16,020 research outputs found
Prediction of payload vibration environments by mechanical admittance test techniques
A series of experiments was conducted with simple beam and mass launch vehicle and payload models in order to determine the validity of mechanical admittance/impedance techniques applied to development of improved payload vibration tests. Admittances and impedances were measured from tests of the individual components to form matrices which were combined analytically to allow prediction of responses for the complete system. Results were computed for a transmission matrix approach and an admittance matrix approach. Both a rigid body and a flexible payload model were considered. The results clearly demonstrate that the transmission matrix method is too sensitive to measurement error to be practical for this application, while the pure admittance matrix method produces quite satisfactory results. The effects of various errors on the final results are demonstrated
Thermodynamics of Two Dimensional Magnetic Nanoparticles
A two dimensional magnetic particle in the presence of an external magnetic
field is studied. Equilibrium thermodynamical properties are derived by
evaluating analytically the partition function. When the external field is
applied perpendicular to the anisotropy axis the system exhibits a second order
phase transition with order parameter being the magnetization parallel to the
field. In this case the system is isomorph to a mechanical system consisting in
a particle moving without friction in a circle rotating about its vertical
diameter. Contrary to a paramagnetic particle, equilibrium magnetization shows
a maximum at finite temperature. We also show that uniaxial anisotropy in a
system of noninteracting particles can be missinterpreted as a ferromagnetic or
antiferromagnetic coupling among the magnetic particles depending on the angle
between anisotropy axis and magnetic field.Comment: 4 pages 6 figures 19 reference
A 300 GHz "Always-in-Focus" Focusing System for Target Detection
A focusing system for a 300 GHz radar with 5 m target distance and 10 mm diameter spot size resolution is proposed. The focusing system is based on a Gaussian telescope scheme and its main parameters have been de¬signed using Gaussian beam quasi-optical propagation theory with an in-house developed MATLAB® based analysis tool. Then, this approach has been applied to a real focusing system based on two elliptical mirrors in order to reduce the distortion and cross-polar level and a plane mirror to provide scanning capabilities. The over¬all system has been simulated with a full-wave electromag¬netic simulator and its behavior is presented. With this approach, the focusing system always works "in-focus" since the only mirror that is rotated when scanning is the output plane mirror, so the beam is almost not distorted. The design process, although based in the well-known Gaussian beam quasi-optical propagation theory, provides a fast and accurate method and minimizes the overall size of the mirrors. As a consequence, the size of the focusing system is also reduced
Manejo de buva resistente ao glifosato.
bitstream/item/127511/1/ID-41256-FL-8506-manejo-de-buva-resistente-ao-glifosato.pd
Manejo de buva resistente ao glifosato.
Manejo das plantas resistentes. Manejo no inverno. Cultivo da área. Uso de herbicida. Manejo pré-semeadura (dessecação). Controle em pré-emergência. Controle em pós-emergência. Conclusões. Tabelabitstream/item/31188/1/doc.91.trigo.pd
Azevém resistente ao glifosato: características, manejo e controle.
bitstream/item/62590/1/2011comunicadotecnicoonline298.pd
Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene
We investigate the transmission properties of quasiperiodic or aperiodic
structures based on graphene arranged according to the Cantor sequence. In
particular, we have found self-similar behaviour in the transmission spectra,
and most importantly, we have calculated the scalability of the spectra. To do
this, we implement and propose scaling rules for each one of the fundamental
parameters: generation number, height of the barriers and length of the system.
With this in mind we have been able to reproduce the reference transmission
spectrum, applying the appropriate scaling rule, by means of the scaled
transmission spectrum. These scaling rules are valid for both normal and
oblique incidence, and as far as we can see the basic ingredients to obtain
self-similar characteristics are: relativistic Dirac electrons, a self-similar
structure and the non-conservation of the pseudo-spin. This constitutes a
reduction of the number of conditions needed to observe self-similarity in
graphene-based structures, see D\'iaz-Guerrero et al. [D. S. D\'iaz-Guerrero,
L. M. Gaggero-Sager, I. Rodr\'iguez-Vargas, and G. G. Naumis,
arXiv:1503.03412v1, 2015]
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