Now showing items 21-40 of 20301

    • Direct Growth of Single Crystalline GaN Nanowires on Indium Tin Oxide-Coated Silica

      Prabaswara, Aditya; Min, Jung-Wook; Subedi, Ram Chandra; Tangi, Malleswararao; Holguin Lerma, Jorge Alberto; Zhao, Chao; Priante, Davide; Ng, Tien Khee; Ooi, Boon S. (Springer Nature, 2019-02-05)
      In this work, we demonstrated the direct growth of GaN nanowires on indium tin oxide (ITO)-coated fused silica substrate. The nanowires were grown catalyst-free using plasma-assisted molecular beam epitaxy (PA-MBE). The effect of growth condition on the morphology and quality of the nanowires is systematically investigated. Structural characterization indicates that the nanowires grow in the (0001) direction directly on top of the ITO layer perpendicular to the substrate plane. Optical characterization of the nanowires shows that yellow luminescence is absent from the nanowire's photoluminescence response, attributed to the low number of defects. Conductive atomic force microscopy (C-AFM) measurement on n-doped GaN nanowires shows good conductivity for individual nanowires, which confirms the potential of using this platform for novel device applications. By using a relatively low-temperature growth process, we were able to successfully grow high-quality single-crystal GaN material without the degradation of the underlying ITO layer.
    • Numerical study on the jet formation of simple-geometry heavy gas inhomogeneities

      Fan, E.; Guan, Ben; WEN, Chih-Yung; Shen, Hua (AIP Publishing, 2019-02-05)
      The jet formation of gas inhomogeneities under the impact of a planar shock wave is an interesting phenomenon that is closely related to shock convergence. In this study, a series of heavy gas inhomogeneities with very simple geometries (square, rectangle, circle, and triangle) are numerically reproduced to trace the source of the jet formation. Special attention is given to the wave patterns that lead to the formation of specific jet forms. The shock-accelerated multicomponent flow is simulated by solving inviscid compressible Euler equations. An up-wind characteristic space-time conservation element and solution element scheme is adopted, and a five-equation model is used to treat the gas interface. The jet types that emerge in the experimental images are explained based on the numerical results, and a typical shock pattern that ensures the jet formation is uncovered. It is found that, physically, the jet is initiated by the impact of the internal Mach stem, and the jet growth is nourished by the high speed gas flow induced by this Mach stem. The width of the jet is determined by the height of the internal Mach stem. Geometrically, a focal wedge enveloped by slip lines emerges in the gas inhomogeneity, in which the gas is accelerated. It is found that the existence of the focal wedge and the coordinates of the wedge tip can be used as qualitative criteria to illustrate the mechanism of the jet formation. These criteria provide a more intuitive basis for understanding the direction, scale, and process of jet formation.
    • Nutrient stress arrests tentacle growth in the coral model Aiptasia

      Radecker, Nils; Chen, Jit Ern; Pogoreutz, Claudia; Herrera Sarrias, Marcela; Aranda, Manuel; Voolstra, Christian R. (Springer Nature, 2019-02-04)
      The symbiosis between cnidarians and dinoflagellate algae of the family Symbiodiniaceae builds the foundation of coral reef ecosystems. The sea anemone Aiptasia is an emerging model organism promising to advance our functional understanding of this symbiotic association. Here, we report the observation of a novel phenotype of symbiotic Aiptasia likely induced by severe nutrient starvation. Under these conditions, developing Aiptasia no longer grow any tentacles. At the same time, fully developed Aiptasia do not lose their tentacles, yet produce asexual offspring lacking tentacles. This phenotype, termed ‘Wurst’ Aiptasia, can be easily induced and reverted by nutrient starvation and addition, respectively. Thereby, this observation may offer a new experimental framework to study mechanisms underlying phenotypic plasticity as well as nutrient cycling within the Cnidaria – Symbiodiniaceae symbiosis.
    • Data for "grain-displacive gas migration in fine-grained sediments"

      Sun, Zhonghao; Santamarina, Carlos (2019-02-03)
    • Thin Peptide Hydrogel Membranes Suitable as Scaffolds for Engineering Layered Biostructures

      Seow, Wei Yang; Kandasamy, Karthikeyan; Purnamawati, Kristy; Sun, William; Hauser, Charlotte (Elsevier BV, 2019-02-02)
      A short tetramer peptide, Ac-IVKC, spontaneously formed a hydrogel in water. Disulfide bonds were introduced via hydrogen peroxide (H2O2)-assisted oxidation, resulting in (Ac-IVKC)2 dimers. The extent of disulfide bond formation and gel stiffness increased with the amount of H2O2 used and 100% dimerization was achieved with 0.2% H2O2. The resultant gel achieved an elastic modulus of ∼0.9 MPa, which to our knowledge, has not been reported for peptide-based hydrogels. The enhanced mechanical property enabled the fabrication of thin and transparent membranes. The hydrogel could also be handled with forceps at mm thickness, greatly increasing its ease of physical manipulation. Excess H2O2 was removed and the membrane was then infused with cell culture media. Various cells, including primary human corneal stromal and epithelial cells, were seeded onto the hydrogel membrane and demonstrated to remain viable. Depending on the intended application, specific cell combination or membrane stacking order could be used to engineer layered biostructures. STATEMENT OF SIGNIFICANCE: A short tetramer peptide - Ac-IVKC - spontaneously formed a hydrogel in water and disulfide bonds were introduced via hydrogen peroxide (H2O2)-assisted oxidation. The extent of disulfide-bond formation and gel stiffness were modulated by the amount of H2O2. At maximum disulfide-bond formation, the hydrogel achieved an elastic modulus of ∼0.9 MPa, which to our knowledge, has not been reported for peptide-based hydrogels. The enhanced mechanical property enabled the fabrication of thin transparent membranes that can be physically manipulated at mm thickness. The gels also supported 3D cell growth, including primary human corneal stromal and epithelial cells. Depending on the intended application, specific combination of cells or individual membrane stacking order could be used to engineer layered biostructures.
    • Formal axioms in biomedical ontologies improve analysis and interpretation of associated data

      Smaili, Fatima Z.; Gao, Xin; Hoehndorf, Robert (Cold Spring Harbor Laboratory, 2019-02-02)
      Motivation: There are now over 500 ontologies in the life sciences. Over the past years, significant resources have been invested into formalizing these biomedical ontologies. Formal axioms in ontologies have been developed and used to detect and ensure ontology consistency, find unsatisfiable classes, improve interoperability, guide ontology extension through the application of axiom-based design patterns, and encode domain background knowledge. At the same time, ontologies have extended their amount of human-readable information such as labels and definitions as well as other meta-data. As a consequence, biomedical ontologies now form large formalized domain knowledge bases and have a potential to improve ontology-based data analysis by providing background knowledge and relations between biological entities that are not otherwise connected. Results: We evaluate the contribution of formal axioms and ontology meta-data to the ontology-based prediction of protein-protein interactions and gene-disease associations. We find that the formal axioms that have been created for the Gene Ontology and several other ontologies significantly improve ontology- based prediction models through provision of domain-specific background knowledge. Furthermore, we find that the labels, synonyms and definitions in ontologies can also provide background knowledge that may be exploited for prediction. The axioms and meta-data of different ontologies contribute in varying degrees to improving data analysis. Our results have major implications on the further development of formal knowledge bases and ontologies in the life sciences, in particular as machine learning methods are more frequently being applied. Our findings clearly motivate the need for further development, and the systematic, application-driven evaluation and improvement, of formal axioms in ontologies
    • Noninvasive Featherlight Wearable Compliant “Marine Skin”: Standalone Multisensory System for Deep-Sea Environmental Monitoring

      Shaikh, Sohail F.; Mazo-Mantilla, Harold F.; Qaiser, Nadeem; Khan, Sherjeel M.; Nassar, Joanna M.; Geraldi, Nathan R.; Duarte, Carlos M.; Hussain, Muhammad Mustafa (Wiley, 2019-02-01)
      Advances in marine research to understand environmental change and its effect on marine ecosystems rely on gathering data on species physiology, their habitat, and their mobility patterns using heavy and invasive biologgers and sensory telemetric networks. In the past, a lightweight (6 g) compliant environmental monitoring system: Marine Skin was demonstrated. In this paper, an enhanced version of that skin with improved functionalities (500–1500% enhanced sensitivity), packaging, and most importantly its endurance at a depth of 2 km in the highly saline Red Sea water for four consecutive weeks is reported. A unique noninvasive approach for attachment of the sensor by designing a wearable, stretchable jacket (bracelet) that can adhere to any species irrespective of their skin type is also illustrated. The wearable featherlight (<0.5 g in air, 3 g with jacket) gadget is deployed on Barramundi, Seabream, and common goldfish to demonstrate the noninvasive and effective attachment strategy on different species of variable sizes which does not hinder the animals' natural movement or behavior.
    • Dip-angle image gathers computation using Poynting vector in elastic reverse-time migration and their application for noise suppression

      Liu, Qiancheng (Society of Exploration Geophysicists, 2019-02-01)
      Angle-domain common-imaging gathers (ADCIGs) are important in analyzing the subsurface discontinuities where the reflection-waves take place. In elastic reverse-time migration (E-RTM), the dip-angle ADCIGs can be computed post-migration via the subsurface offset extension. We here obtain dip-angle ADCIG pre-migration in E-RTM by using Poynting vector, which is likely to compute during wavefield propagation. The reflection normal of PP imaging is the bisector of the scattering angle while that of PS imaging is not. We derive formulas to estimate PP and PS dip-angle ADCIGs, respectively, with some straightforward vector operations. Similar to the subsurface-offset method, our method also has dip-angle ADCIGs with the appearance of blocky horizontal coherence. According to the theory of local semblance analysis, the signal with better horizontal coherence has a higher semblance score, and vice versa. We can thus design a specularity filter to suppress incoherent noises according to their corresponding local semblance scores. We validate our methods with numerical examples. Both the Graben data and Marmousi data show that our methods work effectively in dip-angle ADCIG computation and the following noise suppression in E-RTM. We also apply our methods to the field data.
    • CpG traffic lights are markers of regulatory regions in human genome

      Lioznova, Anna V.; Khamis, Abdullah M.; Artemov, Artem V.; Besedina, Elizaveta; Ramensky, Vasily; Bajic, Vladimir B.; Kulakovskiy, Ivan V.; Medvedeva, Yulia A. (Springer Nature, 2019-02-01)
      Background:DNA methylation is involved in the regulation of gene expression. Although bisulfite-sequencing based methods profile DNA methylation at a single CpG resolution, methylation levels are usually averaged over genomic regions in the downstream bioinformatic analysis. Results:We demonstrate that on the genome level a single CpG methylation can serve as a more accurate predictor of gene expression than an average promoter / gene body methylation. We define CpG traffic lights (CpG TL) as CpG dinucleotides with a significant correlation between methylation and expression of a gene nearby. CpG TL are enriched in all regulatory regions. Among all promoters, CpG TL are especially enriched in poised ones, suggesting involvement of DNA methylation in their regulation. Yet, binding of only a handful of transcription factors, such as NRF1, ETS, STAT and IRF-family members, could be regulated by direct methylation of transcription factor binding sites (TFBS) or its close proximity. For the majority of TF, an alternative scenario is more likely: methylation and inactivation of the whole regulatory element indirectly represses functional TF binding with a CpG TL being a reliable marker of such inactivation. Conclusions: CpG TL provide a promising insight into mechanisms of enhancer activity and gene regulation linking methylation of single CpG to gene expression. CpG TL methylation can be used as reliable markers of enhancer activity and gene expression in applications, e.g. in clinic where measuring DNA methylation is easier compared to directly measuring gene expression due to more stable nature of DNA.
    • Ecohydrographic control on the community structure and vertical distribution of pelagic Chaetognatha in the Red Sea

      Karati, Kusum Komal; Al-aidaroos, Ali M.; Devassy, Reny P.; El-Sherbiny, Mohsen M.; Jones, Burton; Sommer, Ulrich; Kürten, Benjamin (Springer Nature, 2019-01-31)
      The present study details the effects of basin-scale hydrographic characteristics of the Red Sea on the macroecology of Chaetognatha, a major plankton component in the pelagic realm. The hydrographic attributes and circulation of the Red Sea as a result of its limited connection with the northern Indian Ocean make it a unique ecohydrographic region in the world ocean. Here, we aimed to identify the prime determinants governing the community structure and vertical distribution of the Cheatognatha in this ecologically significant world ocean basin. The intrusion of Gulf of Aden Water influenced the Chaetognatha community composition in the south, whereas the overturning circulation altered their vertical distribution in the north. The existence of hypoxic waters (< 100 µmol kg−1) at mid-depth also influenced their vertical distribution. The detailed evaluation of the responses of the different life stages of Chaetognatha revealed an increased susceptibility of adult individuals to hypoxic waters compared to immature stages. Higher oxygen demands of the adults for the egg and sperm production might have prevented them from inhabiting the oxygen-deficient mid-depth zones. The carbon and nitrogen content of the Copepoda and Chaetognatha communities and the quantification of the predation impact of Chaetognatha on Copepoda based on the feeding rate helped in corroborating the significant trophic link between these two prey–predator taxa. The observed influences of physical and chemical attributes on the distribution of Chaetognatha can be used as a model example for the role of the hydrography on the zooplankton community of the Red Sea.
    • Marine biofilms constitute a bank of hidden microbial diversity and functional potential

      Zhang, Weipeng; Ding, Wei; Li, Yong-Xin; Tam, Chunkit; Bougouffa, Salim; Wang, Ruojun; Pei, Bite; Chiang, Hoyin; Leung, Pokman; Lu, Yanhong; Sun, Jin; Fu, He; Bajic, Vladimir B.; Liu, Hongbin; Webster, Nicole S.; Qian, Pei-Yuan (Springer Nature, 2019-01-31)
      Recent big data analyses have illuminated marine microbial diversity from a global perspective, focusing on planktonic microorganisms. Here, we analyze 2.5 terabases of newly sequenced datasets and the Tara Oceans metagenomes to study the diversity of biofilm-forming marine microorganisms. We identify more than 7,300 biofilm-forming ‘species’ that are undetected in seawater analyses, increasing the known microbial diversity in the oceans by more than 20%, and provide evidence for differentiation across oceanic niches. Generation of a gene distribution profile reveals a functional core across the biofilms, comprised of genes from a variety of microbial phyla that may play roles in stress responses and microbe-microbe interactions. Analysis of 479 genomes reconstructed from the biofilm metagenomes reveals novel biosynthetic gene clusters and CRISPR-Cas systems. Our data highlight the previously underestimated ocean microbial diversity, and allow mining novel microbial lineages and gene resources.
    • Structure and Phase Regulation in MoxC (α-MoC1-x/β-Mo2C) to Enhance Hydrogen Evolution

      Zhang, Xiangyong; Wang, Junchao; Guo, Ting; Liu, Tianying; Wu, Zhuangzhi; Cavallo, Luigi; Cao, Zhen; Wang, Dezhi (Elsevier BV, 2019-01-30)
      Non-precious metal-based efficient electrocatalysts with superior activity and stability for the hydrogen evolution reaction (HER) are useful in solving energy and environmental crises. Herein, monodisperse inverse opal-like MoxC (α-MoC1-x/β-Mo2C) nanospheres were synthesized via a facile strategy to adjust the intrinsic activity and maximize the exposed active sites. In particular, the MoxC-0.4 with the optimal composition of α-MoC1-x/β-Mo2C (0.56/0.44) demonstrated a superior HER performance in 0.5 M H2SO4 with a small Tafel slope of 48 mV dec-1 and remarkable stability. Such prominent performance not only benefits from the inverse opal-like structure that provides more active sites for HER, but also should be ascribed to the strong synergistic effect between α-MoC1-x and β-Mo2C. Based on theoretical calculations, it is further verified that the synergistic effect of MoxC-0.4 is originated from the optimization of interaction with the H* induced by the heterostructure. Furthermore, this work will broaden our vision for highly efficient hydrogen production by bridging the microscopic structure with macroscopic catalytic performance.
    • Dual RNA-seq identifies human mucosal immunity protein Mucin-13 as a hallmark of Plasmodium exoerythrocytic infection

      LaMonte, Gregory M.; Orjuela-Sanchez, Pamela; Calla, Jaeson; Wang, Lawrence T.; Li, Shangzhong; Swann, Justine; Cowell, Annie N.; Zou, Bing Yu; Abdel-Haleem Mohamed, Alyaa M.; Villa Galarce, Zaira Hellen; Moreno, Marta; Tong Rios, Carlos; Vinetz, Joseph M.; Lewis, Nathan; Winzeler, Elizabeth A. (Springer Nature, 2019-01-30)
      The exoerythrocytic stage of Plasmodium infection is a critical window for prophylactic intervention. Using genome-wide dual RNA sequencing of flow-sorted infected and uninfected hepatoma cells we show that the human mucosal immunity gene, mucin-13 (MUC13), is strongly upregulated during Plasmodium exoerythrocytic hepatic-stage infection. We confirm MUC13 transcript increases in hepatoma cell lines and primary hepatocytes. In immunofluorescence assays, host MUC13 protein expression distinguishes infected cells from adjacent uninfected cells and shows similar colocalization with parasite biomarkers such as UIS4 and HSP70. We further show that localization patterns are species independent, marking both P. berghei and P. vivax infected cells, and that MUC13 can be used to identify compounds that inhibit parasite replication in hepatocytes. This data provides insights into host-parasite interactions in Plasmodium infection, and demonstrates that a component of host mucosal immunity is reprogrammed during the progression of infection.
    • Engineering Point Defect States in Monolayer WSe2

      Zhang, Chendong; Wang, Cong; Yang, Feng; Huang, Jing-Kai; Li, Lain-Jong; Yao, Wang; Ji, Wei; Shih, Chih-Kang (American Chemical Society (ACS), 2019-01-29)
      Defect engineering is a key approach for tailoring the properties of the emerging two-dimensional semiconductors. Here, we report an atomic engineering of the W vacancy in monolayer WSe2 by single potassium atom decoration. The K decoration alters the energy states and reshapes the wave-function such that previously hidden mid-gap states become visible with well-resolved multiplets in scanning tunneling spectroscopy. Their energy levels are in good agreement with first principle calculations. More interestingly, the calculations show that an unpaired electron donated by the K atom can lead to a local magnetic moment, exhibiting an on-off switching by the odd-even number of electron filling. Experimentally the Fermi level is pinned above all defect states due to the graphite substrate, corresponding to an off state. The close agreement between theory and experiment in the off state, on the other hand, suggest a possibility of gate-programmable magnetic moments at the defects.
    • Scattering Radiation Pattern Atlas: What anisotropic elastic properties can body waves resolve?

      Kazei, Vladimir; Alkhalifah, Tariq Ali (American Geophysical Union (AGU), 2019-01-29)
      Full-waveform inversion (FWI) optimizes the subsurface properties of geophysical earth models in such a way that the modeled data, based on these subsurface properties, match the observed data. The anisotropic properties, whether monoclinic, orthorhombic, triclinic, or vertical transversally isotropic (VTI), of the subsurface, be it a fractured reservoir or the core-mantle boundary, are necessary to describe the observed wave phenomena. There are no principal limitations on the complexity of the anisotropy that can be inverted using FWI. However, the question remains – what kind of anisotropic descriptions of the elastic properties of the earth can or cannot be inverted reliably from seismic waveforms? We reveal the resolution that can be achieved through reconstructions of each elastic parameter by building vertical resolution patterns from the scattering radiation patterns of body waves. A visual analysis of these patterns indicates
    • Hyperdiverse Macrofauna Communities Associated with a Common Sponge, Stylissa carteri, Shift across Ecological Gradients in the Central Red Sea

      Kandler, Nora; Wooster, Michael; Leray, Matthieu; Knowlton, Nancy; de Voogd, Nicole; Paulay, Gustav; Berumen, Michael L. (MDPI AG, 2019-01-29)
      Sponges act as important microhabitats in the marine environment and promote biodiversity by harboring a wide variety of macrofauna, but little is known about the magnitude and patterns of diversity of sponge-associated communities. This study uses DNA barcoding to examine the macrofaunal communities associated with Stylissa carteri in the central Saudi Arabian Red Sea, an understudied ecosystem with high biodiversity and endemism. In total, 146 operational taxonomic units (OTUs) were distinguished from 938 successfully-sequenced macrofauna individuals from 99 sponges. A significant difference was found in the macrofaunal community composition of S. carteri along a cross-shelf gradient using OTU abundance (Bray–Curtis dissimilarity index), with more amphipods associated with offshore sponges and more brittle stars and fishes associated with inshore sponges. The abundance of S. carteri also showed a gradient, increasing with proximity to shore. However, no significant differences in macrofaunal community composition or total macrofauna abundance were observed between exposed and sheltered sides of the reefs and there was no significant change in total macrofauna abundance along the inshore–offshore gradient. As climate change and ocean acidification continue to impact coral reef ecosystems, understanding the ecology of sponges and their role as microhabitats may become more important for understanding their full ramifications for biodiversity.
    • Joint Trajectory and Precoding Optimization for UAV-Assisted NOMA Networks

      Zhao, Nan; Pang, Xiaowei; Li, Zan; Chen, Yunfei; Li, Feng; Ding, Zhiguo; Alouini, Mohamed-Slim (Institute of Electrical and Electronics Engineers (IEEE), 2019-01-29)
      The explosive data traffic and connections in 5G networks require the use of non-orthogonal multiple access (NOMA) to accommodate more users. Unmanned aerial vehicle (UAV) can be exploited with NOMA to improve the situation further. In this paper, we propose a UAV-assisted NOMA network, in which the UAV and base station (BS) cooperate with each other to serve ground users simultaneously. The sum rate is maximized by jointly optimizing the UAV trajectory and the NOMA precoding. To solve the optimization, we decompose it into two steps. First, the sum rate of the UAV-served users is maximized via alternate user scheduling and UAV trajectory, with its interference to the BS-served users below a threshold. Then, the optimal NOMA precoding vectors are obtained using two schemes with different constraints. The first scheme intends to cancel the interference from the BS to the UAV-served user, while the second one restricts the interference to a given threshold. In both schemes, non-convex optimization problems are converted into tractable ones. An iterative algorithm is designed. Numerical results are provided to evaluate the effectiveness of the proposed algorithms for the hybrid NOMA and UAV network.
    • Mixed-gas sorption in polymers via a new barometric test system: sorption and diffusion of CO2-CH4 mixtures in polydimethylsiloxane (PDMS)

      Genduso, Giuseppe; Litwiller, Eric; Ma, Xiaohua; Zampini, Stefano; Pinnau, Ingo (Elsevier BV, 2019-01-29)
      Mixed-gas sorption of CO2-CH4 mixtures in rubbery polydimethylsiloxane (PDMS) at 35 °C demonstrated that the presence of CH4 changed the behavior of CO2 sorption and vice versa. This mutual interaction indicated that gases in mixtures do not sorb independently in rubbery membranes. Moreover, we observed that at increasing pressures the interaction between PDMS and CO2-CH4 mixtures enhanced the solubility selectivity of PDMS. Mixed-gas solubility coefficients of CH4 in PDMS were lower than 0.5 cm3(STP) cm−3 atm−1. To accurately measure these values, a new sorption system was designed, constructed, and optimized for low solubility coefficients; an operator-friendly approach to mixed-gas sorption experiments is also discussed in this work. CO2-CH4 mixed-gas diffusivity trends were evaluated from Maxwell-Stefan model fitting of mixed-gas permeation and sorption data. The analysis of both mixed-gas diffusion and sorption data demonstrated that CO2/CH4 mixed-gas permselectivity of PDMS was mainly influenced by CO2 sorption. In mixtures, CH4 diffusion coefficients increased with higher volumetric CO2 concentration, whereas CO2 diffusion coefficients were essentially concentration independent in both pure- and mixed-gas environments.
    • Improved solar hydrogen production by engineered doping of InGaN/GaN axial heterojunctions

      Zhang, Huafan; Ebaid, Mohamed; Tan, Jeremy; Liu, Guangyu; Min, Jungwook; Ng, Tien Khee; Ooi, Boon S. (The Optical Society, 2019-01-28)
      InGaN-based nanowires (NWs) have been investigated as efficient photoelectrochemical (PEC) water splitting devices. In this work, the InGaN/GaN NWs were grown by molecular beam epitaxy (MBE) having InGaN segments on top of GaN seeds. Three axial heterojunction structures were constructed with different doping types and levels, namely n-InGaN/n-GaN NWs, undoped (u)-InGaN/p-GaN NWs, and p-InGaN/p-GaN NWs. With the carrier concentrations estimated by Mott–Schottky measurements, a PC1D simulation further confirmed the band structures of the three heterojunctions. The u-InGaN/p-GaN and p-InGaN/p-GaN NWs exhibited optimized stability in pH 0 electrolytes for over 10 h with a photocurrent density of about –4.0 and –9.4 mA/cm2, respectively. However, the hydrogen and oxygen evolution rates of the Pt-treated u-InGaN/p-GaN NWs exhibited a less favorable stoichiometric ratio. On the other hand, the Pt-decorated p-InGaN/p-GaN NWs showed the best PEC performance, generating approximately 1000 µmol/cm2 hydrogen and 550 µmol/cm2 oxygen in 10 h. The band-engineered p-InGaN/p-GaN axial NWs-heterojunction demonstrated a great potential for highly efficient and durable photocathodes.
    • On the opposing effects of methanol and ethanol addition on PAH and soot formation in ethylene counterflow diffusion flames

      Yan, Fuwu; Xu, Lei; Wang, Yu; Park, Sungwoo; Sarathy, Mani; Chung, Suk-Ho (Elsevier BV, 2019-01-28)
      An experimental and numerical analysis of the effects of methanol and ethanol addition on polycyclic aromatic hydrocarbon (PAH) and soot formation in non-premixed ethylene flames is reported here. Laser-induced incandescence (LII) and laser-induced fluorescence (LIF) techniques were used to measure soot volume fractions and relative PAH concentrations in counterflow diffusion flames, respectively. A comprehensive chemical kinetic analysis was performed by modeling soot with detailed gas-phase chemistry and a sectional method. The results showed that although both methanol and ethanol are typically regarded as clean fuels, their presence in ethylene diffusion flames had the opposite effects on PAH and soot formation. The LIF and LII signals decreased significantly as methanol fraction increased, suggesting a soot-inhibiting role for methanol. Apart from the fact that methanol addition reduced the carbon supply for soot thus having a fuel-dilution effect (methanol converted primarily to CO), the increased H2 concentration from methanol decomposition was seen to chemically suppress incipient benzene ring formation and subsequent PAH and soot growth processes. In contrast, a small amount of ethanol addition enhanced soot formation, which was well captured by the numerical model. Reaction pathway analysis showed that ethanol decomposition produced a relatively large amount of methyl radicals, enhancing the chemical interaction between CH3 and C2 species and, thereby promoting the formation of propargyl and C4 species. As a result, benzene formation was promoted through reactions between C2H2 and C4 species and via C3H3 recombination reaction, leading sequentially to the enhancement of PAH growth and soot formation.