537 research outputs found
An Alternative to Spinning Dust for the Microwave Emission of LPH 201.663+1.643: an Ultracompact HII Region
The microwave spectral energy distribution of the dusty, diffuse H II region
LPH 201.663+1.643 has been interpreted by others as tentative evidence for
microwave emission from spinning dust grains. We present an alternative
interpretation for that particular object; specifically, that an ultracompact H
II region embedded within the dust cloud would explain the available
observations as well or better than spinning dust. Parameters for the size,
surface brightness, and flux density of the putative ultracompact HII region,
derived from the microwave observations, are within known ranges. A possible
candidate for such an ultracompact H II region is IRAS 06337+1051, based upon
its infrared colors. However, IRAS 06337+1051's infrared flux appears to be too
small to be consistent with the microwave flux required for this alternative
model to explain the observations.Comment: 11 pages, 3 figures, accepted to ApJ Letter
Near-infrared images of star forming regions containing masers. Las Campanas observations of 31 southern sources
We present sensitive high resolution near infrared (NIR) broad band (J, H, and K) observations of a sample of 31 Star Forming Regions (SFRs) which contain H_2O and OH maser sources. The observations are aimed at the detection and characterization of Young Stellar Objects (YSOs) which may be the source of excitation of the maser emission. In spite of the large number of sources detected in the regions, using positional coincidence and NIR colours we are able to reliably identify K-band sources related to the masing gas in a large fraction of the observed regions. The NIR infrared sources selected from close positional coincidence with the maser show strong NIR excesses and most probably represent the YSOs still embedded in their parental cocoon where the maser emission occurs
MERLIN radio detection of an interaction zone within a binary Orion proplyd system
Presented here are high angular resolution MERLIN 5 GHz (6 cm) continuum
observations of the binary proplyd system, LV 1 in the Orion nebula, which
consists of proplyd 168--326SE and its binary proplyd companion 168--326NW
(separation 0.4 arcsec). Accurate astrometric alignment allows a detailed
comparison between these data and published HST PC Halpha and [Oiii] images.
Thermal radio sources coincide with the two proplyds and originate in the
ionized photoevaporating flows seen in the optical emission lines. Flow
velocities of approx 50 km/s from the ionized proplyd surfaces and \geq 100
km/s from a possible micro-jet have been detected using the Manchester Echelle
spectrometer.
A third radio source is found to coincide with a region of extended, high
excitation, optical line emission that lies between the binary proplyds
168--326SE/326NW . This is modelled as a bowshock due to the collision of the
photoevaporating flows from the two proplyds. Both a thermal and a non-thermal
origin for the radio emission in this collision zone are considered.Comment: 23 pages, 9 figures, accepted by Ap
A Semantic Approach to Decidability in Epistemic Planning
The use of Dynamic Epistemic Logic (DEL) in multi-agent planning has led to a widely adopted action formalism that can handle nondeterminism, partial observability and arbitrary knowledge nesting. As such expressive power comes at the cost of undecidability, several decidable fragments have been isolated, mainly based on syntactic restrictions of the action formalism. In this paper, we pursue a novel semantic approach to achieve decidability. Namely, rather than imposing syntactical constraints, the semantic approach focuses on the axioms of the logic for epistemic planning. Specifically, we augment the logic of knowledge S5n and with an interaction axiom called (knowledge) commutativity, which controls the ability of agents to unboundedly reason on the knowledge of other agents. We then provide a threefold contribution. First, we show that the resulting epistemic planning problem is decidable. In doing so, we prove that our framework admits a finitary non-fixpoint characterization of common knowledge, which is of independent interest. Second, we study different generalizations of the commutativity axiom, with the goal of obtaining decidability for more expressive fragments of DEL. Finally, we show that two well-known epistemic planning systems based on action templates, when interpreted under the setting of knowledge, conform to the commutativity axiom, hence proving their decidability
Data-aware conformance checking with SMT
Conformance checking is a key process mining task to confront the normative behavior imposed by a process model with the actual behavior recorded in a log. While this problem has been extensively studied for pure control-flow processes, data-aware conformance checking has received comparatively little attention. In this paper, we tackle the conformance checking problem for the challenging scenario of processes that combine data and control-flow dimensions. Concretely, we adopt the formalism of data Petri nets (DPNs) and show how solid, well-established automated reasoning techniques from the area of Satisfiability Modulo Theories (SMT) can be effectively harnessed to compute conformance metrics and optimal data-aware alignments. To this end, we introduce the CoCoMoT (Computing Conformance Modulo Theories) framework, with a fourfold contribution. First, we show how SMT allows to leverage SAT-based encodings for the pure control-flow setting to the data-aware case. Second, we introduce a novel preprocessing technique based on a notion of property-preserving clustering, to speed up the computation of conformance checking outputs. Third, we show how our approach extends seamlessly to the more comprehensive conformance checking artifacts of multi- and anti-alignments. Fourth, we describe a proof-of-concept implementation based on state-of-the-art SMT solvers, and report on experiments. Finally, we discuss how CoCoMoT directly lends itself to further process mining tasks like log analysis by clustering and model repair, and the use of SMT facilitates the support of even richer multi-perspective models, where, for example, more expressive DPN guards languages are considered or generic datatypes (other than integers or reals) are employed
A dynamic role of mastermind-like 1. A journey through the main (path)ways between development and cancer
Major signaling pathways, such as Notch, Hedgehog (Hh), Wnt/β-catenin and Hippo, are targeted by a plethora of physiological and pathological stimuli, ultimately resulting in the modulation of genes that act coordinately to establish specific biological processes. Many biological programs are strictly controlled by the assembly of multiprotein complexes into the nucleus, where a regulated recruitment of specific transcription factors and coactivators on gene promoter region leads to different transcriptional outcomes. MAML1 results to be a versatile coactivator, able to set up synergistic interlinking with pivotal signaling cascades and able to coordinate the network of cross-talking pathways. Accordingly, despite its original identification as a component of the Notch signaling pathway, several recent reports suggest a more articulated role for MAML1 protein, showing that it is able to sustain/empower Wnt/β-catenin, Hh and Hippo pathways, in a Notch-independent manner. For this reason, MAML1 may be associated to a molecular “switch”, with the function to control the activation of major signaling pathways, triggering in this way critical biological processes during embryonic and post-natal life. In this review, we summarize the current knowledge about the pleiotropic role played by MAML proteins, in particular MAML1, and we recapitulate how it takes part actively in physiological and pathological signaling networks. On this point, we also discuss the contribution of MAML proteins to malignant transformation. Accordingly, genetic alterations or impaired expression of MAML proteins may lead to a deregulated crosstalk among the pathways, culminating in a series of pathological disorders, including cancer development. Given their central role, a better knowledge of the molecular mechanisms that regulate the interplay of MAML proteins with several signaling pathways involved in tumorigenesis may open up novel opportunities for an attractive molecular targeted anticancer therapy
Compact Radio Sources in Orion: New Detections, Time Variability, and Objects in OMC-1S
We present the analysis of four 3.6 cm radio continuum archival observations
of Orion obtained using the Very Large Array in its A-configuration, with
angular resolution. The observations were made during the period
1994-1997. In a region of , we detect a total of 77 compact radio
sources. Of the total of detected sources, 54 are detected in one or more of
the individual observations and 36 of these show time variability (by more than
30%) between the observed epochs. A deep image made from averaging all data
shows an additional 23 faint sources, in the range of 0.1 to 0.3 mJy. Of the
total of 77 sources, 39 are new centimeter detections. However, only 9 of the
77 sources do not have a previously reported counterpart at near-infrared,
optical, or X-ray wavelengths. In particular, we detect three faint sources in
the OMC-1S region that may be related to the sources that power the multiple
outflows that emanate from this part of the Orion nebula. %We discuss the
nature of these sources and its relation with the %near-infrared, optical, and
X-ray objects in the region.Comment: 29 pages, 9 figure
Proper Motion of Water Masers Associated with IRAS 21391+5802: Bipolar Outflow and an AU-Scale Dusty Circumstellar Shell
We present VLBA observations of water maser emission associated with the
star-forming region IRAS 21391+5802, which is embedded in a bright rimmed
cometary globule in IC1396. The angular resolution of the maps is about 0.8
mas, corresponding to a spatial resolution of about 0.6 AU, at an estimated
distance of 750 pc. Proper motions are derived for 10 maser features identified
consistently over three epochs, which were separated by intervals of about one
month. The masers appear in four groups, which are aligned linearly on the sky,
roughly along a northeast-southwest direction, with a total separation of about
520 AU (about 0.7 arcseconds). The 3-D velocities of the masers have a maximum
value of about 42 km/s (about 9 AU/yr). The average error on the derived proper
motions is about 4 km/s. The overall pattern of proper motions is indicative of
a bipolar outflow. Proper motions of the masers in a central cluster, with a
projected extent of about 20 AU, show systematic deviations from a radial
outflow. However, we find no evidence of Keplerian rotation, as has been
claimed elsewhere. A nearly circular loop of masers lies near the middle of the
cluster. The radius of this loop is 1 AU and the line-of-sight velocities of
the masers in the loop are within 2 km/s of the systemic velocity of the
region. These masers presumably exist at the radial distance where significant
dust condensation occurs in the outflow emanating from the star.Comment: 15 pages, 4 figures. Accepted for publication in the Astrophysical
Journal. Version 2.12.00: Astrometric coordinates of maser revise
3-He in the Milky Way Interstellar Medium: Ionization Structure
The cosmic abundance of the 3-He isotope has important implications for many
fields of astrophysics. We are using the 8.665 GHz hyperfine transition of
3-He+ to determine the 3-He/H abundance in Milky Way HII regions and planetary
nebulae. This is one in a series of papers in which we discuss issues involved
in deriving accurate 3-He/H abundance ratios from the available measurements.
Here we describe the ionization correction we use to convert the 3-He+/H+
abundance, y3+, to the 3-He/H abundance, y3. In principle the nebular
ionization structure can significantly influence the y3 derived for individual
sources. We find that in general there is insufficient information available to
make a detailed ionization correction. Here we make a simple correction and
assess its validity. The correction is based on radio recombination line
measurements of H+ and 4-He+, together with simple core-halo source models. We
use these models to establish criteria that allow us to identify sources that
can be accurately corrected for ionization and those that cannot. We argue that
this effect cannot be very large for most of the sources in our observational
sample. For a wide range of models of nebular ionization structure we find that
the ionization correction factor varies from 1 to 1.8. Although large
corrections are possible, there would have to be a conspiracy between the
density and ionization structure for us to underestimate the ionization
correction by a substantial amount.Comment: 36 pages, 4 figures To appear Astrophysical Journal, 20 August 2007,
vol 665, no
A multiwavelength study of Galactic HII region Sh2-294
We present the observational results of Galactic HII region S294, using
optical photometry, narrow-band imaging and radio continuum mapping at 1280
MHz, together with archival data from 2MASS, MSX and IRAS surveys. The stellar
surface density profile indicates that the radius of the cluster associated
with the S294 region is ~ 2.3 arcmin. We found an anomalous reddening law for
the dust inside the cluster region and the ratio of total-to-selective
extinction is found to be 3.8+-0.1. We estimate the minimum reddening E (B-V) =
1.35 mag and distance of 4.8+-0.2 kpc to the region from optical CC and CM
diagrams. We identified the ionizing source of the HII region, and spectral
type estimates are consistent with a star of spectral type ~ B0 V. The 2MASS
JHKs images reveal a partially embedded cluster associated with the ionizing
source along with a small cluster towards the eastern border of S294. The
ionization front seen along the direction of small cluster in radio continuum
and Halpha images, might be due to the interaction of ionizing sources with the
nearby molecular cloud. We found an arc shaped diffuse molecular hydrogen
emission at 2.12 micron and a half ring of MSX dust emission which surrounds
the ionized gas in the direction of the ionization front. Self consistent
radiative transfer model of mid- to far-infrared continuum emission detected
near small cluster is in good agreement with the observed spectral energy
distribution of a B1.5 ZAMS star. The morphological correlation between the
ionised and molecular gas, along with probable time scale involved between the
ionising star, evolution of HII region and small cluster, indicates that the
star-formation activity observed at the border is probably triggered by the
expansion of HII region.Comment: 50 pages, 21 figures: Accepted by The Astrophysical Journal; Also
available at http://www.tifr.res.in/~ojha/S294.pd
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