The valuable result from the investigation is that an increase in the length of the point heat source leads to the enhancement of the velocity profiles. Moreover, it is noticeable that an enhancement of Hall current has a direct connection with the primary factor of the volumetric flow rate and skin friction. © 2020, Indian Academy of Sciences.
Effect of qGN4.1 QTL for Grain Number per Panicle in Genetic Backgrounds of Twelve Different Mega Varieties of Rice
(Springer New York LLC, 2018) Vijay Kumar Singh; Ranjith Kumar Ellur; Ashok Kumar Singh; M. Nagarajan; Brahma Deo Singh; Nagendra Kumar Singh
Background: Rice is a major source of food, particularly for the growing Asian population; hence, the utilization of genes for enhancing its yield potential is important for ensuring food security. Earlier, we have mapped a major quantitative trait loci (QTL) for the grain number per panicle, qGN4.1, using biparental recombinant inbred line (RIL) populations involving a new plant type Indica rice genotype Pusa 1266. Later, three independent studies have confirmed the presence of a major QTL for spikelet number by three different names (SPIKE, GPS and LSCHL4) in the same chromosomal region, and have implicated the overexpression of Nal1 gene as the causal factor for high spikelet number. However, the effect of qGN4.1 in different rice genetic backgrounds and expression levels of the underlying candidate genes is not known. Results: Here, we report the effect of qGN4.1 QTL in the genetic backgrounds of 12 different high-yielding mega varieties of rice, introgressed by marker assisted-backcross breeding (MABB) using two QTL positive markers for foreground selection and two QTL negative flanking markers for recombinant selection together with phenotypic selection for the recovery of recipient parent genetic background. Analysis of the performance of BC2F3 plants showed a significant increase in the average number of well-filled grains per panicle in all the backgrounds, ranging from 21.6 in CSR 30-GN4.1 to 147.6 in Samba Mahsuri-GN4.1. Furthermore, qGN4.1 caused a significant increase in flag leaf width and panicle branching in most backgrounds. We identified BC3F3qGN4.1 near-isogenic lines (NILs) with 92.0–98.0% similarity to the respective recipient parent by background analysis using a 50 K rice SNP genotyping chip. Three of the NILs, namely Pusa Basmati 1121-GN4.1, Samba Mahsuri-GN4.1 and Swarna-GN4.1, showed a significant yield superiority to their recipient parents. Analysis of differential gene expression revealed that high grain number in these QTL-NILs was unlikely due to the overexpression of Nal1 gene (LOC_Os04g52479). Instead, another tightly linked gene (LOC_Os04g52590) coding for a protein kinase domain-containing protein was consistently overexpressed in the high grain number NILs. Conclusion: We have successfully introgressed the qGN4.1 QTL for high grain number per panicle into 12 different mega varieties of rice using marker-assisted backcross breeding. The advanced near-isogenic lines are promising for the development of even higher yielding versions of these high-yielding mega varieties of rice. © 2018, The Author(s).
Effects of nonuniform heating and viscosity variation on transient natural convection around a vertical plate in a porous medium
(American Institute of Physics, 2025) n. Anurag; Anand Kumar; Richa Rajora; Vijay Kumar Sukariya; Ashok Kumar Singh
This study investigates the effect of nonuniform heating and temperature-dependent viscosity on transient free convective flow in a porous material adjacent to a semi-infinite upright plate. Such scenarios are relevant to applications such as the cooling of electronic devices, solar energy systems, and geophysical processes. The governing equations are transformed into dimensionless form and subsequently solved using the Crank–Nicolson technique. The results reveal that velocity increases with increasing viscosity parameter ζ = 0, 2, 4 at all cross-sections, while the temperature decreases at x = 0.25 and 0.5, but rises at x = 0.75, with the maximum free-stream velocity occurring at x = 0.75 for ζ = 2. Additionally, velocity and temperature attain their highest values near the plate, with the boundary layers growing over time. Eventually, both velocity and temperature stabilize, signifying the attainment of a steady-state condition. The local Nusselt number exhibits an increasing trend with increasing Darcy, Prandtl, and Grashof numbers, indicating improved heat transfer, while increasing viscosity contributes to a reduction in local skin friction. Moreover, nonuniform heating leads to the highest temperature at x = 0.5, which decreases at x = 0.75, and reaches its lowest value at x = 0.25. © 2025 Author(s).
Efficient tillage and nutrient management practices for sustainable yields, profitability and energy use efficiency for rice-based cropping system in different soils and agro-climatic conditions
(2013) G. R. Maruthi Sankar; K.L. Sharma; K. Srinivas Reddy; G. Pratibha; Reshma Shinde; S.R. Singh; A.K. Nema; R.P. Singh; B.S. Rath; A. Mishra; B.D. Behera; C.R. Subudhi; Bhagwan Singh; H.C. Singh; Ashok Kumar Singh; D.K. Rusia; M.S. Yadava; C.R. Thyagaraj; P.K. Mishra; M. Suma Chandrika; B. Venkateswarlu
Long-term tillage and fertilizer experiments were conducted in rice in kharif followed by lentil in dry subhumid Inceptisols at Varanasi and Faizabad; horse gram at Phulbani and linseed at Ranchi in moist subhumid Alfisols in rabi during 2001 to 2010. The study was conducted to assess the effect of conventional tillage (CT), low tillage + interculture (LT1) and low tillage + herbicide (LT2) together with 100% N (organic) (F1), 50% N (organic) + 50% N (inorganic) (F2) and 100% N (inorganic) (F3) on productivity, profitability, rainwater and energy use efficiencies. The results at Varanasi revealed that CT was superior with mean yield of 2389 kg ha-1, while F1 was superior with 2378 kg ha-1 in rice. At Faizabad, CT was superior with mean rice yield of 1851 kg ha-1 and lentil yield of 977 kg ha -1, while F1 was superior with 1704 and 993 kg ha-1 of rice and lentil, respectively. At Phulbani, F2 was superior with rice yield of 1170 kg ha-1. At Ranchi, F2 with rice yield of 986 kg ha-1 and F3 with linseed yield of 224 kg ha-1 were superior. The regression model of crop seasonal rainfall and yield deviations indicated an increasing trend in rice yield over mean (positive deviation) with increase in rainfall at all locations; while a decreasing trend (negative deviation) was found for lentil at Faizabad, horse gram at Phulbani and linseed at Ranchi. Based on economic analysis, CTF1 at Varanasi and Faizabad, CTF2 at Phulbani and LT2F2 at Ranchi were superior. Copyright © 2013 Cambridge University Press.
Geomorphic Evidences of Neotectonic Activity in the Lower Chambal River Basin (Central India) Using Geospatial Technology
(Pleiades Publishing, 2025) Pawan Kumar Gautam; B. Vishwakarma; Dhirendra Kumar; Ashok Kumar Singh; Narendra Kumar; Sh Patel
Abstract: The Chambal River is a significant tributary of the Yamuna River. It originates from the Janapav Valley, Malwa Ridge of Madhya Pradesh, India, which is characterized by rugged geomorphic features such as gullies, ravines, and badland topography. The objective of the study is to understand the surface variability of the river by identifying the geomorphic evidence with the help of remote sensing (RS) and mathematical equations. The computing and numerical formulas of drainage parameters (linear, areal, relief, morpho-tectonic, and geometric) and the geo-processing model give the linear method. The Chambal River has 8th order and dendritic drainage pattern. The Chambal River has 8th order and dendritic drainage pattern. It has seven sub-basins: Mej, Banas, Kshipra, Choti Kali Sindh, Kali Sindh, Parbati, and Kuno. The estimated bifurcation ratio (3.32 to 6.46) and mean bifurcation ratio (4.32) show the geological and structural control of the drainage pattern. A drainage density value of 0.58 km/km2 suggests a relatively efficient drainage system, where streams meander gently across a flat landscape, facilitating moderate yet steady water flow. A drainage texture of 17.19 km–1 indicates a very fine texture, characterized by numerous small, closely spaced channels. This contributes to intricate erosion patterns, commonly observed in badlands. The escarpment heights along the left and right banks of the Chambal River are typical 13.64 to 13.72 m respectively. The Chambal River exhibits a gradual elevation decrease, though the profile shows localized ups and downs, indicating tectonic disturbances. The asymmetry factor of 44.98 indicates that the basin is tilted toward the left bank. The hypsometric integral of 0.50 suggests the river is moderately eroded. The rugged terrain of the Chambal River basin necessitates protection measures to control the degradation of natural resources, including soil and water, emphasizing the importance of sustainable management practices in this ecologically sensitive region. © Pleiades Publishing, Ltd. 2025.
Ground-state structures in ordered binary h.c.p. alloys
(1991) Ashok Kumar Singh; Shrikant Lele
Ground-state ordered structures in binary h.c.p. alloys have been studied. Nonideal axial ratios and pairwise interactions up to third-nearest neighbours have been considered. Ordered structures have been constructed by dividing the atomic sites into several sublattices ranging from a minimum of 6 to a maximum of 28. Ordered structures have been generated by identifying distinct layers arising for each sublattice division by populating them with two types of atoms, A and B, and then stacking such layers. Twelve energetically distinct structures with lowest energies for certain values of the interchange energy parameters have been identified. Three other structures have been found which probably belong to the ground-state. Complete structural details have been worked out and energy expressions found for these. Degeneracy occurs in several ways. The first is associated with the occurrence of several stoichiometric structures with the same energy. A second type of degeneracy is exhibited by stoichiometric structures with compositions intermediate to two terminal ground-state structures and energies equal to those of a mixture of the latter. For off-stoichiometric situations, composition regions corresponding to the presence of miscibility gaps or solid solutions are discussed. The latter show a third type of degeneracy where the solid solution, which is partially ordered, has the same energy as that of an ordered structure. © 1991 Taylor & Francis Ltd.
Hydromagnetic free convection in a vertical channel with induced magnetic field: Open and short circuits
(Springer, 2022) Naveen Dwivedi; Ashok Kumar Singh; Pallath Chandran; Nirmal C Sacheti
This theoretical paper deals with a fully developed free convective flow of an incompressible viscous and electrically conducting fluid in an infinitely long rigid vertical channel in the presence of an externally applied magnetic field. By retaining the induced magnetic field, we have carried out a detailed analysis of the field equations and obtained a host of interesting results corresponding to both open-circuit and short-circuit arrangements. The governing PDEs, which under the chosen physical configuration get transformed to a set of ordinary differential equations together with appropriate boundary conditions, have further been subjected to non-dimensionalisation. Using the theory of simultaneous ordinary differential equations, the analytical solutions for velocity, temperature field and induced magnetic field were obtained. These solutions were used to obtain important quantities of engineering interest such as current density, wall skin friction and volumetric flux for both open and short circuits. The effect of Hartmann number on the velocity, induced magnetic field and induced current density were shown quite extensively. Furthermore, the results for the symmetric and asymmetric heating of the vertical walls of the channel for open- and short-circuit arrangements were compared. It is found that for the open-circuit arrangement, the velocity, induced current density and induced magnetic field are higher than that for the short-circuit arrangement. © 2022, Indian Academy of Sciences.
Hydromagnetic free convective flow in vertical cylinder due to point/line heat source/sink
(Springer, 2022) Naveen Dwivedi; Ashok Kumar Singh
The current study is to explore the phenomena of the hydromagnetic free convective flow of an electrically conducting and incompressible viscous fluid through an impermeable vertical cylinder, with the point heat source under the influence of the transversely applied magnetic field of uniform strength in the radial direction. The free convection phenomenon in the working fluid occurs due to the presence of the point/line heat source as it appears in many real-world mechanisms. The main motive of this analytical study is thus to examine the effect of point and line heat source on this buoyancy-dominated developing flow. The governing equations thus framed for the prescribed flow namely energy and momentum, simplify to steady linear differential equations in the physical setup assumed in this investigation. These equations, in non-dimensional forms, have been solved, in turn, employed simultaneous ordinary differential equations (ODEs) theory. The resulting closed form solutions for the physical variables, namely fluid temperature and fluid velocity have been presented in terms of Bessel, modified Bessel, and Regularized Hypergeometric functions. Additionally, skin friction coefficient, Nusselt number, and mass flow rate are numerically discussed for the involved parameters. There arises a number of pertinent physical parameters in our analysis: Heat source, Hartman number, and point heat source whose influence on the developing velocity and some temperature profiles have been illustrated through a number of plots. Major outcomes show that the enhancement in Hartmann number motivates a reduction in the velocity profile for the point and line heat source cases. In addition, the fluid motion rises due to the line and point heat source, and the velocity and temperature profiles have a higher value in the case of the line heat source as compared to the point heat source. © 2021, Indian Association for the Cultivation of Science.
Influence of Hall current on hydromagnetic natural convective flow between two vertical concentric cylinders in presence of heat source/sink
(John Wiley and Sons Inc, 2020) Naveen Dwivedi; Ashok Kumar Singh
The fully developed laminar magnetohydrodynamic free convection between two concentric vertical cylinders with Hall currents and heat source/sink, in the presence of the radial magnetic field, are studied. The governing thermal energy and momentum equations are changed into ordinary differential equations whose solutions are determined in closed-form expressions of the Bessel and modified Bessel functions of order zero. A parametric investigation illustrating the impacts of the Hall current, magnetic field, heat source, and radii ratio has been accomplished graphically to examine the changes in temperature as well as velocity while the Nusselt number, mass flux, and skin friction values have been presented in tabular forms. The results ensure that the Hall current has a strong and direct impact on the flow character, such that the influence of the Hall parameter enhances the velocity fields in the appearance of heat source and sink. The velocity remains almost constant as the Hall parameter value is greater than four. Moreover, the velocity and temperature fields have an increasing tendency due to the heat source and inversely for the heat sink. © 2020 Wiley Periodicals, Inc.
Influence of heat source/sink on free convection in annular porous region
(International Information and Engineering Technology Association, 2021) Anurag; Shyam Lal Yadav; Ashok Kumar Singh
The significant interpretation of this model is to explore the influence of temperature-dependent heat source/sink on laminar free-convective flow in an annular porous region such as petroleum engineering, thermal technique and groundwater hydrology. For a unified solution of the Brinkman-Darcy model, the regulatory equations solved analytically by applying the variation of parameter technique in terms of Bessel's functions for the heat source and sink. Moreover, we have investigated the Variations of Darcy number, Heat source/sink and viscosity ratio in the presence of isothermal and constant heat flux sequentially. As a result, we received the critical value of the velocity for the radii ratio (R = 2.05 and 2.92) in both the cases of source and sink (S = 1.0 and Si = 0.1) respectively which is exhibited through the graphs. Further, the numerical outcomes present of the skin friction including volume flow with annular gap by the graphs as well as tables. © 2021 International Information and Engineering Technology Association. All rights reserved.