Li(2)Ti(6)O(13) and H(2)Ti(6)O(13) were easily synthesized from Na(2)Ti(6)O(13) by successive Na(+)-Li(+)-H(+) ion exchange. The crystal structures of Na(2)Ti(6)O(13), Li(2)Ti(6)O(13) and ...H(2)Ti(6)O(13) were investigated using neutron powder diffraction. Monovalent A(+) cations (Na, Li and H) have been located using difference Fourier analysis. Although monoclinic lattice parameters (space group C2/m) of the three titanates remain almost unchanged with retention of the basic Ti(6)O(13)(2-) network, monovalent Na, Li and H cations occupy different sites in the tunnel space. By comparing the structural details concerning the A(+) oxygen coordination, i.e. NaO(8) square prismatic coordination, LiO(4) square planar coordination and covalently bond H atoms, with results from (23)Na, (7)Li and (1)H NMR spectroscopy we were able to obtain a more detailed insight into the respective local distortions and anharmonic motions. We were able to show that the site that the A(+) cation occupies in the hexatitanate channel structure strongly influences the lithium insertion properties of these compounds and therefore their usefulness as electrode materials for energy storage.
En los últimos años se ha producido un espectacular aumento de los estudios y trabajos realizados sobre la migración en España, en la medida en la que ha habido un aumento de la población extranjera ...residente en el país así como una mayor visibilización social de la misma. En este marco general, en la literatura sobre migraciones se ha ido produciendo un giro en la orientación de buena parte de estos estudios que corresponde a la progresiva madurez que estas investigaciones han ido alcanzando.
A new family of non-toxic biocides based on low melting point (1250 degree C) transparent glasses with high content of ZnO (15-40wt%) belonging to the miscibility region of the B2O3-SiO2-Na2O-ZnO ...system has been developed. These glasses have shown an excellent biocide activity (logarithmic reduction >3) against Gram- (E. coli), Gram+ (S. aureus) and yeast (C. krusei); they are chemically stable in different media (distilled water, sea-like water, LB and DMEN media) as well as biocompatible. The cytotoxicity was evaluated by the Neutral Red Uptake using NIH-3T3 (mouse embryonic fibroblast cells) and the cell viability was >80%. These new glasses can be considered in several and important applications in the field of inorganic non-toxic biocide agents such as medical implants, surgical equipment, protective apparels in hospitals, water purifications systems, food packaging, food storages or textiles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dennettine, a new 2,6-dimethoxychromone and three known phenanthrene alkaloids (uvariopsine, stephenanthrine and argentinine) in addition to the phenolic and known compound vanillin were isolated ...from the roots of Dennettia tripetala. Their structures were determined by physical and spectroscopical one dimensional (1D) and 2D-NMR analysis, including heteronuclear multiple bond correlation and nuclear Overhauser enhancement spectroscopy.
We show how B-series may be used to derive in a systematic way the analytical expressions of the high-order stroboscopic averaged equations that approximate the slow dynamics of highly oscillatory ...systems. For first-order systems we give explicitly the form of the averaged systems with
errors,
j
=1,2,3 (2
π
ε
denotes the period of the fast oscillations). For second-order systems with large
forces, we give the explicit form of the averaged systems with
errors,
j
=1,2. A variant of the Fermi–Pasta–Ulam model and the inverted Kapitsa pendulum are used as illustrations. For the former it is shown that our approach establishes the adiabatic invariance of the oscillatory energy. Finally we use B-series to analyze multiscale numerical integrators that implement the method of averaging. We construct integrators that are able to approximate not only the simplest, lowest-order averaged equation but also its high-order counterparts.
The paper considers non-autonomous oscillatory systems of ordinary differential equations with
d
≥1 non-resonant constant frequencies
ω
1
,…,
ω
d
. Formal series like those used nowadays to analyze ...the properties of numerical integrators are employed to construct higher-order averaged systems and the required changes of variables. With the new approach, the averaged system and the change of variables consist of vector-valued functions that may be written down immediately and scalar
coefficients
that are universal in the sense that they do not depend on the specific system being averaged and may therefore be computed once and for all given
ω
1
,…,
ω
d
. The new method may be applied to obtain a variety of averaged systems. In particular, we study the
quasi-stroboscopic
averaged system characterized by the property that the true oscillatory solution and the averaged solution coincide at the initial time. We show that quasi-stroboscopic averaging is a geometric procedure, because it is independent of the particular choice of co-ordinates used to write the given system. As a consequence, quasi-stroboscopic averaging of a canonical Hamiltonian (respectively, of a divergence-free) system results in a canonical (respectively, in a divergence-free) averaged system. We also study the averaging of a family of near-integrable systems where our approach may be used to construct explicitly
d
formal first integrals for both the given system and its quasi-stroboscopic averaged version. As an application we construct three first integrals of a system that arises as a nonlinear perturbation of five coupled harmonic oscillators with one slow frequency and four resonant fast frequencies.
The origin of the intricate nanostructure of La
0.5−
x
Li
0.5−
x
Sr
2
x
TiO
3
(0.0625 ≤
x
≤ 0.25) perovskite-type Li ion conductors has been investigated. Reciprocal space electron diffraction ...analysis and aberration-corrected STEM by combining annular bright field (ABF) and high angle annular dark field (HAADF) imaging methods have been used to elucidate the complex local atomic arrangements which cannot be adequately described by average crystal structure models. Two different local crystal structures endotaxially-related at the nanoscale without compositional phase separation associated, constituting the crystals. Self-organization of the two different ordered regions arises as a consequence of the competition between two distortive forces in the crystal lattice: octahedral tilting and second-order Jahn-Teller distortion of TiO
6
octahedra. Changes in the distribution of A species suggest different Li ion conduction pathways for the two structures and this scenario has difficult long-range Li mobility. The detailed study performed may be helpful in understanding the local structural changes affecting Li and their relation to the conductivity in LLTO-derived ionic conductors.
The intricate nanostructure of La
0.5−
x
Li
0.5−
x
Sr
2
x
TiO
3
Li-ion conductors has been elucidated. Advanced transmission electron microscopy has allowed investigation where average structure models cannot account for the changeable local atomic arrangements detected.
Li sub(0.5-y)Na sub(y)La sub(0.5)Nb sub(2)O sub(6) samples (y= 0-0.5) were synthesized by the solid-state reaction (SSR). Structural features of the a sub(p) a sub(p) 2a sub(p) perovskite series were ...investigated by X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and density functional theory DFT simulation techniques. The location of La ions was assessed by Rietveld analysis of XRD patterns, and structural sites occupied by Li, Na and Nb ions investigated by MAS-NMR spectroscopy. In Li-rich samples, La and Li ions are preferentially located at z/c= 0 planes, but as the Na content increases, La and Na occupy both z/c= 0 and 0.5 planes. To analyze La and Li possible arrangements, different structural models have been considered in DFT simulations, confirming the cation ordering deduced from XRD patterns and the impediment of Na ions to move through square windows of the perovskite. The structural information deduced has been used to discuss transport properties deduced by Impedance Spectroscopy (IS). In Li rich samples, the La arrangement in alternating planes favors a 2D-dimensional Li conductivity. The incorporation of Na in two crystallographic planes reduces La ordering and increases Li conductivity. La disorder favours the change from 2D to 3D Li conductivity, which could explain the broad maximum detected in the Li conductivity as a function of the Na content.
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