18,119 research outputs found
Within- and between-pen transmission of Classical Swine Fever Virus: a new method to estimate the basic reproduction ratio from transmission experiments
We present a method to estimate basic reproduction ratio R0 from transmission experiments. By using previously published data of experiments with Classical Swine Fever Virus more extensively, we obtained smaller confidence intervals than the martingale method used in the original papers. Moreover, our method allows simultaneous estimation of a reproduction ratio within pens R0w and a modified reproduction ratio between pens R'0b. Resulting estimates of R0w and R'0b for weaner pigs were 100 (95% CI 54.4-186) and 7.77 (4.68-12.9), respectively. For slaughter pigs they were 15.5 (6.20-38.7) and 3.39 (1.54-7.45), respectively. We believe, because of the smaller confidence intervals we were able to obtain, that the method presented here is better suited for use in future experiments
Sustainable Soesterkwartier
The municipality of Amersfoort wants to construct an endurable and sustainable eco-town in the Soesterkwartier neighbourhood, by taking future climate change into account. The impact of climate change at the location of the proposed eco-town was studied by a literature review
Electronic orders near the type-II van Hove singularity in BC
Using the functional renormalization group, we investigate the electron
instability in the single-sheet BC when the electron filling is near a
type-II van Hove singularity. For a finite Hubbard interaction, the
ferromagnetic-like spin density wave order dominates in the immediate vicinity
of the singularity. Elsewhere near the singularity the p-wave superconductivity
prevails. We also find that a small nearest-neighbor Coulomb repulsion can
enhance the superconductivity. Our results show that BC would be a
promising candidate to realize topological superconductivity, but the
transition temperature is practically sizable only if the local interaction is
moderately strong.Comment: 6 pages, 6 color figures. arXiv admin note: text overlap with
arXiv:1503.0047
Transport of interacting electrons in arrays of quantum dots and diffusive wires
We develop a detailed theoretical investigation of the effect of Coulomb
interaction on electron transport in arrays of chaotic quantum dots and
diffusive metallic wires. Employing the real time path integral technique we
formulate a new Langevin-type of approach which exploits a direct relation
between shot noise and interaction effects in mesoscopic conductors. With the
aid of this approach we establish a general expression for the Fano factor of
1D quantum dot arrays and derive a complete formula for the interaction
correction to the current which embraces all perturbative results previously
obtained for various quasi-0D and quasi-1D disordered conductors and extends
these results to yet unexplored regimes.Comment: 12 pages, 2 figure
On Star Formation and the Non-Existence of Dark Galaxies
We investigate whether a baryonic dark galaxy or `galaxy without stars' could
persist indefinitely in the local universe, while remaining stable against star
formation. To this end, a simple model has been constructed to determine the
equilibrium distribution and composition of a gaseous protogalactic disk.
Specifically, we determine the amount of gas that will transit to a Toomre
unstable cold phase via the H2 cooling channel in the presence of a UV--X-ray
cosmic background radiation field.
All but one of the models are predicted to become unstable to star formation.
Moreover, we find that all our model objects would be detectable via HI line
emission, even in the case that star formation is potentially avoided. These
results are consistent with the non-detection of isolated extragalactic HI
clouds with no optical counterpart (galaxies without stars) by HIPASS.
Additionally, where star formation is predicted to occur, we determine the
minimum interstellar radiation field required to restore gravothermal
stability, which we then relate to a minimum global star formation rate. This
leads to the prediction of a previously undocumented relation between HI mass
and star formation rate that is observed for a wide variety of dwarf galaxies
in the HI mass range 10^8--10^10 M_sun. The existence of such a relation
strongly supports the notion that the well observed population of dwarf
galaxies represent the minimum rates of self-regulating star formation in the
universe. (Barely abridged)Comment: 19 pages, 8 figures, TeX using emulateapj.cls, v2 accepted for
publication in ApJ (16/8/5) with one figure deleted and a number of minor
clarifying revision
The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies
Although numerous simulations have been done to understand the effects of
intense bursts of star formation on high surface brightness galaxies, few
attempts have been made to understand how localized starbursts would affect
both the color and surface brightness of low surface brightness (LSB) galaxies.
To remedy this, we have run 53 simulations involving bursts of star formation
activity on LSB galaxies, varying both the underlying galaxy properties and the
parameters describing the starbursts. We discovered that although changing the
total color of a galaxy was fairly straightforward, it was virtually impossible
to alter a galaxy's central surface brightness and thereby remove it from the
LSB galaxy classification without placing a high (and fairly artificial)
threshold for the underlying gas density. The primary effect of large amounts
of induced star formation was to produce a centralized core (bulge) component
which is generally not observed in LSB galaxies. The noisy morphological
appearance of LSB galaxies as well as their noisy surface brightness profiles
can be reproduced by considering small bursts of star formation that are
localized within the disk. The trigger mechanism for such bursts is likely
distant/weak tidal encounters. The stability of disk central surface brightness
to these periods of star formation argues that the large space density of LSB
galaxies at z = 0 should hold to substantially higher redshifts.Comment: 38 pages, 5 figures, 4 tables, tarred and compressed Also available
on http://guernsey.uoregon.edu/~kare
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
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