347 research outputs found
Assessing similarity of dynamic geographic phenomena in spatiotemporal databases.
The growing availability of routine observations from satellite imagery and other remote sensors holds great promise for improved understanding of processes that act in the landscape. However, geographers' ability to effectively use such spatiotemporal data is challenged by large data volume and limitations of conventional data models in geographic information systems (GIS), which provide limited support for querying and exploration of spatiotemporal data other than simple comparisons of temporally referenced snapshots. Current GIS representations allow measurement of change but do not address coherent patterns of change that reflects the working of geographic events and processes. This dissertation presents a representational and query framework to overcome the limitations and enable assessing similarity of dynamic phenomena. The research includes three self contained but related studies: (1) development of a representational framework that incorporates spatiotemporal properties of geographic phenomena, (2) development of a framework to characterize events and processes that can be inferred from GIS databases, and (3) development of a method to assess similarity of events and processes based on the temporal sequences of spatiotemporal properties. Collectively the studies contribute to scientific understanding of spatiotemporal components of geographic processes and technological advances in representation and analysis
Combination of selenium and green tea improves the efficacy of chemoprevention in a rat colorectal cancer model by modulating genetic and epigenetic biomarkers
Dietary supplementation of selenium and green tea holds promise in cancer prevention. In this study, we evaluated the
efficacies of selenium and green tea administered individually and in combination against colorectal cancer in an
azoxymethane (AOM)-induced rat colonic carcinogenesis model and determined the underlying mechanisms of the
protection. Four-week old Sprague-Dawley male rats were fed with diets containing 0.5% green tea extract, 1ppm selenium
as selenium-enriched milk protein, or combination of 1ppm selenium and 0.5% green tea extract. Animals received 2 AOM
(15 mg/kg) treatments to induce colonic oncogenesis. Rats were killed 8 or 30 wk later after the last AOM to examine the
effect of dietary intervention on aberrant crypt foci (ACF) formation or tumor development. On sacrifice, colons were
examined for ACF and tumors, the mRNA levels of SFRP5 and Cyclin D1, and the proteins levels of ß-catenin, COX-2, Ki-67,
DNMT1 and acetyl histone H3. The combination of selenium and green tea resulted in a significant additive inhibition of
large ACF formation, this effect was greater than either selenium or green tea alone, P,0.01; the combination also had a
significant additive inhibition effect on all tumor endpoints, the effect of the combination diet on tumor incidence,
multiplicity and size was greater than selenium or green tea alone, P,0.01. Rats fed the combination diet showed marked
reduction of DNMT1 expression and induction of histone H3 acetylation, which were accompanied by restoration of SFRP5
mRNA in normal-appearing colonic crypts. The combination diet also significantly reduced ß-catenin nuclear translocation,
Cyclin D1 expression and cell proliferation. These data show, for the first time, that combination of selenium and green tea is
more effective in suppressing colorectal oncogenesis than either agent alone. The preventive effect is associated with
regulation of genetic and epigenetic biomarkers implicated in colonic carcinogenesis
A lithostratigraphical and chronological study of Oligocene-Miocene sequences on eastern King George Island, South Shetland Islands (Antarctica) and correlation of glacial episodes with global isotope events
King George Island (South Shetland Islands, Antarctic Peninsula) is renowned for its terrestrial palaeoenvironmental record, which includes evidence for potentially up to four Cenozoic glacial periods. An advantage of the glacigenic outcrops on the island is that they are associated with volcanic formations that can be isotopically dated. As a result of a new mapping and chronological study, it can now be shown that the published stratigraphy and ages of many geological units on eastern King George Island require major revision. The Polonez Glaciation is dated as c. 26.64 ± 1.43 Ma (Late Oligocene (Chattian Stage)) and includes the outcrops previously considered as evidence for an Eocene glacial ('Krakow Glaciation'). It was succeeded by two important volcanic episodes (Boy Point and Cinder Spur formations) formed during a relatively brief interval (< 2 Ma), which also erupted within the Oligocene Chattian Stage. The Melville Glaciation is dated as c. 21–22 Ma (probably 21.8 Ma; Early Miocene (Aquitanian Stage)), and the Legru Glaciation is probably ≤ c. 10 Ma (Late Miocene or younger). As a result of this study, the Polonez and Melville glaciations can now be correlated with increased confidence with the Oi2b and Mi1a isotope zones, respectively, and thus represent major glacial episodes
Ar-Ar age constraints on the timing of Havre Trough opening and magmatism
The age and style of opening of the Havre Trough back-arc system is uncertain due to a lack of geochronologic constraints for the region. 40Ar/39Ar dating of 19 volcanic rocks from across the southern Havre Trough and Kermadec Arc was conducted in three laboratories to provide age constraints on the system. The results are integrated and interpreted as suggesting that this subduction system is young (<2 Ma) and coeval with opening of the continental Taupo Volcanic Zone of New Zealand. Arc magmatism was broadly concurrent across the breadth of the Havre Trough
Evolution in the Disks and Bulges of Group Galaxies since z=0.4
We present quantitative morphology measurements of a sample of optically
selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope
(HST) Advanced Camera for Surveys (ACS) and the GIM2D surface
brightness--fitting software package. The group sample is derived from the
Canadian Network for Observational Cosmology Field Redshift survey (CNOC2) and
follow-up Magellan spectroscopy. We compare these measurements to a similarly
selected group sample from the Millennium Galaxy Catalogue (MGC) at 0.05 < z <
0.12. We find that, at both epochs, the group and field fractional bulge
luminosity (B/T) distributions differ significantly, with the dominant
difference being a deficit of disk--dominated (B/T < 0.2) galaxies in the group
samples. At fixed luminosity, z=0.4 groups have ~ 5.5 +/- 2 % fewer
disk--dominated galaxies than the field, while by z=0.1 this difference has
increased to ~ 19 +/- 6 %. Despite the morphological evolution we see no
evidence that the group environment is actively perturbing or otherwise
affecting the entire existing disk population. At both redshifts, the disks of
group galaxies have similar scaling relations and show similar median
asymmetries as the disks of field galaxies. We do find evidence that the
fraction of highly asymmetric, bulge--dominated galaxies is 6 +/- 3 % higher in
groups than in the field, suggesting there may be enhanced merging in group
environments. We replicate our group samples at z=0.4 and z=0 using the
semi-analytic galaxy catalogues of Bower et al (2006). This model accurately
reproduces the B/T distributions of the group and field at z=0.1. However, the
model does not reproduce our finding that the deficit of disks in groups has
increased significantly since z=0.4.Comment: Accepted for publication in MNRAS. 20 pages, 17 figure
Natural selection shaped the rise and fall of passenger pigeon genomic diversity.
The extinct passenger pigeon was once the most abundant bird in North America, and possibly the world. Although theory predicts that large populations will be more genetically diverse, passenger pigeon genetic diversity was surprisingly low. To investigate this disconnect, we analyzed 41 mitochondrial and 4 nuclear genomes from passenger pigeons and 2 genomes from band-tailed pigeons, which are passenger pigeons' closest living relatives. Passenger pigeons' large population size appears to have allowed for faster adaptive evolution and removal of harmful mutations, driving a huge loss in their neutral genetic diversity. These results demonstrate the effect that selection can have on a vertebrate genome and contradict results that suggested that population instability contributed to this species's surprisingly rapid extinction
An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 58 (2011): 173-185, doi:10.1016/j.dsr.2010.12.002.Unprecedented summer-season sampling of the Arctic Ocean during the period 2006−2008 makes
possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins.
In comparison to observations from 1992−1999, LFW content relative to a salinity of 35 in the layer
from the surface to the 34 isohaline increased by 8400 ± 2000 km3 in the Arctic Ocean (water depth
greater than 500m). This is close to the annual export of freshwater (liquid and solid) from the Arctic
Ocean reported in the literature.
Observations and a model simulation show regional variations in LFW were both due to changes
in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a
mean freshening of the water column above this depth, associated with an increased net sea ice melt
and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic
Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in
LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a
quarter of the salinity contribution, and non-linear effects due to both factors were negligible.This work was supported by the Co-Operative Project “The
North Atlantic as Part of the Earth System: From System Comprehension to Analysis of Regional
Impacts” funded by the German Federal Ministry for Education and Research (BMBF) and by the European Union Sixth Framework Programme project DAMOCLES (Developing Arctic Modelling and
Observing Capabilities for Long-term Environment Studies), contract number 018509GOCE
Timing of detachment faulting in the Bullfrog Hills and Bare Mountain area, southwest Nevada: Inferences from 40Ar/39Ar, K-Ar, U-Pb and fission track thermochronology
Crustal extension in the Bullfrog Hills and Bare Mountain area of southwest Nevada is associated with movement along a regional detachment fault. Normal faulting in the upper plate and rapid cooling (denudation) of the lower plate were coeval with Miocene silicic volcanism and with west-northwest transport along the detachment fault. A west-northwest progression of tilting along upper plate normal faults is indicated by ages of the volcanic rocks in relation to angular unconformities. Near the breakaway, tilting in the upper plate occurred between 12.7 and 11.6 Ma, continued less strongly past 10.7 Ma, and was over by 8.2 Ma. Ten to 20 km west of the breakaway, tilting occurred between 10.7 and 10.33 Ma, continued less strongly after 10.33 Ma, and was over by 8.1 Ma. The cooling histories of the lower plate metamorphic rocks were determined by thermochronologic dating methods: K-Ar and Ar-40/(39)A on muscovite, biotite, and hornblende, Ar-40/(39)A on K-feldspar, U-Pb on apatite, zircon, and sphene, and fission track on apatite, zircon, and sphene. Lower plate rocks 10 km west of the breakaway cooled slowly from Early Cretaceous lower-amphibolite facies conditions through 350+/-50 degrees to 300+/-50 degrees C between 57 and 38 Ma, then cooled rapidly from 205+/-50 degrees to 120+/-5O degrees C between 12.6+/-1.6 and 11.1+/-1.9 Ma. Lower plate rocks 20 km west of the breakaway cooled slowly from Early Cretaceous upper-amphibolite facies conditions through 500+/-50 degrees C at 78-67 Ma, passed through 350+/-50 degrees to 300+/-50 degrees C between 16.3+/-0.4 and 10.5+/-0.3 Ma, then cooled rapidly from 285+/-50 degrees to 120+/-50 degrees C between 10.2 and 8.6 Ma. Upper plate tilting and rapid cooling (denudation) of the lower plate occurred simultaneously in the respective areas. The early slow-cooling part of the lower plate thermal histories was probably related to erosion at the Earth's surface, which stripped off about 9 km of material in 50 to 100 m.y. The results indicate an initial fault dip greater than or equal to 30 degrees and a 12 mm yr(-1) west-northwest migration of the locus of rapid tilting in the upper plate
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