166 research outputs found
Trace fossil Artichnus pholeoides igen. nov. isp. nov. in Eocene turbidites, Polish Carpathians : possible ascription to holothurians
A hitherto unknown trace fossil was found in some abundance in turbidites of the Polish Outer Carpathians. The occurrence is within the Hieroglyphic Beds of the Silesian Nappe, within the Szczyrzyc Synclinorium, of Middle Eocene age. The trace fossil is a wide, J-shaped structure having a narrow, upward tapering shaft as a connection to the seafloor. The distal end also tapers, to a blind termination. The burrow lumen is surrounded by an irregular spreite structure. The trace fossil is compared with the work of burrowing holothurians, which show some comparative features that suggest a tracemaker belonging to the Apodida
S’Estret des Temps: registro cuaternario, eolianitas y estructuras asociadas
Abstract not availabl
Problems in Interpreting Unusually Large Burrows
Although marine burrows of unusually large dimensions have long been known in certain areas, they are probably much more widespread in the rock record than is generally recognized. Such burrows constitute a heterogeneous group, having little in common other than exceptional size. Yet their size alone unites them in difficulty of interpretation: e.g., densely spaced-dwelling burrows of combined dwelling-escape burrows as much as 12 cm in diameter and 5 m long; vertical dwelling burrows only 0.5 cm in diameter but up to 9 m long; possible escape structures as much as 24 cm in diameter and 3 m long, subsequently penetrated in some cases by secondary burrow-like structures.
Numerous special problems are encountered in the study and interpretation of burrows of these extreme dimensions: (1) field exposure and accessibility, so that the full extent, or a large part, of the structures can be studied; (2) preservation of the burrows in continuity, not merely in places where they pass through certain beds or within concretion horizons; (3) the fossilization barrier ; our knowledge of comparable modern structures of similar dimensions or of the animals responsible for them is negligible; and (4) the possibility that certain of these unusual structures were formed by physical rather than organic processes; again, our criteria for comparisons are limited.
The examples selected by us—from the Permian of Montana, Idaho, and Wyoming, the Cretaceous and Paleocene of northwestern Europe, and the Pleistocene of North Carolina—are intended primarily (1) to call additional attention to such intriguing structures, and (2) to illustrate some of the problems involved in interpreting their origin and function. Hopefully, future work will solve many of these problems
Bioerosion of Lower Ordovician Hardgrounds in Southern Scandinavia and Western North America.
Trace fossils produced by macroboring invertebrates can be found in carbonate hardgrounds of early Ordovician age in southern Sweden, southern Norway and western Utah (U.S.A.). The bioeroded rocks are highly fossiliferous, thinly bedded, shallow-marine li-mestones. The macroborings in each of the three localities are vase-shaped cavities with diameters and lengths ranging from one to a few centimeters. At least some of the Swedish specimens apparently belong to the ichnogenus Gastrochaenolites LEYMERIE. These bioerosion trace fossils appear to be the oldest macroborings in carbonate hardgrounds, and they indicate that the macroboring niche was firmly established in shallow-marine carbonate shelf environments at least by Arenig time in the Ordovician Period
The Periodic Standing-Wave Approximation: Overview and Three Dimensional Scalar Models
The periodic standing-wave method for binary inspiral computes the exact
numerical solution for periodic binary motion with standing gravitational
waves, and uses it as an approximation to slow binary inspiral with outgoing
waves. Important features of this method presented here are: (i) the
mathematical nature of the ``mixed'' partial differential equations to be
solved, (ii) the meaning of standing waves in the method, (iii) computational
difficulties, and (iv) the ``effective linearity'' that ultimately justifies
the approximation. The method is applied to three dimensional nonlinear scalar
model problems, and the numerical results are used to demonstrate extraction of
the outgoing solution from the standing-wave solution, and the role of
effective linearity.Comment: 13 pages RevTeX, 5 figures. New version. A revised form of the
nonlinearity produces better result
Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA
Inclusive photoproduction of D*+- mesons has been measured for photon-proton
centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality
Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of
37 pb^-1. Total and differential cross sections as functions of the D*
transverse momentum and pseudorapidity are presented in restricted kinematical
regions and the data are compared with next-to-leading order (NLO) perturbative
QCD calculations using the "massive charm" and "massless charm" schemes. The
measured cross sections are generally above the NLO calculations, in particular
in the forward (proton) direction. The large data sample also allows the study
of dijet production associated with charm. A significant resolved as well as a
direct photon component contribute to the cross section. Leading order QCD
Monte Carlo calculations indicate that the resolved contribution arises from a
significant charm component in the photon. A massive charm NLO parton level
calculation yields lower cross sections compared to the measured results in a
kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure
Measurement of Jet Shapes in Photoproduction at HERA
The shape of jets produced in quasi-real photon-proton collisions at
centre-of-mass energies in the range GeV has been measured using the
hadronic energy flow. The measurement was done with the ZEUS detector at HERA.
Jets are identified using a cone algorithm in the plane with a
cone radius of one unit. Measured jet shapes both in inclusive jet and dijet
production with transverse energies GeV are presented. The jet
shape broadens as the jet pseudorapidity () increases and narrows
as increases. In dijet photoproduction, the jet shapes have been
measured separately for samples dominated by resolved and by direct processes.
Leading-logarithm parton-shower Monte Carlo calculations of resolved and direct
processes describe well the measured jet shapes except for the inclusive
production of jets with high and low . The observed
broadening of the jet shape as increases is consistent with the
predicted increase in the fraction of final state gluon jets.Comment: 29 pages including 9 figure
Gravitating discs around black holes
Fluid discs and tori around black holes are discussed within different
approaches and with the emphasis on the role of disc gravity. First reviewed
are the prospects of investigating the gravitational field of a black
hole--disc system by analytical solutions of stationary, axially symmetric
Einstein's equations. Then, more detailed considerations are focused to middle
and outer parts of extended disc-like configurations where relativistic effects
are small and the Newtonian description is adequate.
Within general relativity, only a static case has been analysed in detail.
Results are often very inspiring, however, simplifying assumptions must be
imposed: ad hoc profiles of the disc density are commonly assumed and the
effects of frame-dragging and completely lacking. Astrophysical discs (e.g.
accretion discs in active galactic nuclei) typically extend far beyond the
relativistic domain and are fairly diluted. However, self-gravity is still
essential for their structure and evolution, as well as for their radiation
emission and the impact on the environment around. For example, a nuclear star
cluster in a galactic centre may bear various imprints of mutual star--disc
interactions, which can be recognised in observational properties, such as the
relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be
available from http://www.iop.org/EJ/journal/CQ
OpenET : filling a critical data gap in water management for the western United States.
The lack of consistent, accurate information on evapotranspiration (ET) and consumptive use of water by irrigated agriculture is one of the most important data gaps for water managers in the western United States (U.S.) and other arid agricultural regions globally. The ability to easily access information on ET is central to improving water budgets across the West, advancing the use of data-driven irrigation management strategies, and expanding incentive-driven conservation programs. Recent advances in remote sensing of ET have led to the development of multiple approaches for field-scale ET mapping that have been used for local and regional water resource management applications by U.S. state and federal agencies. The OpenET project is a community-driven effort that is building upon these advances to develop an operational system for generating and distributing ET data at a field scale using an ensemble of six well-established satellite-based approaches for mapping ET. Key objectives of OpenET include: Increasing access to remotely sensed ET data through a web-based data explorer and data services; supporting the use of ET data for a range of water resource management applications; and development of use cases and training resources for agricultural producers and water resource managers. Here we describe the OpenET framework, including the models used in the ensemble, the satellite, meteorological, and ancillary data inputs to the system, and the OpenET data visualization and access tools. We also summarize an extensive intercomparison and accuracy assessment conducted using ground measurements of ET from 139 flux tower sites instrumented with open path eddy covariance systems. Results calculated for 24 cropland sites from Phase I of the intercomparison and accuracy assessment demonstrate strong agreement between the satellite-driven ET models and the flux tower ET data. For the six models that have been evaluated to date (ALEXI/DisALEXI, eeMETRIC, geeSEBAL, PT-JPL, SIMS, and SSEBop) and the ensemble mean, the weighted average mean absolute error (MAE) values across all sites range from 13.6 to 21.6 mm/month at a monthly timestep, and 0.74 to 1.07 mm/day at a daily timestep. At seasonal time scales, for all but one of the models the weighted mean total ET is within ±8% of both the ensemble mean and the weighted mean total ET calculated from the flux tower data. Overall, the ensemble mean performs as well as any individual model across nearly all accuracy statistics for croplands, though some individual models may perform better for specific sites and regions. We conclude with three brief use cases to illustrate current applications and benefits of increased access to ET data, and discuss key lessons learned from the development of OpenET
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