Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects

Investigations of the magnetic properties of graphenes prepared by different methods reveal that dominant ferromagnetic interactions coexist along with antiferromagnetic interactions in all the samples. Thus, all the graphene samples exhibit room-temperature magnetic hysteresis. The magnetic properties depend on the number of layers and the sample area, small values of both favoring larger magnetization. Molecular charge-transfer affects the magnetic properties of graphene, interaction with a donor molecule such as tetrathiafulvalene having greater effect than an electron-withdrawing molecule such as tetracyanoethyleneComment: 16 pges, 5 figure

Quenching of fluorescence of aromatic molecules by graphene due to electron transfer

Investigations on the fluorescence quenching of graphene have been carried out with two organic donor molecules, pyrene butanaoic acid succinimidyl ester (PyBS, I) and oligo(p-phenylenevinylene) methyl ester (OPV-ester, II). Absorption and photoluminescence spectra of I and II recorded in mixture with increasing the concentrations of graphene showed no change in the former, but remarkable quenching of fluorescence. The property of graphene to quench fluorescence of these aromatic molecules is shown to be associated with photo-induced electron transfer, on the basis of fluorescence decay and time-resolved transient absorption spectroscopic measurements.Comment: 18 pages, 6 figure

Femtosecond carrier dynamics and saturable absorption in graphene suspensions

Nonlinear optical properties and carrier relaxation dynamics in graphene, suspended in three different solvents, are investigated using femtosecond (80 fs pulses) Z-scan and degenerate pumpprobe spectroscopy at 790 nm. The results demonstrate saturable absorption property of graphene with a nonlinear absorption coefficient, $beta$, of ~2 to 9x10^-8 cm/W. Two distinct time scales associated with the relaxation of photoexcited carriers, a fast one in the range of 130-330 fs (related to carrier-carrier scattering) followed by a slower one in 3.5-4.9 ps range (associated with carrier-phonon scattering) are observed.Comment: 3 pages, 2 figures, 2 table

Catalytic decomposition of N2O over CeO2 supported Co3O4 catalysts

This work was aimed to design efficient catalysts for N2O decomposition at low temperatures. Cobalt oxide (Co3O4) was prepared by hydrothermal, precipitation and combustion methods and tested for N2O decomposition. It was found that the catalysts prepared by solution combustion synthesis were most active for this reaction. Subsequently, a series of ceria (CeO2) supported Co3O4 catalysts (xCeCo) were prepared by solution combustion method and used them for N2O decomposition. All the catalysts were characterized by analytical methods like XRD, TEM, BET, XPS, UV-Vis, Raman and H (2)-TPR. It was found that 10 and 20 wt..% loading of CeO2 on Co3O4 promoted the activity of Co3O4 towards N2O decomposition, whereas, higher loading of CeO2 reduced the activity. Typical results indicated that addition of CeO2 increases the surface area of Co3O4, and improves the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step for the N2O decomposition over Co3O4 spinel catalysts. Optimal CeO2 loading can increase both dispersion and surface area of Co3O4 catalysts and weaken the Co-O bond strength to promote N2O decomposition

Dynamics of Metallic Particle Contamination in Gas Insulated Substation (GIS)

This paper analyses the movement of free conducting particles inside a single phase Gas Insulated Bus duct(GIB).A two dimensional mathematical model was proposed for determining the movement pattern of metallic particle in GIB by considering all the forces acting on the particle like gravitational, drag and the electric field forces. These particles may be free to move in the electric field or may be fixed on the conductors, thus enhancing local surface fields. Electric fields at the instantaneous contaminated particle locations were computed using Charge Simulation Method (CSM).To determine the particle trajectory in a single phase Gas Insulated Bus duct (GIB), an enclosure diameter 152 mm and conductor diameter 55 mm is considered. The simulation of the particle movement was carried under different AC voltage levels like 100KV, 132KV, 145KV and 175KV class enclosure of GIB for aluminum, copper and silver particles. The results of the simulation have been presented and analyzed in this paper

Determination of In-Situ Stress at Desilting Chamber of Punatsangchhu Hydroelectric Project (Bhutan), to Reconfirm Its Orientation Influenced by Topography — A Case Study

Punatsangchhu Hydroelectric Project stage-I was conceptualized in Wangdue- Phodrang district of Bhutan for harnessing the hydro-power potentiality of Punatsangchhu River. Regionally the project area is located within a part of a gneissic terrain of Tethyan Belt of Bhutan Himalayas. The project envisages construction of 195m high concrete gravity dam across the river Punatsangchhu. For Desilting chamber and Powerhouse, it is always desirable to carry out in-situ stress measurement in such huge underground openings for designing of the support types. The stability of the underground cavern gets enhanced if the long axis of the cavern is oriented along or sub-parallel to that of maximum principal stress. National Institute of Rock Mechanics, a premier Research Institute under Ministry of Mines, Government of India, carried out stress measurements at RD 100m and RD 150m inside an exploratory drift approaching towards desilting chamber with a rock cover of 100m. This test was required to freeze the orientation of desilting chamber vis. a vis. orientation of maximum compression (σH) which was found to be N 150°. As it was only 100 to 150 m away from the portal, a topography effect on the orientation of (σH) was not completely ruled out. So when the adit to Desilting chamber reached at RD 360m with a rock cover of 410m, it is necessary to carry out stress measurement at RD 360m to confirm the results of earlier tests at RD100m and RD 150m to find out the influence of topography on which the present paper is based was primarily for determination of in-situ stress measurements. The stress orientation as evaluated at RD 360m reconfirms the orientations revealed from earlier stress measurements at RD 100 and RD 150m.Thus it is recommended to freeze the direction of Desilting chamber along N 150°. It also confirms that the earlier stress measurement results do not suffer from topography related influence

Synthetic Aspects and Selected Properties of Graphene

Graphene has generated great sensation owing to its fascinating properties with possible potential applications. This two‐dimensional material exhibits half‐ integer quantum Hall effect and an ambipolar electric field effect, along with ballistic conduction of charge carriers. In this article, we provide a overview on some aspects of graphene devoting the special attention to synthesis, functionalization, self‐assembly, surface properties, gas adsorption and fluorescence quenching ability of graphene. Graphenes with varying number of layers can be synthesized by using different strategies. Graphene can be functionalized by different means in order to disperse it in various solvents. We also present the self‐assembly of graphene at the liquid‐liquid interface besides its surface properties including adsorption of hydrogen, carbon dioxide and methane. The remarkable property of graphene of quenching fluorescence of aromatic molecules is shown to be associated with photo‐induced electron transfe