3,823 research outputs found
Security Attributes Based Digital Rights Management
Most real-life systems delegate responsibilities to different authorities. We apply this model to a digital rights management system, to achieve flexible security. In our model a hierarchy of authorities issues certificates that are linked by cryptographic means. This linkage establishes a chain of control, identity-attribute-rights, and allows flexible rights control over content. Typical security objectives, such as identification, authentication, authorization and access control can be realised. Content keys are personalised to detect illegal super distribution. We describe a working prototype, which we develop using standard techniques, such as standard certificates, XML and Java. We present experimental results to evaluate the scalability of the system. A formal analysis demonstrates that our design is able to detect a form of illegal super distribution
Cranial anatomy of the giant Middle Triassic temnospondyl Cherninia megarhina and a review of feeding in mastodonsaurids
The skull of Cherninia (,Parotosuchus') megarhina, a giant but poorly known mastodonsaurid temnospondyl from the Upper Horizon of the Middle Triassic N'tawere Formation of the Upper Luangwa Valley, Zambia, is redescribed and refigured in detail for the first time. Cherninia megarhina is highly derived in most aspects of its cranial morphology and is characterised by the presence of a massively broad and elongated snout, relatively tiny orbits that are set well back on the skull roof, small, near-laterally directed tabular horns, an occipital sensory sulcus, and prominent, forked ridges on the skull roof. The palate is characterised by the presence of a ventral exoccipital-pterygoid contact, a short basicranial suture, a narrow parasphenoid body, a broad pterygoid body, and choanae that are placed far forward of the interpterygoid vacuities. The presence in Cherninia megarhina of numerous cranial autapomorphies justifies its separation from Parotosuchus. These autapomorphies are shared with Cherninia (‘Parotosuchus') denwaifrom the Middle Triassic Denwa Formation of India. The lateral orientation of the tabular horns and morphology of the otic region suggests that Cherninia megarhina is slightly more derived than the Indian species. Mastodonsaurids have traditionally been perceived as passive, benthic suction-feeders. However, recent work on the anatomy and functional morphology of the skeleton of mastodonsaurids suggests that they were designed for active swimming and predation. As such, it is hypothesised that prey capture was achieved using sideways sweeps of the head rather than suction-feeding.The Council's Research Committee, University of the Witwatersrand; National Research Foundation (NRF); Palaeo-Anthropology Scientific Trust (PAST)
A brachyopid temnospondyl from the lower Cynognathus Assemblage Zone In the northern Karoo Basin, South Africa
Main articleA new brachyopid temnospondyl is described from the Early to Middle Triassic Cynognathus
Assemblage Zone of the upper Beaufort Group, Karoo Basin of South Africa. It is the fourth named
brachyopid from the Karoo and the first from the northern part of the basin. Despite the incomplete
nature of the holotype skull, the new brachyopid apparently shows closest affinities to Batrachosuchus
watsoni. However, differences in the width of the sensory sulci, the absence of a transverse occipital
sulcus, and the presence of a unique narial morphology, warrants separation at the species level. The
holotype skull also provides insight into the morphology of the ventral surface of the skull roof and
the configuration of the bones between the orbit and the nostril. A referred right mandibular ramus,
the most complete yet recovered of a brachyopid, also shows several unique features. A reconsideration
of the taxonomy of the brachyopid genus Batrachosuchus reveals that Batrachosuchus watsoni
possesses several characters distinct from the type species, Batrachosuchus browni, and is thus
transferred to a new genus. In addition, 'Batrachosuchus' henwoodi and Batrachosuchus concordi
probably do not pertain to the genus Batrachosuchus. Brachyopid diversity in the Karoo is exceeded
only by the Mastodonsauridae and Rhinesuchidae, and they may eventually prove to be important aids
in the biostratigraphy of the Cynognathus Assemblage Zone.Palaeo-Anthropology Scientific Trust; French Embassy in South Africa; Co-operation and Cultural Service
A taxonomic note concerning a dicynodont (Synapsida: Anomodontia) from the Middle Triassic of East Africa
Main articleThe complicated histories of the Indian dicynodont Rechnisaurus and the East African dicynodont Kannemeyeria cristarhynchus has led to
the incorrect use of the name ‘cristarhynchus’ for the latter taxon. This paper therefore proposes a new species name and diagnosis.The National
Research Foundation and University Research Committee of the University of the
Witwatersran
Unveiling the Cygnus OB2 stellar population with Chandra
The aim of this work is to identify the so far unknown low mass stellar
population of the ~2Myr old Cygnus OB2 region, and to investigate the X-ray and
near-IR stellar properties of its members. We analyzed a 97.7 ksec Chandra
ACIS-I observation pointed at the core of the Cygnus OB2 region. X-ray
variability ans spectral analysis of sources was characterized through the
KS-test and XSPEC thermal models, respectively. We detected 1003 X-ray sources.
Of these, 775 have near-IR counterparts associated with Cygnus OB2 members. We
estimate a typical absorption toward Cygnus OB2 of Av~7.0 mag. Although the
region is young, very few stars (~4.4 %) show disk-induced excesses in the
near-IR. X-ray variability is detected in ~13 % of the sources. Flares account
for at least 60 % of the variability. O- that early B-type stars are not
significantly variable. Typical X-ray spectral parameters are log(Nh)~22.25 and
kT~1.35 keV. Variable and flaring sources have harder spectra with median
kT=3.3 and 3.8 keV, respectively. OB stars are typically softer (kT~0.75 keV).
X-ray luminosities range between 1E+30 and 1E+31 erg/s for intermediate- and
low-mass stars, and 2.5x10^30 and between 6.3E+33 erg/s for OB stars. The
Cygnus OB2 region has a very rich population of low-mass X-ray emitting stars.
Circumstellar disks seem to be very scarce.Comment: Accepted for publication in A&A. 20 pages, 17 figure
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