Distribution anisotropy: the influence of magnetic interactions on the anisotropy of magnetic remanence

The anisotropy of magnetic remanence (AMR) is often used as a tool for examining magnetic anisotropy of rocks. However, the influence of magnetostatic interactions on AMR has not been previously rigorously addressed either theoretically or experimentally, though it is widely thought to be highly significant. Using a three-dimensional micromagnetic algorithm, we have conducted a systematic numerical study of the role of magnetostatic interactions on AMR. We have considered both lineation and foliation, by modelling assemblages of ideal single domain grains and magnetically non-uniform magnetite-like cubic grains. We show that magnetostatic interactions strongly affect the measured AMR signal. It is found that depending on the orientation of the single-grain anisotropy and grain spacing it is possible for the AMR signal from a chain or grid of grains to be either oblate or prolate. For non-uniform grains, the degree of anisotropy generally increases with increasing interactions. In the modelling of AMR anisotropy, saturation isothermal remanence was chosen for numerical tractability. The influence of interactions on other types of more commonly measured AMR, are considered in light of the results in this paper. © The Geological Society of London 2004.Accepted versio

Using permeable membranes to produce hydrogen and oxygen from water

Concept may make it profitable to obtain hydrogen fuel from water. Laboratory tests have demonstrated that method enables decomposition of water several orders of magnitude beyond equilibrium state where only small amounts of free hydrogen are present

The Hilbert Action in Regge Calculus

The Hilbert action is derived for a simplicial geometry. I recover the usual Regge calculus action by way of a decomposition of the simplicial geometry into 4-dimensional cells defined by the simplicial (Delaunay) lattice as well as its dual (Voronoi) lattice. Within the simplicial geometry, the Riemann scalar curvature, the proper 4-volume, and hence, the Regge action is shown to be exact, in the sense that the definition of the action does not require one to introduce an averaging procedure, or a sequence of continuum metrics which were common in all previous derivations. It appears that the unity of these two dual lattice geometries is a salient feature of Regge calculus.Comment: 6 pages, Plain TeX, no figure

Jet-cloud interations and the brightening of the narrow line region in Seyfert galaxies

We study the kinematical and brightness evolution of emission line clouds in the narrow line region (NLR) of Seyfert galaxies during the passage of a jet. We derive a critical density above which a cloud remains radiative after compression by the jet cocoon. The critical density depends mainly on the cocoon pressure. Super-critical clouds increase in emission line brightness, while sub-critical clouds generally are highly overheated reducing their luminosity below that of the inter-cloud medium. Due to the pressure stratification in the bow-shock of the jet, a cylindrical structure of nested shells develops around the jet. The most compact and brightest compressed clouds surround the cloud-free channel of the radio jet. To support our analytical model we present a numerical simulation of a supersonic jet propagating into a clumpy NLR. The position-velocity diagram of the simulated H_alpha emission shows total line widths of the order of 500 km/s with large-scale variations in the radial velocities of the clouds due to the stratified pressure in the bow-shock region of the jet. Most of the luminosity is concentrated in a few dense clouds surrounding the jet. These morphological and kinematic signatures are all found in the well observed NLR of NGC1068 and other Seyfert galaxies.Comment: 11 pages, 3 figures, accepted for publication in The Astrophysical Journal Letter

The Construction of Sorkin Triangulations

Some time ago, Sorkin (1975) reported investigations of the time evolution and initial value problems in Regge calculus, for one triangulation each of the manifolds $R*S^3$ and $R^4$. Here we display the simple, local characteristic of those triangulations which underlies the structure found by Sorkin, and emphasise its general applicability, and therefore the general validity of Sorkin's conclusions. We also make some elementary observations on the resulting structure of the time evolution and initial value problems in Regge calculus, and add some comments and speculations.Comment: 5 pages (plus one figure not included, available from author on request), Plain Tex, no local preprint number (Only change: omitted "\magnification" command now replaced

The clumpiness of molecular clouds: HCO+ (3--2) survey near Herbig-Haro objects

Some well-studied Herbig Haro objects have associated with them one or more cold, dense, and quiescent clumps of gas. We propose that such clumps near an HH object can be used as a general measure of clumpiness in the molecular cloud that contains that HH object. Our aim is to make a survey of clumps around a sample of HH objects, and to use the results to make an estimate of the clumpiness in molecular clouds. All known cold, dense, and quiescent clumps near HH objects are anomalously strong HCO+ emitters. Our method is, therefore, to search for strong HCO+ emission as an indicator of a clump near to an HH object. The searches were made using JCMT and SEST in the HCO+ 3-2 and also H13CO+ 1-0 lines, with some additional searches for methanol and sulphur monoxide lines. The sources selected were a sample of 22 HH objects in which no previous HCO+ emission had been detected. We find that half of the HH objects have clumps detected in the HCO+ 3-2 line and that all searches in H13CO$+ 1-0 lines show evidence of clumpiness. All condensations have narrow linewidths and are evidently unaffected dynamically by the HH jet shock. We conclude that the molecular clouds in which these HH objects are found must be highly heterogeneous on scales of less than 0.1 pc. An approximate calculation based on these results suggests that the area filling factor of clumps affected by HH objects is on the order of 10%. These clumps have gas number densities larger than 3e4 cm-2.Comment: 11 pages, 14 figures. Accepted for publication in Astronomy and Astrophysic

Geodesic Deviation in Regge Calculus

Geodesic deviation is the most basic manifestation of the influence of gravitational fields on matter. We investigate geodesic deviation within the framework of Regge calculus, and compare the results with the continuous formulation of general relativity on two different levels. We show that the continuum and simplicial descriptions coincide when the cumulative effect of the Regge contributions over an infinitesimal element of area is considered. This comparison provides a quantitative relation between the curvature of the continuous description and the deficit angles of Regge calculus. The results presented might also be of help in developing generic ways of including matter terms in the Regge equations.Comment: 9 pages. Latex 2e with 5 EPS figures. Submitted to CQ

Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent compound, TiSe2, which shows a charge density wave transition and no superconductivity. The crystal structure, characterized by high resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements suggest that the superconductivity is induced by charge transfer from the PbSe layers to the TiSe2 layers.Comment: 17 pages, 4 figures. To be published in Physical Review

Global analysis of muon decay measurements

We have performed a global analysis of muon decay measurements to establish model-independent limits on the space-time structure of the muon decay matrix element. We find limits on the scalar, vector and tensor coupling of right- and left-handed muons to right- and left-handed electrons. The limits on those terms that involve the decay of right-handed muons to left-handed electrons are more restrictive than in previous global analyses, while the limits on the other non-standard model interactions are comparable. The value of the Michel parameter eta found in the global analysis is -0.0036 \pm 0.0069, slightly more precise than the value found in a more restrictive analysis of a recent measurement. This has implications for the Fermi coupling constant G_F.Comment: 5 pages, 3 table

Quantum phases of bosons in double-well optical lattices

We study the superfluid to Mott insulator transition of bosons in a two-legged ladder optical lattice, of a type accessible in current experiments on double-well optical lattices. The zero-temperature phase diagram is mapped out, with a focus on its dependence upon interchain hopping and the tilt between double wells. We find that the unit-filling Mott phase exhibits a non-monotonic behavior as a function of the tilt parameter, producing a reentrant phase transition between Mott insulator and superfluid phases.Comment: 5 pages, 5 figure