2,542 research outputs found
Matching Conditions in Atomistic-Continuum Modeling of Materials
A new class of matching condition between the atomistic and continuum regions
is presented for the multi-scale modeling of crystals. They ensure the accurate
passage of large scale information between the atomistic and continuum regions
and at the same time minimize the reflection of phonons at the interface. These
matching conditions can be made adaptive if we choose appropriate weight
functions. Applications to dislocation dynamics and friction between
two-dimensional atomically flat crystal surfaces are described.Comment: 6 pages, 4 figure
Drag Reduction by Polymers in Wall Bounded Turbulence
We address the mechanism of drag reduction by polymers in turbulent wall
bounded flows. On the basis of the equations of fluid mechanics we present a
quantitative derivation of the "maximum drag reduction (MDR) asymptote" which
is the maximum drag reduction attained by polymers. Based on Newtonian
information only we prove the existence of drag reduction, and with one
experimental parameter we reach a quantitative agreement with the experimental
measurements.Comment: 4 pages, 1 fig., included, PRL, submitte
Molecular imaging of atherosclerosis with integrated PET imaging
Atherosclerotic diseases account for nearly half of all deaths and are leading causes of adult disability. Our understanding of how atherosclerosis leads to cardiovascular disease events has evolved: from a concept of progressive luminal narrowing, to that of sudden rupture and thrombosis of biologically active atheroma. In concert with this conceptual shift, contemporary imaging techniques now allow imaging of biological processes that associate with plaque instability: active calcification and plaque inflammation. This review focuses on opportunities provided by positron emission tomography/computed tomography, to identify these high-risk biological features of atherosclerosis.BH is supported by Research Training grant from Alexandria University. NRE is supported by a Research Training Fellowship from The Dunhill Medical Trust [Grant Number RTF44/0114]. JHFR is part supported by the NIHR Cambridge Biomedical Research Centre, the British Heart Foundation, EPSRC, and the Wellcome Trust. AT reports grants from NIH/NHLBI, Actelion, Genentech and Takeda, and personal fees from Actelion, Amgen AstraZeneca, and Takeda, all outside the submitted work
Nucleation and Growth of GaN/AlN Quantum Dots
We study the nucleation of GaN islands grown by plasma-assisted
molecular-beam epitaxy on AlN(0001) in a Stranski-Krastanov mode. In
particular, we assess the variation of their height and density as a function
of GaN coverage. We show that the GaN growth passes four stages: initially, the
growth is layer-by-layer; subsequently, two-dimensional precursor islands form,
which transform into genuine three-dimensional islands. During the latter
stage, island height and density increase with GaN coverage until the density
saturates. During further GaN growth, the density remains constant and a
bimodal height distribution appears. The variation of island height and density
as a function of substrate temperature is discussed in the framework of an
equilibrium model for Stranski-Krastanov growth.Comment: Submitted to PRB, 10 pages, 15 figure
Dynamic of a non homogeneously coarse grained system
To study materials phenomena simultaneously at various length scales,
descriptions in which matter can be coarse grained to arbitrary levels, are
necessary. Attempts to do this in the static regime (i.e. zero temperature)
have already been developed. In this letter, we present an approach that leads
to a dynamics for such coarse-grained models. This allows us to obtain
temperature-dependent and transport properties. Renormalization group theory is
used to create new local potentials model between nodes, within the
approximation of local thermodynamical equilibrium. Assuming that these
potentials give an averaged description of node dynamics, we calculate thermal
and mechanical properties. If this method can be sufficiently generalized it
may form the basis of a Molecular Dynamics method with time and spatial
coarse-graining.Comment: 4 pages, 4 figure
Bioresorbable composite bone fracture repair plates: manufacture and characterisation
This study reports on Bioresorbable composites manufactured using PLA as matrix and phosphate-based glass fibres as reinforcement. Composites were manufactured with varying volume fraction (from 25% - 45%) and mechanically tested
Cisplatin-induced emesis: systematic review and meta-analysis of the ferret model and the effects of 5-HT3 receptor antagonists
PURPOSE: The ferret cisplatin emesis model has been used for ~30ย years and enabled identification of clinically used anti-emetics. We provide an objective assessment of this model including efficacy of 5-HT(3) receptor antagonists to assess its translational validity. METHODS: A systematic review identified available evidence and was used to perform meta-analyses. RESULTS: Of 182 potentially relevant publications, 115 reported cisplatin-induced emesis in ferrets and 68 were included in the analysis. The majority (nย =ย 53) used a 10ย mgย kg(โ1) dose to induce acute emesis, which peaked after 2ย h. More recent studies (nย =ย 11) also used 5ย mgย kg(โ1), which induced a biphasic response peaking at 12ย h and 48ย h. Overall, 5-HT(3) receptor antagonists reduced cisplatin (5ย mgย kg(โ1)) emesis by 68% (45โ91%) during the acute phase (day 1) and by 67% (48โ86%) and 53% (38โ68%, all Pย <ย 0.001), during the delayed phase (days 2, 3). In an analysis focused on the acute phase, the efficacy of ondansetron was dependent on the dosage and observation period but not on the dose of cisplatin. CONCLUSION: Our analysis enabled novel findings to be extracted from the literature including factors which may impact on the applicability of preclinical results to humans. It reveals that the efficacy of ondansetron is similar against low and high doses of cisplatin. Additionally, we showed that 5-HT(3) receptor antagonists have a similar efficacy during acute and delayed emesis, which provides a novel insight into the pharmacology of delayed emesis in the ferret
Three-dimensional molecular dynamics simulations of void coalescence during dynamic fracture of ductile metals
Void coalescence and interaction in dynamic fracture of ductile metals have
been investigated using three-dimensional strain-controlled multi-million atom
molecular dynamics simulations of copper. The correlated growth of two voids
during the coalescence process leading to fracture is investigated, both in
terms of its onset and the ensuing dynamical interactions. Void interactions
are quantified through the rate of reduction of the distance between the voids,
through the correlated directional growth of the voids, and through correlated
shape evolution of the voids. The critical inter-void ligament distance marking
the onset of coalescence is shown to be approximately one void radius based on
the quantification measurements used, independent of the initial separation
distance between the voids and the strain-rate of the expansion of the system.
The interaction of the voids is not reflected in the volumetric asymptotic
growth rate of the voids, as demonstrated here. Finally, the practice of using
a single void and periodic boundary conditions to study coalescence is examined
critically and shown to produce results markedly different than the coalescence
of a pair of isolated voids.Comment: Accepted for publication in Physical Review
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