Digital Processing of Electron Energy Loss Spectra and Images

Processing in electron energy loss spectroscopy involves both data acquisition and analysis. The interface of an analytical electron microscope to a laboratory computer with a satellite microcomputer dedicated to data acquisition results in a system with a high degree of flexibility. In spectrum acquisition, channels may be selected around specific core edges, or dwell times may be varied continuously as a function of energy loss to reduce the dynamic range of the signal. Data transfer to the host computer allows further analysis such as the removal of plural scattering by spectral deconvolution. Elemental maps and line-scans can be recorded with real-time processing of energy loss data at each pixel. Images may be analyzed to provide quantitative information by means of pixel intensity histograms. If parameters for the background are stored at each pixel, the image data may sometimes be further processed to improve the signal-to-noise ratio

Biological Electron Energy Loss Spectroscopy in the Field-Emission Scanning Transmission Electron Microscope

The dedicated scanning transmission electron microscope (STEM) combined with parallel electron energy loss spectroscopy (EELS) provides a very sensitive means of detecting specific elements in small structures. EELS is more sensitive than optimized energy-dispersive X-ray spectroscopy by a factor of about three for calcium. Measurement of such low concentrations requires special processing methods such as difference-acquisition techniques and multiple least squares procedures for fitting reference spectra. By analyzing data recorded at each pixel in a spectrum-image it is possible to map quantitatively the elemental distributions in a specimen. It is possible to prepare cryosections that are sufficiently thin to avoid excessive plural inelastic scattering so analysis can be performed at 100 keV beam energy. Under optimal conditions, a resolution of 10 nm and detection limits of a few atoms are achievable for elements such as calcium, phosphorus and iron. In the field emission STEM certain types of chemical information can be extracted from biological specimens. Valence EELS has been exploited to measure water distributions in frozen hydrated cryosections

X-ray absorption spectroscopy systematics at the tungsten L-edge

A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, has been interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W<sup>0</sup>(PMe<sub>3</sub>)<sub>6</sub>], [W<sup>II</sup>Cl<sub>2</sub>(PMePh<sub>2</sub>)<sub>4</sub>], [W<sup>III</sup>Cl<sub>2</sub>(dppe)<sub>2</sub>][PF<sub>6</sub>] (dppe = 1,2-bis(diphenylphosphino)ethane), [W<sup>IV</sup>Cl<sub>4</sub>(PMePh<sub>2</sub>)<sub>2</sub>], [W<sup>V</sup>(NPh)Cl<sub>3</sub>(PMe<sub>3</sub>)<sub>2</sub>], and [W<sup>VI</sup>Cl<sub>6</sub>] correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio (EBR) of the L<sub>3,2</sub>-edges and the L<sub>1</sub> rising-edge energy with metal Z<sub>eff</sub>, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W<sup>IV</sup>(mdt)<sub>2</sub>(CO)<sub>2</sub>] and [W<sup>IV</sup>(mdt)<sub>2</sub>(CN)<sub>2</sub>]<sup>2–</sup> (mdt<sup>2–</sup> = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W<sup>IV</sup> species. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: 1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Z<sub>eff</sub> in the species of interest; 2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS; 3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate the difference between formal oxidation state and metal Z<sub>eff</sub> or, as in the case of [W<sup>IV</sup>(mdt)<sub>2</sub>(CO)<sub>2</sub>], add other subtlety by modulating the redox level of other ligands in the coordination sphere

Dynamics of social class contempt in contemporary British television comedy

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2010 Taylor & Francis.British television comedy has often ridiculed the complexities and characteristics of social class structures and identities. In recent years, poor white socially marginalised groups, now popularly referred to as “chavs”, have become a prevalent comedy target. One of the most popular and controversial television “comedy chavs” is Little Britain's fictional teenage single mother, Vicky Pollard. This article examines the representation of Vicky Pollard in light of contemporary widespread abuse of the white working class. Highlighting the polysemic and ambivalent nature of Vicky Pollard's representation, the article argues that whilst Little Britain's characterisation of Vicky Pollard largely contributes to contemporary widespread demonisation of the working class, there are moments within Little Britain when a more sympathetic tone towards the poor working class may be read, and where chav identities are used to ridicule the pretensions, superficiality, and falsity of middle-class identities. The article concludes that television comedy has been, and continues to be, a significant vehicle through which serious concerns, anxieties, and questions about social class and class identities are discursively constructed and contested