Spectral analysis is an important signal processing tool for seismic data. The transformation of a seismogram into the frequency domain is the basis for a significant number of processing algorithms and interpretive methods. However, for seismograms whose frequency content vary with time, a simple 1-D (Fourier) frequency transformation is not sufficient. Improved spectral decomposition in frequency-time (FT) space is provided by the sliding window (short time) Fourier transform, although this method suffers from the timefrequency resolution limitation. Recently developed transforms based on the new mathematical field of wavelet analysis bypass this resolution limitation and offer superior spectral decomposition. The continuous wavelet transform with its scale-translation plane is conceptually best understood when contrasted to a short time Fourier transform. The discrete wavelet transform and matching pursuit algorithm are alternative wavelet transforms that map a seismogram into FT space. Decomposition into FT space of synthetic and calibrated explosive-source seismic data suggest that the matching pursuit algorithm provides excellent spectral localization, and reflections, direct and surface waves, and artifact energy are clearly identifiable. Wavelet-based transformations offer new opportunities for improved processing algorithms and spectral interpretation methods.
This report describes the acquisition and reduction of deep-crustal onshore-offshore seismic refraction/wide-angle reflection data in the Inner California Borderland-Los Angeles metropolitan region, conducted in October 1994 as part of the Los Angeles Regional Seismic Experiment (LARSE). LARSE is a cooperative study of the crustal structure of southern California involving earth scientists from the U.S. Geological Survey (USGS), California Institute of Technology (Caltech), the University of Southern California (USC), the University of California Los Angeles (UCLA), and other institutions of the Southern California Earthquake Center (SCEC). During LARSE, the R/V Ewing's 20-element air gun array, totaling 137.7 liters (8470 cu. in.), was primarily used as a seismic source for wide-angle recording along three main onshore-offshore lines centered on the Los Angeles basin and the epicenters of the 1933 Long Beach and 1994 Northridge earthquakes. The LARSE onshore-offshore lines were each 200-250 km long, with the offshore source lines being between 90 and 150 km long. The 22,128 air gun signals generated by the Ewing were recorded by an array of 174 PASSCAL Reftek recorders deployed at 2 km intervals along all three of the onshore lines and 9 ocean bottom seismometers (OBSs) deployed along two of the lines. The Ewing's 4.2-km, 160-channel, digital streamer was also used to record approximately 1250 km of 40-fold multichannel seismic-reflection data.To enhance the fold of the wide-angle data recorded onshore, mitigating against cultural and wind noise in the Los Angeles basin, the entire ship track was repeated at least once resulting in fewer than about 660 km of unique trackline coverage in the Inner Borderland. Portions of the seismic-reflection lines were repeated up to 6 times. The marine air-gun signals were recorded by portable land recorders which were deployed in continuous recording mode. With the use of accurate GPS timing at both sources and receivers, seismograms were extracted from the continuously recorded data. In this report, we describe the equipment and procedures used to acquire the onshore-offshore seismic refraction/wide angle reflection data, discuss the reduction of the data, and present reduced travel-time seismic sections of the acquired common-station-gather profiles. A more complete description of the marine seismic data collected by the Ewing is available in Brocher et al. (1995) and ten Brink et al. (1996). A third portion of the full LARSE experiment involved onland explosive sources collected by onland portable recorders which is described in Murphy et al. (1996). Local earthquakes which occurred during the acquisition of the air-gun data are described in Okaya et al. (1996). A separate LARSE experiment in 1993 to collect earthquakes over a several week period along Line 1 is described in Kohler et al. (1996).
<p>This paper investigates the behavior of a high frequency parallel quasiresonant<br />inverter fitted domestic induction heater with different switching frequencies. The power semiconductor switch Insulated Gate Bipolar Junction Transistor (IGBT) is incorporated in this high frequency inverter that can operate under ZVS and ZCS conditions during the switching operations at certain switching frequency to reduce switching losses. The proposed induction heating system responds to three different switching frequencies with providing different results. An Insulated Gate Bipolar Junction Transistor (IGBT) provides better efficiency and faster switching operations. After the complete study of the proposed induction heating system at the selected switching frequencies, the results are compared and it is decided that most reliable, efficient and effective operations from the proposed induction heater can be obtained if the switching frequency is selected slightly above the resonant frequency of the tank circuit of the resonant inverter. The proposed scheme is analyzed using Power System<br />Simulator (PSIM) environment.</p>
This paper presents the performance analysis of high frequency parallel quasi-resonant converter for domestic induction heating application as well as industrial application. The power semiconductor switch like IGBT is incorporated in this high frequency converter. Parallel Quasi-resonant topology is selected to provide ZVS and ZCS operation during switching conditions to reduce switching losses. Here, IGBT provides better efficiency and faster switching technique. In the proposed topology, a diode is connected across the IGBT ensuring the ZVS operation during turn-ON that enhances the possibility of less turn-ON loss. On the other hand, the switching frequency nearly equal to the resonant frequency ensures the ZCS operation of the IGBT during turn-OFF, which also ensures a reduction of turn-OFF loss. As a result, the performance of the induction heating system gets improved. The proposed scheme is analyzed using PSIM software environment.
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