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I. De Pater, University of California, Berkeley Berkeley, California, USA,
D. P. Hamilton, University of Maryland College Park, Maryland, USA,
M. R. Showalter, SETI Institute Mountain View, California, USA,
H. B. Throop, Planetary Science Institute Tucson, Arizona, USA,
J. A. Burns, Cornell University Ithaca, New York, USA
M. M. Hedman, University of Idaho Moscow, Idaho, USA,
F. Postberg, University of Heidelberg Heidelberg, GERMANY,
D. P. Hamilton, University of Maryland College Park, Maryland, USA,
S. Renner, University of Lille Lille, FRANCE,
H.-W. Hsu, University of Colorado Boulder, Colorado, USA
All of the giant planets in the outer Solar System possess rings composed primarily of particles less than 100 microns across. Such small particles are conventionally referred to as “dust grains” regardless of their composition, and so these rings are considered “dusty rings” (as opposed to the more famous main rings of Saturn and Uranus, whose particles are more than a millimeter across). Dusty rings are often very tenuous and so can be much more difficult to observe than Saturn's broad, bright, and dense main rings. Nevertheless, dusty rings are extremely interesting because they have very rich dynamics and are extremely sensitive probes of their environment.
The high surface-area-to-volume ratio of dust-sized grains makes them much more responsive to non-gravitational forces like solar radiation pressure, plasma drag, and torques from the planet's electromagnetic field. Furthermore, sub-millimeter particles can be lost from the ring system on relatively short timescales due to erosion via charged-particle and micrometeoroid bombardment or through ejection by the non-gravitational forces listed above. This means that small particles need to be constantly supplied to these rings from larger bodies, and indeed all of the known dusty rings are associated with larger objects that are the likely sources of dusty debris. The most dramatic example of this is Saturn's E ring, which is clearly supplied by material erupting from beneath the surface of the geologically active moon Enceladus. However, this is a special case, and most dusty rings are instead associated with denser rings (which are composed primarily of millimeter-to-metersized particles) or small moons. These objects can serve as dust sources because they are constantly being bombarded by micrometeoroids, and these impacts release fine debris that can escape the weak gravitational fields of these small bodies and go into orbit around the planet. Note that the amount of dust released by this process depends on the size, mass, and regolith properties of the source object, and calculations of the dust production rate based on simple estimates of impact ejecta velocity distributions suggest that source moons that are several kilometers across are the most efficient at producing dusty rings (Burns et al., 1999).
We examine whether the dark, orbitally-leading hemisphere of Saturn's satellite Iapetus might be coated by debris from low-albedo Phoebe, which orbits retrograde well exterior to Iapetus. Using simplified analytical models along with more complete numerical integrations, we follow the paths of various-sized particles launched gently off Phoebe following collisions with interplanetary and interstellar meteoroids. Micron grains can quickly reach Iapetus since (due to solar radiation) they trace elliptical orbits; larger grains may only hit after their more-circular orbits collapse due to Poynting-Robertson drag; few very large and very small Phoebe grains strike Iapetus. Despite some inconsistencies with observations, we conclude that Phoebe may possibly be the agent that has darkened Iapetus.
Shallow ice cores were obtained from widely distributed sites across the West Antarctic ice sheet, as part of the United States portion of the International Trans-Antarctic Scientific Expedition (US ITASE) program. The US ITASE cores have been dated by annual-layer counting, primarily through the identification of summer peaks in non-sea-salt sulfate (nssSO42–) concentration. Absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores, Tambora, Indonesia (1815), being the most prominent. Independent validation is provided by the tracing of isochronal layers from site to site using high-frequency ice-penetrating radar observations, and by the timing of mid-winter warming events in stable-isotope ratios, which demonstrate significantly better than 1 year accuracy in the last 20 years. Dating precision to ±1 month is demonstrated by the occurrence of summer nitrate peaks and stable-isotope ratios in phase with nssSO42–, and winter-time sea-salt peaks out of phase, with phase variation of <1 month. Dating precision and accuracy are uniform with depth, for at least the last 100 years.
An updated compilation of published and new data of major-ion (Ca, Cl, K, Mg, Na, NO3, SO4) and methylsulfonate (MS) concentrations in snow from 520 Antarctic sites is provided by the national ITASE (International Trans-Antarctic Scientific Expedition) programmes of Australia, Brazil, China, Germany, Italy, Japan, Korea, New Zealand, Norway, the United Kingdom, the United States and the national Antarctic programme of Finland. The comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across Antarctica and exhibit distinct geographical patterns. The Antarctic-wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples. This paper aims to initiate data compilation and administration in order to provide a framework for facilitation of Antarctic-wide snow chemistry discussions across all ITASE nations and other contributing groups. The data are made available through the ITASE web page (http://www2.umaine.edu/itase/content/syngroups/snowchem.html) and will be updated with new data as they are provided. In addition, recommendations for future research efforts are summarized.
Six radio telescopes were operated as the first southern hemisphere VLBI array in April and May 1982. Observations were made at 2.3 and 8.4 Ghz. This array produced VLBI images of 28 southern hemisphere radio sources, high accuracy VLBI geodesy between southern hemisphere sites, and subarcsecond radio astrometry of celestial sources south of declination −45 degrees. This paper discusses only the astrophysical aspects of the experiment.
VLBI observations of the nucleus of Centaurus A were made in April, 1982 at two frequencies with an array of five Australian radio antennas as part of the Southern Hemisphere VLBI Experiment (SHEVE). Observations were undertaken at 2.29 GHz with all five antennas, while only two were operational at 8.42 GHz. The 2.29 GHz data yielded significant information on the structure of the nuclear jet. At 8.42 GHz a compact unresolved core was detected as well.
Cryogenic detectors for gravitational wave astronomy promise greatly improved sensitivity over room temperature detectors. The 3 mK detector which we have under construction should give an improvement of 106 over existing detectors. The cryogenic antennae are described and the calculated low temperature performance is detailed. New superconducting instrumentation is described.
The Southern Hemisphere VLBI Experiment (SHEVE) program is aimed at producing high-resolution images of southern radio sources. The radio telescopes of the present SHEVE array are described below and some recent results presented.
The radiocarbon results (and Bayesian modeling) of 15 samples of carbonized food residues removed from the external surface of rim sherds of cooking pots indicate that shellyware pottery first appeared in Perth, Scotland, around cal AD 910–1020 (95% probability) and that it had disappeared by cal AD 1020–1140 (95% probability). Previously, it had been suggested that this pottery could not date to before AD 1150. These data, together with 14C analyses carried out on leather artifacts and a sample of wattle from a ditch lining, also demonstrate that there was occupation in Perth about 100 yr or more prior to the granting of royal burgh status to Perth in the 1120s.
Observations at a number of frequencies indicate that for at least two pulsars the average pulse shape has a slow but quite definite frequency dependence. Figure 1 shows average pulse shapes for CP 1919, CP 0950 and CP 1133. With the exception of those at 408 MHz these results were obtained at Parkes. The 408 MHz pulse shapes were obtained at Jodrell Bank by Lyne and Rickett. Circumstances of the observations are listed in Table I. Linearly polarized feeds were used at all frequencies.
The supernova SN1986j resembles the prototypical Type V supernova SN1961v in the relatively slow ∼1000km/s expansion velocity, the slow light curve, and also in the Hα dominated spectrum. The optical spectrum is similar to the spectra of some novae, and some OB stars with massive winds, being characteristic of a nebular plasma at about 1010cm−3 and 104K. What makes SN1986j exceptional is its tremendous radio luminosity, the brightest radio supernova observed to date. The radio emission indicates the presence of a massive circumstellar wind, with which the SN ejecta are now colliding. Since the cooling time of the optically emitting gas is about an hour, a heat source is required to power the light curve. Shocks moving back into the ejecta offer a natural heat source, and account quantitatively for the observed luminosity and spectral character of SN1986j. The large Hα/Hβ ratio is attributed to trapping of Ly α, which pumps the n = 2 level of hydrogen, causing a finite optical depth in Balmer lines, and converting Hβ to Pα and Hα. The ratio of the derived H(n = 2) density and column density yields a size for the Hα emitting region consistent with the thickness of a cooling shock, but less than 10−7 of the 1017cm VLBI size. An important discriminant between shock models and photoionization models of the spectrum is that shocks predict Lyman 2-photon emission. The mass of the optically emitting material in SN1986j is about 1M⊙, substantially less than the 2000 M⊙ argued in the case of SN1961v by Utrobin. However, there may be, and probably is, considerably more unobserved ejecta. This material should reveal itself as the remnant of SN1986j continues to evolve.
Background: Ependymomas are rare tumors of the central nervous system whose management is controversial. This population-based study of adults and children with ependymoma aims to (1) identify clinical and treatment-related factors that impact survival and (2) determine if postoperative radiotherapy (RT) can improve survival of patients with subtotal resection (STR) to levels similar to patients who had gross total resection (GTR). Methods: This retrospective population-based study evaluated 158 patients with ependymoma diagnosed between 1975-2007 in Alberta, Canada. Results: Younger patients (<7 years of age) were more likely to be diagnosed with grade III tumors compared with adults in whom grade I tumors were more common (p=0.003). Adults were more likely to have spinally located tumors compared to young children whose tumors were typically found in the brain. Overall, young children with ependymoma were more likely to die than older children or adults (p=0.001). An equivalent number of patients underwent GTR as compared with STR (48% vs 45%, respectively). Overall, older age, spinal tumor location, lower grade, and GTR were associated with improved progression free survival but only GTR was associated with significant improvement in overall survival. Median survival after STR and RT was 82 months compared with 122 months in patients who had GTR (p=0.0022). Conclusions: This is the first Canadian population-based analysis of patients with ependymoma including adults and children. Extent of resection appears to be the most important factor determining overall survival. Importantly, the addition of RT to patients initially treated with STR does not improve survival to levels similar to patients receiving GTR.
This study builds on existing research on the prevalence and consequences of mental illness discrimination by investigating and quantifying the relationships between experienced discrimination and costs of healthcare and leisure activities/social participation among secondary mental health service users in England.
We use data from the Mental Illness-Related Investigations on Discrimination (MIRIAD) study (n = 202) and a subsample of the Viewpoint study (n = 190). We examine experiences of discrimination due to mental illness in the domains of personal relationships, community activities, and health care, and how such experienced discrimination relates to patterns of service use and engagement in leisure activities.
Our findings show that the cost of health services used for individuals who reported previous experiences of discrimination in a healthcare setting was almost twice as high as for those who did not report any discrimination during the last 12 months (Relative Risk: 1.73; 95% Confidence Interval (CI): 1.39, 2.17) and this was maintained after controlling for symptoms and functioning. Experienced discrimination in healthcare (Relative Risk: 0.83; 95% CI: 0.81, 0.84) or in relationships (Relative Risk: 0.89; 95% CI: 0.87, 0.91), however, was associated with lower participation in, and hence lower costs of, leisure activities. Individuals who reported any discrimination in a healthcare setting had, on average, £434 higher costs associated with health service use while reported discrimination in the community was associated with increased leisure costs of £32.
These findings make an important initial step towards understanding the magnitude of the costs of mental health-related discrimination.
Experiments in the system NaAlSiO4(Ne)−KAlSiO4(Ks)−SiO2(Qz)−H2O at 100 MPa show that the maximum content of NaAlSi2O6 in leucite is ∼4 wt.% and that analcime is close to the stoichiometric composition (NaAlSi2O6.H2O). Analcime forms metastably on quenching the higher-temperature experiments; it is secondary after leucite in experiments quenched from 780°C, while from 850°C it forms by alteration of leucite, and by devitrification of water-saturated glass. Both processes involve reaction with Na-rich aqueous fluids. Stable analcime forms at 500°C, well below the solidus, and cannot form as phenocrysts in shallow volcanic systems. New data for natural analcime macrocrysts in blairmorites are presented for the Crowsnest volcanics, Alberta, Canada. Other researchers have suggested that primary analcime occurs as yellow-brown, glassy, analcime phenocrysts. Our microprobe analyses show that such primary analcime is close to stoichiometric, with very low K2O (<0.1 wt.%), minor Fe2O3 (0.5−0.8 wt.%) and CaO (∼0.5 wt.%). An extrapolation of published experimental data for Ne−Ks−Qz at >500 MPa PH2O, where Anl + melt coexist, suggests that at >800 MPa two invariant points are present: (1) a reaction point involving Kf + Ab + Anl + melt + vapour; and (2) a eutectic with Kf + Anl + Ne + melt + vapour. We suggest that the nepheline-free equilibrium mineral assemblage for Crowsnest samples is controlled by reaction point (1). In contrast, blairmorites from Lupata Gorge, Mozambique, form at eutectic (2), consistent with the presence of nepheline phenocrysts. Our conclusions, based on high- vs. low-pressure experiments, confirm the suggestion made by other authors, that Crowsnest volcanic rocks must have been erupted explosively to preserve glassy analcime phenocrysts during very rapid, upward transport from deep in the crust (H2O pressures ≫500 MPa). Only rare examples survived the deuteric and hydrothermal alteration that occurred during and after eruption.
The Cumberland Infirmary, Carlisle, serves a largely remote, rural population of 330 000. The aim of this study was to report the treatment and survival figures for patients treated for laryngeal cancer at this centre.
The study included 209 consecutive patients with squamous cell carcinoma of the larynx diagnosed between 1996 and 2010 at the Cumberland Infirmary.
Disease-specific survival was 100 per cent for stage one, 76 per cent for stage two, 87 per cent for stage three and 46 per cent for stage four. In total, 76 patients (36 per cent) had a laryngectomy, either as primary treatment or as a salvage procedure.
Our tumour-specific survival rate was very high, and this success may be due in part to high rates of surgical intervention. Survival data compared favourably with other centres, despite less radical radiotherapy regimes. Laryngeal cancer can be managed effectively in a small, relatively remote, multidisciplinary team setting.
We demonstrate the novel use of CV simulation to determine the level of charge at each interface in multilayer GaAs/AlGaAs heterostructures. The gettering of charged centres at the earliest grown interfaces is quantitatively appraised and the parallel application of PL decay lifetime measurements determines their effectiveness as recombination centres. A direct relationship is found between the magnitude of the charged states and the recombination velocity. Estimates of a 1eV activation energy and a hole capture cross section of 10−15 cm2 were also obtained. This suggests that the dominant recombination centre could be observed as a hole trap.