Finite element approximation of a model for phase separation of a multi-component alloy with a concentration-dependent mobility matrix

We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented.     

Chemical synthesis of oligoribonucleotides containing 2-aminopurine: substrates for the investigation of ribozyme function

The chemical synthesis of a fully protected ribonucleoside phosphoramidite, containing 2-aminopurine as the base component, and its incorporation into short oligoribonucleotides as substrates for an engineered ribozyme from Tetrahymena is described.     

Surface photovoltage,band-bending and surface states on a-Si : H

We have measured the surface photovoltage (SPV) of intrinsic (i.e., undoped) and phosphorus-doped amorphous Si : H between ?168 and 25°C in the spectral range from 0.5 to 2.5 eV. The a-Si : H was grown in a silane glow discharge. Vibrating Kelvin probe techniques were used for the SPV measurements; Auger spectroscopy was used for monitoring surface cleanliness and chemistry. At all temperatures and for both materials, (1) the SPV was invariably negative, (2) there was no correlation between the spectral, thermal and response-time properties of the SPV and the bulk photoconductivity, and (3) surface treatments such as sputtering and oxygen physisorption strongly affected the SPV but not the photoconductivity. These facts indicated that the SPV was due to the emptying of surface-states via surface transitions, and corresponded to the flattening of bands which, when unilluminated, were bent upwards. Intrinsic material showed a maximum SPV of about 0.2 V. The SPV was characterized at ?168°C by strong electronic isolation between surface-states and valence band (i.e., once light was removed, there was no surface-state refilling or decay of the SPV), slow rise times (～min), saturation at photon fluxes of about 10¹¹/cm² · s, and a SPV spectral threshold occurring at 0.7 eV. At 25°C, all SPV responses were much faster (<0.5 s) and the optical threshold was 0.9 eV. The thermal activation energies associated with the SPV were 0.11 eV for surface-state emptying and 0.22 eV for surface-state refilling. For P-doped material the maximum SPV at ?168°C was 0.3 V and its properties indicated less electronic isolation between surface-states and valence band. There was no SPV at room temperature. Our results are discussed in terms of an energy level scheme which contains a distribution of filled surface states isolated from both conduction and valence bands. The surface-state density is estimated to be about (1?2) × 10¹¹/ cm², a relatively low value which is consistent with the observed lack of Fermi level pinning. In both materials there is a very fast component of the SPV which suggests the presence of additional surface states below the valence band edge.     

Fine-structure and tensor polarizabilities of 1snd 3 D levels of He I (n=3 to 7)

Zeitschrift für Physik A Hadrons and nuclei - Using level crossing techniques the fine-structure splittings and tensor polarizabilities of the 1snd 3 D levels of He I withn=3 to 7 have been...     

Silver(I) chloride-polypyrrole composite: electrochemical preparation,characterization, and application as a SERS platform

Journal of Solid State Electrochemistry - A new electrochemical-chemical-electrochemical synthetic route to silver(I) chloride nanoparticle-polypyrrole composites is presented. The chemical...     

Template-Directed Copying of RNA by Non-enzymatic Ligation

The non-enzymatic replication of the primordial genetic material is thought to have enabled the evolution of early forms of RNA-based life. However, the replication of oligonucleotides long enough to encode catalytic functions is problematic due to the low efficiency of template copying with mononucleotides. We show that template-directed ligation can assemble long RNAs from shorter oligonucleotides, which would be easier to replicate. The rate of ligation can be greatly enhanced by employing a 3′-amino group at the 3′-end of each oligonucleotide, in combination with an N-alkyl imidazole organocatalyst. These modifications enable the copying of RNA templates by the multistep ligation of tetranucleotide building blocks, as well as the assembly of long oligonucleotides using short splint oligonucleotides. We also demonstrate the formation of long oligonucleotides inside model prebiotic vesicles, which suggests a potential route to the assembly of artificial cells capable of evolution.     

Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.