Whales before whaling in the North Atlantic     

Roman J  Palumbi SR 《Science (New York, N.Y.)》2003,301(5632):508-510

It is well known that hunting dramatically reduced all baleen whale populations, yet reliable estimates of former whale abundances are elusive. Based on coalescent models for mitochondrial DNA sequence variation, the genetic diversity of North Atlantic whales suggests population sizes of approximately 240,000 humpback, 360,000 fin, and 265,000 minke whales. Estimates for fin and humpback whales are far greater than those previously calculated for prewhaling populations and 6 to 20 times higher than present-day population estimates. Such discrepancies suggest the need for a quantitative reevaluation of historical whale populations and a fundamental revision in our conception of the natural state of the oceans.  相似文献   

The effect of spin splitting on the metallic behavior of a two-dimensional system     

Papadakis SJ  De Poortere EP  Manoharan HC  Shayegan M  Winkler R 《Science (New York, N.Y.)》1999,283(5410):2056-2058

Experiments on a constant-density two-dimensional hole system in a gallium arsenide quantum well revealed that the metallic behavior observed in the zero-magnetic-field temperature dependence of the resistivity depends on the symmetry of the confinement potential and the resulting spin splitting of the valence band.  相似文献   

Potato tuber development I. The Russet Burbank variety; influence of seedpiece origin and spacing on tuber size and shape     

G. H. Rieman  D. C. Cooper  Melvin Rominsky 《American Journal of Potato Research》1953,30(4):98-103

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First call for nominations for honorary life membership in PAA     

David Curwen  Joe Siezcka 《American Journal of Potato Research》1993,70(11):863-863

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Root diseases, weeds, and nematodes with poultry litter and conservation tillage in a sweet corn–snap bean double crop     

Donald R. Sumner  Melvin R. Hall  J. Danny Gay  Greg MacDonald  Stanley I. Savage  R. Keith Bramwell 《Crop Protection》2002,21(10):963-972

The effect of continuous applications of poultry litter on root diseases, nematodes, and weeds with different tillage practices in vegetable production in Georgia was investigated. Litter treatments (noncomposted and composted broiler or breeder litter) applied 3–5 weeks before planting were compared with no litter. In sweet corn and snap bean there were differences among years, and tillage and litter treatments had a variable effect on yield, post-emergence damping-off and plant stand. Crown and brace root rot in corn induced by Rhizoctonia solani AG 2-2 increased after 3 years conservation tillage, but there were no differences among litter treatments. Population densities of R. solani AG-4 were increased by conservation tillage before planting snap bean the first year but not in later years, while litter treatments had no effect. After 3 years, populations of Pythium spp., Fusarium solani, and Fusarium spp. did not differ among treatments, but noncomposted broiler litter increased populations of saprophytic fungi in soil compared with no litter. Population densities of stylet-bearing nematodes were low and usually not different among treatments. After 3 years of sweet corn populations of Meloidogyne incognita increased with conventional tillage compared with conservation tillage, populations of Paratrichodorus christiei were reduced by litter treatments and populations of Helicotylenchus dihystera were reduced by noncomposted broiler litter compared with no litter. Weed infestation increased in both tillage systems with time, but in snap bean there was a greater infestation in conservation tillage than in conventional tillage. Litter treatments had little effect on weed infestation.  相似文献   

Feeding cotton products to cattle.   总被引：1，自引：0，他引：1  

Glenn M Rogers  Matthew H Poore  Joe C Paschal 《Veterinary Clinics of North America: Food Animal Practice》2002,18(2):267-294

Despite the potential for gossypol toxicosis (particularly in pre-ruminants) and risk factors associated with impaired fertility in bulls, cottonseed products offer a safe alternative feed for cattle producers when fed at recommended levels. Beef producers seeking to lower production costs should consider using cotton byproducts in their feeding programs. If carefully incorporated, cotton byproduct feeds can reduce feed costs while maintaining or increasing the level of cattle performance. Cottonseed meal will remain a standard protein supplement for beef cattle throughout the country. Whole cottonseed has much potential for Southern producers near cotton gins if it is purchased in a timely fashion and fed according to recommendations. Cotton gin trash, cottonseed hulls, and cotton textile mill waste also have potential economic benefits, especially to producers located near cotton and cottonseed processing facilities.  相似文献