Visualising mouse neuroanatomy and function by metal distribution using laser ablation-inductively coupled plasma-mass spectrometry imaging

Metals have a number of important roles within the brain. We used laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to map the three-dimensional concentrations and distributions of transition metals, in particular iron (Fe), copper (Cu) and zinc (Zn) within the murine brain. LA-ICP-MS is one of the leading analytical tools for measuring metals in tissue samples. Here, we present a complete data reduction protocol for measuring metals in biological samples, including the application of a pyramidal voxel registration technique to reproducibly align tissue sections. We used gold (Au) nanoparticle and ytterbium (Yb)-tagged tyrosine hydroxylase antibodies to assess the co-localisation of Fe and dopamine throughout the entire mouse brain. We also examined the natural clustering of metal concentrations within the murine brain to elucidate areas of similar composition. This clustering technique uses a mathematical approach to identify multiple ‘elemental clusters’, avoiding user bias and showing that metal composition follows a hierarchical organisation of neuroanatomical structures. This work provides new insight into the distinct compartmentalisation of metals in the brain, and presents new avenues of exploration with regard to region-specific, metal-associated neurodegeneration observed in several chronic neurodegenerative diseases.     

The surface geometry of GaAs(110): A response

A brief survey of the various surface structure analyses for GaAs(110) is presented. The interplay between studies based on low-energy-electron diffraction (LEED), ion channeling, ion scattering, photoemission and isochromat spectroscopy leads to a structure in which a relaxation within the top layer (characterized by a perpendicular displacement of the As and Ga species by $\text{Δ}{}_{\mathrm{1,\; \perp }}\text{= 0.69±0.05}\text{A}\text{?}$ with the As species relaxing outward by $\text{0.21±0.05}\text{A}\text{?}$ and the Ga species inward by $\text{0.48±0.05}\text{A}\text{?}$) is accompanied by a uniform relaxation of the top layer by $\text{0.05±0.1}\text{A}\text{?}$ toward the substrate and a perpendicular displacement in the second layer in the opposite sense by $\text{0.06±0.1}\text{A}\text{?}$. The displacements of the top-layer Ga and As species parallel to the surface remain controversial. LEED and medium-energy ion-scattering analysis favor bond-length-conserving rotated top-layer structures (i.e., large $\text{(Δd}{}_{\mathrm{|}}\text{～ 0.3}\text{A}\text{?}\text{)}$ displacements parallel to the surface) whereas high-energy ion-channeling and isochromat spectroscopy experiments favor small displacements $\text{(Δd}{}_{\mathrm{|}}\text{? 0.1}\text{A}\text{?}\text{)}$ parallel to the surface.     

Schur complement preconditioners for anisotropic problems

We present two new variants of Schur complement domain decompositionpreconditioners suitable for 2D anisotropic problems. Thesevariants are based on adaptations of the probing idea, describedby Chan et al (1992 Fifth Int. Symp. on Domain DecompositionMethods for Partial Differential Equations, Philadelphia: SIAM,pp 236-249), used in conjunction with a coarse grid approximationas introduced by Bramble et al (1986 Math. Comput. 47, 103-134).The new methods are specifically designed for situations wherethe coupling between neighbouring interfaces is stronger thanthe coupling within an interface. Taking into account this strongcoupling, one variant uses a multicolour probing technique toavoid distortion in the probe approximations that appear whenusing the method proposed by Chan et al. The second techniqueuses additional probe matrices to approximate not only the couplingwithin the interfaces but also the coupling between interfacepoints across the subdomains. This latter procedure looks somewhatlike an alternating line relaxation method for anisotropic problems,see Brandt (1977 Math. Comput.. 31, 333-390). To assess therelevance of the new preconditioners, we compare their numericalbehaviour with well known robust preconditioners such as thebalanced Neumann-Neumann method proposed by Mandel (1993 Commun.Numer. Methods Eng.. 9, 233-241).     

Stereoretention in styrene heterodimerisation promoted by one-electron oxidants

Radical cations generated from the oxidation of C C π-bonds are synthetically useful reactive intermediates for C–C and C–X bond formation. Radical cation formation, induced by sub-stoichiometric amounts of external oxidant, are important intermediates in the Woodward–Hoffmann thermally disallowed [2 + 2] cycloaddition of electron-rich alkenes. Using density functional theory (DFT), we report the detailed mechanisms underlying the intermolecular heterodimerisation of anethole and β-methylstyrene to give unsymmetrical, tetra-substituted cyclobutanes. Reactions between trans-alkenes favour the all-trans adduct, resulting from a kinetic preference for anti-addition reinforced by reversibility at ambient temperatures since this is also the thermodynamic product; on the other hand, reactions between a trans-alkene and a cis-alkene favour syn-addition, while exocyclic rotation in the acyclic radical cation intermediate is also possible since C–C forming barriers are higher. Computations are consistent with the experimental observation that hexafluoroisopropanol (HFIP) is a better solvent than acetonitrile, in part due to its ability to stabilise the reduced form of the hypervalent iodine initiator by hydrogen bonding, but also through the stabilisation of radical cationic intermediates along the reaction coordinate.

A computational study details the mechanism, catalytic cycle and origins of stereoselectivity underlying hole-catalyzed intermolecular alkene heterodimerisation to give unsymmetrical, tetra-substituted cyclobutanes.     

评《马氏决策过程》

（《马氏决策过程》,侯振挺、郭先平著,长沙,湖南科技出版社,1997,中文版,386页,定价：28元）马尔可夫决策过程是概率论的运筹学的理论研究和实际应用中极其重要的领域之一．随着中国和国际上对马尔可夫决策过程（MarkovDecisionProcesses,简记为MDP）研究的新进展,许     

A novel asymmetrically coupled quantum well infrared modulator

A novel high-speed infrared modulator is proposed which uses resonant tunneling and intersubband optical transitions within the conduction band of a semiconductor quantum well. Variations of the applied bias voltage control the amount of light transmitted through the device.     

The thermal fragmentation of 1,3,4-diathiazol-2-ones

Thermal expulsion of carbon oxusulphide from 1,3,4-dithiazol-2-ones in the presence of DMAD affords nitrile sulphide-derived dimethyl isothiazole-4,5-dicarboxylates.