212,341 research outputs found
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Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets: artificial and historic records
A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011-2001 design spectrum to a parametrically defined evolutionary power spectrum (EPS). Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned design spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response spectrum is in a close agreement with the considered design spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signalsâ response spectra with the GB 50011-2001 design spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice
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A mission synthesis algorithm for fatigue damage analysis
This paper presents a signal processing based algorithm, the Mildly Nonstationary Mission Synthesis
(MNMS), which produces a short mission signal from long records of experimental data. The
algorithm uses the Discrete Fourier Transform, Orthogonal Wavelet Transform and bump reinsertion
procedures. In order to observe the algorithm effectiveness a fatigue damage case study was
performed for a vehicle lower suspension arm using signals containing tensile and compressive
preloading. The mission synthesis results were compared to the original road data in terms of both the
global signal statistics and the fatigue damage variation as a function of compression ratio. Three
bump reinsertion methods were used and evaluated. The methods differed in the manner in which
bumps (shock events) from different wavelet groups (frequency bands) were synchronised during the
reinsertion process. One method, based on time synchronised section reinsertion, produced the best
results in terms of mission signal kurtosis, crest factor, root-mean-square level and power spectral
density. For improved algorithm performance, bump selection was identified as the main control
parameter requiring optimisation
A Low Bit Rate Audio Coder based on Segmental Sinusoidal Model
Audio signal information with high quality would help the television audience to increase the perception of the information displayed. Transmission channel capacity will become limited, while the need of channel communication is increased. The research aim is coding the audio signal on the low bit rate for saving the channel communication usage for digital television broadcasting. The research will be done is develop an audio signal coder on the low bit rate with the suitable decoder. The proposed audio signal coder consists of signal existention detector, period width detector, average amplitude counter, separation of the vibrating and the nonvibrating signal, determination of the period signal and parameters coding. One period signal is coded using sinusoidal model. The decoder consists of the parameters detector, signal synthesizer, and the periodic signal generator. The research results contribution for digital broadcasting is the method developing for decreasing the audio signal rate. So that the communication channel usage can be saved
Diffuse polarized emission associated with the Perseus cluster
We report on full-polarization radio observations of the Perseus cluster
(Abell 426) using the Westerbork Synthesis Radio Telescope (WSRT) at
wavelengths from 81-95 cm. We have employed a novel technique, Rotation Measure
synthesis (Brentjens and de Bruyn, 2005) to unravel the polarization properties
of the emission across the full field of view and detect polarized emission
over a wide range of RM from about 0 to 90 rad m^-2. The low RM emission is
associated with our Galaxy, while the high RM emission is associated with the
Perseus cluster. The latter reaches typical surface brightness levels of 0.5-1
mJy per beam and must be rather highly polarized. Most of the peripheral
polarized emission appears too bright, by about 1-2 orders of magnitude, to be
explainable as Thomson scattered emission of the central radio source off the
thermal electrons in the cluster. The bulk of the emission associated with the
Perseus cluster is probably related to buoyant bubbles of relativistic plasma,
probably relics from still active or now dormant AGN within the cluster. A
lenticular shaped structure measuring 0.5-1 Mpc is strikingly similar to the
structures predicted by Ensslin et al. (1998). At the western edge of the
cluster, we detect very long, linear structures that may be related to shocks
caused by infall of gas into the Perseus cluster.Comment: 18 pages, 17 figures, accepted by A&A, corrected small typo, added
referenc
Lattice structures for optimal design and robust implementation of two-channel perfect-reconstruction QMF banks
A lattice structure and an algorithm are presented for the design of two-channel QMF (quadrature mirror filter) banks, satisfying a sufficient condition for perfect reconstruction. The structure inherently has the perfect-reconstruction property, while the algorithm ensures a good stopband attenuation for each of the analysis filters. Implementations of such lattice structures are robust in the sense that the perfect-reconstruction property is preserved in spite of coefficient quantization. The lattice structure has the hierarchical property that a higher order perfect-reconstruction QMF bank can be obtained from a lower order perfect-reconstruction QMF bank, simply by adding more lattice sections. Several numerical examples are provided in the form of design tables
A Phase Vocoder based on Nonstationary Gabor Frames
We propose a new algorithm for time stretching music signals based on the
theory of nonstationary Gabor frames (NSGFs). The algorithm extends the
techniques of the classical phase vocoder (PV) by incorporating adaptive
time-frequency (TF) representations and adaptive phase locking. The adaptive TF
representations imply good time resolution for the onsets of attack transients
and good frequency resolution for the sinusoidal components. We estimate the
phase values only at peak channels and the remaining phases are then locked to
the values of the peaks in an adaptive manner. During attack transients we keep
the stretch factor equal to one and we propose a new strategy for determining
which channels are relevant for reinitializing the corresponding phase values.
In contrast to previously published algorithms we use a non-uniform NSGF to
obtain a low redundancy of the corresponding TF representation. We show that
with just three times as many TF coefficients as signal samples, artifacts such
as phasiness and transient smearing can be greatly reduced compared to the
classical PV. The proposed algorithm is tested on both synthetic and real world
signals and compared with state of the art algorithms in a reproducible manner.Comment: 10 pages, 6 figure
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