Dissociation of individual isotopic peaks: predicting isotopic distributions of product ions in MSn

Traditional practice in tandem mass spectrometry is to select the mono-isotopic ion for dissociation. However, high molecular weight compounds often have weak mono-isotopic peaks, which limit that approach. Furthermore, the traditional approach does not take advantage of the very rich store of information available in the isotopic patterns from the dissociation of individual non-mono-isotopic peaks. Interpretation of these isotopic patterns requires a theory capable of predicting the patterns. However, a general theory for the prediction of these patterns has been lacking. This paper shows that the patterns can be obtained from a certain vector product, the outer product, of the full isotopic distribution of the product ion with the full isotopic distribution of the complementary product. Unlike previous approaches, the method is applicable to systems of arbitrary isotopic complexity. The patterns are potentially useful for elucidation of dissociation pathways, elemental composition, and chemical structure. The paper presents several applications of the theory.     

Frequency response design of uncertain systems using performance indices and meta-models

Systems that are operated near their resonance frequencies experience vibrations that can lead to impaired performance, overstressing, fatigue fracture and adverse human reactions. Frequency response (FR) analysis can be invoked to mitigate the effects. When components of a system are described by random variables, modal frequencies and modal shapes, or, amplitudes and phases, are also random variables and the frequency response (FR) design of the system becomes more complex since it requires the solution of a frequency-variant probability problem. This paper presents a methodology to provide the frequency response design of uncertain systems using a transfer function approach. The methodology is found to be robust, expandable and flexible and can be applied to multi-disciplinary systems with n-dof and multiple design constraints. The novelty of the approach is the creation of a frequency-invariant probability problem through: (a) the discretization of the frequency band of interest into multiple contiguous point frequencies, (b) the introduction of new performance indices that measure the probability of success over the entire frequency band, and (c) the introduction of explicit meta-models to provide sufficiently fast probability evaluations through Monte Carlo simulation. The key to the performance indices are limit-state functions formed at all discrete, contiguous, frequencies. Each limit-state function establishes a conformance region in terms of the random design variables. The probabilities of the conformance regions are correctly combined to provide a single series-system index to be maximized by adjusting distribution parameters. The simple explicit meta-model is based on Kriging and performance measures at arbitrary design sets are efficiently calculated. Error analysis suggests ways to predict and control the errors with regards to meta-model fitting and probability calculations and so the method appears sufficiently accurate for engineering applications. The proposed methodology has applications in numerous areas such as electrical filters and structural mechanics – all with n-dof and multiple responses. The Performance indices can be evaluated at any frequency over any number of frequency ranges. A case study of a vibration absorber mechanism shows how the new methodology provides an improved and timely design with controllable accuracy when compared with previous proposals that employed modal frequencies.     

Band Assignments in the Infrared Spectra of Some Metal(II) Complexes of Pyrazine

The IR spectra of [Co(pz)₂X₂]_n (pz = pyrazine; X = C1, Br, I), [Cu(pz)X₂]_n (X = C1, Br), [Cu(pz)₂](C10₄)₂ and [Cu(py)₄] (C10₄)₂ (py = pyridine) derived from deuterated pz and py, and their unlabelled analogues are discussed. Assignments of the metal-ligand vibrations are based on the effects of the isotopic substitutions.     

The Industrial Research Program at the European Synchrotron Radiation Facility: The Past,the Present,and Challenges for the Future

The challenge of harnessing the power of third-generation synchrotron sources for industrial R&D has been taken up by the ESRF ever since the first users arrived in 1994. However, working with industry has its own special requirements, and often mismatches and clashes between a traditional scientific “ivory tower” culture and the needs of the market-driven commercial world. After more than 15 years of industrial research at the ESRF, during which strong industrial programs in protein crystallography and microtomography have been established, we continue to build bridges between the two worlds.     

Hemisystems of small flock generalized quadrangles

In this paper, we describe a complete computer classification of the hemisystems in the two known flock generalized quadrangles of order (5², 5) and give numerous further examples of hemisystems in all the known flock generalized quadrangles of order (s ², s) for s ≤ 11. By analysing the computational data, we identify two possible new infinite families of hemisystems in the classical generalized quadrangle H(3, s ²).     

Prior decisions and experiences about mathematics of students in bridging courses

We report on the survey responses of 51 students attending mathematics bridging courses at a major Australian university, investigating what mathematics, if any, these students had studied in the senior years of schooling and what factors affected their decisions about the level of mathematics chosen. Quantitative findings are augmented by qualitative responses to open-ended questions in the survey as well as excerpts from follow-up emails. The findings show that the major reasons for students taking lower levels of mathematics in senior year(s), or dropping mathematics, include finding enough time for non-mathematics subjects, confidence in mathematical capability, advice and maximizing potential ranking for university admission.     

On L-spaces and left-orderable fundamental groups

Examples suggest that there is a correspondence between L-spaces and three-manifolds whose fundamental groups cannot be left-ordered. In this paper we establish the equivalence of these conditions for several large classes of manifolds. In particular, we prove that they are equivalent for any closed, connected, orientable, geometric three-manifold that is non-hyperbolic, a family which includes all closed, connected, orientable Seifert fibred spaces. We also show that they are equivalent for the twofold branched covers of non-split alternating links. To do this we prove that the fundamental group of the twofold branched cover of an alternating link is left-orderable if and only if it is a trivial link with two or more components. We also show that this places strong restrictions on the representations of the fundamental group of an alternating knot complement with values in $\text{ Homeo}_+(S^1)$ .     

Investigating statistical approximations with computer graphics

This paper describes the use of interactive computer graphics software to explore the notion of the approximation of one statistical distribution by another. In particular, the authors illustrate how such programs can be used to investigate the normal approximation to the binomial distribution, the Poisson approximation to the binomial distribution, the convergence of t‐distributions to the normal distribution, and the limiting behaviour of the chi‐squared distribution. The discussions include possible methods using such programs, either in a classroom setting on a demonstration basis or on an individual student basis for independent study in a computer laboratory setting.     

Nonaqueous synthesis of TiO2 nanocrystals using TiF4 to engineer morphology, oxygen vacancy concentration, and photocatalytic activity

Control over faceting in nanocrystals (NCs) is pivotal for many applications, but most notably when investigating catalytic reactions which occur on the surfaces of nanostructures. Anatase titanium dioxide (TiO(2)) is one of the most studied photocatalysts, but the shape dependence of its activity has not yet been satisfactorily investigated and many questions still remain unanswered. We report the nonaqueous surfactant-assisted synthesis of highly uniform anatase TiO(2) NCs with tailorable morphology in the 10-100 nm size regime, prepared through a seeded growth technique. Introduction of titanium(IV) fluoride (TiF(4)) preferentially exposes the {001} facet of anatase through in situ release of hydrofluoric acid (HF), allowing for the formation of uniform anatase NCs based on the truncated tetragonal bipyramidal geometry. A method is described to engineer the percentage of {001} and {101} facets through the choice of cosurfactant and titanium precursor. X-ray diffraction studies are performed in conjunction with simulation to determine an average NC dimension which correlates with results obtained using electron microscopy. In addition to altering the particle shape, the introduction of TiF(4) into the synthesis results in TiO(2) NCs that are blue in color and display a broad visible/NIR absorbance which peaks in the infrared (λ(max) ≈ 3400 nm). The blue color results from oxygen vacancies formed in the presence of fluorine, as indicated by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) studies. The surfactants on the surface of the NCs are removed through a simple ligand exchange procedure, allowing the shape dependence of photocatalytic hydrogen evolution to be studied using monodisperse TiO(2) NCs. Preliminary experiments on the photoreforming of methanol, employed as a model sacrificial agent, on platinized samples resulted in high volumes of evolved hydrogen (up to 2.1 mmol h(-1) g(-1)) under simulated solar illumination. Remarkably, the data suggest that, under our experimental conditions, the {101} facets of anatase are more active than the {001}.     

Giant magnetoelastic effect at the opening of a spin-gap in Ba3BiIr2O9

As compared to 3d (first-row) transition metals, the 4d and 5d transition metals have much more diffuse valence orbitals. Quantum cooperative phenomena that arise due to changes in the way these orbitals overlap and interact, such as magnetoelasticity, are correspondingly rare in 4d and 5d compounds. Here, we show that the 6H-perovskite Ba(3)BiIr(2)O(9), which contains 5d Ir(4+) (S = 1/2) dimerized into isolated face-sharing Ir(2)O(9) bioctahedra, exhibits a giant magnetoelastic effect, the largest of any known 5d compound, associated with the opening of a spin-gap at T* = 74 K. The resulting first-order transition is characterized by a remarkable 4% increase in Ir-Ir distance and 1% negative thermal volume expansion. The transition is driven by a dramatic change in the interactions among Ir 5d orbitals, and represents a crossover between two very different, competing, ground states: one that optimizes direct Ir-Ir bonding (at high temperature), and one that optimizes Ir-O-Ir magnetic superexchange (at low temperature).