Second harmonic AC calorimetry technique within a diamond anvil cell

Tuning the energy density of matter at high pressures gives rise to exotic and often unprecedented properties, e.g., structural transitions, insulator-metal transitions, valence fluctuations, topological order, and the emergence of superconductivity. The study of specific heat has long been used to characterize these kinds of transitions, but their application to the diamond anvil cell (DAC) environment has proved challenging. Limited work has been done on the measurement of specific heat within DACs, in part due to the difficult experimental setup. To this end we have developed a novel method for the measurement of specific heat within a DAC that is independent of the DAC design and therefore readily compatible with any DACs already performing high pressure resistance measurements. As a proof-of-concept, specific heat measurements of the MgB2 superconductor were performed, showing a clear anomaly at the transition temperature (Tc), indicative of bulk superconductivity. This technique allows for specific heat measurements at higher pressure than previously possible.Comment: 5 pages with 5 figure

Post-drought decline of the Amazon carbon sink

Amazon forests have experienced frequent and severe droughts in the past two decades. However, little is known about the large-scale legacy of droughts on carbon stocks and dynamics of forests. Using systematic sampling of forest structure measured by LiDAR waveforms from 2003 to 2008, here we show a significant loss of carbon over the entire Amazon basin at a rate of 0.3 ± 0.2 (95% CI) PgC yr−1 after the 2005 mega-drought, which continued persistently over the next 3 years (2005–2008). The changes in forest structure, captured by average LiDAR forest height and converted to above ground biomass carbon density, show an average loss of 2.35 ± 1.80 MgC ha−1 a year after (2006) in the epicenter of the drought. With more frequent droughts expected in future, forests of Amazon may lose their role as a robust sink of carbon, leading to a significant positive climate feedback and exacerbating warming trends.The research was partially supported by NASA Terrestrial Ecology grant at the Jet Propulsion Laboratory, California Institute of Technology and partial funding to the UCLA Institute of Environment and Sustainability from previous National Aeronautics and Space Administration and National Science Foundation grants. The authors thank NSIDC, BYU, USGS, and NASA Land Processes Distributed Active Archive Center (LP DAAC) for making their data available. (NASA Terrestrial Ecology grant at the Jet Propulsion Laboratory, California Institute of Technology)Published versio

Tropical nighttime warming as a dominant driver of variability in the terrestrial carbon sink

The terrestrial biosphere is currently a strong carbon (C) sink but may switch to a source in the 21st century as climate-driven losses exceed CO2-driven C gains, thereby accelerating global warming. Although it has long been recognized that tropical climate plays a critical role in regulating interannual climate variability, the causal link between changes in temperature and precipitation and terrestrial processes remains uncertain. Here, we combine atmospheric mass balance, remote sensing-modeled datasets of vegetation C uptake, and climate datasets to characterize the temporal variability of the terrestrial C sink and determine the dominant climate drivers of this variability. We show that the interannual variability of global land C sink has grown by 50–100% over the past 50 y. We further find that interannual land C sink variability is most strongly linked to tropical nighttime warming, likely through respiration. This apparent sensitivity of respiration to nighttime temperatures, which are projected to increase faster than global average temperatures, suggests that C stored in tropical forests may be vulnerable to future warming

Vertebrate telomeres and telomere-interacting proteins

We have characterized telomere dynamics of normal and immortalized chicken cells in order to explore the possibility of using chicken cells as an alternate vertebrate model system to study telomere biology. We chose to study chicken cells because: (1) chicken primary cells have a limited life span in culture and exhibit low rates of spontaneous immortalization, and (2) chicken DT40 cells can be used to generate gene “knock-outs” in cell culture. After optimizing the conditions to isolate genomic DNA with minimal aggregation, we measured the length of telomeres from normal chicken cells using a novel non-denaturing Southern hybridization. We report that chicken telomeres are rather short (8–23kb). The telomerase expression profile in normal chicken tissues (three different donor ages) was also examined and we have found that telomerase is constitutively expressed in the germ line and in most somatic tissues examined. This expression profile mimics that observed in mice and differs from that of humans. The robust telomerase activity in embryonic tissues was rapidly down-regulated when a primary culture was established from this tissue and the culture senesced after undergoing 22–32 population doublings. The down-regulation of telomerase activity correlated well the with gradual loss of telomere length exhibited by the aging chicken embryonic fibroblasts. Therefore, like their human counterparts, telomere shortening acts as the signal that limits the proliferation of chicken cells in culture. The gene encoding chicken ortholog of human Tankyrase1, a protein with poly(ADP-ribose) polymerase activity localized to telomeres, has been isolated and found to be very well conserved (∼98% identical). The gene encoding another molecule called Tankyrase2, that has a similar modular architecture to Tankyrase1 and significant overall sequence identity, has also been isolated from chicken cells (∼85%). While Tankyrase1 displays a complex cellular localization, and is present at telomeres, the pericentriolar matrix and at nuclear pores, the cellular localization of Tankyrase2 is currently unknown. Based on sequence analysis, we hypothesize that Tankyrase1 and 2 may have both common and unique roles in cells. Their function(s) are currently being studied

Feedbacks of Vegetation on Summertime Climate Variability over the North American Grasslands. Part I: Statistical Analysis

ABSTRACT: Feedbacks of vegetation on summertime climate variability over the North American Grasslands are analyzed using the statistical technique of Granger causality. Results indicate that normalized difference vegetation index (NDVI) anomalies early in the growing season have a statistically measurable effect on precipitation and surface temperature later in summer. In particular, higher means and/or decreasing trends of NDVI anomalies tend t

Feedbacks of Vegetation on Summertime Climate Variability over the North American Grasslands: 1. Statistical Analysis

Feedbacks of vegetation on summertime climate variability over the North American Grasslands are analyzed using the statistical technique of Granger causality. Results indicate that NDVI (normalized difference vegetation index) anomalies early in the growing season have a statistically measurable effect on precipitation and surface temperature later in summer. In particular, higher means and/or decreasing trends of NDVI anomalies tend to be followed by lower rainfall but higher temperatures during July through September. These results suggest that initially enhanced vegetation may deplete soil moisture faster than normal, and thereby induce drier and warmer climate anomalies via the strong soil moisture/precipitation coupling in these regions. Consistent with this soil moisture/precipitation feedback mechanism, interactions between temperature and precipitation anomalies in this region indicate that moister and cooler conditions are also related to increases in precipitation during the preceding months. Because vegetation responds to soil moisture variations, interactions between vegetation and precipitation generate oscillations in NDVI anomalies at growing-season time scales