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  • 1
    Electronic Resource
    Electronic Resource
    Magnetometer array studies (1983)
    Springer
    Surveys in geophysics 6 (1983), S. 153-172 
    Details
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A review of experiments in which arrays of recording magnetometers deployed over an area of land to study induction problems is presented. Intensive array activities take place on a continual basis in North America, Australia, Scotland and Africa and array studies have been conducted in India, Scandinavia, and Russia. The main results are summarised. Analysis, presentation and interpretation of array data have also enjoyed significant developments which are discussed with illustrations. The use of multi-techniques in the analysis of array data has improved the reliability of the interpretational inferences. One-dimensional conductivity profiles can now be deduced by the simple inversion of the inductive response functionC(w, t) estimated from the vertical field Z and spatial gradient of the horizontal field components (ΔX/Δx+ΔY/Δy) of magnetometer array data with large gradient. Bounds can be placed on accepted profiles using the Monte Carlo process just as it is done in magnetotelluric data inversion. The results from array studies continue to improve our understanding of the synthesis of realistic tectonic models of the continents. The structure under some geothermal zones are now known through a number of recent studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01453999
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The collective review papers presented at the 7th IAGA Workshop on Electromagnetic Induction in the Earth and Moon (1986)
    Springer
    Surveys in geophysics 8 (1986), S. 235-238 
    Details
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01904060
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    Paper (German National Licenses)
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  • 3
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    Developing shellfish industry in Nigeria: technology and economics (2021)
    Fisheries Society of Nigeria | Lagos (Nigeria)
    In:  http://aquaticcommons.org/id/eprint/23534 | 19325 | 2018-05-10 09:44:16 | 23534 | Fisheries Society of Nigeria
    Details
    Publication Date: 2021-07-14
    Description: The paper asserted that shellfish resources are poorly developed and utilized in West Africa. This was proved by the fact that in 2008 total marine shellfish capture production in West Africa was only 29,815 tonnes. The advantages of Nigeria in beefing up its production are highlighted. Some of these advantages are on extensive coast line which has not been affected by industrial pollution. The tropical climate is also an advantage for growing of cultured shellfish. The paper highlighted that to maximize the potential of shellfish Mari-culture development requires education, training, seed production technology, grow-out technology, processing and marketing. These requirements are discussed in details in the paper.
    Description: FISON EKO 2010: Invited paper Includes:- 3 tables.;9 figs.;60 refs.
    Keywords: Biology ; Aquaculture ; ASE ; Nigeria ; Coast ; marine environment ; Shellfish ; Shellfish culture ; Shellfish fisheries
    Repository Name: AquaDocs
    Type: conference_item , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 1-21
    Format: 21
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    PAPER (OA)
  • 4
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    The mass discrepancy acceleration relation in early-type galaxies: extended mass profiles and the phantom menace to MOND (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-15
    Description: The dark matter (DM) haloes around spiral galaxies appear to conspire with their baryonic content: empirically, significant amounts of DM are inferred only below a universal characteristic acceleration scale. Moreover, the discrepancy between the baryonic and dynamical mass, which is usually interpreted as the presence of DM, follows a very tight mass discrepancy acceleration (MDA) relation. Its universality, and its tightness in spiral galaxies, poses a challenge for the DM interpretation and was used to argue in favour of MOdified Newtonian Dynamics (MOND). Here, we test whether or not this applies to early-type galaxies. We use the dynamical models of fast-rotator early-type galaxies by Cappellari et al. based on ATLAS 3D and SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) data, which was the first homogenous study of this kind, reaching ~4 R e , where DM begins to dominate the total mass budget. We find the early-type galaxies to follow an MDA relation similar to spiral galaxies, but systematically offset. Also, while the slopes of the mass density profiles inferred from galaxy dynamics show consistency with those expected from their stellar content assuming MOND, some profiles of individual galaxies show discrepancies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    The SLUGGS survey: exploring the globular cluster systems of the Leo II group and their global relationships (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-06
    Description: We present an investigation of the globular cluster (GC) systems of NGC 3607 and NGC 3608 as part of the ongoing SLUGGS (SAGES Legacy Unifying Globulars and GalaxieS) survey. We use wide-field imaging data from the Subaru telescope in the g, r and i filters to analyse the radial density, colour and azimuthal distributions of both GC systems. With the complementary kinematic data obtained from the Keck II telescope, we measure the radial velocities of a total of 81 GCs. Our results show that the GC systems of NGC 3607 and NGC 3608 have a detectable spatial extent of ~15 and 13 galaxy effective radii, respectively. Both GC systems show a clear bimodal colour distribution. We detect a significant radial colour gradient for the GC subpopulations in both galaxies. NGC 3607 exhibits an overabundance of red GCs on the galaxy minor axis and NGC 3608 shows a misalignment in the GC subpopulation position angles with respect to the galaxy stellar component. With the aid of literature data, we discuss several relationships between the properties of GC systems and their host galaxies. A one-to-one relation between the ellipticities of red GCs and the galaxy stellar light emphasizes the evolutionary similarities between them. In our sample of four slowly rotating galaxies with kinematically decoupled cores, we observe a higher ellipticity for the blue GC subpopulation than their red counterparts. Also, we notice the flattening of negative colour gradients for the blue GC subpopulations with increasing galaxy stellar mass. Finally, we discuss the formation scenarios associated with the blue GC subpopulation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The SLUGGS survey: chromodynamical modelling of the lenticular galaxy NGC 1023 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-02
    Description: Globular clusters (GCs) can be considered discrete, long-lived, dynamical tracers that retain crucial information about the assembly history of their parent galaxy. In this paper, we present a new catalogue of GC velocities and colours for the lenticular galaxy NGC 1023, we study their kinematics and spatial distribution, in comparison with the underlying stellar kinematics and surface brightness profile, and we test a new method for studying GC properties. Specifically, we decompose the galaxy light into its spheroid (assumed to represent the bulge+halo components) and disc components and use it to assign to each GC a probability of belonging to one of the two components. Then we model the galaxy kinematics, assuming a disc and spheroidal component, using planetary nebulae and integrated stellar light. We use this kinematic model and the probability previously obtained from the photometry to recalculate for each GC its likelihood of being associated with the disc, the spheroid, or neither. We find that the reddest GCs are likely to be associated with the disc, as found for faint fuzzies in this same galaxy, suggesting that the disc of this S0 galaxy originated at z ~= 2. The majority of blue GCs are found likely to be associated with the spheroidal (hot) component. The method also allows us to identify objects that are unlikely to be in equilibrium with the system. In NGC 1023 some of the rejected GCs form a substructure in phase space that is connected with NGC 1023 companion galaxy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The SLUGGS survey: combining stellar and globular cluster metallicities in the outer regions of early-type galaxies (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-15
    Description: The outer halo regions of early-type galaxies carry key information about their past accretion history. However, spectroscopically probing the stellar component at such galactocentric radii is still challenging. Using the DEep Imaging Multi-Object Spectrograph on the Keck, we have been able to measure the metallicities of the stellar and globular cluster components in 12 early-type galaxies out to more than 10 R e . We find similar metallicity gradients for the metal-poor and metal-rich globular cluster subpopulations, suggesting a common formation process for the two subpopulations. This is in conflict with most current theoretical predictions, where the metal-poor globular clusters are thought to be purely accreted and metal-rich globular clusters mostly formed in situ . Moreover, we find that the globular cluster metallicity gradients show a trend with galaxy mass, being steeper in lower mass galaxies than in higher mass galaxies. This is similar to what we find for the outermost galaxy stars and suggests a more active accretion history, with a larger role played by major mergers, in the most massive galaxies. This conclusion is qualitatively consistent with expectations from two-phase galaxy assembly models. Finally, we find that the small difference in metallicity between galaxy stars and metal-rich globular clusters at 1 R e may correlate with galaxy mass. The origin of this difference is not currently clear.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    The SLUGGS survey: the mass distribution in early-type galaxies within five effective radii and beyond (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-26
    Description: We study mass distributions within and beyond 5 effective radii ( R e ) in 23 early-type galaxies from the SAGES Legacy Unifying Globulars and Galaxies Survey, using their globular cluster (GC) kinematic data. The data are obtained with Keck/DEep Imaging Multi-Object Spectrograph, and consist of line-of-sight velocities for ~3500 GCs, measured with a high precision of ~15 km s –1 per GC and extending out to ~13 R e . We obtain the mass distribution in each galaxy using the tracer mass estimator of Watkins et al. and account for kinematic substructures, rotation of the GC systems and galaxy flattening in our mass estimates. The observed scatter between our mass estimates and results from the literature is less than 0.2 dex. The dark matter fraction within 5 R e ( f DM ) increases from ~0.6 to ~0.8 for low- and high-mass galaxies, respectively, with some intermediate-mass galaxies ( M * ~ 10 11 M ) having low f DM ~ 0.3, which appears at odds with predictions from simple galaxy models. We show that these results are independent of the adopted orbital anisotropy, stellar mass-to-light ( M / L ) ratio, and the assumed slope of the gravitational potential. However, the low f DM in the ~10 11 M galaxies agrees with the cosmological simulations of Wu et al. where the pristine dark matter distribution has been modified by baryons during the galaxy assembly process. We find hints that these M * ~ 10 11 M galaxies with low f DM have very diffuse dark matter haloes, implying that they assembled late. Beyond 5 R e , the M / L gradients are steeper in the more massive galaxies and shallower in both low and intermediate mass galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The SLUGGS survey: globular clusters and the dark matter content of early-type galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-25
    Description: A strong correlation exists between the total mass of a globular cluster (GC) system and the virial halo mass of the host galaxy. However, the total halo mass in this correlation is a statistical measure conducted on spatial scales that are some 10 times that of a typical GC system. Here we investigate the connection between GC systems and galaxy's dark matter on comparable spatial scales, using dynamical masses measured on a galaxy-by-galaxy basis. Our sample consists of 17 well-studied massive (~10 11 M ) early-type galaxies from the SLUGGS survey. We find the strongest correlation to be that of the blue (metal-poor) GC subpopulation and the dark matter content. This correlation implies that the dark matter mass of a galaxy can be estimated to within a factor of 2 from careful imaging of its GC system. The ratio of the GC system mass to that of the enclosed dark matter is nearly constant. We also find a strong correlation between the fraction of blue GCs and the fraction of enclosed dark matter, so that a typical galaxy with a blue GC fraction of 60 per cent has a dark matter fraction of 86 per cent over similar spatial scales. Both halo growth and removal (via tidal stripping) may play some role in shaping this trend. In the context of the two-phase model for galaxy formation, we find galaxies with the highest fractions of accreted stars to have higher dark matter fractions for a given fraction of blue GCs.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Geophysical Evaluation of Gold Potential in Southeastern Part of Kafin-Koro, Northwestern Nigeria (2018)
    Science and Education Publishing
    Details
    Publication Date: 2018-12-12
    Description: Gold mineralization in Nigeria is traversed by regional northwest - southeast lineaments or shear zone which have been considered as continental extension of oceanic transform fault - fracture zone, and it is suggested that the migmatization and metamorphic deformation of the metasedimentary and metavolcanic rocks gave rise to dispersion of gold in quartz veins within the Nigeria basement complex. Combined geophysical methods have been used in the exploration for ore mineral bodies. Induced polarization (IP) technique has proved favourable for mineral exploration in hard rock terrain, as well as for ground water exploration and environmental geology studies. Also, magnetic technique has been used in identifying massive sulfide hosted quartz veins. The study area lies within the Kushaka schist Formation of the north-western block of Nigeria basement complex and Nigeria metallogeny province, the formation has been intruded by large volumes of granitic rocks that led to extensive migmatization of metasedimentary and metavolcanic rocks carrying substantial gold mineralization. Combined magnetic and IP and resistivity imaging technique was used in the study. The magnetic profiles in the study area showed anomalies of varying amplitudes. The variation in amplitudes of the residual intensity may be due to the presence of geological structures such as faults, dykes and contacts in the area. The total magnetic intensity map of the area exhibits zonation and alteration that indicates hydrothermal alteration which is usually associated with mineralization probably as a result of intrusion. Observed apparent resistivity and IP data presented as pseudo-section and 2-D inverted resistivity-IP mode show a qualitative idea of resistivity and chargeability distribution in the subsurface. The ground magnetic survey generally suggests a step or an edge structures like dyke or intrusion, such structures are of interest may hold mineralization at certain depth.
    Print ISSN: 2373-6690
    Electronic ISSN: 2373-6704
    Topics: Geosciences
    Published by Science and Education Publishing
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