1,862 research outputs found
A theory on the vertical dispersal of splash-borne pathogen units influenced by arable crop characteristics
An analytical mechanistic model was proposed to study the vertical spread of splash-borne spores in arable crop canopies. Three crop types were considered, with different LAI distributions. The influences of crop characteristics and rain properties on vertical spread were investigated. The LAI affected the amount of rain being intercepted by the canopy and the vertical displacement of splashed spores. Splash dispersal was concentrated in the upper canopy layers in a crop having LAI constant or increasing with height. Splash probabilities were greatest and most spores were intercepted in the layers just beneath the upper layers in a crop having LAI decreasing with height
A theory on the vertical dispersal of splash-borne pathogen units influenced by arable crop characteristics
An analytical mechanistic model was proposed to study the vertical spread of splash-borne spores in arable crop canopies. Three crop types were considered, with different LAI distributions. The influences of crop characteristics and rain properties on vertical spread were investigated. The LAI affected the amount of rain being intercepted by the canopy and the vertical displacement of splashed spores. Splash dispersal was concentrated in the upper canopy layers in a crop having LAI constant or increasing with height. Splash probabilities were greatest and most spores were intercepted in the layers just beneath the upper layers in a crop having LAI decreasing with height
Self-interacting dark matter and Higgs bosons in the SU(3)_C x SU(3)_L x U(1)_N model with right-handed neutrinos
We investigate the possibility that dark matter could be made from CP-even
and CP- odd Higgs bosons in the SU(3)_C X SU(3)_L X U(1)_N (3-3-1) model with
right-handed neutrinos. This self-interacting dark matters are stable without
imposing of new symmetry and should be weak-interacting.Comment: 7 pages, Latex, To appear in Europhys. Let
Semi-Analytical Models for the Formation of Disk Galaxies II. Dark Matter versus Modified Newtonian Dynamics
We present detailed semi-analytical models for the formation of disk galaxies
both in a Universe dominated by dark matter (DM), and in one for which the
force law is given by modified Newtonian dynamics (MOND). We tune the models to
fit the observed near-infrared Tully-Fisher (TF) relation, and compare numerous
predictions of the resulting models with observations. The DM and MOND models
are almost indistinguishable. They both yield gas mass fractions and dynamical
mass-to-light ratios which are in good agreement with observations. Both models
reproduce the narrow relation between global mass-to-light ratio and central
surface brightness, and reveal a characteristic acceleration, contrary to
claims that these relations are not predicted by DM models. Both models require
SN feedback in order to reproduce the lack of high surface brightness dwarf
galaxies. However, the introduction of feedback to the MOND models steepens the
TF relation and increases the scatter, making MOND only marginally consistent
with observations. The most serious problem for the DM models is their
prediction of steep central rotation curves. However, the DM rotation curves
are only slightly steeper than those of MOND, and are only marginally
inconsistent with the poor resolution data on LSB galaxies.Comment: 26 pages, 11 figures. Accepted for publication in Ap
Reliability and efficiency at global level in power systems
In EU project E-Price it is proposed to attribute reliability to the Transmission System Operator (TSO) and the drive for efficiency to the Balance Responsible Parties (BRP). Two main ideas are proposed. The first idea is to make BRPs themselves responsible for estimating their uncertainty in real time and hedge their imbalance risks, yielding the proposal to introduce dual-sided markets for ancillary services. The second idea is to reduce the conservatism in exploiting the inter-area transmission capacity (ATC), while still guaranteeing sufficient degrees of reliability. This paper explains, elucidates and concludes, based on qualitative arguments and supported by quantitative simulations and calculations, that both proposals are beneficial to improve the stated compromise between reliability and economy
Cannibalism as a life boat mechanism
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one
The low dark matter content of the lenticular galaxy NGC 3998
We observed the lenticular galaxy NGC 3998 with the Mitchell Integral-Field Spectrograph and extracted line-of-sight velocity distributions out to three half-light radii. We constructed collisionless orbit models in order to constrain NGC 3998's dark and visible structure, using kinematics from both the Mitchell and SAURON instruments. We find NGC 3998 to be almost axisymmetric, seen nearly face-on with a flattened intrinsic shape â i.e. a face-on fast rotator. We find an I-band mass-to-light ratio of 4.7 +0.32/â0.45 in good agreement with previous spectral fitting results for this galaxy. Our best-fitting orbit model shows a both a bulge and a disc component, with a non-negligible counter-rotating component also evident. We find that relatively little dark matter is needed to model this galaxy, with an inferred dark mass fraction of just 7.1 +8.1/â7.1 percent within one half-light radius.Publisher PDFPeer reviewe
Nuclear stellar discs in low-luminosity elliptical galaxies: NGC 4458 and NGC 4478
We present the detection of nuclear stellar discs in the low-luminosity
elliptical galaxies NGC 4458 and NGC 4478, which are known to host a
kinematically-decoupled core. Using archival HST imaging, and available
absorption line-strength index data based on ground-based spectroscopy, we
investigate the photometric parameters and the properties of the stellar
populations of these central structures. Their scale length, h, and face-on
central surface brightness, mu_0^c, fit on mu_0^c-h relation for galaxy discs.
For NGC 4458 these parameters are typical for nuclear discs, while the same
quantities for NGC 4478 lie between those of nuclear discs and the discs of
discy ellipticals. We present Lick/IDS absorption line-strength measurements of
Hbeta, Mgb, along the major and minor axes of the galaxies. We model these
data with simple stellar populations that account for the alpha/Fe
overabundance. The counter-rotating central disc of NGC 4458 is found to have
similar properties to the decoupled cores of bright ellipticals. This galaxy
has been found to be uniformly old despite being counter-rotating. In contrast,
the cold central disc of NGC 4478 is younger, richer in metals and less
overabundant than the main body of the galaxy. This points to a prolonged star
formation history, typical of an undisturbed disc-like, gas-rich (possibly
pre-enriched) structure.Comment: 11 pages, 8 figures, accepted for pubblication on MNRA
Detection of non-ordered central gas motions in a sample of four low surface brightness galaxies
We present integral-field spectroscopy of the ionized gas in the central
regions of four galaxies with a low surface brightness disk taken with the
Visible Multi Object Spectrograph at the Very Large Telescope and aimed at
testing the accuracy in the determination of the central logarithmic slope
of the mass density radial profile in this
class of objects. For all the sample galaxies we subtracted from the observed
velocity field the best-fit model of gas in circular motions and derived the
residuals. Only ESO-LV 5340200 is characterized by a regular velocity field. We
extracted the velocity curves of this galaxy along several position angles, in
order to estimate the uncertainty in deriving the central gradient of the total
mass density from long-slit spectroscopy. We report the detection of strong
non-ordered motions of the ionized gas in three out of four sample galaxies.
The deviations have velocity amplitudes and spatial scales that make not
possible to disentangle between cuspy and core density radial profiles.Comment: 7 pages, 4 figures, accepted for publication in A&
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