4,424 research outputs found
The sedimentology of some Transvaal hominid cave deposits and its environmental and chronological implications
Abstract of paper presented at 5th SASQUA Conference, July 1979The sedimentology of cave deposits is principally influenced by two sets of factors:
(1) those relating to the morphology of the depository and its evolution through time; and
(2) those resulting from external influences, including the production of sediments and their
introduction into the cave under varying conditions of climate and vegetation cover.
The interaction of these two sets of factors often poses unique sedimentological problems
which differ markedly from those encountered in other sedimentary environments. In particular,
the imprint of intracavernous conditions on specific sedimentary facies frequently complicates
interpretations relative to extracavernous environmental influences. Inferences from
sedimentological studies should, therefore, be supplemented as far as possible with other evidence
- for example from isotope analyses, palynology and faunal studies - in any meaningful
attempt to reconstruct ancient environments from these deposits.
The sequence of intracavernous events which occurred during the accumulation of the
Makapansgat and Sterkfontein Formations will be outlined in relation to the probable imprint
of external changes. When viewed in conjunction with the evidence of variations in the
concentrations of 13C and 18O in the various stratigraphic units and with interpretations relative
to the extent of the cover of woody vegetation near each site, a fairly consistent picture
of climate fluctuations emerges. These early fluctuations may, in a general way, parallel those
recorded by Shackleton and Opdyke in the northern hemisphere for the period between 3,2
My B.P. and the beginning of the Quaternary.Non
The stratigraphy of the Sterkfontein hominid deposit and its relationship to the underground cave system
A programme of orientated core drilling was carried out during 1989 to elucidate stratigraphic relationships within the Sterkfontein Formation and to obtain a representative suite of samples for palaeomagnetic analysis. The cores have revealed that the hominid-bearing cave deposits occur as a continuous succession comprising 6 Members and extending to a maximum depth of about 30 m below present surface. Of these Member I (comprising a sterile, residual fill) and Member 3 are the most extensive. This sequence has been displaced vertically downwards within a zone of decalcification coinciding with the central part of the deposit. This zone has been the focus of recent deep excavations at the site. The results of the drilling, in conjunction with recent surveys of the underground cave system, confirm that a dolomite floor existed at an average depth of about 20 m at the time offirst cave filling. Subsequent cavern development down to depths in excess of 50 m caused the local collapse of some lower units of the Sterkfontein Formation and, as new openings developed to the surface, permitted the ingress of younger fills below the base of the hominid-bearing succession
The nature and genesis of solution cavities (Makondos) in Transvaal Cave breccias
Main articleThe discovery of a large part of the cranium of a
hominid, evidently closely related to Homo habilis
(Hughes and Tobias 1977) in a solution cavity
within the calcified Member 5 of the Sterkfontein
Formation (Partridge 1978) has again drawn attention
to the frequent occurrence of these features
in the hominid-bearing breccias of the Transvaal.
The authors first studied these features at
Makapansgat (fig. 1) some fifteen years ago and
have since then become aware of their very widespread
occurrence in soluble rocks in many parts
of the world. All subsequent information has
served to confirm the origin of these features, but,
since these were never published, it is worthwhile
to place these findings on record.
Solution cavities, or Makondos, in the Transvaal
cave breccias are soil-filled pits shaped like an
inverted cone. Their walls and intervening areas of
the calcified cave deposit are usually rough, and
the coalescing of adjacent cavities below the surface
is common. They seldom exceed 2 m in diameter
and 6 m in depth and occur at intervals of 2 to
3 m in the calcified cave deposit.Non
The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
We present new evolution sequences for very low mass stars, brown dwarfs and
giant planets and use them to explore a variety of influences on the evolution
of these objects. We compare our results with previous work and discuss the
causes of the differences and argue for the importance of the surface boundary
condition provided by atmosphere models including clouds.
The L- to T-type ultracool dwarf transition can be accommodated within the
Ackerman & Marley (2001) cloud model by varying the cloud sedimentation
parameter. We develop a simple model for the evolution across the L/T
transition. By combining the evolution calculation and our atmosphere models,
we generate colors and magnitudes of synthetic populations of ultracool dwarfs
in the field and in galactic clusters. We focus on near infrared color-
magnitude diagrams (CMDs) and on the nature of the ``second parameter'' that is
responsible for the scatter of colors along the Teff sequence. Variations in
metallicity and cloud parameters, unresolved binaries and possibly a relatively
young population all play a role in defining the spread of brown dwarfs along
the cooling sequence. We find that the transition from cloudy L dwarfs to
cloudless T dwarfs slows down the evolution and causes a pile up of substellar
objects in the transition region, in contradiction with previous studies. We
apply the same model to the Pleiades brown dwarf sequence. Taken at face value,
the Pleiades data suggest that the L/T transition occurs at lower Teff for
lower gravity objects. The simulated populations of brown dwarfs also reveal
that the phase of deuterium burning produces a distinctive feature in CMDs that
should be detectable in ~50-100 Myr old clusters.Comment: Accepted for publication in the ApJ. 52 pages including 20 figure
Bright soliton trains of trapped Bose-Einstein condensates
We variationally determine the dynamics of bright soliton trains composed of
harmonically trapped Bose-Einstein condensates with attractive interatomic
interactions. In particular, we obtain the interaction potential between two
solitons. We also discuss the formation of soliton trains due to the quantum
mechanical phase fluctuations of a one-dimensional condensate.Comment: 4 pages, 2 figures, submitted to PR
Deformation of a Trapped Fermi Gas with Unequal Spin Populations
The real-space densities of a polarized strongly-interacting two-component
Fermi gas of Li atoms reveal two low temperature regimes, both with a
fully-paired core. At the lowest temperatures, the unpolarized core deforms
with increasing polarization. Sharp boundaries between the core and the excess
unpaired atoms are consistent with a phase separation driven by a first-order
phase transition. In contrast, at higher temperatures the core does not deform
but remains unpolarized up to a critical polarization. The boundaries are not
sharp in this case, indicating a partially-polarized shell between the core and
the unpaired atoms. The temperature dependence is consistent with a tricritical
point in the phase diagram.Comment: Accepted for publication in Physical Review Letter
The Bayesian Decision Tree Technique with a Sweeping Strategy
The uncertainty of classification outcomes is of crucial importance for many
safety critical applications including, for example, medical diagnostics. In
such applications the uncertainty of classification can be reliably estimated
within a Bayesian model averaging technique that allows the use of prior
information. Decision Tree (DT) classification models used within such a
technique gives experts additional information by making this classification
scheme observable. The use of the Markov Chain Monte Carlo (MCMC) methodology
of stochastic sampling makes the Bayesian DT technique feasible to perform.
However, in practice, the MCMC technique may become stuck in a particular DT
which is far away from a region with a maximal posterior. Sampling such DTs
causes bias in the posterior estimates, and as a result the evaluation of
classification uncertainty may be incorrect. In a particular case, the negative
effect of such sampling may be reduced by giving additional prior information
on the shape of DTs. In this paper we describe a new approach based on sweeping
the DTs without additional priors on the favorite shape of DTs. The
performances of Bayesian DT techniques with the standard and sweeping
strategies are compared on a synthetic data as well as on real datasets.
Quantitatively evaluating the uncertainty in terms of entropy of class
posterior probabilities, we found that the sweeping strategy is superior to the
standard strategy
Semantic Transformation of Web Services
Web services have become the predominant paradigm for the development of distributed software systems. Web services provide the means to modularize software in a way that functionality can be described, discovered and deployed in a platform independent manner over a network (e.g., intranets, extranets and the Internet). The representation of web services by current industrial practice is predominantly syntactic in nature lacking the fundamental semantic underpinnings required to fulfill the goals of the emerging Semantic Web. This paper proposes a framework aimed at (1) modeling the semantics of syntactically defined web services through a process of interpretation, (2) scop-ing the derived concepts within domain ontologies, and (3) harmonizing the semantic web services with the domain ontologies. The framework was vali-dated through its application to web services developed for a large financial system. The worked example presented in this paper is extracted from the se-mantic modeling of these financial web services
Planck Observations of M33
We have performed a comprehensive investigation of the global integrated flux
density of M33 from radio to ultraviolet wavelengths, finding that the data
between 100 GHz and 3 THz are accurately described by a single modified
blackbody curve with a dust temperature of = 21.670.30 K
and an effective dust emissivity index of = 1.350.10,
with no indication of an excess of emission at millimeter/sub-millimeter
wavelengths. However, sub-dividing M33 into three radial annuli, we found that
the global emission curve is highly degenerate with the constituent curves
representing the sub-regions of M33. We also found gradients in
and across the disk of M33, with both
quantities decreasing with increasing radius. Comparing the M33 dust emissivity
with that of other Local Group members, we find that M33 resembles the
Magellanic Clouds rather than the larger galaxies, i.e., the Milky Way and M31.
In the Local Group sample, we find a clear correlation between global dust
emissivity and metallicity, with dust emissivity increasing with metallicity. A
major aspect of this analysis is the investigation into the impact of
fluctuations in the Cosmic Microwave Background (CMB) on the integrated flux
density spectrum of M33. We found that failing to account for these CMB
fluctuations would result in a significant over-estimate of
by 5 K and an under-estimate of by 0.4.Comment: Accepted for publication in MNRA
Post-Den Emergence Behavior of Polar Bears (Ursus maritimus) in Northern Alaska
We observed polar bear (Ursus maritimus) maternity den sites on Alaska’s North Slope in March 2002 and 2003 in an effort to describe bears’ post-den emergence behavior. During 40 sessions spanning 459 h, we observed 8 adults and 14 dependent cubs outside dens for 37.5 h (8.2% of total observation time). There was no significant difference between den emergence dates in 2002 (mean = 15 Mar ± 4.1 d) and 2003 (mean = 21 Mar ± 2.1 d). Following initial den breakout, polar bears remained at their den sites for 1.5 to 14 days (mean = 8.1 ± 5.1 d). The average length of stay in dens between emergent periods was significantly shorter in 2002 (1.79 h) than in 2003 (4.82 h). While outside, adult bears were inactive 49.5% of the time, whereas cubs were inactive 13.4% of the time. We found no significant relationships between den emergence activity and weather. Adult polar bears at den sites subjected to industrial activity exhibited significantly fewer bouts of vigilance than denned bears in undisturbed areas (t = -5.5164, df = 4, p = 0.00). However, the duration of vigilance behaviors at sites near industrial activity was not significantly shorter than at the other sites studied (t = -1.8902, df = 4, p = 0.07). Results for these bears were within the range of findings in other studies of denned polar bears.Nous avons observé des tanières de maternité d’ours polaires (Ursus maritimus) sur le versant nord de l’Alaska aux mois de mars 2002 et 2003 dans le but de décrire le comportement de sortie des ours après leur séjour dans la tanière. Dans le cadre de 40 séances d’observation ayant duré 459 heures, nous avons observé 8 ours adultes et 14 oursons à charge en dehors des tanières pendant 37,5 heures (soit 8,2 % de la durée d’observation totale). Il n’y avait pas de différence importante entre les dates de sortie des tanières en 2002 (moyenne = 15 mars ± 4,1 j) et 2003 (moyenne = 21 mars ± 2,1 j). Après la première sortie de la tanière, les ours polaires restaient à l’emplacement de leur tanière pendant 1,5 à 14 jours (moyenne = 8,1 ± 5.1 j). La longueur moyenne du séjour en tanière entre les périodes de sortie était beaucoup plus courte en 2002 (1,79 h) qu’en 2003 (4,82 h). Une fois sortis, les ours adultes étaient inactifs pendant 49,5 % du temps, tandis que les oursons étaient inactifs pendant 13,4 % du temps. Nous n’avons pas trouvé de lien important entre l’activité une fois sorti de la tanière et le temps qu’il faisait. Les ours polaires adultes à l’emplacement de tanières assujetties à des activités industrielles affichaient beaucoup moins de séquences de vigilance que les ours en tanière des régions tranquilles (t = -5,5164, dl = 4, p = 0,00). Cependant, la durée des comportements de vigilance aux emplacements situés près d’activités industrielles n’était pas beaucoup plus courte qu’aux autres emplacements étudiés (t = - 1,8902, dl = 4, p = 0,07). Les résultats enregistrés pour ces ours tombaient dans l’étendue des constatations découlant d’autres études d’ours polaires en tanière
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