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41.
M. Goreti F. Sales M. Carmo V. F. Vaz Cristina Delerue-Matos Sofia A. A. Almeida M. Fátima Barroso Helder A. O. Ferreira 《International journal of environmental analytical chemistry》2013,93(1):37-49
Abstract The sorption of pentachlorophenol (PCP) onto the aquatic humic matter (HM) for very wide concentration range (60 ng PCP/L - 1 mg PCP/L) was investigated. The binding affinity increased significantly with the acidity of the solution. The dissolved organic carbon (DOC) normalized sorption coefficients (log KOC) of PCP were 3.39 at pH 3, 3.19 at pH 5.5 and 3.01 at pH 7. The binding of PCP took place via a two step binding mechanism: the rapid first step was followed by a second much slower one indicating that the surface of the HM is very heterogeneous containing binding sites with different binding affinities. It was possible to obtain a “fully saturated” HM-PCP adduct (also all possible micro-voids of the HM were occupied) in a very high PCP concentration. The log KOC value for the whole concentration range was slightly smaller than that obtained under very low PCP concentration level. The Langmuir isotherm was the most suitable for the whole concentration range of PCP, whereas the Freundlich model was the most suitable for the low concentration range of PCP. The dissimilarities between different sorption models were as a whole marginal and thus it is possible without significant loss of information to describe the PCP sorption with a linear model. The results verify that the conventional humic (HA) and fulvic (FA) acid type humic solutes of fresh waters account for the main part of the PCP sorption. 相似文献
42.
Helder Fleury Pinheiro Attílio José Giarola Carlos Le?nidas da Silva Souza Sobrinho 《International Journal of Infrared and Millimeter Waves》1995,16(11):1965-1975
The formulation is developed in the frequency domain and the finite difference method is used for the numerical solution of the scalar wave equation, written in terms of the transverse components of the magnetic field. As a result a conventional eigenvalue problem is obtained without the presence of spurious modes due to the implicit inclusion of the divergence of the magnetic field equal to zero. The formulation is developed to include biaxial anisotropic dielectrics with an index profile varying arbitrarily in the cross section of the waveguide under analysis. This formulation is then applied to the analysis of the influence on the dispersion characteristics of the dimensions of asymmetric coupled rectangular uniaxial anisotropic dielectric waveguides. As expected, the reduction of the height or the width of one of the rectangular dielectric waveguides causes the dispersion curves to move towards higher frequencies. 相似文献
43.
Rita Araújo Tatiana J. Carneiro Paula Marinho Marisa Maltez da Costa Ana Roque Odete A. B. da Cruz e Silva Maria Helena Fernandes Paula M. Vilarinho Ana M. Gil 《Magnetic resonance in chemistry : MRC》2019,57(11):919-933
Untargeted nuclear magnetic resonance (NMR) metabolomics was employed, for the first time to our knowledge, to characterize the metabolome of human osteoblast (HOb) cells and extracts in the presence of non-poled or negatively poled poly-L-lactic acid (PLLA). The metabolic response of these cells to this polymer, extensively used in bone regeneration strategies, may potentially translate into useful markers indicative of in vivo biomaterial performance. We present preliminary results of multivariate and univariate analysis of NMR spectra, which have shown the complementarity of lysed cells and extracts in terms of information on cell metabolome, and unveil that, irrespective of poling state, PLLA-grown cells seem to experience enhanced oxidative stress and activated energy metabolism, at the cost of storage lipids and glucose. Possible changes in protein and nucleic acid metabolisms were also suggested, as well as enhanced membrane biosynthesis. Therefore, the presence of PLLA seems to trigger cell catabolism and anti-oxidative protective mechanisms in HOb cells, while directing them towards cellular growth. This was not sufficient, however, to lead to a visible cell proliferation enhancement in the presence of PLLA, although a qualitative tendency for negatively poled PLLA to be more effective in sustaining cell growth than non-poled PLLA was suggested. These preliminary results indicate the potential of NMR metabolomics in enlightening cell metabolism in response to biomaterials and their properties, justifying further studies of the fine effects of poled PLLA on these and other cells of significance in tissue regeneration strategies. 相似文献
44.
W. Kleemann S. Bedanta P. Borisov V. V. Shvartsman S. Miga J. Dec A. Tkach P. M. Vilarinho 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(3):407-410
“Multiglass” materials with simultaneous occurrence of
two different glassy states extend the frame of conventional
multiferroicity, which is devoted to crystalline materials with coexisting
uniform long-range electric and magnetic ordering. The concept applies to
Sr0.98Mn0.02TiO3 ceramics, where A-site substituted Mn2+
ions are at the origin of both a polar and a spin cluster glass. Spin
freezing is initiated below the dipolar glass temperature,
Tg
e ≈ 38 K, which is seemingly indicated by a divergence
of the nonlinear susceptibility, χ3. Below Tg
m ≈ 34 K both glass phases are independently verified by memory and
rejuvenation effects. Biquadratic interaction of the Mn2+ spins with
ferroelectric correlations of their off-center pseudospins in the incipient
ferroelectric host crystal SrTiO3 explains the high spin glass
temperature and comparably strong third-order magnetoelectric coupling
between the polar and the magnetic degrees of freedom. Preliminary results
on the related compound K0.97Mn0.03TaO3 favorably comply with
the magnetoelectric multiglass concept. 相似文献
45.
Johan M. Carlsson Helder S. Domingos Bo Hellsing Paul D. Bristowe 《Interface Science》2001,9(3-4):143-148
We have investigated Bi doping in the bulk and in a = 13 tilt grain boundary in ZnO using ab-initio DFT-calculations. We obtain a negative segregation energy suggesting that bismuth accumulates in the grain boundary. The Bi-atom causes considerable atomic displacements in the grain boundary increasing the local Bi–O bond length and attracting an O-atom on the opposite side of the structural unit in the grain boundary. The results suggest the formation of a Bi–rich phase in the grain boundary. The Bi-atoms act as donors and the conduction electrons are quasi-localised in the grain boundary region. 相似文献
46.
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48.
We give an application of a topological dynamics version of multidimensional Brown’s lemma to tiling theory: given a tiling of an Euclidean space and a finite geometric pattern of points $F$ , one can find a patch such that, for each scale factor $\lambda $ , there is a vector $\vec {t}_\lambda $ so that copies of this patch appear in the tilling “nearly” centered on $\lambda F+\vec {t}_\lambda $ once we allow “bounded perturbations” in the structure of the homothetic copies of $F$ . Furthermore, we introduce a new unifying setting for the study of tiling spaces which allows rather general group “actions” on patches and we discuss the local isomorphism property of tilings within this setting. 相似文献
49.
Tkach A Almeida A Moreira JA Chaves MR Espinha A Vilarinho PM 《J Phys Condens Matter》2012,24(4):045906
Polar behaviour in K(1-x)Li(x)TaO(3) ceramics with x = 0:02, 0.05 and 0.10, processed by the conventional solid state method, is studied by Raman spectroscopy and thermally stimulated depolarization current (TSDC) techniques between 10 and 290 K. The TO1 mode of KTaO(3) is revealed to harden in the whole temperature range and to split in the low-temperature range by Li doping. One splitting is observed for x = 0:02 and two consequent splittings are detected for x = 0:05 and 0.10. The temperatures, where TO1 mode splitting occurs, are found to correspond to those of the peaks of TSDC, and hence to the onset of the electric polarization. Such behaviour provides evidence for the order-disorder ferroelectric phase transition induced in KTaO(3) by lithium doping, which emerges from deformations of the cubic phase developed on cooling either in one (for x = 0:02) or two steps (for x = 0:05 and 0.10). 相似文献
50.
Varadwaj PR Cukrowski I Perry CB Marques HM 《The journal of physical chemistry. A》2011,115(24):6629-6640
The structure of the complexes of the type [Ni(L)(H(2)O)(2)](2+), where L is an amino alcohol ligand, L = N,N'-bis(2-hydroxyethyl)-ethane-1,2-diamine (BHEEN), N,N'-bis(2-hydroxycyclohexyl)-ethane-1,2-diamine (Cy(2)EN), and N,N'-bis(2-hydroxycyclopentyl)-ethane-1,2-diamine, (Cyp(2)EN) were investigated at the X3LYP/6-31+G(d,p) level of theory both in the gas phase and in solvent (CPCM model) to gain insight into factors that control the experimental log K(1) values. We find that (i) analyses based on Bader's quantum theory of atoms in molecules (QTAIM) are useful in providing significant insight into the nature of metal-ligand bonding and in clarifying the nature of weak "nonbonded" interactions in these complexes and (ii) the conventional explanation of complex stability in these sorts of complexes (based on considerations of bond lengths, bite angles and H-clashes) could be inadequate and indeed might be misleading. The strength of metal-ligand bonds follows the order Ni-N > Ni-OH ≥ Ni-OH(2); the bonds are predominantly ionic with some covalent character decreasing in the order Ni-N > Ni-OH > Ni-OH(2), with Ni-OH(2) being close to purely ionic. We predict that the cis complexes are preferred over the trans complexes because of (i) stronger bonding to the alcoholic O-donor atoms and (ii) more favorable intramolecular interactions, which appear to be important in determining the conformation of a metal-ligand complex. We show that (i) the flexibility of the ligand, which controls the Ni-OH bond length, and (ii) the ability of the ligand to donate electron density to the metal are likely to be important factors in determining values of log K(1). We find that the electron density at the ring critical point of the cyclopentyl moieties in Cyp(2)EN is much higher than that in the cyclohexyl moieties of Cy(2)EN and interpret this to mean that Cyp(2)EN is a poorer donor of electron density to a Lewis acid than Cy(2)EN. 相似文献