ΓD‐convergence for a class of quasilinear elliptic equations in thin structures

We study the asymptotic behaviour of the solution of a stationary quasilinear elliptic problem posed in a domain Ω^(ε) of asymptotically degenerating measure, i.e. meas Ω^(ε) → 0 as ε → 0, where ε is the parameter that characterizes the scale of the microstructure. We obtain the convergence of the solution and the homogenized model of the problem is constructed using the notion of convergence in domains of degenerating measure. Proofs are given using the method of local characteristics of the medium Ω^(ε) associated with our problem in a variational form. Copyright © 2005 John Wiley & Sons, Ltd.     

Structure determination of Na3DySi6O15 and crystal chemistry of zektzerite related compounds

The crystal structure of Na₃DySi₆O₁₅ has been solved and refined to an R₁=2.97% (wR₂=8.25%) for 1311 independent reflections. The compound was found to crystallize within the orthorhombic system with the space group Cmca (Z=8) and the lattice parameters: a=14.590(7) Å, b=17.813(4) Å, c=10.519(2) Å, V=2734.0 Å³, D_cal=3.11 g/cm³. The structure of Na₃DySi₆O₁₅ is a filled variant of the zektzerite with S like corrugated double chains of [SiO₄] tetrahedral, connected via Na⁺ and Dy³⁺ cations and running parallel to c-axis. The three-dimensional network results from the packing of these chains along [100] by skewering them in rods represented by the tunnels delimited by the S shape of the silicate chains. One of the main peculiar features of the Na₃DySi₆O₁₅ structure is the location of Na⁺ in tetrahedral sites with rather short Na-O bond lengths (2×2.243 and 2×2.262 Å).     

Collisional dynamics of Ag19 on Pd(100): a molecular dynamics study

By means of molecular dynamics simulations based on realistic n-body potentials we investigate structural and dynamical features inherent to the energetic collision of a silver cluster (Ag₁₉) on the Pd(100) substrate. Both the system and the impact energy (E_i = 95 eV) adopted have been chosen to parallel an experimental study of size selected Ag cluster deposition on Pd(100). Our results indicate that the experimental cross section obtained via thermal energy atom scattering at the same collision energy is well reproduced by the simulations.The modeling allows to rationalize the collision outcome in terms of defect production and cluster atoms implantation. The adsorbed structures have an heterogenous nature and are mostly two-dimensional.     

Crystal structures of two allotropic forms of Na2CoP2O7

Na₂CoP₂O₇ may be prepared in two allotropie forms:I, rose,M _r =278.85, triclinic, P1,a=9.735(2),b=10.940(3),c=12.289(4) Å,=148.78,=121.76(1), =68.38(2)°,V=566.8(2) ų,Z=4,D _meas=3.28(5) g cm^–3,D _calc=3.267 g cm^–3, (MoK)=0.71069 Å,=37.12 cm^–1, F(000)=540,T=298 K,R=5.4% for 2911 observed reflections; andII, blue,M _r =278.85, orthorhombic, P2₁cn,a=7.713(2) Å,b=10.271(4),c=15.378(6)°,V=1218.2(8) ų,Z=8,D _meas=3.06(5) g cm^–3,D _calc=3.040 g cm^–1, (MoK ) Å,=34.55 cm^–1, F(000)=1080,T=298 K,R=9.9% for 1450 observed reflections. Cobalt displays octahedral coordination to six oxygen atoms in the rose form whereas the metal coordination is tetrahedral in the blue form.     

Mechanism for resonant O electron stimulated desorption from condensed O2. Non-adiabatic transitions and dynamics

Absolute kinetic energy distributions and yields associated with ground state ³P and excited state ¹D oxygen atoms have been obtained for O⁻ anion electron stimulated desorption from condensed O₂ in the electron energy range 6–15 eV. The observed yields are understood as resulting essentially from dissociative electron attachment reactions via the two lowest ²Σ⁺_g O⁻₂ resonance states through adiabatic and non-adiabatic transitions to the limits O⁻(²P) + O(³P) and O⁻(²P) + O(¹D). The kinetic energy distributions show the prominent role of electron multiple collision processes and post-dissociation interactions of the O⁻ anions in the condensed phase.     

Unprecedented hour-long residence time of a cation in a left-handed G-quadruplex

Cations are critical for the folding and assembly of nucleic acids. In G-quadruplex structures, cations can bind between stacked G-tetrads and coordinate with negatively charged guanine carbonyl oxygens. They usually exchange between binding sites and with the bulk in solution with time constants ranging from sub-millisecond to seconds. Here we report the first observation of extremely long-lived K⁺ and NH₄⁺ ions, with an exchange time constant on the order of an hour, when coordinated at the center of a left-handed G-quadruplex DNA. A single-base mutation, that switched one half of the structure from left- to right-handed conformation resulting in a right–left hybrid G-quadruplex, was shown to remove this long-lived behaviour of the central cation.

An extremely long-lived cation has been detected in left-handed G-quadruplexes.     

The unexpected rearrangement of 1,5‐benzodiazepin‐2,4‐dione to a benzimidazol‐2‐one derivative during N,N'‐diglucosylation

Reaction of 1,5‐benzodiazepin‐2,4‐dione with 3‐O‐substituted‐5,6‐anhydro‐1,2‐isopropylidene‐α‐D‐glucofuranose gave the unexpected N,N'‐di‐glucofuranosyl benzimidazol‐2‐one by a novel rearrangement and ring closure reaction. A mechanism is proposed.     

Crystal Structure of a New Ammonium Potassium Selenomolybdate Compound K3.31(NH4)0.69[Se2Mo5O21]·2H2O

An inorganic compound formulated as K_3.31(NH₄)_0.69[Se₂Mo₅O₂₁]·2H₂O has been synthesized by conventional solution method and characterized by scanning electron microscopy, IR, UV-Vis spectroscopies behaviors. The structure of the title compound has been determined from a single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P2₁/n, with a?=?9.9371(2) ?, b?=?23.3545(2) ?, c?=?10.5179(2) ?, β?=?114.12(3)°, V?=?2227.7(5) ?³ and Z?=?4. It was revealed that the Strandberg-type polyoxoselenomolybdate cluster can be considered as a ring formed by five distorted edge- and corner-sharing MoO₆ octahedra, capped on both poles by a selenate pyramids sharing three vertices with the ring molybdenum centers. The Strandberg clusters are connected with ammonium ions and water molecules through hydrogen-bonding interactions which ensure the cohesion of the structure into a three-dimensional network.