Tribology of soot suspension in hexadecane as distinguished by the physical structure and chemistry of soot particles

Ethylene gas is burnt to generate soot which is collected thermophoretically from different locations of the flame. Tribological performance of the collected soot in hexadecane suspension is compared with that of carbon black and diesel soot. The soots are analysed to yield a range of mechanical properties, physical structures and chemistry. The paper correlates these property variations with the corresponding variations in friction and wear when the soot suspended in hexadecane is used to lubricate a steel on steel sliding interaction. The particles are dispersed in hexadecane by a non-ionic surfactant, poly-isobutylene succinimide (PIBS), which is mono-functional with no free amine group. The grafting of the surfactant on the soot particles is found to have a profound effect on the dispersion of the soot, in general, while, between the different soot types, the tribology is differentiated by the physical structure and chemistry.

Structure and deformation correlation of closed-cell aluminium foam subject to uniaxial compression

We report the results of an experimental and numerical study conducted on a closed-cell aluminium foam that was subjected to uniaxial compression with lateral constraint. X-ray computed tomography was utilized to gain access into the three-dimensional (3-D) structure of the foam and some aspects of the deformation mechanisms. A series of advanced 3-D image analyses are conducted on the 3-D images aimed at characterizing the strain localization regions. We identify the morphological/geometrical features that are responsible for the collapse of the cells and the strain localization. A novel mathematical approach based on a Minkowski tensor analysis along with the mean intercept length technique were utilized to search for signatures of anisotropy across the foam sample and its evolution as a function of loading. Our results show that regions with higher degrees of anisotropy in the undeformed foam have a tendency to initiate the onset of cell collapse. Furthermore, we show that strain hardening occurs predominantly in regions with large cells and high anisotropy. We combine the finite element method with the tomographic images to simulate the mechanical response of the foam. We predict further deformation in regions where the foam is already deformed. Crown Copyright (C) 2012 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.

Mixed-ligand aroylhydrazone complexes of molybdenum: Synthesis, structure and biological activity

The reaction of the benzoylhydrazone of 2-hydroxybenzaldehyde (H2L) with MoO2(acac)(2)] proceeds smoothly in refluxing ethanol to afford an orange complex MoO2L(C2H5OH)] (1). The substrate binding capacity of 1 has been demonstrated by the formation and isolation of two mononuclear MoO2L(Q)] {where Q = imidazole (2a) and 1-methylimidazole (2b)} and one dinuclear (MoO2L)(2)(Q)] {Q = 4,4'-bipyridine (3)} mixed-ligand oxomolybdenum complex. All the complexes have been characterized by elemental analysis, magnetic and spectroscopic (IR, UV-Vis and NMR) measurements. The molecular structures of all the oxomolybdenum(VI) complexes (1, 2a, 2b and 3) have been determined by X-ray crystallography. In each complex, the dianionic planar ligand is coordinated to the metal centre via one enolate oxygen, one phenolate oxygen and an azomethine nitrogen atom. The complexes have been screened for their antibacterial activity against Escherichia coli, Bacillus and Pseudomonas aeruginosa. The minimum inhibitory concentration of these complexes and their antibacterial activity indicates that compounds 2a and 2b are potential lead molecules for drug designing. (C) 2012 Elsevier Ltd. All rights reserved.

Stabilization of O-Mn-O clusters (Mn-5) in three dimensionally extended MOF structures: synthesis, structure and properties

Four new three-dimensional Mn2+ ion-containing compounds have been prepared by employing a hydrothermal reaction between Mn(CH3COO)(2)center dot 4H(2)O, sulfodibenzoic acid (H(2)SDBA), imidazole, alkali hydroxide and water at 220 degrees C for 1 day. The compounds have Mn-5 (1-4) clusters connected by SDBA, forming the three-dimensional structure. A time and temperature dependent study on the synthesis mixture revealed the formation of a one-dimensional compound, Mn(SDBA)(H2O)(2), at lower temperatures (T <= 180 degrees C). The stabilization of the fcu related topology in the compounds is noteworthy. Magnetic studies indicate strong anti-ferromagnetic interactions between the Mn2+ ions within the clusters in the temperature range 75-300 K. The rare participation of a sulfonyl group in the bonding is important and can pave way for the design of new structures.

Study of molecular structure and vibrational spectra of poly (beta,-1-malic acid) PMLA] using DFT approach

Poly (beta-L-malic acid) (PMLA) is a biodegradable polymer and it has various important applications in the biomedical field. In the present work the structural and spectral characteristics of PMLA have been studied by methods of infrared. Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) using oligomeric approach employing B3LYP with complete relaxation in the potential energy surface using 6-311++G (d, p) basis set. Based on results, we have discussed the correlation between the vibrational modes and the structure of the PMLA. A complete analysis of the experimental infrared and Raman spectra has been reported on the basis of wavenumber of the vibrational bands and potential energy distribution. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The calculated infrared and the Raman spectra of the polymer based on DFT calculations show reasonable agreement with the experimental results. (c) 2012 Elsevier Ltd. All rights reserved.

Structure and mechanical properties of Ti-C films deposited using combination of pulsed DC and normal DC magnetron co-sputtering

Titanium-carbon (Ti-C) thin films of different compositions were prepared by a combination of pulsed DC (for Ti target) and normal DC (for graphite target) magnetron co-sputtering on oxidized silicon and fused quartz substrates. At 33.7 at.% of C content, pure hcp Ti transforms into fcc-TiC with a preferential orientation of (2 2 0) along with (1 1 1) and (2 0 0). A clear transformation in the preferential orientation from (2 2 0) to (1 1 1) has been observed when the C content was increased to 56 at.%. At 62.5 at.% of C, TiC precipitates in an amorphous carbon matrix whereas further increase in C leads to X-ray amorphous films. The cross-sectional scanning electron microscope images reveal that the films with low carbon content consists of columnar grains, whereas, randomly oriented grains are in an amorphous carbon matrix at higher carbon content. A dramatic variation was observed in the mechanical properties such as hardness, H, from 30 to 1 GPa and in modulus, E, from 255 to 25 GPa with varying carbon content in the films. Resistance to plastic deformation parameter was observed as 0.417 for films containing 62.5 at.% of C. Nanoscratch test reveals that the films are highly scratch resistant with a coefficient of friction ranging from 0.15 to 0.04. (C) 2012 Elsevier B.V. All rights reserved.

Structure and morphology studies of chromium film at elevated temperature in hypersonic environment

This paper presents the after shock heated structural and morphological studies of chromium film coated on hypersonic test model as a passive drag reduction element. The structural changes and the composition of phases of chromium due to shock heating (2850 K) are characterized using X-ray diffraction studies. Surface morphology changes of chromium coating have been studied using scanning electron microscopy (SEM) before and after shock heating. Significant amount of chromium ablation and sublimation from the model surface is noticed from SEM micrographs. Traces of randomly oriented chromium oxides formed along the coated surface confirm surface reaction of chromium with oxygen present behind the shock. Large traces of amorphous chromium oxide phases are also observed.

A Rare Phenoxido/Acetato/Azido Bridged Trinuclear and an Unprecedented Phenoxido/Azido Bridged One-Dimensional Polynuclear Nickel(II) Complexes: Synthesis, Crystal Structure, and Magnetic Properties with Theoretical Investigations on the Exchange Mechanism

The reaction of a tridentate Schiff base ligand HL (2-(3-dimethylaminopropylimino)-methyl]-phenol) with Ni(II) acetate or perchlorate salts in the presence of azide as coligand has led to two new Ni(II) complexes of formulas Ni3L2(OAc)(2)(mu(1,1)-N-3)(2)(H2O)(2)]center dot 2H(2)O (1) and Ni2L2(mu(1,1)-N-3) (mu(1,3)-N-3)](n)(2). Single crystal X-ray structures show that complex 1 is a linear trinuclear Ni(II) compound containing a mu(2)-phenwddo, an end-on (EO) azido and a syn-syn acetato bridge between the terminal and the central Ni(II) ions. Complex 2 can be viewed as a one-dimensional (1D) chain in which the triply bridged (di-mu(2)-phenoxido and EO azido) dimeric Ni-2 units are linked to each other in a zigzag pattern by a single end-to-end (EE) azido bridge. Variable-temperature magnetic susceptibility studies indicate the presence of moderate ferromagnetic exchange coupling in complex 1 with J value of 16.51(6) cm(-1). The magnetic behavior of 2 can be fitted in an alternating ferro- and antiferromagnetic model J(FM) = +34.2(2.8) cm(-1) and J(AF) = -21.6(1.1) cm(-1)] corresponding to the triple bridged dinuclear core and EE azido bridge respectively. Density functional theory (DFT) calculations were performed to corroborate the magnetic results of 1 and 2. The contributions of the different bridges toward magnetic interactions in both compounds have also been calculated.

Theory and Algorithms for Hop-Count-Based Localization with Random Geometric Graph Models of Dense Sensor Networks

Wireless sensor networks can often be viewed in terms of a uniform deployment of a large number of nodes in a region of Euclidean space. Following deployment, the nodes self-organize into a mesh topology with a key aspect being self-localization. Having obtained a mesh topology in a dense, homogeneous deployment, a frequently used approximation is to take the hop distance between nodes to be proportional to the Euclidean distance between them. In this work, we analyze this approximation through two complementary analyses. We assume that the mesh topology is a random geometric graph on the nodes; and that some nodes are designated as anchors with known locations. First, we obtain high probability bounds on the Euclidean distances of all nodes that are h hops away from a fixed anchor node. In the second analysis, we provide a heuristic argument that leads to a direct approximation for the density function of the Euclidean distance between two nodes that are separated by a hop distance h. This approximation is shown, through simulation, to very closely match the true density function. Localization algorithms that draw upon the preceding analyses are then proposed and shown to perform better than some of the well-known algorithms present in the literature. Belief-propagation-based message-passing is then used to further enhance the performance of the proposed localization algorithms. To our knowledge, this is the first usage of message-passing for hop-count-based self-localization.

Spirodiazaselenuranes: synthesis, structure and antioxidant activity

In this paper, the synthesis, characterization and glutathione peroxidase and peroxynitrite scavenging activities of a series of stable spirodiazaselenuranes are described. The spiro compounds were synthesized in good yields by oxidative cyclization of diaryl selenides bearing amide moieties. All the selenides and spiro derivatives were characterized by H-1, C-13 and Se-77 NMR spectroscopy, mass spectral techniques and the structures of some of the spirodiazaselenuranes were confirmed by single crystal X-ray crystallography. The structures reveal that the selenium atom occupies the center of a distorted trigonal bipyramid core with two nitrogen atoms occupying the apical positions and two carbon atoms and the selenium lone pair occupying the equatorial positions. Mechanistic investigations indicate that the spirocyclization occurs via the formation of selenoxide intermediates. The new compounds were evaluated for their glutathione peroxidase (GPx) mimetic activity by using H2O2 as a substrate and glutathione (GSH) as a co-substrate. It was found that the substituents attached to the nitrogen atom of the selenazole ring have a significant effect on the GPx activity. While the introduction of electron withdrawing groups such as -Cl, -Br etc. to the phenyl ring decreases the activity, the introduction of electron donating groups such as -OH, -OMe significantly enhances the GPx activity of both diaryl selenides and spirodiazaselenuranes. In addition to GPx activity, the selenides and spiro derivatives were studied for their ability to inhibit peroxynitrite (PN)-mediated nitration of bovine serum albumin (BSA) and oxidation of dihydrorhodamine 123. These studies indicate that the diarylselenides effectively inhibit the PN-mediated nitration and oxidation reactions by reacting with PN to produce the corresponding spirodiazaselenuranes.

Confined fluids in a Janus pore: influence of surface asymmetry on structure and solvation forces

Density distribution, fluid structure and solvation forces for fluids confined in Janus slit-shaped pores are investigated using grand canonical Monte Carlo simulations. By varying the degree of asymmetry between the two smooth surfaces that make up the slit pores, a wide variety of adsorption situations are observed. The presence of one moderately attractive surface in the asymmetric pore is sufficient to disrupt the formation of frozen phases observed in the symmetric case. In the extreme case of asymmetry in which one wall is repulsive, the pore fluid can consist of a frozen contact layer at the attractive surface for smaller surface separations (H) or a frozen contact layer with liquid-like and gas-like regions as the pore width is increased. The superposition approximation, wherein the solvation pressure and number density in the asymmetric pores can be obtained from the results on symmetric pores, is found to be accurate for H > 4 sigma(ff), where sigma(ff) is the Lennard-Jones fluid diameter and within 10% accuracy for smaller surface separations. Our study has implications in controlling stick slip and overcoming static friction `stiction' in micro and nanofluidic devices.

1-D Hydrogen bonded water in Cu(II)-picolinate coordination polymer: synthesis, crystal structure, and thermogravimetric analysis

A new Cu(II)-picolinate complex was synthesized and characterized by single crystal X-ray crystallography. The complex crystallizes in the centrosymmetric triclinic space group P (1) over bar (no. 2). Picolinate in the complex extends the neutral unit into a 1-D chain through mu(2)-bridging carboxylate. The complex has a hydrogen bonding acceptor in the second coordination sphere allowing lattice water to assemble neighboring chains. Water self-assembles to form a zig-zag 1-D chain. The adjacent chains are assembled by C-H center dot center dot center dot O interactions result in the formation 2-D hydrogen bonded network. The overall hydrogen bonding between water chain and Cu-picolinate network yields a 3-D hydrogen bonded coordination network. X-ray structural analysis, FTIR and thermal analysis have been used to characterize the reported compound in the solid state.

Synthesis of a mixed-metal spinel, NiMn2O4, through site-selective substitution in MOF, (NiMn2){C6H3(COO)(3)}(2)]: synthesis, structure and magnetic studies

A mixed-metal metal-organic framework (MOF) compound NiMn2{C6H3(COO)(3)}(2)], I, is prepared hydrothermally by replacing one of the octahedral Mn2+ ions in Mn-3{C6H3(COO)(3)}(2)] by Ni2+ ions. Magnetic studies on I suggest antiferromagnetic interactions with weak canted antiferromagnetism below 8 K. On heating in flowing air I transforms to NiMn2O4 spinel at low temperature (T < 400 degrees C). The thermal decomposition of I at different temperatures results in NiMn2O4 with particle sizes in the nano regime. The nanoparticle nature of NiMn2O4 was confirmed using PXRD and TEM studies. Magnetic studies on the nanoparticles of NiMn2O4 indicate ferrimagnetism. The transition temperature of NiMn2O4 nanoparticles exhibits a direct correlation with the particle size. This study highlights the usefulness of MOF compound as a single-source precursor for the preparation of important ceramic oxides with better control on the stoichiometry and particle size.

Joint data detection and dominant singular mode estimation in time varying reciprocal MIMO systems

This paper proposes an algorithm for joint data detection and tracking of the dominant singular mode of a time varying channel at the transmitter and receiver of a time division duplex multiple input multiple output beamforming system. The method proposed is a modified expectation maximization algorithm which utilizes an initial estimate to track the dominant modes of the channel at the transmitter and the receiver blindly; and simultaneously detects the un known data. Furthermore, the estimates are constrained to be within a confidence interval of the previous estimate in order to improve the tracking performance and mitigate the effect of error propagation. Monte-Carlo simulation results of the symbol error rate and the mean square inner product between the estimated and the true singular vector are plotted to show the performance benefits offered by the proposed method compared to existing techniques.

New metal-organic precursors for MOCVD applications: Synthesis, characterization, crystal structure and thermal properties of mixed-ligand Mg(II) complexes

In an effort to develop new MOCVD precursors, mixed-ligand metal-organic complexes, bis (acetylacetonato-k(2)O,O') (2,2'-bipyridine-k(2)N,N') magnesium(II), and his (acetylacetonato-k(2)O,O') (1,10-phenanthroline-k(2)N,N') magnesium(II) were synthesized. Spectroscopic characterization and crystal structures confirmed them to be monomeric and stable complexes. Crystal structure analysis suggests in each of the magnesium(II) complexes, the metal center has a distorted octahedral coordination geometry. Thermo-gravimetric analysis (TGA/DTA) suggests that these complexes are volatile and thermally stable. The thermal characteristics of newly designed complexes make them attractive precursors for MOCVD applications. (c) 2012 Elsevier B.V. All rights reserved.