Recent Submissions

  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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.
  • 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.
  • 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.
  • Giant enhancement of superconductivity in arrays of ultrathin gallium and zinc sub-nanowires embedded in zeolite

    Zhang, B.; Lyu, J.; Rajan, A.; Li, X.; Zhang, X.; Zhang, T.; Dong, Z.; Pan, Jie; Liu, Y.; Zhang, J.; Lortz, R.; Lai, Z.; Sheng, P. (Elsevier BV, 2018-09-08)
    We have fabricated superconducting samples comprising gallium (Ga) or zinc (Zn) infiltrated into the one-dimensional (1D) linear channels of AlPO-5 (AFI) zeolite, which have an internal pore diameter of 7 Å and are separated by an insulating wall of ∼7–9 Å. The Angstrom-scale Ga and Zn sub-nanowires, arranged in Josephson-coupled triangular arrays with an ab-plane lattice constant of 14.4 Å, display bulk superconductivity with Tc values of 7.2 K and 3.7 K, respectively, which are significantly enhanced by a factor of 7 and 4 compared with their bulk values. While the zeolite template of our composite superconductor dictates the nanostructure of Ga and Zn to be 1D in the electronic sense with a highly advantageous effect for the superconducting pairing, the arrangement in a densely packed array structure avoids the shortcomings of other typical 1D superconductors, in which the coherence is usually completely suppressed by strong phase fluctuations.
  • 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.
  • 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.
  • 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.
  • Porous Hollow Fiber Nickel Electrodes for Effective Supply and Reduction of Carbon Dioxide to Methane through Microbial Electrosynthesis

    Alqahtani, Manal F.; Katuri, Krishna P.; Bajracharya, Suman; Yu, Yuanlie; Lai, Zhiping; Saikaly, Pascal Elias (Wiley, 2018-09-06)
    Microbial electrochemical reduction of CO2 gas to value-added chemical products requires the development of an electrode architecture with a three-phase interface for efficient mass transport. A hybrid bioinorganic system for CO2 reduction to CH4 is developed by coupling a new electrode architecture with enriched methanogenic community. The novel electrode design consists of porous nickel hollow fibers, which act as an inorganic electrocatalyst for hydrogen generation from proton reduction and as a gas-transfer membrane for direct CO2 delivery to CO2-fixing hydrogenotrophic methanogens (biological catalyst) on the cathode through the pores of the hollow fibers. These unique features of the electrode create a suitable environment for the enrichment of methanogens, which utilize the hydrogen as a source of reducing equivalents for the conversion of CO2 to CH4. The performance of the nickel electrode is tested in microbial electrosynthesis cells operated at cathode potential of −1 V versus Ag/AgCl, achieving high faradaic efficiency of 77% for CH4. The superior performance of the hybrid bioinorganic system is attributed to the electrode architecture, which provides a three-phase boundary for gas–liquid reactions, with the reactions supported by the inorganic and biological catalysts.
  • Capturing the Diurnal Cycle of Land Surface Temperature Using an Unmanned Aerial Vehicle

    Malbéteau, Yoann; Parkes, Stephen; Aragon, Bruno; Rosas, Jorge; McCabe, Matthew (MDPI AG, 2018-09-05)
    Characterizing the land surface temperature (LST) and its diurnal cycle is important in understanding a range of surface properties, including soil moisture status, evaporative response, vegetation stress and ground heat flux. While remote-sensing platforms present a number of options to retrieve this variable, there are inevitable compromises between the resolvable spatial and temporal resolution. For instance, the spatial resolution of geostationary satellites, which can provide sub-hourly LST, is often too coarse (3 km) for many applications. On the other hand, higher-resolution polar orbiting satellites are generally infrequent in time, with return intervals on the order of weeks, limiting their capacity to capture surface dynamics. With recent developments in the application of unmanned aerial vehicles (UAVs), there is now the opportunity to collect LST measurements on demand and at ultra-high spatial resolution. Here, we detail the collection and analysis of a UAV-based LST dataset, with the purpose of examining the diurnal surface temperature response: something that has not been possible from traditional satellite platforms at these scales. Two separate campaigns were conducted over a bare desert surface in combination with either Rhodes grass or a recently harvested maize field. In both cases, thermal imagery was collected between 0800 and 1700 local solar time. The UAV-based diurnal cycle was consistent with ground-based measurements, with a mean correlation coefficient and root mean square error (RMSE) of 0.99 and 0.68 °C, respectively. LST retrieved over the grass surface presented the best results, with an RMSE of 0.45 °C compared to 0.67 °C for the single desert site and 1.28 °C for the recently harvested maize surface. Even considering the orders of magnitude difference in scale, an exploratory analysis comparing retrievals of the UAV-based diurnal cycle with METEOSAT geostationary data yielded pleasing results (R = 0.98; RMSE = 1.23 °C). Overall, our analysis revealed a diurnal range over the desert and maize surfaces of ~20 °C and ~17 °C respectively, while the grass showed a reduced amplitude of ~12 °C. Considerable heterogeneity was observed over the grass surface at the peak of the diurnal cycle, which was likely indicative of the varying crop water status. To our knowledge, this study presents the first spatially varying analysis of the diurnal LST captured at ultra-high resolution, from any remote platform. Our findings highlight the considerable potential to utilize UAV-based retrievals to enhance investigations across multi-disciplinary studies in agriculture, hydrology and land-atmosphere investigations.
  • 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.

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