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1.
In both humans and mice the number of hair cells in the inner ear sensory epithelia declines with age, indicating cell death
(Park et al. 1987; Rosenhall 1973). However, recent reports demonstrate the ability of the vestibular sensory epithelia to
regenerate after injury (Forge et al. 1993, 1998; Kuntz and Oesterle 1998; Li and Forge 1997; Rubel et al. 1995; Tanyeri et
al. 1995). Still, a continuous hair cell turnover in the vestibular epithelia has not previously been demonstrated in mature
mammals. Bats are the only flying mammals, and they are known to live to a higher age than animals of equal size. The maximum
age of many species is 20 years, with average lifespans of 4–6 years (Schober and Grimmberger 1989). Further, the young are
fully developed and able to fly at the age of 2 months, and thus the vestibular organs are thought to be differentiated at
that age. Consequently, long-lived mammals such as bats might compensate for the loss of hair cells by producing new hair
cells in their postembryonic life. Here we show that the utricular macula of adult Daubenton's bats (more than 6 months old)
contains innervated immature hair cells as well as apoptotic hair cells, which strongly indicates a continuous turnover of
hair cells, as previously demonstrated in birds.
Received: 30 August 1999 / Accepted in revised form: 20 October 1999 相似文献
2.
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
3.
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
4.
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
5.
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
6.
Jia Liu Yunshan Ge Xin Wang Lijun Hao Jianwei Tan Zihang Peng Chuanzhen Zhang Huiming Gong Ying Huang 《环境科学学报(英文版)》2017,29(7):238-248
In this study, the particle size-resolved distribution from a China-3 certificated light-duty diesel vehicle was measured by using a portable emission measurement system (PEMS). In order to examine the influences of vehicle specific power (VSP) and high-altitude operation, measurements were conducted at 8 constant speeds, which ranged from 10 to 80 km/hr at 10 km/hr intervals, and two different high altitudes, namely 2200 and 3200 m. The results demonstrated that the numbers of particles in all size ranges decreased significantly as VSP increased when the test vehicle was running at lower speeds (< 20 km/hr), while at a moderate speed (between 30 and 60 km/hr), the particle number was statistically insensitive to increase VSP. Under high-speed cruising conditions, the numbers of ultrafine particles and PM2.5 were insensitive to changes in VSP, but the numbers of nanoparticles and PM10 surged considerably. An increase in the operational altitude of the test vehicle resulted in increased particle number emissions at low and high driving speeds; however, particle numbers obtained at moderate speeds decreased as altitude rose. When the test vehicle was running at moderate speeds, particle numbers measured at the two altitudes were very close, except for comparatively higher number concentrations of nanoparticles measured at 2200 m. 相似文献
7.
Vincent WF Gibson JA Pienitz R Villeneuve V Broady PA Hamilton PB Howard-Williams C 《Die Naturwissenschaften》2000,87(3):137-141
The Ward Hunt Ice Shelf (83°N, 74°W) is the largest remaining section of thick (>10 m) landfast sea ice along the northern
coastline of Ellesmere Island, Canada. Extensive meltwater lakes and streams occur on the surface of the ice and are colonized
by photosynthetic microbial mat communities. This High Arctic cryo-ecosystem is similar in several of its physical, biological
and geochemical features to the McMurdo Ice Shelf in Antarctica. The ice-mats in both polar regions are dominated by filamentous
cyanobacteria but also contain diatoms, chlorophytes, flagellates, ciliates, nematodes, tardigrades and rotifers. The luxuriant
Ward Hunt consortia also contain high concentrations (107–108 cm–2) of viruses and heterotrophic bacteria. During periods of extensive ice cover, such as glaciations during the Proterozoic,
cryotolerant mats of the type now found in these polar ice shelf ecosystems would have provided refugia for the survival,
growth and evolution of a variety of organisms, including multicellular eukaryotes.
Received: 30 August 1999 / Accepted in revised form: 15 December 1999 相似文献
8.
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
9.
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
10.
Human observers achieve a surprising precision in many visual judgements, such as estimating relative position, colinearity
and the regularity of shape. We measured the sensitivity in detecting shape deformations by presenting a square simultaneously
with a rectangle of variable aspect ratio, or a circle with an ellipsoid. Weber fractions approach 3–5% and improve to approximately
1% when subjects are asked to tell which of the two objects was 'oriented more vertically′, instead of identifying the square
or circle. Contour position can be judged with a precision of 10–20 arc s, clearly in the hyperacuity range and also beyond
the thresholds known for detecting differences in the curvature of comparable line segments. Our results suggest that detecting
deformation in rectangles seems to rely on aspect ratio, whereas performance is improved for ellipsoids by a high sensitivity
for changes in local curvature.
Received: 21 January 1999 / Accepted in revised form: 16 June 1999 相似文献
11.
Rodlet cells have been found in the head and trunk kidneys of the common carp (Cyprinus carpio L.). From an experimental sample of 50 carps of various ages, we detected these cells in only seven fishes, contradicting the
hypothesis that they constitute a normal component of the fish epithelia. The rodlet cells have a typical structure: 12–16 μm
in diameter, with a basal nucleus various in form, and an encasing layer of fibrillar structure. The cells contain rodlets,
composed of elongated, opaque sacs featuring dark rods in the center, which strongly elongate in ripening cells. Remarkable
pseudopodia-like extensions from the apical parts of the rodlet cells penetrate into the delicate blood vessels and sinusoids
of the organs. The encasing layer at the cell apex then opens to release the rodlets into the bloodstream. No junctions were
found between the rodlet cells and neighboring cells. It is suggested that these cells comprise some kind of "symbiosis" between
leukocyte, possible granulocyte cells, and the parasitic rodlets. The cells serve the rodlets as an incubation chamber, as
well as a means of transportation into the bloodstream after ripening.
Received: 29 December 1998 / Accepted in revised form: 3 March 1999 相似文献
12.
Ants have a well developed olfactory sense, which they need both for the perception of environmental chemicals, and for a
highly sophisticated intraspecific communication system based on pheromones. The question arises therefore as to how different
odors are coded in the antennal lobe, the first central neuropil to process olfactory information. We measured odor-evoked
activity patterns using in vivo neuropil calcium recording in the antennal lobe of the ant Camponotus rufipes. We found that (a) odors elicit focal activity spots (diameter ca. 20 μm) which most probably represent the olfactory glomeruli;
(b) different odors are coded in odor specific patterns of such activated spots, and a particular spot can participate in
the pattern for different odors; (c) calcium increased in the activated spots within the 2-s stimulation period and slowly
declined thereafter.
Received: 10 March 1999 / Accepted in revised form: 5 July 1999 相似文献
13.
This paper reports study of day-to-day instability in the locomotor activity rhythm of the nocturnal field mouse Mus booduga. The free-running period (τ) of this rhythm was estimated in constant darkness in n=347 adult male mice. The "onset" and "offset" of locomotor activity rhythm were used as phase markers of the circadian clock.
The precision of the onset of locomotor activity was observed to be a non-linear function of τ, with maximal precision at
τ close to 24 h. The precision of the offset of locomotor activity was found to increase with increasing τ. These results
suggest that the homeostasis of τ is tighter when τ is close to 24 h.
Received: 5 May 1998 / Accepted: 11 February 1999 相似文献
14.
Summer phytoplankton assemblages from surface waters off Kuwait were enriched with levels of eolian dust (105, 106, and 107 mg/m3), similar to seasonal dust fallout for this region. Algal growth was positive and dose dependent. Highest biomass was up
to 527 μg chlorophyll a/l on day 5. The maximum doublings of biomass per day were 0.64, 0.77, and 1.42, corresponding to 105, 106, and 107 mg/m3 enrichment and were significantly higher than the 0.56 for control. Changes in the phytoplankton species composition occurred
with changes in biomass, with small algae dominating peak populations. It is suggested that through enrichment of trace elements
via eolian dust, a high level of phytoplankton biomass and growth can be sustained in this arid environment.
Received: 15 October / Accepted in revised form: 16 June 1999 相似文献
15.
Alexander Lerchl 《Die Naturwissenschaften》1999,86(7):340-342
The relationship between average monthly air temperature and sex ratios at birth (SRB) was analyzed for children born in
Germany during the period 1946–1995. Both the absolute temperature and – more markedly – the monthly temperature deviations
from the overall mean were significantly positively correlated with the SRB (P<0.01) when temperatures were time-lagged against the SRB data by –10 or –11 months. It is concluded that the sex of the offspring
is partially determined by environmental temperatures prior to conception.
Received: 26 August 1998 / Accepted in revised form: 18 February 1999 相似文献
16.
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
17.
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
18.
There have been many reports characterizing DNA from amber, which is a fossil version of plant resin. Here we report an investigation
of the effects of plant resin (from Pseudotsuga menziesii) and drying conditions on the preservation of DNA in biological tissues. We examined the degree of degradation of the DNA
by agarose gel electrophoresis of extracted DNA, by polymerase chain reaction, and by DNA sequencing. The plant resin alone
appeared to cause little or no damage to DNA. Tissue immersed in plant resin that dried rapidly (exposed to sunlight) contained
DNA with little apparent damage. Tissue immersed in the resin that was dried slowly (in shade without sunlight) contained
DNA with some degradation (3.5% nucleotide changes). The tissue that was immersed in the resin that was constantly hydrated
(by immersion in water) yielded DNA that was severely damaged (50–62% nucleotide changes). Transversions outnumbered transitions
in these samples by a ratio of 1.4 : 1. A piece of Baltic amber immersed in water for 5 days appeared to be impervious to
the water. Thus amber inclusions that initially dried rapidly have the potential to yield undamaged DNA. Those that dried
slowly may contain damaged DNA and may be unsuitable for phylogenetic and other studies.
Received: 23 March 1999 / Accepted in revised form: 16 September 1999 相似文献
19.
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
20.
An experimental group of homing pigeons (Columba livia f. domestica) learned to associate food with a magnetic anomaly produced by bar magnets that were fixed to the bowl in which they received
their daily food ration in their home loft; the control group lacked this experience. Both groups were trained to search for
two hidden food depots in a rectangular sand-filled arena without obvious visual cues; for the experimental birds, these depots
were also marked with three 1.15 × 106 μT bar magnets. During the tests, there were two food depots, one marked with the magnets, the other unmarked; their position
within the arena was changed from test to test. The experimental birds searched within 10 cm of the magnetically marked depot
in 49% of the test sessions, whereas the control birds searched there in only 11% of the sessions. Both groups searched near
the control depot in 11 and 13% of the sessions, respectively. The significant preference of the magnetically marked food
depot by the experimental birds shows that homing pigeons cannot only detect a magnetic anomaly but can also use it as a cue
for locating hidden food in an open arena. 相似文献