Origin of multikilometer earth- and mars-crossing asteroids: A quantitative simulation     

F Migliorini  P Michel  A Morbidelli  D Nesvorny  V Zappala 《Science (New York, N.Y.)》1998,281(5385):2022-2024

Orbital dynamic simulations show that many asteroids in the main asteroid belt are driven toward Mars-crossing orbits by numerous weak mean motion resonances, which slowly increase the orbital ellipticity of the asteroids. In addition, half of the Mars-crossing asteroids (MCAs) transition to Earth-crossing asteroids (ECAs) in less than 20 million years. This scenario quantitatively explains the observed number of large ECAs and MCAs.  相似文献   

Biological Activity of Two Stereoisomers of the N-Thienyl Chloroacetamide Herbicide Dimethenamid     

Michel Couderchet  Pierre F. Bocion  Reynold Chollet  Karl Seckinger  Peter Bger 《Pest management science》1997,50(3):221-227

Due to the presence of an asymmetrically substituted C atom, dimethenamid [2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide], a recently introduced N-thienyl chloroacetamide herbicide, exists as two stereoisomers (S and R) having differing herbicidal activities as demonstrated with a selection of weeds and Lemna minor. The activity of the two isomers was investigated in greater detail with the green alga Scenedesmus acutus and compared to that of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide]. As with alachlor, the S isomer (5 μM ) strongly inhibited algal growth and fatty acid desaturation while the R isomer had no effect. In short-term experiments (up to 5·5 h), the S isomer and alachlor (100 μM ) inhibited [¹⁴C]acetate uptake and its incorporation into fatty acids in the same manner, while the R isomer did not. Incorporation of [¹⁴C]acetate into a non-lipid fraction of the algae was strongly inhibited by alachlor and the S isomer (100 μM ) and only slightly by the R isomer. A 50% inhibition of incorporation of [¹⁴C]oleic acid into the same non-lipid fraction was attained with less than 10^-7 M of the S isomer while 10^-5 M of the R form of dimethenamid achieved only a 40% inhibition. The same stereospecificity of the compound on growth, fatty acid desaturation, acetate uptake and oleic acid incorporation provides strong evidence that dimethenamid may act upon a primary, specific target in lipid metabolism. Furthermore, the comparable biological activities of dimethenamid and alachlor indicate that this target is common to both N-phenyl and N-thienyl chloroacetamide herbicides. © 1997 SCI.  相似文献   

Interaction between acetylcholinesterase and choline acetyltransferase: an hypothesis to explain unusual toxicological responses     

Denis Bourguet  Michel Raymond  Saïd Berrada  Didier Fournier 《Pest management science》1997,51(3):276-282

Organophosphorus and carbamate insecticides are thought to have only one target site, acetylcholinesterase (EC 3.1.1.7). When this enzyme is inhibited, the neurotransmitter acetylcholine is not metabolized and polarization of the post-synaptic membrane does not take place. But, what happens when the cholinesterase becomes resistant or when neurotransmitter levels are diminished? Here, we report results suggesting that choline acetyltransferase (EC 2.3.1.6), the enzyme responsible for the acetylcholine production, may be involved either as an alternative pesticide target site or as a factor enhancing survival during insecticide exposure. This underlines the concept that the pivotal step for insecticide toxicology is not the acetylcholinesterase activity but the amount of acetylcholine present. This latter can only fluctuate between an upper and a lower threshold, and crossing one of these two thresholds leads to the death of the insect. The interaction between acetylcholinesterase and choline acetyltransferase activities would explain the astonishing toxicological phenomenon that, in some conditions, mortality decreases when insecticide concentration increases. ©1997 SCI  相似文献   

The limitations of locust preventive management faced with spatial uncertainty: exploration with a multi‐agent model     

Pierre‐Emmanuel Gay  Michel Lecoq  Cyril Piou 《Pest management science》2020,76(3):1094-1102

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Mitigating the impact of selective phenotyping in training populations on the prediction ability by multi-trait pedigree and genomic selection models     

Sebastian Michel  Franziska Löschenberger  Ellen Sparry  Christian Ametz  Hermann Bürstmayr 《Plant Breeding》2020,139(6):1067-1075

Training populations for pedigree and genomic prediction in plant breeding programmes are largely updated with superior genotypes from multi-environment trials, where they are tested with the goal of variety development. Such a selective phenotyping has, however, a negative impact on prediction abilities, especially when only a subset of breeding lines can be tested, as for laborious and costly to phenotype traits. This study focused, thus, on investigating the impact of selective phenotyping in the training population of an applied wheat breeding programme, and assessing the potential to mitigate this impact by pedigree and genomic multi-trait prediction models as well as bi-directionally selected training populations for several baking quality parameters. Combining both pedigree and genomic information in multi-trait prediction models with pre-existing phenotypic information for protein content and sedimentation value compensated for the observed loss in prediction ability, while entering few inferior breeding lines into the training population further mitigated the impact of selective phenotyping and even led to a slight increase of prediction ability in comparison to a randomly chosen training population.  相似文献   

Mitochondrial complex III Qi‐site inhibitor resistance mutations found in laboratory selected mutants and field isolates     

Pierre Mounkoro  Thomas Michel  Rafik Benhachemi  Georgiana Surpateanu  Bogdan I Iorga  Nicholas Fisher  Brigitte Meunier 《Pest management science》2019,75(8):2107-2114

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Spatial analysis of soil surface hydraulic properties: Is infiltration method dependent?     

Ibrahim Mubarak  Rafael Angulo-Jaramillo  Jean Claude Mailhol  Mohammadreza Khaledian  Michel Vauclin 《Agricultural Water Management》2010,97(10):1517-150

The management of irrigated agricultural fields requires reliable information about soil hydraulic properties and their spatio-temporal variability. The spatial variability of saturated hydraulic conductivity, K_s and the alpha-parameter α_vG-2007 of the van Genuchten equation was reviewed on an agricultural loamy soil after a 17-year period of repeated conventional agricultural practices for tillage and planting. The Beerkan infiltration method and its algorithm BEST were used to characterize the soil through the van Genuchten and Brooks and Corey equations. Forty field measurements were made at each node of a 6 m × 7.5 m grid. The soil hydraulic properties and their spatial structure were compared to those recorded in 1990 on the same field soil, through the exponential form of the soil hydraulic conductivity given by the Gardner equation, using the Guelph Pressure Infiltrometer technique. No significant differences in the results obtained in 1990 and 2007 were observed for either particle-size distribution or dry bulk density. The mean value of α_vG-2007 was found to be identical to that of α_G-1990, while that of K_s-2007 was significantly smaller than that of K_s-1990. In contrast to the Gardner equation, the van Genuchten/Brooks and Corey expression was found to be more representative of a well-graded particle-size distribution of a loamy soil. The geostatistical analysis showed the two parameters, K_s and α_vG-2007, were autocorrelated up to about 30 and 21 m, respectively, as well as spatially positively correlated within a range of 30 m. Despite the difference in the mean values of K_s between the two studies, the spatial structures were similar to those found in the 1990 experiment except for the covariance sign. The similarity in autocorrelation ranges indicate that the spatial analysis of soil hydraulic properties is independent of the infiltration methods (i.e., measurement of an infiltration flux) used in the two studies, while the difference in the covariance sign may be linked to the use of two different techniques of soil hydraulic parameterization. The covariance values found in the 2007 campaign indicates a positive relationship between the two parameters, K_s and α_vG-2007. The spatial correlations of soil hydraulic parameters appear to be temporally stabilized, at least within the agro-pedo-climatic context of the study. This may be attributed to the soil textural properties which remain constant in time and to the structural properties which are constantly renewed by the cyclic agricultural practices. However, further experiments are needed to strengthen this result.  相似文献   

Natural cyclopeptides as leads for novel pesticides: tentoxin and destruxin     

Florine Cavelier  Jean Verducci  Franois Andr  Francis Haraux  Claude Sigalat  Michel Traris  Alain Vey 《Pest management science》1998,52(1):81-89

Difficulties in synthesis make natural cyclopeptides challenging targets for chemists. Our interest focused on two natural toxic cyclopeptide series produced by pathogenic fungi: tentoxin, [cyclo-(N-MeAla¹-Leu²-N-Meδ^zPhe³-Gly⁴)] and the destruxins [cyclo-(Pro¹-Ile²-N-MeVal³-N-MeAla⁴-β-Ala⁵-HA⁶)]. The total syntheses of these two bioactive series were optimised, and several analogues were designed and synthesised to establish structure–activity relationships. The importance of synthetic analogues in the identification of molecular targets and the explanation of mechanisms of action was demonstrated. Such systematic investigations can determine the crucial features responsible for the activity of the natural compound and help the design of more powerful or more selective products. © 1998 SCI.  相似文献