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Search Results: 1 - 10 of 139117 matches for " Pradip K. Bhowmik "
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A New Method of Synthesizing Black Birnessite Nanoparticles: From Brown to Black Birnessite with Nanostructures
Marcos A. Cheney,Pradip K. Bhowmik,Shizhi Qian,Sang W. Joo,Wensheng Hou,Joseph M. Okoh
Journal of Nanomaterials , 2008, DOI: 10.1155/2008/763706
Abstract: A new method for preparing black birnessite nanoparticles is introduced. The initial synthesis process resembles the classical McKenzie method of preparing brown birnessite except for slower cooling and closing the system from the ambient air. Subsequent process, including wet-aging at 7°C for 48 hours, overnight freezing, and lyophilization, is shown to convert the brown birnessite into black birnessite with complex nanomorphology with folded sheets and spirals. Characterization of the product is performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and N2 adsorption (BET) techniques. Wet-aging and lyophilization times are shown to affect the architecture of the product. XRD patterns show a single phase corresponding to a semicrystalline birnessite-based manganese oxide. TEM studies suggest its fibrous and petal-like structures. The HRTEM images at 5 and 10 nm length scales reveal the fibrils in folding sheets and also show filamentary breaks. The BET surface area of this nanomaterial was found to be 10.6 m2/g. The TGA measurement demonstrated that it possessed an excellent thermal stability up to 400°C. Layer-structured black birnessite nanomaterial containing sheets, spirals, and filamentary breaks can be produced at low temperature (?49°C) from brown birnessite without the use of cross-linking reagents.
The Effect of Stirring on the Morphology of Birnessite Nanoparticles
Marcos A. Cheney,Pradip K. Bhowmik,Shingo Moriuchi,Mario Villalobos,Shizhi Qian,Sang W. Joo
Journal of Nanomaterials , 2008, DOI: 10.1155/2008/168716
Abstract: The effect of mechanical stirring on the morphology of hexagonal layer-structure birnessite nanoparticles produced from decomposition of KMnO4 in dilute aqueous H2SO4 is investigated, with characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and N2 adsorption (BET). Mechanical stirring during an initial stage of synthesis is shown to produce black birnessite containing nanofibers, whereas granular particulates of brown birnessite are produced without stirring. This is the first reduction synthesis of black birnessite nanoparticles with dendritic morphology without any use of organic reductant, and suggests that a particular morphology can arise from structural preferences of Mn in acidic conditions rather than particular organic reactants. These results enlighten the possibility of synthesizing nanoparticles with controlled size and morphology.
Synthesis and Characterization of Birnessite and Cryptomelane Nanostructures in Presence of Hoffmeister Anions
Marcos A. Cheney,Robin Jose,Arghya Banerjee,Pradip K. Bhowmik,Shizhi Qian,Joseph M. Okoh
Journal of Nanomaterials , 2009, DOI: 10.1155/2009/940462
Abstract: The effect of Hoffmeister anions Cl?, SO42?, and ClO4? on the structure and morphology of birnessite and cryptomelane-type manganese dioxide nanostructures, produced by the reduction reaction of KMnO4 and MnSO4 in aqueous acidic media, was studied. The syntheses were based on the decomposition of aqueous KMnO4 in presence of HCl for birnessite-type and acidified MnSO4 for cryptomelane-type manganese dioxide under soft hydrothermal conditions. They were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) techniques. XRD patterns show the formation of birnessite for the first synthesis and a mixture of cryptomelane and birnessite-types MnO2 for the second synthesis. XRD data revealed that the Hoffmeister anions have a significant effect on the nanostructures of birnessite. The sulphate ion-treated birnessite has the smallest crystals, whereas the chloride ion-treated birnessite has the largest crystals. Their TEM and HRTEM studies revealed a transformation from nanoplatelet morphology for chloride-treated samples to nanofibrous morphology for sulphate-treated birnessite. For the cryptomelane nanostructures, Hoffmeister anions also show a profound effect on their crystalline structures as determined by XRD analyses revealing a transformation of the cryptomelane phase to birnessite phase of MnO2. This transformation is also supported by TEM and HRTEM studies.
Systematics of Anti magnetic rotation in even-even Cd isotopes
Santosh Roy,S. Chattopadhyay,S. Pal,S. Bhattacharya,A. Goswami,Pradip Datta,H. C. Jain,R. Palit,R. K. Bhowmik,R. Kumar,S. Muralithar,R. P. Singh
Physics , 2010, DOI: 10.1016/j.physletb.2010.10.018
Abstract: The lifetimes for the high spin levels of the yrast band of $^{110}$Cd has been measured. The estimated B(E2) values decrease with increase in angular momentum. This is the characteristic of Anti magnetic rotation as reported in $^{106,108}$Cd. However, alignment behavior of $^{110}$Cd is completely different from its even-even neighbors. A model based on classical particle plus rotor has been used to explore the underlying systematics and develop a self consistent picture for the observed behavior of these isotopes.
Band crossing in Shears band of $^{108}$Cd
Santosh Roy,Pradip Datta,S. Pal,S. Chattopadhyay,S. Bhattacharya,A. Goswami,H. C. Jain,P. K. Joshi,R. K. Bhowmik,R. Kumar,S. Muralithar,R. P. Singh,N. Madhavan,P. V. Madhusudhana Rao
Physics , 2010, DOI: 10.1103/PhysRevC.81.054311
Abstract: The level lifetimes have been measured for a Shears band of $^{108}$Cd which exhibits bandcrossing. The observed level energies and B(M1) rates have been successfully described by a semi-classical geometric model based on shear mechanism. In this geometric model, the bandcrossing in Shears band has been described as the reopening of the angle between the blades of a shear.
Guest Editor's Introduction
Pradip K. Srimani
VLSI Design , 1995, DOI: 10.1155/1995/87424
Abstract:
Strange matter and its stability in presence of magnetic field
Pradip K Sahu
Physics , 1995,
Abstract: We study the effect of a magnetic field on the interacting quark matter and apply to strange star. We considere the low temperature approximation to strange matter. We find that the interacting strange quark matter is more stable compare to free quark gas in presence of strong external magnetic field with zero and finite temperature. We then calculate strange star structure parameters such as mass and radius and find that the strange star is more compact for interacting quark matter than free quark matter in presence of strong magnetic field.
Two-loop QED with External Magnetic Field
Pradip K Sahu
Physics , 1995,
Abstract: In two - loop effective Lagrangian, the low - temperature expansion of the $QED_{3+1}$ with a constant magnetic field and a finite chemical potential is performed. We then calculate the total fermion density, some components of polarization operator and de Hass -van Alphen oscillations. We find that there is a significant contribution from two-loop expansion to magnetization and fermion density for higher values of chemical potentials.
Soft Electromagnetic Radiations from Heavy Ion Colisions
Pradip K. Roy
Physics , 1997,
Abstract: The production of low mass dileptons and soft photons from thermalized Quark Gluon Plasma (QGP) and hadronic matter in relativistic heavy ion collisions is evaluated. A boost invariant longitudinal and cylindrically symmetric transverse expansion of the systems created in central collision of lead nuclei at CERN SPS, BNL RHIC, and CERN LHC, and undergoing a first order phase transition to hadronic matter is considered. A large production of low mass ($M<$ 0.3 GeV) dileptons, and soft photons ($p_T<$ 0.4 GeV) is seen to emanate from the bremsstrahlung of quarks and pions. We find an increase by a factor of 2--4 in the low mass dilepton and soft photon yield as we move from SPS to RHIC energies, and an increase by an order of magnitude as we move from SPS to LHC energies. Most of the soft radiations are found to originate from pion driven processes at SPS and RHIC energies, while at the LHC energies the quark and the pion driven processes contribute by a similar amount. The study of the transverse mass distribution is seen to provide interesting details of the evolution. We also find a unique universal behaviour for the ratio of $M^2$ weighted transverse mass distribution for $M=$ 0.1 GeV to that for $M=$ 0.2 and 0.3 GeV, as a function of $M_T$, for SPS, RHIC, and LHC energies, in the absence of transverse expansion of the system. A deviation from this universal behaviour is seen as a clear indication of the flow.
Conditional Disconnection Probability in Star Graphs
Walid Najjar,Pradip K. Srimani
VLSI Design , 1993, DOI: 10.1155/1993/84924
Abstract:
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