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    Wyświetlanie 1-3 z 3
    Tytuł:
    Sound Diffusers with Fabric Covering
    Autorzy:
    Kamisiński, T.
    Brawata, K.
    Pilch, A.
    Rubacha, J.
    Zastawnik, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/176693.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    fabric covering
    Schroeder diffusers
    absorption
    scattering
    Opis:
    Fabric covering is often used by designers, as it can easily mask acoustic structures that do not match an interior. However, in the case of sound diffusers based on change in the phase of the reflected wave, the use of fabric covering is not without its effect on acoustics. It reduces the effectiveness of these structures and raises acoustic absorption. In the paper, the authors analyzed the acoustical properties of a selected fabric used to cover sound diffusers. Sound absorption and scattering coefficients for a system composed of sound diffusers and a fabric situated at different distances d were measured. The results were compared to the sound absorption predicted on the basis of Kuttruff’s and Mechel’s theoretical models. Analysis of the results indicates that the fabric has a significant influence on the system’s acoustic parameters. It is also observed, that fabric applied directly on a phase grating diffuser, produces higher absorption than when it is at some distance from it.
    Źródło:
    Archives of Acoustics; 2012, 37, 3; 317-322
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Test Signal Selection for Determining the Sound Scattering Coefficient in a Reverberation Chamber
    Autorzy:
    Kamisiński, T.
    Brawata, K.
    Pilch, A.
    Rubacha, J.
    Zastawnik, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/176622.pdf
    Data publikacji:
    2012
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    Schroeder diffusers
    scattering
    MLS
    sine sweep
    Opis:
    The paper focuses on the problem of test signal selection in determining the sound scattering coefficient in accordance with ISO 17497-1. Research shows that the use of MLS signal is preferred in this procedure. The sine sweep signal, despite its advantages, presents certain limitations if the sample is moving during measurement. An attempt has been made to develop a method that allows for minimization of error, demonstrating the dependence of the obtained values of the sound scattering coefficient on the rotational speed of the turntable and type of test signal. Conditions for the application of the sine sweep signals in continuous and discrete measurements were defined.
    Źródło:
    Archives of Acoustics; 2012, 37, 4; 405-409
    0137-5075
    Pojawia się w:
    Archives of Acoustics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Northwest Africa 7915: A New approved LL5 chondrite from Morocco
    Autorzy:
    Brawata, M.
    Kryza, R.
    Jakubowski, T.
    Przylibski, T. A.
    Ćwiąkalski, J.
    Łuszczek, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/411506.pdf
    Data publikacji:
    2014
    Wydawca:
    Polskie Towarzystwo Meteorytowe
    Tematy:
    chondrite
    NWA 7915
    Morocco
    chondrule
    chondrite chemistry
    chondrite weathering
    Opis:
    A 415 g single meteorite was purchased in 2010 by T. Jakubowski from a dealer in Morocco. The meteorite was isometric in shape, ca. 8 cm in size, with distinct regmaglypts on the original ablated surface, and covered mostly in primary crust with one broken surface. The weight of the sample studied was 69 g. The meteorite is composed of several types of chondrules including porphyritic-Ol-Px, barred-Ol, radial-Px, granular and cryptocrystalline with distinct and diffused (not sharp) boundaries, and opaque grains and aggregates, enclosed in a very fine-grained matrix. The average compositions of minerals are: olivine (both in chondrules and matrix) − Fo70.4Fa29.1Te0.5, pyroxenes, represented by Mg-Fe (Ca-poor) orthopyroxene (and minor clinopyroxene?) − En73.9Fs24.1Wo2.0, feldspars (small in the matrix and in barred chondrules), with An12-37, and Or~3-4, taenite − Fe 70.80, Ni 25.50 and Co 1.67 wt. %, troilite − Fe0.98S1.00, chromite (Fe2+ 0.96Mg0.12Mn0.01Zn0.01) (Cr1.52Al0.23Fe3+ 0.02Ti0.10Si0.02)O4; altered accessory minerals including apatite and iron-rich secondary phases have also been identified and analyzed. The meteorite is of petrologic type 5, as evidenced by the observed recrystallization of the matrix, relatively good preservation of the chondrule structures, homogeneous composition of olivine and pyroxene, and the presence of only secondary small feldspar grains. The shock stage, S2, is based on the presence of undulatory extinction and irregular fractures in olivine crystals. The weathering grade, W3, is confirmed by the observation that kamacite is totally altered into secondary iron phases, whereas Nirich taenite, and troilite are only partly weathered. The specimen shows many bulk- and mineral-chemical parameters corresponding, mostly, to the LL chondrite group (e.g., Fe/SiO2 0.49, SiO2/MgO 1.62, Fa in olivine 29.05). However, concentrations of several other elements, including REE, are not fully consistent with the average values for the LL ordinary chondrites. Apparently, the parent body of the studied NWA 7915 meteorite was depleted in Dy, Tm, and Yb, compared to typical LL-type ordinary chondrite parent bodies. Also, relatively high concentrations of other elements, including Ba and Sr, have been measured, which may result from terrestrial weathering in hot desert conditions. The meteorite has been classified as LL5 ordinary chondrite, S2, W3, and registered in the Meteoritical Society database as NWA 7915. The type specimen is deposited in the Mineralogical Museum of the University of Wrocław.
    Źródło:
    Meteorites; 2014, 3, No. 1-2; 45-58
    2299-0313
    2299-1220
    Pojawia się w:
    Meteorites
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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