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Caltech Authors (160.918 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 1.516

  1. Spatial and temporal distributions of air pollutant emissions from open crop straw and biomass burnings in China from 2002 to 2016

    Mehmood, Khalid; Chang, Shucheng; Yu, Shaocai; Wang, Liqiang; Li, Pengfei; Li, Zhen; Liu, Weiping; Rosenfeld, Daniel; Seinfeld, John H.
    Open biomass burning (OBB) with a main contribution from open crop straw burning (OCSB) plays a key role in the formation of heavy haze episodes during harvest seasons in China through release of particulate matter (PM) and gaseous pollutants. Here we analyze spatial and temporal distributions of air pollutant emissions from OCSB and OBB in China from 2002 to 2016 on the basis of daily and highly resolved (1 km) emissions from the latest FINNv1.5 inventory. Estimated annual emissions of black carbon, organic carbon, PM_(2.5), PM_(10), CH_4, CO, CO_2, NH_3, NO_x, SO_2 and NMVOCS from OBB in China from 2002...

  2. Post-collisional deposits in the Zagros foreland basin: Implications for diachronous underthrusting

    Pirouz, Mortaza
    Detailed sedimentology of the Neogene foreland basin deposits is investigated and classified into 11 lithofacies associations with respect to their paleo-sedimentary environments. The foreland deposits reveal a single coarsening-upward mega-sequence with continuous passage from back-bulge to forebulge, foredeep, and wedge-top sedimentary environments. The Gachsaran deposits form the base of the foreland strata and consist mainly of three different lithofacies associations including fluvial, marine, and sabkha deposits in the eastern Zagros in Fars, and are typically dominated with evaporites toward the west in the Dezful and Kirkuk embayments. The Mishan Formation has three different shallow-marine lithofacies associations in a vertical succession...

  3. Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals

    Feuda, Roberto; Dohrmann, Martin; Pett, Walker; Philippe, Hervé; Rota-Stabelli, Omar; Lartillot, Nicolas; Wörheide, Gert; Pisani, Davide
    The relationships at the root of the animal tree have proven difficult to resolve, with the current debate focusing on whether sponges (phylum Porifera) or comb jellies (phylum Ctenophora) are the sister group of all other animals [1; 2; 3; 4 ; 5]. The choice of evolutionary models seems to be at the core of the problem because Porifera tends to emerge as the sister group of all other animals (“Porifera-sister”) when site-specific amino acid differences are modeled (e.g., [6 ; 7]), whereas Ctenophora emerges as the sister group of all other animals (“Ctenophora-sister”) when they are ignored (e.g., [8;...

  4. Earth System Modeling 2.0: A Blueprint for Models That Learn From Observations and Targeted High-Resolution Simulations

    Schneider, Tapio; Lan, Shiwei; Stuart, Andrew; Teixeira, João
    Climate projections continue to be marred by large uncertainties, which originate in processes that need to be parameterized, such as clouds, convection, and ecosystems. But rapid progress is now within reach. New computational tools and methods from data assimilation and machine learning make it possible to integrate global observations and local high-resolution simulations in an Earth system model (ESM) that systematically learns from both and quantifies uncertainties. Here we propose a blueprint for such an ESM. We outline how parameterization schemes can learn from global observations and targeted high-resolution simulations, for example, of clouds and convection, through matching low-order statistics...

  5. Expected seismicity and the seismic noise environment of Europa

    Panning, Mark P.; Stähler, Simon C.; Huang, Hsin-Hua; Vance, Steven D.; Kedar, Sharon; Tsai, Victor C.; Pike, William T.; Lorenz, Ralph D.
    Seismic data will be a vital geophysical constraint on internal structure of Europa if we land instruments on the surface. Quantifying expected seismic activity on Europa both in terms of large, recognizable signals and ambient background noise is important for understanding dynamics of the moon, as well as interpretation of potential future data. Seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans. We define a range of models of seismic activity in Europa's ice shell by assuming each model follows a Gutenberg-Richter relationship with varying parameters. A range of cumulative seismic moment...

  6. Eph-ephrin signaling modulated by polymerization and condensation of receptors

    Ojosnegros, Samuel; Cutrale, Francesco; Rodríguez, Daniel; Otterstrom, Jason J.; Chiu, Chi Li; Hortigüela, Verónica; Tarantino, Carolina; Seriola, Anna; Mieruszynski, Stephen; Martínez, Elena; Lakadamyali, Melike; Raya, Angel; Fraser, Scott E.
    Eph receptor signaling plays key roles in vertebrate tissue boundary formation, axonal pathfinding, and stem cell regeneration by steering cells to positions defined by its ligand ephrin. Some of the key events in Eph-ephrin signaling are understood: ephrin binding triggers the clustering of the Eph receptor, fostering transphosphorylation and signal transduction into the cell. However, a quantitative and mechanistic understanding of how the signal is processed by the recipient cell into precise and proportional responses is largely lacking. Studying Eph activation kinetics requires spatiotemporal data on the number and distribution of receptor oligomers, which is beyond the quantitative power offered...

  7. Stabilization of hybrid perovskite CH_3NH_3PbI_3 thin films by graphene passivation

    Tseng, Wei-Shiuan; Jao, Meng-Huan; Hsu, Chen-Chih; Huang, Jing-Shun; Wu, Chih-I.; Yeh, N.-C.
    We report the long-term stability of water-sensitive hybrid perovskites CH_3NH_3PbI_3 that were protected with monolayer graphene. This successful passivation was enabled by our development of a new water-free and polymer-free graphene transfer method. Monolayer graphene samples grown by plasma-enhanced chemical vapor deposition and transferred onto different substrates with the water/polymer-free method were found to preserve their high-quality characteristics after the transfer, as manifested by the studies of Raman, X-ray and ultraviolet photoemission spectroscopy (XPS and UPS), optical absorption, and sheet resistance. Additionally, XPS, UPS and optical absorption studies of fully graphene-covered CH_3NH_3PbI_3 thin films showed spectral invariance even after 3...

  8. Isocanthine Synthesis via Rh(III)-Catalyzed Intramolecular C-H Functionalization

    Chen, Anthony Y.; Lu, Qianqian; Fu, Yao; Sarpong, Richmond; Stoltz, Brian M.; Zhang, Haiming
    An efficient synthesis of substituted isocanthines has been achieved using an intramolecular Rh(III)-catalyzed C─H functionalization of alkyne-tethered indoles in the presence of catalytic tris(acetonitrile)pentamethyl-cyclopentadienylrhodium(III) hexafluoroantimonate and stoichiometric copper(II) acetate. This isocanthine synthesis tolerates a variety of electronically diverse 5- or 6-substituted indoles with N-tethered alkyne coupling partners and can also be extended to pyrrole derivatives for the synthesis of annulated 5-azaindoles.

  9. Genetically programmed chiral organoborane synthesis

    Kan, S. B. Jennifer; Huang, Xiongyi; Gumulya, Yosephine; Chen, Kai; Arnold, Frances H.
    Recent advances in enzyme engineering and design have expanded nature’s catalytic repertoire to functions that are new to biology. However, only a subset of these engineered enzymes can function in living systems. Finding enzymatic pathways that form chemical bonds that are not found in biology is particularly difficult in the cellular environment, as this depends on the discovery not only of new enzyme activities, but also of reagents that are both sufficiently reactive for the desired transformation and stable in vivo. Here we report the discovery, evolution and generalization of a fully genetically encoded platform for producing chiral organoboranes in...

  10. Extension of the Polarizable Charge Equilibration Model to Higher Oxidation States with Applications to Ge, As, Se, Br, Sn, Sb, Te, I, Pb, Bi, Po, and At Elements

    Oppenheim, Julius J.; Naserifar, Saber; Goddard, William A., III
    We recently developed the Polarizable Charge Equilibration (PQEq) model to predict accurate electrostatic interactions for molecules and solids and optimized parameters for H, C, N, O, F, Si, P, S, and Cl elements to fit polarization energies computed by quantum mechanics (QM). Here, we validate and optimize the PQEq parameters for other p-block elements including Ge, As, Se, Br, Sn, Sb, Te, I, Pb, Bi, Po, and At using 28 molecular structures containing these elements. For elements in the Se column of the periodic table, we now include molecules with higher oxidation states: III and V for the As column,...

  11. Copper-Catalyzed Alkylation of Aliphatic Amines Induced by Visible Light

    Matier, Carson D.; Schwaben, Jonas; Peters, Jonas C.; Fu, Gregory C.
    Although the alkylation of an amine by an alkyl halide serves as a “textbook example” of a nucleophilic substitution reaction, the selective mono-alkylation of aliphatic amines by unactivated, hindered halides persists as a largely unsolved challenge in organic synthesis. We report herein that primary aliphatic amines can be cleanly mono-alkylated by unactivated secondary alkyl iodides in the presence of visible light and a copper catalyst. The method operates under mild conditions (–10 °C), displays good functional-group compatibility, and employs commercially available catalyst components. A trapping experiment with TEMPO is consistent with C–N bond formation via an alkyl radical in an...

  12. Geochemistry of the Serifos calc-alkaline granodiorite pluton, Greece: constraining the crust and mantle contributions to I-type granitoids

    Stouraiti, C.; Baziotis, I.; Asimow, P. D.; Downes, H.
    The Late Miocene (11.6–9.5 Ma) granitoid intrusion on the island of Serifos (Western Cyclades, Aegean Sea) is composed of syn- to post-tectonic granodiorite with quartz monzodiorite enclaves, cut by dacitic and aplitic dikes. The granitoid, a typical I-type metaluminous calcic amphibole-bearing calc-alkaline pluton, intruded the Cycladic Blueschists during thinning of the Aegean plate. Combining field, textural, geochemical and new Sr–Nd–O isotope data presented in this paper, we postulate that the Serifos intrusion is a single-zoned pluton. The central facies has initial ^(87)Sr/^(86)Sr = 0.70906 to 0.7106, ε_(Nd)(t) = − 5.9 to −  7.5 and δ^(18)Ο_(qtz) = + 10 to + 10.6‰, whereas the marginal...

  13. Seismic and Aseismic Moment Budget and Implication for the Seismic Potential of the Parkfield Segment of the San Andreas Fault

    Michel, Sylvain; Avouac, Jean-Philippe; Jolivet, Romain; Wang, Lifeng
    This study explores methods to assess the seismic potential of a fault based on geodetic measurements, geological information of fault‐slip rate, and seismicity data. The methods are applied to the Parkfield section along the San Andreas fault (SAF) at the transition zone between the SAF creeping segment in the north and the locked section of Cholame to the south, where M_w ∼6 earthquakes occurred every 24.5 yrs on average since the 1857 M_w 7.7 Fort Tejon earthquake. We compare the moment released by the known earthquakes and associated postseismic deformation with the moment deficit accumulated during the interseismic period derived...

  14. Structural Basis for the Inhibitory Effects of Ubistatins in the Ubiquitin-Proteasome Pathway

    Nakasone, Mark A.; Lewis, Timothy A.; Walker, Olivier; Thakur, Anita; Mansour, Wissam; Castañeda, Carlos A.; Goeckeler-Fried, Jennifer L.; Parlati, Frank; Chou, Tsui-Fen; Hayat, Ortal; Zhang, Daoning; Camara, Christina M.; Bonn, Steven M.; Nowicka, Urszula K.; Krueger, Susan; Glickman, Michael H.; Brodsky, Jeffrey L.; Deshaies, Raymond J.; Fushman, David
    The discovery of ubistatins, small molecules that impair proteasomal degradation of proteins by directly binding to polyubiquitin, makes ubiquitin itself a potential therapeutic target. Although ubistatins have the potential for drug development and clinical applications, the lack of structural details of ubiquitin-ubistatin interactions has impeded their development. Here, we characterized a panel of new ubistatin derivatives using functional and binding assays. The structures of ubiquitin complexes with ubistatin B and hemi-ubistatin revealed direct interactions with ubiquitin's hydrophobic surface patch and the basic/polar residues surrounding it. Ubistatin B binds ubiquitin and diubiquitin tighter than a high-affinity ubiquitin receptor and shows strong...

  15. Structural basis for the initiation of eukaryotic transcription-coupled DNA repair

    Xu, Jun; Lahiri, Indrajit; Wang, Wei; Wier, Adam; Cianfrocco, Michael A.; Chong, Jenny; Hare, Alissa A.; Dervan, Peter B.; DiMaio, Frank; Leschziner, Andres E.; Wang, Dong
    Eukaryotic transcription-coupled repair (TCR) is an important and well-conserved sub-pathway of nucleotide excision repair that preferentially removes DNA lesions from the template strand that block translocation of RNA polymerase II (Pol II). Cockayne syndrome group B (CSB, also known as ERCC6) protein in humans (or its yeast orthologues, Rad26 in Saccharomyces cerevisiae and Rhp26 in Schizosaccharomyces pombe) is among the first proteins to be recruited to the lesion-arrested Pol II during the initiation of eukaryotic TCR. Mutations in CSB are associated with the autosomal-recessive neurological disorder Cockayne syndrome, which is characterized by progeriod features, growth failure and photosensitivity1. The molecular...

  16. Predictive simulation of non-steady-state transport of gases through rubbery polymer membranes

    Soniat, Marielle; Tesfaye, Meron; Brooks, Daniel; Merinov, Boris; Goddard, William A., III; Weber, Adam Z.; Houle, Frances A.
    A multiscale, physically-based, reaction-diffusion kinetics model is developed for non-steady-state transport of simple gases through a rubbery polymer. Experimental data from the literature, new measurements of non-steady-state permeation and a molecular dynamics simulation of a gas-polymer sticking probability for a typical system are used to construct and validate the model framework. Using no adjustable parameters, the model successfully reproduces time-dependent experimental data for two distinct systems: (1) O_2 quenching of a phosphorescent dye embedded in poly(n-butyl(amino) thionylphosphazene), and (2) O_2, N_2, CH_4 and CO_2 transport through poly(dimethyl siloxane). The calculations show that in the pre-steady-state regime, permeation is only correctly...

  17. The DNA Pol ϵ stimulatory activity of Mrc1 is modulated by phosphorylation

    Zhang, Zhong-Xin; Zhang, Jingjing; Cao, Qinhong; Campbell, Judith L.; Lou, Huiqiang
    DNA replication checkpoint (Mec1-Mrc1-Rad53 in budding yeast) is an evolutionarily conserved surveillance system to ensure proper DNA replication and genome stability in all eukaryotes. Compared to its well-known function as a mediator of replication checkpoint, the exact role of Mrc1 as a component of normal replication forks remains relatively unclear. In this study, we provide in vitro biochemical evidence to support that yeast Mrc1 is able to enhance the activity of DNA polymerase ϵ (Pol ϵ), the major leading strand replicase. Mrc1 can selectively bind avidly to primer/template DNA bearing a single-stranded region, but not to double-stranded DNA (dsDNA). Mutations...

  18. Interrogating marine virus-host interactions and elemental transfer with BONCAT and nanoSIMS-based methods

    Pasulka, Alexis L.; Thamatrakoln, Kimberlee; Kopf, Sebastian H.; Guan, Yunbin; Poulos, Bonnie; Moradian, Annie; Sweredoski, Michael J.; Hess, Sonja; Sullivan, Mathew B.; Bidle, Kay D.; Orphan, Victoria J.
    While the collective impact of marine viruses has become more apparent over the last decade, a deeper understanding of virus-host dynamics and the role of viruses in nutrient cycling would benefit from direct observations at the single-virus level. We describe two new complementary approaches - stable isotope probing coupled with nanoscale secondary ion mass spectrometry (nanoSIMS) and fluorescence-based biorthogonal non-canonical amino acid tagging (BONCAT) - for studying the activity and biogeochemical influence of marine viruses. These tools were developed and tested using several ecologically relevant model systems (Emiliania huxleyi/EhV207, Synechococcus sp. WH8101/Syn1, and Escherichia coli/T7). By resolving carbon and nitrogen...

  19. The Station Information System (SIS): A Centralized Repository for Populating, Managing, and Distributing Metadata of the Advanced National Seismic System Stations

    Yu, Ellen; Acharya, Prabha; Jaramillo, Justin; Kientz, Sue; Thomas, Valerie; Hauksson, Egill
    Creating, maintaining, and archiving accurate station metadata is critical for successful seismic network operations, data discovery, and research. The Station Information System (SIS) is a centralized repository of seismic station equipment inventory, instrument response, and site information of stations operated by regional seismic networks (RSNs) of the Advanced National Seismic System (ANSS; Filson and Arabasz, 2017). It has a web‐based user interface that enables the creation and manipulation of the corresponding metadata. The system can track the installation, maintenance, and removal of equipment from a site, which often results in the creation of new metadata epochs. SIS also computes the...

  20. The Kirchberg–Wassermann operator system is unique

    Lupini, Martino
    In 1998, Kirchberg and Wassermann constructed a separable nuclear operator system with the property that the canonical unital ⁎-homomorphism from the maximal C*-algebra onto the C*-envelope is injective. We show that such an operator system is unique, and completely order isomorphic to the operator system associated with the noncommutative Poulsen simplex.

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