1,801 research outputs found
Star Formation in Southern Seyfert Galaxies
We have produced radio maps, using the ATCA, of the central regions of six
southern Seyfert 2 galaxies (NGC 1365, 4945, 6221, 6810, 7582, and Circinus)
with circumnuclear star formation, to estimate the relative contribution of
star formation activity compared to activity from the active galactic nucleus
(AGN). The radio morphologies range from extended diffuse structures to compact
nuclear emission, with no evidence, even in the relatively compact sources, for
synchrotron self--absorption. In each case the radio to far--infrared (FIR)
ratio has a value consistent with star formation, and in all but one case the
radio to [FeII] ratio is also consistent with star formation. We derive
supernova rates and conclude that, despite the presence of a Seyfert nucleus in
these galaxies, the radio, FIR, and [FeII] line emission are dominated by
processes associated with the circumnuclear star formation (i.e. supernova
remnants and HII regions) rather than with the AGN.Comment: 26 pages, Latex, 13 figures, submitted to MNRA
Cold gas and star formation in a merging galaxy sequence
We explore the evolution of the cold gas and star-formation activity during
galaxy interactions, using a merging galaxy sequence comprising both pre- and
post-mergers. Data for this study come from the literature but supplemented by
new radio observations presented here. Firstly, we confirm that the
star-formation efficiency (SFE) increases close to nuclear coalescence. At
post-merger stages there is evidence that the SFE declines to values typical of
ellipticals. This trend can be attributed to M(H_2) depletion due to
interaction induced star-formation. However, there is significant scatter,
likely to arise from differences in the interaction details of individual
systems. Secondly, we find that the central molecular hydrogen surface density,
increases close to the final stages of the merging of the two nuclei. Such a
trend is also predicted by numerical simulations. Furthermore, there is
evidence for a decreasing fraction of cold gas mass from early interacting
systems to merger remnants, attributed to gas conversion into other forms. The
evolution of the total-radio to blue-band luminosity ratio, reflecting the
disk+nucleus star-formation activity, is also investigated. Although this ratio
is on average higher than that of isolated spirals, we find a marginal increase
along the merging sequence, attributed to the relative insensitivity of disk
star-formation to interactions. However, a similar result is also obtained for
the nuclear radio emission, although galaxy interactions are believed to
significantly affect the activity in the central galaxy regions. Finally, we
find that the FIR--radio flux ratio distribution of interacting galaxies is
consistent with star-formation being the main energising source.Comment: 18 pages, 17 figures, accepted for publication in MNRA
Radio Observations of Super Star Clusters in Dwarf Starburst Galaxies
We present new radio continuum observations of two dwarf starburst galaxies,
NGC3125 and NGC5408, with observations at 4.80GHz (6cm) and 8.64GHz (3cm),
taken with the Australia Telescope Compact Array (ATCA). Both galaxies show a
complex radio morphology with several emission regions, mostly coincident with
massive young star clusters. The radio spectral indices of these regions are
negative (with alpha ~ -0.5 - -0.7), indicating that the radio emission is
dominated by synchrotron emission associated with supernova activity from the
starburst. One emission region in NGC5408 has a flatter index (alpha ~ -0.1)
indicative of optically thin free-free emission, which could indicate it is a
younger cluster. Consequently, in these galaxies we do not see regions with the
characteristic positive spectral index indicative of optically obscured
star-formation regions, as seen in other dwarf starbursts such as Hen 2-10.Comment: Accepted for publication in MNRA
Responding to ash dieback (Hymenoscyphus fraxineus) in the UK: woodland composition and replacement tree species
Common ash (Fraxinus excelsior L.) is an important timber species that is widespread in broadleaved woodlands across Europe, where it is currently declining due to the fungal pathogen (Hymenoscyphus fraxineus (T. Kowal) Baral et al., 2014) causing ash dieback. Using the UK as our case study, we assess: (1) likely woodland composition following ash dieback and (2) choice of replacement species for production planting. The greatest impacts on woodland composition will occur where ash forms a larger proportion of the canopy. In such woodlands, larger gaps formed from the loss of ash, are likely to be filled by sycamore (Acer pseudoplatanus L.) and beech (Fagus sylvatica L.) under current climatic conditions and where there is little management intervention. Native woodland policy regarding sycamore and beech may need to be reviewed in UK-designated woodlands where these species are considered non-native. For actively managed production woodlands, 27 replacement tree species for ash are considered, some of these are non-native and present options for continuing production forestry objectives on former ash sites. An assessment of replacement species shows there is no single species that can substitute for the wide range of site conditions associated with the good growth of ash. In deciding to replace ash with another tree species, the decision on selection should be made based on particular site conditions and woodland objectives
Investigation of a tilt-wing proof of concept for a high-speed VTOL jet UAV using thrust vectoring for balance
Success of Special operations forces (SOF) missions depends on a high level of situational awareness within sensitive areas of interest, especially when arriving in volatile, sensitive environments. Oftentimes intelligence, surveillance, and reconnaissance (ISR) UAS platforms expand situational awareness for small, clandestine teams for Special Operations; however, there is a demonstrable need for a high-speed, long-range platform capable of point launches and landings to improve outcomes of rapid response missions. This thesis intends to provide the fundamental mechanics of one solution to that platform centered on the premise of a conventional jet UAV being modified into a tilt-wing V/STOL UAV using its existing features.The proof of concept being explored emulates modifying a fast, conventional UAV configuration. That concept possessed a tubular carbon spar that was used as a point of rotation. Motor pods were attached to the wing for the lift system and only used during takeoffs and landings, after which, the propellers were folded away to reduce drag in cruise. Additionally, a thrust vectoring unit was added to the central propulsion system for balance under stall-speeds. The final configuration culminated into a novel tilt-wing VTOL system with the potential to add minimal weight and drag increases to the base configuration. This configuration was then scrutinized for its fundamental challenges to evaluate its effectiveness.Through the research and development of the proof of concept, several milestones were met. Solidworks Flow Simulation (SWFS) was validated for unsteady propeller analyses. Using lessons learned from this validation effort, the tilt-wing concept was found to have the best net lift characteristics over the tilt-rotor after verifying the effects of download experienced in tilt-rotors in SWFS. In fact, the tilt-rotor expressed a net loss in lift of 25% whereas the tilt-wing saw negligible losses. This fully rationalized the tilt-wing as a viable system for the mission profile. After construction and preliminary testing of a prototype, a CG condition was discovered for balancing novel VTOL concepts using separated propulsion systems. This discovery was key in demonstrating the tilt-wing proof of concept where it was shown to execute point launches and landings as intended through simulated testing where the runway footprint of the prototype model was reduced significantly
Probability of economic success for Netherlands dairy farmers moving operations to the United States
Dairy producers in the Netherlands are struggling to stay in business due to
increased environmental legislation, population density, intensity of farming systems,
costs of production and quota restrictions. One option available to Netherlands dairy
farmers is to liquidate the value of their assets, put the money into an international bank,
and buy an established dairy farm in the United States. The primary objective of this
research is to compare the economic viability of a Netherlands dairy farmer staying in
the Netherlands versus moving to the United States, assuming they will bring over all of
their equity to put towards the purchase of a U.S. farm.
The hypothesis that a Dutch dairy farmer would have a greater probability of
economic success by relocating to the U.S was tested using a whole farm simulation
model (FLIPSIM) to simulate the economic activity of a representative dairy farm in the
Netherlands and 23 representative U.S. dairy farms in the major dairy producing regions
over the 2002-2011 planning horizon. FLIPSIM generated an empirical probability
distribution for net present value to rank the representative farms using stochastic
efficiency with respect to a function (SERF) for risk neutral and risk averse decision
makers.
The FLIPSIM results showed that six of the twenty-three U.S. dairy farms would
give the Dutch farmer a 99% chance of economic success. The added risk on income in
the U.S. would result in these U.S. farms having a 1 to 99% chance of negative ending
cash reserves (ECR) and a 1 to 99% chance of negative net cash farm income (NCFI).
In a complete SERF analysis, seventeen of the twenty-three U.S. farms were preferred
over the Dutch farm. In conclusion, the research shows Dutch dairy farmers with
adequate equity would be financially better off by relocating to the U.S. if they desire to
continue dairying, rather than staying in the Netherlands
\u27Academic Capitalism\u27: Universities\u27 Consultancy Agendas
Recent debate in Higher Education (HE) has attempted to identify the legitimate components at the core of academic scholarship. Teaching and research, are recognized activities of modern academia; although their nexus is at times questioned. This paper seeks to understand the role of a rising academic activity, academic consultancy, and to portray its impact onto HE. A two-stage research design including a web-based survey and semi-structured interviews was implemented to gather the experiences and perceptions of academics in information technology/information systems/information management (IT/IS/IM) in the United Kingdom (UK). The findings reveal that the majority of consultancy activities undertaken by the study participants are of small scale, of technical nature and in areas strongly related to the research interest of the academics in questions. Although a shared understanding of what consultancy is can be found among academics, the perception of how consultancy impacts teaching practices and research differs significantly within research-led or teaching-led universities. Such findings are significant as they portray entrepreneurship as a contributing factor that may help universities to shape their policy, culture and structure
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