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  • 1995-1999  (6)
  • 1940-1944
  • 1860-1869
  • 1996  (6)
  • 1
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ground-based optical observations coordinated with Yohkoh/SXT X-ray observations of an old, disintegrating bipolar active region AR NOAA 7493 (May 1, 1993) provided a multiwavelength data base to study a flaring ‘active region’ X-ray bright point (XBP) of about 16 hr lifetime, and the activity related to it in different layers of the solar atmosphere. The XBP appeared to be related to a new minor bipole of about 1020 Mx. Superposed on a global evolution of soft X-ray brightness, the XBP displayed changes of brightness, lasting for 1–10 min. During the brightenings the XBP apparently had a spatial structure, which was (tiny) loop-like rather than point-like. The X-ray brightenings were correlated with chromospheric activity: (i) brightenings of underlying chromospheric faculae, and (ii) appearance of strong turbulent velocities in the arch filament system. We propose that the XBP brightenings were due to reconnection of the magnetic field lines (sketched in 3D) between the new bipole and a pre-existing plage field induced by the motion of one of the new pores (v = 0.2 km s−1) towards the plage, and that the XBP itself was a reconnected hot loop between them.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract On May 1, 1993, a flaring X-ray bright point (XBP) was observed for about 16 hours in the old, disintegrating, bipolar active region (AR) NOAA 7493. During this period, a minor magnetic bipole (1020 Mx) emerged in the region. We have found observational evidence showing that the XBP brightenings were due to magnetic reconnection between the new bipole and pre-existing plage fields. The aim of the present work is to substantiate with magnetic modelling what has been shown by the observations. For this purpose we extrapolate the observed photospheric magnetic fields in the linear force-free approximation and follow its evolution during the lifetime of the XBP. From the computed coronal field lines we determine the location of regions of drastic change in field-line linkage, called ‘quasi-separatrix layers’ or QSLs. QSLs are open layers that behave physically like separatrices: the break down of ideal magnetohydrodynamics and the release of free magnetic energy may occur at these locations when their thickness is small enough. The extrapolated field lines, with photospheric footpoints on both sides of QSLs, match the observed chromospheric and coronal structures (arch filament system, XBP and faint X-ray loops (FXL)). We study also the evolution of the width of the QSL located over the new negative polarity pore: the calculated QSL is very thin (typically less than 100 m) during the lifetime of the XBP, but becomes much thicker (≥ 104 m) after the XBP has faded. Furthermore we show that peaks in X-ray brightness propagate along the FXL with a velocity of ≈ 670 km s-1, starting from the XBP location, implying that the energy is released where the emerging bipole impacts against pre-existing coronal loops. We discuss the possible mechanism of energy transport and conclude that the energy is conducted to the remote footpoints of the FXL by a thermal front. These results strongly support the supposition that the XBP brightness and flaring are due to the interaction of different flux systems, through 3D magnetic reconnection, at QSLs.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  In the central Vetreny Belt, southeastern Baltic Shield, an areally extensive 110 m deep lava lake is exposed consisting of remarkably fresh differentiated komatiitic basalt. During eruption, the liquid had a temperature of 1380–1400 °C and contained ∼15% MgO. The lava ponded in a large topographic depression soon after eruption. The differentiation of the lava lake was controlled by settling of transported olivine and chromite phenocrysts and caused the origin of prominent internal layering. The last portions of the trapped liquid crystallized at temperatures of 1250– 1070 °C. A Sm-Nd isochron of 2410±34 Ma for whole rock samples, olivine, augite and pigeonite separates from the lava lake provides a reliable estimate for the time of formation of the uppermost sequences in the Vetreny Belt. This age is in good agreement with the Sm-Nd and Pb-Pb isochron ages of 2449±35 and 2424±178 Ma for the volcanic rocks from the same stratigraphic level in the northwestern Vetreny Belt. Modeling of Nd-isotopes and major and trace elements shows that the komatiitic basalts at Lion Hills may have had a komatiite parent depleted in highly incompatible elements. It can be shown that this initial liquid was contaminated by 7–9% of Archaean upper crustal material from the adjacent Vodla and Belomorian Blocks en route to the surface thus acquiring the observed geochemical and isotope signatures including relative enrichment in Zr, Ba, and LREE, negative Nb- and Ti-anomalies and ɛNd(T) of −1.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Mantle peridotites of the Internal Liguride (IL) units (Northern Apennines) constitute a rare example of the depleted lithosphere of the Jurassic Ligurian Tethys. Detailed chemical (ICP-MS and SIMS techniques) and isotopic investigations on very fresh samples have been performed with the major aim to constrain the timing and mechanism of their evolution and to furnish new data for the geodynamic interpretation. The data are also useful to discuss some general geochemical aspects of oceanic-type mantle. The studied samples consist of clinopyroxene-poor spinel lherzolites, showing incipient re-equilibration in the plagioclase-facies stability field. The spinel-facies assemblage records high (asthenospheric) equilibration temperatures (1150–1250° C). Whole rocks, and constituent clinopyroxenes, show a decoupling between severe depletion in highly incompatible elements [light rare earth elements (LREE), Sr, Zr, Na, Ti] and less pronounced depletion in moderate incompatible elements (Ca, Al, Sc, V). Bulk rocks also display a relatively strong M(middle)REE/H(heavy)REE fractionation. These compositional features indicate low-degree (〈10%) fractional melting, which presumably started in the garnet stability field, as the most suitable depletion mechanism. In this respect, the IL ultramafics show strong similarity to abyssal peridotites. The Sr and Nd isotopic compositions, determined on carefully handpicked clinopyroxene separates, indicate an extremely depleted signature (87Sr/86Sr=0.702203–0.702285; 143Nd/144Nd=0.513619–0.513775). The Sm/Nd model ages suggest that the IL peridotites melted most likely during Permian times. They could record, therefore, the early upwelling and melting of mid ocean ridge basalt (MORB) type asthenosphere, in response to the onset of extensional mechanisms which led to the opening of the Western Tethys. They subsequently cooled and experienced a composite subsolidus evolution testified by multiple episodes of gabbroic intrusions and HT-LP retrograde metamorphic re-equilibration, prior to their emplacement on the sea floor. The trace element chemistry of IL peridotites also provides useful information about the composition of oceanic-type mantle. The most important feature concerns the occurrence of Sr and Zr negative anomalies (relative to “adjacent” REE) in both clinopyroxenes and bulk rocks. We suggest that such anomalies reflect changes in the relative magnitude of Sr, Zr and REE partition coefficients, depending on the specific melting conditions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Der Chirurg 67 (1996), S. 779-787 
    ISSN: 1433-0385
    Keywords: Key words: Malignant melanoma ; Lymph node metastases ; Lymph node dissection ; Prognosis. ; Schlüsselwörter: Malignes Melanom ; Lymphknotenmetastasierung ; Lymphknotendissektion ; Prognose.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung. Die Indikation zur elektiven Lymphknotendissektion, ihre evtl. zukünftige Bedeutung als Stagingmaßnahme vor adjuvanten Therapieverfahren, die Prognose der therapeutischen Dissektion sowie die Identifizierung des Pförtner-Lymphknotens und die daraus sich ergebenden therapeutischen Konsequenzen sind die wichtigsten Aspekte der Lymphknotendissektion beim malignen Melanom. Die Indikation zur elektiven Dissektion orientiert sich nicht nur an der pT-Kategorie, sondern auch an der Tumorlokalisation, dem Tumortyp und dem Geschlecht des Patienten. Ein allgemein akzeptierter Konsens zur Auswahl der in Frage kommenden Patienten besteht noch nicht. Da die ersten Studien mit Chemo-/Immuntherapie bei nodal positiven Patienten eine Prognoseverbesserung zeigen, muß zukünftig auch die Lymphknotendissektion als Stagingmaßnahme diskutiert werden. Neue Anregungen wurden in den letzten Jahren durch die Identifikation des Pförtner(„sentinel“)-Lymphknotens eingebracht. Diese Methodik bedarf noch der weiteren Evaluierung, dürfte aber zukünftig einen wesentlichen Einfluß auf die Indikation zur elektiven Lymphknotendissektion nehmen. Mit eingetretener Lymphknotenmetastasierung verschlechtert sich die Prognose des malignen Melanoms global um 20–50 %, abhängig vom Ausmaß der Metastasierung. Die Thematik wird anhand der eigenen Ergebnisse diskutiert.
    Notes: Summary. Elective lymph node dissection and its potential as a staging procedure, the prognosis of established lymph node metastases and the sentinel lymph node identification procedure are the most important aspects of lymph node dissection in malignant melanoma. It is widely accepted that subgroups of patients benefit from elective lymph node dissection. The question of which parameters identify the relevant patients properly is still under discussion. pT-categories are the most important prognostic factor; however, localisation and type of tumour and the sex of the patients are additional parameters influencing patient selection. Recently, the first studies have identified subgroups of nodal positive patients who would profit from adjuvant chemo-/immunotherapy. Therefore, lymph node dissection as a staging procedure has to be discussed in the future. Identification of the sentinel lymph node is receiving increasing attention because of its potential influence on the reassessment of elective lymph node dissection. However, this method needs further evaluation. If lymph node metastases have occurred, the prognosis of malignant melanoma decreases by 20 %–50 %, depending on the extent of metastasis in the individual case. The relevant topics and results are discussed on the basis of data of the Surgical Department of the University Hospital of Erlangen-Nuremberg.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 164 (1996), S. 321-332 
    ISSN: 1573-093X
    Keywords: Polarimetry ; Sunspots
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A Fabry-Perot interferometer is being used for two-dimensional spectropolarimetric measurements. We demonstrate the suitability of the setup for the measurement of the magnetic field and present some preliminary results from first observations.
    Type of Medium: Electronic Resource
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