42,266 research outputs found
A theory and its metatheory in FS 0
Feferman has proposed FS0, a theory of finitary inductive systems, as a framework theory suitable for various purposes, including reasoning both in and about encoded theories. I look here at how practical FS0 really is. I formalise of a sequent calculus presentation of classical propositional logic in FS0 and show this can be used for work in both the theory and the metatheory. the latter is illustrated with a discussion of a proof of Gentzen's Hauptsatz
Charging and Growth of Fractal Dust Grains
The structure and evolution of aggregate grains formed within a plasma
environment are dependent upon the charge acquired by the micron-sized dust
grains during the coagulation process. The manner in which the charge is
arranged on developing irregular structures can affect the fractal dimension of
aggregates formed during collisions, which in turn influences the coagulation
rate and size evolution of the dust within the plasma cloud. This paper
presents preliminary models for the charge and size evolution of fractal
aggregates immersed in a plasma environment calculated using a modification to
the orbital-motion-limited (OML) theory. Primary electron and ion currents
incident on points on the aggregate surface are determined using a
line-of-sight (LOS) approximation: only those electron or ion trajectories
which are not blocked by another grain within the aggregate contribute to the
charging current. Using a self-consistent iterative approach, the equilibrium
charge and dipole moment are calculated for the dust aggregate. The charges are
then used to develop a heuristic charging scheme which can be implemented in
coagulation models. While most coagulation theories assume that it is difficult
for like-charged grains to coagulate, the OML_LOS approximation indicates that
the electric potentials of aggregate structures are often reduced enough to
allow significant coagulation to occur
WINDOW: A computer program for planning astronomical observations
A FORTRAN computer program called WINDOW was written to simplify the planning of astronomical observations of a number of objects in a limited time. The program lists the azimuths at 15 minute intervals of up to 20 objects while they are in a given range of elevation angles - the window - and gives the elevation angle of each object at its time of transit. This work was motivated by the need to use observing time efficiently on flights of NASA-Ames' Lear Jet and C-141 observatories; WINDOW permits the investigator to prepare preliminary flight plans. However, the program is suited to planning ground-based observations as well. The program and a sample flight plan are described
Analytical calculation of the areas of Saturn's disk and rings
The area of the visible disk, the area of the ansae (visible rings not overlapping the disk), and the area of overlap (visible rings overlapping the disk) were analytically determined to account for the thermal emission from the rings. These parameters were available in the ephemeris
Body dissatisfaction, appearance investment and wellbeing: how older obese men orient to 'aesthetic health' [forthcoming]
Most research on male body image to date has focused on young men using quantitative methods. The study reported here is based on qualitative interviews with a sample of older men (n = 30) on a weight management programme, and we asked them about body-related feelings. The interviews were all transcribed and analysed using thematic analysis. Our results indicate that although body weight was typically minimised, body image was a key concern, with many examples of body consciousness and body dissatisfaction evident. On the other hand, post-programme weight loss was associated with a transformative shift in body image, with the men emphasising enhanced body confidence, self-esteem and psychological wellbeing. We conclude by highlighting the need to recognise and address appearance issues and/as health concerns for middle-aged and older men
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Citation and peer review of data: moving towards formal data publication
This paper discusses many of the issues associated with formally publishing data in academia, focusing primarily on the structures that need to be put in place for peer review and formal citation of datasets. Data publication is becoming increasingly important to the scientific community, as it will provide a mechanism for those who create data to receive academic credit for their work and will allow the conclusions arising from an analysis to be more readily verifiable, thus promoting transparency in the scientific process. Peer review of data will also provide a mechanism for ensuring the quality of datasets, and we provide suggestions on the types of activities one expects to see in the peer review of data. A simple taxonomy of data publication methodologies is presented and evaluated, and the paper concludes with a discussion of dataset granularity, transience and semantics, along with a recommended human-readable citation syntax
Charging and coagulation of dust in protoplanetary plasma environments
Combining a particle-particle, particle-cluster and cluster-cluster
agglomeration model with an aggregate charging model, the coagulation and
charging of dust particles in various plasma environments relevant for
proto-planetary disks have been investigated. The results show that charged
aggregates tend to grow by adding small particles and clusters to larger
particles and clusters, leading to greater sizes and masses as compared to
neutral aggregates, for the same number of monomers in the aggregate. In
addition, aggregates coagulating in a Lorentzian plasma (containing a larger
fraction of high-energy plasma particles) are more massive and larger than
aggregates coagulating in a Maxwellian plasma, for the same plasma densities
and characteristic temperature. Comparisons of the grain structure, utilizing
the compactness factor, {\phi}{\sigma}, demonstrate that a Lorentzian plasma
environment results in fluffier aggregates, with small {\phi}{\sigma}, which
exhibit a narrow compactness factor distribution. Neutral aggregates are more
compact, with larger {\phi}{\sigma}, and exhibit a larger variation in
fluffiness. Measurement of the compactness factor of large populations of
aggregates is shown to provide information on the disk parameters that were
present during aggregation
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