974 research outputs found
Towards Intelligent Databases
This article is a presentation of the objectives and techniques
of deductive databases. The deductive approach to databases aims at extending
with intensional definitions other database paradigms that describe
applications extensionaUy. We first show how constructive specifications can
be expressed with deduction rules, and how normative conditions can be defined
using integrity constraints. We outline the principles of bottom-up and
top-down query answering procedures and present the techniques used for
integrity checking. We then argue that it is often desirable to manage with
a database system not only database applications, but also specifications of
system components. We present such meta-level specifications and discuss
their advantages over conventional approaches
Shift-Symmetric Configurations in Two-Dimensional Cellular Automata: Irreversibility, Insolvability, and Enumeration
The search for symmetry as an unusual yet profoundly appealing phenomenon,
and the origin of regular, repeating configuration patterns have long been a
central focus of complexity science and physics. To better grasp and understand
symmetry of configurations in decentralized toroidal architectures, we employ
group-theoretic methods, which allow us to identify and enumerate these inputs,
and argue about irreversible system behaviors with undesired effects on many
computational problems. The concept of so-called configuration shift-symmetry
is applied to two-dimensional cellular automata as an ideal model of
computation. Regardless of the transition function, the results show the
universal insolvability of crucial distributed tasks, such as leader election,
pattern recognition, hashing, and encryption. By using compact enumeration
formulas and bounding the number of shift-symmetric configurations for a given
lattice size, we efficiently calculate the probability of a configuration being
shift-symmetric for a uniform or density-uniform distribution. Further, we
devise an algorithm detecting the presence of shift-symmetry in a
configuration.
Given the resource constraints, the enumeration and probability formulas can
directly help to lower the minimal expected error and provide recommendations
for system's size and initialization. Besides cellular automata, the
shift-symmetry analysis can be used to study the non-linear behavior in various
synchronous rule-based systems that include inference engines, Boolean
networks, neural networks, and systolic arrays.Comment: 22 pages, 9 figures, 2 appendice
A complementary view on the growth of directory trees
Trees are a special sub-class of networks with unique properties, such as the
level distribution which has often been overlooked. We analyse a general tree
growth model proposed by Klemm {\em et. al.} (2005) to explain the growth of
user-generated directory structures in computers. The model has a single
parameter which interpolates between preferential attachment and random
growth. Our analysis results in three contributions: First, we propose a more
efficient estimation method for based on the degree distribution, which is
one specific representation of the model. Next, we introduce the concept of a
level distribution and analytically solve the model for this representation.
This allows for an alternative and independent measure of . We argue that,
to capture real growth processes, the estimations from the degree and the
level distributions should coincide. Thus, we finally apply both
representations to validate the model with synthetically generated tree
structures, as well as with collected data of user directories. In the case of
real directory structures, we show that measured from the level
distribution are incompatible with measured from the degree distribution.
In contrast to this, we find perfect agreement in the case of simulated data.
Thus, we conclude that the model is an incomplete description of the growth of
real directory structures as it fails to reproduce the level distribution. This
insight can be generalised to point out the importance of the level
distribution for modeling tree growth.Comment: 16 pages, 7 figure
Recommended from our members
Measurements of the velocity distribution for granular flow in a Couette cell
Š 2018 American Physical Society. In this paper, magnetic resonance velocimetry is used to measure the spatially resolved velocity and velocity fluctuations for granular flow in a Couette cell for four different particle sizes. The largest particles studied (dp=1.7mm) showed significant slip at the inner wall. The remaining particles showed no slip and all exhibit the same behavior in the profiles of the mean velocity and variance of velocity. The measurements demonstrate that the velocity and variance in velocity scale with the inner wall velocity U; the variance does not scale with U2. The experimental data were compared with a kinetic theory based model of granular flow and a hydrodynamic model. It was found that the shear rate scales with an exponent of 1.5-2.0 with respect to the velocity fluctuations (uy2), compared with the value of 1.0 expected from kinetic theory. The difference in the exponent is consistent with the effect of collective dynamics as described by the hydrodynamic model
Recognising Desire: A psychosocial approach to understanding education policy implementation and effect
It is argued that in order to understand the ways in which teachers experience their work - including the idiosyncratic ways in which they respond to and implement mandated education policy - it is necessary to take account both of sociological and of psychological issues. The paper draws on original research with practising and beginning teachers, and on theories of social and psychic induction, to illustrate the potential benefits of this bipartisan approach for both teachers and researchers. Recognising the significance of (but somewhat arbitrary distinction between) structure and agency in teachersâ practical and ideological positionings, it is suggested that teachersâ responses to local and central policy changes are governed by a mix of pragmatism, social determinism and often hidden desires. It is the often underacknowledged strength of desire that may tip teachers into accepting and implementing policies with which they are not ideologically comfortable
The significance of 'the visit' in an English category-B prison: Views from prisoners, prisoners' families and prison staff
A number of claims have been made regarding the importance of prisoners staying in touch with their family through prison visits, firstly from a humanitarian perspective of enabling family members to see each other, but also regarding the impact of maintaining family ties for successful rehabilitation, reintegration into society and reduced re-offending. This growing evidence base has resulted in increased support by the Prison Service for encouraging the family unit to remain intact during a prisonerâs incarceration. Despite its importance however, there has been a distinct lack of research examining the dynamics of families visiting relatives in prison. This paper explores perceptions of the same event â the visit â from the familiesâ, prisonersâ and prison staffs' viewpoints in a category-B local prison in England. Qualitative data was collected with 30 prisonersâ families, 16 prisoners and 14 prison staff, as part of a broader evaluation of the visitorsâ centre. The findings suggest that the three parties frame their perspective of visiting very differently. Prisonersâ families often see visits as an emotional minefield fraught with practical difficulties. Prisoners can view the visit as the highlight of their time in prison and often have many complaints about how visits are handled. Finally, prison staff see visits as potential security breaches and a major organisational operation. The paper addresses the current gap in our understanding of the prison visit and has implications for the Prison Service and wider social policy
The bridge between social identity and community capital on the path to recovery and desistance
It has long been recognised that changes in social networks (and the underpinning changes in personal and social identity) are strong predictors of both desistance from crime and recovery from substance use. Building on existing work attempting to measure and shift social networks and transitions to prosocial groups, the current study provides pilot data from prisoners and family members about a visualisation technique widely used in specialist addiction treatment (node-link mapping) to map opportunities for linkage to prosocial groups and networks. The data presented in the paper are from a small-scale feasibility pilot. This suggests both bonding and bridging capital in prisoner populations due for release and the diversity of community capital opportunities that exists in this population. The implications of this work are significant for substance users and offenders pending return to the community, and has implications around resettlement and reintegration support for probation staff in prisons and in the community. The paper emphasises the importance of mapping connectedness as a key component of planning for reintegration back into the community for those working with offenders who are aspiring to achieve desistance and recovery
Complexes Formed in Solution Between Vanadium(IV)/(V) and the Cyclic Dihydroxamic Acid Putrebactin or Linear Suberodihydroxamic Acid
The ability of microbial siderophores to coordinate metal ions, particularly Fe(III), continues to generate interest in the poten-tial applications of these bioligands in the environment and medicine.13 Siderophores produced by terrestrial and marin
Organizing research data
Research relies on ever larger amounts of data from experiments, automated production equipment, questionnaries, times series such as weather records, and so on. A major task in science is to combine, process and analyse such data to obtain evidence of patterns and correlations
âIt was just like we were a family againâ: play as a means to maintain family ties for children visiting an imprisoned parent
Children can find the process of visiting a prison traumatic and as a result of parental incarceration may experience a range of adverse outcomes. When children stay in contact with their imprisoned parent through prison visiting, however, this seems to be a protective factor. This paper reports on a play visits service based at Her Majesty's Prison Leeds, UK. The service provides supervised play work provision for children visiting their father. Data were derived from prisoners and prisoners' families and were triangulated as a means of achieving a level of validity. The findings reveal that play visits do produce positive outcomes for children and play visits are effective in maintaining and strengthening family ties. These effects may be stronger when compared to standard prison visits, but further research is needed to confirm this
- âŚ