Re-entrant behavior in dynamics of binary mixtures of soft hybrid nanocolloids and homopolymers

We present results of measurements of temperature and wavevector dependent dynamics in binary mixtures of soft polymer grafted nanoparticles and linear homopolymers. We find evidence of melting of the dynamically arrested state of the soft nanocolloids with addition of linear polymers followed by a re-entrant slowing down of the dynamics with further increase in polymer density, depending on the size ratio, delta, of the polymers and the nanocolloids. For higher delta the re-entrant behavior is not observed, even for the highest added polymer density, explored here. Possible explanation of the observed dynamics in terms of the presence of a double - glass phase is provided. (C) 2011 American Institute of Physics. [doi:10.1063/1.3644930]

Corrosion of 310 stainless steel in H2 H2O-H2S gas mixtures; studies at constant temperature and fixed oxygen potential

Corrosion of SAE 310 stainless steel in H2-H2O-H2S gas mixtures was studied at a constant temperature of 1150 K. Reactive gas mixtures were chosen to yield a constant oxygen potential of approximately 6 × 10-13 Nm-2 and sulfur potentials ranging from 0.19 × 10-2 Nm-2 to 33 × 10-2 Nm-2. The kinetics of corrosion were determined using a thermobalance, and the scales were analyzed using metallography, scanning electron microscopy, and energy dispersive X-ray analysis. Two corrosion regimes, which were dependent on sulfur potential, were identified. At high sulfur potentials (P S 2 ± 2.7 × 10-2 Nm-2) the corrosion rates were high, the kinetics obeyed a linear rate equation, and the scales consisted mainly of sulfide phases similar to those observed from pure sulfidation. At low sulfur potentials (P S 2 ± 0.19 × 10-2 Nm-2) the corrosion rates were low, the kinetics obeyed a parabolic rate equation, and scales consisted mainly of oxide phases. Thermochemical diagrams for the Fe-Cr-S-O, Fe-Ni-S-O, Cr-Ni-S-O, and Si-Cr-S-O systems were constructed, and the experimental results are discussed in relation to these diagrams. Based on this comparison, reasonable corrosion mechanisms were developed. At high sulfur potentials, oxide and sulfide phases initially nucleate as separate islands. Overgrowth of the oxide by the sulfide occurs and an exchange reaction governs the corrosion process. Preoxidation at low oxygen potentials and 1150 K is beneficial in suppressing sulfidation at high sulfur potentials.

Population inversions behind normal shock waves in CO2‐N2‐He mixtures seeded with solid particles: Further results

The analysis of propagation of a normal shock wave in CO2‐N2‐He or H2 or H2O system seeded with solid particles is presented. The variation of translational and vibrational temperatures of gas phase and the particle temperatures in the relaxation zone behind the shock front are given in graphical form. These results show that the peak value of population inversion and the width of the inversion zone are highest for He catalyst and lowest for H2O catalyst.

Evaluation of bentonite and sand mixtures as liners

Compacted clay liners are widely used for waste contaminant facilities because of their low cost, large leachate attenuation capacity and resistance to damage and puncture. Commonly used bentonite possess many limitations such as high swelling and shrinkage potential, sensitivity to waste fluid characteristics etc. The paper proposes the use of bentonite-sand mixture containing optimal clay content as liner material. It has been brought out, based on detailed geotechnical investigations, that a mixture containing only about 20 to 39% of bentonite is more suited than the clay alone and they possess.

Composition of Extrafloral Nectar Influences Interactions between the Myrmecophyte Humboldtia brunonis and its Ant Associates

Ant-plant interactions often are mediated by extrafloral nectar (EFN) composition that may influence plant visitation by ants. Over a 300 km range in the Indian Western Ghats, we investigated the correlation between the EFN composition of the myrmecophytic ant-plant Humboldtia brunonis (Fabaceae) and the number and species of ants visiting EFN. EFN composition varied among H. brunonis populations and between plant organs (floral bud vs. young leaf EFN). In general, EFN was rich in sugars with small quantities of amino acids, especially essential amino acids, and had moderate invertase activity. In experiments at the study sites with sugar and amino acid solutions and with leaf or floral bud EFN mimics, dominant EFN-feeding ants differentiated between solutions as well as between mimics. The castration parasite Crematogaster dohrni (northern study site) was the least selective and did not exhibit any clear feeding preferences, while the largely trophobiont-tending non-protective Myrmicaria brunnea (middle study site) preferred higher sucrose concentrations and certain essential/non-essential amino acid mixtures. The mutualistic Technomyrmex albipes (southern study site) preferred sucrose over glucose or fructose solutions and consumed the leaf EFN mimic to a greater extent than the floral bud EFN mimic. This young leaf EFN mimic had low sugar concentrations, the lowest viscosity and sugar: amino acid ratio, was rich in essential amino acids, and appeared ideally suited to the digestive physiology of T. albipes. This preference for young leaf EFN may explain the greater protection afforded to young leaves than to floral buds by T. albipes, and may also help to resolve ant-pollinator conflicts. The differential response of dominant ants to sugar, amino acids, or solution viscosity suggests that plants can fine-tune their interactions with local ants via EFN composition. Thus, EFN can mediate local partner-choice mechanisms in ant-plant interactions.

Structural Transformations, Composition Anomalies and a Dramatic Collapse of Linear Polymer Chains in Dilute Ethanol-Water Mixtures

Water-ethanol mixtures exhibit many interesting anomalies, such as negative excess partial molar volume of ethanol, excess sound absorption coefficient at low concentrations, and positive deviation from Raoult's law for vapor pressure, to mention a few. These anomalies have been attributed to different, often contradictory origins, but a quantitative understanding is still lacking. We show by computer simulation and theoretical analyses that these anomalies arise from the sudden emergence of a bicontinuous phase that occurs at a relatively low ethanol concentration of x(eth) approximate to 0.06-0.10 (that amounts to a volume fraction of 0.17-0.26, which is a significant range!). The bicontinuous phase is formed by aggregation of ethanol molecules, resulting in a weak phase transition whose nature is elucidated. We find that the microheterogeneous structure of the mixture gives rise to a pronounced nonmonotonic composition dependence of local compressibility and nonmonotonic dependence in the peak value of the radial distribution function of ethyl groups. A multidimensional free energy surface of pair association is shown to provide a molecular explanation of the known negative excess partial volume of ethanol in terms of parallel orientation and hence better packing of the ethyl groups in the mixture due to hydrophobic interactions. The energy distribution of the ethanol molecules indicates additional energy decay channels that explain the excess sound attenuation coefficient in aqueous alcohol mixtures. We studied the dependence of the solvation of a linear polymer chain on the composition of the water-ethanol solvent. We find that there is a sudden collapse of the polymer at x(eth) approximate to 0.05-a phenomenon which we attribute to the formation of the microheterogeneous structures in the binary mixture at low ethanol concentrations. Together with recent single molecule pulling experiments, these results provide new insight into the behavior of polymer chain and foreign solutes, such as enzymes, in aqueous binary mixtures.

Semi empirical models for selectivity of supercritical carbon dioxide for solid mixtures

Selectivity of the particular solvent to separate a mixture is essential for the optimal design of a separation process. Supercritical carbon dioxide (SCCO2) is widely used as a solvent in the extraction, purification and separation of specialty chemicals. The effect of the temperature and pressure on selectivity is complicated and varies from system to system. The effect of temperature and pressure on selectivity of SCCO2 for different solid mixtures available in literature was analyzed. In this work, we have developed two model equations to correlate the selectivity in terms of temperature and pressure. The model equations have correlated the selectivity of SCCO2 satisfactorily for 18 solid mixtures with an average absolute relative deviation (AARD) of around 5%. (C) 2012 Elsevier B.V. All rights reserved.

Detection of sugar-lectin interactions by multivalent dendritic sugar functionalized single-walled carbon nanotubes

We show that single walled carbon nanotubes (SWNTs) decorated with sugar functionalized poly (propyl ether imine) (PETIM) dendrimer is a very sensitive platform to quantitatively detect carbohydrate recognizing proteins, namely, lectins. The changes in electrical conductivity of SWNT in field effect transistor device due to carbohydrate-protein interactions form the basis of present study. The mannose sugar attached PETIM dendrimers undergo charge-transfer interactions with the SWNTs. The changes in the conductance of the dendritic sugar functionalized SWNT after addition of lectins in varying concentrations were found to follow the Langmuir type isotherm, giving the concanavalin A (Con A)-mannose affinity constant to be 8.5 x 10(6) M-1. The increase in the device conductance observed after adding 10 nM of Con A is same as after adding 20 mu M of a non-specific lectin peanut agglutinin, showing the high specificity of the Con A-mannose interactions. The specificity of sugar-lectin interactions was characterized further by observing significant shifts in Raman modes of the SWNTs. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4739793]

A versatile resolving agent for diffusion edited separation of enantiomers, complex mixtures and constitutional isomers

The study is the first report of the utilization of a crown ether as a new and versatile resolving agent for the diffusion edited separation of enantiomers, complex mixtures and constitutional isomers. As a consequence of different binding affinities of enantiomers of a chiral molecule and individual components of the complex mixtures with the crown ether, the molecules diffuse at different rates. The enhanced separation achieved due to matrix assisted diffusion permitted their separation in the diffusion dimension. The generality and wide utility of the new resolving agent and the methodology are demonstrated on diverse examples, such as an organic chiral molecule, constitutional isomers and complex mixture of molecules possessing different functional groups that possess nearly identical molecular weights.

Anomalous structural and dynamical phase transitions of soft colloidal binary mixtures

We report microscopic structural and dynamical measurements on binary mixtures of homopolymers and polymer grafted nanoparticles at high densities in good solvent. We find strong and unexpected anomalies in the structure and dynamics of these binary mixtures, including appearance of spontaneous orientational alignment, as a function of added homopolymers of different molecular weights. Our experiments point to the possibility of exploiting the phase space in density and homopolymer size, of such hybrid systems, to create new materials with novel structural and physical properties.

2,3-Unsaturated enoses. A Pummerer rearrangement route to sugar vinyl sulfides and synthesis of 3-deoxy-3-alkyl/arylsulfinyl pyranosides

A Pummerer rearrangement of 2,3-dideoxy-3-alkyl/arylsulfinyl-arabino-hexopyranosides is reported. Treatment of sulfinyl-arabino-hexopyranoside derivatives, obtained through oxidation of the corresponding thio-derivatives, with trifluoroacetic anhydride (TFAA)/pyridine led to a facile formation of 2,3-dideoxy-3-alkyl/arylthio-hex-2-enopyranosides. Upon conversion of sugar vinyl sulfides to vinyl sulfoxides, conjugate addition reactions were conducted with alkoxides, to afford 3-deoxy-3-alkyl/arylsulfinyl pyranosides, in the manno-configuration exclusively. Whereas the conjugate addition reaction did not proceed with ether protecting groups, ester protecting groups and free hydroxyl groups in the sugar vinyl sulfoxide permitted the reaction. (C) 2012 Elsevier Ltd. All rights reserved.

GFT projection NMR for efficient H-1/C-13 sugar spin system identification in nucleic acids

A newly implemented G-matrix Fourier transform (GFT) (4,3)D HC(C)CH experiment is presented in conjunction with (4,3)D HCCH to efficiently identify H-1/C-13 sugar spin systems in C-13 labeled nucleic acids. This experiment enables rapid collection of highly resolved relay 4D HC(C)CH spectral information, that is, shift correlations of C-13-H-1 groups separated by two carbon bonds. For RNA, (4,3)D HC(C)CH takes advantage of the comparably favorable 1'- and 3'-CH signal dispersion for complete spin system identification including 5'-CH. The (4,3)D HC(C)CH/HCCH based strategy is exemplified for the 30-nucleotide 3'-untranslated region of the pre-mRNA of human U1A protein.

Identification of Active Sources in Single-Channel Convolutive Mixtures Using Known Source Models

We address the problem of identifying the constituent sources in a single-sensor mixture signal consisting of contributions from multiple simultaneously active sources. We propose a generic framework for mixture signal analysis based on a latent variable approach. The basic idea of the approach is to detect known sources represented as stochastic models, in a single-channel mixture signal without performing signal separation. A given mixture signal is modeled as a convex combination of known source models and the weights of the models are estimated using the mixture signal. We show experimentally that these weights indicate the presence/absence of the respective sources. The performance of the proposed approach is illustrated through mixture speech data in a reverberant enclosure. For the task of identifying the constituent speakers using data from a single microphone, the proposed approach is able to identify the dominant source with up to 8 simultaneously active background sources in a room with RT60 = 250 ms, using models obtained from clean speech data for a Source to Interference Ratio (SIR) greater than 2 dB.

Evaluation of isopentane, R-245fa and their mixtures as working fluids for organic Rankine cycles

Low grade thermal energy from sources such as solar, geothermal and industrial waste heat in the temperature range of 380-425 K can be converted to electrical energy with reasonable efficiency using isopentane and R-245fa. While the former is flammable and the latter has considerable global warming potential, their mixture in 0.7/0.3 mole fraction is shown to obviate these disadvantages and yet retain dominant merits of each fluid. A realistic thermodynamic analysis is carried out wherein the possible sources of irreversibilities such as isentropic efficiencies of the expander and the pump and entropy generation in the regenerator, boiler and condenser are accounted for. The performance of the system in the chosen range of heat source temperatures is evaluated. A technique of identifying the required source temperature for a given output of the plant and the maximum operating temperature of the working fluid is developed. This is based on the pinch point occurrence in the boiler and entropy generation in the boiling and superheating regions of the boiler. It is shown that cycle efficiencies of 10-13% can be obtained in the range investigated at an optimal expansion ratio of 7-10. (C) 2012 Elsevier Ltd. All rights reserved.