Non-Gaussianity in three fluid curvaton model

The generation of non-gaussianity is studied in a three fluid curvaton model. By utilizing second order perturbation theory we derive general formulae for the large scale temperature fluctuation and non-gaussianity parameter, $f_{NL}$, that includes the possibility of a non-adiabatic final state. In the adiabatic limit we recover previously known results. The results are applied to a three fluid curvaton model where the curvaton decays into radiation and matter. We find that the amount of non-gaussianity decreases as the final state of the system becomes more adiabatic and that the generated non-gaussianity in the scenario is small, $|f_{NL}| \sim \mathcal{O}(1)$.Comment: 10 pages, 2 figure

Non-Gaussianity Generated by the Entropic Mechanism in Bouncing Cosmologies Made Simple

Non-gaussianity in the microwave background radiation is bound to play a key role in giving us clues about the physics of the very early universe. However, the associated calculations, at second and even third order in perturbation theory, tend to be complicated to the point of obscuring simple underlying physical processes. In this note, we present a simple analytic procedure for approximating the non-linearity parameters f_{NL} and g_{NL} for cyclic models in which the cosmological perturbations are generated via the entropic mechanism. Our approach is quick, physically transparent and agrees well with the results of numerical calculations.Comment: 9 pages, 1 figur

Existential Second-Order Logic Over Graphs: A Complete Complexity-Theoretic Classification

Descriptive complexity theory aims at inferring a problem's computational complexity from the syntactic complexity of its description. A cornerstone of this theory is Fagin's Theorem, by which a graph property is expressible in existential second-order logic (ESO logic) if, and only if, it is in NP. A natural question, from the theory's point of view, is which syntactic fragments of ESO logic also still characterize NP. Research on this question has culminated in a dichotomy result by Gottlob, Kolatis, and Schwentick: for each possible quantifier prefix of an ESO formula, the resulting prefix class either contains an NP-complete problem or is contained in P. However, the exact complexity of the prefix classes inside P remained elusive. In the present paper, we clear up the picture by showing that for each prefix class of ESO logic, its reduction closure under first-order reductions is either FO, L, NL, or NP. For undirected, self-loop-free graphs two containment results are especially challenging to prove: containment in L for the prefix $\exists R_1 \cdots \exists R_n \forall x \exists y$ and containment in FO for the prefix $\exists M \forall x \exists y$ for monadic $M$. The complex argument by Gottlob, Kolatis, and Schwentick concerning polynomial time needs to be carefully reexamined and either combined with the logspace version of Courcelle's Theorem or directly improved to first-order computations. A different challenge is posed by formulas with the prefix $\exists M \forall x\forall y$: We show that they express special constraint satisfaction problems that lie in L.Comment: Technical report version of a STACS 2015 pape

The theory of planned behaviour predicts self-reports of walking, but does not predict step count

Objectives This paper compares multiple measures of walking in two studies, and the second study compares how well Theory of Planned Behaviour (TPB) constructs perform in predicting these different measures. Methods In Study 1, 41 participants wore a New Lifestyles NL-2000 pedometer for 1 week. Subsequently, participants completed a questionnaire containing measures of the TPB constructs and two self-report measures of walking, followed by two interview measures of walking. For Study 2, 200 RAF trainee aircraftsmen wore pedometers for 2 weeks. At the end of each week, participants completed the questionnaire and interview measures of walking. Results Both studies found no significant association between questionnaire measures of walking and pedometer measures. In Study 1, the interview measures produced significant, large correlations with the pedometer measure, but these relationships were markedly weaker in the second study. TPB variables were found to explain 22% of variance in intention to walk in Study 1 and 45% of the variance in Study 2. In Study 2, prediction of subsequent measures of behaviour was found to be weak, except when using a single-item measure of walking. Conclusions Recall of walking is poor, and accurate measurement by self-report is problematic. Although the TPB predicts intentions to walk well, it does not predict actual amount of walking, as assessed by pedometer. Possible reasons for these findings include the unique nature of walking as an activity primarily used to facilitate higher order goals. The use of single-item measures may exaggerate the effectiveness of the TPB model for walking, and possibly other forms of physical activity.</p

Analysis of all-optical generation of graphene surface plasmons by a frequency-difference process

The generation of graphene surface plasmons (SPs) by a frequency-difference nonlinear (NL) process caused by the interaction of two optical beams was experimentally demonstrated several years ago by measuring the differential reflectance of the probe beam. However, the understanding of these results requires much larger second-order optical conductivities of graphene than calculations performed so far can yield. In this work, we carefully calculate the relevant NL conductivities and show that, indeed, the experimental observations of the differential reflectance must have originated from physical processes beyond the coherent frequency-difference generation of SPs described by the density-matrix perturbation theory approach, presumably by hot-electron effects. We also suggest an alternative way of detecting optically generated SPs, which can be feasible at lower powers of the optical pulses. Such additional experiments are expected to help understand the remaining discrepancy between the theory and the existing experimental data.This research was funded by the Portuguese Foundation for Science and Technology (FCT) through project Ref. PTDC/NAN-OPT/29265/2017 “Towards high speed optical devices by exploiting the unique electronic properties of engineered 2D materials”, the European Commission within the project “Graphene-Driven Revolutions in ICT and Beyond” (Ref. No. 696656), and the Strategic Funding UID/FIS/04650/2020

The potential for networked learning in environmental assessment teaching in Sweden

This paper explores the current teaching of Environmental assessment (EA) in Sweden. EA processes aim at identifying the potential advantages and disadvantages of a proposed action mainly applied in physical landuse planning and for the approval of projects. EA not achieving best practice has been an issue within research for a long period of time. At the same time, the competence requirements on EA practitioners are very high. Recent court verdicts have raised a concern about the competence status among Swedish practitioners in the field of EA.The aim of this paper is to explore and analyse the current teaching in EA in Sweden in order to develop this field through influence from other disciplines, in this case Network Learning (NL). The paper builds on two different analyses. The first being an analysis of Swedish EA courses. The second being a comparison of the International Association for Impact Assessment (IAIA) Best Practice Principles for Teaching, and the Design dimensions for NL.The analysis shows that most of the courses are leaning more towards practical training than integration of research contribution and research training. This means that there is a risk that the students will leave the university with a low absorptive capacity. The analysis has also identified that vital competences are lacking in current teaching. These are the awareness of EA being an interdisciplinary process and integrative and systems thinking. This despite, the ability to synthesize information from different sources to develop a holistic understanding is central to EA practise.The comparison with the design dimensions for NL experiences shows a clear correlation with the category pedagogy of the IAIA Principles an indirect correlation with content and skills. The social dimension in NL is not visible in the analysed course syllabuses, and notions of conflict management and reflective practice are weak.The backbone of EA teaching is the same in all countries and there are good opportunities, with technology, to build international teaching networks. This would enable more knowledge sharing in larger teaching communities in the field of EA teaching. Therefore, network learning offers a potential for EA teaching, bridging the gap between theory and practice

Obtaining the lattice energy of the anthracene crystal by modern yet affordable first-principles methods

The non-covalent interactions in organic molecules are known to drive their self-assembly to form molecular crystals. We compare, in the case of anthracene and against experimental (electronic-only) sublimation energy, how modern quantum-chemical methods are able to calculate this cohesive energy taking into account all the interactions between occurring dimers in both first-and second-shells. These include both O(N 6)- and O(N 5)-scaling methods, Local Pair Natural Orbital-parameterized Coupled-Cluster Single and Double, and Spin-Component-Scaled-Møller-Plesset perturbation theory at second-order, respectively, as well as the most modern family of conceived density functionals: double-hybrid expressions in several variants (B2-PLYP, mPW2-PLYP, PWPB95) with customized dispersion corrections (–D3 and –NL). All-in-all, it is shown that these methods behave very accurately producing errors in the 1–2 kJ/mol range with respect to the experimental value taken into account the experimental uncertainty. These methods are thus confirmed as excellent tools for studying all kinds of interactions in chemical systems.Financial support by the “Ministerio de Economía y Competitividad” of Spain and the “European Regional Development Fund” through projects CTQ2011-27253, CTQ2012-31914, and Consolider-Ingenio CSD2007-00010 in Molecular Nanoscience, and by the Generalitat Valenciana (ISIC 2012/008 and PROMETEO/2012/053) is acknowledged. The work in Mons is supported by the Belgian National Fund for Scientific Research (FNRS). Y.O. is a FNRS Post-doctoral Research Fellow. J.C.S.G. is a FNRS Visiting Professor

On enhanced corrections from quasi-degenerate states to heavy quarkonium observables

It is well known that in perturbation theory existence of quasi-degenerate states can rearrange the order counting. For a heavy quarkonium system, naively, enhanced effects ($l$-changing mixing effects) could contribute already to the first-order and third-order corrections to the wave function and the energy level, respectively, in expansion in $\alpha_s$. We present a formulation and note that the corresponding (lowest-order) corrections vanish due to absence of the relevant off-diagonal matrix elements. As a result, in the quarkonium energy level and leptonic decay width, the enhanced effects are expected to appear, respectively, in the fifth- and fourth-order corrections and beyond.Comment: 9 page