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  • 1
    Electronic Resource
    Electronic Resource
    Productivity and nutritive value of some cultivated perennial grasses and mixtures in the alpine region of the Tibetan Plateau (2003)
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 58 (2003), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The productivity and nutritive value of some cultivated perennial grasses, Bromus inermis (B), Elymus sibricus (S), E. nutans (N), Agropyron cristatum (A), Poa crymophila (P) and mixtures B + N, S + A, B + S + A, S + B + N, N + S + A, B + S + N + A, B + N + A + P, B + S +A + P and S + N + A + P, in the alpine region of the Tibetan Plateau were investigated. Elymus nutans and E. sibricus and the mixtures, B + S + N + A, B + S +A + P and S + N + A + P, were most productive with yields of dry matter (DM) of between 11 000 and 14 000 kg−1 of biomass annually in the second harvest year. Acid-detergent fibre (ADF) concentrations increased (P 〈 0·05), and crude protein (CP) concentrations and in sacco DM degradability values decreased (P 〈 0·05) with the maturity of the cultivated grasses. Swards, based on these species and mixtures, have the potential to be the main choices for cultivation in the Tibetan Plateau because they produce more nutrients than other grass species and mixtures. Late August (flowering stage of dominant grasses) is the optimum time for harvesting as the yield of rumen-degradable CP is highest that of DM relatively high and the DM degradability is satisfactory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2494.2003.00382.x
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  • 2
    Electronic Resource
    Electronic Resource
    Productivity and persistence of perennial grass mixtures under competition from annual weeds in the alpine region of the Qinghai-Tibetan Plateau (2005)
    Oxford, UK : Blackwell Science Ltd
    Weed research 45 (2005), S. 0 
    Details
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In the alpine region of the Qinghai-Tibetan Plateau four indigenous perennial grass species Bromus inermis (BI), Elymus sibiricus (ES), Elymus nutans (EN) and Agropyron cristatum (AC) were cultivated as three mixtures with different compositions and seeding rates, BI + EN, BI + ES + AC and BI + ES + EN + AC. From 1998 to 2001 there were three different weeding treatments: never weeded (CK); weeded on three occasions in the first year (1-y) and weeded on three occasions in both the first and second year (2-y) and their effect of grass combination and interactions on sward productivity and persistence was measured. Intense competitive interference by weedy annuals reduced dry matter (DM) yield of the swards. Grass combination significantly affected sward DM yields, leaf area index (LAI) and foliar canopy cover and also species composition DM and LAI, and species plant cover. Interaction between weeding treatments and grass combination was significant for sward DM yield, LAI and canopy cover, but not on species composition for DM, LAI or species plant cover. Grass mixture BI + ES + EN + AC gave the highest sward DM yield and LAI for both weeding and non-weeding treatments. Species ES and EN were competitively superior to the others. Annual weedy forbs must be controlled to obtain productive and stable mixtures of perennial grasses, and germination/emergence is the most important time for removal. Weeding three times (late May, late June and mid-July) in the establishment year is enough to maintain the production and persistence of perennial grass mixtures in the following growing seasons. Extra weeding three times in the second growing year makes only a slight improvement in productivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3180.2004.00440.x
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  • 3
    Electronic Resource
    Electronic Resource
    A Correlation between the Spectra of Non-thermal Radio Sources and their Brightness Temperatures (1962)
    [s.l.] : Nature Publishing Group
    Nature 195 (1962), S. 692-693 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1 shows the spectra of the eleven sources which show a marked deviation from a simple power law spectrum. Of these, Cygnus A has long been known to have a spectrum of this type2'3. Fig, 1 Spectra which have been found to show considerable curvature. The sources CTA 21 and CTA 102 are taken ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/195692a0
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  • 4
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    A discrete chemo-dynamical model of the giant elliptical galaxy NGC 5846: dark matter fraction, internal rotation, and velocity anisotropy out to six effective radii (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-03
    Description: We construct a suite of discrete chemo-dynamical models of the giant elliptical galaxy NGC 5846. These models are a powerful tool to constrain both the mass distribution and internal dynamics of multiple tracer populations. We use Jeans models to simultaneously fit stellar kinematics within the effective radius R e , planetary nebula (PN) radial velocities out to 3 R e , and globular cluster (GC) radial velocities and colours out to 6 R e . The best-fitting model is a cored dark matter halo which contributes ~10 per cent of the total mass within 1 R e , and 67 per cent ± 10 per cent within 6 R e , although a cusped dark matter halo is also acceptable. The red GCs exhibit mild rotation with v max / 0  ~ 0.3 in the region R 〉 R e , aligned with but counter-rotating to the stars in the inner parts, while the blue GCs and PNe kinematics are consistent with no rotation. The red GCs are tangentially anisotropic, the blue GCs are mildly radially anisotropic, and the PNe vary from radially to tangentially anisotropic from the inner to the outer region. This is confirmed by general made-to-measure models. The tangential anisotropy of the red GCs in the inner regions could stem from the preferential destruction of red GCs on more radial orbits, while their outer tangential anisotropy – similar to the PNe in this region – has no good explanation. The mild radial anisotropy of the blue GCs is consistent with an accretion scenario.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Assessing the Jeans Anisotropic Multi-Gaussian Expansion method with the Illustris simulation (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-03
    Description: We assess the effectiveness of the Jeans Anisotropic Multi-Gaussian Expansion (JAM) technique with a state-of-the-art cosmological hydrodynamic simulation, the Illustris project. We perform JAM modelling on 1413 simulated galaxies with stellar mass M * 〉 10 10 M , and construct an axisymmetric dynamical model for each galaxy. Combined with a Markov chain Monte Carlo simulation, we recover the projected root-mean-square velocity ( V rms ) field of the stellar component, and investigate constraints on the stellar mass-to-light ratio, M */ L , and the fraction of dark matter f DM within 2.5 effective radii ( R e ). We find that the enclosed total mass within 2.5 R e is well constrained to within 10 per cent. However, there is a degeneracy between the dark matter and stellar components with correspondingly larger individual errors. The 1 scatter in the recovered M */ L is 30–40 per cent of the true value. The accuracy of the recovery of M */ L depends on the triaxial shape of a galaxy. There is no significant bias for oblate galaxies, while for prolate galaxies the JAM-recovered stellar mass is on average 18 per cent higher than the input values. We also find that higher image resolutions alleviate the dark matter and stellar mass degeneracy and yield systematically better parameter recovery.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    A Schwarzschild model of the Galactic bar with initial density from N-body simulations (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-12
    Description: Using the potential from N -body simulations, we construct the Galactic bar models with the Schwarzschild method. By varying the pattern speed and the position angle of the bar, we find that the best-fitting bar model has pattern speed p  = 40 km s –1 kpc –1 , and bar angle bar  = 45°. N -body simulations show that the best-fitting model is stable for more than 1.5 Gyr. Combined with the results in Wang et al., we find that the bar angle and/or the pattern speed are not well constrained by Bulge Radial Velocity Assay data in our Schwarzschild models. The proper motions predicted from our model are slightly larger than those observed in four fields. In the future, more kinematic data from the ground- and space-based observations will enable us to refine our model of the Milky Way bar.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Determining the local dark matter density with LAMOST data (2016)
    Oxford University Press
    Details
    Publication Date: 2016-04-08
    Description: Measurement of the local dark matter density plays an important role in both Galactic dynamics and dark matter direct detection experiments. However, the estimated values from previous works are far from agreeing with each other. In this work, we provide a well-defined observed sample with 1427 G- and K-type main-sequence stars from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope spectroscopic survey, taking into account selection effects, volume completeness, and the stellar populations. We apply a vertical Jeans equation method containing a single exponential stellar disc, a razor thin gas disc, and a constant dark matter density distribution to the sample, and obtain a total surface mass density of $78.7 ^{+3.9}_{-4.7}\,\rm M_{{\odot }}\,\rm pc^{-2}$ up to 1 kpc and a local dark matter density of $0.018\pm 0.0054\,\rm M_{{\odot }}\,\rm pc^{-3}$ . We find that the sampling density (i.e. number of stars per unit volume) of the spectroscopic data contributes to about two-third of the uncertainty in the estimated values. We discuss the effect of the tilt term in the Jeans equation and find it has little impact on our measurement. Other issues, such as a non-equilibrium component due to perturbations and contamination by the thick-disc population, are also discussed.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    SDSS-IV MaNGA: environmental dependence of stellar age and metallicity gradients in nearby galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-30
    Description: We present a study on the stellar age and metallicity distributions for 1105 galaxies using the starlight software on MaNGA (Mapping Nearby Galaxies at APO) integral field spectra. We derive age and metallicity gradients by fitting straight lines to the radial profiles, and explore their correlations with total stellar mass M * , NUV  –  r colour and environments, as identified by both the large-scale structure (LSS) type and the local density. We find that the mean age and metallicity gradients are close to zero but slightly negative, which is consistent with the inside-out formation scenario. Within our sample, we find that both the age and metallicity gradients show weak or no correlation with either the LSS type or local density environment. In addition, we also study the environmental dependence of age and metallicity values at the effective radii. The age and metallicity values are highly correlated with M * and NUV  –  r and are also dependent on LSS type as well as local density. Low-mass galaxies tend to be younger and have lower metallicity in low-density environments while high-mass galaxies are less affected by environment.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Made-to-measure galaxy models - III. Modelling with Milky Way observations (2013)
    Oxford University Press
    Details
    Publication Date: 2013-01-03
    Description: We demonstrate how the Syer and Tremaine made-to-measure method of stellar dynamical modelling can be adapted to model a rotating galactic bar. We validate our made-to-measure changes using observations constructed from the existing Shen et al. N -body model of the Milky Way bar, together with kinematic observations of the Milky Way bulge and bar taken by the Bulge Radial Velocity Assay. Our results for a combined determination of the bar angle and bar pattern speed (30° and 40 km s –1 kpc –1 ) are consistent with those determined by the N -body model. Whilst the made-to-measure techniques we have developed are applied using a particular N -body model and observational data set, they are in fact general and could be applied to other Milky Way modelling scenarios utilizing different N -body models and data sets. Additionally, we use the exercise as a vehicle for illustrating how N -body and made-to-measure methods might be combined into a more effective method.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Star formation rates of star-forming galaxies from the WISE All-Sky Survey (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-16
    Description: We explore correlations between extinction-corrected Hα, Hβ and ${\rm [O\,\small {II}]_{double}}$ luminosities versus 12- and 22-μm band luminosities, based on matching samples from the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer ( WISE ). All the coefficients show strong correlations between Balmer lines and mid-infrared (MIR) luminosities, while the extinction-corrected ${\rm [O\,\small {II}]_{double}}$ shows a weaker correlation with MIR luminosities. The extinction-corrected emission-line (EL) luminosities are more tightly correlated with linear combinations of EL(obs) and MIR luminosities than with pure MIR luminosities. Linear combinations include both direct and dust-obscured star formation activity in galaxies and offer an improved star formation rate (SFR) indicator for star-forming galaxies. The factor that causes log 10 L MIR /log 10 L Hα to vary is the metallicity. We find that log 10 ( L Hα (obs) + α  L MIR ) and ${\log _{10}(L[{\rm O}\,\small {II}]_{\rm double}(\mathrm{obs})+\alpha \times L_{\rm MIR})}$ , rather than pure MIR luminosities or ${\rm [O\,\small {II}]_{double}}$ alone, are good proxies for extinction-corrected log 10 L Hα , with a residual that is independent of metallicity. The morphologies have weak correlations with log 10 L MIR /log 10 L EL ratios. E ( B  – V ) can be estimated by log 10 [ L MIR / L Hα (obs)].
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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