K-Rational D-Brane Crystals

In this paper the problem of constructing spacetime from string theory is addressed in the context of D-brane physics. It is suggested that the knowledge of discrete configurations of D-branes is sufficient to reconstruct the motivic building blocks of certain Calabi-Yau varieties. The collections of D-branes involved have algebraic base points, leading to the notion of K-arithmetic D-crystals for algebraic number fields K. This idea can be tested for D0-branes in the framework of toroidal compactifications via the conjectures of Birch and Swinnerton-Dyer. For the special class of D0-crystals of Heegner type these conjectures can be interpreted as formulae that relate the canonical Neron-Tate height of the base points of the D-crystals to special values of the motivic L-function at the central point. In simple cases the knowledge of the D-crystals of Heegner type suffices to uniquely determine the geometry.Comment: 36 page

Data processing and computer techniques for marine seismic interpretation

This work is divided into two sections, the first containing results and interpretations from marine seismic reflection profiling performed by Durham University (1972) in a region to the north of the Faeroe Islands, and the second containing theories for the removal of multiple reflection effects from marine seismic records by means of digital data processing techniques. The seismic profiling investigations were carried out to ascertain the geological structure causing the gravity 'low' north of the Faeroes which had previously been proposed by Bott, Browitt and Stacey (1971) to be caused by an infilled valley. Results from the 1972 survey shows that this infilled valley has a limited aerial extent containing relatively large basement undulations. Further work was carried out to obtain information about the sedimentary' sequencies and to try and correlate these with sediments in surrounding regions where data had been obtained by previous workers. The profiling work (1972) indicated three major sequencies within the sedimentary column with an overall thickening of sediments away from the uplifted areas of the Iceland - Faeroe Ridge and Faeroe Islands. The data processing section deals principally with the removal of multiple reflections from marine seismic records. An introduction is given to the basic concepts involved throughout this work, and includes a description of noise theory and types of multiple reflections encountered in marine seismic profiling. Some previous methods for multiple elimination are improved upon and then two new techniques are developed, applied to seismic sections, and finally a comparison made between the techniques used. All programs are written in FORTRAN IV for use on the IBM 360 computer, and for displaying purposes, facilities available with the Durham IBM 1130 plotting system were used

Precise measurements of UV atomic lines: Hyperfine structure and isotope shifts in the 398.8 nm line of Yb

We demonstrate a technique for frequency measurements of UV transitions with sub-MHz precision. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the $D_2$ line of $^{87}$Rb. We have used this to measure the 398.8 nm ${^1S}_0 \leftrightarrow {^1P}_1$ line of atomic Yb. We report isotope shifts of all the seven stable isotopes, including the rarest isotope $^{168}$Yb. We have been able to resolve the overlapping $^{173}$Yb($F = 3/2$) and $^{172}$Yb transitions for the first time. We also obtain high-precision measurements of excited-state hyperfine structure in the odd isotopes, $^{171}$Yb and $^{173}$Yb. The measurements resolve several discrepancies among earlier measurements.Comment: 7 pages, 6 figure

A contribution to understanding the complex nature of peisleyite

The type specimen of peisleyite has been reinvestigated by a combination of scanning electron microscopy, electron probe microanalysis (EPMA) and synchrotron powder X-ray diffraction. Morphological investigation showed that mats of peisleyite crystals, individually <3 μm across, are intergrown with wavellite veinlets to form the white cryptocrystalline material that is typical of 'peisleyite'. New EPMA data (mean of 12 analyses) gave the empirical formula of peisleyite as (Na_(1.69)Ca_(0.18))_(Σ1.87)(Al_(9.04)Fe_(0.03))_(Σ9.07)[(P_(6.28)S_(1.38)Si_(0.25))O_4]_(Σ7.91)(OH)_(6.66)·27.73H_2O, or ideally Na_2Al_9[(P,S)O_4]_8(OH)_6·28H_2O. The associated wavellite was found to be F-rich. Synchrotron powder data were indexed and refined and gave the following unit cell: P1, a = 9.280(19), b = 11.976(19), c = 13.250(18) Å, α = 91.3(1), β = 75.6(1), γ = 67.67(1)º, V = 1308(5) Å3 and Z = 4. These data are significantly different to those reported in the original description of peisleyite

Cumulative Effect of the Application of N and P Fertilizers on Soil Total and Labile Concentrations After 12 Cereal Crops on a Black Vertosol

Soil organic carbon is commonly used as a key indicator of sustainability of farming systems due to effects on nutrient availability, structural stability and its central role in soil biotic processes. Trends in total carbon content (CT) and lability of carbon (CL) in soil have been measured in a long-term nitrogen (N) x phosphorus (P) fertiliser experiment in continuous cereal cropping to assess the effect of increasing crop nutrient supply on soil carbon accretion and partitioning. Increasing N supply in each crop by 80 kg/ha or more was effective in creating significantly different total and labile carbon content

Birth, death and diffusion of interacting particles

Individual-based models of chemical or biological dynamics usually consider individual entities diffusing in space and performing a birth-death type dynamics. In this work we study the properties of a model in this class where the birth dynamics is mediated by the local, within a given distance, density of particles. Groups of individuals are formed in the system and in this paper we concentrate on the study of the properties of these clusters (lifetime, size, and collective diffusion). In particular, in the limit of the interaction distance approaching the system size, a unique cluster appears which helps to understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A: Condensed matte

On certain relationships between cosmological observables in the Einstein-Cartan gravity

We show that in the Einstein-Cartan gravity it is possible to obtain a relation between Hubble's expansion and the global rotation (vorticity) of the Universe. Gravitational coupling can be reduced to dimensionless quantity of order unity, fixing the scalar mass density and the resulting negative cosmological constant at spacelike infinity. Current estimates of the expansion and rotation (see also astro-ph/9703082) of the Universe favour the massive spinning particles as candidate particles for cold and hot dark matter. Nodland and Ralston vorticity (Phys. Rev. Lett. 78 (1997) 3043) overestimates the value favoured by the Einstein-Cartan gravity for three orders of magnitude.Comment: 7 pages, LaTeX styl

Developmental changes in the balance of disparity, blur and looming/proximity cues to drive ocular alignment and focus

Accurate co-ordination of accommodation and convergence is necessary to view near objects and develop fine motor co-ordination. We used a remote haploscopic videorefraction paradigm to measure longitudinal changes in simultaneous ocular accommodation and vergence to targets at different depths, and to all combinations of blur, binocular disparity, and change-in-size (“proximity”) cues. Infants were followed longitudinally and compared to older children and young adults, with the prediction that sensitivity to different cues would change during development. Mean infant responses to the most naturalistic condition were similar to those of adults from 6-7 weeks (accommodation) and 8-9 weeks (vergence). Proximity cues influenced responses most in infants less than 14 weeks of age, but sensitivity declined thereafter. Between 12-28 weeks of age infants were equally responsive to all three cues, while in older children and adults manipulation of disparity resulted in the greatest changes in response. Despite rapid development of visual acuity (thus increasing availability of blur cues), responses to blur were stable throughout development. Our results suggest that during much of infancy, vergence and accommodation responses are not dependent on the development of specific depth cues, but make use of any cues available to drive appropriate changes in response