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Now showing items 1 - 16 of 136

  • Strength Prediction in NiCo Alloys - The Role of Composition and Nanotwins

    Chowdhury, P.   Sehitoglu, H.   Maier, H.J.   Rateick, R.  

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  • On the Design of Energy-Efficient Mixed-Line-Rate (MLR) Optical Networks

    Chowdhury, P.   Tornatore, M.   Nag, A.   Ip, E.   Ting Wang   Mukherjee, B.  

    With increasing energy consumption of the Internet, it is now imperative to design energy-efficient network architectures and protocols. Optical technologies have significant promise in improving the energy efficiency of network infrastructures. Future optical backbone networks will be heterogeneous in nature where a single link may carry various line-rate signals. This mixed-line-rate (MLR) network architecture is shown to be cost effective in satisfying heterogeneous traffic demands. In this study, we present mathematical models that can act as references for designing energy- and cost-efficient MLR optical networks. We also perform a comparative study of the energy efficiency of MLR and special cases of MLR design, named as single-line-rate networks (where all the links have same line rates). We explore the scenarios where the MLR networks minimize energy consumption. Finally, we investigate the relationship between energy-minimized and cost-minimized MLR network design.
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  • Mechanisms of fatigue crack growth - a critical digest of theoretical developments

    Chowdhury, P.   Sehitoglu, H.  

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  • Building a Green Wireless-Optical Broadband Access Network (WOBAN)

    Chowdhury, P.   Tornatore, M.   Sarkar, S.   Mukherjee, B.  

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  • Nano-structured Exchange-spring Hard Magnetic Thin Films

    Chowdhury, P.   Krishnan, M.   Barshilia, H.C.   Rao, D.V. Sridhara   Shivakumar, C.  

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  • Structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films

    Chowdhury, P.   Krishnan, M.   Barshilia, Harish C.   Sridhara Rao, D.V.   Kumar, Deepak   Shivakumara, C.  

    We investigated the structural and magnetic properties of SmCo5/Co exchange coupled nanocomposite thin films grown by magnetron sputtering from Sm and Co multitargets successively. The growth of the films was carried out at elevated substrate temperature followed by in situ annealing. On Si (100) substrate, X-ray diffraction confirms the formation of textured (110) SmCo5 hard phase, whereas on MgO(110) substrate, the diffraction pattern shows the epitaxial growth of SmCo5 phase with crystalline orientation along [100] direction. Secondary Ion Mass Spectroscopy reveals the structural transformation from multilayered (Sm/Co) to SmCo5/Co nano-composite films due to high reactivity of Sm at elevated temperature. Transmission electron microscopy indicates the existence of nanocrystalline phase of SmCo5 along with unreacted Co. Observed single phase behavior in magnetic hysteresis measurements indicates well exchange coupling between the soft and the hard phases in these nano-composite films. For samples with samarium layer thickness, tSm=3.2 nm and cobalt layer thickness, tCo=11.4 nm, the values of were obtained as 20.1 MGOe and 12.38 MGOe with Hc value grown on MgO and Si substrates, respectively.
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  • Synthesis of Quaternized poly(4-Vinyl Pyridine) and the Study of its Ion Exchange Property

    Chowdhury, P.   Saha, S. K.   Bayen, S. P.  

    Lightly cross-linked poly(4-vinyl pyridine) has been synthesized from 4-vinyl pyridine and a small amount of ethylene glycol dimethacrylate (EGDMA) in aqueous medium through micelle technique. The polymer is then quaternized with 1,4-dibromobutane to develop an anion exchange resin with high selectivity and ion exchange capacity at a wide range of pH and temperature. The material exhibits high ion exchange capacity and reverse anion selectivity order compared to commercially available anion exchanger. A method has been designed to separate chromate and sulfate using the synthesized material.
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  • single crystals by SQUID magnetometer and micro-Hall sensor

    Chowdhury, P.   Kim, Heon-Jung   Kang, W. N.   Zang, Dong-Jin   Lee, Sung-Ik   Kim, D. H.  

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  • Structural evolution and giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers

    Chowdhury, P.   Ghosh, S. K.   Dogra, Anjana   Dey, G. K.   Gowda, Yashwant G.   Gupta, S. K.   Ravikumar, G.   Grover, A. K.   Suri, A. K.  

    Structural transformations and their effect on giant magnetoresistance (GMR) were investigated in electrodeposited Co/Cu multilayers with varying Co-layer thicknesses (t(Co)) in the range of 0.2-10 nm while keeping the Cu layer thickness (t(Cu)) fixed at 4 nm. X-ray diffraction, scanning electron microscopy, cross-sectional transmission electron microscopy, and magnetization measurements were carried out to probe the structural transition from granular to semicontinuous to continuous Co layers. An unexpected result of the study is the observation of variations in GMR characteristics with a sharp peak in GMR at t(Co)=0.5 nm followed by a broad peak at t(Co)=3 nm. The GMR results have been analyzed in terms of ferromagnetic and superparamagnetic components for samples with varying t(Co) to understand the structural evolution of the magnetoresistance behavior.
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  • Synthesis and Characterization of Poly(Methyl Methacrylate) Grafted from Acacia Gum

    Chowdhury, P.   Samui, S.   Kundu, T.   Saha, B.  

    Graft polymerization of methyl methacrylate onto acacia gum has been studied in detail.The grafting was found to be optimal under the following reaction conditions:gum at 0.4 g/dL,monomer at 7.52X10~(-2)approxmol/dL,eerie ammonium sulfate at 15.81X10%~(-4) mol/dL,H_2SO_4 at 0.037 mol/dL,temperature at 50 deg C and time at 3.0 h.Fourier transform infrared spectroscopy was sed for the confirmation of grafting.Thermal and physical properties of the copolymer were studied.A probable mechanism of polymerization has been suggested based on reaction kinetics.
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  • Comparison of conventional RT-PCR, One step and Two step qRT-PCR for diagnosis of West Nile virus

    Chowdhury, P.   Khan, S.A.   Bora, T.  

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  • Towards Superheavies: Spectroscopy of 94 < Z < 98, 150 < N < 154 Nuclei

    Chowdhury, P.   Hota, S. S.   Qiu, Y   Ahmad, I.   Carpenter, M. P.   Greene, J. P.   Janssens, R. V. F.   Khoo, T. L.   Kondev, F. G.   Lauritsen, T.   Lister, C. J.   Seweryniak, D.   Zhu, S.   Reed, M.W.   Simpson, E.C.   Mitchell, A.J.  

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  • Effect of coherent to incoherent structural transition on magnetic anisotropy in Co/Pt multilayers

    Chowdhury, P.   Kulkarni, P. D.   Krishnan, M.   Barshilia, Harish C.   Sagdeo, A.   Rai, S. K.   Lodha, G. S.   Sridhara Rao, D. V.  

    The crystallographic structure and magnetic anisotropy have been investigated in Co/Pt multilayers deposited by direct current magnetron sputtering on two different buffer layers, Ta and Pt. Detail theoretical and experimental investigations reveal the presence of three effects: magneto-elastic, interface and shape anisotropies, and their competition results in three distinct regions based on the Co layer thickness (t Co). In the region I, with t Co< 6Aring, the coherent lattice strain modifies the volume anisotropy through magneto-elastic contribution and it leads to overall positive volume anisotropy energy. With further increase in t Co, lattice mismatch initiates and this results in a decrease in magneto-elastic effect and it enhances the interface anisotropy. The presence of both diminished magneto-elastic effect and enhanced interface anisotropy results in an intermediate region (region II) with negative volume anisotropy energy which is relatively wider (6 Aring < t Co< 12 Aring) for multilayer stacks with Ta underlayer. In the region III, with t Co > 12 Aring, the magneto-elastic effect emerges as an interface phenomena and the shape anisotropy becomes dominant.
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  • Graft copolymerization of methyl acrylate onto polyvinyl alcohol using Ce(IV) initiator

    Chowdhury, P.   Pal, C.M.  

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  • Graft copolymerization of methyl acrylate onto polyvinyl alcohol using Ce(IV) initiator

    Chowdhury, P.   Pal, C.M.  

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  • Use of Group IVB Metal Oxides for Curing Polyacrylic Rubber

    Chowdhury, P.   Chakravorti, M. C.   Das, C. K.  

    Group IVB metal oxides, both with and without ethylene thiourea (ETU) have been used to cure polyacrylic rubber (ACM). Curing characteristics and properties of the vulcanizates have been studied with a view to elucidate curing mechanism with special reference to the role of metal oxides (e.g. SnO, SnO2, PbO, PbO2 and Pb3O4). Best results are obtained with Pb3O4, in the presence of ETU and with SnO in the absence of ETU. PbO-SnO or PbO2-SnO blends provide no synergistic effect. In the presence of ETU, the formation of metal sulphide and metal chloride in the vulcanizate is confirmed by XRD and XPS. Studies on IR spectra show that crosslink occurs at the C-Cl cure site of the polymer. Based on the experimental results a mechanistic reaction scheme has been put forward.
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