381 research outputs found
Ion-doped brushite cements for bone regeneration
Decades of research in orthopaedics has culminated in the quest for formidable yet resorbable biomaterials using bioactive materials. Brushite cements most salient features embrace high biocompatibility,
bioresorbability, osteoconductivity, self-setting characteristics, handling, and injectability properties. Such
type of materials is also effectively applied as drug delivery systems. However, brushite cements possess limited mechanical strength and fast setting times. By means of incorporating bioactive ions, which
are incredibly promising in directing cell fate when incorporated within biomaterials, it can yield biomaterials with superior mechanical properties. Therefore, it is a key to develop fine-tuned regenerative
medicine therapeutics. A comprehensive overview of the current accomplishments of ion-doped brushite
cements for bone tissue repair and regeneration is provided herein. The role of ionic substitution on
the cements physicochemical properties, such as structural, setting time, hydration products, injectability,
mechanical behaviour and ion release is discussed. Cell-material interactions, osteogenesis, angiogenesis,
and antibacterial activity of the ion-doped cements, as well as its potential use as drug delivery carriers
are also presented.This study was funded by the Portuguese Foundation for Science and Technology (FCT) and the German Academic Exchange
Service (Deutscher Akademischer Austauschdienst, DAAD) for the
transnational cooperation FCT/DAAD 2018-2019. The authors also
thank the funds provided under the distinctions attributed to JMO
(IF/01285/2015) and SP (CEECIND/03673/2017). Furthermore, funding by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG), Grant Nr. HU 2498/1-1; GB 1/22-1, and the
Emerging Talents Initiative of the FAU is acknowledged
Testimony at court: a randomised controlled trial investigating the art and science of persuading witnesses and victims to attend trial
The presence of civilian witnesses and victims in court is central to the effective operation of the criminal justice system. However, there is evidence of significant non-attendance which can result in ineffective and cracked trials. To address this, West Midlands Police Witness Care Unit and the Behavioural Insights Team designed an intervention using behavioural insight principles consisting of (1) a new conversation guide for Witness Care Officers (WCOs); (2) a redesigned ‘Warning Letter’ confirming details of the proceedings; and (3) a new reminder call and SMS. The impact of the new approach was evaluated through a randomised controlled trial in which 36 WCOs were randomly assigned to either “business as usual” (control) or treatment. The evaluation used an intention-to-treat design with implementation guided and encouraged at several points. Subgroup analysis was undertaken to explore whether differential effects were seen for domestic violence cases or between those that were victims and witnesses. Results indicated that the treatment approach was directionally positive in all cases, but that the increase in attendance was not statistically significant. This is in line with findings of other similar research in this area
Pattern formation in directional solidification under shear flow. I: Linear stability analysis and basic patterns
An asymptotic interface equation for directional solidification near the
absolute stabiliy limit is extended by a nonlocal term describing a shear flow
parallel to the interface. In the long-wave limit considered, the flow acts
destabilizing on a planar interface. Moreover, linear stability analysis
suggests that the morphology diagram is modified by the flow near the onset of
the Mullins-Sekerka instability. Via numerical analysis, the bifurcation
structure of the system is shown to change. Besides the known hexagonal cells,
structures consisting of stripes arise. Due to its symmetry-breaking
properties, the flow term induces a lateral drift of the whole pattern, once
the instability has become active. The drift velocity is measured numerically
and described analytically in the framework of a linear analysis. At large flow
strength, the linear description breaks down, which is accompanied by a
transition to flow-dominated morphologies, described in a companion paper.
Small and intermediate flows lead to increased order in the lattice structure
of the pattern, facilitating the elimination of defects. Locally oscillating
structures appear closer to the instability threshold with flow than without.Comment: 20 pages, Latex, accepted for Physical Review
Bistability of Slow and Fast Traveling Waves in Fluid Mixtures
The appearence of a new type of fast nonlinear traveling wave states in
binary fluid convection with increasing Soret effect is elucidated and the
parameter range of their bistability with the common slower ones is evaluated
numerically. The bifurcation behavior and the significantly different
spatiotemporal properties of the different wave states - e.g. frequency, flow
structure, and concentration distribution - are determined and related to each
other and to a convenient measure of their nonlinearity. This allows to derive
a limit for the applicability of small amplitude expansions. Additionally an
universal scaling behavior of frequencies and mixing properties is found.
PACS: 47.20.-k, 47.10.+g, 47.20.KyComment: 4 pages including 5 Postscript figure
On the principal bifurcation branch of a third order nonlinear long-wave equation
We study the principal bifurcation curve of a third order equation which
describes the nonlinear evolution of several systems with a long--wavelength
instability. We show that the main bifurcation branch can be derived from a
variational principle. This allows to obtain a close estimate of the complete
branch. In particular, when the bifurcation is subcritical, the large amplitude
stable branch can be found in a simple manner.Comment: 11 pages, 3 figure
Eutectic Colony Formation: A Stability Analysis
Experiments have widely shown that a steady-state lamellar eutectic
solidification front is destabilized on a scale much larger than the lamellar
spacing by the rejection of a dilute ternary impurity and forms two-phase cells
commonly referred to as `eutectic colonies'. We extend the stability analysis
of Datye and Langer for a binary eutectic to include the effect of a ternary
impurity. We find that the expressions for the critical onset velocity and
morphological instability wavelength are analogous to those for the classic
Mullins-Sekerka instability of a monophase planar interface, albeit with an
effective surface tension that depends on the geometry of the lamellar
interface and, non-trivially, on interlamellar diffusion. A qualitatively new
aspect of this instability is the occurence of oscillatory modes due to the
interplay between the destabilizing effect of the ternary impurity and the
dynamical feedback of the local change in lamellar spacing on the front motion.
In a transient regime, these modes lead to the formation of large scale
oscillatory microstructures for which there is recent experimental evidence in
a transparent organic system. Moreover, it is shown that the eutectic front
dynamics on a scale larger than the lamellar spacing can be formulated as an
effective monophase interface free boundary problem with a modified
Gibbs-Thomson condition that is coupled to a slow evolution equation for the
lamellar spacing. This formulation provides additional physical insights into
the nature of the instability and a simple means to calculate an approximate
stability spectrum. Finally, we investigate the influence of the ternary
impurity on a short wavelength oscillatory instability that is already present
at off-eutectic compositions in binary eutectics.Comment: 26 pages RevTex, 14 figures (28 EPS files); some minor changes;
references adde
Experimental studies of front propagation and mode-locking in an advection-reaction-diffusion system
First-principles study of As interstitials in GaAs: Convergence, relaxation, and formation energy
Convergence of density-functional supercell calculations for defect formation
energies, charge transition levels, localized defect state properties, and
defect atomic structure and relaxation is investigated using the arsenic split
interstitial in GaAs as an example. Supercells containing up to 217 atoms and a
variety of {\bf k}-space sampling schemes are considered. It is shown that a
good description of the localized defect state dispersion and charge state
transition levels requires at least a 217-atom supercell, although the defect
structure and atomic relaxations can be well converged in a 65-atom cell.
Formation energies are calculated for the As split interstitial, Ga vacancy,
and As antisite defects in GaAs, taking into account the dependence upon
chemical potential and Fermi energy. It is found that equilibrium
concentrations of As interstitials will be much lower than equilibrium
concentrations of As antisites in As-rich, -type or semi-insulating GaAs.Comment: 10 pages, 5 figure
Twinning superlattices in indium phosphide nanowires
Here, we show that we control the crystal structure of indium phosphide (InP)
nanowires by impurity dopants. We have found that zinc decreases the activation
barrier for 2D nucleation growth of zinc-blende InP and therefore promotes the
InP nanowires to crystallise in the zinc blende, instead of the commonly found
wurtzite crystal structure. More importantly, we demonstrate that we can, by
controlling the crystal structure, induce twinning superlattices with
long-range order in InP nanowires. We can tune the spacing of the superlattices
by the wire diameter and the zinc concentration and present a model based on
the cross-sectional shape of the zinc-blende InP nanowires to quantitatively
explain the formation of the periodic twinning.Comment: 18 pages, 4 figure
- …