Ion angular distributions in electron stimulated desorption: Oxygen and CO on W(111)

The ion angular distributions resulting from electron stimulated desorption (ESD) of oxygen and carbon monoxide chemisorbed on a tungsten (111) crystal have been determined. The O⁺ ions released during ESD of adsorbed oxygen exhibit three-fold symmetric angular distributions in orientational registry with the W(111) substrate. The CO⁺ and O⁺ ions released during ESD of a monolayer of CO are desorbed normal to the (111) surface. Models for both oxygen and CO adsorption are discussed. The data for CO are consistent with adsorption of CO in “standing up” carbonyl structures in the virgin and α-CO binding states.     

Discrete-continuous model conversion

This paper presents methods for model conversions of continuous-time state-space equations and discrete-time state-space equations. An improved geometric-series method is presented for converting continuous-time models to equivalent discrete-time models. Also, a direct truncation method, a matrix continued fraction method and a geometric-series method are presented for converting discrete models to equivalent continuous models. As a result, many well-developed theorems and methods in either continuous or discrete domains can be effectively applied to a suitable model in either domain.     

A “high-pressure” electron spectrometer for surface studies

A photoelectron spectrometer which permits the study of solids in the presence of gas at up to 1 Torr pressure has been developed and the main factors considered in its design and construction are described. The inelastic mean free path of 890 eV kinetic energy electrons through argon at 1 Torr has been measured and shown to be 4.5 ± 1 mm. The X-ray induced valence band spectrum of liquid mercury is also reported. It is in good agreement with calculation (S.C. Keeton and T.L. Loucks, Phys. Rev. 152 (1966) 548), but shows some differences from that of condensed mercury monolayers at 163 K (S. Svensson et al., J. Electron Spectrosc. 9 (1976) 51).     

Local spectroscopy of image-potential-derived states: from single molecules to monolayers of benzene on Cu(111)

Stark-shifted image-potential states were measured with an STM tip for benzene adsorbed on a Cu(111) surface. A single benzene molecule locally shifts the position of the first image state toward the Fermi level by 0.2 eV relative to its position on the clean surface. The energetic position of this molecule-modified state shifts to lower energy with increasing coverage of benzene on the surface. This is attributed to local surface potential changes that are correlated with the lowering of the crystal work function due to adsorption of benzene.     

The influence of N-substitution on the reductive elimination behaviour of hydrocarbyl-palladium-carbene complexes--a DFT study

The reductive elimination of 2-hydrocarbyl-imidazolium salts from hydrocarbyl-palladium complexes bearing N-heterocyclic carbene (NHC) ligands represents an important deactivation route for catalysts of this type. We have explored the influence that carbene N-substituents have on both the activation energy and the overall thermodynamics of the reductive elimination reaction using density functional theory (DFT). Given the proximity of the N-substituent to the three-centred transition structure, steric bulk has little influence on the activation barrier and it is electronic factors that dominate the barriers' magnitude. Increased electron donation from the departing NHC ligand acts to stabilise the associated complex against reductive elimination, with stability following the trend: Cl < H < Ph < Me < Cy < iPr < neopentyl < tBu. The intimate involvement of the carbene p pi-orbital in determining the barrier to reductive elimination means N-substituents that are capable of removing pi-density (e.g. phenyl) act to promote a more facile reductive elimination.     

Phenyl species formation and preferential hydrogen abstraction in the decomposition of chemisorbed benzoate on Cu(110)

The adsorption and decomposition of benzoic acid on the Cu(110) surface has been investigated using temperature-programmed reaction (TPR) spectroscopy and scanning tunneling microscopy (STM). The benzoate species is found to exist in two conformations--a phase containing upright species at monolayer saturation and a phase containing many lying-down species at lower coverages. Thermal decomposition begins to occur near 500 K, yielding benzene and CO(2). It is found that phenyl species, generated preferentially from the lying-down benzoate species, efficiently abstract H atoms from undecomposed benzoate species to produce benzene in a rate-controlling process with an activation energy of about 29 kcal/mol. Using deuterium-atom substitution at the 4-C position on the benzoate ring it is found that the hydrogen-abstraction reaction is selective for 2,3 and 5,6 C-H bonds. This observation indicates that the mobile phenyl species is surface bound and preferentially attacks C-H bonds which are nearest the Cu surface and bind the benzoate species as either an upright species or a tilted species.     

Engineered bio-active polysaccharides from heparin

[Image: see text] Heparin, the well-known anticoagulant polysaccharide, is also active in many other biological systems owing to its structural similarity to HS, but usually lacks selectivity because it is more highly sulfated. A series of straightforward chemical reactions (de-O-sulfation, de-N-sulfation and re-N-acetylation), carried out to partial or complete extent, were combined, resulting in a number of modified heparin polysaccharide derivatives with altered properties. These exhibited a range of abilities to promote cell signalling through the FGF/FGFR tyrosine kinase signalling system, in an in vitro cell assay with combinations of FGF-1, -2, -3 and FGFR 1 and 3. One polysaccharide (N-acetylated, 6-O- and 2-O-sulfated heparin), with only a fraction (<10(-3)) of the anticoagulant activity of heparin (200 U . mg(-1)), promoted FGF-2-mediated angiogenesis (10-fold) and therefore had an improved ratio of pro-angiogenic activity to anticoagulant activity in excess of 10(4) compared to heparin. These results demonstrate that heparin-derived polysaccharides can be engineered for selected activities and have potential in a wide range of medical, biotechnological and tissue-engineering applications. Effect of selected engineered heparin polysaccharides on angiogenesis.     

The landscape of cancer genes and mutational processes in breast cancer

All cancers carry somatic mutations in their genomes. A subset, known as driver mutations, confer clonal selective advantage on cancer cells and are causally implicated in oncogenesis, and the remainder are passenger mutations. The driver mutations and mutational processes operative in breast cancer have not yet been comprehensively explored. Here we examine the genomes of 100 tumours for somatic copy number changes and mutations in the coding exons of protein-coding genes. The number of somatic mutations varied markedly between individual tumours. We found strong correlations between mutation number, age at which cancer was diagnosed and cancer histological grade, and observed multiple mutational signatures, including one present in about ten per cent of tumours characterized by numerous mutations of cytosine at TpC dinucleotides. Driver mutations were identified in several new cancer genes including AKT2, ARID1B, CASP8, CDKN1B, MAP3K1, MAP3K13, NCOR1, SMARCD1 and TBX3. Among the 100 tumours, we found driver mutations in at least 40 cancer genes and 73 different combinations of mutated cancer genes. The results highlight the substantial genetic diversity underlying this common disease.     

The multipliers‐free domain decomposition methods

This article concludes the development and summarizes a new approach to dual‐primal domain decomposition methods (DDM), generally referred to as “the multipliers‐free dual‐primal method.” Contrary to standard approaches, these new dual‐primal methods are formulated without recourse to Lagrange‐multipliers. In this manner, simple and unified matrix‐expressions, which include the most important dual‐primal methods that exist at present are obtained, which can be effectively applied to floating subdomains, as well. The derivation of such general matrix‐formulas is independent of the partial differential equations that originate them and of the number of dimensions of the problem. This yields robust and easy‐to‐construct computer codes. In particular, 2D codes can be easily transformed into 3D codes. The systematic use of the average and jump matrices, which are introduced in this approach as generalizations of the “average” and “jump” of a function, can be effectively applied not only at internal‐boundary‐nodes but also at edges and corners. Their use yields significant advantages because of their superior algebraic and computational properties. Furthermore, it is shown that some well‐known difficulties that occur when primal nodes are introduced are efficiently handled by the multipliers‐free dual‐primal method. The concept of the Steklov–Poincaré operator for matrices is revised by our theory and a new version of it, which has clear advantages over standard definitions, is given. Extensive numerical experiments that confirm the efficiency of the multipliers‐free dual‐primal methods are also reported here. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2010