Estimating the mass of asteroid 253 mathilde from tracking data during the NEAR flyby   总被引：1，自引：0，他引：1  

DK Yeomans  J Barriot  DW Dunham  RW Farquhar  JD Giorgini  CE Helfrich  AS Konopliv  JV McAdams  JK Miller  WM Owen  DJ Scheeres  SP Synnott  BG Williams 《Science (New York, N.Y.)》1997,278(5346):2106-2109

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter.  相似文献   

A two-stage optimal motion planner for autonomous agricultural vehicles   总被引：1，自引：0，他引：1  

S. Vougioukas  S. Blackmore  J. Nielsen  S. Fountas 《Precision Agriculture》2006,7(5):361-377

This paper presents a two-stage motion planning algorithm which can compute low-cost motions for autonomous agricultural vehicles, for a given cost function defined over the entire path (e.g., shortest path, maximum clearance, etc.). In the first stage, the algorithm utilizes randomized motion planning to explore the space of possible motions and computes a feasible sub-optimal trajectory. In the second stage, the optimization of the stage-1 motion is formulated within the optimal control framework and function-space gradient descent is used to minimize the cost of the entire motion. The numerical results suggest that the two-stage motion planner can compute optimal or quasi-optimal motions in free space very quickly. In the presence of obstacles however, the execution time increases significantly. Furthermore, kino-dynamic, or dynamic motion models seem to be necessary in order to produce smooth motion trajectories.  相似文献   

The epidemiological interpretation of serological responses to leptospiral serovars in sheep.     

D.K. Blackmore  A.R. Bahaman  R.B. Marshall 《New Zealand veterinary journal》2013,61(4):38-42

Serum samples were examined for evidence of leptospiral agglutinins from 928 sheep from 45 lines and kidneys from 12 of these lines for evidence of leptospiral infection. All sheep had been submitted for slaughter at meat works in the Manawatu.

Serological results were analysed using the results at a minimum serum dilution in the microscopic agglutination test (MAT) of 1:24 and at a minimum dilution of 1:48. It was shown that a minimum dilution of 1:24 resulted in many non-specific or cross-reactions. A minimum dilution of 1:48 was more accurate for detecting the serological prevalence of specific agglutinins to leptospires in ovine sera. Twenty percent of the sheep had titres of 1:48 or greater to hardjo, 3.8% to pomona, 2.6% to tarassovi, 2.3% to copenhageni and 2.7% to ballum. No titres of 1:48 or greater to australis were detected. Serovar hardjo was isolated from the kidneys of three animals in one line.

Eighteen months later 291 serum samples and 95 urine samples were collected from live animals on the property from which the three hardjo infected animals originated. No titres to hardjo were detected in the sera of lambs, but a serological prevalence of 44% and 84% to this serovar was demonstrated in the hoggets and ewes respectively. No leptospires were demonstrated in any of the urine samples.

These results show that sporadic infection of sheep with hardjo can occur but they also indicate that infection with this serovar is not endemic and that sheep are unlikely to act as maintenance hosts for hardjo in New Zealand.  相似文献   

Epidemiology of leptospirosis in dairy farm workers in the Manawatu. Part II. A case-control study of high and low risk farms     

C.G. Mackintosh  L.M. Schollum  D.K. Blackmore  R.B. MarshalI 《New Zealand veterinary journal》2013,61(6):73-76

Subsequent to a cross-sectional serological survey of Manawatu dairy farm workers, a case-control study was carried out to investigate the correlation between titres to leptospiral serovars in workers and those in cattle in their herds. A total of 52 herds was investigated, 25 of which were ‘high risk’ where milkers had titres of 1:96 or greater, and 27 were case-controls where milkers had no detectable agglutinin titres at a minimum serum dilution of 1:24.

The serological prevalence of titres to hardjo in cattle on ‘high risk’ farms (76.5%) was significantly higher (P<0.05) than on the case-control farms (60.0%). The geometric mean titres of seropositive cattle on ‘high risk’ farms were also significantly higher (P<0.0l) than in the cattle from the case-control farms, especially in the younger cohorts. These findings suggest that there was active endemic hardjo infection in the two- to three-year-old cattle on the ‘high risk’ farms.

Titres to pomona were demonstrated in only 5.2% of the cattle from both types of farm. Workers with titres to pomona tended to be from farms on which stock, especially calves, were bought-in and pigs were kept.

Conventional measures for protecting milkers from contact with infected urine appeared to be ineffective and it is concluded that prevention of leptospirosis in dairy farm workers can only be achieved by elimination of infection in the herd by vaccination of cattle.  相似文献   

Isolation of Leptospira interrogans serovar hardjo from sheep in New Zealand     

A.R. Bahaman  R.B. Marshall  D.K. Blackmore  S.W. Hathaway 《New Zealand veterinary journal》2013,61(8)

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Light intensity and fur-chewing in rabbits     

David K. Blackmore  Wendy H. Schultze  Gillian C. Absolon 《New Zealand veterinary journal》2013,61(9)

Extract

Madam:-, Fur-chewing is a relatively common apparent behavioural problem of farmed rabbits. Unlike the preparturient doe, who pulls out fur from ventral body surfaces to line her nest, rabbits of either sex which fur-chew, bite off hair from any part of the body which is accessible and may partially denude more than 50% of their body surface. The condition often appears to be self-inflicted, and unlike whisker chewing in mice, or feather plucking in chickens, a rabbit may either chew its own fur or that of others. The condition is a serious problem for commercial producers of rabbit pelts and for those attempting to carry out nutritional studies which require analysis and comparison of food intake and faecal output. For instance, in digestibility studies, fur-chewing constitutes a confounding variable in relation to nitrogen analysis.  相似文献   

Effect of infectious bursal disease virus insult on iron, copper, and zinc concentration in liver, bursa of Fabricius, spleen, pancreas, and serum of chickens     

Blackmore C  Klasing K  Wakenell P 《Avian diseases》2006,50(2):303-305

The effect of a systemic disease on the dynamics of iron, zinc, and copper in chickens fed ad libitum was examined by infecting 10-day-old specific pathogen-free chickens with infectious bursal disease virus (IBDV). Liver, bursa of Fabricius, pancreas, spleen, and serum were sampled in 10 controls and 10 challenged chickens at 3-day intervals postinfection (PI) for 15 days. The samples were analyzed using atomic absorption spectroscopy. Serum levels were similar to that reported in the literature. Concentrations of iron and zinc did not change significantly in the pancreas, but there was an increase in copper in infected pancreatic tissue on days 9 and 15 PI. Iron concentration in the spleen showed a significant increase on days 6, 9, and 15 PI, whereas zinc was only significantly increased on day 15 PI. There was no significant change in copper concentrations in the spleens of infected chickens vs. controls. This finding is in line with previously reported data. The results showed that the liver was not a major tissue where iron and zinc were sequestered, as previous data have shown in mammals. Instead, the bursa of Fabricius had significantly increased levels of both iron and zinc in infected tissue vs. control tissue from 9 days PI on. Furthermore, the bursa had increased levels of copper in the latter portion of the study. These findings suggest that the bursa of Fabricius rather than the liver is the major organ for metallic ion sequestering during IBDV infection.  相似文献   

A generalised individual‐based algorithm for modelling the evolution of quantitative herbicide resistance in arable weed populations          下载免费PDF全文

Chun Liu  Shiv S Kaundun  Les Glasgow  Micheal DK Owen  Paul Neve 《Pest management science》2017,73(2):462-474

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How well will stacked transgenic pest/herbicide resistances delay pests from evolving resistance?          下载免费PDF全文

Jonathan Gressel  Aaron J Gassmann  Micheal DK Owen 《Pest management science》2017,73(1):22-34

Resistance has evolved to single transgenic traits engineered into crops for arthropod and herbicide resistances, and can be expected to evolve to the more recently introduced pathogen resistances. Combining transgenes against the same target pest is being promoted as the solution to the problem. This solution will work if used pre‐emptively, but where resistance has evolved to one member of a stack, resistance should easily evolve for the second gene in most cases. We propose and elaborate criteria that could be used to evaluate the value of stacked traits for pest resistance management. Stacked partners must: target the same pest species; be in a tandem construct to preclude segregation; be synchronously expressed in the same tissues; have similar tissue persistence; target pest species that are still susceptible to at least two stacked partners. Additionally, transgene products must not be degraded in the same manner, and there should be a lack of cross‐resistance to stacked transgenes or to their products. With stacked herbicide resistance transgenes, both herbicides must be used and have the same persistence. If these criteria are followed, and integrated with other pest management practices, resistance may be considerably delayed. © 2016 Society of Chemical Industry  相似文献   

Effect of Roscovitine‐Treated Donor Cells on Development of Porcine Cloned Embryos     

HJ Park  OJ Koo  DK Kwon  JT Kang  G Jang  BC Lee 《Reproduction in domestic animals》2010,45(6):1082-1088

Synchronization of the donor cell cycle is an important factor for successful animal cloning by nuclear transfer. To improve the efficiency of porcine cloning, in the present report, we evaluated effects of contact inhibition, serum starvation and roscovitine treatment of donor cells on in vitro and in vivo developmental potency of cloned porcine embryos. Fibroblasts derived from a porcine foetus at day 30 of gestation were isolated and cultured to 70% confluency. Then, cells were either cultured to 100% confluency for contact inhibition, or cultured in 0.5% serum for 72 h for serum starvation or with 15 μm roscovitine for 24 h. Cells were most effectively synchronized at G0/G1 in the serum starvation group (87.5%) compared with the contact inhibition and roscovitine treatment groups (76.3% and 79.9% respectively p < 0.05). However, after somatic cell nuclear transfer followed by in vitro culture, the serum starvation group showed a significantly lower blastocyst formation rate (5.6%) compared with the contact inhibition and roscovitine treatment groups (11.6% and 20.0% respectively). Differential expression of apoptosis‐related genes and the level of apoptosis in each treatment group explain the variation in developmental competence among the groups. Significantly higher level of apoptosis was observed in the serum starvation group. On the other hand, the roscovitine treatment group shows the lowest level of apoptosis and the best in vitro development among the groups. Cloned embryos derived from roscovitine‐treated donor cells were transferred to surrogate pigs. Three healthy live piglets were produced. In conclusion, we suggest that roscovitine treatment of donor cells improves development of cloned porcine embryos and can raise the efficiency of cloned piglet production.  相似文献