To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
A theoretical and experimental investigation of two-dimensional (2-D) liquid curtains (gravitationally thinning liquid sheets) is provided under conditions where the curtain issues from a thin slot whose centreline is inclined with respect to the vertical. This analysis is motivated in part by recent works where it has been proposed that oblique liquid curtains (those exiting a non-vertical slot) may bend upwards against gravity when the relevant Weber number at the slot is less than unity ($We <1$). By contrast, Weinstein et al. (J. Fluid Mech., vol. 876, 2019, R3) have proposed that such $We<1$ curtains must be vertical and downward falling regardless of the inclination of the slot. Under low-Reynolds-number ($Re$) conditions typical of liquid film coating operations, our experiments show that the curtain shape follows the classic ballistic (parabolic) trajectory in the supercritical regime ($We>1$). In subcritical conditions ($We<1$), experiments show that the downward-falling curtain is vertical except in a relatively small region near the slot, where the combined effects of viscosity and surface tension induce the so-called teapot effect. These experimental results are confirmed by 2-D numerical simulations, which predict the curtain behaviour ranging from highly viscous ($Re = O(1)$) to nearly inviscid conditions. The one-dimensional (1-D) inviscid model of Weinstein et al. is recast in a different form to facilitate comparisons with the 2-D model, and 1-D and 2-D results agree favourably for supercritical and subcritical conditions. Despite the large parameter range explored, we have found no evidence that upward-bending curtains exist in an oblique configuration.
Natural habitats are being rapidly lost due to human activities. It is therefore vital to understand how these activities influence biodiversity so that suitable guidelines can be established for conservation. This is particularly important in understudied, high biodiversity, areas such as the Angolan Escarpment. Here we examine which habitat characteristics drive bird diversity and endemic species presence at Kumbira Forest, a key site in the Central Escarpment Forest. Bird diversity was sampled by 10 min bird point counts, whereas habitat characteristics were measured by a combination of ground-based vegetation surveys and remotely sensed data modelling of Landsat images. GLM, multi-model inference and model averaging were used to determine the most important variables driving species richness and the presence of endemics. The remote sensing variables performed poorly in predicting presence of Red-crested Turaco Tauraco erythrolophus and Gabela Bushshrike Laniarius amboimensis but they contributed significantly to explain species richness and Gabela Akalat Sheppardia gabela presence, both of which were associated with greater canopy cover. Liana density and elevation were also important explanatory variables in certain cases. Conservation actions at Kumbira should focus on increasing canopy cover and maintaining forest integrity (as measured by liana density), as these actions are likely to have the most positive outcomes for the avifauna.
A consensus conference on the reasons for the undertreatment of depression was organized by the National Depressive and Manic Depressive Association (NDMDA) on January 17–18,1996. The target audience included health policymakers, clinicians, patients and their families, and the public at large. Six key questions were addressed: (1) Is depression undertreated in the community and in the clinic? (2) What is the economic cost to society of depression? (3) What have been the efforts in the past to redress undertreatment and how successful have they been? (4) What are the reasons for the gap between our knowledge of the diagnosis and treatment of depression and actual treatment received in this country? (5) What can we do to narrow this gap? (6) What can we do immediately to narrow this gap?
Kumbira Forest is the best representative area of Angola's Central Escarpment and the only site known to hold significant populations of four of the five threatened endemic bird species of this habitat. However, the forest is disappearing as a result of human activities. Remote-sensing techniques were used to assess changes in forest cover, and bird and habitat surveys were performed to assess the effect of land-use changes on endemic species and the bird community. No relationships could be established between the presence of endemics and habitat and landscape variables. This lack of effect may be attributable to the low number of records and compounded by the mosaic structure of the landscape. Although forest cover has been maintained in Kumbira, old-growth forest has been replaced by secondary growth in many areas. Nevertheless these secondary-growth forest patches can maintain a bird community similar to that found in old-growth forest.
Pregnancy outcome and characteristics of women who conceive following subfertility treatment remains a subject of great interest. We analyzed these variables among 199 women who delivered a registerable twin birth compared with 1773 women who delivered a naturally conceived twin birth in a population-based obstetric cohort drawn from around Oxford, England. Treatment was restricted to conceptions involving simple ovulation induction only. Treated mothers were of significantly higher social class and older, more likely to deliver girls and to be delivered by cesarean section, and significantly less likely to be smokers at the time of antenatal booking and to have delivered previous pregnancies. Pregnancy outcome was similar between the two groups for most measures, with the exception of birthweight which was lower in treated twins, though not significantly so. Overall the results are reassuring with respect to outcome in twin pregnancies following simple ovulation induction.
We present Herschel PACS and SPIRE images of the dust shells around the planetary nebulae NGC 650, NGC 6853, and NGC 6720, as well as images showing the dust temperature in their shells. The latter show a rich structure, which indicates that internal extinction in the UV is important despite the highly evolved status of the nebulae.
A comparison between the past four decades of astrophysical space missions and those expected to be launched over the next decade shows a marked decrease in numbers. However, missions such as Gaia and the JWST are expected to have a major impact on planetary nebula research. The capabilities of these and other anticipated space missions are discussed.
The extraction of chemical abundances of ionised nebulae from a limited spectral range is usually hampered by the lack of emission lines corresponding to certain ionic stages. So far, the missing emission lines have been accounted for by the ionisation correction factors (ICFs), constructed under simplistic assumptions like spherical geometry by using 1-D photoionisation modelling.
In this contribution we discuss the results (Gonçalves et al. 2011, in prep.) of our ongoing project to find a new set of ICFs to determine total abundances of N, O, Ne, Ar, and S, with optical spectra, in the case of non-spherical PNe. These results are based on a grid of 3-D photoionisation modelling of round, elliptical and bipolar shaped PNe, spanning the typical PN luminosities, effective temperatures and densities.
We show that the additional corrections to the widely used Kingsburgh & Barlow (1994) ICFs are always higher for bipolars than for ellipticals. Moreover, these additional corrections are, for bipolars, up to: 17% for oxygen, 33% for nitrogen, 40% for neon, 28% for argon and 50% for sulphur. Finally, on top of the fact that corrections change greatly with shape, they vary also greatly with the central star temperature, while the luminosity is a less important parameter.
Post-AGB stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the Asymptotic Giant Branch (AGB) towards the planetary nebula stage. There is growing evidences that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VISIR/VLT, T-Recs/Gemini South and Michelle/Gemini North. We found that all the the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non resolved. The resolved targets can be divided in two categories. The nebulae with a dense central core, that are either bipolar and multipolar. The nebulae with no central core have an elliptical morphology. The dense central torus observed likely host binary systems which triggered fast outflows that shaped the nebulae.
Little is known about the effectiveness of advance care planning in the United Kingdom, although policy documents recommend that it should be available to all those with life-limiting illness.
An exploratory patient preference randomized controlled trial of advance care planning discussions with an independent mediator (maximum three sessions) was conducted in London outpatient oncology clinics and a nearby hospice. Seventy-seven patients (mean age 62 years, 39 male) with various forms of recurrent progressive cancer participated, and 68 (88%) completed follow-up at 8 weeks. Patients completed visual analogue scales assessing perceived ability to discuss end-of-life planning with healthcare professionals or family and friends (primary outcome), happiness with the level of communication, and satisfaction with care, as well as a standardized measure of anxiety and depression.
Thirty-eight patients (51%) showed preference for the intervention. Discussions with professionals or family and friends about the future increased in the intervention arms, whether randomized or preference, but happiness with communication was unchanged or worse, and satisfaction with services decreased. Trial participation did not cause significant anxiety or depression and attrition was low.
Significance of results:
A randomized trial of advance care planning is possible. This study provides new evidence on its acceptability and effectiveness for patients with advanced cancer.
Advance care planning (ACP) provides patients with an opportunity to consider, discuss, and plan their future care with health professionals. Numerous policy documents recommend that ACP should be available to all with life-limiting illness.
Forty patients with recurrent progressive cancer completed one or more ACP discussions with a trained planning mediator using a standardized topic guide. Fifty-two interviews were transcribed verbatim and analyzed for qualitative thematic content.
Most patients had not spoken extensively to health professionals or close persons about the future. Their concerns related to experiencing distressing symptoms or worrying how family members would cope. Some patients wished for more accurate information and were unaware of their options for care. Many felt it was doctors' responsibility to initiate such discussions, but perceived that their doctors were reluctant to do so. However, some patients felt that the time was not yet right for these conversations.
Significance of results:
This article reports on the recorded content of ACP discussions. The extent to which patients want to engage in ACP is variable, and support and training are needed for health professionals to initiate such discussions. Our findings do not fully support the current United Kingdom policy of introducing ACP early in life-threatening disease.
The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?
In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life.
The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.
EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates.
The Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r′-Hα)-(r′-i′) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks.
The relative role of the stellar radiation field, the stellar outflows and the interstellar radiation field (ISRF) in transforming the molecular ejecta into atomic gas was the subject of our ISO LWS and SWS spectroscopy study of 24 evolved stars which span the range from AGB stars to proto-planetary nebulae (PPNs) and PNs. The far-infrared (FIR) atomic fine-structure lines are powerful probes of the warm atomic gas in photodissociation regions (PDRs) and shocks. This paper summarizes and compares the ISO spectroscopy studies of carbon-rich (C-rich) and oxygen-rich (O-rich) evolved stars, published by Fong et al. (2001) and Castro-Carrizo et al. (2001), respectively. We find that photodissociation, not shocks, is responsible for the chemical change from molecular to atomic gas.
A three-dimensional self-consistent photo-ionisation code is developed using Monte Carlo techniques in order to build realistic models of photoionised nebulae of arbitrary geometry and density distribution. The code's results are benchmarked against those of estabilished codes. Two models are computed for the planetary nebula NGC 3918 using two different density distributions. The results of the two models are compared with the observations.
The sensitivity of bat species to stochastic disturbance was investigated by exploiting the natural experiment provided by Hurricane Georges, which struck the island of Puerto Rico (Caribbean) in September 1998. Six forest habitats and three cave roost sites sampled for bats prior to the hurricane were sampled in the same way after the hurricane. Populations showed significant declines in abundance and species richness across all forest habitats sampled. Species' sensitivity to disturbance were not equal: larger species were significantly more affected by disturbance than smaller species, once the effects of phylogenetic non-independence were removed. There was some evidence that frugivorous and nectarivorous species are more affected by hurricane disturbance than insectivorous species. These findings have important implications for maintaining viable populations of species in areas that experience a high degree of environmental fluctuation.