4,551 research outputs found
Generalised Kinematics for Double Field Theory
We formulate a kinematical extension of Double Field Theory on a
-dimensional para-Hermitian manifold where the
metric is supplemented by an almost symplectic two-form
. Together and define an almost bi-Lagrangian structure
which provides a splitting of the tangent bundle
into two Lagrangian subspaces. In this paper a
canonical connection and a corresponding generalised Lie derivative for the
Leibniz algebroid on are constructed. We find integrability
conditions under which the symmetry algebra closes for general and
, even if they are not flat and constant. This formalism thus provides
a generalisation of the kinematical structure of Double Field Theory. We also
show that this formalism allows one to reconcile and unify Double Field Theory
with Generalised Geometry which is thoroughly discussed.Comment: 41 pages, v2: typos corrected, references added, published versio
Two-Dimensional Forward Scattering – Comparisons of Approximate and Exact Solutions
Various methods for analyses of scattering are mentioned and new approximate relationships are derived. Experimental results for thin wire and several numerical simulations of forward scattering using approximate estimations, physical optics and exact solutions for two-dimensional scattering are presented both for far and near fields. That allows not only accuracy analyses but also conclusions about scattering and total fields in the presence of objects, which are important for many applications such as communications, bistatic and multistatic radars and electromagnetic compatibility
Coloured mulch as a weed control technology and yield booster for summer savory
An investigation into the effect of coloured mulch technology as a technique to control weeds when growing the essential oil plant, summer savory (Satureja hortensis) was made. As well as weed control, the effects on the production of crop biomass and essential oil content and quality were also considered. The mulch treatments produced significantly more biomass than either of the control treatments (which used no mulch either with or without herbicide). The white mulch treatment produced the greatest biomass, closely followed by the red mulch treatment. The blue mulch treatment was third in ranking, although not significantly greater than the black mulch. Estimates of the quantity of essential oil produced by each treatment followed a similar trend to that shown by biomass production
Anomalous TWTA output power spikes and their effect on a digital satellite communications system
Several 30 GHz, 60 W traveling wave tube amplifiers (TWTA) were manufactured for the NASA Lewis Research Center's High Burst Rate Link Evaluation Terminal Project. An unusual operating problem characterized by anomalous nonperiodic output power spikes, common to all of the TWTAs proved during testing to significantly affect the performance of a digitally-modulated data transmission test system. Modifications made to the TWTAs significantly curtailed the problem and allowed acceptable system performance to be obtained. This paper presents a discussion of the TWTA output power spike problem, possible causes of the problem, and the solutions implemented by the manufacturer which improved the TWTA performance to an acceptable level. The results of the testing done at NASA Lewis on the TWTAs both before and after the improvement made by Hughes are presented, and the effects of the output power spikes on the performance of the test system are discussed
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