9,451 research outputs found
Justification for inclusion dependency normal form
Functional dependencies (FDs) and inclusion dependencies (INDs) are the most fundamental integrity constraints that arise in practice in relational databases. In this paper, we address the issue of normalization in the presence of FDs and INDs and, in particular, the semantic justification for Inclusion Dependency Normal Form (IDNF), a normal form which combines Boyce-Codd normal form with the restriction on the INDs that they be noncircular and key-based. We motivate and formalize three goals of database design in the presence of FDs and INDs: noninteraction between FDs and INDs, elimination of redundancy and update anomalies, and preservation of entity integrity. We show that, as for FDs, in the presence of INDs being free of redundancy is equivalent to being free of update anomalies. Then, for each of these properties, we derive equivalent syntactic conditions on the database design. Individually, each of these syntactic conditions is weaker than IDNF and the restriction that an FD not be embedded in the righthand side of an IND is common to three of the conditions. However, we also show that, for these three goals of database design to be satisfied simultaneously, IDNF is both a necessary and sufficient condition
DTKI: a new formalized PKI with no trusted parties
The security of public key validation protocols for web-based applications
has recently attracted attention because of weaknesses in the certificate
authority model, and consequent attacks.
Recent proposals using public logs have succeeded in making certificate
management more transparent and verifiable. However, those proposals involve a
fixed set of authorities. This means an oligopoly is created. Another problem
with current log-based system is their heavy reliance on trusted parties that
monitor the logs.
We propose a distributed transparent key infrastructure (DTKI), which greatly
reduces the oligopoly of service providers and allows verification of the
behaviour of trusted parties. In addition, this paper formalises the public log
data structure and provides a formal analysis of the security that DTKI
guarantees.Comment: 19 page
On the uniqueness of kinematical signatures of intermediate-mass black holes in globular clusters
Finding an intermediate-mass black hole (IMBH) in a globular cluster (GC), or
proving its absence, is a crucial ingredient in our understanding of galaxy
formation and evolution. The challenge is to identify a unique signature of an
IMBH that cannot be accounted for by other processes. Observational claims of
IMBH detection are often based on analyses of the kinematics of stars, such as
a rise in the velocity dispersion profile towards the centre. In this
contribution we discuss the degeneracy between this IMBH signal and pressure
anisotropy in the GC. We show that that by considering anisotropic models it is
possible to partially explain the innermost shape of the projected velocity
dispersion profile, even though models that do not account for an IMBH do not
exhibit a cusp in the centre.Comment: 4 pages, 2 figures. To be published in the Proceedings IAU Symposium
No. 312, Star Clusters and Black Holes in Galaxies Across Cosmic Tim
The effect of stellar-mass black holes on the central kinematics of omega Cen: a cautionary tale for IMBH interpretations
The search for intermediate-mass black holes (IMBHs) in the centre of
globular clusters is often based on the observation of a central cusp in the
surface brightness profile and a rise towards the centre in the velocity
dispersion profiles. Similar signatures, however, could result from other
effects, that need to be taken into account in order to determine the presence
(or the absence) of an IMBH in these stellar systems. Following our previous
exploration of the role of radial anisotropy in shaping these observational
signatures, we analyse here the effects produced by the presence of a
population of centrally concentrated stellar-mass black holes. We fit dynamical
models to omega Cen data, and we show that models with ~5% of their mass in
black holes (consistent with ~100% retention fraction after natal kicks) can
reproduce the data. When simultaneously considering both radial anisotropy and
mass segregation, the best-fit model includes a smaller population of remnants,
and a less extreme degree of anisotropy with respect to the models that include
only one of these features. These results underline that before conclusions
about putative IMBHs can be made, the effects of stellar-mass black holes and
radial anisotropy need to be properly accounted for.Comment: 13 pages, 5 figures. Accepted for publication in MNRA
Query management in a sensor environment
Traditional sensor network deployments consisted of fixed infrastructures and were relatively small in size. More and more, we see the deployment of ad-hoc sensor networks with heterogeneous devices on a larger scale, posing new challenges for device management and query processing. In this paper, we present our design and prototype implementation of XSense, an architecture supporting metadata and query services for an underlying large scale dynamic P2P sensor network. We cluster sensor devices into manageable groupings to optimise the query process and automatically locate appropriate clusters based on keyword abstraction from queries. We present experimental analysis to show the benefits of our approach and demonstrate improved query performance and scalability
Small Mercury Relativity Orbiter
The accuracy of solar system tests of gravitational theory could be very much improved by range and Doppler measurements to a Small Mercury Relativity Orbiter. A nearly circular orbit at roughly 2400 km altitude is assumed in order to minimize problems with orbit determination and thermal radiation from the surface. The spacecraft is spin-stabilized and has a 30 cm diameter de-spun antenna. With K-band and X-band ranging systems using a 50 MHz offset sidetone at K-band, a range accuracy of 3 cm appears to be realistically achievable. The estimated spacecraft mass is 50 kg. A consider-covariance analysis was performed to determine how well the Earth-Mercury distance as a function of time could be determined with such a Relativity Orbiter. The minimum data set is assumed to be 40 independent 8-hour arcs of tracking data at selected times during a two year period. The gravity field of Mercury up through degree and order 10 is solved for, along with the initial conditions for each arc and the Earth-Mercury distance at the center of each arc. The considered parameters include the gravity field parameters of degree 11 and 12 plus the tracking station coordinates, the tropospheric delay, and two parameters in a crude radiation pressure model. The conclusion is that the Earth-Mercury distance can be determined to 6 cm accuracy or better. From a modified worst-case analysis, this would lead to roughly 2 orders of magnitude improvement in the knowledge of the precession of perihelion, the relativistic time delay, and the possible change in the gravitational constant with time
The short-lived MATα2 transcriptional regulator is ubiquitinated in vivo
The substrates of ubiquitin-dependent proteolytic pathways include both damaged or otherwise abnormal proteins and undamaged proteins that are naturally short-lived. Few specific examples of the latter class have been identified, however. Previous work has shown that the cell type-specific MAT-alpha-2 repressor of the yeast Saccharomyces cerevisiae is an extremely short-lived protein. We now demonstrate that alpha-2 is conjugated to ubiquitin in vivo. More than one lysine residue of alpha-2 can be joined to ubiquitin, and some of the ubiquitin moieties form a Lys48-linked multiubiquitin chain. Overexpression of degradation-impaired ubiquitin variants was used to show that at least a significant fraction of alpha-2 degradation is dependent on its ubiquitination
Testing lowered isothermal models with direct N-body simulations of globular clusters - II: Multimass models
Lowered isothermal models, such as the multimass Michie-King models, have
been successful in describing observational data of globular clusters. In this
study we assess whether such models are able to describe the phase space
properties of evolutionary -body models. We compare the multimass models as
implemented in (Gieles \& Zocchi) to -body models of star clusters with
different retention fractions for the black holes and neutron stars evolving in
a tidal field. We find that multimass models successfully reproduce the density
and velocity dispersion profiles of the different mass components in all
evolutionary phases and for different remnants retention. We further use these
results to study the evolution of global model parameters. We find that over
the lifetime of clusters, radial anisotropy gradually evolves from the low-mass
to the high-mass components and we identify features in the properties of
observable stars that are indicative of the presence of stellar-mass black
holes. We find that the model velocity scale depends on mass as ,
with for almost all models, but the dependence of central
velocity dispersion on can be shallower, depending on the dark remnant
content, and agrees well with that of the -body models. The reported model
parameters, and correlations amongst them, can be used as theoretical priors
when fitting these types of mass models to observational data.Comment: 28 pages, 22 figures, published in MNRA
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