Study of the polyoxymethylene and its sputtered fragments: Implications for comets

Laboratory mass spectra of sputtered polyoxymethylene (POM) reveals a fragmentation pattern consistent with observed peaks in the PICCA experiment on board the Giotto spacecraft. Both commercially available POM and radiation synthesized POM have been used in the studies. Synthesized POM was identified using infrared absorption spectra after proton irradiation of H2CO ice on silicate grains at 20 K. Laboratory results suggest that similar type sputtering is a possible mechanism for removing species from comet grains

The stabilisation of the Nx phase in mixtures

The phase behaviour of mixtures between two symmetric dimers, CBC9CB and the ether-linked analogue CBOC9OCB was investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) studies. The dimeric constituents are fully miscible and the construction of a temperature-composition phase diagram reveals a surprising amplification of the stability of the Nx phase in compositions of up to 37 wt% of CBOC9OCB in CBC9CB. The origin for this enhancement of stability is discussed and an explanation based on chiral recognition is developed

Novel Charge-Transfer Materials via Cocrystallization of Planar Aromatic Donors and Spherical Polyoxometalate Acceptors

Spherical polyoxometalates (POMs) such as M6O192- and SiM12O404- (with M = Mo or W) and planar arene donors (anthracenes and pyrenes) can be cocrystallized (despite their structural incompatibility) by attaching a cationic “anchor” onto the arene which then clings to the POM anion by Coulombic forces. As a result, novel charge-transfer (CT) salts are prepared from arene donors and Lindqvist-type [M6O19]2- and Keggin-type [SiM12O40]4- acceptors with overall 2:1 and 4:1 stoichiometry, respectively. The CT character of the dark-colored (yellow to red) crystalline materials is confirmed by the linear Mulliken correlation between the CT transition energies and the reduction potentials of the POM acceptors, as well as by the transient (diffuse reflectance) absorption spectra (upon picosecond laser excitation) of anthracene or pyrene cation radicals (in monomeric and π-dimeric forms). X-ray crystallographic studies reveal a unique “dimeric” arrangement of the cofacially oriented arene couples which show contact points with the oxygen surface of the POMs that vary with distance, depending on the POM/arene combination. Moreover, the combination of X-ray crystallographic and spectroscopic techniques results in the observation of a logical structure/property relationshipthe shorter the distance between the POM surface and the arene nucleus, the darker is the color of the CT crystal and the faster is the decay of the laser-excited charge-transfer state (due to back-electron transfer)

Electrochemical study of H3PMo12 retention on Vulcan carbon grafted with NH2 and OH groups

In this work, we show a comparative study based on the effects of specific chemical functional groups (–OH, –NH2), grafted on Vulcan carbon (VC) with the incorporation of a specific polyoxometalate (POM), PMo12 (H3PMo12O40), to improve electrochemical performance. We observed a decrease in the specific surface area of the grafted matrices (VC-OH and VC-NH2) [1], and the same trend was observed for PMo12 (POM) incorporation. Our electrochemical studies showed low concentrations of POM in unmodified VCs and higher POM concentrations for grafted matrices (VC-OH and VC-NH2) after 500 voltammetric cycles, especially for the VC grafted with –OH groups (VC-OH-POM). Mechanisms have been proposed for POM interaction with the grafted groups in carbon, emphasizing the role of aqueous medium and redox activity of POM. Cyclic voltammograms suggested the POM anchoring through –OH groups with a strong interaction as a covalent bond, resulting in a surface coverage of 1.66 × 10−11 mol cm−2. Surface modifications could be extrapolated to other carbons, and the materials could be employed for different potential applications such as photocatalysis, amperometric sensors, fuel cells, and supercapacitors.Fil: Cuentas Gallegos, Ana Karina. Universidad Nacional Autónoma de México; México. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: López Cortina, S.. Universidad Autonoma de Nuevo Leon; MéxicoFil: Brousse, T.. Université de Nantes. Institut Des Materiaux Jean Rouxel; FranciaFil: Pacheco Catalán, D.. Centro de Investigación Científica de Yucatán; MéxicoFil: Fuentes Quezada, Eduardo. Centro de Investigación y Desarrollo Tecnológico en Electroquímica; México. Universidad Nacional Autónoma de México; México. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mosqueda, H.. Universidad Autonoma de Nuevo Leon; MéxicoFil: Orozco Gamboa, G.. Centro de Investigación y Desarrollo Tecnológico en Electroquímica; Méxic

Photochemical transformation of particulate organic carbon and its impact on mercury cycling in aqueous systems

Thesis: S.M. in Environmental Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.Cataloged from PDF version of thesis. Errors in Table of Content. Pagination reflects how thesis was delivered to MIT LIbraries.Includes bibliographical references (pages 35-37).Mercury (Hg) is a global pollutant with high toxicity that accumulates in biota and biomagnifies, posing a risk to organisms throughout the food chain. Mercury is known to strongly associate with natural organic matter (NOM), which, in turn, affects its speciation, solubility, mobility and toxicity. Numerous studies have examined Hg coordination with dissolved organic carbon (DOC), an important aqueous constituent that alters the reactivity and fate of Hg primarily through complexation with carboxyl and reduced sulfur (e.g. sulfhydryl) groups. However, less is understood of Hg reactions with particulate organic matter (POM), an important reservoir of NOM found within soils, sediments, and suspended in aqueous systems. Moreover, the chemistry of NOM changes when irradiated by sunlight, altering the composition and distribution of functional groups available for complexation with aqueous Hg. Accordingly, we investigate Hg complexation with POM derived from a natural source, Phragmites australis ("common reed"), and examined how photochemical processes impact Hg adsorption through chemical alteration of POM. Mercury adsorption to irradiated and non-irradiated POM was examined through performing isotherm experiments, using an environmentally-relevant range of Hg concentrations (2-500 ppb). First, we find that non-irradiated POM is a powerful sorbent of Hg²+. Adsorption characteristics are indeed altered during POM photolysis, with a three-fold (based on Kd) increase in Hg adsorption observed for irradiated POM compared to dark controls. Further, we examine the speciation and oxidation state of adsorbed Hg²+, and deciphered functional groups that contribute to mercury association with POM. Measurements of C, S, and Hg speciation and oxidation state were performed using synchrotron-based X-ray adsorption spectroscopy (XAS) and scanning transmission x-ray microscopy (STXM). These revealed a marked decrease in POM-reduced sulfur following irradiation, leading to fewer R-SH groups capable of strongly binding Hg. However, decreased Hg binding to irradiated POM was not observed owing to a large increase in the quantity of carboxyl groups formed through photochemical processes, which resulted in a higher overall capacity of irradiated POM to bind Hg. The large capacity of POM for binding Hg, as well as enhanced Hg binding following irradiation illustrates that POM is a chemically dynamic pool of NOM that warrants consideration when evaluating reservoirs and processes governing the global Hg cycle.by Claudia E. Gelfond.S.M. in Environmental Engineerin

Selective targeting of proteins by hybrid polyoxometalates: Interaction between a bis-biotinylated hybrid conjugate and avidin

The Keggin-type polyoxometalate [\u3b3-SiW10O36]8 12 was covalently modified to obtain a bis-biotinylated conjugate able to bind avidin. Spectroscopic studies such as UV-vis, fluorimetry, circular dichroism, coupled to surface plasmon resonance technique were used to highlight the unique interplay of supramolecular interactions between the homotetrameric protein and the bis-functionalized polyanion. In particular, the dual recognition mechanism of the avidin encompasses (i) a complementary electrostatic association between the anionic surface of the polyoxotungstate and each positively charged avidin subunit and (ii) specific host-guest interactions between each biotinylated arm and a corresponding pocket on the tetramer subunits. The assembly exhibits peroxidase-like reactivity and it was used in aqueous solution for L-methionine methyl ester oxidation by H2O2. The recognition phenomenon was then exploited for the preparation of layer-by-layer films, whose structural evolution was monitored in situ by ATR-FTIR spectroscopy. Finally, cell tracking studies were performed by exploiting the specific interactions with a labeled streptavidin

Operations Management Curricula: Literature Review and Analysis

A review and analysis of studies on the interface between Operations Management (OM) academicians and industry practitioners indicate the existence of a persistent gap between what is being taught and what is relevant to practitioners in their daily jobs. The majority of practitioner studies have been directed at upper management levels, yet academia typically educates students for entry level or management trainee (undergraduate) and mid-management (MBA) positions. A recurring finding was that academicians prefer to teach quantitative techniques while practitioners favor qualitative concepts. The OM curricula literature shows some disagreements between academicians concerning subject matter, and a wide variety of teaching opinions. This paper provides an extensive analytical review of OM curricula literature along with their respective authors’ conclusions. From this analysis we suggest a customer-focused business plan to close the gap between industry and academia. This plan can be modified to account for faculty teaching and research interests, local industry requirements and institution specific factors such as class sizes and resources

A Randomized Controlled Trial of a Play-Based, Peer-Mediated Pragmatic Language Intervention for Children With Autism

Purpose: This randomized controlled trial evaluated the effectiveness of a play-based pragmatic language intervention for children with autism. Methods: A sample of 71 children with autism were randomized to an intervention-first group (n = 28 analyzed) or waitlist-first (n = 34 analyzed) group. Children attended 10, weekly clinic play-sessions with a typically developing peer, and parents mediated practice components at home. The Pragmatics Observational Measure (POM-2) and the Social Emotional Evaluation (SEE) evaluated pragmatics before, after and 3-months following the intervention. Results: POM-2 gains were greatest for intervention-first participants (p = 0.031, d = 0.57). Treatment effects were maintained at 3-month follow-up (p < 0.001–0.05, d = 0.49–0.64). POM-2 scores were not significantly different in the clinic and home settings at follow-up. Conclusion: Findings support the combination of play, peer-mediation, video-feedback and parent training to enhance pragmatic language in children with autism