Localization and physical properties experiments conducted by Spirit at Gusev Crater     

Arvidson RE  Anderson RC  Bartlett P  Bell JF  Blaney D  Christensen PR  Chu P  Crumpler L  Davis K  Ehlmann BL  Fergason R  Golombek MP  Gorevan S  Grant JA  Greeley R  Guinness EA  Haldemann AF  Herkenhoff K  Johnson J  Landis G  Li R  Lindemann R  McSween H  Ming DW  Myrick T  Richter L  Seelos FP  Squyres SW  Sullivan RJ  Wang A  Wilson J 《Science (New York, N.Y.)》2004,305(5685):821-824

The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials.  相似文献   

Identification of non-precious metal alloy catalysts for selective hydrogenation of acetylene     

Studt F  Abild-Pedersen F  Bligaard T  Sørensen RZ  Christensen CH  Nørskov JK 《Science (New York, N.Y.)》2008,320(5881):1320-1322

The removal of trace acetylene from ethylene is performed industrially by palladium hydrogenation catalysts (often modified with silver) that avoid the hydrogenation of ethylene to ethane. In an effort to identify catalysts based on less expensive and more available metals, density functional calculations were performed that identified relations in heats of adsorption of hydrocarbon molecules and fragments on metal surfaces. This analysis not only verified the facility of known catalysts but identified nickel-zinc alloys as alternatives. Experimental studies demonstrated that these alloys dispersed on an oxide support were selective for acetylene hydrogenation at low pressures.  相似文献   

Initial results from the Mini-TES experiment in Gusev Crater from the Spirit Rover     

Christensen PR  Ruff SW  Fergason RL  Knudson AT  Anwar S  Arvidson RE  Bandfield JL  Blaney DL  Budney C  Calvin WM  Glotch TD  Golombek MP  Gorelick N  Graff TG  Hamilton VE  Hayes A  Johnson JR  McSween HY  Mehall GL  Mehall LK  Moersch JE  Morris RV  Rogers AD  Smith MD  Squyres SW  Wolff MJ  Wyatt MB 《Science (New York, N.Y.)》2004,305(5685):837-842

The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils.  相似文献   

Viking first encounter of phobos: preliminary results     

Tolson RH  Duxbury TC  Born GH  Christensen EJ  Diehl RE  Farless D  Hildebrand CE  Mitchell RT  Molko PM  Morabito LA  Palluconi FD  Reichert RJ  Taraji H  Veverka J  Neugebauer G  Findlay JT 《Science (New York, N.Y.)》1978,199(4324):61-64

During the last 2 weeks of February 1977, an intensive scientific investigation of the martian satellite Phobos was conducted by the Viking Orbiter-1 (VO-1) spacecraft. More than 125 television pictures were obtained during this period and infrared observations were made. About 80 percent of the illuminated hemisphere was imaged at a resolution of about 30 meters. Higher resolution images of limited areas were also obtained. Flyby distances within 80 kilometers of the surface were achieved. An estimate of the mass of Phobos (GM) was obtained by observing the effect of Phobos's gravity on the orbit of VO-1 as sensed by Earth-based radiometric tracking. Preliminary results indicate a value of GM of 0.00066 +/- 0.00012 cubic kilometer per second squared (standard deviation of 3) and a mean density of about 1.9 +/- 0.6 gram per cubic centimeter (standard deviation of 3). This low density, together with the low albedo and the recently determined spectral reflectance, suggest that Phobos is compositionally similar to type I carbonaceous chondrites. Thus, either this object formed in the outer part of the asteroid belt or Lewis's theory that such material cannot condense at 1.5 astronomical units is incorrect. The data on Phobos obtained during this first encounter period are comparable in quantity to all of the data on Mars returned by Mariner flights 4, 6, and 7.  相似文献   

Changes in potato starch quality during growth   总被引：2，自引：0，他引：2  

D. H. Christensen  Marianne H. Madsen 《Potato Research》1996,39(1):43-50

Summary Potato starch quality parameters (amylose concentration, glucose-6-phosphate content and granule size) were analyzed in relation to the harvesting date and tuber size of four cultivars. A significant increase in the glucose-6-phosphate content and granule size of starch was observed during tuber growth, whereas the amylose concentration was constant. Granule size increased markedly, whereas glucose-6-phosphate content showed slightly increasing values with increasing tuber size. Amylose concentration showed no correlation with tuber size. We conclude that the changes in the granule size, glucose-6-phosphate and amylose content of potato starch during growth are independent of each other.  相似文献   

Addendum     

Kenneth A. Rykbost  Randy L. Dovel  Neil W. Christensen 《American Journal of Potato Research》1991,68(11):798-799

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Management of hydrops amnion in a mare resulting in birth of a live foal     

Christensen BW  Troedsson MH  Murchie TA  Pozor MA  Macpherson ML  Estrada AH  Carrillo NA  Mackay RJ  Roberts GD  Langlois J 《Journal of the American Veterinary Medical Association》2006,228(8):1228-1233

CASE DESCRIPTION: A 19-year-old Thoroughbred mare was evaluated at 265 days of gestation with a markedly distended abdomen and edema of the ventral portion of the abdomen. CLINICAL FINDINGS: The uterus was distended over the pelvic rim, making transrectal palpation of the fetus impossible. Transabdominal ultrasonography revealed excessive amounts of fetal fluid. Results of analysis of fluid obtained via amnio- and allantocentesis confirmed that the amniotic cavity was large. TREATMENT AND OUTCOME: The mare was monitored for signs of weakness of the prepubic tendon and abdominal wall. The fetus and placenta were monitored for signs of stress and pending abortion. Flunixin meglumine and altrenogest were administered to the mare. Parturition was attended and occurred at 321 days' gestation. Postpartum complications in the mare included hypovolemic shock and cardiac arrhythmias. Both conditions were treated, and the mare recovered. The foal was considered small, had bilateral angular limb deformities, and was unable to nurse. The foal was given plasma for failure of passive transfer of immunity. Ten months later, the foal underwent procedures to correct limb deformities. CONCLUSIONS AND CLINICAL RELEVANCE: Hydrops conditions are rare in horses, with hydrops allantois occurring more frequently than hydrops amnion; reportedly result in fetal or neonatal death; and may result in death of or injury to the mare. Close monitoring of maternal and fetal health in combination with supportive treatment of the mare can result in the safe progression of a hydrops pregnancy and the birth of a live foal.  相似文献   

Simultaneous determination of ginsenosides and polyacetylenes in American ginseng root (Panax quinquefolium L.) by high-performance liquid chromatography     

Christensen LP  Jensen M  Kidmose U 《Journal of agricultural and food chemistry》2006,54(24):8995-9003

A method for simultaneous determination of ginsenosides and polyacetylenes in Panax quinquefolium L. (American ginseng) roots was developed. The ginsenosides Rb1, Rb2, Rc, Rd, Re, Rg1, Ro, malonyl-Rb1, malonyl-Rc, and malonyl-Rd and the polyacetylenes falcarinol and panaxydol were extracted from fresh ginseng roots in a sequential extraction process with 100% methanol followed by 80% aqueous methanol and quantified simultaneously in extracts by high-performance liquid chromatography using diode array detection. Separations were achieved with a phosphate buffer-acetonitrile gradient system using an RP-C18 column. Except for Rd, the present extraction method resulted in similar or significantly higher concentrations of both ginsenosides and polyacetylenes in comparison to commonly used extraction methods for these compounds. The contents of polyacetylenes and ginsenosides were determined in the root hairs, lateral roots, and main roots of 6 year old ginseng plants. The total mean concentrations of ginsenosides and polyacetylenes in root hairs were 31.0 g/kg fresh weight (FW) and 2.6 g/kg FW, respectively, whereas the concentrations of these bioactive compounds in the main roots were significantly lower with total mean concentrations of 17.8 g/kg FW for ginsenosides and 0.6 g/kg FW for polyacetylenes. The concentration of individual and total ginsenosides and polyacetylenes did not differ significantly between main roots of different sizes. Consequently, it is possible to do quantitative screening for ginsenosides and polyacetylenes to breed ginseng roots with higher levels of bioactive compounds.  相似文献   

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M C Gjessing  D H Christensen  F Manji  S Mohammad  P E Petersen  B Saure  C Skjengen  S C Weli  O B Dale 《Journal of fish diseases》2018,41(7):i-i

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The occurrence of rust disease,and biochemical and physiological responses on <Emphasis Type="Italic">Apocynum venetum</Emphasis> plants grown at four soil water contents,following inoculation with <Emphasis Type="Italic">Melampsora apocyni</Emphasis>     

Peng Gao  Ting-Yu Duan  Michael J. Christensen  Zhi-Biao Nan  Qi-Tang Liu  Fan-Jie Meng  Jing-Feng Huang 《European journal of plant pathology / European Foundation for Plant Pathology》2018,150(3):549-563

We studied the development of rust disease, and biochemical and physiological responses, on Apocynum venetum plants inoculation with Melampsora apocyni that were growing in a greenhouse at four relative soil water contents. The soil conditions were 25% (severe drought), 50% (mild drought), 75% (optimal) and 100% (waterlogging) relative soil water content. Plants exposed to drought and waterlogging stress had a lower number of open stomata before inoculation, corresponding with the disease index on the 10th day after inoculation being lower than that of the optimal soil water condition. Inoculated plants exposed to severe and mild drought stress had a gradually enhanced resistance to the rust disease from the 10th day after inoculation, corresponding with the enhanced activity of polyphenol oxidase and phenylalanine ammonialyase. For the inoculated plants exposed to severe drought stress, hydrogen peroxide always remained at the highest level for any treatment, and they had a rapidly enhanced activity of peroxidase, two factors that were associated with suppression of disease development. A. venetum plants exposed to double stress of waterlogging and disease had a high activity of peroxidase that not only removed reactive oxygen to prevent or reduce cell injury but also enhanced resistance to the rust disease. In addition, a rapidly enhanced activity of phenylalanine ammonialyase in the waterlogging condition from the 25th day after inoculation was also associated with an enhanced resistance to the rust disease. Drought and waterlogging stress had a negative effect on the leaf photosystem, and in particular, there was a significant decrease in the net photosynthetic rate with an increase in the duration and degree of drought stress, and this lead to a statistically significant decrease in the weight of aboveground tissue compared with that of plants under optimal soil water condition (P < 0.05). Inoculating with M. apocyni had a slight effect on photosynthesis of plants during early disease development, but the physiological function of diseased leaves under the drought stress was damaged more seriously than that of non-inoculated plants in later disease development, leading to a large reduction in the net photosynthetic rate. However, this reduction did not cause a statistically significant (P > 0.05) decrease in the weight of aboveground tissue compared with that of non-inoculated plants under drought stress.  相似文献