Differential cross sections for ionization of laser-aligned atoms by electron impact

The first experimental data are given for (e,2e) ionization from laser-aligned atoms. A linearly polarized laser excited Mg atoms to the 31P? state prior to ionization by low energy electrons. The scattered and ejected electrons were detected in coincidence and the differential cross section determined for a range of alignment angles. An asymmetric coplanar geometry was used, with one electron fixed and the other detected at different angles. The data are compared to that from the spherically symmetric 31S? state. Significant differences are found, in both magnitude and angular distribution.     

Optically controlled tunable dispersion compensators based on pumped fiber gratings

We demonstrate optically tunable dispersion compensators based on pumping fiber Bragg gratings made in Er/Yb codoped fiber. The tunable dispersion for a chirped grating and also a uniform-period grating was successfully demonstrated in the experiment. The dispersion of the chirped grating was tuned from 900 to 1990 ps/nm and also from -600 to -950 ps/nm in the experiment.     

Room-temperature C-H arylation: merger of Pd-catalyzed C-H functionalization and visible-light photocatalysis

This communication describes the development of a room-temperature ligand-directed C-H arylation reaction using aryldiazonium salts. This was achieved by the successful merger of palladium-catalyzed C-H functionalization and visible-light photoredox catalysis. The new method is general for a variety of directing groups and tolerates many common functional groups.     

Detection of Protein S‐Sulfhydration by a Tag‐Switch Technique

Protein S‐sulfhydration (forming ‐S‐SH adducts from cysteine residues) is a newly defined oxidative posttranslational modification and plays an important role in H₂S‐mediated signaling pathways. In this study we report the first selective, “tag‐switch” method which can directly label protein S‐sulfhydrated residues by forming stable thioether conjugates. Furthermore we demonstrate that H₂S alone cannot lead to S‐sulfhydration and that the two possible physiological mechanisms include reaction with protein sulfenic acids (P‐SOH) or the involvement of metal centers which would facilitate the oxidation of H₂S to HS^..     

Unexpected behaviour of monospirothiacalix[4]arene under acidic conditions

Treatment of the monospirodienone derivative of thiacalix[4]arene with various acidic agents (HCl and HBr) results in rearrangement of the thiacalixarene skeleton leading to the formation of a phenoxanthiin derivative in high yields (up to 80%). The structure of the unexpected product is confirmed using ¹H and ¹³C NMR spectroscopy, and X-ray crystallography.     

Magnetic and mechanical AC loss of the ITER CS1 model coil conductor under transverse cyclic loading

The magnetic field in a coil results in a transverse force on the strands pushing the cable towards one side of the jacket. A special cryogenic press has been built to study in a unique way the mechanical and electrical properties of full-size ITER Cable-in-Conduit (CIC) samples under a transverse, mechanical load. The press can transmit a variable (cyclic) force of at least 650 kN/m to a cable section of 400 mm at 4.2 K. The jacket around the cable is partly opened in order to transmit the transverse force directly onto the cable. A superconducting dipole coil provides the AC magnetic field required to perform magnetisation measurements with pick-up coils. In addition the interstrand resistance (R_c) between various strands selected from topologically different positions inside the cable is measured. The force on the cable as well as the displacement are monitored simultaneously in order to determine the effective cable Young's modulus and the mechanical heat generation due to friction and deformation as the force is cycled. The mechanical heat generation, the coupling loss time constant nτ and R_c of a full-size ITER conductor have been studied under load for the first time. An important result is the significant decrease of nτ, after cyclic loading. It is also observed that the mechanical heat generation decreases with cycling.     

Manganese(I)‐Catalyzed C−H Activation: The Key Role of a 7‐Membered Manganacycle in H‐Transfer and Reductive Elimination

Manganese‐catalyzed C?H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven‐membered Mn^I intermediate is detected and characterized that is effective for H‐transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at Mn^I by judicious choice of an electron‐deficient 2‐pyrone substrate containing a 2‐pyridyl directing group, which undergoes regioselective C?H bond activation, serving as a valuable system for probing the mechanistic features of Mn C?H bond activation chemistry.     

Extremals for Logarithmic Hardy-Littlewood-Sobelov Inequalities on Compact Manifolds

Let M be a closed, connected surface and let Γ be a conformal class of metrics on M with each metric normalized to have area V. For a metric g Γ, denote the area element by dV and the Laplace–Beltrami operator by Δ _g . We define the Robin mass m(x) at the point x M to be the value of the Green’s function G(x, y) at y = x after the logarithmic singularity has been subtracted off. The regularized trace of Δ _g ⁻¹ is then defined by trace Δ⁻¹ = ∫ _M m dV. (This essentially agrees with the zeta functional regularization and is thus a spectral invariant.) Let be the Laplace–Beltrami operator on the round sphere of volume V. We show that if there exists g Γ with trace Δ _g ⁻¹ < trace then the minimum of trace Δ⁻¹ over Γ is attained by a metric in Γ for which the Robin mass is constant. Otherwise, the minimum of trace Δ⁻¹ over Γ is equal to trace . In fact we prove these results in the general setting where M is an n-dimensional closed, connected manifold and the Laplace–Beltrami operator is replaced by any non-negative elliptic operator A of degree n which is conformally covariant in the sense that for the metric g we have . In this case the role of is assumed by the Paneitz or GJMS operator on the round n-sphere of volume V. Explicitly these results are logarithmic HLS inequalities for (M, g). By duality we obtain analogs of the Onofri–Beckner theorem. Received: February 2006, Accepted: March 2006