Two‐dimensional non‐close‐packed arrays of nanoparticles via core‐shell nanospheres and reactive ion etching

Nanosized PTFE/polystyrene core‐shell particles were prepared by seed emulsion polymerization technique starting from PTFE seeds of 20 nm. At the end of the reaction, no residual PTFE nor secondary nucleation was observed and by appropriately choosing the ratio between the monomer and the PTFE seed it was possible to obtain particles, with predetermined size in the range 60–100 nm, featuring an extremely narrow size distribution. These particles were successfully employed as building blocks for the preparation of large scale nanosized monolayers through the floating technique. Reactive ion etching was further applied to modulate the size characteristics of the resulting 2D ordered nanostructure. Although for relatively short RIE times a peculiar continuous morphology was observed in which the particles are interconnected through thin arms, on further increasing the RIE time a well‐organized 2D arrangement of particles with size of about 30 nm was obtained. Considering the shell as an expendable ordering and spacing tool, the use of core‐shell nanospheres allows a wide variety of controlled morphologies to be designed and prepared thus opening new perspectives for nanostructure fabrication processes through nanosphere lithography (NSL). Copyright © 2011 John Wiley & Sons, Ltd.     

Orientational drawing of polymers and their blends

Pecularities of deformation of two-phase blends is considered depending on drawing conditions and mechanical properties of each phase. Significant anisotropy of mechanical properties of polymer blends film can take place because of particle orientation of dispersed polymer. This significant anisotropy exists also when there is no orientation of macromolecules in each phase. Possibility is demonstrated to regulate properties of each phase in polymer blends by addition of selective plasticizer which can act only on one polymer phase in two-phase polymer mixture.     

On efficient stopping times

This paper is devoted to efficient sequential estimation in stochastic processes whose corresponding sufficient statistics are processes with stationary independent increments. It is proved that a stopping time is efficient if and only if it represents a time of the first attaining of a hyperplane., which cannot ‘be passed’, in the sense which is made precise below. The problem of determining the explicit form of the hyperplanes which cannot ‘be passed’ is also discussed.     

A note on the relativistic covariance of the B-cyclic relations

It is shown that the Evans-Vigier modified electrodynamics is compatible with relativity theory.     

The law of large numbers for weakly correlated random elements in the spaces lp, 1 ⩽ p < ∞

Lithuanian Mathematical Journal - We prove an analogue of Khinchin’s theorem for weakly correlated random elements with values in the spaces lp, 1 ? p &lt; ∞.     

Acyclic tautomers in crystalline carbohydrates: the keto forms of 1-deoxy-1-carboxymethylamino-D-2-pentuloses (pentulose-glycines)

NMR and X-ray diffraction studies on acyclic carbohydrate keto tautomers of N-(1-deoxy-d-erythro-2-pentulos-1-yl)- and N-(1-deoxy-d-threo-2-pentulos-1-yl)glycines (ribulose-glycine, 1 and xylulose-glycine, 2), are reported. In aqueous solutions, both 1 and 2 exist as a tautomeric mixture, with the beta-furanose as a major form, followed by the alpha-furanose and the acyclic keto tautomer. Both 1 and 2 crystallize as zwitterions in the acyclic keto form. Solid-state 13C NMR spectra reveal the existence of two crystallographically independent molecules in 2 but only one in crystalline 1. The structure of 2 was solved by X-ray diffraction; in the crystal, two conformational isomers, 2a and 2b in a 1:1 ratio, were identified. The conformers are packed in stacks of similar molecules, with a system of intermolecular hydrogen bonds involving all hydroxyl, ammonium, and carboxyl groups. The structural data indicate that the sugar portion of acyclic 2 adopts conformations similar to those proposed for the parent d-xylulose.     

Fluorescence detection of DNA by the catalytic activation of an aptamer/thrombin complex

A conjugate consisting of a thrombin aptamer tethered to the thrombin, Th, with a sensing nucleic acid (1) is used for the optical detection of DNA. The thrombin/aptamer complex blocks the biocatalytic functions of Th. Hybridization of the analyte DNA (2) to the sensing nucleic acid 1 yields a rigid duplex that detaches the aptamer from Th, a process that activates the protein toward the hydrolysis of bis(p-tosyl-Gly-Pro-Arg)-R110 (3) to the rhodamine 110 fluorophore (4). The system allows the DNA sensing with a sensitivity limit of 1 x 10-8 M. The aptamer/Th conjugate is also immobilized on glass slides for the optical detection of DNA. The dissociation of the aptamer/Th complex upon hybridization and the subsequent dehybridization of the duplex and the regeneration of the catalytically inactive Th/aptamer complex duplicate machinery functions.     

Spin polarized photoemission from molecular beam epitaxy-grown be-doped GaAs

We have made a comparative study of the performance of spin polarized photocathodes based on molecular beam epitaxy (MBE) grown GaAs with Be-doping and on liquid phase epitaxy (LPE) grown GaAs with Zn-doping. The experiments were performed on GaAs (100), (110), and (111) surfaces atT-300 K. The photoelectron spin polarization (P) of the MBE-photocathodes is face dependent reaching 49% for the (111) surface, a value close to P=50% predicted by theory. In contrast for the LPE-photocathodes P is significantly lower (19P36%). Possible causes for the higher polarization of the MBE-photocathodes are investigated. The influence of the Zn- and Be-dopant is elucidated by theoretical model calculations which shows that replacing the Zn-dopant by Be reduces significantly the depolarization at very low temperatures, but not at room temperature. It is therefore concluded that theinterface region between the GaAs substrate and the MBE-GaAs layer grown on top of it strongly influences the performance of the source.On leave from the Istituto di Fisica Universitá di Modena I-41100 Modena Italy.