157 research outputs found
Pultenaea williamsii (Fabaceae: Mirbelieae), a new species endemic to the New England Tableland Bioregion of New South Wales
Pultenaea williamsii I.Telford, Clugston & R.L.Barrett (Fabaceae, Faboideae, Mirbelieae), endemic to the New England Bioregion, New South Wales, Australia, is described as new, segregated from the P. flexilis–P. juniperina–P. blakelyi species assemblage. Its distribution is mapped, and habitat and conservation status discussed
Single crystal, luminescent carbon nitride nanosheets formed by spontaneous dissolution
A primary method for the production of 2D nanosheets is liquid-phase delamination from their 3D layered bulk analogues. Most strategies currently achieve this objective by significant mechanical energy input or chemical modification but these processes are detrimental to the structure and properties of the resulting 2D nanomaterials. Bulk poly(triazine imide) (PTI)-based carbon nitrides are layered materials with a high degree of crystalline order. Here, we demonstrate that these semiconductors are spontaneously soluble in select polar aprotic solvents, that is, without any chemical or physical intervention. In contrast to more aggressive exfoliation strategies, this thermodynamically driven dissolution process perfectly maintains the crystallographic form of the starting material, yielding solutions of defect-free, hexagonal 2D nanosheets with a well-defined size distribution. This pristine nanosheet structure results in narrow, excitation-wavelength-independent photoluminescence emission spectra. Furthermore, by controlling the aggregation state of the nanosheets, we demonstrate that the emission wavelengths can be tuned from narrow UV to broad-band white. This has potential applicability to a range of optoelectronic devices
The Astropy Problem
The Astropy Project (http://astropy.org) is, in its own words, "a community
effort to develop a single core package for Astronomy in Python and foster
interoperability between Python astronomy packages." For five years this
project has been managed, written, and operated as a grassroots,
self-organized, almost entirely volunteer effort while the software is used by
the majority of the astronomical community. Despite this, the project has
always been and remains to this day effectively unfunded. Further, contributors
receive little or no formal recognition for creating and supporting what is now
critical software. This paper explores the problem in detail, outlines possible
solutions to correct this, and presents a few suggestions on how to address the
sustainability of general purpose astronomical software
ADHD in children and young people: prevalence, care pathways & service provision
Attention-Deficit/Hyperactivity Disorder (ADHD) is a common childhood behavioural disorder – systematic reviews indicate that the community prevalence of ADHD globally is between 2% to 7%, with an average of around 5%. In addition, a further 5% of children have significant difficulties with over-activity, inattention and impulsivity that are just sub-threshold to meet full diagnostic criteria for ADHD. Estimates of the administrative (clinically diagnosed and/or recorded) prevalence vary worldwide and although increasing over time, ADHD is still relatively under-recognised and under-diagnosed in most countries, particularly in girls and older children. ADHD often persists into adulthood and is a risk factor for other mental health disorders and negative outcomes including educational under-achievement, difficulties with employment and relationships, and criminality. The timely recognition and treatment of children with ADHD-type difficulties provides an opportunity to improve their long-term outcomes. This review includes a systematic review of the community and administrative prevalence of ADHD in children and adolescents; an overview of the barriers to accessing care for ADHD; a description of costs associated with ADHD; and a broad discussion of evidence-based pathways for the delivery of clinical care, including a focus on key issues for two specific age groups - pre-school children and adolescents requiring transition of care from child to adult services
Constraining bedrock erosion during extreme flood events
The importance of high-magnitude, short-lived flood events in controlling the
evolution of bedrock landscapes is not well understood. During such events, erosion
processes can shift from one regime to another upon the passing of thresholds,
resulting in abrupt landscape changes that can have a long lasting legacy on
landscape morphology.
Geomorphological mapping and topographic analysis document the evidence for,
and impact of, extreme flood events within the Jökulsárgljúfur canyon (North-East
Iceland). Surface exposure dating using cosmogenic 3He of fluvially sculpted
bedrock surfaces determines the timing of the floods that eroded the canyon and
helps constrain the mechanisms of bedrock erosion during these events. Once a
threshold flow depth has been exceeded, the dominant erosion mechanism
becomes the toppling and transportation of basalt lava columns and erosion occurs
through the upstream migration of knickpoints. Surface exposure ages allow
identification of three periods of rapid canyon cutting during erosive flood events
about 9, 5 and 2 ka ago, when multiple active knickpoints retreated large distances
(> 2 km), each leading to catastrophic landscape change within the canyon. A single
flood event ~9 ka ago formed, and then abandoned, Ásbyrgi canyon, eroding 0.14
km3 of rock. Flood events ~5 and ~2 ka ago eroded the upper 5 km of the
Jökulsárgljúfur canyon through the upstream migration of vertical knickpoints such
as Selfoss, Dettifoss and Hafragilsfoss. Despite sustained high discharge of
sediment-rich glacial meltwater (ranging from 100 to 500 m3 s-1); there is no
evidence for a transition to an abrasion-dominated erosion regime since the last
erosive flood: the vertical knickpoints have not diffused over time and there is no
evidence of incision into the canyon floor. The erosive signature of the extreme
events is maintained in this landscape due to the nature of the bedrock, the
discharge of the river, large knickpoints and associated plunge pools. The influence
of these controls on the dynamics of knickpoint migration and morphology are
explored using an experimental study. The retreat rate of knickpoints is independent
of both mean discharge, and temporal variability in the hydrograph. The dominant
control on knickpoint retreat is the knickpoint form which is set by the ratio of
channel flow depth to knickpoint height. Where the knickpoint height is five times
greater than the flow depth, the knickpoints developed undercutting plunge pools,
accelerating the removal of material from the knickpoint base and the overall retreat
rate. Smaller knickpoints relative to the flow depth were more likely to diffuse from a
vertical step into a steepened reach or completely as the knickpoint retreated up the
channel. These experiments challenge the established assumption in models of
landscape evolution that a simple relationship exists between knickpoint retreat and
discharge/drainage area. In order to fully understand how bedrock channels, and
thus landscapes, respond and recover to transient forcing, further detailed study of
the mechanics of erosion processes at knickpoints is required
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