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Sample records for periodically structured montmorillonite

  1. Effects of water on the structure and bonding of resorcinol in the interlayer of montmorillonite nanocomposite: a periodic first principle study.

    PubMed

    Chatterjee, Abhijit; Ebina, Takeo; Mizukami, Fujio

    2005-04-21

    Resorcinol forms a novel nanocomposite in the interlayer of montmorillonite. This resorcinol oligomer is stable inside the clay matrixes even above the boiling point of the monomer. A periodic ab initio calculation was performed with hydrated and nonhydrated montmorillonite before and after intercalation of resorcinol. For the most feasible dimer and tetramer shaped oligomer of resorcinol, the intramolecular and intermolecular hydrogen bonding feasibility has been tested using the DFT-BLYP approach and the DNP basis set in the gas phase and in the presence of aqueous solvent. After locating the active site through Fukui functions within the helm of the hard-soft acid-base principle, the relative nucleophilicity of the active cation sites in their hydrated state has been calculated. A novel quantitative scale in terms of the relative nucleophilicity and electrophilicity of the interacting resorcinol oligomers before and after solvation is proposed. Besides that, a comparison with a hydration situation and also the strength of the hydrogen bridges have been evaluated using mainly the dimer and cyclic tetramer type oligomers of resorcinol. Using periodic ab initio calculations, the formation mechanism was traced by the following two ways: (1) resorcinol molecules combine without any interaction with water or (2) resorcinol oligomerizes through water. Both the mechanism is compared and the effect of water on the process is elucidated. The results show that resorcinol molecules combine after hydration only and hence they are stable at higher temperature. The fittings of the oligomers were also tested as well by periodic calculation to compare the stability of the oligomers inside the newly formed clay nanocomposite. PMID:16851836

  2. Structural properties of reduced Upton montmorillonite

    NASA Astrophysics Data System (ADS)

    Gates, W. P.; Stucki, J. W.; Kirkpatrick, R. J.

    1996-12-01

    Reduction of octahedral Fe in the crystalline structure of smectites influences, possibly controls, surface-sensitive physical and chemical properties. The purpose of this study was to investigate if reduction of structural Fe by Na-dithionite or bacteria affects the chemical environment of constituent cations in montmorillonite, employing solid state multinuclear (29Si and 27Al) magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Reduction of structural Fe resulted in a positive (down field) chemical shift of the main Si Q3 (Q3(0Al)) site which was strongly correlated with Fe(II) content and inferred that distortions in Si-OT (T=Si, Al) bond angles and Si-O bond lengths occur with increasing layer charge. The line width (W) of the 29Si Q3 signal also increased with increasing levels of reduction. No change occurred in the position of the peak maximum for the octahedral Al (27AlVI) signal; however, an increased W was observed for this peak with increasing Fe(II) content. These results are attributed to decreases in Si-O-T bond angles and Si-O bond distances, corresponding to a better fit between the tetrahedral and octahedral sheets brought about by the presence of Fe(II) in the clay structure. The increased 27AlVI signal width (W) may also be due to a lessening of the paramagnetic influence of Fe(III) nuclei and enhancement of 27AlVI signals with different quadrupole coupling constants (QCC). Multinuclear MAS NMR analyses of dithioniteand microbially-reduced montmorillonite indicate that reduction of structural Fe caused reversible changes in the smectite structure, at least as far as this method could discern.

  3. 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.

  4. 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

  5. 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

  6. The structure of montmorillonites modified with zwitterionic surfactants and their sorption ability

    NASA Astrophysics Data System (ADS)

    Zhu, Jianxi; Qing, Yanhong; Ma, Lingya; Zhu, Runliang; He, Hongping

    2015-06-01

    In this work, a novel organo-clays, zwitterionic surfactant modified montmorillonites (ZSMMs) were synthesized by using sulphobetaine and montmorillonites. The structures of ZSMMs were characterized by X ray diffraction (XRD) methods; the surfactant loading levels were measured by Total organic carbon (TOC) analysis, and their sorptive characteristics toward p-nitrophenol and nitrobenzene were investigated. XRD and TOC measurements indicated that the amount of adsorbed surfactants and the basal spacing of the ZSMMs increase with alkyl chain length and surfactant concentration. Sorption experiments showed that the capacity of p-nitrophenol to sorb onto the ZSMMs is higher than that of nitrobenzene. Both capacities increase with surfactant loading level; However, sorption capacity decreases when the surfactant concentration is higher than 2.0 CEC. Under the same surfactant loading level, the sorption capacities of p-nitrophenol and nitrobenzene increase with alkyl chain length. Under this experimental condition, the longer alkyl chain leads to a higher sorption capacity for hydrophobic organic compounds. On the basis of the ability of p-nitrophenol and nitrobenzene to sorb onto the montmorillonites, we conclude that the contaminant sorption coefficients, normalized with organic carbon content, highly depend on surfactant loading levels.

  7. Electrospun dual-porosity structure and biodegradation morphology of Montmorillonite reinforced PLLA nanocomposite scaffolds.

    PubMed

    Lee, Yun Hui; Lee, Jong Hoon; An, In-Gu; Kim, Chan; Lee, Doo Sung; Lee, Young Kwan; Nam, Jae-Do

    2005-06-01

    Combining a nanocomposite technique and the electrospinning process, a robust dual-porosity scaffold structure was developed for a facile transport of metabolic nutrients and wastes through the nano-sized pores and for the cell implantation and blood vessel invasion through the micro-sized pores. The montmorillonite (MMT) nano-sized platelets were incorporated into poly(L-lactic acid) (PLLA) solution, which was subsequently electrospun and mechanically entangled by a cold compression molding process for a robust 3-dimensional scaffold structure. Using a salt leaching/gas forming method, micro-sized pores were developed in the electrospun fiber bundles giving a dual-porosity scaffold structure. Compared with the pristine PLLA scaffold, the developed nanocomposite fibrous scaffold structure exhibited increased strength and improved structural integrity during the biodegradation process. The nanocomposite scaffold systems also exhibited many tiny pinholes desirably generated on the scaffold walls without serious fragmentation during biodegradation reactions. PMID:15603811

  8. 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.

  9. 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.

  10. The structure of montmorillonite gels revealed by sequential cryo-XHR-SEM imaging.

    PubMed

    Mouzon, Johanne; Bhuiyan, Iftekhar U; Hedlund, Jonas

    2016-03-01

    Imaging by extreme high resolution-scanning electron microscopy (XHR-SEM) with a monochromated and decelerated beam was applied on 5% (wt/wt) Na and Ca-montmorillonite gels frozen by high pressure freezing (HPF). In order to visualize the three-dimensional structure and the contacts between clay platelets, a new approach was developed. It consists in recording a sequence of micrographs on a region of interest during controlled sublimation. This simple method allows to rewind and to relate the instantaneous configuration between several particles to their original position in the hydrated state. Consequently, aggregates of parallel platelets (i.e. curved tactoids) were present in the Ca-sample and the instantaneous position of these aggregates in the course of sedimentation was revealed. The Na-sample consisted of a continuous network of flexible platelets sharing mostly face-to-face (FF) contacts caused by jamming at the relatively high concentration of the suspension (5% (wt/wt)), which was above the gel transition. Yet individual platelets belonging to the smallest size fraction were observed to be fully dispersed within the entangled structure, which confirmed the repulsive character of the gel. Substructures consisting of several platelets connected by FF-associations were also evidenced. The origin and potential impact of such substructures on the occurrence of the sol-gel transition and birefringence are discussed. PMID:26641566

  11. Effect of pullulan/poly(vinyl alcohol) blend system on the montmorillonite structure with property characterization of electrospun pullulan/poly(vinyl alcohol)/montmorillonite nanofibers.

    PubMed

    Islam, Md Shahidul; Yeum, Jeong Hyun; Das, Ajoy Kumar

    2012-02-15

    Nanofibers of the composite of pullulan (PULL), poly(vinyl alcohol) (PVA), and montmorillonite clay (MMT) were prepared using electrospinning method in aqueous solutions. Pullulan is an interesting natural polymer for many of its merits and good properties. Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were done to characterize the PULL/PVA/MMT nanofibers morphology and properties. XRD patterns and FTIR data demonstrated that there were good interactions between PULL and PVA caused by possibly hydrogen bonds. Moreover, XRD data and TEM images indicated that intercalated and exfoliated MMT nanoplatelets can be obtained within the PULL/PVA/MMT nanofibers depending on the PULL/PVA blend ratios. Furthermore, the thermal stability and mechanical property (tensile strength) of PULL/PVA/MMT nanofibers could be enhanced more by exfoliated MMT nanoplatelets than intercalated structures of that nanoplatelets. PMID:22172694

  12. Structure modification of montmorillonite nanoclay by surface coating with soy protein.

    PubMed

    Jin, Minfeng; Zhong, Qixin

    2012-12-01

    To achieve exfoliated and/or intercalated structures, montmorillonite (MMT) was surface-coated by soy protein at 60 °C, at MMT/soy protein powder mass ratios of 49:1, 9:1, 4:1, and 2:1 and pH 2.0-10.0. The protein-coated MMT was triple-washed and lyophilized for characterization. Protein coating was observed at all pH conditions, based on data from X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential, and quantification of protein remaining in the continuous phase and present in the triple-washed MMT. At a mass ratio of 4:1, >90% protein bound with MMT, with the largest d-spacing at pH 9.0. When the mass ratio was increased to 2:1, protein-coated MMT at pH 9.0 demonstrated the highest degree of intercalation/exfoliation, corresponding to disappearance of the diffraction peak characteristic of pristine MMT. This study thus demonstrated that intercalation/exfoliation of MMT can be easily achieved by coating with low-cost soy protein for manufacturing nanocomposite materials. PMID:23163488

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

    PubMed

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

    2012-07-01

    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. PMID:22642874

  14. 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.

  15. 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

  16. Doubly Resonant Optical Periodic Structure.

    PubMed

    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

  17. 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

  18. Integrating structural and thermodynamic mechanisms for sorption of PCBs by montmorillonite.

    PubMed

    Liu, Cun; Gu, Cheng; Yu, Kai; Li, Hui; Teppen, Brian J; Johnston, Cliff T; Boyd, Stephen A; Zhou, Dongmei

    2015-03-01

    Strong sorption of planar nonionic organic chemicals by clay minerals has been observed for important classes of organic contaminants including polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and dioxins, and such affinity was hypothesized to relate to the interlayer hydrophobicity of smectite clays. In batch sorption experiments of two trichlorobiphenyls on homoionic Na-, K-, Cs-montmorillonites, considerably greater sorption coefficient (Kw) was observed for coplanar 3,3',5-trichlorobiphenyl (PCB 36); log Kw for Na-, K-, and Cs-montmorillonite were 3.69, 3.72, and 4.53 for coplanar PCB 36 vs 1.21, 1.46, and 0.87 for the nonplanar 2,2',6-trichlorobiphenyl (PCB 19). MD simulations were conducted utilizing X-ray diffraction determined clay interlayer distances (d-spacing). The trajectory, density distribution, and radial distribution function of interlayer cation, water, and PCBs collectively indicated that the hydrophobic nature of the interlayer regions was determined by the hydration status of exchangeable cations and the associated d-spacing. The sorption free energies calculated for both coplanar and nonplanar PCB molecules by adaptive biasing force (ABF) method with an extended interlayer-micropore two-phase model consisting of cleaved clay hydrates and "bulk water" are consistent with the Gibbs free energies derived from the measured log Kw, manifesting enhanced sorption of coplanar PCBs was attributed to shape selectivity and hydrophobic interactions. PMID:25629399

  19. Modeling the Adsorption of Oxalate onto Montmorillonite.

    PubMed

    Ramos, M Elena; Emiroglu, Caglayan; García, David; Sainz-Díaz, C Ignacio; Huertas, F Javier

    2015-11-01

    In this work, a multiscale modeling of the interaction of oxalate with clay mineral surfaces from macroscale thermodynamic equilibria simulations to atomistic calculations is presented. Previous results from macroscopic adsorption data of oxalate on montmorillonite in 0.01 M KNO3 media at 25 °C within the pH range from 2.5 to 9 have been used to develop a surface complexation model. The experimental adsorption edge data were fitted using the triple-layer model (TLM) with the aid of the FITEQL 4.0 computer program. Surface complexation of oxalate is described by two reactions: >AlOH + Ox(2-) + 2H(+) = >AlOxH + H2O (log K = 14.39) and >AlOH + Ox(2-) + H(+) = >AlOx(-) + H2O (log K = 10.39). The monodentate complex >AlOxH dominated adsorption below pH 4, and the bidentate complex >AlOx(-) was predominant at higher pH values. Both of the proposed inner-sphere oxalate species are qualitatively consistent with previously published diffuse reflectance FTIR spectroscopic results for oxalate on montmorillonite edge surface (Chem. Geol. 2014, 363, 283-292). Atomistic computational studies have been performed to understand the interactions at the molecular level between adsorbates and mineral surface, showing the atomic structures and IR frequency shifts of the adsorption complexes of oxalate with the edge surface of a periodic montmorillonite model. PMID:26444928

  20. On composites with periodic structure

    NASA Technical Reports Server (NTRS)

    Nemat-Nasser, S.; Iwakuma, T.; Hejazi, M.

    1982-01-01

    The overall moduli of a composite with an isotropic elastic matrix containing periodically distributed (anisotropic) inclusions or voids, can be expressed in terms of several infinite series which only depend on the geometry of the inclusions or voids, and hence can be computed once and for all for given geometries. For solids with periodic structures these infinite series play exactly the same role as does Eshelby's tensor for a single inclusion or void in an unbounded elastic medium. For spherical and circular-cylindrical geometries, the required infinite series are calculated and the results are tabulated. These are then used to estimate the overall elastic moduli when either the overall strains or the overall stresses are prescribed, obtaining the same results. These results are compared with other estimates and with experimental data. It is found that the model of composites with periodic structure yields estimates in excellent agreement with the experimental observations.

  1. 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.

  2. 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. PMID:21932797

  3. 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. PMID:25322875

  4. 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. PMID:25965492

  5. 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

    2015-02-01

    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, (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. PMID:25459719

  6. 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.

  7. 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. PMID:26254868

  8. Dispersibility of Amphibious Montmorillonite

    NASA Astrophysics Data System (ADS)

    Yeh, Meng-Heng; Hwang, Weng-Sing; Kuo, Wuei-Jueng

    2005-09-01

    The objective of this study is to develop a suitable method to convert hydrophilic montmorillonite into amphibious montmorillonite by replacing the sodium ions normally found in clay with poly(oxyethylene) (POE)-amide chlorite cations. Amphibious montmorillonite has a high d-spacing and good dispersion characteristics in many different types of solutions, including those having an intermediate hydrophilic lipophilic balance (HLB) value. Four different modifying cations are tested and X-ray diffraction analysis is performed to measure the resulting changes in the d-spacing of the MMT. Scanning electron microscopy is employed to investigate the morphology of the modified clays. A laser-doppler particle analyzer is used to measure the particle size of the clays in various solutions. Dobrat’s method is applied to calculate the dispersibility of each clay and Stoke’s law is used to evaluate the settling rate. The results indicate that the d-spacing of the POE-amide chlorite cation modified montmorillonite increases from 1.28 to 3.51 nm. The amphibious montmorillonite demonstrates good dispersion characteristics in eight commonly employed coating solutions with intermediate HLB values.

  9. 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.

  10. Sorption of trivalent lanthanides and actinides onto montmorillonite: Macroscopic, thermodynamic and structural evidence for ternary hydroxo and carbonato surface complexes on multiple sorption sites.

    PubMed

    Fernandes, M Marques; Scheinost, A C; Baeyens, B

    2016-08-01

    The credibility of long-term safety assessments of radioactive waste repositories may be greatly enhanced by a molecular level understanding of the sorption processes onto individual minerals present in the near- and far-fields. In this study we couple macroscopic sorption experiments to surface complexation modelling and spectroscopic investigations, including extended X-ray absorption fine structure (EXAFS) and time-resolved laser fluorescence spectroscopies (TRLFS), to elucidate the uptake mechanism of trivalent lanthanides and actinides (Ln/An(III)) by montmorillonite in the absence and presence of dissolved carbonate. Based on the experimental sorption isotherms for the carbonate-free system, the previously developed 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) model needed to be complemented with an additional surface complexation reaction onto weak sites. The fitting of sorption isotherms in the presence of carbonate required refinement of the previously published model by reducing the strong site capacity and by adding the formation of Ln/An(III)-carbonato complexes both on strong and weak sites. EXAFS spectra of selected Am samples and TRLFS spectra of selected Cm samples corroborate the model assumptions by showing the existence of different surface complexation sites and evidencing the formation of Ln/An(III) carbonate surface complexes. In the absence of carbonate and at low loadings, Ln/An(III) form strong inner-sphere complexes through binding to three Al(O,OH)6 octahedra, most likely by occupying vacant sites in the octahedral layers of montmorillonite, which are exposed on {010} and {110} edge faces. At higher loadings, Ln/An(III) binds to only one Al octahedron, forming a weaker, edge-sharing surface complex. In the presence of carbonate, we identified a ternary mono- or dicarbonato Ln/An(III) complex binding directly to one Al(O,OH)6 octahedron, revealing that type-A ternary complexes form with the one

  11. Magnon band structure of periodic composites

    NASA Astrophysics Data System (ADS)

    Vasseur, J. O.; Dobrzynski, L.; Djafari-Rouhani, B.; Puszkarski, H.

    1996-07-01

    innodata J. O. VASSEUR et al. MAGNON BAND STRUCTURE OF PERIODIC COMPOSITES We calculate the spin-wave spectra of two-dimensional composite materials consisting of periodic square arrays of parallel cylinders made of a ferromagnetic material embedded in a ferromagnetic background. Each material is described by its spontaneous magnetization MS and exchange constant A. An external static magnetic field is applied along the direction of the cylinders and both ferromagnetic materials are assumed to be magnetized parallel to this magnetic field. We consider the spin-waves propagation in the plane perpendicular to the cylinders. We reveal the existence of gaps in the magnon band structure of composite systems such as the periodic array of Fe cylinders in an EuO matrix. We investigate the existence of these gaps in relation to the physical parameters of the materials involved. We also study the influence of the lattice parameter (i.e., the square array periodicity) and the effect of the filling fraction of the cylinders on the magnon band structure.

  12. Spatially variant periodic structures in electromagnetics.

    PubMed

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

    2015-08-28

    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

  13. 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

  14. Electromagnetic scattering from three dimensional periodic structures

    NASA Astrophysics Data System (ADS)

    Barnes, Andrew L.

    We have developed a numerical method for solving electromagnetic scattering problems from arbitrary, smooth, three dimensional structures that are periodic in two directions and of finite thickness in the third direction. We solve Maxwell's equations via an integral equation that was first formulated by Claus Muller. The Muller integral equation is Fredholm of the second kind, so it is a well-posed problem. The original Muller formulation was for compact scatterers and it used a free space Green's function for the Helmholtz equation. We solve a periodic problem with a periodic Helmholtz Green's function. This Green's function has the same degree of singularity as the free space Helmholtz Green's function, but it is an infinite sum that converges very slowly. We use a resummation technique (due to P. P. Ewald) to perform an efficient calculation of the periodic Green's function. We solve the integral equation by a Galerkin method and use RWG vector basis functions to discretize surface currents on the scatterer. We perform a careful extraction of all singularities from the integrals that we compute. We use a triangular Gaussian quadrature method for calculation of the non-singular parts of the integrals. We analytically compute the remaining singular and nearly singular integrals. We also perform an acceleration technique that treats several frequencies simultaneously and leads to decreased computational times. In addition to the numerical code, we present an alternative way of looking at electromagnetic scattering in terms of Calderon projection operators. We have validated our computer code by comparing the numerical results with results from two separate cases. The first case is that of a flat dielectric slab of finite thickness, for which exact formulae are available. The second case is a periodic array of a row of infinite cylinders. In this case, we compare our results with those obtainedv from a two dimensional code developed by S. P. Shipman, S. Venakides

  15. 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.

  16. Spherical LDH-Ag°-montmorillonite heterocoagulated system with a pH-dependent sol-gel structure for controlled accessibility of AgNPs immobilized on the clay lamellae.

    PubMed

    Deák, Ágota; Janovák, László; Tallósy, Szabolcs Péter; Bitó, Tamás; Sebők, Dániel; Buzás, Norbert; Pálinkó, István; Dékány, Imre

    2015-02-17

    Aqueous suspensions of spherical ZnMgAl-layered double hydroxides [LDH(sph)] and antibacterial silver nanoparticles (AgNPs) deposited on the lamellae of montmorillonite were used for the synthesis of composites, which behave like coherent gels at low pH (≲4.5) and incoherent sols at higher pH (≳4.5). The composition of the composite was chosen as LDH(sph)/Ag°-montm. = 25:75 wt % in order to ensure a sol-gel transition that can also be characterized by viscometry. This pH-sensitive heterocoagulated system consisting of oppositely charged colloid particles was suitable for the release of antimicrobial AgNPs immobilized on the clay lamellae via a pH-controlled gel-sol transition. The heterocoagulation process was also characterized by surface charge titration measurements. Spherical LDH/Ag°-montmorillonite composite samples were identified by X-ray diffraction (XRD) measurements. The morphological properties of the composites were studied, and the presence of the heterocoagulated structure was confirmed by scanning electron microscopy (SEM). The nanoscale structure of the LDH(sph)-Ag°-montmorillonite composite obtained was also verified by small-angle X-ray scattering (SAXS), and the rheological characteristics were studied at various pH values. The viscosity and yield value of the composite decreased by an order of magnitude upon increasing the pH from 3.0 to 5.5. The sol-gel transition of the composite suspension was reversible in the previously mentioned pH range. PMID:25619227

  17. Effect of aging on morphology of organo-montmorillonite modified bitumen by atomic force microscopy.

    PubMed

    Zhang, H L; Wang, H C; Yu, J Y

    2011-04-01

    The morphology of unmodified and organo-montmorillonite modified bitumens was investigated by atomic force microscopy. The influence of thin film oven test and ultraviolet aging on the morphology of the binders was also analysed. The atomic force microscopy results showed that bitumen displayed a 'bee-like' structure and the dimension of the 'bee-like' structures was decreased to some extent with the introduction of organo-montmorillonite. Organo-montmorillonite showed a better interaction with the dispersed domains in comparison with the matrix in bitumen, which led to an obvious increase in the contrast between the dispersed domains and the matrix in bitumen. Compared with the unmodified bitumen, the single-phase trend in the organo-montmorillonite modified bitumen could be effectively prevented during thin film oven test and ultraviolet aging, indicating its good aging resistance which was in accordance with changes in physical properties of the organo-montmorillonite modified bitumen before and after aging. PMID:21118229

  18. Effective propagation in a perturbed periodic structure

    NASA Astrophysics Data System (ADS)

    Maurel, Agnès; Pagneux, Vincent

    2008-08-01

    In a recent paper [D. Torrent, A. Hakansson, F. Cervera, and J. Sánchez-Dehesa, Phys. Rev. Lett. 96, 204302 (2006)] inspected the effective parameters of a cluster containing an ensemble of scatterers with a periodic or a weakly disordered arrangement. A small amount of disorder is shown to have a small influence on the characteristics of the acoustic wave propagation with respect to the periodic case. In this Brief Report, we inspect further the effect of a deviation in the scatterer distribution from the periodic distribution. The quasicrystalline approximation is shown to be an efficient tool to quantify this effect. An analytical formula for the effective wave number is obtained in one-dimensional acoustic medium and is compared with the Berryman result in the low-frequency limit. Direct numerical calculations show a good agreement with the analytical predictions.

  19. Effective propagation in a perturbed periodic structure

    SciTech Connect

    Maurel, Agnes; Pagneux, Vincent

    2008-08-01

    In a recent paper [D. Torrent, A. Hakansson, F. Cervera, and J. Sanchez-Dehesa, Phys. Rev. Lett. 96, 204302 (2006)] inspected the effective parameters of a cluster containing an ensemble of scatterers with a periodic or a weakly disordered arrangement. A small amount of disorder is shown to have a small influence on the characteristics of the acoustic wave propagation with respect to the periodic case. In this Brief Report, we inspect further the effect of a deviation in the scatterer distribution from the periodic distribution. The quasicrystalline approximation is shown to be an efficient tool to quantify this effect. An analytical formula for the effective wave number is obtained in one-dimensional acoustic medium and is compared with the Berryman result in the low-frequency limit. Direct numerical calculations show a good agreement with the analytical predictions.

  20. [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. PMID:27337898

  1. Preparation and characterization of zwitterionic surfactant-modified montmorillonites.

    PubMed

    Zhu, Jianxi; Qing, Yanhong; Wang, Tong; Zhu, Runliang; Wei, Jingming; Tao, Qi; Yuan, Peng; He, Hongping

    2011-08-15

    A series of zwitterionic surfactant-modified montmorillonites (ZSMMs) were synthesized using montmorillonite and three zwitterionic surfactants with different alkyl chain lengths at different concentrations [0.2-4.0 cation exchange capacity (CEC)]. These ZSMMs were characterized by X-ray diffraction (XRD), thermo-gravimetric analysis and differential thermo-gravimetric (TG/DTG) analyses. The zwitterionic surfactant could be intercalated into the interlayer spaces of montmorillonites and causing interlayer space-swelling. From XRD measurements, the amount of the surfactants loaded and the basal spacing increased with surfactant concentration and alkyl chain length. One endothermic DTG peak occurred at ~390 °C, which was assigned to the decomposition of the zwitterionic surfactant on the organo-montmorillonites from 0.2 to 0.6 CEC. When the surfactant loading was increased, a new endothermic peak appeared at ~340 °C. From the microstructures of these ZSMMs, the mechanism of zwitterionic surfactant adsorption was proposed. At relatively low loadings of the zwitterionic surfactant, most of surfactants enter the spacing by an ion-exchange mechanism and are adsorbed onto the interlayer cation sites. When the concentration of the zwitterionic surfactant exceeds the CEC of montmorillonite, the surfactant molecules then adhere to the surface-adsorbed surfactant. Some surfactants enter the interlayers, whereas the others are attached to the clay surface. When the concentration of surfactant increases further beyond 2.0 CEC, the surfactants may occupy the inter-particle space within the house-of-cards aggregate structure. PMID:21575956

  2. Sparse phonon modes of a limit-periodic structure

    NASA Astrophysics Data System (ADS)

    Marcoux, Catherine; Socolar, Joshua E. S.

    2016-05-01

    Limit-periodic structures are well ordered but nonperiodic, and hence have nontrivial vibrational modes. We study a ball and spring model with a limit-periodic pattern of spring stiffnesses and identify a set of extended modes with arbitrarily low participation ratios, a situation that appears to be unique to limit-periodic systems. The balls that oscillate with large amplitude in these modes live on periodic nets with arbitrarily large lattice constants. By studying periodic approximants to the limit-periodic structure, we present numerical evidence for the existence of such modes, and we give a heuristic explanation of their structure.

  3. Femtosecond laser-induced periodic surface structure formation on tungsten

    SciTech Connect

    Vorobyev, A. Y.; Guo Chunlei

    2008-09-15

    In this paper, we demonstrate the generation of periodic surface structures on a technologically important material, tungsten, at both 400 and 800 nm, despite that the table values of dielectric constants for tungsten at these two wavelengths suggest the absence of surface plasmons, a wave necessary for forming periodic structures on metals. Furthermore, we find that the structure periods formed on tungsten are significantly less than the laser wavelengths. We believe that the dielectric constants of tungsten change significantly due to intense laser pulse heating and surface structuring and roughening at nanometer scales, permitting surface plasmon excitation and periodic structure formation.

  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. PMID:16759775

  6. A Highly Permeable Aligned Montmorillonite Mixed-Matrix Membrane for CO2 Separation.

    PubMed

    Qiao, Zhihua; Zhao, Song; Wang, Jixiao; Wang, Shichang; Wang, Zhi; Guiver, Michael D

    2016-08-01

    Highly permeable montmorillonite layers bonded and aligned with the chain stretching orientation of polyvinylamineacid are immobilized onto a porous polysulfone substrate to fabricate aligned montmorillonite/polysulfone mixed-matrix membranes for CO2 separation. High-speed gas-transport channels are formed by the aligned interlayer gaps of the modified montmorillonite, through which CO2 transport primarily occurs. High CO2 permeance of about 800 GPU is achieved combined with a high mixed-gas selectivity for CO2 that is stable over a period of 600 h and independent of the water content in the feed. PMID:27312314

  7. Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure.

    PubMed

    Ait-Akbour, Rachid; Boustingorry, Pascal; Leroux, Fabrice; Leising, Frédéric; Taviot-Guého, Christine

    2015-01-01

    This study deals with the adsorption of PolyCarboxylate Poly(ethylene glycol) esters (PCP) superplasticizers on Na-, Mg- and Ca-saturated Montmorillonite (Mmt) clays. The interactions have been examined through different experimental methods: adsorption isotherms, zeta potential measurements and sedimentation experiments. It was found that PCP adsorption depends both on the architecture of PCP molecules and the nature of cation located on the interlayer exchange sites of the Montmorillonite. Whatever the PCP, a larger amount was adsorbed on Na-Mont than on Mg-Mont or Ca-Mont. This indicates the occurrence of two adsorption mechanisms: (i) a superficial adsorption via electrostatic interactions between the carboxylate groups of PCP and positively charged sites on clay surfaces, (ii) intercalation of ether units of the PCP grafts in the interlayer space by displacement of water molecules coordinated to the exchangeable cations. Furthermore, despite the weak negative values of the zeta potential, the addition of PCP promotes the stability of the suspensions which is attributed to steric repulsion acting between particles. PMID:25313488

  8. 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.

  9. Electrolyte diffusion in compacted montmorillonite engineered barriers

    SciTech Connect

    Jahnke, F.M.; Radke, C.J.

    1985-09-01

    The bentonite-based engineered barrier or packing is a proposed component of several designs conceived to dispose of high-level nuclear waste in geologic repositories. Once radionuclides escape the waste package, they must first diffuse through the highly impermeable clay-rich barrier before they reach the host repository. To determine the effectiveness of the packing as a sorption barrier in the transient release period and as a mass-transfer barrier in the steady release period over the geologic time scales involved in nuclear waste disposal, a fundamental understanding of the diffusion of electrolytes in compacted clays is required. We present, and compare with laboratory data, a model quantifying the diffusion rates of cationic cesium and uncharged tritium in compacted montmorillonite clay. Neutral tritium characterizes the geometry (i.e., tortuosity) of the particulate gel. After accounting for cation exchange, we find that surface diffusion is the dominant mechanism of cation transport, with an approximate surface diffusion coefficient of 2 x 10 W cmS/s for cesium. This value increases slightly with increasing background ionic strength. The implications of this work for the packing as a migration barrier are twofold. During the transient release period, K/sub d/ values are of little importance in retarding ion migration. This is because sorption also gives rise to a surface diffusion path, and it is surface diffusion which controls the diffusion rate of highly sorbing cations in compacted montmorillonite. During the steady release period, the presence of surface diffusion leads to a flux through the packing which is greatly enhanced. In either case, if surface diffusion is neglected, the appropriate diffusion coefficient of ions in compacted packing will be in considerable error relative to current design recommendations. 11 refs., 4 figs., 1 tab.

  10. 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

  11. 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.

  12. Green's Function Analysis of Periodic Structures in Computational Electromagnetics

    NASA Astrophysics Data System (ADS)

    Van Orden, Derek

    2011-12-01

    Periodic structures are used widely in electromagnetic devices, including filters, waveguiding structures, and antennas. Their electromagnetic properties may be analyzed computationally by solving an integral equation, in which an unknown equivalent current distribution in a single unit cell is convolved with a periodic Green's function that accounts for the system's boundary conditions. Fast computation of the periodic Green's function is therefore essential to achieve high accuracy solutions of complicated periodic structures, including analysis of modal wave propagation and scattering from external sources. This dissertation first presents alternative spectral representations of the periodic Green's function of the Helmholtz equation for cases of linear periodic systems in 2D and 3D free space and near planarly layered media. Although there exist multiple representations of the periodic Green's function, most are not efficient in the important case where the fields are observed near the array axis. We present spectral-spatial representations for rapid calculation of the periodic Green's functions for linear periodic arrays of current sources residing in free space as well as near a planarly layered medium. They are based on the integral expansion of the periodic Green's functions in terms of the spectral parameters transverse to the array axis. These schemes are important for the rapid computation of the interaction among unit cells of a periodic array, and, by extension, the complex dispersion relations of guided waves. Extensions of this approach to planar periodic structures are discussed. With these computation tools established, we study the traveling wave properties of linear resonant arrays placed near surfaces, and examine the coupling mechanisms that lead to radiation into guided waves supported by the surface. This behavior is especially important to understand the properties of periodic structures printed on dielectric substrates, such as periodic

  13. Characteristic Structures of Power Spectra in Periodic Chaos

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Tomita, K.

    1986-10-01

    The power spectra of periodic chaos are shown to have characteristic structures which are governed by the universal recursion relations. By periodic chaos we mean a chaos which emerges via period-doubling bifurcations, and the recursion relations are based on similarity structures in the process of band-splitting bifurcations of periodic chaos. To derive these relations, the asymmetric tent map is used, and the universal applicability of these relations to other classes of maps including the logistic map, where the rescaling factors are replaced by proper ones, is verified by numerical experiment. Some affirmative results for the H&{acutee}non maps are also given.

  14. 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

  15. Reliability analysis of structures under periodic proof tests in service

    NASA Technical Reports Server (NTRS)

    Yang, J.-N.

    1976-01-01

    A reliability analysis of structures subjected to random service loads and periodic proof tests treats gust loads and maneuver loads as random processes. Crack initiation, crack propagation, and strength degradation are treated as the fatigue process. The time to fatigue crack initiation and ultimate strength are random variables. Residual strength decreases during crack propagation, so that failure rate increases with time. When a structure fails under periodic proof testing, a new structure is built and proof-tested. The probability of structural failure in service is derived from treatment of all the random variables, strength degradations, service loads, proof tests, and the renewal of failed structures. Some numerical examples are worked out.

  16. Silylation of montmorillonite surfaces: dependence on solvent nature.

    PubMed

    Su, Linna; Tao, Qi; He, Hongping; Zhu, Jianxi; Yuan, Peng; Zhu, Runliang

    2013-02-01

    Silylation of clay mineral surfaces has attracted much attention due to their extensive applications in materials science and environmental engineering. Silylation of montmorillonite surfaces with 3-aminopropyltriethoxysilane was carried out in polar-protic and nonpolar solvents. The swelling property of the silylated montmorillonites was investigated by intercalating with cetyltrimethylammonium bromide. Silylated montmorillonites prepared in nonpolar solvents showed a larger amount of loaded silane and a higher extent of condensation among different silane molecules, comparing with those prepared in polar-protic solvents with high dielectric constant. Meanwhile, the silylated montmorillonites prepared in nonpolar solvents displayed poor swelling property due to the linkage between silane oligomers and clay layers, that is, the neighboring clay layers were locked by the silane oligomers. The present study demonstrated that the polarity of the solvents used had an important influence on the extent of grafting, interlayer structure, and swelling property of the silylated products. This is of high importance for synthesis and application of silylated clay minerals. PMID:23123026

  17. Manifold structures of unstable periodic orbits and the appearance of periodic windows in chaotic systems.

    PubMed

    Kobayashi, Miki U; Saiki, Yoshitaka

    2014-02-01

    Manifold structures of the Lorenz system, the Hénon map, and the Kuramoto-Sivashinsky system are investigated in terms of unstable periodic orbits embedded in the attractors. Especially, changes of manifold structures are focused on when some parameters are varied. The angle between a stable manifold and an unstable manifold (manifold angle) at every sample point along an unstable periodic orbit is measured using the covariant Lyapunov vectors. It is found that the angle characterizes the parameter at which the periodic window corresponding to the unstable periodic orbit finishes, that is, a saddle-node bifurcation point. In particular, when the minimum value of the manifold angle along an unstable periodic orbit at a parameter is small (large), the corresponding periodic window exists near (away from) the parameter. It is concluded that the window sequence in a parameter space can be predicted from the manifold angles of unstable periodic orbits at some parameter. The fact is important because the local information in a parameter space characterizes the global information in it. This approach helps us find periodic windows including very small ones. PMID:25353542

  18. 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.

  19. First-principles study of water desorption from montmorillonite surface.

    PubMed

    Zhang, Yao; Meng, Yingfeng; Liu, Houbin; Yang, Mingli

    2016-05-01

    Knowledge about water desorption is important to give a full picture of water diffusion in montmorillonites (MMT), which is a driving factor in MMT swelling. The desorption paths and energetics of water molecules from the surface of MMT with trapped Li(+), Na(+) or K(+) counterions were studied using periodic density functional theory calculations. Two paths--surface and vacuum desorption--were designed for water desorption starting from a stationary structure in which water bonds with both the counterion and the MMT surface. Surface desorption is energetically more favorable than vacuum desorption due to water-surface hydrogen bonds that help stabilize the intermediate structure of water released from the counterion. The energy barriers of water desorption are in the order of Li(+) > Na(+) > K(+), which can be attributed to the short ionic radius of Li(+), which favors strong binding with the water molecule. The temperature dependence of water adsorption and desorption rates were compared based on the computed activation energies. Our calculations reveal that the water desorption on the MMT surface has a different mechanism from water adsorption, which results from surface effects favoring stabilization of water conformers during the desorption process. PMID:27083565

  20. 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

  1. Nuclear shell structures in terms of classical periodic orbits

    NASA Astrophysics Data System (ADS)

    Arita, Ken-ichiro

    2016-06-01

    Semiclassical periodic-orbit theory (POT) theory is applied to the physics of nuclear structures, with the use of a realistic nuclear mean-field model given by the radial power-law potential. Evolution of deformed shell structures, which are responsible for various nuclear deformations, are clearly understood from the contribution of short classical periodic orbits (POs). Bifurcations of short POs, which imply underlying local dynamical symmetry, play significant role there. The effect of the spin degree of freedom is also investigated in relevance to the pseudospin symmetry in spherical nuclei and the prolate–oblate asymmetry in shell structures of nuclei with quadrupole-type deformations.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Montmorillonite Clay-Catalyzed Synthesis of RNA Oligomers

    NASA Astrophysics Data System (ADS)

    Ferris, J. P.; Miyakawa, S.; Huang, W.; Joshi, P.

    2005-12-01

    It is proposed that catalysis had a central role in the origins of life. This will be illustrated using the montmorillonite clay-catalyzed synthesis of oligomers of RNA from activated monomers, (Ferris and Ertem, 1993) a possible step in the origin of the RNA world (Ferris, 2005). Structural analysis of oligomers formed in the reaction of the activated monomer of 5'-AMP with that of 5'-CMP demonstrated that the oligomers formed were not produced by random synthesis but rather the sequences observed were directed by the montmorillonite catalyst (Miyakawa and Ferris, 2003). RNA oligomers containing up to 40 mers have been synthesized in reactions performed in water at 25 oC in the presence of montmorillonite (Huang and Ferris, 2003). Analysis of the structure elements in these oligomers from the 7 to 39 mers showed that they did not vary. Reaction of D, L-mixtures of the activated monomers of A and U resulted in the formation of greater amounts of the homochiral amounts of dimers and trimers of A than would be expected if there was no selectivity in the reaction. A limited number of the dimers and trimers of U were also formed but here the selectivity was for the formation of an excess of heterochiral products (Joshi et al., 2000). A postulate that explains why homochiral trimers of U are not formed and the significance of catalysis in prebiotic synthesis will be discussed. Ferris, J.P. (2005) Origins of life, molecular basis of. In R.A. Meyers, Ed. Encyclopedia of Molecular Cell Biology and Molecular Medicine, 10. Wiley-VCH Verlag, Weinheim, Germany. Ferris, J.P., and Ertem, G. (1993) Montmorillonite catalysis of RNA oligomer formation in aqueous solution. A model for the prebiotic formation of RNA. J. Am. Chem. Soc., 115, 12270-12275. Huang, W., and Ferris, J.P. (2003) Synthesis of 35-40 mers of RNA oligomers from unblocked monomers. A simple approach to the RNA world. Chem. Commun., 1458-1459. Joshi, P.C., Pitsch, S., and Ferris, J.P. (2000) Homochiral selection

  7. 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).

  8. 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.

  9. 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.

  10. 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

  11. Novel hydrophilic carboxymethyl starch/montmorillonite nanocomposite films.

    PubMed

    Wilpiszewska, Katarzyna; Antosik, Adrian Krzysztof; Spychaj, Tadeusz

    2015-09-01

    Preparation of novel carboxymethyl starch (CMS)-based biodegradable films with calcium montmorillonite has been described. The biocomposites were obtained by casting method, glycerol and citric acid were used as plasticizer and crosslinking agent, respectively. The effect of calcium montmorillonite (MMT-Ca) on hydrophilicity (moisture absorption, solubility in water as well as contact angle measurements) was evaluated. Moreover, thermomechanical and mechanical properties of nanocomposites were determined. For all the systems tested intercalated structure of MMT-Ca was revealed, however the most efficient clay platelets dispersion was noted for film containing 5 wt.% MMT-Ca. Such biodegradable CMS/MMT-Ca films exhibiting relatively good mechanical properties could find application in controlled delivery systems as well as in agriculture for seed tapes production where hydrophilicity of polymer carrier is strongly advantageous. PMID:26005142

  12. Center mode of a doubly resonant optical periodic structure

    NASA Astrophysics Data System (ADS)

    Alagappan, G.; Png, C. E.

    2016-07-01

    An optical periodic structure with a single spatial resonance exhibits a stopband. When a second spatial resonance very close to the first one is added, the resulting doubly resonant structure exhibits a Gaussian enveloped, high quality factor transmission state right at the center of the original stopband. Using a slowly varying envelope approximation, we describe the optical characteristics of this transmission state analytically. The transmission state exists despite an optical structure of low refractive index contrast, and has potential applications in nano-optics, and photonics.

  13. 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

  14. Spin wave damping in periodic and quasiperiodic magnonic structures

    NASA Astrophysics Data System (ADS)

    Rychły, J.; Kłos, J. W.; Krawczyk, M.

    2016-05-01

    We investigated the lifetime of spin wave (SW) eigenmodes in periodic and quasiperiodic sequences of Py and Co wires. These materials differ significantly in damping coefficients, therefore, the spatial distribution of the mode’s amplitude within the structure is important for the lifetime of collective SW excitations. Modes of the lower frequencies prefer to concentrate in Py wires, because of the lower ferromagnetic resonance (FMR) frequency for this material. This inhomogeneous distribution of amplitude of modes (with lower amplitude in material of higher damping and with higher amplitude in material of lower damping) is preferable for extending the lifetime of the collective excitations beyond the volume average of lifetimes for solid materials. We established the relation between the profile of the mode and its lifetime for periodic and quasiperiodic structures. We also performed comparative studies in order to find the differences resulting from complexity of the structure and enhancement of localization in the quasiperiodic system on the lifetime of SWs.

  15. Self-assembly protocol design for periodic multicomponent structures.

    PubMed

    Jacobs, William M; Frenkel, Daan

    2015-12-14

    Assembling molecular superstructures with many distinct components will allow unprecedented control over morphology at the nanoscale. Recently, this approach has been used to assemble periodic structures with precisely defined features, such as repeating arrays of pores and channels, using a large number of building blocks. Here we propose a predictive tool that allows us to optimize the nucleation and growth of unbounded, ordered structures. In what follows, we call these structures 'crystals', even though they may only be periodic in one or two dimensions. We find that the nucleation barriers and growth pathways for crystals consisting of many components exhibit generic features that are very different from those of simple crystals. To illustrate the very non-classical nature of the nucleation and growth of such structures, we study the formation of one and two-dimensional crystals with multicomponent unit cells. We find that, whilst the boundaries in the non-periodic dimensions significantly affect the stabilities of these crystals, the nucleation barriers are largely determined by the local connectivity of the associated bulk crystal and are independent of the number of distinct components in the unit cell. We predict that the self-assembly of crystals with complex morphologies can be made to follow specific pathways toward the target structure that successively incorporate key features of the three-dimensional target structure. In contrast with simple crystals, it is possible to tune the kinetics of nucleation and growth separately, thus minimizing defect formation. We show how control over self-assembly pathways can be used to optimize the kinetics of formation of extended structures with arbitrary nanoscale patterns. PMID:26404794

  16. A Periodic Dielectric Resonator Structure for Terahertz Wave Amplification

    NASA Astrophysics Data System (ADS)

    Fawole, Olutosin; Tabib-Azar, Massood

    2014-03-01

    We present a periodic Slow Wave Structure (SWS) that consists of an arrangement of closely spaced cylindrical resonators with low dielectric constant. In this compact arrangement, coupling between resonators was via evanescent field coupling. This arrangement contrasts earlier infinite high dielectric constant SWSs with widely spaced resonators coupled via magnetic dipole moments. The presented periodic structure is an alternative to the metallic slow wave structures that have been proposed for TWT THz amplifiers. The fabricated low frequency (8 GHz) prototype of our structure consists of an array of cylindrical resonators with dielectric constant 9.2, diameter 12 mm, and height 6.35 mm. Slow waves, which setup a TE01δ-like electric field mode in each resonator, propagate in the structure when then the structure was excited with a microstrip line. We will present detailed simulation and experimental results of this prototype at the conference. Furthermore, efforts to scale the SWS to THz frequency and to interact the SWS with high-energy particle beams will be presented.

  17. 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.

  18. 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.

  19. Periodically structured Si pillars for high-performing heterojunction photodetectors

    NASA Astrophysics Data System (ADS)

    Melvin David Kumar, M.; Yun, Ju-Hyung; Kim, Joondong

    2015-03-01

    A periodical array of silicon (Si) micro pillar structures was fabricated on Si substrates using PR etching process. Indium tin oxide (ITO) layer of 80 nm thickness was deposited over patterned Si substrates so as to make ITO/n-Si heterojunction devices. The influences of width and period of pillars on the optical and electrical properties of prepared devices were investigated. The surface morphology of the Si substrates revealed the uniform array of pillar structures. The 5/10 (width/period) Si pillar pattern reduced the optical reflectance to 6.5% from 17% which is of 5/7 pillar pattern. The current rectifying ratio was found higher for the device in which the pillars are situated in optimum periods. At both visible (600 nm) and near infrared (900 nm) range of wavelengths, the 5/7 and 5/10 pillar patterned device exhibited the better photoresponses which are suitable for making advanced photodetectors. This highly transmittance and photoresponsive pillar patterned Si substrates with an ITO layer would be a promising device for various photoelectric applications.

  20. Iron-montmorillonite - A spectral analog of Martian soil

    NASA Technical Reports Server (NTRS)

    Banin, A.; Margulies, L.; Chen, Y.

    1985-01-01

    Spectral data for smectite clays, particularly for montmorillonite, which contain various adsorbed ions and are measured in the UV, VIS, and NIR ranges are analyzed and compared with Martian soil and dust spectra. It is shown that the structural octahedral iron in smectite clays affects their light absorbance in the UV at 240-260 nm, which results from an O(2-) to Fe(3+) charge transfer, similar to one observed in the Martian spectrum. Adsorbed iron affects, via crystal field absorptions, the reflectance of montmorillonite in the VIS and NIR ranges, resulting in stronger absorption and higher opacity in the range 0.40-0.65 micron. Both in spectral contrast and presence of (or lack of) spectral features, the Fe-montmorillonite spectra in the VIS and NIR are in reasonable agreement with the Martian spectrum. It is found that the spectral characteristics of iron-saturated smectite clays cannot be used to preclude the presence of clays in Martian soils and dust.

  1. 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.

  2. 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.

  3. Unidirectional Invisibility Induced by PT-Symmetric Periodic Structures

    SciTech Connect

    Lin Zin; Ramezani, Hamidreza; Kottos, Tsampikos; Eichelkraut, Toni; Christodoulides, Demetrios N.; Cao Hui

    2011-05-27

    Parity-time (PT) symmetric periodic structures, near the spontaneous PT-symmetry breaking point, can act as unidirectional invisible media. In this regime, the reflection from one end is diminished while it is enhanced from the other. Furthermore, the transmission coefficient and phase are indistinguishable from those expected in the absence of a grating. The phenomenon is robust even in the presence of Kerr nonlinearities, and it can also effectively suppress optical bistabilities.

  4. 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.

  5. Characterization of electronic structure of periodically strained graphene

    DOE PAGESBeta

    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.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

  6. Simulation of period doubling of recurrent solar wind structures

    NASA Technical Reports Server (NTRS)

    Whang, Y. C.; Burlaga, L. F.

    1990-01-01

    Based on satellite observations of a recurrent solar wind structure conducted in 1974, an MHD simulation model, and input functions generated from plasma and magnetic field data, the continuing evolution of the solar wind structure outside 5 AU is studied. The model uses the Rankine-Hugoniot relations to describe the jumps in flow properties across the shocks, and it treats shocks as surfaces of discontinuity with zero thickness. Two interaction processes (the collision and the merging of shocks) play important roles in restructuring the solar wind in the outer heliosphere. The simulation result shows that period doubling occurs between 5 and 10 AU. The recurrent solar wind appears to be a persistent new structure between 10 and 20 AU, and it consists of one merged interaction region per solar rotation.

  7. 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.

  8. 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.

  9. 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.

  10. Diffusion and mobility of anisotropic particles in tilted periodic structures

    NASA Astrophysics Data System (ADS)

    Wu, Jian-chun; Chen, Qun; Wang, Rang; Ai, Bao-quan

    2015-02-01

    We numerically investigated the transport of anisotropic particles in tilted periodic structures. The diffusion and mobility of the particles demonstrate distinct behaviors dependence on the shape of the particles. In two-dimensional (2D) periodic potentials, we find that the mobility is influenced a little by the anisotropy of the particle, while the diffusion increases monotonically with the increasing of the particle anisotropy for large enough biased force. However, due to the sensitivity of the channels for the particle anisotropy, the transport in smooth channels is obviously different from that in energy potentials. The mobility decreases monotonically with the increasing of the particle anisotropy, while the diffusion can be a non-monotonic function of the particle anisotropy with a peak under appropriate biased force.

  11. Nanocomposites prepared from acrylonitrile butadiene rubber and organically modified montmorillonite with vinyl groups

    NASA Astrophysics Data System (ADS)

    Han, Mijeong; Kim, Hoonjung; Kim, Eunkyoung

    2006-01-01

    Nanocomposites were prepared from acrylonitrile-butadiene rubber (NBR), vinyl groups containing organically modified montmorillonite and additives, such as zinc oxide, stearic acid, and sulfur. The organically modified montmorillonites used in these nanocomposites were prepared by ion exchange reactions of N,N'-dimethylalkyl-(p-vinylbenzyl)-ammonium chlorides (DAVBAs, alkyl = octyl, dodecyl, and octadecyl) with sodium montmorillonite (Na+-MMT). NBR nanocomposites were obtained by controlling both the mixing and vulcanization conditions, by using a Brabender mixer and hot-press process. X-ray diffraction (XRD) analysis shows that, depending on the amount of montmorillonite that is added, both exfoliated and intercalated nanocomposite structures are formed. The NBR/DAVBA-MMT nanocomposites exhibit much higher mechanical properties (e.g., tensile strength, Young's modulus, 300% modulus, and hardness) as well as gas barrier properties as compared to NBR Na+-MMT or NBR composites generated from modified montmorillonites without vinyl groups. Consistent with the results of XRD, transmission electron microscopy (TEM) reveals that the intercalation and exfoliation structures of the nanocomposites coexist and that the DAVBA-MMT layers are well dispersed in NBR.

  12. A study of purified montmorillonite intercalated with 5-fluorouracil as drug carrier.

    PubMed

    Lin, F H; Lee, Y H; Jian, C H; Wong, Jau-Min; Shieh, Ming-Jium; Wang, Cheng-Yi

    2002-05-01

    Since its introduction over 40 years ago, 5-fluorouracil (5-FU) has remained the only effective chemotherapy option available for the treatment of colorectal cancer (CRC). However, this cytotoxic anticancer drug often causes severe side effects because it does not act selectively on the tumor. It has been reported that the 5-FU showed considerable toxicity when administered by intravenous injections or via alimentary tract. Although, many materials have been developed for carrying 5-FU, there has been no clinically acceptable carrier for 5-FU till now. Montmorillonite, one of the clay minerals, consists of hydrated aluminum silicates with fine grains and large spaces between the layers. Isomorphous substitution of cations is common. In the study, we attempt to intercalate 5-FU into interlayers of montmorillonite through ion exchange. Montmorillonite was purified from crude clays of bentonite in Tai-dong, Taiwan by filtration and sedimentation. Solutions of 5-FU with different concentrations were prepared by dissolving various amounts of 5-FU into 10 ml NaOH solution. Purified montmorillonite powder was soaked in 5-FU solution for a period of time with different pH values and temperatures. In this study, we try to intercalate 5-FU into interlayers of montmorillonite to find out optimum conditions, such as soaking time, temperature, pH value, initial 5-FU concentration, etc., to prepare composites of 5-FU and montmorillonite (5-FU/mont). UV, SDT, FTIR, XRD are used to characterize the 5-FU/mont composite. From the results. 5-FU was successfully intercalated into the interlayer of montmorillonite both by free surface absorption and OH replacement. The optimum condition for 5-FU/mont preparations is 1.185 wt% of 5-FU as initial concentration under a pH value of 11.6 at a temperature of 80 degrees C and a soaking time of 2 h. The total amount of 5-FU in montmorillonite is about 87.5 mg for each gram of montmorillonite, which can be proved by thermal gravimetric analysis

  13. Periodic transmission peak splitting in one dimensional disordered photonic structures

    NASA Astrophysics Data System (ADS)

    Kriegel, Ilka; Scotognella, Francesco

    2016-08-01

    In the present paper we present ways to modulate the periodic transmission peaks arising in disordered one dimensional photonic structures with hundreds of layers. Disordered structures in which the optical length nd (n is the refractive index and d the layer thickness) is the same for each layer show regular peaks in their transmission spectra. A proper variation of the optical length of the layers leads to a splitting of the transmission peaks. Notably, the variation of the occurrence of high and low refractive index layers, gives a tool to tune also the width of the peaks. These results are of highest interest for optical application, such as light filtering, where the manifold of parameters allows a precise design of the spectral transmission ranges.

  14. Exfoliation of montmorillonite in protein solutions.

    PubMed

    Kolman, Krzysztof; Steffen, Werner; Bugla-Płoskońska, Gabriela; Skwara, Aleksandra; Pigłowski, Jacek; Butt, Hans-Jürgen; Kiersnowski, Adam

    2012-05-15

    In the study we demonstrate a method to obtain stable, exfoliated montmorillonite-protein complexes by adsorption of the proteins extracted from hen-egg albumen. Analysis of the process by means of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the complexes are formed by sequential adsorption of ovotransferrin, ovalbumins, ovomucoid and lysozyme on the surface of the silicate. Structural studies performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the adsorption of ovotransferrin and albumins is accompanied by disintegration of clay stacks into discrete platelets. Further analysis by dynamic light scattering (DLS) revealed that at protein to silicate weight ratios exceeding 20, the synergistic adsorption of albumen components leads to reaggregation of silicate platelets into disordered, microgel-like particles. By means of DLS it was found that exfoliation predominantly leads to formation of particles with average hydrodynamic radii (R(h)) of 0.19 μm while their aggregation causes formation of particles having R(h) in of approx. 0.5 μm and larger. PMID:22405581

  15. 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.

  16. 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.

  17. REVIEW ARTICLE: Slow light enhanced nonlinear optics in periodic structures

    NASA Astrophysics Data System (ADS)

    Monat, C.; de Sterke, M.; Eggleton, B. J.

    2010-10-01

    We review recent advances related to slow light in periodic structures, where the refractive index varies along one or two directions, i.e. gratings and planar photonic crystals. We focus on how these geometries are conducive to enhancing the nonlinear interaction between light and matter. We describe the underlying theory developed for shallow gratings, but whose conclusions can be extended to planar photonic crystal waveguides, in particular the enhancement of third-order nonlinear processes with slow light. We review some experiments showing how gratings have been used for pulse compression and the generation of slow gap solitons. We then present recent nonlinear experiments performed in photonic crystal waveguides that demonstrate the strong reinforcement of nonlinear third-order optical phenomena with slow light. We discuss the challenges associated with slow light in these 2D structures and their unique advantage—dispersion engineering—for creating broadband nonlinear devices for all-optical signal processing. By breaking down the relation between dispersion and group velocity imposed in gratings, these structures also offer new opportunities for generating soliton-like effects over short length scales, at low powers and with short pulses.

  18. Brittle fracture in a periodic structure with internal potential energy

    PubMed Central

    Mishuris, Gennady S.; Slepyan, Leonid I.

    2014-01-01

    We consider a brittle fracture taking account of self-equilibrated distributed stresses existing at microlevel in the absence of external forces. To determine how the latter can affect the crack equilibrium and growth, a model of a structured linearly elastic body is introduced, consisting of two equal symmetrically arranged layers (or half-planes) connected by an interface as a prospective crack path. The interface comprises a discrete set of elastic bonds. In the initial state, the bonds are assumed to be stressed in such a way that tensile and compressive forces of the same value alternate. In the general considerations, the layers are assumed to be of an unspecified periodic structure, where such self-equilibrated stresses may also exist. A two-line chain and a lattice are examined as the specified structure. We consider the states of the body-with-a-crack under such microlevel stresses (MS) and under a combined action of the remote forces and MS. Analytical solutions to the considered problems are presented based on the introduction of a selective discrete transform. We demonstrate that MS can increase as well as decrease the crack resistance depending on the internal energy level. We also discuss different scenarios of the crack growth. PMID:24808756

  19. 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.

  20. MALDI analysis of oligonucleotides directly from montmorillonite.

    PubMed

    Zagorevskii, Dmitri V; Aldersley, Michael F; Ferris, James P

    2006-09-01

    Oligonucleotides synthesized on a montmorillonite catalyst were analyzed directly. By mixing the catalyst with a matrix (2,4,6-trihydroxyacetophenone or 6-aza-2-thiothymine) and dibasic ammonium citrate, higher molecular weight products were detected compared with "classical" methods such as gel electrophoresis and HPLC with UV as a detector. The oligomers (30-mers and higher) were detected by mass spectrometry even though their concentration was less than 10(-4)% of the total content of the RNA. This method is different from the (MALDI) analysis of the eluates from montmorillonite, which otherwise requires desalting. Placing reaction mixtures with a high concentration of buffers on homoionic, preferably Li-containing, montmorillonite does not require desalting. PMID:16809045

  1. A curcumin activated carboxymethyl cellulose-montmorillonite clay nanocomposite having enhanced curcumin release in aqueous media.

    PubMed

    Madusanka, Nadeesh; de Silva, K M Nalin; Amaratunga, Gehan

    2015-12-10

    A novel curcumin activated carboxymethylcellulose-montmorillonite nanocomposite is reported. A superabsorbent biopolymer; carboxymethyl cellulose (CMC) was used as an emulsifier for curcumin which is a turmeric derived water insoluble polyphenolic compound with antibacterial/anti-cancer properties. Montmorillonite (MMT) nanoclay was incorporated in the formulation as a matrix material which also plays a role in release kinetics. It was observed that water solubility of curcumin in the nanocomposite has significantly increased (60% release within 2h and 30 min in distilled water at pH 5.4) compared to pure curcumin. The prepared curcumin activated carboxymethylcellulose-montmorillonite nanocomposite is suitable as a curcumin carrier having enhanced release and structural properties. PMID:26428174

  2. Magneto-electro-elastic polariton coupling in a periodic structure

    NASA Astrophysics Data System (ADS)

    Piliposyan, D. G.; Ghazaryan, K. B.; Piliposian, G. T.

    2015-05-01

    Propagation of electro-magneto-acoustic waves in a magneto-electro-elastic (MEE) periodic structure has been investigated with a three phase coupling between mechanical, electric and magnetic fields in each constituent layer. Due to this coupling electromagnetic waves couple with lattice vibrations resulting in both dielectric and magnetic phonon-polaritons which couple via the magneto-electric effect. Propagation properties of acoustic longitudinal and transverse vibrations in this superlattice have been investigated. For longitudinal acoustic vibrations perpendicular to the poling direction, the coupling of piezoelectric and piezomagnetic polaritons results in a propagating mode. For transverse lattice vibrations with the coupled MEE wave propagating parallel to the poling direction, there is a coupled piezoelectric-piezomagnetic phonon polariton gap. The MEE superlattice produces either negative permittivity or negative permeability functions but not double negativity to result in negative refraction crystal.

  3. 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.

  4. 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.

  5. Structural Anisotropy in Polar Fluids Subjected to Periodic Boundary Conditions

    PubMed Central

    2011-01-01

    A heuristic model based on dielectric continuum theory for the long-range solvation free energy of a dipolar system possessing periodic boundary conditions (PBCs) is presented. The predictions of the model are compared to simulation results for Stockmayer fluids simulated using three different cell geometries. The boundary effects induced by the PBCs are shown to lead to anisotropies in the apparent dielectric constant and the long-range solvation free energy of as much as 50%. However, the sum of all of the anisotropic energy contributions yields a value that is very close to the isotropic one derived from dielectric continuum theory, leading to a total system energy close to the dielectric value. It is finally shown that the leading-order contribution to the energetic and structural anisotropy is significantly smaller in the noncubic simulation cell geometries compared to when using a cubic simulation cell. PMID:22303290

  6. Nonasymptotic homogenization of periodic electromagnetic structures: Uncertainty principles

    NASA Astrophysics Data System (ADS)

    Tsukerman, Igor; Markel, Vadim A.

    2016-01-01

    We show that artificial magnetism of periodic dielectric or metal/dielectric structures has limitations and is subject to at least two "uncertainty principles." First, the stronger the magnetic response (the deviation of the effective permeability tensor from identity), the less accurate ("certain") the predictions of any homogeneous model. Second, if the magnetic response is strong, then homogenization cannot accurately reproduce the transmission and reflection parameters and, simultaneously, power dissipation in the material. These principles are general and not confined to any particular method of homogenization. Our theoretical analysis is supplemented with a numerical example: a hexahedral lattice of cylindrical air holes in a dielectric host. Even though this case is highly isotropic, which might be thought of as conducive to homogenization, the uncertainty principles remain valid.

  7. Molecular dynamics simulations of turbostratic dry and hydrated montmorillonite with intercalated carbon dioxide.

    PubMed

    Myshakin, Evgeniy M; Makaremi, Meysam; Romanov, Vyacheslav N; Jordan, Kenneth D; Guthrie, George D

    2014-09-01

    Molecular dynamics simulations using classical force fields were carried out to study energetic and structural properties of rotationally disordered clay mineral-water-CO2 systems at pressure and temperature relevant to geological carbon storage. The simulations show that turbostratic stacking of hydrated Na- and Ca-montmorillonite and hydrated montmorillonite with intercalated carbon dioxide is an energetically demanding process accompanied by an increase in the interlayer spacing. On the other hand, rotational disordering of dry or nearly dry smectite systems can be energetically favorable. The distributions of interlayer species are calculated as a function of the rotational angle between adjacent clay layers. PMID:24745358

  8. Highly ordered periodic mesoporous organosilica nanoparticles with controllable pore structures

    NASA Astrophysics Data System (ADS)

    Guan, Buyuan; Cui, Yan; Ren, Zhongyuan; Qiao, Zhen-An; Wang, Li; Liu, Yunling; Huo, Qisheng

    2012-09-01

    A general synthetic procedure for highly ordered and well-dispersed periodic mesoporous organosilica (PMO) nanoparticles is reported based on a single cationic surfactant cetyltrimethylammonium bromide (CTAB) and simple silica sources with organic bridging groups via an ammonia-catalyzed sol-gel reaction. By changing the bridging group in the silica sources, the pore structures of the as-made particles with three-dimensional hexagonal (P63/mmc), cubic (Pm3n), two-dimensional hexagonal (P6mm), and wormlike structure were evidenced by powder X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The size range of the nanoparticles can be adjusted from 30 nm to 500 nm by variation of the ammonia concentration or the co-solvent content of the reaction medium. The PMO nanoparticles with high concentration of organic groups in the framework offered good thermal stability, good dispersion in low polarity solvent and high adsorption of small hydrophobic molecules. Finally, the dye functionalized PMO nanoparticles show low cytotoxicity and excellent cell permeability, which offers great potential for biomedical applications.A general synthetic procedure for highly ordered and well-dispersed periodic mesoporous organosilica (PMO) nanoparticles is reported based on a single cationic surfactant cetyltrimethylammonium bromide (CTAB) and simple silica sources with organic bridging groups via an ammonia-catalyzed sol-gel reaction. By changing the bridging group in the silica sources, the pore structures of the as-made particles with three-dimensional hexagonal (P63/mmc), cubic (Pm3n), two-dimensional hexagonal (P6mm), and wormlike structure were evidenced by powder X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The size range of the nanoparticles can be adjusted from 30 nm to 500 nm by variation of the ammonia concentration or the co-solvent content of the reaction medium. The PMO nanoparticles with high concentration of organic

  9. Pu(V) and Pu(IV) sorption to montmorillonite.

    PubMed

    Begg, James D; Zavarin, Mavrik; Zhao, Pihong; Tumey, Scott J; Powell, Brian; Kersting, Annie B

    2013-05-21

    Plutonium (Pu) adsorption to and desorption from mineral phases plays a key role in controlling the environmental mobility of Pu. Here we assess whether the adsorption behavior of Pu at concentrations used in typical laboratory studies (≥10(-10) [Pu] ≤ 10(-6) M) are representative of adsorption behavior at concentrations measured in natural subsurface waters (generally <10(-12) M). Pu(V) sorption to Na-montmorillonite was examined over a wide range of initial Pu concentrations (10(-6)-10(-16) M). Pu(V) adsorption after 30 days was linear over the wide range of concentrations studied, indicating that Pu sorption behavior from laboratory studies at higher concentrations can be extrapolated to sorption behavior at low, environmentally relevant concentrations. Pu(IV) sorption to montmorillonite was studied at initial concentrations of 10(-6)-10(-11) M and was much faster than Pu(V) sorption over the 30 day equilibration period. However, after one year of equilibration, the extent of Pu(V) adsorption was similar to that observed for Pu(IV) after 30 days. The continued uptake of Pu(V) is attributed to a slow, surface-mediated reduction of Pu(V) to Pu(IV). Comparison between rates of adsorption of Pu(V) to montmorillonite and a range of other minerals (hematite, goethite, magnetite, groutite, corundum, diaspore, and quartz) found that minerals containing significant Fe and Mn (hematite, goethite, magnetite, and groutite) adsorbed Pu(V) faster than those which did not, highlighting the potential importance of minerals with redox couples in increasing the rate of Pu(V) removal from solution. PMID:23614502

  10. Heterostructured nanohybrid of zinc oxide-montmorillonite clay.

    PubMed

    Hur, Su Gil; Kim, Tae Woo; Hwang, Seong-Ju; Hwang, Sung-Ho; Yang, Jae Hun; Choy, Jin-Ho

    2006-02-01

    We have synthesized heterostructured zinc oxide-aluminosilicate nanohybrids through a hydrothermal reaction between the colloidal suspension of exfoliated montmorillonite nanosheets and the sol solution of zinc acetate. According to X-ray diffraction, N2 adsorption-desorption isotherm, and field emission-scanning electron microscopic analyses, it was found that the intercalation of zinc oxide nanoparticles expands the basal spacing of the host montmorillonite clay, and the crystallites of the nanohybrids are assembled to form a house-of-cards structure. From UV-vis spectroscopic investigation, it becomes certain that calcined nanohybrid contains two kinds of the zinc oxide species in the interlayer space of host lattice and in mesopores formed by the house-of-cards type stacking of the crystallites. Zn K-edge X-ray absorption near-edge structure/extended X-ray absorption fine structure analyses clearly demonstrate that guest species in the nanohybrids exist as nanocrystalline zinc oxides with wurzite-type structure. PMID:16471722

  11. 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.

  12. Mechanisms of CO2 Interaction with Montmorillonite

    NASA Astrophysics Data System (ADS)

    Romanov, V.; Myshakin, E. M.; Howard, B.; Guthrie, G.

    2013-12-01

    Improved understanding of basic fluid-rock interactions can lead to more accurate models of the coupled fluid-flow and geomechanics in engineered geological systems. We studied carbon dioxide (CO2) interaction with source clay samples from The Clay Minerals Society. The manometric, infrared (IR) and X-ray diffraction (XRD) data indicated that montmorillonite can permanently trap CO2 molecules in its interlayer, after dynamic exposure to supercritical CO2. Such trapping is quite secure and appears to result in partial carbonate formation. Molecular dynamics simulations were carried out to investigate CO2 intercalation into the interlayer and its interaction with interlayer species. Previously reported results of simulations using simplified smectite models suggested that the experimentally observed red shift of the asymmetric-stretch vibrational mode for the trapped carbon dioxide can be attributed to induced polarization of the CO2 molecule by the interlayer water molecules. Modified smectite models were designed to account for the naturally occurring structural disorder that allows guest molecules to occupy localized interlamellar voids. In such models, energy dependences and structural rearrangements of the interlayer species are governed by rotational misalignment in turbostratically disordered clay. CO2 invasion in the interlayer disrupts the long-range ordering of water molecules and cations thus forcing the system to adopt energetically unfavorable configurations. New findings indicate that interaction between intercalated CO2 and H2O is limited and, with the increasing interlayer hydration, CO2 preferentially accumulates in interlamellar voids. The vibrational spectra produced by the new model, assuming that clay systems can exist in fractional hydration states, show either a combination of undisturbed and red-shifted asymmetric-stretch modes or a broad peak consistent with the multiple smeared peaks, which explain the multi-mode features that have appeared

  13. 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.

  14. 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...

  15. 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

  16. 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.

  17. 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

  18. 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

  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. 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

  1. 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.

  2. 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.

  3. Synthesis and Characterization of the Hybrid Clay- Based Material Montmorillonite-Melanoidin: A Potential Soil Model

    SciTech Connect

    V Vilas; B Matthiasch; J Huth; J Kratz; S Rubert de la Rosa; P Michel; T Schäfer

    2011-12-31

    The study of the interactions among metals, minerals, and humic substances is essential in understanding the migration of inorganic pollutants in the geosphere. A considerable amount of organic matter in the environment is associated with clay minerals. To understand the role of organic matter in the environment and its association with clay minerals, a hybrid clay-based material (HCM), montmorillonite (STx-1)-melanoidin, was prepared from L-tyrosine and L-glutamic acid by the Maillard reaction. The HCM was characterized by elemental analysis, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), scanning transmission x-ray microscopy (STXM), and thermal analysis. The presence of organic materials on the surface was confirmed by XPS and STXM. The STXM results showed the presence of organic spots on the surface of the STx-1 and the characterization of the functional groups present in those spots. Thermal analysis confirmed the existence of organic materials in the montmorillonite interlayer, indicating the formation of a composite of melanoidin and montmorillonite. The melanoidin appeared to be located partially between the layers of montmorillonite and partially at the surface, forming a structure that resembles the way a cork sits on the top of a champagne bottle.

  4. 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

  5. Adsorption of ferrous ions onto montmorillonites

    NASA Astrophysics Data System (ADS)

    Qin, Dawei; Niu, Xia; Qiao, Min; Liu, Gang; Li, Hongxin; Meng, Zhenxiao

    2015-04-01

    The adsorption of Fe (II) onto montmorillonites was investigated through initial concentration, contact time, pH and temperature. During the whole adsorption process, the ascorbic acid (Vitamin C) was added as a kind of antioxidant, at the same time, deionized water (after boiling) and nitrogen protection were also used to avoid oxidation. The Fe2+/Fetotal ratio of the iron exists in the Fe-montmorillonites was found more than 95%. Two kinetic models, including pseudo-first-order and pseudo-second-order model, were used to analyze the adsorption process of Fe (II) on montmorillonites. The results of our study showed that adsorption process fitted with pseudo-second-order well. Adsorption isotherms showed that Langmuir model was better than Freundlich model. The thermodynamic parameters ΔG0 and ΔH0 were 3.696 kJ/mol and 6.689 kJ/mol (we just gave the values at 298 K), respectively. The positive values at different temperatures showed that the adsorption process was non-spontaneous and endothermic. The characteristics of materials were determined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Surface area and porosity analyzer, Thermogravimetric analysis (TGA), Differential scanning calorimeter (DSC) and Zeta potential distribution.

  6. 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

  7. Theoretical characterization of formamide on the inner surface of montmorillonite

    NASA Astrophysics Data System (ADS)

    Shi, Jing; Lou, Zhaoyang; Yang, Mingli; Zhang, Yao; Liu, Houbin; Meng, Yingfeng

    2014-06-01

    Density functional theory calculations were performed to characterize the low-lying structures of formamide (FA) and protonated formamide (FAH) in the interlayer space of montmorillonite (MMT). The interactions among FA/FAH, H2O, Na+, and the inner surface of MMT were systematically analyzed. The carbonyl-O of FA/FAH has strong coulomb interaction with Na+, while its amide-H forms hydrogen bonds (HBs) with water and MMT surface. The adsorption of FA is promoted by H2O, which exhibits a cooperative adsorption effect by enhancing the FA-Na+ coulomb interaction and by forming HBs with FA. Our study reveals the structural basis of FA/FAH as an intercalator for MMT splitting.

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

    DOEpatents

    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.

  9. 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

  10. 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

  11. Compressional and torsional wave amplitudes in rods with periodic structures

    NASA Astrophysics Data System (ADS)

    Morales, A.; Flores, J.; Gutierrez, L.; Mendez-Sanchez, R. A.

    2002-11-01

    To measure and detect elastic waves in metallic rods a low-frequency electromagnetic-acoustic transducer has been developed. Frequencies range from a few hertz up to hundreds of kilohertz. With appropriate configuration of the transducer, compressional or torsional waves can be selectively excited or detected. Although the transducer can be used in many different situations, it has been tested and applied to a locally periodic rod, which consists of a finite number of unit cells. The measured wave amplitudes are compared with theoretical ones, obtained with the one-dimensional transfer matrix method, and excellent agreement is obtained. copyright 2002 Acoustical Society of America.

  12. 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

  13. Optimization of Periodic Composite Structures for Sub-Wavelength Focusing

    SciTech Connect

    Dobson, David C.; Simeonova, Lyubima B.

    2009-08-15

    Recently, there has been plenty of work in designing and fabricating materials with an effective negative refractive index. Veselago realized that a slab of material with a refractive index of -1 would act as a lens. Pendry suggested that the Veselago lens would act as a superlens, providing a perfect image of an object in contrast to conventional lenses which are only able to focus a point source to an image having a diameter of the order of the wavelength of the incident field.Recent work has shown that similar focusing effects can be obtained with certain slabs of 'conventional' periodic composite materials: photonic crystals. The present work seeks to answer the question of what periodic dielectric composite medium (described by dielectric coefficient with positive real part) gives an optimal image of a point source. An optimization problem is formulated and it is shown that a solution exists provided the medium has small absorption. Solutions are characterized by an adjoint-state gradient condition, and several numerical examples illustrate both the plausibility of this design approach, and the possibility of obtaining smaller image spot sizes than with typical photonic crystals.

  14. 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.

  15. Characterization of the geometry of microscale periodic structures using acoustic microscopy.

    PubMed

    Shaw, Anurupa; Liu, Jingfei; Yoon, Suk Wang; Declercq, Nico F

    2016-08-01

    Periodic structures are very common in both scientific investigations and engineering applications. The geometry of the periodic structure is important for its designed functionality. Although the techniques such as optical and electron microscopy are capable of measuring the periodicity of microscale periodically-corrugated structures, they cannot be used to measure the height or depth of the corrugation. The technique of acoustic microscopy has been developed rapidly and it has been applied in the studies of steel integrated structures, ferro-elastic ceramics, human retina, semiconductors, composites, etc. In acoustic microscopy, V(z) curves have been used to investigate the visco-elastic parameters of thin sliced samples of composites, animal tissue, etc., while in this work it is applied in characterizing the geometry of periodically corrugated structures. The measurements of the geometry of periodic structures obtained using acoustic microscopy are compared with those obtained using optical microscopy, and the reliability of this acoustic technique is also examined. PMID:27259118

  16. Comments on energy confinement in non-periodic structures

    NASA Astrophysics Data System (ADS)

    Costa, S. N. J.; Balthazar, J. M.; Brasil, R. M. L. R. F.

    2008-09-01

    In this study, we investigate the possibility of mode localization occurrence in a non-periodic Pflüger's column model of a rocket with an intermediate concentrated mass at its middle point. We discuss the effects of varying the intermediate mass magnitude and its position and the resulting energy confinement for two cases. Free vibration analysis and the severity of mode localization are appraised, without decoupling the system, by considering as a solution basis the fundamental free response or dynamical solution. This allows for the reduction of the dimension of the algebraic modal equation that arises from satisfying the boundary and continuity conditions. By using the same methodology, we also consider the case of a cantilevered Plüger's column with rotational stiffness at the middle support instead of an intermediate concentrated mass.

  17. 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

  18. Influence of montmorillonites exchange capacity on the basal spacing of cation–anion organo-montmorillonites

    SciTech Connect

    Sanqin, Wu; Zepeng, Zhang; Yunhua, Wang; Libing, Liao; Jiansheng, Zhang

    2014-11-15

    Graphical abstract: This picture shows the distribution of organic modifier (CTAB and SDS) in Mt interlayer and the basal spacing changes of Mt modified by CTAB and SDS. Organic modifier molecule in Mt interlayer is more and more orderly. The basal spacing of Mt is from 1.5 nm to 5 nm as modifier added. - Highlights: • The d{sub 001} of Ca-Mt, R-Na-Mt, Na-Mt modified by CTAB and SDS can reach 5 nm. • It is easier to get cation–anion OMt with greater d{sub 001} if CEC is lower. • The organic molecules distribution in cation–anion OMt was analyzed. • The influence mechanism of Ca-Mt CEC on the d{sub 001} was discussed. - Abstract: With cationic and anionic surfactants cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfonate (SDS) as modifiers, Ca-montmorillonites (Ca-Mt), artificial Na-montmorillonites (R-Na-Mt) and natural Na-montmorillonites (Na-Mt) with different cation exchange capacity (CEC) were modified by solution intercalation method, respectively. Then cation–anion organo-montmorillonites (OMt) were prepared. The influence of CEC on the basal spacing of cation–anion OMt and the influence mechanism were discussed by X-ray diffraction (XRD) and zeta potential testing. The results indicate that the basal spacing of cation–anion OMt is related to CEC. For the same type montmorillonites, the basal spacing of cation–anion OMt decreases with the increase of CEC and it is easier to get cation–anion OMt with greater basal spacing when CEC is lower. Moreover, the CEC of Na-Mt has the greatest influence on the basal spacing of cation–anion OMt.

  19. Preparation and characterization of microporous SiO{sub 2}-ZrO{sub 2} pillared montmorillonite

    SciTech Connect

    Han, Yang-Su . E-mail: yshan@inanospace.com; Yamanaka, Shoji

    2006-04-15

    SiO{sub 2}-ZrO{sub 2} pillared montmorillonite (SZM) was prepared by the reaction of Na-montmorillonite with colloidal silica-zirconia particles which were prepared by depositing zirconium hydroxy cations on silica particles. By pillaring with the colloidal particles, the basal spacing of montmorillonite was expanded to ca. 45 A and the calcined SZM samples showed large specific surface areas up to 320 m{sup 2}/g at 400 deg. C. In spite of large interlayer separation, adsorption results indicated the presence of micropores generated between the colloidal particles. The microporous structure was maintained at least up to 600 deg. C and exhibited specific shape selectivity for the adsorption of large organic molecules, especially between toluene and mesitylene. According to the temperature-programmed-desorption (TPD) spectra of ammonia, the calcined SZM showed weakly acidic sites.

  20. 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.

  1. 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

  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. Poisson structures for lifts and periodic reductions of integrable lattice equations

    NASA Astrophysics Data System (ADS)

    Kouloukas, Theodoros E.; Tran, Dinh T.

    2015-02-01

    We introduce and study suitable Poisson structures for four-dimensional maps derived as lifts and specific periodic reductions of integrable lattice equations. These maps are Poisson with respect to these structures and the corresponding integrals are in involution.

  4. 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

  5. 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).

  6. Spiral organization of periodic structures in the Lorenz–Stenflo system

    NASA Astrophysics Data System (ADS)

    Rech, Paulo C.

    2016-07-01

    This paper reports the existence of organized periodic structures embedded in chaotic regions of a parameter plane of the Lorenz–Stenflo system. More specifically, this work reports on spiral organization of periodic structures observed in the (σ, s) parameter plane of the Lorenz–Stenflo system.

  7. Effects of pH on dielectric relaxation of montmorillonite, allophane, and imogolite suspensions

    SciTech Connect

    Ishida, Tomoyuki; Makino, Tomoyuki

    1999-04-01

    Dielectric measurements were performed on montmorillonite, allophane, and imogolite suspensions under various pH conditions, using time domain reflectometry over the frequency range 10 kHz--20 GHz. A dielectric relaxation peak due to bound water could be observed for all the clays. Allophane has two peaks, indicating that its peaks are very similar to those of silica-alumina gels. Although imogolite has a similar chemical composition, only one peak was found. The relaxation strength of montmorillonite is greater than that of the other two clays. For all the clays, the relaxation strength depended on the pH. A change in the relaxation strength according to a change in pH is explained in terms of the different network structures of the clay particles. It is suggested that bound water influences the network structure formation. In montmorillonite, a great relaxation process detected at low frequency is caused by surface polarization of counterions. The change in measure of the structural unit with the pH, identified from Schwartz`s theory, has a tendency similar to that postulated by other experimental techniques, and surface charge densities identified are close to those estimated from CEC.

  8. 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. PMID:24930689

  9. 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.

  10. Preparation and properties of poly HTBN-based urethane-urea/organo reactive montmorillonite nanocomposites

    NASA Astrophysics Data System (ADS)

    Li, Zai-Feng; Wu, Yuan; Zhang, Fu-Tao; Cao, Yu-Yang; Wu, Shou-Peng; Wang, Ting

    2012-12-01

    With ultrasonic assistant mixing way, an intercalated mixture of polyol/organo reactive montmorillonite (ORMMT) was pretreated. The prepolymer composed MMT clay was prepared by reaction of polyol/ORMMT mixture with toluene diisocyanate (TDI). The resultant prepolymer reacted with extender (DMTDA) and then the polyurethane-urea/organo reactive montmorillonite (PUU/ORMMT) nanocomposites were obtained. The structure, morphology and properties of PUU/ORMMT nanocomposites were characterized by FT-IR, TEM, AFM, strain-stress machine, TGA, and dynamic mechanical analysis (DMA). The results showed that when the OMMT content is 3%, the PUU/ORMMT nanocomposities performed super mechanical properties. Because of the presence of ORMMT, both T g of the soft segment and tan δ of the PUU increased, and the decomposition temperature for the first step and the second step increased respectively. TEM images showed that the organophilic MMT particles in the PUU composite exhibit a high degree of intercalation and exfoliation.

  11. 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.

  12. Polymerization of serine guanylate in the presence of montmorillonite

    NASA Technical Reports Server (NTRS)

    Paecht-Horowitz, M.

    1981-01-01

    Serine guanylate was prepared and its polymerization studied in the presence of montmorillonite and in its absence. In water, without clay, serine guanylate polymerizes in the same way as does serine adenylate. In the presence of montmorillonite, serine guanylate polymerizes to a lesser extent and produces also lower degrees of polymerization than does serine adenylate. It is postulated that the reason for this difference in behavior might lie in the fact that guanylic acid is much more acidic than adenylic acid; hence would bind much more strongly to the edges of montmorillonite and thus, by blocking these sites, would inhibit the catalytic activity of the clay.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Adsorption mechanism and structure of the montmorillonite complexes with (CH{sub 3}){sub 2}XO (X = C, and S), (CH{sub 3}O){sub 3}PO, and CH{sub 3}-CN molecules

    SciTech Connect

    Dios-Cancela, G.; Alfonso-Mendez, L.; Huertas, F.J.; Romero-Taboada, E.; Sainz-Diaz, C.I.; Hernandez-Laguna, A.

    2000-02-01

    The formation of complexes with different ligands in the interlayer space of montmorillonite saturated in Na{sup +}, Mg{sup 2+}, Ca{sup 2+}, Co{sup 2+}, Cu{sup 2+}, Ni{sup 2+}, Fe{sup 3+}, and Cr{sup 3+} was studied. Acetone, acetonitrile, dimethyl sulfoxide, and trimethylphosphate were used as ligands. The nature of the complexes was studied by means of X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, microcalorimetry, and ab initio quantum mechanical methods. In all cases, the organic ligands penetrate into the interlayer space at room temperature, forming complexes stable in vacuum with the interlayer cations. The ligand-cation ratio depends on the valence of the saturating cation. The cation-ligand interaction in these complexes has an ion-dipole electrostatic nature. The complexes are formed by the direct interaction of the oxygen or nitrogen atom of ligand and the interlayer cation. Using the quantum mechanical approach allows the authors to determine the disposition of the ligand in these complexes. In all cases, only one layer of ligands is present in the stable complexes.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Methanogens were grown in media containing bicarbonate buffer, nontronite or montmorillonite clay, and hydrogen gas. No other nutrients were added. These results suggest that martian clays may provide adequate nutrients to support organism growth.

  19. 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.

  20. 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.

  1. 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.

  2. 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

    2015-07-01

    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. PMID:26029791

  3. Analysis of Oligonucleotide DNA Binding and Sedimentation Properties of Montmorillonite Clay Using Ultraviolet Light Spectroscopy

    PubMed Central

    Beall, Gary W.; Sowersby, Drew S.; Roberts, Rachel D.; Robson, Michael H.; Lewis, L. Kevin

    2009-01-01

    Smectite clays such as montmorillonite form complexes with a variety of biomolecules, including the nucleic acids DNA and RNA. Most previous studies of DNA adsorption onto clay have relied upon spectrophotometric analysis after separation of free nucleic acids from bound complexes by centrifugation. In the current work we demonstrate that such studies produce a consistent error due to (a) incomplete sedimentation of montmorillonite and (b) strong absorbance of the remaining clay at 260 nm. Clay sedimentation efficiency was strongly dependent upon cation concentration (Na+ or Mg2+) and on the level of dispersion of the original suspension. An improved clay:DNA adsorption assay was developed and utilized to assess the impact of metal counterions on binding of single-stranded DNA to montmorillonite. X-ray diffraction demonstrated, for the first time, formation of intercalated structures consistent with orientation of the DNA strands parallel to the clay surface. Observed gallery spacings were found to closely match values calculated utilizing atomistic modeling techniques. PMID:19061334

  4. 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.

  5. Key parameters governing the dynamic response of long-period structures

    NASA Astrophysics Data System (ADS)

    Fukuwa, N.; Tobita, J.

    2008-04-01

    The present study describes the important factors (period, duration, and intensity) involved in evaluating input ground motion and structural response for the design of long-period structures such as high-rise buildings and base-isolated buildings. First, the fundamental dynamic properties of high-rise buildings are explained based on the results of newly introduced vibration observations programs. Next, the distribution of the predominant period and duration of seismic ground motion within the Nobi Plain, one of the largest sedimentary plains in Japan, is discussed with respect to the possibility of resonance of long-period structures. Finally, we introduce a recently developed long-stroke shaking table that is intended to convince structural engineers and building owners to take adequate countermeasures against large floor response in high-rise buildings because of resonance.

  6. 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.

  7. Periodic magnetic structures generated by spin–polarized currents in nanostripes

    SciTech Connect

    Volkov, Oleksii M. Sheka, Denis D.; Kravchuk, Volodymyr P.; Gaididei, Yuri; Mertens, Franz G.

    2013-11-25

    The influence of a transverse spin–polarized current on long ferromagnetic nanostripes is studied numerically. The magnetization behavior is analyzed for all range of the applied currents, up to the saturation. It is shown that the saturation current is a nonmonotonic function of the stripe width. A number of stable periodic magnetization structures are observed below the saturation. Type of the periodical structure depends on the stripe width. Besides the one–dimensional domain structure, typical for narrow wires, and the two–dimensional vortex–antivortex lattice, typical for wide films, a number of intermediate structures are observed, e.g., cross–tie and diamond state.

  8. Laser-induced periodic annular surface structures on fused silica surface

    SciTech Connect

    Liu, Yi; Brelet, Yohann; Forestier, Benjamin; Houard, Aurelien; Yu, Linwei; Deng, Yongkai; Jiang, Hongbing

    2013-06-24

    We report on the formation of laser-induced periodic annular surface structures on fused silica irradiated with multiple femtosecond laser pulses. This surface morphology emerges after the disappearance of the conventional laser induced periodic surface structures, under successive laser pulse irradiation. It is independent of the laser polarization and universally observed for different focusing geometries. We interpret its formation in terms of the interference between the reflected laser field on the surface of the damage crater and the incident laser pulse.

  9. 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.

  10. Effect of tool eccentricity on surface periodic banded structures in friction stir welding

    NASA Astrophysics Data System (ADS)

    Guo, N.; Wang, M. R.; Meng, Q.; Zhou, L.; Tang, D. Y.

    2015-12-01

    This paper describes the relationship between tool eccentricity and surface formation of periodic banded structures in friction stir welding. Motion characteristics of welding tool are calculated to explore the forming mechanism of banded structures. The results reveal that the welding tool motion differences on advancing side and retreating side caused by eccentricity are crucial for the formation of banded structures. The crests and troughs of banded structures form during tool motion on retreating side and advancing side, respectively.

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

    NASA Astrophysics Data System (ADS)

    Rebollar, Esther; Vázquez de Aldana, Javier R.; Pérez-Hernández, José A.; Ezquerra, Tiberio A.; Moreno, Pablo; Castillejo, Marta

    2012-01-01

    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.

  12. 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.

  13. 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.

  14. Response of seismic-isolated structures under long-period motions

    SciTech Connect

    Ma, D.C.

    1991-01-01

    In the past decade, considerable progress has been made on reducing the seismic response of structures through seismic isolation. Application of seismic-isolation techniques to nuclear power facilities is currently being investigated. This paper presents an analysis of the effect of long period motions on a seismic-isolated nuclear structure. Preliminary analysis indicates that long-period earthquake motions increase structural accelerations and relative displacements between the upper and lower mats. Relative displacement between the mats can be represented by spectral displacement at the frequency of the structure, and can be effectively reduced by increasing viscous damping in the isolator. The isolated structure behaves as a system with one degree of freedom. Future analysis of seismic effects on seismic-isolated structures should include the linear and nonlinear effects of soil-structure interactions. 3 refs., 12 figs., 3 tabs.

  15. Montmorillonite-levan nanocomposites with improved thermal and mechanical properties.

    PubMed

    Chen, Xiaoming; Gao, Hongsheng; Ploehn, Harry J

    2014-01-30

    This work reports on the structure and properties of novel nanocomposites composed of exfoliated montmorillonite clay blended with levan, a polysaccharide produced by Bacillus sp. Dry levan is very brittle, making it difficult to obtain stand-alone films. MMT-levan composites were prepared by solution blending in water, coating on plastic surfaces, partial drying at 50°C, and conditioning in air at 50-60% relative humidity. This process results in freestanding, transparent, and flexible films of pure levan and MMT-levan composites plasticized by 10-15 wt% water. XRD patterns from levan-MMT composites indicate an MMT interlayer spacing 0.62 nm greater than that of the starting MMT, suggesting re-stacking of MMT platelets coated by adsorbed, uncoiled levan molecules. FTIR results suggest that levan adheres to MMT via water-mediated hydrogen bonding between the levan's hydroxyl groups and MMT surface oxygens. MMT-levan composites have improved thermal stability and a well-defined glass transition temperature that increases with MMT loading. The tensile moduli of levan-MMT composites increase by as much as 480% relative to pure levan. The XRD and mechanical property results suggest that MMT reinforces levan through a filler network structure composed of MMT platelets bridged by adsorbed levan molecules, enhanced when the MMT loading becomes high enough (5-10wt% MMT) to induce an isotropic-nematic transition in MMT platelet orientation. PMID:24299812

  16. Bifurcation structure of the C-type period-doubling transition

    NASA Astrophysics Data System (ADS)

    Laugesen, Jakob L.; Mosekilde, Erik; Zhusubaliyev, Zhanybai T.

    2012-03-01

    The period-doubling transition to chaos along the edge of an Arnold tongue is known to display unusual organization and scaling behavior (Kuznetsov et al. (2005) [7]). It is also known that forced period-doubling systems may be associated with the appearance of so-called period-doubled tori (Arneodo et al. (1983) [15]). Using the Rössler system as an example, we present a detailed analysis of the bifurcation structure associated with the forcing of a three-dimensional period-doubling system. We explain how this structure is related to the recently discovered phenomenon of multi-layered tori and discuss different bifurcation scenarios that transform a resonance torus into a period-doubled ergodic torus. Similar bifurcation phenomena have recently been observed in a biologically relevant model of kidney blood flow regulation in response to fluctuations in arterial pressure.

  17. 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)

  18. 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.

  19. 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

  20. 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. PMID:27066069

  1. Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

    NASA Astrophysics Data System (ADS)

    Abere, Michael J.; Torralva, Ben; Yalisove, Steven M.

    2016-04-01

    The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period <0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/interstitial pairs. Stress relaxation, via diffusing defects, forms the 350-400 nm tall and ˜90 nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiometry.

  2. 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.

  3. 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.

  4. Heteroepitaxial formation of aligned mesostructured silica films with large structural periodicities from mixed surfactant systems.

    PubMed

    Hayase, Saeko; Kanno, Yosuke; Watanabe, Masatoshi; Takahashi, Masahiko; Kuroda, Kazuyuki; Miyata, Hirokatsu

    2013-06-11

    Liquid-crystal phases consisting of cylindrical micelles of amphiphilic block copolymers and silica precursors are epitaxially built up on aligned surface micelles formed by an alkyl-PEO surfactant, Brij56, irrespective of the large difference in the intrinsic structural periodicities resulting in the formation of fully aligned mesostructured silica films with large lattice constants. Brij56 works as an alignment controlling agent on rubbing-treated polyimide through selective adsorption from a precursor solution containing the two surfactants, a block copolymer and Brij56, through strong hydrophobic interactions to form an anisotropic surface micelle structure. Aligned mesostructured silica layers with larger periodicities, which dominantly consist of block copolymers, form on these aligned surface micelles by gradually changing the vertical periodicity keeping the lateral intermicelle distance constant. This can be regarded as a kind of heteroepitaxy because the lattice constant at the surface is different from that of the bulk of the film. On the basis of this new concept, highly aligned mesostructured silica films with structural periodicities as large as 10 nm are successfully formed, which has never been achieved when the block copolymers are used alone as the structure-directing agent. The periodicity of the aligned films can precisely be controlled by an appropriate choice of block copolymers and the mixing ratio of the two surfactants, which increases the opportunity for applications of these films with highly anisotropic mesoscale structure. PMID:23721098

  5. 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.

  6. 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. PMID:24357622

  7. Catalytic Ethanol Dehydration over Different Acid-activated Montmorillonite Clays.

    PubMed

    Krutpijit, Chadaporn; Jongsomjit, Bunjerd

    2016-01-01

    In the present study, the catalytic dehydration of ethanol to obtain ethylene over montmorillonite clays (MMT) with mineral acid activation including H2SO4 (SA-MMT), HCl (HA-MMT) and HNO3 (NA-MMT) was investigated at temperature range of 200 to 400°C. It revealed that HA-MMT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. At 400°C, the HA-MMT yielded 82% of ethanol conversion having 78% of ethylene yield. At lower temperature (i.e. 200 to 300°C), diethyl ether (DEE) was a major product. The highest activity obtained from HA-MMT can be attributed to an increase of weak acid sites and acid density by the activation of MMT with HCl. It can be also proven by various characterization techniques that in most case, the main structure of MMT did not alter by acid activation (excepted for NA-MMT). Upon the stability test for 72 h during the reaction, the MMT and HA-MMT showed only slight deactivation due to carbon deposition. Hence, the acid activation of MMT by HCl is promising to enhance the catalytic dehydration of ethanol. PMID:27041515

  8. 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

  9. Montmorillonite nanodevices for the colon metronidazole delivery.

    PubMed

    Calabrese, Ilaria; Cavallaro, Gennara; Scialabba, Cinzia; Licciardi, Mariano; Merli, Marcello; Sciascia, Luciana; Turco Liveri, Maria Liria

    2013-11-30

    The adsorption profiles of the antibiotic metronidazole (MNE) into the K10-montmorillonite (MMT-K10) clay and the subsequent release have been investigated as a function of pH and MNE/MMT-K10 ratio, in order to evaluate the potential of the MNE/MMT-K10 hybrids as controlled drug delivery system. The adsorption mechanism has been first elucidated by performing complementary equilibrium and kinetic studies and through the X-ray diffractometry (XRD) characterization of the obtained composite materials. The gathered results allowed us to propose a mechanism consisting of a multi-step pathway involving the neutral and the cationic form of the drug, which interact with different sites of the clay surfaces, i.e. the interlayer region and the faces of the lamella. In a second step the drug release kinetics has been studied under physiological pH mimicking conditions simulating the oral drug administration and delivery. For the sake of comparison the commercial formulation has also been employed for the release studies. The investigation of the release profiles and the comparison with the commercial formulation of the drug reveal that the new-tailor made formulation could be fruitful exploited for successfully prolonged the action of drug in the desired site. PMID:24076230

  10. 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).

  11. 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

  12. 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. PMID:24329377

  13. 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.

  14. Floquet wave-based analysis of transient scattering from doubly periodic, discretely planar, perfectly conducting structures

    NASA Astrophysics Data System (ADS)

    Chen, Nan-Wei; Lu, Mingyu; Capolino, Filippo; Shanker, Balasubramaniam; Michielssen, Eric

    2005-08-01

    A Floquet wave-based algorithm for solving an electric field time domain integral equation pertinent to the analysis of transient plane wave scattering from doubly periodic, discretely planar, perfect electrically conducting structures is presented. The proposed scheme accelerates the evaluation of fields generated by periodic constellations of band-limited transient currents via their expansion in time domain Floquet waves and use of blocked fast Fourier transforms. The validity and effectiveness of the resulting algorithm are demonstrated through a number of examples.

  15. Experimental evaluation of natural period of masonry and reinforced concrete structures during operative conditions

    NASA Astrophysics Data System (ADS)

    Carlo Ponzo, Felice; Ditommaso, Rocco; Auletta, Gianluca; Nigro, Antonella; Iacovino, Chiara; Salvatore Nigro, Domenico

    2016-04-01

    This work focuses on the experimental evaluation of the fundamental period of buildings of various types (masonry and reinforced concrete) using measurements of ambient vibrations on real buildings located in Basilicata (Italy) and numerical analyses. The results are compared with the simplified formula provided by the Seismic Italian Code (NTC2008), that is function of structural typology and height for both near collapse and limited damage limit states and experimental results provided by the recent scientific literature. With the intention of proposing simplified relationships to evaluate the fundamental period of buildings, several numerical and experimental campaigns, on different structures all around the world, have been carried out in the last years in order to calibrate different kind of formulas. Most of formulas retrieved from both numerical and experimental analyses provides vibration periods smaller than those suggested by the NTC2008. However, it is well known that the fundamental period of a structure play a key role in the correct evaluation of the spectral acceleration for seismic static analyses. Generally, simplified approaches impose the use of safety factors greater than those related to in depth nonlinear analyses with the aim to cover possible unexpected uncertainties. Using the simplified formula proposed by the Italian seismic code the fundamental period is quite higher than fundamental periods experimentally evaluated on real structures, with the consequence that the spectral acceleration adopted in the seismic static analysis may be significantly different than real spectral acceleration. This approach could produces a decreasing in safety factors obtained using linear seismic static analyses. Based on numerical and experimental evidences, the authors suggest a possible update of the seismic codes formula for the simplified estimation of the fundamental period of vibration of existing masonry and RC buildings. Acknowledgements This study

  16. 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.

  17. A novel sensitivity-based method for damage detection of structures under unknown periodic excitations

    NASA Astrophysics Data System (ADS)

    Naseralavi, S. S.; Salajegheh, E.; Fadaee, M. J.; Salajegheh, J.

    2014-06-01

    This paper presents a technique for damage detection in structures under unknown periodic excitations using the transient displacement response. The method is capable of identifying the damage parameters without finding the input excitations. We first define the concept of displacement space as a linear space in which each point represents displacements of structure under an excitation and initial condition. Roughly speaking, the method is based on the fact that structural displacements under free and forced vibrations are associated with two parallel subspaces in the displacement space. Considering this novel geometrical viewpoint, an equation called kernel parallelization equation (KPE) is derived for damage detection under unknown periodic excitations and a sensitivity-based algorithm for solving KPE is proposed accordingly. The method is evaluated via three case studies under periodic excitations, which confirm the efficiency of the proposed method.

  18. Distributed Feedback in and Distributed Bragg Reflection from Periodic Chiral Structures.

    NASA Astrophysics Data System (ADS)

    Flood, Kevin Michael

    1995-01-01

    In this study, we examine the combined effects of electromagnetic chirality and periodicity on wave interactions in active and passive media. Isotropic chiral media have the unique property of possessing two intrinsic indices of refraction without the additional complication of anisotropy. The two refractive indices arise from different propagation velocities for right-circularly-polarized (RCP) and left -circularly-polarized (LCP) waves (i.e., circular birefringence), and their existence suggests that chiral media may be used in conjunction with the coherent feedback characteristics of periodic structures to create structures that favor either RCP or LCP solutions. In this study, we develop the theory that describes the wave interactions in such periodic chiral structures, and we examine several representative cases, including active devices, to identify specific characteristics. Bandgap characteristics are developed here for finite-length slabs of periodic chiral media using coupled -mode theory. The theory shows that stratified, periodic, isotropic media fall into one of three categories: subchiral, chiral, or superchiral. The superchiral periodic medium possesses three stop bands for the fundamental Bragg condition where the three stop bands are associated with LCP rightarrow RCP coupling, LCP to LCP coupling, and RCP to RCP coupling. We examine the reflectivity for superchiral periodic media to show the degree of polarization mode isolation for both passive and active structures. We also study the relationships among the chiral constitutive parameters (i.e., permittivity, permeability, and chirality admittance) based on a canonical chiral media model, and we address how the presence of chirality may enhance the reflectivity from periodic slabs. In addition to periodic media, we investigate the role of chirality for mode coupling in symmetric planar waveguides with periodic boundaries. Such structures are of current interest as mode converters, filters, and

  19. Vertex-connectivity in periodic graphs and underlying nets of crystal structures.

    PubMed

    Eon, Jean Guillaume

    2016-05-01

    Periodic nets used to describe the combinatorial topology of crystal structures have been required to be 3-connected by some authors. A graph is n-connected when deletion of less than n vertices does not disconnect it. n-Connected graphs are a fortiari n-coordinated but the converse is not true. This article presents an analysis of vertex-connectivity in periodic graphs characterized through their labelled quotient graph (LQG) and applied to a definition of underlying nets of crystal structures. It is shown that LQGs of p-periodic graphs (p ≥ 2) that are 1-connected or 2-connected, but not 3-connected, are contractible in the sense that they display, respectively, singletons or pairs of vertices separating dangling or linker components with zero net voltage over every cycle. The contraction operation that substitutes vertices and edges, respectively, for dangling components and linkers yields a 3-connected graph with the same periodicity. 1-Periodic graphs can be analysed in the same way through their LQGs but the result may not be 3-connected. It is claimed that long-range topological properties of periodic graphs are respected by contraction so that contracted graphs can represent topological classes of crystal structures, be they rods, layers or three-dimensional frameworks. PMID:27126114

  20. 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.

  1. 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.

  2. 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. PMID:26518526

  3. Silicon surface periodic structures produced by plasma flow induced capillary waves

    SciTech Connect

    Dojcinovic, I. P.; Kuraica, M. M.; Obradovic, B. M.; Puric, J.

    2006-08-14

    Silicon single crystal surface modification by the action of nitrogen quasistationary compression plasma flow generated by a magnetoplasma compressor is studied. It has been found that highly oriented silicon periodic cylindrical shape structures are produced during a single pulse surface treatment. The periodical structure formation can be related to the driven capillary waves quenched during fast cooling and resolidification phase of the plasma flow interaction with silicon surface. These waves are induced on the liquid silicon surface due to the compression plasma flow intrinsic oscillations.

  4. 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

  5. Measuring the isoelectric point of the edges of clay mineral particles: the case of montmorillonite.

    PubMed

    Pecini, Eliana M; Avena, Marcelo J

    2013-12-01

    The isoelectric point (IEP) of the edge surface of a montmorillonite sample was determined by using electrophoretic mobility measurements. This parameter, which is fundamental for the understanding of the charging behavior of clay mineral surfaces, was never measured so far because of the presence of permanent negative charges within the montmorillonite structure, charges that mask the electrokinetic behavior of the edges. The strategy was to block or neutralize the structural charges with two different cations, methylene blue (MB(+)) and tetraethylenepentaminecopper(II) ([Cu(tetren)](2+)), so that the charging behavior of the particles becomes that of the edge surfaces. Adsorption isotherms of MB(+) and [Cu(tetren)](2+) at different ionic strengths (NaCl) were performed to establish the uptakes that neutralize the cation exchange capacity (CEC, 0.96 meq g(-1)) of the sample. At high adsorptive concentrations, there was a superequivalent adsorption of MB(+) (adsorption exceeding the CEC) and an equivalent adsorption of [Cu(tetren)](2+) (adsorption reaching the CEC). In both cases, structural charges were neutralized at uptakes very close to the CEC. Zeta potential (ζ) vs pH data at different ionic strengths of montmorillonite with adsorbed MB(+) allowed to estimate an upper limit of the edge's IEP, 5.3 ± 0.2. The same kind of data obtained with adsorbed [Cu(tetren)](2+) provided a lower limit of the IEP, 4.0 ± 0.2. These values are in agreement with previously informed IEP and point of zero charge of pyrophyllite, which is structurally analogous to montmorillonite but carries no permanent charges. The importance of knowing the IEP of the edge surface of clay minerals is discussed. This value characterizes the intrinsic reactivity of edges, that is, the protonating capacity of edge groups in absence of any electric field generated by structural charges. It also allows us to correct relative edge charge vs pH curves obtained by potentiometric titrations and to

  6. Electromagnetic scattering from a structured slab comprised of periodically placed resistive cards

    NASA Astrophysics Data System (ADS)

    Jorgenson, Roy E.; Mittra, Raj

    1989-05-01

    The structured slab, which is constructed by arranging cells composed of thin, lossy, dielectric cards on a one- or two-dimensional lattice, is an important material in the aerospace industry because of its high strength-to-weight ratio. Recently, the structured slab has also been used to reduce the radar cross section of various aircraft. It is important, therefore, to characterize how an electromagnetic wave scatters from this slab. The structured slabs discussed herein are constructed by repeating lossy strips periodically in one dimension or lossy plates in two dimensions. An electric field integral equation is formulated which has as its unknown the electric current flowing in a single unit cell of the structure. The periodicity of the structure is accounted for by using an efficiently calculated periodic Green's function. The loss is modeled by resistive boundary condition. The integral equation is solved by the method of moments using subdomain basis functions. The generalized scattering matrix is calculated and the propagating reflection coefficients are plotted as a function of frequency for various structures. The oblique scattering from one-dimensional arrays of strips is examined for various configurations of unit cells and various resistances. A depolarizing effect of the structure is found to be a function of incident angle and symmetry in the unit cell. The reflection from two-dimensional arrays of plates connected to form slabs of zigzag plates and honeycomb is also examined.

  7. Design and fabrication of infrared antireflecting bi-periodic micro-structured surfaces

    NASA Astrophysics Data System (ADS)

    Bouffaron, R.; Escoubas, L.; Simon, J. J.; Torchio, Ph.; Flory, F.; Berginc, G.; Masclet, Ph.; Perret, C.; Schiavone, P.

    2008-04-01

    Broadband antireflection properties of material surfaces are of primary interest for a wide variety of applications: to enhance the efficiency of photovoltaic cells, to increase the sensitivity of photodetectors, to improve the performance of light emitting diodes, etc... In the past, broadband antireflection multilayer coatings were widely used and recently very low refractive index materials in thin film form have been fabricated by several groups. The research work presented in this paper aims at modeling and fabricating bi-periodic micro-structured silicon surfaces exhibiting broadband antireflection properties in the infrared range. These structures of pyramidal shape, which typical dimensions are smaller than the wavelength, are not in the Effective Medium Theory (EMT) validity domain. The optimization of the optical properties of such patterned surfaces needs a fully Finite Difference Time Domain (FDTD) rigorous description of light propagation phenomena. The influence of various opto-geometrical parameters such as period, depth, shape of the pattern is examined. The antireflective properties of such bi-periodic patterned surfaces is then discussed using the photonic crystal theory and photonic band diagrams description. The structure is considered as a two dimensional periodic structure with a nonuniform third dimension. Correlations between the density of Bloch modes, flatness of dispersion curves and the surface reflectance are presented. The last part of this paper is devoted to the presentation of the fabrication and the characterization of the structures. Low cost and large surface processing techniques are proposed using wet anisotropic etching through a silica mask obtained by photolithography or nanoimprinting.

  8. [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. PMID:19271513

  9. 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.

  10. 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.

  11. 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.

  12. 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. PMID:16182436

  13. Hybrid collagen-based hydrogels with embedded montmorillonite nanoparticles.

    PubMed

    Nistor, Manuela Tatiana; Vasile, Cornelia; Chiriac, Aurica P

    2015-08-01

    Montmorillonite nanoparticles have been physically incorporated within a crosslinked collagen/poly(N-isopropyl acrylamide) network in order to adjust the properties of the stimuli-responsive hybrid systems. The research underlines both the influence of hydrogel composition and nanoparticle type on hybrid hydrogel properties. The dispersion of the montmorillonite nanoparticles in polymeric matrix have been visualized by SEM, TEM and AFM techniques and quantitatively and qualitatively estimated using near infrared chemical imaging. The electrical charge of the nanoparticles influenced the polymeric chain arrangement and the pore size. The morphologies of the nanoparticulated layers are partially exfoliated or intercalated and uniformly dispersed through the polymeric semi-interpenetrated network based on collagen and poly(N-isopropyl acrylamide). The hybrid hydrogels exhibit pseudoplastic behavior and the addition of nanoparticles has resulted in the increase of the complex viscosity. The adhesion capacity was affected mainly by the presence of organically modified montmorillonites. PMID:26042709

  14. 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

  15. The adsorption and reaction of adenine nucleotides on montmorillonite.

    PubMed

    Ferris, J P; Hagan, W J

    1986-01-01

    The binding of AMP to Zn(2+)-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 Zn(2+)-montmorillonite are 13 and 15 angstroms in the presence of PIPES, while a value of 12.8 angstroms 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 of DISN to 3'-AMP bound to Zn(2+)-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 inplicates surface catalysis by the montmorillonite. PMID:11540864

  16. 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. PMID:16488006

  17. 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.

  18. Phase matching in second-harmonic generation using artificial periodic structures.

    NASA Technical Reports Server (NTRS)

    Tang, C. L.; Bey, P. P.

    1973-01-01

    The use of artificial periodic structures, consisting of spatial modulations of the linear and nonlinear susceptibilities of a nonlinear optical medium, to achieve phase matching in second-harmonic generation is analyzed. Dispersion relations and approximate formulas for the second-harmonic fields generated under various conditions are obtained and used to evaluate the experimental situation.

  19. Multiple-grid frequency-selective surfaces as periodically loaded structures

    NASA Astrophysics Data System (ADS)

    Orta, R.; Tascone, R.; Zich, R.

    1988-04-01

    An novel approach to the analysis of multiple-grid frequency-selective surfaces (FSS) is presented. In this case, the multiple grid FSS is thought of as a periodically loaded structure where the unit cell consists of a grid with its adjacent layers. The Bloch wave passband and stopband are used to create the transmission and reflection bands.

  20. Possible selective adsorption of enantiomers by Na-montmorillonite

    NASA Technical Reports Server (NTRS)

    Friebele, E.; Shimoyama, A.; Ponnamperuma, C.

    1981-01-01

    Racemic amino acids including (D,L) alpha-alamine, (D,L) alpha-aminobutyric acid, (D,L) valine, and (D,L) norvaline were incubated with Na-montmorillonite at 100% CEC at three hydrogen ion concentrations, and amino acid adsorption was determined by ion exchange chromatography. Enantiomers were analyzed by gas chromatography. Differences in the quantities of D and L enantiomers in any of the fractions was no larger than a few percent. Although a large difference in the adsorption of the amino acid enantiomers was not observed, the analysis may indicate a small preferential adsorption (0.5-2%) of L-amino acids by Na-montmorillonite.

  1. Alkylammonium montmorillonites as adsorbents for organic vapors from air

    SciTech Connect

    Harper, M.; Purnell, C.J. )

    1990-01-01

    Montmorillonite clays may be modified by the exchange of the inorganic interlayer cations with alkylammonium ions, resulting in a fixed internal porosity. The pore size and shape depend on the nature of the alkylammonium ion. A number of different ions were used to prepare adsorbents with varying properties, and these were examined for their potential application to sampling organic vapors in air. Characterization involved determination of nitrogen and water contents, surface area, interlayer spacing, thermal stability, and breakthrough volumes of organic vapors. The adsorbent that showed the most promise (tetramethylammonium montmorillonite (TMA)) was further evaluated for use as an adsorbent in both thermal- and solvent-desorable sampling systems.

  2. Modeling laser-induced periodic surface structures: Finite-difference time-domain feedback simulations

    SciTech Connect

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

    2014-03-14

    A model predicting the formation of laser-induced periodic surface structures (LIPSSs) is presented. That is, the finite-difference time domain method is used to study the interaction of electromagnetic fields with rough surfaces. In this approach, the rough surface is modified by “ablation after each laser pulse,” according to the absorbed energy profile, in order to account for inter-pulse feedback mechanisms. LIPSSs with a periodicity significantly smaller than the laser wavelength are found to “grow” either parallel or orthogonal to the laser polarization. The change in orientation and periodicity follow from the model. LIPSSs with a periodicity larger than the wavelength of the laser radiation and complex superimposed LIPSS patterns are also predicted by the model.

  3. Changing dynamic behavior of periodic structures by using piezoelectric circuitry with negative resistance

    NASA Astrophysics Data System (ADS)

    Zhao, J.; Wang, X.; Tang, J.

    2009-03-01

    Integrating a piezoelectric circuitry, which consists of a piezoelectric transducer connected with electrical circuitry elements, to a mechanical structure can alter the dynamic behavior of the structural system. From a system dynamics standpoint, these circuitry elements are analogous to the mass, damping, and stiffness elements in the mechanical regime. Using op amp circuits we can synthesize circuitry elements with interesting characteristics such as tunable or negative elements. In this research, we demonstrate that the negative resistance element can reduce the overall system damping, thereby changing the dynamic response of mechanical structures. In particular, it will be shown that not only the response amplitude can be amplified; the response pattern in the mistuned periodic structure can be altered significantly upon the change of local structural properties. Such phenomena are analyzed systematically, and the potential advantage for structural damage detection is highlighted.

  4. 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.

  5. 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.

  6. 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. PMID:20028057

  7. 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)

  8. Perfect coupling of light to a periodic dielectric/metal/dielectric structure

    SciTech Connect

    Wang, Zhengling E-mail: shiqiangli2013@u.northwestern.edu; Li, Shiqiang E-mail: shiqiangli2013@u.northwestern.edu; Chang, R. P. H.; Ketterson, John B.

    2014-07-21

    Using the finite difference time domain method, it is demonstrated that perfect coupling can be achieved between normally incident light and a periodic dielectric/metal/dielectric structure. The structure serves as a diffraction grating that excites modes related to the long range surface plasmon and short range surface plasmon modes that propagate on continuous metallic films. By optimizing the structural dimensions, perfect coupling is achieved between the incident light and these modes. A high Q of 697 and an accompanying ultrasharp linewidth of 0.8 nm are predicted for a 10 nm silver film for optimal conditions.

  9. 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.

  10. Polarisation-dependent generation of fs-laser induced periodic surface structures

    NASA Astrophysics Data System (ADS)

    Gräf, Stephan; Müller, Frank A.

    2015-03-01

    The formation of laser induced periodic surface structures (LIPPS) was investigated on polished stainless steel surfaces under irradiation with fs-laser pulses characterised by a pulse duration τ = 300 fs, a laser wavelength λ = 1025 nm, a repetition frequency frep = 250 Hz and a laser fluence F = 1 J/cm2. For this purpose line scans with a scanning velocity v = 0.5 mm/s were performed in air environment at normal incidence utilising a well-defined temporal control of the electrical field vector. The generated surface structures were characterised by optical microscopy, by scanning electron microscopy and by atomic force microscopy in combination with Fourier transformation. The results reveal the formation of a homogenous and highly periodic surface pattern of ripples with a period Λexp ≈ 925 nm aligned perpendicular to the incident electric field vector for static linear polarisation states. Utilising a motor-driven rotation device it was demonstrated that a continuously rotating electric field vector allows to transfer the originally well-ordered periodic ripples into tailored disordered surface structures that could be of particular interest for e.g. absorbing surfaces, plasmonic enhanced optoelectronic devices and biomedical applications.

  11. 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.

  12. 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.

  13. Pump-probe imaging of laser-induced periodic surface structures after ultrafast irradiation of Si

    SciTech Connect

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

    2013-09-30

    Ultrafast pump-probe microscopy has been used to investigate laser-induced periodic surface structure (LIPSS) formation on polished Si surfaces. A crater forms on the surface after irradiation by a 150 fs laser pulse, and a second, subsequent pulse forms LIPSS within the crater. Sequentially delayed images show that LIPSS with a periodicity slightly less than the fundamental laser wavelength of 780 nm appear on Si surfaces ∼50 ps after arrival of the second pump laser pulse, well after the onset of melting. LIPSS are observed on the same timescale as material removal, suggesting that their formation involves material ejection.

  14. 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. PMID:19905235

  15. 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.

  16. Footprints of Lagrangian flow structures in Eulerian concentration distributions in periodic mixing flows

    NASA Astrophysics Data System (ADS)

    Speetjens, M. F. M.; Lauret, M.; Nijmeijer, H.; Anderson, P. D.

    2013-05-01

    Transport of passive tracers may be described through the spatio-temporal evolution of Eulerian concentration distributions or via the geometrical composition of the Lagrangian flow structure. The present study seeks to deepen insight into the connection between the Eulerian and Lagrangian perspectives by investigating the role of Lagrangian coherent structures (LCSs) in the Eulerian concentration distributions in time-periodic and spatially-periodic mixing flows. Representation of the Eulerian transport by the mapping method, describing realistic transport problems by distribution matrices, admits a generic analysis based on matrix and graph theory. This reveals that LCSs-and the transport barriers that separate them-leave a distinct “footprint” in the eigenmode spectrum of the distribution matrix and, by proxy, of the underlying Eulerian transport operator. Transport barriers impart a block-diagonal structure upon the mapping matrix, where each block matrix A corresponds with a given LCS. Its kind is reflected in the spectrum of A; higher-order periodicity yields a distinct permutation within A. The composition of the distribution matrix versus the Lagrangian flow structure thus predicted is demonstrated by way of examples. These findings increase fundamental understanding of transport phenomena and have great practical potential for e.g. flow and mixing control.

  17. Electric birefringence spectroscopy of montmorillonite particles.

    PubMed

    Arenas-Guerrero, Paloma; Iglesias, Guillermo R; Delgado, Ángel V; Jiménez, María L

    2016-06-14

    Electric birefringence (EB) of suspensions of anisotropic particles can be considered an electrokinetic phenomenon in a wide sense, as both liquid motions and polarization of the electrical double layer (EDL) of the particles participate in the process of particle orientation under the applied field. The EB spectrum can be exploited for obtaining information on the dimensions, average value and anisotropy of the surface conductivity of the particles, and the concentration and Maxwell-Wagner polarization of the EDLs. It is thus a highly informative technique, applicable to non-spherical particles. In this paper, we investigate the birefringent response of plate-like montmorillonite particles as a function of the frequency and amplitude of the applied AC electric field, for different compositions (pH, ionic strength, particle concentration) of the suspensions. The transient electric birefringence (i.e., the decay of the refractive index anisotropy with time when the field is switched off) is used for estimating the average dimensions of the particle axes, by modeling it as an oblate spheroid. The obtained values are very similar to those deduced from electron microscopy determinations. The frequency spectra show a very distinct behaviour at low (on the order of a few Hz) and high (up to several MHz) frequencies: the α and Maxwell-Wagner-O'Konski relaxations, characteristic of EDLs, are detected at frequencies above 10 kHz, and they can be well explained using electrokinetic models for the polarization of EDLs. At low frequencies, in contrast, the birefringence changes to negative, an anomalous response meaning that the particles tend to orient with their symmetry axis parallel to the field. This anomaly is weaker at basic pH values, high ionic strengths and low concentrations. The results can be explained by considering the polydispersity of real samples: the fastest particles redistribute around the slowest ones, inducing a hydrodynamic torque opposite to that of

  18. Adsorption of aniline and toluidines on montmorillonite

    SciTech Connect

    Essington, M.E. )

    1994-09-01

    Bentonite clay liners are commonly employed to mitigate the movement of contaminants from waste disposal sites. In order to assess the ability of clay liner material to restrict the mobility of amine compounds under a variety of chemical conditions and to further elucidate amine adsorption characteristics, the adsorption of aniline and o-, m-, and p-toluidine on Ca[sup 2+]- and K[sup +]-saturated Wyoming bentonite (SWy-1) was investigated. Adsorption experiments were performed under conditions of varied pH and ionic environment. Amine adsorption on montmorillonite is pH dependent. Maximum amine adsorption occurs when solution pH is approximately equal to the pK[sub a] of the anilinium ion deprotonation reaction (pH 4.45-5.08). An amine adsorption envelope results from the combined influence of increasing anilinium ion and anilinium-aniline complex formation (as pH decreases to the pK[sub a]) and amine competition with H[sup +] for surface sites, decreasing anilinium-aniline complex concentration, and decreasing aniline available for water bridging with exchangeable Ca[sup 2+] and K[sup +] (as solution pH decreases below the pK[sub a]). For any given amine, maximum adsorption increases with decreasing ionic strength. Maximum amine adsorption is greater in the Ca[sup 2+] systems than in the K[sup +] systems at equivalent cation charge and reflects the formation of an amine water bridge with the exchangeable Ca[sup 2+]. Amine adsorption is also greater in chloride systems compared with sulfate systems at comparable cation concentrations, possibly due to the formation of aqueous anilinium-sulfate complexes. The amine compounds are retained mainly by bentonite through a cation exchange process, the capacity of the clay to adsorb the amine compounds being a significant percentage of the exchange capacity at the pK[sub a]. However, amine retention decreases with increasing pH and is minimal at solution pH values greater than 7. 19 refs., 6 figs.

  19. 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. PMID:26122570

  20. Synthesis and characterization of a novel chitosan/montmorillonite/hydroxyapatite nanocomposite for bone tissue engineering.

    PubMed

    Katti, Kalpana S; Katti, Dinesh R; Dash, Rajalaxmi

    2008-09-01

    Recently, biopolymer-based nanocomposites have been replacing synthetic polymer composites for various biomedical applications. This is often because of the biocompatible and biodegradable behavior of natural polymers. Several studies have been reported pertaining to the synthesis and characterization of chitosan(chi)/montmorillonite(MMT) and chitosan (chi)/hydroxyapatite (HAP) for tissue engineering applications. In the present work, a biopolymer-based novel nanocomposite chitosan/montmorillonite (MMT)/hydroxyapatite (HAP) was developed for biomedical applications. The composite was prepared from chitosan, unmodified MMT and HAP precipitate in aqueous media. The properties of the composites were investigated using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and thermogravimetric analysis (TGA). Nanomechanical properties were measured using nanoindentation. Cell culture experiments were also conducted in order to ascertain the biocompatibility of the composite. The XRD results indicate that an intercalated structure was formed with an increase in d-spacing of montmorillonite. FTIR studies provide the evidence of molecular interaction among the three different constituents of the composite. AFM images show well-distributed nanoparticles in the chitosan matrix. The composites also exhibit a significant enhancement in nanomechanical property as compared to pure chitosan as well as the chi/HAP and chi/MMT composites. The TGA results indicate that an intercalated nanocomposite was formed with improved thermal properties even compared to chi/MMT composites. The results of cell culture experiments show that the composite is biocompatible and has a better cell proliferation rate compared to chi/HAP composites. This work represents the design of a novel clay-chitosan-hydroxyapatite composite with improved mechanical properties that has potential applications in bone tissue engineering. PMID:18765898

  1. 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.

  2. Ion exchange and surface charge on montmorillonite clay

    SciTech Connect

    Sperry, J.M.; Peirce, J.J.

    1999-05-01

    An ion-exchange model originally developed for pure oxides prepared in the laboratory is extended to study of ion exchange and surface charge on a naturally occurring montmorillonite clay. The range of surface charges measured for montmorillonite with various electrolyte solutions and clay pretreatments is within the range of those measured for a wide variety of oxides prepared in the laboratory, including MnO{sub 2}-IC1, MnO{sub 2}-IC12, MnO{sub 2}-IC22, titanium dioxide, ferric oxide, and aluminum oxide. In addition, fitted parameter values for lateral interaction constants and equilibrium constants for the acid sites that characterize ion exchange on montmorillonite are on the same order of magnitude as those obtained for pure oxides. Surface charge of montmorillonite in sodium nitrate solution is measured to be approximately 15 to 25% greater than that measured between a pH of 4 and 9 in calcium chloride solution. This difference is attributed to the greater charge on the calcium (2{sup +}) ion; thus, its stronger electrostatic attraction to the acid hydroxyl site. An order of magnitude change in solids concentration (C{sub p}) can lead to a difference in measured net surface charge density of the same oxide sample of several orders of magnitude. This difference increases at higher pH, indicating the importance of reporting the corresponding C{sub p} at which experiments are conducted.

  3. Influence of Ca2+ on tetracycline adsorption on montmorillonite.

    PubMed

    Parolo, M Eugenia; Avena, Marcelo J; Pettinari, Gisela R; Baschini, Miria T

    2012-02-15

    The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca(2+) concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca(2+), TC adsorption was high at low pH and decreased as the pH increased. In the presence of Ca(2+), at least two different adsorption processes took place in the studied systems, i.e., cation exchange and Ca-bridging. Cation exchange was the prevailing process at pH<5, and thus, TC adsorption decreased by increasing total Ca(2+) concentration. On the contrary, Ca-bridging was the prevailing process at pH>5, and thus, TC adsorption increased by increasing Ca(2+) concentration. The pH 5 represents an isoadsorption pH where both adsorption processes compensate each other. TC adsorption became independent of Ca(2+) concentration at this pH. For TC adsorption on Ca(2+)-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca(2+) was close to 1 in the pH range of 5-9, indicating an important participation of Ca(2+) in the binding of TC to montmorillonite. X-ray diffraction and transmission electron microscopy showed that TC adsorption induced intercalation between montmorillonite layers forming a multiphase system with stacking of layers with and without intercalated TC. PMID:22189389

  4. Generation of laser-induced periodic surface structures on transparent material-fused silica

    NASA Astrophysics Data System (ADS)

    Schwarz, Simon; Rung, Stefan; Hellmann, Ralf

    2016-05-01

    We report on a comparison between simulated and experimental results for the generation of laser-induced periodic surface structures with low spatial frequency on dielectrics. Using the established efficacy factor theory extended by a Drude model, we determine the required carrier density for the generation of low spatial frequency LIPSS (LSFL) and forecast their periodicity and orientation. In a subsequent calculative step, we determine the fluence of ultrashort laser pulses necessary to excite this required carrier density in due consideration of the pulse number dependent ablation threshold. The later calculation is based on a rate equation including photo- and avalanche ionization and derives appropriate process parameters for a selective generation of LSFL. Exemplarily, we apply this approach to the generation of LSFL on fused silica using a 1030 nm femtosecond laser. The experimental results for the orientation and spatial periodicity of LSFL reveal excellent agreement with the simulation.

  5. 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. PMID:25076541

  6. 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.

  7. 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.

  8. Temporal femtosecond pulse shaping dependence of laser-induced periodic surface structures in fused silica

    SciTech Connect

    Shi, Xuesong; Jiang, Lan; Li, Xin Zhang, Kaihu; Yu, Dong; Yu, Yanwu; Lu, Yongfeng

    2014-07-21

    The dependence of periodic structures and ablated areas on temporal pulse shaping is studied upon irradiation of fused silica by femtosecond laser triple-pulse trains. Three types of periodic structures can be obtained by using pulse trains with designed pulse delays, in which the three-dimensional nanopillar arrays with ∼100–150 nm diameters and ∼200 nm heights are first fabricated in one step. These nanopillars arise from the break of the ridges of ripples in the upper portion, which is caused by the split of orthogonal ripples in the bottom part. The localized transient electron dynamics and corresponding material properties are considered for the morphological observations.

  9. Three-dimensionality of space in the structure of the periodic table of chemical elements

    SciTech Connect

    Veremeichik, T. F.

    2006-07-15

    The effect of the dimension of the 3D homogeneous and isotropic Euclidean space, and the electron spin on the self-organization of the electron systems of atoms of chemical elements is considered. It is shown that the finite dimension of space creates the possibility of periodicity in the structure of an electron cloud, while the value of the dimension determines the number of stable systems of electrons at different levels of the periodic table of chemical elements and some characteristics of the systems. The conditions for the stability of systems of electrons and the electron system of an atom as a whole are considered. On the basis of the results obtained, comparison with other hierarchical systems (nanostructures and biological structures) is performed.

  10. 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.

  11. 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.

  12. Desymmetrized Vertex Design for the Synthesis of Covalent Organic Frameworks with Periodically Heterogeneous Pore Structures.

    PubMed

    Zhu, Youlong; Wan, Shun; Jin, Yinghua; Zhang, Wei

    2015-11-01

    Two novel porous 2D covalent organic frameworks (COFs) with periodically heterogeneous pore structures were successfully synthesized through desymmetrized vertex design strategy. Condensation of C(2v) symmetric 5-(4-formylphenyl)isophthalaldehyde or 5-((4-formylphenyl)ethylene)isophthalaldehyde with linear hydrazine linker under the solvothermal or microwave heating conditions yields crystalline 2D COFs, HP-COF-1 and HP-COF-2, with high specific surface areas and dual pore structures. PXRD patterns and computer modeling study, together with pore size distribution analysis confirm that each of the resulting COFs exhibits two distinctively different hexagonal pores. The structures were characterized by FT-IR, solid state (13)C NMR, gas adsorption, SEM, TEM, and theoretical simulations. Such rational design and synthetic strategy provide new possibilities for preparing highly ordered porous polymers with heterogeneous pore structures. PMID:26478274

  13. Statistical analysis of digital images of periodic fibrous structures using generalized Hurst exponent distributions

    NASA Astrophysics Data System (ADS)

    Blachowicz, Tomasz; Ehrmann, Andrea; Domino, Krzysztof

    2016-06-01

    Distinction of diverse two-dimensional periodic structures can be based on a large number of methods and parameters, while the quantitative description of differences between similar samples is usually difficult. This article aims, by the use of statistical random walk in a generalized q-order dimensional space, at introducing a methodology to qualify the networked structures on the basis of exemplary textile samples. The presented results were obtained at 1-bit monochromatic maps obtained from optical microscopic pictures. Significant features of samples were represented by the obtained distributions of Hurst exponents and Shannon entropy calculations.

  14. 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.

  15. Thermal behaviour of a periodic structure supported by dielectric rods in vacuum

    NASA Astrophysics Data System (ADS)

    Gahlaut, V.; Alvi, P. A.; Ghosh, S.

    2014-06-01

    In a traveling-wave tube (TWT) the helical periodic slow-wave structure (SWS) is supported by dielectric supports in a metal envelope in high vacuum. The heat generated in the helix during beam-wave interaction, restricts the average power handling capability of a TWT, dissipated by conduction through support rods. Thermal contact resistances, arises at different joints of different materials, affect heat dissipation from the helix which have been studied and presented here.

  16. Periodic and aperiodic liquid crystal-polymer composite structures realized via spatial light modulator direct holography.

    PubMed

    Infusino, M; De Luca, A; Barna, V; Caputo, R; Umeton, C

    2012-10-01

    In this work we present the first realization and characterization of two-dimensional periodic and aperiodic POLICRYPS (Polymer Liquid Crystal Polymer Slices) structures, obtained by means of a single-beam holographic technique exploiting a high resolution spatial light modulator (SLM). A first investigation shows that the gratings, operating in the Raman Nath regime, exhibit a morphology and a electro-optical behavior that are typical of the POLICRYPS gratings realized by two-beam interference holography. PMID:23188278

  17. Periodic oscillation and fine structure of wedge-induced oblique detonation waves

    NASA Astrophysics Data System (ADS)

    Gui, Ming-Yue; Fan, Bao-Chun; Dong, Gang

    2011-12-01

    An oblique detonation wave for a Mach 7 inlet flow over a long enough wedge of 30° turning angle is simulated numerically using Euler equation and one-step rection model. The fifth-order WENO scheme is adopted to capture the shock wave. The numerical results show that with the compression of the wedge wall the detonation wave front structure is divided into three sections: the ZND model-like strcuture, single-sided triple point structure and dual-headed triple point strucuture. The first structure is the smooth straight, and the second has the characteristic of the triple points propagating dowanstream only with the same velocity, while the dual-headed triple point structure is very complicated. The detonation waves facing upstream and downstream propagate with different velocities, in which the periodic collisions of the triple points cause the oscillation of the detonation wave front. This oscillation process has temporal and spatial periodicity. In addition, the triple point trace are recorded to obtain different cell structures in three sections.

  18. A comparative study of the acidity toward the aqueous phase and adsorptive properties of Al{sub 13}-pillared montmorillonite and Al{sub 13}-pillared saponite

    SciTech Connect

    Bergaoui, L.; Mrad, I.; Ghorbel, A.; Lambert, J.F.

    1999-04-15

    The selectivity of an Al{sub 13}-pillared saponite and an Al{sub 13}-pillared montmorillonite for Cd{sup 2+} and Cu{sup 2+} adsorption was studied. The quantity of metal adsorbed on both pillared clays depends on the pH of the solution and the pillars density. Adsorption equilibria are regulated by the protonation equilibria of the amphoteric sites on the pillars. Pillared clays adsorb more cadmium and copper than classic aluminum hydroxides which is simply attributable to a higher density of surface aluminum groups. Significant differences in behavior are observed between pillared montmorillonite and pillared saponite. Pillared montmorillonite appears to be more acidic, which is correlated with a more advanced degree of structural modification of the pillars on calcination. The authors propose a tentative, partial structural model of pillar transformation compatible with these differences. At the same time, both pillared clays have similar affinities for cadmium II at low pH (5--6), but pillared montmorillonite seems to be a more efficient cadmium trap at pH = 8 when its surface groups are negatively ionized. Thus, the nature of the clay layers conditions the structural modifications of the intercalated [Al{sub 13}] polycations, which in turn determine adsorptive behavior.

  19. 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

  20. 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.

  1. Mechanically induced long period fiber gratings in Er3+ fiber for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Pulido-Navarro, M. G.; Alvarez-Chavez, J. A.; Ceballos-Herrera, D. E.; Escamilla-Ambrosio, P. J.

    2013-09-01

    This work presents preliminary results on wavelength sensitivity due to mechanically induced long period fiber grating (LPFG) on both standard single-mode and Er-doped fibers. The work presents and compares results for both types of fibers under different torsion conditions. In order to apply the torsion one of the fiber ends is fixed while torsion is applied on the other end. A LPFG whose period is 503μm is used to press on the fiber after the torsion, this will allow for micro curvatures to be formed on the fiber, which will in turn generate a periodical index perturbation on it. Here, it was noted that the rejection band shifts to shorter wavelengths for Er-doped fibers. It was detected that for torsion of 6 turns applied to 10cm doped fiber the wavelength peaks can shift up to 25nm, which is longer than similar results reported on standard fibers. Therefore, by using Er-doped fibers this technique will give more sensitive and accurate results on the real conditions of the structure under study. These results can be employed for sensing applications, especially for small to medium size structures, being these structures mechanical, civil or aeronautical. Theoretical calculations and simulations are employed for experimental results validation.

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

    PubMed

    Prakash, Kirti; 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

    2015-11-24

    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

  3. 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.

  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. Buckling in 2D periodic, soft and porous structures: effect of pore shape and lattice pattern

    NASA Astrophysics Data System (ADS)

    Shan, Sicong; Bertoldi, Katia; Shim, Jongmin; Overvelde, Johannes T. B.; Kang, Sung Hoon

    2013-03-01

    Adaptive structures allowing dramatic shape changes offer unique opportunities for the design of responsive and reconfigurable devices. Traditional morphing and foldable structures with stiff structural members and mechanical joints remains a challenge in manufacturing at small length scales. Soft structures where the folding mechanisms are induced by a mechanical instability represent a new class of novel adaptive materials which can be easily manufactured over a wide range of length scales. More specifically, soft porous structures with deliberately designed patterns can significantly change their architecture in response to diverse stimuli, opening avenues for reconfigurable devices that change their shapes to respond to their environment. While so far only two-dimensional periodic porous structures with circular holes arranged on a square or triangular lattice have been investigated, here we investigate both numerically and experimentally the effects of pore shape and lattice pattern on the macroscopic properties of the structures. Our results show that both the pore shape and lattice pattern can be used to effectively design desired materials and pave the way for the development of a new class of soft, active and reconfigurable devices over a wide range of length scales.

  6. 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. PMID:19090186

  7. 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.

  8. Can log-periodic power law structures arise from random fluctuations?

    NASA Astrophysics Data System (ADS)

    Wosnitza, Jan Henrik; Leker, Jens

    2014-05-01

    Recent research has established log-periodic power law (LPPL) patterns prior to the detonation of the German stock index (DAX) bubble in 1998. The purpose of this article is to explore whether a Langevin equation extracted from real world data can generate synthetic time series with comparable LPPL structures. To this end, we first estimate the stochastic process underlying the DAX log-returns during the period from mid-1997 until end-2003. The employed data set contains about 3.93ṡ106 intraday DAX quotes at a sampling rate of 15 s. Our results indicate that the DAX log-returns can be described as a Markov process. As a consequence, a Langevin equation is derived. Based on this model equation, we run extensive simulations in order to generate 100 synthetic DAX trajectories each covering 3000 trading days. We find LPPL behavior in ten artificial time series. Moreover, we can establish a link between LPPL patterns and ensuing bubble bursts in seven synthetic 600-week windows. However, the LPPL components in most synthetic trajectories differ fundamentally from those LPPL structures that have previously been detected in real financial time series. Summarized, this paper demonstrates that LPPL structures are not necessarily the signature of imitative behavior among investors but can also stem from noise, even though the likelihood of this is extremely low. Thus, our findings confirm with high statistical confidence that the LPPL structures in the DAX development are rooted deeper than only in the random fluctuations of the German stock market.

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

    DOE PAGESBeta

    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

  10. 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.

  11. Fabrication of two-dimensional periodic structures on silicon after scanning irradiation with femtosecond laser multi-beams

    NASA Astrophysics Data System (ADS)

    Pan, An; Si, Jinhai; Chen, Tao; Li, Cunxia; Hou, Xun

    2016-04-01

    Two-dimensional (2D) periodic structures were fabricated on silicon surfaces by femtosecond laser irradiation in air and water, with the assistance of a microlens array (MLA) placed in the beam's path. By scanning the laser beam along the silicon surface, multiple grooves were simultaneously fabricated in parallel along with smaller laser-induced ripples. The 2D periodic structures contained long-periodic grooves and perpendicular short-periodic laser-induced ripples, which had periods of several microns and several hundred nanometers, respectively. We investigated the influence of laser power and scanning velocity on the morphological evolution of the 2D periodic structures in air and water. Large-area grid-like structures with ripples were fabricated by successively scanning once along each direction of the silicon's surface, which showed enhanced optical absorption. Hydrofluoric acid was then used to remove any oxygen and laser-induced defects for all-silicon structures.

  12. 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.

  13. Height control for small periodic structures using x-ray radiography

    NASA Astrophysics Data System (ADS)

    Schüttler, M.; Meyer, P.; Schaff, F.; Yaroshenko, A.; Kunka, D.; Besser, H.; Pfeiffer, F.; Mohr, J.

    2016-02-01

    We report on a method to characterize the height of periodic x-ray absorbing structures. Such structures are used for example in grating-based x-ray interferometry. In contrast to other techniques, our approach allows for a non-destructive determination of the height based on a few transmission measurements. It can be used with conventional laboratory-based x-ray setups and is therefore of great interest at the application sites of the structures, as it allows further characterization without the need of additional hardware. Here we present the principle of the method, show first results acquired with an absorption grating and compare them with theoretical calculations and those obtained using a destructive method.

  14. Sonic Stop-Bands for Periodic Arrays of Metallic Rods: Honeycomb Structure

    NASA Astrophysics Data System (ADS)

    Kushwaha, M. S.; Djafari-Rouhani, B.

    1998-12-01

    Extensive band structures have been computed for periodic arrays (in the honeycomb structure) of rigid metallic rods in air. Multiple complete acoustic stop bands have been obtained within which sound and vibrations are forbidden. These gaps start opening up for a filling fractionf≥8% and tend to increase with the filling fraction, exhibiting a maximum at the close-packing. A tandem structure has also been proposed that allows an ultrawideband filter for environmental or industrial noise to be achieved in the desired frequency range. This work is motivated by the recent experimental observation of sound attenuation on the sculpture by Eusebio Sempere, exhibited at the Juian March Foundation in Madrid [21] and complements the corresponding theoretical work [22, 23].

  15. 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.

  16. 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.

  17. Stability and pH-independence of nano-zero-valent iron intercalated montmorillonite and its application on Cr(VI) removal.

    PubMed

    Wu, Limei; Liao, Libing; Lv, Guocheng; Qin, Faxiang

    2015-08-01

    Composite of nano-zero-valent iron and montmorillonite (NZVI/MMT) was prepared by inserting NZVI into the interlayer of montmorillonite. The unique structure montmorillonite with isolated exchangeable Fe(III) cations residing near the sites of structural negative charges inhibited the agglomeration of ZVI and result in the formation of ZVI particles in the montmorillonite interlayer regions. NZVI/MMT was demonstrated to possess large specific surface area and outstanding reducibility that encourage rapid and stable reaction with Cr (VI). Besides, the intercalation also makes NZVI well dispersed and more stable in the interlayer, thereby improving the reaction capacity by 16 times. The effects of pH value, initial concentration of Cr (VI) and reaction time on Cr (VI) removal have also been investigated in detail. According to PXRD and XPS characterization, NZVI/Cr (VI) redox reaction occurred in the interlayer of MMT. The study of NZVI/MMT is instrumental to the development of remediation technologies for persistent environmental contaminants. PMID:26011800

  18. Alignment structures and diffraction properties of chiral nematic liquid crystal cells with periodically patterned photoalignment films

    NASA Astrophysics Data System (ADS)

    Sasaki, Tomoyuki; Shimura, Rei; Kawai, Kotaro; Noda, Kohei; Sakamoto, Moritsugu; Kawatsuki, Nobuhiro; Ono, Hiroshi

    2016-01-01

    Liquid crystal (LC) cells with periodic alignment distributions were fabricated using chiral nematic LCs (N*LCs), which were prepared using mixtures of a nematic LC and a chiral dopant, along with photoreactive liquid crystalline polymer (PLCP) films. Periodic structures were formed by polarization holographic recording in the PLCP films. The director distribution in each cell depended on the ratio of chiral dopant present, i.e., the inherent helical pitch of the N*LCs. These periodic alignment structures with line defects in the LC grating cells were well explained on the basis of the elastic continuum theory of the N*LCs and the photoalignment effect of the PLCP films. The diffraction properties of the grating LC cells were also investigated using a polarized visible laser. The observed intensity and polarization states of the diffracted beams were consistent with theoretical ones calculated using the director distribution models. Our results clarify that the diffraction properties of the grating LC cells can be controlled by the helical pitch of the N*LCs.

  19. Evolution of open magnetic structures on the sun - The Skylab period

    NASA Technical Reports Server (NTRS)

    Levine, R. H.

    1977-01-01

    High-resolution harmonic analysis of the measured photospheric magnetic field of the sun is used to construct models of open magnetic structures over a period of 11 solar rotations. The models successfully reproduce the surface location and topology of all coronal holes during the Skylab period. In addition, there is persistent evidence in the models that open field lines are associated with active regions in a systematic way. These associations are listed for the period studied; they suggest that open field lines are a basic feature of solar magnetism. Specific examples of the evolution of coronal holes and of calculated open structures are presented. Quantitative study of the measured field strength within and neighboring a hole confirms the fact that coronal hole regions are indistinguishable by local magnetic properties. However, the calculated field strengths at the footpoints of open field lines within coronal holes show distinct evolutionary patterns and may indicate that, at least in young coronal holes, a significant amount of magnetic flux is closed. Problems of studying magnetic field divergence by using these models are discussed.

  20. 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.

  1. Femtosecond laser induced periodic surface structures on multi-layer graphene

    SciTech Connect

    Beltaos, Angela Kovačević, Aleksander G.; Matković, Aleksandar; Ralević, Uroš; Savić-Šević, Svetlana; Jovanović, Djordje; Jelenković, Branislav M.; Gajić, Radoš

    2014-11-28

    In this work, we present an observation of laser induced periodic surface structures (LIPSS) on graphene. LIPSS on other materials have been observed for nearly 50 years, but until now, not on graphene. Our findings for LIPSS on multi-layer graphene were consistent with previous reports of LIPSS on other materials, thus classifying them as high spatial frequency LIPSS. LIPSS on multi-layer graphene were generated in an air environment by a linearly polarized femtosecond laser with excitation wavelength λ of 840 nm, pulse duration τ of ∼150 fs, and a fluence F of ∼4.3–4.4 mJ/cm{sup 2}. The observed LIPSS were perpendicular to the laser polarization and had dimensions of width w of ∼30–40 nm and length l of ∼0.5–1.5 μm, and spatial periods Λ of ∼70–100 nm (∼λ/8–λ/12), amongst the smallest of spatial periods reported for LIPSS on other materials. The spatial period and width of the LIPSS were shown to decrease for an increased number of laser shots. The experimental results support the leading theory behind high spatial frequency LIPSS formation, implying the involvement of surface plasmon polaritons. This work demonstrates a new way to pattern multi-layer graphene in a controllable manner, promising for a variety of emerging graphene/LIPSS applications.

  2. Confined stripe structure in periodically grooved NdCo Films with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Martin, Jose I.; Hierro-Rodriguez, Aurelio; Cid, Rosalia; Rodriguez-Rodriguez, Gabriel; Velez, Maria; Alvarez-Prado, Luis M.; Alameda, Jose M.

    2012-02-01

    Magnetic multilayers are broad research field with many interesting phenomena depending on interlayer coupling. Also, since the development of nanolithography techniques, magnetic nanowires and dots have been intensively investigated [1]. Recently, as a combination of these two fields, the concept of magnetic lateral superlattice has emerged: continuous magnetic films with a lateral modulation of their magnetic properties at submicrometric length scale [2]. In this work, we have fabricated amorphous Nd-Co films with perpendicular magnetic anisotropy and a periodic thickness modulation by e-beam lithography and ion milling. Lateral periods range from 2 μm - 500 nm and groove depths from 10 to 30 nm. MFM and Kerr magnetometry have been used for characterization. Lateral patterning modifies the interplay between magnetostatic energy, perpendicular and in plane anisotropy and exchange interaction resulting in confined magnetic stripe structures. The different regimes that appear depending on the size of the periodic thickness modulation relative to the magnetic stripe period will be discussed. [1] J.I Martin et al, JMMM, 256 (2003) 449 [2] S. P. Li et al, PRL 88 (2002) 087202; N. Martin et al, PRB 83 (2010) 174423

  3. 3D parameter to quantify the anisotropy measurement of periodic structures on rough surfaces.

    PubMed

    Guillemot, G; Bigerelle, M; Khawaja, Z

    2014-01-01

    In this paper, a new 3D roughness parameter, Sreg, is proposed to quantify the regularity of a surface, independent of the amplitude and the scanning length units of the surface. The efficiency of this parameter is tested on noisy periodical surfaces with degrees of anisotropy. This parameter lies between zero (perfect noise) and 100% (a perfect periodic surface). This parameter enables the identification of the anisotropy directions of regularity for a given surface. For a periodical surface, the greater the noise, the lower the anisotropy. A direction function is proposed to analyse the direction of regularity of a rough surface, which then permits characterization of the directional regularity of the topography. The regularity parameter can be used for several purposes: to identify the direction of periodical structures formed by laser-pulsed radiations on the surface of solid workpieces; to examine the reproducibility of surface machining methods such as finishing process; and to identify the surface regularity produced by abrasive machining, such as precision surface grain, abrasive slotting, and lapping. PMID:23824916

  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. Structural and technological changes of greenhouse gas emissions during the transition period in Polish industry

    NASA Astrophysics Data System (ADS)

    Pasierb, Slawomir; Niedziela, Karol; Wojtulewicz, Jerzy

    1996-01-01

    We analyzed the patterns of energy use and greenhouse gas (GHG) emissions in Polish industry arising during the transition from a centrally planned economy to a market economy. A method of analyzing industry energy use and GHG emissions is discussed. Using this method, the impact of changes in industrial production value, the share of specific industry branches in the total industrial production, energy intensity, and the mix of the energy carriers in the 1989 1993 period has been analyzed. The last year of the analyzed period shows favorable trends in efficiency and signs of production structure shift to a less energy-intensive one. Economic reform implemented after 1989, which released energy carriers' prices from government control, had important effects on the industrial sector. Energy efficiency and emission intensity trends of 1992 1994 were favorable; if they continue, production will return to 1989 levels with much lower energy consumption and significantly decreased GHG emissions.

  6. 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.

  7. Formation of low-frequency periodic structures in a pulsed magnetron discharge

    NASA Astrophysics Data System (ADS)

    Kaziev, A. V.; Khodachenko, G. V.; Kharkov, M. M.

    2016-01-01

    Periodic plasma structures are observed in non-sputtering magnetron discharge (NSMD) that is the transient quasi-stationary low-voltage regime between the high-current magnetron discharge (HCIMD) and an arc. The fast camera imaging synchronized with the magnetic probe diagnostics reveals the correlation between the observed rotation of the plasma inhomogeneities and the magnetic field perturbation behaviour. The frequencies of the periodic processes fall into kHz-range. A simple analytical model of the ionization instability in crossed electric and magnetic fields is suggested for the low-pressure discharge case. Using the model, the possible ranges of wavelengths and frequencies for the plasma inhomogeneities are evaluated. The results show good agreement between the experimental data and theory.

  8. 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.

  9. 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.

  10. 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.

  11. Periodic solutions of a nonautonomous predator-prey system with stage structure and time delays

    NASA Astrophysics Data System (ADS)

    Xu, Rui; Wang, Zhiqiang

    2006-11-01

    A nonautonomous Lotka-Volterra type predator-prey model with stage structure and time delays is investigated. It is assumed in the model that the individuals in each species may belong to one of two classes: the immatures and the matures, the age to maturity is presented by a time delay, and that the immature predators do not feed on prey and do not have the ability to reproduce. By some comparison arguments we first discuss the permanence of the model. By using the continuation theorem of coincidence degree theory, sufficient conditions are derived for the existence of positive periodic solutions to the model. By means of a suitable Lyapunov functional, sufficient conditions are obtained for the uniqueness and global stability of the positive periodic solutions to the model.

  12. Simultaneous gain and phase-shift enhancements in periodic gain structures

    SciTech Connect

    Yan, R.H.; Chuang, Z.M.; Corzine, S.W.; Coldren, L.A. )

    1990-05-01

    The recently proposed concept of periodic gain, i.e., dividing the active region into segments placed at optical electric-field standing wave maxima, has been shown to greatly reduce the threshold gain requirement of the active media by up to a factor of 2 in high-finesse vertical cavity surface-emitting lasers. The lasing wavelength is determined by the period of the standing wave; however, previous analyses of these structures have failed to show that a similar enhancement effect occurs for the index shift resulting from the active segments as well. In this communication, we show that effects on both gain and index can be rigorously derived from conventional transmission scattering theory.

  13. 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.

  14. 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. PMID:24863798

  15. Periodic Structure in the Megaparsec-scale Jet of PKS 0637-752

    NASA Astrophysics Data System (ADS)

    Godfrey, L. E. H.; Lovell, J. E. J.; Burke-Spolaor, S.; Ekers, R.; Bicknell, G. V.; Birkinshaw, M.; Worrall, D. M.; Jauncey, D. L.; Schwartz, D. A.; Marshall, H. L.; Gelbord, J.; Perlman, E. S.; Georganopoulos, M.

    2012-10-01

    We present 18 GHz Australia Telescope Compact Array imaging of the megaparsec-scale quasar jet PKS 0637-752 with angular resolution ~0farcs58. We draw attention to a spectacular train of quasi-periodic knots along the inner 11'' of the jet, with average separation ~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 jet ~ 1046 erg s-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 × 103 yr < τ < 3 × 105 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 <~ a <~ 30 pc, which corresponds to a maximum angular separation of ~0.1-5 mas.

  16. 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.

  17. 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.

  18. 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.

  19. Half-spectral unidirectional invisibility in non-Hermitian periodic optical structures.

    PubMed

    Longhi, Stefano

    2015-12-01

    The phenomenon of half-spectral unidirectional invisibility is introduced for one-dimensional periodic optical structures with tailored real and imaginary refractive index distributions in a non PT-symmetric configuration. The effect refers to the property in which the optical medium appears to be invisible, both in reflection and transmission, below the Bragg frequency when probed from one side and above the Bragg frequency when probed from the opposite side. Half-spectral invisibility is obtained by a combination of in-phase index and gain gratings whose spatial envelopes are related to each other by a Hilbert transform. PMID:26625084

  20. Displacement reactions in the Ni-Al-O system resulting in periodic layer structures

    SciTech Connect

    Song, D.W.; Subramanian, R.; Dieckmann, R.

    1995-10-01

    Displacement reactions may play an important role in in situ processing technologies for the production of metal-ceramic composites. To better understand such reactions displacement reactions between NiO and Al were studied at high temperatures. Different reaction layers with periodic structures were observed involving Al{sub 2}O{sub 3}, Al{sub 3}Ni, Al{sub 3}Ni{sub 2}, Ni and Al. The experimental observations are presented and discussed with regard to the reaction mechanism.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. Structure of Periodic Crystals and Quasicrystals in Ultrathin Films of Ba-Ti-O

    PubMed Central

    Cockayne, Eric; Mihalkovič, Marek; Henley, Christopher L.

    2016-01-01

    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. PMID:26998528

  6. 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

  7. 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. PMID:26372330

  8. Multi-Cell High Latitude Density Structure Induced by Ion Drag during Active Periods

    NASA Astrophysics Data System (ADS)

    Walterscheid, R. L.; Crowley, G.

    2012-12-01

    During active periods two-cell convection patterns can produce four-cell density structure in the high-latitude thermosphere. During these periods density perturbations approaching 50% are possible. The occurrence of density structures that are more complex than the forcing itself suggests that the structure is caused by a profound change in the balance of forces. Using a General Circulation Model of the thermosphere, we compare the balance of forces in the upper and lower thermosphere during active and quiet times. We also examine the thermal structure caused by the dynamical adjustment to ion-drag forcing in relation to the other terms as a balanced state is approached. Simulations reveal that where ion drag is unable to accelerate the atmosphere into rapid motion (during quiet times or at low thermospheric altitudes) the Coriolis force is the dominant inertial term, and for fixed pressure levels centers of cyclonic motion are (per the usual meteorology relations) colder and denser than the surrounding air, while centers of anticyclonic motion are warmer and less dense. At fixed heights, densities are high in the evening anticyclonic gyre, and low in the dawn cyclonic gyre. However, this situation is radically changed during active periods when the atmosphere is spun up to rapid motion and the centrifugal force resulting from curved trajectories is the dominant inertial force. When this occurs, the high latitude anticyclones and cyclones both become centers of relatively cold high density air at fixed height. Cold low-density centers are found on both the dawn and dusk sides with a trough of low density air over the pole connecting them. This intrusion of low density splits the evening high density region that exists under quiet conditions giving the four cell pattern found by Crowley et al. [1989; 1996a, b]. Crowley, G., J. Schoendorf, R. G. Roble, F. A. Marcos (1996a). Cellular structures in the high latitude lower thermosphere, J. Geophys. Res. 101, 211

  9. 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. PMID:26836289

  10. Pulsewidth dependence of laser-induced periodic surface structure formed on yttria-stabilized zirconia polycrystal

    NASA Astrophysics Data System (ADS)

    Kakehata, Masayuki; Yashiro, Hidehiko; Oyane, Ayako; Ito, Atsuo; Torizuka, Kenji

    2016-03-01

    Three-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) is a fine engineering ceramic that offers high fracture resistance and flexural strength. Thus, it is often applied in mechanical components and medical implants. The surface roughness can be controlled to improve the device characters in some applications. Ultrashort pulse lasers can form laser-induced periodic surface structures (LIPSS) on 3Y-TZP, which have never been investigated in detail. Therefore, this paper reports the formation and characteristics of LIPSS formed on 3Y-TZP, focusing on the pulsewidth dependence. The LIPSS was formed by a Ti:sapphire chirped-pulse amplification system, which generates 810 nmcentered 80-fs pulses at a 570 Hz repetition rate. The measured ablation threshold peak fluence was ~1.5 J/cm2 and the LIPSS was formed at the peak fluence of 2.7-7.7 J/cm2. For linearly polarized pulses, the lines of the LIPSS were oriented parallel to the polarization direction, and their period was comparable to or larger than the center wavelength of the laser. These characteristics differ from the reported characteristics of LIPSS on metals and dielectrics. The pulsewidth dependence of the ablation and LIPSS was investigated for different pulsewidths and signs of chirp. Under the investigated fluence condition, the LIPSS period increased with increasing pulsewidth for both signs of chirp. Similar pulsewidth dependencies were observed for circularly polarized pulses.

  11. Quasi phase matching through periodic step structure: modeling of frequency conversion in consideration of heat influence

    NASA Astrophysics Data System (ADS)

    Ohfuchi, Takafumi; Hirano, Nobuyuki; Matsukawa, Hiroya; Nakayama, Koichiro; Kumagai, Hiroshi; Inoue, Norihiro; Fukuda, Naoaki; Takiya, Toshio

    2012-02-01

    Periodic inversion of spontaneous polarization in a ferroelectric substrate has realized quasi phase matching (QPM) and thereby revolutionized nonlinear optics. In this paper, we report on the heat influence on the frequency conversion in birefringence phase matching (BPM) by use of BaB2O4 (BBO) crystals as preparatory for efficient generation of the second harmonics (SHs) by QPM we suggest. Indeed, QPM is achieved normally by polarization inversion, but we suggest the periodic step structure to achieve QPM. Polarization inversion is generally formed by superimposed voltage. However, the shorter wavelength region is, the shorter inversion cycle is. Therefore, if the vacuum ultraviolet (VUV) region is treated, it becomes more difficult to form periodic inversion and the accuracy is more necessary. Accordingly, it is necessary to consider the influence of crystal's heat, caused by absorption of laser, which affects frequency conversion. We discuss validity of analytical approach about crystal's heat and frequency conversion by comparing between both results of experiment and simulation with BBO crystals.

  12. 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.

  13. Enthalpy changes accompanying the collapse of montmorillonite layers and the penetration of electrolyte into interlayer space

    SciTech Connect

    Yan, L.; Low, P.F.; Roth, C.B.

    1996-09-25

    The enthalpy changes, {Delta}H, in suspensions of Li-, Na-, and K-montmorillonite were determined as functions of the molal concentrations of LiCl, NaCl, and KCl, respectively, by microcalorimetry. These changes were compared with the corresponding changes in interlayer distance, {lambda}, as determined by X-ray diffraction. It was found that {Delta}H values accompanying the collapse of the montmorillonite layers from {lambda} > 14 nm to {lambda} {approx_equal} 1.0 nm were essentially negligible; however, {Delta}H values accompanying the collapse of layers of Li- and Na-montmorillonite from {lambda} {approx_equal} 1.0 nm to {lambda} {approx_equal} 0.6 nm, and the collapse of layers of K-montmorillonite from {lambda} {approx_equal} 0.6 nm, were not negligible. No additional collapse of Li- and Na-montmorillonite layers occurred after {lambda} {approx_equal} 0.6 nm, and for K-montmorillonite layers after {lambda} {approx_equal} 0.3 nm, but {Delta}H continued to change with increasing salt addition. This change was attributed to the penetration of electrolyte into the interlayer space. A notable observation was that the value of {Delta}H was positive for Li-montmorillonite, but negative for Na- and K-montmorillonite. These observations were interpreted to mean that {Delta}H changes in the montmorillonite suspension were largely attributable to reorganization of the interlayer space by the added electrolytes.

  14. Analysis of peptides synthesized in the presence of SAz-1 montmorillonite and Cu(2+) exchanged hectorite.

    PubMed

    Porter, T L; Eastman, M P; Bain, E; Begay, S

    2001-07-01

    We have investigated the synthesis of oligopeptides containing glycine and tyrosine in the presence of the clay minerals montmorillonite (non-exchanged, SAz-1) and Cu(2+) exchanged hectorite. In both cases, homopolymers of the two amino acids are formed, as are mixed peptides. In the case of Cu(2+) hectorite, mixed oligopeptides up to trimers are detected in small amounts. For montmorillonite, heterogeneous oligopeptides up to hexamers are detected. Our experiments indicate montmorillonite is more effective in promoting oligopeptide formation than Cu(2+) hectorite. Analysis of the oligopeptide sequences formed on the montmorillonite surfaces indicates preferential synthesis of certain Gly-Tyr sequences over others. PMID:11429201

  15. 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.

  16. 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.

  17. Assessment of femtosecond laser induced periodic surface structures on polymer films.

    PubMed

    Rebollar, Esther; Vázquez de Aldana, Javier R; Martín-Fabiani, Ignacio; Hernández, Margarita; Rueda, Daniel R; Ezquerra, Tiberio A; Domingo, Concepción; Moreno, Pablo; Castillejo, Marta

    2013-07-21

    In this work we present the formation of laser induced periodic surface structures (LIPSS) on spin-coated thin films of several model aromatic polymers including poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly carbonate bis-phenol A upon irradiation with femtosecond pulses of 795 and 265 nm at fluences well below the ablation threshold. LIPSS are formed with period lengths similar to the laser wavelength and parallel to the direction of the laser polarization vector. Formation of LIPSS upon IR irradiation at 795 nm, a wavelength at which the polymers absorb weakly, contrasts with the absence of LIPSS in this spectral range upon irradiation with nanosecond pulses. Real and reciprocal space characterization of LIPSS obtained by Atomic Force Microscopy (AFM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), respectively, yields well correlated morphological information. Comparison of experimental and simulated GISAXS patterns suggests that LIPSS can be suitably described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice. Fluorescence measurements, after laser irradiation, provide indirect information about dynamics and structure of the polymer at the molecular level. Our results indicate that the LIPSS are formed by interference of the incident and surface scattered waves. As a result of this process, heating of the polymer surface above its glass transition temperature takes place enabling LIPSS formation. PMID:23728307

  18. Optical filter including a sub-wavelength periodic structure and method of making

    DOEpatents

    Kaushik, S.; Stallard, B.R.

    1998-03-10

    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. 17 figs.

  19. 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.

  20. 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.

  1. Femtosecond laser-induced periodic surface structures on steel and titanium alloy for tribological applications

    NASA Astrophysics Data System (ADS)

    Bonse, J.; Koter, R.; Hartelt, M.; Spaltmann, D.; Pentzien, S.; Höhm, S.; Rosenfeld, A.; Krüger, J.

    2014-10-01

    Laser-induced periodic surface structures (LIPSS, ripples) were generated on stainless steel (100Cr6) and titanium alloy (Ti6Al4V) surfaces upon irradiation with multiple femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas (5 × 5 mm2) covered homogeneously by the nanostructures. The irradiated surface regions were subjected to white light interference microscopy and scanning electron microscopy revealing spatial periods around 600 nm. The tribological performance of the nanostructured surface was characterized by reciprocal sliding against a ball of hardened steel in paraffin oil and in commercial engine oil as lubricants, followed by subsequent inspection of the wear tracks. For specific conditions, on the titanium alloy a significant reduction of the friction coefficient by a factor of more than two was observed on the laser-irradiated (LIPSS-covered) surface when compared to the non-irradiated one, indicating the potential benefit of laser surface structuring for tribological applications.

  2. Facile Synthesis of Yolk-Shell-Structured Triple-Hybridized Periodic Mesoporous Organosilica Nanoparticles for Biomedicine.

    PubMed

    Teng, Zhaogang; Zhang, Junjie; Li, Wei; Zheng, Yuanyi; Su, Xiaodan; Tang, Yuxia; Dang, Meng; Tian, Ying; Yuwen, Lihui; Weng, Lixing; Lu, Guangming; Wang, Lianhui

    2016-07-01

    The synthesis of mesoporous nanoparticles with controllable structure and organic groups is important for their applications. In this work, yolk-shell-structured periodic mesoporous organosilica (PMO) nanoparticles simultaneously incorporated with ethane-, thioether-, and benzene-bridged moieties are successfully synthesized. The preparation of the triple-hybridized PMOs is via a cetyltrimethylammonium bromide-directed sol-gel process using mixed bridged silsesquioxanes as precursors and a following hydrothermal treatment. The yolk-shell-structured triple-hybridized PMO nanoparticles have large surface area (320 m(2) g(-1) ), ordered mesochannels (2.5 nm), large pore volume (0.59 cm(3) g(-1) ), uniform and controllable diameter (88-380 nm), core size (22-110 nm), and shell thickness (13-45 nm). In vitro cytotoxicity, hemolysis assay, and histological studies demonstrate that the yolk-shell-structured triple-hybridized PMO nanoparticles have excellent biocompatibility. Moreover, the organic groups in the triple-hybridized PMOs endow them with an ability for covalent connection of near-infrared fluorescence dyes, a high hydrophobic drug loading capacity, and a glutathione-responsive drug release property, which make them promising candidates for applications in bioimaging and drug delivery. PMID:27183872

  3. Evolution and mechanism of the periodical structures formed on Ti plate under femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Liu, Dong; Chen, Chuansong; Man, Baoyuan; Meng, Xue; Sun, Yanna; Li, Feifei

    2016-08-01

    This work investigates the femtosencond laser (fs-laser) induced periodical surface structures (FLIPSS) on titanium plate including the concentric rings, microgrooves and subwavelength ripples. The evolution of the three types of the structures at different laser fluence and shot number is investigated experimentally in detail. The competition mechanisms exist among the different FLIPSS. A processing window for each resulting FLIPSS is obtained. In order to give an overall understanding of the FLIPSS, the formation mechanisms of each type of FLIPSS are discussed. The formation of the ripples is well explained by the propagating of the surface plasma wave (SPW) on the air/Ti interface. The evolutions of the ripple distribution are well understood according to this model as well. It is concluded that the interaction of the scattered wave of the laser light with the surface wave is concluded to give rise to the microgroove structure. According to our observation, the shape of the concentric rings does not change with the variation of the laser fluence and pulse number. The structure could be originated from the optical interference between the transmitted and reflected laser beams by the two surfaces of the biconvex lens. This investigation could not only make a further understanding of the formations of FLIPSS but also provide the possibility to control the surface morphologies in laser processing.

  4. 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. PMID:27302334

  5. Cut-off period for slow magnetoacoustic waves in coronal plasma structures

    NASA Astrophysics Data System (ADS)

    Afanasyev, A. N.; Nakariakov, V. M.

    2015-10-01

    Context. There is abundant observational evidence of longitudinal compressive waves in plasma structures of the solar corona, which are confidently interpreted in terms of slow magnetoacoustic waves. The uses of coronal slow waves in plasma diagnostics, as well as analysis of their possible contribution to coronal heating and the solar wind acceleration, require detailed theoretical modelling. Aims: We investigate the effects of obliqueness, magnetic field, and non-uniformity of the medium on the evolution of long-wavelength slow magnetoacoustic waves guided by field-aligned plasma non-uniformities, also called tube waves. Special attention is paid to the cut-off effect due to the gravity stratification of the coronal plasma. Methods: We study the behaviour of linear tube waves in a vertical untwisted straight field-aligned isothermal plasma cylinder. We apply the thin flux tube approximation, taking into account effects of stratification caused by gravity. The dispersion due to the finite radius of the flux tube is neglected. We analyse the behaviour of the cut-off period for an exponentially divergent magnetic flux tube filled in with a stratified plasma. The results obtained are compared with the known cases of the constant Alfven speed and the pure acoustic wave. Results: We derive the wave equation for tube waves and reduce it to the form of the Klein-Gordon equation with varying coefficients, which explicitly contains the cut-off frequency. The cut-off period is found to vary with height, decreasing significantly in the low-beta plasma and in the plasma with the beta of the order of unity. The depressions in the cut-off period profiles can affect the propagation of longitudinal waves along coronal plasma structures towards the higher corona and can form coronal resonators.

  6. Application of Modified Nanonaturally Montmorillonite in Monochlorobenzene Remediation in River Water

    NASA Astrophysics Data System (ADS)

    Liu, Chen; Chen, Jun-Feng; Li, Yun; Chen, Rong-Chang; Asaoka, Sachio; Yuan, Guo-Li

    2012-12-01

    As the inland waterway transportation developed rapidly in China, the frequency of hazardous chemical leakage accidents is increasing every year. Such pollution to inland river environment has become a world-wide issue. Montmorillonite (Mont) is typical 2:1 layer type silicate clay and due to their special structure, it has been used in organic pollution removal process. In order to improve their ability in pollution adsorption, the pillared Mont was made in this work. Since the common toxic structure in most chemical pollutants is the halogen atom-benzene ring part, we select a typical compound Monochlorobenzene (MCB) as the aim contaminant. In this research, the original Mont, Na-Mont, TiO2 and TiO2-Mont were prepared and used in MCB degradation experiment as catalysts. The influence of catalyst amount, promoter (H2O2) amount, MCB concentration and reaction time to MCB removal rate were studied, respectively in detail.

  7. 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. PMID:24752811

  8. 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.

  9. 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.

  10. Structure analysis of the protein transduction domain of human Period1 and its mutant analogs.

    PubMed

    Yang, Xiao Lin; Xie, Jun; Niu, Bo; Hu, Xiao Nian; Gao, Yang; Xiang, Qian; Zhang, Yue Hong; Guo, Yong; Zhang, Zheng Guo

    2005-04-01

    Human Period1 (hPer1) has been proved to be able to translocate into cells in a protein transduction manner. The segment of amino acids 830-845 of hPer1 is its protein transduction domain (PTD). In order to explore the membrane penetrating mechanism of hPer1-PTD and the physico-chemical properties necessary in the process, Ala scanning mutation method was used to investigate the variation in the peptide internalization. To further investigate the related physico-chemical requirements, the three dimensional structures of hPer1-PTD and its mutant analogs were simulated by Rosetta method. The electrostatic potentials and energies of these structures were calculated using the Delphi algorithm to solve Poisson-Boltzman equation. The hydrophobicity was assessed by the percentage of the nonpolar area in SAS (solvent accessible surface (SAS)). It has been proved that the Arg836 was the key residue for peptide internalization. When this Arg mutated into Ala, the peptide could not cross the membrane. The large enough area with positive charge was the decisive factor for hPer1-PTD. The alpha-helical structure seemed to play an assistant role so as to enable the positive charge connected in spatial arrangement. PMID:15781181

  11. ''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.

  12. 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.

  13. 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

  14. 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. PMID:20854214

  15. 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.

  16. Unconventional band structure for a periodically gated surface of a three dimensional Topological Insulator

    NASA Astrophysics Data System (ADS)

    Ghosh, Sankalpa; Mondal, Puja

    The surface states of the three dimensional (3D) Topological Insulators are described by two-dimensional (2D) massless dirac equation. A gate voltage induced one dimensional potential barrier on such surface creates a discrete bound state in the forbidden region outside the dirac cone. Even for a single barrier it is shown such bound state can create electrostatic analogue of Shubnikov de Haas oscillation which can be experimentally observed for relatively smaller size samples. However when these surface states are exposed to a periodic arrangement of such gate voltage induced potential barriers, the band structure of the same got nontrivially modified. This is expected to significantly alters the properties of macroscopic system. We also suggest that in suitable limit the system may offer ways to control electron spin electrostatically which may be practically useful Supported by UGC Fellowship (PM) and a UKIERI-UGC Thematic Partnership.

  17. Unconventional band structure for a periodically gated surface of a three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Mondal, Puja; Ghosh, Sankalpa

    2015-12-01

    The surface states of the three-dimensional (3D) topological insulators are described by a two-dimensional (2D) massless dirac equation. A gate-voltage-induced one-dimensional potential barrier on such surfaces creates a discrete bound state in the forbidden region outside the dirac cone. Even for a single barrier it is shown that such a bound state can create an electrostatic analogue of Shubnikov de Haas oscillation which can be experimentally observed for relatively smaller size samples. However, when these surface states are exposed to a periodic arrangement of such gate-voltage-induced potential barriers, the band structure of the same was significantly modified. This is expected to significantly alter the properties of the macroscopic system. We also suggest that, within suitable limits, the system may offer ways to control electron spin electrostatically, which may be practically useful.

  18. 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.

  19. Stochasticity, periodicity and localized light structures in partially mode-locked fibre lasers

    NASA Astrophysics Data System (ADS)

    Churkin, D. V.; Sugavanam, S.; Tarasov, N.; Khorev, S.; Smirnov, S. V.; Kobtsev, S. M.; Turitsyn, S. K.

    2015-05-01

    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.

  20. 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.

  1. 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.

  2. 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

  3. Stochasticity, periodicity and localized light structures in partially mode-locked fibre lasers.

    PubMed

    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

  4. Generation of periodic accelerating structures in plasma by colliding laser pulses.

    PubMed

    Shvets, G; Fisch, N J; Pukhov, A; Meyer-Ter-Vehn, J

    1999-08-01

    A mechanism for generating large (>1 GeV/m) accelerating wakes in a plasma is proposed. Two slightly detuned counterpropagating laser beams, an ultrashort timing pulse and a long pump, exchange photons and deposit the recoil momentum in plasma electrons. This produces a localized region of electron current, which acts as a virtual electron beam, inducing intense plasma wakes with phase velocity equal to the group velocity of the short pulse. Modulating the pumping beam generates periodic accelerating structures in the plasma ("plasma linac") which can be used for particle acceleration unlimited by the dephasing between the particles and the wake. An important difference between this type of plasma accelerator and the conventional wakefield accelerators is that this type can be achieved with laser intensities I<10(18) W/cm(2). PMID:11970016

  5. Fabrication of a periodic structure with a high refractive-index difference by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Takeshima, Nobuhito; Kuroiwa, Yutaka; Narita, Yoshihiro; Tanaka, Shuhei; Hirao, Kazuyuki

    2004-08-01

    A microfabrication process using ultrafast laser pulses in glass was investigated. We investigated the formation of semiconductors by the irradiation of glasses with femtosecond laser pulses. ZnS- or PbS-doped SiO2-Al2O3-B2O3-CaO-ZnO-Na2O-K2O glasses were prepared by a melting method and irradiated by femtosecond laser pulses. Periodic structures in the sample glasses with a high refractive index difference were produced by femtosecond laser pulses. The maximum relative refractive index difference between the irradiated area and the nonirradiated areas was 20%. Diffraction gratings were also fabricated inside the ZnS- or PbS-doped silicate glasses. The diffraction efficiency of these gratings was approximately 90% in the infrared region.

  6. GaN-based vertical cavity surface emitting lasers with periodic gain structures

    NASA Astrophysics Data System (ADS)

    Matsui, Kenjo; Kozuka, Yugo; Ikeyama, Kazuki; Horikawa, Kosuke; Furuta, Takashi; Akagi, Takanobu; Takeuchi, Tetsuya; Kamiyama, Satoshi; Iwaya, Motoaki; Akasaki, Isamu

    2016-05-01

    We have achieved room-temperature CW operations of GaN-based vertical cavity surface emitting lasers (VCSELs) with periodic gain structures (PGSs). The PGS-VCSEL consisted of 4.5λ-thick optical cavity length and two GaInN 5-quantum-well (QW) active regions separated with a Mg-doped GaN intermediate layer. The uniform carrier injection into the two active regions was also investigated using light-emitting diodes (LEDs). It is found that the use of an optimum Mg concentration in the intermediate layers improves the uniform carrier injection in the two active regions. From these results, we realized the CW operation of VCSELs with PGSs grown on AlInN/GaN distributed Bragg reflectors (DBRs). The VCSEL under CW operation showed a threshold current density of 16.5 kA/cm2 and its operation wavelength was 409.9 nm.

  7. Free electron terahertz wave radiation source with two-section periodical waveguide structures

    SciTech Connect

    Liu Weihao; Gong Sen; Zhang Yaxin; Zhou Jun; Zhang Ping; Liu Shenggang

    2012-03-15

    We analyze a free electron terahertz wave radiation source with two-section periodical waveguide structure (PWS), where the first section (section-I) is used to pre-modulate the electron beam and the second section (section-II) is for terahertz wave generation. By means of theoretical analysis and numerical simulations, we demonstrate that the starting current density of the beam-wave interaction in section-II can be significantly reduced provided that the operation frequency is the harmonic of electron beam's pre-modulation frequency. This kind of source can generate relatively high power terahertz wave radiation but only need moderate beam current density. And it may have great potential application in developing the compact and high power terahertz wave radiation source.

  8. 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.

  9. 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.

  10. 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.

  11. Mechanically induced long period fiber gratings on single mode tapered optical fiber for structure sensing applications

    NASA Astrophysics Data System (ADS)

    Pulido-Navarro, María. G.; Marrujo-García, Sigifredo; Álvarez-Chávez, José A.; Velázquez-González, Jesús S.; Martínez-Piñón, Fernando; Escamilla-Ambrosio, Ponciano J.

    2015-08-01

    The modal characteristics of tapered single mode optical fibers and its strain sensing characteristics by using mechanically induced long period fiber gratings are presented in this work. Both Long Period Fiber Gratings (LPFG) and fiber tapers are fiber devices that couple light from the core fiber into the fiber cladding modes. The mechanical LPFG is made up of two plates, one flat and the other grooved. For this experiment the grooved plate was done on an acrylic slab with the help of a computer numerical control machine. The manufacturing of the tapered fiber is accomplished by applying heat using an oxygen-propane flame burner and stretching the fiber, which protective coating has been removed. Then, a polymer-tube-package is added in order to make the sensor sufficiently stiff for the tests. The mechanical induced LPFG is accomplished by putting the tapered fiber in between the two plates, so the taper acquires the form of the grooved plate slots. Using a laser beam the transmission spectrum showed a large peak transmission attenuation of around -20 dB. The resultant attenuation peak wavelength in the transmission spectrum shifts with changes in tension showing a strain sensitivity of 2pm/μɛ. This reveals an improvement on the sensitivity for structure monitoring applications compared with the use of a standard optical fiber. In addition to the experimental work, the supporting theory and numerical simulation analysis are also included.

  12. 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.

  13. 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

  14. 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.

  15. 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

  16. In vitro biodegradation and biocompatibility of gelatin/montmorillonite-chitosan intercalated nanocomposite.

    PubMed

    Zhuang, Hong; Zheng, Jun Ping; Gao, Hong; De Yao, Kang

    2007-05-01

    The intercalated nanocomposite of gelatin/montmorillonite-chitosan (Gel/MMT-CS) was prepared via the solution intercalation process. In vitro degradation tests showed that the nanocomposite had a lower degradation rate than Gel-CS composite. And the introduced intercalation structure endowed Gel/MMT-CS nanocomposite with a controllable degradation rate when changing the MMT content. Cells attachment, spread and proliferation on the Gel/MMT-CS membranes were investigated by scanning electron microscopy (SEM) and mitochondrial activity assay. The results provided evidences of good adhesion, proliferation and morphology of rat stromal stem cells on Gel/MMT-CS membranes compared to the tissue culture plates (TCPs), making the Gel/MMT-CS nanocomposite a promising candidate towards tissue engineering. PMID:17221313

  17. Modification of nanosized natural montmorillonite for ultrasound-enhanced adsorption of Acid Red 17.

    PubMed

    Acisli, Ozkan; Khataee, Alireza; Karaca, Semra; Sheydaei, Mohsen

    2016-07-01

    This work aims to modify montmorillonite (MMT) via dodecyltrimethylammonium bromide (DTMA) and investigate its ability in ultrasound (US) assisted decolorization of a polluted solution. BET surface area of MMT was increased from 19.76 to 42.57 m(2)/g and basal spacing of MMT structural layers was increased from 1.13 to 1.69 nm by DTMA modification. The application of DTMA-modified MMT (DTMA-MMT) and US for the decolorization of Acid Red 17 (AR17) showed that US could improve the ability of DTMA-MMT on decolorization of AR17 solution due to simultaneous adsorption and sonocatalysis. The ability of US assisted DTMA-MMT was slightly decreased with pH, the initial dye concentration and the presence of inorganic anions. PMID:26964930

  18. Development of chitosan/montmorillonite nanocomposites with encapsulated α-tocopherol.

    PubMed

    Dias, Marali Vilela; Machado Azevedo, Viviane; Borges, Soraia Vilela; Soares, Nilda de Fátima Ferreira; de Barros Fernandes, Regiane Victória; Marques, João José; Medeiros, Eber Antonio Alves

    2014-12-15

    Nanocomposites of chitosan (CS) were developed and characterized in a full factorial design with varying levels of montmorillonite (MMTNa) and encapsulated tocopherol (toc-encap). The structural properties (XRD, FTIR), morphology (TEM), hygroscopic properties (water vapour permeability, hydrophobicity, sorption isotherms) and optical properties (haze, CIELab parameters) of the resulting materials were evaluated. Toc-encap contents up to 10% influenced the intercalation of MMTNa in the CS matrix, resulting in films with reduced water vapour permeability (3.48×10(-11)(g/msPa)), increased hydrophobicity (ΔGHydroph |7.93-59.54|mJm(-2)) and lower equilibrium moisture content (EMC), thus showing potential for active food packaging materials. At levels above 10%, toc-encap agglomerates occurred, which deteriorated the properties of the resulting films, as shown with the TEM. As the toc-encap content increased, the films became slightly more yellow, more irregular and less transparent, with a higher haze index. PMID:25038682

  19. Free vibrations of finite periodic structures in pass- and stop-bands of the counterpart infinite waveguides

    NASA Astrophysics Data System (ADS)

    Hvatov, Alexander; Sorokin, Sergey

    2015-07-01

    The existence of frequency stop-bands, in which transmission of the vibro-acoustic energy is impossible, suggests that the periodic structures may be used for vibro-isolation. In any technical application, however, only a finite segment of such a structure can be used. This paper is concerned with comparison of the eigenfrequency spectra of finite periodic structures with location of stop-bands for their infinite counterparts. A hierarchy of four mathematical models is considered. In each case, special attention is paid to eigenfrequencies and eigenmodes of a single periodicity cell with appropriate boundary conditions. The influence of the amount of periodicity cells in a finite compound structure on its eigenfrequency spectrum is analyzed. Several features common for the considered models are found and discussed in the context of the existing knowledge on the subject.

  20. Development of Periodic and Three-Dimensional Structures in Acrylic-Monomer Photopolymer Materials by Holographic Methods

    NASA Astrophysics Data System (ADS)

    Vorzobova, N. D.; Bulgakova, V. G.; Moskalenko, A. I.; Pavlovets, I. M.; Denisyuk, I. Yu.; Burunkova, Yu. É.

    2015-01-01

    We show the possibility and advantages of using photopolymer materials based on acrylic monomers and nanocomposites in holography. Holographic characteristics of these materials and conditions for forming periodic structures and three-dimensional elements in them are determined.

  1. 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

  2. Effect of phosphate on U(VI) sorption to montmorillonite: Ternary complexation and precipitation barriers

    NASA Astrophysics Data System (ADS)

    Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh S.; Giammar, Daniel E.; Catalano, Jeffrey G.

    2016-02-01

    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

  3. 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

  4. Periodic structure formation and surface morphology evolution of glassy carbon surfaces applying 35-fs-200-ps laser pulses

    NASA Astrophysics Data System (ADS)

    Csontos, J.; Toth, Z.; Pápa, Z.; Budai, J.; Kiss, B.; Börzsönyi, A.; Füle, M.

    2016-06-01

    In this work laser-induced periodic structures with lateral dimensions smaller than the central wavelength of the laser were studied on glassy carbon as a function of laser pulse duration. To generate diverse pulse durations titanium-sapphire (Ti:S) laser (center wavelength 800 nm, pulse durations: 35 fs-200 ps) and a dye-KrF excimer laser system (248 nm, pulse durations: 280 fs, 2.1 ps) were used. In the case of Ti:S laser treatment comparing the central part of the laser-treated areas a striking difference is observed between the femtoseconds and picoseconds treatments. Ripple structure generated with short pulse durations can be characterized with periodic length significantly smaller than the laser wavelength (between 120 and 165 nm). At higher pulse durations the structure has a higher periodic length (between 780 and 800 nm), which is comparable to the wavelength. In case of the excimer laser treatment the different pulse durations produced similar surface structures with different periodic length and different orientation. One of the structures was parallel with the polarization of the laser light and has a higher periodic length (~335 nm), and the other was perpendicular with smaller periodic length (~78-80 nm). The possible mechanisms of structure formation will be outlined and discussed in the frame of our experimental results.

  5. 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. PMID:26354233

  6. 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. PMID:24000131

  7. Nanoscale elastic properties of montmorillonite upon water adsorption.

    PubMed

    Ebrahimi, Davoud; Pellenq, Roland J-M; Whittle, Andrew J

    2012-12-11

    Smectites are an important group of clay minerals that experience swelling upon water adsorption. This paper uses molecular dynamics with the CLAYFF force field to simulate isothermal isobaric water adsorption of interlayer Wyoming Na-montmorillonite, a member of the smectite group. Nanoscale elastic properties of the clay-interlayer water system are calculated from the potential energy of the model system. The transverse isotropic symmetry of the elastic constant matrix was assessed by calculating Euclidean and Riemannian distance metrics. Simulated elastic constants of the clay mineral are compared with available results from acoustic and nanoindentation measurements. PMID:23181550

  8. The periparturient period is associated with structural and transcriptomic adaptations of rumen papillae in dairy cattle.

    PubMed

    Steele, M A; Schiestel, C; AlZahal, O; Dionissopoulos, L; Laarman, A H; Matthews, J C; McBride, B W

    2015-04-01

    The structural and functional adaption of the rumen epithelium during the transition period is largely undescribed. To characterize the adaptation of the rumen epithelium during transition, multiparous dairy cattle (n=12) fitted with rumen fistulas and fed a low-energy dry cow diet (1.37 Mcal/kg, net energy for lactation) were transitioned abruptly to a high-energy lactating cow diet (1.68 Mcal/kg, net energy for lactation) immediately after parturition. Rumen papillae were biopsied at -3, +1, and +6 wk relative to calving. The histology of morphology of the rumen papillae was evaluated under the light microscope and electron microscope, and mRNA profiling was performed using an Affymetrix GeneChip Bovine Gene 1.0 ST Array (Affymetrix, Santa Clara, CA). Data preprocessing was conducted using the robust multi-array average method, and detection of significant genes was conducted using ANOVA. Also, the Benjamini-Hochberg false discovery rate of 0.1 was applied. Microscopic examination of rumen papillae revealed an increase in epithelial desquamation during early lactation as sloughing scores increased from 1.7 ± 0.2 at -3 wk to 4.1 ± 0.3 and 3.4 ± 0.2 at +1 and + 6 wk, respectively. A total of 1,011 (-3 vs. +1 wk) and 729 (-3 vs. +6 wk) differentially expressed genes were identified (false discovery rate of 0.10, P<10(-3), fold-change ± 1.2 cut-off). A group of differentially expressed genes involved in desmosome assembly (DSG1, CDSN), epidermal growth factor signaling (EGFR, EREG), transforming growth factor β signaling (TGFB1), and the insulin-like growth factor-axis (GHR, IGFBP2, IGFBP3, CTGF) was also validated using PCR. Gene network analysis found that EGFR, GHR, and TGFB1 were focal points of the top pathways, thereby supporting the importance of these regulatory genes to the adaptive response of rumen papillae in early lactation. The microscopic and transcriptomic changes in this study provide insight into the mechanisms responsible for the rapid rate of

  9. 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(+). PMID:22894657

  10. 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

    2013-08-01

    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. PMID:23822729

  11. 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.

  12. 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.

  13. Electronic structure, stacking energy, partial charge, and hydrogen bonding in four periodic B-DNA models

    NASA Astrophysics Data System (ADS)

    Poudel, Lokendra; Rulis, Paul; Liang, Lei; Ching, W. Y.

    2014-08-01

    We present a theoretical study of the electronic structure of four periodic B-DNA models labeled (AT)10,(GC)10, (AT)5(GC)5, and (AT-GC)5 where A denotes adenine, T denotes thymine, G denotes guanine, and C denotes cytosine. Each model has ten base pairs with Na counterions to neutralize the negative phosphate group in the backbone. The (AT)5(GC)5 and (AT-GC)5 models contain two and five AT-GC bilayers, respectively. When compared against the average of the two pure models, we estimate the AT-GC bilayer interaction energy to be 19.015 Kcal/mol, which is comparable to the hydrogen bonding energy between base pairs obtained from the literature. Our investigation shows that the stacking of base pairs plays a vital role in the electronic structure, relative stability, bonding, and distribution of partial charges in the DNA models. All four models show a highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) gap ranging from 2.14 to 3.12 eV with HOMO states residing on the PO4 + Na functional group and LUMO states originating from the bases. Our calculation implies that the electrical conductance of a DNA molecule should increase with increased base-pair mixing. Interatomic bonding effects in these models are investigated in detail by analyzing the distributions of the calculated bond order values for every pair of atoms in the four models including hydrogen bonding. The counterions significantly affect the gap width, the conductivity, and the distribution of partial charge on the DNA backbone. We also evaluate quantitatively the surface partial charge density on each functional group of the DNA models.

  14. CMOS-compatible polarization rotator design based on asymmetrical periodic loaded waveguide structure

    NASA Astrophysics Data System (ADS)

    Sun, Yao; Ye, Winnie N.

    2016-03-01

    Silicon-on-insulator (SOI) technology has been a promising platform for photonic applications. However, the high index-contrast between silicon and the top cladding (SiO2 or air) of the SOI waveguides makes the modal birefringence hard to control. Consequently, SOI based photonics integrated circuits (PICs) are in general highly polarization-sensitive, making polarization management important. In this paper, a polarization rotator (PR) design on the 220 nm SOI platform is demonstrated through numerical simulations and experiments. The demonstrated PR design is based on asymmetrical periodic loaded waveguide structures. The demonstrated design features compact device footprint and can be fabricated by CMOS compatible process. In addition, no special cladding is required to break the vertical symmetry of the waveguide. The design has shown promising performance over the C-band wavelengths (1530 nm-1565 nm) by simulations. However, the fabrication requirements are stringent for the design, thus the performance of the fabricated devices are limited by the current fabrication technology.

  15. 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.

  16. Codon usage affects the structure and function of the Drosophila circadian clock protein PERIOD.

    PubMed

    Fu, Jingjing; Murphy, Katherine A; Zhou, Mian; Li, Ying H; Lam, Vu H; Tabuloc, Christine A; Chiu, Joanna C; Liu, Yi

    2016-08-01

    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

  17. Box length search algorithm for molecular simulation of systems containing periodic structures.

    PubMed

    Schultz, A J; Hall, C K; Genzer, J

    2004-01-22

    We have developed a box length search algorithm to efficiently find the appropriate box dimensions for constant-volume molecular simulation of periodic structures. The algorithm works by finding the box lengths that equalize the pressure in each direction while maintaining constant total volume. Maintaining the volume at a fixed value ensures that quantitative comparisons can be made between simulation and experimental, theoretical or other simulation results for systems that are incompressible or nearly incompressible. We test the algorithm on a system of phase-separated block copolymers that has a preferred box length in one dimension. We also describe and test a Monte Carlo algorithm that allows the box lengths to change while maintaining constant volume. We find that the box length search algorithm converges at least two orders of magnitude more quickly than the variable box length Monte Carlo method. Although the box length search algorithm is not ergodic, it successfully finds the box length that minimizes the free energy of the system. We verify this by examining the free energy as determined by the Monte Carlo simulation. PMID:15268341

  18. Analysis of the genetic structure of allopatric populations of Lutzomyia umbratilis using the period clock gene.

    PubMed

    de Souza Freitas, Moises Thiago; Ríos-Velasquez, Claudia Maria; da Silva, Lidiane Gomes; Costa, César Raimundo Lima; Marcelino, Abigail; Leal-Balbino, Tereza Cristina; Balbino, Valdir de Queiroz; Pessoa, Felipe Arley Costa

    2016-02-01

    In South America, Lutzomyia umbratilis is the main vector of Leishmania guyanensis, one of the species involved in the transmission of American tegumentary leishmaniasis. In Brazil, L. umbratilis has been recorded in the Amazon region, and an isolated population has been identified in the state of Pernambuco, Northeastern region. This study assessed the phylogeographic structure of three allopatric Brazilian populations of L. umbratilis. Samples of L. umbratilis were collected from Rio Preto da Eva (north of the Amazon River, Amazonas), from Manacapuru (south of the Amazon River), and from the isolated population in Recife, Pernambuco state. These samples were processed to obtain sequences of the period gene. Phylogenetic analysis revealed the presence of two distinct monophyletic clades: one clade comprised of the Recife and Rio Preto da Eva samples, and one clade comprised of the Manacapuru samples. Comparing the Manacapuru population with the Recife and Rio Preto da Eva populations revealed high indices of interpopulational divergence. Phylogenetic analysis indicated that geographical distance and environmental differences have not modified the ancestral relationship shared by the Recife and Rio Preto da Eva populations. Genetic similarities suggest that, in evolutionary terms, these populations are more closely related to each other than to the Manacapuru population. These results confirm the existence of an L. umbratilis species complex composed of at least two incipient species. PMID:26655040

  19. Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

    PubMed

    Almeida, G F B; Martins, R J; Otuka, A J G; Siqueira, J P; Mendonca, C R

    2015-10-19

    We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring. PMID:26480419

  20. Object reconstruction in multilayer neural network based profilometry using grating structure comprising two regions with different spatial periods

    NASA Astrophysics Data System (ADS)

    Ganotra, Dinesh; Joseph, Joby; Singh, Kehar

    2004-08-01

    Feed-forward backpropagation neural network has been used in fringe projection profilometry for reconstruction of a three-dimensional (3D) object. A grating structure comprising two regions of different spatial periods is projected on the reference surface over which the object is placed. The shorter spatial period part of the grating is projected over the object, whereas the longer spatial period part is projected on the reference surface only. 3D object shape is reconstructed with the help of neural networks using images of the projected grating. During training phase of the network, the shorter spatial period grating along with the longer spatial period grating is used. Experimental results are presented for a diffuse object, showing that the 3D shape of the object is recovered using the above-mentioned method. However, the phases wrapping takes place in Fourier transform profilometry by using only one grating of shorter spatial period.

  1. Molecular modeling of polymer-clay nanocomposite precursors: Lysine in montmorillonite interlayers.

    PubMed

    Davis, Alicia M; Joanis, Gary; Tribe, Lorena

    2008-04-30

    The layered structure of clays with interlayer cations leads to unique chemical and mechanical properties, which have been capitalized on in the field of polymer/layered silicate nanocomposites. Hydrophilic silica surfaces can become organophilic with the inclusion of alkylammonium cations, which improve the wetting characteristics of the polymer matrix. In fact, the molecular level interactions of amino acids, either natural or non-natural, with clay surfaces are at the heart of fields of study as diverse as nanocomposites fabrication, drug delivery, bio-remediation of soils and catalysis of biological polymers, to name a few. The ubiquity of these systems and the potential uses to which they could be put suggests the necessity of a deeper understanding of the interplay of bonds, conformations, and configurations between the molecules and the hosts. The interactions of the amino acid lysine with sodium montmorillonite were studied using theoretical molecular modeling methods. The interlayer spacing of montmorillonite was increased by incorporating water molecules and allowing the system to evolve with molecular mechanics. Care was taken to retain the sodium cations in the interlayer. The initial amino acid conformation was obtained surrounding the molecule with numerous discrete water molecules and minimizing the system at the semi empirical level. The optimized amino acid was then placed in the interlayer space in a series of initial positions. Molecular mechanics calculations were performed and the final positions were analyzed. The results tended to indicate the preponderance of configurations which included surface-sodium-amino acid complexes with a variety of spatial arrangements. These results were compared with molecular dynamics calculations of similar systems from the literature. PMID:17987601

  2. Mechanism of smectic arrangement of montmorillonite and bentonite clay platelets incorporated in gels of poly(acrylamide) induced by the interaction with cationic surfactants.

    PubMed

    Starodoubtsev, S G; Lavrentyeva, E K; Khokhlov, A R; Allegra, G; Famulari, A; Meille, S V

    2006-01-01

    Structure transitions, induced by the interaction with the cationic surfactant cetylpyridinium chloride in nanocomposite gels of poly(acrylamide) with incorporated suspensions of the two closely related layered clays bentonite and montmorillonite, were studied. Unexpectedly, different behaviors were revealed. X-ray diffraction measurements confirm that, due to the interaction with the surfactant, initially disordered bentonite platelets arrange into highly ordered structures incorporating alternating clay platelets and surfactant bilayers. The formation of these smectic structures also in the cross-linked polymer gels, upon addition of the surfactant, is explained by the existence of preformed, poorly ordered aggregates of the clay platelets in the suspensions before the gel formation. In the case of montmorillonite, smectic ordering of the disordered platelets in the presence of the surfactant is observed only after drying the suspensions and the clay-gel composites. Rheology studies of aqueous suspensions of the two clays, in the absence of both surfactant and gel, evidence a much higher viscosity for bentonite than for montmorillonite, suggesting smaller clay-aggregate size in the latter case. Qualitatively consistent results are obtained from optical micrographs. PMID:16378447

  3. 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

  4. 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

  5. Montmorillonite-based porous clay heterostructures (PCHs) intercalated with silica-titania pillars-synthesis and characterization

    SciTech Connect

    Chmielarz, Lucjan; Gil, Barbara; Kustrowski, Piotr; Piwowarska, Zofia; Dudek, Barbara; Michalik, Marek

    2009-05-15

    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 deg. 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 Bronsted acid sites. - Graphical abstract: Synthesis of the montmorillonite based porous clay heterostructures (PCHs) intercalated with silica-titania pillars has been performed. The mechanism of the thermal degradation of organic templates in the pore system of PCHs was studied. PCHs were characterized with respect to structure, texture, composition, surface acidity, thermal stability and form of introduced titanium.

  6. 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. PMID:24906646

  7. 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. PMID:25562752

  8. 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.

  9. 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

  10. 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.

  11. Study on light extraction efficiency of light-emitting diodes having periodically corrugated enhancement structures with different duty cycles

    NASA Astrophysics Data System (ADS)

    Ku, Hao Ming; Wang, Huei Tsz; Huang, Chen Yang; Pan, Huang Wei; Chao, Shiuh

    2016-02-01

    The duty cycle effect on the light extraction efficiency of light-emitting diodes having different periodically corrugated enhancement structures placed opposite to the emission surface was studied. The experimental results were compared with numerical simulation results. The numerical simulation was performed using a rigorous-coupled-wave-analysis method. In the case of common structures such as a patterned-sapphire structure, we found that, in general, extraction efficiency increased drastically when duty cycle was increased from zero, and then it varied relatively slowly as the duty cycle was increased further; after that, the extraction efficiency dropped drastically as the duty cycle approached 100%. However, for a structure that was composed of autocloned-photonic crystals super-imposing on the periodical corrugation, the efficiency increased monotonically with the duty cycle and reached 83.4% (corresponding to 589% enhancement efficiency) when the duty cycle approached 100%. A method for the fabrication of such high-efficiency structures was proposed.

  12. On the use of a hierarchical multi-level building block basis function scheme in periodic plasmonic structures

    NASA Astrophysics Data System (ADS)

    Zheng, X.; Valev, V. K.; Volskiy, V.; Vandenbosch, Guy A. E.; Moshchalkov, V. V.

    2014-05-01

    A Volumetric Method of Moments algorithm is applied to predict the plasmonic responses of chiral metamaterials. This algorithm is based on the use of a multi-level building block basis function scheme, in combination with a dedicated Kummer transformation in the calculation of periodic Green's functions. The validity of the algorithm is demonstrated by analyzing a Ninja Star periodic structure. A good agreement can be found between simulation and experiment.

  13. Observation of self-assembled periodic nano-structures induced by femtosecond laser in both ablation and deposition regimes

    NASA Astrophysics Data System (ADS)

    Tang, Mingzhen; Zhang, Haitao; Her, Tsing-Hua

    2008-02-01

    We observed the spontaneous formation of periodic nano-structures in both femtosecond laser ablation and deposition. The former involved 400-nm femtosecond pulses from a 250-KHz regenerated amplified mode-locked Ti:sapphire laser and periodic nanocracks and the nano-structure are in the form of periodic nanocracks in the substrate, the latter applied an 80-MHz mode-locked Ti:sapphire oscillator with pulse energy less than half nanojoule in a laser-induced chemical vapor deposition configuration and tungsten nanogratings grow heterogeneously on top of the substrates. These two observed periodic nanostructures have opposite orientations respecting to laser polarization: the periodic nanocracks are perpendicular to, whereas the deposited tungsten nanogratings are parallel to laser polarization direction. By translating the substrate respecting to the laser focus, both the periodic nanocrack and tungsten nanograting extend to the whole scanning range. The deposited tungsten nanogratings possess excellent uniformity on both the grating period and tooth length. Both the attributes can be tuned precisely by controlling the laser power and scanning speed. Furthermore, we discovered that the teeth of transverse tungsten nanogratings are self aligned along their axial direction during multiple scanning with appropriate offset between scans. We demonstrate the feasibility of fabricating large-area one-dimensional grating by exploiting such unique property. These distinct phenomena of nanocracks and tungsten nanogratings indicate different responsible mechanisms.

  14. New method for analyzing the periodic structure of multilayer by differential anomalous small-angle x-ray scattering

    NASA Astrophysics Data System (ADS)

    Kato, K.; Matsubara, E.; Saito, M.; Kosaka, T.; Waseda, Y.; Inomata, K.

    1995-03-01

    A new method has been proposed for analyzing the periodic structure of a multilayered sample by the differential anomalous small-angle X-ray scattering method in the reflection geometry. The scattering peaks due to the periodically layered structure in the small angle region are often observed with a large background intensity. These peak intensities strongly depend upon the anomalous dispersion terms of the constituent element near its absorption edge. Thus, by taking a difference of these peak intensities observed at two energies near the edge, the scattering intensity attributed to various causes can be accurately eliminated except the periodically layered structure. Namely, only the intrinsic peak intensities are precisely determined by this method. Furthermore, this method is the most effective for analyzing the periodic structures of multilayers composed of the next neighboring elements in the periodic table. The experimental details and the usefulness of the present new method have been presented by obtaining the concentration profile of a Cu/Co multilayer using the peak intensity variation arising from the anomalous dispersion terms of Cu and Co near their K absorption edges.

  15. Adsorption of Lysine on Na-Montmorillonite and Competition with Ca(2+): A Combined XRD and ATR-FTIR Study.

    PubMed

    Yang, Yanli; Wang, Shengrui; Liu, Jingyang; Xu, Yisheng; Zhou, Xiaoyun

    2016-05-17

    Lysine adsorption at clay/aqueous interfaces plays an important role in the mobility, bioavailability, and degradation of amino acids in the environment. Knowledge of these interfacial interactions facilitates our full understanding of the fate and transport of amino acids. Here, X-ray diffraction (XRD) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) measurements were used to explore the dynamic process of lysine adsorption on montmorillonite and the competition with Ca(2+) at the molecular level. Density functional theory (DFT) calculations were employed to determine the peak assignments of dissolved lysine in the solution phase. Three surface complexes, including dicationic, cationic, and zwitterionic structures, were observed to attach to the clay edge sites and penetrate the interlayer space. The increased surface coverage and Ca(2+) competition did not affect the interfacial lysine structures at a certain pH, whereas an elevated lysine concentration contributed to zwitterionic-type coordination at pH 10. Moreover, clay dissolution at pH 4 could be inhibited at a higher surface coverage with 5 and 10 mM lysine, whereas the inhibition effect was inconspicuous or undetected at pH 7 and 10. The presence of Ca(2+) not only could remove a part of the adsorbed lysine but also could facilitate the readsorption of dissolved Si(4+) and Al(3+) and surface protonation. Our results provide new insights into the process of lysine adsorption and its effects on montmorillonite surface sites. PMID:27118104

  16. Effect of clay modification on the morphological, mechanical, and thermal properties of epoxy/polypropylene/montmorillonite shape memory materials

    NASA Astrophysics Data System (ADS)

    Tan, Huifeng; Sun, He; Liu, Yuyan; Tong, Linbao; Du, Xingwen

    2012-04-01

    A series of montmorillonite (DK2) modified shape memory polyurethane-epoxy (UEP) composites had been prepared. The effect of DK2 modification on the morphological, mechanical and thermal properties of epoxy/polypropylene/Montmorillonite nano-composites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile test, scanning electron microscope (SEM) and dynamic mechanical analysis (DMA). The shape memory performance was investigated by fold-deploy shape memory tests. The XRD and TEM results indicated the formation of exfoliated structure for epoxy/polypropylene nano-composites had been prepared using 2~ 3wt.% DK2. On the other hand, a mixture of intercalated and exfoliated structure was found in 4~5wt.% DK2/ epoxy/polypropylene polymers. Further more, the toughness, tensile strength, enlongation at break had been improved by adding DK2, while glass transition temperature, storage modulus and shape recovery ratio was unaffected. The composite materials possessed excellent shape memory properties, they could fully recover their original shapes within 3 min under the maximum bending angle of 180°, and there were little effect by fold-deploy ten times.

  17. Effect of clay modification on the morphological, mechanical, and thermal properties of epoxy/polypropylene/montmorillonite shape memory materials

    NASA Astrophysics Data System (ADS)

    Tan, Huifeng; Sun, He; Liu, Yuyan; Tong, Linbao; Du, Xingwen

    2011-11-01

    A series of montmorillonite (DK2) modified shape memory polyurethane-epoxy (UEP) composites had been prepared. The effect of DK2 modification on the morphological, mechanical and thermal properties of epoxy/polypropylene/Montmorillonite nano-composites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile test, scanning electron microscope (SEM) and dynamic mechanical analysis (DMA). The shape memory performance was investigated by fold-deploy shape memory tests. The XRD and TEM results indicated the formation of exfoliated structure for epoxy/polypropylene nano-composites had been prepared using 2~ 3wt.% DK2. On the other hand, a mixture of intercalated and exfoliated structure was found in 4~5wt.% DK2/ epoxy/polypropylene polymers. Further more, the toughness, tensile strength, enlongation at break had been improved by adding DK2, while glass transition temperature, storage modulus and shape recovery ratio was unaffected. The composite materials possessed excellent shape memory properties, they could fully recover their original shapes within 3 min under the maximum bending angle of 180°, and there were little effect by fold-deploy ten times.

  18. 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.

  19. Kinetic and Conformational Insights of Protein Adsorption onto Montmorillonite Revealed Using in Situ ATR-FTIR/2D-COS.

    PubMed

    Schmidt, Michael P; Martínez, Carmen Enid

    2016-08-01

    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

  20. Periodic structure with a periodicity of 2-3.5 μm on crystalline TiO2 induced by unpolarized KrF excimer lasers

    NASA Astrophysics Data System (ADS)

    He, Rong; Ma, Hongliang; Zheng, Jiahui; Han, Yongmei; Lu, Yuming; Cai, Chuanbing

    2016-08-01

    Laser-induced periodic surface structures (LIPSS) were processed on the TiO2 bulk surface under the irradiation of 248 nm unpolarized KrF excimer laser pulses in air. Spatial LIPSS periods ranging from 2 to 3.5 μm are ascribed to the capillary wave. These microstructures were analyzed at different laser pulse numbers with the laser energy from 192 to 164 mJ. The scanning electron microscopy results indicated eventually stripes that have been disrupted as the increase in the laser pulse numbers, which is reasonably explained by the energy accumulating effect. In addition, investigations were concentrated on the surface modifications at pre-focal plane, focal plane and post-focal plane in the same defocusing amount. Compared with condition at pre-focal plane, in addition to the plasma produced at target, the air was also breakdown for the situation of post-focal plane. So it was reasonable that stripes appeared at pre-focal plane but not at post-focal plane.

  1. A hybrid wave-mode formulation for the vibro-acoustic analysis of 2D periodic structures

    NASA Astrophysics Data System (ADS)

    Droz, C.; Zhou, C.; Ichchou, M. N.; Lainé, J.-P.

    2016-02-01

    In the framework of vibrational analysis of 2D periodic waveguides, Floquet-Bloch theorem is widely applied for the determination of wave dispersion characteristics. In this context, the Wave Finite Element Method (WFEM) combines Periodic Structure Theory (PST) with standard FE packages, enabling wave dispersion analysis of waveguides involving structurally realistic unit-cells. For such applications, the computational efficiency of the WFEM depends on the choice of the formulation and can lead to numerical issues, worsen by extensive computational cost. This paper presents a coupled wave-mode approach for the determination of wave dispersion characteristics in structurally advanced periodic structures. It combines two scales of model order reduction. At the unit-cell's scale, Component Mode Synthesis (CMS) provides the displacement field associated with local resonances of the periodic structure, while the free wave propagation is considered using a spectral problem projection on a reduced set of shape functions associated with propagating waves, thus providing considerable reduction of the computational cost. An application is provided for a bi-directionally stiffened panel and the influence of reduction parameters is discussed, as well as the robustness of the numerical results.

  2. [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

  3. Intergrown mica and montmorillonite in the Allende carbonaceous chondrite

    NASA Technical Reports Server (NTRS)

    Tomeoka, K.; Buseck, P. R.

    1982-01-01

    High resolution transmission electron microscopy (HRTEM) observations were made of a mixture of mica and montmorillonite from fine-grained calcium, aluminum inclusions (CAI) in the Allende C3(V) meteorite. A petrographic thin section having a diameter of 4 mm contained CAI fragments ranging from less than 1 to 50 microns. The observed textural and chemical characteristics placed the inclusion in the fine-grained alkali-rich spinel aggregate category of Warks' (1979) classifications of CAIs and as type 3 in Kornacki's classifications of fine grains in Allende. Chemical analyses were performed on the phyllosilicate grains observed in the TEM scan by means of an X ray observed, and the proximity to the matrix boundary suggests a metamorphism which included aqueous alteration at a relatively low temperature.

  4. Intergrown mica and montmorillonite in the Allende carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Tomeoka, K.; Buseck, P. R.

    1982-09-01

    High resolution transmission electron microscopy (HRTEM) observations were made of a mixture of mica and montmorillonite from fine-grained calcium, aluminum inclusions (CAI) in the Allende C3(V) meteorite. A petrographic thin section having a diameter of 4 mm contained CAI fragments ranging from less than 1 to 50 microns. The observed textural and chemical characteristics placed the inclusion in the fine-grained alkali-rich spinel aggregate category of Warks' (1979) classifications of CAIs and as type 3 in Kornacki's classifications of fine grains in Allende. Chemical analyses were performed on the phyllosilicate grains observed in the TEM scan by means of an X ray observed, and the proximity to the matrix boundary suggests a metamorphism which included aqueous alteration at a relatively low temperature.

  5. 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.

  6. Steady-state droplet size in montmorillonite stabilised emulsions.

    PubMed

    Ganley, William J; van Duijneveldt, Jeroen S

    2016-08-14

    The formation of hexadecane-in-water emulsions stabilised by montmorillonite platelets was studied. In this system the platelets form a monolayer around the droplets and the droplet size decreases with increasing platelet volume fraction. However, the number of platelets present exceeds that required for monolayer coverage. The kinetics of emulsification were investigated and coalescence of droplets during turbulent mixing was found to continue even after the droplets had reached their ultimate size. Non-spherical droplets, resulting from arrested coalescence, were not observed suggesting that particles may be desorbing from the interface during the turbulent flow. A kinetic model based on a competition between droplet break-up and coalescence, mediated by particle adsorption and desorption, reproduces experimental trends in droplet diameter. The model can be used to predict the most efficient formulation to minimise droplet diameters for given materials and mixing conditions and sheds light on the processes occurring during emulsification in this system. PMID:27407026

  7. Pomegranate peel pectin films as affected by montmorillonite.

    PubMed

    Oliveira, Túlio Ítalo S; Zea-Redondo, Luna; Moates, Graham K; Wellner, Nikolaus; Cross, Kathryn; Waldron, Keith W; Azeredo, Henriette M C

    2016-05-01

    The industrial production of pomegranate juice has been favored by its alleged health benefits derived from its antioxidant properties. The processing of pomegranate juice involves squeezing juice from the fruit with the seeds and the peels together, leaving a pomace consisting of approximately 73 wt% peels. In this study, pectin was extracted from pomegranate peels, and used to produce films with different contents of montmorillonite (MMT) as a nanoreinforcement material. The nanoreinforcement improved the tensile strength and modulus of films when added at up to 6 wt%, while the further addition of MMT (to 8 wt%) reduced the reinforcement effect, probably because of dispersion problems. The elongation was decreased with increasing MMT concentrations. The water vapor permeability decreased with increasing MMT contents up to 8 wt% MMT, indicating that the increased tortuosity of the permeant path was effective on barrier properties of the film. PMID:26769511

  8. Biodegradable nanocomposites from toughened polyhydroxybutyrate and titanate-modified montmorillonite clay

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Montmorillonite clay treated with neopentyl (diallyl)oxy tri( dioctyl) pyrophosphato-titanate was used as a reinforcement for toughened bacterial bioplastic, Polyhydroxybutyrate (PHB) in order to develop novel biodegradable nanocomposites. The modified clay, PHB, toughening partner and specific comp...

  9. 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...

  10. Neptunium(V) sorption behavior on clinoptilolite, quartz and montmorillonite

    SciTech Connect

    Bertetti, F.P.; Pabalan, R.T.; Turner, D.R.; Almendarez, M.G.

    1996-08-01

    Performance assessment models have identified {sup 237}Np as a radionuclide of concern in meeting release limits established for the geologic disposal of high-level nuclear waste at the proposed repository at Yucca Mountain, Nevada. In this study, quartz, clinoptilolite, and montmorillonite, which are minerals representative of phases that occur both in the rock matrix and as fracture coatings at Yucca Mountain, were reacted with {sup 237}Np-bearing solutions to characterize the sorption behavior of Np(V) on these minerals. Batch experiments were conducted over a wide range of conditions in which pH of solution, surface loading, sorbent surface area, initial concentration of Np(V), and partial pressure of CO{sub 2} were varied. Initial Np(V) concentrations were between 1 {times} 10{sup {minus}7} and 1 {times} 10{sup {minus}6} M in electrolyte solutions of 0.1 or 0.01 M NaNO{sub 3}. The oxidation state of Np in solution was verified with NIR spectroscopy and by solvent extraction. Prior to the start of experiments, minerals were pretreated to eliminate impurities, and the clinoptilolite and montmorillonite were converted to Na-form by ion exchange with NaCl solutions. Results indicate that, for all three minerals, Np(V) sorption begins at pH values coincident with the start of hydrolysis in solution ({approximately}7). For solutions undersaturated with respect to atmospheric CO{sub 2}, sorption increases continuously with increasing pH. Under equilibrium with atmospheric CO{sub 2}, Np(V) sorption is important in the pH range (7--9.5) where NpO{sub 2}(OH){sup 0}(aq) is significant, whereas sorption is inhibited at higher pH where neptunyl carbonate complexes are the predominant species.

  11. Hierarchical structure of the European countries based on debts as a percentage of GDP during the 2000-2011 period

    NASA Astrophysics Data System (ADS)

    Kantar, Ersin; Deviren, Bayram; Keskin, Mustafa

    2014-11-01

    We investigate hierarchical structures of the European countries by using debt as a percentage of Gross Domestic Product (GDP) of the countries as they change over a certain period of time. We obtain the topological properties among the countries based on debt as a percentage of GDP of European countries over the period 2000-2011 by using the concept of hierarchical structure methods (minimal spanning tree, (MST) and hierarchical tree, (HT)). This period is also divided into two sub-periods related to 2004 enlargement of the European Union, namely 2000-2004 and 2005-2011, in order to test various time-window and observe the temporal evolution. The bootstrap techniques is applied to see a value of statistical reliability of the links of the MSTs and HTs. The clustering linkage procedure is also used to observe the cluster structure more clearly. From the structural topologies of these trees, we identify different clusters of countries according to their level of debts. Our results show that by the debt crisis, the less and most affected Eurozone’s economies are formed as a cluster with each other in the MSTs and hierarchical trees.

  12. 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…

  13. 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.

  14. 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.

  15. Characterization of montmorillonite doped PVA/SA blends using X-ray diffraction

    NASA Astrophysics Data System (ADS)

    Hemalatha, K.; Mahadevaiah, Somashekarappa, H.; Somashekar, R.

    2014-04-01

    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.

  16. 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.

  17. 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

  18. Ultrahigh spatial-frequency, high-contrast periodic structures produced by interference lithography

    SciTech Connect

    Nguyen, H. T.; Britten, J. A.; Boyd, R. D.; Shore, B. D.; Perry, M. D.

    1996-04-01

    We have developed a process to produce high-aspect ratio, high- frequency periodic profiles recorded in a photoresist layer by interference lithography. We are able to independently control the period, duty cycle, and sidewall angle of the profiles. High-contrast diazonapthoquinone-based photoresist and single mode operation of the exposure laser are critical. The high-aspect ratio profiles are necessary for many applications such as transfer etch masks for etching oxides and field emitter array patterning. 5 refs., 5 figs.

  19. 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.

  20. In situ polarized micro-Raman investigation of periodic structures realized in liquid-crystalline composite materials.

    PubMed

    Castriota, Marco; Fasanella, Angela; Cazzanelli, Enzo; De Sio, Luciano; Caputo, Roberto; Umeton, Cesare

    2011-05-23

    In situ polarized micro-Raman Spectroscopy has been utilized to determine the liquid crystal configuration inside a periodic liquid crystalline composite structure made of polymer slices alternated to films of liquid crystal. Liquid crystal, Norland Optical Adhesive (NOA-61) monomer and its polymerized form have been investigated separately. The main Raman features, used as markers for the molecular orientation estimation, have been identified. In situ polarized Raman spectra indicate that the orientation of the liquid crystal director inside the structure is perpendicular to its polymeric slices. Results show the usefulness of in situ polarized micro-Raman spectroscopy to investigate liquid crystalline composite structures. PMID:21643304

  1. 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.

  2. 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. PMID:19250893

  3. 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.

  4. Seawater pH sensor based on the long period grating in a single-mode-multimode-single-mode structure

    NASA Astrophysics Data System (ADS)

    Wang, Ke; Klimov, Denis; Kolber, Zbigniew

    2009-03-01

    A pH sensor is developed based on the long-period grating (LPG) inscribed into a single-mode-multimode-single-mode (SMS) structure in order to measure the pH in seawater. The LPG is formed by using a focused CO2 laser at LPG's critical period (1 mm). The transmission characteristics are similar to that of a multimode fiber. However, the SMS structure has a higher sensitivity because mode coupling only happens between the fundamental mode and higher-order modes in the SMS structure. The pH-sensitive hydrogel is made by the thermal cross-link of poly vinyl alcohol and poly acrylic acid. This sensor has been utilized in seawater pH sensing in the range of 6-8. Experiments have confirmed that the sensor is sensitive and repeatable.

  5. 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. PMID:17222420

  6. 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.

  7. Design of Fabry-Perot surface-emitting lasers with a periodic gain structure

    SciTech Connect

    Corzine, S.W.; Geels, R.S.; Scott, J.W.; Yan, R.H.; Coldren, L.A.

    1989-06-01

    In this paper, the authors present a detailed analysis of a Fabry-Perot surface-emitting laser (FP-SEL) which utilizes the recently proposed concept of periodic gain. They show that by employing the periodic gain concept, close to a factor of two reduction in threshold current should be possible, the ideal reduction of a factor of two being limited by the internal loss of the cavity. Multiple quantum well active regions are also considered and shown to provide greater than a factor of two improvement over bulk GaAs periodic and uniform gain configurations. The effects of index perturbations within the cavity created by interleaving active and passive segments are treated for different Al mole fractions within the passive segments. The effects are found to be small for chi < 0.3. In addition, optical pumping results on periodic gain DBR-SEL samples which exhibit very low optical power density thresholds (<3 x 10/sup 4/ W/cm/sup 2/) and narrow above-threshold linewidths (<2 A) are included.

  8. Design of Fabry-Perot surface-emitting lasers with a periodic gain structure

    SciTech Connect

    Corzine, S.W.; Geels, R.S.; Scott, J.W.; Yan, R.H.; Coldren, L.A.

    1989-06-01

    This reprint presents a detailed analysis of a Fabry-Perot Surface-Emitting Laser (FP-SEL) which utilizes the recently proposed concept of periodic gain. By employing the periodic gain concept, close to a factor of two reduction in threshold current should be possible, the ideal reduction of a factor of two being limited by the internal loss of the cavity. Multiple quantum-well active regions are also considered and shown to provide greater than a factor of two improvement over bulk-GaAs periodic and uniform gain configurations. The effects of index perturbations within the cavity created by interleaving active and passive segments are treated for different Al mole fractions within the passive segments. The effects are found to be small for x<0.3. In addition, optical pumping results on periodic gain DBR-SEL samples which exhibit very low optical power density thresholds (<30000 W/sq cm) and narrow above-threshold linewidth (<2A) are included.

  9. Periodic variation in side-chain polarities of T-cell antigenic peptides correlates with their structure and activity.

    PubMed Central

    Cornette, J L; Margalit, H; Berzofsky, J A; DeLisi, C

    1995-01-01

    We present an analysis that synthesizes information on the sequence, structure, and motifs of antigenic peptides, which previously appeared to be in conflict. Fourier analysis of T-cell antigenic peptides indicates a periodic variation in amino acid polarities of 3-3.6 residues per period, suggesting an amphipathic alpha-helical structure. However, the diffraction patterns of major histocompatibility complex (MHC) molecules indicate that their ligands are in an extended non-alpha-helical conformation. We present two mutually consistent structural explanations for the source of the alpha-helical periodicity, based on an observation that the side chains of MHC-bound peptides generally partition with hydrophobic (hydrophilic) side chains pointing into (out of) the cleft. First, an analysis of haplotype-dependent peptide motifs indicates that the locations of their defining residues tend to force a period 3-4 variation in hydrophobicity along the peptide sequence, in a manner consistent with the spacing of pockets in the MHC. Second, recent crystallographic determination of the structure of a peptide bound to a class II MHC molecule reveals an extended but regularly twisted peptide with a rotation angle of about 130 degrees. We show that similar structures with rotation angles of 100-130 degrees are energetically acceptable and also span the length of the MHC cleft. These results provide a sound physical chemical and structural basis for the existence of a haplotype-independent antigenic motif which can be particularly important in limiting the search time for antigenic peptides. Images Fig. 3 PMID:7667297

  10. Structure formation during the crystallization induction period of a short chain-molecule system: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Takeuchi, Hisao

    1998-10-01

    A molecular dynamics simulation has been performed for a short chain-molecule system to study structure formation during the crystallization induction period. A model simulating n-alkane having 20 methylene units was used for the short-chain molecule. A model system containing either 250 or 2000 chains was quenched from a high temperature, and the structure formation was examined at constant temperature and pressure. The model system containing 250 chains eventually forms an ordered phase after the induction period, during which macroscopic quantities, such as volume, remain almost constant. In spite of these small changes in the macroscopic quantities, development of local parallel order is significant during the induction period. We also found that the development of local parallel order causes density fluctuations which appear as a weak small-angle peak in the structure factor. A characteristic length scale corresponding to the density fluctuations becomes larger as time elapses in the induction period. These features are qualitatively in accord with recent experimental findings on a different polymer system [M. Imai et al., Phys. Rev. B 52, 12 696 (1995)].

  11. 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

  12. 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

  13. Multiple periodic solutions of a delayed predator–prey model with non-monotonic functional response and stage structure

    PubMed Central

    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. PMID:24963983

  14. 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

  15. Characteristics of microstrip dipole antennas in a periodic structure with dielectric layers

    NASA Astrophysics Data System (ADS)

    Grinev, A. Iu.; Kotov, Iu. V.

    Microstrip dipole antennas in a periodic antenna array with dielectric layers are analyzed on the basis of a rigorous solution of an integral equation of the first kind with respect to the electric-field distribution on the dipole. Numerical results are presented on the partial radiation pattern of the antenna, the total input impedance, and the amplitude-phase distribution of the electric current on the dipole. The optimization of the antenna is considered.

  16. Liquid-bridging in particle self-assemblies toward constructing periodic nano-mesh structures and nano-dot arrays

    NASA Astrophysics Data System (ADS)

    Chul Park, Seung; Lee, In-Ho; Na, Jun-Hee; Lee, Sin-Doo

    2013-10-01

    We demonstrate a simple generic principle of constructing periodic nano-mesh structures and nano-dot arrays by liquid-bridging in particle self-assemblies. A self-assembly of nano- to micro-sized spheres of polystyrene, produced in a close-packed monolayer on a substrate by a convective method, is used as a template for liquid-bridging of a functional fluid in the pores among the neighboring particles. After the solidification of the fluid, followed by the detachment of the particles from the substrate, a periodic mesh structure is directly obtained. Moreover, deposition of a desired substance onto such mesh structure made of a sacrificial material, which is subsequently removable through a lift-off process, enables to produce a periodic dot array of the substance. Depending on the size of the particle and the nature of liquid bridging in the particle assembly, a variety of nano-mesh structures of silver-ink and nano-dot arrays of gold are constructed. This simple liquid bridging-based methodology is easily applicable for different classes of functional fluids such as soluble organic semiconductors.

  17. Single-step optical realization of bio-inspired dual-periodic motheye and gradient-index-array photonic structures.

    PubMed

    Behera, Saraswati; Joseph, Joby

    2016-08-01

    This Letter demonstrates a single-step optical realization method for hexagonal and square lattice-based dual periodic motheye and gradient-index-array photonic structures over large areas. Computed phase mask of gradient interference patterns are used as inputs to a phase-only spatial light modulator (SLM), and the first-order diffracting beams are coherently superposed with the help of a 2f-2f Fourier filtering setup to avoid complex optical geometry for generation and control of individual beams. The simulated interference patterns are verified experimentally through a CMOS camera. The fabricated micro-structures on a positive photoresist are shown to have a major periodicity of 638 μm and minor periodicity of 25.2 μm, with the air hole diameter varying from 22.7 to 6.9 μm along the X and Y axes. The depth of the fabricated structure gradually varies from 4.203 μm at the center to 1.818 μm at the corner. These structures may be scaled down to submicron features that can show improved anti-reflection properties for solar energy harvesting and GRIN lens for optical wavelength region. PMID:27472623

  18. 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.

  19. Interactions between Nafion resin and protonated dodecylamine modified montmorillonite: a solid state NMR study.

    PubMed

    Zhang, Limin; Xu, Jun; Hou, Guangjin; Tang, Huiru; Deng, Feng

    2007-07-01

    A series of nanocomposites have been prepared from perfluorosulfonylfluoride copolymer resin (Nafion) and layered montmorillonite (MMT) modified with protonated dodecylamine by conventional sol-gel intercalation. The structure of these nanocomposite materials have been characterized using FT-IR, elemental analysis, XRD and solid state NMR techniques, including 19F magic-angle spinning (MAS) NMR, 19F NMR relaxation time measurements, 29Si MAS, 1H MAS, 1H-13C cross-polarization magic-angle spinning (CPMAS), and 1H-13C heteronuclear correlation (HETCOR) 2D NMR. The results showed that thermal stability of Nafion was improved moderately by the addition of dodecylamine modified MMT without intercalation. FT-IR and 29Si MAS NMR results indicated that dodecylamine modification did not result in obvious changes in the MMT lattice structure. The XRD results showed that the protonated dodecylamine has been embedded and intercalated into the MMT interlayers, whereas Nafion was not. Elemental analysis results also suggested that some dodecylamine was adsorbed on the surface of MMT. 1H-13C HETCOR 2D NMR experiment clearly indicated that strong electrostatic interactions were present between the NH+3 group of dodecylamine and the fluorine-containing groups (CF3, OCF2, and SCF2) of Nafion resin. Such electrostatic interactions are probably the major contributors for the improved thermal stability of the resultant composite materials. PMID:17382953

  20. Molecular dynamics study of montmorillonite crystalline swelling: Roles of interlayer cation species and water content

    NASA Astrophysics Data System (ADS)

    Sun, Linlin; Tanskanen, Jukka T.; Hirvi, Janne T.; Kasa, Seppo; Schatz, Timothy; Pakkanen, Tapani A.

    2015-07-01

    Molecular dynamic simulations are employed to study the crystalline swelling behavior of montmorillonites (MMTs) with different interlayer Na+ and Ca2+ ion compositions, and the effect of temperature and pressure on the swelling behavior. Non-linear increases in d-spacing are observed with increasing water content. Plateaus in the swelling curve for Na-MMT around d-spacings of 12 and 15 Å demonstrate the formation of 1- and 2-layer hydrate structures. Ca-MMT and mixed Na/Ca-MMTs exhibit similar swelling behavior with exception of showing stronger swelling at water contents corresponding to the 1-layer hydrate in Na-MMT. The stronger swelling in the calcium containing systems is attributed to the preference of Ca2+ to be fully coordinated to water molecules, which favors a 2-layer hydrate structure and increased d-spacings. The larger hydration energy of Ca2+ ions relative to Na+ ions promotes increased water coordination numbers and more pronounced association of water molecules with Ca2+ ions. The 1- and 2-layer hydrates for Na-MMT and the 2-layer hydrate for Ca-MMT were relatively stable to changes in temperature and pressure.

  1. Hemicelluloses/montmorillonite hybrid films with improved mechanical and barrier properties.

    PubMed

    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

  2. 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.

  3. Synthesis and photocatalytic performances of the TiO2 pillared montmorillonite.

    PubMed

    Chen, Daimei; Zhu, Qian; Zhou, Fengsan; Deng, Xutao; Li, Fatang

    2012-10-15

    TiO(2) pillared clay materials were prepared by montmorillonite (Mt) and acidic solutions of hydrolyzed Ti alkoxides in the presence of high-molecular-weight polyoxypropylene (POP)-backboned di-quaternary salts (POP). The as-prepared materials were characterized by means of XRD, FTIR, TG-DTA, XRF, specific surface area and porosity determinations, TEM and SEM, respectively. The experiments showed that the resulting material was a porous delaminated structure containing pillared fragments and nano-scaled TiO(2) particles well dispersed among each other. Introducing polymer surfactant POP as an expanding agent of Mt cannot only promote the formation of the delaminated structure, but significantly improve the porosity and surface area of the composites. The resulting TiO(2) pillared Mt exhibited a good thermal stability as indicated by its surface area after calcination at 800 °C. No phase transformation from anatase to rutile was observed even under calcination at 900 °C. The grain size of anatase in as-prepared sample decreased with the increase of the POP concentration, but increased with the increment of calcination temperature. The photocatalytic performances of these new porous materials were evaluated by using methylene blue degradation. The composite solid exhibited superior photocatalyic property and the maximum removal efficiency was up to 98% within 90 min. PMID:22884731

  4. Activity of laccase immobilized on TiO2-montmorillonite complexes.

    PubMed

    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

  5. 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

  6. 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

  7. 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

  8. Determining the response of infinite, one-dimensional, non-uniform periodic structures by substructuring using waveshape coordinates

    NASA Astrophysics Data System (ADS)

    Brown, G. P.; Byrne, K. P.

    2005-10-01

    A method is presented for determining the wavenumbers, waveshapes and point receptances for an infinite, one-dimensional, non-uniform periodic structure with distributed periodic attachments or supports. The approach is based on a general theory of harmonic wave propagation in one-dimensional periodic systems. Ill-conditioning was previously reported as an impediment to applying the theory to problems of practical importance. In this paper ill-conditioning problems are overcome and a method of substructuring using waveshape coordinates is presented that dramatically improves computational efficiency. The accuracy and generality of the new method are tested by comparing computed and measured receptances for a typical TGV railway track with UIC60 rail, rail pad, ballast and concrete sleepers. The computed results are found to correlate well with measured data.

  9. Micro-contacting of single and periodically arrayed columnar silicon structures by focused ion beam techniques

    SciTech Connect

    Friedrich, F. Herfurth, N.; Teodoreanu, A.-M.; Boit, C.

    2014-06-16

    Micron-sized, periodic crystalline Silicon columns on glass substrate were electrically contacted with a transparent conductive oxide front contact and a focused ion beam processed local back contact. Individual column contacts as well as arrays of >100 contacted columns were processed. Current-voltage characteristics of the devices were determined. By comparison with characteristics obtained from adapted device simulation, the absorber defect density was reconstructed. The contacting scheme allows the fabrication of testing devices in order to evaluate the electronic potential of promising semiconductor microstructures.

  10. Surface-emitting lasers with periodic gain and a parallel driven nipi structure

    SciTech Connect

    Coldren, L.A.; Scott, J.W.; Yan, R.H.

    1989-10-10

    This patent describes a distributed-Bragg-Reflector semiconductor laser. It comprises a nipinipi...gain-producing active section comprised of a plurality of gain segments disposed at periodic intervals with respect to the wavelength of an intended operating frequency of the laser; a pair of distributed-Bragg-Reflector stacks disposed at the respective ends of the nipinipi...active section; and, electrode means operably connected to the nipinipi...active section in electrical contact therewith for applying a driving current to the nipinipi...active section.

  11. Optical-assembly periodic structure of ferrofluids in a liquid core/metal cladding optical waveguide.

    PubMed

    Wang, Xianping; Yin, Cheng; Sun, Jingjing; Han, Qingbang; Li, Honggen; Sang, Minghuang; Yuan, Wen; Cao, Zhuangqi

    2013-11-01

    We present a novel and simple mechanism for the fabrication of periodic microstructure based on a ferrofluids core/metal cladding optical waveguide chip. The ultrahigh-order modes excited in the millimeter scale guiding layer lead to the ordered particle aggregates in ferrofluids without applying a magnetic field. Since the absorption of photons by the extremely dilute ferrofluids is extremely small and the Soret effect is not noticeable, a tentative explanation in terms of the optical trapping effect is proposed. Furthermore, this scheme exhibits all-optically tunable reflectivity and lateral Goos-Hänchen shift, which potentially may be for practical use in novel optical devices. PMID:24216657

  12. 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

  13. Mimicking bicolor by changing the reflectance of the substrate in a one-dimensional periodic structure.

    PubMed

    Wang, Bin; Ye, Yong-Hong; Yang, Li

    2013-11-01

    In nature, some beetles can display bicolor on their elytra. In order to explore the bicolor mechanism, we experimentally studied the optical and structural properties of the Carabus lafossei beetle. We found a multilayer structure in the cuticle of the beetle. Due to the different multilayer thicknesses in different areas, the beetle displayed bicolor. Here, we provide another approach to fabricate bicolor by depositing the same multilayer stack on a substrate with different reflectances at different areas. In this paper, the substrate with different reflectances is achieved by prefabricating sculpted hexagons (SU-8) on a silicon substrate. By coating a (ZnS/MgF2)3.5 multilayer, the sculpted structure displays green color at the ridges (SU-8/silicon area) and yellow color at the basins (silicon area). PMID:24216662

  14. Ultra-short-pulsed laser-machined nanogratings of laser-induced periodic surface structures on thin molybdenum layers

    NASA Astrophysics Data System (ADS)

    Scorticati, Davide; Römer, Gert-Willem; de Lange, Dirk Frederik; Huis in't Veld, Bert

    2012-01-01

    Large areas of regular diffraction nanogratings were produced consisting of so-called laser-induced periodic surface structures (LIPSS) on thin molybdenum layers (<400 nm) deposited on a borosilicate glass substrate. The aim was to produce these structures without ablating nor cracking the molybdenum layer. Ultra short laser pulses were applied using a focused Gaussian beam profile. Processing parameters such as laser fluence, pulse overlap, number of overscans, repetition frequency, wavelength and polarization were varied to study the effect on periodicity, height, and especially regularity of the obtained LIPSS. It was found that a careful choice of the correct laser parameters is required to avoid detrimental mechanical stresses, cracking, and delamination during the laser processing of the layer in order to remain in its correct range of ductility as well as to ensure regular LIPSS. A possible photovoltaic application of these nanogratings could be found in texturing of thin film cells to enhance light trapping mechanisms.

  15. Effect of interaction between periodic δ-doping in both well and barrier layers on modulation of superlattice band structure

    NASA Astrophysics Data System (ADS)

    Xu, Huaizhe; Yan, Qiqi; Wang, Tianmin

    2007-08-01

    The modulation of superlattice band structure via periodic δ-doping in both well and barrier layers have been theoretically investigated, and the importance of interaction between the δ-function potentials in the well layers and those in the barrier layers on SL band structure have been revealed. It is pointed out that the energy dispersion relation Eq. (3) given in [G. Ihm, S.K. Noh, J.I. Lee, J.-S. Hwang, T.W. Kim, Phys. Rev. B 44 (1991) 6266] is an incomplete one, as the interaction between periodic δ-doping in both well and barrier layers had been overlooked. Finally, we have shown numerically that the electron states of a GaAs/Ga0.7Al0.3As superlattice can be altered more efficiently by intelligent tuning the two δ-doping's positions and heights.

  16. Effects of axial load and structural damping on wave propagation in periodic Timoshenko beams on elastic foundations under moving loads

    NASA Astrophysics Data System (ADS)

    Ding, Lan; Zhu, Hong-Ping; Wu, Li

    2016-07-01

    The propagation and attenuation properties of waves in ordered and disordered periodic composite Timoshenko beams, which consider the effects of axial static load and structural damping, resting on elastic foundations are studied when the system is subjected to moving loads of constant amplitude with a constant velocity. The transfer matrix methodology is adopted to formulate the model in a reference coordinate system moving with the load. The localization factor is calculated to determine the wave velocity pass bands and stop bands. The interactions between the static axial load and moving load, structural damping and disorder on the bands are analyzed.

  17. Led InGaN/GaN Structures with Short-Period Superlattice Grown on Flat and Patterned Sapphire Substrates

    NASA Astrophysics Data System (ADS)

    Romanov, I. S.; Prudaev, I. A.; Brudnyi, V. N.; Kop'ev, V. V.; Novikov, Vad. A.; Marmalyuk, A. A.; Kureshov, V. A.; Sabitov, D. R.; Mazalov, A. V.

    2015-03-01

    The results of studies of blue LED InGaN/GaN heterostructures with a short-period InGaN/GaN superlattice in front of an active region of the structure grown on flat and patterned Al2O3 substrates are presented. In these structures, an increase of the internal quantum efficiency is observed. The high-resolution X-ray diffraction spectra and the integrated PL intensity are measured for two temperatures - 10 and 300 K - at different levels of optical YAG-laser pumping.

  18. Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

    SciTech Connect

    Sedao, Xxx; Garrelie, Florence Colombier, Jean-Philippe; Reynaud, Stéphanie; Pigeon, Florent; Maurice, Claire; Quey, Romain

    2014-04-28

    The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

  19. Nonlinear dynamics of fluid-structure systems. Final technical report for period January 5, 1991 - December 31, 1997

    SciTech Connect

    Moon, Francis C.

    1999-07-20

    The technical research was directed at problems involving the dynamics of fluid flow and elastic structures. Such problems occur in heat-exchange systems in energy generating plants. Fluid excited vibrations of structures can result in unwanted impact forces which can lead to metal fatigue failures. Mathematical theories based on linear models have been used for several decades. In this research the authors explored the phenomena associated with nonlinear effects using experimental models, mathematical models and numerical computation. A number of nonlinear effects were observed experimentally including chaotic dynamics, multi-fractal Poincare maps, quasi-periodic vibrations, subcritical Hopf bifurcations, helical waves in a tube row and spatial localization.

  20. On the Structure of the Two-Dimensional Spatially Periodic Inner Transition Layers in a Gas-Discharge Plasma

    SciTech Connect

    Voronov, A.Ya.

    2005-07-01

    We investigate the structure of the spatially periodic inner boundary layers in the plasma of a positive glow-discharge column produced in a long cylindrical tube with an electropositive gas inside. Asymptotic methods, namely, the method of boundary functions, are used to analyze the initial mathematical model. We consider the formation of contrast burst-type structures. We have found all principal terms of the boundary-layer asymptotics of the solution. The results obtained are compared with the available probe measurements of basic physical parameters of ionization waves (strata) in neon at low pressures.

  1. Quantum states of charge carriers and longitudinal conductivity in double periodic n-type semiconductor lattice structures in electric field

    SciTech Connect

    Perov, A. A. Penyagin, I. V.

    2015-07-15

    Quantum states of charge carriers in double periodic semiconductor superlattices of n-type quantum dots with Rashba spin–orbit coupling in an electron gas have been calculated in the one-electron approximation in the presence of mutually perpendicular electric and magnetic fields. For these structures in weak constant electric field, the solution to the quasi-classical kinetic Boltzmann equation shows that the states of carriers in magnetic Landau minibands with negative differential conductivity are possible.

  2. Extinction in periodic competitive stage-structured Lotka-Volterra model with the effects of toxic substances

    NASA Astrophysics Data System (ADS)

    Li, Zhong; Chen, Fengde

    2009-09-01

    In this paper, we consider a periodic competitive stage-structured Lotka-Volterra model with the effects of toxic substances. It is shown that toxic substances play an important role in the extinction of species. We obtain a set of sufficient conditions which guarantee that one of the components is driven to extinction while the other is globally attractive. The numerical simulation of an example verifies our main results.

  3. Experimental study on dynamics of coherent structures formed by inertial solid particles in three-dimensional periodic flows

    NASA Astrophysics Data System (ADS)

    Gotoda, Masakazu; Melnikov, Denis E.; Ueno, Ichiro; Shevtsova, Valentina

    2016-07-01

    We present experimental results obtained under normal gravity on the dynamics of solid particles in periodic oscillatory thermocapillary-driven flows in a non-isothermal liquid bridge made of decane. Inertial particles of different densities and in the size range approximately 0.75 - 75 μm are able to form stable coherent structures (particle accumulation structures, or PASs). Two image processing techniques were developed and successfully applied to compute time required for an ensemble of particles to form a structure. It is shown that the formation time grows with the decrease of the Stokes number. The observations indicate the probable irrelevance of the memory term for these experiments. Two types of PAS were observed—single (SL-I) and double-loop (SL-II)—which sometimes co-existed. Only large or very dense particles may form an SL-II type structure. A number of novel features of the system were perceived. In some cases, intermittently stable structures emerged (their dynamics is characterized by alternating time intervals during which a structure exists and is destroyed). Whereas in most experiments we observed a conventional symmetric and centered PAS, there were cases when a long-term stable asymmetric structure appeared. Experiments wherein two different types of PAS-forming particles were used simultaneously revealed the destructive role of collisions between the particles on formation of structures.

  4. A Study of the Structure of Piagetian Logical and Infralogical Grouping Within the Concrete Operational Period.

    ERIC Educational Resources Information Center

    Dettrick, Graham W.

    This study investigated a problem within the theoretical structure of cognitive development proposed by Jean Piaget, and used the concepts of classification and projective spatial relationships to investigate the nature of attainment and sequencing of three corresponding logical and infralogical groupings according to the models proposed by…

  5. 75 FR 24501 - Fatigue Tolerance Evaluation of Metallic Structures; Extension of Comment Period

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-05

    ... Notice No. 10-04, Fatigue Tolerance Evaluation of Metallic Structures (75 FR 11799, 3/12/2010). Comments... Federal Aviation Administration 14 CFR Part 27 RIN 2120-AJ51 Fatigue Tolerance Evaluation of Metallic... airworthiness standards for fatigue tolerance evaluation (FTE) of transport category metallic...

  6. Structural Aging Program technical progress for period, January 1, 1992--December 31, 1992

    SciTech Connect

    Naus, D.J.; Oland, C.B.

    1993-07-01

    The Structural Aging (SAG) Program is conducted for the Nuclear Regulatory Commission (NRC) by the Oak Ridge National Laboratory (ORNL). The program has the overall objective of preparing an expandable handbook or report which will provide potential structural safety issues and acceptance criteria for use by the NRC in nuclear power plant evaluations of continued service. Initial focus of the program is on concrete and concrete-related materials which comprise safety-related (Category I) structures in light-water reactor facilities. The SAG Program is organized into four tasks: Task S.1 -- Program Management, Task S.2 -- Materials Property Data Base, Task S.3 -- Structural Component Assessment/Repair Technology, and Task S.4 -- Quantitative Methodology for Continued Service Determinations. In meeting the individual objectives of these tasks resources are drawn from ORNL with subcontract support from universities and other research laboratories. This report provides an overview of principal developments in each of the four program tasks from January 1, 1992 to December 31, 1992. Planned activities under each of these tasks are also presented.

  7. Early doors (Edo) mutant mouse reveals the importance of period 2 (PER2) PAS domain structure for circadian pacemaking

    PubMed Central

    Militi, Stefania; Maywood, Elizabeth S.; Sandate, Colby R.; Chesham, Johanna E.; Parsons, Michael J.; Vibert, Jennifer L.; Joynson, Greg M.; Partch, Carrie L.; Hastings, Michael H.; Nolan, Patrick M.

    2016-01-01

    The suprachiasmatic nucleus (SCN) defines 24 h of time via a transcriptional/posttranslational feedback loop in which transactivation of Per (period) and Cry (cryptochrome) genes by BMAL1–CLOCK complexes is suppressed by PER–CRY complexes. The molecular/structural basis of how circadian protein complexes function is poorly understood. We describe a novel N-ethyl-N-nitrosourea (ENU)-induced mutation, early doors (Edo), in the PER-ARNT-SIM (PAS) domain dimerization region of period 2 (PER2) (I324N) that accelerates the circadian clock of Per2Edo/Edo mice by 1.5 h. Structural and biophysical analyses revealed that Edo alters the packing of the highly conserved interdomain linker of the PER2 PAS core such that, although PER2Edo complexes with clock proteins, its vulnerability to degradation mediated by casein kinase 1ε (CSNK1E) is increased. The functional relevance of this mutation is revealed by the ultrashort (<19 h) but robust circadian rhythms in Per2Edo/Edo; Csnk1eTau/Tau mice and the SCN. These periods are unprecedented in mice. Thus, Per2Edo reveals a direct causal link between the molecular structure of the PER2 PAS core and the pace of SCN circadian timekeeping. PMID:26903623

  8. Nanophotonic light trapping in polycrystalline silicon thin-film solar cells using periodically nanoimprint-structured glass substrates

    NASA Astrophysics Data System (ADS)

    Becker, Christiane; Xavier, Jolly; Preidel, Veit; Wyss, Philippe; Sontheimer, Tobias; Rech, Bernd; Probst, Jürgen; Hülsen, Christoph; Löchel, Bernd; Erko, Alexei; Burger, Sven; Schmidt, Frank; Back, Franziska; Rudigier-Voigt, Eveline

    2013-09-01

    A smart light trapping scheme is essential to tap the full potential of polycrystalline silicon (poly-Si) thin-film solar cells. Periodic nanophotonic structures are of particular interest as they allow to substantially surpass the Lambertian limit from ray optics in selected spectral ranges. We use nanoimprint-lithography for the periodic patterning of sol-gel coated glass substrates, ensuring a cost-effective, large-area production of thin-film solar cell devices. Periodic crystalline silicon nanoarchitectures are prepared on these textured substrates by high-rate silicon film evaporation, solid phase crystallization and chemical etching. Poly-Si microhole arrays in square lattice geometry with an effective thickness of about 2μm and with comparatively large pitch (2 μm) exhibit a large absorption enhancement (A900nm = 52%) compared to a planar film (A900nm ~ 7%). For the optimization of light trapping in the desired spectral region, the geometry of the nanophotonic structures with varying pitch from 600 nm to 800 nm is tailored and investigated for the cases of poly-Si nanopillar arrays of hexagonal lattice geometry, exhibiting an increase in absorption in comparison to planar film attributed to nanophotonic wave optic effects. These structures inspire the design of prospective applications such as highly-efficient nanostructured poly-Si thin-film solar cells and large-area photonic crystals.

  9. Theoretical investigation of surface acoustic wave propagation characteristics in periodic (AlN/ZnO)N /diamond multilayer structures

    NASA Astrophysics Data System (ADS)

    Qian, Lirong; Li, Cuiping; Li, Mingji; Wang, Fang; Yang, Baohe

    2014-11-01

    Propagation characteristics of surface acoustic wave (SAW) in periodic (AlN/ZnO)N/diamond multilayer structures were theoretically investigated using effective permittivity method. The phase velocity Vp, electromechanical coupling coefficient K2, and temperature coefficient of frequency (TCF) of the Sezawa mode are analyzed for different thicknesses-to-wavelength H/λ, thickness ratios of AlN to ZnO Rh, and periods of alternating ZnO and AlN layers N. Results show that, comparing with AlN/ZnO/diamond multilayer structure, the periodic (AlN/ZnO)N/diamond multilayer structure (N ≥ 2) shows excellent electromechanical coupling and temperature stable characteristics with significantly improved K2 and TCF. The largest coupling coefficient of 3.0% associated with a phase velocity of 5726 m/s and a TCF of -29.2 ppm/°C can be reached for Rh = 0.2 and N = 2. For a low TCF of -24.4 ppm/°C, a large coupling coefficient of 2.0% associated with a phase velocity of 7058 m/s can be obtained for Rh = 1.0 and N = 5. The simulated results can be used to design the low loss and good temperature stability SAW devices of gigahertz-band application.

  10. Effects of graded levels of montmorillonite on performance, hematological parameters and bone mineralization in weaned pigs.

    PubMed

    Duan, Q W; Li, J T; Gong, L M; Wu, H; Zhang, L Y

    2013-11-01

    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

  11. 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

  12. Diffraction from tunable periodic structures: application for the determination of electro-optic coefficients.

    PubMed

    Yang, X; Wood, L T; Miller, J H

    2001-11-01

    We discuss a method for measuring electro-optic coefficients by measuring diffraction from a tunable grating. The method involves measuring the changes in the diffraction pattern of a reflection grating, where applied electric fields of alternating direction induce changes in the index of refraction through the electro-optic effect. For certain geometries, these applied fields cause period-doubling effects that produce new peaks in the diffraction pattern. Numerically calculated diffraction patterns are presented for the assumptions of both homogeneous and inhomogeneous fields. Peak splitting, as a function of both the number of slits illuminated and the induced change in the index of refraction, is observed and discussed. Finally, the usefulness of our method for the measurement of electro-optic coefficients is discussed. PMID:18364844

  13. Capillary instability of periodic polymer structures: Influence of viscosity, substrate confinement and local curvature

    NASA Astrophysics Data System (ADS)

    Zhang, Zheng; Ding, Yifu

    2015-03-01

    NMR spectrum and spin-lattice relaxation time(T1) of CaF2 thin film samples deposited on a silicon cantilever tip were obtained by magnetic resonance force microscopy(MRFM). Thickness of the thin films were 50nm and 150nm. In order to measure T1, a cyclic adiabatic inversion method was used with periodic phase inversion. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental conditions such as temperature and magnetic field.

  14. Structure and Evolution of Nearby Stars with Planets. I. Short-Period Systems

    NASA Astrophysics Data System (ADS)

    Ford, Eric B.; Rasio, Frederic A.; Sills, Alison

    1999-03-01

    Using the Yale stellar evolution code, we have calculated theoretical models for nearby stars with planetary-mass companions in short-period nearly circular orbits: 51 Pegasi, τ Bootis, υ Andromedae, ρ1 Cancri, and ρ Coronae Borealis. We present tables listing key stellar parameters such as mass, radius, age, and size of the convective envelope as a function of the observable parameters (luminosity, effective temperature, and metallicity), as well as the unknown helium fraction. For each star we construct best models based on recently published spectroscopic data and the present understanding of galactic chemical evolution. We discuss our results in the context of planet formation theory and, in particular, tidal dissipation effects and stellar metallicity enhancements.

  15. Constructing molecular structures on periodic superstructure of graphene/Ru(0001)

    PubMed Central

    Li, Geng; Huang, Li; Xu, Wenyan; Que, Yande; Zhang, Yi; Lu, Jianchen; Du, Shixuan; Liu, Yunqi; Gao, Hong-Jun

    2014-01-01

    We review the way to fabricate large-scale, high-quality and single crystalline graphene epitaxially grown on Ru(0001) substrate. A moiré pattern of the graphene/Ru(0001) is formed due to the lattice mismatch between graphene and Ru(0001). This superstructure gives rise to surface charge redistribution and could behave as an ordered quantum dot array, which results in a perfect template to guide the assembly of organic molecular structures. Molecules, for example iron phthalocyanine and C60, on this template show how the molecule–substrate interaction makes different superstructures. These results show the possibility of constructing ordered molecular structures on graphene/Ru(0001), which is helpful for practical applications in the future. PMID:24615151

  16. [Diagnostic problems in recognizing structural pathology of the heart during the prenatal period].

    PubMed

    Włoch, Agata; Rokicki, Władysław; Krzystolik-Ładzińska, Joanna; Włoch, Stanisław; Sikora, Jerzy; Bilewicz-Wyrozumska, Teresa

    2002-01-01

    The aim of our study was to analyse the results of echocardiographic examinations of 28 fetuses with structural heart abnormalities referred for echocardiographic examination from January 1996 to May 2001 along with their follow-up. Fetal heart anomalies were diagnosed in 2.1% of all of the examined fetuses (28/1319). Among 28 cases of structural anomalies, there were 23 cases of heart defects, 4 cases of cardiomyopathy, and one case of intracardiac tumors. In 5 cases, heart defects were accompanied by arrhythmias while in 2 cases, heart defects were accompanied by congestive heart failure. Extracardiac malformations coexisted with heart defects in 11 fetuses. Eight newborns were operated shortly after birth. The mortality rate in the examined group was 64%. PMID:12632900

  17. Origin of the periodic structure in the conductance curve of gold nanojunctions in hydrogen environment

    NASA Astrophysics Data System (ADS)

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2016-03-01

    The evolution of the atomic structure and the vibrational and electronic transport properties of gold atomic junctions incorporating molecular and atomic hydrogen upon elongation have been investigated with the nonequilibrium Green's function formalism combined with density functional theory. Our calculations show that for the case of gold junctions doped with a single H2 molecule the low-bias conductance drops rapidly with the electrodes' separation, while it remains almost constant if a single H atom replaces the molecule. In contrast, when one considers two H atoms adsorbed on a gold monatomic chain forming an Au-H-Au-H-Au double-bridge structure, the low-bias conductance increases first and then shows a plateau upon stretching the junction, in perfect agreement with experiments on gold nanocontacts in hydrogen environment. Furthermore, also the distribution of the calculated vibrational energies of the two H atoms is consistent with the experimental result in the low-conductance region, demonstrating clear evidence that hydrogen molecules can dissociate on stretched gold monatomic chains. These findings are helpful to improve our understanding of the structure-property relation of gold nanocontacts and also provide a new prospect for gold nanowires being used as chemical sensors and catalysts.

  18. Phase diagrams of Wyoming Na-montmorillonite clay. Influence of particle anisotropy.

    PubMed

    Michot, Laurent J; Bihannic, Isabelle; Porsch, Katharina; Maddi, Solange; Baravian, Christophe; Mougel, Julien; Levitz, Pierre

    2004-12-01

    Natural Na-Wyoming montmorillonite was size fractionated by successive centrifugation. Polydisperse particles with average sizes of 400, 290, and 75 nm were then obtained. As the structural charge of the particles belonging to three fractions (determined by cationic exchange capacity measurements) is the same, such a procedure allows studying the effect of particle anisotropy on the colloidal phase behavior of swelling clay particles. Osmotic stress experiments were carried out at different ionic strengths. The osmotic pressure curves display a plateau whose beginning systematically coincides with the sol/gel transition determined by oscillatory stress measurements. The concentration corresponding to the sol/gel transition increases linearly with particle anisotropy, which shows that the sol/gel transition is not directly related to an isotropic/nematic transition of individual clay particles. Indeed, a reverse evolution should be observed for an I/N transition involving the individual clay particles. Still, when observed between crossed polarizer and analyzer, the gel samples exhibit permanent birefringent textures, whereas in the "sol" region, transient birefringence is observed when the samples are sheared. This suggests that interacting clay particles are amenable to generate, at rest and/or under shear, large anisotropic particle associations. PMID:15568830

  19. Preparation of polyethersulfone-organophilic montmorillonite hybrid particles for the removal of bisphenol A.

    PubMed

    Cao, Fuming; Bai, Pengli; Li, Haocheng; Ma, Yunli; Deng, Xiaopei; Zhao, Changsheng

    2009-03-15

    Polyethersulfone (PES)-organophilic montmorillonite (OMMT) hybrid particles, with various proportions of OMMT, were prepared by using a liquid-liquid phase separation technique, and then were used for the removal of bisphenol A (BPA) from aqueous solution. The adsorbed BPA amounts increased significantly when the OMMT were embedded into the particles. The structure of the particle was characterized by using scanning electron microscopy (SEM); and these particles hardly release small molecules below 250 degrees C which was testified by using thermogravimetric analysis (TGA). The experimental data of BPA adsorption were adequately fitted with Langmuir equations. Three simplified kinetics model including the pseudo-first-order (Lagergren equation), the pseudo-second-order, and the intraparticle diffusion model were used to describe the adsorption process. Kinetic studies showed that the adsorbed BPA amount reached an equilibrium value after 300 min, and the experimental data could be expressed by the intraparticular mass transfer diffusion model. Furthermore, the adsorbed BPA could be effectively removed by ethanol, which indicated that the hybrid particles could be reused. These results showed that the PES-OMMT hybrid particles have the potential to be used in the environmental application. PMID:18597933

  20. Nanocomposites of rice and banana flours blend with montmorillonite: partial characterization.

    PubMed

    Rodríguez-Marín, María L; Bello-Pérez, Luis A; Yee-Madeira, Hernani; Zhong, Qixin; González-Soto, Rosalía A

    2013-10-01

    Rice and banana flours are inexpensive starchy materials that can form films with more improved properties than those made with their starch because flour and starch present different hydrophobicity. Montmorillonite (MMT) can be used to further improve the properties of starch-based films, which has not received much research attention for starchy flours. The aim of this work was to evaluate the mechanical and barrier properties of nanocomposite films of banana and rice flours as matrix material with addition of MMT as a nanofiller. MMT was modified using citric acid to produce intercalated structures, as verified by the X-ray diffraction pattern. The intercalated MMT was blended with flour slurries, and films were prepared by casting. Nanocomposite films of banana and rice flours presented an increase in the tensile at break and elongation percentage, respectively, more than their respective control films without MMT. This study showed that banana and rice flours could be alternative raw materials to use in making nanocomposite films. PMID:23910294

  1. Hybrid materials: Magnetite-Polyethylenimine-Montmorillonite, as magnetic adsorbents for Cr(VI) water treatment.

    PubMed

    Larraza, Iñigo; López-Gónzalez, Mar; Corrales, Teresa; Marcelo, Gema

    2012-11-01

    Hybrid materials formed by the combination of a sodium rich Montmorillonite (MMT), with magnetite nanoparticles (40 nm, Fe(3)O(4) NPs) coated with Polyethylenimine polymer (PEI 800 g/mol or PEI 25000 g/mol) were prepared. The intercalation of the magnetite nanoparticles coated with PEI among MMT platelets was achieved by cationic exchange. The resulting materials presented a high degree of exfoliation of the MMT sheets and a good dispersion of Fe(3)O(4) NPs on both the surface and among the layers of MMT. The presence of amine groups in the PEI structure not only aids the exfoliation of the MMT layers, but also gives to the hybrid material the necessary functionality to interact with heavy metals. These hybrid materials were used as magnetic sorbent for the removal of hexavalent chromium from water. The effect that pH, Cr(VI) concentration, and adsorbent material composition have on the Cr(VI) removal efficiency was studied. A complete characterization of the materials was performed. The hybrid materials showed a slight dependence of the removal efficiency with the pH in a wide range (1-9). A maximum amount of adsorption capacity of 8.8 mg/g was determined by the Langmuir isotherm. Results show that these hybrid materials can be considered as potential magnetic adsorbent for the Cr(VI) removal from water in a wide range of pH. PMID:22841705

  2. Formulation and evaluation of transdermal composite films of chitosan-montmorillonite for the delivery of curcumin.

    PubMed

    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

  3. Microstructural Response of Variably Hydrated Ca-Rich Montmorillonite to Supercritical CO2

    SciTech Connect

    Lee, Mal Soon; McGrail, B. Peter; Glezakou, Vassiliki Alexandra

    2014-08-05

    We report on ab initio molecular dynamics simulations of Ca-rich montmorillonite systems, in different hydration states in the presence of supercritical CO2. Analysis of the molecular trajectories provides estimates of the relative H2O:CO2 ratio per interspatial cation. The vibrational density of states in direct comparison with dipole moment derived IR spectra for these systems provide unique signatures that can used to follow molecular transformation. In a co-sequestration scenario, these signatures could be used to identify the chemical state and fate of Sulfur compounds. Interpretation of CO2 asymmetric stretch shift is given based on a detailed analysis of scCO2 structure and intermolecular interactions of the intercalated species. Based on our simulations, smectites with higher charge interlayer cations at sub-single to single hydration states should be more efficient in capturing CO2, while maintaining caprock integrity. This research would not have been possible without the support of the office of Fossil Energy, Department of Energy. The computational resources were made available through a user proposal of the EMSL User facility, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

  4. 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

    2016-11-01

    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. PMID:27318738

  5. 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. PMID:26118641

  6. 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.

  7. 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. PMID:26609925

  8. 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. PMID:22985953

  9. 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

  10. 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

  11. Design and implementation of novel nonlinear processes in bulk and waveguide periodic structures

    NASA Astrophysics Data System (ADS)

    Kajal, Meenu

    The telecommunication networks are facing increasing demand to implement all-optical network infrastructure for enabling the wide deployment of new triple play high-speed services (e.g. IPTV, Video On Demand, Voice over IP). One of the challenges with such video broadcasting applications is that these are much more distributed and multi-point in nature unlike the traditional point-to-point communication networks. Currently deployed high-speed electronic components in the optical networks are incapable of handling the unprecedented bandwidth demand for real-time multimedia based broadcasting. The solution essentially lies in increasing the transparency of networks i.e. by replacing high speed signal processing electronics with all-optical signal processors capable of performing signal manipulations such as wavelength switching, time and wavelength division multiplexing, optical pulse compression etc. all in optical domain. This thesis aims at providing an all-optical solution for broadband wavelength conversion and tunable broadcasting, a crucial optical network component, based on quasi-phase-matched wave mixing in nonlinear materials. The quasi phase matching (QPM) technique allows phase matching in long crystal lengths by employing domain-inverted gratings to periodically reverse the sign of nonlinearity, known as periodic poling. This results into new frequency components with high conversion efficiency and has been successfully implemented towards various processes such as second harmonic generation (SHG), sum- and difference- frequency generation (SFG and DFG). Conventionally, the optical networks has an operation window of ˜35 nm centered at 1.55 mum, known as C-band. The wavelength conversion of a signal channel in C-band to an output channel also in the C-band has been demonstrated in periodically poled lithium niobate (PPLN) waveguides via the process of difference frequency mixing, cascaded SHG/DFG and cascaded SFG/DFG. While a DFG process utilized a

  12. New polyelectrolyte complex from pectin/chitosan and montmorillonite clay.

    PubMed

    da Costa, Marcia Parente Melo; de Mello Ferreira, Ivana Lourenço; de Macedo Cruz, Mauricio Tavares

    2016-08-01

    A new nanocomposite hydrogel was prepared by forming a crosslinked hybrid polymer network based on chitosan and pectin in the presence of montmorillonite clay. The influence of clay concentration (0.5 and 2% wt) as well as polymer ratios (1:1, 1:2 and 2:1) was investigated carefully. The samples were characterized by different techniques: transmission and scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, swelling degree and compression test. Most samples presented swelling degree above 1000%, which permits characterizing them as superabsorbent material. Images obtained by transmission electron microscopy showed the presence of clay nanoparticles into hydrogel. The hydrogels' morphological properties were evaluated by scanning electron microscope in high and low-vacuum. The micrographs showed that the samples presented porous. The incorporation of clay produced hydrogels with differentiated morphology. Thermogravimetric analysis results revealed that the incorporation of clay in the samples provided greater thermal stability to the hydrogels. The compression resistance also increased with addition of clay. PMID:27112858

  13. 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. PMID:18572177

  14. 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 different water saturation, salinity, interlayer space and humic substances. The molecular configuration, density profile, diffusion coefficient and aggregation intensity were determined by molecular dynamic simulation, while the 3D topography and particle size of the aggregates were characterized by atomic force microscopy. Results indicated that the diffusivity of asphaltenes was up to 5-fold higher in the MMT interlayer filled with fresh water than with saline water (salinity: 35‰). However, salinity had little impact on the asphaltene aggregation. This study also showed a marked decrease in the mobility of asphaltenes with decrease in the pore water content and the interlayer space of MMT. This was more pronounced in the organo-MMT where the humic substances were present. The co-aggregation process resulted in the sequestration of asphaltenes in the hollow cone-shaped cavity of humic substances in the MMT interlayer, which decreased the asphaltene diffusion by up to one-order of magnitude and increased the asphaltene aggregation by about 33%. These findings have important ramifications for evaluating the fate and transport of heavy fractions of the residual oil in the contaminated soils. PMID:27362529

  15. Preparation and characterization of bone cements incorporated with montmorillonite.

    PubMed

    Kwon, Soon Yong; Cho, Eun Hee; Kim, Sung Soo

    2007-10-01

    Bone cements incorporated with montmorillonite (MMT) were prepared in an attempt to improve their mechanical properties. The cements were characterized using particle size analysis, gel permeation chromatography, viscosity measurements, unreacted monomer analysis, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and mechanical properties. The average particle size and molecular weight of the PMMA powders used were 47 microm and 100,000 g/mol, respectively. The incorporation of MMT led to an increase in viscosity of the bone cement but did not severely affect its setting temperature or the amount of residual monomer. Regardless of the MMT mixing methods used, in this case MMT being mixing in liquid and powder components, sodium MMT (SMMT) was not well dispersed in the bone cements, which was believed to be due to its hydrophilicity. Organophilic MMT (OMMT) was better dispersed in the liquid component than in the powder component. The compressive and tensile strength of the bone cement containing the OMMT mixed into the liquid component were significantly higher than those of the bone cement without MMT (p < 0.05). PMID:17385224

  16. Adsorption of trace elements from poultry litter by montmorillonite clay.

    PubMed

    Subramanian, Bhaskaran; Gupta, Gian

    2006-01-16

    Poultry litter (PL) is used as fertilizer on agricultural lands because of its high nutrient content. However, the litter also contains trace elements such as As, Cd, Cu, Pb, and Zn. On land application of PL, these trace elements may be absorbed by crops, leach into groundwater, or enter the aquatic system as run-off. The objective of this research was to study the effect of the addition of montmorillonite clay-mineral (CM) in reducing the release of trace elements from PL. Cd, Cu, and Zn showed significant decreases of 29, 34, and 22%, respectively, in PL aqueous leachate (compared with the control-PL without CM) on mixing with 0.05 g CM but no change in As, Co, and Cr concentrations was observed. Lead showed a significant increase in PL aqueous leachate on mixing with 0.2 g CM but Pb concentration was two orders of magnitude less than in CM aqueous leachate alone. On washing, the settled precipitate (PL+CM) in the centrifuge tubes with water (desorption study) most of the adsorbed metals (Cd 85%, Cu 61%, and Zn 100%) were released. The results of this study show that the addition of CM resulted in significant adsorption of Cd and Cu from PL. PMID:16298051

  17. Mechanism of amitriptyline adsorption on Ca-montmorillonite (SAz-2).

    PubMed

    Chang, Po-Hsiang; Jiang, Wei-Teh; Li, Zhaohui; Kuo, Chung-Yih; Jean, Jiin-Shuh; Chen, Wan-Ru; Lv, Guocheng

    2014-07-30

    The uptake of amitriptyline (AMI) from aqueous environment by Ca-montmorillonite (SAz-2) was studied in a batch system under different physicochemical conditions. The adsorbent was characterized by X-ray diffraction and Fourier transform infrared (FTIR) analyses. The AMI adsorption on SAz-2 obeyed the Langmuir isotherm with a capacity of 330mg/g (1.05mmol/g) at pH 6-7. The adsorption kinetics was fast, almost reaching equilibrium in 2h, and followed a pseudo-second-order kinetic model. Desorption of exchangeable cations correlated with the AMI adsorption well, indicating that cation exchange was the major mechanism. X-ray diffraction patterns showing significant expansions of the d001 spacing and characteristic FTIR band shifts toward higher frequencies after AMI adsorption onto SAz-2 indicated that the adsorbed AMI molecules were intercalated into the interlayers of the mineral. Thermodynamic parameters based on partitioning coefficients suggested that the AMI adsorption was an endothermic physisorption at high adsorption levels. At low and higher AMI adsorption levels, the intercalated AMI molecules take a horizontal monolayer and bilayer conformation, respectively. The higher adsorption capacity suggested that SAz-2 could be a good candidate to remove AMI from wastewater and would be an important environmental sink for the fate and transport of AMI in soils and groundwater. PMID:24373983

  18. The effect of dispersion technique of montmorillonite on polyisocyanurate nanocomposites

    NASA Astrophysics Data System (ADS)

    Cabulis, U.; Fridrihsone, A.; Andersons, J.; Vlcek, T.

    2014-05-01

    The biomass represents an abundant, renewable, competitive and low cost resource that can play an alternative role to petrochemical resources. The central topic of the research activity reported is the use of rape seed oil (RO) as a raw material for the production of rigid polyisocyanurate foams (PIR). The content of the renewable resource-derived polymers achieved in ready foams is up to 20%. By using biopolymers as a matrix, a prospective way is to reinforce them with nanoparticles, organically modified clays, for improvement of mechanical properties while, at the same time, replacing petrochemical raw materials. Organoclay Cloisite® 15A was tested as a filler of PIR foams. Three different techniques - ultrasonification, mixing by three-roll mills, and high-pressure homogenization were used for dispergation of nanoclays in polyols. Composite polyisocyanurate foams and solid polymer samples were produced and tested for stiffness and strength. This paper discusses the studies into the use of RO as a renewable source in rigid PIR foams filled with organomodified montmorillonite clay with loadings from 1 to 5% by weight.

  19. Synthesis of silver nanoparticles in montmorillonite and their antibacterial behavior

    PubMed Central

    Shameli, Kamyar; Ahmad, Mansor Bin; Zargar, Mohsen; Yunus, Wan Md Zin Wan; Rustaiyan, Abdolhossein; Ibrahim, Nor Azowa

    2011-01-01

    Silver nanoparticles (Ag NPs) were synthesized by the chemical reducing method in the external and interlamellar space of montmorillonite (MMT) as a solid support at room temperature. AgNO3 and NaBH4 were used as a silver precursor and reducing agent, respectively. The most favorable experimental conditions for synthesizing Ag NPs in the MMT are described in terms of the initial concentration of AgNO3. The interlamellar space limits changed little (d-spacing = 1.24–1.47 nm); therefore, Ag NPs formed on the MMT suspension with d-average = 4.19–8.53 nm diameter. The Ag/MMT nanocomposites (NCs), formed from AgNO3/MMT suspension, were characterizations with different instruments, for example UV-visible, PXRD, TEM, SEM, EDXRF, FT-IR, and ICP-OES analyzer. The antibacterial activity of different sizes of Ag NPs in MMT were investigated against Gram-positive, ie, Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) and Gram-negative bacteria, ie, Escherichia coli, Escherichia coli O157:H7, and Klebsiella pneumoniae, by the disk diffusion method using Mueller-Hinton agar (MHA). The smaller Ag NPs were found to have significantly higher antibacterial activity. These results showed that Ag NPs can be used as effective growth inhibitors in different biological systems, making them applicable to medical applications. PMID:21674015

  20. Momentum and mass fluxes in a gas confined between periodically structured surfaces at different temperatures.

    PubMed

    Donkov, Alexander A; Tiwari, Sudarshan; Liang, Tengfei; Hardt, Steffen; Klar, Axel; Ye, Wenjing

    2011-07-01

    It is well known that in a gas-filled duct or channel along which a temperature gradient is applied, a thermal creep flow is created. Here we show that a mass and momentum flux can also be induced in a gas confined between two parallel structured surfaces at different temperatures, i.e., orthogonal to the temperature gradient. We use both analytical and numerical methods to compute the resulting fluxes. The momentum flux assumes its maximum value in the free-molecular flow regime, the (normalized) mass flux in the transition flow regime. The discovered phenomena could find applications in methods for energy-conversion and thermal pumping of gases. PMID:21867301