Historically, long-term records of Normalized Difference Vegetation Index (NDVI) have been the most useful data source among various optical remote sensing datasets derived from sun-synchronous sensors such as the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) 9. While efforts to monitor Amazon forests in situ continue, 7, 8 optical remote sensing plays a major role in monitoring vegetation dynamics for broad regions in the Amazon.
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Despite the importance of Amazon vegetation dynamics in climate change studies, the lack of ground observations still leaves large uncertainties in how to represent tropical evergreen forests in Earth system models 6. For instance, severe Amazon droughts are expected to occur more frequently as a result of global warming 3, 4 and modeling forests’ responses to drought is crucial for climate projections 5. Understanding the interactions of Amazon forests with the climate system is a key to predicting climate changes in the 21st century 1, 2. Though additional work is needed in converting the observed changes in seasonality into meaningful changes in canopy dynamics, our results highlight the potential of the new generation geostationary satellites to help us better understand tropical ecosystems, which has been a challenge with only polar orbiting satellites.Īmazon forests have a strong influence on global climate, carbon, and water cycles.
The analyses show statistically significant changes in seasonality over 85% of Amazon forest pixels, an area about three times greater than previously reported using MODIS data. Our analysis of NDVI data collected over the Amazon during 2018–19 shows that ABI provides 21–35 times more cloud-free observations in a month than MODIS. ABI is similar to the widely used polar orbiting sensor, the Moderate Resolution Imaging Spectroradiometer (MODIS), but provides observations every 10–15 min. Here, we use data from a new generation of geostationary satellites that carry the Advanced Baseline Imager (ABI) to study the Amazon canopy. All rights reserved.Assessing the seasonal patterns of the Amazon rainforests has been difficult because of the paucity of ground observations and persistent cloud cover over these forests obscuring optical remote sensing observations. Unlike acute infection, chronic carriers contain only a low level of HBV core-antigen-specific T cell activity, contributing to the lack of viral clearance.Ĭopyright © 2018 Elsevier Ltd. Persistent HBV infection is caused mainly by ccc DNA and immune tolerance to HBV antigens in the liver. Capsids containing a mature rc DNA genome target to the nucleus for ccc DNA synthesis. Reverse transcription occurs in the capsids by using the pgRNA as a template for the synthesis of single-stranded linear and then partially double-stranded relaxed circular (rc) DNA. Its covalently closed circular (ccc) DNA in the nucleus encodes a pregenomic RNA (pgRNA), which can be encapsidated by HBV polymerase. HBV replicates via reverse transcription. An HBV surface-antigen vaccine is effective, but treatments are currently not curative.
Chronic hepatitis B can progress to an inactive carrier state, and then, in some patients, give rise to cirrhosis and cancer of the liver, leading to death. Hepatitis B virus (HBV) is a common worldwide blood-borne pathogen. This infographic about hepatitis B virus explores its replication cycle, natural history of infection and pathogenesis, and how this can be controlled and treated.
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