ABSTRACT Exact locations of spawning areas used by marine fishes are needed to design marine reserves and estimate spawning stocks. The location of spawning areas of soniferous fishes such as weakfish Cynoscion regalis can be determined by means of passive hydroacoustic surveys. We conducted nocturnal hydrophone surveys at 12 locations in Pamlico Sound in May of 1996 and 1997. Digital audio tapes were made of weakfish “purring” sounds, the tapes were analyzed spectrographically and compared with ichthyoplankton surveys taken at the same stations and times. All weakfish “purring” sounds were recorded at stations near inlets. Maximum sound pressure levels recorded after sunset were 127 dB (re 1 (μPa) for individual weakfish, but reached a maximum of 147 dB when weakfish and other fish were producing sounds simultaneously. The maximum distance that an individual weakfish “purr” can be detected above the background sound, assuming a cylindrical spreading model, is approximately 50 m. There was a strong association (r = 0.78) between the log10— transformed abundance of early-stage sciaenid-type eggs and maximum sound pressure levels, with the greatest numbers occurring at the inlet stations. These results suggest that passive hydroacoustic surveys can be used to delimit spawning areas for conservation and management purposes. 相似文献
Near‐infrared (NIR) radiation has been employed using one‐ and two‐photon excitation of fluorescence imaging at wavelengths 650–950 nm (optical window I) for deep brain imaging; however, longer wavelengths in NIR have been overlooked due to a lack of suitable NIR‐low band gap semiconductor imaging detectors and/or femtosecond laser sources. This research introduces three new optical windows in NIR and demonstrates their potential for deep brain tissue imaging. The transmittances are measured in rat brain tissue in the second (II, 1,100–1,350 nm), third (III, 1,600–1,870 nm), and fourth (IV, centered at 2,200 nm) NIR optical tissue windows. The relationship between transmission and tissue thickness is measured and compared with the theory. Due to a reduction in scattering and minimal absorption, window III is shown to be the best for deep brain imaging, and windows II and IV show similar but better potential for deep imaging than window I.
The formation of biofilms in the endotracheal tubes (ETTs) of intubated patients on mechanical ventilation is associated with a greater risk of ventilator‐associated pneumonia and death. New technologies are needed to detect and monitor ETTs in vivo for the presence of these biofilms. Longitudinal OCT imaging was performed in mechanically ventilated subjects at 24‐hour intervals until extubation to detect the formation and temporal changes of in vivo ETT biofilms. OCT‐derived attenuation coefficient images were used to differentiate between mucus and biofilm. Extubated ETTs were examined with optical and electron microscopy, and all imaging results were correlated with standard‐of‐care clinical test reports. OCT and attenuation coefficient images from four subjects were positive for ETT biofilms and were negative for two subjects. The processed and stained extubated ETTs and clinical reports confirmed the presence/absence of biofilms in all subjects. Our findings confirm that OCT can detect and differentiate between biofilm‐positive and biofilm‐negative groups (P < 10?5). OCT image‐based features may serve as biomarkers for direct in vivo detection of ETT biofilms and help drive investigation of new management strategies to reduce the incidence of VAP. 相似文献
The underwater light field has been studied in a hypertrophic, gravel-pit lake close to Madrid (Spain) during a one year cycle. Both the inherent and the apparent properties of the underwater light field have been weekly surveyed. As theoretically expected, there is a link between inherent and apparent properties in this lake. Evidence is given suggesting that a seasonal trend in the underwater light field seems to occur. The main factor attenuating light in the vertical column is phytoplankton chlorophyll “a” but humic substances also appear to play an importtant role in light attenuation. 相似文献
The underwater light field is described as a stochastic process, with the vertical attenuation as a random variable. It is shown that the vertical attenuation integral is well described as a Normal process with uncorrelated increments. The attenuation processes within a water body are found to be quite independent of the incoming irradiance. Thus, the relative light intensity at any depth can be approximated by a Lognormal random variable. Based upon the expectation of this Lognormal variable, and the mean value of the incident irradiance, the irradiance delivered at any depth can be estimated, as well as the statistical distribution of the irradiance. Light data from a number of Norwegian soft-water lakes showed good fit to the model. Two productive lakes included in this study also had a light regime well described by the statistical model. However, the model should be extended to cater for seasonal variations in these applications. 相似文献
Bilayer liposomes from a mixture of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPC:DPPE=8:2, molar ratio) or DPPC labeled with 14C-DPPC (DPPC:14C-DPPC) were bombarded with thermally activated tritium atoms. The tritiated liposomes were hydrolyzed by phospholipase C, and the tritium incorporation into different parts of the bilayer along its thickness was determined. The tritium flux attenuation coefficients were calculated for the headgroup (k1=0.176±0.032 Å–1) and acylglycerol residue (k2=0.046±0.004 Å–1) layers indicating a preferential attenuation of the tritium flux in the headgroup region and relative transparence of the membrane hydrophobic part. The finding is potentially important to apply tritium bombardment for investigation of spatial organization of transmembrane proteins in their native lipid environment. 相似文献
A Periconia sp was isolated from Torreya grandifolia (a relative of yew that does not synthesize taxol) near Huangshan National Park in the People’s Republic of China. This fungus,
not previously known as a tree endophyte, was isolated from the inner bark of a small lower limb. When freshly isolated from
the tree and placed in a semi-synthetic medium, the fungus produced readily detectable quantities of the anticancer drug taxol.
Other taxol-producing endophytes were also isolated from this source. The production of taxol by Periconiasp was demonstrated unequivocally via spectroscopic and immunological methods. However, successive transfers of the fungus in
semi-synthetic medium resulted in gradual attenuation until low production occurred even though fungal growth was relatively
unaffected. Several compounds, known previously as activators of microbial metabolism, including serinol, p-hydroxybenzoic acid, and a mixture of phenolic acids, were capable of fully or partially restoring taxol production to otherwise
taxol-attenuated cultures. The compound with the most impressive ability to activate taxol production was benzoic acid at
0.01 mM. Benzoic acid was not a taxol precursor.
Received 19 December 1997/ Accepted in revised form 19 February 1998 相似文献
We addressed potential sources of error in estimating the water clarity of mountain lakes by investigating the use of beam
transmissometer measurements to estimate Secchi disk depth. The optical properties Secchi disk depth (SD) and beam transmissometer
attenuation (BA) were measured in Crater Lake (Crater Lake National Park, Oregon, USA) at a designated sampling station near
the maximum depth of the lake. A standard 20 cm black and white disk was used to measure SD. The transmissometer light source
had a nearly monochromatic wavelength of 660 nm and a path length of 25 cm. We created a SD prediction model by regression
of the inverse SD of 13 measurements recorded on days when environmental conditions were acceptable for disk deployment with
BA averaged over the same depth range as the measured SD. The relationship between inverse SD and averaged BA was significant
and the average 95% confidence interval for predicted SD relative to the measured SD was ±1.6 m (range = −4.6 to 5.5 m) or ±5.0%.
Eleven additional sample dates tested the accuracy of the predictive model. The average 95% confidence interval for these
sample dates was ±0.7 m (range = −3.5 to 3.8 m) or ±2.2%. The 1996–2000 time-series means for measured and predicted SD varied
by 0.1 m, and the medians varied by 0.5 m. The time-series mean annual measured and predicted SD’s also varied little, with
intra-annual differences between measured and predicted mean annual SD ranging from −2.1 to 0.1 m. The results demonstrated
that this prediction model reliably estimated Secchi disk depths and can be used to significantly expand optical observations
in an environment where the conditions for standardized SD deployments are limited. 相似文献
External phosphorus load to a wetland with two shallow lakes in the Botshol Nature Reserve, The Netherlands, was reduced,
resulting in a rapid reduction of phytoplankton biomass and turbidity, and after 4 years, explosive growth of Characeae. The
clear water state was unstable, however, and the ecosystem then alternated between clear, high-vegetation and turbid, low-vegetation
states. A model of water quality processes was used in conjunction with a 14-year nutrient budget for Botshol to determine
if fluctuations in precipitation and nutrient load caused the ecosystem instability. The results indicate that, during wet
winters when groundwater level rose above surface water level, phosphorus from runoff was stored in the lake bottom and banks.
Stored phosphorus was released the following spring and summer under anaerobic sediment conditions, resulting in increased
phytoplankton density and light attenuation in the water column. During years with high net precipitation, flow from land
to surface water also transported humic acids, further increasing light attenuation. In years with dry winters, the phosphorus
and humic acid loads to surface water were reduced, and growth of submerged macrophytes was enhanced by clear water. Thus,
the temporal pattern of precipitation and flow from land to water gave a coherent, quantitative explanation of the observed
dynamics in phosphorus, phytoplankton, turbidity, and Characeae. Global warming has caused winters in The Netherlands to become
warmer and wetter during the last 50 years, increasing flow from land to water of humic acids and phosphorus and, ultimately,
enhancing instability of Characeae populations. In the first half of the 20th century interannual variation in precipitation
was not sufficient to cause large changes in internal P flux in Botshol, and submerged macrophyte populations were stable. 相似文献