58,703 research outputs found
WHEN PRICES MISS THE MARK: METHODS FOR VALUING ENVIRONMENTAL CHANGE
Environmental Economics and Policy,
A VLBA Search for a Stimulated Recombination Line from the Accretion Region in NGC1275
The radio source 3C84, in NGC1275, has a two sided structure on parsec
scales. The northern feature, presumed to be associated with a jet moving away
from the Earth, shows strong evidence for free-free absorption. The ionized gas
responsible for that absorption would be a source of detectable stimulated
recombination line emission for a wide range of physical conditions. The VLBA
has been used to search for the H65 hydrogen recombination line. The
line is only expected to be seen against the northern feature which contains a
small fraction of the total radio flux density. This spatial discrimination
significantly aids the search for a weak line. No line was seen, with upper
limits of roughly 15% of the continuum over a velocity range of 1486 km/s with
resolutions up to 6.6 km/s. In the absence of a strong radiation field, this
would imply that the free-free absorbing gas has a wide velocity width, is
moving rapidly relative to the systemic velocity, or is concentrated in a thin,
high density structure. All of these possibilities are reasonably likely close
to an AGN. However, in the intense radiation environment of the AGN, even
considering only the radiation we actually observe passing through the
free-free absorbing gas, the non-detection is probably assured by a combination
of saturation and radiation damping.Comment: 14 pages with 4 postscript figures. Accepted for publication in the
April 2003 Astronomical Journa
Understanding the different rotational behaviors of No and No
Total Routhian surface calculations have been performed to investigate
rapidly rotating transfermium nuclei, the heaviest nuclei accessible by
detailed spectroscopy experiments. The observed fast alignment in No
and slow alignment in No are well reproduced by the calculations
incorporating high-order deformations. The different rotational behaviors of
No and No can be understood for the first time in terms of
deformation that decreases the energies of the
intruder orbitals below the N=152 gap. Our investigations reveal the importance
of high-order deformation in describing not only the multi-quasiparticle states
but also the rotational spectra, both providing probes of the single-particle
structure concerning the expected doubly-magic superheavy nuclei.Comment: 5 pages, 4 figures, the version accepted for publication in Phys.
Rev.
Aircraft flight test trajectory control
Two design techniques for linear flight test trajectory controllers (FTTCs) are described: Eigenstructure assignment and the minimum error excitation technique. The two techniques are used to design FTTCs for an F-15 aircraft model for eight different maneuvers at thirty different flight conditions. An evaluation of the FTTCs is presented
Modelling the impact of referral guideline changes for mild dyskaryosis on colposcopy services in England
Objectives: This model examines the effects of changing referral strategies within the established structure of NHS cervical screening driven colposcopy practice. It considers the effects of the new strategy on colposcopy workload, patient waiting times, and associated costs and health benefits.
Methods: By postal survey, the current operational strategies of colposcopy services were established by questionnaire with respect to referral practices and management protocols. After first-cut piloting, and utilising published and original research, a Markovian model was constructed, and the impact of the new strategy was determined on colposcopy workload and patient waiting times for three hypothetical clinic types. Expected costs and benefits of the new policy were assessed through the adaptation of a previous ScHARR cervical screening model.
Results: Clinic workload is expected to increase by between 21% and 35% within three years of the policy change, depending on clinic efficiency in other areas; the majority of this impact would be seen within the first year. It is predicted that particularly inefficient clinics would struggle to meet the existing waiting time requirements for women referred with low-grade disease, owing to the increased level of workload seen throughout the patient pathway as a result of the implementation of the new policy.
The impact of the new policy can, however, be mitigated through improving the efficiency of existing clinics, by altering policies relating to surveillance of low grade disease, post-treatment follow-up, treatment policy (whether or not treatment is performed at the initial colposcopy visit), and through adherence to national guidelines.
A cost-effectiveness analysis using the ScHARR liquid-based cytology model suggests that the policy change is likely to be have a cost per quality-adjusted lifeyear gained of between £1,400 and £5,500 per quality-adjusted life-year gained (excluding the costs of follow-up), which would be deemed acceptable to organisations such as the National Institute for Health and Clinical Excellence
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