8,261 research outputs found
C2D Spitzer-IRS spectra of disks around T Tauri stars V. Spectral decomposition
(Abridged) Dust particles evolve in size and lattice structure in
protoplanetary disks, due to coagulation, fragmentation and crystallization,
and are radially and vertically mixed in disks. This paper aims at determining
the mineralogical composition and size distribution of the dust grains in disks
around 58 T Tauri stars observed with Spitzer/IRS. We present a spectral
decomposition model that reproduces the IRS spectra over the full spectral
range. The model assumes two dust populations: a warm component responsible for
the 10\mu m emission arising from the disk inner regions and a colder component
responsible for the 20-30\mu m emission, arising from more distant regions. We
show evidence for a significant size distribution flattening compared to the
typical MRN distribution, providing an explanation for the usual boxy 10\mu m
feature profile generally observed. We reexamine the crystallinity paradox,
observationally identified by Olofsson et al. (2009), and we find a
simultaneous enrichment of the crystallinity in both the warm and cold regions,
while grain sizes in both components are uncorrelated. Our modeling results do
not show evidence for any correlations between the crystallinity and either the
star spectral type, or the X-ray luminosity (for a subset of the sample). The
size distribution flattening may suggests that grain coagulation is a slightly
more effective process than fragmentation in disk atmospheres, and that this
imbalance may last over most of the T Tauri phase. This result may also point
toward small grain depletion via strong stellar winds or radiation pressure in
the upper layers of disk. The non negligible cold crystallinity fractions
suggests efficient radial mixing processes in order to distribute crystalline
grains at large distances from the central object, along with possible nebular
shocks in outer regions of disks that can thermally anneal amorphous grains
Early Greek Thought and Perspectives for the Interpretation of Quantum Mechanics: Preliminaries to an Ontological Approach
It will be shown in this article that an ontological approach for some
problems related to the interpretation of Quantum Mechanics could emerge from a
re-evaluation of the main paradox of early Greek thought: the paradox of Being
and non-Being, and the solutions presented to it by Plato and Aristotle.
Plato's and Aristotle's systems are argued here to do on the ontological level
essentially the same: to introduce stability in the world by introducing the
notion of a separable, stable object, for which a principle of contradiction is
valid: an object cannot be and not-be at the same place at the same time. After
leaving Aristotelian metaphysics, early modern science had to cope with these
problems: it did so by introducing ``space'' as the seat of stability, and
``time'' as the theater of motion. But the ontological structure present in
this solution remained the same. Therefore the fundamental notion `separable
system', related to the notions observation and measurement, themselves related
to the modern concepts of space and time, appears to be intrinsically
problematic, because it is inextricably connected to classical logic on the
ontological level. We see therefore the problems dealt with by quantum logic
not as merely formal, and the problem of `non-locality' as related to it,
indicating the need to re-think the notions `system', `entity', as well as the
implications of the operation `measurement', which is seen here as an
application of classical logic (including its ontological consequences) on the
material world.Comment: 18 page
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