Self-stabilizing cluster routing in Manet using link-cluster architecture

We design a self-stabilizing cluster routing algorithm based on the link-cluster architecture of wireless ad hoc networks. The network is divided into clusters. Each cluster has a single special node, called a clusterhead that contains the routing information about inter and intra-cluster communication. A cluster is comprised of all nodes that choose the corresponding clusterhead as their leader. The algorithm consists of two main tasks. First, the set of special nodes (clusterheads) is elected such that it models the link-cluster architecture: any node belongs to a single cluster, it is within two hops of the clusterhead, it knows the direct neighbor on the shortest path towards the clusterhead, and there exist no two adjacent clusterheads. Second, the routing tables are maintained by the clusterheads to store information about nodes both within and outside the cluster. There are two advantages of maintaining routing tables only in the clusterheads. First, as no two neighboring nodes are clusterheads (as per the link-cluster architecture), there is no need to check the consistency of the routing tables. Second, since all other nodes have significantly less work (they only forward messages), they use much less power than the clusterheads. Therefore, if a clusterhead runs out of power, a neighboring node (that is not a clusterhead) can accept the role of a clusterhead. (Abstract shortened by UMI.)

Elastic properties and spectroscopic studies of fast ion conducting Li2O-ZnO-B2O3 glass system

Glass systems of the composition xLi(2)O-20ZnO-(80 - x)B2O3 where (x = 5, 10, 15, 20, 25 and 30 mol%) have been prepared by melt quenching technique. Elastic properties, 1 B-11 MAS-NMR and IR spectroscopic studies have been employed to study the structure of Li2O-ZnO-B2O3 glasses. Elastic properties have been investigated using sound velocity measurements at 10 MHz. Elastic moduli reveal trends in their compositional dependence. The bulk modulus and shear modulus increases monotonically with increase of BO4 units, which increase the dimensionality of the network. B-11 MAS-NMR and IR spectra show characteristic features of borate network and compositional dependent trends as a function of Li2O/ZnO concentration. The results are discussed in view of berate network and the dual structural role of Zn2+ ions. The results indicate that the Zn2+ are likely to occupy network-forming positions in this glass system. (C) 2006 Elsevier Ltd. All rights reserved

Synthesis, structural and transport properties of nanocrystalline La1−xBaxMnO3 (0.0≤x≤0.3) powders

Nanocrystalline La1−xBaxMnO3 (0.0≤x≤0.3) manganites have been prepared by a simple and instantaneous solution combustion method, which is a low temperature initiated synthetic route to obtain fine-grained powders with relatively high surface area. The phase purity and crystal structure of the combustion products are carried out by powder X-ray diffraction. The as-made nanopowders are in cubic phase. On calcination to 900 °C, barium doped manganites retain cubic phase, whereas barium free manganite transformed to rhombohedral phase. The scanning electron microscope (SEM) results revealed that the combustion-derived compounds are agglomerated with fine primary particles. The doped manganites have surface area in the range 24–44 m2/g. The surface area of the manganites increases with barium content, whereas it decreases on calcination. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 cm−1. The low temperature resistivity measurements have been carried out by four-probe method down to 77 K. All the samples exhibit metal–insulator behaviour and metal–insulator transition temperature (TM–I) in the range 184–228 K and it is interesting to note that, as the barium content increases the TM–I shifts to lower temperature side. The maximum TM–I of 228 K is observed for La0.9Ba0.1MnO3 sample

Swift heavy ion irradiation induced phase transformation in calcite single crystals

Ion irradiation induced phase transformation in calcite single crystals have been studied by means of Raman and infrared spectroscopy using 120 MeV Au 9+ ions. The observed bands have been assigned according to group theory analysis. For higher fluence of 5Ã10 12 ion/cm 2, an extra peak on either side of the 713 cm -1 peak and an increase in the intensity of 1085 cm -1 peak were observed in Raman studies. FTIR spectra exhibit extra absorption bands at 674, 1589 cm -1 and enhancement in bands at 2340 and 2374 cm -1 was observed. This might be due to the phase transformation from calcite to vaterite. The damage cross section (Ï) for all the Raman and FTIR active modes was determined. The increase of FWHM, shift in peak positions and appearance of new peaks indicated that calcite phase is converted into vaterite. © 2009 Elsevier Ltd. All rights reserved

Solution combustion derived nanocrystalline Zn2SiO4 : Mn phosphors: A spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn2-xMnxSiO4 (0.1less than or equal toxless than or equal to0.5) have been synthesized by a low-temperature initiated, self-propagating, gas producing solution combustion process. The phosphors have been characterized by using x-ray diffraction (XRD), energy dispersive spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and photo luminescence (PL) spectroscopic techniques. The lattice parameters calculated from XRD confirm that Zn2-xMnxSiO4 has a rhombohedral space group R (3) over barH. The XRD patterns confirm that Zn2-xMnxSiO4 phosphor samples undergo a phase transformation from beta-willemite to alpha-willemite phase at 950 degreesC. The EPR spectra of Mn2+ ions exhibit resonance signals at gcongruent to3.24 and gcongruent to2.02, with a sextet hyperfine structure centered around gcongruent to2.02. The EPR signals of Mn2+ give a clear indication of the presence of two different Mn2+ sites. The magnitude of the hyperfine splitting (A) indicates that the Mn2+ is in an ionic environment. The number of spins participating in resonance (N), the paramagnetic susceptibility (chi), and the zero-field splitting parameter (D) have been evaluated as function of x. It is interesting to observe that the variation of N with temperature obeys Boltzmann. The paramagnetic susceptibility is calculated from the EPR data at various temperatures and the Curie constant and Curie paramagnetic temperature was evaluated from the 1/chi versus T graph. The luminescence of Mn2+ ion in Zn2SiO4 shows a strong green emission peak around 520 nm from the synthesized phosphor particles under UV excitation (251 nm). The luminescence is assigned to a transition from the upper T-4(1)-->(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied. (C) 2004 American Institute of Physics

Effect of Li+-​ion on enhancement of photoluminescence in Gd2O3:Eu3+ nanophosphors prepared by combustion technique

Gd2O3:Eu3+ (4 mol​%) nanophosphor co-​doped with Li+ ions have been synthesized by low-​temp. soln. combustion technique in a short time. Powder X-​ray diffractometer (PXRD)​, SEM, Fourier transform IR spectroscopy (FT-​IR)​, UV-​VIS and photoluminescence (PL) techniques have been employed to characterize the synthesized nanoparticles. It is found that the lattice of Gd2O3:Eu3+ phosphor transforms from monoclinic to cubic as the Li+-​ions are doped. Upon 254 nm excitation, the phosphor showed characteristic luminescence 5D0 → 7FJ (J = 0-​4) of the Eu3+ ions. The electronic transition located at 626 nm (5D0 → 7F2) of Eu3+ ions was stronger than the magnetic dipole transition located at 595 nm (5D0 → 7F1)​. Furthermore, the effects of the Li+ co-​doping as well as calcinations temp. on the PL properties have been studied. The results show that incorporation of Li+ ions in Gd2O3:Eu3+ lattice could induce a remarkable improvement of their PL intensity. The emission intensity was obsd. to be enhanced four times than that of with out Li+-​doped Gd2O3:Eu3+

EPR and Optical Studies of Mo5+ Ions in Lithium Molybdoborate Glasses

Electron paramagnetic resonance (EPR) and optical absorption studies of Li2O–MoO3–B2O3 with varying concentrations of Li2O, MoO3 and B2O3 have been carried out at room temperature. Two series of glasses, one with constant MoO3 (CM) and another with constant borate (CB), have been investigated. Characteristic EPR spectra of Mo5+ have been observed centered around g ≅ 2.00, which are attributed to Mo5+ ion in an octahedral coordination sphere with an axial distortion. The spectra also show strong dependence on the concentration of Li2O and B2O3. Spin concentrations (N) and magnetic susceptibilities (χ) have been calculated. In the CM series, the N values decrease with increasing Li2O content up to 30 mol%, while in the CB series variation of N is found to increase initially up to 20 mol%, and with further increase in the Li2O content the N values tend to decrease. The variation of magnetic susceptibilities is almost similar to that observed with the variation of N. From the optical absorption spectra, an absorption edge (α) has been evaluated. In the CM series, the values of α show a blueshift. On the other hand, in the CB series a redshift is observed. The observed variations in spectral parameters are explained by considering the molybdoborate network. Addition of Li2O to the CM and CB series results in modification of [MoO6/2]0 → [MoOO5/2]− and [BO3/2]0 → [BO4/2]− → [BOO2/2]− groups, respectively, leading to creation of nonbridging oxygens. The optical basicity of the glasses has been evaluated in both the CM and the CB glasses. The optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity indicates decreasing covalency. It is observed that the covalency between Mo5+ ions and oxygen ligands increases in the CB series, whereas in the CM series the covalency between Mo5+ ions and oxygen ligands decreases

Magnetoresistive studies on nanocrystalline la0.8Sr 0.2MnO3+δ manganite

Low-temperature magnetoresistance (MR) measurement has been carried out on nanocrystalline La0.8Sr0.2MnO3+δ manganites prepared by combustion synthesis. This preparation method yields voluminous powders with large surface area (â¼40m2/g) having crystalline nanosize(-50 nm) products. Formation and homogeneity of the solid solutions have been confirmed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Rietveld refinement of X-ray data indicates that as-formed compound exhibits cubic phase with space group Pm3m. However, calcined sample transforms into rhombohedral phase with space group R-3c. The stabilization of the cubic phase in as-formed manganite is due to the substitution of Sr2+ on La3+ sites, resulting in higher Mn4+ content. The low-temperature resistivity measurements down to 70 K exhibit a broad metal-insulator transition (TM-I) at around 257 K. MR measurements on sintered pellets show â¼5 MR at 1T, whereas for 4 and 7T, the MR values are found as 22 and 28, respectively, at TM-I. © 2008 Elsevier B.V. All rights reserved

Synthesis, characterization and TL studies of porous CaSiO3 ceramic powders

Nanocryst. porous CaSiO3 ceramic powders have been synthesized by a novel low temp. initiated self-​propagating, gas producing soln. combustion process and characterized by XRD, SEM, EDS (energy dispersive spectroscopy)​, porosity, surface area and thermoluminescence (TL) studies. The effect of temp. on cryst. phase formation, amt. of porogens and particle size of porous CaSiO3 have been investigated. Single phase β-​CaSiO3 and α-​CaSiO3 were formed at 950° and 1200°C resp. The phase transformation temps. of combustion derived CaSiO3 were found to be low compared to the powders obtained via solid state reaction method. The microstructure and morphol. were studied by SEM and it was noted that with increase in calcination temp., the samples became more porous and the pore diam. increased from 0.25 to 8 μm. The samples calcined at 950°C for 3 h had 17.5​% porosity, however, the porosity increased to 31.6​% on calcination at 1200°C for 3 h. The surface areas of the as-​formed and calcined (at 950° and 1200°C) CaSiO3 samples were found to be 31.93, 0.585 and 3.48 m2·g-​1 resp. The TL intensity in powder sample was more intense when compared to the pelletized CaSiO3 and it was further obsd. that there was a shift in glow peak temps. in pelletized sample. This is attributed to the interparticle spacing and pressure-​induced defects