11,183 research outputs found
Dispersion corrections in graphenic systems: a simple and effective model of binding
We combine high-level theoretical and \emph{ab initio} understanding of
graphite to develop a simple, parametrised force-field model of interlayer
binding in graphite, including the difficult non-pairwise-additive
coupled-fluctuation dispersion interactions. The model is given as a simple
additive correction to standard density functional theory (DFT) calculations,
of form where is the interlayer
distance. The functions are parametrised by matching contact properties, and
long-range dispersion to known values, and the model is found to accurately
match high-level \emph{ab initio} results for graphite across a wide range of
values. We employ the correction on the difficult bigraphene binding and
graphite exfoliation problems, as well as lithium intercalated graphite
LiC. We predict the binding energy of bigraphene to be 0.27 J/m^2, and the
exfoliation energy of graphite to be 0.31 J/m^2, respectively slightly less and
slightly more than the bulk layer binding energy 0.295 J/m^2/layer. Material
properties of LiC are found to be essentially unchanged compared to the
local density approximation. This is appropriate in view of the relative
unimportance of dispersion interactions for LiC layer binding
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Bridging the research to practice gap in transfusion: the need for a multidisciplinary and evidence-based approach
Binding and interlayer force in the near-contact region of two graphite slabs: experiment and theory
Via a novel experiment, Liu \emph{et al.} [Phys. Rev. B, {\bf 85}, 205418
(2012)] estimated the graphite binding energy, specifically the cleavage
energy, an important physical property of bulk graphite. We re-examine the data
analysis and note that within the standard Lennard-Jones model employed, there
are difficulties in achieving internal consistency in the reproduction of the
graphite elastic properties. By employing similar models which guarantee
consistency with the elastic constant, we find a wide range of model dependent
binding energy values from the same experimental data. We attribute some of the
difficulty in the determination of the binding energy to: i) limited
theoretical understanding of the van der Waals dispersion of graphite cleavage,
ii) the mis-match between the strong bending stiffness of the graphite-SiO
cantilever and the weak asymptotic inter-layer forces that are integrated over
to produce the binding energy. We find, however, that the data does support
determination of a maximum inter-layer force that is relatively model
independent. We conclude that the peak force per unit area is GPa
for cleavage, and occurs at an inter-layer spacing of nm
New constraints on primordial black holes abundance from femtolensing of gamma-ray bursts
The abundance of primordial black holes is currently significantly
constrained in a wide range of masses. The weakest limits are established for
the small mass objects, where the small intensity of the associated physical
phenomenon provides a challenge for current experiments. We used gamma- ray
bursts with known redshifts detected by the Fermi Gamma-ray Burst Monitor (GBM)
to search for the femtolensing effects caused by compact objects. The lack of
femtolensing detection in the GBM data provides new evidence that primordial
black holes in the mass range 5 \times 10^{17} - 10^{20} g do not constitute a
major fraction of dark matter.Comment: 7 pages, 6 figures, submitted to Physical Review
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How do hospitals respond to feedback about blood transfusion practice? A multiple case study investigation
National clinical audits play key roles in improving care and driving system-wide change. However, effects of audit and feedback depend upon both reach (e.g. relevant staff receiving the feedback) and response (e.g. staff regulating their behaviour accordingly). This study aimed to investigate which hospital staff initially receive feedback and formulate a response, how feedback is disseminated within hospitals, and how responses are enacted (including barriers and enablers to enactment). Using a multiple case study approach, we purposively sampled four UK hospitals for variation in infrastructure and resources. We conducted semi-structured interviews with staff from transfusion-related roles and observed Hospital Transfusion Committee meetings. Interviews and analysis were based on the Theoretical Domains Framework of behaviour change. We coded interview transcripts into theoretical domains, then inductively identified themes within each domain to identify barriers and enablers. We also analysed data to identify which staff currently receive feedback and how dissemination is managed within the hospital. Members of the hospitalâs transfusion team initially received feedback in all cases, and were primarily responsible for disseminating and responding, facilitated through the Hospital Transfusion Committee. At each hospital, key individuals involved in prescribing transfusions reported never having received feedback from a national audit. Whether audits were discussed and actions explicitly agreed in Committee meetings varied between hospitals. Key enablers of action across all cases included clear lines of responsibility and strategies to remind staff about recommendations. Barriers included difficulties disseminating to relevant staff and needing to amend feedback to make it appropriate for local use. Appropriate responses by hospital staff to feedback about blood transfusion practice depend upon supportive infrastructures and role clarity. Hospitals could benefit from support to disseminate feedback systematically, particularly to frontline staff involved in the behaviours being audited, and practical tools to support strategic decision-making (e.g. action-planning around local response to feedback)
Small world effects in evolution
For asexual organisms point mutations correspond to local displacements in
the genotypic space, while other genotypic rearrangements represent long-range
jumps. We investigate the spreading properties of an initially homogeneous
population in a flat fitness landscape, and the equilibrium properties on a
smooth fitness landscape. We show that a small-world effect is present: even a
small fraction of quenched long-range jumps makes the results indistinguishable
from those obtained by assuming all mutations equiprobable. Moreover, we find
that the equilibrium distribution is a Boltzmann one, in which the fitness
plays the role of an energy, and mutations that of a temperature.Comment: 13 pages and 5 figures. New revised versio
Topology and Evolution of Technology Innovation Networks
The web of relations linking technological innovation can be fairly described
in terms of patent citations. The resulting patent citation network provides a
picture of the large-scale organization of innovations and its time evolution.
Here we study the patterns of change of patents registered by the US Patent and
Trademark Office (USPTO). We show that the scaling behavior exhibited by this
network is consistent with a preferential attachment mechanism together with a
Weibull-shaped aging term. Such attachment kernel is shared by scientific
citation networks, thus indicating an universal type of mechanism linking ideas
and designs and their evolution. The implications for evolutionary theory of
innovation are discussed.Comment: 6 pages, 5 figures, submitted to Physical Review
On the âDuelâ Nature of History: Revisiting Contingency versus Determinism
Are we âhistorical accidentsâ of an undirected evolutionary history? In his recent book, Islands in the Cosmos, Dale Russell addresses this question, and Brian Swartz reviews his synthesis of this âcosmicâ evolutionary debate
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