The top priority of fire management agencies in Canada is to protect human life and property. Here we investigate if decades of aggressive fire suppression in the boreal biome of Canada has reduced ...the proportion of recently burned forests (RBF; <30 years) near human communities, and thereby inadvertently increased the risk of wildfire. We measured the percentage of RBF, which are usually less flammable than older forests, up to a 25-km radius around communities compared to that in the surrounding regional fire regime zone. Our analysis of 160 communities across boreal Canada shows that 54.4% exhibited a deficit or lack of RBF, whereas only 15.0% showed a surplus. Overall, a majority (74.4%) of communities are surrounded by a low (≤10%) proportion of RBF, indicating a higher vulnerability of those communities to wildfire. These findings suggest that suppression policies are increasing flammability in the wildland-urban interface of boreal Canada.
A diverse range of materials and properties are exhibited by layered perovskites. We report on the synthesis, characterization, and computational investigation of a new ferroelectricCsBi2Ti2NbO10an ...n = 3 member of the Dion–Jacobson (DJ) family. Structural studies using variable-temperature neutron powder diffraction indicate that a combination of octahedral rotations and polar displacements result in the polar structure. Density functional theory calculations reveal that the wider perovskite blocks in CsBi2Ti2NbO0 stabilize proper ferroelectricity, in contrast to the hybrid-improper ferroelectricity reported for all other DJ phases. Our results raise the possibility of a new class of proper ferroelectric materials analogous to the well-known Aurivillius phases.
Fire seasons have become increasingly variable and extreme due to changing climatological, ecological, and social conditions. Earth observation data are critical for monitoring fires and their ...impacts. Herein, we present a whole‐system framework for identifying and synthesizing fire monitoring objectives and data needs throughout the life cycle of a fire event. The four stages of fire monitoring using Earth observation data include the following: (1) pre‐fire vegetation inventories, (2) active‐fire monitoring, (3) post‐fire assessment, and (4) multi‐scale synthesis. We identify the challenges and opportunities associated with current approaches to fire monitoring, highlighting four case studies from North American boreal, montane, and grassland ecosystems. While the case studies are localized to these ecosystems and regional contexts, they provide insights for others experiencing similar monitoring challenges worldwide. The field of remote sensing is experiencing a rapid proliferation of new data sources, providing observations that can inform all aspects of our fire monitoring framework; however, significant challenges for meeting fire monitoring objectives remain. We identify future opportunities for data sharing and rapid co‐development of information products using cloud computing that benefits from open‐access Earth observation and other geospatial data layers.
Earth observation data are critical for monitoring fires and their impacts as fire seasons become less predictable. In this manuscript, we draw upon multiple disciplines to present a whole‐system framework for identifying and synthesizing fire monitoring objectives and data needs throughout the life cycle of a fire event. By applying our framework to four North American case studies, we identify challenges and future opportunities for fire monitoring to benefit from broader advances in Earth observations.
Abstract
SN 2014C was originally classified as a Type Ib supernova, but at phase
ϕ
= 127 days, post-explosion strong H
α
emission was observed. SN 2014C has since been observed in radio, infrared, ...optical and X-ray bands. Here we present new optical spectroscopic and photometric data spanning
ϕ
= 947–2494 days post-explosion. We address the evolution of the broadened H
α
emission line, as well as broad O
iii
emission and other lines. We also conduct a parallel analysis of all publicly available multiwavelength data. From our spectra, we find a nearly constant H
α
FWHM velocity width of ∼2000 km s
−1
that is significantly lower than that of other broadened atomic transitions (∼3000–7000 km s
−1
) present in our spectra (O
i
λ
6300; O
iii
λ
λ
4959, 5007; He
i
λ
7065; Ca
ii
λ
λ
7291, 7324). The late radio data demand a fast forward shock (∼10,000 km s
−1
at
ϕ
= 1700 days) in rarified matter that contrasts with the modest velocity of the H
α
. We propose that the infrared flux originates from a toroidal-like structure of hydrogen surrounding the progenitor system, while later emission at other wavelengths (radio, X-ray) likely originates predominantly from the reverse shock in the ejecta and the forward shock in the quasi-spherical progenitor He-wind. We propose that the H
α
emission arises in the boundary layer between the ejecta and torus. We also consider the possible roles of a pulsar and a binary companion.
We used repeat oblique photography to quantify and determine the drivers of vegetation change, particularly forest closure and encroachment, in the Rocky Mountains of southern Alberta, Canada, from ...the beginning of the twentieth century to the present. We classified the landscape into seven distinct vegetation types (closed‐canopy conifer forest, broadleaf deciduous forest, mixedwood forest, open‐canopy woodlands, shrublands, grasslands and meadows, non‐vegetated) and assessed vegetation change between the two time periods. We found that closed‐canopy coniferous forest, broadleaf deciduous forest, and mixedwood forest increased on an area basis by 35%, 45%, and 80%, respectively, over this time period; concomitantly, grasslands and open‐canopy woodlands declined by 25% and 39%, respectively. Overall, 28% of the landscape was in a more advanced successional state in 2008 as compared to the early twentieth century. The Montane and Subalpine Natural Subregions (NSR) experienced the most change (42% and 26%, respectively, in a more advanced successional state). The loss of open‐canopy woodlands was observed across the entire landscape, while grassland and meadow losses were most acute in the Subalpine and Alpine NSRs. The probability of vegetation change to a more advanced successional condition was greater at higher elevations and in areas receiving lower amounts of solar insolation. The changes observed are consistent with what we would expect to see due to lengthening of fire return intervals. Understanding the magnitude of change in vegetation types and the drivers of this change is important for the development of effective contemporary ecosystem management and restoration practices.
Montane regions throughout western North America have experienced increases in forest canopy closure and forest encroachment into grasslands over the past century; this has been attributed to climate ...change and fire suppression/exclusion. These changes threaten ecological values and potentially increase probabilities of intense wildfire. Restoration of landscapes to historical conditions has been proposed as a potential solution. We used historical oblique photographs of an area in the Rocky Mountains of Alberta, Canada, to determine the vegetation composition in 1909 and then asked whether restoration to a historical vegetation condition would: (1) reduce the overall burn probability of fire; (2) reduce the probability of high‐intensity fires; and (3) change the spatial pattern of burn probabilities, as compared to current conditions. We used the Burn‐P3 model to calculate the overall and high‐intensity burn probabilities in two scenarios: (1) the baseline (current (2014) vegetation composition) and (2) historical restoration (vegetation in the study area as of 1909 with the surrounding landscape in its current condition). In the baseline, the landscape had 50% less grassland and more coniferous forest than 100 yr ago. Except for the fuel grids, we ensured all input parameters (number and locations of ignitions, weather conditions, etc.) were identical between the two scenarios; therefore, any differences in outputs are solely attributable to the changed fuels. The historical restoration scenario reduced the overall burn probability by only 1.3%, but the probability of high‐intensity wildfires was reduced by nearly half (44.2%), as compared to the baseline scenario. There were also differences in the spatial pattern of overall burn probabilities between the two scenarios. While 6.7% of the landscape burned with half (or less) the probability in the restoration scenario (compared to the baseline), other areas (3.2%) had burn probabilities two to five times higher. More than 21.5% had high‐intensity burn probabilities that were 20% or less of those in the baseline scenario. Differences in burn probabilities between the two scenarios were largely attributable to the effects of the vegetation difference on rate of fire spread. Restoration to historical vegetation structure significantly lowered wildfire risk to the landscape.
Carbonic anhydrase VA deficiency is a recently described inherited cause of paediatric hyperammonaemia. Most published cases describe patients with only one episode of hyperammonaemia whilst others ...report patients who had up to three metabolic crises with the first invariably being the most severe. We describe a patient with carbonic anhydrase VA deficiency who experienced 7 hyperammonemic episodes over a 3‐year period, up to age 5 years 9 months. These episodes did not clearly decrease in severity over time. This report expands the clinical phenotype and the age window for metabolic crises associated with this condition.
Long-Term Radio Monitoring of SN 1993J Weiler, Kurt W; Williams, Christopher L; Panagia, Nino ...
The Astrophysical journal,
12/2007, Letnik:
671, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present our extensive observations of the radio emission from supernova (SN) 1993J, in M81 (NGC 3031), made with the Very Large Array, at 90, 20, 6, 3.6, 2, 1.2, and 0.7 cm, as well as numerous ...measurements from other telescopes and at other wavelengths. The combined data set constitutes probably the most detailed set of measurements ever established for any SN outside of the Local Group in any wavelength range. The radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well. However, (1) The highest frequency measurements at 85-110 GHz at early times (<40 days) are not well fitted by the parameterization which describes the centimeter wavelength measurements. (2) At midcentimeter wavelengths there is often deviation from the fitted radio light curves. (3) At a time similar to 3100 days after shock breakout, the decline rate of the radio emission steepens from (t super(+ beta )) beta similar to -0.7 to -2.7 without change in the spectral index (v super(+ alpha ); alpha similar to -0.81); however, this decline is best described not as a power-law, but as an exponential decay with an e-folding time of similar to 1100 days. (4) The best overall fit to all of the data is a model including both nonthermal synchrotron self-absorption (SSA) and thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate until the break. (5) The radio and X-ray light curves display quite similar behavior and both suggest a sudden increase in the supernova progenitor mass-loss rate occurred at similar to 8000 yr prior to shock breakout.
We present and discuss the radio observations of 27 Type Ia supernovae (SNe Ia), observed over two decades with the Very Large Array. No SN Ia has been detected so far in the radio, implying a very ...low density for any possible circumstellar material established by the progenitor, or progenitor system, before explosion. We derive 2 s upper limits to a steady mass-loss rate for individual SN systems as low as 63 x 10 super(-8) M sub(z) yr super(-1), which argues strongly against white dwarf accretion via a stellar wind from a massive binary companion in the symbiotic star, an example of the "single-degenerate" scenario. However, a white dwarf accreting from a relatively low mass companion via a sufficiently high efficiency (>60%-80%) Roche lobe overflow is still consistent with our limits. The "double-degenerate" merger scenario also cannot be excluded.
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