Finite temperature molecular dynamics study of unstable stacking fault free energies in silicon

We calculate the free energies of unstable stacking fault (USF) configurations on the glide and shuffle slip planes in silicon as a function of temperature, using the recently developed Environment Dependent Interatomic Potential (EDIP). We employ the molecular dynamics (MD) adiabatic switching method with appropriate periodic boundary conditions and restrictions to atomic motion that guarantee stability and include volume relaxation of the USF configurations perpendicular to the slip plane. Our MD results using the EDIP model agree fairly well with earlier first-principles estimates for the transition from shuffle to glide plane dominance as a function of temperature. We use these results to make contact to brittle-ductile transition models.Comment: 6 pages revtex, 4 figs, 16 refs, to appear in Phys. Rev.

Experimental cross sections of Ho 165 (α,n) Tm 168 and Er 166 (α,n) Yb 169 for optical potential studies relevant for the astrophysical γ process

Background: Optical potentials are crucial ingredients for the prediction of nuclear reaction rates needed in simulations of the astrophysical γ process. Associated uncertainties are particularly large for reactions involving α particles. This includes (γ,α) reactions which are of special importance in the γ process. Purpose: The measurement of (α,n) reactions allows for an optimization of currently used α-nucleus potentials. The reactions Ho165(α,n) and Er166(α,n) probe the optical model in a mass region where γ process calculations exhibit an underproduction of p nuclei which is not yet understood. Method: To investigate the energy-dependent cross sections of the reactions Ho165(α,n) and Er166(α,n) close to the reaction threshold, self-supporting metallic foils were irradiated with α particles using the FN tandem Van de Graaff accelerator at the University of Notre Dame. The induced activity was determined afterwards by monitoring the specific β-decay channels. Results: Hauser-Feshbach predictions with a widely used global α potential describe the data well at energies where the cross sections are almost exclusively sensitive to the α widths. Increasing discrepancies appear towards the reaction threshold at lower energy. Conclusions: The tested global α potential is suitable at energies above 14 MeV, while a modification seems necessary close to the reaction threshold. Since the γ and neutron widths show non-negligible impact on the predictions, complementary data are required to judge whether or not the discrepancies found can be solely assigned to the α width. © 2014 American Physical Society.Peer reviewedFinal Accepted Versio

Embedding formalism for N{\mathcal N}-extended AdS superspace in four dimensions

The supertwistor and bi-supertwistor formulations for ${\mathcal N}$-extended anti-de Sitter (AdS) superspace in four dimensions, ${\rm AdS}^{4|4\mathcal N}$, were derived two years ago in arXiv:2108.03907. In the present paper, we introduce a novel realisation of the ${\mathcal N}$-extended AdS supergroup $\mathsf{OSp}(\mathcal{N}|4;\mathbb{R})$ and apply it to develop a coset construction for ${\rm AdS}^{4|4\mathcal N}$ and the corresponding differential geometry. This realisation naturally leads to an atlas on ${\rm AdS}^{4|4\mathcal N}$ (that is a generalisation of the stereographic projection for a sphere) that consists of two charts with chiral transition functions for ${\mathcal N}>0$. A manifestly $\mathsf{OSp}(\mathcal{N}|4;\mathbb{R})$ invariant model for a superparticle in ${\rm AdS}^{4|4\mathcal N}$ is proposed. Additionally, by employing a conformal superspace approach, we describe the most general conformally flat $\mathcal N$-extended supergeometry. This construction is then specialised to the case of ${\rm AdS}^{4|4\mathcal N}$.Comment: 49 page

Measurements of Gd 152 (p,γ) Tb 153 and Gd 152 (p,n) Tb 152 reaction cross sections for the astrophysical γ process

The total cross sections for the Gd152(p,γ)Tb153 and Gd152(p,n)152Tb reactions have been measured by the activation method at effective center-of-mass energies 3.47≤Ec.m.eff≤7.94 MeV and 4.96≤Ec.m.eff≤7.94 MeV, respectively. The targets were prepared by evaporation of 30.6% isotopically enriched Gd152 oxide on aluminum backing foils, and bombarded with proton beams provided by a cyclotron accelerator. The cross sections were deduced from the observed γ-ray activity, which was detected off-line by an HPGe detector in a low background environment. The results are presented and compared with predictions of statistical model calculations. This comparison supports a modified optical proton+Gd152 potential suggested earlier.Peer reviewedFinal Accepted Versio

Developmental Alcohol-Specific Parenting Profiles in Adolescence and their Relationships with Adolescents’ Alcohol Use

Previous studies on general parenting have demonstrated the relevance of strict parenting within a supportive social context for a variety of adolescent behaviors, such as alcohol use. Yet, alcohol-specific parenting practices are generally examined as separate predictors of adolescents’ drinking behavior. The present study examined different developmental profiles of alcohol-specific parenting (rule-setting, quality and frequency of communication about alcohol use) and how these patterns relate to the initiation and growth of adolescents’ drinking. A longitudinal sample of 883 adolescents (47 % female) including four measurements (between ages 12 and 16) was used. Latent class growth analysis revealed that five classes of parenting could be distinguished. Communication about alcohol appeared to be fairly stable over time in all parenting classes, whereas the level of rule-setting declined in all subgroups of parents as adolescents grow older. Strict rule-setting in combination with a high quality and frequency of communication was associated with the lowest amount of drinking; parents scoring low on all these behaviors show to be related to the highest amount of drinking. This study showed that alcohol-specific rule-setting is most effective when it coincides with a good quality and frequency of communication about alcohol use. This indicates that alcohol-specific parenting behaviors should be taken into account as an alcohol-specific parenting context, rather than single parenting practices. Therefore, parent-based alcohol interventions should not only encourage strict rule setting, the way parents communicate with their child about alcohol is also of major importance

Population-based mammography screening below age 50: balancing radiation-induced vs prevented breast cancer deaths

Introduction:Exposure to ionizing radiation at mammography screening may cause breast cancer. Because the radiation risk increases with lower exposure age, advancing the lower age limit may affect the balance between screening benefits and risks. The present study explores the benefit-risk ratio of screening before age 50.Methods:The benefits of biennial mammography screening, starting at various ages between 40 and 50, and continuing up to age 74 were examined using micro-simulation. In contrast with previous studies that commonly used excess relative risk models, we assessed the radiation risks using the latest BEIR-VII excess abso

Insurability of export credit risks

Firms exporting their goods and services abroad face risks that are different from the risks faced by firms who do not engage in international trade. It is common practice to allow the receiving party to pay in instalments. The exporting firm faces credit risk, but as in most countries, Dutch firms can insure such risks. To some extent, such export credit risks can be insured on the private market. There are private insurance companies that insure short-term risks. On the Dutch market, Gerling NCM, Coface, and Euler-Cobac operate as insurers. The Dutch government acts as reinsurer of long-term export credit risks (three years or more). A reinsurance agreement exists with Gerling NCM for this purpose. Short-term and medium-term contracts can be reinsured in the private reinsurance market. In almost all OECD countries export credits are officially supported. This can take the form of direct finance (e.g. US, Canada) or the government can insure the export credit risks (directly as for example in the United Kingdom or indirectly by reinsuring a private insurer such as in the Netherlands). The role of this government-backed insurance on exports to certain countries is important as experience has shown that the private market is very reluctant to cover long term export risks to non-OECD countries. Considering the government involvement in this market, one can raise the following questions: 1. What are the key determinants of export credit risk insurability by the private market? 2. Which export credit risks can be covered by the private market? In the report, an answer to these questions is provided by means of a literature review and an extensive field study, with special emphasis on the role of the Dutch government as a reinsurer of export credit risks. The main conclusions are as follows. Economic theory predicts that firms that operate risk averse are willing to pay an insurance premium. Large (say listed) firms operate at a relative low degree of risk aversion. These firms can use internal risk hedging as a useful alternative to private export credit risk insurance. Medium-sized firms are more likely to apply for export credit risk insurance, while small firms probably face problems (since for this group there is only one supplier of insurance active in the Dutch market). Small firms do not have the knowledge to hedge export risks differently than by export credit insurance in the Netherlands. They lack the resources and knowledge to have access to the international insurance markets. Moreover, the duration of the coverage is often not as long as exporting companies would like (this is experienced by both large and small companies). This is partly due to reinsurance restrictions faced by the insurance companies. A related problem to insurability is the high market concentration of supply. Market dominance leads to monopolistic rent extraction. In the case of the Netherlands this might apply to Gerling NCM. On the other hand relationship insurance seems to be a popular model. In our field study, firms point at a preference for long-lasting relations. Most exporters seem to have low price elasticity of insurance demand. Economic theory predicts moral hazard to be an important determinant of insurability. The issue of moral hazard, though recognized by insurance companies, does not dominate the perception of insurability. The price of export credit insurance is largely determined by macroeconomic risk factors, such as political risk. This leads us to the second main issue: what role should the government play on the market for export credit risk insurance and which risks should be covered by the governement? We argue the following: ? In markets with asymmetric information it is likely that profitable projects will be denied insurance. If the government considers export growth as one of its main goals, it should interfere in the market by lowering relative prices; ? The government is equipped to hedge intertemporal risks due to a low social cost of capital. In our field study some market participants point at the responsibility the government should take, especially in the case of small exporting companies; ? The government should offer opportunities to hedge macroeconomic risks, such as political/country risk. These risk types are seen as the main drivers of export insurance premium contracts; ? Moral hazard of public (re-)insurance might be a problem, but is not perceived as such in our field study by (re)insurance companies operating in the private market. The relation between the Dutch government and Gerling NCM is different, though. Gerling NCM retains no risk on its public account, and the government cannot end its relation with Gerling NCM. Therefore, moral hazard could be a problem in this insurer/reinsurer relation; ? Besides direct interference, the government should take care of prudential regulation of the insurance sector. Monopolistic behaviour should be avoided by appropriate regulation. Especially contracts that have a large geographical nature are subject to at least monopolistic competition. Clients who are not satisfied with the monopoly supplier should be able to meet other suppliers (at home or abroad). This holds especially for long-term contracts. In all cases the government should operate in a prudential way. No involvement may prevent profitable projects from being insured, too much involvement may crowd out the market for private export credit risk insurance. Finally, based on the research, we recommend the following. ? It seems that the industrial organization of the market for export credit risks insurance is an important issue. Some firms that were interviewed mentioned the large number of alternatives in the London market. This reinforces the idea of increasing competition in the Netherlands. ? There is a large barrier to entry on the Dutch market: an insurance company needs extensive datasets to go into business. Old firms have a competitive advantage by controlling such databases. Perhaps public data collection (at EU level) could mitigate this problem. ? Especially smaller firms are not aware of possibilities on the international market for export credit risk insurance. A national campaign explaining and informing about alternative risk products (not necessarily insurance products) will help exporters to find a better solution for reducing the risks they are exposed to. Keywords: export credit risk, insurance, moral hazard, ratin