摘要 :
Hydrogen (H-2) is a crucial electron donor for many processes in the environment including nitrate-, sulfate-and, iron-reduction, homoacetogenesis, and methanogenesis, and is a major determinant of microbial competition and metabo...
展开
Hydrogen (H-2) is a crucial electron donor for many processes in the environment including nitrate-, sulfate-and, iron-reduction, homoacetogenesis, and methanogenesis, and is a major determinant of microbial competition and metabolic pathways in groundwater, sediments, and soils. Despite the importance of H-2 for many microbial processes in the environment, the total H-2 consuming capacity (or H-2 demand) of soils is generally unknown. Using soil microcosms with added H-2, the aims of this study were 1) to measure the H-2 demand of geochemically diverse soils and 2) to define the processes leading to this demand. Study results documented a large range of H(2 )demand in soil (0.034-1.2 millielectron equivalents H(2 )g(-1) soil). The measured H-2 demand greatly exceeded the theoretical demand predicted based on measured concentrations of common electron acceptors initially present in a library of 15 soils. While methanogenesis accounted for the largest fraction of H(2 )demand, humic acid reduction and acetogenesis were also significant contributing H-2-consuming processes. Much of the H-2 demand could be attributed to CO(2 )produced during incubation from fermentation and/or acetoclastic methanogenesis.The soil initial total organic carbon showed the strongest correlation to H-2 demand. Besides external additions, H(2 )was likely generated or cycled in the microcosms. Apart from fermentative H-2 production, carboxylate elongation to produce C4-C7 fatty acids may have accounted for additional H(2 )production in these soils. Many of these processes, especially the organic carbon contribution is underestimated in microbial models for H-2 consumption in natural soil ecosystems or during bioremediation of contaminants in soils.
收起
摘要 :
This paper reviews materials challenges and recent progress for selective area regrowth and doping for vertical gallium nitride (GaN) power devices. The purpose is to realize randomly placed, reliable, contactable, and generally u...
展开
This paper reviews materials challenges and recent progress for selective area regrowth and doping for vertical gallium nitride (GaN) power devices. The purpose is to realize randomly placed, reliable, contactable, and generally useable laterally patterned p-n junctions, which are the building blocks for various advanced power rectifiers and transistors. The general regrowth process and regrowth dynamics in trenches were discussed, where the effects of trench geometries, growth methods, and bulk substrates were elucidated. Comprehensive materials characterization techniques were utilized to analyze the regrown structures, including scanning electron microscopy, transmission electron microscopy, atom probe tomography, scanning probe microscopy, and secondary-ion mass spectrometry. Cathodoluminescence and secondary electrons in scanning electron microscopy and atom probe tomography were used to achieve lateral and vertical dopant profiling at a sub-micron scale. The regrowth interface after dry etching accumulated a high density of impurities and charges, contributing to the formation of a p+-n+ tunneling junction. This hypothesis was further confirmed by the electrostatic potential profile at the regrowth interface using electron holography. Novel etching technologies were investigated to improve the regrowth interface. It was found that low-power dry etching significantly reduced the interfacial charges and the reverse leakage currents of regrown p-n junctions. Photoelectrochemical wet etching was found to be effective in reducing deep-level defects near the regrowth interface. Atomic layer etching uses self-limiting chemical processes, thus removing the damaged layers without inducing further etching damage. Tertiarybutylchloride-based in situ etching may serve as an alternative etching method to dry etching with reduced etching damage. In terms of devices, regrown p-n junctions with low leakage currents and vertical junction field-effect transistors were demonstrated. Further improvements in selective area regrowth and associated devices can be expected using regrowth optimization and regrowth interface engineering via surface treatments and low-damage etching. These results represent an important step towards realizing selective area regrowth and doping for high performance GaN power electronics devices and systems.
收起
摘要 :
Urban Search and Rescue (USAR) missions continue to benefit from the incorporation of human-robot teams (HRTs). USAR environments can be ambiguous, hazardous, and unstable. The integration of robot teammates into USAR missions has...
展开
Urban Search and Rescue (USAR) missions continue to benefit from the incorporation of human-robot teams (HRTs). USAR environments can be ambiguous, hazardous, and unstable. The integration of robot teammates into USAR missions has enabled human teammates to access areas of uncertainty, including hazardous locations. For HRTs to be effective, it is pertinent to understand the factors that influence team effectiveness, such as having shared goals, mutual understanding, and efficient communication. The purpose of our research is to determine how to (1) better establish human trust, (2) identify useful levels of robot transparency and robot explanations, (3) ensure situation awareness, and (4) encourage a bipartisan role amongst teammates. By implementing robot transparency and robot explanations, we found that the driving factors for effective HRTs rely on robot explanations that are context-driven and are readily available to the human teammate.
收起
摘要 :
Human G-protein coupled receptor kinase 6 (GRK6) belongs to the GRK4 kinase subfamily of the G proteincoupled receptor kinase family which comprises of GRK1, GRK2, and GRK4. These kinases phosphorylate ligand-activated G-protein c...
展开
Human G-protein coupled receptor kinase 6 (GRK6) belongs to the GRK4 kinase subfamily of the G proteincoupled receptor kinase family which comprises of GRK1, GRK2, and GRK4. These kinases phosphorylate ligand-activated G-protein coupled receptors (GPCRs), driving heterotrimeric G protein coupling, desensitization of GPCR, and beta-arrestin recruitment. This reaction series mediates cellular signal pathways for cell survival, proliferation, migration and chemotaxis. GRK6 is a kinase target in multiple myeloma since it is highly expressed in myeloma cells compared to epithelial cells and has a significant role in mediating the chemotactic responses of T and B-lymphocytes. To support structure-based drug design, we describe three human GRK6 constructs, GRK6, GRK6His/EK, and GRK6His/TEV, designed for protein expression in Spodoptera frugiperda Sf9 insect cells. The first construct did not contain any purification tag whereas the other two constructs contained the His10 affinity tag, which increased purification yields. We report here that all three constructs of GRK6 were overexpressed in Sf9 insect cells and purified to homogeneity at levels that were suitable for co-crystallization of GRK6 with potential inhibitors. The yields of purified GRK6, GRK6His/EK, and GRK6His/TEV were 0.3 mg, 0.8 mg and 0.7 mg per liter of cell culture, respectively. In addition, we have shown that GRK6His/TEV with the His10 tag removed was highly homogeneous and monodisperse as observed by dynamic light scattering measurement and actively folded as exhibited by circular dichroism spectroscopy. The described methods will support the structure-based development of additional therapeutics against multiple myeloma.
收起
摘要 :
Promoting prosocial behaviour towards those who are dissimilar from oneself is an urgent contemporary issue. Because children spend much time in same-gender relationships, promoting other-gender prosociality could help them develo...
展开
Promoting prosocial behaviour towards those who are dissimilar from oneself is an urgent contemporary issue. Because children spend much time in same-gender relationships, promoting other-gender prosociality could help them develop more inclusive relationships. Our goals were to better understand the development of school-age children's intergroup prosocial behavior and the extent to which elementary school-age children consider their own and the recipient's gender in prosocial behaviour. Participants included 515 3rd, 4th and 5th graders (263, 51.1% boys, M-ageinyears = 9.08, SD = 1.00) surveyed in the fall (T1) and spring (T2). We assessed children's prosociality using peer nominations. Children became more prosocial toward same-gender peers over time but prosocial behavior toward other-gender peers remained stable. We found that gender mattered: Children showed an ingroup bias in prosociality favouring members of their own-gender group. Having other-gender friendships positively predicted children's prosocial behaviour towards other-gender peers over time. Children's felt similarity to other-gender peers was not directly, but indirectly, related to more prosocial behaviour toward other-gender peers. Findings shed light on potential pathways to fostering school-age children's intergroup prosocial behaviors.
收起
摘要 :
Improvements in global sustainability, health, and equity will largely be determined by the extent to which cities are able to become more efficient, hospitable, and productive places. The development and evolution of urban areas ...
展开
Improvements in global sustainability, health, and equity will largely be determined by the extent to which cities are able to become more efficient, hospitable, and productive places. The development and evolution of urban areas has a significant impact on local and regional weather and climate, which subsequently affect people and other organisms that live in and near cities. Biometeorologists, researchers who study the impact of weather and climate on living creatures, are well positioned to help evaluate and anticipate the consequences of urbanization on the biosphere. Motivated by the 60th anniversary of the International Society of Biometeorology, we reviewed articles published in the Society's International Journal of Biometeorology over the period 1974-2017 to understand if and how biometeorologists have directed attention to urban areas. We found that interest in urban areas has rapidly accelerated; urban-oriented articles accounted for more than 20% of all articles published in the journal in the most recent decade. Urban-focused articles in the journal span five themes: measuring urban climate, theoretical foundations and models, human thermal comfort, human morbidity and mortality, and ecosystem impacts. Within these themes, articles published in the journal represent a sizeable share of the total academic literature. More explicit attention from urban biometeorologists publishing in the journal to low- and middle-income countries, indoor environments, animals, and the impacts of climate change on human health would help ensure that the distinctive perspectives of biometeorology reach the places, people, and processes that are the foci of global sustainability, health, and equity goals.
收起
摘要 :
Cellular import of D-xylose, the second most abundant sugar in typical lignocellulosic biomass, has been evidenced to be an energy-depriving process in bacterial biocatalysts. The sugar facilitator of Zymomonas mobilis, Glf, is ca...
展开
Cellular import of D-xylose, the second most abundant sugar in typical lignocellulosic biomass, has been evidenced to be an energy-depriving process in bacterial biocatalysts. The sugar facilitator of Zymomonas mobilis, Glf, is capable of importing xylose at high rates without extra energy input, but is inhibited by D-glucose (the primary biomass sugar), potentially limiting the utility of this transporter for fermentation of sugar mixtures derived from lignocellulose. In this work we developed an Escherichia coli platform strain deficient in glucose and xylose transport to facilitate directed evolution of Glf to overcome glucose inhibition. Using this platform, we isolated nine Glf variants created by both random and site-saturation mutagenesis with increased xylose utilization rates ranging from 4.8-fold to 13-fold relative to wild-type Glf when fermenting 100 g l(-1) glucose-xylose mixtures. Diverse point mutations such as A165M and L445I were discovered leading to released glucose inhibition. Most of these mutations likely alter sugar coordinating pocket for the 6-hydroxymethyl group of D-glucose. These discovered glucose-resistant Glf variants can be potentially used as energy-conservative alternatives to the native sugar transport systems of bacterial biocatalysts for fermentation of lignocellulose-derived sugars.
收起
摘要 :
Thermal interface materials based on room temperature liquid metals (LMs) are promising candidates for improving thermal management of flexible electronics, microelectronics packaging, and energy storage devices. However, use of t...
展开
Thermal interface materials based on room temperature liquid metals (LMs) are promising candidates for improving thermal management of flexible electronics, microelectronics packaging, and energy storage devices. However, use of these materials is limited by their corrosivity and reactivity. Here, the fabrication and thermal characterization of multiphase soft composites consisting of LM and non-reactive silicon carbide (SiC) particles that are either uncoated or Ag-coated (Ag-SiC) are demonstrated. The LM-SiC (and LM-Ag-SiC) mixtures show thermal conductivities approaching 50 W m(-1) K-1 at 40 vol% particles. Corrosion issues with aluminum-based components are addressed through a multiphase composite consisting of hybrid LM-Ag-SiC fillers in a silicone oil matrix. This composite achieves an effective thermal conductivity of 9.9 W m(-1)K(-1) with a particle:LM:oil volumetric ratio of 30:20:50 (or intrinsic thermal conductivity of 17 W m(-1)K(-1) when accounting for contact resistance). It is shown that the Ag-coating plays a critical role in these oil-based composites by preventing LM de-wetting during blending. Upon mechanical compression, the LM thermally-bridges the solid fillers together within the oil matrix and thereby improves thermal performance. This insight into processing of LM-based materials opens additional avenues for designing thermally conductive soft composites.
收起
摘要 :
Thermal interface materials based on room temperature liquid metals (LMs) are promising candidates for improving thermal management of flexible electronics, microelectronics packaging, and energy storage devices. However, use of t...
展开
Thermal interface materials based on room temperature liquid metals (LMs) are promising candidates for improving thermal management of flexible electronics, microelectronics packaging, and energy storage devices. However, use of these materials is limited by their corrosivity and reactivity. Here, the fabrication and thermal characterization of multiphase soft composites consisting of LM and non-reactive silicon carbide (SiC) particles that are either uncoated or Ag-coated (Ag-SiC) are demonstrated. The LM-SiC (and LM-Ag-SiC) mixtures show thermal conductivities approaching 50 W m(-1) K-1 at 40 vol% particles. Corrosion issues with aluminum-based components are addressed through a multiphase composite consisting of hybrid LM-Ag-SiC fillers in a silicone oil matrix. This composite achieves an effective thermal conductivity of 9.9 W m(-1)K(-1) with a particle:LM:oil volumetric ratio of 30:20:50 (or intrinsic thermal conductivity of 17 W m(-1)K(-1) when accounting for contact resistance). It is shown that the Ag-coating plays a critical role in these oil-based composites by preventing LM de-wetting during blending. Upon mechanical compression, the LM thermally-bridges the solid fillers together within the oil matrix and thereby improves thermal performance. This insight into processing of LM-based materials opens additional avenues for designing thermally conductive soft composites.
收起
摘要 :
Build time is a critical contributor to overall part cost in the Laser Powder Bed Fusion (L-PBF) process, which in turn plays an important role in whether a part is made with this process or not. While there are many ways to impro...
展开
Build time is a critical contributor to overall part cost in the Laser Powder Bed Fusion (L-PBF) process, which in turn plays an important role in whether a part is made with this process or not. While there are many ways to improve productivity in the L-PBF process, this work focuses on one specific approach in the context of L-PBF of Inconel 718: increasing layer thickness, which reduces the number of slices for a given part, but is accompanied with the potential for a degradation in mechanical properties. The study is separated into two parts: the first establishes an optimal process at each of three different layer thicknesses (30, 60 and 80 mu m). Having developed an optimum process, the study then obtains density, surface roughness and mechanical property data on specimens fabricated with the selected processes, along with SEM micrographs. Half the specimens are characterized and tested in the as-built condition, the other half go through a heat treatment process that includes Hot Isostatic Pressing (HIP). This study of a total of 600 specimens across six builds confirms that an increase in layer thickness has no significant effect on elastic modulus, but does show reductions in density and strength, along with slight increases in surface roughness. Microstructural studies show no significant differences in grain size and orientation, with a slight increase in carbides and delta precipitates with increasing thickness. Post-heat treatment mechanical strength for all thicknesses is comparable to forged values for Inconel 718, and limited data suggest improvements in excess of forged values can be obtained if specimens are machined prior to testing, with a narrowing of the differences attributable to layer thickness. This study also showed correlations between strength and density and revealed build location dependence for UTS.
收起
原文获取