Now showing items 1-20 of 49897

    • Spreading of Normal Liquid Helium Drops

      Mallin, David; Langley, Kenneth; Aguirre-Pablo, Andres A.; Wallace, Matthew L.; Milgie, Michael; Thoroddsen, Sigurdur T; Taborek, P. (Physical Review E, American Physical Society (APS), 2020-10-21) [Article]
      We have used video imaging and interferometric techniques to investigate the dynamics of spreading of drops of 4He on a solid surface for temperatures ranging from 5.2 K (near the critical point) to 2.2 K (near Tλ). After an initial transient, the drops become pancake-shaped with a radius that grows as R(t) ≈ t α, with α =0.149 ± 0.002. The drops eventually begin to shrink due to evaporation driven by gravitational and curvature effects, which limits their lifetime to about 1000 s. Although helium completely wets the substrate, and the spreading takes place over a pre-existing adsorbed film, a distinct contact line with a contact angle of order one degree is visible throughout this process.
    • Electropolymerization of robust conjugated microporous polymer membranes for rapid solvent transport and narrow molecular sieving

      Zhou, Zongyao; Li, Xiang; Guo, Dong; Shinde, Digambar; Lu, Dongwei; Chen, Long; Liu, Xiaowei; Cao, Li; Aboalsaud, Ammar M.; Hu, Yunxia; Lai, Zhiping (Nature Communications, Springer Science and Business Media LLC, 2020-10-21) [Article]
      Abstract Pore size uniformity is one of the most critical parameters in determining membrane separation performance. Recently, a novel type of conjugated microporous polymers (CMPs) has shown uniform pore size and high porosity. However, their brittle nature has prevented them from preparing robust membranes. Inspired by the skin-core architecture of spider silk that offers both high strength and high ductility, herein we report an electropolymerization process to prepare a CMP membrane from a rigid carbazole monomer, 2,2’,7,7’-tetra(carbazol-9-yl)-9,9’-spirobifluorene, inside a robust carbon nanotube scaffold. The obtained membranes showed superior mechanical strength and ductility, high surface area, and uniform pore size of approximately 1 nm. The superfast solvent transport and excellent molecular sieving well surpass the performance of most reported polymer membranes. Our method makes it possible to use rigid CMPs membranes in pressure-driven membrane processes, providing potential applications for this important category of polymer materials.
    • Enrichment of salt-tolerant CO2-fixing communities in microbial electrosynthesis systems using porous ceramic hollow tube wrapped with carbon cloth as cathode and for CO2 supply.

      AlQahtani, Manal Faisal; Bajracharya, Suman; Katuri, Krishna; Ali, Muhammad; Xu, Jiajie; Alarawi, Mohammed S; Saikaly, Pascal (The Science of the total environment, Elsevier BV, 2020-10-20) [Article]
      Microbial inocula from marine origins are less explored for CO2 reduction in microbial electrosynthesis (MES) system, although effective CO2-fixing communities in marine environments are well-documented. We explored natural saline habitats, mainly salt marsh (SM) and mangrove (M) sediments, as potential inoculum sources for enriching salt-tolerant CO2 reducing community using two enrichment strategies: H2:CO2 (80:20) enrichment in serum vials and enrichment in cathode chamber of MES reactors operated at -1.0 V vs. Ag/AgCl. Porous ceramic hollow tube wrapped with carbon cloth was used as cathode and for direct CO2 delivery to CO2 reducing communities growing on the cathode surface. Methanogenesis was dominant in both the M- and SM-seeded MES and the methanogenic Archaea Methanococcus was the most dominant genus. Methane production was slightly higher in the SM-seeded MES (4.9 ± 1.7 mmol) compared to the M-seeded MES (3.8 ± 1.1 mmol). In contrast, acetate production was almost two times higher in the M-seeded MES (3.1 ± 0.9 mmol) than SM-seeded MES (1.5 ± 1.3 mmol). The high relative abundance of the genus Acetobacterium in the M-seeded serum vials correlates with the high acetate production obtained. The different enrichment strategies affected the community composition, though the communities in MES reactors and serum vials were performing similar functions (methanogenesis and acetogenesis). Despite similar operating conditions, the microbial community composition of M-seeded serum vials and MES reactors differed from the SM-seeded serum vials and MES reactors, supporting the importance of inoculum source in the evolution of CO2-reducing microbial communities.
    • Characterizing envelopes of moving rotational cones and applications in CNC machining

      Skopenkov, Mikhail; Bo, Pengbo; Bartoň, Michael; Pottmann, Helmut (Elsevier, 2020-10-20) [Article]
      Motivated by applications in CNC machining, we provide a characterization of surfaces which are enveloped by a one-parametric family of congruent rotational cones. As limit cases, we also address developable surfaces and ruled surfaces. The characterizations are higher order nonlinear PDEs generalizing the ones by Gauss and Monge for developable surfaces and ruled surfaces, respectively. The derivation includes results on local approximations of a surface by cones of revolution, which are expressed by contact order in the space of planes. These results are themselves of interest in geometric computing, for example in cutter selection and positioning for flank CNC machining.
    • Role of Oxidized Mo Species on the Active Surface of Ni–Mo Electrocatalysts for Hydrogen Evolution under Alkaline Conditions

      Bau, Jeremy; Kozlov, Sergey; Azofra Mesa, Luis; Ould-Chikh, Samy; Emwas, Abdul-Hamid M.; Idriss, Hicham; Cavallo, Luigi; Takanabe, Kazuhiro (ACS Catalysis, American Chemical Society (ACS), 2020-10-20) [Article]
      A Ni–Mo composite functions as a promising non-noble metal electrocatalyst for the hydrogen evolution reaction (HER) in alkaline water. Despite its industrial relevance, the kinetic origin of the high catalytic activity remains under debate. The present report discusses a reaction mechanism of HER on Ni–Mo catalysts by combining experimental and theoretical studies. In contrast to a Ni catalyst, a Ni–Mo catalyst is insensitive to CO gas introduced during HER. In situ spectroscopic measurements including Raman spectroscopy and electron paramagnetic resonance (EPR) show that Mo3+ prevails during HER catalysis. Density functional theory (DFT) simulations corroborate the thermodynamic stability and HER activity of Mo3+-containing centers on Ni(111) at HER potentials. Notably, Ni is demonstrated to play no direct role as a catalytic site but to effectively disperse and activate the oxidized catalytic Mo species. The results illustrate how to improve the electrocatalytic activity for alkaline HER.
    • Electrification at water–hydrophobe interfaces

      Nauruzbayeva, Jamilya; Sun, Zhonghao; Gallo Junior, Adair; Ibrahim, Mahmoud; Santamarina, Carlos; Mishra, Himanshu (Nature Communications, Springer Science and Business Media LLC, 2020-10-20) [Article]
      Abstract The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science. A clear understanding of these mechanisms could, for instance, aid the rational design of triboelectric generators and micro- and nano-fluidic devices. Here, we investigate the origins of the excess positive charges incurred on water droplets that are dispensed from capillaries made of polypropylene, perfluorodecyltrichlorosilane-coated glass, and polytetrafluoroethylene. Results demonstrate that the magnitude and sign of electrical charges vary depending on: the hydrophobicity/hydrophilicity of the capillary; the presence/absence of a water reservoir inside the capillary; the chemical and physical properties of aqueous solutions such as pH, ionic strength, dielectric constant and dissolved CO2 content; and environmental conditions such as relative humidity. Based on these results, we deduce that common hydrophobic materials possess surface-bound negative charge. Thus, when these surfaces are submerged in water, hydrated cations form an electrical double layer. Furthermore, we demonstrate that the primary role of hydrophobicity is to facilitate water-substrate separation without leaving a significant amount of liquid behind. These results advance the fundamental understanding of water-hydrophobe interfaces and should translate into superior materials and technologies for energy transduction, electrowetting, and separation processes, among others.
    • RepAHR: an improved approach for de novo repeat identification by assembly of the high-frequency reads.

      Liao, Xingyu; Gao, Xin; Zhang, Xiankai; Wu, Fang-Xiang; Wang, Jianxin (BMC bioinformatics, Springer Science and Business Media LLC, 2020-10-20) [Article]
      BACKGROUND:Repetitive sequences account for a large proportion of eukaryotes genomes. Identification of repetitive sequences plays a significant role in many applications, such as structural variation detection and genome assembly. Many existing de novo repeat identification pipelines or tools make use of assembly of the high-frequency k-mers to obtain repeats. However, a certain degree of sequence coverage is required for assemblers to get the desired assemblies. On the other hand, assemblers cut the reads into shorter k-mers for assembly, which may destroy the structure of the repetitive regions. For the above reasons, it is difficult to obtain complete and accurate repetitive regions in the genome by using existing tools. RESULTS:In this study, we present a new method called RepAHR for de novo repeat identification by assembly of the high-frequency reads. Firstly, RepAHR scans next-generation sequencing (NGS) reads to find the high-frequency k-mers. Secondly, RepAHR filters the high-frequency reads from whole NGS reads according to certain rules based on the high-frequency k-mer. Finally, the high-frequency reads are assembled to generate repeats by using SPAdes, which is considered as an outstanding genome assembler with NGS sequences. CONLUSIONS:We test RepAHR on five data sets, and the experimental results show that RepAHR outperforms RepARK and REPdenovo for detecting repeats in terms of N50, reference alignment ratio, coverage ratio of reference, mask ratio of Repbase and some other metrics.
    • Learning from Scholarly Attributed Graphs for Scientific Discovery

      Akujuobi, Uchenna Thankgod (2020-10-18) [Dissertation]
      Advisor: Zhang, Xiangliang
      Committee members: Moshkov, Mikhail; Hoehndorf, Robert; Zhang, Min
      Research and experimentation in various scientific fields are based on the knowledge and ideas from scholarly literature. The advancement of research and development has, thus, strengthened the importance of literary analysis and understanding. However, in recent years, researchers have been facing massive scholarly documents published at an exponentially increasing rate. Analyzing this vast number of publications is far beyond the capability of individual researchers. This dissertation is motivated by the need for large scale analyses of the exploding number of scholarly literature for scientific knowledge discovery. In the first part of this dissertation, the interdependencies between scholarly literature are studied. First, I develop Delve – a data-driven search engine supported by our designed semi-supervised edge classification method. This system enables users to search and analyze the relationship between datasets and scholarly literature. Based on the Delve system, I propose to study information extraction as a node classification problem in attributed networks. Specifically, if we can learn the research topics of documents (nodes in a network), we can aggregate documents by topics and retrieve information specific to each topic (e.g., top-k popular datasets). Node classification in attributed networks has several challenges: a limited number of labeled nodes, effective fusion of topological structure and node/edge attributes, and the co-existence of multiple labels for one node. Existing node classification approaches can only address or partially address a few of these challenges. This dissertation addresses these challenges by proposing semi-supervised multi-class/multi-label node classification models to integrate node/edge attributes and topological relationships. The second part of this dissertation examines the problem of analyzing the interdependencies between terms in scholarly literature. I present two algorithms for the automatic hypothesis generation (HG) problem, which refers to the discovery of meaningful implicit connections between scientific terms, including but not limited to diseases, drugs, and genes extracted from databases of biomedical publications. The automatic hypothesis generation problem is modeled as a future connectivity prediction in a dynamic attributed graph. The key is to capture the temporal evolution of node-pair (term-pair) relations. Experiment results and case study analyses highlight the effectiveness of the proposed algorithms compared to the baselines’ extension.
    • Dynamic Programming Multi-Objective Combinatorial Optimization

      Mankowski, Michal (2020-10-18) [Dissertation]
      Advisor: Moshkov, Mikhail
      Committee members: Keyes, David E.; Shihada, Basem; Boros, Endre
      In this dissertation, we consider extensions of dynamic programming for combinatorial optimization. We introduce two exact multi-objective optimization algorithms: the multi-stage optimization algorithm that optimizes the problem relative to the ordered sequence of objectives (lexicographic optimization) and the bi-criteria optimization algorithm that simultaneously optimizes the problem relative to two objectives (Pareto optimization). We also introduce a counting algorithm to count optimal solution before and after every optimization stage of multi-stage optimization. We propose a fairly universal approach based on so-called circuits without repetitions in which each element is generated exactly one time. Such circuits represent the sets of elements under consideration (the sets of feasible solutions) and are used by counting, multi-stage, and bi-criteria optimization algorithms. For a given optimization problem, we should describe an appropriate circuit and cost functions. Then, we can use the designed algorithms for which we already have proofs of their correctness and ways to evaluate the required number of operations and the time. We construct conventional (which work directly with elements) circuits without repetitions for matrix chain multiplication, global sequence alignment, optimal paths in directed graphs, binary search trees, convex polygon triangulation, line breaking (text justi cation), one-dimensional clustering, optimal bitonic tour, and segmented least squares. For these problems, we evaluate the number of operations and the time required by the optimization and counting algorithms, and consider the results of computational experiments. If we cannot nd a conventional circuit without repetitions for a problem, we can either create custom algorithms for optimization and counting from scratch or can transform a circuit with repetitions into a so-called syntactical circuit, which is a circuit without repetitions that works not with elements but with formulas representing these elements. We apply both approaches to the optimization of matchings in trees and apply the second approach to the 0/1 knapsack problem. We also brie y introduce our work in operation research with applications to health care. This work extends our interest in the optimization eld from developing new methods included in this dissertation towards the practical application.
    • Impact of osmotic and thermal isolation barrier on concentration and temperature polarization and energy efficiency in a novel FO-MD integrated module

      Son, Hyuk Soo; Kim, Youngjin; Nawaz, Muhammad Saqib; Al-Hajji, Mohammed Ali; Abu-Ghdaib, Muhannad; Soukane, Sofiane; Ghaffour, NorEddine (Journal of Membrane Science, Elsevier BV, 2020-10-18) [Article]
      In this study, a novel integrated forward osmosis - membrane distillation (FO-MD) module equipped with an isolation barrier carefully placed between the FO and MD membranes is experimentally investigated, and its performance is compared with a conventional hybrid module. The function of the isolation barrier is to osmotically and thermally separate the FO draw solution (DS) and MD feed channels. A systematic approach is adopted to compare the flux through both modules under (i) different and similar hydrodynamic conditions, (ii) different DS concentrations and temperatures, and (iii) different feed solution concentrations. All experiments were performed for 9 h each in batch mode using a custom-made compact module. New FO and MD membrane sheets were mounted for each experiment to ensure similarity in operating conditions. The proposed module design increased the flux by 22.1% using the same module dimensions but different hydrodynamic conditions. The flux increased by 16.6% using the same hydrodynamic conditions but different module dimensions. The FO/MD energy ratio reduced from 0.89 to 0.64 for the novel module, indicating better utilization of energy (primarily from MD). The gain output ratio (GOR) increased on average by 15.8% for the novel module compared to the conventional module, with a maximum increment of 20.7%. The temperature and concentration polarization coefficients in the MD operations showed improvements of 17.4% and 2.6%, respectively. The presence of the isolation barrier inside the integrated module indicated promising improvements of the flux and internal heat recovery, and further significant enhancements are expected for larger scale modules. Additionally, the novel module design offers unprecedented process integration opportunities for FO-MD as well as other membrane hybrid systems.
    • High summer temperatures amplify functional differences between coral- and algae-dominated reef communities

      Roth, Florian; Rädecker, Nils; Carvalho, Susana; Duarte, Carlos M.; Saderne, Vincent; Anton Gamazo, Andrea; Silva, Luis; Calleja Cortes, Maria de Lluch; Moran, Xose Anxelu G.; Voolstra, Christian R.; Kürten, Benjamin; Jones, Burton; Wild, Christian (Ecology, Wiley, 2020-10-17) [Article]
      Shifts from coral to algal dominance are expected to increase in tropical coral reefs as a result of anthropogenic disturbances. The consequences for key ecosystem functions such as primary productivity, calcification, and nutrient recycling are poorly understood, particularly under changing environmental conditions. We used a novel in situ incubation approach to compare functions of coral- and algae-dominated communities in the central Red Sea bi-monthly over an entire year. In situ gross and net community primary productivity, calcification, dissolved organic carbon fluxes, dissolved inorganic nitrogen fluxes, and their respective activation energies were quantified to describe the effects of seasonal changes. Overall, coral-dominated communities exhibited 30% lower net productivity and 10 times higher calcification than algae-dominated communities. Estimated activation energies indicated a higher thermal sensitivity of coral-dominated communities. In these communities, net productivity and calcification were negatively correlated with temperature (>40% and >65% reduction, respectively, with +5°C increase from winter to summer), while carbon losses via respiration and dissolved organic carbon release were more than doubled at higher temperatures. In contrast, algae-dominated communities doubled net productivity in summer, while calcification and dissolved organic carbon fluxes were unaffected. These results suggest pronounced changes in community functioning associated with phase shifts. Algae-dominated communities may outcompete coral-dominated communities due to their higher productivity and carbon retention to support fast biomass accumulation while compromising the formation of important reef framework structures. Higher temperatures likely amplify these functional differences, indicating a high vulnerability of ecosystem functions of coral-dominated communities to temperatures even below coral bleaching thresholds. Our results suggest that ocean warming may not only cause but also amplify coral-algal phase shifts in coral reefs.
    • Diatom modulation of select bacteria through use of two unique secondary metabolites

      Shibl, Ahmed A.; Isaac, Ashley; Ochsenkühn, Michael A.; Cardenas, Anny; Fei, Cong; Behringer, Gregory; Arnoux, Marc; Drou, Nizar; Santos, Miraflor P.; Gunsalus, Kristin C.; Voolstra, Christian R.; Amin, Shady A. (Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, 2020-10-17) [Article]
      Unicellular eukaryotic phytoplankton, such as diatoms, rely on microbial communities for survival despite lacking specialized compartments to house microbiomes (e.g., animal gut). Microbial communities have been widely shown to benefit from diatom excretions that accumulate within the microenvironment surrounding phytoplankton cells, known as the phycosphere. However, mechanisms that enable diatoms and other unicellular eukaryotes to nurture specific microbiomes by fostering beneficial bacteria and repelling harmful ones are mostly unknown. We hypothesized that diatom exudates may tune microbial communities and employed an integrated multiomics approach using the ubiquitous diatom Asterionellopsis glacialis to reveal how it modulates its naturally associated bacteria. We show that A. glacialis reprograms its transcriptional and metabolic profiles in response to bacteria to secrete a suite of central metabolites and two unusual secondary metabolites, rosmarinic acid and azelaic acid. While central metabolites are utilized by potential bacterial symbionts and opportunists alike, rosmarinic acid promotes attachment of beneficial bacteria to the diatom and simultaneously suppresses the attachment of opportunists. Similarly, azelaic acid enhances growth of beneficial bacteria while simultaneously inhibiting growth of opportunistic ones. We further show that the bacterial response to azelaic acid is numerically rare but globally distributed in the world’s oceans and taxonomically restricted to a handful of bacterial genera. Our results demonstrate the innate ability of an important unicellular eukaryotic group to modulate select bacteria in their microbial consortia, similar to higher eukaryotes, using unique secondary metabolites that regulate bacterial growth and behavior inversely across different bacterial populations.
    • Spin transport in multilayer graphene away from the charge neutrality point

      He, Xin; Wen, Yan; Zhang, Chenhui; Li, Peng; Zheng, Dongxing; Chen, Aitian; Manchon, Aurelien; Zhang, Xixiang (Carbon, Elsevier BV, 2020-10-17) [Article]
      Graphene is considered as a promising material in spintronics due to its long spin relaxation time and long spin relaxation length. However, its spin transport properties have been studied at low carrier density only, beyond which much is still unknown. In this study, we explore the spin transport and spin precession properties in multilayer graphene at high carrier density using ionic liquid gating. We find that the spin relaxation time is directly proportional to the momentum relaxation time, indicating that the Elliott-Yafet mechanism still dominates the spin relaxation in multilayer graphene away from the charge neutrality point.
    • How many alien species will there be in 2050?

      Anton Gamazo, Andrea (Global Change Biology, Wiley, 2020-10-17) [Article]
      The introduction of non-native species into new regions is on the rise due to humanity's increasing global connectivity (Seebens et al., 2017). Many studies have identified the widespread ecological, economic, and social damage that these alien species can cause (Doherty et al., 2016; Hoffmann & Broadhurst, 2016). Advanced statistical analysis has recently been employed to predict ecological patterns of alien species, such as how alien species may be globally distributed in the future. Previous studies that have attempted to answer this question have been restricted to single species, taxa, or regions (Seebens et al., 2015, 2016).
    • Guest Editorial Special Issue on “Wireless Networks Empowered by Reconfigurable Intelligent Surfaces”

      Di Renzo, Marco; Debbah, Merouane; Alouini, Mohamed-Slim; Yuen, Chau; Marzetta, Thomas; Zappone, Alessio (IEEE Journal on Selected Areas in Communications, Institute of Electrical and Electronics Engineers (IEEE), 2020-10-16) [Article]
      Future wireless networks will be as pervasive as the air we breathe, not only connecting us but embracing us through a web of systems that support personal and societal well-being. That is, the ubiquity, speed and low latency of such networks will allow currently disparate devices and services to become a distributed intelligent communications, sensing, and computing platform.
    • Pan-regional marine benthic cryptobiome biodiversity patterns revealed by metabarcoding Autonomous Reef Monitoring Structures.

      Pearman, John K.; Chust, G; Aylagas, E; Villarino, E; Watson, J R; Chenuil, A; Borja, A; Cahill, A E; Carugati, L; Danovaro, R; David, R; Irigoien, X; Mendibil, I; Moncheva, S; Rodríguez-Ezpeleta, N; Uyarra, M C; Carvalho, Susana (Molecular ecology, Wiley, 2020-10-16) [Article]
      Autonomous Reef Monitoring Structures (ARMS) have been applied worldwide to characterize the critical yet frequently overlooked biodiversity patterns of marine benthic organisms. In order to disentangle the relevance of environmental factors in benthic patterns, here, through standardized metabarcoding protocols, we analyze sessile and mobile (
    • Total alkalinity production in a mangrove ecosystem reveals an overlooked Blue Carbon component

      Saderne, Vincent; Fusi, Marco; Thomson, Timothy; Dunne, Aislinn; Mahmud, Fatima; Roth, Florian; Carvalho, Susana; Duarte, Carlos M. (Limnology and Oceanography Letters, Wiley, 2020-10-16) [Article]
      Mangroves have the capacity to sequester organic carbon (Corg) in their sediments permanently. However, the carbon budget of mangroves is also affected by the total alkalinity (TA) budget. Principally, TA emitted from carbonate sediment dissolution is a perennial sink of atmospheric CO2. The assessment of the TA budget of mangrove carbonate sediments in the Red Sea revealed a large TA emission of 403 ± 17 mmol m−2 d−1, independent of light, seasons, or the presence of pneumatophores, compared to −36 ± 10 mmol m−2 d−1 in lagoon sediment. We estimate the TA emission from carbonate dissolution in Red Sea mangroves supported a CO2 uptake of 345 ± 15 gC m−2 yr−1, 23-fold the Corg burial rate of 15 gC m−2 yr−1. The focus on Corg burial in sediments may substantially underestimate the role of mangroves in CO2 removal. Quantifying the role of mangroves in climate change mitigation requires carbonate dissolution to be included in assessments.
    • Bulk and Interfacial Properties of the Decane + Water System in the Presence of Methane, Carbon Dioxide, and Their Mixture

      Yang, Yafan; Nair, Arun Kumar Narayanan; Anwari Che Ruslan, Mohd Fuad; Sun, Shuyu (The Journal of Physical Chemistry B, American Chemical Society (ACS), 2020-10-16) [Article]
      Molecular dynamics simulations are carried out to study the two-phase behavior of the n-decane + water system in the presence of methane, carbon dioxide, and their mixture under reservoir conditions. The simulation studies were complemented by theoretical modeling using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) and density gradient theory. Our results show that the presence of methane and carbon dioxide decreases the interfacial tension (IFT) of the decane + water system. In general, the IFT increases with increasing pressure and decreasing temperature for the methane + decane + water and carbon dioxide + decane + water systems, similar to what has been found for the corresponding decane + water system. The most important finding of this study is that the presence of carbon dioxide decreases the IFT of the methane + decane + water system. The atomic density profiles provide evidence of the local accumulation of methane and carbon dioxide at the interface, in most of the studied systems. The results of this study show the preferential dissolution in the water-rich phase and enrichment at the interface for carbon dioxide in the methane + carbon dioxide + decane + water system. This indicates the preferential interaction of water with carbon dioxide relative to methane and decane. Notably, there is an enrichment of the interface by decane at high mole fractions of methane in the methane/decane-rich or methane/carbon dioxide/decane-rich phase. Overall, the solubility of methane and carbon dioxide in the water-rich phase increases with increasing pressure and temperature. Additionally, we find that the overall performance of the PC-SAFT EoS and the cubic-plus-association EoS is similar with respect to the calculation of bulk and interfacial properties of these systems.
    • Understanding High-Salt and Cold Adaptation of a Polyextremophilic Enzyme

      Karan, Ram; Mathew, Sam; Muhammad, Reyhan; Bautista, Didier B.; Vogler, Malvina M.; Eppinger, Jörg; Oliva, Romina; Cavallo, Luigi; Arold, Stefan T.; Rueping, Magnus (Microorganisms, MDPI AG, 2020-10-16) [Article]
      The haloarchaeon Halorubrum lacusprofundi is among the few polyextremophilic organisms capable of surviving in one of the most extreme aquatic environments on Earth, the Deep Lake of Antarctica (−18 °C to +11.5 °C and 21–28%, w/v salt content). Hence, H. lacusprofundi has been proposed as a model for biotechnology and astrobiology to investigate potential life beyond Earth. To understand the mechanisms that allow proteins to adapt to both salinity and cold, we structurally (including X-ray crystallography and molecular dynamics simulations) and functionally characterized the β-galactosidase from H. lacusprofundi (hla_bga). Recombinant hla_bga (produced in Haloferax volcanii) revealed exceptional stability, tolerating up to 4 M NaCl and up to 20% (v/v) of organic solvents. Despite being cold-adapted, hla_bga was also stable up to 60 °C. Structural analysis showed that hla_bga combined increased surface acidity (associated with halophily) with increased structural flexibility, fine-tuned on a residue level, for sustaining activity at low temperatures. The resulting blend enhanced structural flexibility at low temperatures but also limited protein movements at higher temperatures relative to mesophilic homologs. Collectively, these observations help in understanding the molecular basis of a dual psychrophilic and halophilic adaptation and suggest that such enzymes may be intrinsically stable and functional over an exceptionally large temperature range.
    • A comprehensive experimental and kinetic modeling study of 1- and 2-pentene

      Dong, Shijun; Zhang, Kuiwen; Ninnemann, Erik; Najjar, Ahmed; Kukkadapu, Goutham; Baker, Jessica; Arafin, Farhan; Wang, Zhandong; Pitz, William J.; Vasu, Subith S.; Sarathy, Mani; Senecal, Peter K.; Curran, Henry J. (Combustion and Flame, Elsevier BV, 2020-10-15) [Article]
      1- and 2-pentene are components in gasoline and are also used as representative alkene components in gasoline surrogate fuels. Most of the available ignition delay time data in the literature for these fuels are limited to low pressures, high temperatures and highly diluted conditions, which limits the kinetic model development and validation potential of these fuels. Therefore, ignition delay time measurements under engine-like conditions are needed to provide target data to understand their low-temperature fuel chemistry and extend their chemical kinetic validation to lower temperatures and higher pressures. In this study, both a high-pressure shock tube and a rapid compression machine have been employed to measure ignition delay times of 1- and 2-pentene over a wide temperature range (600–1300 K) at equivalence ratios of 0.5, 1.0 and 2.0 in ‘air’, and at pressures of 15 and 30 atm. At high-temperatures (> 900 K), the experimental ignition delay times show that the fuel reactivities of 1- and 2-pentene are very similar at all equivalence ratios and pressures. However, at low temperatures, 1-pentene shows negative temperature coefficient behavior and a higher fuel reactivity compared to 2-pentene. Moreover, carbon monoxide time-histories for both 1- and 2-pentene were measured in a high-pressure shock tube for a stoichiometric mixture at 10 atm and at high temperatures. Furthermore, species versus temperature profiles were measured in a jet-stirred reactor at φ = 1.0 and 1 atm over a temperature range of 700–1100 K. All of these experimental data have been used to validate the current chemistry mechanism. Starting from a published pentane mechanism, modifications have been made to the 1- and 2-pentene sub-mechanisms resulting in overall good predictions. Moreover, flux and sensitivity analyses were performed to highlight the important reactions involved in the oxidation process.