7,299 research outputs found
Boundary states, matrix factorisations and correlation functions for the E-models
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
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) 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 (1 Myr) for
stars more massive than 0.4 M. 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, 5 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 1
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
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Rotating Machine Technologies for Integration of Pulsed and High Power Loads in Naval Electric Power Systems
Advanced electric sensors and weapons are placing increasing demands on the electric power distribution systems of future naval vessels and energy storage is viewed as a critical technology for effective integration of IPS architectures in these platforms. This paper shows that kinetic energy storage, i.e. stored in the angular momentum of a rotating mass, can be applied in differing topologies to address a range of ship power system applications. Rotating machine technologies are presented for UPS and load leveling applications as well as for high cycle rate pulsed power applications.Center for Electromechanic
Interstellar water chemistry: from laboratory to observations
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
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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