3,389 research outputs found
37 GHz methanol masers : Horsemen of the Apocalypse for the class II methanol maser phase?
We report the results of a search for class II methanol masers at 37.7, 38.3
and 38.5 GHz towards a sample of 70 high-mass star formation regions. We
primarily searched towards regions known to show emission either from the 107
GHz class II methanol maser transition, or from the 6.035 GHz excited OH
transition. We detected maser emission from 13 sources in the 37.7 GHz
transition, eight of these being new detections. We detected maser emission
from three sources in the 38 GHz transitions, one of which is a new detection.
We find that 37.7 GHz methanol masers are only associated with the most
luminous 6.7 and 12.2 GHz methanol maser sources, which in turn are
hypothesised to be the oldest class II methanol sources. We suggest that the
37.7 GHz methanol masers are associated with a brief evolutionary phase (of
1000-4000 years) prior to the cessation of class II methanol maser activity in
the associated high-mass star formation region.Comment: 14 pages, 4 figures, accepted for publication in Ap
12.2-GHz methanol maser MMB follow-up catalogue - II. Longitude range 186 to 330 degrees
We present the second portion of a catalogue of 12.2-GHz methanol masers
detected towards 6.7-GHz methanol masers observed in the unbiased Methanol
Multibeam (MMB) Survey. Using the Parkes radio telescope we have targeted all
207 6.7-GHz methanol masers in the longitude range 186 to 330 degrees for
12.2-GHz counterparts. We report the detection of 83 12.2-GHz methanol masers,
and one additional source which we suspect is thermal emission, equating to a
detection rate of 40 per cent. Of the 83 maser detections, 39 are reported here
for the first time. We discuss source properties, including variability and
highlight a number of unusual sources. We present a list of 45 candidates that
are likely to harbor methanol masers in the 107.0-GHz transition.Comment: Accepted MNRAS 19 July 201
12.2-GHz methanol maser MMB follow-up catalogue - I. Longitude range 330 to 10 degrees
We present a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz
methanol masers observed in the unbiased Methanol Multibeam (MMB) survey in the
longitude range 330\circ (through 360\circ) to 10\circ. This is the first
portion of the catalogue which, when complete, will encompass all of the MMB
detections. We report the detection of 184 12.2-GHz sources towards 400 6.7-GHz
methanol maser targets, equating to a detection rate of 46 per cent. Of the 184
12.2-GHz detections, 117 are reported here for the first time. We draw
attention to a number of 'special' sources, particularly those with emission at
12.2-GHz stronger than their 6.7-GHz counterpart and conclude that these
unusual sources are not associated with a specific evolutionary stage.Comment: accepted to MNRAS 21 Dec 201
USING INFORMATIONAL LABELING TO INFLUENCE THE MARKET FOR QUALITY IN FOOD PRODUCTS
In the United States, the federal government is increasingly using requirements for informational labeling on food products to influence 1) consumers' knowledge and purchasing patterns and 2) manufacturers' product offerings and marketing practices. We discuss the economic rationale behind these regulations and issues related to judging their success or failure.Food labeling, food quality, food safety, information, Food Consumption/Nutrition/Food Safety,
Statistical properties of 12.2 GHz methanol masers associated with a complete sample of 6.7 GHz methanol masers
We present definitive detection statistics for 12.2 GHz methanol masers
towards a complete sample of 6.7 GHz methanol masers detected in the Methanol
Multibeam survey south of declination -20 degrees. In total, we detect 250 12.2
GHz methanol masers towards 580 6.7 GHz methanol masers. This equates to a
detection rate of 43.1%, which is lower than that of previous significant
searches of comparable sensitivity. Both the velocity ranges and the flux
densities of the target 6.7 GHz sources surpass that of their 12.2 GHz
companion in almost all cases. 80 % of the detected 12.2 GHz methanol maser
peaks are coincident in velocity with the 6.7 GHz maser peak. Our data support
an evolutionary scenario whereby the 12.2 GHz sources are associated with a
somewhat later evolutionary stage than the 6.7 GHz sources devoid of this
transition. Furthermore, we find that the 6.7 GHz and 12.2 GHz methanol sources
increase in luminosity as they evolve. In addition to this, evidence for an
increase in velocity range with evolution is presented. This implies that it is
not only the luminosity, but also the volume of gas conducive to the different
maser transitions, that increases as the sources evolve. Comparison with
GLIMPSE mid-infrared sources has revealed a coincidence rate between the
locations of the 6.7 GHz methanol masers and GLIMPSE point sources similar to
that achieved in previous studies. Overall, the properties of the GLIMPSE
sources with and without 12.2 GHz counterparts are similar. There is a higher
12.2 GHz detection rate towards those 6.7 GHz methanol masers that are
coincident with extended green objects.Comment: Accepted to ApJ March 2011. 28 pages, 9 figure
Variability monitoring of the hydroxyl maser emission in G12.889+0.489
Through a series of observations with the Australia Telescope Compact Array
we have monitored the variability of ground-state hydroxyl maser emission from
G12.889+0.489 in all four Stokes polarisation products. These observations were
motivated by the known periodicity in the associated 6.7-GHz methanol maser
emission. A total of 27 epochs of observations were made over 16 months. No
emission was seen from either the 1612 or 1720 MHz satellite line transitions
(to a typical five sigma upper limit of 0.2 Jy). The peak flux densities of the
1665 and 1667 MHz emission were observed to vary at a level of ~20% (with the
exception of one epoch which dropped by <40%). There was no distinct flaring
activity at any epoch, but there was a weak indication of periodic variability,
with a period and phase of minimum emission similar to that of methanol. There
is no significant variation in the polarised properties of the hydroxyl, with
Stokes Q and U flux densities varying in accord with the Stokes I intensity
(linear polarisation, P, varying by <20%) and the right and left circularly
polarised components varying by <33% at 1665-MHz and <38% at 1667-MHz. These
observations are the first monitoring observations of the hydroxyl maser
emission from G12.889+0.489.Comment: 7 pages, 6 figures, accepted for publication in MNRA
Traceability Adoption at the Farm Level: An Empirical Analysis of the Portuguese Pear Industry
Traceability is becoming a condition for doing business in European food markets. Retailers are adopting standards that are more stringent than what is mandatory. An example is EurepGAP, a quality standard for good agricultural practices that includes traceability as a main requirement. We analyze EurepGAP implementation in the Portuguese pear industry and find that implementation cannot be distinguished from sales to British supermarkets. Discrete choice models show the odds of traceability adoption increase with farm size and previous compliance with quality assurance schemes, while farm productivity has a negative impact on the probability of adoption.Research and Development/Tech Change/Emerging Technologies,
Optimal choice of Voluntary traceability as a food risk management tool
Traceability systems are information tools implemented within and between firms in food chains to improve logistics and transparency or to reduce total food safety damage costs. Information about location and condition of products is critical when food safety incidents arise. This paper uses a principal-agent model to investigate the optimal choice of voluntary traceability in terms of precision of information on a given attribute at each link of a food chain. The results suggest that four scenarios may emerge for the supply chain depending on the costs of a system and whether or not the industry can internalize total food safety damages: no traceability, traceability for one link, equal traceability for all links, or different positive traceability levels across all links.Traceability, food safety, principal-agent model, Food Consumption/Nutrition/Food Safety,
The Economics of Traceability for Multi-Ingredient Products: A Network Approach
The consumption of multi-ingredient foods is increasing across the globe as consumers spend less time preparing meals. Traceability is now extensively used to reduce information imperfections in food markets and recent EU law suggests it will be implemented for manufactured meals as well. We present a model developed to understand how information on different ingredients flows through supply chains for multi-ingredient food products. The network model has three tiers linked by contracts for levels of quality and information. The model is useful for analyzing tradeoffs and network effects emerging in the choice of traceability levels.Traceability, multi-ingredient foods, network models, Food Consumption/Nutrition/Food Safety,
High Order QED Corrections in Physics of Positronium
High-order perturbative corrections to positronium decays and hyperfine
splitting are briefly reviewed. Theoretical predictions are compared to the
most recent experimental data. Perspectives of future calculations are
discussed.Comment: 8 pages, LaTeX, talk given at Workshop on Positronium Physics, ETH
Honggerberg, Zurich, May 30-31, 2003, a misprint in Eq. (1) correcte
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