We report on very small fossil eggs from the Lower Cretaceous of Thailand, one of them containing a theropod embryo, which display a remarkable mosaic of characters. While the surficial ornamentation is typical of non-avian saurischian dinosaurs, the three-layered prismatic structure of the eggshell is currently known only in extant and fossil eggs associated with birds. These eggs, about the size of a goldfinch's, mirror at the reproductive level the retention of small body size that was paramount in the transition from non-avian theropods to birds. The egg-layer may have been a small feathered theropod similar to those recently found in China. 相似文献
The possible effect of Alexandrium spp. containing paralytic shellfish poisoning (PSP) toxins on the hemocytes of oysters was tested experimentally. In one
trial, eastern oysters, Crassostrea virginica Gmelin, were exposed to bloom concentrations of the sympatric dinoflagellate, Alexandrium fundyense Balech, alone and in a mixture with a non-toxic diatom, Thalassiosira weissflogii (Grun) Fryxell et Hasle. Subsequently, another experiment exposed Pacific oysters, Crassostrea gigas Thunberg, to a mixed suspension of the sympatric, toxic species Alexandrium catenella (Whedon et Kofoid) Balech, with T. weissflogii. Measurements of numbers of oyster hemocytes, percentages of different cell types, and functions (phagocytosis, reactive
oxygen species (ROS) production, and mortality) were made using flow-cytometry. During and after exposure, almost no significant
effects of Alexandrium spp. upon hemocyte numbers, morphology, or functions were detected, despite observations of adductor-muscle paralysis in
C. virginica and measured toxin accumulation in C. gigas. The only significant correlation found was between toxin accumulation at one temperature and higher numbers of circulating
live and dead hemocytes in C. gigas. The PSP toxins are known to interfere specifically with sodium-channel function; therefore, the finding that the toxins
had no effect on measured hemocyte functions suggests that sodium-channel physiology is not important in these hemocyte functions.
Finally, because oysters were exposed to the living algae, not purified toxins, there was no evidence of bioactive compounds
other than PSP toxins affecting hemocytes in the two species of Alexandrium studied. 相似文献
Hepatocytes cultures prepared from castrated pig hepatocytes (Great Yorkshire x Dutch Landrace), as a model for human liver, were used to study the effect of twenty polychlorinated biphenyls (PCBs) on CYP1A activity, measured as the dealkylation of either ethoxyresorufin or methoxyresorufin. The selection of the PCBs was based on their differences in physico-chemical properties. The non-ortho and mono-ortho substituted PCBs were the most potent CYP1A inducers in pig hepatocytes. In addition, several multiple-ortho substituted congeners, with five or more chlorine atoms, were inducers of CYP1A activity as well. Their relative effect potencies (REP) were proximately 10,000 times lower than the most potent congener, 3,3',4,4',5 PeCB (PCB#126). Using partial least-squares (PLS) modeling, predictions of CYP1A activity could be made for all tetra to hepta substituted congeners. Several multiple-ortho substituted PCBs, which are highly abundant in the biotic and abiotic environment, have been found to induce CYP1A activity in pig hepatocytes. Because induction of CYP1A activity is used as biomarker for Ah-receptor mediated responses, it is suggested to include these congeners in future risk assessment. 相似文献
Laboratory tests of photocatalytic air purifiers are usually performed with a single pollutant, in the parts per million by volume domain and at airflow rates < or =0.1 m3/hr. Clearly, it is necessary to probe photocatalytic materials and apparatuses under real conditions or conditions closely mimicking reality. Photocatalytic prototypes were placed in an ordinary room. To collect hydrocarbons over a shorter period (15 min) than with adsorbent-containing cartridges, solid-phase microextraction (SPME) was used. Typically, concentrations in substituted benzene hydrocarbons and tetrachloroethene were decreased to 20-35% of initial values; toluene and m- + p-xylene concentrations dropped to 2-6 parts per billion by volume, and o-xylene and benzene concentrations were still lower. In the absence of appropriate, commercialized SPME fibers, carbonyl compounds (both formed and destroyed by photocatalysis) were extracted using cartridges containing 2,4- dinitrophenylhydrazine-coated silica. The concentration ranges (in parts per billion by volume) were shifted to higher values in treated air: from 9-15.5 to 12.5-18 for methanal, from 1.5-3 to 8-11.5 for ethanal, and from 4.5-19 to 8-26.5 for propanone with the prototype used; these unprecedented results do not exclude using photocatalysis to treat air, but they illustrate that improvement is needed. Because these tests are time-consuming, preliminary tests are useful; results obtained with a 225-L closed-loop, airtight, photocatalytic reactor with an external turbine enabling the ambient air inside the reactor to be circulated through the purifier device at 15-450 m3/hr flow rates are reported. 相似文献
Emission factors for selected volatile organic compounds (VOCs) and particulate emissions were developed while processing eight commercial grades of polycarbonate (PC) and one grade of a PC/acrylonitrile-butadiene-styrene (ABS) blend. A small commercial-type extruder was used, and the extrusion temperature was held constant at 304 degrees C. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere/million pounds of polymer resin processed [ppm (wt/wt)]. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar PC processing operations. 相似文献
The activity and surface sediment displacement by the terebellid polychaete Eupolymnia nebulosa were monitored, using new image acquisition and image analysis procedures. We used a video sensor mounted on a motorized
table, to acquire adjacent images of the whole studied aquarium within about 2 s. These images were then grouped within a
composite image acquired every 15 s. Consecutive composite images were compared to infer activity and surface sediment displacement.
This procedure proved efficient for E. nebulosa as indicated by (1) the continuity of the tentacles within composite images, and (2) the direct comparison of images and
detected activities. There were important temporal changes in the relative importance of the three main types of activity:
feeding, tube-building and (both partial and total) emergence from the tube, accounting, respectively, for 75, 15 and 10%
of the entire experiment duration. Activity intensity (cm2 min-1) was assessed through the surface of pixels with grey levels differing by more than 20 (on a 0–255 scale) between two consecutive
images. Feeding was associated with low activity intensity, whereas tube-building and emergence from the tubes were associated
with high activity intensities. Surface sediment displacement mostly resulted from tentacle activity both during feeding and
tube-building and was almost zero when worms emerged from their tube. We used our experimental set up to assess spatial changes
in activity intensity and particle displacements along the tentacles. Most of the activity occurred within the first 4–6 cm
from the tube aperture. Particle loss during their transfer along the tentacles preferentially affected larger particles as
postulated by the model of particle selection and transport in tentaculate deposit-feeders. Moreover, the speed of the particles
along the tentacles correlated negatively with their size. This contributed to increase in the residence time of larger particles
on the tentacles and thus, to further enhance their probability of being lost. The size distributions of particles during
feeding and tube-building did not differ significantly although visual observations confirmed the preferential use of larger
particles for tube-building. This suggests the existence of a sorting step occurring elsewhere than on the tentacles as already
demonstrated for spionid polychaetes. 相似文献
Objective: We compared the differences in the braking response to vehicle collision between an active human emergency braking (control condition) and cruise control (CC) or adaptive cruise control (ACC).
Methods: In 11 male subjects, age 22 to 67 years, we measured the active emergency braking response during manual driving using the accelerator pedal (control condition) or in condition mimicking CC or ACC. In both conditions, we measured the brake reaction time (BRT), delay to produce the peak braking force (PBD), total emergency braking response (BRT + PBD), and peak braking force (PBF). Electromyograms of leg and thigh muscles were recorded during braking. The tonic vibratory response (TVR), Hoffman reflex (HR), and M-waves were recorded in leg muscles to explore the change in sensorimotor control.
Results: No difference in PBF, TVR amplitude, HR latency, and Hmax/Mmax ratio were found between the control and CC/ACC conditions. On the other hand, BRT and PBD were significantly lengthened in the CC/ACC condition (240 ± 13 ms and 704 ± 70 ms, respectively) compared to control (183 ± 7 ms and 568 ± 36 ms, respectively). BRT increased with the age of participants and the driving experience shortened PBD and increased PBF.
Conclusions: In male subjects, driving in a CC/ACC condition significantly delays the active emergency braking response to vehicle collision. This could result from higher amplitude of leg motion in the CC/ACC condition and/or by the age-related changes in motor control. Car and truck drivers must take account of the significant increase in the braking distance in a CC/ACC condition. 相似文献
The Eulerian Chemistry-Transport Model BelEUROS was used to calculate the concentrations of airborne PM10 and PM2.5 over Europe. Both primary as well as secondary particulate matter in the respirable size-range was taken into account. Especially PM2.5 aerosols are often formed in the atmosphere from gaseous precursor compounds. Comprehensive computer codes for the calculation of gas phase chemical reactions and thermodynamic equilibria between compounds in the gas-phase and the particulate phase had been implemented into the BelEUROS-model. Calculated concentrations of PM10 and PM2.5 are compared to observations, including both the spatial and daily, temporal distribution of particulate matter in Belgium for certain monitoring locations and periods. The concentrations of the secondary compounds ammonium, nitrate and sulfate have also been compared to observed values. BelEUROS was found to reproduce the observed concentrations rather well. The model was applied to assess the contribution of emissions derived from the sector agriculture in Flanders, the northern part of Belgium, to PM10- and PM2.5-concentrations. The results demonstrate the importance of ammonia emissions in the formation of secondary particulate matter. Hence, future European emission abatement policy should consider more the role of ammonia in the formation of secondary particles. 相似文献