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  • 1
    Electronic Resource
    Electronic Resource
    A power-stable CO2 laser with ceramic resonator frame (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3735-3737 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A CO2 laser with a resonator frame made of low expansion ceramics has been developed to provide superior passive stability properties. High stiffness, low specific weight, and very good electric insulation properties recommend ceramic as an attractive material for many laser applications. The long-term power stability of a first prototype was better than ±0.44% measured over 15 min, the short-term stability was better than ±0.24%. Both values were achieved without any active stabilization technique, without damping of external vibrations, and with a non-temperature-controlled coolant. With a new switch mode power supply without ballast resistor a wall-plug efficiency of about 14% has been achieved under quasi-sealed-off conditions. The specific laser output power was about 20 W/m at a gas pressure of 18.5 mbar and a gas mixture He:N2:CO2=75:15:10+5.5% Xe. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145430
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    Paper (German National Licenses)
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  • 2
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    A power‐stable CO2 laser with ceramic resonator frame (1995)
    American Institute of Physics
    Details
    Publication Date: 1995-07-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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  • 3
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    Wavelet Coherence Analysis of Broadband Array Data Recorded at Stromboli Volcano, Italy (2004)
    Seismological Society of America
    Details
    Publication Date: 2004-02-01
    Description: We present a wavelet coherence method that is capable of displaying local coherence information between two seismic stations in the sense of a spectrogram. We have analyzed the vertical components of a 20-min-long time series from four stations that were situated in the seismic near field of Stromboli volcano. Typical volcanic seismic signals recorded in the near field of Stromboli volcano consist of continuous volcanic tremor superimposed on frequent Strombolian explosion signals. The tremor exhibits a banded and frequency-stable structure, whereas the broadband explosion signals span two or three frequency decades. We demonstrate that signals related to explosion earthquakes are strongly correlated within the network over 1.5 frequency decades. Using synthetic data, we show how coherent signal portions can be extracted out of noisy data using a coherence-filtering method. A time delay analysis using coherence information results in a coarse source location estimation that lies within the crater region. With the exception of randomly fluctuating coherence peaks, low correlations have been observed in the characteristic bands that are assumed to be generated by continuous tremor. In the low-frequency band that is related to the ocean microseisms (period nearly equal 4-8 sec), we observe mostly high correlation that breaks down during the appearance of explosion earthquake signals. Based on further analysis using the inverse wavelet transformation, we propose a model that describes the breakdown phenomenon as a super-position of two independent events.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 4
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    Best-basis analysis of broadband tremor signals (2006)
    Details
    Publication Date: 2019-11-04
    Description: Active volcanoes usually generate highly non-stationary broadband tremor signals. Short-time shock events with a frequency content of several decades are superimposed on a stationary narrow band continuous tremor. Tremor signals of this type can be observed in the near field of many active volcanoes. In this paper we will demonstrate the analysis of such signals using a specific tremor signal of Mt. Stromboli (Sicily). We used the Best-Basis Algorithm (BBA) in order to compute a spectrogram which is adapted to signal properties on highly different scales. It turns out that the BBA can reveal better fitting properties of the tremor in the time-frequency plane compared to standard methods like Short-Time Fourier Transformation (STFT). Moreover, this very effective algorithm can be used for real time monitoring in the time-frequency plane, for data compression or for de-noising of the tremor signals.
    Description: JCR Journal
    Description: open
    Keywords: adaptive spectrogram analysis ; broadband tremor ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2503690 bytes
    Format: application/pdf
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  • 5
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    Spectrogram analysis of selected tremor signals using short-time Fourier transform and continuous wavelet transform (2006)
    Details
    Publication Date: 2019-11-04
    Description: Among a variety of spectrogram methods Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) were selected to analyse transients in non-stationary tremor signals. Depending on the properties of the tremor signal a more suitable representation of the signal is gained by CWT. Three selected broadband tremor signals from the volcanos Mt. Stromboli, Mt. Semeru and Mt. Pinatubo were analyzed using both methods. The CWT can also be used to extend the definition of coherency into a time-varying coherency spectrogram. An example is given using array data from the volcano Mt. Stromboli.
    Description: JCR Journal
    Description: open
    Keywords: spectrogram ; wavelet transform ; broadband tremor ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 3407816 bytes
    Format: application/pdf
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