7,747 research outputs found
How to do things without words
Clark and Chalmers (1998) defend the hypothesis of an âExtended Mindâ, maintaining that beliefs and other paradigmatic mental states can be implemented outside the central nervous system or body. Aspects of the problem of âlanguage acquisitionâ are considered in the light of the extended mind hypothesis. Rather than âlanguageâ as typically understood, the object of study is something called âutterance-activityâ, a term of art intended to refer to the full range of kinetic and prosodic features of the on-line behaviour of interacting humans. It is argued that utterance activity is plausibly regarded as jointly controlled by the embodied activity of interacting people, and that it contributes to the control of their behaviour. By means of specific examples it is suggested that this complex joint control facilitates easier learning of at least some features of language. This in turn suggests a striking form of the extended mind, in which infantsâ cognitive powers are augmented by those of the people with whom they interact
The Puzzling Spectrum of HD 94509
The spectral features of HD 94509 are highly unusual, adding an extreme to
the zoo of Be and shell stars. The shell dominates the spectrum, showing lines
typical for spectral types mid-A to early-F, while the presence of a late/mid
B-type central star is indicated by photospheric hydrogen line wings and helium
lines. Numerous metallic absorption lines have broad wings but taper to narrow
cores. They cannot be fit by Voigt profiles.
We aim to describe and illustrate unusual spectral features of this star, and
make rough calculations to estimate physical conditions and abundances in the
shell. Furthermore, the central star is characterized.
We assume mean conditions for the shell. An electron density estimate is made
from the Inglis-Teller formula. Excitation temperatures and column densities
for Fe I and Fe II are derived from curves of growth. The neutral H column
density is estimated from high Paschen members. The column densities are
compared with calculations made with the photoionization code Cloudy.
Atmospheric parameters of the central star are constrained employing non-LTE
spectrum synthesis.
Overall chemical abundances are close to solar. Column densities of the
dominant ions of several elements, as well as excitation temperatures and the
mean electron density are well accounted for by a simple model. Several
features, including the degree of ionization, are less well described.
HD 94509 is a Be star with a stable shell, close to the terminal-age main
sequence. The dynamical state of the shell and the unusually shaped, but
symmetric line profiles, require a separate study.Comment: 10 pages, 9 tables, 13 figures; accepted for publication by Astronomy
and Astrophysic
Nonlinear mirror instability
Slow dynamical changes in magnetic-field strength and invariance of the
particles' magnetic moments generate ubiquitous pressure anisotropies in weakly
collisional, magnetized astrophysical plasmas. This renders them unstable to
fast, small-scale mirror and firehose instabilities, which are capable of
exerting feedback on the macroscale dynamics of the system. By way of a new
asymptotic theory of the early nonlinear evolution of the mirror instability in
a plasma subject to slow shearing or compression, we show that the instability
does not saturate quasilinearly at a steady, low-amplitude level. Instead, the
trapping of particles in small-scale mirrors leads to nonlinear secular growth
of magnetic perturbations, . Our theory explains
recent collisionless simulation results, provides a prediction of the mirror
evolution in weakly collisional plasmas and establishes a foundation for a
theory of nonlinear mirror dynamics with trapping, valid up to .Comment: 5 pages, submitte
Jupiter's polar ionospheric flows: measured intensity and velocity variations poleward of the main auroral oval
Recent analysis of high-resolution spectra of Doppler-shifted H3+ emission from the auroral/polar regions of Jupiter revealed a complex wind system, with a persistent auroral electrojet and strong anti-sunward flows in a region of lesser intensity centred around the magnetic pole [ Stallard et al., 2001 ]. This region, which we have called the Dark Polar Region (DPR), is re-investigated, transforming the observed line-of-sight velocities into a frame of reference fixed with respect to the magnetic pole. The DPR is shown to include a region essentially stagnant in this frame of reference (the f-DPR). We identify it as a region coupled to open magnetotail field lines. There is also a transition region in which the ion velocity returns to corotation (the r-DPR)
Lanthanides and other spectral oddities in a Centauri
Context: There is considerable interest in the helium variable a Cen as a
bridge between helium-weak and helium-strong CP stars. Aims: We investigate Ce
III and other possible lanthanides in the spectrum the of hottest chemically
peculiar (CP) star in which these elements have been found. A {Kr II line
appears within a broad absorption which we suggest may be due to a high-level
transition in C II. Methods: Wavelengths and equivalent widths are measured on
high-resolution UVES spectra, analyzed, and their phase-variations
investigated. Results: New, robust identifications of Ce III and Kr II are
demonstrated. Nd III is likely present. A broad absorption near 4619[A] is
present at all phases of a Cen, and in some other early B stars. Conclusions:
The presence of lanthanides in a Cen strengthens the view that this star is a
significant link between the cooler CP stars and the hotter helium-peculiar
stars. Broad absorptions in a Cen are not well explained.Comment: Research Note accepted by Astronomy and Astrophysics; 4 pages, 4
Figs. 2 Table
National Policies for Local Urban Sustainability: A New Governance Approach?
Cities have become a focal point for efforts to transition towards a more sustainable, low-carbon society, with many municipal agencies championing âeco cityâ initiatives of one kind or another. And yet, national policy initiatives frequently play an important â if sometimes overlooked â role, too. This chapters provides comparative perspectives on four recent national sustainable city programmes from France, India, Japan, and the United Kingdom. The analysis reveals two key insights: first, national policy is found to exercise a strong shaping role in what sustainable development for future cities is understood to be, which helps explain the considerable differences in priorities and approaches across countries. Second, beyond articulating strategic priorities, national policy may exercise a âsoftâ governance function by incentivising and facilitating wider, voluntary governance networks in the effort to implement sustainable city projects locally. This innovative role, however, depends on the ability of national policy to produce resonance among societal actors and on its effective interaction with formal planning processes
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