Search PubMed⌕ Search

Biomedical subjects

R Kirk

Publications and source records attributed to R Kirk.

At least 19 recordsLinked to original sources
PubMed2007

The lakes of Titan.

The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70 degrees north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.

Journal Article↗
PubMed2006

Titan Radar Mapper observations from Cassini's T3 fly-by.

Cassini's Titan Radar Mapper imaged the surface of Saturn's moon Titan on its February 2005 fly-by (denoted T3), collecting high-resolution synthetic-aperture radar and larger-scale radiometry and scatterometry data. These data provide the first definitive identification of impact craters on the surface of Titan, networks of fluvial channels and surficial dark streaks that may be longitudinal dunes. Here we describe this great diversity of landforms. We conclude that much of the surface thus far imaged by radar of the haze-shrouded Titan is very young, with persistent geologic activity.

Journal Article↗
PubMed2006

The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Extraterrestrial Environment↗
PubMed2005

Rain, winds and haze during the Huygens probe's descent to Titan's surface.

The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent.

Atmosphere↗
PubMed2005

Cassini radar views the surface of Titan.

The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of approximately 0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons.

Atmosphere↗
PubMed2001

The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros.

The NEAR-Shoemaker spacecraft was designed to provide a comprehensive characterization of the S-type asteroid 433 Eros (refs 1,2,3), an irregularly shaped body with approximate dimensions of 34 x 13 x 13 km. Following the completion of its year-long investigation, the mission was terminated with a controlled descent to its surface, in order to provide extremely high resolution images. Here we report the results of the descent on 12 February 2001, during which 70 images were obtained. The landing area is marked by a paucity of small craters and an abundance of 'ejecta blocks'. The properties and distribution of ejecta blocks are discussed in a companion paper. The last sequence of images reveals a transition from the blocky surface to a smooth area, which we interpret as a 'pond'. Properties of the 'ponds' are discussed in a second companion paper. The closest image, from an altitude of 129 m, shows the interior of a 100-m-diameter crater at 1-cm resolution.

Journal Article↗
PubMed2001

Imaging of small-scale features on 433 Eros from NEAR: evidence for a complex regolith.

On 25 October 2000, the Near Earth Asteroid Rendevous (NEAR)-Shoemaker spacecraft executed a low-altitude flyover of asteroid 433 Eros, making it possible to image the surface at a resolution of about 1 meter per pixel. The images reveal an evolved surface distinguished by an abundance of ejecta blocks, a dearth of small craters, and smooth material infilling some topographic lows. The subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter-sized blocks.

Journal Article↗
PubMed2001

The epidemiology of emergency department attendances in Christchurch.

AIM: To describe the characteristics of patients who attended Christchurch Hospital's emergency department (ED) in 1998. METHODS: Non-identifiable data about all the attendances to the ED during 1998 were obtained from Christchurch Hospital's management information services database. Demographic data, time and date of arrival, source of referral, diagnosis, triage category, and discharge destination were analysed. RESULTS: In 1998 there were 65,024 attendances, on average 178 people per day (95% confidence interval 145-211). Children and the elderly were the most frequent attenders except in weekends when visits by young people were more common. The elderly had the highest age specific rates of attendance. Most attendances were between 8am and midnight, and Mondays and July were the day and month with most attendances respectively. 43% of people referred themselves and 38% were referred by their general practitioner (GP). GP referrals were significantly more common during the day, the working week and in the winter. The elderly frequently presented with medical problems, their attendances were classified as more urgent and 75% of their visits resulted in hospital admission. CONCLUSIONS: These findings are generally consistent with the few previously published descriptions of ED attendance in New Zealand and most overseas studies. ED attendance data have important implications for funders and providers of ED services and a national dataset should be established.

Adolescent↗
PubMed2001

Glass particles in footwear of members of the public in south-eastern Australia--a survey.

A total of 776 pairs of shoes collected from random members of the public in south-eastern Australia were examined for the presence of glass fragments. From the samples collected a total of 110 fragments were recovered from 57 pairs of shoes (7.3% of the pairs examined). This study shows that the prevalence of glass fragments in footwear is dependent upon the area of the shoe from which the fragments were recovered. A much higher percentage of shoes were found to have fragments embedded in the sole (5.9%) than in the upper area of the shoe (1.9%). These shoes were also more likely to have multiple fragments from multiple sources of glass. Only a very small percentage of shoes contained fragments in both the upper and the sole (0.3%). These findings and their significance for the interpretation of glass evidence involving footwear are discussed in this study.

Adolescent↗
PubMed2000

NEAR at eros: imaging and spectral results

Eros is a very elongated (34 kilometers by 11 kilometers by 11 kilometers) asteroid, most of the surface of which is saturated with craters smaller than 1 kilometer in diameter. The largest crater is 5.5 kilometers across, but there is a 10-kilometer saddle-like depression with attributes of a large degraded crater. Surface lineations, both grooves and ridges, are prominent on Eros; some probably exploit planes of weakness produced by collisions on Eros and/or its parent body. Ejecta blocks (30 to 100 meters across) are abundant but not uniformly distributed over the surface. Albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith. On scales of 200 meters to 1 kilometer, Eros is more bland in terms of color variations than Gaspra or Ida. Spectra (800 to 2500 nanometers) are consistent with an ordinary chondrite composition for which the measured mean density of 2.67 +/- 0.1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent.

Journal Article↗
PubMed2000

Establishment of a smoking cessation programme in primary and secondary care in Canterbury.

AIMS: Smokescreen for the 1990's is a smoking cessation programme devised for use in primary care in Australia. It is based on the 'readiness to change' model where smokers are categorised as being 'ready', 'unsure', or 'not ready' to quit smoking. Those in the 'ready' group are encouraged to set a quit date and offered nicotine replacement therapy. Those in the unsure group receive brief motivational intervention, and those 'not ready' are given simple health advice. The aims of the study were to evaluate the process and outcome of establishing this program in primary and secondary care in Christchurch. METHODS: Process evaluation involved all staff participating in the program. Patient outcomes including quit rates were assessed by interview six months after enrollment. RESULTS: Implementation was successful with 59 general practitioners, 49 practice nurses and 294 hospital staff receiving education in the use of the programme. Nine hundred and seven patients (smokers) were enrolled in the study, 347 from primary care and 560 from Christchurch Hospital. The point prevalence abstinence rate at 6 months was 10.4% for the primary care sample and 17% for the secondary care group, with an overall rate of 14.4%. CONCLUSIONS: The programme was successfully implemented across primary and secondary care with an acceptable quit rate at 6 months.

Attitude of Health Personnel↗
PubMed1999

Mitochondrial genetic analyses suggest selection against maternal lineages in bipolar affective disorder.

Previous reports of preferential transmission of bipolar affective disorder (BP) from the maternal versus the paternal lines in families suggested that this disorder may be caused by mitochondrial DNA mutations. We have sequenced the mitochondrial genome in 25 BP patients with family histories of psychiatric disorder that suggest matrilineal inheritance. No polymorphism identified more than once in this sequencing showed any significant association with BP in association studies using 94 cases and 94 controls. To determine whether our BP sample showed evidence of selection against the maternal lineage, we determined genetic distances between all possible pairwise comparisons within the BP and control groups, based on multilocus mitochondrial polymorphism haplotypes. These analyses revealed fewer closely related haplotypes in the BP group than in the matched control group, suggesting selection against maternal lineages in this disease. Such selection is compatible with recurrent mitochondrial mutations, which are associated with slightly decreased fitness. Although such mismatch distribution comparisons have been used previously for analyses of population histories, this is, as far as we are aware, the first report of this method being used to study disease.

Alleles↗
PubMed1997

Transcatheter closure of patent arterial ducts using controlled-release coils.

OBJECTIVE: To determine the efficacy of transcatheter closure of patent arterial ducts using controlled-release coils. DESIGN: Transcatheter closure of patent arterial ducts was attempted in 52 patients using controlled-release coils. SETTING: For the study, four tertiary paediatric cardiology units were used, two of which were in the U.K., one in Italy and one in Turkey. PATIENTS: The 52 patients ranged in age between 3-5 months and 61 years (median 3-5 years), and weighted between 4.5 kg and 62 kg. The duct diameters were 1 mm to 6.5 mm. RESULTS: In four patients the ducts were too large for safe release of the coils. In the remaining 48, one coil was inserted in 33 patients, two coils in nine, three coils in four and four coils in two patients. Immediately at the end of the procedure, the duct was completely occluded in 26/47 (55%) patients. Haemolysis occurred in one patient, in whom the coil was removed by a snare catheter and a large umbrella device was implanted with resolution of the haemolysis. Coil embolization to the pulmonary artery occurred in five (10%) patients. All were easily retrieved and replaced by larger coils. At the latest follow-up by colour Doppler echocardiography, the duct was completely occluded in 44/47 (94%) patients. CONCLUSIONS: Transcatheter closure of patent arterial ducts by controlled-release coils is effective and safe. Even when more than one coil is inserted the technique is still less cumbersome and considerably cheaper than transcatheter umbrella closure.

Child, Preschool↗