Interface dynamics and crystal phase switching in GaAs nanowires.

Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.D.J., S.L. and K.A.D. acknowledge financial support from the Knut and Alice Wallenberg Foundation (KAW), the Swedish Research Council (VR) and the Nanometer Structure Consortium at Lund University (nmC@LU). F.P. and S.H. acknowledge support from ERC Grant 279342: InSituNANO. We acknowledge A. Ellis for technical support.This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature1714

A Dimension-Adaptive Multi-Index Monte Carlo Method Applied to a Model of a Heat Exchanger

We present an adaptive version of the Multi-Index Monte Carlo method, introduced by Haji-Ali, Nobile and Tempone (2016), for simulating PDEs with coefficients that are random fields. A classical technique for sampling from these random fields is the Karhunen-Lo\`eve expansion. Our adaptive algorithm is based on the adaptive algorithm used in sparse grid cubature as introduced by Gerstner and Griebel (2003), and automatically chooses the number of terms needed in this expansion, as well as the required spatial discretizations of the PDE model. We apply the method to a simplified model of a heat exchanger with random insulator material, where the stochastic characteristics are modeled as a lognormal random field, and we show consistent computational savings

Can Genetics Predict Response to Complex Behavioral Interventions? Evidence from a Genetic Analysis of the Fast Track Randomized Control Trial.

Early interventions are a preferred method for addressing behavioral problems in high-risk children, but often have only modest effects. Identifying sources of variation in intervention effects can suggest means to improve efficiency. One potential source of such variation is the genome. We conducted a genetic analysis of the Fast Track randomized control trial, a 10-year-long intervention to prevent high-risk kindergarteners from developing adult externalizing problems including substance abuse and antisocial behavior. We tested whether variants of the glucocorticoid receptor gene NR3C1 were associated with differences in response to the Fast Track intervention. We found that in European-American children, a variant of NR3C1 identified by the single-nucleotide polymorphism rs10482672 was associated with increased risk for externalizing psychopathology in control group children and decreased risk for externalizing psychopathology in intervention group children. Variation in NR3C1 measured in this study was not associated with differential intervention response in African-American children. We discuss implications for efforts to prevent externalizing problems in high-risk children and for public policy in the genomic era

Impairing autophagy in retinal pigment epithelium leads to inflammasome activation and enhanced macrophage-mediated angiogenesis

Age-related decreases in autophagy contribute to the progression of age-related macular degeneration (AMD). We have now studied the interaction between autophagy impaired in retinal pigment epithelium (RPE) and the responses of macrophages. We find that dying RPE cells can activate the macrophage inflammasome and promote angiogenesis. In vitro, inhibiting rotenone-induced autophagy in RPE cells elicits caspase-3 mediated cell death. Co-culture of damaged RPE with macrophages leads to the secretion of IL-1β, IL-6 and nitrite oxide. Exogenous IL-6 protects the dysfunctional RPE but IL-1β causes enhanced cell death. Furthermore, IL-1β toxicity is more pronounced in dysfunctional RPE cells showing reduced IRAK3 gene expression. Co-culture of macrophages with damaged RPE also elicits elevated levels of pro-angiogenic proteins that promote ex vivo choroidal vessel sprouting. In vivo, impaired autophagy in the eye promotes photoreceptor and RPE degeneration and recruitment of inflammasome-activated macrophages. The degenerative tissue environment drives an enhanced pro-angiogenic response, demonstrated by increased size of laser-induced choroidal neovascularization (CNV) lesions. The contribution of macrophages was confirmed by depletion of CCR2 + monocytes, which attenuates CNV in the presence of RPE degeneration. Our results suggest that the interplay between perturbed RPE homeostasis and activated macrophages influences key features of AMD development

Is 'oil pulling' a 'snake oil'? : a clinical trial

The traditional Ayurveda practice of ‘oil pulling’ has become a recent phenomenon and concerns about its efficacy have been raised. Objectives: (1) to determine awareness about the practice of ‘oil pulling’ among a group of young adults, and to determine variations in awareness with respect to socio-demographic factors, oral health behaviours (oral hygiene and dental attendance) and use of natural health products; (2) to determine the effectiveness of ‘oil pulling’ and conventional oral hygiene practice compared to the use of conventional oral hygiene practice alone in terms of oral hygiene and (3) to determine the effectiveness of ‘oil pulling’ and conventional oral hygiene practice compared to the use of conventional oral hygiene practice alone in terms of gingival health. Methods: Group members recruited seventy-four young adults to participate in a clinical trial over a two-month period comparing the effectiveness of (a) ‘oil pulling’ and conventional oral hygiene methods (toothbrush and toothpaste) versus (b) conventional oral hygiene methods alone. Oral hygiene was assessed using the Plaque Index - PI (Silness and Löe, 1964) and the proportion of sites with visible plaque (PVP). Gingival health was assessed using the Gingival Index – GI (Silness and Löe,1963) and the proportion of sites with gingival bleeding (PGB). Participants were block randomized in groups of four to a cross over clinical trial and assessments were conducted at one-month and two-months. Results: Approximately a quarter (28.4%, 21) of participants was aware of the practice of ‘oil pulling’. Awareness of the practice was associated with reported use of natural dental/oral health products (p0.05). There were observed significant differences in gingival health among both the test and control groups from baseline to one-month (p0.05). No significant differences were observed in oral health parameters from one-month to two-month among neither the test nor control groups (p>0.05). Conclusion: Awareness of the practice of ‘oil pulling’ is relatively common and is associated with use of natural dental/oral health products. Findings from the clinical trial failed to support the adjunct use of ‘oil pulling’ in addition to conventional oral hygiene practices.published_or_final_versio

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

Deletion of the gabra2 gene results in hypersensitivity to the acute effects of ethanol but does not alter ethanol self administration

Human genetic studies have suggested that polymorphisms of the GABRA2 gene encoding the GABA(A) α2-subunit are associated with ethanol dependence. Variations in this gene also convey sensitivity to the subjective effects of ethanol, indicating a role in mediating ethanol-related behaviours. We therefore investigated the consequences of deleting the α2-subunit on the ataxic and rewarding properties of ethanol in mice. Ataxic and sedative effects of ethanol were explored in GABA(A) α2-subunit wildtype (WT) and knockout (KO) mice using a Rotarod apparatus, wire hang and the duration of loss of righting reflex. Following training, KO mice showed shorter latencies to fall than WT littermates under ethanol (2 g/kg i.p.) in both Rotarod and wire hang tests. After administration of ethanol (3.5 g/kg i.p.), KO mice took longer to regain the righting reflex than WT mice. To ensure the acute effects are not due to the gabra2 deletion affecting pharmacokinetics, blood ethanol concentrations were measured at 20 minute intervals after acute administration (2 g/kg i.p.), and did not differ between genotypes. To investigate ethanol's rewarding properties, WT and KO mice were trained to lever press to receive increasing concentrations of ethanol on an FR4 schedule of reinforcement. Both WT and KO mice self-administered ethanol at similar rates, with no differences in the numbers of reinforcers earned. These data indicate a protective role for α2-subunits, against the acute sedative and ataxic effects of ethanol. However, no change was observed in ethanol self administration, suggesting the rewarding effects of ethanol remain unchange

Management of high-risk corneal grafts

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