Friedmann universe as a limit of dust shell model     

A. Eid  J. Langer 《Astrophysics and Space Science》2012,337(2):747-752

We generalize the equations of motion of a shell for a sequence of thin shells and derive the general form of the expansion law of the dust shell model which represents the FRW universe when we take an appropriate limit. The three Friedmann model for the three possible values of k:0,±1 are satisfied.  相似文献   

Prediction of ground motion parameters for the volcanic area of Mount Etna     

Giuseppina Tusa  Horst Langer 《Journal of Seismology》2016,20(1):1-42

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Life cycles of spots on Jupiter from Cassini images     

Liming Li  Andrew P. Ingersoll  Carolyn C. Porco  Shawn P. Ewald 《Icarus》2004,172(1):9-23

Using the sequence of 70-day continuum-band (751 nm) images from the Cassini Imaging Science System (ISS), we record over 500 compact oval spots and study their relation to the large-scale motions. The ∼100 spots whose vorticity could be measured—the large spots in most cases—were all anticyclonic. We exclude cyclonic features (chaotic regions) because they do not have a compact oval shape, but we do record their interactions with spots. We distinguish probable convective storms from other spots because they appear suddenly, grow rapidly, and are much brighter than their surroundings. The distribution of lifetimes for spots that appeared and disappeared during the 70-day period follows a decaying exponential with time constant (mean lifetime) of 3.5 days for probable convective storms and 16.8 days for all other spots. Extrapolating the exponential beyond 70 days seriously underestimates the number of spots that existed for the entire 70-day period. This and other evidences (size, shape, distribution in latitude) suggest that these long-lived spots with lifetime larger than 70 days are from a separate population. The zonal wind profile obtained manually by tracking individual features (this study) agrees with that obtained automatically by correlating brightness variations in narrow latitude bands (Porco et al., 2003). Some westward jets have developed more curvature and some have developed less curvature since Voyager times, but the number of westward jets that violate the barotropic stability criterion is about the same. In the northern hemisphere the number of spots is greatest at the latitudes of the westward jets, which are the most unstable regions according to the barotropic stability criterion. During the 70-day observation period the Great Red Spot (GRS) absorbed nine westward-moving spots that originated in the South Equatorial Belt (SEB), where most of the probable convective storms originate. Although the probable convective storms do not directly transform themselves into westward-moving spots, their common origin in the SEB suggests that moist convection and the westward jet compose a system that has maintained the GRS over its long lifetime.  相似文献   

The IRS 1 circumstellar disk, and the origin of the jet and CO outflow in B5     

Langer WD  Velusamy T  Xie T 《The Astrophysical journal》1996,468(1):L41-L44

We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall.  相似文献   

Statistical analyses and characteristics of volcanic tremor on Stromboli Volcano (Italy)     

S. Falsaperla  H. Langer  S. Spampinato 《Bulletin of Volcanology》1998,60(2):75-88

 A study of volcanic tremor on Stromboli is carried out on the basis of data recorded daily between 1993 and 1995 by a permanent seismic station (STR) located 1.8 km away from the active craters. We also consider the signal of a second station (TF1), which operated for a shorter time span. Changes in the spectral tremor characteristics can be related to modifications in volcanic activity, particularly to lava effusions and explosive sequences. Statistical analyses were carried out on a set of spectra calculated daily from seismic signals where explosion quakes were present or excluded. Principal component analysis and cluster analysis were applied to identify different classes of spectra. Three clusters of spectra are associated with two different states of volcanic activity. One cluster corresponds to a state of low to moderate activity, whereas the two other clusters are present during phases with a high magma column as inferred from the occurrence of lava fountains or effusions. We therefore conclude that variations in volcanic activity at Stromboli are usually linked to changes in the spectral characteristics of volcanic tremor. Site effects are evident when comparing the spectra calculated from signals synchronously recorded at STR and TF1. However, some major spectral peaks at both stations may reflect source properties. Statistical considerations and polarization analysis are in favor of a prevailing presence of P-waves in the tremor signal along with a position of the source northwest of the craters and at shallow depth. Received: 15 December 1996 / Accepted: 31 March 1998  相似文献   

Input parameters for estimating seismic loading     

H. Langer 《Natural Hazards》1990,3(2):125-139

The estimation of seismic loading requires both the featuring of the seismotectonic environment as well as a prognosis of site-specific strong ground-motion parameters. Due to the long recurrence times of larger events, there is a lack of high quality strong motion recordings at many sites. The use of seismograms obtained from different seismotectonic regions, additionally recorded under different subsoil conditions, poses several questions as to the significance of the assessment of seismic loading. A way to overcome these problems is the generation of synthetic seismograms, e.g. by the use of Boore's stochastic procedure. Subsoil conditions may be explicitly included in the simulation as proposed by Kunze et al. In this context, the seismotectonic environment forms the deterministic frame of any stochastic strong ground-motion simulation. In terms of Boore's approach, seismic moment, global stress drop, high frequency cut off, and focal depth act as controlling parameters. In order to achieve a more realistic assessment of possible seismic loading, a classification of seismoactive zones should account for parameter vectors as described above rather than for single parameters like magnitudes or intensities. A tool to attack this task may be found in cluster analysis, which is a type of pattern recognition based on statistical considerations. Crucial to this technique, however, is the use of properly estimated parameters, which still cause discussion in the seismological community. Problems and chances of the approach are discussed with examples from the Swabian Jura and the Rhine graben.Paper presented at the 21st General Assembly of the European Seismological Commission held in Sofia, 1988.  相似文献   

On the origin of tunnel valleys of the Saginaw Lobe of the Laurentide Ice Sheet; Michigan,USA     

Alan E. Kehew  Stephanie K. Ewald  John M. Esch  Andrew L. Kozlowski 《Boreas: An International Journal of Quaternary Research》2013,42(2):442-462

Tunnel valleys are common throughout the terrain of the Saginaw Lobe of the Laurentide Ice Sheet in southern Michigan. The set of valleys described in this paper is regularly spaced in a radial pattern behind the Kalamazoo Moraine, an ice‐marginal position formed during retreat from the Last Glacial Maximum. These valleys are divided into proximal and distal groups lying north and south, respectively, of a major river valley that cross‐cuts the tunnel valleys at right angles. Based on a series of rotasonic borings and core analysis, the proximal valleys are shallow, contain minimal sediment fill, and overlie fine‐grained diamicton and glaciolacustrine sediment, whereas the distal valleys are deeply incised into the substrate and are partially filled with coarse sediment. The distal valleys terminate within a broad zone of high‐relief, hummocky topography representing stagnation and collapse behind the Kalamazoo ice margin. The proximal valleys occur within a more subdued landscape located farther from the ice margin. Although some elements of existing genetic models are consistent with these valleys, none appears to be completely compatible with their stratigraphy and morphology. Initial incision of the valleys could have involved short‐lived moderate‐ to high‐discharge flows, followed by deposition during or after the events. The deep incision and thick, coarse sediment in distal valleys in the stagnant marginal zone probably involved supraglacial meltwater draining to the bed as the margin downwasted. Fining‐upward eskers inset into the valleys were formed by flows of declining energy in small late‐stage conduits.  相似文献   

ANTARES – A Numerical Tool for Astrophysical RESearch with applications to solar granulation     

H.J. Muthsam  F. Kupka  B. Löw-Baselli  C. Obertscheider  M. Langer  P. Lenz 《New Astronomy》2010,15(5):460-475

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Deep alpine valleys: examples of geophysical explorations in Austria     

Ewald Brückl  Johanna Brückl  Werner Chwatal  Christian Ullrich 《Swiss Journal of Geoscience》2010,103(3):329-344

Results from geophysical explorations of three deep valleys, selected from different tectonic regimes in the Eastern Alps (Ötz-, Oichten-, and Drau Valley), are presented and discussed. Ongoing tectonic deformation may use tectonic structures related to these valleys. However, seismic activity is low there. During the Würm ice age, the thickness of the ice cover ranged between 300 and 1,500 m above present ground elevation. The geophysical investigations comprised reflection seismology, gravity- and resistivity surveys. The maximum depth down to the erosional base of the valleys varies from ~340 to 700 m. Distinct layer packages of the valley-infill at depths greater than 250 m were termed “old valley-fill”. Geophysical parameters and a comparison with the reflection seismic image of an intermediate layer at the recent Pasterze glacier suggest that the top of the “old valley-fill” represents the glacier bed during the decay of the Würm glaciation. Deep erosion is not related to high basal shear stress. The confluence of tributary glaciers is apparently not a significant factor for deep erosion in our examples of deep alpine valleys. We conclude that deep erosion may be related to high water pressure at the glacier bed, supported by specific processes of tectonic weakening.  相似文献   

Waves in Jupiter's atmosphere observed by the Cassini ISS and CIRS instruments     

Liming Li  Andrew P. Ingersoll  Amy A. Simon-Miller  Shawn P. Ewald  Carolyn C. Porco  F. Michael Flasar 《Icarus》2006,185(2):416-429

The Cassini Imaging Science Subsystem (ISS) and Composite Infrared Spectrometer (CIRS) reported a North Equatorial Belt (NEB) wave in Jupiter's atmosphere from optical images [Porco, C.C., and 23 colleagues, 2003. Science 299, 1541-1547] and thermal maps [Flasar, F.M., and 39 colleagues, 2004. Nature 427, 132-135], respectively. The connection between the two waves remained uncertain because the two observations were not simultaneous. Here we report on simultaneous ISS images and CIRS thermal maps that confirm that the NEB wave shown in the ISS ultraviolet (UV1) and strong methane band (MT3) images is correlated with the thermal wave in the CIRS temperature maps, with low temperatures in the CIRS maps (upwelling) corresponding to dark regions in the UV1 images (UV-absorbing particles) and bright regions in the MT3 images (high clouds and haze). The long period of the NEB wave suggests that it is a planetary (Rossby) wave. The combined observations from the ISS and CIRS are utilized to discuss the vertical and meridional propagation of the NEB wave, which offers a possible explanation for why the NEB wave is confined to specific latitudes and altitudes. Further, the ISS UV1 images reveal a circumpolar wave centered at 48.5° S (planetocentric) and probably located in the stratosphere, as suggested by the ISS and CIRS observations. The simultaneous comparison between the ISS and CIRS also implies that the large dark oval in the polar stratosphere of Jupiter discovered in the ISS UV1 images [Porco, C.C., and 23 colleagues, 2003. Science 299, 1541-1547] is the same feature as the warm regions at high northern latitudes in the CIRS 1-mbar temperature maps [Flasar, F.M., and 39 colleagues, 2004. Nature 427, 132-135]. This comparison supports a previous suggestion that the dark oval in the ISS UV1 images is linked to auroral precipitation and heating [Porco, C.C., and 23 colleagues, 2003. Science 299, 1541-1547].  相似文献