Computational study of boron nitride nanotube synthesis: how catalyst morphology stabilizes the boron nitride bond

In an attempt to understand why catalytic methods for the growth of boron nitride nanotubes work much worse than for their carbon counterparts, we use first-principles calculations to study the energetics of elemental reactions forming N2, B2 and BN molecules on an iron catalyst. We observe that in the case of these small molecules, the catalytic activity is hindered by the formation of B2 on the iron surface. We also observe that the local morphology of a step edge present in our nanoparticle model stabilizes the boron nitride molecule with respect to B2 due to the ability of the step edge to offer sites with different coordination simultaneously for nitrogen and boron. Our results emphasize the importance of atomic steps for a high yield chemical vapor deposition growth of BN nanotubes and may outline new directions for improving the efficiency of the method.Comment: submitted to physical review

Structural models for the Si(553)-Au atomic chain reconstruction

Recent photoemission experiments on the Si(553)-Au reconstruction show a one-dimensional band with a peculiar ~1/4 filling. This band could provide an opportunity for observing large spin-charge separation if electron-electron interactions could be increased. To this end, it is necessary to understand in detail the origin of this surface band. A first step is the determination of the structure of the reconstruction. We present here a study of several structural models using first-principles density functional calculations. Our models are based on a plausible analogy with the similar and better known Si(557)-Au surface, and compared against the sole structure proposed to date for the Si(553)-Au system [Crain JN et al., 2004 Phys. Rev. B 69 125401 ]. Results for the energetics and the band structures are given. Lines for the future investigation are also sketched

Cascaded exciton emission of an individual strain-induced quantum dot

Single strain-induced quantum dots are isolated for optical experiments by selective removal of the inducing InP islands from the sample surface. Unpolarized emission of single, bi- and triexciton transitions are identified by power-dependent photoluminescence spectroscopy. Employing time-resolved experiments performed at different excitation powers we find a pronounced shift of the rise and decay times of these different transitions as expected from cascaded emission. Good agreement is found for a rate equation model for a three step cascade

Sub-monolayers of carbon on alpha-iron facets: an ab-initio study

Motivated by recent in situ studies of carbon nanotube growth from large transition-metal nanoparticles, we study various alpha-iron (ferrite) facets at different carbon concentrations using ab initio methods. The studied (110), (100) and (111) facets show qualitatively different behaviour when carbon concentration changes. In particular, adsorbed carbon atoms repel each other on the (110) facet, resulting in carbon dimer and graphitic material formation. Carbon on the (100) facet forms stable structures at concentrations of about 0.5 monolayer and at 1.0 monolayer this facet becomes unstable due to a frustration of the top layer iron atoms. The stability of the (111) facet is weakly affected by the amount of adsorbed carbon and its stability increases further with respect to the (100) facet with increasing carbon concentration. The exchange of carbon atoms between the surface and sub-surface regions on the (111) facet is easier than on the other facets and the formation of carbon dimers is exothermic. These findings are in accordance with a recent in situ experimental study where the existence of graphene decorated (111) facets is related to increased carbon concentration

First-principles study of the atomic and electronic structure of the Si(111)-(5x2-Au surface reconstruction

We present a systematic study of the atomic and electronic structure of the Si(111)-(5x2)-Au reconstruction using first-principles electronic structure calculations based on the density functional theory. We analyze the structural models proposed by Marks and Plass [Phys. Rev. Lett.75, 2172 (1995)], those proposed recently by Erwin [Phys. Rev. Lett.91, 206101 (2003)], and a completely new structure that was found during our structural optimizations. We study in detail the energetics and the structural and electronic properties of the different models. For the two most stable models, we also calculate the change in the surface energy as a function of the content of silicon adatoms for a realistic range of concentrations. Our new model is the energetically most favorable in the range of low adatom concentrations, while Erwin's "5x2" model becomes favorable for larger adatom concentrations. The crossing between the surface energies of both structures is found close to 1/2 adatoms per 5x2 unit cell, i.e. near the maximum adatom coverage observed in the experiments. Both models, the new structure and Erwin's "5x2" model, seem to provide a good description of many of the available experimental data, particularly of the angle-resolved photoemission measurements

‘Hey, teach these kids to eat their own food!’: Institutional intergroup contact in immigrant mothers' talk

Although informal segregation often persists in multiethnic neighbourhoods, local institutions offering public services may act as an important setting for intergroup contact. Therefore, we studied how immigrant mothers of young children discursively construct institutional intergroup contact with workers of public playgrounds and kindergartens. We conducted longitudinal interviews with 10 immigrant mothers three times over the period of a year in 2 multi-ethnic neighbourhoods in Helsinki, Finland. Using Critical Discursive Psychology, we analysed respondents' talk about the encounters and identified three interpretative repertoires: 'contact as asserting rights', 'contact as helping', and 'contact as cultural rectification'. Our analysis showed how mothers positioned themselves and the workers differently in terms of agency and power in each repertoire. Our findings stress the importance of studying people's own sense-making of institutional contact, with different roles for participants, and that construction of agency within institutional contact is important for building equal membership in society. Please refer to the Supplementary Material section to find this article's Community and Social Impact Statement

Long-term clinical and economic outcomes in previously untreated paediatric patients with severe haemophilia A : A nationwide real-world study with 700 person-years

AimFor previously untreated patients (PUPs) with severe haemophilia A in Finland for the past 2 decades, the standard practice has been to start early primary prophylaxis. We evaluated the long-term clinical outcomes and costs of treatment with high-dose prophylaxis in PUPs from birth to adolescence, including immune tolerance induction (ITI). MethodsFrom the medical records of all PUPs born between June 1994 and May 2013 in Finland, we retrospectively extracted data on clinical outcomes and healthcare use. Using linear mixed models, we analysed longitudinal clinical outcome data. To analyse skewed cost data, including zero costs, we applied hurdle regression. ResultsAll 62 patients received early regular prophylaxis; totally, they have had treatment for nearly 700 patient-years. The median age of starting home treatment was 1.1years. The mean (SD) annual treatment costs (Europerkg) were 4391Euro (3852). For ages 1-3, ITI comprised over half of the costs; in other groups, prophylactic FVIII treatment dominated. With these high costs, however, clinical outcomes were desirable; median (IQR) ABR was low at 0.19 (0.07-0.46) and so was AJBR at 0.06 (0-0.24). Thirteen (21%) patients developed a clinically significant inhibitor, 10 (16%) with a high titre. All ITIs were successful. The mean costs for ITI were 383448Euro (259085). The expected ITI payback period was 1.81 (95% CI 0.62-12.12) years. ConclusionsEarly high-dose prophylaxis leads to excellent long-term clinical outcomes, and early childhood ITI therapy seems to turn cost-neutral generally already in 2years.Peer reviewe

Epistemic roles of materiality within a collaborative invention project at a secondary school

In this study, we examined maker‐centred learning from an epistemic perspective, highlighting the agentic role of material engagement and artefacts in learning and creativity. The use of physical materials plays a crucial role in maker activities where the socio‐epistemic aspects of knowledge creation entangle with the designing and making of physical artefacts. By taking a case study perspective, we analysed video data from nine design sessions involving a team of students (aged 13 to 14) developing an invention. First, we analysed knowledge that was built during the process. Our analysis revealed how design ideas evolved from preliminary to final stages and, together with the expressed design problems and conversations preceding the ideas, formed an epistemic object pursued by the team. Next, we included non‐human agencies into the analysis to understand the role of materials in the process. Features of materials and human design intentions both constrained and enabled idea improvement and knowledge creation, intermixing meanings and materials. Material making invited the students to not only rely on human rationalisation, but also to think together with the materials.In this study, we examined maker-centred learning from an epistemic perspective, highlighting the agentic role of material engagement and artefacts in learning and creativity. The use of physical materials plays a crucial role in maker activities where the socio-epistemic aspects of knowledge creation entangle with the designing and making of physical artefacts. By taking a case study perspective, we analysed video data from nine design sessions involving a team of students (aged 13 to 14) developing an invention. First, we analysed knowledge that was built during the process. Our analysis revealed how design ideas evolved from preliminary to final stages and, together with the expressed design problems and conversations preceding the ideas, formed an epistemic object pursued by the team. Next, we included non-human agencies into the analysis to understand the role of materials in the process. Features of materials and human design intentions both constrained and enabled idea improvement and knowledge creation, intermixing meanings and materials. Material making invited the students to not only rely on human rationalisation, but also to think together with the materials.Peer reviewe

Luotanko vai enkö luota? Nuorten luottamus sosiaalisessa mediassa leviävään informaatioon ja siihen liittyviä tekijöitä.

The increasing role that social media plays as a source of news and information has both positive and negative effects from the viewpoint of democratic societies. As sharing information on social media is easy, it has also become easier to spread false information. False news, which can render manipulation of people’s views and thoughts remarkably easy, can be extremely challenging to detect. We approached youngsters’ trust in social media content as a potential risk factor; trust can reduce uncertainty and suspicion of information and thus predict the spread of disinformation and conspiracy theories. This may have negative effects on societal security. We aimed to examine what factors explain Finnish youngsters’ (15–19 years) trust in news and information in social media. The analysis was based on a survey (N=800) collected in 2019– 2020. Using regression analysis we found four factors that were positively associated with youngsters’ trust in news and information in social media; trust in traditional media, daily use of social media, following social media influencers, and the belief that approval ratings predict the trustworthiness of news. In addition, the belief that social media gives a distorted view of other people’s lives was negatively connected to trust in news and information. From a national security perspective, youngsters’ social media use is often harmless. However, as their identities and worldviews are still developing, they may act as a target group for information campaigns which aim to undermine the stability of society and disrupt national security. Therefore, it is crucial to understand more about youngsters’ trust in social media content and their ability to detect false information

Treatment of infantile spasms: emerging insights from clinical and basic science perspectives.

Infantile spasms is an epileptic encephalopathy of early infancy with specific clinical and electroencephalographic (EEG) features, limited treatment options, and a poor prognosis. Efforts to develop improved treatment options have been hindered by the lack of experimental models in which to test prospective therapies. The neuropeptide adrenocorticotropic hormone (ACTH) is effective in many cases of infantile spasms, although its mechanism(s) of action is unknown. This review describes the emerging candidate mechanisms that can underlie the therapeutic effects of ACTH in infantile spasms. These mechanisms can ultimately help to improve understanding and treatment of the disease. An overview of current treatments of infantile spasms, novel conceptual and experimental approaches to infantile spasms treatment, and a perspective on remaining clinical challenges and current research questions are presented here. This summary derives from a meeting of specialists in infantile spasms clinical care and research held in New York City on June 14, 2010