Thermoanalysis of ammonium perchlorate and sodium nitrate mixture

A binary mixture of ammonium perchlorate-sodium nitrate in molar proportion undergoes partial fusion at 223°C and the transformation of the mixture to sodium perchlorate-ammonium nitrate occurs in the broad endothermic region. The mixture was heated and quenched at various temperatures in a differential thermal analysis assembly. Thermogravimetric analysis, X-ray diffraction, and infrared spectroscopic techniques were used to determine the composition of the quenched sample in order to explain the overall thermal phenomenon. Visual observations of the morphological changes that occur during the course of heating were made using a hot-stage microscope, 30–350°C.

Study of the effect of alkali mixture on V-O bond length in Oxyfluoro Vanadate glasses using Raman spectroscopy

Raman spectroscopic study on Oxyfluoro Vanadate glasses containing various proportions of lithium fluoride and rubidium fluoride was carried out to see an effect of mixture of alkali on vanadium-oxygen (V-O) bond length. Glasses with a general formula 40V(2)O(5) - 30BaF(2) - (30 - x) LiF - xRbF (x = 0-30) were prepared. Room temperature Raman spectra of these glass samples were recorded in back scattering geometry. The data presented is in ``reduced Raman intensity'' form with maximum peak scaled to 100. We have used v = Aexp(BR), where A and B are fitting parameters, to correlate the bond length R with Raman scattering frequency v. We observed that variation in bond length and its distribution about a most probable value can be correlated to the alkali environment present in these glasses. We also observed that all rubidium environment around the network forming unit is more homogenous than all lithium environment.

Experimental determination and activity coefficient based models for mixture solubilities of nitrophenol isomers in supercritical carbon dioxide

The experimental solubilities of the mixture of nitrophenol (m- and p-) isomers were determined at 308, 318 and 328 K over a pressure range of 10-17.55 MPa. Compared to the binary solubilities, the ternary solubilities of m-nitrophenol increased at 308, 318 and 328 K. The ternary solubilities of p-nitrophenol increased at 308 K, while the ternary solubilities decreased at lower pressures and increased at higher pressure at 318 and 328 K. The solubilities of the solid mixtures in supercritical carbon dioxide (SCCO2) were correlated with solution models by incorporating the non-idealities using activity coefficient based models. The Wilson and NRTL activity coefficient models were applied to determine the nature of the interactions between the molecules. The equation developed by using the NRTL model has three parameters and correlates mixture solubilities of solid solutes in terms of temperature and cosolute composition. The equation derived from the Wilson model contains five parameters and correlates solubilities in terms of temperature, density and cosolute composition. These two new equations developed in this work were used to correlate the solubilities of 25 binary solid mixtures including the current data. The average AARDs of the model equations derived using the NRTL and Wilson models for the solid mixtures were found to be 7% and 4%, respectively. (C) 2012 Elsevier B.V. All rights reserved.

Thermally Induced Demixing in an LCST Mixture in the Presence of Densely Grafted Nanoparticles: Tuning the Graft Chain Length To Induce Thermodynamic Miscibility

The demixing in an LCST mixture of PS/PVME (polystyrene/poly(vinyl methyl ether)) was probed here by melt rheology in the presence of gold nanoparticles which were densely coated with varying graft lengths of PS. The graft density for the gold nanoparticles coated with 3 kDa PS was ca. Sigma = 1.7 chains/nm(2), and that for 53 kDa PS was ca. Sigma = 1.2 chains/nm(2). The evolution of morphology, as the blends transit through the metastable and the unstable envelopes of the phase diagram, and the localization of the gold nanoparticles upon demixing were monitored using in situ hot-stage AFM and confocal Raman imaging. Interestingly, gold nanoparticles coated with 3 kDa polystyrene (PS(3 kDa)-g-nAu) were localized in the PVME phase, whereas gold nanoparticles coated with 53 kDa polystyrene (PS(53 kDa)-g-nAu) were localized in the PS phase of the blend. While the localization of PS(3 kDa)-g-nAu in the PVME phase can be expected to be of entropic origin due to expulsion from the PS phase as R-g,R-matrix chains > R-g,R-grafted chains (where R-g is the radius of gyration of the polymer chain), the localization of PS(53 kDa)-g-nAu in the PS phase is believed to be facilitated by favorable melt/graft interactions. The latter nanoparticles also delayed the demixing by 12 degrees C with respect to the neat mixture. The observed changes were addressed in context to enthalpic interactions between the grafted PS and the free PS, the entropic losses (deformational entropic losses on blending, translational entropic loss of the free PS, and the conformational entropic loss of the grafted PS), and the interface of the grafted and the free chains.

Equilibration of a liquid droplet-vapor-gas mixture downstream of a shock wave

The equations of motion for the flow of a mixture of liquid droplets, their vapor, and an inert gas through a normal shock wave are derived. A set of equations is obtained which is solved numerically for the equilibrium conditions far downstream of the shock. The equations describing the process of reaching equilibrium are also obtained. This is a set of first-order nonlinear differential equations and must also be solved numerically. The detailed equilibration process is obtained for several cases and the results are discussed.

I. The attenuation and dispersion of sound in a condensing medium. II. The flow of a gas-particle mixture downstream of a normal shock in a nozzle

I. The attenuation of sound due to particles suspended in a gas was first calculated by Sewell and later by Epstein in their classical works on the propagation of sound in a two-phase medium. In their work, and in more recent works which include calculations of sound dispersion, the calculations were made for systems in which there was no mass transfer between the two phases. In the present work, mass transfer between phases is included in the calculations.

The attenuation and dispersion of sound in a two-phase condensing medium are calculated as functions of frequency. The medium in which the sound propagates consists of a gaseous phase, a mixture of inert gas and condensable vapor, which contains condensable liquid droplets. The droplets, which interact with the gaseous phase through the interchange of momentum, energy, and mass (through evaporation and condensation), are treated from the continuum viewpoint. Limiting cases, for flow either frozen or in equilibrium with respect to the various exchange processes, help demonstrate the effects of mass transfer between phases. Included in the calculation is the effect of thermal relaxation within droplets. Pressure relaxation between the two phases is examined, but is not included as a contributing factor because it is of interest only at much higher frequencies than the other relaxation processes. The results for a system typical of sodium droplets in sodium vapor are compared to calculations in which there is no mass exchange between phases. It is found that the maximum attenuation is about 25 per cent greater and occurs at about one-half the frequency for the case which includes mass transfer, and that the dispersion at low frequencies is about 35 per cent greater. Results for different values of latent heat are compared.

II. In the flow of a gas-particle mixture through a nozzle, a normal shock may exist in the diverging section of the nozzle. In Marble’s calculation for a shock in a constant area duct, the shock was described as a usual gas-dynamic shock followed by a relaxation zone in which the gas and particles return to equilibrium. The thickness of this zone, which is the total shock thickness in the gas-particle mixture, is of the order of the relaxation distance for a particle in the gas. In a nozzle, the area may change significantly over this relaxation zone so that the solution for a constant area duct is no longer adequate to describe the flow. In the present work, an asymptotic solution, which accounts for the area change, is obtained for the flow of a gas-particle mixture downstream of the shock in a nozzle, under the assumption of small slip between the particles and gas. This amounts to the assumption that the shock thickness is small compared with the length of the nozzle. The shock solution, valid in the region near the shock, is matched to the well known small-slip solution, which is valid in the flow downstream of the shock, to obtain a composite solution valid for the entire flow region. The solution is applied to a conical nozzle. A discussion of methods of finding the location of a shock in a nozzle is included.

Convex relaxation of mixture regression with efficient algorithms

We develop a convex relaxation of maximum a posteriori estimation of a mixture of regression models. Although our relaxation involves a semidefinite matrix variable, we reformulate the problem to eliminate the need for general semidefinite programming. In particular, we provide two reformulations that admit fast algorithms. The first is a max-min spectral reformulation exploiting quasi-Newton descent. The second is a min-min reformulation consisting of fast alternating steps of closed-form updates. We evaluate the methods against Expectation-Maximization in a real problem of motion segmentation from video data.

Separation of ethyl acetate-ethanol azeotropic mixture using hydrophilic ionic liquids

The separation of ethyl acetate and ethanol (EtOH) is important but difficult due to their close boiling points and formation of an azeotropic mixture. The separation of the azeotropic mixture of ethyl acetate and EtOH using the hydrophilic ionic liquids (ILs) 1-alkyl-3-methylimidazolium chloride (alkyl = butyl, hexyl, and octyl) ([C(n)mim]Cl, n = 4, 6, 8) and 1-allyl-3-methylimidazolium chloride and bromide ([Amim]Cl and [Amim]Br) has been investigated. Triangle phase diagrams of five ILs with ethyl acetate and EtOH were constructed, and the biphasic regions were found as follows: [Amim]Cl > [Amim]Br > [C(4)mim]Cl > [C(6)mim]Cl > [C(8)mim]Cl. The mechanisms of the ILs including cation, anion, and polarity effect were discussed.

Later Life Consequences of Subteratogenic Exposure to a Complex PAH Mixture in the Atlantic Killifish (Fundulus heteroclitus)

Subteratogenic and other low-level chronic exposures to toxicant mixtures are an understudied threat to environmental and human health. It is especially important to understand the effects of these exposures for contaminants, such as polycyclic aromatic hydrocarbons (PAHs) a large group of more than 100 individual compounds, which are important environmental (including aquatic) contaminants. Aquatic sediments constitute a major sink for hydrophobic pollutants, and studies show PAHs can persist in sediments over time. Furthermore, estuarine systems (namely breeding grounds) are of particular concern, as they are highly impacted by a wide variety of pollutants, and estuarine fishes are often exposed to some of the highest levels of contaminants of any vertebrate taxon. Acute embryonic exposure to PAHs results in cardiac teratogenesis in fish, and early life exposure to certain individual PAHs and PAH mixtures cause heart alterations with decreased swimming capacity in adult fish. Consequently, the heart and cardiorespiratory system are thought to be targets of PAH mixture exposure. While many studies have investigated acute, teratogenic PAH exposures, few studies have longitudinally examined the impacts of subtle, subteratogenic PAH mixture exposures, which are arguably more broadly applicable to environmental contamination scenarios. The goal of this dissertation was to highlight the later-life consequences of early-life exposure to subteratogenic concentrations of a complex, environmentally relevant PAH mixture.

A unique population of Fundulus heteroclitus (the Atlantic killifish or mummichog, hereafter referred to as killifish), has adapted to creosote-based polycyclic aromatic hydrocarbons (PAHs) found at the Atlantic Wood Industries (AW) Superfund site in the southern branch of the Elizabeth River, VA, USA. This killifish population survives in a site heavily contaminated with a mixture of PAHs from former creosote operations. They have developed resistance to the acute toxicity and teratogenic effects caused by the mixture of PAHs in sediment from the site. The primary goal of this dissertation was to compare and contrast later-life outcomes of early-life, subteratogenic PAH mixture exposure in both the Atlantic Wood killifish (AW) and a naïve reference population of killifish from King’s Creek (KC; a relatively uncontaminated tributary of the Severn River, VA). Killifish from both populations were exposed to subteratogenic concentrations of a complex PAH-sediment extract, Elizabeth River Sediment Extract (ERSE), made by collecting sediment from the AW site. Fish were reared over a 5-month period in the laboratory, during which they were examined for a variety of molecular, physiological and behavioral responses.

The central aims of my dissertation were to determine alterations to embryonic gene expression, larval swimming activity, adult behavior, heart structure, enzyme activity, and swimming/cardiorespiratory performance following subteratogenic exposure to ERSE. I hypothesized that subteratogenic exposure to ERSE would impair cardiac ontogenic processes in a way that would be detectable via gene expression in embryos, and that the misregulation of cardiac genes would help to explain activity changes, behavioral deficits, and later-life swimming deficiencies. I also hypothesized that fish heart structure would be altered. In addition, I hypothesized that the AW killifish population would be resistant to developmental exposures and perform normally in later life challenges. To investigate these hypotheses, a series of experiments were carried out in PAH-adapted killifish from Elizabeth River and in reference killifish. As an ancillary project to the primary aims of the dissertation, I examined the toxicity of weaker aryl hydrocarbon receptor (AHR) agonists in combination with fluoranthene (FL), an inhibitor of cytochrome P4501A1 (CYP1A1). This side project was conducted in both Danio rerio (zebrafish) and the KC and AW killifish.

Embryonic gene expression was measured in both killifish populations over an ERSE dose response with multiple time points (12, 24, 48, and 144 hours post exposure). Genes known to play critical roles in cardiac structure/development, cardiac function, and angiogenesis were elevated, indicating cardiac damage and activation of cardiovascular repair mechanisms. These data helped to inform later-life swimming performance and cardiac histology studies. Behavior was assessed during light and dark cycles in larvae of both populations following developmental exposure to ERSE. While KC killifish showed activity differences following exposure, AW killifish showed no significant changes even at concentrations that would cause overt cardiac toxicity in KC killifish. Juvenile behavior experiments demonstrated hyperactivity following ERSE exposure in KC killifish, but no significant behavioral changes in AW killifish. Adult swimming performance via prolonged critical swimming capacity (Ucrit) demonstrated performance costs in the AW killifish. Furthermore, swimming performance decline was observed in KC killifish following exposure to increasing dilutions of ERSE. Lastly, cardiac histology suggested that early-life exposure to ERSE could result in cardiac structural alteration and extravasation of blood into the pericardial cavity.

Responses to AHR agonists resulted in a ranking of relative potency for agonists, and determined which agonists, when combined with FL, caused cardiac teratogenesis. These experiments showed interesting species differences for zebrafish and killifish. To probe mechanisms responsible for cardiotoxicity, a CYP1A-morpholino and a AHR2-morpholino were used to mimic FL effects or attempt to rescue cardiac deformities respectively. Findings suggested that the cardiac toxicity elicited by weak agonist + FL exposure was likely driven by AHR-independent mechanisms. These studies stand in contrast to previous research from our lab showing that moderate AHR agonist + FL caused cardiac toxicity that can be partially rescued by AHR-morpholino knockdown.

My findings will form better characterization of mechanisms of PAH toxicity, and advance our understanding of how subteratogenic mixtures of PAHs exert their toxic action in naïve killifish. Furthermore, these studies will provide a framework for investigating how subteratogenic exposures to PAH mixtures can impact aquatic organismal health and performance. Most importantly, these experiments have the potential to help inform risk assessment in fish, mammals, and potentially humans. Ultimately, this research will help protect populations exposed to subtle PAH-contamination.

Mutual Solubilities of Ammonium-Based Ionic Liquids with Water and with Water/Methanol Mixture

Over the last two decades, ionic liquids have gained importance as alternative solvents to conventional VOCs in the field of homogeneous catalysis. This success is not only due to their ability to dissolve a large amount of metal catalysts, but it is also due to their potential to enhance yields of enantiopure products. The art of preparation of a specific enantiomer is a highly desired one and searched for in pharmaceutical industry. This work presents a study on solubility in water and in water/methanol mixture of a set of ILs composed of the bis (trifluoromethylsulfonyl) imide anion and of the N-alkyl-triethyl-ammonium cation (abbrev. [NR,222][NTf2]) with the alkyl chain R ranging from 6 to 12 carbons. Mutual solubilities between ILs and water, as well as between ILs and methanol/water mixture were investigated in detail. These solubilities were measured using two well-known and accurate experimental techniques based on a volumetric and a cloud-point methods. Both methods enabled us to measure the Tx diagrams reflecting the mutual solubilities between water (or water/methanol) and selected ILs in the temperature range from 293.15 to 338.15 K. The data were fitted by using the modified Flory-Huggins equation proposed by de Sousa and Rebelo and compared also with the prediction carried out by the Cosmo-RS methodology

Probe-level linear model fitting and mixture modeling results in high accuracy detection of differential gene expression

Affiliation: Institut de recherche en immunologie et en cancérologie, Université de Montréal

Equivalence of truncated count mixture distributions and mixtures of truncated count distributions

This article is about modeling count data with zero truncation. A parametric count density family is considered. The truncated mixture of densities from this family is different from the mixture of truncated densities from the same family. Whereas the former model is more natural to formulate and to interpret, the latter model is theoretically easier to treat. It is shown that for any mixing distribution leading to a truncated mixture, a (usually different) mixing distribution can be found so. that the associated mixture of truncated densities equals the truncated mixture, and vice versa. This implies that the likelihood surfaces for both situations agree, and in this sense both models are equivalent. Zero-truncated count data models are used frequently in the capture-recapture setting to estimate population size, and it can be shown that the two Horvitz-Thompson estimators, associated with the two models, agree. In particular, it is possible to achieve strong results for mixtures of truncated Poisson densities, including reliable, global construction of the unique NPMLE (nonparametric maximum likelihood estimator) of the mixing distribution, implying a unique estimator for the population size. The benefit of these results lies in the fact that it is valid to work with the mixture of truncated count densities, which is less appealing for the practitioner but theoretically easier. Mixtures of truncated count densities form a convex linear model, for which a developed theory exists, including global maximum likelihood theory as well as algorithmic approaches. Once the problem has been solved in this class, it might readily be transformed back to the original problem by means of an explicitly given mapping. Applications of these ideas are given, particularly in the case of the truncated Poisson family.

A bagging-based correction for the mixture model estimator of population size

Estimation of a population size by means of capture-recapture techniques is an important problem occurring in many areas of life and social sciences. We consider the frequencies of frequencies situation, where a count variable is used to summarize how often a unit has been identified in the target population of interest. The distribution of this count variable is zero-truncated since zero identifications do not occur in the sample. As an application we consider the surveillance of scrapie in Great Britain. In this case study holdings with scrapie that are not identified (zero counts) do not enter the surveillance database. The count variable of interest is the number of scrapie cases per holding. For count distributions a common model is the Poisson distribution and, to adjust for potential heterogeneity, a discrete mixture of Poisson distributions is used. Mixtures of Poissons usually provide an excellent fit as will be demonstrated in the application of interest. However, as it has been recently demonstrated, mixtures also suffer under the so-called boundary problem, resulting in overestimation of population size. It is suggested here to select the mixture model on the basis of the Bayesian Information Criterion. This strategy is further refined by employing a bagging procedure leading to a series of estimates of population size. Using the median of this series, highly influential size estimates are avoided. In limited simulation studies it is shown that the procedure leads to estimates with remarkable small bias.

Further monoterpene chromane esters from Peperomia obtusifolia: VCD determination of the absolute configuration of a new diastereomeric mixture

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrical properties of YSZ/NiO composites prepared by a liquid mixture technique

We report the preparation and characterization of yttria-stabilized zirconia/nickel oxide composites (YSZ/NiO). This composite is the precursor material of the cermet YSZ/Ni, which is used as solid oxide fuel cell anode material. The performance of the anode is strongly dependent on the microstructural properties of the cermet. Therefore, the control of the microstructure of the YSZ/NiO composite is a key step for the fabrication of high-performance anodes. In this study, the composites were prepared by a modified liquid mixture technique. Scanning electron microscopy analysis evidenced the good dispersion of the phases and that NiO nanoparticles are spread over the YSZ surface. Sintered pellets were studied by X-ray diffraction and impedance spectroscopy. The main results show that the composite is comprised of a well-dispersed mixture of the two phases. The electrical conductivity data show that there is a strong dependence of the transport mechanism on the relative composition of phases. (c) 2005 Elsevier Ltd. All rights reserved.