1,341 research outputs found
Vegetation structure and inferred patterns of functional group attrition in a shrub encroached old field and tallgrass prairie mosaic
Tallgrass prairie is an endangered ecosystem and encroachment by woody species threatens many remnants. Insights are needed into the differences in diversity and species and functional group composition along a gradient of woody encroachment to help gauge restoration potential and gain insights into patterns of disassembly in grassland communities. The study site is a 65 ha (160 acre) tallgrass prairie and old field mosaic in Lake County, Illinois. The three main objectives in this study are to: (1) analyze and classify plant communities, (2) explore seed bank dynamics and its contribution to old field colonization, and (3) determine the patterns of species and functional group richness and cover in a tallgrass prairie:old field mosaic with varying levels of shrub invasion and assess whether there are ordered patterns of loss in richness and cover with increasing shrub canopy cover. Ground layer and shrub layer data were collected from 45 sample plots including 37 located on stratified transects and eight located randomly in high-quality reference prairie habitat. Two community types were identified through field observation and reinforced by cluster analysis, indicator species analysis, and Nonmetric Multidimensional Scaling (NMS). The communities differed significantly in species density, species richness, ground layer cover, floristic quality indices, shrub canopy cover, and percent bare ground. To assess whether germination from the seed bank was limited by the lack of fire at the site, soil samples were heat treated prior to placement in greenhouse flats and germination rates were compared to a control. Heat shock had a variable effect on germination, and the species germinating from the seed bank were dependant upon the treatment. S??rensen Similarity Index indicated that there was very little similarity between the species present in the seed bank and the standing vegetation. To determine if prairie remnants were responsible for the recolonization of the site after agricultural disturbance, species data were examined on a distance gradient to the nearest remnant. Overall species richness, proportion of prairie species, and Floristic Quality Index had no relationship with distance to remnants. Results suggests that many areas of the site are seed limited, further complicating the restoration of plant communities. Possible causes of seed bank failure as a refugium could be attributed to the past history of rigorous cultivation at the site and the recent history of shrub encroachment. Species composition data were converted to plant functional groups based on species traits to assess whether increasing shrub canopy cover leads to loss or decline in richness and cover in species with shared traits. The relationships between functional group richness and ground layer cover to shrub canopy cover were examined with linear regression, discriminant analysis, ANOVA followed by Tukey post-hoc tests, and NMS. Cover of C4 grass, perennial legume, perennial forb, perennial sedge, C3 grass and annual forb functional groups and richness of C4 grass, perennial legume, and perennial forb functional groups follow ordered decline with increasing shrub canopy cover and differences among canopy cover classes were significant. NMS provides a graphical summary indicating functional groups representative of prairie communities are associated with low canopy cover plots compared with closed canopy plots. Comparisons with previous studies at this site suggest shrub species have increased in density three fold in the past fourteen years. Results from this study highlight ordered patterns of losses in the cover and richness of plant functional groups that can be used as a guideline to evaluate sites undergoing shrub encroachment that have important management implications for restoration and management of grassland ecosystems
Internal Motility in Stiffening Actin-Myosin Networks
We present a study on filamentous actin solutions containing heavy meromyosin
subfragments of myosin II motor molecules. We focus on the viscoelastic phase
behavior and internal dynamics of such networks during ATP depletion. Upon
simultaneously using micro-rheology and fluorescence microscopy as
complementary experimental tools, we find a sol-gel transition accompanied by a
sudden onset of directed filament motion. We interpret the sol-gel transition
in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain
the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure
A Search for X-Ray Bright Distant Clusters of Galaxies
We present the results of a search for X--ray luminous distant clusters of
galaxies. We found extended X--ray emission characteristic of a cluster towards
two of our candidate clusters of galaxies. They both have a luminosity in the
ROSAT bandpass of and a redshift of ;
thus making them two of the most distant X--ray clusters ever observed.
Furthermore, we show that both clusters are optically rich and have a known
radio source associated with them. We compare our result with other recent
searches for distant X--ray luminous clusters and present a lower limit of
for the number density of such high redshift
clusters. This limit is consistent with the expected abundance of such clusters
in a standard (b=2) Cold Dark Matter Universe. Finally, our clusters provide
important high redshift targets for further study into the origin and evolution
of massive clusters of galaxies. Accepted for publication in the 10th September
1994 issue of ApJ.Comment: 20 pages Latex file + 1 postscript figure file appende
The Global Star Formation Rate from the 1.4 GHz Luminosity Function
The decimetric luminosity of many galaxies appears to be dominated by
synchrotron emission excited by supernova explosions. Simple models suggest
that the luminosity is directly proportional to the rate of supernova
explosions of massive stars averaged over the past 30 Myr. The proportionality
may be used together with models of the evolving 1.4 GHz luminosity function to
estimate the global star formation rate density in the era z < 1. The local
value is estimated to be 0.026 solar masses per year per cubic megaparsec, some
50% larger than the value inferred from the Halpha luminosity density. The
value at z ~ 1 is found to be 0.30 solar masses per year per cubic megaparsec.
The 10-fold increase in star formation rate density is consistent with the
increase inferred from mm-wave, far-infrared, ultra-violet and Halpha
observations.Comment: 10 pages, 2 figures, Astrophysical Journal Letters (in press); new PS
version has improved figure placemen
Cultural respect encompassing simulation training: being heard about health through broadband
Background. Cultural Respect Encompassing Simulation Training (CREST) is a learning program that uses simulation to provide health professional students and practitioners with strategies to communicate sensitively with culturally and linguistically diverse (CALD) patients. It consists of training modules with a cultural competency evaluation framework and CALD simulated patients to interact with trainees in immersive simulation scenarios. The aim of this study was to test the feasibility of expanding the delivery of CREST to rural Australia using live video streaming; and to investigate the fidelity of cultural sensitivity â defined within the process of cultural competency which includes awareness, knowledge, skills, encounters and desire â of the streamed simulations. Design and Methods. In this mixed-methods evaluative study, health professional trainees were recruited at three rural academic campuses and one rural hospital to pilot CREST sessions via live video streaming and simulation from the city campus in 2014. Cultural competency, teaching and learning evaluations were conducted. Results. Forty-five participants rated 26 reliable items before and after each session and reported statistically significant improvement in 4 of 5 cultural competency domains, particularly in cultural skills (P<0.05). Qualitative data indicated an overall acknowledgement amongst participants of the importance of communication training and the quality of the simulation training provided remotely by CREST. Conclusions. Cultural sensitivity education using live video-streaming and simulation can contribute to health professionalsâ learning and is effective in improving cultural competency. CREST has the potential to be embedded within health professional curricula across Australian universities to address issues of health inequalities arising from a lack of cultural sensitivity training
Flood-risk mapping: contributions towards an enhanced assessment of extreme events and associated risks
Currently, a shift from classical flood protection as engineering task towards integrated flood risk management concepts can be observed. In this context, a more consequent consideration of extreme events which exceed the design event of flood protection structures and failure scenarios such as dike breaches have to be investigated. Therefore, this study aims to enhance existing methods for hazard and risk assessment for extreme events and is divided into three parts. In the first part, a regionalization approach for flood peak discharges was further developed and substantiated, especially regarding recurrence intervals of 200 to 10 000 years and a large number of small ungauged catchments. Model comparisons show that more confidence in such flood estimates for ungauged areas and very long recurrence intervals may be given as implied by statistical analysis alone. The hydraulic simulation in the second part is oriented towards hazard mapping and risk analyses covering the whole spectrum of relevant flood events. As the hydrodynamic simulation is directly coupled with a GIS, the results can be easily processed as local inundation depths for spatial risk analyses. For this, a new GIS-based software tool was developed, being presented in the third part, which enables estimations of the direct flood damage to single buildings or areas based on different established stage-damage functions. Furthermore, a new multifactorial approach for damage estimation is presented, aiming at the improvement of damage estimation on local scale by considering factors like building quality, contamination and precautionary measures. The methods and results from this study form the base for comprehensive risk analyses and flood management strategies
Activity Assay of Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Triple-Negative Breast Cancer Cells Using Peptide-Conjugated Magnetic Beads
Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer with limited treatment options. Epidermal growth factor receptor I (EGFR) has emerged as a promising target in TNBC. Limited success of the EGFR kinase inhibiting small molecules in clinical trials may be attributed in part to inaccuracy in identifying EGFR signatures in patient tumors. In light of the absence of a simple correlation between EGFR expression and its degree of activation, a simple and reliable tool that can quantify EGFR kinase activity in tumor samples may be of therapeutic value in predicting patient-specific EGFR targeted therapies. This study reports the development of an assay that can quantitatively profile EGFR kinase activities and inhibitor sensitivities in TNBC cell lysates by using peptide reporters covalently tethered to magnetic beads in a controlled orientation. The use of magnetic beads provides rapid sample handling and easy product isolation. The potential of this approach was demonstrated by screening a set of five clinically relevant EGFR tyrosine kinase inhibitors. Formatted for microwell plates, this magnetic bead-based kinase assay may be used as a complementary approach for direct high-throughput screening of small molecule inhibitors.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140099/1/adt.2012.454.pd
Measurement of radiotherapy x-ray skin dose on a chest wall phantom
Sufficient skin dose needs to be delivered by a radiotherapy chest wall treatment regimen to ensure the probability of a near surface tumor recurrence is minimized. To simulate a chest wall treatment a hemicylindrical solid water phantom of 7.5 cm radius was irradiated with 6 MV x-rays using 20Ă20âcm2 and 10Ă20âcm2 fields at 100 cm source surface distance (SSD) to the base of the phantom. A surface dose profile was obtained from 0 to 180°, in 10° increments around the circumference of the phantom. Dosimetry results obtained from radiochromic film (effective depth of 0.17 mm) were used in the investigation, the superficial doses were found to be 28% (of Dmax) at the 0° beam entry position and 58% at the 90° oblique beam position. Superficial dose results were also obtained using extra thin thermoluminescent dosimeters (TLD) (effective depth 0.14 mm) of 30% at 0°, 57% at 90°, and a metal oxide semiconductor field effect transistor (MOSFET) detector (effective depth 0.5 mm) of 43% at 0°, 62% at 90°. Because the differences in measured superficial doses were significant and beyond those related to experimental error, these differences are assumed to be mostly attributable to the effective depth of measurement of each detector. We numerically simulated a bolus on/bolus off technique and found we could increase the coverage to the skin. Using an alternate âbolus on,â âbolus offâ regimen, the skin would receive 36.8 Gy at 0° incidence and 46.4 Gy at 90° incidence for a prescribed midpoint dose of 50 Gy. From this work it is evident that, as the circumference of the phantom is traversed the SSD increases and hence there is an inverse square fluence fall-off, this is more than offset by the increase in skin dose due to surface curvature to a plateau at about 90°. Beyond this angle it is assumed that beam attenuation through the phantom and inverse square fall-off is causing the surface dose to reduce
Radio Wavelength Constraints on the Sources of the Far Infrared Background
The cosmic far infrared background detected recently by the COBE-DIRBE team
is presumably due, in large part, to the far infrared (FIR) emission from all
galaxies. We take the well-established correlation between FIR and radio
luminosity for individual galaxies and apply it to the FIR background. We find
that these sources make up about half of the extragalactic radio background,
the other half being due to AGN. This is in agreement with other radio
observations, which leads us to conclude that the FIR-radio correlation holds
well for the very faint sources making up the FIR background, and that the FIR
background is indeed due to star-formation activity (not AGN or other possible
sources). If these star-forming galaxies have a radio spectral index between
0.4 and 0.8, and make up 40 to 60% of the extragalactic radio background, we
find that they have redshifts between roughly 1 and 2, in agreement with recent
estimates by Madau et al. of the redshift of peak star-formation activity. We
compare the observed extragalactic radio background to the integral over the
logN-logS curve for star-forming radio sources, and find that the slope of the
curve must change significantly below about 1 microjansky. At 1 microjansky,
the faint radio source counts predict about 25 sources per square arcminute,
and these will cause SIRTF to be confusion limited at 160micron.Comment: 10 pages including 1 figure, AASTeX, accepted by Ap
Pleuroperitoneal shunts as treatment for refractory chylothorax following surgery for congenital beast disease
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