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351.
Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments. 相似文献
352.
An approach for factoring the effects of a planetary thermal history into a predicted set of crater statistics for an icy satellite is developed and forms the basis for subsequent data inversion studies. The key parameter is a thermal evolution-dependent critical time for which craters of a particular size forming earlier do not contribute to present-day statistics. An example is given for the satellite Ganymede and the effect of the thermal history is easily seen in the resulting predicted crater statistics. A preliminary comparison with the data, subject to the uncertainties in ice rheology and impact flux history, suggests a surface age of 3.8 x 10(9) years and a radionuclide abundance of 0.3 times the chondritic value. 相似文献
353.
Chemical anatomy of the brain 总被引:14,自引:0,他引:14
The development of sensitive histochemical-neuroanatomical techniques has made it possible to analyze the content of specific compounds in single nerve cells and their processes. In consequence, it has been possible to construct detailed maps of the distribution of various types of neurons on the basis of their transmitter substance. There are now many examples of neurons containing both a classical transmitter and a peptide. In some instances the peptides seem to support the action of the classical transmitters. This interaction may have applications in the prevention and treatment of nervous disease states. 相似文献
354.
355.
Soderblom LA Anderson RC Arvidson RE Bell JF Cabrol NA Calvin W Christensen PR Clark BC Economou T Ehlmann BL Farrand WH Fike D Gellert R Glotch TD Golombek MP Greeley R Grotzinger JP Herkenhoff KE Jerolmack DJ Johnson JR Jolliff B Klingelhöfer G Knoll AH Learner ZA Li R Malin MC McLennan SM McSween HY Ming DW Morris RV Rice JW Richter L Rieder R Rodionov D Schröder C Seelos FP Soderblom JM Squyres SW Sullivan R Watters WA Weitz CM Wyatt MB Yen A Zipfel J 《Science (New York, N.Y.)》2004,306(5702):1723-1726
The soils at the Opportunity site are fine-grained basaltic sands mixed with dust and sulfate-rich outcrop debris. Hematite is concentrated in spherules eroded from the strata. Ongoing saltation exhumes the spherules and their fragments, concentrating them at the surface. Spherules emerge from soils coated, perhaps from subsurface cementation, by salts. Two types of vesicular clasts may represent basaltic sand sources. Eolian ripples, armored by well-sorted hematite-rich grains, pervade Meridiani Planum. The thickness of the soil on the plain is estimated to be about a meter. The flatness and thin cover suggest that the plain may represent the original sedimentary surface. 相似文献
356.
Lars B. Johansson 《Potato Research》1988,31(1):145-149
Summary A new method is presented for anther culture. Anthers are cultivated on cubes of solid medium, surrounded by liquid medium.
This allows changes of media composition at any time. When embryos or callus were produced, the liquid initiation medium was
removed and replaced with regeneration medium. The best yield of embryos and the best regeneration frequency were obtained
when the initiation medium contained 2,4-dichlorophenoxyacetic acid (2,4-D). Regeneration of shoots from callus was stimulated
on double layer medium, with the callus placed on top of a solid medium, partly submerged in the overlaying liquid medium.
The best gelling agent for shoot multiplication media was agarose, but gellan gum was a good alternative. Both the production
of flower buds and embryogenesis in anther cultures was inhibited by an increased concentration of CO2 in the air surrounding the donor plants. 相似文献
357.
Malin E Jonsson Erik Eriksson Sofia Boqvist Anne Margrete Urdahl Anna Aspán 《Acta veterinaria Scandinavica》2009,51(1):43
Background
In Sweden, a particular subtype of verocytotoxin-producing Escherichia coli (VTEC) O157:H7, originally defined as being of phage type 4, and carrying two vtx2 genes, has been found to cause the majority of reported human infections during the past 15 years, including both sporadic cases and outbreaks. One plausible explanation for this could be that this particular subtype is better adapted to colonise cattle, and thereby may be excreted in greater concentrations and for longer periods than other VTEC O157:H7 subtypes.Methods
In an experimental study, 4 calves were inoculated with 109 colony forming units (cfu) of strain CCUG 53931, representative of the subtype VTEC O157:H7 (PT4;vtx2;vtx2c). Two un-inoculated calves were co-housed with the inoculated calves. Initially, the VTEC O157:H7 strain had been isolated from a dairy herd with naturally occurring infection and the farm had previously also been linked to human infection with the same strain. Faecal samples were collected over up to a 2-month period and analysed for VTEC O157 by immuno-magnetic separation (IMS), and IMS positive samples were further analysed by direct plating to elucidate the shedding pattern. Samples were also collected from the pharynx.Results
All inoculated calves proved culture-positive in faeces within 24 hours after inoculation and the un-inoculated calves similarly on days 1 and 3 post-inoculation. One calf was persistently culture-positive for 43 days; in the remainder, the VTEC O157:H7 count in faeces decreased over the first 2 weeks. All pharyngeal samples were culture-negative for VTEC O157:H7.Conclusion
This study contributes with information concerning the dynamics of a specific subtype of VTEC O157:H7 colonisation in dairy calves. This subtype, VTEC O157:H7 (PT4;vtx2;vtx2c), is frequently isolated from Swedish cattle and has also been found to cause the majority of reported human infections in Sweden during the past 15 years. In most calves, inoculated with a representative strain of this specific subtype, the numbers of shed bacteria declined over the first two weeks. One calf could possibly be classified as a high-shedder, excreting high levels of the bacterium for a prolonged period. 相似文献358.
359.
Wiinberg B Jensen AL Rozanski E Johansson PI Kjelgaard-Hansen M Tranholm M Kristensen AT 《Veterinary journal (London, England : 1997)》2009,179(1):121-129
The ability of a laboratory assay to correlate to clinical phenotype is crucial for the accurate diagnosis and monitoring of haemostasis and is therefore challenging with currently used routine haemostasis assays. Thromboelastography (TEG) is increasingly used to evaluate haemostasis in humans and may well be of value in the workup of dogs suspected of having a haemostatic disorder. This study was undertaken to evaluate prospectively how tissue factor (TF) activated TEG correlated to clinical signs of bleeding in dogs, compared to a routine coagulation profile. A prospective case-control study was performed over a 2 year period from 2004-2006. Eligible dogs were those where the primary clinician requested a coagulation profile to evaluate haemostasis. The dogs were simultaneously evaluated with a TF-activated TEG assay. Twenty-seven dogs, characterised as hypo-coagulable based on the TEG parameter G (<3.2 Kdyn/cm(2)), were included in the study as cases. Size matched control groups of TEG normo- (G=3.2K-7.2 Kdyn/cm(2)) and hyper-coagulable (G>7.2 Kdyn/cm(2)) dogs were selected retrospectively from the eligible dogs. For all dogs, clinical signs of bleeding were noted at time of analysis. There were statistically significant differences between all TEG values of hypo- and normo- and hyper-coagulable dogs. Thromboelastography correctly identified dogs with clinical signs of bleeding with a positive predictive value (PPV) of 89% and a negative predictive value (NPV) of 98% based on G alone. In comparison, the coagulation profile had a PPV between 50-81% and a NPV between 92-93% for detection of bleeding, depending on the observer. In conclusion, a TF-activated TEG G value<3.2K dyn/cm(2) correctly identified dogs with clinical signs of bleeding with very high PPV and NPV, irrespective of observer. The findings strongly suggest that TF- activated TEG may be of value in the workup of dogs suspected of having a haemostatic disorder. 相似文献
360.
Pivi Ekholm Liisa Virkki Maija Ylinen Liisa Johansson Pertti Varo 《Cereal Chemistry》2000,77(5):562-566
The solubility of mineral elements from oat bran and flake samples was studied by a method using equilibrium dialysis after enzymatic digestion of starch and proteins. The effects of six potential chelating agents common in food were tested on the solubility of mineral elements. The minerals studied were calcium, magnesium, iron, manganese, zinc and potassium, and the chelating agents were citric, lactic, malic, and ascorbic acids, glucose and xylitol. The mineral elements were tightly bound to the dietary fiber of the samples. Bran fiber bound even the zinc and calcium contributed through the enzymes used. Adding citric, malic, or lactic acids increased the solubility of the mineral elements studied, except for potassium which was easily dialyzable as such. Iron was insoluble in all situations. Citric acid was the most efficient chelating agent in solubilizing the mineral elements. The effect of malic and lactic acids on the solubility of minerals was small. No effect was found with glucose, ascorbic acid, and xylitol. Thus, the intestinal availability of mineral elements may be affected by dietary hydroxy acids such as citric and malic acids in high dietary fiber diets. 相似文献