Adsorption of aqueous Pb(II), Cu(II), Zn(II) ions by amorphous tin(VI) hydrogen phosphate: an excellent inorganic adsorbent     

C. Zhu  X. Dong  Z. Chen  R. Naidu 《International Journal of Environmental Science and Technology》2016,13(5):1257-1268

Amorphous tin(VI) hydrogen phosphate (ATHP) was synthesized using the liquid phase precipitation method and served as an adsorbent to remove Pb(II), Cu(II), and Zn(II) from aqueous solutions. The ATHP was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption techniques. Adsorption properties were evaluated as a function of pH, reaction time, concentration of reactants, and salinity. Their equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich isotherms, respectively. The results revealed that adsorption equilibrium reached within 180 min. ATHP indicated good adsorption even below the pH_ZPC, and best adsorption at pH 5 for Pb(II) and Cu(II) and at pH 5.5 for Zn(II) was observed. Equilibrium data fitted better to the Langmuir model for Pb(II) and Cu(II) and fitted better to the Freundlich model for Zn(II). The saturated adsorption capacities deduced from the Langmuir model were 2.425, 1.801, and 0.600 mmol/g for Cu(II), Pb(II), and Zn(II), respectively, indicating an adsorption affinity order of Cu > Pb > Zn. There is a negative correlation between the concentration of NaCl and adsorption capacity of ATHP, yet ATHP still exhibited excellent adsorption having an adsorption capacity of 19.35, 15.16, 6.425 mg/g when the concentration of NaCl was 0.6 mol/L. The free energy (E) was 12.33, 10.70, and 14.74 kJ/mol for Pb(II), Cu(II), and Zn(II), respectively. An adsorption mechanism based on ion exchange between heavy metal ions and H⁺ in the ATHP is proposed. Furthermore, the used ATHP was regenerated by HCl solution and the adsorbent was used repeatedly.  相似文献   

Axially Symmetric Cosmic Strings in a Scalar-Tensor Theory     

D. R. K. Reddy  R. L. Naidu  V. U. M. Rao 《Astrophysics and Space Science》2006,306(4):185-188

Axially symmetric cosmological models with cosmic string source are obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A113, 467, 1985). The models obtained give us axially symmetric geometric (Nambu) string, p-string and Reddy string (Astrophys. Space Sci. 286, 2003b) in Saez-Ballester theory. Some physical properties of the models are also discussed.  相似文献   

Bianchi type-IX cosmic strings in a scalar-tensor theory of gravitation     

D. R. K. Reddy  R. L. Naidu 《Astrophysics and Space Science》2007,312(1-2):99-102

Bianchi type-IX space-time is considered in the presence of cosmic string source in the frame work of a scalar- tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1985). Exact cosmological models representing geometric (Nambu) string, p string and baratropic string are discussed in this theory. Some physical and kinematical properties of the models are also studied.  相似文献   

Approximate solutions for isothermal flows behind strong spherical shocks with variable energy     

G. Narasimhulu Naidu  M. P. Ranga Rao  Hira Lal Yadav 《Astrophysics and Space Science》1983,89(1):77-87

Self-similar unsteady flows with zero temperature gradient behind strong spherical shocks propagating in non-uniform perfect gas at rest are investigated. The total energy of the flow is assumed to be varying with the shock radius obeying a power law. Approximate solutions in a closed analytical form are obtained using the integral method. Also these solutions are shown to be useful to calculate easily and quickly the shock temperature, X-ray surface brightness and luminosity which are important in astrophysical problems. It is found that these approximate solutions are in close agreement with numerical solutions.  相似文献   

Textural studies on red sediments of Bhimunipatnam,Andhra Pradesh,east coast of India     

K. N. Murali Krishna  K. S. N. Reddy  Ch. Ravi Sekhar  P. Ganapathi Rao  K. Bangaku Naidu 《Journal of the Geological Society of India》2017,89(1):111-111

The study presents the textural characteristics of late Quaternary red sediments of Bhimunipatnam to understand the process of formation of these sediments. The red sediments are classified into (a) yellow sediments (b) reddish brown sediments (c) brick red sediments and (d) light yellow sediments sequence in the vertical litho section. The yellow sediments, rests on the khondalite basement, comprises of medium grained, moderate to poorly sorted and positively skewed. The rounded pebble beds with trough cross bedding indicate high energy turbulent conditions of deposition. The fining upward sequences indicate sediments were deposited under decreasing energy conditions under fluvial regime.The iron bearing minerals like garnets and pyriboles have undergone chemical weathering under high oxidizing environment resulting in addition of silt and clay to the reddish brown and brick red sediments and concretions were formed by carbonate precipitation. These processes caused changes in the mean grain size and sorting nature of these sediments which are originally aeolian in origin. The light yellow sediments were medium to fine grained, well sorted and similar to modern dune sands in terms of textural parameters. These sediments were deposited under low oxidation environmental conditions and acquired yellow colour due to Fe hydroxides.  相似文献   

Multiple Regressive Pattern Recognition Technique: An Adapted Approach for Improved Georesource Estimation     

Thomas?Oommen  Debasmita?MisraEmail author  Anupma?Prakash  Sukumar?Bandopadhyay  Sathy?Naidu  John?J.?Kelley 《Natural Resources Research》2011,20(1):11-24

Multiple Regressive Pattern Recognition Technique (MRPRT) is an adapted approach for improved geologic resource estimation. We developed and tested this approach for the Platinum (Pt) bearing region near Goodnews Bay, Alaska, which presents an example of a complex depositional environment. We applied geospatial and pattern recognition methods to assess the spatial distribution of offshore Pt in the Goodnews Bay area from point data collected by various agencies. We used the coefficient of correlation (r) and the Nash–Sutcliffe efficiency (E) to quantitatively assess the degree of accuracy of the estimated Pt distribution. We split the study area, based on trend analysis, into two regions: inside the Bay and outside the Bay. We could not obtain appreciable estimates from the geospatial and pattern recognition methods. Using MRPRT, we were able to improve r from 0.57 to 0.93 and the E from 28.31 to 92.91 inside the Bay. We achieved improvement in r from 0.55 to 0.61 and E from 28.46 to 34.52 outside the Bay. The reasons for a non-significant improvement outside the Bay have been discussed. The results indicate that the proposed MRPRT has wide application potential in georesource estimation where input data is often scarce.  相似文献   

An integrated approach to investigate saline water intrusion and to identify the salinity sources in the Central Godavari delta, Andhra Pradesh, India     

Naidu L.S.  G. Rao V.V.S.  T. Rao G.  Mahesh J.  Padalu G.  Sarma V.S.  Prasad P.R.  Rao S.M.  R. Rao B.M. 《Arabian Journal of Geosciences》2013,6(10):3709-3724

The Central Godavari delta is located along the Bay of Bengal Coast, Andhra Pradesh, India, and is drained by Pikaleru, Kunavaram and Vasalatippa drains. There is no groundwater pumping for agriculture as wells as for domestic purpose due to the brackish nature of the groundwater at shallow depths. The groundwater table depths vary from 0.8 to 3.4 m and in the Ravva Onshore wells, 4.5 to 13.3 m. Electrical Resistivity Tomography (ERT) surveys were carried out at several locations in the delta to delineate the aquifer geometry and to identify saline water aquifer zones. Groundwater samples collected and analyzed for major ions for assessing the saline water intrusion and to identify the salinity origin in the delta region. The results derived from ERT indicated low resistivity values in the area, which can be attributed to the existence of thick marine clays from ground surface to 12–15 m below ground level near the coast and high resistivity values are due to the presence of coarse sand with freshwater away from the coast. The resistivity values similar to saline water <0.01 Ω m is attributed to the mixing of the saline water along surface water drains. In the Ravva Onshore Terminal low resistivity values indicated up coning of saline water and mixing of saline water from Pikaleru drain. The SO ₄ ^?2 /Cl^?and Na⁺²/Cl^?ratios did not indicate saline water intrusion and the salinity is due to marine palaeosalinity, dilution of marine clays and dissolution of evaporites.  相似文献   

A five dimensional Kaluza-Klein bulk viscous string cosmological model in Brans-Dicke scalar-tensor theory of gravitation     

R. L. Naidu  K. Dasu Naidu  K. Shobhan Babu  D. R. K. Reddy 《Astrophysics and Space Science》2013,347(1):197-201

In this paper, we have investigated a five dimensional Kaluza-Klein space-time in the frame work of Brans-Dicke (Phys. Rev. 124:925, 1961) scalar-tensor theory of gravitation when the source of energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. We have obtained a determinate solution of the field equations using the special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) We have also used a barotropic equation of state for the pressure and density. Some physical properties of the model are also discussed.  相似文献   

Causal temperature profiles in horizon-free collapse     

N. F. Naidu  M. Govender 《Journal of Astrophysics and Astronomy》2007,28(4):167-174

We investigate the causal temperature profiles in a recent model of a radiating star undergoing dissipative gravitational collapse without the formation of a horizon. It is shown that this simple exact model provides physically reasonable behaviour for the temperature profile within the framework of extended irreversible thermodynamics.  相似文献   

Computation of telluric field and apparent resistivity over an anticline     

K. K. Roy  P. S. Naidu 《Pure and Applied Geophysics》1970,80(1):205-217

Summary A combination of Schwarz-Christofel method and numerical methods of solving non-linear differential equations has enabled us to solve for the effect of an anticline on the telluric field and apparent resistivity. From the computed anomaly curves we conclude that complete information about an anticline can be obtained only if its height is at least thirty per cent of the total depth to the basement. However, partial information; e.g., depth to the top of an anticline, can be obtained even for smaller anticlines.  相似文献