Current Interruption at Powers up to 1 GW with Crossed-Field Tubes

This paper describes the current interruption and voltage holdoff capabilities of a wide range of crossed-field tubes (XFTs). The XFTs investigated have active electrode areas ranging from 96 to 8000 cm2 with mean diameters from 2 to 56 cm. For the larger XFTs, currents up to 10 kA have been interrupted at voltages up to 100 kV, corresponding to a switched power of 1 GW. Experiments have shown the peak interruptible current to vary linearly with tube radius. The mechanism responsible for the limitation may be related to the self-generated magnetic field, but other factors are also shown to play a role.     

The stability of an interface between miscible fluids in a porous medium

Résumé On étudie la nature de stabilité de l'interface horizontale de deux fluides miscibles qui se filtrent verticalement à travers une couche poreuse. Initialement, le profile de densité vertical est une fonction de Heaviside; on admet l'existence d'un déplacement ondé d'une amplitude infinitésimale à l'interface. Subséquemment, la diffusion moléculaire et la dispersion mécanique font décroître les gradients de densité et des autres caractéristiques des fluides. La vitesse d'accroissement d'amplitude de la perturbation dépend de la répartition de densité variable et du nombre d'onde et de l'amplitude initiale de chaque composante de Fourier de cette perturbation. On obtient une expansion en séries d'une composante typique, et de résultants numériques pour la perturbation symétrique qui se trouve par suite des conditions initiales.     

Molybdenum blue: binding to collagen fibres and microcrystal formation

Collagen fibres have been shown by transmission electron microscopy to progressively bind the polyoxomolybdate ring-complex, termed molybdenum blue. Nucleation of cuboidal molybdenum blue microcrystals occurs on the surface of the collagen fibres, leading eventually to extensive coating of the fibres with microcrystals.     

Factors affecting d-block metal-ligand bond lengths: toward an automated library of molecular geometry for metal complexes

Metal-ligand (M-L) bond lengths for a range of ligands (carboxylates, chlorides, pyridines, water, tertiary phosphines, and alkenes) and a variety of metals have been retrieved from the Cambridge Structural Database, CSD. Analysis of the factors which affect M-L bond lengths (for example, ligand coordination mode, oxidation state, metal coordination number and geometry, spin and Jahn-Teller effects, and ligand trans to M-L bond) shows that it is generally possible to subdivide the M-L data sets systematically to obtain better defined, unimodal, bond length distributions with means and sample standard deviations (SSDs) which reflect the nature of the bond in question. Typically, the SSDs for the M-L data sets can be reduced to 0.04-0.05 A by these methods. This work is an extension to tables of bond lengths in organometallic compounds and coordination complexes published in 1989. The importance of the factors which affect M-L bond lengths for particular metal-ligand groups are discussed. From the case studies reported, an algorithm is proposed by which compilation of a library of molecular geometry for metal complexes may be automated. The points that need to be considered to produce such a molecular library from the data stored in the CSD are discussed. The development of such a library would allow users to retrieve chemically well-defined geometric data rapidly and accurately. This should be of use, for example, to crystallographers and molecular modelers.     

High-accuracy optical clock via three-level coherence in neutral bosonic 88Sr

An optical atomic clock scheme is proposed that utilizes two lasers to establish coherent coupling between the 5s2 1S0 ground state of 88Sr and the first excited state, 5s5p 3P0. The coupling is mediated by the broad 5s5p 1P1 state, exploiting the phenomenon of electromagnetically induced transparency. The effective linewidth of the clock transition can be chosen at will by adjusting the laser intensity. By trapping the 88Sr atoms in an optical lattice, long interaction times with the two lasers are ensured; Doppler and recoil effects are eliminated. Based on a careful analysis of systematic errors, a clock accuracy of better than 2 x 10(-17) is expected.