209 research outputs found
Dark-ages reionization & galaxy formation simulation IV: UV luminosity functions of high-redshift galaxies
In this paper we present calculations of the UV luminosity function from the
Dark-ages Reionization And Galaxy-formation Observables from Numerical
Simulations (DRAGONS) project, which combines N-body, semi-analytic and
semi-numerical modelling designed to study galaxy formation during the Epoch of
Reionization. Using galaxy formation physics including supernova feedback, the
model naturally reproduces the UV LFs for high-redshift star-forming galaxies
from through to . We investigate the luminosity--star
formation rate (SFR) relation, finding that variable SFR histories of galaxies
result in a scatter around the median relation of -- dex depending on
UV luminosity. We find close agreement between the model and observationally
derived SFR functions. We use our calculated luminosities to investigate the
luminosity function below current detection limits, and the ionizing photon
budget for reionization. We predict that the slope of the UV LF remains steep
below current detection limits and becomes flat at
. We find that () per cent of the total
UV flux at () has been detected above an observational limit of
, and that galaxies fainter than
are the main source of ionizing photons for
reionization. We investigate the luminosity--stellar mass relation, and find a
correlation for galaxies with that has the form
, in good agreement with observations, but
which flattens for fainter galaxies. We determine the luminosity--halo mass
relation to be , finding that
galaxies with reside in host dark matter haloes of
at , and that this mass decreases
towards high redshift.Comment: 17 pages, 14 figures, Accepted for publication in MNRA
Modification of the 21-cm power spectrum by X-rays during the epoch of reionisation
We incorporate a contribution to reionization from X-rays within analytic and
semi-numerical simulations of the 21-cm signal arising from neutral hydrogen
during the epoch of reionization. We explore the impact that X-ray ionizations
have on the power spectrum (PS) of 21-cm fluctuations by varying both the
average X-ray MFP and the fractional contribution of X-rays to reionization. In
general, prior to the epoch when the intergalactic medium is dominated by
ionized regions (H {\sevensize II} regions), X-ray-induced ionization enhances
fluctuations on spatial scales smaller than the X-ray MFP, provided that X-ray
heating does not strongly supress galaxy formation. Conversely, at later times
when \H2 regions dominate, small-scale fluctuations in the 21-cm signal are
suppressed by X-ray ionization. Our modelling also shows that the modification
of the 21-cm signal due to the presence of X-rays is sensitive to the relative
scales of the X-ray MFP, and the characteristic size of \H2 regions. We
therefore find that X-rays imprint an epoch and scale-dependent signature on
the 21-cm PS, whose prominence depends on fractional X-ray contribution. The
degree of X-ray heating of the IGM also determines the extent to which these
features can be discerned. We show that the MWA will have sufficient
sensitivity to detect this modification of the PS, so long as the X-ray photon
MFP falls within the range of scales over which the array is most sensitive
( Mpc). In cases in which this MFP takes a much smaller value,
an array with larger collecting area would be required.Comment: 15 pages, 6 figures, Accepted for publication in MNRAS X-ray heating
contribution now adde
The Impact of HI in Galaxies on 21-cm Intensity Fluctuations During the Reionisation Epoch
We investigate the impact of neutral hydrogen (HI) in galaxies on the
statistics of 21-cm fluctuations using analytic and semi-numerical modelling.
Following the reionisation of hydrogen the HI content of the Universe is
dominated by damped absorption systems (DLAs), with a cosmic density in HI that
is observed to be constant at a level equal to ~2% of the cosmic baryon density
from z~1 to z~5. We show that extrapolation of this constant fraction into the
reionisation epoch results in a reduction of 10-20% in the amplitude of 21-cm
fluctuations over a range of spatial scales. The assumption of a different
percentage during the reionisation era results in a proportional change in the
21-cm fluctuation amplitude. We find that consideration of HI in galaxies/DLAs
reduces the prominence of the HII region induced shoulder in the 21-cm power
spectrum (PS), and hence modifies the scale dependence of 21-cm fluctuations.
We also estimate the 21cm-galaxy cross PS, and show that the cross PS changes
sign on scales corresponding to the HII regions. From consideration of the
sensitivity for forthcoming low-frequency arrays we find that the effects of HI
in galaxies/DLAs on the statistics of 21-cm fluctuations will be significant
with respect to the precision of a PS or cross PS measurement. In addition,
since overdense regions are reionised first we demonstrate that the
cross-correlation between galaxies and 21-cm emission changes sign at the end
of the reionisation era, providing an alternative avenue to pinpoint the end of
reionisation. The sum of our analysis indicates that the HI content of the
galaxies that reionise the universe will need to be considered in detailed
modelling of the 21-cm intensity PS in order to correctly interpret
measurements from forthcoming low-frequency arrays.Comment: 11 pages, 6 figures. Submitted to MNRA
Relaxation in the glass-former acetyl salicylic acid studied by deuteron magnetic resonance and dielectric spectroscopy
Supercooled liquid and glassy acetyl salicylic acid was studied using
dielectric spectroscopy and deuteron relaxometry in a wide temperature range.
The supercooled liquid is characterized by major deviations from thermally
activated behavior. In the glass the secondary relaxation exhibits the typical
features of a Johari-Goldstein process. Via measurements of spin-lattice
relaxation times the selectively deuterated methyl group was used as a
sensitive probe of its local environments. There is a large difference in the
mean activation energy in the glass with respect to that in crystalline acetyl
salicylic acid. This can be understood by taking into account the broad energy
barrier distribution in the glass.Comment: 8 pages, 3 figures, Submitted to Phys. Rev.
A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses
We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants
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Evaluating Knowledge to Support Climate Action: A Framework for Sustained Assessment. Report of an Independent Advisory Committee on Applied Climate Assessment
As states, cities, tribes, and private interests cope with climate damages and seek to increase preparedness and resilience, they will need to navigate myriad choices and options available to them. Making these choices in ways that identify pathways for climate action that support their development objectives will require constructive public dialogue, community participation, and flexible and ongoing access to science- and experience-based knowledge. In 2016, a Federal Advisory Committee (FAC) was convened to recommend how to conduct a sustained National Climate Assessment (NCA) to increase the relevance and usability of assessments for informing action. The FAC was disbanded in 2017, but members and additional experts reconvened to complete the report that is presented here. A key recommendation is establishing a new nonfederal "climate assessment consortium" to increase the role of state/local/tribal government and civil society in assessments. The expanded process would 1) focus on applied problems faced by practitioners, 2) organize sustained partnerships for collaborative learning across similar projects and case studies to identify effective tested practices, and 3) assess and improve knowledge-based methods for project implementation. Specific recommendations include evaluating climate models and data using user-defined metrics; improving benefit-cost assessment and supporting decision-making under uncertainty; and accelerating application of tools and methods such as citizen science, artificial intelligence, indicators, and geospatial analysis. The recommendations are the result of broad consultation and present an ambitious agenda for federal agencies, state/local/tribal jurisdictions, universities and the research sector, professional associations, nongovernmental and community-based organizations, and private-sector firms.New York State Energy Research and Development Authority [123416]; Columbia University's Earth Institute; American Meteorological Society; Kresge Foundation6 month embargo; published online: 21 May 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Imaging neutral hydrogen on large-scales during the Epoch of Reionization with LOFAR
The first generation of redshifted 21 cm detection experiments, carried out
with arrays like LOFAR, MWA and GMRT, will have a very low signal-to-noise
ratio per resolution element (\sim 0.2). In addition, whereas the variance of
the cosmological signal decreases on scales larger than the typical size of
ionization bubbles, the variance of the formidable galactic foregrounds
increases, making it hard to disentangle the two on such large scales. The poor
sensitivity on small scales on the one hand, and the foregrounds effect on
large scales on the other hand, make direct imaging of the Epoch of
Reionization of the Universe very difficult, and detection of the signal
therefore is expected to be statistical.Despite these hurdles, in this paper we
argue that for many reionization scenarios low resolution images could be
obtained from the expected data. This is because at the later stages of the
process one still finds very large pockets of neutral regions in the IGM,
reflecting the clustering of the large-scale structure, which stays strong up
to scales of \sim 120 comoving Mpc/h (\sim 1 degree). The coherence of the
emission on those scales allows us to reach sufficient S/N (\sim 3) so as to
obtain reionization 21 cm images. Such images will be extremely valuable for
answering many cosmological questions but above all they will be a very
powerful tool to test our control of the systematics in the data. The existence
of this typical scale (\sim 120 comoving Mpc/h) also argues for designing
future EoR experiments, e.g., with SKA, with a field of view of at least 4
degree.Comment: Replaced with final version (minor changes), 9 figures, 11 pages,
accepted for publication in MNRA
Validity and reliability of a novel 3D scanner for assessment of the shape and volume of amputees’ residual limb models
Objective assessment methods to monitor residual limb volume following lower-limb amputation are required to enhance practitioner-led prosthetic fitting. Computer aided systems, including 3D scanners, present numerous advantages and the recent Artec Eva scanner, based on laser free technology, could potentially be an effective solution for monitoring residual limb volumes.
The aim of this study was to assess the validity and reliability of the Artec Eva scanner (practical measurement) against a high precision laser 3D scanner (criterion measurement) for the determination of residual limb model shape and volume. Three observers completed three repeat assessments of ten residual limb models, using both the scanners. Validity of the Artec Eva scanner was assessed (mean percentage error <2%) and Bland-Altman statistics were adopted to assess the agreement between the two scanners. Intra and inter-rater reliability (repeatability coefficient <5%) of the Artec Eva scanner was calculated for measuring indices of residual limb model volume and shape (i.e. residual limb cross sectional areas and perimeters). Residual limb model volumes ranged from 885 to 4399 ml. Mean percentage error of the Artec Eva scanner (validity) was 1.4% of the criterion volumes. Correlation coefficients between the Artec Eva and the Romer determined variables were higher than 0.9. Volume intra-rater and inter-rater reliability coefficients were 0.5% and 0.7%, respectively. Shape percentage maximal error was 2% at the distal end of the residual limb, with intra-rater reliability coefficients presenting the lowest errors (0.2%), both for cross sectional areas and perimeters of the residual limb models.
The Artec Eva scanner is a valid and reliable method for assessing residual limb model shapes and volumes. While the method needs to be tested on human residual limbs and the results compared with the current system used in clinical practice, it has the potential to quantify shape and volume fluctuations with greater resolution
Projected changes of rainfall seasonality and dry spells in a high greenhouse gas emissions scenario
In this diagnostic study we analyze changes of rainfall seasonality and dry spells by the end of the twenty-first century under the most extreme IPCC5 emission scenario (RCP8.5) as projected by twenty-four coupled climate models contributing to Coupled Model Intercomparison Project 5 (CMIP5). We use estimates of the centroid of the monthly rainfall distribution as an index of the rainfall timing and a threshold-independent, information theory-based quantity such as relative entropy (RE) to quantify the concentration of annual rainfall and the number of dry months and to build a monsoon dimensionless seasonality index (DSI). The RE is projected to increase, with high inter-model agreement over Mediterranean-type regions---southern Europe, northern Africa and southern Australia---and areas of South and Central America, implying an increase in the number of dry days up to 1Â month by the end of the twenty-first century. Positive RE changes are also projected over the monsoon regions of southern Africa and North America, South America. These trends are consistent with a shortening of the wet season associated with a more prolonged pre-monsoonal dry period. The extent of the global monsoon region, characterized by large DSI, is projected to remain substantially unaltered. Centroid analysis shows that most of CMIP5 projections suggest that the monsoonal annual rainfall distribution is expected to change from early to late in the course of the hydrological year by the end of the twenty-first century and particularly after year 2050. This trend is particularly evident over northern Africa, southern Africa and western Mexico, where more than 90% of the models project a delay of the rainfall centroid from a few days up to 2Â weeks. Over the remaining monsoonal regions, there is little inter-model agreement in terms of centroid changes
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