5,677 research outputs found
Motlles naturals de microperforacions a eolianites del Pleistocè i Pliocè mallorquí
En aquest treball estudiem els motlles naturalis de microperforacions, actualment de LMC, en substrats de fragments de mol·luscs. L'aragonita de les closques fou dissolt en condicions vadoses continentals, amb la consegüent posada en relleu dels motlles i de la "micritic envelope".Els materials estudiats son eolianites d'edat Riss i Pliocenes, de diversos afloraments de Mallorca. Hi hem observat quatre tipus de motlles que suposem que foren produits per l'acció perforant de quatre microorganismes diferents. S'hi analitza la història diagenètica dels motlles
Wavelet versus Detrended Fluctuation Analysis of multifractal structures
We perform a comparative study of applicability of the Multifractal Detrended
Fluctuation Analysis (MFDFA) and the Wavelet Transform Modulus Maxima (WTMM)
method in proper detecting of mono- and multifractal character of data. We
quantify the performance of both methods by using different sorts of artificial
signals generated according to a few well-known exactly soluble mathematical
models: monofractal fractional Brownian motion, bifractal Levy flights, and
different sorts of multifractal binomial cascades. Our results show that in
majority of situations in which one does not know a priori the fractal
properties of a process, choosing MFDFA should be recommended. In particular,
WTMM gives biased outcomes for the fractional Brownian motion with different
values of Hurst exponent, indicating spurious multifractality. In some cases
WTMM can also give different results if one applies different wavelets. We do
not exclude using WTMM in real data analysis, but it occurs that while one may
apply MFDFA in a more automatic fashion, WTMM has to be applied with care. In
the second part of our work, we perform an analogous analysis on empirical data
coming from the American and from the German stock market. For this data both
methods detect rich multifractality in terms of broad f(alpha), but MFDFA
suggests that this multifractality is poorer than in the case of WTMM.Comment: substantially extended version, to appear in Phys.Rev.
Cronoestratigrafía (Palinología) del Triásico Sudpirenaico y del Pirineo Vasco-Cantábrico
This paper presients a general chronostratigraphy of the south Pyrenean Triassic basi:d on palynological studies. The Triassic in Les Nogueres-Cadí and the Basque Country areas is divided into the Buntsandstein, Muschelkalk and Keuper facies and the Isábena Forrnation. The Conglomeratic, sandstone and lutitic Unit of the Buntsandstein in the Puerto dr Otxondo (Basque Country) presents Stellapollenites thiergartii and together with the absence of Praecirculina granifer, suggests a Lower-middle Anisian age. The Lutitic Unit of the Buntsandstein in Igüem, Sant Sebastia de Buseu and Baga (Les Nogueres-Cadí) presenits Illinites kosankeii and Stellapollenites thiergartii, and the absence of Praecirculina granifer, indicates a Lower Anisian age. The Muschelkailk in Hostalets (Les Nogueres) presents Camerosporites secatus, suggesting an upper Ladinian age. The transit zone between the Muschelkaik and the Keuper facies in Odkn (Cadí) shows a palynological assemblage with Patinasporites densus, Partitisporites quadruplicis and Staurosaccites quadrifidus, indicating a Camain age, possibly Middie-upper Camian. The lower part of the Keuper in Noguera de Tor and Adons, in the Les Nogueres area, presents a palynological assemblage with Classopollis, Granuloperculatipollis rudis, Ovalipollis ovalis, Praecirculina granifer and Triadispora. The abundance of Classopollis and the presence of Granul~p~erculatipollrius dis suggest a Norian age, possibly lower-middle. The upper part of the Keuper in La Nou (Pedraforca) is Rhaetian in age due to the presence of cf. Deltaidospora and cf. Taeniasporites. The base of tlie Isábena Formation in Noves de Segre presents Corollina zwolinskae and Cerebropollenites pseudomassulae, indicating a Rhaetian age. The palynological studies, together with the forarninifera and conodonta data, deteimine the existence of important stratigraphicc hiatuses in the south Pyrenean Triassic supercycle
Quantitative features of multifractal subtleties in time series
Based on the Multifractal Detrended Fluctuation Analysis (MFDFA) and on the
Wavelet Transform Modulus Maxima (WTMM) methods we investigate the origin of
multifractality in the time series. Series fluctuating according to a qGaussian
distribution, both uncorrelated and correlated in time, are used. For the
uncorrelated series at the border (q=5/3) between the Gaussian and the Levy
basins of attraction asymptotically we find a phase-like transition between
monofractal and bifractal characteristics. This indicates that these may solely
be the specific nonlinear temporal correlations that organize the series into a
genuine multifractal hierarchy. For analyzing various features of
multifractality due to such correlations, we use the model series generated
from the binomial cascade as well as empirical series. Then, within the
temporal ranges of well developed power-law correlations we find a fast
convergence in all multifractal measures. Besides of its practical significance
this fact may reflect another manifestation of a conjectured q-generalized
Central Limit Theorem
The Spatial Distribution of Fluorescent H Near T Tau
New subarcsecond FUV observations of T Tau with HST/STIS show spatially
resolved structures in the 2"x2" area around the star. The structures show in
multiline emission of fluorescent H_2 pumped by Lyman alpha. One emission
structure follows the cavity walls observed around T Tau N in scattered light
in the optical. A temperature greater or equal to 1000K is required to have
enough population in the H_2 to produce the observed fluorescent lines; in the
cool environment of the T Tau system, shock heating is required to achieve this
temperature at distances of a few tens of AU. Fluorescent H_2 along the cavity
wall represents the best evidence to date for the action of low-density,
wide-opening-angle outflows driving cavities into the molecular medium at
scales smaller than 100 AU. A southern region of emission consists of two arcs,
with shape and orientation similar to the arcs of H_2 2.12 microns and
forbidden line emission crossing the outflow associated with the embedded
system T Tau S. This region is located near the centroid of forbidden line
emission at the blueshifted lobe of the N-S outflow.Comment: To appear in ApJ, vol. 591. Color figures available online at
http://cfa-www.harvard.edu/cfa/youngstars
Laser Guide Star Adaptive Optics Integral Field Spectroscopy of a Tightly Collimated Bipolar Jet from the Herbig Ae star LkHa 233
We have used the integral field spectrograph OSIRIS and laser guide star
adaptive optics at Keck Observatory to obtain high angular resolution (0.06"),
moderate spectral resolution (R ~ 3800) images of the bipolar jet from the
Herbig Ae star LkHa 233, seen in near-IR [Fe II] emission at 1.600 & 1.644
microns. This jet is narrow and tightly collimated, with an opening angle of
only 9 degrees, and has an average radial velocity of ~ 100 km/s. The jet and
counterjet are asymmetric, with the red-shifted jet much clumpier than its
counterpart at the angular resolution of our observations. The observed
properties are in general similar to jets seen around T Tauri stars, though it
has a relatively large mass flux of (1.2e-7 +- 0.3e-7) M_sun/year, near the
high end of the observed mass flux range around T Tauri stars. We also
spatially resolve an inclined circumstellar disk around LkHa 233, which
obscures the star from direct view. By comparison with numerical radiative
transfer disk models, we estimate the disk midplane to be inclined i = 65 +- 5
degrees relative to the plane of the sky. Since the star is seen only in
scattered light at near-infrared wavelengths, we detect only a small fraction
of its intrinsic flux. Because previous estimates of its stellar properties did
not account for this, either LkHa 233 must be located closer than the
previously believed, or its true luminosity must be greater than previously
supposed, consistent with its being a ~4 M_sun star near the stellar birthline.Comment: Accepted for publication in the Ap
Interferometría SAR en las islas Shetland del Sur: modelo numérico de elevaciones de la Isla Decepción
Satellite Synthetic Aperture Radar (SAR) interferometry is a technique that allows the generation of altimetric information. The technique is higly useful in remote areas and this paper shows an application of SAR interferometry in the South Shetland Islands (Antarctica). SAR images obtained by the ERS (European Remote Sensing) satellites of the European Space Agency (ESA) have been processed with an interferometric processor developed by the Departament de Geodinàmica i Geofísica of the Universitat de Barcelona in collaboration with the Institut Cartogràfic de Catalunya
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