247 research outputs found
Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis
We report the results of spectroscopic mapping observations carried out
toward small (1 x 1 arcmin) regions within the supernova remnants W44, W28,
IC443, and 3C391 using the Infrared Spectrograph of the Spitzer Space
Telescope. These observations, covering the 5.2 - 37 micron spectral region,
have led to the detection of a total of 15 fine structure transitions of Ne+,
Ne++, Si+, P+, S, S++, Cl+, Fe+, and Fe++; the S(0) - S(7) pure rotational
lines of molecular hydrogen; and the R(3) and R(4) transitions of hydrogen
deuteride. In addition to these 25 spectral lines, the 6.2, 7.7, 8.6, 11.3 and
12.6 micron PAH emission bands were also observed. Most of the detected line
transitions have proven strong enough to map in several sources, providing a
comprehensive picture of the relative distribution of the various line
emissions observable in the Spitzer/IRS bandpass. A principal component
analysis of the spectral line maps reveals that the observed emission lines
fall into five distinct groups, each of which may exhibit a distinct spatial
distribution: (1) lines of S and H2 (J > 2); (2) the H2 S(0) line; (3) lines of
ions with appearance potentials less than 13.6 eV; (4) lines of ions with
appearance potentials greater than 13.6 eV, not including S++; (5) lines of
S++. Lines of group (1) likely originate in molecular material subject to a
slow, nondissociative shock that is driven by the overpressure within the
supernova remnant, and lines in groups (3) - (5) are associated primarily with
dissociative shock fronts with a range of (larger) shock velocities. The H2
S(0) line shows a low-density diffuse emission component, and - in some sources
- a shock-excited component.Comment: 43 pages, including 21 figures. Accepted for publication in Ap
Im-Promptu: In-Context Composition from Image Prompts
Large language models are few-shot learners that can solve diverse tasks from
a handful of demonstrations. This implicit understanding of tasks suggests that
the attention mechanisms over word tokens may play a role in analogical
reasoning. In this work, we investigate whether analogical reasoning can enable
in-context composition over composable elements of visual stimuli. First, we
introduce a suite of three benchmarks to test the generalization properties of
a visual in-context learner. We formalize the notion of an analogy-based
in-context learner and use it to design a meta-learning framework called
Im-Promptu. Whereas the requisite token granularity for language is well
established, the appropriate compositional granularity for enabling in-context
generalization in visual stimuli is usually unspecified. To this end, we use
Im-Promptu to train multiple agents with different levels of compositionality,
including vector representations, patch representations, and object slots. Our
experiments reveal tradeoffs between extrapolation abilities and the degree of
compositionality, with non-compositional representations extending learned
composition rules to unseen domains but performing poorly on combinatorial
tasks. Patch-based representations require patches to contain entire objects
for robust extrapolation. At the same time, object-centric tokenizers coupled
with a cross-attention module generate consistent and high-fidelity solutions,
with these inductive biases being particularly crucial for compositional
generalization. Lastly, we demonstrate a use case of Im-Promptu as an intuitive
programming interface for image generation
Distribution of Water Vapor in Molecular Clouds
We report the results of a large-area study of water vapor along the Orion
Molecular Cloud ridge, the purpose of which was to determine the
depth-dependent distribution of gas-phase water in dense molecular clouds. We
find that the water vapor measured toward 77 spatial positions along the
face-on Orion ridge, excluding positions surrounding the outflow associated
with BN/KL and IRc2, display integrated intensities that correlate strongly
with known cloud surface tracers such as CN, C2H, 13CO J =5-4, and HCN, and
less well with the volume tracer N2H+. Moreover, at total column densities
corresponding to Av < 15 mag., the ratio of H2O to C18O integrated intensities
shows a clear rise approaching the cloud surface. We show that this behavior
cannot be accounted for by either optical depth or excitation effects, but
suggests that gas-phase water abundances fall at large Av. These results are
important as they affect measures of the true water-vapor abundance in
molecular clouds by highlighting the limitations of comparing measured water
vapor column densities with such traditional cloud tracers as 13CO or C18O.
These results also support cloud models that incorporate freeze-out of
molecules as a critical component in determining the depth-dependent abundance
of water vapor
Identification of Ambient Molecular Clouds Associated with Galactic Supernova Remnant IC443
The Galactic supernova remnant (SNR) IC443 is one of the most studied
core-collapse SNRs for its interaction with molecular clouds. However, the
ambient molecular clouds with which IC443 is interacting have not been
thoroughly studied and remain poorly understood. Using Five College Radio
Astronomy Observatory 14m telescope, we obtained fully sampled maps of ~
1{\deg} \times 1{\deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0
lines. In addition to the previously known molecular clouds in the velocity
range v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new
ambient molecular cloud components: small (~ 1') bright clouds in v_lsr = -8 to
-3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds).
Our data also reveal the detailed kinematics of the shocked molecular gas in
IC443, however the focus of this paper is the physical relationship between the
shocked clumps and the ambient cloud components. We find strong evidence that
the SCs are associated with the shocked clumps. This is supported by the
positional coincidence of the SCs with shocked clumps and other tracers of
shocks. Furthermore, the kinematic features of some shocked clumps suggest that
these are the ablated material from the SCs upon the impact of the SNR shock.
The SCs are interpreted as dense cores of parental molecular clouds that
survived the destruction by the pre-supernova evolution of the progenitor star
or its nearby stars. We propose that the expanding SNR shock is now impacting
some of the remaining cores and the gas is being ablated and accelerated
producing the shocked molecular gas. The morphology of the +5 km/s clouds
suggests an association with IC443. On the other hand, the -3 km/s clouds show
no evidence for interaction.Comment: Accepted for publication in ApJ. 15 pages (with emulateapj.cls), 17
figures, and 2 table
Noticias de BahÃa Academia
El Vivero de la ECCD. Las Amenazadas Tortugas de Cerro Paloma, Isabel. El Daño de los Chivos al Volcán Alcedo. Las Colecciones del Museo de la ECCD. Chivos en Pinta, Otra Vez? Existe un Guadalupe River en Galápagos? Avistamiento de un Tirano del Este. Tomar Palabras del Pasado. ¡Es Scalesia Atractyloides! El Beagle, Bote de Investigación de la ECCD. Alcedo al DÃa. Exposición de Arte a Beneficio de Alcedo. Nueva Construcción. Actividad Geológica? Ciencia de Alta TecnologÃa. Mas Noticias Sobre Pinta. Primer Registro de la Garza Verde (Butorides Viriscens) en las Islas Galápagos. Un Vuelo sobre los Volcanes del Norte de Isabela
Giant Galápagos tortoises; molecular genetic analyses identify a trans-island hybrid in a repatriation program of an endangered taxon
BACKGROUND: Giant Galápagos tortoises on the island of Española have been the focus of an intensive captive breeding-repatriation programme for over 35 years that saved the taxon from extinction. However, analysis of 118 samples from released individuals indicated that the bias sex ratio and large variance in reproductive success among the 15 breeders has severely reduced the effective population size (N(e)). RESULTS: We report here that an analysis of an additional 473 captive-bred tortoises released back to the island reveals an individual (E1465) that exhibits nuclear microsatellite alleles not found in any of the 15 breeders. Statistical analyses incorporating genotypes of 304 field-sampled individuals from all populations on the major islands indicate that E1465 is most probably a hybrid between an Española female tortoise and a male from the island of Pinzón, likely present on Española due to human transport. CONCLUSION: Removal of E1465 as well as its father and possible (half-)siblings is warranted to prevent further contamination within this taxon of particular conservation significance. Despite this detected single contamination, it is highly noteworthy to emphasize the success of this repatriation program conducted over nearly 40 years and involving release of over 2000 captive-bred tortoises that now reproduce in situ. The incorporation of molecular genetic analysis of the program is providing guidance that will aid in monitoring the genetic integrity of this ambitious effort to restore a unique linage of a spectacular animal
Herschel Search for O_2 toward the Orion Bar
We report the results of a search for molecular oxygen (O_2) toward the Orion Bar, a prominent photodissociation region at the southern edge of the H II region created by the luminous Trapezium stars. We observed the spectral region around the frequency of the O_2 NJ = 33-12 transition at 487 GHz and the 5_(4)-3_(4) transition at 774 GHz using the Heterodyne Instrument for the Far-Infrared on the Herschel Space Observatory. Neither line was detected, but the 3σ upper limits established here translate to a total line-of-sight O2 column density <1.5 × 10^(16) cm^(–2) for an emitting region whose temperature is between 30 K and 250 K, or <1 × 10^(16) cm^(–2) if the O_2 emitting region is primarily at a temperature of ≲100 K. Because the Orion Bar is oriented nearly edge-on relative to our line of sight, the observed column density is enhanced by a factor estimated to be between 4 and 20 relative to the face-on value. Our upper limits imply that the face-on O_2 column density is less than 4 × 10^(15) cm^(–2), a value that is below, and possibly well below, model predictions for gas with a density of 10^(4)-10^(5) cm^(–3) exposed to a far-ultraviolet flux 10^4 times the local value, conditions inferred from previous observations of the Orion Bar. The discrepancy might be resolved if (1) the adsorption energy of O atoms to ice is greater than 800 K; (2) the total face-on A V of the Bar is less than required for O_2 to reach peak abundance; (3) the O_2 emission arises within dense clumps with a small beam filling factor; or (4) the face-on depth into the Bar where O_2 reaches its peak abundance, which is density dependent, corresponds to a sky position different from that sampled by our Herschel beams
Mouse Estrous Cycle Identification Tool and Images
The efficiency of producing timed pregnant or pseudopregnant mice can be increased by identifying those in proestrus or estrus. Visual observation of the vagina is the quickest method, requires no special equipment, and is best used when only proestrus or estrus stages need to be identified. Strain to strain differences, especially in coat color can make it difficult to determine the stage of the estrous cycle accurately by visual observation. Presented here are a series of images of the vaginal opening at each stage of the estrous cycle for 3 mouse strains of different coat colors: black (C57BL/6J), agouti (CByB6F1/J) and albino (BALB/cByJ). When all 4 stages (proestrus, estrus, metestrus, and diestrus) need to be identified, vaginal cytology is regarded as the most accurate method. An identification tool is presented to aid the user in determining the stage of estrous when using vaginal cytology. These images and descriptions are an excellent resource for learning how to determine the stage of the estrous cycle by visual observation or vaginal cytology
Pion-nucleus elastic scattering on 12C, 40Ca, 90Zr, and 208Pb at 400 and 500 MeV
Pion-nucleus elastic scattering at energies above the Delta(1232) resonance
is studied using both pi+ and pi- beams on 12C, 40Ca, 90Zr, and 208Pb. The
present data provide an opportunity to study the interaction of pions with
nuclei at energies where second-order corrections to impulse approximation
calculations should be small. The results are compared with other data sets at
similar energies, and with four different first-order impulse approximation
calculations. Significant disagreement exists between the calculations and the
data from this experiment
Spitzer observations of hydrogen deuteride
We report the detection of interstellar hydrogen deuteride (HD) toward the
supernova remnant IC443, and the tentative detection of HD toward the Herbig
Haro objects HH54 and HH7 and the star forming region GGD37 (Cepheus A West).
Our detections are based upon spectral line mapping observations of the R(3)
and R(4) rotational lines of HD, at rest wavelengths of 28.502 and 23.034
micron respectively, obtained using the Infrared Spectrograph onboard the
Spitzer Space Telescope. The HD R(4)/R(3) line intensity ratio promises to be a
valuable probe of the gas pressure in regions where it can be observed. The
derived HD/H2 abundance ratios are 1.19(+0.35/-0.24)E-5, 1.80(+0.54/-0.32)E-5,
and 1.41(+0.46/-0.33)E-5 respectively (68.3% confidence limits, based upon
statistical errors alone) for IC443 (clump C), HH54, and HH7. If HD is the only
significant reservoir of gas-phase deuterium in these sources, the inferred
HD/H2 ratios are all consistent with a gas-phase elemental abundance
[n(D)/n(H)](gas) ~ 7.5E-6, a factor 2 - 3 below the values obtained previously
from observations of atomic deuterium in the local bubble and the Galactic
halo. However, similarly low gas-phase deuterium abundances have been inferred
previously for molecular gas clouds in the Orion region, and in atomic clouds
along sight-lines within the Galactic disk to stars more distant than 500 pc
from the Sun.Comment: 12 pages, including 5 figures. Accepted for publication in ApJ
Letter
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