The origin of scaling in the galaxy distribution     

Bernard J. T. Jones 《Monthly notices of the Royal Astronomical Society》1999,307(2):376-386

I present an analytic model for non‐linear clustering of the luminous (baryonic) material in a universe in which the gravitational field is dominated by dark matter. The model is based on a two-component generalization of the adhesion approximation in which the gravitational potential of the dark component is determined by the standard Zel'dovich approximation or one of its variants, or by an N ‐body simulation. The baryonic matter flow is dissipative and is driven by this dark matter gravitational potential. The velocity potential of the matter is described by a generalization of the Burgers equation: the random heat equation ('RH equation') with a spatially correlated Gaussian driving potential.
The properties of the RH equation are well understood: it is closely related to the equation for the Anderson model and to Brownian motion in a random potential: the solution can be expressed in terms of path integrals. Using this it is possible to derive the scaling properties of the solution and, in particular, those of the resultant velocity field. Even though the flow is non‐linear, the velocity field remains Gaussian and inherits its scaling properties from the gravitational potential. This provides an underlying dynamical reason why the density field in the baryonic component is lognormally distributed and manifests multifractal scaling.
By explicitly putting dark and luminous matter on different footings, the model provides an improved framework for considering the growth of large‐scale cosmic structure. It provides a solution for the velocity potential of the baryonic component in closed form (albeit a path integral) from which the statistical properties of the baryonic flow can be derived.  相似文献   

A multifrequency maximum-entropy joint analysis of COBE and Tenerife data     

A. W. Jones  A. N. Lasenby  P. Mukherjee  C. M. Gutierrez  R. D. Davies  R. A. Watson  R. Hoyland  R. Rebolo 《Monthly notices of the Royal Astronomical Society》1999,310(1):105-109

We use data from the Tenerife 10-, 15- and 33‐GHz beam-switching experiments along with the COBE 53- and 90‐GHz data to separate the cosmic microwave background (CMB) signal from the Galactic signal, and create two maps at high Galactic latitude. The new multi-MEM technique is used to obtain the best reconstruction of the two channels. The two maps are presented, and known features are identified within each. We find that the Galactic contribution to both the 15- and 33-GHz Tenerife data is small enough to be ignored when compared with the errors in the data and the magnitude of the CMB signal.  相似文献   

Surface-sediment and epilithic diatom pH calibration sets for remote European mountain lakes (AL:PE Project) and their comparison with the Surface Waters Acidification Programme (SWAP) calibration set   总被引：1，自引：0，他引：1  

N. G. Cameron  H. J. B. Birks  V. J. Jones  F. Berges  J. Catalan  R. J. Flower  J. Garcia  B. Kawecka  K. A. Koinig  A. Marchetto  P. Sánchez-Castillo  R. Schmidt  M. Šiško  N. Solovieva  E. Štefková  M. Toro 《Journal of Paleolimnology》1999,22(3):291-317

A modern diatom-pH calibration data-set consisting of surface-sediment diatom assemblages from 118 lakes and 530 taxa is presented. The AL:PE data-set is from high-altitude or high-latitude lakes in the Alps, Norway, Svalbard, Kola Peninsula, UK, Slovenia, Slovakia, Poland, Portugal, and Spain (pH range = 4.5-8.0; DOC range = 0.2-3.2 mg l^-1). In addition, 92 epilithon samples from 22 high-altitude or high-latitude lakes comprise an AL:PE epilithon diatom-pH data-set. Weighted averaging partial least squares regression is used to develop pH-inference models. The AL:PE data-set has a root-mean-square-error of prediction (RMSEP) of 0.33 and a maximum bias of 0.36 pH units and r² of 0.82, as assessed by leave-one-out cross-validation. The epilithon data-set has, after data-screening and the deletion of one very obvious outlier, a RMSEP of 0.23 and a maximum bias of 0.18 pH units and r² of 0.88. The 167 sample SWAP diatom-pH data-set from lowland or upland lakes in the UK, Norway, and Sweden has a RMSEP of 0.29 and a maximum bias of 0.23 pH units and r² of 0.86.The pH optima, as estimated by weighted averaging and Gaussian regression, are compared for the three data-sets (AL:PE, SWAP, AL:PE epilithon). There is a good correspondence between the AL:PE and the AL:PE epilithon optima, but a consistent bias between the AL:PE and SWAP optima, with the SWAP optima being lower than the AL:PE estimates.The predictive performances of the AL:PE and SWAP calibration data-sets are compared using independent test samples and six core sequences, all from high-altitude lakes, one in south-east Siberia and five in eastern Scotland. The results show the importance of using the AL:PE data-set for inferring lake-water pH from diatom assemblages in high-altitude or high latitude lakes with low DOC concentrations.  相似文献   

Anisotropy in multi-offset deep-crustal seismic experiments   总被引：1，自引：0，他引：1  

K. Jones  M. Warner  & J. Brittan 《Geophysical Journal International》1999,138(2):300-318

Modelling of deep-seismic wide-angle data commonly assumes that the Earth is heterogeneous and isotropic. It is important to know the magnitudes of errors that may be introduced by isotropic-based wide-angle models when the Earth is anisotropic. It is equally important to find ways of detecting anisotropy and determining its properties.
  This paper explores the errors introduced by interpreting anisotropic seismic data with isotropic models. Errors in P -wave reflector depths are dependent on the magnitude of the velocity anisotropy and the direction of the fast axis. The interpreted, isotropic, model velocity function is found to correspond closely to the horizontal velocity of the anisotropic medium. An additional observed parameter is the time mismatch , which we define to be the difference between the vertical two-way traveltime to a reflector and the time-converted wide-angle position of the reflector. The magnitude of the time mismatch is typically <1.0  s (when the whole crust is anisotropic) and is found to be closely related to the magnitude and sign of the anisotropic anellipticity. The relationships are extendible to more complicated models, including those with vertical velocity gradients, crustal zonation, and lower symmetry orders.
  A time mismatch may be symptomatic of the presence of anisotropy. We illustrate the observation of a time mismatch for a real multi-offset seismic data set collected north of Scotland and discuss the implications for crustal anisotropy in that region.  相似文献   

Researching local elites: reflexivity, ‘situatedness’ and political-temporal contingency     

Kevin G. Ward  Martin Jones   《Geoforum》1999,30(4):70

Since the late 1970s, the UK has experienced a series of changes in the mechanisms of governing local economic development. This paper considers the methodological consequences of these recent changes. Drawing on two local elite-based case studies, involving semi-structured interviews, we reflect on our acquired ‘situated knowledge’ and argue that this is related to the contingent nature of our respective research access. We advocate that an approach sensitive to ‘research situatedness’ (with respect to the politics of time as a ‘research moment’) is essential to avoid over generalising from our experiences. To address this concern, the paper offers two concepts for debate – political-temporal contingency and the mode of entry.  相似文献   

Diatom responses to late-glacial and early-Holocene environmental changes at Kråkenes, western Norway   总被引：1，自引：0，他引：1  

E.G. Bradshaw  V. J. Jones  H.J.B. Birks  Hilary H. Birks 《Journal of Paleolimnology》2000,23(1):21-34

A stratigraphic diatom sequence is presented for the period from 13,870-9,170 cal BP from Kråkenes Lake, western Norway. Changes in species assemblages are discussed with reference to the changing environmental conditions in the Allerød, Younger Dryas, and the early Holocene and to the development of the aquatic ecosystem. The site is sensitive to acidification, and diatom-based transfer functions are applied to estimate the past pH status. The combination of rapid sediment accumulation together with an excellent calibrated radiocarbon chronology means that the rate of inferred pH change and associated increase in [H⁺] can be assessed and compared with recent, anthropogenically acidified situations.The Allerød diatom assemblages are dominated by benthic taxa particularly Fragilaria species, indicating an unproductive, alkaline, turbid, and immature system. Diatoms are absent in the early part of the Younger Dryas, but subsequently a sparse planktonic flora develops reflecting decreased turbidity and/or increased nutrient supply. A clear sequence of diatom assemblages is seen in the early Holocene. A short-lived peak of Stephanodiscus species indicating a period of increased nutrient availability occurred at ca. 11,500 cal BP. Throughout the early Holocene, acid-tolerant species increasingly replaced less acidophilous, circumneutral taxa.The lake became slightly more acid during the Allerød, but this was statistically insignificant in a trend test involving regression of pH or [H⁺] in relation to age. Diatom-inferred pH declined rapidly during the early Holocene period investigated (9,175-11,525 cal BP) with a statistically significant overall rate of 0.024 pH units per 100 yrs. This consisted of an older (ca. 11,525-10,255 cal BP) phase, where pH fell more rapidly at up to 0.095 pH units per 100 yrs; and a younger phase after ca. 10,500 cal BP where the pH fall was extremely slow (0.008 pH units per 100 yrs) and was not statistically significant.In the Allerød a combination of low catchment productivity together with disturbance, weathering, and minerogenic inwash ensured that the base-cation status remained relatively high. In the Holocene the catchment soils stabilised and base cations were sequestered by terrestrial vegetation and soil. This resulted in reduced base-cation leaching and this, together with the production of organic acids caused the lake to acidify, reaching an equilibrium by ca. 10,000 cal BP.  相似文献   

Multiscale Terrain and Topographic Modelling with the Implicit TIN   总被引：1，自引：0，他引：1  

David B. Kidner  J. Mark Ware  rew J. Sparkes  & Christopher B. Jones 《Transactions in GIS》2000,4(4):361-378

It is often assumed that real land surfaces demonstrate the statistically self-affine scaling behaviour of fractional Brownian surfaces. Tests of this assumption against empirical data, however, show many deviations. Estimates of fractal properties vary between methods and over different scale ranges. So far, this empirical evidence has come from the analysis of variograms for DEMs representing areas up to tens of kilometres in diameter. Here we report results obtained by using variograms to analyse land surface DEMs at the continental scale, with a grid resolution of 30 arc seconds. Results reveal variogram curvature and breaks of slope, but also linear sections over distance lags of hundreds of kilometres. The estimated mean fractal dimension calculated from these sections is 2.66, substantially higher for all continents at these broad scales (around 200 km) than values calculated at the erosional landscape scale (around 200 m). Thus the land surface is not self-affine, and it is not clear that it follows any simple multifractal model. At the longest wavelengths, patterns found in the variograms appear to be related to broad tectonic features of the Earth's surface. For the reader to assess their quality and generality, estimates of fractal dimension should always be accompanied by statements of the scale range covered and the goodness of fit to a log-linear relationship.  相似文献   

Multiwavelength observations of an evolved galaxy group: an end-point of galaxy merging?     

L. R. Jones  T. J. Ponman  Duncan A. Forbes 《Monthly notices of the Royal Astronomical Society》2000,312(1):139-150

The group of galaxies RXJ1340.6+4018 has approximately the same bolometric X-ray luminosity as other bright galaxy groups and poor clusters such as the Virgo cluster. However, 70 per cent of the optical luminosity of the group comes from a dominant giant elliptical galaxy, compared with 5 per cent from M87 in Virgo.The second brightest galaxy in RXJ1340.6+4018 is a factor of 10 fainter (Δ m ₁₂=2.5 mag) than the dominant elliptical, and the galaxy luminosity function has a gap at about L *.
We interpret the properties of the system as a result of galaxy merging within a galaxy group. We find that the central galaxy lies on the Fundamental Plane of ellipticals, has an undisturbed, non-cD morphology, and has no spectral features indicative of recent star formation, suggesting that the last major merger occurred ≳4 Gyr ago. The deviation of the system from the cluster L _X− T relation in the opposite sense to most groups may be caused by an early epoch of formation of the group or a strong cooling flow.
The unusual elongation of the X-ray isophotes and the similarity between the X-ray and optical ellipticities at large radii (∼230 kpc) suggest that both the X-ray gas and the outermost stars of the dominant galaxy are responding to an elongated dark matter distribution. RXJ1340.6+4018 may be part of a filamentary structure related to infall in the outskirts of the cluster A1774.  相似文献   

Book Review: Regression Analysis of Count Data. By A. Colin Cameron and Pravin K. Trivedi Cambridge University Press,Cambridge, UK, 1998, 411 p., US$64.95/US$24.95, ISBN 0-521-63201-3 (hardbound), ISBN 0-521-63567-5 (paperbound)     

Jones  Thomas A. 《Mathematical Geosciences》2000,32(8):1001-1003

Mathematical Geosciences -  相似文献   

Late quaternary sediment sources, storage and transfers within mountain basins using clast lithological analysis: Pineta Basin, central Pyrenees, Spain     

Dr. A. P. Jones 《Geomorphology》2000,34(3-4)

Understanding basin-wide sediment dynamics, both spatially and temporally, is an important antecedent to eventual quantitative interpretation of sediment transfer within mountain fluvial systems. This paper describes an attempt to trace sediment transfer modes and pathways using clast lithological analysis in a small mountain basin strongly influenced by glaciation: the Pineta Basin in the central Pyrenees of Spain. The paper interprets slope–channel interaction by encompassing the whole basin, enabling staged sedimentary pathways to be revealed. Additionally, bed-material textures of the modern rivers and youngest La Sarra Terrace were investigated to provide further information on the geomorphic coupling of the system. Relatively few studies have taken this approach. Glacial and later, fluvial systems transferred the sediments creating laterally extensive, polylithological sediment stores. Local depositional systems overprint this inherited signature. To what extent depends on the size and energy of the local system. Significant impacts are made by conduits, such as large-scale fluvially dominated fans and waterfalls, which deliver local lithologies to the main river. Conduits may be part of the main river system or part of the tributary system. Conduits are the most important elements when considering provenance studies and theoretical modelling.  相似文献