M.marcia West - Academia.edu (original) (raw)

Papers by M.marcia West

Journal of Polymer Science Part A, 2001

membranes which define concentrating and diluting flow channels between adjacent membrane pairs. ... more membranes which define concentrating and diluting flow channels between adjacent membrane pairs. The diluting channels include cation and anion exchange materials, fixed in close contact, to provide conductive paths for ions of the adjacent membranes and flow passages for water between the material. The packing material can include one or more macro-structural elements made of smaller micro-structural elements. The first and second stages can be used to purify water including calcium, carbon dioxide and its hydrates. The ion-exchange material differs in the diluting flow channel of each stage, and the concentrating flow channels can include a brine channel between two guard channels.

Geochimica et Cosmochimica Acta Supplement, Sep 1, 2003

ACS Catalysis, Jul 1, 2020

The interface between perfluorosulfonic acid polymer electrolytes and Pt nanoparticles in a model... more The interface between perfluorosulfonic acid polymer electrolytes and Pt nanoparticles in a model hydrogen fuel cell catalyst layer was analyzed using high-resolution scanning transmission x-ray mi...

Seed Science Research, Jun 1, 1994

Inorganic P, total P and phytic acid-P leakage from imbibing whole soybean, bean, and pea seeds, ... more Inorganic P, total P and phytic acid-P leakage from imbibing whole soybean, bean, and pea seeds, as well as whole maize and barley grains were measured The amounts of P and phytic acid leaked during a 6-h soaking period varied for the five species Soybeans leaked the most P and phytic acid of the species examined Peas, beans and barley leaked little or no phytic acid Based on reported levels of total P and phytic acid in the dry seeds/grains that were studied, total P leakage ranged from 0 5 to 1 2%, while phytic acid leakage ranged from 0 01 to 0 5% No relationship was found between initial levels of total P or phytic acid in the dry seeds/grains and the amount of total P or phytic acid leaked by the imbibed seed/grain Similarly, the amounts of phytic acid leaked by the seeds/grams of this study did not appear to be related to the water solubility of the phytic acid in the dry seeds/grains

Journal of Power Sources, Nov 1, 2014

Scanning Transmission X-ray Microscopy (STXM) at the C 1s, F 1s and S 2p edges has been used to i... more Scanning Transmission X-ray Microscopy (STXM) at the C 1s, F 1s and S 2p edges has been used to investigate degradation of proton exchange membrane fuel cell (PEM-FC) membrane electrode assemblies (MEA) subjected to accelerated testing protocols. Quantitative chemical maps of the catalyst, carbon support and ionomer in the cathode layer are reported for beginning-of-test (BOT), and end-of-test (EOT) samples for two types of carbon support, low surface area carbon (LSAC) and medium surface area carbon (MSAC), that were exposed to accelerated stress testing with upper potentials (UPL) of 1.0, 1.2, and 1.3 V. The results are compared in order to characterize catalyst layer degradation in terms of the amounts and spatial distributions of these species. Pt agglomeration, Pt migration and corrosion of the carbon support are all visualized, and contribute to differing degrees in these samples. It is found that there is formation of a distinct Pt-in-membrane (PTIM) band for all EOT samples. The cathode thickness shrinks due to loss of the carbon support for all MSAC samples that were exposed to the different upper potentials, but only for the most aggressive testing protocol for the LSAC support. The amount of ionomer per unit volume significantly increases indicating it is being concentrated in the cathode as the carbon corrosion takes place. S 2p spectra and mapping of the cathode catalyst layer indicates there are still sulfonate groups present, even in the most damaged material.

Geomicrobiology Journal, Mar 1, 2004

The oxidation of ferrous ions in the presence of an excess of dissolved oxygen at neutral pH gene... more The oxidation of ferrous ions in the presence of an excess of dissolved oxygen at neutral pH generally leads to the formation of lepidocrocite. The effect of inorganic ligands (PO4, SO4, or Si(OH)4) in concentrations typical of those in sediment pore waters, and of microorganisms (Escherichia coli K12, Pseudomonas aeruginosa PA01, Bacillus subtilis or Bacillus licheniformis) on the mineralogy, chemical

Nucleation and Atmospheric Aerosols, 2016

Proton-Exchange Membrane Fuel Cell (PEM-FC) based engines are being developed rapidly for near-te... more Proton-Exchange Membrane Fuel Cell (PEM-FC) based engines are being developed rapidly for near-term implementation in hydrogen fueled, mass production, personal automobiles. Research is focused on understanding and controlling various degradation processes (carbon corrosion, Pt migration, cold start), and reducing cost by reducing or eliminating Pt catalyst. We are using soft X-ray scanning transmission X-ray microscopy (STXM) at the S 2p, C 1s, O 1s and F 1s edges to study a variety of issues related to optimization of PEM-FC materials for automotive applications. A method to efficiently and accurately measure perfluorosulfonic acid distributions was developed and is being used to better understand how different loadings and preparation methods affect the ionomer distribution in the cathode. Progress towards an environmental cell capable of controlling the temperature and humidity of a PEM-FC sample in the STXM is described. Methods for studying the 3D chemical structure of PEM-FC are outlined.

Protoplasma, Sep 1, 1998

Iron-rich particles, previously reported in seeds of members of the genus Pinus, were found in ra... more Iron-rich particles, previously reported in seeds of members of the genus Pinus, were found in radicle-hypocotyI tissues of dry embryos from eight other genera in the family Pinaceae. Thus, these Fe-rich particles are of common occurrence in seeds of this conifer family. These particles were most difficult to locate in Pseudolarix amabilis, which has green embryos. Energy-dispersive X-ray analysis was used to determine the elements present in conifer Fe-rich particles and phytoferritin deposits in pea embryo axes. Fetich particles from all species studied contained mainly Fe and P but also contained considerable K and Mg. Abietoideae group I (genera Cedrus and Abies) had lower Fe : P ratios compared to all the other combined subfamilies within the Pinaceae. Pea phytoferritin deposits contained markedly lower amounts of P relative to Fe based on peakto-background ratios and quantitative values calculated by using a ferric phosphate standard. We also found, for the first time, that pea phytoferritin contained considerable K. A strong similarity was found between the energy-dispersive X-ray analysis spectra from Ferich particles and portions of a laboratory-synthesized Fe, K, Mg phytate salt. Phytate is a common mineral-nutrient storage compound in seeds. The possibility of these Fe-rich particles being phytoferritin cannot be ruled out, but if they are phytoferritin, they have lower Fe : P ratios than almost all other ferritins reported to date.

Environmental Science & Technology, Sep 29, 1999

The microfloras of sediments control the biogeochemical cycling of heavy metals in natural waters... more The microfloras of sediments control the biogeochemical cycling of heavy metals in natural waters, thereby determining, in large part, the ecological effects of the metals. However, little is known about interactions of metals with individual benthic microbes in nature owing to the technical difficulty of studying such small-scale processes in complex, heterogeneous sedimentary ecosystems. Seeking to overcome this obstacle, we used energy-dispersive X-ray microanalysis and transmission electron microscopy to investigate the accumulation of Cu and other elements by the cell walls, cytoplasm, cytoplasmic inclusions, fibrils, and mineral coatings of individual bacterial cells in the sediments of a lake polluted with heavy metals. Data from statistically meaningful numbers of specimens revealed various associations of elements with each other and with specific microstructures. The results imply (i) common occurrence of Fe and Mn oxyhydroxide coatings on cell walls and fibrils; (ii) strong sorption of Cu by these coatings and the inability of Ca, Mg, and K to displace the Cu from the binding sites; (iii) weaker but more extensive direct sorption of Cu by cell walls from which the Cu is readily displaced by Ca, Mg, and K; (iv) blockage of cell wall ligands by Si-, Al-, and Fe-bearing mineral deposits; and (v) preferential accumulation of Cu in the coatings or in cytoplasmic inclusions enriched in Fe and usually enriched in P as well (with or without measurable enrichment in Mn) with respect to the cytoplasm. Our findings help to elucidate the accumulation of heavy metals by microbes in aquatic ecosystems and suggest the existence of diverse mechanisms of detoxification.

Physical Chemistry Chemical Physics, 2012

Applied Geochemistry, Aug 1, 2013

Journal of Power Sources, Mar 1, 2018

Abstract 4D imaging - the three-dimensional distributions of chemical species determined using mu... more Abstract 4D imaging - the three-dimensional distributions of chemical species determined using multi-energy X-ray tomography - of cathode catalyst layers of polymer electrolyte membrane fuel cells (PEM-FC) has been measured by scanning transmission x-ray microscopy (STXM) spectro-tomography at the C 1s and F 1s edges. In order to monitor the effects of radiation damage on the composition and 3D structure of the perfluorosulfonic acid (PFSA) ionomer, the same volume was measured 3 times sequentially, with spectral characterization of that same volume at several time points during the measurements. The changes in the average F 1s spectrum of the ionomer in the cathode as the measurements progressed gave insights into the degree of chemical modification, fluorine mass loss, and changes in the 3D distributions of ionomer that accompanied the spectro-tomographic measurement. The PFSA ionomer-in-cathode is modified both chemically and physically by radiation damage. The 3D volume decreases anisotropically. By reducing the incident flux, partial defocusing (50 nm spot size), limiting the number of tilt angles to 14, and using compressed sensing reconstruction, we show it is possible to reproducibly measure the 3D structure of ionomer in PEM-FC cathodes at ambient temperature while causing minimal radiation damage.

European Journal of Mineralogy, Jul 18, 2001

Abstract Natural iron-oxides are often found in close association with bacterial cells in aquatic... more Abstract Natural iron-oxides are often found in close association with bacterial cells in aquatic environments, but the effect of bacteria on their formation is still under investigation. The present study was undertaken to assess the effect of two common bacteria, Bacillus ...

Seed Science Research, Jun 1, 1995

The endosperm and cotyledon tissues o1 Ricinus communis seeds and young seedlings were examined f... more The endosperm and cotyledon tissues o1 Ricinus communis seeds and young seedlings were examined for changes in the mineral nutrient composition of globoids during early seedling growth. The effect on globoid composition of providing mineral nutrients to the developing seedling was also investigated. Globoids in endosperm and cotyledon tissues of castor bean seeds contained P, Mg and K, as well as trace amounts of Ca, Fe and Zn. Irrespective of the addition of mineral nutrients, K content in globoids of endosperm and cotyledon tissues declined significantly during initial seedling growth. During early seedling growth, amounts of Fe, Zn and Ca increased in cotyledon globoids. Ca contents of globoids of endosperm tissues also increased.The changes in Fe, Zn and Ca globoid contents were not influenced by providing mineral nutrients to growing castor bean seedlings.

Canadian journal of botany, Jun 1, 1995

The mature seeds of some angiosperms contain perisperm tissue derived from remains of the nucellu... more The mature seeds of some angiosperms contain perisperm tissue derived from remains of the nucellus tissue of the ovule. In our transmission electron microscopy studies, the perisperm tissues of the seeds of Yucca brevifolia, Coffea arabica, Beta vulgaris, Piper nigrum, and Zostera capricorni contained naturally electron-dense globoids. Energy dispersive X-ray analysis of globoids from the perisperm tissues of these seeds revealed varying levels of phosphorus, potassium, magnesium, and calcium, results that are consistent with the presence of the mineral nutrient store called phytate. Phosphorus, potassium, magnesium, calcium, and other mineral nutrients, likely stored as phytate, have routinely been located in globoids of endosperm, female gametophyte, and embryo tissues of seeds. Key words: perisperm, globoids, mineral nutrient reserves, phosphorus, seeds, energy dispersive X-ray analysis.

Canadian Journal of Forest Research, Sep 1, 1996

The cotyledons of Pinusbanksiana Lamb, from dry seeds and seedlings were studied for differences ... more The cotyledons of Pinusbanksiana Lamb, from dry seeds and seedlings were studied for differences in the elements present in globoids. Globoids are mineral nutrient storage bodies. Parallel studies were conducted on iron-rich particles. A comparison of globoids from cotyledons of dry seeds with those of seedlings found that P, K, and Mg levels declined markedly, while Ca, Fe, Zn, and Mn levels increased significantly. A comparison of iron-rich particles showed that levels of P, K, Mg, and Ca changed, while Fe, Zn, and Mn remained unchanged. The iron-rich particles persisted during cotyledon greening and were definitely located in chloroplasts. This is the first report of such particles in chloroplasts of conifers.

Geomicrobiology Journal, Jan 18, 2011

Energy dispersive X-ray microanalysis and transmission electron microscopy were used to investiga... more Energy dispersive X-ray microanalysis and transmission electron microscopy were used to investigate heavy metal accumulation and partitioning by a statistically meaningful assortment of bacteria and colloidal minerals in metal-polluted lake sediment. Visually selected external and internal parts of bacterial cells were analysed individually. Variations in element distribution and relationships provided clues to small-scale biogeochemical processes and their implications for microbial

Canadian Journal of Fisheries and Aquatic Sciences, Oct 1, 1997

Organic colloids from the Adriatic Sea, covering the full colloid size range, were characterized ... more Organic colloids from the Adriatic Sea, covering the full colloid size range, were characterized on a per-colloid basis by transmission electron microscopy applied to ultrathin sections of embedded colloids. To detect, assess, and minimize artifacts, a multimethod correlative approach to analysis was used. A colloid classification scheme was developed from the characterizations, with individual colloid species defined in the broad sense established by environmental analytical aquatic chemists. The basic scheme is related to derivative classification schemes in which abundant colloid species are listed according to activities known from the literature, with a focus on activities related to carbon transformations and transport. Morphological criteria show that abundant colloid species occupy broad size ranges, such that colloid fractionation protocols based on sizing alone are likely to be of questionable scientific utility. Image analysis revealed that small colloids, designated as humic substances, represented 91% of the total organic colloid burden of the bulk water during a summer period of high biological productivity. At this time, fibrils were rare in the bulk water while representing the most abundant colloid in marine snow. Résumé : Des coupes ultra minces de colloïdes sous inclusion, examinées au microscope électronique à transmission, ont permis d'établir les caractéristiques individuelles de colloïdes organiques provenant de la mer Adriatique et couvrant toute la gamme des dimensions. Afin de déceler, d'évaluer et de minimiser les éventuels artefacts, une approche multiméthode de corrélation a été utilisée pour l'analyse. Un modèle de classification des colloïdes a été mis au point à partir des caractérisations, les espèces colloïdales individuelles étant définies au sens large par des spécialistes de la chimie analytique du milieu aquatique. Le modèle de base est lié à des modèles de classification détaillée dans lesquels une liste des espèces colloïdales abondantes est donnée en fonction des activités documentées dans les études publiées; on a mis l'accent sur les activités en rapport avec les transformations et le transport du carbone. Selon des critères morphologiques, il apparaît qu'un grand nombre d'espèces de colloïdes présentent une gamme étendue de dimensions, de sorte que les protocoles de fractionnement des colloïdes fondés uniquement sur la taille sont d'un intérêt scientifique douteux. L'analyse d'images a révélé que les petits colloïdes, qu'on appelle les substances humiques, représentent 91 % de toute la charge colloïdale organique de l'eau libre durant une période estivale de productivité biologique élevée. Au moment de l'étude, les fibrilles étaient rares dans l'eau libre, alors qu'elles représentent l'espèce colloïdale la plus abondante dans la neige marine. [Traduit par la Rédaction]

Journal of Environmental Quality, Nov 1, 2003

along with their associated metals. The highest resolution electron-optical technology cannot be ... more along with their associated metals. The highest resolution electron-optical technology cannot be employed Activated sludge floc from a wastewater treatment system was directly in a cost-effective manner, however. It must characterized, with regard to principal structural, chemical, and microbe used as the last stage in a multimethod correlative biological components and properties, in relation to contaminantapproach (Leppard, 1992b), which requires several difcolloid associations and settling. Multiscale analytical microscopies, in conjunction with multimethod sample preparations, were used cor-ferent but complementary multiscale visualization relatively to characterize diverse colloidal matrices within microbial methods (Droppo et al., 1996a) and methods of specifloc. Transmission electron microscopy, in conjunction with energy men preparation (Liss et al., 1996). Only through this dispersive spectroscopy (EDS), revealed specific associations of conapproach can one address the long-term goals of relating taminant heavy metals with individual bacterial cells and with extracelthe (i) usually ill-defined surface features, (ii) complex lular polymeric substances (EPS). Floc structure was mapped from internal pore structure, and (iii) spatial arrangements the level of gross morphology down to the nano-scale, and flocs were of microbial populations and extracellular colloids of described with respect to settling properties, size, shape, density, poflocs to the metal accumulation activities of the various rosity, bound water content, and EPS chemical composition; gross colloidal floc components, information that is potensurface properties were also measured for correlation with principal tially useful for future manipulation of flocs. floc features. Compartmentalization results based on 171 EDS analy-The correlative use of novel analytical tools from (i) ses and representative high-resolution images showed that nano-scale agglomerations of (i) silver (100%) and (ii) zinc (91%) were confined molecular, (ii) cell biology, and (iii) molecular chemistry almost entirely to EPS matrices while (iii) Pb (100%) was confined is increasingly helpful in ascertaining the activities of to intracellular granules and (iv) aluminum was partitioned between microbes and their extracellular products in complex EPS matrices (41%) and intracellular matrices (59%). The results ecosystems (Leppard and Buffle, 1998; Logan and Rittsuggest that engineered changes in microbial physiology and/or in

Applied and Environmental Microbiology, Sep 1, 2003

Confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), and soft X-ray... more Confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), and soft X-ray scanning transmission X-ray microscopy (STXM) were used to map the distribution of macromolecular subcomponents (e.g., polysaccharides, proteins, lipids, and nucleic acids) of biofilm cells and matrix. The biofilms were developed from river water supplemented with methanol, and although they comprised a complex microbial community, the biofilms were dominated by heterotrophic bacteria. TEM provided the highestresolution structural imaging, CLSM provided detailed compositional information when used in conjunction with molecular probes, and STXM provided compositional mapping of macromolecule distributions without the addition of probes. By examining exactly the same region of a sample with combinations of these techniques (STXM with CLSM and STXM with TEM), we demonstrate that this combination of multimicroscopy analysis can be used to create a detailed correlative map of biofilm structure and composition. We are using these correlative techniques to improve our understanding of the biochemical basis for biofilm organization and to assist studies intended to investigate and optimize biofilms for environmental remediation applications.