You and Your Neighbor

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What Limits Fire? An Examination of Driver\u27s of Burnt Area in Southern Africa

The factors controlling the extent of fire in Africa south of the equator were investigated using moderate resolution (500 m) satellite-derived burned area maps and spatial data on the environmental factors thought to affect burnt area. A random forest regression tree procedure was used to determine the relative importance of each factor in explaining the burned area fraction and to address hypotheses concerned with human and climatic influences on the drivers of burnt area. The model explained 68% of the variance in burnt area. Tree cover, rainfall in the previous 2 years, and rainfall seasonality were the most important predictors. Human activities – represented by grazing, roads per unit area, population density, and cultivation fraction – were also shown to affect burnt area, but only in parts of the continent with specific climatic conditions, and often in ways counter to the prevailing wisdom that more human activity leads to more fire. The analysis found no indication that ignitions were limiting total burnt area on the continent, and most of the spatial variation was due to variation in fuel load and moisture. Split conditions from the regression tree identified (i) low rainfall regions, where fire is rare; (ii) regions where fire is under human control; and (iii) higher rainfall regions where burnt area is determined by rainfall seasonality. This study provides insights into the physical, climatic, and human drivers of fire and their relative importance across southern Africa, and represents the beginnings of a predictive framework for burnt area

Quantifying the Human Influence on Fire Ignition Across the Western USA

Humans have a profound effect on fire regimes by increasing the frequency of ignitions. Although ignition is an integral component of understanding and predicting fire, to date fire models have not been able to isolate the ignition location, leading to inconsistent use of anthropogenic ignition proxies. Here, we identified fire ignitions from the Moderate Resolution Imaging Spectrometer (MODIS) Burned Area Product (2000–2012) to create the first remotely sensed, consistently derived, and regionally comprehensive fire ignition data set for the western United States. We quantified the spatial relationships between several anthropogenic land-use/disturbance features and ignition for ecoregions within the study area and used hierarchical partitioning to test how the anthropogenic predictors of fire ignition vary among ecoregions. The degree to which anthropogenic features predicted ignition varied considerably by ecoregion, with the strongest relationships found in the Marine West Coast Forest and North American Desert ecoregions. Similarly, the contribution of individual anthropogenic predictors varied greatly among ecoregions. Railroad corridors and agricultural presence tended to be the most important predictors of anthropogenic ignition, while population density and roads were generally poor predictors. Although human population has often been used as a proxy for ignitions at global scales, it is less important at regional scales when more specific land uses (e.g., agriculture) can be identified. The variability of ignition predictors among ecoregions suggests that human activities have heterogeneous impacts in altering fire regimes within different vegetation types and geographies

The effect of fire on tree–grass coexistence in savannas: a simulation study

The savanna biome has the greatest burned area globally. Whereas the global distribution of most biomes can be predicted successfully from climatic variables, this is not so for savannas. Attempts to dynamically model the distribution of savannas, including a realistically varying tree : grass ratio are fraught with difficulties. In a simulation study using the dynamic vegetation model LPJ-GUESS we investigate the effect of fire on the tree : grass ratios as well as the biome distribution on the African continent. We performed simulations at three spatial scales: locally, at four sites inside Kruger National Park (South Africa); regionally, along a precipitation gradient; and for the African continent. We evaluated the model using results of a fire experiment and found that the model underestimates the effect of fire on tree cover slightly. On a regional scale, high frequencies were able to prevent trees from outcompeting grasses in mesic regions between ~700 and 900 mm mean annual precipitation. Across the African continent, incorporation of fire improved notably the simulated distribution of the savanna biome. Our model results confirm the role of fire in determining savanna distributions, a notion that has been challenged by competing theories of tree–grass coexistence

Computer simulations of developmental change: The contributions of working memory capacity and long-term knowledge

Increasing working memory (WM) capacity is often cited as a major influence on children’s development and yet WM capacity is difficult to examine independently of long-term knowledge. A computational model of children’s nonword repetition (NWR) performance is presented that independently manipulates long-term knowledge and WM capacity to determine the relative contributions of each in explaining the developmental data. The simulations show that (1) both mechanisms independently cause the same overall developmental changes in NWR performance; (2) increase in long-term knowledge provides the better fit to the child data; and (3) varying both long-term knowledge and WM capacity adds no significant gains over varying long-term knowledge alone. Given that increases in long-term knowledge must occur during development, the results indicate that increases in WM capacity may not be required to explain developmental differences. An increase in WM capacity should only be cited as a mechanism of developmental change when there are clear empirical reasons for doing so

Extending the Limited Transfer Window Hypothesis to Inter-organelle DNA Migration

Mitochondrial genomes often contain large amounts of plastid DNA (ptDNA)-derived sequences (MTPTs). It has been suggested that the intercompartmental transfer of ptDNA is greatly reduced in species with only a single plastid per cell (monoplastidic) as compared with those with many plastids per cell (polyplastidic). This hypothesis has not been applied to the movement of DNA from plastids to mitochondria. By analyzing the organelle genomes from diverse mono- and polyplastidic taxa, I show that MTPTs are restricted to the mitochondrial genomes of species with many plastids per cell and are absent from those with one plastid per cell or with monoplastidic meristematic systems. Moreover, the most bloated mitochondrial genomes that were explored had the largest MTPT contents. These data, like previous results on ptDNA-derived sequences in nuclear genomes, support the hypothesis that plastid number and the forces governing the expansion and contraction of noncoding mitochondrial DNA (mtDNA) influence MTPT abundance. I also show that plastid genomes are depauperate in mtDNA-derived sequences (PTMTs), irrespective of the number of mitochondria per cell and plastid genome size, which may reflect the lack of a DNA uptake system in plastids

The Lantern Vol. 27, No. 2, Spring 1959

• The Case for a Stratified Society • Education Courses • Some Thoughts for God\u27s Thinking Creatures • Sawdust to the Oats? • To Change the Things I Can... • Vignette • I Meet Goliath • Reverie and Reminiscence • On Flight • In Defense of Jazz • A Description • Line of Retreat • Alan Lomax and the American Folk Song • Dawn Stillness • Seasons • Two Poems • Despair • Too Late • Education • For All Practical Purposes He Was Bald • Contrast • I Belong to the Sea • Waves • Love • The Glory and the Dreamhttps://digitalcommons.ursinus.edu/lantern/1077/thumbnail.jp

Radio imaging observations of PSR J1023+0038 in an LMXB state

The transitional millisecond pulsar (MSP) binary system PSR J1023+0038 re-entered an accreting state in 2013 June in which it bears many similarities to low-mass X-ray binaries (LMXBs) in quiescence or near-quiescence. At a distance of just 1.37 kpc, PSR J1023+0038 offers an unsurpassed ability to study low-level accretion onto a highly magnetized compact object. We have monitored PSR J1023+0038 intensively using radio imaging with the Karl G. Jansky Very Large Array, the European VLBI Network and the Low Frequency Array, seeing rapidly variable, flat spectrum emission that persists over a period of six months. The flat spectrum and variability are indicative of synchrotron emission originating in an outflow from the system, most likely in the form of a compact, partially self-absorbed jet, as is seen in LMXBs at higher accretion rates. The radio brightness, however, greatly exceeds extrapolations made from observations of more vigorously accreting neutron star LMXB systems. We postulate that PSR J1023+0038 is undergoing radiatively inefficient "propeller-mode" accretion, with the jet carrying away a dominant fraction of the liberated accretion luminosity. We confirm that the enhanced ?-ray emission seen in PSR J1023+0038 since it re-entered an accreting state has been maintained; the increased ?-ray emission in this state can also potentially be associated with propeller-mode accretion. Similar accretion modes can be invoked to explain the radio and X-ray properties of the other two known transitional MSP systems XSS J12270-4859 and PSR J1824-2452I (M28I), suggesting that radiatively inefficient accretion may be a ubiquitous phenomenon among (at least one class of) neutron star binaries at low accretion rates

The role of non-initial clusters in the Children’s test of Nonword Repetition: evidence from children with language impairment and typically developing children

One of the most used tests of nonword repetition is the Children’s test of Nonword Repetition (CNRep, Gathercole et al., 1994, Gathercole & Baddeley, 1996). The test is composed of nonwords of different length, and normative data suggest that children experience more difficulties in repeating long nonwords. An analysis of the distribution of phonological clusters in the test shows that non-initial clusters are unequally distributed in the test, and they always appear in long nonwords. For this reason, we hypothesised that the difficulties children encounter with long nonwords may be influenced by the phonological complexity of the clusters, and not just by the challenge for working memory associated with long nonwords. To test the hypothesis, we compared performance in long nonwords with and without a non-initial cluster in 18 children with language impairment and 18 typically developing children. Without questioning the validity of the test as a diagnostic tool, our analysis shows that, in line with our prediction, long nonwords with non-initial clusters are repeated less accurately by both groups. In addition, there was an interaction of the effect of cluster and age: specifically, it is absent in younger children and it gradually increases with age. These findings suggest that phonological complexity may be impacting on the length effect normally observed in the CNRep task, and this impact may be particularly evident in older children