Science.gov

Sample records for forming incomplete monolayer

  1. Algodystrophy: complex regional pain syndrome and incomplete forms

    PubMed Central

    Giannotti, Stefano; Bottai, Vanna; Dell’Osso, Giacomo; Bugelli, Giulia; Celli, Fabio; Cazzella, Niki; Guido, Giulio

    2016-01-01

    Summary The algodystrophy, also known as complex regional pain syndrome (CRPS), is a painful disease characterized by erythema, edema, functional impairment, sensory and vasomotor disturbance. The diagnosis of CRPS is based solely on clinical signs and symptoms, and for exclusion compared to other forms of chronic pain. There is not a specific diagnostic procedure; careful clinical evaluation and additional test should lead to an accurate diagnosis. There are similar forms of chronic pain known as bone marrow edema syndrome, in which is absent the history of trauma or triggering events and the skin dystrophic changes and vasomotor alterations. These incomplete forms are self-limited, and surgical treatment is generally not needed. It is still controversial, if these forms represent a distinct self-limiting entity or an incomplete variant of CRPS. In painful unexplained conditions such as frozen shoulder, post-operative stiff shoulder or painful knee prosthesis, the algodystrophy, especially in its incomplete forms, could represent the cause. PMID:27252736

  2. HAMLET forms annular oligomers when deposited with phospholipid monolayers.

    PubMed

    Baumann, Anne; Gjerde, Anja Underhaug; Ying, Ming; Svanborg, Catharina; Holmsen, Holm; Glomm, Wilhelm R; Martinez, Aurora; Halskau, Oyvind

    2012-04-20

    Recently, the anticancer activity of human α-lactalbumin made lethal to tumor cells (HAMLET) has been linked to its increased membrane affinity in vitro, at neutral pH, and ability to cause leakage relative to the inactive native bovine α-lactalbumin (BLA) protein. In this study, atomic force microscopy resolved membrane distortions and annular oligomers (AOs) produced by HAMLET when deposited at neutral pH on mica together with a negatively charged lipid monolayer. BLA, BAMLET (HAMLET's bovine counterpart) and membrane-binding Peptide C, corresponding to BLA residues 75-100, also form AO-like structures under these conditions but at higher subphase concentrations than HAMLET. The N-terminal Peptide A, which binds to membranes at acidic but not at neutral pH, did not form AOs. This suggests a correlation between the capacity of the proteins/peptides to integrate into the membrane at neutral pH-as observed by liposome content leakage and circular dichroism experiments-and the formation of AOs, albeit at higher concentrations. Formation of AOs, which might be important to HAMLET's tumor toxic action, appears related to the increased tendency of the protein to populate intermediately folded states compared to the native protein, the formation of which is promoted by, but not uniquely dependent on, the oleic acid molecules associated with HAMLET.

  3. Phase equilibria in model surfactants forming Langmuir monolayers.

    PubMed

    Ramírez, E; Santana, A; Cruz, A; López, G E

    2007-12-14

    The study of Langmuir monolayers has generated the attention of researchers because of their unique properties and their not well understood phase equilibrium. These monolayers exhibit interesting phase diagrams where the unusual liquid-liquid equilibrium can be observed for a single component monolayer. Monte Carlo computer simulations in the virtual Gibbs ensemble were used to obtain the phase diagram of Langmuir monolayers. The liquid-vapor and liquid-liquid phase equilibria were considered by constructing the Cailletet-Mathias phase diagrams. By using the Ising model and the rectilinear approximations the identification of the critical properties for both equilibria was determined. These critical parameters were calculated as a function of the strength of the interaction between the surfactant molecules and the aqueous subphase. As a result, we have identified the coexistence between a liquid expanded state (LES)-vapor and the liquid condensed state-LES, in agreement with experimental and theoretical evidence in the literature. We obtained a clear separation of phases and a strong dependence on the strength of the solvent used. Namely, as the interaction between the solvent and the head of the surfactant increases, the critical properties also increase. Equilibrium states were characterized by computing thermodynamic quantities as a function of temperature and solvent strength.

  4. Method for forming monolayer graphene-boron nitride heterostructures

    DOEpatents

    Sutter, Peter Werner; Sutter, Eli Anguelova

    2016-08-09

    A method for fabricating monolayer graphene-boron nitride heterostructures in a single atomically thin membrane that limits intermixing at boundaries between graphene and h-BN, so as to achieve atomically sharp interfaces between these materials. In one embodiment, the method comprises exposing a ruthenium substrate to ethylene, exposing the ruthenium substrate to oxygen after exposure to ethylene and exposing the ruthenium substrate to borazine after exposure to oxygen.

  5. Thermodynamics of monolayers formed by mixtures of phosphatidylcholine/phosphatidylserine.

    PubMed

    Luna, Carlos; Stroka, Kimberly M; Bermudez, Harry; Aranda-Espinoza, Helim

    2011-07-01

    In this work we obtain the thermodynamic properties of mixed (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) PC and (1-stearoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (sodium salt)) PS monolayers. Measurements of compressibility (isotherms, bulk modulus, and excess area per molecule) and surface potential show that the properties of monolayers at the air-water interface depend on the concentration of ions (Na(+) and K(+)) and the proportion of PS in the mixture. The dependence on PS arises because the molecule is originally bound to a Na(+) counterion; by increasing the concentration of ions the entropy changes, creating a favorable system for the bound counterions of PS to join the bulk, leaving a negatively charged molecule. This change leads to an increase in electrostatic repulsions which is reflected by the increase in area per molecule versus surface pressure and a higher surface potential. The results lead to the conclusion that this mixture of phospholipids follows a non ideal behavior and can help to understand the thermodynamic behavior of membranes made of binary mixtures of a zwitterionic and an anionic phospholipid with a bound counterion.

  6. MDM2 regulates a novel form of incomplete neoplastic transformation of Theileria parva infected lymphocytes.

    PubMed

    Hayashida, Kyoko; Kajino, Kiichi; Hattori, Masakazu; Wallace, Maura; Morrison, Ivan; Greene, Mark I; Sugimoto, Chihiro

    2013-02-01

    Our efforts are concerned with identifying features of incomplete malignant transformation caused by non viral pathogens. Theileria parva (T. parva) is a tick-transmitted protozoan parasite that can cause a fatal lymphoproliferative disease in cattle. The T. parva-infected lymphocytes display a transformed phenotype and proliferate in culture media like the other tumor cells, however those cells will return to normal after antiprotozoal treatment reflecting the incomplete nature of transformation. To identify signaling pathways involved in this form of transformation of T. parva-infected cells, we screened a library of anticancer compounds. Among these, TIBC, a specific inhibitor of MDM2, markedly inhibited proliferation of T. parva-infected lymphocytes and promoted apoptosis. Therefore we analyzed MDM2 function in T. parva-infected cells. Several T. parva-infected cell lines showed increased expression level of MDM2 with alternatively spliced isoforms compared to the lymphoma cells or ConA blasts. In addition, buparvaquone affected MDM2 expression in T. parva transformed cells. Moreover, p53 protein accumulation and function were impaired in T. parva-infected cells after cisplatin induced DNA damage despite the increased p53 transcription level. Finally, the treatment of T. parva-infected cells with boronic-chalcone derivatives TIBC restored p53 protein accumulation and induced Bax expression. These results suggest that the overexpression of MDM2 is closely linked to the inhibition of p53-dependent apoptosis of T. parva-infected lymphocytes. Aberrant expression of host lymphocyte MDM2 induced by cytoplasmic existence of T. parva, directly and/or indirectly, is associated with aspects of this type of transformation of T. parva-infected lymphocytes. This form of transformation shares features of oncogene induced malignant phenotype acquisition.

  7. Identification and structural characterization of two incompletely processed forms of the fourth component of human complement.

    PubMed Central

    Chan, A C; Atkinson, J P

    1983-01-01

    Immunoprecipitates of human C4 from EDTA-plasma were incubated with [14C]methylamine and analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and fluorography. In addition to finding label in the alpha-chains of the secreted (C4s) and predominant plasma (C4p) forms of C4, two additional molecules with apparent molecular weights of approximately 168,000 (p168) and approximately 125,000 (p125) covalently incorporated methylamine, indicating the presence of an internal thioester bond. These two molecules were present at a concentration of approximately 5% of total plasma C4 and were not immunoprecipitated by antisera to C3 or alpha 2-macroglobulin. A human hepatoma-derived cell line (HepG2), in addition to synthesizing C4s and small quantities of the polypeptide precursor of C4 (pro-C4), was found to secrete p168 and p125 at concentrations of 14 +/- 4.8 and 21 +/- 9.2% (mean +/- SD), respectively, of total secreted C4. These molecules were not found intracellularly. Both molecules were present on reduced, but not nonreduced, SDS-polyacrylamide gels. Chido (C4B) and Rodgers' (C4A) alloantisera precipitated the C4A and C4B variants of pro-C4, p168, p125, and C4s. Both tryptic and Staphylococcus aureus V8 protease peptide analyses showed homology between p168 and the beta- and alpha-chains and between p125 and the alpha- and gamma-chains. Partial NH2-terminal sequencing revealed that the beta-chain was NH2-terminal in p168 and that the alpha-chain was NH2-terminal in p125. Taken together, these data indicate that p168 and p125 represent uncleaved beta-alpha- and alpha-gamma-fragments of pro-C4, respectively. Thus, in most individuals, plasma C4 consists of five structurally distinct molecules, the single polypeptide precursor (pro-C4), the three-subunit secreted (C4s) and predominant plasma (C4p) forms of C4, and two incompletely processed two-subunit molecules with uncleaved beta-alpha- (p168) or uncleaved alpha-gamma (p125)-subunits. In addition

  8. Genetically improved monolayer-forming tobacco mosaic viruses to generate nanostructured semiconducting bio/inorganic hybrids.

    PubMed

    Atanasova, Petia; Stitz, Nina; Sanctis, Shawn; Maurer, Johannes H M; Hoffmann, Rudolf C; Eiben, Sabine; Jeske, Holger; Schneider, Jörg J; Bill, Joachim

    2015-04-07

    The genetically determined design of structured functional bio/inorganic materials was investigated by applying a convective assembly approach. Wildtype tobacco mosaic virus (wt TMV) as well as several TMV mutants were organized on substrates over macroscopic-length scales. Depending on the virus type, the self-organization behavior showed pronounced differences in the surface arrangement under the same convective assembly conditions. Additionally, under varying assembly parameters, the virus particles generated structures encompassing morphologies emerging from single micrometer long fibers aligned parallel to the triple-contact line through disordered but dense films to smooth and uniform monolayers. Monolayers with diverse packing densities were used as templates to form TMV/ZnO hybrid materials. The semiconducting properties can be directly designed and tuned by the variation of the template architecture which are reflected in the transistor performance.

  9. Fullerene-derivative PC61BM forms three types of phase-pure monolayer on the surface of Au(111)

    NASA Astrophysics Data System (ADS)

    Li, Wen-Jie; Du, Ying-Ying; Zhang, Han-Jie; Chen, Guang-Hua; Sheng, Chun-Qi; Wu, Rui; Wang, Jia-Ou; Qian, Hai-Jie; Ibrahim, Kurash; He, Pi-Mo; Li, Hong-Nian

    2016-12-01

    We have studied the packing structures of C60-derivative PC61BM on the surface of Au(111) in ultrahigh vacuum using scanning tunneling microscopy. The Au(111) has a triangle-like reconstructed surface, which results in some packing structures different from those reported for low coverages. PC61BM can form three types of phase-pure monolayer, namely, the compact straight molecular double-row monolayer, the hexagonal-packing monolayer and the glassy monolayer. The different types of monolayer form for different molecular densities and different annealing temperatures. In addition to the already known inter-molecular interactions (Van de Waals interaction and hydrogen bond), the steric effect of the phenyl-butyric-acid-methyl-ester side tail plays conspicuous role in the molecular self-assembly at high coverages. The steric effect makes it difficult to prepare a hexagonal-packing monolayer at room temperature and decides the instability of the hexagonal-packing monolayer prepared by thermal annealing.

  10. Towards a new paradigm of microscopic colitis: Incomplete and variant forms

    PubMed Central

    Guagnozzi, Danila; Landolfi, Stefania; Vicario, Maria

    2016-01-01

    Microscopic colitis (MC) is a chronic inflammatory bowel disease that has emerged in the last three decades as a leading cause of chronic watery diarrhoea. MC classically includes two main subtypes: lymphocytic colitis (LC) and collagenous colitis (CC). Other types of histopathological changes in the colonic mucosa have been described in patients with chronic diarrhoea, without fulfilling the conventional histopathological criteria for MC diagnosis. Whereas those unclassified alterations remained orphan for a long time, the use of the term incomplete MC (MCi) is nowadays universally accepted. However, it is still unresolved whether CC, LC and MCi should be considered as one clinical entity or if they represent three related conditions. In contrast to classical MC, the real epidemiological impact of MCi remains unknown, because only few epidemiological studies and case reports have been described. MCi presents clinical characteristics indistinguishable from complete MC with a good response to budesonide and cholestiramine. Although a number of medical treatments have been assayed in MC patients, currently, there is no causal treatment approach for MC and MCi, and only empirical strategies have been performed. Further studies are needed in order to identify their etiopathogenic mechanisms, and to better classify and treat MC. PMID:27784958

  11. Correlation of mutant menin stability with clinical expression of multiple endocrine neoplasia type 1 and its incomplete forms.

    PubMed

    Shimazu, Satoko; Nagamura, Yuko; Yaguchi, Hiroko; Ohkura, Naganari; Tsukada, Toshihiko

    2011-11-01

    Germline mutations of the tumor suppressor gene MEN1 are found not only in typical multiple endocrine neoplasia type 1 (MEN1) but also in its incomplete forms such as familial isolated hyperparathyroidism (FIHP) and apparently sporadic parathyroid tumor (ASPT). No definitive genotype-phenotype correlation has been established between these clinical forms and MEN1 gene mutations. We previously demonstrated that mutant menin proteins associated with MEN1 are rapidly degraded by the ubiquitin-proteasome pathway. To examine whether the intracellular stability of mutant menin is correlated with clinical phenotypes, we developed a method of evaluating menin stability and examined 20 mutants associated with typical MEN1 (17 missense, two in-frame deletion, one nonsense) and 21 mutants associated with FIHP or ASPT (19 missense, two in-frame deletion). All tested mutants associated with typical MEN1 showed reduced stability. Some missense and in-frame deletion mutants (G28A, R171W, T197I, E255K, E274A, Y353del and E366D) associated with FIHP or ASPT were almost as stable as or only slightly less stable than wild-type menin, while others were as unstable as those associated with typical MEN1. Some stable mutants exhibited substantial biological activities when tested by JunD-dependent transactivation assay. These findings suggest that certain missense and in-frame mutations are fairly stable and retain intrinsic biological activity, and might be specifically associated with incomplete clinical phenotypes. The menin stability test will provide useful information for the management of patients carrying germline MEN1 mutations especially when they have missense or in-frame variants of ambiguous clinical significance.

  12. Low adhesion, non-wetting phosphonate self-assembled monolayer films formed on copper oxide surfaces.

    PubMed

    Hoque, E; DeRose, J A; Bhushan, B; Hipps, K W

    2009-07-01

    Self-assembled monolayer (SAM) films have been formed on oxidized copper (Cu) substrates by reaction with 1H,1H,2H,2H-perfluorodecylphosphonic acid (PFDP), octadecylphosphonic acid (ODP), decylphosphonic acid (DP), and octylphosphonic acid (OP) and then investigated by X-ray photoelectron spectroscopy (XPS), contact angle measurement (CAM), and atomic force microscopy (AFM). The presence of alkyl phosphonate molecules, PFDP, ODP, DP, and OP, on Cu were confirmed by CAM and XPS analysis. No alkyl phosphonate molecules were seen by XPS on unmodified Cu as a control. The PFDP/Cu and ODP/Cu SAMs were found to be very hydrophobic having water sessile drop static contact angles of more than 140 degrees , while DP/Cu and OP/Cu have contact angles of 119 degrees and 76 degrees , respectively. PFDP/Cu, ODP/Cu, DP/Cu, and OP/Cu SAMs were studied by friction force microscopy, a derivative of AFM, to better understand their micro/nanotribological properties. PFDP/Cu, ODP/Cu, and DP/Cu had comparable adhesive force, which is much lower than that for unmodified Cu. ODP/Cu had the lowest friction coefficient followed by PFDP/Cu, DP/Cu, and OP/Cu while unmodified Cu had the highest. XPS data gives some indication that a bidentate bond forms between the alkyl phosphonate molecules and the oxidized Cu surface. Hydrophobic phosphonate SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for anti-wetting, low adhesion surfaces.

  13. Increasing the light extraction and longevity of TMDC monolayers using liquid formed micro-lenses

    NASA Astrophysics Data System (ADS)

    Woodhead, C. S.; Roberts, J.; Noori, Y. J.; Cao, Y.; Bernardo-Gavito, R.; Tovee, P.; Kozikov, A.; Novoselov, K.; Young, R. J.

    2017-03-01

    The recent discovery of semiconducting two-dimensional materials is predicted to lead to the introduction of a series of revolutionary optoelectronic components that are just a few atoms thick. Key remaining challenges for producing practical devices from these materials lie in improving the coupling of light into and out of single atomic layers, and in making these layers robust to the influence of their surrounding environment. We present a solution to tackle both of these problems simultaneously, by deterministically placing an epoxy based micro-lens directly onto the materials’ surface. We show that this approach enhances the photoluminescence of tungsten diselenide (WSe2) monolayers by up to 300%, and nearly doubles the imaging resolution of the system. Furthermore, this solution fully encapsulates the monolayer, preventing it from physical damage and degradation in air. The optical solution we have developed could become a key enabling technology for the mass production of ultra-thin optical devices, such as quantum light emitting diodes.

  14. Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene

    DOE PAGES

    Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib; ...

    2015-03-24

    Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO₂/Si substrates using transverse shear microscope.more » We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.« less

  15. Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene

    SciTech Connect

    Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib; Lee, Mi Jung; Jia, Quanxi; Park, Minwoo; Lee, Hoonkyung; Park, Bae Ho

    2015-03-24

    Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO₂/Si substrates using transverse shear microscope. We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.

  16. Chemical stability of nonwetting, low adhesion self-assembled monolayer films formed by perfluoroalkylsilanization of copper.

    PubMed

    Hoque, E; DeRose, J A; Hoffmann, P; Bhushan, B; Mathieu, H J

    2007-03-21

    A self-assembled monolayer (SAM) has been produced by reaction of 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS) with an oxidized copper (Cu) substrate and investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, and contact angle measurement. FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. The perfluoroalkyl SAM on Cu is found to be extremely hydrophobic, yielding sessile drop static contact angles of more than 130 degrees for pure water and a "surface energy" (which is proportional to the Zisman critical surface tension for a Cu surface with 0 rms roughness) of 14.5 mJm2(nMm). Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH=12, 60 degrees C) solutions for at least 30 min. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70 min at 60 degrees C or 50 min at 80 degrees C. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for antiwetting, low adhesion surfaces or dropwise condensation on heat exchange surfaces.

  17. Triblock polyphiles through click chemistry: self-assembled thermotropic cubic phases formed by micellar and monolayer vesicular aggregates.

    PubMed

    Tan, Xiaoping; Kong, Leiyang; Dai, Heng; Cheng, Xiaohong; Liu, Feng; Tschierske, Carsten

    2013-11-25

    Three series of triblock polyphiles consisting of a rigid 4-phenyl-1,2,3-triazole or 1,4-diphenyl-1,2,3-triazole core with three lipophilic and flexible alkoxyl chains at one end and a polar glycerol group at the opposite end were synthesized by copper-catalyzed azide-alkyne click reactions. Their mesophase behavior was studied by polarizing optical microscopy, differential scanning calorimetry, and XRD. Depending on alkyl chain length and core length, a transition from hexagonal columnar to Pm3n-type cubic phases was observed. In the cubic phases, the molecules are organized as spherical objects. Remarkably, compounds with a longer core unit have a higher tendency to form these cubic phases, and their stability is strongly enhanced over those of the compounds with a shorter core, despite longer cores having a smaller cone angle and therefore being expected to disfavor the formation of spherical objects. There is a large difference in the number of molecules involved in the spherical aggregates formed by compounds with long and short cores. Whereas the aggregates in the cubic phases of the compounds with short rod units are small and could be regarded as micellar, the long-core compounds form much larger aggregates which are regarded as a kind of monolayer vesicular aggregate.

  18. Understanding Peptide Oligomeric State in Langmuir Monolayers of Amphiphilic 3-Helix Bundle-Forming Peptide-PEG Conjugates

    PubMed Central

    Shu, Jessica Y.; Xu, Ting

    2016-01-01

    Coiled-coil peptide–polymer conjugates are an emerging class of biomaterials. Fundamental understanding of the coiled-coil oligomeric state and assembly process of these hybrid building blocks is necessary to exert control over their assembly into well-defined structures. Here, we studied the effect of peptide structure and PEGylation on the self-assembly process and oligomeric state of a Langmuir monolayer of amphiphilic coiled-coil peptide–polymer conjugates using X-ray reflectivity (XR) and grazing-incidence X-ray diffraction (GIXD). Our results show that the oligomeric state of PEGylated amphiphiles based on 3-helix bundle-forming peptide is surface pressure dependent, a mixture of dimers and trimers was formed at intermediate surface pressure but transitions into trimers completely upon increasing surface pressure. Moreover, the interhelical distance within the coiled-coil bundle of 3-helix peptide-PEG conjugate amphiphiles was not perturbed under high surface pressure. Present studies provide valuable insights into the self-assembly process of hybrid peptide–polymer conjugates and guidance to develop biomaterials with controlled multivalency of ligand presentation. PMID:27784156

  19. Structure and stability characterization of anti-adhesion self-assembled monolayers formed by vapour deposition for NIL use

    NASA Astrophysics Data System (ADS)

    Garidel, Sophie; Zelsmann, Marc; Voisin, Pauline; Rochat, Nevine; Michallon, Philippe

    2007-03-01

    Anti-sticking efficiency remains a key issue in nanoimprint lithography. In order to address this problem, a selfassembled monolayer (SAM) of a fluorinated silane release agent is generally applied to the stamp surface, either in wet or in vapour phase. We present here the study on vapour deposition of (tridecafluoro-1,1,2,2-tetrahydrooctyl)TriChloroSilane (F 13-TCS) and wet and vapour deposition of a commercial product, OPTOOL DSX from Daikin. They are both fluorinated silanes used for the formation of anti-adhesive layers in nanoimprint lithography. Results will be compared in term of anti-adhesion properties and homogeneity for the obtained layers. Characterizations are made by means of contact angle measurements, Fourier Transform Infra-Red analysis and Atomic Force Microscopy observations. The vapour phase deposition of F 13-TCS allows us to reach surface energies as low as 11mN/m without increasing initial roughness. OPTOOL DSX TM deposition in wet phase presents comparable results, but with an increased roughness mainly due to the deposition procedure. The durability of the formed layers was investigated as a function of number of prints. For both materials, a significant degradation of the anti-adhesion properties occurs after few imprinted dies.

  20. Pt monolayer coating on complex network substrate with high catalytic activity for the hydrogen evolution reaction

    PubMed Central

    Li, Man; Ma, Qiang; Zi, Wei; Liu, Xiaojing; Zhu, Xuejie; Liu, Shengzhong (Frank)

    2015-01-01

    A deposition process has been developed to fabricate a complete-monolayer Pt coating on a large-surface-area three-dimensional (3D) Ni foam substrate using a buffer layer (Ag or Au) strategy. The quartz crystal microbalance, current density analysis, cyclic voltammetry integration, and X-ray photoelectron spectroscopy results show that the monolayer deposition process accomplishes full coverage on the substrate and the deposition can be controlled to a single atomic layer thickness. To our knowledge, this is the first report on a complete-monolayer Pt coating on a 3D bulk substrate with complex fine structures; all prior literature reported on submonolayer or incomplete-monolayer coating. A thin underlayer of Ag or Au is found to be necessary to cover a very reactive Ni substrate to ensure complete-monolayer Pt coverage; otherwise, only an incomplete monolayer is formed. Moreover, the Pt monolayer is found to work as well as a thick Pt film for catalytic reactions. This development may pave a way to fabricating a high-activity Pt catalyst with minimal Pt usage. PMID:26601247

  1. Monolayer coated aerogels and method of making

    DOEpatents

    Zemanian, Thomas Samuel; Fryxell, Glen; Ustyugov, Oleksiy A.

    2006-03-28

    Aerogels having a monolayer coating are described. The aerogel and a monolayer forming precursor are provided in a supercritical fluid, whereupon the aerogel and the monolayer forming precursor are reacted in said supercritical fluid to form a covalent bond between the aerogel and the monolayer forming precursor. Suitable aerogels are ceramic oxides such as silica, alumina, aluminosilicate, and combinations thereof. Suitable monolayer forming precursors include alkyl silanes, chlorosilanes, boranes, chloroboranes, germanes, and combinations thereof. The method may also include providing a surface preparation agent such as water, or hydroetching an aerogel to enhance the coating of the monolayer.

  2. Ray Calculations of Ocean Sound Channels Using a Pocket Programmable Calculator and Extended Forms of the Hirsch-Carter Mathematical Model with Tables of the Incomplete Beta Function.

    DTIC Science & Technology

    1978-10-01

    pocket programmable calculator on two Sargasso Sea profiles, one from the center of a cold ring eddy are given. Necessary tables of the incomplete beta-function and calculator programs are included in a supplement.

  3. Kinetic bottleneck to the self-organization of bidisperse hard disk monolayers formed by random sequential adsorption.

    PubMed

    Doty, R Christopher; Bonnecaze, Roger T; Korgel, Brian A

    2002-06-01

    We study the self-organization of bidisperse mixtures of hard spheres in two dimensions by simulating random sequential adsorption (RSA) of tethered hard disks that undergo limited Monte Carlo surface diffusion. The tethers place a control on the local entropy of the disks by constraining their movement within a specified distance from their original adsorption positions. By tuning the tether length, from zero (the pure RSA process) to infinity (near-equilibrium conditions), the kinetic pathway to monolayer formation can be varied. Previously [J. J. Gray et al., Phys. Rev. Lett. 85, 4430 (2000); Langmuir 17, 2317 (2001)], we generated nonequilibrium phase diagrams for size-monodisperse and size-polydisperse hard disks as a function of surface coverage, size distribution, and tether length to reveal the occurrence of hexagonal close-packed, hexatic, and disordered phases. Bidisperse hard disks potentially offer increasingly diverse phase diagrams, with the possible occurrence of spatially and compositionally organized superlattices. Geometric packing calculations anticipate the formation of close-packed lattices in two dimensions for particle size ratios sigma=R(S)/R(L)=0.53, 0.414, and 0.155. The simulations of these systems presented here, however, reveal that RSA kinetics frustrate superlattice ordering, even for infinite tethers. The calculated jamming limits fall well below the minimum surface coverages necessary for stable ordering, as determined by melting simulations.

  4. Electrical parameters and water permeability properties of monolayers formed by T84 cells cultured on permeable supports.

    PubMed

    Ozu, M; Toriano, R; Capurro, C; Parisi, M

    2005-01-01

    T84 is an established cell line expressing an enterocyte phenotype whose permeability properties have been widely explored. Osmotic permeability (POSM), hydraulic permeability (PHYDR) and transport-associated net water fluxes (JW-transp), as well as short-circuit current (ISC), transepithelial resistance (RT), and potential difference (deltaVT) were measured in T84 monolayers with the following results: POSM 1.3 +/- 0.1 cm.s-1 x 10-3; PHYDR 0.27 +/- 0.02 cm.s-1; RT 2426 +/- 109 omega.cm2, and deltaVT 1.31 +/- 0.38 mV. The effect of 50 microM 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DCEBIO), a "net Cl- secretory agent", on T84 cells was also studied. We confirm the reported important increase in ISC induced by DCEBIO which was associated here with a modest secretory deltaJW-transp. The present results were compared with those reported using the same experimental approach applied to established cell lines originating from intestinal and renal epithelial cells (Caco-2, LLC-PK1 and RCCD-1). No clear association between PHYDR and RT could be demonstrated and high PHYDR values were observed in an electrically tight epithelium, supporting the view that a "water leaky" barrier is not necessarily an "electrically leaky" one. Furthermore, the modest secretory deltaJW-transp was not consistent with previous results obtained with RCCD-1 cells stimulated with vasopressin (absorptive fluxes) or with T84 cells secreting water under the action of Escherichia coli heat stable enterotoxin. We conclude that, while the presence of aquaporins is necessary to dissipate an external osmotic gradient, coupling between water and ion transport cannot be explained by a simple and common underlying mechanism.

  5. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-01-01

    Our research over this past grant period has focused on (1) developing methods for making in situ permeation measurements at the air-water interface, (2) defining the structural and conformational behavior of selected calix(4)arenes, (3) defining the metal complexation properties of certain upper-rim functionalized calix(4)arenes, and (4) synthesizing a broad series of polymerizable calixarenes, to be used for constructing perforated monolayers and multilayers.

  6. Binding structure and kinetics of surfactin monolayer formed at the air/water interface to counterions: A molecular dynamics simulation study.

    PubMed

    Gang, Hongze; Liu, Jinfeng; Mu, Bozhong

    2015-10-01

    The binding structure and kinetics of ionized surfactin monolayer formed at the air/water interface to five counterions, Li+, Na+, K+, Ca2+, and Ba2+ (molar ratios of surfactin to monovalent and divalent counterions are 1:2 and 1:1 respectively), have been studied using molecular dynamics simulation. The results show that surfactin exhibits higher binding affinity to divalent counterions, Ca2+, and Ba2+, and smaller monovalent counterion, Li+, than Na+ and K+. Both carboxyl groups in surfactin are accessible for counterions, but the carboxyl group in Glu1 is easier to access by counterions than Asp5. Salt bridges are widely built between carboxyl groups by counterions, and the probability of the formation of intermolecular salt bridge is markedly larger than that of intramolecular salt bridge. Divalent counterions perform well in forming salt bridges between carboxyl groups. The salt bridges mediated by Ca2+ are so rigid that the lifetimes are about 0.13 ns, and the break rates of these salt bridges are 1-2 orders of magnitude smaller than those mediated by K+ which is about 5 ps in duration. The positions of the hydration layer of carboxyl groups are independent of counterions, but the bound counterions induce the dehydration of carboxyl groups and disturb the hydrogen bonds built between carboxyl group and hydration water.

  7. Grazing incidence X-ray diffraction studies of condensed double-chain phospholipid monolayers formed at the soft air/water interface.

    PubMed

    Stefaniu, Cristina; Brezesinski, Gerald

    2014-05-01

    The use of highly brilliant synchrotron light sources in the middle of the 1980s for X-ray diffraction has revolutionized the research of condensed monolayers. Since then, monolayers gained popularity as convenient quasi two-dimensional model systems widely used in biophysics and material science. This review focuses on structures observed in one-component phospholipid monolayers used as simplified two-dimensional models of biological membranes. In a monolayer system the phase transitions can be easily triggered at constant temperature by increasing the packing density of the lipids by compression. Simultaneously the monolayer structure changes are followed in situ by grazing incidence X-ray diffraction. Competing interactions between the different parts of the molecule are responsible for the different monolayer structures. These forces can be modified by chemical variations of the hydrophobic chain region, of the hydrophilic head group region or of the interfacial region between chains and head groups. Modifications of monolayer structures triggered by changes of the chemical structure of double-chain phospholipids are highlighted in this paper.

  8. Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001{sup ¯}) surfaces

    SciTech Connect

    Tochihara, Hiroshi E-mail: tochihara.hiroshi.146@m.kyushu-u.ac.jp; Suzuki, Takayuki; Yagyu, Kazuma; Shirasawa, Tetsuroh; Takahashi, Toshio; Miyamachi, Toshio; Yoshizawa, Shunsuke; Komori, Fumio; Kajiwara, Takashi; Tanaka, Satoru

    2014-02-03

    An epitaxial silicon-oxide monolayer of chemical composition of Si{sub 2}O{sub 3} (the Si{sub 2}O{sub 3} layer) formed on hexagonal SiC(0001{sup ¯}) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si{sub 2}O{sub 3} layer are found to be missing SiO{sub n} (n = 1, 2, 3) molecules. The band gap of the Si{sub 2}O{sub 3} layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO{sub 2}, 8.9 eV. It is proposed that the Si{sub 2}O{sub 3} layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

  9. Reasoning from Incomplete Knowledge.

    ERIC Educational Resources Information Center

    Collins, Allan M.; And Others

    People use a variety of plausible, but uncertain inferences to answer questions about which their knowledge is incomplete. Such inferential thinking and reasoning is being incorporated into the SCHOLAR computer-assisted instruction (CAI) system. Socratic tutorial techniques in CAI systems such as SCHOLAR are described, and examples of their…

  10. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7[angstrom] diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using perforated monolayer''-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N[sub 2] and SF[sub 6]. Results of derivative studies that have also been completed are also described in this report.

  11. I. Enabling Single-Chain Surfactants to Form Vesicles by Nonamphiphilic Liquid Crystals in Water II. Controlling Attachment and Ligand-Mediated Adherence of Candida albicans on Monolayers

    NASA Astrophysics Data System (ADS)

    Varghese, Nisha

    . Adhesion of C. albicans to a surface is a complex process and is governed by nonspecific attachment or multiple ligand-receptor interactions. The work demonstrates that the multiple ligand-receptor interactions used by C. albicans for adherence to a surface can be individually studied using self-assembled monolayers (SAMs) decorated with minimal motif of the ligands. The SAMs were also used to differentiate between the interactions of the two different morphological forms of C. albicans.. Chapter 5 presents a study on small molecules that were used to inhibit biofilm formed by C. albicans. The acyclic triazoles used in the study were not toxic to the C. albicans and were capable of inhibiting biofilm formed by C. albicans. The acyclic triazole can be used as promising candidates to design new antifungal agents. The chapter also reports the synthesis of squarylated homoserine lactones (SHLs) structural mimics of bacterial acyl homoserine lactones (AHLs) to study the inhibitory effects of SHLs on fungal biofilm. The bacterial AHLs are known to repress the growth of C. albicans and control fungal biofilm in native host environment. The synthesized SHLs were non-toxic to C. albicans and failed to inhibit biofilm formed by C. albicans. . Chapter 6 uses gradient nanotopography combined with controlled surface chemistry to confine bacterial biofilm formed by Escherichia coli. The E. coli biofilm were confined within micrometer sized regions of hydrophobic SAMs surrounded by polyol-terminated SAMs. The study reveals that surface with higher topography enhances the ability of the bioinert SAMs to resist bacterial adherence to surface.

  12. Modeling Stimuli-Responsive Nanoparticle Monolayer

    NASA Astrophysics Data System (ADS)

    Yong, Xin

    2015-03-01

    Using dissipative particle dynamics (DPD), we model a monolayer formed at the water-oil interface, which comprises stimuli-responsive nanoparticles. The solid core of the nanoparticle encompasses beads arranged in an fcc lattice structure and its surface is uniformly grafted with stimuli-responsive polymer chains. The surface-active nanoparticles adsorb to the interface from the suspension to minimize total energy of the system and create a monolayer covering the interface. We investigate the monolayer formation by characterizing the detailed adsorption kinetics. We explore the microstructure of the monolayer at different surface coverage, including the particle crowding and ordering, and elucidate the response of monolayer to external stimuli. The collective behavior of the particles within the monolayer is demonstrated quantitatively by vector-vector autocorrelation functions. This study provides a fundamental understanding of the interfacial behavior of stimuli-responsive nanoparticles.

  13. Incomplete invention of drugs.

    PubMed

    Hisa, Tomoyuki

    2007-02-01

    Scientists seldom know the differences between "rejected invention", "non-invention", "incomplete invention", "invention yet to be completed" and "defective invention". The Japanese Supreme Court appointed me as a specialist member (Article 92-2, Code of Civil Procedure) of intellectual property division for medical and biological patents. Herein, I present scientists to the differences and which of them are patentable. In order to prevent oneself from being taken for granted for the scientists' noblesse oblige by clever business administrations, the scientists must know the borderline between patentable or non-patentable.

  14. Semantic Borders and Incomplete Understanding.

    PubMed

    Silva-Filho, Waldomiro J; Dazzani, Maria Virgínia

    2016-03-01

    In this article, we explore a fundamental issue of Cultural Psychology, that is our "capacity to make meaning", by investigating a thesis from contemporary philosophical semantics, namely, that there is a decisive relationship between language and rationality. Many philosophers think that for a person to be described as a rational agent he must understand the semantic content and meaning of the words he uses to express his intentional mental states, e.g., his beliefs and thoughts. Our argument seeks to investigate the thesis developed by Tyler Burge, according to which our mastery or understanding of the semantic content of the terms which form our beliefs and thoughts is an "incomplete understanding". To do this, we discuss, on the one hand, the general lines of anti-individualism or semantic externalism and, on the other, criticisms of the Burgean notion of incomplete understanding - one radical and the other moderate. We defend our understanding that the content of our beliefs must be described in the light of the limits and natural contingencies of our cognitive capacities and the normative nature of our rationality. At heart, anti-individualism leads us to think about the fact that we are social creatures, living in contingent situations, with important, but limited, cognitive capacities, and that we receive the main, and most important, portion of our knowledge simply from what others tell us. Finally, we conclude that this discussion may contribute to the current debate about the notion of borders.

  15. Semifluorinated Alkylphosphonic Acids Form High-Quality Self-Assembled Monolayers on Ag-Coated Yttrium Barium Copper Oxide Tapes and Enable Filamentization of the Tapes by Microcontact Printing.

    PubMed

    Park, Chul Soon; Lee, Han Ju; Lee, Dahye; Jamison, Andrew C; Galstyan, Eduard; Zagozdzon-Wosik, Wanda; Freyhardt, Herbert C; Jacobson, Allan J; Lee, T Randall

    2016-08-30

    A custom-designed semifluorinated phosphonic acid, (9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,16-heptadecafluorohexadecyl)phosphonic acid (F8H8PA), and a normal hexadecylphosphonic acid (H16PA) were synthesized and used to generate self-assembled monolayers (SAMs) on commercially available yttrium barium copper oxide (YBCO) tapes. In this study, we wished to evaluate the effectiveness of these monolayer films as coatings for selectively etching YBCO. Initial films formed by solution deposition and manual stamping using a non-patterned polydimethylsiloxane stamp allowed for a comparison of the film-formation characteristics. The resulting monolayers were characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To prepare line-patterned (filamentized) YBCO tapes, standard microcontact printing (μ-CP) procedures were used. The stamped patterns on the YBCO tapes were characterized by scanning electron microscopy (SEM) before and after etching to confirm the effectiveness of the patterning process on the YBCO surface and energy-dispersive X-ray spectroscopy (EDX) to obtain the atomic composition of the exposed interface.

  16. ENAM Mutations with Incomplete Penetrance

    PubMed Central

    Seymen, F.; Lee, K.-E.; Koruyucu, M.; Gencay, K.; Bayram, M.; Tuna, E.B.; Lee, Z.H.; Kim, J.-W.

    2014-01-01

    Amelogenesis imperfecta (AI) is a genetic disease affecting tooth enamel formation. AI can be an isolated entity or a phenotype of syndromes. To date, more than 10 genes have been associated with various forms of AI. We have identified 2 unrelated Turkish families with hypoplastic AI and performed mutational analysis. Whole-exome sequencing identified 2 novel heterozygous nonsense mutations in the ENAM gene (c.454G>T p.Glu152* in family 1, c.358C>T p.Gln120* in family 2) in the probands. Affected individuals were heterozygous for the mutation in each family. Segregation analysis within each family revealed individuals with incomplete penetrance or extremely mild enamel phenotype, in spite of having the same mutation with the other affected individuals. We believe that these findings will broaden our understanding of the clinical phenotype of AI caused by ENAM mutations. PMID:25143514

  17. Incomplete periacetabular acetabuloplasty

    PubMed Central

    2014-01-01

    Background Residual acetabular dysplasia is one of the most common complications after treatment for developmental dysplasia of the hip. The acetabular growth response after reduction of a dislocated hip varies. The options are to wait and add a redirectional osteotomy as a secondary procedure at an older age, or to perform a primary acetabuloplasty at the time of the open reduction to stimulate acetabular development. We present the early results of such a procedure—open reduction and an incomplete periacetabular acetabuloplasty—as a one-stop procedure for developmental dysplasia of the hip. Patients and methods We retrospectively reviewed the results obtained with 55 hips (in 48 patients, 43 of them girls) treated between September 2004 and February 2011. This cohort included late presentations and failures of nonoperative treatment and excluded unsuccessful previous surgical treatment (including closed reductions), neuromuscular disease, and other teratological conditions. Patients were treated once the ossific nucleus was present or when they reached one year of age. 31 cases were late presentations while 17 represented failures of nonoperative treatment. The mean age of the patients at surgery was 1.3 (0.6–2.6) years. The mean follow-up period was 4 (2–8) years. According to the IHDI classification, 1 was grade I, 9 were grade II, 13 were grade III, and 32 were grade IV. Results The mean acetabular index fell from 38 (23–49) preoperatively to 21 (10–27) at the last follow-up. There were no infections, nerve palsies, or graft extrusions. None of the cases required secondary surgery for residual acetabular dysplasia. 8 patients developed avascular necrosis (AVN) of grade II or more. The incidence of AVN was significantly associated with previous, failed nonoperative treatment. 1 patient developed coxa magna requiring shelf arthroplasty 4 years after the index procedure and 1 patient with lateral growth arrest required medial screw epiphysiodesis

  18. Nonlinear light scattering by a dipole monolayer

    NASA Astrophysics Data System (ADS)

    Averbukh, B. B.; Averbukh, I. B.

    2013-08-01

    Scattering of a strong p-polarized monochromatic field by a dipole monolayer is considered. It is shown that a triplet should be observed at incident angles (between the wave vector of the incident wave and the normal to the monolayer surface) not too close to π/2 in the spectrum of the scattered radiation. For grazing incidence of a strong field on the monolayer, waves with frequencies of the strong field and the high-frequency component of the triplet scatter forward and backward. In this case, radiation with frequency of the low-frequency component of the triplet propagates in the form of two inhomogeneous waves along the monolayer on both sides of it, exponentially decaying with distance from the monolayer.

  19. Incompletely compacted equilibrated ordinary chondrites

    SciTech Connect

    Sasso, M.R.; Macke, R.J.; Boesenberg, J.S.; Britt, D.T.; Rovers, M.L.; Ebel, D.S.; Friedrich, J.M.

    2010-01-22

    We document the size distributions and locations of voids present within five highly porous equilibrated ordinary chondrites using high-resolution synchrotron X-ray microtomography ({mu}CT) and helium pycnometry. We found total porosities ranging from {approx}10 to 20% within these chondrites, and with {mu}CT we show that up to 64% of the void space is located within intergranular voids within the rock. Given the low (S1-S2) shock stages of the samples and the large voids between mineral grains, we conclude that these samples experienced unusually low amounts of compaction and shock loading throughout their entire post accretionary history. With Fe metal and FeS metal abundances and grain size distributions, we show that these chondrites formed naturally with greater than average porosities prior to parent body metamorphism. These materials were not 'fluffed' on their parent body by impact-related regolith gardening or events caused by seismic vibrations. Samples of all three chemical types of ordinary chondrites (LL, L, H) are represented in this study and we conclude that incomplete compaction is common within the asteroid belt.

  20. The analysis of incomplete data.

    NASA Technical Reports Server (NTRS)

    Hartley, H. O.; Hocking, R. R.

    1971-01-01

    In this paper, we attempt to provide a simple taxonomy for incomplete-data problems and at the same time develop unified methods of analysis. The emphasis is on techniques which are natural extensions of the complete-data analysis and which will handle rather general classes of incomplete-data problems as opposed to custom-made techniques for special problems. The principle of estimation is either maximum likelihood or is at least based on maximum likelihood.

  1. Multicellular density fluctuations in epithelial monolayers

    NASA Astrophysics Data System (ADS)

    Zehnder, Steven M.; Wiatt, Marina K.; Uruena, Juan M.; Dunn, Alison C.; Sawyer, W. Gregory; Angelini, Thomas E.

    2015-09-01

    Changes in cell size often accompany multicellular motion in tissue, and cell number density is known to strongly influence collective migration in monolayers. Density fluctuations in other forms of active matter have been explored extensively, but not the potential role of density fluctuations in collective cell migration. Here we investigate collective motion in cell monolayers, focusing on the divergent component of the migration velocity field to probe density fluctuations. We find spatial patterns of diverging and converging cell groups throughout the monolayers, which oscillate in time with a period of approximately 3-4 h. Simultaneous fluorescence measurements of a cytosol dye within the cells show that fluid passes between groups of cells, facilitating these oscillations in cell density. Our findings reveal that cell-cell interactions in monolayers may be mediated by intercellular fluid flow.

  2. Advanced incomplete factorization algorithms for Stiltijes matrices

    SciTech Connect

    Il`in, V.P.

    1996-12-31

    The modern numerical methods for solving the linear algebraic systems Au = f with high order sparse matrices A, which arise in grid approximations of multidimensional boundary value problems, are based mainly on accelerated iterative processes with easily invertible preconditioning matrices presented in the form of approximate (incomplete) factorization of the original matrix A. We consider some recent algorithmic approaches, theoretical foundations, experimental data and open questions for incomplete factorization of Stiltijes matrices which are {open_quotes}the best{close_quotes} ones in the sense that they have the most advanced results. Special attention is given to solving the elliptic differential equations with strongly variable coefficients, singular perturbated diffusion-convection and parabolic equations.

  3. Solvent polarity effect on quality of n-octadecanethiol self-assembled monolayers on copper and oxidized copper

    NASA Astrophysics Data System (ADS)

    Zhang, Yaozhong; Zhou, Jun; Zhang, Xiaoli; Hu, Jun; Gao, Han

    2014-11-01

    This article reports the effect of solvent polarity on the formation of n-octadecanethiol self-assembled monolayers (C18SH-SAMs) on pure copper surface and oxidized copper surface. The quality of SAMs prepared in different solvents (n-hexane, toluene, trichloroethylene, chloroform, acetone, acetonitrile, ethanol) was monitored by EIS, RAIRS and XPS. The results indicated that C18SH-SAMs formed in these solvents were in good barrier properties on pure copper surface and the structures of monolayers formed in high polarity solvents were more compact and orderly than that formed in low polarity solvents. For comparison, C18SH adsorbed on the surface of oxidized copper in these solvents were studied and the results indicated that C18SH could be adsorbed on oxidized copper surface after the reduction of copper oxide layer by thiols. Compared with high polarity solvents, a limited reduction process of oxidized copper by thiols led to the incompletely formation of monolayers in low polarity solvents. This can be interpreted that the generated water on solid-liquid interface and a smaller reaction force restrict the continuous reduction reaction in low polarity solvents

  4. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2013-10-29

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  5. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli [El Cerrito, CA; Fabbri, Jason D [San Francisco, CA; Melosh, Nicholas A [Menlo Park, CA; Hussain, Zahid [Orinda, CA; Shen, Zhi-Xun [Stanford, CA

    2012-04-10

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  6. Dewetting of a solid monolayer.

    PubMed

    Pierre-Louis, O; Chame, Anna; Saito, Yukio

    2007-09-28

    We report on the dewetting of a monolayer on a solid substrate, where mass transport occurs via surface diffusion. For a wide range of parameters, a labyrinthine pattern of bilayer islands is formed. An irreversible regime and a thermodynamic regime are identified. In both regimes, the velocity of a dewetting front, the wavelength of the bilayer island pattern, and the rate of nucleation of dewetted zones are obtained. We also point out the existence of a scaling behavior, which is analyzed by means of a geometrical model.

  7. Incomplete intestinal absorption of fructose.

    PubMed Central

    Kneepkens, C M; Vonk, R J; Fernandes, J

    1984-01-01

    Intestinal D-fructose absorption in 31 children was investigated using measurements of breath hydrogen. Twenty five children had no abdominal symptoms and six had functional bowel disorders. After ingestion of fructose (2 g/kg bodyweight), 22 children (71%) showed a breath hydrogen increase of more than 10 ppm over basal values, indicating incomplete absorption: the increase averaged 53 ppm, range 12 to 250 ppm. Four of these children experienced abdominal symptoms. Three of the six children with bowel disorders showed incomplete absorption. Seven children were tested again with an equal amount of glucose, and in three of them also of galactose, added to the fructose. The mean maximum breath hydrogen increases were 5 and 10 ppm, respectively, compared with 103 ppm after fructose alone. In one boy several tests were performed with various sugars; fructose was the only sugar incompletely absorbed, and the effect of glucose on fructose absorption was shown to be dependent on the amount added. It is concluded that children have a limited absorptive capacity for fructose. We speculate that the enhancing effect of glucose and galactose on fructose absorption may be due to activation of the fructose carrier. Apple juice in particular contains fructose in excess of glucose and could lead to abdominal symptoms in susceptible children. PMID:6476870

  8. Profile Likelihood and Incomplete Data.

    PubMed

    Zhang, Zhiwei

    2010-04-01

    According to the law of likelihood, statistical evidence is represented by likelihood functions and its strength measured by likelihood ratios. This point of view has led to a likelihood paradigm for interpreting statistical evidence, which carefully distinguishes evidence about a parameter from error probabilities and personal belief. Like other paradigms of statistics, the likelihood paradigm faces challenges when data are observed incompletely, due to non-response or censoring, for instance. Standard methods to generate likelihood functions in such circumstances generally require assumptions about the mechanism that governs the incomplete observation of data, assumptions that usually rely on external information and cannot be validated with the observed data. Without reliable external information, the use of untestable assumptions driven by convenience could potentially compromise the interpretability of the resulting likelihood as an objective representation of the observed evidence. This paper proposes a profile likelihood approach for representing and interpreting statistical evidence with incomplete data without imposing untestable assumptions. The proposed approach is based on partial identification and is illustrated with several statistical problems involving missing data or censored data. Numerical examples based on real data are presented to demonstrate the feasibility of the approach.

  9. Nanoparticle interaction with model lung surfactant monolayers

    PubMed Central

    Harishchandra, Rakesh Kumar; Saleem, Mohammed; Galla, Hans-Joachim

    2010-01-01

    One of the most important functions of the lung surfactant monolayer is to form the first line of defence against inhaled aerosols such as nanoparticles (NPs), which remains largely unexplored. We report here, for the first time, the interaction of polyorganosiloxane NPs (AmorSil20: 22 nm in diameter) with lipid monolayers characteristic of alveolar surfactant. To enable a better understanding, the current knowledge about an established model surface film that mimics the surface properties of the lung is reviewed and major results originating from our group are summarized. The pure lipid components dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol have been used to study the biophysical behaviour of their monolayer films spread at the air–water interface in the presence of NPs. Film balance measurements combined with video-enhanced fluorescence microscopy have been used to investigate the formation of domain structures and the changes in the surface pattern induced by NPs. We are able to show that NPs are incorporated into lipid monolayers with a clear preference for defect structures at the fluid–crystalline interface leading to a considerable monolayer expansion and fluidization. NPs remain at the air–water interface probably by coating themselves with lipids in a self-assembly process, thereby exhibiting hydrophobic surface properties. We also show that the domain structure in lipid layers containing surfactant protein C, which is potentially responsible for the proper functioning of surfactant material, is considerably affected by NPs. PMID:19846443

  10. Item Calibration in Incomplete Testing Designs

    ERIC Educational Resources Information Center

    Eggen, Theo J. H. M.; Verhelst, Norman D.

    2011-01-01

    This study discusses the justifiability of item parameter estimation in incomplete testing designs in item response theory. Marginal maximum likelihood (MML) as well as conditional maximum likelihood (CML) procedures are considered in three commonly used incomplete designs: random incomplete, multistage testing and targeted testing designs.…

  11. Abscisic acid-lipid interactions: a phospholipid monolayer study.

    PubMed

    Bürner, H; Benz, R; Gimmler, H; Hartung, W; Stillwell, W

    1993-08-15

    Lipid monolayer studies were performed on a Langmuir trough in the absence and in the presence of the plant hormone abscisic acid (ABA). The ABA-induced effects on the lipid monolayers can be summarized as follows: (i) ABA as the free acid (pH below 5.3) increased the molecular area and slightly decreased the surface pressure in the collapse points of monolayers made of saturated, unsaturated and of mixed lipids; ABA as the anion showed only minor effects. (ii) The ABA-induced area increase of the lipid monolayers decreased when the surface pressure increased, but some ABA remained in the monolayers made of unsaturated phospholipids even at collapse pressure. (iii) The incorporation of ABA into the monolayers could be inhibited by adding the plant sterol beta-sitosterol to the monolayer forming phospholipids. (iv) There was no substantial difference of ABA action on plant phospholipids as compared with other phospholipids. (v) ABA had a much stronger influence on unsaturated phospholipids than on saturated ones. (vi) ABA decreased the phase-transition temperature of saturated phospholipids. These results, which agree with those obtained from phospholipid vesicle studies, indicate that the physical state of the lipid is important for the ability of ABA penetrating into the lipid monolayer. Finally, a possible relevance of these results is discussed in terms of the action of ABA on guard cell membranes of plants.

  12. Molecular structure of cysteamine monolayers on silver and gold substrates. Comparative studies by surface-enhanced Raman scattering

    NASA Astrophysics Data System (ADS)

    Michota, Agnieszka; Kudelski, Andrzej; Bukowska, Jolanta

    2002-04-01

    Monolayers of cysteamine (2-aminoethanethiol) frequently work as linkage layers for adsorption of other molecules on metal surfaces. We compared the structure of cysteamine monolayers formed on gold and silver and the influence of various electrolytes on the structure of monolayers formed on both substrates. The monolayers formed on silver contain significantly higher portion of a trans conformer than monolayers on gold. Probably monolayers on silver are self-assembled in such a way that higher portion of the amino groups is unbonded to the surface, thus being available for attaching other molecules. The structure of cysteamine monolayers formed on gold is considerably more stable and resistive to the influence of electrolytes as compared to the silver substrate. The greater stability of the monolayers on Au surface was ascribed to the strong affinity of the amine groups toward this metal.

  13. Quantum Stackelberg duopoly with incomplete information [rapid communication

    NASA Astrophysics Data System (ADS)

    Lo, C.-F.; Kiang, D.

    2005-10-01

    We investigate the quantum version of the Stackelberg duopoly with incomplete information, especially how the quantum entanglement affects the first-mover advantage in the classical form. It is found that while positive entanglement enhances the first-mover advantage beyond the classical limit, the advantage is dramatically suppressed by negative entanglement. Moreover, despite that positive quantum entanglement improves the first-mover's tolerance for the informational incompleteness, the quantum effect does not change the basic fact that Firm A's lack of complete information of Firm B's unit cost is eradicating the first-mover advantage.

  14. Interaction of prazosin with model membranes--a Langmuir monolayer study.

    PubMed

    Gzyl-Malcher, Barbara; Handzlik, Jadwiga; Klekowska, Ewelina

    2012-10-01

    In this study, the effect of prazosin on the molecular interactions between cholesterol and 1,2-dipalmitoylphosphatidylcholine (DPPC) within a monolayer at an air-water interface was studied. A mixed cholesterol/DPPC monolayer was employed as a model lipid membrane. From a detailed analysis of surface pressure-area isotherms, it was concluded that DPPC and cholesterol were miscible and formed non-ideal monolayers on prazosin solution. The thermodynamic stability of the mixed monolayers was investigated by analyzing the free energy of mixing. It was found that the mixed monolayers were more stable than the single component monolayers. Monolayers spread over a subphase with prazosin were more compressible than those spread on pure water. To quantify the effect of prazosin on the monolayer stability, the Gibbs free energy due to the presence of prazosin in the water subphase was calculated. It was found that prazosin penetrated and destabilized mixed cholesterol/DPPC monolayers. However, a comparison of the drug penetration into the pure DPPC monolayer and the mixed cholesterol/DPPC monolayer showed that the presence of cholesterol in the DPPC monolayer considerably restricted the drug penetration.

  15. Cation-induced monolayer collapse at lower surface pressure follows specific headgroup percolation.

    PubMed

    Das, Kaushik; Sah, Bijay Kumar; Kundu, Sarathi

    2017-02-01

    A Langmuir monolayer can be considered as a two-dimensional (2D) sheet at higher surface pressure which structurally deform with mechanical compression depending upon the elastic nature of the monolayer. The deformed structures formed after a certain elastic limit are called collapsed structures. To explore monolayer collapses at lower surface pressure and to see the effect of ions on such monolayer collapses, out-of-plane structures and in-plane morphologies of stearic acid Langmuir monolayers have been studied both at lower (≈6.8) and higher (≈9.5) subphase pH in the presence of Mg^{2+},Ca^{2+},Zn^{2+},Cd^{2+}, and Ba^{2+} ions. At lower subphase pH and in the presence of all cations, the stearic acid monolayer remains as a monolayer before collapse, which generally takes place at higher surface pressure (π_{c}>50mN/m). However, at higher subphase pH, structural changes of stearic acid monolayers occur at relatively lower surface pressure depending upon the specific dissolved ions. Among the same group elements of Mg^{2+},Ca^{2+}, and Ba^{2+}, only for Ba^{2+} ions does monolayer to multilayer transition take place from a much lower surface pressure of the monolayer, remaining, however, as a monolayer for Mg^{2+} and Ca^{2+} ions. For another same group elements of Zn^{2+} and Cd^{2+} ions, a less covered bilayer structure forms on top of the monolayer structure at lower surface pressure, which is evidenced from both x-ray reflectometry and atomic force microscopy. Fourier transform infrared spectroscopy confirms the presence of two coexisting conformations formed by the two different metal-headgroup coordinations and the monolayer to trilayer or multilayer transformation takes place when the coverage ratio of the two molecular conformations changes from the critical value (p_{c}) of ≈0.66. Such ion-specific monolayer collapses are correlated with the 2D lattice percolation model.

  16. Optically Reconfigurable Monolayer of Azobenzene Donor Molecules on Oxide Surfaces.

    PubMed

    McElhinny, Kyle M; Huang, Peishen; Joo, Yongho; Kanimozhi, Catherine; Lakkham, Arunee; Sakurai, Kenji; Evans, Paul G; Gopalan, Padma

    2017-03-07

    The structural configuration of molecules assembled at organic-inorganic interfaces within electronic materials strongly influences the functional electronic and vibrational properties relevant to applications ranging from energy storage to photovoltaics. Controlling and characterizing the structural state of an interface and its evolution under external stimuli is crucial both for the fundamental understanding of the factors influenced by molecular structure and for the development of methods for material synthesis. It has been challenging to create complete molecular monolayers that exhibit external reversible control of the structure and electronic configuration. We report a monolayer/inorganic interface consisting of an organic monolayer assembled on an oxide surface, exhibiting structural and electronic reconfiguration under ultraviolet illumination. The molecular monolayer is linked to the surface through a carboxylate link, with the backbone bearing an azobenzene functional group and the head group consisting of a rhenium-bipyridine group. Optical spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray reflectivity show that closely packed monolayers are formed from these molecules via the Langmuir-Blodgett technique. Reversible photoisomerization is observed in solution and in monolayers assembled on Si and quartz substrates. The reconfiguration of these monolayers provides additional means to control excitation and charge transfer processes that are important in applications in catalysis, molecular electronics, and solar energy conversion.

  17. Dynamics of a monolayer of microspheres on an elastic substrate

    NASA Astrophysics Data System (ADS)

    Wallen, S. P.; Maznev, A. A.; Boechler, N.

    2015-11-01

    We present a model for wave propagation in a monolayer of spheres on an elastic substrate. The model, which considers sagittally polarized waves, includes: horizontal, vertical, and rotational degrees of freedom; normal and shear coupling between the spheres and substrate, as well as between adjacent spheres; and the effects of wave propagation in the elastic substrate. For a monolayer of interacting spheres, we find three contact resonances, whose frequencies are given by simple closed-form expressions. For a monolayer of isolated spheres, only two resonances are present. The contact resonances couple to surface acoustic waves in the substrate, leading to mode hybridization and "avoided crossing" phenomena. We present dispersion curves for a monolayer of silica microspheres on a silica substrate, assuming adhesive Hertzian interactions, and compare calculations using an effective medium approximation (including elasticity of the substrate) to a discrete model of a monolayer on a rigid substrate. While the effective medium model does not describe discrete lattice effects occurring at short wavelengths, we find that it is well suited for describing the interaction between the monolayer and substrate in the long wavelength limit. We suggest that a complete picture of the dynamics of a monolayer adhered to an elastic substrate can be found by combining the dispersion curves generated with the effective medium model for the elastic substrate and the discrete model for the rigid substrate. This model is potentially scalable for use with nano- to macroscale systems, and offers the prospect of experimentally extracting contact stiffnesses from measurements of acoustic dispersion.

  18. 32 CFR 651.44 - Incomplete information.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 32 National Defense 4 2013-07-01 2013-07-01 false Incomplete information. 651.44 Section 651.44 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY (CONTINUED) ENVIRONMENTAL QUALITY ENVIRONMENTAL ANALYSIS OF ARMY ACTIONS (AR 200-2) Environmental Impact Statement § 651.44 Incomplete...

  19. 32 CFR 651.44 - Incomplete information.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 32 National Defense 4 2014-07-01 2013-07-01 true Incomplete information. 651.44 Section 651.44 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY (CONTINUED) ENVIRONMENTAL QUALITY ENVIRONMENTAL ANALYSIS OF ARMY ACTIONS (AR 200-2) Environmental Impact Statement § 651.44 Incomplete...

  20. 32 CFR 651.44 - Incomplete information.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 32 National Defense 4 2012-07-01 2011-07-01 true Incomplete information. 651.44 Section 651.44 National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY (CONTINUED) ENVIRONMENTAL QUALITY ENVIRONMENTAL ANALYSIS OF ARMY ACTIONS (AR 200-2) Environmental Impact Statement § 651.44 Incomplete...

  1. Unsupported single-atom-thick copper oxide monolayers

    NASA Astrophysics Data System (ADS)

    Yin, Kuibo; Zhang, Yu-Yang; Zhou, Yilong; Sun, Litao; Chisholm, Matthew F.; Pantelides, Sokrates T.; Zhou, Wu

    2017-03-01

    Oxide monolayers may present unique opportunities because of the great diversity of properties of these materials in bulk form. However, reports on oxide monolayers are still limited. Here we report the formation of single-atom-thick copper oxide layers with a square lattice both in graphene pores and on graphene substrates using aberration-corrected scanning transmission electron microscopy. First-principles calculations find that CuO is energetically stable and its calculated lattice spacing matches well with the measured value. Furthermore, free-standing copper oxide monolayers are predicted to be semiconductors with band gaps ∼3 eV. The new wide-bandgap single-atom-thick copper oxide monolayers usher a new frontier to study the highly diverse family of two-dimensional oxides and explore their properties and their potential for new applications.

  2. Electrochemical Properties of Organosilane Self Assembled Monolayers on Aluminum 2024

    NASA Technical Reports Server (NTRS)

    Hintze, Paul E.; Calle, Luz Marina

    2004-01-01

    Self assembled monolayers are commonly used to modify surfaces. Within the last 15 years, self assembled monolayers have been investigated as a way to protect from corrosion[1,2] or biofouling.[3] In this study, self assembled monolayers of decitriethoxysilane (C10H21Si(OC2H5)3) and octadecyltriethoxysilane (C18H37Si(OC2H5)3) were formed on aluminum 2024-T3. The modified surfaces and bare Al 2024 were characterized by dynamic water contact angle measurements, x-ray photoelectron spectroscopy (XIPS) and infrared spectroscopy. Electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl was used to characterize the monolayers and evaluate their corrosion protection properties. The advancing water contact angle and infrared measurements show that the mono layers form a surface where the hydrocarbon chains are packed and oriented away from the surface, consistent with what is found in similar systems. The contact angle hysteresis measured in these systems is relatively large, perhaps indicating that the hydrocarbon chains are not as well packed as monolayers formed on other substrates. The results of the EIS measurements were modeled using a Randle's circuit modified by changing the capacitor to a constant phase element. The constant phase element values were found to characterize the monolayer. The capacitance of the monolayer modified surface starts lower than the bare Al 2024, but approaches values similar to the bare Al 2024 within 24 hours as the monolayer is degraded. The n values found for bare Al 2024 quickly approach the value of a true capacitor and are greater than 0.9 within hours after the start of exposure. For the monolayer modified structure, n can stay lower than 0.9 for a longer period of time. In fact, n for the monolayer modified surfaces is different from the bare surface even after the capacitance values have converged. This indicates that the deviation from ideal capacitance is the most sensitive indicator of the presence of the monolayer.

  3. Nonallelic heterogeneity in autosomal dominant retinitis pigmentosa with incomplete penetrance

    SciTech Connect

    Kim, S.K.; Berson, E.L.; Dryja, T.P.

    1994-08-01

    Retinitis pigmentosa is a group of retinal diseases in which photoreceptor cells throughout the retina degenerate. Although there is considerable genetic heterogeneity (autosomal dominant, autosomal recessive, and X-linked forms exist), there is a possibility that some clinically defined subtypes of the disease may be the result of mutations at the same locus. One possible clinically defined subtype is that of autosomal dominant retinitis pigmentosa (ADRP) with incomplete penetrance. Whereas in most families with ADRP, carriers can be clearly identified because of visual loss, ophthalmological findings, or abnormal electroretinograms (ERGs), in occasional families some obligate carriers are asymptomatic and have normal or nearly normal ERGs even late in life. A recent paper reported the mapping of the diseases locus in one pedigree (designated adRP7) with ADRP with incomplete penetrance to chromosome 7p. To test the idea that ADRP with incomplete penetrance may be genetically homogeneous, we have evaluated whether a different family with incomplete penetrance also has a disease gene linked to the same region. 4 refs., 1 fig., 1 tab.

  4. On the characteristics of mixed Langmuir monolayer templates containing dipalmitoyl phosphatidylcholine for gold nanoparticle formation.

    PubMed

    Hsiao, Fang-Wei; Lee, Yuh-Lang; Chang, Chien-Hsiang

    2009-10-01

    Mixed Langmuir monolayers containing dipalmitoyl phosphatidylcholine (DPPC) were applied as two-dimensional templates to incorporate with gold precursor AuCl4- in the subphases. The organic monolayer templates were then transferred onto solid substrates to form ultra-thin films by the Langmuir-Blodgett (LB) deposition technique. With an UV irradiation approach, gold nanoparticles were thus fabricated in the LB films of monolayer templates. Characteristics of the monolayer templates were studied by the surface pressure-area isotherm measurements and Brewster angle microscopy (BAM) observation. The factors affecting the formation of gold nanoparticle structures in the LB films of organic monolayer templates were elucidated by the atomic force microscopy (AFM). The monolayer isotherms and BAM images suggested that by changing the gold precursor concentration in the subphase, one could control the adsorption behavior of the gold precursor onto the monolayer templates. It was found that the association of the gold precursor with a pure DPPC monolayer template resulted in an unstable Langmuir monolayer, which was inappropriate for the following LB deposition. With the presence of n-hexadecanol in a DPPC monolayer, the monolayer template stability and corresponding LB deposition quality could be tremendously improved. Moreover, the distribution of DPPC molecules in the monolayer templates was possible to be regulated by the addition of n-hexadecanol, and the association behavior of the gold precursor with the monolayer templates was thus controlled. The AFM analysis then indicated that the number and size of gold nanoparticles fabricated in the LB films of the mixed DPPC/n-hexadecanol monolayer templates by a photoreduction reaction could be manipulated by the mole fraction of n-hexadecanol and UV irradiation time.

  5. 7 CFR 763.8 - Incomplete applications.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... days of receipt of an incomplete application, the Agency will provide the seller and buyer written notice of any additional information that must be provided. The seller or buyer, as applicable,...

  6. Reconstruction of Unilateral Incomplete Cryptophthalmos in Fraser Syndrome.

    PubMed

    Tran, Ann Q; Lee, Bradford W; Alameddine, Ramzi M; Korn, Bobby S; Kikkawa, Don O

    2015-03-25

    A full-term baby girl with Fraser syndrome was born with right incomplete cryptophthalmos. On examination, the globe was completely covered with skin with partially formed eyelids laterally. At 3 years of age, she underwent an evisceration with orbital implant and reconstruction of the eyelids and fornices using the pre-existing scleral remnant. Custom ocular prosthetic fitting was performed 5 weeks postoperatively. At 4 years follow up, she continued to successfully retain an ocular prosthesis.

  7. Grafted silane monolayers: reconsideration of growth mechanisms

    NASA Astrophysics Data System (ADS)

    Ivanov, D. A.; Nysten, B.; Jonas, A. M.; Legras, R.

    1998-03-01

    Chemical force microscopy is a new technique devised to image chemical heterogeneities on surfaces. It requires the chemical modification of Atomic Force Microscopy (AFM) tips in order to create chemical probes. In this respect, self-assembled monolayers (SAM) of alkylchlorosilanes are particularly interesting as modifying agents for AFM tips. We report here our results on the kinetics of silanization and on the structure of such SAM's grafted on model surfaces (hydroxylated Si(100) wafers). AFM, contact angle measurements, X-ray reflectivity and X-ray photoelectron spectroscopy were used to characterize SAM's of octadecyltrichlorosilane (OTS) and octadecyldimethylchlorosilane (ODMS) grown from hexadecane and toluene solutions. The mechanism of grafting of OTS follows two stages. The first rapid stage corresponds to the nucleation and growth of island-like monolayer domains. The second slower stage is related to the densification of the monolayer. SAM's of ODMS were found to form thinner layers as compared to OTS, due to their lower grafting density probably resulting in a more disordered state of grafted alkyl chains. We also address the problems concerning the relationships between the quality of final SAM structures and the water content as well as the nature of the solvent used for silanization.

  8. Treponema pallidum Invades Intercellular Junctions of Endothelial Cell Monolayers

    NASA Astrophysics Data System (ADS)

    Thomas, D. Denee; Navab, Mahamad; Haake, David A.; Fogelman, Alan M.; Miller, James N.; Lovett, Michael A.

    1988-05-01

    The pathogenesis of syphilis reflects invasive properties of Treponema pallidum, but the actual mode of tissue invasion is unknown. We have found two in vitro parallels of treponemal invasiveness. We tested whether motile T. pallidum could invade host cells by determining the fate of radiolabeled motile organisms added to a HeLa cell monolayer; 26% of treponemes associated with the monolayer in a trypsin-resistant niche, presumably between the monolayer and the surface to which it adhered, but did not attain intracellularity. Attachment of T. pallidum to cultured human and rabbit aortic and human umbilical vein endothelial cells was 2-fold greater than to HeLa cells. We added T. pallidum to aortic endothelial cells grown on membrane filters under conditions in which tight intercellular junctions had formed. T. pallidum was able to pass through the endothelial cell monolayers without altering tight junctions, as measured by electrical resistance. In contrast, heat-killed T. pallidum and the nonpathogen Treponema phagedenis biotype Reiter failed to penetrate the monolayer. Transmission electron micrographs of sections of the monolayer showed T. pallidum in intercellular junctions. Our in vitro observations suggest that these highly motile spirochetes may leave the circulation by invading the junctions between endothelial cells.

  9. Phenomenological Modeling for Langmuir Monolayers

    NASA Astrophysics Data System (ADS)

    Baptiste, Dimitri; Kelly, David; Safford, Twymun; Prayaga, Chandra; Varney, Christopher N.; Wade, Aaron

    Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. Research reported in this abstract was supported by UWF NIH MARC U-STAR 1T34GM110517-01.

  10. Incomplete reactions in nanothermite composites

    NASA Astrophysics Data System (ADS)

    Jacob, Rohit J.; Ortiz-Montalvo, Diana L.; Overdeep, Kyle R.; Weihs, Timothy P.; Zachariah, Michael R.

    2017-02-01

    Exothermic reactions between oxophilic metals and transition/post transition metal-oxides have been well documented owing to their fast reaction time scales (≈10 μs). This article examines the extent of the reaction in nano-aluminum based thermite systems through a forensic inspection of the products formed during reaction. Three nanothermite systems (Al/CuO, Al/Bi2O3, and Al/WO3) were selected owing to their diverse combustion characteristics, thereby providing sufficient generality and breadth to the analysis. Microgram quantities of the sample were coated onto a fine platinum wire, which was resistively heated at high heating rates (≈105 K/s) to ignite the sample. The subsequent products were captured/quenched very rapidly (≈500 μs) in order to preserve the chemistry/morphology during initiation and subsequent reaction and were quantitatively analyzed using electron microscopy and focused ion beam cross-sectioning followed by energy dispersive X-ray spectroscopy. Elemental examination of the cross-section of the quenched particles shows that oxygen is predominantly localized in the regions containing aluminum, implying the occurrence of the redox reaction. The Al/CuO system, which has simultaneous gaseous oxygen release and ignition (TIgnition ≈ TOxygen Release), shows a substantially lower oxygen content within the product particles as opposed to Al/Bi2O3 and Al/WO3 thermites, which are postulated to undergo a condensed phase reaction (TIgnition ≪ TOxygen Release). An effective Al:O composition for the interior section was obtained for all the mixtures, with the smaller particles generally showing a higher oxygen content than the larger ones. The observed results were further corroborated with the reaction temperature, obtained using a high-speed spectro-pyrometer, and bomb calorimetry conducted on larger samples (≈15 mg). The results suggest that thermites that produce sufficient amounts of gaseous products generate smaller product particles and

  11. Processing of monolayer materials via interfacial reactions

    DOEpatents

    Sutter, Peter Werner; Sutter, Eli Anguelova

    2014-05-20

    A method of forming and processing of graphene is disclosed based on exposure and selective intercalation of the partially graphene-covered metal substrate with atomic or molecular intercalation species such as oxygen (O.sub.2) and nitrogen oxide (NO.sub.2). The process of intercalation lifts the strong metal-carbon coupling and restores the characteristic Dirac behavior of isolated monolayer graphene. The interface of graphene with metals or metal-decorated substrates also provides for controlled chemical reactions based on novel functionality of the confined space between a metal surface and a graphene sheet.

  12. CIMGS: An incomplete orthogonal factorization preconditioner

    SciTech Connect

    Wang, X.; Bramley, R.; Gallivan, K.

    1994-12-31

    This paper introduces, analyzes, and tests a preconditioning method for conjugate gradient (CG) type iterative methods. The authors start by examining incomplete Gram-Schmidt factorization (IGS) methods in order to motivate the new preconditioner. They show that the IGS family is more stable than IC, and they successfully factor any full rank matrix. Furthermore, IGS preconditioners are at least as effective in accelerating convergence of CG type iterative methods as the incomplete Cholesky (IC) preconditioner. The drawback of IGS methods are their high cost of factorization. This motivates finding a new algorithm, CIMGS, which can generate the same factor in a more efficient way.

  13. Adaptive schemes for incomplete quantum process tomography

    SciTech Connect

    Teo, Yong Siah; Englert, Berthold-Georg; Rehacek, Jaroslav; Hradil, Zdenek

    2011-12-15

    We propose an iterative algorithm for incomplete quantum process tomography with the help of quantum state estimation. The algorithm, which is based on the combined principles of maximum likelihood and maximum entropy, yields a unique estimator for an unknown quantum process when one has less than a complete set of linearly independent measurement data to specify the quantum process uniquely. We apply this iterative algorithm adaptively in various situations and so optimize the amount of resources required to estimate a quantum process with incomplete data.

  14. Cochlear implant in incomplete partition type I.

    PubMed

    Berrettini, S; Forli, F; De Vito, A; Bruschini, L; Quaranta, N

    2013-02-01

    In this investigation, we report on 4 patients affected by incomplete partition type I submitted to cochlear implant at our institutions. Preoperative, surgical, mapping and follow-up issues as well as results in cases with this complex malformation are described. The cases reported in the present study confirm that cochlear implantation in patients with incomplete partition type I may be challenging for cochlear implant teams. The results are variable, but in many cases satisfactory, and are mainly related to the surgical placement of the electrode and residual neural nerve fibres. Moreover, in some cases the association of cochlear nerve abnormalities and other disabilities may significantly affect results.

  15. 32 CFR 651.44 - Incomplete information.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... National Defense Department of Defense (Continued) DEPARTMENT OF THE ARMY (CONTINUED) ENVIRONMENTAL QUALITY ENVIRONMENTAL ANALYSIS OF ARMY ACTIONS (AR 200-2) Environmental Impact Statement § 651.44 Incomplete information. When the proposed action will have significant adverse effects on the human environment, and there...

  16. 40 CFR 725.33 - Incomplete submissions.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... ACT REPORTING REQUIREMENTS AND REVIEW PROCESSES FOR MICROORGANISMS Administrative Procedures § 725.33 Incomplete submissions. (a) A submission under this part is not complete, and the review period does not... attachments are not in English, except for published scientific literature. (4) The submitter does not...

  17. Higher Education's Grade for Data: "Incomplete"

    ERIC Educational Resources Information Center

    Hebel, Sara

    2008-01-01

    The latest national report card on higher education, as in the past, handed out a lot of "incompletes." Like the student who keeps forgetting to turn in that lab report, the grades can't be computed without all the data. There's a lot policy makers don't know about their states' higher-education performance, and the gaps in information limit the…

  18. Electromelting of confined monolayer ice.

    PubMed

    Qiu, Hu; Guo, Wanlin

    2013-05-10

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  19. Numerical evaluation of the incomplete airy functions and their application to high frequency scattering and diffraction

    NASA Technical Reports Server (NTRS)

    Constantinides, E. D.; Marhefka, R. J.

    1992-01-01

    The incomplete Airy integrals serve as canonical functions for the uniform ray optical solutions to several high frequency scattering and diffraction problems that involve a class of integrals characterized by two stationary points that are arbitrarily close to one another or to an integration endpoint. Integrals of such analytical properties describe transition region phenomena associated with composite shadow boundaries. An efficient and accurate method for computing the incomplete Airy functions would make the solutions to such problems useful for engineering purposes. Here, a convergent series solution form for the incomplete Airy functions is derived. Asymptotic expansions involving several terms were also developed and serve as large argument approximations. The combination of the series solution form with the asymptotic formulae provides for an efficient and accurate computation of the incomplete Airy functions. Validation of accuracy is accomplished using direct numerical integration data.

  20. Coupled dust-lattice solitons in monolayer plasma crystals.

    PubMed

    Ivlev, A V; Zhdanov, S K; Morfill, G E

    2003-12-01

    Nonlinearly coupled dust-lattice (DL) waves in monolayer plasma crystals are studied theoretically. It is shown that the high-frequency transverse (vertical) oscillations can form localized wave envelopes--solitons coupled with "slow" longitudinal DL perturbations. Using the molecular dynamics simulations, the derived soliton solution is shown to be stable.

  1. Extraordinary optical transmission through metal-coated colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Landström, L.; Brodoceanu, D.; Piglmayer, K.; Bäuerle, D.

    2006-09-01

    Extraordinary optical transmission through metal-coated close-packed monolayers has been observed. The monolayers consist of silica (a-SiO2) or polystyrene microspheres that form two-dimensional close-packed lattices by self-assembly. Metal layers of Ag, Au and Ni with different thicknesses (larger than the skin depth) were evaporated onto such lattices by means of standard techniques. The optical transmission spectra investigated between 300 and 2500 nm show pronounced peaks that scale with the diameter and the optical properties of the composite slabs. The enhanced transmission observed is most likely mediated via plasmons.

  2. Coincidence of Incomplete Pentalogy of Cantrell and Meningomyelocele in a Dizygotic Twin Pregnancy

    PubMed Central

    Timur, Hakan; Tokmak, Aytekin; Bayram, Hatice; Şükran Çakar, Esra; Danışman, Nuri

    2015-01-01

    Pentalogy of Cantrell is an extremely rare and lethal syndrome. Ectopia cordis is frequently found in fetuses with POC but not required for incomplete forms. Likewise, meningomyelocele is a relatively uncommon neural tube defect affecting central nervous system and associated with neurological problems. Herein, we presented a woman with dizygotic twin pregnancy having coincidence of incomplete POC and MMC in each individual fetus, which has never been reported previously. PMID:26421202

  3. Controlling enantiomeric populations in fluctuating Brownian monolayers of chiral colloids.

    PubMed

    Rossi, L; Mason, T G

    2015-03-28

    An ideal parallelogram platelet, although achiral in 3D, has an identifiable chirality when confined in a 2D monolayer. We lithographically fabricate microscale parallelogram platelets, disperse them in an aqueous surfactant solution, and allow them to settle towards a lower glass wall. To reduce the thermal-gravitational height, we add polystyrene nanospheres as a depletion agent to create a depletion attraction between the parallelograms and the wall. Surprisingly, by increasing the volume fraction of the depletion agent, we show that a nearly enantiopure monolayer can be created. We explain this by developing a model of 2D monolayer formation based on anisotropic facial attractions; one face of a platelet is more strongly attracted to the wall than the other as a consequence of an anisotropy introduced by the lithographic process. We study enantiopure Brownian systems of parallelograms as a function of particle area fraction and show that oblique chiral crystals form at high densities. By mixing parallelogram platelets printed in opposite senses, we also dictate the chiral ratio in the monolayer over the entire possible range. This approach is not limited to parallelograms and provides a means for tuning the chiral ratio in fluctuating 2D monolayers composed of a wide variety of chiral shapes.

  4. Carbon phosphide monolayers with superior carrier mobility

    NASA Astrophysics Data System (ADS)

    Wang, Gaoxue; Pandey, Ravindra; Karna, Shashi P.

    2016-04-01

    promise for applications in high-performance electronics and optoelectronics. Electronic supplementary information (ESI) available: Fig. S1 cohesive energy and structure of the CP monolayer with various stoichiometric compositions obtained using CALYPSO, Fig. S2 history of CALYPSO steps and structure of the CP monolayer, Fig. S3 phonon dispersion with DFT-D2 functional, Fig. S4 band structure for β-CP using the DFT-PBE and DFT-D2 functional forms, Fig. S5 strain energy curves, Fig. S6 projected band structure for α-CP, Fig. S7 projected band structure for β-CP, Fig. S8 projected band structure for γ-CP, Fig. S9 band structures obtained with the GGA-PBE and HSE06 functional; Table S1 lattice parameters with the DFT-D2 functional form; Video S1 AIMD simulation of α-CP at 300 K, Video S2 AIMD simulation of β-CP at 300 K, Video S3 AIMD simulation of γ-CP at 300 K. See DOI: 10.1039/c6nr00498a

  5. Structural and electronic properties of arsenic nitrogen monolayer

    NASA Astrophysics Data System (ADS)

    Liu, Pei; Nie, Yao-zhuang; Xia, Qing-lin; Guo, Guang-hua

    2017-03-01

    We present our first-principles calculations of a new two-dimensional material, arsenic nitrogen monolayer. The structural, electronic, and mechanical properties are investigated in detail by means of density functional theory computations. The calculated binding energy and the phonon spectra demonstrate that the AsN can form stable monolayer in puckered honeycomb structure. It is a semiconductor with indirect band gap of 0.73 eV, and displays highly anisotropic mechanical properties. Strain has obvious influence on the electronic properties of AsN monolayer. It is found that in the armchair direction, a moderate compression strain (-12%) can trigger an indirect to direct band gap transition and a tensile strain of 18% can make the AsN becoming a stable metal. In the zigzag direction, a rather smaller strain than armchair direction (12% for compression and 8% for stretch) can induce the indirect band gap to metal transition.

  6. Computational prediction of the diversity of monolayer boron phosphide allotropes

    NASA Astrophysics Data System (ADS)

    Zhu, Zhili; Cai, Xiaolin; Niu, Chunyao; Wang, Chongze; Jia, Yu

    2016-10-01

    We propose previously unrecognized allotropes of monolayer boron phosphorus (BP) based on ab initio density functional calculations. In addition to the hexagonal structure of h-BP, four types of boron phosphide compounds were predicted to be stable as monolayers. They can form sp2 hybridized planar structures composed of 6-membered rings, and buckled geometries including 4-8 or 3-9 membered rings with sp3 like bonding for P atoms. The calculated Bader charges illustrate their ionic characters with the charge transfers from B to P atoms. The competing between the electrostatic energy and the bonding energy of sp2 and sp3 hybridizations reflected in P atoms results in multiple structures of BP. These 2D BP structures can be semiconducting or metallic depending on their geometric structures. Our findings significantly broaden the diversity of monolayer BP allotropes and provide valuable guidance to other 2D group-III-V allotropes.

  7. Incomplete exponential sums and Diffie-Hellman triples

    NASA Astrophysics Data System (ADS)

    Banks, William D.; Friedlander, John B.; Konyagin, Sergei V.; Shparlinski, Igor E.

    2006-03-01

    Let p be a prime and vartheta an integer of order t in the multiplicative group modulo p. In this paper, we continue the study of the distribution of Diffie-Hellman triples (vartheta(x,) vartheta(y,) vartheta(xy) ) by considering the closely related problem of estimating exponential sums formed from linear combinations of the entries in such triples. We show that the techniques developed earlier for complete sums can be combined, modified and developed further to treat incomplete sums as well. Our bounds imply uniformity of distribution results for Diffie-Hellman triples as the pair (x,y) varies over small boxes.

  8. Tuning Oleophobicity of Silicon Oxide Surfaces with Mixed Monolayers of Aliphatic and Fluorinated Alcohols.

    PubMed

    Lee, Austin W H; Gates, Byron D

    2016-12-13

    We demonstrate the formation of mixed monolayers derived from a microwave-assisted reaction of alcohols with silicon oxide surfaces in order to tune their surface oleophobicity. This simple, rapid method provides an opportunity to precisely tune the constituents of the monolayers. As a demonstration, we sought fluorinated alcohols and aliphatic alcohols as reagents to form monolayers from two distinct constituents for tuning the surface oleophobicity. The first aspect of this study sought to identify a fluorinated alcohol that formed monolayers with a relatively high surface coverage. It was determined that 1H,1H,2H,2H-perfluoro-1-octanol yielded high quality monolayers with a water contact angle (WCA) value of ∼110° and contact angle values of ∼80° with toluene and hexadecane exhibiting both an excellent hydrophobicity and oleophobicity. Tuning of the oleophobicity of the modified silicon oxide surfaces was achieved by controlling the molar ratio of 1H,1H,2H,2H-perfluoro-1-octanol within the reaction mixtures. Surface oleophobicity progressively decreased with a decrease in the fluorinated alcohol content while the monolayers maintained their hydrophobicity with WCA values of ∼110°. The simple and reliable approach to preparing monolayers of a tuned composition that is described in this article can be utilized to control the fluorocarbon content of the hydrophobic monolayers on silicon oxide surfaces.

  9. Tuning the structure of thermosensitive gold nanoparticle monolayers.

    PubMed

    Rezende, Camila A; Shan, Jun; Lee, Lay-Theng; Zalczer, Gilbert; Tenhu, Heikki

    2009-07-23

    Gold nanoparticles grafted with poly(N-isopropylacrylamide) (PNIPAM) are rendered amphiphilic and thermosensitive. When spread on the surface of water, they form stable Langmuir monolayers that exhibit surface plasmon resonance. Using Langmuir balance and contrast-matched neutron reflectivity, the detailed structural properties of these nanocomposite monolayers are revealed. At low surface coverage, the gold nanoparticles are anchored to the interface by an adsorbed PNIPAM layer that forms a thin and compact pancake structure. Upon isothermal compression (T=20 degrees C), the adsorbed layer thickens with partial desorption of polymer chains to form brush structures. Two distinct polymer conformations thus coexist: an adsorbed conformation that assures stability of the monolayer, and brush structures that dangle in the subphase. An increase in temperature to 30 degrees C results in contractions of both adsorbed and brush layers with a concomitant decrease in interparticle distance, indicating vertical as well as lateral contractions of the graft polymer layer. The reversibility of this thermal response is also shown by the contraction-expansion of the polymer layers in heating-cooling cycles. The structure of the monolayer can thus be tuned by compression and reversibly by temperature. These compression and thermally induced conformational changes are discussed in relation to optical properties.

  10. Methods for incomplete Bessel function evaluation

    NASA Astrophysics Data System (ADS)

    Harris, Frank E.; Fripiat, J. G.

    Presented here are detailed methods for evaluating the incomplete Bessel functions arising when Gaussian-type orbitals are used for systems periodic in one spatial dimension. The scheme is designed to yield these incomplete Bessel functions with an absolute accuracy of ±1 × 10-10, for the range of integer orders 0 ≤ n ≤ 12 [a range sufficient for a basis whose members have angular momenta of up to three units (s, p, d, or f atomic functions)]. To reach this accuracy level within acceptable computation times, new rational approximations were developed to compute the special functions involved, namely, the exponential integral E1(x) and the modified Bessel functions K0(x) and K1(x), to absolute accuracy ±1 × 10-15.

  11. Past incompleteness of a bouncing multiverse

    SciTech Connect

    Vilenkin, Alexander; Zhang, Jun E-mail: jun.zhang@tufts.edu

    2014-06-01

    According to classical GR, Anti-de Sitter (AdS) bubbles in the multiverse terminate in big crunch singularities. It has been conjectured, however, that the fundamental theory may resolve these singularities and replace them by nonsingular bounces. This may have important implications for the beginning of the multiverse. Geodesics in cosmological spacetimes are known to be past-incomplete, as long as the average expansion rate along the geodesic is positive, but it is not clear that the latter condition is satisfied if the geodesic repeatedly passes through crunching AdS bubbles. We investigate this issue in a simple multiverse model, where the spacetime consists of a patchwork of FRW regions. The conclusion is that the spacetime is still past-incomplete, even in the presence of AdS bounces.

  12. The undirected incomplete perfect phylogeny problem.

    PubMed

    Satya, Ravi Vijaya; Mukherjee, Amar

    2008-01-01

    The incomplete perfect phylogeny (IPP) problem and the incomplete perfect phylogeny haplotyping (IPPH) problem deal with constructing a phylogeny for a given set of haplotypes or genotypes with missing entries. The earlier approaches for both of these problems dealt with restricted versions of the problems, where the root is either available or can be trivially re-constructed from the data, or certain assumptions were made about the data. In this paper, we deal with the unrestricted versions of the problems, where the root of the phylogeny is neither available nor trivially recoverable from the data. Both IPP and IPPH problems have previously been proven to be NP-complete. Here, we present efficient enumerative algorithms that can handle practical instances of the problem. Empirical analysis on simulated data shows that the algorithms perform very well both in terms of speed and in terms accuracy of the recovered data.

  13. Stochastic approximation boosting for incomplete data problems.

    PubMed

    Sexton, Joseph; Laake, Petter

    2009-12-01

    Boosting is a powerful approach to fitting regression models. This article describes a boosting algorithm for likelihood-based estimation with incomplete data. The algorithm combines boosting with a variant of stochastic approximation that uses Markov chain Monte Carlo to deal with the missing data. Applications to fitting generalized linear and additive models with missing covariates are given. The method is applied to the Pima Indians Diabetes Data where over half of the cases contain missing values.

  14. Control of Radiative Exciton Recombination by Charge Transfer Induced Surface Dipoles in MoS2 and WS2 Monolayers

    PubMed Central

    Hu, Peng; Ye, Jun; He, Xuexia; Du, Kezhao; Zhang, Keke K.; Wang, Xingzhi; Xiong, Qihua; Liu, Zheng; Jiang, Hui; Kloc, Christian

    2016-01-01

    Due to the two dimensional confinement of electrons in a monolayer of 2D materials, the properties of monolayer can be controlled by electrical field formed on the monolayer surface. F4TCNQ was evaporated on MoS2 and WS2 monolayer forming dipoles between strong acceptor, F4TCNQ, and monolayers of MoS2 or WS2. The strong acceptor attracts electrons (charge transfer) and decreases the number of the ionized excitons. Free excitons undergo radiative recombination in both MoS2 and WS2. Moreover, the photoluminescence enhancement is stronger in WS2 where the exciton-phonon coupling is weaker. The theoretical model indicates that the surface dipole controls the radiative exciton recombination and enhances photoluminescence radiation. Deposition of F4TCNQ on the 2D monolayers enables a convenient control of the radiative exciton recombination and leads to the applications of these materials in lasers or LEDs. PMID:27053440

  15. Cation-induced monolayer collapse at lower surface pressure follows specific headgroup percolation

    NASA Astrophysics Data System (ADS)

    Das, Kaushik; Sah, Bijay Kumar; Kundu, Sarathi

    2017-02-01

    A Langmuir monolayer can be considered as a two-dimensional (2D) sheet at higher surface pressure which structurally deform with mechanical compression depending upon the elastic nature of the monolayer. The deformed structures formed after a certain elastic limit are called collapsed structures. To explore monolayer collapses at lower surface pressure and to see the effect of ions on such monolayer collapses, out-of-plane structures and in-plane morphologies of stearic acid Langmuir monolayers have been studied both at lower (≈6.8) and higher (≈9.5) subphase p H in the presence of M g2 +,C a2 +,Z n2 +,C d2 + , and B a2 + ions. At lower subphase p H and in the presence of all cations, the stearic acid monolayer remains as a monolayer before collapse, which generally takes place at higher surface pressure (πc>50 mN /m ). However, at higher subphase p H , structural changes of stearic acid monolayers occur at relatively lower surface pressure depending upon the specific dissolved ions. Among the same group elements of M g2 +,C a2 + , and B a2 + , only for B a2 + ions does monolayer to multilayer transition take place from a much lower surface pressure of the monolayer, remaining, however, as a monolayer for M g2 + and C a2 + ions. For another same group elements of Z n2 + and C d2 + ions, a less covered bilayer structure forms on top of the monolayer structure at lower surface pressure, which is evidenced from both x-ray reflectometry and atomic force microscopy. Fourier transform infrared spectroscopy confirms the presence of two coexisting conformations formed by the two different metal-headgroup coordinations and the monolayer to trilayer or multilayer transformation takes place when the coverage ratio of the two molecular conformations changes from the critical value (pc) of ≈0.66 . Such ion-specific monolayer collapses are correlated with the 2D lattice percolation model.

  16. Predicting Two-Dimensional Silicon Carbide Monolayers.

    PubMed

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.

  17. Quantitative analysis of molecular orientation in chlorophyll a Langmuir monolayer: a polarized visible reflection spectroscopic study.

    PubMed Central

    Okamura, E; Hasegawa, T; Umemura, J

    1995-01-01

    Polarized visible reflection spectra of a chlorophyll a (Chl.a) Langmuir monolayer have been measured in situ at various surface pressures. By applying Hansen's optics to the three-phase plane-bounded system (air/Chl.a monolayer/water), the negative reflection absorbances observed were reproduced satisfactorily by the theoretical calculation. Molecular orientation of Chl.a in the monolayer was evaluated quantitatively as a function of surface pressure, from the reflection absorbance of p- and s-polarized spectra of the red (Qy) band. It has been proven that Chl.a molecules in the monolayer form aggregates (islands) even in the low surface pressure region and that during the monolayer compression the molecules are gradually reorganized from inhomogeneous islands to ordered structures, with the chromophores oriented on the average vertically to the water surface. Images FIGURE 1 PMID:8519968

  18. Classification and data acquisition with incomplete data

    NASA Astrophysics Data System (ADS)

    Williams, David P.

    In remote-sensing applications, incomplete data can result when only a subset of sensors (e.g., radar, infrared, acoustic) are deployed at certain regions. The limitations of single sensor systems have spurred interest in employing multiple sensor modalities simultaneously. For example, in land mine detection tasks, different sensor modalities are better-suited to capture different aspects of the underlying physics of the mines. Synthetic aperture radar sensors may be better at detecting surface mines, while infrared sensors may be better at detecting buried mines. By employing multiple sensor modalities to address the detection task, the strengths of the disparate sensors can be exploited in a synergistic manner to improve performance beyond that which would be achievable with either single sensor alone. When multi-sensor approaches are employed, however, incomplete data can be manifested. If each sensor is located on a separate platform ( e.g., aircraft), each sensor may interrogate---and hence collect data over---only partially overlapping areas of land. As a result, some data points may be characterized by data (i.e., features) from only a subset of the possible sensors employed in the task. Equivalently, this scenario implies that some data points will be missing features. Increasing focus in the future on using---and fusing data from---multiple sensors will make such incomplete-data problems commonplace. In many applications involving incomplete data, it is possible to acquire the missing data at a cost. In multi-sensor remote-sensing applications, data is acquired by deploying sensors to data points. Acquiring data is usually an expensive, time-consuming task, a fact that necessitates an intelligent data acquisition process. Incomplete data is not limited to remote-sensing applications, but rather, can arise in virtually any data set. In this dissertation, we address the general problem of classification when faced with incomplete data. We also address the

  19. Hydrodynamics of domain relaxation in a polymer monolayer

    NASA Astrophysics Data System (ADS)

    Mann, E. K.; Hénon, S.; Langevin, D.; Meunier, J.; Léger, L.

    1995-06-01

    The line tension between two phases within a monolayer can be determined from the characteristic relaxation time of deformed domains, if the hydrodynamics of that relaxation, in particular the relative roles of surface and bulk viscosity, can be established. This is accomplished here for a polymer monolayer by varying the viscosity of the bulk substrate. A Poly(dimethyl)siloxane monolayer segregates into dense and dilute polymer domains on aqueous glycerol and glucose solutions (of viscosity 1.2<η/ ηwater<75) as well as on pure water. The surface pressures of these polymer films are, for moderate surface pressures and within experimental precision, independent of the glycerol and glucose content of the substrate solutions. Isolated polymer domains relax toward the circular form, linearly for the early ``bola'' form and exponentially for moderate deformations. Relaxation times Tc are measured for domains of size 10 μmmonolayer domains in the two limits, in which surface or bulk viscosity dominates, is discussed. All data are consistent with dissipation dominated by viscosity in the substrate. The deduced line tension is λ=(1.1+/-0.3)×10-12 N.

  20. Essays on incomplete contracts in regulatory activities

    NASA Astrophysics Data System (ADS)

    Saavedra, Eduardo Humberto

    This dissertation consists of three essays. The first essay, The Hold-Up Problem in Public Infrastructure Franchising, characterizes the equilibria of the investment decisions in public infrastructure franchising under incomplete contracting and ex-post renegotiation. The parties (government and a firm) are unable to credibly commit to the contracted investment plan, so that a second step investment is renegotiated by the parties at the revision stage. As expected, the possibility of renegotiation affects initial non-verifiable investments. The main conclusion of this essay is that not only underinvestment but also overinvestment in infrastructure may arise in equilibrium, compared to the complete contracting case. The second essay, Alternative Institutional Arrangements in Network Utilities: An Incomplete Contracting Approach, presents a theoretical assessment of the efficiency implications of privatizing natural monopolies which are vertically related to potential competitive firms. Based on the incomplete contracts and asymmetric information paradigm. I develop a model that analyzes the relative advantages of different institutional arrangements---alternative ownership and market structures in the industry--- in terms of their allocative and productive efficiencies. The main policy conclusion of this essay is that both ownership and the existence of conglomerates in network industries matter. Among other conclusions, this essay provides an economic rationale for a mixed economy in which the network is public and vertical separation of the industry when the natural monopoly is under private ownership. The last essay, Opportunistic Behavior and Legal Disputes in the Chilean Electricity Sector, analyzes post-contractual disputes in this newly privatized industry. It discusses the presumption that opportunistic behavior and disputes arise due to inadequate market design, ambiguous regulation, and institutional weaknesses. This chapter also assesses the presumption

  1. Incomplete figure perception and invisible masking.

    PubMed

    Chikhman, Valery; Shelepin, Yuri; Foreman, Nigel; Merkuljev, Aleksey; Pronin, Sergey

    2006-01-01

    The Gollin test (measuring recognition thresholds for fragmented line drawings of everyday objects and animals) has traditionally been regarded as a test of incomplete figure perception or 'closure', though there is a debate about how such closure is achieved. Here, figural incompleteness is considered to be the result of masking, such that absence of contour elements of a fragmented figure is the result of the influence of an 'invisible' mask. It is as though the figure is partly obscured by a mask having parameters identical to those of the background. This mask is 'invisible' only consciously, but for the early stages of visual processing it is real and has properties of multiplicative noise. Incomplete Gollin figures were modeled as the figure covered by the mask with randomly distributed transparent and opaque patches. We adjusted the statistical characteristics of the contour image and empty noise patches and processed those using spatial and spatial-frequency measures. Across 73 figures, despite inter-subject variability, mean recognition threshold was always approximately 15% of total contour in naive observers. Recognition worsened with increasing spectral similarity between the figure and the 'invisible' mask. Near threshold, the spectrum of the fragmented image was equally similar to that of the 'invisible' mask and complete image. The correlation between spectral parameters of figures at threshold and complete figures was greatest for figures that were most easily recognised. Across test sessions, thresholds reduced when either figure or mask parameters were familiar. We argue that recognition thresholds for Gollin stimuli in part reflect the extraction of signal from noise.

  2. Dynamic pattern matcher using incomplete data

    NASA Technical Reports Server (NTRS)

    Johnson, Gordon G. (Inventor); Wang, Lui (Inventor)

    1993-01-01

    This invention relates generally to pattern matching systems, and more particularly to a method for dynamically adapting the system to enhance the effectiveness of a pattern match. Apparatus and methods for calculating the similarity between patterns are known. There is considerable interest, however, in the storage and retrieval of data, particularly, when the search is called or initiated by incomplete information. For many search algorithms, a query initiating a data search requires exact information, and the data file is searched for an exact match. Inability to find an exact match thus results in a failure of the system or method.

  3. Incomplete Dirac reduction of constrained Hamiltonian systems

    SciTech Connect

    Chandre, C.

    2015-10-15

    First-class constraints constitute a potential obstacle to the computation of a Poisson bracket in Dirac’s theory of constrained Hamiltonian systems. Using the pseudoinverse instead of the inverse of the matrix defined by the Poisson brackets between the constraints, we show that a Dirac–Poisson bracket can be constructed, even if it corresponds to an incomplete reduction of the original Hamiltonian system. The uniqueness of Dirac brackets is discussed. The relevance of this procedure for infinite dimensional Hamiltonian systems is exemplified.

  4. Catalytic combustion with incompletely vaporized residual fuel

    NASA Technical Reports Server (NTRS)

    Rosfjord, T. J.

    1981-01-01

    Catalytic combustion of fuel lean mixtures of incompletely vaporized residual fuel and air was investigated. The 7.6 cm diameter, graded cell reactor was constructed from zirconia spinel substrate and catalyzed with a noble metal catalyst. Streams of luminous particles exited the rector as a result of fuel deposition and carbonization on the substrate. Similar results were obtained with blends of No. 6 and No. 2 oil. Blends of shale residual oil and No. 2 oil resulted in stable operation. In shale oil blends the combustor performance degraded with a reduced degree of fuel vaporization. In tests performed with No. 2 oil a similar effect was observed.

  5. Phospholipid monolayers between fluid and solid states.

    PubMed Central

    Helm, C A; Möhwald, H; Kjaer, K; Als-Nielsen, J

    1987-01-01

    Monolayers of the phospholipid dimyristoyl phosphatidic acid on the surface of water have been studied by a combination of the new techniques of synchrotron x-ray diffraction and fluorescence microscopy with classical surface pressure data. The pressure vs. area isotherm changes slope at the surface pressures pi c and pi s. The optical technique demonstrates that between pi c and pi s the fluid phase coexists with a denser "gel" phase. Electron diffraction data have shown that the gel phase has bond orientational order over tens of micrometers. However, the x-ray data demonstrate that positional correlations extend only over tens of angstroms. Thus, the gel phase is not crystalline. Above pi s a solid phase is formed with a positional correlation range that is eight times longer for the chemically purest films. Images FIGURE 1 FIGURE 2 PMID:3651557

  6. 49 CFR 529.4 - Requirements for incomplete automobile manufacturers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 6 2010-10-01 2010-10-01 false Requirements for incomplete automobile... AUTOMOBILES § 529.4 Requirements for incomplete automobile manufacturers. (a) Except as provided in paragraph (c) of this section, §§ 529.5 and 529.6, each incomplete automobile manufacturer is considered,...

  7. 49 CFR 529.4 - Requirements for incomplete automobile manufacturers.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 6 2014-10-01 2014-10-01 false Requirements for incomplete automobile... AUTOMOBILES § 529.4 Requirements for incomplete automobile manufacturers. (a) Except as provided in paragraph (c) of this section, §§ 529.5 and 529.6, each incomplete automobile manufacturer is considered,...

  8. 49 CFR 529.4 - Requirements for incomplete automobile manufacturers.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 6 2011-10-01 2011-10-01 false Requirements for incomplete automobile... AUTOMOBILES § 529.4 Requirements for incomplete automobile manufacturers. (a) Except as provided in paragraph (c) of this section, §§ 529.5 and 529.6, each incomplete automobile manufacturer is considered,...

  9. 49 CFR 529.4 - Requirements for incomplete automobile manufacturers.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 6 2012-10-01 2012-10-01 false Requirements for incomplete automobile... AUTOMOBILES § 529.4 Requirements for incomplete automobile manufacturers. (a) Except as provided in paragraph (c) of this section, §§ 529.5 and 529.6, each incomplete automobile manufacturer is considered,...

  10. 49 CFR 529.4 - Requirements for incomplete automobile manufacturers.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 6 2013-10-01 2013-10-01 false Requirements for incomplete automobile... AUTOMOBILES § 529.4 Requirements for incomplete automobile manufacturers. (a) Except as provided in paragraph (c) of this section, §§ 529.5 and 529.6, each incomplete automobile manufacturer is considered,...

  11. The monolayer structure of 1,2-bis(4-pyridyl)ethylene physisorbed on a graphite surface

    NASA Astrophysics Data System (ADS)

    Brewer, Adam Y.; Friscic, Tomislav; Day, G. M.; Overvoorde, Lois M.; Parker, Julia E.; Richardson, Chris N.; Clarke, Stuart M.

    2013-01-01

    The crystalline monolayer of 1,2-bis(4-pyridyl)ethylene physisorbed on a graphite surface at 0.44 monolayers coverage has been observed and characterized by synchrotron X-ray diffraction and differential scanning calorimetry. The experimentally determined monolayer structure has p2 symmetry with lattice parameters a = 17.77 Å, b = 13.69 Å and ν = 39.7°. The unit cell contains two molecules, which are oriented in a plane parallel to the surface. It is proposed that the molecules are arranged such that they are able to form a weak C-H ... N hydrogen bond between pyridine groups. The monolayer melts at 414 K, which is unusually close to the bulk melting point for a sub-monolayer coverage system. This molecule is chiral when adsorbed on the surface, but both isomers appear in the unit cell leading to no overall chirality in the monolayer.

  12. Rate-dependent incompleteness of earthquake catalogs

    NASA Astrophysics Data System (ADS)

    Hainzl, Sebastian

    2016-04-01

    Important information about the earthquake generation process can be gained from instrumental earthquake catalogs, but this requires complete recordings to avoid biased results. The local completeness magnitude Mc is known to depend on general conditions such as the seismographic network and the environmental noise, which generally limit the possibility to detect small events. The detectability can be additionally reduced by an earthquake-induced increase of the noise-level leading to short-term variations of Mc, which cannot be resolved by traditional methods relying on the analysis of the frequency-magnitude distribution. Based on simple assumptions, I propose a new method to estimate such temporal excursions of Mc solely based on the estimation of the earthquake rate resulting in a high temporal resolution of Mc. The approach is shown to be in agreement with the apparent decrease of the estimated Gutenberg-Richter b-value in high-activity phases of recorded data sets and the observed incompleteness periods after mainshocks. Furthermore, an algorithm to estimate temporal changes of Mc is introduced and applied to empirical aftershock and swarm sequences from California and central Europe, indicating that observed b-value fluctuations are often related to rate-dependent incompleteness of the earthquake catalogs.

  13. Robust pulmonary lobe segmentation against incomplete fissures

    NASA Astrophysics Data System (ADS)

    Gu, Suicheng; Zheng, Qingfeng; Siegfried, Jill; Pu, Jiantao

    2012-03-01

    As important anatomical landmarks of the human lung, accurate lobe segmentation may be useful for characterizing specific lung diseases (e.g., inflammatory, granulomatous, and neoplastic diseases). A number of investigations showed that pulmonary fissures were often incomplete in image depiction, thereby leading to the computerized identification of individual lobes a challenging task. Our purpose is to develop a fully automated algorithm for accurate identification of individual lobes regardless of the integrity of pulmonary fissures. The underlying idea of the developed lobe segmentation scheme is to use piecewise planes to approximate the detected fissures. After a rotation and a global smoothing, a number of small planes were fitted using local fissures points. The local surfaces are finally combined for lobe segmentation using a quadratic B-spline weighting strategy to assure that the segmentation is smooth. The performance of the developed scheme was assessed by comparing with a manually created reference standard on a dataset of 30 lung CT examinations. These examinations covered a number of lung diseases and were selected from a large chronic obstructive pulmonary disease (COPD) dataset. The results indicate that our scheme of lobe segmentation is efficient and accurate against incomplete fissures.

  14. Social Interactions under Incomplete Information: Games, Equilibria, and Expectations

    NASA Astrophysics Data System (ADS)

    Yang, Chao

    Interactions under Incomplete Information", is an application of the first chapter to censored outcomes, corresponding to the situation when agents" behaviors are subjected to some binding restrictions. In an interesting empirical analysis for property tax rates set by North Carolina municipal governments, it is found that there is a significant positive correlation among near-by municipalities. Additionally, some private information about its own residents is used by a municipal government to predict others' tax rates, which enriches current empirical work about tax competition. The third chapter, "Social Interactions under Incomplete Information with Multiple Equilibria", extends the first chapter by investigating effective estimation methods when the condition for a unique equilibrium may not be satisfied. With multiple equilibria, the previous model is incomplete due to the unobservable equilibrium selection. Neither conventional likelihoods nor moment conditions can be used to estimate parameters without further specifications. Although there are some solutions to this issue in the current literature, they are based on strong assumptions such as agents with the same observable characteristics play the same strategy. This paper relaxes those assumptions and extends the all-solution method used to estimate discrete choice games to a setting with both discrete and continuous choices, bounded and unbounded outcomes, and a general form of incomplete information, where the existence of a pure strategy equilibrium has been an open question for a long time. By the use of differential topology and functional analysis, it is found that when all exogenous characteristics are public information, there are a finite number of equilibria. With privately known exogenous characteristics, the equilbria can be represented by a compact set in a Banach space and be approximated by a finite set. As a result, a finite-state probability mass function can be used to specify a probability measure

  15. Self-Assembled Monolayers: a Molecular Resolution STM Study

    NASA Astrophysics Data System (ADS)

    Dhirani, Al-Amin

    Building on studies of self-assembled monolayers (SAMs) based on the (CH_3(CH _2)_{rm n{-}1}SH) + Au(111) prototype, we have designed and constructed a high impedance STM to consider the formation and properties of new SAM systems with molecular resolution. On Au-, Ag-, and Pt-(111), the monolayer structures of n-decanethiol were found to be (1) ordered on gold and silver but not platinum (2) strongly correlated with the structures formed by simpler sulfur components. In addition the potential formation and properties of new molecular classes of ordered SAMs were considered by studying monolayers of H(C _6H_4Cequiv C)_{rm n}C _6H_4SH (n = 0 - 2) (1a - c) on Au(111). An increase in order with chain length as well as the formation of an ordered SAM by 1c were observed. Finally, current-voltage (I-V) measurements of 1 monolayers displayed an increasing nonlinearity with chain length and an asymmetry for 1c. The electrical behavior is consistent with a model based on a semi-classical tunneling formalism using the barrier height and molecular polarizability of 1.

  16. Graphene Biosensor Programming with Genetically Engineered Fusion Protein Monolayers.

    PubMed

    Soikkeli, Miika; Kurppa, Katri; Kainlauri, Markku; Arpiainen, Sanna; Paananen, Arja; Gunnarsson, David; Joensuu, Jussi J; Laaksonen, Päivi; Prunnila, Mika; Linder, Markus B; Ahopelto, Jouni

    2016-03-01

    We demonstrate a label-free biosensor concept based on specific receptor modules, which provide immobilization and selectivity to the desired analyte molecules, and on charge sensing with a graphene field effect transistor. The receptor modules are fusion proteins in which small hydrophobin proteins act as the anchor to immobilize the receptor moiety. The functionalization of the graphene sensor is a single-step process based on directed self-assembly of the receptor modules on a hydrophobic surface. The modules are produced separately in fungi or plants and purified before use. The modules form a dense and well-oriented monolayer on the graphene transistor channel and the receptor module monolayer can be removed, and a new module monolayer with a different selectivity can be assembled in situ. The receptor module monolayers survive drying, showing that the functionalized devices can be stored and have a reasonable shelf life. The sensor is tested with small charged peptides and large immunoglobulin molecules. The measured sensitivities are in the femtomolar range, and the response is relatively fast, of the order of one second.

  17. Nano-scale characterization of binary self-assembled monolayers under an ambient condition with STM and TERS.

    PubMed

    Horimoto, Noriko N; Tomizawa, Shigeru; Fujita, Yasuhiko; Kajimoto, Shinji; Fukumura, Hiroshi

    2014-09-07

    Gold surfaces were modified by benzyl-mercaptan (BM) and then partly replaced with benzenethiol (BT), which formed binary self-assembled monolayers (SAM). Initially BT randomly replaced BM in the monolayer, but at long exchange times >15 nm radius domains were observed with specific relative composition of BT and BM.

  18. Structure and shear response of lipid monolayers

    SciTech Connect

    Dutta, P.; Ketterson, J.B.

    1990-02-01

    Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this Progress Report, we describe our X-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension.

  19. Equilibrating Nanoparticle Monolayers Using Wetting Films

    SciTech Connect

    Pontoni, D.; Alvine, K; Checco, A; Gang, O; Ocko, B; Pershan, P

    2009-01-01

    Monolayers of bimodal gold nanoparticles on silicon are investigated by a combination of microscopy (dry monolayers) and x-ray diffraction (dry and wet monolayers). In the presence of an excess of small particles, the nanoscale packing structure closely resembles the small-particle-rich scenario of the structural crossover transition that has been predicted and also observed with micron-scale hard-sphere colloids. Structural morphology is monitored in situ during monolayer dissolution and reassembly within the thin liquid wetting film. This approach allows investigation of size and solvent effects on nanoparticles in quasi-two-dimensional confinement.

  20. Anti-fouling chemistry of chiral monolayers: enhancing biofilm resistance on racemic surface.

    PubMed

    Bandyopadhyay, Debjyoti; Prashar, Deepali; Luk, Yan-Yeung

    2011-05-17

    This work reports the resistance to protein adsorption and bacterial biofilm formation by chiral monolayers of polyol-terminated alkanethiols surrounding micrometer-sized patterns of methyl-terminated alkanethiols on gold films. We discover that patterned surfaces surrounded by chiral polyol monolayers can distinguish different stages of biofilm formation. After inoculation on the surfaces, bacteria first reversibly attached on the chiral polyol monolayers. Over time, the bacteria detached from the polyol surfaces, and attached on the hydrophobic micropatterns to form biofilms. Interestingly, while both enantiomers of gulitol- and mannonamide-terminated monolayer resisted adsorption of proteins (bovine serum albumin, lysozyme, and fibrinogen) and confined biofilms formed on the micropatterns, the monolayers formed by the racemic mixture of either pair of enantiomers exhibited stronger antifouling chemistry against both protein adsorption and biofilm formation than monolayers formed by one enantiomer alone. These results reveal the different chemistries that separate the different stages of biofilm formation, and the stereochemical influence on resisting biofoulings at a molecular-level.

  1. Dynamic microtubule-dependent interactions position homotypic neurones in regular monolayered arrays during retinal development.

    PubMed

    Galli-Resta, Lucia; Novelli, Elena; Viegi, Alessandro

    2002-08-01

    In the vertebrate retina cell layers support serial processing, while monolayered arrays of homotypic neurones tile each layer to allow parallel processing. How neurones form layers and arrays is still largely unknown. We show that monolayered retinal arrays are dynamic structures based on dendritic interactions between the array cells. The analysis of three developing retinal arrays shows that these become regular as a net of dendritic processes links neighbouring array cells. Molecular or pharmacological perturbations of microtubules within dendrites lead to a stereotyped and reversible disruption of array organization: array cells lose their regular spacing and the arrangement in a monolayer. This leads to a micro-mechanical explanation of how monolayers of regularly spaced 'like-cells' are formed.

  2. Series expansions for the incomplete Lipschitz-Hankel integral Je 0(a, z)

    NASA Astrophysics Data System (ADS)

    Mechaik, Mehdi M.; Dvorak, Steven L.

    1995-09-01

    Bessel series expansions are derived for the incomplete Lipschitz-Hankel integralJe0(a, z). These expansions are obtained by using contour integration techniques to evaluate the inverse Laplace transform representation for Je0(a, z). It is shown that one of the expansions can be used as a convergent series expansion for one definition of the branch cut and as an asymptotic expansion if the branch cut is chosen differently. The effects of the branch cuts are demonstrated by plotting the terms in the series for interesting special cases. The Laplace transform technique used in this paper simplifies the derivation of the series expansions, provides information about the resulting branch cuts, yields integral representations for Je0(a, z), and allows the series expansions to be extended to complex values of z. These series expansions can be used together with the expansions for Ye0(a, z), which are obtained in a separate paper, to compute numerous other special functions, encountered in electromagnetic applications. These include: incomplete Lipschitz-Hankel integrals of the Hankel and modified Bessel form, incomplete cylindrical functions of Poisson form (incomplete Bessel, Struve, Hankel, and Macdonald functions), and incomplete Weber integrals (Lommel functions of two variables).

  3. Bereavement: an incomplete rite of passage.

    PubMed

    Hunter, Jennifer

    A bereavement ritual observed during anthropological fieldwork in Peru gives basis to this article which asserts that bereavement has become an incomplete rite of passage. The article reviews the role of ritual and rites of passage, examines other anthropologic examples of death and bereavement rituals, and identifies the lack of post-funeral ritual for many bereaved individuals in the United States. While funerary rituals which end with the funeral and burial of the dead are helpful in providing immediate structure for the bereaved, they are not congruent with the long-term emotional needs and reconstruction of meaning within grief. The author acknowledges value of both private ritual and reunions of the community of mourners, and recommends that bereavement counselors and/or the funeral industry offer to help bereaved construct a "ritual of remembrance and new meaning" after time has allowed them to move along in meaning reconstruction processes of making sense, finding benefits, and identity change.

  4. Shape reconstruction methods with incomplete data

    NASA Astrophysics Data System (ADS)

    Nakahata, K.; Kitahara, M.

    2000-05-01

    Linearized inverse scattering methods are applied to the shape reconstruction of defects in elastic solids. The linearized methods are based on the Born approximation in the low frequency range and the Kirchhoff approximation in the high frequency range. The experimental measurement is performed to collect the scattering data from defects. The processed data from the measurement are fed into the linearized methods and the shape of the defect is reconstructed by two linearized methods. The importance of scattering data in the low frequency range is pointed out not only for Born inversion but also for Kirchhoff inversion. In the ultrasonic measurement for the real structure, the access points of the sensor may be limited to one side of the structural surfaces and a part of the surface. From the viewpoint of application, the incomplete scattering data are used as inputs for the shape reconstruction methods and the effect of the sensing points are discussed.

  5. Inflaton dark matter from incomplete decay

    NASA Astrophysics Data System (ADS)

    Bastero-Gil, Mar; Cerezo, Rafael; Rosa, João G.

    2016-05-01

    We show that the decay of the inflaton field may be incomplete, while nevertheless successfully reheating the Universe and leaving a stable remnant that accounts for the present dark matter abundance. We note, in particular, that since the mass of the inflaton decay products is field dependent, one can construct models, endowed with an appropriate discrete symmetry, where inflaton decay is kinematically forbidden at late times and only occurs during the initial stages of field oscillations after inflation. We show that this is sufficient to ensure the transition to a radiation-dominated era and that inflaton particles typically thermalize in the process. They eventually decouple and freeze out, yielding a thermal dark matter relic. We discuss possible implementations of this generic mechanism within consistent cosmological and particle physics scenarios, for both single-field and hybrid inflation.

  6. Regulatory perspective on incomplete control rod insertions

    SciTech Connect

    Chatterton, M.

    1997-01-01

    The incomplete control rod insertions experienced at South Texas Unit 1 and Wolf Creek are of safety concern to the NRC staff because they represent potential precursors to loss of shutdown margin. Even before it was determined if these events were caused by the control rods or by the fuel there was an apparent correlation of the problem with high burnup fuel. It was determined that there was also a correlation between high burnup and high drag forces as well as with rod drop time histories and lack of rod recoil. The NRC staff initial actions were aimed at getting a perspective on the magnitude of the problem as far as the number of plants and the amount of fuel that could be involved, as well as the safety significance in terms of shutdown margin. As tests have been performed and data has been analyzed the focus has shifted more toward understanding the problem and the ways to eliminate it. At this time the staff`s understanding of the phenomena is that it was a combination of factors including burnup, power history and temperature. The problem appears to be very sensitive to these factors, the interaction of which is not clearly understood. The model developed by Westinghouse provides a possible explanation but there is not sufficient data to establish confidence levels and sensitivity studies involving the key parameters have not been done. While several fixes to the problem have been discussed, no definitive fixes have been proposed. Without complete understanding of the phenomena, or fixes that clearly eliminate the problem the safety concern remains. The safety significance depends on the amount of shutdown margin lost due to incomplete insertion of the control rods. Were the control rods to stick high in the core, the reactor could not be shutdown by the control rods and other means such as emergency boration would be required.

  7. Hyperthermal Carbon Dioxide Interactions with Self-Assembled Monolayer Surfaces

    DTIC Science & Technology

    2013-09-08

    time as well as density measurements of the thermosphere. The sensor under current development is based on the charge conversion of hyperthermal...oxygen atoms (O) to their anionic form (O−) upon collision with an organosilane/silicon self-assembled monolayer (SAM). The measured current of O− can...efficiency at charge conversion. The original goals of this project were to (1) measure the lifetimes of AFRL-provided SAMs under hyperthermal O

  8. Second harmonic generation study of liquid surface and amphilphile monolayer

    SciTech Connect

    Zhao, X.

    1992-12-31

    This thesis contains the following topics. In Chapter 2, we use temperature dependent SHC to study the surface structure of some neat liquids. It was found all the hydrogen bonding liquids have a stronger SHG dependence of temperature while for the non-hydrogen bonding liquids SH response is insensitive to temperature change. In Chapter 3, we discussed the general feature of the electric field induced second harmonic generation (EFISHG). We experimentally established the importance of the {chi}{sup (3)} mechanism at the air/water charged interface. In Chapter 4, we used SHG to study the p-nitrophenol (PNP) penetration into the insoluble monolayer of hexadecyl and pentadecyl acid. It was found that PNP preferentially adsorbs at the fatty acid monolayer. The population and orientation of PNP is strongly dependent on the fatty acid monolayer packing. In Chapter 5, SH signal fluctuation spectroscopy was used to study the surface self-diffusion within the monolayer gas-liquid co-existence region. Assuming the uniform distribution of the liquid phase cluster size, a diffusion model was developed to fit the experimental measured autocorrelation function. In Chapter 6, SH fluctuation spectroscopy was used to study the monolayer orientation spontaneous fluctuation. It was found that only the electron rich aromatic head groups exhibit the orientational fluctuation while the electron poor aromatic molecules do not have a fluctuation anomalies. Fluctuation time scale is strongly influenced by the hydrophobic chain length. A quantitative theory was presented based on Landau-Ginzburg theory to fit the time dependent orientation fluctuation. In Chapter 7, we focused on the acid-base equilibrium constant measurement at the air/water interface using both {chi}{sup (2)} and {chi}{sup (2)} method. We have measured pKa of aniline, phenol, amine, and acid at the interface. It turned out that for all these species, the neutral form is more stable at the interface.

  9. Classification with Incomplete Data Using Dirichlet Process Priors

    PubMed Central

    Wang, Chunping; Liao, Xuejun; Carin, Lawrence; Dunson, David B.

    2013-01-01

    A non-parametric hierarchical Bayesian framework is developed for designing a classifier, based on a mixture of simple (linear) classifiers. Each simple classifier is termed a local “expert”, and the number of experts and their construction are manifested via a Dirichlet process formulation. The simple form of the “experts” allows analytical handling of incomplete data. The model is extended to allow simultaneous design of classifiers on multiple data sets, termed multi-task learning, with this also performed non-parametrically via the Dirichlet process. Fast inference is performed using variational Bayesian (VB) analysis, and example results are presented for several data sets. We also perform inference via Gibbs sampling, to which we compare the VB results. PMID:23990757

  10. Specific effects of monovalent counterions on the structural and interfacial properties of dodecyl sulfate monolayers.

    PubMed

    Allen, Daniel T; Saaka, Yussif; Pardo, Luis Carlos; Lawrence, M Jayne; Lorenz, Christian D

    2016-11-09

    A series of molecular dynamics simulations have been conducted in order to study the specific ion effects of Li(+), Na(+), Cs(+) and NH4(+) cations on dodecyl sulfate (DS(-)) monolayers. Varying the counterion had no appreciable effect on the structure of the surfactant molecules within the different monolayers. However, the different counterions have a significant effect on the interfacial properties of the monolayer. In particular, we have investigated to what extent each of the counterions is dehydrated when interacting with the DS(-) headgroup, the specific interactions between the counterions and the headgroup and the salt bridging of the headgroups caused by each counterion. The NH4(+) ions are found to directly compete with water molecules to form hydrogen bonds with the DS(-) headgroup and as a result the ammonium dodecyl sulfate monolayer is the least hydrated of any of those studied. The Cs(+) ions are strongly bound to the headgroup and weakly hydrated, such that they would prefer to displace water in the DS(-) hydration shell to interact with the headgroups. In the case of the Li(+) ions, they interact almost as strongly with the DS(-) headgroups as the Na(+) ions, but are generally less hydrated than the Na(+) ions and consequently the lithium dodecyl sulfate monolayers are less hydrated than the sodium dodecyl sulfate monolayers. Therefore, by changing the counterion, one can modify the interfacial properties of the surfactant monolayer, and thus affect their ability to encapsulate poorly water soluble drug molecules, which we discuss further in the manuscript.

  11. Broadband ultra-high transmission of terahertz radiation through monolayer MoS{sub 2}

    SciTech Connect

    Deng, Xue-Yong; Deng, Xin-Hua; Su, Fu-Hai; Liu, Nian-Hua; Liu, Jiang-Tao

    2015-12-14

    In this study, the terahertz (THz) absorption and transmission of monolayer MoS{sub 2} with different carrier concentrations were investigated theoretically. The calculation shows that the THz absorption of monolayer MoS{sub 2} is very low even under high carrier concentrations and large incident angles. The sum of reflection and absorption losses of monolayer MoS{sub 2} is lower than that of graphene by one to three orders of magnitude. The transmission of monolayer MoS{sub 2} is higher than that of two-dimensional electron gases in traditional GaAs and InAs. The field-effect tube structure formed by monolayer MoS{sub 2}-insulation-layer-graphene is also studied. The THz absorption of graphene can reach saturation under low voltage by tuning the voltage between MoS{sub 2} and graphene layers in the structure. The maximum THz absorption of monolayer MoS{sub 2} is approximately 5%. Thus, monolayer MoS{sub 2} is a promising candidate for THz transparent electrodes.

  12. Calcium carbonate crystal growth beneath Langmuir monolayers of acidic β-hairpin peptides.

    PubMed

    Gong, Haofei; Yang, Yi; Pluntke, Manuela; Marti, Othmar; Majer, Zsuzsa; Sewald, Norbert; Volkmer, Dirk

    2014-11-28

    Four amphiphilic peptides with designed hairpin structure were synthesized and their monolayers were employed as model systems to study biologically inspired calcium carbonate crystallization. Langmuir monolayers of hairpin peptides were investigated by surface pressure area isotherms, surface potential isotherms, Brewster angle microscopy (BAM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. A β-hairpin conformation was found for all peptides at the air-water interface although their packing arrangements seem to be different. Crystallization of calcium carbonate under these peptide monolayers was investigated at different surface pressures and growth times both by in situ optical microscopy, BAM and ex situ investigations such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An amorphous calcium carbonate precursor was found at the initial crystallization stage. The crystallization process occurred in three stages. It starts from the nucleation of amorphous particles being a kinetically controlled process. Crystal nuclei subsequently aggregate to large particles and vaterite crystals start to form inside the amorphous layer, with the monolayer fluidity exerting an important role. The third process includes the re-crystallization of vaterite to calcite, which is thermodynamically controlled by monolayer structural factors including the monolayer flexibility and packing arrangement of the polar headgroups. Thus, the kinetic factors, monolayer fluidity and flexibility as well as structure factors govern the crystal morphology and polymorph distribution simultaneously and synergistically.

  13. Molecular Packing of Functionalized Fluorinated Lipids in Langmuir Monolayers

    SciTech Connect

    Landsberg, Michael J.; Ruggles, Jeremy L.; Hussein, Waleed M.; McGeary, Ross P.; Gentle, Ian R.; Hankamer, Ben

    2012-01-20

    Fluorinated amphipaths are a fascinating class of compounds, which, despite significant challenges associated with their syntheses, have found use across a number of areas of biotechnology. Applications range from the in vitro stabilization of membrane proteins to the development of enhanced stability intravenous drug and gene delivery systems. More recently, monolayer-forming fluorinated lipids have found use in the 2D crystallization of detergent-solubilized hydrophobic or partially hydrophobic proteins at the air-water interface. In this study, we investigate the surface properties of a novel suite of monolayer forming, partially fluorinated lipids. These modular lipid structures contain a densely fluorinated insertion in the hydrocarbon tail and a synthetically modifiable headgroup. Analyses of surface-pressure area isotherms and X-ray reflectometry profiles reveal that the lipids spread into fluid monolayers and are more compressible than their non-fluorinated counterparts. Furthermore, the data support a model whereby the partially fluorinated chains of the lipid tails form a film which is fundamentally incompatible with detergents and other destabilizing amphipaths.

  14. Multifunctional self-assembled monolayers

    SciTech Connect

    Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F.; Ferrais, J.

    1996-06-01

    This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

  15. Stilling Waves with Ordered Molecular Monolayers

    ERIC Educational Resources Information Center

    Vitz, Ed

    2008-01-01

    A demonstration of the damping effect of an oil monolayer on water waves is described. The history of this remarkable demonstration--with a 2000 (or more) year span--and a brief explanation in terms of the properties of water and the monolayer are presented. If a layer of olive oil, one molecule thick (about one-ten millionth of a centimeter), is…

  16. Variable temperature STM study of Co deposition on a dodecanethiol self assembled monolayer

    NASA Astrophysics Data System (ADS)

    Breitwieser, Romain; Campiglio, Paolo; Chacon, Cyril; Repain, Vincent; Nemausat, Ruidy; Girard, Yann; Lagoute, Jérôme; Rousset, Sylvie

    2012-02-01

    The present scanning tunneling microscopy study reports on the growth processes of Co vapor-deposited on a dodecanethiol (DDT) self-assembled monolayer (SAM)/Au(111). We observe strongly modified surface and depth diffusions of Co adatoms depending on the growth temperature. Co deposited at 300 K shows an extremely incomplete regime of condensation on the organic layer. Besides, Co penetrates the DDT monolayer and resides at the DDT/Au(111) interface as 2D clusters. This phenomenon takes place through defects in the SAM which are transient channels. In contrast, Co deposited at 50 K shows a complete condensation and nucleates on defects of the SAM layer as 3D islands sitting most likely on top of the DDTs. These results are of interest in the growing field of organic spintronics where the quality of the organic/ferromagnetic interface is a key issue.

  17. Structure of Freund's complete and incomplete adjuvants

    PubMed Central

    Dvorak, Ann M.; Dvorak, H. F.

    1974-01-01

    Emulsions of complete (CFA) and incomplete (IFA) Freund's adjuvants were examined in the light and electron microscopes, and the resulting morphological findings were correlated with the effectiveness of the emulsions as immunological adjuvants. Thick (viscous) emulsions of both IFA and CFA consisted of highly stable, three-dimensional meshworks composed of interconnecting strands of antigen-containing water droplets interspersed in oil phase. Included mycobacteria were confined to this meshwork and were coated with an adherent surface layer of water droplets. Thin Freund's adjuvants were less stable, relatively coarse emulsions, but even in such preparations mycobacteria showed a striking affinity for the surface of water droplets when these contained low concentrations of antigens such as human serum albumin (HSA). The characteristic adjuvant effect of CFA was observed only when associations between mycobacteria and water droplets took place. Thus, no adjuvant effect occurred with oil-in-water (o/w) emulsions, nor when antigen and mycobacteria-in-oil were injected into separate foot pads. Further, a good adjuvant effect was observed even with thin emulsions when mycobacteria-water droplet associations were abundant. These morphological and immunological data suggest that CFA is a device for bringing extrinsic, water-soluble antigens into intimate, stable contact with myco-bacteria, thereby conferring on them the ability to elicit an immunological response qualitatively similar to that induced by mycobacteria-in-oil to the intrinsic antigen, tuberculin. ImagesFIG. 1FIG. 2FIG. 3FIG. 4FIG. 5 PMID:4605156

  18. The Treatment of the Incompletely Descended Testis

    PubMed Central

    Wilson, D. S. Poole

    1939-01-01

    (1) Under three years of age the diagnosis of the incompletely descended testis is uncertain. (2) The policy of awaiting spontaneous descent may be pursued until 10 years of age but, unless the testis lies in the superior scrotal position, this policy should not be persisted in thereafter. (3) Hormonal therapy may be employed before operative treatment as a means of determining testes which will descend spontaneously. It should only be used in the prepuberty period. (4) Operative treatment may be safely carried out at any age after 3 years and should be completed before puberty. The optimum period is between 8 and 11 years. The Bevan operation may be successful when the testis is very mobile but the most consistent results are obtained by the septal transposition or Keetley-Torek operations. ImagesFig. 1Fig. 2Fig. 3Fig. 4Fig. 5Fig. 8Fig. 9Fig. 10Fig. 13Fig. 14Fig. 15Fig. 16Fig. 18Fig. 19Fig. 20Fig. 21Fig. 22 PMID:19991991

  19. Analyzing incomplete longitudinal clinical trial data.

    PubMed

    Molenberghs, Geert; Thijs, Herbert; Jansen, Ivy; Beunckens, Caroline; Kenward, Michael G; Mallinckrodt, Craig; Carroll, Raymond J

    2004-07-01

    Using standard missing data taxonomy, due to Rubin and co-workers, and simple algebraic derivations, it is argued that some simple but commonly used methods to handle incomplete longitudinal clinical trial data, such as complete case analyses and methods based on last observation carried forward, require restrictive assumptions and stand on a weaker theoretical foundation than likelihood-based methods developed under the missing at random (MAR) framework. Given the availability of flexible software for analyzing longitudinal sequences of unequal length, implementation of likelihood-based MAR analyses is not limited by computational considerations. While such analyses are valid under the comparatively weak assumption of MAR, the possibility of data missing not at random (MNAR) is difficult to rule out. It is argued, however, that MNAR analyses are, themselves, surrounded with problems and therefore, rather than ignoring MNAR analyses altogether or blindly shifting to them, their optimal place is within sensitivity analysis. The concepts developed here are illustrated using data from three clinical trials, where it is shown that the analysis method may have an impact on the conclusions of the study.

  20. Deep community detection in topologically incomplete networks

    NASA Astrophysics Data System (ADS)

    Xin, Xin; Wang, Chaokun; Ying, Xiang; Wang, Boyang

    2017-03-01

    In this paper, we consider the problem of detecting communities in topologically incomplete networks (TIN), which are usually observed from real-world networks and where some edges are missing. Existing approaches to community detection always consider the input network as connected. However, more or less, even nearly all, edges are missing in real-world applications, e.g. the protein-protein interaction networks. Clearly, it is a big challenge to effectively detect communities in these observed TIN. At first, we bring forward a simple but useful method to address the problem. Then, we design a structured deep convolutional neural network (CNN) model to better detect communities in TIN. By gradually removing edges of the real-world networks, we show the effectiveness and robustness of our structured deep model on a variety of real-world networks. Moreover, we find that the appropriate choice of hop counts can improve the performance of our deep model in some degree. Finally, experimental results conducted on synthetic data sets also show the good performance of our proposed deep CNN model.

  1. All-Carbon Electrode Molecular Electronic Devices Based on Langmuir-Blodgett Monolayers.

    PubMed

    Sangiao, Soraya; Martín, Santiago; González-Orive, Alejandro; Magén, César; Low, Paul J; De Teresa, José M; Cea, Pilar

    2017-02-01

    Nascent molecular electronic devices, based on monolayer Langmuir-Blodgett films sandwiched between two carbonaceous electrodes, have been prepared. Tightly packed monolayers of 4-((4-((4-ethynylphenyl)ethynyl)phenyl)ethynyl)benzoic acid are deposited onto a highly oriented pyrolytic graphite electrode. An amorphous carbon top contact electrode is formed on top of the monolayer from a naphthalene precursor using the focused electron beam induced deposition technique. This allows the deposition of a carbon top-contact electrode with well-defined shape, thickness, and precise positioning on the film with nm resolution. These results represent a substantial step toward the realization of integrated molecular electronic devices based on monolayers and carbon electrodes.

  2. Coulomb excitations of monolayer germanene

    NASA Astrophysics Data System (ADS)

    Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa

    2017-01-01

    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes.

  3. Coulomb excitations of monolayer germanene

    PubMed Central

    Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa

    2017-01-01

    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes. PMID:28091555

  4. Thermoelectric transport in monolayer phosphorene

    NASA Astrophysics Data System (ADS)

    Zare, Moslem; Rameshti, Babak Zare; Ghamsari, Farnood G.; Asgari, Reza

    2017-01-01

    We apply the generalized Boltzmann theory to describe thermoelectric transport properties of monolayer phosphorene in the presence of short- and long-range charged impurity interactions. First, we propose a low-energy Hamiltonian to explore the accurate electronic band structure of phosphorene in comparison with those results obtained by density-functional simulations. We explain the effect of the coupling between the conduction and valence bands on the thermoelectric properties. We show that the electric conductivity of phosphorene is highly anisotropic, while the Seebeck coefficient and figure of merit, without being influenced via either the presence or absence of the coupling term, are nearly isotropic. Furthermore, we demonstrate that the conductivity for the n type of doping is more influenced by the coupling term than that of the p type. Along with thermopower sign change, profound thermoelectric effects can be achieved.

  5. Mixed multilayered vertical heterostructures utilizing strained monolayer WS2

    NASA Astrophysics Data System (ADS)

    Sheng, Yuewen; Xu, Wenshuo; Wang, Xiaochen; He, Zhengyu; Rong, Youmin; Warner, Jamie H.

    2016-01-01

    Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by CVD directly on Si substrates with SiO2 surface are easily washed off by water and this makes aqueous based transfer methods challenging for creating vertical stacks on the growth substrate. 2D hexagonal Boron Nitride films are used to provide an insulating layer that limits interactions with a top graphene layer and preserve the strong photoluminescence from the WS2. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with atomic thickness depth control and large area coverage.Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by

  6. Electronic structure of graphene oxide and reduced graphene oxide monolayers

    SciTech Connect

    Sutar, D. S.; Singh, Gulbagh; Divakar Botcha, V.

    2012-09-03

    Graphene oxide (GO) monolayers obtained by Langmuir Blodgett route and suitably treated to obtain reduced graphene oxide (RGO) monolayers were studied by photoelectron spectroscopy. Upon reduction of GO to form RGO C1s x-ray photoelectron spectra showed increase in graphitic carbon content, while ultraviolet photoelectron spectra showed increase in intensity corresponding to C2p-{pi} electrons ({approx}3.5 eV). X-ray excited Auger transitions C(KVV) and plasmon energy loss of C1s photoelectrons have been analyzed to elucidate the valence band structure. The effective number of ({pi}+{sigma}) electrons as obtained from energy loss spectra was found to increase by {approx}28% on reduction of GO.

  7. An array of layers in silicon sulfides: Chainlike and monolayer

    NASA Astrophysics Data System (ADS)

    Alonso-Lanza, T.; Ayuela, A.; Aguilera-Granja, F.

    2016-12-01

    While much is known about isoelectronic materials related to carbon nanostructures, such as boron-nitride layers and nanotubes, rather less is known about equivalent silicon-based materials. Following the recent discovery of phosphorene, here we discuss isoelectronic silicon-monosulfide monolayers. We describe a set of anisotropic structures that clearly have a high stability with respect to previously reported silicon-monosulfide monolayers. The source of the layer anisotropy is related to the presence of Si-S double chains linked by some Si-Si covalent bonds together with a remarkable spd hybridization on Si. The increased stability is related to silicon forming four bonds, including an additional double-bond-like Si-Si bond. The involvement of d orbitals brings more variety to silicon-sulfide-based nanostructures that are isoelectronic to phosphorene, which could be relevant for future applications, adding extra degrees of freedom.

  8. WILLIAM SEAL REJECTING AN INCOMPLETE OR IMPROPERLY SET BEARDSLEY AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    WILLIAM SEAL REJECTING AN INCOMPLETE OR IMPROPERLY SET BEARDSLEY AND PIPER ROTOMOLD CORMATIC CORE. - Southern Ductile Casting Company, Core Making, 2217 Carolina Avenue, Bessemer, Jefferson County, AL

  9. Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers.

    PubMed

    Giner-Casares, Juan J; Pérez-Morales, Marta; Bolink, Henk J; Muñoz, Eulogia; de Miguel, Gustavo; Martín-Romero, María T; Camacho, Luis

    2007-11-01

    In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)(2)(tmphen)]PF(6), (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as pi-A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at pi approximately equal to 37 mNm(-1). Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.

  10. Studies on behaviors of dipalmitoylposphatidylcholine and bilirubin in mixed monolayer at the air/water interface

    NASA Astrophysics Data System (ADS)

    Shen, Yuhua; Tang, Yufeng; Xie, Anjian; Zhu, Jinmiao; Li, Shikuo; Zhang, Yong

    2006-06-01

    Mixed monolayers of dipalmitoylposphatidylcholine (DPPC) and bilirubin (BR) were prepared on different subphases. The properties of DPPC/BR monolayer, such as collapse pressure ( πcoll), limiting area per molecule ( Alim), surface compressibility modulus, free energy (Δ Gmix) and excess free energy (Δ Gex), were investigated based on the analysis of the surface pressure-area isotherms on pure water. The results showed that DPPC and BR were miscible and formed non-ideal mixed monolayers at the air/water interface. With the molar fraction of BR ( XBR) increasing, the LE-LC coexistence region of DPPC monolayer was eliminated gradually. The DPPC/BR complex (M D-B) of 1:2 stoichiometry formed as a result of the strong hydrogen bonds between the polar groups of DPPC and BR. The studies of effects of pH values and calcium ions in subphase on the DPPC/BR monolayers showed that the mixed monolayer became expanded on alkali aqueous solution and on 1 mmol/L CaCl 2 aqueous solution. The orientation of DPPC and BR at air/water interface was also discussed.

  11. Monolayer II-VI semiconductors: A first-principles prediction

    NASA Astrophysics Data System (ADS)

    Zheng, Hui; Li, Xian-Bin; Chen, Nian-Ke; Xie, Sheng-Yi; Tian, Wei Quan; Chen, Yuanping; Xia, Hong; Zhang, S. B.; Sun, Hong-Bo

    2015-09-01

    A systematic study of 32 honeycomb monolayer II-VI semiconductors is carried out by first-principles methods. While none of the two-dimensional (2D) structures can be energetically stable, it appears that BeO, MgO, CaO, ZnO, CdO, CaS, SrS, SrSe, BaTe, and HgTe honeycomb monolayers have a good dynamic stability. The stability of the five oxides is consistent with the work published by Zhuang et al. [Appl. Phys. Lett. 103, 212102 (2013), 10.1063/1.4831972]. The rest of the compounds in the form of honeycomb are dynamically unstable, revealed by phonon calculations. In addition, according to the molecular dynamic (MD) simulation evolution from these unstable candidates, we also find two extra monolayers dynamically stable, which are tetragonal BaS [P 4 /n m m (129 ) ] and orthorhombic HgS [P 21/m (11 ) ] . The honeycomb monolayers exist in the form of either a planar perfect honeycomb or a low-buckled 2D layer, all of which possess a band gap and most of them are in the ultraviolet region. Interestingly, the dynamically stable SrSe has a gap near visible light, and displays exotic electronic properties with a flat top of the valence band, and hence has a strong spin polarization upon hole doping. The honeycomb HgTe has recently been reported to achieve a topological nontrivial phase under appropriate in-plane tensile strain and spin-orbital coupling (SOC) [J. Li et al., arXiv:1412.2528]. Some II-VI partners with less than 5 % lattice mismatch may be used to design novel 2D heterojunction devices. If synthesized, potential applications of these 2D II-VI families could include optoelectronics, spintronics, and strong correlated electronics.

  12. Highly doped silicon nanowires by monolayer doping.

    PubMed

    Veerbeek, Janneke; Ye, Liang; Vijselaar, Wouter; Kudernac, Tibor; van der Wiel, Wilfred G; Huskens, Jurriaan

    2017-02-23

    Controlling the doping concentration of silicon nanostructures is challenging. Here, we investigated three different monolayer doping techniques to obtain silicon nanowires with a high doping dose. These routes were based on conventional monolayer doping, starting from covalently bound dopant-containing molecules, or on monolayer contact doping, in which a source substrate coated with a monolayer of a carborane silane was the dopant source. As a third route, both techniques were combined to retain the benefits of conformal monolayer formation and the use of an external capping layer. These routes were used for doping fragile porous nanowires fabricated by metal-assisted chemical etching. Differences in porosity were used to tune the total doping dose inside the nanowires, as measured by X-ray photoelectron spectroscopy and secondary ion mass spectrometry measurements. The higher the porosity, the higher was the surface available for dopant-containing molecules, which in turn led to a higher doping dose. Slightly porous nanowires could be doped via all three routes, which resulted in highly doped nanowires with (projected areal) doping doses of 10(14)-10(15) boron atoms per cm(2) compared to 10(12) atoms per cm(2) for a non-porous planar sample. Highly porous nanowires were not compatible with the conventional monolayer doping technique, but monolayer contact doping and the combined route resulted for these highly porous nanowires in tremendously high doping doses up to 10(17) boron atoms per cm(2).

  13. Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

    DOE PAGES

    Wood, M. R.; Kanedy, K.; Lopez, F.; ...

    2015-02-23

    In this paper, we use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-by-monolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Finally, although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellentmore » quantitative match to all important aspects of the x-ray data.« less

  14. Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

    SciTech Connect

    Wood, M. R.; Kanedy, K.; Lopez, F.; Weimer, M.; Klem, J. F.; Hawkins, S. D.; Shaner, E. A.; Kim, J. K.

    2015-02-23

    In this paper, we use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-by-monolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Finally, although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellent quantitative match to all important aspects of the x-ray data.

  15. Auditory Compensation for Head Rotation Is Incomplete

    PubMed Central

    2016-01-01

    Hearing is confronted by a similar problem to vision when the observer moves. The image motion that is created remains ambiguous until the observer knows the velocity of eye and/or head. One way the visual system solves this problem is to use motor commands, proprioception, and vestibular information. These “extraretinal signals” compensate for self-movement, converting image motion into head-centered coordinates, although not always perfectly. We investigated whether the auditory system also transforms coordinates by examining the degree of compensation for head rotation when judging a moving sound. Real-time recordings of head motion were used to change the “movement gain” relating head movement to source movement across a loudspeaker array. We then determined psychophysically the gain that corresponded to a perceptually stationary source. Experiment 1 showed that the gain was small and positive for a wide range of trained head speeds. Hence, listeners perceived a stationary source as moving slightly opposite to the head rotation, in much the same way that observers see stationary visual objects move against a smooth pursuit eye movement. Experiment 2 showed the degree of compensation remained the same for sounds presented at different azimuths, although the precision of performance declined when the sound was eccentric. We discuss two possible explanations for incomplete compensation, one based on differences in the accuracy of signals encoding image motion and self-movement and one concerning statistical optimization that sacrifices accuracy for precision. We then consider the degree to which such explanations can be applied to auditory motion perception in moving listeners. PMID:27841453

  16. Electrochemical Deposition Of Thiolate Monolayers On Metals

    NASA Technical Reports Server (NTRS)

    Porter, Marc D.; Weissharr, Duane E.

    1995-01-01

    Electrochemical method devised for coating metal (usually, gold) surfaces with adherent thiolate monolayers. Affords greater control over location and amount of material deposited and makes it easier to control chemical composition of deposits. One important potential use for this method lies in fabrication of chemically selective thin-film resonators for microwave oscillators used to detect pollutants: monolayer formulated to bind selectively pollutant chemical species of interest, causing increase in mass of monolayer and corresponding decrease in frequency of resonance. Another important potential use lies in selective chemical derivatization for purposes of improving adhesion, lubrication, protection against corrosion, electrocatalysis, and electroanalysis.

  17. Monolayer coated gold nanoparticles for delivery applications

    PubMed Central

    Rana, Subinoy; Bajaj, Avinash; Mout, Rubul; Rotello, Vincent M.

    2011-01-01

    Gold nanoparticles (AuNPs) provide attractive vehicles for delivery of drugs, genetic materials, proteins, and small molecules. AuNPs feature low core toxicity coupled with the ability to parametrically control particle size and surface properties. In this review, we focus on engineering of the AuNP surface monolayer, highlighting recent advances in tuning monolayer structures for efficient delivery of drugs and biomolecules. This review covers two broad categories of particle functionalization, organic monolayers and biomolecule coatings, and discusses their applications in drug, DNA/RNA, protein and small molecule delivery. PMID:21925556

  18. Semi-metallic Be5C2 monolayer global minimum with quasi-planar pentacoordinate carbons and negative Poisson's ratio

    PubMed Central

    Wang, Yu; Li, Feng; Li, Yafei; Chen, Zhongfang

    2016-01-01

    Designing new materials with novel topological properties and reduced dimensionality is always desirable for material innovation. Here we report the design of a two-dimensional material, namely Be5C2 monolayer on the basis of density functional theory computations. In Be5C2 monolayer, each carbon atom binds with five beryllium atoms in almost the same plane, forming a quasi-planar pentacoordinate carbon moiety. Be5C2 monolayer appears to have good stability as revealed by its moderate cohesive energy, positive phonon modes and high melting point. It is the lowest-energy structure with the Be5C2 stoichiometry in two-dimensional space and therefore holds some promise to be realized experimentally. Be5C2 monolayer is a gapless semiconductor with a Dirac-like point in the band structure and also has an unusual negative Poisson's ratio. If synthesized, Be5C2 monolayer may find applications in electronics and mechanics. PMID:27139572

  19. 40 CFR 86.085-20 - Incomplete vehicles, classification.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... and Heavy-Duty Engines, and for 1985 and Later Model Year New Gasoline Fueled, Natural Gas-Fueled, Liquefied Petroleum Gas-Fueled and Methanol-Fueled Heavy-Duty Vehicles § 86.085-20 Incomplete vehicles... 40 Protection of Environment 19 2014-07-01 2014-07-01 false Incomplete vehicles,...

  20. Calculating Balanced Incomplete Block Design for Educational Assessments.

    ERIC Educational Resources Information Center

    van der Linden, Wim J.; Carlson, James E.

    A popular design in large-scale educational assessments is the balanced incomplete block design. The design assumes that the item pool is split into a set of blocks of items that are assigned to assessment booklets. This paper shows how the technique of 0-1 linear programming can be used to calculate a balanced incomplete block design. Several…

  1. Loss of Information in Estimating Item Parameters in Incomplete Designs

    ERIC Educational Resources Information Center

    Eggen, Theo J. H. M.; Verelst, Norman D.

    2006-01-01

    In this paper, the efficiency of conditional maximum likelihood (CML) and marginal maximum likelihood (MML) estimation of the item parameters of the Rasch model in incomplete designs is investigated. The use of the concept of F-information (Eggen, 2000) is generalized to incomplete testing designs. The scaled determinant of the F-information…

  2. 49 CFR 630.6 - Late and incomplete reports.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 7 2012-10-01 2012-10-01 false Late and incomplete reports. 630.6 Section 630.6 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL TRANSIT ADMINISTRATION, DEPARTMENT OF TRANSPORTATION NATIONAL TRANSIT DATABASE § 630.6 Late and incomplete reports. (a) Late...

  3. 49 CFR 630.6 - Late and incomplete reports.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 7 2013-10-01 2013-10-01 false Late and incomplete reports. 630.6 Section 630.6 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL TRANSIT ADMINISTRATION, DEPARTMENT OF TRANSPORTATION NATIONAL TRANSIT DATABASE § 630.6 Late and incomplete reports. (a) Late...

  4. 49 CFR 630.6 - Late and incomplete reports.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 7 2011-10-01 2011-10-01 false Late and incomplete reports. 630.6 Section 630.6 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL TRANSIT ADMINISTRATION, DEPARTMENT OF TRANSPORTATION NATIONAL TRANSIT DATABASE § 630.6 Late and incomplete reports. (a) Late...

  5. 49 CFR 630.6 - Late and incomplete reports.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 7 2014-10-01 2014-10-01 false Late and incomplete reports. 630.6 Section 630.6 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL TRANSIT ADMINISTRATION, DEPARTMENT OF TRANSPORTATION NATIONAL TRANSIT DATABASE § 630.6 Late and incomplete reports. (a) Late...

  6. Treatment of Intravenous Leiomyomatosis with Cardiac Extension following Incomplete Resection

    PubMed Central

    Doyle, Mathew P.; Li, Annette; Villanueva, Claudia I.; Peeceeyen, Sheen C. S.; Cooper, Michael G.; Hanel, Kevin C.; Fermanis, Gary G.; Robertson, Greg

    2015-01-01

    Aim. Intravenous leiomyomatosis (IVL) with cardiac extension (CE) is a rare variant of benign uterine leiomyoma. Incomplete resection has a recurrence rate of over 30%. Different hormonal treatments have been described following incomplete resection; however no standard therapy currently exists. We review the literature for medical treatments options following incomplete resection of IVL with CE. Methods. Electronic databases were searched for all studies reporting IVL with CE. These studies were then searched for reports of patients with inoperable or incomplete resection and any further medical treatments. Our database was searched for patients with medical therapy following incomplete resection of IVL with CE and their results were included. Results. All studies were either case reports or case series. Five literature reviews confirm that surgery is the only treatment to achieve cure. The uses of progesterone, estrogen modulation, gonadotropin-releasing hormone antagonism, and aromatase inhibition have been described following incomplete resection. Currently no studies have reviewed the outcomes of these treatments. Conclusions. Complete surgical resection is the only means of cure for IVL with CE, while multiple hormonal therapies have been used with varying results following incomplete resection. Aromatase inhibitors are the only reported treatment to prevent tumor progression or recurrence in patients with incompletely resected IVL with CE. PMID:26783463

  7. Dynamic Phase Engineering of Bendable Transition Metal Dichalcogenide Monolayers.

    PubMed

    Berry, Joel; Zhou, Songsong; Han, Jian; Srolovitz, David J; Haataja, Mikko P

    2017-03-14

    Current interest in two-dimensional (2D) materials is driven in part by the ability to dramatically alter their optoelectronic properties through strain and phase engineering. A combination of these approaches can be applied in quasi-2D transition metal dichalcogenide (TMD) monolayers to induce displacive structural transformations between semiconducting (H) and metallic/semimetallic (T') phases. We classify such transformations in Group VI TMDs, and formulate a multiscale, first-principles-informed modeling framework to describe evolution of microstructural domain morphologies in elastically bendable 2D monolayers. We demonstrate that morphology and mechanical response can be controlled via application of strain either uniformly or through local probes to generate functionally patterned conductive T' domains. Such systems form dynamically programmable electromechanical 2D materials, capable of rapid local switching between domains with qualitatively different transport properties. This enables dynamic "drawing" of localized conducting regions in an otherwise semiconducting TMD monolayer, opening several interesting device-relevant functionalities such as the ability to dynamically "rewire" a device in real time.

  8. On Monolayer Formation of Pyrenebutyric Acid on Graphene.

    PubMed

    Hinnemo, Malkolm; Zhao, Jie; Ahlberg, Patrik; Hägglund, Carl; Djurberg, Viktor; Scheicher, Ralph H; Zhang, Shi-Li; Zhang, Zhi-Bin

    2017-04-04

    As a two-dimensional material with high charge carrier mobility, graphene may offer ultrahigh sensitivity in biosensing. To realize this, the first step is to functionalize the graphene. This is commonly done by using 1-pyrenebutyric acid (PBA) as a linker for biomolecules. However, the adsorption of PBA on graphene remains poorly understood despite reports of successful biosensors functionalized via this route. Here, the PBA adsorption on graphene is characterized through a combination of Raman spectroscopy, ab initio calculations, and spectroscopic ellipsometry. The PBA molecules are found to form a self-assembled monolayer on graphene, the formation of which is self-limiting and Langmuirian. Intriguingly, in concentrated solutions, the PBA molecules are found to stand up and stack horizontally with their edges contacting the graphene surface. This morphology could facilitate a surface densely populated with carboxylic functional groups. Spectroscopic analyses show that the monolayer saturates at 5.3 PBA molecules per nm(2) and measures ∼0.7 nm in thickness. The morphology study of this PBA monolayer sheds light on the π-π stacking of small-molecule systems on graphene and provides an excellent base for optimizing functionalization procedures.

  9. Neutral amino acid transport across brain microvessel endothelial cell monolayers

    SciTech Connect

    Audus, K.L.; Borchardt, R.T.

    1986-03-01

    Brain microvessel endothelial cells (BMEC) which form the blood-brain barrier (BBB) possess an amino acid carrier specific for large neutral amino acids (LNAA). The carrier is important for facilitating the delivery of nutrient LNAA's and centrally acting drugs that are LNAA's, to the brain. Bovine BMEC's were isolated and grown up to complete monolayers on regenerated cellulose-membranes in primary culture. To study the transendothelial transport of leucine, the monolayers were placed in a side-by-side diffusion cell, and transport across the monolayers followed with (/sup 3/H)-leucine. The transendothelial transport of leucine in this in vitro model was determined to be bidirectional, and time-, temperature-, and concentration-dependent. The transport of leucine was saturable and the apparent K/sub m/ and V/sub max/, 0.18 mM and 6.3 nmol/mg/min, respectively. Other LNAA's, including the centrally acting drugs, ..cap alpha..-methyldopa, L-DOPA, ..cap alpha..-methyl-tyrosine, and baclofen, inhibited leucine transport. The leucine carrier was also found to be stereospecific and not sensitive to inhibitors of active transport. These results are consistent with previous in vitro and in vivo studies. Primary cultures of BMEC's appear to be a potentially important tool for investigating at the cellular level, the transport mechanisms of the BBB.

  10. Induction of homochirality in achiral enantiomorphous monolayers.

    PubMed

    Parschau, Manfred; Romer, Sara; Ernst, Karl-Heinz

    2004-12-01

    We report the induction of homochirality in enantiomorphous layers of achiral succinic acid on a Cu(110) surface after doping with tartaric acid (TA) enantiomers. Succinic acid becomes chiral upon adsorption due to symmetry-breaking interactions with the Cu(110) surface. The doubly deprotonated bisuccinate forms mirror domains on the surface, which leads to a superposition of (11,-90) and (90,-11) patterns observed by low-energy electron diffraction (LEED). On average, however, the surface layer is racemic. An amount of 2 mol % of (R,R)- or (S,S)-tartaric acid in the monolayer, corresponding to an absolute coverage of 0.001 tartaric acid molecule per surface copper atom, is sufficient to make the LEED spots of one enantiomorphous lattice disappear. After thermally induced desorption of TA, the succinic acid lattice turns racemic again. In analogy to the "sergeants-and-soldiers" principle described for helical polymers, this effect is explained by a lateral cooperative interaction within the two-dimensional lattice.

  11. Technique for etching monolayer and multilayer materials

    DOEpatents

    Bouet, Nathalie C. D.; Conley, Raymond P.; Divan, Ralu; Macrander, Albert

    2015-10-06

    A process is disclosed for sectioning by etching of monolayers and multilayers using an RIE technique with fluorine-based chemistry. In one embodiment, the process uses Reactive Ion Etching (RIE) alone or in combination with Inductively Coupled Plasma (ICP) using fluorine-based chemistry alone and using sufficient power to provide high ion energy to increase the etching rate and to obtain deeper anisotropic etching. In a second embodiment, a process is provided for sectioning of WSi.sub.2/Si multilayers using RIE in combination with ICP using a combination of fluorine-based and chlorine-based chemistries and using RF power and ICP power. According to the second embodiment, a high level of vertical anisotropy is achieved by a ratio of three gases; namely, CHF.sub.3, Cl.sub.2, and O.sub.2 with RF and ICP. Additionally, in conjunction with the second embodiment, a passivation layer can be formed on the surface of the multilayer which aids in anisotropic profile generation.

  12. Accurate Molecular Dimensions from Stearic Acid Monolayers.

    ERIC Educational Resources Information Center

    Lane, Charles A.; And Others

    1984-01-01

    Discusses modifications in the fatty acid monolayer experiment to reduce the inaccurate moleculary data students usually obtain. Copies of the experimental procedure used and a Pascal computer program to work up the data are available from the authors. (JN)

  13. Method to synthesize metal chalcogenide monolayer nanomaterials

    SciTech Connect

    Hernandez-Sanchez, Bernadette A.; Boyle, Timothy J.

    2016-12-13

    Metal chalcogenide monolayer nanomaterials can be synthesized from metal alkoxide precursors by solution precipitation or solvothermal processing. The synthesis routes are more scalable, less complex and easier to implement than other synthesis routes.

  14. Penetration of Milk-Derived Antimicrobial Peptides into Phospholipid Monolayers as Model Biomembranes

    PubMed Central

    Rogalska, Ewa; Więcław-Czapla, Katarzyna

    2013-01-01

    Three antimicrobial peptides derived from bovine milk proteins were examined with regard to penetration into insoluble monolayers formed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DPPG). Effects on surface pressure (Π) and electric surface potential (ΔV) were measured, Π with a platinum Wilhelmy plate and ΔV with a vibrating plate. The penetration measurements were performed under stationary diffusion conditions and upon the compression of the monolayers. The two type measurements showed greatly different effects of the peptide-lipid interactions. Results of the stationary penetration show that the peptide interactions with DPPC monolayer are weak, repulsive, and nonspecific while the interactions with DPPG monolayer are significant, attractive, and specific. These results are in accord with the fact that antimicrobial peptides disrupt bacteria membranes (negative) while no significant effect on the host membranes (neutral) is observed. No such discrimination was revealed from the compression isotherms. The latter indicate that squeezing the penetrant out of the monolayer upon compression does not allow for establishing the penetration equilibrium, so the monolayer remains supersaturated with the penetrant and shows an under-equilibrium orientation within the entire compression range, practically. PMID:24455264

  15. Surface activity coefficients of spread monolayers of behenic acid salts at air-water interface.

    PubMed

    Chattoraj, D K; Halder, E; Das, K P; Mitra, A

    2006-11-16

    The pressure-area isotherms of ionized monolayers of behenic acid at air-water interface at pH 12.0 have been obtained from the Langmuir film balance experiments under various physico-chemical conditions. The value of the measured surface pressure at a given area per molecule is equal to the sum of the ideal pressure, cohesive pressure and electrical pressure. The electrical pressure term is regarded as the sum of the pressure originating from the Gouy-Chapman double layer including discrete ion effect, ion binding and monolayer hydration effect. At a given area, the deviation of the measured surface pressure from its ideal value has been calculated in terms of the apparent surface compressibility coefficients, surface fugacity coefficients for gaseous monolayer and surface activity coefficients of solute forming two-dimensional solutions in the monolayer phase respectively. Values of all these coefficients have been calculated for different compositions of the monolayer using non-ideal gas model and Raoult's and Henry's laws modified for two-dimensional non-ideal solutions respectively. Values of these coefficients may be higher or lower than unity depending upon ionic strengths and nature of inorganic salts present in the sub-phase. Using these values of surface activity coefficients, the standard free energies of formation, of spread monolayers of salts of behenic acid have been calculated at different standard states of reference.

  16. Reactive Capture of Gold Nanoparticles by Strongly Physisorbed Monolayers on Graphite

    SciTech Connect

    Wei, Xiaoliang; Tong, Wenjun; Fidler, Vlastimil; Zimmt, Matthew B.

    2012-12-01

    Anthracene Diels Alder adducts (DAa) bearing two long side chains (H-(CH2)22O(CH2)6OCH2-) at the 1- and 5-positions form self-assembled monolayers (SAMs) at the phenyloctane - highly oriented pyrolytic graphite (HOPG) interface. The long DAa side chains promote strong physisorption of the monolayer to HOPG and maintain the monolayer morphology upon rinsing or incubation in ethanol and air-drying of the substrate. Incorporating a carboxylic acid group on the DAa core enables capture of 1 - 4 nm diameter gold nanoparticles (AuNP) provided (i) the monolayer containing DAa-carboxylic acids is treated with Cu2+ ions and (ii) the organic coating on the AuNP contains carboxylic acids (11-mercaptoundecanoic acid, MUA-AuNP). AuNP capture by the monolayer proceeds with formation of Cu2+ - carboxylate coordination complexes. The captured AuNP appear as mono- and multi-layered clusters at high coverage on HOPG. The surface density of the captured AuNPs can be adjusted from AuNP multi-layers to isolated AuNPs by varying incubation times, MUA-AuNP concentration, the number density of carboxylic acids in the monolayer, the number of MUA per AuNP, and the post-incubation treatments.

  17. Well-ordered monolayers of alkali-doped coronene and picene: Molecular arrangements and electronic structures

    SciTech Connect

    Yano, M.; Endo, M.; Hasegawa, Y.; Okada, R.; Yamada, Y. Sasaki, M.

    2014-07-21

    Adsorptions of alkali metals (such as K and Li) on monolayers of coronene and picene realize the formation of ordered phases, which serve as well-defined model systems for metal-intercalated aromatic superconductors. Upon alkali-doping of the monolayers of coronene and picene, scanning tunneling microscopy and X-ray absorption spectroscopy revealed the rearrangement of the entire molecular layer. The K-induced reconstruction of both monolayers resulted in the formation of a structure with a herringbone-like arrangement of molecules, suggesting the intercalation of alkali metals between molecular planes. Upon reconstruction, a shift in both the vacuum level and core levels of coronene was observed as a result of a charge transfer from alkali metals to coronene. In addition, a new density of states near the Fermi level was formed in both the doped coronene and the doped picene monolayers. This characteristic electronic feature of the ordered monolayer has been also reported in the multilayer picene films, ensuring that the present monolayer can model the properties of the metal-intercalated aromatic hydrocarbons. It is suggested that the electronic structure near the Fermi level is sensitive to the molecular arrangement, and that both the strict control and determinations of the molecular structure in the doped phase should be important for the determination of the electronic structure of these materials.

  18. Cobalt monolayer islands on Ag(111) for ORR catalysis.

    PubMed

    Loglio, Francesca; Lastraioli, Elisa; Bianchini, Claudio; Fontanesi, Claudio; Innocenti, Massimo; Lavacchi, Alessandro; Vizza, Francesco; Foresti, Maria Luisa

    2011-08-22

    The design of a catalyst for one of the most important electrocatalytic reactions, the oxygen reduction reaction (ORR), was done following the most recent guidelines of theoretical studies on this topic. Aim of this work was to achieve a synergic effect of two different metals acting on different steps of the ORR. The catalytic activity of Ag, already known and characterized, was enhanced by the presence of a monolayer of cobalt subdivided into nanosized islands. To obtain such a controlled nanostructure, a novel method utilizing self-assembled monolayers (SAMs) as templates was employed. In a recent study, we were able to perform a confined electrodeposition of cobalt onto Ag(111) in a template formed by selectively desorbing a short-chain thiol (3-mercaptopropionic acid, MPA) from binary SAMs using 1-dodecanthiols (DDT). This method allows for an excellent control of the morphology of the deposit by varying the molar ratio of the two thiols. Because cobalt does not deposit on silver at an underpotential, the alternative approach of surface limited redox replacement (SLRR) was used. This method, recently developed by Adžić et al., consists of the use of a monolayer of a third metal, which can be deposited at an underpotential, as a template for the spontaneous deposition of a more noble metal. Herein, we choose zinc as template for the deposition of cobalt. Ag(111) crystals were covered by monolayer islands consisting of cobalt, with the surface atomic ratios ranging from 12 to 39% for cobalt. The catalytic activity of such samples towards ORR was evaluated and the best improvement in activity was found to be that of the sample with a cobalt percentage of approximately 30% with respect to the bare silver, which is in good agreement with theoretical hypotheses.

  19. C60 fullerene promotes lung monolayer collapse

    PubMed Central

    Barnoud, Jonathan; Urbini, Laura; Monticelli, Luca

    2015-01-01

    Airborne nanometre-sized pollutants are responsible for various respiratory diseases. Such pollutants can reach the gas-exchange surface in the alveoli, which is lined with a monolayer of lung surfactant. The relationship between physiological effects of pollutants and molecular-level interactions is largely unknown. Here, we determine the effects of carbon nanoparticles on the properties of a model of lung monolayer using molecular simulations. We simulate phase-separated lipid monolayers in the presence of a model pollutant nanoparticle, C60 fullerene. In the absence of nanoparticles, the monolayers collapse only at very low surface tensions (around 0 mN m−1). In the presence of nanoparticles, instead, monolayer collapse is observed at significantly higher surface tensions (up to ca 10 mN m−1). Collapse at higher tensions is related to lower mechanical rigidity of the monolayer. It is possible that similar mechanisms operate on lung surfactant in vivo, which suggests that health effects of airborne carbon nanoparticles may be mediated by alterations of the mechanical properties of lung surfactant. PMID:25589571

  20. Studies on monolayers. Part 1. Surface tension and absorption spectroscopic measurements of monolayers of surface-active azo and stilbene dyes

    SciTech Connect

    Heesemann, J.

    1980-03-26

    In order to develop new molecules as function components of monolayer assemblies, a series of 9 surface-active azo and stilbene compounds are synthesized. Their monolayer properties at the air-water interface are studied by surface pressure-surface area measurements and spectroscopic techniques. The results show that small changes in the molecular structure of the surfactants (such as, length of the fatty acid chain and type of the chromphore) have an immense influence on the monolayer properties. For monolayers of compounds I and III-VIII, van der Walls-like isotherms are obtained, which show a liquid expanded state, a phase transition region, and a condensed state. From monolayer absorbance spectra it is found that in the liquid expanded state at 100 to 110 sq angstroms/molecule the chromphores lie flatly on the water surface, forming monomers. The phase transition region of the isotherms can be assigned to a change of orientation of the chromophore axis (horizontal to vertical) and an aggregation process of the chromophores (monomers to H aggregates). 20 references.

  1. The topology of integrable systems with incomplete fields

    SciTech Connect

    Aleshkin, K R

    2014-09-30

    Liouville's theorem holds for Hamiltonian systems with complete Hamiltonian fields which possess a complete involutive system of first integrals; such systems are called Liouville-integrable. In this paper integrable systems with incomplete Hamiltonian fields are investigated. It is shown that Liouville's theorem remains valid in the case of a single incomplete field, while if the number of incomplete fields is greater, a certain analogue of the theorem holds. An integrable system on the algebra sl(3) is taken as an example. Bibliography: 11 titles.

  2. Double Incomplete Internal Biliary Fistula: Coexisting Cholecystogastric and Cholecystoduodenal Fistula

    PubMed Central

    Beksac, Kemal; Erkan, Arman; Kaynaroglu, Volkan

    2016-01-01

    Internal biliary fistula is a rare complication of a common surgical disease, cholelithiasis. It is seen in 0.74% of all biliary tract surgeries and is thought to be a result of repeated inflammatory periods of the gallbladder. In this report we present a case of incomplete cholecystogastric and cholecystoduodenal fistulae in a single patient missed by ultrasonography and endoscopic retrograde cholangiopancreatography and diagnosed intraoperatively. In the literature there is only one report of an incomplete cholecystogastric fistula. To our knowledge this is the first case of double incomplete internal biliary fistulae. PMID:26904348

  3. Transport pathways of solid lipid nanoparticles across Madin-Darby canine kidney epithelial cell monolayer.

    PubMed

    Chai, Gui-Hong; Hu, Fu-Qiang; Sun, Jihong; Du, Yong-Zhong; You, Jian; Yuan, Hong

    2014-10-06

    An understanding of drug delivery system transport across epithelial cell monolayer is very important for improving the absorption and bioavailability of the drug payload. The mechanisms of epithelial cell monolayer transport for various nanocarriers may differ significantly due to their variable components, surface properties, or diameter. Solid lipid nanoparticles (SLNs), conventionally formed by lipid materials, have gained increasing attention in recent years due to their excellent biocompatibility and high oral bioavailability. However, there have been few reports about the mechanisms of SLNs transport across epithelial cell monolayer. In this study, the molecular mechanisms utilized by SLNs of approximately 100 nm in diameter crossing intestinal epithelial monolayer were carefully studied using a simulative intestinal epithelial monolayer formed by Madin-Darby canine kidney (MDCK) epithelial cells. The results demonstrated that SLNs transportation did not induce a significant change on tight junction structure. We found that the endocytosis of SLNs into the epithelial cells was energy-dependent and was significantly greater than nanoparticle exocytosis. The endocytosis of SLNs was found to be rarely mediated via macropinocytosis, as confirmed by the addition of 5-(N-ethyl-N-isopropyl)amiloride (EIPA) as an inhibitory agent, and mainly depended on lipid raft/caveolae- and clathrin-mediated pathways. After SLNs was internalized into MDCK cells, lysosome was one of the main destinations for these nanoparticles. The exocytosis study indicated that the endoplasmic reticulum, Golgi complex, and microtubules played important roles in the transport of SLNs out of MDCK cells. The transcytosis study indicated that only approximately 2.5% of the total SLNs was transported from the apical side to the basolateral side. For SLNs transportation in MDCK cell monolayer, greater transport (approximately 4-fold) was observed to the apical side than to the basolateral side. Our

  4. Plant development, auxin, and the subsystem incompleteness theorem.

    PubMed

    Niklas, Karl J; Kutschera, Ulrich

    2012-01-01

    Plant morphogenesis (the process whereby form develops) requires signal cross-talking among all levels of organization to coordinate the operation of metabolic and genomic subsystems operating in a larger network of subsystems. Each subsystem can be rendered as a logic circuit supervising the operation of one or more signal-activated system. This approach simplifies complex morphogenetic phenomena and allows for their aggregation into diagrams of progressively larger networks. This technique is illustrated here by rendering two logic circuits and signal-activated subsystems, one for auxin (IAA) polar/lateral intercellular transport and another for IAA-mediated cell wall loosening. For each of these phenomena, a circuit/subsystem diagram highlights missing components (either in the logic circuit or in the subsystem it supervises) that must be identified experimentally if each of these basic plant phenomena is to be fully understood. We also illustrate the "subsystem incompleteness theorem," which states that no subsystem is operationally self-sufficient. Indeed, a whole-organism perspective is required to understand even the most simple morphogenetic process, because, when isolated, every biological signal-activated subsystem is morphogenetically ineffective.

  5. [Age and aging as incomplete architecture of human ontogenesis].

    PubMed

    Baltes, P B

    1999-12-01

    The focus is on the basic biological-genetic and social-cultural architecture of human development across the life span. The starting point is the frame provided by past evolutionary forces. A first conclusion is that for modern times and the relative brevity of the time windows involved in modernity, further change in human functioning is primarily dependent on the evolution of new cultural forms of knowledge rather than evolution-based changes in the human genome. A second conclusion concerns the general architecture of the life course. Three governing lifespan developmental principles coexist. First, because long-term evolutionary selection evince a negative age correlation, genome-based plasticity and biological potential decrease with age. Second, for growth aspects of human development to extend further into the life span, culture-based resources are required at ever increasing levels. Third, because of age-related losses in biological plasticity and negative effects associated with some principles of learning (e.g., negative transfer), the efficiency of culture is reduced as lifespan development unfolds. Joint application of these principles suggests that the lifespan architecture becomes more and more incomplete with age. Three examples are given to illustrate the implications of the lifespan architecture outlined. The first is a general theory of development involving the orchestration of three component processes and their age-related dynamics: Selection, optimization, and compensation. The second example is theory and research on lifespan intelligence that distinguishes between the biology-based mechanics and culture-based pragmatics of intelligence and specifies distinct age gradients for the two categories of intellectual functioning. The third example considers the goal of evolving a positive biological and cultural scenario for the last phase of life (fourth age). Because of the general lifespan architecture outlined, this objective becomes

  6. Nanopattern formation in self-assembled monolayers of thiol-capped Au nanocrystals

    NASA Astrophysics Data System (ADS)

    Banerjee, R.; Hazra, S.; Banerjee, S.; Sanyal, M. K.

    2009-11-01

    The structure and the stability of the transferred monolayers of gold-thiol nanoparticles, formed at air-water interface at different surface pressure, on to silicon surface have been studied using two complementary techniques, x-ray reflectivity and atomic force microscopy (AFM). Networklike nanopatterns, observed through AFM, of the in-plane aggregated nanoparticles can be attributed to the late stage drying of the liquid trapped in the islands formed by nanoparticles. During drying process the trapped liquid leaves pinholes in the islands which by the process of nucleation and growth carry the mobile nanoparticles on their advancing fronts such that the nanoparticles are trapped at the boundaries of similar adjacent holes. This process continues bringing about in-plane as well as out-of-plane restructuring in the monolayer until the liquid evaporates completely rendering a patterned structure to the islands and instability in the monolayer is then stabilized.

  7. Universal Area Distributions in the Monolayers of Confluent Mammalian Cells

    NASA Astrophysics Data System (ADS)

    Wilk, Gary; Iwasa, Masatomo; Fuller, Patrick E.; Kandere-Grzybowska, Kristiana; Grzybowski, Bartosz A.

    2014-04-01

    When mammalian cells form confluent monolayers completely filling a plane, these apparently random "tilings" show regularity in the statistics of cell areas for various types of epithelial and endothelial cells. The observed distributions are reproduced by a model which accounts for cell growth and division, with the latter treated stochastically both in terms of the sizes of the dividing cells as well as the sizes of the "newborn" ones—remarkably, the modeled and experimental distributions fit well when all free parameters are estimated directly from experiments.

  8. Phase structure of a holographic double monolayer Dirac semimetal

    NASA Astrophysics Data System (ADS)

    Grignani, Gianluca; Marini, Andrea; Pigna, Adriano-Costantino; Semenoff, Gordon W.

    2016-06-01

    We study a holographic D3/probe-D5-brane model of a double monolayer Dirac semimetal in a magnetic field and in the presence of a nonzero temperature. Intra-and inter-layer exciton condensates can form by varying the balanced charge density on the layers, the spatial separation and the temperature. Constant temperature phase diagrams for a wide range of layer separations and charge densities are found. The presence of a finite temperature makes the phase diagrams extremely rich and in particular leads to the appearance of a symmetric phase which was missing at zero temperature.

  9. Incomplete and transitory decrease of glycolysis

    PubMed Central

    Schoors, Sandra; Cantelmo, Anna Rita; Georgiadou, Maria; Stapor, Peter; Wang, Xingwu; Quaegebeur, Annelies; Cauwenberghs, Sandra; Wong, Brian W; Bifari, Francesco; Decimo, Ilaria; Schoonjans, Luc; De Bock, Katrien; Dewerchin, Mieke; Carmeliet, Peter

    2014-01-01

    During vessel sprouting, a migratory endothelial tip cell guides the sprout, while proliferating stalk cells elongate the branch. Tip and stalk cell phenotypes are not genetically predetermined fates, but are dynamically interchangeable to ensure that the fittest endothelial cell (EC) leads the vessel sprout. ECs increase glycolysis when forming new blood vessels. Genetic deficiency of the glycolytic activator PFKFB3 in ECs reduces vascular sprouting by impairing migration of tip cells and proliferation of stalk cells. PFKFB3-driven glycolysis promotes the tip cell phenotype during vessel sprouting, since PFKFB3 overexpression overrules the pro-stalk activity of Notch signaling. Furthermore, PFKFB3-deficient ECs cannot compete with wild-type neighbors to form new blood vessels in chimeric mosaic mice. In addition, pharmacological PFKFB3 blockade reduces pathological angiogenesis with modest systemic effects, likely because it decreases glycolysis only partially and transiently. PMID:24335389

  10. Enantiomeric interactions between liquid crystals and organized monolayers of tyrosine-containing dipeptides.

    PubMed

    Bai, Yiqun; Abbott, Nicholas L

    2012-01-11

    We have examined the orientational ordering of nematic liquid crystals (LCs) supported on organized monolayers of dipeptides with the goal of understanding how peptide-based interfaces encode intermolecular interactions that are amplified into supramolecular ordering. By characterizing the orientations of nematic LCs (4-cyano-4'-pentylbiphenyl and TL205 (a mixture of mesogens containing cyclohexane-fluorinated biphenyls and fluorinated terphenyls)) on monolayers of l-cysteine-l-tyrosine, l-cysteine-l-phenylalanine, or l-cysteine-l-phosphotyrosine formed on crystallographically textured films of gold, we conclude that patterns of hydrogen bonds generated by the organized monolayers of dipeptides are transduced via macroscopic orientational ordering of the LCs. This conclusion is supported by the observation that the ordering exhibited by the achiral LCs is specific to the enantiomers used to form the dipeptide-based monolayers. The dominant role of the -OH group of tyrosine in dictating the patterns of hydrogen bonds that orient the LCs was also evidenced by the effects of phosphorylation of the tyrosine on the ordering of the LCs. Overall, these results reveal that crystallographic texturing of gold films can direct the formation of monolayers of dipeptides with long-range order, thus unmasking the influence of hydrogen bonding, chirality, and phosphorylation on the macroscopic orientational ordering of LCs supported on these surfaces. These results suggest new approaches based on supramolecular assembly for reporting the chemical functionality and stereochemistry of synthetic and biological peptide-based molecules displayed at surfaces.

  11. Endothelial monolayers and transendothelial migration depend on mechanical properties of the substrate.

    PubMed

    Onken, Michael D; Mooren, Olivia L; Mukherjee, Suranjana; Shahan, Stefanie T; Li, Jinmei; Cooper, John A

    2014-12-01

    Endothelial cells (ECs) line the microvasculature and constitute a barrier between the vessel lumen and surrounding tissues. ECs inform circulating immune cells of the health and integrity of surrounding tissues, recruiting them in response to pathogens and tissue damage. ECs play an active role in the transmigration of immune cells across the vessel wall. We have discovered important differences in the properties of ECs on soft hydrogel substrates of varying stiffness, in comparison to glass. Primary ECs from several human sources were tested; all formed monolayers normally on soft substrates. EC monolayers formed more mature cell-cell junctions on soft substrates, relative to glass, based on increased recruitment of vinculin and F-actin. EC monolayers supported transendothelial migration (TEM) on soft substrates. Immune cells, including peripheral blood lymphocytes (PBLs) and natural killer cells, showed decreasing numbers of paracellular (between-cell) transmigration events with decreasing substrate stiffness, while the number of transcellular (through-cell) events increased for PBLs. Melanoma cancer cells showed increased transmigration with decreased stiffness. Our findings demonstrate that endothelial monolayers respond to the mechanical properties of their surroundings, which can regulate the integrity and function of the monolayer independently from inflammatory signals. Soft hydrogel substrates are a more appropriate and physiological model for tissue environments than hard substrates, with important implications for the experimental analysis of TEM.

  12. Efficient and accurate computation of the incomplete Airy functions

    NASA Technical Reports Server (NTRS)

    Constantinides, E. D.; Marhefka, R. J.

    1993-01-01

    The incomplete Airy integrals serve as canonical functions for the uniform ray optical solutions to several high-frequency scattering and diffraction problems that involve a class of integrals characterized by two stationary points that are arbitrarily close to one another or to an integration endpoint. Integrals with such analytical properties describe transition region phenomena associated with composite shadow boundaries. An efficient and accurate method for computing the incomplete Airy functions would make the solutions to such problems useful for engineering purposes. In this paper a convergent series solution for the incomplete Airy functions is derived. Asymptotic expansions involving several terms are also developed and serve as large argument approximations. The combination of the series solution with the asymptotic formulae provides for an efficient and accurate computation of the incomplete Airy functions. Validation of accuracy is accomplished using direct numerical integration data.

  13. Phase-Specific Diffusivity of DPPG Monolayers

    NASA Astrophysics Data System (ADS)

    Dewitt, Joel; Thapa, Prem; Flanders, Bret

    2004-03-01

    The primary role of lung surfactant is to reduce the alveolar surface tension during exhalation in a reversible manner. Failure to do so results in respiratory distress syndrome. Model lung surfactants provide simplified systems for studying the mechanisms that underlie this essential role of alveolar surfactant. Dipalmitoyl-phosphatidylglycerol (DPPG) monolayers exhibit reversible folding when compressed to a critical surface tension. This process may exemplify how the compression-expansion cycle attains reversibility and, thus, requires penetrating study. The buckling theory for reversible collapse provides a promising though untested description of this process, but poor knowledge of domain boundary widths in DPPG monolayers impedes the evaluation of this theory as a model for the observed behavior. In turn, the measurement of the domain boundary widths requires knowledge of the phase-specific viscosities of the monolayer. In this study, multi-particle tracking has been used to determine the phase-specific diffusion coefficients of polystyrene spheres embedded in DPPG monolayers. By invoking a Stokes-Einstein relationship that is appropriate for spheres diffusing in a viscous surfactant, the phase specific viscosities of the monolayers have been estimated. The rationale for this work is that this knowledge will promote the quantitative evaluation of buckling as a model for reversible folding and, thus, promote growth in understanding of the folding mechanism in model lung surfactants.

  14. Constructivism and empiricism: An incomplete divorce

    NASA Astrophysics Data System (ADS)

    Matthews, Michael R.

    1992-12-01

    The paper outlines the significant influence of constructivism in contemporary science and mathematics education, and emphasises the central role that epistemology plays in constructivist theory and practice. It is claimed that despite the anti-empiricism of much constructivist writing, in most forms its epistemology is nevertheless firmly empiricist. In particular it is subject-centered and experience-based. It is argued that its relativist, if not skeptical conclusions, only follow given these empiricist assumptions. Further it is suggested that such assumptions belong to Aristotelian science, and were effectively overthrown with the modern science of Galileo and Newton. Thus constructivism cannot provide understanding of post-Aristotelian science.

  15. Effect of the degree of dissociation of molecules in a monolayer at an air/water interface on the force between the monolayer and a like-charged particle in the subphase.

    PubMed

    McNamee, Cathy E; Kappl, Michael; Butt, Hans-Juergen; Nguyen, Hang; Sato, Shinichiro; Graf, Karlheinz; Healy, Thomas W

    2012-11-26

    We used the monolayer particle interaction apparatus to measure the force between a monolayer of stearic acid or octadecanol at the air/water interface and a colloidal silica sphere. The silica sphere approached the monolayer from the aqueous subphase. The aim was to analyze how the magnitude of the charge of a deformable interface affects the interaction between that interface and a like-charged hard particle. The charge density of the stearic acid monolayer was controlled by adjusting the pH (5.8-9) and the surface pressure. The octadecanol monolayer acted as a reference; the alcohol headgroup did not dissociate between pH 5.8-9.0. Stable monolayers of dissociated stearic acid molecules were formed at the air/water interface by dissolving stearic acid into the subphase to give a saturated concentration at each pH value studied. The approach force curve showed that the electrostatic repulsion increased with an increasing degree of dissociation and therefore the charge of the monolayer. The strength of the repulsion corresponded to that measured between two like-charged hard surfaces, but the apparent range of the repulsion was larger for a deformable interface. Retracting force curves displayed a significant adhesion, whose magnitude and range depended on the surface pressure and subphase pH.

  16. The melting of pulmonary surfactant monolayers.

    PubMed

    Yan, Wenfei; Biswas, Samares C; Laderas, Ted G; Hall, Stephen B

    2007-05-01

    Monomolecular films of phospholipids in the liquid-expanded (LE) phase after supercompression to high surface pressures (pi), well above the equilibrium surface pressure (pi(e)) at which fluid films collapse from the interface to form a three-dimensional bulk phase, and in the tilted-condensed (TC) phase both replicate the resistance to collapse that is characteristic of alveolar films in the lungs. To provide the basis for determining which film is present in the alveolus, we measured the melting characteristics of monolayers containing TC dipalmitoyl phosphatidylcholine (DPPC), as well as supercompressed 1-palmitoyl-2-oleoyl phosphatidylcholine and calf lung surfactant extract (CLSE). Films generated by appropriate manipulations on a captive bubble were heated from < or =27 degrees C to > or =60 degrees C at different constant pi above pi(e). DPPC showed the abrupt expansion expected for the TC-LE phase transition, followed by the contraction produced by collapse. Supercompressed CLSE showed no evidence of the TC-LE expansion, arguing that supercompression did not simply convert the mixed lipid film to TC DPPC. For both DPPC and CLSE, the melting point, taken as the temperature at which collapse began, increased at higher pi, in contrast to 1-palmitoyl-2-oleoyl phosphatidylcholine, for which higher pi produced collapse at lower temperatures. For pi between 50 and 65 mN/m, DPPC melted at 48-55 degrees C, well above the main transition for bilayers at 41 degrees C. At each pi, CLSE melted at temperatures >10 degrees C lower. The distinct melting points for TC DPPC and supercompressed CLSE provide the basis by which the nature of the alveolar film might be determined from the temperature-dependence of pulmonary mechanics.

  17. The melting of pulmonary surfactant monolayers

    PubMed Central

    Yan, Wenfei; Biswas, Samares C.; Laderas, Ted G.; Hall, Stephen B.

    2012-01-01

    Monomolecular films of phospholipids in the liquid-expanded (LE) phase after supercompression to high surface pressures (π), well above the equilibrium surface pressure (πe) at which fluid films collapse from the interface to form a three-dimensional bulk phase, and in the tilted-condensed (TC) phase both replicate the resistance to collapse that is characteristic of alveolar films in the lungs. To provide the basis for determining which film is present in the alveolus, we measured the melting characteristics of monolayers containing TC dipalmitoyl phosphatidylcholine (DPPC), as well as supercompressed 1-palmitoyl-2-oleoyl phosphatidylcholine and calf lung surfactant extract (CLSE). Films generated by appropriate manipulations on a captive bubble were heated from ≤27°C to ≥60°C at different constant π above πe. DPPC showed the abrupt expansion expected for the TC-LE phase transition, followed by the contraction produced by collapse. Supercompressed CLSE showed no evidence of the TC-LE expansion, arguing that supercompression did not simply convert the mixed lipid film to TC DPPC. For both DPPC and CLSE, the melting point, taken as the temperature at which collapse began, increased at higher π, in contrast to 1-palmitoyl-2-oleoyl phosphatidylcholine, for which higher π produced collapse at lower temperatures. For π between 50 and 65 mN/m, DPPC melted at 48–55°C, well above the main transition for bilayers at 41°C. At each π, CLSE melted at temperatures >10°C lower. The distinct melting points for TC DPPC and supercompressed CLSE provide the basis by which the nature of the alveolar film might be determined from the temperature-dependence of pulmonary mechanics. PMID:17194731

  18. Electrical Performance of Monolayer MoS2 Field-Effect Transistors Prepared by Chemical Vapor Deposition

    DTIC Science & Technology

    2013-05-16

    REPORT Electrical performance of monolayer MoS2 field-effect transistors prepared by chemical vapor deposition 14. ABSTRACT 16. SECURITY CLASSIFICATION...OF: Molybdenum disulfide ( MoS2 ) field effect transistors (FET) were fabricated on atomically smooth large-area single layers grown by chemical vapor...Standard Form 298 (Rev 8/98) Prescribed by ANSI Std. Z39.18 - Electrical performance of monolayer MoS2 field-effect transistors prepared by chemical

  19. Giant piezoelectricity of monolayer group IV monochalcogenides

    NASA Astrophysics Data System (ADS)

    Fei, Ruixiang; Li, Wenbin; Li, Ju; Yang, Li

    We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M =Sn or Ge, X =Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS2 and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique ``puckered'' C2v symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.

  20. Edge plasmons in monolayer black phosphorus

    NASA Astrophysics Data System (ADS)

    Bao, Zhi-Wei; Wu, Hong-Wei; Zhou, Yu

    2016-12-01

    In this paper, we numerically investigate the edge plasmons in monolayer black phosphorus. It is found that the complex effective indexes of these modes depend on the molecular configuration of the edge. We have calculated the ratio of the real over the imaginary part of the mode effective index, and the results indicate that such edge modes indeed possess outstanding propagation performances in the mid-infrared. In the case of black phosphorus nanoribbon, it seems that only the anti-symmetric modes have low losses, and may be of use in applications. Compared with those at the edge of monolayer black phosphorus, the propagation performances can be further enhanced due to the mode coupling between the two edges. In the end, the effects of substrates are discussed. Our study shows that monolayer black phosphorus may be regarded as a promising candidate for plasmonic applications in the mid-infrared.

  1. Magneto photoluminescence measurements of tungsten disulphide monolayers

    NASA Astrophysics Data System (ADS)

    Kuhnert, Jan; Rahimi-Iman, Arash; Heimbrodt, Wolfram

    2017-03-01

    Layered transition-metal dichalcogenides have attracted great interest in the last few years. Thinned down to the monolayer limit they change from an indirect band structure to a direct band gap in the visible region. Due to the monolayer thickness the inversion symmetry of the crystal is broken and spin and valley are coupled to each other. The degeneracy between the two equivalent valleys, K and K‧, respectively, can be lifted by applying an external magnetic field. Here, we present photoluminescence measurements of CVD-grown tungsten disulphide (WS2) monolayers at temperatures of 2 K. By applying magnetic fields up to 7 T in Faraday geometry, a splitting of the photoluminescence peaks can be observed. The magnetic field dependence of the A-exciton, the trion and three bound exciton states is discussed and the corresponding g-factors are determined.

  2. Monolayer culture systems with respiratory epithelial cells for evaluation of bacterial invasiveness.

    PubMed

    Hirakata, Yoichi; Yano, Hisakazu; Arai, Kazuaki; Endo, Shiro; Kanamori, Hajime; Aoyagi, Tetsuji; Hirotani, Ayako; Kitagawa, Miho; Hatta, Masumitsu; Yamamoto, Natsuo; Kunishima, Hiroyuki; Kawakami, Kazuyoshi; Kaku, Mitsuo

    2010-01-01

    Pseudomonas (P.) aeruginosa is a major opportunistic pathogen especially in immunocompromised patients. To evaluate the invasiveness of respiratory pathogens, we developed monolayer culture systems and examined the degree of invasion by P. aeruginosa and invasive Salmonella (S.) typhimurium strains using human respiratory cell lines: A549 (derived from lung cancer), BEAS-2B (normal bronchial epithelium), and Calu-3 (pleural effusion of a patient with adenocarcinoma of the lung). Cells were seeded into filter units containing 0.33 cm(2) filter membranes with 3.0 microm pores, and were incubated at 37 degrees C under 5% CO(2) for 4-10 days. By monitoring the trans-monolayer electrical resistance (TER), we judged that BEAS-2B cells (TER values: 436.2 +/- 16.8 to 628.8 +/- 66.3 Omega cm(2)) and Calu-3 cells (TER values: 490.5 +/- 25.2 to 547.8 +/- 21.6 Omega cm(2)) formed monolayers with tight junctions, but not A549 cells. On day 8 of culture, monolayer cultures were infected with bacteria, and the number of microorganisms penetrating into the basolateral medium was counted. Wild-type P. aeruginosa PAO1 (PAO1 WT) and S. typhimurium SL1344 were detected in the basolateral medium of BEAS-2B monolayer system by 3 h after inoculation, while only P. aeruginosa PAO1 WT was detected in the basolateral medium of Calu-3 monolayer, indicating poor invasiveness of S. typhimurium SL1344 in the Calu-3 system. These findings suggest that BEAS-2B or Calu-3 monolayer system could be useful for evaluating the invasiveness of respiratory pathogens. Because of the difference in bacterial invasiveness, we may need to choose a suitable cell system for each target pathogen.

  3. Incomplete Relaxation between Beats after Myocardial Hypoxia and Ischemia

    PubMed Central

    Weisfeldt, Myron L.; Armstrong, Paul; Scully, Hugh E.; Sanders, Charles A.; Daggett, Willard M.

    1974-01-01

    Recovery from hypoxia has been shown to prolong cardiac muscle contraction, particularly the relaxation phase. The present studies were designed to examine whether incomplete relaxation between beats can result from this prolongation of contraction and relaxation in isolated muscle after hypoxia and in the canine heart after both hypoxia and acute ischemia. The relationship between heart rate and the extent of incomplete relaxation is emphasized in view of the known enhancement of the velocity of contraction caused by increasing heart rate. The extent of incomplete relaxation during 10-s periods of pacing at increasing rates was examined before and after hypoxia in isometric cat right ventricular papillary muscle (12-120 beats/min) and in the canine isovolumic left ventricle (120-180 beats/min). Incomplete relaxation was quantified by measuring the difference between the lowest diastolic tension or pressure during pacing and the true resting tension or pressure determined by interruption of pacing at each rate. In eight cat papillary muscles (29°C), there was significantly greater incomplete relaxation 5 min after hypoxia at rates of 96 and 120 beats/min (P < 0.02 vs. before hypoxia). In seven canine isovolumic left ventricles, recovery from hypoxia and higher heart rates also resulted in incomplete relaxation. Incomplete relaxation before hypoxia at a rate of 180 beats/min was 0.8±0.5 cm H2O and at 5 min of recovery from hypoxia was 12.6±3.5 cm H2O (P < 0.01). 12 hearts were subjected to a 1.5-3-min period of acute ischemia and fibrillation. There was significant incomplete relaxation at a rate of 140 beats/min for 5 min after defibrillation and reperfusion. These data indicate that incomplete relaxation is an important determinant of diastolic hemodynamics during recovery from ischemia or hypoxia. The extent of incomplete relaxation appears to be a function of the rate of normalization of the velocity of relaxation and tension development after ischemia or

  4. Effect of perfluoroalkyl chain length on monolayer behavior of partially fluorinated oleic acid molecules at the air-water interface.

    PubMed

    Baba, Teruhiko; Takai, Katsuki; Takagi, Toshiyuki; Kanamori, Toshiyuki

    2013-01-01

    A series of oleic acid (OA) analogs containing terminal perfluoroalkyl groups (CF3, C2F5, n-C3F7, n-C4F9 or n-C8F17) was synthesized to clarify how the fluorinated chain length affects the stability and molecular packing of liquid-expanded OA monolayers at the air-water interface. Although the substitution of terminal CF3 group for CH3 in OA had no effect on monolayer stability, further fluorination led to a gradual increase in monolayer stability at 25 °C. Surface pressure-area isotherm revealed that partially fluorinated OA analogs form more expanded monolayers than OA at low surface pressures, and that the monolayer behavior of OA analogs with the even-carbon numbered fluorinated chain is almost the same as that of OA upon monolayer compression, whereas the behavior of OA analogs with the odd-carbon numbered fluorinated chain significantly differs from that of OA. These results indicate: (i) the terminal short part (at least C2 residue) in OA predominantly determines the liquid-expanded monolayer stability; (ii) the molecular packing state of OA may be perturbed by the substitution of a short odd-carbon numbered fluorinated chain; (iii) hence, OA analogs with even-carbon numbered chain are considered to be preferable as hydrophobic building blocks for the synthesis of fluorinated phospholipids.

  5. Stiffness of lipid monolayers with phase coexistence.

    PubMed

    Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia

    2013-08-27

    The surface dilational modulus--or compressibility modulus--has been previously studied for monolayers composed of pure materials, where a jump in this modulus was related with the onset of percolation as a result of the establishment of a connected structure at the molecular level. In this work, we focused on monolayers composed of two components of low lateral miscibility. Our aim was to investigate the compressibility of mixed monolayers at pressures and compositions in the two-phase region of the phase diagram, in order to analyze the effect of the mechanical properties of each phase on the stiffness of the composite. In nine different systems with distinct molecular dipoles and charges, the stiffness of each phase and the texture at the plane of the monolayer were studied. In this way, we were able to analyze the general compressibility of two-phase lipid monolayers, regardless of the properties of their constituent parts. The results are discussed in the light of the following two hypotheses: first, the stiffness of the composite could be dominated by the stiffness of each phase as a weighted sum according to the percentage of each phase area, regardless of the distribution of the phases in the plane of the monolayer. Alternatively, the stiffness of the composite could be dominated by the mechanical properties of the continuous phase. Our results were better explained by this latter proposal, as in all the analyzed mixtures it was found that the mechanical properties of the percolating phase were the determining factors. The value of the compression modulus was closer to the value of the connected phase than to that of the dispersed phase, indicating that the bidimensional composites displayed mechanical properties that were related to the properties of each phases in a rather complex manner.

  6. Active Tensile Modulus of an Epithelial Monolayer

    NASA Astrophysics Data System (ADS)

    Vincent, Romaric; Bazellières, Elsa; Pérez-González, Carlos; Uroz, Marina; Serra-Picamal, Xavier; Trepat, Xavier

    2015-12-01

    A general trait of cell monolayers is their ability to exert contractile stresses on their surroundings. The scaling laws that link such contractile stresses with the size and geometry of constituent cells remain largely unknown. In this Letter, we show that the active tension of an epithelial monolayer scales linearly with the size of the constituent cells, a surprisingly simple relationship. The slope of this relationship defines an active tensile modulus, which depends on the concentration of myosin and spans more than 2 orders of magnitude across cell types and molecular perturbations.

  7. Monochromatic electron photoemission from diamondoid monolayers

    SciTech Connect

    Yang, Wanli; Yang, Wanli L.; Fabbri, J.D.; Willey, T.M.; Lee, J.R.I.; Dahl, J.E.; Carlson, R.M.K.; Schreiner, P.R.; Fokin, A.A.; Tkachenko, B.A.; Fokina, N.A.; Meevasana, W.; Mannella, N.; Tanaka, K.; Zhou, X.J.; van Buuren, T.; Kelly, M.A.; Hussain, Z.; Melosh, N.A.; Shen, Z.-X.

    2007-02-27

    We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68percent of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flatpanel displays.

  8. Monochromatic Electron Photoemission from DiamondoidMonolayers

    SciTech Connect

    Yang, W.L.

    2010-04-15

    We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68% of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flat-panel displays.

  9. Low temperature photoresponse of monolayer tungsten disulphide

    SciTech Connect

    Cao, Bingchen; Shen, Xiaonan; Shang, Jingzhi; Cong, Chunxiao; Yang, Weihuang; Eginligil, Mustafa E-mail: meginligil@ntu.edu.sg; Yu, Ting E-mail: meginligil@ntu.edu.sg

    2014-11-01

    High photoresponse can be achieved in monolayers of transition metal dichalcogenides. However, the response times are inconveniently limited by defects. Here, we report low temperature photoresponse of monolayer tungsten disulphide prepared by exfoliation and chemical vapour deposition (CVD) method. The exfoliated device exhibits n-type behaviour; while the CVD device exhibits intrinsic behaviour. In off state, the CVD device has four times larger ratio of photoresponse for laser on/off and photoresponse decay–rise times are 0.1 s (limited by our setup), while the exfoliated device has few seconds. These findings are discussed in terms of charge trapping and localization.

  10. Interface exciton at lateral heterojunction of monolayer semiconductors

    NASA Astrophysics Data System (ADS)

    Lau, Ka Wai; Gong, Zhirui; Yu, Hongyi; Yao, Wang

    Heterostructures based on 2D transition metal dichalcogenides (TMDs) have attracted extensive research interest recently due to the appealing physical properties of TMDs and new geometries for forming heterostructures. One such heterostructure is the lateral heterojunctions seamlessly formed in a monolayer crystal between two different types of TMDs, e.g. WSe2 and MoSe2. Such heterojunction exhibits a type II band alignment, with electrons (holes) having lower energy on the MoSe2 (WSe2) region. Here we present the study of an interface exciton at the 1D lateral junction of monolayer TMDs. With the distance dependent screening, we find that the interface exciton can have strong binding even though the electron-hole separation is much larger compare to the 2D excitons in TMDs. Neutral excitons are studied using two different approaches: the solution based on a real-space tight binding model, and the perturbation expansion in a hydrogen-like basis in an effective mass model. We have also used the latter method to study charged excitons at a MoSe2-WSe2-MoSe2 nanoscale junction. The work is supported by the Research Grant Council of Hong Kong (HKU705513P, HKU9/CRF/13G), the Croucher Foundation, and the HKU OYRA.

  11. Observation of negative terahertz photoconductivity in monolayer MoS2 under femtosecond laser excitation

    NASA Astrophysics Data System (ADS)

    Lui, Chun Hung; Frenzel, Alex J.; Pilon, Daniel V.; Lee, Yi-Hsien; Kong, Jing; Gedik, Nuh

    2014-03-01

    We observed a pronounced transient decrease of terahertz conductivity in doped monolayer molybdenum disulfide (MoS2) after pulsed laser excitation. This anomalous phenomenon arises from the strong many-body interactions in the system, where optically produced electron-hole pairs join the doped charges to form trions, bound states of two electrons and one hole, and substantially diminish the carrier conductivity by the resulting increase of effective mass. Our results reveal the ultrafast formation and decay of trions in monolayer MoS2 and their influence on the conductivity of the material.

  12. Mediatorless solar energy conversion by covalently bonded thylakoid monolayer on the glassy carbon electrode.

    PubMed

    Lee, Jinhwan; Im, Jaekyun; Kim, Sunghyun

    2016-04-01

    Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C-C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230 nA cm(-2) was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification.

  13. More than a monolayer: relating lung surfactant structure and mechanics to composition.

    PubMed

    Alonso, Coralie; Alig, Tim; Yoon, Joonsung; Bringezu, Frank; Warriner, Heidi; Zasadzinski, Joseph A

    2004-12-01

    Survanta, a clinically used bovine lung surfactant extract, in contact with surfactant in the subphase, shows a coexistence of discrete monolayer islands of solid phase coexisting with continuous multilayer "reservoirs" of fluid phase adjacent to the air-water interface. Exchange between the monolayer, the multilayer reservoir, and the subphase determines surfactant mechanical properties such as the monolayer collapse pressure and surface viscosity by regulating solid-fluid coexistence. Grazing incidence x-ray diffraction shows that the solid phase domains consist of two-dimensional crystals similar to those formed by mixtures of dipalmitoylphosphatidylcholine and palmitic acid. The condensed domains grow as the surface pressure is increased until they coalesce, trapping protrusions of liquid matrix. At approximately 40 mN/m, a plateau exists in the isotherm at which the solid phase fraction increases from approximately 60 to 90%, at which the surface viscosity diverges. The viscosity is driven by the percolation of the solid phase domains, which depends on the solid phase area fraction of the monolayer. The high viscosity may lead to high monolayer collapse pressures, help prevent atelectasis, and minimize the flow of lung surfactant out of the alveoli due to surface tension gradients.

  14. Continuity of Monolayer-Bilayer Junctions for Localization of Lipid Raft Microdomains in Model Membranes

    PubMed Central

    Ryu, Yong-Sang; Wittenberg, Nathan J.; Suh, Jeng-Hun; Lee, Sang-Wook; Sohn, Youngjoo; Oh, Sang-Hyun; Parikh, Atul N.; Lee, Sin-Doo

    2016-01-01

    We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed between the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates. PMID:27230411

  15. Continuity of monolayer-bilayer junctions for localization of lipid raft microdomains in model membranes

    SciTech Connect

    Ryu, Yong -Sang; Wittenberg, Nathan J.; Suh, Jeng -Hun; Lee, Sang -Wook; Sohn, Youngjoo; Oh, Sang -Hyun; Parikh, Atul N.; Lee, Sin -Doo

    2016-05-27

    We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed between the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Furthermore, our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates.

  16. Formation of protein molecular imprints within Langmuir monolayers: a quartz crystal microbalance study.

    PubMed

    Turner, Nicholas W; Wright, Bryon E; Hlady, Vladimir; Britt, David W

    2007-04-01

    Protein imprinting leading to enhanced rebinding of ferritin to ternary lipid monolayers is demonstrated using a quartz crystal microbalance. Monolayers consisting of cationic dioctadecyldimethylammonium bromide, non-ionic methyl stearate, and poly(ethylene glycol) bearing phospholipids were imprinted with ferritin at the air/water interface of a Langmuir-Blodgett trough and transferred hydrated to hydrophobic substrates for study. This immobilization was shown by fluorescence correlation spectroscopy to significantly hinder any further diffusion of lipids, while rebinding studies demonstrated up to a six-fold increase in ferritin adsorption to imprinted versus control monolayers. A diminished rebinding of ferritin to its imprint was observed through pH reduction to below the protein isoelectric point, demonstrating the electrostatic nature of the interaction. Rebinding to films where imprint pockets remained occupied by the template protein was also minimal. Studies with a smaller acidic protein revealed the importance of the steric influence of poly(ethylene glycol) in forming the protein binding pockets, as albumin-imprinted monolayers showed low binding of ferritin, while ferritin-imprinted monolayers readily accommodated albumin. The controllable structure-function relationship and limitations of this system are discussed with respect to the application of protein imprinting in sensor development as well as fundamental studies of proteins at dynamic interfaces.

  17. Transport of Antihypertensive Peptide RVPSL, Ovotransferrin 328-332, in Human Intestinal Caco-2 Cell Monolayers.

    PubMed

    Ding, Long; Wang, Liying; Zhang, Yan; Liu, Jingbo

    2015-09-23

    The objective of this study was to investigate the transepithelial transport of RVPSL (Arg-Val-Pro-Ser-Leu), an egg-white-derived peptide with angiotensin I-converting enzyme (ACE) inhibitory and antihypertensive activity, in human intestinal Caco-2 cell monolayers. Results revealed that RVPSL could be passively transported across Caco-2 cell monolayers. However, during the process of transport, 36.31% ± 1.22% of the initial RVPSL added to the apical side was degraded, but this degradation decreased to 23.49% ± 0.68% when the Caco-2 cell monolayers were preincubated with diprotin A (P < 0.001), suggesting that RVPSL had a low resistance to various brush border membrane peptidases. When transport from the apical side to the basolateral side was investigated, the apparent permeability coefficient (Papp) was (6.97 ± 1.11) × 10(-6) cm/s. The transport route of RVPSL appears to be the paracellular pathway via tight junctions, as only cytochalasin D, a disruptor of tight junctions (TJs), significantly increased the transport rate (P < 0.001). In addition, the relationship between the structure of RVPSL and transport across Caco-2 cell monolayers was studied by mutation of RVPSL. It was found that N-terminal Pro residues were more beneficial for transport of pentapeptides across Caco-2 cell monolayers than Arg and Val. Furthermore, RVPSL could be more easily transported as smaller peptides, especially in the form of dipeptides and tripeptides.

  18. Continuity of monolayer-bilayer junctions for localization of lipid raft microdomains in model membranes

    DOE PAGES

    Ryu, Yong -Sang; Wittenberg, Nathan J.; Suh, Jeng -Hun; ...

    2016-05-27

    We show that the selective localization of cholesterol-rich domains and associated ganglioside receptors prefer to occur in the monolayer across continuous monolayer-bilayer junctions (MBJs) in supported lipid membranes. For the MBJs, glass substrates were patterned with poly(dimethylsiloxane) (PDMS) oligomers by thermally-assisted contact printing, leaving behind 3 nm-thick PDMS patterns. The hydrophobicity of the transferred PDMS patterns was precisely tuned by the stamping temperature. Lipid monolayers were formed on the PDMS patterned surface while lipid bilayers were on the bare glass surface. Due to the continuity of the lipid membranes over the MBJs, essentially free diffusion of lipids was allowed betweenmore » the monolayer on the PDMS surface and the upper leaflet of the bilayer on the glass substrate. The preferential localization of sphingomyelin, ganglioside GM1 and cholesterol in the monolayer region enabled to develop raft microdomains through coarsening of nanorafts. Furthermore, our methodology provides a simple and effective scheme of non-disruptive manipulation of the chemical landscape associated with lipid phase separations, which leads to more sophisticated applications in biosensors and as cell culture substrates.« less

  19. Visualizing X-ray Beam Damage of a Langmuir Monolayer via GIXD and Brewster Angle Microscopy

    NASA Astrophysics Data System (ADS)

    Lin, B.; Danauskas, S.; Ishitsuka, Y.; Ratajczak, M.; Lee, K. Y. C.; Gebhardt, J.; Schultz, D.; Meron, M.

    2007-03-01

    The extent and form of radioactive beam damage from high brilliance x-ray sources has been debated among researchers who study biological membranes. It has been shown that radiation damage increases during x-ray measurements as a function of time. However, this damage has not been optically observed on the micrometer scale for lipid membranes. Here we report the observation on the effect of radiation on a lipid monolayer of DMPS (1,2-Dimyristoyl-sn-Glycero-3-[Phospho-L-Serine]) with grazing incident x-ray diffraction in conjunction with in situ Brewster Angle Microscopy (BAM). The measurements were done in an oxygenated atmosphere, at a surface pressure of 25 mN/m and at room temperature. Under these conditions the monolayer is fully condensed, and the GIXD measurement shows a single first order diffraction peak. When the surface pressure is held constant, the GIXD peak height decreases over time. In addition, the BAM shows patches of lowered refractive index for the monolayer, indicating that these areas no longer contain lipids in the condensed phase. When the surface area is held constant, irradiation of the monolayer leads to a dramatic change in surface morphology as part of the condensed phase of the monolayer becomes disordered.

  20. Azobenzene-based photomechanical monolayers as light-addressable nano-engineered structures.

    NASA Astrophysics Data System (ADS)

    Dahdah, J. M.; Furtak, T. E.; Walba, D. M.; Fang, G.; Yi, Y.; Maclennan, J. E.; Clark, N. A.

    2007-03-01

    Azobenzene-based photomechanical monolayers have received a great deal of attention for their potential as platforms for light-addressable nano-engineered structures in bioscience, photonics, and display technologies. We have developed an aminoazobenzene material (d-MR), derived from methyl red, which forms high-quality, covalently anchored monolayers on glass. These monolayers demonstrate unusually high sensitivity to polarized light, which controls the molecular orientation distribution through optical anisotropy of the trans-cis isomerization. In an effort to understand and optimize this phenomenon we are studying the influence of the two-dimensional molecular field on the dynamics of the light-driven reorganization. We have correlated the behavior of d-MR monolayers, as determined by spectral studies of dichroism and differential reflection ellipsometry, to dilute solutions of d-MR in a variety of solvents, as characterized by absorption cross sections, quantum yields, and characteristic time constants. The resulting information has helped to clarify the details of how these molecules respond to light leading to design strategies for even higher performing monolayers.

  1. Strictly monolayer large continuous MoS2 films on diverse substrates and their luminescence properties

    NASA Astrophysics Data System (ADS)

    Mohapatra, P. K.; Deb, S.; Singh, B. P.; Vasa, P.; Dhar, S.

    2016-01-01

    Despite a tremendous interest on molybdenum disulfide as a thinnest direct band gap semiconductor, single step synthesis of a large area purely monolayer MoS2 film has not yet been reported. Here, we report a CVD route to synthesize a continuous film of strictly monolayer MoS2 covering an area as large as a few cm2 on a variety of different substrates without using any seeding material or any elaborate pretreatment of the substrate. This is achieved by allowing the growth to take place in the naturally formed gap between a piece of SiO2 coated Si wafer and the substrate, when the latter is placed on top of the former inside a CVD reactor. We propose a qualitative model to explain why the MoS2 films are always strictly monolayer in this method. The photoluminescence study of these monolayers shows the characteristic excitonic and trionic features associated with monolayer MoS2. In addition, a broad defect related luminescence band appears at ˜1.7 eV. As temperature decreases, the intensity of this broad feature increases, while the band edge luminescence reduces.

  2. Characterization and reactivity of organic monolayers on gold and platinum surfaces

    SciTech Connect

    Wu, Chien-Ching

    1995-12-06

    Purpose is to understand how the mobilization, dielectric, orientation, composition, coverage, and structure of self-assembled organic monolayers on metal surfaces affects the surface reactivities and properties of these films in order to facilitate the construction of desired films. Two model systems were used: tiols at Au and aromatic acids at Pt. Surface analysis methods, including contact angle, electrochemistry, ellipsometry, infrared reflection absorption spectroscopy (IRRAS), and x-ray photospectroscopy, were used to study the self-assembled organic monolayers on Au and Pt. IRRAS, contact angle, and electrochemistry were used to determine the surface pKa of phenylcarboxylic acids and pyridylcarboxylic acids monolayers on Pt. These techniques were also used to determine the orientation of polymethylene chain axis and the carboxylic follow the structural evolution of the chains and end group of the thiolate monolayers during formation. IRRAS was also used to assess the carboxylic acid group in terms of its possible existence as the non-hydrogen-bonded species, the hydrogen-bonded dimeric group, and the hydrogen-bonded polymeric group. These different forms of the end group were also followed vs coverage, as well as the reactivity vs solution pH. IRRAS and contact angle were used to calculate the rate constant of the esterification of carboxylic acid-terminated monolayers on Au.

  3. Monolayer-to-bilayer transformation of silicenes and their structural analysis

    PubMed Central

    Yaokawa, Ritsuko; Ohsuna, Tetsu; Morishita, Tetsuya; Hayasaka, Yuichiro; Spencer, Michelle J. S.; Nakano, Hideyuki

    2016-01-01

    Silicene, a two-dimensional honeycomb network of silicon atoms like graphene, holds great potential as a key material in the next generation of electronics; however, its use in more demanding applications is prevented because of its instability under ambient conditions. Here we report three types of bilayer silicenes that form after treating calcium-intercalated monolayer silicene (CaSi2) with a BF4− -based ionic liquid. The bilayer silicenes that are obtained are sandwiched between planar crystals of CaF2 and/or CaSi2, with one of the bilayer silicenes being a new allotrope of silicon, containing four-, five- and six-membered sp3 silicon rings. The number of unsaturated silicon bonds in the structure is reduced compared with monolayer silicene. Additionally, the bandgap opens to 1.08 eV and is indirect; this is in contrast to monolayer silicene which is a zero-gap semiconductor. PMID:26847858

  4. Reversible monolayer-to-crystalline phase transition in amphiphilic silsesquioxane at the air-water interface

    PubMed Central

    Banerjee, R.; Sanyal, M. K.; Bera, M. K.; Gibaud, A.; Lin, B.; Meron, M.

    2015-01-01

    We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initial monolayer state. The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate. PMID:25687953

  5. Identification of a Novel Parallel β‐Strand Conformation within Molecular Monolayer of Amyloid Peptide

    PubMed Central

    Liu, Lei; Li, Qiang; Zhang, Shuai; Wang, Xiaofeng; Hoffmann, Søren Vrønning; Li, Jingyuan; Liu, Zheng

    2016-01-01

    The differentiation of protein properties and biological functions arises from the variation in the primary and secondary structure. Specifically, in abnormal assemblies of protein, such as amyloid peptide, the secondary structure is closely correlated with the stable ensemble and the cytotoxicity. In this work, the early Aβ33‐42 aggregates forming the molecular monolayer at hydrophobic interface are investigated. The molecular monolayer of amyloid peptide Aβ33‐42 consisting of novel parallel β‐strand‐like structure is further revealed by means of a quantitative nanomechanical spectroscopy technique with force controlled in pico‐Newton range, combining with molecular dynamic simulation. The identified parallel β‐strand‐like structure of molecular monolayer is distinct from the antiparallel β‐strand structure of Aβ33‐42 amyloid fibril. This finding enriches the molecular structures of amyloid peptide aggregation, which could be closely related to the pathogenesis of amyloid disease. PMID:27818898

  6. Monolayer-to-bilayer transformation of silicenes and their structural analysis

    NASA Astrophysics Data System (ADS)

    Yaokawa, Ritsuko; Ohsuna, Tetsu; Morishita, Tetsuya; Hayasaka, Yuichiro; Spencer, Michelle J. S.; Nakano, Hideyuki

    2016-02-01

    Silicene, a two-dimensional honeycomb network of silicon atoms like graphene, holds great potential as a key material in the next generation of electronics; however, its use in more demanding applications is prevented because of its instability under ambient conditions. Here we report three types of bilayer silicenes that form after treating calcium-intercalated monolayer silicene (CaSi2) with a BF4- -based ionic liquid. The bilayer silicenes that are obtained are sandwiched between planar crystals of CaF2 and/or CaSi2, with one of the bilayer silicenes being a new allotrope of silicon, containing four-, five- and six-membered sp3 silicon rings. The number of unsaturated silicon bonds in the structure is reduced compared with monolayer silicene. Additionally, the bandgap opens to 1.08 eV and is indirect; this is in contrast to monolayer silicene which is a zero-gap semiconductor.

  7. Neutron reflectivity studies on the DNA adsorption on lipid monolayers at the air liquid interface

    NASA Astrophysics Data System (ADS)

    Wu, Jui-Ching; Lin, Tsang-Lang; Jeng, U.-Ser; Torikai, Naoya

    2006-11-01

    In situ neutron reflectivity was used to study the DC-Chol and TC-Chol monolayers at the air-liquid interface in the presence and absence of DNA in the subphase. It was found that the DC-Chol is more effective in adsorbing the DNA than the TC-Chol. It was also found that a compact DNA layer formed beneath the DC-Chol monolayer with a DNA gap spacing around 20 Å and a less compact DNA layer adsorbed to the TC-Chol monolayer with a DNA spacing around 60 Å, as estimated from the determined neutron scattering length density. From the determined neutron scattering length density profiles, the adsorbed DNA somewhat penetrates into the head group region of the charged lipids.

  8. Strain-Modulated Electronic Structure and Infrared Light Adsorption in Palladium Diselenide Monolayer

    NASA Astrophysics Data System (ADS)

    Liu, Xiaobiao; Zhou, Hongcai; Yang, Bo; Qu, Yuanyuan; Zhao, Mingwen

    2017-01-01

    Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit intriguing properties for both fundamental research and potential application in fields ranging from electronic devices to catalysis. Based on first-principles calculations, we proposed a stable form of palladium diselenide (PdSe2) monolayer that can be synthesized by selenizing Pd(111) surface. It has a moderate band gap of about 1.10 eV, a small in-plane stiffness, and electron mobility larger than that of monolayer black phosphorus by more than one order. Additionally, tensile strain can modulate the band gap of PdSe2 monolayer and consequently enhance the infrared light adsorption ability. These interesting properties are quite promising for application in electronic and optoelectronic devices.

  9. Strain-Modulated Electronic Structure and Infrared Light Adsorption in Palladium Diselenide Monolayer

    PubMed Central

    Liu, Xiaobiao; Zhou, Hongcai; Yang, Bo; Qu, Yuanyuan; Zhao, Mingwen

    2017-01-01

    Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit intriguing properties for both fundamental research and potential application in fields ranging from electronic devices to catalysis. Based on first-principles calculations, we proposed a stable form of palladium diselenide (PdSe2) monolayer that can be synthesized by selenizing Pd(111) surface. It has a moderate band gap of about 1.10 eV, a small in-plane stiffness, and electron mobility larger than that of monolayer black phosphorus by more than one order. Additionally, tensile strain can modulate the band gap of PdSe2 monolayer and consequently enhance the infrared light adsorption ability. These interesting properties are quite promising for application in electronic and optoelectronic devices. PMID:28051184

  10. Ordering and defects in self-assembled monolayers on nanoporous gold

    NASA Astrophysics Data System (ADS)

    Patel, Dipna A.; Weller, Andrew M.; Chevalier, Robert B.; Karos, Constantine A.; Landis, Elizabeth C.

    2016-11-01

    Self-assembled monolayers are commonly used to tailor nanoporous structures for applications, and they also provide a model system for determining the effects of nanoscale structure on self-assembly. We have investigated the ordering and defects in alkanethiol self-assembled monolayers on nanoporous gold, a high surface area mesoporous material. Infrared reflection absorption spectroscopy was used to characterize the effects of alkyl chain length and nanoporous gold pore size on molecular layer ordering. Cyclic voltammetry was used to characterize the monolayer density and ordering, with ferrocenylalkylthiolates used to quantify and characterize defect sites. We find that dense and well-ordered molecular layers form quickly with low defect levels. However, we do not observe differences in molecular layer ordering or defects with changes in pore size.

  11. Two-dimensional binary and ternary nanocrystal superlattices: the case of monolayers and bilayers.

    PubMed

    Dong, Angang; Ye, Xingchen; Chen, Jun; Murray, Christopher B

    2011-04-13

    The modular assembly of multicomponent nanocrystal (NC) superlattices enables new metamaterials with programmable properties. While self-assembly of three-dimensional (3D) binary NC superlattices (BNSLs) has advanced significantly in the past decade, limited progress has been made to grow 2D BNSLs such as monolayers and bilayers over extended areas. Here, we report the growth of large-area (∼ 1 cm(2)), transferable BNSL monolayers using the liquid-air interfacial assembly approach. The BNSL monolayers are formed by an entropy-driven assembly process with structures tunable by varying the NC size ratio. We further demonstrate the liquid-air interfacial assembly of BNSL bilayers which exhibit unique superlattice structures that have not been observed in the 3D BNSLs. As a further extension, bilayered ternary NC superlattices (TNSLs) are obtained by the cocrystallization of three types of NCs at the liquid-air interface.

  12. Solvent Effect on Formation of Cysteamine Self-Assembled Monolayers on Au(111)

    NASA Astrophysics Data System (ADS)

    Lee, Sang Yun; Noh, Jaegeun; Ito, Eisuke; Lee, Haiwon; Hara, Masahiko

    2003-01-01

    Cysteamine (CA) self-assembled monolayers (SAMs) formed in various solutions on Au(111) were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to understand the solvent effect on the SAM structure. The STM study revealed that the surface structure of CA SAMs prepared in polar protic solutions was strongly influenced by immersion time, while there were no significant structural changes in the SAMs prepared in nonpolar and polar aprotic solutions. This result implies that the proticity of the solvent and the immersion time play important roles in determining the surface structures of the amino-terminated CA SAMs due to the coadsorptoin of solvent molecules onto the clean monolayers, which are stabilized by hydrogen bonding between polar protic solvents and the clean monolayers. In addition, our STM and XPS results for CA SAMs on Au(111) suggest the existence of two different structural conformations, i.e., trans and gauche conformers.

  13. Reversible monolayer-to-crystalline phase transition in amphiphilic silsesquioxane at the air-water interface

    DOE PAGES

    Banerjee, R.; Sanyal, M. K.; Bera, M. K.; ...

    2015-02-17

    We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initialmore » monolayer state. The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate.« less

  14. Reversible monolayer-to-crystalline phase transition in amphiphilic silsesquioxane at the air-water interface

    SciTech Connect

    Banerjee, R.; Sanyal, M. K.; Bera, M. K.; Gibaud, A.; Lin, B.; Meron, M.

    2015-02-17

    We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initial monolayer state. The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate.

  15. A statistical approach for distinguishing hybridization and incomplete lineage sorting.

    PubMed

    Joly, Simon; McLenachan, Patricia A; Lockhart, Peter J

    2009-08-01

    The extent and evolutionary significance of hybridization is difficult to evaluate because of the difficulty in distinguishing hybridization from incomplete lineage sorting. Here we present a novel parametric approach for statistically distinguishing hybridization from incomplete lineage sorting based on minimum genetic distances of a nonrecombining locus. It is based on the idea that the expected minimum genetic distance between sequences from two species is smaller for some hybridization events than for incomplete lineage sorting scenarios. When applied to empirical data sets, distributions can be generated for the minimum interspecies distances expected under incomplete lineage sorting using coalescent simulations. If the observed distance between sequences from two species is smaller than its predicted distribution, incomplete lineage sorting can be rejected and hybridization inferred. We demonstrate the power of the method using simulations and illustrate its application on New Zealand alpine buttercups (Ranunculus). The method is robust and complements existing approaches. Thus it should allow biologists to assess with greater accuracy the importance of hybridization in evolution.

  16. Incomplete caries removal: a systematic review and meta-analysis.

    PubMed

    Schwendicke, F; Dörfer, C E; Paris, S

    2013-04-01

    Increasing numbers of clinical trials have demonstrated the benefits of incomplete caries removal, in particular in the treatment of deep caries. This study systematically reviewed randomized controlled trials investigating one- or two-step incomplete compared with complete caries removal. Studies treating primary and permanent teeth with primary caries lesions requiring a restoration were analyzed. The following primary and secondary outcomes were investigated: risk of pulpal exposure, post-operative pulpal symptoms, overall failure, and caries progression. Electronic databases were screened for studies from 1967 to 2012. Cross-referencing was used to identify further articles. Odds ratios (OR) as effect estimates were calculated in a random-effects model. From 364 screened articles, 10 studies representing 1,257 patients were included. Meta-analysis showed risk reduction for both pulpal exposure (OR [95% CI] 0.31 [0.19-0.49]) and pulpal symptoms (OR 0.58 [0.31-1.10]) for teeth treated with one- or two-step incomplete excavation. Risk of failure seemed to be similar for both complete and incomplete excavation, but data for this outcome were of limited quality and inconclusive (OR 0.97 [0.64-1.46]). Based on reviewed studies, incomplete caries removal seems advantageous compared with complete excavation, especially in proximity to the pulp. However, evidence levels are currently insufficient for definitive conclusions because of high risk of bias within studies.

  17. Handling incomplete smoking history data in survival analysis.

    PubMed

    Furukawa, Kyoji; Preston, Dale L; Misumi, Munechika; Cullings, Harry M

    2014-10-26

    While data are unavoidably missing or incomplete in most observational studies, consequences of mishandling such incompleteness in analysis are often overlooked. When time-varying information is collected irregularly and infrequently over a long period, even precisely obtained data may implicitly involve substantial incompleteness. Motivated by an analysis to quantitatively evaluate the effects of smoking and radiation on lung cancer risks among Japanese atomic-bomb survivors, we provide a unique application of multiple imputation to incompletely observed smoking histories under the assumption of missing at random. Predicting missing values for the age of smoking initiation and, given initiation, smoking intensity and cessation age, analyses can be based on complete, though partially imputed, smoking histories. A simulation study shows that multiple imputation appropriately conditioned on the outcome and other relevant variables can produce consistent estimates when data are missing at random. Our approach is particularly appealing in large cohort studies where a considerable amount of time-varying information is incomplete under a mechanism depending in a complex manner on other variables. In application to the motivating example, this approach is expected to reduce estimation bias that might be unavoidable in naive analyses, while keeping efficiency by retaining known information.

  18. High-temperature superconductivity in FeSe monolayers

    NASA Astrophysics Data System (ADS)

    Sadovskii, M. V.

    2016-10-01

    This paper reviews the basic experimental and theoretical aspects of high-temperature superconductivity in intercalated FeSe compounds and FeSe monolayer films on SrTiO_3 and similar substrates. The paper examines in detail the electronic structure of these systems, how it is calculated, and how the calculated results compare with ARPES experiments. It is emphasized that the reviewed systems have qualitatively different electronic spectra from the typical pattern of well-studied FeAs superconductors and explores the implications of these differences for a theoretical description of how these spectra form. Possible mechanisms of Cooper pairing in FeSe monolayers are discussed and the associated problems are examined. Because FeSe monolayer films on SrTiO_3 are typical Ginzburg 'sandwiches', the possibility of increasing their T_c via 'excitonic' superconductivity mechanisms is considered. It is shown that, while the classical version of this mechanism (as proposed for such systems by Allender, Bray, and Bardeen) fails to explain the observed values of T_c, the situation changes when optical phonons in SrTiO_3 (with energy of about 100 meV) are considered to be 'excitons'. Both the simplest possible model of T_c enhancement due to interaction with such phonons and more complex ones with dominant 'forward' scattering that explain successfully the increase in T_c compared to bulk FeSe and intercalated FeSe systems are verified. Problems related to the antiadiabatic nature of this superconductivity mechanism are also discussed.

  19. Compressibility study of quaternary phospholipid blend monolayers.

    PubMed

    Cavalcanti, Leide P; Tho, Ingunn; Konovalov, Oleg; Fossheim, Sigrid; Brandl, Martin

    2011-07-01

    The mechanical properties of liposome membranes are strongly dependent on type and ratio of lipid compounds, which can have important role in drug targeting and release processes when liposome is used as drug carrier. In this work we have used Brewster's angle microscopy to monitor the lateral compression process of lipid monolayers containing as helper lipids either distearoyl phosphatidylethanolamine (DSPE) or dioleoyl phophatidylethanolamine (DOPE) molecules on the Langmuir trough. The compressibility coefficient was determined for lipid blend monolayers containing the helper lipids above, cholesterol, distearoyl phosphatidylcholine (DSPC) and pegylated-DSPE at room temperature. Two variables, the cholesterol fraction and the ratio ρ between the helper lipid (either DSPE or DOPE) and the reference lipid DSPC, were studied by multivariate analysis to evaluate their impact on the compressibility coefficient of the monolayers. The cholesterol level was found to be the most significant variable for DSPE blends while the ratio ρ was the most significant one for DOPE blend monolayers. It was also found that these two variables can exhibit positive interaction and the same compressibility value can be obtained with different blend compositions.

  20. Adsorption of Ions at Uncharged Insoluble Monolayers.

    PubMed

    Peshkova, Tatyana V; Minkov, Ivan L; Tsekov, Roumen; Slavchov, Radomir I

    2016-09-06

    A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3-30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na(+) is specifically adsorbed, while Cl(-) remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na(+) seems to be the interaction of the ion with the dipole moment of the monolayer.

  1. Hydrolytic kinetics of biodegradable polyester monolayers

    SciTech Connect

    Lee, W.K.; Gardella, J.A. Jr.

    2000-04-04

    The rate of hydrolysis of Langmuir monolayer films of a series of biodegradable polyesters was investigated at the air/water interface. The present study investigated parameters such as degradation medium, pH, and time. The hydrolysis of polyester monolayers strongly depended on both the degradation medium used to control subphase pH and the concentration of active ions. Under the conditions studied here, polymer monolayers showed faster hydrolysis when they were exposed to a basic subphase rather than that of acidic or neutral subphase. The basic (pH = 10) hydrolysis of [poly(l-lactide)/polycaprolactone](l-PLA/PCL 1/1 by mole) blend was faster than that of each homopolymer at the initial stage. This result is explained by increasing numbers of base attack sites per unit area owing to the very slow hydrolysis of PCL, a dilution effect on the concentration of l-PLA monolayers. Conversely the hydrolytic behavior of l-lactide-co-caprolactone (1/1 by mole) was similar to that of PCL even though the chemical compositions of the blend and the copolymer are very similar to each other. The resistance of the copolymer to hydrolysis might be attributed to the hydrophobicity and the steric hindrance of caprolactone unit in the copolymer.

  2. Adsorption of Ions at Uncharged Insoluble Monolayers

    NASA Astrophysics Data System (ADS)

    Peshkova, T. V.; Minkov, I. L.; Tsekov, R.; Slavchov, R. I.

    2016-08-01

    A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3–30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na+ is specifically adsorbed, while Cl– remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na+ seems to be the interaction of the ion with the dipole moment of the monolayer.

  3. Modulation of dipalmitoylphosphatidylcholine monolayers by dimethyl sulfoxide.

    PubMed

    Dabkowska, Aleksandra P; Collins, Louise E; Barlow, David J; Barker, Robert; McLain, Sylvia E; Lawrence, M Jayne; Lorenz, Christian D

    2014-07-29

    The action of the penetration-enhancing agent, dimethyl sulfoxide (DMSO), on phospholipid monolayers was investigated at the air-water interface using a combination of experimental techniques and molecular dynamics simulations. Brewster angle microscopy revealed that DPPC monolayers remained laterally homogeneous at subphase concentrations up to a mole fraction of 0.1 DMSO. Neutron reflectometry of the monolayers in combination with isotopic substitution enabled the determination of solvent profiles as a function of distance perpendicular to the interface for the different DMSO subphase concentrations. These experimental results were compared to those obtained from molecular dynamic (MD) simulations of the corresponding monolayer systems. There was excellent agreement found between the MD-derived reflectivity curves and the measured data for all of the H/D contrast variations investigated. The MD provide a detailed description of the distribution of water and DMSO molecules around the phosphatidylcholine headgroup, and how this distribution changes with increasing DMSO concentrations. Significantly, the measurements and simulations that are reported here support the hypothesis that DMSO acts by dehydrating the phosphatidylcholine headgroup, and as such provide the first direct evidence that it does so primarily by displacing water molecules bound to the choline group.

  4. The structure and dynamics of Nano Particles encapsulated by the SDS monolayer collapse at the water/TCE interface

    PubMed Central

    Shi, Wenxiong

    2016-01-01

    The super-saturated surfactant monolayer collapses with the nanoparticles (NPs) at the water/trichloroethylene (TCE) interface are investigated using molecular dynamics (MD) simulations. The results show that sodium alkyl sulfate (SDS) monolayer collapse is initiated by buckling and followed primarily by budding and the bud encapsulating the NPs and oil molecules. The developed bud detaches from the monolayer into a water phase and forms the swollen micelle emulsion with NPs and oil molecules. We investigate the wavelength of the initial budding and the theoretical description of the budding process. The wavelength of the monolayer increases with bending modulus. The energy barrier of the budding can be easily overcome by thermal fluctuation energy, which indicates that budding process proceeds rapidly. PMID:27853312

  5. The structure and dynamics of Nano Particles encapsulated by the SDS monolayer collapse at the water/TCE interface

    NASA Astrophysics Data System (ADS)

    Shi, Wenxiong

    2016-11-01

    The super-saturated surfactant monolayer collapses with the nanoparticles (NPs) at the water/trichloroethylene (TCE) interface are investigated using molecular dynamics (MD) simulations. The results show that sodium alkyl sulfate (SDS) monolayer collapse is initiated by buckling and followed primarily by budding and the bud encapsulating the NPs and oil molecules. The developed bud detaches from the monolayer into a water phase and forms the swollen micelle emulsion with NPs and oil molecules. We investigate the wavelength of the initial budding and the theoretical description of the budding process. The wavelength of the monolayer increases with bending modulus. The energy barrier of the budding can be easily overcome by thermal fluctuation energy, which indicates that budding process proceeds rapidly.

  6. Incomplete fuzzy data processing systems using artificial neural network

    NASA Technical Reports Server (NTRS)

    Patyra, Marek J.

    1992-01-01

    In this paper, the implementation of a fuzzy data processing system using an artificial neural network (ANN) is discussed. The binary representation of fuzzy data is assumed, where the universe of discourse is decartelized into n equal intervals. The value of a membership function is represented by a binary number. It is proposed that incomplete fuzzy data processing be performed in two stages. The first stage performs the 'retrieval' of incomplete fuzzy data, and the second stage performs the desired operation on the retrieval data. The method of incomplete fuzzy data retrieval is proposed based on the linear approximation of missing values of the membership function. The ANN implementation of the proposed system is presented. The system was computationally verified and showed a relatively small total error.

  7. A comparison of incomplete-data methods for categorical data.

    PubMed

    van der Palm, Daniël W; van der Ark, L Andries; Vermunt, Jeroen K

    2016-04-01

    We studied four methods for handling incomplete categorical data in statistical modeling: (1) maximum likelihood estimation of the statistical model with incomplete data, (2) multiple imputation using a loglinear model, (3) multiple imputation using a latent class model, (4) and multivariate imputation by chained equations. Each method has advantages and disadvantages, and it is unknown which method should be recommended to practitioners. We reviewed the merits of each method and investigated their effect on the bias and stability of parameter estimates and bias of the standard errors. We found that multiple imputation using a latent class model with many latent classes was the most promising method for handling incomplete categorical data, especially when the number of variables used in the imputation model is large.

  8. A Novel Method to Assess Incompleteness of Mammography Reports

    PubMed Central

    Gimenez, Francisco J.; Wu, Yirong; Burnside, Elizabeth S.; Rubin, Daniel L.

    2014-01-01

    Mammography has been shown to improve outcomes of women with breast cancer, but it is subject to inter-reader variability. One well-documented source of such variability is in the content of mammography reports. The mammography report is of crucial importance, since it documents the radiologist’s imaging observations, interpretation of those observations in terms of likelihood of malignancy, and suggested patient management. In this paper, we define an incompleteness score to measure how incomplete the information content is in the mammography report and provide an algorithm to calculate this metric. We then show that the incompleteness score can be used to predict errors in interpretation. This method has 82.6% accuracy at predicting errors in interpretation and can possibly reduce total diagnostic errors by up to 21.7%. Such a method can easily be modified to suit other domains that depend on quality reporting. PMID:25954448

  9. A novel method to assess incompleteness of mammography reports.

    PubMed

    Gimenez, Francisco J; Wu, Yirong; Burnside, Elizabeth S; Rubin, Daniel L

    2014-01-01

    Mammography has been shown to improve outcomes of women with breast cancer, but it is subject to inter-reader variability. One well-documented source of such variability is in the content of mammography reports. The mammography report is of crucial importance, since it documents the radiologist's imaging observations, interpretation of those observations in terms of likelihood of malignancy, and suggested patient management. In this paper, we define an incompleteness score to measure how incomplete the information content is in the mammography report and provide an algorithm to calculate this metric. We then show that the incompleteness score can be used to predict errors in interpretation. This method has 82.6% accuracy at predicting errors in interpretation and can possibly reduce total diagnostic errors by up to 21.7%. Such a method can easily be modified to suit other domains that depend on quality reporting.

  10. Self-assembled monolayer films of C[sub 60]/on cysteamine-modified gold

    SciTech Connect

    Caldwell, W.B.; Chen, K.; Mirkin, C.A.; Babinec, S.J. Dow Chemical Company, Midland, MI )

    1993-08-01

    Self-assembled monolayer films (SAMs) of C[sub 60] on cysteamine-modified and cysteamine/ethanethiol-modified Au are reported. The monolayers were characterized via contact angle measurements, X-ray photoelectron spectroscopy, electrochemistry, and quartz crystal microbalance (QCM) measurements. C[sub 60] surface coverage (2.0 [times] 10[sup [minus]10] mol/cm[sup 2]) for a film formed on pure cysteamine was determined by QCM measurements and compares remarkably well with monolayer coverage (1.9 [times] 10[sup [minus]10] mol/cm[sup 2]) predicted by a model based on crystallographic data for C[sub 60]. These experiments demonstrate the utility of the QCM in characterizing and monitoring the growth of fullerene SAMs. C[sub 60] SAMs formed on pure cysteamine yield strikingly different electrochemical responses than those formed on prelayers consisting of varying ratios of ethanethiol and cysteamine and previously reported monolayers of C[sub 60] on (aminopropyl)silanized oxide surfaces. Although the C[sub 60] SAMs are stable under ambient conditions, the fullerenes may be desorbed from the surface through electrochemical reduction of the films for extended periods of time (> 10 min). 11 refs., 2 figs.

  11. SOME CODES WHICH ARE INVARIENT UNDER A DOUBLY-TRANSITIVE PERMUTATION GROUP AND THEIR CONNECTION WITH BALANCED INCOMPLETE BLOCK DESIGNS

    DTIC Science & Technology

    If a binary code is invariant under a doubly-transitive permutation group, then the set of all code words of weight j forms a balanced incomplete...codes are properly arranged, and if the first digit is omitted, then all Reed-Muller codes are cyclic.

  12. Incomplete use of condoms: the importance of sexual arousal.

    PubMed

    Graham, Cynthia A; Crosby, Richard A; Milhausen, Robin R; Sanders, Stephanie A; Yarber, William L

    2011-10-01

    The purpose of this study was to identify associations between incomplete condom use (not using condoms from start to finish of sex) and sexual arousal variables. A convenience sample of heterosexual men (n = 761) completed a web-based questionnaire. Men who scored higher on sexual arousability were more likely to put a condom on after sex had begun (AOR = 1.58). Men who reported difficulty reaching orgasm were more likely to report removing condoms before sex was over (AOR = 2.08). These findings suggest that sexual arousal may be an important, and under-studied, factor associated with incomplete use of condoms.

  13. Incomplete and False Identification Distributions: Group Screening Models.

    DTIC Science & Technology

    1981-05-01

    AD-AO99 310 MARYLAND LUN1V COLLEGE PARK F/6 12/1 INCOMPLETE AND FALSE IDENTIFICATION DISTRIBUTIONS: GROUP SCREEN--ETC(U) MAY 8l S KOTZ. N L JOHNSON...present paper, we extend some of these results to the case of screeningw’mpling schemes. KeyWords and Phrases: group screening; binomial distribution...Johnson and Kotz (1981a). la) Incomplete identification. Consider a sample of size n without replacement from a lot of size N conforming X defective (or

  14. X-ray specular reflection studies of silicon coated by organic monolayers (alkylsiloxanes)

    NASA Astrophysics Data System (ADS)

    Tidswell, I. M.; Ocko, B. M.; Pershan, P. S.; Wasserman, S. R.; Whitesides, G. M.; Axe, J. D.

    1990-01-01

    X-ray specular reflectivity has been used to characterize the structure of silicon-silicon-oxide surfaces coated with chemisorbed hydrocarbon monolayer films (alkylsiloxanes). Using synchrotron radiation the reflectivity was followed over 9 orders of magnitude, from grazing incidence to an incident angle of φ~=6.5°, or q=(4π/λ)sin(φ)=0.8 Å-1, allowing a spatial resolution of features approximately π/0.8~=4.0 Å along the surface normal. Analysis was performed by fitting the data to reflectivities calculated from models of the surface electron density and by calculating Patterson functions directly from the data. Although the measured reflectivities could be equally well described by different sets of model parameters, the electron densities calculated from these different parameters were remarkably alike. Inspection of the electron densities allowed identification of a layer of SiO2 (~=17-Å thick), a layer of head-group region where the alkylsiloxane adsorbs to the SiO2, and the hydrocarbon layer. Fitting the data also required that the various interfaces have different widths. The fact that the same local hydrocarbon density of 0.85 g/cm3 was observed for both fully formed and partially formed monolayers with alkane chains of varying length excluded a model in which the partially formed monolayer was made up of separated islands of well-formed monolayers. Measurements before and after chemical reaction of a monolayer in which the alkyl chain was terminated by an olefinic group demonstrated the ability to use x-ray reflectivity to characterize chemical changes. The effects of radiation damage on these types of measurements are described.

  15. Microstructure analysis of monodisperse ferrofluid monolayers: theory and simulation.

    PubMed

    Kantorovich, Sofia; Cerdà, Juan J; Holm, Christian

    2008-04-14

    We try to elucidate the microstructure formation in a monodisperse ferrofluid monolayer. The system under study consists of soft sphere magnetic dipolar particles confined to a thin fluid layer. The positions of the particles are constrained to a 2D geometry, whereas the particle magnetic dipole moments are not fixed to the body systems, and are free to rotate in 3 dimensions, hence forming in what we call a quasi-2D geometry. Using a combination of analytical density functional theory and molecular dynamics (MD) simulations, we find that for the studied range of parameters the majority of aggregates might be divided into two types: chains and rings. Their sizes and area fractions are strongly influenced by the geometrical constraints. We show that for quasi-2D systems the excluded area effects play one of the most important parts in the microstructure formation. The simulation technique and the theoretical model put forward in the present paper agree qualitatively with the results of recent in situ observations of the microstructures observed in ferrofluid monolayers [M. Klokkenberg, R. P. A. Dullens, W. K. Regel, B. H. Erné, A. P. Philipse, Phys. Rev. Lett., 2006, 96, 037203].

  16. Grains and grain boundaries in highly crystalline monolayer molybdenum disulphide.

    PubMed

    van der Zande, Arend M; Huang, Pinshane Y; Chenet, Daniel A; Berkelbach, Timothy C; You, YuMeng; Lee, Gwan-Hyoung; Heinz, Tony F; Reichman, David R; Muller, David A; Hone, James C

    2013-06-01

    Recent progress in large-area synthesis of monolayer molybdenum disulphide, a new two-dimensional direct-bandgap semiconductor, is paving the way for applications in atomically thin electronics. Little is known, however, about the microstructure of this material. Here we have refined chemical vapour deposition synthesis to grow highly crystalline islands of monolayer molybdenum disulphide up to 120 μm in size with optical and electrical properties comparable or superior to exfoliated samples. Using transmission electron microscopy, we correlate lattice orientation, edge morphology and crystallinity with island shape to demonstrate that triangular islands are single crystals. The crystals merge to form faceted tilt and mirror twin boundaries that are stitched together by lines of 8- and 4-membered rings. Density functional theory reveals localized mid-gap states arising from these 8-4 defects. We find that mirror twin boundaries cause strong photoluminescence quenching whereas tilt boundaries cause strong enhancement. Meanwhile, mirror twin boundaries slightly increase the measured in-plane electrical conductivity, whereas tilt boundaries slightly decrease the conductivity.

  17. Molecular and electronic structure of electroactive self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Méndez De Leo, Lucila P.; de la Llave, Ezequiel; Scherlis, Damián; Williams, Federico J.

    2013-03-01

    Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

  18. Molecular and electronic structure of electroactive self-assembled monolayers.

    PubMed

    Méndez De Leo, Lucila P; de la Llave, Ezequiel; Scherlis, Damián; Williams, Federico J

    2013-03-21

    Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

  19. Negative dipole potentials of uncharged langmuir monolayers due to fluorination of the hydrophilic heads.

    PubMed

    Petrov, Jordan G; Andreeva, Tonya D; Kurth, Dirk G; Möhwald, Helmuth

    2005-07-28

    The dipole potential, affecting the structure, functions, and interactions of biomembranes, lipid bilayers, and Langmuir monolayers, is positive toward the hydrocarbon moieties. We show that uncharged Langmuir monolayers of docosyl trifluoroethyl ether (DFEE) exhibit large negative dipole potentials, while the nonfluorinated docosyl ethyl ether (DEE) forms films with positive dipole potentials. Comparison of the Delta V values for these ethers with those of the previously studied(37-39) monolayers of trifluoroethyl ester (TFEB) and ethyl ester of behenic acid (EB) shows that the reversal of the sign of Delta V causes the same change Delta(Delta V) = -706 +/- 16 mV due to fluorination of heads. The Delta V values of both TFEB and EB films differ by -122 +/- 16 mV from those of DFEE and DEE monolayers, respectively, with the same density. Such quantitative coincidence points to a common mechanism of reversal of the sign of the dipole potential for the ether and ester films despite the different structure of their heads. The mechanical properties and phase behaviors of these monolayers show that both fluorinated heads are less hydrated, suggesting that the change of the sign of Delta V could, at least partially, be related to different hydration water structure. The same negative contribution of the carbonyl bond in both TFEB and EB films contrasts with the generally accepted positive contribution of the C(delta+)=O(delta-) bond in condensed Langmuir monolayers of fatty acids, their alcohol esters, glycerides, and phospholipids but concurs with the theoretical analysis of Delta V of stearic acid monolayers. Both results question the literature values of the molecular dipole moments of these substances calculated via summation of bonds and atomic group contributions. Mixed monolayers of DFEE and DEE show smooth monotonic variation of Delta V from +450 to -235 mV, indicating a way for adjustment of the sign and magnitude of the dipole potential at the membrane

  20. Augmented multisensory feedback enhances locomotor adaptation in humans with incomplete spinal cord injury.

    PubMed

    Yen, Sheng-Che; Landry, Jill M; Wu, Ming

    2014-06-01

    Different forms of augmented feedback may engage different motor learning pathways, but it is unclear how these pathways interact with each other, especially in patients with incomplete spinal cord injury (SCI). The purpose of this study was to test whether augmented multisensory feedback could enhance aftereffects following short term locomotor training (i.e., adaptation) in patients with incomplete SCI. A total of 10 subjects with incomplete SCI were recruited to perform locomotor adaptation. Three types of augmented feedback were provided during the adaptation: (a) computerized visual cues showing the actual and target stride length (augmented visual feedback); (b) a swing resistance applied to the leg (augmented proprioceptive feedback); (c) a combination of the visual cues and resistance (augmented multisensory feedback). The results showed that subjects' stride length increased in all conditions following the adaptation, but the increase was greater and retained longer in the multisensory feedback condition. The multisensory feedback provided in this study may engage both explicit and implicit learning pathways during the adaptation and in turn enhance the aftereffect. The results implied that multisensory feedback may be used as an adjunctive approach to enhance gait recovery in humans with SCI.

  1. Inference and sample size calculation for clinical trials with incomplete observations of paired binary outcomes.

    PubMed

    Zhang, Song; Cao, Jing; Ahn, Chul

    2017-02-20

    We investigate the estimation of intervention effect and sample size determination for experiments where subjects are supposed to contribute paired binary outcomes with some incomplete observations. We propose a hybrid estimator to appropriately account for the mixed nature of observed data: paired outcomes from those who contribute complete pairs of observations and unpaired outcomes from those who contribute either pre-intervention or post-intervention outcomes. We theoretically prove that if incomplete data are evenly distributed between the pre-intervention and post-intervention periods, the proposed estimator will always be more efficient than the traditional estimator. A numerical research shows that when the distribution of incomplete data is unbalanced, the proposed estimator will be superior when there is moderate-to-strong positive within-subject correlation. We further derive a closed-form sample size formula to help researchers determine how many subjects need to be enrolled in such studies. Simulation results suggest that the calculated sample size maintains the empirical power and type I error under various design configurations. We demonstrate the proposed method using a real application example. Copyright © 2016 John Wiley & Sons, Ltd.

  2. Omega-Terminated Alkanethiolate Monolayers on Surfaces of Copper, Silver and Gold Have Similar Wettabilities

    DTIC Science & Technology

    1991-12-01

    metal cxides and form oriented, oleophobic monolayers,25 0-hydroxy- and W-amino-alkanoic acids adsorb and form poorly organized films that are not wet...gold. Experinental Materials . 1l-Bromo-undecyl t-butyldimethylsilyl ether and most alkanethiols were available from pcrevious studies;6, 2 1, 4 8 ctn...er materials were obtained from Aldrich and used as received unless Specified. Octadecanethiol was distilled under reduced pressure prior to use

  3. Endodontic and restorative management of incompletely fractured molar teeth.

    PubMed

    Gutmann, J L; Rakusin, H

    1994-11-01

    The treatment of fractured teeth poses significant problems for the practitioner. However, once the treatment planning decision has been made to attempt to retain the tooth, various practical regimens are available to effect this goal. This paper addresses the specific use of glass ionomer in the restorative management of incompletely, vertically fractured molar teeth integrated with specific root canal treatment techniques.

  4. Robustness of shape descriptors to incomplete contour representations.

    PubMed

    Ghosh, Anarta; Petkov, Nicolai

    2005-11-01

    With inspiration from psychophysical researches of the human visual system, we propose a novel aspect and a method for performance evaluation of contour-based shape recognition algorithms regarding their robustness to incompleteness of contours. We use complete contour representations of objects as a reference (training) set. Incomplete contour representations of the same objects are used as a test set. The performance of an algorithm is reported using the recognition rate as a function of the percentage of contour retained. We call this evaluation procedure the ICR test. We consider three types of contour incompleteness, viz. segment-wise contour deletion, occlusion, and random pixel depletion. As an illustration, the robustness of two shape recognition algorithms to contour incompleteness is evaluated. These algorithms use a shape context and a distance multiset as local shape descriptors. Qualitatively, both algorithms mimic human visual perception in the sense that recognition performance monotonously increases with the degree of completeness and that they perform best in the case of random depletion and worst in the case of occluded contours. The distance multiset method performs better than the shape context method in this test framework.

  5. 19 CFR 122.74 - Incomplete (pro forma) manifest.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 1 2011-04-01 2011-04-01 false Incomplete (pro forma) manifest. 122.74 Section 122.74 Customs Duties U.S. CUSTOMS AND BORDER PROTECTION, DEPARTMENT OF HOMELAND SECURITY; DEPARTMENT...; Electronic Manifest Requirements for Passengers, Crew Members, and Non-Crew Members Onboard...

  6. Computer Simulation of Incomplete-Data Interpretation Exercise.

    ERIC Educational Resources Information Center

    Robertson, Douglas Frederick

    1987-01-01

    Described is a computer simulation that was used to help general education students enrolled in a large introductory geology course. The purpose of the simulation is to learn to interpret incomplete data. Students design a plan to collect bathymetric data for an area of the ocean. Procedures used by the students and instructor are included.…

  7. Gender under Incomplete Acquisition: Heritage Speakers' Knowledge of Noun Categorization

    ERIC Educational Resources Information Center

    Polinsky, Maria

    2008-01-01

    The author discusses a study of gender assignment (noun categorization) in heritage Russian and presents issues in the methodology of heritage language study. To anticipate the conclusions of this article, the gender assignment data presented argue for the systematicity of what emerges under incomplete acquisition. The system is different from its…

  8. Root cause of incomplete control rod insertions at Westinghouse reactors

    SciTech Connect

    Ray, S.

    1997-01-01

    Within the past year, incomplete RCCA insertions have been observed on high burnup fuel assemblies at two Westinghouse PWRs. Initial tests at the Wolf Creek site indicated that the direct cause of the incomplete insertions observed at Wolf Creek was excessive fuel assembly thimble tube distortion. Westinghouse committed to the NRC to perform a root cause analysis by the end of August, 1996. The root cause analysis process used by Westinghouse included testing at ten sites to obtain drag, growth and other characteristics of high burnup fuel assemblies. It also included testing at the Westinghouse hot cell of two of the Wolf Creek incomplete insertion assemblies. A mechanical model was developed to calculate the response of fuel assemblies when subjected to compressive loads. Detailed manufacturing reviews were conducted to determine if this was a manufacturing related issue. In addition, a review of available worldwide experience was performed. Based on the above, it was concluded that the thimble tube distortion observed on the Wolf Creek incomplete insertion assemblies was caused by unusual fuel assembly growth over and above what would typically be expected as a result of irradiation exposure. It was determined that the unusual growth component is a combination of growth due to oxide accumulation and accelerated growth, and would only be expected in high temperature plants on fuel assemblies that see long residence times and high power duties.

  9. Limit Pricing with Incomplete Information: Answers to Frequently Asked Questions

    ERIC Educational Resources Information Center

    Sorenson, Timothy L.

    2004-01-01

    Strategic pricing is an important and exciting topic in industrial organization and the economics of strategy. A wide range of texts use what has become a standard version of the Milgrom and Roberts (1982a) limit-pricing model to convey the essential ideas of strategic pricing under incomplete information. In addition to providing a formal, but…

  10. An Interactive Approach to Analyzing Incomplete Multivariate Data.

    ERIC Educational Resources Information Center

    Raymond, Mark R.

    This paper examines some of the problems that arise when conducting multivariate analyses with incomplete data. The literature on the effectiveness of several missing data procedures (MDP) is summarized. The most widely used MDPs are: (1) listwise deletion; (2) pairwise deletion; (3) variable mean; (4) correlational methods. No MDP should be used…

  11. 40 CFR 86.085-20 - Incomplete vehicles, classification.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 18 2010-07-01 2010-07-01 false Incomplete vehicles, classification... PROGRAMS (CONTINUED) CONTROL OF EMISSIONS FROM NEW AND IN-USE HIGHWAY VEHICLES AND ENGINES General Provisions for Emission Regulations for 1977 and Later Model Year New Light-Duty Vehicles, Light-Duty...

  12. Studies of dipalmitoylphosphatidylcholine (DPPC) monolayers embedded with endohedral metallofullerene (Dy@C82).

    PubMed

    Wang, Zhining; Li, Xiaofang; Yang, Shihe

    2009-11-17

    Toxicological effects of carbon nanomaterials have attracted increasing attention. In this work, we studied the interaction between Dy@C(82) and dipalmitoylphosphatidylcholine (DPPC) in a monolayer at the N(2)/Tris buffer interface by thermodynamic analysis of surface pressure-area (pi-A) and surface potential-area (DeltaV-A) isotherms. Dy@C(82) was found to impact considerably more on the physical properties of the monolayers than C(60) because of its elliptical structure and distinctive dipole. The addition of Dy@C(82) essentially closed down the liquid expanded-liquid condensed (LE-LC) phase coexistence region of the mixed monolayers. Furthermore, Dy@C(82) reduced elasticity of the monolayers, as indicated by the decreasing elastic modulus (C(s)(-1)) with increasing molar ratio of Dy@C(82) (X(Dy@C82)). Brewster angle microscopy (BAM) and atomic force microscopy (AFM) revealed that the dispersion of Dy@C(82) depend on the state of the mixed films. Dy@C(82) formed flocs from aggregation of Dy@C(82) towers in the LE and LE-LC coexistence regions, accompanied by gradual falling down of Dy@C(82) from the towers and permeation of the falling metallofullerenes into the LE phase during their compression-induced reorientation process. In the LC and solid phases, the Dy@C(82) flocs were dispersed into isolated towers, accompanied by the partial squeezing out of the embedded metallofullerenes to above the DPPC monolayer. The continuous falling down of Dy@C(82) from the towers resulted in their height decrease but diameter enlargement. When the surface pressure was increased to the kink value (53 mN/m), Dy@C(82) was almost completely extruded from the DPPC monolayers. These findings are believed to be important for understanding the impact of fullerenes, metallofullerenes, and nanomaterials in general on biological membranes.

  13. Isoelectronic tungsten doping in monolayer MoSe2 for carrier type modulation

    SciTech Connect

    Li, Xufan; Lin, Ming -Wei; Basile, Leonardo; Hus, Saban M.; Puretzky, Alexander A.; Lee, Jaekwang; Kuo, Yen -Chien; Chang, Lo -Yueh; Wang, Kai; Idrobo, Juan C.; Li, An -Ping; Chen, Chia-Hao; Rouleau, Christopher M.; Geohegan, David B.; Xiao, Kai

    2016-07-06

    Doping and alloying are effective ways to engineer the band structure and modulate the optoelectronic functionality of monolayer transition metal dichalcogenides (TMDs). In this work, we explore the synthesis and electronic properties of monolayer Mo1-xWxSe2 (0 < x < 0.18) alloys with almost 100% alloying degree. The isoelectronic substitutional doping of tungsten for molybdenum in the monolayer MoSe2 is shown to suppress its intrinsically n-type conduction behavior, with p-type conduction gradually emerging to become dominant with increasing W concentration in the alloys. Atomic resolution Z-contrast electron microscopy show that W is shown to substitute directly for Mo without the introduction of noticeable vacancy or interstitial defects, however with randomly-distributed W-rich regions ~2 nm in diameter. Scanning tunneling microscopy/spectroscopy measurements reveal that these W-rich regions exhibit a local band structure with the valence band maximum (VBM) closer to the Fermi level as compared with the Mo-rich regions in the monolayer Mo1-xWxSe2 crystal. These localized upshifts of the VBM in the local band structure appear responsible for the overall p-type behavior observed for the monolayer Mo1-xWxSe2 crystals. Stacked monolayers of n-type MoSe2 and p-type Mo1-xWxSe2 were demonstrated to form atomically thin, vertically stacked p n homojunctions with gate-tunable characteristics, which appear useful for future optoelectronic applications. Lastly, these results indicate that alloying with isoelectronic dopant atoms appears to be an effective and advantageous alternate strategy to doping or alloying with electron donors or acceptors in two-dimensional TMDs.

  14. Isoelectronic tungsten doping in monolayer MoSe2 for carrier type modulation

    DOE PAGES

    Li, Xufan; Lin, Ming -Wei; Basile, Leonardo; ...

    2016-07-06

    Doping and alloying are effective ways to engineer the band structure and modulate the optoelectronic functionality of monolayer transition metal dichalcogenides (TMDs). In this work, we explore the synthesis and electronic properties of monolayer Mo1-xWxSe2 (0 < x < 0.18) alloys with almost 100% alloying degree. The isoelectronic substitutional doping of tungsten for molybdenum in the monolayer MoSe2 is shown to suppress its intrinsically n-type conduction behavior, with p-type conduction gradually emerging to become dominant with increasing W concentration in the alloys. Atomic resolution Z-contrast electron microscopy show that W is shown to substitute directly for Mo without the introductionmore » of noticeable vacancy or interstitial defects, however with randomly-distributed W-rich regions ~2 nm in diameter. Scanning tunneling microscopy/spectroscopy measurements reveal that these W-rich regions exhibit a local band structure with the valence band maximum (VBM) closer to the Fermi level as compared with the Mo-rich regions in the monolayer Mo1-xWxSe2 crystal. These localized upshifts of the VBM in the local band structure appear responsible for the overall p-type behavior observed for the monolayer Mo1-xWxSe2 crystals. Stacked monolayers of n-type MoSe2 and p-type Mo1-xWxSe2 were demonstrated to form atomically thin, vertically stacked p n homojunctions with gate-tunable characteristics, which appear useful for future optoelectronic applications. Lastly, these results indicate that alloying with isoelectronic dopant atoms appears to be an effective and advantageous alternate strategy to doping or alloying with electron donors or acceptors in two-dimensional TMDs.« less

  15. Effect of shear stress on water and LDL transport through cultured endothelial cell monolayers.

    PubMed

    Kang, Hongyan; Cancel, Limary M; Tarbell, John M

    2014-04-01

    Previous animal experiments have shown that the transport of LDL into arterial walls is shear stress dependent. However, little work has probed shear effects on LDL transport in vitro where conditions are well defined and mechanisms are more easily explored. Therefore, we measured shear induced water and LDL fluxes across cultured bovine aortic endothelial (BAEC) monolayers in vitro and developed a three-pore model to describe the transport dynamics. Cell apoptosis was quantified by TdT-mediated dUTP nick end labeling (TUNEL) assay. We also examined the role of nitric oxide (NO) in shear induced water and LDL fluxes by incubating BAEC monolayers with an NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). Our results show that direct exposure of endothelial monolayers to 12 dyn/cm2 shear stress for 3 h elicited a 2.37-fold increase in water flux (Jv), a 3.00-fold increase in LDL permeability (Pe), a 1.32-fold increase in LDL uptake, and a 1.68-fold increase in apoptotic rate. L-NMMA treatment of BAEC monolayers blocked shear induced Jv response, but had no significant effect on shear responses of Pe and cell apoptosis. A long time shear exposure (12 h) of endothelial monolayers reduced Pe and apoptotic rate close to the baseline. These results suggest that an acute change in shear stress from a static baseline state induces increases in water flux that are mediated by an NO dependent mechanism. On the other hand, the permeability of endothelial monolayers to LDL is enhanced by a short term-shear application and reduced nearly to the baseline level by a longer time shear exposure, positively correlated to the leaky junctions forming around apoptotic cells.

  16. Structural and electric properties of two semifluorinated alkane monolayers compressed on top of a controlled hydrophobic monolayer substrate

    NASA Astrophysics Data System (ADS)

    El Abed, Abdel-Illah; Ionov, Radoslav; Goldmann, Michel

    2007-10-01

    We investigate the dynamic behavior upon lateral compression of two mixed films made with one of the two semifluorinated alkanes F(CF2)8(CH2)18H and F(CF2)10(CH2)10H and the natural α -helix alamethicin peptide. Surface pressure, surface potential versus molecular area isotherms, and grazing-incidence x-ray diffraction were applied to characterize this system. We show that both mixed films demix vertically to form two asymmetric flat bilayers where the lower layer is made of alamethicin and the upper layer is made of semifluorinated molecules. The structure matching of the semifluorinated alkanes (where the hydrophilic group is missing) with a suitable organization of the underlying alamethicin monolayer allows for a continuous compression of the upper semifluorinated layers while the density of the lower alamethicin monolayer remains constant. Comparing data of the two studied mixed films enables us to evaluate the effect of chain length on the in-plane organization of the molecules and on the electric properties of the upper layers.

  17. Significance of the amide functionality on DOPA-based monolayers on gold.

    PubMed

    Rībena, Dina; Alekseev, Alexander; van Asselen, Otto; Mannie, Gilbère J A; Hendrix, Marco M R M; van der Ven, Leendert G J; Sommerdijk, Nico A J M; de With, Gijsbertus

    2012-12-11

    The adhesive proteins secreted by marine mussels contain an unusual amino acid, 3,4-dihydroxyphenylalanine (DOPA), that is responsible for the cohesive and adhesive strength of this natural glue and gives mussels the ability to attach themselves to rocks, metals, and plastics. Here we report a detailed structural and spectroscopic investigation of the interface between N-stearoyldopamine and a single-crystalline Au(111) model surface and an amide-absent molecule, 4-stearylcatechol, also on Au(111), with the aim of understanding the role of the amide functionality in the packing, orientation, and fundamental interaction between the substrate and the monolayer formed from an aqueous environment by the Langmuir-Blodgett technique. The organization of monolayers on gold was observed directly and studied in detail by X-ray photoelectron spectroscopy (XPS), contact angle measurements (CA), surface-enhanced Raman spectroscopy (SERS), infrared reflection-absorption spectroscopy (IRRAS), and atomic force microscopy (AFM). Our study shows that within the monolayer the catecholic oxygen atoms are coordinated to the gold surface, having a more perpendicular orientation with respect to the aromatic ring and the apparently tilted alkyl chains, whereas the amide functionality stabilizes the monolayer that is formed.

  18. Realization of continuous Zachariasen carbon monolayer.

    PubMed

    Joo, Won-Jae; Lee, Jae-Hyun; Jang, Yamujin; Kang, Seog-Gyun; Kwon, Young-Nam; Chung, Jaegwan; Lee, Sangyeob; Kim, Changhyun; Kim, Tae-Hoon; Yang, Cheol-Woong; Kim, Un Jeong; Choi, Byoung Lyong; Whang, Dongmok; Hwang, Sung-Woo

    2017-02-01

    Rapid progress in two-dimensional (2D) crystalline materials has recently enabled a range of device possibilities. These possibilities may be further expanded through the development of advanced 2D glass materials. Zachariasen carbon monolayer, a novel amorphous 2D carbon allotrope, was successfully synthesized on germanium surface. The one-atom-thick continuous amorphous layer, in which the in-plane carbon network was fully sp(2)-hybridized, was achieved at high temperatures (>900°C) and a controlled growth rate. We verified that the charge carriers within the Zachariasen carbon monolayer are strongly localized to display Anderson insulating behavior and a large negative magnetoresistance. This new 2D glass also exhibited a unique ability as an atom-thick interface layer, allowing the deposition of an atomically flat dielectric film. It can be adopted in conventional semiconductor and display processing or used in the fabrication of flexible devices consisting of thin inorganic layers.

  19. Ground state structures in ferrofluid monolayers.

    PubMed

    Prokopieva, Taisia A; Danilov, Victor A; Kantorovich, Sofia S; Holm, Christian

    2009-09-01

    A combination of analytical calculations and Monte Carlo simulations is used to find the ground state structures in monodisperse ferrofluid monolayers. Taking into account the magnetic dipole-dipole interaction between all particles in the system we observe different topological structures that are likely to exist at low temperatures. The most energetically favored structures we find are rings, embedded rings, and rings side by side, and we are able to derive analytical expressions for the total energy of these structures. A detailed analysis of embedded rings and rings side by side shows that the interring interactions are negligible. We furthermore find that a single ideal ring is the ground state structure for a ferrofluid monolayer. We compared our theoretical predictions to the results of simulated annealing data and found them to be in excellent agreement.

  20. Piezoelectric monolayers as nonlinear energy harvesters.

    PubMed

    López-Suárez, Miquel; Pruneda, Miguel; Abadal, Gabriel; Rurali, Riccardo

    2014-05-02

    We study the dynamics of h-BN monolayers by first performing ab-initio calculations of the deformation potential energy and then solving numerically a Langevine-type equation to explore their use in nonlinear vibration energy harvesting devices. An applied compressive strain is used to drive the system into a nonlinear bistable regime, where quasi-harmonic vibrations are combined with low-frequency swings between the minima of a double-well potential. Due to its intrinsic piezoelectric response, the nonlinear mechanical harvester naturally provides an electrical power that is readily available or can be stored by simply contacting the monolayer at its ends. Engineering the induced nonlinearity, a 20 nm2 device is predicted to harvest an electrical power of up to 0.18 pW for a noisy vibration of 5 pN.

  1. Collective cell motion in endothelial monolayers

    PubMed Central

    Szabó, A.; Ünnep, R.; Méhes, E.; Twal, W. O.; Argraves, S. W.; Cao, Y.; Czirók, A.

    2011-01-01

    Collective cell motility is an important aspect of several developmental and pathophysiological processes. Despite its importance, the mechanisms that allow cells to be both motile and adhere to one another are poorly understood. In this study we establish statistical properties of the random streaming behavior of endothelial monolayer cultures. To understand the reported empirical findings, we expand the widely used cellular Potts model to include active cell motility. For spontaneous directed motility we assume a positive feedback between cell displacements and cell polarity. The resulting model is studied with computer simulations, and is shown to exhibit behavior compatible with experimental findings. In particular, in monolayer cultures both the speed and persistence of cell motion decreases, transient cell chains move together as groups, and velocity correlations extend over several cell diameters. As active cell motility is ubiquitous both in vitro and in vivo, our model is expected to be a generally applicable representation of cellular behavior. PMID:21076204

  2. Visualizing Individual Nitrogen Dopants in Monolayer Graphene

    SciTech Connect

    L Zhao; R He; K Rim; T Schiros; K Kim; H Zhou; C Gutierrez; S Chockalingam; C Arguello; et al.

    2011-12-31

    In monolayer graphene, substitutional doping during growth can be used to alter its electronic properties. We used scanning tunneling microscopy, Raman spectroscopy, x-ray spectroscopy, and first principles calculations to characterize individual nitrogen dopants in monolayer graphene grown on a copper substrate. Individual nitrogen atoms were incorporated as graphitic dopants, and a fraction of the extra electron on each nitrogen atom was delocalized into the graphene lattice. The electronic structure of nitrogen-doped graphene was strongly modified only within a few lattice spacings of the site of the nitrogen dopant. These findings show that chemical doping is a promising route to achieving high-quality graphene films with a large carrier concentration.

  3. Fracture characteristics of monolayer CVD-graphene.

    PubMed

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo

    2014-03-24

    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. The fracture toughness, describing the ability of a material containing inherent flaws to resist catastrophic failure, of the CVD-graphene has turned out to be exceptionally high, as compared to other carbon based 3D materials. These results imply that the CVD-graphene could be an ideal candidate as a structural material notwithstanding environmental susceptibility. In addition, the measurements reported here suggest that specific non-continuum fracture behaviors occurring in 2D monoatomic structures can be macroscopically well visualized and characterized.

  4. Fracture Characteristics of Monolayer CVD-Graphene

    NASA Astrophysics Data System (ADS)

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo

    2014-03-01

    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. The fracture toughness, describing the ability of a material containing inherent flaws to resist catastrophic failure, of the CVD-graphene has turned out to be exceptionally high, as compared to other carbon based 3D materials. These results imply that the CVD-graphene could be an ideal candidate as a structural material notwithstanding environmental susceptibility. In addition, the measurements reported here suggest that specific non-continuum fracture behaviors occurring in 2D monoatomic structures can be macroscopically well visualized and characterized.

  5. Realization of continuous Zachariasen carbon monolayer

    PubMed Central

    Joo, Won-Jae; Lee, Jae-Hyun; Jang, Yamujin; Kang, Seog-Gyun; Kwon, Young-Nam; Chung, Jaegwan; Lee, Sangyeob; Kim, Changhyun; Kim, Tae-Hoon; Yang, Cheol-Woong; Kim, Un Jeong; Choi, Byoung Lyong; Whang, Dongmok; Hwang, Sung-Woo

    2017-01-01

    Rapid progress in two-dimensional (2D) crystalline materials has recently enabled a range of device possibilities. These possibilities may be further expanded through the development of advanced 2D glass materials. Zachariasen carbon monolayer, a novel amorphous 2D carbon allotrope, was successfully synthesized on germanium surface. The one-atom-thick continuous amorphous layer, in which the in-plane carbon network was fully sp2-hybridized, was achieved at high temperatures (>900°C) and a controlled growth rate. We verified that the charge carriers within the Zachariasen carbon monolayer are strongly localized to display Anderson insulating behavior and a large negative magnetoresistance. This new 2D glass also exhibited a unique ability as an atom-thick interface layer, allowing the deposition of an atomically flat dielectric film. It can be adopted in conventional semiconductor and display processing or used in the fabrication of flexible devices consisting of thin inorganic layers. PMID:28246635

  6. Fracture Characteristics of Monolayer CVD-Graphene

    PubMed Central

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo

    2014-01-01

    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. The fracture toughness, describing the ability of a material containing inherent flaws to resist catastrophic failure, of the CVD-graphene has turned out to be exceptionally high, as compared to other carbon based 3D materials. These results imply that the CVD-graphene could be an ideal candidate as a structural material notwithstanding environmental susceptibility. In addition, the measurements reported here suggest that specific non-continuum fracture behaviors occurring in 2D monoatomic structures can be macroscopically well visualized and characterized. PMID:24657996

  7. Insights about α-tocopherol and Trolox interaction with phosphatidylcholine monolayers under peroxidation conditions through Brewster angle microscopy.

    PubMed

    Castro, Carla M; Pinheiro, Marina; Lúcio, Marlene; Giner-Casares, Juan J; Camacho, Luis; Lima, José L F C; Reis, Salette; Segundo, Marcela A

    2013-11-01

    Membranes are major targets to oxidative damage, particularly due to lipid oxidation, which has been associated to aging. The role, efficacy and membrane interaction of antioxidants is still unclear, requiring further understanding of molecular interaction. Hence, the objective of this work was to evaluate the interaction between antioxidants (α-tocopherol and its aqueous soluble analog Trolox) and the monolayer formed by phosphatidylcholine molecules at air/liquid interface upon peroxidation conditions, promoted by peroxyl radicals from thermal decomposition of 2,2'-azobis(2-methylpropionamidine) (AAPH). The interaction with three different monolayers, containing (i) 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine (DPPC), (ii) DDPC+α-linolenic acid, or (iii) egg yolk l-α-phosphatidylcholine (EPC), was ascertain by surface pressure (π)-molecular area (A) isotherms and by monitoring monolayer features through Brewster angle microscopy (BAM). The interaction of antioxidants with DPPC monolayers was confirmed by modifications on DPPC domain shape for α-tocopherol and through the maintenance of typical multilobed domain shape during an extended surface pressure interval for Trolox. Under peroxidation conditions, BAM images showed a clear interaction between components of AAPH subphase with the monolayer through changes on DPPC domain shape and appearance of white dots, located mainly at the frontier between the condensed and expanded liquid phases. White branched structures were also observed whenever both α-linolenic acid and α-tocopherol were present, indicating the segregation of these components within the monolayer, which is highly significant in biological systems. For EPC monolayers, no information from BAM was obtained but π-A isotherms confirmed the existence of the same interactions observed within the other two monolayers.

  8. Exploring atomic defects in molybdenum disulphide monolayers

    PubMed Central

    Hong, Jinhua; Hu, Zhixin; Probert, Matt; Li, Kun; Lv, Danhui; Yang, Xinan; Gu, Lin; Mao, Nannan; Feng, Qingliang; Xie, Liming; Zhang, Jin; Wu, Dianzhong; Zhang, Zhiyong; Jin, Chuanhong; Ji, Wei; Zhang, Xixiang; Yuan, Jun; Zhang, Ze

    2015-01-01

    Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment–theory investigation of point defects in monolayer molybdenum disulphide prepared by mechanical exfoliation, physical and chemical vapour deposition. Defect species are systematically identified and their concentrations determined by aberration-corrected scanning transmission electron microscopy, and also studied by ab-initio calculation. Defect density up to 3.5 × 1013 cm−2 is found and the dominant category of defects changes from sulphur vacancy in mechanical exfoliation and chemical vapour deposition samples to molybdenum antisite in physical vapour deposition samples. Influence of defects on electronic structure and charge-carrier mobility are predicted by calculation and observed by electric transport measurement. In light of these results, the growth of ultra-high-quality monolayer molybdenum disulphide appears a primary task for the community pursuing high-performance electronic devices. PMID:25695374

  9. Investigation on gallium ions impacting monolayer graphene

    SciTech Connect

    Wu, Xin; Zhao, Haiyan Yan, Dong; Pei, Jiayun

    2015-06-15

    In this paper, the physical phenomena of gallium (Ga{sup +}) ion impacting monolayer graphene in the nanosculpting process are investigated experimentally, and the mechanisms are explained by using Monte Carlo (MC) and molecular dynamics (MD) simulations. Firstly, the MC method is employed to clarify the phenomena happened to the monolayer graphene target under Ga{sup +} ion irradiation. It is found that substrate has strong influence on the damage mode of graphene. The mean sputtering yield of graphene under 30 keV Ga{sup +} ion irradiation is 1.77 and the least ion dose to completely remove carbon atoms in graphene is 21.6 ion/nm{sup 2}. Afterwards, the focused ion beam over 21.6 ion/nm{sup 2} is used for the irradiation on a monolayer graphene supported by SiO2 experimentally, resulting in the nanostructures, i.e., nanodot and nanowire array on the graphene. The performances of the nanostructures are characterized by atomic force microscopy and Raman spectrum. A plasma plume shielding model is put forward to explain the nanosculpting results of graphene under different irradiation parameters. In addition, two damage mechanisms are found existing in the fabrication process of the nanostructures by using empirical MD simulations. The results can help us open the possibilities for better control of nanocarbon devices.

  10. Phase transitions of monolayers on graphene

    NASA Astrophysics Data System (ADS)

    Kahn, Joshua; Dzyubenko, Boris; Vilches, Oscar; Cobden, David

    We have studied physisorbed layers of monatomic and diatomic gases on graphene. We used devices in which few-layer graphene, ranging from monolayer to trilayer, is suspended across a trench between two platinum contacts and are cleaned by thermal and current annealing. We found that the density of adsorbates is revealed by the conductance, similar to the case with nanotubes. The conductance change for a monolayer can be large. On trilayer graphene the adsorbed gases can be seen to exhibit transitions between two-dimensional phases identical to those on bulk graphite, including incommensurate and commensurate solid, fluid and vapor and multiple layers. New features appear in the conductance at the boundaries of the commensurate phase of Kr. We are able to measure single-particle binding energies very accurately and see how it depends on thickness; investigate the effects of changing disorder by gradually current annealing; and search for new phases in the case of monolayer graphene where atoms adsorbed on both sides can interact. We can map out the 2d phase diagrams very quickly by ohmic heating, which gives nearly instantaneous control of the temperature.

  11. Biocompatible Ferromagnetic Cr-Trihalide Monolayers

    NASA Astrophysics Data System (ADS)

    Sun, Qiang

    Cr with an electronic configuration of 3d54s1 possesses the largest atomic magnetic moment (6µB) of all elements in the 3d transition metal series. Furthermore, the trivalent chromium (Cr3+) is biocompatible and is widely found in food and supplements. Here using first principles calculations combined with Monte Carlo simulations based on Ising model, we systematically study a class of 2D ferromagnetic monolayers CrX3 (X = Cl, Br, I). The feasibility of exfoliation from their layered bulk phase is confirmed by the small cleavage energy and high in-plane stiffness. Spin-polarized calculations, combined with self consistently determined Hubbard U that accounts for strong correlation energy, demonstrate that CrX3 (X =Cl, Br, I) monolayers are ferromagnetic and Cr is trivalent and carries a magnetic moment of 3µB, the resulting Cr3+ ions are biocompatible. The corresponding Curie temperatures for CrCl3 CrBr3 CrI3 are are found to 66, 86, and 107 K, respectively, which can be increased to 323, 314, 293 K by hole doping. The biocompatibility and ferromagnetism render these Cr-containing trichalcogenide monolayers unique for applications.

  12. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers

    PubMed Central

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-01-01

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10−15 cm2 s−1, 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value. PMID:26227342

  13. Insertion of liquid crystal molecules into hydrocarbon monolayers

    SciTech Connect

    Popov, Piotr Mann, Elizabeth K.; Lacks, Daniel J.; Jákli, Antal

    2014-08-07

    Atomistic molecular dynamics simulations were carried out to investigate the molecular mechanisms of vertical surface alignment of liquid crystals. We study the insertion of nCB (4-Cyano-4{sup ′}-n-biphenyl) molecules with n = 0,…,6 into a bent-core liquid crystal monolayer that was recently found to provide good vertical alignment for liquid crystals. The results suggest a complex-free energy landscape for the liquid crystal within the layer. The preferred insertion direction of the nCB molecules (core or tail first) varies with n, which can be explained by entropic considerations. The role of the dipole moments was found to be negligible. As vertical alignment is the leading form of present day liquid crystal displays (LCD), these results will help guide improvement of the LCD technology, as well as lend insight into the more general problem of insertion of biological and other molecules into lipid and surfactant layers.

  14. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers

    NASA Astrophysics Data System (ADS)

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-07-01

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10-15 cm2 s-1, 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value.

  15. Nanoscale Nitrogen Doping in Silicon by Self-Assembled Monolayers.

    PubMed

    Guan, Bin; Siampour, Hamidreza; Fan, Zhao; Wang, Shun; Kong, Xiang Yang; Mesli, Abdelmadjid; Zhang, Jian; Dan, Yaping

    2015-07-31

    This Report presents a nitrogen-doping method by chemically forming self-assembled monolayers on silicon. Van der Pauw technique, secondary-ion mass spectroscopy and low temperature Hall effect measurements are employed to characterize the nitrogen dopants. The experimental data show that the diffusion coefficient of nitrogen dopants is 3.66 × 10(-15) cm(2) s(-1), 2 orders magnitude lower than that of phosphorus dopants in silicon. It is found that less than 1% of nitrogen dopants exhibit electrical activity. The analysis of Hall effect data at low temperatures indicates that the donor energy level for nitrogen dopants is located at 189 meV below the conduction band, consistent with the literature value.

  16. Photoluminescence of monolayer transition metal dichalcogenides integrated with VO2

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chuan; DeLello, Kursti; Zhang, Hai-Tian; Zhang, Kehao; Lin, Zhong; Terrones, Mauricio; Engel-Herbert, Roman; Robinson, Joshua A.

    2016-12-01

    Integrating a phase transition material with two-dimensional semiconductors can provide a route towards tunable opto-electronic metamaterials. Here, we integrate monolayer transition metal dichalcogenides with vanadium dioxide (VO2) thin films grown via molecular beam epitaxy to form a 2D/3D heterostructure. Vanadium dioxide undergoes an insulator-to-metal transition at 60-70 °C, which changes the band alignment between MoS2 and VO2 from a semiconductor-insulator junction to a semiconductor-metal junction. By switching VO2 between insulating and metallic phases, the modulation of photoluminescence emission in the 2D semiconductors was observed. This study demonstrates the feasibility to combine TMDs and functional oxides to create unconventional hybrid optoelectronic properties derived from 2D semiconductors that are linked to functional properties of oxides through proximity coupling.

  17. Graphene-like monolayer low-buckled honeycomb germanium film

    NASA Astrophysics Data System (ADS)

    He, Yezeng; Luo, Haibo; Li, Hui; Sui, Yanwei; Wei, Fuxiang; Meng, Qingkun; Yang, Weiming; Qi, Jiqiu

    2017-04-01

    Molecular dynamics simulations have been performed to study the cooling process of two-dimensional liquid germanium under nanoslit confinement. The results clearly indicates that the liquid germanium undergoes an obvious liquid-solid phase transition to a monolayer honeycomb film with the decrease of temperature, accompanying the rapid change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the solidification process, some hexagonal atomic islands first randomly emerge in the disordered liquid film and then grow up to stable crystal grains which keep growing and finally connect together to form a honeycomb polycrystalline film. It is worth noting that the honeycomb germanium film is low-buckled, quite different from the planar graphene.

  18. A primary battery-on-a-chip using monolayer graphene

    NASA Astrophysics Data System (ADS)

    Iost, Rodrigo M.; Crespilho, Frank N.; Kern, Klaus; Balasubramanian, Kannan

    2016-07-01

    We present here a bottom-up approach for realizing on-chip on-demand batteries starting out with chemical vapor deposition-grown graphene. Single graphene monolayers contacted by electrode lines on a silicon chip serve as electrodes. The anode and cathode are realized by electrodeposition of zinc and copper respectively onto graphene, leading to the realization of a miniature graphene-based Daniell cell on a chip. The electrolyte is housed partly in a gel and partly in liquid form in an on-chip enclosure molded using a 3d printer or made out of poly(dimethylsiloxane). The realized batteries provide a stable voltage (∼1.1 V) for many hours and exhibit capacities as high as 15 μAh, providing enough power to operate a pocket calculator. The realized batteries show promise for deployment as on-chip power sources for autonomous systems in lab-on-a-chip or biomedical applications.

  19. Degradation of octanethiol self-assembled monolayers from hydrogen-atom exposure: A molecular-scale study using scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Kautz, Natalie A.; Fogarty, Daniel P.; Kandel, S. Alex

    2007-08-01

    Octanethiol self-assembled monolayers were exposed to gas-phase hydrogen atoms, and the resulting changes in the order and chemical structure of the surface were monitored using scanning tunneling microscopy (STM). Extensive damage to the monolayer was observed in the form of both dark and bright features in STM images. These changes began along domain boundaries and moved into close-packed regions of the monolayer as hydrogen-atom exposure time increased. Increasing exposure also results in an accelerated rate of observed surface changes, indicating that the reactivity of the surface increases as a result of initial gas-surface reactions. Complex restructuring of the alkanethiol monolayer is observed, including defect formation and the disordering of the alkanethiol monolayer. However, in some cases the monolayer demonstrates the capability of self-healing, with local annealing and reordering of close-packed domains. This annealing and reordering likely results from increased mobility of surface-bound alkanethiolates in the vicinity of monolayer defects, or from diffusion and readsorption of transiently formed alkanethiol molecules.

  20. Reticulate evolution and incomplete lineage sorting among the ponderosa pines.

    PubMed

    Willyard, Ann; Cronn, Richard; Liston, Aaron

    2009-08-01

    Interspecific gene flow via hybridization may play a major role in evolution by creating reticulate rather than hierarchical lineages in plant species. Occasional diploid pine hybrids indicate the potential for introgression, but reticulation is hard to detect because ancestral polymorphism is still shared across many groups of pine species. Nucleotide sequences for 53 accessions from 17 species in subsection Ponderosae (Pinus) provide evidence for reticulate evolution. Two discordant patterns among independent low-copy nuclear gene trees and a chloroplast haplotype are better explained by introgression than incomplete lineage sorting or other causes of incongruence. Conflicting resolution of three monophyletic Pinus coulteri accessions is best explained by ancient introgression followed by a genetic bottleneck. More recent hybridization transferred a chloroplast from P. jeffreyi to a sympatric P. washoensis individual. We conclude that incomplete lineage sorting could account for other examples of non-monophyly, and caution against any analysis based on single-accession or single-locus sampling in Pinus.

  1. Incomplete Stevens-Johnson syndrome secondary to atypical pneumonia.

    PubMed

    Ramasamy, Anantharaman; Patel, Chiraush; Conlon, Christopher

    2011-10-04

    Steven-Johnson syndrome is a common condition characterised by erythematous target lesions on the skin and involvement of the oral mucosa, genitals and conjunctivae. It has been documented as one of the extra-pulmonary manifestations of Mycoplasma pneumoniae infection. Recently, there has been several documentation of an incomplete presentation of this syndrome - without the typical rash but with mucosal, conjunctival and genital involvement. Our case illustrates that the incomplete Steven-Johnson syndrome may present with oral mucosal and conjunctival involvement alone without skin or genital involvement. This important clinical diagnosis should not be missed due to its atypical presentation. Treatment of Steven-Johnson syndrome remains supportive along with treating the underlying infection if recognised.

  2. Investigations on the Incompletely Developed Plane Diagonal-Tension Field

    NASA Technical Reports Server (NTRS)

    Kuhn, Paul

    1940-01-01

    This report presents the results of an investigation on the incompletely developed diagonal-tension field. Actual diagonal-tension beams work in an intermediate stage between pure shear and pure diagonal tension; the theory developed by wagner for diagonal tension is not directly applicable. The first part of the paper reviews the most essential items of the theory of pure diagonal tension as well as previous attempts to formulate a theory of incomplete diagonal tension. The second part of the paper describes strain measurement made by the N. A. C. A. to obtain the necessary coefficients for the proposed theory. The third part of the paper discusses the stress analysis of diagonal-tension beams by means of the proposed theory.

  3. Survey incompleteness and the evolution of the QSO luminosity function

    NASA Technical Reports Server (NTRS)

    Majewski, Steven R.; Munn, Jeffrey A.; Kron, Richard G.; Bershady, Matthew A.; Smetanka, John J.; Koo, David C.

    1993-01-01

    We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88.

  4. Α Markov model for longitudinal studies with incomplete dichotomous outcomes.

    PubMed

    Efthimiou, Orestis; Welton, Nicky; Samara, Myrto; Leucht, Stefan; Salanti, Georgia

    2017-03-01

    Missing outcome data constitute a serious threat to the validity and precision of inferences from randomized controlled trials. In this paper, we propose the use of a multistate Markov model for the analysis of incomplete individual patient data for a dichotomous outcome reported over a period of time. The model accounts for patients dropping out of the study and also for patients relapsing. The time of each observation is accounted for, and the model allows the estimation of time-dependent relative treatment effects. We apply our methods to data from a study comparing the effectiveness of 2 pharmacological treatments for schizophrenia. The model jointly estimates the relative efficacy and the dropout rate and also allows for a wide range of clinically interesting inferences to be made. Assumptions about the missingness mechanism and the unobserved outcomes of patients dropping out can be incorporated into the analysis. The presented method constitutes a viable candidate for analyzing longitudinal, incomplete binary data.

  5. Α Markov model for longitudinal studies with incomplete dichotomous outcomes

    PubMed Central

    Welton, Nicky; Samara, Myrto; Leucht, Stefan; Salanti, Georgia

    2016-01-01

    Missing outcome data constitute a serious threat to the validity and precision of inferences from randomized controlled trials. In this paper, we propose the use of a multistate Markov model for the analysis of incomplete individual patient data for a dichotomous outcome reported over a period of time. The model accounts for patients dropping out of the study and also for patients relapsing. The time of each observation is accounted for, and the model allows the estimation of time‐dependent relative treatment effects. We apply our methods to data from a study comparing the effectiveness of 2 pharmacological treatments for schizophrenia. The model jointly estimates the relative efficacy and the dropout rate and also allows for a wide range of clinically interesting inferences to be made. Assumptions about the missingness mechanism and the unobserved outcomes of patients dropping out can be incorporated into the analysis. The presented method constitutes a viable candidate for analyzing longitudinal, incomplete binary data. PMID:27917593

  6. Noise effects on conflicting interest quantum games with incomplete information

    NASA Astrophysics Data System (ADS)

    Situ, Haozhen; Huang, Zhiming; Zhang, Cai

    2016-09-01

    Noise effects can be harmful to quantum information systems. In the present paper, we study noise effects in the context of quantum games with incomplete information, which have more complicated structure than quantum games with complete information. The effects of several paradigmatic noises on three newly proposed conflicting interest quantum games with incomplete information are studied using numerical optimization method. Intuitively noises will bring down the payoffs. However, we find that in some situations the outcome of the games under the influence of noise effects are counter-intuitive. Sometimes stronger noise may lead to higher payoffs. Some properties of the game, like quantum advantage, fairness and equilibrium, are invulnerable to some kinds of noises.

  7. Bayesian Inference of Natural Rankings in Incomplete Competition Networks

    NASA Astrophysics Data System (ADS)

    Park, Juyong; Yook, Soon-Hyung

    2014-08-01

    Competition between a complex system's constituents and a corresponding reward mechanism based on it have profound influence on the functioning, stability, and evolution of the system. But determining the dominance hierarchy or ranking among the constituent parts from the strongest to the weakest - essential in determining reward and penalty - is frequently an ambiguous task due to the incomplete (partially filled) nature of competition networks. Here we introduce the ``Natural Ranking,'' an unambiguous ranking method applicable to a round robin tournament, and formulate an analytical model based on the Bayesian formula for inferring the expected mean and error of the natural ranking of nodes from an incomplete network. We investigate its potential and uses in resolving important issues of ranking by applying it to real-world competition networks.

  8. Einstein's Boxes: Incompleteness of Quantum Mechanics Without a Separation Principle

    NASA Astrophysics Data System (ADS)

    Held, Carsten

    2015-09-01

    Einstein made several attempts to argue for the incompleteness of quantum mechanics (QM), not all of them using a separation principle. One unpublished example, the box parable, has received increased attention in the recent literature. Though the example is tailor-made for applying a separation principle and Einstein indeed applies one, he begins his discussion without it. An analysis of this first part of the parable naturally leads to an argument for incompleteness not involving a separation principle. I discuss the argument and its systematic import. Though it should be kept in mind that the argument is not the one Einstein intends, I show how it suggests itself and leads to a conflict between QM's completeness and a physical principle more fundamental than the separation principle, i.e. a principle saying that QM should deliver probabilities for physical systems possessing properties at definite times.

  9. Thiolated cyclodextrin self-assembled monolayer-like characterized with secondary ion mass spectrometry

    NASA Astrophysics Data System (ADS)

    Rabara, L.; Aranyosiova, M.; Velic, D.

    2011-01-01

    In the work the focus is on the preparation of self-assembled monolayer-like films consisting of thiolated cyclodextrin on gold substrate and a characterization by using secondary ion mass spectrometry. The short (1 min) and long (1 h) time preparations of self-assembled monolayer-like films, resulting in submonolayer and monolayer regimes, are investigated, respectively. The observed species of thiolated cyclodextrin (M as molecular ion) self-assembled monolayer-like films are assigned to three groups: Au xH yS z clusters, fragments with origin in cyclodextrin molecule associated with Au, and molecular ions. The group of Au xH yS z ( x = 2-17, y = 0-2, z = 1-5) clusters have higher intensities than other species in the positive and even more in negative mass spectra. Interestingly, the dependence between the number of Au and S atoms shows that with the increasing size of Au xH yS z clusters up to 11 Au atoms, the number of associated S atoms is also increasing and then decreasing. Molecular species as (M-S+H)Na +, (M+H)Na +, AuMNa +, (M 2-S)Na +, and M 2Na + are determined, and also in cationized forms with K +. The intensities of thiolated cyclodextrin fragments at the long time preparation are approximately 10 times higher than the intensities of the same fragments observed at the short time. The largest observed ions in thiolated cyclodextrin self-assembled monolayer-like films are AuM 2 and Au 2M. The thiolated cyclodextrin molecular ions are compared with hexadecanethiol molecular ions in the form of Au xM w where the values of x and w are smaller for thiolated cyclodextrin than for hexadecanethiol. This result is supported with larger, more compact, and more stabile thiolated cyclodextrin molecule.

  10. Contributions to the theory of incomplete tension bay

    NASA Technical Reports Server (NTRS)

    Schapitz, E

    1937-01-01

    The present report offers an approximate theory for the stress and deformation condition after buckling of the skin in reinforced panels and shells loaded in simple shear and compression and under combined stresses. The theory presents a unified scheme for stresses of these types. It is based upon the concept of a nonuniform stress distribution in the metal panel and its marked power of resistance against compressive stresses ("incomplete" tension bay).

  11. Distributed control systems with incomplete and uncertain information

    NASA Astrophysics Data System (ADS)

    Tang, Jingpeng

    Scientific and engineering advances in wireless communication, sensors, propulsion, and other areas are rapidly making it possible to develop unmanned air vehicles (UAVs) with sophisticated capabilities. UAVs have come to the forefront as tools for airborne reconnaissance to search for, detect, and destroy enemy targets in relatively complex environments. They potentially reduce risk to human life, are cost effective, and are superior to manned aircraft for certain types of missions. It is desirable for UAVs to have a high level of intelligent autonomy to carry out mission tasks with little external supervision and control. This raises important issues involving tradeoffs between centralized control and the associated potential to optimize mission plans, and decentralized control with great robustness and the potential to adapt to changing conditions. UAV capabilities have been extended several ways through armament (e.g., Hellfire missiles on Predator UAVs), increased endurance and altitude (e.g., Global Hawk), and greater autonomy. Some known barriers to full-scale implementation of UAVs are increased communication and control requirements as well as increased platform and system complexity. One of the key problems is how UAV systems can handle incomplete and uncertain information in dynamic environments. Especially when the system is composed of heterogeneous and distributed UAVs, the overall system complexity is increased under such conditions. Presented through the use of published papers, this dissertation lays the groundwork for the study of methodologies for handling incomplete and uncertain information for distributed control systems. An agent-based simulation framework is built to investigate mathematical approaches (optimization) and emergent intelligence approaches. The first paper provides a mathematical approach for systems of UAVs to handle incomplete and uncertain information. The second paper describes an emergent intelligence approach for UAVs

  12. Radiopaque Tagging Masks Caries Lesions following Incomplete Excavation in vitro.

    PubMed

    Schwendicke, F; Meyer-Lueckel, H; Schulz, M; Dörfer, C E; Paris, S

    2014-06-01

    One-step incomplete excavation seals caries-affected dentin under a restoration and appears to be advantageous in the treatment of deep lesions. However, it is impossible to discriminate radiographically between intentionally left, arrested lesions and overlooked or active lesions. This diagnostic uncertainty decreases the acceptance of minimally invasive excavation and might lead to unnecessary re-treatment of incompletely excavated teeth. Radiopaque tagging of sealed lesions might mask arrested lesions and assist in discrimination from progressing lesions. Therefore, we microradiographically screened 4 substances (SnCl2, AgNO3, CsF, CsCH3COO) for their effect on artificial lesions. Since water-dissolved tin chloride (SnCl2×Aq) was found to stably mask artificial lesions, we then investigated its radiographic effects on progressing lesions. Natural lesions were incompletely excavated and radiopaque tagging performed. Grey-value differences (△GV) between sound and carious dentin were determined and radiographs assessed by 20 dentists. While radiographic effects of SnCl2×Aq were stable for non-progressing lesions, they significantly decreased during a second demineralization (p < .001, t test). For natural lesions, tagging with SnCl2×Aq significantly reduced △GV (p < .001, Wilcoxon). Tagged lesions were detected significantly less often than untagged lesions (p < .001). SnCl2×Aq was suitable to mask caries-affected dentin and discriminate between arrested and progressing lesions in vitro. Radiopaque tagging could resolve diagnostic uncertainties associated with incomplete excavation.

  13. Simulated data supporting inbreeding rate estimates from incomplete pedigrees

    USGS Publications Warehouse

    Miller, Mark P.

    2017-01-01

    This data release includes:(1) The data from simulations used to illustrate the behavior of inbreeding rate estimators. Estimating inbreeding rates is particularly difficult for natural populations because parentage information for many individuals may be incomplete. Our analyses illustrate the behavior of a newly-described inbreeding rate estimator that outperforms previously described approaches in the scientific literature.(2) Python source code ("analytical expressions", "computer simulations", and "empricial data set") that can be used to analyze these data.

  14. 3D ultrasound image segmentation using multiple incomplete feature sets

    NASA Astrophysics Data System (ADS)

    Fan, Liexiang; Herrington, David M.; Santago, Peter, II

    1999-05-01

    We use three features, the intensity, texture and motion to obtain robust results for segmentation of intracoronary ultrasound images. Using a parameterized equation to describe the lumen-plaque and media-adventitia boundaries, we formulate the segmentation as a parameter estimation through a cost functional based on the posterior probability, which can handle the incompleteness of the features in ultrasound images by employing outlier detection.

  15. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111).

    PubMed

    Mendoza, Sandra M; Arfaoui, Imad; Zanarini, Simone; Paolucci, Francesco; Rudolf, Petra

    2007-01-16

    We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

  16. Monolayer contact doping of silicon surfaces and nanowires using organophosphorus compounds.

    PubMed

    Hazut, Ori; Agarwala, Arunava; Subramani, Thangavel; Waichman, Sharon; Yerushalmi, Roie

    2013-12-02

    Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures(1). MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms. In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

  17. Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

    PubMed Central

    Hazut, Ori; Agarwala, Arunava; Subramani, Thangavel; Waichman, Sharon; Yerushalmi, Roie

    2013-01-01

    Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms. In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station. PMID:24326774

  18. Electroactive self-assembled monolayers of unique geometric structures by using rigid norbornylogous bridges.

    PubMed

    Darwish, Nadim; Eggers, Paul K; Da Silva, Paulo; Zhang, Yi; Tong, Yujin; Ye, Shen; Gooding, J Justin; Paddon-Row, Michael N

    2012-01-02

    Herein, we describe the synthesis of straight (S) and L-shaped (L) norbornylogous bridges (NBs) with an anthraquinone moiety at the distal end as the redox-active head group and two thiol feet at the proximal end, by which the molecules assemble on gold surfaces. The NB molecules were shown to form self-assembled monolayers (SAMs) with a well-behaved surface redox process. The SAMs were characterized by using in situ IR spectroscopy, cyclic voltammetry, scanning tunnelling microscopy and electrochemical impedance spectroscopy. The surface selection rules associated with the IR band intensities allowed the estimation of the position of the anthraquinone moiety with respect to the surface and the tilt of the bridge with respect to the surface normal, both in pure and diluted monolayers. It is shown that the S- and L-NBs hold the plane of the anthraquinone moiety close to the surface normal or the surface tangent, respectively. Neither NB molecule changes its orientation if spaced by diluents on the surface. The difference in the structure of the S- and L-NB SAMs provides a suitable framework for the investigation of factors that govern electron transfer of anthraquinone moieties across self-assembled monolayers with limited structural ambiguity, as compared with the commonly used structurally flexible alkanethiol monolayers.

  19. Influence of bioregulators on the phospholipid Langmuir monolayers.

    PubMed

    Mogilevich, A S; Mogilevich, S E; Luik, A L

    1997-01-01

    Influence of bioregulators on the phospholipid Langmuir monolayers made of distearoylphosphatidylcholine and its equimolar mixture with dimitrystoylphosphatidylcholine was investigated. The results obtained allow concluding that the presence of physiologically active compounds in the subphase weakens the lipid-lipid interaction and increases the free energy change of air-liquid interface in the case of pure distearoylphosphatidylcholine monolayers, but in the case of mixed monolayers it leads both to the increase and decrease of these parameters. Presence of the dimirystoylphosphatidylcholine molecules with the short fatty acyl chains in the monolayer destabilizes it. This effect is partially compensated by the interaction between lipid and subphase molecules.

  20. Determination of the upper and lower limits of the mechanistic stoichiometry of incompletely coupled fluxes. Stoichiometry of incompletely coupled reactions.

    PubMed

    Beavis, A D; Lehninger, A L

    1986-07-15

    A rationale is formulated for the design of experiments to determine the upper and lower limits of the mechanistic stoichiometry of any two incompletely coupled fluxes J1 and J2. Incomplete coupling results when there is a branch at some point in the sequence of reactions or processes coupling the two fluxes. The upper limit of the mechanistic stoichiometry is given by the minimum value of dJ2/dJ1 obtained when the fluxes are systematically varied by changes in steps after the branch point. The lower limit is given by the maximum value of dJ2/dJ1 obtained when the fluxes are varied by changes in steps prior to the branch point. The rationale for determining these limits is developed from both a simple kinetic model and from a linear nonequilibrium thermodynamic treatment of coupled fluxes, using the mechanistic approach [Westerhoff, H. V. & van Dam, K. (1979) Curr. Top. Bioenerg. 9, 1-62]. The phenomenological stoichiometry, the flux ratio at level flow and the affinity ratio at static head of incompletely coupled fluxes are defined in terms of mechanistic conductances and their relationship to the mechanistic stoichiometry is discussed. From the rationale developed, experimental approaches to determine the mechanistic stoichiometry of mitochondrial oxidative phosphorylation are outlined. The principles employed do not require knowledge of the pathway or the rate of transmembrane leaks or slippage and may also be applied to analysis of the stoichiometry of other incompletely coupled systems, including vectorial H+/O and K+/O translocation coupled to mitochondrial electron transport.

  1. Metal monolayer deposition by replacement of metal adlayers on electrode surfaces

    NASA Astrophysics Data System (ADS)

    Brankovic, S. R.; Wang, J. X.; Adžić, R. R.

    2001-03-01

    A new metal deposition method is demonstrated by deposition of a submonolayer of Pt, a monolayer of Pd and a bilayer of Ag on Au(1 1 1) surfaces by using a Cu adlayer as a template. The deposition of these metals occurs as a spontaneous irreversible redox process in which a Cu adlayer, obtained by underpotential deposition, is oxidized by more noble metal cations, which are reduced and simultaneously deposited. The Pt deposit is a two-dimensional submonolayer consisting of partially interconnected nano-clusters of monoatomic height. Pd forms a uniform, but textured monolayer, while Ag forms a bilayer. The deposit of each metal uniformly covers the entire gold surface without preferential deposition along the step edges. This method provides surface adlayer-controlled growth, as compared to the current distribution controlled growth in conventional electrodeposition.

  2. Chiral solidification of a phospholipid monolayer

    NASA Technical Reports Server (NTRS)

    Langer, J. S.

    1985-01-01

    The formation of chiral solidlike domains observed by Weiss and McConnell (1984) in monolayers of depalmitoylphosphatidylcholine (DPPC) floating on an air-water interface is investigated theoretically. It is proposed that the diffusion tensor for the two-dimensional fluidlike phase of the DPPC molecules has a chiral component acting perpendicular to the concentration gradient and coupled to the rotational motion of a pinwheellike molecule by the viscous forces. Diagrams are provided, and numerical estimates of the forces involved are shown to be in agreement with the observed behavior of the structures.

  3. Fluidization of a horizontally driven granular monolayer.

    PubMed

    Heckel, Michael; Sack, Achim; Kollmer, Jonathan E; Pöschel, Thorsten

    2015-06-01

    We consider the transition of a horizontally vibrated monodisperse granular monolayer between its condensed state and its three-dimensional gaseous state as a function of the vibration parameters, amplitude, and frequency as well as particle number density. The transition is characterized by an abrupt change of the dynamical state which leaves its fingerprints in several measurable quantities including dissipation rate, sound emission, and a gap size which characterizes the sloshing motion of the material. The transition and its pronounced hysteresis is explained through the energy due to the collective motion of the particles relative to the container.

  4. Spontaneously adsorbed monolayer films: Fabrication, characterization, and application of monolayers of alkanethiol and sulfur-bearing cyclodestrin derivatives

    SciTech Connect

    Chinkap, Chung.

    1991-03-12

    Monolayers of n-alkanethiols (CH{sub 3}(CH{sub 2}){sub n}SH, n=1--17) and sulfur-bearing cyclodextrin derivatives spontaneously adsorbed on Ag and Au have been studied with a variety of surface characterization methods, such as infrared inflection spectroscopy, contact angle measurements, electro-chemistry, optical ellipsometry, and scanning tunneling microscopy. Long chain n-alkanethiols monolayers on Ag and Au are insulating to electron transfer and have contact angles indicative of well-ordered hydrocarbon terminated structures. Infrared and contact angle data indicate a different orientation of the methyl group with respect to the surface for chains with odd and even numbers of methylene groups. Compared to monolayers on Au, the alkanethiol monolayers on Ag are oriented more towards the surface normal. The observed odd-even effect methyl group orientation for these monolayers on Ag is offset by a methylene group from that on Au. The relationships between the structure and packing of the monolayers on Ag and Au and the composition, roughness, and crystallinity of the substrate are also discussed. Monolayers of sulfur-bearing cyclodextrin derivatives on Au and Ag are fabricated by spontaneous adsorption and characterized by the above techniques. Size-selectively and molecular recognition of the {alpha}- and {beta}- cyclodextrin cavity are shown with our monolayers. Because of molecular recognition, p-nitrophenol is retained preferrentially by the cyclodextrin monolayers over o-nitrophenol. 146 refs., 44 figs., 5 tabs.

  5. Polarized neutron reflectivity from monolayers of self-assembled magnetic nanoparticles.

    PubMed

    Mishra, D; Petracic, O; Devishvili, A; Theis-Bröhl, K; Toperverg, B P; Zabel, H

    2015-04-10

    We prepared monolayers of iron oxide nanoparticles via self-assembly on a bare silicon wafer and on a vanadium film sputter deposited onto a plane sapphire substrate. The magnetic configuration of nanoparticles in such a dense assembly was investigated by polarized neutron reflectivity. A theoretical model fit shows that the magnetic moments of nanoparticles form quasi domain-like configurations at remanence. This is attributed to the dipolar coupling amongst the nanoparticles.

  6. High school incompletion and childhood maltreatment among street-involved young people in Vancouver, Canada.

    PubMed

    Barker, Brittany; Kerr, Thomas; Dong, Huiru; Wood, Evan; DeBeck, Kora

    2017-03-01

    While the link between educational attainment and future health and wellness is well understood, little investigation has considered the potential impacts of distinct forms of childhood maltreatment on high school completion. In the present study, the relationship between five categories of childhood maltreatment (physical, emotional, and sexual abuse, and physical and emotional neglect) and completion of high school education were examined using the Childhood Trauma Questionnaire (CTQ). From September 2005 to May 2013, data were collected for the At-Risk Youth Study (ARYS), a cohort of street-involved young people who use illicit drugs in Vancouver, Canada. We used logistic regression to examine the relationship between childhood maltreatment and high school completion, while controlling for a range of potential confounding variables. Specifically, five separate models for each category of maltreatment and two combined models were employed to examine the relative associations between, and cumulative impact of, different forms of childhood maltreatment and educational attainment. Among 974 young people, 737 (76%) reported not completing high school. In separate multivariable analyses physical abuse, emotional abuse, physical neglect, and emotional neglect remained positively and independently associated with an incomplete high school education. In a combined multivariable model with all forms of childhood maltreatment considered together, emotional abuse (adjusted odds ratio = 2.08; 95% confidence interval: 1.51-2.86) was the only form of maltreatment that remained significantly associated with an incomplete high school education. The cumulative impact assessment indicated a moderate dose-dependent trend where the greater the number of different forms of childhood maltreatment the greater the risk of not completing a high school education. These findings point to the need for trauma-informed interventions to improve educational attainment among vulnerable young

  7. Monolayer film behavior of lipopolysaccharide from Pseudomonas aeruginosa at the air-water interface.

    PubMed

    Abraham, Thomas; Schooling, Sarah R; Beveridge, Terry J; Katsaras, John

    2008-10-01

    Lipopolysaccharide (LPS) is an essential biomacromolecule making up approximately 50% of the outer membrane of gram-negative bacteria. LPS chemistry facilitates cellular barrier and permeability functions and mediates interactions between the cell and its environment. To better understand the local interactions within LPS membranes, the monolayer film behavior of LPS extracted from Pseudomonas aeruginosa, an opportunistic pathogen of medical importance, was investigated by Langmuir film balance. LPS formed stable monolayers at the air-water interface and the measured lateral stresses and modulus (rigidity) of the LPS film in the compressed monolayer region were found to be appreciable. Scaling theories for two-dimensional (2D) polymer chain conformations were used to describe the pi-A profile, in particular, the high lateral stress region suggested that the polysaccharide segments reside at the 2D air-water interface. Although the addition of monovalent and divalent salts caused LPS molecules to adopt a compact conformation at the air-water interface, they did not appear to have any influence on the modulus (rigidity) of the LPS monolayer film under biologically relevant stressed conditions. With increasing divalent salt (CaCl2) content in the subphase, however, there is a progressive reduction of the LPS monolayer's collapse pressure, signifying that, at high concentrations, divalent salts weaken the ability of the membrane to withstand elevated stress. Finally, based on the measured viscoelastic response of the LPS films, we hypothesize that this property of LPS-rich outer membranes of bacteria permits the deformation of the membrane and may consequently protect bacteria from catastrophic structural failure when under mechanical-stress.

  8. Chemical films and monolayers on the water surface and their interactions with ultraviolet radiation: a pilot investigation

    NASA Astrophysics Data System (ADS)

    Schouten, Peter; Lemckert, Charles; Turnbull, David; Parisi, Alfio; Downs, Nathan; Underhill, Ian; Turner, Geoff

    2011-06-01

    Over the past 50 years numerous types of chemical films and monolayers have been deployed on top of a wide variety of water reserves in an endeavour to reduce evaporation. To date very little knowledge has been assimilated on how these chemical films and monolayers, once applied to a water surface, influence the underwater UV light field and, in turn, the delicate ecosystems that exist in aquatic environments. This manuscript presents underwater UV exposure profiles weighted to the DNA damage action spectrum measured under an octadecanol/hexadecanol/lime chemical film mixture, a silicone-based chemical film and an octadecanol monolayer applied to the water surface. UV transmission and absorption properties were also evaluated for each of these chemical films and monolayers. From this it was found that when chemical films/monolayers are applied to surface water they can reduce the penetration of biologically effective UV into the water column by up to 85% at a depth as small as 1 cm. This could have a positive influence on the aquatic ecosystem, as harmful UV radiation may be prevented from reaching and consequently damaging a variety of life forms or it could have a negative effect by potentially stopping aquatic organisms from adapting to solar ultraviolet radiation over extended application intervals. Additionally, there is currently no readily applicable system or technique available to readily detect or visualize chemical films and monolayers on the water surface. To overcome this problem a new method of monolayer and chemical film visualization, using a UV camera system, is detailed and tested and its applicability for usage in both laboratory-based trials and real-world operations is evaluated.

  9. Mixing behavior of a poly(ethylene glycol)-grafted phospholipid in monolayers at the air/water interface.

    PubMed

    Tsoukanova, Valeria; Salesse, Christian

    2008-11-18

    Mixed phospholipid monolayers hosting a poly(ethylene glycol) (PEG)-grafted distearoylphosphatidylethanolamine with a PEG molecular weight of 5000 (DSPE-PEG5000) spread at the air/water interface were used as model systems to study the effect of PEG-phospholipids on the lateral structure of PEG-grafted membrane-mimetic surfaces. DSPE-PEG5000 has been found to mix readily with distearoylphosphoethanolamine-succinyl (DSPE-succynil), a phospholipid whose structure resembles closely that of the phospholipid part of the DSPE-PEG5000 molecule. However, properties of mixed monolayers such as morphology and stability varied significantly with DSPE-PEG5000 content. In particular, our surface pressure, epifluorescence microscopy (EFM), and Brewster angle microscopy (BAM) studies have shown that mixtures containing 1-9 mol % of DSPE-PEG5000 form stable condensed monolayers with no sign of microscopic phase separation at surface pressures above approximately 25 mN/m. Yet, at 1 mol % of DSPE-PEG5000 in mixed monolayers, the two components have been found to behave nearly immiscibly at surface pressures below approximately 25 mN/m. For monolayers containing 18-75 mol % of DSPE-PEG5000, a high-pressure transition has been observed in the low-compressibility region of their isotherms, which has been identified on the basis of continuous BAM imaging of monolayer morphology, as reminiscent of the collapse nucleation in a pure DSPE-PEG5000 monolayer. Thus, the comparative analysis of our surface pressure, EFM, and BAM data has revealed that there exists a rather narrow range of mixture compositions with DSPE-PEG5000 content between 3 and 9 mol %, where somewhat homogeneous distribution of DSPE-PEG5000 molecules and high pressure stability can be achieved. This finding can be useful to "navigating" through possible mixture compositions while developing guidelines to the rational design of membrane-mimetic surfaces with highly controlled bio-nonfouling properties.

  10. Adsorption and dissociation of H2S on monometallic and monolayer bimetallic Ni/Pd(111) surfaces: A first-principles study

    NASA Astrophysics Data System (ADS)

    Li, Yi; Huang, Pan; Tao, Dandan; Wu, Juan; Qiu, Mei; Huang, Xin; Ding, Kaining; Chen, Wenkai; Su, Wenyue; Zhang, Yongfan

    2016-11-01

    Periodic density functional theory calculations have been performed to investigate the adsorption structures and dissociative reaction pathways for H2S molecule on Ni(111), Pd(111) and Ni/Pd(111) monolayer bimetallic surfaces with surface monolayer and subsurface monolayer structures. Our results indicate that, for the molecular adsorption mode, the introducing Pd atoms on Ni(111) can enhance the binding strength between H2S and the surface, while an opposite effect is achieved when the Ni monolayer is formed on Pd(111) surface. The decompositions of H2S molecule on all Ni/Pd(111) surfaces are exothermic, especially for the surfaces that the top layer is composed of Ni atoms. According to the predicted minimum energy paths that connect the molecular and dissociative states, two elementary steps are found for all Ni/Pd(111) metal surfaces, and the breaking of the first Hsbnd S bond is the rate-determining step for the H2S dissociation. Our results reveal that in most cases, the decomposition of H2S molecule on the monometallic and Ni/Pd(111) monolayer bimetallic surfaces is easy to happen. However, on the monolayer Ni-Pd(111) surface, there is a competition between the trapping-desorption channel and activated dissociation channel, which implies that depositing one monolayer Ni on a Pd(111) surface may help reducing sulfur poisoning by hindering the dissociation of H2S molecule.

  11. Study of structural order in porphyrin-fullerene dyad ZnDHD6ee monolayers by electron diffraction and atomic force microscopy

    SciTech Connect

    D'yakova, Yu. A.; Suvorova, E. I.; Orekhov, Andrei S.; Orekhov, Anton S.; Alekseev, A. S.; Gainutdinov, R. V.; Klechkovskaya, V. V. Tereschenko, E. Yu.; Tkachenko, N. V.; Lemmetyinen, H.; Feigin, L. A.; Kovalchuk, M. V.

    2013-11-15

    The structure of porphyrin-fullerene dyad ZnDHD6ee monolayers formed on the surface of aqueous subphase in a Langmuir trough and transferred onto solid substrates has been studied. The data obtained are interpreted using simulation of the structure of isolated molecules and their packing in monolayer and modeling of diffraction patterns from molecular aggregates having different sizes and degrees of order. Experiments on the formation of condensed ZnDHD6ee monolayers are described. The structure of these monolayers on a water surface is analyzed using {pi}-A isotherms. The structure of the monolayers transferred onto solid substrates is investigated by electron diffraction and atomic force microscopy. The unit-cell parameters of two-dimensional domains, which are characteristic of molecular packing in monolayers and deposited films, are determined. Domains are found to be organized into a texture (the molecular axes are oriented by the [001] direction perpendicular to the substrate). The monolayers contain a limited number of small 3D domains.

  12. Compartmentalization and delivery via asymmetric copolymer monolayers with swollen or inverse swollen micelles

    SciTech Connect

    Guo, Hong Xia; Olvera de la Cruz, Monica

    2011-01-01

    We investigate the equilibrium properties and the underlying dynamics of emulsions formed in asymmetric A-B copolymers in matrices of immiscible B and C molecular fluids using coarse-grained molecular dynamics simulations. The emulsions are generated by introducing net attractions among the A units of the copolymers and the C molecules. They coexist with an absorbed copolymer monolayer. We determine the interfacial properties as the emulsions are forming. In general, highly asymmetric copolymers self-assemble within the B-matrix phase into swollen micelles; the cores of which are composed of C-component material. Less asymmetric copolymers, however, after initially budding and eventually fissioning from the interfacial copolymer monolayer, generate emulsified “inverse swollen micelles” within the C-matrix phase. These stable inverse (crew-cut) swollen micelles, which form under the inward bending of the saturated or oversaturated interfaces toward the longer B-block due to the attraction between the A and C units, can encapsulate large amounts of B-matrix component in their cores. This monolayer collapse mechanism can be exploited to generate nanoreactors or containers that enhance the delivery of molecular components into immiscible molecular fluid environments.

  13. Analytical Solution for Reactive Solute Transport Considering Incomplete Mixing

    NASA Astrophysics Data System (ADS)

    Bellin, A.; Chiogna, G.

    2013-12-01

    The laboratory experiments of Gramling et al. (2002) showed that incomplete mixing at the pore scale exerts a significant impact on transport of reactive solutes and that assuming complete mixing leads to overestimation of product concentration in bimolecular reactions. We consider here the family of equilibrium reactions for which the concentration of the reactants and the product can be expressed as a function of the mixing ratio, the concentration of a fictitious non reactive solute. For this type of reactions we propose, in agreement with previous studies, to model the effect of incomplete mixing at scales smaller than the Darcy scale assuming that the mixing ratio is distributed within an REV according to a Beta distribution. We compute the parameters of the Beta model by imposing that the mean concentration is equal to the value that the concentration assumes at the continuum Darcy scale, while the variance decays with time as a power law. We show that our model reproduces the concentration profiles of the reaction product measured in the Gramling et al. (2002) experiments using the transport parameters obtained from conservative experiments and an instantaneous reaction kinetic. The results are obtained applying analytical solutions both for conservative and for reactive solute transport, thereby providing a method to handle the effect of incomplete mixing on multispecies reactive solute transport, which is simpler than other previously developed methods. Gramling, C. M., C. F. Harvey, and L. C. Meigs (2002), Reactive transport in porous media: A comparison of model prediction with laboratory visualization, Environ. Sci. Technol., 36(11), 2508-2514.

  14. A Supernodal Approach to Incomplete LU Factorization with Partial Pivoting

    SciTech Connect

    Li, Xiaoye Sherry; Shao, Meiyue

    2009-06-25

    We present a new supernode-based incomplete LU factorization method to construct a preconditioner for solving sparse linear systems with iterative methods. The new algorithm is primarily based on the ILUTP approach by Saad, and we incorporate a number of techniques to improve the robustness and performance of the traditional ILUTP method. These include the new dropping strategies that accommodate the use of supernodal structures in the factored matrix. We present numerical experiments to demonstrate that our new method is competitive with the other ILU approaches and is well suited for today's high performance architectures.

  15. Bayesian model updating using incomplete modal data without mode matching

    NASA Astrophysics Data System (ADS)

    Sun, Hao; Büyüköztürk, Oral

    2016-04-01

    This study investigates a new probabilistic strategy for model updating using incomplete modal data. A hierarchical Bayesian inference is employed to model the updating problem. A Markov chain Monte Carlo technique with adaptive random-work steps is used to draw parameter samples for uncertainty quantification. Mode matching between measured and predicted modal quantities is not required through model reduction. We employ an iterated improved reduced system technique for model reduction. The reduced model retains the dynamic features as close as possible to those of the model before reduction. The proposed algorithm is finally validated by an experimental example.

  16. Conditioning Analysis of Incomplete Cholesky Factorizations with Orthogonal Dropping

    SciTech Connect

    Napov, Artem

    2013-08-01

    The analysis of preconditioners based on incomplete Cholesky factorization in which the neglected (dropped) components are orthogonal to the approximations being kept is presented. General estimate for the condition number of the preconditioned system is given which only depends on the accuracy of individual approximations. The estimate is further improved if, for instance, only the newly computed rows of the factor are modified during each approximation step. In this latter case it is further shown to be sharp. The analysis is illustrated with some existing factorizations in the context of discretized elliptic partial differential equations.

  17. Incomplete block factorization preconditioning for indefinite elliptic problems

    SciTech Connect

    Guo, Chun-Hua

    1996-12-31

    The application of the finite difference method to approximate the solution of an indefinite elliptic problem produces a linear system whose coefficient matrix is block tridiagonal and symmetric indefinite. Such a linear system can be solved efficiently by a conjugate residual method, particularly when combined with a good preconditioner. We show that specific incomplete block factorization exists for the indefinite matrix if the mesh size is reasonably small. And this factorization can serve as an efficient preconditioner. Some efforts are made to estimate the eigenvalues of the preconditioned matrix. Numerical results are also given.

  18. Incompletely-Condensed Fluorinated Silsesquioxane: Synthesis and Crystal Structure

    DTIC Science & Technology

    2011-11-29

    other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a ...ABSTRACT A recently developed sub-class of POSS, fluorinated polyhedral oligomeric silsesquioxane (F-POSS), consists of a Si-O core with a periphery of...incompletely-condensed silsesquioxane, (CF3(CF2)7CH2CH2)8Si8O11(OH)2, has been synthesized via a multi-step synthesis (52% yield). The structure was

  19. A computer program for estimation from incomplete multinomial data

    NASA Technical Reports Server (NTRS)

    Credeur, K. R.

    1978-01-01

    Coding is given for maximum likelihood and Bayesian estimation of the vector p of multinomial cell probabilities from incomplete data. Also included is coding to calculate and approximate elements of the posterior mean and covariance matrices. The program is written in FORTRAN 4 language for the Control Data CYBER 170 series digital computer system with network operating system (NOS) 1.1. The program requires approximately 44000 octal locations of core storage. A typical case requires from 72 seconds to 92 seconds on CYBER 175 depending on the value of the prior parameter.

  20. Incomplete block SSOR preconditionings for high order discretizations

    SciTech Connect

    Kolotilina, L.

    1994-12-31

    This paper considers the solution of linear algebraic systems Ax = b resulting from the p-version of the Finite Element Method (FEM) using PCG iterations. Contrary to the h-version, the p-version ensures the desired accuracy of a discretization not by refining an original finite element mesh but by introducing higher degree polynomials as additional basis functions which permits to reduce the size of the resulting linear system as compared with the h-version. The suggested preconditionings are the so-called Incomplete Block SSOR (IBSSOR) preconditionings.

  1. Chronic incomplete atrioventricular block induced by radiofrequency catheter ablation

    SciTech Connect

    Huang, S.K.; Bharati, S.; Graham, A.R.; Gorman, G.; Lev, M. )

    1989-10-01

    To determine if catheter ablation of the atrioventricular (AV) junction with radiofrequency energy can induce chronic incomplete (first- and second-degree) AV block to avoid the need for a permanent pacemaker, 20 closed-chest dogs were studied. Group 1 (10 dogs) received radiofrequency energy (750 kHz) with a fixed power setting (5 or 10 W) while increasing the pulse duration from 10 to 50 seconds for each application. Group 2 (10 dogs) received energy with a fixed pulse duration (20 or 30 seconds) while increasing the power setting from 5 to 10 W or from 10 to 20 W during each energy delivery. Radiofrequency energy was delivered between a chest-patch electrode and the distal electrode of a regular 7F tripolar His bundle catheter. For each application, the energy delivery was interrupted when (1) the PR interval prolonged (greater than 50%) or (2) second-degree or complete AV block occurred and persisted up to 5 seconds. The ablation procedure ended when there was (1) persistent PR prolongation (greater than 50%) or persistent second-degree AV block (lasting greater than 30 minutes) after ablation, (2) occurrence of two consecutive transient (less than 1 minute) complete AV blocks after each energy delivery, or (3) complete AV block (lasting greater than 2 minutes) after ablation. Of seven dogs in group 1 and five dogs in group 2 in which incomplete AV block was achieved 1 hour after the procedure, six in group 1 and five in group 2 remained in incomplete AV block 2-3 months after ablation. One dog in group 1 progressed into complete AV block. Of the remaining three dogs in group 1 and five dogs in group 2 in which complete AV block was initially achieved 1 hour after ablation, two in group 1 and four in group 2 continued to have complete AV block, whereas one in each group had AV conduction returned to incomplete at 1-2 months of follow-up.

  2. Uniform Asymptotic Expansion for the Incomplete Beta Function

    NASA Astrophysics Data System (ADS)

    Nemes, Gergő; Olde Daalhuis, Adri B.

    2016-10-01

    In [Temme N.M., Special functions. An introduction to the classical functions of mathematical physics, A Wiley-Interscience Publication, John Wiley & Sons, Inc., New York, 1996, Section 11.3.3.1] a uniform asymptotic expansion for the incomplete beta function was derived. It was not obvious from those results that the expansion is actually an asymptotic expansion. We derive a remainder estimate that clearly shows that the result indeed has an asymptotic property, and we also give a recurrence relation for the coefficients.

  3. Incomplete optical shielding in cold sodium atom traps

    SciTech Connect

    Yurovsky, Vladimir; Ben-Reuven, Abraham

    1997-01-05

    A simple two-channel model, based on the semiclassical Landau-Zener (LZ) approximation, with averaging over angle-dependent exponents, is proposed as a fast means for accounting for the incomplete optical shielding of collisions, as observed in recent experiments conducted by Weiner and co-workers on ultracold sodium-atom traps, and its dependence on the laser polarization. The model yields a reasonably good agreement with the recent quantum close-coupling calculations of Julienne and co-workers. The remaining discrepancy between both theories and the data is qualitatively attributed to a partial overlap of the collision ranges at which loss processes and optical shielding occur.

  4. Synthesis of copper monolayer and particles at aqueous organic interface

    NASA Astrophysics Data System (ADS)

    Yang, Jian-guang; Yang, Sheng-hai; Okamoto, Takeshi; Bessho, Takeshi; Satake, Shigeru; Ichino, Ryoichi; Okido, Masazumi

    2006-12-01

    Using aqueous-organic interface (water-oleic acid) reduction of Cu 2+ by ascorbic acid, hydrophobic copper monolayer and copper particles have been prepared and characterized. The resultant monolayer could be transferred from the interface onto solid substrate or be dissolved to yield an organosol and copper nanoparticles.

  5. Hydrogen exchange mass spectrometry of proteins at Langmuir monolayers

    PubMed Central

    Pirrone, Gregory F.; Vernon, Briana C.; Kent, Michael S.; Engen, John R.

    2015-01-01

    Hydrogen exchange (HX) mass spectrometry (MS) is valuable for providing conformational information for proteins/peptides that are very difficult to analyze with other methods such as peripheral membrane proteins and peptides that interact with membranes. We developed a new type of HX MS measurement that integrates Langmuir monolayers. A lipid monolayer was generated, a peptide or protein associated with it, and then the monolayer-associated peptide or protein was exposed to deuterium. The deuterated species was recovered from the monolayer, digested, and deuterium incorporation monitored by MS. Test peptides showed that deuterium recovery in an optimized protocol was equivalent to deuterium recovery in conventional solution HX MS. The reproducibility of the measurements was high despite the requirement of generating a new monolayer for each deuterium labeling time. We validated that known conformational changes in the presence of a monolayer/membrane could be observed with the peptide melittin and the myristoylated protein Arf-1. Results in an accompanying paper show that the method can reveal details of conformational changes in a protein (HIV-1 Nef) which adopts a different conformation depending on if it can insert into the lipid layer. Overall, the HX MS Langmuir monolayer method provided new and meaningful conformational information for proteins that associate with lipid layers. The combination of HX MS results with neutron or X-ray reflection of the same proteins in Langmuir monolayers can be more informative than isolated use of either method. PMID:26134943

  6. Topological, Valleytronic, and Optical Properties of Monolayer PbS.

    PubMed

    Wan, Wenhui; Yao, Yugui; Sun, Liangfeng; Liu, Cheng-Cheng; Zhang, Fan

    2017-03-01

    A PbS monolayer is demonstrated to be a novel platform for topological, valleytronic, and optical phenomena. Compressive strain can turn the trivial monolayer into a topological insulator. Optical pumping can facilitate charge, spin, and valley Hall effects tunable by external strain and light ellipticity. Similar results apply to other IV-VI semiconductors.

  7. SYNCHROTRON X - RAY OBSERVATIONS OF A MONOLAYER TEMPLATE FOR MINERALIZATION.

    SciTech Connect

    DIMASI,E.; GOWER,L.B.

    2000-11-27

    Mineral nucleation at a Langmuir film interface has been studied by synchrotron x-ray scattering. Diluted calcium bicarbonate solutions were used as subphases for arachidic and stearic acid monolayers, compressed in a Langmuir trough. Self-assembly of the monolayer template is observed directly, and subsequent crystal growth monitored in-situ.

  8. m-Terphenyl thiols: rigid and bulky molecules for the formation of bioactive self-assembled monolayers on gold.

    PubMed

    Dickie, Diane A; Chan, Andy Y C; Jalali, Hanifa; Jenkins, Hilary A; Yu, Hua-Zhong; Clyburne, Jason A C

    2004-11-07

    The m-terphenyl 4-mercaptomethyl-2,6-diphenylbenzoic acid (3), was prepared and shown to form omega-carboxyl terminated self-assembled monolayers (SAMs) on gold with high surface pKa(10.1 +/- 0.2) and low density favourable for the binding of biological macromolecules.

  9. Influence of buried hydrogen-bonding groups within monolayer films on gas-surface energy exchange and accommodation.

    PubMed

    Ferguson, M K; Lohr, J R; Day, B S; Morris, J R

    2004-02-20

    Self-assembled monolayers (SAMs) of carbonyl-containing alkanethiols on gold are employed to explore the influence of hydrogen-bonding interactions on gas-surface energy exchange and accommodation. H-bonding, COOH-terminated SAMs are found to produce more impulsive scattering and less thermal accommodation than non-H-bonding, COOCH3-terminated monolayers. For carbamate-functionalized SAMs of the form Au/S(CH2)16OCONH(CH2)(n-1)CH3, impulsive scattering decreases and accommodation increases as the H-bonding group is positioned farther below the terminal CH3.

  10. Methylene blue adsorption on a DMPA lipid langmuir monolayer.

    PubMed

    Giner Casares, Juan José; Camacho, Luis; Martín-Romero, Maria Teresa; López Cascales, José Javier

    2010-07-12

    Adsorption of methylene blue (MB) onto a dimyristoylphosphatidic acid (DMPA) Langmuir air/water monolayer is studied by molecular dynamics (MD) simulations, UV reflection spectroscopy and surface potential measurements. The free-energy profile associated with MB transfer from water to the lipid monolayer shows two minima of -66 and -60 kJ mol(-1) for its solid and gas phase, respectively, corresponding to a spontaneous thermodynamic process. From the position of the free-energy minima, it is possible to predict the precise location of MB in the interior of the DMPA monolayer. Thus, MB is accommodated in the phosphoryl or carbonyl region of the DMPA Langmuir air/water interface, depending on the isomorphic state (solid or gas phase, respectively). Reorientation of MB, measured from the bulk solution to the interior of the lipid monolayer, passes from a random orientation in bulk solution to an orientation parallel to the surface of the lipid monolayer when MB is absorbed.

  11. Reorientation of a dipolar monolayer and dipolar solvent.

    PubMed

    Yi, Taeil; Lichter, Seth

    2014-06-01

    The reliable persistence of an adhered monolayer film on a substrate is critical for film function. The process by which monolayers degrade or disperse remains unclear. Our study investigates the properties and dynamics of a solute of dipolar molecules initially adhered as a monolayer on a substrate in a water-like Stockmayer solvent. We find that for a rigid solute, both the solute and solvent show qualitatively different dynamics than for a flexible solute and its solvent. For the rigid solute, spreading is hindered and solvent orientation is more pronounced. We formulate a simple kinetic model that shows qualitatively similar results to the molecular dynamics simulations of the time evolution of the monolayer. Simple kinetics of molecules on substrates is a starting point for understanding important industrial monolayer applications and complex interactions on membranes.

  12. Dynamically Tuning Particle Interactions and Assemblies at Soft Interfaces: Reversible Order-Disorder Transitions in 2D Particle Monolayers.

    PubMed

    Park, Bum Jun; Lee, Daeyeon

    2015-09-16

    Particles trapped at fluid interfaces experience long-range interactions that determine their assembly behavior. Because particle interactions at fluid interfaces tend to be unusually strong, once particles organize themselves into a 2D assembly, it is challenging to induce changes in their microstructure. In this report, a new approach is presented to induce reversible order-disorder transitions (ODTs) in the 2D monolayer of colloidal particles trapped at a soft gel-fluid interface. Particles at the soft interface, consisting of a nonpolar superphase and a weakly gelled subphase, initially form a monolayer with a highly ordered structure. The structure of this monolayer can be dynamically varied by the addition or removal of the oil phase. Upon removing the oil via evaporation, the initially ordered particle monolayer undergoes ODT, driven by capillary attractions. The ordered monolayer can be recovered through disorder-to-order transition by simply adding oil atop the particle-laden soft interface. The possibility to dynamically tune the interparticle interactions using soft interfaces can potentially enable control of the transport and mechanical properties of particle-laden interfaces and provide model systems to study particle-laden soft interfaces that are relevant to biological tissues or organs.

  13. Strictly monolayer large continuous MoS{sub 2} films on diverse substrates and their luminescence properties

    SciTech Connect

    Mohapatra, P. K.; Deb, S.; Singh, B. P.; Vasa, P.; Dhar, S.

    2016-01-25

    Despite a tremendous interest on molybdenum disulfide as a thinnest direct band gap semiconductor, single step synthesis of a large area purely monolayer MoS{sub 2} film has not yet been reported. Here, we report a CVD route to synthesize a continuous film of strictly monolayer MoS{sub 2} covering an area as large as a few cm{sup 2} on a variety of different substrates without using any seeding material or any elaborate pretreatment of the substrate. This is achieved by allowing the growth to take place in the naturally formed gap between a piece of SiO{sub 2} coated Si wafer and the substrate, when the latter is placed on top of the former inside a CVD reactor. We propose a qualitative model to explain why the MoS{sub 2} films are always strictly monolayer in this method. The photoluminescence study of these monolayers shows the characteristic excitonic and trionic features associated with monolayer MoS{sub 2}. In addition, a broad defect related luminescence band appears at ∼1.7 eV. As temperature decreases, the intensity of this broad feature increases, while the band edge luminescence reduces.

  14. The response of phytoplankton and microlayer-adapted bacteria to monolayer application in a humic, eutrophic irrigation dam.

    PubMed

    Pittaway, P; Matveev, V

    2017-01-01

    Repeat applications of artificial monolayers to farm irrigation dams to reduce evaporative loss may adversely affect water quality by enhancing populations of microlayer-adapted bacteria and blue-green algae. The microlayer, subsurface and water column of a 16 ha dam were monitored every two weeks for 18 months, to benchmark the seasonal dynamics of phytoplankton and microlayer-adapted bacteria prior to monolayer application. Results for Secchi depth, total P, total N, chlorophyll a, phytobiovolume and UV254 absorbance, characterise Logan's Dam as humic and hypereutrophic. Seasonal peaks in the cyanobacterial species Microcystis aeruginosa and Anabaena sp. associated with regular thermal stratification periods over summer, exceeded the Queensland algal bloom alert level. Dissolved organic matter derived from aromatic char in the black soil used to construct the dam was the main substrate for microlayer-adapted bacteria. Intermittent monolayer application over seven weeks in late summer temporarily increased surface pressure, indicating a condensed monolayer had formed, with no increase in chemical oxygen demand or in populations of cyanobacteria or microlayer-adapted bacteria. The increase in dissolved organic carbon was well below the concentration recorded after a pump ingress event in late spring. In this humic hypereutrophic irrigation dam, repeat applications of the experimental monolayer formulation did not adversely affect water quality.

  15. Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence.

    PubMed

    Yuan, Cailei; Cao, Yingjie; Luo, Xingfang; Yu, Ting; Huang, Zhenping; Xu, Bo; Yang, Yong; Li, Qinliang; Gu, Gang; Lei, Wen

    2015-11-07

    The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis.

  16. Phase winding of a nematic liquid crystal by dynamic localized reorientation of an azo-based self-assembled monolayer.

    PubMed

    Shi, Yue; Fang, Guanjiu; Glaser, Matthew A; Maclennan, Joseph E; Korblova, Eva; Walba, David M; Clark, Noel A

    2014-08-12

    Azobenzene-based molecules forming a self-assembled monolayer (SAM) tethered to a glass surface are highly photosensitive and readily reorient liquid crystals in contact with them when illuminated with polarized actinic light. We probe the coupling of such monolayers to nematic liquid crystal in a hybrid cell by studying the dynamics of liquid crystal reorientation in response to local orientational changes of the monolayer induced by a focused actinic laser with a rotating polarization. The steady increase in the azimuth of the mean molecular orientation of the SAM around the laser beam locally reorients the nematic, winding up an extended set of nested rings of splay-bend nematic director reorientation until the cumulative elastic torque exceeds that of the surface coupling within the beam, after which the nematic director starts to slip. Quantitative analyses of the ring dynamics allow measurements of the anchoring strength of the azo-SAM and its interaction with the nematic liquid crystal.

  17. Dynamic Financial Constraints: Distinguishing Mechanism Design from Exogenously Incomplete Regimes*

    PubMed Central

    Karaivanov, Alexander; Townsend, Robert M.

    2014-01-01

    We formulate and solve a range of dynamic models of constrained credit/insurance that allow for moral hazard and limited commitment. We compare them to full insurance and exogenously incomplete financial regimes (autarky, saving only, borrowing and lending in a single asset). We develop computational methods based on mechanism design, linear programming, and maximum likelihood to estimate, compare, and statistically test these alternative dynamic models with financial/information constraints. Our methods can use both cross-sectional and panel data and allow for measurement error and unobserved heterogeneity. We estimate the models using data on Thai households running small businesses from two separate samples. We find that in the rural sample, the exogenously incomplete saving only and borrowing regimes provide the best fit using data on consumption, business assets, investment, and income. Family and other networks help consumption smoothing there, as in a moral hazard constrained regime. In contrast, in urban areas, we find mechanism design financial/information regimes that are decidedly less constrained, with the moral hazard model fitting best combined business and consumption data. We perform numerous robustness checks in both the Thai data and in Monte Carlo simulations and compare our maximum likelihood criterion with results from other metrics and data not used in the estimation. A prototypical counterfactual policy evaluation exercise using the estimation results is also featured. PMID:25246710

  18. An information propagation model considering incomplete reading behavior in microblog

    NASA Astrophysics Data System (ADS)

    Su, Qiang; Huang, Jiajia; Zhao, Xiande

    2015-02-01

    Microblog is one of the most popular communication channels on the Internet, and has already become the third largest source of news and public opinions in China. Although researchers have studied the information propagation in microblog using the epidemic models, previous studies have not considered the incomplete reading behavior among microblog users. Therefore, the model cannot fit the real situations well. In this paper, we proposed an improved model entitled Microblog-Susceptible-Infected-Removed (Mb-SIR) for information propagation by explicitly considering the user's incomplete reading behavior. We also tested the effectiveness of the model using real data from Sina Microblog. We demonstrate that the new proposed model is more accurate in describing the information propagation in microblog. In addition, we also investigate the effects of the critical model parameters, e.g., reading rate, spreading rate, and removed rate through numerical simulations. The simulation results show that, compared with other parameters, reading rate plays the most influential role in the information propagation performance in microblog.

  19. Observable Priors: Limiting Biases in Estimated Parameters for Incomplete Orbits

    NASA Astrophysics Data System (ADS)

    Kosmo, Kelly; Martinez, Gregory; Hees, Aurelien; Witzel, Gunther; Ghez, Andrea M.; Do, Tuan; Sitarski, Breann; Chu, Devin; Dehghanfar, Arezu

    2017-01-01

    Over twenty years of monitoring stellar orbits at the Galactic center has provided an unprecedented opportunity to study the physics and astrophysics of the supermassive black hole (SMBH) at the center of the Milky Way Galaxy. In order to constrain the mass of and distance to the black hole, and to evaluate its gravitational influence on orbiting bodies, we use Bayesian statistics to infer black hole and stellar orbital parameters from astrometric and radial velocity measurements of stars orbiting the central SMBH. Unfortunately, most of the short period stars in the Galactic center have periods much longer than our twenty year time baseline of observations, resulting in incomplete orbital phase coverage--potentially biasing fitted parameters. Using the Bayesian statistical framework, we evaluate biases in the black hole and orbital parameters of stars with varying phase coverage, using various prior models to fit the data. We present evidence that incomplete phase coverage of an orbit causes prior assumptions to bias statistical quantities, and propose a solution to reduce these biases for orbits with low phase coverage. The explored solution assumes uniformity in the observables rather than in the inferred model parameters, as is the current standard method of orbit fitting. Of the cases tested, priors that assume uniform astrometric and radial velocity observables reduce the biases in the estimated parameters. The proposed method will not only improve orbital estimates of stars orbiting the central SMBH, but can also be extended to other orbiting bodies with low phase coverage such as visual binaries and exoplanets.

  20. Topological effects of data incompleteness of gene regulatory networks

    PubMed Central

    2012-01-01

    Background The topological analysis of biological networks has been a prolific topic in network science during the last decade. A persistent problem with this approach is the inherent uncertainty and noisy nature of the data. One of the cases in which this situation is more marked is that of transcriptional regulatory networks (TRNs) in bacteria. The datasets are incomplete because regulatory pathways associated to a relevant fraction of bacterial genes remain unknown. Furthermore, direction, strengths and signs of the links are sometimes unknown or simply overlooked. Finally, the experimental approaches to infer the regulations are highly heterogeneous, in a way that induces the appearance of systematic experimental-topological correlations. And yet, the quality of the available data increases constantly. Results In this work we capitalize on these advances to point out the influence of data (in)completeness and quality on some classical results on topological analysis of TRNs, specially regarding modularity at different levels. Conclusions In doing so, we identify the most relevant factors affecting the validity of previous findings, highlighting important caveats to future prokaryotic TRNs topological analysis. PMID:22920968

  1. Incomplete oxidation of ethylenediaminetetraacetic acid in chemical oxygen demand analysis.

    PubMed

    Anderson, James E; Mueller, Sherry A; Kim, Byung R

    2007-09-01

    Ethylenediaminetetraacetic acid (EDTA) was found to incompletely oxidize in chemical oxygen demand (COD) analysis, leading to incorrect COD values for water samples containing relatively large amounts of EDTA. The degree of oxidation depended on the oxidant used, its concentration, and the length of digestion. The COD concentrations measured using COD vials with a potassium dichromate concentration of 0.10 N (after dilution by sample and sulfuric acid) were near theoretical oxygen demand values. However, COD measured with dichromate concentrations of 0.010 N and 0.0022 N were 30 to 40% lower than theoretical oxygen demand values. Similarly, lower COD values were observed with manganic sulfate as oxidant at 0.011 N. Extended digestion yielded somewhat higher COD values, suggesting incomplete and slower oxidation of EDTA, as a result of lower oxidant concentrations. For wastewater in which EDTA is a large fraction of COD, accurate COD measurement may not be achieved with methods using dichromate concentrations less than 0.1 N.

  2. Analysis of recurrent event data with incomplete observation gaps.

    PubMed

    Kim, Yang-Jin; Jhun, Myoungshic

    2008-03-30

    In analysis of recurrent event data, recurrent events are not completely experienced when the terminating event occurs before the end of a study. To make valid inference of recurrent events, several methods have been suggested for accommodating the terminating event (Statist. Med. 1997; 16:911-924; Biometrics 2000; 56:554-562). In this paper, our interest is to consider a particular situation, where intermittent dropouts result in observation gaps during which no recurrent events are observed. In this situation, risk status varies over time and the usual definition of risk variable is not applicable. In particular, we consider the case when information on the observation gap is incomplete, that is, the starting time of intermittent dropout is known but the terminating time is not available. This incomplete information is modeled in terms of an interval-censored mechanism. Our proposed method is applied to the study of the Young Traffic Offenders Program on conviction rates, wherein a certain proportion of subjects experienced suspensions with intermittent dropouts during the study.

  3. Cannabinoids induce incomplete maturation of cultured human leukemia cells

    SciTech Connect

    Murison, G.; Chubb, C.B.H.; Maeda, S.; Gemmell, M.A.; Huberman, E.

    1987-08-01

    Monocyte maturation markers were induced in cultured human myeloblastic ML-2 leukemia cells after treatment for 1-6 days with 0.03-30 ..mu..M ..delta../sup 9/-tetrahydrocannabinol (THC), the major psychoactive component of marijuana. After a 2-day or longer treatment, 2- to 5-fold increases were found in the percentages of cells exhibiting reactivity with either the murine OKM1 monoclonal antibody of the Leu-M5 monoclonal antibody, staining positively for nonspecific esterase activity, and displaying a promonocyte morphology. The increases in these differentiation markers after treatment with 0.03-1 ..mu..M THC were dose dependent. At this dose range, THC did not cause an inhibition of cell growth. The THC-induced cell maturation was also characterized by specific changes in the patterns of newly synthesized proteins. The THC-induced differentiation did not, however, result in cells with a highly developed mature monocyte phenotype. However, treatment of these incompletely matured cells with either phorbol 12-myristate 13-acetate of 1..cap alpha..,25-dihydroxycholecalciferol, which are inducers of differentiation in myeloid leukemia cells (including ML-2 cells), produced cells with a mature monocyte morphology. The ML-2 cell system described here may be a useful tool for deciphering critical biochemical events that lead to the cannabinoid-induced incomplete cell differentiation of ML-2 cells and other related cell types. Findings obtained from this system may have important implications for studies of cannabinoid effects on normal human bone-marrow progenitor cells.

  4. Semiparametric pseudoscore for regression with multidimensional but incompletely observed regressor.

    PubMed

    Hu, Zonghui; Qin, Jing; Follmann, Dean

    2017-02-16

    We study the regression fβ (Y|X,Z), where Y is the response, Z∈Rd is a vector of fully observed regressors and X is the regressor with incomplete observation. To handle missing data, maximum likelihood estimation via expectation-maximisation (EM) is the most efficient but is sensitive to the specification of the distribution of X. Under a missing at random assumption, we propose an EM-type estimation via a semiparametric pseudoscore. Like in EM, we derive the conditional expectation of the score function given Y and Z, or the mean score, over the incompletely observed units under a postulated distribution of X. Instead of directly using the 'mean score' in estimating equation, we use it as a working index to construct the semiparametric pseudoscore via nonparametric regression. Introduction of semiparametric pseudoscore into the EM framework reduces sensitivity to the specified distribution of X. It also avoids the curse of dimensionality when Z is multidimensional. The resulting regression estimator is more than doubly robust: it is consistent if either the pattern of missingness in X is correctly specified or the working index is appropriately, but not necessarily correctly, specified. It attains optimal efficiency when both conditions are satisfied. Numerical performance is explored by Monte Carlo simulations and a study on treating hepatitis C patients with HIV coinfection. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

  5. Gradual molecular evolution of a sex determination switch through incomplete penetrance of femaleness.

    PubMed

    Beye, Martin; Seelmann, Christine; Gempe, Tanja; Hasselmann, Martin; Vekemans, Xavier; Fondrk, M Kim; Page, Robert E

    2013-12-16

    Some genes regulate phenotypes that are either present or absent. They are often important regulators of developmental switches and are involved in morphological evolution. We have little understanding of the molecular mechanisms by which these absence/presence gene functions have evolved, because the phenotype and fitness of molecular intermediate forms are unknown. Here, we studied the sex-determining switch of 14 natural sequence variants of the csd gene among 76 genotypes of the honeybee (Apis mellifera). Heterozygous genotypes (different specificities) of the csd gene determine femaleness, while hemizygous genotypes (single specificity) determine maleness. Homozygous genotypes of the csd gene (same specificity) are lethal. We found that at least five amino acid differences and length variation between Csd specificities in the specifying domain (PSD) were sufficient to regularly induce femaleness. We estimated that, on average, six pairwise amino acid differences evolved under positive selection. We also identified a natural evolutionary intermediate that showed only three amino acid length differences in the PSD relative to its parental allele. This genotype showed an intermediate fitness because it implemented lethality regularly and induced femaleness infrequently (i.e., incomplete penetrance). We suggest incomplete penetrance as a mechanism through which new molecular switches can gradually and adaptively evolve.

  6. Incomplete vertical integration in the health care industry: pseudomarkets and pseudopolicies.

    PubMed

    Evans, R G

    1983-07-01

    Most economic relationships are either arm's-length exchange transactions, each party seeking his or her own interest, or command structures, such as a firm or public agency, integrating joint efforts toward a common goal. The health care industry, however, displays a pattern of incomplete vertical integration--relationships which are neither truly arm's-length nor completely hierarchical. The doctor-patient relationship is archetypical. Physicians appear to sell services in private markets; yet they reach through the exchange process to direct the consumer-patient's utilization decisions, implicity undertaking to act in the patient's interest, and thus integrate forward. But they also integrate backward to control the public regulatory process--self-government--and some forms of insurance. The health care systems of different countries--Canada, the United Kingdom, and the United States--can be interpreted as different patterns of incomplete integration among five basic classes of transactors: consumer-patients, first-line providers, second-line providers, insurers, and governments. Each system of linkage has characteristic strengths and weaknesses. Nowhere, however, do we find a predominance of arm's-length market relationships. Where they exist, markets in health care are usually pseudomarkets dominated by one side of the transaction. The rhetoric of market relationships serves principally to obscure political struggles over shifting patterns of integration.

  7. Confidence-interval construction for rate ratio in matched-pair studies with incomplete data.

    PubMed

    Li, Hui-Qiong; Chan, Ivan S F; Tang, Man-Lai; Tian, Guo-Liang; Tang, Nian-Sheng

    2014-01-01

    Matched-pair design is often used in clinical trials to increase the efficiency of establishing equivalence between two treatments with binary outcomes. In this article, we consider such a design based on rate ratio in the presence of incomplete data. The rate ratio is one of the most frequently used indices in comparing efficiency of two treatments in clinical trials. In this article, we propose 10 confidence-interval estimators for the rate ratio in incomplete matched-pair designs. A hybrid method that recovers variance estimates required for the rate ratio from the confidence limits for single proportions is proposed. It is noteworthy that confidence intervals based on this hybrid method have closed-form solution. The performance of the proposed confidence intervals is evaluated with respect to their exact coverage probability, expected confidence interval width, and distal and mesial noncoverage probability. The results show that the hybrid Agresti-Coull confidence interval based on Fieller's theorem performs satisfactorily for small to moderate sample sizes. Two real examples from clinical trials are used to illustrate the proposed confidence intervals.

  8. The impact of solution agglomeration on the deposition of self-assembled monolayers

    SciTech Connect

    BUNKER,BRUCE C.; CARPICK,ROBERT W.; ASSINK,ROGER A.; THOMAS,MICHAEL L.; HANKINS,MATTHEW G.; VOIGT,JAMES A.; SIPOLA,DIANA L.; DE BOER,MAARTEN P.; GULLEY,GERALD L.

    2000-04-17

    Self-assembled monolayers (SAMS) are commonly produced by immersing substrates in organic solutions containing trichlorosilane coupling agents. Unfortunately, such deposition solutions can also form alternate structures including inverse micelles and lamellar phases. The formation of alternate phases is one reason for the sensitivity of SAM depositions to factors such as the water content of the deposition solvent. If such phases are present, the performance of thin films used for applications such as minimization of friction and stiction in micromachines can be seriously compromised. Inverse micelle formation has been studied in detail for depositions involve 1H-, 1H-, 2H-, 2H-perfluorodecyltrichlorosilane (FDTS) in isooctane. Nuclear magnetic resonance experiments have been used to monitor the kinetics of hydrolysis and condensation reactions between water and FDTS. Light scattering experiments show that when hydrolyzed FDTS concentrations reach a critical concentration, there is a burst of nucleation to form high concentrations of spherical agglomerates. Atomic force microscopy results show that the agglomerates then deposit on substrate surfaces. Deposition conditions leading to monolayer formation involve using deposition times that are short relative to the induction time for agglomeration. After deposition, inverse micelles can be converted into lamellar or monolayer structures with appropriate heat treatments if surface concentrations are relatively low.

  9. Tunable redox potential of nonmetal doped monolayer MoS2: First principle calculations

    NASA Astrophysics Data System (ADS)

    Lu, S.; Li, C.; Zhao, Y. F.; Gong, Y. Y.; Niu, L. Y.; Liu, X. J.

    2016-10-01

    Doping is an effective method to alter the electronic behavior of materials by forming new chemical bonds and bringing bond relaxation. With this aid of first principle calculations, the crystal configuration and electronic properties of monolayer MoS2 have been modulated by the nonmetal (NM) dopants (H, B, C, N, O, F, Si, P, Cl, As, Se, Br, Te and I), and the thermodynamic stability depending on the preparation conditions (Mo-rich and S-rich conditions) were discussed. Results shown that, the NM dopants substituted preferentially for S under Mo-rich condition, the electronic distribution around the dopants and the nearby Mo atoms are changed by the new formed Mo-NM bonds and bands relaxation. Compared to pristine monolayer MoS2, the NM ions with odd chemical valences enhance the oxidation potential and reduce the reduction potential of specimens, but the NM ions with even chemical valences have the opposite effects on the redox potentials. Compared to the NM ions with even chemical valences, the lone pair electrons in NM ions with odd chemical valences can extra interact with the Mo ions and reduces the ECBM and EVBM values of specimens. It offers a simple way to design various monolayer MoS2 based catalysts in order to catalyze different materials by chose the reasonable dopants for stronger oxidation or reduction potential.

  10. Reduced graphene oxide directed self-assembly of phospholipid monolayers in liquid and gel phases.

    PubMed

    Rui, Longfei; Liu, Jiaojiao; Li, Jingliang; Weng, Yuyan; Dou, Yujiang; Yuan, Bing; Yang, Kai; Ma, Yuqiang

    2015-05-01

    The response of cell membranes to the local physical environment significantly determines many biological processes and the practical applications of biomaterials. A better understanding of the dynamic assembly and environmental response of lipid membranes can help understand these processes and design novel nanomaterials for biomedical applications. The present work demonstrates the directed assembly of lipid monolayers, in both liquid and gel phases, on the surface of a monolayered reduced graphene oxide (rGO). The results from atomic force microscopy indicate that the hydrophobic aromatic plane and the defect holes due to reduction of GO sheets, along with the phase state and planar surface pressure of lipids, corporately determine the morphology and lateral structure of the assembled lipid monolayers. The DOPC molecules, in liquid phase, probably spread over the rGO surface with their tails associating closely with the hydrophobic aromatic plane, and accumulate to form circles of high area surrounding the defect holes on rGO sheets. However, the DPPC molecules, in gel phase, prefer to form a layer of continuous membrane covering the whole rGO sheet including defect holes. The strong association between rGO sheets and lipid tails further influences the melting behavior of lipids. This work reveals a dramatic effect of the local structure and surface property of rGO sheets on the substrate-directed assembly and subsequent phase behavior of the supported lipid membranes.

  11. The interaction of mefloquine hydrochloride with cell membrane models at the air-water interface is modulated by the monolayer lipid composition.

    PubMed

    Goto, Thiago Eichi; Caseli, Luciano

    2014-10-01

    The antiparasitic properties of antiparasitic drugs are believed to be associated with their interactions with the protozoan membrane, encouraging research on the identification of membrane sites capable of drug binding. In this study, we investigated the interaction of mefloquine hydrochloride, known to be effective against malaria, with cell membrane models represented by Langmuir monolayers of selected lipids. It is shown that even small amounts of the drug affect the surface pressure-area isotherms as well as surface vibrational spectra of some lipid monolayers, which points to a significant interaction. The effects on the latter depend on the electrical charge of the monolayer-forming molecules, with the drug activity being particularly distinctive for negatively charged lipids. Therefore, the lipid composition of the monolayer modulates the interaction with the lipophilic drug, which may have important implications in understanding how the drug acts on specific sites of the protozoan membrane.

  12. First principles study of metal contacts to monolayer black phosphorous

    SciTech Connect

    Chanana, Anuja; Mahapatra, Santanu

    2014-11-28

    Atomically thin layered black phosphorous (BP) has recently appeared as an alternative to the transitional metal dichalcogenides for future channel material in a metal-oxide-semiconductor transistor due to its lower carrier effective mass. Investigation of the electronic property of source/drain contact involving metal and two-dimensional material is essential as it impacts the transistor performance. In this paper, we perform a systematic and rigorous study to evaluate the Ohmic nature of the side-contact formed by the monolayer BP (mBP) and metals (gold, titanium, and palladium), which are commonly used in experiments. Employing the Density Functional Theory, we analyse the potential barrier, charge transfer and atomic orbital overlap at the metal-mBP interface in an optimized structure to understand how efficiently carriers could be injected from metal contact to the mBP channel. Our analysis shows that gold forms a Schottky contact with a higher tunnel barrier at the interface in comparison to the titanium and palladium. mBP contact with palladium is found to be purely Ohmic, where as titanium contact demonstrates an intermediate behaviour.

  13. Vacancy and Doping States in Monolayer and bulk Black Phosphorus

    PubMed Central

    Guo, Yuzheng; Robertson, John

    2015-01-01

    The atomic geometries and transition levels of point defects and substitutional dopants in few-layer and bulk black phosphorus are calculated. The vacancy is found to reconstruct in monolayer P to leave a single dangling bond, giving a negative U defect with a +/− transition level at 0.24 eV above the valence band edge. The V− state forms an unusual 4-fold coordinated site. In few-layer and bulk black P, the defect becomes a positive U site. The divacancy is much more stable than the monovacancy, and it reconstructs to give no deep gap states. Substitutional dopants such as C, Si, O or S do not give rise to shallow donor or acceptor states but instead reconstruct to form non-doping sites analogous to DX or AX centers in GaAs. Impurities on black P adopt the 8-N rule of bonding, as in amorphous semiconductors, rather than simple substitutional geometries seen in tetrahedral semiconductors. PMID:26383634

  14. Valley depolarization in monolayer WSe2

    PubMed Central

    Yan, Tengfei; Qiao, Xiaofen; Tan, Pingheng; Zhang, Xinhui

    2015-01-01

    We have systematically examined the circular polarization of monolayer WSe2 at different temperature, excitation energy and exciton density. The valley depolarization in WSe2 is experimentally confirmed to be governed by the intervalley electron-hole exchange interaction. More importantly, a non-monotonic dependence of valley circular polarization on the excitation power density has been observed, providing the experimental evidence for the non-monotonic dependence of exciton intervalley scattering rate on the excited exciton density. The physical origination of our experimental observations has been proposed to be in analogy to the D′yakonov-Perel′ mechanism that is operative in conventional GaAs quantum well systems. Our experimental results are fundamentally important for well understanding the valley pseudospin relaxation in atomically thin transition metal dichalcogenides. PMID:26490157

  15. Ultrafast response of monolayer molybdenum disulfide photodetectors

    PubMed Central

    Wang, Haining; Zhang, Changjian; Chan, Weimin; Tiwari, Sandip; Rana, Farhan

    2015-01-01

    The strong light emission and absorption exhibited by single atomic layer transitional metal dichalcogenides in the visible to near-infrared wavelength range make them attractive for optoelectronic applications. In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz. The fast photodetector response is a result of the short electron–hole and exciton lifetimes in this material. Recombination of photoexcited carriers in most two-dimensional metal dichalcogenides is dominated by nonradiative processes, most notable among which is Auger scattering. The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links. PMID:26572726

  16. Metastability of a Supercompressed Fluid Monolayer

    PubMed Central

    Smith, Ethan C.; Crane, Jonathan M.; Laderas, Ted G.; Hall, Stephen B.

    2003-01-01

    Previous studies showed that monomolecular films of extracted calf surfactant collapse at the equilibrium spreading pressure during quasi-static compressions but become metastable at much higher surface pressures when compressed faster than a threshold rate. To determine the mechanism by which the films become metastable, we studied single-component films of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC). Initial experiments confirmed similar metastability of POPC if compressed above a threshold rate. Measurements at different surface pressures then showed that rates of collapse, although initially increasing above the equilibrium spreading pressure, reached a sharply defined maximum and then slowed considerably. When heated, rapidly compressed films recovered their ability to collapse with no discontinuous change in area, arguing that the metastability does not reflect transition of the POPC film to a new phase. These observations indicate that in several respects, the supercompression of POPC monolayers resembles the supercooling of three-dimensional liquids toward a glass transition. PMID:14581205

  17. Covalently networked monolayer-protected nanoparticle films.

    PubMed

    Tognarelli, D J; Miller, Robert B; Pompano, Rebecca R; Loftus, Andrew F; Sheibley, Daniel J; Leopold, Michael C

    2005-11-22

    Covalently networked films of nanoparticles can be assembled on various substrates from functionalized monolayer-protected clusters (MPCs) via ester coupling reactions. Exposure of a specifically modified substrate to alternating solutions of 11-mercaptoundecanoic acid exchanged and 11-mercaptoundecanol exchanged MPCs, in the presence of ester coupling reagents, 1,3-dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine, results in the formation of a multilayer film with ester bridges between individual nanoparticles. These films can be grown in a controlled manner to various thicknesses and exhibit certain properties that are consistent with films having other types of interparticle connectivity, including chemical vapor response behavior and quantized double layer charging. Ester coupling of MPCs into assembled films is a straightforward and highly versatile approach that results in robust films that can endure harsher chemical environments than other types of films. The stability of these covalent films is assessed and compared to other more traditional MPC film assemblies.

  18. Novel Behavior in Self-Assembled Superparamagnetic Nanoparticle Monolayers at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Stanley, Jacob; Boucheron, Leandra; Dai, Yeling; Lin, Binhua; Meron, Mati; Shpyrko, Oleg

    2013-03-01

    Iron oxide nanoparticles, coated with an oleic acid ligand, have been found to form self-assembled monolayers when deposited at the air-water interface. Even for low particle densities these particles aggregate into hexagonally close-packed islands which merge into a uniform layer at higher densities. Using Grazing Incidence Small Angle X-Ray Scattering (GISAXS) we were able to measure the first through fifth order diffraction peaks. By analyzing the positions and shapes of these peaks we investigated the in-plane structure of these monolayers and characterized how the structure changes as a function of compression in a Langmuir-Blodgett trough. Since iron oxide nanoparticles are known to be super-paramagnetic, we sought to investigate the role magnetic effects may have on the interparticle interactions and ordering within the film. We performed Grazing Incidence Diffraction (GID) measurements on the film while varying an external magnetic field. We will discuss the results of our findings.

  19. Phase diagram for controlled crystallization of calcium phosphate under acidic organic monolayers

    NASA Astrophysics Data System (ADS)

    Cui, F. Z.; Zhou, L. F.; Cui, H.; Ma, C. L.; Lu, H. B.; Li, H. D.

    1996-12-01

    The effect of ionic concentration and pH on matrix-regulated crystallization may be important in biomineralization processes and biomimetic synthesis of materials. This effect in the system of calcium phosphate solution under stearic acid monolayers was investigated. In experiments, the solution conditions ranged in concentration of Ca ion of 0.1-20mM and in pH of 5.3-7.0. It was found that at the initial stage of the controlled crystallization, the (0001)-oriented hydroxyapatite (HAp) precipitations under the acidic monolayers always occur. At solution conditions near the solubility isotherms of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) in the solubility phase diagram, precipitations of OCP and DCPD phases can form together with HAp precipitation, respectively. Orientations of DCPD or OCP phase precipitations were irregular.

  20. Perfect Spin-filtering in graphene monolayer-bilayer superlattice with zigzag boundaries

    PubMed Central

    Yu, Hang; Liu, Jun-Feng

    2016-01-01

    We show that the spontaneous magnetization is formed at the zigzag boundary between monolayer and bilayer graphene by the self-consistent calculation based on Hubbard model. In a monolayer- bilayer graphene superlattice with zigzag boundaries, it is surprising that nearly 100% spin polarization is achieved in the energy window around the Dirac point, no matter the magnetization configuration at two boundaries is parallel or antiparallel. The reason is that the low-energy transport is only influenced by the magnetization at one edge, but not by that at the other. The underlying physics is unveiled by the spin-split band structure and the distribution of the wave-function pertaining to the lowest (highest) subband of electron (hole). PMID:27140666

  1. Highly conductive and transparent Ag honeycomb mesh fabricated using a monolayer of polystyrene spheres

    NASA Astrophysics Data System (ADS)

    Kwon, Namyong; Kim, Kyohyeok; Sung, Sihyun; Yi, Insook; Chung, Ilsub

    2013-06-01

    We describe the design principles and fabrication of Ag honeycomb mesh as a transparent conductive electrode using a polystyrene (PS) sphere template. Monolayers of PS spheres with different diameters, such as 600 nm, 3 μm, and 10 μm, are studied as templates to form Ag mesh with high transmittance. Since the parasitic Ag islands degrade the transmittance, both heat pretreatment and wet etching are used to control the area covered by parasitic Ag islands. The trade-off between transmittance and conductivity forces us to use larger diameter PS spheres. Ten-micron PS spheres are chosen as the template for the PS sphere monolayer, and heat pretreatment and Ag wet etching are used to demonstrate that the Ag honeycomb mesh transparent electrodes have high performance. The transmittance and the sheet resistance are 83% and 20 Ω/sq, which are comparable to commercial ITO electrodes.

  2. Highly oriented, self-assembled alkanephosphate monolayers on tantalum(V) oxide surfaces

    SciTech Connect

    Brovelli, D.; Haehner, G.; Ruiz, L.

    1999-06-22

    Octadecyl phosphoric acid ester has been found to produce oriented, well-ordered monolayers on a flat tantalum(V) oxide surface, via self-assembly from a heptane/propan-2-ol solution. By means of contact angle, optical waveguide lightmode spectroscopy (OWLS), near-edge X-ray absorption fine structure spectroscopy (NEXASFS), and X-ray photoelectron spectroscopy (XPS) measurements, it has been shown that these layers closely resemble those formed by the corresponding thiol-gold system, with respect to packing density, inclination, and order. The system shows promise as an approach to functionalizing oxide surfaces with well-ordered organic monolayers, with potential applications in the fields of biochemical analysis and sensors.

  3. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

    SciTech Connect

    Ihli, Johannes; Clark, Jesse N.; Côté, Alexander S.; Kim, Yi-Yeoun; Schenk, Anna S.; Kulak, Alexander N.; Comyn, Timothy P.; Chammas, Oliver; Harder, Ross J.; Duffy, Dorothy M.; Robinson, Ian K.; Meldrum, Fiona C.

    2016-06-15

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. In this study, we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. In conclusion, this work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates.

  4. Ordered structure upon deposition of Ge on the monolayer silicene on Ag(111)

    NASA Astrophysics Data System (ADS)

    Chen, Han-De; Lin, Dengsung

    The growth of monolayer silicene on Ag (111) has been a hot research in recent years. The akin structure of the same group IV element: Germanene, has also been grown successfully on different metal substrates. In this investigation, Ge has been deposited by molecular beam epitaxy on the monolayer-thick silicene grown on Ag(111). Low-temperature scanning tunneling microscopy (LT-STM) has been employed to observed the surface morphology and atomic structure. On the (3 x 3)Si phase, only one Ge adatom is found on each (3 x 3)Si unit cell on two different sites, A and B. The deposited Ge adatoms prefer to settle around a unit cell that has already incorporated one Ge adatom, thereby forming two domains (3 x 3)A and (3 x 3)B. Results on (r7 x r7)Si superstructure showing local ordering will also be presented.

  5. Monolayer to Bilayer Structural Transition in Confined Pyrrolidinium-Based Ionic Liquids.

    PubMed

    Smith, Alexander M; Lovelock, Kevin R J; Gosvami, Nitya Nand; Licence, Peter; Dolan, Andrew; Welton, Tom; Perkin, Susan

    2013-02-07

    Ionic liquids can be intricately nanostructured in the bulk and at interfaces resulting from a delicate interplay between interionic and surface forces. Here we report the structuring of a series of dialkylpyrrolidinium-based ionic liquids induced by confinement. The ionic liquids containing cations with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement to a thin film, whereas a cation with a longer alkyl chain substituent leads to bilayer formation. The crossover from monolayer to bilayer structure occurs between chain lengths of n = 8 and 10 for these pyrrolidinium-based ionic liquids. The bilayer structure for n = 10 involves full interdigitation of the alkyl chains; this is in contrast with previous observations for imidazolium-based ionic liquids. The results are pertinent to these liquids' application as electrolytes, where the electrolyte is confined inside the pores of a nanoporous electrode, for example, in devices such as supercapacitors or batteries.

  6. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

    PubMed Central

    Ihli, Johannes; Clark, Jesse N.; Côté, Alexander S.; Kim, Yi-Yeoun; Schenk, Anna S.; Kulak, Alexander N.; Comyn, Timothy P.; Chammas, Oliver; Harder, Ross J.; Duffy, Dorothy M.; Robinson, Ian K.; Meldrum, Fiona C.

    2016-01-01

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates. PMID:27302863

  7. Monolayer semiconductor nanocavity lasers with ultralow thresholds.

    PubMed

    Wu, Sanfeng; Buckley, Sonia; Schaibley, John R; Feng, Liefeng; Yan, Jiaqiang; Mandrus, David G; Hatami, Fariba; Yao, Wang; Vučković, Jelena; Majumdar, Arka; Xu, Xiaodong

    2015-04-02

    Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

  8. Anomalous thermal conductivity of monolayer boron nitride

    NASA Astrophysics Data System (ADS)

    Tabarraei, Alireza; Wang, Xiaonan

    2016-05-01

    In this paper, we use nonequilibrium molecular dynamics modeling to investigate the thermal properties of monolayer hexagonal boron nitride nanoribbons under uniaxial strain along their longitudinal axis. Our simulations predict that hexagonal boron nitride shows an anomalous thermal response to the applied uniaxial strain. Contrary to three dimensional materials, under uniaxial stretching, the thermal conductivity of boron nitride nanoribbons first increases rather than decreasing until it reaches its peak value and then starts decreasing. Under compressive strain, the thermal conductivity of monolayer boron nitride ribbons monolithically reduces rather than increasing. We use phonon spectrum and dispersion curves to investigate the mechanism responsible for the unexpected behavior. Our molecular dynamics modeling and density functional theory results show that application of longitudinal tensile strain leads to the reduction of the group velocities of longitudinal and transverse acoustic modes. Such a phonon softening mechanism acts to reduce the thermal conductivity of the nanoribbons. On the other hand, a significant increase in the group velocity (stiffening) of the flexural acoustic modes is observed, which counteracts the phonon softening effects of the longitudinal and transverse modes. The total thermal conductivity of the ribbons is a result of competition between these two mechanisms. At low tensile strain, the stiffening mechanism overcomes the softening mechanism which leads to an increase in the thermal conductivity. At higher tensile strain, the softening mechanism supersedes the stiffening and the thermal conductivity slightly reduces. Our simulations show that the decrease in the thermal conductivity under compressive strain is attributed to the formation of buckling defects which reduces the phonon mean free path.

  9. Monolayer semiconductor nanocavity lasers with ultralow thresholds

    SciTech Connect

    Wu, Sanfeng; Buckley, Sonia; Schaibley, John R.; Feng, Liefeng; Yan, Jiaqiang; Mandrus, David G.; Hatami, Fariba; Yao, Wang; Vučković, Jelena; Majumdar, Arka; Xu, Xiaodong

    2015-03-16

    Engineering the electromagnetic environment of a nanoscale light emitter by a photonic cavity can significantly enhance its spontaneous emission rate through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter1–5, providing the ultimate low-threshold laser system with small footprint, low power consumption and ultrafast modulation. A state-of-the-art ultra-low threshold nanolaser has been successfully developed though embedding quantum dots into photonic crystal cavity (PhCC)6–8. However, several core challenges impede the practical applications of this architecture, including the random positions and compositional fluctuations of the dots7, extreme difficulty in current injection8, and lack of compatibility with electronic circuits7,8. Here, we report a new strategy to lase, where atomically thin crystalline semiconductor, i.e., a tungsten-diselenide (WSe2) monolayer, is nondestructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PhCC. A new type of continuous-wave nanolaser operating in the visible regime is achieved with an optical pumping threshold as low as 27 nW at 130 K, similar to the value achieved in quantum dot PhCC lasers7. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within 1 nm of the PhCC surface. The surface-gain geometry allows unprecedented accessibilities to multi-functionalize the gain, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

  10. Monolayer semiconductor nanocavity lasers with ultralow thresholds

    DOE PAGES

    Wu, Sanfeng; Buckley, Sonia; Schaibley, John R.; ...

    2015-03-16

    Engineering the electromagnetic environment of a nanoscale light emitter by a photonic cavity can significantly enhance its spontaneous emission rate through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter1–5, providing the ultimate low-threshold laser system with small footprint, low power consumption and ultrafast modulation. A state-of-the-art ultra-low threshold nanolaser has been successfully developed though embedding quantum dots into photonic crystal cavity (PhCC)6–8. However, several core challenges impede the practical applications of this architecture, including the random positions and compositional fluctuations of the dots7, extreme difficulty in current injection8, and lackmore » of compatibility with electronic circuits7,8. Here, we report a new strategy to lase, where atomically thin crystalline semiconductor, i.e., a tungsten-diselenide (WSe2) monolayer, is nondestructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PhCC. A new type of continuous-wave nanolaser operating in the visible regime is achieved with an optical pumping threshold as low as 27 nW at 130 K, similar to the value achieved in quantum dot PhCC lasers7. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within 1 nm of the PhCC surface. The surface-gain geometry allows unprecedented accessibilities to multi-functionalize the gain, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.« less

  11. Electronic correlations in monolayer VS2

    NASA Astrophysics Data System (ADS)

    Isaacs, Eric B.; Marianetti, Chris A.

    2016-07-01

    The layered transition metal dichalcogenide vanadium disulfide (VS2), which nominally has one electron in the 3 d shell, is potent for strong-correlation physics and is possibly another realization of an effective one-band model beyond the cuprates. Here monolayer VS2 in both the trigonal prismatic and the octahedral phases is investigated using density functional theory plus Hubbard U (DFT +U ) calculations. Trigonal prismatic VS2 has an isolated low-energy band that emerges from a confluence of crystal-field splitting and direct V-V hopping. Within spin density functional theory, ferromagnetism splits the isolated band of the trigonal prismatic structure, leading to a low-band-gap, S =1/2 , ferromagnetic Stoner insulator; the octahedral phase is higher in energy. Including the on-site interaction U increases the band gap, leads to Mott insulating behavior, and, for sufficiently high values, stabilizes the ferromagnetic octahedral phase. The validity of DFT and DFT +U for these two-dimensional materials with potential for strong electronic correlations is discussed. A clear benchmark is given by examining the experimentally observed charge density wave in octahedral VS2, for which DFT grossly overestimates the bond length differences compared to known experiments; the presence of charge density waves is also probed for the trigonal prismatic phase. Finally, we investigate why only the octahedral phase has been observed in experiments and discuss the possibility of realizing the trigonal prismatic phase. Our work suggests that trigonal prismatic VS2 is a promising candidate for strongly correlated electron physics that, if realized, could be experimentally probed in an unprecedented fashion due to its monolayer nature.

  12. Surface-segregated monolayers: a new type of ordered monolayer for surface modification of organic semiconductors.

    PubMed

    Wei, Qingshuo; Tajima, Keisuke; Tong, Yujin; Ye, Shen; Hashimoto, Kazuhito

    2009-12-09

    We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.

  13. Surface modification of silicon oxide with trialkoxysilanes toward close-packed monolayer formation.

    PubMed

    Tanaka, Mutsuo; Sawaguchi, Takahiro; Kuwahara, Masashi; Niwa, Osamu

    2013-05-28

    In order to scrutinize potential of trialkoxysilanes to form close-packed monolayer, surface modification of silicon oxide was carried out with the trialkoxysilanes bearing a ferrocene moiety for analysis by electrochemical methods. As it was found that hydrogen-terminated silicon reacts with trialkoxysilane through natural oxidation in organic solvents, where the silicon oxide layer is thin enough to afford conductivity for electrochemical analysis, hydrogen-terminated silicon wafer was immersed in trialkoxysilane solution for surface modification without oxidation treatment. Cyclic voltammetry measurements to determine surface concentrations of the immobilized ferrocene-silane on silicon surface were carried out with various temperature, concentration, solvent, and molecular structure, while the blocking effect in the cyclic voltammogram was investigated to obtain insight into density leading to the close-packed layer. The results suggested that a monolayer modification tended to occur under milder conditions when the ferrocene-silane had a longer alkyl chain, and formation of a close-packed layer to show significant blocking effect was observed. However, the surface modification proceeded even when surface concentration of the immobilized ferrocene-silane was greater than that expected for the monolayer. On the basis of these tendencies, the surface of silicon oxide modified with trialkoxysilane is considered to be a partial multilayer rather than monolayer although a close-packed layer is formed. This result is supported by the comparison with carbon surface modified with ferrocene-diazonium, in which a significant blocking effect was observed when surface concentrations of the immobilized ferrocene moiety are lower than that for silicon oxide modified with ferrocene-silane.

  14. Electrons and phonons in layered and monolayer vanadium pentoxide

    NASA Astrophysics Data System (ADS)

    Lambrecht, Walter R. L.

    Vanadium pentoxide (V2O5) is a layered material with the potential for interesting new properties when made in 2D mono- or few-layer form. Its band structure is characterized by a split-off conduction band. The lowest conduction band is separated from the rest of the conduction bands by about 1 eV and consists of V-dxy orbitals, non-bonding to the oxygens by symmetry. This narrow band has dispersion essentially along the direction of chains occurring in the layer. When this band becomes half-filled by doping, spin-splitting occurs accompanied by an antiferromagnetic coupling between nearest neighbors along the chain direction. This situation is well known to occur in the so-called ladder compound NaV2O5 , which was extensively studied in the late 90s as a potential spin-Peierls or charge ordering compound. However, the monolayer form of V2O5 may allow for other ways to control the doping by gating, removing vanadyl oxygens, adsorption of alkali metals, nanoribbon formation, etc. Our calculations predict a switch from antiferromagnetic to ferromagnetic coupling for doping slightly less than half filling of the split-off band. In this talk we will discuss our recent work on the electronic band structure of both bulk and monolayer V2O5 as well as the phonons. We find that the quasi-particle self-consistent GW method strongly overestimates the band gap. Lattice polarization corrections of the screening are required because of the large LO/TO phonon frequency ratios. Excitonic effects may also be expected to be fairly large. We find that some of the vibrational modes, notably the vanadyl-oxygen bond stretch perpendicular to the layer, unexpectedly shows a strong blue shift. This is explained in terms of reduced screening affecting the long-range dipole components of the force constants. Supported by AFOSR and DOE. Work done with Churna Bhandari, Mark van Schilfgaarde and Andre Schleiffe.

  15. Translational Diffusion in Phospholipid Monolayers Measured by Fluorescence Microphotolysis

    NASA Astrophysics Data System (ADS)

    Peters, Reiner; Beck, Konrad

    1983-12-01

    A method is described that eliminates surface flow in monolayers at the air-water interface and makes possible diffusion measurements by fluorescence microphotolysis (``photobleaching''). In contrast to previous studies that did not account for surface flow, lipid probe diffusion has been found to be similar in densely packed monolayers and in related bilayers. Furthermore, it seems that lipid diffusion is based on the same molecular mechanism in monolayers, bilayers, and potentially also cell membranes. In monolayers of L-α -dilauroylphosphatidylcholine (Lau2-PtdCho) the translational diffusion coefficient D of the fluorescent lipid probe N-4-nitrobenzo-2-oxa-1,3 diazole egg phosphatidylethanolamine decreased from 110 μ m2/s at a surface pressure Pi =1 mN/m to 15 μ m2/s at Pi =38 mN/m (T = 21-22 degrees C). Data could be fitted by the ``free volume model.'' In monolayers of L-α -dipalmitoylphosphatidylcholine (Pam2-PtdCho) D decreased by >3 orders of magnitude upon increasing Pi at constant temperature, thus indicating a fluid-to-crystalline phase transition. In Lau2-PtdCho/Pam2-PtdCho monolayers phase separation has been visualized in the fluorescence microscope and the effect on D measured. These results suggest that monolayers are a promising model system for studying the molecular mobility of lipids and other cell membrane components.

  16. The Modeling of Pulmonary Particulate Matter Transport Using Langmuir Monolayers

    NASA Astrophysics Data System (ADS)

    Eaton, Jeremy M.

    The effects of a barrier in proximity to the air-water interface on the dynamics of a Langmuir monolayer system are observed. A monolayer of Survanta, bovine lung surfactant, is deposited onto the interface of an aqueous buffer solution. Polystyrene particles one micron in diameter and tagged with fluorescent carboxylate groups are distributed evenly throughout the monolayer surface. The bead-monolayer system is compressed and expanded to induce folding. A polydimethylsiloxane (PDMS) substrate is placed below the monolayer in the buffer solution to study interactions between the folding monolayer and a barrier. The presence of the substrate is shown to shift surface pressure-area isotherms toward regions of lower area by an average of 8.9 mN/m. The surface of the PDMS substrate can be imaged using fluorescence microscopy to detect the presence of particles or surfactant that may have been transported there from the air-water interface during folding. Images show the transferral of particles and monolayer together suggesting the pinch-off of a fold or the direct interaction of a fold with the barrier.

  17. EXCESS FIBRINOGEN ADSORPTION TO MONOLAYERS OF MIXED LIPIDS

    PubMed Central

    Deshmukh, V.; Britt, D.W.; Hlady, V.

    2010-01-01

    Adsorption of fibrinogen to the monolayers of mixed lipids, dipalmitoyl phosphatidyl choline (DPPC) and eicosylamine (EA) was measured at a surface pressure of 20 mN/m by an in situ surface plasmon resonance technique. Pressure-area isotherms of DPPC+EA mixtures on water and buffer subphases indicated good lipid miscibility and some contraction of the monolayers at intermediate and higher surface pressures. Surface electric potential of the DPPC+EA monolayers showed excess values for intermediate DPPC:EA ratios. Fibrinogen adsorption and its adsorption rates from a dilute solution (0.03 mg/ml) were proportional to the fraction of EA in the monolayer indicating that protein binding was primarily driven by electrostatic interactions between positive EA charges in the monolayer and a net negative protein charge. At a higher protein concentration (0.06 mg/ml) both the fibrinogen adsorbed amount and its maximum adsorption rate showed excess values relative to the pure EA for 1:1, 2:1 and 3:1 DPPC+EA monolayers. This excess adsorption could be explained, in part, by the contraction of the monolayers with intermediate DPPC:EA ratios which resulted in an excess surface electric potential. PMID:20829000

  18. Self-Assembled Monolayers as Templates for Heme Crystallization

    SciTech Connect

    Wang, Xuefeng; Ingall, Ellery; Lai, Barry; Stack, Andrew G; Allard Jr, Lawrence Frederick

    2010-01-01

    Homogeneous self-assembled monolayers (SAMs) of alkanethiols (HS(CH{sub 2}){sub n}X) on Au(111) were used as substrates for crystallization of ferriprotoporphyrin IX (heme) in acidic aqueous solution. Different terminal functional groups (X = OH, COOH, NH{sub 2}, CH{sub 3}) were used on the SAMs as models of sites where heme crystallization takes place in blood-feeding organisms. Atomic force microscopy, X-ray diffraction (XRD), and X-ray absorption near edge spectroscopy (XANES) were employed to characterize particle morphology, density, crystallographic orientation, and the coordination environment. It was found that the morphology and extent of growth of particulates were strongly affected by the environment in which they crystallize. As has been previously observed, acicular crystals form in DMSO-methanol solution, whereas irregular aggregates of crystals form in acidic aqueous solution. Here tabular crystals were found to form on -NH{sub 2} and -OH terminated SAMs, whereas inclined crystals formed on -COOH and -CH{sub 3} terminated substrates. Particulate coverage on these SAMs decreased in the order of -NH{sub 2}, -COOH, -CH{sub 3}, and -OH. Chloroquine, a widely used antimalaria drug, slowed particle nucleation rate on the SAMs with varying efficacy but was most efficient on the -COOH SAM. XANES measurements showed that the coordination environment surrounding iron in the particles was found to be the same, regardless of the preparation method and matches existing spectra of hemozoin produced in vivo and synthetic {beta}-hematin. Different crystallographic planes were found to be expressed depending on the identity of the SAM using XRD. The interaction between the terminal functional group of the SAM and the density and orientation of crystals is discussed.

  19. Self-Assembled Monolayers as Templates for Heme Crystallization.

    SciTech Connect

    Wang, Xuefeng; Ingall, Ellery; Lai, Barry; Stack, Andrew G

    2010-01-01

    Homogeneous self-assembled monolayers (SAMs) of alkanethiols (HS(CH{sub 2}){sub n}X) on Au(111) were used as substrates for crystallization of ferriprotoporphyrin IX (heme) in acidic aqueous solution. Different terminal functional groups (X = OH, COOH, NH{sub 2}, CH{sub 3}) were used on the SAMs as models of sites where heme crystallization takes place in blood-feeding organisms. Atomic force microscopy, X-ray diffraction (XRD), and X-ray absorption near edge spectroscopy (XANES) were employed to characterize particle morphology, density, crystallographic orientation, and the coordination environment. It was found that the morphology and extent of growth of particulates were strongly affected by the environment in which they crystallize. As has been previously observed, acicular crystals form in DMSO-methanol solution, whereas irregular aggregates of crystals form in acidic aqueous solution. Here tabular crystals were found to form on -NH{sub 2} and -OH terminated SAMs, whereas inclined crystals formed on -COOH and -CH{sub 3} terminated substrates. Particulate coverage on these SAMs decreased in the order of -NH{sub 2}, -COOH, -CH{sub 3}, and -OH. Chloroquine, a widely used antimalaria drug, slowed particle nucleation rate on the SAMs with varying efficacy but was most efficient on the -COOH SAM. XANES measurements showed that the coordination environment surrounding iron in the particles was found to be the same, regardless of the preparation method and matches existing spectra of hemozoin produced in vivo and synthetic {beta}-hematin. Different crystallographic planes were found to be expressed depending on the identity of the SAM using XRD. The interaction between the terminal functional group of the SAM and the density and orientation of crystals is discussed.

  20. Spectral ordering techniques for incomplete LU preconditoners for CG methods

    NASA Technical Reports Server (NTRS)

    Clift, Simon S.; Simon, Horst D.; Tang, Wei-Pai

    1995-01-01

    The effectiveness of an incomplete LU (ILU) factorization as a preconditioner for the conjugate gradient method can be highly dependent on the ordering of the matrix rows during its creation. Detailed justification for two heuristics commonly used in matrix ordering for anisotropic problems is given. The bandwidth reduction and weak connection following heuristics are implemented through an ordering method based on eigenvector computations. This spectral ordering is shown to be a good representation of the heuristics. Analysis and test cases in two and three dimensional diffusion problems demonstrate when ordering is important, and when an ILU decomposition will be ordering insensitive. The applicability of the heuristics is thus evaluated and placed on a more rigorous footing.

  1. A Coupled Approach for Structural Damage Detection with Incomplete Measurements

    NASA Technical Reports Server (NTRS)

    James, George; Cao, Timothy; Kaouk, Mo; Zimmerman, David

    2013-01-01

    This historical work couples model order reduction, damage detection, dynamic residual/mode shape expansion, and damage extent estimation to overcome the incomplete measurements problem by using an appropriate undamaged structural model. A contribution of this work is the development of a process to estimate the full dynamic residuals using the columns of a spring connectivity matrix obtained by disassembling the structural stiffness matrix. Another contribution is the extension of an eigenvector filtering procedure to produce full-order mode shapes that more closely match the measured active partition of the mode shapes using a set of modified Ritz vectors. The full dynamic residuals and full mode shapes are used as inputs to the minimum rank perturbation theory to provide an estimate of damage location and extent. The issues associated with this process are also discussed as drivers of near-term development activities to understand and improve this approach.

  2. The value of incomplete mouse models of Alzheimer's disease.

    PubMed

    Radde, Rebecca; Duma, Cecilia; Goedert, Michel; Jucker, Mathias

    2008-03-01

    To study Alzheimer's disease (AD), a variety of mouse models has been generated through the overexpression of the amyloid precursor protein and/or the presenilins harboring one or several mutations found in familial AD. With aging, these mice develop several lesions similar to those of AD, including diffuse and neuritic amyloid deposits, cerebral amyloid angiopathy, dystrophic neurites and synapses, and amyloid-associated neuroinflammation. Other characteristics of AD, such as neurofibrillary tangles and nerve cell loss, are not satisfactorily reproduced in these models. Mouse models that recapitulate only specific aspects of AD pathogenesis are of great advantage when deciphering the complexity of the disease and can contribute substantially to diagnostic and therapeutic innovations. Incomplete mouse models have been key to the development of Abeta42-targeted therapies, as well as to the current understanding of the interrelationship between cerebral beta-amyloidosis and tau neurofibrillary lesions, and are currently being used to develop novel diagnostic agents for in vivo imaging.

  3. Multirate control with incomplete information over Profibus-DP network

    NASA Astrophysics Data System (ADS)

    Salt, J.; Casanova, V.; Cuenca, A.; Pizá, R.

    2014-07-01

    When a process field bus-decentralized peripherals (Profibus-DP) network is used in an industrial environment, a deterministic behaviour is usually claimed. However, due to some concerns such as bandwidth limitations, lack of synchronisation among different clocks and existence of time-varying delays, a more complex problem must be faced. This problem implies the transmission of irregular and, even, random sequences of incomplete information. The main consequence of this issue is the appearance of different sampling periods at different network devices. In this paper, this aspect is checked by means of a detailed Profibus-DP timescale study. In addition, in order to deal with the different periods, a delay-dependent dual-rate proportional-integral-derivative control is introduced. Stability for the proposed control system is analysed in terms of linear matrix inequalities.

  4. Iterative reconstruction of images from incomplete spectral data

    NASA Astrophysics Data System (ADS)

    Rhebergen, Jan B.; van den Berg, Peter M.; Habashy, Tarek M.

    1997-06-01

    In various branches of engineering and science, one is confronted with measurements resulting in incomplete spectral data. The problem of the reconstruction of an image from such a data set can be formulated in terms of an integral equation of the first kind. Consequently, this equation can be converted into an equivalent integral equation of the second kind which can be solved by a Neumann-type iterative method. It is shown that this Neumann expansion is an error-reducing method and that it is equivalent to the Papoulis - Gerchberg algorithm for band-limited signal extrapolation. The integral equation can also be solved by employing a conjugate gradient iterative scheme. Again, convergence of this scheme is demonstrated. Finally a number of illustrative numerical examples are presented and discussed.

  5. Traumatic vertebral artery dissection presenting with incomplete congruous homonymous quadrantanopia

    PubMed Central

    2010-01-01

    Background To describe a rare presentation of vertebral artery dissection (VAD) as a small but congruous incomplete homonymous hemianopia demonstrating use of visual field testing in the diagnosis. Case presentation A 30 year old woman had been unwell for 4 months with difficulty focusing, vertigo, dizziness and a feeling of falling to the right. A small but congruous right inferior homonymous quadrantanopia was found on examination leading to further investigation that uncovered a vertebral artery dissection and multiple posterior circulation infarctions including a left occipital stroke matching the field defect. Conclusions We describe an atypical case of VAD presenting with a small congruous quadrantanopia. This is a rare but significant condition that predisposes to multiple thromboembolic infarction that may be easily misdiagnosed and a high index of suspicion is required to make the diagnosis. PMID:20482837

  6. Incomplete Lineage Sorting Is Common in Extant Gibbon Genera

    PubMed Central

    Luca, Francesca; Carbone, Lucia; Mootnick, Alan R.; de Jong, Pieter J.; Di Rienzo, Anna

    2013-01-01

    We sequenced reduced representation libraries by means of Illumina technology to generate over 1.5 Mb of orthologous sequence from a representative of each of the four extant gibbon genera (Nomascus, Hylobates, Symphalangus, and Hoolock). We used these data to assess the evolutionary relationships between the genera by evaluating the likelihoods of all possible bifurcating trees involving the four taxa. Our analyses provide weak support for a tree with Nomascus and Hylobates as sister taxa and with Hoolock and Symphalangus as sister taxa, though bootstrap resampling suggests that other phylogenetic scenarios are also possible. This uncertainty is due to short internal branch lengths and extensive incomplete lineage sorting across taxa. The true phylogenetic relationships among gibbon genera will likely require a more extensive whole-genome sequence analysis. PMID:23341974

  7. Absolute magnitude calibration using trigonometric parallax - Incomplete, spectroscopic samples

    NASA Technical Reports Server (NTRS)

    Ratnatunga, Kavan U.; Casertano, Stefano

    1991-01-01

    A new numerical algorithm is used to calibrate the absolute magnitude of spectroscopically selected stars from their observed trigonometric parallax. This procedure, based on maximum-likelihood estimation, can retrieve unbiased estimates of the intrinsic absolute magnitude and its dispersion even from incomplete samples suffering from selection biases in apparent magnitude and color. It can also make full use of low accuracy and negative parallaxes and incorporate censorship on reported parallax values. Accurate error estimates are derived for each of the fitted parameters. The algorithm allows an a posteriori check of whether the fitted model gives a good representation of the observations. The procedure is described in general and applied to both real and simulated data.

  8. Incomplete rotational cooling in a 22-pole ion trap

    NASA Astrophysics Data System (ADS)

    Endres, E. S.; Egger, G.; Lee, S.; Lakhmanskaya, O.; Simpson, M.; Wester, R.

    2017-02-01

    Cryogenic 22-pole ion traps have found many applications in ion-molecule reaction kinetics and in high resolution molecular spectroscopy. For most of these applications it is important to know the translational and internal temperatures of the trapped ions. Here, we present detailed rotational state thermometry measurements over an extended temperature range for hydroxyl anions in He, HD, and H2. The measured rotational temperatures show a termination of the thermalisation with the buffer gas around 25 K, independent of mass ratio and confinement potential of the trap. Different possible explanations for this incomplete thermalisation are discussed, among them the thermalisation of the buffer gas, room temperature blackbody radiation or warm gas entering the trap, and heating due to energy transfer from rotationally excited hydrogen molecules.

  9. Corrected profile likelihood confidence interval for binomial paired incomplete data.

    PubMed

    Pradhan, Vivek; Menon, Sandeep; Das, Ujjwal

    2013-01-01

    Clinical trials often use paired binomial data as their clinical endpoint. The confidence interval is frequently used to estimate the treatment performance. Tang et al. (2009) have proposed exact and approximate unconditional methods for constructing a confidence interval in the presence of incomplete paired binary data. The approach proposed by Tang et al. can be overly conservative with large expected confidence interval width (ECIW) in some situations. We propose a profile likelihood-based method with a Jeffreys' prior correction to construct the confidence interval. This approach generates confidence interval with a much better coverage probability and shorter ECIWs. The performances of the method along with the corrections are demonstrated through extensive simulation. Finally, three real world data sets are analyzed by all the methods. Statistical Analysis System (SAS) codes to execute the profile likelihood-based methods are also presented.

  10. Pericardio-Amniotic Shunting for Incomplete Pentalogy of Cantrell.

    PubMed

    Engels, Alexander C; Debeer, Anne; Russo, Francesca M; Aertsen, Michael; Aerts, Katleen; Miserez, Marc; Deprest, Jan; Lewi, Liesbeth; Devlieger, Roland

    2017-01-01

    A 27-year-old woman, gravida 2, para 0, presented with an incomplete Pentalogy of Cantrell with an omphalocele, diaphragmatic hernia, and a pericardial defect at 32 weeks' gestation. A large pericardial effusion compressed the lungs and had led to a reduced lung growth with an observed-to-expected total lung volume of 28% as measured by MRI. The effusion disappeared completely after the insertion of a pericardio-amniotic shunt at 33 weeks. After birth, the newborn showed no signs of pulmonary hypoplasia and underwent a surgical correction of the defect. Protracted wound healing and a difficult withdrawal from opioids complicated the neonatal period. The child was discharged on postnatal day 105 in good condition. This case demonstrates that in case of Pentalogy of Cantrell with large pericardial effusion, the perinatal outcome might be improved by pericardio-amniotic shunting.

  11. A flexible acquisition cycle for incompletely defined fieldbus protocols.

    PubMed

    Gaitan, Vasile-Gheorghita; Gaitan, Nicoleta-Cristina; Ungurean, Ioan

    2014-05-01

    Real time data-acquisition from fieldbuses strongly depends on the network type and protocol used. Currently, there is an impressive number of fieldbuses, some of them are completely defined and others are incompletely defined. In those from the second category, the time variable, the main element in real-time data acquisition, does not appear explicitly. Examples include protocols such as Modbus ASCII/RTU, M-bus, ASCII character-based, and so on. This paper defines a flexible acquisition cycle based on the Master-Slave architecture that can be implemented on a Master station, called a Base Station Gateway (BSG). The BSG can add a timestamp for temporal location of data. It also presents a possible extension for the Modbus protocol, developed as simple and low cost solution based on existing hardware.

  12. Quantum Tomography from Incomplete Data via MaxEnt Principle

    NASA Astrophysics Data System (ADS)

    Bužek, Vladimír

    We show how the maximum entropy (MaxEnt) principle can be efficiently used for a reconstruction of states of quantum systems from incomplete tomographic data. This MaxEnt reconstruction scheme can be in specific cases several orders of magnitude more efficient than the standard inverse Radon transformation or the reconstruction via direct sampling using pattern functions. We apply the MaxEnt algorithm for a reconstruction of motional quantum states of neutral atoms. As an example we analyze the experimental data obtained by the group of C. Salomon at the ENS in Paris and we reconstruct Wigner functions of motional quantum states of Cs atoms trapped in an optical lattice. We also reconstruct Wigner functions of a cavity field based on a measurement of the parity operator. We analyze in detail experimental data obtained by the group of S. Haroche at the ENS in Paris.

  13. Incomplete lineage sorting is common in extant gibbon genera.

    PubMed

    Wall, Jeffrey D; Kim, Sung K; Luca, Francesca; Carbone, Lucia; Mootnick, Alan R; de Jong, Pieter J; Di Rienzo, Anna

    2013-01-01

    We sequenced reduced representation libraries by means of Illumina technology to generate over 1.5 Mb of orthologous sequence from a representative of each of the four extant gibbon genera (Nomascus, Hylobates, Symphalangus, and Hoolock). We used these data to assess the evolutionary relationships between the genera by evaluating the likelihoods of all possible bifurcating trees involving the four taxa. Our analyses provide weak support for a tree with Nomascus and Hylobates as sister taxa and with Hoolock and Symphalangus as sister taxa, though bootstrap resampling suggests that other phylogenetic scenarios are also possible. This uncertainty is due to short internal branch lengths and extensive incomplete lineage sorting across taxa. The true phylogenetic relationships among gibbon genera will likely require a more extensive whole-genome sequence analysis.

  14. Missing... presumed at random: cost-analysis of incomplete data.

    PubMed

    Briggs, Andrew; Clark, Taane; Wolstenholme, Jane; Clarke, Philip

    2003-05-01

    When collecting patient-level resource use data for statistical analysis, for some patients and in some categories of resource use, the required count will not be observed. Although this problem must arise in most reported economic evaluations containing patient-level data, it is rare for authors to detail how the problem was overcome. Statistical packages may default to handling missing data through a so-called 'complete case analysis', while some recent cost-analyses have appeared to favour an 'available case' approach. Both of these methods are problematic: complete case analysis is inefficient and is likely to be biased; available case analysis, by employing different numbers of observations for each resource use item, generates severe problems for standard statistical inference. Instead we explore imputation methods for generating 'replacement' values for missing data that will permit complete case analysis using the whole data set and we illustrate these methods using two data sets that had incomplete resource use information.

  15. Analysis of incomplete longitudinal binary data using multiple imputation.

    PubMed

    Li, Xiaoming; Mehrotra, Devan V; Barnard, John

    2006-06-30

    We propose a propensity score-based multiple imputation (MI) method to tackle incomplete missing data resulting from drop-outs and/or intermittent skipped visits in longitudinal clinical trials with binary responses. The estimation and inferential properties of the proposed method are contrasted via simulation with those of the commonly used complete-case (CC) and generalized estimating equations (GEE) methods. Three key results are noted. First, if data are missing completely at random, MI can be notably more efficient than the CC and GEE methods. Second, with small samples, GEE often fails due to 'convergence problems', but MI is free of that problem. Finally, if the data are missing at random, while the CC and GEE methods yield results with moderate to large bias, MI generally yields results with negligible bias. A numerical example with real data is provided for illustration.

  16. Effects of incomplete mixing on chemical reactions under flow heterogeneities.

    NASA Astrophysics Data System (ADS)

    Perez, Lazaro; Hidalgo, Juan J.; Dentz, Marco

    2016-04-01

    Evaluation of the mixing process in aquifers is of primary importance when assessing attenuation of pollutants. In aquifers different hydraulic and chemical properties can increase mixing and spreading of the transported species. Mixing processes control biogeochemical transformations such as precipitation/dissolution reactions or degradation reactions that are fast compared to mass transfer processes. Reactions are local phenomena that fluctuate at the pore scale, but predictions are often made at much larger scales. However, aquifer heterogeities are found at all scales and generates flow heterogeneities which creates complex concentration distributions that enhances mixing. In order to assess the impact of spatial flow heterogeneities at pore scale we study concentration profiles, gradients and reaction rates using a random walk particle tracking (RWPT) method and kernel density estimators to reconstruct concentrations and gradients in two setups. First, we focus on a irreversible bimolecular reaction A+B → C under homogeneous flow to distinguish phenomena of incomplete mixing of reactants from finite-size sampling effects. Second, we analise a fast reversible bimolecular chemical reaction A+B rightleftharpoons C in a laminar Poiseuille flow reactor to determine the difference between local and global reaction rates caused by the incomplete mixing under flow heterogeneities. Simulation results for the first setup differ from the analytical solution of the continuum scale advection-dispersion-reaction equation studied by Gramling et al. (2002), which results in an overstimation quantity of reaction product (C). In the second setup, results show that actual reaction rates are bigger than the obtained from artificially mixing the system by averaging the concentration vertically. - LITERATURE Gramling, C. M.,Harvey, C. F., Meigs, and L. C., (2002). Reactive transport in porous media: A comparison of model prediction with laboratory visualization, Environ. Sci

  17. Ordered Porous Pd Octahedra Covered with Monolayer Ru Atoms.

    PubMed

    Ge, Jingjie; He, Dongsheng; Bai, Lei; You, Rui; Lu, Haiyuan; Lin, Yue; Tan, Chaoliang; Kang, Yan-Biao; Xiao, Bin; Wu, Yuen; Deng, Zhaoxiang; Huang, Weixin; Zhang, Hua; Hong, Xun; Li, Yadong

    2015-11-25

    Monolayer Ru atoms covered highly ordered porous Pd octahedra have been synthesized via the underpotential deposition and thermodynamic control. Shape evolution from concave nanocube to octahedron with six hollow cavities was observed. Using aberration-corrected high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we provide quantitative evidence to prove that only a monolayer of Ru atoms was deposited on the surface of porous Pd octahedra. The as-prepared monolayer Ru atoms covered Pd nanostructures exhibited excellent catalytic property in terms of semihydrogenation of alkynes.

  18. Optical Control of Spin Polarization in Monolayer Transition Metal Dichalcogenides.

    PubMed

    Chen, Xi; Yan, Tengfei; Zhu, Bairen; Yang, Siyuan; Cui, Xiaodong

    2017-02-28

    Optical excitation could generate electrons' spin polarization in some semiconductors with the control of the field polarization. In this article, we report a series of spin-resolved photocurrent experiments on monolayer tungsten disulfide. The experiments demonstrate that the optical excitations with the same helicity could generate opposite spin polarization around the Fermi level by tuning the excitation energy. The mechanism lies in the valley-dependent optical selection rules, the giant spin-orbit coupling, and spin-valley locking in monolayer transition metal dichalcogenides (TMDs). These exotic features make monolayer TMDs promising candidates for conceptual semiconductor-based spintronics.

  19. IMPORTANT BUT INCOMPLETE: PLAN B AS AN AVENUE FOR POST-ASSAULT CARE

    PubMed Central

    Munro, Michelle L.; Martyn, Kristy K.; Campbell, Rebecca; Graham-Bermann, Sandra; Seng, Julia S.

    2016-01-01

    Many survivors of rape do not seek post-assault care. The recent change in status of emergency contraception (EC), such as Plan B, to an over-the-counter (OTC) product may be further changing post-assault care-seeking. This descriptive study will quantify OTC EC use in the post-assault period and elicit survivors’ desires for care. Data were collected from women purchasing OTC EC at university pharmacies (n=55) and students in an undergraduate university class (n=165). Quantitative results indicate annual prevalence rates of post-assault OTC EC use as 5.4%-7.3%. Qualitative analyses indicate OTC EC is an important but incomplete form of post-assault care. Future work should focus on intervention development to provide all OTC EC users with information about post-assault resources to prevent long-term sequelae. PMID:27293493

  20. Incomplete oedipism and chronic suicidality in psychotic depression with paranoid delusions related to eyes

    PubMed Central

    Pompili, Maurizio; Lester, David; Tatarelli, Roberto; Girardi, Paolo

    2006-01-01

    Self-enucleation or oedipism is a term used to describe self-inflicted enucleation. It is a rare form of self-mutilation, found mainly in acutely psychotic patients. We propose the term incomplete oedipism to describe patients who deliberately and severely mutilate their eyes without proper enucleation. We report the case of a 32-year-old male patient with a five-year history of psychotic depression accompanied by paranoid delusions centered around his belief that his neighbors criticized him and stared at him. A central feature of his clinical picture was an eye injury that the patient had caused by pouring molten lead into his right eye during a period of deep hopelessness and suicidality when the patient could not resolve his anhedonia and social isolation. Pharmacotherapy and psychotherapy dramatically improved his disorder. PMID:17118200

  1. Incomplete cytokinesis/binucleation in mammals: The powerful system of hepatocytes.

    PubMed

    Fortier, M; Celton-Morizur, S; Desdouets, C

    2017-01-01

    Polyploidy, the state of having greater than a diploid DNA content (tetraploid, octoploid, etc.) is a characteristic feature of mammalian hepatocytes and accompanies late fetal development and postnatal maturation of the liver. During the weaning period, diploid hepatocytes can engage either into normal cell division cycle giving rise to two diploid hepatocytes or follow a scheduled division program characterized by incomplete cytokinesis. In that case, diploid hepatocytes undergo mitosis, but do not form a contractile ring. Indeed, cleavage-plane specification is never established, because of the deficiencies of actin cytoskeleton reorganization. Furthermore, microtubules fail both to contact the cortex and to deliver their molecular signal, preventing localization and activation of RhoA. Therefore, cytokinesis aborts and a binucleate tetraploid liver cell is generated, which subsequently plays a pivotal role in liver progressive polyploidization. In this chapter, we describe detailed protocols to monitor hepatocyte proliferation and cytokinesis process by in situ and dynamic ex vivo approaches.

  2. Bacterial lipopolysaccharides form physically cross-linked, two-dimensional gels in the presence of divalent cations.

    PubMed

    Herrmann, Moritz; Schneck, Emanuel; Gutsmann, Thomas; Brandenburg, Klaus; Tanaka, Motomu

    2015-08-14

    We established a bacterial membrane model with monolayers of bacterial lipopolysaccharides (LPS Re and LPS Ra) and quantified their viscoelastic properties by using an interfacial stress rheometer coupled to a Langmuir film balance. LPS Re monolayers exhibited purely viscous behaviour in the absence of calcium ions, while the same monolayers underwent a viscous-to-elastic transition upon compression in the presence of Ca(2+). Our results demonstrated for the first time that LPSs in bacterial outer membranes can form two-dimensional elastic networks in the presence of Ca(2+). Different from LPS Re monolayers, the LPS Ra monolayers showed a very similar rheological transition both in the presence and absence of Ca(2+), suggesting that longer saccharide chains can form 2D physical gels even in the absence of Ca(2+). By exposure of the monolayers to the antimicrobial peptide protamine, we could directly monitor the differences in resistance of bacterial membranes according to the presence of calcium.

  3. Contact doping of silicon wafers and nanostructures with phosphine oxide monolayers.

    PubMed

    Hazut, Ori; Agarwala, Arunava; Amit, Iddo; Subramani, Thangavel; Zaidiner, Seva; Rosenwaks, Yossi; Yerushalmi, Roie

    2012-11-27

    Contact doping method for the controlled surface doping of silicon wafers and nanometer scale structures is presented. The method, monolayer contact doping (MLCD), utilizes the formation of a dopant-containing monolayer on a donor substrate that is brought to contact and annealed with the interface or structure intended for doping. A unique feature of the MLCD method is that the monolayer used for doping is formed on a separate substrate (termed donor substrate), which is distinct from the interface intended for doping (termed acceptor substrate). The doping process is controlled by anneal conditions, details of the interface, and molecular precursor used for the formation of the dopant-containing monolayer. The MLCD process does not involve formation and removal of SiO(2) capping layer, allowing utilization of surface chemistry details for tuning and simplifying the doping process. Surface contact doping of intrinsic Si wafers (i-Si) and intrinsic silicon nanowires (i-SiNWs) is demonstrated and characterized. Nanowire devices were formed using the i-SiNW channel and contact doped using the MLCD process, yielding highly doped SiNWs. Kelvin probe force microscopy (KPFM) was used to measure the longitudinal dopant distribution of the SiNWs and demonstrated highly uniform distribution in comparison with in situ doped wires. The MLCD process was studied for i-Si substrates with native oxide and H-terminated surface for three types of phosphorus-containing molecules. Sheet resistance measurements reveal the dependency of the doping process on the details of the surface chemistry used and relation to the different chemical environments of the P═O group. Characterization of the thermal decomposition of several monolayer types formed on SiO(2) nanoparticles (NPs) using TGA and XPS provides insight regarding the role of phosphorus surface chemistry at the SiO(2) interface in the overall MLCD process. The new MLCD process presented here for controlled surface doping

  4. Monte Carlo computer simulation of spreading pressure-area isotherms of Langmuir monolayers of fatty-acid molecules

    NASA Astrophysics Data System (ADS)

    Polimeno, Antonino; Ros, J. Marijin; Levine, Yehudi K.

    2001-10-01

    We describe an off-lattice model with chemical group resolution for investigating the spreading pressure-area isotherms of Langmuir monolayers of fatty-acid molecules at air-water interfaces. It is shown that a balance of the attractive interactions between the methylene chains and longer-range repulsive interactions between the headgroups determines the form of the isotherms. The model reproduces the experimentally observed dependence of the isotherms on the chain length and unsaturation. At 300 K model palmitic acid chains (C16:0) are shown to form liquid-condensed monolayers at all spreading pressures, while the isotherms of monolayers of myristic acid (C14:0) exhibit a liquid-condensed to liquid-expanded transition in agreement with experiments. Moreover, the simulations show that the introduction of cis-unsaturated segments into the 7-8 positions of the C14 chains depresses the phase transition temperature, so that the monolayers undertake a liquid-expanded structure.

  5. Exciton formation assisted by longitudinal optical phonons in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Thilagam, A.

    2016-09-01

    We examine a mechanism by which excitons are generated via the longitudinal optical (LO) phonon-assisted scattering process after optical excitation of monolayer transition metal dichalcogenides. The exciton formation time is computed as a function of the exciton center-of-mass wavevector, electron and hole temperatures, and carrier densities for known values of the Fröhlich coupling constant, LO phonon energy, lattice temperature, and the exciton binding energy in layered structures. For the monolayer MoS2, we obtain ultrafast exciton formation times on the sub-picosecond time scale at charge densities of 5 × 1011 cm-2 and carrier temperatures less than 300 K, in good agreement with recent experimental findings ( ≈0.3 ps). While excitons are dominantly created at zero center-of-mass wavevectors at low charge carrier temperatures ( ≈30 K), the exciton formation time is most rapid at non-zero wavevectors at higher temperatures ( ≥120 K) of charge carriers. The results show the inverse square-law dependence of the exciton formation times on the carrier density, consistent with a square-law dependence of photoluminescence on the excitation density. Our results show that excitons are formed more rapidly in exemplary monolayer selenide-based dichalcogenides (MoSe2 and WSe2) than sulphide-based dichalcogenides (MoS2 and WS2).

  6. Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy.

    PubMed

    Ando, Jun; Kinoshita, Masanao; Cui, Jin; Yamakoshi, Hiroyuki; Dodo, Kosuke; Fujita, Katsumasa; Murata, Michio; Sodeoka, Mikiko

    2015-04-14

    Sphingomyelin (SM) and cholesterol (chol)-rich domains in cell membranes, called lipid rafts, are thought to have important biological functions related to membrane signaling and protein trafficking. To visualize the distribution of SM in lipid rafts by means of Raman microscopy, we designed and synthesized an SM analog tagged with a Raman-active diyne moiety (diyne-SM). Diyne-SM showed a strong peak in a Raman silent region that is free of interference from intrinsic vibrational modes of lipids and did not appear to alter the properties of SM-containing monolayers. Therefore, we used Raman microscopy to directly visualize the distribution of diyne-SM in raft-mimicking domains formed in SM/dioleoylphosphatidylcholine/chol ternary monolayers. Raman images visualized a heterogeneous distribution of diyne-SM, which showed marked variation, even within a single ordered domain. Specifically, diyne-SM was enriched in the central area of raft domains compared with the peripheral area. These results seem incompatible with the generally accepted raft model, in which the raft and nonraft phases show a clear biphasic separation. One of the possible reasons is that gradual changes of SM concentration occur between SM-rich and -poor regions to minimize hydrophobic mismatch. We believe that our technique of hyperspectral Raman imaging of a single lipid monolayer opens the door to quantitative analysis of lipid membranes by providing both chemical information and spatial distribution with high (diffraction-limited) spatial resolution.

  7. Electronic and magnetic properties of nonmetal atoms adsorbed ReS{sub 2} monolayers

    SciTech Connect

    Zhang, Xiaoou; Li, Qingfang

    2015-08-14

    The stable configurations and electronic and magnetic properties of nonmetal atoms (H, N, P, O, S, F, and Cl) adsorbed ReS{sub 2} monolayers have been investigated by first-principles calculations. It is found that H, O, S, F, and Cl prefer to occupy the peak sites of S atoms, while both N and P atoms favor the valley sites of S atoms. The ReS{sub 2} sheet exhibits a good adsorption capability to nonmetal atoms. The reconstruction of the surface is pronounced in N- and P-adsorbed ReS{sub 2} monolayers. In H-adsorbed case, the Fermi level is pulled into the conduction band, which results in the semiconductor-metal transition. The same magnetic moment of 1μ{sub B} is found in the N-, P-, F-, and Cl-adsorbed ReS{sub 2} monolayers, while the mechanisms of forming magnetic moment for N (P)- and F (Cl)-adsorbed cases are different. In addition, the spatial extensions of spin density in P-, F-, and Cl-adsorbed cases are larger than that in N-adsorbed case, which is more suitable to achieve long-range magnetic coupling interaction at low defect concentrations. Our results provide insight for achieving metal-free magnetism and a tunable band gap for various electronic and spintronic devices based on ReS{sub 2}.

  8. Sphingomyelin distribution in lipid rafts of artificial monolayer membranes visualized by Raman microscopy

    PubMed Central

    Ando, Jun; Kinoshita, Masanao; Cui, Jin; Yamakoshi, Hiroyuki; Dodo, Kosuke; Fujita, Katsumasa; Murata, Michio; Sodeoka, Mikiko

    2015-01-01

    Sphingomyelin (SM) and cholesterol (chol)-rich domains in cell membranes, called lipid rafts, are thought to have important biological functions related to membrane signaling and protein trafficking. To visualize the distribution of SM in lipid rafts by means of Raman microscopy, we designed and synthesized an SM analog tagged with a Raman-active diyne moiety (diyne-SM). Diyne-SM showed a strong peak in a Raman silent region that is free of interference from intrinsic vibrational modes of lipids and did not appear to alter the properties of SM-containing monolayers. Therefore, we used Raman microscopy to directly visualize the distribution of diyne-SM in raft-mimicking domains formed in SM/dioleoylphosphatidylcholine/chol ternary monolayers. Raman images visualized a heterogeneous distribution of diyne-SM, which showed marked variation, even within a single ordered domain. Specifically, diyne-SM was enriched in the central area of raft domains compared with the peripheral area. These results seem incompatible with the generally accepted raft model, in which the raft and nonraft phases show a clear biphasic separation. One of the possible reasons is that gradual changes of SM concentration occur between SM-rich and -poor regions to minimize hydrophobic mismatch. We believe that our technique of hyperspectral Raman imaging of a single lipid monolayer opens the door to quantitative analysis of lipid membranes by providing both chemical information and spatial distribution with high (diffraction-limited) spatial resolution. PMID:25825736

  9. A new organofunctional ethoxysilane self-assembly monolayer for promoting adhesion of rubber to aluminum.

    PubMed

    Wang, Fang; Xu, Juan; Luo, Heyi; Wang, Jinggang; Wang, Qian

    2009-10-12

    Practical adhesion of rubber to aluminum is measured for various aluminum silanization treatments. In this study, 6-(3-triethoxysilylpropylamino)-1,3,5-triazine-2,4-dithiol (TES) was used as the coupling agent for preparing self-assembly monolayers (SAMs) on an aluminum surface. The structure and chemical composition of the SAMs were analyzed using Fourier transform infra-red spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The changes in the surface features of the aluminum surface due to TES treatment were investigated by atomic force microscopy (AFM). The adhesive properties of the silanized aluminum surface and EPDM rubber have been evaluated by a T-peel strength test. The results suggested that the Si-O-Al bonding at aluminum TES interface existed and a TES self-assembly monolayer was formed on the aluminum surface. More than 6.0 KN/m adhesion strength is obtained when the aluminum is silanized with 2.5 mmol/dm(3) TES, cured at 160 degrees C and vulcanized with EPDM rubber at 160 degrees C for 30 min. It is suggested that the TES self-assembly monolayer is bound to aluminum through its ethoxysilyl functional group, and the thiol function group is strongly crosslinked to EPDM rubber, respectively.

  10. Atomic Scale Study on Growth and Heteroepitaxy of ZnO Monolayer on Graphene

    PubMed Central

    2016-01-01

    Atomically thin semiconducting oxide on graphene carries a unique combination of wide band gap, high charge carrier mobility, and optical transparency, which can be widely applied for optoelectronics. However, study on the epitaxial formation and properties of oxide monolayer on graphene remains unexplored due to hydrophobic graphene surface and limits of conventional bulk deposition technique. Here, we report atomic scale study of heteroepitaxial growth and relationship of a single-atom-thick ZnO layer on graphene using atomic layer deposition. We demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation. We experimentally determine that the thinnest ZnO monolayer has a wide band gap (up to 4.0 eV), due to quantum confinement and graphene-like structure, and high optical transparency. This study can lead to a new class of atomically thin two-dimensional heterostructures of semiconducting oxides formed by highly controlled epitaxial growth. PMID:28002942

  11. Impact of Anchoring Groups on Ballistic Transport: Single Molecule vs Monolayer Junctions

    PubMed Central

    2015-01-01

    Tuning the transport properties of molecular junctions by chemically modifying the molecular structure is one of the key challenges for advancing the field of molecular electronics. In the present contribution, we investigate current–voltage characteristics of differently linked metal–molecule–metal systems that comprise either a single molecule or a molecular assembly. This is achieved by employing density functional theory in conjunction with a Green’s function approach. We show that the conductance of a molecular system with a specific anchoring group is fundamentally different depending on whether a single molecule or a continuous monolayer forms the junction. This is a consequence of collective electrostatic effects that arise from dipolar elements contained in the monolayer and from interfacial charge rearrangements. As a consequence of these collective effects, the “ideal” choice for an anchoring group is clearly different for monolayer and single molecule devices. A particularly striking effect is observed for pyridine-docked systems. These are subject to Fermi-level pinning at high molecular packing densities, causing an abrupt increase of the junction current already at small voltages. PMID:26401191

  12. Vibrational Spectra of Vinyltriethoxysilane (vtes) Monolayers Adsorbed on Germania and Alumina

    NASA Astrophysics Data System (ADS)

    Craig, Ronald; Mallik, Robert R.

    1997-05-01

    VTES is used as a coupling agent to improve the adhesion of various coatings especially to glass, but also to minerals, metal oxides and other substrates. It has been studied extensively in this context by Infrared, Raman, and other spectroscopic methods; however, few of these methods have the sensitivity to probe effectively the first adsorbed monolayer on the above substrates. Inelastic Electron Tunneling Spectroscopy (IETS), however, is intrinsically capable of detecting fractional monolayer coverage, but, until recently, studies have been limited primarily to the adsorption of monolayers on aluminum oxide which forms the insulating barrier in most metal/insulator/metal IET junctions. IETS has not been used to investigate adorbates on other barriers because it is difficult to make the barriers suitably thin and physically continuous. We are now able to fabricate viable IETS barriers by radio-frequency sputtering, and we present spectra of VTES adsorbed on thermally grown alumina, and sputtered germania films. Germania is chosen as a model for glass to avoid any ambiguity in assigning Si-O related vibrational modes to either the adsorband or adsorbate.

  13. Epithelial monolayer culture system for real‐time single‐cell analyses

    PubMed Central

    Seo, Jong Bae; Moody, Mark; Koh, Duk‐Su

    2014-01-01

    Abstract Many epithelial cells form polarized monolayers under in vivo and in vitro conditions. Typically, epithelial cells are cultured for differentiation on insert systems where cells are plated on a porous filter membrane. Although the cultured monolayers have been a standard system to study epithelial physiology, there are some limits: The epithelial cells growing inside the commercial inserts are not optimal to visualize directly through lenses on inverted microscopes. The cell images are optically distorted and background fluorescence is bright due to the filter membrane positioned between the cells and the lens. In addition, the cells are not easily accessible by electrodes due to the presence of tall side walls. Here, we present the design, fabrication, and practical applications of an improved system for analysis of polarized epithelial monolayers. This new system allows (1) direct imaging of cells without an interfering filter membrane, (2) electrophysiological measurements, and (3) detection of apical secretion with minimal dilution. Therefore, our culture method is optimized to study differentiated epithelial cells at the single‐cell and subcellular levels, and can be extended to other cell types with minor modifications. PMID:24771696

  14. Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects.

    PubMed

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-07

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

  15. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    PubMed Central

    Yang, Guang; Hallinan, Daniel T.

    2016-01-01

    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties. PMID:27762394

  16. Self-Assembled Morphologies of Linear and Miktoarm Star Triblock Copolymer Monolayers.

    PubMed

    Deng, Hanlin; Li, Weihua; Qiu, Feng; Shi, An-Chang

    2017-04-12

    Monolayers of linear and miktoarm star ABC triblock copolymers with equal A and C blocks are investigated using the self-consistent field theory. The monolayers of ABC triblock copolymers are formed between two parallel surfaces that are attractive to the A and C blocks. The repulsive interaction parameter $\\chi_{AC}N$ between the A and C blocks is chosen to be weaker than the A/B and B/C interactions, quantified by $\\chi_{AB}N$ and $\\chi_{BC}N$, such that the B blocks are confined at the A/C interface, resulting in various B-domains with different geometries and arrangements. It is observed that two variables, the strength of the surface fields and the film thickness, are dominant factors controlling the self-assembly of the B blocks into various morphologies. For the linear triblock copolymers, the morphologies of B domains include disks, stripes (parallel cylinders), and hexagonal network (inverse disks). For the miktoarm star triblock copolymers, the competition between the tendency to align the junction points along a straight line and the constraint on their arrangement from the surface interactions leads to richer ordered morphologies. As a result of packing the junction points of the ABC miktoarm star copolymers, a counterintuitive phase sequence from low curvature phases to high curvature phases with increasing the length of B block is predicted. The study indicates that the self-assembly of monolayers of ABC triblock copolymers provides an interesting platform to engineer novel morphologies.

  17. Electrical properties of dog tracheal epithelial cells grown in monolayer culture.

    PubMed

    Coleman, D L; Tuet, I K; Widdicombe, J H

    1984-03-01

    Epithelial cells from dog trachea, when grown in tissue culture, formed confluent monolayers 5-6 days after plating. After 8-10 days, domes [mean diam 356 +/- (SE) 53 micron] appeared in monolayers grown in collagen-coated flasks. When grown on polycarbonate filters coated with collagen, a detectable resistance (greater than 5 omega X cm2) and transepithelial potential difference (PD) (greater than 0.1 mV) developed 6 days after plating and increased to approximately 15 omega X cm2 and 15 mV at 10 days. Serosal ouabain (10(-4) M) abolished PD and short-circuit current (Isc). Luminal ouabain had no effect. Luminal amiloride (10(-4) M) and serosal bumetanide (10(-4) M) each decreased PD and Isc. However, a combination of both of these drugs did not abolish Isc. Isoproterenol (10(-5) M), dibutyryl adenosine 3',5'-cyclic monophosphate (10(-3) M), vasoactive intestinal peptide (10(-7) M), prostaglandin (PG) E2 (10(-5) M), PGF2 alpha (10(-5) M), and bradykinin (10(-5) M) each increased PD and Isc. Thus these monolayer cultures maintain electrical properties resembling those of the original tissue. This preparation may prove useful for the study of water and ion transport by airway epithelia.

  18. Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects

    NASA Astrophysics Data System (ADS)

    Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

    2016-09-01

    Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

  19. Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

    NASA Astrophysics Data System (ADS)

    Lu, Xiaolong; Shi, Ruixin; Hao, Changchun; Chen, Huan; Zhang, Lei; Li, Junhua; Xu, Guoqing; Sun, Runguang

    2016-09-01

    The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics. The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine (DPPE) by analyzing the data of surface pressure-area (π-A) isotherms and surface pressure-time (π-T) curves. Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 mN/m. However, the changes of DPPE are larger than DPPC, indicating stronger interaction of lysozyme with DPPE than DPPC. The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 mN/m. Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers, which leads to self-aggregation and self-assembly, forming irregular multimers and conical multimeric. Through analysis, we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers. Project supported by the National Natural Science Foundation of China (Grant Nos. 21402114 and 11544009), the Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2016JM2010), the Fundamental Research Funds for the Central Universities of China (Grant No. GK201603026), and the National University Science and Technology Innovation Project of China (Grant No. 201610718013).

  20. Synthesis and Monolayer Behaviors of Succinic Acid-Type Gemini Surfactants Containing Semifluoroalkyl Groups.

    PubMed

    Kawase, Tokuzo; Nagase, Youhei; Oida, Tatsuo

    2016-01-01

    In this work, novel succinic acid-type gemini surfactants containing semifluoroalkyl groups, dl- and meso-2,3-bis[Rf-(CH2)n]-succinic acids (Rf = C4F9, C6F13, C8F17; n = 2, 9), were successfully synthesized, and the effects of Rf, methylene chain length (n), and stereochemistry on their monolayer behaviors were studied. Critical micelle concentrations (CMC) of dl- and meso-2,3-bis[C4F9(CH2)9]-succinic acids were one order of magnitude smaller than that of the corresponding 1+1 type surfactant, C4F9(CH2)9COOH. From surface pressure-area (π-A) measurements, the lift-off areas of the geminis were found to decrease in the order C4F9 ≥ C6F13 > C8F17, regardless of methylene chain length and stereochemistry. The zero-pressure molecular areas of the geminis were twice those of the corresponding 1+1 type surfactants. Based on Gibbs compression modulus analysis, it was clarified that 2,3-bis[C8F17(CH2)n]-succinic gemini with short methylene chains (n = 2) would form more rigid monolayers than those having long methylene chains (n = 9). Unlike for 2,3-bis(alkyl)-succinic acids, the effects of stereochemistry on the monolayer behavior of semifluoroalkylated geminis were small.

  1. Monolayer kinetic model of formation of β-cyclodextrin-β-carotene inclusion complex.

    PubMed

    Ivanova, Tz; Mircheva, K; Balashev, K; Panaiotov, I; Boury, F

    2015-11-01

    The carotenoids are sensitive molecules and their chemical integrity must be preserved from pro-oxidant elements which could affect and decrease their physiological benefits. The encapsulation based on the inclusion of the carotenoids into cage molecules is a promising approach for preserving over time of the intrinsic properties of the carotenoids. It is well known that cyclic oligosaccharide β-cyclodextrin (CD) as a cage molecule possesses strong inclusion ability to β-carotene (C) and as a result of the hydrophobic interactions forms an inclusion complex. In the present paper a monolayer kinetic model was established with the notion to extract more information about the influence of the molecular structure and organization to the interfacial interactions between the interacting species as well as about the role of the specific areas, which are often underestimated in previously studied dispersed systems. We developed the monolayer kinetic model for the formation of the inclusion CD-C complex by applying an experimental approach for following the kinetics by means of measuring the decrease of the surface area (ΔA) versus time (t) at constant surface pressure (π) and the decrease of surface pressure (π) versus time (t) at constant surface area (A). We also visualized by AFM the state of the monolayers at the initial and end points of the kinetic process. The values for the degree (d) and constant (Ka) of the association were estimated and compared with those from the studies of dispersed systems.

  2. Synthesis of one-dimensional silver oxide nanoparticle arrays and silver nanorods templated by Langmuir monolayers.

    PubMed

    Liu, Hong-Guo; Xiao, Fei; Wang, Chang-Wei; Xue, Qingbin; Chen, Xiao; Lee, Yong-Ill; Hao, Jingcheng; Jiang, Jianzhuang

    2007-10-01

    One-dimensional (1D) silver oxide nanoparticle arrays were synthesized by illuminating the composite Langmuir-Blodgett monolayers of porphyrin derivatives/Ag(+) and n-hexadecyl dihydrogen phosphate (n-HDP)/Ag(+) deposited on carbon-coated copper grids with daylight and then exposing them to air. Transmission electron microscopy (TEM) observation shows that the nanoparticle size is around 3 nm, with the separation of about 2-3 nm. High-resolution TEM (HRTEM) investigation indicates that the particles are made up of Ag(2)O. Ag nanorods with the width of 15-35 nm and the length of several hundreds of nanometers were synthesized by irradiating the composite Langmuir monolayers of porphyrin derivatives/Ag(+) and n-HDP/Ag(+) by UV-light directly at the air/water interface at room temperature. HRTEM image and selected-area electron diffraction (SAED) pattern indicate that the nanorods are single crystals with the (110) face of the face-centered cubic (fcc) silver parallel to the air/water interface. The formation of the 1D arrays and the nanorods should be attributed to the templating effect of the linear supramolecules formed by porphyrin derivative or n-HDP molecules in Langmuir monolayers through non-covalent interactions.

  3. Surface anchoring structure of a liquid crystal monolayer studied via dual polarization interferometry

    NASA Astrophysics Data System (ADS)

    Tan, Osbert; Cross, Graham H.

    2009-02-01

    The self-organization of liquid crystal molecules of 4- n -pentyl- 4' -cyanobiphenyl (5CB) forming an oriented monolayer by condensation from the vapor phase onto a silicon oxynitride surface has been observed using the evanescent wave dual slab waveguide dual polarization mode interferometry (DPI) technique. Two distinct stages to the layer formation are observed: After the formation of a layer of molecules lying prone on the surface, further condensation begins to densify the layer and produces a gradual mutual alignment of the molecules until the fully condensed, fully aligned monolayer is reached. At this limit the full coverage 5CB monolayer on this surface and at a temperature of 25°C , is found to be anchored with an average molecular axis polar angle of 56±1° and with a measured thickness of 16.6±0.5Å . These results are in reasonable agreement with the molecular dimensions provided by molecular models. The apparent precision and accuracy of these results resolves some wide disparity between earlier studies of such systems. Previous difficulties in determining optogeometrical properties of such ultrathin birefringent films using ellipsometry or in the need for complex modeling of the film layer structure using x-ray reflectivity are overcome in this instance. We provide a technique for analyzing the dual polarization data from DPI such that the bulk refractive index values, when known, can be used to determine the orientation and thickness of a layer that is on the nanometer or subnanometer scale.

  4. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    NASA Astrophysics Data System (ADS)

    Yang, Guang; Hallinan, Daniel T.

    2016-10-01

    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties.

  5. Dipolar interactions between domains in lipid monolayers at the air-water interface.

    PubMed

    Rufeil-Fiori, Elena; Wilke, Natalia; Banchio, Adolfo J

    2016-05-25

    A great variety of biologically relevant monolayers present phase coexistence characterized by domains formed by lipids in an ordered phase state dispersed in a continuous, disordered phase. From the difference in surface densities between these phases, inter-domain dipolar interactions arise. These interactions are relevant for the determination of the spacial distribution of domains as well as their dynamics. In this work, we propose a novel way of estimating the dipolar repulsion using a passive method that involves the analysis of images of the monolayer with phase coexistence. This method is based on the comparison of the pair correlation function obtained from experiments with that obtained from Brownian dynamics simulations of a model system. As an example, we determined the difference in dipolar density of a binary monolayer of DSPC/DMPC at the air-water interface from the analysis of the radial distribution of domains, and the results are compared with those obtained by surface potential determinations. A systematic analysis for the experimentally relevant parameter range is given, which may be used as a working curve for obtaining the dipolar repulsion in different systems.

  6. Asphaltene Adsorption onto Self-Assembled Monolayers of Mixed Aromatic

    SciTech Connect

    Turgman-Cohen, S.; Smith, M; Fischer, D; Kilpatrick, P; Genzer, J

    2009-01-01

    The adsorption of asphaltenes onto flat solid surfaces modified with mixed self-assembled monolayers (SAMs) of aliphatic and aromatic trichlorosilanes with varying wettabilities, aromaticities, and thicknesses is tested. The mixed SAMs are characterized by means of contact angle to assess hydrophobicity and molecular and chemical uniformity, spectroscopic ellipsometry to measure the thickness of the films, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy to assess chemical and molecular composition. The molecular characteristics of the adsorbed asphaltene layer and the extent of asphaltene adsorption are determined using NEXAFS and spectroscopic ellipsometry, respectively. The SAMs are formed by depositing phenyl-, phenethyl-, butyl-, and octadecyl- trichlorosilanes from toluene solutions onto silica-coated substrates; the chemical composition and the wettability of the SAM surface is tuned systematically by varying the trichlorosilane composition in the deposition solutions. The adsorption of asphaltenes on the substrates does not correlate strongly with the SAM chemical composition. Instead, the extent of asphaltene adsorption decreases with increasing SAM thickness. This observation suggests that the leading interaction governing the adsorption of asphaltenes is their interaction with the polar silica substrate and that the chemical composition of the SAM is of secondary importance.

  7. Equilibrium structures of anisometric, quadrupolar particles confined to a monolayer.

    PubMed

    Heinemann, Thomas; Antlanger, Moritz; Mazars, Martial; Klapp, Sabine H L; Kahl, Gerhard

    2016-02-21

    We investigate the structural properties of a two-dimensional system of ellipsoidal particles carrying a linear quadrupole moment in their center. These particles represent a simple model for a variety of uncharged, non-polar conjugated organic molecules. Using optimization tools based on ideas of evolutionary algorithms, we first examine the ground state structures as we vary the aspect ratio of the particles and the pressure. Interestingly, we find, besides the intuitively expected T-like configurations, a variety of complex structures, characterized with up to three different particle orientations. In an effort to explore the impact of thermal fluctuations, we perform constant-pressure molecular dynamics simulations within a range of rather low temperatures. We observe that ground state structures formed by particles with a large aspect ratio are in particular suited to withstand fluctuations up to rather high temperatures. Our comprehensive investigations allow for a deeper understanding of molecular or colloidal monolayer arrangements under the influence of a typical electrostatic interaction on a coarse-grained level.

  8. Monolayer graphene dispersion and radiative cooling for high power LED

    NASA Astrophysics Data System (ADS)

    Hsiao, Tun-Jen; Eyassu, Tsehaye; Henderson, Kimberly; Kim, Taesam; Lin, Chhiu-Tsu

    2013-10-01

    Molecular fan, a radiative cooling by thin film, has been developed and its application for compact electronic devices has been evaluated. The enhanced surface emissivity and heat dissipation efficiency of the molecular fan coating are shown to correlate with the quantization of lattice modes in active nanomaterials. The highly quantized G and 2D bands in graphene are achieved by our dispersion technique, and then incorporated in an organic-inorganic acrylate emulsion to form a coating assembly on heat sinks (for LED and CPU). This water-based dielectric layer coating has been formulated and applied on metal core printed circuit boards. The heat dissipation efficiency and breakdown voltage are evaluated by a temperature-monitoring system and a high-voltage breakdown tester. The molecular fan coating on heat dissipation units is able to decrease the equilibrium junction temperature by 29.1 ° C, while functioning as a dielectric layer with a high breakdown voltage (>5 kV). The heat dissipation performance of the molecular fan coating applied on LED devices shows that the coated 50 W LED gives an enhanced cooling of 20% at constant light brightness. The schematics of monolayer graphene dispersion, undispersed graphene platelet, and continuous graphene sheet are illustrated and discussed to explain the mechanisms of radiative cooling, radiative/non-radiative, and non-radiative heat re-accumulation.

  9. Building high-coverage monolayers of covalently bound magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Williams, Mackenzie G.; Teplyakov, Andrew V.

    2016-12-01

    This work presents an approach for producing a high-coverage single monolayer of magnetic nanoparticles using "click chemistry" between complementarily functionalized nanoparticles and a flat substrate. This method highlights essential aspects of the functionalization scheme for substrate surface and nanoparticles to produce exceptionally high surface coverage without sacrificing selectivity or control over the layer produced. The deposition of one single layer of magnetic particles without agglomeration, over a large area, with a nearly 100% coverage is confirmed by electron microscopy. Spectroscopic techniques, supplemented by computational predictions, are used to interrogate the chemistry of the attachment and to confirm covalent binding, rather than attachment through self-assembly or weak van der Waals bonding. Density functional theory calculations for the surface intermediate of this copper-catalyzed process provide mechanistic insight into the effects of the functionalization scheme on surface coverage. Based on this analysis, it appears that steric limitations of the intermediate structure affect nanoparticle coverage on a flat solid substrate; however, this can be overcome by designing a functionalization scheme in such a way that the copper-based intermediate is formed on the spherical nanoparticles instead. This observation can be carried over to other approaches for creating highly controlled single- or multilayered nanostructures of a wide range of materials to result in high coverage and possibly, conformal filling.

  10. Synthesis and characterizations of heterojunction of monolayer semiconductors

    NASA Astrophysics Data System (ADS)

    Lee, Yi-Hsien; Zhang, Xin-Quan; Tseng, Yu-Wen; Huang, Kuan-Hua; Chen, Chun-An; Chen, Bo-Han

    Monolayers of van der Waals materials, including graphene, and MoS2, offered a burgeoning field in fundamental physics, and optoelectronics.[1-5] Recently, atomically thin heterostructures of monolayer TMDc with various geometrical and energy band alignments are expected to be the key materials for next generation flexible optoelectronics. The individual TMDc monolayers can be adjoined vertically or laterally to construct diverse heterostructures which are difficult to reach with the laborious pick up-and-transfer method of the exfoliated flakes. The ability to produce copious amounts of high quality layered heterostructures on diverse surfaces is highly desirable but it has remained a challenging issue. Here, we have achieved a direct synthesis of various heterostructures of monolayer TMDc. The synthesis was performed using CVD with aromatic molecules as seeding promoters. We will discuss possible growth behaviors, and we examine the symmetry and the interface of these heterostructures using optical analysis and scanning TEM.

  11. Thiophene-based monolayer OFETs prepared by Langmuir techniques

    NASA Astrophysics Data System (ADS)

    Agina, Elena V.; Sizov, Alexey S.; Anisimov, Daniil S.; Trul, Askold A.; Borshchev, Oleg V.; Paraschuk, Dmitry Y.; Shcherbina, Maxim A.; Chvalun, Sergey N.; Ponomarenko, Sergey A.

    2015-08-01

    A novel fast, easily processible and highly reproducible approach to thiophene-based monolayer OFETs fabrication by Langmuir-Blodgett or Langmuir-Schaefer techniques was developed and successfully applied. It is based on selfassembly of organosilicon derivatives of oligothiophenes or benzothienobenzothiophene on the water-air interface. Influence of the conjugation length and the anchor group chemistry of the self-assembling molecules on the monolayer structure and electric performance of monolayer OFETs was systematically investigated. The efficient monolayer OFETs with the charge carrier mobilities up to 0.01 cm2/Vs and on/off ratio up to 106 were fabricated, and their functionality in integrated circuits under normal air conditions was demonstrated.

  12. Phase emerging from intramonolayer cycloaddition on micro-patterned monolayer

    SciTech Connect

    Tajuddin, Hairul A.; Manning, Robert J.; Leggett, Graham J.; Williams, Nicholas H.

    2012-11-27

    Cu(I)-catalyzed cycloaddition between azide and acetylene, followed by hydrolysis of ester were performed on micro-patterned self-assembled monolayer to produce smaller features. The reactions were initially performed on mixed monolayers and analysed by water contact angle (CA) and confirmed by X-ray Photoelectron Spectroscopy (XPS). The contact angle measurement has shown a drastic wetting of water on the surface of mixed monolayer indicating that the terminal groups on mixed monolayer has changed into carboxylic acid and hydroxyl terminals. The reactions work in a similar way on micro-patterned SAM and analyzed by using friction force microscope. The emerging of the new lines with high friction force on the border suggested a successful intramonolayer reactions on the border of the patterned SAM.

  13. The Formation and Stability of Alkylthiol Monolayers on Carbon Substrates

    PubMed Central

    Lockett, Matthew R.; Smith, Lloyd M.

    2010-01-01

    The formation and stability of alkylthiol monolayers on amorphous carbon thin films are investigated. Alkylthiol monolayers were prepared via a two-step, wet chemical process in which the carbon surface was first halogenated and then incubated with (4-(trifluoromethyl)phenyl)methanethiol (4tBM). The 4tBM covalently attaches to the surface in a substitution reaction in which the 4tBM thiol replaces the surface halogen. Studies of the substitution mechanism showed that monolayer formation is affected by the nature of the surface-bound halogen as well as the concentration and nucleophilicity of the 4tBM sulfur atom, consistent with a bimolecular (SN2) substitution reaction mechanism. The alkylthiol monolayers are stable over a wide range of solvent, pH, and temperature conditions. PMID:20706614

  14. Growth of rare-earth monolayers on synthetic fluorine mica

    NASA Astrophysics Data System (ADS)

    Tsui, F.; Han, P. D.; Flynn, C. P.

    1993-05-01

    We have grown single-crystal rare-earth films on cleaved faces of synthetic fluorine mica fluorophlogopite by molecular-beam-epitaxy techniques. This has made it possible to measure material properties such as magnetism in monolayer structures.

  15. Optical emission and vibrational modes of uniform pentacene monolayers (*)

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy; Blanchet, Graciela; Pinczuk, Aron

    2006-03-01

    Pentacene monolayers are probed by photoluminescence and resonant Raman spectroscopies below 10K. Monolayers grown on polymeric substrate of poly-alpha-methyl-styrene (PAMS) exhibit high uniformity within micron size clusters. These films show sharp exciton luminescence bands, and the energy of the exciton optical emission displays a red-shift as the average film thickness increases. The large resonance enhancements of Raman scattering intensities enable the measurements of low-lying (40- 200cm-1) optical lattice vibrations from these monolayers. These experiments demonstrate that luminescence and resonant Raman scattering from single pentacene monolayers are venues for probing 2D properties, studies of interface effects, and thin film characterization. (*) Supported primarily by the Nanoscale Science and Engineering Initiative of the National Science Foundation under NSF Award No. CHE-0117752 and by the New York State Office of Science, Technology, and Academic Research (NYSTAR), and by a research grant of the W. M. Keck Foundation.

  16. Oxidized Monolayers of Epitaxial Silicene on Ag(111)

    PubMed Central

    Johnson, Neil W.; Muir, David I.; Moewes, Alexander

    2016-01-01

    The properties of epitaxial silicene monolayers on Ag(111) at various levels of oxidation are determined through complementary density functional theory calculations and soft X-ray spectroscopy experiments. Our calculations indicate that moderate levels of oxidation do not cause a significant bandgap opening in the epitaxial silicene monolayer, suggesting that oxygen functionalization is not a viable mechanism for bandgap tuning while the silicene monolayer remains on its metallic substrate. In addition, moderate oxidation is calculated to strongly distort the hexagonal Si lattice, causing it to cluster in regions of highest oxygen adatom concentration but retain its 2D sheet structure. However, our experiments reveal that beam-induced oxidation is consistent with the formation of islands of bulk-like SiO2. Complete exposure of the monolayer to ambient conditions results in a fully oxidized sample that closely resembles bulk SiO2, of which a significant portion is completely detached from the substrate. PMID:26936144

  17. Recognition of Salmonella typhimurium by immobilized phage P22 monolayers

    NASA Astrophysics Data System (ADS)

    Handa, Hitesh; Gurczynski, Stephen; Jackson, Matthew P.; Auner, Gregory; Walker, Jeremy; Mao, Guangzhao

    2008-04-01

    Phages are promising alternatives to antibodies as the biorecognition element in a variety of biosensing applications. In this study, a monolayer of bacteriophage P22 whose tailspike proteins specifically recognize Salmonella serotypes was covalently bound to glass substrates through a bifunctional cross linker 3-aminopropyltrimethoxysilane. The specific binding of Salmonella typhimurium to the phage monolayer was studied by enzyme-linked immunosorbent assay and atomic force microscopy. Escherichia coli and a Gram-positive bacterium Listeria monocytogenes were also studied as control bacteria. The P22 particles show strong binding affinity to S. typhimurium. In addition, the dried P22 monolayer maintained 50% binding capacity to S. typhimurium after a one-week storage time. This is a promising method to prepare phage monolayer coatings on surface plasmon resonance and acoustic biosensor substrates in order to utilize the nascent phage display technology.

  18. Monolayers of hard rods on planar substrates. I. Equilibrium.

    PubMed

    Oettel, M; Klopotek, M; Dixit, M; Empting, E; Schilling, T; Hansen-Goos, H

    2016-08-21

    The equilibrium properties of hard rod monolayers are investigated in a lattice model (where position and orientation of a rod are restricted to discrete values) as well as in an off-lattice model featuring spherocylinders with continuous positional and orientational degrees of freedom. Both models are treated using density functional theory and Monte Carlo simulations. Upon increasing the density of rods in the monolayer, there is a continuous ordering of the rods along the monolayer normal ("standing up" transition). The continuous transition also persists in the case of an external potential which favors flat-lying rods in the monolayer. This behavior is found in both the lattice and the continuum models. For the lattice model, we find very good agreement between the results from the specific DFT used (lattice fundamental measure theory) and simulations. The properties of lattice fundamental measure theory are further illustrated by the phase diagrams of bulk hard rods in two and three dimensions.

  19. Monolayers of hard rods on planar substrates. I. Equilibrium

    NASA Astrophysics Data System (ADS)

    Oettel, M.; Klopotek, M.; Dixit, M.; Empting, E.; Schilling, T.; Hansen-Goos, H.

    2016-08-01

    The equilibrium properties of hard rod monolayers are investigated in a lattice model (where position and orientation of a rod are restricted to discrete values) as well as in an off-lattice model featuring spherocylinders with continuous positional and orientational degrees of freedom. Both models are treated using density functional theory and Monte Carlo simulations. Upon increasing the density of rods in the monolayer, there is a continuous ordering of the rods along the monolayer normal ("standing up" transition). The continuous transition also persists in the case of an external potential which favors flat-lying rods in the monolayer. This behavior is found in both the lattice and the continuum models. For the lattice model, we find very good agreement between the results from the specific DFT used (lattice fundamental measure theory) and simulations. The properties of lattice fundamental measure theory are further illustrated by the phase diagrams of bulk hard rods in two and three dimensions.

  20. Dual functions of 2D WS2 and MoS2-WS2 monolayers coupled with a Ag3PO4 photocatalyst

    NASA Astrophysics Data System (ADS)

    Wei, Zeng-Xi; Huang, Wei-Qing; Xu, Liang; Hu, Wangyu; Peng, P.; Huang, Gui-Fang

    2016-09-01

    The photocatalytic performance of semiconductors can be improved by coupling two-dimensional (2D) layered materials. Understanding the underlying mechanism of this phenomenon at the electronic level is important for the development of photocatalysts with a high efficiency. Here, we first present a theoretical elucidation of the dual functions of 2D layered material as a sensitizer and a co-catalyst by performing density functional theory calculations, taking WS2 and a lateral heterogeneous WS2-MoS2 monolayer as examples to couple with a promising photocatalyst Ag3PO4. The band alignment of a staggered type-II is formed between Ag3PO4 and the 2D monolayer with the latter possessing the higher electron affinity, resulting in the robust separation of photoexcited charge carriers between them, and indicating that the 2D monolayer is an effective sensitizer. Interestingly, the W (Mo) atoms, which are catalytically inert in the isolated 2D monolayer, turn into catalytic active sites, making the 2D monolayer a highly active co-catalyst in hybrids. A better photocatalytic performance in the coupled lateral heterogeneous WS2-MoS2 monolayer and Ag3PO4 can be expected. The calculated results can be rationalized by available experiments. These findings provide theoretical evidence supporting the experimental reports and may be used as a foundation for developing highly efficient 2D layered materials-based photocatalysts.

  1. Revealing fibrinogen monolayer conformations at different pHs: electrokinetic and colloid deposition studies.

    PubMed

    Nattich-Rak, Małgorzata; Adamczyk, Zbigniew; Wasilewska, Monika; Sadowska, Marta

    2015-07-01

    Adsorption mechanism of human fibrinogen on mica at different pHs is studied using the streaming potential and colloid deposition measurements. The fibrinogen monolayers are produced by a controlled adsorption under diffusion transport at pH of 3.5 and 7.4. Initially, the electrokinetic properties of these monolayers and their stability for various ionic strength are determined. It is shown that at pH 3.5 fibrinogen adsorbs irreversibly on mica for ionic strength range of 4×10(-4) to 0.15 M. At pH 7.4, a partial desorption is observed for ionic strength below 10(-2) M. This is attributed to the desorption of the end-on oriented molecules whereas the side-on adsorbed molecules remain irreversibly bound at all ionic strengths. The orientation of molecules and monolayer structure is evaluated by the colloid deposition measurements involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential is observed. At pH 3.5 measurable deposition of latex is observed even at low ionic strength where the approach distance of latex particles exceeded 70 nm. At pH 7.4 this critical distance is 23 nm. This confirms that fibrinogen monolayers formed at both pHs are characterized by the presence of the side-on and end-on oriented molecules that prevail at higher coverage range. It is also shown that positive charge is located at the end parts of the αA chains of the adsorbed fibrinogen molecules. Therefore, it is concluded that the colloid deposition method is an efficient tool for revealing protein adsorption mechanisms at solid/electrolyte interfaces.

  2. Direct patterning of self-assembled monolayers on gold using a laser beam.

    PubMed

    Shadnam, Mohammad R; Kirkwood, Sean E; Fedosejevs, Robert; Amirfazli, A

    2004-03-30

    The development of a methodology to manipulate surface properties of a self-assembled monolayer (SAM) of alkanethiol on a gold film using direct laser patterning is the objective of this paper. The present study demonstrates proof of the concept for the feasibility of laser patterning monolayers and outlines theoretical modeling of the process to predict the resulting feature size. This approach is unique in that it eliminates the need for photolithography, is noncontact, and can be extended to other systems such as SAMs on silicon wafers or potentially polymeric substrates. A homogeneous SAM made of 1-hexadecanethiol is formed on a 300-A sputtered film of gold (supported by a soda lime glass substrate). Localized regions are then desorbed by scanning the focal spot of a 488-nm continuous-wave argon ion laser beam under a nitrogen atmosphere. The desorption occurs as a result of a high substrate temperature produced by the moving laser beam with a Gaussian spatial profile at a constant speed of 200 microm/s. After completing the scans, the sample is dipped into a dilute solution of 16-mercaptohexadecanoic acid and a hydrophilic monolayer self-assembles along the previously irradiated regions. The resultant lines are viewed, and line widths are measured using both wetting with tridecane under a light microscope and scanning electron microscopy. Using the direct laser patterning method, we have produced straight line patterns with widths of 28-170 microm. A thermal model was constructed to predict the line width of the desorbed monolayer. The effect of the laser power, beam waist, and temperature dependence of the substrate conductivity on the theoretical predictions is considered. It is shown that the theoretical predictions are in good agreement with the experimental results, and, thus, the model can effectively be used to predict experimental results.

  3. Edge-Controlled Growth and Etching of Two-Dimensional GaSe Monolayers

    DOE PAGES

    Li, Xufan; Dong, Jichen; Idrobo, Juan C.; ...

    2016-12-07

    Understanding the atomistic mechanisms governing the growth of two-dimensional (2D) materials is of great importance in guiding the synthesis of wafer-sized, single-crystalline, high-quality 2D crystals and heterostructures. Etching, in many cases regarded as the reverse process of material growth, has been used to study the growth kinetics of graphene. In this paper, we explore a growth–etching–regrowth process of monolayer GaSe crystals, including single-crystalline triangles and irregularly shaped domains formed by merged triangles. We show that the etching begins at a slow rate, creating triangular, truncated triangular, or hexagonally shaped holes that eventually evolve to exclusively triangles that are rotated 60°more » with respect to the crystalline orientation of the monolayer triangular crystals. The regrowth occurs much faster than etching, reversibly filling the etched holes and then enlarging the size of the monolayer crystals. A theoretical model developed based on kinetic Wulff construction (KWC) theory and density functional theory (DFT) calculations accurately describe the observed morphology evolution of the monolayer GaSe crystals and etched holes during the growth and etching processes, showing that they are governed by the probability of atom attachment/detachment to/from different types of edges with different formation energies of nucleus/dents mediated by chemical potential difference Δμ between Ga and Se. Finally, our growth–etching–regrowth study provides not only guidance to understand the growth mechanisms of 2D binary crystals but also a potential method for the synthesis of large, shape-controllable, high-quality single-crystalline 2D crystals and their lateral heterostructures.« less

  4. Edge-Controlled Growth and Etching of Two-Dimensional GaSe Monolayers

    SciTech Connect

    Li, Xufan; Dong, Jichen; Idrobo, Juan C.; Puretzky, Alexander A.; Rouleau, Christopher M.; Geohegan, David B.; Ding, Feng; Xiao, Kai

    2016-12-07

    Understanding the atomistic mechanisms governing the growth of two-dimensional (2D) materials is of great importance in guiding the synthesis of wafer-sized, single-crystalline, high-quality 2D crystals and heterostructures. Etching, in many cases regarded as the reverse process of material growth, has been used to study the growth kinetics of graphene. In this paper, we explore a growth–etching–regrowth process of monolayer GaSe crystals, including single-crystalline triangles and irregularly shaped domains formed by merged triangles. We show that the etching begins at a slow rate, creating triangular, truncated triangular, or hexagonally shaped holes that eventually evolve to exclusively triangles that are rotated 60° with respect to the crystalline orientation of the monolayer triangular crystals. The regrowth occurs much faster than etching, reversibly filling the etched holes and then enlarging the size of the monolayer crystals. A theoretical model developed based on kinetic Wulff construction (KWC) theory and density functional theory (DFT) calculations accurately describe the observed morphology evolution of the monolayer GaSe crystals and etched holes during the growth and etching processes, showing that they are governed by the probability of atom attachment/detachment to/from different types of edges with different formation energies of nucleus/dents mediated by chemical potential difference Δμ between Ga and Se. Finally, our growth–etching–regrowth study provides not only guidance to understand the growth mechanisms of 2D binary crystals but also a potential method for the synthesis of large, shape-controllable, high-quality single-crystalline 2D crystals and their lateral heterostructures.

  5. Scaling laws for buckling instability in monolayer networks

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1992-01-01

    In this comment a power law is argued to govern the thickening of cell widths relative to their lengths in buckling monolayer networks. A scaling relation is derived for general instabilities in cellular networks, and a reply is given that questions the use of the amplitude of the buckling undulation in an already buckled wall in the Euler relation. Both treatments provided shed light on the stability/instability of wavelengths for buckling monolayer networks.

  6. Nonequilibrium 2-Hydroxyoctadecanoic Acid Monolayers: Effect of Electrolytes

    SciTech Connect

    Lendrum, Conrad D.; Ingham, Bridget; Lin, Binhua; Meron, Mati; Toney, Michael F.; McGrath, Kathryn M.

    2012-02-06

    2-Hydroxyacids display complex monolayer phase behavior due to the additional hydrogen bonding afforded by the presence of the second hydroxy group. The placement of this group at the position {alpha} to the carboxylic acid functionality also introduces the possibility of chelation, a utility important in crystallization including biomineralization. Biomineralization, like many biological processes, is inherently a nonequilibrium process. The nonequilibrium monolayer phase behavior of 2-hydroxyoctadecanoic acid was investigated on each of pure water, calcium chloride, sodium bicarbonate and calcium carbonate crystallizing subphases as a precursor study to a model calcium carbonate biomineralizing system, each at a pH of {approx}6. The role of the bicarbonate co-ion in manipulating the monolayer structure was determined by comparison with monolayer phase behavior on a sodium chloride subphase. Monolayer phase behavior was probed using surface pressure/area isotherms, surface potential, Brewster angle microscopy, and synchrotron-based grazing incidence X-ray diffraction and X-ray reflectivity. Complex phase behavior was observed for all but the sodium chloride subphase with hydrogen bonding, electrostatic and steric effects defining the symmetry of the monolayer. On a pure water subphase hydrogen bonding dominates with three phases coexisting at low pressures. Introduction of calcium ions into the aqueous subphase ensures strong cation binding to the surfactant head groups through chelation. The monolayer becomes very unstable in the presence of bicarbonate ions within the subphase due to short-range hydrogen bonding interactions between the monolayer and bicarbonate ions facilitated by the sodium cation enhancing surfactant solubility. The combined effects of electrostatics and hydrogen bonding are observed on the calcium carbonate crystallizing subphase.

  7. A hierarchical nest survival model integrating incomplete temporally varying covariates

    PubMed Central

    Converse, Sarah J; Royle, J Andrew; Adler, Peter H; Urbanek, Richard P; Barzen, Jeb A

    2013-01-01

    Nest success is a critical determinant of the dynamics of avian populations, and nest survival modeling has played a key role in advancing avian ecology and management. Beginning with the development of daily nest survival models, and proceeding through subsequent extensions, the capacity for modeling the effects of hypothesized factors on nest survival has expanded greatly. We extend nest survival models further by introducing an approach to deal with incompletely observed, temporally varying covariates using a hierarchical model. Hierarchical modeling offers a way to separate process and observational components of demographic models to obtain estimates of the parameters of primary interest, and to evaluate structural effects of ecological and management interest. We built a hierarchical model for daily nest survival to analyze nest data from reintroduced whooping cranes (Grus americana) in the Eastern Migratory Population. This reintroduction effort has been beset by poor reproduction, apparently due primarily to nest abandonment by breeding birds. We used the model to assess support for the hypothesis that nest abandonment is caused by harassment from biting insects. We obtained indices of blood-feeding insect populations based on the spatially interpolated counts of insects captured in carbon dioxide traps. However, insect trapping was not conducted daily, and so we had incomplete information on a temporally variable covariate of interest. We therefore supplemented our nest survival model with a parallel model for estimating the values of the missing insect covariates. We used Bayesian model selection to identify the best predictors of daily nest survival. Our results suggest that the black fly Simulium annulus may be negatively affecting nest survival of reintroduced whooping cranes, with decreasing nest survival as abundance of S. annulus increases. The modeling framework we have developed will be applied in the future to a larger data set to evaluate the

  8. A hierarchical nest survival model integrating incomplete temporally varying covariates.

    PubMed

    Converse, Sarah J; Royle, J Andrew; Adler, Peter H; Urbanek, Richard P; Barzen, Jeb A

    2013-11-01

    Nest success is a critical determinant of the dynamics of avian populations, and nest survival modeling has played a key role in advancing avian ecology and management. Beginning with the development of daily nest survival models, and proceeding through subsequent extensions, the capacity for modeling the effects of hypothesized factors on nest survival has expanded greatly. We extend nest survival models further by introducing an approach to deal with incompletely observed, temporally varying covariates using a hierarchical model. Hierarchical modeling offers a way to separate process and observational components of demographic models to obtain estimates of the parameters of primary interest, and to evaluate structural effects of ecological and management interest. We built a hierarchical model for daily nest survival to analyze nest data from reintroduced whooping cranes (Grus americana) in the Eastern Migratory Population. This reintroduction effort has been beset by poor reproduction, apparently due primarily to nest abandonment by breeding birds. We used the model to assess support for the hypothesis that nest abandonment is caused by harassment from biting insects. We obtained indices of blood-feeding insect populations based on the spatially interpolated counts of insects captured in carbon dioxide traps. However, insect trapping was not conducted daily, and so we had incomplete information on a temporally variable covariate of interest. We therefore supplemented our nest survival model with a parallel model for estimating the values of the missing insect covariates. We used Bayesian model selection to identify the best predictors of daily nest survival. Our results suggest that the black fly Simulium annulus may be negatively affecting nest survival of reintroduced whooping cranes, with decreasing nest survival as abundance of S. annulus increases. The modeling framework we have developed will be applied in the future to a larger data set to evaluate the

  9. A hierarchical nest survival model integrating incomplete temporally varying covariates

    USGS Publications Warehouse

    Converse, Sarah J.; Royle, J. Andrew; Adler, Peter H.; Urbanek, Richard P.; Barzan, Jeb A.

    2013-01-01

    Nest success is a critical determinant of the dynamics of avian populations, and nest survival modeling has played a key role in advancing avian ecology and management. Beginning with the development of daily nest survival models, and proceeding through subsequent extensions, the capacity for modeling the effects of hypothesized factors on nest survival has expanded greatly. We extend nest survival models further by introducing an approach to deal with incompletely observed, temporally varying covariates using a hierarchical model. Hierarchical modeling offers a way to separate process and observational components of demographic models to obtain estimates of the parameters of primary interest, and to evaluate structural effects of ecological and management interest. We built a hierarchical model for daily nest survival to analyze nest data from reintroduced whooping cranes (Grus americana) in the Eastern Migratory Population. This reintroduction effort has been beset by poor reproduction, apparently due primarily to nest abandonment by breeding birds. We used the model to assess support for the hypothesis that nest abandonment is caused by harassment from biting insects. We obtained indices of blood-feeding insect populations based on the spatially interpolated counts of insects captured in carbon dioxide traps. However, insect trapping was not conducted daily, and so we had incomplete information on a temporally variable covariate of interest. We therefore supplemented our nest survival model with a parallel model for estimating the values of the missing insect covariates. We used Bayesian model selection to identify the best predictors of daily nest survival. Our results suggest that the black fly Simulium annulus may be negatively affecting nest survival of reintroduced whooping cranes, with decreasing nest survival as abundance of S. annulus increases. The modeling framework we have developed will be applied in the future to a larger data set to evaluate the

  10. Probabilistic Seismic Hazard Assessment from Incomplete and Uncertain Data

    NASA Astrophysics Data System (ADS)

    Smit, Ansie; Kijko, Andrzej

    2016-04-01

    A question that frequently arises with seismic hazard assessment is why are our assessments so poor? Often the answer is that in many cases the standard applied methodologies do not take into account the nature of seismic event catalogs. In reality these catalogues are incomplete with uncertain magnitude estimates and a significant discrepancy between the empirical data and applied occurrence model. Most probabilistic seismic hazard analysis procedures require knowledge of at least three seismic source parameters: the mean seismic activity rate λ, the Gutenberg-Richter b-value, and the area-characteristic (seismogenic source) maximum possible earthquake magnitude Mmax. In almost all currently used seismic hazard assessment procedures utilizing these three parameters, it's explicitly assumed that all three remain constant over a specified time and space. However, closer examination of most earthquake catalogues indicates that there are significant spatial and temporal variations in the seismic activity rate λ as well as the Gutenberg-Richter b-value. In the proposed methodology the maximum likelihood estimation of these earthquake hazard parameters takes into account the incompleteness of catalogues, uncertainty in the earthquake magnitude determination as well as the uncertainty associated with the applied earthquake occurrence models. The uncertainty in the earthquake occurrence models are introduced by assuming that both, the mean, seismic activity rate λ and the b-value of Gutenberg-Richter are random variables, each described by the Gamma distribution. The approach results in the extension of the classic frequency-magnitude Gutenberg-Richter relation and the Poisson distribution of number of earthquakes, with their compounded counterparts. The proposed procedure is applied in the estimation of the seismic parameters for the area of Ceres-Tulbagh, South Africa, which experienced the strongest earthquake in the country's recorded history. In this example it is

  11. Colloidal polycrystalline monolayers under oscillatory shear

    NASA Astrophysics Data System (ADS)

    Buttinoni, Ivo; Steinacher, Mathias; Spanke, Hendrik Th.; Pokki, Juho; Bahmann, Severin; Nelson, Bradley; Foffi, Giuseppe; Isa, Lucio

    2017-01-01

    In this paper we probe the structural response to oscillatory shear deformations of polycrystalline monolayers of soft repulsive colloids with varying area fraction over a broad range of frequencies and amplitudes. The particles are confined at a fluid interface, sheared using a magnetic microdisk, and imaged through optical microscopy. The structural and mechanical response of soft materials is highly dependent on their microstructure. If crystals are well understood and deform through the creation and mobilization of specific defects, the situation is much more complex for disordered jammed materials, where identifying structural motifs defining plastically rearranging regions remains an elusive task. Our materials fall between these two classes and allow the identification of clear pathways for structural evolution. In particular, we demonstrate that large enough strains are able to fluidize the system, identifying critical strains that fulfill a local Lindemann criterion. Conversely, smaller strains lead to localized and erratic irreversible particle rearrangements due to the motion of structural defects. In this regime, oscillatory shear promotes defect annealing and leads to the growth of large crystalline domains. Numerical simulations help identify the population of rearranging particles with those exhibiting the largest deviatoric stresses and indicate that structural evolution proceeds towards the minimization of the stress stored in the system. The particles showing high deviatoric stresses are localized around grain boundaries and defects, providing a simple criterion to spot regions likely to rearrange plastically under oscillatory shear.

  12. Hopping magnetoresistance in ion irradiated monolayer graphene

    NASA Astrophysics Data System (ADS)

    Shlimak, I.; Zion, E.; Butenko, A. V.; Wolfson, L.; Richter, V.; Kaganovskii, Yu.; Sharoni, A.; Haran, A.; Naveh, D.; Kogan, E.; Kaveh, M.

    2016-02-01

    Magnetoresistance (MR) of ion irradiated monolayer graphene samples with a variable-range hopping (VRH) mechanism of conductivity was measured at temperatures down to T=1.8 K in magnetic fields up to B=8 T. It was observed that in perpendicular magnetic fields, hopping resistivity R decreases, which corresponds to negative MR (NMR), while parallel magnetic field results in positive MR (PMR) at low temperatures. NMR is explained on the basis of the "orbital" model in which perpendicular magnetic field suppresses the destructive interference of many paths through the intermediate sites in the total probability of the long-distance tunneling in the VRH regime. At low fields, a quadratic dependence (| ΔR / R | ∼ B2) of NMR is observed, while at B > B*, the quadratic dependence is replaced by the linear one. It was found that all NMR curves for different samples and different temperatures could be merged into common dependence when plotted as a function of B/B*. It is shown that B* ∼ T1/2 in agreement with predictions of the "orbital" model. The obtained values of B* also allowed us to estimate the localization radius ξ of charge carriers for samples with a different degree of disorder. PMR in parallel magnetic fields is explained by suppression of hopping transitions via double occupied states due to alignment of electron spins.

  13. Photogalvanic effect in monolayer black phosphorus

    NASA Astrophysics Data System (ADS)

    Xie, Yiqun; Zhang, Lei; Zhu, Yu; Liu, Lei; Guo, Hong

    2015-11-01

    We report a first-principles theoretical approach for analyzing linear and circular photogalvanic effects (PGEs) based on density functional theory within the nonequilibrium Green’s function formalism. Using this approach we investigate the PGE phenomena in monolayer black phosphorus (MBP) doped with sulfur atoms. The impurity doping breaks the space inversion symmetry of pristine MBP, leading to a C s symmetry with a mirror reflection plane normal to the zigzag direction of the MBP lattice. Governed by this symmetry, a linear PGE is induced in both zigzag and armchair directions, and a circular PGE is induced along the zigzag direction. A robust broadband photoresponse is found from the near-infrared to the visible range for the MBP device. There is a strong anisotropy in PGE: photoresponse in the zigzag direction can be larger by an order of magnitude than that in the armchair direction. We identify the origin of the observed PGE as the inter-band transitions from the impurity and valence bands to the conduction bands, which involves a transfer of angular momentum from photons to electrons.

  14. Photogalvanic effect in monolayer black phosphorus.

    PubMed

    Xie, Yiqun; Zhang, Lei; Zhu, Yu; Liu, Lei; Guo, Hong

    2015-11-13

    We report a first-principles theoretical approach for analyzing linear and circular photogalvanic effects (PGEs) based on density functional theory within the nonequilibrium Green's function formalism. Using this approach we investigate the PGE phenomena in monolayer black phosphorus (MBP) doped with sulfur atoms. The impurity doping breaks the space inversion symmetry of pristine MBP, leading to a C s symmetry with a mirror reflection plane normal to the zigzag direction of the MBP lattice. Governed by this symmetry, a linear PGE is induced in both zigzag and armchair directions, and a circular PGE is induced along the zigzag direction. A robust broadband photoresponse is found from the near-infrared to the visible range for the MBP device. There is a strong anisotropy in PGE: photoresponse in the zigzag direction can be larger by an order of magnitude than that in the armchair direction. We identify the origin of the observed PGE as the inter-band transitions from the impurity and valence bands to the conduction bands, which involves a transfer of angular momentum from photons to electrons.

  15. Properties of Langmuir monolayers from semifluorinated alkanes

    NASA Astrophysics Data System (ADS)

    Broniatowski, M.; Macho, I. Sandez; Miñones, J.; Dynarowicz-Łątka, P.

    2005-06-01

    The aim of this study was to characterize several semifluorinated alkanes (SFA), of the general formula F(CF 2) m(CH 2) nH (in short F mH n), containing 25 carbon atoms in total (pentacosanes) differing in the m/ n ratio, as Langmuir monolayers at the free water surface. The following compounds have been studied: F6H19, F8H17, F10H15 and F12H13. Surface pressure ( π) and electric surface potential (Δ V) isotherms were recorded in addition to quantitative Brewster angle microscopy results. The negative sign of Δ V evidenced for the orientation of all the investigated semifluorinated pentacosanes, regardless the length of the hydrogenated segment, with their perfluorinated parts directed towards the air. As inferred from apparent dipole moment values and relative reflectivity results, the fluorinated pentacosanes with shorter perfluorinated fragment (F6H19 and F8H17) were found to be vertically oriented at the air/water interface, while those with longer perfluorinated moiety (F10H15 and F12H13) remain titled even in the vicinity of the film collapse.

  16. Surface dilatational viscosity of Langmuir monolayers

    NASA Astrophysics Data System (ADS)

    Lopez, Juan; Vogel, Michael; Hirsa, Amir

    2003-11-01

    With increased interest in microfluidic systems, interfacial phenomena is receiving more attention. As the length scales of fluid problems decrease, the surface to volume ratio increases and the coupling between interfacial flow and bulk flow becomes increasingly dominated by effects due to intrinsic surface viscosities (shear and dilatational), in comparison to elastic effects (due to surface tension gradients). The surface shear viscosity is well-characterized, as cm-scale laboratory experiments are able to isolate its effects from other interfacial processes (e.g., in the deep-channel viscometer). The same is not true for the dilatational viscosity, because it acts in the direction of surface tension gradients. Their relative strength scale with the capillary number, and for cm-scale laboratory flows, surface tension effects tend to dominate. In microfluidic scale flows, the scaling favors viscosity. We have devised an experimental apparatus which is capable of isolating and enhancing the effects of dilatational viscosity at the cm scales by driving the interface harmonically in time, while keeping the interface flat. In this talk, we shall present both the theory for how this works as well as experimental measurements of surface velocity from which we deduce the dilatational viscosity of several monolayers on the air-water interface over a substantial range of surface concentrations. Anomalous behavior over some range of concentration, which superficially indicates negative viscosity, maybe explained in terms of compositional effects due to large spatial and temporal variations in concentration and corresponding viscosity.

  17. Structural phase transitions in monolayer molybdenum dichalcogenides

    NASA Astrophysics Data System (ADS)

    Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo

    2015-03-01

    The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

  18. UV/vis and NIR light-responsive spiropyran self-assembled monolayers.

    PubMed

    Ivashenko, Oleksii; van Herpt, Jochem T; Feringa, Ben L; Rudolf, Petra; Browne, Wesley R

    2013-04-02

    Self-assembled monolayers of a 6-nitro BIPS spiropyran (SP) modified with a disulfide-terminated aliphatic chain were prepared on polycrystalline gold surfaces and characterized by UV/vis absorption, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopies (XPS). The SAMs obtained are composed of the ring-closed form (i.e., spiropyran) only. Irradiation with UV light results in conversion of the monolayer to the merocyanine form (MC), manifested in the appearance of an N(+) contribution in the N 1s region of the XPS spectrum of the SAMs, the characteristic absorption band of the MC form in the visible region at 555 nm, and the C-O stretching band in the SERS spectrum. Recovery of the initial state of the monolayer was observed both thermally and after irradiation with visible light. Several switching cycles were performed and monitored by SERS spectroscopy, demonstrating the stability of the SAMs during repeated switching between SP and MC states. A key finding in the present study is that ring-opening of the surface-immobilized spiropyrans can be induced by irradiation with continuous wave NIR (785 nm) light as well as by irradiation with UV light. We demonstrate that ring-opening by irradiation at 785 nm proceeds by a two-photon absorption pathway both in the SAMs and in the solid state. Hence, spiropyran SAMs on gold can undergo reversible photochemical switching from the SP to the MC form with both UV and NIR and the reverse reaction induced by irradiation with visible light or heating. Furthermore, the observation of NIR-induced switching with a continuous wave source holds important consequences in the study of photochromic switches on surfaces using SERS and emphasizes the importance of the use of multiple complementary techniques in characterizing photoresponsive SAMs.

  19. Thermoelectric properties of SnSe2 monolayer

    NASA Astrophysics Data System (ADS)

    Li, Guanpeng; Ding, Guangqian; Gao, Guoying

    2017-01-01

    The 2H (MoS2-type) phase of 2D transition metal dichalcogenides (TMDCs) has been extensively studied and exhibits excellent electronic and optoelectronic properties, but the high phonon thermal conductivity is detrimental to the thermoelectric performances. Here, we use first-principles methods combined with Boltzmann transport theory to calculate the electronic and phononic transport properties of 1T (CdI2-type) SnSe2 monolayer, a recently realized 2D metal dichalcogenide semiconductor. The calculated band gap is 0.85 eV, which is a little larger than the bulk value. Lower phonon thermal conductivity and higher power factor are obtained in 1T-SnSe2 monolayer compared to 2H-TMDCs monolayers. The low phonon thermal conductivity (3.27 W mK-1 at room temperature) is mainly due to the low phonon frequency of acoustic modes and the coupling of acoustic modes with optical modes. We also find that the p-type has better thermoelectric performance than the n-type, and the figure of merit within p-type can reach 0.94 at 600 K for 1T-SnSe2 monolayer, which is higher than those of most 2H-TMDCs monolayers, making 1T-SnSe2 monolayer a promising candidate for thermoelectric applications.

  20. Monolayer Contact Doping from a Silicon Oxide Source Substrate.

    PubMed

    Ye, Liang; González-Campo, Arántzazu; Kudernac, Tibor; Núñez, Rosario; de Jong, Michel; van der Wiel, Wilfred G; Huskens, Jurriaan

    2017-04-03

    Monolayer contact doping (MLCD) is a modification of the monolayer doping (MLD) technique that involves monolayer formation of a dopant-containing adsorbate on a source substrate. This source substrate is subsequently brought into contact with the target substrate, upon which the dopant is driven into the target substrate by thermal annealing. Here, we report a modified MLCD process, in which we replace the commonly used Si source substrate by a thermally oxidized substrate with a 100 nm thick silicon oxide layer, functionalized with a monolayer of a dopant-containing silane. The thermal oxide potentially provides a better capping effect and effectively prevents the dopants from diffusing back into the source substrate. The use of easily accessible and processable silane monolayers provides access to a general and modifiable process for the introduction of dopants on the source substrate. As a proof of concept, a boron-rich carboranyl-alkoxysilane was used here to construct the monolayer that delivers the dopant, to boost the doping level in the target substrate. X-ray photoelectron spectroscopy (XPS) showed a successful grafting of the dopant adsorbate onto the SiO2 surface. The achieved doping levels after thermal annealing were similar to the doping levels acessible by MLD as demonstrated by secondary ion mass spectrometry measurements. The method shows good prospects, e.g. for use in the doping of Si nanostructures.

  1. Using self-assembled monolayers to model the extracellular matrix.

    PubMed

    Mrksich, Milan

    2009-03-01

    The extracellular matrix is an insoluble aggregate of large proteins and glycosoaminoglycans that comprises the microenvironment of cells in tissue. The matrix displays a host of ligands that interact with cell-surface receptors to mediate the attachment and spreading of cells and regulate signaling processes. Studies of cell-matrix interactions and downstream signaling processes commonly employ substrates having an adsorbed layer of protein and are challenged by the difficulty in controlling the structure and activity of the immobilized protein. Significant effort has been directed towards the development of model substrates that present adhesion ligands in defined densities, orientations and environments. Among these approaches, self-assembled monolayers of alkanethiolates on gold offer a high level of control over the molecular structure of the surface and are well-suited to studies of cell adhesion. This review describes the design and use of monolayers for applications in cell biology, including the use of monolayers to evaluate the roles of peptide and protein ligands in cell-matrix interactions, the development of methods to pattern ligands on monolayers and applications to cell biology, the development of dynamic monolayers that can switch the activities of ligands presented to an adherent cell, and the rewiring of interactions between a cell and its substrate. These examples illustrate the flexibility inherent to monolayers for applications in cell biology.

  2. High Quality Factor Mechanical Resonators Based on WSe2 Monolayers

    PubMed Central

    2016-01-01

    Suspended monolayer transition metal dichalcogenides (TMD) are membranes that combine ultralow mass and exceptional optical properties, making them intriguing materials for opto-mechanical applications. However, the low measured quality factor of TMD resonators has been a roadblock so far. Here, we report an ultrasensitive optical readout of monolayer TMD resonators that allows us to reveal their mechanical properties at cryogenic temperatures. We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 1.6 × 104 at liquid nitrogen temperature and 4.7 × 104 at liquid helium temperature. This surpasses the quality factor of monolayer graphene resonators with similar surface areas. Upon cooling the resonator, the resonant frequency increases significantly due to the thermal contraction of the WSe2 lattice. These measurements allow us to experimentally study the thermal expansion coefficient of WSe2 monolayers for the first time. High Q-factors are also found in resonators based on MoS2 and MoSe2 monolayers. The high quality-factor found in this work opens new possibilities for coupling mechanical vibrational states to two-dimensional excitons, valley pseudospins, and single quantum emitters and for quantum opto-mechanical experiments based on the Casimir interaction. PMID:27459399

  3. Growth of calcium oxalate monohydrate at phospholipid Langmuir monolayers

    NASA Astrophysics Data System (ADS)

    Whipps, Scott; Khan, Saeed R.; Jeffrey O'Palko, F.; Backov, Rénal; Talham, Daniel R.

    1998-08-01

    Calcium oxalate monohydrate crystals have been nucleated from metastable solutions at Langmuir monolayers of the phospholipids dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylserine and dipalmitoylphosphatidylcholine and the fatty acid arachidic acid. The phospholipid monolayers were used as model systems for domains of pure lipid in cellular media as part of investigations of their potential role in the nucleation of calcium oxalate in the urinary tract. Crystal formation was monitored at the air/water interface using Brewster angle microscopy and in transferred films using SEM and TEM. For each Langmuir monolayer, it was observed that nucleation is heterogeneous and is selective with respect to the orientation and morphology of the precipitated crystals with up to 90% of crystals growing with the ( 1 0 1¯) face oriented towards the monolayer interface. The selectivity is attributed to calcium binding at the lipid monolayer favoring formation of the calcium-rich ( 1 0 1¯) face. The behavior at each monolayer was similar, although a higher rate of crystal formation was observed at the anionic DPPG interface.

  4. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solidsa)

    NASA Astrophysics Data System (ADS)

    Greene, J. E.

    2015-03-01

    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (˜1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ˜78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese "floating-ink" art (suminagashi) developed ˜1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO2 and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including controlled wetting

  5. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solids

    SciTech Connect

    Greene, J. E.

    2015-03-15

    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (∼1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ∼78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese “floating-ink” art (suminagashi) developed ∼1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO{sub 2} and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including

  6. Effect of chirality on monoacylglycerol ester monolayer characteristics: 3-monostearoyl-sn-glycerol.

    PubMed

    Vollhardt, D; Brezesinski, G

    2017-03-08

    The effect of chirality on the thermodynamic behavior, the morphological features, and the 2D lattice structures of 3-monostearoyl-sn-glycerol monolayers is studied. The present study focusses on the influence of the alkyl chain length on the chiral discrimination. Surface pressure-area (π-A) isotherms, Brewster angle microscopy (BAM), and particularly, grazing incidence X-ray diffraction (GIXD) are the experimental basis of the presented results. The π-A isotherms of the enantiomeric 3-monostearoyl-sn-glycerol monolayers measured between 25 and 38 °C resemble those of the racemic 1-monostearoyl-rac-glycerol monolayers, thus indicating small energetic differences between the enantiomeric and the racemic forms. The absolute ΔS values increase as the temperature decreases and thus, the ordering of the condensed phase increases at lower temperatures. The extrapolation to zero ΔS provides a critical temperature Tc of 42.1 °C (315.3 K), above which the monolayer cannot be compressed into the condensed state. Despite the great tendency of the 3-monostearoyl-sn-glycerol domains to develop irregular deviations in shape and inner texture, regular domains similar to those of the racemic monoacylglycerol esters are also formed. GIXD measurements performed over a large range of lateral pressures at four different temperatures (5, 10, 15 and 20 °C) indicate the dominance of the chiral nature. Contour plots with three clearly separated diffraction signals are observable in a large pressure range which is shifted to higher lateral pressures with increasing temperature. The comparison with the contour plots of the homologous 3-monopalmitoyl-sn-glycerol monolayers reveals the stronger dominance of the chiral nature with increasing alkyl chain length and thus, demonstrates the stronger influence of the lattice symmetry. The lattice data obtained by fitting the contour plots with 3 or 2 peaks demonstrate the resemblance to orthorhombic structures with NN tilted molecules at

  7. Spectral Regularization Algorithms for Learning Large Incomplete Matrices.

    PubMed

    Mazumder, Rahul; Hastie, Trevor; Tibshirani, Robert

    2010-03-01

    We use convex relaxation techniques to provide a sequence of regularized low-rank solutions for large-scale matrix completion problems. Using the nuclear norm as a regularizer, we provide a simple and very efficient convex algorithm for minimizing the reconstruction error subject to a bound on the nuclear norm. Our algorithm Soft-Impute iteratively replaces the missing elements with those obtained from a soft-thresholded SVD. With warm starts this allows us to efficiently compute an entire regularization path of solutions on a grid of values of the regularization parameter. The computationally intensive part of our algorithm is in computing a low-rank SVD of a dense matrix. Exploiting the problem structure, we show that the task can be performed with a complexity linear in the matrix dimensions. Our semidefinite-programming algorithm is readily scalable to large matrices: for example it can obtain a rank-80 approximation of a 10(6) × 10(6) incomplete matrix with 10(5) observed entries in 2.5 hours, and can fit a rank 40 approximation to the full Netflix training set in 6.6 hours. Our methods show very good performance both in training and test error when compared to other competitive state-of-the art techniques.

  8. Piriformis syndrome in an incomplete paraplegic patient: a case report

    PubMed Central

    Misirlioglu, TO; Palamar, D; Akgun, K

    2015-01-01

    Study design: Single case report. Objectives: We present an incomplete paraplegic patient with lower back and hip pain, diagnosed and treated as the piriformis syndrome (PS). Setting: University hospital, Turkey. Case: A 62-year-old woman with T3 paraplegia of American Spinal Injury Association Impairment Scale grade D presented with lower back and right hip pain accompanied by pain and numbness radiating to her right leg. After detailed anamnesis and physical examination, she was pre-diagnosed as having PS. The marked relief of pain following the ultrasound-guided piriformis muscle injection of 4 cc of lidocaine 2%+1 cc of betametazone confirmed the diagnosis. Conclusion: Although the compressive neuropathies and musculoskeletal injuries of the upper limb leading to neuropathic and musculoskeletal pain in persons with spinal cord injury (SCI) are well described in literature, there is limited information regarding those of lower limbs. To the best of our knowledge, this is the first reported case of PS in a patient with SCI. PS should be kept in mind as a pain generator, especially in active and ambulatory SCI patients. PMID:28053713

  9. Learning with incomplete information and the mathematical structure behind it.

    PubMed

    Kühn, Reimer; Stamatescu, Ion-Olimpiu

    2007-07-01

    We investigate the problem of learning with incomplete information as exemplified by learning with delayed reinforcement. We study a two phase learning scenario in which a phase of Hebbian associative learning based on momentary internal representations is supplemented by an 'unlearning' phase depending on a graded reinforcement signal. The reinforcement signal quantifies the success-rate globally for a number of learning steps in phase one, and 'unlearning' is indiscriminate with respect to associations learnt in that phase. Learning according to this model is studied via simulations and analytically within a student-teacher scenario for both single layer networks and, for a committee machine. Success and speed of learning depend on the ratio lambda of the learning rates used for the associative Hebbian learning phase and for the unlearning-correction in response to the reinforcement signal, respectively. Asymptotically perfect generalization is possible only, if this ratio exceeds a critical value lambda( c ), in which case the generalization error exhibits a power law decay with the number of examples seen by the student, with an exponent that depends in a non-universal manner on the parameter lambda. We find these features to be robust against a wide spectrum of modifications of microscopic modelling details. Two illustrative applications-one of a robot learning to navigate a field containing obstacles, and the problem of identifying a specific component in a collection of stimuli-are also provided.

  10. Incomplete restoration of homeostatic shear stress within arteriovenous fistulae.

    PubMed

    McGah, Patrick M; Leotta, Daniel F; Beach, Kirk W; Eugene Zierler, R; Aliseda, Alberto

    2013-01-01

    Arteriovenous fistulae are surgically created to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is, in part, a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. We present computational hemodynamic simulations in four patient-specific models of mature arteriovenous fistulae reconstructed from 3D ultrasound scans. Our results suggest that these mature fistulae have remodeled to return to ''normal'' shear stresses away from the anastomoses: about 1.0 Pa in the outflow veins and about 2.5 Pa in the inflow arteries. Large parts of the anastomoses were found to be under very high shear stresses >15 Pa, over most of the cardiac cycle. These results suggest that the remodeling process works toward restoring mechanical homeostasis in the fistulae, but that the process is limited or incomplete, even in mature fistulae, as evidenced by the elevated shear at or near the anastomoses. Based on the long term clinical viability of these dialysis accesses, we hypothesize that the elevated nonhomeostatic shear stresses in some portions of the vessels were not detrimental to fistula patency.

  11. General Relativity Theory - Well Proven and Also Incomplete: Further Arguments

    NASA Astrophysics Data System (ADS)

    Brandes, Jürgen

    In the former article "General Relativity Theory - well proven and also incomplete?" with a few arguments it was proven that general relativity (GRT) makes contradictory predictions about the total energy of a particle resting in the gravitational field. With a few further arguments it was proven that this contradiction is resolved by expanding general relativity. General relativity is contradictious in energy questions since on one side the total energy of a particle resting in the gravitational field is lower than its rest mass (there is energy needed to pull out the particle from the gravitational field) while on the other side it is equal to its rest mass (this is a consequence of the equivalence principle). In the following article these considerations are generalized to a moving particle. A particle moving in the gravitational field has a total energy less than its rest mass times the relativistic γ-factor since there is energy needed to pull the particle out without changing its velocity. On the other side total energy of a moving particle is equal to its rest mass times the relativistic γ-factor (this is a consequence of the equivalence principle, too). This contradiction is resolved by expanding general relativity in the same manner as above. The other fact: Though it is not the aim of the author to reject general relativity but to expand it, he is treated as some uncritical anti-relativist - since the start of his considerations and meanwhile for more than 20 years.

  12. Quantum Correlations from the Conditional Statistics of Incomplete Data.

    PubMed

    Sperling, J; Bartley, T J; Donati, G; Barbieri, M; Jin, X-M; Datta, A; Vogel, W; Walmsley, I A

    2016-08-19

    We study, in theory and experiment, the quantum properties of correlated light fields measured with click-counting detectors providing incomplete information on the photon statistics. We establish a correlation parameter for the conditional statistics, and we derive the corresponding nonclassicality criteria for detecting conditional quantum correlations. Classical bounds for Pearson's correlation parameter are formulated that allow us, once they are violated, to determine nonclassical correlations via the joint statistics. On the one hand, we demonstrate nonclassical correlations in terms of the joint click statistics of light produced by a parametric down-conversion source. On the other hand, we verify quantum correlations of a heralded, split single-photon state via the conditional click statistics together with a generalization to higher-order moments. We discuss the performance of the presented nonclassicality criteria to successfully discern joint and conditional quantum correlations. Remarkably, our results are obtained without making any assumptions on the response function, quantum efficiency, and dark-count rate of photodetectors.

  13. Topology and incompleteness for 2+1-dimensional cosmological spacetimes

    NASA Astrophysics Data System (ADS)

    Fajman, David

    2016-12-01

    We study the long-time behavior of the Einstein flow coupled to matter on 2-dimensional surfaces. We consider massless matter models such as collisionless matter composed of massless particles, massless scalar fields and radiation fluids and show that the maximal globally hyperbolic development of homogeneous and isotropic initial data on the 2-sphere is geodesically incomplete in both time directions, i.e. the spacetime recollapses. This behavior also holds for open sets of initial data. In particular, we construct classes of recollapsing 2+1-dimensional spacetimes with spherical spatial topology which provide evidence for a closed universe recollapse conjecture for massless matter models in 2+1 dimensions. Furthermore, we construct solutions with toroidal and higher genus topology for the massless matter fields, which in both cases are future complete. The spacetimes with toroidal topology are 2+1-dimensional analogies of the Einstein-de Sitter model. In addition, we point out a general relation between the energy-momentum tensor and the Kretschmann scalar in 2+1 dimensions and use it to infer strong cosmic censorship for all these models. In view of this relation, we also recall corresponding models containing massive particles, constructed in a previous work and determine the nature of their initial singularities. We conclude that the global structure of non-vacuum cosmological spacetimes in 2+1 dimensions is determined by the mass of particles and—in the homogeneous and isotropic setting studied here—verifies strong cosmic censorship.

  14. Synesthesia in twins: incomplete concordance in monozygotes suggests extragenic factors.

    PubMed

    Bosley, Hannah G; Eagleman, David M

    2015-06-01

    Colored-sequence synesthesia (CSS) is a neurological condition in which sequential stimuli such as letters, numbers, or days of the week trigger simultaneous, involuntary color perception. Although the condition appears to run in families and several studies have sought a genetic link, the genetic contribution to synesthesia remains unclear. We conducted the first comparative twin study of CSS and found that CSS has a pairwise concordance of 73.9% in monozygotic twins, and a pairwise concordance of 36.4% in dizygotic twins. In line with previous studies, our results suggest a heritable element of synesthesia. However, consonant with the findings of previous single-pair case studies, our large sample size verifies that synesthesia is not completely conferred by genetics; if it were, monozygotic twins should have 100% concordance. These findings implicate a genetic mechanism of CSS that may work differently than previously thought: collectively, our data suggest that synesthesia is a heritable condition with incomplete penetrance that is substantially influenced by epigenetic and environmental factors.

  15. Quantum Correlations from the Conditional Statistics of Incomplete Data

    NASA Astrophysics Data System (ADS)

    Sperling, J.; Bartley, T. J.; Donati, G.; Barbieri, M.; Jin, X.-M.; Datta, A.; Vogel, W.; Walmsley, I. A.

    2016-08-01

    We study, in theory and experiment, the quantum properties of correlated light fields measured with click-counting detectors providing incomplete information on the photon statistics. We establish a correlation parameter for the conditional statistics, and we derive the corresponding nonclassicality criteria for detecting conditional quantum correlations. Classical bounds for Pearson's correlation parameter are formulated that allow us, once they are violated, to determine nonclassical correlations via the joint statistics. On the one hand, we demonstrate nonclassical correlations in terms of the joint click statistics of light produced by a parametric down-conversion source. On the other hand, we verify quantum correlations of a heralded, split single-photon state via the conditional click statistics together with a generalization to higher-order moments. We discuss the performance of the presented nonclassicality criteria to successfully discern joint and conditional quantum correlations. Remarkably, our results are obtained without making any assumptions on the response function, quantum efficiency, and dark-count rate of photodetectors.

  16. Projectile - Mass asymmetry systematics for low energy incomplete fusion

    NASA Astrophysics Data System (ADS)

    Singh, Pushpendra P.; Yadav, Abhishek; Sharma, Vijay R.; Sharma, Manoj K.; Kumar, Pawan; Sahoo, Rudra N.; Kumar, R.; Singh, R. P.; Muralithar, S.; Singh, B. P.; Bhowmik, R. K.; Prasad, R.

    2015-06-01

    In the present work, low energy incomplete fusion (ICF) in which only a part of projectile fuses with target nucleus has been investigated in terms of various entrance channel parameters. The ICF strength function has been extracted from the analysis of experimental excitation functions (EFs) measured for different projectile-target combinations from near- to well above- barrier energies in 12C,16O(from 1.02Vb to 1.64Vb)+169Tm systems. Experimental EFs have been analysed in the framework statistical model code PACE4 based on the idea of equilibrated compound nucleus decay. It has been found that the value of ICF fraction (FICF) increases with incident projectile energy. A substantial fraction of ICF (FICF ≈ 7 %) has been accounted even at energy as low as ≈ 7.5% above the barrier (at relative velocity νrel ≈0.027) in 12C+169Tm system, and FICF ≈ 10 % at νrel ≈0.014 in 16O+169Tm system. The probability of ICF is discussed in light of the Morgenstern's mass-asymmetry systematics. The value of FICF for 16O+169Tm systems is found to be 18.3 % higher than that observed for 12C+169Tm systems. Present results together with the re-analysis of existing data for nearby systems conclusively demonstrate strong competition of ICF with CF even at slightly above barrier energies, and strong projectile dependence that seems to supplement the Morgenstern's systematics.

  17. Pathlength scaling in graphs with incomplete navigational information

    NASA Astrophysics Data System (ADS)

    Lee, Sang Hoon; Holme, Petter

    2011-10-01

    The graph-navigability problem concerns how one can find as short paths as possible between a pair of vertices, given an incomplete picture of a graph. We study the navigability of graphs where the vertices are tagged by a number (between 1 and the total number of vertices) in a way to aid navigation. This information is too little to ensure errorfree navigation but enough, as we will show, for the agents to do significantly better than a random walk. In our setup, given a graph, we first assign information to the vertices that agents can utilize for their navigation. To evaluate the navigation, we calculate the average distance traveled over random pairs of source and target and different graph realizations. We show that this type of embedding can be made quite efficiently; the more information is embedded, the more efficient it gets. We also investigate the embedded navigational information in a standard graph layout algorithm and find that although this information does not make algorithms as efficient as the above-mentioned schemes, it is significantly helpful.

  18. A multiple imputation strategy for incomplete longitudinal data.

    PubMed

    Landrum, M B; Becker, M P

    Longitudinal studies are commonly used to study processes of change. Because data are collected over time, missing data are pervasive in longitudinal studies, and complete ascertainment of all variables is rare. In this paper a new imputation strategy for completing longitudinal data sets is proposed. The proposed methodology makes use of shrinkage estimators for pooling information across geographic entities, and of model averaging for pooling predictions across different statistical models. Bayes factors are used to compute weights (probabilities) for a set of models considered to be reasonable for at least some of the units for which imputations must be produced, imputations are produced by draws from the predictive distributions of the missing data, and multiple imputations are used to better reflect selected sources of uncertainty in the imputation process. The imputation strategy is developed within the context of an application to completing incomplete longitudinal variables in the so-called Area Resource File. The proposed procedure is compared with several other imputation procedures in terms of inferences derived with the imputations, and the proposed methodology is demonstrated to provide valid estimates of model parameters when the completed data are analysed. Extensions to other missing data problems in longitudinal studies are straightforward so long as the missing data mechanism can be assumed to be ignorable.

  19. Incomplete water securitization in coupled hydro-human production sytems

    NASA Astrophysics Data System (ADS)

    van den Boom, B.; Pande, S.

    2012-04-01

    Due to the dynamics, the externalities and the contingencies involved in managing local water resource for production, the water allocation at basin-level is a subtle balance between laws of nature (gravity; flux) and laws of economics (price; productivity). We study this balance by looking at inter-temporal basin-level water resource allocations in which subbasins enjoy a certain degree of autonomy. Each subbasin is represented as an economic agent i, following a gravity ordering with i=1 representing the most upstream area and i=I the downstream boundary. The water allocation is modeled as a decentralized equilibrium in a coupled conceptual hydro-human production system. Agents i=1,2,...,I in the basin produce a composite good according to a technology that requires water as a main input and that is specific to the subbasin. Agent i manages her use Xi and her storage Si, conceptualizing surface and subsurface water, of water with the purpose of maximizing the utility derived from consumption Ci of the composite good, where Ci is a scalar and Xi and Si are vectors which are composed of one element for each time period and for each contingency. A natural way to consume the good would be to absorb the own production. Yet, the agent may have two more option, namely, she might get a social transfer from other agents or she could use an income from trading water securities with her contiguous neighbors. To study these options, we compare water allocations (Ci, Xi, Si) all i=1,2,...,I for three different settings. We look at allocations without water securitization (water autarky equilibrium EA) first. Next, we describe the imaginary case of full securitization (contingent water markets equilibrium ECM) and, in between, we study limited securitization (incomplete water security equilibrium EWS). We show that allocations under contingent water markets ECM are efficient in the sense that, for the prevailing production technologies, no other allocation exists that is at

  20. Nanostructure formation by self-assembled monolayers: influence of the isomerization state of azobenzene ligands on monolayer formation

    NASA Astrophysics Data System (ADS)

    Vogel, Florian; Bretthauer, Frauke; Siemeling, Ulrich; Träger, Frank

    2011-03-01

    The monolayer formation of photoswitchable self-assembled monolayers of azobenzene-functionalized molecules was studied in situ and in real time by optical second-harmonic generation. Especially the influence of the isomerization state during the adsorption process was measured in our experiments. As will be shown, the isomerization state has a significant influence on the adsorption process of the investigated molecules. Based on the results of the second-harmonic generation experiments the kinetics of the adsorption process was determined.