Synthesis of modified vermiculite by interaction with aromatic heterocyclic amines

Vermiculite of general formula [Si_6.85Al_1.15][Mg_4.68Al_0.51Fe_0.63]O₂₀(OH)₄Ca_0.128Na_0.032K_0.094 reacted with heteroaromatic amines α-, β-, and γ-picolines from aqueous solution. The products were characterized by elemental analysis, infrared spectroscopy, and X-ray diffraction. The intercalated nanocompounds maintained the crystallinity and changed the original interlayer distance of 1422 pm to 1474, 1456, and 1474 pm, for the sequence of the guest picoline molecules. Natural and intercalated vermiculite can remove copper at the solid/liquid interface; removal 0.40 mmol g⁻¹ was obtained for the original matrix, and 1.10, 0.92, and 1.33 mmol g⁻¹ for the intercalated forms. These values are near the capacity of cation exchange (CEC) of this clay mineral, which can be possibly used as source of copper removal from aqueous solution.     

Fractionation of HDPE on quench cooling

In a previous paper we discussed co-crystallization in a LDPE/HDPE blend using TREF and DSC. As part of that study it was observed that pure HDPE showed an unexpected fractionation behavior when quench crystallized in TREF. The overall peak broadened and two peaks appeared instead of the previously observed single peak for slow cooled HDPE.The development of two peaks was observed for all commercial HDPEs investigated, independent of their melting indices and densities. TREF and GPC were used in an attempt to evaluate the origin of the two HDPE components.The authors appreciate support from CAPES-BRAZIL (C.A.F.). Additional thanks go to Dr. G. W. Knight in Dow Chemical Company for kindly providing the polymer samples and performing the GPC analysis.     

Composition of higher fullerenes obtained by laser ablation of carboniferous materials

The compositions of higher fullerenes produced by ablation of various carboniferous materials are experimentally studied. The yield of fullerenes versus the type of carboniferous materials and laser radiation parameters is found.     

Explicit inverse of a tridiagonal k−Toeplitz matrix

Summary We obtain explicit formulas for the entries of the inverse of a nonsingular and irreducible tridiagonal k–Toeplitz matrix A. The proof is based on results from the theory of orthogonal polynomials and it is shown that the entries of the inverse of such a matrix are given in terms of Chebyshev polynomials of the second kind. We also compute the characteristic polynomial of A which enables us to state some conditions for the existence of A^–1. Our results also extend known results for the case when the residue mod k of the order of A is equal to 0 or k–1 (Numer. Math., 10 (1967), pp. 153–161.).The work was supported by CMUC (Centro de Matemática da Universidade de Coimbra) and by Acção Integrada Luso-Espanhola E-6/03     

Influence of defects on the optical and structural properties of Ge dots embedded in an Si/Ge superlattice

In this work we studied the influence of high-energy proton irradiation on the optical and structural properties of an Si/Ge superlattice (SL) with embedded Ge quantum dots (QDs). The presence of QDs in the as-grown samples was established by transmission electron microscopy and photoluminescence (PL). The samples were irradiated with 2.0 MeV protons to fluences in the range 2×10¹²-2×10¹⁴ cm^-2. The structural characterization made by X-ray reciprocal space mapping, X-ray reflection and Rutherford backscattering/channelling has shown no changes in the as-grown heterostructure due to the irradiation. In spite of the expected high concentration of nonradiative recombination centres caused by the proton-induced damage, the PL emission from the Ge dots has been observed even for the highest irradiation fluence. The studied QD-in-SL structure has shown an extraordinarily high radiation hardness when compared with previously studied QD heterostructures.     

Characteristic Features of Gravitational Wave Lensing as Probe of Lens Mass Model

To recognize gravitational wave lensing events and being able to differentiate between similar lens models will be of crucial importance once one will be observing several lensing events of gravitational waves per year. In this work, the lensing of gravitational waves is studied in the context of LISA sources and wave-optics regime. While different papers before the studied microlensing effects enhanced by simultaneous strong lensing, the focus is on frequency (time) dependent phase effects produced by one lens that will be visible with only one lensed signal. It is shows how, in the interference regime (i.e., when interference patterns are present in the lensed image), one is able to i) distinguish a lensed waveform from an unlensed one, and ii) differentiate between different lens models. In pure wave-optics, on the other hand, the feasibility of the study depends on the signal-to-noise ratio of the signal and/or the amplitude of the lensing effect. To achieve these goals, the phase of the amplification factor of the different lens models and its effect on the unlensed waveform is studied, and the signal-to-noise calculation to provide some quantitative examples is exploited.     

A Highly Stabilizing Silver(I)‐Mediated Base Pair in Parallel‐Stranded DNA

The first parallel‐stranded DNA duplex with Hoogsteen base pairing that readily incorporates an Ag⁺ ion into an internal mispair to form a metal‐mediated base pair has been created. Towards this end, the highly stabilizing 6 FP ‐Ag⁺‐ 6 FP base pair comprising the artificial nucleobase 6‐furylpurine ( 6 FP ) was devised. A combination of temperature‐dependent UV spectroscopy, CD spectroscopy, and DFT calculations was used to confirm the formation of this base pair. The nucleobase 6 FP is capable of forming metal‐mediated base pairs both by the Watson–Crick edge (i.e. in regular antiparallel‐stranded DNA) and by the Hoogsteen edge (i.e. in parallel‐stranded DNA), depending on the oligonucleotide sequence and the experimental conditions. The 6 FP ‐Ag⁺‐ 6 FP base pair within parallel‐stranded DNA is the most strongly stabilizing Ag⁺‐mediated base pair reported to date for any type of nucleic acid, with an increase in melting temperature of almost 15 °C upon the binding of one Ag⁺ ion.     

Six‐Coordinate Group 13 Complexes: The Role of d Orbitals and Electron‐Rich Multi‐Center Bonding

Bonding in six‐coordinate complexes based on Group 13 elements (B, Al, Ga, In, Tl) is usually considered to be identical to that in transition‐metal analogues. We herein demonstrate through sophisticated electronic‐structure analyses that the bonding in these Group 13 element complexes is fundamentally different and better characterized as electron‐rich hypervalent bonding with essentially no role for the d orbitals. This characteristic is carried through to the molecular properties of the complex.