University of St Andrews

About: University of St Andrews is a education organization based out in St Andrews, Fife, United Kingdom. It is known for research contribution in the topics: Population & Laser. The organization has 16260 authors who have published 43364 publications receiving 1636072 citations. The organization is also known as: St Andrews University & University of St. Andrews.

Nanoparticulate TiO2(B): An Anode for Lithium‐Ion Batteries

Abstract: Titanates are being intensively investigated as anodes for lithium-ion batteries due to their superior safety and rate capability compared with graphite, although their higher voltage lowers the overall energy density of the lithium-ion cell. Li4Ti5O12 spinel is now used in commercial lithium-ion batteries. TiO2 possesses twice the theoretical specific capacity (335 mAh g ) compared with Li4Ti5O12 (175 mAhg ), i.e., is comparable to graphite, rendering TiO2 potentially attractive as an anode for Li-ion batteries. 3] TiO2(B) can accommodate more lithium than any other TiO2 polymorph as a bulk material (micrometer-sized particles). 4] It has been shown that nanostructured forms of TiO2(B) enhance rate capability compared to the bulk, with nanotubes of TiO2(B) or TiO2(B)/anatase microspheres exhibiting the highest rate capability to date. Their performance is exceeded by nanoparticulate TiO2(B) described here. Nanoparticulate TiO2(B) was synthesized by a procedure described in the Experimental Section. Briefly, Ti metal is dissolved in a mixture of H2O2 and NH3 in water, to which glycolic acid is added, forming a titanium glycolate complex. This is subjected to hydrothermal treatment at 160 8C for 30 min. The resulting solid was finally calcined in dry air at 300 8C for 1 h. The powder X-ray diffraction pattern (PXRD) of nanoparticulate TiO2(B) is shown in Figure 1, where it is compared with standard TiO2(B). The small particle dimensions necessarily result in peak broadening but the powder diffraction pattern follows the same intensity distribution as that of the bulk material. Confirmation that the nanoparticulate powder is TiO2(B) was obtained by high-resolution TEM (Figure 2); lattice spacings of 0.357 nm and 0.619 nm corresponding to the (110) and (001) reflections from the TiO2(B) structure (ICDD 046-1237) are observed. O NMR spectra of O-enriched TiO2 clearly show characteristic resonances from the three oxygen coordination environments OTi2, OTi3, and OTi4 in intensity ratios of approximately 1:2:1, which is characteristic of the TiO2(B) polymorph (Supporting Information, Figure S2). Rutile and anatase both contain only OTi3 environments. The TEM data demonstrate that the material is composed of nanoparticles of ca. 2.5 4.3 nm size (based on analysis of 100 nanoparticles), with a relatively narrow size distribution, and that form agglomerates of 0.3–3 mm (Figure 2a and S1). The BET surface area determined from N2 adsorption is 251 m g 1 (pore volume 0.12 cm g ) whereas, based on the primary particle size of 2.5 2.5 4.3 nm, the predicted surface area is 567 m g , i.e., more than twice the observed value and consistent with aggregation of the primary particles into porous agglomerates. One problem that often besets nanoparticles is the need to employ molecules (e.g. surfactants) in the synthesis to inhibit particle size growth. Such molecules, if they remain on the Figure 1. PXRD pattern of the TiO2(B) nanoparticles. Bulk TiO2(B) from the ICDD database is shown for comparison.

The ATLAS3D project - XXV. Two-dimensional kinematic analysis of simulated galaxies and the cosmological origin of fast and slow rotators

Abstract: We present a detailed two-dimensional stellar dynamical analysis of a sample of 44 cosmological hydrodynamical simulations of individual central galaxies with stellar masses of 2 × 1010 M⊙ ≲ M* ≲ 6 × 1011 M⊙. Kinematic maps of the stellar line-of-sight velocity, velocity dispersion and higher order Gauss-Hermite moments h3 and h4 are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the λR-parameter. The velocity, velocity dispersion, h3 and h4 fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS3D survey. This includes fast (regular), slow and misaligned rotation, hot spheroids with embedded cold disc components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present-day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a significant influence on the rotation properties resulting in both a spin-down as well as a spin-up of the merger remnant. Lower mass galaxies with significant (≳18 per cent) in situ formation of stars since z ≈ 2, or with additional gas-rich major mergers - resulting in a spin-up - in their formation history, form elongated (ɛ ˜ 0.45) fast rotators (λR ˜ 0.46) with a clear anticorrelation of h3 and v/σ. An additional formation path for fast rotators includes gas-poor major mergers leading to a spin-up of the remnants (λR ˜ 0.43). This formation path does not result in anticorrelated h3 and v/σ. The formation histories of slow rotators can include late major mergers. If the merger is gas rich, the remnant typically is a less flattened slow rotator with a central dip in the velocity dispersion. If the merger is gas poor, the remnant is very elongated (ɛ ˜ 0.43) and slowly rotating (λR ˜ 0.11). The galaxies most consistent with the rare class of non-rotating round early-type galaxies grow by gas-poor minor mergers alone. In general, more massive galaxies have less in situ star formation since z ˜ 2, rotate slower and have older stellar populations. We discuss general implications for the formation of fast and slowly rotating galaxies as well as the weaknesses and strengths of the underlying models.

Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination.

Abstract: Chlorinated natural products include vancomycin and cryptophycin A. Their biosynthesis involves regioselective chlorination by flavin-dependent halogenases. We report the structural characterization of tryptophan 7-halogenase (PrnA), which regioselectively chlorinates tryptophan. Tryptophan and flavin adenine dinucleotide (FAD) are separated by a 10 angstrom-long tunnel and bound by distinct enzyme modules. The FAD module is conserved in halogenases and is related to flavin-dependent monooxygenases. On the basis of biochemical studies, crystal structures, and by analogy with monooxygenases, we predict that FADH2 reacts with O2 to make peroxyflavin, which is decomposed by Cl-. The resulting HOCl is guided through the tunnel to tryptophan, where it is activated to participate in electrophilic aromatic substitution.