122,321 research outputs found
Single stage experimental evaluation of variable geometry guide vanes and stators. Part 1 - Analysis and design
Variable geometry concepts applied to guide vanes and stators in single stage compressor
Magnetic shielding and vacuum test for passive hydrogen masers
Vibration tests on high permeability magnetic shields used in the SAO-NRL Advanced Development Model (ADM) hydrogen maser were made. Magnetic shielding factors were measured before and after vibration. Preliminary results indicate considerable (25%) degradation. Test results on the NRL designed vacuum pumping station for the ADM hydrogen maser are also discussed. This system employs sintered zirconium carbon getter pumps to pump hydrogen plus small ion pumps to pump the inert gases. In situ activation tests and pumping characteristics indicate that the system can meet design specifications
Analytical expressions for fringe fields in multipole magnets
Fringe fields in multipole magnets can have a variety of effects on the
linear and nonlinear dynamics of particles moving along an accelerator
beamline. An accurate model of an accelerator must include realistic models of
the magnet fringe fields. Fringe fields for dipoles are well understood and can
be modelled at an early stage of accelerator design in such codes as MAD8, MADX
or ELEGANT. However, usually it is not until the final stages of a design
project that it is possible to model fringe fields for quadrupoles or higher
order multipoles. Even then, existing techniques rely on the use of a numerical
field map, which will usually not be available until the magnet design is well
developed. Substitutes for the full field map exist but these are typically
based on expansions about the origin and rely heavily on the assumption that
the beam travels more or less on axis throughout the beam line. In some types
of machine (for example, a non-scaling FFAG such as EMMA) this is not a good
assumption.
In this paper, a method for calculating fringe fields based on analytical
expressions is presented, which allows fringe field effects to be included at
the start of an accelerator design project. The magnetostatic Maxwell equations
are solved analytically and a solution that fits all orders of multipoles
derived. Quadrupole fringe fields are considered in detail as these are the
ones that give the strongest effects. Two examples of quadrupole fringe fields
are presented. The first example is a magnet in the LHC inner triplet, which
consists of a set of four quadrupoles providing the final focus to the beam,
just before the interaction point. Quadrupoles in EMMA provide the second
example. In both examples, the analytical expressions derived in this paper for
quadrupole fringe fields provide a good approximation to the field maps
obtained from a numerical magnet modelling code.Comment: 27 pages, 39 figures. The figures are new with respect to the
previous version, Several mistakes also correcte
Benchmark ultra-cool dwarfs in widely separated binary systems
Ultra-cool dwarfs as wide companions to subgiants, giants, white dwarfs and
main sequence stars can be very good benchmark objects, for which we can infer
physical properties with minimal reference to theoretical models, through
association with the primary stars. We have searched for benchmark ultra-cool
dwarfs in widely separated binary systems using SDSS, UKIDSS, and 2MASS. We
then estimate spectral types using SDSS spectroscopy and multi-band colors,
place constraints on distance, and perform proper motions calculations for all
candidates which have sufficient epoch baseline coverage. Analysis of the
proper motion and distance constraints show that eight of our ultra-cool dwarfs
are members of widely separated binary systems. Another L3.5 dwarf, SDSS 0832,
is shown to be a companion to the bright K3 giant Eta Cancri. Such primaries
can provide age and metallicity constraints for any companion objects, yielding
excellent benchmark objects. This is the first wide ultra-cool dwarf + giant
binary system identified.Comment: 4 pages, 3 figures, conference, "New Technologies for Probing the
Diversity of Brown Dwarfs and Exoplanets", oral tal
A Tale of Two Theories: Quantum Griffiths Effects in Metallic Systems
We show that two apparently contradictory theories on the existence of
Griffiths-McCoy singularities in magnetic metallic systems [1,2] are in fact
mathematically equivalent. We discuss the generic phase diagram of the problem
and show that there is a non-universal crossover temperature range T* < T < W
where power law behavior (Griffiths-McCoy behavior) is expect. For T<T* power
law behavior ceases to exist due to the destruction of quantum effects
generated by the dissipation in the metallic environment. We show that T* is an
analogue of the Kondo temperature and is controlled by non-universal couplings.Comment: 4 pages, 2 figure
Critical review of the impacts of grazing intensity on soil organic carbon storage and other soil quality indicators in extensively managed grasslands
Acknowledgements This work contributes to the N-Circle project (grant number BB/N013484/1), and CINAg (BB/N013468/1) Virtual Joint Centres on Agricultural Nitrogen (funded by the Newton Fund via UK BBSRC/NERC), U-GRASS (grant number NE/M016900/1), the Belmont Forum/FACCE-JPI DEVIL project (grant number NE/M021327/1), Soils-R-GGREAT (grant number NE/P019455/1), ADVENT (grant number NE/M019713/1), Sêr Cymru LCEE-NRN project, Climate-Smart Grass and the Scottish Government’s Strategic Research Programme.Peer reviewedPublisher PD
Fail-safe system for activity cooled supersonic and hypersonic aircraft
A fail-safe-system concept was studied as an alternative to a redundant active cooling system for supersonic and hypersonic aircraft which use the heat sink of liquid-hydrogen fuel for cooling the aircraft structure. This concept consists of an abort maneuver by the aircraft and a passive thermal protection system (TPS) for the aircraft skin. The abort manuever provides a low-heat-load descent from normal cruise speed to a lower speed at which cooling is unnecessary, and the passive TPS allows the aircraft skin to absorb the abort heat load without exceeding critical skin temperature. On the basis of results obtained, it appears that this fail-safe-system concept warrants further consideration, inasmuch as a fail-safe system could possibly replace a redundant active cooling system with no increase in weight and would offer other potential advantages
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