How to Mix Molecules with Mathematics

In this paper we develop two methods to calculate thermodynamic properties of mixtures. Starting point are the basic assumptions that also form the basis for the COSMO-RS model. In this approach, the individual molecules are represented by their geometrical shape with an electrical charge density on their surfaces. Next, the surface is split up into surface segments each with its own charge. In COSMO-RS a strong reduction is introduced by treating the segments as if they are completely independent. In the present study we take into account that the coupling between two patches is essentially dependent on the charge distribution on neighboring segments and on the local geometrical structure of the surface. Two approaches are followed. The first one points out how the model equations, which comprise the optimization of the entropy and conservation of internal energy, can efficiently be solved in general, thus also if the dependency between segments and the local geometry is included in the expression for the coupling energy between segments. In the second method the configuration with maximal entropy and prescribed energy is sought via simulation. Successive molecular configurations of the mixture are simulated and updated via a genetic algorithm to optimize the entropy. The second method is more time consuming but very general

Radio observations of active galactic nuclei with mm-VLBI

Over the past few decades, our knowledge of jets produced by active galactic nuclei (AGN) has greatly progressed thanks to the development of very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms involved in the formation of the plasma flow, as well as those driving its exceptional radiative output up to TeV energies, remain to be clarified. Most likely, these physical processes take place at short separations from the supermassive black hole, on scales which are inaccessible to VLBI observations at centimeter wavelengths. Due to their high synchrotron opacity, the dense and highly magnetized regions in the vicinity of the central engine can only be penetrated when observing at shorter wavelengths, in the millimeter and sub-millimeter regimes. While this was recognized already in the early days of VLBI, it was not until the very recent years that sensitive VLBI imaging at high frequencies has become possible. Ongoing technical development and wide band observing now provide adequate imaging fidelity to carry out more detailed analyses. In this article we overview some open questions concerning the physics of AGN jets, and we discuss the impact of mm-VLBI studies. Among the rich set of results produced so far in this frequency regime, we particularly focus on studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also presented.Comment: Published in The Astronomy & Astrophysics Review. Open access: https://link.springer.com/article/10.1007/s00159-017-0105-

Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry

Results are presented from a long-term astrometry program on PSR B0919+06 using the NRAO Very Long Baseline Array. With ten observations (seven epochs) between 1994--2000, we measure a proper motion of 18.35 +/- 0.06 mas/yr in RA, 86.56 +/- 0.12 mas/yr in Dec, and a parallax of 0.83 +/- 0.13 mas (68% confidence intervals). This yields a pulsar distance of 1.21 +/- 0.19 kpc, making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has been obtained, and the implied pulsar transverse speed is 505 +/- 80 km/s. Combining the distance estimate with interstellar scintillation data spanning 20 years, we infer the existence of a patchy or clumpy scattering screen along the line of sight in addition to the distributed electron density predicted by models for the Galaxy, and constrain the location of this scattering region to within about 250 parsecs of the Sun. Comparison with the lines of sight towards other pulsars in the same quadrant of the Galaxy permits refinement of our knowledge of the local interstellar matter in this direction.Comment: 12 pages, includes 4 figures and 3 tables, uses AASTeX 5 (included); ApJ submitte

Convergence in light capture efficiencies among tropical forest understory plants with contrasting crown architectures: a case of morphological compensation

10 páginas, 5 figuras y 4 tablasLeaf and crown characteristics were examined for 24 tree and herbaceous species of contrasting architectures from the understory of a lowland rainforest. Light-capture efficiency was estimated for the crowns of the different species with a three-dimensional geometric modeling program. Causal relationships among traits affecting light absorption at two hierarchical levels (leaf and whole crown) were quantified using path analysis. Light-capture and foliage display efficiency were found to be very similar among the 24 species studied, with most converging on a narrow range of light absorption efficiencies (ratio of absorbed vs. available light of 0.60– 0.75). Exceptionally low values were found for the climber vines and, to a lesser extent, for the Bromeliad Aechmea magdalenae. Differences in photosynthetic photon flux density (PFD) absorbed per unit leaf area by individual plants were mostly determined by site to site variation in PFD and not by the differences in crown architecture among individuals or species. Leaf angle, and to a lesser extent also supporting biomass, specific leaf area, and internode length, had a significant effect on foliage display efficiency. Potential constraints on light capture such as the phyllotactic pattern were generally offset by other compensatory adjustments of crown structure such as internode length, arching stems, and plagiotropy. The variety of shoot morphologies capable of efficiently capturing light in tropical forest understories is greater than initially thought, extending over species with very different phyllotactic patterns, crown architectures, leaf sizes, and morphologies.This research was supported by Mellon foundation/ Smithsonian Institution fellowships to FV and RWP, NSF Grant IBN 96-04424. Manuscript preparation was supported by a train and mobility grant given to FV by the Spanish Ministry of Education, Culture and Sports and a Professional Development Grant to JBS from the California State University.The authors thank Eduardo Sierra for help with the identification of the individuals studied, to Eloisa Lasso for help with data collection, and to Lourens Poorter for fitting criticisms. This research was supported by Mellon foundation/ Smithsonian Institution fellowships to FV and RWP, NSF Grant IBN 96-04424.Peer reviewe

Nofs ta' kelma

Ġabra ta’ poeżiji u proża li tinkludi: Alla kbir bla qies! ta’ R. M. B. – Tantum ergo – Lil kewkba feġġa – Għajjiena le xebagħna ta’ Ros. Briffa – Sliem ta’ Dun Karm – Kewkba ta’ Dun Karm – Nofs ta’ kelma ta’ A. C.N/

Development and Implementation of a Flipped-Classroom Delivery in Engineering Computing and Analysis for First Year Engineering Students

University of Wollongong recently undertook a major restructure of its academic and professional units, after the appointment of a new Vice Chancellor in 2012. As a result, the previous 11 faculties have been merged and rationalised into five new faculties. The Faculty of Engineering and the Faculty of Informatics merged to become the Faculty of Engineering and Information Sciences (EIS), consisting of six schools representing a total of 13 disciplines. Following the restructuring, EIS made the decision to develop a new common first year curriculum for all engineering undergraduate programs, spanning nine disciplines, they being; civil, mining, environmental, electrical, computer, telecommunications, mechanical, materials and mechatronic engineering. The process of developing the new first year subjects was undertaken in 2014 by a Task and Finish (T&F) group aiming for full implementation at the commencement of 2015. Through consultation with key stakeholders from each discipline area, as well as teaching teams from existing first year programs, five new engineering subjects were to be created, to coexist with the unaltered physics and mathematics subjects. The T&F group met regularly over the course of 2014, where they initially tasked with identifying the key mastery skills that all engineering students should have developed by the end of their first year of full time study. These skills were then grouped into themes, leading to the creation of the five new subjects. The final role of the T&F group was to report back to the Heads of School who would then assign key personnel to develop the curriculum content for each new subject. This paper will focus on the development of one of those newly created subjects, ENGG105 Engineering Computing and Analysis, which adopted the flipped-classroom approach to deliver the subject content

Precise absolute astrometry from the VLBA imaging and polarimetry survey at 5 GHz

We present in this paper accurate positions of 857 sources derived from the astrometric analysis of 16 eleven-hour experiments from the Very Long Baseline Array imaging and polarimetry survey at 5 GHz (VIPS). Among observed sources, positions of 430 objects were not determined before at a milliarcsecond level of accuracy. For 95% of the sources the uncertainty of their positions range from 0.3 to 0.9 mas, with the median value of 0.5 mas. This estimate of accuracy is substantiated by the comparison of positions of 386 sources that were previously observed in astrometric programs simultaneously at 2.3/8.6 GHz. Surprisingly, the ionosphere contribution to group delay was adequately modeled with the use of the total electron contents maps derived from GPS observations and only marginally affected estimates of source coordinates.Comment: Accepted for publication by the Astronomical Journal. 7 pages, 2 tables, 4 figures. Submission contains an ascii file with the catalogue. You can get the catalogue by downloading the source of this paper and extracting file table2.tx

L'usage des systèmes d'informations électroniques en recherche scientifique : le cas de la neurophysiologie.

Nous présentons les premiers résultats d'une enquête destinée à mieux connaître les pratiques de recherche d'information bibliographique et documentaire chez les chercheurs scientifiques. 64 chercheurs et étudiants doctorants en neurophysiologie ont répondu à un questionnaire portant sur les méthodes, les outils, et les objectifs des recherches d'information typiques dans leur activité. De plus, 11 personnes parmi les répondants ont participé à un entretien individuel semi structuré. Il en ressort que l'usage d'outils informatisés de recherche d'information bibliographique (RIB) est désormais pratique courante, au détriment des index et autres sources imprimées. Les principaux outils utilisés sont la base de données bibliographiques PubMed et le moteur de recherche Google, avec toutefois de nombreux autres outils plus spécifiques utilisés à titre complémentaire. Les répondants mentionnent des objectifs très variés, comme l'acquisition de connaissances nouvelles, mais aussi la recherche de techniques expérimentales, la veille documentaire, l'alimentation du débat scientifique, ou l'aide à l'enseignement. Les difficultés que rencontrent les experts en neurosciences intégratives dans l'exploitation des outils informatiques de RIB spécialisés semblent surtout liées à l'absence de formation des experts à ces outils. Les chercheurs définissent l'outil informatique de RIB « idéal » comme fiable et exhaustif, mais aussi rapide et facile à utiliser et apprendre . De fait, le facteur temps apparaît déterminant dans leur choix d'utilisation ou non d'un outil particulier. Cette étude ouvre la voie à des expériences plus spécifiques, qui porteront sur les stratégies cognitives des experts dans ce type de tâches