Compared with the measureable but limited K isotope variation in geological samples,biological samples have much larger variations in δ^41 values：from-1.3‰ to＋1.1‰ relative to the international K standard NIST SR...Compared with the measureable but limited K isotope variation in geological samples,biological samples have much larger variations in δ^41 values：from-1.3‰ to＋1.1‰ relative to the international K standard NIST SRM 3141a.Notably,higher plants generally have δ^41 values that are lower than igneous rocks,whereas sea plants（algae）have δ^41 values that are higher than seawater;the range in δ^41K values of plants encompasses the δ^41 values of both igneous rocks and seawater.Plant cells utilize different K uptake mechanisms in response to highand low-K conditions.In a low-K environment,plant cells use energy-consuming ion pumps for active uptake of K;plant cells in high-K environments use non-energy-consuming ion channels.Based on these facts and on K isotope data from sea and land plants,it is hypothesized that the different K uptake mechanisms are accompanied by distinct K isotope fractionation behaviors or vital effects.The enrichment of light K isotopes in terrestrial plants could be attributed to preferential transport of isotopically light K in the energy-consuming active uptake process by K ion pumps in the membranes of plant root cells.On the other hand,the enrichment of heavy K isotopes in algae may be caused by a combination of the lack of K isotope fractionation during K uptake from seawater via ion channels and the preferential efflux of light K isotopes across the cell membrane back to the seawater.The large variation of K isotope compositions in biological samples therefore may reflect the diversity of isotopic vital effects for K in organisms,which implies the great potential of K isotopes in biogeochemical studies.展开更多
The amount of explained variation R2 is an overall measure used to quantify the information in a model and especially how useful the model might be when predicting future observations, explained variation is useful in...The amount of explained variation R2 is an overall measure used to quantify the information in a model and especially how useful the model might be when predicting future observations, explained variation is useful in guiding model choice for all types of predictive regression models, including linear and generalized linear models and survival analysis. In this work we consider how individual observations in a data set can influence the value of various R2 measures proposed for survival analysis including local influence to assess mathematically the effect of small changes. We discuss methodologies for assessing influence on Graf et al.＇s R2G measure, Harrell＇s C-index and Nagelkerke＇s R2N. The ideas are illustrated on data on 1391 patients diagnosed with Diffuse Large B-cell Lymphoma （DLBCL）, a major subtype ofNon-Hodgkin＇s Lymphoma （NHL）.展开更多
基金supported by"1000-talent Program"of China,and National Science Foundation of China(Grant No.41622301)to WL
文摘Compared with the measureable but limited K isotope variation in geological samples,biological samples have much larger variations in δ^41 values：from-1.3‰ to＋1.1‰ relative to the international K standard NIST SRM 3141a.Notably,higher plants generally have δ^41 values that are lower than igneous rocks,whereas sea plants（algae）have δ^41 values that are higher than seawater;the range in δ^41K values of plants encompasses the δ^41 values of both igneous rocks and seawater.Plant cells utilize different K uptake mechanisms in response to highand low-K conditions.In a low-K environment,plant cells use energy-consuming ion pumps for active uptake of K;plant cells in high-K environments use non-energy-consuming ion channels.Based on these facts and on K isotope data from sea and land plants,it is hypothesized that the different K uptake mechanisms are accompanied by distinct K isotope fractionation behaviors or vital effects.The enrichment of light K isotopes in terrestrial plants could be attributed to preferential transport of isotopically light K in the energy-consuming active uptake process by K ion pumps in the membranes of plant root cells.On the other hand,the enrichment of heavy K isotopes in algae may be caused by a combination of the lack of K isotope fractionation during K uptake from seawater via ion channels and the preferential efflux of light K isotopes across the cell membrane back to the seawater.The large variation of K isotope compositions in biological samples therefore may reflect the diversity of isotopic vital effects for K in organisms,which implies the great potential of K isotopes in biogeochemical studies.
文摘The amount of explained variation R2 is an overall measure used to quantify the information in a model and especially how useful the model might be when predicting future observations, explained variation is useful in guiding model choice for all types of predictive regression models, including linear and generalized linear models and survival analysis. In this work we consider how individual observations in a data set can influence the value of various R2 measures proposed for survival analysis including local influence to assess mathematically the effect of small changes. We discuss methodologies for assessing influence on Graf et al.＇s R2G measure, Harrell＇s C-index and Nagelkerke＇s R2N. The ideas are illustrated on data on 1391 patients diagnosed with Diffuse Large B-cell Lymphoma （DLBCL）, a major subtype ofNon-Hodgkin＇s Lymphoma （NHL）.
