Blue phase III widening in CE6-dispersed surface-functionalised CdSe nanoparticles

The phase transition behaviour of the chiral liquid crystal CE6 doped with spherical surface-functionalised CdSe nanoparticles has been examined by means of high-resolution adiabatic scanning calorimetry and polarising microscopy. The addition of nanoparticles results in an essentially stabilised blue phase III. The phase diagram is displayed upon heating and cooling and the enthalpy changes involved in the conversion between the blue phases are determined. The dispersion of functionalised nanoparticles is prominent for the stabilisation of blue phase III, which is potentially useful for applications, especially if applied on liquid crystals that exhibit blue phases close to room temperature.     

Perception of pitch location within a speaker's range: Fundamental frequency, voice quality and speaker sex

How are listeners able to identify whether the pitch of a brief isolated sample of an unknown voice is high or low in the overall pitch range of that speaker? Does the speaker's voice quality convey crucial information about pitch level? Results and statistical models of two experiments that provide answers to these questions are presented. First, listeners rated the pitch levels of vowels taken over the full pitch ranges of male and female speakers. The absolute f0 of the samples was by far the most important determinant of listeners' ratings, but with some effect of the sex of the speaker. Acoustic measures of voice quality had only a very small effect on these ratings. This result suggests that listeners have expectations about f0s for average speakers of each sex, and judge voice samples against such expectations. Second, listeners judged speaker sex for the same speech samples. Again, absolute f0 was the most important determinant of listeners' judgments, but now voice quality measures also played a role. Thus it seems that pitch level judgments depend on voice quality mostly indirectly, through its information about sex. Absolute f0 is the most important information for deciding both pitch level and speaker sex.     

Energetic and spectral properties of triple photon downconversion in a phase-matched KTiOPO4 crystal

We measured the spectrum and energy of infrared triple photons generated in a phase-matched KTiOPO4 crystal pumped by picosecond beams at 532 and 1662 nm. The experimental data are in good agreement with our model, taking into account the spectral linewidths of the incident beams as well as a parasitic Kerr effect.     

Preferential surface oxidation of Gd in Gd5Ge4

Gd oxidizes preferentially at the (0 1 0) surface of Gd₅Ge₄. This is consistent with thermodynamic data for the bulk oxides. Upon oxidation in vacuum, the gadolinium oxide displaces or covers the Ge. Oxidation is more extensive at 600 K than at 300 K, because more oxygen is incorporated into the surface and the shift of the Gd binding energy is larger.     

Raman spectroscopic characterization of the magnesium content in amorphous calcium carbonates

A series of Mg‐bearing synthetic amorphous calcium carbonates (ACC) were characterized by Raman spectroscopy. The spectra showed a systematic increase in the carbonate ν₁ peak position from the control samples that contained 0.0 mol % MgCO₃ to samples that contained up to 43 mol % MgCO₃. The relationship is best described by the function: mol % MgCO₃ = (ν₁ – 1079.66) / 0.2017. The Mg content is equally well‐predicted by a correlation with the instrumentally corrected ν₁ full width at half maximum that is quantified by: mol % MgCO₃ = (ν₁ – 23.26) / 0.1969. An analysis of the Raman data collected for ACC combined with insights from crystalline materials suggests that compositional dependencies arise from changes in the local metal–oxygen bonds as Mg substitutes for Ca. The calibrations described here provide a rapid and nondestructive means of determining the Mg content of ACC, with additional advantages of minimal sample preparation and a high degree of lateral spatial resolution (approximately 1 µm). This method may be appropriate for investigations of heterogeneous samples such as biominerals. Copyright © 2011 John Wiley & Sons, Ltd.     

Exact join detection for convex polyhedra and other numerical abstractions

Deciding whether the union of two convex polyhedra is itself a convex polyhedron is a basic problem in polyhedral computations; having important applications in the field of constrained control and in the synthesis, analysis, verification and optimization of hardware and software systems. In such application fields though, general convex polyhedra are just one among many, so-called, numerical abstractions, which range from restricted families of (not necessarily closed) convex polyhedra to non-convex geometrical objects. We thus tackle the problem from an abstract point of view: for a wide range of numerical abstractions that can be modeled as bounded join-semilattices—that is, partial orders where any finite set of elements has a least upper bound—we show necessary and sufficient conditions for the equivalence between the lattice-theoretic join and the set-theoretic union. For the case of closed convex polyhedra—which, as far as we know, is the only one already studied in the literature—we improve upon the state-of-the-art by providing a new algorithm with a better worst-case complexity. The results and algorithms presented for the other numerical abstractions are new to this paper. All the algorithms have been implemented, experimentally validated, and made available in the Parma Polyhedra Library.     

Can density functional theory (DFT) be used as an aid to a deeper understanding of tandem mass spectrometric fragmentation pathways?

Prediction of tandem mass spectrometric (MS/MS) fragmentation for non‐peptidic molecules based on structure is of immense interest to the mass spectrometrist. If a reliable approach to MS/MS prediction could be achieved its impact within the pharmaceutical industry could be immense. Many publications have stressed that the fragmentation of a molecular ion or protonated molecule is a complex process that depends on many parameters, making prediction difficult. Commercial prediction software relies on a collection of general heuristic rules of fragmentation, which involve cleaving every bond in the structure to produce a list of ‘expected’ masses which can be compared with the experimental data. These approaches do not take into account the thermodynamic or molecular orbital effects that impact on the molecule at the point of protonation which could influence the potential sites of bond cleavage based on the structural motif. A series of compounds have been studied by examining the experimentally derived high‐resolution MS/MS data and comparing it with the in silico modelling of the neutral and protonated structures. The effect that protonation at specific sites can have on the bond lengths has also been determined. We have calculated the thermodynamically most stable protonated species and have observed how that information can help predict the cleavage site for that ion. The data have shown that this use of in silico techniques could be a possible way to predict MS/MS spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Publisher’s note

Experimental Techniques -