We used a mechanistic physical model to examine the effect of variability in dissolved organic carbon (DOC) concentrations on the physical properties of small temperate lakes. The model was validated ...on eight small (6 × 10−4 to 3.8 × 10−2 km²) lakes in Wisconsin and Michigan, with a standard error , 1°C for seven of eight lakes. Attenuation of photosynthetically active radiation (400-700 nm) in these lakes was regulated by DOC concentrations and was important in the vertical structuring of water temperatures. Heat exchange below the surface mixed layer was near the molecular rate, increasing the importance of water clarity as a control on the heat content of deeper waters. To understand the thermal effects of changing DOC concentrations, we applied scenarios of a 50% increase and 50% decrease in DOC concentrations for one lake (Trout Bog) and found water temperatures to vary in response, with the seasonally averaged temperatures in the increased DOC scenario being > 2°C colder than the reduced scenario. We found a nonlinear relationship between DOC and temperature, with clearer (lower DOC) simulations being more sensitive to climate variability, suggesting that DOC may act as a buffer against a warming climate. Our model showed that DOC also influenced epilimnetic depths, as nocturnal mixing (related to the vertical partitioning of heat) was more important than wind-driven mixing. Small lakes are globally important regulators of biogeochemical cycles and are structurally different from larger lakes. Important feedbacks to physical processes must be accounted for when understanding the effects of changing DOC and climate on small lakes.
In this study, 1219 HIV-uninfected, heterosexual adults in Botswana were randomly assigned to tenofovir–emtricitabine (TDF–FTC) or placebo. The TDF–FTC group had a lower incidence of HIV infection ...but increased rates of side effects, including a significant loss of bone density.
Biomedical strategies to prevent sexual transmission of human immunodeficiency virus (HIV) remain limited.
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In animal models, preexposure prophylaxis with tenofovir disoproxil fumarate (TDF) or with the combination of TDF and emtricitabine (TDF–FTC) can prevent infections with HIV or hybrid simian–human immunodeficiency virus after vaginal or rectal challenge.
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,
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In humans, daily preexposure prophylaxis with TDF–FTC has been shown to reduce transmission of HIV by 44% among men who have sex with men
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; however, the findings from studies in heterosexual populations have been mixed.
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Botswana has the world's second highest prevalence of HIV infection, estimated in 2008 to be . . .
Abstract
Atmospheric warming heats lakes, but the causes of variation among basins are poorly understood. Here, multi-decadal profiles of water temperatures, trophic state, and local climate from 345 ...temperate lakes are combined with data on lake geomorphology and watershed characteristics to identify controls of the relative rates of temperature change in water (WT) and air (AT) during summer. We show that differences in local climate (AT, wind speed, humidity, irradiance), land cover (forest, urban, agriculture), geomorphology (elevation, area/depth ratio), and water transparency explain >30% of the difference in rate of lake heating compared to that of the atmosphere. Importantly, the rate of lake heating slows as air warms (
P
< 0.001). Clear, cold, and deep lakes, especially at high elevation and in undisturbed catchments, are particularly responsive to changes in atmospheric temperature. We suggest that rates of surface water warming may decline relative to the atmosphere in a warmer future, particularly in sites already experiencing terrestrial development or eutrophication.
Solid-state quantum emitters that couple coherent optical transitions to long-lived spin qubits are essential for quantum networks. Here we report on the spin and optical properties of individual ...tin-vacancy (SnV) centers in diamond nanostructures. Through cryogenic magneto-optical and spin spectroscopy, we verify the inversion-symmetric electronic structure of the SnV, identify spin-conserving and spin-flipping transitions, characterize transition linewidths, measure electron spin lifetimes, and evaluate the spin dephasing time. We find that the optical transitions are consistent with the radiative lifetime limit even in nanofabricated structures. The spin lifetime is phonon limited with an exponential temperature scaling leading to T_{1}>10 ms, and the coherence time, T_{2}^{*} reaches the nuclear spin-bath limit upon cooling to 2.9 K. These spin properties exceed those of other inversion-symmetric color centers for which similar values require millikelvin temperatures. With a combination of coherent optical transitions and long spin coherence without dilution refrigeration, the SnV is a promising candidate for feasable and scalable quantum networking applications.
Extracellular vesicles and exomere nanoparticles are under intense investigation as sources of clinically relevant cargo. Here we report the discovery of a distinct extracellular nanoparticle, termed ...supermere. Supermeres are morphologically distinct from exomeres and display a markedly greater uptake in vivo compared with small extracellular vesicles and exomeres. The protein and RNA composition of supermeres differs from small extracellular vesicles and exomeres. Supermeres are highly enriched with cargo involved in multiple cancers (glycolytic enzymes, TGFBI, miR-1246, MET, GPC1 and AGO2), Alzheimer's disease (APP) and cardiovascular disease (ACE2, ACE and PCSK9). The majority of extracellular RNA is associated with supermeres rather than small extracellular vesicles and exomeres. Cancer-derived supermeres increase lactate secretion, transfer cetuximab resistance and decrease hepatic lipids and glycogen in vivo. This study identifies a distinct functional nanoparticle replete with potential circulating biomarkers and therapeutic targets for a host of human diseases.
Ecosystem respiration Solomon, Christopher T.; Bruesewitz, Denise A.; Richardson, David C. ...
Limnology and oceanography,
20/May , Letnik:
58, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We assembled data from a global network of automated lake observatories to test hypotheses regarding the drivers of ecosystem metabolism. We estimated daily rates of respiration and gross primary ...production (GPP) for up to a full year in each lake, via maximum likelihood fits of a free-water metabolism model to continuous high-frequency measurements of dissolved oxygen concentrations. Uncertainties were determined by a bootstrap analysis, allowing lake-days with poorly constrained rate estimates to be down-weighted in subsequent analyses. GPP and respiration varied considerably among lakes and at seasonal and daily timescales. Mean annual GPP and respiration ranged from 0.1 to 5.0 mg O2 L−1 d−1 and were positively related to total phosphorus but not dissolved organic carbon concentration. Within lakes, significant day-to-day differences in respiration were common despite large uncertainties in estimated rates on some lake-days. Daily variation in GPP explained 5% to 85% of the daily variation in respiration after temperature correction. Respiration was tightly coupled to GPP at a daily scale in oligotrophic and dystrophic lakes, and more weakly coupled in mesotrophic and eutrophic lakes. Background respiration ranged from 0.017 to 2.1 mg O₂ L−1 d−1 and was positively related to indicators of recalcitrant allochthonous and autochthonous organic matter loads, but was not clearly related to an indicator of the quality of allochthonous organic matter inputs.
Ecosystems are responding to broad‐scale changes in climate and other factors in complex ways. Two key changes occurring in many inland waterbodies are increasing temperatures and increasing ...terrestrial dissolved organic matter (tDOM) inputs. Due in part to tDOM inputs, inland waters play an important role in the global carbon cycle, with release of CO2 from these ecosystems a substantial portion of the combined carbon sinks of terrestrial ecosystems and the oceans.
Ecosystem respiration (ER) is an important mechanism regulating CO2 in aquatic systems, and ER rates are temperature‐dependent. However, it is unknown how ER rates will change in the future because ER is sensitive to factors other than temperature, such as the concentration and source of organic matter. Theory posits that ER rates supported by refractory carbon compounds should exhibit a greater temperature dependence than ER rates supported by labile carbon compounds, but empirical tests of this theory are inconclusive.
We experimentally manipulated temperature and carbon quality in mesocosms while monitoring dissolved oxygen (DO) with in situ high frequency DO sensors. We used two highly divergent, natural DOM sources and diluted the more refractory source so that dissolved organic carbon concentrations were similar in all mesocosms. We calculated daily ER rates over 27 days in each mesocosm.
We found that ER increased more with temperature when tDOM dominated the organic carbon pool. Given widespread increases in temperature and tDOM inputs to aquatic ecosystems, these results highlight important interactions governing how ecosystems may respond to concurrent environmental changes and alter their contributions to the global carbon cycle.
High‐frequency physical observations from 40 temperate lakes were used to examine the relative contributions of wind shear (u*) and convection (w*) to turbulence in the surface mixed layer. Seasonal ...patterns of u* and w* were dissimilar; u* was often highest in the spring, while w*increased throughout the summer to a maximum in early fall. Convection was a larger mixed‐layer turbulence source than wind shear (u*/w* < 0.75) for 18 of the 40 lakes, including all 11 lakes <10 ha. As a consequence, the relative contribution of convection to the gas transfer velocity (k, estimated by the surface renewal model) was greater for small lakes. The average k was 0.54 m day−1 for lakes <10 ha. Because u* and w*differ in temporal pattern and magnitude across lakes, both convection and wind shear should be considered in future formulations of lake‐air gas exchange, especially for small lakes.
Key Points
Convection was consistently a larger turbulence source than wind for small lakes
Convection and wind shear have different diurnal seasonal and geographic pattern
Wind‐only methods for gas exchange are not appropriate for small lakes
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