294 research outputs found
Using Ecological Land Units in a Gap Analysis for Conservation Planning in a Southwestern Ohio Watershed
Gap analysis is a method to identify insufficiency in biodiversity protection. In degraded agricultural landscapes, it requires information on the past, present, and the potential natural distribution of forest vegetation to construct a comprehensive nature reserve network. Using Geographic Information Systems (GIS), I conducted a biodiversity gap analysis to assess the representation of ecological land units (ELUs) supporting forest vegetation both within and external to the current reserve network in the Lower Twin Creek Watershed (LTCW), southwestern Ohio. I used this analysis to make conservation planning recommendations to the local park district. ELUs are based on relatively stable associations of soils, physiography, and potential natural vegetation. In heavily deforested landscapes, such as the LTCW, ELUs model a more intact functioning landscape by predicting the distribution of potential natural forest vegetation. ELUs were classified using multivariate and cluster analyses on forest canopy tree species and seven physiographic and soil variables derived from digital elevation models and a soil series map in GIS. A cluster analysis of the five most significant variables (landform, drainage, hillshade, curvature, and percent slope) influencing vegetation distribution resulted in nine discrete ELUs. They included uplands dominated by Fagus grandifolia â Acer saccharum, dry slopes dominated by Quercus spp. - Carya ovata, mesic slopes dominated by a mixed mesophytic community, and wet floodplains dominated by Platanus occidentalis â Populus deltoides. A reference ecosystem map was constructed using ArcView GIS Spatial Analyst with the five environmental variables identified in the multivariate analysis. To determine the area of forest cover in each ELU within the reserve network and the watershed as a whole, the reference ecosystem map was overlaid with a 1990 land cover type map and the reserve boundaries. The area of forest in each ELU in the reserve network was then compared to the area of forest in each ELU in the watershed as a whole and the potential natural distribution of forest cover as predicted by the reference ecosystem map to determine the percent of forest protected in each condition. The gap analysis, using the current forest distribution, indicated that the well and poorly drained upland ecosystems were underrepresented in the reserve network. A similar pattern emerged using the reference ecosystem map; however, reflecting the degree to which these upland ecosystems are deforested, to meet a 25% representation target would require three to four times more forest than existed in these ELUs in 1990. The results of the gap analysis based on the current vegetation distribution were influenced by the pattern of deforestation in the LTCW. The reference ecosystems map provided a model of an intact functioning landscape from which to establish conservation planning targets. Although the upland matrix forest ecosystems may have lower species richness per land unit area and are relatively common, restoring portions of the matrix forest may be the key to the long-term maintenance of biological diversity in the LTCW
Factors Affecting Bubble Size in Ionic Liquids
This study reports on understanding the formation of bubbles in ionic liquids (ILs), with a view to utilising ILs more efficiently in gas capture processes. In particular, the impact of the IL structure on the bubble sizes obtained has been determined in order to obtain design principles for the ionic liquids utilised. 11 ILs were used in this study with a range of physico-chemical properties in order to determine parametrically the impact on bubble size due to the liquid properties and chemical moieties present. The results suggest the bubble size observed is dictated by the strength of interaction between the cation and anion of the IL and, therefore, the mass transport within the system. This bubble size â ILs structureâphysical property relationship has been illustrated using a series of QSPR correlations. A predictive model based only on the sigma profiles of the anions and cations has been developed which shows the best correlation without the need to incorporate the physico-chemical properties of the liquids. Depending on the IL, selected mean bubble sizes observed were between 56.1 and 766.9 ÎŒm demonstrating that microbubbles can be produced in the IL allowing the potential for enhanced mass transport and absorption kinetics in these systems
Collapsar Accretion and the Gamma-Ray Burst X-Ray Light Curve
We present axisymmetric hydrodynamical simulations of the long-term accretion
of a rotating GRB progenitor star, a "collapsar," onto the central compact
object. The simulations were carried out with the adaptive mesh refinement code
FLASH in two spatial dimensions and with an explicit shear viscosity. The
evolution of the central accretion rate exhibits phases reminiscent of the long
GRB gamma-ray and X-ray light curve, which lends support to the proposal that
the luminosity is modulated by the central accretion rate. After a few tens of
seconds, an accretion shock sweeps outward through the star. The formation and
outward expansion of the accretion shock is accompanied with a sudden and rapid
power-law decline in the central accretion rate Mdot ~ t^{-2.8}, which
resembles the L_X ~ t^{-3} decline observed in the X-ray light curves. The
collapsed, shock-heated stellar envelope settles into a thick, low-mass
equatorial disk embedded within a massive, pressure-supported atmosphere. After
a few hundred seconds, the inflow of low-angular-momentum material in the axial
funnel reverses into an outflow from the surface of the thick disk. Meanwhile,
the rapid decline of the accretion rate slows down, or even settles a in steady
state with Mdot ~ 5x10^{-5} Msun/s, which resembles the "plateau" phase in the
X-ray light curve. While the duration of the "prompt" phase depends on the
resolution in our simulations, we provide an analytical model taking into
account neutrino losses that estimates the duration to be ~20 s. The model
suggests that the steep decline in GRB X-ray light curves is triggered by the
circularization of the infalling stellar envelope at radii where the virial
temperature is below ~10^{10} K, such that neutrino cooling shuts off and an
outward expansion of the accretion shock becomes imminent.Comment: 16 pages, 10 figure
Simulations of Accretion Powered Supernovae in the Progenitors of Gamma Ray Bursts
Observational evidence suggests a link between long duration gamma ray bursts
(LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type
Ic supernovae in LGRB progenitors powered solely by accretion energy. We
present spherically-symmetric hydrodynamic simulations of the long-term
accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto
the central compact object, which we take to be a black hole. The simulations
were carried out with the adaptive mesh refinement code FLASH in one spatial
dimension and with rotation, an explicit shear viscosity, and convection in the
mixing length theory approximation. Once the accretion flow becomes
rotationally supported outside of the black hole, an accretion shock forms and
traverses the stellar envelope. Energy is carried from the central
geometrically thick accretion disk to the stellar envelope by convection.
Energy losses through neutrino emission and nuclear photodisintegration are
calculated but do not seem important following the rapid early drop of the
accretion rate following circularization. We find that the shock velocity,
energy, and unbound mass are sensitive to convective efficiency, effective
viscosity, and initial stellar angular momentum. Our simulations show that
given the appropriate combinations of stellar and physical parameters,
explosions with energies ~5x10^50 ergs, velocities 3000 km/s, and unbound
material masses >6 solar masses are possible in a rapidly rotating 16 solar
mass main sequence progenitor star. Further work is needed to constrain the
values of these parameters, to identify the likely outcomes in more plausible
and massive LRGB progenitors, and to explore nucleosynthetic implications.Comment: 20 Pages, 15 Figures, Accepted to Ap
Evaluation of forest canopy models for estimating isoprene emissions
During the summer of 1992, isoprene emissions were measured in a mixed deciduous forest near Oak Ridge, Tennessee. Measurements were aimed at the experimental scale-up of emissions from the leaf level to the forest canopy to the mixed layer. Results from the scale-up study are compared to different canopy models for determining the leaf microclimate as input to isoprene emission algorithms. These include (1) no canopy effects, (2) a simple vertical scaling canopy model with a leaf energy balance, and (3) a numerical canopy model which accounts for leaf-sun geometries, photosynthesis, respiration, transpiration, and gas transport in the canopy. Initial evaluation of the models was based upon a standard emission rate factor of 90 ΌgC g-1 hr-1 (0.42 nmol g-1 s-1) taken from leaf cuvette measurements and a biomass density factor of 203 g m-2 taken from biomass surveys and a flux footprint analysis. The results indicated that predicted fluxes were consistent among the models to within approximately ±20%, but that the models overestimated the mean flux by about a factor of 2 and overestimated the maximum observed flux by 30 to 50%. Adjusting the standard emission factor and biomass density each downward by 20% yielded predicted means approximately 20% greater than the observed means and predicted maxima approximately 25% less than the observed maxima. Accounting for changes in biomass density as a function of direction upwind of the tower improved the overall model performance
The future of interpretive accounting research:A Polyphonic Debate
In 1997-99 the three of us organised a series of European Commission funded
conferences aimed at building a network of young researchers in the area of
accounting. At the time âyoungâ was defined by the Commission as researchers
under 35 years of age (allowing for maternity leave or national service). Over the
intervening years our network had grown and we wanted to try and take stock of the
field in which we had now been working for a surprising number of years. To that
Page 1 of 29
Accepted Manuscript
2
end we put together the above email and a broad invitation list of people who had
been at those first meetings, and others of the same generation (or even younger)
whom we had met since.
About half of those originally contacted managed to make the meeting where we
spent a stimulating couple of hours of debate on the topics raised belowâso
stimulating that we developed a collective desire to leave a trace of the discussion.
Writing a traditional paper with so many, so widely dispersed authors was not going
to work. Instead we came up with a different form of collective writing that mirrored
the original debate, and that might contribute to ongoing debates in this journal
concerning the nature and status of our research (e.g. Arrington, 2004; Inanga &
Schneider, 2005; Macintosh, 2004). We agreed a process in which each of us in turn
would have one week to add a target of 300 words to a rolling document, going
through the contributors alphabetically. After two rounds we would see what we had
got
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Design and implementation of the canadian kidney disease cohort study (CKDCS): A prospective observational study of incident hemodialysis patients
<p>Abstract</p> <p>Background</p> <p>Many nephrology observational studies use renal registries, which have well known limitations. The Canadian Kidney Disease Cohort Study (CKDCS) is a large prospective observational study of patients commencing hemodialysis in five Canadian centers. This study focuses on delineating potentially reversible determinants of adverse outcomes that occur in patients receiving dialysis for end-stage renal disease (ESRD).</p> <p>Methods/Design</p> <p>The CKDCS collects information on risk factors and outcomes, and stores specimens (blood, dialysate, hair and fingernails) at baseline and in long-term follow-up. Such specimens will permit measurements of biochemical markers, proteomic and genetic parameters (proteins and DNA) not measured in routine care. To avoid selection bias, all consenting incident hemodialysis patients at participating centers are enrolled, the large sample size (target of 1500 patients), large number of exposures, and high event rates will permit the exploration of multiple potential research questions.</p> <p>Preliminary Results</p> <p>Data on the baseline characteristics from the first 1074 subjects showed that the average age of patients was 62 (range; 50-73) years. The leading cause of ESRD was diabetic nephropathy (41.9%), and the majority of the patients were white (80.0%). Only 18.7% of the subjects received dialysis in a satellite unit, and over 80% lived within a 50 km radius of the nearest nephrologist's practice.</p> <p>Discussion</p> <p>The prospective design, detailed clinical information, and stored biological specimens provide a wealth of information with potential to greatly enhance our understanding of risk factors for adverse outcomes in dialysis patients. The scientific value of the stored patient tissue will grow as new genetic and biochemical markers are discovered in the future.</p
Executive Summary of the Second International Guidelines for the Diagnosis and Management of Pediatric Acute Respiratory Distress Syndrome (PALICC-2)
OBJECTIVES: We sought to update our 2015 work in the Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2) guidelines for the diagnosis and management of pediatric acute respiratory distress syndrome (PARDS), considering new evidence and topic areas that were not previously addressed. DESIGN: International consensus conference series involving 52 multidisciplinary international content experts in PARDS and four methodology experts from 15 countries, using consensus conference methodology, and implementation science. SETTING: Not applicable. PATIENTS: Patients with or at risk for PARDS. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Eleven subgroups conducted systematic or scoping reviews addressing 11 topic areas: 1) definition, incidence, and epidemiology; 2) pathobiology, severity, and risk stratification; 3) ventilatory support; 4) pulmonary-specific ancillary treatment; 5) nonpulmonary treatment; 6) monitoring; 7) noninvasive respiratory support; 8) extracorporeal support; 9) morbidity and long-term outcomes; 10) clinical informatics and data science; and 11) resource-limited settings. The search included MEDLINE, EMBASE, and CINAHL Complete (EBSCOhost) and was updated in March 2022. Grading of Recommendations, Assessment, Development, and Evaluation methodology was used to summarize evidence and develop the recommendations, which were discussed and voted on by all PALICC-2 experts. There were 146 recommendations and statements, including: 34 recommendations for clinical practice; 112 consensus-based statements with 18 on PARDS definition, 55 on good practice, seven on policy, and 32 on research. All recommendations and statements had agreement greater than 80%. CONCLUSIONS: PALICC-2 recommendations and consensus-based statements should facilitate the implementation and adherence to the best clinical practice in patients with PARDS. These results will also inform the development of future programs of research that are crucially needed to provide stronger evidence to guide the pediatric critical care teams managing these patients.</p
- âŠ