48,262 research outputs found
Specification of inputs and instrumentation for flutter testing of multivariable systems
The application of system identification methods in flutter testing of aeroelastic structure is discussed. The accuracy with which flutter parameters are estimated depends upon the test plan and on the algorithms used to reduce the data. The techniques for selecting the kinds and optimal positions of inputs and instrumentation, under typical test constraints, are presented. Identification results for both the input/output transfer function and the value of physical parameters are given. Numerical results on the optimal input spectrum and the accelerometer location for estimating flutter parameters of a two dimensional wing are obtained using these algorithms. Current work on applying system identification methods to high order three dimensional aeroelastic structures is reported
Input design for identification of aircraft stability and control derivatives
An approach for designing inputs to identify stability and control derivatives from flight test data is presented. This approach is based on finding inputs which provide the maximum possible accuracy of derivative estimates. Two techniques of input specification are implemented for this objective - a time domain technique and a frequency domain technique. The time domain technique gives the control input time history and can be used for any allowable duration of test maneuver, including those where data lengths can only be of short duration. The frequency domain technique specifies the input frequency spectrum, and is best applied for tests where extended data lengths, much longer than the time constants of the modes of interest, are possible. These technqiues are used to design inputs to identify parameters in longitudinal and lateral linear models of conventional aircraft. The constraints of aircraft response limits, such as on structural loads, are realized indirectly through a total energy constraint on the input. Tests with simulated data and theoretical predictions show that the new approaches give input signals which can provide more accurate parameter estimates than can conventional inputs of the same total energy. Results obtained indicate that the approach has been brought to the point where it should be used on flight tests for further evaluation
FearNot! An Anti-Bullying Intervention: Evaluation of an Interactive Virtual Learning Environment
Original paper can be found at: http://www.aisb.org.uk/publications/proceedings.shtm
Hierarchical structuring of Cultural Heritage objects within large aggregations
Huge amounts of cultural content have been digitised and are available
through digital libraries and aggregators like Europeana.eu. However, it is not
easy for a user to have an overall picture of what is available nor to find
related objects. We propose a method for hier- archically structuring cultural
objects at different similarity levels. We describe a fast, scalable clustering
algorithm with an automated field selection method for finding semantic
clusters. We report a qualitative evaluation on the cluster categories based on
records from the UK and a quantitative one on the results from the complete
Europeana dataset.Comment: The paper has been published in the proceedings of the TPDL
conference, see http://tpdl2013.info. For the final version see
http://link.springer.com/chapter/10.1007%2F978-3-642-40501-3_2
The School Improvement Partnership Programme: Using Collaboration and Enquiry to tackle Educational Inequity
No abstract available
Lattice vibrations and structural instability in Cesium near the cubic to tetragonal transition
Under pressure cesium undergoes a transition from a high-pressure fcc phase
(Cs-II) to a collapsed fcc phase (Cs-III) near 4.2GPa. At 4.4GPa there follows
a transition to the tetragonal Cs-IV phase. In order to investigate the lattice
vibrations in the fcc phase and seek a possible dynamical instability of the
lattice, the phonon spectra of fcc-Cs at volumes near the III-IV transition are
calculated using Savrasov's density functional linear-response LMTO method.
Compared with quasiharmonic model calculations including non-central
interatomic forces up to second neighbours, at the volume (
is the experimental volume of bcc-Cs with =6.048{\AA}), the
linear-response calculations show soft intermediate wavelength
phonons. Similar softening is also observed for
short wavelength and phonons and intermediate
wavelength phonons. The Born-von K\'{a}rm\'{a}n analysis of
dispersion curves indicates that the interplanar force constants exhibit
oscillating behaviours against plane spacing and the large softening of
intermediate wavelength phonons results from a
negative (110)-interplanar force-constant . The frequencies of the
phonons with around 1/3 become imaginary
and the fcc structure becomes dynamically unstable for volumes below .
It is suggested that superstructures corresponding to the
soft mode should be present as a precursor of tetragonal Cs-IV structure.Comment: 12 pages, 5 figure
Textile Diamond Dipole and Artificial Magnetic Conductor Performance under Bending, Wetness and Specific Absorption Rate Measurements
Textile diamond dipole and Artificial Magnetic Conductor (AMC) have been proposed and tested under wearable and body centric measurements. The proposed antenna and AMC sheet are entirely made of textiles for both the substrate and conducting parts, thus making it suitable for wearable communications. Directive radiation patterns with high gain are obtained with the proposed AMC sheet, hence minimizing the radiation towards the human body. In this study, wearable and body centric measurements are investigated which include bending, wetness and Specific Absorption Rate (SAR). Bending is found not to give significant effect to the antenna and AMC performance, as opposed to wetness that yields severe performance distortion. However, the original performance is retrieved once the antenna and AMC dried. Moreover, notable SAR reduction is achieved with the introduction of the AMC sheet, which is appropriate to reduce the radiation that penetrates into human flesh
Flavor at the TeV Scale with Extra Dimensions
Theories where the Standard Model fields reside on a 3-brane, with a low
fundamental cut-off and extra dimensions, provide alternative solutions to the
gauge hierarchy problem. However, generating flavor at the TeV scale while
avoiding flavor-changing difficulties appears prohibitively difficult at first
sight. We argue to the contrary that this picture allows us to lower flavor
physics close to the TeV scale. Small Yukawa couplings are generated by
``shining'' badly broken flavor symmetries from distant branes, and flavor and
CP-violating processes are adequately suppressed by these symmetries. We
further show how the extra dimensions avoid four dimensional disasters
associated with light fields charged under flavor. We construct elegant and
realistic theories of flavor based on the maximal U(3)^5 flavor symmetry which
naturally generate the simultaneous hierarchy of masses and mixing angles.
Finally, we introduce a new framework for predictive theories of flavor, where
our 3-brane is embedded within highly symmetrical configurations of
higher-dimensional branes.Comment: 40 pages, 8 figure
Mountain-Shaped Coupler for Ultra Wideband Applications
This paper demonstrates a novel mountain-shaped design for a compact 3-dB coupler operating at ultra-wideband (UWB) frequencies from 3.1GHz to 10.6 GHz. The proposed design was accomplished using multilayer technology in which the structure is formed by three layers of conductors interleaved by a layer of substrate between each conductor layer. Simulation was carried out using CST Microwave Studio; the result was then compared with results from rectangular and star-shaped couplers that implemented the same technique. The results obtained show that the proposed new coupler has better performance compared to both rectangular and star-shaped coupler designs in terms of return loss, isolation, and phase difference. The coupler was fabricated and measured; the measurement results satisfactorily agree with the simulation results
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