997 research outputs found
WAS FAIR FAIR TO U.S. CORN GROWERS? AN ANALYSIS OF THE PAYMENTS OFFERED TO CORN GROWERS UNDER THE 1996 FEDERAL AGRICULTURAL IMPROVEMENT AND REFORM ACT
The 1996 Farm Bill (FAIR) dramatically changed agricultural policy for producers of many commodities. A series of 7 annual decoupled payments replaced the deficiency-payment program. Option-pricing techniques are used to determine whether program benefits to corn producers are smaller or larger under the new program than the old.Agricultural and Food Policy,
The Chemical and Dynamical Evolution of Isolated Dwarf Galaxies
Using a suite of simulations (Governato et al. 2010) which successfully
produce bulgeless (dwarf) disk galaxies, we provide an analysis of their
associated cold interstellar media (ISM) and stellar chemical abundance
patterns. A preliminary comparison with observations is undertaken, in order to
assess whether the properties of the cold gas and chemistry of the stellar
components are recovered successfully. To this end, we have extracted the
radial and vertical gas density profiles, neutral hydrogen velocity dispersion,
and the power spectrum of structure within the ISM. We complement this analysis
of the cold gas with a brief examination of the simulations' metallicity
distribution functions and the distribution of alpha-elements-to-iron.Comment: To appear in the proceedings of the JENAM 2010 Symposium "Dwarf
Galaxies: Keys to Galaxy Formation and Evolution" (Lisbon, 9-10 September
2010), P. Papaderos, S. Recchi, G. Hensler (eds.), Springer Verlag (2011), in
pres
Systematic problems with using dark matter simulations to model stellar halos
The limits of available computing power have forced models for the structure of stellar halos to adopt one or both of the following simplifying assumptions: (1) stellar mass can be "painted" onto dark matter (DM) particles in progenitor satellites; (2) pure DM simulations that do not form a luminous galaxy can be used. We estimate the magnitude of the systematic errors introduced by these assumptions using a controlled set of stellar halo models where we independently vary whether we look at star particles or painted DM particles, and whether we use a simulation in which a baryonic disk galaxy forms or a matching pure DM simulation that does not form a baryonic disk. We find that the "painting" simplification reduces the halo concentration and internal structure, predominantly because painted DM particles have different kinematics from star particles even when both are buried deep in the potential well of the satellite. The simplification of using pure DM simulations reduces the concentration further, but increases the internal structure, and results in a more prolate stellar halo. These differences can be a factor of 1.5-7 in concentration (as measured by the half-mass radius) and 2-7 in internal density structure. Given this level of systematic uncertainty, one should be wary of overinterpreting differences between observations and the current generation of stellar halo models based on DM-only simulations when such differences are less than an order of magnitude
Galaxy Formation with local photoionisation feedback I. Methods
We present a first study of the effect of local photoionising radiation on
gas cooling in smoothed particle hydrodynamics simulations of galaxy formation.
We explore the combined effect of ionising radiation from young and old stellar
populations. The method computes the effect of multiple radiative sources using
the same tree algorithm used for gravity, so it is computationally efficient
and well resolved. The method foregoes calculating absorption and scattering in
favour of a constant escape fraction for young stars to keep the calculation
efficient enough to simulate the entire evolution of a galaxy in a cosmological
context to the present day. This allows us to quantify the effect of the local
photoionisation feedback through the whole history of a galaxy`s formation. The
simulation of a Milky Way like galaxy using the local photoionisation model
forms ~ 40 % less stars than a simulation that only includes a standard uniform
background UV field. The local photoionisation model decreases star formation
by increasing the cooling time of the gas in the halo and increasing the
equilibrium temperature of dense gas in the disc. Coupling the local radiation
field to gas cooling from the halo provides a preventive feedback mechanism
which keeps the central disc light and produces slowly rising rotation curves
without resorting to extreme feedback mechanisms. These preliminary results
indicate that the effect of local photoionising sources is significant and
should not be ignored in models of galaxy formation.Comment: Accepted for Publication in MNRAS, 13 pages, 13 figure
Being on the Juvenile Dermatomyositis Rollercoaster: a qualitative study
Objectives: Juvenile Dermatomyositis is a rare, potentially life-threatening condition with no known cure. There is no published literature capturinghow children and young people feel about their condition, from their perspective. This study was therefore unique in that it asked children and young people what is it like to live with Juvenile Dermatomyositis.
Methods: Data wereobtained from fifteen young people with Juvenile Dermatomyositis, between eightand nineteen years of age from one Paediatric Rheumatology department using audio-recordedinterpretive phenomenology interviews. Data were analyzed phenomenologically, using a process that derives narratives from transcripts resulting in a collective composite of participants shared experiences, called a‘phenomenon’.
Results:The overarching metaphor of a rollercoaster captures the phenomenon of living withJuvenile Dermatomyositisas a young person, with the ups and downs at different time points clearly described by those interviewed. The five themes plotted on the rollercoaster, began with confusion; followed by feeling different, being sick, steroidal and scared from the medications; uncertainty; and then ended with acceptance of the disease over time.
Conclusion: Young people were able to talk about their experiences about having Juvenile Dermatomyositis. Our findings will aid clinicians in their practice by gaining a deeper understanding of what daily life is like and highlighting ways to enhance psychosocial functioning. Hopefully, this study and any further resulting studies,will raise understanding of Juvenile Dermatomyositis worldwide and will encourage health care professionals to better assess psychosocial needs in the future
The not-so-sterile womb: Evidence that the human fetus is exposed to bacteria prior to birth
The human microbiome includes trillions of bacteria, many of which play a vital role in host physiology. Numerous studies have now detected bacterial DNA in first-pass meconium and amniotic fluid samples, suggesting that the human microbiome may commence in utero. However, these data have remained contentious due to underlying contamination issues. Here, we have used a previously described method for reducing contamination in microbiome workflows to determine if there is a fetal bacterial microbiome beyond the level of background contamination. We recruited 50 women undergoing non-emergency cesarean section deliveries with no evidence of intra-uterine infection and collected first-pass meconium and amniotic fluid samples. Full-length 16S rRNA gene sequencing was performed using PacBio SMRT cell technology, to allow high resolution profiling of the fetal gut and amniotic fluid bacterial microbiomes. Levels of inflammatory cytokines were measured in amniotic fluid, and levels of immunomodulatory short chain fatty acids (SCFAs) were quantified in meconium. All meconium samples and most amniotic fluid samples (36/43) contained bacterial DNA. The meconium microbiome was dominated by reads that mapped to Pelomonas puraquae. Aside from this species, the meconium microbiome was remarkably heterogeneous between patients. The amniotic fluid microbiome was more diverse and contained mainly reads that mapped to typical skin commensals, including Propionibacterium acnes and Staphylococcus spp. All meconium samples contained acetate and propionate, at ratios similar to those previously reported in infants. P. puraquae reads were inversely correlated with meconium propionate levels. Amniotic fluid cytokine levels were associated with the amniotic fluid microbiome. Our results demonstrate that bacterial DNA and SCFAs are present in utero, and have the potential to influence the developing fetal immune system
Magnetic White Dwarfs from the SDSS II. The Second and Third Data Releases
Fifty-two magnetic white dwarfs have been identified in spectroscopic
observations from the Sloan Digital Sky Survey (SDSS) obtained between mid-2002
and the end of 2004, including Data Releases 2 and 3. Though not as numerous
nor as diverse as the discoveries from the first Data Release, the collection
exhibits polar field strengths ranging from 1.5MG to ~1000MG, and includes two
new unusual atomic DQA examples, a molecular DQ, and five stars that show
hydrogen in fields above 500MG. The highest-field example, SDSSJ2346+3853, may
be the most strongly magnetic white dwarf yet discovered. Analysis of the
photometric data indicates that the magnetic sample spans the same temperature
range as for nonmagnetic white dwarfs from the SDSS, and support is found for
previous claims that magnetic white dwarfs tend to have larger masses than
their nonmagnetic counterparts. A glaring exception to this trend is the
apparently low-gravity object SDSSJ0933+1022, which may have a history
involving a close binary companion.Comment: 20 pages, 4 figures Accepted for publication in the Astronomical
Journa
Galaxy formation with local photoionization feedback – II. Effect of X-ray emission from binaries and hot gas
We study how X-rays from stellar binary systems and the hot intracluster medium (ICM) affect the radiative cooling rates of gas in galaxies. Our study uses a novel implementation of gas cooling in the moving-mesh hydrodynamics code arepo. X-rays from stellar binaries do not affect cooling at all as their emission spectrum is too hard to effectively couple with galactic gas. In contrast, X-rays from the ICM couple well with gas in the temperature range 10⁴–10⁶ K. Idealized simulations show that the hot halo radiation field has minimal impact on the dynamics of cooling flows in clusters because of the high virial temperature ( ≳ 10⁷ K), making the interaction between the gas and incident photons very ineffective. Satellite galaxies in cluster environments, on the other hand, experience a high radiation flux due to the emission from the host halo. Low-mass satellites ( ≲ 10¹² M⊙) in particular have virial temperatures that are exactly in the regime where the effect of the radiation field is maximal. Idealized simulations of satellite galaxies including only the effect of host halo radiation (no ram pressure stripping or tidal effects) fields show a drastic reduction in the amount of cool gas formed (∼40 per cent) on a short time-scale of about 0.5 Gyr. A galaxy merger simulation including all the other environmental quenching mechanisms, shows about 20 per cent reduction in the stellar mass of the satellite and about ∼30 per cent reduction in star formation rate after 1 Gyr due to the host hot halo radiation field. These results indicate that the hot halo radiation fields potentially play an important role in quenching galaxies in cluster environments
The stellar metallicity distribution of disc galaxies and bulges in cosmological simulations
By means of high-resolution cosmological hydrodynamical simulations of Milky
Way-like disc galaxies, we conduct an analysis of the associated stellar
metallicity distribution functions (MDFs). After undertaking a kinematic
decomposition of each simulation into spheroid and disc sub-components, we
compare the predicted MDFs to those observed in the solar neighbourhood and the
Galactic bulge. The effects of the star formation density threshold are visible
in the star formation histories, which show a modulation in their behaviour
driven by the threshold. The derived MDFs show median metallicities lower by
0.2-0.3 dex than the MDF observed locally in the disc and in the Galactic
bulge. Possible reasons for this apparent discrepancy include the use of low
stellar yields and/or centrally-concentrated star formation. The dispersions
are larger than the one of the observed MDF; this could be due to simulated
discs being kinematically hotter relative to the Milky Way. The fraction of low
metallicity stars is largely overestimated, visible from the more negatively
skewed MDF with respect to the observational sample. For our fiducial Milky Way
analog, we study the metallicity distribution of the stars born "in situ"
relative to those formed via accretion (from disrupted satellites), and
demonstrate that this low-metallicity tail to the MDF is populated primarily by
accreted stars. Enhanced supernova and stellar radiation energy feedback to the
surrounding interstellar media of these pre-disrupted satellites is suggested
as an important regulator of the MDF skewness.Comment: 20 pages, 14 figures, MNRAS, accepte
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