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  • 1
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    Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains (2014)
    American Geophysical Union
    Details
    Publication Date: 2021-02-17
    Description: Pelagic marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties, including reversible humped low-temperature cycling (LTC) curves. Different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of LTC curves. A dipole spring mechanism in magnetosome chains is introduced to explain reversible LTC curves. This dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite, similar to published results for uniaxial stable single domain (SD) particles. The dipole spring mechanism reversibly restores the remanence during warming in LTC measurements. This supports a previous idea that remanence of magnetosome chains is completely reversible during LTC experiments. We suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains, although the presence of isolated uniaxial stable SD particles and magnetically interacting particles can complicate this test. Magnetic measurements through the Eocene section of ODP Hole 738B reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic “hard” component. Co-occurrence of these two magnetic fingerprints during the late Eocene in the Southern Ocean indicates less oxic conditions, probably due to increased oceanic primary productivity and organic carbon burial.
    Description: Published
    Description: 6049–6065
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: pelagic carbonates ; biogenic magnetite ; rock magnetism ; environmental magnetism ; ODP ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Muroto Project: Scientifi c Drilling of the Late Pliocene Forearc Basin Deposit on the West Coast of Muroto Peninsula, Shikoku, Japan (2006)
    In:  Scientific Drilling
    Details
    Publication Date: 2020-02-12
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 3
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    On the possibility of a complete Ediacaran field collapse (2023)
    In:  XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
    Details
    Publication Date: 2023-09-12
    Description: In the past decade there has been increased multidisciplinary interest in the onset time of inner core nucleation (ICN). A major step forward toward understanding ICN from paleomagnetism was the discovery by Bono et al. (Nature Geoscience, 2019) of ultralow fields in Ediacaran-age (565 Ma) anorthosites of the Sept Îles layered mafic sequence of northern Quebec, Canada. Independent thermal and numerical dynamo modeling (Driscoll, GRL, 2016) predicted the weak-field state prior to ICN. Bono et al. (2019) combined the unusual geomagnetic behavior (a hyper-reversal state) from global studies together with the Sept Îles ultra-low field value to suggest ICN near 565 Ma. We consider whether the internally generated field did not just decline to ultra-low values but might have effectively disappeared for some time interval of the Ediacaran Period. We study whole rock paleointensity values from Ediacaran-age dikes sampled from Ontario, Canada. We find Arai plots with extreme two-slope behavior. The low temperature slope appears to be a thermo-viscous overprint, whereas the high temperature slope, if interpreted as a viable paleointensity measure, records ultra-low fields. The whole rocks almost certainly contain some large multidomain grains. Here we investigate the possibility that the high temperature slope is a field overestimate, reflecting not the true ambient field but rather the dominant viscous overprint that has contaminated higher unblocking temperatures. If correct, it is further possible that this overprint might be concealing even lower ambient fields, or a complete collapse of the dynamo. We will discuss our plans to experimentally assess this hypothesis.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 4
    Electronic Resource
    Electronic Resource
    Versatile millimeter-wave interferometer with two frequencies in the divertor region of JT-60U (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3181-3185 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A millimeter-wave interferometer having a capability of concomitant electron temperature measurement, based on the electron cyclotron absorption (ECA) technique, has been developed for divertor diagnostics in JT-60U. Three lines of sight, which pass through the X point horizontally, the inboard divertor and the outboard divertor, are chosen. Two transmitter/receiver units with frequencies of 217 and 183 GHz are employed in order to eliminate the spurious vibration effect using a two color scheme. The two independent units are also arranged to enable two sight line measurements without the vibration compensation. Furthermore, these units allow us to apply the simultaneous ECA diagnostic. Due to the complexity of the transmission line inside the tokamak, the insertion loss is as large as 65 dB. However, the interferometer system can be operated with the signal-to-noise (S/N) ratio of about 20 dB due to the low equivalent input noise of −90 dB m. The measurements performed for several types of the JT-60U discharges indicate the feasibility of the system and the rapid reduction of the electron density near the X point at the high confinement mode transition is first demonstrated. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149081
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  • 5
    Electronic Resource
    Electronic Resource
    Raman scattering of (GaAs)n(GaP)n short-period superlattices prepared by pulsed jet epitaxy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6713-6715 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have carried out the Raman-scattering measurement of (GaAs)n(GaP)n short-period superlattices (n=1–5) prepared by the atomic layer epitaxy technique called pulsed jet epitaxy (PJE). The zone-folding effects on the longitudinal-acoustic (LA) phonon were observed for all the samples. The Raman peak observed for the (GaAs)1(GaP)1 monolayer superlattice has also been tentatively assigned to the scattering from zone-folded LA phonons. If the assignment is correct, this is the first observation of the zone-folded LA phonon in a semiconductor monolayer superlattice. The present results suggest that the growth proceeds atomic layer by atomic layer in PJE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348893
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  • 6
    Electronic Resource
    Electronic Resource
    Comparative study of self-limiting growth of GaAs using different Ga-alkyl compounds: (CH3)3Ga, C2H5(CH3)2Ga, and (C2H5)3Ga (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5660-5664 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the self-limiting growth of GaAs using three kinds of Ga-alkyl compounds−trimethylgallium (TMGa), ethyldimethylgallium, and triethylgallium−as atomic layer epitaxy (ALE) sources. Perfect self-limiting behavior was found only for TMGa. The self-limiting mechanism could be explained by the surface site selectivity of the metalorganic molecules in the adsorption, desorption, and decomposition processes. We found that the degree of the site selectivity declined as methyl groups attached to a Ga atom were replaced by ethyl groups. We believe that the TMGa molecule is adsorbed without decomposition in the first step, and then fully decomposed into Ga. Three methyl groups of the adsorbed TMGa play an important role in the site selectivity and make the growth self-limited. We studied the evolution of the chemical state of the TMGa-exposed (001) GaAs surface by changing the length of the interruption following a TMGa pulse. There was no change in the surface chemical conditions and in the degree of self-limiting during the H2 purge after TMGa pulse. These results provide a detailed understanding of the surface chemistry and self-limiting growth involved in ALE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346980
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  • 7
    Electronic Resource
    Electronic Resource
    Performance characteristics of a high-pressure pulsed singlet oxygen generator (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5760-5767 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The characteristics of a high-pressure pulsed singlet oxygen generator is investigated. This generator was designed for the energy source of new pulsed chemical lasers. A ceramic porous pipe is devised in it to attain the high-pressure pulsed operation. New methods were developed to measure a water vapor pressure and a reaction efficiency in the pulsed singlet oxygen generator system. The maximum singlet oxygen pressure obtained was 35 Torr, and the estimated initial excitation efficiency was 70%–80%
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350469
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  • 8
    Electronic Resource
    Electronic Resource
    New approach to the atomic layer epitaxy of GaAs using a fast gas stream (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 1509-1511 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new growth method has been developed for the atomic layer epitaxy of GaAs. The gas system was based on a conventional metalorganic vapor phase epitaxial system but the decomposition of methylgallium was suppressed in the stagnant layer by using a fast pulsed gas stream from a jet nozzle. The method enabled us to grow high purity epitaxial layers with a clear self-limiting mechanism even at 560 °C. The variations in the growth rate with respect to various growth parameters were explained by the rate equations based on the selective adsorption of methylgallium on surface As atoms. The decomposition rate of methylgallium on the surface had an activation energy of 42 kcal/mole from 440 to 560 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99941
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  • 9
    Electronic Resource
    Electronic Resource
    Atomic layer epitaxy of GaP and elucidation for self-limiting mechanism (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 827-829 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Atomic layer epitaxy (ALE) of GaP was performed for the first time in a low-pressure metalorganic vapor phase epitaxial (MOVPE) reactor using trimethylgallium (TMG) and phosphine (PH3) as sources. Growth was self-limiting for the exposure time of each reactant. X-ray photoelectron spectroscopy (XPS) analyses were carried out to identify the adsorbates on the growth surface. There were no methyl groups on the surface Ga and the self-limiting mechanism is due to the selective adsorption of TMG by the surface P atoms. When the substrate was exposed to a sufficient TMG flow after a submonolayer Ga was deposited by triethylgallium (TEG), growth was still self-limiting. This supports the selective adsorption model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102675
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  • 10
    Electronic Resource
    Electronic Resource
    In situ x-ray photoelectron spectroscopic study of GaAs grown by atomic layer epitaxy (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 656-657 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We carried out an in situ investigation of GaAs grown by atomic layer epitaxy, using an x-ray photoelectron spectroscopy system combined with a metalorganic vapor phase epitaxial growth chamber, where Ga(CH3)3 and AsH3 were the source gases. It has been proved that Ga(CH3)n molecules (where n=1 or 2) are decomposed into Ga atoms after being adsorbed on the GaAs surface around 500 °C. This means that the self-limited adsorption of Ga in the atomic layer epitaxy of GaAs can be achieved on the surface where the Ga adsorbate is atomic Ga.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100909
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