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Search Results: 1 - 10 of 3181 matches for " Brad Murray "
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Temporal introduction patterns of invasive alien plant species to Australia
Brad Murray,Megan Phillips
NeoBiota , 2012, DOI: 10.3897/neobiota.13.2422
Abstract: We examined temporal introduction patterns of 132 invasive alien plant species (IAPS) to Australia since European colonisation in 1770. Introductions of IAPS were high during 1810–1820 (10 species), 1840–1880 (51 species, 38 of these between 1840 and 1860) and 1930–1940 (9 species). Conspicuously few introductions occurred during 10-year periods directly preceding each introduction peak. Peaks during early European settlement (1810–1820) and human range expansion across the continent (1840-1860) both coincided with considerable growth in Australia’s human population. We suggest that population growth during these times increased the likelihood of introduced plant species becoming invasive as a result of increased colonization and propagule pressure. Deliberate introductions of IAPS (104 species) far outnumbered accidental introductions (28 species) and were particularly prominent during early settlement. Cosmopolitan IAPS (25 species) and those native solely to South America (53 species), Africa (27 species) and Asia (19 species) have been introduced deliberately and accidentally to Australia across a broad period of time. A small number of IAPS, native solely to Europe (5 species) and North America (2 species), were all introduced to Australia prior to 1880. These contrasting findings for native range suggest some role for habitat matching, with similar environmental conditions in Australia potentially driving the proliferation of IAPS native to southern-hemisphere regions. Shrub, tree and vine species dominated IAPS introduced prior to 1840, with no grasses or forbs introduced during early colonisation. Since 1840, all five growth forms have been introduced deliberately and accidentally in relatively large numbers across a broad period of time. In particular, a large number of grass and forb IAPS were deliberately introduced between 1840 and 1860, most likely a direct result of the introduction of legislation promoting intensive agriculture across large areas of the continent. Since the 1980s, only three IAPS have been introduced (all deliberately introduced forbs). The decline in IAPS introductions is most likely a reflection of both increased surveillance and biosecurity efforts and the likelihood that many potential IAPS are still within a pre-expansion lag period.
Testing In Situ Assembly with the Kepler Planet Candidate Sample
Brad Hansen,Norm Murray
Physics , 2013, DOI: 10.1088/0004-637X/775/1/53
Abstract: We present a Monte Carlo model for the structure of low mass (total mass < 25 earth mass) planetary systems that form by the in situ gravitational assembly of planetary embryos into final planets. Our model includes distributions of mass, eccentricity, inclination and period spacing that are based on the simulation of a disk of 20 earth masses, forming planets around a solar mass star, and assuming a power law surface density distribution $\propto a^{-1.5}$. The output of the Monte Carlo model is then subjected to the selection effects that mimic the observations of a transiting planet search such as that performed by the Kepler satellite. The resulting comparison of the output to the properties of the observed sample yields an encouraging agreement in terms of the relative frequencies of multiple planet systems and the distribution of the mutual inclinations, when moderate tidal circularisation is taken into account. The broad features of the period distribution and radius distribution can also be matched within this framework, although the model underpredicts the distribution of small period ratios. This likely indicates that some dissipation is still required in the formation process. The most striking deviation between model and observations is in the ratio of single to multiple systems, in that there are roughly 50% more single planet candidates observed than are produced in any model population. This suggests that some systems must suffer additional attrition to reduce the number of planets or increase the range of inclinations.
Migration then assembly: Formation of Neptune mass planets inside 1 AU
Brad M. S. Hansen,Norm Murray
Physics , 2011, DOI: 10.1088/0004-637X/751/2/158
Abstract: We demonstrate that the observed distribution of `Hot Neptune'/`Super-Earth' systems is well reproduced by a model in which planet assembly occurs in situ, with no significant migration post-assembly. This is achieved only if the amount of mass in rocky material is $\sim 50$--$100 M_{\oplus}$ interior to 1 AU. Such a reservoir of material implies that significant radial migration of solid material takes place, and that it occur before the stage of final planet assembly. The model not only reproduces the general distribution of mass versus period, but also the detailed statistics of multiple planet systems in the sample. We furthermore demonstrate that cores of this size are also likely to meet the criterion to gravitationally capture gas from the nebula, although accretion is rapidly limited by the opening of gaps in the gas disk. If the mass growth is limited by this tidal truncation, then the scenario sketched here naturally produces Neptune-mass objects with substantial components of both rock and gas, as is observed. The quantitative expectations of this scenario are that most planets in the `Hot Neptune/Super-Earth' class inhabit multiple-planet systems, with characteristic orbital spacings. The model also provides a natural division into gas-rich (Hot Neptune) and gas-poor (Super-Earth) classes at fixed period. The dividing mass ranges from $\sim 3 M_{\oplus}$ at 10 day orbital periods to $\sim 10 M_{\oplus}$ at 100 day orbital periods. For orbital periods $< 10$ days, the division is less clear because a gas atmosphere may be significantly eroded by stellar radiation.
Torsion in Groups of Integral Triangles  [PDF]
Will Murray
Advances in Pure Mathematics (APM) , 2013, DOI: 10.4236/apm.2013.31015
Abstract:

Let 0γ<π be a fixed pythagorean angle. We study the abelian group Hr of primitive integral triangles (a,b,c) for which the angle opposite side c is γ. Addition in Hr is defined by adding the angles β opposite side b and modding out by π-γ. The only Hr for which the structure is known is Hπ/2, which is free abelian. We prove that for generalγ, Hr has an element of order two iff 2(1-

Impacts of the Replacement of Native Woodland with Exotic Pine Plantations on Leaf-Litter Invertebrate Assemblages: A Test of a Novel Framework
Brad R. Murray,Andrew C. Baker,Tessa C. Robson
International Journal of Ecology , 2009, DOI: 10.1155/2009/490395
Abstract: We present an empirical comparison of invertebrate community structure between areas of undisturbed native eucalypt woodland and areas that have been cleared and replaced with plantations of exotic radiata pine (Pinus radiata). Implementation of a novel conceptual framework revealed that both insect (in autumn) and arachnid (in winter) assemblages demonstrated inhibition in response to the pine plantations. Species richness declines occurred in several taxonomic Orders (e.g., Hymenoptera, Blattodea, Acari) without compensated increases in other Orders in plantations. This was, however, a seasonal response, with shifts between inhibition and equivalency observed in both insects and arachnids across autumn and winter sampling periods. Equivalency responses were characterized by relatively similar levels of species richness in plantation and native habitats for several Orders (e.g., Coleoptera, Collembola, Psocoptera, Araneae). We propose testable hypotheses for the observed seasonal shifts between inhibition and equivalency that focus on diminished resource availability and the damp, moist conditions found in the plantations. Given the compelling evidence for seasonal shifts between categories, we recommend that seasonal patterns should be considered a critical component of further assemblage-level investigations of this novel framework for invasion ecology.
Maternal Attachment Status, Mother-Child Emotion Talk, Emotion Understanding, and Child Conduct Problems
Brad M. Farrant,Murray T. Maybery,Janet Fletcher
Child Development Research , 2013, DOI: 10.1155/2013/680428
Abstract:
Rapid Development of Adaptive, Climate-Driven Clinal Variation in Seed Mass in the Invasive Annual Forb Echium plantagineum L.
Tara K. Konarzewski, Brad R. Murray, Robert C. Godfree
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0049000
Abstract: We examined adaptive clinal variation in seed mass among populations of an invasive annual species, Echium plantagineum, in response to climatic selection. We collected seeds from 34 field populations from a 1,000 km long temperature and rainfall gradient across the species' introduced range in south-eastern Australia. Seeds were germinated, grown to reproductive age under common glasshouse conditions, and progeny seeds were harvested and weighed. Analyses showed that seed mass was significantly related to climatic factors, with populations sourced from hotter, more arid sites producing heavier seeds than populations from cooler and wetter sites. Seed mass was not related to edaphic factors. We also found that seed mass was significantly related to both longitude and latitude with each degree of longitude west and latitude north increasing seed mass by around 2.5% and 4% on average. There was little evidence that within-population or between-population variation in seed mass varied in a systematic manner across the study region. Our findings provide compelling evidence for development of a strong cline in seed mass across the geographic range of a widespread and highly successful invasive annual forb. Since large seed mass is known to provide reproductive assurance for plants in arid environments, our results support the hypothesis that the fitness and range potential of invasive species can increase as a result of genetic divergence of populations along broad climatic gradients. In E. plantagineum population-level differentiation has occurred in 150 years or less, indicating that the adaptation process can be rapid.
Differences in Leaf Flammability, Leaf Traits and Flammability-Trait Relationships between Native and Exotic Plant Species of Dry Sclerophyll Forest
Brad R. Murray, Lyndle K. Hardstaff, Megan L. Phillips
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0079205
Abstract: The flammability of plant leaves influences the spread of fire through vegetation. Exotic plants invading native vegetation may increase the spread of bushfires if their leaves are more flammable than native leaves. We compared fresh-leaf and dry-leaf flammability (time to ignition) between 52 native and 27 exotic plant species inhabiting dry sclerophyll forest. We found that mean time to ignition was significantly faster in dry exotic leaves than in dry native leaves. There was no significant native-exotic difference in mean time to ignition for fresh leaves. The significantly higher fresh-leaf water content that was found in exotics, lost in the conversion from a fresh to dry state, suggests that leaf water provides an important buffering effect that leads to equivalent mean time to ignition in fresh exotic and native leaves. Exotic leaves were also significantly wider, longer and broader in area with significantly higher specific leaf area–but not thicker–than native leaves. We examined scaling relationships between leaf flammability and leaf size (leaf width, length, area, specific leaf area and thickness). While exotics occupied the comparatively larger and more flammable end of the leaf size-flammability spectrum in general, leaf flammability was significantly correlated with all measures of leaf size except leaf thickness in both native and exotic species such that larger leaves were faster to ignite. Our findings for increased flammability linked with larger leaf size in exotics demonstrate that exotic plant species have the potential to increase the spread of bushfires in dry sclerophyll forest.
Maternal Attachment Status, Mother-Child Emotion Talk, Emotion Understanding, and Child Conduct Problems
Brad M. Farrant,Murray T. Maybery,Janet Fletcher
Child Development Research , 2013, DOI: 10.1155/2013/680428
Abstract: Conduct problems that emerge in childhood often persist into adolescence and are associated with a range of negative outcomes. It is therefore important to identify the factors that predict conduct problems in early childhood. The present study investigated the relations among maternal attachment status, mother-child emotion talk, child emotion understanding, and conduct problems in a sample of 92 (46 males) typically developing children (M age = 61.3 months, SD = 8.3 months). The results support a model in which maternal attachment status predicts the level of appropriate/responsive mother-child emotion talk, which predicts child emotion understanding, which in turn negatively predicts child conduct problems. These findings further underline the developmental role of mother-child emotion talk as well as the importance of involving parents in programs designed to increase children’s emotion understanding and/or decrease the incidence of conduct problems. 1. Introduction Conduct problems involve atypical levels of oppositional behavior, aggression, stealing, and physical destructiveness [1]. These problems can begin in childhood [2] or adolescence [3] and may continue through the lifecycle [4]. Children who display conduct problems in the preschool years are at high risk of having problems that persist into adolescence (see [5] for a brief review). Indeed, this pattern, described as early starter [6], early onset [7], or life-course-persistent [8], is associated with the most negative prognosis including diagnoses of conduct disorder, oppositional defiant disorder, antisocial personality disorder, juvenile delinquency, school dropout, drug abuse, and criminality [1, 4, 9–11]. There is fairly broad theoretical agreement that conduct problems develop and are maintained through dynamic interactions among child, parental, peer, and environmental factors [1, 3, 12–14]. These factors include attachment patterns [15], emotion socialization [16], parenting [14], emotion understanding, and regulation skills [17] among others. These findings fit well with social-constructivist perspectives in which individual characteristics influence the parent-child interaction/socialisation which facilitate children’s sociocognitive and behavioral development [18, 19]. Crittenden [20] argued that attachment patterns are self-protective strategies that are initially learned in interactions with attachment figures in early childhood and continue to develop across the lifespan. Securely attached adults are comfortable depending on others, find it relatively easy to get close to
Cognitive Flexibility, Theory of Mind, and Hyperactivity/Inattention
Brad M. Farrant,Janet Fletcher,Murray T. Maybery
Child Development Research , 2014, DOI: 10.1155/2014/741543
Abstract: The present study analyzed the concurrent and longitudinal relations among cognitive flexibility, theory of mind, and hyperactivity/inattention in a sample of 70 typically developing children ( age = 61.4 months, SD = 8.3 months). Mothers and teachers reported on children’s hyperactivity/inattention using the strengths and difficulties questionnaire (Goodman, 1997), cognitive flexibility was measured using the dimension change card sort task (Zelazo, 2006), and theory of mind was assessed using a battery of tasks. Cognitive flexibility and theory of mind scores were found to be significantly negatively correlated with the level of hyperactivity/inattention at both time points. Furthermore, year 1 cognitive flexibility score was found to be a significant predictor of year 2 hyperactivity/inattention score after controlling for child age, gender, and year 1 hyperactivity/inattention score. Directions for future research include training studies which would further our understanding of these relationships and allow more effective interventions. 1. Introduction The ability to focus attention and regulate behavior is a key determinant of scholastic achievement and occupational success [1–3]. Indeed, these self-control skills are viewed as desirable by parents, teachers, and employers alike [3] and high levels of problems with focusing or sustaining attention and regulating behavior are core clinical features used to diagnose attention-deficit hyperactivity disorder (ADHD). However, many children with symptoms of hyperactivity and inattention do not meet the criteria for a formal ADHD diagnosis and parents and education professionals are confronted with the challenge of working with these children [4]. The present study investigated the cognitive factors associated with symptoms of hyperactivity/inattention in typically developing children during the early school years. Much of the research into the development of children’s self-regulation skills has been conducted within the executive function framework [5]. Inhibitory control, working memory, and cognitive flexibility are components of executive function that contribute to the development of self-regulation [6]. These executive function components follow different trajectories across early development such that the preschool period is characterized by dramatic improvements in inhibitory control, whereas the development of cognitive flexibility accelerates during the early school years [7]. According to cognitive complexity and control (CCC) theory, cognitive flexibility refers to the ability to flexibly
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