722 research outputs found
Effects of forest harvesting on summer stream temperatures in New Brunswick, Canada: an inter-catchment, multiple-year comparison
This paper presents a pre- and post-harvest comparison of stream temperatures collected in five neighbouring streams (sub-catchments) over a period of five years (1994-1998). The aim of the study was to determine whether land cover changes from clear cutting in areas outside forest buffer zones (applied to streams >0.5 m wide) might contribute to an increase in summer mean stream temperatures in buffered streams downslope by infusion of warmed surface and sub-surface water into the streams. Specific relationships were observed in all five forest streams investigated. To assist in the analysis, several spatially-relevant variables, such as land cover change, mid-summer potential solar radiation, flow accumulation, stream location and slope of the land were determined, in part, from existing aerial photographs, GIS-archived forest inventory data and a digital terrain model of the study area. Spatial calculations of insolation levels for July 15<sup>th</sup> were used as an index of mid-summer solar heating across sub-catchments. Analysis indicated that prior to the 1995 harvest, differences in stream temperature could be attributed to <i>(i)</i> topographic position and catchment-to-sun orientation, <i>(ii)</i> the level of cutting that occurred in the upper catchment prior to the start of the study, and <i>(iii)</i> the average slope within harvested areas. Compared to the pre-harvest mean stream temperatures in 1994, mean temperatures in the three streams downslope from the 1995 harvest areas increased by 0.3 to 0.7°C (representing a 4-8% increase; p-value of normalised temperatures <<0.05). The greatest temperature change occurred in the stream that had the greatest proportion of its upper catchment harvested (16.8%), which also had the highest calculated potential solar loading ( ~2749 MJ per stream cell). From the analysis it was determined that the thinning applied to the forest buffer of that stream, with a basal area removal of ~28%, was insufficient to cause significant change in the observed stream temperature. Similar effects were observed following a second harvest in 1997. In general, increases in mean stream temperature coincided with forest harvesting activities outside forest buffers, where conditions promoting stream warming were greatest. In this study, no clear relationship existed between forest buffer strip width (ranging from 30-60 m) and the level of stream warming observed at the monitoring stations.</p> <p style='line-height: 20px;'><b>Keywords:</b> terrain attributes, solar radiation, land cover, forest buffers, New Brunswick regulations, spatial modelling, DEM, forest covertype
Effects of forest harvesting on summer stream temperatures in New Brunswick, Canada: an inter-catchment, multiple-year comparison
International audienceThis paper presents a pre- and post-harvest comparison of stream temperatures collected in five neighbouring streams (sub-catchments) over a period of five years (1994-1998). The aim of the study was to determine whether land cover changes from clear cutting in areas outside forest buffer zones (applied to streams >0.5 m wide) might contribute to an increase in summer mean stream temperatures in buffered streams downslope by infusion of warmed surface and sub-surface water into the streams. Specific relationships were observed in all five forest streams investigated. To assist in the analysis, several spatially-relevant variables, such as land cover change, mid-summer potential solar radiation, flow accumulation, stream location and slope of the land were determined, in part, from existing aerial photographs, GIS-archived forest inventory data and a digital terrain model of the study area. Spatial calculations of insolation levels for July 15th were used as an index of mid-summer solar heating across sub-catchments. Analysis indicated that prior to the 1995 harvest, differences in stream temperature could be attributed to (i) topographic position and catchment-to-sun orientation, (ii) the level of cutting that occurred in the upper catchment prior to the start of the study, and (iii) the average slope within harvested areas. Compared to the pre-harvest mean stream temperatures in 1994, mean temperatures in the three streams downslope from the 1995 harvest areas increased by 0.3 to 0.7°C (representing a 4-8% increase; p-value of normalised temperatures
Optical Polarization and Spectral Variability in the M87 Jet
During the last decade, M87's jet has been the site of an extraordinary
variability event, with one knot (HST-1) increasing by over a factor 100 in
brightness. Variability was also seen on timescales of months in the nuclear
flux. Here we discuss the optical-UV polarization and spectral variability of
these components, which show vastly different behavior. HST-1 shows a highly
significant correlation between flux and polarization, with P increasing from
at minimum to >40% at maximum, while the orientation of its electric
vector stayed constant. HST-1's optical-UV spectrum is very hard
(, ), and displays "hard lags"
during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at
later epochs. We interpret the behavior of HST-1 as enhanced particle
acceleration in a shock, with cooling from both particle aging and the
relaxation of the compression. We set 2 upper limits of
parsecs and 1.02 on the size and advance speed of the flaring region. The
slight deviation of the electric vector orientation from the jet PA, makes it
likely that on smaller scales the flaring region has either a double or twisted
structure. By contrast, the nucleus displays much more rapid variability, with
a highly variable electric vector orientation and 'looping' in the
plane. The nucleus has a much steeper spectrum () but
does not show UV-optical spectral variability. Its behavior can be interpreted
as either a helical distortion to a steady jet or a shock propagating through a
helical jet.Comment: 14 pages, 7 figures, ApJ, in pres
Recommended from our members
Modeling Analysis of Primary Controls on Net Ecosystem Productivity of Seven Boreal and Temperate Coniferous Forests Across a Continental Transect
Process-based models are effective tools to synthesize and/or extrapolate measured carbon (C) exchanges from individual sites to large scales. In this study, we used a C- and nitrogen (N)-cycle coupled ecosystem model named CN-CLASS (Carbon Nitrogen-Canadian Land Surface Scheme) to study the role of primary climatic controls and site-specific C stocks on the net ecosystem productivity (NEP) of seven intermediate-aged to mature coniferous forest sites across an east–west continental transect in Canada. The model was parameterized using a common set of parameters, except for two used in empirical canopy conductance–assimilation, and leaf area–sapwood relationships, and then validated using observed eddy covariance flux data. Leaf Rubisco-N dynamics that are associated with soil–plant N cycling, and depend on canopy temperature, enabled the model to simulate site-specific gross ecosystem productivity (GEP) reasonably well for all seven sites. Overall GEP simulations had relatively smaller differences compared with observations vs. ecosystem respiration (RE), which was the sum of many plant and soil components with larger variability and/or uncertainty associated with them. Both observed and simulated data showed that, on an annual basis, boreal forest sites were either carbon-neutral or a weak C sink, ranging from 30 to 180 g C m−2 yr−1; while temperate forests were either a medium or strong C sink, ranging from 150 to 500 g C m−2 yr−1, depending on forest age and climatic regime. Model sensitivity tests illustrated that air temperature, among climate variables, and aboveground biomass, among major C stocks, were dominant factors impacting annual NEP. Vegetation biomass effects on annual GEP, RE and NEP showed similar patterns of variability at four boreal and three temperate forests. Air temperature showed different impacts on GEP and RE, and the response varied considerably from site to site. Higher solar radiation enhanced GEP, while precipitation differences had a minor effect. Magnitude of forest litter content and soil organic matter (SOM) affected RE. SOM also affected GEP, but only at low levels of SOM, because of low N mineralization that limited soil nutrient (N) availability. The results of this study will help to evaluate the impact of future climatic changes and/or forest C stock variations on C uptake and loss in forest ecosystems growing in diverse environments.Earth and Planetary Science
Spin Waves and Quantum Criticality in the Frustrated XY Pyrochlore Antiferromagnet Er2Ti2O7
We report detailed measurements of the low temperature magnetic phase diagram
of ErTiO. Heat capacity and time-of-flight neutron scattering
studies of single crystals, subject to magnetic fields applied along the
crystallographic [110] direction, reveal unconventional low energy states.
Er magnetic ions reside on a pyrochlore lattice in ErTiO,
where local XY anisotropy and antiferromagnetic interactions give rise to a
unique frustrated system. In zero field, the ground state exhibits coexisting
short and long range order, accompanied by soft collective spin excitations
previously believed to be absent. The application of finite magnetic fields
tunes the ground state continuously through a landscape of non-collinear
phases, divided by a zero temperature phase transition at 1.5
T. The characteristic energy scale for spin fluctuations is seen to vanish at
the critical point, as expected for a second order quantum phase transition
driven by quantum fluctuations.Comment: 5 pages, 4 figures, submitted for publicatio
Developing a decision support tool for assessing land use change and BMPs in ungauged watersheds based on decision rules provided by SWAT simulation
Decision making on water resources management at ungauged, especially
large-scale watersheds relies on hydrological modeling. Physically based
distributed hydrological models require complicated setup, calibration, and
validation processes, which may delay their acceptance among decision makers.
This study presents an approach to develop a simple decision support
tool (DST) for decision makers and economists to evaluate multiyear impacts
of land use change and best management practices (BMPs) on water quantity and quality for ungauged
watersheds. The example DST developed in the present study was based on
statistical equations derived from Soil and Water Assessment Tool (SWAT)
simulations and applied to a small experimental watershed in northwest New
Brunswick. The DST was subsequently tested against field measurements and
SWAT simulations for a larger watershed. Results from DST could reproduce
both field data and model simulations of annual stream discharge and sediment
and nutrient loadings. The relative error of mean annual discharge and
sediment, nitrate–nitrogen, and soluble-phosphorus loadings were −6, −52,
27, and −16 %, respectively, for long-term simulation. Compared with
SWAT, DST has fewer input requirements and can be applied to multiple
watersheds without additional calibration. Also, scenario analyses with DST
can be directly conducted for different combinations of land use and BMPs
without complex model setup procedures. The approach in developing DST can be
applied to other regions of the world because of its flexible structure.</p
Recruitment, augmentation and apoptosis of rat osteoclasts in 1,25-(OH)2D3 response to short-term treatment with 1,25-dihydroxyvitamin D3in vivo
Background
Although much is known about the regulation of osteoclast (OC) formation and activity, little is known about OC senescence. In particular, the fate of of OC seen after 1,25-(OH)2D3 administration in vivo is unclear. There is evidence that the normal fate of OC is to undergo apoptosis (programmed cell death). We have investigated the effect of short-term application of high dose 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on OC apoptosis in an experimental rat model.
Methods
OC recruitment, augmentation and apoptosis was visualised and quantitated by staining histochemically for tartrate resistant acid phosphatase (TRAP), double staining for TRAP/ED1 or TRAP/DAPI, in situ DNA fragmentation end labelling and histomorphometric analysis.
Results
Short-term treatment with high-dose 1,25-(OH)2D3 increased the recruitment of OC precursors in the bone marrow resulting in a short-lived increase in OC numbers. This was rapidly followed by an increase in the number of apoptotic OC and their subsequent removal. The response of OC to 1,25-(OH)2D3 treatment was dose and site dependent; higher doses producing stronger, more rapid responses and the response in the tibiae being consistently stronger and more rapid than in the vertebrae.
Conclusions
This study demonstrates that (1) after recruitment, OC are removed from the resorption site by apoptosis (2) the combined use of TRAP and ED1 can be used to identify OC and their precursors in vivo (3) double staining for TRAP and DAPI or in situ DNA fragmentation end labelling can be used to identify apoptotic OC in vivo
A Unifying Model of Genome Evolution Under Parsimony
We present a data structure called a history graph that offers a practical
basis for the analysis of genome evolution. It conceptually simplifies the
study of parsimonious evolutionary histories by representing both substitutions
and double cut and join (DCJ) rearrangements in the presence of duplications.
The problem of constructing parsimonious history graphs thus subsumes related
maximum parsimony problems in the fields of phylogenetic reconstruction and
genome rearrangement. We show that tractable functions can be used to define
upper and lower bounds on the minimum number of substitutions and DCJ
rearrangements needed to explain any history graph. These bounds become tight
for a special type of unambiguous history graph called an ancestral variation
graph (AVG), which constrains in its combinatorial structure the number of
operations required. We finally demonstrate that for a given history graph ,
a finite set of AVGs describe all parsimonious interpretations of , and this
set can be explored with a few sampling moves.Comment: 52 pages, 24 figure
A Methodological Framework for the Reconstruction of Contiguous Regions of Ancestral Genomes and Its Application to Mammalian Genomes
The reconstruction of ancestral genome architectures and gene orders from homologies between extant species is a long-standing problem, considered by both cytogeneticists and bioinformaticians. A comparison of the two approaches was recently investigated and discussed in a series of papers, sometimes with diverging points of view regarding the performance of these two approaches. We describe a general methodological framework for reconstructing ancestral genome segments from conserved syntenies in extant genomes. We show that this problem, from a computational point of view, is naturally related to physical mapping of chromosomes and benefits from using combinatorial tools developed in this scope. We develop this framework into a new reconstruction method considering conserved gene clusters with similar gene content, mimicking principles used in most cytogenetic studies, although on a different kind of data. We implement and apply it to datasets of mammalian genomes. We perform intensive theoretical and experimental comparisons with other bioinformatics methods for ancestral genome segments reconstruction. We show that the method that we propose is stable and reliable: it gives convergent results using several kinds of data at different levels of resolution, and all predicted ancestral regions are well supported. The results come eventually very close to cytogenetics studies. It suggests that the comparison of methods for ancestral genome reconstruction should include the algorithmic aspects of the methods as well as the disciplinary differences in data aquisition
- …