Experimental and theoretical studies on static and dynamic pressure-concentration isotherms of MmNi(5-x)Al(x) (x=0, 0.3, 0.5 and 0.8) hydrides

The static and dynamic pressure concentration isotherms (PCIs) of MmNi(5-x)Al(x). (x = 0, 0.3, 0.5 and 0.8) hydrides were measured at different temperatures using volumetric method. The effect of Al substitution on PCI and thermodynamic properties were studied. The plateau pressure and maximum hydrogen storage capacity decreased with Al content whereas reaction enthalpy increased. The plateau pressure, plateau slope and hysteresis effect was observed more for dynamic PCIs compared to static PCIs. Different mathematical models used for metal hydride-based thermodynamic devices simulation are compared to select suitable model for static and dynamic PCI simulation of MmNi(5)-based hydrides. Few important physical coefficients (partial molar volume, reaction enthalpy, reaction entropy, etc.) useful for development of thermodynamic devices were estimated. A relation has been proposed to correlate aluminium content and physical coefficients for the prediction of unknown PCI. The simulated and experimental PCIs were found matching closely for both static and dynamic conditions. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Low temperature magnetoresistance and magnetization studies of iron encapsulated multiwall carbon nanotube/polyvinyl chloride composites

We present the experimental results of temperature dependent magnetoresistance (MR) and the magnetization studies of iron encapsulated multiwall carbon nanotube (MWCNT)/polyvinyl chloride (PVC) composites with different wt% of MWCNTs. Transmission electron microscopy characterization shows that MWCNTs are encapsulated with rod-shaped iron nanoparticles of aspect ratio of similar to 3. The MR behavior of 1.9 wt% MWCNT/PVC sample shows dominance of forward scattering and wave function shrinkage whereas, weak localization and electron-electron interactions explain the MR data of higher wt% samples (9.1, 16.6 and 44.4 wt%). The composites of 4.7 and 9.1 wt% exhibit ferromagnetic behavior at all temperatures with room temperature coercivities of similar to 1036 and 628 Oe, respectively. (C) 2014 Elsevier Ltd. All rights reserved.

High Proton Mobility, Solvent Induced Single Crystal to Single Crystal Structural Transformation, and Related Studies on a Family of Compounds Formed from Mn-3 Oxo-Clusters

The reaction between 4,4'-sulfonyldibenzoic acid (H(2)SDBA) and manganese under mild conditions resulted in the isolation of two new three-dimensional compounds, Mn-4(C14H8O6S)(4)(DMA)(2)]center dot 3DMA, I, and Mn-3(C14H8O6S)(3)(DMA)(2)(MeOH)]center dot DMA, IIa. Both structures have Mn-3 trimer oxo cluster units. While the Mn-3 oxoclusters are connected through octahedral manganese forming one-dimensional Mn-O-Mn chains in I, the Mn-3 units are isolated in IIa. The SDBA units connect the Mn-O-Mn chains and the Mn-3 clusters giving rise to the three-dimensional structure. Both compounds have coordinated and free solvent molecules. In IIa, two different solvent molecules are coordinated, of which one solvent can be reversibly exchanged by a variety of other similar solvents via a solvent-mediated single crystal to single crystal (SCSC) transformation. The free lattice DMA solvent molecules in I can be exchanged by water molecules resulting in hydrophilic channels. Proton conductivity studies on I reveals a high proton mobility with conductivity values of similar to 0.87 x 10(-3) Omega(-1) cm(-1) at 34 degrees C and 98% RH, which is comparable to some of the good proton conductivity values observed in inorganic coordination polymers. We have also shown structural transformation of I to IIa through a possible dissolution and recrystallization pathway. In addition, both I and IIa appear to transform to two other manganese compounds H3O]Mn-3(mu(3)-OH)(C14H8O6S)(3)(H2O)](DMF)(5) and H3O](2)Mn-7(mu 3-OH)(4)(C14H8O6S)(6)(H2O)(4)](H2O)(2)(DMF)(8) under suitable reaction conditions. We have partially substituted Co in place of Mn in the Mn-3 trimer clusters forming CoMn2(C14H8O6S)(3)(DMA)(2)(EtOH)]center dot DMA, III, a structure that is closely related to IIa. All the compounds reveal antiferromagnetic behavior. On heating, the cobalt substituted phase (compound III) forms a CoMn2O4 spinel phase with particle sizes in the nanometer range.

Three centered hydrogen bonds of the type C=O...H(N)...X-C in diphenyloxamide derivatives involving halogens and a rotating CF3 group: NMR, QTAIM, NCI and NBO studies

The existence of three centered C=O...H(N)...X-C hydrogen bonds (H-bonds) involving organic fluorine and other halogens in diphenyloxamide derivatives has been explored by NMR spectroscopy and quantum theoretical studies. The three centered H-bond with the participation of a rotating CF3 group and the F...H-N intramolecular hydrogen bonds, a rare observation of its kind in organofluorine compounds, has been detected. It is also unambiguously established by a number of one and two dimensional NMR experiments, such as temperature perturbation, solvent titration, N-15-H-1 HSQC, and F-19-H-1 HOESY, and is also confirmed by theoretical calculations, such as quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) and non-covalent interaction (NCI).

Temperature-Dependent Magnetic and EPR Studies of Bulk and Nanoparticles of Bi0.1Ca0.9MnO3

We report temperature-dependent magnetic and electron paramagnetic resonance (EPR) properties of bulk and nanoparticle samples of Bi0.1Ca0.9MnO3 (BCMO). The nanoparticles of BCMO (dia similar to 50 nm) were prepared by the standard sol-gel technique and bulk samples by solid-state reaction method. We have investigated the magnetic ordering in the two samples by carrying out temperature-dependent magnetic and EPR studies and compared their properties. According to earlier reports, antiferromagnetic and ferromagnetic orders coexist in the bulk sample of Bi0.1Ca0.9MnO3. Our magnetization and EPR results show the existence of ferromagnetism in the bulk sample which is present in the nanosample as well but with somewhat weakened strength with the size reduction.

Effective Degradation of Aqueous Nitrobenzene Using the SrFeO3-delta Photocatalyst under UV Illumination and Its Kinetics and Mechanistic Studies

In this article, the SrFeO3-delta photocatalyst was synthesized by a solution combustion method and applied for the photocatalytic degradation of aqueous nitrobenzene in the presence and absence of H2O2. The SrFeO3-delta photocatalyst was characterized by XRD, FT-IR, FE-SEM, TEM, TG-DTG, XPS, and UV visible spectroscopy. The band gap energy of SrFeO3-delta was found to be 3.75 eV which lies in the UV region. The XPS results indicate that the oxidation state of Sr and Fe in SrFeO3-delta was 2+ and 3+, respectively, and the surface atomic ratio of Sr and Fe is 0.995. The photocatalytic activity reveals that the degradation of nitrobenzene over the SrFeO3-delta catalyst itself (UV/SFO) is superior compared to SrFeO3-delta in the presence of H2O2 (UV/SFO/H2O2) with a degradation efficiency of 99-96%. The degradation of nitrobenzene obeys first-order kinetics in both UV/SFO and UV/SFO/H2O2 processes. The decrease in degradation efficiency with UV/SFO/H2O2 was attributed due to the formation of strontium carbonate on the photocatalyst surface.

Effect of Size Reduction on Magnetic Ordering in Sm1-x Ca (x) MnO3 (x=0.35, 0.65 and 0.92) Manganites: Magnetic and EMR Studies

We have employed the highly sensitive electron magnetic resonance technique complimented by magnetization measurements to study the impact of size reduction on the magnetic ordering in nanosized Sm1-x Ca (x) MnO3 (x = 0.35, 0.65 and 0.92). In the bulk form, x = 0.35 sample shows a charge ordering transition at 235 K followed by a mixed magnetic phase, the sample with x = 0.65 exhibits charge order below 275 K and shows an antiferromagnetic insulator phase below 135 K while that with x = 0.92 has a ferromagnetic-cluster glass ground state. Thus, a comparative study of magnetic ground states of bulk and nanoparticles (diameter similar to 25 nm) enables us to investigate size-induced effects on different types of magnetic ordering. It is seen that in the bulk samples the temperature dependences of the EPR parameters are quite different from each other. This difference diminishes for the nanosamples where all the three samples show qualitatively similar behavior. The magnetization measurements corroborate this conclusion.

Experimental characterisation and performance evaluation of a coaxial current transformer for measurement of insulated gate bipolar transistor switching current

Measurement of device current during switching characterisation of an insulated gate bipolar transistor (IGBT) requires a current sensor with low insertion impedance and high bandwidth. This study presents an experimental procedure for evaluating the performance of a coaxial current transformer (CCT), designed for the above purpose. A prototype CCT, which can be mounted directly on a power terminal of a 1200 V/50 A half-bridge IGBT module, is characterised experimentally. The measured characteristics include insertion impedance, gain and phase of the CCT at different frequencies. The bounds of linearity within which the CCT can operate without saturation are determined theoretically, and are also verified experimentally. The experimental study on linearity of the CCT requires a high-amplitude current source. A proportional-resonant (PR) controller-based current-controlled half-bridge inverter is developed for this purpose. A systematic procedure for selection of PR controller parameters is also reported in this study. This set-up is helpful to determine the limit of linearity and also to measure the frequency response of the CCT at realistic amplitudes of current in the low-frequency range.

Scaling analysis and numerical studies on water vapour adsorption in a columnar porous silica gel bed

This article presents a theoretical analysis of heat and mass transfer in a silica gel + water adsorption process using scaling principles. A two-dimensional columnar packed adsorber domain is chosen for the study, with side and bottom walls cooled and vapour inlet from the top. The adsorption process is initiated from the cold walls with a temperature jump of 15 K, whereas the water vapour supply is maintained at a constant inlet pressure of 1 kPa. The first part of the study is dedicated to deriving relevant scales for the adsorption process by an order of magnitude analysis of energy, continuity and momentum equations. In the latter part, the derived scales are compared with the outcome of numerical studies performed for various domain widths and aspect ratio of bed. A good correlation between scaling and simulation results is observed, thereby validating the scaling approach. (C) 2015 Elsevier Ltd. All rights reserved.

Appraisal of groundwater resource in Holocene soil deposits by resistivity, hydrochemical and granulomerial studies in the Gulf of Mannar Coast from Southern India

This article is aimed to delineate groundwater sources in Holocene deposits area in the Gulf of Mannar Coast from Southern India. For this purpose 2-D electrical resistivity tomography (ERT), hydrochemical and granulomerical studies were carried out and integrated to identify hydrogeological structures and portable groundwater resource in shallow depths which in general appears in the coastal tracts. The 2-D ERT was used to determine the two-dimensional subsurface geological formations by multicore cable with Wenner array. Low resistivity of 1-5 Omega m for saline water appeared due to calcite at the depth of about 5 m below the ground level (bgl). Sea water intrusion was observed around the maximum resistivity as 5 Omega m at the 8 m depth, bgl in the calcite environs, but the calcareous sandstone layer shows around 15-64 Omega m at the 6 m depth, bgl. The hydrochemical variation of TDS, HCO3-, Cl-, Na+, K+, Ca2+, and Mg2+ concentrations was observed for the saline and sea water intrusion in the groundwater system. The granulometic analysis shows that the study area was under the sea between 5400 and 3000 year ago. The events of ice melting an unnatural ice-stone rain/hail among 5000-4000 years ago resulted in the inundation of sea over the area and deposits of late Holocene marine transgression formation up to Puthukottai quartzite region for a stretch of around 17 km.

On the Capacity and Performance of Generalized Spatial Modulation

Generalized spatial modulation (GSM) uses N antenna elements but fewer radio frequency (RF) chains (R) at the transmitter. In GSM, apart from conveying information bits through R modulation symbols, information bits are also conveyed through the indices of the R active transmit antennas. In this letter, we derive lower and upper bounds on the the capacity of a (N, M, R)-GSM MIMO system, where M is the number of receive antennas. Further, we propose a computationally efficient GSM encoding method and a message passing-based low-complexity detection algorithm suited for large-scale GSM-MIMO systems.

COST AND PERFORMANCE TRADEOFFS OF ALTERNATIVE SOLAR-DRIVEN S-CO2 BRAYTON CYCLE CONFIGURATIONS

This paper evaluates cost and performance tradeoffs of alternative supercritical carbon dioxide (s-CO2) closed-loop Brayton cycle configurations with a concentrated solar heat source. Alternative s-CO2 power cycle configurations include simple, recompression, cascaded, and partial cooling cycles. Results show that the simple closed-loop Brayton cycle yielded the lowest power-block component costs while allowing variable temperature differentials across the s-CO2 heating source, depending on the level of recuperation. Lower temperature differentials led to higher sensible storage costs, but cycle configurations with lower temperature differentials (higher recuperation) yielded higher cycle efficiencies and lower solar collector and receiver costs. The cycles with higher efficiencies (simple recuperated, recompression, and partial cooling) yielded the lowest overall solar and power-block component costs for a prescribed power output.