Diffraction and near-zero transmission of flexural phonons at graphene grain boundaries

Graphene grain boundaries are known to affect phonon transport and thermal conductivity, suggesting that they may be used to engineer the phononic properties of graphene. Here, the effect of two buckled grain boundaries on long-wavelength flexural acoustic phonons has been investigated as a function of angle of incidence using molecular dynamics. The flexural acoustic mode has been chosen due to its importance to thermal transport. It is found that the transmission through the boundaries is strongly suppressed for incidence angles close to 35$^\circ$. Also, the grain boundaries are found to act as diffraction gratings for the phonons

Scattering of flexural acoustic phonons at grain boundaries in graphene

We investigate the scattering of long-wavelength flexural phonons against grain boundaries in graphene using molecular dynamics simulations. Three symmetric tilt grain boundaires are considered: one with a misorientation angle of $17.9^\circ$ displaying an out-of-plane buckling 1.5 nm high and 5 nm wide, one with a misorientation angle of $9.4^\circ$ and an out-of-plane buckling 0.6 nm high and 1.7 nm wide, and one with a misorientation angle of $32.2^\circ$ and no out-of-plane buckling. At the flat grain boundary, the phonon transmission exceeds 95 % for wavelengths above 1 nm. The buckled boundaries have a substantially lower transmission in this wavelength range, with a minimum transmission of 20 % for the $17.9^\circ$ boundary and 40 % for the $9.4^\circ$ boundary. At the buckled boundaries, coupling between flexural and longitudinal phonon modes is also observed. The results indicate that scattering of long-wavelength flexural phonons at grain boundaries in graphene is mainly due to out-of-plane buckling. A continuum mechanical model of the scattering process has been developed, providing a deeper understanding of the scattering process as well as a way to calculate the effect of a grain boundary on long-wavelength flexural phonons based on the buckling size.Comment: 11 pages, 14 figure

Oxygen vacancy segregation and space-charge effects in grain boundaries of dry and hydrated BaZrO3

A space-charge model is applied to describe the equilibrium effects of segregation of double-donor oxygen vacancies to grain boundaries in dry and wet acceptor-doped samples of the perovskite oxide BaZrO3. The grain boundary core vacancy concentrations and electrostatic potential barriers resulting from different vacancy segregation energies are evaluated. Density-functional calculations on vacancy segregation to the mirror-symmetric \Sigma 3 (112) [-110] tilt grain boundary are also presented. Our results indicate that oxygen vacancy segregation can be responsible for the low grain boundary proton conductivity in BaZrO3 reported in the literature

Theoretical modeling of defect segregation and space-charge formation in the BaZrO3 (210) 001 tilt grain boundary

Density-functional theory (DFT) has been used to determine the structure and interface energy of different rigid body translations (RBTs) of the (210)10011 grain boundary (GB) in BaZrO3. There exist several different stable structures with almost equally low interfacial energy. Segregation energies of protons and oxygen vacancies have been determined for the most stable (210)10011 grain boundary structure. The results suggest that both defect species favor segregation to the same site at the boundary interface with minimum segregation energies of - 1.45 eV and - 1.32 eV for vacancies and protons respectively. The segregation energies have been used in a thermodynamic space-charge model to obtain equilibrium defect concentrations and space-charge potentials at a 10% dopant concentration. Space-charge,potential barriers around 0.65 V were obtained at intermediate temperatures under hydrated conditions, where protons are the main contributor to the excess core charge. The potential is slightly lower under dry conditions. (C) 2013 Elsevier B.V. All rights reserved

Guest-host electro-optic switching in spin-coated polymer ferroelectric liquid crystal film

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Shoji Okazaki, Sadahito Uto, Masanori Ozaki, Katsumi Yoshino, Kent Skarp, and Bertil Helgee, Appl. Phys. Lett. 71, 3373 (1997) and may be found at https://doi.org/10.1063/1.120399

Electro-optic switching in spin-coated ferroelectric mesomorphic polymer films and its analysis

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Sadahito Uto, Hiroshi Moritake, Masanori Ozaki, Kent Skarp, and Bertil Helgee, Journal of Applied Physics 79, 4444 (1996) and may be found at https://doi.org/10.1063/1.361754

Automatic Filtering and Substantiation of Drug Safety Signals

Drug safety issues pose serious health threats to the population and constitute a major cause of mortality worldwide. Due to the prominent implications to both public health and the pharmaceutical industry, it is of great importance to unravel the molecular mechanisms by which an adverse drug reaction can be potentially elicited. These mechanisms can be investigated by placing the pharmaco-epidemiologically detected adverse drug reaction in an information-rich context and by exploiting all currently available biomedical knowledge to substantiate it. We present a computational framework for the biological annotation of potential adverse drug reactions. First, the proposed framework investigates previous evidences on the drug-event association in the context of biomedical literature (signal filtering). Then, it seeks to provide a biological explanation (signal substantiation) by exploring mechanistic connections that might explain why a drug produces a specific adverse reaction. The mechanistic connections include the activity of the drug, related compounds and drug metabolites on protein targets, the association of protein targets to clinical events, and the annotation of proteins (both protein targets and proteins associated with clinical events) to biological pathways. Hence, the workflows for signal filtering and substantiation integrate modules for literature and database mining, in silico drug-target profiling, and analyses based on gene-disease networks and biological pathways. Application examples of these workflows carried out on selected cases of drug safety signals are discussed. The methodology and workflows presented offer a novel approach to explore the molecular mechanisms underlying adverse drug reactions

Improving Drug Discovery Decision Making using Machine Learning and Graph Theory in QSAR Modeling

During the last decade non-linear machine-learning methods have gained popularity among QSAR modelers. The machine-learning algorithms generate highly accurate models at a cost of increased model complexity where simple interpretations, valid in the entire model domain, are rare. This thesis focuses on maximizing the amount of extracted knowledge from predictive QSAR models and data. This has been achieved by the development of a descriptor importance measure, a method for automated local optimization of compounds and a method for automated extraction of substructural alerts. Furthermore different QSAR modeling strategies have been evaluated with respect to predictivity, risks and information content. To test hypotheses and theories large scale simulations of known relations between activities and de- scriptors have been conducted. With the simulations it has been possible to study properties of methods, risks, implementations and errors in a controlled manner since the correct answer has been known. Sim- ulation studies have been used in the development of the generally applicable descriptor importance measure and in the analysis of QSAR modeling strategies. The use of simulations is spread in many areas, but not that common in the computational chemistry community. The descriptor importance mea- sure developed can be applied to any machine-learning method and validations using both real data and simulated data show that the descriptor importance measure is very accurate for non-linear methods. An automated method for local optimization of compounds was developed to partly replace manual searches made to optimize compounds. The local optimization of compounds make use of the informa- tion in available data and deterministically enumerates new compounds in a space spanned close to the compound of interest. This can be used as a starting point for further compound optimization and aids the chemist in finding new compounds. An other approach to guide chemists in the process of optimiz- ing compounds is through substructural warnings. A fast method for significant substructure extraction has been developed that extracts significant substructures from data with respect to the activity of the compound. The method is at least on par with existing methods in terms of accuracy but is significantly less time consuming. Non-linear machine-learning methods have opened up new possibilities for QSAR modeling that changes the way chemical data can be handled by model algorithms. Therefore properties of Local and Global QSAR modeling strategies have been studied. The results show that Local models come with high risks and are less accurate compared to Global models. In summary this thesis shows that Global QSAR modeling strategies should be applied preferably using methods that are able to handle non-linear relationships. The developed methods can be interpreted easily and an extensive amount of information can be retrieved. For the methods to become easily available to a broader group of users packaging with an open-source chemical platform is needed

Gränsdragningen mellan förhindra skatteflykt och förhindra förlust av skatteintäker : Två separata rättfärdigandegrunder med samma innebörd?

Sammanfattning Inom den direkta beskattningens område har medlemstaterna i den Europeiska Unionen till stor del behållit sin behörighet men ska likväl beakta EU-rätten vid utövandet av denna behörighet. EU-rätten har dock fått ett allt större inflytande på den direkta beskattningens område genom bestämmelserna om den fria rörligheten och etableringsfriheten som till viss del begränsar medlemsstaternas behörighet. Medlemsstaterna måste rättfärdiga en nationell bestämmelse som är i konflikt med etableringsfriheten för att få tillämpa den och ofta åberopas den principiellt accepterade rättfärdigandegrunden förhindra skatteflykt. Det är dock inte ovanligt att nationella bestämmelser anses oförenliga med etableringsfriheten om de syftar till att förhindra förlust av skatteintäkter. Att förhindra förlust av skatteintäkter är inte en accepterad rättfärdigandegrund då den anses vara grundad på rent ekonomiska intressen och således inte utgör ett tvingande hänsyn till allmänintresset. En medlemsstat vars nationella bestämmelse ämnar förhindra skatteflykt åsyftar dock högst sannolikt att indirekt förhindra att de skatteintäkter hänförbara till medlemsstaten går förlorade vilket tyder på att även denna rättfärdigandegrund kan anses grundad i ett ekonomiskt intresse från medlemstaterna. Frågan uppkommer därför om det finns en tydlig gränsdragning mellan dessa två rättfärdigandegrunder. Innebörden av förhindra förlust av skatteintäkter måste anses inrymmas i medlemsstaternas ändamål med att söka förhindra skatteflykt. Dessa två rättfärdigandegrunder har således samma syfte och därför kan uppdelningen av dessa inte anses helt självklar. Gränsdragningen mellan dessa rättfärdigandegrunder anses således inte tillräckligt tydlig för att kunna hävda att förutsebarhet de facto föreligger för medlemsstaterna vid tillämpningen av respektive rättfärdigandegrund.Abstract The Member States in the European Union have kept their authority within the area of direct taxation but must still observe Community law when exercising this authority. However, Community law has received a major influence on the area of direct taxation through the free movement provisions and the freedom of establishment, which limits the authority of the Member States. If a national measure restricts or hinders the freedom of establishment, the Member States must justify the measure in order to be able to apply it and the prevention of tax avoidance is an often referred ground of justification that is accepted in principle. It is however not unusual that a national measure is considered in breach with the freedom of establishment if it refers to the prevention of loss of tax revenue. The loss of tax revenue is not an accepted ground of justification as it is considered to be based on merely economic interests and thus not regarded as a matter of overriding general interest. A Member State whose national measure aims at preventing tax avoidance, most likely also aims to prevent that tax revenues derived from the Member State is not deprived from it. This indicates that prevention of tax avoidance also is based on an economic interest which arise the question whether or not there is a distinct differentiation between these grounds of justification. The meaning of the loss of tax revenue is considered to be included in the objective of the Member States when they seek to prevent tax avoidance. Accordingly, these two grounds of justification have the same purpose and the separation between them can therefore not be considered as obvious. The differentiation between these grounds of justification is hence not obvious enough to be able to claim that predictability is at hand for the Member States when applying concerned ground of justification

Effects of anoxia and sulfide on concentrations of total and methyl mercury in sediment and water in two Hg-polluted lakes

Between May and December 1996, monthly samples of surface sediment (0-1 cm), settling matter, and water were taken at a shallow site and a deep site in each of two consecutive Hg-polluted riverine lakes. In the upper lake, the sediment was polluted also with cellulose fiber. Both hypolimnia turned anoxic, but sulfide was detected only in the upper lake. When sulfide appeared, hypolimnetic methyl mercury (MeHg) increased and reached 47 pM (9.4 ng.L-1), whereas MeHg in the sediment below decreased. The increase in hypolimnetic inorganic Hg (IHg = total Hg - MeHg), which reached a peak of 40 pM (8.0 ng.L-1), was slower, possibly because mobilized IHg was methylated. In the lower lake, hypolimnetic MeHg and IHg increased less dramatically during summer stratification, reaching only 5 and 24 pM (1.0 and 4.8 ng.L-1), respectively. There was no detectable concomitant decrease in sediment MeHg. In both lakes, MeHg appeared to increase simultaneously with total Fe and Mn in the hypolimnion, as did IHg in the lower lake. Our observations suggest that the presence of hydrous ferric and manganese oxides decreased the mobility of Hg in both lakes but increased MeHg production in the upper lake