Characterization and spectroscopic analysis of phenol-ethanol hydrogen bonded clusters

Different hydrogen bonded clusters involving phenol and ethanol are studied theoretically using MP2/aug-cc-pVDZ. Nine different 1: 1 clusters are obtained and analyzed according to their stability and spectroscopic properties. Different isomeric forms of ethanol are considered. Attention is also devoted to the spectral shift of the characteristic pi -> pi* transition of phenol. Using TDHF, CIS, CIS(D) and TDB3LYP in aug-cc-pVDZ basis set, all results agree that a red shift is obtained when phenol is the hydrogen donor and a blue shift is obtained in the opposite case. These results are used to rationalize the red shift observed for phenol in liquid ethanol. (C) 2010 Elsevier B.V. All rights reserved.

Many-body energy decomposition of hydrogen-bonded glycine clusters in gas-phase

A detailed analysis of the many-body contribution to the interaction energies of the gas-phase hydrogen-bonded glycine clusters, (Gly)(N), N = 1-4 is presented. The energetics of the hydrogen-bonded dimer, trimer and tetramer complexes have been analyzed using density-functional theory. The magnitude of the two-through four-body energy terms have been calculated and compared. The relaxation energy and the two-body energy terms are the principal contributors to the total binding energy. Four-body contribution is negligible. However, the three-body contribution is found to be sizable and the formation of the cyclic glycine trimer presents geometric strains that make it less favorable. (C) 2010 Elsevier B.V. All rights reserved.

The imprint of the interaction between dark sectors in galaxy clusters

Based on perturbation theory, we study the dynamics of how dark matter and dark energy in the collapsing system approach dynamical equilibrium when they are in interaction. We find that the interaction between dark sectors cannot ensure the dark energy to fully cluster along with dark matter. When dark energy does not trace dark matter, we present a new treatment on studying the structure formation in the spherical collapsing system. Furthermore we examine the cluster number counts dependence on the interaction between dark sectors and analyze how dark energy inhomogeneities affect cluster abundances. It is shown that cluster number counts can provide specific signature of dark sectors interaction and dark energy inhomogeneities.

Signature of the interaction between dark energy and dark matter in galaxy clusters

We investigate the influence of ail interaction between dark energy and dark matter upon the dynamics of galaxy clusters. We obtain file general Layser-Irvine equation in the presence of interactions, and find how, in that case. the virial theorem stands corrected. Using optical, X-ray and weak lensing data from 33 relaxed galaxy clusters, we put constraints on the strength of the coupling between the dark sectors. Available data Suggests that this coupling is small but positive, indicating that dark energy might be decaying into dark matter. Systematic effects between the several mass estimates, however, should be better known, before definitive conclusions oil the magnitude and significance of this coupling could be established. (C) 2009 Published by Elsevier B.V.

High-density gas aggregation nanoparticle gun applied to the production of SmCo clusters

We describe in this article the application of a high-density gas aggregation nanoparticle gun to the production and characterization of high anisotropy SmCo nanoparticles. We give a detailed description of the simple but efficient experimental apparatus with a focus on the microscopic processes of the gas aggregation technique. Using high values of gas flux (similar to 45 sccm) we are able to operate in regimes of high collimation of material. In this regime, as we explain in terms of a phenomenological model, the power applied to the sputtering target becomes the main variable to change the size of the clusters. Also presented are the morphological, structural, and magnetic characterizations of SmCo nanoparticles produced using 10 and 50 W of sputtering power. These values resulted in mean sizes of similar to 12 and similar to 20 nm. Significant differences are seen in the structural and magnetic properties of the samples with the 50 W sample showing a largely enhanced crystalline structure and magnetic anisotropy.

Hyperfine and magnetic properties of Fe-Cu clusters and Fe precipitates embedded in a Cu matrix

Using the first-principles real-space linear muffin-tin orbital method within the atomic sphere approximation (RS-LMTO-ASA) we study hyperfine and local magnetic properties of substituted pure Fe and Fe-Cu clusters in an fcc Cu matrix. Spin and orbital contributions to magnetic moments, hyperfine fields and the Mossbauer isomer shifts at the Fe sites in Fe precipitates and Fe-Cu alloy clusters of sizes up to 60 Fe atoms embedded in the Cu matrix are calculated and the influence of the local environment on these properties is discussed.

The effect of additional Si and SiGe layers on the confinement potential of GeMn diluted ferromagnetic semiconductor

In this work we analyze the spin-polarized charge density distribution in the GeMn diluted ferromagnetic semiconductors (DFS). The calculations are performed within a self-consistent k.p method, in which the exchange correlation effects in the local density approximation, as well as the strain effects due to the lattice mismatch, are taken into account. Our findings show that the extra confinement potential provided by the barriers and the variation of the Mn content in the DFS are responsible for a separation between the different spin charge densities, giving rise to higher mobility spin-polarized currents or high ferromagnetism transition temperatures systems. (c) 2008 Elsevier B.V. All rights reserved.

Experimental evidence of the spin-glass transition in the diluted magnetic semiconductor Zn(1-x)Mn(x)In(2)Se(4)

This work reports on magnetic measurements of the quasi-two-dimensional (quasi-2D) system Zn(1-x)Mn(x)In(2)Se(4), with 0.01 <= x <= 1.00. For x > 0.67, the quasi-2D system seems to develop a spin-glass behaviour. Evidence of a true phase transition phenomenon is provided by the steep increase of the nonlinear susceptibility chi(nl) when approaching T(C) from above. The static scaling of chi(nl) data yields critical exponents delta = 4.0 +/- 0.2, phi = 4.37 +/- 0.17 and TC = 3.4 +/- 0.1 K for the sample with x = 1.00 and similar values for the sample with x = 0.87. These critical exponents are in good agreement with values reported for other spin-glass systems with short-range interactions.

Capacitive electrolyte-insulator-semiconductor structures functionalised with a polyelectrolyte/enzyme multilayer: New strategy for enhanced field-effect biosensing

A novel strategy for enhanced field-effect biosensing using capacitive electrolyte-insulator-semiconductor (EIS) structures functionalised with pH-responsive weak polyelectrolyte/enzyme or dendrimer/enzyme multilayers is presented. The feasibility of the proposed approach is exemplarily demonstrated by realising a penicillin biosensor based on a capacitive p-Si-SiO(2) EIS structure functionalised with a poly(allylamine hydrochloride) (PAH)/penicillinase and a poly(amidoamine) dendrimer/penicillinase multilayer. The developed sensors response to changes in both the local pH value near the gate surface and the charge of macromolecules induced via enzymatic reaction, resulting in a higher sensitivity. For comparison, an EIS penicillin biosensor with adsorptively immobilised penicillinase has been also studied. The highest penicillin sensitivity of 100 mV/dec has been observed for the EIS sensor functionalised with the PAH/penicillinase multilayer. The lower and upper detection limit was around 20 mu M and 10 mM, respectively. In addition, an incorporation of enzymes in a multilayer prepared by layer-by-layer technique provides a larger amount of immobilised enzymes per sensor area, reduces enzyme leaching effects and thus, enhances the biosensor lifetime (the loss of penicillin sensitivity after 2 months was 10-12%). (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Optical and dielectric relaxor behaviour of Ba(Zr(0.25)Ti(0.75))O(3) ceramic explained by means of distorted clusters

In this work, Ba(Zr(0.25)Ti(0.75))O(3) ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie-Weiss law. The optical properties were analysed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV-vis spectrum indicated that the Ba(Zr(0.25)Ti(0.75))O(3) ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO(6)] distorted clusters into a globally cubic matrix.

Detection of microwaves using the organic semiconductor poly(p-phenylenevinylene)

We report a new procedure to convert the polymer precursor poly(xylylidene tetrahydrothiophenium chloride) (PTHT) into poly(p-phenylenevinylene) (PPV) using microwave irradiation. Spin-coated PTHT films were irradiated at room temperature under ambient conditions in a commercial microwave oven, with varying power from 20W to 100W. Complete conversion was reached within only 5 min of irradiation for powers above 50W, yielding PPV films with absorption and photoluminescence spectra that are practically indistinguishable from the spectra of thermally converted PPV films, which require ca. 2 h of a high temperature (similar to 200 degrees C) thermal treatment. In addition to a much faster conversion procedure, the irradiation with microwaves led to a red shift in the absorption spectrum of a PTHT film, which varied linearly with the time of irradiation. These films can then be used as low-cost, easy-to-use detectors of microwaves. (C) 2010 Elsevier B.V. All rights reserved.

Spin-polarization effects in homogeneous and non-homogeneous diluted magnetic semiconductor heterostructures

Spin polarization is a key characteristic in developing spintronic devices. Diluted magnetic heterostructures (DMH), where subsequent layers of conventional and diluted magnetic semiconductors (DMS) are alternate, are one of the possible ways to obtain it. Si being the basis of modern electronics, Si or other group-IV DMH can be used to build spintronic devices directly integrated with conventional ones. In this work we study the physical properties and the spin-polarization effects of p-type DMH based in group-IV semiconductors (Si, Ge, SiGe, and SiC), by performing self-consistent (k) over right arrow . (p) over right arrow calculations in the local spin density approximation. We show that high spin polarization can be maintained in these structures below certain values of the carrier concentrations. Full spin polarization is attained in the low carrier concentration regime for carrier concentrations in the DMS layer up to similar to 2.0 x 10(19) cm(-3) for Si and up to similar to 6.0 x 10(19) cm(-3) for SiC. Partial, but still important spin polarization can be achieved for all studied group-IV DMH, with the exception of Ge for carrier concentrations up to 6.0 x 10(19) cm(-3). The role played by the effective masses and the energy splitting of the spin-orbit split-off hole bands is also discussed throughout the paper.

Catalytic oxidation of hydrocarbons by trinuclear mu-oxo-bridged ruthenium-acetate clusters: Radical versus non-radical mechanisms

The [Ru(3)O(H(3)CCO(2))(6)(py)(2)(L)]PF(6) clusters, where L=methanol or dimethyl sulfoxide, can be activated by peroxide or oxygen donor species, such as tert-butyl hydroperoxide (TBHP) or iodosylbenzene (PhIO), respectively, generating reactive intermediates of the type [Ru(3)(IV,IV,III)=0](+). In this way, they catalyse the oxidation of cyclohexane or cyclohexene by TBHP and PhIO, via oxygen atom transfer, rather than by the alternative oxygen radical mechanism characteristic of this type of complexes. In addition to their ability to perform efficient olefin epoxydation catalysis, these clusters also promote the cleavage of the C-H bond in hydrocarbons, resembling the oxidation catalysis by metal porphyrins. (C) 2008 Elsevier Inc. All rights reserved.

Triangular ruthenium acetate clusters containing the bis(pyridyl)propane ligand and their inclusion chemistry with beta-cyclodextrin

The triruthenium carboxylate cluster [Ru(3)O(OAc)(6)(py)(2)(bpp)](+) (OAc = acetate) containing the bridging 1,3-bis(4-pyridyl)propane (bpp) ligand, and its dimeric species [{Ru(3)O(OAc)(6)(py(2))}(2)(mu-bpp)](2+) were synthesized in order to investigate their inclusion compounds with beta-cyclodextrin (beta-CD). Characterization of the complexes was carried out based on spectroscopic, electrochemical and spectroelectrochemical techniques, while the formation of inclusion complexes was evaluated using (1)H NMR/NOESY spectroscopy. Since bpp is a flexible ligand, a DFT study was carried out in order to characterize its conformational isomers and their possible role in the host-guest chemistry with beta-CD. Instead of observing the formation of inclusion compounds with different stoichiometries, we observed the formation of 1:1 bpp/beta-CD compounds in which the bpp ligand assumes different conformations. The assembly of polymetallic rotaxane species was successfully demonstrated by monitoring the (1)H NMR spectra of the monomeric cluster species in the presence of aquapentacyanoferrate(II) ions and beta-CD.

A comparison of the leaf-litter ant fauna in a secondary atlantic forest with an adjacent pine plantation in southeastern Brazil

We investigated the influence of Pinus afforestation on the structure of leaf-litter ant communities in the southeastern Brazilian Atlantic Forest, studying an old secondary forest and a nearly 30 year-old never managed Pinus elliottii reforested area. A total of 12,826 individual ants distributed among 95 species and 32 genera were obtained from 50 1 m² samples/ habitat. Of these, 60 species were recorded in the pine plantation and 82 in the area of Atlantic forest; almost 50% of the species found in the secondary forest area were also present in the pine plantation. The number of species per sample was significantly higher in the secondary forest than in the pine plantation. Forest-adapted taxa are the most responsible for ant species richness differences between areas, and the pine plantation is richer in species classified as soil or litter omnivorous-dominants. The specialized ant predators registered in the pine plantation, as seven Dacetini, two Basiceros, two Attini and two Discothyrea, belong to widely distributed species. The NMDS (non-metric multidimensional scaling) ordination also suggested strong differences in similarity among samples of the two areas. Furthermore, this analysis indicated higher sample heterogeneity in the secondary forest, with two clusters of species, while in the pine plantation the species belong to a single cluster. We applied the ant mosaic hypothesis to explain the distribution of the leaf-litter fauna and spatial autocorrelation tests among samples. We argue that the results are likely related to differences in quality and distribution of the leaf-litter between the pine plantation and the secondary area.