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971.
Flavonoid wing pigments increase attractiveness of female common blue (Polyommatus icarus) butterflies to mate-searching males 总被引:1,自引:0,他引:1
Common blue butterflies (Polyommatus icarus) sequester flavonoids from their larval host plants and allocate these UV-absorbing pigments to the wings. In field experiments
using dummies constructed from female butterflies, mate-searching males inspected flavonoid-rich dummies more intensively
than those with little or no flavonoids. Flavonoid content as signalled by UV-wing pattern may indicate ontogenetically determined
female quality or enhance detectability to males.
Received: 21 March 2000 / Accepted in revised form: 17 May 2000 相似文献
972.
The GPS recorder consists of a GPS receiver board, a logging facility, an antenna, a power supply, a DC-DC converter and
a casing. Currently, it has a weight of 33 g. The recorder works reliably with a sampling rate of 1/s and with an operation
time of about 3 h, providing time-indexed data on geographic positions and ground speed. The data are downloaded when the
animal is recaptured. Prototypes were tested on homing pigeons. The records of complete flight paths with surprising details
illustrate the potential of this new method that can be used on a variety of medium-sized and large vertebrates.
Received: 2 February 2000 / Accepted in revised form: 17 April 2000 相似文献
973.
The Mormon cricket, Anabrus simplex, is one of just a few species of katydids (or bushcrickets, Orthoptera: Tettigoniidae) that, like migratory locusts, appear
to have solitary and migratory morphs. Using radio telemetry we studied movements of individuals of two morphs of this flightless
species. Individuals within each migratory band had similar rates of movements along similar directional headings whereas
solitary individuals moved little and showed little evidence of directionality in movement. Our results also add to other
recent radio-telemetry studies showing that flightless insects of 1–2 g in mass can be tracked successfully using these methods.
Received: 28 February 2000 / Accepted in revised form: 19 June 2000 相似文献
974.
High-performance permanent magnets 总被引:2,自引:0,他引:2
High-performance permanent magnets (pms) are based on compounds with outstanding intrinsic magnetic properties as well as
on optimized microstructures and alloy compositions. The most powerful pm materials at present are RE–TM intermetallic alloys
which derive their exceptional magnetic properties from the favourable combination of rare earth metals (RE=Nd, Pr, Sm) with
transition metals (TM=Fe, Co), in particular magnets based on (Nd,Pr)2Fe14B and Sm2(Co,Cu,Fe,Zr)17. Their development during the last 20 years has involved a dramatic improvement in their performance by a factor of >15 compared
with conventional ferrite pms therefore contributing positively to the ever-increasing demand for pms in many (including new)
application fields, to the extent that RE–TM pms now account for nearly half of the worldwide market. This review article
first gives a brief introduction to the basics of ferromagnetism to confer an insight into the variety of (permanent) magnets,
their manufacture and application fields. We then examine the rather complex relationship between the microstructure and the
magnetic properties for the two highest-performance and most promising pm materials mentioned. By using numerical micromagnetic
simulations on the basis of the Finite Element technique the correlation can be quantitatively predicted, thus providing a
powerful tool for the further development of optimized high-performance pms. 相似文献
975.
对长江南京段水、悬浮物及沉积物中多氯有毒有机污染物进行了分析测定,由色谱/质谱测得的结果表明,水和沉积物中多氯有机污染物的浓度较低,低于欧洲主要河流中的含量水平.悬浮物中这类污染物总含量较高,为56.45~62.35μg/kg,而水中总含量仅为14.61~15.83ng/L.由于长江中污染物被充分稀释与混匀,各采样点的水和悬浮物中该类污染物的浓度变化不大,两相间具有较好的相关性.但各采样点的沉积物中多氯有机污染物含量差异甚大,表明悬浮物的沉积极不均一.沉积物中主要污染物是六氯苯(HCB)和它的代谢产物五氯苯(PeCB)以及滴滴涕(DDT)的代谢产物,其他多氯有机污染物含量很低. 相似文献
976.
977.
978.
979.
980.
We use hydra as a model system to understand how growth and differentiation and, as a consequence of this, pattern formation are controlled at the molecular level. We have found that four substances control head and foot formation in hydra: an activator and an inhibitor of head formation and an activator and an inhibitor of foot formation. The two activators are peptides with molecular weights around 1000 daltons, the inhibitors are smaller in molecular weight (<500), have an overall positive charge and do not contain peptide bonds. In normal animals all four substances are present and most likely produced by nerve cells. We hope to understand how these substances act and interact to create the spatial and temporal pattern of growth and differentiation typical for hydra. 相似文献