Recent contrasting winter temperature changes over North America linked to enhanced positive Pacific‐North American pattern

Recently enhanced contrasts in winter (December‐January‐February) mean temperatures and extremes (cold southeast and warm northwest) across North America have triggered intensive discussion both within and outside of the scientific community, but the mechanisms responsible for these contrasts remain unresolved. Here we use a combination of observations and reanalysis data sets to show that the strengthened contrasts in winter mean temperatures and extremes across North America are closely related to an enhancement of the positive Pacific‐North American (PNA) pattern during the second half of the 20th century. Recent intensification of positive PNA events is associated with amplified planetary waves over North America, driving cold‐air outbreaks into the southeast and warm tropical/subtropical air into the northwest. This not only results in a strengthened winter mean temperature contrast but increases the occurrence of the opposite‐signed extremes in these two regions.Key PointsThe enhanced contrasts in winter mean temperatures and extremes in North America are observedRecent enhancement of positive PNA is a main cause of the contrasting winter temperature changesThe study provides a framework for detection and attribution of climate change in North AmericaPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115952/1/grl53404_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/115952/2/grl53404.pd

Two-stage soil infiltration treatment system for treating ammonium wastewaters of low COD/TN ratios

Soil infiltration treatment (SIT) is ineffective to treat ammonium wastewaters of total nitrogen (TN) > 100 mg l−1. This study applied a novel two-stage SIT process for effective TN removal from wastewaters of TN > 100 mg l−1 and of chemical oxygen demand (COD)/TN ratio of 3.2–8.6. The wastewater was first fed into the soil column (stage 1) at hydraulic loading rate (HLR) of 0.06 m3 m−2 d−1 for COD removal and total phosphorus (TP) immobilization. Then the effluent from stage 1 was fed individually into four soil columns (stage 2) at 0.02 m3 m−2 d−1 of HLR with different proportions of raw wastewater as additional carbon source. Over the one-year field test, balanced nitrification and denitrification in the two-stage SIT revealed excellent TN removal (>90%) from the tested wastewaters

Functional soil organic matter fractions in response to long-term fertilization in upland and paddy systems in South China

Soil organic matter (SOM) and its fractions play key roles in optimizing crop yield and improving soil quality. However, how functional SOM fractions responded to long-term fertilization and their relative importance for C sequestration were less addressed. In this study, we determined the effects of long-term fertilization on six functional SOM fractions (unprotected, physically protected, physico-biochemically protected, physico-chemically protected, chemically protected, and biochemically protected) based on two long-term fertilization experiments carried out in South China. The unprotected coarse particulate organic matter (cPOM), the biochemically and chemically protected silt-sized fractions (NH-dSilt and H-dSilt) were the primary C storage fractions under long-term fertilization, accounting for 23.6–46.2%, 15.7–19.4%, and 14.4–17.4% of the total soil organic carbon (SOC) content in upland soil and 19.5–29.3%, 9.9–15.5%, and 14.2–17.2% of the total SOC content in paddy soil, respectively. Compared with the control treatment (CK) in upland soil, the application of manure combined with mineral NPK (NPKM) resulted in an increase in the SOC content in the cPOM, pure physically protected fraction (iPOM), the physico-chemically protected (H-μSilt), and the chemically protected (H-dSilt) fraction by 233%, 166%, 124%, and 58%, respectively. Besides, the SOC increase in upland soil expressed as SOC content per unit of total SOC for iPOM, H-μSilt, cPOM and H-dSilt were the highest and as large as 283%, 248%, 194%, and 105% respectively. In paddy soil, the highest increase per unit of total SOC was H-dSilt (190%), followed by H-dClay (156%) and H-μSilt (155%). These results suggested that the upland soil could stabilize more C through the pure physical, whereas the chemical protection mechanism played a more important role in paddy soil. Chemical protection mechanism within the microaggregates played important roles in sequestrating C in both upland and paddy soils. Overall, the different responses of functional SOM fractions to long-term fertilization indicate different mechanisms for SOM cycling in terms of C sequestration under upland and paddy systems

A synthetic analysis of greenhouse gas emissions from manure amended agricultural soils in China

Application of manure has been recommended as an effective strategy to mitigate climate change. However, the magnitude of greenhouse gases emission derived by application of manure to agricultural soils across environmental conditions still remains unclear. Here, we synthesized data from 379 observations in China and quantified the responses of soil nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) emissions to manure (Org-M) in comparison to chemical fertilizers (Min-F) or non-fertilizers (Non-F). The results showed that N2O, CO2 and CH4 emissions were significantly affected by Org-M compared to Min-F (percentage change: −3, +15 and +60%, P <0.05) and Non-F (percentage change: +289, +84 and +83%, P<0.05), respectively. However, at the same amount of total N input, Org-M decreased soil N2O emission by 13% and CH4 emission by 12%, and increased soil CO2 emission by 26% relative to Min-F in upland soils. For paddy soils, N2O, CO2 and CH4 emissions differed by −3%, −36% and +84% between Org-M and Min-F (i.e., Org-M minus Min-F). Thus, practices such as application of manure instead of chemical fertilizer and decreasing nitrogen input rate need to be highly considered and optimized under different soils and climate conditions to mitigate GHGs emission in China

Human mucosal-associated invariant T cells contribute to antiviral influenza immunity via IL-18–dependent activation

Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes known to elicit potent immunity to a broad range of bacteria, mainly via the rapid production of inflammatory cytokines. Whether MAIT cells contribute to antiviral immunity is less clear. Here we asked whether MAIT cells produce cytokines/chemokines during severe human influenza virus infection. Our analysis in patients hospitalized with avian H7N9 influenza pneumonia showed that individuals who recovered had higher numbers of CD161+Vα7.2+ MAIT cells in peripheral blood compared with those who succumbed, suggesting a possible protective role for this lymphocyte population. To understand the mechanism underlying MAIT cell activation during influenza, we cocultured influenza A virus (IAV)-infected human lung epithelial cells (A549) and human peripheral blood mononuclear cells in vitro, then assayed them by intracellular cytokine staining. Comparison of influenza-induced MAIT cell activation with the profile for natural killer cells (CD56+CD3−) showed robust up-regulation of IFNγ for both cell populations and granzyme B in MAIT cells, although the individual responses varied among healthy donors. However, in contrast to the requirement for cell-associated factors to promote NK cell activation, the induction of MAIT cell cytokine production was dependent on IL-18 (but not IL-12) production by IAV-exposed CD14+ monocytes. Overall, this evidence for IAV activation via an indirect, IL-18–dependent mechanism indicates that MAIT cells are protective in influenza, and also possibly in any human disease process in which inflammation and IL-18 production occur

Effects of Lactobacillus plantarum on the Fermentation Profile and Microbiological Composition of Wheat Fermented Silage Under the Freezing and Thawing Low Temperatures

The corruption and/or poor quality of silages caused by low temperature and freeze-thaw conditions makes it imperative to identify effective starters and low temperature silage fermentation technology that can assist the animal feed industry and improve livestock productivity. The effect of L. plantarum QZ227 on the wheat silage quality was evaluated under conditions at constant low temperatures followed by repeated freezing and thawing at low temperatures. QZ227 became the predominant strain in 10 days and underwent a more intensive lactic acid bacteria fermentation than CK. QZ227 accumulated more lactic acid, but lower pH and ammonia nitrogen in the fermentation. During the repeated freezing and thawing process, the accumulated lactic acid in the silage fermented by QZ227 remained relatively stable. Relative to CK, QZ227 reduced the abundance of fungal pathogens in silage at a constant 5°C, including Aspergillus, Sporidiobolaceae, Hypocreaceae, Pleosporales, Cutaneotrichosporon, Alternaria, and Cystobasidiomycetes. Under varying low temperature conditions from days 40 to days 60, QZ227 reduced the pathogenic abundance of fungi such as Pichia, Aspergillus, Agaricales, and Plectosphaerella. QZ227 also reduced the pathogenic abundance of Mucoromycota after the silage had been exposed to oxygen. In conclusion, QZ227 can be used as a silage additive in the fermentation process at both constant and variable low temperatures to ensure fast and vigorous fermentation because it promotes the rapid accumulation of lactic acid, and reduces pH values and aerobic corruption compared to the CK

Enhanced bioconversion of hydrogen and carbon dioxide to methane using a micro-nano sparger system: mass balance and energy consumption

Simultaneous CO2 removal with renewable biofuel production can be achieved by methanogens through conversion of CO2 and H2 into CH4. However, the low gas–liquid mass transfer (kLa) of H2 limits the commercial application of this bioconversion. This study tested and compared the gas–liquid mass transfer of H2 by using two stirred tank reactors (STRs) equipped with a micro-nano sparger (MNS) and common micro sparger (CMS), respectively. MNS was found to display superiority to CMS in methane production with the maximum methane evolution rate (MER) of 171.40 mmol/LR/d and 136.10 mmol/LR/d, along with a specific biomass growth rate of 0.15 d−1 and 0.09 d−1, respectively. Energy analysis indicated that the energy-productivity ratio for MNS was higher than that for CMS. This work suggests that MNS can be used as an applicable resolution to the limited kLa of H2 and thus enhance the bioconversion of H2 and CO2 to CH4

Hot-Carrier Cooling in High-Quality Graphene is Intrinsically Limited by Optical Phonons

Many promising optoelectronic devices, such as broadband photodetectors, nonlinear frequency converters, and building blocks for data communication systems, exploit photoexcited charge carriers in graphene. For these systems, it is essential to understand, and eventually control, the cooling dynamics of the photoinduced hot-carrier distribution. There is, however, still an active debate on the different mechanisms that contribute to hot-carrier cooling. In particular, the intrinsic cooling mechanism that ultimately limits the cooling dynamics remains an open question. Here, we address this question by studying two technologically relevant systems, consisting of high-quality graphene with a mobility >10,000 cm$^2$V$^{-1}$s$^{-1}$ and environments that do not efficiently take up electronic heat from graphene: WSe$_2$-encapsulated graphene and suspended graphene. We study the cooling dynamics of these two high-quality graphene systems using ultrafast pump-probe spectroscopy at room temperature. Cooling via disorder-assisted acoustic phonon scattering and out-of-plane heat transfer to the environment is relatively inefficient in these systems, predicting a cooling time of tens of picoseconds. However, we observe much faster cooling, on a timescale of a few picoseconds. We attribute this to an intrinsic cooling mechanism, where carriers in the hot-carrier distribution with enough kinetic energy emit optical phonons. During phonon emission, the electronic system continuously re-thermalizes, re-creating carriers with enough energy to emit optical phonons. We develop an analytical model that explains the observed dynamics, where cooling is eventually limited by optical-to-acoustic phonon coupling. These fundamental insights into the intrinsic cooling mechanism of hot carriers in graphene will play a key role in guiding the development of graphene-based optoelectronic devices