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Biomedical subjects

J F Bell

Publications and source records attributed to J F Bell.

At least 37 records · Page 2Linked to original sources
PubMed2004

Pancam multispectral imaging results from the Spirit Rover at Gusev Crater.

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.

Atmosphere↗
PubMed2004

The Spirit Rover's Athena science investigation at Gusev Crater, Mars.

The Mars Exploration Rover Spirit and its Athena science payload have been used to investigate a landing site in Gusev crater. Gusev is hypothesized to be the site of a former lake, but no clear evidence for lacustrine sedimentation has been found to date. Instead, the dominant lithology is basalt, and the dominant geologic processes are impact events and eolian transport. Many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration. Any lacustrine sediments that may exist at this location within Gusev apparently have been buried by lavas that have undergone subsequent impact disruption.

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↗
PubMed1999

Imaging of asteroid 433 eros during NEAR's flyby reconnaissance

During the 23 December 1998 flyby of asteroid 433 Eros, the Near-Earth Asteroid Rendezvous (NEAR) spacecraft obtained 222 images of Eros, as well as supporting spectral observations. The images cover slightly more than two-thirds of Eros (best resolution is approximately 400 meters per pixel) and reveal an elongated, cratered body with a linear feature extending for at least 20 kilometers. Our observations show that Eros has dimensions of 33 x 13 x 13 kilometers. The volume, combined with the mass determined by the NEAR radio science experiment, leads to a density of 2.5 +/- 0.8 grams per cubic centimeter. This relatively high density, and the presence of an extensive linear feature, suggest that Eros may be a structurally coherent body.

Journal Article↗
PubMed1997

Results from the Mars Pathfinder camera.

Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity approximately 0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.

Atmosphere↗
PubMed1991

Solid C triple bond N bearing material on outer solar system bodies.

Using telescopic observations by ourselves and other observers, we have identified cyano-group containing molecules in the very dark solids on the surfaces of a few D-class asteroids, the dust of some comets, and low-albedo hemisphere of Iapetus, and the rings of Uranus, through spectroscopic detection of the 2.2-micrometers overtone of the C triple bond N stretching fundamental mode. The occurrence of this band on all four classes of small Solar System bodies may be diagnostic of the duration of exposure and degree of modification of surface materials, and may also establish a link between outer Solar System and interstellar materials.

Carbon↗
PubMed1986

Blood selenium concentrations of sheep and goats from selected areas of Kenya.

A systematic mapping technique based on blood, forage and soil selenium levels was employed to locate areas of selenium deficiency, adequacy or excess in areas of Kenya where grazing of small ruminants predominates. A total of 1,478 blood samples from both sheep and goats, 180 forage samples and 90 soil samples were analysed for selenium levels. During the wet seasons 28% of the sheep and 15% of the goats had marginal to deficient blood selenium concentrations while during the dry season 20% of the sheep and 12% of the goats had marginal to deficient blood selenium concentrations. Forage samples had a range of 0.03 to 0.66 ppm selenium while soil samples had a range of 0.06 to 0.98 ppm selenium. Although many animals had blood selenium levels of less than 0.05 ppm, below which selenium deficiency signs might occur, none of the animals manifested these signs.

Animals↗
PubMed1985

Tick survey on goats and sheep in Kenya.

A tick survey was done on sheep and goats in Siaya and Kakamega Districts, Kenya between October 1980 and October 1981. Most of the animals were found to carry one to 10 ticks with no significant difference between sheep and goats. The most abundant species was R. appendiculatus followed by R. evertsi. There were more male than female ticks found on the animals. Thirty per cent of the farms visited practised the hand picking method of tick control while 14% regularly dipped their animals.

Animals↗
PubMed1983

Immunofluorescent examination of the skin of rabies-infected animals as a means of early detection of rabies virus antigen.

Correlations were made on immunofluorescence positivity to antirabies conjugate between cranium-derived nerve fibers in skin and traditional samplings of brain tissue from several species and illness categories of animals with naturally acquired rabies. The overall correlation of results from all categories was about 98% (n, 104) for those that were brain positive and 100% (n, 99) for those that were brain negative. Some animals that ultimately developed rabies were found to have immunofluorescence-positive results 2 or more days before the onset of clinical signs in both natural and experimental infections. The percentage of those with positive skin immunofluorescence results increased as the onset of symptoms approached. From the midcourse period of illness to death, the correlation between skin and brain approached 100%. Different vaccines, commonly given to prevent rabies and other diseases of dogs and cats, were administered to groups of mice and were found to not produce false-positive results when their skin was examined by immunofluorescence for rabies virus antigen. These data suggest that examination of surgical biopsy specimens by immunofluorescence for rabies virus antigen is a useful and reliable diagnostic tool to evaluate the rabies status of biting dogs or cats, or to confirm a clinical diagnosis of rabies in the species tested. The biopsy evaluation of any other species as a means of assessing bite risk is not suggested by these data.

Animals↗
PubMed1983

Quantum differences in oral susceptibility of voles, Microtus pennsylvanicus, to virulent Francisella tularensis type B, in drinking water: implications to epidemiology.

Shedding nephritis in voles with chronic tularemia is the probable source of frequent contamination of streams over wide areas of the northern hemisphere. However, voles inoculated parenterally with as few as one dex viable cells of Francisella tularensis palaearctica succumb uniformly to acute tularemia, whereas voles, beavers, and muskrats often thrive in waters contaminated with the organism. Nevertheless, water-borne epizootics do occur in these animals, and at these times streams are heavily contaminated. In attempts to determine the lethal dose, per os, of the bacteria to voles, it was found that there are stable, 'order-of-magnitude' differences in susceptibility of individual weaned voles reared under uniform conditions. Also, voles thus infected often became chronically infected with bacteriuria. It is proposed that the most susceptible voles are responsible for amplification of water contamination and thus for initiation of water-borne epizootics in hygrocolic mammals and for frequent mild infections in man.

Animals↗
PubMed1980

Experimental chronic rabies in the cat.

Two cats, inoculated with a street rabies virus strain, survived with only some progressive debility and atrophy of musculature in the injected limb for 136 weeks. They had continuously increasing titers of neutralizing antibody in serum and in cerebrospinal fluid, and terminally they had high antibody titers in the brain. Virus was isolated from two brain specimens of one cat obtained at necropsy; isolation was successful only by explant culture and inoculation of explanted tissue into mice. Virus antigen was detected in eight sites in the brain and spinal cord of the same cat by frozen-section immunofluorescence. Lesions in the central nervous system consisted of neuronal degeneration and neuronophagia, associated with the prescence of inclusion bodies and widespread inflammatory cell inflitration into brain and spinal cord parenchyma, perineuronal sites, and perivascular spaces. The inflitrates contained lymphocytes, monocytes-macrophages, and a high proportion of plasma cells. These experimental cases of chronic progressive rabies resembled more closely subacute sclerosing panecephalitis of man than the usual subacute fatal rabies encephalitis of man and other mammalian species.

Animals↗
PubMed1979

Allergic encephalitis, rabies antibodies, and the blood/brain barrier.

Similarity of the syndromes of rabies and of encephalomyelitis resulting from rabies vaccination poses a problem in differential diagnosis that has had tragic consequences. That difficulty may also be largely responsible for the traditional belief that rabies is inexorably fatal, in that recovery from paralysis is interpreted as evidence that the disease was postvaccinal encephalomyelitis rather than rabies. Diagnosis is additionally complicated by presence of rabies antibodies in serum in both conditions. However, we have found that rabies antibodies elicited by vaccination do not pass the blood/brain barrier to enter the fluids of the CNS in EAE, the experimental counterpart of postvaccinal encephalomyelitis; whereas antibodies are present in high titer as a result of production in situ after recovery from rabies. Therefore a ratio of antibody concentrations of greater than 1:10 in CSF and serum indicates chronic rabies or recovery from that disease.

Animals↗