7,299 research outputs found

    Boundary states, matrix factorisations and correlation functions for the E-models

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    The open string spectra of the B-type D-branes of the N=2 E-models are calculated. Using these results we match the boundary states to the matrix factorisations of the corresponding Landau-Ginzburg models. The identification allows us to calculate specific terms in the effective brane superpotential of E_6 using conformal field theory methods, thereby enabling us to test results recently obtained in this context.Comment: 20 pages, no figure

    The Rotation of Young Low-Mass Stars and Brown Dwarfs

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    We review the current state of our knowledge concerning the rotation and angular momentum evolution of young stellar objects and brown dwarfs from a primarily observational view point. Periods are typically accurate to 1% and available for about 1700 stars and 30 brown dwarfs in young clusters. Discussion of angular momentum evolution also requires knowledge of stellar radii, which are poorly known for pre-main sequence stars. It is clear that rotation rates at a given age depend strongly on mass; higher mass stars (0.4-1.2 M⊙_\odot) have longer periods than lower mass stars and brown dwarfs. On the other hand, specific angular momentum is approximately independent of mass for low mass pre-main sequence stars and young brown dwarfs. A spread of about a factor of 30 is seen at any given mass and age. The evolution of rotation of solar-like stars during the first 100 Myr is discussed. A broad, bimodal distribution exists at the earliest observable phases (∼\sim1 Myr) for stars more massive than 0.4 M⊙_\odot. The rapid rotators (50-60% of the sample) evolve to the ZAMS with little or no angular momentum loss. The slow rotators continue to lose substantial amounts of angular momentum for up to 5 Myr, creating the even broader bimodal distribution characteristic of 30-120 Myr old clusters. Accretion disk signatures are more prevalent among slowly rotating PMS stars, indicating a connection between accretion and rotation. Disks appear to influence rotation for, at most, ∼\sim5 Myr, and considerably less than that for the majority of stars. If the dense clusters studied so far are an accurate guide, then the typical solar-like star may have only ∼\sim1 Myr for this task. It appears that both disk interactions and stellar winds are less efficient at braking these objects.Comment: Review chapter for Protostars and Planets V. 15 page and 8 figure

    Interstellar water chemistry: from laboratory to observations

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    Water is observed throughout the universe, from diffuse interstellar clouds to protoplanetary disks around young stars, and from comets in our own solar system and exoplanetary atmospheres to galaxies at high redshifts. This review summarizes the spectroscopy and excitation of water in interstellar space as well as the basic chemical processes that form and destroy water under interstellar conditions. Three major routes to water formation are identified: low temperature ion-molecule chemistry, high-temperature neutral-neutral chemistry and gas-ice chemistry. The rate coefficients of several important processes entering the networks are discussed in detail; several of them have been determined only in the last decade through laboratory experiments and theoretical calculations. Astronomical examples of each of the different chemical routes are presented using data from powerful new telescopes, in particular the Herschel Space Observatory. Basic chemical physics studies remain critically important to analyze astronomical data.Comment: Authors' manuscript 138 pages, 34 figures, 4 tables, published in a Thematic Issue "Astrochemistry" in Chemical Reviews (December 2013), volume 113, 9043-9085 following peer review by the American Chemical Society. The published paper is available as open access at http://pubs.acs.org/doi/abs/10.1021/cr400317

    SPISE guidelines on how to make sprayer adjustment at the workshop as an addition to the functional inspection of field crop sprayers

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    In the ambit of SPISE working Group several Technical Working Groups (TWG) have been recently created with the aim to prepare guidelines about the items taken into account by the EU Directive 128/2009/EC but still not considered in the actual ISO/CEN standards. SPISE TWG 6 in particular has defined guidelines on what are the minimum workshop facilities necessary and how to make an appropriate sprayer adjustment of field crop sprayers at the workshop during the inspection/calibration activities.Sprayer adjustment is focused to the adaptation of the sprayer output (both liquid and air) to the specific crop and eventually environmental situations present on the farm. To guide and verify the correct sprayer adjustment at the workshop, it is necessary to use ad hoc test benches that the workshops should have in their set of instruments. It is an operation that shall be made at the end of the functional inspection but before the eventual calibration of the sprayer. It has to be carried out for each crop type and situation present on the farm or at least for the most representative ones, because only a correct adjusted sprayer guarantees that the spray mixture is addressed to the target, the use of PPP is optimized and the risks for the environment (e.g. spray drift) and for the consumers are minimized
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