Now showing items 21-40 of 48943

    • Three-stage auto-ignition of n-heptane and methyl-cyclohexane mixtures at lean conditions in a flat piston rapid compression machine

      AlRamadan, Abdullah; Houidi, Moez Ben; Sotton, Julien; Bellenoue, Marc; Johansson, Bengt; Sarathy, Mani (Proceedings of the Combustion Institute, Elsevier BV, 2020-07-28) [Article]
      One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture.
    • Chemical structure of atmospheric pressure premixed laminar formic acid/hydrogen flames

      Osipova, K.N.; Sarathy, Mani; Korobeinichev, O.P.; Shmakov, A.G. (Proceedings of the Combustion Institute, Elsevier BV, 2020-07-28) [Article]
      The work presents an experimental and kinetic modeling study of laminar premixed formic acid [HC(O)OH]/H2/O2/Ar flames at different equivalence ratios (φ=0.85, 1.1 and 1.3) stabilized on a flat burner at atmospheric pressure, as well as laminar flame speed of HC(O)OH/O2/Ar flames (φ=0.5–1.5) at 1 atm. Flame structure as well as laminar flame speed were simulated using three different detailed chemical kinetic mechanisms proposed for formic acid oxidation. The components in the fuel blends show different consumption profiles, namely, hydrogen is consumed slower than formic acid. According to kinetic analysis, the reason of the observed phenomenon is that the studied flames have hydrogen as a fuel but also as an intermediate product formed from HC(O)OH decomposition. Comparison of the measured and simulated flame structure shows that all the mechanisms satisfactorily predict the mole fraction profiles of the reactants, main products, and intermediates. It is noteworthy that the mechanisms proposed by Glarborg et al., Konnov et al. and the updated AramcoMech2.0 adequately predict the spatial variations in the mole fractions of free radicals, such as H, OH O and HO2. However, some drawbacks of the mechanisms used were identified; in particular, they predict different concentrations of CH2O. As for laminar flame speed simulations, the Konnov et al. mechanism predicts around two times higher values than in experiment, while the Glarborg et al. and updated AramcoMech2.0 show good agreement with the experimental data.
    • Removal of Organic Micropollutants from Water by Macrocycle-Containing Covalent Polymer Networks.

      Sessler, Jonathan L; Ji, Xiaofan; Wang, Hu; Wang, Hongyu; Zhao, Tian; Page, Zachariah A; Khashab, Niveen M. (Angewandte Chemie (International ed. in English), Wiley, 2020-07-28) [Article]
      Access to clean drinking water is a recognized societal need that touches on the health and livelihood of millions of people worldwide. This is providing an incentive to develop new water-treatment technologies. Traditional technologies, while widespread, are usually inefficient at removing organic pollutants from sewage or so-called grey water. Macrocycle-containing covalent polymer networks have begun to attract attention in the context of water treatment owing to the inherent stability provided by the polymer backbones and their ability to capture micropollutant guests as the result of tunable macrocycle-based host-guest interactions. In this minireview, we summarize recent advances (from 2016 to mid-2020) involving the removal of organic micropollutants from water using macrocycle-containing covalent polymer networks. An overview of future challenges within this subfield is also provided.
    • Methanol as the Hydrogen Source in the Selective Transfer Hydrogenation of Alkynes Enabled by a Manganese Pincer Complex

      Sklyaruk, Jan; Zubar, Viktoriia; Borghs, Jannik C.; Rueping, Magnus (Organic Letters, American Chemical Society (ACS), 2020-07-28) [Article]
      The first base metal-catalyzed transfer hydrogenation of alkynes with methanol is described. An air and moisture stable manganese pincer complex catalyzes the reduction of a variety of different alkynes to the corresponding (Z)-olefins in high yields. The reaction is stereo- and chemoselective and scalable.
    • Solar Water Splitting: Over 17% Efficiency Stand-Alone Solar Water Splitting Enabled by Perovskite-Silicon Tandem Absorbers (Adv. Energy Mater. 28/2020)

      Karuturi, Siva Krishna; Shen, Heping; Sharma, Astha; Beck, Fiona J.; Varadhan, Purushothaman; Duong, The; Narangari, Parvathala Reddy; Zhang, Doudou; Wan, Yimao; He, Jr-Hau; Tan, Hark Hoe; Jagadish, Chennupati; Catchpole, Kylie (Advanced Energy Materials, Wiley, 2020-07-28) [Article]
      Realizing solar-to-hydrogen (STH) efficiencies close to 20% using low-cost semiconductors remains a major step toward accomplishing the practical viability of photoelectrochemical (PEC) hydrogen generation technologies. Dual-absorber tandem cells combining inexpensive semiconductors are a promising strategy to achieve high STH efficiencies at a reasonable cost. Here, a perovskite photovoltaic biased silicon (Si) photoelectrode is demonstrated for highly efficient stand-alone solar water splitting. A p+nn+ -Si/Ti/Pt photocathode is shown to present a remarkable photon-to-current efficiency of 14.1% under biased condition and stability over three days under continuous illumination. Upon pairing with a semitransparent mixed perovskite solar cell of an appropriate bandgap with state-of-the-art performance, an unprecedented 17.6% STH efficiency is achieved for self-driven solar water splitting. Modeling and analysis of the dual-absorber PEC system reveal that further work into replacing the noble-metal catalyst materials with earth-abundant elements and improvement of perovskite fill factor will pave the way for the realization of a low-cost high-efficiency PEC system.
    • Enhanced Thermoelectric Performance and Lifetime in Acid-Doped PEDOT:PSS Films via Work Function Modification

      Villalva, Diego Rosas; Haque, Mohammed; Nugraha, Mohamad; Baran, Derya (ACS Applied Energy Materials, American Chemical Society (ACS), 2020-07-28) [Article]
      In recent years, most of the work on p-type organic thermoelectrics focus on improving the thermoelectric properties of PEDOT:PSS through a sequential doping-dedoping process. However, the air-stability of thermoelectric parameters of these systems, which is essential for the realization of reliable devices remains largely unexplored. In this study, Poly (ethyleneimine)-ethoxylate (PEIE) acts as a work function modification agent and encapsulation layer to improve the thermoelectric performance and air-stability of nitric acid (HNO3) doped PEDOT:PSS films. The evaporation of HNO3 is responsible for a simultaneous decrease in electrical conductivity and an increase in the Seebeck coefficient leading to the degradation of the power factor. PEIE reduces the evaporation of HNO3 from PEDOT:PSS, and increases the power factor from 72 to 168 μW m-1K-2. After a week of exposure to air, the films show a power factor of 124 μW m-1K-2, retaining 74% of its initial thermoelectric merits. These results underscore the importance of PEIE as a material for enhancing thermoelectric performance and air-stability in the development of polymer-based thermoelectrics.
    • A statistical analysis of developing knock intensity in a mixture with temperature inhomogeneities

      Luong, Minh Bau; Desai, Swapnil; Pérez, Francisco E. Hernández; Sankaran, Ramanan; Johansson, Bengt; Im, Hong G. (Proceedings of the Combustion Institute, Elsevier BV, 2020-07-27) [Article]
      Knock formation and its intensity for a stoichiometric ethanol/air mixture under a representative endgas auto-ignition condition in IC engines with temperature inhomogeneities are investigated using multidimensional direct numerical simulations (DNS) with a 40-species skeletal mechanism of ethanol. Two- and three-dimensional simulations are performed by systematically varying temperature fluctuations and its most energetic length scale, lT. The volumetric fraction of the mixture regions that have the propensity to detonation development, FD, is proposed as a metric to predict the amplitude of knock intensity.It isfound that with increasing lT, FD shows a good agreement with the heat release fraction of the mixture regions with pressure greater than equilibrium pressure, FH. The detonation peninsula is well captured by FD and FH when plotting them as a function of the volume-averaged ξ , ξ, (ξ = a/Ssp is the ratio of the acoustic speed, a to the ignition front speed, Ssp). Decreasing lT is found to significantly reduce the super-knock intensity. The results suggest that decreasing lT, as in engines with tumble desig
    • Fluorophosphates: Next Generation Cathode Materials for Rechargeable Batteries

      Sharma, Lalit; Adiga, Shashishekar P.; Alshareef, Husam N.; Barpanda, Prabeer (Advanced Energy Materials, Wiley, 2020-07-27) [Article]
      Cost, safety, and cycle life have emerged as prime concerns to build robust batteries to cater to the global energy demand. These concerns are impacted by all battery components, but the realizable energy density of lithium-ion batteries (LIBs) is limited by the performance of cathodes. Thus, cathode materials have a significant role to play in advancing the performance and economics of secondary batteries. To realize next generation Li-ion and post Li-ion batteries, a variety of cathode insertion materials have been explored, but finding a cost effective and stable cathode material that can deliver high energy density has been a daunting task. Oxide cathode materials are ubiquitous in commercial applications, as they can deliver high capacity. In comparison, polyanionic insertion materials can offer tuneable (high) redox potential, operational safety, and structural as well as thermal stability. Indeed, a wide range of polyanionic materials like phosphates, borates, sulfates, and their complexes have been reported. In this article, the alkali metal fluorophosphates class of polyanionic cathodes for secondary batteries is discussed. The various reported fluorophosphate insertion materials are discussed in terms of their electrochemical and electrocatalytic properties. The historical overview, recent progress, and remaining challenges for polyanionic fluorophosphates are presented along with suggested future research directions and potential application.
    • Enriching Context Information for Entity Linking with Web Data

      Wang, Yi Ting; Shen, Jie; Li, Zhi Xu; Yang, Qiang; Liu, An; Zhao, Peng Peng; Xu, Jia Jie; Zhao, Lei; Yang, Xun Jie (Journal of Computer Science and Technology, Springer Science and Business Media LLC, 2020-07-27) [Article]
      Entity linking (EL) is the task of determining the identity of textual entity mentions given a predefined knowledge base (KB). Plenty of existing efforts have been made on this task using either “local” information (contextual information of the mention in the text), or “global” information (relations among candidate entities). However, either local or global information might be insufficient especially when the given text is short. To get richer local and global information for entity linking, we propose to enrich the context information for mentions by getting extra contexts from the web through web search engines (WSE). Based on the intuition above, two novel attempts are made. The first one adds web-searched results into an embedding-based method to expand the mention’s local information, where we try two different methods to help generate high-quality web contexts: one is to apply the attention mechanism and the other is to use the abstract extraction method. The second one uses the web contexts to extend the global information, i.e., finding and utilizing more extra relevant mentions from the web contexts with a graph-based model. Finally, we combine the two models we propose to use both extended local and global information from the extra web contexts. Our empirical study based on six real-world datasets shows that using extra web contexts to extend the local and the global information could effectively improve the F1 score of entity linking.
    • The Role of Adding Bi0.5A0.5ZrO3 in Affecting Orthorhombic-Tetragonal Phase Transition Temperature and Electrical Properties in Potassium Sodium Niobate Ceramics

      Lv, Xiang; Zhang, Nan; Wu, Jiagang; Zhang, Xixiang (Acta Materialia, Elsevier BV, 2020-07-25) [Article]
      By studying the alone and synergetic effects of Zr4+ and Bi3+ on potassium sodium niobate ((K, Na)NbO3, KNN) ceramics, we revealed how Bi0.5A0.5ZrO3 (A = K, Na, Ag, and (Na0.82K0.18)) reduces the orthorhombic-tetragonal phase transition temperature (TO–T) of KNN ceramics. Investigations into the alone effects reveal that aliovalent substitutions on K+/Na+ (Nb5+) with Bi3+ (Zr4+) inevitably destroy long-range ordering (LRO) and thus worsen piezo/ferroelectric properties. Despite this, Zr4+ can replace Nb5+ within a high content, remain an orthorhombic (O) phase, and slightly increase TO–T. Although substituting on K+/Na+ with Bi3+ decreases TO–T, it already significantly destroyed LRO before shifting TO–T to room temperature. Then, investigations into the synergetic effects show that Zr4+ acts as a buffer, Bi3+ is an accelerator, and A+ is a stabilizer. The buffer can exist in KNN ceramics within a high content and neutralizes the charges caused by the accelerator that concentrates on decreasing TO–T, and the stabilizer compensates for the stability of the perovskite phase. Their synergetic effects explain why Bi0.5A0.5ZrO3 can gradually reduce the TO–T of KNN ceramics without significantly destroying LRO. Therefore, this work helps understand how Bi0.5A0.5ZrO3 decreases TO–T and further design the phase boundary for KNN ceramics.
    • Evolution and scaling of the peak flame surface density in spherical turbulent premixed flames subjected to decaying isotropic turbulence

      Kulkarni, Tejas; Bisetti, Fabrizio (Proceedings of the Combustion Institute, Elsevier BV, 2020-07-25) [Article]
      The peak flame surface density within the turbulent flame brush is central to turbulent premixed combustion models in the flamelet regime. This work investigates the evolution of the peak surface density in spherically expanding turbulent premixed flames with the help of direct numerical simulations at various values of the Reynolds and Karlovitz number. The flames propagate in decaying isotropic turbulence inside a closed vessel. The effects of turbulent transport, transport due to mean velocity gradient, and flame stretch on the peak surface density are identified and characterized with an analysis based on the transport equation for the flame surface density function. The three mechanisms are governed by distinct flow time scales; turbulent transport by the eddy turnover time, mean transport by a time scale related to the pressure rise in the closed chamber, and flame stretch by the Kolmogorov time scale. Appropriate scaling of the terms is proposed and shown to collapse the data despite variations in the dimensionless groups. Overall, the transport terms lead to a reduction in the peak value of the surface density, while flame stretch has the opposite effect. In the present configuration, a small imbalance between the two leads to an exponential decay of the peak surface density in time. The dimensionless decay rate is found to be consistent with the evolution of the wrinkling scale as defined in the Bray-Moss-Libby model.
    • Light-Harvesting Two-Photon-Absorbing Polymers

      Goswami, Subhadip; Cekli, Seda; Alarousu, Erkki; Winkel, Russell W.; Younus, Muhammad; Mohammed, Omar F.; Schanze, Kirk (Macromolecules, American Chemical Society (ACS), 2020-07-24) [Article]
      A series of atactic polystyrene-based polymers was synthesized that contains grafted π-conjugated organic and organometallic chromophores to investigate two-photon light-harvesting properties. The polymers feature 4-(diphenylamino)fluorene (DPAF) and Pt−DPAF as π-conjugated units which are known to be moderately efficient two-photon absorption (2PA) chromophores. The polymers were synthesized by reversible addition−fragmentation transfer (RAFT) polymerization of 4-chloromethylstyrene, and following substitution of Cl by N3, the DPAF and Pt−DPAF chromophores were grafted onto the polymer via the coppercatalyzed azide−alkyne click reaction. The loading of Pt−DPAF units in the polymers was varied from 0 to 20% by varying the feed ratio in the click reactions. With an increase in the Pt−DPAF content, the fluorescence quantum yield from the DPAF singlet excited state decreases and fluorescence is replaced by phosphorescence characteristic of the Pt−DPAF units at 530 nm. The emission lifetime and ultrafast transient absorption spectroscopy confirm that rapid and efficient singlet energy transfer occurs from DPAF to DPAF− Pt. Excitation of the polymers with 100 fs, near-infrared pulses gives rise to upconverted emission, and the observed emission spectra are similar to those under one-photon excitation. The results indicate that the DPAF units effectively function as 2-photon absorption light-harvesting units, transferring the excitation to the Pt−DPAF units where intersystem crossing occurs efficiently. Taken together, the results point the way to development of novel polymer-based optical power-limiting materials for ultrashort and long optical pulses.
    • Tuning the Surface Structure of Polyamide Membranes Using Porous Carbon Nitride Nanoparticles for High-Performance Seawater Desalination

      Zhou, Zongyao; Li, Xiang; Shinde, Digambar; Sheng, Guan; Lu, Dongwei; Li, Peipei; Lai, Zhiping (Membranes, MDPI AG, 2020-07-24) [Article]
      Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C3N4) nanoparticle to potentially improve both the water flux and salt rejection of the state-of-the-art polyamide (PA) thin film composite (TFC) membranes. The organic–organic covalent bonds endowed C3N4 with great compatibility with the PA layer, which positively influenced the customization of interfacial polymerization (IP). Benefitting from the positive effects of C3N4, a more hydrophilic, more crumpled thin film nanocomposite (TFN) membrane with a larger surface area, and an increased cross-linking degree of PA layer was achieved. Moreover, the uniform porous structure of the C3N4 embedded in the ”ridge” sections of the PA layer potentially provided additional water channels. All these factors combined provided unprecedented performance for seawater desalination among all the PA-TFC membranes reported thus far. The water permeance of the optimized TFN membrane is 2.1-folds higher than that of the pristine PA-TFC membrane, while the NaCl rejection increased to 99.5% from 98.0%. Our method provided a promising way to improve the performance of the state-of-art PA-TFC membranes in seawater desalination.
    • NonlinearWave Motion in Viscoelasticity and Free Surface Flows

      Ussembayev, Nail (2020-07-24) [Dissertation]
      Advisor: Markowich, Peter A.
      Committee members: Thoroddsen, Sigurdur T; Tzavaras, Athanasios E.; Bona, Jerry L.
      This dissertation revolves around various mathematical aspects of nonlinear wave motion in viscoelasticity and free surface flows. The introduction is devoted to the physical derivation of the stress-strain constitutive relations from the first principles of Newtonian mechanics and is accessible to a broad audience. This derivation is not necessary for the analysis carried out in the rest of the thesis, however, is very useful to connect the different-looking partial differential equations (PDEs) investigated in each subsequent chapter. In the second chapter we investigate a multi-dimensional scalar wave equation with memory for the motion of a viscoelastic material described by the most general linear constitutive law between the stress, strain and their rates of change. The model equation is rewritten as a system of first-order linear PDEs with relaxation and the well-posedness of the Cauchy problem is established. In the third chapter we consider the Euler equations describing the evolution of a perfect, incompressible, irrotational fluid with a free surface. We focus on the Hamiltonian description of surface waves and obtain a recursion relation which allows to expand the Hamiltonian in powers of wave steepness valid to arbitrary order and in any dimension. In the case of pure gravity waves in a two-dimensional flow there exists a symplectic coordinate transformation that eliminates all cubic terms and puts the Hamiltonian in a Birkhoff normal form up to order four due to the unexpected cancellation of the coefficients of all fourth order non-generic resonant terms. We explain how to obtain higher-order vanishing coefficients. Finally, using the properties of the expansion kernels we derive a set of nonlinear evolution equations for unidirectional gravity waves propagating on the surface of an ideal fluid of infinite depth and show that they admit an exact traveling wave solution expressed in terms of Lambert’s W-function. The only other known deep fluid surface waves are the Gerstner and Stokes waves, with the former being exact but rotational whereas the latter being approximate and irrotational. Our results yield a wave that is both exact and irrotational, however, unlike Gerstner and Stokes waves, it is complex-valued.
    • Highly UV Resistant Inch-Scale Hybrid Perovskite Quantum Dot Papers

      Li, Ting-You; Xu, Xuezhu; Lin, Chun-Ho; Guan, Xinwei; Hsu, Wei-Hao; Tsai, Meng-Lin; Fang, Xiaosheng; Wu, Tom; He, Jr-Hau (Advanced Science, Wiley, 2020-07-24) [Article]
      Halide perovskite quantum dots (PQDs) are promising materials for diverse applications including displays, light-emitting diodes, and solar cells due to their intriguing properties such as tunable bandgap, high photoluminescence quantum yield, high absorbance, and narrow emission peaks. Despite the prosperous achievements over the past several years, PQDs face severe challenges in terms of stability under different circumstances. Currently, researchers have overcome part of the stability problem, making PQDs sustainable in water, oxygen, and polar solvents for long-term use. However, halide PQDs are easily degraded under continuous irradiation, which significantly limits their potential for conventional applications. In this study, an oleic acid/oleylamine (traditional surface ligands)-free method to fabricate perovskite quantum dot papers (PQDP) is developed by adding cellulose nanocrystals as long-chain binding ligands that stabilize the PQD structure. As a result, the relative photoluminescence intensity of PQDP remains over ≈90% under continuous ultraviolet (UV, 16 W) irradiation for 2 months, showing negligible photodegradation. This proposed method paves the way for the fabrication of ultrastable PQDs and the future development of related applications.
    • Model-Based Design of Graphite-Compatible Electrolytes in Potassium-Ion Batteries

      Zhang, Jiao; Cao, Zhen; Zhou, Lin; Liu, Gang; Park, Geon-Tae; Cavallo, Luigi; Wang, Limin; Alshareef, Husam N.; Sun, Yang-Kook; Ming, Jun (ACS Energy Letters, American Chemical Society (ACS), 2020-07-24) [Article]
      Potassium-ion batteries (KIBs) are attractive alternatives to lithium-ion batteries (LIBs) because of their lower cost and global potassium sustainability. However, designing compatible electrolytes with graphite anode remains challenging. This is because the electrolyte decomposition and/or graphite exfoliation (due to K+–solvent co-insertion) always exist, which is much harder to overcome compared to the case of LIBs because of the higher activities of K+. Herein, we report a general principle to design compatible electrolytes with the graphite anode, where the K+ can be reversibly (de)intercalated. We find that the electrolyte composition is critical to determining the graphite performance, which can be tuned by the kind of solvent, anion, additives, and concentration. We present a new interfacial model to understand the variation in performance (i.e., K+ (de)intercalation or K+–solvent co-insertion or decomposition). Our model is distinctly different from the solid electrolyte interphase interpretation. This work offers new opportunities to design high-performance KIBs and potassium-ion sulfur batteries. Particularly, we present new guideline to design electrolytes for KIBs and other advanced mobile (ion) batteries.
    • Understanding multi-stage HCCI combustion caused by thermal stratification and chemical three-stage auto-ignition

      Ben Houidi, Moez; AlRamadan, Abdullah; Sotton, Julien; Bellenoue, Marc; Sarathy, Mani; Johansson, Bengt (Proceedings of the Combustion Institute, Elsevier BV, 2020-07-23) [Article]
      The Homogeneous Charge Compression Ignition (HCCI) concept shows great potential for improving engine efficiency and reducing pollutant emissions. However, the operation with this concept in Internal Combustion (IC) engines is still limited to low speed and load conditions, as excessive Pressure Rise Rates (PRR) are generated with its fast auto-ignition. To overcome this limitation, the use of moderate thermal and charge stratification has been promoted. This leads to multi-stage ignition, and thus a potentially acceptable PRR. Recently Sarathy et al. (2019), three-stage auto-ignition has been emphasized as a chemical phenomenon where the thermal runaway is inhibited during the main ignition event. The current paper demonstrates experimental evidence on this phenomenon observed during n-heptane and n-hexane auto-ignition at lean diluted conditions in a flat piston Rapid Compression Machine (RCM). Multi-stage ignition events caused by either chemical kinetics or by the well-known thermal stratification of this type of RCM are clearly identified and differentiated. The combination of these two factors seems to be a suitable solution to overcome PRR limitations.
    • Dissecting new genetic components of salinity tolerance in two-row spring barley at the vegetative and reproductive stages

      saade, stephanie; Brien, Chris; Pailles, Yveline; Berger, Bettina; Shahid, Mohammad; Russell, Joanne; Waugh, Robbie; Negrão, Sónia; Tester, Mark A. (PLOS ONE, Public Library of Science (PLoS), 2020-07-23) [Article]
      Soil salinity imposes an agricultural and economic burden that may be alleviated by identifying the components of salinity tolerance in barley, a major crop and the most salt tolerant cereal. To improve our understanding of these components, we evaluated a diversity panel of 377 two-row spring barley cultivars during both the vegetative, in a controlled environment, and the reproductive stages, in the field. In the controlled environment, a high-throughput phenotyping platform was used to assess the growth-related traits under both control and saline conditions. In the field, the agronomic traits were measured from plots irrigated with either fresh or saline water. Association mapping for the different components of salinity tolerance enabled us to detect previously known associations, such as HvHKT1;5. Using an "interaction model", which took into account the interaction between treatment (control and salt) and genetic markers, we identified several loci associated with yield components related to salinity tolerance. We also observed that the two developmental stages did not share genetic regions associated with the components of salinity tolerance, suggesting that different mechanisms play distinct roles throughout the barley life cycle. Our association analysis revealed that genetically defined regions containing known flowering genes (Vrn-H3, Vrn-H1, and HvNAM-1) were responsive to salt stress. We identified a salt-responsive locus (7H, 128.35 cM) that was associated with grain number per ear, and suggest a gene encoding a vacuolar H+-translocating pyrophosphatase, HVP1, as a candidate. We also found a new QTL on chromosome 3H (139.22 cM), which was significant for ear number per plant, and a locus on chromosome 2H (141.87 cM), previously identified using a nested association mapping population, which associated with a yield component and interacted with salinity stress. Our study is the first to evaluate a barley diversity panel for salinity stress under both controlled and field conditions, allowing us to identify contributions from new components of salinity tolerance which could be used for marker-assisted selection when breeding for marginal and saline regions.
    • Carbon quantum dots enabled tuning of the microphase structures of poly (ether-b-amide) membrane for CO2 separation

      Shi, Fei; Tian, Qianqian; Wang, Jingtao; Wang, Qi; Shi, Feng; Li, Yifan; Nunes, Suzana Pereira (Industrial & Engineering Chemistry Research, American Chemical Society (ACS), 2020-07-23) [Article]
      In this study, molecular-level of mixed matrix membranes are prepared by incorporating two types of carbon quantum dots (QDs), polymer-like QDs (PQD) and graphene oxide QDs (GQD) into Pebax, a poly (ether-b-amide) copolymer. PQD is shown to destroy part of the intrinsic crystalline structure of Pebax as typical fillers do. By comparison, GQD has fewer functional groups and causes an interesting enhancement of the microphase separation of Pebax. The polyether domains become more segregated and more available for the selective CO2 permeation. As a result, the gas separation performance of the membranes is evidently enhanced. GQD outperforms PQD as filler and the encouraging enhancement occurs at lower loading. The membrane with 0.05 wt% GQD loading shows the optimal gas separation property while it is 1 wt% for PQD-doped membranes. A possible mechanism is tentatively proposed based on the findings of this study.
    • DeepKriging: Spatially Dependent Deep Neural Networks for Spatial Prediction

      Li, Yuxiao; Sun, Ying; Reich, Brian J (arXiv, 2020-07-23) [Preprint]
      In spatial statistics, a common objective is to predict the values of a spatial process at unobserved locations by exploiting spatial dependence. In geostatistics, Kriging provides the best linear unbiased predictor using covariance functions and is often associated with Gaussian processes. However, when considering non-linear prediction for non-Gaussian and categorical data, the Kriging prediction is not necessarily optimal, and the associated variance is often overly optimistic. We propose to use deep neural networks (DNNs) for spatial prediction. Although DNNs are widely used for general classification and prediction, they have not been studied thoroughly for data with spatial dependence. In this work, we propose a novel neural network structure for spatial prediction by adding an embedding layer of spatial coordinates with basis functions. We show in theory that the proposed DeepKriging method has multiple advantages over Kriging and classical DNNs only with spatial coordinates as features. We also provide density prediction for uncertainty quantification without any distributional assumption and apply the method to PM$_{2.5}$ concentrations across the continental United States.