Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO
) represents one of the important interactions between anthropogenic emissions related to combustion and natural ...emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO
-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO
-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO
radical, the difficulty of characterizing the spatial distributions of BVOC and NO
within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry-climate models. This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO
-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO
-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.
Symbiotic nitrogen fixation (SNF) by higher plants and their bacterial symbionts is a globally important input of nitrogen. Our understanding of the mechanisms that control SNF and the time‐scales ...over which they operate has been constrained by the limitations of the existing methods for measuring SNF. One method, Acetylene Reduction Assays by Cavity ring‐down laser Absorption Spectroscopy (ARACAS), seems promising, as it is highly sensitive and gives rapid, continuous, repeatable and real‐time measurements of nitrogenase activity. ARACAS has been used to study nitrogen fixation in lichens, mosses and asymbiotic bacteria, but adapting it to higher plants poses challenges because acetylene and ethylene can influence plant function.
Here, we report modifications to ARACAS that allow it to be used on higher plants in an environmentally controlled incubation chamber. The modifications include lower concentrations of acetylene (2%) and ethylene and concurrent measurements of whole‐chamber CO2 exchange, H2O exchange and nitrogenase activity, linking nitrogenase activity to whole‐plant rates of photosynthesis and respiration.
After propagating the error terms from all sources, we establish the following parameters of the method: (a) The detection limit of our method was 2–3 ppbv C2H4 per hour, although it rose substantially when we used tank‐derived acetylene, which has much higher ethylene contamination; (b) Repeated measures at a frequency of 3 days or longer did not diminish nitrogenase activity or photosynthesis, although daily measurements diminished nitrogenase activity; (c) This method can detect changes at time‐scales as short as seconds; (d) Continuous measurement of nitrogenase activity is maintained above 90% of the maximum rate for 7.0 ± 1.3 (M ± SD) hours.
This method has the potential to improve our understanding of the controls over SNF, and therefore, how SNF and global nitrogen and carbon cycling are likely to be affected by global change.
Paranthropus boisei was first described in 1959 based on fossils from the Olduvai Gorge and now includes many fossils from Ethiopia to Malawi. Knowledge about its postcranial anatomy has remained ...elusive because, until recently, no postcranial remains could be reliably attributed to this taxon. Here, we report the first associated hand and upper limb skeleton (KNM-ER 47000) of P. boisei from 1.51 to 1.53 Ma sediments at Ileret, Kenya. While the fossils show a combination of primitive and derived traits, the overall anatomy is characterized by primitive traits that resemble those found in Australopithecus, including an oblique scapular spine, relatively long and curved ulna, lack of third metacarpal styloid process, gracile thumb metacarpal, and curved manual phalanges. Very thick cortical bone throughout the upper limb shows that P. boisei had great upper limb strength, supporting hypotheses that this species spent time climbing trees, although probably to a lesser extent than earlier australopiths. Hand anatomy shows that P. boisei, like earlier australopiths, was capable of the manual dexterity needed to create and use stone tools, but lacked the robust thumb of Homo erectus, which arguably reflects adaptations to the intensification of precision grips and tool use. KNM-ER 47000 provides conclusive evidence that early Pleistocene hominins diverged in postcranial and craniodental anatomy, supporting hypotheses of competitive displacement among these contemporaneous hominins.
Summary
Metagenomics uses gene expression patterns to understand the taxonomy and metabolic activities of microbial communities. Metaproteomics applies the same approach to community proteomes. ...Previously, we used a novel three‐dimensional peptide separation method to identify over 2000 salivary proteins. This study used those data to carry out the first metaproteomic analysis of the human salivary microbiota. The metagenomic software MEGAN generated a phylogenetic tree, which was checked against the Human Oral Microbiome Database (HOMD). Pathway analyses were performed with the Clusters of Orthologous Groups and MetaCyc databases. Thirty‐seven per cent of the peptides were identifiable only at the level of cellular organisms or bacteria. The rest were distributed among five bacterial phyla (61%), archea (0.5%), and viruses (0.8%); 29% were assignable at the genus level, and most belonged to Streptococcus (17%). Eleven per cent of all peptides could be assigned to species. Most taxa were represented in HOMD and they included well‐known species such as periodontal pathogens. However, there also were ‘exotic’ species including aphid endosymbionts; plant, water, and soil bacteria; extremophiles; and archea. The pathway analysis indicated that peptides were linked to translation (37%), followed by glycolysis (19%), amino acid metabolism (8%), and energy production (8%). The taxonomic structure of the salivary metaproteome is very diverse but is dominated by streptococci. ‘Exotic’ species may actually represent close relatives that have not yet been sequenced. Salivary microbes appear to be actively engaged in protein synthesis, and the pathway analysis is consistent with the metabolism of salivary glycoproteins.
Rapid environmental change at high latitudes is predicted to greatly alter the diversity, structure, and function of plant communities, resulting in changes in the pools and fluxes of nutrients. In ...Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying warming is known to impact plant diversity and ecosystem function; however, to date, most studies examining Arctic nutrient enrichment focus on the impact of relatively large (>25x estimated naturally occurring N enrichment) doses of nutrients on plant community composition and net primary productivity. To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming‐induced fertilization. In addition, we compared our measured ecosystem CO2 flux data to a widely used Arctic ecosystem exchange model to investigate the ability to predict the capacity for CO2 exchange with nutrient addition. We observed declines in abundance‐weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to the model, we found that the model explained roughly 30%–50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization—over an order of magnitude or more than warming‐induced rates—significantly alter the capacity for tundra CO2 exchange. Overall, our findings highlight the value of measuring and modeling the impacts of a nutrient enrichment gradient, as warming‐related nutrient availability may impact ecosystems differently than single‐level fertilization experiments.
To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming‐induced fertilization. We observed declines in abundance‐weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to a widely used ecosystem CO2 exchange model, we found that the model explained roughly 30%–50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization—over an order of magnitude or more than warming‐induced rates—significantly alter the capacity for tundra CO2 exchange.
Many piezoelectric microelectromechanical systems (MEMS) measure or generate acoustic signals via the motion of radially non-uniform, thin film composite plates. The composite layers provide ...piezoelectric actuation, structural support, electrode metallization, passivation, etc. Often, the layers are non-uniform over the plate and contain residual stresses introduced during the fabrication process. Accurate models of non-uniform composite plate mechanics are crucial for predicting and optimizing device performance. In this paper, an analytical solution for a radially non-uniform, piezoelectric, circular composite plate incorporating residual stress is derived. The analytical solution is compared to experimental measurements of a MEMS piezoelectric diaphragm. The results show the improved accuracy of the analytical model when including film stress, the speed of the analytical solution as compared to finite element analysis, the sensitivity of device performance to residual stress and the importance of accurate film stresses as model inputs. The analytical model presented is useful as a design optimization tool given the efficiency of the computational time, shown to be 275 times less than a comparable finite element analysis.
Substituted guanines and pyrimidines were tested as inhibitors of cyclin B1/CDK1 and cyclin A3/CDK2 and soaked into crystals of monomeric CDK2. O 6-Cyclohexylmethylguanine (NU2058) was a competitive ...inhibitor of CDK1 and CDK2 with respect to ATP (K i values: CDK1, 5 ± 1 μM; CDK2, 12 ± 3 μM) and formed a triplet of hydrogen bonds (i.e., NH-9 to Glu 81, N-3 to Leu 83, and 2-NH2 to Leu 83). The triplet of hydrogen bonding and CDK inhibition was reproduced by 2,6-diamino-4-cyclohexylmethyloxy-5-nitrosopyrimidine (NU6027, K i values: CDK1, 2.5 ± 0.4 μM; CDK2, 1.3 ± 0.2 μM). Against human tumor cells, NU2058 and NU6027 were growth inhibitory in vitro (mean GI50 values of 13 ± 7 μM and 10 ± 6 μM, respectively), with a pattern of sensitivity distinct from flavopiridol and olomoucine. These CDK inhibition and chemosensitivity data indicate that the distinct mode of binding of NU2058 and NU6027 has direct consequences for enzyme and cell growth inhibition.
We present a method to infer CO2 emissions from
individual power plants based on satellite observations of co-emitted
nitrogen dioxide (NO2), which could serve as complementary verification
of ...bottom-up inventories or be used to supplement these inventories. We
demonstrate its utility on eight large and isolated US power plants, where
accurate stack emission estimates of both gases are available for
comparison. In the first step of our methodology, we infer nitrogen oxides
(NOx) emissions from US power plants using Ozone Monitoring Instrument
(OMI) NO2 tropospheric vertical column densities (VCDs) averaged over
the ozone season (May–September) and a “top-down” approach that we
previously developed. Second, we determine the relationship between NOx
and CO2 emissions based on the direct stack emissions measurements
reported by continuous emissions monitoring system (CEMS) programs,
accounting for coal quality, boiler firing technology, NOx emission
control device type, and any change in operating conditions. Third, we
estimate CO2 emissions for power plants using the OMI-estimated
NOx emissions and the CEMS NOx∕CO2 emission ratio. We find
that the CO2 emissions estimated by our satellite-based method during
2005–2017 are in reasonable agreement with the US CEMS measurements, with a
relative difference of 8 %±41 % (mean ± standard
deviation). The broader implication of our methodology is that it has the
potential to provide an additional constraint on CO2 emissions from
power plants in regions of the world without reliable emissions accounting.
We explore the feasibility by comparing the derived NOx∕CO2
emission ratios for the US with those from a bottom-up emission inventory
for other countries and applying our methodology to a power plant in South
Africa, where the satellite-based emission estimates show reasonable
consistency with other independent estimates. Though our analysis is limited
to a few power plants, we expect to be able to apply our method to more US
(and world) power plants when multi-year data records become available from
new OMI-like sensors with improved capabilities, such as the TROPOspheric
Monitoring Instrument (TROPOMI), and upcoming geostationary satellites, such
as the Tropospheric Emissions: Monitoring Pollution (TEMPO) instrument.
The human forefoot presents an interesting biomechanical problem of clinical importance because loads are distributed unequally across multiple bones. The fact that long bones typically have a ...several-fold safety factor relative to peak loads suggests that metatarsal strengths should be related to their peak loads. This study is the first to systematically examine the cross-sectional geometric properties of the human forefoot and their relationship to external loads during walking and running. We report midlength cross-sectional geometric properties (
CA,
Ix,
Iy,
Imax,
Imin,
J,
Zx, and
Zy) of metatarsals (1–5) and the hallucial proximal phalanx of a shod industrial population (
n = 40) obtained using computed tomography. We then examine the relationship between these measures of shaft strength and published plantar pressure data sets recorded during the following functional activities: standing, at the push-off stage of the walking cycle, the full walking cycle, and running. Cross-sectional geometric properties of the first ray are greater than those of other rays, even when scaled to bone length. This pattern corresponds to the high pressures recorded for the first ray during most activities. The relationships between cross-sectional geometric properties of the lateral metatarsals and peak plantar pressure data are more complex. Metatarsals 2–4 are weakest in most cross-sectional geometric properties. However, metatarsal 2, and to a lesser extent metatarsal 3, experience relatively high peak pressures. On average, geometric measures of axial and bending strengths (adjusted relative to body size) are lower in females than males, and in European Americans than in African Americans, which corresponds to the respective rates of general metatarsal stress fracture in these groups. The discrepancy between strength and plantar pressure values in metatarsals 2 and 3 is consistent with the high incidence of stress fractures in these bones and underscores the importance of soft tissues, such as the plantar fascia and flexor musculature, in moderating metatarsal shaft strain.
Fossil-fuel CO2 emissions and their trends in eight U.S. megacities during 2006–2017 are inferred by combining satellite-derived NOX emissions with bottom-up city-specific NOX-to-CO2 emission ratios. ...A statistical model is fit to a collection NO2 plumes observed from the Ozone Monitoring Instrument (OMI), and is used to calculate top-down NOX emissions. Decreases in OMI-derived NOX emissions are observed across the eight cities from 2006 to 2017 (−17% in Miami to −58% in Los Angeles), and are generally consistent with long-term trends of bottom-up inventories (−25% in Miami to −49% in Los Angeles), but there are some interannual discrepancies. City-specific NOX-to-CO2 emission ratios, used to calculate inferred CO2, are estimated through annual bottom-up inventories of NOX and CO2 emissions disaggregated to 1 × 1 km2 resolution. Over the study period, NOX-to-CO2 emission ratios have decreased by ~40% nationwide (−24% to −51% for our studied cities), which is attributed to a faster reduction in NOX when compared to CO2 due to policy regulations and fuel type shifts. Combining top-down NOX emissions and bottom-up NOX-to-CO2 emission ratios, annual fossil-fuel CO2 emissions are derived. Inferred OMI-based top-down CO2 emissions trends vary between +7% in Dallas to −31% in Phoenix. For 2017, we report annual fossil-fuel CO2 emissions to be: Los Angeles 113 ± 49 Tg/yr; New York City 144 ± 62 Tg/yr; and Chicago 55 ± 24 Tg/yr. A study in the Los Angeles area, using independent methods, reported a 2013–2016 average CO2 emissions rate of 104 Tg/yr and 120 Tg/yr, which suggests that the CO2 emissions from our method are in good agreement with other studies' top-down estimates. We anticipate future remote sensing instruments – with better spatial and temporal resolution – will better constrain the NOX-to-CO2 ratio and reduce the uncertainty in our method.
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•Top-down NOX emissions and inventory-based NOX-to-CO2 ratios are used to infer CO2.•NOX and CO2 emissions are both decreasing, but NOx is decreasing faster over time.•Our inferred CO2 emissions agree well with other top-down methods in the LA basin.
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