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排序方式: 共有204条查询结果,搜索用时 15 毫秒
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Krešimir Begović Jonathan S. Schurman Marek Svitok Jakob Pavlin Thomas Langbehn Kristyna Svobodová Martin Mikoláš Pavel Janda Michal Synek William Marchand Lucie Vitková Daniel Kozák Ondrej Vostarek Vojtech Čada Radek Bače Miroslav Svoboda 《Global Change Biology》2023,29(1):143-164
In a world of accelerating changes in environmental conditions driving tree growth, tradeoffs between tree growth rate and longevity could curtail the abundance of large old trees (LOTs), with potentially dire consequences for biodiversity and carbon storage. However, the influence of tree-level tradeoffs on forest structure at landscape scales will also depend on disturbances, which shape tree size and age distribution, and on whether LOTs can benefit from improved growing conditions due to climate warming. We analyzed temporal and spatial variation in radial growth patterns from ~5000 Norway spruce (Picea abies [L.] H. Karst) live and dead trees from the Western Carpathian primary spruce forest stands. We applied mixed-linear modeling to quantify the importance of LOT growth histories and stand dynamics (i.e., competition and disturbance factors) on lifespan. Finally, we assessed regional synchronization in radial growth variability over the 20th century, and modeled the effects of stand dynamics and climate on LOTs recent growth trends. Tree age varied considerably among forest stands, implying an important role of disturbance as an age constraint. Slow juvenile growth and longer period of suppressed growth prolonged tree lifespan, while increasing disturbance severity and shorter time since last disturbance decreased it. The highest age was not achieved only by trees with continuous slow growth, but those with slow juvenile growth followed by subsequent growth releases. Growth trend analysis demonstrated an increase in absolute growth rates in response to climate warming, with late summer temperatures driving the recent growth trend. Contrary to our expectation that LOTs would eventually exhibit declining growth rates, the oldest LOTs (>400 years) continuously increase growth throughout their lives, indicating a high phenotypic plasticity of LOTs for increasing biomass, and a strong carbon sink role of primary spruce forests under rising temperatures, intensifying droughts, and increasing bark beetle outbreaks. 相似文献
3.
C.Y. Lee Margaret Mcpherson Vojtech Licko J. Ramachandran 《Archives of biochemistry and biophysics》1980,201(2):411-419
The biological properties of the naturally occurring pituitary peptide αh7–38-adrenocorticotropin (ACTH) have been investigated. αh7–38-ACTH is devoid of steroidogenic activity but inhibits competitively ACTH-induced steroidogenesis in vitro as well as in vivo. The long-term actions of ACTH on normal and tumor adrenal cells in culture are also antagonized by αh7–38-ACTH. The apparent Ki for the inhibition of cyclic AMP production by αh7–38-ACTH (301 ± 62 nm) was significantly higher than the apparent Ki for the inhibition of corticosterone synthesis (21.6 ± 6.8 nm). Analysis of the inhibition of ACTH-induced steroidogenesis and cyclic AMP production in normal rat adrenocortical cells indicates that two separate receptors may be involved in mediating these responses. 相似文献
4.
For healthy infants, which were born normally and fully breastfed, the dominant component of the intestinal microflora are bifidobacteria. However, infants born by caesarean section possess clostridia as a dominant intestinal bacterial group. The aim of the present study was to determine whether bifidobacteria and clostridia are able to grow on human milk oligosaccharides (HMOs) and other carbon sources - lactose, cow milk (CM) and human milk (HM). Both bifidobacteria and clostridia grew on lactose and in CM. Bifidobacteria grew in HM and on HMOs. In contrast, 3 out of 5 strains of clostridia were not able to grow in HM. No clostridial strain was able to utilise HMOs. While both bifidobacterial strains were resistant to lysozyme, 4 out of 5 strains of clostridia were lysozyme-susceptible. It seems that HMOs together with lysozyme may act as prebiotic-bifidogenic compounds inhibiting intestinal clostridia. 相似文献
5.
Elevational species richness gradients in a hyperdiverse insect taxon: a global meta‐study on geometrid moths
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Jan Beck Christy M. McCain Jan C. Axmacher Louise A. Ashton Florian Bärtschi Gunnar Brehm Sei‐Woong Choi Oldrich Cizek Robert K. Colwell Konrad Fiedler Cristina L. Francois Steven Highland Jeremy D. Holloway Jurie Intachat Tomas Kadlec Roger L. Kitching Sarah C. Maunsell Thomas Merckx Akihiro Nakamura Erica Odell Weiguo Sang Pagi S. Toko Jaroslav Zamecnik Yi Zou Vojtech Novotny 《Global Ecology and Biogeography》2017,26(4):412-424
6.
Akchheta Karki Joachim Vollbrecht Alexander J. Gillett Philipp Selter Jaewon Lee Zhengxing Peng Nora Schopp Alana L. Dixon Max Schrock Vojtech Ndady Franz Schauer Harald Ade Bradley F. Chmelka Guillermo C. Bazan Richard H. Friend Thuc‐Quyen Nguyen 《Liver Transplantation》2020,10(29)
Even though significant breakthroughs with over 18% power conversion efficiencies (PCEs) in polymer:non‐fullerene acceptor (NFA) bulk heterojunction organic solar cells (OSCs) have been achieved, not many studies have focused on acquiring a comprehensive understanding of the underlying mechanisms governing these systems. This is because it can be challenging to delineate device photophysics in polymer:NFA blends comprehensively, and even more complicated to trace the origins of the differences in device photophysics to the subtle differences in energetics and morphology. Here, a systematic study of a series of polymer:NFA blends is conducted to unify and correlate the cumulative effects of i) voltage losses, ii) charge generation efficiencies, iii) non‐geminate recombination and extraction dynamics, and iv) nuanced morphological differences with device performances. Most importantly, a deconvolution of the major loss processes in polymer:NFA blends and their connections to the complex BHJ morphology and energetics are established. An extension to advanced morphological techniques, such as solid‐state NMR (for atomic level insights on the local ordering and donor:acceptor π? π interactions) and resonant soft X‐ray scattering (for donor and acceptor interfacial area and domain spacings), provide detailed insights on how efficient charge generation, transport, and extraction processes can outweigh increased voltage losses to yield high PCEs. 相似文献
7.
8.
Vera Bunesova Eva Vlkova Vojtech Rada Jiri Killer Vladimir Kmet 《Journal of biosciences》2013,38(2):239-243
Bifidobacteria are considered as one of the key genera in intestinal tracts of animals, and their species composition vary depending on the host. The aim of this study was to identify faecal bifidobacteria from Asian elephants (Elephas maximus), housed in Zoological gardens (Ostrava, Czech Republic). Using culturing, bifidobacteria were found in counts 7.60?±?0.56 log CFU/g. Twenty-six pure strains were isolated from faeces of Asian elephant. The isolates were clustered into two groups according to fingerprinting profiles and fermentation characteristic. Bacteria were identified by a combination of MALDI-TOF MS, PCR methods and sequencing as B. boum (12 isolates) and B. adolescentis (14 isolates). Elephant strains showed different fingerprinting profiles than type and collection strains. Since these two species are frequently isolated from gastrointestinal tract of herbivores, they seem to be typical of animals fed plant diets. 相似文献
9.
Objective
In an effort to understand how results of human clinical trials are made public, we analyze a large set of clinical trials registered at ClinicalTrials.gov, the world’s largest clinical trial registry.Materials and Methods
We considered two trial result artifacts: (1) existence of a trial result journal article that is formally linked to a registered trial or (2) the deposition of a trial’s basic summary results within the registry.Results
The study sample consisted of 8907 completed, interventional, phase 2-or-higher clinical trials that were completed in 2006-2009. The majority of trials (72.2%) had no structured trial-article link present. A total of 2367 trials (26.6%) deposited basic summary results within the registry. Of those , 969 trials (10.9%) were classified as trials with extended results and 1398 trials (15.7%) were classified as trials with only required basic results. The majority of the trials (54.8%) had no evidence of results, based on either linked result articles or basic summary results (silent trials), while a minimal number (9.2%) report results through both registry deposition and publication.Discussion
Our study analyzes the body of linked knowledge around clinical trials (which we refer to as the “trialome”). Our results show that most trials do not report results and, for those that do, there is minimal overlap in the types of reporting. We identify several mechanisms by which the linkages between trials and their published results can be increased.Conclusion
Our study shows that even when combining publications and registry results, and despite availability of several information channels, trial sponsors do not sufficiently meet the mandate to inform the public either via a linked result publication or basic results submission. 相似文献10.
Midpoint attractors and species richness: Modelling the interaction between environmental drivers and geometric constraints
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Robert K. Colwell Nicholas J. Gotelli Louise A. Ashton Jan Beck Gunnar Brehm Tom M. Fayle Konrad Fiedler Matthew L. Forister Michael Kessler Roger L. Kitching Petr Klimes Jürgen Kluge John T. Longino Sarah C. Maunsell Christy M. McCain Jimmy Moses Sarah Noben Katerina Sam Legi Sam Arthur M. Shapiro Xiangping Wang Vojtech Novotny 《Ecology letters》2016,19(9):1009-1022
We introduce a novel framework for conceptualising, quantifying and unifying discordant patterns of species richness along geographical gradients. While not itself explicitly mechanistic, this approach offers a path towards understanding mechanisms. In this study, we focused on the diverse patterns of species richness on mountainsides. We conjectured that elevational range midpoints of species may be drawn towards a single midpoint attractor – a unimodal gradient of environmental favourability. The midpoint attractor interacts with geometric constraints imposed by sea level and the mountaintop to produce taxon‐specific patterns of species richness. We developed a Bayesian simulation model to estimate the location and strength of the midpoint attractor from species occurrence data sampled along mountainsides. We also constructed midpoint predictor models to test whether environmental variables could directly account for the observed patterns of species range midpoints. We challenged these models with 16 elevational data sets, comprising 4500 species of insects, vertebrates and plants. The midpoint predictor models generally failed to predict the pattern of species midpoints. In contrast, the midpoint attractor model closely reproduced empirical spatial patterns of species richness and range midpoints. Gradients of environmental favourability, subject to geometric constraints, may parsimoniously account for elevational and other patterns of species richness. 相似文献