48,375 research outputs found
Replacement of fluid-filter elements without interruption of flow
Gatling-type filter assembly, preloaded with several filter elements enables filter replacement without breaking into the operative fluid system. When the filter element becomes contaminated, a unit inner subassembly is rotated 60 degrees to position a clean filter in the line
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
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
Toda Lattice and Tomimatsu-Sato Solutions
We discuss an analytic proof of a conjecture (Nakamura) that solutions of
Toda molecule equation give those of Ernst equation giving Tomimatsu-Sato
solutions of Einstein equation. Using Pfaffian identities it is shown for Weyl
solutions completely and for generic cases partially.Comment: LaTeX 8 page
Evolving collective behavior in an artificial ecology
Collective behavior refers to coordinated group motion, common to many animals. The dynamics of a group can be seen as a distributed model, each āanimalā applying the same rule set. This study investigates the use of evolved sensory controllers to produce schooling behavior. A set of artificial creatures āliveā in an artificial world with hazards and food. Each creature has a simple artificial neural network brain that controls movement in different situations. A chromosome encodes the network structure and weights, which may be combined using artificial evolution with another chromosome, if a creature should choose to mate. Prey and predators coevolve without an explicit fitness function for schooling to produce sophisticated, nondeterministic, behavior. The work highlights the role of speciesā physiology in understanding behavior and the role of the environment in encouraging the development of sensory systems
Generic approach for deriving reliability and maintenance requirements through consideration of in-context customer objectives
Not all implementations of reliability are equally effective at providing customer and user benefit. Random system failure with no prior warning or failure accommodation will have an immediate, usually adverse impact on operation. Nevertheless, this approach to reliability, implicit in measurements such as āfailure rateā and āMTBFā, is widely assumed without consideration of potential benefits of pro-active maintenance. Similarly, it is easy to assume that improved maintainability is always a good thing. However, maintainability is only one option available to reduce cost of ownership and reduce the impact of failure. This paper discusses a process for deriving optimised reliability and maintenance requirements through consideration of in-context
customer objectives rather than a product in isolation
Bond patterns and charge order amplitude in 1/4-filled charge-transfer solids
Metal-insulator transition accompanied by charge-ordering has been widely
investigated in quasi-one-dimensional conductors, including in particular
organic charge-transfer solids. Among such materials the 1/4-filled band
charge-transfer solids are of strong interest, because of the commensurate
nature of the charge-ordering in these systems. The period-four charge-order
pattern ...1100... here is accompanied by two distinct bond distortion
patterns, giving rise to bond-charge-density waves (BCDW) of types 1 and 2.
Using quantum Monte Carlo methods, we determine the phase diagram within the
extended Hubbard Hamiltonian that gives both types 1 and 2 BCDW in the
thermodynamic limit. We further investigate the effect of electron-electron and
electron-phonon interactions on the amount of charge disproportionation. Our
results show that between these two bond patterns, one (BCDW2) in general
coexists with a large magnitude charge order, which is highly sensitive to
electron-phonon interactions, while the other (BCDW1) is characterized by weak
charge order. We discuss the relevance of our work to experiments on several
1/4-filled conductors, focusing in particular on the materials (EDO-TTF)_2X and
(DMEDO-TTF)_2X with large amplitude charge-order.Comment: 7 pages, 8 figure
Intensive versus standard dose statin therapy: the costs and benefits for patients with acute coronary syndrome
Introduction: Recent NICE guidance in England and Wales states that statin therapy for secondary CVD should "usually be initiated with a drug with a low acquisition cost (taking into account required daily dose and product price per dose)". Intensive dose statin therapy is more costly than standard dose, but offers additional benefits and may potentially be more cost effective for a sub-group of high risk patients.
Objective: To determine if the strategy of treating ACS patients with intensive dose statin compared with standard dose statin can be considered to be cost effective and to what extent these results are influenced by the age of the patient at start of treatment.
Methods: A Markov model was used to explore the costs and health outcomes associated with a lifetime of intensive dose (represented by 80mg atorvastatin) versus standard dose (represented by 20mg simvastatin) treatment for patients with acute coronary syndrome. Health states included unstable angina, MI, stroke, fatal CHD, fatal stroke, or non vascular death. The benefits associated with statin treatment were modelled by applying the relative risks from a meta-analysis of 4 large RCTs reporting clinical endpoints. Costs and utilities assigned to health states were derived from a review of published evidence.
Results: Treatment with intensive dose statin therapy offers additional benefits over standard dose therapy. The cost offsets through avoided events are less than the associated treatment costs and result in a cost per QALY of around Ā£24,000 for patients with ACS starting treatment at 60 years of age and falling to around Ā£14,000 for patients starting treatment at 70 years. The key driver of cost effectiveness is the relative risk for mortality.
Conclusions: This analysis suggests that intensive statin regimens (represented by atorvastatin 80mg/day) are cost effective compared with standard statin regimens (represented by simvastatin 20mg/day) for patients with ACS over the age of 60 years. A recent registry study reports a mean age of 70 years for ACS patients admitted to UK hospitals and hence this comparison applies to the great majority of ACS patients
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