18,953 research outputs found
An infrared proper motion study of the Orion bullets
We report the first IR proper motion measurements of the Herbig-Haro objects
in the Orion Molecular Cloud--One using a four-year time baseline. The [Fe II]
emitting bullets are moving of order 0.08 arcsec per year, or at about 170
\kms. The direction of motion is similar to that inferred from their
morphology. The proper motions of \h2 emitting wakes behind the [Fe II]
bullets, and of newly found \h2 bullets, are also measured. \h2 bullets have
smaller proper motion than [Fe II] bullets, while \h2 wakes with leading [Fe
II] bullets appear to move at similar speeds to their associated bullets. A few
instances of variability in the emission can be attributed to dense, stationary
clumps in the ambient cloud being overrun, setting up a reverse--oriented
bullet. Differential motion between [Fe II] bullets and their trailing \h2
wakes is not observed, suggesting that these are not separating, and also that
they have reached a steady--state configuration over at least 100 years. The
most distant bullets have, on average, larger proper motions, but are not
consistent with free expansion. Nevertheless an impulsive, or short--lived
( 1,000 years) duration for their origin seems likely.Comment: 9 pages, 8 figure
The southern dust pillars of the Carina Nebula
We present preliminary results from a detailed study towards four previously
detected bright mid-infrared sources in the southern part of the Carina Nebula:
G287.73--0.92, G287.84--0.82, G287.93--0.99 and G288.07--0.80. All of these
sources are located at the heads of giant dust pillars that point towards the
nearby massive star cluster, Trumpler 16. It is unclear if these pillars are
the prime sites for a new generation of triggered star formation or if instead
they are the only remaining parts of the nebula where ongoing star fromation
can take place.Comment: 2 pages, to appear in the proceedings of "Hot Star Workshop III: The
Earliest Phases of Massive Star Birth" (ed. P.A. Crowther
Slowing the Loop: the role of grief and hope in building new economic spaces
This is the final version.In this paper we examine how civil society groups are tackling plastics within the South West region of England. We consider the drivers behind the rapid rise in 'plastic activism' in the region and how these groups contribute to wider considerations of the circular economy. We critique the techno-managerial conceptualisations of the circular economy and rational-actor approaches to nudging individual behaviours and call for more attention to be made to the relational, emotional, and affective connections that people have toward place, environment, and non-human beings. We consider the role of emotions and affect in driving new social practices that are, in turn, re-articulating local economic geographies through place-based responses to environmental concerns. We pose that, in response to feelings of grief and loss (for ecological decline and lost futures; see Head 2016), civil society groups are finding small spaces of hope that contribute to a plastics circular economy through new and reclaimed social practices that slow the loop
Vibrations of closed-shell Lennard-Jones icosahedral and cuboctahedral clusters and their effect on the cluster ground state energy
Vibrational spectra of closed shell Lennard-Jones icosahedral and
cuboctahedral clusters are calculated for shell numbers between 2 and 9.
Evolution of the vibrational density of states with the cluster shell number is
examined and differences between icosahedral and cuboctahedral clusters
described. This enabled a quantum calculation of quantum ground state energies
of the clusters in the quasiharmonic approximation and a comparison of the
differences between the two types of clusters. It is demonstrated that in the
quantum treatment, the closed shell icosahedral clusters binding energies
differ from those of cuboctahedral clusters more than is the case in classical
treatment
The distribution of species range size: a stochastic process
The major role played by environmental factors in determining the geographical range sizes of species raises the possibility of describing their long-term dynamics in relatively simple terms, a goal which has hitherto proved elusive. Here we develop a stochastic differential equation to describe the dynamics of the range size of an individual species based on the relationship between abundance and range size, derive a limiting stationary probability model to quantify the stochastic nature of the range size for that species at steady state, and then generalize this model to the species-range size distribution for an assemblage. The model fits well to several empirical datasets of the geographical range sizes of species in taxonomic assemblages, and provides the simplest explanation of species-range size distributions to date
Unlocking the Keyhole - H2 and PAH emission from molecular clumps in the Keyhole Nebula
To better understand the environment surrounding CO emission clumps in the
Keyhole Nebula, we have made images of the region in H2 1-0 S(1) (2.122 um)
emission and polycyclic aromatic hydrocarbon (PAH) emission at 3.29 um. Our
results show that the H2 and PAH emission regions are morphologically similar,
existing as several clumps, all of which correspond to CO emission clumps and
dark optical features. The emission confirms the existence of photodissociation
regions (PDRs) on the surface of the clumps. By comparing the velocity range of
the CO emission with the optical appearance of the H2 and PAH emission, we
present a model of the Keyhole Nebula in which the most negative velocity
clumps are in front of the ionization region, the clumps at intermediate
velocities are in it, and those which have the least negative velocities are at
the far side. It may be that these clumps, which appear to have been swept up
from molecular gas by the stellar winds from eta Car, are now being over-run by
the ionization region and forming PDRs on their surfaces. These clumps comprise
the last remnants of the ambient molecular cloud around eta Car.Comment: 8 pages, 4 figures, to be published in MNRA
A Technique for Correlative Scanning and Transmission Electron Microscopy of Individual Human Placental Villi: An Example Demonstrating Syncytial Sprouts in Early Gestation
Correlating the surface appearances of certain features with their internal structure is made particularly difficult in the human placenta by the complex three-dimensional branching pattern of the villous tree. This places a possible limitation on the use of the scanning electron microscope in this field, both for basic research purposes and as a tool in pathological diagnosis. To help overcome this problem, a technique for handling individual placental villi has been devised. By attaching single villi to glass pipette tips it has proved possible to scan the villi, embed them in resin and then section them in a known pre-determined orientation. Exact correlations between the surface appearances and the internal structure, as seen with either the light or transmission electron microscope, can then be drawn. This paper describes the technique and, using an example based on syncytial sprouts in early pregnancy, illustrates the precision afforded by the method
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