共查询到20条相似文献,搜索用时 46 毫秒
1.
Light-dependent magnetoreception in birds: the effect of intensity of 565-nm green light 总被引:1,自引:0,他引:1
In a previous study, Australian silvereyes tested in autumn under monochromatic 565-nm green light at intensities of 2.1
and 7.5 mW m–2 preferred their normal northerly migratory direction, whereas they showed a significantly different tendency towards northwest
at 15.0 mW m–2. Repeating these experiments in spring with silvereyes migrating southward, we again observed well-oriented tendencies in
the migratory direction at 2.1 and 7.5 mW m–2. At 15.0 mW m–2, however, the birds once more preferred northwesterly directions, i.e. their response under this condition proved to be independent
of the migratory direction. This contradicts the interpretation that monochromatic green light of this high intensity leads
to a rotation of compass information; instead, it appears to produce sensory input that causes birds to give up their migratory
direction in favor of a fixed direction of as yet unknown origin.
Received: 3 April 2000 / Accepted in revised form: 19 June 2000 相似文献
2.
Uda M Sassa S Taniguchi K Nomura S Yoshimura S Kondo J Iskander N Zaghloul B 《Die Naturwissenschaften》2000,87(6):260-263
Some of the pigments painted on the Funerary Stele of Amenemhat (ca. 2000 B.C.) exhibited at the Egyptian Museum, Cairo and
on the walls of the Tomb of Userhat (ca. 1450 B.C.), a rock-cut tomb in Thebes, Egypt, were investigated in situ using both
a convenient home-made hand-held type of X-ray diffractometer and a commercial X-ray fluorescence spectrometer in a complementary
way under touch-free conditions. CaCO3 · 3MgCO3 (huntite) was found in the white-painted parts of these two ancient monuments. An arsenic (As)-bearing phase was detected
in the yellow-painted parts of the latter monument. The occurrence of huntite in Egypt has not been reported previously.
Received: 8 October 1999 / Accepted in revised form: 10 March 2000 相似文献
3.
Numerical dating of the Eckfeld maar fossil site, Eifel, Germany: a calibration mark for the Eocene time scale 总被引:1,自引:0,他引:1
Sediments of the Eckfeld maar (Eifel, Germany) bear a well-preserved Eocene fauna and flora. Biostratigraphically, Eckfeld
corresponds to the Middle Eocene mammal reference level MP (Mammals Paleogene) 13 of the ELMA (European Land Mammal Age) Geiseltalian.
In the maar crater, basalt fragments were drilled, representing explosion crater eruption products. By 40Ar/39Ar dating of the basalt, for the first time a direct numerical calibration mark for an Eocene European mammal locality has
been established. The Eckfeld basalt inverse isochron date of 44.3±0.4 Ma suggests an age for the Geiseltalian/Robiacian boundary
at 44 Ma and, together with the 1995 time scale of Berggren et al., a time span ranging from 49 to 44 Ma for the Geiseltalian
and from 44 to 37 Ma for the Robiacian, respectively. Additional 40Ar/39Ar dating on a genetically related basalt occurrence close to the maar confirms a period of volcanism of ca. 0.6 m.y. in the
Eckfeld area, matching the oldest Eocene volcanic activity of the Hocheifel volcanic field.
Received: 27 December 1999 / Accepted in revised form: 6 April 2000 相似文献
4.
Jie Tang Xiaoming Xu Zhaoyang Li Weizheng Han 《Mitigation and Adaptation Strategies for Global Change》2012,17(1):103-109
The study area of this article, Western Jilin province of China, was a typical area responding to global changing in middle
latitude areas. In this paper, by interpreting the thematic mapper (TM) images of the study area in the years of 1989, 1996,
2000 and 2004, the land use/cover change (LUCC) data were achieved, which included the area of paddy fields and its spatial
distributions. 113 soil samples were collected to obtain soil organic carbon (SOC) data of different land use types. After
that, the organic matter contents of these samples were measured by using the potassium dichromate oxidation-outer heating
method. Based on the data above, the amount of SOC sequestrated by the surface soil (0~30 cm) of paddy fields was calculated.
The result showed that: the area of paddy fields was increasing continuously in western Jilin, from 11.28 × 104 hm2 in 1989 to 22.77 × 104 hm2 in 2004. Paddy fields transferred from wetlands, grasslands and water areas accounted for the main part of the paddy fields
in 2004, the areas were 3.09 × 104 hm2, 2.98 × 104 hm2 and 2.8 × 104 hm2, respectively. And paddy fields with a total area of 0.83 × 104 hm2 degraded into saline-alkali lands. The amount of organic carbon sequestration in the surface layer (0–30 cm) of paddy fields
was 658.86 × 104 t. The primary SOC sinks located around the joint of Baicheng City and Zhenlai County, while the major SOC source located
at Songyuan City and northern Qianguo County. 相似文献
5.
Fisher CR MacDonald IR Sassen R Young CM Macko SA Hourdez S Carney RS Joye S McMullin E 《Die Naturwissenschaften》2000,87(4):184-187
During a research cruise in July 1997 in the Gulf of Mexico we discovered a gas hydrate approximately 1 m thick and over
2 m in diameter which had recently breached the sea floor at a depth of 540 m. The hydrate surface visible from the submarine
was considerably greater than that of any other reported hydrate. Two distinct color bands of hydrate were present in the
same mound, and the entire exposed surface of the hydrate was infested (2500 individuals/m2) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca
methanicola, in the polychaete family Hesionidae (Desbruyères and Toulmond 1998). H.
methanicola tissue stable isotope values are consistent with a chemoautotrophic food source. No evidence of chemoautotrophic symbionts
was detected, but geochemical data support the presence of abundant free living bacteria on the hydrate. The activities of
the polychaetes, grazing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution
of hydrates in surface sediments.
Received: 16 August 1999 / Accepted in revised form: 19 January 2000 相似文献
6.
Yury G. Shckorbatov 《Die Naturwissenschaften》1999,86(9):452-453
Cells of human buccal epithelium were irradiated in vitro by laser light at a wavelength of 632.8 nm and and an intensity
of 1 mW/cm2. The irradiation induced changes in the chromatin condensation state. The effect of irradiation depends on exposure time,
and cells of different donors reveal varying sensitivity to laser light. In some donors 1 s exposure induced decondensation,
but 2.5 min and 5 min condensation of chromatin in all donors.
Received: 10 June 1998 / Accepted in revised form: 7 May 1999 相似文献
7.
The effect of different ambient sulphide concentrations on the internal pH regime of Hediste (Nereis) diversicolor was studied under in vivo conditions using liquid membrane pH microelectrodes, a method which is new to marine sciences.
As a case study, the hypothesis was tested whether organisms exposed to ambient sulphidic conditions are able to lower their
internal pH which, in effect, would reduce sulphide influx into the animals and thus could represent an effective detoxification
mechanism. It was shown that a significant lowering of the internal pH occurred within only 20 min after adding sulphide.
This pH lowering appeared to be dependent on the external sulphide concentration of the ambient medium and showed a saturation
beyond a threshold level of about 130 μM. It is discussed whether this sulphide-induced pH drop is an active regulatory mechanism
and acts as an effective protection mechanism against sulphide during short-term exposures.
Received: 1 June 1999 / Accepted in revised form: 3 May 2000 相似文献
8.
Fruits of Garden Lettuce, imbibed in 0.01 M KNO3, were depleted of maternal active phytochrome B by saturating deep-red exposure and photosensitized by chilling for 1 week
at 4 °C. Twenty saturated fluence-response curves for photoinduced germination were elaborated between 300 and 800 nm, using
exposure periods from 6 to 600 s at 22.5 °C; there is linear and closely parallel regression in the logarithmic probability
net. The reciprocals of the half-response fluences obtained gave the apparent conversion spectrum of the controlling pigments
and this was corrected for the transmittance of the seed-coat. It is a phytochrome spectrum of P
r with photoconversion cross-sections of 1.2·109 and 4.5·103 m2 mol–1 at 666 and 800 nm, respectively. This means that for half-saturated germination of sensitized seed, fewer than 1 out of 200,000
phytochrome A molecules have to be photoconverted to P
fr, and no photo-reversibility by deep-red was found. Therefore, all spectral colours of nightly moon- or skylight should stimulate
the germination of sensitized weed seeds if they are exposed at the soil surface between sequential tillage operations.
Received: 28 April 2000 / Accepted in revised form: 28 July 2000 相似文献
9.
To determine whether the harvester ant Messor barbarus acts as a seed disperser in Mediterranean grasslands, the accuracy level of seed processing was assessed in the field by
quantifying seed drops by loaded foragers. In the vicinity of exploited seed patches 3 times as many diaspores were found
as in controls due to seed losses by foragers. Over trails, up to 30% of harvested seeds were dropped, singly, by workers
but all were recovered by nestmates within 24 h. Seeds were also dropped within temporary caches with very few viable diaspores
being left per cache when ants no longer used the trail. Globally, ant-dispersed diaspores accounted for only 0.1% of seeds
harvested by M. barbarus. We discuss the possible significance for grassland vegetation of harvester-ant-mediated seed dispersal.
Received: 26 January 2000 / Accepted in revised form: 20 June 2000 相似文献
10.
The phonotactic capacity of tachinid flies to acoustically detect and localize a sound source simulating their cricket host
was investigated in a large flight room. Acoustic measurements were performed to estimate the actual stimulus delivered to
the flies, revealing highly heterogeneous sound fields. When presented with a simulated cricket song in red or infrared light
conditions, the flies readily flew to the sound source and landed on it. Behavioural phonotactic thresholds were established
as a function of carrier frequency and were found to coincide well with the frequency of the host's natural song (4.5–5.2 kHz).
Experiments revealed that the same range of frequencies is preferentially attractive to the free-flying flies, and that the
reliability of signal detection in the presence of noise is best at behaviourally relevant frequencies.
Received: 23 February 2000 / Accepted in revised form: 6 June 2000 相似文献
11.
Although turbidite deposits are classically considered to be good reservoir rocks for oil and gas, there are no reports concerning
their source rock potential in the literature. The sediments from the Vallfogona Formation in the South-Eastern Pyrenees present
numerous organic matter-rich levels interbedded in sandstones and coarse turbidite deposits. Two types of organic matter deposits
were differentiated on the basis of organic geochemistry and petrography: type A and type B. Type A was deposited in a carbonate
marine environment under hypersaline conditions as indicated mainly by even/odd n-alkane predominance, pristane and phytane ratio (Pr/Ph) < 1, presence of gammacerane, and trisnorneohopane over trisnorhopane
ratio (Ts/Tm) > 1. Type B was deposited in a more mud-rich marine environment evidenced by the predominance of odd n-alkane, Pr/Ph ≥ 1, Ts/Tm < 1, the absence of gammacerane, similar concentrations of the C27 and C29 regular steranes, and the greater abundance of C27 diasteranes. Turbidite facies can be regarded as an environment where organic matter sedimentation is heterogeneous in type
and amount. This study suggests that turbidite deposits with interbedded organic matter-rich levels may act as a combined
source–reservoir system. 相似文献
12.
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
13.
Cerumen, or propolis, is a mixture of plant resins enriched with bee secretions. In Australia, stingless bees are important
pollinators that use cerumen for nest construction and possibly for colony’s health. While extensive research attests to the
therapeutic properties of honeybee (Apis mellifera) propolis, the biological and medicinal properties of Australian stingless bee cerumen are largely unknown. In this study,
the chemical and biological properties of polar extracts of cerumen from Tetragonula carbonaria in South East Queensland, Australia were investigated using gas chromatography-mass spectrometry (GC-MS) analyses and in
vitro 5-lipoxygenase (5-LOX) cell-free assays. Extracts were tested against comparative (commercial tincture of A. mellifera propolis) and positive controls (Trolox and gallic acid). Distinct GC-MS fingerprints of a mixed diterpenic profile typical
of native bee cerumen were obtained with pimaric acid (6.31 ± 0.97%, w/w), isopimaric acid (12.23 ± 3.03%, w/w), and gallic
acid (5.79 ± 0.81%, w/w) tentatively identified as useful chemical markers. Characteristic flavonoids and prenylated phenolics
found in honeybee propolis were absent. Cerumen extracts from T. carbonaria inhibited activity of 5-LOX, an enzyme known to catalyse production of proinflammatory mediators (IC50 19.97 ± 2.67 μg/ml, mean ± SEM, n = 4). Extracts had similar potency to Trolox (IC50 12.78 ± 1.82 μg/ml), but were less potent than honeybee propolis (IC50 5.90 ± 0.62 μg/ml) or gallic acid (IC50 5.62 ± 0.35 μg/ml, P < 0.001). These findings warrant further investigation of the ecological and medicinal properties of this stingless bee cerumen,
which may herald a commercial potential for the Australian beekeeping industry. 相似文献
14.
Marcelo Perantoni Darci M. S. Esquivel Eliane Wajnberg Daniel Acosta-Avalos Geraldo Cernicchiaro Henrique Lins de Barros 《Die Naturwissenschaften》2009,96(6):685-690
Magnetotactic microorganisms use the interaction of internal biomineralized nanoparticles with the geomagnetic field to orientate.
The movement of the magnetotactic multicellular prokaryote Candidatus Magnetoglobus multicellularis under an applied magnetic field was observed. A method using digital image processing techniques
was used to track the organism trajectory to simultaneously obtain its body radius, velocity, U-turn diameter, and the reorientation
time. The magnetic moment was calculated using a self-consistent method. The distribution of magnetic moments and radii present
two well-characterized peaks at (9 ± 2) × 10−15 and (20 ± 3) × 10−15 A m2 and (3.6 ± 0.1) and (4.3 ± 0.1) μm, respectively. For the first time, simultaneous determination of the distribution of the
organism radii and magnetic moment was obtained from the U-turn method by a new digital imaging processing. The bimodal distributions
support an organism reproduction process model based on electron microscopy observations. These results corroborate the prokaryote
multicellular hypothesis for Candidatus M. multicellularis. 相似文献
15.
Light-Dependent Magnetoreception in Birds: Does Directional Information Change with Light Intensity?
Magnetic compass orientation in birds is based on light-dependent processes, with magnetoreception being possible only under
light containing blue and green wavelengths. To look for possible intensity-dependent effects we tested Australian silvereyes
during autumn migration under monochromatic green light (565 nm) produced by light-emitting diodes at various light levels.
At intensities of 0.0021 and 0.0075 W/m2, the birds showed normal activity and were oriented in their seasonally appropriate migratory direction. Under low light
of 0.0002 W/m2 the birds were less active; scatter increased, but they still oriented in their migratory direction. Under a high light level
of 0.0150 W/m2, however, the test birds showed a counterclockwise shift in direction, preferring west-northwest instead of north. This change
in behavior may reflect a change in the output of the magnetoreception system, resulting from a disruption of the natural
balance between the wavelengths of light.
Received: 18 June 1999 / Accepted in revised form: 20 September 1999 相似文献
16.
How water saving irrigation contributes to climate change resilience—a case study of practices in China 总被引:3,自引:2,他引:1
Xiaoxia Zou Yu-e Li Qingzhu Gao Yunfan Wan 《Mitigation and Adaptation Strategies for Global Change》2012,17(2):111-132
A warming climate system is now an indisputable fact. An effective response to climate change should include both mitigation
and adaptation. Water is essential to human survival and social development. But the shortage of water resources is a worldwide
problem, which in China has been exacerbated by climate change. In order to find out how to cope with climate change successfully,
this study, on the basis of China statistical data 2007–2009, quantitatively analyzes the role of water saving irrigation
(WSI) in addressing climate change. The study shows that water saving irrigation (WSI) can serve as a useful enabler in dealing
with climate change. From the perspective of mitigation, the 3-year total CO2 emission reduction stands at 34.67 (21.83 ~ 47.48) Mt, about per year 11.56(7.28 ~ 15.83)Mt. From the perspective of adaptation,
the total water saved from 2007 to 2009 stands at 96.85 (61.81 ~ 129.66) Gm3. If per unit farmland irrigation takes a 3-year average of agricultural water consumption, the water saved in 2009 is enough
to irrigate additional 5.70 (3.80 ~ 7.80) Mhm2, or to increase the grain yield by 22.04 (14.68 ~ 30.15) Gt. In addition, WSI can reduce soil salinization and conserve soil
to sustain land productivity and environmental benefits. So WSI can be a positive measure in coping with climate change when
it is rightly deployed. However, the costs and local context of such practices call for further studies. 相似文献
17.
There is great potential for conflict within social insect colonies especially when there are multiple inseminated females
laying eggs. One reason that conflict is not always realized may be that these females do not identify their own progeny and
direct their attentions preferentially towards them. Using DNA microsatellite loci we were able to determine exactly which
female was the mother of each larva in eight nests of the social wasp, Polistes carolina. Using 26 h of videotapes of natural nests we observed 2,093 feedings of specific larvae by these adults and found that they
did not preferentially feed their own progeny. Instead feedings were distributed to progeny as predicted based on their frequency
in the nest. The absence of nepotism towards closest kin within colonies in this system is likely to promote colony harmony.
Received: 24 January 2000 / Accepted in revised form: 30 March 2000 相似文献
18.
Honeybees ingested 50% w/w (1.8 M) sucrose solution at a rate feeder offering either 16.5, 32.5 or 65 μl/min. While the time
spent ingesting solution at the feeder decreased significantly with increasing flow of solution, bees attained maximum crop
loads with this range of flows. Different parameters related to mouth-to-mouth food exchange (trophallaxis) showed important
modulations as the offered flow of solution was incremented. Trophallactic transfer rate, i.e. the speed at which liquid food
is transferred from donor to recipient bee, was found to increase along with increasing profitability at the rate feeder.
In the present case, food source profitability could have been evaluated by foragers either by measuring the time invested
in ingesting the solution, or by direct assessment of the flow rate of the feeder. Thus it seems that perception of profitability
conditions at the food sourcesuffices for later representation in the hive through trophallactic contacts, independently of
crop-filling state.
Received: 10 March 2000 / Accepted in revised form: 19 April 2000 相似文献
19.
Self-diffusion coefficients were studied for the highly polar liquid N-methylformamide at pressures up to 200 MPa between the melting pressure curves and 420 K by the spin-echo method. N-Methylformamide exists as a mixture of two conformers in the neat liquid. These conformers have large differences at lower
temperatures in their dynamic and structural properties. The self-diffusion coefficient of the cis-conformer being 17% lower than that of the trans-conformer at the same T and p. This is the first observation of such an effect. The experimental study is supported by Monte Carlo (MC) calculations which
show that the first neighbors around a cis conformer are arranged differently than in an all trans liquid. The difference leads in the simulations to a much lower dielectric constant for the trans-cis mixture and might also explain the retardation of diffusion for the cis conformer.
Received: 15 November 1999 / Accepted in revised form: 28 February 2000 相似文献
20.
Photoperiod and dietary lipids both influence thermal physiology and the pattern of torpor of heterothermic mammals. The aim
of the present study was to test the hypothesis that photoperiod-induced physiological changes are linked to differences in
tissue fatty acid composition of deer mice, Peromyscus maniculatus (∼18-g body mass). Deer mice were acclimated for >8 weeks to one of three photoperiods (LD, light/dark): LD 8:16 (short photoperiod),
LD 12:12 (equinox photoperiod), and LD 16:8 (long photoperiod). Deer mice under short and equinox photoperiods showed a greater
occurrence of torpor than those under long photoperiods (71, 70, and 14%, respectively). The duration of torpor bouts was
longest in deer mice under short photoperiod (9.3 ± 2.6 h), intermediate under equinox photoperiod (5.1 ± 0.3 h), and shortest
under long photoperiod (3.7 ± 0.6 h). Physiological differences in torpor use were associated with significant alterations
of fatty acid composition in ∼50% of the major fatty acids from leg muscle total lipids, whereas white adipose tissue fatty
acid composition showed fewer changes. Our results provide the first evidence that physiological changes due to photoperiod
exposure do result in changes in lipid composition in the muscle tissue of deer mice and suggest that these may play a role
in survival of low body temperature and metabolic rate during torpor, thus, enhancing favourable energy balance over the course
of the winter. 相似文献