1,260 research outputs found
Gravitational tolerance and size of <i>Brachiosaurus brancai</i>
In an earlier study, Gunga et al. (1999) determined body size and body volume distribution by photogrammetry in sauropods from the Upper Jurassic in Tendaguru (Tanzania, East Africa). Specifically, they found a body mass of about 74400 kg for a specimen of Brachiosaurus brancai. By means of dimensional analysis and a theory of biological similarity, moreover, it was possible to estimate the numerical value of the allometric exponent (b = −0.17) for gravitational tolerance (Gmax) of animals living on earth, which changes with the body mass. This theoretical exponent is close to Economos' empirical finding (b = −0.14). Our results show that there remains an unsolved contradiction between the theoretical assumptions for Gmax for the body mass of the largest fully terrestrial animals.
In einer vorangehenden Studie (Gunga et al. 1999) wurde mit Hilfe der Photogrammetrie die Körpermassen und Körpervolumenverteilung von jurassischen Sauropoden aus Tendaguru (Tansania, Ostafrika) ermittelt. Diese Bestimmungen ergaben für Brachiosaurus brancai eine Körpermasse von von ca. 74400 kg. Weitere Studien aus der vergleichenden Physiologie haben gezeigt, dass die Toleranz bei Schwerkraftbelastung (Gmax) mit der Körpermasse variert. Durch dimensionale Analyse und vergleichende Studien konnte ein allometrischer Exponent für die Toleranz bei Schwerkraftbelastung mit b = −0.17 für terrestrische Organismen bestimmt werden. Dieser theoretische Exponent kommt den empirischen Befunden von Economos (b = −0.14) nahe. Dennoch weisen diese vorliegenden Berechnungen damit auf einen Widerspruch bei den bislang vorhandenen theoretischen Überlegungen zur Gmax bei den grössten maximalen Körpermassen für terrestrisch lebende Organismen hin.
doi:10.1002/mmng.20020050115</a
Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations
The irregular satellites of the giant planets are believed to have been
captured during the evolution of the solar system. Knowing their physical
parameters, such as size, density, and albedo is important for constraining
where they came from and how they were captured. The best way to obtain these
parameters are observations in situ by spacecrafts or from stellar occultations
by the objects. Both techniques demand that the orbits are well known. We aimed
to obtain good astrometric positions of irregular satellites to improve their
orbits and ephemeris. We identified and reduced observations of several
irregular satellites from three databases containing more than 8000 images
obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias,
Observatoire de Haute-Provence, and European Southern Observatory - La Silla).
We used the software PRAIA (Platform for Reduction of Astronomical Images
Automatically) to make the astrometric reduction of the CCD frames. The UCAC4
catalog represented the International Celestial Reference System in the
reductions. Identification of the satellites in the frames was done through
their ephemerides as determined from the SPICE/NAIF kernels. Some procedures
were followed to overcome missing or incomplete information (coordinates,
date), mostly for the older images. We managed to obtain more than 6000
positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus
(Sycorax), and 1 of Neptune (Nereid). For some satellites the number of
obtained positions is more than 50\% of what was used in earlier orbital
numerical integrations. Comparison of our positions with recent JPL ephemeris
suggests there are systematic errors in the orbits for some of the irregular
satellites. The most evident case was an error in the inclination of Carme.Comment: 9 pages, with 3 being online materia
Short-Range Ising Spin Glass: Multifractal Properties
The multifractal properties of the Edwards-Anderson order parameter of the
short-range Ising spin glass model on d=3 diamond hierarchical lattices is
studied via an exact recursion procedure. The profiles of the local order
parameter are calculated and analysed within a range of temperatures close to
the critical point with four symmetric distributions of the coupling constants
(Gaussian, Bimodal, Uniform and Exponential). Unlike the pure case, the
multifractal analysis of these profiles reveals that a large spectrum of the
-H\"older exponent is required to describe the singularities of the
measure defined by the normalized local order parameter, at and below the
critical point. Minor changes in these spectra are observed for distinct
initial distributions of coupling constants, suggesting an universal spectra
behavior. For temperatures slightly above T_{c}, a dramatic change in the
function is found, signalizing the transition.Comment: 8 pages, LaTex, PostScript-figures included but also available upon
request. To be published in Physical Review E (01/March 97
Normal transport properties for a classical particle coupled to a non-Ohmic bath
We study the Hamiltonian motion of an ensemble of unconfined classical
particles driven by an external field F through a translationally-invariant,
thermal array of monochromatic Einstein oscillators. The system does not
sustain a stationary state, because the oscillators cannot effectively absorb
the energy of high speed particles. We nonetheless show that the system has at
all positive temperatures a well-defined low-field mobility over macroscopic
time scales of order exp(-c/F). The mobility is independent of F at low fields,
and related to the zero-field diffusion constant D through the Einstein
relation. The system therefore exhibits normal transport even though the bath
obviously has a discrete frequency spectrum (it is simply monochromatic) and is
therefore highly non-Ohmic. Such features are usually associated with anomalous
transport properties
Onset of fluidization in vertically shaken granular material
When granular material is shaken vertically one observes convection, surface
fluidization, spontaneous heap formation and other effects. There is a
controversial discussion in literature whether there exists a threshold for the
Froude number below which these effects cannot be
observed anymore. By means of theoretical analysis and computer simulation we
find that there is no such single threshold. Instead we propose a modified
criterion which coincides with critical Froude number for small
driving frequency .Comment: 7 pages, 5 figure
Simulation for the oblique impact of a lattice system
The oblique collision between an elastic disk and an elastic wall is
numerically studied.
We investigate the dependency of the tangential coefficient of restitution on
the incident angle of impact.
From the results of simulation, our model reproduces experimental results and
can be explained by a phenomenological theory of the oblique impact.Comment: 30 pages, 9 figures, submitted to J. Phys. Soc. Japa
Dynamical Phases of Driven Vortices Interacting with Periodic Pinning
The finite temperature dynamical phases of vortices in films driven by a
uniform force and interacting with the periodic pinning potential of a square
lattice of columnar defects are investigated by Langevin dynamics simulations
of a London model. Vortices driven along the [0,1] direction and at densities
for which there are more vortices than columnar defects () are
considered. At low temperatures, two new dynamical phases, elastic flow and
plastic flow, and a sharp transition between them are identified and
characterized according to the behavior of the vortex spatial order, velocity
distribution and frequency-dependent velocity correlationComment: 4 pages with 4 figures. To be published in Phys. Rev. B Rapid
Communication
Quantitative EEG and Functional Outcome Following Acute Ischemic Stroke
Objective: To identify the most accurate quantitative electroencephalographic (qEEG) predictor(s) of unfavorable post-ischemic stroke outcome, and its discriminative capacity compared to already known demographic, clinical and imaging prognostic markers.
Methods: Prospective cohort of 151 consecutive anterior circulation ischemic stroke patients followed for 12 months. EEG was recorded within 72 h and at discharge or 7 days post-stroke. QEEG (global band power, symmetry, affected/unaffected hemisphere and time changes) indices were calculated from mean Fast Fourier Transform and analyzed as predictors of unfavorable outcome (mRS ≥ 3), at discharge and 12 months poststroke, before and after adjustment for age, admission NIHSS and ASPECTS.
Results: Higher delta, lower alpha and beta relative powers (RP) predicted outcome. Indices with higher discriminative capacity were delta-theta to alpha-beta ratio (DTABR) and alpha RP. Outcome models including either of these and other clinical/imaging stroke outcome predictors were superior to models without qEEG data. In models with qEEG indices, infarct size was not a significant outcome predictor.
Conclusions: DTAABR and alpha RP are the best qEEG indices and superior to ASPECTS in post-stroke outcome prediction. They improve the discriminative capacity of already known clinical and imaging stroke outcome predictors, both at discharge and 12 months after stroke.
Significance: qEEG indices are independent predictors of stroke outcome.info:eu-repo/semantics/publishedVersio
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