2,916 research outputs found
Who Cares about Axiomatization? Representation, Invariance, and Formal Ontologies
The philosophy of science of Patrick Suppes is centered on two important notions that are
part of the title of his recent book (Suppes 2002): Representation and Invariance.
Representation is important because when we embrace a theory we implicitly choose a way to
represent the phenomenon we are studying. Invariance is important because, since invariants
are the only things that are constant in a theory, in a way they give the “objective” meaning of
that theory.
Every scientific theory gives a representation of a class of structures and studies the invariant
properties holding in that class of structures. In Suppes’ view, the best way to define this class
of structures is via axiomatization. This is because a class of structures is given by a
definition, and this same definition establishes which are the properties that a single structure
must possess in order to belong to the class. These properties correspond to the axioms of a
logical theory.
In Suppes’ view, the best way to characterize a scientific structure is by giving a
representation theorem for its models and singling out the invariants in the structure.
Thus, we can say that the philosophy of science of Patrick Suppes consists in the application
of the axiomatic method to scientific disciplines.
What I want to argue in this paper is that this application of the axiomatic method is also at
the basis of a new approach that is being increasingly applied to the study of computer
science and information systems, namely the approach of formal ontologies.
The main task of an ontology is that of making explicit the conceptual structure underlying a
certain domain. By “making explicit the conceptual structure” we mean singling out the most
basic entities populating the domain and writing axioms expressing the main properties of
these primitives and the relations holding among them.
So, in both cases, the axiomatization is the main tool used to characterize the object of
inquiry, being this object scientific theories (in Suppes’ approach), or information systems
(for formal ontologies).
In the following section I will present the view of Patrick Suppes on the philosophy of science
and the axiomatic method, in section 3 I will survey the theoretical issues underlying the work
that is being done in formal ontologies and in section 4 I will draw a comparison of these two
approaches and explore similarities and differences between them
Interacting epidemics and coinfection on contact networks
The spread of certain diseases can be promoted, in some cases substantially,
by prior infection with another disease. One example is that of HIV, whose
immunosuppressant effects significantly increase the chances of infection with
other pathogens. Such coinfection processes, when combined with nontrivial
structure in the contact networks over which diseases spread, can lead to
complex patterns of epidemiological behavior. Here we consider a mathematical
model of two diseases spreading through a single population, where infection
with one disease is dependent on prior infection with the other. We solve
exactly for the sizes of the outbreaks of both diseases in the limit of large
population size, along with the complete phase diagram of the system. Among
other things, we use our model to demonstrate how diseases can be controlled
not only by reducing the rate of their spread, but also by reducing the spread
of other infections upon which they depend.Comment: 9 pages, 3 figure
High-mass star formation in southern disk galaxies
As part of a major study of the physical processes of star formation and the evolution of galactic discs, the detailed distribution of high-mass star formation within southern late-type spirals and Magellanic-type galaxies is being measured by means of narrow-band imaging in Ha and the continuum, spectroscopic studies of prominent HII regions identified in the Ha images, and by radio mapping in neutral hydrogen and the continuum. The radio mapping will be undertaken with the Southern Hemisphere's first large, multi-frequency synthesis array, the Australia Telescope. Some optical imaging and spectroscopic data has already been acquired; the optical data and some preliminary results are described
Superconducting Superstructure for the TESLA Collider
We discuss the new layout of a cavity chain (superstructure) allowing, we
hope, significant cost reduction of the RF system of both linacs of the TESLA
linear collider. The proposed scheme increases the fill factor and thus makes
an effective gradient of an accelerator higher. We present mainly computations
we have performed up to now and which encouraged us to order the copper model
of the scheme, still keeping in mind that experiments with a beam will be
necessary to prove if the proposed solution can be used for the acceleration.Comment: 11 page
The effects of tidally induced disc structure on white dwarf accretion in intermediate polars
We investigate the effects of tidally induced asymmetric disc structure on
accretion onto the white dwarf in intermediate polars. Using numerical
simulation, we show that it is possible for tidally induced spiral waves to
propagate sufficiently far into the disc of an intermediate polar that
accretion onto the central white dwarf could be modulated as a result. We
suggest that accretion from the resulting asymmetric inner disc may contribute
to the observed X-ray and optical periodicities in the light curves of these
systems. In contrast to the stream-fed accretion model for these periodicities,
the tidal picture predicts that modulation can exist even for systems with
weaker magnetic fields where the magnetospheric radius is smaller than the
radius of periastron of the mass transfer stream. We also predict that
additional periodic components should exist in the emission from low mass ratio
intermediate polars displaying superhumps.Comment: 9 pages, 5 figures, accepted for publication in MNRA
WD1953-011 - a magnetic white dwarf with peculiar field structure
We present H-alpha spectra of the magnetic white dwarf star WD1953-011 which
confirm the presence of the broad Zeeman components corresponding to a field
strength of about 500kG found by Maxted & Marsh (1999). We also find that the
line profile is variable over a timescale of a day or less. The core of the
H-alpha line also shows a narrow Zeeman triplet corresponding to a field
strength of of about 100kG which appears to be almost constant in shape. These
observations suggest that the magnetic field on WD1953-011 has a complex
structure and that the star has a rotational period of hours or days which
causes the observed variability of the spectra. We argue that neither an offset
dipole model nor a double-dipole model are sufficient to explain our
observations. Instead, we propose a two component model consisting of a high
field region of magnetic field strength of about 500kG covering about 10% of
the surface area of the star superimposed on an underlying dipolar field of
mean field strength of about 70kG. Radial velocity measurements of the narrow
Zeeman triplet show that the radial velocity is constant to within a few km/s
so this star is unlikely to be a close binary.Comment: Accpeted for publication in MNRAS. 4 pages, 2 figure
Polars Changing State: Multiwavelength Long Term Photometry and Spectroscopy of QS Tel, V834 Cen, and BL Hyi
Long term optical and near-infrared photometric and blue spectroscopic
observations were obtained for QS Tel, V834 Cen, and BL Hyi. The optical light
curves of all three polars displayed large magnitude changes during our
observations. These same high/low state transitions were also apparent in
near-infrared JHK photometry, though with decreased amplitude. The color of the
polar with respect to its state was examined and found not to be a good
indicator of the instantaneous state. During low to high state transitions, a
nearly constant magnitude difference was observed in all three polars. This
m value was found to be consistent with the level expected to occur if
accretion onto the white dwarf reached the Eddington luminosity during the high
state. The high state Balmer decrement was measured for each star and used to
estimate that the temperature of the emission line forming region was ~12,000K
with N near 12.8 dex. No relationship between the Balmer emission line
strength and the white dwarf magnetic field strength was seen, in contrast to a
good correlation between these two parameters observed for UV emission lines.Comment: 9 figures, 4 tables; accepted for publication in PAS
Statistical properties of stochastic 2D Navier-Stokes equations from linear models
A new approach to the old-standing problem of the anomaly of the scaling
exponents of nonlinear models of turbulence has been proposed and tested
through numerical simulations. This is achieved by constructing, for any given
nonlinear model, a linear model of passive advection of an auxiliary field
whose anomalous scaling exponents are the same as the scaling exponents of the
nonlinear problem. In this paper, we investigate this conjecture for the 2D
Navier-Stokes equations driven by an additive noise. In order to check this
conjecture, we analyze the coupled system Navier-Stokes/linear advection system
in the unknowns . We introduce a parameter which gives a
system ; this system is studied for any
proving its well posedness and the uniqueness of its invariant measure
.
The key point is that for any the fields and
have the same scaling exponents, by assuming universality of the
scaling exponents to the force. In order to prove the same for the original
fields and , we investigate the limit as , proving that
weakly converges to , where is the only invariant
measure for the joint system for when .Comment: 23 pages; improved versio
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