SCUBA observations of the Horsehead Nebula - what did the horse swallow?

We present observations taken with SCUBA on the JCMT of the Horsehead Nebula in Orion (B33), at wavelengths of 450 and 850 \mum. We see bright emission from that part of the cloud associated with the photon-dominated region (PDR) at the `top' of the horse's head, which we label B33-SMM1. We characterise the physical parameters of the extended dust responsible for this emission, and find that B33-SMM1 contains a more dense core than was previously suspected. We compare the SCUBA data with data from the Infrared Space Observatory (ISO) and find that the emission at 6.75-\mum is offset towards the west, indicating that the mid-infrared emission is tracing the PDR while the submillimetre emission comes from the molecular cloud core behind the PDR. We calculate the virial balance of this core and find that it is not gravitationally bound but is being confined by the external pressure from the HII region IC434, and that it will either be destroyed by the ionising radiation, or else may undergo triggered star formation. Furthermore we find evidence for a lozenge-shaped clump in the `throat' of the horse, which is not seen in emission at shorter wavelengths. We label this source B33-SMM2 and find that it is brighter at submillimetre wavelengths than B33-SMM1. SMM2 is seen in absorption in the 6.75-\mum ISO data, from which we obtain an independent estimate of the column density in excellent agreement with that calculated from the submillimetre emission. We calculate the stability of this core against collapse and find that it is in approximate gravitational virial equilibrium. This is consistent with it being a pre-existing core in B33, possibly pre-stellar in nature, but that it may also eventually undergo collapse under the effects of the HII region.Comment: 11 pages, 6 figures, accepted by MNRA

Automatically deploying nozzle exit cone extension Patent

Automatically deploying nozzle exit cone extensio

SCUBA polarisation observations of the magnetic fields in the prestellar cores L1498 and L1517B

We have mapped linearly polarized dust emission from the prestellar cores L1498 and L1517B with the James Clerk Maxwell Telescope (JCMT) using the Submillimetre Common User Bolometer Array (SCUBA) and its polarimeter SCUBAPOL at a wavelength of 850um. We use these measurements to determine the plane-of-sky magnetic field orientation in the cores. In L1498 we see a magnetic field across the peak of the core that lies at an offset of 19 degrees to the short axis of the core. This is similar to the offsets seen in previous observations of prestellar cores. To the southeast of the peak, in the filamentary tail of the core, we see that the magnetic field has rotated to lie almost parallel to the long axis of the filament. We hypothesise that the field in the core may have decoupled from the field in the filament that connects the core to the rest of the cloud. We use the Chandrasekhar-Fermi (CF) method to measure the plane-of-sky field strength in the core of L1498 to be 10 +/- 7 uG. In L1517B we see a more gradual turn in the field direction from the northern part of the core to the south. This appears to follow a twist in the filament in which the core is buried, with the field staying at a roughly constant 25 degree offset to the short axis of the filament, also consistent with previous observations of prestellar cores. We again use the CF method and calculate the magnetic field strength in L1517B also to be 30 +/- 10 uG. Both cores appear to be roughly virialised. Comparison with our previous work on somewhat denser cores shows that, for the denser cores, thermal and non-thermal (including magnetic) support are approximately equal, while for the lower density cores studied here, thermal support dominates.Comment: 6 pages, 2 figures; accepted for publication by MNRA

Hydrodynamics of photoionized columns in the Eagle Nebula, M 16

We present hydrodynamical simulations of the formation, structure and evolution of photoionized columns, with parameters based on those observed in the Eagle Nebula. On the basis of these simulations we argue that there is no unequivocal evidence that the dense neutral clumps at heads of the columns were cores in the pre-existing molecular cloud. In our simulations, a variety of initial conditions leads to the formation and maintenance of near-equilibrium columns. Therefore, it is likely that narrow columns will often occur in regions with large-scale inhomogeneities, but that observations of such columns can tell us little about the processes by which they formed. The manner in which the columns in our simulations develop suggests that their evolution may result in extended sequences of radiation-induced star formation.Comment: 12 pages, 9 figures, Latex, MN macros, in press with MNRA

Aeroplane design study STOL airliner (A71). Part 1- configuration description and data

The interest in STOL airliners was reflected in the choice of a 100-118 passenger short range aircraft of this type as the 1971 design project. In addition to the use of the study for detailed investigation by the students of Aircraft Design it also served as the basis for an investigation of the low speed lift and control problems of STOL aircraft. This report is concerned with a description of the configuration adopted and specification of geometric and aerodynamic data. As such it is the first part of the complete reporting of the investigation, subsequent parts being concerned with the more detailed work. The aircraft was designed to operate from 2000 ft long single runways and have a cruising speed of up to 11 - 0.83 at 30,000 ft altitude. The estimated gross weight is 115,000 lb and when landing at 100,000 lb weight the approach speed is 79 knots. The high lift coefficients necessitated by this are obtained either by externally blown jet flaps or an augmenter wing arrangement

Microscopic calculation of transition intensities for vibrational bands and high-K isomers

We investigate the effect of the Coriolis coupling and the residual interactions upon the inter-band transition rates for the vibrational bands and the decay of two-quasiparticle high-K isomers.Comment: 5 pages, RevTex using epsf.sty, 2 postscript figures included. Talk presented at Conference on "Nuclear structure at the extremes" (June 17 - 19, 1998, Lewes, UK

Bounding inconsistency using a novel threshold metric for dead reckoning update packet generation

Human-to-human interaction across distributed applications requires that sufficient consistency be maintained among participants in the face of network characteristics such as latency and limited bandwidth. The level of inconsistency arising from the network is proportional to the network delay, and thus a function of bandwidth consumption. Distributed simulation has often used a bandwidth reduction technique known as dead reckoning that combines approximation and estimation in the communication of entity movement to reduce network traffic, and thus improve consistency. However, unless carefully tuned to application and network characteristics, such an approach can introduce more inconsistency than it avoids. The key tuning metric is the distance threshold. This paper questions the suitability of the standard distance threshold as a metric for use in the dead reckoning scheme. Using a model relating entity path curvature and inconsistency, a major performance related limitation of the distance threshold technique is highlighted. We then propose an alternative time—space threshold criterion. The time—space threshold is demonstrated, through simulation, to perform better for low curvature movement. However, it too has a limitation. Based on this, we further propose a novel hybrid scheme. Through simulation and live trials, this scheme is shown to perform well across a range of curvature values, and places bounds on both the spatial and absolute inconsistency arising from dead reckoning

Exploring the Cost Effectiveness of Land Conservation Auctions and Payment Policies

Until recently public efforts to encourage conservation on private land in many countries has primarily been through uniform payment policies. Auctions are increasingly used as a payment mechanism to acquire public benefits such as conservation actions that provide environmental improvements on private land (e.g. the US Conservation Reserve Program (CRP). The economic rationale for use of auctions is that they create decentralised incentives to offer bids at close to the true landholder opportunity costs, even when the implementing agency holds little information about these opportunity costs. This paper assesses the cost of a case study auction relative to four payment policies that use varying levels of information strategically to reduce rent payment and to prioritise funding based on environmental value. The results suggest that the estimated cost savings achievable with the discriminant price auction for conservation contracts depends on the policy to which the auction outcomes are compared. Auction cost savings are likely to be greatest when compared to policy alternatives involving little effort to discriminate amongst offers based on differences in landholder opportunity costs. A further key finding is that, for this case study, most of the savings resulting from the discriminant price auction could be attributed to the use of the environmental benefits index in project ranking and selection.Land Economics/Use,