• The Influence of Intake Pressure and Ethanol Addition to Gasoline on Single- and Dual-Stage Autoignition in an HCCI Engine

      Vuilleumier, David; Atef, Nour; Kukkadapu, Goutham; Wolk, Benjamin; Selim, Hatem; Kozarac, Darko; Saxena, Samveg; Wang, Zhaowen; Sung, Chih-Jen; Dibble, Robert; Sarathy, S. Mani (American Chemical Society (ACS), 2018-09-11)
      Autoignition in HCCI engines is known to be controlled by the combustion kinetics of the in-cylinder fuel/air mixture which is highly influenced by the amount of low-temperature and intermediate-temperature heat release (LTHR and ITHR) that occurs. At lower intake pressures (typically <1.4 bar absolute), it has been observed that gasoline behaves as a single-stage heat release fuel, while at higher intake pressures (typically >1.8 bar absolute) gasoline behaves as a two-stage heat release fuel. Furthermore, ethanol blending into gasoline strongly affects heat release characteristics, and this warrants further investigation. This paper experimentally investigates the conditions under which gasoline transitions from a single-stage heat release fuel to a two-stage heat release fuel as intake pressure is increased. Experiments were performed in single-cylinder HCCI engine fueled with two research-grade gasolines, FACE A and FACE C. These gasolines were tested neat, and with 10% and 20% (by volume) ethanol addition. In addition, these results were compared to results previously obtained for PRF 85, and new results for PRF 84 with 10% and 20% ethanol addition. Moreover, the engine experiments were supported by rapid compression machine (RCM) ignition delay data for the same fuels. The engine experiments revealed that there were minimal differences between the heat release profiles of the two gasolines, FACE A and FACE C, a result which was supported by the RCM experiments that showed similar ignition delay times for the two FACE fuels and PRF 84. On the other hand, with ethanol addition to these gasolines and PRF 84, the occurrence of LTHR shifted to higher intake pressures compared to ethanol-free cases, from 1.4 bar intake pressure for neat fuel to 2.2 bar with 20% ethanol. Consequently, the intake temperatures required to achieve constant combustion phasing for all mixtures were drastically altered. Simulations using a detailed chemical kinetic model were utilized to understand the effects of ethanol blending on the ignition characteristics of PRF 84. The addition of ethanol was found to act as a radical sink where it inhibits the radical pool formation during the low (<850 K) and intermediate (850–1050 K) temperature chemistry regimes resulting in lower reactivity. These results help explain ethanol’s significant antiknock qualities under boosted conditions in spark-ignition engines.
    • Finding Nemo’s Genes: A chromosome-scale reference assembly of the genome of the orange clownfish Amphiprion percula

      Lehmann, Robert; Lightfoot, Damien J.; Schunter, Celia; Michell, Craig T.; Ohyanagi, Hajime; Mineta, Katsuhiko; Foret, Sylvain; Berumen, Michael L.; Miller, David J.; Aranda, Manuel; Gojobori, Takashi; Munday, Philip L.; Ravasi, Timothy (Wiley, 2018-09-11)
      The iconic orange clownfish, Amphiprion percula, is a model organism for studying the ecology and evolution of reef fishes, including patterns of population connectivity, sex change, social organization, habitat selection and adaptation to climate change. Notably, the orange clownfish is the only reef fish for which a complete larval dispersal kernel has been established and was the first fish species for which it was demonstrated that antipredator responses of reef fishes could be impaired by ocean acidification. Despite its importance, molecular resources for this species remain scarce and until now it lacked a reference genome assembly. Here, we present a de novo chromosome-scale assembly of the genome of the orange clownfish Amphiprion percula. We utilized single-molecule real-time sequencing technology from Pacific Biosciences to produce an initial polished assembly comprised of 1,414 contigs, with a contig N50 length of 1.86 Mb. Using Hi-C-based chromatin contact maps, 98% of the genome assembly were placed into 24 chromosomes, resulting in a final assembly of 908.8 Mb in length with contig and scaffold N50s of 3.12 and 38.4 Mb, respectively. This makes it one of the most contiguous and complete fish genome assemblies currently available. The genome was annotated with 26,597 protein-coding genes and contains 96% of the core set of conserved actinopterygian orthologs. The availability of this reference genome assembly as a community resource will further strengthen the role of the orange clownfish as a model species for research on the ecology and evolution of reef fishes.
    • Single-site ruthenium pincer complex knitted in porous organic polymers for green dehydrogenation of formic acid in aqueous medium

      Huang, Kuo-Wei; Wang, Xinbo; Ang, Eleanor; Guan, Chao; Zhang, Qinggang; Wu, Wenting; Liu, Pengxin; Zheng, Nanfeng; Zhang, Daliang; Lopatin, Sergei; Lai, Zhiping (Wiley, 2018-09-12)
      Owing to its capacity for reversible hydrogen storage, formic acid (FA) holds great promise as an energy carrier alternative to conventional fossil fuels systems. While the decomposition of FA to hydrogen (H2) and carbon dioxide (CO2) through homogeneous catalysis has been well-established, the selective and efficient dehydrogenation of FA by a robust heterogeneous catalyst remains a challenge. Herein, a novel heterogeneous ruthenium-pincer framework with single-atomic sites was prepared in one step by the direct knitting of a phosphorous-nitrogen PN3P-pincer ruthenium complex in a porous organic polymer. The heterogeneous ruthenium complex efficiently dehydrogenates formic acid in both organic and aqueous media with remarkably enhanced stability. Notably, no detectible CO was generated and a turnover number of 145,300 was attained in a continuous experiment with no significant decline in catalytic reactivity (in sharp contrast, total TON of only 5,600 was obtained with the homogeneous analog under the same conditions). The single-atomic sites in the porous framework allowed the combination of the desirable attributes of high reactivity and selectivity of a homogeneous catalyst with the significantly enhanced catalyst stability and reusability benefits of heterogeneous catalysis.
    • Vocal practice regulates singing activity–dependent genes underlying age-independent vocal learning in songbirds

      Hayase, Shin; Wang, Hongdi; Ohgushi, Eri; Kobayashi, Masahiko; Mori, Chihiro; Horita, Haruhito; Mineta, Katsuhiko; Liu, Wan-chun; Wada, Kazuhiro (Public Library of Science (PLoS), 2018-09-12)
      The development of highly complex vocal skill, like human language and bird songs, is underlain by learning. Vocal learning, even when occurring in adulthood, is thought to largely depend on a sensitive/critical period during postnatal development, and learned vocal patterns emerge gradually as the long-term consequence of vocal practice during this critical period. In this scenario, it is presumed that the effect of vocal practice is thus mainly limited by the intrinsic timing of age-dependent maturation factors that close the critical period and reduce neural plasticity. However, an alternative, as-yet untested hypothesis is that vocal practice itself, independently of age, regulates vocal learning plasticity. Here, we explicitly discriminate between the influences of age and vocal practice using a songbird model system. We prevented zebra finches from singing during the critical period of sensorimotor learning by reversible postural manipulation. This enabled to us to separate lifelong vocal experience from the effects of age. The singing-prevented birds produced juvenile-like immature song and retained sufficient ability to acquire a tutored song even at adulthood when allowed to sing freely. Genome-wide gene expression network analysis revealed that this adult vocal plasticity was accompanied by an intense induction of singing activity-dependent genes, similar to that observed in juvenile birds, rather than of age-dependent genes. The transcriptional changes of activity-dependent genes occurred in the vocal motor robust nucleus of the arcopallium (RA) projection neurons that play a critical role in the production of song phonology. These gene expression changes were accompanied by neuroanatomical changes: dendritic spine pruning in RA projection neurons. These results show that self-motivated practice itself changes the expression dynamics of activity-dependent genes associated with vocal learning plasticity and that this process is not tightly linked to age-dependent maturational factors.
    • The Arabidopsis DWARF27 gene encodes an all-trans-/9-cis-β-carotene isomerase and is induced by auxin, abscisic acid and phosphate deficiency

      Abuauf, Haneen; Haider, Imran; Jia, Kun-Peng; Ablazov, Abdugaffor; Mi, Jianing; Blilou, Ikram; Al-Babili, Salim (Elsevier BV, 2018-09-11)
      Strigolactones (SLs) are carotenoid-derived plant hormones that influence various aspects of plant growth and development in response to environmental conditions, especially nutrients deficiency. SLs are synthesized via a strict stereo-specific core pathway that leads to the intermediate carlactone, requiring the iron-containing polypeptide DWARF27 (D27) and the carotenoid cleavage dioxygenases 7 (CCD7) and 8 (CCD8). It has been shown that the rice OsD27 is a β-carotene isomerase catalyzing the interconversion of all-trans- into 9-cis-β -carotene. However, data about the enzymatic activity of D27 from other species are missing. Here, we investigated the activity and substrate specificity of the Arabidopsis AtD27 by testing a broad range of carotenoid substrates. Both in vivo and in vitro assays show that AtD27 catalyzes the reverse isomerization of all-trans-/9-cis-β-carotene. AtD27 did not isomerize 13-cis- or 15-cis-β-carotene, indicating high specificity for the C9-C10 double bond. The isomerization reaction was inhibited in the presence of silver acetate, pointing to the involvement of an iron-sulfur cluster. We further investigated the expression of AtD27, using Arabidopsis transgenic lines expressing β-glucuronidase (GUS) under the control of AtD27 native promoter. AtD27 is ubiquitously expressed throughout the plant with the highest expression in immature flowers. In lateral roots, AtD27 expression was induced by treatment with auxin and ABA, while the application of SL analogs did not show an effect. Lower ABA levels in atd27 mutant indicated an interference with the ABA pathway. Quantitative real-time RT-PCR showed that transcript levels of AtD27 and other SL biosynthetic genes in roots are induced upon phosphate starvation. Taken together, our study on AtD27 confirms the postulated enzymatic function of this enzyme, shows its strict substrate- and regio-specificity and indicates an important role in response to multiple plant hormones and phosphate deficiency.
    • Bio-Glycidol Conversion to Solketal over Acid Heterogeneous Catalysts: Synthesis and Theoretical Approach

      Ricciardi, Maria; Falivene, Laura; Tabanelli, Tommaso; Proto, Antonio; Cucciniello, Raffaele; Cavani, Fabrizio (MDPI AG, 2018-09-11)
      The present work deals with the novel use of heterogeneous catalysts for the preparation of solketal from bio-glycidol. Sustainable feedstocks and mild reaction conditions are considered to enhance the greenness of the proposed process. Nafion NR50 promotes the quantitative and selective acetalization of glycidol with acetone. DFT calculations demonstrate that the favored mechanism consists in the nucleophilic attack of acetone to glycidol concerted with the ring opening assisted by the acidic groups on the catalyst and in the following closure of the five member ring of the solketal.
    • The caseinolytic protease complex component CLPC1 in Arabidopsis maintains proteome and RNA homeostasis in chloroplasts

      Zhang, ShouDong; Zhang, Huoming; Xia, Yiji; Xiong, Liming (Springer Nature America, Inc, 2018-09-12)
      Homeostasis of the proteome is critical to the development of chloroplasts and also affects the expression of certain nuclear genes. CLPC1 facilitates the translocation of chloroplast pre-proteins and mediates protein degradation.We found that proteins involved in photosynthesis are dramatically decreased in their abundance in the clpc1 mutant, whereas many proteins involved in chloroplast transcription and translation were increased in the mutant. Expression of the full-length CLPC1 protein, but not of the N-terminus-deleted CLPC1 (ΔN), in the clpc1 mutant background restored the normal levels of most of these proteins. Interestingly, the ΔN complementation line could also restore some proteins affected by the mutation to normal levels. We also found that that the clpc1 mutation profoundly affects transcript levels of chloroplast genes. Sense transcripts of many chloroplast genes are up-regulated in the clpc1 mutant. The level of SVR7, a PPR protein, was affected by the clpc1 mutation. We showed that SVR7 might be a target of CLPC1 as CLPC1-SVR7 interaction was detected through co-immunoprecipitation.Our study indicates that in addition to its role in maintaining proteome homeostasis, CLPC1 and likely the CLP proteasome complex also play a role in transcriptome homeostasis through its functions in maintaining proteome homeostasis.
    • One-pot synthesis of high-flux b-oriented MFI zeolite membranes for Xe recovery

      Wang, Xuerui; Karakilic, Pelin; Liu, Xinlei; Shan, Meixia; Nijmeijer, Arian; Winnubst, Louis; Gascon, Jorge; Kapteijn, Freek (American Chemical Society (ACS), 2018-09-11)
      We demonstrate that b-oriented MFI zeolite membranes can be manufactured by in-situ crystallization using an intermediate amorphous SiO2 layer. The improved in-plane growth by using a zeolite growth modifier leads to fusion of independent crystals and eliminates boundary gaps, giving good selectivity in the separation of CO2/Xe mixtures. The fast diffusion of CO2 dominates the overall membrane selectivity towards CO2/Xe mixture. Because of the straight and short [010] channels, the obtained CO2 permeation fluxes are several orders of magnitude higher than those of carbon molecular sieving membranes and polymeric membranes, opening opportunities for Xe recovery from waste anaesthetic gas.
    • Coupled Resonators for Sound Trapping and Absorption

      Al Jahdali, Rasha; Wu, Ying (Springer Nature America, Inc, 2018-09-10)
      The leakage of sound waves in a resonance based rainbow trapping device prevents the sound wave being trapped in a specific location. In this study, we report a design of sound trapping device based on coupled Helmholtz resonators, loaded to an air waveguide, which can effectively tackle the wave leakage issue. We show that coupled resonators structure can generate dips in the transmission spectrum by an analytical model derived from Newton’s second law and numerical analysis based on finite-element method. An effective medium theory is derived, which shows that coupled resonators cause a negative effective bulk modulus near the resonance frequency and induce flat bands that give rise to the confinement of the incoming wave inside the resonators. We compute the transmission spectra and band diagram from the effective medium theory, which are consistent with the simulation results. Trapping and high absorption of sound wave energy are demonstrated with our designed device.
    • Behavior of numerical error in pore-scale lattice Boltzmann simulations with simple bounce-back rule: Analysis and highly accurate extrapolation

      Khirevich, Siarhei; Patzek, Tadeusz W. (AIP Publishing, 2018-09-14)
      We perform the viscosity-independent Stokes flow simulations in regular sphere packings using the two-relaxation-times (TRT) lattice Boltzmann method (LBM) with the simple bounce-back (BB) rule. Our special discretization procedure reduces the scatter in integral quantities, such as drag force, and quantifies the solution convergence error. We assume transition to linear (−1) convergence rate for different sets of TRT parameters and use this assumption to provide a simple extrapolation scheme. After establishing the accurate reference values of drag for a wide range of porosities, 0.26–0.78, we show a ten-fold decrease in the drag error using the suggested extrapolations. This error decrease allows the simple LBM/BB scheme to reach an accuracy of the high-order interpolated boundary schemes. The suggested extrapolation approach is straightforward to apply in porous media, whose pore space can be discretized at several resolutions.
    • Bio-inspired Architectures and Hetero-Atom Doping to Construct Metal Oxide based Anode for High Performance Lithium Ion Batteries

      Ming, Jun; Wang, Liming; Sun, Qujiang; Zhou, Lin; Sun, Lianshan; Wang, Chunli; Wu, Yingqiang; Wang, Xuxu (Wiley, 2018-09-11)
      Pursuing the greater energy density and longer life span of lithium ion batteries (LIBs) are urgently needed to satisfy the dramatically increased demand in energy market, where the metal oxide-based anodes are being intensively studied due to the higher capacity over that of the traditional graphite anode. Herein, we introduce a new and sustainable strategy to construct the metal oxide-based anode with high capacity and extremely long cycle life, in which the features of bio-inspired architectures and hetero-atom doping can contribute a lot for great performances. In detail, one-dimensional tube-like metal oxide (e.g., MnO) coated on N-doped carbon framework (i.e., MnO/N-C) is designed using the natural abundant and renewable Metaplexis japonica fibers (MJFs) as the bio-template and hetero-atom sources. Benefiting from the uniqueness of structure and compositions, as-prepared MnO/N-C demonstrates extremely high rate capacities of 951, 777, 497, 435 mAh g-1 at the rates of 0.5, 2, 4 and 5 A g-1 respectively with a good stability more than 1000 cycles. We find that the electrochemical performances are superior to most previous MnO-based anode, in which the faster kinetics of conversion reactions on the merit of the ion/electron transportation and morphological evolution is verified. We hope that the concept of bio-inspired architectures with hetero-atom doping can be applied in the wider applications for greater capabilities.
    • Special Section Guest Editorial: Semiconductor UV Photonics

      Ng, Tien Khee; Yan, Jianchang (SPIE, 2018-09-14)
      This guest editorial summarizes the JNP Special Section on Semiconductor UV Photonics.
    • Conservation of energy for the Euler-Korteweg equations

      Dębiec, Tomasz; Gwiazda, Piotr; Świerczewska-Gwiazda, Agnieszka; Tzavaras, Athanasios (Springer, 2018-09-09)
      In this article we study the principle of energy conservation for the Euler-Korteweg system. We formulate an Onsager-type sufficient regularity condition for weak solutions of the Euler-Korteweg system to conserve the total energy. The result applies to the system of Quantum Hydrodynamics.
    • Measurements of pressure effects on PAH distribution and 2D soot volume fraction diagnostics in a laminar non-premixed coflow flame

      Bennett, Anthony; Amin, Hafiz M.F; Cenker, Emre; Roberts, William L. (American Chemical Society (ACS), 2018-09-07)
      The soot formation process has been investigated at pressures up to 16 bar using a non-premixed laminar coflow flame with nitrogen-diluted ethylene. 2D diffuse line-of-sight attenuation (2D LOSA) and planar laser-induced incandescence (PLII) were used to measure soot volume fraction (SVF). The peak SVF increased exponentially with increasing pressure and the spatial distribution of soot volume fraction changed substantially. At pressures below 6 bar, the two techniques agreed well. At pressures above 6 bar, the techniques began to disagree, with 2D LOSA showing higher peak SVF values at a location lower in the wings of the flame compared to PLII. Errors in the LOSA measurements due to the molecular absorption of PAHs were assessed by performing measurements with bandpass filters centered at 435 nm and at 647 nm. Furthermore, the evolution of polycyclic aromatic hydrocarbons (PAH) in the flame was studied using planar laser-induced fluorescence (PLIF) with the excitation laser set at 282.85 nm and compared to LOSA measurements. Fluorescence signals were captured using bandpass filters (350 nm, 400 nm, 450 nm, and 510 nm) corresponding to increasing PAH size. The peak concentration of PAHs moved closer to the burner nozzle as pressure increased. Absorption by PAH were unable to explain discrepancies between LOSA measurements and PLII measurements. Using the Rayleigh-Debye-Gans approximation for polydisperse fractal aggregates (RDG-PFA), the differences between LOSA and PLII measurements were analyzed, and it was found that LOSA is more sensitive to the soot primary particle diameter due to changes in the scattering to absorption ratio (ρ_sa). The effect of gate duration on SVF imaging with PLII is also reported.
    • Frequency domain multi-parameter acoustic inversion for transversely isotropic media with a vertical axis of symmetry

      Djebbi, Ramzi; Alkhalifah, Tariq (Society of Exploration Geophysicists, 2018-09-07)
      Multi-parameter full waveform inversion (FWI) for transversely isotropic (TI) media with a vertical axis of symmetry (VTI) suffers from the trade-off between the parameters. The trade-off results in the leakage of one parameter’s update into the other. It affects the accuracy and convergence of the inversion. The sensitivity analyses suggested a parameterization using the horizontal velocity vh, Thomsen’s parameter ϵ and the an-elliptic parameter η to reduce the trade-off for surface recorded seismic data. We aim to invert for this parameterization using the scattering integral (SI) method. The available Born sensitivity kernels, within this approach, can be used to calculate additional inversion information. We mainly compute the diagonal of the approximate Hessian, used as a conjugate-gradient preconditioner, and the gradients step lengths. We consider modeling in the frequency domain. The large computational cost of the scattering integral method can be avoided with direct Helmholtz equation solvers.We apply the proposed method to the VTI Marmousi II model for various inversion strategies. We show that we can invert the vh accurately. For the ϵ parameter, only the short wavelengths are well recovered. On the other hand, the η parameter impact is weak on the inversion results and can be fixed. However, a good background η, with accurate long wavelengths, is needed to correctly invert for vh.Furthermore, we invert a real data set acquired by CGG from offshore Australia. We invert simultaneously all three parameters using the proposed inversion approach. The velocity model is improved and additional layers are recovered. We confirm the accuracy of the results by comparing them with well-log information, as well as, looking at the data and angle gathers.
    • A Hybrid Hydrogel with High Water Vapor Harvesting Capacity for Deployable Solar-Driven Atmospheric Water Generator

      Li, Renyuan; Shi, Yusuf; Alsaedi, Mossab; Wu, Mengchun; Shi, Le; Wang, Peng (American Chemical Society (ACS), 2018-09-07)
      The Earth’s atmosphere holds approximately 12,900 billion tons of fresh water and it distributes all over the world with fast replenishment. The atmospheric water harvesting is emerging as a promising strategy for clean water production in arid regions, land-locked, and remote communities. The water vapor sorbent is the key component for atmospheric water harvesting devices based on absorbing-releasing process. In this work, a flexible hybrid photothermal water sorbent composed of deliquescent salt and hydrogel was rationally fabricated. It possesses superior water sorption capacity even in low humidity air thanks to the deliquescent salt and it maintains a solid form after it sorbs a large amount of water owing to the hydrogel platform. The harvested water could be easily released under regular sunlight via the photothermal effect, and it can be directly reused without noticeable capacity fading. An “easy-to-assemble-at-household” prototype device with 35 g of the dry hydrogel was tested outdoors in field conditions and delivered 20 g of fresh water within 2.5 h under natural sunlight. It is estimated that the material cost of making such a device to supply minimum daily water consumption for an adult (i.e., 3 kg) is only $3.2 (USD). This type of atmospheric water generator (AWG) is cheap and affordable, perfectly works with a broad range of humidity, does not need any electricity, and thus is suitable especially for clean water production in remote areas.
    • Dual action of L-Lactate on the activity of NR2B-containing NMDA receptors: from potentiation to neuroprotection

      Jourdain, P.; Rothenfusser, K.; Ben-Adiba, C.; Allaman, I.; Marquet, P.; Magistretti, P. J. (Springer Nature America, Inc, 2018-09-03)
      L-Lactate is a positive modulator of NMDAR-mediated signaling resulting in plasticity gene induction and memory consolidation. However, L-Lactate is also able to protect neurons against excito-toxic NMDAR activity, an indication of a mitigating action of L-Lactate on NMDA signaling. In this study, we provide experimental evidence that resolves this apparent paradox. Transient co-application of glutamate/glycine (1 μM/100 μM; 2 min) in primary cultures of mouse cortical neurons triggers a NMDA-dependent Ca2+ signal positively modulated by L-Lactate (10 mM) or DTT (1 mM) but decreased by Pyruvate (10 mM). This L-Lactate and DTT-induced potentiation is blocked by Ifenprodil (2 μM), a specific blocker of NMDARs containing NR2B sub-units. In contrast, co-application of glutamate/glycine (1 mM/100 μM; 2 min) elicits a NMDAR-dependent excitotoxic death in 49% of neurons. L-Lactate and Pyruvate significantly reduce this rate of cell death processes (respectively to 23% and 9%) while DTT has no effect (54% of neuronal death). This L-Lactate-induced neuroprotection is blocked by carbenoxolone and glibenclamide, respectively blockers of pannexins and KATP. In conclusion, our results show that L-Lactate is involved in two distinct and independent pathways defined as NMDAR-mediated potentiation pathway (or NADH pathway) and a neuroprotective pathway (or Pyruvate/ATP pathway), the prevalence of each one depending on the strength of the glutamatergic stimulus.
    • High summertime aerosol loadings over the Arabian Sea and their transport pathways

      Jin, Qinjian; Wei, Jiangfeng; Pu, Bing; Yang, Zong-Liang; Parajuli, Sagar Prasad (American Geophysical Union (AGU), 2018-09-03)
      Satellite observations show high aerosol loadings over the Arabian Sea in boreal summer, which have great impacts on the Indian monsoon due to absorbing dust aerosols. However, the compositions, origins, transport pathways, and decadal trends of these aerosols have not been well studied. In this study, using multiple satellite retrievals, a back-trajectory model, and reanalysis data, we found that: 1) Aerosol optical depth (AOD) over the Arabian Sea and Arabian Peninsula have a summer peak and dust aerosols dominate the AOD; Aerosol reanalysis data tend to considerably underestimate dust AOD compared to satellite data, indicating challenges of extracting dust from total AOD; 2) Aerosols over the Arabian Sea are largely transported from South and East Arabian Peninsula by cyclonic winds in the lower troposphere (850 hPa) and from Iran–Afghanistan–Pakistan by anticyclonic winds in the middle troposphere (500 hPa); 3) Both case studies and composite analyses show that extremely high aerosol loadings over the Arabian Sea is associated with an abnormally low pressure over the Arabian Sea and the Middle East; and 4) Significant positive trends in AOD over the Arabian Peninsula and the Arabian Sea exist during 2000–2011 but disappear during 2000–2016, indicating a strong interdecadal variability of dust activities. This study revealed pathways linking dust emissions in the Middle East to high summertime AOD over the Arabian Sea and identified the atmospheric conditions favorable for dust emissions and transport.
    • Graphene Oxide Liquid Crystal Membranes in Protic Ionic Liquid for Nanofiltration

      Mahalingam, Dinesh; Wang, Shaofei; Nunes, Suzana P. (American Chemical Society (ACS), 2018-09-04)
      Graphene oxide (GO) liquid crystals are of great interest for membrane preparation. Vacuum filtration has been frequently adopted as small-scale manufacturing method. The main challenge is to obtain thin and robust layers with high permeation and selectivity by methods that could be applied in large scale. GO liquid crystals are mostly formed by dispersion in water. For the first time, we demonstrate that GO can form lyotropic liquid crystalline nematic phase dispersions in protic ionic liquid and be fabricated as membranes for nanofiltration. The well-balanced electrostatic interaction between ionic liquid and GO promotes and stabilizes the alignment of GO nanosheets even when concentrations as low as 9 mg GO /mL are used, providing the ideal rheology for the dispersion casting and membrane preparation. Robust membranes with GO layers as thick as 1 m with high permeance (37 L m-2 h-1 bar-1) and 99.9 % rejection of dyes with molecular weight 697 g/mol were obtained. We confirmed the liquid crystal formation by the detection of birefringence and the rheological behavior and explained the liquid crystal formation as an interplay between hydrogen bonding and electrostatic interactions.
    • Point Defects and Green Emission in Zero-Dimensional Perovskites

      Yin, Jun; Yang, Haoze; Song, Kepeng; El-Zohry, Ahmed M.; Han, Yu; Bakr, Osman M.; Bredas, Jean-Luc; Mohammed, Omar F. (American Chemical Society (ACS), 2018-09-05)
      Zero-dimensional (0D) perovskites have recently opened a new frontier in device engineering for light conversion technologies due to their unprecedented high photoluminescence quantum yield as solids. Although many experimental and theoretical efforts have been made to understand their optical behavior, the origin of their green emission is still opaque. Here, we develop a complete experimental and theoretical picture of point defects in Cs-Pb-Br perovskites and demonstrate that bromide vacancies (VBr) in prototype 0D perovskite Cs4PbBr6 have low formation energy and a relevant defect level to contribute to the mid-gap radiative state. Moreover, the state-of-the-art characterizations including atomic-resolution electron imaging not only confirm the purity of 0D-phase of Br-deficient green-emissive Cs4PbBr6 nanocrystals (NCs), but also exclude the presence of CsPbBr3 NCs impurities. Our findings provide robust evidence for defect-induced green luminescence in 0D perovskite nanoscrystals, which helps extend the scope of the utility of these bulk 0D quantum materials in optoelectronic applications.