79 research outputs found
Nitrate sources and cycling at the Turkey Lakes Watershed: A stable isotope approach
Stable isotopic analysis of nitrate (15N/14N and 18O/16O) was used to trace nitrate sources and cycling under undisturbed conditions and following harvest at the Turkey Lakes Watershed (TLW), located near Sault Ste. Marie, Ontario, Canada.
Bulk precipitation collected biweekly at the TLW from 1995 to 2000 had nitrate isotope values that ranged from +42. 4 to +80. 4‰ for d18O and -6. 3 to +2. 8‰ for d15N. An incubation experiment indicated that the isotopic composition of atmospheric nitrate was not compromised by collection methods whereby unfiltered bulk precipitation samples remain in the collector for up to two weeks.
The first direct measurement of the isotopic composition of microbial nitrate produced in situ was obtained by eliminating precipitation inputs to three forest floor lysimeters and subsequently watering the area with a nitrate-free solution. Microbial nitrate had d18O values that ranged from +3. 1 to +10. 1‰ with a mean value of +5. 2‰, only slightly higher than values predicted based on the d18O-H2O of the watering solution used. d18O values of soil O2 (+23. 2 to +24. 1‰) down to a depth of 55cm were not significantly different from atmospheric O2 (+23. 5‰) and therefore respiratory enrichment of soil O2 did not affect the d18O values of microbial nitrate produced at the TLW.
Nitrate export from two undisturbed first-order stream basins was dominated by microbial nitrate, with the contribution of atmospheric nitrate peaking at about 30% during snowmelt. Clear-cutting of catchment 31 in 1997 resulted in elevated nitrate concentrations, reaching levels that exceeded the drinking water limit of 10 mg N/L. Isotopic analysis indicated that the source of this nitrate was predominantly chemolithoautotrophic nitrification. The d18O values of microbial nitrate in stream 31 progressively increased during the post-harvest period due to an increase in the proportion of nitrification that occurred in the summer months. Despite drastic alteration of nitrogen cycling in the catchment by the harvest, d15N-nitrate values in shallow groundwater did not change from the pre-harvest. Denitrification and plant uptake of nitrate in a small forested swamp in catchment 31 attenuated 65 to 100% of surface water nitrate inputs following harvest, reducing catchment-scale nitrate export by 35 to 80%
MMTV-PyMT and derived Met-1 mouse mammary tumor cells as models for studying the role of the androgen receptor in triple-negative breast cancer progression
Triple-negative breast cancer (TNBC) has a faster rate of metastasis compared to other breast cancer subtypes and no effective targeted therapies are currently FDA-approved. Recent data indicate that the androgen receptor (AR) promotes tumor survival and may serve as a potential therapeutic target in TNBC. Studies of AR in disease progression and the systemic effects of anti-androgens have been hindered by the lack of an AR-positive (AR+) immunocompetent preclinical model. In this study we identified the transgenic MMTV-PyMT (mouse mammary tumor virus-polyoma middle tumor antigen) mouse mammary gland carcinoma model of breast cancer and Met-1 cells derived from this model as tools to study the role of AR in breast cancer progression. AR protein expression was examined in late-stage primary tumors and lung metastases from MMTV-PyMT mice as well as in Met-1 cells by immunohistochemistry (IHC). Sensitivity of Met-1 cells to the AR agonist dihydrotestosterone (DHT) and anti-androgen therapy was examined using cell viability, migration/invasion, and anchorage-independent growth assays. Late-stage primary tumors and lung metastases from MMTV-PyMT mice and Met-1 cells expressed abundant nuclear AR protein, while negative for estrogen and progesterone receptors. Met-1 sensitivity to DHT and AR antagonists demonstrated a reliance on AR for survival, and AR antagonists inhibited invasion and anchorage-independent growth. These data suggest that the MMTV-PyMT model and Met-1 cells may serve as valuable tools for mechanistic studies of the role of AR in disease progression and how anti-androgens affect the tumor microenvironment
Absorption of the Linear Polarization of the Galactic Background Radiation by the 21-cm Line of HI
Absorption lines at 21-cm are detected in the Stokes Q and U
components of the Galactic synchrotron background. The lower limit distance
implied for the emission region is 2 kpc in the direction (l,b) =
(329.5,+1.15). The Australia Telescope Compact Array has
the capability of mapping this absorption over large areas of the Galactic
plane. Observations like these have the potential to reveal the three
dimensional structure of the Galactic synchrotron emission throughout the Milky
Way disk.Comment: 13 pages, 3 figures, Latex, see
http://ast1.spa.umn.edu/john/Galpol.html to be published in Astrophysical
Journal, 1997 October 1
Convergence and translation: attitudes to inter-professional learning and teaching of creative problem-solving among medical and engineering students and staff
Background: Healthcare worldwide needs translation of basic ideas from engineering into the clinic. Consequently, there is increasing demand for graduates equipped with the knowledge and skills to apply interdisciplinary medicine/engineering approaches to the development of novel solutions for healthcare. The literature provides little guidance regarding barriers to, and facilitators of, effective interdisciplinary learning for engineering and medical students in a team-based project context. Methods: A quantitative survey was distributed to engineering and medical students and staff in two universities, one in Ireland and one in Belgium, to chart knowledge and practice in interdisciplinary learning and teaching, and of the teaching of innovation. Results: We report important differences for staff and students between the disciplines regarding attitudes towards, and perceptions of, the relevance of interdisciplinary learning opportunities, and the role of creativity and innovation. There was agreement across groups concerning preferred learning, instructional styles, and module content. Medical students showed greater resistance to the use of structured creativity tools and interdisciplinary teams. Conclusions: The results of this international survey will help to define the optimal learning conditions under which undergraduate engineering and medicine students can learn to consider the diverse factors which determine the success or failure of a healthcare engineering solution
Fine-mapping of the HNF1B multicancer locus identifies candidate variants that mediate endometrial cancer risk.
Common variants in the hepatocyte nuclear factor 1 homeobox B (HNF1B) gene are associated with the risk of Type II diabetes and multiple cancers. Evidence to date indicates that cancer risk may be mediated via genetic or epigenetic effects on HNF1B gene expression. We previously found single-nucleotide polymorphisms (SNPs) at the HNF1B locus to be associated with endometrial cancer, and now report extensive fine-mapping and in silico and laboratory analyses of this locus. Analysis of 1184 genotyped and imputed SNPs in 6608 Caucasian cases and 37 925 controls, and 895 Asian cases and 1968 controls, revealed the best signal of association for SNP rs11263763 (P = 8.4 × 10(-14), odds ratio = 0.86, 95% confidence interval = 0.82-0.89), located within HNF1B intron 1. Haplotype analysis and conditional analyses provide no evidence of further independent endometrial cancer risk variants at this locus. SNP rs11263763 genotype was associated with HNF1B mRNA expression but not with HNF1B methylation in endometrial tumor samples from The Cancer Genome Atlas. Genetic analyses prioritized rs11263763 and four other SNPs in high-to-moderate linkage disequilibrium as the most likely causal SNPs. Three of these SNPs map to the extended HNF1B promoter based on chromatin marks extending from the minimal promoter region. Reporter assays demonstrated that this extended region reduces activity in combination with the minimal HNF1B promoter, and that the minor alleles of rs11263763 or rs8064454 are associated with decreased HNF1B promoter activity. Our findings provide evidence for a single signal associated with endometrial cancer risk at the HNF1B locus, and that risk is likely mediated via altered HNF1B gene expression
Worldwide variations in artificial skyglow
Despite constituting a widespread and significant environmental change,
understanding of artificial nighttime skyglow is extremely limited. Until now,
published monitoring studies have been local or regional in scope, and
typically of short duration. In this first major international compilation of
monitoring data we answer several key questions about skyglow properties.
Skyglow is observed to vary over four orders of magnitude, a range hundreds of
times larger than was the case before artificial light. Nearly all of the
study sites were polluted by artificial light. A non-linear relationship is
observed between the sky brightness on clear and overcast nights, with a
change in behavior near the rural to urban landuse transition. Overcast skies
ranged from a third darker to almost 18 times brighter than clear. Clear sky
radiances estimated by the World Atlas of Artificial Night Sky Brightness were
found to be overestimated by ~25%; our dataset will play an important role in
the calibration and ground truthing of future skyglow models. Most of the
brightly lit sites darkened as the night progressed, typically by ~5% per
hour. The great variation in skyglow radiance observed from site-to-site and
with changing meteorological conditions underlines the need for a long-term
international monitoring program
An artificial intelligence tool for heterogeneous team formation in the classroom
Nowadays, there is increasing interest in the development of teamwork skills
in the educational context. This growing interest is motivated by its
pedagogical effectiveness and the fact that, in labour contexts, enterprises
organize their employees in teams to carry out complex projects. Despite its
crucial importance in the classroom and industry, there is a lack of support
for the team formation process. Not only do many factors influence team
performance, but the problem becomes exponentially costly if teams are to be
optimized. In this article, we propose a tool whose aim it is to cover such a
gap. It combines artificial intelligence techniques such as coalition structure
generation, Bayesian learning, and Belbin's role theory to facilitate the
generation of working groups in an educational context. This tool improves
current state of the art proposals in three ways: i) it takes into account the
feedback of other teammates in order to establish the most predominant role of
a student instead of self-perception questionnaires; ii) it handles uncertainty
with regard to each student's predominant team role; iii) it is iterative since
it considers information from several interactions in order to improve the
estimation of role assignments. We tested the performance of the proposed tool
in an experiment involving students that took part in three different team
activities. The experiments suggest that the proposed tool is able to improve
different teamwork aspects such as team dynamics and student satisfaction
Radio polarization from the inner Galaxy at arcminute resolution
The Southern Galactic Plane Survey (SGPS) is an HI and 1.4-GHz continuum
survey of the 4th quadrant of the Galaxy at arcmin resolution. We present here
results on linearly polarized continuum emission from an initial
28-square-degree Test Region for the SGPS, consisting of 190 mosaiced pointings
of the Australia Telescope Compact Array, and covering the range 325.5 < l <
332.5, -0.5 < b < +3.5. Complicated extended structure is seen in linear
polarization throughout the Test Region, almost all of which has no correlation
with total intensity. We interpret the brightest regions of polarized emission
as representing intrinsic structure in extended polarization, most likely
originating in the Crux spiral arm at a distance of 3.5 kpc; fainter polarized
structure is imposed by Faraday rotation in foreground material. Two large
areas in the field are devoid of polarization. We argue that these voids are
produced by foreground HII regions in which the magnetic field is disordered on
scales of ~0.1-0.2 pc. We also identify a depolarized halo around the HII
region RCW 94, which we suggest results from the interaction of the HII region
with a surrounding molecular cloud.Comment: 21 pages, 5 embedded EPS figures, 9 jpeg figures, uses emulateapj
apjfonts. Accepted to the Astrophysical Journal. Version with all 14 figures
in embedded EPS format available at http://space.mit.edu/~bmg/sgps
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