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71.
Dissolved organic carbon (DOC) plays an important role in surface water chemistry and ecology and trends in DOC concentration
have been also associated with shifts in terrestrial carbon pools. Numerous studies have reported long-term trends in DOC
concentration; however, some studies consider changes in average measured DOC whereas other compute discharge weighted concentrations.
Because of differences in reporting methods and variable record lengths it is difficult to compare results among studies and
make regional generalizations. Furthermore, changes in stream discharge may impact long-term trends in DOC concentration and
the potentially subtle effect of shifts in stream flow may be missed if only measured DOC concentrations are considered. In
this study we compare trends in volume-weighted vs. average measured DOC concentration between 1980 and 2001 at seven headwater
streams in south-central Ontario, Canada that vary in wetland coverage and DOC (22-year mean vol. wt.) from 3.4 to 10.6 mg l−1. On average, annual measured DOC concentrations were 13–34% higher than volume-weighted values, but differences of up to
290% occurred in certain years. Estimates of DOC flux were correspondingly higher using measured concentration values. Both
measured and volume-weighted DOC concentrations increased significantly between 1980 and 2001, but slopes were larger in measured
data (0.04–0.35 mg l−1 year−1 compared with 0.05–0.15 mg l−1 year−1) and proportional increases at the most wetland-influenced sites ranged from 32 to 43% in volume-weighted DOC and from 52
to 75% in measured DOC. In contrast, DOC flux did not change with time when estimated using either method, because of the
predominant influence of stream flow on DOC export. Our results indicate that changes in stream flow have an important impact
on trends in DOC concentration, and extrapolation of trend results from one region to another should be made cautiously and
consider methodological and reporting differences among sites. 相似文献
72.
Michał Bijok Ewelina Gruszczynska Adam Kowalczyk Katarzyna Sikorska Agnieszka Walewska Pawel F. Kukolowicz 《Reports of Practical Oncology and Radiotherapy》2018,23(5):341-345
Aim
The aim of the study was to analyze the long-term stability of electron beams generated by the Novac11? IORT accelerator.Background
Novac11? (NRT®) is a mobile electron accelerator designed to irradiate small areas of tissue, up to 10?cm in diameter, with electron beams during surgical procedures. It is characterized by a great mobility guaranteed by a number of degrees of freedom enabling irradiation in the conditions of an operating theatre.Materials and methods
Over the period of January 2013 and September 2016, the measurement sessions of the output of clinically used beam qualities (6, 8 and 10?MeV) were carried out 41 times. Because of the unsatisfactory long-term stability, an extra procedure of tuning of the magnetron, suggested by the manufacturer, was introduced in October 2015, 15 measurements were performed since then. The output of the Novac11? accelerator was measured in the reference conditions recommended by the IAEA Report 398, the measurements of the charge in the ionization chamber at the reference depth were carried out with a Dose1? electrometer and a plane-parallel chamber PPC05? from IBA®.Results
The introduction of the tuning of the magnetron procedure resulted in satisfactory long-term stability of the measured outputs below 2%.Conclusions
After the introduction of the STV parameter tuning procedure, the long-term stability of the Novac11? output increased considerably and is within the values declared by the manufacturer. 相似文献73.
Rita D.G. Franca Helena M. Pinheiro Mark C.M. van Loosdrecht Nídia D. Lourenço 《Biotechnology advances》2018,36(1):228-246
Aerobic granular sludge technology has been extensively studied over the past 20 years and is regarded as the upcoming new standard for biological treatment of domestic and industrial wastewaters. Aerobic granules (AG) are dense, compact, self-immobilized microbial aggregates that allow better sludge-water separation and thereby higher biomass concentrations in the bioreactor than conventional activated sludge aggregates. This brings potential practical advantages in terms of investment cost, energy consumption and footprint. Yet, despite the relevant advances regarding the process of AG formation, instability of AG during long-term operation is still seen as a major barrier for a broad practical application of this technology. This paper presents an up-to-date review of the literature focusing on AG stability, aiming to contribute to the identification of key factors for promoting long-term stability of AG and to a better understanding of the underlying mechanisms. Operational conditions leading to AG disintegration are described, including high organic loads, particulate substrates in the influent, toxic feed components, aerobic feeding and too short famine periods. These operational and influent wastewater composition conditions were shown to influence the micro-environment of AG, consequently affecting their stability. Granule stability is generally favored by the presence of a dense core, with microbial growth throughout the AG depth being a crucial intrinsic factor determining its structural integrity. Accordingly, possible practical solutions to improve granule long-term stability are described, namely through the promotion of minimal substrate concentration gradients and control of microbial growth rates within AG, including anaerobic, plug-flow feeding and specific sludge removal strategies. 相似文献
74.
对继代17年的玉米花粉胚性细胞系核形态和细胞分裂情况进行了观察分析,结果表明:随着继代培养时间的延长,异形核细胞比率增加,异形核类型和异常分裂增多。分析认为异形核和异常分裂现象出现和增多是导致胚性细胞系分化率降低、异形分化和非整倍体细胞产生的主要原因。并提出来自玉米农家种“八趟白”的部分胚性细胞系能长期保持倍性稳定和胚胎发生并再生,与不断挑选和继代培养中不加2,4-D有关。 相似文献
75.
Ananza M. Rabello Catherine L. Parr Antônio C. M. Queiroz Danielle L. Braga Graziele S. Santiago Carla R. Ribas 《Biotropica》2018,50(1):39-49
Changes in land use strongly influence habitat attributes (e.g., herbaceous ground cover and tree richness) and can consequently affect ecological functions. Most studies have focused on the response of these ecological functions to land‐use changes within only a single vegetation type. These studies have often focused solely on agricultural conversion of forests, making it nearly impossible to draw general conclusions across other vegetation types or with other land‐use changes (e.g., afforestation). We examined the consequences of agricultural conversion for seed removal by ants in native grassland, savanna, and savanna‐forest habitats that had been transformed to planted pastures (Brachiaria decumbens) and tree plantations (Eucalyptus spp.) and explored if changes in seed removal were correlated with differences in habitat attributes between habitat types. We found that land‐use changes affected seed removal across the tree cover gradient and that the magnitude of impact was influenced by similarity in habitat attributes between native and converted habitats, being greater where there was afforestation (Eucalyptus spp in grassland and savanna). Herbaceous ground cover, soil hardness, and tree richness were the most important habitat attributes that correlated with differences in seed removal. Our results reveal that the magnitude of impact of land‐use changes on seed removal varies depending on native vegetation type and is associated with the type of habitat attribute change. Our findings have implications for biodiversity in tropical grassy systems: afforestation can have a greater detrimental impact on ecological function than tree loss. 相似文献
76.
K-7174, a GATA-specific inhibitor, is a putative anti-inflammatory agent that attenuates effects of inflammatory cytokines in certain cell types. However, molecular mechanisms involved have not been elucidated. We found that, in glomerular podocytes, induction of monocyte chemoattractant protein 1 (MCP-1) and inducible nitric oxide synthase (iNOS) by TNF-alpha was abrogated by K-7174. It was correlated with unexpected induction of unfolded protein response (UPR) evidenced by: (1) induction of endogenous indicators 78 kDa glucose-regulated protein and CCAAT/enhancer-binding protein-homologous protein, and (2) suppression of an exogenous indicator, endoplasmic reticulum stress-repressive alkaline phosphatase. In podocytes, induction of UPR by either tunicamycin, thapsigargin, A23187 or AB5 subtilase cytotoxin completely reproduced the suppressive effect of K-7174. Furthermore, K-7174-elicited UPR abrogated induction of MCP-1 and iNOS not only by TNF-alpha but also by medium conditioned by activated macrophages. These results suggested a novel, UPR-dependent mechanism underlying the anti-inflammatory potential of K-7174. 相似文献
77.
Abstract. Structure, diversity and dynamics of five Japanese temperate old-growth forests were compared, differing from each other in, i.a., climate, dominant tree type, topography, disturbance regime. The forests were Aya, Ogawa, Kanumazawa Riparian, Kanumazawa upland and Senju. A permanent plot (1–6 ha) was established in each forest and trees were censused several times at intervals of two years. Mean annual recruitment rates and mortality rates in these forests were both in the range of 0.5 to 4.6 %/yr at the community level. Analyses of the structure and dynamics of populations showed that the underlying process was different among the forests. Some forests experienced compositional shifts in their canopies, others had a constant canopy composition but appeared to lack effective regeneration in recent years. The recruitment rate appeared to be strongly affected by competitive undergrowth vegetation such as dwarf bamboo which has been controlled by natural disturbance or human impact. It is likely that the forests with mostly low recruitment rates had a low species diversity. The current variation in structure, diversity and dynamics of the studied forests might have been determined not only by physical conditions (e.g. climate) but also by chance factors (e.g. disturbance, outbreak of deer population). 相似文献
78.
Evaluation of Voltage-Sensitive Dyes for Long-Term Recording of Neural Activity in the Hippocampus 总被引:3,自引:0,他引:3
Y. Momose-Sato K. Sato Y. Arai I. Yazawa H. Mochida K. Kamino 《The Journal of membrane biology》1999,172(2):145-157
We searched for an optimal voltage-sensitive dye for optical measurements of neural activity in the hippocampal slice by
evaluating several merocyanine-rhodanine and oxonol dyes. The wavelength dependence (action spectra), pharmacological effects
of staining, signal size, signal-to-noise ratio, and the utility of the dyes for long-term continuous recording were examined
for four merocyanine-rhodanine dyes (NK2761, NK2776, NK3224 and NK3225), which had been reported to be optimal in embryonic
nervous systems, and for two oxonol dyes (NK3630 (RH482) and NK3041 (RH155)), which have been among the most popular potentiometric
probes for the hippocampal slice preparation. NK2761, NK3224 and NK3225 provided large signal-to-noise ratios, and proved
to be useful for optical recordings lasting several hours. NK3630 was most suitable for long-term recording, although the
signal-to-noise ratio was slightly inferior to that of the merocyanine-rhodanines. Using NK3630 (RH482) on the hippocampal
slice preparation, we demonstrate here that long-term potentiation can be monitored stably for more than 8 hr.
Received: 16 June 1999/Revised: 4 August 1999 相似文献
79.
Differences in field‐scale N2O flux linked to crop residue removal under two tillage systems in cold climates 下载免费PDF全文
Katelyn A. Congreves Shannon E. Brown Deanna D. Németh Kari E. Dunfield Claudia Wagner‐Riddle 《Global Change Biology Bioenergy》2017,9(4):666-680
Residue removal for biofuel production may have unintended consequences for N2O emissions from soils, and it is not clear how N2O emissions are influenced by crop residue removal from different tillage systems. Thus, we measured field‐scale N2O flux over 5 years (2005–2007, 2010–2011) from an annual crop rotation to evaluate how N2O emissions are influenced by no‐till (NT) compared to conventional tillage (CV), and how crop residue removal (R?) rather than crop residue return to soil (R+) affects emissions from these two tillage systems. Data from all 5 years indicated no differences in N2O flux between tillage practices at the onset of the growing season, but CT had 1.4–6.3 times higher N2O flux than NT overwinter. Nitrous oxide emissions were higher due to R? compared to R+, but the effect was more marked under CT than NT and overwinter than during spring. Our results thus challenge the assumption based on IPCC methodology that crop residue removal will result in reduced N2O emissions. The potential for higher N2O emission with residue removal implies that the benefit of utilizing biomass as biofuels to mitigate greenhouse gas emission may be overestimated. Interestingly, prior to an overwinter thaw event, dissolved organic C (DOC) was negatively correlated to peak N2O flux (r = ?0.93). This suggests that lower N2O emissions with R+ vs. R? may reflect more complete stepwise denitrification to N2 during winter and possibly relate to the heterotrophic microbial capacity for processing crop residue into more soluble C compounds and a shift in the preferential C source utilized by the microbial community overwinter. 相似文献
80.
Coral reef crisis in deep and shallow reefs: 30 years of constancy and change in reefs of Curacao and Bonaire 总被引:1,自引:0,他引:1
Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m.
Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep
reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover
at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent
photo quadrats. About 20 zooxanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies
in deep reefs over the last 30 years. In deep reefs, non-agaricid species are decreasing but agaricid domination will be interrupted
by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in
the deep-reef environment with extremely low temperatures possibly related to deep-reef bleaching.
An erratum to this article can be found at 相似文献