22,955 research outputs found
Made-to-measure galaxy models - III Modelling with Milky Way observations
We demonstrate how the Syer & 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. (2010) 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 (BRAVA). Our results for a combined determination of the bar
angle and bar pattern speed (~30 degrees and ~40 km/s/kpc) 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 utilising 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.Comment: Accepted for publication, 10 pages, 7 figure
How anthropogenic shifts in plant community composition alter soil food webs.
There are great concerns about the impacts of soil biodiversity loss on ecosystem functions and services such as nutrient cycling, food production, and carbon storage. A diverse community of soil organisms that together comprise a complex food web mediates such ecosystem functions and services. Recent advances have shed light on the key drivers of soil food web structure, but a conceptual integration is lacking. Here, we explore how human-induced changes in plant community composition influence soil food webs. We present a framework describing the mechanistic underpinnings of how shifts in plant litter and root traits and microclimatic variables impact on the diversity, structure, and function of the soil food web. We then illustrate our framework by discussing how shifts in plant communities resulting from land-use change, climatic change, and species invasions affect soil food web structure and functioning. We argue that unravelling the mechanistic links between plant community trait composition and soil food webs is essential to understanding the cascading effects of anthropogenic shifts in plant communities on ecosystem functions and services
Global change impacts on forest soils: linkage between soil biota and carbon-nitrogen-phosphorus stoichiometry
orest ecosystems are subjected to global change drivers worldwide, such as increasing temperature, atmospheric carbon dioxide, nutrient pollution, as well as changes in fire and precipitation regimes. These global change drivers have greatly modified the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P), which has an impact on primary productivity in forest ecosystems and in turn, affect the quality and quantity of resources entering the soil food web. However, C, N, and P soil dynamics have been mostly studied without considering their coupling effects on soil organisms. This is of critical interest because changes in nutrient stoichiometry may have a strong effect on soil biota and the ecosystem functions they drive. Further, most studies have focused on global change effects on bacteria and fungi and their C:N:P stoichiometry, while neglecting other soil organisms at higher trophic levels. This has led to an incomplete understanding of how the entire soil food web drives ecosystem processes involved in organic matter turnover and nutrient cycling. Here, we review studies that investigated how global change drivers impact C:N:P stoichiometry of soil organisms at different trophic levels in forest ecosystems and identify important knowledge gaps. We propose future directions for research on global change impacts on the linkages between soil biota and C:N:P stoichiometry
Dynamic magnetic response of infinite arrays of ferromagnetic particles
Recently developed techniques to find the eigenmodes of a ferromagnetic
particle of arbitrary shape, as well as the absorption in the presence of an
inhomogeneous radio-frequency field, are extended to treat infinite lattices of
such particles. The method is applied to analyze the results of recent FMR
experiments, and yields substantially good agreement between theory and
experiment
Made-to-measure galaxy models - II Elliptical and Lenticular Galaxies
We take a sample of 24 elliptical and lenticular galaxies previously analysed
by the SAURON project using three-integral dynamical models created with
Schwarzschild's method, and re-analyse them using the made-to-measure (M2M)
method of dynamical modelling. We obtain good agreement between the two methods
in determining the dynamical mass-to-light (M/L) ratios for the galaxies with
over 80% of ratios differing by < 10% and over 95% differing by < 20%. We show
that (M/L)_M2M is approximately equal to (M/L)_Sch. For the global velocity
dispersion anisotropy parameter delta, we find similar values but with fewer of
the made-to-measure models tangentially anisotropic by comparison with their
SAURON Schwarzschild counterparts. Our investigation is the largest comparative
application of the made-to-measure method to date.Comment: 14 pages, 8 figures and 5 table
Structure and Physical Properties of SrNiRu\u3csub\u3e5\u3c/sub\u3eO\u3csub\u3e11\u3c/sub\u3e Single Crystals: An \u3cem\u3eR\u3c/em\u3e-Type Ferrite Based on Ordered Kagome Nets
Single crystals of the R-type ferrite SrNiRu5O11 were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on distorted kagome nets. The low-temperature dc magnetic susceptibilities (χ⊥ and χ∥, perpendicular and parallel to the c axis, respectively) diverge as T−0.3, and do not exhibit any indication of long-range magnetic order down to 4.5 K. The electrical resistivity varies as T1.6 below 40 K, which is typical of non-Fermi liquids, and may originate from a competition between residual magnetic interactions among Ni2+ (S = 1) spins and geometrical frustration on the two-dimensional kagome lattice of Ru3+ (S = ½) spins. The transverse magnetoresistivity ρxy at constant temperature T = 5 K for current (J) -magnetic field (H) configurations, J⊥H ∥ c axis and J ∥ H⊥c axis, reveals no anomalous contribution, which is consistent with the absence of magnetic order. Fits of the specific heat data below 10 K require a dominant, but unusual electronic term of the form Cel = γT1.2, which is expected for massless Dirac fermion states in topological insulators, or spin-liquid phases
Higgs-gauge boson interactions in the economical 3-3-1 model
Interactions among the standard model gauge bosons and scalar fields in the
framework of SU(3)_C X SU(3)_L X U(1)_X gauge model with minimal (economical)
Higgs content are presented. From these couplings, all scalar fields including
the neutral scalar and the Goldstone bosons can be identified and their
couplings with the usual gauge bosons such as the photon, the charged
and the neutral , without any additional condition, are recovered. In the
effective approximation, full content of scalar sector can be recognized. The
CP-odd part of Goldstone associated with the neutral non-Hermitian bilepton
gauge boson is decouple, while its CP-even counterpart has the mixing
by the same way in the gauge boson sector. Masses of the new neutral Higgs
boson and the neutral non-Hermitian bilepton are dependent on a
coefficient of Higgs self-coupling (). Similarly, masses of the
singly-charged Higgs boson and of the charged bilepton are
proportional through a coefficient of Higgs self-interaction (). The
hadronic cross section for production of this Higgs boson at the LHC in the
effective vector boson approximation is calculated. Numerical evaluation shows
that the cross section can exceed 260 .Comment: 22 pages, 1 figure, submitted to Phys. Rev.
Made-to measure galaxy models - I Methodology
We re-derive the made-to-measure method of Syer and Tremaine 1996, for
modelling stellar systems and individual galaxies, and demonstrate how
extensions to the made-to-measure method may be implemented and used. We
illustrate the enhanced made-to-measure method by determining the mass-to-light
ratio of a galaxy modelled as a Plummer sphere. From the standard galactic
observables of surface brightness and line-of-sight velocity dispersion
together with the h_4 Gauss-Hermite coefficient of the line-of-sight velocity
distribution, we successfully recover the true mass-to-light ratio of our toy
galaxy. Using kinematic data from Kleyna et al 2002, we then estimate the
mass-to-light ratio of the dwarf spheroidal galaxy Draco achieving a V-band
value of 539 \pm 136 M_{\odot} / L_{\odot}. We describe the main aspects of
creating a made-to-measure galaxy model and show how the key modelling
parameters may be determined.Comment: 18 pages, 15 figure
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