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Sample records for periodically structured montmorillonite

  1. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay - The effect of mononucleotide structure on phosphodiester bond formation

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; KAMALUDDIN

    1989-01-01

    The formation of oligomers from deoxynucleotides, catalyzed by Na(+)-montmorillonite, was investigated with special attention given to the effect of the monomer structure on the phosphodiester bond formation. It was found that adenine deoxynucleotides bind more strongly to montmorillonite than do the corresponding ribonucleotides and thymidine nucleotides. Tetramers of 2-prime-dpA were detected in the reaction of 2-prime-d-5-prime-AMP with a water-soluble carbodiimide EDAC in the presence of Na(+)-montmorillonite, illustrating the possible role of minerals in the formation of biopolymers on the primitive earth.

  2. Engineering New Layered Solids from Exfoliated Inorganics: a Periodically Alternating Hydrotalcite – Montmorillonite Layered Hybrid

    PubMed Central

    Chalasani, Rajesh; Gupta, Amit; Vasudevan, Sukumaran

    2013-01-01

    Two-dimensional (2D) nanosheets obtained by exfoliating inorganic layered crystals have emerged as a new class of materials with unique attributes. One of the critical challenges is to develop robust and versatile methods for creating new nanostructures from these 2D-nanosheets. Here we report the delamination of layered materials that belonging to two different classes - the cationic clay, montmorillonite, and the anionic clay, hydrotalcite - by intercalation of appropriate ionic surfactants followed by dispersion in a non-polar solvent. The solids are delaminated to single layers of atomic thickness with the ionic surfactants remaining tethered to the inorganic and consequently the nanosheets are electrically neutral. We then show that when dispersions of the two solids are mixed the exfoliated sheets self-assemble as a new layered solid with periodically alternating hydrotalcite and montmorillonite layers. The procedure outlined here is easily extended to other layered solids for creating new superstructures from 2D-nanosheets by self-assembly. PMID:24336682

  3. Morphology and Structure of Amino-fatty Acid Intercalated Montmorillonite

    NASA Astrophysics Data System (ADS)

    Reyes, Larry; Sumera, Florentino

    2015-04-01

    Natural clays and its modified forms have been studied for their wide range of applications, including polymer-layered silicate, catalysts and adsorbents. For nanocomposite production, montmorillonite (MMT) clays are often modified with organic surfactants to favor its intermixing with the polymer matrix. In the present study, Na+-montmorillonite (Na+-MMT) was subjected to organo-modification with a protonated 12-aminolauric acid (12-ALA). The amount of amino fatty acid surfactants loaded was 25, 50, 100 and 200% the cation exchange capacity (CEC) of Na+-MMT (25CEC-AMMT, 50CEC-AMMT, 100CEC-AMMT and 200CEC-AMMT). Fatty acid-derived surfactants are an attractive resource of intercalating agents for clays due to their renewability and abundance. X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were performed to determine the occurrence of intercalation of 12-ALA and their molecular structure in the clay's silicates. XRD analysis revealed that the interlayer spacing between the alumino-silicate layers increased from 1.25 nm to 1.82 nm with increasing ALA content. The amino fatty acid chains were considered to be in a flat monolayer structure at low surfactant loading, and a bilayered to a pseudotrilayered structure at high surfactant loading. On the other hand, FTIR revealed that the alkyl chains adopt a gauche conformation, indicating their disordered state based on their CH2symmetric and asymmetric vibrations. Thermogravimetric analyses (TGA) allows the determination of the moisture and organic content in clays. Here, TGA revealed that the surfactant in the clay was thermally stable, with Td ranging from 353° C to 417° C. The difference in the melting behavior of the pristine amino fatty acids and confined fatty acids in the interlayer galleries of the clay were evaluated by Differential Scanning Calorimerty (DSC). The melting temperatures (Tm) of the amino fatty acid in the clay were initially found to be higher than those of the free

  4. Structure of tetraalkylammonium ionic liquids in the interlayer of modified montmorillonite

    NASA Astrophysics Data System (ADS)

    Duarte, Daniel; Salanne, Mathieu; Rotenberg, Benjamin; Bizeto, Marcos A.; Siqueira, Leonardo J. A.

    2014-07-01

    We perform molecular dynamics simulations of tetraalkylammonium ionic liquids confined in the interlayer of montmorillonite (MMT). We study the structure and energetics of the systems, which consist of cations with two different alkyl chain lengths and several ionic liquid concentrations. The results we obtained for the structure, namely the presence of a strong layering in all systems and the formation of nonpolar domains with interdigitated alkyl chains in some cases, are largely consistent with previous surface force balance experiments performed on similar systems. Finally, we show that swelling of the organo-modified MMT by a large amount of ionic liquid seems energetically favorable in all cases.

  5. Multidimensional period doubling structures.

    PubMed

    Lee, Jeong Yup; Flom, Dvir; Ben-Abraham, Shelomo I

    2016-05-01

    This paper develops the formalism necessary to generalize the period doubling sequence to arbitrary dimension by straightforward extension of the substitution and recursion rules. It is shown that the period doubling structures of arbitrary dimension are pure point diffractive. The symmetries of the structures are pointed out.

  6. Periodic chiral structures

    NASA Technical Reports Server (NTRS)

    Jaggard, Dwight L.; Engheta, Nader; Pelet, Philippe; Liu, John C.; Kowarz, Marek W.; Kim, Yunjin

    1989-01-01

    The electromagnetic properties of a structure that is both chiral and periodic are investigated using coupled-mode equations. The periodicity is described by a sinusoidal perturbation of the permittivity, permeability, and chiral admittance. The coupled-mode equations are derived from physical considerations and used to examine bandgap structure and reflected and transmitted fields. Chirality is observed predominantly in transmission, whereas periodicity is present in both reflection and transmission.

  7. Structural and thermodynamics properties of organo-modified montmorillonite clay

    NASA Astrophysics Data System (ADS)

    Anoukou, K.; Zaoui, A.; Zaïri, F.; Naït-Abdelaziz, M.; Gloaguen, J. M.

    2015-01-01

    Polymer clay nanocomposites (PCNs) have been seen as the most novel materials in engineering applications since they exhibit significant improvement in mechanical and physical properties. Indeed, with few amount of organoclay, PCNs exhibit enhanced mechanical, optical, thermal and liquid or gas barrier properties compared to pure polymers and to their counterpart microcomposites. Thus, organoclays are extensively used as precursors in the preparation of PCNs. They are the best candidate in reinforcing PCNs because of the lightweight and the high availability of clay minerals in the nature. However, structure and physical phenomena arising at molecular level in organoclays, and subsequently in PCNs, are not completely or difficultly accessible with existing experimental techniques. In this work, molecular dynamics (MD) simulation was conducted using the combination of two force fields (CLAYFF and CHARMM) to evaluate the thermodynamics and structural properties of organoclay such as heat capacities, isothermal bulk modulus, density, basal spacing and chains arrangement in the interlayer spacing. Our results regarding the basal spacing and density are in fairly good agreement with available experimental data. This allows us to validate the use of the two force fields to represent interactions in organoclays. The effect of the cation exchange capacity (CEC) on the basal spacing and the thermodynamics properties is assessed. We found, through our MD simulation, that the calculated isothermal bulk modulus is in good agreement with the density value of organoclays with two different CEC.

  8. High-Resolution of Electron Microscopy of Montmorillonite and Montmorillonite/Epoxy Nanocomposites

    DTIC Science & Technology

    2005-01-01

    AFRL-ML-WP-TP-2006-464 HIGH-RESOLUTION OF ELECTRON MICROSCOPY OF MONTMORILLONITE AND MONTMORILLONITE /EPOXY NANOCOMPOSITES Lawrence F...HIGH-RESOLUTION OF ELECTRON MICROSCOPY OF MONTMORILLONITE AND MONTMORILLONITE /EPOXY NANOCOMPOSITES 5c. PROGRAM ELEMENT NUMBER 62102F 5d...transmission electron microscopy the structure and morphology of montmorillonite (MMT), a material of current interest for use in polymer nanocomposites, was

  9. Role of uniform pore structure and high positive charges in the arsenate adsorption performance of Al13-modified montmorillonite.

    PubMed

    Zhao, Shou; Feng, Chenghong; Huang, Xiangning; Li, Baohua; Niu, Junfeng; Shen, Zhenyao

    2012-02-15

    Four modified montmorillonite adsorbents with varied Al(13) contents (i.e., Na-Mont, AC-Mont, PAC(20)-Mont, and Al(13)-Mont) were synthesized and characterized by N(2) adsorption/desorption, X-ray diffraction, and Fourier-transform infrared analyses. The arsenate adsorption performance of the four adsorbents were also investigated to determine the role of intercalated Al(13), especially its high purity, high positive charge (+7), and special Keggin structure. With increased Al(13) content, the physicochemical properties (e.g., surface area, structural uniformity, basal spacing, and pore volume) and adsorption performance of the modified montmorillonites were significantly but disproportionately improved. The adsorption data well fitted the Freundlich and Redlich-Peterson isotherm model, whereas the kinetic data better correlated with the pseudo-second-order kinetic model. The arsenate sorption mechanism of the montmorillonites changed from physical to chemisorption after intercalation with Al(13). Increasing charges of the intercalated ions enhanced the arsenate adsorption kinetics, but had minimal effect on the structural changes of the montmorillonites. The uniform pore structure formed by intercalation with high-purity Al(13) greatly enhanced the pore diffusion and adsorption rate of arsenate, resulting in the high adsorption performance of Al(13)-Mont.

  10. Structural study of synthetic mica montmorillonite by means of 2D MAS NMR experiments

    NASA Astrophysics Data System (ADS)

    Alba, M. D.; Castro, M. A.; Chain, P.; Naranjo, M.; Perdigón, A. C.

    2005-07-01

    Syn-1, is a synthetic mica montmorillonite interstratified mineral that forms one of the standard clay samples in the Clay Minerals Society Source Clays Project. However, there are still controversies regarding some structural aspects such as the interlayer composition or the location of the extra-aluminium determined by chemical analysis. The main objective of this paper is to shed light on those structural aspects that affect the reactivity of the interstratified minerals. For this purpose, we have used 1 H 29 Si and 1 H 27Al HETCOR MAS NMR to show that it is likely that the interlayer space of the beidellite part is composed of ammonium ions whereas ammonium and aluminium ions are responsible for the charge balance in the mica type layer.

  11. A periodic DFT study of adsorption of water on sodium-montmorillonite (001) basal and (010) edge surface

    NASA Astrophysics Data System (ADS)

    Peng, Chenliang; Min, Fanfei; Liu, Lingyun; Chen, Jun

    2016-11-01

    Water molecules can be easily adsorbed on the surface or in the interlayer space of clay minerals. This process is named hydration which plays an important role in various application fields. In order to find how water interacted with surface through minimizing the interaction among multiple waters, the adsorptions of single water molecule on external surfaces of sodium-montmorillonite (Na-MMT), including (001) basal and (010) edge surface, were theoretically investigated based on periodic density functional theory (DFT) method. The adsorption energies and geometries as well as electronic properties were studied in the work. It was found that water molecule was adsorbed on Na-MMT (001) basal surface mainly through electrostatic interaction between water molecule and Na+ cation, and was adsorbed on (010) edge surface through hydrogen bonding between water and surface sbnd OH or sbnd OH2 groups. The adsorption energy Eads value of water molecule on (010) edge surface was larger than that on (001) basal surface. After adsorption, a part of electron density was transferred from both Na-MMT (001) and (010) surfaces to water molecule. Based on the PDOS, there was the bonding between Na 3s and Ow 2p orbitals on (001) basal surface and between H 1s and O 2p orbitals for hydrogen bonds on (010) edge surface.

  12. Periodic truss structures

    NASA Astrophysics Data System (ADS)

    Zok, Frank W.; Latture, Ryan M.; Begley, Matthew R.

    2016-11-01

    Despite the recognition of the enormous potential of periodic trusses for use in a broad range of technologies, there are no widely-accepted descriptors of their structure. The terminology has been based loosely either on geometry of polyhedra or of point lattices: neither of which, on its own, has an appropriate structure to fully define periodic trusses. The present article lays out a system for classification of truss structure types. The system employs concepts from crystallography and geometry to describe nodal locations and connectivity of struts. Through a series of illustrative examples of progressively increasing complexity, a rational taxonomy of truss structure is developed. Its conceptual evolution begins with elementary cubic trusses, increasing in complexity with non-cubic and compound trusses as well as supertrusses, and, finally, with complex trusses. The conventions and terminology adopted to define truss structure yield concise yet unambiguous descriptions of structure types and of specific (finite) trusses. The utility of the taxonomy is demonstrated by bringing into alignment a disparate set of ad hoc and incomplete truss designations previously employed in a broad range of science and engineering fields. Additionally, the merits of a particular compound truss (comprising two interpenetrating elementary trusses) is shown to be superior to the octet truss for applications requiring high stiffness and elastic isotropy. By systematically stepping through and analyzing the finite number of structure types identified through the present classification system, optimal structures for prescribed mechanical and functional requirements are expected to be ascertained in an expeditious manner.

  13. Mordenite and montmorillonite alteration of glass structures in a rhyolite pipe, northern Black Hills, South Dakota

    SciTech Connect

    Kirchner, J.G. )

    1991-10-01

    Green structures, 0.5 to 1.5 in. across, occur in a Tertiary rhyolite pipe in the northern Black Hills, South Dakota. The structures are of two types: angular to ellipsoidal masses and stretched or smeared structures. Thin section analysis revealed that those of the first type are massive, with no internal structure, and those of the second type are cellular and have classic flame structure characteristics. XRD indicated the composition to be a mixture of secondary mordenite (a zeolite) and montmorillonite. The first type is interpreted to be deuterically altered vitrophyre clasts and the second type to be altered vesicular structures produced by degassing of the magma in the pipe. Chemical analysis of the alteration material indicates a loss of alkalies and silica, with an increase in water, CaO, MgO and ferric iron when compared to the composition of fresh vitrophyre from the same pipe. The changes are in agreement with experimental work on the alteration of rhyolitic glass by a number of researchers. This is the first occurrence of mordenite reported for the Black Hills.

  14. Mechanical Properties of Unsaturated Polyester / Montmorillonite Composites

    DTIC Science & Technology

    2001-11-01

    Montmorillonite Composites DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report: TITLE: Nanophase and...Mechanical Properties of Unsaturated Polyester / Montmorillonite Composites A. Baran Inceoglu and Ulku Yilmazer Middle East Technical University, Chemical...analysed the nature of the curing agent on structure. Kornmann, Berglund and Giannelis [8] studied nanocomposites based on montmorillonite modified

  15. Periodically structured plasmonic waveguides

    NASA Astrophysics Data System (ADS)

    Saj, W. M.; Foteinopoulou, S.; Kafesaki, M.; Soukoulis, C. M.; Economou, E. N.

    2008-04-01

    We study surface plasmon polariton (SPP) guiding structures, which are a modification of the Metal-Insulator-Metal (MIM) waveguide. The designs are constructed by introducing a periodic modulation in a MIM waveguide, with a glass core and silver claddings. This periodic modulation is created either by causing periodic indentations in the silver slabs encompassing the glass core, or by increasing the glass spacer material in certain periodic locations. Our objective is to achieve long range sub-wavelength waveguiding with vast dispersion engineering capabilities. We employ the Finite Difference Time Domain Method (FDTD) with the Auxiliary Differential Equation method (ADE) for the calculation of the dispersion relation of the guided modes, as well as the real time propagation suggests that the guiding mechnism in the examined structures is based on the electromagnetic (EM) couping between the slit plasmon modes. These - depending on the design - exist in the grooves between the silver plates or in the larger areas of the glass core spacer. Put it different, the guiding mechanism in the examined SPP waveguide designs is analogous to the EM energy transfer along metallic nanoparticle chains.

  16. Oligomerization reactions of deoxyribonucleotides on montmorillonite clay - The effect of mononucleotide structure, phosphate activation and montmorillonite composition on phosphodiester bond formation

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; KAMALUDDIN; Ertem, Gozen

    1990-01-01

    The 2(prime)-d-5(prime)-GMP and 2(prime)-d-5(prime)-AMP bind 2 times more strongly to montmorillonite 22A than do 2(prime)-d-5(prime)-CMP and 5(prime)-TMP. The dinucleotide d(pG)2 forms in 9.2 percent yield and the cyclic dinucleotide c(dpG)2 in 5.4 percent yield in the reaction of 2(prime)-d-5(prime)-GMP with EDAC in the presence of montmorillonite 22A. The yield of dimers which contain the phosphodiester bond decreases as the reaction medium is changed from 0.2 M NaCl to a mixture of 0.2 M NaCl and 0.075 M MgCl2. A low yield of d(pA)2 was observed in the condensation reaction of 5(prime)-ImdpA on montmorillonite 22A. The yield of d(pA)2 obtained when EDAC is used as the condensing agent increases with increasing iron content of the Na(+)-montmorillonite used as catalyst. Evidence is presented which shows that the acidity of the Na(+)-montmorillonite is a necessary but not sufficient factor for the montmorillonite catalysis of phosphodiester bond formation.

  17. Transformation of montmorillonite to kaolinite during weathering

    USGS Publications Warehouse

    Altschuler, Z.S.; Dwornik, E.J.; Kramer, H.

    1963-01-01

    Extensive deposits of kaolinite in Florida are formed by transformation of montmorillonite during low-temperature supergene weathering. The transformation occurs by intracrystalline leaching of interlayer cations and tetrahedral silica layers. Interposition of stripped layers within montmorillonite creates a regular 1:1 mixed-layered montmorillonite-kaolinite, a new clay structure. Kaolin-like layers are nourished by lateral epitaxy, as the iron-rich montmorillonite decomposes. Hexagonal outgrowths of new kaolinite develop at the edges of montmorillonite flakes and nucleate new vertical growth. Kaolinitic sands impregnated with goethite are ultimately formed, and the released silica enriches groundwater and forms secondary chert.

  18. Self-healing fish gelatin/sodium montmorillonite biohybrid coacervates: structural and rheological characterization.

    PubMed

    Qazvini, Nader Taheri; Bolisetty, Sreenath; Adamcik, Jozef; Mezzenga, Raffaele

    2012-07-09

    Complex coacervation driven by associative electrostatic interactions was studied in mixtures of exfoliated sodium-montmorillonite (Na(+)-MMT) nanoplatelets and fish gelatin, at a specific mixing ratio and room temperature. Structural and viscoelastic properties of the coacervate phase were investigated as a function of pH by means of different complementary techniques. Independent of the technique used, the results consistently showed that there is an optimum pH value at which the coacervate phase shows the tightest structure with highest elasticity. The solid-like coacervates showed an obvious shear-thinning behavior and network fracture but immediately recovered back into their original elastic character upon removal of the shear strain. The nonlinear mechanical response characterized by single step stress relaxation experiments revealed the same trend for the yield stress and isochronal shear modulus of the coacervates as a function of pH with a maximum at pH 3.0 and lower values at 2.5 and 3.5 pHs, followed by a very sharp drop at pH 4.0. Finally, small-angle X-ray scattering (SAXS) data confirmed that at pHs lower than 4.0 the coacervate phases were dense and structured with a characteristic length scale (ξ(SAXS)) of ~7-9 nm. Comparing the ξ(SAXS) with rheological characteristic length (ξ(rheol)) estimated from low-frequency linear viscoelastic data and network theory, it was concluded that both the strength of the electrostatic interactions and the conformation of the gelatin chains before and during of the coacervation process are responsible for the structure and rigidity of the coacervates.

  19. Relevance of Pore Structure and Diffusion-Accessible Porosity for Calcium-Bromide Diffusion in Na-Montmorillonite

    NASA Astrophysics Data System (ADS)

    Tinnacher, R. M.; Davis, J. A.

    2013-12-01

    Bentonite is an important hydraulic barrier material in many geotechnical applications, such as geosynthetic clay liners at solid waste landfills, or as proposed backfill material in engineered barrier systems at nuclear waste repositories. The limited permeability of bentonite is at least partially the result of its low porosity and the swelling of Na-montmorillonite, its major mineralogical component, in water. Due to these characteristics, the transport of contaminants through bentonite layers is expected to be limited and dominated by diffusion processes. In bentonite, the majority of the connected porosity is associated with montmorillonite particles, which consist of stacks of negatively-charged smectite layers. As a result, compacted smectite has two types of porosities: (1) large pores between clay particles, where diffusion is less affected by electric-double-layer forces, and (2) very thin interlayer spaces within individual clay particles, where diffusion is strongly impacted by surface charge and ionic strength. As diffusion is expected to take place differently in these two volumes, this essentially creates two 'small-scale diffusion pathways', where each may become dominant under different system conditions. Furthermore, for surface-reactive solutes, these two porous regimes differ with regards to surface complexation reactions. Electrostatic and hydration forces only are thought to govern interlayer binding, whereas chemical bonding with surface ligands is dominant for reactions at edge sites of layered clay particles and for iron oxide nanoparticles on outer basal planes. In this presentation, we will demonstrate the relevance of clay pore structure and diffusion-accessible porosity for solute diffusion rates, and hence, contaminant mobility in bentonites. First, we will discuss the effects of chemical solution conditions on montmorillonite properties, such as clay surface charge, diffusion-accessible porosity, clay tortuosity and constrictivity

  20. Doubly Resonant Optical Periodic Structure

    PubMed Central

    Alagappan, G.; Png, C. E.

    2016-01-01

    Periodic structures are well known in various branches of physics for their ability to provide a stopband. In this article, using optical periodic structures we showed that, when a second periodicity – very closed to the original periodicity is introduced, large number of states appears in the stopband corresponding to the first periodicity. In the limit where the two periods matches, we have a continuum of states, and the original stopband completely disappears. This intriguing phenomena is uncovered by noticing that, regardless of the proximities of the two periodicities, there is an array of spatial points where the dielectric functions corresponding to the two periodicities interfere destructively. These spatial points mimic photonic atoms by satisfying the standards equations of quantum harmonic oscillators, and exhibit lossless, atom-like dispersions. PMID:26853945

  1. Doubly Resonant Optical Periodic Structure.

    PubMed

    Alagappan, G; Png, C E

    2016-02-08

    Periodic structures are well known in various branches of physics for their ability to provide a stopband. In this article, using optical periodic structures we showed that, when a second periodicity--very closed to the original periodicity is introduced, large number of states appears in the stopband corresponding to the first periodicity. In the limit where the two periods matches, we have a continuum of states, and the original stopband completely disappears. This intriguing phenomena is uncovered by noticing that, regardless of the proximities of the two periodicities, there is an array of spatial points where the dielectric functions corresponding to the two periodicities interfere destructively. These spatial points mimic photonic atoms by satisfying the standards equations of quantum harmonic oscillators, and exhibit lossless, atom-like dispersions.

  2. Periodic solar wind density structures

    NASA Astrophysics Data System (ADS)

    Viall, Nicholeen Mary

    2010-01-01

    This dissertation addresses a specific aspect of the Sun-Earth connection: we show that coronal activity creates periodic density structures in the solar wind which convect radially outward and interact with Earth's magnetosphere. First, we analyze 11 years (1995-2005) of in situ solar wind density observations from the Wind spacecraft and find that periodic density structures occur at particular sets of radial length-scales more often than others. This indicates that these density fluctuations, which have radial length-scales of hundreds of megameters, cannot be attributed entirely to turbulence. Next, we analyze their effect on Earth's magnetosphere. Though these structures are not waves in the solar wind rest frame, they appear at discrete frequencies in Earth's reference frame. They compress the magnetosphere as they convect past, driving global magnetospheric oscillations at the same discrete frequencies as the periodic density structures. Last, we investigate source regions and mechanisms of the periodic solar wind density structures. We analyze the alpha particle to proton abundance ratio during events of periodic density structures. In many events, the proton and alpha density fluctuations are anti- correlated, which strongly argues for either temporally or spatially varying coronal source plasma. We examine white light images of the solar wind taken with SECCHI HI1 on the STEREO spacecraft and find periodic density structures as near to the Sun as 15 solar radii. The smallest resolvable periodic structures that we identify are of comparable length to those found at 1 AU, providing further evidence that at least some periodic density structures are generated in the solar corona as the solar wind is formed. Guided by the properties observed during previous studies and the characteristics established through the work presented here, we examine possible candidate mechanisms in the solar corona that can form periodic density structures. We conclude that

  3. Immobilization of cobalt(III) Schiff base complexes onto Montmorillonite-K10: Synthesis, experimental and theoretical structural determination.

    PubMed

    Kianfar, Ali Hossein; Kamil Mahmood, Wan Ahmad; Dinari, Mohammad; Farrokhpour, Hossein; Enteshari, Majid; Azarian, Mohammad Hossein

    2015-02-05

    The [Co(naphophen)(PPh3)(OH2)]ClO4 and [Co(naphophen)(PBu3)(OH2)]BF4 (where naphophen=bis(naphthaldehyde)1,2-phenylenediimine) complexes were synthesized and chracterized by FT-IR, UV-Vis, (1)H NMR, (13)C NMR spectroscopy and elemental analysis techniques. The coordination geometry of the synthesized complexes were determined by X-ray crystallography. Cobalt (III) complexes have six-coordinated pseudo-octahedral geometry in which the O(1), O(2), N(1) and N(2) atoms of the Schiff base forms the equatorial plane. These complexes showed a dimeric structure via hydrogen bonding between the phenolate oxygen and the hydrogens of the coordinated H2O molecule. The theoretical calculations were also performed to optimize the structure of the complexes in the gas phase to confirm the structures proposed by X-ray crystallography. In addition, UV-Visible and IR spectra of complexes were calculated and compared with the corresponding experimental spectra to complete the experimental structural identification. The synthesized complexes were incorporated onto the Montmorillonite-K10 nanoclay via simple ion-exchange reaction. The structure and morphology of the obtained nanohybrids were identified by FT-IR, XRD, TGA/DTA, SEM and TEM techniques. Based on the XRD results of the new nanohybrid materials, the Schiff base complexes were intercalated in the interlayer spaces of clay. SEM and TEM micrographs of the clay/complex shows that the resulting hybrid nanomaterials has layer structures.

  4. Immobilization of cobalt(III) Schiff base complexes onto Montmorillonite-K10: Synthesis, experimental and theoretical structural determination

    NASA Astrophysics Data System (ADS)

    Kianfar, Ali Hossein; Kamil Mahmood, Wan Ahmad; Dinari, Mohammad; Farrokhpour, Hossein; Enteshari, Majid; Azarian, Mohammad Hossein

    2015-02-01

    The [Co(naphophen)(PPh3)(OH2)]ClO4 and [Co(naphophen)(PBu3)(OH2)]BF4 (where naphophen = bis(naphthaldehyde)1,2-phenylenediimine) complexes were synthesized and chracterized by FT-IR, UV-Vis, 1H NMR, 13C NMR spectroscopy and elemental analysis techniques. The coordination geometry of the synthesized complexes were determined by X-ray crystallography. Cobalt (III) complexes have six-coordinated pseudo-octahedral geometry in which the O(1), O(2), N(1) and N(2) atoms of the Schiff base forms the equatorial plane. These complexes showed a dimeric structure via hydrogen bonding between the phenolate oxygen and the hydrogens of the coordinated H2O molecule. The theoretical calculations were also performed to optimize the structure of the complexes in the gas phase to confirm the structures proposed by X-ray crystallography. In addition, UV-Visible and IR spectra of complexes were calculated and compared with the corresponding experimental spectra to complete the experimental structural identification. The synthesized complexes were incorporated onto the Montmorillonite-K10 nanoclay via simple ion-exchange reaction. The structure and morphology of the obtained nanohybrids were identified by FT-IR, XRD, TGA/DTA, SEM and TEM techniques. Based on the XRD results of the new nanohybrid materials, the Schiff base complexes were intercalated in the interlayer spaces of clay. SEM and TEM micrographs of the clay/complex shows that the resulting hybrid nanomaterials has layer structures.

  5. Structure and physical properties of starch/poly vinyl alcohol/sodium montmorillonite nanocomposite films.

    PubMed

    Ali, Samer S; Tang, Xiaozhi; Alavi, Sajid; Faubion, Jon

    2011-12-14

    Nanocomposites of starch, poly vinyl alcohol (PVOH), and sodium montmorillonite (Na(+)MMT) were produced by solution mixing and cast into films. Tensile strength (TS) and elongation at the break (E%) of the films ranged from 11.60 to 22.35 MPa and 28.93-211.40%, respectively, while water vapor permeability (WVP) ranged from 0.718 to 1.430 g·mm/kPa·h·m(2). In general, an increase in Na(+)MMT content (0-20%) enhanced TS and decreased E% and WVP. Use of higher molecular weight PVOH increased both TS and E% and also decreased WVP. Mechanical properties were negatively affected, but water vapor barrier properties improved with increasing starch content (0-80%). X-ray diffraction and transmission electron microscopy were used to analyze the nanostructure, and molecular conformations and interactions in the multicomponent nanocomposites were inferred from glass transition behavior. Interactions between starch and PVOH were strongest, followed by polymer/clay interactions. On the basis of this insight, a conceptual model was presented to explain the phenomena of intercalation and exfoliation in the starch/PVOH/Na(+)MMT nanocomposites.

  6. Constructing covalent interface in rubber/clay nanocomposite by combining structural modification and interlamellar silylation of montmorillonite.

    PubMed

    Zha, Chao; Wang, Wencai; Lu, Yonglai; Zhang, Liqun

    2014-11-12

    Strong interfacial interaction and nanodispersion are necessary for polymer nanocomposites with expectations on mechanical performance. In this work, montmorillonite (MMT) was first structurally modified by acid treatment to produce more silanol groups on the layer surface. This was followed by chemical modification of γ-methacryloxy propyl trimethoxysilane molecule (KH570) through covalent grafting with the silanol groups. (29)Si and (27)Al magic angle spinning (MAS) NMR results revealed the microstructural changes of MMT after acid treatment and confirmed the increase of silanol groups on acid-treated MMT surfaces. Thermogravimetric analysis indicated an increase in the grafted amount of organosilane on the MMT surface. X-ray diffraction (XRD) showed that the functionalization process changed the highly ordered stacking structure of the MMT mineral into a highly disordered structure, indicating successful grafting of organosilane to the interlayer surface of the crystalline sheets. The styrene-butadiene rubber (SBR)/MMT nanocomposites were further prepared by co-coagulating with SBR latex and grafted-MMT aqueous suspension. During vulcanization, a covalent interface between modified MMT and rubber was established through peroxide-radical-initiated reactions, and layer aggregation was effectively prevented. The SBR/MMT nanocomposites had highly and uniformly dispersed MMT layers, and the covalent interfacial interaction was finally achieved and exhibited high performance.

  7. Chitosan-Montmorillonite microspheres: A sustainable fertilizer delivery system.

    PubMed

    dos Santos, Bruna Rodrigues; Bacalhau, Fabiana Britti; Pereira, Tamires dos Santos; Souza, Claudinei Fonseca; Faez, Roselena

    2015-08-20

    Controlled release fertilizers are efficient tools that increase the sustainability of agricultural practices. However, the biodegradability of the matrices and the determination of the release into soil still require some investigation. This paper describes the preparation of potassium-containing microspheres based on chitosan and montmorillonite clay and the in situ soil release. The chitosan-montmorillonite microspheres were prepared using a coagulation method and different proportions of montmorillonite. The structural, thermal and morphological properties as well the water swelling and fertilizer sorption capacity were evaluated. The best formulations were applied in soil, and the fertilizer release was monitored using time-domain reflectometry (TDR). Montmorillonite clay provides better sorption properties than the chitosan microspheres because of the rough and porous surface. Due to these properties, high levels of fertilizer were sorbed onto the material. ChMMT33-containing potassium shows two specific periods of fertilizer release: the first one lasted approximately three days and was assigned to the external fertilizer on the microspheres. The second was assigned to the internal fertilizer. TDR is an important and fast tool and was used to determine the fertilizer release and the ion movement in the soil.

  8. Ab initio molecular dynamics study of the interlayer and micropore structure of aqueous montmorillonite clays

    NASA Astrophysics Data System (ADS)

    Suter, James L.; Kabalan, Lara; Khader, Mahmoud; Coveney, Peter V.

    2015-11-01

    Ab initio molecular dynamics simulations have been performed to gain an understanding of the interfacial microscopic structure and reactivity of fully hydrated clay edges. The models studied include both micropore and interlayer water. We identify acidic sites through dissociation mechanisms; the resulting ions can be stabilized by both micropore and interlayer water. We find clay edges possess a complex amphoteric behavior, which depends on the face under consideration and the location of isomorphic substitution. For the neutral (1 1 0) surface, we do not observe any dissociation on the timescale accessible. The edge terminating hydroxyl groups participate in a hydrogen bonded network of water molecules that spans the interlayer between periodic images of the clay framework. With isomorphic substitutions in the tetrahedral layer of the (1 1 0) clay edge, we find the adjacent exposed apical oxygen behaves as a Brönsted base and abstracts a proton from a nearby water molecule, which in turn removes a proton from an AlOH2 group. With isomorphic substitutions in the octahedral layer of the (1 1 0) clay edge the adjacent exposed apical oxygen atom does not abstract a proton from the water molecules, but increases the number of hydrogen bonded water molecules (from one to two). Acid treated clays are likely to have both sites protonated. The (0 1 0) surface does not have the same interfacial hydrogen bonding structure; it is much less stable and we observe dissociation of half the terminal SiOH groups (tbnd Sisbnd Osbnd H → tbnd Sisbnd O- + H+) in our models. The resulting anions are stabilized by solvation from both micropore and interlayer water molecules. This suggests that, when fully hydrated, the (0 1 0) surface can act as a Brönsted acid, even at neutral pH.

  9. Effect of ionic strength and pH on hydraulic properties and structure of accumulating solid assemblages during microfiltration of montmorillonite suspensions.

    PubMed

    Santiwong, Suvinai R; Guan, Jing; Waite, T David

    2008-01-01

    The structure and hydraulic behaviour of colloidal montmorillonite assemblages formed during constant-pressure microfiltration of feed suspensions under various pH and ionic strengths have been investigated with flux versus time data analysed using both conventional cake filtration theory and a more rigorous sorptivity-diffusivity approach. Size distribution and fractal dimension analyses revealed a shift in assemblage structure from porous to compact as a result of a step-increase in electrolyte concentrations. The hydraulic conductivity of the filter cakes was dramatically affected by suspension ionic strength with significantly higher hydraulic conductivity observed at the higher ionic strengths compared to that observed at lower ionic strengths. Results obtained using the sorptivity-diffusivity model were consistent with conventional cake filtration theory and provided useful insights into the bulk properties of the filter cakes. Cake moisture ratio profiles of the montmorillonite system showed that high suspension ionic strength resulted in denser or less voluminous filter cakes that retained less water than was the case at the low ionic strength. These results suggest that, under low ionic strength conditions, the clay particles associate in suspension in assemblages of high aspect ratio which subsequently form highly "cross-linked" voluminous honeycomb type structures of low permeability once deposited upon the membrane. However, under sufficiently high ionic strength conditions, the high aspect ratio montmorillonite assemblages form nematic structures on deposition on the membrane that are denser yet more permeable than the structures formed at lower salt concentration. The distinct change in properties of the deposited clay on increase in salt concentration may well be indicative of transition from a gel to a nematically ordered phase.

  10. Manufacturing, structure and properties of recycled polyethylene terephthalate /liquid crystal polymer/montmorillonite clay nanocomposites

    NASA Astrophysics Data System (ADS)

    Japins, Guntis; Berzina, Rita; Zicans, Janis; Merijs Meri, Remo; Ivanova, Tatjana; Kalkis, Valdis; Reinholds, Ingars

    2013-12-01

    Polyethylene terephthalate (PET)/liquid crystal polymer (LCP)/monthmorillonite clay (MMT) compositions were obtained by melt mixing. Their mechanical, structural, rheological and thermal properties were investigated.

  11. Phenolic removal using phenylamine modified montmorillonite

    NASA Astrophysics Data System (ADS)

    Wiyantoko, Bayu; Lail, Jamalul; Kurniawati, Puji; Purbaningtias, Tri Esti; Nurrohmah, Ashri; Kurniandari, Safitri

    2017-03-01

    Synthesis, characterization, and application of phenylamine modified montmorillonite have been studied. Preparation of phenylamine modified montmorillonite was conducted by intercalation process using simple amine compound. The changes in physical and chemical properties were observed through the crystal structure, functional groups and acidity as well as the application as an adsorbent for phenolic compound. The diffractogram showed characteristic basal spacing of montmorillonite at 2θ = 7.0710° and 19.8856°, also peaks with sharp intense around 20-30° were 2θ = 28.6181° and 35.0112°. The reflection pattern of phenylamine modified montmorillonite exhibited the shifting of d001 basal spacing at 2θ = 7.0710° into 7.1624° that implied the phenylamine was attached to the surface of montmorillonite. The spectra of FTIR gave the difference of wave number for -OH stretching, -OH bending also Mg-O-Al vibration that distinguished between natural montmorillonite and prepared material. The prepared material has lower acidity value and different surface characters which confirmed by gravimetric and infrared spectrum. The phenolic adsorption using prepared material gave maximum pH at 5 and optimum contact time around 2 hours with adsorption capacity was 24.48%.

  12. Structural and thermal properties of inorganic-organic montmorillonite: Implications for their potential environmental applications.

    PubMed

    Rathnayake, Suramya I; Xi, Yunfei; Frost, Ray L; Ayoko, Godwin A

    2015-12-01

    Inorganic-organic clays (IOCs), clays intercalated with both organic cations such as cationic surfactants and inorganic cations such as metal hydroxy polycations have the properties of both organic and pillared clays, and thereby the ability to remove both inorganic and organic contaminants from water simultaneously. In this study, IOCs were synthesised using three different methods with different surfactant concentrations. Octadecyltrimethylammonium bromide (ODTMA) and hydroxy aluminium ([Al13O4(OH)24(H2O)12](7+) or Al13) are used as the organic and inorganic modifiers (intercalation agents). According to the results, the interlayer distance, the surfactant loading amount and the Al/Si ratio of IOCs strictly depend on the intercalation method and the intercalation agent ratio. Interlayers of IOCs synthesised by intercalating ODTMA before Al13 and IOCs synthesised by simultaneous intercalation of ODTMA and Al13 were increased with increasing the ODTMA concentration used in the synthesis procedure and comparatively high loading amounts could be observed in them. In contrast, Al/Si decreased with increasing ODTMA concentration in these two types of IOCs. The results suggest that Al-pillars can be fixed within the interlayers by calcination and any increment in the amount of ODTMA used in the synthesis procedure did not affect the interlayer distance of the IOCs. Overall the study provides valuable insights into the structure and properties of the IOCs and their potential environmental applications.

  13. Deterministic weak localization in periodic structures.

    PubMed

    Tian, C; Larkin, A

    2005-12-09

    In some perfect periodic structures classical motion exhibits deterministic diffusion. For such systems we present the weak localization theory. As a manifestation for the velocity autocorrelation function a universal power law decay is predicted to appear at four Ehrenfest times. This deterministic weak localization is robust against weak quenched disorders, which may be confirmed by coherent backscattering measurements of periodic photonic crystals.

  14. Multiscale periodic structure in the Io wake

    NASA Astrophysics Data System (ADS)

    Smith, P. R.; Wright, A. N.

    1989-06-01

    Preliminary results from an eigenmode synthesis of the Alfven waves launched by Io are presented. It is found that several important periodicities emerge. Observations of the decametric emission reveal fine, medium, and large-scale radio structure. These simulations can provide structure on each of these scales, unlike earlier models.

  15. THz Radiation Source Trough Periodically Modulated Structures

    DTIC Science & Technology

    1997-12-04

    Trough Periodically Modulated Structures C 6. AUTHOR(S) N 68171-96-C-9015 E. Gornik, Ch. Rauch, G. Strasser, K. Unterrainer, R. Kersting 7...is used to ,ad M6 probe the transmittance of undoped GaAs/Ga0.7A10 3As superlattices. The measured ofninjecte elnjectron collector current reflects...period superlattice is shown for different collector biases. The black solid line represents the transfer ratio at flat band condition (UBc=0). A clear

  16. Supratransmission in a disordered nonlinear periodic structure

    NASA Astrophysics Data System (ADS)

    Yousefzadeh, B.; Phani, A. Srikantha

    2016-10-01

    We study the interaction among dispersion, nonlinearity, and disorder effects in the context of wave transmission through a discrete periodic structure, subjected to continuous harmonic excitation in its stop band. We consider a damped nonlinear periodic structure of finite length with disorder. Disorder is introduced throughout the structure by small changes in the stiffness parameters drawn from a uniform statistical distribution. Dispersion effects forbid wave transmission within the stop band of the linear periodic structure. However, nonlinearity leads to supratransmission phenomenon, by which enhanced wave transmission occurs within the stop band of the periodic structure when forced at an amplitude exceeding a certain threshold. The frequency components of the transmitted waves lie within the pass band of the linear structure, where disorder is known to cause Anderson localization. There is therefore a competition between dispersion, nonlinearity, and disorder in the context of supratransmission. We show that supratransmission persists in the presence of disorder. The influence of disorder decreases in general as the forcing frequency moves away from the pass band edge, reminiscent of dispersion effects subsuming disorder effects in linear periodic structures. We compute the dependence of the supratransmission force threshold on nonlinearity and strength of coupling between units. We observe that nonlinear forces are confined to the driven unit for weakly coupled systems. This observation, together with the truncation of higher-order nonlinear terms, permits us to develop closed-form expressions for the supratransmission force threshold. In sum, in the frequency range studied here, disorder does not influence the supratransmission force threshold in the ensemble-average sense, but it does reduce the average transmitted wave energy.

  17. Population structure of the Classic period Maya.

    PubMed

    Scherer, Andrew K

    2007-03-01

    This study examines the population structure of Classic period (A.D. 250-900) Maya populations through analysis of odontometric variation of 827 skeletons from 12 archaeological sites in Mexico, Guatemala, Belize, and Honduras. The hypothesis that isolation by distance characterized Classic period Maya population structure is tested using Relethford and Blangero's (Hum Biol 62 (1990) 5-25) approach to R matrix analysis for quantitative traits. These results provide important biological data for understanding ancient Maya population history, particularly the effects of the competing Tikal and Calakmul hegemonies on patterns of lowland Maya site interaction. An overall F(ST) of 0.018 is found for the Maya area, indicating little among-group variation for the Classic Maya sites tested. Principal coordinates plots derived from the R matrix analysis show little regional patterning in the data, though the geographic outliers of Kaminaljuyu and a pooled Pacific Coast sample did not cluster with the lowland Maya sites. Mantel tests comparing the biological distance matrix to a geographic distance matrix found no association between genetic and geographic distance. In the Relethford-Blangero analysis, most sites possess negative or near-zero residuals, indicating minimal extraregional gene flow. The exceptions were Barton Ramie, Kaminaljuyu, and Seibal. A scaled R matrix analysis clarifies that genetic drift is a consideration for understanding Classic Maya population structure. All results indicate that isolation by distance does not describe Classic period Maya population structure.

  18. Periodic Structures in the Equatorial Ionosphere (Postprint)

    DTIC Science & Technology

    2012-05-13

    AFRL-RV-PS- AFRL-RV-PS- TP-2012-0004 TP-2012-0004 PERIODIC STRUCTURES IN THE EQUATORIAL IONOSPHERE (POSTPRINT) Cheryl Y. Huang...in the Equatorial Ionosphere (Postprint) 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) 5d. PROJECT NUMBER 2301...International Reference Ionosphere model to remove variations in density due to changes in spacecraft altitude and latitude along the orbit. In this

  19. Spatially variant periodic structures in electromagnetics

    PubMed Central

    Rumpf, Raymond C.; Pazos, Javier J.; Digaum, Jennefir L.; Kuebler, Stephen M.

    2015-01-01

    Spatial transforms are a popular technique for designing periodic structures that are macroscopically inhomogeneous. The structures are often required to be anisotropic, provide a magnetic response, and to have extreme values for the constitutive parameters in Maxwell's equations. Metamaterials and photonic crystals are capable of providing these, although sometimes only approximately. The problem still remains about how to generate the geometry of the final lattice when it is functionally graded, or spatially varied. This paper describes a simple numerical technique to spatially vary any periodic structure while minimizing deformations to the unit cells that would weaken or destroy the electromagnetic properties. New developments in this algorithm are disclosed that increase efficiency, improve the quality of the lattices and provide the ability to design aplanatic metasurfaces. The ability to spatially vary a lattice in this manner enables new design paradigms that are not possible using spatial transforms, three of which are discussed here. First, spatially variant self-collimating photonic crystals are shown to flow unguided waves around very tight bends using ordinary materials with low refractive index. Second, multi-mode waveguides in spatially variant band gap materials are shown to guide waves around bends without mixing power between the modes. Third, spatially variant anisotropic materials are shown to sculpt the near-field around electric components. This can be used to improve electromagnetic compatibility between components in close proximity. PMID:26217058

  20. Multiple multipole program computation of periodic structures

    NASA Astrophysics Data System (ADS)

    Hafner, Ch.

    1995-05-01

    The three-dimensional multiple multipole program (MMP) code based on the generalized multipole technique is outlined for readers who are not familiar with its concepts. This code was originally designed for computational electromagnetics. Rayleigh expansions and periodic boundary conditions are two new features that make MMP computations of arbitrary periodic structures efficient and that at the same time allow us to take advantage of the benefits of other MMP features, including surface impedance boundary conditions and a variety of available basis functions for modeling the electromagnetic field. The application of three-dimensional MMP to a simple grating of highly conducting wires with rectangular cross sections illustrates the high accuracy and the fast convergence of the method as well as the use of surface impedance boundary conditions. A more complicated biperiodic array of helical antennas demonstrates the application of thin-wire expansions in conjunction with regular MMP expansions. This model can be considered a simulation of a thin, anisotropic chiral slab with interesting characteristics.

  1. Interactions of sodium montmorillonite with poly(acrylic acid).

    PubMed

    Tran, Nguyen H; Dennis, Gary R; Milev, Adriyan S; Kannangara, G S Kamali; Wilson, Michael A; Lamb, Robert N

    2005-10-15

    The chemical-structural modifications of the natural clay sodium montmorillonite during interaction with poly(acrylic acid) were studied mainly by X-ray photoemission spectroscopy. Samples of modified montmorillonite were prepared from the reaction of sodium montmorillonite ( approximately 0.5 g) and an aqueous solution of poly(acrylic acid) (pH approximately 1.8, 50 g) at varying temperatures. X-ray diffraction indicated that the montmorillonite interlayer space ( approximately 13 A), formed by regular stacking of the silicate layers (dimension approximately 1x1000 nm), expanded to approximately 16 A as the reaction was carried out at room temperature and at 30 degrees C. At 60 degrees C, the interlayer space further expanded to approximately 20 A. The results of X-ray photoemission spectroscopy indicated that poly(acrylic acid) molecules exchange sodium ions on the surface of the silicate layers. These combined results allowed development of a reaction model that explains the dependency of the interlayer expansion with temperature. Information concerning the surface chemical reactions and systematic increases in the interlayer distances is particularly useful if montmorillonite and poly(acrylic acid) are to be used for formation of nanocomposite materials.

  2. Modification of Wyoming montmorillonite surfaces using a cationic surfactant.

    PubMed

    Xi, Yunfei; Frost, Ray L; He, Hongping; Kloprogge, Theo; Bostrom, Thor

    2005-09-13

    Surfaces of Wyoming SWy-2-Na-montmorillonite were modified using ultrasonic and hydrothermal methods through the intercalation and adsorption of the cationic surfactant octadecyltrimethylammonium bromide (ODTMA). Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG), and electron microscopy. The ultrasonic preparation method results in a higher surfactant concentration within the montmorillonite interlayer when compared with that from the hydrothermal method. Three different molecular environments for surfactants within the surface-modified montmorillonite are proposed upon the basis of their different decomposition temperatures. Both XRD patterns and TEM images demonstrate that SWy-2-Na-montmorillonite contains superlayers. TEM images of organoclays prepared at high surfactant concentrations show alternate basal spacings between neighboring layers. SEM images show that modification with surfactant reduces the clay particle size and aggregation. Organoclays prepared at low surfactant concentration display curved flakes, whereas they become flat with increasing intercalated surfactant. Novel surfactant-modified montmorillonite results in the formation of new nanophases with the potential for the removal of organic impurities from aqueous media.

  3. [Adsorptive Stabilization of Soil Cr (VI) Using HDTMA Modified Montmorillonite].

    PubMed

    2016-03-15

    A series of organo-montomorillonites were prepared using Na-montomorillonite and hexadecyl trimethyl ammonium bromide (HDTMA). The organo-montomorillonites were then investigated for the remediation of Cr(VI) contaminated soils. FT-IR, XRD, SEM and N2 -BET, CEC, Zeta potential measurement were conducted to understand the structural changes of montmorillonites as different amounts of HDTMAs were added as modifier. The characterization results indicated that the clay interlayer spacing distance increased from 1. 25 nm to 2. 13 nm, the clay surface roughness decreased, the clay surface area reduced from 38.91 m² · g⁻¹ to 0.42 m² · g⁻¹, the clay exchangeable cation amount reduced from 62 cmol · kg⁻¹ to 9.9 cmol · kg⁻¹ and the clay surface charge changed from -29.1 mV to 5.59 mV as the dosage of HDTMA in montmorillonite was increased. The TCLP (toxicity characteristic leaching procedure) was used to evaluate the leachate toxicity of Cr(VI). The effects of the initial soil Cr(VI) concentration, montmorillonites dosage, reaction time and HDTMA modification amount were investigated, respectively. The results revealed that modification of montmorillonites would manifest an attenuated physical adsorptive effect and an enhanced electrostatic adsorptive effect on Cr(VI), suggesting electrostatic effect was the major force that resulted in improved Cr(VI) adsorption onto HDTMA modified montmorillonites.

  4. Montmorillonite-Alginate Composites as a Drug delivery System: Intercalation and In vitro Release of Diclofenac sodium

    PubMed Central

    Kevadiya, B. D.; Patel, H. A.; Joshi, G. V.; Abdi, S. H. R.; Bajaj, H. C.

    2010-01-01

    Diclofenac sodium and alginate was intercalated into montmorillonite to form uniform sized beads by gelation method. The structure and surface morphology of the synthesized composite beads were characterized by powdered X-ray diffraction, Fourier transform infrared spectroscopy, thermo gravimetric analysis and scanning electron microscopy. Diclofenac release kinetics of the composite in simulated intestinal fluid medium (pH 7.4) and effect of montmorillonite content on the in vitro release of diclofenac from diclofenac-montmorillonite-alginate composites bead was investigated by UV/Vis spectrophotometer. Diclofenac encapsulation efficiency in the montmorillonite-alginate composites bead increases with an increase in the montmorillonite content. The control release of diclofenac from diclofenac-montmorillonite-alginate composites beads was observed to be better as compared to diclofenac-alginate beads. PMID:21969745

  5. Sorption of sodium dodecylbenzene sulfonate by montmorillonite.

    PubMed

    Yang, Kun; Zhu, Lizhong; Xing, Baoshan

    2007-01-01

    Sorption of linear alkylbenzene sulfonates by soils and sediments is an important process that may affect their fate, transport, toxicity and their application in remediation of contaminated soil and groundwater. In this study, batch experiments were conducted to elucidate the sorption of a widely used anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), by montmorillonite. It was observed that: (i) SDBS was sorbed significantly by montmorillonite saturated with Ca(2+), but little by Na-saturated montmorillonite; (ii) the amount of SDBS sorbed by Ca(2+)-montmorillonite was enhanced by NaCl; and (iii) no significant intercalation of SDBS into Ca(2+)-montmorillonite was observed by X-ray diffraction (XRD) analysis. These results indicate that the removal of SDBS by Ca(2+)-montmorillonite was primarily attributed to the precipitation between DBS(-) and Ca(2+) in solution which was released from montmorillonite via cation exchange. These results will help us to understand the sorption behavior and environmental effects of anionic surfactants.

  6. Formation of periodic structures on glass with laser irradiation

    NASA Astrophysics Data System (ADS)

    Peng, Ying Zi; An, Cheng Wu; Wu, Dong Jiang; Hong, Ming Hui; Lu, Yong Feng; Chong, Tow Chong

    2003-07-01

    Regular and tidy periodic structures hae been directly induced on glasses using a CW CO2 laser beam with linear polarization. It is experimentally shown that precise periodic structures with the period of several microns can be formed by means of well-set laser parameters. The orientation of the periodic structures formed is the same as that of the laser polarization no matter what the scanning direction is. The occurrence of periodic structures is very sensitive to laser power level and scanning velocity. To obtain appropriate periodic patterns, a combined condition of laser energy and scanning velocity must be satisfied. The period, width and height of the structures are dependent on processing parameters. An interesting phenomenon is that the period decreases with increasing scanning velocity. Permanent relieves with periods, widths and heights varied with the laser parameters are also studied.

  7. The acid-base titration of montmorillonite

    NASA Astrophysics Data System (ADS)

    Bourg, I. C.; Sposito, G.; Bourg, A. C.

    2003-12-01

    Proton binding to clay minerals plays an important role in the chemical reactivity of soils (e.g., acidification, retention of nutrients or pollutants). If should also affect the performance of clay barriers for waste disposal. The surface acidity of clay minerals is commonly modelled empirically by assuming generic amphoteric surface sites (>SOH) on a flat surface, with fitted site densities and acidity constant. Current advances in experimental methods (notably spectroscopy) are rapidly improving our understanding of the structure and reactivity of the surface of clay minerals (arrangement of the particles, nature of the reactive surface sites, adsorption mechanisms). These developments are motivated by the difficulty of modelling the surface chemistry of mineral surfaces at the macro-scale (e.g., adsorption or titration) without a detailed (molecular-scale) picture of the mechanisms, and should be progressively incorporated into surface complexation models. In this view, we have combined recent estimates of montmorillonite surface properties (surface site density and structure, edge surface area, surface electrostatic potential) with surface site acidities obtained from the titration of alpha-Al2O3 and SiO2, and a novel method of accounting for the unknown initial net proton surface charge of the solid. The model predictions were compared to experimental titrations of SWy-1 montmorillonite and purified MX-80 bentonite in 0.1-0.5 mol/L NaClO4 and 0.005-0.5 mol/L NaNO3 background electrolytes, respectively. Most of the experimental data were appropriately described by the model after we adjusted a single parameter (silanol sites on the surface of montmorillonite were made to be slightly more acidic than those of silica). At low ionic strength and acidic pH the model underestimated the buffering capacity of the montmorillonite, perhaps due to clay swelling or to the interlayer adsorption of dissolved aluminum. The agreement between our model and the experimental

  8. A 'periodic table' for protein structures.

    PubMed

    Taylor, William R

    2002-04-11

    Current structural genomics programs aim systematically to determine the structures of all proteins coded in both human and other genomes, providing a complete picture of the number and variety of protein structures that exist. In the past, estimates have been made on the basis of the incomplete sample of structures currently known. These estimates have varied greatly (between 1,000 and 10,000; see for example refs 1 and 2), partly because of limited sample size but also owing to the difficulties of distinguishing one structure from another. This distinction is usually topological, based on the fold of the protein; however, in strict topological terms (neglecting to consider intra-chain cross-links), protein chains are open strings and hence are all identical. To avoid this trivial result, topologies are determined by considering secondary links in the form of intra-chain hydrogen bonds (secondary structure) and tertiary links formed by the packing of secondary structures. However, small additions to or loss of structure can make large changes to these perceived topologies and such subjective solutions are neither robust nor amenable to automation. Here I formalize both secondary and tertiary links to allow the rigorous and automatic definition of protein topology.

  9. Periodic thermomagnetic structures in solar plasma

    SciTech Connect

    Kovalev, V. A.; Laptukhov, A. I.

    2009-04-15

    Stationary solutions in the form of small-scale periodic cells in a plane perpendicular to the magnetic field are obtained in the framework of two-fluid magnetohydrodynamics. The solutions are established as a result of the development of thermal instability and represent a superposition of standing temperature waves. In solving the problem, an expression is used for a generalized heat source (including heating and radiative cooling) that forms a temperature transition region between the chromosphere and corona.

  10. Formation of terahertz beams produced by artificial dielectric periodical structures

    NASA Astrophysics Data System (ADS)

    Khodzitsky, Mikhail K.; Vozianova, Anna V.; Gill, Viktoria V.; Chernyadiev, Alexander V.; Grebenchukov, Alexandr N.; Minin, Igor V.; Minin, Oleg V.

    2016-09-01

    This paper presents an investigation of terajets formation by dielectric periodic structure at terahertz frequencies in effective medium regime (photonic metamaterial). The dispersions of effective permittivity for three periodic structures formed by different types of plastics (ABS, PLA, Crystal) were analytically obtained for both regimes. Numerical simulation of this structure was performed by using COMSOL Multiphysics. The terajet formation was numerically shown.

  11. Elaboration et caracterisation de nanocomposites polyethylene/montmorillonite

    NASA Astrophysics Data System (ADS)

    Stoeffler, Karen

    This research project consists in preparing polyethylene/montmorillonite nanocomposites for film packaging applications. Montmorillonite is a natural clay with an exceptional aspect ratio. In recent years, its incorporation in polymer matrices has attracted great interest. The pioneer work from Toyota on polyamide-6/montmorillonite composites has shown that it was possible to disperse the clay at a nanometric scale. Such a structure, so-called exfoliated, leads to a significant increase in mechanical, barrier and fire retardant properties, even at low volumetric fractions of clay. This allows a valorization of the polymeric material at moderate cost. Due to its high polarity, montmorilloite exfoliation in polymeric matrices is problematic. In the particular case of polyolefin matrices, the platelets dispersion remains limited: most frequently, the composites obtained exhibit conventional structures (microcomposites) or intercalated structures. To solve this problem, two techniques are commonly employed: the surface treatment of the clay, which allows the expansion of the interfoliar gallery while increasing the affinity between the clay and the polymer, and the use of a polar compatibilizing agent (grafted polyolefin). The first part of this thesis deals with the preparation and the characterization of highly thermally stable organophilic montmorillonites. Commercial organophilic montmorillonites are treated with quaternary ammonium intercalating agents. However, those intercalating agents present a poor thermal stability and are susceptible to decompose upon processing, thus affecting the clay dispersion and the final properties of the nanocomposites. In this work, it was proposed to modify the clay with alkyl pyridinium, alkyl imidazolium and alkyl phosphonium intercalating agents, which are more stable than ammonium based cations. Organophilic montmorillonites with enhanced thermal stabilites compared to commercial organoclays (+20°C to +70°C) were prepared

  12. Determining the cation exchange capacity of montmorillonite by simultaneous thermal analysis method

    NASA Astrophysics Data System (ADS)

    Boeva, N. M.; Bocharnikova, Yu. I.; Belousov, P. E.; Zhigarev, V. V.

    2016-08-01

    A way of determining the cation exchange capacity of montmorillonite by simultaneous thermal analysis is developed using as an example the bentonites of the 10th Khutor deposit (Republic of Khakassia) and the Vodopadnyi area (Sakhalin Island). A correlation is established between the cation exchange capacity of smectite and its weight loss upon heating in the range of dehydration; the enthalpy of dehydration of montmorillonite; and the weight loss and the enthalpy of thermal dissociation of ethylene glycol contained in the interlayer space of the mineral's crystal structure. These data open up new possibilities for determining the cation exchange capacity of montmorillonite, the most important technological indicator of the natural clay nanomineral.

  13. Fabrication and characterization of metallic quasi-periodic structures.

    PubMed

    Wang, Yongjin

    2008-01-21

    A variety of intriguing interference patterns are generated as a template to create metallic quasi-periodic structures using our robust experimental setup. A combination of thermal evaporation and lift-off process, the 2D metallic quasi-periodic structures are generated, a twelve-fold symmetry structure can be clearly observed in fabricated structures with four exposures. The excitation of surface plasmon (SP) resonances, which are determined by the geometry of metallic structures, the incident angle alpha, and the refractive index n(d) of the adjacent dielectric medium, is demonstrated in the optical transmission experiments. The optical transmission of metallic quasi-periodic structures can be tuned by varying the refractive index n(d), changing the period a and altering the incident angle alpha. The experimental results agree well with the predication for SP resonances. It's the first step to investigate the interesting optical properties of metallic quasi-periodic structures.

  14. Exfoliation and intercalation of montmorillonite by small peptides.

    PubMed

    Block, Karin A; Trusiak, Adrianna; Katz, Al; Alimova, Alexandra; Wei, Hui; Gottlieb, Paul; Steiner, Jeffrey C

    2015-04-01

    Understanding structural changes in clay minerals induced by complexation with organic matter is relevant to soil science and agricultural applications. In this study, the effect of peptide storage in montmorillonite and the thermal stability of peptide-clay complexes was examined through characterization by X-ray diffraction (XRD), electron microscopy, UV absorption, and thermogravimetric analysis (TGA). XRD analysis of small peptide-montmorillonite clay complexes produced profiles consisting of reflections associated with the smectite 001 reflection and related peaks similar to that produced by a mixed layer clay mineral structure. Shifts in higher order diffraction maxima were attributed to disorder caused by the intercalation with the peptides. Increasing peptide concentrations resulted in greater shifts towards smaller 2θ from 6.37° (1.39 nm) to 5.45° (1.62 nm) as the interlayer space expanded. The expansion was accompanied by broadening of the 001 reflection (FWHM increases from 0.51 to 1.22° 2θ). The XRD line broadening was interpreted as caused by poorer crystallinity resulting from intercalation and tactoid exfoliation. SEM images revealed montmorillonite platelets with upwardly rolled edges that tend toward cylindrical structures with the production of tubules. High-resolution TEM images revealed bending of montmorillonite platelets, confirming exfoliation. The distribution of basal spacings in the micrographs was determined from the spatial frequencies obtained by Fourier analysis of density profiles. The distribution indicated the presence of discrete coherent crystallite domains. XRD and TGA results indicated that higher peptide concentrations resulted in a greater fraction of intercalated peptides and that surface adsorption of peptides mediated intercalation. Therefore, higher peptide concentration led to more stable organoclay complexes. However, UV absorption and TGA found that peptide adsorption onto montmorillonite had a finite limit at

  15. Exfoliation and intercalation of montmorillonite by small peptides

    PubMed Central

    Block, Karin A.; Trusiak, Adrianna; Katz, Al; Alimova, Alexandra; Wei, Hui; Gottlieb, Paul; Steiner, Jeffrey C.

    2015-01-01

    Understanding structural changes in clay minerals induced by complexation with organic matter is relevant to soil science and agricultural applications. In this study, the effect of peptide storage in montmorillonite and the thermal stability of peptide-clay complexes was examined through characterization by X-ray diffraction (XRD), electron microscopy, UV absorption, and thermogravimetric analysis (TGA). XRD analysis of small peptide-montmorillonite clay complexes produced profiles consisting of reflections associated with the smectite 001 reflection and related peaks similar to that produced by a mixed layer clay mineral structure. Shifts in higher order diffraction maxima were attributed to disorder caused by the intercalation with the peptides. Increasing peptide concentrations resulted in greater shifts towards smaller 2θ from 6.37° (1.39 nm) to 5.45° (1.62 nm) as the interlayer space expanded. The expansion was accompanied by broadening of the 001 reflection (FWHM increases from 0.51 to 1.22° 2θ). The XRD line broadening was interpreted as caused by poorer crystallinity resulting from intercalation and tactoid exfoliation. SEM images revealed montmorillonite platelets with upwardly rolled edges that tend toward cylindrical structures with the production of tubules. High-resolution TEM images revealed bending of montmorillonite platelets, confirming exfoliation. The distribution of basal spacings in the micrographs was determined from the spatial frequencies obtained by Fourier analysis of density profiles. The distribution indicated the presence of discrete coherent crystallite domains. XRD and TGA results indicated that higher peptide concentrations resulted in a greater fraction of intercalated peptides and that surface adsorption of peptides mediated intercalation. Therefore, higher peptide concentration led to more stable organoclay complexes. However, UV absorption and TGA found that peptide adsorption onto montmorillonite had a finite limit at

  16. Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures

    NASA Astrophysics Data System (ADS)

    Lei, Yuxiong; Chen, Zheng; Li, Liangliang

    2015-05-01

    Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures were investigated in this study. The periodic and quasi-periodic structures were designed based on Fibonacci sequence and golden ratio. Ni nanowires arrays were electrodeposited in anodic aluminum oxide (AAO) templates with patterned Cu electrodes, and then the AAO templates were attached to the coplanar waveguide lines fabricated on quartz substrate for measurement. The S21 of both periodic and quasi-periodic structure-patterned Ni nanowire arrays showed an extra absorption peak besides the absorption peak due to the ferromagnetic resonance of Ni nanowires. The frequency of the absorption peak caused by the patterned structure could be higher than 40 GHz when the length and arrangement of the structural units were modified. In addition, the frequency of the absorption peak due to the quasi-periodic structure was calculated based on a simple analytical model, and the calculated value was consistent with the measured one. The experimental data showed that it could be a feasible approach to tune the performance of microwave devices by patterning ferromagnetic nanowires.

  17. Controlled Release of Agrochemicals Intercalated into Montmorillonite Interlayer Space

    PubMed Central

    2014-01-01

    Periodic application of agrochemicals has led to high cost of production and serious environmental pollution. In this study, the ability of montmorillonite (MMT) clay to act as a controlled release carrier for model agrochemical molecules has been investigated. Urea was loaded into MMT by a simple immersion technique while loading of metalaxyl was achieved by a rotary evaporation method. The successful incorporation of the agrochemicals into the interlayer space of MMT was confirmed by several techniques, such as, significant expansion of the interlayer space, reduction of Barrett-Joyner-Halenda (BJH) pore volumes and Brunauer-Emmett-Teller (BET) surface areas, and appearance of urea and metalaxyl characteristic bands on the Fourier-transform infrared spectra of the urea loaded montmorillonite (UMMT) and metalaxyl loaded montmorillonite (RMMT) complexes. Controlled release of the trapped molecules from the matrix was done in water and in the soil. The results reveal slow and sustained release behaviour for UMMT for a period of 10 days in soil. For a period of 30 days, MMT delayed the release of metalaxyl in soil by more than 6 times. It is evident that MMT could be used to improve the efficiency of urea and metalaxyl delivery in the soil. PMID:24696655

  18. Controlled release of agrochemicals intercalated into montmorillonite interlayer space.

    PubMed

    Wanyika, Harrison

    2014-01-01

    Periodic application of agrochemicals has led to high cost of production and serious environmental pollution. In this study, the ability of montmorillonite (MMT) clay to act as a controlled release carrier for model agrochemical molecules has been investigated. Urea was loaded into MMT by a simple immersion technique while loading of metalaxyl was achieved by a rotary evaporation method. The successful incorporation of the agrochemicals into the interlayer space of MMT was confirmed by several techniques, such as, significant expansion of the interlayer space, reduction of Barrett-Joyner-Halenda (BJH) pore volumes and Brunauer-Emmett-Teller (BET) surface areas, and appearance of urea and metalaxyl characteristic bands on the Fourier-transform infrared spectra of the urea loaded montmorillonite (UMMT) and metalaxyl loaded montmorillonite (RMMT) complexes. Controlled release of the trapped molecules from the matrix was done in water and in the soil. The results reveal slow and sustained release behaviour for UMMT for a period of 10 days in soil. For a period of 30 days, MMT delayed the release of metalaxyl in soil by more than 6 times. It is evident that MMT could be used to improve the efficiency of urea and metalaxyl delivery in the soil.

  19. Montmorillonite-induced Bacteriophage φ6 Disassembly

    NASA Astrophysics Data System (ADS)

    Trusiak, A.; Gottlieb, P.; Katz, A.; Alimova, A.; Steiner, J. C.; Block, K. A.

    2012-12-01

    It is estimated that there are 1031 virus particles on Earth making viruses an order of magnitude more prevalent in number than prokaryotes with the vast majority of viruses being bacteriophages. Clays are a major component of soils and aquatic sediments and can react with RNA, proteins and bacterial biofilms. The clays in soils serve as an important moderator between phage and their host bacteria, helping to preserve the evolutionary balance. Studies on the effects of clays on viral infectivity have given somewhat contradictory results; possibly a consequence of clay-virus interactions being dependent on the unique structure of particular viruses. In this work, the interaction between montmorillonite and the bacteriophage φ6 is investigated. φ6 is a member of the cystovirus family that infects Pseudomonas syringe, a common plant pathogen. As a member of the cystovirus family with an enveloped structure, φ6 serves as a model for reoviruses, a human pathogen. Experiments were conducted with φ6 suspended in dilute, purified homoionic commercial-grade montmorillonite over a range of virus:clay ratios. At a 1:100000 virus:clay ratio, the clay reduced viral infectivity by 99%. The minimum clay to virus ratio which results in a measurable reduction of P. syringae infection is 1:1. Electron microscopy demonstrates that mixed suspensions of smectite and virus co-aggregate to form flocs encompassing virions within the smectite. Both free viral particles as well as those imbedded in the flocs are seen in the micrographs to be missing the envelope- leaving only the nucleocapsid (NC) intact; indicating that smectite inactivates the virus by envelope disassembly. These results have strong implications in the evolution of both the φ6 virus and its P. syringae host cells. TEM of aggregate showing several disassembled NCs.

  20. Linear Scaling Electronic Structure Methods with Periodic Boundary Conditions

    SciTech Connect

    Gustavo E. Scuseria

    2008-02-08

    The methodological development and computational implementation of linear scaling quantum chemistry methods for the accurate calculation of electronic structure and properties of periodic systems (solids, surfaces, and polymers) and their application to chemical problems of DOE relevance.

  1. Nontronite and Montmorillonite as Nutrient Sources for Life on Mars

    NASA Technical Reports Server (NTRS)

    Craig, P. I.; Mickol, R. L.; Archer, P. D.; Kral, T. A.

    2017-01-01

    Clay minerals have been identified on Mars' oldest (Noachian) terrain and their presence suggests long-term water-rock interactions. The most commonly identified clay minerals on Mars to date are nontronite (Fe-smectite) and montmorillonite (Al-smectite) [1], both of which contain variable amounts of water both adsorbed on their surface and within their structural layers. Over Mars' history, these clay miner-al-water assemblages may have served as nutrient sources for microbial life.

  2. Periodic and quasi-periodic behavior in resource-dependent age structured population models.

    PubMed

    Dilão, R; Domingos, T

    2001-03-01

    To describe the dynamics of a resource-dependent age structured population, a general non-linear Leslie type model is derived. The dependence on the resources is introduced through the death rates of the reproductive age classes. The conditions assumed in the derivation of the model are regularity and plausible limiting behaviors of the functions in the model. It is shown that the model dynamics restricted to its omega-limit sets is a diffeomorphism of a compact set, and the period-1 fixed points of the model are structurally stable. The loss of stability of the non-zero steady state occurs by a discrete Hopf bifurcation. Under general conditions, and after the loss of stability of the structurally stable steady states, the time evolution of population numbers is periodic or quasi-periodic. Numerical analysis with prototype functions has been performed, and the conditions leading to chaotic behavior in time are discussed.

  3. Periodic instantons and domain structure in a ferromagnetic film

    NASA Astrophysics Data System (ADS)

    Zheng, G.-P.; Liang, J.-Q.; Nie, Y.-H.; Yin, W.

    2003-11-01

    We in this paper study periodic instantons and domain structures in a theoretical film consisting of biaxial-anisotropic ferromagnets. In a proper approximation the equation of motion of the magnetization vector as a space-time function in the film is reduced to the 1 + 2-dimensional sine-Gordon field equation in strong anisotropy limit. Static periodic instantons, which are solutions of Euclidean field equantion, and various new domain structures are obtained analytically. We also investigate the energy density and stability of the periodic instantons.

  4. A Density Functional Theory Study of a Calcium- Montmorillonite: A First Investigation for Medicine Application

    NASA Astrophysics Data System (ADS)

    Dewi Kencana Wungu, Triati; Fauzan, Muhammad Rifqi Al; Widayani; Suprijadi

    2016-08-01

    In this study, we performed structural geometry and electronic properties calculations of calcium - based clay mineral for medicine application using first principles calculation by means of Density Functional Theory. Here, a kind of clay mineral used was Ca- montmorillonite and it is applied as an absorber of dangerous metal contained in a human body, such as Pb, which causes osteoporosis. Osteoporosis is a disease associated with bone mass decreases. Since montmorillonite has ability to exchange its cation (Ca+2), therefore, it plays an important role in preventing or/and cure human bone from osteoporosis. In order to understand how Ca-montmorillonite can do detoxification in the human body, we firstly investigated the mechanism of Pb adsorption on the surface of Ca-montmorillonite in an atomic level point of view. We found that the repulsive interactions between H of OH groups with Ca and Pb yielding the rotation of the H of OH groups of montmorillonite. A relatively small movement of Ca was observed when Pb is adsorbed and the band gap of Ca- montmorillonite becomes 1.87 eV narrow.

  5. Hydrothermal Synthesis and Characterization of Ni-Al Montmorillonite-Like Phyllosilicates

    PubMed Central

    Reinholdt, Marc X.; Brendlé, Jocelyne; Tuilier, Marie-Hélène; Kaliaguine, Serge; Ambroise, Emmanuelle

    2013-01-01

    This work describes the first hydrothermal synthesis in fluoride medium of Ni-Al montmorillonite-like phyllosilicates, in which the only metallic elements in the octahedral sheet are Ni and Al. X-ray diffraction , chemical analysis, thermogravimetric and differential thermal analysis, scanning electron microscopy and transmission electron microscopy confirm that the synthesized samples are montmorillonite-like phyllosilicates having the expected chemical composition. The specific surface areas of the samples are relatively large (>100 m2 g−1) compared to naturally occurring montmorillonites. 29Si and 27Al nuclear magnetic resonance (NMR) indicate substitutions of Al for Si in the tetrahedral sheet. 19F NMR and Ni K-edge extended X-ray absorption fine structure (EXAFS) local probes highlight a clustering of the metal elements and of the vacancies in the octahedral sheet of the samples. These Ni-Al phyllosilicates exhibit a higher local order than in previously synthesized Zn-Al phyllosilicates. Unlike natural montmorillonites, where the distribution of transition metal cations ensures a charge equilibrium allowing a stability of the framework, synthetic montmorillonites entail clustering and instability of the lattice when the content of divalent element in the octahedral sheet exceeds ca. 20%. Synthesis of Ni-Al montmorillonite-like phyllosilicates, was successfully achieved for the first time. These new synthetic materials may find potential applications as catalysts or as materials with magnetic, optical or staining properties. PMID:28348321

  6. Waves in active and passive periodic structures - A review

    NASA Technical Reports Server (NTRS)

    Elachi, C.

    1976-01-01

    The theory and recent applications of waves in periodic structures are reviewed. Both the Floquet and coupled waves approach are analyzed in some detail. The theoretical part of the paper includes wave propagation in unbounded and bounded active or passive periodic media, wave scattering from periodic boundaries, source radiation (dipole, Cerenkov, transition, and Smith-Purcell) in periodic media, and pulse transmission through a periodic slab. The applications part covers the recent development in a variety of fields: distributed feedback oscillators, filters, mode converters, couplers, second-harmonic generators, deflectors, modulators, and transducers in the fields of integrated optics and integrated surface acoustics. Work on insect compound eyes, mechanical structures, ocean waves, pulse compressions, temperature waves, and cholesteric liquid crystals, and particles interaction with crystals is briefly reviewed, especially in the case of zeolite crystals and superlattices. Recent advances in fabrication techniques for very fine gratings are also covered.

  7. Analysis of vibration of two-dimensional periodic cellular structures

    NASA Astrophysics Data System (ADS)

    Jeong, Sang Min (Joseph)

    The vibration of and wave propagation in periodic cellular structures are analyzed. Cellular structures exhibit a number of desirable multifunctional properties, which make them attractive in a variety of engineering applications. These include ultra-light structures, thermal and acoustic insulators, and impact amelioration systems, among others. Cellular structures with deterministic architecture can be considered as example of periodic structures. Periodic structures feature unique wave propagation characteristics, whereby elastic waves propagate only in specific frequency bands, known as "pass band", while they are attenuated in all other frequency bands, known as "stop bands". Such dynamic properties are here exploited to provide cellular structures with the capability of behaving as directional, pass-band mechanical filters, thus complementing their well documented multifunctional characteristics. This work presents a methodology for the analysis of the dynamic behavior of periodic cellular structures, which allows the evaluation of location and spectral width of propagation and attenuation regions in non-dimensional form. The filtering characteristics are tested and demonstrated for structures of various geometry and topology, including cylindrical grid-like structures, Kagome and tetrhedral truss core lattices. Experimental investigations is done on a 2-D lattice manufactured out of aluminum. The complete wave field of the specimen at various frequencies is measured using a Scanning Laser Doppler Vibrometer (SLDV). Experimental results show good agreement with the methodology and computational tools developed in this work. The results demonstrate how wave propagation characteristics are defined by cell geometry and configuration. Numerical and experimental results show the potential of periodic cellular structures as mechanical filters and/or isolators of vibrations.

  8. Laser-induced periodic surface structures: Fingerprints of light localization

    NASA Astrophysics Data System (ADS)

    Skolski, J. Z. P.; Römer, G. R. B. E.; Obona, J. V.; Ocelik, V.; Huis in't Veld, A. J.; de Hosson, J. Th. M.

    2012-02-01

    The finite-difference time-domain (FDTD) method is used to study the inhomogeneous absorption of linearly polarized laser radiation below a rough surface. The results are first analyzed in the frequency domain and compared to the efficacy factor theory of Sipe and coworkers. Both approaches show that the absorbed energy shows a periodic nature, not only in the direction orthogonal to the laser polarization, but also in the direction parallel to it. It is shown that the periodicity is not always close to the laser wavelength for the perpendicular direction. In the parallel direction, the periodicity is about λ/Re(ñ), with ñ being the complex refractive index of the medium. The space-domain FDTD results show a periodicity in the inhomogeneous energy absorption similar to the periodicity of the low- and high-spatial-frequency laser-induced periodic surface structures depending on the material's excitation.

  9. Characterization of sodium dodecyl sulfate modified iron pillared montmorillonite and its application for the removal of aqueous Cu(II) and Co(II).

    PubMed

    Li, Shu-Zhen; Wu, Ping-Xiao

    2010-01-15

    Anionic surfactant modified Fe-pillared montmorillonites were prepared by Fe-hydrate solution and sodium dodecyl sulfate (SDS) solution. These organo-inorgano complex montmorillonites were divided into three types (CM1, CM2 and CM3) depending on different intercalation processes. X-ray diffraction spectra, the Fourier transform infrared (FTIR) spectra were used to analyze the structure of the raw and modified montmorillonites. X-ray photoelectron spectra of the samples have been studied to determine spectral characteristics to allow the identification of Fe(III) hydroxide. The specific surface area of the host montmorillonite (M0) is 73.2m(2)/g, while for the modified montmorillonites it is 114.0m(2)/g, 117.2m(2)/g, and 115.8m(2)/g, respectively. The mesopore volumes of the montmorillonites decrease after modification. Ions of copper and cobalt were selected as adsorbates to evaluate the adsorption performance of each montmorillonite. The adsorption data was analyzed by both Freundlich and Langmuir isotherm models and the data was well fit by the Langmuir isotherm model. The adsorption was efficient and significantly influenced by metal speciation, metal concentration, contact time, and pH. Higher adsorption capacity of the modified montmorillonites were obtained at pH 5-6. The results of desorption indicated that the metal ions were covalently bound to the modified montmorillonites.

  10. Characterization of electronic structure of periodically strained graphene

    SciTech Connect

    Aslani, Marjan; Garner, C. Michael Nishi, Yoshio; Kumar, Suhas; Nordlund, Dennis; Pianetta, Piero

    2015-11-02

    We induced periodic biaxial tensile strain in polycrystalline graphene by wrapping it over a substrate with repeating pillar-like structures with a periodicity of 600 nm. Using Raman spectroscopy, we determined to have introduced biaxial strains in graphene in the range of 0.4% to 0.7%. Its band structure was characterized using photoemission from valance bands, shifts in the secondary electron emission, and x-ray absorption from the carbon 1s levels to the unoccupied graphene conduction bands. It was observed that relative to unstrained graphene, strained graphene had a higher work function and higher density of states in the valence and conduction bands. We measured the conductivity of the strained and unstrained graphene in response to a gate voltage and correlated the changes in their behavior to the changes in the electronic structure. From these sets of data, we propose a simple band diagram representing graphene with periodic biaxial strain.

  11. Characterization of electronic structure of periodically strained graphene

    SciTech Connect

    Aslani, Marjan; Garner, C. Michael; Kumar, Suhas; Nordlund, Dennis; Pianetta, Piero; Nishi, Yoshio

    2015-11-03

    We induced periodic biaxial tensile strain in polycrystalline graphene by wrapping it over a substrate with repeating pillar-like structures with a periodicity of 600 nm. Using Raman spectroscopy, we determined to have introduced biaxial strains in graphene in the range of 0.4% to 0.7%. Its band structure was characterized using photoemission from valance bands, shifts in the secondary electron emission, and x-ray absorption from the carbon 1s levels to the unoccupied graphene conduction bands. It was observed that relative to unstrained graphene, strained graphene had a higher work function and higher density of states in the valence and conduction bands. Furthermore, we measured the conductivity of the strained and unstrained graphene in response to a gate voltage and correlated the changes in their behavior to the changes in the electronic structure. From these sets of data, we propose a simple band diagram representing graphene with periodic biaxial strain.

  12. Laser-induced periodic surface structures, modeling, experiments, and applications

    NASA Astrophysics Data System (ADS)

    Römer, G. R. B. E.; Skolski, J. Z. P.; Oboňa, J. Vincenc; Ocelík, V.; de Hosson, J. T. M.; Huis in't Veld, A. J.

    2014-03-01

    Laser-induced periodic surface structures (LIPSSs) consist of regular wavy surface structures, or ripples, with amplitudes and periodicity in the sub-micrometer range. A summary of experimentally observed LIPSSs is presented, as well as our model explaining their possible origin. Linearly polarized continuous wave (cw) or pulsed laser light, at normal incidence, can produce LIPSSs with a periodicity close to the laser wavelength, and direction orthogonal to the polarization on the surface of the material. Ripples with a periodicity (much) smaller than the laser wavelength develop when applying laser pulses with ultra-short durations in the femtosecond and picosecond regime. The direction of these ripples is either parallel or orthogonal to the polarization direction. Finally, when applying numerous pulses, structures with periodicity larger than the laser wavelength can form, which are referred to as "grooves". The physical origin of LIPSSs is still under debate. The strong correlation of the ripple periodicity to the laser wavelength, suggests that their formation can be explained by an electromagnetic approach. Recent results from a numerical electromagnetic model, predicting the spatially modulated absorbed laser energy, are discussed. This model can explain the origin of several characteristics of LIPSSs. Finally, applications of LIPSSs will be discussed.

  13. Influence of calcium and silica on hydraulic properties of sodium montmorillonite assemblages under alkaline conditions.

    PubMed

    Kinsela, Andrew S; Tjitradjaja, Alice; Collins, Richard N; Waite, T David; Payne, Timothy E; Macdonald, Bennett C T; White, Ian

    2010-03-01

    A sodium-washed montmorillonite was exposed to calcium and silica under alkaline conditions in order to gain insight into possible interactions of engineered clay barriers and cementitious leachates found in many waste storage facilities. The changes in physico-chemical properties of the material were investigated using a combination of dead-end filtration, electrophoresis and scanning electron microscopy. The results show minimal differentiation between unaltered Na-montmorillonite samples at the two pH values tested (9 and 12), with the structure of the resulting assemblages arising from repulsive tactoid interactions. The addition of calcium (50 mM) greatly decreases the size of the structural network, and in doing so, increases the hydraulic conductivity approximately 65-fold, with the effect being greatest at pH 12. Whilst the addition of silica alone (10 mM) produced little change in the hydraulic properties of montmorillonite, its combined effect with calcium produced alterations to the structural assemblages that could not be accounted for by the presence of calcium alone. The likely binding of calcium with multiple silanol groups appears to enhance the retention of water within the Na-montmorillonite assemblage, whilst still allowing the fluent passage of water. The results confirm that polyvalent cations such as Ca(2+) may have a dramatic effect on the structural and hydraulic properties of montmorillonite assemblages while the effects of solutions containing both silicate and calcium are complex and influenced by silica-cation interactions.

  14. Modal approach to Casimir forces in periodic structures

    SciTech Connect

    Davids, P. S.; Intravaia, F.; Rosa, F. S. S.; Dalvit, D. A. R.

    2010-12-15

    We present a modal approach to calculate finite-temperature Casimir interactions between two periodically modulated surfaces. The scattering formula is used and the reflection matrices of the patterned surfaces are calculated by decomposing the electromagnetic field into the natural modes of the structures. The Casimir force gradient from a deeply etched silicon grating is evaluated using the modal approach and compared to experiment for validation. The Casimir force involving a two-dimensional periodic structure is computed and deviations from the proximity force approximation are examined.

  15. Ferric sulfate montmorillonites as Mars soil analogs

    NASA Technical Reports Server (NTRS)

    Bishop, J. L.; Pieters, C. M.; Burns, R. G.

    1993-01-01

    Spectroscopic analyses have shown that Fe(3+)-doped smectites prepared in the laboratory exhibit important similarities to the soils on Mars. Ferrihydrite in these smectites has features in the visible to near-infrared region that resemble the energies and band-strengths of features in reflectance spectra observed for several bright regions on Mars. Ferric - sulfate - montmorillonite samples have been prepared more recently because they are a good compositional match with the surface material on Mars as measured by Viking. Reflectance spectra of montmorillonite doped with ferric sulfate in the interlayer regions include a strong 3 micron band that persists under dry conditions. This is in contrast to spectra of similarly prepared ferric-doped montmorillonites, which exhibit a relatively weaker 3 micron band under comparable dry environmental conditions. Presented here are reflectance spectra of a suite of ferric-sulfate exchanged montmorillonites prepared with variable ferric sulfate concentrations and variable pH conditions.

  16. Enhanced light trapping in periodically truncated cone silicon nanowire structure

    NASA Astrophysics Data System (ADS)

    Kai, Qiu; Yuhua, Zuo; Tianwei, Zhou; Zhi, Liu; Jun, Zheng; Chuanbo, Li; Buwen, Cheng

    2015-10-01

    Light trapping plays an important role in improving the conversion efficiency of thin-film solar cells. The good wideband light trapping is achieved using our periodically truncated cone Si nanowire (NW) structures, and their inherent mechanism is analyzed and simulated by FDTD solution software. Ordered cylinder Si NW structure with initial size of 80 nm and length of 200 nm is grown by pattern transfer and selective epitaxial growth. Truncated cone Si NW array is then obtained by thermal oxidation treatment. Its mean reflection in the range of 300-900 nm is lowered to be 5% using 140 nm long truncated cone Si NW structure, compared with that of 20% using cylinder counterparts. It indicates that periodically truncated Si cone structures trap the light efficiently to enhance the light harvesting in a wide spectral range and have the potential application in highly efficient NW solar cells. Project supported by the National Natural Science Foundation of China (Nos. 51072194, 61021003, 61036001, 61376057).

  17. Optical properties of structures composed of periodic, quasi-periodic, and aperiodic sequences of particulate monolayers

    NASA Astrophysics Data System (ADS)

    Loiko, V. A.; Miskevich, A. A.

    2017-01-01

    The spectra of the coherent transmission and reflection coefficients of multilayers consisting of the periodic, Fibonacci (quasi-periodic), and Thue-Morse (aperiodic) sequences of plane-parallel monolayers of monodisperse spherical alumina and silica particles are investigated using the quasi-crystalline approximation (QCA) and the transfer matrix method (TMM). The additional opportunities for the transmission and reflection spectra manipulation in comparison with the periodic sequence of monolayers are demonstrated. Photonic band gaps in the spectra of the particulate structures are shifted to the short-wavelength range in comparison with those for systems of homogeneous layers. The shift is larger for the Thue-Morse sequence. The widths of the photonic band gaps for particulate systems are narrower than the ones for multilayers consisting of homogeneous layers of an equivalent volume of matter. The results can be used to create optical, optoelectronics, and photonics devices—for example, multispectral filters, light emitting diodes, solar cells, displays.

  18. Coherent structures in 3D viscous time-periodic flow

    NASA Astrophysics Data System (ADS)

    Znaien, J. G.; Speetjens, M. F. M.; Trieling, R. R.; Clercx, H. J. H.

    2010-11-01

    Periodically driven laminar flows occur in many industrial processes from food-mixing devices to micro-mixer in lab-on-a-chip systems. The present study is motivated by better understanding fundamental transport phenomena in three-dimensional viscous time-periodic flows. Both numerical simulation and three-dimensional Particle Tracking Velocimetry measurements are performed to investigate the 3D advection of a passive scalar in a lid-driven cylindrical cavity flow. The flow is forced by a time-periodic in-plane motion of one endwall via a given forcing protocol. We concentrate on the formation and interaction of coherent structures due to fluid inertia, which play an important role in 3D mixing by geometrically determining the tracer transport. The disintegration of these structures by fluid inertia reflects an essentially 3D route to chaos. Data from tracking experiments of small particles will be compared with predictions from numerical simulations on transport of passive tracers.

  19. The period structure of the ZZ Ceti variables

    NASA Technical Reports Server (NTRS)

    Mcgraw, J. T.

    1980-01-01

    The current observational status of the period structure of ZZ Ceti stars is reviewed, and in particular those features which appear to be the most important for theory to explain, or which may be relevant to the directions of theoretical development are discussed. Mechanisms to explain the broad range of period structure are suggested. Multiple nonradial modes, probably corresponding to different radial overtones, may be simultaneously excited in each star. The excitation energy of individual stars is distributed among permitted modes by nonlinear resonant coupling. In addition, rotational splitting of the nonradial modes can produce closely spaced periods which results in modulation of the light curve. Amplitude/spectral complexity correlation results from the appearance in the power spectrum of harmonics and cross-frequencies which are the effects brought on by increasing nonlinearity of the pulsations.

  20. Laser-induced periodic surface structuring of biopolymers

    NASA Astrophysics Data System (ADS)

    Pérez, Susana; Rebollar, Esther; Oujja, Mohamed; Martín, Margarita; Castillejo, Marta

    2013-03-01

    We report here on a systematic study about the formation of laser-induced periodic surface structures (LIPSS) on biopolymers. Self-standing films of the biopolymers chitosan, starch and the blend of chitosan with the synthetic polymer poly (vinyl pyrrolidone), PVP, were irradiated in air with linearly polarized laser beams at 193, 213 and 266 nm, with pulse durations in the range of 6-17 ns. The laser-induced periodic surface structures were topographically characterized by atomic force microscopy and the chemical modifications induced by laser irradiation were inspected via Raman spectroscopy. Formation of LIPSS parallel to the laser polarization direction, with periods similar to the laser wavelength, was observed at efficiently absorbed wavelengths in the case of the amorphous biopolymer chitosan and its blend with PVP, while formation of LIPSS is prevented in the crystalline starch biopolymer.

  1. A Fundamental Study of Heat Transfer Phenomenon in Periodic Structures

    DTIC Science & Technology

    2012-11-09

    household radiators or electric heaters, furnaces, combustion chambers, fires, rocket nozzles , power plants, engines etc. The importance of radiation...can be applied to any other problem related to the wave propagation through periodic structures such as acoustic wave and ultrasonic wave propagation

  2. High-throughput patterning of photonic structures with tunable periodicity

    PubMed Central

    Kempa, Thomas J.; Bediako, D. Kwabena; Kim, Sun-Kyung; Park, Hong-Gyu; Nocera, Daniel G.

    2015-01-01

    A patterning method termed “RIPPLE” (reactive interface patterning promoted by lithographic electrochemistry) is applied to the fabrication of arrays of dielectric and metallic optical elements. This method uses cyclic voltammetry to impart patterns onto the working electrode of a standard three-electrode electrochemical setup. Using this technique and a template stripping process, periodic arrays of Ag circular Bragg gratings are patterned in a high-throughput fashion over large substrate areas. By varying the scan rate of the cyclically applied voltage ramps, the periodicity of the gratings can be tuned in situ over micrometer and submicrometer length scales. Characterization of the periodic arrays of periodic gratings identified point-like and annular scattering modes at different planes above the structured surface. Facile, reliable, and rapid patterning techniques like RIPPLE may enable the high-throughput and low-cost fabrication of photonic elements and metasurfaces for energy conversion and sensing applications. PMID:25870280

  3. Localization of acoustic modes in periodic porous silicon structures

    PubMed Central

    2014-01-01

    The propagation of longitudinal acoustic waves in multilayer structures based on porous silicon and the experimental measurement of acoustic transmission for the structures in the gigahertz range are reported and studied theoretically. The considered structures exhibit band gaps in the transmission spectrum and these are localized modes inside the band gap, coming from defect layers introduced in periodic systems. The frequency at which the acoustic resonances appear can be tuned by changing the porosity and/or thickness of the defect layer. PMID:25206317

  4. A periodic table of coiled-coil protein structures.

    PubMed

    Moutevelis, Efrosini; Woolfson, Derek N

    2009-01-23

    Coiled coils are protein structure domains with two or more alpha-helices packed together via interlacing of side chains known as knob-into-hole packing. We analysed and classified a large set of coiled-coil structures using a combination of automated and manual methods. This led to a systematic classification that we termed a "periodic table of coiled coils," which we have made available at http://coiledcoils.chm.bris.ac.uk/ccplus/search/periodic_table. In this table, coiled-coil assemblies are arranged in columns with increasing numbers of alpha-helices and in rows of increased complexity. The table provides a framework for understanding possibilities in and limits on coiled-coil structures and a basis for future prediction, engineering and design studies.

  5. Table of periodic properties of fullerenes based on structural parameters.

    PubMed

    Torrens, Francisco

    2004-01-01

    The periodic table (PT) of the elements suggests that hydrogen could be the origin of everything else. The construction principle is an evolutionary process that is formally similar to those of Darwin and Oparin. The Kekulé structure count and permanence of the adjacency matrix of fullerenes are related to structural parameters involving the presence of contiguous pentagons p, q and r. Let p be the number of edges common to two pentagons, q the number of vertices common to three pentagons, and r the number of pairs of nonadjacent pentagon edges shared between two other pentagons. Principal component analysis (PCA) of the structural parameters and cluster analysis (CA) of the fullerenes permit classifying them and agree. A PT of the fullerenes is built based on the structural parameters, PCA and CA. The periodic law does not have the rank of the laws of physics. (1) The properties of the fullerenes are not repeated; only, and perhaps, their chemical character. (2) The order relationships are repeated, although with exceptions. The proposed statement is the following: The relationships that any fullerene p has with its neighbor p + 1 are approximately repeated for each period.

  6. Optimal ground motion intensity measure for long-period structures

    NASA Astrophysics Data System (ADS)

    Guan, Minsheng; Du, Hongbiao; Cui, Jie; Zeng, Qingli; Jiang, Haibo

    2015-10-01

    This paper aims to select the most appropriate ground motion intensity measure (IM) that is used in selecting earthquake records for the dynamic time history analysis of long-period structures. For this purpose, six reinforced concrete frame-core wall structures, designed according to modern seismic codes, are studied through dynamic time history analyses with a set of twelve selected earthquake records. Twelve IMs and two types of seismic damage indices, namely, the maximum seismic response-based and energy-based parameters, are chosen as the examined indices. Selection criteria such as correlation, efficiency, and proficiency are considered in the selection process. The optimal IM is identified by means of a comprehensive evaluation using a large number of data of correlation, efficiency, and proficiency coefficients. Numerical results illustrate that peak ground velocity is the optimal one for long-period structures and peak ground displacement is also a close contender. As compared to previous reports, the spectral-correlated parameters can only be taken as moderate IMs. Moreover, the widely used peak ground acceleration in the current seismic codes is considered inappropriate for long-period structures.

  7. Steady state solutions to dynamically loaded periodic structures

    NASA Technical Reports Server (NTRS)

    Kalinowski, A. J.

    1980-01-01

    The general problem of solving for the steady state (time domain) dynamic response (i.e., NASTRAN rigid format-8) of a general elastic periodic structure subject to a phase difference loading of the type encountered in traveling wave propagation problems was studied. Two types of structural configurations were considered; in the first type, the structure has a repeating pattern over a span that is long enough to be considered, for all practical purposes, as infinite; in the second type, the structure has structural rotational symmetry in the circumferential direction. The theory and a corresponding set of DMAP instructions which permits the NASTRAN user to automatically alter the rigid format-8 sequence to solve the intended class of problems are presented. Final results are recovered as with any ordinary rigid format-8 solution, except that the results are only printed for the typical periodic segment of the structure. A simple demonstration problem having a known exact solution is used to illustrate the implementation of the procedure.

  8. Graded period multilayer structures for X-ray optics

    NASA Astrophysics Data System (ADS)

    Biltoft, P. J.; Falabella, S.; Pombo, R. F.; Noble, E. H.

    1993-01-01

    Our goal for FY 91 was to develop the capability to deposit multilayer thin film coatings of prescribed period gradient onto planar and figured substrates. To accomplish this goal we have extended our use of deposition flux masking to create laterally graded multilayer coatings. In addition, we have constructed a planetary substrate rotation fixture for deposition of axisymmetric graded thickness multilayer structures on planar and figured optics. Materials combinations for the layered synthetic microstructures (LSM's) we have fabricated by these techniques include: tungsten/carbon, molybdenum/silicon, molybdenum disilicide/silicon and chromium carbide/carbon. Soft X-ray diffraction characterization of the LSM's has verified that we have deposited controlled thickness graded period structures.

  9. Periodic Cellular Structure Technology for Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Chen, Edward Y.

    2015-01-01

    Shape memory alloys are being considered for a wide variety of adaptive components for engine and airframe applications because they can undergo large amounts of strain and then revert to their original shape upon heating or unloading. Transition45 Technologies, Inc., has developed an innovative periodic cellular structure (PCS) technology for shape memory alloys that enables fabrication of complex bulk configurations, such as lattice block structures. These innovative structures are manufactured using an advanced reactive metal casting technology that offers a relatively low cost and established approach for constructing near-net shape aerospace components. Transition45 is continuing to characterize these structures to determine how best to design a PCS to better exploit the use of shape memory alloys in aerospace applications.

  10. DFTB Parameters for the Periodic Table: Part 1, Electronic Structure.

    PubMed

    Wahiduzzaman, Mohammad; Oliveira, Augusto F; Philipsen, Pier; Zhechkov, Lyuben; van Lenthe, Erik; Witek, Henryk A; Heine, Thomas

    2013-09-10

    A parametrization scheme for the electronic part of the density-functional based tight-binding (DFTB) method that covers the periodic table is presented. A semiautomatic parametrization scheme has been developed that uses Kohn-Sham energies and band structure curvatures of real and fictitious homoatomic crystal structures as reference data. A confinement potential is used to tighten the Kohn-Sham orbitals, which includes two free parameters that are used to optimize the performance of the method. The method is tested on more than 100 systems and shows excellent overall performance.

  11. Locally resonant periodic structures with low-frequency band gaps

    NASA Astrophysics Data System (ADS)

    Cheng, Zhibao; Shi, Zhifei; Mo, Y. L.; Xiang, Hongjun

    2013-07-01

    Presented in this paper are study results of dispersion relationships of periodic structures composited of concrete and rubber, from which the frequency band gap can be found. Two models with fixed or free boundary conditions are proposed to approximate the bound frequencies of the first band gap. Studies are conducted to investigate the low-frequency and directional frequency band gaps for their application to engineering. The study finds that civil engineering structures can be designed to block harmful waves, such as earthquake disturbance.

  12. Calculation of electrostatic fields in periodic structures of complex shape

    NASA Technical Reports Server (NTRS)

    Kravchenko, V. F.

    1978-01-01

    A universal algorithm is presented for calculating electrostatic fields in an infinite periodic structure consisting of electrodes of arbitrary shape which are located in mirror-symmetrical manner along the axis of electron-beam propagation. The method is based on the theory of R-functions, and the differential operators which are derived on the basis of the functions. Numerical results are presented and the accuracy of the results is examined.

  13. Analysis of time-domain scattering by periodic structures

    NASA Astrophysics Data System (ADS)

    Gao, Yixian; Li, Peijun

    2016-11-01

    This paper is devoted to the mathematical analysis of a time-domain electromagnetic scattering by periodic structures which are known as diffraction gratings. The scattering problem is reduced equivalently into an initial-boundary value problem in a bounded domain by using an exact transparent boundary condition. The well-posedness and stability of the solution are established for the reduced problem. Moreover, a priori energy estimates are obtained with minimum regularity requirement for the data and explicit dependence on the time.

  14. Periodic barrier structure in AA-stacked bilayer graphene

    NASA Astrophysics Data System (ADS)

    Redouani, Ilham; Jellal, Ahmed

    2016-06-01

    We study the charge carriers transport in an AA-stacked bilayer graphene modulated by a lateral one-dimensional multibarrier structure. We investigate the band structures of our system, that is made up of two shifted Dirac cones, for finite and zero gap. We use the boundary conditions to explicitly determine the transmission probability of each individual cone (τ =+/- 1) for single, double and finite periodic barrier structure. We find that the Klein tunneling is only possible when the band structure is gapless and can occur at normal incidence as a result of the Dirac nature of the quasiparticles. We observe that the band structure of the barriers can have more than one Dirac points for finite periodic barrier. The resonance peaks appear in the transmission probability, which correspond to the positions of new cones index like associated with τ =+/- 1. Two conductance channels through different cones (τ =+/- 1) are found where the total conductance has been studied and compared to the cases of single layer and AB-stacked bilayer graphene.

  15. Microstructure and mechanical properties of neoprene montmorillonite nanocomposites

    NASA Astrophysics Data System (ADS)

    Yeh, Meng-Heng; Hwang, Weng-Sing; Cheng, Lin-Ri

    2007-03-01

    To investigate the microstructure and mechanical properties of neoprene-montmorillonite nanocomposite, three modified montmorillonite are used. An X-ray diffractometer is used to measure the corresponding change in d-spacing. Scanning electron microscopy is employed to investigate the morphology of the various composites. Transmission electron microscopy is employed to investigate the composite of montmorillonite and neoprene. The results indicate that the addition of montmorillonite enhances the mechanical properties of neoprene significantly.

  16. Characterization of electronic structure of periodically strained graphene

    DOE PAGES

    Aslani, Marjan; Garner, C. Michael; Kumar, Suhas; ...

    2015-11-03

    We induced periodic biaxial tensile strain in polycrystalline graphene by wrapping it over a substrate with repeating pillar-like structures with a periodicity of 600 nm. Using Raman spectroscopy, we determined to have introduced biaxial strains in graphene in the range of 0.4% to 0.7%. Its band structure was characterized using photoemission from valance bands, shifts in the secondary electron emission, and x-ray absorption from the carbon 1s levels to the unoccupied graphene conduction bands. It was observed that relative to unstrained graphene, strained graphene had a higher work function and higher density of states in the valence and conduction bands.more » Furthermore, we measured the conductivity of the strained and unstrained graphene in response to a gate voltage and correlated the changes in their behavior to the changes in the electronic structure. From these sets of data, we propose a simple band diagram representing graphene with periodic biaxial strain.« less

  17. Characterisation, in vitro release study, and antibacterial activity of montmorillonite-gentamicin complex material.

    PubMed

    Rapacz-Kmita, A; Bućko, M M; Stodolak-Zych, E; Mikołajczyk, M; Dudek, P; Trybus, M

    2017-01-01

    The present paper concerns the potential use of montmorillonite as a drug carrier and focusses on the intercalation of the studied clay with gentamicin (an aminoglycoside antibiotic) at various temperatures (20, 50 and 80°C). The experiments were performed to identify the temperature required for the optimum intercalation of gentamicin into the interlayer of montmorillonite. The structural and microstructural properties of gentamicin and the potential for introducing it between smectite clay layers were investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopic techniques, and SEM with EDS analysis. Additionally, the in vitro drug release behaviour of the montmorillonite-gentamicin complex and its antibacterial activity against Escherichia coli (E. coli) bacteria was investigated. Based on these studies, the impact of temperature on the intercalation of the drug between layers of smectite was evaluated. It was found that an intercalation temperature of 50°C resulted in the highest shift in the position of principle peak d(001) as measured by XRD, suggesting, that the greatest amount of gentamicin had been introduced into the interlayer space of montmorillonite at this temperature. Subsequently, the montmorillonite-gentamicin complex material obtained at 50°C revealed the greatest capacity for killing E. coli bacteria during an in vitro test.

  18. Periodization

    PubMed Central

    Lorenz, Daniel S.; Reiman, Michael P.; Walker, John C.

    2010-01-01

    Background: Clinicians are constantly faced with the challenge of designing training programs for injured and noninjured athletes that maximize healing and optimize performance. Periodization is a concept of systematic progression—that is, resistance training programs that follow predictable patterns of change in training variables. The strength training literature is abundant with studies comparing periodization schemes on uninjured, trained, and untrained athletes. The rehabilitation literature, however, is scarce with information about how to optimally design resistance training programs based on periodization principles for injured athletes. The purpose of this review is to discuss relevant training variables and methods of periodization, as well as periodization program outcomes. A secondary purpose is to provide an anecdotal framework regarding implementation of periodization principles into rehabilitation programs. Evidence Acquisition: A Medline search from 1979 to 2009 was implemented with the keywords periodization, strength training, rehabilitation, endurance, power, hypertrophy, and resistance training with the Boolean term AND in all possible combinations in the English language. Each author also undertook independent hand searching of article references used in this review. Results: Based on the studies researched, periodized strength training regimens demonstrate improved outcomes as compared to nonperiodized programs. Conclusions: Despite the evidence in the strength training literature supporting periodization programs, there is a considerable lack of data in the rehabilitation literature about program design and successful implementation of periodization into rehabilitation programs. PMID:23015982

  19. Crescent shaped dielectric periodic structure for light manipulation.

    PubMed

    Kurt, H; Turduev, M; Giden, I H

    2012-03-26

    We present optical properties of crescent-shaped dielectric nano-rods that comprise a square lattice periodic structure named as crescent-shaped photonic crystals (CPC). The circular symmetry of individual cells of periodic dielectric structures is broken by replacing each unit cell with a reduced symmetry crescent shaped structure. The created configuration is assumed to be formed by the intersection of circular dielectric and air rods. The degree of freedom to manipulate the light propagation arises due to the rotational sensitivity of the CPC. The interesting dispersion property of designed CPC occurs due to the anisotropic nature of the iso-frequency contours that yield tilted self-collimated wave guiding. Furthermore, this feature allows focusing, routing, splitting and deflecting light beams along certain routes which are independent of the lattice symmetry directions of regular PCs. The propagation direction of light can be tuned by means of the opening angle of the crescent shape. Finally, the property of being all-dielectric structure ensures the absence of optical absorption losses that are reminiscent of employed metallic nano-particles.

  20. GPS in pioneering dynamic monitoring of long-period structures

    USGS Publications Warehouse

    Celebi, M.; Sanli, A.

    2002-01-01

    Global Positioning System (GPS) technology with 10-20-Hz sampling rates allows scientifically justified dynamic measurements of relative displacements of long-period structures. The displacement response of a simulated tall building in real time and permanent deployment of GPS units at the roof of a building are described. To the authors' best knowledge, this is the first permanent deployment of GPS units (in the world) for continuous dynamic monitoring of a tall building. Data recorded from the building during a windy day is analyzed to determine the structural characteristics. When recorded during extreme motions caused by earthquakes and strong winds, such measurements can be used to compute average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the structural integrity and performance by establishing pre-established thresholds. Such information can be used to secure public safety and/or take steps to improve the performance of the building.

  1. Design of intelligent mesoscale periodic array structures utilizing smart hydrogel

    NASA Technical Reports Server (NTRS)

    Sunkara, H. B.; Penn, B. G.; Frazier, D. O.; Weissman, J. M.; Asher, S. A.

    1996-01-01

    Mesoscale Periodic Array Structures (MPAS, also known as crystalline colloidal arrays), composed of aqueous or nonaqueous dispersions of self-assembled submicron colloidal spheres are emerging toward the development of advanced optical devices for technological applications. This is because of their unique optical diffraction properties and the ease with which these intriguing properties can be modulated experimentally. Moreover our recent advancements in this area which include 'locking' the liquid MPAS into solid or semisolid polymer matrices for greater stability with longer life span, and incorporation of CdS quantum dots and laser dyes into colloidal spheres to obtain nonlinear optical (NLO) responses further corroborate the use of MPAS in optical technology. Our long term goal is fabrication of all-optical and electro-optical devices such as spatial light modulators for optical signal processing and flat panel display devices by utilizing intelligent nonlinear periodic array structural materials. Here we show further progress in the design of novel linear MPAS which have the ability to sense and respond to an external source such as temperature. This is achieved by combining the self-assembly properties of polymer colloidal spheres and thermoshrinking properties of smart polymer gels. At selected temperatures the periodic array efficiently Bragg diffracts light and transmits most of the light at other temperatures. Hence these intelligent systems are of potential use as fixed notch filters optical switches or limiters to protect delicate optical sensors from high intensity laser radiation.

  2. Radiation from relativistic electron beams in periodic structures

    SciTech Connect

    Babzien, M.; Batchelor, K.; Ben-Zvi, I.

    1995-12-31

    We present an experimental study of emission of radiation from relativistic electrons in a novel periodic structure. The MIT microwiggler is a pulsed ferromagnetic-core electromagnet consisting of 70 periods of 8.8 mm periodicity, generating an on-axis peak magnetic field of 4.2 kG. Each field pea in independently tunable. We employed a novel tuning scheme to reduce the RMS spread in the peak amplitudes to 0.08%, the lowest ever attained in a sub-cm magnetic field. A high brightness, 40 MeV pulsed electron beam produced by the LINAC at the Accelerator Test Facility at Brookhaven National Laboratory was injected into the short period wiggler and visible spontaneous emission was produced. Spectral density profiles were measured and the measured peak wavelength was shown to vary appropriately with beam energy. It is shown that the principal spectral broadening mechanisms are longitudinal energy spread in the electron beam and off-axis emission. Further work is planned at 50 MeV.

  3. Tunable multichannel absorber composed of graphene and doped periodic structures

    NASA Astrophysics Data System (ADS)

    Kong, Xiang-kun; Shi, Xiang-zhu; Mo, Jin-jun; Fang, Yun-tuan; Chen, Xin-lei; Liu, Shao-bin

    2017-01-01

    A new design for a tunable multichannel compact absorber, which is achieved by using an asymmetric photonic crystal with graphene monolayers, is theoretically proposed. The graphene monolayers are periodically embedded into the first and last dielectric layers. The absorption, reflection, and transmission spectra of the absorber are studied numerically. A perfect absorption channel is achieved because of impedance matching, and channel number can be modulated by changing periodic number. The characteristic properties of the absorption channel depend on graphene conductivity, which can be controlled via the gate voltage. The proposed structure works as a perfect absorber that is independent from polarization. It has potential applications in the design of multichannel filters, thermal detectors, and electromagnetic wave energy collectors.

  4. Fractionation of humic acids upon adsorption on montmorillonite and palygorskite

    NASA Astrophysics Data System (ADS)

    Alekseeva, T. V.; Zolotareva, B. N.

    2013-06-01

    The adsorption of three humic acid (HA) preparations by clays—montmorillonite (Wyoming, USA) and palygorskite (Kolomenskoe district, Moscow oblast)—has been studied. The HA preparations were isolated from samples of the humus-accumulative horizons of a leached chernozem (Voronezh) and a chestnut soil (Volgograd), and a commercial preparation of sodium humate (Aldrich) was also used. The solid-state 13C NMR spectroscopy and IR spectroscopy revealed the selective adsorption of structural HA fragments (alkyls, O-alkyls (carbohydrates), and acetal groups) on these minerals. As a result, the aromaticity of the organic matter (OM) in the organic-mineral complexes (OMCs) and the degree of its humification have been found to be lower compared to the original HA preparations. The fractionation of HAs is controlled by the properties of the mineral surfaces. The predominant enrichment of OMCs with alkyls has been observed for montmorillonite, as well as an enrichment with O-alkyls (carbohydrates) for palygorskite. A decrease in the C : N ratio has been noted in the elemental composition of the OM in complexes, which reflected its more aromatic nature and (or) predominant sorption of N-containing structural components of HA molecules. The adsorption of HA preparations by montmorillonite predominantly occurs on the external surface of mineral particles, and the interaction of nonpolar alkyl groups of HAs with this mineral belongs to weak (van der Waals, hydrophobic) interactions. The adsorption of HA preparations by palygorskite is at least partly of chemical nature: Si-OH groups of minerals are involved in the adsorption process. The formation of strong bonds between the OM and palygorskite explains the long-term (over 300 million years) retention of fossil fulvate-type OM in its complex with palygorskite, which we revealed previously.

  5. Efficient degradation of phenol using iron-montmorillonite as a Fenton catalyst: Importance of visible light irradiation and intermediates.

    PubMed

    Wei, Xipeng; Wu, Honghai; He, Guangping; Guan, Yufeng

    2017-01-05

    Iron-montmorillonite (Fe-Mt) with delaminated structures was synthesized via the introduction of iron oxides into Na-montmorillonite. Fe-Mt showed significant increases in the available iron content, surface area and pore volume, along with a slight increase in the basal spacing from d001=1.26 (Na-Mt) to 1.53nm (Fe-Mt). The Fenton process was efficient for phenol removal using Fe-Mt as a catalyst under visible light irradiation, and the process had two-stage pseudo-first order kinetics. The overall reaction had a higher degradation rate even when it was only irradiated with visible light for the first 40min period. Further investigation confirmed that the irradiation increased the presence of certain intermediates. Among them, 1,4-benzoquinone, hydroquinone, and catechol all enhanced the Fenton reaction rates. Either catechol or hydroquinone was added to the Fenton system with Fe-Mt/H2O2 with or without visible light irradiation, and they both accelerated phenol degradation because catechol and hydroquinone are capable of reductively and effectively transforming Fe(III) into Fe(II). The concentrations of dissolved total Fe increased with the increase in the oxalic acid concentration, which can strongly chelate Fe(III). Hence, iron was released from Fe-Mt, and reductive transformation played an important role in promoting the Fenton reaction process for phenol removal.

  6. Hybrid transfer-matrix FDTD method for layered periodic structures.

    PubMed

    Deinega, Alexei; Belousov, Sergei; Valuev, Ilya

    2009-03-15

    A hybrid transfer-matrix finite-difference time-domain (FDTD) method is proposed for modeling the optical properties of finite-width planar periodic structures. This method can also be applied for calculation of the photonic bands in infinite photonic crystals. We describe the procedure of evaluating the transfer-matrix elements by a special numerical FDTD simulation. The accuracy of the new method is tested by comparing computed transmission spectra of a 32-layered photonic crystal composed of spherical or ellipsoidal scatterers with the results of direct FDTD and layer-multiple-scattering calculations.

  7. Femtosecond laser-induced periodic surface structures on silica

    SciTech Connect

    Hoehm, S.; Rosenfeld, A.; Krueger, J.; Bonse, J.

    2012-07-01

    The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences ({tau} = 150 fs pulse duration, {lambda} = 800 nm center wavelength, temporal pulse separation {Delta}t < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL)] with different spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the 'dynamics' of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier dependence of the optical properties of fs-laser excited silica. This new approach provides an explanation of the LSFL orientation parallel to the laser beam polarisation in silica - as opposed to the behaviour of most other materials.

  8. Periodic orbits and shell structure in octupole deformed potentials

    SciTech Connect

    Heiss, W.D. ); Nazmitdinov, R.G. ); Radu, S. )

    1995-01-15

    The effect of an octupole term in a quadrupole deformed single-particle potential is studied from the classical and quantum-mechanical viewpoint. Whereas the problem is nonintegrable, the quantum-mechanical spectrum nevertheless shows some shell structure in the superdeformed prolate case for particular, yet fairly large octupole strengths; for spherical or oblate deformation the shell structure disappears. This result is associated with classical periodic orbits that are found by employing the removal of resonances method; this approximation method allows determination of the shape of the orbit and of the approximate octupole coupling strength for which it occurs. The validity of the method is confirmed by solving numerically the classical equations of motion. The quantum-mechanical shell structure is analyzed using the particle-number dependence of the fluctuating part of the total energy. In accordance with the classical result, this dependence turns out to be very similar for a superdeformed prolate potential plus octupole term and a hyperdeformed prolate potential without octupole term. In this way the shell structure is explained at least for some few hundred levels. The Fourier transform of the level density further corroborates these findings.

  9. Development of biodegradable foamlike materials based on casein and sodium montmorillonite clay

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biodegradable foamlike materials based on a naturally occurring polymer (casein protein) and sodium montmorillonite clay (Na+-MMT) were produced through a simple freeze-drying process. By utilizing DL-glyceraldehyde (GC) as a chemical cross-linking agent, the structural integrity of these new aeroge...

  10. Optimum design of structures subject to general periodic loads

    NASA Technical Reports Server (NTRS)

    Reiss, Robert; Qian, B.

    1989-01-01

    A simplified version of Icerman's problem regarding the design of structures subject to a single harmonic load is discussed. The nature of the restrictive conditions that must be placed on the design space in order to ensure an analytic optimum are discussed in detail. Icerman's problem is then extended to include multiple forcing functions with different driving frequencies. And the conditions that now must be placed upon the design space to ensure an analytic optimum are again discussed. An important finding is that all solutions to the optimality condition (analytic stationary design) are local optima, but the global optimum may well be non-analytic. The more general problem of distributing the fixed mass of a linear elastic structure subject to general periodic loads in order to minimize some measure of the steady state deflection is also considered. This response is explicitly expressed in terms of Green's functional and the abstract operators defining the structure. The optimality criterion is derived by differentiating the response with respect to the design parameters. The theory is applicable to finite element as well as distributed parameter models.

  11. Highly Nonlinear Wave Propagation in Elastic Woodpile Periodic Structures

    NASA Astrophysics Data System (ADS)

    Kim, E.; Li, F.; Chong, C.; Theocharis, G.; Yang, J.; Kevrekidis, P. G.

    2015-03-01

    In the present work, we experimentally implement, numerically compute with, and theoretically analyze a configuration in the form of a single column woodpile periodic structure. Our main finding is that a Hertzian, locally resonant, woodpile lattice offers a test bed for the formation of genuinely traveling waves composed of a strongly localized solitary wave on top of a small amplitude oscillatory tail. This type of wave, called a nanopteron, is not only motivated theoretically and numerically, but is also visualized experimentally by means of a laser Doppler vibrometer. This system can also be useful for manipulating stress waves at will, for example, to achieve strong attenuation and modulation of high-amplitude impacts without relying on damping in the system.

  12. GPS in dynamic monitoring of long-period structures

    USGS Publications Warehouse

    Celebi, M.

    2000-01-01

    Global Positioning System (GPS) technology with high sampling rates (??? 10 samples per second) allows scientifically justified and economically feasible dynamic measurements of relative displacements of long-period structures-otherwise difficult to measure directly by other means, such as the most commonly used accelerometers that require post-processing including double integration. We describe an experiment whereby the displacement responses of a simulated tall building are measured clearly and accurately in real-time. Such measurements can be used to assess average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the building performance during extreme motions caused by earthquakes and strong winds. By establishing threshold displacements or drift ratios and identifying changing dynamic characteristics, procedures can be developed to use such information to secure public safety and/or take steps to improve the performance of the building. Published by Elsevier Science Ltd.

  13. Carbon structures with three-dimensional periodicity at optical wavelengths

    PubMed

    Zakhidov; Baughman; Iqbal; Cui; Khayrullin; Dantas; Marti; Ralchenko

    1998-10-30

    Porous carbons that are three-dimensionally periodic on the scale of optical wavelengths were made by a synthesis route resembling the geological formation of natural opal. Porous silica opal crystals were sintered to form an intersphere interface through which the silica was removed after infiltration with carbon or a carbon precursor. The resulting porous carbons had different structures depending on synthesis conditions. Both diamond and glassy carbon inverse opals resulted from volume filling. Graphite inverse opals, comprising 40-angstrom-thick layers of graphite sheets tiled on spherical surfaces, were produced by surface templating. The carbon inverse opals provide examples of both dielectric and metallic optical photonic crystals. They strongly diffract light and may provide a route toward photonic band-gap materials.

  14. Coherence in ultrafast laser-induced periodic surface structures

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Colombier, Jean-Philippe; Li, Chen; Faure, Nicolas; Cheng, Guanghua; Stoian, Razvan

    2015-11-01

    Ultrafast laser irradiation can trigger anisotropically structured nanoscaled gratinglike arrangements of matter, the laser-induced periodic surface structures (LIPSSs). We demonstrate here that the formation of LIPSS is intrinsically related to the coherence of the laser field. Employing several test materials that allow large optical excursions, we observe the effect of randomizing spatial phase in generating finite domains of ripples. Using three-dimensional finite-difference time-domain methods, we evaluate energy deposition patterns below a material's rough surface and show that modulated pattern, i.e., a spatially ordered electromagnetic solution, results from the coherent superposition of waves. By separating the field scattered from a surface rough topography from the total field, the inhomogeneous energy absorption problem is reduced to a simple interference equation. We further distinguish the contribution of the scattered near field and scattered far field on various types of inhomogeneous energy absorption features. It is found that the inhomogeneous energy absorption which could trigger the low-spatial-frequency LIPSSs (LSFLs) and high-spatial-frequency LIPSSs (HSFLs) of periodicity Λ >λ /Re(n ˜) are due to coherent superposition between the scattered far field (propagation) and the refracted field, while HSFLs of Λ <λ /Re(n ˜) are triggered by coherent superposition between the scattered near field (evanescent) and the refracted field. This is a general scenario that involves a topography-induced scattering phenomenon and stationary evanescent fields, being applied to two model case materials that exhibit large optical excursions upon excitation (W, Si) and nonplasmonic to plasmonic transitions. We indicate the occurrence of a general light interference phenomenon that does not necessarily involve wavelike surface plasmonic excitation. Finally, we discuss the role of interference field and scattered field on the enhancement of LIPSSs by

  15. Mixed-layer kaolinite-montmorillonite from the Yucatan Peninsula, Mexico

    USGS Publications Warehouse

    Schultz, L.G.; Shepard, A.O.; Blackmon, P.D.; Starkey, H.C.

    1971-01-01

    Clay beds 1-2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite. Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers. The montmorillonite structural formulas average K0??2Na0??2Ca0??2Mg0??2(Al2??5Fe1??03+Mg0??5)(Al0??75Si7??25)O20+(OH)4-, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers. Nonexchangeable K+ indicates that a few layers are mica-like. Crystals are mostly round plates 1 10 to 1 20 ?? across. The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 A?? after heating at 300 ??C. The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins. ?? 1971.

  16. Spectroscopic study of the polymerization of intercalated anilinium ions in different montmorillonite clays

    NASA Astrophysics Data System (ADS)

    do Nascimento, Gustavo M.; Temperini, Marcia L. A.

    2011-09-01

    The polymerization of the intercalated aniline ions was studied in three different clays, Swy2-montmorillonite (MMT), synthetic mica-montmorillonite (Syn1) and pillarized Swy2-montmorillonite (PILC). PANI is formed between the MMT and Syn1 clay layers, being confirmed by the shift of d001 peak in the X-ray pattern. X-ray Absorption near to Si K edge (Si K XANES) data show that the structures of clays are preserved after the polymerization process and in addition to the SEM images show that morphologies of the clays are maintained after polymerization, indicating no polymerization in their external surface. UV-vis-NIR and resonance Raman data display that the PANI formed in Syn1 galleries has higher amount of phenazinic rings than observed for PANI intercalated in montmorillonite (MMT) clay. No polymer formation was detected in the PILC. N K XANES and EPR spectroscopies show the presence of azo and radical nitrogen in intercalated PANI chains. Hence, the results are rationalized considering the structural differences between the clays for understanding the role of the anilinium polymerization within the clays galleries.

  17. RF properties of periodic accelerating structures for linear colliders

    SciTech Connect

    Wang, J.W.

    1989-07-01

    With the advent of the SLAC electron-positron linear collider (SLC) in the 100 GeV center-of-mass energy range, research and development work on even higher energy machines of this type has started in several laboratories in the United States, Europe, the Soviet Union and Japan. These linear colliders appear to provide the only promising approach to studying e/sup /plus//e/sup /minus// physics at center-of-mass energies approaching 1 TeV. This thesis concerns itself with the study of radio frequency properties of periodic accelerating structures for linear colliders and their interaction with bunched beams. The topics that have been investigated are: experimental measurements of the energy loss of single bunches to longitudinal modes in two types of structures, using an equivalent signal on a coaxial wire to simulate the beam; a method of canceling the energy spread created within a single bunch by longitudinal wakefields, through appropriate shaping of the longitudinal charge distribution of the bunch; derivation of the complete transient beam-loading equation for a train of bunches passing through a constant-gradient accelerator section, with application to the calculation and minimization of multi-bunch energy spread; detailed study of field emission and radio frequency breakdown in disk-loaded structures at S-, C- and X-band frequencies under extremely high-gradient conditions, with special attention to thermal effects, radiation, sparking, emission of gases, surface damage through explosive emission and its possible control through RF-gas processing. 53 refs., 49 figs., 9 tabs.

  18. Mineralization of CO2 in hydrated calcium Montmorillonite

    NASA Astrophysics Data System (ADS)

    Yang, W.; Zaoui, A.

    2016-12-01

    We perform here a theoretical study based on both Monte Carlo and Molecular dynamic simulations in order to investigate CO2 mineral carbonation in hydrated calcium Montmorillonite (Ca-MMT). Thermodynamical, structural and dynamical properties have been evaluated in order to understand the mineral carbonation characteristics of CO2 in Ca-MMT. To simulate the behavior of CO2 through mineral carbonation, we consider calcium Montmorillonite clays at equilibrium with H2 O-CO2-H3O+- CO32- mixture under different hydration and different CO32- concentration. Radial distribution function results indicate that average calcium-oxygen (CO32-) distance is about 2.275 Å, which is rather short because of the charge attraction. These carbonation reactions produce the stable limestone. The carbonation energy for different CO32- concentrations is calculated at different temperatures varying from 280 K to 460 K, gradually with 20 K. The calculated diffusion coefficient indicates that the diffusion of calcium ions decreases with CO32- concentrations. Finally, the obtained mineralization energy was found in increase with carbonate concentration and burial depth.

  19. Montmorillonite, oligonucleotides, RNA and origin of life

    NASA Technical Reports Server (NTRS)

    Ertem, Gozen

    2004-01-01

    Na-montmorillonite prepared from Volclay by the titration method facilitates the self-condensation of ImpA, the 5'-phosphorimidazolide derivative of adenosine. As was shown by AE-HPLC analysis and selective enzymatic hydrolysis of products, oligo(A)s formed in this reaction are 10 monomer units long and contain 67% 3',5'-phosphodiester bonds (Ferris and Ertem, 1992a). Under the same reaction conditions, 5'-phosphorimidazolide derivatives of cytidine, uridine and guanosine also undergo self-condensation producing oligomers containing up to 12-14 monomer units for oligo(C)s to 6 monomer units for oligo(G)s. In oligo(C)s and oligo(U)s, 75-80% of the monomers are linked by 2',5'-phosphodiester bonds. Hexamer and higher oligomers isolated from synthetic oligo(C)s formed by montmorillonite catalysis, which contain both 3',5'- and 2',5'-linkages, serve as catalysts for the non-enzymatic template directed synthesis of oligo(G)s from activated monomer 2-MeImpG, guanosine 5'-phospho-2-methylimidazolide (Ertem and Ferris, 1996). Pentamer and higher oligomers containing exclusively 2',5'-linkages, which were isolated from the synthetic oligo(C)s, also serve as templates and produce oligo(G)s with both 2',5'- and 3',5'-phosphodiester bonds. Kinetic studies on montmorillonite catalyzed elongation rates of oligomers using the computer program SIMFIT demonstrated that the rate constants for the formation of oligo(A)s increased in the order of 2-mer < 3-mer < 4-mer ... < 7-mer (Kawamura and Ferris, 1994). A decameric primer, dA(pdA)8pA bound to montmorillonite was elongated to contain up to 50 monomer units by daily addition of activated monomer ImpA to the reaction mixture (Ferris, Hill and Orgel, 1996). Analysis of dimer fractions formed in the montmorillonite catalyzed reaction of binary and quaternary mixtures of ImpA, ImpC, 2-MeImpG and ImpU suggested that only a limited number of oligomers could have formed on the primitive Earth rather than equal amounts of all possible

  20. Montmorillonite, Oligonucleotides, RNA and Origin of Life

    NASA Astrophysics Data System (ADS)

    Ertem, Gözen

    2004-12-01

    Na-montmorillonite prepared from Volclay by the titration method facilitates the self-condensation of ImpA, the 5'-phosphorimidazolide derivative of adenosine. As was shown by AE-HPLC analysis and selective enzymatic hydrolysis of products, oligo(A)s formed in this reaction are 10 monomer units long and contain 67% 3',5'-phosphodiester bonds (Ferris and Ertem, 1992a). Under the same reaction conditions, 5'-phosphorimidazolide derivatives of cytidine, uridine and guanosine also undergo self-condensation producing oligomers containing up to 12-14 monomer units for oligo(C)s to 6 monomer units for oligo(G)s. In oligo(C)s and oligo(U)s, 75-80% of the monomers are linked by 2',5'-phosphodiester bonds. Hexamer and higher oligomers isolated from synthetic oligo(C)s formed by montmorillonite catalysis, which contain both 3',5'- and 2',5'-linkages, serve as catalysts for the non-enzymatic template directed synthesis of oligo(G)s from activated monomer 2-MeImpG, guanosine 5'-phospho-2-methylimidazolide (Ertem and Ferris, 1996). Pentamer and higher oligomers containing exclusively 2',5'-linkages, which were isolated from the synthetic oligo(C)s, also serve as templates and produce oligo(G)s with both 2',5'- and 3',5'-phosphodiester bonds. Kinetic studies on montmorillonite catalyzed elongation rates of oligomers using the computer program SIMFIT demonstrated that the rate constants for the formation of oligo(A)s increased in the order of 2-mer <3-mer <4-mer ... <7-mer (Kawamura and Ferris, 1994). A decameric primer, dA(pdA)8pA bound to montmorillonite was elongated to contain up to 50 monomer units by daily addition of activated monomer ImpA to the reaction mixture (Ferris, Hill and Orgel, 1996). Analysis of dimer fractions formed in the montmorillonite catalyzed reaction of binary and quaternary mixtures of ImpA, ImpC, 2-MeImpG and ImpU suggested that only a limited number of oligomers could have formed on the primitive Earth rather than equal amounts of all possible isomers

  1. Montmorillonite Dissolution in Simulated Lung Fluids

    NASA Astrophysics Data System (ADS)

    Schmidt, M.; Wendlandt, R. F.

    2008-12-01

    Because lung fluids" first interaction is with the surface of inhaled grains, the surface properties of inhaled mineral dusts may have a generally mitigating effect on cytotoxicity and carcinogenicity. Wendlandt et al. (Appl. Geochem. 22, 2007) investigated the surface properties of respirable-sized quartz grains in bentonites and recognized pervasive montmorillonite surface coatings on silica grains. The purpose of this study was to determine the dissolution rate and biodurability of montmorillonite in simulated lung fluids and to assess its potential to mitigate silica cytotoxicity. Modified batch reaction experiments were conducted on purified and size fractionated calcic (SAz-2; 0.4-5 μm) and sodic (DC-2; 0.4-2 μm) montmorillonites for 120 to 160 days of reaction time at 37°C in both simulated extracellular lung fluid (Lu) and simulated lysosomal fluid (Ly). Modified batch experiments simulated a flow-through setup and minimized sample handling difficulties. Reacted Lu and Ly fluid was analyzed for Mg, Al, and Si on an ICP-OE spectrometer. Steady state dissolution was reached 90-100 days after the start of the experiment and maintained for 40-60 days. Measured montmorillonite dissolution rates based on BET surface areas and Si steady state release range from 4.1x10-15 mol/m2/s at the slowest to 1.0x10-14 mol/m2/s at the fastest with relative uncertainties of less than 10%. Samples reacting in Ly (pH = 4.55) dissolved faster than those in Lu (pH = 7.40), and DC-2 dissolved faster than SAz-2. The measured range of biodurabilities was 1,300 to 3,400 years for a 1 μm grain assuming a spherical volume and a molar volume equal to that of illite. The difference in salinities of the two fluids was too slight to draw conclusions about the relationship of ionic strength to dissolution rate. Results indicate that montmorillonite dissolution is incongruent and edge controlled. Dissolution rates for DC- 2 and SAz-2 clays were comparable to those reported in the

  2. Silver bromide in montmorillonite as visible light-driven photocatalyst and the role of montmorillonite

    NASA Astrophysics Data System (ADS)

    Sohrabnezhad, Sh.; Pourahmad, A.; Razavi, M.

    2016-09-01

    In this study, novel plasmonic photocatalyst, Ag/AgBr-montmorillonite (MMT) nanocomposite, was prepared by dispersion method and light irradiation. The structure, composition and optical properties of such material was investigated by transmission electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The powder X-ray diffraction showed intercalation of Ag/AgBr nanoparticles into the clay interlayer space. The results showed that the prepared sample has a similar phase composition. However, their photocatalytic activity varied significantly. The photocatalytic testing result showed that the Ag/AgBr-MMT nanocomposite was more efficient photocatalyst in the discoloration of methylene blue under visible light illumination. The Ag/AgBr-MMT nanocomposite in pH = 2 and under visible light degraded 92 % of dye at the irradiation time of 20 min. MMT as matrix showed excellent role in separation efficiency of electron-hole pairs. The mechanism of separation of the photogenerated electrons and holes at the Ag/AgBr-MMT nanocomposite was discussed.

  3. S4 : A free electromagnetic solver for layered periodic structures

    NASA Astrophysics Data System (ADS)

    Liu, Victor; Fan, Shanhui

    2012-10-01

    We describe S4, a free implementation of the Fourier modal method (FMM), which has also been commonly referred to as rigorous coupled wave analysis (RCWA), for simulating electromagnetic propagation through 3D structures with 2D periodicity. We detail design aspects that allow S4 to be a flexible platform for these types of simulations. In particular, we highlight the ability to select different FMM formulations, user scripting, and extensibility of program capabilities for eigenmode computations. Program summary Program title: S4 Catalogue identifier: AEMO_v1_0. Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEMO_v1_0..html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 2 No. of lines in distributed program, including test data, etc.: 56910 No. of bytes in distributed program, including test data, etc.: 433883 Distribution format: Programming language: C, C++. Computer: Any computer with a Unix-like environment and a C++ compiler. Developed on 2.3 GHz AMD Phenom 9600. Operating system: Any Unix-like environment; developed under MinGW32 on Windows 7. Has the code been vectorized or parallelized?: Yes. Parallelized using MPI. RAM: Problem dependent (linearly proportional to number of layers and quadratic in number of Fourier components). A single layer calculation with approximately 100 Fourier components uses approximately 10 MB. Classification: 10. Electrostatics and Electromagnetics. External routines: Lua [1] and optionally exploits additional free software packages: FFTW [2], CHOLMOD [3], MPI message-passing interface [4], LAPACK and BLAS linear-algebra software [5], and Kiss FFT [6]. Nature of problem: Time-harmonic electromagnetism in layered bi-periodic structures. Solution method: The Fourier modal method (rigorous coupled wave analysis) and the scattering matrix method. Running time: Problem dependent and highly dependent on quality of the BLAS

  4. Periodic changes in the compact radio structure of SS 433

    NASA Technical Reports Server (NTRS)

    Niell, A. E.; Preston, R. A.; Lockhart, T. G.

    1981-01-01

    VLBI observations of SS 433 at 2.3 GHz made on 12 days between 1979 May and 1980 August yield the following results: (a) the position angle of the radio 'jet' of angular size of about 0.1 arcsec varies approximately sinusoidally about a mean value of 100.2 + or - 1.7 deg with an amplitude of 19.3 + or - 3.4 deg for a period fixed at 163.6 days. This resolves the ambiguity in the two angles of the optical model of Abell and Margon and assigns the inclination of the axis of the precession cone to the 79 deg value; (b) the position angle of the radio structure on this scale lags that of the optical model by 17.4 + or - 1.6 days; and (c) at least some of the radio emitting material appears to propagate away from the core in blobs. Using the rate of change of angular separation of the blobs from the core obtained from measurements on four different days, and assuming that the radio emission is traveling at the speed derived for the optical jets from the kinematic model, a distance to SS 433 of 5.1 + or - 0.5 kpc is obtained.

  5. Further work on sodium montmorillonite as catalyst for the polymerization of activated amino acids

    NASA Technical Reports Server (NTRS)

    Eirich, F. R.; Paecht-Horowitz, M.

    1986-01-01

    When the polycondensation of amino acid acylates was catalyzed with Na-montmorillonite, the polypeptides were consistently found to exhibit a distribution of discrete molecular weights, for as yet undiscovered reasons. One possible explanation was connected to the stepwise mode of monomer addition. New experiments have eliminated this possibility, so that there is the general assumption that this discreteness is the result of a preference of shorter oligomers to add to others of the same length, a feature that could be attributed to some structure of the platelet aggregates of the montmorillonite. The production of optical stereoisomers is anticipated when D,L-amino acids are polymerized on montmorillonite. Having used an optically active surface, the essence of the results lies not only in the occurrence of optically active oligomers and polymers, but also in the fact that the latter exhibit the same molecular weight characteristics as the D,L-polymers. Preparatory to work contemplated on a parallel synthesis of amino acid and nucleotide oligomers, studies were continued on the co-adsorption of amino acids, nucleotides, and amino acid-nucleotides on montmorillonite.

  6. Preparation and Characterization of Novel Montmorillonite Nanocomposites

    NASA Astrophysics Data System (ADS)

    Mansa, Rola

    Clay minerals have historically played a consequential role in human health. While the beginnings were rooted in geophagy, a primitive act of consuming earth, the health-related uses of clay minerals have evolved and diversified over time.. As excipients in pharmaceutical formulations, clay minerals can attribute novel properties onto intercalated compounds. Intercalating oxybenzone, a UV filter, within the interlamellar space of montmorillonite is desirable in order to minimize direct contact with skin. Intercalating resveratrol, a compound known for attributing beneficial effects onto human health, may be advantageous since this compound is susceptible to cis-trans isomerisation. The strategy of using alkylammonium--modified clay was undertaken and proved successful for the intercalation of oxybenzone. The field of biopolymer/layered silicate nanocomposites is heavily researched for use in a multitude of applications. Novel montmorillonite nanocomposites were prepared with neutral guar gum and cationic guar gum, using an environmentally friendly process and are fully characterized.

  7. Simultaneous and sequential adsorption of crystal violet and 2-naphthol onto montmorillonite: a microstructural and thermodynamic study.

    PubMed

    Zhu, Jianxi; Wei, Jingming; Zhu, Runliang; Qing, Yanhong; Ge, Fei; Yuan, Peng; He, Hongping

    2010-01-01

    Thermodynamic analysis of simultaneous and sequential adsorption of crystal violet (CV) and 2-naphthol adsorption on montmorillonite has been conducted, and the changes of microstructure of the clay after adsorption were investigated using X-ray diffraction (XRD). The basal spacing and structural order of CV and 2-naphthol adsorbed montmorillonites varied with different CV loadings. In principle, larger basal spacing was resulted from a higher loading of CV in montmorillonites. The excellent structural order of the resultant hybrids is achieved in samples with 0.50-0.75 CEC (cation exchange capacity) loadings of CV. The effects of temperature and ionic strength on the adsorption of CV and 2-naphthol on montmorillonite were also investigated. The Freundlich isotherm model was applied for curve-fitting of the equilibrium isotherm data. The resulting thermodynamics parameters suggested that the sorption process was a spontaneous exothermic process in the case of low CV concentrations. The negative values of Gibbs free energy in all of the adsorption processes indicated that these processes are spontaneous processes. With the increase of CV concentration, the sequential adsorption of 2-naphthol onto montmorillonite proved to be an endothermic process.

  8. Synthesis of silver/montmorillonite nanocomposites using γ-irradiation

    PubMed Central

    Shameli, Kamyar; Ahmad, Mansor Bin; Yunus, Wan Md Zin Wan; Ibrahim, Nor Azowa; Gharayebi, Yadollah; Sedaghat, Sajjad

    2010-01-01

    Silver nanoparticles (Ag-NPs) were synthesized into the interlamellar space of montmorillonite (MMT) by using the γ-irradiation technique in the absence of any reducing agent or heat treatment. Silver nitrate and γ-irradiation were used as the silver precursor and physical reducing agent in MMT as a solid support. The MMT was suspended in the aqueous AgNO3 solution, and after the absorption of silver ions, Ag+ was reduced using the γ-irradiation technique. The properties of Ag/MMT nanocomposites and the diameters of Ag-NPs were studied as a function of γ-irradiation doses. The interlamellar space limited particle growth (d-spacing [ds] = 1.24–1.42 nm); powder X-ray diffraction and transmission electron microscopy (TEM) measurements showed the production of face-centered cubic Ag-NPs with a mean diameter of about 21.57–30.63 nm. Scanning electron microscopy images indicated that there were structure changes between the initial MMT and Ag/MMT nanocomposites under the increased doses of γ-irradiation. Furthermore, energy dispersive X-ray fluorescence spectra for the MMT and Ag/ MMT nanocomposites confirmed the presence of elemental compounds in MMT and Ag-NPs. The results from ultraviolet-visible spectroscopy and TEM demonstrated that increasing the γ-irradiation dose enhanced the concentration of Ag-NPs. In addition, the particle size of the Ag-NPs gradually increased from 1 to 20 kGy. When the γ-irradiation dose increased from 20 to 40 kGy, the particle diameters decreased suddenly as a result of the induced fragmentation of Ag-NPs. Thus, Fourier transform infrared spectroscopy suggested that the interactions between Ag-NPs with the surface of MMT were weak due to the presence of van der Waals interactions. The synthesized Ag/MMT suspension was found to be stable over a long period of time (ie, more than 3 months) without any sign of precipitation. PMID:21170354

  9. Geochemical studies of clay minerals III. The determination of free silica and free alumina in montmorillonites

    USGS Publications Warehouse

    Foster, M.D.

    1953-01-01

    Determination of free silica by the method proposed made possible the derivation of logical formulas for several specimens of montmorillonites for which the formulas could not be derived from the analyses alone. Other montmorillonites, for which logical formulas could be derived from their analyses, were found to contain small amounts of free silica or free alumina. Others were found to contain neither free silica nor free alumina. The method consists of the following steps: (1) digestion of 1 g of the specimen with 0.5 N NaOH solution in a covered platinum crucible or dish on a steam bath for 4 hrs, stirring the mixture at 30-min intervals, (2) filtration of the undissolved material, followed by washing several times with 1% NaOH solution, (3) neutralization of the filtrate with HCl, addition of 5 ml HCl in excess and determination of SiO and Al2O3 in the usual way and (4) calculation of the amount of free SiO2 or free Al2O3 if any and the amount of attack of the clay structure by the treatment from the ratio of SiO2 to Al2O3 dissolved and the ratio of SiO2 to Al2O3 obtained on analysis. Tests with 5% Na2CO3 solution, the reagent formerly used for the solution of free SiO2 in rocks and minerals, showed that solution of opal by this reagent is always fractional, never complete, no matter how small the amount present or how long the period of treatment. Re-treatment of the sample results in 90-95% solution if 10 mg or less of opal is present, but for larger amounts of opal the percentage dissolved decreases as the amount present increases. On the other hand, 75 ml of 0.5 N NaOH completely dissolves as much as 400 mg of opal in 4 hrs digestion in a covered platinum crucible or dish, on a steam bath. However, a weaker solution or a shorter period of digestion does not effect complete solution. The same amount (75 ml) of 0.5 N NaOH also dissolves 90 mg of cristobalite and 57 mg of quartz having a grain size of less than 2 microns. Use of NaOH also permits determination

  10. Surface catalyzed oxidative oligomerization of 17β-estradiol by Fe(3+)-saturated montmorillonite.

    PubMed

    Qin, Chao; Troya, Diego; Shang, Chao; Hildreth, Sherry; Helm, Rich; Xia, Kang

    2015-01-20

    With widespread detection of endocrine disrupting compounds including hormones in wastewater, there is a need to develop cost-effective remediation technologies for their removal from wastewater. Previous research has shown that Fe(3+)-saturated montmorillonite is effective in quickly transforming phenolic organic compounds such as pentachlorophenol, phenolic acids, and triclosan via surface-catalyzed oligomerization. However, little is known about its effectiveness and reaction mechanisms when reacting with hormones. In this study, the reaction kinetics of Fe(3+)-saturated montmorillonite catalyzed 17β-estradiol (βE2) transformation was investigated. The transformation products were identified using liquid chromatography coupled with mass spectrometry, and their structures were further confirmed using computational approach. Rapid βE2 transformation in the presence of Fe(3+)-saturated montmorillonite in an aqueous system was detected. The disappearance of βE2 follows first-order kinetics, while the overall catalytic reaction follows the second-order kinetics with an estimated reaction rate constant of 200 ± 24 (mmol βE2/g mineral)(−1) h(–1). The half-life of βE2 in this system was estimated to be 0.50 ± 0.06 h. βE2 oligomers were found to be the major products of βE2 transformation when exposed to Fe(3+)-saturated montmorillonite. About 98% of βE2 were transformed into βE2 oligomers which are >10(7) times less water-soluble than βE2 and, therefore, are much less bioavailable and mobile then βE2. The formed oligomers quickly settled from the aqueous phase and were not accumulated on the reaction sites of the interlayer surfaces of Fe(3+)-saturated montmorillonite, the major reason for the observed >84% βE2 removal efficiency even after five consecutive usages of the same of Fe(3+)-saturated montmorillonite. The results from this study clearly demonstrated that Fe(3+)-saturated montmorillonite has a great potential to be used as a cost

  11. Understanding Periodicity as a Process with Gestalt Structure.

    ERIC Educational Resources Information Center

    Shama, Gilli

    1998-01-01

    Presents a two-phase investigation of how Israeli students understand the concept of periodicity. Discusses related research with teachers and students (N=895) employing both qualitative and quantitative research methodologies. Concludes that students understand periodicity as a process. Students' errors and preferences are discussed with…

  12. Desorption of plutonium from montmorillonite: An experimental and modeling study

    NASA Astrophysics Data System (ADS)

    Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

    2017-01-01

    Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. We evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with Kd values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in Kd, indicating that true sorption equilibrium was not achieved within the first 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. A conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50-100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.

  13. Desorption of plutonium from montmorillonite: An experimental and modeling study

    DOE PAGES

    Begg, James D.; Zavarin, Mavrik; Kersting, Annie B.

    2017-01-15

    Desorption of plutonium (Pu) will likely control the extent to which it is transported by mineral colloids. In this article, we evaluated the adsorption/desorption behavior of Pu on SWy-1 montmorillonite colloids at pH 4, pH 6, and pH 8 using batch adsorption and flow cell desorption experiments. After 21 days adsorption, Pu(IV) affinity for montmorillonite displayed a pH dependency, with Kd values highest at pH 4 and lowest at pH 8. The pH 8 experiment was further allowed to equilibrate for 6 months and showed an increase in Kd, indicating that true sorption equilibrium was not achieved within the firstmore » 21 days. For the desorption experiments, aliquots of the sorption suspensions were placed in a flow cell, and Pu-free solutions were then pumped through the cell for a period of 12 days. Changes in influent solution flow rate were used to investigate the kinetics of Pu desorption and demonstrated that it was rate-limited over the experimental timescales. At the end of the 12-day flow cell experiments, the extent of desorption was again pH dependent, with pH 8 > pH 6 > pH 4. Further, at pH 8, less Pu was desorbed after an adsorption contact time of 6 months than after a contact time of 21 days, consistent with an aging of Pu on the clay surface. In addition, a conceptual model for Pu adsorption/desorption that incorporated known surface-mediated Pu redox reactions was used to fit the experimental data. The resulting rate constants indicated processes occurring on timescales of months and even years which may, in part, explain observations of clay colloid-facilitated Pu transport on decadal timescales. Importantly, however, our results also imply that migration of Pu adsorbed to montmorillonite colloids at long (50–100 year) timescales under oxic conditions may not be possible without considering additional phenomena, such as co-precipitation.« less

  14. Broadband electromagnetic analysis of dispersive, periodic structures for radiometer calibration

    NASA Astrophysics Data System (ADS)

    Sandeep, S.

    This thesis primarily focusses on the full wave electromagnetic analysis of radiometer calibration targets using doubly dispersive 3D Finite Difference Time Domain (FDTD) formulation. The boundary conditions are set up to solve for doubly periodic structures. The thesis contains very detailed derivation and equations regarding this formulation. One of the novelty in this formulation is the handling of magnetically and electrically dispersive media (usually it is just the electrical dispersion which is incorporated). Using a custom developed code which can be run on a distributed computing system, the reflectivity spectrum of calibration targets of different geometries, coating thicknesses and aspect ratios are analyzed. The results are well validated using commercial simulation softwares and custom Geometric Optics (GO) code. The geometries analyzed include square pyramids, conical pyramids, truncated square pyramids and truncated conical pyramids with spherical top. The coating thicknesses used are 1 mm, 2 mm and 3 mm. The aspect ratios (ratio of base to height) used include 1 : 1, 1 : 2 and 1 : 4. The nominal target structure has 1 : 4 aspect ratio and 2mm coating thickness. The material used for simulation is ECCOSORB MF112. The material properties of other materials such as MF110 and MF114 are listed. It should be remarked that measured material properties are available only in the frequency range [8, 26] GHz and a Debye series extrapolation was used for simulation at frequencies outside this range. Throughout this work 0.5 inch base was used. Some significant conclusions include the following: (1) 1:4 aspect ratio or better is required to achieve a -50 dB reflectivity or lower. (2) Low frequency reflectivity is independent of the target geometry. (3) At high frequencies, the conical target results in better performance when compared to square pyramids (by about 10 dB). (4) The reflectivity spectrum exhibits a general trend of high reflectivity at low

  15. Preparation and characterization of antibacterial silver/vermiculites and silver/montmorillonites

    NASA Astrophysics Data System (ADS)

    Valášková, Marta; Hundáková, Marianna; Kutláková, Kateřina Mamulová; Seidlerová, Jana; Čapková, Pavla; Pazdziora, Erich; Matějová, Kateřina; Heřmánek, Martin; Klemm, Volker; Rafaja, David

    2010-11-01

    The reason for the preparation and characterization of the novel antibacterial silver/vermiculites (Ag/V) together with the silver/montmorillonites (Ag/M) was that the information on the vermiculite structure change and stability of Ag/V in water as well as its effect on bacteria are sporadic. The vermiculite (V), (Si 3.02Al 0.98) IV (Mg 2.27Al 0.12Fe0.283+Fe0.052+Ti 0.07) VI O 10(OH) 2 Ca 0.09Na 0.21K 0.50 from West China and montmorillonite (M), (Si 3.96Al 0.04) IV (Al 1.20Fe0.343+Mg 0.42Ti 0.02) VI O 10 (OH) 2Ca 0.15Na 0.14K 0.08 from Ivančice (Czech Republic), fraction <0.4 μm were the starting clay materials for sample preparation. The samples V1 and M1 were prepared via reaction of the V and M with the 0.01 mol L -1 AgNO 3 aqueous solution. The samples V2 and M2 were treated with the aqueous solution of AgNO 3 for two times. The cation exchange and reduced metallic silver on M1 and V1 evoked the specific surface area (SSA) diminution, the mean particle-size diameter extension and appearance of micropores with radius (<0.4 nm). Repeated silver cation exchange in M2 and V2 reduced particle size, increased slightly SSA and micropores with radius of 0.4-0.5 nm. Samples Ag/V and Ag/M showed higher content of pores with radius 0.5-1.0 nm than original V and M. The Ag concentration was found higher in Ag/V than in Ag/M and higher in repeatedly treated samples: 0.9 wt.% Ag in V1, 1.4 wt.% Ag in V2, 0.6 wt.% Ag in M1 and 1.0 wt.% Ag in M2. Vermiculite structure consisting of the hydrated interstratified phases and the mica-like phase changed to the cation-one-zero layer hydrate interstratification structure in V1 and to the random of two-one layer hydrate interstratifications in V2. Infrared and Mössbauer spectroscopy revealed no changes in the structure of the clay minerals that could be related directly to the sorption and crystallization of silver. Transmission electron microscopy showed that the silver nanoparticles size distribution was much narrower for the

  16. Structure of the solar oscillation with period near 160 minutes

    NASA Technical Reports Server (NTRS)

    Scherrer, P. H.; Wilcox, J. M.

    1982-01-01

    The solar oscillation with period near 160 minutes is found to be unique in a spectrum computed over the range of periods from about 71 to 278 minutes. A best estimate of the period is 160.0095 + or - 0.001 minutes, which is different from 160 minutes (one ninth of a day) by a highly significant amount. The width of the peak is approximately equal to the limiting resolution that can be obtained from an observation lasting 6 years, which suggests that the damping time of the oscillations is considerably longer than 6 years. A suggestion that this peak might be the result of a beating phenomenon between the five minute data averages and a solar oscillation with period near five minutes is shown to be incorrect by recomputing a portion of the spectrum using 15 second data averages.

  17. Thermal stability of octadecyltrimethylammonium bromide modified montmorillonite organoclay.

    PubMed

    Xi, Yunfei; Zhou, Qin; Frost, Ray L; He, Hongping

    2007-07-15

    Organoclays are significant for providing a mechanism for the adsorption of organic molecules from potable water. As such their thermal stability is important. A combination of thermogravimetric analysis and infrared emission spectroscopy was used to determine this stability. Infrared emission spectroscopy (IES) was used to investigate the changes in the structure and surface characteristics of water and surfactant molecules in montmorillonite, octadecyltrimethylammonium bromide and organoclays prepared with the surfactant octadecyltrimethylammonium bromide with different surfactant loadings. These spectra collected at different temperatures give support to the results obtained from the thermal analysis and also provide additional evidence for the dehydration which is difficult to obtain by normal thermoanalytical techniques. The spectra provide information on the conformation of the surfactant molecules in the clay layers and the thermal decomposition of the organoclays. Infrared emission spectroscopy proved to be a useful tool for the study of the thermal stability of the organoclays.

  18. Samarium Ion Exchanged Montmorillonite for High Temperature Cumene Cracking Reaction

    NASA Astrophysics Data System (ADS)

    Binitha, N. N.; Silija, P. P.; Suraj, V.; Yaakob, Z.; Sugunan, S.

    2011-02-01

    Montmorillonite clay is cation exchanged with samarium and its catalytic influence in cumene cracking reaction is investigated. Effect of exchange with sodium ions on further exchange with samarium ions is also noted. Acidity measurements are done using Temperature Programmed Desorption (TPD) of ammonia. The retention of basic structure is proved from FTIR spectra and XRD patterns. Elemental analysis result shows that samarium exchange has occurred, which is responsible for the higher catalytic activity. Surface area and pore volume remains more or less unaffected upon exchange. Thermogravimetric analysis indicates the enhanced thermal stability on exchanging. Cumene cracking reaction is carried out at atmospheric pressure in a fixed bed glass reactor at 673 K. The predominance of Brønsted acidity is confirmed from high selectivity to benzene.

  19. Coupling into and scattering from cylindrical structures covered periodically with metallic patches

    NASA Technical Reports Server (NTRS)

    Cwik, Tom

    1990-01-01

    Circular cylindrical structures covered periodically with metallic patches are considered. After an analogy to planar periodic surfaces is shown, formulations are presented for calculating induced currents on the curved surface. The equations are solved and results calculated for the specific case of periodic strips on the cylindrical surface. For a cylindrical structure a two-dimensional periodicity exists, as in a planar structure, while a spherical structure allows only a rotational periodicity. When the cylindrical structure is excited by the characteristic harmonic of the system, the spectral response of the transmitted field exhibits resonances that depend on the surface periodicity, as is known for planar structures. Since the cylindrical structure contains finite closed regions, the effects of resonances internal to the structure are seen and give additional information as compared to planar structures.

  20. Vibration reduction for smart periodic structures via periodic piezoelectric arrays with nonlinear interleaved-switched electronic networks

    NASA Astrophysics Data System (ADS)

    Bao, Bin; Guyomar, Daniel; Lallart, Mickaël

    2017-01-01

    Smart periodic structures covered by periodically distributed piezoelectric patches have drawn more and more attention in recent years for wave propagation attenuation and corresponding structural vibration suppression. Since piezoelectric materials are special type of energy conversion materials that link mechanical characteristics with electrical characteristics, shunt circuits coupled with such materials play a key role in the wave propagation and/or vibration control performance in smart periodic structures. Conventional shunt circuit designs utilize resistive shunt (R-shunt) and resonant shunt (RL-shunt). More recently, semi-passive nonlinear approaches have also been developed for efficiently controlling the vibrations of such structures. In this paper, an innovative smart periodic beam structure with nonlinear interleaved-switched electric networks based on synchronized switching damping on inductor (SSDI) is proposed and investigated for vibration reduction and wave propagation attenuation. Different from locally resonant band gap mechanism forming narrow band gaps around the desired resonant frequencies, the proposed interleaved electrical networks can induce new broadly low-frequency stop bands and broaden primitive Bragg stop bands by virtue of unique interleaved electrical configurations and the SSDI technique which has the unique feature of realizing automatic impedance adaptation with a small inductance. Finite element modeling of a Timoshenko electromechanical beam structure is also presented for validating dispersion properties of the structure. Both theoretical and experimental results demonstrate that the proposed beam structure not only shows better vibration and wave propagation attenuation than the smart beam structure with independent switched networks, but also has technical simplicity of requiring only half of the number of switches than the independent switched network needs.

  1. Long-period quasi-periodic oscillations of a small-scale magnetic structure on the Sun

    NASA Astrophysics Data System (ADS)

    Kolotkov, D. Y.; Smirnova, V. V.; Strekalova, P. V.; Riehokainen, A.; Nakariakov, V. M.

    2017-01-01

    Aims: Long-period quasi-periodic variations of the average magnetic field in a small-scale magnetic structure on the Sun are analysed. The structure is situated at the photospheric level and is involved in a facula formation in the chromosphere. Methods: The observational signal obtained from the SDO/HMI line-of-sight magnetograms of the target structure has a non-stationary behaviour, and is therefore processed with the Hilbert-Huang Transform spectral technique. Results: The empirical decomposition of the original signal and subsequent testing of the statistical significance of its intrinsic modes reveal the presence of the white and pink noisy components for the periods shorter and longer than 10 min, respectively, and a significant oscillatory mode. The oscillation is found to have a non-stationary period growing from approximately 80 to 230 min and an increasing relative amplitude, while the mean magnetic field in the oscillating structure is seen to decrease. The observed behaviour could be interpreted either by the dynamical interaction of the structure with the boundaries of supergranula cells in the region of interest or in terms of the vortex shedding appearing during the magnetic flux emergence.

  2. Interactions of aminomethylphosphonic acid and sarcosine with montmorillonite interlayer surfaces

    NASA Astrophysics Data System (ADS)

    Rennig, Amanda; Slutter, Annette; Tribe, Lorena

    The smectite clay, montmorillonite, can be found in many soils throughout the world. In addition to its importance in agriculture and soil remediation, montmorillonite has extensive applications in industry both in its natural form and as a component of composite materials. The adsorptive properties of montmorillonite have been explored in relation to its interactions with the common herbicide glyphosate. This herbicide, when exposed to microorganisms in the soil is degraded, forming two products: aminomethylphosphonic acid (AMPA) and sarcosine. The atomic-level interactions of these compounds with the montmorillonite interlayer surfaces are studied here using molecular mechanics. The final outcomes of these calculations are analyzed in terms of the proximity of the montmorillonite surface to the moieties of the degradation products. The phosphonate moiety was found to be the most important source of interactions for AMPA, while for sarcosine there was an even distribution between the amino and carboxylic moieties, and Na+ ion mediated surface complexes.0

  3. Montmorillonite K-10 catalyzed green synthesis of 2,6-unsubstituted dihydropyridines as potential inhibitors of PDE4.

    PubMed

    Reddy, T Ram; Reddy, G Rajeshwar; Reddy, L Srinivasula; Meda, Chandana Lakshmi T; Parsa, Kishore V L; Kumar, K Shiva; Lingappa, Y; Pal, Manojit

    2013-04-01

    Montmorillonite K-10 mediated MCR of anilines, arylaldehydes and ethyl-3,3-diethoxypropionate in water afforded 2,6-unsubstituted dihydropyridines depending on the nature of anilines employed. A variety of dihydropyridines were prepared by using this green methodology in good yields and montmorillonite K-10 was found to be an inexpensive and reusable catalyst. The structure elaboration of a representative compound was carried out under Heck conditions. Some of the compounds synthesized showed significant inhibition of PDE4B when tested in vitro. Docking studies indicated that one of the ester moieties of these compounds played a key role in their interactions with the PDE4B protein.

  4. Prebiotic RNA Synthesis by Montmorillonite Catalysis

    NASA Astrophysics Data System (ADS)

    Jheeta, Sohan; Joshi, Prakash C.

    2014-08-01

    This review summarizes our recent findings on the role of mineral salts in prebiotic RNA synthesis, which is catalyzed by montmorillonite clay minerals. The clay minerals not only catalyze the synthesis of RNA but also facilitate homochiral selection. Preliminary data of these findings have been presented at the "Horizontal Gene Transfer and the Last Universal Common Ancestor (LUCA)" conference at the Open University, Milton Keynes, UK, 5-6 September 2013. The objective of this meeting was to recognize the significance of RNA in LUCA. We believe that the prebiotic RNA synthesis from its monomers must have been a simple process. As a first step, it may have required activation of the 5'-end of the mononucleotide with a leaving group, e.g., imidazole in our model reaction (Figure 1). Wide ranges of activating groups are produced from HCN under plausible prebiotic Earth conditions. The final step is clay mineral catalysis in the presence of mineral salts to facilitate selective production of functional RNA. Both the clay minerals and mineral salts would have been abundant on early Earth. We have demonstrated that while montmorillonite (pH 7) produced only dimers from its monomers in water, addition of sodium chloride (1 M) enhanced the chain length multifold, as detected by HPLC. The effect of monovalent cations on RNA synthesis was of the following order: Li+ > Na+ > K+. A similar effect was observed with the anions, enhancing catalysis in the following order: Cl- > Br- > I-. The montmorillonite-catalyzed RNA synthesis was not affected by hydrophobic or hydrophilic interactions. We thus show that prebiotic synthesis of RNA from its monomers was a simple process requiring only clay minerals and a small amount of salt.

  5. Prebiotic RNA Synthesis by Montmorillonite Catalysis

    PubMed Central

    Jheeta, Sohan; Joshi, Prakash C.

    2014-01-01

    This review summarizes our recent findings on the role of mineral salts in prebiotic RNA synthesis, which is catalyzed by montmorillonite clay minerals. The clay minerals not only catalyze the synthesis of RNA but also facilitate homochiral selection. Preliminary data of these findings have been presented at the “Horizontal Gene Transfer and the Last Universal Common Ancestor (LUCA)” conference at the Open University, Milton Keynes, UK, 5–6 September 2013. The objective of this meeting was to recognize the significance of RNA in LUCA. We believe that the prebiotic RNA synthesis from its monomers must have been a simple process. As a first step, it may have required activation of the 5'-end of the mononucleotide with a leaving group, e.g., imidazole in our model reaction (Figure 1). Wide ranges of activating groups are produced from HCN under plausible prebiotic Earth conditions. The final step is clay mineral catalysis in the presence of mineral salts to facilitate selective production of functional RNA. Both the clay minerals and mineral salts would have been abundant on early Earth. We have demonstrated that while montmorillonite (pH 7) produced only dimers from its monomers in water, addition of sodium chloride (1 M) enhanced the chain length multifold, as detected by HPLC. The effect of monovalent cations on RNA synthesis was of the following order: Li+ > Na+ > K+. A similar effect was observed with the anions, enhancing catalysis in the following order: Cl− > Br− > I−. The montmorillonite-catalyzed RNA synthesis was not affected by hydrophobic or hydrophilic interactions. We thus show that prebiotic synthesis of RNA from its monomers was a simple process requiring only clay minerals and a small amount of salt. PMID:25370375

  6. Low porosity metallic periodic structures with negative Poisson's ratio.

    PubMed

    Taylor, Michael; Francesconi, Luca; Gerendás, Miklós; Shanian, Ali; Carson, Carl; Bertoldi, Katia

    2014-04-16

    Auxetic behavior in low porosity metallic structures is demonstrated via a simple system of orthogonal elliptical voids. In this minimal 2D system, the Poisson's ratio can be effectively controlled by changing the aspect ratio of the voids. In this way, large negative values of Poisson's ratio can be achieved, indicating an effective strategy for designing auxetic structures with desired porosity.

  7. Three-dimensional periodic dielectric structures having photonic Dirac points

    SciTech Connect

    Bravo-Abad, Jorge; Joannopoulos, John D.; Soljacic, Marin

    2015-06-02

    The dielectric, three-dimensional photonic materials disclosed herein feature Dirac-like dispersion in quasi-two-dimensional systems. Embodiments include a face-centered cubic (fcc) structure formed by alternating layers of dielectric rods and dielectric slabs patterned with holes on respective triangular lattices. This fcc structure also includes a defect layer, which may comprise either dielectric rods or a dielectric slab with patterned with holes. This defect layer introduces Dirac cone dispersion into the fcc structure's photonic band structure. Examples of these fcc structures enable enhancement of the spontaneous emission coupling efficiency (the .beta.-factor) over large areas, contrary to the conventional wisdom that the .beta.-factor degrades as the system's size increases. These results enable large-area, low-threshold lasers; single-photon sources; quantum information processing devices; and energy harvesting systems.

  8. Monomers of cutin biopolymer: sorption and esterification on montmorillonite surfaces

    NASA Astrophysics Data System (ADS)

    Olshansky, Yaniv; Polubesova, Tamara; Chefetz, Benny

    2013-04-01

    One of the important precursors for soil organic matter is plant cuticle, a thin layer of predominantly lipids that cover all primary aerial surfaces of vascular plants. In most plant species cutin biopolymer is the major component of the cuticle (30-85% weight). Therefore cutin is the third most abundant plant biopolymer (after lignin and cellulose). Cutin is an insoluble, high molecular weight bio-polyester, which is constructed of inter-esterified cross linked hydroxy-fatty acids and hydroxyepoxy-fatty acids. The most common building blocks of the cutin are derivatives of palmitic acid, among them 9(10),16 dihydroxy palmitic acid (diHPA) is the main component. These fatty acids and their esters are commonly found in major organo-mineral soil fraction-humin. Hence, the complexes of cutin monomers with minerals may serve as model of humin. Both cutin and humin act as adsorption efficient domains for organic contaminants. However, only scarce information is available about the interactions of cutin with soil mineral surfaces, in particular with common soil mineral montmorillonite. The main hypothesize of the study is that adsorbed cutin monomers will be reconstituted on montmorillonite surface due to esterification and oligomerization, and that interactions of cutin monomers with montmorillonite will be affected by the type of exchangeable cation. Cutin monomers were obtained from the fruits of tomato (Lycopersicon esculentum). Adsorption of monomers was measured for crude Wyoming montmorillonites and montmorillonites saturated with Fe3+ and Ca2+. To understand the mechanism of monomer-clay interactions and to evaluate esterification on the clay surface, XRD and FTIR analyses of the montmorillonite-monomers complexes were performed. Our results demonstrated that the interactions of cutin monomers with montmorillonite are affected by the type of exchangeable cation. Isotherms of adsorption of cutin monomers on montmorillonites were fitted by a dual mode model of

  9. Hyperbolic crystallography of two-periodic surfaces and associated structures.

    PubMed

    Pedersen, Martin Cramer; Hyde, Stephen T

    2017-03-01

    This paper describes the families of the simplest, two-periodic constant mean curvature surfaces, the genus-two HCB and SQL surfaces, and their isometries. All the discrete groups that contain the translations of the genus-two surfaces embedded in Euclidean three-space modulo the translation lattice are derived and enumerated. Using this information, the subgroup lattice graphs are constructed, which contain all of the group-subgroup relations of the aforementioned quotient groups. The resulting groups represent the two-dimensional representations of subperiodic layer groups with square and hexagonal supergroups, allowing exhaustive enumeration of tilings and associated patterns on these surfaces. Two examples are given: a two-periodic [3,7]-tiling with hyperbolic orbifold symbol {\\sf {2223}} and a {\\sf {22222}} surface decoration.

  10. Interface Modeling for Electro-Osmosis in Subgrade Structures

    DTIC Science & Technology

    2004-12-01

    aggregate and different clays ( kaolinite , montmorillonite , limestone and quartz sands) created to simulate below grade structures. A direct current 30...Quartz Sand 100 Sieve Ca Montmorillonite Na Montmorillonite Kaolinite The test setup used a 0.45 water to cement ratio concrete cylinder... Kaolinite cell Figure 4. Measured pH for Concrete and Na Montmorillonite cell 4 Scaling occurred at the interface between the anode

  11. The periodic structure of the natural record, and nonlinear dynamics.

    USGS Publications Warehouse

    Shaw, H.R.

    1987-01-01

    This paper addresses how nonlinear dynamics can contribute to interpretations of the geologic record and evolutionary processes. Background is given to explain why nonlinear concepts are important. A resume of personal research is offered to illustrate why I think nonlinear processes fit with observations on geological and cosmological time series data. The fabric of universal periodicity arrays generated by nonlinear processes is illustrated by means of a simple computer mode. I conclude with implications concerning patterns of evolution, stratigraphic boundary events, and close correlations of major geologically instantaneous events (such as impacts or massive volcanic episodes) with any sharply defined boundary in the geologic column. - from Author

  12. A non-asymptotic homogenization theory for periodic electromagnetic structures

    PubMed Central

    Tsukerman, Igor; Markel, Vadim A.

    2014-01-01

    Homogenization of electromagnetic periodic composites is treated as a two-scale problem and solved by approximating the fields on both scales with eigenmodes that satisfy Maxwell's equations and boundary conditions as accurately as possible. Built into this homogenization methodology is an error indicator whose value characterizes the accuracy of homogenization. The proposed theory allows one to define not only bulk, but also position-dependent material parameters (e.g. in proximity to a physical boundary) and to quantify the trade-off between the accuracy of homogenization and its range of applicability to various illumination conditions. PMID:25104912

  13. Vibration and buckling of general periodic lattice structures

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.; Williams, F. W.

    1984-01-01

    A method is presented for vibration and buckling analysis of arbitrary lattice structures having repetitive geometry in any combination of coordinate directions. The approach is based on exact member theory for representing the stiffness of an individual member subject to axial load, and in the case of vibration, undergoing harmonic oscillation. The method is an extension of previous work that was limited to specific geometries. The resulting eigenvalue problem is of the size associated with the repeating element of the structure. A computer program has been developed incorporating the theory and results are given for vibration of rectangular platforms and a large antenna structure having rotational symmetry. Buckling and vibration results for cable-stiffened rings are also given.

  14. Sorption of tetracycline on organo-montmorillonites.

    PubMed

    Liu, Niu; Wang, Ming-xia; Liu, Ming-ming; Liu, Fan; Weng, Liping; Koopal, Luuk K; Tan, Wen-feng

    2012-07-30

    Tetracycline (TC) is a veterinary antibiotic that is frequently detected as pollutant in the environment. Powerful adsorbents are required for removing TC. The present paper compares the TC adsorption capacity of Na-montmorillonite (Na-mont) with six organo-montmorillonites (organo-monts). Three quaternary ammonium cations (QACs) with different alkyl-chain lengths were used as modifiers. Powder X-ray diffraction indicated that the d(001) values of organo-monts increased with increasing the QACs loading and alkyl-chain length. The CECs of the organo-monts were substantially lower than that of Na-mont and decreased with QACs chain length and increased loading. The modeling of the adsorption kinetics revealed that the processes of TC adsorption on the tested samples could be well fitted by the pseudo-second-order equation. The maximum adsorption capacities of TC on the organo-monts (1000-2000mmol/kg) were considerably higher than that on Na-mont (769mmol/kg). Both the Langmuir and Freundlich model could fit the adsorption isotherms. The TC adsorption to the organo-monts increase significantly with decreasing the pH below 5.5 because of the electrostatic interaction, and a high QACs loading performed better than a low loading at around pH 3.

  15. Fe(II) uptake on natural montmorillonites. I. Macroscopic and spectroscopic characterization.

    PubMed

    Soltermann, Daniela; Marques Fernandes, Maria; Baeyens, Bart; Dähn, Rainer; Joshi, Prachi A; Scheinost, Andreas C; Gorski, Christopher A

    2014-01-01

    Iron is an important redox-active element that is ubiquitous in both engineered and natural environments. In this study, the retention mechanism of Fe(II) on clay minerals was investigated using macroscopic sorption experiments combined with Mössbauer and extended X-ray absorption fine structure (EXAFS) spectroscopy. Sorption edges and isotherms were measured under anoxic conditions on natural Fe-bearing montmorillonites (STx, SWy, and SWa) having different structural Fe contents ranging from 0.5 to 15.4 wt % and different initial Fe redox states. Batch experiments indicated that, in the case of low Fe-bearing (STx) and dithionite-reduced clays, the Fe(II) uptake follows the sorption behavior of other divalent transition metals, whereas Fe(II) sorption increased by up to 2 orders of magnitude on the unreduced, Fe(III)-rich montmorillonites (SWy and SWa). Mössbauer spectroscopy analysis revealed that nearly all the sorbed Fe(II) was oxidized to surface-bound Fe(III) and secondary Fe(III) precipitates were formed on the Fe(III)-rich montmorillonite, while sorbed Fe is predominantly present as Fe(II) on Fe-low and dithionite-reduced clays. The results provide compelling evidence that Fe(II) uptake characteristics on clay minerals are strongly correlated to the redox properties of the structural Fe(III). The improved understanding of the interfacial redox interactions between sorbed Fe(II) and clay minerals gained in this study is essential for future studies developing Fe(II) sorption models on natural montmorillonites.

  16. Velocity structure in long period variable star atmospheres

    NASA Technical Reports Server (NTRS)

    Pilachowski, C.; Wallerstein, G.; Willson, L. A.

    1980-01-01

    A regression analysis of the dependence of absorption line velocities on wavelength, line strength, excitation potential, and ionization potential is presented. The method determines the region of formation of the absorption lines for a given data and wavelength region. It is concluded that the scatter which is frequently found in velocity measurements of absorption lines in long period variables is probably the result of a shock of moderate amplitude located in or near the reversing layer and that the frequently observed correlation of velocity with excitation and ionization are a result of the velocity gradients produced by this shock in the atmosphere. A simple interpretation of the signs of the coefficients of the regression analysis is presented in terms of preshock, post shock, or across the shock, together with criteria for evaluating the validity of the fit. The amplitude of the reversing layer shock is estimated from an analysis of a series of plates for four long period variable stars along with the most probable stellar velocity for these stars.

  17. Nickel sorption to goethite and montmorillonite in presence of citrate.

    PubMed

    Marcussen, Helle; Holm, Peter E; Strobel, Bjarne W; Hansen, Hans Chr B

    2009-02-15

    Mobility and bioavailability of nickel (Ni) in soil strongly depends on the interaction between Ni(II), ligands, and sorbents like organic matter and minerals. Sorption of Ni(II) and Ni(II)-citrate complexes to goethite and montmorillonite was examined in batch experiments with and without citrate as ligand in the pH range pH 4-7.5. Without citrate, montmorillonite shows higher Ni sorption than goethite. Citrate strongly decreases Ni sorption to montmorillonite; in presence of 100 microM citrate goethite becomes a stronger Ni sorbent than montmorillonite. Ni and citrate sorption was modeled successfully using the diffuse double layer model with the following reactions: Goethite: 3 [triple bond]FeOH + Citrate(3-) + 3H+ <=> [triple bond] Fe3Citrate + 3H2O, [triple bond]FeOH + Ni2+ <=> [triple bond] FeONi + H+ and 2 [triple bond] FeOH + Citrate(3)- + Ni2+ <=> [triple bond] FeONiCitrate(2-) + H+. Montmorillonite: 2X- + Ni2+ <=> X2Ni and [triple bond] AIOH + Ni2+ <=> AIONi+ + H+. Sorption of Ni to a mixture of goethite and montmorillonite could be calculated by use of reactions and constants for the monomineral systems. Without citrate, the sorbed amount of Ni per mass unit in the mixture can be found as a simple average of sorption to the two single sorbents, while in presence of citrate Ni sorption to montmorillonite is strongly influenced by citrate sorption to goethite.

  18. Synthesis and characterization of BiOI/montmorillonite composites with high visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Wang, Jizhong; Wang, Xiaojing; Li, Fatang; Zhang, Lei; Chen, Yue

    2015-12-01

    BiOI/montmorillonite composite photocatalysts are synthesized by a facile room temperature method using Bi(NO3)3, KI and montmorillonite (MMT) clay as precursors, and characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and nitrogen adsorption-desorption measurements. The facile synthesis method avoids high temperature treatment, and is based on cheap precursors. The prepared Bi-M-x composites possess a hierarchically nanoplates structure and are composed of BiOI and MMT phases. The degradation rate of the methylene blue reached up to about 95% after 45 min whereas that for the pure BiOI was only 75%. The high photocatalytic Bi-M-x composites would have a potential application in environmental purification owing to its low cost and easy synthesis.

  19. Solid-state synthesis and electrical properties of polyaniline/Cu-montmorillonite nanocomposite

    SciTech Connect

    Bekri-Abbes, Imene; Srasra, Ezzeddine

    2010-12-15

    In this paper, the solid-state synthesis of polyaniline/Cu-montmorillonite nanocomposite is reported. Mixture of anilinium chlorure and Cu exchanged montmorillonite was grinded at room temperature while we vary the molar rate of aniline to interlayer Cu{sup 2+} cations (R) from 0.5 to 6. The properties of the hybrid compounds are characterized by X-ray diffraction, thermogravimetric analysis, SEM, FTIR and impedance spectroscopy. The results showed that the structure and the conductivity of PANI in hybrid materials depend on R. The ac conduction showed a regime of constant dc conductivity at low frequencies and a crossover to a frequency-dependent regime of the type A {omega}{sup s} at high frequencies.

  20. Water radiolysis in exchanged-montmorillonites: the H2 production mechanisms.

    PubMed

    Fourdrin, C; Aarrachi, H; Latrille, C; Esnouf, S; Bergaya, F; Le Caër, S

    2013-08-20

    The radiolysis of water confined in montmorillonites is studied as a function of the composition of the montmorillonite, the nature of the exchangeable cation, and the relative humidity by following the H2 production under electron irradiation. It is shown that the main factor influencing this H2 production is the water amount in the interlayer space. The effect of the exchangeable cation is linked to its hydration enthalpy. When the water amount is high enough to get a basal distance higher than 1.3 nm, then a total energy transfer from the montmorillonite sheets to the interlayer space occurs, and the H2 production measured is very similar to the one obtained in bulk water. For a basal distance smaller than 1.3 nm, the H2 production increases with the relative humidity and thus with the water amount. Lastly, electron paramagnetic resonance measurements evidence the formation of a new defect induced by ionizing radiation. It consists of a hydrogen radical (H2 precursor) trapped in the structure. This implies that structural hydroxyl bonds can be broken under irradiation, potentially accounting for the observed H2 production.

  1. Cerium; crystal structure and position in the periodic table.

    PubMed

    Johansson, Börje; Luo, Wei; Li, Sa; Ahuja, Rajeev

    2014-09-17

    The properties of the cerium metal have intrigued physicists and chemists for many decades. In particular a lot of attention has been directed towards its high pressure behavior, where an isostructural volume collapse (γ phase → α phase) has been observed. Two main models of the electronic aspect of this transformation have been proposed; one where the 4f electron undergoes a change from being localized into an itinerant metallic state, and one where the focus is on the interaction between the 4f electron and the conduction electrons, often referred to as the Kondo volume collapse model. However, over the years it has been repeatedly questioned whether the cerium collapse really is isostructural. Most recently, detailed experiments have been able to remove this worrisome uncertainty. Therefore the isostructural aspect of the α-γ transition has now to be seriously addressed in the theoretical modeling, something which has been very much neglected. A study of this fundamental characteristic of the cerium volume collapse is made in present paper and we show that the localized [rlhar2 ] delocalized 4f electron picture provides an adequate description of this unique behavior. This agreement makes it possible to suggest that an appropriate crossroad position for cerium in The Periodic Table.

  2. Cerium; Crystal Structure and Position in The Periodic Table

    PubMed Central

    Johansson, Börje; Luo, Wei; Li, Sa; Ahuja, Rajeev

    2014-01-01

    The properties of the cerium metal have intrigued physicists and chemists for many decades. In particular a lot of attention has been directed towards its high pressure behavior, where an isostructural volume collapse (γ phase → α phase) has been observed. Two main models of the electronic aspect of this transformation have been proposed; one where the 4f electron undergoes a change from being localized into an itinerant metallic state, and one where the focus is on the interaction between the 4f electron and the conduction electrons, often referred to as the Kondo volume collapse model. However, over the years it has been repeatedly questioned whether the cerium collapse really is isostructural. Most recently, detailed experiments have been able to remove this worrisome uncertainty. Therefore the isostructural aspect of the α-γ transition has now to be seriously addressed in the theoretical modeling, something which has been very much neglected. A study of this fundamental characteristic of the cerium volume collapse is made in present paper and we show that the localized ⇌ delocalized 4f electron picture provides an adequate description of this unique behavior. This agreement makes it possible to suggest that an appropriate crossroad position for cerium in The Periodic Table. PMID:25227991

  3. Strength of Wet and Dry Montmorillonite

    NASA Astrophysics Data System (ADS)

    Morrow, C. A.; Lockner, D. A.; Moore, D. E.

    2015-12-01

    Montmorillonite, an expandable smectite clay, is a common mineral in fault zones to a depth of around 3 km. Its low strength relative to other common fault gouge minerals is important in many models of fault rheology. However, the coefficient of friction is not well constrained in the literature due to the difficulty of establishing fully drained or fully dried states in the laboratory. For instance, in some reported studies, samples were either partially saturated or possibly over pressured, leading to wide variability in reported shear strength. In this study, the coefficient of friction, μ, of both saturated and oven-dried (at 150°C) Na-montmorillonite was measured at normal stresses up to 680 MPa at room temperature and shortening rates from 1.0 to 0.01 μm/s. Care was taken to shear saturated samples slowly enough to avoid pore fluid overpressure in the clay layers. Coefficients of friction are reported after 8 mm of axial displacement in a triaxial apparatus on saw-cut samples containing a layer of montmorillonite gouge, with either granite or sandstone driving blocks. For saturated samples, μ increased from around 0.1 at low pressure to 0.25 at the highest test pressures. In contrast, values for oven-dried samples decreased asymptotically from approximately 0.78 at 10 MPa normal stress to around 0.45 at 400-680 MPa. While wet and dry strengths approached each other with increasing effective normal stress, wet strength remained only about half of the dry strength at 600 MPa effective normal stress. The increased coefficient of friction can be correlated with a reduction in the number of loosely bound lubricating surface water layers on the clay platelets due to applied normal stress under saturated conditions. The steady-state rate dependence of friction, a-b, was positive and dependent on normal stress. For saturated samples, a-b increased linearly with applied normal stress from ~0 to 0.004, while for dry samples a-b decreased with increasing normal

  4. Prediction of the Fundamental Period of Infilled RC Frame Structures Using Artificial Neural Networks.

    PubMed

    Asteris, Panagiotis G; Tsaris, Athanasios K; Cavaleri, Liborio; Repapis, Constantinos C; Papalou, Angeliki; Di Trapani, Fabio; Karypidis, Dimitrios F

    2016-01-01

    The fundamental period is one of the most critical parameters for the seismic design of structures. There are several literature approaches for its estimation which often conflict with each other, making their use questionable. Furthermore, the majority of these approaches do not take into account the presence of infill walls into the structure despite the fact that infill walls increase the stiffness and mass of structure leading to significant changes in the fundamental period. In the present paper, artificial neural networks (ANNs) are used to predict the fundamental period of infilled reinforced concrete (RC) structures. For the training and the validation of the ANN, a large data set is used based on a detailed investigation of the parameters that affect the fundamental period of RC structures. The comparison of the predicted values with analytical ones indicates the potential of using ANNs for the prediction of the fundamental period of infilled RC frame structures taking into account the crucial parameters that influence its value.

  5. Intestinal morphology, brush border and digesta enzyme activities of broilers fed on a diet containing Cu2+-loaded montmorillonite.

    PubMed

    Ma, Y L; Guo, T

    2008-01-01

    1. A total of 320 1-d-old Arbor Acres broiler chicks were used to investigate the effect of Cu(2+)-loaded montmorillonite (CM) on the growth performance, intestinal morphology and activities of brush border enzyme in the intestinal mucosa and digestive enzyme in the intestinal digesta of broilers. 2. The chicks were assigned randomly into 4 groups with 80 chicks per treatment. The 4 dietary treatments were: basal diet only (control group), basal diet + 2 g montmorillonite/kg, basal diet + 1 g CM/kg, and basal diet + 2 g CM/kg. The chicks were raised in cages and feed and water were provided ad libitum for a period of 42 d. 3. The addition of CM to the diet of broilers significantly increased body weight and feed efficiency. Similarly, birds receiving montmorillonite had higher feed efficiency than the control after 42 d of feeding. 4. Data on villus height and crypt depth for duodenum, jejunum and ileum indicated that treating the diet of broilers with either CM or montmorillonite improved the mucosal morphology of the small intestine. 5. The presence of CM in the diet of broilers significantly increased the activities of maltase, aminopeptidase N and alkaline phosphatase in small intestinal mucosa. However, the activities of protease, trypsin, chymotrypsin, amylase and lipase in small intestinal digesta of broilers fed on the CM-supplemented diet were slightly higher than control values.

  6. Polariton Local States in Periodic Bragg Multiple Quantum Well Structures

    NASA Astrophysics Data System (ADS)

    Deych, Lev; Yamilov, Alexey; Lisyansky, Alexander

    2000-11-01

    We analytically study defect polariton states in Bragg MQW structures, and defect induced changes in transmission and reflection spectra. Defect layers can differ from the host layers in three different ways: in the exciton-light coupling strength, in the exciton resonance frequency, and in interwell spacing. We show that a single defect leads to two local polariton modes in the photonic band gap. These modes lead to peculiarities in reflection and transmission spectra. Each type of defect can be reproduced experimentally, and we show that each of them play distinctly different roles in the optical properties of the system. We obtain closed analytical expressions for respective local frequencies, as well as for reflection and transmission coefficients. On the basis of the results obtained, we give practical recommendation for experimental observation of the studied effects in samples used in Refs. [1,2]. [1] M.Hübner, J. Kuhl, T. Stroucken, A. Knorr, S.W. Koch, R. Hey, K. Ploog, Phys. Rev. Lett. 76, 4199 (1996). [2] M.Hübner, J.P. Prineas, C. Ell, P. Brick, E.S. Lee, G. Khitrova, H.M. Gibbs, S.W. Koch, Phys. Rev. Lett. 83, 2841 (1999).

  7. Dissolution of alkaline earth sulfates in the presence of montmorillonite

    USGS Publications Warehouse

    Eberl, D.D.; Landa, E.R.

    1985-01-01

    In a study of the effect of montmorillonite on the dissolution of BaSO4 (barite), SrSO4 (celestite), and 226Ra from U mill tailings, it was found that: (1) More of these substances dissolve in an aqueous system that contains montmorillonite than dissolve in a similar system without clay, due to the ion exchange properties of the clay; (2) Na-montmorillonite is more effective in aiding dissolution than is Ca-montmorillonite; (3) the amount of Ra that moves from mill tailings to an exchanger increases as solution sulfate activity decreases. Leaching experiments suggest that 226Ra from H2SO4-circuit U mill tailings from Edgemont, South Dakota, is not present as pure Ra sulfate or as an impurity in anhydrite or gypsum; it is less soluble, and probably occurs as a trace constituent in barite.

  8. Adsorption of organic phenols onto hexadecyltrimethylammonium-treated montmorillonite

    SciTech Connect

    Kim, Young S.; Song, Dong I.; Jeon, Young W.; Choi, Sang J.

    1996-12-01

    Montmorillonite used as an adsorbent was organically modified by using a cationic surfactant, hexadecyltrimethylammonium (HDTMA), to enhance the removal capacity of organic phenol contaminants dissolved in an aqueous solution. This modification produces a change of the surface property of montmorillonite from hydrophilic to organophilic. The single- and multicomponent competitive adsorptions were performed in a batch reactor to investigate the removal of three toxic organic phenols, 2-chlorophenol, 3-cyanophenol, and 4-nitrophenol, on the modified HDTMA-montmorillonite. It was observed from the experimental results that the adsorption affinity for HDTMA-montmorillonite was 2-chlorophenol, 4-nitrophenol, 3-cyanophenol in decreasing order. Langmuir and the Redlich-Peterson models were used to analyze the single-component adsorption results, while the IAST and the LCM models predicted the multicomponent adsorption equilibria. These models yielded favorable representations of both individual and competitive adsorption behaviors.

  9. Pillared montmorillonite catalysts for coal liquefaction

    SciTech Connect

    Sharma, R.K.; Olson, E.S.

    1994-12-31

    Pillared clays contain large micropores and have considerable potential for catalytic hydrogenation and cleavage of coal macromolecules. Pillared montmorillonite-supported catalysts were prepared by the intercalation of polynuclear hydroxychromium cations and subsequent impregnation of nickel and molybdenum. Infrared and thermogravimetric studies of pyridine-adsorbed catalysts indicated the presence of both Lewis and Bronsted acid sites. Thus, the catalysts have both acidic properties that can aid in hydrocracking and cleavage of carbon-heteroatom bonds as well as hydrogen-activating bimetallic sites. These catalysts were applied to the hydrodesulfurization and liquefaction of coal-derived intermediates. The reactions of model organosulfur compounds and coal liquids were carried out at 300{degrees}-400{degrees}C for 3 hours in the presence of 1000 psi of molecular hydrogen. Reaction products were analyzed by GC/FT-IR/MS/AED. The catalysts have been found to be very effective in removing sulfur from model compounds as well as liquefaction products.

  10. Cuprous Ion Conducting Montmorillonite- Polypyrrole Nanocomposites

    NASA Astrophysics Data System (ADS)

    Krishantha, D. M. M.; Rajapakse, R. M. G.; Tennakoon, D. T. B.; Bandara, W. M. A. T.; Thilakarathna, P. N. L.

    2006-06-01

    Solid state polymer-Silicate nanocomposite based on Polypyrrole-Cu+-montmorilonite were prepared and electrical properties were investigated. In this preparation, Na-montmorillonite (Na+-MMT) was purified by repeated washing with distilled water and the intergallery cations were exchanged for Cu(II). The cupric ions exchanged-MMT(Cu(II)-- MMT) was again exposed to pyrrole in aqueous acidic solution to yield polypyrrole-Cu+-MMT nanocomposite. DC polarization test and AC impedance measurement reveal that the materials are mixed conductors. The ionic conductivity is due to the motion of cuprous ions which is facilitated by microstructure of polypyrrrole present in the intergalleries. An electrochemical cell was fabricated using the materials which can be represented by Cu(s)/ Cu+-PPY-MMT/Cu2SO4 (s)/Na2SO4(S)-Na2S2O8(s)/ and gave a 1.00 V. The cell is rechargeable.

  11. Synthesis and characterization of montmorillonite clay intercalated with molecular magnetic compounds

    SciTech Connect

    Martins, Marcel G.; Martins, Daniel O.T.A.; Carvalho, Beatriz L.C. de; Mercante, Luiza A.; Soriano, Stéphane; Andruh, Marius; Vieira, Méri D.; Vaz, Maria G.F.

    2015-08-15

    In this work montmorillonite (MMT) clay, whose matrix was modified with an ammonium salt (hexadecyltrimethylammonium bromide – CTAB), was employed as an inorganic host for the intercalation of three different molecular magnetic compounds through ion exchange: a nitronyl nitroxide derivative 2-[4-(N-ethyl)-pyridinium]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (p-EtRad{sup +}) and two binuclear coordination compounds, [Ni(valpn)Ln]{sup 3+}, where H{sub 2}valpn stands for 1,3-propanediyl-bis(2-iminomethylene-6-methoxy-phenol), and Ln=Gd{sup III}; Dy{sup III}. The pristine MMT and the intercalated materials were characterized by X-ray powder diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and magnetic measurements. The X-ray diffraction data analysis showed an increase of the interlamellar space of the intercalated MMT, indicating the intercalation of the magnetic compounds. Furthermore, the magnetic properties of the hybrid compounds were investigated, showing similar behavior as the pure magnetic guest species. - Graphical abstract: Montmorillonite clay was employed as inorganic host for the intercalation of three different molecular magnetic compounds through ion exchange - Highlights: • Montmorillonite was employed as a host material. • Three molecular magnetic compounds were intercalated through ion exchange. • The compounds were successful intercalated maintaining the layered structure. • The hybrid materials exhibited similar magnetic behavior as the pure magnetic guest.

  12. Surface complexation modeling of Cd(II) sorption to montmorillonite, bacteria, and their composite

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Du, Huihui; Huang, Qiaoyun; Cai, Peng; Rong, Xingmin; Feng, Xionghan; Chen, Wenli

    2016-10-01

    Surface complexation modeling (SCM) has emerged as a powerful tool for simulating heavy metal adsorption processes on the surface of soil solid components under different geochemical conditions. The component additivity (CA) approach is one of the strategies that have been widely used in multicomponent systems. In this study, potentiometric titration, isothermal adsorption, zeta potential measurement, and extended X-ray absorption fine-structure (EXAFS) spectra analysis were conducted to investigate Cd adsorption on 2 : 1 clay mineral montmorillonite, on Gram-positive bacteria Bacillus subtilis, and their mineral-organic composite. We developed constant capacitance models of Cd adsorption on montmorillonite, bacterial cells, and mineral-organic composite. The adsorption behavior of Cd on the surface of the composite was well explained by CA-SCM. Some deviations were observed from the model simulations at pH < 5, where the values predicted by the model were lower than the experimental results. The Cd complexes of X2Cd, SOCd+, R-COOCd+, and R-POCd+ were the predominant species on the composite surface over the pH range of 3 to 8. The distribution ratio of the adsorbed Cd between montmorillonite and bacterial fractions in the composite as predicted by CA-SCM closely coincided with the estimated value of EXAFS at pH 6. The model could be useful for the prediction of heavy metal distribution at the interface of multicomponents and their risk evaluation in soils and associated environments.

  13. Highly anisotropic conductivity of tablets pressed from polyaniline-montmorillonite nanocomposite

    SciTech Connect

    Tokarský, Jonáš

    2016-03-15

    Highlights: • Montmorillonite (MMT) can be intercalated with polyaniline (PANI) chains. • Tablets pressed from PANI/MMT exhibit high anisotropy in electrical conductivity. • Pressure 28MPa is sufficient to reach the anisotropy. • Tablets pressed from pure PANI also exhibit anisotropy in electrical conductivity. - Abstract: Polyaniline-montmorillonite nanocomposite was prepared from anilinium sulfate (precursor) and ammonium peroxodisulfate (oxidizing agent) using simple one-step method. The resulting nanocomposite obtained in powder form has been pressed into tablets using various compression pressures (28–400 MPa). Electrical conductivities of tablets in two perpendicular directions, i.e. direction parallel with the main surface of tablet (σ=) and in orthogonal direction (σ⊥), and corresponding anisotropy factors (i.e., the ratio σ=/σ⊥) have been studied in dependence on compression pressure used during the preparation. Polyaniline-montmorillonite nanocomposite was characterized using X-ray diffraction analysis, raman spectroscopy, transmission electron microscopy, thermogravimetric analysis and molecular modeling which led to the understanding of the internal structure. Measurement of hardness performed on pressed tablets has been also involved. Taking into account the highest value of anisotropy factor reached (σ=/σ⊥ = 490), present study shows a chance to design conductors with nearly two-dimensional conductivity.

  14. Enhanced Photoreduction of Nitro-aromatic Compounds by Hydrated Electrons Derived from Indole on Natural Montmorillonite.

    PubMed

    Tian, Haoting; Guo, Yong; Pan, Bo; Gu, Cheng; Li, Hui; Boyd, Stephen A

    2015-07-07

    A new photoreduction pathway for nitro-aromatic compounds (NACs) and the underlying degradation mechanism are described. 1,3-Dinitrobenzene was reduced to 3-nitroaniline by the widely distributed aromatic molecule indole; the reaction is facilitated by montmorillonite clay mineral under both simulated and natural sunlight irradiation. The novel chemical reaction is strongly affected by the type of exchangeable cation present on montmorillonite. The photoreduction reaction is initiated by the adsorption of 1,3-dinitrobenzene and indole in clay interlayers. Under light irradiation, the excited indole molecule generates a hydrated electron and the indole radical cation. The structural negative charge of montmorillonite plausibly stabilizes the radical cation hence preventing charge recombination. This promotes the release of reactive hydrated electrons for further reductive reactions. Similar results were observed for the photoreduction of nitrobenzene. In situ irradiation time-resolved electron paramagnetic resonance and Fourier transform infrared spectroscopies provided direct evidence for the generation of hydrated electrons and the indole radical cations, which supported the proposed degradation mechanism. In the photoreduction process, the role of clay mineral is to both enhance the generation of hydrated electrons and to provide a constrained reaction environment in the galley regions, which increases the probability of contact between NACs and hydrated electrons.

  15. Mechanism of the reduction of hexavalent chromium by organo-montmorillonite supported iron nanoparticles.

    PubMed

    Wu, Pingxiao; Li, Shuzhen; Ju, Liting; Zhu, Nengwu; Wu, Jinhua; Li, Ping; Dang, Zhi

    2012-06-15

    Iron nanoparticles exhibit greater reactivity than micro-sized Fe(0), and they impart advantages for groundwater remediation. In this paper, supported iron nanoparticles were synthesized to further enhance the speed and efficiency of remediation. Natural montmorillonite and organo-montmorillonite were chosen as supporting materials. The capacity of supported iron nanoparticles was evaluated, compared to unsupported iron nanoparticles, for the reduction of aqueous Cr(VI). The reduction of Cr(VI) was much greater with organo-montmorillonite supported iron nanoparticles and fitted the pseudo-second order equation better. With a dose at 0.47 g/L, a total removal capacity of 106 mg Cr/g Fe(0) was obtained. Other factors that affect the efficiency of Cr(VI) removal, such as pH values, the initial Cr(VI) concentration and storage time of nanoparticles were investigated. X-ray photoelectron spectrometry (XPS) and X-ray absorption near edge structure (XANES) were used to figure out the mechanism of the removal of Cr(VI). XPS indicated that the Cr(VI) bound to the particle surface was completely reduced to Cr(III) under a range of conditions. XANES confirmed that the Cr(VI) reacted with iron nanoparticles was completely reduced to Cr(III).

  16. Structural and functional analyses of PAS domain interactions of the clock proteins Drosophila PERIOD and mouse PERIOD2.

    PubMed

    Hennig, Sven; Strauss, Holger M; Vanselow, Katja; Yildiz, Ozkan; Schulze, Sabrina; Arens, Julia; Kramer, Achim; Wolf, Eva

    2009-04-28

    PERIOD proteins are central components of the Drosophila and mammalian circadian clocks. The crystal structure of a Drosophila PERIOD (dPER) fragment comprising two PER-ARNT-SIM (PAS) domains (PAS-A and PAS-B) and two additional C-terminal alpha-helices (alphaE and alphaF) has revealed a homodimer mediated by intermolecular interactions of PAS-A with tryptophane 482 in PAS-B and helix alphaF. Here we present the crystal structure of a monomeric PAS domain fragment of dPER lacking the alphaF helix. Moreover, we have solved the crystal structure of a PAS domain fragment of the mouse PERIOD homologue mPER2. The mPER2 structure shows a different dimer interface than dPER, which is stabilized by interactions of the PAS-B beta-sheet surface including tryptophane 419 (equivalent to Trp482dPER). We have validated and quantitatively analysed the homodimer interactions of dPER and mPER2 by site-directed mutagenesis using analytical gel filtration, analytical ultracentrifugation, and co-immunoprecipitation experiments. Furthermore we show, by yeast-two-hybrid experiments, that the PAS-B beta-sheet surface of dPER mediates interactions with TIMELESS (dTIM). Our study reveals quantitative and qualitative differences between the homodimeric PAS domain interactions of dPER and its mammalian homologue mPER2. In addition, we identify the PAS-B beta-sheet surface as a versatile interaction site mediating mPER2 homodimerization in the mammalian system and dPER-dTIM heterodimer formation in the Drosophila system.

  17. Effect of eddy current damping on phononic band gaps generated by locally resonant periodic structures

    NASA Astrophysics Data System (ADS)

    Ozkaya, Efe; Yilmaz, Cetin

    2017-02-01

    The effect of eddy current damping on a novel locally resonant periodic structure is investigated. The frequency response characteristics are obtained by using a lumped parameter and a finite element model. In order to obtain wide band gaps at low frequencies, the periodic structure is optimized according to certain constraints, such as mass distribution in the unit cell, lower limit of the band gap, stiffness between the components in the unit cell, the size of magnets used for eddy current damping, and the number of unit cells in the periodic structure. Then, the locally resonant periodic structure with eddy current damping is manufactured and its experimental frequency response is obtained. The frequency response results obtained analytically, numerically and experimentally match quite well. The inclusion of eddy current damping to the periodic structure decreases amplitudes of resonance peaks without disturbing stop band width.

  18. Influence of montmorillonite on antimicrobial activity of tetracycline and ciprofloxacin

    NASA Astrophysics Data System (ADS)

    Lv, Guocheng; Pearce, Cody W.; Gleason, Andrea; Liao, Libing; MacWilliams, Maria P.; Li, Zhaohui

    2013-11-01

    Antibiotics are used not only to fight infections and inhibit bacterial growth, but also as growth promotants in farm livestock. Farm runoff and other farm-linked waste have led to increased antibiotic levels present in the environment, the impact of which is not completely understood. Soil, more specifically clays, that the antibiotic contacts may alter its effectiveness against bacteria. In this study a swelling clay mineral montmorillonite was preloaded with antibiotics tetracycline and ciprofloxacin at varying concentrations and bioassays were conducted to examine whether the antibiotics still inhibited bacterial growth in the presence of montmorillonite. Escherichia coli was incubated with montmorillonite or antibiotic-adsorbed montmorillonite, and then the number of viable bacteria per mL was determined. The antimicrobial activity of tetracycline was affected in the presence of montmorillonite, as the growth of non-resistant bacteria was still found even when extremely high TC doses were used. Conversely, in the presence of montmorillonite, ciprofloxacin did inhibit E. coli bacterial growth at high concentrations. These results suggest that the effectiveness of antimicrobial agents in clayey soils depends on the amount of antibiotic substance present, and on the interactions between the antibiotic and the clays in the soil, as well.

  19. Periodic vortex pinning by regular structures in Nb thin films: magnetic vs. structural effects

    NASA Astrophysics Data System (ADS)

    Montero, Maria Isabel; Jonsson-Akerman, B. Johan; Schuller, Ivan K.

    2001-03-01

    The defects present in a superconducting material can lead to a great variety of static and dynamic vortex phases. In particular, the interaction of the vortex lattice with regular arrays of pinning centers such as holes or magnetic dots gives rise to commensurability effects. These commensurability effects can be observed in the magnetoresistance and in the critical current dependence with the applied field. In recent years, experimental results have shown that there is a dependence of the periodic pinning effect on the properties of the vortex lattice (i.e. vortex-vortex interactions, elastic energy and vortex velocity) and also on the dots characteristics (i.e. dot size, distance between dots, magnetic character of the dot material, etc). However, there is not still a good understanding of the nature of the main pinning mechanisms by the magnetic dots. To clarify this important issue, we have studied and compared the periodic pinning effects in Nb films with rectangular arrays of Ni, Co and Fe dots, as well as the pinning effects in a Nb film deposited on a hole patterned substrate without any magnetic material. We will discuss the differences on pinning energies arising from magnetic effects as compared to structural effects of the superconducting film. This work was supported by NSF and DOE. M.I. Montero acknowledges postdoctoral fellowship by the Secretaria de Estado de Educacion y Universidades (Spain).

  20. Formation of limit-periodic structures by quadrupole particles confined to a triangular lattice

    NASA Astrophysics Data System (ADS)

    Rutkowski, David M.; Marcoux, Catherine; Socolar, Joshua E. S.; Hall, Carol K.

    2017-01-01

    We have performed Monte Carlo (MC) simulations on two-dimensional systems of quadrupole particles confined to a triangular lattice in order to determine the conditions that permit the formation of a limit-periodic phase. We have found that limit-periodic structures form only when the rotations of the particles are confined to a set of six orientations aligned with the lattice directions. Related structures including striped and unidirectional rattler phases form when π /π 6 rotations or continuous rotations are allowed. Order parameters signaling the formation of the limit-periodic structure and related structures are measured as a function of temperature. Our findings on the formation of the limit-periodic structure elucidate features relevant to the experimental creation of such a structure, which is expected to have interesting vibrational and electromagnetic modes.

  1. The mobility of uranium and other elements during alteration of rhyolite ash to montmorillonite: A case study in the Troublesome Formation, Colorado, U.S.A.

    USGS Publications Warehouse

    Zielinski, R.A.

    1982-01-01

    An unusual occurrence of juxtaposed glassy and clay-altered ash was sampled to estimate the degree and type of element mobility during alteration of glass to montmorillonite. The results are particularly interesting in that major mobilization of uranium is indicated. Closely spaced samples of glassy and montmorillonitic ash were collected from the same 20-50 cm thick stratigraphic horizon in the Troublesome Formation (Miocene) of northwestern Colorado. Sharp contacts exist between glassy ash and underlying pink montmorillonite and indicate that water-saturated conditions were restricted to basal ash layers. Formation of montmorillonite instead of zeolites suggests that the water was not highly saline or alkaline. Isotopic and chemical analyses of glassy and clay-altered samples indicate the following: 1. (1) Montmorillonite has U concentrations which are only 10-15% of the concentrations in coexisting glass. Similarly depleted elements include Cs, Rb, Na and K. Much smaller depletions of these elements in some glassy samples serve as sensitive indicators of incipient alteration of glass to montmorillonite. 2. (2) Abundances of relatively insoluble elements such as Th, Ta, Hf and Al are slightly higher (5-50%) in clay-altered ash and serve as indicators of the maximum levels of enrichment in residual material. Greater enrichment of elements such as Ca, Mg, Sr, Sc, P, Cr and Co indicate structural incorporation, adsorption, or ion-exchange uptake by clay or secondary hydrous oxides of Fe and Mn. 3. (3) The rare-earth-element patterns and abundances in glass are sufficiently mimicked by detritus-free montmorillonite to document the compositional equivalency of the two. 4. (4) Radioactive equilibrium exists between 238U and its decay products 234U and 230Th. This documents minimal open-system mobility of U within the last ??? 0.3 Ma. ?? 1982.

  2. Growth and characterization of periodically polarity-inverted ZnO structures on sapphire substrates

    SciTech Connect

    Park, Jinsub; Yao, Takafumi

    2012-10-15

    We report on the fabrication and characterization of periodically polarity inverted (PPI) ZnO heterostructures on (0 0 0 1) Al{sub 2}O{sub 3} substrates. For the periodically inverted array of ZnO polarity, CrN and Cr{sub 2}O{sub 3} polarity selection buffer layers are used for the Zn- and O-polar ZnO films, respectively. The change of polarity and period in fabricated ZnO structures is evaluated by diffraction patterns and polarity sensitive piezo-response microscopy. Finally, PPI ZnO structures with subnanometer scale period are demonstrated by using holographic lithography and regrowth techniques.

  3. Adenine derivatives as phosphate-activating groups for the regioselective formation of 3',5'-linked oligoadenylates on montmorillonite: possible phosphate-activating groups for the prebiotic synthesis of RNA

    NASA Technical Reports Server (NTRS)

    Prabahar, K. J.; Ferris, J. P.

    1997-01-01

    Methyladenine and adenine N-phosphoryl derivatives of adenosine 5'-monophosphate (5'-AMP) and uridine 5'-monophosphate (5'-UMP) are synthesized, and their structures are elucidated. The oligomerization reactions of the adenine derivatives of 5'-phosphoramidates of adenosine on montmorillonite are investigated. 1-Methyladenine and 3-methyladenine derivatives on montmorillonite yielded oligoadenylates as long as undecamer, and the 2-methyladenine and adenine derivatives on montmorillonite yielded oligomers up to hexamers and pentamers, respectively. The 1-methyladenine derivative yielded linear, cyclic, and A5'ppA-derived oligonucleotides with a regioselectivity for the 3',5'-phosphodiester linkages averaging 84%. The effect of pKa and amine structure of phosphate-activating groups on the montmorillonite-catalyzed oligomerization of the 5'-phosphoramidate of adenosine are discussed. The binding and reaction of methyladenine and adenine N-phosphoryl derivatives of adenosine are described.

  4. Fungal biomineralization of montmorillonite and goethite to short-range-ordered minerals

    NASA Astrophysics Data System (ADS)

    Li, Huan; Hu, Shuijin; Polizzotto, Matthew L.; Chang, Xiaoli; Shen, Qirong; Ran, Wei; Yu, Guanghui

    2016-10-01

    Highly reactive nano-scale minerals, e.g., short-range-ordered minerals (SROs) and other nanoparticles, play an important role in soil carbon (C) retention. Yet, the mechanisms that govern biomineralization from bulk minerals to highly reactive nano-scale minerals remain largely unexplored, which critically hinders our efforts toward managing nano-scale minerals for soil C retention. Here we report the results from a study that explores structural changes during Aspergillus fumigatus Z5 transformation of montmorillonite and goethite to SROs. We examined the morphology and structure of nano-scale minerals, using high-resolution transmission electron microscopy, time-resolved solid-state 27Al and 29Si NMR, and Fe K-edge X-ray absorption fine structure spectroscopy combined with two dimensional correlation spectroscopy (2D COS) analysis. Our results showed that after a 48-h cultivation of montmorillonite and goethite with Z5, new biogenic intracellular and extracellular reactive nano-scale minerals with a size of 3-5 nm became abundant. Analysis of 2D COS further suggested that montmorillonite and goethite were the precursors of the dominant biogenic nano-scale minerals. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectra and their deconvolution results demonstrated that during fungus Z5 growth, carboxylic C (288.4-289.1 eV) was the dominant organic group, accounting for approximately 34% and 59% in the medium and aggregates, respectively. This result suggested that high percentage of the production of organic acids during the growth of Z5 was the driving factor for structural changes during biomineralization. This is, to the best of our knowledge, the first report of the structural characterization of nano-scale minerals by 2D COS, highlighting its potential to elucidate biomineralization pathways and thus identify the precursors of nano-scale minerals.

  5. The formation mechanism of the periodic nanograting structure by the Weibel instability

    NASA Astrophysics Data System (ADS)

    Gouda, A. M.; Sakagami, H.; Ogata, T.; Hashida, M.; Sakabe, S.

    2016-04-01

    The two-dimensional particle in cell code has been used to demonstrated the formation mechanism for the periodic nanograting structure using 500-fs pulses of an ultra-fast laser with wavelength 800 nm, incidence angle 0°, linearly-polarized, and intensity 1018 W/cm2 µm2 in hydrogen plasma. The periodic nanograting structure has been clearly self-organized at the boundary between the preformed plasma and the dense plasma at t = 250 fs. By time evolution of the magnetic field and the current density in the dense plasma, it has been found that the Weibel instability plays a significant role to form the periodic nanograting structure.

  6. Solid state characterisation of silver sulfadiazine loaded on montmorillonite/chitosan nanocomposite for wound healing.

    PubMed

    Aguzzi, Carola; Sandri, Giuseppina; Bonferoni, Cristina; Cerezo, Pilar; Rossi, Silvia; Ferrari, Franca; Caramella, Carla; Viseras, César

    2014-01-01

    Biopolymer chitosan/montmorillonite nanocomposites loaded with silver sulfadiazine for wound healing purposes were prepared via intercalation solution technique. Structure and morphology of loaded nanocomposites were studied and compared with pure components and unloaded nanocomposites. X-ray diffraction, Fourier transformed infrared spectroscopy, high resolution transmission electron microscopy coupled with energy-dispersion X-ray analysis, thermal and elemental analysis were employed for the characterisation. The results confirmed that the drug was effectively loaded in the three-dimensional nanocomposite structures, in which chitosan chains were adsorbed in monolayers into the clay mineral interlayer spaces.

  7. Adsorption of phenol on inorganic-organic pillared montmorillonite in polluted water.

    PubMed

    Wu, P X; Liao, Z W; Zhang, H F; Guo, J G

    2001-05-01

    Both inorganic- and organic-pillared montmorillonites (PMts) were used to adsorb phenol to study suitable conditions for adsorption and adsorption isotherms. The adsorbing capacity of modified clays depends not only surface area, but mainly on micropore structure and surface components. After incandescing at 500 degrees C, the pillar structure and the basal interlayer spacing (1.83 nm) remained stable. Using modified PMt with surfactant can improve adsorbing capacity greatly. The PMt can be recycled, and it is a potential substance for adsorption of environmental pollutants.

  8. Batch sorption and spectroscopic speciation studies of neptunium uptake by montmorillonite and corundum

    NASA Astrophysics Data System (ADS)

    Elo, O.; Müller, K.; Ikeda-Ohno, A.; Bok, F.; Scheinost, A. C.; Hölttä, P.; Huittinen, N.

    2017-02-01

    Detailed information on neptunium(V) speciation on montmorillonite and corundum surfaces was obtained by batch sorption and desorption studies combined with surface complexation modelling using the Diffuse Double-Layer (DDL) model, in situ time-resolved Attenuated Total Reflection Fourier-Transform Infrared (ATR FT-IR) and X-ray absorption (XAS) spectroscopies. The pH-dependent batch sorption studies and the spectroscopic investigations were conducted under carbonate-free conditions in 10 mM NaClO4 or 10 mM NaCl. Solid concentrations of 0.5 g/l and 5 g/l were used depending on the experiment. The neptunium(V) desorption from the two mineral surfaces was investigated at pH values ranging from 8 to 10, using the replenishment technique. Neptunium(V) was found to desorb from the mineral surface, however, the extent of desorption was dependent on the solution pH. The desorption of neptunium(V) was confirmed in the ATR FT-IR spectroscopic studies at pH 10, where all of the identified inner-sphere complexed neptunium(V), characterized by a vibrational band at 790 cm-1, was desorbed from both mineral surfaces upon flushing the mineral films with a blank electrolyte solution. In XAS investigations of neptunium(V) uptake by corundum, the obtained structural parameters confirm the formation of an inner-sphere complex adsorbed on the surface in a bidentate fashion. As the inner-sphere complexes found in the IR-studies are characterized by identical sorption bands on both corundum and montmorillonite, we tentatively assigned the neptunium(V) inner-sphere complex on montmorillonite to the same bidentate complex found on corundum in the XAS investigations. Finally, the obtained batch sorption and spectroscopic results were modelled with surface complexation modelling to explain the neptunium(V) speciation on montmorillonite over the entire investigated pH range. The modelling results show that cation exchange in the interlayer space as well as two pH-dependent surface complexes

  9. CO2-Laser-Induced Regular Periodic Structures on Glass Substrates

    NASA Astrophysics Data System (ADS)

    Peng, Yingzi; An, Chengwu; Hong, Minghui; Lu, Yongfeng; Chong, Tow-chong

    2003-11-01

    A CW CO2 laser was used to induce regular and tidy periodic structures on glass substrates. It is experimentally shown that the wave vector of the ripples is perpendicular to the recording polarization irrespective of the scanning direction. The occurrence of periodic structures is highly sensitive to laser power level and scanning velocity. To obtain appropriate periodic patterns, a combined condition of laser power and scanning velocity must be satisfied. Different directions of laser scanning lead to different occurrence areas. Different kinds of materials seem to develop the occurrence areas with almost similar shape, but their relative positions and dimensions may be different. The maximum laser scanning velocity range to form regular and tidy periodic structures appears at the optimum power condition. Moreover, the maximum period could be obtained at this optimum condition.

  10. Earthquake Induced Damage Mechanism of Long Period Structures Using Energy Response

    SciTech Connect

    Du Yongfeng; Li Hui

    2008-07-08

    This paper presents a method of expounding the damage of RC long period frame structure using energy analysis method. Since the damage of structures usually occurs under major earthquakes, the structure is assumed to be in elasto-plastic state, and degraded Bouc-Wen model is used to describe the hysteretic component of the restoring force. A double index damage criterion defined by the maximum drift and energy absorption is used as the damage criterion. The energy transferring relation in a structure is derived, and both momentary and cumulative energy response is used to reflect the delay of the collapse of a long period structure. The mechanism of collapse delay of the long period structure is suggested through a numerical example combing the energy response and time history response.

  11. Distribution pattern of rare earth ions between water and montmorillonite and its relation to the sorbed species of the ions.

    PubMed

    Takahashi, Yoshio; Tada, Akisa; Shimizu, Hiroshi

    2004-09-01

    REE (rare earth element) distribution coefficients (Kd) between the aqueous phase and montmorillonite surface were obtained to investigate the relation between the REE distribution patterns and the species of REE sorbed on the solid-water interface. It was shown that the features in the REE patterns, such as the slope of the REE patterns, the tetrad effect, and the Y/Ho ratio, were closely related to the REE species at the montmorillonite-water interface. In a binary system (REE-montmorillonite) below pH 5, three features (a larger Kd value for a lighter REE, the absence of the tetrad effect, and the Y/Ho ratio being unchanged from its initial value) suggest that hydrated REE are directly sorbed as an outer-sphere complex at the montmorillonite-water interface. Above pH 5.5, the features in the REE patterns, the larger Kd value for heavier REE, the M-type tetrad effect, and the reduced Y/Ho ratio, showed the formation of an inner-sphere complex of REE with -OH group at the montmorillonite surface. In addition, the REE patterns in the presence of humic acid at pH 5.9 were also studied, where the REE patterns became flat, suggesting that the humate complex is dominant as both dissolved and sorbed species of REE in the ternary system. All of these results were consistent with the spectroscopic data (laser-induced fluorescence spectroscopy) showing the local structure of Eu(III) conducted in the same experimental system. The present results suggest that the features in the REE distribution patterns include information on the REE species at the solid-water interface.

  12. Hybrid FDTD Analysis for Periodic On-Chip Terahertz (THZ) Structures

    SciTech Connect

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    We present electromagnetic analysis and radiation efficiency calculations for on-chip terahertz (THz) structures based on a hybrid, finite-difference, time-domain (HFDTD) technique. The method employs the FDTD technique to calculate S-parameters for one cell of a periodic structure. The transmission ABCD matrix is then estimated and multiplied by itself n times to obtain the n-cell periodic structure ABCD parameters that are then converted back to S-parameters. Validation of the method is carried out by comparing the results of the hybrid technique with FDTD calculations of the entire periodic structure as well as with HFSS which all agree quite well. This procedure reduces the CPU-time and allows efficient design and optimization of periodic THz radiation sources. Future research will involve coupling of Maxwell's equations with a more detailed, physics-based transport model for higher-order effects.

  13. High spatial frequency periodic structures induced on metal surface by femtosecond laser pulses.

    PubMed

    Yao, Jian-Wu; Zhang, Cheng-Yun; Liu, Hai-Ying; Dai, Qiao-Feng; Wu, Li-Jun; Lan, Sheng; Gopal, Achanta Venu; Trofimov, Vyacheslav A; Lysak, Tatiana M

    2012-01-16

    The high spatial frequency periodic structures induced on metal surface by femtosecond laser pulses was investigated experimentally and numerically. It is suggested that the redistribution of the electric field on metal surface caused by the initially formed low spatial frequency periodic structures plays a crucial role in the creation of high spatial frequency periodic structures. The field intensity which is initially localized in the grooves becomes concentrated on the ridges in between the grooves when the depth of the grooves exceeds a critical value, leading to the ablation of the ridges in between the grooves and the formation of high spatial frequency periodic structures. The proposed formation process is supported by both the numerical simulations based on the finite-difference time-domain technique and the experimental results obtained on some metals such as stainless steel and nickel.

  14. On the period of the coherent structure in boundary layers at large Reynolds numbers

    NASA Technical Reports Server (NTRS)

    Narayanan, M. A. B.; Marvin, J. G.

    1978-01-01

    The period of the large coherent structure in a subsonic, compressible, turbulent boundary layer was determined using the autocorrelation of the velocity and pressure fluctuations for Reynolds numbers between 5,000 and 35,000. In low Reynolds number flows the overall correlation period scaled with the outer variables - namely, the free stream velocity and the boundary layer thickness.

  15. The effects of microstructural changes on montmorillonite-microbial interactions

    NASA Astrophysics Data System (ADS)

    Spence, Adrian; Robinson, Claion; Hanson, Richard E.

    2014-01-01

    Clay minerals are important natural adsorbents of soil organic matter (SOM) and therefore are natural modulators of soil-atmospheric carbon fluxes. Although such effects have been reported, little is known about the spatial distribution of organic matter (OM) on the surfaces of soil minerals and even less is known about the effects of microstructural changes on clay-organo interactions. Here we employ acid hydrolysis to induce varying degrees of microstructural changes to montmorillonite clay mineral as a function of time and combine IR spectroscopy, X-ray diffraction, and SEM-EDX as primary techniques to independently provide molecular-level information on the effects these changes on microbial interactions with the mineral. We observed that progressive dissolution of octahedral cations and the simultaneous enrichment of amorphous silica are prominent structural changes induced by hydrolysis, and that the adsorption of microbial-derived components (in particular lipids) on the surfaces of acid-treated clay decreases with increasing acid dissolution time. Although the precise mechanism(s) of interactions remains unclear, we speculate that this adsorption behavior is most likely due to spatial co-variation of microbial-derived OM with octahedral cations in the mineral, acid erosion of biochemically active binding sites, and/or a progressive increase in the hydrophilicity of the mineral surfaces by acid attack over time.

  16. Transport mechanisms of small molecules through polyamide 12/montmorillonite nanocomposites.

    PubMed

    Alexandre, B; Colasse, L; Langevin, D; Médéric, P; Aubry, T; Chappey, C; Marais, S

    2010-07-15

    The aim of this work is to study the transport of small molecules through the hybrid systems polyamide 12 (PA12)/organo-modified montmorillonite (Cloisite 30B, C30B) prepared by melt blending, using two blending conditions. The transport mechanisms were investigated by using three probe molecules: nitrogen, water, and toluene. While a barrier effect appears clearly with nitrogen, this effect changes with the amount of fillers for water and disappears for toluene. The reduction of permeability for nitrogen is mainly due to the increase of tortuosity. For water and toluene, the permeation kinetics reveals many concomitant phenomena responsible for the permeation behavior. Despite the tortuosity effect, the toluene permeability of nanocomposites increases with C30B fraction. The water and toluene molecules interact differently with fillers according to their hydrophilic/hydrophobic character. Moreover, the plasticization effect of water and toluene in the matrix, involving a concentration-dependent diffusion coefficient, is correctly described by the law D = D(0)e(gammaC). On the basis of Nielsen's tortuosity concept, we suggest a new approach for relative permeability modeling, not only based on the geometrical parameters (aspect ratio, orientation, recovery) but also including phenomenological parameters deduced from structural characterization and permeation kinetics.

  17. Disassembly of the cystovirus ϕ6 envelope by montmorillonite clay.

    PubMed

    Block, Karin A; Trusiak, Adrianna; Katz, Al; Gottlieb, Paul; Alimova, Alexandra; Wei, Hui; Morales, Jorge; Rice, William J; Steiner, Jeffrey C

    2014-02-01

    Prior studies of clay-virus interactions have focused on the stability and infectivity of nonenveloped viruses, yielding contradictory results. We hypothesize that the surface charge distribution of the clay and virus envelope dictates how the components react and affect aggregation, viral stability, and infectivity. The bacteriophage Cystoviridae species φ6 used in this study is a good model for enveloped pathogens. The interaction between φ6 and montmorillonite (MMT) clay (the primary component of bentonite) is explored by transmission electron microscopy. The analyses show that MMT-φ6 mixtures undergo heteroaggregation, forming structures in which virtually all the virions are either sequestered between MMT platelet layers or attached to platelet edges. The virions swell and undergo disassembly resulting in partial or total envelope loss. Edge-attached viral envelopes distort to increase contact area with the positively charged platelet edges indicating that the virion surface is negatively charged. The nucleocapsid (NCs) remaining after envelope removal also exhibit distortion, in contrast to detergent-produced NCs which exhibit no distortion. This visually discernible disassembly is a mechanism for loss of infectivity previously unreported by studies of nonenveloped viruses. The MMT-mediated sequestration and disassembly result in reduced infectivity, suggesting that clays may reduce infectivity of enveloped pathogenic viruses in soils and sediments.

  18. Disassembly of the cystovirus ϕ6 envelope by montmorillonite clay

    PubMed Central

    Block, Karin A; Trusiak, Adrianna; Katz, Al; Gottlieb, Paul; Alimova, Alexandra; Wei, Hui; Morales, Jorge; Rice, William J; Steiner, Jeffrey C

    2014-01-01

    Prior studies of clay–virus interactions have focused on the stability and infectivity of nonenveloped viruses, yielding contradictory results. We hypothesize that the surface charge distribution of the clay and virus envelope dictates how the components react and affect aggregation, viral stability, and infectivity. The bacteriophage Cystoviridae species φ6 used in this study is a good model for enveloped pathogens. The interaction between φ6 and montmorillonite (MMT) clay (the primary component of bentonite) is explored by transmission electron microscopy. The analyses show that MMT–φ6 mixtures undergo heteroaggregation, forming structures in which virtually all the virions are either sequestered between MMT platelet layers or attached to platelet edges. The virions swell and undergo disassembly resulting in partial or total envelope loss. Edge-attached viral envelopes distort to increase contact area with the positively charged platelet edges indicating that the virion surface is negatively charged. The nucleocapsid (NCs) remaining after envelope removal also exhibit distortion, in contrast to detergent-produced NCs which exhibit no distortion. This visually discernible disassembly is a mechanism for loss of infectivity previously unreported by studies of nonenveloped viruses. The MMT-mediated sequestration and disassembly result in reduced infectivity, suggesting that clays may reduce infectivity of enveloped pathogenic viruses in soils and sediments. PMID:24357622

  19. Carbonate formation in Wyoming montmorillonite under high pressure carbon dioxide

    SciTech Connect

    Hur, Tae-Bong; Baltrus, John P.; Howard, Bret H.; Harbert, William P.; Romanov, Vyacheslav N.

    2013-03-01

    Carbonation reaction with silicate minerals that are common components of the host rock and cap rock within geological storage reservoirs and the associated structural deformation were investigated for better understanding of the geochemical reactions associated with geologic CO2 storage. Exposure of a model expanding clay, Wyoming montmorillonite, SWy-2, to high-pressure CO2 resulted in the formation of a mineral carbonate phase via dry CO2–clay mineral interactions at two different temperatures. The experimental evidence suggests that the properties of CO2 fluid at 70 °C provide more favorable conditions for carbonate formation at the clay surface less accessible to CO2 at 22 °C. The carbonation reaction occurred predominantly within the first couple of days of exposure to the fluid and then proceeded slower with continuing exposure. As compared to the as-received clay under the same ambient conditions, the (0 0 1) basal spacing of the clay bearing carbonates (after the CO2 exposure) was slightly expanded at a relative humidity (RH) level of 12% but it was slightly collapsed at the RH level of 40%. Finally, experimental observations suggest that the carbonation reaction occurs at the external surface as well as internal surface (interlayer) of the clay particles.

  20. Examining Periodic Solar-Wind Density Structures Observed in the SECCHI Heliospheric Imagers

    NASA Technical Reports Server (NTRS)

    Viall, Nicholeen M.; Spence, Harlan E.; Vourlidas, Angelos; Howard, Russell

    2010-01-01

    We present an analysis of small-scale, periodic, solar-wind density enhancements (length scales as small as approximately equals 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO-A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also nonturbulent, periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper analyzed the alpha-to-proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed at 1 AU, which were generated in the corona, can be observable in coronal and heliospheric white-light images if they possess sufficiently high density contrast. Indeed, we identify such periodic density structures as they enter the HI field of view and follow them as they advect with the solar wind through the images. The smaller, periodic density structures that we identify in the images are comparable in size to the larger structures analyzed in-situ at 1 AU, yielding further evidence that periodic density enhancements are a consequence of coronal activity as the solar wind is formed.

  1. Highly Sensitive and Robust Damage Detection of Periodic Structures with Piezoelectric Networking

    DTIC Science & Technology

    2008-05-01

    REPORT TYPE Final 3. DATES COVERED (From - To) December 15. 2006 to May 3 1. 2008 4. TITLE AND SUBTITLE Highly Sensitive and Robust Damage...localization characteristics of such periodic structures to enhance damage detection sensitivity and robustness through piezoelectric circuitry...ANSI Sid Z39 18 Adobe Professional 7.0 Highly Sensitive and Robust Damage Detection of Periodic Structures with Piezoelectric Networking GRANT

  2. The mechanism of montmorillonite catalysis in RNA synthesis

    NASA Astrophysics Data System (ADS)

    Joshi, Prakash

    The formation of complex prebiotic molecules on the early Earth is likely to have involved a component of mineral catalysis. Amongst the variety of clay minerals that have been investigated by us for their ability to catalyze the formation of RNA oligomers is montmorillonite. These are 2:1 layer silicates that have a wide range of chemical compositions [(Na,Ca)0.33(Al,Fe,Mg)2(Si,Al)4O10(OH)2.nH2O]. They are commonly produced by the weathering of silicic volcanic ashes to form Bentonite. Once formed, montmorillonites gradually transform to Illites at a modest pressure and temperature. Of the many samples of montmorillonite that we have experimentally examined, a selected subset has been observed to be catalytic for RNA synthesis (Joshi et. al., 2009; Aldersley et al., 2011). Those that have been observed to be excellent catalysts come from a restricted range of elemental compositions. The recent identification of phyllosilicates including montmorillonite on Mars (Bishop et al., 2008) raises the possibility that such processes may have taken place there too. The extent of catalysis depended not only upon the magnitude of the negative charge on the montmorillonite lattice and the number of cations associated with it, but also on the pH at which the reaction is promoted. The isotherm and catalysis studies were extended to provide binding information and catalytic outcomes over a wide pH range. When cations in raw montmorillonite are completely replaced by sodium ions, the resulting Na+-montmorillonite does not catalyze oligomer formation because the ions saturate the interlayer between the platelets of montmorillonite, which blocks the binding of the activated monomers. Acid washed montmorillonite titrated to pH 6-8 with alkali metal ions, serves as the model catalyst for this RNA synthesis (Aldersley et. al., 2011). The optimal binding occurred in the region of maximal oligomer formation. X-ray diffraction studies revealed changes in layer separations of

  3. Single-solute and bisolute sorption of phenol and trichloroethylene from aqueous solution onto modified montmorillonite and application of sorption models.

    PubMed

    Wu, C D; Wang, L; Hu, C X; He, M H

    2013-01-01

    The single-solute and bisolute sorption behaviour of phenol and trichloroethylene, two organic compounds with different structures, onto cetyltrimethylammonium bromide (CTAB)-montmorillonite was studied. The monolayer Langmuir model (MLM) and empirical Freundlich model (EFM) were applied to the single-solute sorption of phenol or trichloroethylene from water onto monolayer or multilayer CTAB-montmorillonite. The parameters contained in the MLM and EFM were determined for each solute by fitting to the single-solute isotherm data, and subsequently utilized in binary sorption. The extended Langmuir model (ELM) coupled with the single-solute MLM and the ideal adsorbed solution theory (IAST) coupled with the single-solute EFM were used to predict the binary sorption of phenol and trichloroethylene onto CTAB-montmorillonite. It was found that the EFM was better than the MLM at describing single-solute sorption from water onto CTAB-montmorillonite, and the IAST was better than the ELM at describing the binary sorption from water onto CTAB-montmorillonite.

  4. 1d, 2d, and 3d periodic structures: Electromagnetic characterization, design, and measurement

    NASA Astrophysics Data System (ADS)

    Brockett, Timothy John

    Periodic structures have many useful applications in electromagnetics including phased arrays, frequency selective surfaces, and absorbing interfaces. Their unique properties can be used to provide increased performance in antenna gain, electromagnetic propagation, and electromagnetic absorption. In antenna arrays, repeating elements create a larger eective aperture, increasing the gain of the antenna and the ability to scan the direction of the main beam. Three-dimensional periodic structures, such as an array of shaped pillars such as columns, cones, or prisms have the potential of improving electromagnetic absorption, improving performance in applications such as solar cell eciency and absorbing interfaces. Furthermore, research into periodic structures is a continuing endeavor where novel approaches and analysis in appropriate applications can be sought. This dissertation will address the analysis, diagnostics, and enhancement of 1D, 2D, and 3D periodic structures for antenna array applications and solar cell technology. In particular, a unique approach to array design will be introduced to prevent the appearance of undesirable grating lobes in large antenna arrays that employ subarrays. This approach, named the distortion diagnostic procedure, can apply directly to 1D and 2D periodic structures in the form of planar antenna arrays. Interesting corollaries included here are developments in millimeter-wave antenna measurements including spiral planar scanning, phaseless measurements, and addressing antennas that feature an internal source. Finally, analysis and enhancement of 3D periodic structures in nanostructure photovoltaic arrays and absorbing interfaces will be examined for their behavior and basic operation in regards to improved absorption of electromagnetic waves.

  5. Transformation of Triclosan by Fe(III)-saturated montmorillonite.

    PubMed

    Liyanapatirana, Chamindu; Gwaltney, Steven R; Xia, Kang

    2010-01-15

    Abiotic transformation of triclosan (TCS) was investigated by incubating TCS with Fe(III)- and Na-montmorillonite at 40% relative humidity and room temperature for up to 100 days. The TCS transformation products were characterized using LC/MS, GC/MS, and computational modeling and quantified using HPLC/UV and GC/MS. Within 1-5 days, depending on the initial TCS concentrations, about 55% of the TCS was rapidly transformed in the presence of Fe(III)-montmorillonite, producing 2,4-dichlorophenol, 3-chlorophenol, 2,4-dichlorophenol dimer, chlorophenoxy phenols, and TCS dimers and trimers. Computational modeling based on density functional theory confirmed the formation of four TCS dimer conformers and six TCS trimer conformers. The TCS phenoxy radicals, produced by Fe(III) oxidation of TCS, react with other TCS molecules to form TCS dimers. The TCS trimers were formed by attachment of TCS dimer phenoxy radicals, produced by Fe(III) oxidation of TCS dimers, with TCS molecules. Significantly smaller quantities of TCS transformation products were detected in the reactions with Na-montmorillonite compared to the reactions with Fe(III)-montmorillonite. Formation of a significant amount of 2,4-dichlorophenol, especially in reaction with Fe(III)-montmorillonite, may have negative impact on the environment because of its toxicity. However, mineral-facilitated TCS polymerization may reduce its mobility and bioavailability in soils.

  6. Peptide formation mechanism on montmorillonite under thermal conditions.

    PubMed

    Fuchida, Shigeshi; Masuda, Harue; Shinoda, Keiji

    2014-02-01

    The oligomerization of amino acids is an essential process in the chemical evolution of proteins, which are precursors to life on Earth. Although some researchers have observed peptide formation on clay mineral surfaces, the mechanism of peptide bond formation on the clay mineral surface has not been clarified. In this study, the thermal behavior of glycine (Gly) adsorbed on montmorillonite was observed during heating experiments conducted at 150 °C for 336 h under dry, wet, and dry-wet conditions to clarify the mechanism. Approximately 13.9 % of the Gly monomers became peptides on montmorillonite under dry conditions, with diketopiperazine (cyclic dimer) being the main product. On the other hand, peptides were not synthesized in the absence of montmorillonite. Results of IR analysis showed that the Gly monomer was mainly adsorbed via hydrogen bonding between the positively charged amino groups and negatively charged surface sites (i.e., Lewis base sites) on the montmorillonite surface, indicating that the Lewis base site acts as a catalyst for peptide formation. In contrast, peptides were not detected on montmorillonite heated under wet conditions, since excess water shifted the equilibrium towards hydrolysis of the peptides. The presence of water is likely to control thermodynamic peptide production, and clay minerals, especially those with electrophilic defect sites, seem to act as a kinetic catalyst for the peptide formation reaction.

  7. Thermodynamic properties of water in compacted sodium montmorillonite

    SciTech Connect

    Torikai, Yuji; Sato, Seichi; Ohashi, Hiroshi

    1996-07-01

    Compacted bentonite is a promising material as an engineering barrier to enclose nuclear waste. The migration of nuclides occurs in the water of bentonite, where the major mineral is sodium montmorillonite. To determine the thermodynamic properties of water in compacted sodium montmorillonite, the equilibrium vapor pressure of the water in the montmorillonite was measured as a function of water content and temperature, without external pressure. The thermodynamic properties depend on water content but not on the dry density of unsaturated specimens. In montmorillonite, single-layer adsorption may proceed from 0 to 16 wt% water content, two-layer adsorption from 16 to 27 wt%, and three-layer adsorption above 27 wt%; pore water appears only in the last region. It is probable that 30 wt% of the total water included in saturated montmorillonite is not in the interlayer between platelets at 45.0 wt% water content and 0.80 {times} 10{sup 3} kg/m{sup 3} dry density. There is a very slight amount of water, which is not bound between platelets at dry densities of 1.20 and 1.76 {times} 10{sup 3} kg/m{sup 3}. This water is not a dilute electrolytic solution but has higher ionic strength, like typical seawater of salinity 23{per_thousand} and saturated NaCl.

  8. Sorption of endrin to montmorillonite and kaolinite clays.

    PubMed

    Peng, Xianjia; Wang, Jun; Fan, Bin; Luan, Zhaokun

    2009-08-30

    It has been discovered previously that clay minerals may have a greater potential for sorption of pesticides. In this paper, the sorption of endrin, a nonionic persistent organochlorine pesticide, to montmorillonite and kaolinite was investigated. The effect of pH, ionic strength on the sorption was studied. The effect of intercalation of hydroxyl aluminium species on sorption of endrin to montmorillonite was also investigated. The results show that, the sorption isotherm of endrin to montmorillonite and kaolinite was linear. The sorption increases with the increase in ionic strength. pH has effect on the sorption and the sorption on both montmorillonite and kaolinite has obvious troughs at pH about 7.2 and 5.4, respectively. The intercalation of hydroxyl aluminium species decreases the sorption. Sorption mechanism of endrin to montmorillonite and kaolinite was suggested to be a combination of hydrophobic interaction and charge-dipole interaction and troughs in the effect of pH on sorption was attributed to the proton shift reaction of the broken bonds at the clay edges.

  9. Adsorption mechanism of chloroacetanilide herbicides to modified montmorillonite.

    PubMed

    El-Nahhal, Yasser

    2003-09-01

    This study was undertaken to characterize the adsorption mechanism of alachlor and metolachlor on montmorillonite modified with cationic surfactants. Adsorbed amounts of cationic surfactant on montmorillonite surfaces were determined by CNHSO analyzer. Equilibrium concentrations of alachlor and metolachlor were determined by GC and adsorption results were fit to a linear regression equation. The slope of the isotherms (Kd) was normalized to the fraction of organic carbon on montmorillonite complexes to produce corresponding Koc. Adsorption of surfactants fit very well to Langmuir equation. Increased basal spacing indicates that surfactant molecules could penetrate through the interlayer spacing and arrange themselves in different ways. Equilibrium data of alachlor and metolachlor suggest that adsorption may occur via physical or chemical bonds. Koc values of alachlor or metolachlor decreased as the fraction of the organic carbon increased in montmorillonite complexes indicating independent adsorption process. Changes of the molar free energy of the adsorption reactions were in the range of physical adsorption, indicating that adsorption reactions are spontaneous and the molecules either adsorb on the surface or penetrate into the inter-layers of montmorillonite-surfactant complex. Careful investigation of the adsorption data suggests that interaction may occur via the active groups such as carbonyl group (-C=O), anilidic (C-N) group and/or phenyl rings. This information may provide better understanding on adsorption mechanism and be useful in designing ecologically acceptable herbicide formulations.

  10. Molecular dynamics simulation of TCDD adsorption on organo-montmorillonite.

    PubMed

    Zhu, Runliang; Hu, Wenhao; You, Zhimin; Ge, Fei; Tian, Kaixun

    2012-07-01

    In this work, molecular dynamics simulation was applied to investigate the adsorption of Tetrachlorodibenzo-p-Dioxin (TCDD) on tetramethylammonium (TMA) and tetrapropylammonium (TPA) modified montmorillonite, with the aim of providing novel information for understanding the adsorptive characteristics of organo-montmorillonite toward organic contaminants. The simulation results showed that on both outer surface and interlayer space of TPA modified montmorillonite (TPA-mont), TCDD was adsorbed between the TPA cations with the molecular edge facing siloxane surface. Similar result was observed for the adsorption on the outer surface of TMA modified montmorillonite (TMA-mont). These results indicated that TCDD had stronger interaction with organic cation than with siloxane surface. While in the interlayer space of TMA-mont, TCDD showed a coplanar orientation with the siloxane surfaces, which could be ascribed to the limited gallery height within TMA-mont interlayer. Comparing with TMA-mont, TPA-mont had larger adsorption energy toward TCDD but smaller interlayer space to accommodate TCDD. Our results indicated that molecular dynamics simulation can be a powerful tool in characterizing the adsorptive characteristics of organoclays and provided additional proof that for the organo-montmorillonite synthesized with small organic cations, the available interlayer space rather than the attractive force plays the dominant role for their adsorption capacity toward HOCs.

  11. Polymerization of alanine in the presence of a non-swelling montmorillonite

    NASA Technical Reports Server (NTRS)

    Paecht-Horowitz, M.; Lahav, N.

    1977-01-01

    Alanine, starting from alanine-adenylate, has been polymerized in the presence of non-swelling Al-montmorillonite. The yield of polymerization is much lower than that obtained in the presence of swelling Na-montmorillonite. The possibility that the changing interlayer spacing in Na-montmorillonite might be responsible for its catalytic properties, is discussed.

  12. Montmorillonite Functionalized with Pralidoxime as a Material for Chemical Protection against Organophosphorous Compounds

    DTIC Science & Technology

    2011-03-25

    implied is via iondipole forces.5,6 It is well-known that clays such as montmorillonite and kaolinite accelerate the degradation of insecticides such...REPORT Montmorillonite Functionalized with Pralidoxime As a Material for Chemical Protection against Organophosphorous Compounds 14. ABSTRACT 16...SECURITY CLASSIFICATION OF: Montmorillonite K-10 functionalized with ?-nucleophilic 2-pralidoxime (PAM) and its zwitterionic oximate form (PAMNa) is

  13. Aggregation of Montmorillonite and Organic Matter in Aqueous Media Containing Artificial Seawater

    DTIC Science & Technology

    2009-01-23

    laboratory kaolinite and montmorillonite aggregation in which the dispersion-aggregation properties of pure clay suspensions were found to be primarily...Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Aggregation of montmorillonite and organic matter in aqueous media containing...properties of suspended colloids and aggregates) were determined for systems containing suspended montmorillonite , humic acid, and/or chitin at the

  14. Ultraviolet and infrared femtosecond laser induced periodic surface structures on thin polymer films

    SciTech Connect

    Rebollar, Esther; Castillejo, Marta; Vazquez de Aldana, Javier R.; Moreno, Pablo

    2012-01-23

    This work demonstrates the formation of femtosecond laser induced periodic surface structures (LIPSS) by multipulse irradiation with the fundamental and 3rd harmonic of a linearly polarized Ti:sapphire laser (795 and 265 nm) on thin films of the polymers poly (ethylene terephthalate), poly (trimethylene terephthalate), and poly (carbonate bisphenol A) prepared by spin-coating. LIPSS, inspected by atomic force microscopy, are formed upon multiple pulse UV and IR irradiation with wavelength-sized period in a narrow range of fluences below the ablation threshold. Control and tunability of the size and morphology of the periodic structures become thus possible ensuring photochemical integrity of polymer films.

  15. Analysis of electromagnetic scattering by nearly periodic structures: an LDRD report.

    SciTech Connect

    Johnson, William Arthur; Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Wilton, Donald R. (University of Houston, Houston, TX); Basilio, Lorena I.; Peters, David William; Capolino, F.

    2006-10-01

    In this LDRD we examine techniques to analyze the electromagnetic scattering from structures that are nearly periodic. Nearly periodic could mean that one of the structure's unit cells is different from all the others--a defect. It could also mean that the structure is truncated, or butted up against another periodic structure to form a seam. Straightforward electromagnetic analysis of these nearly periodic structures requires us to grid the entire structure, which would overwhelm today's computers and the computers in the foreseeable future. In this report we will examine various approximations that allow us to continue to exploit some aspects of the structure's periodicity and thereby reduce the number of unknowns required for analysis. We will use the Green's Function Interpolation with a Fast Fourier Transform (GIFFT) to examine isolated defects both in the form of a source dipole over a meta-material slab and as a rotated dipole in a finite array of dipoles. We will look at the numerically exact solution of a one-dimensional seam. In order to solve a two-dimensional seam, we formulate an efficient way to calculate the Green's function of a 1d array of point sources. We next formulate ways of calculating the far-field due to a seam and due to array truncation based on both array theory and high-frequency asymptotic methods. We compare the high-frequency and GIFFT results. Finally, we use GIFFT to solve a simple, two-dimensional seam problem.

  16. The FP4026 Research Database on the fundamental period of RC infilled frame structures.

    PubMed

    Asteris, Panagiotis G

    2016-12-01

    The fundamental period of vibration appears to be one of the most critical parameters for the seismic design of buildings because it strongly affects the destructive impact of the seismic forces. In this article, important research data (entitled FP4026 Research Database (Fundamental Period-4026 cases of infilled frames) based on a detailed and in-depth analytical research on the fundamental period of reinforced concrete structures is presented. In particular, the values of the fundamental period which have been analytically determined are presented, taking into account the majority of the involved parameters. This database can be extremely valuable for the development of new code proposals for the estimation of the fundamental period of reinforced concrete structures fully or partially infilled with masonry walls.

  17. Efficient Modeling of Electromagnetic Scattering by Symmetric Lamellar Periodic Structures at Normal Incidence

    DTIC Science & Technology

    2004-12-01

    SYMMETRIZED MODAL-FIELD METHOD We are interested in a biaxial lamellar structure that is periodic along the x-direction. If a is the size of the primitive cell , then...structure must be symmetric about the center of each primitive cell . Thus if the origin in x is chosen to be at the center of one of the primitive cells

  18. Local field enhancement on metallic periodic surface structures produced by femtosecond laser pulses

    SciTech Connect

    Ionin, Andrei A; Kudryashov, Sergei I; Ligachev, A E; Makarov, Sergei V; Mel'nik, N N; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Khmelnitskii, R A

    2013-04-30

    Periodic surface structures on aluminium are produced by femtosecond laser pulses for efficient excitation of surface electromagnetic waves using a strong objective (NA = 0.5). The local electromagnetic field enhancement on the structures is measured using the technique of surface-enhanced Raman scattering from pyridine molecules. (extreme light fields and their applications)

  19. Formation of RNA oligomers on montmorillonite: site of catalysis

    NASA Technical Reports Server (NTRS)

    Ertem, G.; Ferris, J. P.

    1998-01-01

    Certain montmorillonites catalyze the self condensation of the 5'-phosphorimidazolide of nucleosides in pH 8 aqueous electrolyte solutions at ambient temperatures leading to formation of RNA oligomers. In order to establish the nature of the sites on montmorillonite responsible for this catalytic activity, oligomerization reactions were run with montmorillonites which had been selectively modified (I) at the edges by (a) fluoride treatment, (b) silylation, (c) metaphosphate treatment of the anion exchange sites (II) in the interlayer by (a) saturation with quaternary alkylammonium ions of increasing size, (b) aluminum polyoxo cations. High pressure liquid chromatography, HPLC, analysis of condensation products for their chain lengths and yields indicated that modification at the edges did not affect the catalytic activity to a significant extent, while blocking the interlayer strongly inhibited product formation.

  20. Study of cetyltrimethylammonium and cetylpyridinium adsorption on montmorillonite.

    PubMed

    Praus, Petr; Turicová, Martina; Studentová, Sona; Ritz, Michal

    2006-12-01

    Adsorption of cetyltrimethylammonium (CTA) and cetylpyridinium (CP) onto Na-rich montmorillonite (MMT) was studied. For this purpose, the adsorption isotherms of CTA and CP, along with desorption curves of metal cations (Na+, K+, Ca2+, Mg2+), were obtained by means of capillary isotachophoresis and atomic absorption spectrometry. Infrared, X-ray diffraction pattern, specific surface area, porosity, and moisture adsorption measurements of montmorillonite revealed that CTA and CP were adsorbed in monolayer arrangements. CTA is assumed to be attached to the negatively charged MMT surface mainly by electrostatic forces. On the other hand, CP, adsorbed in higher amounts, can be additionally bound via other interactions of pyridinium rings, such as induced and pi-pi interactions. By the surfactant adsorption, the montmorillonite surface became hydrophobic and its micro- and mesopores were significantly diminished. Using scanning electron microscopy, aggregation of such organically modified MMT particles was observed.

  1. Speciation of uranium(VI) sorption complexes on montmorillonite

    SciTech Connect

    Chisholm-Brause, C.J.; Morris, D.E.; Richard, R.E.

    1992-05-01

    Environmental contaminant releases that contain uranium are among the most serious problems that must be confronted by restoration programs. To facilitate restoration, information concerning the speciation of uranium is needed. Under oxidizing conditions, dissolved uranium is predominantly in the U(VI) (uranyl) form and is quite mobile in the environment, however sorption onto soils may retard its movement. In this study, we have investigated the effects of changes in solution speciation on the nature of uranyl sorption complexes on montmorillonite, a common soil constituent. Aqueous U(VI) solutions between pH 3 to 7 were batch-equilibrated with montmorillonite for several days; specific pH values were selected such that the solutions consisted of dominantly monomeric, oligomeric, or a mix of monomeric and oligomeric aqueous uranyl species. Emission spectroscopy was used to investigate the nature of U(VI) sorbed to montmorillonite.

  2. Retention of gases by hexadecyltrimethylammonium-montmorillonite clays.

    PubMed

    Volzone, C; Rinaldi, J O; Ortiga, J

    2006-05-01

    Intercalated montmorillonite clays with different amounts of organic hexadecyltrimethylammonium (HDTMA) cations were studied to analyse their CO, CH(4), and SO(2) gas retentions. Equilibrium adsorption was measured by using a standard volumetric apparatus at 25 degrees C and 0.1 MPa. The solids were characterised by X-ray diffraction. The levels of adsorption of SO(2) by organo-montmorillonites (0.3595-1.6403 mmol/g) were higher than those of CO (up to 0.0202 mmol/g) and CH(4) (up to 0.0273 mmol/g) gases. HDTMA montmorillonites may be effective adsorbents for removing SO(2) and for its potential separation in the presence of CO and/or CH(4) molecules, which can be present in contaminated air.

  3. The Catalytic Behaviour of NanoAg@montmorillonite Composite Materials

    NASA Astrophysics Data System (ADS)

    Karlíková, Martina; Kvítek, Libor; Prucek, Robert; Panáček, Aleš; Filip, Jan; Pechoušek, Jiří; Adegboyega, Nathaniel F.

    The preparation of nanoAg@montmorillonite composite materials and their catalytic activity is reported in this article. The nanoAg@montmorillonite composite materials were prepared by the adsorption of silver NPs, with an average size about 30 nm, from their aqueous dispersion onto two types of montmorillonite with different chemical composition. Silver NPs were prepared via modified Tollens process, which involves the reduction of [Ag(NH3)2]+ complex cation by maltose. The amount of silver NPs anchored onto the MMT surfaces was determined by UV-VIS spectroscopy; the decrease in absorbance of the dispersion after the adsorption was monitored. Prepared nanocomposite materials were subsequently characterized by means of transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The reduction of 4-nitrophenol by sodium borohydride was chosen to examine the catalytic properties of the synthesized silver nanocomposite materials.

  4. Prediction of the Fundamental Period of Infilled RC Frame Structures Using Artificial Neural Networks

    PubMed Central

    Asteris, Panagiotis G.; Tsaris, Athanasios K.; Cavaleri, Liborio; Repapis, Constantinos C.; Papalou, Angeliki; Di Trapani, Fabio; Karypidis, Dimitrios F.

    2016-01-01

    The fundamental period is one of the most critical parameters for the seismic design of structures. There are several literature approaches for its estimation which often conflict with each other, making their use questionable. Furthermore, the majority of these approaches do not take into account the presence of infill walls into the structure despite the fact that infill walls increase the stiffness and mass of structure leading to significant changes in the fundamental period. In the present paper, artificial neural networks (ANNs) are used to predict the fundamental period of infilled reinforced concrete (RC) structures. For the training and the validation of the ANN, a large data set is used based on a detailed investigation of the parameters that affect the fundamental period of RC structures. The comparison of the predicted values with analytical ones indicates the potential of using ANNs for the prediction of the fundamental period of infilled RC frame structures taking into account the crucial parameters that influence its value. PMID:27066069

  5. Split-field FDTD method for oblique incidence study of periodic dispersive metallic structures.

    PubMed

    Baida, F I; Belkhir, A

    2009-08-15

    The study of periodic structures illuminated by a normally incident plane wave is a simple task that can be numerically simulated by the finite-difference time-domain (FDTD) method. On the contrary, for off-normal incidence, a widely modified algorithm must be developed in order to bypass the frequency dependence appearing in the periodic boundary conditions. After recently implementing this FDTD algorithm for pure dielectric materials, we here extend it to the study of metallic structures where dispersion can be described by analytical models. The accuracy of our code is demonstrated through comparisons with already-published results in the case of 1D and 3D structures.

  6. Acoustic plate mode propagation and interaction with ultraviolet light in periodic AIN-on-sapphire structure

    SciTech Connect

    Chivukula, Venkata; Shur, Michael; Ciplys, Daumantas; Jain, Rakesh; Yang Jinwei; Gaska, Remis

    2011-02-28

    AlN overlay featuring periodic columnar structure fabricated by epitaxial lateral overgrowth technique leads to excitation of acoustic plate modes (APMs) not observed in overlays without such periodic structure. The measured velocities of acoustic plate modes propagating in AlN-on-sapphire structure were verified by numerical simulation. The APM velocity is strongly modulated by UV illumination at wavelengths from 240 to 365 nm, and the corresponding phase response is sensitive to both the UV power and the wavelength with maximum sensitivity of 3.0 ppm/({mu}W/cm{sup 2}) at 240 nm.

  7. Poly(imide)/Organically-Modified Montmorillonite Nanocomposite as a Potential Membrane for Alkaline Fuel Cells

    PubMed Central

    Battirola, Liliane C.; Gasparotto, Luiz H. S.; Rodrigues-Filho, Ubirajara P.; Tremiliosi-Filho, Germano

    2012-01-01

    In this work we evaluated the potentiality of a poly(imide) (PI)/organically-modified montmorillonite (O-MMT) nanocomposite membrane for the use in alkaline fuel cells. Both X-ray diffraction and scanning electron microscopy revealed a good dispersion of O-MMT into the PI matrix and preservation of the O-MMT layered structure. When compared to the pure PI, the addition of O-MMT improved thermal stability and markedly increased the capability of absorbing electrolyte and ionic conductivity of the composite. The results show that the PI/O-MMT nanocomposite is a promising candidate for alkaline fuel cell applications. PMID:24958290

  8. The adsorption and reaction of adenine nucleotides on montmorillonite

    NASA Astrophysics Data System (ADS)

    Ferris, James P.; Hagan, William J.

    1986-03-01

    The binding of AMP to Zn2+-montmorillonite was investigated in the presence of buffers and salts. Good's buffers, piperazine-N,N'-bis(2-ethanesulfonate) [PIPES] and morpholine-N-2-ethanesulfonate [MES], perturbed the exchangeable cations to a lesser extent (only 9% of Zn2+ displaced by 0.2 M buffer) than was observed with imidazole and lutidine buffers or NaCl and KCl salts (up to 80% of Zn2+ displaced). AMP adsorption isotherms measured in the presence of 0.2 M PIPES, MES or Na2SO4 exhibited normal Langmuir-type behavior. The adsorption coefficient, KL, is 3-fold greater in the presence of HEPES or PIPES than it is in the absence of buffers. Basal spacings measured by X-ray diffraction for Zn2+-montmorillonite are 13 and 15 Å in the presence of PIPES, while a value of 12.8 Å was determined in the absence of PIPES. These data are interpreted in a model in which the adsorption of AMP is mediated by a Zn2+ complex of PIPES in different orientations in the interlamellar region of the montmorillonite. The type of exchangeable cation does not affect the ability of the lattice-bound Fe3+ in the montmorillonite to oxidize diaminomaleonitrile (DAMN). Exchangeable Cu2+ oxidizes DAMN, but exchangeable Fe3+ is nearly ineffective as an oxidant. The addition if DISN to 3'-AMP bound to Zn2+-montmorillonite in the presence of 0.2 M PIPES resulted in a higher yield of 2', 3'-cAMP than is observed with a comparable concentration of Zn2+, a result which implicates surface catalystis by the montmorillonite.

  9. The origin of the pozzolanic activity of calcined clay minerals: A comparison between kaolinite, illite and montmorillonite

    SciTech Connect

    Fernandez, Rodrigo; Martirena, Fernando; Scrivener, Karen L.

    2011-01-15

    This paper investigates the decomposition of three clayey structures (kaolinite, illite and montmorillonite) when thermally treated at 600 {sup o}C and 800 {sup o}C and the effect of this treatment on their pozzolanic activity in cementitious materials. Raw and calcined clay minerals were characterized by the XRF, XRD, {sup 27}Al NMR, DTG and BET techniques. Cement pastes and mortars were produced with a 30% substitution by calcined clay minerals. The pozzolanic activity and the degree of hydration of the clinker component were monitored on pastes using DTG and BSE-IA, respectively. Compressive strength and sorptivity properties were assessed on standard mortars. It was shown that kaolinite, due to the amount and location of OH groups in its structure, has a different decomposition process than illite or montmorillonite, which results in an important loss of crystallinity. This explains its enhanced pozzolanic activity compared to other calcined clay-cement blends.

  10. Self-Similar Log-Periodic Structures in Western STOCK Markets from 2000

    NASA Astrophysics Data System (ADS)

    Bartolozzi, M.; Drożdż, S.; Leinweber, D. B.; Speth, J.; Thomas, A. W.

    The presence of log-periodic structures before and after stock market crashes is considered to be an imprint of an intrinsic discrete scale invariance (DSI) in this complex system. The fractal framework of the theory leaves open the possibility of observing self-similar log-periodic structures at different time scales. In the present work, we analyze the daily closures of four of the most important indices worldwide since 2000: the DAX for Germany and the NASDAQ-100, the S&P 500 and the Dow Jones for the United States. The qualitative behavior of these different markets is similar during the temporal frame studied. Evidence is found for decelerating log-periodic oscillations of duration about two years and starting in September 2000. Moreover, a nested sub-structure starting in May 2002 is revealed, bringing more evidence to support the hypothesis of self-similar, log-periodic behavior. Ongoing log-periodic oscillations are also revealed. A Lomb analysis over the aforementioned periods indicates a preferential scaling factor λ~2. Higher order harmonics are also present. The spectral pattern of the data has been found to be similar to that of a Weierstrass-type function, used as a prototype of a log-periodic fractal function.

  11. Adsorption of Ba2+ by Ca-exchange clinoptilolite tuff and montmorillonite clay.

    PubMed

    Chávez, M L; de Pablo, L; García, T A

    2010-03-15

    The adsorption of barium by Ca-exchanged clinoptilolite and montmorillonite is presented. The kinetics of adsorption of Ba(2+) were evaluated contacting 1g portion of each adsorber with 100mL 0.1N BaCl(2) for 200 h. Adsorption by Ca-clinoptilolite is defined by second-order kinetics of rate constant K(v) 8.232 x 10(-2) g mg(-1)h(-1) and maximum removal of 71.885 mg g(-1). It is a two-stage process initiated by a rapid uptake of Ba(2+) followed by more moderate kinetics. The adsorption isotherms were determined contacting 0.2g of each adsorber with 10 mL 0.1-0.005N BaCl(2)+CaCl(2) solution, Ba(2+)/Ca(2+) ratio 1, for periods of 7 days for the tuff and 2 days for the clay. The equilibrium adsorption is described by the Langmuir model, of equilibrium constant K 0.0151 L mg(-1) and maximum adsorption of 15.29 mg g(-1). The adsorption of Ba(2+) by Ca-exchanged montmorillonite also follows a second-order reaction of rate constant K(v) 3.179 x 10(-2) g mg(-1)h(-1), and calculated separation of 36.74 mg g(-1); the Langmuir isotherm is defined by the constant K 0.034 L mg(-1) and maximum adsorption of 15.29 mg g(-1). X-ray diffraction shows that the exchange of Ba(2+) modifies the d(001) of Ca-montmorillonite from 15.4 to 12.4A.

  12. Simple preparation of a cadmium selenide-montmorillonite hybrid.

    PubMed

    Ontam, Areeporn; Khaorapapong, Nithima; Ogawa, Makoto

    2011-05-15

    The immobilization of organically modified cadmium selenide on montmorillonite was investigated by the reaction of modified cadmium selenide nanoparticles with montmorillonite. The intercalation of the nanoparticles was indicated by the expansion of the interlayer space and spectroscopic observations. The diffuse reflectance absorption spectrum of the product showed absorption onset at 567 nm. In comparison to the bulk cadmium selenide, the blue shift of the absorption onset of the hybrid was ascribed to the quantum size effect of the modified cadmium selenide nanoparticles. This study provides a new method for introducing nanoparticles into the interlayer space of layered inorganic materials.

  13. Vibration transmission through periodic structures using a mobility power flow approach

    NASA Technical Reports Server (NTRS)

    Cuschieri, J. M.

    1990-01-01

    The transmission of vibrational power (time averaged) through multiple coupled (periodic) structures is examined. The analysis is performed in the frequency domain and the coupling between the sub-elements of the periodic structure is expressed in terms of structural mobility functions for the junction points and between the junction points of the sub-elements. Equal length spans between stiffeners or supports of the periodic structure are considered. Through the use of the mobility power flow approach, the influence of sub-element and junction parameters, including damping at the joints, can be investigated. The results from the analysis can be in the form of either structural intensity or alternatively structural power content for each of the sub-elements. The examples discussed are for a thin, perfectly periodic beam with a finite number of spans with different types of stiffeners and/or supports between the spans. The excitation of the structure is by a point load located midway along the first span.

  14. Modified montmorillonite as vector for gene delivery.

    PubMed

    Lin, Feng-Huei; Chen, Chia-Hao; Cheng, Winston T K; Kuo, Tzang-Fu

    2006-06-01

    Currently, gene delivery systems can be divided into two parts: viral or non-viral vectors. In general, viral vectors have a higher efficiency on gene delivery. However, they may sometimes provoke mutagenesis and carcinogenesis once re-activating in human body. Lots of non-viral vectors have been developed that tried to solve the problems happened on viral vectors. Unfortunately, most of non-viral vectors showed relatively lower transfection rate. The aim of this study is to develop a non-viral vector for gene delivery system. Montmorillonite (MMT) is one of clay minerals that consist of hydrated aluminum with Si-O tetrahedrons on the bottom of the layer and Al-O(OH)2 octahedrons on the top. The inter-layer space is about 12 A. The room is not enough to accommodate DNA for gene delivery. In the study, the cationic hexadecyltrimethylammonium (HDTMA) will be intercalated into the interlayer of MMT as a layer expander to expand the layer space for DNA accommodation. The optimal condition for the preparation of DNA-HDTMA-MMT is as follows: 1 mg of 1.5CEC HDTMA-MMT was prepared under pH value of 10.7 and with soaking time for 2 h. The DNA molecules can be protected from nuclease degradation, which can be proven by the electrophoresis analysis. DNA was successfully transfected into the nucleus of human dermal fibroblast and expressed enhanced green fluorescent protein (EGFP) gene with green fluorescence emission. The HDTMA-MMT has a great potential as a vector for gene delivery in the future.

  15. Oligomerization of uridine phosphorimidazolides on montmorillonite: a model for the prebiotic synthesis of RNA on minerals

    NASA Technical Reports Server (NTRS)

    Ding, P. Z.; Kawamura, K.; Ferris, J. P.

    1996-01-01

    The 5'-phosphorimidazolide of uridine reacts on Na(+)-montmorillonite 22A in aqueous solution to give oligomers as long as 7 mers. The maximum chain length increases to 9 mers and the overall oligomer yield increases when 9:1 ImpU, A5' ppA mixtures react under the same conditions. The oligomer yield and maximum chain length decreases with the structure of the added pyrophosphate in the order A5' ppA > A5' ppU > U5' ppU. Structure analysis of individual oligomer fractions was performed by selective enzymatic hydrolyses followed by HPLC analysis of the products. The regioselectivity for 3',5'-bond formation is 80-90% in the 9:1 ImpU, A5' ppA reaction, a percentage comparable to that observed in the 9:1 ImpA, A5' ppA reaction. Oligomerization of ImpU is inhibited by addition of dA5' ppdA, and MeppA. No oligomers containing A5' ppU were products of the 9:1 ImpU,A5' ppA reaction, a finding consistent with the simple addition of the ImpU to the A5' ppA and not the rearrangement of an ImpU-A5' ppA adduct. Concentrations of lysine or arginine which were close to that of the ImpU did not inhibit oligomer formation. Treatment of Na(+)-montmorillonite with 1 M arginine yielded arginine-montmorillonite, an amino acid-mineral adduct which did not catalyze ImpU oligomerization. Neither the 4-9 mers formed in the 9:1 ImpU, A5' ppA reaction nor the 4-9 mers formed by the base hydrolysis of poly(U) served as templates for the formation of oligo(A)s.

  16. Uranium uptake by hectorite and montmorillonite: a solution chemistry and polarized EXAFS study.

    PubMed

    Schlegel, Michel L; Descostes, Michael

    2009-11-15

    The mechanism of U(VI) retention on montmorillonite and hectorite at high ionic strength (0.5 M NaCl) was investigated by solution chemistry and, at near-neutral pH, polarized EXAFS spectroscopy. Uranium(VI) sorption increases from pH 3 to 7 on the two clays, but with a steeper edge for hectorite. Uranium(VI) is no longer retained at pH > 9, presumably owing to the formation of soluble anionic complexes. Polarized EXAFS showed that U(VI) retains its uranyl conformation on montmorillonite (U_mont) and hectorite (U_hect), with uranyl O at 1.79(2) A for U_mont and 1.82(2) A for U_hect, and split equatorial O shells at 2.29(2) and 2.47(2) A (U_mont), or 2.35(2) and 2.53(2) A (U_hect). An additional atomic shell of approximately 0.5 Al/Si at 3.3 A is detected for U_mont, but neither the oxygen nor the cationic shell exhibit clear angular dependence. These results indicate the formation of mononuclear complexes at the edges of montmorillonite platelets, with the orientation of the uranyl axis equal to the magic angle, as constrained by the edges' structural properties. In contrast to U_mont, the U-O signal varies with the polarization angle in U_hect, and the cationic Mg/Si contribution at 3.2 A is weak. The structure of this surface complex is not completely elucidated; it may correspond either to sorption on silanol sites, or to coprecipitation. These results lay out the fundamental molecular-scale basis to understand U retention by neoformed clay layers of nuclear glasses.

  17. Low participation ratio vibrational modes in a limit-periodic structure

    NASA Astrophysics Data System (ADS)

    Marcoux, Catherine; Socolar, Joshua E. S.

    Motivated by the demonstration that patterned colloidal particles may form a limit-periodic phase, we study the nature of vibrational modes in a toy model based on the Taylor-Socolar tiling. We consider a triangular lattice of identical point masses with nearest neighbors connected by springs of two different strengths, where the pattern of spring constants reflects the limit-periodic structure of the tiling. Using calculations of the phonon spectra for crystalline approximants to the limit-periodic structure, we identify several hierarchies of modes shared by the full limit-periodic system that have arbitrarily low participation ratios. We present a heuristic explanation of the existence of such modes, which are robust in the presence of vacancies and small amounts of disorder in the spring constants. Supported by the NSF Research Triangle MRSEC (DMR-1121107).

  18. Narrowband DWDM filters based on Fibonacci-class quasi-periodic structures.

    PubMed

    Golmohammadi, S; Moravvej-Farshi, M K; Rostami, A; Zarifkar, A

    2007-08-20

    In this paper, we propose a narrowband DWDM filter structure, whose reflection band characteristics, meets the ITU-T standard. The proposed filter structure is based on Fibonacci quasi-periodic structures composed of multilayers with large index differences. Studying the effects of the optical and geometrical parameters of Fibonacci quasi-periodic structures on its filtering properties, we have realized that to achieve the ITU-T standard, we need to cascade two successive structures both with the same generation numbers j=4 and orders n=25 and apodized refractive indices. The apodization process helps to minimize the stop band sidelobes. We have also demonstrated that beside Fibonacci's order, n, the layers dimensions, and their refractive index ratios are the main design parameters.

  19. Transfer-matrix approach for finite-difference time-domain simulation of periodic structures.

    PubMed

    Deinega, Alexei; Belousov, Sergei; Valuev, Ilya

    2013-11-01

    Optical properties of periodic structures can be calculated using the transfer-matrix approach, which establishes a relation between amplitudes of the wave incident on a structure with transmitted or reflected waves. The transfer matrix can be used to obtain transmittance and reflectance spectra of finite periodic structures as well as eigenmodes of infinite structures. Traditionally, calculation of the transfer matrix is performed in the frequency domain and involves linear algebra. In this work, we present a technique for calculation of the transfer matrix using the finite-difference time-domain (FDTD) method and show the way of its implementation in FDTD code. To illustrate the performance of our technique we calculate the transmittance spectra for opal photonic crystal slabs consisting of multiple layers of spherical scatterers. Our technique can be used for photonic band structure calculations. It can also be combined with existing FDTD methods for the analysis of periodic structures at an oblique incidence, as well as for modeling point sources in a periodic environment.

  20. Transfer-matrix approach for finite-difference time-domain simulation of periodic structures

    NASA Astrophysics Data System (ADS)

    Deinega, Alexei; Belousov, Sergei; Valuev, Ilya

    2013-11-01

    Optical properties of periodic structures can be calculated using the transfer-matrix approach, which establishes a relation between amplitudes of the wave incident on a structure with transmitted or reflected waves. The transfer matrix can be used to obtain transmittance and reflectance spectra of finite periodic structures as well as eigenmodes of infinite structures. Traditionally, calculation of the transfer matrix is performed in the frequency domain and involves linear algebra. In this work, we present a technique for calculation of the transfer matrix using the finite-difference time-domain (FDTD) method and show the way of its implementation in FDTD code. To illustrate the performance of our technique we calculate the transmittance spectra for opal photonic crystal slabs consisting of multiple layers of spherical scatterers. Our technique can be used for photonic band structure calculations. It can also be combined with existing FDTD methods for the analysis of periodic structures at an oblique incidence, as well as for modeling point sources in a periodic environment.

  1. Periodical Micro-Structuring of Hydride Containing Metastable Aluminumoxide using Laser Interference Metallurgy

    SciTech Connect

    Veith, Michael; Andres, Katrin; Petersen, Christian; Daniel, Claus; Holzapfel, Christian; M�cklich, Frank

    2005-01-01

    Layers of the metastable ceramic HAlO are sensitive to heat: These layers transform to biphasic Al/Al2O3 due to elimination of di-hydrogen. Using interfering Nd:YAG laser beams, periodic patterns can be produced. By these methods two dimensional structuring is obtained with the characteristics of distinctly different phases and different chemical compositions at periodic places on the layer.

  2. Integration of periodic structure and highly narrowband MEMS sensor to enhance crack detection ability in steel structures

    NASA Astrophysics Data System (ADS)

    Kabir, Minoo; Ozevin, Didem

    2016-09-01

    Acoustic emission method is a nondestructive evaluation method based on the propagation of elastic waves due to the sudden change in strain field caused by newly formed fracture surfaces. While the method has been successfully applied to many structures, the influence of friction emissions limits the diverse use of the method in large-scale structures. This research integrates the metamaterial geometry to block low frequency friction signals while allowing high frequency signals due to the crack growth. The phononic structure is composed of periodic arrangement of holes in a steel plate that prohibits propagation of elastic waves near the band gap of 60 kHz. The dispersion curve of the periodic structure is calculated using finite element modeling of a unit cell in COMSOL Multiphysics. As the band gap of the periodic structure is highly narrowband, the acoustic sensing is achieved by highly narrowband capacitive type Micro-Electro- Mechanical Systems (MEMS) sensors tuned to the desired stop band frequency. The integration of periodic plate design and MEMS sensors provides wave-field focusing to reduce wave attenuation, and prevent interference of secondary waves sources, such as friction, with the primary waveforms. The waveguiding feature of the designed structure is experimentally investigated and discussed in this paper.

  3. Structure and dating errors in the geologic time scale and periodicity in mass extinctions

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1989-01-01

    Structure in the geologic time scale reflects a partly paleontological origin. As a result, ages of Cenozoic and Mesozoic stage boundaries exhibit a weak 28-Myr periodicity that is similar to the strong 26-Myr periodicity detected in mass extinctions of marine life by Raup and Sepkoski. Radiometric dating errors in the geologic time scale, to which the mass extinctions are stratigraphically tied, do not necessarily lessen the likelihood of a significant periodicity in mass extinctions, but do spread the acceptable values of the period over the range 25-27 Myr for the Harland et al. time scale or 25-30 Myr for the DNAG time scale. If the Odin time scale is adopted, acceptable periods fall between 24 and 33 Myr, but are not robust against dating errors. Some indirect evidence from independently-dated flood-basalt volcanic horizons tends to favor the Odin time scale.

  4. Ordered and isomorphic mapping of periodic structures in the parametrically forced logistic map

    NASA Astrophysics Data System (ADS)

    Maranhão, Dariel M.

    2016-09-01

    We investigate the periodic domains found in the parametrically forced logistic map, the classical logistic map when its control parameter changes dynamically. Phase diagrams in two-parameter spaces reveal intricate periodic structures composed of patterns of intersecting superstable orbits curves, defining the cell of a periodic window. Cells appear multifoliated and ordered, and they are isomorphically mapped when one changes the map parameters. Also, we identify the characteristics of simplest cell and apply them to other more complex, discussing how the topography on parameter space is affected. By use of the winding number as defined in periodically forced oscillators, we show that the hierarchical organization of the periodic domains is manifested in global and local scales.

  5. Dynamics of laser ablative shock waves from one dimensional periodic structured surfaces

    NASA Astrophysics Data System (ADS)

    Chelikani, Leela; Pinnoju, Venkateshwarlu; Paturi, Prem Kiran

    2017-01-01

    Laser ablative shock waves (LASWs) from one dimensional periodic structured surfaces (1D-PSS) on Aluminum metal is studied using time resolved shadowgraphy technique. 1D-PSS of triangular and sinusoidal periodic density profiles consisting of 288 lines per laser focal spot diameter (lp2ω0) with periodicity of 0.83 μm are used as targets. The SW properties such as propagation distance, velocity and pressure behind the shock front were compared with flat Aluminum surface of the target under the same experimental conditions. The possibility of tailoring the nature of LASWs with varying density profile on the surface is presented.

  6. Anti-plane transverse waves propagation in nanoscale periodic layered piezoelectric structures.

    PubMed

    Chen, A-Li; Yan, Dong-Jia; Wang, Yue-Sheng; Zhang, Chuanzeng

    2016-02-01

    In this paper, anti-plane transverse wave propagation in nanoscale periodic layered piezoelectric structures is studied. The localization factor is introduced to characterize the wave propagation behavior. The transfer matrix method based on the nonlocal piezoelectricity continuum theory is used to calculate the localization factor. Additionally, the stiffness matrix method is applied to compute the wave transmission spectra. A cut-off frequency is found, beyond which the elastic waves cannot propagate through the periodic structure. The size effect or the influence of the ratio of the internal to external characteristic lengths on the cut-off frequency and the wave propagation behavior are investigated and discussed.

  7. Analysis of quasi-periodic pore-network structure of centric marine diatom frustules

    NASA Astrophysics Data System (ADS)

    Cohoon, Gregory A.; Alvarez, Christine E.; Meyers, Keith; Deheyn, Dimitri D.; Hildebrand, Mark; Kieu, Khanh; Norwood, Robert A.

    2015-03-01

    Diatoms are a common type of phytoplankton characterized by their silica exoskeleton known as a frustule. The diatom frustule is composed of two valves and a series of connecting girdle bands. Each diatom species has a unique frustule shape and valves in particular species display an intricate pattern of pores resembling a photonic crystal structure. We used several numerical techniques to analyze the periodic and quasi-periodic valve pore-network structure in diatoms of the Coscinodiscophyceae order. We quantitatively identify defect locations and pore spacing in the valve and use this information to better understand the optical and biological properties of the diatom.

  8. Relationship between periodic dinucleotides and the nucleosome structure revealed by alpha shape modeling

    NASA Astrophysics Data System (ADS)

    Zhou, Weiqiang; Yan, Hong

    2010-04-01

    As the fundamental repeating units in eukaryotic chromatin, nucleosomes play an important role in many biological processes. For this reason, the study of the structure of nucleosomes may help to reveal some of the crucial principals of these processes. In our research, we have used alpha shapes to model nucleosome structure and discovered that the periodic DNA dinucleotides AA, TT and GC occupy special positions in nucleosome structure with one nucleotide inside and the other outside the nucleosome surface. This structural feature and other dinucleotide characteristics can provide useful information for the study of nucleosome positioning.

  9. Three-dimensional periodic complex structures in soft matter: investigation using scattering methods

    PubMed Central

    Impéror-Clerc, Marianne

    2012-01-01

    Three-dimensional periodic complex structures are encountered in various soft matter systems such as liquid crystals, block-copolymer phases and the related nano-structured materials. Here, we review several well-defined topologies: two-dimensional hexagonal phase, three-dimensional packing of spheres, tetrahedral close packing (tcp) bi-continuous and tri-continuous cubic phases. We illustrate how small-angle X-ray scattering experiments help us to investigate these different structures and introduce the main available structural models based on both direct and inverse methods. PMID:24098843

  10. Insights into tetracycline adsorption onto kaolinite and montmorillonite: experiments and modeling.

    PubMed

    Zhao, Yanping; Gu, Xueyuan; Li, Shiyin; Han, Ruiming; Wang, Guoxiang

    2015-11-01

    Adsorption of tetracycline (TC) on kaolinite and montmorillonite was investigated using batch adsorption experiments with different pH, ionic strength, and surface coverage. As a result, pH and ionic strength-dependent adsorption of TC was observed for the two clay minerals. The adsorption of TC decreased with the increase of pH and ionic strength, and high initial TC concentration had high adsorption. In addition, a triple-layer model was used to predict the adsorption and surface speciation of TC on the two minerals. As a result, four complex species on kaolinite (≡X(-)∙H3TC(+), ≡X(-)∙H2TC(±), ≡SOH(0)∙H2TC(±), and ≡SOH(0)∙HTC(-)) and three species on montmorillonite (≡X(-)∙H3TC(+), ≡X(-)∙H2TC(±), and ≡SOH(0)∙HTC(-)) were structurally constrained by spectroscopy, and these species were also successfully fitted to the adsorption edges of TC. Three functional groups of TC were involved in these adsorption reactions, including the positively charged dimethylamino group, the C=O amide I group, and the C=O group at the C ring. Combining adsorption experiments and model in this study, the adsorption of TC on kaolinite and montmorillonite was mainly attributed to cation exchange on the surface sites (≡X(-)) compared to surface complexation on the edge sites (≡SOH) at natural soil pH condition. Moreover, the surface adsorption species, the corresponding adsorption modes, and the binding constants for the surface reactions were also estimated.

  11. [Measurement of steel corrosion in concrete structures by analyzing long-period fiber grating spectrum character].

    PubMed

    Wang, Yan; Liang, Da-Kai; Zhou, Bing

    2008-11-01

    The consideration on the durability of concrete structures with reinforcement corrosion has become a most urgent problem. A new technique to measure the corrosion of steel in concrete structures was proposed in the present paper. It is based on the microbending characteristic of long period optical grating (LPFG). The temperature spectum character and curvature spectrum character of long period optical fiber grating were studied first. It was shown that the transmission spectrum of long period optical fiber grating shifted right and the transmission of the resonance wavelength was invariable when the temperature increased, while the transmission spectrum of long period optical fiber grating became shallow when the curvature increased, the transmission of the resonance wavelength would increase and it was linear with the curvature. On the basis of the characteristic, a notch shaped pedestal was designed and a long period optical fiber grating was laid on the steel surface. With this method the radial expansion of the steel resulting from the steel corrosion would translate into the curvature of the long period optical fiber grating. The curvature of long period optical fiber grating could be obtained by analyzing the change of spectrum, and then the steel corrosion depth could be measured. This method is simple and immediate and is independent of the variety in temperature, strain and refractive index owing to the inimitable spectrum characteristic of long period optical fiber grating. From the experiment it was found that the precision of the corrosion depth was better than 1.2 microm, and the corrosion depth of 3 mm could be achieved. This measurement could be used to monitor the early to metaphase corrosion of reinforcing steel in concrete structures.

  12. Debromination of decabromodiphenyl ether by organo-montmorillonite-supported nanoscale zero-valent iron: preparation, characterization and influence factors.

    PubMed

    Pang, Zhihua; Yan, Mengyue; Jia, Xiaoshan; Wang, Zhenxing; Chen, Jianyu

    2014-02-01

    An organo-montmorillonite-supported nanoscale zero-valent iron material (M-NZVI) was synthesized to degrade decabromodiphenyl ether (BDE-209). The results showed that nanoscale zero-valent iron had good dispersion on organo-montmorillonite and was present as a core-shell structure with a particle size range of nanoscale iron between 30-90 nm, characterized by XRD, SEM, TEM, XRF, ICP-AES, and XPS. The results of the degradation of BDE-209 by M-NZVI showed that the efficiency of M-NZVI in removing BDE-209 was much higher than that of NZVI. The efficiency of M-NZVI in removing BDE-209 decreased as the pH and the initial dissolved oxygen content of the reaction solution increased, but increased as the proportion of water in the reaction solution increased.

  13. Capture and sequestration of CO2 in the interlayer space of hydrated calcium Montmorillonite clay under various geological burial depth

    NASA Astrophysics Data System (ADS)

    Yang, W.; Zaoui, A.

    2016-05-01

    We perform, at nanoscale level, the structure and dynamics of carbon dioxide molecules in hydrated Ca-montmorillonite clays. The swelling behaviour of hydrated Wyoming-type Montmorillonite including CO2 molecules and counterions is presented and analysed. In addition, the atom density profile, diffusion behaviours and radial distribution functions of CO2, interlayer water molecules and Calcium ions have been investigated at different geological burial depth of 0 km, 3 km and 6 km, which correspond to various temperature and pressure of simulation conditions. Furthermore, the influence of different hydration state on the dynamical behaviours of carbon dioxide is also explained. The calculated self-diffusion coefficient shows that the carbon dioxide species diffuse more freely with the increase of depth and water content. We also found that the presence of interlayer CO2 inhibits the diffusion of all the mobile species. These results mainly show that the hydrated clay system is an appropriate space capable of absorbing CO2 molecules.

  14. Self-diffusion of sodium ions in compacted sodium montmorillonite

    SciTech Connect

    Kozaki, Tamotsu; Fujishima, Atsushi; Sato, Seichi; Ohashi, Hiroshi

    1998-01-01

    Diffusion of sodium ions through compacted sodium montmorillonite in a water-saturated state was studied to obtain fundamental information for performance assessments of geological disposal of high-level radioactive waste. Basal spacings obtained from X-ray diffraction measurements indicated a decrease in the interlamellar spacing with increasing dry density of the montmorillonite; the three-water-layer hydrate was observed at low dry density, and the two-water-layer hydrate was observed at high dry density, whereas both were observed at dry densities between 1.4 and 1.5 Mg/m{sup 3}. Activation energies from 14.1 to 24.7 kJ/mol were obtained from the temperature dependence of the self-diffusion coefficients of sodium ions. Activation energies lower than that for the diffusion of sodium ions in free water were found for montmorillonite specimens with dry densities of {le} 1.2 Mg/m{sup 3}, while higher activation energies were observed at dry densities {ge} 1.4 Mg/m{sup 3}. The pore water diffusion model, the general model used for migration of nuclides, is based on geometric parameters; however, findings cannot be explained by only the changes in the geometric parameters. Possible explanations for the dry density dependence of the activation energy are changes in the temperature dependence of the distribution coefficients of sodium ions on the montmorillonite, changes in the diffusion process with an increase in dry density, or both.

  15. Modeling of alkyl quaternary ammonium cations intercalated into montmorillonite lattice

    SciTech Connect

    Daoudi, El Mehdi; Boughaleb, Yahia; El Gaini, Layla; Meghea, Irina; Bakasse, Mina

    2013-05-15

    Highlights: ► The modification of montmorillonites by three surfactants increases the basal spacing. ► The model proposed show a bilayer conformation for the surfactant ODTMA. ► The DODMA and TOMA surfactants adopt a paraffin type arrangement. ► Behavior of surfactants in interlayer space was confirmed by TGA and ATR analysis. - Abstract: The objective of this work was to study the conformation of the quaternary ammonium cations viz., octadecyl trimethyl ammonium (ODTMA), dioctadecyl dimethyl ammonium (DMDOA) and trioctadecyl methyl ammonium (TOMA) intercalated within montmorillonite. The modified montmorillonite was characterized by X-ray diffraction in small angle (SAXS), thermal analysis (TGA) and infrared spectroscopy of attenuated total reflection (ATR). The modification of organophilic montmorillonites by the three surfactants ODTMA, DMDOA and TOMA increases the basal spacing from their respective intercalated distances of 1.9 nm, 2.6 nm and 3.4 nm respectively. The increase in the spacing due to the basic organic modification was confirmed by the results of thermal analysis (TGA) and infrared spectroscopy (ATR), and also supported by theoretical calculations of longitudinal and transversal chain sizes of these alkyl quaternary ammonium cations.

  16. Gold-film coating assisted femtosecond laser fabrication of large-area, uniform periodic surface structures.

    PubMed

    Feng, Pin; Jiang, Lan; Li, Xin; Rong, Wenlong; Zhang, Kaihu; Cao, Qiang

    2015-02-20

    A simple, repeatable approach is proposed to fabricate large-area, uniform periodic surface structures by a femtosecond laser. 20 nm gold films are coated on semiconductor surfaces on which large-area, uniform structures are fabricated. In the case study of silicon, cross-links and broken structures of laser induced periodic surface structures (LIPSSs) are significantly reduced on Au-coated silicon. The good consistency between the scanning lines facilitates the formation of large-area, uniform LIPSSs. The diffusion of hot electrons in the Au films increases the interfacial carrier densities, which significantly enhances interfacial electron-phonon coupling. High and uniform electron density suppresses the influence of defects on the silicon and further makes the coupling field more uniform and thus reduces the impact of laser energy fluctuations, which homogenizes and stabilizes large-area LIPSSs.

  17. Rapid analysis of scattering from periodic dielectric structures using accelerated Cartesian expansions

    SciTech Connect

    Baczewski, Andrew David; Miller, Nicholas C.; Shanker, Balasubramaniam

    2012-03-22

    Here, the analysis of fields in periodic dielectric structures arise in numerous applications of recent interest, ranging from photonic bandgap structures and plasmonically active nanostructures to metamaterials. To achieve an accurate representation of the fields in these structures using numerical methods, dense spatial discretization is required. This, in turn, affects the cost of analysis, particularly for integral-equation-based methods, for which traditional iterative methods require Ο(Ν2) operations, Ν being the number of spatial degrees of freedom. In this paper, we introduce a method for the rapid solution of volumetric electric field integral equations used in the analysis of doubly periodic dielectric structures. The crux of our method is the accelerated Cartesian expansion algorithm, which is used to evaluate the requisite potentials in Ο(Ν) cost. Results are provided that corroborate our claims of acceleration without compromising accuracy, as well as the application of our method to a number of compelling photonics applications.

  18. FT-IR study of montmorillonite-chitosan nanocomposite materials

    NASA Astrophysics Data System (ADS)

    Paluszkiewicz, C.; Stodolak, E.; Hasik, M.; Blazewicz, M.

    2011-08-01

    Bone defect is one of the most frequent problems in bone tissue reconstruction in which application of a biomaterial filling is necessary. It creates a still rising demand of biomaterials for bone surgery. Polymer-ceramic nanocomposites (e.g. based on chitosan matrix) is a group of novel materials whose properties such as strength, Young's modulus, bioactivity and controlled degradation time make them suitable materials for filling bone defects. Investigations of nanocomposite foils which consisted of biopolymer-chitosan (CS) matrix and montmorillonite (MMT) as a nano-filler was the subject of the work. The nanocomposite materials were produced by a two-step dispersion of the nanoparticles in the biopolymer matrix. The first stage involved mechanical stirring and the second one - ultrasonic agitation. Mechanical tests were performed on the nanocomposites and their Young's modulus was estimated. Significant improvement of mechanical properties of the nanocomposites in comparison with the pure polymer (CS) was observed. The nanocomposite foils (CS/MMT) were subjected to FT-IR spectroscopy investigations whose objective was to explain the reason of the change in mechanical characteristics of the nanocomposites. Transmission and ATR techniques operating in MIR range were used to study the nanocomposites. The FT-IR techniques were used to determine interactions at nanoparticle-biopolymer matrix interface. A pure unmodified CS foil was used as a reference material for FT-IR studies. It was proven that application of FT-IR techniques allows not only to identify phases, but also to explain structural changes in the systems studied.

  19. Electron acceleration by an electromagnetic wave propagating across a magnetic field in periodic structures

    NASA Astrophysics Data System (ADS)

    Buts, V. A.; Ognivenko, V. V.

    1990-05-01

    The possibility of the acceleration of charged particles captured by an electromagnetic wave propagating across a constant magnetic field in periodic slow-wave structures is demonstrated. A plane waveguide with perfectly conducting walls is examined as an example of an electrodynamic structure in which such an acceleration mechanism is possible. The acceleration rate is determined, and the stability of captured particle motion is investigated.

  20. Abiotic formation of RNA-like oligomers by montmorillonite catalysis: part II

    NASA Astrophysics Data System (ADS)

    Ertem, Gözen; Snellinger-O'Brien, Ann M.; Ertem, M. C.; Rogoff, D. A.; Dworkin, Jason P.; Johnston, Murray V.; Hazen, Robert M.

    2008-01-01

    This work is an extension of our previous studies carried out to investigate the possible catalytic role of minerals in the abiotic synthesis of biologically important molecules. In the presence of montmorillonite, a member of the phyllosilicate group minerals that are abundant on Earth and identified on Mars, activated RNA monomers, namely 5‧-phosphorimidazolides of nucleosides (ImpNs), undergo condensation reactions in aqueous electrolyte solution producing oligomers with similar structures to short RNA fragments. Analysis of the linear trimer isomers formed in the reaction of a mixture of activated adenosine and cytidine monomers (ImpA and ImpC, respectively) employing high-performance liquid chromatography, selective enzymatic hydrolysis and matrix-assisted laser desorption/ionization mass spectroscopy molecular weight measurements demonstrate that montmorillonite catalysis facilitates the formation of hetero-isomers containing 56% A- and 44% C-monomer incorporated in their structure. The results also show that 56% of the monomer units are linked together by RNA-like 3‧, 5‧-phosphodiester bonds. These results follow the same trend observed in our most recent work studying the reaction of activated adenosine and uridine monomers, and support Bernal's hypothesis proposing the possible catalytic role of minerals in the abiotic processes in the course of chemical evolution.

  1. Cotransport of bismerthiazol and montmorillonite colloids in saturated porous media

    NASA Astrophysics Data System (ADS)

    Shen, Chongyang; Wang, Hong; Lazouskaya, Volha; Du, Yichun; Lu, Weilan; Wu, Junxue; Zhang, Hongyan; Huang, Yuanfang

    2015-06-01

    While bismerthiazol [N,N‧-methylene-bis-(2-amino-5-mercapto-1,3,4-thiadiazole)] is one of the most widely used bactericides, the transport of bismerthiazol in subsurface environments is unclear to date. Moreover, natural colloids are ubiquitous in the subsurface environments. The cotransport of bismerthiazol and natural colloids has not been investigated. This study conducted laboratory column experiments to examine the transport of bismerthiazol in saturated sand porous media both in the absence and presence of montmorillonite colloids. Results show that a fraction of bismerthiazol was retained in sand and the retention was higher at pH 7 than at pH 4 and 10. The retention did not change with ionic strength. The retention was attributed to the complex of bismerthiazol with metals/metal oxides on sand surfaces through ligand exchange. The transport of bismerthiazol was enhanced with montmorillonite colloids copresent in the solutions and, concurrently, the transport of montmorillonite colloids was facilitated by the bismerthiazol. The transport of montmorillonite colloids was enhanced likely because the bismerthiazol and the colloids competed for the attachment/adsorption sites on collector surfaces and the presence of bismerthiazol changed the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies between colloids and collectors. The transport of bismerthiazol was inhibited if montmorillonite colloids were pre-deposited in sand because bismerthiazol could adsorb onto the colloid surfaces. The adsorbed bismerthiazol could be co-remobilized with the colloids from primary minima by decreasing ionic strength. Whereas colloid-facilitated transport of pesticides has been emphasized, our study implies that transport of colloids could also be facilitated by the presence of pesticides.

  2. Cotransport of bismerthiazol and montmorillonite colloids in saturated porous media.

    PubMed

    Shen, Chongyang; Wang, Hong; Lazouskaya, Volha; Du, Yichun; Lu, Weilan; Wu, Junxue; Zhang, Hongyan; Huang, Yuanfang

    2015-01-01

    While bismerthiazol [N,N'-methylene-bis-(2-amino-5-mercapto-1,3,4-thiadiazole)] is one of the most widely used bactericides, the transport of bismerthiazol in subsurface environments is unclear to date. Moreover, natural colloids are ubiquitous in the subsurface environments. The cotransport of bismerthiazol and natural colloids has not been investigated. This study conducted laboratory column experiments to examine the transport of bismerthiazol in saturated sand porous media both in the absence and presence of montmorillonite colloids. Results show that a fraction of bismerthiazol was retained in sand and the retention was higher at pH7 than at pH 4 and 10. The retention did not change with ionic strength. The retention was attributed to the complex of bismerthiazol with metals/metal oxides on sand surfaces through ligand exchange. The transport of bismerthiazol was enhanced with montmorillonite colloids copresent in the solutions and, concurrently, the transport of montmorillonite colloids was facilitated by the bismerthiazol. The transport of montmorillonite colloids was enhanced likely because the bismerthiazol and the colloids competed for the attachment/adsorption sites on collector surfaces and the presence of bismerthiazol changed the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies between colloids and collectors. The transport of bismerthiazol was inhibited if montmorillonite colloids were pre-deposited in sand because bismerthiazol could adsorb onto the colloid surfaces. The adsorbed bismerthiazol could be co-remobilized with the colloids from primary minima by decreasing ionic strength. Whereas colloid-facilitated transport of pesticides has been emphasized, our study implies that transport of colloids could also be facilitated by the presence of pesticides.

  3. Form and structure factors for impedance and reflection from periodic layers.

    PubMed

    Pan, Janet L

    2007-01-20

    In an exact treatment of the Maxwell equations, we derive form and structure factors for reflection from periodic layers, and we show that these factors are significantly different from their analogs in kinematic x-ray diffraction. Quite generally, we show that reflection and impedance can be written precisely as the sum of an additive form factor and the product of a structure factor and a second form factor. This additive form factor does not have an analog in kinematic x-ray diffraction. It is demonstrated that the form factors are found by analytic continuation to an arbitrary wavelength of expressions for the impedance both at long wavelengths and at quarter wavelengths. A correction to the Bragg law relating fringe spacing to the total structure thickness is derived. We go beyond previous numerical work by deriving simple analytic exact expressions for reflection and impedance of periodic layers for all frequencies within the reflection passband, and for an arbitrary number of periods in the structure, an arbitrary index profile within each period, arbitrary layer thicknesses (not just quarter-wave layers), and for arbitrary sizes of the refractive index differences.

  4. Judgments of Information Structure in L2 French: Nativelike Performance and the Critical Period Hypothesis

    ERIC Educational Resources Information Center

    Reichle, Robert V.

    2010-01-01

    Previous studies using judgments of morphosyntactic errors have shown mixed evidence for a critical period for L2 acquisition (e.g., Birdsong & Molis, Journal of Memory and Language 44: 235-249, 2001, Johnson & Newport, Cognitive Psychology 21: 60-99, 1989). This study uses anomalies in the domain of information structure, the interface…

  5. A Discontinuous Galerkin Time Domain Framework for Periodic Structures Subject to Oblique Excitation

    NASA Astrophysics Data System (ADS)

    Miller, Nicholas C.; Baczewski, Andrew D.; Albrecht, John D.; Shanker, Balasubramaniam

    2014-08-01

    A nodal Discontinuous Galerkin (DG) method is derived for the analysis of time-domain (TD) scattering from doubly periodic PEC/dielectric structures under oblique interrogation. Field transformations are employed to elaborate a formalism that is free from any issues with causality that are common when applying spatial periodic boundary conditions simultaneously with incident fields at arbitrary angles of incidence. An upwind numerical flux is derived for the transformed variables, which retains the same form as it does in the original Maxwell problem for domains without explicitly imposed periodicity. This, in conjunction with the amenability of the DG framework to non-conformal meshes, provides a natural means of accurately solving the first order TD Maxwell equations for a number of periodic systems of engineering interest. Results are presented that substantiate the accuracy and utility of our method.

  6. Formation of laser-induced periodic surface structures on niobium by femtosecond laser irradiation

    SciTech Connect

    Pan, A.; Dias, A.; Gomez-Aranzadi, M.; Olaizola, S. M.; Rodriguez, A.

    2014-05-07

    The surface morphology of a Niobium sample, irradiated in air by a femtosecond laser with a wavelength of 800 nm and pulse duration of 100 fs, was examined. The period of the micro/nanostructures, parallel and perpendicularly oriented to the linearly polarized fs-laser beam, was studied by means of 2D Fast Fourier Transform analysis. The observed Laser-Induced Periodic Surface Structures (LIPSS) were classified as Low Spatial Frequency LIPSS (periods about 600 nm) and High Spatial Frequency LIPSS, showing a periodicity around 300 nm, both of them perpendicularly oriented to the polarization of the incident laser wave. Moreover, parallel high spatial frequency LIPSS were observed with periods around 100 nm located at the peripheral areas of the laser fingerprint and overwritten on the perpendicular periodic gratings. The results indicate that this method of micro/nanostructuring allows controlling the Niobium grating period by the number of pulses applied, so the scan speed and not the fluence is the key parameter of control. A discussion on the mechanism of the surface topology evolution was also introduced.

  7. Multifractal detrended fluctuation analysis for clustering structures of electricity price periods

    NASA Astrophysics Data System (ADS)

    Wang, Fang; Liao, Gui-ping; Li, Jian-hui; Li, Xiao-chun; Zhou, Tie-jun

    2013-11-01

    A new model is proposed to investigate the structure of electricity price in different time periods. A popular method - the multifractal detrended fluctuation analysis (MF-DFA) method is employed to analyze the features achieved from three types of electricity price data after filtering some trends by Fourier detrended fluctuation function. Twelve multifractal parameters are calculated and selected as the characteristic indicators for comparison. Moreover, the minimum number of indicators is determined so that the discriminant accuracy reaches maximum based on Fisher’s linear discriminant algorithm (Fisher’s LDA) for each time period. These indicators form a multi-dimensional space, in which each point represents a price time series. This allows us to cluster the three price time periods, namely, the low price time periods, the average price time periods and the peak price time periods. Fisher’s LDA is employed to evaluate the discriminant accuracy on these three kinds of time periods. Our analysis is then applied to the data in California1999-2000 and PJM2001-2002 electricity markets to demonstrate the applicability of our methods.

  8. Radial wave crystals: radially periodic structures from anisotropic metamaterials for engineering acoustic or electromagnetic waves.

    PubMed

    Torrent, Daniel; Sánchez-Dehesa, José

    2009-08-07

    We demonstrate that metamaterials with anisotropic properties can be used to develop a new class of periodic structures that has been named radial wave crystals. They can be sonic or photonic, and wave propagation along the radial directions is obtained through Bloch states like in usual sonic or photonic crystals. The band structure of the proposed structures can be tailored in a large amount to get exciting novel wave phenomena. For example, it is shown that acoustical cavities based on radial sonic crystals can be employed as passive devices for beam forming or dynamically orientated antennas for sound localization.

  9. Formation of periodic structures upon laser ablation of metal targets in liquids

    SciTech Connect

    Kazakevich, Pavel V; Simakin, Aleksandr V; Shafeev, Georgii A

    2005-09-30

    Experimental data on the formation of ordered microstructures produced upon ablation of metal targets in liquids irradiated by a copper vapour laser or a pulsed Nd:YAG laser are presented. The structures were obtained on brass, bronze, copper, and tungsten substrates immersed in distilled water or ethanol. As a result of multiple-pulse laser ablation by a scanning beam, ordered microcones with pointed vertexes are formed on the target surface. The structures are separated by deep narrow channels. The structure period was experimentally shown to increase linearly with diameter of the laser spot on the target surface. (interaction of laser radiation with matter)

  10. A microsphere assembly method with laser microwelding for fabrication of three-dimensional periodic structures

    NASA Astrophysics Data System (ADS)

    Takagi, Kenta; Omote, Masanori; Kawasaki, Akira

    2010-03-01

    The orderly build-up of monosized microspheres with sizes of hundreds of micrometres enabled us to develop three-dimensional (3D) photonic crystal devices for terahertz electromagnetic waves. We designed and manufactured an original 3D particle assembly system capable of fabricating arbitrary periodic structures from these spherical particles. This method employs a pick-and-place assembling approach with robotic manipulation and interparticle laser microwelding in order to incorporate a contrivance for highly accurate arraying: an operation that compensates the size deviation of raw monosized particles. Pre-examination of particles of various materials revealed that interparticle laser welding must be achieved with local melting by suppressing heat diffusion from the welding area. By optimizing the assembly conditions, we succeeded in fabricating an accurate periodic structure with a diamond lattice from 400 µm polyethylene composite particles. This structure demonstrated a photonic bandgap in the terahertz frequency range.

  11. Complex layered materials and periodic electromagnetic band-gap structures: Concepts, characterizations, and applications

    NASA Astrophysics Data System (ADS)

    Mosallaei, Hossein

    The main objective of this dissertation is to characterize and create insight into the electromagnetic performances of two classes of composite structures, namely, complex multi-layered media and periodic Electromagnetic Band-Gap (EBG) structures. The advanced and diversified computational techniques are applied to obtain their unique propagation characteristics and integrate the results into some novel applications. In the first part of this dissertation, the vector wave solution of Maxwell's equations is integrated with the Genetic Algorithm (GA) optimization method to provide a powerful technique for characterizing multi-layered materials, and obtaining their optimal designs. The developed method is successfully applied to determine the optimal composite coatings for Radar Cross Section (RCS) reduction of canonical structures. Both monostatic and bistatic scatterings are explored. A GA with hybrid planar/curved surface implementation is also introduced to efficiently obtain the optimal absorbing materials for curved structures. Furthermore, design optimization of the non-uniform Luneburg and 2-shell spherical lens antennas utilizing modal solution/GA-adaptive-cost function is presented. The lens antennas are effectively optimized for both high gain and suppressed grating lobes. The second part demonstrates the development of an advanced computational engine, which accurately computes the broadband characteristics of challenging periodic electromagnetic band-gap structures. This method utilizes the Finite Difference Time Domain (FDTD) technique with Periodic Boundary Condition/Perfectly Matched Layer (PBC/PML), which is efficiently integrated with the Prony scheme. The computational technique is successfully applied to characterize and present the unique propagation performances of different classes of periodic structures such as Frequency Selective Surfaces (FSS), Photonic Band-Gap (PBG) materials, and Left-Handed (LH) composite media. The results are

  12. The influence of continuous rice cultivation and different waterlogging periods on morphology, clay mineralogy, Eh, pH and K in paddy soils.

    PubMed

    Bahmanyar, M A

    2007-09-01

    The effect of different rice cultivation periods on the properties of selected soils in alluvial plain were studied in Mazandaran province (north of Iran) in 2004. Soils were sampled form 0, 6, 16, 26 and over 40 years rice cultivation fields. In each treatment three soil profiles and six nearby auger holes were studied. The present study results indicated that continuous rice cultivation have changed soil moisture regime from xeric to aquic, soil color from brown to grayish, surface horizons from mollic to ochric epipedon and soil structure changed from granular or blocky to massive. Therefore, the soil order has changed from Mollisols to Inceptisols. No illuviation and eluviation of clay minerals occurred as a consequence of rice cultivation. X-ray diffraction analysis showed that clay minerals in non-rice cultivated field were illite, vermiculite, montmorillonite, kaolinite and chlorite, but in rice field were illite, montmorillonite, kaolinite and chlorite, respectively. In contrast of montmorillonite, the amount of illite and vermiculite have been decreased by increasing periods of rice cultivation. The pH values of the saturated soil surface in six weeks past plantation have shifted toward neutrality. While Eh value of non-paddy soils were about +90 mv, surface horizons of paddy soils at field conditions had Eh value about +40, -12, -84, -122 mv, respectively. The amounts of organic matter and available Fe, Mn, Zn and Cu were increased whereas available K was decreased in paddy soils.

  13. Dynamics of laser ablative shock waves from one dimensional periodic structured surfaces

    NASA Astrophysics Data System (ADS)

    Paturi, Prem Kiran; Chelikani, Leela; Pinnoju, Venkateshwarlu; Acrhem Team

    2015-06-01

    Spatio-temporal evolution of Laser ablative shock waves (LASWs) from one dimensional periodic structured surfaces (1D-PSS) of Aluminum is studied using time resolved defocused shadowgraphy technique. LASWs are generated by focusing 7 ns pulses from second harmonic of Nd:YAG (532 nm, 10 Hz) laser on to 1D-PSS with sinusoidal and triangular modulations of varying periodicity. An expanded He-Ne laser (632.8 nm) is used as probe beam for shadowgraphy. Evolution of ablative shock front (SF) with 1.5 ns temporal resolution is used to measure position of the SF, its nature, density and pressure behind the SF. The effect of surface modulation on the LASW and contact front dynamics was compared to those from a flat surface (FS) of Aluminum. SWs from FS and PSS obeyed Taylor's solution for spherical and planar nature, respectively. The velocity of SF from 1D PSS had a twofold increase compared to the FS. This was further enhanced for structures whose periodicity is of the order of excitation wavelength. Variation of SF properties with varying periodicity over a range of 3.3 μm to 0.55 μm has the potential to tailor shockwaves of required parameters. The work is supported by Defence Research and Developement Organization, India through Grants-in-Aid Program. The periodic surfaces were procured with financial support from BRFST project No. NFP-MAT-A12-04.

  14. QUASI-PERIODIC WIGGLES OF MICROWAVE ZEBRA STRUCTURES IN A SOLAR FLARE

    SciTech Connect

    Yu, Sijie; Tan, Baolin; Yan, Yihua; Nakariakov, V. M.; Selzer, L. A.

    2013-11-10

    Quasi-periodic wiggles of microwave zebra pattern (ZP) structures with periods ranging from about 0.5 s to 1.5 s are found in an X-class solar flare on 2006 December 13 at the 2.6-3.8 GHz with the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou). Periodogram and correlation analysis show that the wiggles have two to three significant periodicities and are almost in phase between stripes at different frequencies. The Alfvén speed estimated from the ZP structures is about 700 km s{sup –1}. We find the spatial size of the wave-guiding plasma structure to be about 1 Mm with a detected period of about 1 s. This suggests that the ZP wiggles can be associated with the fast magnetoacoustic oscillations in the flaring active region. The lack of a significant phase shift between wiggles of different stripes suggests that the ZP wiggles are caused by a standing sausage oscillation.

  15. Characterization of power absorption response of periodic three-dimensional structures to partially coherent fields.

    PubMed

    Tihon, Denis; Withington, Stafford; Thomas, Christopher N; Craeye, Christophe

    2016-12-01

    In many applications of absorbing structures it is important to understand their spatial response to incident fields, for example in thermal solar panels, bolometric imaging, and controlling radiative heat transfer. In practice, the illuminating field often originates from thermal sources and is only partially spatially coherent when it reaches the absorbing device. In this paper, we present a method to fully characterize the way a structure can absorb such partially coherent fields. The method is presented for any three-dimensional material and accounts for the partial coherence and partial polarization of the incident light. This characterization can be achieved numerically using simulation results or experimentally using the energy absorption interferometry that has been described previously in the literature. The absorbing structure is characterized through a set of absorbing functions onto which any partially coherent field can be projected. This set is compact for any structure of finite extent, and the absorbing function is discrete for periodic structures.

  16. Periodic Density Structures and the Origin of the Slow Solar Wind

    NASA Technical Reports Server (NTRS)

    Viall-Kepko, Nicholeen M.; Vourlidas, Angelos

    2015-01-01

    The source of the slow solar wind has challenged scientists for years. Periodic density structures (PDSs), observed regularly in the solar wind at 1 AU (Astronomical Unit), can be used to address this challenge. These structures have length scales of hundreds to several thousands of megameters and frequencies of tens to hundreds of minutes. Two lines of evidence indicate that PDSs are formed in the solar corona as part of the slow solar wind release and/or acceleration processes. The first is corresponding changes in compositional data in situ, and the second is PDSs observed in the inner Heliospheric Imaging data on board the Solar Terrestrial Relations Observatory (STEREO)/Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite. The periodic nature of these density structures is both a useful identifier as well as an important physical constraint on their origin. In this paper, we present the results of tracking periodic structures identified in the inner Heliospheric Imager in SECCHI back in time through the corresponding outer coronagraph (COR2) images. We demonstrate that the PDSs are formed around or below 2.5 solar radii-the inner edge of the COR2 field of view. We compute the occurrence rates of PDSs in 10 days of COR2 images both as a function of their periodicity and location in the solar corona, and we find that this set of PDSs occurs preferentially with a periodicity of approximately 90 minutes and occurs near streamers. Lastly, we show that their acceleration and expansion through COR2 is self-similar, thus their frequency is constant at distances beyond 2.5 solar radii.

  17. Application of phase-lock loops to periodic disturbance rejection in smart structures

    NASA Astrophysics Data System (ADS)

    Algrain, Marcelo C.; Ehlers, Douglas E.; Hardt, Steven L.

    1996-05-01

    This paper presents a simple, effective and economical system capable of suppressing periodic vibration (external or self induced) affecting a structure or payload. The approach used integrates piezoelectric materials/actuators, sensors, and low-cost electronics in a novel way. The key innovation is the use of phase-lock-loops (PLL) and switch capacitor filters (SCF) for the on-line identification, tracking and control of periodic vibration. This method concentrates its control action at those frequencies where periodic vibration is detected. Among the advantages of this approach are: it is conceptually simple, easily expandable and modular; the controller does not rely on a model of the structure, and it only needs some approximate notion of the frequency range where the periodic disturbances are expected to occur; it is robust and can be operated at high gain without loss of stability; it is not significantly affected by the presence of random vibration or sensor noise; and it can be implemented with inexpensive electronics. The effectiveness of this new approach was experimentally evaluated using a test unit consisting of a simple structure, accelerometers and Terfenol-D actuators. The structure was excited by driving one of the actuator with sinusoidal and random signals. The resulting periodic disturbances were measured using the accelerometers. The acceleration signals were passed though a bank of PLLs and associated SCFs to detect the fundamental frequency and harmonics. This information was used to drive another actuator that rejected the original disturbances, and attenuation levels as high as 30 dB were achieved.

  18. A phase-lock-loop-based control system for suppressing periodic vibration in smart structural systems

    NASA Astrophysics Data System (ADS)

    Algrain, Marcelo; Hardt, Steve; Ehlers, Douglas

    1997-02-01

    This paper presents a simple, effective and economical system capable of suppressing periodic vibration (external or self-induced) affecting a structure or payload. The approach used integrates piezoelectric materials/actuators, sensors and low-cost electronics in a novel way. The key innovation is the use of phase-lock loops (PLLs) and switch-capacitor filters (SCFs) for the on-line identification, tracking and control of periodic vibration. This method concentrates its control action at those frequencies where periodic vibration is detected. Among the advantages of this approach are the following: it is conceptually simple, easily expandable and modular; the controller does not rely on a model of the structure and it only needs some approximate notion of the frequency range where the periodic disturbances are expected to occur; it is robust and can be operated at high gain without loss of stability; it is not significantly affected by the presence of random vibration or sensor noise and it can be implemented with inexpensive electronics. The effectiveness of this new approach was experimentally evaluated using a test unit consisting of a simple structure, accelerometers and Terfenol-D actuators. The structure was excited by driving one of the actuators with sinusoidal and random signals. The resulting periodic disturbances were measured using the accelerometers. The acceleration signals were passed though a bank of PLLs and associated SCFs to detect the fundamental frequency and harmonics. This information was used to drive another actuator that rejected the original disturbances, and attenuation levels as high as 30 dB were achieved.

  19. Periodic Density Structures and the Origin of the Slow Solar Wind

    NASA Astrophysics Data System (ADS)

    Viall, Nicholeen M.; Vourlidas, Angelos

    2015-07-01

    The source of the slow solar wind has challenged scientists for years. Periodic density structures (PDSs), observed regularly in the solar wind at 1 AU, can be used to address this challenge. These structures have length scales of hundreds to several thousands of megameters and frequencies of tens to hundreds of minutes. Two lines of evidence indicate that PDSs are formed in the solar corona as part of the slow solar wind release and/or acceleration processes. The first is corresponding changes in compositional data in situ, and the second is PDSs observed in the inner Heliospheric Imaging data on board the Solar Terrestrial Relations Observatory (STEREO)/Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite. The periodic nature of these density structures is both a useful identifier as well as an important physical constraint on their origin. In this paper, we present the results of tracking periodic structures identified in the inner Heliospheric Imager in SECCHI back in time through the corresponding outer coronagraph (COR2) images. We demonstrate that the PDSs are formed around or below 2.5 solar radii—the inner edge of the COR2 field of view. We compute the occurrence rates of PDSs in 10 days of COR2 images both as a function of their periodicity and location in the solar corona, and we find that this set of PDSs occurs preferentially with a periodicity of ˜90 minutes and occurs near streamers. Lastly, we show that their acceleration and expansion through COR2 is self-similar, thus their frequency is constant at distances beyond 2.5 solar radii.

  20. Periodic optical rogue waves (PORWs) in parity-time (PT) symmetric Bragg-grating structure

    NASA Astrophysics Data System (ADS)

    Gupta, Samit Kumar; Sarma, Amarendra K.

    2014-10-01

    In this work, we present an analytical investigation of traveling wave solution in a nonlinear Bragg grating structure with the core of the optical fiber having PT-symmetric refractive index distribution. Under the approximation of weak-nonlinearity and above the PT-threshold region, the existence of highly intense, well-localized periodic train of pulses has been explored for the backward-propagating wave for some suitable choice of the parameter values of the system. The result of the present study might be useful in practical purpose in generating high-power, periodic optical pulses.

  1. Doubly periodic structure for the study of inhomogeneous bulk fermion matter with spatial localizations

    SciTech Connect

    Vantournhout, Klaas; Jachowicz, Natalie; Ryckebusch, Jan

    2011-09-15

    We present a method that offers perspectives to perform fully antisymmetrized simulations for inhomogeneous bulk fermion matter. The technique bears resemblance to classical periodic boundary conditions, using localized single-particle states. Such localized states are an ideal tool to discuss phenomena where spatial localization plays an important role. The antisymmetrization is obtained introducing a doubly periodic structure in the many-body fermion wave functions. This results in circulant matrices for the evaluation of expectation values, leading to a computationally tractable formalism to study fully antisymmetrized bulk fermion matter. We show that the proposed technique is able to reproduce essential fermion features in an elegant and computationally advantageous manner.

  2. Nonlinear modulation of Rabi oscillations in a one-dimensional nonlinear periodic photonic structure.

    PubMed

    Zang, Xiao-Fei; Jiang, Chun; Zhu, Hai-Bin

    2009-09-01

    We study nonlinear dynamics of classical electromagnetic wave propagation in a one-dimensional nonlinear periodic photonic structure. It is found that the period of Rabi oscillations can be modulated by the relatively weak nonlinearity (2V0/gamma>1). When nonlinearity is relatively strong compared to the strength of resonant coupling (2V0/gamma<1), Rabi oscillations is suppressed and the system shows a dynamical behavior, i.e., energy localizes in one mode rather than full oscillation between two degenerated modes. Phase plane analysis is applied to explain these dynamical phenomena.

  3. Nonlinear modulation of Rabi oscillations in a one-dimensional nonlinear periodic photonic structure

    NASA Astrophysics Data System (ADS)

    Zang, Xiao-Fei; Jiang, Chun; Zhu, Hai-Bin

    2009-09-01

    We study nonlinear dynamics of classical electromagnetic wave propagation in a one-dimensional nonlinear periodic photonic structure. It is found that the period of Rabi oscillations can be modulated by the relatively weak nonlinearity (2V0/γ>1) . When nonlinearity is relatively strong compared to the strength of resonant coupling (2V0/γ<1) , Rabi oscillations is suppressed and the system shows a dynamical behavior, i.e., energy localizes in one mode rather than full oscillation between two degenerated modes. Phase plane analysis is applied to explain these dynamical phenomena.

  4. Hexadimethrine-montmorillonite nanocomposite: Characterization and application as a pesticide adsorbent

    NASA Astrophysics Data System (ADS)

    Gámiz, B.; Hermosín, M. C.; Cornejo, J.; Celis, R.

    2015-03-01

    The goal of this work was to prepare and characterize a novel functional material by the modification of SAz-1 montmorillonite with the cationic polymer hexadimethrine (SA-HEXAD), and to explore the potential use of this nanocomposite as a pesticide adsorbent. Comparative preparation and characterization with the well-known hexadecyltrimethylammonium-modified SAz-1 montmorillonite (SA-HDTMA) was also assessed. The characterization was performed by elemental analysis, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), physisorption of N2, scanning electron microscopy (SEM) and Z potential measurements. The characterization and adsorption experiments showed that the extent of pesticide adsorption was markedly subjected to the structure and features of the surface of each organo-clay and also to the nature of the considered pesticide. SA-HEXAD displayed a high affinity for anionic pesticides which, presumably, were adsorbed by electrostatic attraction on positively-charged ammonium groups of the polymer not directly interacting with the clay. In contrast, SA-HDTMA displayed great adsorption of both uncharged and anionic pesticides with predominance of hydrophobic interactions. This work provided information about the surface properties of a new organic-inorganic nanohybrid material, SA-HEXAD, and its potential as an adsorbent for the removal of anionic organic pollutants from aqueous solutions.

  5. Solvent-based nanocomposite coatings I. Dispersion of organophilic montmorillonite in organic solvents.

    PubMed

    Burgentzlé, D; Duchet, J; Gérard, J F; Jupin, A; Fillon, B

    2004-10-01

    This study aims to determine the relevant parameters controlling the organophilic montmorillonite dispersion in various organic solvents which can be used as dispersion media for polymer coatings. These suspensions were studied at three scales: At nanometer scale by looking to interlayer distance: When the solvent surface energy is higher than the organophilic clay surface energy, i.e., gamma solvent > or = gamma montmorillonite, the intercalated organic chains of the quaternary ammonium modifier swell, leading to an increase of the interlayer distance. The balance between hydrophilic and hydrophobic character is the key to dispersion of nanoclays. At micrometer scale by studying the rheological behaviour of clay suspensions: Gels are formed by percolation of microgels, based on swollen 3-4 platelet tactoids. The viscoelastic properties and the flow behavior reveal the gel structuration by measuring the gel stiffness and the flowing stress. At macroscopic scale analyzed from the swelling of the nanoclay into solvents: The compatibility between solvent and organophilic clay governs the macroscopic swelling, i.e., interactions between organic chains borne by the intercalated ions and solvents govern the final suspension morphologies. The same methodology can be adopted for monomers or prepolymers selected for one in situ intercalation/exfoliation processing route.

  6. Removal of hexavalent chromium from aqueous solution using exfoliated polyaniline/montmorillonite composite.

    PubMed

    Chen, Jun; Hong, Xiaoqin; Zhao, Yongteng; Zhang, Qianfeng

    2014-01-01

    Exfoliated polyaniline/montmorillonite (PANI/MMT) composites with nanosheet structure were successfully prepared by in situ chemical oxidation polymerization with MMT platelets as the scaffold. Amphoteric polymer, (2-methacryloyloxyethyl)trimethyl ammonium chloride and methacrylate acid copolymer, was used to modify montmorillonite and a large number of carboxylic acids were introduced on the surface of the clay platelets, which can be used as a dopant of PANI and play a 'bridge' role to combine PANI with clay. Adsorption experiments were carried out to study the effects of pH, contact time, Cr(VI) concentration, adsorbent dose and temperature. The adsorption of Cr(VI) on the PANI/MMT was highly pH dependent and the adsorption kinetics followed a pseudo-second-order model. The Langmuir isothermal model described the adsorption isotherm data well and the maximum adsorption capacity increased with the increase in temperature. Thermodynamic investigation indicated that the adsorption process is spontaneous, endothermic and marked with an increase in randomness at the adsorbent - liquid interface. The maximum adsorption capacity of the PANI/MMT composites for Cr(VI) was 308.6 mg/g at 25 °C. The excellent adsorption characteristic of exfoliated PANI/MMT composites will render it a highly efficient and economically viable adsorbent for Cr(VI) removal.

  7. A unique patterned diamond stamp for a periodically hierarchical nanoarray structure

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Shen, Yanting; Xu, Weiqing; Xu, Shuping; Li, Hongdong

    2016-10-01

    A diamond stamp with a hierarchical pattern was designed for the direct preparation of a periodic nanoarray structure, which was prepared by the reactive ion etching technique with a hierarchical ultrathin alumina membrane (HUTAM) as a mask. The optimal etching conditions for fabricating the diamond stamp were discussed in order to realize a vertical nanopore structure, avoiding structural damage from lateral etching. By using this diamond stamp, a polymer film with the desired hierarchical nanorod array structure can be obtained easily via the simple stamping process, which greatly simplifies the processing procedure. More importantly, the stamp is reusable because of its super-hardness, which ensures the reproducibility of the nanorod array pattern. Another merit is that the smooth surface of the etched diamond can avoid the use of a release agent. Our results prove that this hard stamp can be used for quick preparation of an elaborate periodic nanoarray structure. This study is significant in that it solves the problems of high cost and easy damage of stamps in nanoimprint lithography, and it might inspire more sophisticated applications of such an ordered structure in nanoplasmonics, biochemical sensing and nanophotonic devices.

  8. Sol-gel hybrid films based on organosilane and montmorillonite for corrosion inhibition of AA2024.

    PubMed

    Dalmoro, V; dos Santos, J H Z; Armelin, E; Alemán, C; Azambuja, D S

    2014-07-15

    The present work reports the production of films on AA2024-T3 composed of vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS) with incorporation of montmorillonite (sodium montmorillonite and montmorillonite modified with quaternary ammonium salt, abbreviated Na and 30B, respectively), generated by the sol-gel process. According to FT-IR analyses the incorporation of montmorillonite does not affect silica network. Electrochemical characterization was performed by electrochemical impedance spectroscopy measurement in 0.05 mol L(-1) NaCl solution. Results indicate that montmorillonite incorporation improves the corrosion protection compared to the non-modified system. Scanning electron microscopy micrographs reveal that high concentrations of montmorillonite provide agglomerations on the metallic surface, which is in detriment of the anticorrosive performance. The VTMS/TEOS/30B films with the lowest concentration (22 mg L(-1)) of embedded clay provide the highest corrosion protection.

  9. Absorption of lithium in montmorillonite: a density functional theory (DFT) study.

    PubMed

    Wungu, Triati Dewi Kencana; Aspera, Susan Menez; David, Melanie Yadao; Dipojono, Hermawan Kresno; Nakanishi, Hiroshi; Kasai, Hideaki

    2011-04-01

    The absorption of lithium in montmorillonite [LiSi8(Al3Mg)O20(OH)4] was investigated using Density Functional Theory (DFT). The final position of lithium after absorption was found to be in good agreement with an experimental observation where lithium atom migrated from the interlayer into the vacant octahedral site of montmorillonite. The lithium absorbed on montmorillonite was held together by a very strong attraction between ions and exhibited an insulating behavior as depicted from the density of states curve. Due to the presence of lithium in the octahedral site of montmorillonite, the OH group reoriented itself perpendicular to the ab plane and an electron of lithium was transferred in order to compensate the existing net charge of montmorillonite caused by isomorphous substitutions. Relative small charge transfer was observed between lithium and montmorillonite.

  10. Sound transmission through a double panel structure periodically coupled with vibration insulators

    NASA Astrophysics Data System (ADS)

    Legault, Julien; Atalla, Noureddine

    2010-07-01

    In this paper, sound transmission through an aircraft sidewall representative double panel structure is investigated theoretically and parametric and validation studies are conducted. The studied configuration is composed of a trim panel (receiver side panel) attached to a ribbed skin panel (source side panel) with periodically spaced resilient mounts. The structure is considered infinite in order to use space harmonic expansion. The partition is also assumed planar for simplicity. The model allows for a 3D incident field and the panels can be metallic and/or composite. A four-pole formulation is employed for modeling of the mounts and the absorption provided by the fiberglass that fills the cavity between the leaves is addressed with an equivalent fluid model. The investigation of mount stiffness, damping and spacing show that properly designed mounts can increase the TL significantly (up to 20 dB of difference between rigid and resilient mounts). However, they can create undesirable resonances resulting from their interaction with the panels. The influence of cavity absorption is also studied and results illustrate the fact that it is not worth investing in a highly absorbent fiber if the structure-borne transmission path is not adequately insulated, and likewise that it is not worth investing in highly resilient mounts without sufficient cavity absorption. Moreover, the investigation of panel damping confirms that when structure-borne transmission is present, raising skin damping can increase the TL even below coincidence, but that on average, greater improvements are achieved by raising trim damping. Finally, comparison between the periodic model and finite element simulations for structure-borne transmission shows that the average level of transmitted energy is well reproduced with the periodic approach. However, the modes are only captured approximately due to the assumption of an infinite structure.

  11. Spatially Periodic Domain Structure in Coupled Reaction--Diffusion Equations for Segment Formation

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu

    2012-02-01

    Segment formation is an important process of pattern formation in the developing vertebrate embryo. The mechanism of such pattern formation is considered to be different from that of Turing instability. We propose reaction--diffusion equations generating traveling pulses and coupled reaction--diffusion equations for two genes that generate a domain structure. Next, we construct a synthetic model for segment formation by combining the coupled reaction--diffusion equations. A spatially periodic domain structure is found in the numerical simulation of the model equation. It is shown that the wavelength of the spatially periodic pattern and the proportion of the sizes of the anterior and posterior domains in each segment can be controlled by adjusting some system parameters.

  12. Limits of slow sound propagation and transparency in lossy, locally resonant periodic structures

    NASA Astrophysics Data System (ADS)

    Theocharis, G.; Richoux, O.; Romero García, V.; Merkel, A.; Tournat, V.

    2014-09-01

    We investigate sound propagation in lossy, locally resonant periodic structures by studying an air-filled tube periodically loaded with Helmholtz resonators and taking into account the intrinsic viscothermal losses. In particular, by tuning the resonator with the Bragg gap in this prototypical locally resonant structure, we study the limits and various characteristics of slow sound propagation. While in the lossless case the overlapping of the gaps results in slow-sound-induced transparency of a narrow frequency band surrounded by a strong and broadband gap, the inclusion of the unavoidable losses imposes limits to the slowdown factor and the maximum transmission. Experiments, theory, and finite element simulations have been used for the characterization of acoustic wave propagation by tuning the Helmholtz/Bragg frequencies and the total amount of loss both for infinite and finite lattices. This study contributes to the field of locally resonant acoustic metamaterials and slow sound applications.

  13. Characteristic of high temperature structural long period grating fabricated by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Liu, Shujing; Luo, Mingyan; Ji, Qiang

    2015-08-01

    Structural Long period gratings (LPGs) in photonic crystal fiber (PCF) were successfully fabricated using the femtosecond laser micromachining system by introducing periodic side-holes. High temperature characterizations of the fabricated gratings have been performed. The structural gratings written with the femtosecond laser micromachining technique can suffer a low shift of the resonance wavelengths with sensitivity of 23pm/oC while the temperature is increased from 20°C to 1200°C. The LPGs have been found to have negligible temperature sensitivity whilst exhibiting useful strain (-1.86pm/μɛ)and strong directional bend sensitivity with -4.40nm•m (180°) and -2.79nm•m (0°) at low temperature. The unique sensing characteristics enable many potential sensing applications in high temperature environments, such as space aircraft, nuclear power plants, and the chemical industry.

  14. Ultrafast laser induced periodic sub-wavelength aluminum surface structures and nanoparticles in air and liquids

    SciTech Connect

    Kuladeep, Rajamudili; Dar, Mudasir H.; Rao, D. Narayana E-mail: dnr-laserlab@yahoo.com; Deepak, K. L. N.

    2014-09-21

    In this communication, we demonstrate the generation of laser-induced periodic sub-wavelength surface structures (LIPSS) or ripples on a bulk aluminum (Al) and Al nanoparticles (NPs) by femtosecond (fs) laser direct writing technique. Laser irradiation was performed on Al surface at normal incidence in air and by immersing in ethanol (C₂H₅OH) and water (H₂O) using linearly polarized Ti:sapphire fs laser pulses of ~110 fs pulse duration and ~800 nm wavelength. Field emission scanning electron microscope is utilized for imaging surface morphology of laser written structures and it reveals that the spatial periodicity as well as the surface morphology of the LIPSS depends on the surrounding dielectric medium and also on the various laser irradiation parameters. The observed LIPSS have been classified as low spatial frequency LIPSS which are perpendicularly oriented to the laser polarization with a periodicity from 460 to 620 nm and high spatial frequency LIPSS which spectacles a periodicity less than 100 nm with the orientation parallel to the polarization of the incident laser beam. Fabricated colloidal solutions, which contain the Al NPs, were characterized by UV-Vis absorption spectroscopy and transmission electron microscopy (TEM). TEM results reveal the formation of internal cavities in Al NPs both in ethanol and water. Formation mechanism of LIPSS and cavities inside the nanoparticles are discussed in detail.

  15. Finite-difference Time-domain Modeling of Laser-induced Periodic Surface Structures

    NASA Astrophysics Data System (ADS)

    Römer, G. R. B. E.; Skolski, J. Z. P.; Oboňa, J. Vincenc; Veld, A. J. Huis in't.

    Laser-induced periodic surface structures (LIPSSs) consist of regular wavy surface structures with amplitudes the (sub)micrometer range and periodicities in the (sub)wavelength range. It is thought that periodically modulated absorbed laser energy is initiating the growth of LIPSSs. The "Sipe theory" (or "Efficacy factor theory") provides an analytical model of the interaction of laser radiation with a rough surface of the material, predicting modulated absorption just below the surface of the material. To address some limitations of this model, the finite-difference time-domain (FDTD) method was employed to numerically solve the two coupled Maxwell's curl equations, for linear, isotropic, dispersive materials with no magnetic losses. It was found that the numerical model predicts the periodicity and orientation of various types of LIPSSs which might occur on the surface of the material sample. However, it should be noted that the numerical FDTD model predicts the signature or "fingerprints" of several types of LIPSSs, at different depths, based on the inhomogeneously absorbed laser energy at those depths. Whether these types of (combinations of) LIPSSs will actually form on a material will also depend on other physical phenomena, such as the excitation of the material, as well as thermal-mechanical phenomena, such as the state and transport of the material.

  16. Ultrafast laser induced periodic sub-wavelength aluminum surface structures and nanoparticles in air and liquids

    NASA Astrophysics Data System (ADS)

    Kuladeep, Rajamudili; Dar, Mudasir H.; Deepak, K. L. N.; Rao, D. Narayana

    2014-09-01

    In this communication, we demonstrate the generation of laser-induced periodic sub-wavelength surface structures (LIPSS) or ripples on a bulk aluminum (Al) and Al nanoparticles (NPs) by femtosecond (fs) laser direct writing technique. Laser irradiation was performed on Al surface at normal incidence in air and by immersing in ethanol (C2H5OH) and water (H2O) using linearly polarized Ti:sapphire fs laser pulses of ˜110 fs pulse duration and ˜800 nm wavelength. Field emission scanning electron microscope is utilized for imaging surface morphology of laser written structures and it reveals that the spatial periodicity as well as the surface morphology of the LIPSS depends on the surrounding dielectric medium and also on the various laser irradiation parameters. The observed LIPSS have been classified as low spatial frequency LIPSS which are perpendicularly oriented to the laser polarization with a periodicity from 460 to 620 nm and high spatial frequency LIPSS which spectacles a periodicity less than 100 nm with the orientation parallel to the polarization of the incident laser beam. Fabricated colloidal solutions, which contain the Al NPs, were characterized by UV-Vis absorption spectroscopy and transmission electron microscopy (TEM). TEM results reveal the formation of internal cavities in Al NPs both in ethanol and water. Formation mechanism of LIPSS and cavities inside the nanoparticles are discussed in detail.

  17. Acoustic scattering for 3D multi-directional periodic structures using the boundary element method.

    PubMed

    Karimi, Mahmoud; Croaker, Paul; Kessissoglou, Nicole

    2017-01-01

    An efficient boundary element formulation is proposed to solve three-dimensional exterior acoustic scattering problems with multi-directional periodicity. The multi-directional periodic acoustic problem is represented as a multilevel block Toeplitz matrix. By exploiting the Toeplitz structure, the computational time and storage requirements to construct and to solve the linear system of equations arising from the boundary element formulation are significantly reduced. The generalized minimal residual method is implemented to solve the linear system of equations. To efficiently calculate the matrix-vector product in the iterative algorithm, the original matrix is embedded into a multilevel block circulant matrix. A multi-dimensional discrete Fourier transform is then employed to accelerate the matrix-vector product. The proposed approach is applicable to a periodic acoustic problem for any arbitrary shape of the structure in both full space and half space. Two case studies involving sonic crystal barriers are presented. In the first case study, a sonic crystal barrier comprising rigid cylindrical scatterers is modeled. To demonstrate the effectiveness of the proposed technique, periodicity in one, two, or three directions is examined. In the second case study, the acoustic performance of a sonic crystal barrier with locally resonant C-shaped scatterers is studied.

  18. [Adsorption of aflatoxin on montmorillonite modified by low-molecular-weight humic acids].

    PubMed

    Yao, Jia-Jia; Kang, Fu-Xing; Gao, Yan-Zheng

    2012-03-01

    The adsorption of a typical biogenic toxin aflatoxin B1 on montmorillonite modified by low-molecular-weight humic acids (M(r) < 3 500) was investigated. The montmorillonite rapidly adsorbed the aflatoxin B1 until amounting to the maximal capacity, and then the adsorbed aflatoxin B1 slowly released into solution and reached the sorption equilibrium state after 12 h. The sorption isotherm of aflatoxin B1 by montmorillonite could be well described by Langmiur model, while the sorption isotherm by humic acid-modified montmorillonite was well fitted by using the Freundlich model. The modification of the montmorillonite with humic acids obviously enhanced its adsorption capacity for aflatoxin B1, and the amounts of aflatoxin adsorbed by modified montmorillonite were obviously higher than those by montmorillonite. The sorption enhancement by humic acid modification was attributed to (1) the enlarged adsorption sites which owed to the surface collapse of crystal layers induced by organic acids, and (2) the binding of aflatoxin with the humic acid sorbed on mineral surface. In addition, the adsorption amounts of aflatoxin by montmorillonite and modified montmorillonite increased with the increase of pH values in solution, and more significant enhancement was observed for the latter than the former, which attributed to the release of humic acids from the modified montmorillonite with the high pH values in solution. This indicates that increasing the pH values resulted in the enhanced hydrophilic property and the release of the organic acids presented in modified montmorillonite, and more sorption sites were available for aflatoxin on the modified montmorillonite. Results of this work would strengthen our understanding of the behavior and fate of biological contaminants in the environment.

  19. Preparation of Optically Transparent Films of Poly(methyl methacrylate) (PMMA) and Montmorillonite

    DTIC Science & Technology

    2001-11-01

    methacrylate] [PMMA] and Montmorillonite DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report...Society V6.4 Preparation of Optically Transparent Films of Poly(methyl methacrylate) (PMMA) and Montmorillonite Elena Vasiliul, Chyi-Shan Wang"’ 2...exchanged with 1.40 meq/g of dimethyl dehydrogenated tallow ammonium from a sodium montmorillonite , Cloisite Na+ (CNa). Since the cation-exchange

  20. Effect of Dissolved NaC1 on Freezing Curves of Kaolinite, Montmorillonite, and Sand Pastes,

    DTIC Science & Technology

    1999-01-01

    test this procedure. Pastes of kaolinite clay, montmorillonite , and quartz sand were prepared by washing repeatedly with aque- ous solutions of 0.1...Cold Regions Research & Engineering Laboratory Effect of Dissolved NaCI on Freezing Curves of Kaolinite , Montmorillonite , and Sand Pastes S.A...of kaolinite pastes warmed from -66.6°C to 0°C 8 4. Unfrozen-water contents, as measured by pulsed NMR, of montmorillonite pastes cooled from 0

  1. Evanescent-wave amplification studied using a bilayer periodic circuit structure and its effective medium model

    NASA Astrophysics Data System (ADS)

    Liu, Ruopeng; Zhao, Bo; Lin, Xian Qi; Cheng, Qiang; Cui, Tie Jun

    2007-03-01

    In this paper, we present both theoretical analysis and experimental verification of evanescent-wave amplification by using a bilayer periodic circuit structure and its effective medium model. We propose a series-shunt capacitor (C-C) structure to simulate a magnetic plasma, whose permittivity is positive and permeability is negative, and a series-shunt inductor (L-L) structure to simulate an electric plasma, whose permittivity is negative and permeability is positive, in which the structure cells are not required to be electrically small. In addition, we derive and define an effective permittivity and permeability for the C-C and L-L structures in closed forms, which are completely different from the published ones. When the two structures are cascaded together to form a bilayer structure, we show that evanescent waves which exist in two single layers independently can be amplified exponentially if a certain resonant condition is satisfied. Such a resonant condition is equivalent to the antimatching condition for the permittivity and permeability of the effectively electric and magnetic plasmas. To show the accuracy of this equivalent medium model, we compare both circuit-simulation results for the C-C and L-L structures and theoretical-prediction results for the effective magnetic and electric plasmas, which have excellent agreement. Finally, we design an experiment using lumped capacitors and inductors mounted on a printed circuit board to verify the amplification of evanescent waves sufficiently. The measurement results have good agreement with the simulation results.

  2. Radionuclide desorption kinetics on synthetic Zn/Ni-labeled montmorillonite nanoparticles

    NASA Astrophysics Data System (ADS)

    Huber, F. M.; Heck, S.; Truche, L.; Bouby, M.; Brendlé, J.; Hoess, P.; Schäfer, T.

    2015-01-01

    Sorption/desorption kinetics for selected radionuclides (99Tc(VII), 232Th(IV), 233U(VI), 237Np(V), 242Pu and 243Am(III)) under Grimsel (Switzerland) ground water conditions (pH 9.7 and ionic strength of ∼1 mM) in the presence of synthetic Zn or Ni containing montmorillonite nanoparticles and granodiorite fracture filling material (FFM) from Grimsel were examined in batch studies. The structurally bound Zn or Ni in the octahedral sheet of the synthetic colloids rendered them suitable as colloid markers. Only a weak interaction of the montmorillonite colloids with the fracture filling material occurs over the experimental duration of 10,000 h (∼13 months). The tri- and tetravalent radionuclides are initially strongly associated with nanoparticles in contrast to 99Tc(VII), 233U(VI) and 237Np(V) which showed no sorption to the montmorillonite colloids. Radionuclide desorption of the nanoparticles followed by sorption to the fracture filling material is observed for 232Th(IV), 242Pu and 243Am(III). Based on the conceptual model that the driving force for the kinetically controlled radionuclide desorption from nanoparticles and subsequent association to the FFM is the excess in surface area offered by the FFM, the observed desorption kinetics are related to the colloid/FFM surface area ratio. The observed decrease in concentration of the redox sensitive elements 99Tc(VII), 233U(VI) and 237Np(V) may be explained by reduction to lower oxidation states in line with Eh-pH conditions prevailing in the experiments and thermodynamic considerations leading to (i) precipitation of a sparingly soluble phase, (ii) sorption to the fracture filling material, (iii) possible formation of eigencolloids and/or (iv) sorption to the montmorillonite colloids. Subsequent to the sorption/desorption kinetics study, an additional experiment was conducted investigating the potential remobilization of radionuclides/colloids attached to the FFM used in the sorption/desorption kinetic

  3. Laser induced periodic surface structures on pyrolytic carbon prosthetic heart valve

    NASA Astrophysics Data System (ADS)

    Stepak, Bogusz D.; Łecka, Katarzyna M.; Płonek, Tomasz; Antończak, Arkadiusz J.

    2016-12-01

    Laser-induced periodic surface structures (LIPSS) can appear in different forms such as ripples, grooves or cones. Those highly periodic wavy surface features which are frequently smaller than incident light wavelength bring possibility of nanostructuring of many different materials. Furthermore, by changing laser parameters one can obtain wide spectrum of periodicities and geometries. The aim of this research was to determine possibility of nanostructuring pyrolytic carbon (PyC) heart valve leaflets using different irradiation conditions. The study was performed using two laser sources with different pulse duration (15 ps, 450 fs) as well as different wavelengths (1064, 532, 355 nm). Both low and high spatial frequency LIPSS were observed for each set of irradiation parameters. In case femtosecond laser pulses we obtained deep subwavelength ripple period which was even ten times smaller than applied wavelength. Obtained ripple period was ranging from 90 up to 860 nm. Raman spectra revealed the increase of disorder after laser irradiation which was comparable for both pico- and femtosecond laser.

  4. Elastic waves at periodically-structured surfaces and interfaces of solids

    SciTech Connect

    Every, A. G.; Maznev, A. A.

    2014-12-15

    This paper presents a simple treatment of elastic wave scattering at periodically structured surfaces and interfaces of solids, and the existence and nature of surface acoustic waves (SAW) and interfacial (IW) waves at such structures. Our treatment is embodied in phenomenological models in which the periodicity resides in the boundary conditions. These yield zone folding and band gaps at the boundary of, and within the Brillouin zone. Above the transverse bulk wave threshold, there occur leaky or pseudo-SAW and pseudo-IW, which are attenuated via radiation into the bulk wave continuum. These have a pronounced effect on the transmission and reflection of bulk waves. We provide examples of pseudo-SAW and pseudo-IW for which the coupling to the bulk wave continuum vanishes at isloated points in the dispersion relation. These supersonic guided waves correspond to embedded discrete eigenvalues within a radiation continuum. We stress the generality of the phenomena that are exhibited at widely different scales of length and frequency, and their relevance to situations as diverse as the guiding of seismic waves in mine stopes, the metrology of periodic metal interconnect structures in the semiconductor industry, and elastic wave scattering by an array of coplanar cracks in a solid.

  5. Superresolution imaging reveals structurally distinct periodic patterns of chromatin along pachytene chromosomes

    PubMed Central

    Fournier, David; Redl, Stefan; Best, Gerrit; Borsos, Máté; Tiwari, Vijay K.; Tachibana-Konwalski, Kikuë; Ketting, René F.; Parekh, Sapun H.; Cremer, Christoph; Birk, Udo J.

    2015-01-01

    During meiosis, homologous chromosomes associate to form the synaptonemal complex (SC), a structure essential for fertility. Information about the epigenetic features of chromatin within this structure at the level of superresolution microscopy is largely lacking. We combined single-molecule localization microscopy (SMLM) with quantitative analytical methods to describe the epigenetic landscape of meiotic chromosomes at the pachytene stage in mouse oocytes. DNA is found to be nonrandomly distributed along the length of the SC in condensed clusters. Periodic clusters of repressive chromatin [trimethylation of histone H3 at lysine (Lys) 27 (H3K27me3)] are found at 500-nm intervals along the SC, whereas one of the ends of the SC displays a large and dense cluster of centromeric histone mark [trimethylation of histone H3 at Lys 9 (H3K9me3)]. Chromatin associated with active transcription [trimethylation of histone H3 at Lys 4 (H3K4me3)] is arranged in a radial hair-like loop pattern emerging laterally from the SC. These loops seem to be punctuated with small clusters of H3K4me3 with an average spread larger than their periodicity. Our findings indicate that the nanoscale structure of the pachytene chromosomes is constrained by periodic patterns of chromatin marks, whose function in recombination and higher order genome organization is yet to be elucidated. PMID:26561583

  6. Adjustment of minimum seismic shear coefficient considering site effects for long-period structures

    NASA Astrophysics Data System (ADS)

    Guan, Minsheng; Du, Hongbiao; Cui, Jie; Zeng, Qingli; Jiang, Haibo

    2016-06-01

    Minimum seismic base shear is a key factor employed in the seismic design of long-period structures, which is specified in some of the major national seismic building codes viz. ASCE7-10, NZS1170.5 and GB50011-2010. In current Chinese seismic design code GB50011-2010, however, effects of soil types on the minimum seismic shear coefficient are not considered, which causes problems for long-period structures sited in hard or rock soil to meet the minimum base shear requirement. This paper aims to modify the current minimum seismic shear coefficient by taking into account site effects. For this purpose, effective peak acceleration (EPA) is used as a representation for the ordinate value of the design response spectrum at the plateau. A large amount of earthquake records, for which EPAs are calculated, are examined through the statistical analysis by considering soil conditions as well as the seismic fortification intensities. The study indicates that soil types have a significant effect on the spectral ordinates at the plateau as well as the minimum seismic shear coefficient. Modified factors related to the current minimum seismic shear coefficient are preliminarily suggested for each site class. It is shown that the modified seismic shear coefficients are more effective to the determination of minimum seismic base shear of long-period structures.

  7. Imaging of polarization rotation in transmission resonances of periodic plasmonic structures

    NASA Astrophysics Data System (ADS)

    Arora, Pankaj; Krishnan, Ananth

    2014-05-01

    We imaged polarization rotation of transmitted light in 1D Periodic Plasmonic Structures (PPS) fabricated on thin metal coated dielectric substrate. Several PPS of 50% duty cycle and extremely low aspect ratio (height to width ratio) of 0.1 were designed using rigorous coupled wave analysis to exhibit transmission plasmonic resonances at optical wavelengths (400 nm to 700 nm). PPS were fabricated using electron beam lithography, evaporation and lift-off process on glass substrates coated with thin metal. The PPS were characterized using normally incident broadband visible light and crossaxis Polarizer Analyzer setup, with the transmitted light imaged in direct and momentum space using a camera. When the cross axis Polarizer Analyzer were positioned at +45° & -45° respectively w.r.t. plane of incidence, bright emissions of Green, Yellow or Red colors corresponding to transmission plasmonic resonances of the PPS with different periods, were observed in both direct and Fourier planes, instead of completely dark images. From the measured emission momentum in Fourier plane images and spectra of collected light, the emissions were attributed to the excitations of surface plasmons and the reason for surface plasmon excitation in this arrangement is strong coupling of hybrid modes with each other caused by the anisotropy introduced by grating which strongly enhances the efficiency of Polarization rotation. The presented structures behave as frequency selective half wave plates in transmission configuration and could also be used to eliminate the effect of direct beam while imaging the coupling to surface plasmons in periodic structures.

  8. Analysis of all-optically tunable functionalities in subwavelength periodic structures by the Fourier modal method

    NASA Astrophysics Data System (ADS)

    Bej, Subhajit; Tervo, Jani; Francés, Jorge; Svirko, Yuri P.; Turunen, Jari

    2016-05-01

    We propose the nonlinear Fourier Modal Method (FMM) [J. Opt. Soc. Am. B 31, 2371 (2014)] as a convenient and versatile numerical tool for the design and analysis of grating based next generation all-optical devices. Here, we include several numerical examples where the FMM is used to simulate all-optically tunable functionalities in sub-wavelength periodic structures. At first, we numerically investigate a 1-D periodic nonlinear binary grating with amorphous TiO2. We plot the diffraction efficiency in the transmitted orders against the structure depth for normally incident plane wave. Change in diffraction efficiencies for different incident field amplitudes are evident from the plots. We verify the accuracy of our implementation by comparing our results with the results obtained with the nonlinear Split Field-Finite Difference Time Domain (SF-FDTD) method. Next we repeat the same experiment with vertically standing amorphous Titanium dioxide (TiO2) nanowire arrays grown on top of quartz which are periodic in two mutually perpendicular directions and examine the efficiencies in the direct transmitted light for different incident field amplitudes. Our third example includes analysis of a form birefringent linear grating with Kerr medium. With FMM we demonstrate that the birefringence of such a structure can be tuned by all-optical means. As a final example, we design a narrow band Guided Mode Resonance Filter (GMRF). Numerical experiments based on the nonlinear FMM reveal that the spectral tunability of such a filter can be obtained by all-optical means.

  9. Near infrared spectroscopy of stearic acid adsorbed on montmorillonite.

    PubMed

    Lu, Longfei; Cai, Jingong; Frost, Ray L

    2010-03-01

    The adsorption of stearic acid on both sodium montmorillonites and calcium montmorillonites has been studied by near infrared spectroscopy complimented with infrared spectroscopy. Upon adsorption of stearic acid on Ca-Mt additional near infrared bands are observed at 8236 cm(-1) and is assigned to an interaction of stearic acid with the water of hydration. Upon adsorption of the stearic acid on Na-Mt, the NIR bands are now observed at 5671, 5778, 5848 and 5912 cm(-1) and are assigned to the overtone and combination bands of the CH fundamentals. Additional bands at 4177, 4250, 4324, 4337, 4689 and 4809 cm(-1) are attributed to CH combination bands resulting from the adsorption of the stearic acid. Stearic acid is used as a model molecule for adsorption studies. The application of near infrared spectroscopy to the study of this adsorption proved most useful.

  10. The adsorption and reaction of adenine nucleotides on montmorillonite

    NASA Technical Reports Server (NTRS)

    Ferris, James P.; Hagan, William J., Jr.

    1986-01-01

    The binding of AMP to Zn(2+)-montmorillonite is investigated in the presence of salts and Good's zwitterion buffers, PIPES and MES. The initial concentrations of nucleotide and the percent adsorbtion are used to calculate the adsorption isotherms, and the Langmuir adsorption equation is used for the analysis of data. The adsorption coefficient was found to be three times greater in the presence of 0.2 M PIPES than in its absence. In addition, basal spacings measured by X-ray diffraction were increased by the buffer. These results are interpreted in terms of a model in which the adsorption of AMP is mediated by a Zn(2+) complex of PIPES in different orientations in the interlamellar region of the montmorillonite. Mixed ligand complexes of this type are reminiscent of the complexes observed between metal ions and biological molecules in living systems.

  11. Proton conductive montmorillonite-Nafion composite membranes for direct ethanol fuel cells

    NASA Astrophysics Data System (ADS)

    Wu, Xiu-Wen; Wu, Nan; Shi, Chun-Qing; Zheng, Zhi-Yuan; Qi, Hong-Bin; Wang, Ya-Fang

    2016-12-01

    The preparation of Nafion membranes modified with montmorillonites is less studied, and most relative works mainly applied in direct methanol fuel cells, less in direct ethanol fuel cells. Organic/inorganic composite membranes are prepared with different montmorillonites (Ca-montmorillonite, Na-montmorillonite, K-montmorillonite, Mg-montmorillonite, and H-montmorillonite) and Nafion solution via casting method at 293 K in air, and with balance of their proton conductivity and ethanol permeability. The ethanol permeability and proton conductivity of the membranes are comparatively studied. The montmorillonites can well decrease the ethanol permeability of the membranes via inserted them in the membranes, while less decrease the proton conductivities of the membranes depending on the inserted amount and type of montmorillonites. The proton conductivities of the membranes are between 36.0 mS/cm and 38.5 mS/cm. The ethanol permeability of the membranes is between 0.69 × 10-6 cm2/s and 2.67 × 10-6 cm2/s.

  12. Adsorption of phosphate on hydroxyaluminum- and hydroxyiron-montmorillonite complexes.

    PubMed

    Zhu, Mao-Xu; Ding, Kui-Ying; Xu, Shao-Hui; Jiang, Xin

    2009-06-15

    One hydroxyaluminum-montmorillonite complex (HyAl-Mt), two hydroxyiron-montmorillonite complexes (HyFe-Mts) with different iron contents, and three hydroxyiron/aluminum-montmorillonite complexes (HyFeAl-Mts) with various Fe:Al molar ratios were synthesized. Behavior and kinetics of phosphate (P) sorption on selected Mt-complexes mentioned above were investigated under acidic conditions. The results indicated that the intercalations of polymeric HyFe and/or HyAl ions in interlayers of Na-saturated montmorillonite (Na-Mt) caused significant changes in surface properties of the Na-Mt, such as cation exchange capacity, specific surface area, pH at zero point of charge. In pH range tested (3.0-6.5), P adsorption on the Mt-complexes decreased with increasing pH, whereas the effect became weaker with increasing Fe contents in the Mt-complexes. The adsorption capacities of the HyFeAl-Mts were greater than those of the HyAl-Mt and HyFe-Mt, which could be attributed to decreasing crystallinity of Fe and Al oxides in the HyFeAl-Mts. The equilibrium adsorption of P on the Mt-complexes could be well described using the Langmuir isotherm, and the kinetics of P adsorption could be well described by both the pseudo-second-order and Elovich models. An increase in Fe contents in the Mt-complexes could enhance the initial kinetic rate of P adsorption, as suggested by the Elovich models. It is inferred that a great number of Fe-related active sorption sites have been located on the outer surfaces of the HyFe-Mt, as indicated by extremely high alpha value in the Elovich model. Previous studies focusing mainly on P sorption on HyAl-Mt complexes might have underestimated the contributions of Mt-complexes to P retention in acidic soils high in Fe contents.

  13. Self-Assembled, Iridescent, Crustacean-Mimetic Nanocomposites with Tailored Periodicity and Layered Cuticular Structure.

    PubMed

    Wang, Baochun; Walther, Andreas

    2015-11-24

    Natural high-performance materials inspire the pursuit of ordered hard/soft nanocomposite structures at high fractions of reinforcements and with balanced molecular interactions. Herein, we develop a facile, waterborne self-assembly pathway to mimic the multiscale cuticle structure of the crustacean armor by combining hard reinforcing cellulose nanocrystals (CNCs) with soft poly(vinyl alcohol) (PVA). We show iridescent CNC nanocomposites with cholesteric liquid-crystal structure, in which different helical pitches and photonic band gaps can be realized by varying the CNC/PVA ratio. We further show that multilayered crustacean-mimetic materials with tailored periodicity and layered cuticular structure can be obtained by sequential preparation pathways. The transition from a cholesteric to a disordered structure occurs for a critical polymer concentration. Correspondingly, we find a transition from stiff and strong mechanical behavior to materials with increasing ductility. Crack propagation studies using scanning electron microscopy visualize the different crack growth and toughening mechanisms inside cholesteric nanocomposites as a function of the interstitial polymer content for the first time. Different extents of crack deflection, layered delamination, ligament bridging, and constrained microcracking can be observed. Drawing of highly plasticized films sheds light on the mechanistic details of the transition from a cholesteric/chiral nematic to a nematic structure. The study demonstrates how self-assembly of biobased CNCs in combination with suitable polymers can be used to replicate a hierarchical biological structure and how future design of these ordered multifunctional nanocomposites can be optimized by understanding mechanistic details of deformation and fracture.

  14. Octachlorodibenzodioxin formation on Fe(III)-montmorillonite clay.

    PubMed

    Gu, Cheng; Li, Hui; Teppen, Brian J; Boyd, Stephen A

    2008-07-01

    Polychlorinated dibenzo-p-dioxins (PCDDs) are ubiquitous and highly toxic environmental contaminants found in surface and subsurface soils and in clay deposits. Interestingly, the congener profiles of such PCDDs are inexplicably dissimilar to those of known anthropogenic (e.g., pesticide manufacture, waste incineration) or natural (e.g., forest fire) sources. Characteristic features of soil or clay-associated PCDDs are the dominance of octachlorodibenzo-p-dioxin (OCDD) as the most abundant congener and very low levels of polychlorinated dibenzofurans (PCDFs). These propensities led to the hypothesis of in situ PCDD formation in soils and geologic clay deposits. In this study, we demonstrate the formation of OCDD on the naturally occurring and widely distributed clay mineral montmorillonite under environmentally relevant conditions. When pentachlorophenol (PCP)was mixed with Fe(III)-montmorillonite, significant amounts of OCDD were rapidly (minutes to days) formed (approximately 5 mg OCDD/kg clay) at ambient temperature in the presence of water. This reaction is initiated by single electron transfer from PCP to Fe(III)-montmorillonite thereby forming the PCP radical cation. Subsequent dimerization, dechlorination, and ring closure reactions result in formation of OCDD. This study provides the first direct evidence for clay-catalyzed formation of OCDD supporting the plausibility of its in situ formation in soils.

  15. Adsorption of low molecular weight halocarbons by montmorillonite

    SciTech Connect

    Estes, T.J.; Shah, R.V.; Vilker, V.L. )

    1988-04-01

    Montmorillonite clay from Clay Spur, WY, was found to adsorb several low molecular weight, hydrophobic halocarbons from aqueous solution at sub-parts-per-million levels. The halocarbons studied were trichloroethylene, tetrachloroethylene, hexachloroethane, and dibromochloropropane. When the montmorillonite was treated with sodium citrate-bicarbonate-dithionite (CBD), it adsorbed higher levels of halocarbons than the untreated clay. In addition, the CBD-treated clay exhibited a maximum in halocarbon adsorption around pH 4, while untreated clay showed little variation in adsorption over the pH range 2-10. Adsorption of trichloroethylene was inhibited by low concentrations of sodium chloride (0.01 M or greater) in solution. Aging the CBD-treated clay in water decreased its capacity to adsorb trichloroethylene. Desorption studies showed that the sorption of tetrachloroethylene to CBD-treated clay is an irreversible process when compared to sorption by fumed silica. The ability of montmorillonite to adsorb halocarbons and the instability of the clay in water are postulated to involve changes in the oxide surface coating on the clay.

  16. Infrared investigation of organo-montmorillonites prepared from different surfactants.

    PubMed

    Ma, Yuehong; Zhu, Jianxi; He, Hongping; Yuan, Peng; Shen, Wei; Liu, Dong

    2010-07-01

    In this paper, a series of organoclays were prepared from montmorillonites with different CEC and surfactants with different alkyl chain numbers and chain length. Then, FTIR spectroscopy using ATR, DRIFT and KBr pressed disk techniques was used to characterize the local environments of surfactant and host clays in various surfactants modified montmorillonites under wet and dry states. The present study demonstrates that the alkyl chain length and chain number have significant influences on the local environment of the intercalated surfactants. Also, this study indicates that the surface property of the resulting organoclays is affected by the loading and configuration of the intercalated surfactants. In wet state, more gauche conformers are introduced into the alkyl chains in the organoclays with low surfactant loading, evidenced by the shift of CH(2) vibration to higher frequency. Meanwhile, in the case of the organo-montmorillonites with high surfactant loading, the interaction between the surfactant and silicate surface results in a re-arrangement of SiO(4) tetrahedral sheets and a splitting of Si-O stretching vibration. The KBr pressed disk technique is suitable to probe the conformational ordering of the confined amine chains and the reflectance spectroscopy with ATR and/or DRIFT technique is more suitable to probe the water in organoclays. These findings are of high importance to the preparation of organoclays with proper surfactants and investigation of the microstructure of the resulting organoclays using suitable techniques.

  17. Evidence of irreversible CO2 intercalation in montmorillonite

    SciTech Connect

    Romanov, V

    2013-02-13

    Mitigation of the global climate change via sequestration of anthropogenic carbon dioxide (CO2) in geologic formations requires assessment of the reservoir storage capacity and cap rock seal integrity. The typical cap rock is shale or mudstone rich in clay minerals that may significantly affect the effectiveness of the CO2 trapping. Specific objectives of this study were to conduct experimental investigation into the processes associated with CO2 and H2O trapped in swelling clay, namely, Wyoming and Texas montmorillonite powder. Combined (same-sample) multi-technique data ? manometric sorption isotherm hysteresis, diffuse reflectance infrared spectroscopy ?trapped CO2? fingerprints, irreversible X-ray diffraction patterns for the clay interlayer in intermediate hydration state, and HF acid digestion resulting in formation of non-extractable F:CO2 adducts ? corroborate a hypothesis that carbon dioxide molecules can be irreversibly trapped via anomalous extreme confinement in the galleries associated with montmorillonite interlayer, which may result in formation of carbonates in the longer term. Validation on Arizona montmorillonite lumps substantiated the evidence that such processes may occur in natural clay deposits but possibly on a different scale and at a different rate.

  18. In Situ D-periodic Molecular Structure of Type II Collagen

    SciTech Connect

    Antipova, Olga; Orgel, Joseph P.R.O.

    2010-05-06

    Collagens are essential components of extracellular matrices in multicellular animals. Fibrillar type II collagen is the most prominent component of articular cartilage and other cartilage-like tissues such as notochord. Its in situ macromolecular and packing structures have not been fully characterized, but an understanding of these attributes may help reveal mechanisms of tissue assembly and degradation (as in osteo- and rheumatoid arthritis). In some tissues such as lamprey notochord, the collagen fibrillar organization is naturally crystalline and may be studied by x-ray diffraction. We used diffraction data from native and derivative notochord tissue samples to solve the axial, D-periodic structure of type II collagen via multiple isomorphous replacement. The electron density maps and heavy atom data revealed the conformation of the nonhelical telopeptides and the overall D-periodic structure of collagen type II in native tissues, data that were further supported by structure prediction and transmission electron microscopy. These results help to explain the observed differences in collagen type I and type II fibrillar architecture and indicate the collagen type II cross-link organization, which is crucial for fibrillogenesis. Transmission electron microscopy data show the close relationship between lamprey and mammalian collagen fibrils, even though the respective larger scale tissue architecture differs.

  19. Refraction index sensor based on phase resonances in a subwavelength structure with double period.

    PubMed

    Skigin, Diana C; Lester, Marcelo

    2016-10-01

    In this paper, we numerically demonstrate a refraction index sensor based on phase resonance excitation in a subwavelength-slit structure with a double period. The sensor consists of a metal layer with subwavelength slots arranged in a bi-periodic form, separated from a high refraction index medium. Between the metallic structure and the incident medium, a dielectric waveguide is formed whose refraction index is going to be determined. Variations in the refraction index of the waveguide are detected as shifts in the peaks of transmitted intensity originated by resonant modes supported by the compound metallic structure. At normal incidence, the spectral position of these resonant peaks exhibits a linear or a quadratic dependence with the refraction index, which permits us to obtain the unknown refraction index value with a high precision for a wide range of wavelengths. Since the operating principle of the sensor is due to the morphological resonances of the slits' structure, this device can be scaled to operate in different wavelength ranges while keeping similar characteristics.

  20. Rapid analysis of scattering from periodic dielectric structures using accelerated Cartesian expansions

    DOE PAGES

    Baczewski, Andrew David; Miller, Nicholas C.; Shanker, Balasubramaniam

    2012-03-22

    Here, the analysis of fields in periodic dielectric structures arise in numerous applications of recent interest, ranging from photonic bandgap structures and plasmonically active nanostructures to metamaterials. To achieve an accurate representation of the fields in these structures using numerical methods, dense spatial discretization is required. This, in turn, affects the cost of analysis, particularly for integral-equation-based methods, for which traditional iterative methods require Ο(Ν2) operations, Ν being the number of spatial degrees of freedom. In this paper, we introduce a method for the rapid solution of volumetric electric field integral equations used in the analysis of doubly periodic dielectricmore » structures. The crux of our method is the accelerated Cartesian expansion algorithm, which is used to evaluate the requisite potentials in Ο(Ν) cost. Results are provided that corroborate our claims of acceleration without compromising accuracy, as well as the application of our method to a number of compelling photonics applications.« less

  1. Development of biodegradable foamlike materials based on casein and sodium montmorillonite clay.

    PubMed

    Pojanavaraphan, Tassawuth; Magaraphan, Rathanawan; Chiou, Bor-Sen; Schiraldi, David A

    2010-10-11

    Biodegradable foamlike materials based on a naturally occurring polymer (casein protein) and sodium montmorillonite clay (Na+ -MMT) were produced through a simple freeze-drying process. By utilizing DL-glyceraldehyde (GC) as a chemical cross-linking agent, the structural integrity of these new aerogels were remarkably improved when compared to those of the control system (without GC), with a minimal increase in the density from 0.11 to 0.12 g cm⁻³. The degree of perfection of the foamlike structures was another parameter that had a significant influence on the physical and thermal performances of the low density composites. The biodegradability of the aerogels was investigated in terms of the carbon dioxide (CO₂) evolution for up to 8 weeks in compost media under controlled conditions.

  2. Colloidal and polyelectrolyte inks for direct-write assembly of 3D periodic structures

    NASA Astrophysics Data System (ADS)

    Gratson, Gregory Michael

    Novel inks were developed for the direct-write assembly of 3D periodic structures with varying feature size. Specifically, two ink designs were pursued: (1) a model colloidal ink (feature size > 100 mum) and (2) a polyelectrolyte ink (feature size ˜ 1 mum). The rheological properties of both inks were specifically tailored for our direct-write assembly process, which involves ink deposition through a fine scale nozzle that is robotically controlled using a 3-axis stage. Central to this approach is the design of inks that are capable of flowing through deposition nozzles of varying size and then "setting" immediately to facilitate shape retention of the deposited features. In addition, the inks must contain a high solid volume fraction to minimize drying-induced shrinkage after assembly is complete. First, a model colloidal ink based on monodisperse silica microspheres was designed for 3D periodic structures. These colloidal inks suffer difficulties (e.g., nozzle clogging) when used to fabricate structures with feature sizes below ˜ 100 mum, so a different ink design was pursued based on polyelectrolyte complexes. These inks rapidly solidified upon deposition into an IPA/water coagulation reservoir, and the exact coagulation mechanism depended strongly on reservoir composition. The water/IPA ratio in the reservoir (83--88 % IPA) was carefully tailored to produce filaments that could maintain their shape while spanning unsupported regions in the structure, yet were flexible enough to adhere to the substrate or underlying layers. Several micro-periodic structures of varying design were fabricated, revealing the facile nature of our approach. 3D micro-periodic scaffolds were used to create photonic crystals with high refractive index contrast. Silica chemical vapor deposition was performed under ambient conditions to produce a thin inorganic layer around the polymer, which facilitated further high-temperature steps. The polymer was removed through burnout at 475

  3. Rich dynamic of a stage-structured prey-predator model with cannibalism and periodic attacking rate

    NASA Astrophysics Data System (ADS)

    Zhang, Limin; Zhang, Chaofeng

    2010-12-01

    The dynamic behavior of a stage-structure prey-predator model with cannibalism for prey and periodic attacking rate for predator is investigated. Firstly, the permanence, locally and globally asymptotic stability analyses of the model with constant attacking rate are explored. After that, sufficient conditions for the permanence of the corresponding nonautonomous system with periodic attacking rate are obtained. Furthermore, numerical simulations are presented to illustrate the effects of periodic attacking rate. Simulation results show that the system with periodic attacking rate shows a rich behaviors, including period-doubling and period-having bifurcations, chaos and windows of periodicity.

  4. Microwave measurements of energy lost to longitudinal modes by single electron bunches traversing periodic structures

    SciTech Connect

    Wang, J.W.; Loew, G.A.; Weaver, J.N.; Wilson, P.B.

    1981-10-01

    In the design of future linear colliders, it will be important to minimize the loss of beam energy due to the excitation of higher-order modes in the accelerator structure by single bunches of electrons or positrons. This loss is not only detrimental in itself but also gives rise to energy spectrum widening and transverse emittance growth. Microwave measurements made on disk-loaded and alternating-spoke structures to determine the loss to the longitudinal modes are described. In these measurements the Gaussian bunch is simulated by a current pulse of the same shape transmitted through the structure on an axial center conductor. Results to date are presented for the total longitudinal loss parameter per period K in volts per picocoulomb.

  5. Ordering of small particles in one-dimensional coherent structures by time-periodic flows.

    PubMed

    Pushkin, D O; Melnikov, D E; Shevtsova, V M

    2011-06-10

    Small particles transported by a fluid medium do not necessarily have to follow the flow. We show that for a wide class of time-periodic incompressible flows inertial particles have a tendency to spontaneously align in one-dimensional dynamic coherent structures. This effect may take place for particles so small that often they would be expected to behave as passive tracers and be used in PIV measurement technique. We link the particle tendency to form one-dimensional structures to the nonlinear phenomenon of phase locking. We propose that this general mechanism is, in particular, responsible for the enigmatic formation of the "particle accumulation structures" discovered experimentally in thermocapillary flows more than a decade ago and unexplained until now.

  6. Localization of surface modes along a periodic/quasiperiodic structure containing a left-handed material

    NASA Astrophysics Data System (ADS)

    Toledo-Solano, M.; Palomino-Ovando, M. A.; Lozada-Morales, R.

    2015-12-01

    We have investigated the optical properties of a one-dimensional (1-D) photonic periodic/quasiperiodic structure, designed as photonic crystal (PC)-Fibonacci (FN)-photonic crystal (PC) sections. The structure is composed of alternating layers of a right-handed material (RHM) and a left-handed material (LHM). The RHM dielectric function is frequency independent and the LHM (metamaterial) dielectric function and magnetic susceptibility are described according to the Drude model. Using attenuated total reflectivity geometry, we explore the coupling of light with the plasmons on the surface of the metamaterial layers of the hybrid structure. The excitation of surface modes in different frequency regions are investigated. We observed bands of surface modes with a significant selective spatial localization at which the intensity of the electric field is confined almost totally within one of the PC sections or within the FN one.

  7. Fluorescent SiC with pseudo-periodic moth-eye structures

    NASA Astrophysics Data System (ADS)

    Ou, Yiyu; Aijaz, Imran; Ou, Haiyan

    2012-10-01

    White light-emitting diodes (LEDs) consisting of a nitride-based blue LED chip and phosphor are very promising candidates for the general lighting applications as energy-saving sources. Recently, donor-acceptor doped fluorescent SiC has been proven as a highly efficient wavelength converter material much superior to the phosphors in terms of high color rendering index value and long lifetime. The light extraction efficiency of the fluorescent SiC based all semiconductor LED light sources is usually low due to the large refractive index difference between the semiconductor and air. In order to enhance the extraction efficiency, we present a simple method to fabricate the pseudo-periodic moth-eye structures on the surface of the fluorescent SiC. A thin gold layer is deposited on the fluorescent SiC first. Then the thin gold layer is treated by rapid thermal processing. After annealing, the thin gold layer turns into discontinuous nano-islands. The average size of the islands is dependent on the annealing condition which could be well controlled. By using the reactive-ion etching, pseudo-periodic moth-eye structures would be obtained using the gold nano-islands as a mask layer. Reactive-ion etching conditions are carefully optimized to obtain the lowest surface reflection performance of the fabricated structures. Significant omnidirectional luminescence enhancement (226.0 %) was achieved from the angle-resolved photoluminescence measurement, which proves the pseudo-periodic moth-eye structure as an effective and simple method to enhance the extraction efficiency of fluorescent SiC based white LEDs.

  8. Sub-Diffraction Limited Writing based on Laser Induced Periodic Surface Structures (LIPSS)

    PubMed Central

    He, Xiaolong; Datta, Anurup; Nam, Woongsik; Traverso, Luis M.; Xu, Xianfan

    2016-01-01

    Controlled fabrication of single and multiple nanostructures far below the diffraction limit using a method based on laser induced periodic surface structure (LIPSS) is presented. In typical LIPSS, multiple lines with a certain spatial periodicity, but often not well-aligned, were produced. In this work, well-controlled and aligned nanowires and nanogrooves with widths as small as 40 nm and 60 nm with desired orientation and length are fabricated. Moreover, single nanowire and nanogroove were fabricated based on the same mechanism for forming multiple, periodic structures. Combining numerical modeling and AFM/SEM analyses, it was found these nanostructures were formed through the interference between the incident laser radiation and the surface plasmons, the mechanism for forming LIPSS on a dielectric surface using a high power femtosecond laser. We expect that our method, in particular, the fabrication of single nanowires and nanogrooves could be a promising alternative for fabrication of nanoscale devices due to its simplicity, flexibility, and versatility. PMID:27721428

  9. Formation of nanoporous structures in metallic materials by pulse-periodic laser treatment

    NASA Astrophysics Data System (ADS)

    Murzin, Serguei P.

    2015-09-01

    A method of the formation of nanoporous structures in metallic materials by pulse-periodic laser treatment was developed. In this study, the multicomponent aluminum-iron brass was considered and the nanoporous structure across the entire cross section of the material with a thickness of 50 μm was formed. The method was implemented using a CO2 laser processing unit. The pulse-periodic laser treatment of the Cu-Zn-Al-Fe alloy with pulse frequency of 5 Hz has led to the formation of nanosized cavities due to accumulation of internal stresses during cyclic heating and cooling at high speeds. It was determined that the pores of a channel type with average widths of 80-100 nm are formed in the central region of the heat-affected zone during laser action with thermocycling. When implementing the chosen conditions of the pulse-periodic laser processing, the localness in depth and area of the physical processes occurring in the heat-affected zone is ensured, while maintaining the original properties of the material and the absence of significant deformations in the rest of the volume. This patented process is perspective for the production not only catalysts for chemical reactions, but for ultrafiltration and microfiltration membranes as well.

  10. Detecting Repetitions and Periodicities in Proteins by Tiling the Structural Space

    PubMed Central

    2013-01-01

    The notion of energy landscapes provides conceptual tools for understanding the complexities of protein folding and function. Energy landscape theory indicates that it is much easier to find sequences that satisfy the “Principle of Minimal Frustration” when the folded structure is symmetric (Wolynes, P. G. Symmetry and the Energy Landscapes of Biomolecules. Proc. Natl. Acad. Sci. U.S.A.1996, 93, 14249–14255). Similarly, repeats and structural mosaics may be fundamentally related to landscapes with multiple embedded funnels. Here we present analytical tools to detect and compare structural repetitions in protein molecules. By an exhaustive analysis of the distribution of structural repeats using a robust metric, we define those portions of a protein molecule that best describe the overall structure as a tessellation of basic units. The patterns produced by such tessellations provide intuitive representations of the repeating regions and their association toward higher order arrangements. We find that some protein architectures can be described as nearly periodic, while in others clear separations between repetitions exist. Since the method is independent of amino acid sequence information, we can identify structural units that can be encoded by a variety of distinct amino acid sequences. PMID:23758291

  11. Optical and thermal properties of periodic photonic structures on a silicon-on-insulator platform

    NASA Astrophysics Data System (ADS)

    Song, Weiwei

    Silicon photonics is the leading candidate to fulfill the high bandwidth requirement for the future communication networks. Periodic photonic structures, due to their fascinating properties including compact size, high efficiency, and ease of design, play an important role in photonic systems. In this dissertation, SOI-based one-dimensional and two-dimensional periodic photonic structures are studied. Low crosstalk, high density integration of bus waveguides is demonstrated by employing a novel waveguide array structure. Inspired by the low coupling strength shown by initial pair waveguide experiments, novel waveguide array structures are studied by generalizing the nearest-neighbor tight-bonding model. Based on the theory, waveguide arrays have been designed and fabricated. The waveguide arrays have been characterized to demonstrate high density bus waveguides with minimal crosstalk. Two-dimensional photonic crystal waveguide (PCW) structure was then investigated aiming at reducing the propagation loss. A general cross-sectional eigenmode orthogonality relation is first derived for a one dimensional periodic system. Assisted by this orthogonality, analytic formulas are obtained to describe the propagation loss in PCW structures. By introducing the radiation and backscattering loss factors alpha1 and alpha2, the total loss coefficient alpha can be written as alpha = alpha1ng + alpha2ng2 ( ng is the group index). It is analytically shown the backscattering loss generally dominates the radiation loss for ng>10. Combined with systematic simulations of loss dependences on key structure parameters, this analytic study helps identify promising strategies to reduce the slow light loss. The influence of the substrate on the performance of a thermo-optic tuning photonic crystal device was studied in the following section. The substrate-induced thermo-optic tuning is obtained as a function of key physical parameters, based on a semi-analytic theory that agrees well with

  12. Fabrication and characterization of periodically patterned silica fiber structures for enhanced second-order nonlinearity.

    PubMed

    Daengngam, Chalongrat; Kandas, Ishac; Ashry, Islam; Wang, Anbo; Heflin, James R; Xu, Yong

    2015-03-23

    We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

  13. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, Ekmel; Tuttle, Gary; Michel, Erick; Ho, Kai-Ming; Biswas, Rana; Chan, Che-Ting; Soukoulis, Costas

    1995-01-01

    A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

  14. Periodic dielectric structure for production of photonic band gap and method for fabricating the same

    DOEpatents

    Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

    1995-04-11

    A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

  15. Polarization dependent formation of femtosecond laser-induced periodic surface structures near stepped features

    SciTech Connect

    Murphy, Ryan D.; Torralva, Ben; Adams, David P.; Yalisove, Steven M.

    2014-06-09

    Laser-induced periodic surface structures (LIPSS) are formed near 110 nm-tall Au microstructured edges on Si substrates after single-pulse femtosecond irradiation with a 150 fs pulse centered near a 780 nm wavelength. We investigate the contributions of Fresnel diffraction from step-edges and surface plasmon polariton (SPP) excitation to LIPSS formation on Au and Si surfaces. For certain laser polarization vector orientations, LIPSS formation is dominated by SPP excitation; however, when SPP excitation is minimized, Fresnel diffraction dominates. The LIPSS orientation and period distributions are shown to depend on which mechanism is activated. These results support previous observations of the laser polarization vector influencing LIPSS formation on bulk surfaces.

  16. Band structure engineering of graphene by a local gate defined periodic potential

    NASA Astrophysics Data System (ADS)

    Forsythe, Carlos; Maher, Patrick; Scarabelli, Diego; Dean, Cory; Kim, Philip

    Recent improvements in 2-dimensional (2D) material layering have resulted in enhanced device quality and created pathways for new device architectures. We fabricate periodic arrays from a patterned local back gate and a uniform top gate on hBN encapsulated graphene channels. The symmetry and lattice size of the periodic potential can be determined by state-of-art electron beam lithography and etching, achieving a lattice constant of 35 nm. The strength of the electric potential modulation can be controlled through applied voltage on the patterned gate. We observe signatures of superlattice modulation near the main Dirac peak in the density dependent resistance measurement at zero magnetic field. Current studies focus on the exploration of Hofstadter fractal band structures under magnetic fields. Our nano-patterned engineered superlattices on graphene hold great promise for wider applications.

  17. Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

    NASA Astrophysics Data System (ADS)

    Ertem, Gözen; Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-09-01

    The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH3-(CH2)n-NH3]+, where n = 3-16 and 18, and then measuring d(001), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

  18. Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

    PubMed Central

    Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-01-01

    Abstract The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH3-(CH2)n-NH3]+, where n = 3–16 and 18, and then measuring d(001), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed. Key Words: Mars—Origin of life—Montmorillonite—Mineral catalysis—Layer charge density—X–ray diffractometry. Astrobiology 10, 743–749. PMID:20854214

  19. Correlation between the extent of catalytic activity and charge density of montmorillonites.

    PubMed

    Ertem, Gözen; Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

    2010-09-01

    The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH₃-(CH₂)(n)-NH₃](+), where n = 3-16 and 18, and then measuring d(₀₀₁), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

  20. Reflectance spectroscopy and GEX simulation of palagonite and iron-rich montmorillonite clay mixtures: Implications for the surface composition of Mars

    NASA Technical Reports Server (NTRS)

    Orenberg, J. B.; Handy, J.; Quinn, R.

    1992-01-01

    Because of the power of remote sensing reflectance spectroscopy in determining mineralogy, it has been used as the major method of identifying a possible mineral analogue of the martian surface. A summary of proposed martian surface compositions from reflectance spectroscopy before 1979 was presented by Singer et al. Since that time, iron-rich montmorillonite clay, nanocrystalline or nanophase hematite, and palagonite have been suggested as Mars soil analogue materials. Palagonite in petrological terms is best described as an amorphous, hydrated, ferric iron, silica gel. Montmorillonite is a member of the smectite clay group, and its structure is characterized by an octahedral sheet in coordination with two tetrahedral sheets in which oxygen atoms are shared. The crystal unity of montmorillonite is well defined in contrast to palagonite where it is considered amorphous or poorly crystalline at best. Because of the absence of the diagnostic strong 2.2-micron reflectance band characteristic of clays in the near-infrared (NIR) spectrum of Mars and palagonite and based upon a consideration of wide wavelength coverage (0.3-50 microns), Roush et al. concluded that palagonite is a more likely Mars surface analogue. In spite of the spectral agreement of palagonite and the Mars reflectance spectrum in the 2.2-micron region, palagonite shows poor correspondence with the results of the Viking LR experiment. In contrast, iron-rich montmorillonite clays show relatively good agreement with the results of the Viking LR experiment. This spectral study was undertaken to evaluate the spectral properties of mixtures of palagonite and Mars analogue iron-rich montmorillonite clay (16-18 wt. percent Fe as Fe2O3) as a Mars surface mineralogical model. Mixtures of minerals as Mars surface analogue materials have been studied before, but the mixtures were restricted to crystalline clays and iron oxides.

  1. Periodic F-actin structures shape the neck of dendritic spines.

    PubMed

    Bär, Julia; Kobler, Oliver; van Bommel, Bas; Mikhaylova, Marina

    2016-11-14

    Most of the excitatory synapses on principal neurons of the forebrain are located on specialized structures called dendritic spines. Their morphology, comprising a spine head connected to the dendritic branch via a thin neck, provides biochemical and electrical compartmentalization during signal transmission. Spine shape is defined and tightly controlled by the organization of the actin cytoskeleton. Alterations in synaptic strength correlate with changes in the morphological appearance of the spine head and neck. Therefore, it is important to get a better understanding of the nanoscale organization of the actin cytoskeleton in dendritic spines. A periodic organization of the actin/spectrin lattice was recently discovered in axons and a small fraction of dendrites using super-resolution microscopy. Here we use a small probe phalloidin-Atto647N, to label F-actin in mature hippocampal primary neurons and in living hippocampal slices. STED nanoscopy reveals that in contrast to β-II spectrin antibody labelling, phalloidin-Atto647N stains periodic actin structures in all dendrites and the neck of nearly all dendritic spines, including filopodia-like spines. These findings extend the current view on F-actin organization in dendritic spines and may provide new avenues for understanding the structural changes in the spine neck during induction of synaptic plasticity, active organelle transport or tethering.

  2. Periodic F-actin structures shape the neck of dendritic spines

    PubMed Central

    Bär, Julia; Kobler, Oliver; van Bommel, Bas; Mikhaylova, Marina

    2016-01-01

    Most of the excitatory synapses on principal neurons of the forebrain are located on specialized structures called dendritic spines. Their morphology, comprising a spine head connected to the dendritic branch via a thin neck, provides biochemical and electrical compartmentalization during signal transmission. Spine shape is defined and tightly controlled by the organization of the actin cytoskeleton. Alterations in synaptic strength correlate with changes in the morphological appearance of the spine head and neck. Therefore, it is important to get a better understanding of the nanoscale organization of the actin cytoskeleton in dendritic spines. A periodic organization of the actin/spectrin lattice was recently discovered in axons and a small fraction of dendrites using super-resolution microscopy. Here we use a small probe phalloidin-Atto647N, to label F-actin in mature hippocampal primary neurons and in living hippocampal slices. STED nanoscopy reveals that in contrast to β-II spectrin antibody labelling, phalloidin-Atto647N stains periodic actin structures in all dendrites and the neck of nearly all dendritic spines, including filopodia-like spines. These findings extend the current view on F-actin organization in dendritic spines and may provide new avenues for understanding the structural changes in the spine neck during induction of synaptic plasticity, active organelle transport or tethering. PMID:27841352

  3. Infrared light-induced protein crystallization. Structuring of protein interfacial water and periodic self-assembly

    NASA Astrophysics Data System (ADS)

    Kowacz, Magdalena; Marchel, Mateusz; Juknaité, Lina; Esperança, José M. S. S.; Romão, Maria João; Carvalho, Ana Luísa; Rebelo, Luís Paulo N.

    2017-01-01

    We show that a physical trigger, a non-ionizing infrared (IR) radiation at wavelengths strongly absorbed by liquid water, can be used to induce and kinetically control protein (periodic) self-assembly in solution. This phenomenon is explained by considering the effect of IR light on the structuring of protein interfacial water. Our results indicate that the IR radiation can promote enhanced mutual correlations of water molecules in the protein hydration shell. We report on the radiation-induced increase in both the strength and cooperativeness of H-bonds. The presence of a structured dipolar hydration layer can lead to attractive interactions between like-charged biomacromolecules in solution (and crystal nucleation events). Furthermore, our study suggests that enveloping the protein within a layer of structured solvent (an effect enhanced by IR light) can prevent the protein non-specific aggregation favoring periodic self-assembly. Recognizing the ability to affect protein-water interactions by means of IR radiation may have important implications for biological and bio-inspired systems.

  4. Periodic dielectric structure for production of photonic band gap and devices incorporating the same

    DOEpatents

    Ho, Kai-Ming; Chan, Che-Ting; Soukoulis, Costas

    1994-08-02

    A periodic dielectric structure which is capable of producing a photonic band gap and which is capable of practical construction. The periodic structure is formed of a plurality of layers, each layer being formed of a plurality of rods separated by a given spacing. The material of the rods contrasts with the material between the rods to have a refractive index contrast of at least two. The rods in each layer are arranged with their axes parallel and at a given spacing. Adjacent layers are rotated by 90.degree., such that the axes of the rods in any given layer are perpendicular to the axes in its neighbor. Alternating layers (that is, successive layers of rods having their axes parallel such as the first and third layers) are offset such that the rods of one are about at the midpoint between the rods of the other. A four-layer periocity is thus produced, and successive layers are stacked to form a three-dimensional structure which exhibits a photonic band gap. By virtue of forming the device in layers of elongate members, it is found that the device is susceptible of practical construction.

  5. PERIODIC STRUCTURE IN THE MEGAPARSEC-SCALE JET OF PKS 0637-752

    SciTech Connect

    Godfrey, L. E. H.; Ekers, R.; Lovell, J. E. J.; Burke-Spolaor, S.; Bicknell, G. V.; Jauncey, D. L.; Birkinshaw, M.; Worrall, D. M.; Schwartz, D. A.; Marshall, H. L.; Gelbord, J.; Perlman, E. S.; Georganopoulos, M.

    2012-10-20

    We present 18 GHz Australia Telescope Compact Array imaging of the megaparsec-scale quasar jet PKS 0637-752 with angular resolution {approx}0.''58. We draw attention to a spectacular train of quasi-periodic knots along the inner 11'' of the jet, with average separation {approx}1.1 arcsec (7.6 kpc projected). We consider two classes of model to explain the periodic knots: those that involve a static pattern through which the jet plasma travels (e.g., stationary shocks) and those that involve modulation of the jet engine. Interpreting the knots as re-confinement shocks implies the jet kinetic power Q{sub jet} {approx} 10{sup 46} erg s{sup -1}, but the constant knot separation along the jet is not expected in a realistic external density profile. For models involving modulation of the jet engine, we find that the required modulation period is 2 Multiplication-Sign 10{sup 3} yr < {tau} < 3 Multiplication-Sign 10{sup 5} yr. The lower end of this range is applicable if the jet remains highly relativistic on kiloparsec scales, as implied by the IC/CMB model of jet X-ray emission. We suggest that the periodic jet structure in PKS 0637-752 may be analogous to the quasi-periodic jet modulation seen in the microquasar GRS 1915+105, believed to result from limit cycle behavior in an unstable accretion disk. If variations in the accretion rate are driven by a binary black hole, the predicted orbital radius is 0.7 pc {approx}< a {approx}< 30 pc, which corresponds to a maximum angular separation of {approx}0.1-5 mas.

  6. Analysis of waves in the plasma guided by a periodical vane-type slow wave structure

    SciTech Connect

    Wu, T.J.; Kou, C.S.

    2005-10-01

    In this study, the dispersion relation has been derived to characterize the propagation of the waves in the plasma guided by a periodical vane-type slow wave structure. The plasma is confined by a quartz plate. Results indicate that there are two different waves in this structure. One is the plasma mode that originates from the plasma surface wave propagating along the interface between the plasma and the quartz plate, and the other is the guide mode that originally travels along the vane-type slow wave structure. In contrast to its original slow wave characteristics, the guide mode becomes a fast wave in the low-frequency portion of the passband, and there exists a cut-off frequency for the guide mode. The vane-type guiding structure has been shown to limit the upper frequency of the passband of the plasma mode, compared with that of the plasma surface wave. In addition, the passband of the plasma mode increases with the plasma density while it becomes narrower for the guide mode. The influences of the parameters of the guiding structure and plasma density on the propagation of waves are also presented.

  7. Photonic-magnonic crystals: Multifunctional periodic structures for magnonic and photonic applications

    SciTech Connect

    Kłos, J. W. Krawczyk, M.; Dadoenkova, Yu. S.; Dadoenkova, N. N.; Lyubchanskii, I. L.

    2014-05-07

    We investigate the properties of a photonic-magnonic crystal, a complex multifunctional one-dimensional structure with magnonic and photonic band gaps in the GHz and PHz frequency ranges for spin waves and light, respectively. The system consists of periodically distributed dielectric magnetic slabs of yttrium iron garnet and nonmagnetic spacers with an internal structure of alternating TiO{sub 2} and SiO{sub 2} layers which form finite-size dielectric photonic crystals. We show that the spin-wave coupling between the magnetic layers, and thus the formation of the magnonic band structure, necessitates a nonzero in-plane component of the spin-wave wave vector. A more complex structure perceived by light is evidenced by the photonic miniband structure and the transmission spectra in which we have observed transmission peaks related to the repetition of the magnetic slabs in the frequency ranges corresponding to the photonic band gaps of the TiO{sub 2}/SiO{sub 2} stack. Moreover, we show that these modes split to very high sharp (a few THz wide) subpeaks in the transmittance spectra. The proposed novel multifunctional artificial crystals can have interesting applications and be used for creating common resonant cavities for spin waves and light to enhance the mutual influence between them.

  8. Sound propagation in a duct of periodic wall structure. [numerical analysis

    NASA Technical Reports Server (NTRS)

    Kurze, U.

    1978-01-01

    A boundary condition, which accounts for the coupling in the sections behind the duct boundary, is given for the sound-absorbing duct with a periodic structure of the wall lining and using regular partition walls. The soundfield in the duct is suitably described by the method of differences. For locally active walls this renders an explicit approximate solution for the propagation constant. Coupling may be accounted for by the method of differences in a clear manner. Numerical results agree with measurements and yield information which has technical applications.

  9. A numerical investigation of the dynamics of non-periodic micromagnetic structures

    NASA Astrophysics Data System (ADS)

    Redjdal, Makhlouf

    1998-02-01

    The dynamics of a domain wall and non-periodic domain wall structures in magnetic garnet material are numerically investigated in the presence of fields either perpendicular or parallel to the film plane. This is the first investigation that has been made of these structures as single elements since all previous attempts, both analytical and numerical, have used mathematics only appropriate to periodic structures. Domain wall structures of a single π-vertical Bloch line (VBL) and 2πVBL are of interest to the design of a VBL memory. The static shapes of all structures are calculated. When a field normal to the film plane is applied, the wall moves and gyrotropically drives any structure present in the wall. VBL to wall velocity ratio at dynamic equilibrium is calculated for the range of perpendicular fields of interest to the VBL memory. At high fields (>10 Oe), a considerable magnetization due to Horizontal Bloch lines (HBLs) nucleation on each side of the VBL structure is observed. When a field is applied parallel to the film plane and the domain wall, the πVBL moves first and drives the domain wall gyrotropically. Steady state is reached when an HBL-like distortion, occurring at the beginning, is overcome. The steady state VBL to wall velocity ratio is calculated. A 2πVBL is split into two single πVBLs. This operation is dominated by the extreme magnetization distortion occurring at the beginning in the wall center. Surprisingly, this distortion alone was capable of splitting the 2πVBL structure when the field is turned off. A large scale computer simulation technique has been developed for this investigation. The technique is based on a comoving formulation of the Landau-Lifshitz-Gilbert equation and is implemented on the Connection Machine System CM5. The LLG equation is solved in a rectangular lattice using free boundary conditions. The simulation takes as input a characterization of the phenomenological magnetic parameters exchange, anisotropy

  10. High school chemistry students' learning of the elements, structure, and periodicity of the periodic table: Contributions of inquiry-based activities and exemplary graphics

    NASA Astrophysics Data System (ADS)

    Roddy, Knight Phares, Jr.

    The main research question of this study was: How do selected high school chemistry students' understandings of the elements, structure, and periodicity of the Periodic Table change as they participate in a unit study consisting of inquiry-based activities emphasizing construction of innovative science graphics? The research question was answered using a multiple case study/mixed model design which employed elements of both qualitative and quantitative methodologies during data collection and analyses. The unit study was conducted over a six-week period with 11th -grade students enrolled in a chemistry class. A purposive sample of six students from the class was selected to participate in interviews and concept map coconstruction (Wandersee & Abrams, 1993) periodically across the study. The progress of the selected students of the case study was compared to the progress of the class as a whole. The students of the case study were also compared to a group of high school chemistry students at a comparative school. The results show that the students from both schools left traditional instruction on the periodic table (lecture and textbook activities) with a very limited understanding of the topic. It also revealed that the inquiry-based, visual approach of the unit study helped students make significant conceptual progress in their understanding of the periodic table. The pictorial periodic table (which features photographs of the elements), used in conjunction with the graphic technique of data mapping, enhanced students understanding of the patterns of the physical properties of the elements on the periodic table. The graphic technique of compound mapping helped students learn reactivity patterns between types and groups of elements on the periodic table. The recreation of the periodic table with element cards created from the pictorial periodic table helped students progress in their understanding of periodicity and its key concepts. The Periodic Table Literacy

  11. Wetting transition of a nematic liquid crystal on a periodic wedge-structured substrate.

    PubMed

    Patricio, P; Pham, C-T; Romero-Enrique, J M

    2008-01-01

    It is known that the wetting behaviour of a fluid is deeply altered by the presence of rough or structured substrates. We first review some simple considerations about isotropic fluids and rough substrates, and then we generalize Wenzel's law, which assigns an effective contact angle to a droplet on a rough substrate, when the wetting layer has an ordered phase, like a nematic. We estimate the conditions for which the wetting behavior of an ordered fluid can be qualitatively different from that usually found in a simple fluid. To support our general considerations, we use the Landau-de Gennes mean field approach to investigate theoretically and numerically the wetting transition of a nematic phase on a periodic triangular structured substrate.

  12. Observation of Exchange Anisotropy in Single-Phase Layer-Structured Oxides with Long Periods

    PubMed Central

    Huang, Yan; Wang, Guopeng; Sun, Shujie; Wang, Jianlin; Peng, Ranran; Lin, Yue; Zhai, Xiaofang; Fu, Zhengping; Lu, Yalin

    2015-01-01

    A remarkable exchange bias effect arising from the temperature-dependent interaction among the ferromagnetic-like cluster glasses and antiferromagnetic regions was observed in a newly developed single-phase multiferroic compound of Bi10Fe6Ti3O30 which has a nine-layer Aurivillius structure. Inhomogeneous distribution of magnetic Fe ions inside this long-period layered structure was experimentally identified via the atomic level imaging. The results confirmed the presence of the short-range magnetic ordering (the cluster glassy state) and the canted antiferromagnetism, and then the direct interaction among them was further confirmed. Finding of this new single-phase material accompanying this remarkable exchange bias effect would be beneficial to both basic physics understanding and the potential device development. PMID:26487509

  13. Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O

    DOE PAGES

    Cockayne, Eric; Mihalkovič, Marek; Henley, Christopher L.

    2016-01-07

    Here, we model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structue is a simple decoration of three types of tiles: square, triangle and 30° rhombus, with edge lengths 6.85 Å, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, and identify the brightmore » protrusions as Ba atoms. The models are consistent with all experimental observations.« less

  14. Periodic responses of a structure with 3:1 internal resonance

    NASA Astrophysics Data System (ADS)

    Shaw, A. D.; Hill, T. L.; Neild, S. A.; Friswell, M. I.

    2016-12-01

    This work presents a conceptually simple experiment consisting of a cantilever beam with a nonlinear spring at the tip. The configuration allows manipulation of the relative spacing between the modal frequencies of the underlying linear structure, and this permits the deliberate introduction of internal resonance. A 3:1 resonance is studied in detail; the response around the first mode shows a classic stiffening response, with the addition of more complex dynamic behaviour and an isola region. Quasiperiodic responses are also observed but in this work the focus remains on periodic responses. Predictions using Normal Form analysis and continuation methods show good agreement with experimental observations. The experiment provides valuable insight into frequency responses of nonlinear modal structures, and the implications of nonlinearity for vibration tests.

  15. Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O

    SciTech Connect

    Cockayne, Eric; Mihalkovič, Marek; Henley, Christopher L.

    2016-01-07

    Here, we model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O, and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structue is a simple decoration of three types of tiles: square, triangle and 30° rhombus, with edge lengths 6.85 Å, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally, and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.

  16. Analysis of the moiré pattern of moving periodic structures using reciprocal vector approach

    NASA Astrophysics Data System (ADS)

    Rasouli, S.; Tavassoly, M. T.

    2012-03-01

    Several mathematical approaches have been used to explore the moiré pattern. All of them have been considered for superimposing the static structures. In this paper, we have presented a theoretical approach to take into account the relative motion in superimposed gratings and its effect on the moiré fringe patterns. We have used a reciprocal vector approach and consequently obtained a comprehensive description of the dynamic behavior of the moiré patterns in a cinematic viewpoint. Formulations of the rotation and parallel moiré patterns of superposition of static and dynamic periodic structures have been derived in an unified form. Besides, some applications of moiré technique that have been already carried out in dynamical phenomena will be briefly reviewed.

  17. Effect of modified montmorillonites on the biodegradation and adsorption of biomarkers such as hopanes, steranes and diasteranes.

    PubMed

    Ugochukwu, Uzochukwu C; Head, Ian M; Manning, David A C

    2013-12-01

    The effect of modified montmorillonites on the biodegradation and adsorption of selected steranes, diasteranes and hopanes was investigated in aqueous clay/oil microcosm experiments with a hydrocarbon degrading microorganism community. The unmodified montmorillonite was treated with didecyldimethylammonium bromide, hydrochloric acid and the relevant metallic chloride to produce organomontmorillonite, acid activated montmorillonite and homoionic montmorillonite respectively which were used in this study. The study indicated that organomontmorillonite, acid activated montmorillonite and potassium montmorillonite did not support the biodegradation of the selected steranes, diasteranes and hopanes as alteration of the biomarkers via biodegradation varied from a paltry 2-6 %. The adsorption of the selected biomarkers on acid activated montmorillonite and organomontmorillonite was also poor. However, adsorption of the biomarkers on potassium montmorillonite was relatively high. Sodium montmorillonite and unmodified montmorillonite appear to stimulate the biodegradation of the selected biomarkers moderately (30-35 %) with adsorption occurring at low level. Calcium montmorillonite and ferric montmorillonite effected significant biodegradation (51-60 %) of the selected biomarkers.

  18. Unwinding the differences of the mammalian PERIOD clock proteins from crystal structure to cellular function.

    PubMed

    Kucera, Nicole; Schmalen, Ira; Hennig, Sven; Öllinger, Rupert; Strauss, Holger M; Grudziecki, Astrid; Wieczorek, Caroline; Kramer, Achim; Wolf, Eva

    2012-02-28

    The three PERIOD homologues mPER1, mPER2, and mPER3 constitute central components of the mammalian circadian clock. They contain two PAS (PER-ARNT-SIM) domains (PAS-A and PAS-B), which mediate homo- and heterodimeric mPER-mPER interactions as well as interactions with transcription factors and kinases. Here we present crystal structures of PAS domain fragments of mPER1 and mPER3 and compare them with the previously reported mPER2 structure. The structures reveal homodimers, which are mediated by interactions of the PAS-B β-sheet surface including a highly conserved tryptophan (Trp448(mPER1), Trp419(mPER2), Trp359(mPER3)). mPER1 homodimers are additionally stabilized by interactions between the PAS-A domains and mPER3 homodimers by an N-terminal region including a predicted helix-loop-helix motive. We have verified the existence of these homodimer interfaces in solution and inside cells using analytical gel filtration and luciferase complementation assays and quantified their contributions to homodimer stability by analytical ultracentrifugation. We also show by fluorescence recovery after photobleaching analyses that destabilization of the PAS-B/tryptophan dimer interface leads to a faster mobility of mPER2 containing complexes in human U2OS cells. Our study reveals structural and quantitative differences between the homodimeric interactions of the three mouse PERIOD homologues, which are likely to contribute to their distinct clock functions.

  19. Propagation of SH waves in an infinite/semi-infinite piezoelectric/piezomagnetic periodically layered structure.

    PubMed

    Pang, Yu; Liu, Yu-Shan; Liu, Jin-Xi; Feng, Wen-Jie

    2016-04-01

    In this paper, SH bulk/surface waves propagating in the corresponding infinite/semi-infinite piezoelectric (PE)/piezomagnetic (PM) and PM/PE periodically layered composites are investigated by two methods, the stiffness matrix method and the transfer matrix method. For a semi-infinite PE/PM or PM/PE medium, the free surface is parallel to the layer interface. Both PE and PM materials are assumed to be transversely isotropic solids. Dispersion equations are derived by the stiffness/transfer matrix methods, respectively. The effects of electric-magnetic (ME) boundary conditions at the free surface and the layer thickness ratios on dispersion curves are considered in detail. Numerical examples show that the results calculated by the two methods are the same. The dispersion curves of SH surface waves are below the bulk bands or inside the frequency gaps. The ratio of the layer thickness has an important effect not only on the bulk bands but also on the dispersion curves of SH surface waves. Electric and magnetic boundary conditions, respectively, determine the dispersion curves of SH surface waves for the PE/PM and PM/PE semi-infinite structures. The band structures of SH bulk waves are consistent for the PE/PM and PM/PE structures, however, the dispersive behaviors of SH surface waves are indeed different for the two composites. The realization of the above-mentioned characteristics of SH waves will make it possible to design PE/PM acoustic wave devices with periodical structures and achieve the better performance.

  20. Variable Temperature Infrared Spectroscopy Studies of Aromatic Acid Adsorbate Effects on Montmorillonite Dehydration.

    PubMed

    Ingram, Audrey L; Nickels, Tara M; Maraoulaite, Dalia K; White, Robert L

    2017-02-01

    Molecular interactions between benzoic, salicylic, and acetylsalicylic acids and water contained within montmorillonite clay interlayer spaces are characterized by using variable temperature diffuse reflection infrared Fourier transform spectroscopy (VT-DRIFTS). By using sample perturbation and difference spectroscopy, infrared (IR) spectral variations resulting from the removal of interlayer water are used to characterize aromatic acid local environment changes. Difference spectra features representing functional group perturbations are correlated with changes in IR absorptions associated with -O-H and -C = O stretching vibrations. Results suggest that adsorbate carboxylic acid functionalities participate in extensive hydrogen bonding and that the strengths of these interactions are diminished when clays are dehydrated. The nature of these interactions and their temperature-dependent properties are found to depend on adsorbate structure and concentration as well as the clay interlayer cation.

  1. What causes periodic beating in sperm flagella: synchronized internal forcing or fluid-structure interaction?

    NASA Astrophysics Data System (ADS)

    Prabhakar, Ranganathan; Nandagiri, Ashwin; Jadhav, Sameer

    2016-11-01

    Eucaryotic cells such as sperm propel themselves using internally driven flagella. Two different models for the origin of the whip-like beating observed in such flagella are compared. The first model assumes that internal protein motors actuate synchronously to cause a traveling active-force wave within the filament. The forcing wave is chosen such that its resultant and the total torque on the filament are zero. In contrast, the second model assumes that forces and torques exerted by the motors locally sum to zero across the scale of the filament diameter. The only effect of the motor activity is to give rise to a stresslet distribution across the filament length. In either model, the slender filament is modeled as a bead-spring chain with hydrodynamic interactions. Flagellar waveforms and trajectory patterns obtained are compared systematically while keeping the dissipation rates the same for the two models. Periodic beating emerges in freely swimming filaments with the second model without any imposed periodicity in the stresslet distribution. This suggests that periodic waveforms in eucaryotic flagella can emerge by fluid-structure interactions alone without significant internal synchronization of protein motor activity.

  2. Femtosecond laser-induced periodic surface structure on the Ti-based nanolayered thin films

    SciTech Connect

    Petrović, Suzana M.; Gaković, B.; Peruško, D.; Stratakis, E.; Bogdanović-Radović, I.; Čekada, M.; Fotakis, C.; Jelenković, B.

    2013-12-21

    Laser-induced periodic surface structures (LIPSSs) and chemical composition changes of Ti-based nanolayered thin films (Al/Ti, Ni/Ti) after femtosecond (fs) laser pulses action were studied. Irradiation is performed using linearly polarized Ti:Sapphire fs laser pulses of 40 fs pulse duration and 800 nm wavelength. The low spatial frequency LIPSS (LSFL), oriented perpendicular to the laser polarization with periods slightly lower than the irradiation wavelength, was typically formed at elevated laser fluences. On the contrary, high spatial frequency LIPSS (HSFL) with uniform period of 155 nm, parallel to the laser light polarization, appeared at low laser fluences, as well as in the wings of the Gaussian laser beam distribution for higher used fluence. LSFL formation was associated with the material ablation process and accompanied by the intense formation of nanoparticles, especially in the Ni/Ti system. The composition changes at the surface of both multilayer systems in the LSFL area indicated the intermixing between layers and the substrate. Concentration and distribution of all constitutive elements in the irradiated area with formed HSFLs were almost unchanged.

  3. Valley-dependent band structure and valley polarization in periodically modulated graphene

    NASA Astrophysics Data System (ADS)

    Lu, Wei-Tao

    2016-08-01

    The valley-dependent energy band and transport property of graphene under a periodic magnetic-strained field are studied, where the time-reversal symmetry is broken and the valley degeneracy is lifted. The considered superlattice is composed of two different barriers, providing more degrees of freedom for engineering the electronic structure. The electrons near the K and K' valleys are dominated by different effective superlattices. It is found that the energy bands for both valleys are symmetric with respect to ky=-(AM+ξ AS) /4 under the symmetric superlattices. More finite-energy Dirac points, more prominent collimation behavior, and new crossing points are found for K' valley. The degenerate miniband near the K valley splits into two subminibands and produces a new band gap under the asymmetric superlattices. The velocity for the K' valley is greatly renormalized compared with the K valley, and so we can achieve a finite velocity for the K valley while the velocity for the K' valley is zero. Especially, the miniband and band gap could be manipulated independently, leading to an increase of the conductance. The characteristics of the band structure are reflected in the transmission spectra. The Dirac points and the crossing points appear as pronounced peaks in transmission. A remarkable valley polarization is obtained which is robust to the disorder and can be controlled by the strain, the period, and the voltage.

  4. Optical filter including a sub-wavelength periodic structure and method of making

    DOEpatents

    Kaushik, Sumanth; Stallard, Brian R.

    1998-01-01

    An optical filter includes a dielectric layer formed within a resonant optical cavity, with the dielectric layer having formed therein a sub-wavelength periodic structure to define, at least in part, a wavelength for transmission of light through the resonant optical cavity. The sub-wavelength periodic structure can be formed either by removing material from the dielectric layer (e.g. by etching through an electron-beam defined mask), or by altering the composition of the layer (e.g. by ion implantation). Different portions of the dielectric layer can be patterned to form one or more optical interference filter elements having different light transmission wavelengths so that the optical filter can filter incident light according to wavelength and/or polarization. For some embodiments, the optical filter can include a detector element in optical alignment with each optical interference filter element to quantify or measure the filtered light for analysis thereof. The optical filter has applications to spectrometry, colorimetry, and chemical sensing.

  5. Fraunhofer diffraction of electromagnetic radiation by finite periodic structures with regular or irregular overall shapes.

    PubMed

    Xu, Yu-Lin

    2015-01-01

    Based on an essentially different theoretical foundation than common classical diffraction theories that remain in extensive use, this paper discusses from a fresh perspective the theoretical interpretation and prediction of the far-field diffraction of a plane monochromatic wave by a finite periodic array (PA) of identical obstacles. The theoretical treatment rests on the PA extension of the rigorous generalized multiparticle Mie solution (GMM). The truncated periodic structures may have an irregular overall shape with an arbitrary spatial orientation with respect to the incident beam. It is shown that the overall shape and intrinsic geometrical structure of a finite PA play a decisive role in giving rise to an associated far-field diffraction pattern. It is also shown that, when the physical dimensions of individual component units are much smaller than the incident wavelength, the extracted diffraction pattern of a densely packed PA of such small volumes in forward directions exhibits the distinct features predicted from classical diffraction theories for an aperture with the same shape as the overall finite PA. Several typical examples are presented, including two complementary arrays used in the specific discussion concerning Babinet's principle. There are brief preliminary discussions on some fundamental concepts in connection with the involved theoretical basis and on potential further development and application of the present GMM-PA approach.

  6. Vortex structure of a plane impinging jet with spanwise periodic forcing

    NASA Astrophysics Data System (ADS)

    Sakakibara, Jun; Anzai, Tomokuni

    1999-11-01

    Vortex structure of a plane impinging jet of water with spanwise periodic forcing has been experimentally measured using PIV. A plane nozzle, having a width of ( B=30 ) mm and aspect ratio of 10, issued water jet vertically and impinged on a plate set at a distance ( H=5.5B ) from the nozzle exit. Sixty rectangular slots (1mm (×) 4mm cross-section) aligned in spanwise direction are installed both side of the nozzle exit with 5mm interval. Each slots are connected via vinyl tubes to four of speaker boxes to add suction/blowing perturbations to the initial shear layer of the jet. The perturbation added by successive 3 slots, 15mm in spanwise length, have a phase lag (α) behind the perturbation by next 3 slots, and repeated in whole row of the slots. This configuration could make spanwise periodic perturbations, which have a wave length (λ=30)mm, to excite the secondary instability of the shear layer. As increasing phase lag (α) the intensity of the vorticity of the streamwise counter-rotating vortices on the stagnation plate was increased, and maximum intensity was achieved at (α=π). Time and spatial evolution of the vortex structures will be shown in the presentation.

  7. Surface Modulation of Graphene Field Effect Transistors on Periodic Trench Structure.

    PubMed

    Jin, Jun Eon; Choi, Jun Hee; Yun, Hoyeol; Jang, Ho-Kyun; Lee, Byung Chul; Choi, Ajeong; Joo, Min-Kyu; Dettlaff-Weglikowska, Urszula; Roth, Siegmar; Lee, Sang Wook; Lee, Jae Woo; Kim, Gyu Tae

    2016-07-20

    In this work, graphene field effect transistors (FETs) were fabricated on a trench structure made by carbonized poly(methylmethacrylate) to modify the graphene surface. The trench-structured devices showed different characteristics depending on the channel orientation and the pitch size of the trenches as well as channel area in the FETs. Periodic corrugations and barriers of suspended graphene on the trench structure were measured by atomic force microscopy and electrostatic force microscopy. Regular barriers of 160 mV were observed for the trench structure with graphene. To confirm the transfer mechanism in the FETs depending on the channel orientation, the ratio of experimental mobility (3.6-3.74) was extracted from the current-voltage characteristics using equivalent circuit simulation. It is shown that the number of barriers increases as the pitch size decreases because the number of corrugations increases from different trench pitches. The noise for the 140 nm pitch trench is 1 order of magnitude higher than that for the 200 nm pitch trench.

  8. The study of structural color filter based on periodic nanohole arrays for bio-detection

    NASA Astrophysics Data System (ADS)

    Kim, Seunguk; Shin, Jeonghee; Yoo, Seungjun; Kim, Samhwan; Jeon, Byoungok; Moon, Cheil; Jang, Jae-Eun

    2015-07-01

    A nanostructure which induces localized surface plasmon resonance (LSPR) can be utilized in visible light and near infrared (NIR) regions and it shows promising features as a bio-detector because LSPR state is changed easily by different bio-related materials. Owing to transparent property of many biomolecules as well as diluted states in base solutions, it is hard to distinguish each other by eye or microscope analysis. However, difference in molecular structure and composition makes difference in optical characteristics such as a refractive index or a dielectric constant. Therefore, our LSPR-based nanohole array structure which has high sensitivity to detect small changes in optical characteristics can be a great candidate for a bio detector. Here, we fabricated structural color filters (SCFs) to detect wavelength shifts for several biomolecules and optimized the nanohole array structures for high sensitivity. Periodic nanohole arrays were designed to present resonance peaks in visible light region for optical analysis and fabricated in Au or Al thin film layer. The spectral shifts were detected caused by biomolecules.

  9. Enhanced interlayer trapping of a tetracycline antibiotic within montmorillonite layers in the presence of Ca and Mg.

    PubMed

    Aristilde, Ludmilla; Lanson, Bruno; Miéhé-Brendlé, Jocelyne; Marichal, Claire; Charlet, Laurent

    2016-02-15

    The formation of a ternary antibiotic-metal-clay complex is hypothesized as the primary adsorption mechanism responsible for the increased adsorption of tetracycline antibiotics on smectites in the presence of divalent metal cations under circumneutral and higher pH conditions. To evaluate this hypothesis, we conducted a spectroscopic investigation of oxytetracycline (OTC) interacting with Na-montmorillonite in the presence and absence of Ca or Mg salts at pH 6 and pH 8. Despite a two-fold increase in OTC adsorbed in the presence of Ca or Mg, both solid-state nuclear magnetic resonance and infrared signatures of the OTC functional groups involved in metal complexation implied that the formation of an inner-sphere ternary complexation was not significant in stabilizing the adsorbate structures. The spectroscopic data further indicated that the positively-charged amino group mediated the OTC adsorption both in the absence and presence of the divalent metal cations. Focusing on the experiments with Mg, X-ray diffraction analysis revealed that the metal-promoted adsorption was coupled with an increased intercalation of OTC within the montmorillonite layers. The resulting interstratified clay layers were characterized by simulating X-ray diffraction of theoretical stacking compositions using molecular dynamics-optimized montmorillonite layers with and without OTC. The simulations uncovered the evolution of segregated interstratification patterns that demonstrated how increased access to smectite interlayers in the presence of the divalent metal cations enhanced adsorption of OTC. Our findings suggest that specific aqueous structures of the clay crystallites in response to the co-presence of Mg and OTC in solution served as precursors to the interlayer trapping of the antibiotic species. Elucidation of these structures is needed for further insights on how aqueous chemistry influences the role of smectite clay minerals in trapping organic molecules in natural and

  10. Investigation of hidden periodic structures on SEM images of opal-like materials using FFT and IFFT.

    PubMed

    Stephant, Nicolas; Rondeau, Benjamin; Gauthier, Jean-Pierre; Cody, Jason A; Fritsch, Emmanuel

    2014-01-01

    We have developed a method to use fast Fourier transformation (FFT) and inverse fast Fourier transformation (IFFT) to investigate hidden periodic structures on SEM images. We focused on samples of natural, play-of-color opals that diffract visible light and hence are periodically structured. Conventional sample preparation by hydrofluoric acid etch was not used; untreated, freshly broken surfaces were examined at low magnification relative to the expected period of the structural features, and, the SEM was adjusted to get a very high number of pixels in the images. These SEM images were treated by software to calculate autocorrelation, FFT, and IFFT. We present how we adjusted SEM acquisition parameters for best results. We first applied our procedure on an SEM image on which the structure was obvious. Then, we applied the same procedure on a sample that must contain a periodic structure because it diffracts visible light, but on which no structure was visible on the SEM image. In both cases, we obtained clearly periodic patterns that allowed measurements of structural parameters. We also investigated how the irregularly broken surface interfered with the periodic structure to produce additional periodicity. We tested the limits of our methodology with the help of simulated images.

  11. Uranium(VI) Diffusion in Sodium-Montmorillonite at Alkaline pH Conditions

    NASA Astrophysics Data System (ADS)

    Tinnacher, R. M.; Davis, J. A.; Tournassat, C.; Birkholzer, J. T.

    2015-12-01

    Diffusive transport of uranium(VI) in montmorillonite clay and bentonite has important implications for uranium(VI) mobility in engineered barrier systems or host rocks in high level radioactive waste repositories, and clay-rich soils and sediments in the environment. The prediction of uranium(VI) adsorption and diffusion in clay-rich media, however, is complicated by (1) the complexity of the mineralogical structure of montmorillonite, in terms of its pore-size distributions and available surface site types, and (2) the complex uranium(VI) solution speciation, which can include cationic, uncharged, and anionic complexes, depending on solution conditions. For instance, a partial or full exclusion of anions from negatively charged clay interlayer spaces could change the effective 'anion-accessible' porosity and decrease the diffusive flux of these solutes under steady state conditions. In contrast, weak cation exchange reactions can result in 'surface diffusion' of adsorbed cations, such as UO2OH+, in addition to diffusion in the liquid phase, resulting in greater diffusive fluxes at steady state. In order to investigate these complex interactions, we performed two, lab-scale uranium(VI) through-diffusion experiments in lightly compacted Na-montmorillonite at slightly different, alkaline pH conditions (average pH values of 8.69 and 8.87). Observed uranium(VI) diffusive fluxes were decreased by approximately an order of magnitude in comparison to a tritium tracer. This indicates a relevance of 'anion exclusion' effects, the full or partial exclusion of anionic U(VI)-carbonato species from clay interlayer spaces. In addition, uranium(VI) sorption reactions were shown to be relevant in the diffusion experiments, even at alkaline pH values of around 8.7 and 8.9, where uranium(VI) sorption is low compared to other pH conditions. Despite the similarity of pH conditions, different degrees of uranium(VI) retardation were determined for the two systems. Additionally, we

  12. Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

    SciTech Connect

    Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh; Giammar, Daniel; Catalano, Jeffrey G.

    2016-02-15

    Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work

  13. Reaction of montmorillonite in alkaline solution at 60 C, 90 C, 120 C and 180 C

    SciTech Connect

    Amaya, Takayuki; Shimojo, Mikio; Fujihara, Hiroshi; Yokoyama, Katsuhiko

    1999-07-01

    The reaction of montmorillonite was investigated. Three kinds of bentonites with different montmorillonite composition were mixed with 0.3M NaOH solution and 0.3M Ca(OH){sub 2} slurry. They were immersed at 60 C, 90 C, 120 C, and 180 C for one month, three months and six months. The concentrations of the soluble ions were measured and the bentonites were analyzed quantitatively after the immersion. 50% of the montmorillonite was reacted within two weeks at greater than 90 C. Montmorillonite reacts less when mixed with Si-minerals. It extensively reacted in 0.3M Ca(OH){sub 2} slurry. These results suggest that the reaction mechanism of the montmorillonite in alkaline solution was dominantly Si dissolution, and would decrease by controlling the concentration of Si ion. The cement/bentonite system under Si saturated conditions is discussed.

  14. Coherent X-ray radiation by relativistic electron in a structure “amorphous layer-vacuum-periodic layered medium”

    NASA Astrophysics Data System (ADS)

    Blazhevich, S. V.; Gladkikh, J. P.; Nemtsev, S. N.; Zagorodnyuk, R. A.; Noskov, A. V.

    2016-07-01

    The dynamic theory of coherent X-ray radiation by relativistic electron crossing a three-layer structure consisting of an amorphous substance layer, a layer of vacuum and a layer with artificial periodic structure has been developed. The process of radiation and propagation of X-ray waves in an artificial periodic structure have been considered based on two-wave approximation of dynamic diffraction theory in Laue scattering geometry.

  15. Radio Induced Fluorescence (RIF) Imaging Of E-region Quasi-periodic Structures

    NASA Astrophysics Data System (ADS)

    Bernhardt, P. A.

    The horizontal structure of sporadic-E layers has been imaged using artificial airglow excited by high power radio waves. In January 1998, the HF facility at Arecibo, Puerto Rico beamed a 80 MW signal upward at 3.175 MHz. The beam reflected in the E- region near 120 km altitude to excite green-line emissions at 557.7 nm. Ground based images showed quasi-periodic structures with periods near 2 and 10 km. These struc- tures been interpreted as being produced by Kelvin-Helmholtz (K-H) instabilities in the neutral atmosphere. The excitation of radio induced fluorescence (RIF) emissions has been studied with both one-dimensional and two-dimensional computer simulations of the conversion of electromagnetic waves into electron plasma waves. The steep gradients on the bottomside of the E-layer provide conditions for efficient mode conversion. The re- sulting Langmuir waves accelerate electrons to energies between 2 and 10 eV. These suprathermal electrons collide with oxygen atoms to produce green-line emissions. The optical glow only occurs in the parts of the E-region where the plamsa is dense enough to reflect the 3.175 MHz radio waves. Results of the E-layer observations using the RIF technique have shown horizontal stuctures that are most likely produced by the K-H instability. A numerical model has been generated to demonstrate the effects of neutral wind shears on the E-region structures. The model includes the effects of both speed-shear and turning shear dy- namics. The results of the numerical model are used to suggest future research using high-power radio wave to study the ion dynamics of the lower thermosphere.

  16. Analysis of bandgap characteristics of two-dimensional periodic structures by using the source-model technique.

    PubMed

    Ludwig, Alon; Leviatan, Yehuda

    2003-08-01

    We introduce a solution based on the source-model technique for periodic structures for the problem of electromagnetic scattering by a two-dimensional photonic bandgap crystal slab illuminated by a transverse-magnetic plane wave. The proposed technique takes advantage of the periodicity of the slab by solving the problem within the unit cell of the periodic structure. The results imply the existence of a frequency bandgap and provide a valuable insight into the relationship between the dimensions of a finite periodic structure and its frequency bandgap characteristics. A comparison shows a discrepancy between the frequency bandgap obtained for a very thick slab and the bandgap obtained by solving the corresponding two-dimensionally infinite periodic structure. The final part of the paper is devoted to explaining in detail this apparent discrepancy.

  17. Acidity of edge surface sites of montmorillonite and kaolinite

    NASA Astrophysics Data System (ADS)

    Liu, Xiandong; Lu, Xiancai; Sprik, Michiel; Cheng, Jun; Meijer, Evert Jan; Wang, Rucheng

    2013-09-01

    Acid-base chemistry of clay minerals is central to their interfacial properties, but up to now a quantitative understanding on the surface acidity is still lacking. In this study, with first principles molecular dynamics (FPMD) based vertical energy gap technique, we calculate the acidity constants of surface groups on (0 1 0)-type edges of montmorillonite and kaolinite, which are representatives of 2:1 and 1:1-type clay minerals, respectively. It shows that tbnd Si-OH and tbnd Al-OH2OH groups of kaolinite have pKas of 6.9 and 5.7 and those of montmorillonite have pKas of 7.0 and 8.3, respectively. For each mineral, the calculated pKas are consistent with the experimental ranges derived from fittings of titration curves, indicating that tbnd Si-OH and tbnd Al-OH2OH groups are the major acidic sites responsible to pH-dependent experimental observations. The effect of Mg substitution in montmorillonite is investigated and it is found that Mg substitution increases the pKas of the neighboring tbnd Si-OH and tbnd Si-OH2 groups by 2-3 pKa units. Furthermore, our calculation shows that the pKa of edge tbnd Mg-(OH2)2 is as high as 13.2, indicating the protonated state dominates under common pH. Together with previous adsorption experiments, our derived acidity constants suggest that tbnd Si-O- and tbnd Al-(OH)2 groups are the most probable edge sites for complexing heavy metal cations.

  18. Structural heterogeneity modulates effective refractory period: a mechanism of focal arrhythmia initiation.

    PubMed

    Bishop, Martin J; Connolly, Adam; Plank, Gernot

    2014-01-01

    Reductions in electrotonic loading around regions of structural and electrophysiological heterogeneity may facilitate capture of focal triggered activity, initiating reentrant arrhythmias. How electrotonic loading, refractoriness and capture of focal ectopics depend upon the intricate nature of physiological structural anatomy, as well as pathological tissue remodelling, however, is not well understood. In this study, we performed computational bidomain simulations with anatomically-detailed models representing the rabbit left ventricle. We used these models to quantify the relationship between local structural anatomy and spatial heterogeneity in action potential (AP) characteristics, electrotonic currents and effective refractory periods (ERPs) under pacing and restitution protocols. Regions surrounding vessel cavities, in addition to tissue surfaces, had significantly lower peak downstream electrotonic currents than well coupled myocardium (72.6 vs 220.4 μA/cm2), with faster maximum AP upstroke velocities (257.3 vs 147.3 mV/ms), although noticeably very similar APDs (167.7 vs 168.4 ms) and AP restitution properties. Despite similarities in APDs, ERPs in regions of low electrotonic load in the vicinity of surfaces, intramural vessel cavities and endocardial structures were up to 40 ms shorter compared to neighbouring well-coupled tissue, leading to regions of sharp ERP gradients. Consequently, focal extra-stimuli timed within this window of ERP heterogeneity between neighbouring regions readily induced uni-directional block, inducing reentry. Most effective induction sites were within channels of low ERPs between large vessels and epicardium. Significant differences in ERP driven by reductions in electrotonic loading due to fine-scale physiological structural heterogeneity provides an important mechanism of capture of focal activity and reentry induction. Application to pathological ventricles, particularly myocardial infarction, will have important implications

  19. Influence of the intercalated cations on the surface energy of montmorillonites: consequences for the morphology and gas barrier properties of polyethylene/montmorillonites nanocomposites.

    PubMed

    Picard, E; Gauthier, H; Gérard, J-F; Espuche, E

    2007-03-15

    Organically modified montmorillonites obtained by cation exchange from the same natural layered silicate were studied. The surface properties of the pristine and a series of organically modified clays were determined by inverse gas chromatography and the water adsorption mechanisms were studied by a gravimetric technique coupled with a microcalorimeter. A significant increase of the specific surface area, a decrease of the water adsorption, and a decrease of the dispersive component of the surface energy were observed when the sodium cations of the natural montmorillonite were exchanged for a quaternary ammonium. Slighter differences in surface properties were observed, on the other hand, between the different types of organically modified montmorillonites. Indeed, similar dispersive components of the surface energy were determined on the organoclays. Nevertheless, the specific surface area increased in the range 48-80 m(2)/g with increasing d-spacing values and the presence of specific groups attached to the quaternary ammonium, such as phenyl rings or hydroxyl groups, led to some specific behaviors, i.e., a more pronounced base character and a higher water adsorption at high activity, respectively. Differences in interlayer cation chain organization, denoted as crystallinity, were also observed as a function of the nature of the chains borne by the quaternary ammonium. In a later step, polyethylene-based nanocomposites were prepared with those organically modified montmorillonites. The clay dispersion and the barrier properties of the nanocomposites were discussed as a function of the montmorillonite characteristics and of the matrix/montmorillonite interactions expected from surface energy characterization.

  20. Spectroscopic study for a chromium-adsorbed montmorillonite

    NASA Astrophysics Data System (ADS)

    Nurtay, Maidina ·; Tuersun, Maierdan ·; Cai, Yuanfeng; Açıkgöz, Muhammed; Wang, Hongtao; Pan, Yuguan; Zhang, Xiaoke; Ma, Xiaomei

    2017-02-01

    Samples of purified montmorillonite with trace amounts of quartz were subjected to different concentrations of chromium sulphate solutions for one week to allow cation exchange. The chromium-bearing montmorillonites were verified and tested using powder X-ray diffractometry (XRD), X-ray fluorescence spectrometry, electron spin resonance (ESR) spectrometry and Fourier transformation infrared (FTIR) spectroscopy to explore the occupation sites of the chromium. The ESR spectra recorded before and after the chromium exchange show clear differences: a strong and broad resonance with two shoulders at the lower magnetic field side was present to start, and its intensity as well as that of the ferric iron resonance, increased with the concentration of added chromium. The signals introduced by the chromium, for example at g = 1.975 and 2.510 etc., suggested that the chromium had several occupational sites. The ESR peak with g = 2.510 in the second derivative spectrum suggested that Cr3+ was weakly bounded to TOT with the form of [Cr(H2O)3]3+ in hexagonal cavities. This was verified by comparing the FTIR spectra of the pure and modified montmorillonite. The main resonance centred at g = 1.975 indicated that the majority of Cr3+ occupied the interlayer region as [Cr(H2O)6]3+. The substitution of Ca2 + by Cr3+ also greatly affected the vibration of the hydrogens associate to water, ranged from 3500 to 2600 cm-1 in FTIR. Furthermore, the presence of two diffraction lines in the XRD results (specifically those with d-values of 1.5171 and 1.2673 nm) and the calculations of the size of the interlayer space suggested the presence of two types of montmorillonite with different hydration cations in the sample exposed to 0.2 M chromium sulphate. The two diffraction lines were assigned to [Cr(H2O)6]3+ and [Cr(H2O)3O3]3+, respectively. This also suggested that the species of hydration cation was constrained by the concentration of the chromium solution.

  1. The growth of carbon nanotubes on montmorillonite and zeolite (clinoptilolite)

    NASA Astrophysics Data System (ADS)

    Kadlečíková, M.; Breza, J.; Jesenák, K.; Pastorková, K.; Luptáková, V.; Kolmačka, M.; Vojačková, A.; Michalka, M.; Vávra, I.; Križanová, Z.

    2008-06-01

    Synthesis of carbon nanotubes described in the present work is based on activation of methane in a hot filament CVD reactor and subsequent creation of nanostructures on a catalyst pre-treated polished surface of silicon. An essential step of the synthesis is the use of natural minerals as catalysts. We have studied the catalyst parameters, the way of its application and the amount of Fe 3+ cations on the surface of aluminosilicates on the quality of the grown nanotube layers. The growth of carbon nanotubes catalyzed by montmorillonite and zeolite (clinoptilolite) was confirmed by scanning electron microscopy and Raman spectroscopy.

  2. Improved detecting sensitivity of long period fiber gratings by polyelectrolyte multilayers: The effect of film structures

    NASA Astrophysics Data System (ADS)

    Li, Qiu-Shun; Zhang, Xu-Lin; He, Hao; Meng, Qingjun; Shi, Jianguo; Wang, Jun-Nan; Dong, Wen-Fei

    2014-11-01

    Novel polyelectrolyte multilayer (PEM) coated long period fiber gratings (LPFGs) are emerging as one of high-performance optical refractive index (RI) sensors. The influence of PEM film structures (i.e film thickness and chemical structures) on the transmission spectra and detecting sensitivity of LPFG sensors had been investigated theoretically and experimentally. The results demonstrated that the central wavelength of the attenuation bands of LPFGs will shift to the low value with increasing PEM film thickness. The optimized film thickness, where the highest variation of the resonant wavelength may take place, is strongly governed by the inner chemical structure of PEM film. For the dense and less-responsive film coated LPFG, its optimized film thickness will decrease when the RI of surrounding medium increases. This behavior is different with the responsive film coated one. In addition, the detecting sensitivity of PEM coated one is improved by two orders of magnitude as compared with the uncoated one. Therefore, these PEM coated LPFGs have great potentials in diverse fields of molecular diagnostic, environmental monitoring, food safety testing and homeland security.

  3. Pulsed second-harmonic generation in nonlinear, one-dimensional, periodic structures

    NASA Astrophysics Data System (ADS)

    Scalora, M.; Bloemer, M. J.; Manka, A. S.; Dowling, J. P.; Bowden, C. M.; Viswanathan, R.; Haus, J. W.

    1997-10-01

    We present a numerical study of second-harmonic (SH) generation in a one-dimensional, generic, photonic band-gap material that is doped with a nonlinear χ(2) medium. We show that a 20-period, 12-μm structure can generate short SH pulses (similar in duration to pump pulses) whose energy and power levels may be 2-3 orders of magnitude larger than the energy and power levels produced by an equivalent length of a phase-matched, bulk medium. This phenomenon comes about as a result of the combination of high electromagnetic mode density of states, low group velocity, and spatial phase locking of the fields near the photonic band edge. The structure is designed so that the pump pulse is tuned near the first-order photonic band edge, and the SH signal is generated near the band edge of the second-order gap. This maximizes the density of available field modes for both the pump and SH field. Our results show that the χ(2) response is effectively enhanced by several orders of magnitude. Therefore, mm- or cm-long, quasi-phase-matched devices could be replaced by these simple layered structures of only a few micrometers in length. This has important applications to high-energy lasers, Raman-type sources, and frequency up- and down-conversion schemes.

  4. ''Inelastic Neutron Scattering and Periodic Density Functional Studies of Hydrogen Bonded Structures''

    SciTech Connect

    Bruce S. Hudson

    2004-10-27

    This project is directed at a fundamental understanding of hydrogen bonding, the primary reversible interaction leading to defined geometries, networks and supramolecular aggregates formed by organic molecules. Hydrogen bonding is still not sufficiently well understood that the geometry of such supramolecular aggregates can be predicted. In the approach taken existing quantum chemical methods capable of treating periodic solids have been applied to hydrogen bonded systems of known structure. The equilibrium geometry for the given space group and packing arrangement were computed and compared to that observed. The second derivatives and normal modes of vibration will then be computed and from this inelastic neutron scattering (INS) spectra were computed using the normal mode eigenvectors to compute spectral intensities. Appropriate inclusion of spectrometer line width and shape was made in the simulation and overtones, combinations and phonon wings were be included. These computed spectra were then compared with experimental results obtained for low-temperature polycrystalline samples at INS spectrometers at several facilities. This procedure validates the computational methodology for describing these systems including both static and dynamic aspects of the material. The resulting description can be used to evaluate the relative free energies of two or more proposed structures and so ultimately to be able to predict which structure will be most stable for a given building block.

  5. Monte Carlo study of the adsorption and aggregation of alkyltrimethylammonium chloride on the montmorillonite-water interface.

    PubMed

    Klebow, Birthe; Meleshyn, Artur

    2012-09-18

    Organically modified clays exhibit adsorption capacities for cations, anions, and nonpolar organic compounds, which make them valuable for various environmental technical applications. To improve the understanding of the adsorption processes, the molecular-scale characterization of the structures of organic aggregates assembled on the external basal surfaces of clay particles is essential. The focus of this Monte Carlo simulation study was on the effects of the surface coverage and the alkyl chain length n on the structures of alkyltrimethylammonium chloride ((C(n)TMA)Cl) aggregates assembled on the montmorillonite-water interface. We found that the amount of adsorbed C(n)TMA(+) ions is independent of the alkyl chain length and increases with the C(n)TMA(+) surface coverage. The C(n)TMA(+) ions predominantly adsorb as inner-sphere complexes; the fraction of outer-sphere adsorbed ions equals only about 10%. The conformational order of the C(n)TMA(+) alkyl chains substantially decreases with decreasing alkyl chain length. In agreement with previous experiments, the amount of C(n)TMA(+) ions that are aggregated at the mineral surface increases with increasing chain length. The maximum value of 0.66 C(n)TMA(+) adsorption complex per unit cell area of the clay surface considerably exceeds the amount of cations required to compensate the negative charge of the montmorillonite surface. Furthermore, in most of the studied systems, fractions of Na(+) surface cations remain adsorbed on montmorillonite. The resulting interfacial positive charge excess is counterbalanced by coadsorbed chloride ions forming ion pairs with both C(n)TMA(+) and Na(+).

  6. Nanocomposite PAAm/methyl cellulose/montmorillonite hydrogel: evidence of synergistic effects for the slow release of fertilizers.

    PubMed

    Bortolin, Adriel; Aouada, Fauze A; Mattoso, Luiz H C; Ribeiro, Caue

    2013-08-07

    In this work, we synthesized a novel series of hydrogels composed of polyacrylamide (PAAm), methylcellulose (MC), and calcic montmorillonite (MMt) appropriate for the controlled release of fertilizers, where the components presented a synergistic effect, giving very high fertilizer loading in their structure. The synthesized hydrogel was characterized in relation to morphological, hydrophilic, spectroscopic, structural, thermal, and kinetic properties. After those characterizations, the application potential was verified through sorption and desorption studies of a nitrogenated fertilizer, urea (CO(NH2)2). The swelling degree results showed that the clay loading considerably reduces the water absorption capability; however, the hydrolysis process favored the urea adsorption in the hydrogel nanocomposites, increasing the load content according to the increase of the clay mass. The FTIR spectra indicated that there was incorporation of the clay with the polymeric matrix of the hydrogel and that incorporation increased the water absorption speed (indicated by the kinetic constant k). By an X-ray diffraction technique, good nanodispersion (intercalation) and exfoliation of the clay platelets in the hydrogel matrix were observed. Furthermore, the presence of the montmorillonite in the hydrogel caused the system to liberate the nutrient in a more controlled manner than that with the neat hydrogel in different pH ranges. In conclusion, excellent results were obtained for the controlled desorption of urea, highlighting the hydrolyzed hydrogels containing 50% calcic montmorillonite. This system presented the best desorption results, releasing larger amounts of nutrient and almost 200 times slower than pure urea, i.e., without hydrogel. The total values of nutrients present in the system show that this material is potentially viable for application in agriculture as a nutrient carrier vehicle.

  7. Periodic dielectric structures for light-trapping in InGaAs/GaAs quantum well solar cells.

    PubMed

    Turner, Sam; Mokkapati, Sudha; Jolley, Greg; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati

    2013-05-06

    We study dielectric diffraction gratings for light-trapping in quantum well solar cells and compare their performance with plasmonic and Lambertian light-trapping structures. The optimum structural parameters are identified for symmetric uni-periodic, symmetric bi-periodic and asymmetric bi-periodic gratings. The enhancement in short-circuit current density from the quantum well region with respect to a reference cell with no diffraction grating is calculated. The ratio of this enhancement to the maximum achievable enhancement (i.e. no transmission losses) is 33%, 75% and 74%, respectively for these structures. The optimum asymmetric and symmetric bi-periodic structures perform closest to Lambertian light-trapping, while all three optimum grating structures outperform optimum plasmonic light-trapping. We show that the short-circuit current density from the quantum well region is further enhanced by incorporating a rear reflector.

  8. Stochasticity, periodicity and localized light structures in partially mode-locked fibre lasers

    PubMed Central

    Churkin, D. V.; Sugavanam, S.; Tarasov, N.; Khorev, S.; Smirnov, S. V.; Kobtsev, S. M.; Turitsyn, S. K.

    2015-01-01

    Physical systems with co-existence and interplay of processes featuring distinct spatio-temporal scales are found in various research areas ranging from studies of brain activity to astrophysics. The complexity of such systems makes their theoretical and experimental analysis technically and conceptually challenging. Here, we discovered that while radiation of partially mode-locked fibre lasers is stochastic and intermittent on a short time scale, it exhibits non-trivial periodicity and long-scale correlations over slow evolution from one round-trip to another. A new technique for evolution mapping of intensity autocorrelation function has enabled us to reveal a variety of localized spatio-temporal structures and to experimentally study their symbiotic co-existence with stochastic radiation. Real-time characterization of dynamical spatio-temporal regimes of laser operation is set to bring new insights into rich underlying nonlinear physics of practical active- and passive-cavity photonic systems. PMID:25947951

  9. Rectification of Lamb wave propagation in thin plates with piezo-dielectric periodic structures

    NASA Astrophysics Data System (ADS)

    Iwasaki, Yuhei; Tsuruta, Kenji; Ishikawa, Atsushi

    2016-07-01

    Based on a heterostructured plate consisting of piezoelectric-ceramic/epoxy-resin composites with different periodicities, we design a novel acoustic diode for the symmetrical/asymmetrical (S/A) mode of Lamb wave at audible ranges. The acoustic diode is constructed with two parts, i.e., the mode conversion part and the mode selection part, and the mode conversion mechanism at the interface is applied to the mode hybridization from S to S+A and for the mode conversion from A to S. The phonon band structures for each part are calculated and optimized so that the mode selection is realized for a specific mode at the junction. Finite-element simulations prove that the proposed acoustic diode achieves efficient rectification at audio frequency ranges for both S and A mode incidences of the Lamb wave.

  10. Laser-induced periodic surface structure in nickel-fullerene composites

    NASA Astrophysics Data System (ADS)

    Vacik, J.; Lavrentiev, V.; Havranek, V.; Horak, P.; Hnatowicz, V.; Fajgar, R.

    2016-02-01

    The phase separation of a thin film of the binary composite of Ni and C60 has been studied using laser illumination of the sample through an array of pinholes (with a diameter of 10-µm and 60-µm × 80-µm spacing). The mesh with pinholes enabled splitting of the probing beam into an array of close-spaced laser micro-beams. The simultaneous illumination of the composite, with a set of micro-beams, resulted in a fast phase separation of the hybrid matter and an occurrence of unusual laser-induced periodic surface structures - a net of complex Ni and C allotropes (C60 and amorphous C) concentric rings and a fine array of the C60 - based islands, regularly distributed over the Ni + C60 thin film matrix. The results confirmed the high proclivity of the hybrid Ni + C60 composites to a correlated separation of the Ni and C-allotrope phases.

  11. AM CVn Stars: Structure and Evolution of Ultra-Short Period Interacting Binaries

    NASA Technical Reports Server (NTRS)

    Froning, Cynthia

    2005-01-01

    This is the final report of a FUSE program to study the physics of accretion and outflows in ultra-compact, helium dominated, disk-accreting binaries. With FUSE, we observed the AM CVn binary V803 Cen, which is one of only two AM CVn systems observed by FUSE to date. V803 Cen is a short-period interacting binary in which a hydrogen-deficient white dwarf transfers mass to another white dwarf via a hot, steady-state accretion disk. Unlike other cataclysmic variables (CVs), AM CVn stars have undergone double common envelope evolution (one for each white dwarf in the binary) and so probe an alternate route of evolution in binary stars. Our goals in this project were to investigate how the structure of the accretion disk and the link between the disk and wind outflows are affected by the absence of hydrogen in the system and by the compact size of the binary and the accretion disk.

  12. Endoscopic system for automated high dynamic range inspection of moving periodic structures

    NASA Astrophysics Data System (ADS)

    Hahlweg, Cornelius; Rothe, Hendrik

    2015-09-01

    In the current paper an advanced endoscopic system for high resolution and high dynamic range inspection of periodic structures in rotating machines is presented. We address the system architecture, short time illumination, special optical problems, such as excluding the specular reflex, image processing, forward velocity prediction and metrological image processing. There are several special requirements to be met, such as the thermal stability above 100°C, robustness of the image field, illumination in view direction and the separation of metallic surface diffuse scatter. To find a compromise between image resolution and frame rate, an external sensor system was applied for synchronization with the moving target. The system originally was intended for inspection of thermal engines, but turned out to be of a more general use. Beside the theoretical part and dimensioning issues, practical examples and measurement results are included.

  13. A comprehensive study for the plasmonic thin-film solar cell with periodic structure.

    PubMed

    Sha, Wei E I; Choy, Wallace C H; Chew, Weng Cho

    2010-03-15

    A comprehensive study of the plasmonic thin-film solar cell with the periodic strip structure is presented in this paper. The finite-difference frequency-domain method is employed to discretize the inhomogeneous wave function for modeling the solar cell. In particular, the hybrid absorbing boundary condition and the one-sided difference scheme are adopted. The parameter extraction methods for the zeroth-order reflectance and the absorbed power density are also discussed, which is important for testing and optimizing the solar cell design. For the numerical results, the physics of the absorption peaks of the amorphous silicon thin-film solar cell are explained by electromagnetic theory; these peaks correspond to the waveguide mode, Floquet mode, surface plasmon resonance, and the constructively interference between adjacent metal strips. The work is therefore important for the theoretical study and optimized design of the plasmonic thin-film solar cell.

  14. Dynamics of periodic mechanical structures containing bistable elastic elements: From elastic to solitary wave propagation

    NASA Astrophysics Data System (ADS)

    Nadkarni, Neel; Daraio, Chiara; Kochmann, Dennis M.

    2014-08-01

    We investigate the nonlinear dynamics of a periodic chain of bistable elements consisting of masses connected by elastic springs whose constraint arrangement gives rise to a large-deformation snap-through instability. We show that the resulting negative-stiffness effect produces three different regimes of (linear and nonlinear) wave propagation in the periodic medium, depending on the wave amplitude. At small amplitudes, linear elastic waves experience dispersion that is controllable by the geometry and by the level of precompression. At moderate to large amplitudes, solitary waves arise in the weakly and strongly nonlinear regime. For each case, we present closed-form analytical solutions and we confirm our theoretical findings by specific numerical examples. The precompression reveals a class of wave propagation for a partially positive and negative potential. The presented results highlight opportunities in the design of mechanical metamaterials based on negative-stiffness elements, which go beyond current concepts primarily based on linear elastic wave propagation. Our findings shed light on the rich effective dynamics achievable by nonlinear small-scale instabilities in solids and structures.

  15. Influence of substrate microcrystallinity on the orientation of laser-induced periodic surface structures

    SciTech Connect

    Nürnberger, P.; Reinhardt, H.; Kim, H-C.; Yang, F.; Peppler, K.; Janek, J.; Hampp, N.

    2015-10-07

    The research in this paper deals with the angular dependence of the formation of laser-induced periodic surface structures (LIPSS) by linearly polarized nanosecond laser pulses on polycrystalline austenitic stainless steel. Incident angles ranging from 45° to 70° lead to the generation of superimposed merely perpendicular oriented LIPSS on steel as well as on monocrystalline (100) silicon which was used as a reference material. Additional extraordinary orientations of superimposing LIPSS along with significantly different periodicities are found on polycrystalline steel but not on (100) silicon. Electron backscatter diffraction measurements indicate that the expansion of these LIPSS is limited to the grain size and affected by the crystal orientation of the individual grains. Atomic force microscopy imaging shows that LIPSS fringe heights are in good agreement with the theoretically predicted penetration depths of surface plasmon polaritons into stainless steel. These results indicate that optical anisotropies must be taken into account to fully describe the theory of light-matter interaction leading to LIPSS formation.

  16. Liquidity crisis detection: An application of log-periodic power law structures to default prediction

    NASA Astrophysics Data System (ADS)

    Wosnitza, Jan Henrik; Denz, Cornelia

    2013-09-01

    We employ the log-periodic power law (LPPL) to analyze the late-2000 financial crisis from the perspective of critical phenomena. The main purpose of this study is to examine whether LPPL structures in the development of credit default swap (CDS) spreads can be used for default classification. Based on the different triggers of Bear Stearns’ near bankruptcy during the late-2000 financial crisis and Ford’s insolvency in 2009, this study provides a quantitative description of the mechanism behind bank runs. We apply the Johansen-Ledoit-Sornette (JLS) positive feedback model to explain the rise of financial institutions’ CDS spreads during the global financial crisis 2007-2009. This investigation is based on CDS spreads of 40 major banks over the period from June 2007 to April 2009 which includes a significant CDS spread increase. The qualitative data analysis indicates that the CDS spread variations have followed LPPL patterns during the global financial crisis. Furthermore, the univariate classification performances of seven LPPL parameters as default indicators are measured by Mann-Whitney U tests. The present study supports the hypothesis that discrete scale-invariance governs the dynamics of financial markets and suggests the application of new and fast updateable default indicators to capture the buildup of long-range correlations between creditors.

  17. Model independent x-ray standing wave analysis of periodic multilayer structures

    SciTech Connect

    Yakunin, S. N.; Pashaev, E. M.; Subbotin, I. A.; Makhotkin, I. A.; Kruijs, R. W. E. van de; Zoethout, E.; Chuev, M. A.; Louis, E.; Seregin, S. Yu.; Novikov, D. V.; Bijkerk, F.; Kovalchuk, M. V.

    2014-04-07

    We present a model independent approach for the analysis of X-ray fluorescence yield modulated by an X-ray standing wave (XSW), that allow a fast reconstruction of the atomic distribution function inside a sample without fitting procedure. The approach is based on the direct regularized solution of the system of linear equations that characterizes the fluorescence yield. The suggested technique was optimized for, but not limited to, the analysis of periodic layered structures where the XSW is formed under Bragg conditions. The developed approach was applied to the reconstruction of the atomic distribution function for LaN/BN multilayers with 50 periods of 43 Å thick layers. The object is especially difficult to analyze with traditional methods, as the estimated thickness of the interface region between the constituent materials is comparable to the individual layer thicknesses. However, using the suggested technique, it was possible to reconstruct width of the La atomic distribution showing that the La atoms stay localized within the LaN layers and interfaces and do not diffuse into the BN layer. The analysis of the reconstructed profiles showed that the positions of the center of the atomic distribution function can be estimated with an accuracy of 1 Å.

  18. Magneto-optical response of a periodic metallic nano-structure

    NASA Astrophysics Data System (ADS)

    Strelniker, Yakov M.; Bergman, David J.

    2015-08-01

    When an applied magnetic field has an arbitrary direction with respect to the lattice axes of a periodically nano-structured metal-dielectric metamaterial, the macroscopic or bulk effective permittivity tensor becomes anisotropic and all its components can be nonzero. This effect can be especially strong and significant in the vicinity of surface plasmon and cyclotron resonances (the frequencies of which are also sensitive to the value and direction of the applied external magnetic field). A similar effect for the case of dc effective conductivity is already verified experimentally (since magneto-conductivity tensor can be measured directly). However, this prediction for the permittivity has not yet been tested experimentally (since the permittivity tensor cannot be measured directly). What can be measured directly is the Voigt rotation, for which general exact analytical expressions were not published previously. In this work we have studied analytically and numerically the rotation and ellipticity of polarization of the light propagating through a metamaterial film with periodic nanostructure for arbitrary direction of the applied static magnetic field, including both Voigt and Faraday configurations. In the Voigt configuration we found a strong dependence of the above mentioned effects on the direction of the applied magnetic field.

  19. An Infrared Spectroscopy Study Of Pb(II) And Siderophore Sorption To Montmorillonite

    NASA Astrophysics Data System (ADS)

    Maurice, P. A.; Hunter, E. L.; Quicksall, A. N.; Haack, E.; Johnston, C. T.

    2010-12-01

    Aerobic microorganisms exude low molecular weight organic ligands known as siderophores in order to acquire nutrient Fe. Because siderophores can also bind other metals such as Pb, Zn, and Cd, they may affect metal sorption, fate, and transport. This study combined batch sorption experiments, thermodynamic modeling, X-ray diffraction (XRD), and spectroscopic analysis, to investigate Pb(II) and desferrioxamine B (DFOB) sorption to montmorillonite, alone and in combination, at pH 3-9, ~22 C, and in 0.1 M NaCl. Samples at pH 3, 5.5, and 7.5 were analyzed by XRD and Fourier-Transform Infrared Spectroscopy (FTIR) and samples at pH5.5 were analyzed by in-situ Attenuated Total Reflection Infrared Spectroscopy (ATR-FTIR). DFOB does not bind Pb substantially at pH 3, and sorption results showed that the ligand only minimally affects Pb sorption at this pH. However, combination of batch sorption experiments with XRD, FTIR, and ATR-FTIR analysis suggested that Pb(II)/DFOB (co)absorption in the interlayer is likely an important sorption mechanism at pH 5.5 and 7.5 under both air-dried and aqueous conditions. The precise structure of the sorption complex(es) could not be determined by these methods. Some adsorption of Pb(II)/DFOB to the external clay surface is also possible. In the absence of DFOB, a Pb-carbonate complex or precipitate (perhaps hydrocerrusite) was detected by FTIR. Overall, results showed that a microbial siderophore may affect Pb sorption to montmorillonite, that (co)absorption in the interlayer region can be important, and that sorption effects can vary substantially depending upon solution conditions.

  20. Surface-mounted periodic field eddy current sensors for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Goldfine, Neil J.; Zilberstein, Vladimir A.; Schlicker, Darrell E.; Sheiretov, Yanko; Walrath, Karen; Washabaugh, Andrew P.; Van Otterloo, Douglas

    2001-07-01

    Surface mountable eddy current sensors are a revolutionary new concept in nondestructive inspection. These eddy current sensors can be mounted, like a strain gage, at critical locations for detection of crack initiation and monitoring of crack growth. This can be accomplished on a fatigue test article, as well as on in-service aircraft or other structures (patents pending). The mountable periodic field eddy current sensors, described in this paper, can be used as a replacement for standard eddy-current sensors without introducing new requirements. This is not the case with other proposed health monitoring sensors. For critical structures, substantially reduced inspection costs and life extension is possible with permanently mounted eddy current sensors. This is particularly true for difficult-to-access locations that require surface preparation (e.g., sealant or insulation removal) and disassembly when conventional eddy current testing is performed. By enabling eddy current testing in areas currently not accessible to conventional inspection, such as locations deep in an aircraft structure, damage tolerance can be achieved with low cost inspections. Embedded versions might even be mounted between layers, such as in a lapjoint. Surface mountable eddy current sensors are suitable for on-line monitoring and in-service inspections. This paper provides an introduction to surface mountable eddy current sensors, presents specific results from fatigue coupon tests and describes upcoming full-scale aircraft fatigue tests. Also, ongoing efforts to implement this technology on commercial and military aircraft are described. This research has been funded in part by the U.S. Navy, U.S. Air Force, JENTEK Sensors, Inc., and Lockheed Martin Aeronautics Company. The goal of this paper is to provide a basic understanding of surface mounted eddy current sensor capabilities and potential, and to promote their broader use in fatigue testing, aircraft health monitoring as well as for

  1. Fabrication and structural properties of AlN submicron periodic lateral polar structures and waveguides for UV-C applications

    NASA Astrophysics Data System (ADS)

    Alden, D.; Guo, W.; Kirste, R.; Kaess, F.; Bryan, I.; Troha, T.; Bagal, A.; Reddy, P.; Hernandez-Balderrama, Luis H.; Franke, A.; Mita, S.; Chang, C.-H.; Hoffmann, A.; Zgonik, M.; Collazo, R.; Sitar, Z.

    2016-06-01

    Periodically poled AlN thin films with submicron domain widths were fabricated for nonlinear applications in the UV-VIS region. A procedure utilizing metalorganic chemical vapor deposition growth of AlN in combination with laser interference lithography was developed for making a nanoscale lateral polarity structure (LPS) with domain size down to 600 nm. The Al-polar and N-polar domains were identified by wet etching the periodic LPS in a potassium hydroxide solution and subsequent scanning electron microscopy (SEM) characterization. Fully coalesced and well-defined vertical interfaces between the adjacent domains were established by cross-sectional SEM. AlN LPSs were mechanically polished and surface roughness with a root mean square value of ˜10 nm over a 90 μm × 90 μm area was achieved. 3.8 μm wide and 650 nm thick AlN LPS waveguides were fabricated. The achieved domain sizes, surface roughness, and waveguides are suitable for second harmonic generation in the UVC spectrum.

  2. Comparison between periodic and stochastic parabolic light trapping structures for thin-film microcrystalline Silicon solar cells.

    PubMed

    Peters, M; Battaglia, C; Forberich, K; Bläsi, B; Sahraei, N; Aberle, A G

    2012-12-31

    Light trapping is of very high importance for silicon photovoltaics (PV) and especially for thin-film silicon solar cells. In this paper we investigate and compare theoretically the light trapping properties of periodic and stochastic structures having similar geometrical features. The theoretical investigations are based on the actual surface geometry of a scattering structure, characterized by an atomic force microscope. This structure is used for light trapping in thin-film microcrystalline silicon solar cells. Very good agreement is found in a first comparison between simulation and experimental results. The geometrical parameters of the stochastic structure are varied and it is found that the light trapping mainly depends on the aspect ratio (length/height). Furthermore, the maximum possible light trapping with this kind of stochastic structure geometry is investigated. In a second step, the stochastic structure is analysed and typical geometrical features are extracted, which are then arranged in a periodic structure. Investigating the light trapping properties of the periodic structure, we find that it performs very similar to the stochastic structure, in agreement with reports in literature. From the obtained results we conclude that a potential advantage of periodic structures for PV applications will very likely not be found in the absorption enhancement in the solar cell material. However, uniformity and higher definition in production of these structures can lead to potential improvements concerning electrical characteristics and parasitic absorption, e.g. in a back reflector.

  3. A period of structural plasticity at the axon initial segment in developing visual cortex

    PubMed Central

    Gutzmann, Annika; Ergül, Nursah; Grossmann, Rebecca; Schultz, Christian; Wahle, Petra; Engelhardt, Maren

    2014-01-01

    Cortical networks are shaped by sensory experience and are most susceptible to modifications during critical periods characterized by enhanced plasticity at the structural and functional level. A system particularly well-studied in this context is the mammalian visual system. Plasticity has been documented for the somatodendritic compartment of neurons in detail. A neuronal microdomain not yet studied in this context is the axon initial segment (AIS) located at the proximal axon segment. It is a specific electrogenic axonal domain and the site of action potential (AP) generation. Recent studies showed that structure and function of the AIS can be dynamically regulated. Here we hypothesize that the AIS shows a dynamic regulation during maturation of the visual cortex. We therefore analyzed AIS length development from embryonic day (E) 12.5 to adulthood in mice. A tri-phasic time course of AIS length remodeling during development was observed. AIS first appeared at E14.5 and increased in length throughout the postnatal period to a peak between postnatal day (P) 10 to P15 (eyes open P13–14). Then, AIS length was reduced significantly around the beginning of the critical period for ocular dominance plasticity (CP, P21). Shortest AIS were observed at the peak of the CP (P28), followed by a moderate elongation toward the end of the CP (P35). To test if the dynamic maturation of the AIS is influenced by eye opening (onset of activity), animals were deprived of visual input before and during the CP. Deprivation for 1 week prior to eye opening did not affect AIS length development. However, deprivation from P0 to 28 and P14 to 28 resulted in AIS length distribution similar to the peak at P15. In other words, deprivation from birth prevents the transient shortening of the AIS and maintains an immature AIS length. These results are the first to suggest a dynamic maturation of the AIS in cortical neurons and point to novel mechanisms in the development of neuronal

  4. A new method for the characterization of micro-/nano-periodic structures based on microscopic Moiré fringes.

    PubMed

    Wu, Dan; Xie, Huimin; Tang, Minjin; Hu, Zhenxing

    2014-01-01

    Linewidth and opening ratio (ratio of linewidth to period) are important parameters in characterizing micro-/nano-periodic and quasi-periodic structures. Periodic structures are conventionally characterized by the direct observation of specimens under a microscope. However, the field of view is relatively small, and only certain details can be acquired under a microscope. Moreover, the non-uniformity of the linewidth in quasi-periodic structures cannot be detected. This paper proposes a new characterization method for determining the linewidth and opening ratio of periodic structures based on Moiré fringe analysis. This method has the advantage of full-field characterization of the linewidth of micro-/nano-structures over a larger area than that afforded by direct observation. To validate the method, the linewidth of scanning electron microscope (SEM) scan lines was first calibrated with a standard grating. Next, a microperiodic structure with known geometry was characterized using this calibrated SEM system. The results indicate that the proposed method is simple and effective, indicating a potential approach for the characterization of gratings over large areas. This technique can be extended to various high-power scanning microscopes to characterize micro-/nano-structures.

  5. Microstructural investigation of MX-80 bentonite and Na/Ca-montmorillonite using basal spacing determination

    NASA Astrophysics Data System (ADS)

    Holmboe, M.; Wold, S.

    2010-12-01

    Knowledge about the microstructure of saturated compacted bentonite is of fundamental importance in order to describe and predict diffusive transport through the bentonite barrier in a deep geological repository. If the mineral composition is well characterized, microstructural models of compacted bentonite on the nanoscale can be based on accurate information of the basal spacings and corresponding interlayer distances within the montmorillonite particles. From the average basal spacing, the interlayer and the so-called interparticle or free porosity can be calculated [1]. The basal spacings of the montmorillonite particles can be measured by neutron and X-ray small-angle scattering or diffraction. However, due to microstructural heterogeneity and interstratification of different hydration states, profile fitting through mixed layered modeling is necessary although challenging [2,3]. In this study, we have used low-angle XRD in reflection mode together with one-dimensional analysis of mixed layered clays [2] in order to compare both the relative layer distribution and average basal spacing of MX-80 bentonite and Na/Ca-montmorillonite samples. Two different methods for water saturation commonly used in the literature were compared, saturation by constant relative humidity (adsorption and desorption) and saturation under constant volume conditions, forming compacted clay with dry densities of 0.5-1.8 g/cm3. No significant difference in basal spacings was observed between highly compacted (< 4 H2O layers) homoionic montmorillonite and MX-80 bentonite samples saturated under volume constricted conditions, if the accessory minerals and lower smectite content was accounted for. This was however not the case for the samples saturated at constant RH%, which indicates mixing of the exchangeable cations in the interlayers. Interestingly, even if the total water content was the same water uptake restricted by water activity did not always result in the same magnitude of

  6. Molecular simulation of preferential adsorption of CO2 over CH4 in Na-montmorillonite clay material

    NASA Astrophysics Data System (ADS)

    Yang, Nannan; Liu, Shuyan; Yang, Xiaoning

    2015-11-01

    Grand canonical Monte Carlo simulations have been conducted to study the adsorption of carbon dioxide and methane, as well as their binary mixtures on Na-montmorillonite clay material. It was found that the adsorption behavior near the clay structure for the two species is distinctively different. The Na-montmorillonite clay shows obviously high adsorption capacity for CO2, as compared with CH4. The adsorption behavior and mechanism have been characterized by the interlayer interfacial structures and isosteric heats of adsorption. Meanwhile, the mixture adsorption demonstrates that CO2 molecules with enhanced adsorption strength are able to competitively replace CH4 molecules within the clay structure. The high separation selectivity of CO2 over CH4 implies the possibility of separating CO2 from natural gas mixtures using the clay minerals. The interlayer sodium cations and negatively charged clay surface can provide enhanced interaction with CO2 molecules that have high quadrupole moment, which is responsible for the higher adsorption loading of CO2.

  7. Sodium montmorillonite silylation: unexpected effect of the aminosilane chain length.

    PubMed

    Piscitelli, Filomena; Posocco, Paola; Toth, Radovan; Fermeglia, Maurizio; Pricl, Sabrina; Mensitieri, Giuseppe; Lavorgna, Marino

    2010-11-01

    In this work, the silylation of sodium montmorillonite (Na-MMT) was performed in glycerol using 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and 3-[2-(2-aminoethylamino)ethylamino]-propyl-trimethoxysilane. The effects on the d-spacing of sodium montmorillonite (Na-MMT) upon reaction with three aminosilanes of different chain length were studied in details by combining experimental and computational techniques. Infrared spectroscopy was used to monitor the grafting process, while the degree of grafting was calculated using thermogravimetric analysis. X-ray diffraction experiments were carried out to evaluate the shift of the (0 0 1) basal spacing. It was found that the degree of silylation of Na-MMT increases with increasing the length of the aminosilane organic moieties, the overall aminosilane concentration, and temperature. The same beneficial effects were observed on the silicate d-spacing, as its value increases with increasing silane concentration and reaction temperature. Remarkably, however, increasing the length of the organic chains in the silane modifiers resulted in decreasing values of the Na-MMT interlayer distance. A rationale for this behavior is proposed on the basis of atomistic molecular dynamics simulation evidences.

  8. Heterogeneous freezing of water droplets containing kaolinite and montmorillonite particles

    NASA Astrophysics Data System (ADS)

    Murray, Benjamin J.; Broadley, Sarah; Wilson, Theodore; Bull, Sophia; Wills, Rebecca

    2010-05-01

    Clouds composed of both ice particles and supercooled liquid water droplets, known as mixed phase clouds, exist at temperatures above ~236 K. These clouds, which strongly impact climate, are very sensitive to the presence of particles that can catalyse ice particle formation. In this paper we describe experiments to determine at which temperatures water droplets containing clay mineral particles froze. Water droplets containing a known amount of clay mineral were supported on a hydrophobic surface and the temperatures at which individual droplets froze, as they were cooled down, was determined by optical microscopy. The hydrophobic substrate does not significantly catalyse ice formation in droplets and pure water droplets freeze around 236 K. Droplets containing kaolinite and montmorillonite nucleate ice at warmer temperatures. The mean nucleation temperature increases from close to or at the homogeneous nucleation limit (236 K) to 240.8 ± 0.6 K as the kaolinite concentration is increased from 0.005 wt% to 1 wt%. In contrast, ice always nucleates at 245.8 ± 0.6 K when water droplets are contaminated with montmorillonite independent of mineral concentration. These results highlight the importance of understanding the ice nucleating properties of individual minerals rather than complex mixtures of minerals found in natural dusts and so-called test dusts. In addition we parameterise the results in a form suitable for modelling studies and also derive contact angles for kaolinite.

  9. Sorption of perfluorooctane sulfonate on organo-montmorillonites.

    PubMed

    Zhou, Qin; Deng, Shubo; Yu, Qiang; Zhang, Qiaoying; Yu, Gang; Huang, Jun; He, Hongping

    2010-02-01

    Perfluorinated compound as one of the emerging pollutants has caused great attention in recent years. In this study, the organo-montmorillonites (organo-Mts) with different amounts and arrangements of hexadecyltrimethylammonium bromide (HDTMAB) were prepared as effective sorbents for PFOS removal from water. Batch sorption experiments including sorption kinetics, sorption isotherm as well as effect of solution pH were studied. The Elovich and pseudo-second-order models were selected to fit the kinetic data and the latter described the sorption kinetic better. Sorption isotherms showed that the sorption amount of PFOS increased with increasing amount of HDTMAB loaded in the montmorillonites, indicating that hydrophobic interaction played an important role in the sorption process. Comparative sorption of other perfluorinated compounds (PFCs) with different length of C-F chains and different functional groups further verified that hydrophobic interaction was the main force for the sorption of PFCs on the organo-Mts. X-ray diffraction (XRD) analysis demonstrated the significant decrease of interlayer distance after PFOS sorption, suggesting that the HDTMAB molecules were rearranged in the interlayer of organo-Mts. The PFOS molecules first diffused into the organo-Mts via hydrophobic interaction, and then the rearrangement occurred through electrostatic interaction between the two surfactants, resulting in the microstructure change within the organo-Mts.

  10. Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot

    NASA Astrophysics Data System (ADS)

    Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

    2015-01-01

    In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

  11. Terahertz surface plasmon polaritons on a semiconductor surface structured with periodic V-grooves.

    PubMed

    Li, Shanshan; Jadidi, Mohammad M; Murphy, Thomas E; Kumar, Gagan

    2013-03-25

    We demonstrate propagation of terahertz waves confined to a semiconductor surface that is periodically corrugated with V-shaped grooves. A one-dimensional array of V-grooves is fabricated on a highly-doped silicon surface, using anisotropic wet-etching of crystalline silicon, thereby forming a plasmonic waveguide. Terahertz time domain spectroscopy is used to characterize the propagation of waves near the corrugated surface. We observe that the grating structure creates resonant modes that are confined near the surface. The degree of confinement and frequency of the resonant mode is found to be related to the pitch and depth of the V-grooves. The surface modes are confirmed through both numerical simulations and experimental measurements. Not only does the V-groove geometry represent a new and largely unexplored structure for supporting surface waves, but it also enables the practical fabrication of terahertz waveguides directly on semiconductor surfaces, without relying on reactive-ion etching or electroplating of sub-millimeter metallic surfaces.

  12. Controlled structuring of binary hard-disk mixtures via a periodic, external potential.

    PubMed

    Franzrahe, K; Nielaba, P

    2009-05-01

    Ordering phenomena on surfaces or in monolayers can be successfully studied by model systems as binary hard-disk mixtures, the influence of a substrate being modeled by an external potential. For the field-free case the thermodynamic stability of space-filling lattice structures for binary hard-disk mixtures is studied by Monte Carlo computer simulations. As these structures prove to be thermodynamically stable only in high pressure environments, the phase behavior of an equimolar binary mixture with a diameter ratio of sigma_{B}/sigma_{A}=0.414 exposed to an external, one-dimensional, periodic potential is analyzed in detail. The underlying ordering mechanisms and the resulting order differ considerably, depending on which components of the mixture interact with the external potential. The simulations show that slight deviations in the concentration of large particles x_{A} or the diameter ratio sigma_{B}/sigma_{A} have no impact on the occurrence of the various field-induced phenomena as long as the mixture stays in the relevant regime of the packing fraction eta . Furthermore the importance of the commensurability of the external potential to the S1(AB) square lattice for the occurrence of the induced ordering is discussed.

  13. The structure of the distanct geomagnetic tail during long periods of northward IMF

    NASA Technical Reports Server (NTRS)

    Raeder, J.; Walker, R. J.; Ashour-Abdalla, M.

    1995-01-01

    We have used a newly developed, parallelized, global MHD magnetosphere - ionosphere simulation model with a 400 R(sub E) long tail to study the evolution, structure, and dynamics of the distant magnetotail during extended periods of northward interplanetary magnetic field (IMF). We find that the tail evolves to a nearly time stationary structure about one solar wind transit time after the IMF turns northward. Four regions of different magnetic topology can be distinguished which extend at least to the end of the simulation box at 400 R(sub E). Besides lobe field lines and open solar wind field lines tailward of an X-line, there is a broad boundary layer of closed field lines which we call the tail flank boundary layer (TFBL). Just inside the TFBL there is a region of closed field loops. Besides the X-line we find two O-lines which are enclosed by the closed field loops and are roughly aligned with the tail axis. Together they form a U shaped separator between the northward and the southward plasma sheet fields.

  14. Forced snaking: Localized structures in the real Ginzburg-Landau equation with spatially periodic parametric forcing

    NASA Astrophysics Data System (ADS)

    Ponedel, Benjamin C.; Knobloch, Edgar

    2016-11-01

    We study spatial localization in the real subcritical Ginzburg-Landau equation ut = m0u + Q(x)u + uxx + d|u|2u -|u|4u with spatially periodic forcing Q(x). When d>0 and Q ≡ 0 this equation exhibits bistability between the trivial state u = 0 and a homogeneous nontrivial state u = u0 with stationary localized structures which accumulate at the Maxwell point m0 = -3d2/16. When spatial forcing is included its wavelength is imprinted on u0 creating conditions favorable to front pinning and hence spatial localization. We use numerical continuation to show that under appropriate conditions such forcing generates a sequence of localized states organized within a snakes-and-ladders structure centered on the Maxwell point, and refer to this phenomenon as forced snaking. We determine the stability properties of these states and show that longer lengthscale forcing leads to stationary trains consisting of a finite number of strongly localized, weakly interacting pulses exhibiting foliated snaking.

  15. Enhanced third harmonic generation using the surface states of light in periodic photonic structures

    NASA Astrophysics Data System (ADS)

    Zaytsev, Kirill I.; Gorelik, Vladimir S.; Katyba, Gleb M.; Yurchenko, Stanislav O.

    2014-10-01

    Third harmonic generation enhancement in periodic photonic structures was experimentally observed and theoretically interpreted. Nonlinear optical effects in opal globular photonic crystals (PC) have been studied under the femtosecond laser pumping. Strong dependence of the third harmonic generation efficiency on the ratio between the central pumping wavelength and the spectral location of the PC band gaps was found. Numerical simulations based on the finite difference time-domain technique for the solution of the Maxwell's equations were applied for investigations of the observed phenomenon origin. The simulation results have shown that the origin of the efficient nonlinear conversion is related with the surface state of electromagnetic field in PC. Interacting with the PC surface the light wavefront distorts coherently, and the effect of structure light focusing appears. Coherent wavefront distortion leads to the strong optical field localization, hence the light intensity within the certain PC regions increases. In case of the band gap pumping dramatic light redistribution appears; very sharp peaks of light intensity emerge in the region of the quartz globules, which leads to the high-efficient PC pumping.

  16. Plutonium(IV) sorption to montmorillonite in the presence of organic matter.

    PubMed

    Boggs, Mark A; Dai, Zurong; Kersting, Annie B; Zavarin, Mavrik

    2015-03-01

    The effect of altering the order of addition in a ternary system of plutonium(IV), organic matter (fulvic acid, humic acid and desferrioxamine B), and montmorillonite was investigated. A decrease in Pu(IV) sorption to montmorillonite in the presence of fulvic and humic acid relative to the binary Pu-montmorillonite system, is attributed to strong organic aqueous complex formation with aqueous Pu(IV). No dependence on the order of addition was observed. In contrast, in the system where Pu(IV) was equilibrated with desferrioxamine B (DFOB) prior to addition of montmorillonite, an increase in Pu(IV) sorption was observed relative to the binary system. When DFOB was equilibrated with montmorillonite prior to addition of Pu(IV), Pu(IV) sorption was equivalent to the binary system. X-ray diffraction and transmission electron microscopy revealed that DFOB accumulated in the interlayer of montmorillonite. The order of DFOB addition plays an important role in the observed sorption/desorption behavior of Pu. The irreversible nature of DFOB accumulation in the montmorillonite interlayer leads to an apparent dependence of Pu sorption on the order of addition in the ternary system. This work demonstrates that the order of addition will be relevant in ternary systems in which at least one component exhibits irreversible sorption behavior.

  17. Montmorillonite enhanced ciprofloxacin transport in saturated porous media with sorbed ciprofloxacin showing antibiotic activity

    NASA Astrophysics Data System (ADS)

    Chen, Hao; Gao, Bin; Yang, Liu-Yan; Ma, Lena Q.

    2015-02-01

    Antibiotic ciprofloxacin (CIP) is immobile in the subsurface but it has been frequently detected in the aquatic system. Therefore it is important to investigate the factors impacting CIP's mobilization in aquifer. Laboratory columns packed with sand were used to test colloid-facilitated CIP transport by 1) using kaolinite or montmorillonite to mobilize presorbed-CIP in a column or 2) co-transporting with CIP by pre-mixing them before transport. The Langmuir model showed that CIP sorption by montmorillonite (23 g kg- 1) was 100 times more effective than sand or kaolinite. Even with strong CIP complexation ability to Fe/Al coating on sand surface, montmorillonite promoted CIP transport, but not kaolinite. All presorbed-CIP by sand was mobilized by montmorillonite after 3 pore volumes through co-transporting of CIP with montmorillonite. The majority of CIP was fixed onto the montmorillonite interlayer but still showed inhibition of bacteria growth. Our results suggested that montmorillonite with high CIP sorption ability can act as a carrier to enhance CIP's mobility in aquifer.

  18. Molecular dynamics simulation of the intercalation behaviors of methane hydrate in montmorillonite.

    PubMed

    Yan, KeFeng; Li, XiaoSen; Xu, ChunGang; Lv, QiuNan; Ruan, XuKe

    2014-06-01

    The formation and mechanism of CH4 hydrate intercalated in montmorillonite are investigated by molecular dynamics (MD) simulation. The formation process of CH4 hydrate in montmorillonite with 1 ~ 8 H2O layers is observed. In the montmorillonite, the "surface H2O" constructs the network by hydrogen bonds with the surface Si-O ring of clay, forming the surface cage. The "interlayer H2O" constructs the network by hydrogen bonds, forming the interlayer cage. CH4 molecules and their surrounding H2O molecules form clathrate hydrates. The cation of montmorillonite has a steric effect on constructing the network and destroying the balance of hydrogen bonds between the H2O molecules, distorting the cage of hydrate in clay. Therefore, the cages are irregular, which is unlike the ideal CH4 clathrate hydrates cage. The pore size of montmorillonite is another impact factor to the hydrate formation. It is quite easier to form CH4 hydrate nucleation in montmorillonite with large pore size than in montmorillonite with small pore. The MD work provides the constructive information to the investigation of the reservoir formation for natural gas hydrate (NGH) in sediments.

  19. Montmorillonite catalysis of RNA oligomer formation in aqueous solution. A model for the prebiotic formation of RNA

    NASA Technical Reports Server (NTRS)

    Ferris, J. P.; Ertem, G.

    1993-01-01

    Oligomers of adenylic acid of up to the 11-mer in length are formed by the reaction of the phosphorimidazolide of adenosine (ImpA) in pH 8 aqueous solution at room temperature in the presence of Na(+)-montmorillonite. These oligomers are joined by phosphodiester bonds in which the 3',5'-linkage predominates over the 2',5'-linkage by a 2:1 ratio. Reaction of a 9:1 mixture of ImpA, A5'ppA results in the formation of oligomers with a 3:1 ratio of 3',5'- to 2',5'-linked phosphodiester bonds. A high proportion of these oligomers contain the A5'ppA grouping. A5'ppA reacts much more rapidly with ImpA than does 5'-ADP (ppA) or 5'-ATP (pppA). The exchangeable cation associated with the montmorillonite effects the observed catalysis with Li+, Na+, NH4+, and Ca2+ being the more effective while Mg2+ and Al3+ are almost ineffective catalysts. 2',5'-Linked oligomers, up to the tetramer in length, are formed using UO2(2+)-montmorillonite. The structure analysis of individual oligomer fractions was performed by selective enzymatic and KOH hydrolytic studies followed by HPLC analysis of the reaction products. It is concluded from the composition of the oligomers that the rate of addition ImpA to a 3'-terminus containing a 2',5'-linkage is slower than the addition to a nucleoside joined by a 3',5'-linked phosphodiester bond. The potential importance of mineral catalysis of the formation of RNA and other oligomers on primitive Earth is discussed.

  20. Hierarchical periodic micro/nano-structures on nitinol and their influence on oriented endothelialization and anti-thrombosis.

    PubMed

    Nozaki, Kosuke; Shinonaga, Togo; Ebe, Noriko; Horiuchi, Naohiro; Nakamura, Miho; Tsutsumi, Yusuke; Hanawa, Takao; Tsukamoto, Masahiro; Yamashita, Kimihiro; Nagai, Akiko

    2015-12-01

    The applications of hierarchical micro/nano-structures, which possess properties of two-scale roughness, have been studied in various fields. In this study, hierarchical periodic micro/nano-structures were fabricated on nitinol, an equiatomic Ni-Ti alloy, using a femtosecond laser for the surface modification of intravascular stents. By controlling the laser fluence, two types of surfaces were developed: periodic nano- and micro/nano-structures. Evaluation of water contact angles indicated that the nano-surface was hydrophilic and the micro/nano-surface was hydrophobic. Endothelial cells aligned along the nano-structures on both surfaces, whereas platelets failed to adhere to the micro/nano-surface. Decorrelation between the responses of the two cell types and the results of water contact angle analysis were a result of the pinning effect. This is the first study to show the applicability of hierarchical periodic micro/nano-structures for surface modification of nitinol.

  1. Biological and spatial structure of an early classic period cemetery at Charco Redondo, Oaxaca.

    PubMed

    Paul, Kathleen S; Stojanowski, Christopher M; Butler, Michelle M

    2013-10-01

    This article presents an analysis of biological and spatial patterning of an Early Classic (A.D. 250-500) Chatino cemetery at the archaeological site of Charco Redondo, located in the lower Río Verde Valley, Oaxaca, Mexico. The Early Classic was a time of political instability positioned between two phases of state-level centralization within the coastal valley. The communal cemetery at Charco Redondo adds significantly to the inventory of excavated graves from this time period and provides novel data on mortuary practices during a critical phase in the development of state level polities in the region. Cluster analysis of mortuary data is combined with intracemetery biodistance approaches to reconstruct how the Charco Redondo cemetery was organized with respect to biological relationships. Cluster analysis of mortuary data identified three groupings of burials. Multidimensional scaling of Euclidean distances and Gower coefficients based on 45 odontometric and 13 dental morphological variables suggests a strong relationship between grave characteristics and locations and phenotypic variation. In other words, the cemetery at Charco Redondo appears biologically kin-structured. The communal nature of the cemetery conflicts with the assumed "household" burial model for this time period. We propose the observed combination of features represents a transitional practice in which aspects of community, kin, and individual identity were signaled simultaneously within the funerary environment during a time of political transition in the Valley. This article highlights the utility of intracemetery biodistance analyses for examining dimensions of kinship, "house," and community throughout Mesoamerica where overarching models often mask regional variability.

  2. Population structure and reproductive period of two introduced fish species in a Brazilian semiarid region reservoir.

    PubMed

    Sousa, Marla Melise de Oliveira; Lopes, Suzany Iasnaya Moreira; da Costa, Rodrigo Silva; Novaes, José Luís Costa

    2015-09-01

    The Amazonian fish species Plagioscion squamosissimus (Sciaenidae) and Cichla monoculus Cichlidae), have been widely introduced into different reservoirs in Brazil, and have caused many negative mpacts on local fish fauna. The aim of this study was to evaluate the population structure (abundance, length structure, length-weight relationship, sex ratio, and length at first maturity) and the reprodutive period of these wo species in the Santa Cruz Reservoir (built in 2002), located in the Brazilian semiarid region, for their adequate management and local species conservation policies. Specimens were collected quarterly in eight sites from February 2010 to November 2013 using gillnets (12 to 70 mm mesh between adjacent knots). The specimens captured were counted and the following biometric and biological data were analysed: standard length, total weight, and reproductive data, such as, sex, weight and gonadal maturity stage. The species abundances were estimated by CPUE and expressed as the number of individuals per gill net area x gill net exposition time (m2 x h); length frequency histograms were built with intervals of 5 cm. The length-weight parameters were estimated with a linear regression after a logarithmic transformation of the data. With the reproductive data we estimated sex ratio, reproduction period and length at first maturity (L50). We captured a total of 1,071 specimens of P. squamosissimus and 156 specimens of C. monoculus. Both species showed higher abundances in 2010, 0.004306 m2 x h and 0.00022 m2 x h, respectively, but this parameter decreased from 2010 to 2013. Standard length ranged between 6.4 and 46.2 cm for P. squamosissimus (20.025.0 cm was the most frequent class), and 7.0 and 38.7 cm for C. monocidus (10.0-15.0 cm was the most frequent class). The length-weight relationships were described by the following equations: log10Wt = -1.8349+3.0899log10Lp and R2= 0.9795 for P. squamosissimus, and log10 Wt = -1.7944+3.0885log10Lp and Wt = 0

  3. The effect of pillaring montmorillonite and beidellite on the conversion of trimethylbenzenes

    SciTech Connect

    Kojima, M.; Hartford, R.; O'Connor, C.T. )

    1991-04-01

    Natural montmorillonite, synthetic mica-montmorillonite (SMM), and Ni-substituted SMM were treated with hydroxy-Al solutions and the activities of the respective unpillared and pillared clays were tested using 1,2 4-trimethylbenzene as a reactant. Pillaring montmorillonite and, to a lesser extent, synthetic beidellite gave the largest % increase in the conversion level. The selectivity to 1,2,4,5-tetramethylbenzene, the smallest of the tetramethylbenzene isomers, was found to be a function not of the extent of pillaring, but rather of the extent of isomerization of the alkylbenzenes.

  4. Kinetic and Conformational Insights of Protein Adsorption onto Montmorillonite Revealed Using in Situ ATR-FTIR/2D-COS.

    PubMed

    Schmidt, Michael P; Martínez, Carmen Enid

    2016-08-09

    Protein adsorption onto clay minerals is a process with wide-ranging impacts on the environmental cycling of nutrients and contaminants. This process is influenced by kinetic and conformational factors that are often challenging to probe in situ. This study represents an in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic investigation of the adsorption of a model protein (bovine serum albumin (BSA)) onto a clay mineral (montmorillonite) at four concentrations (1.50, 3.75, 7.50, and 15.0 μM) under environmentally relevant conditions. At all concentrations probed, FTIR spectra show that BSA readily adsorbs onto montmorillonite. Adsorption kinetics follow an Elovich model, suggesting that primary limitations on adsorption rates are surface-related heterogeneous energetic restrictions associated with protein rearrangement and lateral protein-protein interaction. BSA adsorption onto montmorillonite fits the Langmuir model, yielding K = 5.97 × 10(5) M(-1). Deconvolution and curve fitting of the amide I band at the end of the adsorption process (∼120 min) shows a large extent of BSA unfolding upon adsorption at 1.50 μM, with extended chains and turns increasing at the expense of α-helices. At higher concentrations/surface coverages, BSA unfolding is less pronounced and a more compact structure is assumed. Two-dimensional correlation spectroscopic (2D-COS) analysis reveals three different pathways corresponding to adsorbed conformations. At 1.50 μM, adsorption increases extended chains, followed by a loss in α-helices and a subsequent increase in turns. At 3.75 μM, extended chains decrease and then aggregated strands increase and side chains decrease, followed by a decrease in turns. With 7.50 and 15.0 μM BSA, the loss of side-chain vibrations is followed by an increase in aggregated strands and a subsequent decrease in turns and extended chains. Overall, the BSA concentration and resultant surface coverage have a profound

  5. Global upper mantle structure from long-period differential travel times

    SciTech Connect

    Woodward, R.L.; Masters, G. )

    1991-04-10

    The authors have made over ten thousand measurements of PP-P and SS-S differential travel times from long-period Global Digital Seismograph Network recordings of all events with m{sub b} {ge} 5.5 which occurred during the years 1976 and 1986. The experiments indicate that lower-mantle structure and source-receiver structure can each contribute approximately {plus minus}0.5 s to the measured PP-P residuals so there is considerable signal to be explained. The pattern observed in the PP-P measurements is similar to the pattern observed in the SS-S measurements, with the SS-S residuals 2 to 4 times larger in magnitude. Comparisons of measured residuals to those predicted by the upper-mantle models of Woodhouse and Dziewonski show that the overall patterns are quite similar but the amplitude of the model residuals is roughly a factor of 2 too small. Comparisons with the predictions of a whole-mantle model of Tanimoto again shows that the predicted pattern of residuals is reasonably consistent with the observations but now the predicted residuals are too large by about a factor of 2. They have also binned the measurements according to the tectonic regionalization GTR1 of Jordan and find a qualitative correlation of average residual with tectonic region. In particular, Precambrian shields show a strong anomaly, and there is a correlation of residual size with the age of oceanic crust at the bounce point. For all tectonic regions the ratio of SS-S to PP-P residuals is approximately 2. This ratio is consistent with a thermal origin for the observed signal. Finally, measurements show no compelling evidence for azimuthal anisotroph which might be related to fossil spreading direction or the direction of absolute plate motion.

  6. Why credit risk markets are predestined for exhibiting log-periodic power law structures

    NASA Astrophysics Data System (ADS)

    Wosnitza, Jan Henrik; Leker, Jens

    2014-01-01

    Recent research has established the existence of log-periodic power law (LPPL) patterns in financial institutions’ credit default swap (CDS) spreads. The main purpose of this paper is to clarify why credit risk markets are predestined for exhibiting LPPL structures. To this end, the credit risk prediction of two variants of logistic regression, i.e. polynomial logistic regression (PLR) and kernel logistic regression (KLR), are firstly compared to the standard logistic regression (SLR). In doing so, the question whether the performances of rating systems based on balance sheet ratios can be improved by nonlinear transformations of the explanatory variables is resolved. Building on the result that nonlinear balance sheet ratio transformations hardly improve the SLR’s predictive power in our case, we secondly compare the classification performance of a multivariate SLR to the discriminative powers of probabilities of default derived from three different capital market data, namely bonds, CDSs, and stocks. Benefiting from the prompt inclusion of relevant information, the capital market data in general and CDSs in particular increasingly outperform the SLR while approaching the time of the credit event. Due to the higher classification performances, it seems plausible for creditors to align their investment decisions with capital market-based default indicators, i.e., to imitate the aggregate opinion of the market participants. Since imitation is considered to be the source of LPPL structures in financial time series, it is highly plausible to scan CDS spread developments for LPPL patterns. By establishing LPPL patterns in governmental CDS spread trajectories of some European crisis countries, the LPPL’s application to credit risk markets is extended. This novel piece of evidence further strengthens the claim that credit risk markets are adequate breeding grounds for LPPL patterns.

  7. Tribological performance of sub-100-nm femtosecond laser-induced periodic surface structures on titanium

    NASA Astrophysics Data System (ADS)

    Bonse, J.; Höhm, S.; Koter, R.; Hartelt, M.; Spaltmann, D.; Pentzien, S.; Rosenfeld, A.; Krüger, J.

    2016-06-01

    Sub-100-nm laser-induced periodic surface structures (LIPSS) were processed on bulk titanium (Ti) surfaces by femtosecond laser pulse irradiation in air (30 fs pulse duration, 790 nm wavelength). The laser peak fluence, the spatial spot overlap, and the number of overscans were optimized in a sample-scanning geometry in order to obtain large surface areas (5 mm × 5 mm) covered homogeneously by the LIPSS. The laser-processed regions were characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). The friction coefficient of the nanostructured surfaces was tested during 1000 cycles under reciprocal sliding conditions (1 Hz, 1.0 N normal load) against a 10-mm diameter ball of hardened 100Cr6 steel, both in paraffin oil and in engine oil used as lubricants. Subsequently, the corresponding wear tracks were qualified by OM, SEM, and energy dispersive X-ray analyses (EDX). The results of the tribological tests are discussed and compared to that obtained for near wavelength-sized fs-LIPSS, processed under somewhat different irradiation conditions. Some constraints for a beneficial effect of LIPSS on the tribological performance are provided.

  8. Periodic actin structures in neuronal axons are required to maintain microtubules

    PubMed Central

    Qu, Yue; Hahn, Ines; Webb, Stephen E.D.; Pearce, Simon P.; Prokop, Andreas

    2017-01-01

    Axons are cable-like neuronal processes wiring the nervous system. They contain parallel bundles of microtubules as structural backbones, surrounded by regularly spaced actin rings termed the periodic membrane skeleton (PMS). Despite being an evolutionarily conserved, ubiquitous, highly ordered feature of axons, the function of PMS is unknown. Here we studied PMS abundance, organization, and function, combining versatile Drosophila genetics with superresolution microscopy and various functional readouts. Analyses with 11 actin regulators and three actin-targeting drugs suggest that PMS contains short actin filaments that are depolymerization resistant and sensitive to spectrin, adducin, and nucleator deficiency, consistent with microscopy-derived models proposing PMS as specialized cortical actin. Upon actin removal, we observed gaps in microtubule bundles, reduced microtubule polymerization, and reduced axon numbers, suggesting a role of PMS in microtubule organization. These effects become strongly enhanced when carried out in neurons lacking the microtubule-stabilizing protein Short stop (Shot). Combining the aforementioned actin manipulations with Shot deficiency revealed a close correlation between PMS abundance and microtubule regulation, consistent with a model in which PMS-dependent microtubule polymerization contributes to their maintenance in axons. We discuss potential implications of this novel PMS function along axon shafts for axon maintenance and regeneration. PMID:27881663

  9. Experimental characterization of periodic frequency-steerable arrays for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Senesi, Matteo; Xu, Buli; Ruzzene, Massimo

    2010-05-01

    Beam steering through phased arrays is a well-established technique, used extensively in ultrasonic imaging for medical, NDE and SHM applications. Phased arrays typically need individual control of their elements, which involves hardware and software complexity. This paper presents the characterization of a novel frequency-steerable array for structural health monitoring. In the considered configuration, beam steering is achieved by exploiting interference phenomena generated by the spatial lay-out of the array elements, and their simultaneous activation at specific frequencies. Such frequencies correspond to wavenumbers which are associated with radiation in determined spatial directions. In essence, the array acts as a spatial filter, which preferentially radiates at wavenumbers defined by the spatial arrangement of the elements. As such, the array is also effective at tuning its radiation to specific wave modes. In this paper, a simple quadrilateral periodic topology illustrates the directional properties of the array and shows its tuning capabilities. The investigations are supported by a preliminary numerical analysis, which is used to design an experimental prototype. Tests successfully validate the numerical predictions and demonstrate the directional and tuning capabilities of the proposed array design.

  10. Sleep structure in patients with periodic limb movements and obstructive sleep apnea syndrome.

    PubMed

    Iriarte, Jorge; Murie-Fernandez, Manuel; Toledo, Estefania; Urrestarazu, Elena; Alegre, Manuel; Viteri, Cesar; Salvador, Javier; Baptista, Peter; Alcaide, Belen; Artieda, Julio

    2009-08-01

    Periodic limb movements (PLM) and obstructive sleep apnea syndrome (OSAS) are two frequent sleep disorders which often occur in the same patient. The goal of this study was to know the influence of the presence of PLM in the sleep architecture in patients with and without OSAS. Two hundred twenty consecutive patients (69 women and 151 men) participated in this transversal study. They were patients with clinical suspicion of dysomnia, including snoring, OSAS, and PLM. All of them underwent a full polysomnography and were interviewed using questionnaires about the sleep quality. The sleep parameters (percentage of sleep stages, rapid eye movement latency, sleep efficiency, awakenings, PLM presence, apnea-hypopnea index) were calculated and compared between groups. Descriptive statistics and nonparametric distribution techniques were used for the analysis. Patients with PLM when compared with patients with OSAS had lower sleep efficiency and less rapid eye movement percentage. The presence of PLM in patients with sleep apnea was less relevant being responsible only for an increase in the rapid eye movement latency and a decrease in the duration of the three to four sleep stages. However, the presence of OSAS was related to a better sleep efficiency (patients with PLM plus OSAS had a better sleep efficiency than patients with only PLM). PLM alters the structure of sleep. In patients with sleep apnea, the presence of PLM is less relevant.

  11. Codon usage affects the structure and function of the Drosophila circadian clock protein PERIOD

    PubMed Central

    Fu, Jingjing; Murphy, Katherine A.; Zhou, Mian; Li, Ying H.; Lam, Vu H.; Tabuloc, Christine A.; Chiu, Joanna C.; Liu, Yi

    2016-01-01

    Codon usage bias is a universal feature of all genomes, but its in vivo biological functions in animal systems are not clear. To investigate the in vivo role of codon usage in animals, we took advantage of the sensitivity and robustness of the Drosophila circadian system. By codon-optimizing parts of Drosophila period (dper), a core clock gene that encodes a critical component of the circadian oscillator, we showed that dper codon usage is important for circadian clock function. Codon optimization of dper resulted in conformational changes of the dPER protein, altered dPER phosphorylation profile and stability, and impaired dPER function in the circadian negative feedback loop, which manifests into changes in molecular rhythmicity and abnormal circadian behavioral output. This study provides an in vivo example that demonstrates the role of codon usage in determining protein structure and function in an animal system. These results suggest a universal mechanism in eukaryotes that uses a codon usage “code” within genetic codons to regulate cotranslational protein folding. PMID:27542830

  12. Genotoxicity of unmodified and organo-modified montmorillonite.

    PubMed

    Sharma, Anoop Kumar; Schmidt, Bjørn; Frandsen, Henrik; Jacobsen, Nicklas Raun; Larsen, Erik Husfeldt; Binderup, Mona-Lise

    2010-07-19

    The natural clay mineral montmorillonite (Cloisite) Na+) and an organo-modified montmorillonite (Cloisite 30B) were investigated for genotoxic potential as crude suspensions and as suspensions filtrated through a 0.2-microm pore-size filter to remove particles above the nanometre range. Filtered and unfiltered water suspensions of both clays did not induce mutations in the Salmonella/microsome assay at concentrations up to 141microg/ml of the crude clay, using the tester strains TA98 and TA100. Filtered and unfiltered Cloisite) Na+ suspensions in culture medium did not induce DNA strand-breaks in Caco-2 cells after 24h of exposure, as tested in the alkaline comet assay. However, both the filtered and the unfiltered samples of Cloisite 30B induced DNA strand-breaks in a concentration-dependent manner and the two highest test concentrations produced statistically significantly different results from those seen with control samples (p<0.01 and p<0.001) and (p<0.05 and p<0.01), respectively. The unfiltered samples were tested up to concentrations of 170microg/ml and the filtered samples up to 216microg/ml before filtration. When tested in the same concentration range as used in the comet assay, none of the clays produced ROS in a cell-free test system (the DCFH-DA assay). Inductively coupled plasma mass-spectrometry (ICP-MS) was used to detect clay particles in the filtered samples using aluminium as a tracer element characteristic to clay. The results indicated that clay particles were absent in the filtered samples, which was independently confirmed by dynamic light-scattering measurements. Detection and identification of free quaternary ammonium modifier in the filtered sample was carried out by HPLC-Q-TOF/MS and revealed a total concentration of a mixture of quaternary ammonium analogues of 1.57microg/ml. These findings suggest that the genotoxicity of organo-modified montmorillonite was caused by the organo-modifier. The detected organo-modifier mixture was

  13. Microwave transmission through one-dimensional hybrid quasi-regular (fibonacci and Thue-Morse)/periodic structures

    NASA Astrophysics Data System (ADS)

    Trabelsi, Youssef; Benali, Naim; Bouazzi, Yassine; Kanzari, Mounir

    2013-09-01

    The transmission properties of hybrid quasi-periodic photonic systems (HQPS) made by the combination of one-dimensional periodic photonic crystals (PPCs) and quasi-periodic photonic crystals (QPCs) were theoretically studied. The hybrid quasi-periodic photonic lattice based on the hetero-structures was built from the Fibonacci and Thue-Morse sequences. We addressed the microwave properties of waves through the one-dimensional symmetric Fibonacci, and Thue-Morse system i.e., a quasi-periodic structure was made up of two different dielectric materials (Rogers and air), in the quarter wavelength condition. It shows that controlling the Fibonacci parameters permits to obtain selective optical filters with the narrow passband and polychromatic stop band filters with varied properties which can be controlled as desired. From the results, we presented the self-similar features of the spectra, and we also presented the fractal process through a return map of the transmission coefficients. We extracted powerfully the band gaps of hybrid quasi-periodic multilayered structures, called "pseudo band gaps", often containing resonant states, which could be considered as a manifestation of numerous defects distributed along the structure. The results of transmittance spectra showed that the cutoff frequency could be manipulated through the thicknesses of the defects and the type of dielectric layers of the system. Taken together, the above two properties provide favorable conditions for the design of an all-microwave intermediate reflector.

  14. Controlling electromagnetic fields using periodic structures: Gratings, metamaterials, and photonic crystals

    NASA Astrophysics Data System (ADS)

    Memarian, Mohammad

    This thesis presents novel devices and techniques that enable new methods for enhancement, concentration, refraction, shaping, collimation, and directive beaming of electromagnetic fields. These unprecedented methods to control electromagnetic fields are achieved by exploring and harnessing the unique wave-interactions in periodic gratings, metamaterials, and photonic crystals, with emphasis on Epsilon-Near-Zero (ENZ) metamaterials and zero-index media. The presented solutions impact a wide variety of applications ranging from microwave to optical frequencies. A discovery of dramatic radiation enhancement of an invisible array of sources next to a sub-wavelength periodic metal strip grating is reported, both theoretically and experimentally. The phenomenon is first systematically theorized by introducing the 'spectral impulse response' approach for the aperiodic excitation problem, followed by the 'spectral array factor' approach for designing the near-field of array of sources. Such radiation enhancement has applications in sensing, detection, and accurate measurement of distance. The shaping and collimation of radiation of a simple dipole source near or buried inside a general anisotropic ENZ half-space is then systematically studied using the Lorentz reciprocity method. Various elliptic and hyperbolic anisotropic ENZ media are considered, showing how the air-side radiation can be enhanced and shaped using certain ENZs. A novel device and technique is proposed for collecting, refracting and concentrating incident waves into an area of high power concentration, at extremely short distances. This flat low-profile light-concentrator comprises a hetero-junction of anisotropic ENZ metamaterials (hyperbolic or elliptic), and is realized with plasmonic layered media at optical frequencies. By harnessing an extremely oblique refraction process in ENZs, the light-concentrator significantly outperforms the size requirements of existing thick high curvature lenses, useful

  15. Eco-Friendly Magnetic Iron Oxide Pillared Montmorillonite for Advanced Catalytic Degradation of Dichlorophenol

    EPA Science Inventory

    Eco-friendly pillared montmorillonites, in which the pillars consist of iron oxide are expected to have interesting and unusual magnetic properties that are applicable for environmental decontamination. Completely “green” and effective composite was synthesized using mild reactio...

  16. Bioavailability of labile and desorption-resistant phenanthrene sorbed to montmorillonite clay containing humic fractions

    SciTech Connect

    Lahlou, M.; Ortega-Calvo, J.J.

    1999-12-01

    The biodegradation of {sup 14}C-labeled phenanthrene in the presence of particles of montmorillonite and fulvic and humic acid-montmorillonite complexes was studied in a batch system. A mathematical model that takes into account the contribution to mineralization by the slowly desorbing compound was used to calculate the initial mineralization rates. Sorption of phenanthrene to the particles was determined in sorption isotherms, and desorption was measured during successive water extractions. Mineralization rates in equilibrated suspensions were higher than predicted from aqueous equilibrium concentrations, and in some cases, montmorillonite and fulvic acid-montmorillonite complexes stimulated the phenanthrene transformation rates. In contrast with the high bioavailability exhibited by phenanthrene sorbed as a labile form, biodegradation of the desorption-resistant phenanthrene occurred slowly and followed zero-order kinetics, which indicated a limitation caused by slow desorption. The results suggest that the mechanism of sorption may cause a differential bioavailability of the sorbed compound.

  17. Theoretical Studies on the Extrinsic Defects of Montmorillonite in Soft Rock

    NASA Astrophysics Data System (ADS)

    He, Man-Chao; Fang, Zhi-Jie; Zhang, Ping

    Using the first-principles methods, we study the formation energetics and charge doping properties of the extrinsic substitutional defects in montmorillonite. Especially, we choose Be, Mg, Ca, Fe, Cr, Mn, Cu, Zn as extrinsic defects to substitute for Al atoms. By systematically calculating the impurity formation energies and transition energy levels, we find that all Group II defects introduce the relative shallow transition energy levels in montmorillonite. Among them, MgAl has the shallowest transition energy level at 0.10 eV above the valence band maximum. The transition-elemental defects FeAl, CrAl, and MnAl are found to have relatively low formation energies, suggesting their easy formation in montmorillonite under natural surrounding conditions. Our calculations show that the defects CuAl and ZnAl have high formation energies, which exclude the possibility of their formation in montmorillonite.

  18. Removal of 8-quinolinecarboxylic acid pesticide from aqueous solution by adsorption on activated montmorillonites.

    PubMed

    Mekhloufi, M; Zehhaf, A; Benyoucef, A; Quijada, C; Morallon, E

    2013-12-01

    Sodium montmorillonite (Na-M), acidic montmorillonite (H-M), and organo-acidic montmorillonite (Org-H-M) were applied to remove the herbicide 8-quinolinecarboxylic acid (8-QCA). The montmorillonites containing adsorbed 8-QCA were investigated by transmission electron microscopy, FT-IR spectroscopy, X-ray diffraction analysis, X-ray fluorescence thermogravimetric analysis, and physical adsorption of gases. Experiments showed that the amount of adsorbed 8-QCA increased at lower pH, reaching a maximum at pH 2. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. The Langmuir model provided the best correlation of experimental data for adsorption equilibria. The adsorption of 8-QCA decreased in the order Org-H-M > H-M > Na-M. Isotherms were also used to obtain the thermodynamic parameters. The negative values of ΔG indicated the spontaneous nature of the adsorption process.

  19. Characterization of synthesized polyurethane/montmorillonite nanocomposites foams

    NASA Astrophysics Data System (ADS)

    Ansari, Farahnaz; Sachse, Sophia; Michalowski, S.; Kavosh, Masoud; Pielichowski, Krzysztof; Njuguna, James

    2014-08-01

    Nanophased hybrid composites based on polyurethane/montmorillonite (PU/MMT) have been fabricated. The nanocomposite which was formed by the addition of a polyol premix with 4,4'-diphenylmethane diisocyanate to obtain nanophased polyurethane foams which were then used for fabrication of nanocomposite panels has been shown to have raised strength, stiffness and thermal insulation properties. The nanophased polyurethane foam was characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM) measurements and X-ray diffraction (XRD). TEM and SEM analysis indicated that nanophased particles are dispersed homogeneously in the polyurethane matrix on the nanometer scale indicating that PU/MMT is an intercalated nanocomposite with a 2-3 nm nanolayer thickness.

  20. Adsorption of polyetheramines on montmorillonite at high pH.

    PubMed

    Cui, Yannan; van Duijneveldt, Jeroen S

    2010-11-16

    Adsorption of a series of polyetheramines on montmorillonite in aqueous suspension was investigated by a range of methods: elemental analysis, atomic absorption spectroscopy, measurement of pH, conductivity and electrophoretic mobility, and small-angle X-ray scattering. Adsorption proceeds through an ion exchange mechanism. The maximum surface coverage attained is equivalent to about 40% of the cationic exchange capacity of the clay. Adsorption of the poly(oxypropylene) block adjacent to the amine group onto the clay surface may contribute to this. Surprisingly the adsorption takes place at pH conditions well above the pK(a) of the amine surfactants, where they are not protonated in the bulk solution. The surface coverage as a function of molar mass broadly agrees with predictions assuming adsorbed polymers adopt a densely packed mushroom configuration at the clay surface.

  1. Maghemite Intercalated Montmorillonite as New Nanofillers for Photopolymers

    PubMed Central

    Tarablsi, Bassam; Delaite, Christelle; Brendle, Jocelyne; Croutxe-Barghorn, Celine

    2012-01-01

    In this work, maghemite intercalated montmorillonite (γFe2O3-MMT)/polymer nanocomposites loaded with 1 or 2 wt.% of nanofillers were obtained by photopolymerization of difunctional acrylate monomers. The γFe2O3-MMT nanofillers were prepared by a new method based on the in situ formation of maghemite in the interlayer space of Fe-MMT using a three step process. X-ray diffraction (XRD), chemical analysis, TG/DTA and transmission electron microscopy (TEM) characterization of these nanofillers indicated the efficiency of the synthesis. When following the kinetics of the photopolymerization of diacrylate-γFe2O3-MMT nanocomposites using FTIR spectroscopy no significant inhibition effect of the nanofillers was observed at a loading up to 2 wt.%. These innovative nanocomposites exhibit improved mechanical properties compared to the crude polymer. PMID:28348316

  2. Study of montmorillonite clay for the removal of copper (II) by adsorption: full factorial design approach and cascade forward neural network.

    PubMed

    Turan, Nurdan Gamze; Ozgonenel, Okan

    2013-01-01

    An intensive study has been made of the removal efficiency of Cu(II) from industrial leachate by biosorption of montmorillonite. A 2(4) factorial design and cascade forward neural network (CFNN) were used to display the significant levels of the analyzed factors on the removal efficiency. The obtained model based on 2(4) factorial design was statistically tested using the well-known methods. The statistical analysis proves that the main effects of analyzed parameters were significant by an obtained linear model within a 95% confidence interval. The proposed CFNN model requires less experimental data and minimum calculations. Moreover, it is found to be cost-effective due to inherent advantages of its network structure. Optimization of the levels of the analyzed factors was achieved by minimizing adsorbent dosage and contact time, which were costly, and maximizing Cu(II) removal efficiency. The suggested optimum conditions are initial pH at 6, adsorbent dosage at 10 mg/L, and contact time at 10 min using raw montmorillonite with the Cu(II) removal of 80.7%. At the optimum values, removal efficiency was increased to 88.91% if the modified montmorillonite was used.

  3. Study of Montmorillonite Clay for the Removal of Copper (II) by Adsorption: Full Factorial Design Approach and Cascade Forward Neural Network

    PubMed Central

    Turan, Nurdan Gamze; Ozgonenel, Okan

    2013-01-01

    An intensive study has been made of the removal efficiency of Cu(II) from industrial leachate by biosorption of montmorillonite. A 24 factorial design and cascade forward neural network (CFNN) were used to display the significant levels of the analyzed factors on the removal efficiency. The obtained model based on 24 factorial design was statistically tested using the well-known methods. The statistical analysis proves that the main effects of analyzed parameters were significant by an obtained linear model within a 95% confidence interval. The proposed CFNN model requires less experimental data and minimum calculations. Moreover, it is found to be cost-effective due to inherent advantages of its network structure. Optimization of the levels of the analyzed factors was achieved by minimizing adsorbent dosage and contact time, which were costly, and maximizing Cu(II) removal efficiency. The suggested optimum conditions are initial pH at 6, adsorbent dosage at 10 mg/L, and contact time at 10 min using raw montmorillonite with the Cu(II) removal of 80.7%. At the optimum values, removal efficiency was increased to 88.91% if the modified montmorillonite was used. PMID:24453833

  4. Characterization of montmorillonite doped PVA/SA blends using X-ray diffraction

    SciTech Connect

    Hemalatha, K.; Somashekarappa, H.; Mahadevaiah,; Somashekar, R.

    2014-04-24

    PVA films doped with Montmorillonite was prepared by slow evaporation technique. These films have been used to record X-ray patterns at room temperature. Correlation lengths and microstructural parameters were computed using in-house program employing X-ray data. Results show that correlation lengths as well as crystallite size increases with increase in the concentration of Montmorillonite which is inconformity with the conductivity studies.

  5. Influence of the organic complex concentration on adsorption of herbicide in organic modified montmorillonite

    NASA Astrophysics Data System (ADS)

    Kaludjerovic, Lazar; Tomic, Zorica; Djurovic, Rada; Milosevic, Maja

    2016-04-01

    Pesticides are recognized as an important source of potential pollution to soil and water due to their mobility and degradation in soils. Results presented in this paper show impact of the organic complex concentration on the adsorption of herbicides (acetochlor) at the surface of the organic modified montmorillonite. In this work, natural montmorillonite from Bogovina, located near Boljevac municipality, was used for organic modification. Cation-exchange capacity of this montmorillonite was determined by extraction with ammonium acetate (86 mmol/100g of clay). Montmorillonite have been modified first with NaCl and than with two organic complexes, hexadecyltrimethylammonium bromide (HDTMA) and phenyltrimethylammonium chloride (PTMA). For both organic complexes, three saturation concentrations were selected for monitoring of the herbicide adsorption (43 mmol/100g of clay (0.5 CEC), 86 mmol/100g of clay (1 CEC) and 129 mmol/100g of clay (1.5 CEC)). Changes in the properties of the inorganic and organic bentonite have been examined using the X-ray powder diffraction (XRPD) and batch equilibrium method. Increase in basal spacing (d) of montmorillonites saturated with 1.5 CEC of organic cation indicate that sorption of PTMA and HDTMA can exceed the saturation of 1 CEC. Both organic montmorillonites have shown higher uptake of the herbicide, compared to the inorganic montmorillonite. Comparing the values Freundlich coefficients in batch equilibrium method, (presented in the form of log Kf and 1/n), it can be seen that the sorption decreases in the series: 0.5CEC> 1CEC> 1.5CEC> NaM, for both organic montmorillonites.

  6. Heterogeneous allylsilylation of aromatic and aliphatic alkenes catalyzed by proton-exchanged montmorillonite.

    PubMed

    Motokura, Ken; Matsunaga, Shigekazu; Miyaji, Akimitsu; Sakamoto, Yasuharu; Baba, Toshihide

    2010-04-02

    Allylsilylation of an alkene is the only known procedure to install both silyl and allyl groups onto a carbon-carbon double bond directly. Proton-exchanged montmorillonite showed excellent catalytic performances for the allylsilylation of alkenes. For example, the reaction of p-chlorostyrene with allyltrimethylsilane proceeded smoothly to afford the corresponding allylsilylated product in 95% yield. We also attempted to isolate the reaction intermediate on the montmorillonite surface to investigate the reaction mechanism.

  7. Comparison between the removal of phenol and catechol by modified montmorillonite with two novel hydroxyl-containing Gemini surfactants.

    PubMed

    Liu, Yuening; Gao, Manglai; Gu, Zheng; Luo, Zhongxin; Ye, Yage; Lu, Laifu

    2014-02-28

    Na-montmorillonites were modified with two novel hydroxyl-containing Gemini surfactants, 1,3-bis(hexadecyldimethylammonio)-2-hydroxypropane dichloride (BHHP) and 1,3-bis(octyldimethylammonio)-2-hydroxypropane dichloride (BOHP), via ion-exchange reaction in this study. The modified samples were characterized by X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy. Phenol and catechol were removed from aqueous solution by these two kinds of organo-montmorillonites in a batch system. Important parameters have been investigated, which affect the adsorption efficiency, such as the amount of modifier, temperature, pH and contact time. The adsorption kinetics of phenol and catechol were discussed using pseudo-first-order, pseudo-second-order and intra-particle diffusion model. It indicated that the experimental data fitted very well with the pseudo-second-order kinetic model, and the equilibrium adsorption data was proved in good agreement with the Langmuir isotherm. The result also showed the adsorption capacity of catechol was higher than that of phenol in the same conditions, which might result from the extra hydroxyl in the structure of catechol. Thermodynamic quantities such as Gibbs free energy (ΔG°), the enthalpy (ΔH°), and the entropy change of sorption (ΔS°) were also determined. These parameters suggested the adsorption of phenol was a spontaneous and exothermic process, while the sorption of catechol was endothermic.

  8. Ancient cellular structures and modern humans: change of survival strategies before prolonged low solar activity period

    NASA Astrophysics Data System (ADS)

    Ragulskaya, Mariya; Rudenchik, Evgeniy; Gromozova, Elena; Voychuk, Sergei; Kachur, Tatiana

    The study of biotropic effects of modern space weather carries the information about the rhythms and features of adaptation of early biological systems to the outer space influence. The influence of cosmic rays, ultraviolet waves and geomagnetic field on early life has its signs in modern biosphere processes. These phenomena could be experimentally studied on present-day biological objects. Particularly inorganic polyphosphates, so-called "fossil molecules", attracts special attention as the most ancient molecules which arose in inanimate nature and have been accompanying biological objects at all stages of evolution. Polyphosphates-containing graves of yeast's cells of Saccharomyces cerevisiae strain Y-517, , from the Ukrainian Collection of Microorganisms was studied by daily measurements during 2000-2013 years. The IZMIRAN daily data base of physiological parameters dynamics during 2000-2013 years were analyzed simultaneously (25 people). The analysis showed significant simultaneous changes of the statistical parameters of the studied biological systems in 2004 -2006. The similarity of simultaneous changes of adaptation strategies of human organism and the cell structures of Saccharomyces cerevisiae during the 23-24 cycles of solar activity are discussed. This phenomenon could be due to a replacement of bio-effective parameters of space weather during the change from 23rd to 24th solar activity cycle and nonstandard geophysical peculiarities of the 24th solar activity cycle. It could be suggested that the observed similarity arose as the optimization of evolution selection of the living systems in expectation of probable prolonged period of low solar activity (4-6 cycles of solar activity).

  9. Modelling Line Edge Roughness in Periodic Line-Space Structures by Fourier Optics to Improve Scatterometry

    NASA Astrophysics Data System (ADS)

    Gross, H.; Heidenreich, S.; Henn, M.-A.; Dai, G.; Scholze, F.; Bär, M.

    2014-01-01

    In the present paper, we propose a 2D-Fourier transform method as a simple and efficient algorithm for stochastical and numerical studies to investigate the systematic impacts of line edge roughness on light diffraction pattern of periodic line-space structures. The key concept is the generation of ensembles of rough apertures composed of many slits, to calculate the irradiance of the illuminated rough apertures far away from the aperture plane, and a comparison of their light intensities to those of the undisturbed, 'non-rough' aperture. We apply the Fraunhofer approximation and interpret the rough apertures as binary 2D-gratings to compute their diffraction patterns very efficiently as the 2D-Fourier transform of the light distribution of the source plane. The rough edges of the aperture slits are generated by means of power spectrum density (PSD) functions, which are often used in metrology of rough geometries. The mean efficiencies of the rough apertures reveal a systematic exponential decrease for higher diffraction orders if compared to the diffraction pattern of the unperturbed aperture. This confirms former results, obtained by rigorous calculations with computational expensive finite element methods (FEM) for a simplified roughness model. The implicated model extension for scatterometry by an exponential damping factor for the calculated efficiencies allows to determine the standard deviation σ_r of line edge roughness along with the critical dimensions (CDs), i.e., line widths, heights and other profile properties in the sub-micrometer range. First comparisons with the corresponding roughness value determined by 3D atomic force microscopy (3D AFM) reveal encouraging results.

  10. Electromagnetic modeling of periodically-structured fiber-reinforced single-layer laminate with multiple fibers missing

    NASA Astrophysics Data System (ADS)

    Liu, Z.-C.; Li, C.-Y.; Lesselier, D.; Zhong, Y.

    2016-12-01

    Modeling of periodically-structured, fiber-reinforced laminates with fibers missing is investigated, this applying as well to similarly disorganized photonic crystals at optical frequencies. Parallel cylindrical fibers are periodically embedded within a layer sandwiched between two half-spaces. Absent fibers destroy the periodicity. The supercell concept involving an auxiliary periodic structure provides subsidiary solutions, wherein plane-wave illumination can be analyzed with the help of the Floquet theorem, while the field response due to a line source can be calculated from the pertinent plane-wave expansion. Accuracy, computational efficacy and versatility of the above approaches are illustrated by comprehensive numerical simulations with in particular comparisons to results provided by a finite-element code, all-purpose but computationally demanding, this work seen as the first step to the localization of missing fibers in a damaged laminate and imaging thereof.

  11. Organo-montmorillonite Barrier Layers Formed by Combustion: Nanostructure and Permeability

    SciTech Connect

    Fox, James B; Ambuken, Preejith V.; Stretz, Holly A; Meisner, Roberta Ann; Payzant, E Andrew

    2010-01-01

    Self-assembly of nanoparticles into barrier layers has been the most cited theoretical explanation for the significant reduction in flammability often noted for nanocomposites formed from polymers and montmorillonite organoclays. Both mass and heat transport reductions have been credited for such improvements, and in most cases a coupled mechanism is expected. To provide validation for early models, new model barrier layers were produced from organoclays, and these barrier layers subjected to novel permeability analysis to obtain a flux. The effects of surfactant, temperature and pressure on barrier layer structure were examined. XRD versus TGA results suggest that chemical degradation of four different organoclays and physical collapse on heating are not correlated. Addition of pressure as low as 7kPa also altered the structure produced. Permeability of Ar through the ash was found to be sensitive to structural change/self assembly of high aspect ratio MMT nanoparticles. Actual fluxes ranged from 0.139 to 0.151 mol(m2.sec)-1, values which will provide useful limits in verifying models for the coupled contribution of mass and heat transfer to flammability parameters such as peak heat release rate.

  12. An investigation of the adsorption of organic dyes onto organo-montmorillonite.

    PubMed

    Lee, S H; Song, D I; Jeon, Y W

    2001-03-01

    Adsorption of organic dyes, crystal violet (CV), orange II (OR), and phenol red (PR), onto organo-clay was investigated in a batch type reactor at 25 degrees C. The organo-clay was obtained by modifying montmorillonite with a cationic surfactant, cetylpyridinium (CP), and used as an adsorbent. We conducted experiments to find out the effect of pH and solvent on the adsorption affinity of organic dyes for the modified montmorillonite. From the results, we observed that the adsorption capacity on the organo-montmorillonite decreased in the order CV > OR > PR at all pH values examined (pH 3, pH 7, and pH 11). It mostly resulted from the difference in solubility and the molecular weight of the solutes. In a 30-V/V % methanol/water cosolvent solution, the adsorption capacity of the dyes decreased compared to that in aqueous solution. In addition, the adsorption capacities of OR and PR on CV-montmorillonite were lower than those on CP-montmorillonite. These results might show that partitioning by CP was superior to the adsorption by CV to hold the solute molecules on the surface of montmorillonite. The Langmuir and Redlich-Peterson (RP) models were used to represent the adsorption equilibria of the organic dyes.

  13. Adsorption of phenol and nitrophenol isomers onto montmorillonite modified with hexadecyltrimethylammonium cation

    SciTech Connect

    Kwon, S.C.; Song, D.I.; Jeon, Y.W.

    1998-09-01

    Single- and two-component competitive adsorptions were carried out in a batch adsorber to investigate the adsorption behavior of phenol and 2-, 3-, and 4-nitrophenols in aqueous solution at 25 C onto hexadecyltrimethylammonium (HDTMA)-treated montmorillonite. HDTMA cation was exchanged for metal cations on the montmorillonite to prepare HDTMA-montmorillonite, changing its surface property from hydrophilic to organophilic. Effective solid diffusivity of HDTMA cation in the montmorillonite particle was estimated to be about 3 {times} 10{sup {minus}12} cm{sup 2}/s by fitting the film-solid diffusion model to a set of HDTMA adsorption kinetic data onto montmorillonite. Adsorption affinity on HDTMA-montmorillonite was found to be in the order 3-nitrophenol {approx} 4-nitrophenol > 2-nitrophenol > phenol. The Langmuir and the Redlich-Peterson (RP) adsorption models were used to analyze the single component adsorption equilibria. The ideal adsorbed solution theory (IAST) and the Langmuir competitive model (LCM) were used to predict the multicomponent competitive adsorption equilibria. These models yielded favorable representations of both individual and competitive adsorption behaviors.

  14. Effect of phosphate activating group on oligonucleotide formation on montmorillonite: the regioselective formation of 3',5'-linked oligoadenylates

    NASA Technical Reports Server (NTRS)

    Prabahar, K. J.; Cole, T. D.; Ferris, J. P.

    1994-01-01

    The effects of amine structure on the montmorillonite-catalyzed oligomerization of the 5'-phosphoramidates of adenosine are investigated. 4-Aminopyridine derivatives yielded oligoadenylates as long as dodecamers with a regioselectivity for 3',5'-phosphodiester bond formation averaging 88%. Linear and cyclic oligomers are obtained and no A5'ppA-containing products are detected. Oligomers as long as the hexanucleotide are obtained using 2-aminobenzimidazole as the activating group. A predominance of pA2'pA is detected in the dimer fraction along with cyclic 3',5'-trimer; no A5'ppA-containing oligomers were detected. Little or no oligomer formation was observed when morpholine, piperidine, pyrazole, 1,2,4-triazole, and 2-pyridone are used as phosphate-activating groups. The effects of the structure of the phosphate activating group on the oligomer structure and chain lengths are discussed.

  15. A vector method for synthesis of orbits and the structure of satellite constellations for multiswath periodic coverage of the Earth

    NASA Astrophysics Data System (ADS)

    Saulskiy, V. K.

    2016-07-01

    Single satellites and multisatellite constellations for the periodic coverage of the Earth are considered. The main feature is the use of several cameras with different swath widths. A vector method is proposed which makes it possible to find orbits minimizing the periodicities of coverage of a given area of Earth uniformly for all swaths. Their number is not limited, but the relative dimensions should satisfy the Fibonacci series or some new numerical sequences. The results apply to constellations of any number of satellites. Formulas were derived for calculating their structure, i.e., relative position in the constellation. Examples of orbits and the structure of constellations for the Earth's multiswath coverage are presented.

  16. Topology of the space of periodic ground states in the antiferromagnetic Ising and Potts models in selected spatial structures

    NASA Astrophysics Data System (ADS)

    Krawczyk, Małgorzata J.

    2010-05-01

    Topology of the space of periodic ground states in the antiferromagnetic Ising and Potts (3-state) models is analysed in selected spatial structures. The states are treated as graph nodes, connected by one-spin-flip transitions. The spatial structures are the triangular lattice, the Archimedean ( 3,12) lattice and the cubic Laves C15 lattice with the periodic boundary conditions. In most cases the ground states are isolated nodes, but for selected systems we obtain connected graphs. The latter means that the magnetisation can vary in time with zero energy cost. The ground states are classified according to their degree and type of neighbours.

  17. [Research on the hospital construction and structure in Daehan empire and colonial modern period].

    PubMed

    Han, Dong Gwan; Ryu, Chang Ug; Ko, Sang Kyun; Jung, Jae Kook; Moon, Jong Youn; Park, Yoon Hyung

    2011-12-31

    It was the late Chosun Dynasty and Daehan Empire era that Western Medicine has firstly been introduced to Korea, previously operating on a basis of Korean traditional medicine. Western Medicine has been introduced by American missionary and Japanese Imperialism. An introduction of Western Medicine made it feasible to proceed new type medical care including operation, leading to require a new form of medical facilities. In the beginning, new facilities were constructed by Japanese Imperialism. Other hand many of facilities including Severance Hospital were established by missionaries. First of all, Daehan Empire established and managed a modern type of medical facility named "Jejoongwon" in 1885 as a government institution hospital. The Red Cross Hospital built in 1889. Afterwards, Jejoongwon and the Red Cross Hospital were taken over to missionary hospital and Japanese Imperialism, respectively. Japanese Imperialists firstly have protected their nationals residing in Chosun but have proceeded care a few Chosun people to exploit medical treatment as a mean to advertise superiority of the Empire of Japan. The facility that has firstly been established and managed was Jeseang Hospital in Busan in 1877, leading to establish in Wonju, Wonsan, and Mokpo. Afterwards, Japan has organized "Donginhoi" as a civil invasion organization, leading for "Donginhoi" to established "Dongin Hospital" in Pyeongyang, Daegu, and Seoul. Since 1909, governmental leading medical facility named Jahye Hospital was established according to an imperial order, leading to establish 32 hospitals all over the nation. American missionaries have established and managed 28 hospitals started from Severance Hospital built in 1904. However, Chosun doctors started to having educated and opening up their own hospital since 1920, leading for many of medical facilities to be established, but most of them have taken different roles followed by 6.25 War and economic development period. However, some of them

  18. Short-Term Safety and Efficacy of Calcium Montmorillonite Clay (UPSN) in Children

    PubMed Central

    Mitchell, Nicole J.; Kumi, Justice; Aleser, Mildred; Elmore, Sarah E.; Rychlik, Kristal A.; Zychowski, Katherine E.; Romoser, Amelia A.; Phillips, Timothy D.; Ankrah, Nii-Ayi

    2014-01-01

    Recently, an association between childhood growth stunting and aflatoxin (AF) exposure has been identified. In Ghana, homemade nutritional supplements often consist of AF-prone commodities. In this study, children were enrolled in a clinical intervention trial to determine the safety and efficacy of Uniform Particle Size NovaSil (UPSN), a refined calcium montmorillonite known to be safe in adults. Participants ingested 0.75 or 1.5 g UPSN or 1.5 g calcium carbonate placebo per day for 14 days. Hematological and serum biochemistry parameters in the UPSN groups were not significantly different from the placebo-controlled group. Importantly, there were no adverse events attributable to UPSN treatment. A significant reduction in urinary metabolite (AFM1) was observed in the high-dose group compared with placebo. Results indicate that UPSN is safe for children at doses up to 1.5 g/day for a period of 2 weeks and can reduce exposure to AFs, resulting in increased quality and efficacy of contaminated foods. PMID:25135766

  19. Stability of Na-, K-, and Ca-montmorillonite at high temperatures and pressures: a Monte Carlo simulation.

    PubMed

    de Pablo, Liberto; Chávez, Maria L; de Pablo, Juan J

    2005-11-08

    Monte Carlo grand canonical molecular simulations on the hydration of Na-, K-, and Ca-montmorillonite show that between 333 and 533 K and 300-1300 bar Na-montmorillonite forms stable one-layer hydrates of d(001) spacings 12.64-12.38 Angstroms, K-montmorillonite of 12.78-12.59 Angstroms, and Ca-montmorillonite of 12.48-12.32 Angstroms. A two-layer hydrate of 14.80 Angstroms occurs for Na-montmorillonite at 533 K and 1300 bar, for K-montmorillonite of 15.32 Angstroms at 533 K and 1300 bar and of 14.74 Angstroms at 533 K and 2000 bar, and for Ca-montmorillonite of 13.83 Angstroms at 473 K and 1000 bar. Three-layer hydrates may possibly form within these same ranges. Outside of them, one-layer hydrates simulate as the only stable hydrates. In sedimentary basins, the two-layer hydrate of Ca-montmorillonite will locate at 6.7 km depth and those of Na- and K-montmorillonite at 8.7 km depth; above and below these depths, the one-layer hydrates are the stable phases.

  20. Hemicelluloses/montmorillonite hybrid films with improved mechanical and barrier properties

    NASA Astrophysics Data System (ADS)

    Chen, Ge-Gu; Qi, Xian-Ming; Li, Ming-Peng; Guan, Ying; Bian, Jing; Peng, Feng; Yao, Chun-Li; Sun, Run-Cang

    2015-11-01

    A facile and environmentally friendly method was introduced to incorporate montmorillonite (MMT) as an inorganic phase into quaternized hemicelluloses (QH) for forming hemicellulose-based films. Two fillers, polyvinyl alcohol (PVA) and chitin nanowhiskers (NCH), were added into the hemicelluloses/MMT hybrid matrices to prepare hybrid films, respectively. The hybrid films were nanocomposites with nacre-like structure and multifunctional characteristics including higher strength and good oxygen barrier properties via the electrostatic and hydrogen bonding interactions. The addition of PVA and NCH could induce changes in surface topography, and effectively enhance mechanical strength, thermal stability, transparency, and oxygen barrier properties. The tensile strengths of the composite films FPVA(0.3), FPVA(0.5), and FNCH(0.8) were 53.7, 46.3, and 50.1 MPa, respectively, which were 171%, 134%, and 153% larger than the FQH-MMT film (19.8 MPa). The tensile strength, and oxygen transmission rate of QH-MMT-PVA film were better than those of quaternized hemicelluloses/MMT films. Thus, the proper filler is very important for the strength of the hybrid film. These results provide insights into the understanding of the structural relationships of hemicellulose-based composite films in coating and packaging application for the future.

  1. Adsorption property of Rhodamine 6G onto chitosan-g-(N-vinyl pyrrolidone)/montmorillonite composite.

    PubMed

    Vanamudan, Ageetha; Bandwala, Khusbu; Pamidimukkala, Padmaja

    2014-08-01

    A series of chitosan-g-(N-vinyl pyrrolidone)/montmorillonite hydrogel composites were synthesized by in situ intercalative polymerization. The properties of the composites were investigated by FTIR, XRD, scanning electron microscopy and differential scanning calorimetry. The morphologies of the hydrogel composites were sponge like with a homogeneous structure. The effects of clay on the swelling, morphology, glass transition (Tg), and water structure were studied. The swelling of the hydrogel composites formed was found to be affected by the pH of the medium and the electrolyte. Maximum swelling was observed in the hydrogel containing low percentage of clay (H-0.2) and was used to investigate the adsorption of a water soluble cationic dye Rhodamine 6G (Rh6G). The results show that the adsorption capacity for the dye increased with increase in dose, contact time but there was no change observed with respect to increase in temperature. The adsorption kinetics of Rh6G followed Pseudo second order model and the equilibrium data was found to fit Freundlich model.

  2. Activity of Laccase Immobilized on TiO2-Montmorillonite Complexes

    PubMed Central

    Wang, Qingqing; Peng, Lin; Li, Guohui; Zhang, Ping; Li, Dawei; Huang, Fenglin; Wei, Qufu

    2013-01-01

    The TiO2-montmorillonite (TiO2-MMT) complex was prepared by blending TiO2 sol and MMT with certain ratio, and its properties as an enzyme immobilization support were investigated. The pristine MMT and TiO2-MMT calcined at 800 °C (TiO2-MMT800) were used for comparison to better understand the immobilization mechanism. The structures of the pristine MMT, TiO2-MMT, and TiO2-MMT800 were examined by HR-TEM, XRD and BET. SEM was employed to study different morphologies before and after laccase immobilization. Activity and kinetic parameters of the immobilized laccase were also determined. It was found that the TiO2 nanoparticles were successfully introduced into the MMT layer structure, and this intercalation enlarged the “d value” of two adjacent MMT layers and increased the surface area, while the calcination process led to a complete collapse of the MMT layers. SEM results showed that the clays were well coated with adsorbed enzymes. The study of laccase activity revealed that the optimum pH and temperature were pH = 3 and 60 °C, respectively. In addition, the storage stability for the immobilized laccase was satisfactory. The kinetic properties indicated that laccase immobilized on TiO2-MMT complexes had a good affinity to the substrate. It has been proved that TiO2-MMT complex is a good candidate for enzyme immobilization. PMID:23771020

  3. Hemicelluloses/montmorillonite hybrid films with improved mechanical and barrier properties

    PubMed Central

    Chen, Ge-Gu; Qi, Xian-Ming; Li, Ming-Peng; Guan, Ying; Bian, Jing; Peng, Feng; Yao, Chun-Li; Sun, Run-Cang

    2015-01-01

    A facile and environmentally friendly method was introduced to incorporate montmorillonite (MMT) as an inorganic phase into quaternized hemicelluloses (QH) for forming hemicellulose-based films. Two fillers, polyvinyl alcohol (PVA) and chitin nanowhiskers (NCH), were added into the hemicelluloses/MMT hybrid matrices to prepare hybrid films, respectively. The hybrid films were nanocomposites with nacre-like structure and multifunctional characteristics including higher strength and good oxygen barrier properties via the electrostatic and hydrogen bonding interactions. The addition of PVA and NCH could induce changes in surface topography, and effectively enhance mechanical strength, thermal stability, transparency, and oxygen barrier properties. The tensile strengths of the composite films FPVA(0.3), FPVA(0.5), and FNCH(0.8) were 53.7, 46.3, and 50.1 MPa, respectively, which were 171%, 134%, and 153% larger than the FQH-MMT film (19.8 MPa). The tensile strength, and oxygen transmission rate of QH-MMT-PVA film were better than those of quaternized hemicelluloses/MMT films. Thus, the proper filler is very important for the strength of the hybrid film. These results provide insights into the understanding of the structural relationships of hemicellulose-based composite films in coating and packaging application for the future. PMID:26549418

  4. Molecular Simulation of Carbon Dioxide Capture by Montmorillonite Using an Accurate and Flexible Force Field

    SciTech Connect

    Romanov, V N; Cygan, R T; Myshakin, E M

    2012-06-21

    Naturally occurring clay minerals provide a distinctive material for carbon capture and carbon dioxide sequestration. Swelling clay minerals, such as the smectite variety, possess an aluminosilicate structure that is controlled by low-charge layers that readily expand to accommodate water molecules and, potentially, CO2. Recent experimental studies have demonstrated the efficacy of intercalating CO2 in the interlayer of layered clays, but little is known about the molecular mechanisms of the process and the extent of carbon capture as a function of clay charge and structure. A series of molecular dynamics simulations and vibrational analyses have been completed to assess the molecular interactions associated with incorporation of CO2 and H2O in the interlayer of montmorillonite clay and to help validate the models with experimental observation. An accurate and fully flexible set of interatomic potentials for CO2 is developed and combined with Clayff potentials to help evaluate the intercalation mechanism and examine the effect of molecular flexibility onthe diffusion rate of CO2 in water.

  5. Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materials

    NASA Technical Reports Server (NTRS)

    Bishop, J. L.; Pieters, C. M.; Burns, R. G.; Edwards, J. O.; Mancinelli, R. L.; Froschl, H.

    1995-01-01

    Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mossbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mossbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mossbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water

  6. Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materials.

    PubMed

    Bishop, J L; Pieters, C M; Burns, R G; Edwards, J O; Mancinelli, R L; Fröschl, H

    1995-09-01

    Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mössbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mössbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mössbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the

  7. Nonequilibrium superconducting states with temporal periodic structures under high quasiparticle injection

    SciTech Connect

    CHEN Shi-gang; CHEN Xiao-lan; WANG You-qin

    1984-07-01

    Based on the Scalapino-Huberman ..mu..* model, the possibility of temporally oscillating structures appearing in a superconducting film under high quasiparticle injection is discussed. The range of parameters in which these structures may occur is also given.

  8. FOREWORD: IX International Symposium on Radiation from Relativistic Electrons in Periodic Structures (RREPS-2011)

    NASA Astrophysics Data System (ADS)

    Potylitsyn, Alexander; Karataev, Pavel

    2012-05-01

    This volume contains papers presented at the IX International Symposium on Radiation from Relativistic Electrons in Periodic Structures (RREPS'11) which was held at Royal Holloway, University of London on September 12-16, Egham, United Kingdom. The symposium was organized jointly by Royal Holloway, University of London and Tomsk Polytechnic University, Tomsk, Russia. RREPS is a biennial series of symposia founded in September 1993 as an initiative of the Nuclear Physics Institute at Tomsk Polytechnic University. The intention was to strengthen the basic and applied research focused on radiation from relativistic electrons in condensed media, particularly from natural and artificial periodic structures, and to review the research activity in this area. Since then, the symposium has developed into a forum attracting young scientists from different areas of research and from many countries. Previous successful symposia were held at Tomsk, Russia (1993, 1995, 1997, 2003), Lake Baikal, Russia (1999), Lake Aiya, Altai, Russia (2001), Czech Technical University in Prague, Czech Republic (2007) and Zvenigorod, Moscow region, Russia (2009). As an outcome of the symposia the conference proceedings have been published in Nuclear Instruments and Methods in Physics Research, Section B (Vol. 145 No 1-2, October 1998; Vol. 173 No 1-2, January 2001; Vol. 201 No 1 January 2003; Vol. 227 No 1-2, January 2005; Vol. 266 No 17, September 2008) and Journal of Physics: Conference Series (Vol. 236, June 2010). The purpose of the present RREPS'11 symposium was to review the up-to-date situation in the area of electromagnetic radiation generated by relativistic charged particles in condensed media, and to discuss the research strategy for the near future. Nowadays, electromagnetic radiation studies cover electron energies from a few MeV up to hundreds of GeV in many laboratories throughout the world. The goal is to study the physics of the generation of various kinds of radiation and their

  9. Montmorillonite-based porous clay heterostructures (PCHs) intercalated with silica-titania pillars—synthesis and characterization

    NASA Astrophysics Data System (ADS)

    Chmielarz, Lucjan; Gil, Barbara; Kuśtrowski, Piotr; Piwowarska, Zofia; Dudek, Barbara; Michalik, Marek

    2009-05-01

    Porous clay heterostructures (PCHs) were synthesized using natural montmorillonite as a raw material. Apart from pure silica pillars also silica-titania pillars were intercalated into the interlayer space of the parent clay. The detailed studies of the calcination process of the as-prepared PCH samples as well as thermal stability of the pillared structure of these materials were performed. The pillared structure of PCHs intercalated with both silica and silica-titania clusters was found to be thermally stable up to temperatures exceeding 600 °C. It was found that titanium incorporated into the silica pillars was present mainly in the form of separated tetracoordinated cations. For the samples with the higher Ti loading also small contribution of titanium in the form of the polymeric oxide species was detected. Titanium incorporated into the PCH materials significantly increased their surface acidity forming mainly Brønsted acid sites.

  10. The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds

    NASA Astrophysics Data System (ADS)

    Couzi, Michel; Guillaume, François; Harris, Kenneth D. M.; Palmer, Benjamin A.; Christensen, Kirsten; Collins, Stephen P.

    2016-12-01

    The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3 + 1)-dimensional superspace groups.

  11. Effect of Programmed Instruction on Students' Attitude towards Structure of the Atom and the Periodic Table among Kenyan Secondary Schools

    ERIC Educational Resources Information Center

    Wangila, M. J.; Martin, W.; Ronald, M.

    2015-01-01

    This study examined the effect of Programmed Instruction on students' attitude towards Structure of the Atom and the Periodic Table (SAPT) among mixed (co-educational) secondary schools of Butere district, Kakamega county, Kenya. The quasi-experimental research design was adopted, using the nonrandomized Solomon four-group as a model. The sample…

  12. The influence of continuous rice cultivation and different waterlogging periods on the morphology, clay mineralogy, Eh, pH and K in paddy soils

    NASA Astrophysics Data System (ADS)

    Bahmaniar, M. A.

    2008-01-01

    The effect of different rice plantation periods on the properties of selected soils on an alluvial plain was studied. Soils were sampled in fields cultivated for 6, 16, 26, and over forty years. In each rice cultivated and nonrice cultivated field, three soil profiles and six nearby auger holes were studied. This study indicated that continuous rice cultivation changed the soil moisture regime from xeric to aquic, the soil color from brown to grayish, and the surface horizons from mollic to ochric epipedon. With increasing duration of cultivation, the abundance of redoximorphic features increased and the soil structure changed from granular or blocky to massive. Therefore, the soil order changed from Mollisols to Inceptisols. No illuviation and eluviation of clay minerals occurred as a consequence of the rice cultivation. X-ray diffraction analysis showed that the clay minerals in the nonrice cultivated field were illite, vermiculite, montmorillonite, kaolinite, and chlorite, and, in the rice field, they were illite, montmorillonite, kaolinite, and chlorite, respectively. However, with increasing the period of cultivation, the amount of illite and vermiculite decreased while the amount of montmorillonite increased. The pH values of the saturated soil surface during the middle stage of rice growth shifted toward neutrality. The Eh of the surface horizons of the paddy soils under the field conditions were +40, -12, -84, and -122 mV, respectively, while the Eh in the nonpaddy soils were close to +90 mV. The amounts of organic matter and available Fe, Mn, Zn, and Cu increased, while the available K decreased in the paddy soils.

  13. Sorption/Desorption Interactions of Plutonium with Montmorillonite

    NASA Astrophysics Data System (ADS)

    Begg, J.; Zavarin, M.; Zhao, P.; Kersting, A. B.

    2012-12-01

    Plutonium (Pu) release to the environment through nuclear weapon development and the nuclear fuel cycle is an unfortunate legacy of the nuclear age. In part due to public health concerns over the risk of Pu contamination of drinking water, predicting the behavior of Pu in both surface and sub-surface water is a topic of continued interest. Typically it was assumed that Pu mobility in groundwater would be severely restricted, as laboratory adsorption studies commonly show that naturally occurring minerals can effectively remove plutonium from solution. However, evidence for the transport of Pu over significant distances at field sites highlights a relative lack of understanding of the fundamental processes controlling plutonium behavior in natural systems. At several field locations, enhanced mobility is due to Pu association with colloidal particles that serve to increase the transport of sorbed contaminants (Kersting et al., 1999; Santschi et al., 2002, Novikov et al., 2006). The ability for mineral colloids to transport Pu is in part controlled by its oxidation state and the rate of plutonium adsorption to, and desorption from, the mineral surface. Previously we have investigated the adsorption affinity of Pu for montmorillonite colloids, finding affinities to be similar over a wide range of Pu concentrations. In the present study we examine the stability of adsorbed Pu on the mineral surface. Pu(IV) at an initial concentration of 10-10 M was pre-equilibrated with montmorillonite in a background electrolyte at pH values of 4, 6 and 8. Following equilibration, aliquots of the suspensions were placed in a flow cell and Pu-free background electrolyte at the relevant pH was passed through the system. Flow rates were varied in order to investigate the kinetics of desorption and hence gain a mechanistic understanding of the desorption process. The flow cell experiments demonstrate that desorption of Pu from the montmorillonite surface cannot be modeled as a simple

  14. Log-periodic oscillations for diffusion on self-similar finitely ramified structures.

    PubMed

    Padilla, L; Mártin, H O; Iguain, J L

    2010-07-01

    Under certain circumstances, the time behavior of a random walk is modulated by logarithmic-periodic oscillations. Using heuristic arguments, we give a simple explanation of the origin of this modulation for diffusion on a substrate with two properties: self-similarity and finite ramification order. On these media, the time dependence of the mean-square displacement shows log-periodic modulations around a leading power law, which can be understood on the basis of a hierarchical set of diffusion constants. Both the random walk exponent and the period of oscillations are analytically obtained for a pair of examples, one is fractal and the other is nonfractal, and confirmed by Monte Carlo simulations. The last example shows that the anomalous diffusion can arise from substrates without holes of all sizes.

  15. A search for periodic structure in solar 2 cm microwave radiation. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Sentman, D. D.

    1973-01-01

    A power spectral analysis of 285 hr of 2 cm microwave intensity data showed no statistically significant ( 96% confidence) periodicities in the frequency range 1 to 15 mHz. No correlation was found between 2 cm periodicities and solar activity in H alpha, X-ray, and several microwave frequencies. A small shift of power toward higher frequencies in the power spectrum of the 2 cm data was found to be correlated with solar H alpha and X-ray activity. Using the statistical properties of power spectra, an expression for the ratio of the minimum detectable peak-to-peak to ambient temperature at chromospheric heights may be derived. Applied to a model for oscillation bursts in quiescent supergranules, and using the most significant results of experiments to detect the microwave periodicities, this expression yields an upper limit of approximately .0015.

  16. Effects of Graded Levels of Montmorillonite on Performance, Hematological Parameters and Bone Mineralization in Weaned Pigs

    PubMed Central

    Duan, Q. W.; Li, J. T.; Gong, L. M.; Wu, H.; Zhang, L. Y.

    2013-01-01

    The aim of this study was to investigate the effects of graded levels of montmorillonite, a constituent of clay, on performance, hematological parameters and bone mineralization in weaned pigs. One hundred and twenty, 35-d-old crossbred pigs (Duroc×Large White×Landrace, 10.50±1.20 kg) were used in a 28-d experiment and fed either an unsupplemented corn-soybean meal basal diet or similar diets supplemented with 0.5, 1.0, 2.5 or 5.0% montmorillonite added at the expense of wheat bran. Each treatment was replicated six times with four pigs (two barrows and two gilts) per replicate. Feed intake declined (linear and quadratic effect, p< 0.01) with increasing level of montmorillonite while feed conversion was improved (linear and quadratic effect, p<0.01). Daily gain was unaffected by dietary treatment. Plasma myeloperoxidase declined linearly (p = 0.03) with increasing dietary level of montmorillonite. Plasma malondialdehyde and nitric oxide levels were quadratically affected (p<0.01) by montmorillonite with increases observed for pigs fed the 0.5 and 1.0% levels which then declined for pigs fed the 2.5 and 5.0% treatments. In bone, the content of potassium, sodium, copper, iron, manganese and magnesium were decreased (linear and quadratic effect, p<0.01) in response to an increase of dietary montmorillonite. These results suggest that dietary inclusion of montmorillonite at levels as high as 5.0% does not result in overt toxicity but could induce potential oxidative damage and reduce bone mineralization in pigs. PMID:25049749

  17. Spatial structure of periodicity in the conifer tree radial increment in the Republic of Komi

    NASA Astrophysics Data System (ADS)

    Raspopov, O. M.; Lopatin, E. V.; Kolström, T.; Dergachev, V. A.; Dmitriev, P. B.; Kahle, H.-P.; Spiecker, H.

    2013-12-01

    Spectral analysis of tree ring data sets of Siberian spruce ( Picea obovata) and Scots pine ( Pinus sylvestris L.) was carried out to study the effects of climatic factors on the conifer tree radial growth in the territory of the Komi Republic. Analyses were performed for different natural subzones in the Komi Republic: the forest-tundra transition zone and the northern, middle, and southern taiga. The results show that several groups of periodicities can be found in the tree radial growth. One from groups of periodicities is related to internal processes in the atmosphere-ocean system; the other is related to the fluctuations in solar activity.

  18. INTERACTION OF LASER RADIATION WITH MATTER: Formation of periodic structures upon laser ablation of metal targets in liquids

    NASA Astrophysics Data System (ADS)

    Kazakevich, Pavel V.; Simakin, Aleksandr V.; Shafeev, Georgii A.

    2005-09-01

    Experimental data on the formation of ordered microstructures produced upon ablation of metal targets in liquids irradiated by a copper vapour laser or a pulsed Nd:YAG laser are presented. The structures were obtained on brass, bronze, copper, and tungsten substrates immersed in distilled water or ethanol. As a result of multiple-pulse laser ablation by a scanning beam, ordered microcones with pointed vertexes are formed on the target surface. The structures are separated by deep narrow channels. The structure period was experimentally shown to increase linearly with diameter of the laser spot on the target surface.

  19. Laser-induced periodic structures for light extraction efficiency enhancement of GaN-based light emitting diodes.

    PubMed

    Chen, Jiun-Ting; Lai, Wei-Chih; Kao, Yu-Jui; Yang, Ya-Yu; Sheu, Jinn-Kong

    2012-02-27

    The laser-induced periodic surface structure technique was used to form simultaneously dual-scale rough structures (DSRS) with spiral-shaped nanoscale structure inside semi-spherical microscale holes on p-GaN surface to improve the light-extraction efficiency of light-emitting diodes (LEDs). The light output power of DSRS-LEDs was 30% higher than that of conventional LEDs at an injection current of 20 mA. The enhancement in the light output power could be attributed to the increase in the probability of photons to escape from the increased surface area of textured p-GaN surface.

  20. Nanoscaled periodic surface structures of medical stainless steel and their effect on osteoblast cells.

    PubMed

    Elter, Patrick; Sickel, Franka; Ewald, Andrea

    2009-06-01

    Nanoscaled lamellar surface structures have been prepared on medical stainless steel AISI 316LVM surfaces by chemical etching of the decomposed phases. The effect of this structure on osteoblastic cells has been investigated. Long filopodia were developed by the cells perpendicular to the lamellar structure while almost no or only short filopodia were formed parallel to the lamellae. These results are explained in terms of a topographical influence of the nanostructure. During the growth process of the filopodia a nearly flat surface was recognized parallel to the lamellae while a topographical change was sensed perpendicular to the structure, which was preferred by the cells.

  1. First principles simulation of laser-induced periodic surface structure using the particle-in-cell method

    NASA Astrophysics Data System (ADS)

    Mitchell, Robert A.; Schumacher, Douglass W.; Chowdhury, Enam A.

    2015-11-01

    We present our results of a fundamental simulation of a periodic grating structure formation on a copper target during the femtosecond-pulse laser damage process, and compare our results to recent experiment. The particle-in-cell (PIC) method is used to model the initial laser heating of the electrons, a two-temperature model (TTM) is used to model the thermalization of the material, and a modified PIC method is employed to model the atomic transport leading to a damage crater morphology consistent with experimental grating structure formation. This laser-induced periodic surface structure (LIPSS) is shown to be directly related to the formation of surface plasmon polaritons (SPP) and their interference with the incident laser pulse.

  2. Comment on ``Steady-state properties of a totally asymmetric exclusion process with periodic structure''

    NASA Astrophysics Data System (ADS)

    Jiang, Rui; Hu, Mao-Bin; Wu, Qing-Song

    2008-07-01

    Lakatos [Phys. Rev. E 71, 011103 (2005)] have studied a totally asymmetric exclusion process that contains periodically varying movement rates. They have presented a cluster mean-field theory for the problem. We show that their cluster mean-field theory leads to redundant equations. We present a mean-field analysis in which there is no redundant equation.

  3. Powerful surface-wave oscillators with two-dimensional periodic structures

    SciTech Connect

    Ginzburg, N. S.; Zaslavsky, V. Yu.; Malkin, A. M.; Sergeev, A. S.

    2012-04-02

    We propose planar relativistic surface-wave oscillators with two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from the wide sheet rectilinear electron beam which allows realizing a Cherenkov millimeter wave oscillator with gigawatt output power.

  4. Dynamics of Vortices in Nano-Structured Superconductors with Periodic Arrays of Various Antidots

    NASA Astrophysics Data System (ADS)

    Fujibayashi, David E.; Kato, Masaru

    2012-12-01

    Stable vortex configurations and its dynamics in superconductors with various types of antidotes are examined, using the molecular dynamics simulation. A pinning potential function, which parameterizes spatial shapes and pinning potential structure of the antidot, is introduced. Dependence of saturation number, which is a maximum number of vortices pinned in a single antidot, on these spatial shape and potential structure are investigated.

  5. Electrochemical energy storage in montmorillonite K10 clay based composite as supercapacitor using ionic liquid electrolyte.

    PubMed

    Maiti, Sandipan; Pramanik, Atin; Chattopadhyay, Shreyasi; De, Goutam; Mahanty, Sourindra

    2016-02-15

    Exploring new electrode materials is the key to realize high performance energy storage devices for effective utilization of renewable energy. Natural clays with layered structure and high surface area are prospective materials for electrical double layer capacitors (EDLC). In this work, a novel hybrid composite based on acid-leached montmorillonite (K10), multi-walled carbon nanotube (MWCNT) and manganese dioxide (MnO2) was prepared and its electrochemical properties were investigated by fabricating two-electrode asymmetric supercapacitor cells against activated carbon (AC) using 1.0M tetraethylammonium tetrafluroborate (Et4NBF4) in acetonitrile (AN) as electrolyte. The asymmetric supercapacitors, capable of operating in a wide potential window of 0.0-2.7V, showed a high energy density of 171Whkg(-1) at a power density of ∼1.98kWkg(-1). Such high EDLC performance could possibly be linked to the acid-base interaction of K10 through its surface hydroxyl groups with the tetraethylammonium cation [(C2H5)4N(+) or TEA(+)] of the ionic liquid electrolyte. Even at a very high power density of 96.4kWkg(-1), the cells could still deliver an energy density of 91.1Whkg(-1) exhibiting an outstanding rate capability. The present study demonstrates for the first time, the excellent potential of clay-based composites for high power energy storage device applications.

  6. Total mineralization of sulfamethoxazole and aromatic pollutants through Fe2+-montmorillonite catalyzed ozonation.

    PubMed

    Shahidi, Dariush; Moheb, Amira; Abbas, Rabah; Larouk, Safa; Roy, René; Azzouz, Abdelkrim

    2015-11-15

    The catalytic activity and selectivity of montmorillonite exchanged with Na(+), Fe(2+), Co(2+), Ni(2+) and Cu(2+) cations were comparatively investigated in the ozonation of sulfamethoxazole (SMX). Chlorobenzene, benzoic acid, 4-nitrobenzoic acid, 3-hydroxybenzaldehyde, 4-nitrophenol and phenol were used as probe molecules having structural similarity with SMX oxidation intermediates. UV-vis spectrophometry and chemical oxygen demand (COD) measurements showed that Fe(II)-Mt and, to a lesser extent, Co(II)-Mt produce total mineralization of all organic substrates in less than 40 min. Combined HPLC-mass spectrometry revealed a reverse proportionality between the degradation time and molecular size of the organic substrates. Oxalic acid was recognized as a common bottleneck in the ozonation of any organic substrates. Ozonation initially obeyed a first order kinetics, but adsorption took place after 3-5 min, inducing changes in the mechanisms pathways. These findings may be useful for tailoring optimum oxidative treatment of waters without accumulation of hazardous derivatives.

  7. Ultrasonic treatment and synthesis of sugar alcohol modified Na+-montmorillonite clay.

    PubMed

    Chaudhary, Deeptangshu; Liu, Huihua

    2013-01-01

    Na(+)-montmorillonite clay (generally referred to as MMT) is very useful for reinforcing polymeric matrix at very low concentrations (typically, 2-5% wt). These clay particles are typically exfoliated before they can demonstrate the significant gains in heat deflection temperature, modulus, and elongation properties. In the case of hydrophilic biopolymer based matrices, such as carbohydrates and chitosan, exfoliating these nanoclay particles needs greater attention because the exfoliation is typically carried out using hydrophobic oligomers through ion-exchange. This study reports a new method of synthesizing completely hydrophilic MMT-assemblages using hydrophilic plasticizers for biopolymers. We used sugar alcohols (glycerol, xylitol with 3 and 5 hydroxyl groups) and polysaccharide maltodextrin to exfoliate the MMT. Sonication was conducted for MMT nanoclay and plasticizers at different weight ratios. It was confirmed that all plasticizer/modifier led to expansion of MMT gallery spacing (d-spacing) and the change in d-spacing could be related to the molecular structure of the plasticizer. Meanwhile, the extent of exfoliation was maximum with maltodextrin (fully exfoliation with 1:10 and 1:20 ratio of MMT:plasticizer) across all test samples and interestingly, glycerol and xylitol samples quickly established within the MMT galleries and exhibited minimal influence with further increase in relative concentrations.

  8. Biodegradable gelatin-ciprofloxacin-montmorillonite composite hydrogels for controlled drug release and wound dressing application.

    PubMed

    Kevadiya, Bhavesh D; Rajkumar, Shalini; Bajaj, Hari C; Chettiar, Shiva Shankaran; Gosai, Kalpeshgiri; Brahmbhatt, Harshad; Bhatt, Adarsh S; Barvaliya, Yogesh K; Dave, Gaurav S; Kothari, Ramesh K

    2014-10-01

    This work reports intercalation of a sparingly soluble antibiotic (ciprofloxacin) into layered nanostructure silicate, montmorillonite (MMT) and its reaction with bone derived polypeptide, gelatin that yields three-dimensional composite hydrogel. Drug intercalation results in changes in MMT layered space and drug loaded MMT and gelatin creates 3D morphology with biodegradable composite hydrogels. These changes can be correlated with electrostatic interactions between the drug, MMT and the gelatin polypeptides as confirmed by X-ray diffraction patterns, thermal, spectroscopic analyses, computational modeling and 3D morphology revealed by SEM and TEM analysis. No significant changes in structural and functional properties of drug was found after intercalation in MMT layers and composite hydrogels. In vitro drug release profiles showed controlled release up to 150h. The drug loaded composite hydrogels were tested on lung cancer cells (A549) by MTT assay. The results of in vitro cell migration and proliferation assay were promising as composite hydrogels induced wound healing progression. In vitro biodegradation was studied using proteolytic enzymes (lysozyme and protease K) at physiological conditions. This new approach of drug intercalation into the layered nanostructure silicate by ion-exchange may have significant applications in cost-effective wound dressing biomaterial with antimicrobial property.

  9. Sequence Analysis of Trimer Isomers Formed by Montmorillonite Catalysis in the Reaction of Binary Monomer Mixtures

    NASA Astrophysics Data System (ADS)

    Ertem, Gözen; Hazen, Robert M.; Dworkin, Jason P.

    2007-10-01

    Oligonucleotides are structurally similar to short RNA strands. Therefore, their formation via non-enzymatic reactions is highly relevant to Gilbert's RNA world scenario (1986) and the origin of life. In laboratory synthesis of oligonucleotides from monomers, it is necessary to remove the water molecules from the reaction medium to shift the equilibrium in favor of oligonucleotide formation, which would have been impossible for reactions that took place in dilute solutions on the early Earth. Model studies designed to address this problem demonstrate that montmorillonite, a phyllosilicate common on Earth and identified on Mars, efficiently catalyzes phosphodiester-bond formation between activated mononucleotides in dilute solutions and produces RNA-like oligomers. The purpose of this study was to examine the sequences and regiospecificity of trimer isomers formed in the reaction of 5'-phosphorimidazolides of adenosine and uridine. Results demonstrated that regiospecificity and sequence specificity observed in the dimer fractions are conserved in their elongation products. With regard to regiospecificity, 61% of the linkages were found to be RNA-like 3',5'-phosphodiester bonds. With regard to sequence specificity, we found that 88% of the linear trimers were hetero-isomers with 61% A-monomer and 39% U-monomer incorporation. These results lend support to Bernal's hypothesis that minerals may have played a significant role in the chemical processes that led to the origin of life by catalyzing the formation of phosphodiester bonds in RNA-like oligomers.

  10. A novel material of cross-linked styrylpyridinium salt intercalated montmorillonite for drug delivery

    PubMed Central

    2014-01-01

    A facile synthesis of a styrylpyridinium salt (SbQ)/montmorillonite (MMT) via cationic exchange interactions between styrylpyridinium species (specifically SbQ) and MMT platelets is reported in this work. The SbQ-MMT solutions were irradiated under ultraviolet (UV) light for a specific time to obtain the cross-linked SbQ-MMT materials. Scanning electron microscopy and atomic force microscopy analyses revealed the structures and morphologies of MMT and modified MMT. X-ray diffraction and transmission electron microscope analyses indicated that the basal spacing increased from 1.24 to 1.53 nm compared with the pristine MMT, which proved that SbQ had interacted with MMT. Thermal gravimetric analysis curves showed that the amount of SbQ in the MMT interlayers was 35.71 meq/100 g. Fourier transform infrared spectroscopy also confirmed the intercalation of SbQ species into MMT interlayers, and UV spectroscopy was used to follow up the cross-linking of SbQ-MMT. This novel material has potential applications in drug delivery, and it can also be used as an additive to improve the mechanical properties of polymers. PMID:25170328

  11. Chitosan-Montmorillonite Polymer Composites: Formulation and Evaluation of Sustained Release Tablets of Aceclofenac

    PubMed Central

    Thakur, Garima; Singh, Amrinder; Singh, Inderbir

    2015-01-01

    The present study reports the preparation and evaluation of polymer composites of chitosan and montmorillonite. The prepared polymer composites were evaluated for various powder properties and characterized by FTIR-ATR (Fourier Transform Infrared Spectroscopy- Attenuated Total Reflectance), XRD (X Ray Diffraction), and SEM (Scaning Electron Microscopy) techniques. Heckel and Kawakita equations indicated good compression characteristics of the composites. The polymer composites were employed in formulating sustained release tablets of aceclofenac. The formation of intercalated lamellar structures due to the entrapment of clay particles in the polymeric matrix network was found to be responsible for the drug release retardant behavior of the composites. The in vitro drug release data were fitted to various models like zero-order, first-order, Higuchi, Korsmeyer-Peppas, and Hixon and Crowell for studying the mechanism of drug release from the formulation. The value of release exponent (n) was found to range between 0.59 and 0.82, indicating non-Fickian (anomalous) drug release behavior. Swelling-induced diffusion of the drug through the polymer matrix and polymer matrix chain relaxation appeared to play a role in the release of the drug from the polymer composites.

  12. Formulation and evaluation of transdermal composite films of chitosan-montmorillonite for the delivery of curcumin

    PubMed Central

    Thakur, Garima; Singh, Amrinder; Singh, Inderbir

    2016-01-01

    Composite transdermal films of chitosan (CS)/montmorillonite K 10 (MMT) clay were prepared for the delivery of curcumin. CS/MMT films were evaluated for various physicochemical parameters. The films were characterized by Fourier transform infrared spectroscopy and X-ray diffraction analysis. Water uptake and swelling ratio of the films was found to decrease with increase in concentration of clay. Mechanical properties of the films were assessed in terms of tensile strength and extensibility using texture analyzer. Increase in tensile strength and reduction in extensibility was reported with increase in the clay content. This was attributed to the formation of intercalated structure and restriction in mobility of CS polymeric chains with the inclusion of clay particles. In vitro drug release study on transdermal films indicated pronounced sustained release of curcumin by the incorporation of clay particles in the CS polymer matrix. Stability study indicated no significant effect on physicochemical properties of films kept at 40°C and 75% RH for 3 months. Overall CS/MMT composite transdermal films exhibited improved mechanical and sustained drug release properties. PMID:27014616

  13. Encaging Palladium Nanoparticles in Chitosan Modified Montmorillonite for Efficient, Recyclable Catalysts.

    PubMed

    Zeng, Minfeng; Wang, Yudong; Liu, Qi; Yuan, Xia; Zuo, Shufeng; Feng, Ruokun; Yang, Jing; Wang, Baoyi; Qi, Chenze; Lin, Yao

    2016-12-07

    Metal nanoparticles, once supported by a suitable scaffolding material, can be used as highly efficient heterogeneous catalysts for numerous organic reactions. The challenge, though, is to mitigate the continuous loss of metals from the supporting materials as reactions proceed, so that the catalysts can be recycled multiple times. Herein, we combine the excellent chelating property of chitosan (CS) and remarkable stability of montmorillonite (MMT) into a composite material to support metal catalysts such as palladium (Pd). The in situ reduction of Pd(2+) into Pd(0) in the interstices of MMT/CS composites effectively encages the Pd(0) nanoparticles in the porous matrices, while still allowing for reactant and product molecules of relatively small sizes to diffuse in and out the matrices. The prepared Pd(0)@MMT/CS catalysts are highly active for the Heck reactions of aromatic halides and alkenes, and can be recycled 30 times without significant loss of activities. Positron annihilation lifetime analysis and other structural characterization methods are implemented to elucidate the unique compartmentalization of metal catalysts in the composite matrices. As both CS and MMT are economical and abundant materials in nature, this approach may facilitate a versatile platform for developing highly recyclable, heterogeneous catalysts containing metal nanoparticles.

  14. The disinfection performance and mechanisms of Ag/lysozyme nanoparticles supported with montmorillonite clay.

    PubMed

    Jiang, Jing; Zhang, Chang; Zeng, Guang-Ming; Gong, Ji-Lai; Chang, Ying-Na; Song, Biao; Deng, Can-Hui; Liu, Hong-Yu

    2016-11-05

    The fabrication of montmorillonite (Mt) decorated with lysozyme-modified silver nanoparticles (Ag/lyz-Mt) was reported. The lysozyme (lyz) was served as both reducing and capping reagent. Coupling the bactericidal activity of the lyz with AgNPs, along with the high porous structure and large specific surface area of the Mt, prevented aggregation of AgNPs and promoted nanomaterial-bacteria interactions, resulting in a greatly enhanced bactericidal capability against both Gram positive and Gram negative bacteria. This paper systematically elucidated the bactericidal mechanisms of Ag/lyz-Mt. Direct contact between the Ag/lyz-Mt surface and the bacterial cell was essential to the disinfection. Physical disruption of bacterial membrane was considered to be one of the bactericidal mechanisms of Ag/lyz-Mt. Results revealed that Ag(+) was involved in the bactericidal activity of Ag/lyz-Mt via tests conducted using Ag(+) scavengers. A positive ROS (reactive oxygen species) scavenging test indirectly confirmed the involvement of ROS (O2(-), H2O2, and OH) in the bactericidal mechanism. Furthermore, the concentrations of individual ROS were quantified. Results showed that Ag/lyz-Mt nanomaterial could be a promising bactericide for water disinfection.

  15. Peculiar magnetism of BiFeO3 nanoparticles with size approaching the period of the spiral spin structure

    PubMed Central

    Huang, Fengzhen; Wang, Zhijun; Lu, Xiaomei; Zhang, Junting; Min, Kangli; Lin, Weiwei; Ti, Ruixia; Xu, TingTing; He, Ju; Yue, Chen; Zhu, Jinsong

    2013-01-01

    Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO3)? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO3 nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO3 nanoparticles. Our result provides another insight into the size effect of BiFeO3, and also a clue to the magnetic structure at nanoscale. PMID:24105027

  16. Syngap1 haploinsufficiency damages a postnatal critical period of pyramidal cell structural maturation linked to cortical circuit assembly

    PubMed Central

    Aceti, Massimiliano; Creson, Thomas K.; Vaissiere, Thomas; Rojas, Camilo; Huang, Wen-Chin; Wang, Ya-Xian; Petralia, Ronald S.; Page, Damon T.; Miller, Courtney A.; Rumbaugh, Gavin

    2014-01-01

    Background Genetic haploinsufficiency of Syngap1 commonly occurs in developmental brain disorders, such as intellectual disability (ID), epilepsy, schizophrenia (SCZ), and autism spectrum (ASD) disorder. Thus, studying mouse models of Syngap1 haploinsufficiency may uncover pathological developmental processes common among distinct brain disorders. Methods A Syngap1 haploinsufficiency model was used to explore the relationship between critical period dendritic spine damage, cortical circuit assembly and the window for genetic rescue in order to understand how damaging mutations disrupt key substrates of mouse brain development. Results Syngap1 mutations broadly disrupted a developmentally sensitive period that corresponded to the period of heightened postnatal cortical synaptogenesis. Pathogenic Syngap1 mutations caused a coordinated acceleration of dendrite elongation and spine morphogenesis, and pruning of these structures in neonatal cortical pyramidal neurons. These mutations also prevented a form of developmental structural plasticity associated with experience-dependent reorganization of brain circuits. Consistent with these findings, Syngap1 mutant mice displayed an altered pattern of long-distance synaptic inputs into a cortical area important for cognition. Interestingly, the ability to genetically improve the behavioral endophenotype of Syngap1 mice decreased slowly over postnatal development and mapped onto the developmental period of coordinated dendritic insults. Conclusions Pathogenic Syngap1 mutations have a profound impact on the dynamics and structural integrity of pyramidal cell postsynaptic structures known to guide the de novo wiring of nascent cortical circuits. These findings support the idea that disrupted critical periods of dendritic growth and spine plasticity may be a common pathological process in developmental brain disorders. PMID:25444158

  17. Multiple periodic solutions of a delayed predator-prey model with non-monotonic functional response and stage structure.

    PubMed

    Liu, Yingyuan; Zhang, Xiaolan; Zhou, Tiejun

    2014-01-01

    The paper studies a periodic and delayed predator-prey system with non-monotonic functional responses and stage structure. In the system, both the predator and prey are divided into immature individuals and mature individuals by two fixed ages. It is assumed that the immature predators cannot attack preys, and the case of the mature predators attacking the immature preys is also ignored. Based on Mawhin's coincidence degree, sufficient conditions are obtained for the existence of two positive periodic solutions of the system. An example is presented to illustrate the feasibility of the main results.

  18. Effect of sonication on the particle size of montmorillonite clays.

    PubMed

    Poli, Alessandra L; Batista, Tatiana; Schmitt, Carla C; Gessner, Fergus; Neumann, Miguel G

    2008-09-15

    This paper reports on the effect of sonication on SAz-1 and SWy-1 montmorillonite suspensions. Changes in the size of the particles of these materials and modifications of their properties have been investigated. The variation of the particle size has been analyzed by DLS (dynamic light scattering). In all cases the clay particles show a bimodal distribution. Sonication resulted in a decrease of the larger modal diameter, as well as a reduction of its volume percentage. Simultaneously, the proportion of the smallest particles increases. After 60 min of sonication, SAz-1 presented a very broad particle size distribution with a modal diameter of 283 nm. On the other hand, the SWy-1 sonicated for 60 min presents a bimodal distribution of particles at 140 and 454 nm. Changes in the properties of the clay suspensions due to sonication were evaluated spectroscopically from dye-clay interactions, using Methylene Blue. The acidic sites present in the interlamellar region, which are responsible for dye protonation, disappeared after sonication of the clay. The changes in the size of the scattering particles and the lack of acidic sites after sonication suggest that sonication induces delamination of the clay particles.

  19. Insights into asphaltene aggregation in the Na-montmorillonite interlayer.

    PubMed

    Zhu, Xinzhe; Chen, Daoyi; Wu, Guozhong

    2016-10-01

    This study aimed to provide insights into the diffusion and aggregation of asphaltenes in the Na-montmorillonite (MMT) interlayer with dif