Asymptotic exactness of an a posteriori error estimator based on the equilibrated residual method

In this paper we analyze an a posteriori error estimator based on the equilibrated residual method. We prove that this estimator is asymptotically exact in the energy norm for regular solutions and meshes. Numerical examples are included to illustrate the theoretical results.     

Practical synthesis of 1,4-dioxane derivative of the closo-dodecaborate anion and its ring opening with acetylenic alkoxides

Practical method of synthesis of the 1,4-dioxane derivative of the closo-dodecaborate anion was developed. The cleavage of the dioxonium ring in [B₁₂H₁₁O(CH₂CH₂)₂O]⁻ with acetylenic alcohols gave rise to the preparation of closo-dodecaborate derivatives with terminal acetylene group. These compounds can be introduced into click reactions with phenylazide leading to the corresponding triazoles. The structures of (Bu₄N)[B₁₂H₁₁O(CH₂CH₂)₂O] and (Bu₄N)₂[B₁₂H₁₁(OCH₂CH₂)₂OCH₂CCH] · 0.5HOCH₂CCH were determined by single-crystal X-ray diffraction.     

Versatile coordination chemistry towards multifunctional carbon nanotube nanohybrids

Dispersible single-walled carbon nanotubes grafted with poly(4-vinylpyridine), SWNT-PVP, were tested in coordination assays with zinc tetraphenylporphyrin (ZnP). Kinetic and spectroscopic evidence corroborates the successful formation of a SWNT-PVPZnP nanohybrid. Within this SWNT-PVPZnP nanohybrid, static electron-transfer quenching (2.0+/-0.1) x 10(9) s(-1) converts the photoexcited-ZnP chromophore into a radical-ion-pair state with a microsecond lifetime, namely one-electron oxidized-ZnP and reduced-SWNT.     

A general and efficient pseudopotential Fourier filtering scheme for real space methods using mask functions

A scheme for the Fourier filtering of pseudopotentials in real space calculations is proposed, in order to reduce the artifact of positional energy dependence ("egg box" effect). It is based on an improved version of the mask function method poposed by Wang [Phys. Rev. B 64, 201107/1 (2001)]. It is easy to implement, efficient, and accurate. By using atom-centered compensation charges, the local part of the pseudopotential becomes short ranged and can be filtered on the same footing as the nonlocal parts. A major advantage of the approach is that a generic set of parameters can be used for different pseudopotentials. A balanced parameter set is derived and validated. In this context a strategy to monitor the extent of grid dependence is introduced. It is found that, given a sufficiently fine grid spacing is used to represent the atomic valence density, the positional energy dependence can be reduced below 0.1 mhartree for all investigated atoms. On the example of a D(3h) symmetric Si(5) cluster and the C(60) molecule it is demonstrated that the artificial symmetry breaking of both bond lengths and orbital energies can substantially be reduced by the filtering scheme.     

Ionic conductivity and thermal expansion of anion-deficient Sr11Mo4O23 perovskite

Transport properties of perovskite-type Sr₁₁Mo₄O₂₃ and composite Sr₁₁Mo₄O₂₃ - 1 wt% Al₂O₃ were studied at 400–1300 K in the oxygen partial pressure range from 0.21 down to 10⁻¹⁹ atm. The electromotive force and faradaic efficiency measurements, in combination with the energy-dispersive spectroscopy of the fractured electrochemical cells, unambiguously showed prevailing role of the oxygen ionic conductivity under oxidizing conditions. At temperatures above 600 K, protonic and cationic transport can be neglected. The oxygen ion transference numbers vary in the range of 0.95–1.00 at 973–1223 K. At temperatures lower than 550 K, the total conductivity of Sr₁₁Mo₄O₂₃ - 1 wt% Al₂O₃ composite measured by impedance spectroscopy tends to increase in wet atmospheres, thus indicating that hydration and protonic transport become significant. Reducing oxygen partial pressure below 10⁻¹⁰–10⁻⁹ atm leads to a significant increase in the n-type electronic conduction. The average thermal expansion coefficients in oxidizing atmospheres are (14.3–15.0) × 10⁻⁶ K⁻¹ at 340–740 K and (18.3–19.2) × 10⁻⁶ K⁻¹ at 870–1370 K.

     

Combinatorial discovery of fluorescent pharmacophores by multicomponent reactions in droplet arrays

Fluorescence imaging in clinical diagnostics and biomedical research relies to a great extent on the use of small organic fluorescent probes. Because of the difficulty of combining fluorescent and molecular-recognition properties, the development of such probes has been severely restricted to a number of well-known fluorescent scaffolds. Here we demonstrate that autofluorescing druglike molecules are a valuable source of bioimaging probes. Combinatorial synthesis and screening of chemical libraries in droplet microarrays allowed the identification of new types of fluorophores. Their concise and clean assembly by a multicomponent reaction presents a unique potential for the one-step synthesis of thousands of structurally diverse fluorescent molecules. Because they are based upon a druglike scaffold, these fluorophores retain their molecular recognition potential and can be used to design specific imaging probes.     

TOF MS Investigation of Nickel Oxide CVD

NiO layers were deposited by metal-organic chemical vapor deposition using bis-(ethylcyclopentadienyl) nickel (EtCp)₂Ni and oxygen or ozone. As a continuation of kinetic study of NiO MOCVD the gas-phase, transformations of (EtCp)₂Ni were studied in the temperature range of 380–830 K. Time of reactions corresponding to the residence time of the gas stream in hot zone of the reactor was about 0.1 s under conditions studied. The interaction of (EtCp)₂Ni with oxygen started at 450 K and its conversion rate reached the maximum at 700 K. The interaction of (EtCp)₂Ni with ozone started at 400 K and its conversion rate reached the maximum at 600 K. Transformations of the gas phase with the temperature in the reaction zone were studied, the model reaction schemes illustrating (EtCp)₂Ni transformations in the reaction systems containing oxygen and ozone have developed. In the reaction system (EtCp)₂Ni–O₂–Ar the main gas-phase products at 380–500 K were CO, CO₂, HCO, C₂H₅OH, CpCOOH, and CpO. Formation of the C₂H₂O, C₃H₄O, and C₅H₈O was found at 630–830 K. The same gas-phase species, (C₄H₃O)₂Ni and dialdehydes was formed in the reaction system (EtCp)₂Ni–O₃–O₂–Ar.

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Distribution of benzo-substituted crown-ethers between chloroform and water: effects of macrocycle ring size and lithium chloride

Small size benzo-substituted crown ethers are attractive complexing agents for lithium isotope separation by solvent extraction. Low transfer of the crown ethers from solvent to water is a key point for applicability of the extractants. In the present study, 9- and 12-membered crown ethers were synthesized, and their distribution between chloroform and water was studied. Polyether ring size, benzene substituents and addition of LiCl to water were found to effect on distribution constants. Low losses of the macrocycles were observed at single-stage contact with aqueous phase. However, these losses should be taken into account in the design of multistage processes for the preparation of highly enriched lithium isotopes.