共查询到20条相似文献,搜索用时 10 毫秒
1.
Gary L. Larson Robert L. Hoffman Bruce R. Hargreaves Robert W. Collier 《Hydrobiologia》2007,574(1):141-148
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
2.
Anna von Bonsdorff-Nikander Jukka Rantanen Leena Christiansen Jouko Yliruusi 《AAPS PharmSciTech》2003,4(3):116-123
The aim of this work was to survey how processing parameters affect the crystal growth of β-sitosterol in suspension. The
process variables studied were the cooling temperature, stirring time and stirring rate during recrystallization. In addition,
we investigated the effect a commonly used surfactant, polysorbate 80, has on crystal size distribution and the polymorphic
form. This study describes the optimization of the crystallization process, with the object of preparing crystals as small
as possible. Particle size distribution and habit were analyzed using optical microscopy, and the crystal structure was analyzed
using X-ray diffractometry. The cooling temperature had a remarkable influence on the crystal size. Crystals with a median
crystal length of ≈23 μm were achieved with a low cooling temperature (<10°C); however, a fairly large number of crystals
over 50 μm appeared. Higher cooling temperatures (>30°C) caused notable crystal growth both in length and width. Rapid (250
rpm), continuous stirring until the suspensions had cooled to room temperature created small, less than 50 μm long (median
<20 μm), needle-shaped crystals. The addition of surfactant slightly reduced the size of the initially large crystals. Both
hemihydrate and monohydrate crystal forms occurred throughout, regardless of the processing parameters. By using an optimized
process, it was possible to obtain a microcrystalline suspension, with a smooth texture. 相似文献
3.
Ute Mühlenhardt-Siegel 《Helgoland Marine Research》1988,42(1):37-65
Macrobenthic fauna and sediment structure were studied at 6 stations from June 1979 to April 1981. The investigations were
carried out in the outer estuary of the River Elbe at depths of 15–38 m near a sewage sludge dumping site. The sediment near
this area consisted of a high portion of silt. Usually, very few species and small numbers of individuals were found near
that dumping ground. During summer 1980, a mass development ofAbra alba and several polychaete species caused an increase in species number which broke down during the following winter. The mass
development observed in the study area was apparently not directly caused by the sludge dumping itself, but reflects the natural
variability of the community structure. The number of species recorded was significantly correlated with a grain size fraction>31
μm, especially in summer. The seasonal and spatial fluctuation of the benthic community could be well documented by the abundance
per species (N/S index). The Shannon-Wiener-Index (H′) and eveness (J) were also useful indicators of community variability.
The log-normal distribution did not show the seasonal and the spatial differences of the stations. Possible reasons are discussed.
The biomass at the stations near the dumping area was less except during the mass development ofA. alba. The average individual weight (B/N) was shown to be a good indicator of population fluctuations; polychaete biomass was
positively correlated to a grain size fraction≦6 μm, that of molluscs to a grain size fraction>31 μm.
相似文献
4.
Embryogenic cell suspension cultures of Santalum album were transformed with Agrobacterium tumefaciens harboring pD35SHER plant expression vector having hepatitis B small surface antigen (HBsAg) with a C-terminal ER retention
signal. The transformed colonies were selected on culture medium supplemented with kanamycin and subsequently the transgenic
nature of these colonies was confirmed by PCR analysis. The expression of HBsAg was confirmed by RT-PCR analysis and Western
blot analysis and the expression was quantified using monoclonal antibody-based ELISA. Cell suspension cultures were initiated
from the colony with expression of 11.09 μg(HBsAg) g−1(f.m.). To further increase the expression of HBsAg, transgenic S. album suspensions were cultured on media with various medium additives and cells growing in medium with 30 mM trehalose showed
the expression of 19.95 μg(HBsAg) g−1(f.m.). 相似文献
5.
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7.
Preparation of gelatin microbeads with a narrow size distribution using microchannel emulsification 总被引:1,自引:0,他引:1
The purpose of this study was to prepare monodisperse gelatin microcapsules containing an active agent using microchannel (MC) emulsification, a novel technique for preparing water-in-oil (W/O) and oil-in-water (O/W) emulsions. As the first step in applying MC emulsification to the preparation of monodisperse gelatin microcapsules, simple gelatin microbeads were prepared using this technique. A W/O emulsion with a narrow size distribution containing gelatin in the aqueous phase was created as follows. First, the aqueous disperse phase was fed into the continuous phase through the MCs at 40°C (operating pressure: 3.9 kPa). The emulsion droplets had an average particle diameter of 40.7 μm and a relative standard deviation of 5.1%. The temperature of the collected emulsion was reduced and maintained at 25°C overnight. The gelatin microbeads had a smooth surface after overnight gelation; the average particle diameter was calculated to be 31.6 μm, and the relative standard deviation, 7.3%. The temperature was then lowered to 5°C by rapid air cooling and finally dried. The gelatin beads were dried and could be resuspended well in iso-octane. The had an average particle diameter of 15.6 μm, and a relative standard deviation of 5.9%. Using MC emulsification, we were able to prepare gelatin microbeads with a narrow size distribution. Since this emulsification technique requires only a low-energy input, it may create desirable experimental conditions for microencapsulation of unstable substances such as peptides and proteins. This method is promising for making monodisperse microbeads. 相似文献
8.
High resolution measurements of sediment resuspension above an accumulation bottom in a stratified lake 总被引:6,自引:3,他引:3
A detailed record of suspended particulate matter (SPM) concentrations in the benthic boundary layer (BBL) 1.5 m above an accumulation bottom and 13.5 m below the surface was obtained from frequent (30 min interval) beam attenuation measurements made with a Sea Tech transmissometer in the main basin of Lake Erken, a moderately deep (mean depth 9 m, maximum depth 21 m) dimictic lake in central Sweden. Concentrations of SPM (g m–3) were not as strongly correlated to the beam attenuation coefficient (c, [m–1]), as were concentrations of the inorganic SPM fraction. Apparently, this was caused by large optically inactive organic particles which significantly affected the measurements of SPM, but had little effect on the attenuation of light.When the water column was thermally stratified, SPM concentrations in the BBL showed a seasonal increase which was related to an increase in the thermocline depth. As the epilimnion deepened, there was also a marked increase in the occurrence of rapid and large changes in SPM concentration. After the loss of stratification, the amount of SPM and the temporal variability in its concentration was reduced. Since surface waves could not influence sediment resuspension at the depth of measurement, these data show the importance of internal waves in promoting sediment resuspension in areas of sediment accumulation. The relatively short period in each summer, when the thermocline reaches a sufficient depth to allow for resuspension over accumulation bottoms, can have important consequences for both the redistribution of lake sediments and the internal loading of phosphorus. 相似文献
9.
Wenbing Li Longjiang Yu Pengpeng Zhou Min Zhu 《World journal of microbiology & biotechnology》2007,23(10):1489-1492
Summary A helical shaped bacterium capable of producing magnetosomes, designated WM-1, was isolated from freshwater sediment through
an improved isolated method that combined magnetic separation and the “race track” method. The strain WM-1 was Gram-negative,
0.2–0.4 μm in diameter and 3–4 μm in length. The strain WM-1 was identified as genus Magnetospirillum in the α-Proteobacteria according to the sequence analysis of the 16S rDNA, the morphology and physiological characteristics.
The shape of the magnetosomes in WM-1was cuboidal by electron microscopy. Statistical analysis of WM-1 magnetosome crystals
showed that the average number of magnetosomes in a WM-1 bacterium was 8 ± 3.4, and the average length was 54 ± 12.3 nm, and
the average width was 43 ± 10.9 nm. 相似文献
10.
The purpose of this research was to compare three different methods for the aerodynamic assessment of (1) chloroflurocarbon
(CFC)-fluticasone propionate (Flovent), (2) CFC-sodium cromoglycate (Intal), and (3) hydrofluoroalkane (HFA)-beclomethasone
dipropionate (Qvar) delivered by pressurized metered dose inhaler. Particle size distributions were compared determining mass
median aerodynamic diameter (MMAD), geometric standard deviation (GSD), and fine particle fraction <4.7 μm aerodynamic diameter
(FPF<4.7 μm). Next Generation Pharmaceutical Impactor (NGI)-size distributions for Flovent comprised finer particles than determined
by Andersen 8-stage impactor (ACI) (MMAD=2.0±0.05 μm [NGI]; 2.8±0.07 μm [ACI]); however FPF<4.7 μm by both impactors was in the narrow range 88% to 93%. Size distribution agreement for Intal was better (MMAD=4.3±0.19 μm
(NGI), 4.2±0.13 μm (ACI), with FPF<4.7 μm ranging from 52% to 60%. The Aerodynamic Particle Sizer (APS) undersized aerosols produced with either formulation (MMAD=1.8±0.07
μm and 3.2±0.02 μm for Flovent and Intal, respectively), but values of FPF<4.7 μm from the single-stage impactor (SSI) located at the inlet to the APS (82.9%±2.1% [Flovent], 46.4%±2.4% [Intal]) were fairly
close to corresponding data from the multi-stage impactors. APS-measured size distributions for Qvar (MMAD=1.0±0.03 μm; FPF<4.7 μm=96.4% ±2.5%), were in fair agreement with both NGI (MMAD=0.9±0.03 μm; FPF<4.7 μm=96.7%±0.7%), and ACI (MMAD=1.2±0.02 μm, FPF<4.7 μm=98%±0.5%), but FPF<4.7 μm from the SSI (67.1%±4.1%) was lower than expected, based on equivalent data obtained by the other techniques. Particle bounce,
incomplete evaporation of volatile constituents and the presence of surfactant particles are factors that may be responsible
for discrepancies between the techniques. 相似文献
11.
Toshi Nagata 《Ecological Research》1986,1(2):207-221
The seasonal changes in the size-fractionated chlorophylla concentrations (<3 μm, 3 to 25 μm, and >25 μm) were investigated at a pelagic site of the north basin of Lake Biwa during
June to December 1985. Autofluorescing plankton cells in the <3-μm fractions were also examined using the fluorescein isothiocyanate
staining epifluorescence microscopic technique. The <3-μm phytoplankton (usually dominated by chroococcoid cyanobacteria except
for a few cases dominated by small eukaryotes) showed a clearly different pattern of seasonal change compared with the larger
fractions. That is, from August to early September, chlorophylla of the larger fractions declined considerably, while the <3-μm chlorophylla did not decrease significantly. Moreover, cyanobacterial cell density in the <3-μm fraction showed a maximum value (2–3.5×105 cells·ml−1) during this period. The relative contribution of the <3-μm chlorophylla to the total chlorophylla increased from <5% to 45% during the course of this change. No clear vertical trend in the distribution and composition of
the <3-μm phytoplankton was found, except that relatively large cyanobacteria (>4 μm3) appeared at a depth of 15m but not at 0,5 and 10 m from late July to August. These large cells were also found in November
and December. The drastic seasonal change of phytoplankton size structure occurring in this basin was discussed in relation
to grazing, nutrient depletion and sinking.
Contribution from Otsu Hydrobiological Station, Kyoto Univeristy (No. 308, foreign language series). 相似文献
12.
Richard J. Thomas Daniel Webber William Sellors Aaron Collinge Andrew Frost Anthony J. Stagg Stephen C. Bailey Pramukh N. Jayasekera Rosa R. Taylor Steve Eley Richard W. Titball 《Aerobiologia》2009,25(2):75-84
Flow-focussing technology was harnessed to enable generation of large droplet aerosols within high-level microbiological containment.
The Collison nebuliser and flow-focussing aerosol generator (FFAG) produced aerosols from distilled water with average mass
median aerodynamic diameters (MMAD) of 4.19 and 11.93 μm, respectively. The medium type [water, phosphate buffered saline
(PBS) or microbiological broth] had minimal effect on the droplet size generated by the FFAG. The FFAG can be modulated to
generate reproducible aerosols with a wide range of MMADs (9–105 μm). The number of particulates (i.e. fluospheres) contained
within the droplets increased as the MMAD increased from 12 to 50 μm. The technology described can be used for the exposure
of small-animal models to large droplet aerosols (>10 μm) and has applications in healthcare, pharmaceutical, agricultural
and biodefence environments. 相似文献
13.
Environmental conditions in high mountain lakes containing toxic benthic cyanobacteria 总被引:6,自引:0,他引:6
In glacial lakes on an alpine pasture in Switzerland, benthic cyanobacteria produced microcystin, a cyclic hepatotoxic heptapeptide.
The cyanobacteria formed dense mats on sediments and submerged stones. The mats consisted mainly of Oscillatoria limosa, Phormidium
konstantinosum (= Oscillatoria tenuis) and Tychonema granulatum (= Oscillatoria granulata). In order to characterize the ecological
conditions of these cyanobacteria, nutrient concentrations were determined, and an automatic data acquisition station was
installed in one of the lakes. It continuously recorded air temperature, global irradiance, precipitation, atmospheric pressure,
wind speed and direction; as well as temperature, pH, oxygen content and conductivity of the lake water. The nutrient situation
in the lakes was mainly influenced by the erosion of the gneissic catchment by glacial meltwater and by precipitation. In
the glacial lakes, the concentrations of calcium, iron, magnesium, sodium and sulphate increased throughout the summer season.
Conductivity values of 4–110 μS cm-1 represent generally low nutrient concentrations. Nevertheless, iron concentrations of up to 20 μM occurred. Biomass, expressed
as protein concentration, as well as the microcystin content of the cyanobacterial mats varied within one season and between
different years (1994 and 1995). In one cyanobacterial mat community, biomass and microcystin concentrations were highest
at the same time, in an other one the microcystin content was maximal three weeks after the highest biomass concentration
was reached. Our observations suggest that biomass and toxin production in the mats were strongly influenced by mechanical
stress, temporary desiccation and high irradiation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Isolation and Characterization of Acetate-Utilizing Anaerobes from a Freshwater Sediment 总被引:1,自引:0,他引:1
Acetate-degrading anaerobic microorganisms in freshwater sediment were quantified by the most probable number technique. From
the highest dilutions a methanogenic, a sulfate-reducing, and a nitrate-reducing microorganism were isolated with acetate
as substrate. The methanogen (culture AMPB-Zg) was non-motile and rod-shaped with blunted ends (0.5–1 μm × 3–4 μm long). Doubling
times with acetate at 30–35°C were 5.6–8.1 days. The methanogen grew only on acetate. Analysis of the 16S rRNA sequence showed
that AMPB-Zg is closely related toMethanosaeta concilii. The isolated sulfate-reducing bacterium (strain ASRB-Zg) was rod-shaped with pointed ends (0.5–0.7 μm × 1.5–3.5 μm long),
weakly motile, spore forming, and gram positive. At the optimum growth temperature of 30°C the doubling times with acetate
were 3.9–5.3 days. The bacterium grew on a range of organic acids, such as acetate, butyrate, fumarate, and benzoate, but
did not grow autotrophically with H2, CO2, and sulfate. The closest relative of strain ASRB-Zg isDesulfotomaculum acetoxidans. The nitrate-reducing bacterium (strain ANRB-Zg) was rod-shaped (0.5–0.7 μm × 0.7–1 μm long), weakly motile, and gram negative.
Optimum growth with acetate occurred at 20–25°C. The bacterium grew on a range of organic substrates, such as acetate, butyrate,
lactate, and glucose, and did grow autotrophically with H2, CO2, and oxygen but not with nitrate. In the presence of acetate and nitrate, thiosulfate was oxidized to sulfate. Phylogenetically,
the closest relative of strain ANRB-Zg isVariovorax paradoxus. 相似文献
15.
To clarify the ecological significance of the association of sulfate-reducing bacteria (SRB) with sediment particle size,
SRB utilizing lactate (l-SRB), propionate (p-SRB) and acetate (a-SRB) were examined with different sizes of sediment particles in a hypertrophic freshwater lake using the anaerobic plate
count method. The numbers ofl-SRB anda-SRB were 104–105 colony forming units (CFU) per ml in the 0–3 cm layer and 102–103 CFU ml−1 in the 10–13 cm layer while the numbers ofp-SRB were one or two orders lower than those ofl-SRB anda-SRB. A sediment suspension was fractionated into four fractions (<1, 1–10, 10–94 and >94 μm). The highest proportions ofl-SRB anda-SRB were found in the 10–94 μm fraction: 66–97% forl-SRB and 53–98% fora-SRB. The highest proportion ofp-SRB was found in the >94 μm fraction (70–74%). These results indicate that most SRB were associated with sediment particles.
One isolate from an acetate-utilizing enrichment culture was similar toDesulfotomaculum acetoxidans, a spore-forming sulfate-reducing bacterium. When lactate and sulfate were added to sediment samples,l-SRB anda-SRB in the <10 μm-fraction grew more rapidly than those in whole sediment for the first 2 days. This result suggests that
nutrients uptake by free-living and small particle-associated (<10 μm) SRB is higher than that by SRB associated with larger
particles. 相似文献
16.
Anna Padovan Niels Munksgaard Belinda Alvarez Keith McGuinness David Parry Karen Gibb 《Hydrobiologia》2012,687(1):275-288
Major and trace elements were measured in sponges, seawater and sediment in Darwin Harbour (Australia) to test the hypothesis
that metals are elevated in sponges closer to a sewage outfall compared with unimpacted sites. Seawater and sediment at the
sewage discharge site contained high, but localised, concentrations of phosphorus (P), manganese (Mn), iron (Fe), cobalt (Co),
nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) compared with background sites. Metal concentrations in the
sponge Spheciospongia vagabunda were highly elevated compared with other sponges and, although site specific, high metal concentrations were unrelated to
the presence of sewage effluent. X-ray fluorescence microprobe imaging was used to investigate the metal distribution pattern
in S. vagabunda. High Fe, Ni and Zn concentrations were either localised in circular patches (100–200 μm size) near water canals or in the
pinacoderm, or scattered in spots (approximately 10 μm) throughout the tissue. This supports a microflora-mediated metal bioaccumulation
hypothesis. In contrast, Co and Mn were highly dispersed and probably associated with aluminium- and iron-oxide rich sediment
inclusions. Although the lack of association between sewage effluent and metal accumulation precludes the use of S. vagabunda as a biomonitor, the apparent differential mechanisms of metal accumulation warrants further investigation. 相似文献
17.
A new methanogenic isolate, designated as strain O1M9704 (=OCM 667), was isolated from the sediment of the estuarine environment
in Eriln Shi, Taiwan. This strain grew on trimethylamine and methanol, but it did not catabolize H2-CO2, acetate, or formate. Cells grew optimally at 37°C with 0.5% NaCl in neutral pH. The cells were stained Gram-negative, nonmotile,
irregular coccus 0.3–0.6 μm in diameter. A comparison of 16S rDNA sequences phylogenetically related strain O1M9704 to Methanosarcina mazei. Gas vacuoles were observed both under phase contrast microscope and in thin sections in the electron microscope. Negative
stain of electron micrographs showed a novel character of strain O1M9704 with tubule structure extended out of the cells.
The tubule structure and gas vacuoles may benefit the adaptation of methanoarchaea in estuarine environment.
Received: 10 December 1999 / Accepted: 10 January 2000 相似文献
18.
Total synaptonemal complex (SC) lengths were estimated from Oreochromis aureus Steindachner (which has a WZ/ZZ sex determination system), O. mossambicus Peters and O. niloticus L. (both of which have XX/XY sex determination systems). The total SC length in oocytes was greater than that in spermatocytes
in all three species (194 ± 30 μm and 134 ± 13 μm, 187 ± 22 μm and 127 ± 17 μm, 193 ± 37 μm and 144 ± 19 μm, respectively).
These sex-specific differences did not appear to be influenced by the type of sex determination system (the female/male total
SC length ratio was 1.45 in O. aureus, 1.47 in O. mossambicus and 1.34 in O. niloticus) and do not correlate with the lack of any overall sex-specific length differences in the current Oreochromis linkage map. Although based on data from relatively few species, there appears to be no consistent relationship between sex-specific
SC lengths and linkage map lengths in fish. Neomale (hormonally masculinized genetic female) O. aureus and O. mossambicus had total SC lengths of 138 ± 13 μm and 146 ± 13 μm respectively, more similar to normal males than to normal females. These
findings agree with data from other vertebrate species that suggest that phenotypic sex, rather than genotype, determines
traits such as total SC length, chiasmata position and recombination pattern, at least for the autosomes. 相似文献
19.
Spatial and Temporal Variability in Sediment Denitrification Within an Agriculturally Influenced Reservoir 总被引:2,自引:1,他引:1
Reservoirs are intrinsically linked to the rivers that feed them, creating a river–reservoir continuum in which water and
sediment inputs are a function of the surrounding watershed land use. We examined the spatial and temporal variability of
sediment denitrification rates by sampling longitudinally along an agriculturally influenced river–reservoir continuum monthly
for 13 months. Sediment denitrification rates ranged from 0 to 63 μg N2O g ash free dry mass of sediments (AFDM)−1 h−1 or 0–2.7 μg N2O g dry mass of sediments (DM)−1 h−1 at reservoir sites, vs. 0–12 μg N2O gAFDM−1 h−1 or 0–0.27 μg N2O gDM−1 h−1 at riverine sites. Temporally, highest denitrification activity traveled through the reservoir from upper reservoir sites
to the dam, following the load of high nitrate (NO3−-N) water associated with spring runoff. Annual mean sediment denitrification rates at different reservoir sites were consistently
higher than at riverine sites, yet significant relationships among theses sites differed when denitrification rates were expressed
per gDM vs. per gAFDM. There was a significant positive relationship between sediment denitrification rates and NO3−-N concentration up to a threshold of 0.88 mg NO3− -N l−1, above which it appeared NO3−-N was no longer limiting. Denitrification assays were amended seasonally with NO3−-N and an organic carbon source (glucose) to determine nutrient limitation of sediment denitrification. While organic carbon
never limited sediment denitrification, all sites were significantly limited by NO3−-N during fall and winter when ambient NO
3−-N was low. 相似文献
20.
Food size-range for 13 species of Tintinnina and 18 species of Oligotrichina were studied using electronic particle counting
and in situ observation of food vacuole contents. Tintinnids consume nanoplankton in the size range 2–20 μm. Oligotrichous naked ciliates
consume particles in the size range 0.5–10 μm. Ciliates smaller than 30 μm take 72% picoplankton and 28% nanoplankton. For
ciliates between 30 μm and 50 μm the proportions are reversed (30% pico- and 70% nanoplankton), while the larger ciliates
(> 50 μm) take nanoplankton almost exclusively (95% nano- and 5% picoplankton). A seasonal study of total Oligotrichida grazing
showed that natural particles were consumed at rates that varied from 1 to 20 μg C 1−1 day−1. This included between 1 and 38% of the bacterioplankton production and 9 to 52% of the nanoplankton production. In the N-W
Mediterranean the total ciliate production varied from 0.4 to 8.2 μg C 1−1 day−1.
Research supported by CNRS-PIROCEAN AIP-RTM-953146-GRECO P4 and by CNRS-UA 716 (FR), and by the University of Nice and by
the CNRS-GRECO 88 (MLP) 相似文献