Rational surface design for molecular dynamics simulations of porous polymer adsorbent media

The construction and use of nonflat agarose surfaces in a simulation box, together with the employment of criteria for the immobilization of a set of dextran polymer chains on the nonflat agarose surfaces whose mathematical physics is compatible with that of the criteria used for the immobilization of the same set of dextran polymer chains on flat agarose surfaces, are shown to generate, through the use of molecular dynamics simulations whose simulation box has linear dimensions along the lateral directions that are the same when flat and nonflat agarose surfaces are used, dextran porous polymer structures whose pore sizes at the outermost surface and in the vicinity of the outermost surface of the porous medium can be controlled by an indirect manner through the variation of the parameters that characterize the nonflat surface. The use of a nonflat surface for the generation of desired large pores requires only a small or modest increase in the number of solvent molecules in the simulation box, while the use of a flat surface for the construction of the same desired large pores requires significant increases in the size of the linear dimensions of the flat surface. This increases so substantially the number of solvent molecules that the computational loads become intractable. The results in this work show that through the use of nonflat surfaces porous dextran polymer layers having pores of desired sizes can be effectively constructed, and this approach could be used for the design and construction of polymer-based porous adsorbent media that could effectively facilitate the transport and adsorption of an adsorbate biomolecule of interest that must be separated from a mixture of components. A useful definition about the properties that a porous polymer structure must have in order to become, for an adsorbate biomolecule of interest of known molecular size, a useful adsorbent medium, is presented and is used to (1) evaluate the porous polymer structures generated through the employment of different nonflat surface models and (2) determine and select the nonflat surface model from a set of nonflat surface models that is effective in producing promising porous structures. Then a procedure is presented by which a set of porous polymer media is generated through the use of the selected nonflat surface model, and the desired porous structure from this set is determined and could be considered to be used for the transport and immobilization of the selected affinity groups/ligands and the subsequent transport and adsorption of the desired to be separated adsorbate.     

Experimental quantum communication without a shared reference frame

We present an experimental realization of a robust quantum communication scheme [Phys. Rev. Lett. 93, 220501 (2004)] using pairs of photons entangled in polarization and time. Our method overcomes errors due to collective rotation of the polarization modes (e.g., birefringence in optical fiber or misalignment), is insensitive to the phase's fluctuation of the interferometer, and does not require any shared reference frame including time reference, except the need to label different photons. The practical robustness of the scheme is further shown by implementing a variation of the Bennett-Brassard 1984 quantum key distribution protocol over 1 km optical fiber.     

Dynamical identification of a threshold instability in Si-doped heterofullerenes

We rationalize the origins of a threshold instability and the mechanism of finite temperature fragmentation in highly Si-doped C(60-m)Si(m) heterofullerenes via a first-principles approach. Cage disruption is driven by enhanced fluctuations of the most internal Si atoms. These are located within fully segregated Si regions neighboring the C-populated part of the cage. The predominance of inner Si atoms over those involved in Si-C bonds marks the transition from thermally stable to unstable C(60-m)Si(m) systems at m = 20.     

Uranyl complexation by chloride ions. Formation of a tetrachlorouranium(VI) complex in room temperature ionic liquids [Bmim][Tf2N] and [MeBu3N][Tf2N

The tetrachlorouranium(VI) complex is formed in [Bmim][Tf2N] and [MeBu3N][Tf2N] from a uranium(VI) solution in the presence of a stoichiometric quantity of chloride ions. The [UVIO2Cl4]2- absorption and emission spectra show bands splitting in comparison with the [UVIO2]2+ spectra, as observed in the solid state, organic solvents, and chloroaluminate-based ionic liquids. The fluorescence lifetime of [UO2Cl4]2- in [MeBu3N][Tf2N] is 0.7 +/- 0.1 mus. The reduction potential of this complex is -1.44 and -1.8 V vs Ag/Ag+ respectively in [Bmim][Tf2N] and [MeBu3N][Tf2N] and does not depend on the chloride concentration. The mechanism proposed for the redox process is a monoelectronic reduction to form [UVO2Cl4]3-, followed by a chemical reaction. The tetrachlorouranium(V) complex seems more stable in [Bmim][Tf2N] than in [MeBu3N][Tf2N]. The electrochemical analysis put in evidence specific interactions of the ionic liquid cation with the uranium anionic species.     

AlN on nanocrystalline diamond piezoelectric cantilevers for sensors/actuators

Micro-cantilevers can be used as both sensors and actuators. In this work, the design, fabrication and characterization of piezoelectrically driven nano-crystalline diamond (NCD) cantilevers are reported Diamond films were grown on silicon (100) substrates by microwave plasma enhanced chemical vapor deposition (MW-PECVD). Cantilevers are coated by DC pulsed piezoelectric with AlN films that is sandwiched between two metallic electrodes. The thicknesses of AlN and diamond layers are 1μm and 700nm, respectively. The influence on the electromechanical response of cantilevers length was studied. The motion of the electrically driven cantilevers is performed by measuring the evolution of the electrical impedance at the resonant frequencies that varies between 10 kHz and 130 kHz for the resonant mode.