Introduction to the EU-network on trace element speciation: preparing for the 21st century

The main objective of the EU-network is to bring together scientists with a background in analytical chemistry interested in speciation method development with potential users from industry and representatives from legislative bodies. The network started on 1/10/1997 for a duration of 2 years. A series of meetings are being organised to debate all the important questions for collecting information on environmental, food and occupational health aspects of speciation and to define possible future projects. The findings and conclusions will be summarised as a series of general papers that will be published in the open literature, recapitulating the essential information gathered to date, outlining the state of the art for each topic and recommending legislative actions. A first meeting was held in Überlingen, Germany on 5–6 December 1997. The representatives from industry explained their interest in the network and the participants from the academic and national institutes gave a state-of-the-art presentation of their research. Out of this, a program was compiled for the following meeting in Segovia from 16 to 20 March 1998. The topics dealt with were: organotin compounds in the environmental session; the speciation and bioavailability of trace element species (Cr, Fe, Se), the quality of the data and new legislation in the food session; and identification of inhaled particles and the search for bioindicators for exposure to Ni and Pt in the occupational health/hygiene session. In each session about half of the participants came from industry. The delegates agreed on a list of priorities in speciation analysis. A www-page has been created: hhtp://www. speciation 21.plymouth.ac.uk. Everybody interested in adding information to the page is requested to mail this to lpitts@plymouth.ac.uk     

Anthropogenic ozone,acids and mutagens: Half a century of Pandora’S Nox

It has been four decades since the phenomenon of photochemical air pollution was first characterized and, in the same year, a tragic London smog episode caused 4,000 excess deaths. Since then, there has been a substantial increase in our understanding of the chemistry involved in both types of air pollution, and a recognition that there is a very close chemical interrelationship between them. In this overview, we provide a brief historical perspective on the atmospheric chemistry of photochemical smog and illustrate how fundamental studies on the gas-phase chemistry of uv-irradiated mixtures of volatile organic compounds (VOC) and oxides of nitrogen (NO_x in polluted laboratory and ambient air masses have contributed to our understanding of three environmental problems: the atmospheric formation of ozone, nitric acid and airborne mutagens. In particular, we demonstrate the central role played by nitrogen dioxide and the hydroxyl radical in each case. We also show how certain reactive toxic and acidic species, e.g., formaldehyde and nitrous and formic acids, have been characterized in smog chambers and ambient smog by long pathlength spectroscopic techniques. It is shown that by using the same methods they now have been identified unequivocally, along with NO₂, in certain common types of polluted indoor atmospheres ... and at much higher concentrations than outdoors. This has significant health implications for indoor HCHO and quite possibly the acids. We then trace the history of the direct mutagenicity of respirable particles in polluted ambient air and show how, through use of the Ames test in biologically-directed assays of products coupled with fundamental studies of gas-phase reactions of polycyclic aromatic hydrocarbons (PAH) and NO_x in irradiated air, much of this activity can be accounted for in terms of the formation of nitro-PAH and oxygenated derivatives. Finally, we discuss the application of basic kinetic, mechanistic and analytical, experimental techniques and theoretical concepts to the development of a new set of “reactivity-based” regulatory controls on motor vehicle emissions of VOC’s. This novel regulatory approach applied by California’s Air Resources Board, which takes effect in 1994, illustrates the continuing need for fundamental research in the area of atmospheric chemistry and how it may be applied to “real world” environmental problems.     

Growth of InAsSb/InAs MQWs on GaSb for mid-IR photodetector applications

We report the OMVPE growth and characterization of InAsSb/InAs strain balanced multiple quantum wells lattice-matched to GaSb substrates for potential application as mid-infrared detectors for wavelengths beyond 4 μm$\mathrm{\mu }\mathrm{m}$. Detailed transmission electron microscopy measurements were performed to evaluate the degree of Ga and Sb intermixing at the GaSb/InAsSb and InAs/InAsSb interfaces. Photoluminescence emission up to 5 μm$\mathrm{\mu }\mathrm{m}$ was observed for superlattice structures with only 15% antimony. The dependence of PL on wavelength is red shifted compared to expectations based on type I band alignment.     

Decompounding random sums: a nonparametric approach

A compound distribution is the distribution of a random sum, which consists of a random number N of independent identically distributed summands, independent of N. Buchmann and Grübel (Ann Stat 31:1054–1074, 2003) considered decompounding a compound Poisson distribution, i.e. given observations on a random sum when N has a Poisson distribution, they constructed a nonparametric plug-in estimator of the underlying summand distribution. This approach is extended here to that of general (but known) distributions for N. Asymptotic normality of the proposed estimator is established, and bootstrap methods are used to provide confidence bounds. Finally, practical implementation is discussed, and tested on simulated data. In particular we show how recursion formulae can be inverted for the Panjer class in general, as well as for an example drawn from the Willmot class.     

Lundberg-type Bounds and Asymptotics for the Moments of the Time to Ruin

We obtain analogues of Lundberg’s inequality and the Cramér—Lundberg asymptotic relationship for the k-th moment of the time to ruin in the classical risk model. We also derive the asymptotic behaviour of the mean time to ruin when the claim size distribution has a heavy or intermediate tail.     

Pentafluoro(aryl)‐λ6‐tellanes and Tetrafluoro(aryl)(trifluoromethyl)‐λ6‐tellanes: From SF5 to the TeF5 and TeF4CF3 Groups

The TeF₅ group is significantly underexplored as a highly fluorinated substituent on an organic framework, despite it being a larger congener of the acclaimed SF₅ group. In fact, only one aryl‐TeF₅ compound (phenyl‐TeF₅) has been reported to date, synthesized using XeF₂. Our recently developed mild TCICA/KF approach to oxidative fluorination provides an affordable and scalable alternative to XeF₂. Using this method, we report a scope of extensively characterized aryl‐TeF₅ compounds, along with the first SC‐XRD data on this compound class. The methodology was also extended to the synthesis and structural study of heretofore unknown aryl‐TeF₄CF₃ compounds. Additionally, preliminary reactivity studies unveiled some inconsistencies with previous literature regarding phenyl‐TeF₅. Although our studies conclude that the arene‐based TeF₅ (and TeF₄CF₃) group is not quite as robust as the SF₅ group, we find that the TeF₅ group is more stable than previously thought, thus opening a door to explore new applications of this motif.     

Performance of the constrained minimization of the total energy in density functional approximations: the electron repulsion density and potential

In the constrained minimization method of Gidopoulos and Lathiotakis [N.I. Gidopoulos, N.N. Lathiotakis, J. Chem. Phys. 136, 224109 (2012)], the Hartree exchange and correlation Kohn-Sham potential of a finite N-electron system is replaced by the electrostatic potential of an effective charge density that is everywhere positive and integrates to a charge of N ? 1 electrons. The optimal effective charge density (electron repulsion density, ρ_rep) and the corresponding optimal effective potential (electron repulsion potential v_rep) are obtained by minimizing the electronic total energy in any density functional approximation. The two constraints are sufficient to remove the self-interaction errors from v_rep, correcting its asymptotic behavior at large distances from the system. In the present work, we describe, in complete detail, the constrained minimization method, including recent refinements. We also assess its performance in removing the self-interaction errors for three popular density functional approximations, namely LDA, PBE and B3LYP, by comparing the obtained ionization energies to their experimental values for an extended set of molecules. We show that the results of the constrained minimizations are almost independent of the specific approximation with average percentage errors 15%, 14%, 13% for the above DFAs respectively. These errors are substantially smaller than the corresponding errors of the plain (unconstrained) Kohn-Sham calculations at 38%, 39% and 27% respectively. Finally, we showed that this method correctly predicts negative values for the HOMO energies of several anions.